Core-shell fiber reinforced epoxy resin composite material and preparation method thereof

Abstract

The invention discloses a core-shell fiber reinforced epoxy resin composite material and a preparation method thereof.The core-shell fiber reinforced epoxy resin composite material is UHMWPE fiber with the surface coated with a silicon dioxide nano layer, the surface is evenly coated with a SiO2 nano layer, the interface bonding performance of the fiber and an epoxy resin matrix is effectively improved, and the core-shell fiber reinforced epoxy resin composite material is prepared; the physical properties of the composite material can also be greatly improved, specifically, (1) the composite material has high insulativity, wherein the breakdown field strength is improved by 50% or above compared with that of an uncoated fiber composite material; (2) high heat conductivity: the out-of-plane heat conductivity coefficient reaches 1-2W / (m.K) and is improved by 3-7 times compared with the traditional epoxy resin; and (3) light weight and high strength. The method is simple in process, controllable in cost, free of complex equipment and suitable for large-scale production. The material can be widely applied to the fields with strict requirements on insulation and heat dissipation performance, such as high-voltage insulation devices, high-power electronic packaging and new energy motor insulation systems.

Description

Technical Field

[0001] This invention belongs to the field of epoxy resin materials technology, specifically relating to a core-shell fiber reinforced epoxy resin composite material and its preparation method. Background Technology

[0002] Epoxy resin (EP), as a typical insulating material in encapsulated electronic products, possesses excellent chemical resistance, processability, corrosion resistance, and electrical insulation properties. However, due to the cross-linking of its molecular chains to form a network structure after heat curing, the system tends to saturate, reducing the number of freely moving electrons within. Furthermore, its relatively large molecular mass makes molecular movement relatively difficult, resulting in a low thermal conductivity of only 0.17~0.2 W / (m·K). This fails to meet the ever-increasing heat dissipation requirements of modern electronic devices. Therefore, improving its thermal conductivity is crucial for addressing the overall heat dissipation problem of encapsulation materials. Currently, methods to improve the thermal conductivity of epoxy resin mainly include intrinsic modification and filler reinforcement. Intrinsic modification improves polymer chain regularity through molecular design, but the process is complex and the improvement is limited. Filler reinforcement, on the other hand, introduces high thermal conductivity fillers (such as alumina, boron nitride, and carbon nanotubes) to construct a thermally conductive network, offering greater practical value. However, traditional filler reinforcement faces challenges in filler dispersibility, interfacial compatibility, and processing performance. While high thermal conductivity inorganic fillers improve thermal conductivity, insulation performance rapidly declines. For example, ultra-high molecular weight polyethylene (UHMWPE) fibers possess excellent thermal conductivity and high mechanical strength, making them suitable as a reinforcing phase to improve the thermal conductivity of composite insulation. However, their non-polar surface exhibits poor adhesion to epoxy resin, and direct lamination can introduce interfacial thermal resistance and insulation defects. Therefore, there is an urgent need to develop a novel preparation process to improve the interfacial bonding of UHMWPE fibers in epoxy resin composite media. Summary of the Invention

[0003] To overcome the problems existing in the prior art, one objective of this invention is to provide a core-shell fiber-reinforced epoxy resin composite material. A second objective of this invention is to provide a method for preparing the aforementioned core-shell fiber-reinforced epoxy resin composite material. To achieve the above objectives, the technical solution adopted by this invention is as follows: The first aspect of the present invention provides a core-shell fiber reinforced epoxy resin composite material, comprising the following raw materials: modified polyethylene fiber and epoxy resin; The modified polyethylene fiber includes ultra-high molecular weight polyethylene fiber (UHMWPE), and the surface of the UHMWPE fiber is coated with a silica nanolayer.

[0004] Preferably, the method for preparing the modified polyethylene fiber includes the following steps: Ultra-high molecular weight polyethylene fiber, alkaline catalyst, template agent and silicon source are mixed in a solvent and subjected to condensation reaction to obtain ultra-high molecular weight polyethylene fiber coated with silica nanolayer. The modified polyethylene fiber was prepared by modifying the ultra-high molecular weight polyethylene fiber coated with a silica nanolayer using a silane coupling agent.

[0005] Preferably, the process includes the following steps: mixing ultra-high molecular weight polyethylene fiber, alkaline catalyst and template agent in water to obtain solution A, mixing silicon source in alcohol solvent to obtain solution B, and mixing solution A and solution B to carry out a condensation reaction.

[0006] More preferably, the alcohol solvent is selected from at least one of methanol, ethanol, and isopropanol.

[0007] More preferably, the ratio of ultra-high molecular weight polyethylene fiber to water is 1 g:(100-300) mL.

[0008] More preferably, the ratio of the ultra-high molecular weight polyethylene fiber to the alcohol solvent is 1 g:(2-6) mL.

[0009] More preferably, the method further includes the following steps: adding ultra-high molecular weight polyethylene fiber, alkaline catalyst and template agent to water, stirring and mixing at room temperature, and then stirring and mixing at 50-70°C to obtain solution A.

[0010] Preferably, the silicon source includes at least one of tetramethoxysilane, tetraethoxysilane, trimethylethoxysilane, ethyltriethoxysilane, and propyltriethoxysilane.

