Wrapping method for reducing loss of Fe-Si-Al magnetic core and Fe-Si-Al magnetic core prepared by wrapping method

Abstract

The invention discloses a wrapping method for reducing the loss of an iron-silicon-aluminum magnetic core and the iron-silicon-aluminum magnetic core prepared by the wrapping method. The wrapping method for reducing the loss of the iron-silicon-aluminum magnetic core comprises the following steps: preheating and activating an iron-silicon-aluminum magnetic powder matrix, mixing the iron-silicon-aluminum magnetic powder matrix with a coating agent, pressing and annealing. The magnetic conductivity and the insulativity of the Fe-Si-Al magnetic powder core prepared through the wrapping method are improved in a coordinated mode, and meanwhile the product is remarkable in high-temperature-resistant and corrosion-resistant stability effect. According to the wrapping method, the problem that the wrapping layer of the magnetic powder core is not uniform can be solved, and local eddy current concentration is prevented, so that eddy current loss is reduced, and the direct current bias performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of Sendust powder coating, and in particular to a coating method for reducing Sendust core loss and a Sendust core prepared therefrom. Background Art

[0002] Sendust cores are widely used in high-frequency inductor devices due to their high saturation magnetic induction and low loss properties. In traditional processes, the coating of magnetic powder cores is prone to problems such as unevenness and poor insulation, forming microscopic short-circuit paths, leading to local eddy current concentration, increasing eddy current losses, and reducing DC bias performance. In addition, existing technologies mostly use a single organic resin coating. The organic coating has non-magnetic characteristics. After being compounded with metal magnetic particles, it will also reduce the saturation magnetization intensity of the material to a certain extent, resulting in insufficient temperature resistance of the Sendust core and difficulty in balancing magnetic permeability and loss. Therefore, there is an urgent need for a packaging method that can achieve a synergistic improvement in magnetic permeability, loss, and DC bias through composite coating agents and process optimization. Summary of the Invention

[0003] The purpose of the present invention is to propose a wrapping method for reducing the loss of Sendust core and the Sendust core prepared therefrom, so as to solve the problem that the coating layer of the above-mentioned magnetic powder core is prone to unevenness and the coating layer type is single, resulting in reduced magnetic permeability, increased loss and decreased DC bias performance.

[0004] To achieve this object, the present invention adopts the following technical solutions:

[0005] The present invention provides a wrapping method for reducing sendust core loss, comprising the following steps:

[0006] S1: preheating and activating the sendust magnetic powder matrix, wherein the preheating and activation treatment includes pickling activation, heat treatment and plasma activation to obtain pretreated powder;

[0007] S2: mixing the pretreated powder with the coating agent and stirring at a speed of 500-600 rpm for 30-40 minutes; then curing the pretreated powder mixed with the coating agent at 120-150° C. for 2-3 hours to form a uniform insulating layer to obtain a coated powder;

[0008] The coating agent comprises the following components by weight: 0.2 to 0.6 parts of phosphoric acid, 0.4 to 1.0 parts of silicone resin, 0.2 to 0.6 parts of nano-boron nitride, 0.3 to 0.5 parts of silane coupling agent ethanol solution, 0.2 to 0.3 parts of phosphate dispersant and 5 to 8 parts of isopropyl alcohol solvent;

[0009] S3: mixing the coated powder with a release agent, and pressing the mixture into a shape at a pressure of 1900 to 2100 MPa to obtain a blank magnetic powder core;

[0010] S4: Under nitrogen protection, the blank magnetic powder core is heated to 750-830°C at a rate of 5°C / min and kept at this temperature for 60-100 minutes to obtain a Sendust magnetic powder core.

[0011] In the wrapping method for reducing sendust core loss, in step S2, the preparation of the coating agent includes the following steps: first, mixing nano-boron nitride with a silane coupling agent ethanol solution, stirring for 2 to 2.5 hours at 58 to 65° C., and centrifugally drying to obtain coupled nano-boron nitride; and then mixing the coupled nano-boron nitride with phosphoric acid, silicone resin, phosphate ester dispersant, and isopropyl alcohol solvent.

[0012] In the wrapping method for reducing sendust core loss, the particle size of the nano-boron nitride is 50-100 nm; and the concentration of the silane coupling agent in the ethanol solution of the silane coupling agent is 4-6 wt %.

