A thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler, the composite filler and its application.

Abstract

The application discloses a heat-conducting epoxy resin film containing embedded Fe3O4 / BN composite fillers, the composite fillers and application, and belongs to the field of high polymer composite materials and thermal management technology.The method can uniformly embed Fe3O4 nanoparticles in the interior and edge of boron nitride while forming the boron nitride through a controllable oxidation method of high-temperature pyrolysis of an iron-containing precursor; the fillers are dispersed in a polymer matrix, under the action of an applied magnetic field, the BN fillers are induced to be oriented and arranged by using the magnetic response of Fe3O4, and finally a polymer composite material with high thermal conductivity is obtained.The application overcomes the defects of uncontrollable orientation of fillers and poor repeatability of thermal conductivity in the traditional method.The obtained heat-conducting epoxy resin film has wide application prospects in the fields of electronic packaging, thermal interface materials and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials and thermal management technology, specifically relating to a thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler, the composite filler and its application. In particular, by constructing an embedded boron nitride sheet structure of iron tetroxide and combining it with magnetic field-induced orientation, a significant improvement in thermal conductivity is achieved. Background Technology

[0002] As electronic devices evolve towards higher integration and higher power density, heat dissipation has become a key factor restricting their performance and reliability. Polymer materials, due to their lightweight, ease of processing, electrical insulation, and corrosion resistance, are widely used in electronic packaging and thermal management. However, most polymers have extremely low intrinsic thermal conductivity (around 0.2 W / (m·K), making it difficult to meet the requirements for efficient heat dissipation. Therefore, adding high thermal conductivity fillers (such as boron nitride (BN), aluminum nitride (AlN), and graphene) to the polymer matrix is ​​a common method to improve the thermal conductivity of polymers. Boron nitride (BN) is favored due to its high thermal conductivity and good electrical insulation. However, simple blending alone is insufficient to form an effective thermally conductive network with low filler content. Studies have shown that inducing anisotropic fillers to oriented in a specific direction through an external force field can significantly improve their thermal conductivity. To improve the thermal conductivity of polymers in the vertical direction, magnetic field induction technology has attracted widespread attention due to its non-contact nature and lack of impact on the intrinsic structure of the matrix. Patent CN119331381A discloses a method for preparing and applying a vertically oriented boron nitride / epoxy resin thermally conductive composite material under a magnetic field. This method induces boron nitride to exfoliate and physically bond with iron(III) oxide (Fe3O4), resulting in a boron nitride nanosheet solution with Fe3O4 adhering to its surface. However, since the Fe3O4 only adheres to the surface of the boron nitride and does not exist within the boron nitride itself, the material's vertical orientation ability within the resin is limited under magnetic field induction, and the stability of the Fe3O4 in use is also insufficient. Patent CN121427313A discloses a flexible thermally conductive composite material with chain-like boron nitride and its preparation method, which can control the orientation of the material by further increasing the magnetic field strength. This method achieves the chain-like vertical alignment of the boron nitride sheets by extending the magnetic field treatment time and optimizes the balance between magnetic responsiveness and thermal conductivity by controlling the Fe3O4 modification amount. However, this method is limited by the sacrifice of the thermal conductivity of the boron nitride itself due to the Fe3O4 surface modification. Meanwhile, because Fe3O4 has a much lower thermal conductivity than BN, excessive loading will occupy the BN surface, forming interfacial thermal resistance and reducing the intrinsic thermal conductivity potential of the composite material. On the other hand, insufficient loading will lead to insufficient magnetic responsiveness, making orientation difficult in a magnetic field. Therefore, how to balance magnetic responsiveness and thermal conductivity to achieve precise and quantitative control of filler orientation and final thermal conductivity remains an unsolved problem in current technology. Summary of the Invention

[0003] This invention addresses the common technical deficiency in current boron nitride epoxy resin-based polymer thermally conductive composite materials, where the vertical thermal conductivity (out-of-plane thermal conductivity) is significantly lower than the in-plane thermal conductivity. It provides a thermally conductive epoxy resin film containing an embedded Fe3O4 / BN composite filler, the composite filler, and its applications. This thermally conductive epoxy resin film material possesses excellent out-of-plane thermal conductivity, good mechanical properties, and stable dielectric characteristics.

[0004] The first aspect of the present invention discloses a thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler, wherein the thermally conductive epoxy resin film is prepared by mixing embedded Fe3O4 / BN composite filler, epoxy resin, curing agent and diluent in a mass ratio of 1~4:9~11:2~3:1~2.

[0005] The embedded Fe3O4 / BN composite filler is prepared by high-temperature pyrolysis of an iron-containing precursor to generate Fe / Fe3C / BN, followed by oxidation treatment. The iron-containing precursor is prepared by iron source, boron source, and nitrogen source. The high-temperature pyrolysis is carried out under an inert atmosphere, which reduces the iron species into nano-Fe / Fe3C particles and embeds them into BN sheets. The oxidation treatment is carried out under an air atmosphere, which converts Fe / Fe3C into Fe3O4 in situ, thus obtaining the embedded Fe3O4 / BN composite filler.

[0006] In a preferred embodiment, in the iron-containing precursor, the mass ratio of iron source to boron source is 1:1 to 1:15; with melamine as the nitrogen source and boric acid as the boron source, the mass ratio of nitrogen source to boron source is 1:3 to 3.5 (the molar amount of boron atoms is slightly greater than the molar amount of nitrogen atoms).

