Flexible rubber material with a multi-stage interpenetrating thermal conduction network and methods of making and using the same

Abstract

This invention provides a flexible rubber material with a multi-level interpenetrating thermally conductive network, its preparation method, and its applications. The preparation method includes: differentially treating sheet-like hexagonal boron nitride and bimodal graded spherical α-alumina with silane using a stepwise surface modification process, and then compounding them to obtain a compound thermally conductive filler; pre-concentrating the compound filler in 20%–35% of seed-phase raw rubber to prepare a pre-structured seed rubber; and performing stepwise shear mixing of the seed rubber and the remaining raw rubber, followed by vulcanization locking. This invention achieves an excellent balance between thermal conductivity ≥1.0 W / (m·K) and elongation at break ≥300% under a total filler content of 50–80 phr through a synergistic strategy of "stepwise modification—graded compounding—seed rubber pre-structuring—stepwise shear growth." Furthermore, the process is based on conventional rubber equipment, is cost-controllable, and highly reproducible, making it widely applicable in the field of thermal management for electronic equipment.

Description

Technical Field

[0001] This invention relates to the field of flexible rubber material preparation technology, specifically to flexible rubber materials with multi-level interpenetrating thermal conductive networks, their preparation methods, and applications. Background Technology

[0002] As electronic devices evolve towards higher power density, miniaturization, and thinner designs, the heat flux density of core components such as chips, power modules, and power batteries continues to rise. Efficient thermal management has become a key bottleneck restricting system reliability and lifespan. Thermal interface materials, acting as thermal bridges between heat sources and heat sinks, must simultaneously possess high thermal conductivity to reduce interface temperature differences and good flexibility to fill rough contact surfaces, absorb thermal stress, and meet assembly tolerances. Flexible rubber-based thermally conductive composite materials are widely used as thermal management components such as thermal pads, thermally conductive insulating sheets, and battery pack buffer layers due to their advantages of high processability, good insulation, and controllable cost.

[0003] Currently, the mainstream strategy for improving the thermal conductivity of rubber-based composites is to fill the matrix with high thermal conductivity fillers, such as boron nitride, alumina, and aluminum nitride, into matrices like silicone rubber and epoxy resin. However, this strategy faces a long-standing thermal conductivity-flexibility paradox: the rubber matrix itself has extremely low thermal conductivity, requiring a large amount of thermally conductive filler, typically >60 vol%, to form a percolation thermally conductive network within the matrix, achieving a thermal conductivity of over 1.0 W / (m·K). However, such a high filler content causes the rubber matrix to be penetrated by a rigid filler skeleton, severely restricting the movement of polymer chain segments, leading to a sharp drop in the material's elongation at break to below 100%, thus losing the adhesion and cushioning capabilities required for flexible gaskets.

[0004] To address these contradictions, researchers have explored several technical approaches: first, using blends of fillers with different shapes to increase bulk density at lower filler levels; second, modifying the surface of fillers to reduce interfacial thermal resistance; and third, using external force fields to induce filler orientation and create directional heat-conducting channels. However, these methods still suffer from the following shortcomings: simple physical blending makes it difficult to control the microscopic distribution of fillers, resulting in a predominantly random "point-to-point" contact network with high interfacial thermal resistance; while external field orientation can improve thermal conductivity in specific directions, it typically requires specialized equipment and is difficult to form a continuous interpenetrating network in three-dimensional space; high filler levels lead to a dramatic increase in compound viscosity, a narrow processing window, and poor batch reproducibility. More critically, existing technologies have consistently failed to overcome the performance limitations of high thermal conductivity and high flexibility, with few solutions capable of simultaneously achieving thermal conductivity ≥1.0 W / (m·K) and elongation at break ≥300% with filler loadings below 80 phr.

[0005] Therefore, this application proposes a flexible rubber material with a multi-level interpenetrating thermal conductive network, its preparation method and application, which can construct an efficient thermal conductive network with a low filler content, while maintaining the excellent flexibility and processability of the rubber matrix to meet the increasingly stringent requirements of electronic thermal management. Summary of the Invention

[0006] To address the existing technical problems, this invention provides a flexible rubber material with a multi-level interpenetrating thermally conductive network, its preparation method, and its applications. The flexible rubber material of this invention overcomes the technical biases of traditional blending, such as poor filler dispersion, difficulty in orientation, and significant loss of flexibility, through the synergistic effect of stepwise modification, gradation, and seed rubber. Even with a total filler content as high as 50-80 parts by mass, this flexible rubber material maintains an excellent balance of performance, with an elongation at break ≥300% and a thermal conductivity ≥1.0 W / (m·K). Furthermore, the preparation process is entirely based on conventional rubber processing equipment, requiring no complex chemical synthesis, resulting in controllable production costs and high reproducibility. It can be widely applied in the field of thermal management for electronic devices, such as CPU / GPU heat sinks, power module thermal pads, thermally conductive buffer layers for power battery packs, and flexible circuit heat dissipation films.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a method for preparing a flexible rubber material with a multi-level interpenetrating thermally conductive network, comprising the following steps:

[0009] S1 Preparation of Prestructured Thermally Conductive Seed Gel:

[0010] S11 Stepwise Surface Modification: A silane coupling agent is prepared into an alcohol-water solution, wherein the mass ratio of alcohol to water is 90:10 to 95:5. The pH is adjusted to 4.5 to 5.5 with acetic acid, and hydrolyzed at room temperature for 30 to 60 min to obtain a pre-hydrolyzed solution. The pre-hydrolyzed solution is sprayed independently onto the surface of flake-shaped hexagonal boron nitride, coarse-grained spherical α-alumina, and medium-fine-grained spherical α-alumina by atomization. After drying at 60 to 120℃ for 1 to 3 h until the water content is ≤0.3 wt%, the solution is passed through a 100 to 200 mesh sieve to obtain the respective modified fillers. The silane coupling agent is selected from γ-glycidoxypropyltrimethoxysilane or γ-mercaptopropyltrimethoxysilane, and the amount used is 0.6% to 1.5% of the corresponding filler mass, respectively.

