Preparation method of flexible permanent magnetic composite material

Abstract

The application discloses a preparation method of a flexible permanent magnetic composite material. The application firstly uses a KH550 coupling agent to perform surface pretreatment on magnetic powder, improves the combination of the powder and a copolyamide coating layer interface; then uses an alcohol-soluble copolyamide to coat the powder, forms a compact copolyamide protective layer on the surface of the magnetic powder; and then mixes the magnetic powder after the copolyamide resin coating treatment, TPE resin and plastic additives such as lubricants and stabilizers, and then performs mixing, extrusion and granulation; thus, in the mixing process, before the TPE binder completely and fully wraps the magnetic powder, the magnetic powder is previously isolated from the surrounding air, and the molten or softened copolyamide is in a very flexible state, plays a role of buffering and lubrication, effectively reduces the damage of high shear between the sheared powders and between the powders and the screw to the powders, significantly reduces the loss of magnetic properties such as coercive force, but does not affect the mixing effect of the strong shear on the whole material formula system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of bonded magnetic composites, and relates to a preparation method of a flexible permanent magnetic composite material with high toughness suitable for injection molding and extrusion molding. BACKGROUND

[0002] Flexible magnetic materials are widely used in toys, door seals and micro-motors. With the development of new technologies and new demands of people on electronic consumer goods, flexible magnetic materials have many new applications in the field of consumer electronics, such as wireless charging, magnetic data line absorption, magnetic watchband, etc. TPE resin refers to thermoplastic elastomer (Thermoplastic Elastomer) resin, a special type of polymer material with rubber elasticity and plastic processability. It has both thermoplasticity and high elasticity, combining the advantages of thermoplastic and elastic rubber. Compared with rubber with high elasticity, TPE can form a relatively complex workpiece in one step by injection molding, and can be recycled for reuse, increasing the use rate of materials and reducing waste. TPE is safe and non-toxic to the human body, suitable for long-term skin contact environment, and the material can be injection molded to obtain products of different shapes by changing the mold. Therefore, from the comprehensive evaluation of processing performance and environmental protection, TPE matrix is an ideal choice as a binder for flexible permanent magnetic composites.

[0003] Permanent magnetic materials mainly include samarium iron nitride (SmFeN), neodymium iron boron (NdFeB) and ferrite. Ferrite has low magnetic performance, but it is resistant to salt mist corrosion and has low price, and is usually suitable for low magnetic performance requirements, large material consumption and price-sensitive applications; neodymium iron boron magnets have high magnetic performance advantages, but are prone to rust and corrosion and the raw material is expensive; samarium iron nitride also has much higher magnetic performance than ferrite, uses surplus rare earth element samarium, has relatively low and stable price, is resistant to salt mist corrosion and not prone to rust, and is suitable for high-end applications with high magnetic performance requirements.

[0004] The flexible permanent magnetic composite material uses samarium iron nitrogen, ferrite, neodymium iron boron, or a composite magnetic powder thereof as a magnetic component, and uses TPE as a resin matrix binder. In a twin-screw extruder or other mixing equipment, the resin matrix and magnetic powder filler are fully dispersed and mixed by using the effects of heating, rotating stirring, shearing, and pressure. In the process of mixing and extruding the magnetic powder and the TPE resin, the magnetic properties of the material, especially the coercive force, are mainly affected by high-temperature oxidation and high shear. The temperature of the extrusion mixing is usually not lower than the melting point of the binder resin matrix; the chemical properties of the rare earth magnetic powder are active, and high-temperature oxidation and screw shearing can affect the magnetic properties, especially the coercive force; the ferrite magnetic powder is resistant to oxidation, but the strong shear force during mixing can also damage the crystal structure of the magnetic powder, reducing its magnetic properties. The damage of high shear to the magnetic powder mainly occurs before the magnetic powder is completely coated by the resin. When the resin and the magnetic powder are fully mixed, the magnetic powder is fully coated by the molten resin. Due to the lubricating effect of the molten resin, the magnetic powder is separated by the molten resin between the magnetic powder and the magnetic powder, and between the magnetic powder and the screw. The shear damage and oxidation are greatly reduced. In the process of mixing and extruding and granulating, when the magnetic powder and the TPE resin pass through the screw conveying section to the screw shearing and mixing section and are fully mixed, the TPE resin has not yet completely melted, and the magnetic powder has not been completely coated by the TPE. At this time, the magnetic powder is in a high-temperature, oxygen-containing, and high-shear environment. The shear friction between the magnetic powders, the shear friction between the magnetic powder and the screw, and the high-temperature oxidation of the rare earth magnetic powder (samarium iron nitrogen, neodymium iron boron, etc.) can cause a significant reduction in the magnetic properties, especially the coercive force.