[0007] In existing technologies, when preparing boron nitride alone, with melamine as the nitrogen source and boric acid as the boron source, the preferred mass ratio of nitrogen source to boron source is approximately 1:2.2 (the molar amount of boron atoms is less than the molar amount of nitrogen atoms). This invention discovers that when the molar amount of boron atoms is slightly greater than the molar amount of nitrogen atoms, the Fe / Fe3C phase can be more stably embedded in the less defective BN sheet structure during high-temperature pyrolysis.

[0008] In a preferred embodiment, the high-temperature pyrolysis step is as follows: a stepped temperature increase is performed from 20~30℃ to 350~450℃ to 750~850℃ to 1050~1150℃ and back to 20~30℃. In the 20~30℃-350~450℃ stage, the temperature is increased at a rate of 1.5~2.5℃; in the 350~450℃-750~850℃ stage, the temperature is increased at a rate of 2.5~3.5℃, until the temperature reaches 750~30℃. After reaching 850℃, maintain for 1.5-2.5h; in the 750~850℃-1050~1150℃ stage, increase the temperature at a rate of 4~6℃, and maintain for 2.5-3.5h after reaching 1050~1150℃; the oxidation treatment steps are as follows: heat Fe / Fe3C / BN to 450~550℃, hold for 1~2 hours, cool naturally to room temperature, and use a magnet to adsorb and wash to obtain embedded Fe3O4 / BN composite filler.

[0009] The temperature and time of the oxidation process need to be controlled. If the oxidation temperature is too high or the time is too long, over-oxidation will occur, and some of the Fe3O4 will be converted into ferric oxide. The non-magnetic ferric oxide reduces the magnetic field-induced orientation effect. If the oxidation temperature is too low or the time is too short, the Fe / Fe3C oxidation will be incomplete, leaving a residual metallic phase. The residual metallic phase is less stable than Fe3O4. Fe / Fe3C catalyzes the local curing of epoxy resin or undergoes side reactions with the curing agent, resulting in a decrease in the mechanical properties of the membrane material. At the same time, the bonding force between the residual Fe / Fe3C and the interior and edges of the BN sheets is lower than that between Fe3O4 and the interior and edges of the BN sheets.

[0010] Furthermore, the iron source is a ferric salt, which is at least one of ferric chloride hexahydrate, ferric nitrate nonahydrate, and ferric triacetylacetone.

[0011] In a preferred embodiment, the preparation process of the iron-containing precursor is as follows: at room temperature, trivalent iron source and boric acid are dissolved in deionized water at a mass ratio of 1:1 to 1:15, heated to 60-70°C, and the pH of the solution is adjusted to 5-5.5. The solution is then mixed to obtain a pale yellow transparent solution. Melamine is dissolved in water and heated to 85-95°C. The hot melamine solution is slowly added dropwise to the above iron-containing boric acid mixture while stirring. During the addition process, iron-containing boron nitride precursor precipitates gradually appear. Stirring is continued for 2-3 hours, and the mixture is allowed to stand at room temperature for 8-15 hours. After washing and drying, a pale yellow precursor powder is obtained.

[0012] Specifically, the preparation method of the embedded Fe3O4 / BN composite filler includes the following steps:

[0013] Step 1: Preparation of iron-containing boron nitride precursor: At room temperature, dissolve trivalent iron source and boric acid in 150 mL of deionized water at a mass ratio of 1:1 to 1:15. Heat the solution in an oil bath to 60–70 °C (this temperature causes partial dehydration and condensation of boric acid to form BOB chains, promoting the formation of Fe). 3+ (Pre-coordination with boric acid) Add an alkaline pH adjuster to adjust the pH of the solution to 5-5.5 (to prevent premature Fe reaction and precipitation), and sonicate in a 540-600W ultrasonic machine for 0.5-1 hour to obtain a pale yellow transparent solution. Dissolve a certain amount of melamine in 100-150 ml of water, heat an oil bath to 90°C for polycondensation, and slowly add the hot melamine solution dropwise to the above iron-containing boric acid mixture while stirring vigorously. During the addition process, the solution gradually precipitates iron-containing boron nitride precursor. Continue stirring for 2-3 hours, and let it stand at room temperature for 12 hours. Wash three times with deionized water, then wash twice with anhydrous ethanol, and vacuum dry at 60°C for 12 hours to obtain a pale yellow precursor powder.

[0014] Step 2, Preparation of Fe / Fe3C / BN composite filler: The dried precursor powder was placed into an alumina boat, leveled, and then pushed into the center of the quartz tube of a tube furnace. The temperature was increased in stages: 25℃-400℃-800℃-1100℃-25℃, with nitrogen protection applied simultaneously. After the tube furnace cooled naturally to room temperature, the atmosphere was turned off, and the product was removed, yielding a grayish-black Fe / Fe3C / BN powder. This powder was gently ground in an agate mortar and pestle and passed through a 200-mesh sieve.

[0015] Step 3: Preparation of Fe3O4 / BN filler by in-situ conversion: Fe / Fe3C / BN powder is evenly spread in a ceramic boat and placed in a muffle furnace. The temperature is raised to 500℃ according to the above procedure, held for 2 hours, and then naturally cooled to room temperature. The filler is then adsorbed using a magnet and washed 3 to 5 times with ethanol and water respectively. The black Fe3O4 / BN filler is then removed.

[0016] Furthermore, in step 1, the ferric salt is one of ferric chloride hexahydrate, ferric nitrate nonahydrate, or ferric triacetylacetone; the alkaline pH adjuster is one of sodium hydroxide solution, ammonia, or sodium bicarbonate solution.

[0017] In step 1, the mixed precursor suspension is left to stand and age at room temperature for 12 hours in order to make the iron ions evenly distributed as the melamine-boric acid-iron complex grows in an orderly manner, which is beneficial to the formation of embedded fine and dispersed Fe / Fe3C nanoparticles in the BN sheets after pyrolysis.

