Liquid metal-based composite heat-conducting silicone grease as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of heat-conducting materials, and provides liquid metal-based composite heat-conducting silicone grease as well as a preparation method and application thereof. The modified silicone oil, the liquid metal, the heat-conducting auxiliary filler and the hydrophobic fumed silica in a specific ratio are used as main components of the liquid metal-based composite heat-conducting silicone grease, and the liquid metal-based composite heat-conducting silicone grease prepared by the invention has high heat conductivity coefficient (up to 6.05-10.0 W / mk) and low heat resistance (as low as 0.01-0.03 DEG C * cm < 2 > / W), can maintain a good appearance in double-85, high temperature 125 DEG C and temperature cycle aging tests, and has a wide application prospect. Therefore, the structure is suitable for an assembly interface of a power module and a radiator with high-power heat dissipation requirements, and the heat dissipation efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal conductive materials, and more specifically, to a liquid metal-based composite thermal conductive silicone grease, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the development of communication and computing power product businesses, the integration and power consumption of chips have increased significantly. The thermal management problem of power devices has gradually become one of the current research hotspots and key competitiveness indicators of products. Thermal interface materials play an indispensable role in improving the heat dissipation efficiency, and the requirements for their thermal conductivity are also getting higher and higher. In addition, with the gradual increase in application scenarios, the application reliability requirements for thermal interface materials are also getting higher and higher.

[0003] Common thermal interface materials mainly include thermal conductive silicone grease, thermal conductive gel, thermal conductive gasket, and thermal conductive phase change material. Among them, thermal conductive silicone grease has been widely used due to its excellent processability and heat dissipation efficiency. However, thermal conductive silicone grease still lacks in the heat dissipation efficiency of high-power devices and cannot effectively meet the requirements of high thermal conductivity (≥6 W / mK), low thermal resistance (≤0.03 °C·cm 2 / W), and appearance reliability. It cannot maintain a good appearance in the double 85 (i.e., 85 °C and 85% RH, an environment that simultaneously meets a temperature of 85 °C and a humidity of 85%), 125 °C, and temperature cycle aging tests.

[0004] Due to its unique physical properties, liquid metal has high thermal conductivity and can significantly improve the heat dissipation efficiency. However, there are also potential problems such as electrical conductivity, corrosiveness, and complex processes, which require high manufacturing processes and installation and maintenance requirements. This has led to the fact that liquid metal has not been widely used in the field of interface heat dissipation. To improve these problems, there are currently two main improvement directions: one is to use liquid metal as the liquid phase and mix it with other thermal conductive auxiliary fillers (metal powder or inorganic thermal conductive auxiliary fillers) to form a liquid metal paste, which improves thixotropy, improves the wetting problem of liquid metal at the heat dissipation interface, and reduces the risk of liquid metal leakage. However, it cannot improve the corrosiveness problem for certain specific interfaces (such as aluminum); at the same time, since the surface of liquid metal (mainly metal gallium and alloys) is not coated, the continuous oxidation problem of liquid metal under double 85 conditions cannot be solved. The other is to use silicone oil, liquid metal, and other thermal conductive auxiliary fillers to compound and make silicone grease. Currently, methyl silicone oil is mainly used as the auxiliary liquid phase. This method can improve the corrosiveness problem of liquid metal. However, the formed liquid metal surface coating structure has poor stability and is prone to problems such as liquid metal precipitation, hydrolysis, and cracking in scraping operations, vibration tests, and appearance reliability tests (double 85, high temperature 125 °C, and temperature cycle aging tests).

[0005] Therefore, there is an urgent need to develop a liquid metal-based thermal conductive material with high thermal conductivity, low thermal resistance and excellent reliability. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. For this purpose, the present invention provides a liquid metal-based composite thermal conductive silicone grease and its preparation method and application. The liquid metal-based composite thermal conductive silicone grease provided by the present invention has high thermal conductivity (reaching 6.05 - 10.0 W / mk), low thermal resistance (can be as low as 0.01 - 0.03 °C·cm 2 / W), a thixotropic index of 3.3 - 4.2, and high reliability (under the test conditions of double 85, high temperature of 125 °C and temperature cycle aging test, the appearance remains good, without cracking or slipping).

[0007] The first aspect of the present invention provides a liquid metal-based composite thermal conductive silicone grease.