[0013] In the wrapping method for reducing sendust core loss, the mixing ratio of the pretreated powder to the coating agent is 5:(3-4).

[0014] In the wrapping method for reducing the core loss of Sendust, in the step S1, the Sendust magnetic powder matrix is sequentially subjected to pickling activation, heat treatment and plasma activation;

[0015] The pickling activation step comprises: placing the sendust magnetic powder matrix in a hydrochloric acid solution for ultrasonic treatment for 20 to 30 minutes, then washing the sendust magnetic powder matrix with water, washing the sendust magnetic powder matrix with water until it is neutral, and vacuum drying to obtain an acid-washed sendust magnetic powder matrix;

[0016] The heat treatment step comprises: placing the pickled Sendust magnetic powder matrix in an argon atmosphere, heating it to 500-550° C., keeping it warm for 1-2 hours, and cooling it to room temperature to obtain a heat-treated Sendust magnetic powder matrix;

[0017] The plasma activation step comprises: placing the heat-treated Sendust magnetic powder matrix in a protective gas atmosphere for plasma treatment, with a plasma power of 300-400W and a plasma treatment time of 10-15 minutes.

[0018] In the wrapping method for reducing the loss of the sendust core, in the pickling and activation step, the concentration of hydrochloric acid is 8-12%, and the ultrasonic power in the ultrasonic treatment is 200-300W;

[0019] In the plasma activation step, the protective gas is obtained by mixing argon and nitrogen, the mixing ratio of argon and nitrogen is 9:1, the gas flow rate is 20-30 sccm, and the chamber pressure is 50-100 Pa.

[0020] In the wrapping method for reducing sendust core loss, in step S2, the curing process includes a pre-curing stage and a final curing stage. In the pre-curing stage, the pre-curing temperature is 118-125° C., and the pre-curing time is 1-1.5 hours; in the final curing stage, the final curing temperature is 148-155° C., and the final curing time is 1-1.5 hours.

[0021] In the wrapping method for reducing the core loss of Sendust, the components of the Sendust magnetic powder matrix, calculated by mass percentage, include 7.5-8.5 wt% Si and 5.0-5.8 wt% Al, with the remainder being Fe.

[0022] In the wrapping method for reducing sendust core loss, in step S4, the purity of nitrogen is ≥99.99% and the dew point is ≤-40°C.

[0023] The present invention also provides a Sendust core, which is prepared by the above-mentioned wrapping method for reducing Sendust core loss.

[0024] A technical solution in the present invention can have the following beneficial effects:

[0025] The wrapping method for reducing sendust core loss involves preheating and activating the sendust magnetic powder matrix, mixing it with a coating agent, and then performing a pressing and heat treatment process to produce a sendust magnetic powder core. The sendust magnetic powder core prepared by this wrapping method exhibits coordinated improvements in magnetic permeability and insulation properties, while also significantly improving the product's high-temperature resistance and corrosion stability. This wrapping method can address the problem of uneven coating on the magnetic powder core, preventing local eddy current concentration, thereby reducing eddy current losses and improving DC bias performance. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be further illustrated below by way of specific embodiments. To facilitate understanding of the present invention, the present invention will be described in more detail below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0027] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] The present invention provides a wrapping method for reducing sendust core loss, comprising the following steps:

[0030] S1: preheating and activating the sendust magnetic powder matrix, wherein the preheating and activation treatment includes pickling activation, heat treatment and plasma activation to obtain pretreated powder;

[0031] S2: mixing the pretreated powder with the coating agent and stirring at a speed of 500-600 rpm for 30-40 minutes; then curing the pretreated powder mixed with the coating agent at 120-150° C. for 2-3 hours to form a uniform insulating layer to obtain a coated powder;

[0032] The coating agent comprises the following components by weight: 0.2 to 0.6 parts of phosphoric acid, 0.4 to 1.0 parts of silicone resin, 0.2 to 0.6 parts of nano-boron nitride, 0.3 to 0.5 parts of silane coupling agent ethanol solution, 0.2 to 0.3 parts of phosphate dispersant and 5 to 8 parts of isopropyl alcohol solvent;

[0033] S3: mixing the coated powder with a release agent, and pressing the mixture into a shape at a pressure of 1900 to 2100 MPa to obtain a blank magnetic powder core;

[0034] S4: Under nitrogen protection, the blank magnetic powder core is heated to 750-830°C at a rate of 5°C / min and kept at this temperature for 60-100 minutes to obtain a Sendust magnetic powder core.