[0018] Washing with anhydrous ethanol can reduce the surface tension of the precursor, reduce agglomeration during the drying process, and make the precursor powder more loose, which is beneficial for the escape of gaseous products and the uniform transfer of heat during subsequent pyrolysis.

[0019] The stepped heating in step 2 is because the reaction mainly consists of three stages. The first stage (25℃→400℃): In this stage, the temperature is slowly increased to 400℃ at a rate of 2℃ / min. The purpose is to slowly remove the water of crystallization and structural water from the precursor and to initially decompose the organic matter. The melamine-boric acid-iron complex contains a large number of hydrogen-bonded water molecules and hydroxyl groups. If the temperature is increased too quickly, the rapid escape of water vapor will cause powder splashing, resulting in material loss and contamination of the tubular furnace. By slowly heating to 400℃, the early decomposition rate of the organic matter is slowed down, preventing uneven distribution of iron ions during the decomposition process. The second stage (400℃→800℃): In this stage, the temperature is increased to 800℃ at a rate of 3℃ / min and held for 2 hours. The purpose is to gradually and completely carbonize and nitride the precursor. Melamine further decomposes into carbon and nitrogen compounds, and boric acid is converted into boron oxide. The two undergo a condensation reaction to form BN bonds, forming an amorphous BN framework. At the same time, Fe3C begins to nucleate. The holding temperature of 800℃ ensures that Fe3C slowly grows into fine particles (Fe3C is mainly formed in this stage) and is evenly distributed in the amorphous BN framework. The third stage (800℃→1100℃): In this stage, the temperature is increased to 1100℃ at a rate of 5℃ / min. The purpose is to promote the crystallization and grain growth of BN, while completely reducing iron species to Fe / Fe3C, forming a BN lamellar structure. Fe / Fe3C is embedded in the BN lamellars and edges in the form of nanoparticles.

[0020] In existing technologies (e.g., Sun Changhong, Zhang Wangxi, Liang Baoyan, et al. Synthesis and characterization of hexagonal boron nitride [J]. Inorganic Salt Industry, 2019, 51(03):45-48.), h-BN is prepared by calcination at 1000℃ for 2 h and 1400℃ for 2 h, which differs significantly from the present invention. For example, the present invention cannot calcine at 1400℃, as Fe3C decomposes at this temperature to obtain elemental iron and free carbon. At this temperature, Fe competes with N for the opportunity to combine with B, resulting in a reduction in the layered structure and structural defects of BN, greatly reducing the mass of BN in the system, which is detrimental to subsequent oxidation steps and unfavorable for interfacial bonding and magnetic field-induced orientation in the preparation of composite materials.

[0021] The preparation of the thermally conductive epoxy resin film includes the following steps: First, a release agent is sprayed onto the mold 2-3 times. Then, the obtained embedded Fe3O4 / BN composite filler, epoxy resin, curing agent, and diluent are mixed in a mass ratio of 1-4:9-11:2-3:1-2 and placed in the mold. The mixture is heated and stirred on a hot plate at 40-50℃ for 10-20 minutes. Subsequently, the mold is placed in a prepared magnetic field with a magnetic field strength controlled at 20-30 mT. Under the action of the magnetic field, the mixture is cured at 40℃-100℃ for 8-10 hours to obtain a thermally conductive epoxy resin film with a thickness of 0.8-1 mm.

[0022] In a preferred embodiment, the release agent includes at least one of silicone oil, wax, and fluorinated release agent; the mold material is at least one of silicone and tetrafluoroethylene; the curing agent is at least one of amines and acid anhydrides; and the diluent is at least one of ethyl acetate, dibutyl phthalate, and phenyl glycidyl ether.

[0023] The second aspect of this invention discloses an embedded Fe3O4 / BN composite filler, wherein the composite filler is formed by high-temperature pyrolysis of an iron-containing precursor to generate Fe / Fe3C / BN, followed by oxidation treatment to form an embedded Fe3O4 / BN composite structure; the iron-containing precursor is prepared by an iron source, a boron source, and a nitrogen source; the high-temperature pyrolysis is carried out under an inert atmosphere, reducing iron species to nano-Fe / Fe3C particles and embedding them into BN sheets; the oxidation treatment is carried out under an air atmosphere, converting Fe / Fe3C in situ into Fe3O4, thereby obtaining the embedded Fe3O4 / BN composite filler.

[0024] In a preferred embodiment, in the iron-containing precursor, the mass ratio of iron source to boron source is 1:1 to 1:15; the mass ratio of nitrogen source to boron source is 1:3 to 3.5; the high-temperature pyrolysis step is: a stepped temperature increase of 20~30℃-350~450℃-750~850℃-1050~1150℃-20~30℃; the oxidation treatment step is: heating Fe / Fe3C / BN to 450~550℃, holding at that temperature for 1~2 hours, naturally cooling to room temperature, adsorbing and washing with a magnet to obtain the embedded Fe3O4 / BN composite filler.

[0025] A third aspect of this invention is to provide the application of the aforementioned thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler, or the aforementioned embedded Fe3O4 / BN composite filler, in the electronic packaging of wearable electronic devices and pressure sensors, wherein the thermally conductive epoxy resin film is attached to the surface of the wearable electronic device or pressure sensor. Besides wearable electronic devices and pressure sensors, it can also be used in the electronic packaging of other electronic devices. The thermally conductive epoxy resin film has broad application prospects in the fields of electronic packaging and thermal interface materials.