[0008] Specifically, a liquid metal-based composite thermal conductive silicone grease, by weight, comprises the following components:

[0009] 100 parts of modified silicone oil, 2000 - 5000 parts of liquid metal, 0 - 500 parts of thermal conductive auxiliary filler, 0.2 - 10 parts of hydrophobic fumed silica;

[0010] The modified silicone oil includes a single-end alkoxy-terminated silicone oil containing an ethylene short chain and a branched structure silicone oil;

[0011] The structure of the single-end alkoxy-terminated silicone oil containing an ethylene short chain is shown in the following formula (Ⅰ):

[0012]

[0013] Among them, R1 is an alkoxy group containing 1 - 3 carbons, R2 is CH3— or CH2=CH—, n represents the average degree of polymerization, and n is an integer of 10 - 50;

[0014] The structure of the branched structure silicone oil is shown in the following formula (Ⅱ):

[0015]

[0016] Among them, the sum of α + β + γ represents the average degree of polymerization, the sum of α + β + γ is an integer of 2 - 30, and 1 ≤ β ≤ 2, α, β and γ are all integers, and R3 is m represents the average degree of polymerization, and m is an integer of 10 - 50.

[0017] Different from the Si-O-Si structure of the silicone oil main chain, the ethylene short-chain in the main chain structure of the single-end alkoxy-capped silicone oil containing ethylene short-chain used in the present invention has a higher bond energy than the Si-O-Si chain, so it has better thermal stability. When performing surface treatment with liquid metal, it can improve the stability of the coating structure and improve the problem of liquid metal precipitation. The siloxane chain segment in the branched structure silicone oil belongs to a flexible chain segment. By increasing its degree of branching, the present invention enhances the cohesion of the liquid metal-based composite thermal conductive silicone grease, thereby improving its anti-cracking ability and appearance reliability. The present invention uses two different modified silicone oils in combination. One end of the single-end alkoxy-capped silicone oil containing ethylene short-chain is linked to the liquid metal, and the other end is embedded in the branched structure silicone oil, thereby effectively ensuring the stability of the liquid metal in the modified silicone oil system.

[0018] Preferably, the liquid metal-based composite thermal conductive silicone grease, by weight, comprises the following components: 100 parts of modified silicone oil, 3000 - 4500 parts of liquid metal, 0 - 300 parts of thermal conductive auxiliary filler, and 5 - 10 parts of hydrophobic fumed silica.

[0019] More preferably, the liquid metal-based composite thermal conductive silicone grease, by weight, comprises the following components: 100 parts of modified silicone oil, 3200 - 4500 parts of liquid metal, 60 - 200 parts of thermal conductive auxiliary filler, and 8 - 10 parts of hydrophobic fumed silica.

[0020] Preferably, the viscosity of the single-end alkoxy-capped silicone oil containing ethylene short-chain at 25°C is 10 - 40 mPa·s.

[0021] More preferably, the viscosity of the single-end alkoxy-capped silicone oil containing ethylene short-chain at 25°C is 15 - 30 mPa·s.

[0022] Preferably, the viscosity of the branched structure silicone oil at 25°C is 50 - 10000 mPa·s.

[0023] More preferably, the viscosity of the branched structure silicone oil at 25°C is 100 - 5000 mPa·s.

[0024] Even more preferably, the viscosity of the branched structure silicone oil at 25°C is 100 - 400 mPa·s.

[0025] Preferably, the mass ratio of the single - end alkoxy - capped silicone oil containing an ethylene short chain to the branched - structure silicone oil is 1:1 to 9. In the present invention, the two kinds of silicone oils are combined in a suitable ratio to coat the liquid metal, thereby obtaining excellent anti - aging performance and appearance reliability. If the mass ratio of the single - end alkoxy - capped silicone oil containing an ethylene short chain in the total mass of the modified silicone oil is less than 10%, the coating effect of the modified silicone oil on the liquid metal will be poor, affecting the appearance reliability. If the mass ratio of the single - end alkoxy - capped silicone oil containing an ethylene short chain in the total mass of the modified silicone oil is higher than 50%, problems such as aging cracks and slippage will also occur.

[0026] Preferably, the single - end alkoxy - capped silicone oil containing an ethylene short chain is at least one of the structures shown in the following formulas (Ⅲ) to (Ⅴ):

[0027]

[0028]

[0029] Among them, a represents the average degree of polymerization, and a is an integer from 10 to 30.

[0030] More preferably, the single - end alkoxy - capped silicone oil containing an ethylene short chain is at least one of the structures shown in the following Formulas One to Four:

[0031]

[0032] Preferably, the sum of α + β + γ is an integer from 10 to 30, and m is an integer from 20 to 50.

[0033] More preferably, the structure of the branched - structure silicone oil is at least one of the structures shown in the following Formulas Five to Seven:

[0034]

[0035] Preferably, the preparation method of the single - end alkoxy - capped silicone oil containing an ethylene short chain includes the following steps:

[0036] Mix vinyl - capped silicone oil, trialkoxysilane (or trimethoxysilane, triethoxysilane) and Karstedt platinum catalyst, react at 60 - 110 °C for 30 - 60 min, carry out vacuum to remove by - products, and cool down to obtain the single - end alkoxy - capped silicone oil containing an ethylene short chain.