[0011] Preferably, the alkaline catalyst includes at least one of ammonia and sodium hydroxide.

[0012] Preferably, the template agent includes at least one of hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, didodecyldimethylammonium chloride, and didodecyldimethylammonium bromide.

[0013] Preferably, the reaction temperature of the condensation reaction is 50-80°C.

[0014] Preferably, the reaction time of the condensation reaction is 8-16 h.

[0015] Preferably, the ratio of ultra-high molecular weight polyethylene fiber to silicon source is 1 g:(2-6) mL.

[0016] Preferably, the ratio of ultra-high molecular weight polyethylene fiber to alkaline catalyst is 1 g:(1-4) mL.

[0017] Preferably, the ratio of ultra-high molecular weight polyethylene fiber to template agent is 1 g:(0.01-0.1) g.

[0018] Preferably, the silane coupling agent includes at least one of aminosilanes, epoxysilanes, vinylsilanes, mercaptosilanes, and methacryloxysilanes.

[0019] Preferably, the modification step using a silane coupling agent includes the following steps: adding the silane coupling agent and ultra-high molecular weight polyethylene fiber coated with a silica nanolayer to an alcohol solvent, and stirring the reaction at 50-80°C.

[0020] Preferably, the mass ratio of the silane coupling agent to the ultra-high molecular weight polyethylene fiber coated with a silica nanolayer is 1:(50-200).

[0021] The main purpose and effect of this invention in further treating the ultra-high molecular weight polyethylene fiber with silane coupling agent after coating it with SiO2 is as follows: (1) Chemical bonding "bridging" effect: After the ethoxy group at one end of the aminosilane coupling agent molecule is hydrolyzed, it condenses with the silanol group (-Si-OH) on the surface of SiO2 to form a stable Si-O-Si covalent bond; the amino group (-NH2) at the other end can undergo a ring-opening reaction with the epoxy group of the epoxy resin matrix, which is equivalent to establishing a strong chemical bonding "bridge" between the SiO2 coating layer of the fiber and the resin matrix. (2) Further optimization of interface structure and performance: Although the SiO2 coating layer itself has greatly improved the physical compatibility between inert UHMWPE and epoxy resin, the introduction of silane coupling agent can enhance this bond from physical anchoring / wetting to a stronger level of chemical bonding. The specific beneficial effects are: ① Further reduce the interfacial thermal resistance and improve the heat conduction efficiency along the fiber axis; ② Enhance the interfacial mechanical interlocking and inhibit the initiation and propagation of microcracks; ③ Make the electric field distribution in the interfacial region more uniform, reduce charge capture and accumulation, and have a positive effect on long-term insulation reliability.

[0022] Furthermore, current composite material design relies heavily on trial and error, lacking multi-scale simulation guidance from electronic structure to macroscopic performance, resulting in long development cycles and high costs. To ensure the safe and long-term operation of electronic devices, developing high-performance thermally conductive materials using multi-scale simulation has become a top priority.

[0023] More preferably, the preparation method of the modified polyethylene fiber further includes the following steps: constructing a model of ultra-high molecular weight polyethylene fiber and silica, and calculating its energy level distribution and density of electronic states (DOS) using first-principles calculations; establishing a finite element simulation model to simulate the effect of silica nanolayer coating on the fiber before and after coating.

[0024] The second aspect of the present invention provides a method for preparing the core-shell fiber reinforced epoxy resin composite material described in the first aspect, comprising the following steps: softening / melting epoxy resin, mixing the softened / melted epoxy resin with a curing agent, an accelerator and modified polyethylene fiber, and carrying out a curing reaction to obtain the core-shell fiber reinforced epoxy resin composite material.

[0025] Preferably, the epoxy resin includes at least one of aliphatic epoxy resin, bisphenol A type epoxy resin, bisphenol S type epoxy resin, and bisphenol F type epoxy resin.

[0026] Preferably, the modified polyethylene fiber accounts for 4%-15% of the mass percentage in the core-shell fiber reinforced epoxy resin composite material.

[0027] Preferably, the process includes the following steps: heating the epoxy resin to 70-100°C, mixing it with a curing agent and an accelerator, and then mixing the resulting mixture with modified polyethylene fibers.

[0028] Preferably, the curing temperature is 60-150℃.

[0029] More preferably, the curing process is as follows: first, heating in a high vacuum environment at 50-70°C for 1-3 hours, then heating in an atmospheric environment at 70-90°C for 1-3 hours, at 90-110°C for 1-3 hours, and at 110-130°C for 1-3 hours.

[0030] Preferably, the curing agent is an epoxy resin curing agent.

[0031] More preferably, the curing agent is an acid anhydride-based curing agent.

[0032] Preferably, the accelerator is an epoxy accelerator.

[0033] More preferably, the accelerator is a tertiary amine accelerator.

[0034] Preferably, the preparation method of the core-shell fiber reinforced epoxy resin composite material is guided by multi-scale simulation.

