Flame-retardant magnetic composite material and method for producing the same

Abstract

The present application belongs to the field of bonded magnetic composite material. The present application provides a kind of flame-retardant magnetic composite material and its preparation method, the preparation method includes the following steps, magnetic powder is dispersed in anhydrous organic alcohol solvent, add the salt containing flame-retardant metal element, add weak base solution, adjust pH to 7~10, stir, use magnetic powder as nucleation site, induce the flame-retardant metal hydroxide in situ growth and coating on its surface, obtain the magnetic powder of coated flame-retardant material;Add coupling agent, obtain the surface modified coated flame-retardant material of magnetic powder;The surface modified coated flame-retardant material of magnetic powder, flame-retardant modified resin and processing aid are mixed uniformly, then extruded granulation, obtain flame-retardant magnetic composite material.The preparation method of the present application, compared with prior art, the amount of flame retardant is significantly reduced, after testing, the prepared flame-retardant magnetic composite material grade reaches UL94-V0, with excellent flame retardancy, magnetic performance and mechanical performance.

Description

Technical Field

[0001] This invention belongs to the field of bonded magnetic composite materials, specifically relating to a method for preparing a flame-retardant magnetic composite material suitable for injection molding and extrusion molding. Background Technology

[0002] Bonded magnetic composites are functional materials made by using polymers (such as nylon, polyphenylene sulfide, and elastic plastics) as binders and magnetic powders (such as samarium iron nitrogen, neodymium iron boron, samarium cobalt, and ferrite) as magnetic components, which are then extruded or injection molded after high-temperature mixing. Compared with magnetic materials made through sintering, bonded magnetic composites exhibit significant advantages in processing performance. They can typically be processed and shaped using extrusion, injection molding, and other processes, making it easy to manufacture products with complex shapes and precise dimensions. They can also be used to prepare flexible magnetic materials. Therefore, bonded magnetic composites have found wide applications in the automotive, home appliance, office equipment, industrial machinery, and children's toys industries.

[0003] Most polymer matrices are inherently flammable, and rare earth magnetic powders typically possess high activity and fine particle size, making them highly flammable. The flammability of composite materials limits their application in fields with higher safety requirements. Even when flame-retardant modified resins are used as binders to mix with conventional rare earth magnetic powders, the high activity of the rare earth magnetic powders causes them to generate intense heat upon contact with high temperatures and oxygen, significantly reducing the material's flame retardancy rating.

[0004] To improve the flame retardancy of rare-earth magnetic composite materials, the conventional method is to directly add large doses of flame retardants to the composite system. Common flame retardants include inorganic flame retardants such as aluminum hydroxide, graphite, and red phosphorus, as well as halogenated and phosphorus-nitrogen-based organic flame retardants. When the flame retardancy rating of the product reaches V0, a ​​large amount of flame retardant is usually required. However, flame retardants are also fillers, and increasing their amount inevitably leads to a decrease in the proportion of magnetic powder or polymer binders, resulting in a reduction in the magnetic and mechanical properties of the corresponding product. Therefore, a smaller amount of flame retardant helps to ensure the flowability, formability, and magnetic properties of the composite material. However, current technologies cannot achieve good flame retardant effects with small amounts of flame retardant.

[0005] In addition, flame retardant powders, especially micro- and nano-sized flame retardants, are difficult to disperse uniformly in high-filling magnetic composite materials and are prone to agglomeration. This not only affects the flame retardant efficiency but also disrupts the continuous phase of the material, leading to a further reduction in flowability and formability and impairing mechanical properties.

[0006] In addition, many existing technologies have not effectively modified the surface of magnetic powders or flame retardants, resulting in poor interfacial compatibility between components. Due to the lack of effective interfacial interaction, the flame retardant and magnetic powder have poor compatibility, which ultimately affects the overall performance of the material.