[0037] Preferably, the vinyl - capped silicone oil is a vinyl - capped silicone oil with an average degree of polymerization of 5 - 40.

[0038] More preferably, the vinyl - capped silicone oil is a vinyl - capped silicone oil with an average degree of polymerization of 10 - 30.

[0039] Preferably, the vacuum degree for vacuum removal is -0.095 to -0.098 MPa, and / or the temperature for vacuum removal is 100 to 190 °C, and / or the time for vacuum removal is 30 to 120 min.

[0040] Preferably, the method for preparing the branched structure silicone oil comprises the following steps:

[0041] Mix a single-end vinyl-terminated silicone oil, a side hydrogen-containing polysiloxane, and a Karstedt platinum catalyst, react at 60 to 110 °C for 30 to 60 min. After the vinyl groups completely react, perform vacuum removal and cool down to obtain the branched structure silicone oil.

[0042] Preferably, the single-end vinyl-terminated silicone oil is a single-end vinyl-terminated silicone oil.

[0043] More preferably, the single-end vinyl-terminated silicone oil is a single-end vinyl-terminated silicone oil with an average degree of polymerization of 10 to 60.

[0044] Even more preferably, the single-end vinyl-terminated silicone oil is a single-end vinyl-terminated silicone oil with an average degree of polymerization of 20 to 50.

[0045] Preferably, the side hydrogen-containing polysiloxane is a side hydrogen-containing polysiloxane with a hydrogen content of 0.1 to 0.3%.

[0046] Preferably, the vacuum degree for vacuum removal is -0.095 to -0.098 MPa, and / or the temperature for vacuum removal is 100 to 190 °C, and / or the time for vacuum removal is 30 to 120 min.

[0047] Preferably, the melting point of the liquid metal is -20 to 50 °C.

[0048] Preferably, the liquid metal is at least one of gallium, gallium-indium alloy, gallium-indium-tin, and gallium-indium-bismuth alloy.

[0049] Preferably, the average particle size of the thermal conductivity assisting filler is 0.1 to 5 μm, and / or the particle size D 100 ≤ 15 μm, and / or the shape of the thermal conductivity assisting filler is spherical or quasi-spherical. The spherical or quasi-spherical thermal conductivity assisting filler helps to increase the filling amount and helps to reduce the viscosity and thermal resistance.

[0050] Preferably, the thermal conductivity assisting filler is at least one of zinc oxide, aluminum oxide, aluminum nitride, silver, copper, and nickel.

[0051] Preferably, the hydrophobic fumed silica is at least one of silicon nitride-modified hydrophobic fumed silica, polydimethylsiloxane-modified hydrophobic fumed silica, and chlorosilane-modified hydrophobic fumed silica.

[0052] Further preferably, the hydrophobic fumed silica is at least one of TS-720 produced by Cabot, TS-530 produced by Cabot, KS-20SC produced by Tokuyama Corporation of Japan, and DM-20S produced by Tokuyama Corporation of Japan.

[0053] The second aspect of the present invention provides a method for preparing a liquid metal-based composite thermal conductive silicone grease.

[0054] A method for preparing a liquid metal-based composite thermal conductive silicone grease includes the following steps:

[0055] Add a modified silicone oil and a liquid metal in sequence to obtain a paste, and then add the remaining components to prepare the liquid metal-based composite thermal conductive silicone grease.

[0056] Preferably, before use, the liquid metal is melted to a liquid state at 30-40 °C.

[0057] Preferably, the modified silicone oil and the liquid metal are added in sequence, and then stirring is started. The stirring speed is 1400-2000 r / min, and / or the stirring time is 1-20 min.

[0058] Preferably, the stirring is carried out in a planetary gravity stirring kettle.

[0059] Preferably, after obtaining the paste, a thermal conductive auxiliary filler and a hydrophobic fumed silica are added in sequence to prepare the liquid metal-based composite thermal conductive silicone grease.

[0060] Further preferably, after obtaining the paste, the paste is transferred to a planetary kettle, and then a thermal conductive auxiliary filler and a hydrophobic fumed silica are added in sequence, and stirring is carried out. The stirring speed is 10-15 Hz, and / or the vacuum degree of the planetary kettle is -0.09 MPa to -0.1 MPa, and the stirring is carried out until a uniform paste is formed.

[0061] The third aspect of the present invention provides an application of a liquid metal-based composite thermal conductive silicone grease.