[0035] The wrapping method for reducing the loss of the Sendust core involves preheating and activating the Sendust magnetic powder matrix, mixing it with a coating agent, and then performing a pressing and heat treatment process to obtain a Sendust magnetic powder core. The magnetic permeability and insulation properties of the Sendust magnetic powder core prepared by the wrapping method are improved in a coordinated manner, while the product also has significant high-temperature resistance and corrosion stability. The above method can solve the problem of uneven coating of the magnetic powder core, prevent local eddy current concentration, thereby reducing eddy current losses and improving DC bias performance.

[0036] The coating agent contains nano-boron nitride and silicone resin. The silicone resin has excellent dielectric strength, effectively isolating the magnetic core from surrounding circuits and preventing short-circuit risks. Furthermore, the silicone resin has a wide temperature range, withstanding temperatures of 700-800°C, making it suitable for the thermal environments of high-frequency applications. It prevents oxidation and magnetic degradation of the core due to high temperatures without compromising its insulation properties. The nano-boron nitride fills the gaps in the Sendust magnetic powder matrix, improving the material's internal structure, enhancing its mechanical and magnetic properties, and reducing power loss. It also improves insulation, significantly increasing resistivity and reducing high-frequency eddy current losses. This enhances the product's frequency characteristics, making it suitable for high-frequency environments. By mixing the pretreated powder with the coating agent, the insulation of the Sendust magnetic powder core is enhanced, the saturation magnetization of the material is increased, and the core's inherent temperature resistance, low permeability, and high losses are avoided.

[0037] Phosphoric acid can react with other components to form a cross-linked structure, enhancing the stability, high temperature resistance, and adhesion of the coating. Phosphoric acid also has excellent dispersibility, which can improve the compatibility between materials.

[0038] The silane coupling agent ethanol solution is formed by mixing a silane coupling agent and ethanol. The silane coupling agent is dissolved in ethanol so that the silane coupling agent and the nano-boron nitride can be fully mixed. In a specific embodiment of the present invention, the silane coupling agent is specifically a commercially available model KH-560 (silane coupling agent, and the concentration of the silane coupling agent ethanol solution is 5wt%. The silane coupling agent can enhance the compatibility and adhesion between the silicone resin and the nano-boron nitride, enhance the overall performance of the encapsulant, thereby improving its moisture resistance and chemical corrosion resistance.

[0039] Phosphate dispersants help improve the dispersibility of the components in the coating agent, avoid the agglomeration of nano-boron nitride, effectively improve the stability of the solution, make the coating agent more uniform during the construction process, and ensure the uniformity and stability of the final coating or coating effect.

[0040] Isopropyl alcohol is used as a solvent to dissolve and dilute other components, helping to evenly mix the formulation. It has low volatility and evaporates quickly, helping the coating form a uniform coating or wrapping effect during application.

[0041] Specifically, in step S2, the preparation of the coating agent includes the following steps: first, mixing nano-boron nitride with an ethanol solution of a silane coupling agent, stirring for 2 to 2.5 hours at 58 to 65° C., and centrifugally drying to obtain coupled nano-boron nitride; then, mixing the coupled nano-boron nitride with phosphoric acid, an organosilicon resin, a phosphate dispersant, and an isopropyl alcohol solvent.

[0042] By adopting the above steps, the nano-boron nitride is firstly fully mixed with the silane coupling agent to enhance the adhesion between the nano-boron nitride and the organic material, and then the nano-boron nitride is mixed with other components to make the bond between the silicone resin and the nano-boron nitride stronger.

[0043] Specifically, the particle size of the nano-boron nitride is 50-100 nm; the concentration of the silane coupling agent in the silane coupling agent ethanol solution is 4-6 wt %.

[0044] Nano-boron nitride has excellent electrical insulation properties and can effectively reduce eddy current losses in Sendust cores during high-frequency operation, helping to improve the efficiency and stability of the core. Using nano-boron nitride with the above particle size allows for a more secure bond to the Sendust core and excellent dispersion, preventing magnetic powder agglomeration and sedimentation, thereby improving material uniformity and ensuring stable core performance.

[0045] The use of the silane coupling agent ethanol solution with the above-mentioned concentration of the silane coupling agent can enhance the adhesion between the nano-boron nitride and the organic material while avoiding waste caused by excessive silane coupling agent.

