A soft magnetic powder composite, a magnetic powder core material, and an insulating coating method based on organic growth.

Abstract

This application discloses a soft magnetic powder composite, a magnetic powder core material, and an insulating coating method based on organic growth, belonging to the field of soft magnetic materials technology. The soft magnetic powder composite of this application includes soft magnetic powder and an insulating coating layer, with the insulating coating layer encapsulating the soft magnetic powder. The insulating coating layer is prepared by a crosslinking reaction of dopamine hydrochloride (hereinafter referred to as dopamine) and polyethyleneimine. The soft magnetic powder is selected from metals and / or alloys containing Fe. The insulating coating method of this application has low hazard, achieves high stability within a certain temperature range, features scalable and controllable insulating film thickness, high film uniformity, and effectively isolates interparticle eddy currents. Simultaneously, the insulating coating layer has strong adhesion, reducing the amount of insulating adhesive used, facilitating molding, reducing the dilution effect of non-magnetic phases, and further improving the magnetic properties of the matrix.

Description

Technical Field

[0001] This application specifically relates to a soft magnetic powder composite, a magnetic powder core material, and an insulating coating method based on organic growth, belonging to the field of magnetic powder core preparation technology. Background Technology

[0002] Magnetic powder cores are soft magnetic composite materials prepared by mixing soft magnetic powder with an insulating medium. The pressing and molding technology of the soft magnetic powder and the insulating medium largely determines the density of the magnetic powder core. The amount and volume fraction of magnetic powder and insulating coating material, the thickness of the insulating coating film, the uniformity of the insulating coating layer, and the bonding effect between the coating layer and the matrix are crucial to the resistivity, permeability, coercivity, hysteresis loss, and eddy current loss of the magnetic powder core.

[0003] Eddy current loss is the primary cause of power loss in composite materials based on metal and alloy powders. Eddy current loss is directly proportional to the square of the operating frequency and inversely proportional to resistivity. Typically, metal and alloy powders require insulating coating in applications such as soft magnetic powder cores to reduce eddy current loss. Therefore, the insulating coating process for powder particles requires the coated powder to possess characteristics such as high resistivity, good thermal stability, high coating integrity, and high uniformity.

[0004] Currently, commonly used coating methods fall into four categories: organic, inorganic, organic-inorganic composite coating, and magnetic phase coating. Most existing coating methods are limited to phosphate coating and metal oxide coating in inorganic coatings, and silicone resin coating in organic coatings. These existing insulating coating methods suffer from drawbacks such as high preparation difficulty, poor process stability, high environmental pollution, significant health hazards, easy cracking of the coating layer, low temperature stability, and poor coating uniformity.

[0005] (1) Most existing organic coating methods employ sol-gel and chemical vapor deposition, resulting in thick coating layers that are difficult to control, thus deteriorating magnetic permeability. Commonly used organic coating materials are resins, including epoxy resins, phenolic resins, and silicone resins. Since organic resins and metal magnetic powders have different polarities, silane coupling agents are typically used to pretreat the magnetic powder surface to improve the wetting and bonding between the resin and the magnetic powder.

[0006] Thermoplastic resins were used earlier in organic coating, but their disadvantages were quickly exposed. They are easily soluble in industrial solutions and have a low melting point that limits the heat treatment temperature. Therefore, thermosetting resins such as epoxy resins were applied and promoted. However, their thermal stability is not high enough, and most resins have weak anti-aging ability and short service life.

[0007] On the other hand, in terms of the affinity between soft magnetic powder and resin, resin is hydrophobic and soft magnetic powder is hydrophilic. Therefore, the surface properties of the two are opposite, which weakens the wetting between soft magnetic powder and organic coating agent. This results in the organic coating agent not being able to completely and uniformly coat the surface of soft magnetic powder, which increases the effective particle size, reduces resistivity, and increases eddy current loss.

[0008] (2) Due to the generally low melting point of organic coating agents, inorganic coating agents have gradually emerged. Currently, commonly used inorganic coating methods include phosphate coating, metal oxide coating, and ferrite coating, which can be roughly divided into two categories. One category is to directly react (passivate) the magnetic powder with phosphoric acid, chromic acid, or oxidizing nitric acid to form an insulating coating film with high resistivity on its surface. The other category is the sol-gel method in which the magnetic powder does not participate in the formation of the insulating layer. For example, Al(NO3)3 hydrolyzes and precipitates on the surface of Fe-Si-Al magnetic powder to form Al(OH)3, which is then annealed and heat-treated to form a coating layer mainly composed of Al2O3.

