Flexible magnetic fiber and preparation method thereof

Abstract

The invention relates to the technical field of electromagnetic wave absorbing materials, and provides a flexible magnetic fiber and a preparation method thereof.The flexible magnetic fiber comprises an insulating polymer fiber substrate, the outer side of the insulating polymer fiber substrate is connected with a Sn / Pd catalyst layer, the outer side of the catalyst layer is connected with a Cu layer, and the outer side of the Cu layer is connected with a magnetically soft alloy layer. According to the invention, the high-performance bimetallic layer is constructed on the flexible insulating fiber, so that the defects of weak binding force, poor conductivity, uneven magnetic performance and the like in the prior art are comprehensively overcome.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing materials technology, specifically to a flexible magnetic fiber and its preparation method. Background Technology

[0002] With the rapid development of 5G communication and electronic devices, the electromagnetic waves radiated by 5G networks and equipment have made electromagnetic pollution problems such as electromagnetic radiation, electromagnetic interference, and electromagnetic leakage increasingly prominent, raising public concerns about the adverse health effects of exposure to radio frequency fields. Meanwhile, with the continuous development of radar technology, the development of new stealth technologies has become urgent to improve the battlefield penetration capabilities of military equipment. To solve the electromagnetic pollution problem and improve stealth capabilities, using microwave absorbing materials to convert electromagnetic energy into Joule heat dissipation is a common method.

[0003] Flexible magnetic fibers, due to their anisotropic shape and high mechanical strength, are advantageous for processing and manufacturing, and meet the requirements of microwave absorbing materials for "thin thickness, light weight, wide bandwidth, and high mechanical strength." Using flexible fibers as a substrate to load inorganic materials with magnetic properties to prepare composite materials is a feasible method for producing flexible magnetic fibers with high aspect ratios. The journal *Journal of Magnetism and Magnetic Materials*, 2016, 399:252–259, discloses a method for preparing magnetic carbon fibers by electroplating FeCo onto carbon fibers. A uniform and dense FeCo coating is constructed on the carbon fiber surface through electrodeposition. The saturation magnetization of this FeCo composite carbon fiber reaches 50 emu / g, and the coercivity is 114 Oe.

[0004] Patent CN111155197A discloses a method for preparing flexible magnetic fibers using electrospinning technology. During electrospinning, the rapid evaporation of the solvent allows the polymer and magnetic loading material to be rapidly precipitated and deposited in situ. The fiber is then swollen in a coagulation bath, allowing the solute components in the coagulation bath to contact the magnetic loading material within the fiber, resulting in an in-situ reaction and the formation of monomolecularly dispersed magnetic materials, thus yielding polymer fibers containing uniformly dispersed magnetic materials. Patent CN119465686A discloses a low-frequency microwave absorbing composite material of aramid fibers loaded with FeCo nanoparticles. Magnetic fibers are obtained by treating the surface of para-aramid fibers with a hyperbranched polysiloxane modifier, followed by chemical crosslinking to adsorb FeCo nanoparticles.

[0005] However, existing technologies have certain technical shortcomings:

[0006] First, the method of directly electroplating magnetic alloys is only suitable for growing magnetic materials on the surface of conductive fibers, and cannot be used for fibers with insulating surfaces. Moreover, the deposited metal layer has a rough surface that is prone to oxidation, resulting in weak adhesion to the fiber substrate.

[0007] Secondly, while electrospinning generates magnetic materials in situ within the fiber, the resulting magnetic fibers exhibit a discrete distribution of magnetic particles, making it impossible to form continuous magnetic alloy channels. Furthermore, since the magnetic material is located inside the fiber, if it is an alloy, its high conductivity will lead to a skin effect, preventing effective utilization of the central magnetic alloy under high-frequency electromagnetic waves. Simultaneously, the fiber surface is an insulating layer, preventing the formation of effective conductive pathways through overlapping.

[0008] Third, while using chemical cross-linking to adsorb magnetic particles onto polymer fibers can reduce the skin effect, the coated magnetic particles tend to cluster, making it difficult to form a continuous and uniform coating layer. Furthermore, due to the weak inter-particle bonding within the clusters, the nanoparticles are prone to detachment during processing.

[0009] In view of this, the present invention proposes a method for preparing flexible magnetic fibers. Summary of the Invention

[0010] This invention proposes a flexible magnetic fiber and its preparation method, which solves the problem of weak bonding between the directly electroplated magnetic alloy and the fiber substrate in the prior art.

[0011] The technical solution of the present invention is as follows: a flexible magnetic fiber, comprising an insulating polymer fiber substrate, an outer side of which is connected to a Sn / Pd catalyst layer, an outer side of which is connected to a Cu layer, and an outer side of which is connected to a soft magnetic alloy layer.

[0012] This invention also provides a method for preparing flexible magnetic fibers, comprising the following steps:

[0013] Step 1: Select insulating polymer fiber filaments as the substrate, and then perform acid washing pretreatment on the insulating polymer fibers;

[0014] Step 2: The acid-washed fiber bundles are passed through a colloidal Sn / Pd reaction tank, and a colloidal Sn / Pd catalytic layer is constructed on the fiber surface by chemical plating. Pd particles, as a highly efficient catalyst, provide active sites with a high specific surface area, reduce interfacial stress, promote uniform nucleation of Cu in subsequent chemical plating, and ensure that the metal layer is tightly bonded to the insulating polymer fiber substrate.

[0015] Step 3: Pass the fiber bundle with the Sn / Pd catalyst layer through the chemical Cu plating reaction tank. A thin Cu layer is deposited on the fiber surface by chemical plating, creating a continuous metal channel and avoiding the increase in resistance caused by discrete particles. This provides the fiber with preliminary conductivity and lays the foundation for subsequent electroplating to thicken the Cu layer and electroplating of magnetic alloys.

[0016] Step 4: Pass the Cu-plated fiber bundle through the Cu electroplating reaction tank to increase the thickness of the Cu layer on the fiber surface by electrodeposition, so that it can meet the requirements for electroplating magnetic materials.

