Preparation of epoxy binder coated modified magnetic powder

Abstract

The invention discloses preparation of epoxy binder coated modified magnetic powder, which comprises 90-95 wt% of modified magnetic powder and 5-10 wt% of epoxy binder, the epoxy binder is uniformly diluted by using butanone as a diluent, the volume ratio of butanone to epoxy binder is 10-20, after uniform stirring and mixing, the modified magnetic powder is added, stirring and mixing are continued, the stirring temperature is controlled at 50-60 DEG C, stirring is carried out for 2-4 hours, and the epoxy binder coated modified magnetic powder is obtained. According to the preparation method disclosed by the invention, the magnetic powder is modified by the coupling agent in a two-step method, so that the modified magnetic powder and the porous structure of the porous chitosan fine powder are well combined and fixed, and the magnetic powder which is less in agglomeration, good in dispersity and good in insulation effect is obtained; therefore, the purpose of production and use of the inductor is achieved, and the product obtained through the method is high in resistivity and low in loss.

Description

Technical Field

[0001] The present invention relates to the field of magnetic core materials, and in particular to the preparation of epoxy binder-coated modified magnetic powder. Background Art

[0002] During the production process of an integrally molded inductor, a winding body is embedded in a metal magnetic powder and die-cast. To improve the bonding properties of the metal magnetic powder, an inorganic or organic binder is added to the metal magnetic powder to ensure that the metallic powder is compacted and bonded together. In existing integral die-casting technology, magnetic powder is dispersed in a binder and die-cast. However, this method has the following problems: conventional magnetic powder has a higher density than organic binders and is prone to sedimentation and agglomeration, resulting in poor dispersibility. Even when the magnetic powder and binder are prepared and used immediately, the magnetic powder will precipitate or agglomerate during the die-casting process, causing uneven dispersion of the magnetic powder. The binder cannot effectively wrap the magnetic powder to achieve the purpose of insulating and bonding the magnetic powder. As a result, the resistivity of the magnetic powder core obtained after die-casting is too low, resulting in large eddy current losses, especially at high frequencies. Therefore, it is necessary to modify the magnetic powder to obtain magnetic powder with less agglomeration, good dispersion, and good insulation effect. Moreover, this magnetic powder can achieve a better bonding effect when bonded with the binder, which is the problem solved by the present invention, thereby meeting the purpose of inductor production and use. Summary of the Invention

[0003] In response to the above problems, the present invention proposes a method for preparing epoxy binder-coated modified magnetic powder. By modifying the magnetic powder, highly dispersible modified magnetic powder is obtained, and the modified magnetic powder is coated with an epoxy resin binder, so that the modified magnetic powder has a good dispersion effect, and the epoxy resin binder completely coats the modified magnetic powder, thereby achieving the purpose of meeting the use of the inductor.

[0004] To achieve the above-mentioned purpose, the embodiment of the present invention adopts the following technical solutions: A method for preparing epoxy binder-coated modified magnetic powder comprises: preparing 90-95 wt% of modified magnetic powder and 5-10 wt% of epoxy binder; the epoxy binder is evenly diluted with butanone as a diluent; the volume ratio of butanone to epoxy binder is 10-20; after stirring and mixing evenly, the modified magnetic powder is added; the stirring and mixing is continued while controlling the stirring temperature at 50-60° C. for 2-4 hours; and filtering through a 300-500 mesh nylon sieve to obtain the epoxy binder-coated modified magnetic powder; Wherein, the modified magnetic powder is prepared by the following steps: S1: adding the magnetic powder to anhydrous ethanol solvent, ultrasonically washing, filtering and drying to obtain anhydrous ethanol-washed magnetic powder A; S2: adding a first coupling agent in anhydrous ethanol at a mass ratio of 0.5-2 wt% of magnetic powder A to magnetic powder A in a 1:1 ratio, and mixing to obtain a first modified solution; S3: adding a second coupling agent in anhydrous ethanol at a mass ratio of 0.5-2 wt% of magnetic powder A to magnetic powder A in a 1:1 ratio, and mixing to obtain a second modified solution; S4: Place the magnetic powder A on a slow roller and slowly roll it, add the first modifying liquid, and roll it for 2 to 8 hours. After mixing evenly, add the second modifying liquid and continue rolling for 2 to 8 hours. The rolling speed of the slow roller is 1 to 3 rpm. After the second modifying liquid is completely mixed, separate the magnetic powder A from the mixed slurry through a 1000 to 2500 mesh nylon sieve, and vacuum dry it at 80 to 90°C to constant weight to obtain magnetic powder surface treated with a coupling agent; S5: Magnetic powder surface treated with a coupling agent is mixed with porous chitosan fine powder in a mass ratio of 1:0.25~0.45, and anhydrous ethanol is used as the solvent. The oil bath is heated to 60~80°C, and the anhydrous ethanol is refluxed. After stirring and mixing under ultrasonic conditions for 2~4 hours, a cross-linking agent is slowly added, and stirring and mixing is continued under ultrasonic conditions for 2~4 hours to obtain a composite of porous chitosan-coated modified magnetic powder. The composite is separated from the mixed solution by a 500~800 mesh nylon sieve, and vacuum dried at 80~90°C to constant weight to obtain modified magnetic powder.

