Low porosity high insulation resistance magnetic powder, and preparation method and application thereof

Abstract

The application discloses a kind of low porosity high insulation resistance magnetic powder and preparation method and application thereof, belong to soft magnetic composite material technical field.The specific preparation steps are as follows: phosphoric acid solution is mixed with high hydrophilic-lipophilic balance (HLB>10) surfactant, as phosphating solution;Phosphating solution and magnetic powder are mixed, to obtain inorganic coated magnetic powder;Organic resin-acetone solution is mixed with surfactant, as organic coating liquid;Organic coating liquid is mixed with inorganic coated magnetic powder, to obtain inorganic organic double-coated magnetic powder, it is low porosity high insulation resistance magnetic powder;Then by pressing, solidification or heat treatment, to obtain magnetic powder core.The application adds high hydrophilic-lipophilic balance (HLB>10) surfactant in inorganic coated phosphating solution, reduces the porosity of phosphating layer;And soluble surfactant is added in organic coating liquid, increases the insulation performance and bonding performance of organic coating, and prepares a kind of low porosity high insulation resistance soft magnetic composite material.

Description

Technical Field

[0001] This invention relates to the field of soft magnetic composite materials technology, and more specifically to a low-porosity, high-insulation-resistance magnetic powder, its preparation method, and its application. Background Technology

[0002] Soft magnetic composite materials are composite materials composed of soft magnetic powder and insulating materials, mainly including a soft magnetic phase responsible for basic inductance and a non-magnetic phase used for inter-powder insulation. Insulation coating is a key technology of soft magnetic composite materials and a research focus of academia and industry, including inorganic coating and organic coating. Insulation coating plays two important roles in soft magnetic composite materials: (1) to electrically insulate the metal magnetic powder and reduce eddy current losses; (2) to bind the powder and improve formability and core strength. The advantages of inorganic coating are high insulation, high temperature stability and high heat resistance, and it can withstand long-term high-temperature annealing. Organic coating has good insulation and excellent formability, but most organic resins decompose above 300°C. Therefore, these two coating technologies each have their advantages. In industry, inorganic coating and organic coating are generally used simultaneously for complementarity, with inorganic coating performed first and then organic coating performed.

[0003] Inorganic coatings are typically used as the first insulating layer on the surface of magnetic powder. Inorganic coatings include phosphating, oxide, and other coatings. Phosphating technology has been developed for a long time in the steel and other alloy industries due to its low cost and simple process, and is therefore the most widely used in the field of magnetic powder cores.

[0004] Organic coatings serve as a second insulating layer on the surface of magnetic powder. Organic coating materials include thermoplastic and thermosetting resins. Most thermoplastic resins are malleable and can withstand harsh application environments. However, thermoplastic resins are insoluble in industrially acceptable solvents such as ethanol and acetone, and cannot uniformly coat the magnetic powder surface. Furthermore, some thermoplastic resins exhibit excessively high viscosity, making them unsuitable for molding. In contrast, thermosetting resins are much easier to process and can significantly reduce the impact of high temperatures on the magnetic and mechanical properties of soft magnetic composites. Therefore, thermosetting resins are currently the primary choice for organic coatings.

[0005] Phosphating is typically performed using a phosphoric acid-water / alcohol / acetone solution. During phosphating, phosphate nucleates and grows at the grain boundary surface, rapidly forming a phosphate crystal layer. However, due to multi-point nucleation and inconsistent growth directions, a porous structure is formed. This structure essentially implies the existence of cracks and channels penetrating the intergranular region to the metal matrix. Furthermore, because the magnetic powder has a small particle size (a few μm to tens of μm), it is prone to agglomeration. Insufficient contact between the magnetic powder and the phosphating solution results in some magnetic powder surfaces failing to form phosphate crystals, while others are over-phosphated, leading to excessively thick and irregular crystals. All of these factors affect the coating effect and insulation performance of the soft magnetic composite material.

[0006] Organic coating is performed using a resin-acetone solution, where the resin is coated onto the surface of the magnetic powder through mechanical stirring of the solution. Due to the agglomeration of the magnetic powder and the low wettability of the solution, uneven resin layers, including uncoated and over-coated layers, are formed. This reduces the insulation and adhesion properties of the soft magnetic composite material.

