Heat-conducting silicone grease and preparation process thereof

Abstract

The invention relates to the technical field of thermal management materials, and discloses heat-conducting silicone grease and a preparation process thereof, and the heat-conducting silicone grease comprises 80-120 parts of vinyl-containing high molecular weight polysiloxane, 1-10 parts of a surface treating agent, 800-2400 parts of a heat-conducting filler, 0.5-20 parts of a hydrogen-containing cross-linking agent, 0.2-5 parts of a polymerization inhibition capsule, 1-10 parts of a heat-resistant additive, 0.01-2 parts of a retarder and 0.01-5 parts of a platinum catalyst. A continuous heat-conducting network is constructed by adopting a high-filling-amount heat-conducting filler, and the compatibility of the filler and a matrix interface is improved in cooperation with a surface treating agent, so that the interface thermal resistance is effectively reduced. The preparation process comprises the following steps: carrying out ball milling and centrifugal grading pretreatment on the heat-conducting filler to optimize the particle stacking density and control the final particle size; a step-by-step mixing process is adopted to ensure uniform dispersion of the components; and volatile matters are thoroughly removed through heating and vacuum treatment. The heat conductivity coefficient of the obtained heat-conducting silicone grease can reach 6W / (m.K) or above, the heat resistance is as low as 0.01 DEG C * in / W or below, and the problems that in the prior art, the heat conductivity coefficient is low, and failure is prone to occurring at high temperature are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of thermal management materials technology, specifically to a thermally conductive silicone grease and its preparation process. Background Technology

[0002] As electronic devices evolve towards miniaturization, integration, and high power density, the heat flux generated by chips and power modules during operation increases dramatically. Thermal management systems have become a crucial element in ensuring the stable operation of electronic equipment, and thermal interface materials connecting heat-generating components and heat sinks play a vital role in this process. The main function of thermal interface materials is to fill the microscopically rough and uneven gaps between the heat-generating and heat-dissipating surfaces, expel air with extremely low thermal conductivity, and establish a continuous heat conduction path, thereby reducing contact thermal resistance.

[0003] Among various thermal interface materials, thermal grease is widely used due to its excellent wettability, extremely low interfacial contact thermal resistance, and ease of repair. Traditional thermal grease is usually a physical blend of liquid polysiloxane and thermally conductive filler. To achieve higher thermal conductivity, the current technological trend is to continuously increase the filling ratio of thermally conductive filler. However, there is a significant surface energy difference between inorganic fillers and the silicone oil matrix. Excessive filling leads to an exponential increase in system viscosity, causing a sharp decrease in material flowability and making application difficult. Simultaneously, high viscosity makes the material difficult to spread under installation pressure, increasing the minimum adhesive layer thickness, which macroscopically offsets the heat transfer advantages brought by high thermal conductivity.

[0004] Furthermore, traditional non-curing thermal greases have significant drawbacks in long-term reliability. During frequent power-on / off cycles or high / low load switching in electronic devices, periodic relative displacement occurs between the heat-generating components and the heat sink due to the mismatch in their coefficients of thermal expansion. This thermomechanical stress acts like a pump, gradually squeezing the fluid-like thermal grease out of the interface region, creating a so-called "pump-out effect." Simultaneously, under high temperature and gravity, the low-surface-tension base silicone oil tends to migrate and seep out from the filler network, leading to "base oil segregation." These phenomena can cause voids, dryness, or poor contact at the interface, resulting in a significant increase in contact thermal resistance over service time, ultimately causing overheating failure of electronic devices.

[0005] To address the issues of pumping out and oil separation, existing technologies attempt to introduce reactive organosilicon systems to prepare thermally conductive gels that can undergo cross-linking and curing upon heating. These materials, after curing, form a cross-linked network with a certain degree of elasticity, thereby limiting silicone oil migration and resisting mechanical deformation. However, introducing a curing system introduces new technical challenges: if the catalytic activity is too high, the material is prone to premature cross-linking during room temperature storage or mixing, leading to unstable viscosity or even gelation, failing to meet the requirements of industrial production and storage; if the catalytic activity is reduced to extend the pot life, extremely high curing temperatures or extremely long curing times are often required, which limits its application in heat-sensitive devices. Therefore, developing a thermally conductive silicone grease that combines high thermal conductivity, low interfacial thermal resistance, excellent anti-pumping performance, and long storage stability remains a pressing technical challenge in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a thermally conductive silicone grease and its preparation process, which solves the problems of low thermal conductivity, easy segregation of base oil and pumping effect under high temperature conditions leading to increased contact thermal resistance, and the difficulty in balancing the application period and storage stability of cross-linked thermally conductive materials while pursuing curing stability.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The first aspect of the present invention provides a thermal grease comprising the following components in parts by weight:

[0009] 80-120 parts of high molecular weight polysiloxane containing vinyl groups

[0010] 1-10 parts of surface treatment agent

[0011] 800-2400 parts of thermally conductive filler

[0012] 0.5-20 parts of hydrogen-containing crosslinking agent,

[0013] Polymerization inhibitor capsules: 0.2-5 parts

[0014] Heat-resistant additive 1-10 parts,

[0015] Delay agent 0.01-2 parts,

[0016] Platinum catalyst 0.01-5 parts.

