Diamond / boron nitride high-temperature-resistant and heat-conducting composite material and preparation method thereof

Abstract

The application discloses a kind of diamond / boron nitride high-temperature-resistant heat-conducting composite materials and preparation method, belong to high-temperature-resistant heat-conducting material technical field;The application adopts "liquid silane coupling agent+solid titanate coupling agent" sequential addition process, in combination with liquid nitrogen low-temperature dry type ball milling technology, realizes the selective surface modification of diamond / hexagonal boron nitride double filler, and constructs the high-temperature-resistant gradient interface structure of "filler-coupling agent-matrix";The prepared composite material is under 50wt% filler filling amount, room temperature thermal conductivity is greater than or equal to 2.0W / (m·K), and in the high temperature range of 25-200 DEG C, thermal conductivity rises with temperature rising, tensile strength is greater than or equal to 80MPa, notched impact strength is greater than or equal to 6kJ / m², and the maximum long-term use temperature can reach 310 DEG C;Solve the core problems such as poor interface compatibility, high-temperature interface failure and thermal conductivity attenuation in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature resistant thermally conductive engineering plastics technology, specifically relating to a diamond / boron nitride high-temperature resistant thermally conductive composite material and its preparation method. Background Technology

[0002] As electronic devices evolve towards higher power, miniaturization, and integration, their thermal management becomes increasingly critical, especially in fields such as aerospace, new energy vehicles, and military electronics, where devices operate at temperatures above 150°C for extended periods. While general-purpose ultra-high temperature engineering plastics (such as PEEK, PI, and PBI, with long-term operating temperatures ≥180°C) possess excellent heat resistance and mechanical properties, their thermal conductivity is extremely low (0.2-0.5 W / (m·K)). Therefore, thermally conductive composite materials must be prepared by filling them with highly thermally conductive fillers.

[0003] Diamond and hexagonal boron nitride (h-BN) are ideal composite fillers: diamond has extremely high thermal conductivity, while h-BN has both high thermal conductivity and excellent electrical insulation. However, existing technologies suffer from the following core defects: poor interface compatibility: the inorganic filler surface is inert and has weak bonding with the organic matrix, resulting in high interfacial thermal resistance and easy interface failure under high-temperature conditions, leading to a significant decrease in thermal conductivity; deterioration of processing and mechanical properties: high filler content easily leads to agglomeration, causing a sharp drop in melt fluidity and becoming stress concentration points, severely deteriorating the mechanical properties of the composite material; defects in modification processes: traditional wet processes use large amounts of organic solvents, resulting in severe pollution and residual impurities affecting temperature resistance; ordinary dry ball milling easily leads to the volatilization and self-agglomeration of coupling agents, uneven modification, and may damage the filler lattice; lack of selective modification schemes: existing composite coupling agent technologies mostly involve simultaneous addition without designing for the differences in surface chemical properties between diamond and boron nitride, leading to grafting competition and poor synergistic effect; therefore, a green, efficient, and high-temperature resistant stable interface filler modification method and a high-performance thermally conductive composite material are proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a liquid nitrogen dry ball milling modified diamond / boron nitride dual-filler high-temperature thermally conductive composite material and its preparation method, so as to achieve uniform dispersion and strong interfacial bonding of fillers in an ultra-high temperature resistant matrix, solve the problems of interfacial failure and thermal conductivity decay at high temperatures, and enable the composite material to have high thermal conductivity, excellent mechanical properties, good processability and high-temperature thermal conductivity stability.

[0005] To achieve the above objectives, the present invention provides a method for preparing a diamond / boron nitride high-temperature resistant and thermally conductive composite material, comprising the following steps: Step 1: Pre-treatment of dual-filler gradation: Micron-sized diamond and nano-sized diamond are graded at a mass ratio of 68:24 to obtain graded diamond; micron-sized hexagonal boron nitride and nano-sized hexagonal boron nitride are graded at a mass ratio of 57:35 to obtain graded hexagonal boron nitride; the graded diamond and graded hexagonal boron nitride are mixed evenly at a mass ratio of 35:57 to obtain diamond / boron nitride dual filler; Step 2, Selective modification by dry ball milling with liquid nitrogen: First, add liquid silane coupling agent to the double packing material obtained in Step 1, and premix at room temperature for 30 minutes until the packing material is uniformly wetted; then add the ground and refined solid titanate coupling agent, and continue to premix for 12 minutes to obtain a mixture; put the mixture into a ball mill jar, evacuate it, and then purge it with high-purity nitrogen three times, immerse it in liquid nitrogen for precooling for 5~10 minutes until the material temperature drops to -180~196℃, and then perform intermittent high-energy dry ball milling for a total ball milling time of 36 hours. After the ball milling is completed, take out the material and vacuum dry it to obtain the surface-modified double packing material; Step 3, melt composite molding: The surface-modified double filler obtained in Step 2 is mixed with the matrix resin at a mass ratio of 36:47, and then added to a twin-screw extruder for melt extrusion. After water cooling / air cooling and pelletizing, composite granules are obtained. After the composite granules are fully dried, they are molded by injection molding machine or compression molding machine to obtain the diamond / boron nitride double filler@high temperature thermally conductive composite material. The matrix resin is polyamide 6 (PA6), or any one of polybenzimidazole (PBI), thermoplastic polyimide (PI), polyamide-imide (PAI), polyetheretherketone (PEEK), polyaryletherketone (PAEK), polyetherketoneketone (PEKK), polyetherketone (PEK), polyetherimide (PEI), polyphenylene sulfide (PPS), polyphenylene sulfone (PPSU), polyethersulfone (PES), polysulfone (PSF), liquid crystal polymer (LCP), polytetrafluoroethylene (PTFE), perfluoroalkoxy resin (PFA), and polyethylene naphthalate (PEN).