[0005] The invention patent CN201911250259.0 provides a method for preparing a permanent magnetic composite material by coating with a silane coupling agent. The surface of the magnetic powder is coated with 0.01-1.0wt% of a silane or titanate coupling agent, and then mixed with a resin. Although the surface of the magnetic powder is coated, which improves the interfacial adhesion and isolates air to some extent, it cannot alleviate the shear force, and the non-flexible coating layer is easily worn out during the shearing process, causing part of the magnetic powder surface to be exposed.

[0006] Co-polyamide is different from homopolymer polyamide. Its structure is disordered and mixed, which destroys the sequence structure regularity of the molecular chain and hinders the hydrogen bond connection between the molecular chains. It is a kind of polyamide material with low melting point and high flexibility. Alcohol-soluble co-polyamide is a kind of co-polyamide material that shows good solubility in alcohol solvents. By introducing functional monomers with alcohol groups (-OH) (such as hydroxyacetic acid and hydroxybutyric acid) during the polymerization of co-polyamide, these alcohol groups can interact with alcohol solvents through hydrogen bonds, so that this kind of co-polyamide can be dissolved in alcohol solvents. SUMMARY

[0007] The application aims to provide a preparation method of TPE-based flexible permanent magnetic composite material by modifying the surface resin coating treatment of magnetic powder, so as to prepare a magnetic composite material with excellent magnetism, mechanics and processability.

[0008] The application comprises the following steps:

[0009] Step 1, magnetic powder pretreatment

[0010] After the coupling agent is appropriately diluted, it is added to the magnetic powder and uniformly mixed at 20-70°C, and vacuum dried at 70-150°C.

[0011] Step 2, magnetic powder coating copolyamide

[0012] The alcohol-soluble copolyamide is dissolved in an appropriate amount of alcohol solvent, and stirred at 20-70°C to make it fully dissolved.

[0013] The solution is added to the magnetic powder obtained in step 1 while hot, and uniformly mixed.

[0014] After vacuum drying at 70-150°C, the magnetic powder with the surface completely wrapped by the copolyamide is obtained.

[0015] Step 3, mixing and granulation of flexible permanent magnetic composite material

[0016] The magnetic powder obtained in step 2, the flexible resin binder and the plastic additive are uniformly mixed, and granulated by a double-screw extruder at 150-200°C to obtain the flexible permanent magnetic composite material.

[0017] The flexible permanent magnetic composite material is prepared by pre-wrapping the copolyamide on the magnetic powder and then mixing and extruding with the TPE binder, and has the following advantages:

[0018] First, the coupling agent is used to pretreat the surface of the magnetic powder in the application, which improves the bonding force between the powder and the copolyamide coating layer, so that the copolyamide coating layer can be firmly wrapped on the surface of the magnetic powder.

[0019] Second, the alcohol-soluble copolyamide is used to coat the surface of the magnetic powder in the application, and even in the state that the TPE resin and the magnetic powder have not been fully mixed during the extrusion process, there is always a dense and flexible copolyamide coating layer on the surface of the magnetic powder. On the one hand, it effectively isolates the air and avoids the oxidation of the rare earth magnetic powder at the mixing temperature; on the other hand, the molten or softened copolyamide coating layer is in a very flexible state, which plays a role of buffering and lubrication, effectively reducing the damage of the friction and strong shearing between the powder and the powder and between the powder and the screw on the magnetic powder, and significantly reducing the loss of magnetic properties such as coercivity during the mixing process, but not affecting the mixing effect of the strong shearing on the entire material formula system. DETAILED DESCRIPTION

[0020] The present application will be described in more detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

[0021] The basic concept of the present application is that the raw materials used in the present application include flexible resin binder, permanent magnetic powder, copolyamide and plastic additive. Based on the above-mentioned raw materials, the present application uses alcohol-soluble copolyamide to coat the surface of the pretreated magnetic powder, forming a dense copolyamide coating layer on the surface, so as to effectively buffer the damage of the strong shearing force between the magnetic powders and between the magnetic powders and the screw during the mixing process, and isolate the air to avoid the oxidation of the magnetic powders, thereby protecting the magnetic powders and significantly improving the performance of the product.