[0011] S12 gradation and compounding: Modified lamellar hexagonal boron nitride, modified coarse-grained spherical α-alumina, and modified medium-fine-grained spherical α-alumina are added to a V-type mixer or a double-cone mixer and mixed at a speed of 10-30 rpm for 10-20 min to obtain a compounded thermally conductive filler; the total mass ratio of lamellar hexagonal boron nitride to coarse and medium-fine-grained spherical α-alumina is 1:1-2.5, and the mass ratio of coarse-grained spherical α-alumina to medium-fine-grained spherical α-alumina is 1.5-3:1;

[0012] The overall particle size distribution of the composite thermally conductive filler satisfies the following: (D90-D10) / D50≤3.8, where D10 is 0.8~3μm, D50 is 6~18 μm, and D90 is 30~55μm; and the median diameter of the plate-like hexagonal boron nitride, D50≥20μm, and the main peak D50 of the coarse and medium-fine spherical α-alumina is ≤15μm.

[0013] S13 High Shear Dispersion: Take 20% to 35% of the raw rubber in the formula as the seed phase rubber, and gradually add the compounded thermally conductive filler into the seed phase rubber in 3 to 5 batches. Grind repeatedly 4 to 10 times with a three-roll mill, and gradually reduce the gap to 0.2 to 0.4 mm, or treat with a high shear disperser at 3000 to 6000 rpm for 5 to 20 minutes to make the thermally conductive filler uniformly dispersed, and obtain a seed rubber paste with high filler content.

[0014] S14 Molding and Pelletizing: The seed adhesive paste is introduced into a slit casting or twin-roll calendering device and repeatedly passed through the rolls 2 to 6 times under the conditions of a slit gap of 0.12 to 0.22 mm and a roll temperature of 40 to 60°C, to calender into a continuous thin strip with a thickness of 0.10 to 0.30 mm, so that the flake hexagonal boron nitride is oriented and aligned along the in-plane direction of the thin strip under the shear flow field; the thin strip is cooled to ≤35°C and cut into particles or fragments with a side length of 1 to 5 mm to obtain prestructured seed adhesive particles;

[0015] S2 stepped shear mixing:

[0016] S21 Primary Mixing: Place the remaining 65% to 80% of raw rubber and seed rubber granules together in an internal mixer or mixing equipment, and mix for 2 to 8 minutes at a rotor speed of 15 to 40 rpm and a material temperature of ≤80℃, so that the seed rubber granules are evenly dispersed in the base raw rubber, while maintaining the morphological integrity of the seed rubber granules and the orientation structure of their internal fillers.

[0017] S22 Secondary Shearing: Increase the rotor speed to 50-75 rpm, raise the material temperature to 80-120℃, and continue mixing for 1.5-6 min. This allows the seed rubber particles to be stretched, extended, and torn in a viscoelastic state. The pre-oriented lamellar hexagonal boron nitride inside is pulled out of the particle boundary and extends outward to form a filler enrichment band as the particles deform. The enrichment bands extended from different particles contact and overlap each other, forming a through-network-like interpenetrating structure in the matrix. When the appearance of the material changes from a speckled particle feel to a gray fibrous / dendritic interwoven texture and the material temperature reaches 85-115℃, stop mixing and quickly unload the material to a two-roll mill with a roller temperature ≤40℃ for cooling.

[0018] S3 vulcanization lock-in:

[0019] After adding the vulcanizing agent to the compound obtained in step S2, the final mixing is passed through a thin tube 2 to 4 times and then sheeted with a thickness of 2 to 6 mm. The sheet is then injected or placed into a mold and vulcanized at 150 to 190°C and 5 to 15 MPa for 3 to 15 minutes. The rubber matrix is ​​cross-linked and cured, and then cured at 140 to 180°C for 1 to 4 hours to obtain a flexible rubber material with a multi-level interpenetrating thermal conductive network.

[0020] This application addresses the competitive adsorption problem between hexagonal boron nitride and alumina due to differences in surface activity through stepwise surface modification, enabling both fillers to obtain uniform silane coupling agent coating layers. Furthermore, it employs a bimodal gradation of spherical α-alumina and lamellar hexagonal boron nitride to construct a high-packing-density composite filler system with a large plate framework and hierarchical spherical embedding. All composite fillers are then pre-concentrated in 20%–35% seed-based adhesive, and calendered into highly oriented thin strips, which are then granulated to obtain pre-structured seed adhesive. Finally, stepwise shear mixing allows the seed adhesive particles to grow controllably in a viscoelastic state, pulling the pre-oriented lamellar boron nitride particles beyond the particle boundaries and overlapping them to form a multi-level interpenetrating thermally conductive network with high-concentration seed nodes as thermal hubs and extended filler enrichment bands as connecting ribs, which is then permanently locked in place through vulcanization.

[0021] In some embodiments, based on 100 parts by weight of raw rubber, the total amount of compounded thermally conductive filler is 50 to 80 parts by weight, including 18 to 30 parts by weight of flake hexagonal boron nitride, 18 to 35 parts by weight of coarse-grained spherical α-alumina, and 8 to 20 parts by weight of medium-fine spherical α-alumina.

[0022] This application limits the total amount of compound filler and the ratio of lamellar hexagonal boron nitride to bimodal spherical α-alumina to create high-density nodes by overlapping lamellar hexagonal boron nitride within the seed glue. Bimodal spherical α-alumina is used to fill the gaps and increase the effective thermal conductivity within the nodes. Then, through shear growth, the nodes are bridged by lamellar extensions, forming a multi-level interpenetrating pathway mainly based on face-to-face / near-face overlap, so that λ can stably cross ≥1.0 W / (m·K) without excessively relying on higher fillers.