[0046] Specifically, the mixing ratio of the pretreated powder to the coating agent is 5:(3-4).

[0047] In a specific embodiment of the present invention, the mixing ratio of the pretreated powder and the coating agent is 5:3. By adopting the above mixing ratio, the periphery of the pretreated powder can be evenly coated with the coating agent while avoiding excessive thickness of the coating layer.

[0048] Specifically, in step S1, the sendust magnetic powder matrix is sequentially subjected to pickling activation, heat treatment, and plasma activation;

[0049] The pickling activation step comprises: placing the sendust magnetic powder matrix in a hydrochloric acid solution for ultrasonic treatment for 20 to 30 minutes, then washing the sendust magnetic powder matrix with water, washing the sendust magnetic powder matrix with water until it is neutral, and vacuum drying to obtain an acid-washed sendust magnetic powder matrix;

[0050] The heat treatment step comprises: placing the pickled Sendust magnetic powder matrix in an argon atmosphere, heating it to 500-550° C., keeping it warm for 1-2 hours, and cooling it to room temperature to obtain a heat-treated Sendust magnetic powder matrix;

[0051] The plasma activation step comprises: placing the heat-treated Sendust magnetic powder matrix in a protective gas atmosphere for plasma treatment, with a plasma power of 300-400W and a plasma treatment time of 10-15 minutes.

[0052] The pickling activation treatment can effectively remove the oxide layer or impurities on the surface of the Sendust magnetic powder matrix, reduce the impact on the magnetic properties, and at the same time make the surface of the Sendust magnetic powder matrix more uniform and smooth, improve the adhesion between the sendust magnetic powder matrix and the coating agent, and avoid the problem of uneven coating layer.

[0053] Heat treatment can change the crystal structure of Sendust magnetic powder, increasing its saturation magnetic induction intensity and magnetic permeability, and improving its magnetic properties, making it perform better in high-frequency and high-power applications. Furthermore, heat treatment can change the particle morphology of Sendust magnetic powder, making it more uniform and regular, thereby improving its dispersion and filling properties.

[0054] Plasma activation ionizes the gas and generates plasma, which can form chemically active groups on the surface of Sendust magnetic powder, change the chemical reactivity of the surface, and increase its surface roughness. It can improve the adhesion between the magnetic powder and the coating agent, thereby enhancing its dispersion and stability in the composite material.

[0055] Specifically, in the pickling activation step, the hydrochloric acid concentration is 8-12%, and the ultrasonic power in the ultrasonic treatment is 200-300W;

[0056] In the plasma activation step, the protective gas is obtained by mixing argon and nitrogen, the mixing ratio of argon and nitrogen is 9:1, the gas flow rate is 20-30 sccm, and the chamber pressure is 50-100 Pa.

[0057] In a specific embodiment of the present invention, in the pickling activation step, the hydrochloric acid concentration is 10%, and the ultrasonic power is 250W; in the plasma activation step, the gas flow rate is 205sccm, and the chamber pressure is 80Pa.

[0058] Specifically, in step S2, the curing process includes a pre-curing stage and a final curing stage. In the pre-curing stage, the pre-curing temperature is 118-125°C, and the pre-curing time is 1-1.5 hours; in the final curing stage, the final curing temperature is 148-155°C, and the final curing time is 1-1.5 hours.

[0059] A pre-curing stage at a lower temperature is carried out first, which can help the coating agent to initially adhere to the sendust magnetic powder matrix, so that the nano-boron nitride and silicone resin can better combine with the surface of the sendust magnetic powder and enhance the adhesion of the coating; then, a final curing stage at a higher temperature is carried out to ensure that the coating agent fully reacts at high temperature, obtaining a more uniform and dense coating layer, thereby improving the high temperature resistance and corrosion resistance.

[0060] Specifically, the Sendust magnetic powder matrix comprises, by weight percentage, 7.5-8.5 wt% Si and 5.0-5.8 wt% Al, with the remainder being Fe. This composition avoids the problem of excessive Si / Al content hindering the movement of magnetic domain walls and reducing magnetic permeability.

[0061] Specifically, in step S4, the purity of nitrogen is ≥99.99% and the dew point is ≤-40° C. The above nitrogen purity and dew point help improve the stability of the annealing process and effectively prevent the metal surface from being oxidized or corroded by moisture.

