Highly thermally conductive core-shell structure material and preparation method thereof

Abstract

The application discloses a kind of high heat-conducting core-shell structure material and preparation method thereof, by functional design to core-shell structure, introduce and fix high heat-conducting network in shell layer, realize high heat-conducting, high toughness, high insulation and solvent resistance and other multi-performance balance under low filler global filling amount.The high heat-conducting core-shell structure material of the application is formed by the melt blending of heat-conducting core-shell functional particles and thermoplastic resin or thermoplastic elastomer matrix resin;The heat-conducting core-shell functional particles are crosslinked polyacrylate rubber as core, and the surface hydrophobic heat-conducting filler grafted with styrene-acrylonitrile copolymer and embedded in the shell layer by in-situ polymerization is as shell;The mass ratio of the core and shell is 45:55 to 30:70;The mass fraction of the heat-conducting core-shell functional particles in the high heat-conducting core-shell structure material is 20%-45%;The mass fraction of the surface hydrophobic heat-conducting filler in the shell layer is 30%-50%.

Description

Technical Field

[0001] This invention relates to a high thermal conductivity material and its preparation method, specifically to a high thermal conductivity core-shell structure material and its preparation method, belonging to the technical field of polymer composite materials and thermal management materials. Background Technology

[0002] As new energy vehicles develop towards ultra-high voltage and ultra-high current fast charging, liquid-cooled charging technology has become crucial for solving the heat dissipation bottleneck. The core component of liquid-cooled charging cables—the liquid-cooled tube—has its material properties that directly determine charging efficiency and safety. Currently, the thermal conductivity of mainstream liquid-cooled tube materials is generally low (0.2-0.5 W / (m•K)), making it unable to efficiently dissipate the large amount of Joule heat generated during charging at 900kW or even higher power. Simultaneously, to meet environmental protection requirements, new low-toxicity, biodegradable hydrocarbon coolants will gradually replace the traditional ethylene glycol / water system, posing a severe challenge to the solvent resistance performance (strength and elongation retention rate after long-term immersion) of liquid-cooled tube materials.

[0003] In existing technologies, the main method to improve the thermal conductivity of polymers is to fill the matrix resin with highly thermally conductive inorganic fillers (such as BN and Al2O3). However, while high filler content (typically >50%) increases thermal conductivity, it severely impairs the material's mechanical properties (especially toughness) and processing fluidity, and increases cable weight. On the other hand, preparing polymer alloys through blending technology is an effective way to obtain materials with comprehensive performance. Therefore, there is an urgent need to develop a new type of polymer material that can inherit the advantages of high toughness, good weather resistance, and easy processing of polymer materials, while fundamentally and significantly improving its intrinsic thermal conductivity through structural design, and simultaneously meeting the requirements for tolerance to new environmentally friendly coolants, in order to solve the technical bottleneck in the field of high-power liquid-cooled supercharging. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high thermal conductivity core-shell structure material and its preparation method. By functionalizing the core-shell structure and introducing and fixing a high thermal conductivity network in the shell, a balance of multiple properties such as high thermal conductivity, high toughness, high insulation and solvent resistance is achieved under low global filler content. At the same time, the preparation method is simple and easy to implement.

[0005] The technical solution of the present invention is as follows: The high thermal conductivity core-shell structure material of the present invention is formed by melt blending thermally conductive core-shell functional particles with thermoplastic resin or thermoplastic elastomer matrix resin; the thermally conductive core-shell functional particles have cross-linked polyacrylate rubber as the core and styrene-acrylonitrile copolymer grafted onto the shell and a surface hydrophobic thermally conductive filler embedded in the shell layer through in-situ polymerization as the shell; the mass ratio of the core to the shell is 45:55 to 30:70; the mass fraction of the thermally conductive core-shell functional particles in the high thermal conductivity core-shell structure material is 20%-45%; the mass percentage of the surface hydrophobic thermally conductive filler in the shell layer is 30%-50%.