[0007] Literature reports that using liquid flame retardants to coat magnetic powder can effectively reduce the amount of flame retardant added. However, liquid flame retardants have problems such as volatility and poor bonding stability with the matrix. Small molecules are easy to precipitate on the material surface, affecting the appearance and aging resistance. In addition, liquid flame retardants may produce a large amount of dense smoke, corrosive gases or toxic substances when burning. The production cost of liquid flame retardants, typically synthetic organophosphorus, is also relatively high, resulting in a low cost-performance ratio for composite materials. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a method for preparing a flame-retardant magnetic composite material. The method involves in-situ growth of metal hydroxide on the surface of magnetic powder to form a core flame-retardant coating layer. Subsequently, the coating layer is surface-modified using a coupling agent to obtain surface-modified magnetic powder with good interfacial compatibility. Finally, the modified magnetic powder is mixed with a resin binder and processing aids in a certain proportion, and then melt-extruded and granulated to obtain the flame-retardant magnetic composite material. Compared with the prior art, the amount of flame retardant used is significantly reduced, and the resulting flame-retardant magnetic composite material achieves a UL94-V0 rating, possessing excellent flame retardancy, magnetic properties, and mechanical properties.

[0009] The purpose of this invention is to provide a method for preparing a flame-retardant magnetic composite material, comprising the following steps:

[0010] (1) Disperse the magnetic powder in anhydrous organic alcohol solvent, add a salt containing flame-retardant metal elements that is soluble in organic alcohol, add a weak alkaline solution, adjust the pH of the solution to 7~10, stir at 25~70℃ for 0.5~2 h, use the magnetic powder as a nucleation site, induce the generated flame-retardant metal hydroxide to grow in situ on its surface and coat it, wash with anhydrous organic alcohol solvent, vacuum dry, and obtain magnetic powder coated with flame-retardant material;

[0011] (2) After the coupling agent is diluted with anhydrous organic alcohol solvent, it is added to the magnetic powder of the flame-retardant material obtained in step (1), mixed evenly at 25℃~70℃, and vacuum dried to obtain the surface-modified flame-retardant material magnetic powder.

[0012] (3) After the magnetic powder, flame-retardant modified resin and processing aid obtained in step (2) are mixed evenly, they are extruded and granulated at 150~220℃ to obtain flame-retardant magnetic composite material.

[0013] The preparation method of this invention first involves growing a metal hydroxide in situ on the surface of magnetic powder to form a core flame-retardant coating layer. Then, a coupling agent is used to modify the surface of this coating layer, resulting in surface-modified magnetic powder with good interfacial compatibility. Finally, the modified magnetic powder is mixed with a resin binder and processing aids in a certain proportion, and then melt-extruded and granulated to obtain a flame-retardant magnetic composite material. The key to this method is that by directly constructing a flame-retardant coating layer on the surface of the magnetic powder, the composite material can possess excellent flame retardancy, magnetic properties, and mechanical properties without the need for additional flame retardants, while requiring a small amount of flame-retardant component and achieving high efficiency.

[0014] Further, in step (1), the anhydrous organic alcohol solvent is anhydrous ethanol, and the salt containing a flame-retardant metal element soluble in the organic alcohol includes at least one of aluminum salt and magnesium salt, and the weak alkaline solution is ammonia. The aluminum salt or magnesium salt is preferably basic aluminum acetate or magnesium acetate.

[0015] Further, in step (1), the magnetic powder includes at least one of samarium iron nitrogen, neodymium iron boron, and samarium cobalt, or a mixture of at least one of samarium iron nitrogen, neodymium iron boron, and samarium cobalt with ferrite.

[0016] Further, in step (3), the flame-retardant modified resin includes a thermoplastic elastomer. Preferably, the flame-retardant modified resin includes at least one of styrene-based thermoplastic elastomers and polyurethane-based thermoplastic elastomers.

[0017] Furthermore, in step (3), the processing aids include at least one of compatibilizer, lubricant, and antioxidant.