[0009] Phosphate coating: This method was used earlier, but phosphate coating materials have low resistivity, large eddy current losses at high frequencies, poor plating solution stability, and complex operation. At the same time, harmful substances such as phosphoric acid are highly harmful to the human body, making it unsuitable for large-scale industrial production and application.

[0010] Metal oxide coating: This type of method is currently the mainstream coating method because it generally has high thermal stability and good electrical insulation, which meets the requirements of heat treatment. However, it is brittle and the insulating coating layer is prone to cracking during the pressing process, resulting in poor coating effect.

[0011] Ferrite coating: This type of method can minimize the influence of the coating material on the magnetic properties of the matrix and can ensure the stability of magnetic properties in the megahertz range, so it is widely used. However, ferrite coating has low uniformity and low compaction density.

[0012] (3) Organic-inorganic composite coating combines the advantages of inorganic and organic coatings and has been widely used and studied in recent years. Nano SiO2 and ZnSO4 are added to the resin to suppress the water molecules generated during the curing process, thereby improving the stability of the resin. Nano silica is generated in situ in the resin through the gel sol method, so that a stable chemical bond is formed between the resin and inorganic nanoparticles.

[0013] (4) Magnetic phase coating uses materials with ferromagnetic magnetic properties as coating / adhesives to enhance or maintain the soft magnetic coupling effect between the main powder particles in the soft magnetic composite material, and improve or maintain the overall saturation magnetic induction intensity and other performance regulation. Summary of the Invention

[0014] This application employs a co-deposition growth method to deposit a polydopamine / polyethyleneimine layer on the surface of metal and alloy soft magnetic powders, providing an insulating coating for the soft magnetic powder particles. The insulating film is very thin with highly controllable thickness and high uniformity, which improves resistivity, effectively reduces eddy currents between magnetic powder particles, and lowers eddy current losses in the magnetic powder core. Simultaneously, the highly uniform thin insulating film reduces the proportion of other non-magnetic materials added during the insulation bonding process, improving the soft magnetic coupling effect between soft magnetic particles, effectively increasing permeability and saturation magnetic induction, and reducing hysteresis losses.

[0015] According to one aspect of this application, a soft magnetic powder composite is provided, comprising soft magnetic powder and an insulating coating layer, wherein the insulating coating layer encapsulates the soft magnetic powder;

[0016] The insulating coating material is prepared by cross-linking dopamine hydrochloride (hereinafter referred to as dopamine) with polyethyleneimine; the soft magnetic powder is selected from metals and / or alloys containing Fe.

[0017] Optionally, the insulating coating layer is formed by co-depositing dopamine and polyethyleneimine to encapsulate the soft magnetic powder.

[0018] Optionally, the molecular weight of dopamine is 189.64, and the weight-average molecular weight of polyethyleneimine (PEI) is 600 to 70,000.

[0019] Optionally, the thickness of the insulating coating is less than 1000 nm.

[0020] Optionally, the thickness of the insulating coating layer is 100–1000 nm.

[0021] Optionally, the upper limit of the thickness of the insulating coating is independently selected from 900nm, 800nm, 700nm, 600nm, 500nm, and 300nm, and the lower limit is independently selected from 200nm, 300nm, 500nm, 600nm, and 700nm.

[0022] Optionally, the cumulative distribution of soft magnetic powder particles is 50% of the particle size D. 50 <75μm.

[0023] Optionally, the soft magnetic powder has a particle size of 15–45 μm.

[0024] According to one aspect of this application, a method for preparing a soft magnetic powder composite is provided, comprising the following steps:

[0025] (1) After sonicating the soft magnetic powder in an acidic or alkaline solution, it is washed with deionized water until neutral, which increases the surface roughness of the soft magnetic powder. Then, it is sonicated in a polyethyleneimine solution to obtain pretreated soft magnetic powder.

[0026] (2) Prepare a Tris-HCl buffer solution containing dopamine and polyethyleneimine, and sonicate it to obtain co-precipitation solution A;

[0027] (3) The pretreated soft magnetic powder is immersed in co-deposition solution A and stirred at a constant temperature of 25-60°C for 8-30 hours to obtain the soft magnetic powder composite.

[0028] Optionally, the soft magnetic powder is sonicated in an acidic or alkaline solution for 30–40 min; the concentration of the polyethyleneimine solution is 50 mg / mL, and the ultrasonic treatment time in the polyethyleneimine solution is 30–40 min.

[0029] Optionally, the concentration of the Tris-HCl buffer solution is 0.05–1 mol / L, and the pH value is 8.5–10.