[0017] In this technical solution, the components form a stable thermally conductive system through specific physical and chemical interactions. The specific mechanism is as follows:

[0018] The vinyl-containing high-molecular-weight polysiloxane serves as a continuous phase matrix, providing a dispersion medium for the thermally conductive filler. The hydrogen-containing crosslinking agent is a hydrogen-containing polysiloxane, whose active hydrogen groups on its molecular chain undergo a hydrosilylation reaction with the vinyl groups in the matrix resin under the action of a platinum catalyst. This reaction constructs a crosslinked network structure within the system, increasing the cohesive strength of the material, limiting the migration of the matrix silicone oil at high temperatures, thereby inhibiting base oil segregation and pump-out effects, and preventing slippage or flow of the silicone grease during vertical coating.

[0019] The thermally conductive filler is added in an amount of 800-2400 parts. This high filling ratio aims to form a close-packed structure in the matrix resin, constructing a continuous heat conduction pathway. The surface treatment agent is adsorbed or chemically bonded to the surface of the thermally conductive filler, reducing the surface energy of the filler and increasing its wettability with the silicone matrix. This interface modification reduces the contact thermal resistance at the solid-liquid interface and lowers the viscosity of the high-filler system, thus maintaining the rheological processing properties of the material while preserving its high thermal conductivity.

[0020] The polymerization inhibitor capsule is a microencapsulated polymerization inhibitor. This component physically isolates the polymerization inhibitor from the catalytic system or releases it slowly at room temperature, inhibiting the activity of the platinum catalyst during storage and preventing premature cross-linking (dead glue) of the adhesive during mixing or storage. When subjected to shear force or reaching a specific temperature, the polymerization inhibitor capsule releases its active ingredient, synergistically regulating the curing induction period with the delay agent to ensure sufficient time for application.

[0021] The heat-resistant additive is dispersed in the matrix to capture free radicals generated by high-temperature oxidation or to shield oxidative active sites, maintain the chemical stability of the polysiloxane backbone under high-temperature conditions, and prevent the material from hardening and pulverizing due to thermal oxidative degradation.

[0022] In one specific embodiment, the vinyl-containing high molecular weight polysiloxane has a vinyl mass fraction of 0.1%-5.0% and a viscosity of 500-100,000 mPa·s at 25°C; the hydrogen-containing crosslinking agent has an active hydrogen mass fraction of 0.1%-1.6%. This parameter range ensures that the crosslinking density after curing is between the gelation point and that of a fully elastomer, giving the material both thixotropic and deformation-resistant properties.

[0023] In one specific embodiment, the thermally conductive filler is selected from at least one of alumina, zinc oxide, aluminum nitride, boron nitride, and silicon carbide; the surface treatment agent is selected from silane coupling agents or titanate coupling agents; the polymerization inhibitor capsule is a microencapsulated polymerization inhibitor; and the delay agent is an alkynyl alcohol compound.

[0024] A second aspect of this invention provides a process for preparing thermal grease, comprising the following steps:

[0025] S1: The thermally conductive packing is ball-milled to obtain ball milling fluid. The ball milling fluid is centrifuged to separate the precipitate, and the precipitate is collected and dried to remove moisture.

[0026] This step involves ball milling to deagglomerate the thermally conductive filler and modify its particle morphology. Centrifugation is used for classification and screening, removing small-diameter microparticles from the upper layer of the ball milling slurry and excessively large particles from the lower layer, while retaining the middle layer particles with a concentrated particle size distribution. Removing microparticles reduces the specific surface area, decreases the amount of adsorbed matrix resin, and thus lowers the system viscosity. Removing large particles reduces the minimum adhesive layer thickness, thereby reducing thermal resistance. Drying removes adsorbed water from the filler surface, preventing moisture from consuming active hydrogen in the hydrogen-containing crosslinking agent or causing catalyst poisoning.

[0027] S2: Mix the full amount of vinyl-containing high molecular weight polysiloxane, the full amount of surface treatment agent and part of the thermally conductive filler treated by S1 evenly to obtain a preliminary mixture; then add the remaining thermally conductive filler, hydrogen-containing crosslinking agent, polymerization inhibitor capsule, heat-resistant additive, delay agent and platinum catalyst to the preliminary mixture and stir evenly.

[0028] This stepwise feeding process first ensures that the high molecular weight polysiloxane, surface treatment agent, and some thermally conductive filler are in full contact under high shear force, ensuring that the coupling agent preferentially coats the filler surface for modification; then the remaining components are added to prevent the active components (such as crosslinking agents and catalysts) from being prematurely deactivated or reacted due to heat or shear during the modification reaction stage.

[0029] S3: Grind the mixture obtained in S2 to control the particle size to not exceed 100μm.

[0030] This step utilizes shear force to further break up the aggregates, ensuring uniform distribution of each component at the microscale and controlling the maximum particle diameter of the system within a set range to meet the micro-gap filling requirements of precision electronic devices.

[0031] S4: Heat the ground mixture to 50-80℃ and evacuate it under a vacuum of ≤-0.095MPa to remove bubbles and volatiles.