[0018] Furthermore, in step (2), the coupling agent includes an amino-based coupling agent, the amount of which is 0.3 to 2 wt% of the original magnetic powder.

[0019] Furthermore, in step (1), the actual coating amount of metal hydroxide is 3 to 10 wt% of the original magnetic powder amount.

[0020] Another objective of this invention is to provide a flame-retardant magnetic composite material, which is prepared by the above-described preparation method.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) In this invention, aluminum hydroxide or magnesium hydroxide, which are used as flame retardants, are introduced onto the surface of magnetic powder. A flame retardant coating layer is formed on the surface of the magnetic powder through a chemical reaction. The flame retardant layer is firmly bonded to the magnetic powder, is not easy to migrate, and there is no compatibility problem between the magnetic powder and the flame retardant. During combustion, it can decompose and absorb heat, release crystal water, and form a dense metal oxide ceramic barrier, thus achieving multi-effect synergistic flame retardancy. The coating layer can not only improve the flame retardant performance of the powder, but also protect the highly active magnetic powder and prevent its performance from deteriorating in subsequent processing.

[0023] (2) In this invention, the flame retardant is directly coated on the surface of the magnetic powder in situ, which avoids the problem of uneven dispersion of the flame retardant in the magnetic powder-resin composite system during the mixing process, and achieves "point-to-point" high-efficiency flame retardancy. Under the premise of achieving the same flame retardant effect, the amount of flame retardant added can be significantly reduced. The reduction in the amount of flame retardant provides more room for adjusting the ratio of magnetic powder to resin, which makes it easier to synergistically optimize the magnetic properties and mechanical properties of the material.

[0024] (3) The present invention uses inorganic hydroxide flame retardant, which decomposes into water and oxides during combustion, does not produce toxic or corrosive gases, and the decomposed oxides can adsorb smoke particles, thus having an excellent smoke suppression effect.

[0025] (4) In this invention, the combination of flame retardant and coupling agent synergistically enhances interfacial compatibility. By utilizing the efficient combination of hydroxyl groups on the surface of metal hydroxide and amino coupling agent, the interfacial compatibility between inorganic magnetic powder and flame retardant modified resin matrix is ​​significantly improved. Attached Figure Description

[0026] Figure 1 The image shows an electron microscope image of the flame-retardant magnetic composite material particles prepared in Example 2. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] The raw materials used in this invention include magnesium or aluminum salts, coupling agents, permanent magnet powder, modified flame-retardant flexible resin, and plastic additives. Based on the above raw materials, this invention uses alcohol-soluble magnesium or aluminum salts, and induces the formation of metal hydroxides by adding ammonia water to adjust the pH of the solution, which grow on the surface of the magnetic powder to achieve coating. A dense flame-retardant coating layer is formed on the surface of the magnetic powder. After surface coupling treatment, it is blended with modified flame-retardant flexible resin and plastic additives, and then extruded and granulated to obtain a flame-retardant magnetic composite material.

[0029] The components and their mass percentages in the composite material of this invention are as follows:

[0030] Surface coated with 80%~92% modified magnetic powder

[0031] Flame-retardant modified resin 8%~20%

[0032] Plastic additives 0.3%~1%

[0033] The actual amount of hydroxide coating in the surface-coated modified magnetic powder is 3 to 10% of the relative weight of the magnetic powder, and the amount of coupling agent is 0.3 to 2 wt% of the relative weight of the magnetic powder.

[0034] The preparation method of this invention includes the following steps:

[0035] Step 1: Coating the surface of magnetic powder with metal hydroxide

[0036] Magnetic powder is dispersed in anhydrous ethanol solvent, aluminum or magnesium salt is added, and ammonia is added dropwise to adjust the pH of the solution to 7-10. The mixture is stirred at 25-70℃ for 0.5-2 h. During stirring, the magnetic powder will be continuously agitated in the solvent, forming a slurry state. The magnetic powder is uniformly dispersed in the solvent. Using the magnetic powder as nucleation sites, metal hydroxides are induced to grow in situ on their surface and coat the powder. After the reaction is complete, the resulting powder is washed with anhydrous ethanol and dried to obtain surface-coated magnetic powder.