[0007] Therefore, improving upon the shortcomings of phosphating and organic coating in the prior art, and providing a magnetic powder coating method with low porosity and high insulation resistance is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] In view of this, the present invention provides a low-porosity, high-insulation-resistance magnetic powder, its preparation method, and its application. By adding a surfactant with a high hydrophilic-lipophilic balance value (HLB>10) to the inorganic coating phosphating solution, the porosity of the phosphating layer is reduced; and by adding a soluble surfactant to the organic coating solution, the insulation and bonding properties of the organic coating are increased, thus preparing a low-porosity, high-insulation-resistance magnetic powder.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] First, this invention provides a method for preparing low-porosity, high-insulation-resistance magnetic powder, specifically including the following steps:

[0011] S1, the phosphating solution is mixed with magnetic powder and reacted to form a uniform phosphating layer on the surface of the magnetic powder. Then, the powder is washed and dried to obtain inorganic coated magnetic powder. The phosphating solution is prepared by mixing phosphoric acid solution with a surfactant.

[0012] S2, an organic coating solution is prepared by mixing an organic resin-acetone solution with a surfactant;

[0013] S3, the organic coating liquid is mixed with the inorganic coating magnetic powder and reacted to form a continuous and uniform resin coating layer on the surface of the inorganic coating magnetic powder. Then it is dried to obtain inorganic and organic double-coated magnetic powder, which is the low porosity and high insulation resistance magnetic powder.

[0014] The solvent for the phosphoric acid solution in step S1 is any one of water, ethanol, or acetone;

[0015] The phosphoric acid solution contains phosphoric acid at a mass of 0.01 wt.% to 10 wt.% of the magnetic powder mass, and the solvent at a mass of 10 wt.% to 100 wt.% of the magnetic powder mass.

[0016] The surfactant mentioned in step S1 is a surfactant with HLB > 10;

[0017] The surfactant in the phosphating solution is 0.1 wt.% to 10 wt.% of the magnetic powder mass;

[0018] The surfactant is preferably any one of the OP series emulsifiers, TX series emulsifiers, or NP series emulsifiers with HLB > 10.

[0019] Its beneficial effects are as follows: HLB (Hydrophilic-lipophilic balance) is an indicator that measures the relative strength of hydrophilic and lipophilic groups in a surfactant molecule. Surfactants can prevent magnetic powder agglomeration, ensuring uniform dispersion in the coating solution and improving coating uniformity. They can also reduce the surface tension of the coating solution, improving its wettability on the magnetic powder. From a wetting effect perspective, when the wetting angle θ = 0°, the coating solution can completely spread and wet the magnetic powder surface, achieving maximum contact and forming a uniform and complete coating layer. When 0° < θ < 90°, the coating solution can effectively wet the magnetic powder surface; as the angle increases, the wetting effect deteriorates, but a certain degree of coating can still be achieved, although the integrity and uniformity of the coating layer may be affected. When θ ≥ 90°, the coating solution barely wets the magnetic powder surface, making it difficult for the liquid to spread and form an effective coating. The coating solution tends to agglomerate into droplets, failing to adhere evenly to the magnetic powder surface. From a coating process perspective, in the coating process where magnetic powder is coated in a coating solution, magnetic powder with a small wetting angle is easily wetted and dispersed by the coating solution, which facilitates sufficient contact and reaction between the coating solution and the magnetic powder, improving coating efficiency and quality. Magnetic powder with a large wetting angle tends to agglomerate in the coating solution, making it difficult for the coating solution to reach the interior of the magnetic powder, thus affecting the coating effect.

[0020] High-HLB surfactants possess high hydrophilicity, effectively increasing the wettability of solvents (water / ethanol / acetone), thereby increasing the contact area between the phosphating solution and magnetic powder. This also prevents magnetic powder agglomeration, promoting the formation of a uniform and dense phosphating layer and reducing its porosity. BET adsorption curves demonstrate that the addition of high-HLB surfactants to the phosphating solution significantly reduces the micropores (pore size <2 nm) and mesopores (pore size 2–50 nm) of the phosphating layer.

[0021] The magnetic powder mentioned in step S1 is one or a mixture of several of the following: carbonyl iron powder, atomized iron powder, reduced iron powder, FeSi-based alloy powder, FeCo-based alloy powder, FeNi-based alloy powder, and amorphous / nanocrystalline powder.

[0022] The reaction conditions are mechanical stirring or ultrasonic dispersion, temperature of 10–100℃, and time of 20–180 min;

[0023] The cleaning process involves using water, ethanol, or acetone.

[0024] The drying temperature is 60–150°C, and the time is 30–120 min;

[0025] The organic resin in the organic resin-acetone solution mentioned in step S2 is one or a mixture of several of epoxy resin, silicone resin, polyurethane, and phenolic resin.