[0030] Optionally, in step (2), the mass ratio of dopamine to polyethyleneimine is (0.5-4):1.

[0031] Optionally, in step (3), the ratio of co-deposition solution A to soft magnetic powder is 10-20 mL / g.

[0032] Optionally, the upper limit of the ratio of co-deposition solution A to soft magnetic powder is independently selected from 18, 17, 16, 14 mL / g, and the lower limit is independently selected from 11, 12, 13, 15 mL / g.

[0033] The mass ratio of dopamine to polyethyleneimine is independently selected from 0.7:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, or any value between the two points mentioned above.

[0034] Optionally, the weight-average molecular weight of polyethyleneimine (PEI) is 600–70,000; and the size of the soft magnetic powder is 15–45 μm.

[0035] According to one aspect of this application, a magnetic powder core material is provided, comprising the above-described soft magnetic powder composite or the soft magnetic powder composite prepared by the above-described preparation method.

[0036] Optionally, the magnetic powder core material also includes an adhesive; the mass ratio of the insulating adhesive to the soft magnetic powder composite is (0.5–4):100.

[0037] The mass ratio of the insulating adhesive to the soft magnetic powder composite is independently selected from 3.5:100, 3:100, 2.5:100, 2:100, 1.5:100, 1:100, or any value between the above two points.

[0038] Optionally, the insulating adhesive is selected from at least one of silicone resin, epoxy resin, phenolic resin, and zinc stearate.

[0039] Optionally, the magnetic permeability of the magnetic powder core material can be stabilized at around 40 within 20kHz, the saturation magnetic induction is 0.9T, and the iron loss is W. 0.1 / 100k The lowest value can reach 511.6 mW / cm. 3 .

[0040] According to one aspect of this application, a method for preparing a magnetic powder core material is provided, comprising mixing any of the above-mentioned soft magnetic powder composites or soft magnetic powder composites prepared by any of the above-mentioned preparation methods with an insulating adhesive, pressing and molding the mixture, and then subjecting it to heat treatment to obtain the magnetic powder core material.

[0041] Optionally, the compression molding method is cold pressing, and the cold pressing process parameters are: pressure 1800MPa and holding time 60s.

[0042] The heat treatment temperature is 300–500℃, and the heat treatment time is 1 hour.

[0043] As one specific embodiment of this application, a method for preparing a soft magnetic powder composite includes the following steps:

[0044] (1) Obtaining soft magnetic powder;

[0045] (2) Dissolve NaOH in deionized water to prepare a 0.1-1 mol / L NaOH solution for later use;

[0046] (3) Add the soft magnetic powder to the above NaOH solution and sonicate for 30 minutes. Then remove the soft magnetic powder and wash it with deionized water until the pH value of the aqueous solution of the soft magnetic powder is neutral.

[0047] (4) Dissolve tris(hydroxymethyl)aminomethane (Tris) in deionized water and disperse it by ultrasonication to prepare a 0.05-0.1 mol / L Tris solution for later use;

[0048] (5) Take concentrated hydrochloric acid solution (HCl) and add it to deionized water to dilute it;

[0049] (6) Add the diluted hydrochloric acid solution to Tris solution to adjust its pH value to 8.5-10;

[0050] (7) Add dopamine (DA) and polyethyleneimine (PEI) to the above Tris solution with a pH of 8.5-10, and disperse them evenly by ultrasonication to obtain Tris-HCl / DA+PEI solution;

[0051] (8) The soft magnetic powder that has been treated and cleaned with NaOH solution is added to Tris-HCl / DA+PEI solution and mechanically stirred, while being heated in a water bath and dried to obtain the soft magnetic powder composite.

[0052] In this application, dopamine is added to Tris-HCl solution and dissolves therein, gradually growing into polydopamine aggregates. At the same time, it is oxidized and reacts with the amino groups in polyethyleneimine. Polyethyleneimine itself is a white viscous liquid. After being added to Tris-HCl solution, it is dissolved by ultrasound and completely dispersed in the solution.

[0053] The dopamine and polyethyleneimine co-deposition coating method is adopted. After the phenolic hydroxyl groups in dopamine are oxidized to quinone groups, the amino groups in polyethyleneimine can quickly undergo cross-linking reaction with dopamine. Polyethyleneimine not only participates in the cross-linking reaction of dopamine to form a copolymer coating layer, but also provides amino groups to the surface of the copolymer coating layer. On the one hand, it can accelerate the co-deposition rate with polydopamine, and on the other hand, it can inhibit the excessive aggregation of polydopamine by destroying the non-covalent bond forces inside polydopamine, thereby obtaining a co-deposited layer with a more uniform and smooth surface morphology.