[0062] An application of a liquid metal-based composite thermal conductive silicone grease in the fields of communication networks, new energy vehicles, electronic products, or artificial intelligence devices.

[0063] The fourth aspect of the present invention provides a thermal interface material.

[0064] A thermal interface material includes the liquid metal-based composite thermal conductive silicone grease.

[0065] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0066] The present invention uses modified silicone oil, liquid metal, heat conduction auxiliary filler, and hydrophobic fumed silica with specific ratios as the main components of the liquid metal-based composite thermal grease. The modified silicone oil includes single-end alkoxy-terminated silicone oil containing ethylene short chains and branched structure silicone oil. The ethylene short chains in the single-end alkoxy-terminated silicone oil containing ethylene short chains have a higher bond energy than the Si-O-Si chain, showing better thermal stability. Moreover, when the alkoxy group containing the ethylene short chain structure is used for surface treatment of the liquid metal, it can improve the stability of the coating structure and alleviate the problem of liquid metal precipitation. The Si-O-Si chain segments in the branched structure silicone oil belong to flexible chain segments with a high degree of branching, thereby improving the anti-cracking ability of the liquid metal-based composite thermal grease and enhancing the appearance reliability. The liquid metal-based composite thermal grease prepared by the present invention has both a high thermal conductivity coefficient (reaching 6.05 - 10.0 W / mk), a low thermal resistance (as low as 0.01 - 0.03 °C·cm 2 / W), and good reliability. Under high temperature (125 °C), high temperature and high humidity (double 85), and temperature cycling conditions, the appearance can remain good (without cracking or slipping), making it suitable for the assembly interface between power modules and heat sinks with high-power heat dissipation requirements, and improving the heat dissipation efficiency. Description of the Drawings

[0067] Figure 1 The figures are the appearance diagrams of the samples of the liquid metal-based composite thermal grease prepared in Example 1 of the present invention after being tested under three different conditions: double 85, 125 °C, and cyclic aging;

[0068] Figure 2 The figures are the appearance diagrams of the samples of the liquid metal-based composite thermal grease prepared in Example 2 of the present invention after being tested under three different conditions: double 85, 125 °C, and cyclic aging;

[0069] Figure 3 The figures are the appearance diagrams of the samples of the liquid metal-based composite thermal grease prepared in Example 3 of the present invention after being tested under three different conditions: double 85, 125 °C, and cyclic aging;

[0070] Figure 4 The figures are the appearance diagrams of the samples of the liquid metal-based composite thermal grease prepared in Example 4 of the present invention after being tested under three different conditions: double 85, 125 °C, and cyclic aging;

[0071] Figure 5 The figures are the appearance diagrams of the samples of the liquid metal-based composite thermal grease prepared in Example 5 of the present invention after being tested under three different conditions: double 85, 125 °C, and cyclic aging;

[0072] Figure 6 The figures are the appearance diagrams of the samples of the liquid metal-based composite thermal grease prepared in Example 6 of the present invention after being tested under three different conditions: double 85, 125 °C, and cyclic aging;

[0073] Figure 7 Appearance diagrams of the liquid metal-based composite thermal conductive silicone grease prepared in Example 7 of the present invention after being tested under three different conditions of double 85, 125°C, and cyclic aging;

[0074] Figure 8 Appearance diagrams of the liquid metal-based composite thermal conductive silicone grease prepared in Example 8 of the present invention after being tested under three different conditions of double 85, 125°C, and cyclic aging;

[0075] Figure 9 Appearance diagrams of the liquid metal-based composite thermal conductive silicone grease prepared in Example 9 of the present invention after being tested under three different conditions of double 85, 125°C, and cyclic aging;

[0076] Figure 10 Appearance diagrams of the liquid metal-based composite thermal conductive silicone grease prepared in Comparative Example 1 after being tested under three different conditions of double 85, 125°C, and cyclic aging;

[0077] Figure 11 Appearance diagrams of the liquid metal-based composite thermal conductive silicone grease prepared in Comparative Example 2 after being tested under three different conditions of double 85, 125°C, and cyclic aging;

[0078] Figure 12 Appearance diagrams of the liquid metal-based composite thermal conductive silicone grease prepared in Comparative Example 3 after being tested under three different conditions of double 85, 125°C, and cyclic aging;

[0079] Figure 13 Appearance diagrams of the liquid metal-based composite thermal conductive silicone grease prepared in Comparative Example 5 after being tested under three different conditions of double 85, 125°C, and cyclic aging;

[0080] Figure 14 Optical microscope images of the liquid metal-based composite thermal conductive silicone grease prepared in Example 1 of the present invention;

[0081] Figure 15 Optical microscope images of the liquid metal-based composite thermal conductive silicone grease prepared in Example 2 of the present invention;

[0082] Figure 16 Optical microscope images of the liquid metal-based composite thermal conductive silicone grease prepared in Example 3 of the present invention;

[0083] Figure 17 Optical microscope images of the liquid metal-based composite thermal conductive silicone grease prepared in Example 4 of the present invention. Detailed implementation manners

[0084] To enable those skilled in the art to more clearly understand the technical solutions of the present invention, the following embodiments are listed for illustration. It should be noted that the following embodiments do not limit the scope of protection required by the present invention.