[0022] According to the above concept, the composite material of the present application includes the following components and their mass percentages:

[0023] Copolyamide-coated magnetic powder 80% to 92%

[0024] TPE resin 8% to 20%

[0025] Plastic additive package 0.3% to 1%

[0026] The solubility of the copolyamide at 70°C is not less than 2g / 100g alcohol solvent, otherwise it is difficult to meet the required amount of copolyamide addition; the flexible resin binder is TPE resin, preferably SEBS (styrene-ethylene-butylene-styrene block copolymer) TPE resin; the plastic additive package is a commercially available mixture, the main components of which are plastic processing lubricant, stabilizer, release agent, etc., and other additives can also be added according to the actual use and needs of the product, such as ultraviolet absorber for outdoor use, etc.

[0027] The present application includes the following steps:

[0028] Step 1, magnetic powder pretreatment

[0029] A certain amount of KH550 coupling agent is dissolved in a suitable amount of anhydrous ethanol or isopropanol for dilution, and the amount of KH550 coupling agent is 0.3-2wt.% relative to the weight of the magnetic powder, and the amount of solvent added for dilution is sufficient to wet the surface of the magnetic powder;

[0030] Then add samarium iron nitrogen, ferrite, neodymium iron boron, or composite magnetic powder, and stir at 20-70°C until uniformly mixed; vacuum drying at 70-150°C.

[0031] Step 2, magnetic powder coating with copolyamide

[0032] Dissolve 0.5-3 wt.% of the alcohol-soluble copolyamide relative to the magnetic powder in an appropriate amount of anhydrous ethanol or isopropanol, stir at 20-70℃ to fully dissolve the copolyamide, and the amount of solvent should be enough to completely dissolve the copolyamide and completely wet the magnetic powder;

[0033] Mix the solution into the powder obtained in the above step while hot, and the magnetic powder should be preheated to the temperature of the copolyamide solution, and the mixing process should be maintained at not less than this temperature, otherwise the temperature of the solution will decrease after mixing, which can cause the homopolyamide to precipitate prematurely, which is not conducive to uniform mixing (note that the temperature should not be higher than 70℃, so as to reduce solvent evaporation); then vacuum dry at 70-150℃ to obtain magnetic powder with a surface completely and densely coated with copolyamide.

[0034] Step 3, mixing and granulation of the flexible permanent magnetic composite material

[0035] Mix the magnetic powder, flexible resin binder, and plastic additives obtained in step 2 through a high-speed mixer, and granulate using a twin-screw extruder at 150-200℃ to obtain a TPE-based flexible permanent magnetic composite material.

[0036] The TPE-based flexible permanent magnetic composite material is prepared using the process of mixing, extruding, and granulating: first, the magnetic powder is pre-treated on the surface using KH550 coupling agent to improve the bonding between the powder and the copolyamide coating layer, so that the copolyamide coating layer can be more uniformly and firmly wrapped around the surface of the samarium iron nitride powder in the subsequent process; then the powder is coated with alcohol-soluble copolyamide to form a dense polyamide protective layer on the surface of the magnetic powder; then the magnetic powder coated with copolyamide resin is mixed with TPE resin and plastic additives such as lubricants and stabilizers, and then mixed, extruded, and granulated; thus, during the mixing process, the magnetic powder is pre-encapsulated and isolated from the surrounding air before the TPE binder fully and completely wraps the magnetic powder, and the molten or softened copolyamide is in a very flexible state, which plays a role in buffering and lubrication, effectively reducing the damage of high shear between the magnetic powder and the magnetic powder, and between the magnetic powder and the screw (including the protection of the crystal structure of the magnetic powder and the coupling agent coating layer after pre-treatment), significantly reducing the loss of magnetic properties such as coercivity, but not affecting the mixing effect of the high shear on the entire material formulation system.