[0023] In some embodiments, the stepwise surface modification of lamellar hexagonal boron nitride and spherical α-alumina employs different process conditions:

[0024] For plate-shaped hexagonal boron nitride: the mass ratio of alcohol to water in the alcohol-water solution is 93:7 to 95:5, the hydrolysis time is 45 to 60 min, the drying temperature is 100 to 120℃, and the dried solution is passed through a 200-mesh sieve.

[0025] For spherical α-alumina: the mass ratio of alcohol to water in the alcohol-water solution is 90:10 to 92:8, the hydrolysis time is 30 to 45 min, the drying temperature is 60 to 80℃, and the dried product is passed through a 100-mesh sieve.

[0026] This application utilizes a modification process that defines plate-like hexagonal boron nitride and spherical α-alumina. The plate-like hexagonal boron nitride has an inert basal surface and a small number of hydroxyl groups at the edges. A high-alcohol environment inhibits the beading / agglomeration of water on the surface of plate-like hexagonal boron nitride, allowing the pre-hydrolyzed solution to spread to the edge active sites. This reduces the risk of premature silane self-condensation and prolongs the hydrolysis time, allowing silanes to more fully complete the –OR to –OH conversion. This overcomes the problem of sparse edge active sites and large steric hindrance in plate-like hexagonal boron nitride, thereby improving edge site coverage and forming a thinner organic transition layer. The spherical α-alumina surface is rich in hydroxyl groups and highly hydrophilic, requiring an appropriate amount of water to promote the condensation grafting of ≡Si–OH and Al–OH. This also reduces the hydrolysis time and avoids excessive self-condensation between adsorbed silane molecules, preventing the formation of a thick and brittle polysiloxane layer and increasing interfacial thermal resistance.

[0027] In some embodiments, the number of times the roller passes through the object in step S14 is 3 to 6, and the pressing direction is kept consistent to strengthen the orientation, or the object is rotated 90° after every 2 to 3 times and then pressed again to achieve quasi-isotropic orientation; the cutting method is stamping, rotary cutting or shearing, and the particle shape is square, rhomboid or irregular fragments with an average feature size of 1.5 to 3.0 mm.

[0028] This application achieves precise control over the internal orientation, geometric dimensions, and morphological angles of seed gum particles by limiting the number of roll passes, pressing direction, cutting method, and particle size. During subsequent stepped shear mixing, each seed gum particle deforms, extends, and overlaps in a predictable manner in the shear field, ultimately constructing a high-density, low-thermal-resistance, multi-level interpenetrating thermally conductive network with predominantly surface-to-surface contact within the low-filled matrix phase.

[0029] In some embodiments, the amount of vulcanizing agent used is 1.5 to 3.5 parts by weight per 100 parts by weight of raw rubber, specifically a peroxide vulcanization system selected from one or more of dicumyl peroxide (DCP), 2,4-dichlorobenzoyl peroxide (DBP), and bis(tert-butylperoxide)dicumyl peroxide.

[0030] In some embodiments, the raw rubber is silicone rubber, selected from at least one of methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber, or room temperature vulcanizing silicone rubber.

[0031] This application avoids foaming, discoloration, or insulation degradation of the filler / silane system due to acid, alkali, or metal catalysis by limiting the type and amount of vulcanizing agent; the dosage window is just right to form a moderately cross-linked network in the rubber raw matrix, which not only permanently locks the multi-level interpenetrating thermally conductive structure, but also retains the entropy elasticity of the continuous low-filler phase.

[0032] In the existing technology, modified fillers are usually directly physically mixed with the matrix. This method involves adding all thermally conductive fillers to the rubber matrix in one go or in batches after simple surface modification, and achieving macroscopic dispersion through open milling or internal milling. However, this method has the following inherent defects: the fillers are randomly distributed in the matrix, making it difficult to form an orderly thermal conduction path. The thermal conduction network depends on the point-to-point contact between filler particles, resulting in high contact thermal resistance and low efficiency in improving thermal conductivity. In order to achieve higher thermal conductivity, the filler loading must be greatly increased, which leads to the rubber matrix being penetrated by the rigid filler skeleton, severely restricting the movement of chain segments, and causing the elongation at break to drop sharply to below 100%, resulting in loss of flexibility. (3) Fillers with different shapes and different surface chemical properties compete for adsorption and selectively aggregate during the blending process, resulting in uneven interface modification and further deteriorating the balance between thermal conductivity and mechanical properties.

[0033] To address the aforementioned issues, this application employs a synergistic approach combining stepwise surface modification, graded composite fillers, and seed adhesive pre-structuring. First, a stepwise surface modification process is used, with differentiated alcohol-to-water ratios, hydrolysis times, and drying temperatures tailored to the surface chemical characteristics of both lamellar hexagonal boron nitride and spherical α-alumina. This ensures that each filler achieves a uniformly compatible organic transition layer, avoiding interfacial defects caused by competitive adsorption. Second, the modified lamellar hexagonal boron nitride and spherical α-alumina are composited to construct a high-packing-density system consisting of a large-plate framework and graded spherical particles. Lamellar hexagonal boron nitride is used to establish in-plane oriented dominant thermal channels, while bimodal graded spherical α-alumina efficiently fills the gaps between the lamellar layers, upgrading the thermal conductivity network from point-to-point contact to surface-to-surface / near-surface overlap, significantly reducing interfacial thermal resistance. Finally, all the compound fillers are pre-concentrated in seed-based adhesives that account for only 20% to 35% of the total amount. The adhesives are then calendered into oriented thin strips and granulated. The seed adhesive particles are then controlled to grow in a viscoelastic state through step-by-step shearing and mixing. The pre-oriented BN sheets inside are pulled out of the particle boundaries and overlap with each other in the matrix, forming a multi-level interpenetrating heat-conducting network with high-concentration seed nodes as hubs and extended filler enrichment zones as connecting ribs.