[0017] Step 5: Prepare mixed solutions of ferrous sulfate heptahydrate (FeSO4·7H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), nickel sulfate hexahydrate (NiSO4·6H2O), and nickel chloride hexahydrate (NiCl2·6H2O) as electroplating precursors. Then, pass the Cu-plated fiber bundle through the reaction tank for electroplating magnetic alloys to electrodeposit a soft magnetic alloy layer with a corresponding atomic ratio on its surface.

[0018] Step 6: After the magnetic fibers have been dried in a drying oven, they are wound up to obtain a bimetallic layer coated fiber with an inner core of insulating polymer fiber, a second outer layer of Cu, and an outermost layer of magnetic alloy.

[0019] Preferably, the insulating polymer fiber is selected from any one of para-aramid fiber, meta-aramid fiber, PBO fiber, PI fiber, and nylon fiber.

[0020] Preferably, in step one, the specific implementation process of the acid washing pretreatment of the insulating polymer fibers is as follows:

[0021] A1. Prepare a hydrochloric acid solution with a concentration of 50 ml / L, and then place it in the pretreatment tank;

[0022] A2. Immerse a 15μm insulating polymer fiber bundle into a hydrochloric acid pretreatment tank at a uniform speed using a winding device. The immersion time is 1-3 minutes.

[0023] A3. Immediately after pickling, transfer to a deionized water tank and rinse with bidirectional flow for 60 seconds to thoroughly remove residual acid.

[0024] A4. After being purged with compressed air, dry with hot air at 80℃ for 5 minutes.

[0025] Preferably, the hydrochloric acid pretreatment tank is equipped with an ultrasonic vibrator with a frequency of 40kHz, and the fiber bundle passes through the ultrasonically vibrating pretreatment tank at a speed of 5-10m / min to enhance the impurity removal effect.

[0026] Preferably, in step two, the specific implementation process of the fiber bundle electroless plating deposition is as follows:

[0027] B1. Mix 10-20 g / L SnCl2·2H2O with 40-60 ml / L HCl at 28-30℃ to obtain a sensitizing solution;

[0028] B2. Immerse the acid-washed fiber bundles in the sensitizing solution for 3-4 minutes. Sn 2+ Adsorbed onto the fiber surface to form a colloidal layer;

[0029] B3. Dissolve 0.1-0.5 g / L of PdCl2 in 10-20 ml / L of HCl solution, then dilute to obtain the activation solution, avoiding direct sunlight;

[0030] B4. Immerse the sensitized fiber bundles in the activation solution for 3-4 minutes. Pd particles are generated on the surface of the fiber bundles through an oxidation-reduction reaction.

[0031] B5. Transfer the reacted fiber bundles into a deionized water bath and rinse with bidirectional flow for 60 seconds to remove free Sn. 4+ / Pd 2+ The ions are then immersed in ammonia water for 90 seconds, gently shaken to neutralize residual acid and prevent plating solution contamination.

[0032] Preferably, in step three, the specific implementation process of electroless Cu plating of the fiber bundle is as follows:

[0033] C1. Dissolve CuSO4·5H2O, formaldehyde, and disodium EDTA in deionized water, then add sodium hydroxide to adjust the pH to 12.5-12.7, then preheat to 50℃ and magnetically stir for 30 minutes until completely dissolved to obtain the plating solution. Add a stabilizer (2-mercaptobenzothiazole) to prevent the plating solution from self-decomposing.

[0034] C2. The fiber bundle with the Sn / Pd catalyst layer deposited is immersed in the plating bath at a speed of 8 m / min for 2 minutes. After reduction reaction, a Cu layer is generated on the surface of the fiber bundle.

[0035] C3. Immerse the Cu-plated fiber bundle in a deionized water bath and rinse bidirectionally for 60 seconds to remove residual plating solution;

[0036] C4. After being purged with compressed air, dry with hot air at 70°C for 3 minutes, then roll up and set aside.

[0037] Preferably, in step four, the specific implementation process of electroplating Cu onto the fiber bundle is as follows:

[0038] D1. In the electroplating reaction tank, a titanium basket is set at the anode to suspend phosphor bronze balls, parallel to the fiber bundle direction; the fiber bundle is connected to the negative terminal of the power supply through a conductive guide roller;

[0039] D2. Dissolve CuSO4·5H2O in deionized water, then acidify with H2SO4, and finally adjust the Cl- by adding HCl. - Finally, a brightener (sodium polydisulfide dipropane sulfonate) and a leveling agent (polyethyleneimine) are added to obtain the electroplating solution, which is then placed in the electroplating reaction tank.

[0040] D3. The thickness of the fiber bundle is measured every 30 seconds using an online film thickness gauge, and the thickness is controlled using the following formula: Where δ is the thickness increment, k is the electrochemical equivalent, I is the current, t is the time, ρ is the density, and A is the fiber surface area. When the fluctuation is > ±0.1μm, the current is automatically adjusted to control the Cu layer thickness to 1±0.1μm.

[0041] D4. Immerse the Cu-plated fiber bundles in a deionized water bath and rinse bidirectionally for 60 seconds to remove residual Cu. 2+ .

[0042] Preferably, in step five, the specific implementation process of electroplating the magnetic alloy onto the fiber bundle is as follows:

[0043] E1. Prepare an ionic solution with an atomic ratio of Fe:Ni = 64:36 using ferrous sulfate heptahydrate (FeSO4·7H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), nickel sulfate hexahydrate (NiSO4·6H2O), and nickel chloride hexahydrate (NiCl2·6H2O) as the plating bath. Then add a buffer (H3BO3), a stabilizer (2-mercaptobenzothiazole), a complexing agent (sodium citrate), and a softener (polyethylene glycol).

[0044] E2. The anode of the electroplating tank is equipped with a titanium basket to suspend the metal ingot. The Cu-plated fiber is immersed in 10% H2SO4 for 30 seconds to remove the oxide film. Then it is rinsed by spraying with deionized water. Finally, the fiber bundle is connected to the negative terminal of the power supply through a conductive guide roller.

[0045] E3. The thickness of the fiber bundle is measured every 30 seconds using an online film thickness gauge, and the thickness is controlled using the following formula: Where δ is the thickness increment, k is the electrochemical equivalent, I is the current, t is the time, ρ is the density, and A is the fiber surface area. When the fluctuation is > ±0.2μm, the current is automatically adjusted to control the soft magnetic alloy layer to be 2±0.2μm thick.