[0085] In the following embodiments, the raw materials, reagents or devices used can be obtained from conventional commercial channels or can be obtained by existing known methods without special instructions.

[0086] The main raw materials involved in the embodiments and comparative examples of the present invention are as follows:

[0087] 1. Preparation of mono - end alkoxy - terminated silicone oil containing ethylene short chain

[0088] Formula One: Add 100 g of vinyl - terminated silicone oil with an average degree of polymerization of 30, 5.52 g of trimethoxyhydrosilane, and 0.1 g of Karstedt platinum catalyst into a reaction kettle, mix evenly, slowly heat up to 80 °C with stirring, and react for 60 min; after detecting that the vinyl reaction is complete, under the conditions of a vacuum degree of - 0.098 MPa and a temperature of 150 °C, carry out vacuum removal for 60 min, and then cool down to obtain Formula One.

[0089] The structural formula of Formula One is shown as follows:

[0090]

[0091] Formula Two: Add 100 g of vinyl - terminated silicone oil with an average degree of polymerization of 20, 8.11 g of trimethoxyhydrosilane, and 0.1 g of Karstedt platinum catalyst into a reaction kettle, mix evenly, slowly heat up to 80 °C with stirring, and react for 60 min; under the conditions of a vacuum degree of - 0.098 MPa and a temperature of 150 °C, carry out vacuum removal for 60 min, and then cool down to obtain Formula Two.

[0092] The structural formula of Formula Two is shown as follows:

[0093]

[0094] Formula Three: Add 100 g of vinyl - terminated silicone oil with an average degree of polymerization of 10, 15.25 g of trimethoxyhydrosilane, and 0.1 g of Karstedt platinum catalyst into a reaction kettle, mix evenly, slowly heat up to 80 °C with stirring, and react for 60 min; under the conditions of a vacuum degree of - 0.098 MPa and a temperature of 150 °C, carry out vacuum removal for 60 min, and then cool down to obtain Formula Three.

[0095] The structural formula of Formula Three is shown as follows:

[0096]

[0097] Formula Four: 100 g of vinyl-terminated silicone oil with an average degree of polymerization of 15, 14.23 g of triethoxyhydroxysilane, and 0.1 g of Karstedt's platinum catalyst were added to a reaction kettle, mixed evenly, slowly heated to 80 °C while stirring, and reacted for 60 min; after detecting that the vinyl reaction was complete, under the conditions of a vacuum degree of -0.098 MPa and a temperature of 150 °C, vacuum degassing was carried out for 60 min, and then cooled to obtain Formula Four.

[0098] The structural formula of Formula Four is as follows:

[0099]

[0100] 2. Preparation of branched silicone oil

[0101] Formula Five: 100 g of mono-vinyl-terminated silicone oil with an average degree of polymerization of 50, 30 g of side hydrogen-containing polysiloxane with a hydrogen content of 0.1%, and 0.1 g of Karstedt's platinum catalyst were added to a reaction kettle, mixed evenly, slowly heated to 80 °C while stirring, and reacted for 60 min; after the vinyl reaction was complete, under the conditions of a vacuum degree of -0.098 MPa and a temperature of 150 °C, vacuum degassing was carried out for 60 min; then cooled to obtain Formula Five.

[0102] The structural formula of Formula Five is as follows:

[0103]

[0104] Formula Six: 100 g of mono-vinyl-terminated silicone oil with an average degree of polymerization of 30, 44 g of side hydrogen-containing polysiloxane with a hydrogen content of 0.1%, and 0.01 g of Karstedt's platinum catalyst were added to a reaction kettle, mixed evenly, slowly heated to 80 °C while stirring, and reacted for 60 min; under the conditions of a vacuum degree of -0.098 MPa and a temperature of 150 °C, vacuum degassing was carried out for 60 min; then cooled to obtain Formula Six.

