Preparation of epoxy binder-coated modified magnetic powder

Abstract

This invention discloses a method for preparing epoxy binder-coated modified magnetic powder, comprising 90-95 wt% modified magnetic powder and 5-10 wt% epoxy binder. The epoxy binder is diluted uniformly with methyl ethyl ketone (MEK) as a diluent, and the volume ratio of MEK to epoxy binder is 10-20. After uniform mixing, the modified magnetic powder is added, and mixing continues while maintaining a stirring temperature of 50-60℃ for 2-4 hours. The mixture is then sieved through a 300-500 mesh nylon sieve to obtain epoxy binder-coated modified magnetic powder. This invention utilizes a two-step coupling agent to modify the magnetic powder, enabling the modified magnetic powder and porous chitosan fine powder to form a good bond and fix within the porous structure, resulting in magnetic powder with low agglomeration, good dispersibility, and good insulation effect, thus meeting the purpose of inductor production and use. The product obtained by this invention has high resistivity and low loss.

Description

Technical Field

[0001] This invention relates to the field of magnetic core materials, and more specifically to the preparation of epoxy binder-coated modified magnetic powder. Background Technology

[0002] In the production process of integrally molded inductors, the winding body is embedded inside the metal magnetic powder and die-cast. To improve the adhesion of the metal magnetic powder, inorganic or organic binders are added to the metal magnetic powder to ensure that the metal powder is pressed and bonded together. In existing integral die-casting technology, magnetic powder is dispersed in binder and die-cast. However, this method has the following problems: the density of ordinary magnetic powder is relatively high compared with organic binders, and it is easy to precipitate and agglomerate, resulting in poor dispersibility. Even when the magnetic powder and binder are prepared and used on the spot, the magnetic powder will still precipitate or agglomerate during the die-casting process, resulting in uneven dispersion of magnetic powder. The binder cannot effectively encapsulate the magnetic powder to achieve the purpose of insulation and adhesion of 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, better dispersibility, and better insulation effect. Furthermore, the magnetic powder should have a better adhesion effect when bonded with the binder. This is the problem solved by the present invention, thereby meeting the purpose of inductor production and use. Summary of the Invention

[0003] To address the aforementioned problems, this invention proposes a method for preparing epoxy-coated modified magnetic powder. By modifying the magnetic powder to obtain highly dispersible modified magnetic powder, and then coating it with an epoxy resin binder, the modified magnetic powder exhibits excellent dispersion, achieving complete coating of the modified magnetic powder by the epoxy resin binder, thereby fulfilling the purpose of inductor use.

[0004] To achieve the above-mentioned objectives, the embodiments of the present invention employ the following technical solutions:

[0005] The preparation of epoxy binder-coated modified magnetic powder includes 90-95 wt% modified magnetic powder and 5-10 wt% epoxy binder. The epoxy binder is diluted evenly with methyl ethyl ketone (MEK) as a diluent. The volume ratio of MEK to epoxy binder is 10-20. After stirring and mixing evenly, the modified magnetic powder is added, and stirring and mixing are continued. The stirring temperature is controlled at 50-60℃ and stirred for 2-4 hours. The mixture is then filtered through a 300-500 mesh nylon sieve to obtain epoxy binder-coated modified magnetic powder.

[0006] The modified magnetic powder is prepared through the following steps:

[0007] S1: Add magnetic powder to anhydrous ethanol solvent, ultrasonically wash, filter and dry to obtain magnetic powder A washed with anhydrous ethanol;

[0008] S2: Add a first coupling agent of 0.5~2wt% of magnetic powder A to anhydrous ethanol. The mass ratio of anhydrous ethanol to magnetic powder A is 1:1. After mixing, the first modified solution is obtained.

[0009] S3: Add a second coupling agent at 0.5~2wt% of magnetic powder A to anhydrous ethanol, where the mass ratio of anhydrous ethanol to magnetic powder A is...

[0010] The ratio is 1:1, and after mixing, a second modified solution is obtained;

[0011] S4: Place the above magnetic powder A on a slow rolling machine and roll it slowly, add the first modifying liquid, and roll for 2~8 hours.