[0054] In this application, when the reaction raw materials are involved, they are all dopamine + polyethyleneimine (DA + PEI), and when the deposition reaction and the post-reaction coating layer are involved, they are all polydopamine / polyethyleneimine (PDA / PEI).

[0055] In this application,

[0056] (1) Magnetic loss (iron loss W): When a metal magnetic powder core works in an alternating magnetic field, it is magnetized on the one hand and loses energy on the other. The total value of energy loss is called magnetic loss. Magnetic loss consists of magnetostrictive loss, eddy current loss, and residual loss.

[0057] (2) Eddy current loss: When the external magnetic field changes with frequency, an induced current will be generated in the material due to electromagnetic induction, which will cause eddy current loss. The higher the frequency of the alternating magnetic field, the greater the eddy current. The insulating coating can block the eddy current inside the magnetic powder particles, thereby reducing the eddy current between the magnetic powder particles and thus reducing the eddy current loss of the magnetic powder core.

[0058] (3) Magnetoinduced loss: When a magnetic material is magnetized in an alternating magnetic field, the power loss caused by the magnetoinduced phenomenon is related to the coercivity of the magnetic powder core. If too much non-magnetic material is added, the coercivity will increase, which will increase the hysteresis loss. Therefore, the nano and micron-level insulating coating film in this application can maintain a low hysteresis loss.

[0059] (4) Residual loss: In low-frequency weak field, the residual loss is mainly magnetic aftereffect loss. In high-frequency case, the residual loss is mainly size resonance loss, domain wall resonance loss and natural resonance loss.

[0060] (5) Resistivity: The property of a substance to impede the flow of electric current, which is related to the type of material, pressure, temperature, magnetic field and other factors.

[0061] (6) Coercivity: After a magnetic material is saturated with magnetization, its magnetic flux density B does not return to zero when the external magnetic field returns to zero. A magnetic field of a certain magnitude needs to be applied in the opposite direction of the original magnetization field to make the magnetic flux density return to zero. This magnetic field is called coercivity. The type and proportion of substances other than soft magnetic powder will affect the soft magnetic coupling effect between magnetic powder particles. The addition and increase of non-magnetic substances and the excessively low pressing density will also increase the coercivity of the magnetic powder core, leading to an increase in hysteresis loss.

[0062] (7) Saturation magnetic induction intensity: The maximum magnetization intensity that a magnetic material can achieve when magnetized in an applied magnetic field is called the saturation magnetic induction intensity, which provides the conditions for miniaturization of electronic components. The saturation magnetic induction intensity directly affects the power output capability of the magnetic core and is a core performance characteristic of power devices, thus providing the conditions for miniaturization of electronic components. For magnetic powder cores, under the same bulk magnetic powder conditions, the higher the proportion of the bulk soft magnetic powder participating in magnetization, the higher its saturation magnetic induction intensity. In this application, the ultra-thin insulating film thickness maintains the good high saturation magnetic induction intensity of the amorphous magnetic powder core.

[0063] The beneficial effects that this application can produce include:

[0064] The insulating coating method employed in this application achieves high stability within a certain temperature range, with no change in the insulating coating layer structure. It results in highly uniform and dense film formation with a thin and controllable film thickness (achieved by adjusting parameters such as time, concentration, and solution pH). This effectively isolates interparticle eddy currents. While improving resistivity, it ensures the high permeability and high saturation magnetization of the substrate, maintaining excellent intrinsic soft magnetic properties. Furthermore, the coating layer exhibits strong adhesion, reducing the ineffective addition of insulating adhesives, facilitating molding, minimizing the dilution effect of non-magnetic phases, further improving the magnetic properties of the substrate, and posing minimal risks. The preparation process is simple and easily repeatable.

[0065] The insulating-coated magnetic powder was pressed into shape at 1800 MPa and stress-relieved annealed at 300–500 °C. A rough coating layer was visible on the surface of the soft magnetic powder under a scanning electron microscope. The insulation layer thickness of the magnetic powder particles with different insulation coating effects ranged from 100 to 1000 nm under a transmission electron microscope. The magnetic properties of the obtained magnetic powder core were compared with those of magnetic powder without dopamine / polyethyleneimine co-deposition insulation coating under the same preparation conditions. The iron loss W... 0.1 / 50k Reduced by 17-43% (W) 0.1 / 50k It refers to the iron loss measured under the operating conditions of magnetic induction intensity of 0.1T and frequency of 50kHz, with the initial permeability μ stable within megahertz. Attached Figure Description

[0066] Figure 1 This is a flowchart of the dopamine / polyethyleneimine co-deposition coating process of this application;

[0067] Figure 2 SEM images of the surface morphology of the original powder and the soft magnetic powder composites of Examples 1-4;

[0068] Figure 3 The images show the cross-sectional morphology of the soft magnetic powder composites in Examples 1-4, obtained via FIB-SEM. Detailed Implementation

[0069] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0070] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased commercially. The silicone resin was purchased from Dongguan Sanjin Facial Materials Co., Ltd. as SJ-106 polyester-modified silicone resin.