[0105] The structural formula of Formula Six is as follows:

[0106]

[0107] Formula Seven: 100 g of mono-vinyl-terminated silicone oil with an average degree of polymerization of 20, 32.3 g of side hydrogen-containing polysiloxane with a hydrogen content of 0.2%, and 0.1 g of Karstedt's platinum catalyst were added to a reaction kettle, mixed evenly, slowly heated to 80 °C while stirring, and reacted for 60 min; under the conditions of a vacuum degree of -0.098 MPa and a temperature of 150 °C, vacuum degassing was carried out for 60 min; then cooled to obtain Formula Seven.

[0108] The structural formula of Formula Seven is as follows:

[0109]

[0110] Formula VIII: Add 100 g of single-end vinyl-capped silicone oil with an average degree of polymerization of 20, 21.5 g of side hydrogen-containing polysiloxane with a hydrogen content of 0.3%, and 0.1 g of Karstedt platinum catalyst into a reaction kettle, mix evenly, slowly heat up to 80 °C while stirring, and react for 60 min; under the conditions of a vacuum degree of -0.098 MPa and a temperature of 150 °C, conduct vacuum degassing for 60 min; cool down to obtain the silicone oil of Formula VIII with a branched structure.

[0111] The structural formula of Formula VIII is shown as follows:

[0112]

[0113] 3. Preparation of single-end alkoxy-capped silicone oil without ethylene short chain

[0114] Formula IX: Add 100 g of single-end hydroxyl-methyl silicone oil with an average degree of polymerization of 20, 10.1 g of methyl orthosilicate, and 0.2 g of dibutylamine formate into a reaction kettle, mix evenly, slowly heat up to 80 °C while stirring, and react for 60 min; under the conditions of a vacuum degree of -0.098 MPa and a temperature of 150 °C, conduct vacuum degassing for 60 min, and cool down to obtain Formula IX.

[0115] The structural formula of Formula IX is shown as follows:

[0116]

[0117] 4. Thermal conductivity auxiliary filler:

[0118] The average particle size of zinc oxide is 0.6 μm, and D 100 is 5 μm;

[0119] The average particle size of silver powder is 3 μm, and D 100 is 12 μm;

[0120] The average particle size of alumina is 2.5 μm, and D 100 is 8 μm;

[0121] The average particle size of aluminum nitride is 2.6 μm, and D 100 is 10 μm.

[0122] 5. Hydrophobic fumed silica: The manufacturer is Cabot, and the model is TS-720.

[0123] Example 1

[0124] A liquid metal-based composite thermal conductive silicone grease comprises the components shown in Table 1 below.

[0125] The preparation method of the above liquid metal-based composite thermal conductive silicone grease comprises the following steps:

[0126] (1) placing the liquid metal in an oven at 35° C. to melt it into a liquid state, wherein the average particle size of the liquid metal after dispersion is 30 to 60 μm, and the liquid metal is set aside;

[0127] (2) adding a single-end alkoxy-terminated silicone oil containing ethylene short chains (Formula 1), a branched structure silicone oil (Formula 6) and a liquid metal in sequence into a planetary gravity stirred kettle, rotating at 1600 r / min, and dispersing at high speed for 10 min until a uniform paste is obtained;

[0128] (3) The paste is transferred to a planetary reactor, and a thermal conductive auxiliary filler and a hydrophobic fumed silica are added in sequence. The mixture is stirred at a stirring frequency of 12 Hz and a vacuum degree of -0.098 MPa until a uniform paste product is formed, which is a liquid metal-based composite thermal conductive silicone grease.

[0129] Embodiment 2-9

[0130] Embodiment 2-9 provides liquid metal-based composite thermal conductive silicone grease, which is different from Embodiment 1 in that the components are different, as shown in Table 1. The preparation method is the same as that of Embodiment 1.

[0131] Comparative Examples 1-5

[0132] Comparative Examples 1-5 provide liquid metal-based composite thermal conductive silicone grease, and the specific components are shown in Table 1. Comparative Examples 1-3 and Comparative Example 5 have different components from Example 1, and the preparation method is the same as Example 1. Comparative Example 4 has the same components as Example 1, but a different preparation method. The preparation method of Comparative Example 4 is as follows:

[0133] (1) Place the liquid metal in a 35°C oven to melt it into a liquid state for later use;

[0134] (2) Adding a single-end alkoxy-terminated silicone oil containing ethylene short chains, a branched structure silicone oil, a thermal conductive auxiliary filler, and a hydrophobic fumed silica in a planetary gravity stirred kettle in sequence, setting the speed to 1600 r / min, and dispersing at high speed for 10 min until a uniform paste is obtained;

[0135] (3) The paste is transferred to a planetary reactor, liquid metal is added, and the mixture is stirred at a stirring frequency of 12 Hz and a vacuum degree of -0.098 MPa until a uniform paste product is formed, which is a liquid metal-based composite thermal conductive silicone grease.

