Magnetic functional film and thermal interface material

Abstract

This invention relates to the field of thermal management technology, specifically to a magnetic functional thin film and a thermal interface material. The magnetic functional thin film comprises an acrylate polymer matrix and iron oxide-coated carbon fibers dispersed in the acrylate polymer matrix; the iron oxide-coated carbon fibers are oriented along the thickness direction of the magnetic functional thin film. This invention achieves efficient oriented alignment of carbon fibers under low magnetic field strength through a strategy of "magnetic coating + low magnetic field induction + ultrasonic vibration synergy," significantly improving the vertical thermal conductivity of the film while endowing it with excellent flexibility and mechanical strength. It can be widely used in fields such as chip heat dissipation, flexible electronics, and 5G communication equipment.

Description

Technical Field

[0001] This invention relates to the field of thermal management technology, specifically to a magnetic functional thin film and thermal interface material. Background Technology

[0002] As electronic devices evolve towards higher integration, higher power density, and thinner designs, heat dissipation has become a key bottleneck restricting their performance and reliability. This is especially true in emerging fields such as flexible electronics, wearable devices, and 5G communications, where there is an urgent need for thermal interface materials that combine high thermal conductivity, flexibility, and lightweight properties.

[0003] Traditional thermal conductive materials, such as thermal grease and thermal pads, often use ceramic particles (such as alumina and boron nitride) to fill a polymer matrix, but their thermal conductivity is generally low (typically <10 W·m). -1 ·K -1 This makes it difficult to meet the heat dissipation requirements of high-power devices.

[0004] Carbon fiber is known for its excellent axial thermal conductivity (up to 900 W·m). -1 ·K -1 Carbon fibers, with their low density and high mechanical strength, are ideal fillers for preparing high-performance thermally conductive composite materials. Acrylic resins have good film-forming properties, are transparent and flexible, and have strong adhesion; combining them with acrylic resins can balance mechanical properties and processability. However, pure carbon fibers are non-magnetic, have a single function, and are usually randomly distributed in the polymer matrix, failing to fully utilize their high axial thermal conductivity. To improve the directional alignment of carbon fibers, researchers have attempted to use external field induction techniques such as electric and magnetic fields. Among these, magnetic field induction has attracted much attention because it requires no contact and causes no damage to the material. However, carbon fibers themselves are diamagnetic materials, and their response in magnetic fields is weak, usually requiring extremely high magnetic field strengths (>10 T) to achieve effective orientation, limiting their practical applications. In addition, the poor dispersion of carbon fibers and weak interfacial bonding with the matrix in existing technologies also restrict the overall performance of composite materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide a Fe3O4@CF / acrylate magnetic functional thin film and its preparation method.

[0006] The present invention provides a carbon fiber composite film comprising, by mass fraction, 10% to 60% of iron oxide-coated carbon fiber and 40% to 90% of acrylate polymer matrix; wherein the iron oxide-coated carbon fiber is oriented along the thickness direction in the film.

[0007] Furthermore, the magnetic functional film uses Fe3O4-coated carbon fiber as the functional phase and acrylate resin as the matrix phase.

[0008] Furthermore, the magnetic functional film comprises an acrylate polymer matrix and carbon fibers coated with iron oxide.

[0009] Furthermore, the carbon fiber is at least one of mesophase pitch-based carbon fiber and polyacrylonitrile-based carbon fiber, with a diameter of 5μm to 20μm, a length of 50μm to 500μm, and an aspect ratio of (5 to 100):1.

[0010] Furthermore, in the magnetic functional film, the carbon fibers rotate and orient themselves in a magnetic field, thereby achieving directional alignment of the carbon fibers along the thickness direction within the polymer matrix.

[0011] Furthermore, the carbon fiber is modified by Fe3O4 coating to impart strong magnetism, enabling directional driving under low magnetic field conditions.

[0012] Furthermore, the acrylate resin is a blend of polyurethane acrylate (PUA) and epoxy acrylate (EA), which provides the film with good flexibility and film-forming properties.

[0013] Furthermore, the solvent is ethyl acetate.

[0014] Furthermore, the low magnetic field strength is 100 mT to 500 mT, the ultrasonic power is 80 W to 300 W, the frequency is 20 kHz to 40 kHz, the vibration frequency is 10 Hz to 50 Hz, and the amplitude is 0.5 mm to 3 mm.

