A magnetooriented PA6CF magnetic composite material and its preparation method

Abstract

This invention discloses a magneto-oriented PA6CF magnetic composite material and its preparation method. The composite material, from the inside out, comprises short-cut carbon fibers, highly polar nylon and magnetic powder coating the outer wall of the short-cut carbon fibers, nylon formed by in-situ polymerization on the surface of the highly polar nylon and magnetic powder through heterogeneous nucleation and induced crystallization, and a matrix polymerized in situ on the periphery. The magnetic powder loaded on the surface of the magnetized fibers provides heterogeneous nucleation sites for the composite material system, promoting the formation of a homogeneous core-shell structure of the APA6 matrix on the surface of the magnetic powder. The crystallization behavior of the nylon formed by in-situ polymerization on the surface of the highly polar nylon and magnetic powder through heterogeneous nucleation and induced crystallization is higher than that of the matrix polymerized in situ on the periphery, thereby improving the interfacial strength of the composite material, reducing interfacial defects, and enhancing the tensile strength of the composite material.

Description

Technical Field

[0001] This invention belongs to the field of high-performance bonded permanent magnet manufacturing, and particularly relates to a magnetically oriented PA6CF magnetic composite material and its preparation method. Background Technology

[0002] "Bonded permanent magnets" are magnetic materials made by combining high-performance permanent magnet powder with a polymer matrix and then using a specific molding process. This technology combines the excellent magnetic properties of metal magnets with the processing flexibility of plastics. With its superior molding flexibility, it can directly manufacture high-precision, impact-resistant, complex integrated components, significantly reducing manufacturing costs.

[0003] The core of bonded permanent magnets lies in uniformly dispersing fine powder of a hard magnetic phase in a non-magnetic binder, such as nylon (PA), polytetrafluoroethylene (PTFE), or epoxy resin. This is then formed through molding, injection molding, or calendering, followed by curing. During the forming process, a strong magnetic field is applied to align the easily magnetized directions of the magnetic powder along the magnetic field direction. Magnets that have undergone this orientation treatment exhibit significantly improved magnetic properties, especially remanence (Br) and maximum energy product (BH)max.

[0004] Traditional methods involve blending polymers with hard magnetic phases and molding, injection, or calendering, with magnetic powder dispersed in a liquid or semi-solid resin binder. When the powder particles are rotated and oriented, they must overcome the viscous resistance of the binder; the higher the viscosity of the binder, the greater the resistance. Heating is often used to reduce viscosity, but viscous resistance remains a significant obstacle. Summary of the Invention

[0005] The purpose of this invention is to provide a magnetically oriented PA6CF magnetic composite material and its preparation method, so as to solve the problem that the magnetic powder must overcome the viscous resistance of the binder during the preparation of traditional bonded permanent magnets.

[0006] The present invention adopts the following technical solution: a magnetically oriented PA6CF magnetic composite material, which, from the inside out, comprises short-cut carbon fibers, strong polar nylon and magnetic powder covering the outer wall of the short-cut carbon fibers, nylon formed by in-situ polymerization on the surface of the strong polar nylon and magnetic powder through heterogeneous nucleation and induced crystallization, and a matrix formed by in-situ polymerization on the periphery.

[0007] A method for preparing a magnetooriented PA6CF magnetic composite material, comprising: Step 1: Desorb impurities from the chopped carbon fibers; Step 2: Modify the short-cut carbon fibers obtained in Step 1 to form Si-OC covalent bonds through the dehydration reaction of hydroxyl groups on the surface of the short-cut carbon fibers. Step 3: Dissolve the magnetic powder and highly polar nylon powder in the dispersion, and also place the modified short carbon fiber from Step 2 in the dispersion, so that the magnetic powder and highly polar nylon powder adhere to the outer wall of the short carbon fiber. Step 4: Mix and stir the short-cut carbon fibers obtained in Step 3 with sodium caprolactam, then add a polymerization activator and stir to melt to obtain a magnetized fiber prepolymer; Step 5: Fill a mold equipped with a DC steady magnetic field device at both ends with a layer of magnetized fiber prepolymer obtained in step 4, and turn on the magnetic field in a predetermined direction. When the magnetized fiber prepolymer layer polymerizes to a semi-solid state, fill a second layer of magnetized fiber prepolymer obtained in step 4 on top of the first layer of magnetized fiber prepolymer, and change the direction of the magnetic field so that the arrangement directions of the two layers of magnetized fiber prepolymer are different. Repeat this process until a composite material of a predetermined thickness is obtained.