[0005] Furthermore, the magnetic powder is one or more of Mn-Zn ferrite, Ni-Zn ferrite, Fe-Si alloy, and Fe-Ni alloy.

[0006] Furthermore, the magnetic powder has a particle size of 2-4 μm.

[0007] Furthermore, in S2, the first coupling agent is a titanate coupling agent, and the titanate coupling agent is one or more of isopropyl tri(dioctyl pyrophosphate) titanate, isopropyl tri(dodecylbenzenesulfonyl) titanate, and isopropyl trioleyl titanate.

[0008] Furthermore, in S3, the second coupling agent is a silane coupling agent containing an amino group, and the silane coupling agent is one or more of KH550, KH540, KH553, KH554, and KH990.

[0009] Furthermore, in S5, the cross-linking agent is one or both of glutaraldehyde and epichlorohydrin.

[0010] Furthermore, in S5, the porous chitosan powder is prepared by the following steps: Chitosan with a deacetylation degree of 90-95% is dissolved in a 1-2 wt% acetic acid aqueous solution and stirred until completely dissolved to form a uniform chitosan acetic acid aqueous solution; silica gel powder with a particle size of 5-10 μm is stirred and uniformly dispersed in the chitosan acetic acid aqueous solution to obtain a mixed solution, wherein the weight of the silica gel powder is 5-10 times the weight of the chitosan; the mixed solution is coated on a glass plate and dried at 35-40°C to form a chitosan film, and the dried chitosan film is placed on a 2-10 wt% The chitosan membrane was boiled in NaOH solution at 60-90°C for 1-2 hours to remove silica gel powder; the chitosan membrane was rinsed with water until neutral, and the chitosan membrane was immersed in glycerol for 30-60 minutes, then rinsed with water to remove surface glycerol, and allowed to stand at room temperature to obtain a porous chitosan membrane with a porosity of 40-50%; the porous chitosan membrane was vacuum dried at 80-90°C to constant weight, and after drying, ground into porous chitosan fine powder with a particle size of 20-40 μm.

[0011] Furthermore, the epoxy adhesive includes, by weight, 40-50 wt% of bisphenol A liquid epoxy resin, 10-20 wt% of low molecular solid bisphenol A epoxy resin, 5-10 wt% of solvent, 5-10 wt% of acrylic modified epoxy resin, 5-10 wt% of polyurethane modified epoxy resin, 4-8 wt% of dicyandiamide, 2-5 wt% of accelerator, 0.2-0.8 wt% of hydrophobic fumed silica, and 1-3 wt% of glass microspheres with a particle size of 50-100 μm.

[0012] Furthermore, the solvent is one or both of methyl isobutyl ketone and butanone.

[0013] Furthermore, the accelerator is one or more of polyurea, 2-methylimidazole, and modified amine.

[0014] The epoxy binder-coated modified magnetic powder obtained by the present invention can be die-casted by a hydraulic press under the conditions of a pressure of 15-20 MPa and a curing temperature of 120° C. to obtain a magnetic powder core with high resistivity and low eddy current loss.

[0015] Compared with the prior art, after the surface of the magnetic powder is modified by the first coupling agent in the present invention, since the titanate coupling agent of the first coupling agent has good adhesion to the outer surface of the magnetic powder metal, the first coupling agent can well wrap the outer surface of the magnetic powder to form a first insulating layer, and the second coupling agent wraps the outer surface of the magnetic powder again to form a second insulating layer. Since the second coupling agent adopts a silane coupling agent having an amino group, the silane coupling agent can not only well form a strong bonding effect with the surface of the first coupling agent, but also introduce amino active groups on the surface of the second insulating layer of the magnetic powder.