[0071] Example 1

[0072] 30g of particles with a diameter D 50 Fe-Si-BC-Cr alloy soft magnetic powder with a particle size of 25 μm was placed in 500 mL of 0.5 mol / L NaOH solution and ultrasonically treated for 30 min. Then it was taken out and washed with deionized water until the pH value was neutral.

[0073] The soft magnetic powder extracted above was placed in 60 mL of a 50 mg / mL solution of polyethyleneimine (molecular weight 1800) and sonicated for 30 min.

[0074] Dopamine and polyethyleneimine were added to 500 mL of 0.05 mol / L Tris-HCl solution at a mass ratio of 2:1, with the concentrations of dopamine and polyethyleneimine being 8 mg / mL and 4 mg / mL, respectively, to obtain a Tris-HCl / DA+PEI solution. The soft magnetic powder that had been ultrasonically treated in the polyethyleneimine solution was then added to the Tris-HCl / DA+PEI solution.

[0075] The above mixed solution was heated at a constant temperature of 40°C while being mechanically stirred for 24 hours, and then dried to obtain a soft magnetic powder composite.

[0076] The surface morphology of its soft magnetic powder composite is as follows Figure 2 Figure 1 of Embodiment 1 shows the cross-sectional morphology as follows: Figure 3 Figure 1 of Example 1 shows that the average thickness of the polydopamine / polyethyleneimine insulating coating is 415±100nm. The upper layer of the coating is a platinum protective layer (to protect the organic coating from being melted by ion beam bombardment in the FIB experiment), and the lower layer is a soft magnetic powder matrix.

[0077] The adhesive (silicone resin) was mixed with the soft magnetic powder composite at a mass ratio of 2:100 and dissolved in acetone solution. After mixing evenly, the mixture was stirred continuously until the acetone was completely evaporated. Then, the mixed powder was taken out and placed in a vacuum drying oven at 60°C for 3 hours.

[0078] The dried mixed powder was placed in a hydraulic molding machine and pressed into a magnetic ring blank with an outer diameter of 20.3 mm and an inner diameter of 12.7 mm by applying a pressure of 1800 MPa and holding the pressure for 60 seconds.

[0079] The above-mentioned magnetic ring blank was placed in a vacuum heat treatment furnace and kept at 450°C for 0.5 hours to obtain a magnetic powder core sample.

[0080] Example 2

[0081] 30g of particles with a diameter D 50 Fe-Si-BC-Cr soft magnetic powder with a particle size of 25 μm was placed in 500 mL of 0.5 mol / L NaOH solution and ultrasonically treated for 30 min. After that, it was taken out and washed with deionized water until the pH value was neutral.

[0082] The soft magnetic powder extracted above was placed in 60 mL of a 50 mg / mL solution of polyethyleneimine (molecular weight 600) and sonicated for 30 min.

[0083] Dopamine and polyethyleneimine in a mass ratio of 1:1 were simultaneously added to a 0.1 mol / L Tris-HCl solution, wherein the concentrations of dopamine and polyethyleneimine were both 12 mg / mL, to obtain a Tris-HCl / DA+PEI solution. The soft magnetic powder that had been ultrasonically treated in the polyethyleneimine solution was then added to the Tris-HCl / DA+PEI solution.

[0084] The above mixed solution was heated at a constant temperature of 25°C while being mechanically stirred for 30 hours and then dried to obtain a soft magnetic powder composite.

[0085] The surface morphology of its soft magnetic powder composite is as follows Figure 2 Figure 2 of Embodiment 2 shows the cross-sectional morphology as follows: Figure 3 In Example 2, the dopamine / polyethyleneimine insulating coating layer has an average thickness of 800±100nm, and the lower layer is a soft magnetic powder matrix.

[0086] The adhesive (silicone resin) was mixed with the soft magnetic powder composite at a mass percentage ratio of 2:100 and dissolved in acetone solution. After mixing evenly, the mixture was stirred continuously until the acetone was completely evaporated. Then, the mixed powder was taken out and placed in a vacuum drying oven at 60°C for 3 hours.