[0136] Product effect testing

[0137] 1. Test methods

[0138] (1) Thermal conductivity: The thermal conductivity of each paste was tested using an interface material thermal resistance and thermal conductivity tester (model: LW-9389) at a temperature of 80°C and a pressure of 30 psi.

[0139] (2) Viscosity @ 25°C: Use a CAP 2000 viscometer to measure the viscosity of each paste under the conditions of 4# @ 5r.

[0140] (3) Thixotropy index: Use an HA type rotational viscometer to measure the viscosity of each paste at low shear (7# @ 1rpm) and high shear (7# @ 10rpm), and then calculate the viscosity ratio at low shear and high shear.

[0141] (4) Thermal resistance: Use an interface material thermal resistance and thermal conductivity measuring instrument (model: LW-9389) to measure the thermal resistance of each paste at a temperature of 80°C @ a pressure of 30 psi.

[0142] (5) Appearance reliability:

[0143] Uniformly coat the sample between two glass slides for assembly. After assembly, the sample should be centered as much as possible and control the thickness of the sample to be 0.1 - 0.15 mm and the diameter to be 26 - 30 mm. The sample is made. Then, three parallel samples are tested under the following three different aging test conditions:

[0144] Condition ① - Double 85: Under the relative conditions of a temperature of 80°C and a humidity of 80%, keep the appearance fixture vertical throughout the process, and observe the appearance state of the sample after 1000h of aging test.

[0145] Condition ② - 125°C: Under the condition of a temperature of 125°C, keep the appearance fixture vertical throughout the process, and observe the appearance state of the sample after 1000h of aging test.

[0146] Condition ③ - Temperature cycle: Under the condition of -40 to 125°C (temperature change rate: 11°C / min, dwell time: 30 min), keep the appearance fixture vertical throughout the process, and observe the appearance state of the sample after 200 cycles of aging test.

[0147] 2. Test results

[0148] Table 1 Components and their dosages (parts by weight) of each example and comparative example

[0149]

[0150]

[0151] As can be seen from the above table, the thermal conductivity of the liquid metal-based composite thermal conductive silicone grease prepared in Examples 1 - 9 reaches 6.05 - 10.0 W / mk, the viscosity reaches 80000 - 127000 mPa·s, the thixotropy index is 3.3 - 4.2, and the thermal resistance is as low as 0.01 - 0.03 °C·cm 2 / W, showing good thermal conductivity. After the liquid metal-based composite thermal conductive silicone grease of Examples 1-9 was subjected to aging tests under three different conditions of double 85, 125 °C high temperature, and temperature cycling, the results were respectively as Figure 1 A-C, Figure 2 A-C, Figure 3 A-C, Figure 4 A-C, Figure 5 A-C, Figure 6 A-C, Figure 7 A-C, Figure 8 A-C, Figure 9 shown in A-C. It can be seen that even after different aging tests, the appearance remains intact, without obvious cracking or slipping, indicating good appearance reliability and excellent stability.

[0152] From the results of Comparative Example 1, it can be seen that when the degree of branching of the branched silicone oil is high (i.e., the number of branched chains exceeds 3), the viscosity of the composite silicone grease increases significantly, reducing the wetting performance of the composite silicone grease with the radiator surface and increasing the difficulty of screen printing operation. At the same time, the degree of branching has a great influence on the cohesive strength of the composite silicone grease. With a high degree of branching, the toughness of the system is poor. After aging treatment, there are obvious cracking situations in the appearance of Comparative Example 1, such as Figure 10 A-C.

[0153] In Comparative Example 2, the amount of liquid metal was reduced. Due to the reduction of heat transfer channels under the effective path, the contact thermal resistance increased, resulting in a decrease in thermal conductivity and thixotropic index. The appearance is as shown in Figure 11 A-C.

[0154] From Comparative Example 3 and Comparative Example 5, in Comparative Example 3, a single-end alkoxysilane without an ethylene short chain was used, and in Comparative Example 5, a single-end alkoxysilane containing an ethylene short chain was not used. Although the thermal conductivity performance is good, the thixotropic index is lower than 3, and the binding ability to liquid metal is insufficient, resulting in easy precipitation and oxidation of liquid metal and poor reliability. This shows that the ethylene short chain in the single-end alkoxysilane of the present invention has an obvious promoting effect on improving the thixotropic effect of the composite silicone grease. The appearance of Comparative Example 3 and Comparative Example 5 are respectively as Figure 12 A-C and Figure 13 A-C.