[0032] Heating reduces the viscosity of the resin system, facilitating the removal of air bubbles; a high-vacuum environment forcibly removes air introduced during mixing and grinding, as well as residual small-molecule volatiles from the raw materials. Removing air bubbles and volatiles increases the breakdown voltage of the material and prevents voids caused by the expansion of volatiles during high-temperature use, maintaining the integrity of the thermal conductivity pathway.

[0033] S5: Cool the mixture to room temperature, stir it evenly under vacuum, and then discharge and package it.

[0034] Cooling and secondary vacuum stirring are used to eliminate thermal history differences and ensure consistent performance of batch products.

[0035] In one specific embodiment, in S1, the ball-to-material ratio of the ball mill is (5:1)-(10:1), the rotation speed is 300-600 r / min, and the time is 4-24 hours; the centrifugal separation speed is 2000-5000 r / min, and the centrifugation time is 10-30 minutes.

[0036] In one specific embodiment, in S2, the amount of thermally conductive filler added is 40%-60% of the total weight of the thermally conductive filler; the mixing temperature of the initial mixture is 40-60℃; and the stirring temperature after adding the remaining components is 20-30℃.

[0037] In one specific implementation, in S3, a three-roll mill is used for grinding, and the grinding is performed 2-4 times. The roller gap of the three-roll mill is set as follows: 80-100μm for the first pass, 40-60μm for the second pass, and 10-30μm for the third pass.

[0038] In one specific implementation, in S4, the heating and vacuum treatment time is 60-120 minutes, and the stirring method is low-speed stirring with a revolution speed of 10-20 r / min.

[0039] In one specific embodiment, in S5, the cooling termination temperature is 20-25°C, the stirring pressure under vacuum is ≤-0.090MPa, and the stirring time is 15-30 minutes.

[0040] The thermally conductive silicone grease obtained by the present invention through the above-mentioned component combination and preparation process has a density of about 3g / cm³, a thermal conductivity of ≥6W / (m·K), a BLT thermal resistance of ≤0.01℃·in² / W, a moderate viscosity, a volume resistivity of ≥10^12Ω·cm, and a flame retardancy rating of V0.

[0041] In summary, this application includes at least one of the following beneficial technical effects:

[0042] 1. This invention improves the interfacial compatibility between inorganic fillers and organosilicon matrix by using surface treatment agents, and combines it with 800-2400 parts of high-filler thermally conductive filler to construct a dense and continuous thermal conduction network in polysiloxane matrix; combined with filler pretreatment to optimize particle size distribution and grinding and dispersion to control final particle size, it effectively reduces solid-liquid interface thermal resistance and minimum adhesive layer thickness, so that the thermal conductivity of thermal grease reaches above 6W / (m·K) and the BLT thermal resistance is reduced to below 0.01℃·in² / W.

[0043] 2. This invention utilizes the addition reaction of a hydrogen-containing crosslinking agent and a vinyl-containing high molecular weight polysiloxane under the action of a platinum catalyst to form a moderately chemically crosslinked network structure within the system, thereby enhancing the cohesive force of the material. This network structure restricts the free migration of the matrix silicone oil molecules, effectively suppressing the segregation of the matrix oil under high-temperature conditions and the pumping effect during thermal cycling, thus preventing the thermal grease from drying out, powdering, cracking, or sag during long-term use.

[0044] 3. This invention introduces a composite control system composed of microencapsulated polymerization inhibitors and delay agents, which achieves physical isolation and chemical regulation of platinum catalytic activity, preventing premature curing of the adhesive during mixing, grinding, and storage. Combined with a stepwise resin mixing process, it ensures that the surface treatment agent preferentially coats and fully wets the high-filler content filler, thereby maintaining suitable viscosity and rheological properties of the system while ensuring high thermal conductivity, and ensuring the material's construction operation time and storage stability. Detailed Implementation

[0045] Example:

[0046] Example 1

[0047] This embodiment provides a thermal grease, the raw material components and their weight parts are as follows:

[0048] Vinyl-containing high molecular weight polysiloxane (viscosity 10,000 mPa·s, vinyl content 0.5%): 100 parts;

[0049] Surface treatment agent (dodecyltrimethoxysilane): 5 parts;

[0050] Thermally conductive filler (a mixture of alumina and zinc oxide with different average particle sizes): 1600 parts;

[0051] Hydrogen-containing crosslinking agent (hydrogen-containing polysiloxane, active hydrogen content 0.8%): 10 parts;

[0052] Polymerization-inhibiting capsules (microencapsulated ethynylcyclohexanol): 2.5 parts;

[0053] Heat-resistant additive (nano cerium oxide): 5 parts;

[0054] Delaying agent (methylbutynol): 1 part;

[0055] Platinum catalyst: 2.5 parts.

[0056] The preparation process of this thermal grease includes the following steps:

[0057] S1: Place the thermally conductive packing material in a planetary ball mill, set the ball-to-material ratio to 8:1, the rotation speed to 450 r / min, and the milling time to 12 hours to obtain the ball milling slurry. Place the ball milling slurry in a centrifuge and centrifuge at 3500 r / min for 20 minutes to remove the supernatant and the bottom precipitate, collecting the middle layer of ball mill precipitate. Dry the collected precipitate in a 110℃ forced-air drying oven for 6 hours to remove moisture.