[0012] After mixing evenly, add the second modified liquid and continue rolling for 2-8 hours. The rolling speed of the slow roller is 1-3 rpm. After the second modified liquid is completely mixed, separate the magnetic powder A from the mixed slurry through a 1000-2500 mesh nylon sieve. Vacuum dry to constant weight at 80-90℃ to obtain magnetic powder with coupling agent surface treatment.

[0013] S5: Magnetic powder surface-treated with coupling agent is mixed with porous chitosan fine powder at a mass ratio of 1:0.25~0.45. Anhydrous ethanol is used as solvent. The mixture is heated in an oil bath at 60~80℃ with anhydrous ethanol refluxed. After stirring and mixing under ultrasonic conditions for 2~4 hours, a crosslinking agent is slowly added. The mixture is stirred and mixed under ultrasonic conditions for another 2~4 hours to obtain a composite of porous chitosan-coated modified magnetic powder. The composite is separated from the mixture by passing it through a 500~800 mesh nylon sieve and vacuum dried to constant weight at 80~90℃ to obtain modified magnetic powder.

[0014] Furthermore, the magnetic powder is one or more of Mn-Zn ferrite, Ni-Zn ferrite, Fe-Si alloy, and Fe-Ni alloy.

[0015] Furthermore, the magnetic powder has a particle size of 2~4μm.

[0016] Further, in S2, the first coupling agent is a titanate coupling agent, which is one or more of isopropyl tris(dioctylpyrophosphate) titanate, isopropyl tris(dodecylbenzenesulfonyl) titanate, and isopropyl trioleoyloxy titanate.

[0017] Further, in S3, the second coupling agent is a silane coupling agent containing an amino group, wherein the silane coupling agent is one or more of KH550, KH540, KH553, KH554, and KH990.

[0018] Furthermore, in S5, the crosslinking agent is one or both of glutaraldehyde and epichlorohydrin.

[0019] Further, in S5, the porous chitosan fine powder is obtained by the following steps:

[0020] Chitosan with a degree of deacetylation of 90-95% was dissolved in a 1-2 wt% aqueous acetic acid solution and stirred until completely dissolved to form a homogeneous chitosan-acetic acid aqueous solution. Silica gel powder with a particle size of 5-10 μm was stirred and uniformly dispersed in the chitosan-acetic acid aqueous solution to obtain a mixture, with the weight of the silica gel powder being 5-10 times the weight of the chitosan. The mixture was coated onto a glass plate and dried at 35-40°C to form a chitosan film. The dried chitosan film was then placed in a 2-10 wt% aqueous acetic acid solution. Boil the chitosan membrane in NaOH solution at 60-90℃ for 1-2 hours to remove silica gel powder; rinse the chitosan membrane with water until neutral, immerse the chitosan membrane in glycerol for 30-60 minutes, then rinse with water to remove surface glycerol, and let it stand at room temperature to obtain a porous chitosan membrane with a porosity of 40-50%; vacuum dry the porous chitosan membrane at 80-90℃ to constant weight, and grind it into porous chitosan fine powder with a particle size of 20-40μm.

[0021] Further, the epoxy adhesive, by weight, comprises 40-50 wt% bisphenol A type liquid epoxy resin, 10-20 wt% low molecular weight solid bisphenol A type epoxy resin, 5-10 wt% solvent, 5-10 wt% acrylic modified epoxy resin, 5-10 wt% polyurethane modified epoxy resin, 4-8 wt% dicyandiamide, 2-5 wt% accelerator, 0.2-0.8 wt% hydrophobic fumed silica, and 1-3 wt% glass microspheres with a particle size of 50-100 μm.

[0022] Furthermore, the solvent is one or both of methyl isobutyl ketone and butanone.

[0023] Furthermore, the accelerator is one or more of polyurea, 2-methylimidazole, and modified amine.

[0024] The epoxy binder-coated modified magnetic powder obtained by this invention can be die-cast using a hydraulic press at a pressure of 15~20MPa and a curing temperature of 120℃ to obtain a magnetic powder core with high resistivity and low eddy current loss.