[0026] This invention involves preparing a precursor solution by co-forming an iron source with a boron source and a nitrogen source. This solution is then subjected to high-temperature pyrolysis, which generates boron nitride sheets while simultaneously reducing iron species into nano-sized Fe / Fe3C particles that are embedded within the matrix. Further oxidation converts the Fe / Fe3C particles in situ into Fe3O4, forming a Fe3O4 embedded pinned structure. Utilizing the magnetic responsiveness of Fe3O4, an external magnetic field induces the composite filler to align vertically within the polymer, constructing a thermally conductive network that penetrates the entire thickness, thereby significantly improving the out-of-plane thermal conductivity of the material.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. Iron ions enter the supramolecular network of melamine and boric acid through coordination, achieving atomic-level uniform embedding rather than simple physical adsorption. Since iron ions achieve atomic-level dispersion in the precursor stage, and since Fe / Fe3C nanoparticles are already embedded inside or at the edges of BN sheets during pyrolysis, Fe3O4 retains its embedding position after oxidation. The resulting Fe3O4 nanoparticles exhibit a highly uniform distribution within the BN sheets, avoiding the particle agglomeration, local enrichment, or uneven distribution problems common in traditional mechanical mixing or impregnation methods. This results in a stronger interface between Fe3O4 and BN, significantly improving the structural stability of the composite material.

[0029] 2. Improved stability and durability of magnetic components: The embedded structure partially or semi-embeds Fe3O4 particles in BN sheets, protecting them from harsh environments such as acidic, alkaline, or high-temperature conditions, significantly enhancing corrosion and oxidation resistance. Furthermore, Fe3O4 particles are less prone to detachment during mechanical stirring, ultrasonic dispersion, or repeated magnetic separation, ensuring the material's performance stability during multiple cycles of use.

[0030] 3. Significantly improved vertical thermal conductivity of epoxy resin composites. Under the induction of an external magnetic field, the embedded Fe3O4 / BN composite filler is highly oriented vertically within the epoxy resin (its orientation capability is superior to that of surface-attached boron nitride with iron oxide), constructing a continuous thermally conductive network that runs through the thickness of the material. This provides a rapid channel for phonon transport, enabling the composite material to achieve a vertical thermal conductivity exceeding that of similar materials with traditional random dispersion or in-plane orientation, as well as epoxy resin composites containing surface-attached boron nitride with iron oxide. This effectively meets the urgent need for efficient heat dissipation through the surface in high-power electronic devices. This stable embedded structure also prevents Fe3O4 from agglomerating on both sides of the thermally conductive epoxy resin film under a magnetic field, further improving the overall thermal conductivity.

[0031] 4. Synergistic optimization of thermal conductivity, mechanical properties, and dielectric properties is achieved. The embedded Fe3O4 / BN composite filler improves thermal conductivity while enhancing the bonding ability between Fe3O4 and BN, balancing the interfacial compatibility and bonding ability between the composite filler and epoxy resin, and simultaneously improving the modulus and strength of the composite material in the vertical direction. The Fe3O4 loading design avoids the deterioration of dielectric properties caused by the introduction of excessive magnetic filler, and the composite material still maintains excellent electrical insulation properties and low dielectric loss. Its outstanding comprehensive performance makes it suitable for electronic packaging fields with high requirements for reliability and safety.

[0032] 5. This invention provides a scalable preparation route for high-performance thermal interface materials. The process route of this invention is simple and efficient, the raw materials are readily available, and the magnetic field orientation step is highly compatible with existing composite material molding processes, making it easy to transform from laboratory to industrial production. It has broad application prospects in thermal management fields such as 5G communication, power devices, and aerospace. Attached Figure Description

[0033] Figure 1 The images shown are SEM images of the products in Example 3 of the present invention. (a) is an SEM image of the embedded Fe3O4 / BN composite filler in Example 3, and (b) is a cross-sectional view of Fe3O4 / BN / EP (i.e., a thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler) in Example 3.

[0034] Figure 2 The following are EDS energy spectrum diagrams of the thermally conductive epoxy resin film material in Example 3: a is the EDS energy spectrum diagram of the embedded Fe3O4 / BN composite filler in Example 3, and b is the EDS energy spectrum diagram of Fe3O4 / BN / EP in Example 3.

[0035] Figure 3 The X-ray diffraction patterns of the embedded Fe3O4 / BN composite fillers in Examples 1-5 of this invention are shown. The horizontal axis represents the diffraction angle, and the vertical axis represents the intensity. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0037] Example 1

[0038] Step 1: Preparation of the iron-containing boron nitride precursor: At room temperature, ferric salt (ferric chloride hexahydrate), boric acid, and deionized water were mixed and stirred until completely dissolved at a mass ratio of 1:15:300. The mixture was heated to 65°C in an oil bath, and dilute ammonia was added dropwise to adjust the pH of the solution to 5.5. The solution was then sonicated for 0.5 hours using a 600W ultrasonic machine to obtain a pale yellow transparent solution. Melamine (the mass ratio of melamine to boric acid added in the previous step was 1:3.3) was dissolved in 120 ml of water. The oil bath was heated to 90°C, and the hot melamine solution was slowly added dropwise to the above boric acid-iron mixture while stirring vigorously. During the addition process, the iron-containing boron nitride precursor gradually precipitated in the solution. Stirring was continued for 2 hours, and the mixture was allowed to stand at room temperature for 12 hours. The solution was washed three times with deionized water and then twice with anhydrous ethanol. It was then vacuum dried at 60°C for 12 hours to obtain a pale yellow precursor powder.