[0008] The beneficial effects of this invention are: This invention precisely controls the orientation of magnetic powder on the surface of the magnetized fiber prepolymer along the direction of the magnetic field by applying a constant DC magnetic field of 0.8~1.5T. By controlling the magnetic field, the fiber arrangement direction in different layers of the magnetized fiber prepolymer is different, which effectively reduces the problem of magnetic domain disorder caused by magnetic powder agglomeration, and improves the residual magnetization (Mr) of the composite material, thus realizing the directional control and efficient utilization of magnetic properties. The magnetic powder of this invention is bonded to the surface of carbon fiber to form a whole. The magnetic powder particles contact each other to form a continuous magnetic path. Combined with the orderly arrangement of subsequent fibers, this facilitates the conduction of magnetic flux and the formation of a closed magnetic circuit, thereby increasing the maximum magnetic energy product (BH)max of the permanent magnet. The contact of the magnetic powder to form a continuous magnetic path essentially transforms a high-resistance "break" in the magnetic circuit into a low-resistance "path". Macroscopically, this plugs the magnetic leakage gap, which is beneficial for the conduction of magnetic flux and the formation of a closed magnetic circuit. This invention completes the ring-opening polymerization reaction of caprolactam, composite material molding, magnetized fiber orientation, and magnetization of the magnetized fiber in one step, eliminating the need for a separate subsequent magnetization process; in-situ polymerization and molding are carried out simultaneously, and combined with process conditions such as nitrogen protection and humidity control, it avoids the problems of contamination, moisture absorption, and performance degradation caused by material transfer in traditional step-by-step processes; The magnetic powder loaded on the surface of the magnetized fiber in this invention provides heterogeneous nucleation sites for the composite material system, which promotes the formation of a homogeneous core-shell structure of the APA6 matrix (anionic polymerized PA6) on the surface of the magnetic powder. The crystallization behavior of the nylon formed by in-situ polymerization on the surface of the highly polar nylon and the magnetic powder through heterogeneous nucleation and induced crystallization is higher than that of the matrix polymerized in situ on the periphery. This improves the interfacial strength of the composite material, reduces interfacial defects, and enhances the tensile strength of the composite material. The Si-OC covalent bonds formed on the surface of the short-cut carbon fibers modified by the coupling agent significantly improve the interfacial bonding strength between the fiber and the matrix, thereby enhancing the notched impact strength of the composite material and avoiding failure problems such as fiber pull-out and magnetic powder shedding under stress. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the structure of the magnetic composite material of the present invention; Figure 2 This is a cross-sectional view of the magnetic composite material of the present invention; Figure 3 The structure of the mold. Detailed Implementation

[0010] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0011] This invention discloses a magnetically oriented PA6CF magnetic composite material, such as... Figure 1 and Figure 2 As shown, from the inside out, it includes short-cut carbon fibers, strong polar nylon and magnetic powder covering the outer wall of the short-cut carbon fibers, nylon formed by in-situ polymerization on the surface of the strong polar nylon and magnetic powder through heterogeneous nucleation and induced crystallization, and the outer matrix formed by in-situ polymerization.

[0012] The present invention also discloses a method for preparing a magnetooriented PA6CF magnetic composite material, comprising five steps.

[0013] Step 1: Desorb impurities from the short-cut carbon fibers.

[0014] Organic solvents such as acetone, anhydrous ethanol, and chloroform are selected, and chopped carbon fibers are immersed in the solvent at a solid-liquid mass ratio of 1:10 to 1:20. Preferably, the length of the chopped carbon fibers is 6 mm and the diameter is 7 to 10 μm. The fibers are cleaned by ultrasonic vibration (power: 200 to 300 W, time: 30 to 60 min). The fibers are separated by filtration and washed repeatedly with organic solvents 2 to 3 times to remove residual solvent. The chopped carbon fibers are then placed in a vacuum drying oven and dried at 60 to 80 °C for 2 to 4 h to remove the solvent. Preferably, drying is done at 80 °C for 4 h.