[0034] The second aspect of the present invention provides a flexible rubber material having a multi-level interpenetrating thermally conductive network. In the flexible rubber material, the total amount of the rubber matrix is ​​100 parts by mass; the total amount of thermally conductive filler is 50 to 80 parts by mass, of which 20 to 35 parts by mass are used as seed phase rubber to form a prestructured seed rubber with all the thermally conductive fillers, and the remaining 65 to 80 parts by mass are used as matrix phase rubber to form a continuous low-filling phase.

[0035] Multi-level interpenetrating heat conduction networks include:

[0036] Primary structure: Locally ordered lamellar microregions formed by the preferential orientation of sheet-like hexagonal boron nitride along a specific direction;

[0037] Secondary structure: at least one high thermal conductivity node region evolved from a high filler concentration prestructured seed glue, the node region is enriched with lamellar hexagonal boron nitride, coarse-grained spherical α-alumina and medium and fine-grained spherical α-alumina, and the lamellar hexagonal boron nitride has an in-plane orientation in the node region;

[0038] The three-level structure consists of filler-rich zones that extend outward from the nodal regions through viscoelastic deformation under the action of a shear field. These filler-rich zones overlap with each other between different nodal regions, forming a continuous thermal conductive path in the rubber matrix.

[0039] In the multi-level interpenetrating thermal conductivity network of this application, the primary structure is a locally ordered sheet micro-region formed by the preferential orientation of sheet-like hexagonal boron nitride along a specific direction. The strong shear flow field during the slit calendering process forces the two-dimensional BN sheets to lie flat along the in-plane direction of the thin strip, allowing phonons to propagate rapidly along the low-resistance channels in the sheet surface. This avoids the frequent passage of heat flow across the high-resistance polymer interface caused by the random orientation of the sheets, thereby pre-establishing multiple micro-regions with in-plane thermal conductivity advantages inside the seed adhesive, laying the structural foundation for efficient thermal conductivity in the subsequent node region. The secondary structure is a high thermal conductivity node region evolved from a high-filler-concentration prestructured seed adhesive. This node region is enriched with lamellar hexagonal boron nitride, coarse-grained spherical α-alumina, and medium-fine-grained spherical α-alumina, and the BN maintains an in-plane orientation within the node region. All the compounded fillers are concentrated in a seed-based adhesive that accounts for only 20% to 35% of the total volume, making the local filler volume fraction in the node region as high as 40% to 48%. At the same time, the bimodal gradation of spherical alumina efficiently fills the ineffective voids between the BN lamellars, upgrading the thermal conductivity network inside the node from the traditional point-to-point contact to a surface-to-surface / near-surface overlap, significantly reducing the local interfacial thermal resistance. This makes the node region a low-resistance heat transfer station, allowing the heat flow to diffuse rapidly along the dense solid contact path after entering the node without being blocked by the polymer interlayer. The tertiary structure consists of filler-enriched bands extending outward from the nodal regions through viscoelastic deformation under the action of a stepped shear field. These enriched bands overlap between different nodal regions, forming a continuous thermally conductive pathway within the rubber matrix. High-temperature, high-speed shearing causes the seed rubber particles to undergo controllable viscoelastic stretching and tearing. The internally pre-oriented BN sheets, along with the filled alumina particles, are pulled out of the particle boundaries, forming slender filler-enriched bridge arms. These bridge arms contact and overlap with the bridge arms extending from adjacent nodules in a face-to-edge or face-to-face manner, thereby connecting isolated nodal regions into a continuous network across the low-filled matrix phase. This allows heat flow to be efficiently transferred between nodules along the solid enriched bands, avoiding the pathway interruption caused by the random distribution of fillers in traditional blending systems. The primary structure stores highly efficient lamellar oriented micro-regions for each node region. The secondary structure transforms the node regions into low thermal resistance heat conduction hubs. The tertiary structure connects the hubs into an overall network through directional bridging. All three are indispensable and together they enable the construction of a quasi-continuous solid heat conduction path with high-concentration nodes as heat reservoirs and extended enrichment zones as connecting ribs, under the conditions of a total filler of 50-80 phr and a global average volume fraction of only 14%-22%. This results in a thermal conductivity of ≥1.0 W / (m·K). At the same time, because the low-filling matrix phase, which accounts for 65%-80% of the main volume, remains continuous and bears macroscopic strain, the elongation at break of the material can still be maintained at ≥300%.

[0040] In some embodiments, the flexible rubber material has a thermal conductivity ≥1.0 W / (m·K) and an elongation at break ≥300%; preferably, a thermal conductivity ≥1.2 W / (m·K), an elongation at break ≥350%, a Shore A hardness of 50–80, and a volume resistivity ≥10.14 Ω·cm.

[0041] The third aspect of this invention provides an application of a flexible rubber material used as a thermal management component for electronic devices, selected from one or more of the following: thermally conductive pads, thermally conductive insulating sheets, CPU / GPU heat dissipation gap filling materials, power module thermally conductive pads, battery pack thermally conductive buffer layers, LED heat dissipation interface materials, and flexible circuit heat dissipation films.

[0042] In use, the preferred orientation surfaces of the lamellar hexagonal boron nitride in the multi-level interpenetrating heat conduction network are arranged parallel to the heat source surface to utilize the advantage of in-plane thermal conductivity to form a heat flow path with low interfacial thermal resistance.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] (1) The flexible rubber material with multi-level interpenetrating thermal conductive network provided by the present invention, under the conditions of total filler of 50 to 80 phr and global average volume fraction of 14% to 22%, can increase the thermal conductivity to more than 1.0 W / (m·K) while maintaining the elongation at break of ≥300%, so that the material has both high-efficiency heat dissipation capability and flexible service characteristics.

[0045] (2) This invention achieves the transition of the heat conduction network from random point contact to oriented surface-to-surface overlap through seed glue pre-concentration + oriented thin strip + controllable growth process. The node density, bridging direction and anisotropy can be flexibly adjusted by the number of roll passes and shearing parameters, giving the material the ability to customize the heat conduction path as needed.