[0046] E4. Immerse the electroplated fiber bundle in benzotriazole for 60 seconds to form a passivation film.

[0047] E5. Immerse the fiber bundle after electroplating the soft magnetic alloy layer into a deionized water bath and rinse bidirectionally for 60 seconds to remove residual ions.

[0048] Preferably, the magnetic coating composition is selected from any one of Ni, Fe0.2Ni0.8, Fe0.5Ni0.5, Fe0.64Ni0.36, Fe0.1Co0.9Niy, Fe0.3Co0.7Niy, and Fe0.64Co0.36Niy.

[0049] The working principle and beneficial effects of this invention are as follows:

[0050] 1. By adjusting the atomic ratio of Fe, Co, and Ni (e.g., Fe:Ni = 64:36), the saturation magnetization can reach 85 emu / g (experimental data), and the coercivity can be as low as 10 Oe. Figure 7 As shown in the figure, this is significantly superior to existing technologies, with a wide range of adjustable magnetic properties, supporting customized applications. The electroplating process ensures that the magnetic alloy layer is continuous and dense, avoiding the problem of particle clusters.

[0051] 2. The synergistic effect of the magnetic alloy layer and the Cu interlayer endows the fiber with excellent conductivity. Experimental examples show that the sample with high Ni content (S2) has a line resistance of only 2.6 Ω / m and a volume conductivity of 1.87 × 10⁻⁶. 7 S / m, which is better than existing technologies (such as FeCo semiconductor materials, with conductivity <1×10⁻⁶). 4 The S / m ratio is increased by more than 40 times. Because the metal layer covers the fiber surface and its thickness is less than the skin depth, the effect of the skin effect is weakened, allowing the magnetic alloy to be effectively utilized under high-frequency electromagnetic waves.

[0052] 3. The electroless Cu layer serves as a conductive substrate, and combined with electroplating for thickening, it forms a continuous metal channel, achieving complete surface metal coverage. Simultaneously, the metal layer (Cu and magnetic alloy) has a smooth and dense surface, does not alter the overall morphology of the fiber, exhibits strong adhesion, and is not easily detached during processing.

[0053] 4. EDS elemental mapping confirms that Fe, Co, and Ni are uniformly distributed on the fiber surface, and the atomic ratio is highly consistent with the target ratio (e.g., Fe:Ni=64:36), which avoids the performance unevenness caused by particle clusters in the prior art.

[0054] 5. The base is made of flexible polymer fibers (such as aramid, PBO or PI fibers), which retain high ductility and mechanical strength after treatment, and are easy to wind and rewind, meeting the needs of wearable or curved surface applications.

[0055] 6. The bimetallic layer structure has high magnetic permeability and high electrical conductivity, making it suitable for 5G equipment, radar stealth materials and military equipment, and helping to solve the problem of electromagnetic pollution. Attached Figure Description

[0056] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0057] Figure 1 This is a schematic diagram of the structure of a flexible magnetic fiber according to the present invention;

[0058] Figure 2 This is a flowchart of a method for preparing flexible magnetic fibers according to the present invention;

[0059] Figure 3 SEM images of FexNi1-x-AF surfaces with different element ratios in this invention;

[0060] Figure 4 The images show cross-sectional SEM images of the PAF (Polyester Aluminum Encapsulated Foil) with Cu plating as an intermediate product in this invention, and the PAF with Ni and Fe0.64Ni0.36 plating as the final product.

[0061] Figure 5 SEM images of FexCo1-xNiy-AF surfaces with different element ratios according to the present invention;

[0062] Figure 6 The elemental mapping spectra of Fe and Ni obtained from the EDS scan of Fe0.5Ni0.5-AF in this invention are shown.

[0063] Figure 7 The elemental mapping spectrum of Fe, Co, and Ni given by EDS scan of Fe0.64Co0.36Niy-AF in this invention;

[0064] Figure 8 The figure shows the hysteresis loop test results of FexNi1-x-AF and FexCo1-xNiy-AF in this invention. Detailed Implementation

[0065] The technical solutions 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.

[0066] Example 1:

[0067] Reference Figure 1 This embodiment proposes a flexible magnetic fiber, including an insulating polymer fiber substrate 101, an Sn / Pd catalyst layer 102 connected to the outside of the insulating polymer fiber substrate 101, a Cu layer 103 connected to the outside of the catalyst layer 102, and a soft magnetic alloy layer 104 connected to the outside of the Cu layer 103.

[0068] Example 2:

[0069] This embodiment proposes a method for preparing flexible magnetic fibers, including the following steps:

[0070] Step 1: Select para-aramid fiber filament as the substrate, and then perform acid washing pretreatment on the para-aramid fiber. The specific implementation process is as follows:

[0071] A1. Prepare a hydrochloric acid solution with a concentration of 50 ml / L, and then place it in the pretreatment tank;

[0072] A2. Immerse a 15μm para-aramid fiber bundle into a hydrochloric acid pretreatment tank at a uniform speed using a winding device for 1 minute.

[0073] A3. Immediately after pickling, transfer to a deionized water tank and rinse with bidirectional flow for 60 seconds to thoroughly remove residual acid.

[0074] A4. After being purged with compressed air, dry with hot air at 80℃ for 5 minutes;

[0075] Step 2: The acid-washed fiber bundles are passed through a colloidal Sn / Pd reaction tank. A colloidal Sn / Pd catalytic layer is constructed on the fiber surface by electroless plating. Pd particles, acting as a highly efficient catalyst, provide active sites with a high specific surface area, reducing interfacial stress and promoting uniform nucleation of Cu in subsequent electroless plating. This ensures a tight bond between the metal layer and the insulating polymer fiber substrate. The specific implementation process is as follows:

[0076] B1. Mix 10 g / L SnCl2·2H2O with 40 ml / L HCl at 28-30℃ to obtain the sensitization solution;

[0077] B2. Immerse the acid-washed fiber bundles in the sensitizing solution for 3 minutes. Sn 2+ Adsorbed onto the fiber surface to form a colloidal layer;

[0078] B3. Dissolve 0.1 g / L PdCl2 in 100 ml / L HCl solution, then dilute to obtain the activation solution, avoiding direct sunlight;

[0079] B4. Immerse the sensitized fiber bundles in the activation solution for 3 minutes. Pd particles are generated on the surface of the fiber bundles through an oxidation-reduction reaction.