[0006] Further, in step two, the micron-sized diamond has a particle size of 1~150μm, and the nano-sized diamond has a particle size of 50~500nm; the micron-sized hexagonal boron nitride has a particle size of 1~30μm, and the nano-sized hexagonal boron nitride has a particle size of 200~500nm; the mass ratio of graded diamond to graded hexagonal boron nitride is 4:6. Through multi-particle-size gradation, small-particle-size fillers can fill the gaps between large-particle-size fillers, reducing the porosity of the filler packing and increasing the packing density. This is beneficial for constructing a continuous and dense three-dimensional thermally conductive network, and also meets the filling and dispersion requirements of high-viscosity melts of ultra-high temperature engineering plastics.

[0007] Further, in step two, the liquid silane coupling agent is any one of 3-aminopropyltriethoxysilane (KH-550), methyltrimethoxysilane (MTMS), and γ-glycidoxypropyltrimethoxysilane (KH-560); the solid titanate coupling agent is any one of triisostearoyl titanate isopropyl ester (TC-114) and isopropyltrioleoyloxytitanate.

[0008] Further, in step two, the mass ratio of the silane coupling agent to the titanate coupling agent is 68:24, preferably 7:3; the total addition amount of the two coupling agents is 0.1~15wt% of the total mass of the diamond / boron nitride dual filler. At this ratio, the silane coupling agent can fully achieve hydroxylation modification of the diamond surface, and the titanate coupling agent can precisely bind to the boron active sites on the boron nitride surface. The two complement each other, without competitive reactions, and the constructed interface structure is suitable for the high-temperature processing and use conditions of ultra-high temperature engineering plastics.

[0009] Further, in step two, the solid titanate coupling agent is ground to a particle size ≤100μm before use; the ball milling process parameters are: ball-to-material mass ratio 10:90:1, grinding balls are Φ5mm and Φ10mm zirconia grinding balls mixed at a mass ratio of 1:1, ball milling speed 100~600rpm, liquid nitrogen replenishment is paused every 10 minutes of ball milling, and the temperature inside the tank is maintained below -150℃ and the oxygen content below 100ppm throughout the process. The low-temperature environment of liquid nitrogen can effectively inhibit the volatilization and self-polymerization of the coupling agent, and at the same time, the low-temperature embrittlement effect makes the filler easier to peel off and break, exposing more active sites and improving the efficiency of mechanochemical grafting; the oxygen-free environment can avoid oxidation of the filler and coupling agent during high-energy ball milling, ensuring the high-temperature stability of the modified filler.

[0010] Furthermore, in step three, the mass ratio of the surface-modified double filler to the matrix resin is 45:56; the matrix resin needs to be vacuum dried before melt processing, and the drying temperature is set to 80~200℃ according to the temperature resistance characteristics of the matrix, and the drying time is 6~12h, so as to fully remove the moisture in the resin, avoid the hydrolytic degradation of the resin during high-temperature processing, and ensure the stability of the composite material performance.

[0011] Furthermore, in step three, the processing temperature of the twin-screw extruder is adjusted according to the type of matrix resin, specifically: PA6 processing temperature 220~250℃, PEN processing temperature 280~300℃, PPS processing temperature 280~300℃, LCP processing temperature 290~320℃, PES / PSF / PPSU processing temperature 320~350℃, PEI processing temperature 340~370℃, PAI processing temperature 350~380℃, PEEK / PEKK / PEK / PAEK processing temperature 360~400℃, thermoplastic PI processing temperature 380~410℃, PBI processing temperature 400~430℃, and PTFE / PFA processing temperature 350~380℃.