[0058] S2: Add 100 parts of vinyl-containing high molecular weight polysiloxane, 5 parts of surface treatment agent, and 800 parts (accounting for 50% of the total filler) of thermally conductive filler treated by S1 to a double planetary vacuum mixer. Stir at 50°C for 45 minutes at a revolution speed of 25 r / min and a rotation speed of 45 r / min to obtain the initial mixture.

[0059] Subsequently, the temperature was lowered to 25°C, and the remaining 800 parts of thermally conductive filler, 10 parts of hydrogen-containing crosslinking agent, 2.5 parts of polymerization inhibitor capsules, 5 parts of heat-resistant additive, 1 part of retarder, and 2.5 parts of platinum catalyst were added to the initial mixture. The mixture was then stirred for 45 minutes at 25°C at a revolution speed of 30 rpm and a rotation speed of 60 rpm to obtain the final mixture.

[0060] S3: Grind the mixture obtained in S2 using a three-roll mill, for a total of 3 passes. The roller gap of the three-roll mill is set as follows: 90μm for the first pass, 50μm for the second pass, and 20μm for the third pass. The particle size test results after grinding show that the maximum particle size is 45μm (meeting the requirement of ≤100μm).

[0061] S4: Place the ground mixture in a mixer and heat to 65°C. While stirring at a low speed of 15 r / min, evacuate to -0.098 MPa and maintain for 90 minutes to remove bubbles and volatiles.

[0062] S5: Cool the mixture to 23°C by passing cooling water through it. Stir for 20 minutes under a vacuum of -0.095MPa to ensure homogeneity, then discharge the mixture and package it in a light-proof and moisture-proof container.

[0063] Example 2

[0064] This embodiment provides a thermal grease, the raw material components and their weight parts are as follows:

[0065] Vinyl-containing high molecular weight polysiloxane (viscosity 500 mPa·s, vinyl content 0.1%): 80 parts;

[0066] Surface treatment agent (octyltrimethoxysilane): 1 part;

[0067] Thermally conductive filler (alumina powder): 800 parts;

[0068] Hydrogen-containing crosslinking agent (hydrogen-containing polysiloxane, active hydrogen content 0.1%): 0.5 parts;

[0069] Polymerization-inhibiting capsules (microencapsulated dimethyl maleate): 0.2 parts;

[0070] Heat-resistant additive (iron oxide): 1 part;

[0071] Delaying agent (ethynylcyclohexanol): 0.01 parts;

[0072] Platinum catalyst (platinum content 1000ppm): 0.01 parts.

[0073] The preparation process of this thermal grease includes the following steps:

[0074] S1: Place the thermally conductive packing material in a planetary ball mill, set the ball-to-material ratio to 5:1, the rotation speed to 300 r / min, and the milling time to 4 hours to obtain a ball milling slurry. Place the ball milling slurry in a centrifuge and centrifuge at 2000 r / min for 10 minutes, collecting the intermediate layer of ball mill precipitate. Dry the precipitate at 100℃ for 4 hours to remove moisture.

[0075] S2: Add 80 parts of vinyl-containing high molecular weight polysiloxane, 1 part of surface treatment agent, and 320 parts (accounting for 40% of the total filler) of thermally conductive filler treated in S1 to the mixer. Stir at 40°C for 30 minutes at a revolution speed of 15 r / min and a rotation speed of 30 r / min to obtain the initial mixture.

[0076] Subsequently, the temperature was lowered to 20°C, and the remaining 480 parts of thermally conductive filler, 0.5 parts of hydrogen-containing crosslinking agent, 0.2 parts of polymerization inhibitor capsules, 1 part of heat-resistant additive, 0.01 parts of retarder, and 0.01 parts of platinum catalyst were added. The mixture was stirred for another 30 minutes at 20°C, with a revolution speed of 20 rpm and a rotation speed of 40 rpm.

[0077] S3: The mixture obtained in S2 was ground using a three-roll mill, for a total of two passes. The roller gaps were set as follows: 100 μm for the first pass, 60 μm for the second pass, and 30 μm for the third pass. The maximum particle size of the material after grinding was found to be 85 μm.

[0078] S4: Heat the mixture to 50°C. With stirring at 10 rpm, evacuate to -0.095 MPa and maintain for 60 minutes to remove bubbles and volatiles.

[0079] S5: Cool the mixture to 20°C. Stir under a vacuum of -0.090 MPa for 15 minutes, then discharge and package.

[0080] Example 3

[0081] This embodiment provides a thermal grease, the raw material components and their weight parts are as follows:

[0082] Vinyl-containing high molecular weight polysiloxane (viscosity 100,000 mPa·s, vinyl content 5.0%): 120 parts;

[0083] Surface treatment agent (titanium ester coupling agent): 10 parts;

[0084] Thermally conductive filler (mixture of spherical alumina and aluminum nitride): 2400 parts;

[0085] Hydrogen-containing crosslinking agent (hydrogen-containing polysiloxane, active hydrogen content 1.6%): 20 parts;

[0086] Polymerization-inhibiting capsules (microencapsulated methylbutynol): 5 parts;

[0087] Heat-resistant additive (hindered phenolic antioxidant): 10 parts;

[0088] Delaying agent (2-methyl-3-butyn-2-ol): 2 parts;

[0089] Platinum catalyst (platinum content 5000ppm): 5 parts.