[0037] The following examples and comparative examples are given in conjunction with the above steps:

[0038] Example 1

[0039] The various raw materials and their mass percentages in this example are as follows:

[0040]

[0041] The process steps are as follows:

[0042] Step 1, Pretreatment of magnetic powder

[0043] Dissolve KH550 coupling agent equivalent to 0.5wt.% of the weight of the magnetic powder in an appropriate amount of anhydrous ethanol, then add samarium-iron-nitrogen magnetic powder, stir and mix at 50°C for 1 h, and vacuum dry at 100°C.

[0044] Step 2, Coating of magnetic powder with copolyamide

[0045] Add alcohol-soluble copolyamide equivalent to 1.5wt.% of the weight of the magnetic powder pretreated in Step 1 to an appropriate amount of anhydrous isopropanol, heat and stir at 60°C to fully dissolve; then add to the samarium-iron-nitrogen magnetic powder prepared in Step 1 and preheated to 60°C, stir and mix at 60°C for 1 h, and then vacuum dry at 100°C to obtain samarium-iron-nitrogen magnetic powder coated with copolyamide on the surface.

[0046] Step 3, Mixing and granulation of flexible permanent magnetic composite material

[0047] Mix the magnetic powder prepared in Step 2, TPE resin, and plastic additives uniformly by a high-speed mixer, and mix and granulate by a twin-screw extruder at 175°C to obtain a TPE-bonded samarium-iron-nitrogen magnetic composite material.

[0048] Example 2

[0049] The various raw materials and mass percentages of the raw materials in this example are as follows:

[0050]

[0051] The process steps are as follows:

[0052] Step 1, Pretreatment of magnetic powder

[0053] Dissolve KH550 coupling agent equivalent to 0.5wt.% of the weight of the magnetic powder in an appropriate amount of anhydrous ethanol, then add samarium-iron-nitrogen magnetic powder, stir and mix at 50°C for 1 h, and vacuum dry at 100°C.

[0054] Step 2, Coating of magnetic powder with copolyamide

[0055] Add alcohol-soluble copolyamide equivalent to 1.0wt.% of the weight of the magnetic powder pretreated in Step 1 to an appropriate amount of anhydrous isopropanol, heat and stir at 60°C to fully dissolve; then add to the samarium-iron-nitrogen magnetic powder prepared in Step 1 and preheated to 60°C, stir and mix at 60°C for 1 h, and then vacuum dry at 100°C to obtain samarium-iron-nitrogen magnetic powder coated with copolyamide on the surface.

[0056] Step 3, Mixing and granulation of flexible permanent magnetic composite material

[0057] The magnetic powder prepared in step 2, TPE resin and plastic additives are mixed uniformly by a high-speed mixer, and then granulated by a twin-screw extruder at 175°C to obtain a TPE bonded samarium-nitrogen-iron magnetic composite material.

[0058] Example 3

[0059] The various raw materials and the mass percentage of the raw materials in this example are as follows:

[0060]

[0061] The process steps are as follows:

[0062] Step 1, Pretreatment of magnetic powder

[0063] KH550 coupling agent equivalent to 0.5wt.% of the weight of the magnetic powder is dissolved in an appropriate amount of anhydrous ethanol, and then the samarium-nitrogen-iron magnetic powder is added, stirred and mixed at 50°C for 1h, and vacuum dried at 100°C.

[0064] Step 2, Coating of magnetic powder with copolyamide

[0065] Alcohol-soluble copolyamide equivalent to 2.5wt.% of the weight of the magnetic powder pretreated in step 1 is added to an appropriate amount of anhydrous isopropyl alcohol, heated and stirred at 60°C to dissolve it completely; then added to the samarium-nitrogen-iron magnetic powder prepared in step 1 and preheated to 60°C, stirred and mixed at 60°C for 1h, and then vacuum dried at 100°C to obtain samarium-nitrogen-iron magnetic powder coated with copolyamide on the surface.

[0066] Step 3, Mixing and granulation of flexible permanent magnetic composite material

[0067] The magnetic powder prepared in step 2, TPE resin and plastic additives are mixed uniformly by a high-speed mixer, and then granulated by a twin-screw extruder at 175°C to obtain a TPE bonded samarium-nitrogen-iron magnetic composite material.