[0012] Furthermore, in step three, the injection molding process parameters are adjusted according to the type of matrix resin, the barrel temperature is matched with the extrusion temperature, the mold temperature is 60~200℃, the injection pressure is 80~120MPa, and the holding pressure is 40~70MPa; for difficult-to-process matrices such as PTFE and ultra-high molecular weight PI, compression molding is adopted, with a compression molding temperature of 360~420℃ and a compression molding pressure of 10~20MPa.

[0013] This invention also provides a diamond / boron nitride high-temperature resistant thermally conductive composite material, prepared by the above-described method; in the composite material, surface-modified diamond / boron nitride dual fillers are uniformly dispersed in an ultra-high temperature resistant engineering plastic matrix to form a continuous three-dimensional thermally conductive network; the composite material, with a filler content of 50wt%, has a room temperature thermal conductivity ≥1.9W / (m·K), and the thermal conductivity increases with temperature in the range of 25~200℃; tensile strength ≥80MPa; notched impact strength of simply supported beam ≥6kJ / m²; heat distortion temperature (1.82MPa) ≥120℃; and a maximum long-term service temperature of up to 310℃.

[0014] Compared with the prior art, the beneficial effects of the present invention are: (1) In view of the difference in surface chemical properties between diamond and boron nitride, the invention designed a sequential addition process of "liquid silane first, then solid titanate", which realizes the hydroxylation modification of diamond by silane and the interface optimization of boron nitride by titanate. The two have no competitive reaction and complement each other. At the same time, the constructed gradient interface structure can form strong chemical bonds with 16 kinds of ultra-high temperature resistant engineering plastics, which solves the core problem of interface debonding and performance failure under high temperature conditions in traditional modification processes, and greatly improves the high temperature stability of composite materials.

[0015] (2) The invention adopts a dry process throughout, without water, organic solvents, or acid and alkali catalysts, which completely avoids the environmental pollution and solvent recovery problems of wet process. At the same time, it eliminates the degradation of the high temperature resistance and insulation performance of ultra-high temperature engineering plastics by solvent and acid and alkali ion residues, and perfectly meets the requirements of high purity and high stability of materials in aerospace, military electronics and other fields.

[0016] (3) In this invention, the synergistic effect of liquid nitrogen low temperature and high energy ball milling greatly improves the grafting efficiency of coupling agent, and the utilization rate of coupling agent is close to 100%. The surface energy of the modified filler is significantly reduced, and it can be uniformly dispersed in high viscosity ultra-high temperature engineering plastic melts such as PEEK, PI, and PBI without obvious agglomeration. This greatly improves the processing fluidity of the melt under high filling and reduces the molding difficulty.

[0017] (4) With a filler content of 50wt%, the room temperature thermal conductivity of this invention can reach 1.9~2.5W / (m·K), which is more than 500% higher than that of pure ultra-high temperature resistant engineering plastics and more than 80% higher than that of unmodified filler-filled composite materials. It has achieved a breakthrough in realizing the positive temperature coefficient characteristic of thermal conductivity increasing with temperature in the range of 25~200℃, which solves the fatal defect of traditional polymer-based thermally conductive composite materials that "the higher the temperature, the worse the heat dissipation capacity". The heat dissipation performance under high temperature conditions is significantly superior, which is perfectly suited to the application scenario where the temperature rises and the heat dissipation demand increases simultaneously when high-power devices are working. At the same time, the tensile strength of the composite material is maintained at 80~95MPa and the notched impact strength of the simply supported beam is maintained at 68kJ / m², which perfectly solves the contradiction between "increased thermal conductivity and deterioration of mechanical and processing performance" in traditional high-filler thermally conductive composite materials. It has high thermal conductivity, excellent mechanical properties, processing performance and ultra-high temperature stability, and is suitable for different extreme working conditions of 16 kinds of ultra-high temperature resistant engineering plastics.

[0018] (5) The invention covers 16 mainstream ultra-high temperature resistant engineering plastics in the matrix, providing a wide range of protection and adapting to the application requirements of different temperature resistance levels. The equipment used is all general industrial equipment, with stable and controllable process parameters, simple procedures, high production efficiency, and low cost. It can realize continuous large-scale production and has extremely high economic value and broad application prospects. Attached Figure Description

[0019] Figure 1 This is a process flow diagram for preparing the diamond / boron nitride dual-filler@high-temperature thermally conductive composite material described in this invention; Figure 2 The Fourier transform infrared (FTIR) spectra of the modified fillers obtained in Example 1 and Comparative Example 1 are compared. Figure 3 The X-ray photoelectron spectroscopy (XPS) B1s peak pattern of the modified filler obtained in Example 1; Figure 4 The images show the impact fracture surface scanning electron microscope (SEM) morphology of the composite materials obtained in Example 1 and Comparative Example 1. Figure 5 A bar chart comparing the thermal conductivity of the composite materials obtained in the examples and comparative examples under different filler loading amounts; Figure 6 The graph shows the trend of thermal conductivity variation of the composite materials obtained in Example 1 and Comparative Example 1 at different temperatures. Detailed Implementation

[0020] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0021] The following examples will further illustrate the above-mentioned content of the present invention in detail. However, it should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following examples. All technologies implemented based on the above-mentioned content of the present invention are within the scope of the present invention.