[0046] (3) All processes of this invention are based on conventional rubber processing equipment such as internal mixers, open mills, and molding presses. No chemical synthesis or special equipment is required. Production costs are controllable, the process window is wide, and batch reproducibility is high. It has the engineering foundation to directly transform from laboratory to industrialization. Attached Figure Description

[0047] Figure 1 This is a flowchart illustrating the preparation process of the flexible rubber material with a multi-level interpenetrating thermal conductive network according to the present invention. Detailed Implementation

[0048] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope. A flexible rubber material with a multi-level interpenetrating thermally conductive network is prepared according to the proportions of the raw materials and the preparation methods specified in the following embodiments and comparative examples.

[0049] To facilitate implementation of this invention by those skilled in the art, the following description is provided regarding the manufacturers of some raw materials used in the embodiments and comparative examples: Flaky hexagonal boron nitride with a thickness of 0.3-2 μm, flake / plate-like, non-aggregated spherical powder, BN purity ≥ 98.5 wt%, D 50 =20-40μm, D90≤55 μm, magnetic impurities such as Fe / Co / Ni ≤50-200 ppm; coarse-grained spherical α-alumina is specifically spherical / quasi-spherical, Al2O3 purity ≥99.0-99.5%, D 50 =10-14μm; medium to fine-grained spherical α-alumina, specifically near-spherical / polished finish, Al2O3 purity ≥99.0%, D 50 =2-3μm; methyl vinyl silicone rubber is selected from Shin-Etsu's KE-900 series, methyl phenyl vinyl silicone rubber is selected from Shin-Etsu's PVMQ / phenyl methyl series; room temperature vulcanizing silicone rubber is selected from Wacker's ELASTOSIL® N620 / N 670; the other compounds and related reagents used can be purchased from the market.

[0050] Preparation Example 1

[0051] Based on 100 parts by weight of raw rubber, the raw material ratio for seed rubber is as follows:

[0052]

[0053] Stepwise surface modification process:

[0054] Modification conditions for plate-shaped hexagonal boron nitride: 0.22 phr of KH-560 was prepared into an alcohol-water solution with an alcohol-water ratio of 94:6. The solution was hydrolyzed at room temperature for 50 min to obtain a pre-hydrolyzed solution. The pre-hydrolyzed solution was sprayed onto the surface of plate-shaped hexagonal boron nitride by atomization, and then dried at 110 °C for 3 h and passed through a 200 mesh sieve.

[0055] Modification conditions for spherical α-alumina: 0.304 phr of KH-560 was prepared into an alcohol-water solution with an alcohol-water ratio of 91:9. The solution was hydrolyzed at room temperature for 35 min to obtain a pre-hydrolyzed solution. The pre-hydrolyzed solution was sprayed onto the surface of spherical α-alumina by atomization, and then dried at 70 °C for 3 h and passed through a 100-mesh sieve.

[0056] Compounding and dispersion: The three modified fillers were put into a V-type mixer and mixed at 20 rpm for 15 min; they were added to the seed-based adhesive in 4 batches and ground 6 times with a three-roll mill, with the gap gradually reduced to 0.3 mm.

[0057] Molding and pelletizing: slit gap 0.15 mm, roller temperature 50℃, consistent direction, 4 passes through the roller, thin strip thickness 0.18 mm; cool to 30℃, cut into 2.0 mm square particles to obtain prestructured thermally conductive seed adhesive.

[0058] Preparation Example 2

[0059] Based on 100 parts by weight of raw rubber, the raw material ratio for seed rubber is as follows:

[0060]

[0061] Stepwise surface modification process:

[0062] Modification conditions for plate-shaped hexagonal boron nitride: 0.336 phr of KH-560 was prepared into an alcohol-water solution with an alcohol-water ratio of 95:5. The solution was hydrolyzed at room temperature for 55 min to obtain a pre-hydrolyzed solution. The pre-hydrolyzed solution was sprayed onto the surface of plate-shaped hexagonal boron nitride by atomization, and then dried at 115 °C for 2 h and passed through a 200-mesh sieve.

[0063] Modification conditions for spherical α-alumina: 0.480 phr of KH-560 was prepared into an alcohol-water solution with an alcohol-water ratio of 90:10. The solution was hydrolyzed at room temperature for 30 min to obtain a pre-hydrolyzed solution. The pre-hydrolyzed solution was sprayed onto the surface of spherical α-alumina by atomization, and then dried at 65℃ for 3 h and passed through a 100-mesh sieve.

[0064] Compounding and dispersion: The three modified fillers were put into a V-type mixer and mixed at 25 rpm for 12 min; then added to the seed-based adhesive in 5 batches and treated in a high-shear disperser at 5000 rpm for 12 min.

[0065] Molding and pelletizing: slit gap 0.18mm, roller temperature 45℃, passing through the roller 5 times, rotating 90° after every 2 times, thin strip thickness 0.22mm; cooling to 28℃, cutting into 2.5 mm diamond-shaped particles to obtain prestructured thermally conductive seed adhesive.

[0066] Preparation Example 3

[0067] Based on 100 parts by weight of raw rubber, the raw material ratio for seed rubber is as follows:

[0068]

[0069] Stepwise surface modification process:

[0070] Modification conditions for plate-shaped hexagonal boron nitride: 0.144 phr of KH-590 was prepared into an alcohol-water solution with an alcohol-water ratio of 93:7. The solution was hydrolyzed at room temperature for 60 min to obtain a pre-hydrolyzed solution. The pre-hydrolyzed solution was sprayed onto the surface of plate-shaped hexagonal boron nitride by atomization, and then dried at 120 °C for 1 h and passed through a 200-mesh sieve.