[0016] The present invention utilizes the porous structure of porous chitosan fine powder. The porous structure inside the porous chitosan contains multiple amino groups and hydroxyl groups. These amino groups and hydroxyl groups all contain residual electron pairs. The amino groups have certain chemical activity and are easy to produce an adsorption effect on magnetic powder with active amino groups on the surface, so that the magnetic powder can be adsorbed and dispersed and filled in the porous structure inside the porous chitosan. At the same time, the hydroxyl groups of the porous chitosan and the amino groups introduced on the surface of the magnetic powder are cross-linked to produce a chemical bonding effect, so that the magnetic powder can be firmly positioned inside the porous structure of the porous chitosan. After the magnetic powder is positioned inside the porous structure of the porous chitosan, the porous structure of the porous chitosan is further cross-linked and sealed by a cross-linking agent, so that the magnetic powder can be completely enclosed inside the porous structure wrapped in the porous chitosan.

[0017] Therefore, after the magnetic powder is wrapped by porous chitosan powder and sealed with a cross-linking agent, it not only solves the problem of agglomeration between the magnetic powders, but also realizes the dispersion effect of the magnetic powders through the dispersed filling of the porous structure. Moreover, after the porous chitosan powder is wrapped around the magnetic powder, the porous chitosan powder's low density and light weight are utilized to improve the problem of gravity sedimentation in the binder due to its high density.

[0018] The present invention targets modified magnetic powder and then implements epoxy coating on the modified magnetic powder, thereby further improving the insulation effect and bonding performance of the magnetic powder after die-casting. The reaction between the amino active groups on the modified magnetic powder and the epoxy groups of the epoxy resin is utilized to cause chemical bonding between the modified magnetic powder and the epoxy binder, which is beneficial to improving the coating stability between the modified magnetic powder and the epoxy binder. Moreover, the epoxy binder-coated modified magnetic powder produces an excellent curing effect during the subsequent processing and die-casting process due to the presence of the amino group. The hydroxyl groups on the porous chitosan in the modified magnetic powder and the excess carboxyl groups in the acrylic modified epoxy resin are esterified and connected together during the subsequent processing and die-casting process, which not only makes the bonding between the porous chitosan and the epoxy binder more firm, but also reduces the acidity of the epoxy binder through the esterification reaction, so that the acid corrosion of the modified magnetic powder on the winding of the inductor after die-casting is greatly reduced, making the modified magnetic powder have a better prospect for use. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a SEM scan of the internal cross-section of product 1 of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be described in detail below with reference to the examples. It should also be understood that the following examples are only used to further illustrate the present invention and are not to be construed as limiting the scope of the present invention. The specific mass, reaction time, temperature, process parameters, etc. in the examples are only examples within the appropriate ranges, and any non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention fall within the scope of the present invention.

[0021] The preparation of epoxy binder coated modified magnetic powder includes modified magnetic powder and epoxy binder. Modified magnetic powder 1 is prepared as follows: Mn-Zn ferrite magnetic powder with a particle size of 2~4μm is taken, the magnetic powder is added to anhydrous ethanol solution, ultrasonic washing is performed to clean impurities in the magnetic powder by anhydrous ethanol, and the anhydrous ethanol-washed magnetic powder A is obtained by filtration and drying. 1wt% of isopropyl tris (dioctyl pyrophosphate acyloxy) titanate of magnetic powder A is added to the anhydrous ethanol, the mass ratio of anhydrous ethanol to magnetic powder A is 1:1, and the first modified solution is obtained after mixing. 1 wt% KH550 of magnetic powder A was added to the mixture, and the mass ratio of anhydrous ethanol: magnetic powder A was 1:1. After mixing, the second modified liquid was obtained. The above magnetic powder A was placed on a slow roller and slowly rolled. The first modified liquid was added and the rolling time was 8 hours. After mixing evenly, the second modified liquid was added and continued to roll for 8 hours. The rolling rate of the slow roller was 2 rpm. After the second modified liquid was completely mixed, the magnetic powder A was separated from the mixed slurry through a 1500 mesh nylon sieve and vacuum dried at 90°C to constant weight to obtain magnetic powder surface treated with a coupling agent.

[0022] 1200 g of the magnetic powder surface-treated with the coupling agent prepared above was taken, and 300 g of porous chitosan fine powder with a porosity of 50% was taken. The magnetic powder and porous chitosan were adsorbed and mixed. Anhydrous ethanol was used as a solvent, and the oil bath temperature was heated to 80°C. The anhydrous ethanol was refluxed and stirred under ultrasonic conditions for 2 hours. After that, the cross-linking agent glutaraldehyde was slowly added, and the stirring and mixing under ultrasonic conditions was continued for 2 hours to obtain a composite of porous chitosan-coated modified magnetic powder. The composite was separated from the mixed solution by passing through a 600-mesh nylon sieve and vacuum-dried at 90°C to constant weight to obtain modified magnetic powder 1.