[0006] A further technical solution of the high thermal conductivity core-shell structure material of the present invention is that the particle size of the cross-linked polyacrylate rubber core is 100-450 nm. A further technical solution is that the cross-linked polyacrylate rubber core is formed by copolymerization and cross-linking of one or more acrylate monomers and a cross-linking agent, and the degree of cross-linking of the cross-linked polyacrylate rubber core is 50%-90%.

[0007] A further technical solution to the high thermal conductivity core-shell structure material described above in this invention may be that the surface hydrophobic thermally conductive filler is one or a combination of boron nitride, alumina, and silicon carbide. A further technical solution is that the surface hydrophobic thermally conductive filler is preferably surface-modified with a silane coupling agent or a C12-C18 long-chain alkyl acid.

[0008] The method for preparing the high thermal conductivity core-shell structure material described above in this invention includes the following steps: S1. Using seed emulsion polymerization with nonionic emulsifier, a large-particle-size cross-linked polyacrylate rubber core pre-emulsion is synthesized through seed preparation and diameter expansion stages. S2. Disperse the surface hydrophobic thermally conductive filler in a mixed monomer solution of styrene and acrylonitrile to form a stable thermally conductive filler dispersion. S3. Mix the rubber core emulsion obtained in step S1, the thermally conductive filler dispersion obtained in step S2, the emulsifier, and the initiator, and carry out a graft copolymerization reaction by continuous drop-addition of pre-emulsion, so that the styrene-acrylonitrile copolymer is polymerized in situ on the surface of the rubber core, and simultaneously encapsulate / embed the surface hydrophobic thermally conductive filler in the shell to obtain a thermally conductive core-shell structure emulsion. S4. Demulsify, wash, and dry the emulsion obtained in step S3, or spray dry it to obtain thermally conductive core-shell structured powder. S5. The thermally conductive core-shell structure powder obtained in step S4 is melt-blended and granulated with thermoplastic resin or thermoplastic elastomer matrix resin through a screw extruder to obtain a high thermal conductivity core-shell structure material.

[0009] The preparation method of the high thermal conductivity core-shell structure material of the present invention further includes the following technical solution: in step S1, the nonionic emulsifier is alkylphenol polyoxyethylene ether or fatty acid polyoxyethylene ester; the diameter expansion stage adopts the continuous dripping method of pre-emulsion to control the monomer dripping rate and achieve precise control of the rubber core particle size.

[0010] The core concept of this invention lies in: ① Core Structure Design and Control: Using nonionic emulsifiers (such as OP-10) and seed emulsion polymerization technology, and through precise control of seed preparation and diameter expansion processes, cross-linked polyacrylate rubber cores with adjustable particle sizes (0.2-0.8 μm) and moderate cross-linking degrees (50%-90%) can be prepared. ② Functionalized Shell Construction: Innovatively, surface-hydrophobic modified high thermal conductivity fillers (such as BN and Al2O3) are pre-dispersed in styrene / acrylonitrile (St / AN) mixed monomers, and then emulsified graft copolymerization is carried out in the presence of a polyacrylic acid copolyester core. During this process, the hydrophobic thermal conductivity filler, due to its compatibility with the monomers and polymers, can be more uniformly dispersed and partially embedded in the growing copolystyrene-acrylonitrile (SAN) shell molecular chains, thereby constructing preliminary thermal conductivity pathways within the shell. This differs from the traditional method of simply blending fillers into the resin matrix, achieving the construction of thermal conductivity pathways with low thermal conductivity filler content. ③ Construction of a three-dimensional thermally conductive network: The core-shell structured particles (referred to as "thermally conductive microspheres") with thermally conductive fillers in the shell layer are melt-blended with polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC), or thermoplastic elastomers (such as TPO, TPU) matrix resins. Under the shearing and kneading action of screw extrusion, when the content of "thermally conductive microspheres" reaches a certain threshold, an interconnected three-dimensional thermally conductive network constructed of thermally conductive fillers is formed in the matrix, thereby achieving a leap in the thermal conductivity of the material (target ≥0.70 W / (m·K)) with a relatively low total filler addition (10-30%). The mass fraction of the thermally conductive core-shell functional particles in the overall material is preferably 20%-45%. ④ Synergistic effect of multiple properties: When the matrix is ​​a solvent-resistant thermoplastic resin or thermoplastic elastomer, this structure enables the material to maintain high toughness and high insulation (volume resistivity not less than 1×10⁻⁶). 12 (Ω·m), excellent weather resistance, and the ability to resist swelling and corrosion from environmentally friendly coolants.