[0071] Modification conditions for spherical α-alumina: 0.108 phr of KH-590 was prepared into an alcohol-water solution with an alcohol-water ratio of 92:8. The solution was hydrolyzed at room temperature for 45 min to obtain a pre-hydrolyzed solution. The pre-hydrolyzed solution was sprayed onto the surface of spherical α-alumina by atomization, and then dried at 80 °C for 3 h and passed through a 100-mesh sieve.

[0072] Compounding and dispersion: The three modified fillers were put into a V-type mixer and mixed at 15 rpm for 18 min; they were added to the seed-based adhesive in 3 batches and ground 8 times with a three-roll mill, with the gap gradually reduced to 0.25 mm.

[0073] Molding and pelletizing: slit gap 0.12mm, roller temperature 55℃, consistent direction, pass through the roller 3 times, thin strip thickness 0.14mm; cool to 32℃, cut into 1.8mm irregular fragments to obtain prestructured thermally conductive seed adhesive.

[0074] Example 1

[0075] Stepped shear mixing:

[0076] Primary mixing: The remaining 75 phr of methyl vinyl silicone rubber and the prestructured thermally conductive seed rubber prepared in Preparation Example 1 were placed together in an internal mixer and mixed for 5 min at a rotor speed of 30 rpm and a material temperature of ≤75℃, so that the seed rubber particles were evenly dispersed in the matrix raw rubber, while maintaining the morphological integrity of the seed rubber particles and the orientation structure of their internal fillers.

[0077] Secondary shearing: Increase the rotor speed to 55 rpm, raise the material temperature to 105℃, continue mixing for 3.5 min, when the material appearance changes from a speckled granular feel to a gray fibrous / dendritic interwoven texture and the material temperature reaches 110℃, stop mixing and quickly unload the material to an open mill with a roller temperature ≤40℃ to cool down.

[0078] Vulcanization lock-in:

[0079] After adding 2.8 phr of DCP vulcanizing agent to the above-mentioned compounded rubber, it is subjected to three final thin-passing processes and then sheeted with a thickness of 2 mm. Subsequently, it is injected into a mold and vulcanized at 170°C and 10 MPa pressure for 8 min, and then cured at 150°C for 2 h to obtain a flexible rubber material with a multi-level interpenetrating thermal conductive network.

[0080] Example 2

[0081] Stepped shear mixing:

[0082] Primary mixing: The remaining 72 phr of methylphenyl vinyl silicone rubber and the prestructured thermally conductive seed rubber prepared in Preparation Example 2 were placed together in a mixer and mixed for 6 min at a rotor speed of 25 rpm and a material temperature of ≤70℃, so that the seed rubber particles were evenly dispersed in the matrix raw rubber, while maintaining the morphological integrity of the seed rubber particles and the orientation structure of their internal fillers.

[0083] Secondary shearing: Increase the rotor speed to 65 rpm, raise the material temperature to 112℃, continue mixing for 4 minutes, when the material appearance changes from a speckled granular texture to a gray fibrous / dendritic interwoven texture and the material temperature reaches 115℃, stop mixing and quickly unload the material to an open mill with a roller temperature ≤40℃ to cool down.

[0084] Vulcanization lock-in:

[0085] After adding 3 phr of DBP vulcanizing agent to the above-mentioned rubber compound, the final mixing and thinning were carried out three times and then sheeted with a thickness of 2 mm. The sheet was then injected into a mold and vulcanized at 165°C and 12 MPa pressure for 10 min, and then cured at 160°C for 2 h to obtain a flexible rubber material with a multi-level interpenetrating thermal conductive network.

[0086] Example 3

[0087] Stepped shear mixing:

[0088] Primary mixing: The remaining 78 phr of vinyl-terminated VMQ-based adhesive, 5 phr of hydrogen-containing silicone oil crosslinking agent, and 0.1 phr of inhibitor were placed together with the prestructured thermally conductive seed adhesive prepared in Preparation Example 3 in a mixing device equipped with a planetary mixer and a high-shear dispersing head. The mixture was mixed for 5 min at a paddle speed of 200 rpm and a material temperature ≤40℃ to maintain the seed particle outline.

[0089] Secondary shearing: Increase the rotor speed to 800 rpm, raise the material temperature to 60℃, continue mixing for 3 minutes, stop when the material shows fibrous texture, and quickly unload to an open mill with a roller temperature ≤40℃ to cool down;

[0090] Vulcanization lock-in:

[0091] After injecting the above-mentioned rubber compound into a mold and adding 3 phr of DBP vulcanizing agent, it is cured at room temperature for 24 hours or accelerated vulcanization at 60°C for 2 hours to obtain a flexible rubber material with a multi-level interpenetrating thermal conductive network.

[0092] Comparative Example 1

[0093] All 100 phr of methyl vinyl silicone rubber was directly fed into an internal mixer with 22 phr of stepwise modified compound filler flake hexagonal boron nitride + 26 phr of coarse spherical α-alumina + 12 phr of medium and fine spherical α-alumina. The mixture was mixed at 60 rpm and 90°C for 10 min. Then, 2.8 phr of DCP was added, and the open milling, flake forming, and vulcanization processes and parameters were the same as in Example 1 to obtain the comparative rubber material.

[0094] Comparative Example 2

[0095] The stepped shearing process in Preparation Example 1 was replaced with a rotor speed of 30 rpm, a material temperature of ≤75℃, and a total mixing time of 8.5 min. The rest of the process was the same as in Preparation Example 1 to obtain a prestructured thermally conductive seed rubber. Then, the comparative rubber material was obtained according to the same preparation process as in Example 1.

[0096] Comparative Example 3

[0097] The stepped shear mixing in Preparation Example 1 was replaced with a rotor speed of 55 rpm, a material temperature of 105°C, and a mixing time of 8.5 min. The rest of the process was the same as in Preparation Example 1 to obtain a prestructured thermally conductive seed rubber. Then, the comparative rubber material was obtained according to the same preparation process as in Example 1.