[0015] Step 2: Modify the short-cut carbon fibers obtained in Step 1 to form Si-OC covalent bonds through the dehydration reaction of hydroxyl groups on the surface of the short-cut carbon fibers.

[0016] The coupling agent is mixed with a water / ethanol mixture at a mass ratio of 1:10 to 1:20, wherein the water / ethanol mass ratio of the water / ethanol mixture is 2:1. The pH is adjusted to 4-5 with acetic acid, and the mixture is stirred at room temperature to allow the coupling agent to be fully hydrolyzed to generate silanol groups, thus obtaining a hydrolysate.

[0017] The chopped carbon fibers obtained in step 1 were immersed in a hydrolysate at a mass ratio of 1:15. The solution was soaked at 25°C for 3–8 hours to allow the coupling agent to adsorb onto the surface of the chopped carbon fibers. The resulting wet chopped carbon fibers were then obtained by filtration. The wet chopped carbon fibers were placed in a forced-air drying oven at 100–120°C for 2 hours to allow the silanol groups to undergo a dehydration condensation reaction with the hydroxyl groups on the surface of the chopped carbon fibers, forming stable Si-OC covalent bonds. After cooling, the fibers were passed through a 100–200 mesh sieve to remove agglomerated fibers, ensuring dispersibility, and then dried and stored.

[0018] Step 3: Dissolve the magnetic powder and highly polar nylon powder in the dispersion, and also place the modified short carbon fiber from Step 2 into the dispersion, so that the magnetic powder and highly polar nylon powder adhere to the outer wall of the short carbon fiber.

[0019] Magnetic powder and highly polar nylon powder were vacuum dried at 110℃ for 2 hours to remove surface adsorbed water. The magnetic powder used was preferably a permanent magnet such as ferrite, samarium cobalt (SmCo), or neodymium iron boron (NdFeB). The magnetic powder was preferably 2000 mesh. The highly polar nylon could be PA6 powder, PA66, or PA22 powder. The highly polar nylon was preferably 150-200 mesh. The mass ratio of modified chopped carbon fiber:magnetic powder:highly polar nylon was 50:(1~5):10.

[0020] Magnetic powder and highly polar nylon powder were added to a three-necked flask and uniformly dispersed in a dispersion of trifluoroacetic acid and hexafluoroisopropanol. The short-cut carbon fibers modified in step 2 were also placed in the dispersion. The mass ratio of dispersion to solid was 6-12:1. The temperature was raised to 30-60℃ and maintained for 2-4 hours before filtration. The mixture was then vacuum dried at 80℃ until the water content was less than 50ppm. Finally, it was passed through a 100-200 mesh sieve to remove agglomerated fibers and ensure dispersibility.

[0021] Step 4: Mix and stir the short-cut carbon fibers obtained in Step 3 with sodium caprolactam, then add a polymerization activator and stir to melt and obtain magnetized fiber prepolymer.

[0022] First, caprolactam is distilled to a purity of over 99.9%. Then, caprolactam is added to a container under a nitrogen atmosphere, heated to 70–80°C, and stirred until completely melted. The activated molecular sieve is then added at a caprolactam:molecular sieve mass ratio of 10:1. Moisture is adsorbed for 4 hours under nitrogen protection and stirring at 70–80°C. The caprolactam is then filtered into a dry, sealed bottle and stored under nitrogen protection. Because anionic polymerization is sensitive to moisture, polymerization can only be initiated when the moisture content is below 200 ppm. To ensure the moisture content of the subsequent prepolymer meets the standard and to avoid caprolactam decomposition due to high-temperature dehydration, molecular sieves are used to dehydrate the caprolactam at its melting point, ensuring a moisture content below 50 ppm.