[0062] The present invention also provides a Sendust core, which is prepared by the above-mentioned wrapping method for reducing Sendust core loss.

[0063] Example 1

[0064] A wrapping method for reducing sendust core loss comprises the following steps:

[0065] The sendust magnetic powder matrix is sequentially subjected to pickling activation, heat treatment, and plasma activation; the components of the sendust magnetic powder matrix, calculated by mass percentage, include 8wt% Si and 5.5wt% Al, with the balance being Fe;

[0066] The pickling activation step comprises: placing the sendust magnetic powder matrix in a 10% hydrochloric acid solution and performing ultrasonic treatment at an ultrasonic power of 250 W for 25 minutes, then washing the sendust magnetic powder matrix with water, washing the sendust magnetic powder matrix with water until it is neutral, and vacuum drying to obtain an acid-washed sendust magnetic powder matrix;

[0067] The heat treatment step comprises: placing the pickled Sendust magnetic powder matrix in an argon atmosphere, heating to 550° C., keeping the temperature for 11.5 hours, and cooling to room temperature to obtain a heat-treated Sendust magnetic powder matrix;

[0068] The plasma activation step includes: placing the heat-treated sendust magnetic powder substrate in a protective gas atmosphere for plasma treatment at a plasma power of 350 W and a plasma treatment time of 12 minutes to obtain a pretreated powder; the protective gas is a mixture of argon and nitrogen at a mixing ratio of 9:1, a gas flow rate of 25 seem, and a chamber pressure of 70 Pa;

[0069] The pretreated powder and the coating agent were mixed in a ratio of 5:3; the mixture was stirred at a speed of 550 rpm for 35 minutes; the pretreated powder mixed with the coating agent was then subjected to pre-curing and final curing treatments in sequence, with a pre-curing temperature of 120° C. and a pre-curing time of 1 hour; and a final curing temperature of 150° C. and a final curing time of 1 hour to form a uniform insulating layer, thereby obtaining a coated powder;

[0070] The coating agent comprises the following components by weight: 0.4 parts of phosphoric acid, 0.7 parts of silicone resin, 0.4 parts of nano-boron nitride with a particle size of 80 nm, 0.4 parts of silane coupling agent ethanol solution with a concentration of 5 wt% of silane coupling agent, 0.25 parts of phosphate dispersant and 6.5 parts of isopropyl alcohol solvent;

[0071] After mixing the coated powder with the release agent, the mixture is pressed into shape at a pressing pressure of 2000 MPa to obtain a blank magnetic powder core; based on 100 parts of the coated powder, the amount of the release agent added is 0.5 parts, and the release agent is zinc stearate;

[0072] The blank magnetic powder core is heated to 780°C at a rate of 5°C / min under nitrogen protection and kept warm for 80 minutes to obtain a sendust magnetic powder core. The purity of the nitrogen is ≥99.99% and the dew point is ≤-40°C.

[0073] Example 2

[0074] The steps of Example 2 are the same as those of Example 1, except that the components of the Sendust magnetic powder matrix, calculated by mass percentage, include 7.5 wt % Si and 5.8 wt % Al, with the balance being Fe.

[0075] In the pickling activation step, the hydrochloric acid solution concentration is 8%, the ultrasonic power is 300W, and the ultrasonic treatment time is 20min;

[0076] In the heat treatment step, heat treatment was performed at 500°C in argon for 2 hours;

[0077] In the plasma activation step, the gas flow rate was 20 sccm and the chamber pressure was 100 Pa;

[0078] The coating agent comprises the following components by weight: 0.2 parts of phosphoric acid, 1 part of organic silicone resin, 0.6 parts of nano-boron nitride with a particle size of 100 nm, 0.3 parts of silane coupling agent ethanol solution with a concentration of 6 wt % of silane coupling agent, 0.3 parts of phosphate dispersant and 5 parts of isopropyl alcohol solvent;

[0079] The pre-treated powder and the coating agent were mixed in a ratio of 5:3; the mixture was stirred at a speed of 600 rpm for 30 minutes; the pre-treated powder mixed with the coating agent was then subjected to pre-curing and final curing treatments in sequence, with a pre-curing temperature of 118° C. and a pre-curing time of 1.5 hours; and a final curing temperature of 148° C. and a final curing time of 1.5 hours, to form a uniform insulating layer to obtain a coated powder;

[0080] After mixing the coated powder with the release agent, the mixture is pressed into shape at a pressing pressure of 2000 MPa to obtain a blank magnetic powder core; based on 100 parts of the coated powder, the amount of the release agent added is 0.5 parts, and the release agent is zinc stearate;

[0081] The blank magnetic powder core was heated to 800°C at a rate of 5°C / min under nitrogen protection and kept at that temperature for 90 minutes to obtain a Sendust magnetic powder core.