[0039] Step 2, Preparation of Fe / Fe3C / BN Composite Filler: The dried precursor powder was placed into an alumina boat, leveled, and then pushed into the center of the quartz tube of a tubular furnace. The temperature was increased in stages: 25℃-400℃-800℃-1100℃-25℃ (First stage (25℃→400℃): Slowly increased to 400℃ at 2℃ / min; Second stage (400℃→800℃): Increased to 800℃ at 3℃ / min and held for 2 hours; Third stage (800℃→1100℃): Increased to 1100℃ at 5℃ / min and held for 3 hours), while simultaneously applying nitrogen protection. After the tubular furnace cooled naturally to room temperature, the atmosphere was turned off, and the product was removed, yielding a grayish-black Fe / Fe3C / BN powder. This powder was gently ground in an agate mortar and pestle and passed through a 200-mesh sieve.

[0040] Step 3: Preparation of in-situ conversion Fe3O4 / BN (i.e., embedded Fe3O4 / BN) composite filler: Fe / Fe3C / BN powder was evenly spread in a ceramic boat and placed in a muffle furnace. The temperature was increased to 500℃ at 2℃ / min and held for 2 hours. After natural cooling to room temperature, the filler was adsorbed using a magnet and washed three times with anhydrous ethanol and water, respectively. The black Fe3O4 / BN filler was then removed (named 5%Fe3O4 / BN, where 5% is the percentage of Fe3O4).

[0041] Step 4, Preparation of thermally conductive epoxy resin film: First, spray the release agent twice on the silicone mold. Then, mix the embedded Fe3O4 / BN composite filler obtained in Step 3, epoxy resin, T-31 phenolic amine epoxy curing agent, and diluent (dibutyl phthalate) in a mass ratio of 3:10:2.5:1.5 (composite filler content is 17.6wt%). Heat the beaker on a hot plate at 45℃ and stir for 15 minutes. Then, place the mold in the prepared magnetic field with a magnetic field strength of 30mT. Under the action of the magnetic field, change the oven temperature stepwise and maintain it at 40℃ for 1 hour, 60℃ for 1 hour, 80℃ for 1 hour, and 100℃ for 2 hours to obtain a thermally conductive epoxy resin film material with a thickness of 0.8-1mm.

[0042] Example 2: The difference between this example and Example 1 is that the trivalent iron salt, melamine and boric acid mentioned in step two are mixed in a mass ratio of 1:2.16:7.12 to prepare a 10% Fe3O4 / BN loaded filler (named 10%Fe3O4 / BN), and then a corresponding thermally conductive epoxy resin film is obtained.

[0043] Example 3: The difference between this example and Example 1 is that the trivalent iron salt, melamine and boric acid mentioned in step two are prepared in a mass ratio of 1:0.72:2.37 to obtain a 25% Fe3O4 / BN loaded filler (named 25%Fe3O4 / BN), and then a corresponding thermally conductive epoxy resin film is obtained.

[0044] Example 4: The difference between this example and Example 1 is that the trivalent iron salt, melamine and boric acid mentioned in step 2 are prepared in a mass ratio of 1:0.49:1.61 to obtain a 33% Fe3O4 / BN filler (named 33%Fe3O4 / BN), and then a corresponding thermally conductive epoxy resin film is obtained.

[0045] Example 5: The difference between this example and Example 1 is that the trivalent iron salt, melamine and boric acid mentioned in step two are prepared in a mass ratio of 1:0.36:1.19 to obtain a 40% Fe3O4 / BN loaded filler (named 40%Fe3O4 / BN), and then a corresponding thermally conductive epoxy resin film is obtained.

[0046] Elemental analysis of the Fe3O4 / BN prepared in Examples 1-5 was performed using inductively coupled plasma atomic emission spectrometry (ICP-AES), and the amount of Fe3O4 precipitate was calculated. The results are shown in Table 1.

[0047] Table 1. ICP test results of the packing materials prepared in Examples 1-5

[0048]

[0049] The surface structure of the material obtained in Example 3 was observed using a scanning electron microscope; Figure 1 The images shown are SEM images of the products in Example 3 of this invention. (a) is an SEM image of the embedded Fe3O4 / BN composite filler in Example 3, and (b) is a cross-sectional view of the Fe3O4 / BN / EP (i.e., the thermally conductive epoxy resin film containing the embedded Fe3O4 / BN composite filler) in Example 3. Figure 1 As can be seen in (a), the prepared composite filler has uniformly precipitated nano-sized Fe3O4 particles inside and on its surface; according to Figure 1 As can be seen from (b), under the induction of the magnetic field, the Fe3O4 / BN inside the thermally conductive epoxy resin composite material is oriented in a uniform manner, forming a denser and more continuous thermally conductive network.

[0050] Figure 2 The following are the EDS energy spectrum diagrams of the thermally conductive epoxy resin film material in Example 3: (a) is the EDS energy spectrum diagram of the embedded Fe3O4 / BN composite filler in Example 3, and (b) is the EDS energy spectrum diagram of Fe3O4 / BN / EP in Example 3. Figure 2 (b) in the paper demonstrates that under the action of a magnetic field, the composite filler has a good magnetic field effect and forms a heat conduction path.

[0051] X-ray diffraction test: The Fe3O4 embedded BN composite particles (i.e. embedded Fe3O4 / BN composite filler) obtained in Examples 1-5 were tested using an X-ray spectrometer. Figure 3The X-ray diffraction patterns of the embedded Fe3O4 / BN composite fillers in Examples 1-5 of this invention show that standard BN and Fe3O4 peaks are present in fillers with different Fe3O4 loadings, proving that there are no residual impurities inside the samples and that the sample components are pure.

[0052] Thermal conductivity test: The vertical thermal conductivity of Fe3O4 / BN / EP obtained in Examples 1-5 was tested using a laser flare thermal conductivity meter, as shown in the figure.