[0023] The caprolactam used must have a purity of 99.9% or higher and a water content ≤50ppm; the NaOH and toluene diisocyanate (TDI) must also have a water content ≤50ppm. Nitrogen gas is purged into the reactor for 10 minutes beforehand to reduce the water content to less than 50ppm. The caprolactam, after being dehydrated by molecular sieves, is melted in the reactor at 80℃ until clear and transparent. The temperature is then raised to 110℃, and NaOH (caprolactam:NaOH = 200mol:1-4mol) is added. The reaction proceeds for 20 minutes until a large number of bubbles emerge. This temperature is then maintained for 10 minutes to obtain sodium caprolactam. Preparing sodium caprolactam at 110℃ avoids the decomposition and yellowing problems associated with high-temperature preparation.

[0024] The prepared sodium caprolactam was transferred to a three-necked flask and melted at 80°C until clear and transparent. Then, the short-cut carbon fibers obtained in step 3 were added to the flask, and the temperature was raised to 130°C. A polymerization activator was added, and the mixture was stirred and melted for 5 minutes to form a magnetized fiber prepolymer. 130°C was chosen because the minimum stable polymerization temperature for caprolactam anionic polymerization is 130°C. To avoid premature curing of the prepolymer, 130°C was selected as the prepolymer preparation temperature.

[0025] The molar ratio of caprolactam, NaOH, and polymerization activator is 200:2:(1~3). Too little initiator will result in incomplete polymerization, while too much initiator will lead to a too fast polymerization rate, which is not conducive to the orientation of the magnetized fiber under the magnetic field.

[0026] The polymerization activator is TDI, and the end-capping group is an isocyanate group.

[0027] In step 3, the short-cut carbon fibers have a mass ratio of 5%-15% of sodium caprolactam.

[0028] Step 5: Fill a mold equipped with a DC steady magnetic field device at both ends with a layer of magnetized fiber prepolymer obtained in step 4, and turn on the magnetic field in a predetermined direction. When the magnetized fiber prepolymer layer polymerizes to a semi-solid state, fill a second layer of magnetized fiber prepolymer obtained in step 4 on top of the first layer of magnetized fiber prepolymer, and change the direction of the magnetic field so that the arrangement directions of the two layers of magnetized fiber prepolymer are different. Repeat this process until a composite material of a predetermined thickness is obtained.

[0029] The magnetic field strength is set to 0.8~1.5T, and the direction of the magnetic field is determined according to the requirements. Different magnetic field directions can be set for different layers. Since the monomer viscosity in the magnetized fiber prepolymer is similar to that of water, a weaker magnetic field can be used to control the fiber orientation. However, traditional resin-based high-viscosity magnetized fibers cannot be rapidly oriented under a weak magnetic field. Therefore, a medium-strong magnetic field of 0.8-1.5T is sufficient to rapidly orient the fibers and complete the magnetization process.

[0030] The number of filling layers of magnetized fiber prepolymer can be increased or decreased as needed. Nitrogen pressurization pressure is 90~130MPa, and the transfer filling speed is 40~80mm / s.

[0031] After the final layer of magnetized fiber prepolymer fills the mold, close the filling channel to prevent backflow. Heat the mold to 160-200℃ for reaction. The mold preheating temperature is 150℃ because this is the optimal temperature for initiating anionic polymerization, with a moderate and easily controllable reaction rate. After injecting the first layer of fiber prepolymer, apply a 0.8-1.5T magnetic field for 3 minutes to allow the resin to semi-cur. At this point, some active reactive groups remain on the surface. Injecting the next layer at this time facilitates chemical bonding and molecular chain entanglement between the two layers, ensuring good interlayer bonding. This also helps maintain the fiber orientation within the first layer of magnetized fiber prepolymer, preventing changes in the magnetic fibers of the first layer due to the different magnetic field direction of the second layer. Then, inject the next layer of magnetized fiber prepolymer, ensuring the magnetic field direction of this layer is perpendicular to the previous layer, and repeat this process.

[0032] The magnetic orientation of the first and second layers of magnetized fiber prepolymers is perpendicular because the fiber orientation of composite materials has anisotropic effects on mechanical properties. To ensure that the composite material has certain strength in all directions, the fiber orientation of the first and second layers of magnetized fiber prepolymers is perpendicular. Furthermore, the magnetic field direction of the third layer of magnetized fiber prepolymers is perpendicular to the magnetic field direction of the second layer of magnetized fiber prepolymers, and this process is repeated.