[0025] Compared with the prior art, the present invention modifies the surface of the magnetic powder by means of a first coupling agent. 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 initially coat the outer surface of the magnetic powder well to form a first insulating layer. The second coupling agent further coats the outer surface of the magnetic powder to form a second insulating layer. Since the second coupling agent is a silane coupling agent with amino groups, the silane coupling agent can not only form a strong adhesion to 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.

[0026] This invention utilizes the porous structure of fine chitosan powder. The porous structure within the chitosan contains multiple amino and hydroxyl groups, each with a residual electron pair. The amino groups exhibit chemical activity, readily adsorbing the magnetic powder containing active amino groups on their surface. This allows the magnetic powder to be adsorbed and dispersed within the porous structure of the chitosan. Simultaneously, the hydroxyl groups of the chitosan and the introduced amino groups on the surface of the magnetic powder cross-link, creating chemical bonds that firmly position the magnetic powder within the porous structure. Furthermore, by using a cross-linking agent to further cross-link and seal the porous structure of the chitosan, the magnetic powder is completely enclosed within the porous structure of the chitosan.

[0027] Therefore, after the magnetic powder is encapsulated by porous chitosan fine powder and sealed with a crosslinking agent, not only can the problem of magnetic powder agglomeration be solved, and the magnetic powder can be dispersed and filled through the porous structure, but also the porous chitosan fine powder, with its low density and light weight, can improve the problem of magnetic powder settling due to gravity in the binder.

[0028] This invention targets modified magnetic powder, specifically by applying an epoxy coating to it. This further enhances the insulation and bonding properties of the magnetic powder after die casting. The reaction between the amino active groups on the modified magnetic powder and the epoxy groups in the epoxy resin creates a chemical bond between the modified magnetic powder and the epoxy binder. This improves the stability of the coating. Furthermore, the presence of amino groups in the epoxy binder-coated modified magnetic powder results in excellent curing during subsequent die casting. The hydroxyl groups on the porous chitosan in the modified magnetic powder and the excess carboxyl groups in the acrylic-modified epoxy resin undergo esterification during the subsequent die casting process. This not only strengthens the bond between the porous chitosan and the epoxy binder but also reduces the acidity of the epoxy binder through the esterification reaction. Consequently, the modified magnetic powder significantly reduces acid corrosion of the inductor windings after die casting, giving it a promising future application prospect. Attached Figure Description

[0029] Figure 1 This is a SEM scan image of the internal cross-section of Product 1 of the present invention. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to embodiments. It should also be understood that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. The specific mass, reaction time, temperature, process parameters, etc., in the examples are merely examples within a suitable range. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0031] 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 2-4 μm is taken and added to anhydrous ethanol solution. The powder is ultrasonically washed to remove impurities from the magnetic powder. After filtration and drying, anhydrous ethanol-washed magnetic powder A is obtained. 1 wt% of isopropyltris(dioctyl pyrophosphate) titanate of magnetic powder A is added to anhydrous ethanol. The mass ratio of anhydrous ethanol to magnetic powder A is 1:1. After mixing, the first modification solution is obtained. [The text abruptly ends here, likely due to an incomplete sentence or missing information.] 1 wt% KH550 of magnetic powder A was added to the mixture, and the mass ratio of anhydrous ethanol to magnetic powder A was 1:1. After mixing, a second modified liquid was obtained. The magnetic powder A was placed on a slow tumbler 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 the rolling continued for 8 hours. The rolling speed of the slow tumbler was 2 rpm. After the second modified liquid was completely mixed, the magnetic powder A was separated from the mixed slurry by passing it through a 1500-mesh nylon sieve. The mixture was then vacuum dried at 90°C to constant weight to obtain magnetic powder with coupling agent surface treatment.