[0080] B5. Transfer the reacted fiber bundles into a deionized water bath and rinse with bidirectional flow for 60 seconds to remove free Sn. 4+ / Pd 2+ Ions are then immersed in ammonia water for 90 seconds, gently agitated to neutralize residual acid and prevent plating solution contamination;

[0081] Step 3: Pass the fiber bundle with the deposited Sn / Pd catalyst layer through the chemical Cu plating reaction tank. A thin Cu layer is deposited on the fiber surface through chemical plating, creating a continuous metal channel and avoiding the increase in resistance caused by discrete particles. This provides the fiber with preliminary conductivity, laying the foundation for subsequent electroplating to thicken the Cu layer and electroplating magnetic alloys. The specific implementation process is as follows:

[0082] C1. Dissolve CuSO4·5H2O, formaldehyde, and disodium EDTA in deionized water, then add sodium hydroxide to adjust the pH to 12.5, then preheat to 50℃ and magnetically stir for 30 minutes until completely dissolved to obtain the plating solution. Add a stabilizer (2-mercaptobenzothiazole) to prevent the plating solution from self-decomposing.

[0083] C2. The fiber bundle with the Sn / Pd catalyst layer deposited is immersed in the plating bath at a speed of 8 m / min for 2 minutes. After reduction reaction, a Cu layer is generated on the surface of the fiber bundle.

[0084] C3. Immerse the Cu-plated fiber bundle in a deionized water bath and rinse bidirectionally for 60 seconds to remove residual plating solution;

[0085] C4. After being purged with compressed air, dry with hot air at 70℃ for 3 minutes, then roll up and set aside.

[0086] Step 4: Pass the Cu-plated fiber bundle through the Cu electroplating reaction tank. The thickness of the Cu layer on the fiber surface is increased by electrodeposition to meet the requirements for electroplating magnetic materials. The specific implementation process is as follows:

[0087] D1. In the electroplating reaction tank, a titanium basket is set at the anode to suspend phosphor bronze balls, parallel to the fiber bundle direction; the fiber bundle is connected to the negative terminal of the power supply through a conductive guide roller;

[0088] D2. Dissolve CuSO4·5H2O in deionized water, then acidify with H2SO4, and finally adjust the Cl- by adding HCl. - Finally, a brightener (sodium polydisulfide dipropane sulfonate) and a leveling agent (polyethyleneimine) are added to obtain the electroplating solution, which is then placed in the electroplating reaction tank.

[0089] D3. The thickness of the fiber bundle is measured every 30 seconds using an online film thickness gauge, and the thickness is controlled using the following formula: Where δ is the thickness increment, k is the electrochemical equivalent, I is the current, t is the time, ρ is the density, and A is the fiber surface area. When the fluctuation is > ±0.1μm, the current is automatically adjusted to control the Cu layer to be 1μm thick.

[0090] D4. Immerse the Cu-plated fiber bundles in a deionized water bath and rinse bidirectionally for 60 seconds to remove residual Cu. 2+ ;

[0091] Step 5: Prepare mixed solutions of different concentrations of ferrous sulfate heptahydrate (FeSO4·7H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), nickel sulfate hexahydrate (NiSO4·6H2O), and nickel chloride hexahydrate (NiCl2·6H2O) as electroplating precursors. Then, pass the Cu-plated fiber bundles through the reaction tank for electroplating magnetic alloys, so that a soft magnetic alloy layer with the corresponding atomic ratio is electrodeposited on its surface. The specific implementation process is as follows:

[0092] E1. Prepare an ionic solution with an atomic ratio of Fe:Ni = 64:36 using ferrous sulfate heptahydrate (FeSO4·7H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), nickel sulfate hexahydrate (NiSO4·6H2O), and nickel chloride hexahydrate (NiCl2·6H2O) as the plating bath. Then add a buffer (H3BO3), a stabilizer (2-mercaptobenzothiazole), a complexing agent (sodium citrate), and a softener (polyethylene glycol).

[0093] E2. The anode of the electroplating tank is equipped with a titanium basket to suspend the metal ingot. The Cu-plated fiber is immersed in 10% H2SO4 for 30 seconds to remove the oxide film. Then it is rinsed by spraying with deionized water. Finally, the fiber bundle is connected to the negative terminal of the power supply through a conductive guide roller.

[0094] E3. The thickness of the fiber bundle is measured every 30 seconds using an online film thickness gauge, and the thickness is controlled using the following formula: Where δ is the thickness increment, k is the electrochemical equivalent, I is the current, t is the time, ρ is the density, and A is the fiber surface area. When the fluctuation is > ±0.2μm, the current is automatically adjusted to control the soft magnetic alloy layer to be 2μm thick.

[0095] E4. Immerse the electroplated fiber bundle in benzotriazole for 60 seconds to form a passivation film.

[0096] E5. Immerse the fiber bundle after electroplating the soft magnetic alloy layer into a deionized water bath and rinse bidirectionally for 60 seconds to remove residual ions.

[0097] Step 6: After the magnetic fibers have been dried in a drying oven, they are wound up to obtain a bimetallic layer coated fiber with an inner core of insulating polymer fiber, a second outer layer of Cu, and an outermost layer of magnetic alloy.

[0098] Furthermore, the hydrochloric acid pretreatment tank is equipped with an ultrasonic vibrator with a frequency of 40kHz. The fiber bundle passes through the ultrasonically vibrating pretreatment tank at a speed of 5m / min, which enhances the impurity removal effect.

