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

Abstract

The invention discloses low-porosity high-insulation resistance magnetic powder and a preparation method and application thereof, and belongs to the technical field of soft magnetic composite materials. The preparation method comprises the following specific steps: mixing a phosphoric acid solution with a high hydrophilic-lipophilic balance value (HLBgt; 10) to serve as a phosphating solution; mixing the phosphating solution with the magnetic powder to obtain inorganic coated magnetic powder; mixing an organic resin-acetone solution with a surfactant to obtain an organic coating solution; mixing the organic coating liquid with the inorganic coating magnetic powder to obtain inorganic and organic double-coated magnetic powder, namely the low-porosity high-insulation resistance magnetic powder; and then the magnetic powder core is obtained through pressing, curing or heat treatment. According to the invention, a high hydrophilic-lipophilic balance value (HLBgt; the surface active agent (10) reduces the pores of the phosphate coating; and a soluble surfactant is added into the organic coating liquid, so that the insulating property and the bonding property of the organic coating are improved, and the low-porosity and high-insulation resistance soft magnetic composite material is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of soft magnetic composite materials, and more specifically, to a magnetic powder with low porosity and high insulation resistance, a preparation method thereof, and an application thereof. Background Art

[0002] Soft magnetic composite materials are composite materials composed of soft magnetic powders and insulating materials, mainly including a soft magnetic phase responsible for the basic inductance function and a non-magnetic phase for insulation between powders. Insulating coating is a key technology for soft magnetic composite materials and is also a research focus in academia and industry, including inorganic coating and organic coating. Insulating coating has two important functions in soft magnetic composite materials: (1) electrically insulating the metal magnetic powder to reduce eddy current loss; (2) bonding the powders to improve formability and the strength of the magnetic powder core. 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 will decompose when the temperature exceeds 300°C. Therefore, these two coating technologies each have their own advantages, and in industry, inorganic coating and organic coating are generally used complementarily, with inorganic coating first and then organic coating.

[0003] The inorganic coating layer is usually the first layer for surface insulation of magnetic powders. Inorganic coating includes phosphating coating, oxide coating, and other coatings. Phosphating technology has been developed for a long time in the fields of steel and other alloys. Its cost is low and the process is relatively simple, so it is also the most widely used in the field of magnetic powder cores.

[0004] The organic coating layer is the second layer for surface insulation of magnetic powders. Organic coating materials include thermoplastic resins and thermosetting resins. Most thermoplastic resins are plastic and can withstand harsh application environments. However, thermoplastic resins are insoluble in industrially acceptable solvents such as ethanol and acetone and cannot be uniformly coated on the surface of magnetic powders. In addition, some thermoplastic resins exhibit too high viscosity to be formed. In contrast, the process control of thermosetting resins is much easier, and it can greatly reduce the influence of high temperature on the magnetic properties and mechanical properties of soft magnetic composite materials. Therefore, currently, thermosetting resins are mainly used for organic coating.

[0005] Phosphating is usually carried out using a phosphoric acid - water / alcohol / acetone solution. During the phosphating process, phosphate nucleates and grows on the grain boundary surface, and a crystal layer of phosphate is rapidly formed. However, due to multi-point nucleation and inconsistent growth directions, a porous structure is formed. This structure essentially means that there are cracks and channels passing through the intergranular region to the metal matrix. In addition, due to the small particle size of magnetic powders (a few μm to dozens of μm), they are prone to agglomeration, and the contact between magnetic powders and the phosphating solution is insufficient. On the surface of some magnetic powders, phosphate crystals are not formed, while on the surface of some magnetic powders, over-phosphating occurs, and the generated crystals are too thick and irregular. All of these will affect the coating effect and insulation performance of soft magnetic composite materials.

[0006] The organic coating is carried out using a resin-acetone solution, and the resin is coated on the surface of the magnetic powder through mechanical stirring of the solution and the magnetic powder. Due to the agglomeration of the magnetic powder and the low wettability of the solution, an uneven resin layer with uncoated and over-coated parts will be formed. This will reduce the insulation performance and bonding performance of the soft magnetic composite material.

[0007] Therefore, improving the disadvantages existing in phosphating and organic coating in the prior art and providing a method for coating magnetic powder with low porosity and high insulation resistance are problems that those skilled in the art urgently need to solve. Summary of the Invention

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

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] First, the present invention provides a method for preparing a magnetic powder with low porosity and high insulation resistance, which specifically includes the following steps:

[0011] S1, Mix the phosphating solution with the magnetic powder and react to uniformly form a phosphating layer on the surface of the magnetic powder, then wash and dry to obtain an inorganic-coated magnetic powder; the phosphating solution is prepared by mixing a phosphoric acid solution and a surfactant;

[0012] S2, Mix the organic resin-acetone solution with the surfactant to obtain an organic coating solution;

[0013] S3, Mix the organic coating solution with the inorganic-coated magnetic powder and react to form a continuous and uniform resin coating layer on the surface of the inorganic-coated magnetic powder, then dry to obtain an inorganic-organic double-coated magnetic powder, which is the magnetic powder with low porosity and high insulation resistance.

