A low-density weight-reducing and heat-conducting silica gel and its preparation method

Abstract

The present invention belongs to the technical field of silicone rubber, and discloses a low-density weight-reducing heat-conducting silicone rubber and a preparation method thereof. The preparation method comprises the following steps: surface-modifying boron nitride and / or aluminum nitride powder with an aluminate coupling agent, and then calcining under air or oxygen conditions to obtain porous alumina-coated heat-conducting powder; then surface-modifying with a silane coupling agent to obtain silane-coupling-agent-modified heat-conducting powder; mixing the obtained silane-coupling-agent-modified heat-conducting powder with vinyl silicone oil, hydrogen-containing silicone oil and a catalyst uniformly, then removing bubbles under vacuum, and then hot-pressing and curing by a calender to obtain the low-density weight-reducing heat-conducting silicone rubber. The present invention uses low-density boron nitride and / or aluminum nitride powder to replace alumina powder, and can achieve better heat-conducting performance and weight-reducing performance. At the same time, through further surface treatment with porous alumina combined with a silane coupling agent, the heat-conducting performance and mechanical properties of the obtained heat-conducting silicone rubber can be significantly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicone rubber, and particularly relates to a low-density weight-reducing thermal conductive silicone rubber and a preparation method thereof. Background Art

[0002] For electronic products, new energy, artificial intelligence, and smart wearables, the weight requirements for products are getting higher and higher. Under the same performance conditions, the lower the density, the lower the weight, the smaller the loss of potential energy, and the better the user experience. For example, especially VR glasses, headphones, mobile phones, and smart wearables are more sensitive to weight and have greater requirements for lightweight.

[0003] At present, the main components of thermal conductive silicone rubber in the industry are thermal conductive powder + flame retardant + silicone oil + hydrogen-containing + additives. The main component of the thermal conductive powder is alumina, and its structure is a solid spherical metal body with a conventional density of 3.5 - 4.0 g / cm 3 , with a large density and specific gravity. Other raw materials for thermal conductive fillers also include boron nitride, aluminum nitride, etc. The density of conventional hexagonal boron nitride is usually 1.5 - 2.5 g / cm 3 , and the density of cubic boron nitride is usually 3.0 - 3.5 g / cm 3 ; the conventional density of raw material aluminum nitride is 2.5 - 3.3 g / cm 3 . And the thermal conductivity of boron nitride and aluminum nitride is better than that of alumina. Therefore, using boron nitride or aluminum nitride to replace alumina as the thermal conductive filler can achieve the purpose of low density and weight reduction.

[0004] To improve the thermal conductivity of thermal conductive silicone rubber products, it is necessary to increase the content of thermal conductive fillers. However, the compatibility and bonding force between thermal conductive fillers such as boron nitride and aluminum nitride and the silicone rubber matrix are poor. The increase in thermal conductive fillers will lead to a decrease in the mechanical properties of the silicone rubber, unable to meet the usage requirements. Generally speaking, the better the dispersion performance of the thermal conductive filler in the silicone rubber matrix, the better its thermal conductivity and mechanical properties. Therefore, the same thermal conductivity and mechanical properties can be achieved under the condition of lower thermal conductive filler dosage, and the density of the silicone rubber matrix is relatively low. By reducing the dosage of thermal conductive fillers, the purpose of low density and weight reduction can also be achieved. Therefore, by improving the dispersion and bonding force of thermal conductive fillers such as boron nitride and aluminum nitride in the silicone rubber matrix, the purpose of low density and weight reduction and the purpose of strengthening mechanical properties can be achieved.

[0005] Patent CN 110343391 A discloses a low-density and high-thermal-conductivity silicone gasket. By using modification aids such as KH-151, KH-171, KH-540, KH-550, titanate, etc. to modify alumina, aluminum hydroxide, and boron nitride, the dispersibility and bonding force of the thermal-conductivity fillers in the silicone rubber matrix are improved. However, directly using the above modification aids has poor modification effects on boron nitride and aluminum nitride, and has limited effects on improving the thermal conductivity and mechanical properties of the products. Summary of the Invention

[0006] Based on the above-mentioned drawbacks and deficiencies of the prior art, the primary object of the present invention is to provide a preparation method of a low-density weight-reducing and thermal-conductivity silicone.

[0007] Another object of the present invention is to provide a thermal-conductivity silicone prepared by the above method.