[0011] The present invention has the following beneficial effects: 1) Excellent thermal conductivity: Through a strategy combining "core-shell structure functionalization" and "three-dimensional network construction," the thermal conductivity of the polymer material is significantly improved with a low total filler content, meeting the requirements of high-power liquid cooling. 2) Balanced comprehensive performance: The material simultaneously possesses high toughness and high insulation (volume resistivity not less than 1×10⁻⁶). 121) Excellent performance: long-term operating temperature not lower than 150℃, good processing fluidity, and excellent weather resistance and resistance to new environmentally friendly coolants. 2) Novel structural design: a brand-new "thermally conductive core-shell particle" unit has been created, opening up new avenues for its application in the field of thermal management. 3) Controllable preparation method: the emulsion polymerization and melt blending processes are adopted, the raw materials are readily available, the process parameters are easy to control, and it is suitable for large-scale production.

[0012] Furthermore, the structure described in this invention, which is "with cross-linked polyacrylate as the core and SAN as the shell," is different from conventional ASA resin: in addition to SAN, its shell layer also contains thermally conductive fillers embedded through in-situ polymerization, and the core and shell particles are only intermediate components that must be blended with the second matrix. The overall material is thermally conductive and resistant to coolant scenarios, and does not belong to the category of general ASA materials. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the microstructure of the "thermally conductive core-shell particles" in the high thermal conductivity material of this invention.

[0014] Figure 2 This is a schematic diagram of the formation of a three-dimensional thermally conductive network in the high thermal conductivity structural material of the present invention. Detailed Implementation

[0015] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, but the present invention is not limited to the embodiments.

[0016] Example 1 S1. 200g of deionized water and 2.0g of nonionic emulsifier OP-10 were added to the polymerization reactor and stirred until dissolved. 50g of butyl acrylate (BA) and 0.25g of crosslinking agent allyl methacrylate (AMA) were added, and pre-emulsification was carried out for 0.5h. The temperature was raised to 80℃, and 0.125g of potassium persulfate (KPS) aqueous solution was added. The reaction was carried out under nitrogen for 3h to obtain a polyacrylate seed emulsion (particle size approximately 100nm). S2. Dilute the above seed emulsion with 200g of water, and separately prepare a pre-emulsion by mixing 100g of BA, 0.4g of AMA, 0.25g of OP-10 with 200g of water; S3. Heat the seed emulsion to 80°C, and add the above pre-emulsion and an aqueous solution of 0.15 g KPS at a uniform rate over 3 hours while stirring. After the addition is complete, react for another 1 hour to obtain a PBA core pre-emulsion with a particle size of approximately 380 nm and a crosslinking degree of approximately 85%. S4. Disperse 100g of boron nitride (BN) powder with a particle size of ~1μm in 200g of ethanol, add 5g of silane coupling agent KH-550, and reflux at 80℃ for 4h. Filter, wash, and dry to obtain surface-hydrophobicated BN; S5. Mix the above-mentioned surface-hydrophobic BN with 100g styrene (St), 50g acrylonitrile (AN), and 0.5g OP-10, and sonicate for 30min to form a uniform thermally conductive filler / monomer dispersion. S6. Add the BN thermally conductive filler / monomer dispersion to the PBA core pre-emulsion, and simultaneously add 0.2g KPS. Heat the mixture to 80℃ and stir for 4h to obtain a BN thermally conductive core-shell emulsion. The core-shell mass ratio is approximately 37.5:62.5 based on the solid content of the feed, and the BN content in the shell is approximately 40%. S7. Add 5wt% MgSO4 solution to the emulsion to break the emulsion, filter, wash with water, and vacuum dry at 80℃ to obtain thermally conductive core-shell powder.