[0015] The present invention also provides a method for preparing the aforementioned magnetic functional thin film, comprising the following steps:

[0016] 1. Preparation of Fe3O4@CF: Short-cut carbon fibers were acid-washed, alkali-washed, and washed with deionized water until neutral, introducing carboxyl and hydroxyl groups, and then dried. Fe3O4 was coated on the surface of the carbon fibers by chemical co-precipitation: The pretreated carbon fibers were added to a mixed solution of FeCl2·4H2O and FeCl3·6H2O (molar ratio 1:2), stirred evenly, and reacted at 55-65℃ for 30-60 min under N2 protection. Ammonia water was slowly added to adjust the pH to 9-10, and the mixture was ultrasonically dispersed (20 kHz-40 kHz) for 30-40 min. The mixture was filtered, washed with deionized water until neutral, and vacuum dried at 60℃ for 12 h to obtain Fe3O4@CF.

[0017] 2. Preparation of magnetic functional slurry: 10% to 60% of magnetic carbon fiber is added to a mixed solution of acrylic resin and solvent, and dispersed evenly under ultrasonic and vibration assistance to obtain a mixed slurry;

[0018] 3. Synergistic film formation: The slurry is rapidly transferred to a specific mold with a release film and placed on a multi-field synergistic film formation platform; first, ultrasonic waves (20-40 kHz, 80-300 W) and low-frequency vibrations (10 Hz-50 Hz, amplitude 0.5 mm-3 mm) are activated to break up agglomerates and assist in leveling; then, an in-plane parallel low magnetic field (100 mT-500 mT) is applied, and the three work synergistically for 10-30 minutes to cause Fe3O4@CF to be oriented along the magnetic field direction.

[0019] 4. Gradient Temperature Curing: Remove the mold and quickly transfer it to a vacuum oven for curing (curing under a magnetic field). First, pre-cur in a vacuum oven at 40–50°C for 2 hours to quickly fix the fiber orientation; then adjust the temperature to 80°C and cure for 8–12 hours to improve resin cross-linking and enhance the mechanical properties and water resistance of the film; finally, peel off the release film to obtain the target film.

[0020] This invention utilizes carbon fiber as the vertical "main channel" to perform the core heat conduction function, fully leveraging the high axial thermal conductivity of carbon fiber. Furthermore, Fe3O4 coating imparts its properties to the carbon fiber, enabling induced orientation under low magnetic field strength to achieve a highly oriented in-plane alignment of Fe3O4@CF within the acrylate matrix, thereby enhancing the vertical thermal conductivity of the film.

[0021] Furthermore, in step (1) of the preparation method, the carbon fiber surface oxidation treatment is as follows: using a mixed acid of HNO3 and H2SO4 (volume ratio 1:3), treating at 60℃ for 30 min, introducing carboxyl and hydroxyl functional groups, and improving the coating strength of Fe3O4.

[0022] Furthermore, in step (2) of the preparation method, the ultrasonic power is 80–300 W / 20–40 kHz, the vibration frequency is 10–50 Hz, and the amplitude is 0.5–3 mm. Through mechanical stirring and ultrasonic dispersion, the carbon fibers are uniformly and stably present in the polymer, eliminating the need for a dispersant. The cavitation effect of ultrasound can effectively break up carbon fiber agglomerations, and the shearing effect of vibration can promote the uniform distribution of carbon fibers in the matrix.

[0023] Furthermore, in the preparation method, the timing sequence of multi-field coordination in step (3) is as follows: first, turn on the ultrasound and vibration for 5 minutes, then apply a low magnetic field and maintain the coordination of the three until leveling is completed. The bottom surface of the container is perpendicular to the direction of magnetic induction intensity.

[0024] Furthermore, in step (4) of the preparation method, the curing is carried out using gradient temperature curing, first pre-curing at 40-50℃ for 2 hours, and then curing at 80℃ for 8-12 hours.

[0025] In summary, compared with the prior art, the present invention achieves the following technical effects:

[0026] (1) This invention modifies carbon fiber by coating it with iron oxide to give it a strong magnetic response, so that it can rotate and orient under low magnetic field strength. This solves the problem that pure carbon fiber has strong antimagnetism and requires an extremely high magnetic field to orient, and greatly reduces equipment cost and energy consumption.