[0033] The holding pressure is 50-70 MPa (50%-60% of the injection pressure), and the holding time is 15-30 min. The reaction temperature during the holding stage is 150-200℃ because at 150℃, the increased viscosity hinders the diffusion of the sodium caprolactam monomer and its collision with the active centers, resulting in incomplete polymerization. Therefore, high-temperature supplementary polymerization is required. The preferred supplementary polymerization temperature is 180℃ for 30 min. Excessive time or temperature can easily lead to cross-linking structures.

[0034] Cooling, demolding, and post-treatment stages: After pressure holding and polymerization, the magnetic field is turned off, and the mold temperature is reduced to ≤60-80℃ using a staged cooling method at a cooling rate of 5-15℃ / min. This ensures complete curing of the composite material and reduces internal stress. The composite material is ejected by a mechanical ejection device to prevent the short-cut carbon fibers from being pulled out. Vacuum annealing post-treatment: Vacuum annealing at 80~100℃ for 2~4 hours eliminates internal stress, yielding the molded composite material.

[0035] The magnetic properties (GB / T 3217-GB / T 3658-2022), mechanical properties (GB / T 1040.2-2022), flexural properties (GB / T 9341-2008), impact properties (GB / T 1843-2008), heat distortion temperature (GB / T 1634.2-2004), Vicat softening temperature (GB / T 1633-2000), thermogravimetric analysis, and surface antistatic properties (GB / T 1410-2006) of the obtained composite materials were measured.

[0036] like Figure 3 As shown, the mold is a frame structure with openings at both the top and bottom. The mold is preferably a cuboid or a cube. A stable magnetic field device is set around the mold. A base is set at the bottom of the mold to close the bottom of the mold, so that the magnetized fiber prepolymer is placed in the area enclosed by the base and the mold. A top cover is set at the top of the mold. The top cover has an inlet and an outlet. The inlet is used for the magnetized fiber prepolymer to enter, and the outlet is used for the discharge of excess magnetized fiber prepolymer in the area.

[0037] Example 1 In this embodiment, the caprolactam was sourced from Zhejiang Quzhou Juhua Industrial Caprolactam, and the toluene-2,4-diisocyanate (TDI) was sourced from Maclean's reagent, with analytical grade (AR) purity. The 6 mm chopped carbon fiber was sourced from Zhongfu Shenying Carbon Fiber Co., Ltd., with analytical grade (AR) purity. The magnetic powder was sourced from Qinghe County Benyu Metal Materials Co., Ltd., and the neodymium iron boron magnetic powder was 2000 mesh. The specifications of the chopped carbon fiber were: length 6 mm, diameter 7~10 μm.

[0038] Step 1: Desorb impurities from the short-cut carbon fibers.

[0039] Acetone was selected as the organic solvent, and the chopped carbon fibers were immersed in acetone at a solid-liquid mass ratio of 1:15. Ultrasonic cleaning (power: 250W, time: 45min) was used to remove residual additives and other impurities from the fiber surface. The fibers and acetone were separated by a vacuum filter, and the fibers were washed three times with clean acetone to remove residual solvent. The chopped carbon fibers were then placed in a vacuum drying oven and dried at 80℃ for 4 hours to completely remove the solvent adsorbed on the fibers.

[0040] Step 2: Modify the short-cut carbon fibers obtained in Step 1 to form Si-OC covalent bonds through the dehydration reaction of hydroxyl groups on the surface of the short-cut carbon fibers.

[0041] An aminosilane coupling agent (model: KH550) was selected and mixed at a mass ratio of coupling agent to water / ethanol mixture = 1:15; wherein the water / ethanol mixture had a water-to-ethanol mass ratio of 2:1. The pH of the mixture was adjusted to 4.5 with acetic acid, and stirred at room temperature for 30 min to allow the silane coupling agent to be fully hydrolyzed to generate silanol groups, thus obtaining a hydrolysate.