[0008] The object of the present invention is achieved by the following technical solutions:

[0009] A preparation method of a low-density weight-reducing and thermal-conductivity silicone, comprising the following steps:

[0010] (1) Surface-modify boron nitride and / or aluminum nitride powder with an aluminate coupling agent, and then calcine it under air or oxygen conditions to obtain porous alumina-coated boron nitride and / or aluminum nitride powder;

[0011] (2) Surface-modify the obtained porous alumina-coated boron nitride and / or aluminum nitride powder with a silane coupling agent to obtain silane-coupling-agent-modified boron nitride and / or aluminum nitride powder;

[0012] (3) Mix the obtained silane-coupling-agent-modified boron nitride and / or aluminum nitride powder with vinyl silicone oil, hydrogen-containing silicone oil, and a catalyst evenly, then remove air bubbles under vacuum, and then hot-press and cure it through a calender to obtain a low-density weight-reducing and thermal-conductivity silicone.

[0013] Preferably, in step (1), the particle size of the boron nitride and / or aluminum nitride powder is 0.5 - 10 μm.

[0014] Preferably, the method of the surface modification in step (1) is as follows:

[0015] Add the boron nitride and / or aluminum nitride powder into a fluidized bed to make it in a suspended motion state, heat it up to 60 - 100 °C, and then spray an aluminate coupling agent solution for reaction to obtain aluminate-coupling-agent-surface-modified boron nitride and / or aluminum nitride powder.

[0016] The present invention adopts the method of surface modification by spraying an aluminate coupling agent in a fluidized bed, which has the advantages of uniform coating and good modification effect.

[0017] Preferably, the dosage of the aluminate coupling agent is 5% - 20% of the mass of boron nitride and / or aluminum nitride powder.

[0018] Preferably, in step (1), the calcination temperature is 300 - 800 °C, and the calcination time is 2 - 24 h.

[0019] In the present invention, the surface of boron nitride and / or aluminum nitride powder is pre-modified by an aluminate coupling agent, and then a porous alumina coating layer with strong binding force to boron nitride and / or aluminum nitride powder is obtained through calcination. This porous alumina coating layer has the characteristic of high specific surface area, which can effectively enhance the reactivity with the silane coupling agent and the binding force with the silicone rubber matrix, improve the dispersion effect of the thermal conductive powder in the silicone rubber matrix, thereby improving the thermal conductivity and mechanical properties. At the same time, this porous alumina coating layer has the characteristic of low density, and has no obvious weight gain effect on boron nitride and / or aluminum nitride powder, and can better maintain the low density characteristic of boron nitride and / or aluminum nitride thermal conductive powder.

[0020] Preferably, in step (2), the silane coupling agent is at least one of an alkyl silane coupling agent, a vinyl silane coupling agent, and an epoxy silane coupling agent; more preferably, the silane coupling agent is a vinyl silane coupling agent.

[0021] In the present invention, the surface of the porous alumina-coated boron nitride and / or aluminum nitride powder is further modified by a silane coupling agent, which can further improve the compatibility between the thermal conductive powder and the silicone rubber matrix and reduce the adverse effect of the thermal conductive filler on the mechanical properties of the silicone rubber. In addition, the thermal conductive filler surface-modified by a vinyl silane coupling agent can also generate a chemical cross-linking reaction with the silicone rubber matrix during the subsequent hot pressing and curing process, further significantly improving the mechanical strength of the thermal conductive silicone rubber.

[0022] Preferably, the addition amount of the silane coupling agent is 1% - 10% of the mass of the porous alumina-coated boron nitride and / or aluminum nitride powder.

[0023] Preferably, in step (3), the mass ratio of the silane coupling agent-modified boron nitride and / or aluminum nitride powder to vinyl silicone oil and hydrogen-containing silicone oil is 100:30 - 80:20 - 50.

[0024] Preferably, in step (3), the catalyst is chloroplatinic acid or Karstedt's platinum catalyst; the catalyst dosage is 0.005% - 0.02% of the total mass of the reaction materials.

[0025] Preferably, in step (3), the mixing means first mixing the silane coupling agent-modified boron nitride and / or aluminum nitride powder with vinyl silicone oil and hydrogen-containing silicone oil evenly at 100 - 160 °C in a vacuum kneader, and then cooling to room temperature and adding the catalyst and mixing evenly.

[0026] Preferably, in step (3), the temperature for hot pressing and curing is 100 - 150°C, and the time is 5 - 15 min.

[0027] A low - density weight - reducing thermally conductive silicone is prepared by the above - mentioned method.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) In the present invention, the thermally conductive filler uses low - density boron nitride and / or aluminum nitride powder to replace alumina powder, which can achieve better thermal conductivity and weight - reducing performance.