[0023] Modified magnetic powder 2 was prepared as follows: the preparation method was the same as that of modified magnetic powder 1, except that Ni-Zn ferrite was used for the magnetic powder, the first coupling agent of the first modifying liquid was isopropyl tri(dodecylbenzenesulfonyl) titanate, and the second coupling agent of the second modifying liquid was KH553. 1200 g of the magnetic powder surface-treated with the coupling agent prepared above was taken, 500 g of porous chitosan fine powder with a porosity of 40% was taken, and the magnetic powder and porous chitosan were adsorbed and mixed. Anhydrous ethanol was used as the solvent, the oil bath was heated to 80°C, the anhydrous ethanol was refluxed, and the mixture was stirred and mixed under ultrasonic conditions for 2 hours. Then, the cross-linking agent epichlorohydrin was slowly added, and the stirring and mixing was continued under ultrasonic conditions for 2 hours to obtain a composite of porous chitosan-coated modified magnetic powder. The composite was separated from the mixed solution by a 600-mesh nylon sieve and vacuum-dried at 90°C to constant weight to obtain modified magnetic powder 2.

[0024] Among them, porous chitosan fine powder with a porosity of 50% was prepared as follows: chitosan with a deacetylation degree of 90-95% was dissolved in a 2wt% acetic acid aqueous solution and stirred until completely dissolved to form a uniform chitosan acetic acid aqueous solution; silica gel powder with a particle size of 5 μm was stirred and evenly dispersed in the chitosan acetic acid aqueous solution to obtain a mixed solution, wherein the weight of the silica gel powder was 10 times the weight of the chitosan; the mixed solution was coated on a glass plate and dried at 40°C to form a chitosan film, the dried chitosan film was placed in an 8wt% NaOH solution, and the silica gel powder was boiled at 90°C for 1 hour; the chitosan film was rinsed with water until neutral, the chitosan film was immersed in glycerol for 60 minutes, and then rinsed with water to remove the surface glycerol, and allowed to stand at room temperature to obtain a porous chitosan film with a porosity of 50%; the porous chitosan film was vacuum dried at 90°C to constant weight, and after drying, it was ground into porous chitosan fine powder with a particle size of 20-40 μm.

[0025] Porous chitosan powder with a porosity of 40% was prepared as follows: chitosan with a deacetylation degree of 90-95% was dissolved in a 1 wt % acetic acid aqueous solution and stirred until completely dissolved to form a uniform chitosan acetic acid aqueous solution; silica gel powder with a particle size of 5 μm was stirred and uniformly dispersed in the chitosan acetic acid aqueous solution to obtain a mixed solution, wherein the weight of the silica gel powder was 6 times the weight of the chitosan; the mixed solution was coated on a glass plate and dried at 40°C to form a chitosan film, the dried chitosan film was placed in a 6 wt % NaOH solution, and the silica gel powder was boiled at 80°C for 2 h; the chitosan film was rinsed with water until neutral, the chitosan film was immersed in glycerol for 30 min, and then rinsed with water to remove the surface glycerol, and allowed to stand at room temperature to obtain a porous chitosan film with a porosity of 40%; the porous chitosan film was vacuum dried at 90°C to constant weight, and after drying, it was ground into porous chitosan fine powder with a particle size of 20-40 μm.

[0026] The porosity of the porous chitosan membrane was measured according to the following method: the prepared porous chitosan membrane was cut into 1×1 cm squares and immersed in double distilled water at 20°C for 24 h to allow the porous chitosan membrane to fully absorb water and swell. The porous chitosan membrane was taken out and excess water was absorbed by filter paper to make the surface of the porous chitosan membrane free of water dripping and water seepage. The membrane was weighed m1 (g), and the thickness and area of ​​the porous chitosan membrane were measured to obtain the volume V (cm) of the porous chitosan membrane after water absorption. 3 ), then place the porous chitosan membrane in a vacuum drying oven and dry it at 80℃ for 1~2h. After taking it out, weigh m0 (g) and get its porosity (%) = (m1 - m0) × 100% / (0.9982 × V). Where 0.9982 is the density of double distilled water at 20℃ (g / cm 3 ). Example

[0027] The invention discloses a preparation method for epoxy binder-coated modified magnetic powder, comprising 90 wt% of modified magnetic powder and 10 wt% of epoxy binder, wherein the epoxy binder is evenly diluted with butanone as a diluent, and the volume ratio of butanone to epoxy binder is 10. After stirring and mixing evenly, the modified magnetic powder is added, and stirring and mixing is continued while controlling the stirring temperature at 50° C. for 4 hours. The epoxy binder-coated modified magnetic powder is obtained by filtering through a 400-mesh nylon sieve.