[0098] Comparative Example 4

[0099] In Preparation Example 1, the compound filler was replaced with 22 phr modified flake hexagonal boron nitride, and the rest of the process was the same as in Preparation Example 1 to obtain a prestructured thermally conductive seed adhesive. Then, according to the same preparation process as in Example 1, a comparative rubber material was obtained.

[0100] Comparative Example 5

[0101] In Preparation Example 1, the compound filler was replaced with 26 phr modified coarse-grained spherical α-alumina and 12 phr modified medium-fine-grained spherical α-alumina. The rest of the process was the same as in Preparation Example 1 to obtain a prestructured thermally conductive seed adhesive. Then, according to the same preparation process as in Example 1, a comparative rubber material was obtained.

[0102] Comparative Example 6

[0103] After mixing flake-shaped hexagonal boron nitride and spherical α-alumina in the same proportions as in Preparation Example 1, the mixture was subjected to co-modification using the same alcohol-to-water ratio of 94:6, hydrolysis time of 50 min, drying temperature of 110°C, and sieve passing through a 200-mesh sieve as in Preparation Example 1. The remaining processes were the same as in Preparation Example 1, resulting in a pre-structured thermally conductive seed adhesive. A comparative rubber material was then obtained using the same processes and steps as in Example 1.

[0104] Performance testing:

[0105] The vulcanized rubber sheets obtained in Examples 1-3 and Comparative Examples 1-6 were cut into specimens of uniform size and conditioned for ≥24 h at 23±2℃ and 50±5% relative humidity. The following tests were then performed: Thermal conductivity (in-plane direction, heat flow direction parallel to the in-plane / calendering direction of the strip) was measured using the steady-state heat flow method according to ASTM D5470-17; the specimens were cut into strips along the calendering direction, approximately 30 mm × 10 mm × original thickness, with a contact pressure of 0.5 MPa between the upper and lower heaters; tensile properties were measured according to GB / T 528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber", using type 2 dumbbell-shaped specimens at a tensile speed of 500 mm / min, and the elongation at break was determined; Shore A hardness was measured according to GB / T 531.1-2008 "Test Method for Indentation Hardness of Vulcanized Rubber or Thermoplastic Rubber Part 1: Shore Hardness Tester Method (Shore Hardness)"; volume resistivity was measured according to GB / T According to GB / T 1692-2008, "Determination of Insulation Resistivity of Vulcanized Rubber", the three-electrode method was used, a DC voltage of 500 V was applied, and the steady-state current was read for calculation. The results are shown in Table 1.

[0106] Table 1

[0107]

[0108] As shown in Table 1, the flexible rubber materials with multi-level interpenetrating thermally conductive networks prepared in Examples 1-3 exhibit good thermal conductivity, mechanical properties, and insulation properties. Among them, Example 1 demonstrates the best balance, with a thermal conductivity of 1.28 W / (m·K), while maintaining an elongation at break of 385%, moderate hardness, and a high volume resistivity of 2.3 × 10⁻⁶. 14 Ω·cm, exhibiting excellent overall performance.

[0109] The comparison between Example 1 and Comparative Example 1 shows that simple physical blending is difficult to form an effective heat conduction pathway, heat transfer is hindered, and thermal conductivity is significantly reduced, proving that the prestructured seed adhesive plays a key skeletal support role in constructing the heat conduction network.

[0110] As can be seen from the comparison between Example 1 and Comparative Example 2, although the presence of seed glue can provide a certain thermal conductivity basis, the lack of subsequent directional shear-induced growth results in the filler failing to form a highly oriented thermally conductive network in the matrix, thus limiting the thermal conductivity efficiency.

[0111] As can be seen from the comparison between Example 1 and Comparative Example 3, high-speed shearing destroys the outline of the seed glue particles, breaks the growing filler network, and causes the filler agglomerates to be of uneven size. This not only reduces the probability of the formation of thermal conductivity pathways, but also increases the internal stress of the material, resulting in a significant reduction in elongation at break.

[0112] As can be seen from the comparison between Example 1 and Comparative Examples 4 and 5, single large-sized sheet-like fillers tend to form dense accumulations in the matrix. Although spherical fillers are beneficial for dispersion, their isotropic characteristics prevent them from forming continuous heat conduction links under shear force like sheet-like fillers. Neither can construct a through-type three-dimensional heat conduction network, resulting in limited thermal conductivity.

[0113] As can be seen from the comparison between Example 1 and Comparative Example 6, when co-modified, the silane coupling agent is difficult to simultaneously meet the optimal reaction conditions of hydrophilic and oleophobic plate-like hexagonal boron nitride and oleophilic and hydrophobic α-alumina. Unmodified or weakly bonded fillers are prone to agglomeration, which hinders their uniform dispersion and directional migration in the matrix, thereby affecting the final thermal conductivity density and overall material performance.

[0114] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present application in any way. Although the present application has been disclosed above with reference to preferred embodiments, it is not intended to limit the present application. For those skilled in the art, it will be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method of making a flexible rubber material having a multi-stage interpenetrating heat conducting network, characterized in that, Includes the following steps: S1 Preparation of Prestructured Thermally Conductive Seed Gel: S11 stepwise surface modification: The surfaces of plate-like hexagonal boron nitride, coarse-grained spherical α-alumina and medium-fine-grained spherical α-alumina were sprayed with pre-hydrolysate, dried to a water content of ≤0.3wt%, and then sieved to obtain their respective independent modified fillers; The pre-hydrolyzed solution is prepared using a silane coupling agent; S12 packing compound: All modified packings are put into a V-type mixer or a double cone mixer and mixed at a speed of 10-30 rpm for 10-20 min to obtain a compound thermally conductive packing. The overall particle size distribution of the compound thermally conductive packing satisfies: (D90-D10) / D50≤3.8, where D10 is 0.8-3μm, D50 is 6-18μm, and D90 is 30-55μm. S13 High Shear Dispersion: Take 20% to 35% of the raw rubber in the formula and mix it evenly with the compound thermally conductive filler to obtain a seed rubber paste with high filler content. S14 Molding and Pelletizing: The seed adhesive paste is introduced into a slot casting or twin-roll calendering device, and after repeated rolling, it is calendered into a continuous thin strip with a thickness of 0.10 to 0.30 mm, and then cut into granules or fragments to obtain prestructured seed adhesive granules. S2 stepped shear mixing: S21 Primary Mixing: Place the remaining raw rubber in the formula and the prestructured seed rubber particles together in an internal mixer or mixing equipment, and mix for 2 to 8 minutes at a rotor speed of 15 to 40 rpm and a material temperature of ≤80℃. S22 Secondary Shear: Increase the rotor speed to 50-75 rpm, increase the material temperature to 80-120℃, and continue mixing for 1.5-6 min. When the appearance of the material changes from a speckled granular texture to a gray fibrous / dendritic interwoven texture, stop mixing to obtain the compound. S3 vulcanization lock-in: After adding a vulcanizing agent to the compounded rubber, it is finally refined and sheeted, then injected or placed into a mold, and after vulcanization and curing treatment, a flexible rubber material with a multi-level interpenetrating thermal conductive network is obtained.