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

[0015] The mass of phosphoric acid in the phosphoric acid solution is 0.01 wt.% to 10 wt.% of the mass of the magnetic powder, and the mass of the solvent is 10 wt.% to 100 wt.% of the mass of the magnetic powder;

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

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

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

[0019] Its beneficial effects are as follows: HLB is the hydrophilic-lipophilic balance value, which is an index to measure the relative strength of hydrophilic groups and lipophilic groups in surfactant molecules. The surfactant can prevent the agglomeration of magnetic powder, make it uniformly dispersed in the coating liquid, and improve the uniformity of coating. It can also reduce the surface tension of the coating liquid and improve the wettability of the coating liquid to the magnetic powder. From the perspective of wetting effect, when the wetting angle θ = 0°, the coating liquid can completely spread on the surface of the magnetic powder and can be completely wetted. At this time, the coating liquid can contact the surface of the magnetic powder to the greatest extent, forming a uniform and complete coating layer. When 0° < θ < 90°, the coating liquid can wet the surface of the magnetic powder well. As the angle increases, the wetting effect becomes worse, but a certain degree of coating can still be achieved, and the integrity and uniformity of the coating layer may be affected. When θ ≥ 90°, the coating liquid basically does not wet the surface of the magnetic powder, and the liquid is difficult to spread on the surface of the magnetic powder and form an effective coating. The coating liquid is easy to aggregate into droplets and cannot be evenly attached to the surface of the magnetic powder; from the perspective of the coating process, in the process of coating magnetic powder in the coating liquid, magnetic powder with a small wetting angle is easy to be wetted and dispersed by the coating liquid, which is beneficial to the full contact and reaction between the coating liquid and the magnetic powder, improving the coating efficiency and quality. Magnetic powder with a large wetting angle is easy to agglomerate in the coating liquid, resulting in difficulty for the coating liquid to contact the inside of the magnetic powder and affecting the coating effect.

[0020] Surfactants with high HLB have high hydrophilicity, can effectively increase the wettability of solvents (water / ethanol / acetone), thereby increasing the contact area between the phosphating solution and the magnetic powder, and can also avoid the agglomeration of magnetic powder, promote the formation of a uniform and dense phosphating layer, and reduce the pores of the phosphating layer. The BET adsorption curve proves that the micropores (pore diameter < 2nm) and mesopores (pore diameter 2 - 50nm) of the phosphating layer are significantly reduced after adding a surfactant with high HLB to the phosphating solution.

[0021] The magnetic powder in step S1 is one or a mixture of carbonyl iron powder, atomized iron powder, reduced iron powder, FeSi-based alloy powder, FeCo-based alloy powder, FeNi-based alloy powder, amorphous / nanocrystalline powder;

[0022] The conditions for the reaction are mechanical stirring or ultrasonic dispersion, the temperature is 10 - 100 °C, and the time is 20 - 180 min;

[0023] The cleaning is carried out by any one of water, ethanol, and acetone;

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

[0025] In the organic resin-acetone solution described in step S2, the organic resin is one or a mixture of epoxy resin, silicone resin, polyurethane, and phenolic resin;

[0026] In the organic resin-acetone solution, the mass of the organic resin is 1 wt.% to 10 wt.% of the mass of the magnetic powder, and the mass of the solvent is 10 wt.% to 100 wt.% of the mass of the magnetic powder;

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

[0028] The surfactant is any one of OP series emulsifiers, tx series emulsifiers, np series emulsifiers, Span series emulsifiers, and Arlacel series emulsifiers;

[0029] Its beneficial effects are as follows: The surfactant can not only prevent magnetic powder agglomeration but also increase the compatibility between the surface of the magnetic powder and the organic resin, uniformly coat the organic resin on the surface of the magnetic powder, and increase the insulation performance and bonding performance.

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

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

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

[0033] Thirdly, the present invention also provides an application of the low-porosity high-insulation-resistance magnetic powder. The low-porosity high-insulation-resistance magnetic powder is put into a mold, pressed and formed by a press, and cured or heat-treated to obtain a magnetic powder core.

[0034] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a low-porosity high-insulation-resistance magnetic powder, its preparation method and application, and its beneficial effects are as follows:

[0035] The present invention adds a surfactant with a high HLB (HLB > 10) 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 performance and bonding performance of the organic coating, and prepares a low-porosity high-insulation-resistance magnetic powder for the preparation of magnetic powder cores. Description of the Drawings

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0037] Figure 1 BET curves of the magnetic powder after inorganic coating in the comparative example and the embodiment. Specific embodiments

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0039] Example 1

[0040] (1) Mix the phosphating solution and carbonyl iron powder, mechanically stir for 30 min at a temperature of 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 phosphoric acid - aqueous solution with surfactant TritonX-100. The masses of phosphoric acid, water, and surfactant TritonX-100 are 0.5 wt.%, 40 wt.%, and 0.6 wt.% of the mass of the carbonyl iron powder, respectively.