[0037] Step 2: Surface modification with coated magnetic powder

[0038] The coupling agent diluted with anhydrous ethanol was added to the surface-coated magnetic powder obtained in step (1), mixed evenly at 25-70°C, and vacuum dried at 70-150°C to remove excess solvent to obtain surface-modified magnetic powder.

[0039] Step 3: Mixing and granulating flame-retardant magnetic composite materials

[0040] After the magnetic powder, flame-retardant modified resin and plastic processing aid obtained in step (2) are mixed evenly, they are extruded and granulated at 150~220℃ through a twin-screw extruder to obtain a flame-retardant magnetic composite material.

[0041] The following are examples and comparative examples based on the steps described above.

[0042] Example 1

[0043] 1. Metal hydroxides coated on the surface of magnetic powder

[0044] Samarium iron nitrogen magnetic powder was dispersed in anhydrous ethanol solvent, basic aluminum acetate was added, and the mixture was stirred to dissolve it. Ammonia water was added dropwise to adjust the pH of the solution to 8. The mixture was stirred at 50°C for 0.5 h. After the reaction was completed, excess solvent was removed and the powder was washed multiple times with anhydrous ethanol. The powder was then vacuum dried at 100°C to obtain magnetic powder with aluminum hydroxide coating. The coating amount was calculated to be approximately 3.1% of the weight of the magnetic powder after weighing.

[0045] 2. Surface modification of coated magnetic powder

[0046] Dissolve KH550 (γ-aminopropyltriethoxysilane) equivalent to 0.5 wt% of the magnetic powder weight in an appropriate amount of anhydrous ethanol and add it to the magnetic powder obtained in step 1. Stir at 5°C for 1 h and vacuum dry at 100°C to obtain surface-modified coated magnetic powder.

[0047] 3. Flame-retardant magnetic composite material compounding and granulation

[0048] (1) Feeding ratio: 88.16 wt% of magnetic powder obtained in step 2 (including 85 wt% of original magnetic powder + 2.72 wt% of metal hydroxide + 0.44 wt% of coupling agent), 11.34 wt% of TPE resin (styrene thermoplastic elastomer), and 0.5 wt% of plastic processing aids.

[0049] (2) Weigh the magnetic powder, thermoplastic elastomer and plastic processing aid obtained in step 2 according to the above proportions and add them to the high-speed mixer to mix evenly. Then, use a twin-screw extruder to knead and granulate at 180°C to obtain a flame-retardant magnetic composite material.

[0050] Example 2

[0051] 1. Metal hydroxides coated on the surface of magnetic powder

[0052] Samarium iron nitrogen magnetic powder was dispersed in anhydrous ethanol solvent, basic aluminum acetate was added, and the mixture was stirred to dissolve it. Ammonia water was added dropwise to adjust the pH of the solution to 8. The mixture was stirred at 50°C for 1 h. After the reaction was completed, excess solvent was removed and the powder was washed multiple times with anhydrous ethanol. The powder was then vacuum dried at 100°C to obtain magnetic powder with aluminum hydroxide coating. The coating amount was calculated to be approximately 5.9% of the weight of the magnetic powder after weighing.

[0053] 2. Surface modification of coated magnetic powder

[0054] Dissolve KH550 equivalent to 0.5 wt% of the magnetic powder weight in an appropriate amount of anhydrous ethanol and add it to the magnetic powder obtained in step 1. Stir at 50°C for 1 h and vacuum dry at 100°C to obtain surface-modified coated magnetic powder.