[0035] The beneficial effects of this invention are: This invention provides a core-shell fiber-reinforced epoxy resin composite material. By uniformly coating the surface of UHMWPE fibers with a SiO2 nanolayer, the interfacial bonding between the fibers and the epoxy resin matrix is ​​effectively improved, and the insulation and thermal conductivity of the composite material are significantly enhanced. The specific modification mechanism is as follows: the SiO2 coating layer not only fills the micro-defects at the fiber-resin interface and reduces local electric field distortion, but also inhibits the development of electrical dendrites through its high dielectric strength, thus significantly improving the breakdown field strength of the composite medium. At the same time, the high thermal conductivity of SiO2 (~1.4 W / (m·K)) and the heat conduction of UHMWPE fibers work synergistically to construct an efficient heat conduction network, giving the composite material both excellent electrical insulation and heat dissipation capabilities.

[0036] The SiO2-coated UHMWPE fiber / epoxy resin composite dielectric prepared using this invention exhibits superior comprehensive performance in the following aspects: (1) High insulation: The breakdown field strength is increased by more than 50% compared to the uncoated UHMWPE fiber composite material; (2) High thermal conductivity: The out-of-plane thermal conductivity reaches 1-2 W / (m·K), which is 3-7 times higher than that of traditional epoxy resin; (3) Lightweight and high strength: The low density and high tensile strength of UHMWPE fiber give the composite material significant advantages in aerospace, high-voltage cables and other fields. The process of this invention is simple, cost-controllable, and does not require complex equipment, making it suitable for large-scale production. This material can be widely used in fields with stringent requirements for insulation and heat dissipation performance, such as high-voltage insulation devices, high-power electronic packaging, and new energy motor insulation systems, providing an innovative solution for the lightweighting and reliability improvement of high-power density electrical equipment. Attached Figure Description

[0037] Figure 1 First-principles calculations of energy level distribution and electronic density of states (DOS) plots for (a) UHMWPE and (b) SiO2.

[0038] Figure 2 Temperature field distribution diagrams of composite media obtained from finite element simulations of pure epoxy resin, 12wt%UHMWPE / EP, and 12wt%UHMWPE@SiO2 / EP.

[0039] Figure 3 Scanning electron microscope images and silicon element distribution diagrams of the prepared UHMWPE fibers, silica-coated UHMWPE fibers, and UHMWPE fibers and silica-coated UHMWPE fibers respectively reinforced high thermal conductivity epoxy resin-based composite media.

[0040] Figure 4 X-ray diffraction patterns of the prepared UHMWPE fibers and silica-coated UHMWPE fibers, respectively, for reinforcing high thermal conductivity epoxy resin-based composite media.

[0041] Figure 5 Fourier transform infrared spectra of the prepared UHMWPE fibers and silica-coated UHMWPE fibers, respectively, for enhancing the high thermal conductivity epoxy resin-based composite media.

[0042] Figure 6 The figure shows the thermal conductivity test results of the prepared pure epoxy resin reinforced with UHMWPE fiber and silica-coated UHMWPE fiber, respectively, for high thermal conductivity epoxy resin-based composite media.

[0043] Figure 7 The AC breakdown Weibull distribution diagrams of the pure epoxy resin, UHMWPE fiber, and silica-coated UHMWPE fiber reinforced high thermal conductivity epoxy resin-based composite media are shown.

[0044] Figure 8 The AC conductivity of the prepared pure epoxy resin reinforced with UHMWPE fiber and silica-coated UHMWPE fiber as a function of frequency is shown in the curves.

[0045] Figure 9 The relative permittivity of the prepared pure epoxy resin reinforced with UHMWPE fiber and silica-coated UHMWPE fiber as a function of frequency is shown in the curves.

[0046] Figure 10 The dielectric loss tangent of the prepared pure epoxy resin reinforced with UHMWPE fiber and silica-coated UHMWPE fiber is shown as a function of frequency.

[0047] Figure 11 Differential scanning calorimetry curves of the prepared UHMWPE fibers and silica-coated UHMWPE fibers.

[0048] Figure 12 The diagram illustrates the principle of enhancing the thermal conductivity of high thermal conductivity epoxy resin-based composite media by preparing UHMWPE fibers and silica-coated UHMWPE fibers, respectively. Detailed Implementation

[0049] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments can be obtained from conventional commercial channels or prepared and isolated through simple synthesis; unless otherwise specified, the processes employed are conventional processes in the art.

[0050] Before the experimental preparation, the following multi-scale simulation analysis was performed: (1) First-principles calculations: Using software, UHMWPE and SiO2 models were constructed, and their energy level distribution and density of electronic states (DOS) were calculated. The results show that the UHMWPE surface coated with SiO2 has a wide bandgap and an extremely wide energy level range.

[0051] (2) Finite element simulation of thermal conductivity: A finite element simulation model was established to simulate the effect of fiber coating on the thermal conductivity of the composite medium. The simulation results show that UHMWPE with SiO2 coating has a higher heat dissipation effect.

[0052] Specific Implementation Method 1: This embodiment describes a silica-coated UHMWPE fiber-reinforced high thermal conductivity epoxy resin-based composite medium and its preparation method. Based on first-principles calculations and finite element simulation results, the following proportions and process conditions are determined: Step 1: Add ultra-high molecular weight polyethylene (UHMWPE) fiber, ammonia, and hexadecyltrimethylammonium bromide to deionized water and stir to obtain mixed solution A. Add tetraethyl silicate to anhydrous ethanol and stir to obtain mixed solution B. Slowly add mixed solution A dropwise to mixed solution B and stir to obtain mixed solution C.