[0087] The dried mixed powder was placed in a hydraulic molding machine and pressed into a magnetic ring blank with an outer diameter of 20.3 mm and an inner diameter of 12.7 mm by applying a pressure of 1800 MPa and holding the pressure for 60 seconds.

[0088] The above-mentioned magnetic ring blank was placed in a vacuum heat treatment furnace and kept at 480°C for 1 hour to obtain a magnetic powder core sample.

[0089] Example 3

[0090] 30g of particles with a diameter D 50 Fe-Si-BC-Cr soft magnetic powder with a particle size of 25 μm was placed in 500 mL of 0.5 mol / L NaOH solution and ultrasonically treated for 30 min. After that, it was taken out and washed with deionized water until the pH value was neutral.

[0091] The soft magnetic powder extracted above was placed in 60 mL of a 50 mg / mL solution of polyethyleneimine (molecular weight 600) and sonicated for 30 min.

[0092] Dopamine and polyethyleneimine (molecular weight 600) in a mass ratio of 2:1 were simultaneously added to a 0.1 mol / L Tris-HCl solution, with the concentrations of dopamine and polyethyleneimine being 8 mg / mL and 4 mg / mL, respectively, to obtain a Tris-HCl / DA+PEI solution.

[0093] The soft magnetic powder that has been ultrasonically treated in polyethyleneimine solution was added to the above Tris-HCl / DA+PEI solution, heated at 60 degrees Celsius and mechanically stirred for 8 hours, and then dried to obtain a soft magnetic powder composite.

[0094] The adhesive (silicone resin) was mixed with the soft magnetic powder composite at a mass percentage ratio of 2:100 and dissolved in acetone solution. After mixing evenly, the mixture was stirred continuously until the acetone was completely evaporated. Then, the mixed powder was taken out and placed in a vacuum drying oven at 60°C for 3 hours.

[0095] The surface morphology of its soft magnetic powder composite is as follows Figure 2 Figure 3 of Example 3 shows the cross-sectional morphology as follows: Figure 3 Figure 3 of Example 3 shows that the average thickness of the polydopamine / polyethyleneimine insulating coating is 680±100nm.

[0096] The dried mixed powder was placed in a hydraulic molding machine and pressed into a magnetic ring blank with an outer diameter of 20.3 mm and an inner diameter of 12.7 mm by applying a pressure of 1800 MPa and holding the pressure for 60 seconds.

[0097] The above-mentioned magnetic ring blank was placed in a vacuum heat treatment furnace and kept at 480°C for 1 hour to obtain a magnetic powder core sample.

[0098] Example 4

[0099] 30g of particles with a diameter D 50 Fe-Si-BC-Cr soft magnetic powder with a particle size of 25 μm was placed in 500 mL of 0.5 mol / L NaOH solution and ultrasonically treated for 30 min. After that, it was taken out and washed with deionized water until the pH value was neutral.

[0100] The soft magnetic powder extracted above was placed in 60 mL of a 50 mg / mL solution of polyethyleneimine (molecular weight 600) and sonicated for 30 min.

[0101] Dopamine and polyethyleneimine (molecular weight 600) in a mass ratio of 1:1 were simultaneously placed in a 0.1 mol / L Tris-HCl solution, wherein the concentration of both dopamine and polyethyleneimine was 24 mg / mL, to obtain a Tris-HCl / DA+PEI solution. The soft magnetic powder that had been ultrasonically treated in the polyethyleneimine solution was then added to the Tris-HCl / DA+PEI solution.

[0102] The above mixed solution was heated at a constant temperature of 50°C for 20 hours while being mechanically stirred and then dried to obtain a soft magnetic powder composite.

[0103] The surface morphology of its soft magnetic powder composite is as follows Figure 2 Figure 4 of Example 4 shows the cross-sectional morphology as follows: Figure 3 In Example 4, the average thickness of the polydopamine / polyethyleneimine insulating coating layer is 600±100nm, and the lower layer is a soft magnetic powder matrix.

[0104] The adhesive (silicone resin) was mixed with the soft magnetic powder composite at a mass percentage ratio of 2:100 and dissolved in acetone solution. After mixing evenly, the mixture was stirred continuously until the acetone was completely evaporated. Then, the mixed powder was taken out and placed in a vacuum drying oven at 60°C for 3 hours.

[0105] The dried mixed powder was placed in a hydraulic molding machine and pressed into a magnetic ring blank with an outer diameter of 20.3 mm and an inner diameter of 12.7 mm by applying a pressure of 1800 MPa and holding the pressure for 60 seconds.