[0028] The modified magnetic powder adopts modified magnetic powder 1, wherein the epoxy binder includes, by weight, 45 wt % of bisphenol A type liquid epoxy resin 128 epoxy resin, 15 wt % of low molecular solid bisphenol A type epoxy resin 901 epoxy resin, 10 wt % of methyl isobutyl ketone, 10 wt % of acrylic acid modified epoxy resin A102, 10 wt % of polyurethane modified epoxy resin E20, 4 wt % of dicyandiamide, 3 wt % of accelerator polyurea, 0.5 wt % of hydrophobic fumed silica, and 2.5 wt % of glass microspheres with a particle size of 50-100 μm.

[0029] The epoxy binder-coated modified magnetic powder obtained in Example 1 was die-casted by a hydraulic press at a pressure of 15-20 MPa and a curing temperature of 120° C. to obtain a product 1 of a magnetic powder core with high resistivity and low eddy current loss.

[0030] After cutting open the interior of product 1, perform SEM scanning on the internal cross section. Figure 1 As shown, after the modified magnetic powder is coated with the porous chitosan fine powder, the modified magnetic powder can be well dispersed inside the porous chitosan fine powder.

[0031] The results of various performance tests of Product 1 are as follows: tensile strength σ MThe effective magnetic permeability is 20.18MPa, the effective magnetic permeability is 30.65, and the density of the magnetic powder core is 4.72g / cm 3 , the resistivity is 1.37×10 9 Ω•m, quality factor 75, loss 554.17 mW / cm³.

[0032] Among them, the various performance measurement methods of product 1 are as follows: Tensile strength σ M (Unit: MPa), the magnetic powder is pressed into a long strip and tested on a tensile testing machine. The tensile force F (unit: N) at the time of fracture and the original cross-sectional area A (unit: mm) of the fracture surface of the magnetic powder core are measured. 2 ), the tensile strength is calculated according to the formula σ M =F / A, and the tensile strength of the magnetic powder core is obtained.

[0033] The effective permeability is measured by winding 37.5 turns of coil around a powder core ring using an impedance analyzer at a frequency of 1 MHz. The effective permeability can be calculated by combining the frequency with the sample size.

[0034] Density ρ is measured by weighing the mass m of the magnetic powder core sample, and then the volume v of the magnetic powder core is measured by the water displacement method, and then calculated using the formula ρ=m / v.

[0035] Resistivity: Use a resistivity tester to test the resistivity of the sample. Place the magnetic powder core sample on the test bench, operate the probe bench to press down the four probe heads, connect the sample to the power supply, and test and read the resistivity value.

[0036] Quality factor,The quality factor of the magnetic powder core is measured using an impedance analyzer, by winding 37.5 turns of coil on the magnetic powder core magnetic ring and then testing it. The test frequency is 1MHz.

[0037] Loss: A BH analyzer is used to test the loss of the magnetic powder core. 37.5 turns of coil are wound around the magnetic powder core ring and then tested. The test conditions are a magnetic flux density Bm of 20mT, a frequency f of 1MHz, and a test temperature T of 25℃. Example

[0038] As in Example 1, a preparation of an epoxy binder-coated modified magnetic powder is prepared, comprising 95 wt% of modified magnetic powder and 5 wt% of epoxy binder, wherein the epoxy binder is evenly diluted with butanone as a diluent, and the volume ratio of butanone to the epoxy binder is 20. After stirring and mixing evenly, the modified magnetic powder is added, and stirring and mixing is continued, and the stirring temperature is controlled at 60°C for 2 hours. The epoxy binder-coated modified magnetic powder is obtained by filtering through a 400-mesh nylon sieve, wherein the modified magnetic powder adopts modified magnetic powder 2, and the ratio of the epoxy binder is the same as in Example 1.

[0039] The epoxy binder-coated modified magnetic powder obtained in Example 2 was die-casted by a hydraulic press at a pressure of 15-20 MPa and a curing temperature of 120° C. to obtain Product 2, a magnetic powder core with high resistivity and low eddy current loss.

[0040] The various performance tests of product 2 refer to Example 1, and the tensile strength σ of product 2 is M The effective magnetic permeability is 21.64MPa, the effective magnetic permeability is 33.92, and the density of the magnetic powder core is 4.19g / cm 3 , the resistivity is 2.13×10 9 Ω•m, quality factor 76, loss 548.53 mW / cm³.