[0090] The preparation process of this thermal grease includes the following steps:

[0091] S1: Place the thermally conductive packing material in a planetary ball mill, set the ball-to-material ratio to 10:1, the rotation speed to 600 r / min, and the milling time to 24 hours to obtain a ball milling slurry. Place the ball milling slurry in a centrifuge and centrifuge at 5000 r / min for 30 minutes, collecting the intermediate layer of ball mill precipitate. Dry the precipitate at 120℃ for 8 hours.

[0092] S2: Add 120 parts of vinyl-containing high molecular weight polysiloxane, 10 parts of surface treatment agent, and 1440 parts (60% of the total filler) of thermally conductive filler treated in S1 to a mixer. Stir at 60°C for 60 minutes at a revolution speed of 30 r / min and a rotation speed of 60 r / min to obtain the initial mixture.

[0093] Subsequently, the temperature was lowered to 30°C, and the remaining 960 parts of thermally conductive filler, 20 parts of hydrogen-containing crosslinking agent, 5 parts of polymerization inhibitor capsules, 10 parts of heat-resistant additive, 2 parts of retarder, and 5 parts of platinum catalyst were added. The mixture was then stirred for 60 minutes at 30°C at a revolution speed of 40 rpm and a rotation speed of 80 rpm.

[0094] S3: The mixture obtained in S2 was ground using a three-roll mill for a total of four passes. The roller gaps were set as follows: 80 μm for the first pass, 40 μm for the second pass, and 10 μm for the third pass. The maximum particle size of the material after grinding was measured to be 25 μm.

[0095] S4: Heat the mixture to 80°C. With stirring at 20 rpm, evacuate to -0.099 MPa and maintain for 120 minutes to thoroughly remove bubbles and volatiles.

[0096] S5: Cool the mixture to 25°C. Stir under a vacuum of -0.098 MPa for 30 minutes, then discharge and package.

[0097] Comparative Example 1:

[0098] Compared with Example 1, the difference is that in S1, the thermally conductive filler was not subjected to ball milling, centrifugal separation and drying pretreatment. Instead, the same commercially available thermally conductive filler was directly used for resin mixing in S2. The remaining components and process steps are the same.

[0099] Comparative Example 2:

[0100] Compared with Example 1, the difference is that no surface treatment agent (dodecyltrimethoxysilane) was added to the raw material components. During the S2 resin mixing process, the vinyl-containing high molecular weight polysiloxane was directly mixed with the thermally conductive filler treated by S1. The remaining components and process steps are the same.

[0101] Comparative Example 3:

[0102] Compared with Example 1, the difference is that no hydrogen-containing crosslinking agent and platinum catalyst were added to the raw material components, while the remaining components and process steps are the same.

[0103] Comparative Example 4:

[0104] Compared with Example 1, the difference is that the polymerization inhibitor capsules in the raw material components are replaced with an equal weight of ordinary ethynylcyclohexanol polymerization inhibitor that has not undergone microencapsulation treatment, while the remaining components and process steps are the same.

[0105] Comparative Example 5:

[0106] Compared with Example 1, the difference is that the resin mixing process of S2 is changed from stepwise mixing to one-step mixing, that is, the vinyl-containing high molecular weight polysiloxane, surface treatment agent, full amount of thermally conductive filler, hydrogen-containing crosslinking agent, polymerization inhibitor capsule, heat-resistant additive, delay agent and platinum catalyst are added into a double planetary vacuum mixer at one time and stirred at 25°C for 90 minutes. The remaining components and subsequent process steps are the same.

[0107] Test Example 1: Basic Physical Properties and Thermal Conductivity Test

[0108] This test case aims to test the viscosity, thermal conductivity, and interfacial thermal resistance of the thermal greases prepared in Examples 1-3 and Comparative Examples 1, 2, and 5.

[0109] Experimental steps

[0110] Viscosity test

[0111] Take an appropriate amount of the thermal grease sample to be tested and place it in a constant temperature water bath at 25℃±0.5℃. Use a TF rotor and set the rotation speed to 5 rpm. Immerse the rotor vertically into the center of the sample and record the viscosity value after the reading stabilizes for 30 seconds. Repeat the test 3 times for each sample and take the arithmetic mean as the final test result.

[0112] Thermal conductivity test

[0113] According to ASTM D5470 (Standard Test Method for Thermal Transfer Properties of Thermally Conductive Electrical Insulating Materials), the thermal resistance and thermal conductivity were measured using a TIM thermal resistance and thermal conductivity tester.

[0114] A sample of thermally conductive silicone grease was applied between the upper and lower copper rods of the testing instrument, with the sample thickness controlled to 0.5 mm using a thickness gauge. The heating block temperature was set to 80°C, the cooling block temperature to 50°C, and the applied pressure to 40 psi. After the system reached steady-state thermal equilibrium, the heat flux density and the temperature difference between the upper and lower contact surfaces were recorded. The apparent thermal conductivity of the sample was calculated using Fourier's law of thermal conductivity. Five different thickness points were tested for each sample, and the volumetric thermal conductivity of the sample was calculated through linear fitting.