[0155] In Comparative Example 4, the preparation process of the composite silicone grease was adjusted, and a layering phenomenon occurred. This is because liquid metal has a very high surface tension, and the process of Comparative Example 4 is extremely likely to cause the thermal conductivity auxiliary filler and liquid metal to form an incompatible phase, resulting in poor stability of the silicone grease, so that some liquid metals cannot be well dispersed in the silicone grease, and the appearance shows layering. Therefore, relevant performance tests were not carried out.

[0156] In summary, the preparation method of the present invention is simple and easy to operate. First, the liquid metal is highly dispersed with the modified silicone oil, and the liquid metal is uniformly cut into droplets with the same particle size by high-speed shearing (the average particle size of the liquid metal in the liquid metal-based composite thermal conductive silicone grease is 30-60 μm, such as Figures 14 - 17 ), and then it reacts with the modified silicone oil to form a stable coating structure, thus ensuring the structural stability when adding the thermal conductive auxiliary material. With the cooperation of other thermal conductive auxiliary fillers, the characteristics of high thermal conductivity and low thermal resistance are achieved, and the thermal resistance can even be as low as 0.01 °C·cm 2 / W. It shows excellent stability during the double 85, 125 °C and temperature cycle aging tests, the liquid metal does not precipitate, and the process reliability and appearance reliability are high. It can be further applied to the stencil printing operation, and the liquid metal is not easy to precipitate.

Claims

1. A liquid metal-based composite thermal conductive silicone grease, characterized in that, By weight, it comprises the following components: 100 parts of modified silicone oil, 2000 - 5000 parts of liquid metal, 0 - 500 parts of heat conduction auxiliary filler, 0.2 - 10 parts of hydrophobic fumed silica; The modified silicone oil includes a single - end alkoxy - terminated silicone oil containing an ethylene short chain and a branched - structure silicone oil; The structure of the single - end alkoxy - terminated silicone oil containing an ethylene short chain is shown in the following formula (Ⅰ): Wherein, R1 is an alkoxy group containing 1 - 3 carbons, R2 is CH3— or CH2=CH—, n represents the average degree of polymerization, and n is an integer of 10 - 50; The structure of the branched - structure silicone oil is shown in the following formula (Ⅱ): Among them, the sum of α + β + γ represents the average degree of polymerization. The sum of α + β + γ is an integer from 2 to 30, and 1 ≤ β ≤ 2. α, β, and γ are all integers. R3 is m represents the average degree of polymerization, and m is an integer from 10 to 50.

2. The liquid metal-based composite thermal conductive silicone grease according to claim 1, wherein By weight, it comprises the following components: 100 parts of modified silicone oil, 3000 - 4500 parts of liquid metal, 0 - 300 parts of heat conduction auxiliary filler, 5 - 10 parts of hydrophobic fumed silica.

3. The liquid metal-based composite thermal conductive silicone grease according to claim 1, characterized in that, The single - end alkoxy - terminated silicone oil containing an ethylene short chain is at least one of the structures shown in the following formula (Ⅲ) to formula (Ⅴ): Wherein, a represents the average degree of polymerization, and a is an integer of 10 - 30.

4. The liquid metal-based composite heat-conducting silicone grease according to claim 1, wherein, The sum of α + β + γ is an integer of 10 - 30, and m is an integer of 20 - 50.

5. The liquid metal-based composite thermal conductive silicone grease according to claim 1, wherein The liquid metal is at least one of gallium, gallium - indium alloy, gallium - indium - tin, gallium - indium - bismuth alloy.

6. The liquid metal-based composite thermal conductive silicone grease according to claim 1, wherein The average particle size of the heat conduction auxiliary filler is 0.1 to 5 μm, and / or the particle size D 100 of the heat conduction auxiliary filler is ≤ 15 μm, and / or the shape of the heat conduction auxiliary filler is spherical or quasi-spherical.

7. The liquid metal-based composite thermal conductive silicone grease according to claim 1, wherein The hydrophobic fumed silica is at least one of silicon nitride - modified hydrophobic fumed silica, polydimethylsiloxane - modified hydrophobic fumed silica, chlorosilane - modified hydrophobic fumed silica.

8. The preparation method of the liquid metal-based composite thermal conductive silicone grease according to any one of claims 1-7, characterized in that, It includes the following steps: Sequentially add the modified silicone oil and the liquid metal to obtain a paste, and then add the remaining components to prepare the liquid - metal - based composite thermal conductive silicone grease.

9. Application of the liquid - metal - based composite thermal conductive silicone grease according to any one of claims 1 - 7 in the fields of communication networks, new energy vehicles, electronic products or artificial intelligence devices.

10. A thermal interface material, characterized in that, It includes the liquid - metal - based composite thermal conductive silicone grease.

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