[0041] Comparative Example 1: As in Example 1, the epoxy binder-coated modified magnetic powder comprises 90 wt% of modified magnetic powder and 10 wt% of epoxy binder, the epoxy binder is evenly diluted with butanone as a diluent, the volume ratio of butanone to epoxy binder is 10, and after stirring and mixing evenly, the modified magnetic powder is added, and stirring and mixing is continued, and the stirring temperature is controlled to 50 ° C. and stirred for 4 hours, and filtered through a 400 mesh nylon sieve to obtain the epoxy binder-coated modified magnetic powder. The step of modifying the magnetic powder adopts the process step of the coupling agent surface treatment of the modified magnetic powder 1, but does not adopt the porous chitosan coating treatment. The epoxy binder is the same as the epoxy binder in Example 1. The obtained epoxy binder-coated modified magnetic powder is die-cast by a hydraulic press at a pressure of 15~20 MPa and a curing temperature of 120 ° C to obtain the magnetic powder core product 3.

[0042] The various performance tests of product 3 refer to Example 1, and the tensile strength σ of product 3 is M The effective magnetic permeability is 23.21, and the density of the magnetic powder core is 5.81g / cm 3 , the resistivity is 3.52×10 8 Ω•m, quality factor 65, loss 1304.42 mW / cm³.

[0043] Comparative Example 2: As in Example 1, the epoxy binder-coated modified magnetic powder comprises 90 wt% of modified magnetic powder and 10 wt% of epoxy binder. The epoxy binder is evenly diluted with butanone as a diluent, and the volume ratio of butanone to the epoxy binder is 10. After stirring and mixing evenly, the modified magnetic powder is added, and stirring and mixing is continued. The stirring temperature is controlled at 50 ° C. and stirred for 4 hours. The epoxy binder-coated modified magnetic powder is obtained by filtering through a 400-mesh nylon sieve. The step of modifying the magnetic powder adopts the process step of surface treatment with a first coupling agent, and is coated with porous chitosan. The epoxy binder is the same as the epoxy binder in Example 1. The obtained epoxy binder-coated modified magnetic powder is die-cast by a hydraulic press at a pressure of 15-20 MPa and a curing temperature of 120 ° C to obtain a magnetic powder core product 4.

[0044] The various performance tests of product 4 refer to Example 1, and the tensile strength σ of product 4 is M The effective magnetic permeability is 18.17MPa, the effective magnetic permeability is 22.47, and the density of the magnetic powder core is 4.96g / cm 3 , the resistivity is 7.38×10 8 Ω•m, quality factor 63, loss 985.76 mW / cm³.

[0045] Comparative Example 3: As in Example 1, the epoxy binder-coated modified magnetic powder comprises 90 wt % of modified magnetic powder and 10 wt % of epoxy binder, the epoxy binder is evenly diluted with butanone as a diluent, the volume ratio of butanone to epoxy binder is 10, and after stirring and mixing evenly, the modified magnetic powder is added, and stirring and mixing is continued, and the stirring temperature is controlled to 50 ° C. and stirred for 4 hours, and filtered through a 400 mesh nylon sieve to obtain the epoxy binder-coated modified magnetic powder. The step of modifying the magnetic powder adopts the process step of surface treatment with a second coupling agent, and is coated with porous chitosan. The epoxy binder is the same as the epoxy binder in Example 1. The obtained epoxy binder-coated modified magnetic powder is die-cast by a hydraulic press at a pressure of 15-20 MPa and a curing temperature of 120 ° C to obtain a magnetic powder core product 5.

[0046] The various performance tests of product 5 refer to Example 1, and the tensile strength σ of product 5 is M The effective magnetic permeability is 18.65MPa, the effective magnetic permeability is 24.32, and the density of the magnetic powder core is 4.87g / cm 3 , the resistivity is 8.67×10 8 Ω•m, quality factor 68, loss 948.23 mW / cm³.

[0047] Examples 1 and 2 are products 1 and 2 obtained by using the modified magnetic powder coated with the epoxy binder of the present invention. Performance tests of the products show that since the modified magnetic powder is coated through the pores of porous chitosan and then coated with the epoxy binder, the obtained products are used to fix the metal magnetic powder in the pores of the porous chitosan so that the metal magnetic powder can be effectively dispersed with each other, reducing the agglomeration of the magnetic powder. Therefore, the products have high dispersed resistivity and low loss (mainly eddy current loss). The problems of poor dispersion and agglomeration of magnetic powder, poor insulation effect of magnetic powder, too low resistivity of magnetic powder core, and large eddy current loss resulting in large loss at high frequency are effectively solved, which well meets the use of modified magnetic powder in one-piece molded inductors.