[0053] Step 2: Vacuum filter the mixed solution C, wash the filtered product, and dry it to obtain silica-coated UHMWPE (UHMWPE@SiO2) fibers.

[0054] Step 3: Weigh UHMWPE@SiO2 fibers and silane coupling agent, add them to anhydrous ethanol, stir, vacuum filter, and then wash and dry to obtain surface-modified UHMWPE@SiO2 fiber cake.

[0055] Step 4: Add epoxy resin to the container and stir; then add methylhexahydrophthalic anhydride as a curing agent, and continue magnetic stirring until the solution is evenly mixed. Then add 2, 4, 6 Tris(dimethylaminomethyl)phenol was used as an accelerator. After being magnetically stirred until homogeneous, an epoxy resin mixture was obtained. The epoxy resin mixture was then poured into a mold with surface-modified UHMWPE@SiO2 fiber cakes to obtain the UHMWPE@SiO2 / EP composite medium to be cured.

[0056] Step 5: Vacuum the UHMWPE@SiO2 / EP composite medium to be cured to remove air bubbles and cure it to obtain a silica-coated UHMWPE fiber-reinforced high thermal conductivity epoxy resin-based composite medium (UHMWPE@SiO2 / EP).

[0057] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method Two in that: before step 1, it also includes calculating the electronic state density of the UHMWPE surface and the SiO2 surface using first-principles calculation software to determine that the silica coating enhances the electrical properties of the fiber / epoxy resin composite medium; and establishing a thermal conduction model of the composite medium using a finite element model to simulate the temperature field distribution of the composite medium before and after silica coating of UHMWPE fibers, thus determining that the silica coating enhances the thermal properties of the fiber / epoxy resin composite medium.

[0058] Specific Implementation Method 3: The difference between this implementation method and Specific Implementation Method 2 is as follows: In step 1, the UHMWPE fiber, ammonia, hexadecyltrimethylammonium bromide, deionized water, tetraethyl silicate, and anhydrous ethanol are 5g, 10mL, 0.2g, 1L, 20mL, and 20mL, respectively, and the ammonia content is 25%; the stirring conditions are: ultrasonic stirring at 300r / min for 15min at room temperature, followed by stirring at 300r / min for 30min at 60℃; the stirring conditions for mixed solution B are: stirring at 500r / min for 1h at room temperature; and the stirring conditions for mixed solution A and B are: stirring at 300r / min for 12h at 60℃.

[0059] The other steps are the same as those in specific implementation methods one and two.

[0060] Specific Implementation Method Four: The difference between this implementation method and Specific Implementation Method One or Two is that: the multiple cleaning method in step 2 is to first stir with 1L of deionized water at 300r / min for 30min and then filter, and then stir with 1L of anhydrous ethanol at 300r / min for 30min and then filter; the drying conditions are to first dry at 60℃ for 30min in a forced-air drying oven, and then dry at 80℃ for 1h.

[0061] The other steps are the same as those in Specific Implementation Methods One to Three.

[0062] Specific Implementation Method 5: The difference between this implementation method and Specific Implementation Methods 1 to 3 is that: in step 3, the UHMWPE@SiO2 fiber, silane coupling agent and anhydrous ethanol are 1g, 10mg and 100mL respectively; the multiple washing method is the same as in step 2; the stirring conditions are stirring at 300r / min for 30min under heating at 60℃; the drying conditions are drying at 60℃ for 1h in a forced-air drying oven.

[0063] The other steps are the same as those in Specific Implementation Methods One through Four.

[0064] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Four in that: in step 4, epoxy resin, methylhexahydrophthalic anhydride, and 2,4,6... The mass of tris(dimethylaminomethyl)phenol was 11.32 g, 9.62 g and 0.11 g respectively; the preheating conditions were 300 r / min stirring at 80℃ for 30 min; the epoxy resin mixture was ultrasonicated at 60℃ for 30 min to remove air bubbles before casting.

[0065] The other steps are the same as those in Specific Implementation Methods 1 to 5.

[0066] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods One to Five is that the mold size in step 4 is 3*3*2cm; the total mass of the epoxy resin mixed solution is 21.06g; and the final pre-cured UHMWPE@SiO2 / EP composite medium has a mass percentage of 0%, 6wt%, and 12wt% for UHMWPE@SiO2 fibers.

[0067] The other steps are the same as those in Specific Implementation Methods 1 to 6.

[0068] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One through Six in that: the vacuuming and gradient temperature curing conditions in step 5 are first at 2×10 -1 Heated at 60°C for 2 hours in a high vacuum environment of Pa, and then heated at 80°C for 2 hours, 100°C for 2 hours, and 120°C for 2 hours under normal pressure.

[0069] The other steps are the same as those in Specific Implementation Methods 1 to 7.