[0032] Take 1200g of the magnetic powder surface-treated with the coupling agent prepared above, and 300g of porous chitosan fine powder with a porosity of 50%. Adsorb and mix the magnetic powder and porous chitosan. Use anhydrous ethanol as solvent, heat in an oil bath at 80℃, reflux with anhydrous ethanol, and stir and mix under ultrasonic conditions for 2h. Slowly add the crosslinking agent glutaraldehyde, and continue stirring and mixing under ultrasonic conditions for 2h to obtain a composite of porous chitosan-coated modified magnetic powder. Separate the composite from the mixture by passing it through a 600-mesh nylon sieve, and vacuum dry it to constant weight at 90℃ to obtain modified magnetic powder 1.

[0033] Modified magnetic powder 2 was prepared as follows: The preparation method was the same as that of modified magnetic powder 1, except that the magnetic powder used was Ni-Zn ferrite, the first coupling agent of the first modifying liquid was isopropyltris(dodecylbenzenesulfonyl) titanate, and the second coupling agent of the second modifying liquid was KH553. 1200g of the magnetic powder surface-treated with the above-prepared coupling agent and 500g of porous chitosan fine powder with a porosity of 40% were taken and adsorbed and mixed. Anhydrous ethanol was used as the solvent, and the mixture was heated in an oil bath at 80℃. Anhydrous ethanol was refluxed and stirred under ultrasonic conditions for 2 hours. Then, the crosslinking agent epichlorohydrin was slowly added and stirred under ultrasonic conditions for another 2 hours to obtain a composite of porous chitosan-coated modified magnetic powder. The composite was separated from the mixture by passing it through a 600-mesh nylon sieve and vacuum dried to constant weight at 90℃ to obtain modified magnetic powder 2.

[0034] The 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 5μm was stirred and evenly dispersed in the chitosan-acetic acid aqueous solution to obtain a mixed solution, the weight of the silica gel powder being 10 times the weight of the chitosan; the mixed solution was coated onto a glass plate and dried at 40℃ to form a chitosan film; the dried chitosan film was placed in an 8wt% NaOH solution and boiled at 90℃ for 1 hour to remove the silica gel powder; the chitosan film was rinsed with water until neutral, then soaked in glycerol for 60 minutes, and then rinsed with water to remove the surface glycerol. After standing at room temperature, a porous chitosan film with a porosity of 50% was obtained; the porous chitosan film was vacuum dried at 90℃ to constant weight, and then ground into porous chitosan fine powder with a particle size of 20-40μm.

[0035] The porous chitosan fine 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, the weight of the silica gel powder being 6 times the weight of the chitosan; the mixed solution was coated onto a glass plate and dried at 40℃ to form a chitosan film; the dried chitosan film was placed in a 6 wt% NaOH solution and boiled at 80℃ for 2 hours to remove the silica gel powder; the chitosan film was rinsed with water until neutral, then immersed in glycerol for 30 minutes, and then rinsed with water to remove the surface glycerol. After standing at room temperature, a porous chitosan film with a porosity of 40% was obtained; the porous chitosan film was vacuum dried at 90℃ to constant weight, and then ground into porous chitosan fine powder with a particle size of 20-40 μm.

[0036] The porosity of the porous chitosan membrane was determined as follows: The prepared porous chitosan membrane was cut into 1×1cm squares and immersed in double-distilled water at 20℃ for 24 hours to allow it to fully absorb water and swell. The membrane was then removed, and excess water was absorbed with filter paper until the surface was neither dripping nor seeping. The membrane was weighed (m1, g), and its thickness and area were measured to obtain the volume V (cm³) of the porous chitosan membrane after water absorption. 3 Then, the porous chitosan membrane was placed in a vacuum drying oven and dried at 80℃ for 1-2 hours. After removal, it was weighed m0 (g), and its porosity (%) was calculated as (m1 - m0) × 100% / (0.9982 × V). Where 0.9982 is the density (g / cm³) of double-distilled water at 20℃. 3 ). Example 1:

[0037] The preparation of epoxy binder-coated modified magnetic powder includes 90 wt% modified magnetic powder and 10 wt% epoxy binder. The epoxy binder is diluted evenly with methyl ethyl ketone (MEK) as a diluent, and the volume ratio of MEK to epoxy binder is 10. After stirring and mixing evenly, the modified magnetic powder is added, and stirring and mixing are 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.