[0115] BLT thermal resistance test

[0116] Using the same testing equipment as the thermal conductivity test described above, the sample was coated onto the surface of the test head, and a constant pressure of 40 psi was applied. After the sample spread under pressure and reached the minimum adhesive layer thickness, and the heat flow stabilized, the total thermal resistance value was recorded. This value reflects the interfacial heat transfer resistance of the material under actual high-pressure installation conditions.

[0117] The experimental data are shown in Table 1.

[0118] Table 1. Test data of basic physical properties and thermal conductivity of the embodiments and comparative examples.

[0119] Group Viscosity (cP, 25℃) Thermal conductivity (W / m·K) BLT thermal resistance (°C·in² / W) Remark Example 1 104800 6.03 0.0098 - Example 2 63400 4.21 0.0123 - Example 3 182100 7.48 0.0089 - Comparative Example 1 147500 5.18 0.0245 No S1 preprocessing Comparative Example 2 >500,000 Unable to test Unable to test It's a dry powder and cannot be applied. Comparative Example 5 123600 5.42 0.0176 One-step mixing

[0120] Table 1 shows that the viscosity of Comparative Example 1 is significantly higher than that of Example 1, and the BLT thermal resistance is approximately 2.5 times that of Example 1. This difference stems from the ball milling and centrifugal classification operations performed on the thermally conductive filler during the filler pretreatment step. Ball milling modifies the surface morphology of the filler and deagglomerates it, while centrifugal separation removes excessively fine particles (micropowder) and excessively large particles, optimizing the particle packing density in the matrix. Removing micropowder with high specific surface area reduces the amount of filler adsorbed onto the matrix resin, thereby reducing the system viscosity; removing large particles reduces the minimum adhesive layer thickness, allowing the thermally conductive silicone grease to form a thinner heat transfer interface under pressure, thus reducing contact thermal resistance. Comparative Example 1, lacking this classification treatment, has uneven particle size distribution, resulting in increased contact thermal resistance and decreased thermal conductivity.

[0121] Comparative Example 2, lacking a surface treatment agent, was a dry powder and could not be properly coated or tested. This is because the thermally conductive filler content in this technical solution is high, resulting in a significant surface energy difference between the inorganic filler and the silicone matrix. One end of the surface treatment agent molecule can chemically bond or physically adsorb onto the surface of the inorganic filler, while the other end is compatible with the silicone resin, thereby reducing the surface energy of the filler and improving wettability. Without the modifying effect of the surface treatment agent, a large amount of thermally conductive filler cannot be effectively wetted and coated by the limited matrix resin, leading to a sharp increase in friction within the system, preventing the formation of a continuous paste-like structure, and consequently, the construction of an effective thermally conductive network.

[0122] Although the component contents of Comparative Example 5 were the same as in Example 1, its thermal conductivity was lower than that of Example 1, and its viscosity increased. This confirms the necessity of a stepwise mixing process for constructing a thermally conductive network. In the first stage of stepwise mixing, the high concentration of surface treatment agent and some of the thermally conductive filler preferentially contact each other in the matrix resin, ensuring that the coupling agent molecules are efficiently and uniformly coated on the filler surface. In contrast, Comparative Example 5 used a one-step mixing method, in which multiple active components such as surface treatment agent, crosslinking agent, and catalyst compete for adsorption simultaneously. Furthermore, the instantaneous high concentration of filler led to a decrease in shear efficiency, hindering the grafting efficiency of the surface treatment agent, causing some filler to agglomerate, disrupting the continuity of the thermally conductive pathway, and resulting in a decrease in macroscopic thermal conductivity and an increase in processing viscosity.

[0123] Test Example 2: Storage Stability and Service Life Test

[0124] This test case aims to test the viscosity change characteristics and anti-gelling properties of the thermal greases prepared in Example 1 and Comparative Example 4 under different storage environments, in order to evaluate their pot life and storage stability.

[0125] Experimental steps

[0126] Applicability period test

[0127] The prepared thermal grease samples from Example 1 and Comparative Example 4 were dispensed into several 50ml sealed aluminum containers. The samples were then stored in a constant temperature and humidity chamber at 25℃±1℃ and 50%±5% relative humidity.

[0128] Set the test time points as the initial time (0 hours), 4 hours, 8 hours, 24 hours, and 48 hours. Record the viscosity values ​​and calculate the growth rate relative to the initial viscosity. When the viscosity growth rate exceeds 100% (i.e., reaches twice the initial viscosity), the service life is considered to have ended.

[0129] Accelerated aging storage stability test

[0130] Take 200g of each sample from Example 1 and Comparative Example 4, and place them into polypropylene plastic containers, sealing them tightly. Place the samples in a forced-air drying oven set at 40℃ for accelerated thermal aging experiments.

[0131] The sample was left to stand for 7 days (168 hours). After the experiment, the sample was removed and cooled to room temperature. First, the sample was visually inspected to see if it remained in a paste-like state or had transformed into an elastic solid (gel). Then, the sample was stirred with a spatula to check for any hard lumps or crusting caused by local cross-linking.

[0132] The experimental data are shown in Table 2.

[0133] Table 2. Practical application period and accelerated aging test data of the examples and comparative examples.