[0099] This invention uses flexible, insulating polymer fibers as a substrate, including aramid fibers, PBO fibers, nylon fibers, PI fibers, etc. After surface metallization modification, the fibers retain good flexibility and ductility, exhibiting a core-shell structure with organic fibers as the inner core, magnetic alloys as the shell, and a copper layer as the intermediate dielectric layer. Various soft magnetic alloy shells (Fe, Co, Ni / FeCo, FeNi, CoNi / FeCoNi) are applied to the fiber surface through a combination of chemical plating and electroplating. The prepared fibers exhibit high saturation magnetization and low coercivity. By adjusting the Fe:Co:Ni ratio, the saturation magnetization and coercivity of the magnetic fibers can be adjusted within a certain range. The electroplated metal layer has a smooth and dense surface, without altering the overall morphology of the fiber, thus constituting a conformal coating. The metal layer has strong adhesion to the fiber and is not easily detached. By controlling the reaction conditions, the thickness of the metal layer can be controlled within a few micrometers, resulting in a continuous and complete surface metal layer that gives the fiber good conductivity.

[0100] Example 3:

[0101] This embodiment proposes a method for preparing flexible magnetic fibers, including the following steps:

[0102] Step 1: Select PBO fiber filament as the substrate, and then perform acid washing pretreatment on the PBO fiber. The specific implementation process is as follows:

[0103] A1. Prepare a hydrochloric acid solution with a concentration of 50 ml / L, and then place it in the pretreatment tank;

[0104] A2. Immerse a 15μm PBO fiber bundle into a hydrochloric acid pretreatment tank at a uniform speed using a winding device for 2 minutes.

[0105] A3. Immediately after pickling, transfer to a deionized water tank and rinse with bidirectional flow for 60 seconds to thoroughly remove residual acid.

[0106] A4. After being purged with compressed air, dry with hot air at 80℃ for 5 minutes;

[0107] Step 2: The acid-washed fiber bundles are passed through a colloidal Sn / Pd reaction tank, and a colloidal Sn / Pd catalytic layer is constructed on the fiber surface by chemical plating. The specific implementation process is as follows:

[0108] B1. Mix 15 g / L SnCl2·2H2O with 50 ml / L HCl at 28-30℃ to obtain the sensitization solution;

[0109] B2. Immerse the acid-washed fiber bundles in the sensitizing solution for 3.5 minutes. Sn 2+ Adsorbed onto the fiber surface to form a colloidal layer;

[0110] B3. Dissolve 0.3 g / L PdCl2 in 15 ml / L HCl solution, then dilute to obtain the activation solution, avoiding direct sunlight;

[0111] B4. Immerse the sensitized fiber bundles in the activation solution for 3.5 minutes. Pd particles are generated on the surface of the fiber bundles through an oxidation-reduction reaction.

[0112] B5. Transfer the reacted fiber bundles into a deionized water bath and rinse with bidirectional flow for 60 seconds to remove free Sn. 4+ / Pd 2+ Ions are then immersed in ammonia water for 90 seconds, gently agitated to neutralize residual acid and prevent plating solution contamination;

[0113] Step 3: Pass the fiber bundle with the deposited Sn / Pd catalyst layer through the chemical Cu plating reaction tank. A thin Cu layer is deposited on the fiber surface by chemical plating to make it conductive. The specific implementation process is as follows:

[0114] C1. Dissolve CuSO4·5H2O, formaldehyde, and disodium EDTA in deionized water, then add sodium hydroxide to adjust the pH to 12.6, then preheat to 50℃ and stir magnetically for 30 minutes until completely dissolved to obtain the plating solution. Add a stabilizer (2-mercaptobenzothiazole) to prevent the plating solution from self-decomposing.

[0115] C2. The fiber bundle with the Sn / Pd catalyst layer deposited is immersed in the plating bath at a speed of 8 m / min for 2 minutes. After reduction reaction, a Cu layer is generated on the surface of the fiber bundle.

[0116] C3. Immerse the Cu-plated fiber bundle in a deionized water bath and rinse bidirectionally for 60 seconds to remove residual plating solution;

[0117] C4. After being purged with compressed air, dry with hot air at 70℃ for 3 minutes, then roll up and set aside.

[0118] Step 4: Pass the Cu-plated fiber bundle through the Cu electroplating reaction tank. The thickness of the Cu layer on the fiber surface is increased by electrodeposition to meet the requirements for electroplating magnetic materials. The specific implementation process is as follows:

[0119] D1. In the electroplating reaction tank, a titanium basket is set at the anode to suspend phosphor bronze balls, parallel to the fiber bundle direction; the fiber bundle is connected to the negative terminal of the power supply through a conductive guide roller;

[0120] D2. Dissolve CuSO4·5H2O in deionized water, then acidify with H2SO4, and finally adjust the Cl- by adding HCl. - Finally, a brightener (sodium polydisulfide dipropane sulfonate) and a leveling agent (polyethyleneimine) are added to obtain the electroplating solution, which is then placed in the electroplating reaction tank.

[0121] D3. The thickness of the fiber bundle is measured every 30 seconds using an online film thickness gauge, and the thickness is controlled using the following formula: Where δ is the thickness increment, k is the electrochemical equivalent, I is the current, t is the time, ρ is the density, and A is the fiber surface area. When the fluctuation is > ±0.1μm, the current is automatically adjusted to control the Cu layer to be 1μm thick.

[0122] D4. Immerse the Cu-plated fiber bundles in a deionized water bath and rinse bidirectionally for 60 seconds to remove residual Cu. 2+ ;

[0123] Step 5: Prepare mixed solutions of different concentrations of ferrous sulfate heptahydrate (FeSO4·7H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), nickel sulfate hexahydrate (NiSO4·6H2O), and nickel chloride hexahydrate (NiCl2·6H2O) as electroplating precursors. Then, pass the Cu-plated fiber bundles through the reaction tank for electroplating magnetic alloys, so that a soft magnetic alloy layer with the corresponding atomic ratio is electrodeposited on its surface. The specific implementation process is as follows:

[0124] E1. Prepare an ionic solution with an atomic ratio of Fe:Ni = 64:36 using ferrous sulfate heptahydrate (FeSO4·7H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), nickel sulfate hexahydrate (NiSO4·6H2O), and nickel chloride hexahydrate (NiCl2·6H2O) as the plating bath. Then add a buffer (H3BO3), a stabilizer (2-mercaptobenzothiazole), a complexing agent (sodium citrate), and a softener (polyethylene glycol).