[0055] 3. Flame-retardant magnetic composite material compounding and granulation

[0056] (1) Feeding ratio: 89.72 wt% of magnetic powder obtained in step 2 (including 84 wt% of original magnetic powder + 5.27 wt% of metal hydroxide + 0.45 wt% of coupling agent), 9.78 wt% of TPE resin (styrene thermoplastic elastomer), and 0.5 wt% of plastic processing aids.

[0057] (2) Weigh the magnetic powder, thermoplastic elastomer, and plastic processing aids obtained in step 2 according to the above proportions and add them to a high-speed mixer to mix evenly. Then, use a twin-screw extruder to knead and granulate at 180°C to obtain a flame-retardant magnetic composite material. The electron microscope image of the flame-retardant magnetic composite material granules prepared in Example 2 is shown below. Figure 1 As shown.

[0058] Example 3

[0059] 1. Metal hydroxides coated on the surface of magnetic powder

[0060] Samarium iron nitrogen magnetic powder was dispersed in anhydrous ethanol solvent, basic aluminum acetate was added, and the mixture was stirred to dissolve it. Ammonia water was added dropwise to adjust the pH of the solution to 8. The mixture was stirred at 50°C for 2 h. After the reaction was completed, excess solvent was removed and the powder was washed multiple times with anhydrous ethanol. The powder was then vacuum dried at 100°C to obtain magnetic powder with aluminum hydroxide coating on the surface. The calculated coating amount was approximately 9.7% of the weight of the magnetic powder.

[0061] 2. Surface modification of coated magnetic powder

[0062] Dissolve KH550 equivalent to 0.5 wt% of the magnetic powder weight in an appropriate amount of anhydrous ethanol and add it to the magnetic powder obtained in step 1. Stir at 50°C for 1 h and vacuum dry at 100°C to obtain surface-modified coated magnetic powder.

[0063] 3. Flame-retardant magnetic composite material compounding and granulation

[0064] (1) Feeding ratio: 91.26 wt% of magnetic powder obtained in step 2 (including 82 wt% of original magnetic powder + 8.81 wt% of metal hydroxide + 0.45 wt% of coupling agent), 8.24 wt% of TPE resin (styrene thermoplastic elastomer), and 0.5 wt% of plastic processing aids.

[0065] (2) Weigh the magnetic powder, thermoplastic elastomer and plastic processing aid obtained in step 2 according to the above proportions and add them to the high-speed mixer to mix evenly. Then, use a twin-screw extruder to knead and granulate at 180°C to obtain a flame-retardant magnetic composite material.

[0066] Example 4

[0067] 1. Metal hydroxides coated on the surface of magnetic powder

[0068] Samarium iron nitrogen magnetic powder was dispersed in anhydrous ethanol solvent, magnesium acetate was added, and the mixture was stirred to dissolve it. Ammonia was added dropwise to adjust the pH of the solution to 9. The mixture was stirred at 50°C for 1 h. After the reaction was completed, excess solvent was removed and the powder was washed multiple times with anhydrous ethanol. The powder was then vacuum dried at 100°C. After weighing, the coating amount was calculated to be approximately 6.2% of the magnetic powder weight.

[0069] 2. Surface modification of coated magnetic powder

[0070] Dissolve KH550 equivalent to 0.5 wt% of the magnetic powder weight in an appropriate amount of anhydrous ethanol and add it to the magnetic powder obtained in step 1. Stir at 50°C for 1 h and vacuum dry at 100°C to obtain surface-modified coated magnetic powder.

[0071] 3. Flame-retardant magnetic composite material compounding and granulation

[0072] (1) Feeding ratio: 90.00 wt% of magnetic powder obtained in step 2 (including 84 wt% of original magnetic powder + 5.55 wt% of metal hydroxide + 0.45 wt% of coupling agent), 9.50 wt% of TPE resin (styrene thermoplastic elastomer), and 0.5 wt% of plastic processing aids.