[0134] Group Initial viscosity (cP) 4-hour viscosity (cP) 8-hour viscosity (cP) 24-hour viscosity (cP) 48-hour viscosity (cP) 40℃ aging for 7 days Example 1 104800 105300 106100 108400 111200 Maintain the paste consistency without forming a skin. Comparative Example 4 105200 168500 294000 >500,000 (already gelled) - The whole body is cured into an elastomer

[0135] Table 2 shows that after 48 hours at 25°C, the viscosity of Example 1 increased by less than 10%, and it maintained a uniform paste structure without gelation even after 7 days of accelerated aging at 40°C. In contrast, the viscosity of Comparative Example 4 increased significantly after only 4 hours, with a growth rate exceeding 60%; after 8 hours, the viscosity was nearly three times the initial value, exceeding the shelf life limit; and in the 24-hour and 40°C accelerated aging tests, the sample completely lost its fluidity and transformed into an elastic solid.

[0136] This difference is attributed to the different reaction control mechanisms between encapsulated polymerization inhibitors and ordinary polymerization inhibitors. In Comparative Example 4, the unencapsulated alkynyl alcohol polymerization inhibitor was directly dispersed in the matrix resin. Although it could temporarily inhibit the activity of the platinum catalyst through complexation, in the system where the hydrogen-containing crosslinking agent and vinyl polysiloxane coexisted, the free polymerization inhibitor would gradually volatilize over time or dissociate during the catalytic cycle, leading to a gradual recovery of catalyst activity. This would trigger a slow crosslinking reaction at room temperature, causing the viscosity to increase exponentially over time and significantly shortening the material's application window.

[0137] Example 1 utilizes microencapsulation technology to encapsulate a polymerization inhibitor within a capsule wall. Under normal temperature and static storage conditions, the capsule wall physically isolates the polymerization inhibitor component and its complexed catalytic active centers from the active functional groups in the matrix resin. This physical barrier blocks the contact pathway for the crosslinking reaction, allowing the system to remain chemically inert during storage. The active ingredient is only released and participates in reaction regulation when the material is subjected to shear forces (such as during coating application) or heated to a specific temperature, causing the capsule wall to rupture or its permeability to change. Therefore, this technical solution can significantly extend the shelf life and application time of thermal grease while ensuring curing performance.

[0138] Test Example 3: High Temperature Reliability and Sagging Resistance Test

[0139] This test case aims to test the anti-sagging performance, oil separation degree and thermal shock resistance of the thermal grease prepared in Example 1 and Comparative Example 3 under high temperature environment, so as to evaluate the structural stability of the material under long-term service conditions.

[0140] Experimental steps

[0141] For the vertical flow (anti-sagging) test, two clean aluminum alloy plates (100mm × 50mm × 2mm in size) were used. 1.0g of each of the thermal grease samples from Example 1 and Comparative Example 3 were weighed and applied to the center area of ​​the aluminum plates. Using a stainless steel scraper and thickness gauge, the coating was trimmed into a circle with a diameter of 20mm, controlling the coating thickness to 1.0mm. The initial lower edge position of the coating was marked. The aluminum plates were placed vertically (at a 90° angle to the horizontal plane) in a forced-air drying oven and kept at a constant temperature of 150°C for 24 hours. After the experiment, the vertical displacement distance of the lower edge of the sample coating relative to the initial marked position was measured.

[0142] For the oil separation degree test, standard qualitative filter paper was placed on a watch glass. 0.5g of samples from Example 1 and Comparative Example 3 were weighed and placed in the center of the filter paper. The watch glass was placed in a 150°C constant temperature oven for 24 hours. The samples were then removed and cooled to room temperature. The maximum diameter of the oil ring formed by the diffusion of silicone oil on the filter paper and the diameter of the remaining portion of the sample were measured. The percentage of oil separation degree was calculated based on the ratio of the oil ring diffusion area to the original coverage area of ​​the sample.

[0143] For the thermal shock test, a sample of thermally conductive silicone grease was applied between two pieces of quartz glass (25mm × 25mm). Pressure was applied to control the grease layer thickness to 0.1mm, creating a sandwich structure test specimen. The specimen was placed in a thermal shock test chamber with a low temperature of -40℃ and a high temperature of 125℃, each with a dwell time of 30 minutes and a transition time of less than 10 seconds. 500 cycles of testing were performed. After the test, the silicone grease layer within the glass interlayer was observed using an optical microscope to check for voids, cracks, or edge overflow.

[0144] The experimental data are shown in Table 3.

[0145] Table 3. High-temperature reliability and aging test data of the examples and comparative examples.

[0146] Group Vertical flow displacement at 150°C (mm) Oil separation degree at 150℃ (%) Appearance after 500 thermal shocks Example 1 0 0.12 The adhesive layer is intact, with no overflow at the edges and no voids inside. Comparative Example 3 >50.0 (slipped to the bottom plate) 5.86 The edges show jagged edges, and irregular cracks and cavities appear in the central area.