[0022] Micron-sized diamond: particle size 1~5μm, purity ≥99.9%, commercially available; Nanoscale diamond: particle size 50~200nm, purity ≥99.9%, commercially available; Micron-sized hexagonal boron nitride: particle size 1~3μm, purity ≥99.9%, commercially available; Nano-sized hexagonal boron nitride: particle size 200~500nm, purity ≥99.9%, commercially available; Liquid silane coupling agent: KH-550 (3-aminopropyltriethoxysilane), commercially available; Solid titanate coupling agent: TC-114 (isopropyl triisostearoyl titanate), commercially available; Matrix resins: PA6 (relative viscosity 2.6, melt index 20g / 10min), PEN, PPS, LCP, PES, PPSU, PEI, PAI, PEEK, PEKK, thermoplastic PI, PBI, PTFE, all of which are commercially available industrial-grade ultra-high temperature resistant engineering plastics.

[0023] Planetary high-energy ball mill: Nanjing University Instrument Factory; Twin-screw extruder: Nanjing Keya Chemical Equipment Co., Ltd., model SHJ-20 (customized model for ultra-high temperature resistance, maximum processing temperature 450℃); Injection molding machine: Ningbo Haitian Plastics Machinery Group Co., Ltd., Model MA1200 (High Temperature Customized Model); Flat vulcanizing molding press: Shanghai No.1 Rubber Machinery Factory, model XLB-D; Laser flare thermal conductivity tester: Netzsch GmbH, Germany, model LFA467 (capable of testing at varying temperatures from room temperature to 300°C). Universal electronic testing machine: Shenzhen Xin Sansi Materials Testing Co., Ltd., model CMT5105; Simply supported beam impact testing machine: Chengde Jinjian Testing Instruments Co., Ltd., model XJJ-5; Heat distortion Vicat softening point tester: Netzsch GmbH, Germany, model HDT / Vicat 312; Scanning electron microscope (SEM): Hitachi, Japan, model SU8010; Fourier transform infrared spectrometer (FTIR): Thermo Fisher Scientific, USA, model Nicolet iS50; X-ray photoelectron spectroscopy (XPS): Thermo Fisher Scientific, USA, model ESCALAB 250Xi.

[0024] Thermal conductivity test: The laser flash method was used, and the test temperatures were 25℃, 150℃ and 200℃. The sample size was Φ12.7mm×1mm. Each sample was tested 5 times at each temperature point, and the average value was taken.

[0025] Mechanical property testing: Tensile properties were tested according to GB / T 1040.2-2006, with a tensile rate of 50 mm / min; Impact properties were tested according to GB / T 1843-2008, using a simply supported beam notched impact specimen with a notch radius of 0.25 mm.

[0026] Thermal stability test: Heat distortion temperature (HDT) was tested according to GB / T 1634.2-2004, with a test load of 1.82 MPa; Thermogravimetric analysis (TGA) was used to test the thermal decomposition temperature of the composite material under nitrogen atmosphere at a heating rate of 10℃ / min.

[0027] Microscopic morphology testing: The morphology of the impact fracture surface of the composite material was observed using SEM. The sample fracture surface was treated with gold sputtering.

[0028] Surface functional groups and chemical bonding tests: FTIR and XPS were used to test and analyze the modified filler to verify the grafting effect and chemical bonding state of the coupling agent. Example