[0026] The organic resin in the organic resin-acetone solution has a mass of 1 wt.% to 10 wt.% of the magnetic powder mass, and the solvent has a mass of 10 wt.% to 100 wt.% of the magnetic powder mass.

[0027] The surfactant in the organic coating solution is 0.1 wt.% to 10 wt.% of the magnetic powder mass;

[0028] The surfactant is any one of the following: OP series emulsifiers, TX series emulsifiers, NP series emulsifiers, Span series emulsifiers, and Arlacel series emulsifiers;

[0029] Its beneficial effects are: surfactants can prevent magnetic powder from agglomerating and increase the compatibility between the magnetic powder surface and organic resin, uniformly coating the magnetic powder surface with organic resin, thereby increasing insulation and adhesion properties.

[0030] The reaction conditions described in step S3 are mechanical stirring or ultrasonic dispersion, and the time is 20 to 180 min;

[0031] The drying temperature is 50–90°C, and the drying time is 30–120 min.

[0032] Secondly, the present invention also provides a low-porosity, high-insulation-resistance magnetic powder prepared by the method described above.

[0033] Furthermore, the present invention also provides the application of the low porosity, high insulation resistance magnetic powder, wherein the low porosity, high insulation resistance magnetic powder is placed into a mold, pressed into shape by a press, and cured or heat-treated to obtain a magnetic powder core.

[0034] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a low-porosity, high-insulation-resistance magnetic powder, its preparation method, and its application, with the following beneficial effects:

[0035] This invention adds a high HLB (HLB>10) surfactant to the inorganic coating phosphating solution to reduce the porosity of the phosphating layer; and adds a soluble surfactant to the organic coating solution to increase the insulation and bonding properties of the organic coating, thus preparing a magnetic powder with low porosity and high insulation resistance for use in the preparation of magnetic powder cores. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0037] Figure 1 BET curves of inorganic-coated magnetic powder in comparative examples and embodiments. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] (1) Mix the phosphating solution and carbonyl iron powder, stir mechanically for 30 min at 25°C, then wash off the excess solution with water, and dry at 120°C for 60 min to obtain inorganic coated magnetic powder.

[0041] The phosphating solution is prepared by mixing an aqueous phosphoric acid solution with a surfactant Triton X-100, wherein the mass percentages of phosphoric acid, water, and surfactant Triton X-100 are 0.5 wt.%, 40 wt.%, and 0.6 wt.%, respectively, based on the mass percentage of the carbonyl iron powder.

[0042] (2) A bisphenol A epoxy resin-acetone solution was mixed with surfactant OP-9 to form an organic coating solution. The mass percentages of bisphenol A epoxy resin, acetone, and surfactant OP-9 were 3 wt.%, 40 wt.%, and 0.6 wt.%, respectively, based on the mass of carbonyl iron powder.

[0043] (3) Mix the organic coating liquid with the inorganic coating magnetic powder, stir mechanically for 30 min, coat the surface of the inorganic coating magnetic powder with a resin layer, and dry at 70°C for 60 min to obtain inorganic and organic double-coated magnetic powder.

[0044] (4) The inorganic-organic double-coated magnetic powder is pressed into a ring with a size of 26.9*14.7*11.2 by 600MPa and cured at 180℃ to make a magnetic powder core.

[0045] Example 2

[0046] (1) Mix the phosphating solution and carbonyl iron powder, stir mechanically for 30 min at 25°C, then wash off the excess solution with water, and dry at 120°C for 60 min to obtain inorganic coated magnetic powder.

[0047] The phosphating solution was prepared by mixing an aqueous solution of phosphoric acid with a surfactant, Triton X-100. The mass percentages of phosphoric acid, water, and surfactant Triton X-100 were 0.5 wt.%, 40 wt.%, and 1 wt.%, respectively, based on the mass of the carbonyl iron powder.

[0048] (2) A bisphenol A epoxy resin-acetone solution was mixed with 0.6 wt% surfactant OP-9 to form an organic coating solution. The mass percentages of bisphenol A epoxy resin, acetone, and surfactant OP-9 were 3 wt.%, 40 wt.%, and 1 wt.%, respectively, of the carbonyl iron powder.

[0049] (3) Mix the organic coating liquid with the inorganic coating magnetic powder, stir mechanically for 30 min, coat the surface of the inorganic coating magnetic powder with a resin layer, and dry at 70°C for 60 min to obtain inorganic and organic double-coated magnetic powder.

[0050] (4) The inorganic-organic double-coated magnetic powder is pressed into a ring with a size of 26.9*14.7*11.2 by 600MPa and cured at 180℃ to make a magnetic powder core.