[0027] (2) The present invention adopts ultrasonic-assisted and vibration-assisted synergistic dispersion technology. The cavitation effect of ultrasound can effectively break the carbon fiber agglomeration, and the shearing effect of vibration can promote the uniform distribution of carbon fiber in the matrix and provide a good initial state for subsequent magnetic field orientation, avoiding the orientation unevenness caused by agglomeration.

[0028] (3) The carbon fibers of the present invention are oriented in a magnetic field. Since the axial thermal conductivity of carbon fibers is much higher than that of radial fibers, the oriented carbon fibers form a continuous "vertical thermal conduction path" along the thickness direction of the film, which minimizes the directional deflection and interface scattering in heat flow transfer and significantly improves the vertical thermal conductivity of the film.

[0029] (4) The magnetic functional film prepared by the present invention has ultra-thin characteristics and the thickness can be controlled between 20 and 200 μm. At the same time, the acrylate matrix gives the film excellent flexibility and mechanical strength, which can meet the heat dissipation requirements of flexible electronic devices.

[0030] (5) The preparation method of the present invention is simple and convenient, the process is highly controllable, and it is easy to promote and scale up production. Attached Figure Description

[0031] Figure 1 This is a process flow diagram for the preparation of the magnetic functional thin film of the present invention.

[0032] Figure 2 This is a SEM image of the magnetic functional thin film prepared in Example 1.

[0033] Figure 3 This is a SEM image of the magnetic functional thin film prepared in Example 2.

[0034] Figure 4 SEM image of the magnetic functional thin film prepared for Comparative Example 1.

[0035] Figure 5 SEM image of the magnetic functional thin film prepared for Comparative Example 2. Detailed Implementation

[0036] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0037] The present invention will be further illustrated below with reference to specific embodiments and comparative embodiments. The following specific embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the following embodiments, and are not in particular limited to the types of raw materials used in the following specific embodiments.

[0038] I. Sources of Raw Materials for Examples and Comparative Examples

[0039] Unless otherwise specified, all raw materials used in the embodiments and comparative examples of this invention are commercially available.

[0040] II. Performance Testing Methods

[0041] (1) Thermal conductivity test: The test shall be conducted in accordance with the standard of ASTM D5470-2012;

[0042] (2) Orientation test: The orientation effect is judged based on the degree of improvement in the final thermal conductivity or based on the SEM image.

[0043] Example 1 (Fe3O4@CF mass fraction is 20 wt%)

[0044] 1. Preparation of Fe3O4@CF: 5 g of carbon fiber (10 μm in diameter and 100 μm in length) was treated with a mixed acid of concentrated HNO3:H2SO4 = 1:3 at 60℃ for 30 min, and washed with deionized water until neutral. A mixed solution of FeCl2·4H2O (0.05 mol) and FeCl3·6H2O (0.1 mol) was added, and the mixture was reacted at 60℃ for 45 min under N2 protection. The pH was adjusted to 9.5 with ammonia water, and the mixture was ultrasonically dispersed (35 kHz) for 15 min. The mixture was then filtered, washed, and vacuum dried at 60℃ for 12 h to obtain Fe3O4@CF.

[0045] 2. Preparation of magnetic functional slurry: Take 2 g Fe3O4@CF (mass fraction of 20%) and add it to a mixed solution of 8 g acrylic resin (PUA:EA mass ratio of 1:1, containing 0.5% photoinitiator 1173) and solvent. Disperse the mixture for 30 min by ultrasonic power 300W, vibration frequency 35Hz, amplitude 0.5mm and mechanical stirring (1000 rpm) to obtain the mixed slurry.

[0046] 3. Synergistic film formation: The slurry is quickly transferred to a specific mold with a release film. The mold is then transferred to a multi-field synergistic platform. First, ultrasound (35 kHz, 100 W) and vibration (50 Hz, 1 mm amplitude) are turned on for 5 min. Then, a low magnetic field of 150 mT is applied and synergistically acted for 20 min to orient the carbon fibers along the direction of the magnetic field.