2. The production method according to claim 1, characterized by, In step S11, the specific process conditions for the stepwise surface modification of the sheet-like hexagonal boron nitride and the spherical α-alumina are as follows: For plate-shaped hexagonal boron nitride: prepare an alcohol-water solution with a silane coupling agent, wherein the mass ratio of alcohol to water is 93:7 to 95:5, adjust the pH to 4.5 to 5.5 with acetic acid, and hydrolyze at room temperature for 45 to 60 min to obtain a pre-hydrolyzed solution. The subsequent drying temperature is 100 to 120℃, and the dried solution is passed through a 200-mesh sieve. For spherical α-alumina: Prepare an alcohol-water solution with silane coupling agent, wherein the mass ratio of alcohol to water is 90:10 to 92:8, adjust the pH to 4.5 to 5.5 with acetic acid, and hydrolyze at room temperature for 30 to 45 min to obtain a pre-hydrolyzed solution. The subsequent drying temperature is 60 to 80℃, and the dried solution is passed through a 100-mesh sieve. The amount of the silane coupling agent is 0.6% to 1.5% of the corresponding filler mass, and it is selected from γ-glycidoxypropyltrimethoxysilane or γ-mercaptopropyltrimethoxysilane.

3. The preparation method according to claim 2, characterized in that, Based on a total raw rubber volume of 100 parts by mass, the total amount of the compounded thermally conductive filler is 50-80 parts by mass, including 18-30 parts by mass of flake-shaped hexagonal boron nitride, 18-35 parts by mass of coarse-grained spherical α-alumina, and 8-20 parts by mass of medium-fine spherical α-alumina.

4. The production method according to claim 1 or 3, characterized by, In step S14, the number of times the roller is repeatedly pressed is 3 to 6, and the pressing direction is kept consistent to strengthen the orientation, or after every 2 to 3 times, the roller is rotated 90° and pressed again to achieve quasi-isotropic orientation; the cutting method is punching, rotary cutting or shearing, and the particle shape is square, rhomboid or irregular fragments with an average feature size of 1.5 to 3.0 mm.

5. The preparation method according to claim 1, characterized in that, The amount of the vulcanizing agent is 1.5 to 3.5 parts by weight per 100 parts by weight of raw rubber, specifically a peroxide vulcanization system selected from one or more of dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, and bis(tert-butylperoxide)dicumyl peroxide.

6. The production method according to claim 5, characterized by, The raw rubber is silicone rubber, selected from at least one of methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber, or room temperature vulcanizing silicone rubber.

7. A flexible rubber material having a multi-stage interpenetrating heat conducting network, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 6.

8. The flexible rubber material of claim 7, wherein, In the flexible rubber material, the total amount of thermally conductive filler is 50 to 80 parts by mass per 100 parts by mass of rubber matrix. Based on the total amount of rubber matrix as 100 parts by mass, 20 to 35 parts by mass are used as seed phase raw rubber to form a prestructured seed rubber with all thermally conductive fillers, and the remaining 65 to 80 parts by mass form a continuous low-filling matrix phase. The flexible rubber material has a thermal conductivity ≥1.0 W / (m·K), an elongation at break ≥300%, a Shore A hardness of 50–80, and a volume resistivity ≥10. 14 Ω·cm.

9. The flexible rubber material of claim 8, wherein, The thermally conductive filler forms a multi-level interpenetrating thermally conductive network within the rubber matrix, the multi-level interpenetrating thermally conductive network comprising: Primary structure: Locally ordered lamellar microregions formed by the preferential orientation of sheet-like hexagonal boron nitride along a specific direction; Secondary structure: at least one high thermal conductivity node region evolved from a high filler concentration prestructured seed glue, wherein the node region is enriched with lamellar hexagonal boron nitride, coarse-grained spherical α-alumina and medium-fine-grained spherical α-alumina, and the lamellar hexagonal boron nitride has an in-plane orientation within the node region; The three-level structure consists of filler-rich bands that extend outward from the nodal regions under the action of a shear field through viscoelastic deformation. These filler-rich bands overlap with each other between different nodal regions, forming a continuous thermally conductive path in the rubber matrix.

10. Use of a flexible rubber material according to any one of claims 7 to 9, characterized in that, The flexible rubber material is used as a thermal management component for electronic devices and is selected from one or more of the following: thermally conductive pads, thermally conductive insulating sheets, CPU / GPU heat dissipation gap filling materials, power module thermally conductive pads, battery pack thermally conductive buffer layers, LED heat dissipation interface materials, and flexible circuit heat dissipation films. In use, the preferred orientation planes of the lamellar hexagonal boron nitride in the multi-level interpenetrating heat conduction network are arranged parallel to the heat source surface to utilize the advantage of in-plane thermal conductivity to form a heat flow path with low interfacial thermal resistance.

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