[0070] The beneficial effects of the present invention are verified using the following embodiments: Example 1 This embodiment provides a 6wt% silica-coated UHMWPE fiber-reinforced high thermal conductivity epoxy resin-based composite medium (6wt% UHMWPE@SiO2 / EP), the preparation method of which is as follows: Step 1: Add 5g of ultra-high molecular weight polyethylene (UHMWPE) fiber, 10mL of ammonia water, and 0.2g of hexadecyltrimethylammonium bromide to 1L of deionized water. Sonicate the solution at room temperature for 15min, then heat at 60℃ and stir at 300rpm for 30min to obtain mixed solution A. Add 20mL of tetraethyl silicate to 20mL of anhydrous ethanol and magnetically stir at 500rpm for 1h at room temperature to obtain mixed solution B. Slowly add mixed solution A dropwise to mixed solution B and stir at 300rpm for 12h at 60℃ to obtain mixed solution C.

[0071] Step 2: Vacuum filter the mixed solution C, and wash the filtered product by first stirring with 1L of deionized water at 300r / min for 30min and then filtering, then stirring with 1L of anhydrous ethanol at 300r / min for 30min and then filtering. Then dry it in a forced-air oven at 60℃ for 30min and then at 80℃ for 1h to obtain silica-coated UHMWPE (UHMWPE@SiO2) fibers.

[0072] Step 3: Weigh 1g of UHMWPE@SiO2 fiber and 10mg of silane coupling agent (KH550) and add them to 100mL of anhydrous ethanol in proportion. Heat at 60℃ and stir at 300r / min for 30min. Vacuum filter and wash the product by first stirring with 1L of deionized water at 300r / min for 30min and then filtering, then stirring with 1L of anhydrous ethanol at 300r / min for 30min and then filtering. Dry the product in a forced-air oven at 60℃ for 1h to obtain the surface-modified UHMWPE@SiO2 fiber cake.

[0073] Step 4: Add 11.32g of bisphenol A type epoxy resin (brand name E-51) to the container and stir at 300r / min for 30min at 80℃; then add 9.62g of methylhexahydrophthalic anhydride as a curing agent, and continue magnetic stirring until the solution is uniformly mixed. Finally, add 0.11g of 2,4,6 Tris(dimethylaminomethyl)phenol was used as an accelerator. After magnetic stirring until homogeneous, 21.06 g of epoxy resin mixture was obtained. The epoxy resin mixture was then ultrasonicated at 60°C for 30 min to remove air bubbles. The epoxy resin mixture was then poured into a 3*3*2 cm mold containing 1.34 g of surface-modified UHMWPE@SiO2 fiber cake to obtain a 6 wt% UHMWPE@SiO2 / EP composite medium to be cured.

[0074] Step 5: Pre-cure the 6wt% UHMWPE@SiO2 / EP composite medium to be cured at 2×10⁻⁶ ℃. -1 Heating at 60°C for 2 hours in a high vacuum environment of Pa, and then heating at 80°C for 2 hours, 100°C for 2 hours, and 120°C for 2 hours under normal pressure, respectively, yields a 6wt% silica-coated UHMWPE fiber-reinforced high thermal conductivity epoxy resin-based composite medium (6wt% UHMWPE@SiO2 / EP).

[0075] Example 2 This embodiment provides a 12wt% silica-coated UHMWPE fiber-reinforced high thermal conductivity epoxy resin-based composite medium (12wt% UHMWPE@SiO2 / EP), the preparation method of which is as follows: In this embodiment, the silica-coated UHMWPE fiber accounts for 12 wt% of the epoxy resin. That is, 21.06 g of epoxy resin mixture is poured into a 3*3*2 cm mold containing 4.01 g of surface-modified UHMWPE@SiO2 fiber cake. All other experimental conditions are the same as in Example 1.

[0076] Comparative Example 1 This comparative example provides a method for preparing a pure epoxy resin medium: Step 1: Add 11.32g of epoxy resin to a container and stir at 300r / min for 30min at 80℃; then add 9.62g of methylhexahydrophthalic anhydride as a curing agent, and continue magnetic stirring until the solution is uniformly mixed. Finally, add 0.11g of 2,4,6 Tris(dimethylaminomethyl)phenol was used as an accelerator. After magnetic stirring until the mixture was homogeneous, 21.06g of epoxy resin mixture solution was obtained. The epoxy resin mixture solution was then ultrasonicated at 60℃ for 30min to remove air bubbles. The epoxy resin mixture solution was then poured into a 3*3*2cm mold to obtain epoxy resin to be cured.

[0077] Step 2: Heat the epoxy resin to be cured at 80℃ for 2 hours, 100℃ for 2 hours, and 120℃ for 2 hours respectively to obtain pure epoxy resin medium.

[0078] Comparative Example 2 This comparative example provides a 6wt% UHMWPE fiber-reinforced high thermal conductivity epoxy resin-based composite medium (6wt% UHMWPE / EP), the specific preparation method of which is as follows: Step 1: Weigh 1g of UHMWPE fiber and 10mg of silane coupling agent and add them to 100mL of anhydrous ethanol in proportion. Heat at 60℃ and stir at 300r / min for 30min. Vacuum filter and wash by first stirring with 1L of deionized water at 300r / min for 30min and then filtering, then stirring with 1L of anhydrous ethanol at 300r / min for 30min and then filtering. Dry in a forced-air oven at 60℃ for 1h to obtain surface-modified UHMWPE fiber cake.