[0073] Weigh the magnetic powder, thermoplastic elastomer, and plastic processing aids obtained in step 2 according to the above proportions and add them to a high-speed mixer to mix evenly. Then, use a twin-screw extruder to knead and granulate the mixture at 180°C to obtain a flame-retardant magnetic composite material.

[0074] Example 5

[0075] 1. Metal hydroxides coated on the surface of magnetic powder

[0076] A mixture of samarium iron nitrogen and ferrite magnetic powder (samarium iron nitrogen: ferrite mass ratio of 3:1) was dispersed in anhydrous ethanol solvent. Basic aluminum acetate was added and stirred to dissolve the powder. Ammonia water was added dropwise to adjust the pH of the solution to 8. The mixture was stirred at 50°C for 1 h. After the reaction was completed, excess solvent was removed and the powder was washed multiple times with anhydrous ethanol. The powder was then vacuum dried at 100°C to obtain magnetic powder with aluminum hydroxide coating. The coating amount was calculated to be approximately 6.1% of the weight of the magnetic powder after weighing.

[0077] 2. Surface modification of coated magnetic powder

[0078] Dissolve KH550 equivalent to 0.5 wt% of the magnetic powder weight in an appropriate amount of anhydrous ethanol and add it to the magnetic powder obtained in step 1. Stir at 50°C for 1 h and vacuum dry at 100°C to obtain surface-modified coated magnetic powder.

[0079] 3. Flame-retardant magnetic composite material compounding and granulation

[0080] (1) Feeding ratio: 89.91 wt% of magnetic powder obtained in step 2 (including 84 wt% of original magnetic powder + 5.46 wt% of metal hydroxide + 0.45 wt% of coupling agent), 9.59 wt% of TPE resin (styrene thermoplastic elastomer), and 0.5 wt% of plastic processing aids.

[0081] (2) Weigh the magnetic powder, thermoplastic elastomer and plastic processing aid obtained in step 2 according to the above proportions and add them to the high-speed mixer to mix evenly. Then, use a twin-screw extruder to knead and granulate at 180°C to obtain a flame-retardant magnetic composite material.

[0082] Example 6

[0083] 1. Metal hydroxides coated on the surface of magnetic powder

[0084] Neodymium iron boron magnetic powder was dispersed in anhydrous ethanol solvent, and basic aluminum acetate was added in proportion. The mixture was stirred to dissolve the powder, and ammonia was added dropwise to adjust the pH of the solution to 8. The mixture was stirred at 50°C for 1 h. After the reaction was completed, excess solvent was removed and the powder was washed multiple times with anhydrous ethanol. The powder was then vacuum dried at 100°C to obtain magnetic powder with aluminum hydroxide coating. The calculated coating amount was approximately 5.6% of the weight of the magnetic powder.

[0085] 2. Surface modification of coated magnetic powder

[0086] Dissolve KH550 equivalent to 0.5 wt% of the magnetic powder weight in an appropriate amount of anhydrous ethanol and add it to the magnetic powder obtained in step 1. Stir at 50°C for 1 h and vacuum dry at 100°C to obtain surface-modified coated magnetic powder.

[0087] 3. Flame-retardant magnetic composite material compounding and granulation

[0088] (1) Feeding ratio: 89.42 wt% of magnetic powder obtained in step 2 (including 84 wt% of original magnetic powder + 4.98 wt% of metal hydroxide + 0.44 wt% of coupling agent), 10.08 wt% of TPE resin (styrene thermoplastic elastomer), and 0.5 wt% of plastic processing aids.

[0089] (2) Weigh the magnetic powder, thermoplastic elastomer and plastic processing aid obtained in step 2 according to the above proportions and add them to the high-speed mixer to mix evenly. Then, use a twin-screw extruder to knead and granulate at 180°C to obtain a flame-retardant magnetic composite material.