[0051] Comparative Example 1

[0052] (1) Mix the phosphating solution and carbonyl iron powder at 25°C, then wash away the excess solution with water, and dry at 120°C for 60 min to obtain inorganic coated magnetic powder.

[0053] The phosphating solution is a 0.5 wt% phosphoric acid-water solution, where the mass of phosphoric acid and water is 0.5 wt.% and 40 wt.% of the mass of carbonyl iron powder, respectively.

[0054] (2) A bisphenol A epoxy resin-acetone solution was used as the organic coating solution. The mass percentages of the bisphenol A epoxy resin and acetone were 3 wt.% and 40 wt.% of the carbonyl iron powder, respectively.

[0055] (3) Mix the organic coating liquid with the inorganic coating magnetic powder, stir mechanically for 30 min, coat the surface of the inorganic coating magnetic powder with a resin layer, and dry at 70°C for 60 min to obtain inorganic and organic double-coated magnetic powder.

[0056] (4) The inorganic-organic double-coated magnetic powder is pressed into a ring with a size of 26.9*14.7*11.2 by 600MPa and cured at 180℃ to make a magnetic powder core.

[0057] Comparative Example 2

[0058] (1) Mix the phosphating solution and carbonyl iron powder, stir mechanically for 30 min at 25°C, then wash off the excess solution with water, and dry at 120°C for 60 min to obtain inorganic coated magnetic powder.

[0059] The phosphating solution was prepared by mixing an aqueous solution of phosphoric acid with the surfactant Triton X-100. The mass percentages of phosphoric acid, water, and surfactant Triton X-100 were 0.5 wt.%, 40 wt.%, and 0.6 wt.%, respectively, based on the mass of the carbonyl iron powder.

[0060] (2) A bisphenol A epoxy resin-acetone solution was used as the organic coating solution. The mass percentages of the bisphenol A epoxy resin and acetone were 3 wt.% and 40 wt.% of the carbonyl iron powder, respectively.

[0061] (3) Mix the organic coating liquid with the inorganic coating magnetic powder, stir mechanically for 30 min, coat the surface of the inorganic coating magnetic powder with a resin layer, and dry at 70°C for 60 min to obtain inorganic and organic double-coated magnetic powder.

[0062] (4) The inorganic-organic double-coated magnetic powder is pressed into a ring with a size of 26.9*14.7*11.2 by 600MPa and cured at 180℃ to make a magnetic powder core.

[0063] Comparative Example 3

[0064] (1) Mix the phosphating solution and carbonyl iron powder, stir mechanically for 30 min at 25°C, then wash off the excess solution with water, and dry at 120°C for 60 min to obtain inorganic coated magnetic powder.

[0065] The phosphating solution is a 0.5 wt% phosphoric acid-water solution, where the mass of phosphoric acid and water is 0.5 wt.% and 40 wt.% of the mass of the carbonyl iron powder, respectively.

[0066] (2) A bisphenol A epoxy resin-acetone solution was mixed with surfactant OP-9 to form an organic coating solution. The mass percentages of bisphenol A epoxy resin, acetone, and surfactant OP-9 were 3 wt.%, 40 wt.%, and 0.6 wt.%, respectively, based on the mass of carbonyl iron powder.

[0067] (3) Mix the organic coating liquid with the inorganic coating magnetic powder, stir mechanically for 30 min, coat the surface of the inorganic coating magnetic powder with a resin layer, and dry at 70°C for 60 min to obtain inorganic and organic double-coated magnetic powder.

[0068] (5) The inorganic-organic double-coated magnetic powder is pressed into a ring with a size of 26.9*14.7*11.2 by 600MPa and cured at 180℃ to make a magnetic powder core.

[0069] Performance testing

[0070] The inorganic-coated magnetic powders of the examples and comparative examples were subjected to nitrogen isothermal adsorption-desorption (BET) tests, and the results are shown in the figure. Figure 1 The nitrogen isotherm adsorption curves of Examples 1, 2, and Comparative Example 2 are Type III isotherms. In the low relative pressure region (P / P0≤0.05), none of the samples showed an inflection point B, indicating that monolayer adsorption is not saturated and micropores (pore size <2nm) are absent. In the multilayer adsorption region (0.1≤P / P0≤0.8), the adsorption amounts of Examples 1 and Comparative Example 2 only increased slightly, indicating very few mesopores (2nm<pore size<50nm). The adsorption amount of Example 2 showed almost no increase, indicating the absence of mesopores. The nitrogen isotherm adsorption curves of Comparative Examples 1 and 3 are Type II isotherms, with a significant increase in adsorption amount, indicating the presence of numerous micropores and mesopores. In conclusion, the addition of the surfactant Triton X-100 to the phosphating solution can effectively reduce the porosity of the phosphating layer.