[0079] Step 2: Add 11.32g of epoxy resin to the container and stir at 300r / min for 30min at 80℃; then add 9.62g of methylhexahydrophthalic anhydride as a curing agent, and continue magnetic stirring until the solution is uniformly mixed. Finally, add 0.11g of 2,4,6 Tris(dimethylaminomethyl)phenol was used as an accelerator. After magnetic stirring until homogeneous, 21.06g of epoxy resin mixture was obtained. The epoxy resin mixture was ultrasonically heated at 60℃ for 30min to remove air bubbles. Then, the epoxy resin mixture was poured into a 3*3*2cm mold with 4.01g of surface-modified UHMWPE fiber cake, to obtain 6wt% UHMWPE / EP composite medium to be cured.

[0080] Step 3: Pre-cure the 6wt% UHMWPE / EP composite medium to be cured at 2×10⁻⁶ ℃. -1 Heating at 60°C for 2 hours in a high vacuum environment of Pa, and then heating at 80°C for 2 hours, 100°C for 2 hours, and 120°C for 2 hours under normal pressure, respectively, yields a 6wt% UHMWPE fiber-reinforced high thermal conductivity epoxy resin-based composite medium (6wt% UHMWPE / EP).

[0081] Comparative Example 3 This comparative example provides a 12wt% UHMWPE fiber-reinforced high thermal conductivity epoxy resin-based composite medium (12wt% UHMWPE / EP), and its preparation method is as follows: In this comparative example, the UHMWPE fiber accounted for 12 wt% of the epoxy resin. Specifically, 21.06 g of epoxy resin mixture was poured into a 3*3*2 cm mold containing 1.34 g of surface-modified UHMWPE fiber cake. All other experimental conditions were the same as in Comparative Example 2.

[0082] Performance Characterization Figure 1 First-principles calculations of energy level distribution and electronic density of states (DOS) plots for (a) UHMWPE and (b) SiO2 are shown. The figures reveal that the wide bandgap and low DOS of SiO2 construct a high-barrier, low-mobility insulating shell on the UHMWPE fiber surface, effectively suppressing charge injection, migration, and accumulation. Simultaneously, it optimizes the interfacial electric field distribution, thereby increasing the breakdown field strength of the coated epoxy resin composite medium by more than 50% compared to the uncoated state.

[0083] Figure 2 This is a finite element analysis (FEM) diagram of the temperature field distribution of composite media for pure epoxy resin, 12wt% UHMWPE / EP, and 12wt% UHMWPE@SiO2 / EP. Under the same heating conditions, materials with higher thermal conductivity have stronger heat transfer efficiency. Specifically, within the same time frame, the overall temperature of the material is lower, the temperature distribution is more uniform, heat is dissipated more quickly, and it is less prone to localized heat accumulation.

[0084] Figure 3Scanning electron microscope (SEM) images of (a) silica-coated UHMWPE fibers, (b) UHMWPE fibers, (c) UHMWPE fibers, and (d) silica-coated UHMWPE fibers reinforcing high thermal conductivity epoxy resin-based composite media, and their silicon element distribution maps (a1), (b1), (c1), and (d1). Figures (a) and (b) show that the thickness of the UHMWPE fibers before and after coating is approximately 20 μm. The silicon element distribution maps (a1) and (b1) show that the silicon content on the surface of the UHMWPE fibers is significantly higher after coating, indicating that silica was successfully coated onto the surface of the UHMWPE fibers. The more uneven surface of the UHMWPE fibers after coating also facilitates interfacial bonding between the fibers and the epoxy resin. The cross-sectional scanning electron microscope images of the UHMWPE / EP composite medium and the UHMWPE@SiO2 / EP composite medium in (c) and (d) and the silicon element distribution diagrams in (c1) and (d1) show that the cross-sectional structure is dense. The UHMWPE@SiO2 / EP composite medium has a significantly higher silicon content than the UHMWPE / EP composite medium, and has relatively fewer pores and defects, indicating that the prepared UHMWPE@SiO2 / EP composite medium meets the expected design.

[0085] Figure 4 X-ray diffraction patterns of UHMWPE fibers and silica-coated UHMWPE fibers reinforced with high thermal conductivity epoxy resin-based composite media were prepared. The high crystallinity of UHMWPE fibers is key to their excellent mechanical properties. As shown in the figure, three distinct crystallization peaks were observed in the 18°-28° range, corresponding to the tetragonal (110) and (200) crystal systems at 21.7° and 24.1°, and the monoclinic (010) crystal system at 19.7°, respectively. The crystallization diffraction patterns of UHMWPE fibers before and after coating were basically consistent, with only a slight decrease in intensity for UHMWPE@SiO2 fibers. This is because the SiO2 coating layer causes X-ray absorption and scattering, reducing the amount of X-rays reaching the UHMWPE crystal plane. Epoxy resin and amorphous SiO2 only showed broad diffuse peaks (2) in XRD. θ =15-30°), and there was no significant change before and after modification, indicating that the composite of fiber and epoxy resin did not produce new crystalline substances.