[0017] Example 2 The difference from Example 1 is as follows: In S1, the polyacrylate seed emulsion contains 30g of butyl methacrylate (BMA), 20g of ethyl methacrylate (EMA), and 0.25g of crosslinking agent allyl methacrylate (AMA); in S2, the pre-emulsion contains 60g of BMA, 40g of EMA, and 0.4g of AMA; in S6, the BN thermally conductive filler / monomer dispersion is added to the polyacrylate copolymer core pre-emulsion, and 0.2g of KPS is added simultaneously. The mixture is heated to 80°C and stirred for 4 hours to obtain a BN thermally conductive core-shell emulsion, wherein the core-shell mass ratio is approximately 37.5:62.5 based on the solid content of the feed, and the BN content in the shell layer is approximately 40%.

[0018] Example 3 The difference from Example 1 is as follows: S4. 50g of boron nitride (BN) powder with a particle size of ~1.5μm is dispersed in 100g of ethanol, and 2.5g of silane coupling agent KH-550 is added. The mixture is refluxed at 80°C for 4h. After filtration, washing, and drying, surface-hydrophobic BN is obtained; S6. The BN thermally conductive filler / monomer dispersion is added to the PBA core pre-emulsion, and 0.2g of KPS is added simultaneously. The mixture is heated to 80°C and stirred for 4h to obtain a BN thermally conductive core-shell emulsion. The core-shell mass ratio is approximately 37.5:62.5 based on the solid content of the feed, and the BN content in the shell is approximately 25%.

[0019] Example 4 The difference from Example 1 is as follows: S5. The above-mentioned surface-hydrophobicated BN is mixed with 80g of styrene (St), 20g of acrylonitrile (AN), and 0.3g of OP-10; S6. The BN thermally conductive filler / monomer dispersion is added to the PBA core pre-emulsion, and 0.15g of KPS is added at the same time. The mixture is heated to 80°C and stirred for 4h to obtain a BN thermally conductive core-shell emulsion. The core-shell mass ratio is about 37.5:62.5 based on the solid content of the feed, and the BN content in the shell is about 50%.

[0020] Example 5 The difference from Example 1 is as follows: S4. 100g of alumina (Al2O3) powder with a particle size of about 2 μm is dispersed in 200g of ethanol, and 5g of stearic acid (C... 17 H 35 COOH (C18 alkyl acid) was refluxed at 75–85°C for 3–5 h, filtered, washed with ethanol, and vacuum dried at 60–80°C to obtain alumina filler with hydrophobic surface treatment of long-chain alkyl acid. Subsequent steps were the same as in Example 1 to prepare thermally conductive core-shell powder.

[0021] Example 6 The thermally conductive core-shell powder obtained in Example 1 was mixed with TPO at a mass ratio of 30:70, and compatibilizers, UV absorbers, antioxidants, etc. were added. The mixture was then melt-blended in a twin-screw extruder (temperature from zone one to the die head: 140-180℃), granulated, to obtain a high thermal conductivity core-shell structure material. The thermal conductivity of this material was tested using a thermal conductivity meter. The test results showed a thermal conductivity of 0.75 W / (m·K). After immersing the material in a low-toxicity, biodegradable hydrocarbon coolant at 90℃ for 168 h (referencing ISO 1817 and commonly used accelerated aging cycles for cable materials), the tensile strength retention rate was ≥85%, and the elongation at break retention rate was ≥80%. This material can be used in liquid-cooled pipes for high-power charging piles.

[0022] Example 7 The thermally conductive core-shell powder obtained in Example 1 was mixed with PVC at a mass ratio of 40:60, and 0.5–3 phr of PVC processing aid ACR (acrylate processing aid), 1–4 phr of environmentally friendly calcium-zinc composite stabilizer, and 0.1–0.5 phr of antioxidant (hindered phenolic or phosphite ester) were added. The mixture was melt-blended in a twin-screw extruder (zone 1 to die head temperature: 160–190°C), granulated, and a high thermal conductivity core-shell structure material was obtained. The thermal conductivity of this material was tested using a thermal flow thermal conductivity meter, and the test results showed a thermal conductivity of 0.80 W / (m·K). This material can be used in thermal management system components for new energy vehicles.