[0030] (2) In the present invention, the boron nitride and / or aluminum nitride thermally conductive powder is surface - coated with porous alumina and further surface - treated with a silane coupling agent, which can significantly improve the thermal conductivity and mechanical properties of the obtained thermally conductive silicone, reduce the amount of thermally conductive filler used, and thus reduce the density of the thermally conductive silicone product. Specific embodiments

[0031] The present invention will be further described in detail below with reference to embodiments, but the embodiments of the present invention are not limited thereto.

[0032] Example 1

[0033] A preparation method of a low - density weight - reducing thermally conductive silicone, comprising the following steps:

[0034] (1) Boron nitride powder with a D50 particle size of 1.5 μm and a density of 2.25 g / cm 3 is added to a fluidized bed, and high - pressure circulating nitrogen at 80°C is introduced to make it in a suspended motion state, and then an ethyl acetate solution of aluminum aluminate coupling agent DL - 411 is sprayed for reaction. The dosage of the aluminum aluminate coupling agent is 12% of the mass of the boron nitride powder, and boron nitride powder surface - modified with aluminum aluminate coupling agent is obtained. Then air is introduced, and the temperature is raised to 650°C for calcination treatment for 8 h to obtain boron nitride powder coated with porous alumina.

[0035] (2) The boron nitride powder coated with porous alumina obtained in step (1) is cooled to 60°C by air cooling, and then a methyltrimethoxysilane coupling agent solution is sprayed for surface modification. The addition amount of the silane coupling agent is 5% of the mass of the boron nitride powder coated with porous alumina, and silane coupling agent - modified boron nitride powder is obtained.

[0036] (3) Add the obtained silane coupling agent - modified boron nitride powder, vinyl silicone oil, and hydrogen - containing silicone oil into a kneader at a mass ratio of 100:50:30, fully knead at 150 °C, then cool down to room temperature, add 0.01% of Kast platinum catalyst, mix evenly, remove bubbles under vacuum, and then inject the material onto a calender by vacuum extraction to extrude a product with a corresponding thickness. The pressed material passes through a tunnel furnace at 140 °C for 12 m and 3 min, 125 °C for 10 m and 3 min, and 110 °C for 10 m and 2 min for thermal curing and forming, and is naturally cooled by air, then wound up to obtain a low - density weight - reducing thermal - conductive silica gel.

[0037] Example 2

[0038] A preparation method of a low - density weight - reducing thermal - conductive silica gel, comprising the following steps:

[0039] (1) Add boron nitride powder with a D50 particle size of 1.5 μm and a density of 2.25 g / cm 3 into a fluidized bed, introduce high - pressure circulating nitrogen at 80 °C to make it in a suspended motion state, and then spray an ethyl acetate solution of aluminate coupling agent DL - 411 for reaction. The dosage of the aluminate coupling agent is 5% of the mass of the boron nitride powder to obtain aluminate coupling agent - surface - modified boron nitride powder. Then introduce air and heat up to 400 °C for calcination treatment for 12 h to obtain porous alumina - coated boron nitride powder.

[0040] (2) Cool down the porous alumina - coated boron nitride powder obtained in step (1) to 60 °C by air cooling, and then spray a methyltrimethoxysilane coupling agent solution for surface modification. The addition amount of the silane coupling agent is 1% of the mass of the porous alumina - coated boron nitride powder to obtain silane coupling agent - modified boron nitride powder.

[0041] (3) Add the obtained silane coupling agent - modified boron nitride powder, vinyl silicone oil, and hydrogen - containing silicone oil into a kneader at a mass ratio of 100:30:20, fully knead at 150 °C, then cool down to room temperature, add 0.01% of Kast platinum catalyst, mix evenly, remove bubbles under vacuum, and then inject the material onto a calender by vacuum extraction to extrude a product with a corresponding thickness. The pressed material passes through a tunnel furnace at 140 °C for 12 m and 3 min, 125 °C for 10 m and 3 min, and 110 °C for 10 m and 2 min for thermal curing and forming, and is naturally cooled by air, then wound up to obtain a low - density weight - reducing thermal - conductive silica gel.

[0042] Example 3

[0043] A preparation method of a low - density weight - reducing thermal - conductive silica gel, comprising the following steps:

[0044] (1) Add boron nitride powder with a D50 particle size of 1.5 μm and a density of 2.25 g / cm 3Add the boron nitride powder into the fluidized bed, introduce 80℃ high pressure circulating nitrogen to make it in suspension, then spray the ethyl acetate solution of aluminate coupling agent DL-411 to react, the amount of aluminate coupling agent is 20% of the mass of boron nitride powder, and obtain boron nitride powder with surface modified by aluminate coupling agent. Then introduce air, heat to 750℃ and calcine for 3h to obtain porous alumina coated boron nitride powder.