[0068] Example 4

[0069] The various raw materials and the mass percentage of the raw materials in this example are as follows:

[0070]

[0071] The process steps are as follows:

[0072] Step 1, Pretreatment of magnetic powder

[0073] KH550 coupling agent equivalent to 0.5wt.% of the weight of the magnetic powder is dissolved in an appropriate amount of anhydrous ethanol, and then the samarium-nitrogen-iron magnetic powder is added, stirred and mixed at 50°C for 1h, and vacuum dried at 100°C.

[0074] Step 2, magnetic powder coated with copolyamide

[0075] The alcohol-soluble copolyamide equivalent to 1.5 wt.% of the weight of the magnetic powder after pretreatment in step 1 was added to an appropriate amount of anhydrous isopropyl alcohol, heated and stirred at 60°C to fully dissolve it, and then added to the composite magnetic powder prepared in step 1 and preheated to 60°C, stirred and mixed at 60°C for 1 h, and then vacuum dried at 100°C to obtain the composite magnetic powder coated with copolyamide on the surface.

[0076] Step 3, mixing and granulation of flexible permanent magnetic composite material

[0077] The magnetic powder prepared in step 2, TPE resin, and plastic additives were uniformly mixed by a high-speed mixer, and then mixed and granulated by a twin-screw extruder at 175°C to obtain the TPE-bonded composite magnetic material.

[0078] Example 5

[0079] The various raw materials and the mass percentage of the raw materials in this example are as follows:

[0080]

[0081] The process steps are as follows:

[0082] Step 1, pretreatment of magnetic powder

[0083] The KH550 coupling agent equivalent to 0.5 wt.% of the weight of the magnetic powder after pretreatment in step 1 was dissolved in an appropriate amount of anhydrous ethanol, and then added to the composite magnetic powder obtained by mixing samarium-iron-nitrogen and neodymium-iron-boron in a mass ratio of 4:6, stirred and mixed at 50°C for 1 h, and then vacuum dried at 100°C.

[0084] Step 2, magnetic powder coated with copolyamide

[0085] The alcohol-soluble copolyamide equivalent to 1.5 wt.% of the weight of the magnetic powder was added to an appropriate amount of anhydrous isopropyl alcohol, heated and stirred at 60°C to fully dissolve it, and then added to the composite magnetic powder prepared in step 1 and preheated to 60°C, stirred and mixed at 60°C for 1 h, and then vacuum dried at 100°C to obtain the composite magnetic powder coated with copolyamide on the surface.

[0086] Step 3, mixing and granulation of flexible permanent magnetic composite material

[0087] The magnetic powder prepared in step 2, TPE resin, and plastic additives were uniformly mixed by a high-speed mixer, and then mixed and granulated by a twin-screw extruder at 175°C to obtain the TPE-bonded composite rare earth magnetic material.

[0088] Comparative Example 1

[0089] The various raw materials and the mass percentage of the raw materials in this example are as follows:

[0090] Magnetic powder (without KH550 pretreatment) 88%, magnetic powder is samarium iron nitride

[0091] SEBS-based TPE resin 11.5%

[0092] Plastic additive package 0.5%

[0093] The process steps are as follows:

[0094] Step 1, flexible permanent magnetic composite material mixing and granulation

[0095] The original magnetic powder (samarium iron nitride, without KH550 pretreatment, and without polyamide coating), TPE resin and plastic additive are mixed uniformly by high-speed mixer, and then granulated by double screw extruder at 175°C to obtain TPE bonded samarium iron nitride magnetic composite material.

[0096] Comparative Example 2

[0097] The various raw materials and mass percentages of the raw materials in this example are as follows:

[0098] Magnetic powder pretreated with KH550 88%, magnetic powder is samarium iron nitride

[0099] SEBS-based TPE resin 11.5%

[0100] Plastic additive package 0.5%

[0101] The process steps are as follows:

[0102] Step 1, pretreatment of magnetic powder

[0103] Dissolve 0.5wt.% of KH550 coupling agent in an appropriate amount of anhydrous ethanol, then add samarium iron nitride magnetic powder, stir and mix at 50°C for 1h, and dry at 100°C under vacuum.

[0104] Step 2, flexible permanent magnetic composite material mixing and granulation

[0105] The magnetic powder is not coated with polyamide, and the magnetic powder obtained in step 1, TPE resin and plastic additive are mixed uniformly by high-speed mixer, and then granulated by double screw extruder at 175°C to obtain TPE bonded samarium iron nitride magnetic composite material.