[0125] E2. The anode of the electroplating tank is equipped with a titanium basket to suspend the metal ingot. The Cu-plated fiber is immersed in 10% H2SO4 for 30 seconds to remove the oxide film. Then it is rinsed by spraying with deionized water. Finally, the fiber bundle is connected to the negative terminal of the power supply through a conductive guide roller.

[0126] E3. The thickness of the fiber bundle is measured every 30 seconds using an online film thickness gauge, and the thickness is controlled using the following formula: Where δ is the thickness increment, k is the electrochemical equivalent, I is the current, t is the time, ρ is the density, and A is the fiber surface area. When the fluctuation is > ±0.2μm, the current is automatically adjusted to control the soft magnetic alloy layer to be 2μm thick.

[0127] E4. Immerse the electroplated fiber bundle in benzotriazole for 60 seconds to form a passivation film.

[0128] E5. Immerse the fiber bundle after electroplating the soft magnetic alloy layer into a deionized water bath and rinse bidirectionally for 60 seconds to remove residual ions.

[0129] Step 6: After the magnetic fibers have been dried in a drying oven, they are wound up to obtain a bimetallic layer coated fiber with an inner core of insulating polymer fiber, a second outer layer of Cu, and an outermost layer of magnetic alloy.

[0130] Example 4:

[0131] This embodiment proposes a method for preparing flexible magnetic fibers, including the following steps:

[0132] Step 1: Select PI fiber filament as the substrate, and then perform acid washing pretreatment on the PI fiber. The specific implementation process is as follows:

[0133] A1. Prepare a hydrochloric acid solution with a concentration of 50 ml / L, and then place it in the pretreatment tank;

[0134] A2. Immerse a 15μm PI fiber bundle into the hydrochloric acid pretreatment tank at a uniform speed using a winding device for 3 minutes.

[0135] A3. Immediately after pickling, transfer to a deionized water tank and rinse with bidirectional flow for 60 seconds to thoroughly remove residual acid.

[0136] A4. After being purged with compressed air, dry with hot air at 80℃ for 5 minutes;

[0137] Step 2: The acid-washed fiber bundles are passed through a colloidal Sn / Pd reaction tank, and a colloidal Sn / Pd catalytic layer is constructed on the fiber surface by chemical plating. The specific implementation process is as follows:

[0138] B1. Mix 20 g / L SnCl2·2H2O with 60 ml / L HCl at 28-30℃ to obtain the sensitization solution;

[0139] B2. Immerse the acid-washed fiber bundles in the sensitizing solution for 4 minutes. Sn 2+ Adsorbed onto the fiber surface to form a colloidal layer;

[0140] B3. Dissolve 0.5 g / L PdCl2 in 20 ml / L HCl solution, then dilute to obtain the activation solution, avoiding direct sunlight;

[0141] B4. Immerse the sensitized fiber bundles in the activation solution for 4 minutes. Pd particles are generated on the surface of the fiber bundles through an oxidation-reduction reaction.

[0142] B5. Transfer the reacted fiber bundles into a deionized water bath and rinse with bidirectional flow for 60 seconds to remove free Sn. 4+ / Pd 2+ Ions are then immersed in ammonia water for 90 seconds, gently agitated to neutralize residual acid and prevent plating solution contamination;

[0143] Step 3: Pass the fiber bundle with the deposited Sn / Pd catalyst layer through the chemical Cu plating reaction tank. A thin Cu layer is deposited on the fiber surface by chemical plating to make it conductive. The specific implementation process is as follows:

[0144] C1. Dissolve CuSO4·5H2O, formaldehyde, and disodium EDTA in deionized water, then add sodium hydroxide to adjust the pH to 12.7, then preheat to 50℃ and stir magnetically for 30 minutes until completely dissolved to obtain the plating solution. Add a stabilizer (2-mercaptobenzothiazole) to prevent the plating solution from self-decomposing.

[0145] C2. The fiber bundle with the Sn / Pd catalyst layer deposited is immersed in the plating bath at a speed of 8 m / min for 2 minutes. After reduction reaction, a Cu layer is generated on the surface of the fiber bundle.

[0146] C3. Immerse the Cu-plated fiber bundle in a deionized water bath and rinse bidirectionally for 60 seconds to remove residual plating solution;

[0147] C4. After being purged with compressed air, dry with hot air at 70℃ for 3 minutes, then roll up and set aside.

[0148] Step 4: Pass the Cu-plated fiber bundle through the Cu electroplating reaction tank. The thickness of the Cu layer on the fiber surface is increased by electrodeposition to meet the requirements for electroplating magnetic materials. The specific implementation process is as follows:

[0149] D1. In the electroplating reaction tank, a titanium basket is set at the anode to suspend phosphor bronze balls, parallel to the fiber bundle direction; the fiber bundle is connected to the negative terminal of the power supply through a conductive guide roller;

[0150] D2. Dissolve CuSO4·5H2O in deionized water, then acidify with H2SO4, and finally adjust the Cl- by adding HCl. - Finally, a brightener (sodium polydisulfide dipropane sulfonate) and a leveling agent (polyethyleneimine) are added to obtain the electroplating solution, which is then placed in the electroplating reaction tank.

[0151] D3. The thickness of the fiber bundle is measured every 30 seconds using an online film thickness gauge, and the thickness is controlled using the following formula: Where δ is the thickness increment, k is the electrochemical equivalent, I is the current, t is the time, ρ is the density, and A is the fiber surface area. When the fluctuation is > ±0.1μm, the current is automatically adjusted to control the Cu layer to be 1μm thick.

[0152] D4. Immerse the Cu-plated fiber bundles in a deionized water bath and rinse bidirectionally for 60 seconds to remove residual Cu. 2+ ;

[0153] Step 5: Prepare mixed solutions of different concentrations of ferrous sulfate heptahydrate (FeSO4·7H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), nickel sulfate hexahydrate (NiSO4·6H2O), and nickel chloride hexahydrate (NiCl2·6H2O) as electroplating precursors. Then, pass the Cu-plated fiber bundles through the reaction tank for electroplating magnetic alloys, so that a soft magnetic alloy layer with the corresponding atomic ratio is electrodeposited on its surface. The specific implementation process is as follows:

[0154] E1. Prepare an ionic solution with an atomic ratio of Fe:Ni = 64:36 using ferrous sulfate heptahydrate (FeSO4·7H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), nickel sulfate hexahydrate (NiSO4·6H2O), and nickel chloride hexahydrate (NiCl2·6H2O) as the plating bath. Then add a buffer (H3BO3), a stabilizer (2-mercaptobenzothiazole), a complexing agent (sodium citrate), and a softener (polyethylene glycol).