[0071] Furthermore, the insulation resistance and core fracture strength of the prepared magnetic powder core were tested, and the results are shown in the table below.

[0072]

[0073]

[0074] The data in the table show that Comparative Examples 1 and 2 (organic coating solution without added surfactant OP-9) have very low insulation resistance and magnetic core fracture strength. Examples 1 and 3 (organic coating solution with added 0.6 wt.% surfactant OP-9) show increased insulation resistance and core fracture strength, while Example 2 (organic coating solution with added 1 wt.% surfactant OP-9) exhibits the highest insulation resistance and core fracture strength. This indicates that adding surfactant OP-9 to the organic coating solution can effectively increase the insulation resistance and core fracture strength of the magnetic powder core.

[0075] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a low-porosity, high-insulation-resistance magnetic powder, characterized in that, Specifically, the following steps are included: S1, the phosphating solution is mixed with magnetic powder and reacted to form a uniform phosphating layer on the surface of the magnetic powder. The mixture is then washed and dried to obtain inorganic coated magnetic powder. The phosphating solution is prepared by mixing a phosphoric acid solution with a surfactant, wherein the surfactant is any one of the OP series emulsifiers, TX series emulsifiers, or NP series emulsifiers with HLB > 10, and the mass of the surfactant is 0.1 wt.%~10 wt.% of the magnetic powder mass. S2, an organic coating solution is prepared by mixing an organic resin-acetone solution with a surfactant, wherein the surfactant is any one of the following: OP series emulsifiers, TX series emulsifiers, NP series emulsifiers, Span series emulsifiers, and Arlacel series emulsifiers, and the mass of the surfactant is 0.1 wt.%~10 wt.% of the magnetic powder mass. S3, the organic coating liquid is mixed with the inorganic coating magnetic powder and reacted to form a continuous and uniform resin coating layer on the surface of the inorganic coating magnetic powder. Then it is dried to obtain inorganic and organic double-coated magnetic powder, which is the low porosity and high insulation resistance magnetic powder.

2. The method for preparing a low-porosity, high-insulation-resistance magnetic powder according to claim 1, characterized in that, The solvent for the phosphoric acid solution in step S1 is any one of water, ethanol, or acetone; The phosphoric acid solution contains phosphoric acid at a mass of 0.01 wt.% to 10 wt.% of the magnetic powder mass, and the solvent at a mass of 10 wt.% to 100 wt.% of the magnetic powder mass.

3. The method for preparing a low-porosity, high-insulation-resistance magnetic powder according to claim 1, characterized in that, The magnetic powder mentioned in step S1 is one or a mixture of several of the following: carbonyl iron powder, atomized iron powder, reduced iron powder, FeSi-based alloy powder, FeCo-based alloy powder, FeNi-based alloy powder, and amorphous / nanocrystalline powder. The reaction conditions are mechanical stirring or ultrasonic dispersion, temperature of 10~100℃, and time of 20~180min; The cleaning process involves using water, ethanol, or acetone. The drying temperature is 60~150℃ and the time is 30~120min.

4. The method for preparing a low-porosity, high-insulation-resistance magnetic powder according to claim 1, characterized in that, The organic resin in the organic resin-acetone solution mentioned in step S2 is one or a mixture of several of epoxy resin, silicone resin, polyurethane, and phenolic resin. The organic resin in the organic resin-acetone solution has a mass of 1 wt.% to 10 wt.% of the magnetic powder mass, and the solvent has a mass of 10 wt.% to 100 wt.% of the magnetic powder mass.

5. The method for preparing a low-porosity, high-insulation-resistance magnetic powder according to claim 1, characterized in that, The reaction conditions in step S3 are mechanical stirring or ultrasonic dispersion for 20-180 min; the drying temperature is 50-90℃ and the drying time is 30-120 min.

6. A low-porosity, high-insulation-resistance magnetic powder prepared by the method according to any one of claims 1-5.

7. The application of a low-porosity, high-insulation-resistance magnetic powder prepared by the method described in claim 1 or the low-porosity, high-insulation-resistance magnetic powder described in claim 6, characterized in that, The low-porosity, high-insulation-resistance magnetic powder is placed into a mold, pressed into shape by a press, and then cured or heat-treated to obtain a magnetic powder core.

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