[0147] Table 3 shows that Example 1 maintained its morphological integrity during high-temperature vertical placement and thermal cycling tests, while Comparative Example 3 experienced severe flow and phase separation. Example 1 contains a vinyl-containing high molecular weight polysiloxane, a hydrogen-containing crosslinking agent, and a platinum catalyst. During heating, the platinum catalyst initiates a hydrosilylation reaction, forming chemical bonds between the linear polysiloxane molecular chains to construct a three-dimensional crosslinked network structure. This network structure endows the material with high yield stress and high-temperature shear modulus, enabling it to resist gravity at 150°C, maintaining the coating position and preventing vertical displacement. Comparative Example 3 lacks the crosslinking agent and catalyst, belonging to a physical blend system. The increased temperature causes a sharp decrease in the viscosity of the matrix resin, making it unable to resist gravity and filler settling stress, resulting in overall slippage.

[0148] In the oil separation test, the high oil separation degree of Comparative Example 3 stemmed from the difference in thermal expansion coefficients between the inorganic thermally conductive filler and the organic silicone oil. At high temperatures, low-viscosity free silicone oil molecules easily migrate capillarily from the gaps between the filler and permeate into the filter paper. In Example 1, the elastic network formed by the cross-linking reaction restricted the free movement of the polysiloxane molecular chains, effectively binding the liquid components within the framework structure constructed by the thermally conductive filler, preventing the precipitation and migration of small-molecule silicone oil, thereby maintaining the uniformity of the material composition.

[0149] The thermal shock test results reflect the material's ability to resist the pump-out effect. In Comparative Example 3, during repeated thermal expansion and contraction, due to the lack of elastic recovery force, the silicone grease was gradually squeezed out of the interface edge, and air was drawn into the interface during the contraction phase, resulting in voids and cracks in the central area, which would significantly increase the contact thermal resistance. Example 1, after curing, formed a soft gel-like elastomer with rubber elasticity. Under the thermal stress generated by temperature cycling, this material undergoes reversible elastic deformation rather than plastic flow, maintaining close contact with the substrate and avoiding the generation of interface defects.

Claims

1. A thermally conductive silicone grease, characterized in that, The components include the following parts by weight: 80-120 parts of vinyl-containing high molecular weight polysiloxane; Surface treatment agent 1-10 parts; 800-2400 parts of thermally conductive filler; 0.5-20 parts of hydrogen-containing crosslinking agent; Polymerization-inhibiting capsules: 0.2-5 parts; 1-10 parts of heat-resistant additive; Delaying agent 0.01-2 parts; Platinum catalyst 0.01-5 parts.

2. The thermal grease according to claim 1, characterized in that, The vinyl-containing high molecular weight polysiloxane has a vinyl mass fraction of 0.1%-5.0% and a viscosity of 500-100,000 mPa·s at 25°C. The hydrogen-containing crosslinking agent is a hydrogen-containing polysiloxane with an active hydrogen mass fraction of 0.1%-1.6%.

3. The thermal grease according to claim 1, characterized in that, The thermally conductive filler is selected from at least one of alumina, zinc oxide, aluminum nitride, boron nitride, and silicon carbide; The surface treatment agent is selected from silane coupling agents or titanate coupling agents.

4. The thermal grease according to claim 1, characterized in that, The polymerization inhibitor capsule is a microencapsulated polymerization inhibitor; The delaying agent is an alkynol compound.

5. A process for preparing the thermal grease as described in any one of claims 1-4, characterized in that, Includes the following steps: S1: The thermally conductive packing is ball-milled to obtain ball milling fluid, the ball milling fluid is centrifuged to separate it, the ball milling precipitate is collected and dried to remove moisture; S2: Mix the full amount of vinyl-containing high molecular weight polysiloxane, the full amount of surface treatment agent and part of the thermally conductive filler treated by S1 evenly to obtain the initial mixture. Then, the remaining thermally conductive filler, hydrogen-containing crosslinking agent, polymerization inhibitor capsule, heat-resistant additive, delay agent and platinum catalyst are added to the initial mixture and stirred evenly. S3: Grind the mixture obtained in S2 to control the particle size to not exceed 100μm; S4: Heat the ground mixture to 50-80℃ and evacuate it under a vacuum of ≤-0.095MPa to remove bubbles and volatiles; S5: Cool the mixture to room temperature, stir it evenly under vacuum, and then discharge and package it.

6. The preparation process according to claim 5, characterized in that, In S1, the ball-to-material ratio of the ball mill is (5:1)-(10:1), the rotation speed is 300-600 r / min, and the time is 4-24 hours; The centrifugation speed is 2000-5000 r / min, and the centrifugation time is 10-30 minutes.

7. The preparation process according to claim 5, characterized in that, In S2, the amount of thermally conductive filler added is 40%-60% of the total weight of the thermally conductive filler; The mixing temperature of the initial mixture is 40-60℃; The stirring temperature after adding the remaining components is 20-30℃.

8. The preparation process according to claim 5, characterized in that, In S3, a three-roll mill is used for grinding, with 2-4 passes. The roller gap of the three-roll mill is set as follows: The first pass is 80-100μm, the second pass is 40-60μm, and the third pass is 10-30μm.

9. The preparation process according to claim 5, characterized in that, In S4, the heating and vacuum treatment time is 60-120 minutes, and the stirring method is low-speed stirring with a revolution speed of 10-20 r / min.

10. The preparation process according to claim 5, characterized in that, In S5, the cooling termination temperature is 20-25℃, the stirring pressure under vacuum is ≤-0.090MPa, and the stirring time is 15-30 minutes.