[0023] Example 8 The thermally conductive core-shell powder obtained in Example 5 was mixed with PC at a mass ratio of 40:60, and antioxidants were added. The mixture was then melt-blended in a twin-screw extruder (zone 1 to die head temperature: 180-220℃), granulated, and a high thermal conductivity core-shell structure material was obtained. The thermal conductivity of this material was tested using a thermal flow thermal conductivity meter. The test results showed a thermal conductivity of 0.78 W / (m·K). This material can be used in engineering plastic products with high thermal conductivity and high toughness.

Claims

1. A high thermal conductivity core-shell structure material, characterized in that, It is formed by melt blending thermally conductive core-shell functional particles with thermoplastic resin or thermoplastic elastomer matrix resin; the thermally conductive core-shell functional particles have cross-linked polyacrylate rubber as the core and styrene-acrylonitrile copolymer grafted onto the shell and a surface hydrophobic thermally conductive filler embedded in the shell layer through in-situ polymerization as the shell; the mass ratio of the core to the shell is 45:55 to 30:70; the mass fraction of the thermally conductive core-shell functional particles in the high thermal conductivity core-shell structure material is 20%-45%; the mass percentage of the surface hydrophobic thermally conductive filler in the shell layer is 30%-50%.

2. The high thermal conductivity core-shell structure material according to claim 1, characterized in that, The cross-linked polyacrylate rubber core has a particle size of 100-450 nm.

3. The high thermal conductivity core-shell structure material according to claim 2, characterized in that, The crosslinked polyacrylate rubber core is formed by copolymerization and crosslinking of one or more acrylate monomers and a crosslinking agent, and the degree of crosslinking of the crosslinked polyacrylate rubber core is 50%-90%.

4. The high thermal conductivity core-shell structure material according to claim 1, characterized in that, The surface hydrophobic thermally conductive filler is one or a combination of boron nitride, aluminum oxide, and silicon carbide.

5. The high thermal conductivity core-shell structure material according to claim 4, characterized in that, The aforementioned surface-hydrophobic thermally conductive filler is surface-modified with a silane coupling agent or a C12-C18 long-chain alkyl acid.

6. A method for preparing a high thermal conductivity core-shell structure material as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Using seed emulsion polymerization with nonionic emulsifiers, a large-particle-size cross-linked polyacrylate rubber core pre-emulsion is synthesized through seed preparation and diameter expansion stages; S2. A surface-hydrophobic thermally conductive filler is dispersed in a mixed monomer solution of styrene and acrylonitrile to form a stable thermally conductive filler dispersion; S3. The rubber core emulsion obtained in step S1, the thermally conductive filler dispersion obtained in step S2, the emulsifier, and the initiator are mixed and graft copolymerization is carried out by continuous drop-addition of pre-emulsion, so that the styrene-acrylonitrile copolymer is polymerized in situ on the surface of the rubber core, and the surface hydrophobic thermally conductive filler is simultaneously coated / embedded in the shell to obtain a thermally conductive core-shell structure emulsion. S4. Demulsify, wash, and dry the emulsion obtained in step S3, or spray dry it to obtain thermally conductive core-shell structured powder; S5. The thermally conductive core-shell structure powder obtained in step S4 is melt-blended and granulated with thermoplastic resin or thermoplastic elastomer matrix resin through a screw extruder to obtain a high thermal conductivity core-shell structure material.

7. The method for preparing a high thermal conductivity core-shell structure material according to claim 6, characterized in that, In step S1, the nonionic emulsifier is alkylphenol polyoxyethylene ether or fatty acid polyoxyethylene ester; the diameter expansion stage adopts the continuous dripping method of pre-emulsion to control the monomer dripping rate and achieve precise control of the rubber core particle size.

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