[0106] Comparative Example 3

[0107] The various raw materials and mass percentages of the raw materials in this example are as follows:

[0108]

[0109] The process steps are as follows:

[0110] Step 1, magnetic powder coating copolyamide

[0111] The alcohol-soluble copolyamide equivalent to 1.5 wt.% of the weight of the magnetic powder (without KH550 pretreatment) was added to an appropriate amount of anhydrous isopropyl alcohol, heated and stirred at 60°C to fully dissolve it, and then added to the samarium-iron-nitrogen magnetic powder without coupling pretreatment and preheated to 60°C, stirred and mixed at 60°C for 1 h, and then vacuum dried at 100°C to obtain the samarium-iron-nitrogen magnetic powder coated with copolyamide on the surface.

[0112] Step 2, mixing and granulation of flexible permanent magnetic composite material

[0113] The magnetic powder prepared in step 1, TPE resin, and plastic additives were uniformly mixed by a high-speed mixer, and then mixed and granulated by a twin-screw extruder at 175°C to obtain a TPE-bonded samarium-iron-nitrogen magnetic composite material.

[0114] Comparative Example 4

[0115] The various raw materials and the mass percentage of the raw materials in this example are as follows:

[0116]

[0117] The process steps are as follows:

[0118] Step 1, pretreatment of magnetic powder

[0119] The KH550 coupling agent equivalent to 0.5 wt.% of the weight of the magnetic powder was dissolved in an appropriate amount of anhydrous ethanol, and then the samarium-iron-nitrogen magnetic powder was added, stirred and mixed at 50°C for 1 h, and then vacuum dried at 100°C.

[0120] Step 2, magnetic powder coating copolyamide

[0121] The alcohol-soluble copolyamide equivalent to 0.25 wt.% of the weight of the pretreated magnetic powder in step 1 was added to an appropriate amount of anhydrous isopropyl alcohol, heated and stirred at 60°C to fully dissolve it, and then added to the samarium-iron-nitrogen magnetic powder prepared in step 1 and preheated to 60°C, stirred and mixed at 60°C for 1 h, and then vacuum dried at 100°C to obtain the samarium-iron-nitrogen magnetic powder coated with copolyamide on the surface.

[0122] Step 3, mixing and granulation of flexible permanent magnetic composite material

[0123] The magnetic powder prepared in step 2, TPE resin, and plastic additives were uniformly mixed by a high-speed mixer, and then mixed and granulated by a twin-screw extruder at 175°C to obtain a TPE-bonded samarium-iron-nitrogen magnetic composite material.

[0124] Comparative Example 5

[0125] The various raw materials and the mass percentage of the raw materials in this example are as follows:

[0126]

[0127] The process steps are as follows:

[0128] Step 1, Pretreatment of magnetic powder

[0129] Dissolve 0.5 wt.% of KH550 coupling agent in an appropriate amount of anhydrous ethanol, then add samarium-iron-nitrogen magnetic powder, stir and mix at 50°C for 1 h, and vacuum dry at 100°C.

[0130] Step 2, Coating of magnetic powder with copolyamide

[0131] Dissolve 3.5 wt.% of alcohol-soluble copolyamide in an appropriate amount of anhydrous isopropyl alcohol, heat and stir at 60°C until fully dissolved. Then add to the samarium-iron-nitrogen magnetic powder prepared in Step 1 and preheated to 60°C, stir and mix at 60°C for 1 h, and then vacuum dry at 100°C to obtain samarium-iron-nitrogen magnetic powder coated with copolyamide.

[0132] Step 3, Mixing and granulation of flexible permanent magnetic composite material

[0133] Mix the magnetic powder prepared in Step 2, TPE resin, and plastic additives uniformly by high-speed mixer, and then mix and granulate by double-screw extruder at 175°C to obtain TPE-bonded samarium-iron-nitrogen magnetic composite material.