[0048] Similarly, in Comparative Example 1, although the modified magnetic powder is subjected to a two-step coupling agent surface treatment process, since porous chitosan coating is not used, the dispersion effect of the modified magnetic powder is relatively higher than that of Examples 1 and 2, and the loss (mainly eddy current loss) is also relatively large, indicating that the dispersion effect of the modified magnetic powder after the porous chitosan coating treatment is excellent, and the agglomeration problem is also well solved.

[0049] Similarly, in Comparative Examples 2 and 3, the modified magnetic powder adopts a single coupling agent surface treatment process step. Compared with Example 1 or Example 2, no two coupling agents are used in the coupling agent treatment step. The obtained product performance test surface adopts a single coupling agent surface treatment process step. After the porous chitosan coating treatment is used, the resistivity is greatly improved compared with Comparative Example 1, and the loss (mainly eddy current loss) is relatively much lower than that of Comparative Example 1, indicating that the use of a single coupling agent surface treatment process step is improved by using The porous chitosan coating treatment can effectively improve the performance of the product. However, due to the single coupling agent surface treatment process step, the bonding effect between the modified magnetic powder and the porous chitosan is not good during the porous chitosan coating process, which greatly reduces the dispersion effect of the modified magnetic powder on the magnetic powder through the porous chitosan. This is because the titanate coupling agent of the first coupling agent has a good adhesion to the outer surface of the magnetic powder metal. The first coupling agent can be well wrapped with the outer surface of the magnetic powder to form a first insulating layer, and the second coupling agent is used to coat the outer surface of the magnetic powder. Wrap again to form the second insulating layer. Since the second coupling agent uses a silane coupling agent with an amino group, the silane coupling agent can not only form a strong bonding effect with the surface of the first coupling agent, but also introduce amino active groups on the surface of the second insulating layer of the magnetic powder. The porous structure of the porous chitosan fine powder contains multiple amino groups and hydroxyl groups on the porous structure inside the porous chitosan. These amino groups and hydroxyl groups contain residual electron pairs. The amino group has a certain chemical activity and is easy to adsorb the magnetic powder containing the active amino group on the surface, so that The obtained magnetic powder can be adsorbed and dispersed in the porous structure inside the porous chitosan. At the same time, the hydroxyl groups of the porous chitosan and the amino groups introduced on the surface of the magnetic powder are cross-linked to produce chemical bonding, so that the magnetic powder can be firmly positioned inside the porous structure of the porous chitosan. The magnetic powder is positioned inside the porous structure of the porous chitosan, so that the dispersion effect after positioning is good. Finally, the porous structure of the porous chitosan is cross-linked and sealed by a cross-linking agent, so that the magnetic powder can be completely enclosed in the porous structure wrapped in the porous chitosan, thereby ensuring the dispersion effect of the magnetic powder.

[0050] Therefore, in summary, the present invention uses the porous structure of porous chitosan fine powder to coat the modified magnetic powder, which is a key technology for achieving the dispersibility of the modified magnetic powder and preventing agglomeration. The present invention uses a two-step method to modify the magnetic powder with a coupling agent, so that the modified magnetic powder and the porous structure of the porous chitosan fine powder form a good bond and fixation. Therefore, the present invention uses a two-step method to modify the magnetic powder with a coupling agent, which is also another key technology for achieving the dispersibility of the modified magnetic powder and preventing agglomeration. It is precisely because the present invention adopts the combination of the above-mentioned key technical solutions that the product obtained by the present invention has the product technical effects of high resistivity and low loss (mainly eddy current loss).