[0106] The above-mentioned magnetic ring blank was placed in a vacuum heat treatment furnace and kept at 480°C for 1 hour to obtain a magnetic powder core sample.

[0107] Examples 2 and 4 are comparative experiments with different concentrations of polydopamine / polyethyleneimine. Due to the difference in concentration of dopamine / polyethyleneimine, the particle size, growth quantity and stacking thickness of polydopamine / polyethyleneimine nanoaggregates in the reaction solution are different, which in turn causes the thickness of the polydopamine / polyethyleneimine insulating coating layer to be different, thus having a certain impact on the soft magnetic properties of the corresponding magnetic powder core.

[0108] Examples 1 and 3 are comparative experiments on different molecular weights of polyethyleneimine (PEI). When the molecular weight of PEI increases, on the one hand, the distance between the "anchor points" providing interaction increases, leading to a decrease in its relative density within the formed cross-linked network; on the other hand, branched molecules such as polydopamine are more likely to form in the solution rather than cross-linked networks. Figure 2 As can be seen, the surface morphology of Example 1 is relatively rough, while the coating layer of Example 3 is thicker.

[0109] Comparative Example 1

[0110] Sodium silicate is mixed with deionized water until homogeneous, then alcohol ether phosphate is added and mixed until homogeneous to obtain a sodium silicate solution.

[0111] Take iron-silicon powder with an average particle size of 35μm, raise the temperature of the coating furnace to 80℃, add lignin sulfonate into the coating furnace, and stir for 30min.

[0112] Add sodium silicate solution to the soft magnetic metal powder and stir for 30 minutes;

[0113] The coating oven temperature was raised to 150℃ and baked for 60 minutes to obtain the coated powder.

[0114] Add 1% by weight of aluminum oxide and 1% by weight of zinc stearate lubricant to the coated powder and mix thoroughly;

[0115] The uniformly mixed soft magnetic powder was molded into a magnetic ring blank with an outer diameter of 27.0 mm and an inner diameter of 14.7 mm under a molding pressure of 2300 MPa. The blank was then kept at 800℃ in an H2 atmosphere for 90 min to obtain a sodium silicate-coated magnetic powder core.

[0116] Comparative Example 2

[0117] 30g of particles with a diameter D 50 Fe-Si-BC-Cr soft magnetic powder with a diameter of 25μm and organosilicon resin were dissolved together in acetone solution at a mass ratio of 100:2. The mixture was stirred evenly and continuously until the acetone solution was completely evaporated. The mixed powder was then placed in a vacuum drying oven and dried at 60℃ for 3 hours.

[0118] The dried mixed powder was placed in a hydraulic molding machine and pressed into a magnetic ring blank with an outer diameter of 20.3 mm and an inner diameter of 12.7 mm by applying a pressure of 1800 MPa and holding the pressure for 60 seconds.

[0119] The above-mentioned magnetic ring blank was placed in a vacuum heat treatment furnace and kept at 480°C for 1 hour to obtain a magnetic powder core sample.

[0120] Comparative Example 3

[0121] Mix phosphoric acid and deionized water thoroughly to prepare a phosphoric acid solution for later use.

[0122] Take a soft magnetic powder of iron-silicon-aluminum (iron 87.8 wt.%, silicon 6.8 wt.%, aluminum 5.4 wt.%) with an average particle size of 38 μm and put it into a coating furnace and start stirring.

[0123] Add the phosphoric acid solution to the coating furnace and continue stirring for 30 minutes; add nano-calcium carbonate with a particle size of less than 100 nm and continue stirring for 30 minutes.

[0124] The coating furnace is heated to 120°C and stirred until dry to obtain pretreated magnetic powder;

[0125] Add 0.3% zinc stearate by weight of the pretreated magnetic powder and stir until homogeneous;

[0126] The magnetic ring blank is pressed into a shape with an outer diameter of 27.0 mm and an inner diameter of 14.7 mm under a pressure of 2300 MPa.

[0127] The magnetic powder core was annealed by holding it at 700℃ in a N2 atmosphere for 30 minutes to obtain a secondary coating of phosphoric acid and nano-calcium carbonate.

[0128] Test case

[0129] The iron loss of magnetic powder core material under the working conditions of magnetic induction intensity of 0.1T and frequency of 50kHz was measured using a Hunan Lianzhong 2335A broadband energy analyzer, where the number of coil turns N1=20 and N2=5.

[0130] The permeability of the magnetic powder core was measured using an Agilent 4294A precision impedance analyzer under operating conditions of 1kHz to 110MHz frequency range and an applied magnetic field H≈0.1A / m, where the number of coil turns N1=20 and N2=5.