[0042] (2) Mix the bisphenol A epoxy resin - acetone solution with surfactant OP-9 as the organic coating solution. The masses of bisphenol A epoxy resin, acetone, and surfactant OP-9 are 3 wt.%, 40 wt.%, and 0.6 wt.% of the mass of the carbonyl iron powder, respectively.

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

[0044] (4) Press the inorganic-organic double-coated magnetic powder into a ring with dimensions of 26.9 * 14.7 * 11.2 at 600 MPa and cure at 180 °C to make a magnetic powder core.

[0045] Example 2

[0046] (1) The phosphating solution and carbonyl iron powder are mixed and mechanically stirred for 30 minutes at a temperature of 25° C., and then the excess solution is washed off with water and dried at 120° C. for 60 minutes to obtain inorganic coated magnetic powder.

[0047] The phosphating solution is prepared by mixing a phosphoric acid-water solution with a surfactant TritonX-100, wherein the masses of phosphoric acid, water and the surfactant TritonX-100 are 0.5wt.%, 40wt.% and 1wt.% of the mass of the carbonyl iron powder respectively.

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

[0049] (3) The organic coating liquid and the inorganic coated magnetic powder are mixed, mechanically stirred for 30 minutes, a resin layer is coated on the surface of the inorganic coated magnetic powder, and dried at 70° C. for 60 minutes to obtain an inorganic and organic double coated magnetic powder.

[0050] (4) The inorganic and organic double-coated magnetic powder was pressed into a ring shape with a size of 26.9*14.7*11.2 at 600 MPa and cured at 180° C. to prepare a magnetic powder core.

[0051] Comparative Example 1

[0052] (1) The phosphating solution and carbonyl iron powder are mixed at a temperature of 25° C., and then the excess solution is washed off with water, and the mixture is dried at 120° C. for 60 min to obtain inorganic coated magnetic powder.

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

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

[0055] (3) The organic coating liquid and the inorganic coated magnetic powder are mixed, mechanically stirred for 30 minutes, a resin layer is coated on the surface of the inorganic coated magnetic powder, and dried at 70° C. for 60 minutes to obtain an inorganic and organic double coated magnetic powder.

[0056] (4) The inorganic and organic double-coated magnetic powder was pressed into a ring shape with a size of 26.9*14.7*11.2 at 600 MPa and cured at 180° C. to prepare a magnetic powder core.

[0057] Comparative Example 2

[0058] (1) The phosphating solution and carbonyl iron powder are mixed and mechanically stirred for 30 minutes at a temperature of 25° C., and then the excess solution is washed off with water and dried at 120° C. for 60 minutes to obtain inorganic coated magnetic powder.

[0059] The phosphating solution is prepared by mixing a phosphoric acid-water solution with a surfactant Triton X-100. The mass of phosphoric acid, water and the surfactant Triton X-100 are 0.5wt.%, 40wt.% and 0.6wt.% of the mass of the carbonyl iron powder respectively.

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

[0061] (3) The organic coating liquid and the inorganic coated magnetic powder are mixed, mechanically stirred for 30 minutes, a resin layer is coated on the surface of the inorganic coated magnetic powder, and dried at 70° C. for 60 minutes to obtain an inorganic and organic double coated magnetic powder.

[0062] (4) The inorganic and organic double-coated magnetic powder was pressed into a ring shape with a size of 26.9*14.7*11.2 at 600 MPa and cured at 180° C. to prepare a magnetic powder core.

[0063] Comparative Example 3

[0064] (1) The phosphating solution and carbonyl iron powder are mixed and mechanically stirred for 30 minutes at a temperature of 25° C., and then the excess solution is washed off with water and dried at 120° C. for 60 minutes to obtain inorganic coated magnetic powder.

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

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

[0067] (3) The organic coating liquid and the inorganic coated magnetic powder are mixed, mechanically stirred for 30 minutes, a resin layer is coated on the surface of the inorganic coated magnetic powder, and dried at 70° C. for 60 minutes to obtain an inorganic and organic double coated magnetic powder.

[0068] (5) The inorganic and organic double-coated magnetic powder was pressed into a ring shape with a size of 26.9*14.7*11.2 at 600 MPa and cured at 180°C to prepare a magnetic powder core.