[0090] Comparative Example 1

[0091] 1. Magnetic powder surface modification

[0092] Dissolve KH550 (equivalent to 0.5 wt.% of the magnetic powder weight) in an appropriate amount of anhydrous ethanol and add it to samarium iron nitrogen magnetic powder. Stir at 50°C for 1 h and dry under vacuum at 100°C to obtain coupling modified magnetic powder.

[0093] 2. Flame-retardant magnetic composite material compounding and granulation

[0094] (1) Feeding ratio: In this example, the magnetic powder obtained in step 1 is 84.42 wt% (including 84 wt% of the original magnetic powder + 0.42 wt% of the coupling agent), aluminum hydroxide flame retardant is 5.27 wt%, TPE resin (styrene thermoplastic elastomer) is 9.81 wt%, and plastic processing aids are 0.5 wt%.

[0095] (2) Weigh the magnetic powder, thermoplastic elastomer and plastic processing aid obtained in step 1 of this example according to the above proportion and add them to the high-speed mixer to mix evenly. Then, use a twin-screw extruder to knead and granulate at 180°C to obtain a flame-retardant magnetic composite material.

[0096] Comparative Example 2

[0097] 1. Coating the surface of magnetic powder with metal hydroxide (same as step 1 in Example 2)

[0098] Samarium iron nitrogen magnetic powder was dispersed in anhydrous ethanol solvent, basic aluminum acetate was added, and the mixture was stirred to dissolve it. Ammonia water was added dropwise to adjust the pH of the solution to 8. The mixture was stirred at 50°C for 1 h. After the reaction was completed, excess solvent was removed and the powder was washed multiple times with anhydrous ethanol. The powder was then vacuum dried at 100°C to obtain magnetic powder with aluminum hydroxide coating. The coating amount was calculated to be approximately 5.9% of the weight of the magnetic powder after weighing.

[0099] 2. Flame-retardant magnetic composite material compounding and granulation

[0100] (1) Feeding ratio: 89.27 wt% of magnetic powder obtained in step 2 (including 84 wt% of original magnetic powder + 5.27 wt% of metal hydroxide, without the addition of coupling agent), 10.23 wt% of TPE resin (styrene thermoplastic elastomer), and 0.5 wt% of plastic processing aids.

[0101] (2) Weigh the magnetic powder, thermoplastic elastomer and plastic processing aid obtained in step 2 according to the above proportions and add them to the high-speed mixer to mix evenly. Then, use a twin-screw extruder to knead and granulate at 180°C to obtain a flame-retardant magnetic composite material.

[0102] Performance testing

[0103] The composite material particles obtained in Examples 1-6 and Comparative Examples 1 and 2 were made into standard test strips on an injection molding machine for performance testing.

[0104] Test method:

[0105] The magnetic properties were tested according to GB / T 3217-2013 "Test Methods for Magnetic Properties of Permanent Magnet (Hard Magnetic) Materials";

[0106] The tensile fracture strain test method was performed in accordance with GB / T 1040.2-2022 Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics;

[0107] Flame retardancy rating tests are conducted according to UL94:2016, Clause 8, V0, V1, V2.

[0108] The test results are shown in the table below:

[0109] As can be seen from the data in the table, Examples 1-6 achieved a flame retardant rating of V0 by constructing a uniform flame retardant coating layer on the surface of the magnetic powder, provided that the content of the flame retardant component relative to the magnetic powder was no higher than 10%. Even when the content of the flame retardant component relative to the magnetic powder was as low as 3.1%, it still achieved a V1 rating. Compared with Comparative Examples 1 and 2, when the content of the flame retardant component relative to the magnetic powder was the same (5.9%), the flame retardant rating of Comparative Example 1 (directly adding an equal amount of flame retardant) was only HB, while both Examples 2 and Comparative Example 2 (generating flame retardant components through in-situ coating) achieved a V0 rating. This indicates that generating flame retardant components through in-situ coating can effectively improve the flame retardancy of the material. However, the tensile fracture strain of Comparative Example 2 was lower than that of Example 2 because the magnetic powder was not surface modified after coating. This indicates that performing surface modification after coating the magnetic powder is an effective measure to improve the mechanical properties of the material. This coating structure not only achieves effective flame retardancy but also protects the magnetic powder and reduces the performance loss of the magnetic powder during processing. Furthermore, the process exhibits stable performance improvement in different magnetic powder systems (such as Examples 2, 4, 5, and 6), demonstrating good versatility and process reliability.