[0042] The chopped carbon fibers obtained in step 1 were immersed in a hydrolysate at a solid-liquid mass ratio of 1:15 for 5 hours at 25°C to allow the coupling agent to be fully adsorbed onto the surface of the chopped carbon fibers. The resulting wet chopped carbon fibers were then filtered. These wet chopped carbon fibers were placed in a 110°C forced-air drying oven for 2 hours to allow the silanol groups generated from the hydrolysis of the coupling agent to undergo a dehydration condensation reaction with the hydroxyl groups on the surface of the chopped carbon fibers, forming stable Si-OC covalent bonds. After cooling, the fibers were passed through a 150-mesh sieve to remove agglomerated fibers and ensure fiber dispersibility. The modified chopped carbon fibers were then stored in a dry environment for later use.

[0043] Step 3: Dissolve the magnetic powder and highly polar nylon powder in the dispersion, and also place the modified short carbon fiber from Step 2 into the dispersion, so that the magnetic powder and highly polar nylon powder adhere to the outer wall of the short carbon fiber.

[0044] Neodymium iron boron (NdFeB) permanent magnet powder (particle size: 1~5μm) and PA6 powder (150-200 mesh) were dried separately in a vacuum drying oven at 110℃ for 2 hours to remove surface adsorbed water. Modified chopped carbon fibers, dried NdFeB magnetic powder, and PA6 powder were added to a three-necked flask at a mass ratio of 50:3:10. Trifluoroacetic acid dispersion was added, with a dispersion-to-solid material mass ratio of 9:1. The mixture was stirred and dispersed at 60℃ for 3 hours. It was then filtered and dried in a vacuum drying oven at 80℃ until the moisture content was less than 50ppm. Finally, it was passed through a 150-mesh sieve to remove agglomerated fibers and ensure dispersibility.

[0045] Step 4: Mix and stir the short-cut carbon fibers obtained in Step 3 with sodium caprolactam, then add a polymerization activator and stir to melt and obtain magnetized fiber prepolymer.

[0046] Caprolactam was distilled to achieve a purity of over 99.9%. The distilled caprolactam was then added to a nitrogen-protected container, heated to 75°C, and stirred until completely melted. Activated molecular sieves were added at a mass ratio of caprolactam:molecular sieve = 10:1. The mixture was then subjected to adsorption of moisture for 4 hours at 75°C under nitrogen protection and stirring. The caprolactam was then filtered into a dry, sealed bottle and stored under nitrogen protection. The water content of the caprolactam used was ≤50 ppm, and the water content of both NaOH and toluene diisocyanate (TDI) was ≤50 ppm. Nitrogen gas was purged into the reactor beforehand for 10 minutes to ensure the water content inside the reactor was less than 50 ppm. The caprolactam, after being dehydrated by the molecular sieves, was added to the reactor and heated to 80°C until clear and transparent. The temperature was then raised to 110°C, and the reaction was carried out for 20 minutes at a caprolactam:NaOH molar ratio of 200:2 until a large number of bubbles emerged. This reaction was then maintained at this temperature for 10 minutes to obtain sodium caprolactam.

[0047] The prepared sodium caprolactam was transferred to a three-necked flask and melted at 80°C until clear and transparent. Short-cut carbon fibers obtained in step 3, comprising 10% of the total mass of sodium caprolactam, were added. The temperature was raised to 130°C, and the polymerization activator TDI (end-capped with isocyanate groups) was added and stirred for 5 minutes to form a homogeneous magnetized fiber prepolymer. The molar ratio of caprolactam, NaOH, and TDI during the entire magnetized fiber prepolymer preparation process was 200 mol: 2 mol: 2 mol.

[0048] Step 5: Fill a mold equipped with a DC steady magnetic field device at both ends with a layer of magnetized fiber prepolymer obtained in step 4, and turn on the magnetic field in a predetermined direction. When the magnetized fiber prepolymer layer polymerizes to a semi-solid state, fill a second layer of magnetized fiber prepolymer obtained in step 4 on top of the first layer of magnetized fiber prepolymer, and change the direction of the magnetic field so that the arrangement directions of the two layers of magnetized fiber prepolymer are different. Repeat this process until a composite material of a predetermined thickness is obtained.