[0029] This embodiment provides a diamond / boron nitride high-temperature resistant and thermally conductive composite material, the preparation method of which includes the following steps: Step 1: Pretreatment of dual-filler gradation: Mix 2.8g of micron-sized diamond with 1.2g of nano-sized diamond to obtain 4g of graded diamond; mix 3.6g of micron-sized hexagonal boron nitride with 2.4g of nano-sized hexagonal boron nitride to obtain 6g of graded hexagonal boron nitride; mix the graded diamond and graded hexagonal boron nitride evenly to obtain 10g of diamond / boron nitride dual filler; Step 2: Selective modification by dry ball milling with liquid nitrogen: First, add 0.07g of liquid KH-550 to the above dual-filler mixture and premix at room temperature for 1 min until the filler is uniformly wetted; then add 0.03g of solid TC-114 ground to a particle size ≤100μm, and continue premixing for 1 min to obtain a mixture; load the mixture into a 500mL zirconia ball mill jar, add Φ5mm and Φ10mm zirconia grinding balls, with a ball-to-material ratio of 12:1 and a grinding ball mass ratio of 1:1; seal the ball mill jar and vacuum pump. The pressure was lowered to -0.1 MPa, and high-purity nitrogen was introduced to purge the material three times. The entire ball milling jar was then immersed in liquid nitrogen for pre-cooling for 6 minutes until the material temperature dropped to -190℃. Subsequently, intermittent ball milling was performed at a speed of 500 rpm, with a 2-minute pause in liquid nitrogen replenishment every 10 minutes of ball milling. The total ball milling time was 4 hours, and the temperature inside the jar was maintained below -150℃ and the oxygen content below 100 ppm throughout the process. After ball milling, the material was removed and placed in an 80℃ vacuum drying oven for 10 hours to obtain surface-modified double filler. Step 3: Melt Composite Molding: Take 500g of the above-mentioned surface-modified double filler and 500g of... PEEK resin (5:5 by mass, 50wt% filler) was mixed uniformly at high speed. The PEEK resin was pre-dried under vacuum at 150℃ for 12 hours. The mixture was then added to a twin-screw extruder for melt extrusion. The temperatures of each zone of the twin screw were: zone 1 360℃, zone 2 370℃, zone 3 380℃, zone 4 385℃, zone 5 380℃, and die head temperature 375℃. The screw speed was 280 rpm, and the feeding frequency was 12 Hz. The extruded strip was air-cooled and pelletized to obtain composite granules. The composite granules were dried in a vacuum drying oven at 150℃ for 10 hours, and then injection molded in a high-temperature injection molding machine. The injection molding process parameters were: barrel temperature 370~390℃, mold temperature 180℃, injection pressure 100MPa, holding pressure 60MPa, holding time 8s, and cooling time 20s. The diamond / boron nitride dual-filler@PEEK thermally conductive composite material, designated S1, was obtained. Example

[0030] In Example 1, the matrix resin in step 3 was replaced with thermoplastic PI resin, and the filler to PI mass ratio remained at 5:5. The PI resin was vacuum dried at 200°C for 12 hours in advance. The twin-screw extrusion temperature was adjusted to 380-410°C, the injection molding temperature was adjusted to 390-420°C, and the mold temperature was 200°C. The remaining process parameters were completely consistent with those in Example 1, and the resulting composite material was designated as S2. Example

[0031] In Example 1, the matrix resin in step 3 was replaced with PBI resin, and the mass ratio of filler to PBI remained at 5:5. The PBI resin was pre-dried in vacuum at 200°C for 12 hours. A compression molding process was adopted with a molding temperature of 420°C, a molding pressure of 15 MPa, and a holding time of 15 minutes. The composite material was then cooled and demolded. All other process parameters were completely consistent with those in Example 1. The resulting composite material was designated as S3. Example

[0032] In Example 1, the matrix resin in step 3 was replaced with PEI resin, and the filler to PEI mass ratio remained at 5:5. The PEI resin was pre-dried in vacuum at 150°C for 12 hours. The twin-screw extrusion temperature was adjusted to 340-370°C, the injection molding temperature was adjusted to 350-370°C, and the mold temperature was 160°C. The remaining process parameters were completely consistent with those in Example 1, and the resulting composite material was designated as S4. Example

[0033] In Example 1, the matrix resin in step 3 was replaced with PPS resin, and the filler to PPS mass ratio remained at 5:5. The PPS resin was pre-dried in vacuum at 120°C for 8 hours. The twin-screw extrusion temperature was adjusted to 280-300°C, the injection molding temperature was adjusted to 290-310°C, and the mold temperature was 120°C. The remaining process parameters were completely consistent with those in Example 1, and the resulting composite material was designated as S5. Example

[0034] In step three of Example 1, the mass ratio of surface-modified double filler to PEEK resin was modified to 4:6 (filler loading 40wt%), and the remaining process parameters were completely consistent with those of Example 1. The resulting composite material was designated as S6. Example

[0035] In step three of Example 1, the mass ratio of surface-modified double filler to PEEK resin was modified to 6:4 (filler loading amount 60wt%), and the remaining process parameters were completely consistent with those of Example 1. The resulting composite material was designated as S7. Example

[0036] The amount of coupling agent added in step two of Example 1 was modified to 1.2wt%, including 0.084g of KH-550 and 0.036g of TC-114. The remaining process parameters were completely consistent with those of Example 1, and the resulting composite material was numbered S8.

[0037] In step two of Example 1, without adding any coupling agent or performing liquid nitrogen dry ball milling modification, the unmodified diamond / boron nitride dual filler was directly compounded with PEEK resin at a mass ratio of 5:5. All other process parameters were completely consistent with those in Example 1. The resulting composite material was designated as D1.

[0038] In step two of Example 1, KH-550 and TC-114 were added to the dual filler simultaneously without any sequential addition steps. The remaining process parameters were completely consistent with those of Example 1, and the resulting composite material was designated as D2.