[0038] The modified magnetic powder uses modified magnetic powder 1, wherein the epoxy binder, by weight, includes 45 wt% of bisphenol A type liquid epoxy resin 128 epoxy resin, 15 wt% of low molecular weight solid bisphenol A type epoxy resin 901 epoxy resin, 10 wt% of methyl isobutyl ketone, 10 wt% of acrylic 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 50~100μm.

[0039] The epoxy binder-coated modified magnetic powder obtained in Example 1 was die-cast using a hydraulic press at a pressure of 15~20MPa and a curing temperature of 120℃ to obtain product 1, a magnetic powder core with high resistivity and low eddy current loss.

[0040] After cutting open the interior of product 1, its internal cross-section was scanned using electron microscopy (SEM). Figure 1 As shown, after the modified magnetic powder is coated with porous chitosan fine powder, the modified magnetic powder can be well dispersed inside the porous chitosan fine powder.

[0041] The results of various performance tests for Product 1 are as follows: Tensile strength σ MIt has a strength of 20.18 MPa, an effective permeability of 30.65, and a core density of 4.72 g / cm³. 3 The resistivity is 1.37 × 10⁻⁶. 9 Ω•m, quality factor 75, loss 554.17 mW / cm³.

[0042] The various performance testing methods for Product 1 are as follows:

[0043] Tensile strength σ M (Unit: MPa) The magnetic powder is die-cast 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 σ is calculated using the formula. M =F / A, which gives the tensile strength of the magnetic powder core.

[0044] Effective permeability was measured using an impedance analyzer with 37.5 turns of coil wound around a magnetic powder core ring at a frequency of 1 MHz. The effective permeability could then be calculated by combining the frequency with the sample size.

[0045] The density ρ is obtained by first weighing the magnetic powder core sample (m) using the weighing method, then determining the volume v of the magnetic powder core using the displacement method, and finally calculating it using the formula ρ=m / v.

[0046] Resistivity is measured using a resistivity meter. The magnetic powder core sample is placed on the test stage, and the probe stage is operated to press down the four probe heads to connect the sample to the power supply. The resistivity value is then read out.

[0047] The quality factor was measured using an impedance analyzer by winding a 37.5-turn coil around the magnetic core ring and then testing it at a frequency of 1MHz.

[0048] Loss was tested using a BH analyzer. A coil of 37.5 turns was wound around the magnetic core ring and then tested. The test conditions were a magnetic flux density Bm of 20mT, a frequency f of 1MHz, and a test temperature T of 25℃. Example 2:

[0049] Similar to Example 1, the preparation of epoxy binder-coated modified magnetic powder includes 95 wt% modified magnetic powder and 5 wt% epoxy binder. The epoxy binder is diluted evenly with methyl ethyl ketone (MEK) as a diluent, and the volume ratio of MEK to epoxy binder is 20. After stirring and mixing evenly, the modified magnetic powder is added, and stirring and mixing are continued. The stirring temperature is controlled at 60°C and stirred for 2 hours. The mixture is then filtered through a 400-mesh nylon sieve to obtain epoxy binder-coated modified magnetic powder. The modified magnetic powder used is modified magnetic powder 2, and the epoxy binder ratio is the same as in Example 1.

[0050] The epoxy binder-coated modified magnetic powder obtained in Example 2 was die-cast using a hydraulic press at a pressure of 15~20MPa and a curing temperature of 120℃ to obtain product 2, a magnetic powder core with high resistivity and low eddy current loss.

[0051] The various performance tests for Product 2 are conducted in accordance with Example 1. The tensile strength σ of Product 2 is... M It has a strength of 21.64 MPa, an effective permeability of 33.92, and a core density of 4.19 g / cm³. 3 The resistivity is 2.13 × 10⁻⁶. 9 Ω•m, quality factor 76, loss 548.53 mW / cm³.