[0049] The mold's internal dimensions are 200mm x 200mm x 20mm. A magnetic field strength of 1.2T is set. The mold is preheated to 150℃, and the first layer of magnetized fiber prepolymer is filled in. The magnetic field direction of the first layer is parallel to the bottom plane of the mold. The second layer is also parallel to the bottom plane of the mold and perpendicular to the first layer. The magnetic field direction of the third layer is the same as the first layer, and the fourth layer is the same as the second layer, for a total of four layers. The magnetic field is applied to each layer for 3 minutes after filling the mold, continuing until the holding pressure is finished. Before injection molding, the mold is purged with nitrogen to replace internal moisture and oxygen.

[0050] Nitrogen gas was applied at a pressure of 120 MPa, with a transfer filling rate of 60 mm / s. After the magnetized fiber prepolymer filled the mold, the filling channel was closed to prevent melt backflow. The mold was then heated to 180°C to initiate a polymerization reaction, forming a bonded permanent magnet. The holding pressure was 60 MPa (55% of the injection pressure) for 20 minutes. The pressure changes inside the mold were monitored in real time, and pressure was appropriately increased when the pressure dropped to control the shrinkage rate of the product within 2.5%.

[0051] After the pressure holding and polymerization is completed, the magnetic field is turned off, and the mold temperature is reduced to 70°C using a staged cooling method at a cooling rate of 10°C / min to ensure complete curing of the composite material and reduce internal stress. The composite material is ejected by a mechanical ejection device to prevent the short carbon fibers from being pulled out. The composite material is then placed in an 80°C vacuum annealing furnace for 3 hours to eliminate internal stress and obtain the composite material.

[0052] Example 2 This embodiment operates the same as Embodiment 1, except that: 1. In step 4, the short-cut carbon fibers obtained in step 3 account for 5% of the total mass of sodium caprolactam.

[0053] Example 3 This embodiment operates the same as Embodiment 1, except that: 1. In step 3, the mass ratio of short-cut carbon fiber, NdFeB magnetic powder and PA6 powder is 50:5:10.

[0054] Example 4 This embodiment operates the same as Embodiment 1, except that: 1. In step 3, the mass ratio of short-cut carbon fiber, NdFeB magnetic powder and PA6 powder is 50:5:10.

[0055] 2. In step 4, the short-cut carbon fibers obtained in step 3 account for 5% of the total mass of sodium caprolactam.

[0056] Example 5 This embodiment operates the same as Embodiment 1, except that: 1. In step 4, the short-cut carbon fibers obtained in step 3 account for 15% of the total mass of sodium caprolactam.

[0057] 2. The internal dimensions of the mold in step 5 are 200mm x 200mm x 10mm.

[0058] Example 6 This embodiment operates the same as Embodiment 1, except that: 1. In step 4, the short-cut carbon fibers obtained in step 3 account for 15% of the total mass of sodium caprolactam.

[0059] 2. The internal dimensions of the mold in step 5 are 200mm x 200mm x 10mm.

[0060] 3. The transfer filling rate in step 5 is 80 mm / s. The test results of the composite materials prepared in each embodiment are shown in Tables 1-3.

[0061] Table 1 Mechanical properties of composite materials Table 2 Magnetic properties of composite materials Table 3 Vicat softening temperature of composite materials As can be seen from Table 1-3: 1. Under the same conditions of adding magnetized carbon fiber, when the proportion of magnetic powder increases, the magnetic powder provides more heterogeneous nucleation sites on the surface of carbon fiber, and the induced core-shell structure and the surrounding in-situ polymerized matrix significantly enhance the interfacial bonding between the fiber and the matrix, effectively improving the interfacial structure of the composite material.

[0062] 2. By controlling the magnetic field layer by layer, the magnetic powder in the magnetized fiber prepolymer is arranged in an orderly manner along a specific direction; at the same time, since the magnetic powder is tightly loaded on the surface of the short-cut carbon fiber to form a continuous physical contact magnetic path, the magnetic resistance and leakage flux are effectively reduced.