[0045] (2) The porous alumina-coated boron nitride powder obtained in step (1) is cooled to 60° C. by air cooling, and then sprayed with a methyltrimethoxysilane coupling agent solution for surface modification, wherein the amount of the silane coupling agent added is 10% of the mass of the porous alumina-coated boron nitride powder to obtain a silane coupling agent-modified boron nitride powder.

[0046] (3) The obtained silane coupling agent modified boron nitride powder, vinyl silicone oil and hydrogen-containing silicone oil are added into a kneader in a mass ratio of 100:80:50 and fully kneaded at 150° C., then cooled to room temperature, 0.01% Custer platinum catalyst is added and mixed evenly, vacuum defoamed, and then the material is added to a calender in a vacuum extraction manner to press out a product of corresponding thickness, and the pressed material is passed through a tunnel furnace at 140° C., 12 m, 3 min; 125° C., 10 m, 3 min; 110° C., 10 m, 2 min, thermally cured and formed, naturally cooled by air, and rolled to obtain a low-density weight-reducing thermally conductive silicone.

[0047] Example 4

[0048] A method for preparing low-density weight-reducing thermally conductive silica gel, compared with Example 1, using an equal amount of D50 particle size of 2 μm and a density of 3.25 g / cm 3 Aluminum nitride powder replaces boron nitride powder.

[0049] Example 5

[0050] A method for preparing low-density weight-reducing thermally conductive silica gel, compared with Example 1, using an equal amount of epoxy silane coupling agent KH-560 to replace methyl trimethoxy silane coupling agent.

[0051] Example 6

[0052] A method for preparing a low-density, weight-reducing, thermally conductive silica gel, compared with Example 1, using an equal amount of vinyl trimethoxy silane coupling agent to replace the methyl trimethoxy silane coupling agent.

[0053] Comparative Example 1

[0054] A method for preparing low-density weight-reducing thermally conductive silica gel comprises the following steps:

[0055] (1) The particle size of D50 is 1.5 μm and the density is 2.25 g / cm 3The boron nitride powder is added into a fluidized bed, and then a methyltrimethoxysilane coupling agent solution is sprayed for surface modification, wherein the amount of the silane coupling agent added is 5% of the mass of the boron nitride powder, to obtain silane coupling agent-modified boron nitride powder.

[0056] (2) The obtained silane coupling agent modified boron nitride powder, vinyl silicone oil and hydrogen-containing silicone oil are added into a kneader in a mass ratio of 100:50:30 and fully kneaded at 150° C., then cooled to room temperature, 0.01% Custer platinum catalyst is added and mixed evenly, vacuum defoamed, and then the material is added to a calender in a vacuum extraction manner to extrude a product of corresponding thickness, and the pressed material is passed through a tunnel furnace at 140° C., 12 m, 3 min; 125° C., 10 m, 3 min; 110° C., 10 m, 2 min, thermally cured and formed, naturally cooled by air, and rolled to obtain a low-density weight-reducing thermal conductive silicone.

[0057] Comparative Example 2

[0058] A method for preparing low-density weight-reducing thermally conductive silica gel comprises the following steps:

[0059] (1) The particle size of D50 is 1.5 μm and the density is 2.25 g / cm 3 The boron nitride powder is added into the fluidized bed, and 80°C high-pressure circulating nitrogen is introduced to make it in a suspended motion state, and then the ethyl acetate solution of aluminate coupling agent DL-411 is sprayed to react. The amount of aluminate coupling agent is 12% of the mass of the boron nitride powder, and the boron nitride powder with the surface modified by the aluminate coupling agent is obtained.

[0060] (2) The boron nitride powder surface-modified with the aluminate coupling agent obtained in step (1) is cooled to 60° C. by air cooling, and then sprayed with a methyltrimethoxysilane coupling agent solution for surface modification, wherein the amount of the silane coupling agent added is 5% of the mass of the boron nitride powder surface-modified with the aluminate coupling agent, to obtain a silane coupling agent-modified boron nitride powder.

[0061] (3) The obtained silane coupling agent modified boron nitride powder, vinyl silicone oil and hydrogen-containing silicone oil are added into a kneader in a mass ratio of 100:50:30 and fully kneaded at 150° C., then cooled to room temperature, 0.01% Custer platinum catalyst is added and mixed evenly, vacuum defoamed, and then the material is added to a calender in a vacuum extraction manner to press out a product of corresponding thickness, and the pressed material is passed through a tunnel furnace at 140° C., 12 m, 3 min; 125° C., 10 m, 3 min; 110° C., 10 m, 2 min, thermally cured and formed, naturally cooled by air, and rolled to obtain a low-density weight-reducing thermal conductive silicone.