[0052] Comparative Example 1:

[0053] Similar to Example 1, the epoxy binder-coated modified magnetic powder consists of 90 wt% modified magnetic powder and 10 wt% epoxy binder. The epoxy binder is diluted evenly with methyl ethyl ketone (MEK) as a diluent, and the volume ratio of MEK to epoxy binder is 10. After stirring and mixing evenly, the modified magnetic powder is added, and stirring and mixing are continued. The stirring temperature is controlled at 50°C and stirred for 4 hours. The mixture is then filtered through a 400-mesh nylon sieve to obtain the epoxy binder-coated modified magnetic powder. The modification of the magnetic powder follows the same process as the coupling agent surface treatment of modified magnetic powder 1, but without the porous chitosan coating treatment. The epoxy binder is the same as that in Example 1. The resulting epoxy binder-coated modified magnetic powder is then die-cast using 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.

[0054] The various performance tests for Product 3 are conducted in accordance with Example 1. The tensile strength σ of Product 3 is... M It has a strength of 19.24 MPa, an effective permeability of 23.21, and a core density of 5.81 g / cm³. 3 The resistivity is 3.52 × 10⁻⁶. 8 Ω•m, quality factor 65, loss 1304.42 mW / cm³.

[0055] Comparative Example 2:

[0056] Similar to Example 1, the epoxy binder-coated modified magnetic powder consists of 90 wt% modified magnetic powder and 10 wt% epoxy binder. The epoxy binder is diluted evenly with methyl ethyl ketone (MEK) as a diluent, and the volume ratio of MEK to epoxy binder is 10. After stirring and mixing evenly, the modified magnetic powder is added, and stirring and mixing are continued. The stirring temperature is controlled at 50°C and stirred for 4 hours. The mixture is then filtered through a 400-mesh nylon screen to obtain the epoxy binder-coated modified magnetic powder. The modified magnetic powder is produced using the same process as the first coupling agent surface treatment and is coated with porous chitosan. The epoxy binder is the same as that in Example 1. The resulting epoxy binder-coated modified magnetic powder is then die-cast using a hydraulic press at a pressure of 15-20 MPa and a curing temperature of 120°C to obtain the magnetic powder core product 4.

[0057] The various performance tests for Product 4 are conducted in accordance with Example 1. The tensile strength σ of Product 4 is... M It has a strength of 18.17 MPa, an effective permeability of 22.47, and a core density of 4.96 g / cm³. 3 The resistivity is 7.38 × 10⁻⁶. 8 Ω•m, quality factor 63, loss 985.76 mW / cm³.

[0058] Comparative Example 3:

[0059] Similar to Example 1, the epoxy binder-coated modified magnetic powder consists of 90 wt% modified magnetic powder and 10 wt% epoxy binder. The epoxy binder is diluted evenly with methyl ethyl ketone (MEK) as a diluent, and the volume ratio of MEK to epoxy binder is 10. After stirring and mixing evenly, the modified magnetic powder is added, and stirring and mixing are continued. The stirring temperature is controlled at 50°C and stirred for 4 hours. The mixture is then filtered through a 400-mesh nylon screen to obtain the epoxy binder-coated modified magnetic powder. The modified magnetic powder is produced using a process step involving surface treatment with a second coupling agent, and is coated with porous chitosan. The epoxy binder is the same as that in Example 1. The resulting epoxy binder-coated modified magnetic powder is then die-cast using a hydraulic press at a pressure of 15-20 MPa and a curing temperature of 120°C to obtain the magnetic powder core product 5.

[0060] The various performance tests of Product 5 are conducted in accordance with Example 1. The tensile strength σ of Product 5 is... M It has a strength of 18.65 MPa, an effective permeability of 24.32, and a core density of 4.87 g / cm³. 3 The resistivity is 8.67 × 10⁻⁶. 8 Ω•m, quality factor 68, loss 948.23 mW / cm³.

[0061] Examples 1 and 2 are products 1 and 2 obtained by coating modified magnetic powder with the epoxy binder of the present invention. Performance tests of the products show that because the modified magnetic powder is coated with porous chitosan pores and then coated with epoxy binder, the resulting products are used to fix the metal magnetic powder in the porous chitosan pores, so that the magnetic powder can be effectively dispersed among each other, reducing the agglomeration of magnetic powder. Therefore, the products have high dispersion resistivity and low loss (mainly eddy current loss). They effectively solve the problems of poor dispersion, agglomeration, poor insulation effect of magnetic powder, low resistivity of magnetic powder core, and large eddy current loss at high frequencies, which well meet the requirements of the use of modified magnetic powder in integrally molded inductors.