[0053] Example 6: Effect of changes in filler content on thermally conductive epoxy resin films

[0054] The difference between this embodiment and Example 3 is the change in filler content; in step 3, the embedded Fe3O4 / BN composite filler, epoxy resin, curing agent, and diluent are mixed in mass ratios of 1:10:2.5:1.5 and 4:10:2.5:1.5, respectively; 10% Fe3O4 / BN / EP materials with filler contents of 6.7wt% and 22.2wt% are prepared respectively, and are named Example 6 6.7wt% and Example 6 22.2wt%, respectively.

[0055] Example 7: Effect of Magnetic Field Strength Change on Thermally Conductive Epoxy Resin Film

[0056] For the scheme of Example 3, the magnetic field strength is changed to 20mT, while the rest remain unchanged. The resulting thermally conductive epoxy resin film is named Example 3 Modified 20mT.

[0057] For the 22.2wt% scheme in Example 6, the magnetic field strength was changed to 20mT, while the rest remained unchanged. The resulting thermally conductive epoxy resin film was named Example 6 22.2wt% modified 20mT.

[0058] Comparative Example 1 (Pure Epoxy Resin): Preparation of Pure Epoxy Resin Film: First, a release agent was sprayed twice onto a silicone mold. Then, epoxy resin, curing agent, and diluent were mixed in a mass ratio of 10:2.5:1.5. The beaker was placed on a hot plate at 45°C and heated and stirred for 15 minutes. The temperature was maintained at 40°C for 1 hour, 60°C for 1 hour, 80°C for 1 hour, and 100°C for 2 hours to obtain a thermally conductive epoxy resin film material with a thickness of 0.8–1 mm.

[0059] Comparative Example 2 (Direct Blending): Step 1, Preparation of Boron Nitride Precursor: At room temperature, boric acid was dissolved in 150 mL of deionized water and stirred until completely dissolved. The mixture was then heated to 65°C in an oil bath. A certain amount of melamine was dissolved in 150 mL of water, and the oil bath was heated to 90°C. The hot melamine solution was slowly added dropwise to the above boric acid mixture; the mass ratio of melamine to boric acid was 1:3.3. Stirring was continued for 2 hours, followed by aging at room temperature for 12 hours. The mixture was washed three times with deionized water, then twice with anhydrous ethanol, and finally vacuum dried at 60°C for 12 hours to obtain the precursor powder.

[0060] Step 2, Preparation of BN by High-Temperature Pyrolysis: The dried precursor powder is placed into an alumina boat, leveled, and then pushed into the center of the quartz tube of a tube furnace. The temperature is increased in stages: 25℃-400℃-800℃-1100℃-25℃, while nitrogen protection is applied. After the tube furnace cools naturally to room temperature, the atmosphere is turned off, and the product is removed to obtain BN powder.

[0061] Step 3: Add 9g of boron nitride and 1g of iron oxide to 1L of isopropanol and sonicate for 20min to obtain a mixed solution of boron nitride and iron oxide; the Fe3O4 particles are in the nanoscale; use a high-pressure homogenizer to circulate and wash the mixed solution of boron nitride and iron oxide 20 times. Through various fluid dynamics such as shearing, turbulence and collision caused by liquid phase washing, boron nitride is induced to peel off and physically bond with iron oxide to obtain a solution of boron nitride nanosheets with iron oxide attached to the surface. Vacuum filter and wash to obtain boron nitride nanosheets with iron oxide attached to the surface.

[0062] Step 4, Preparation of thermally conductive epoxy resin film: First, spray the release agent twice on the silicone mold. Then, mix the boron nitride nanosheets with iron oxide adhering to the surface, epoxy resin, curing agent: diluent in a mass ratio of 3:10:2.5:1.5. Heat the beaker on a hot plate at 45℃ and stir for 15 minutes. Then, place the mold in a prepared magnetic field with a magnetic field strength of 30mT. Under the action of the magnetic field, change the oven temperature stepwise and maintain it at 40℃ for 1 hour, 60℃ for 1 hour, 80℃ for 1 hour, and 100℃ for 2 hours to obtain a thermally conductive epoxy resin film material with a thickness of 0.8-1mm.

[0063] Comparative Example 3 (changing the mass ratio of melamine to boric acid)

[0064] Compared to Example 2, only the mass ratio of melamine to boric acid was changed to 1:2.2. Everything else was the same as in Example 2.

[0065] Comparative Example 4 (Changing High-Temperature Pyrolysis Conditions)

[0066] Compared to Example 2, only the high-temperature pyrolysis conditions were changed: a stepwise temperature increase was performed from 25℃ to 400℃ to 1100℃ and back to 25℃ (first stage (25℃→400℃): this stage involves a slow temperature increase to 400℃ at a rate of 2℃ / min; second stage (400℃→1100℃): this stage involves a temperature increase to 1100℃ at a rate of 5℃ / min, and holding at that temperature for 3 hours). All other conditions remained the same as in Example 2.

[0067] Comparative Example 5 (Changing Oxidation Temperature)

[0068] Compared to Example 2, only the oxidation temperature was changed to 300°C. Everything else was the same as in Example 2.

[0069] The thermally conductive epoxy resin film materials prepared in Examples 1-7 and Comparative Examples 1-5 were subjected to performance testing, and the results are shown in Table 2. Thermal conductivity was tested using a laser flare scanner (Netzsch LFA 467); mechanical properties were examined using an electronic universal testing machine, and tensile properties were tested according to Chinese National Standard GB528-2009 at a tensile rate of 10 mm / min.

[0070] Table 2. Test results of thermally conductive epoxy resin film materials prepared in Examples 1-7 and Comparative Examples 1-5

[0071]

[0072] The dielectric properties of the thermally conductive epoxy resin film materials prepared in Examples 3, 6 (22.2 wt%), Example 3 modified with 20 mT, and Example 6 (22.2 wt%) modified with 20 mT were tested using a broadband dielectric impedance relaxation spectrometer (Novocontrol Concept 80). The results are shown in Table 3.