[0131] parameter <![CDATA[Iron loss W 0.1 / 50k (mW / cm 3 )]]> initial permeability μ Example 1 316 34 Example 2 229 32 Example 3 256 46 Example 4 268 35 Comparative Example 1 898 26 Comparative Example 2 371 39 Comparative Example 3 520 26

[0132] As shown in the table above, comparing the iron loss and initial permeability data measured under the conditions of 0.1T excitation and 50kHz frequency, Examples 1, 2, 3, and 4 of this invention patent show lower iron loss than Comparative Examples 1, 2, and 3, while Examples 1, 2, 3, and 4 show higher initial permeability than Comparative Examples 1 and 3. The initial permeability of Comparative Example 2 is 39, which is still lower than that of Example 3 of this invention patent. In summary, the insulation coating process, adhesive coating process, and cold pressing process in this invention patent have significant advantages in the preparation of magnetic powder cores, and can obtain high initial permeability, low iron loss, and excellent high-frequency stability characteristics.

[0133] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A magnetic powder core material, characterized by, The magnetic powder core material includes a soft magnetic powder composite. The soft magnetic powder composite comprises soft magnetic powder and an insulating coating layer, wherein the insulating coating layer encapsulates the soft magnetic powder; The insulating coating material is prepared by a crosslinking reaction of dopamine and polyethyleneimine. The soft magnetic powder is selected from metals and / or alloys containing Fe. The insulating coating layer is used to encapsulate the soft magnetic powder by in-situ co-deposition of dopamine and polyethyleneimine. The thickness of the insulating coating layer is 100~1000 nm; The magnetic powder core material also includes an insulating adhesive; the mass ratio of the insulating adhesive to the soft magnetic powder composite is (0.5~4):100; The preparation method of the soft magnetic powder composite includes the following steps: (1) After sonicating the soft magnetic powder in an acidic or alkaline solution, wash it with deionized water until it is neutral, and then sonicate it in a polyethyleneimine solution to obtain pretreated soft magnetic powder. (2) Prepare a Tris-HCl buffer solution containing dopamine and polyethyleneimine, and sonicate it to obtain a co-precipitation solution Tris-dopamine / polyethyleneimine (Tris-DA / PEI); (3) The pretreated soft magnetic powder is immersed in the co-deposition solution Tris-DA / PEI and stirred at 25~60℃ for 8~30h to obtain the soft magnetic powder composite.

2. The magnetic powder core material according to claim 1, characterized in that, The weight-average molecular weight of the polyethyleneimine is 600-70000.

3. The magnetic powder core material according to claim 1, characterized in that, The soft magnetic powder has a particle size of 50% of the cumulative distribution D 50 <75 μm.

4. The magnetic powder core material according to claim 1, characterized by The soft magnetic powder has a particle size of 15~45μm.

5. The magnetic powder core material according to claim 1, characterized by The concentration of the Tris-HCl buffer solution is 0.05~1 mol / L, and the pH value is 8.5~10.

6. The magnetic powder core material according to claim 1, characterized by In step (2), the mass ratio of dopamine to polyethyleneimine is (0.5~4):1; The concentration of dopamine in the coprecipitation solution Tris-DA / PEI is 6 mg / mL to 30 mg / mL; the concentration of polyethyleneimine in the coprecipitation solution Tris-DA / PEI is 6 mg / mL to 30 mg / mL.

7. The magnetic powder core material according to claim 1, characterized by In step (3), the ratio of the co-deposition solution Tris-DA / PEI to the soft magnetic powder is 10~20mL / g.

8. The magnetic powder core material according to claim 1, characterized in that, The insulating adhesive is selected from at least one of silicone resin, epoxy resin, phenolic resin, and zinc stearate.

9. The magnetic powder core material according to claim 1, characterized in that, The initial permeability of the magnetic powder core material is stable between 20 and 70 within 20 kHz, the saturation magnetic induction is 0.9 T, and the iron loss is [not specified]. W 0.1 / 100k The lowest is 511.6 mW / cm 3 .

10. A method for preparing the magnetic powder core material according to any one of claims 1 to 9, characterized in that, The soft magnetic powder composite is mixed with an insulating adhesive, pressed into shape, and then heat-treated to obtain the magnetic powder core material.

11. The preparation method according to claim 10, characterized in that, The pressing and molding method is cold pressing, and the cold pressing process parameters are: pressure 800~2000MPa, holding time 30~120s. The heat treatment temperature is 300~500℃, and the heat treatment time is 0.5~2h.

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