[0082] Example 3

[0083] The steps of Example 3 are the same as those of Example 1, except that the components of the Sendust magnetic powder matrix, calculated by mass percentage, include 8.5 wt % Si and 5.0 wt % Al, with the balance being Fe.

[0084] In the pickling activation step, the hydrochloric acid solution concentration is 12%, the ultrasonic power is 200W, and the ultrasonic treatment time is 30min;

[0085] In the heat treatment step, heat treatment was performed at 525°C in argon for 1.5 hours;

[0086] In the plasma activation step, the gas flow rate was 30 sccm and the chamber pressure was 50 Pa;

[0087] The coating agent comprises the following components by weight: 0.6 parts of phosphoric acid, 0.4 parts of organic silicone resin, 0.2 parts of nano-boron nitride with a particle size of 50 nm, 0.5 parts of silane coupling agent ethanol solution with a concentration of 6 wt % of silane coupling agent, 0.2 parts of phosphate dispersant and 8 parts of isopropyl alcohol solvent;

[0088] The pre-treated powder and the coating agent were mixed in a ratio of 5:3; the mixture was stirred at a speed of 500 rpm for 40 minutes; the pre-treated powder mixed with the coating agent was then subjected to pre-curing and final curing treatments in sequence, with a pre-curing temperature of 125° C. and a pre-curing time of 1 hour; and a final curing temperature of 155° C. and a final curing time of 1.5 hours, to form a uniform insulating layer to obtain a coated powder;

[0089] After mixing the coated powder with the release agent, the mixture is pressed into shape at a pressing pressure of 1900 MPa to obtain a blank magnetic powder core; based on 100 parts of the coated powder, the amount of the release agent added is 0.5 parts, and the release agent is zinc stearate;

[0090] The blank magnetic powder core was heated to 830°C at a rate of 5°C / min under nitrogen protection and kept at that temperature for 100 minutes to obtain a sendust magnetic powder core.

[0091] Comparative Example 1

[0092] The steps of Comparative Example 1 are basically the same as those of Example 1, except that the plasma activation step is omitted in step S1, and the pretreated powder after acid washing, activation and heat treatment is directly mixed with the coating agent and directly coated.

[0093] Comparative Example 2

[0094] The steps of Comparative Example 2 are the same as those of Example 1, except that no nano-boron nitride is added to the coating agent in step S2.

[0095] Comparative Example 3

[0096] The steps of Comparative Example 3 are the same as those of Example 1, except that the coating agent in step S2 uses epoxy resin instead of silicone resin.

[0097] According to the standard SJ20966-2006, the effective permeability, DC bias and loss performance of the Sendust magnetic powder cores obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were tested using a BH analyzer. The test results are shown in Table 1.

[0098] Table 1 - Test results

[0099]

[0100] By comparing Example 1 with Comparative Example 1, it can be seen that the loss is reduced by 29%. The plasma activation treatment can significantly improve the bonding strength of the coating layer, thereby reducing the loss.

[0101] By comparing Example 1 and Comparative Example 2, it can be seen that the DC bias performance is improved by 7%. After adding nano-boron nitride to the encapsulating agent, the insulation performance can be effectively enhanced.

[0102] By comparing Example 1 with Comparative Example 3, it can be seen that the loss is reduced by 40%, and the insulating coating performance of the silicone resin is better than that of the epoxy resin.

[0103] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are intended solely to illustrate the principles of the present invention and are not to be construed in any way as limiting the scope of protection of the present invention. Based on the explanations herein, those skilled in the art will be able to devise other specific embodiments of the present invention without inventive effort, and such equivalent variations or substitutions are intended to be encompassed within the scope of the claims of this application.