[0073] Table 3. Test results of dielectric properties of the prepared epoxy resin film material

[0074]

[0075] Data from Examples 1-5 show that thermal conductivity initially increases and then decreases with increasing Fe3O4 loading. The Fe3O4 / BN / EP composite film prepared in Example 3 exhibits the best thermal conductivity, indicating that at 30 mT, the BN / EP film loaded with 25% Fe3O4 most easily achieves a thermally conductive channel. Simultaneously, the addition of embedded Fe3O4 composite filler affects the interfacial stability of the thermally conductive epoxy resin film. The proportion of embedded Fe3O4 in the composite filler and the proportion of the composite filler in the thermally conductive epoxy resin film both influence the mechanical properties of the material.

[0076] Data from Examples 3, 6, and 7 show that the amount of filler added to the composite material is not necessarily better the higher it is; rather, there exists an optimal threshold that matches the applied magnetic field strength. When the filler content is too low, it is difficult to form an effective and continuous thermal conductivity pathway within the matrix, resulting in limited improvement in thermal conductivity. Conversely, when the filler content is excessive, problems such as agglomeration, increased interface defects, and increased internal stress can easily occur, which in turn increases thermal resistance and dielectric loss, leading to a decline in overall performance. Data from Example 3 shows that when the magnetic field strength is 30 mT and the filler content is 17.6 wt%, the system can form the most uniform, continuous, and complete thermal conductivity network. At this point, the phonon transport path is the shortest, interface scattering is minimal, and the thermal conductivity of the composite material reaches its maximum value.

[0077] Compared to Examples 3, 6, and 7, the 20mT magnetic field strength is relatively low, resulting in insufficient driving force and difficulty in effectively guiding the composite filler of the same content to orderly arrange and oriented assemblies within the matrix. This makes it difficult for the filler to form continuous, interconnected, and efficient thermal conductivity pathways, limiting the improvement in thermal conductivity. As the magnetic field strength increases to 30mT, the magnetic field force is significantly enhanced, enabling more effective driving of the composite filler to align along the magnetic field direction, constructing a complete and interconnected thermal conductivity network. This significantly reduces interfacial thermal resistance and phonon scattering, thereby substantially improving the thermal conductivity of the composite material. This result demonstrates that a suitable magnetic field strength can effectively enhance the orientation control of the composite filler, playing a crucial role in improving the thermal conductivity of the composite material. Simultaneously, due to the enhanced bonding force, the compatibility with epoxy resin is also improved, and the mechanical properties are greatly enhanced.

[0078] A comparison of Examples 3, 6, and 7 shows that a suitable magnetic field can effectively induce the embedded Fe3O4 / BN composite filler to align and disperse uniformly within the epoxy resin matrix, thereby forming a continuous and ordered thermally conductive path within the composite material. This magnetic field-induced microstructural reorganization significantly reduces thermal resistance caused by filler agglomeration or poor interfacial contact, and lowers interfacial scattering and energy loss during phonon transmission. The continuous thermally conductive network effectively suppresses local electric field distortion and directional migration of charge carriers, significantly reducing interfacial polarization loss and electrical conductivity loss, ultimately resulting in a significant reduction in the dielectric loss of the composite material, achieving both high thermal conductivity and low dielectric loss.

[0079] As can be seen from Example 2 and Comparative Example 1, the embedded Fe3O4 / BN composite filler significantly improves the thermal conductivity of the thermally conductive epoxy resin film.

[0080] As shown in Example 2 and Comparative Example 2, the surface-treated Fe3O4 and the calcined BN filler, when blended, exhibit only weak physical bonding, resulting in insufficient interfacial compatibility and adhesion. During magnetic field-induced orientation, Fe3O4 struggles to effectively drive BN to form a stable and continuous thermally conductive pathway, leading to uneven dispersion and interfacial separation. This hinders phonon transport, thus reducing the material's thermal conductivity. Furthermore, the lack of sufficient interfacial bonding between fillers and between the filler and the matrix ultimately reduces both the material's mechanical strength and structural stability. This result indicates that a stable and strong interfacial bond between embedded Fe3O4 and BN is crucial for achieving efficient magnetic field-induced orientation and improving the thermal and mechanical properties of the composite material.

[0081] As can be seen from Example 2 and Comparative Example 3, an appropriate amount of boron source can make the Fe / Fe3C phase more stably embedded in the less defective BN sheet structure during high-temperature pyrolysis, thereby improving the thermal conductivity and mechanical properties of the thermally conductive epoxy resin film.

[0082] As can be seen from Example 2 and Comparative Example 4, the step of heat preservation at 800℃ is missing, and Fe3C nucleation is completed directly at 1100℃. Fe3C grows rapidly and forms larger particles, which affects the particle size of the final embedded Fe3O4 and the uniformity of its distribution in BN. It also reduces the interfacial compatibility, and the overall interfacial bonding force shows a decrease and non-uniformity, ultimately affecting the thermal conductivity and mechanical properties.