[0039] In step two of Example 1, TC-114 premix was added first, followed by KH-550 premix. The remaining process parameters were completely consistent with those of Example 1. The resulting composite material was designated as D3.

[0040] In Example 1, step 2 was performed without liquid nitrogen cooling, and dry ball milling was carried out at room temperature and pressure. All other process parameters were exactly the same as in Example 1, and the resulting composite material was designated as D4.

[0041] In step two of Example 1, only 0.1g of KH-550 was added, and TC-114 was not added. All other process parameters were completely consistent with those of Example 1. The resulting composite material was designated as D5.

[0042] In step two of Example 1, only 0.1g of TC-114 was added, and KH-550 was not added. All other process parameters were completely consistent with those of Example 1. The resulting composite material was designated as D6.

[0043] In this embodiment, the existing mainstream wet modification process is adopted: 10g of diamond / boron nitride dual filler is added to 100mL of anhydrous ethanol, ultrasonically dispersed for 30min, 0.07g of KH-550 and 0.03g of TC-114 are added, the pH is adjusted to 4~5 with glacial acetic acid, and the reaction is stirred in a 60℃ water bath for 4h. After centrifugation and washing with anhydrous ethanol 3 times, the mixture is vacuum dried at 80℃ for 12h to obtain the wet modified filler. Subsequently, the modified filler is compounded with PEEK resin at a mass ratio of 5:5. The remaining process parameters are completely consistent with those in Example 1. The composite material prepared is numbered D7.

[0044] Table 1. Comprehensive performance test results of the composite materials obtained in the examples and comparative examples.

[0045] The test results in Table 1 clearly show that: (1) The composite materials obtained in Examples S1 to S8 of the present invention have a comprehensive performance that is far superior to each comparative example: Taking the optimal example S1 as an example, with a filler content of 50wt%, the room temperature thermal conductivity reaches 2.18W / (m·K), which is 651.7% higher than that of pure PEEK, 83.2% higher than that of the unmodified comparative example D1, and 26.7% higher than that of the conventional wet-modified comparative example D7; at the same time, the tensile strength of S1 remains at 88.7MPa, which is basically the same as that of pure PEEK, the notched impact strength reaches 7.5kJ / m², and the heat distortion temperature is slightly improved, which perfectly solves the industry problem of "increased thermal conductivity and deterioration of mechanical properties" under high filler content of ultra-high temperature engineering plastics.

[0046] (2) Comparing Example S1 with Comparative Examples D2 and D3, it can be seen that the sequential addition of coupling agent has a great impact on the performance of composite material. Both synchronous and reverse addition will cause competition for active sites of coupling agent, making selective grafting impossible, resulting in a decrease in coupling agent grafting efficiency, weakening the interfacial bonding force between filler and matrix, and ultimately a significant decrease in the thermal conductivity and mechanical properties of composite material. This verifies the necessity and superiority of the sequential addition process of "silane first, titanate later" in this invention.

[0047] (3) Comparing Example S1 and Comparative Example D4, it can be seen that room temperature dry ball milling modification cannot suppress the self-polymerization and volatilization of coupling agent, resulting in low modification efficiency. At the same time, high-energy ball milling is prone to causing lattice damage to filler, introducing phonon scattering defects, and cannot achieve uniform dispersion of coupling agent, leading to a significant decrease in the thermal conductivity and mechanical properties of composite material. This verifies the core role of the liquid nitrogen low-temperature dry ball milling process of the present invention.

[0048] (4) Comparing Example S1 with Comparative Examples D5 and D6, it can be seen that: single coupling agent modification cannot meet the dual filler modification requirements of diamond and boron nitride, single silane has poor interface modification effect on boron nitride, and single titanate cannot achieve efficient hydroxylation. All of these will lead to high interfacial thermal resistance. The overall performance of the composite material is far lower than the effect of sequential modification of the composite coupling agent of the present invention, which verifies the synergistic effect of the composite system of the present invention.

[0049] (5) Comparing Example S1 and Comparative Example D7, it can be seen that the traditional wet modification process not only has environmental pollution problems, but its modification effect is also far lower than that of the dry modification process of the present invention. In the wet process, the coupling agent is prone to self-polymerization, which cannot achieve selective grafting, and the residual solvent will affect the processing performance and high temperature resistance of PEEK, resulting in the overall performance of the composite material being inferior to that of the present invention.

[0050] (6) Examples S2 to S5 verified the universality of the process of the present invention for 16 kinds of ultra-high temperature resistant engineering plastics. For matrices with different temperature resistance levels such as PI, PBI, PEI, and PPS, the modified filler of the present invention can achieve excellent interfacial bonding. The prepared composite material has high thermal conductivity, high mechanical properties and high temperature resistance, covering the long-term service temperature requirements from 110℃ to 310℃, with a wide protection range and adaptable to the application requirements of different extreme working conditions.