[0110] In summary, the preparation method of this invention first forms a core flame-retardant coating layer by in-situ growth of metal hydroxide on the surface of magnetic powder; then, the coating layer is surface-modified using a coupling agent to obtain surface-modified magnetic powder with good interfacial compatibility. Finally, the modified magnetic powder is mixed with resin binder and processing aids in a certain proportion, and then melt-extruded and granulated to obtain a flame-retardant magnetic composite material. The key to this method is that by directly constructing a flame-retardant coating layer on the surface of magnetic powder, the composite material can possess excellent flame retardancy, magnetic properties, and mechanical properties without the need for additional flame retardants, and the amount of flame-retardant component used is small and highly efficient.

[0111] The above embodiments are for illustrative purposes only and are not intended to limit the invention. Those skilled in the art can make various changes or modifications without departing from the spirit and scope of the invention. Therefore, all equivalent technical solutions should also fall within the scope of the invention and should be defined by the claims.

Claims

1. A method for preparing a flame-retardant magnetic composite material, characterized in that, Includes the following steps, (1) Disperse the magnetic powder in anhydrous organic alcohol solvent, add a salt containing flame-retardant metal elements that is soluble in organic alcohol, add a weak alkaline solution, adjust the pH of the solution to 7~10, stir at 25~70℃ for 0.5~2 h, use the magnetic powder as a nucleation site, induce the generated flame-retardant metal hydroxide to grow in situ on its surface and coat it, wash with anhydrous organic alcohol solvent, vacuum dry, and obtain magnetic powder coated with flame-retardant material; (2) After the coupling agent is diluted with anhydrous organic alcohol solvent, it is added to the magnetic powder of the flame-retardant material obtained in step (1), mixed evenly at 25℃~70℃, and vacuum dried to obtain the surface-modified flame-retardant material magnetic powder. (3) After the magnetic powder, flame-retardant modified resin and processing aid obtained in step (2) are mixed evenly, they are extruded and granulated at 150~220℃ to obtain flame-retardant magnetic composite material.

2. The preparation method according to claim 1, characterized in that, In step (1), the anhydrous organic alcohol solvent is anhydrous ethanol, the salt containing flame-retardant metal elements soluble in organic alcohol includes at least one of aluminum salt and magnesium salt, and the weak alkaline solution is ammonia water.

3. The preparation method according to claim 1, characterized in that, In step (1), the magnetic powder includes at least one of samarium iron nitrogen, neodymium iron boron, and samarium cobalt, or a mixture of at least one of samarium iron nitrogen, neodymium iron boron, and samarium cobalt with ferrite.

4. The preparation method according to claim 1, characterized in that, In step (3), the flame-retardant modified resin includes a thermoplastic elastomer.

5. The preparation method according to claim 4, characterized in that, The thermoplastic elastomer includes at least one of styrene-based thermoplastic elastomers and polyurethane-based thermoplastic elastomers.

6. The preparation method according to claim 1, characterized in that, In step (3), the processing aid includes at least one of compatibilizer, lubricant, and antioxidant.

7. The preparation method according to claim 1, characterized in that, In step (2), the coupling agent includes an amino-based coupling agent, and its dosage is 0.3 to 2 wt% of the original magnetic powder dosage.

8. The preparation method according to claim 1, characterized in that, In step (1), the actual coating amount of metal hydroxide is 3 to 10 wt% of the original magnetic powder.

9. A flame-retardant magnetic composite material, prepared by the preparation method according to any one of claims 1-8.

Images