[0083] As shown in Example 2 and Comparative Example 5, when the reduction temperature is low, trace amounts of Fe in Fe / Fe3C / BN may react at low temperatures to form trace amounts of Fe3O4. However, most of the Fe3C remains stable at this temperature and does not easily change. During the composite material preparation process, curing temperatures of 40–100°C can cause Fe / Fe3C to catalyze localized curing of the epoxy resin or undergo side reactions with the curing agent, resulting in a decrease in the mechanical properties of the membrane material.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way. All technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler, characterized in that, This thermally conductive epoxy resin film is made by mixing embedded Fe3O4 / BN composite filler, epoxy resin, curing agent and diluent in a mass ratio of 1~4:9~11:2~3:1~2; The embedded Fe3O4 / BN composite filler is prepared by high-temperature pyrolysis of an iron-containing precursor to generate Fe / Fe3C / BN, followed by oxidation treatment. The iron-containing precursor is prepared by iron source, boron source, and nitrogen source. The high-temperature pyrolysis is carried out under an inert atmosphere, which reduces the iron species into nano-Fe / Fe3C particles and embeds them into BN sheets. The oxidation treatment is carried out under an air atmosphere, which converts Fe / Fe3C into Fe3O4 in situ, thus obtaining the embedded Fe3O4 / BN composite filler.

2. The thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler according to claim 1, characterized in that, In the iron-containing precursor, the mass ratio of iron source to boron source is 1:1 to 1:15; the mass ratio of nitrogen source to boron source is 1:3 to 3.

5.

3. The thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler according to claim 1, characterized in that, The high-temperature pyrolysis steps are as follows: A stepped temperature increase is performed from 20~30℃ to 350~450℃, then to 750~850℃, then to 1050~1150℃, and back to 20~30℃. In the 20~30℃ to 350~450℃ stage, the temperature is increased at a rate of 1.5~2.5℃; in the 350~450℃ to 750~850℃ stage, the temperature is increased at a rate of 2.5~3.5℃. After reaching 750~850℃... Maintain for 1.5-2.5h; during the 750~850℃-1050~1150℃ stage, increase the temperature at a rate of 4~6℃, and maintain for 2.5-3.5h after reaching 1050~1150℃; the oxidation treatment steps are as follows: heat Fe / Fe3C / BN to 450~550℃, maintain the temperature for 1~2 hours, cool naturally to room temperature, and use a magnet to adsorb and wash to obtain embedded Fe3O4 / BN composite filler.

4. The thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler according to claim 1, characterized in that, The iron source is a ferric salt, which is at least one of ferric chloride hexahydrate, ferric nitrate nonahydrate, and ferric triacetylacetone.

5. The thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler according to claim 1, characterized in that, The preparation process of the iron-containing precursor is as follows: At room temperature, trivalent iron source and boric acid are dissolved in deionized water at a mass ratio of 1:1 to 1:15, heated to 60-70℃, and the pH of the solution is adjusted to 5-5.

5. After mixing, a light yellow transparent solution is obtained. Melamine is dissolved in water and heated to 85-95℃. The hot melamine solution is slowly added dropwise to the above iron-containing boric acid mixture while stirring. During the addition process, iron-containing boron nitride precursor precipitates gradually appear. Stirring is continued for 2-3 hours, and the mixture is allowed to stand at room temperature for 8-15 hours. After washing and drying, a light yellow precursor powder is obtained.

6. The thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler according to claim 1, characterized in that, The preparation of the thermally conductive epoxy resin film includes the following steps: First, a release agent is sprayed onto the mold 2-3 times. Then, the obtained embedded Fe3O4 / BN composite filler, epoxy resin, curing agent, and diluent are mixed in a mass ratio of 1-4:9-11:2-3:1-2 and placed in the mold. The mixture is heated and stirred on a hot plate at 40-50℃ for 10-20 minutes. Subsequently, the mold is placed in a prepared magnetic field with a magnetic field strength controlled at 20-30 mT. Under the action of the magnetic field, the mixture is cured at 40℃-100℃ for 8-10 hours to obtain a thermally conductive epoxy resin film material with a thickness of 0.8-1 mm.

7. The thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler according to claim 6, characterized in that, The release agent includes at least one of silicone oil, wax, and fluorinated release agent; the mold material is at least one of silicone and tetrafluoroethylene; the curing agent is at least one of amine and acid anhydride; and the diluent is at least one of ethyl acetate, dibutyl phthalate, and phenyl glycidyl ether.

8. An embedded Fe3O4 / BN composite filler, characterized in that, The composite filler is prepared by high-temperature pyrolysis of an iron-containing precursor to generate Fe / Fe3C / BN, followed by oxidation to form an embedded Fe3O4 / BN composite structure. The iron-containing precursor is prepared by iron source, boron source, and nitrogen source. The high-temperature pyrolysis is carried out in an inert atmosphere to reduce iron species into nano-Fe / Fe3C particles and embed them into BN sheets. The oxidation treatment is carried out in an air atmosphere to convert Fe / Fe3C into Fe3O4 in situ, thus obtaining the embedded Fe3O4 / BN composite filler.

9. The embedded Fe3O4 / BN composite filler according to claim 8, characterized in that, In the iron-containing precursor, the mass ratio of iron source to boron source is 1:1 to 1:15; the mass ratio of nitrogen source to boron source is 1:3 to 3.5; the high-temperature pyrolysis step is: the temperature is increased in stages from 20 to 30℃ to 350 to 450℃ to 750 to 850℃ to 1050 to 1150℃ to 20 to 30℃; the oxidation treatment step is: the Fe / Fe3C / BN is heated to 450 to 550℃, held for 1 to 2 hours, naturally cooled to room temperature, and then adsorbed and washed using a magnet to obtain the embedded Fe3O4 / BN composite filler.

10. The application of the thermally conductive epoxy resin film containing embedded Fe3O4 / BN composite filler as described in any one of claims 1-7, or the embedded Fe3O4 / BN composite filler as described in claim 8 or 9, in the electronic packaging of wearable electronic devices and pressure sensors, characterized in that... The thermally conductive epoxy resin film is attached to the surface of wearable electronic devices or pressure sensors.

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