[0051] Table 2. Variable-temperature thermal conductivity test results of the composite materials obtained in Example 1 and Comparative Example 1.

[0052] As can be seen from the test results in Table 2, the composite material obtained in Example S1 of this invention exhibits breakthrough high-temperature thermal conductivity: within the test range of 25~200℃, the thermal conductivity continues to increase with the temperature, and the thermal conductivity at 200℃ is 9.17% higher than that at room temperature of 25℃, which is completely different from the general rule that the thermal conductivity of traditional thermally conductive composite materials decreases significantly at high temperatures; while the unmodified comparative example D1 shows a significant decrease in thermal conductivity of 31.09% at 200℃ compared to room temperature, and its high-temperature heat dissipation performance deteriorates sharply.

[0053] The test results fully demonstrate that the strong bonding gradient interface of "filler-coupling agent-matrix" constructed by this invention, along with the continuous and interconnected three-dimensional thermal conductive network, not only completely solves the core problems of interface debonding and increased phonon scattering under high-temperature conditions, but also achieves a positive improvement in thermal conductivity at high temperatures. It is perfectly suited to the application scenarios where the temperature rises and the heat dissipation demand increases simultaneously when high-power devices are working, and has extremely high practical engineering application value.

[0054] (1) FTIR test results: The modified filler obtained in Example S1 has a compressibility of 3200~3500 cm⁻¹ - A strong and broad hydroxyl stretching vibration peak appeared at ¹, at 1100 cm⁻¹. - The characteristic absorption peak of the Si–O–C covalent bond appeared at ¹, at 1380 cm⁻¹. - The characteristic absorption peak of Ti←B coordination bond appeared at position ¹; while the unmodified filler of Comparative Example D1 did not have the above characteristic peak, and the intensity of the above characteristic peak of Comparative Examples D2 and D3 was significantly reduced, proving that the modification process of the present invention can achieve efficient grafting and selective chemical bonding of coupling agent.

[0055] (2) XPS test results: In the B1s peak spectrum of the modified filler obtained in Example S1, a characteristic peak of Ti←B coordination bond appeared at 190.8eV, and a characteristic peak of Si–O–C covalent bond appeared in the Si 2p peak spectrum, which further verified the selective grafting mechanism of the present invention.

[0056] (3) SEM morphology test results: In the impact fracture of the composite material obtained in Example S1, the filler was uniformly dispersed in the PEEK matrix without obvious agglomeration. The interface between the filler and the matrix was tightly bonded, with no obvious interface gaps or filler pull-out. In contrast, in the impact fracture of Comparative Example D1, the filler was severely agglomerated, with obvious interface gaps between it and the matrix. A large amount of filler was pulled out of the matrix, proving that the modification process of the present invention can significantly improve the interface compatibility and dispersibility between the filler and the ultra-high temperature resistant matrix.

[0057] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0058] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a diamond / boron nitride high-temperature resistant and thermally conductive composite material, characterized in that, Includes the following steps: Step 1: Pre-treatment of dual-filler gradation: Micron-sized diamond and nano-sized diamond are graded at a mass ratio of 68:24 to obtain graded diamond; micron-sized hexagonal boron nitride and nano-sized hexagonal boron nitride are graded at a mass ratio of 57:35 to obtain graded hexagonal boron nitride; the graded diamond and graded hexagonal boron nitride are mixed evenly at a mass ratio of 35:57 to obtain diamond / boron nitride dual filler; Step 2, Selective modification by dry ball milling with liquid nitrogen: First, add liquid silane coupling agent to the double packing material obtained in Step 1, and premix at room temperature for 30 minutes until the packing material is uniformly wetted; then add the ground and refined solid titanate coupling agent, and continue to premix for 30 minutes to obtain a mixture; put the mixture into a ball mill jar, evacuate it, and then purge it with high-purity nitrogen three times, immerse it in liquid nitrogen for precooling for 10 minutes until the material temperature drops to -180-196℃, and then perform intermittent high-energy dry ball milling for a total ball milling time of 36 hours. After the ball milling is completed, take out the material and vacuum dry it to obtain the surface-modified double packing material; Step 3, melt composite molding: The surface-modified double filler obtained in Step 2 is mixed with the matrix resin at a mass ratio of 36:47, and then added to a twin-screw extruder for melt extrusion. After water cooling / air cooling and pelletizing, composite granules are obtained. After the composite granules are fully dried, they are molded by injection molding machine or compression molding machine to obtain the diamond / boron nitride double filler@high temperature thermally conductive composite material. The matrix resin is polyamide 6 (PA6), or any one of polybenzimidazole (PBI), thermoplastic polyimide (PI), polyamide-imide (PAI), polyetheretherketone (PEEK), polyaryletherketone (PAEK), polyetherketoneketone (PEKK), polyetherketone (PEK), polyetherimide (PEI), polyphenylene sulfide (PPS), polyphenylene sulfone (PPSU), polyethersulfone (PES), polysulfone (PSF), liquid crystal polymer (LCP), polytetrafluoroethylene (PTFE), perfluoroalkoxy resin (PFA), and polyethylene naphthalate (PEN).