[0062] Similarly, in Comparative Example 1, although the modified magnetic powder was processed using a two-step coupling agent surface treatment, the dispersion effect of the modified magnetic powder was relatively high compared to Examples 1 and 2 because it was not coated with porous chitosan. The resistivity was relatively high and the loss (mainly eddy current loss) was also relatively large. This indicates that the magnetic powder was well dispersed after being coated with porous chitosan, and the agglomeration problem was well solved.

[0063] Similarly, in Comparative Examples 2 and 3, the modified magnetic powder, using a single coupling agent surface treatment process step, compared to Examples 1 or 2, did not employ a surface treatment process using two coupling agents. The resulting product performance test surfaces, after using a single coupling agent surface treatment process and encapsulating with porous chitosan, showed a significantly higher resistivity and a much lower loss (mainly eddy current loss) compared to Comparative Example 1. This indicates that using a single coupling agent surface treatment process, through the application of... Porous chitosan coating can effectively improve product performance. However, due to a single coupling agent surface treatment step, the bonding effect between the modified magnetic powder and porous chitosan is poor during the porous chitosan coating process. This significantly reduces the dispersion effect of the modified magnetic powder through the inclusion of porous chitosan. This is because 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 initially coat the outer surface of the magnetic powder well, forming a first insulating layer. The second coupling agent then binds the outer surface of the magnetic powder... The mixture is then coated again to form a second insulating layer. Because the second coupling agent is a silane coupling agent with amino groups, it not only forms a strong bond with the surface of the first coupling agent, but also introduces amino active groups onto the surface of the second insulating layer of the magnetic powder. The porous structure of the porous chitosan powder contains multiple amino and hydroxyl groups, all of which have residual electron pairs. The amino groups possess chemical activity and readily adsorb the magnetic powder containing the active amino groups on its surface. The magnetic powder can be adsorbed and dispersed within the porous structure of the porous chitosan. Simultaneously, the hydroxyl groups of the porous chitosan and the amino groups introduced on the surface of the magnetic powder undergo cross-linking to form chemical bonds, allowing the magnetic powder to be firmly positioned within the porous structure of the chitosan. Because the magnetic powder is positioned within the porous structure of the chitosan, the dispersion effect after positioning is good. Finally, the porous structure of the porous chitosan is cross-linked and sealed with a cross-linking agent, so that the magnetic powder can be completely sealed within the porous structure of the chitosan, ensuring the dispersion effect of the magnetic powder.

[0064] Therefore, in summary, the use of porous chitosan fine powder to coat modified magnetic powder is a key technology for achieving dispersibility and preventing agglomeration of modified magnetic powder. Furthermore, the use of a two-step coupling agent to modify the magnetic powder allows for a good bond and fixation between the modified magnetic powder and the porous structure of the porous chitosan fine powder. Thus, the use of a two-step coupling agent to modify the magnetic powder is another key technology for achieving dispersibility and preventing agglomeration of the modified magnetic powder. It is precisely because of the combination of the above-mentioned key technical solutions that the product obtained by this invention exhibits high resistivity and low loss (mainly eddy current loss).

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing epoxy binder-coated modified magnetic powder, characterized in that, The mixture includes 90-95 wt% modified magnetic powder and 5-10 wt% epoxy binder. The epoxy binder is diluted evenly with methyl ethyl ketone (MEK) as a diluent. The volume ratio of MEK to epoxy binder is 10-20. After stirring and mixing evenly, the modified magnetic powder is added, and stirring and mixing are continued. The stirring temperature is controlled at 50-60℃ and stirred for 2-4 hours. The mixture is then sieved through a 300-500 mesh nylon sieve to obtain epoxy binder-coated modified magnetic powder. The modified magnetic powder is prepared through the following steps: S1: Add magnetic powder to anhydrous ethanol solution, ultrasonically wash, filter and dry to obtain magnetic powder A washed with anhydrous ethanol; S2: Add a first coupling agent of 0.5~2wt% of magnetic powder A to anhydrous ethanol. The mass ratio of anhydrous ethanol to magnetic powder A is 1:

1. After mixing, the first modified solution is obtained. S3: Add a second coupling agent at 0.5~2wt% of magnetic powder A to anhydrous ethanol, where the mass ratio of anhydrous ethanol to magnetic powder A is... The ratio is 1:1, and after mixing, a second modified solution is obtained; S4: Place the above magnetic powder A on a slow rolling machine and roll it slowly. Add the first modified liquid and roll for 2-8 hours. After mixing evenly, add the second modified liquid and continue rolling for 2-8 hours. The rolling speed of the slow rolling machine is 1-3 rpm. After the second modified liquid is completely mixed, pass it through a 1000-2500 mesh nylon sieve to separate the magnetic powder A from the mixed slurry. Vacuum dry it at 80-90℃ to constant weight to obtain magnetic powder with coupling agent surface treatment. S5: Magnetic powder surface-treated with coupling agent and porous chitosan fine powder are mixed at a mass ratio of 1:0.25~0.

45. Anhydrous ethanol is used as solvent. The mixture is heated in an oil bath at 60~80℃ with anhydrous ethanol refluxed. After stirring and mixing under ultrasonic conditions for 2~4 hours, a crosslinking agent is slowly added. The mixture is stirred and mixed under ultrasonic conditions for another 2~4 hours to obtain a composite of porous chitosan-coated modified magnetic powder. The composite is separated from the mixture by passing it through a 500~800 mesh nylon sieve and vacuum dried at 80~90℃ to constant weight to obtain modified magnetic powder. In step S5, the porous chitosan fine powder is prepared by the following steps: Chitosan with a degree of deacetylation of 90-95% was dissolved in a 1-2 wt% aqueous acetic acid solution and stirred until completely dissolved to form a homogeneous chitosan-acetic acid aqueous solution. Silica gel powder with a particle size of 5-10 μm was stirred and uniformly dispersed in the chitosan-acetic acid aqueous solution to obtain a mixture, with the weight of the silica gel powder being 5-10 times the weight of the chitosan. The mixture was coated onto a glass plate and dried at 35-40°C to form a chitosan film. The dried chitosan film was then placed in a 2-10 wt% aqueous acetic acid solution. Boil the chitosan membrane in NaOH solution at 60-90℃ for 1-2 hours to remove silica gel powder; rinse the chitosan membrane with water until neutral, immerse the chitosan membrane in glycerol for 30-60 minutes, then rinse with water to remove surface glycerol, and let it stand at room temperature to obtain a porous chitosan membrane with a porosity of 40-50%; vacuum dry the porous chitosan membrane at 80-90℃ to constant weight, and grind it into porous chitosan fine powder with a particle size of 20-40μm.

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 2~4μm.

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, which is one or more of isopropyl tris(dioctylpyrophosphate) titanate, isopropyl tris(dodecylbenzenesulfonyl) titanate, and isopropyl trioleoyloxy 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 crosslinking 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, The epoxy adhesive, by weight, comprises 40-50 wt% bisphenol A type liquid epoxy resin, 10-20 wt% low molecular weight solid bisphenol A type epoxy resin, 5-10 wt% solvent, 5-10 wt% acrylic modified epoxy resin, 5-10 wt% polyurethane modified epoxy resin, 4-8 wt% dicyandiamide, 2-5 wt% accelerator, 0.2-0.8 wt% hydrophobic fumed silica, and 1-3 wt% glass microspheres with a particle size of 50-100 μm.

8. The preparation of epoxy binder-coated modified magnetic powder according to claim 7, characterized in that, The solvent is one or both of methyl isobutyl ketone and butanone.

9. The preparation of epoxy binder-coated modified magnetic powder according to claim 7, characterized in that, The accelerator is one or more of polyurea, modified imidazole, and modified amine.

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