Claims

1. A wrapping method for reducing sendust core loss, characterized in that: The following steps are involved: S1: preheating and activating the sendust magnetic powder matrix, wherein the preheating and activation treatment includes pickling activation, heat treatment and plasma activation to obtain pretreated powder; S2: mixing the pretreated powder with the coating agent and stirring at a speed of 500-600 rpm for 30-40 minutes; then curing the pretreated powder mixed with the coating agent at 120-150° C. for 2-3 hours to form a uniform insulating layer to obtain a coated powder; The coating agent comprises the following components by weight: 0.2 to 0.6 parts of phosphoric acid, 0.4 to 1.0 parts of silicone resin, 0.2 to 0.6 parts of nano-boron nitride, 0.3 to 0.5 parts of silane coupling agent ethanol solution, 0.2 to 0.3 parts of phosphate dispersant and 5 to 8 parts of isopropyl alcohol solvent; S3: mixing the coated powder with a release agent, and pressing the mixture into a shape at a pressure of 1900 to 2100 MPa to obtain a blank magnetic powder core; S4: Under nitrogen protection, the blank magnetic powder core is heated to 750-830°C at a rate of 5°C / min and kept at this temperature for 60-100 minutes to obtain a Sendust magnetic powder core.

2. The wrapping method for reducing Sendust core loss according to claim 1, characterized in that: In step S2, the preparation of the coating agent includes the following steps: firstly, mixing nano-boron nitride with an ethanol solution of a silane coupling agent, stirring for 2 to 2.5 hours at 58 to 65° C., and centrifugally drying to obtain coupled nano-boron nitride; and then mixing the coupled nano-boron nitride with phosphoric acid, an organosilicon resin, a phosphate dispersant, and an isopropyl alcohol solvent.

3. The wrapping method for reducing Sendust core loss according to claim 1, characterized in that: The particle size of the nano boron nitride is 50-100 nm; the concentration of the silane coupling agent in the silane coupling agent ethanol solution is 4-6 wt %.

4. The wrapping method for reducing Sendust core loss according to claim 1, characterized in that: The mixing ratio of the pretreated powder to the coating agent is 5:(3-4).

5. The wrapping method for reducing Sendust core loss according to claim 1, characterized in that: In the step S1, the sendust magnetic powder matrix is sequentially subjected to pickling activation, heat treatment and plasma activation; The pickling activation step comprises: placing the sendust magnetic powder matrix in a hydrochloric acid solution for ultrasonic treatment for 20 to 30 minutes, then washing the sendust magnetic powder matrix with water, washing the sendust magnetic powder matrix with water until it is neutral, and vacuum drying to obtain an acid-washed sendust magnetic powder matrix; The heat treatment step comprises: placing the pickled Sendust magnetic powder matrix in an argon atmosphere, heating it to 500-550° C., keeping it warm for 1-2 hours, and cooling it to room temperature to obtain a heat-treated Sendust magnetic powder matrix; The plasma activation step comprises: placing the heat-treated Sendust magnetic powder matrix in a protective gas atmosphere for plasma treatment, with a plasma power of 300-400W and a plasma treatment time of 10-15 minutes.

6. The wrapping method for reducing Sendust core loss according to claim 5, characterized in that: In the pickling and activation step, the hydrochloric acid concentration is 8-12%, and the ultrasonic power in the ultrasonic treatment is 200-300W; In the plasma activation step, the protective gas is obtained by mixing argon and nitrogen, the mixing ratio of argon and nitrogen is 9:1, the gas flow rate is 20-30 sccm, and the chamber pressure is 50-100 Pa.

7. The wrapping method for reducing Sendust core loss according to claim 1, characterized in that: In step S2, the curing process includes a pre-curing stage and a final curing stage. In the pre-curing stage, the pre-curing temperature is 118-125°C and the pre-curing time is 1-1.5 hours; in the final curing stage, the final curing temperature is 148-155°C and the final curing time is 1-1.5 hours.

8. The wrapping method for reducing Sendust core loss according to claim 1, characterized in that: The components of the Sendust magnetic powder matrix, calculated by mass percentage, include 7.5-8.5 wt% Si and 5.0-5.8 wt% Al, with the remainder being Fe.

9. The wrapping method for reducing Sendust core loss according to claim 1, characterized in that: In step S4, the purity of nitrogen is ≥99.99% and the dew point is ≤-40°C.

10. A Sendust core, characterized in that: The Sendust core is prepared by the wrapping method for reducing Sendust core loss according to any one of claims 1 to 9.

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