[0063] 3. When the proportion of magnetic powder increases from 3 parts to 5 parts, (BH)max increases from 13 kJ / m 3 Increased to 16 kJ / m 3 This increased (BH)max by about 23%, confirming that the increase in magnetic powder content is beneficial to improving the continuous magnetic pathway, thereby directly increasing the magnetic energy product. The tensile strength also increased simultaneously, indicating that the interface crystallization induced by magnetic powder did not cause deterioration.

[0064] 4. The Vicat softening temperature of all embodiments remained above 180°C (up to 188°C). This indicates that the magnetic powder loaded on the fiber surface acts as a heterogeneous nucleating agent, promoting a higher crystallinity of the matrix at the interface compared to the surrounding matrix. This highly crystalline interface layer not only enhances mechanical strength but also endows the composite material with excellent thermal dimensional stability, ensuring that it maintains the integrity of the magnetic circuit structure even under high-temperature operating conditions. The Vicat softening temperature of all embodiments was ≥180°C, far higher than that of conventional PA6 matrix (approximately 160°C), demonstrating that the heterogeneous nucleation effect of the magnetic powder significantly improves the crystallinity and thermal stability of the matrix at the fiber interface.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A magneto-oriented PA6CF magnetic composite material, characterized in that, From the inside out, it includes short-cut carbon fibers, highly polar nylon and magnetic powder covering the outer wall of the short-cut carbon fibers, nylon formed by in-situ polymerization on the surface of the highly polar nylon and magnetic powder through heterogeneous nucleation and induced crystallization, and the outer matrix formed by in-situ polymerization.

2. A method for preparing a magneto-oriented PA6CF magnetic composite material, characterized in that, include: Step 1: Desorb impurities from the chopped carbon fibers; Step 2: Modify the short-cut carbon fibers obtained in Step 1 to form Si-OC covalent bonds through the dehydration reaction of hydroxyl groups on the surface of the short-cut carbon fibers. Step 3: Dissolve the magnetic powder and highly polar nylon powder in the dispersion, and also place the modified short carbon fiber from Step 2 in the dispersion, so that the magnetic powder and highly polar nylon powder adhere to the outer wall of the short carbon fiber. Step 4: Mix and stir the short-cut carbon fibers obtained in Step 3 with sodium caprolactam, then add a polymerization activator and stir to melt to obtain a magnetized fiber prepolymer; Step 5: Fill a mold equipped with a DC steady magnetic field device at both ends with a layer of magnetized fiber prepolymer obtained in step 4, and turn on the magnetic field in a predetermined direction. When the magnetized fiber prepolymer layer polymerizes to a semi-solid state, fill a second layer of magnetized fiber prepolymer obtained in step 4 on top of the first layer of magnetized fiber prepolymer, and change the direction of the magnetic field so that the arrangement directions of the two layers of magnetized fiber prepolymer are different. Repeat this process until a composite material of a predetermined thickness is obtained.

3. The method for preparing a magneto-oriented PA6CF magnetic composite material according to claim 2, characterized in that, The modification method in step 2 is as follows: A hydrolysate was prepared by mixing a coupling agent with a water / ethanol mixture at a mass ratio of 1:10 to 1:20 and adjusting the pH to 4 to 5 with acetic acid. The mixture was stirred at room temperature until the coupling agent was completely hydrolyzed to generate silanol groups. The short-cut carbon fibers obtained in step 1 were immersed in the hydrolysate at a mass ratio of 1:15 and soaked at 25°C for 3 to 8 hours to allow the coupling agent to be adsorbed onto the surface of the short-cut carbon fibers. The mixture was then filtered to obtain wet short-cut carbon fibers. The wet short-cut carbon fibers were placed in a forced-air drying oven at 100 to 120°C for 2 hours to form stable Si-OC covalent bonds through the dehydration condensation reaction between the silanol groups and the hydroxyl groups on the surface of the short-cut carbon fibers.

4. The method for preparing a magnetooriented PA6CF magnetic composite material according to claim 3, characterized in that, The coupling agent in step 2 is an aminosilane coupling agent.

5. The method for preparing a magneto-oriented PA6CF magnetic composite material according to claim 2, characterized in that, In step 3, the mass ratio of modified short-cut carbon fiber: magnetic powder: PA6 powder is 50:(1~5):10.

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