[0047] 4. Gradient temperature curing: Under magnetic field conditions, the film is first pre-cured in a vacuum oven at 45℃ for 2 hours, and then cured at 80℃ for 8 hours. The release film is then peeled off after cooling to obtain a magnetic functional film.

[0048] from Figure 1 The scanning electron microscope shows that the carbon fibers are arranged regularly and parallel to the direction of the applied magnetic field.

[0049] Example 2 (Fe3O4@CF mass fraction 40 wt%)

[0050] The difference from Example 1 is that the amount of Fe3O4@CF added was adjusted to 4 g (40% by mass), and the amount of acrylic resin added was 6 g, while other conditions remained the same as in Example 1, resulting in a magnetic functional film. Figure 2 The scanning electron microscope shows that the carbon fibers are arranged regularly and parallel to the direction of the applied magnetic field.

[0051] Example 3 (Fe3O4@CF mass fraction 60 wt%)

[0052] The difference from Example 1 is that the amount of Fe3O4@CF added was adjusted to 6 g (60% by mass), the amount of acrylic resin added was 4 g, and other conditions were the same as in Example 1, thus obtaining a magnetic functional film.

[0053] Comparative Example 1 (Orientation without magnetic field)

[0054] The difference from Example 1 is that no magnetic field-induced orientation step is applied, while other conditions are the same as in Example 1, to obtain a magnetic functional thin film.

[0055] Comparative Example 2 (non-magnetic coating)

[0056] The difference from Example 1 is that uncoated carbon fibers were used, and the other conditions were the same as in Example 1 to obtain a magnetic functional film.

[0057] Comparative Example 3 (without ultrasonic vibration assistance)

[0058] The difference from Example 1 is that only mechanical stirring (300 rpm, 30 min) was performed, without ultrasonic and vibration assistance, and other conditions were the same as in Example 1, to obtain a magnetic functional thin film.

[0059] Test Results

[0060] Table 1. Performance test results of magnetic functional thin films prepared in Examples 1-3 and Comparative Examples 1-3

[0061]

[0062] As can be seen from Table 1:

[0063] (1) In Examples 1-3, as the carbon fiber content increased from 20% to 60%, the vertical thermal conductivity increased from 18.5 W·m. -1· ·K -1· Increased to 35.2 W·m -1· ·K -1· This indicates that the increased carbon fiber content helps to form a denser heat-conducting network.

[0064] (2) The thermal conductivity of Comparative Example 1 (without magnetic field orientation) is only 6.2 W·m. -1· ·K -1 This is significantly lower than the 18.5 W·m⁻¹ in Example 1. -1· ·K -1 This demonstrates that magnetic field-induced orientation is crucial for improving vertical thermal conductivity.

[0065] (3) The thermal conductivity of Comparative Example 2 (non-magnetic coating) is 8.5 W·m. -1· ·K -1 The value was slightly higher than that of Comparative Example 1 but still much lower than that of Example 1, indicating that the orientation effect of uncoated carbon fibers in a 0.5 T magnetic field was limited, and magnetic coating significantly enhanced the magnetic field response capability of carbon fibers.

[0066] (4) The thermal conductivity of Comparative Example 3 (without ultrasonic vibration assistance) is 10.1 W·m. -1· ·K -1 Furthermore, the resistance change rate was as high as 12.3%, indicating that ultrasonic vibration assistance plays an important role in improving the dispersion of carbon fibers and reducing agglomeration defects.

[0067] In summary, this invention imparts a strong magnetic response to carbon fibers by coating them with iron oxide (Fe3O4), achieving efficient directional alignment even under low magnetic field strength. Combined with ultrasonic-vibration synergistic dispersion technology, a magnetic functional film exhibiting high thermal conductivity, high flexibility, and ultrathinness was successfully prepared. When the carbon fiber content is 60%, the vertical thermal conductivity reaches 35.2 W·m. -1· ·K -1 With a film thickness of approximately 100 μm, it has broad application prospects in the field of heat dissipation for electronic devices.

[0068] Examples 1-3 all use the carbon fiber and polymer matrix and other components specific to this invention to prepare thin films. Through special formulation design, the carbon fiber in the prepared thin film has directional orientation and can maintain excellent thermal conductivity.

[0069] 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 magnetic functional thin film, characterized in that, The magnetic functional film comprises an acrylate polymer matrix and iron oxide-coated carbon fibers dispersed in the acrylate polymer matrix; The iron oxide-coated carbon fibers are oriented along the thickness direction of the magnetic functional film.