[0069] Performance Testing

[0070] The nitrogen isothermal adsorption and desorption (BET) tests were carried out on the magnetically powdered materials after inorganic coating in the examples and comparative examples, and the results are shown in Figure 1 , the nitrogen isothermal adsorption curves of Example 1, Example 2 and Comparative Example 2 are type III isothermal curves. In the low relative pressure region (P / P0≤0.05), there is no inflection point B for all samples, indicating that the monolayer adsorption will not saturate and there are no micropores (pore diameter <2nm). In the multilayer adsorption region (0.1≤P / P0≤0.8), the adsorption amounts of Example 1 and Comparative Example 2 only increase slightly, indicating that there are few mesopores (2nm < pore diameter < 50nm). The adsorption amount of Example 2 hardly increases, indicating that there are no mesopores. The nitrogen isothermal adsorption curves of Comparative Example 1 and Comparative Example 3 are type II isothermal curves, and the adsorption amounts increase more, indicating that there are more micropores and mesopores. In summary, adding surfactant Triton X-100 to the phosphating solution can effectively reduce the porosity of the phosphating layer.

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

[0072]

[0073]

[0074] It can be seen from the data in the table that the insulation resistance and magnetic breakage strength of Comparative Example 1 and Comparative Example 2 (without adding surfactant OP-9 in the organic coating solution) are very low. The insulation resistance and magnetic core breakage strength of Example 1 and Comparative Example 3 (adding 0.6wt.% surfactant OP-9 in the organic coating solution) increase, and the insulation resistance and magnetic core breakage strength of Example 2 (adding 1wt.% surfactant OP-9 in the organic coating solution) are the highest. It shows that adding surfactant OP-9 to the organic coating solution can effectively increase the insulation resistance and magnetic core breakage strength of the magnetic powder core.

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

Claims

1. A method for preparing a magnetic powder with low porosity and high insulation resistance, characterized in that, Specifically, it includes the following steps: S1. Mix the phosphating solution with magnetic powder and react to uniformly form a phosphating layer on the surface of the magnetic powder, then wash and dry to obtain inorganic-coated magnetic powder; the phosphating solution is prepared by mixing a phosphoric acid solution and a surfactant; S2. Mix the organic resin-acetone solution with a surfactant to obtain an organic coating solution; S3. Mix the organic coating solution with the inorganic-coated magnetic powder and react to form a continuous and uniform resin coating layer on the surface of the inorganic-coated magnetic powder, then dry to obtain inorganic-organic double-coated magnetic powder, which is the low-porosity and high-insulation-resistance magnetic powder.

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

3. The preparation method of a kind of magnetic powder with low porosity and high insulation resistance according to claim 1, characterized in that, In step S1, the surfactant is a surfactant with HLB > 10; In the phosphating solution, the mass of the surfactant is 0.1 wt.% - 10 wt.% of the mass of the magnetic powder.

4. The preparation method of a magnetic powder with low porosity and high insulation resistance according to claim 3, characterized in that, The surfactant is preferably any one of OP series emulsifiers, TX series emulsifiers, and NP series emulsifiers with HLB > 10.

5. The preparation method of a low-porosity and high-insulation-resistance magnetic powder according to claim 1, wherein, In step S1, the magnetic powder is one or a mixture of several of carbonyl iron powder, atomized iron powder, reduced iron powder, FeSi-based alloy powder, FeCo-based alloy powder, FeNi-based alloy powder, amorphous / nanocrystalline powder; The reaction conditions are mechanical stirring or ultrasonic dispersion, the temperature is 10 - 100 °C, and the time is 20 - 180 min; The washing is carried out with any one of water, ethanol, and acetone; The drying temperature is 60 - 150 °C, and the time is 30 - 120 min.

6. The preparation method of a kind of magnetic powder with low porosity and high insulation resistance according to claim 1, characterized in that, In step S2, the organic resin in the organic resin-acetone solution is one or a mixture of several of epoxy resin, silicone resin, polyurethane, and phenolic resin; In the organic resin-acetone solution, the mass of the organic resin is 1 wt.% - 10 wt.% of the mass of the magnetic powder, and the mass of the solvent is 10 wt.% - 100 wt.% of the mass of the magnetic powder; In the organic coating solution, the mass of the surfactant is 0.1 wt.% - 10 wt.% of the mass of the magnetic powder, The surfactant is any one of OP series emulsifiers, tx series emulsifiers, np series emulsifiers, Span series emulsifiers, and Arlacel series emulsifiers.

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

8. A low-porosity and high-insulation-resistance magnetic powder prepared by the method according to any one of claims 1 - 7.

9. Use of a low-porosity and high-insulation-resistance magnetic powder prepared by the method as described in claim 1 or the low-porosity and high-insulation-resistance magnetic powder as described in claim 8, characterized in that, Put the low-porosity and high-insulation-resistance magnetic powder into a mold, press and form it through a press, and cure or heat-treat it to obtain a magnetic powder core.

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