[0155] E2. The anode of the electroplating tank is equipped with a titanium basket to suspend the metal ingot. The Cu-plated fiber is immersed in 10% H2SO4 for 30 seconds to remove the oxide film. Then it is rinsed by spraying with deionized water. Finally, the fiber bundle is connected to the negative terminal of the power supply through a conductive guide roller.

[0156] E3. The thickness of the fiber bundle is measured every 30 seconds using an online film thickness gauge, and the thickness is controlled using the following formula: Where δ is the thickness increment, k is the electrochemical equivalent, I is the current, t is the time, ρ is the density, and A is the fiber surface area. When the fluctuation is > ±0.2μm, the current is automatically adjusted to control the soft magnetic alloy layer to be 2μm thick.

[0157] E4. Immerse the electroplated fiber bundle in benzotriazole for 60 seconds to form a passivation film.

[0158] E5. Immerse the fiber bundle after electroplating the soft magnetic alloy layer into a deionized water bath and rinse bidirectionally for 60 seconds to remove residual ions.

[0159] Step 6: After the magnetic fibers have been dried in a drying oven, they are wound up to obtain a bimetallic layer coated fiber with an inner core of insulating polymer fiber, a second outer layer of Cu, and an outermost layer of magnetic alloy.

[0160] Experimental example:

[0161] This experiment was used to verify the conductivity of the magnetic fibers in Example 1. Fibers with magnetic coating compositions of Fe0.64Ni0.36, Ni, and FeCo (existing technology materials) were prepared as experimental samples, numbered S1 (Fe0.64Ni0.36), S2 (Ni), and S3 (FeCo), respectively. The samples were then tested using a four-probe resistance meter, and the specific test results are shown in the table below:

[0162]

[0163] As shown above, the volumetric conductivity of sample S2 is 1.87 × 10⁻⁶. 7 S / m is close to that of pure nickel (1.43×10). 7 The resistance of the high-Ni alloy was verified to be more than 40 times higher than that of the existing technology (S / m). The resistance of the magnetic fiber wire with high Ni content was 2.6 Ω / m, while the resistance of the Fe0.64Ni0.36-AF wire with low Ni content was 10.2 Ω / m. The electroplated metal layer has good conductivity.

[0164] Combined with appendix Figure 2-7 ,Depend on Figure 2 As shown in sections 3 and 4, the metal layer on the surface of the magnetic fiber is smooth and dense, with close adhesion between the fiber and the metal layer, and between the Cu layer and the magnetic alloy layer. The metal layer on the fiber surface exhibits good continuity, with no obvious gaps or cracks, indicating that it forms a monolithic alloy layer rather than a simple accumulation of metal particles; Figure 5 As shown in Figure 6, Fe, Co, and Ni elements are uniformly distributed on the surface of the magnetic fiber. The atomic ratios of elements in the actual product were determined by EDS scanning of the magnetic fiber surface, and the specific results are shown in the table below:

[0165]

[0166] As can be seen from the above, the Fe:Co:Ni atomic ratio in the actual product is close to the target ratio, which meets the requirements for element ratio control.

[0167] Depend on Figure 7 It can be seen that by changing Fe:Ni, the saturation magnetization of the magnetic fiber is greatly improved. The saturation magnetization of Fe0.64Ni0.36-AF can reach 85 emu / g, while its coercivity is only 11Oe.

[0168] The above are merely preferred embodiments of the present invention and are 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 flexible magnetic fiber, characterized in that, It includes an insulating polymer fiber substrate (101), an outer Sn / Pd catalyst layer (102) connected to the outside of the insulating polymer fiber substrate (101), a Cu layer (103) connected to the outside of the catalyst layer (102), and a soft magnetic alloy layer (104) connected to the outside of the Cu layer (103).

2. A method for preparing flexible magnetic fibers according to claim 1, characterized in that, Includes the following steps: Step 1: Select insulating polymer fiber filaments as the substrate, and then perform acid washing pretreatment on the insulating polymer fibers; Step 2: The acid-washed fiber bundles are passed through a colloidal Sn / Pd reaction tank, and a colloidal Sn / Pd catalytic layer is constructed on the fiber surface by chemical plating. Pd particles, as a highly efficient catalyst, provide active sites with a high specific surface area, reduce interfacial stress, promote uniform nucleation of Cu in subsequent chemical plating, and ensure that the metal layer is tightly bonded to the insulating polymer fiber substrate. Step 3: Pass the fiber bundle with the Sn / Pd catalyst layer through the chemical Cu plating reaction tank. A thin Cu layer is deposited on the fiber surface by chemical plating, creating a continuous metal channel and avoiding the increase in resistance caused by discrete particles. This provides the fiber with preliminary conductivity and lays the foundation for subsequent electroplating to thicken the Cu layer and electroplating of magnetic alloys. Step 4: Pass the Cu-plated fiber bundle through the Cu electroplating reaction tank to increase the thickness of the Cu layer on the fiber surface by electrodeposition, so that it can meet the requirements for electroplating magnetic materials. Step 5: Prepare mixed solutions of ferrous sulfate heptahydrate (FeSO4·7H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), nickel sulfate hexahydrate (NiSO4·6H2O), and nickel chloride hexahydrate (NiCl2·6H2O) as electroplating precursors. Then, pass the Cu-plated fiber bundle through the reaction tank for electroplating magnetic alloys to electrodeposit a soft magnetic alloy layer with a corresponding atomic ratio on its surface. Step 6: After the magnetic fibers have been dried in a drying oven, they are wound up to obtain a bimetallic layer coated fiber with an inner core of insulating polymer fiber, a second outer layer of Cu, and an outermost layer of magnetic alloy.

3. The method for preparing flexible magnetic fibers according to claim 2, characterized in that, The insulating polymer fiber is selected from any one of para-aramid fiber, meta-aramid fiber, PBO fiber, PI fiber, and nylon fiber.