2. The magnetic functional thin film according to claim 1, characterized in that, By mass fraction, the magnetic functional film comprises 10% to 60% iron oxide-coated carbon fiber and 40% to 90% acrylate polymer matrix.

3. The magnetic functional thin film according to claim 1 or 2, characterized in that, The carbon fiber is selected from at least one of mesophase pitch-based carbon fiber and polyacrylonitrile-based carbon fiber; And / or, the carbon fiber has a diameter of 5 μm to 20 μm, a length of 50 μm to 500 μm, and an aspect ratio of 5:1 to 100:1; And / or, in the iron oxide-coated carbon fibers, the thickness of the iron oxide coating layer is 20–200 nm, and the loading of iron oxide is 12–28 wt%; And / or, the acrylate polymer matrix is ​​a blend of polyurethane acrylate and epoxy acrylate.

4. The magnetic functional thin film according to claim 1, characterized in that, The coating method for the iron oxide-coated carbon fiber is selected from at least one of the following: chemical coprecipitation, solvothermal method, and in-situ polymerization method.

5. A method for preparing a magnetic functional thin film according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Preparation of Fe3O4-coated carbon fiber: After surface oxidation treatment, iron salt is added to the carbon fiber, stirred, reacted under an inert atmosphere, ultrasonically dispersed, filtered, washed with water until neutral, and dried to obtain Fe3O4-coated carbon fiber material. (2) Preparation of magnetic functional slurry: The iron oxide coated carbon fiber material prepared in step (1) is added to a mixed solution of acrylate polymer matrix and solvent, and dispersed under ultrasonic and vibration assistance to obtain magnetic functional slurry; (3) Synergistic film formation: turn on ultrasound and low-frequency vibration; then apply a magnetic field to make the iron oxide-coated carbon fiber material oriented along the direction of the magnetic field; (4) Curing: The wet film is cured at a gradient temperature to obtain a magnetic functional film.

6. The preparation method according to claim 5, characterized in that, The carbon fiber surface oxidation treatment process described in step (1) is as follows: treatment with a mixed acid of HNO3 and H2SO4; And / or, the iron salts described in step (1) include ferric chloride and / or ferric chloride; And / or, the power of the ultrasound assistance in step (2) is 80 W to 300 W and the frequency is 20 kHz to 40 kHz; And / or, the vibration assistance in step (2) has a frequency of 10 kHz to 50 Hz and an amplitude of 0.5 mm to 3 mm; And / or, the power of the ultrasound in step (3) is 80 W to 300 W and the frequency is 20 kHz to 40 kHz; And / or, the frequency of the low-frequency vibration in step (3) is 10 Hz to 50 Hz and the amplitude is 0.5 mm to 3 mm; And / or, the conditions of the magnetic field in step (2) include: 100 mT to 500 mT; And / or, the gradient temperature curing conditions in step (4) include: pre-curing at 40℃~50℃ for 1h~4h, and then curing at 70℃~90℃ for 8h~12h.

7. The preparation method according to claim 6, characterized in that, In step (1), the volume ratio of HNO3 to H2SO4 in the carbon fiber surface oxidation treatment is 1:2 to 5; And / or, the iron salts mentioned in step (1) include FeCl2 and FeCl3 in a molar ratio of 1:2; And / or, the reaction conditions under an inert atmosphere in step (1) include: under N2, reaction at 55℃~65℃ for 30 min~60 min; And / or, the timing of the multi-field coordination in step (3) is as follows: first turn on the ultrasound and vibration, then apply the magnetic field and keep the three coordinated until the leveling is completed, and the bottom surface of the container is perpendicular to the direction of magnetic induction intensity.

8. A thermal interface material, characterized in that, This includes the magnetic functional thin film according to any one of claims 1 to 4 and the magnetic functional thin film prepared by the preparation method according to any one of claims 6 or 7.

9. An electronic device, characterized in that, Includes the thermal interface material as described in claim 8.

10. The electronic device according to claim 9, characterized in that, The electronic device includes at least one of flexible magnetic sensing, electromagnetic shielding, flexible heat dissipation, and magnetically driven micro-actuators.

Images