[0134] Comparative Example 6

[0135] The various raw materials and their mass percentages in this example are as follows:

[0136] Magnetic powder (not pretreated with KH550) 88%, mass ratio of samarium-iron-nitrogen to neodymium-iron-boron in composite magnetic powder 4:6

[0137] SEBS-based TPE resin 11.5%

[0138] Plastic additive package 0.5%

[0139] The process steps are as follows:

[0140] Step 1, Mixing and granulation of flexible permanent magnetic composite material

[0141] Mix the raw magnetic powder (composite magnetic powder with mass ratio of samarium-iron-nitrogen to neodymium-iron-boron 4:6, not pretreated with KH550 and not coated with copolyamide), TPE resin, and plastic additives uniformly by high-speed mixer, and then mix and granulate by double-screw extruder at 175°C to obtain TPE-bonded composite rare earth magnetic material.

[0142] The TPE-based flexible permanent magnetic composite prepared in the above examples and comparative examples was injection molded using an injection molding machine to prepare magnetic performance test samples (Φ10x10mm cylinder, the orientation direction is the axial direction) and mechanical test standard samples (GB.11997-2008); an orientation magnetic field of 0.8 Tesla was applied during injection molding, the injection molding temperature was 195°C, and the mold temperature was 20°C. The test results are shown in Table 1.

[0143] Table 1 test results

[0144]

[0145] As can be seen from the above table, using alcohol-soluble copolyamide to coat the powder forms a dense polyamide protective layer on the surface of the magnetic powder, which can effectively reduce the damage of friction and high shear between the magnetic powder and the magnetic powder and between the magnetic powder and the screw to the powder without affecting the mixing effect, and isolate air to protect the magnetic powder, significantly improve the magnetic performance of the product, especially the coercive force. It is necessary to use KH550 coupling agent for surface pretreatment of the magnetic powder; when the amount of copolyamide is too small, the samarium iron nitrogen powder cannot be completely coated, although it has a certain protective effect, but it is not significant; when the amount of copolyamide is too much, although it has a protective effect, the decrease in tensile strain at break caused by the decrease in TPE ratio is relatively large.

Claims

1. A method of making a flexible permanent magnetic composite material, characterized in that The method comprises the following steps: Step 1, magnetic powder pretreatment After the coupling agent is appropriately diluted, it is added to the magnetic powder and mixed uniformly at 20-70°C, and vacuum dried at 70-150°C; Step 2, magnetic powder coating with copolyamide Dissolve the alcohol-soluble copolyamide in an appropriate amount of alcohol solvent, stir at 20-70°C to fully dissolve it; Add the solution to the magnetic powder obtained in step 1 while hot, mix uniformly; After vacuum drying at 70-150°C, the magnetic powder with a complete and dense coating of copolyamide on the surface is obtained; Step 3, mixing and granulation of flexible permanent magnetic composite material Mix the magnetic powder obtained in step 2, flexible resin binder and plastic additives uniformly, and granulate at 150-200°C using a twin-screw extruder to obtain a flexible permanent magnetic composite material.

2. The method for preparing a flexible permanent magnet composite material as described in claim 1, characterized in that: The coupling agent in step 1 is KH550 coupling agent, and its amount is 0.3-2 wt.% relative to the weight of the magnetic powder.

3. A method of producing a flexible permanent magnetic composite material according to claim 1 or 2, characterized in that: The magnetic powder is one or a mixture of samarium iron nitrogen, ferrite and neodymium iron boron.

4. The method for preparing a flexible permanent magnet composite material as described in claim 1, characterized in that: The alcohol solvent in step 2 is one or a mixture of anhydrous ethanol or anhydrous isopropanol, and the amount of solvent is sufficient to completely dissolve the alcohol-soluble copolyamide and completely wet the magnetic powder.

5. The method for preparing a flexible permanent magnet composite material as described in claim 4, characterized in that: The alcohol-soluble copolyamide in step 2 has a solubility of not less than 2 g / 100 g at 70°C.

6. A method for preparing a flexible permanent magnet composite material as described in claim 1 or 4, characterized in that: The amount of alcohol-soluble copolyamide in step 2 is 0.5-3 wt.% of the pretreated magnetic powder in step 1.

7. The method for preparing a flexible permanent magnet composite material as described in claim 1, characterized in that: The magnetic powder in step 2 needs to be preheated to the temperature of the copolyamide solution, and the mixing process is maintained at not less than this temperature and not higher than 70°C.

8. The method for preparing a flexible permanent magnet composite material as described in claim 1, characterized in that: The flexible resin binder in step 3 is a TPE resin.

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