[0051] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. Preparation of epoxy binder coated modified magnetic powder, characterized in that, The method comprises 90-95 wt% of modified magnetic powder and 5-10 wt% of epoxy binder, wherein the epoxy binder is evenly diluted with butanone as a diluent, and the volume ratio of butanone to epoxy binder is 10-20. After being stirred and mixed evenly, the modified magnetic powder is added, and the stirring and mixing is continued while controlling the stirring temperature at 50-60° C. for 2-4 hours. The modified magnetic powder is sieved through a 300-500 mesh nylon sieve to obtain the epoxy binder-coated modified magnetic powder. Wherein, the modified magnetic powder is prepared by the following steps: S1: adding magnetic powder to an anhydrous ethanol solution, ultrasonically washing, filtering and drying to obtain an anhydrous ethanol-washed magnetic powder A; S2: adding a first coupling agent in anhydrous ethanol at a mass ratio of 0.5-2 wt% of magnetic powder A to magnetic powder A in a 1:1 ratio, and mixing to obtain a first modified solution; S3: adding a second coupling agent in anhydrous ethanol at a mass ratio of 0.5-2 wt% of magnetic powder A to magnetic powder A in a 1:1 ratio, and mixing to obtain a second modified solution; S4: Place the magnetic powder A on a slow roller and slowly roll it, add the first modifying liquid, and roll it for 2 to 8 hours. After mixing evenly, add the second modifying liquid and continue rolling for 2 to 8 hours. The rolling speed of the slow roller is 1 to 3 rpm. After the second modifying liquid is completely mixed, separate the magnetic powder A from the mixed slurry through a 1000 to 2500 mesh nylon sieve, and vacuum dry it at 80 to 90°C to constant weight to obtain magnetic powder surface treated with a coupling agent; S5: Magnetic powder surface treated with a coupling agent is mixed with porous chitosan fine powder in a mass ratio of 1:0.25~0.45, and anhydrous ethanol is used as the solvent. The oil bath is heated to 60~80°C, and the anhydrous ethanol is refluxed. After stirring and mixing under ultrasonic conditions for 2~4 hours, a cross-linking agent is slowly added, and stirring and mixing is continued under ultrasonic conditions for 2~4 hours to obtain a composite of porous chitosan-coated modified magnetic powder. The composite is separated from the mixed solution by a 500~800 mesh nylon sieve, and vacuum dried at 80~90°C to constant weight to obtain modified magnetic powder.

2. The preparation of epoxy binder coated modified magnetic powder according to claim 1, characterized in that: The magnetic powder is one or more of Mn-Zn ferrite, Ni-Zn ferrite, Fe-Si alloy, and Fe-Ni alloy.

3. The preparation of epoxy binder coated modified magnetic powder according to claim 1, characterized in that: The magnetic powder has a particle size of 2-4 μm.

4. The preparation of epoxy binder coated modified magnetic powder according to claim 1, characterized in that: In S2, the first coupling agent is a titanate coupling agent, and the titanate coupling agent is one or more of isopropyl tri(dioctyl pyrophosphate) titanate, isopropyl tri(dodecylbenzenesulfonyl) titanate, and isopropyl trioleyl titanate.

5. The preparation of epoxy binder coated modified magnetic powder according to claim 1, characterized in that: In S3, the second coupling agent is a silane coupling agent containing an amino group, and the silane coupling agent is one or more of KH550, KH540, KH553, KH554, and KH990.

6. The preparation of epoxy binder coated modified magnetic powder according to claim 1, characterized in that: In S5, the cross-linking agent is one or both of glutaraldehyde and epichlorohydrin.

7. The preparation of epoxy binder coated modified magnetic powder according to claim 1, characterized in that: In S5, the porous chitosan powder is prepared by the following steps: Chitosan with a deacetylation degree of 90-95% is dissolved in a 1-2 wt% acetic acid aqueous solution and stirred until completely dissolved to form a uniform chitosan acetic acid aqueous solution; silica gel powder with a particle size of 5-10 μm is stirred and uniformly dispersed in the chitosan acetic acid aqueous solution to obtain a mixed solution, wherein the weight of the silica gel powder is 5-10 times the weight of the chitosan; the mixed solution is coated on a glass plate and dried at 35-40°C to form a chitosan film, and the dried chitosan film is placed on a 2-10 wt% The chitosan membrane was boiled in NaOH solution at 60-90°C for 1-2 hours to remove silica gel powder; the chitosan membrane was rinsed with water until neutral, and the chitosan membrane was immersed in glycerol for 30-60 minutes, then rinsed with water to remove surface glycerol, and allowed to stand at room temperature to obtain a porous chitosan membrane with a porosity of 40-50%; the porous chitosan membrane was vacuum dried at 80-90°C to constant weight, and after drying, ground into porous chitosan fine powder with a particle size of 20-40 μm.

8. The preparation of epoxy binder coated modified magnetic powder according to claim 1, characterized in that: The epoxy adhesive comprises, by weight, 40-50 wt% of bisphenol A liquid epoxy resin, 10-20 wt% of low molecular solid bisphenol A epoxy resin, 5-10 wt% of solvent, 5-10 wt% of acrylic acid modified epoxy resin, 5-10 wt% of polyurethane modified epoxy resin, 4-8 wt% of dicyandiamide, 2-5 wt% of accelerator, 0.2-0.8 wt% of hydrophobic fumed silica, and 1-3 wt% of glass microspheres with a particle size of 50-100 μm.

9. The preparation of epoxy binder coated modified magnetic powder according to claim 8, characterized in that: The solvent is one or both of methyl isobutyl ketone and butanone.

10. The method for preparing epoxy binder coated modified magnetic powder according to claim 8, wherein: The accelerator is one or more of polyurea, modified imidazole and modified amine.

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