2. The method for preparing a diamond / boron nitride high-temperature resistant and thermally conductive composite material according to claim 1, characterized in that, In step one, the particle size of the micron-sized diamond is 1~150μm, and the particle size of the nano-sized diamond is 5-500nm; the particle size of the micron-sized hexagonal boron nitride is 1~30μm, and the particle size of the nano-sized hexagonal boron nitride is 200~500nm; the mass ratio of graded diamond to graded hexagonal boron nitride is 4:

6.

3. The method for preparing a diamond / boron nitride high-temperature resistant and thermally conductive composite material according to claim 2, characterized in that, In step two, the liquid silane coupling agent is any one of 3-aminopropyltriethoxysilane (KH-550), methyltrimethoxysilane (MTMS), and γ-glycidoxypropyltrimethoxysilane (KH-560); the solid titanate coupling agent is any one of triisostearoyl titanate isopropyl ester (TC-114) and isopropyltrioleoyloxytitanate.

4. The method for preparing a diamond / boron nitride high-temperature resistant and thermally conductive composite material according to claim 3, characterized in that, In step two, the mass ratio of the silane coupling agent to the titanate coupling agent is 68:24, preferably 7:3; the total amount of the two coupling agents added is 0.1~15wt% of the total mass of the diamond / boron nitride dual filler.

5. The method for preparing a diamond / boron nitride high-temperature resistant and thermally conductive composite material according to claim 4, characterized in that, In step two, the solid titanate coupling agent is ground to a particle size ≤100μm before use; the ball milling process parameters are: ball-to-material mass ratio 10:90:1, grinding balls are Φ5mm and Φ10mm zirconia grinding balls mixed at a mass ratio of 1:1, ball milling speed 100~600rpm, liquid nitrogen replenishment is paused every 10 minutes of ball milling, and the temperature inside the tank is maintained below -150℃ and the oxygen content is maintained below 100ppm throughout the process.

6. The method for preparing a diamond / boron nitride high-temperature resistant and thermally conductive composite material according to claim 5, characterized in that, In step three, the mass ratio of the surface-modified double filler to the matrix resin is 45:56; the matrix resin needs to be vacuum dried before melt processing, and the drying temperature is set to 80~200℃ according to the temperature resistance characteristics of the matrix, and the drying time is 6~12h.

7. The method for preparing a diamond / boron nitride high-temperature resistant and thermally conductive composite material according to claim 6, characterized in that, In step three, the processing temperature of the twin-screw extruder is adjusted according to the type of matrix resin, specifically: PA6 processing temperature 220~250℃, PEN processing temperature 280~300℃, PPS processing temperature 280~300℃, LCP processing temperature 290~320℃, PES / PSF / PPSU processing temperature 320~350℃, PEI processing temperature 340~370℃, PAI processing temperature 350~380℃, PEEK / PEKK / PEK / PAEK processing temperature 360~400℃, thermoplastic PI processing temperature 380~410℃, PBI processing temperature 400~430℃, and PTFE / PFA processing temperature 350~380℃.

8. The method for preparing a diamond / boron nitride high-temperature resistant and thermally conductive composite material according to claim 7, characterized in that, In step three, the injection molding process parameters are adjusted according to the type of matrix resin. The barrel temperature matches the extrusion temperature, the mold temperature is 60~200℃, the injection pressure is 80~120MPa, and the holding pressure is 40~70MPa. For difficult-to-process matrices such as PTFE and ultra-high molecular weight PI, compression molding is used, with a compression molding temperature of 360-420℃ and a compression molding pressure of 10~20MPa.

9. A diamond / boron nitride high-temperature resistant thermally conductive composite material, prepared using the preparation method of the diamond / boron nitride high-temperature resistant thermally conductive composite material according to any one of claims 1-8, characterized in that, In the composite material, surface-modified diamond / boron nitride dual fillers are uniformly dispersed in an ultra-high temperature resistant engineering plastic matrix to form a continuous three-dimensional thermally conductive network. With a filler content of 50wt%, the composite material has a room temperature thermal conductivity ≥1.9W / (m·K), and the thermal conductivity increases with temperature in the range of 25~200℃. The tensile strength is ≥80MPa, the notched impact strength of a simply supported beam is ≥6kJ / m², the heat distortion temperature (1.82MPa) is ≥120℃, and the maximum long-term service temperature can reach 310℃.

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