[0086] Figure 5 Fourier transform infrared (FTIR) spectra of the prepared UHMWPE fibers and silica-coated UHMWPE fibers, respectively, reinforced high thermal conductivity epoxy resin-based composite media. As shown in the figure, the 12wt% UHMWPE / EP composite media and the 12wt% UHMWPE@SiO2 / EP composite media are located at 1100 cm⁻¹. -1 and 800 cm -1The characteristic absorption peaks correspond to the asymmetric and symmetric stretching vibration peaks of the Si-O-Si bond, respectively. These two characteristic peaks demonstrate that the SiO2 coating layer has been successfully introduced into the composite medium.

[0087] Figure 6 The graph shows the thermal conductivity test results of the prepared pure epoxy resin reinforced with UHMWPE fiber and silica-coated UHMWPE fiber, respectively, for high thermal conductivity epoxy resin-based composite media. From the graph, the thermal conductivity of pure epoxy resin, 6wt% UHMWPE / EP composite medium and UHMWPE@SiO2 / EP composite medium, 12wt% UHMWPE / EP composite medium and UHMWPE@SiO2 / EP composite medium are 0.243, 0.571, 0.756, 1.613 and 2.511 W / (m·K), respectively. As can be seen from the figure, the 12wt% UHMWPE@SiO2 / EP composite medium has a thermal conductivity more than 9 times higher than that of pure epoxy resin. This significant improvement is due to two main factors: firstly, the high thermal conductivity of UHMWPE itself, as evidenced by the 1-7 times increase in thermal conductivity of the 6wt% and 12wt% UHMWPE / EP composite medium compared to pure epoxy resin; and secondly, the improved interfacial bonding due to the SiO2 coating layer, which is also evident from the more than 50% increase in thermal conductivity of the UHMWPE@SiO2 / EP composite medium compared to the UHMWPE / EP composite medium at the same concentration.

[0088] Figure 7 This paper presents the AC breakdown Weibull distribution for pure epoxy resin reinforced with UHMWPE fibers and silica-coated UHMWPE fibers, respectively, as well as the breakdown of high thermal conductivity epoxy resin-based composite media. The AC breakdown strength was tested according to ASTM-D149-81, using a cylindrical electrode structure. The electrode height and diameter were both 25 mm, and the voltage increase rate was 2 kV / s throughout the test, with the sample immersed in transformer oil. After the sample broke down, the pressure was stopped, and the breakdown data were recorded. Ten samples were tested in each group. The breakdown strength was statistically analyzed using a two-parameter Weibull distribution. The Weibull distribution is commonly used to assess material reliability; its cumulative distribution function (CDF) is as follows: F ( E )=1 exp[ ( E / η ) β ],in: E To break down the electric field strength (kV / mm). η The characteristic breakdown field strength (scale parameter, field strength at which 63.2% of the samples break down). βThe shape parameters (reflecting the degree of data dispersion; the larger the value, the higher the reliability) are used. The characteristic breakdown field strengths of pure epoxy resin, 6wt% UHMWPE / EP composite dielectric and UHMWPE@SiO2 / EP composite dielectric, and 12wt% UHMWPE / EP composite dielectric and UHMWPE@SiO2 / EP composite dielectric are 61.23, 11.31, 25.4, 19.74, and 34.66 kV / mm, respectively, with shape parameters of 5.26, 9.36, 4.89, 6.66, and 8.22, respectively. Compared with pure epoxy resin, the breakdown strength of UHMWPE / EP composite dielectric and UHMWPE@SiO2 / EP composite dielectric is slightly lower. This is because the surface of UHMWPE fibers has an inert, non-polar structure (mainly -CH2-), which has severe interfacial incompatibility with epoxy resin (containing -O- and other groups). However, silica coating alleviates this problem to some extent. Both the thermal conductivity and breakdown field strength are improved compared to the uncoated fiber epoxy composite medium, which also confirms that the UHMWPE@SiO2 / EP composite medium prepared in this patent meets the expected design.