4. The method for preparing flexible magnetic fibers according to claim 2, characterized in that, In step one, the specific implementation process of the acid washing pretreatment of the insulating polymer fibers is as follows: A1. Prepare a hydrochloric acid solution with a concentration of 50 ml / L, and then place it in the pretreatment tank; A2. Immerse a 15μm insulating polymer fiber bundle into a hydrochloric acid pretreatment tank at a uniform speed using a winding device. The immersion time is 1-3 minutes. A3. Immediately after pickling, transfer to a deionized water tank and rinse with bidirectional flow for 60 seconds to thoroughly remove residual acid. A4. After being purged with compressed air, dry with hot air at 80℃ for 5 minutes.

5. The method for preparing a flexible magnetic fiber according to claim 4, characterized in that, The hydrochloric acid pretreatment tank is equipped with an ultrasonic vibrator with a frequency of 40kHz. The fiber bundle passes through the ultrasonically vibrating pretreatment tank at a speed of 5-10m / min, which enhances the impurity removal effect.

6. The method for preparing a flexible magnetic fiber according to claim 2, characterized in that, In step two, the specific implementation process of the fiber bundle electroless plating deposition is as follows: B1. Mix 10-20 g / L SnCl2·2H2O with 40-60 ml / L HCl at 28-30℃ to obtain a sensitizing solution; B2. Immerse the acid-washed fiber bundles in the sensitizing solution for 3-4 minutes. Sn 2+ Adsorbed onto the fiber surface to form a colloidal layer; B3. Dissolve 0.1-0.5 g / L of PdCl2 in 10-20 ml / L of HCl solution, then dilute to obtain the activation solution, avoiding direct sunlight; B4. Immerse the sensitized fiber bundles in the activation solution for 3-4 minutes. Pd particles are generated on the surface of the fiber bundles through an oxidation-reduction reaction. B5. Transfer the reacted fiber bundles into a deionized water bath and rinse with bidirectional flow for 60 seconds to remove free Sn. 4+ / Pd 2+ The ions are then immersed in ammonia water for 90 seconds, gently shaken to neutralize residual acid and prevent plating solution contamination.

7. The method for preparing flexible magnetic fibers according to claim 2, characterized in that, In step three, the specific implementation process of electroless Cu plating of the fiber bundle is as follows: C1. Dissolve CuSO4·5H2O, formaldehyde, and disodium EDTA in deionized water, then add sodium hydroxide to adjust the pH to 12.5-12.7, then preheat to 50℃ and stir magnetically for 30 minutes until completely dissolved to obtain the plating solution. Add a stabilizer to prevent the plating solution from self-decomposing. C2. The fiber bundle with the Sn / Pd catalyst layer deposited is immersed in the plating bath at a speed of 8 m / min for 2 minutes. After reduction reaction, a Cu layer is generated on the surface of the fiber bundle. C3. Immerse the Cu-plated fiber bundle in a deionized water bath and rinse bidirectionally for 60 seconds to remove residual plating solution; C4. After being purged with compressed air, dry with hot air at 70°C for 3 minutes, then roll up and set aside.

8. The method for preparing a flexible magnetic fiber according to claim 2, characterized in that, In step four, the specific implementation process of electroplating Cu onto the fiber bundle is as follows: D1. In the electroplating reaction tank, a titanium basket is set at the anode to suspend phosphor bronze balls, parallel to the fiber bundle direction; the fiber bundle is connected to the negative terminal of the power supply through a conductive guide roller; D2. Dissolve CuSO4·5H2O in deionized water, then acidify with H2SO4, and finally adjust the Cl- by adding HCl. - Finally, brightener and leveling agent are added to obtain the electroplating solution, which is then placed in the electroplating reaction tank; D3. The thickness of the fiber bundle is measured every 30 seconds using an online film thickness gauge, and the thickness is controlled using the following formula: Where δ is the thickness increment, k is the electrochemical equivalent, I is the current, t is the time, ρ is the density, and A is the fiber surface area. When the fluctuation is > ±0.1μm, the current is automatically adjusted to control the Cu layer thickness to 1±0.1μm. D4. Immerse the Cu-plated fiber bundles in a deionized water bath and rinse bidirectionally for 60 seconds to remove residual Cu. 2+ .

9. The method for preparing a flexible magnetic fiber according to claim 2, characterized in that, In step five, the specific implementation process of electroplating the magnetic alloy onto the fiber bundle is as follows: E1. Prepare an ionic solution with an atomic ratio of Fe:Ni = 64:36 by mixing ferrous sulfate heptahydrate (FeSO4·7H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), nickel sulfate hexahydrate (NiSO4·6H2O), and nickel chloride hexahydrate (NiCl2·6H2O) as the plating bath, and then add buffer, stabilizer, complexing agent and softener. E2. The anode of the electroplating tank is equipped with a titanium basket to suspend the metal ingot. The Cu-plated fiber is immersed in 10% H2SO4 for 30 seconds to remove the oxide film. Then it is rinsed by spraying with deionized water. Finally, the fiber bundle is connected to the negative terminal of the power supply through a conductive guide roller. E3. The thickness of the fiber bundle is measured every 30 seconds using an online film thickness gauge, and the thickness is controlled using the following formula: Where δ is the thickness increment, k is the electrochemical equivalent, I is the current, t is the time, ρ is the density, and A is the fiber surface area. When the fluctuation is > ±0.2μm, the current is automatically adjusted to control the soft magnetic alloy layer to be 2±0.2μm thick. E4. Immerse the electroplated fiber bundle in benzotriazole for 60 seconds to form a passivation film. E5. Immerse the fiber bundle after electroplating the soft magnetic alloy layer into a deionized water bath and rinse bidirectionally for 60 seconds to remove residual ions.

10. The method for preparing a flexible magnetic fiber according to claim 9, characterized in that, The magnetic coating composition is selected from any one of Ni, Fe0.2Ni0.8, Fe0.5Ni0.5, Fe0.64Ni0.36, Fe0.1Co0.9Niy, Fe0.3Co0.7Niy, and Fe0.64Co0.36Niy.

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