[0089] Figure 8 The AC conductivity of the prepared pure epoxy resin reinforced with UHMWPE fiber and silica-coated UHMWPE fiber as a function of frequency is shown in the curves. Figure 9 The relative permittivity of the prepared pure epoxy resin reinforced with UHMWPE fiber and silica-coated UHMWPE fiber as a function of frequency is shown in the curves. Figure 10The dielectric loss tangent of the prepared high thermal conductivity epoxy resin-based composite media reinforced with pure epoxy resin and UHMWPE fibers, and silica-coated UHMWPE fibers, are shown as a function of frequency. All three curves are from broadband dielectric spectroscopy measurements, performed using an Alpha-A broadband dielectric spectrometer manufactured by Novocontrol, Germany, with a test electrode diameter of 20 mm and a voltage of 1 V across the sample. Compared to pure epoxy resin, the composite media with uncoated UHMWPE fibers exhibit a slight decrease in both relative permittivity and AC conductivity. This is mainly due to the low relative permittivity of the non-polar UHMWPE fibers, which directly reduces the overall polarization of the composite media; simultaneously, their insulating properties limit carrier migration, leading to a decrease in conductivity. Notably, the dielectric loss of all composite media is lower than that of pure epoxy resin, indicating that the introduction of fibers suppresses the relaxation loss of dipoles under alternating electric fields to some extent. The dielectric behavior of the composite media changes significantly after SiO2 coating. The relative permittivity of the 6wt% UHMWPE@SiO2 / EP composite dielectric and the 12wt% UHMWPE@SiO2 / EP composite dielectric increased to 3.73 and 3.72, respectively, higher than that of pure epoxy resin and other uncoated components. This is because SiO2 itself has a higher permittivity than UHMWPE, and its coating layer forms an interface region with higher polarization capability between the fiber and the matrix, thereby improving the overall polarization intensity of the composite dielectric. Despite the increase in permittivity, the dielectric loss of the SiO2-coated composite dielectric remains at a low level, and the dielectric loss tangent (tan φ) of 12wt% UHMWPE@SiO2 is also high. δ The dielectric loss value was the lowest among all composite media. This indicates that the SiO2 coating layer improved interfacial polarization without introducing significant dielectric loss. This is because the SiO2 layer effectively improved the interfacial bonding between the fiber and epoxy resin, reducing charge accumulation and scattering caused by interfacial defects, thereby lowering dielectric loss. The AC conductivity test results were basically consistent with the above analysis; all composite media maintained a low conductivity level, which can well meet the requirements of electronic packaging.

[0090] Figure 11 Differential scanning calorimetry (DSC) curves of the prepared UHMWPE fibers and silica-coated UHMWPE fibers are shown. Based on crystallinity (… X c The formula for calculating ) is: X c =Δ H m / Δ H 0m ×100%, where: Δ H m The enthalpy of melting from the DSC sample; Δ H0m The standard enthalpy of fusion for fully crystalline UHMWPE is typically taken as 293 J / g, which is the theoretical enthalpy of fusion when UHMWPE is fully crystallized. The crystallinity of both UHMWPE and UHMWPE@SiO2 is 68.3%. The high crystallinity of the fiber is a necessary condition for its high thermal conductivity, providing a physical basis for the high thermal conductivity of the composite medium.

[0091] Figure 12 The diagram illustrates the principle of enhancing the thermal conductivity of high thermal conductivity epoxy resin-based composite media by preparing UHMWPE fibers and silica-coated UHMWPE fibers, respectively. The coating effectively fills the gap between UHMWPE and epoxy resin, thus achieving a significant increase in thermal conductivity.

[0092] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A core-shell fiber-reinforced epoxy resin composite material, characterized in that, The raw materials include: modified polyethylene fiber and epoxy resin; The modified polyethylene fiber includes ultra-high molecular weight polyethylene fiber, and the surface of the ultra-high molecular weight polyethylene fiber is coated with a silica nanolayer.

2. The core-shell fiber-reinforced epoxy resin composite material according to claim 1, characterized in that, The method for preparing the modified polyethylene fiber includes the following steps: Ultra-high molecular weight polyethylene fiber, alkaline catalyst, template agent and silicon source are mixed in a solvent and subjected to condensation reaction to obtain ultra-high molecular weight polyethylene fiber coated with silica nanolayer. The modified polyethylene fiber was prepared by modifying the ultra-high molecular weight polyethylene fiber coated with a silica nanolayer using a silane coupling agent.

3. The core-shell fiber-reinforced epoxy resin composite material according to claim 2, characterized in that, The silicon source includes at least one of tetramethoxysilane, tetraethoxysilane, trimethylethoxysilane, ethyltriethoxysilane, and propyltriethoxysilane.

4. The core-shell fiber-reinforced epoxy resin composite material according to claim 2, characterized in that, The alkaline catalyst includes at least one of ammonia and sodium hydroxide; And / or, the template agent comprises at least one of hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, didodecyldimethylammonium chloride, and didodecyldimethylammonium bromide.

5. The core-shell fiber-reinforced epoxy resin composite material according to claim 2, characterized in that, The reaction temperature for the condensation reaction is 50-80℃; And / or, the reaction time of the condensation reaction is 8-16 h.

6. The core-shell fiber-reinforced epoxy resin composite material according to claim 2, characterized in that, The ratio of ultra-high molecular weight polyethylene fiber to silicon source is 1 g:(2-6) mL.

7. The core-shell fiber-reinforced epoxy resin composite material according to claim 2, characterized in that, The types of silane coupling agents include at least one of aminosilanes, epoxysilanes, vinylsilanes, mercaptosilanes, and methacryloxysilanes.

8. The method for preparing the core-shell fiber-reinforced epoxy resin composite material according to any one of claims 1-7, characterized in that, The process includes the following steps: softening / melting epoxy resin, mixing the softened / melted epoxy resin with a curing agent, an accelerator and modified polyethylene fiber, and carrying out a curing reaction to obtain the core-shell fiber reinforced epoxy resin composite material.

9. The method for preparing the core-shell fiber-reinforced epoxy resin composite material according to claim 8, characterized in that, The modified polyethylene fiber accounts for 4%-15% of the mass percentage in the core-shell fiber reinforced epoxy resin composite material.

10. The method for preparing the core-shell fiber-reinforced epoxy resin composite material according to claim 8, characterized in that, The curing temperature is 60-150℃.

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