[0062] Comparative Example 3

[0063] This comparative example uses an equivalent D50 particle size of 1.5 μm and a density of 3.82 g / cm3 Replace the boron nitride powder with alumina powder, and the rest is the same as in Example 1.

[0064] The density (measured by the drainage method), thermal conductivity (according to the ASTM D5470-2006 standard), and tensile strength (according to GB / T 528-2009) of the thermal conductive silicone rubbers obtained in the above examples and comparative examples were tested, and the results are shown in Table 1 below.

[0065] Table 1

[0066]

[0067]

[0068] From the comparison results of Examples 1 to 4 and Comparative Example 3 in Table 1, it can be seen that in the present invention, boron nitride or aluminum nitride powder is used to replace alumina powder, and the obtained thermal conductive silicone rubber has the characteristics of low density and high thermal conductivity. From the comparison results of Example 1 and Examples 5 to 6, it can be seen that compared with other silane coupling agents for modification, the use of vinyl silane coupling agent results in a thermal conductive silicone rubber with higher thermal conductivity and tensile strength. The reason is that the vinyl silane coupling agent can generate a chemical cross-linking reaction with the silicone rubber matrix during the subsequent hot pressing and curing process, thereby improving the bonding force and compatibility between the thermal conductive filler and the silicone rubber matrix. From the result of Comparative Example 1, it can be seen that when the boron nitride thermal conductive powder is not pre-coated with porous alumina on the surface, the thermal conductivity and mechanical strength of the obtained thermal conductive silicone rubber are significantly reduced. The reason is that the porous alumina coating layer can effectively enhance the reactivity of the thermal conductive filler with the silane coupling agent and the bonding force with the silicone rubber matrix, improve the dispersion effect of the thermal conductive filler in the silicone rubber matrix, and thus improve the thermal conductivity and mechanical properties. From the result of Comparative Example 2, it can be seen that the simultaneous surface modification with aluminate coupling agent and silane coupling agent has little effect on the thermal conductivity and mechanical properties of the obtained thermal conductive silicone rubber compared with the single silane coupling agent surface modification, further proving that the formation of a porous alumina coating layer by high-temperature calcination is the key to improving the thermal conductivity and mechanical strength of the product.

[0069] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing low-density weight-reducing thermally conductive silica gel, characterized in that: The steps include: (1) surface-modifying boron nitride and / or aluminum nitride powder with an aluminate coupling agent, and then calcining in air or oxygen to obtain porous alumina-coated boron nitride and / or aluminum nitride powder; (2) surface-modifying the obtained porous alumina-coated boron nitride and / or aluminum nitride powder using a silane coupling agent to obtain silane coupling agent-modified boron nitride and / or aluminum nitride powder; (3) uniformly mixing the obtained silane coupling agent-modified boron nitride and / or aluminum nitride powder with vinyl silicone oil, hydrogen-containing silicone oil and a catalyst, degassing the mixture in vacuum, and then hot-pressing and curing the mixture through a calender to obtain a low-density, weight-reducing, thermally conductive silicone rubber; The surface modification method in step (1) is as follows: Boron nitride and / or aluminum nitride powder is added into a fluidized bed to make it in a suspended motion state, the temperature is raised to 60-100°C, and then an aluminate coupling agent solution is sprayed to react to obtain boron nitride and / or aluminum nitride powder with surface modified by an aluminate coupling agent; the amount of the aluminate coupling agent used is 5%-20% of the mass of the boron nitride and / or aluminum nitride powder.

2. The method for preparing a low-density weight-reducing thermally conductive silica gel according to claim 1, characterized in that: The particle size of the boron nitride and / or aluminum nitride powder in step (1) is 0.5-10 μm.

3. The method for preparing a low-density weight-reducing thermally conductive silica gel according to claim 1, characterized in that: The calcination temperature in step (1) is 300-800°C, and the calcination time is 2-24 hours.

4. The method for preparing a low-density weight-reducing thermally conductive silica gel according to claim 1, characterized in that: The silane coupling agent in step (2) is at least one of an alkyl silane coupling agent, a vinyl silane coupling agent, and an epoxy silane coupling agent.

5. The method for preparing a low-density weight-reducing thermally conductive silica gel according to claim 4, characterized in that: The silane coupling agent is a vinyl silane coupling agent.

6. A method for preparing a low-density weight-reducing thermally conductive silica gel according to claim 4 or 5, characterized in that: The added amount of the silane coupling agent is 1% to 10% of the mass of the porous alumina-coated boron nitride and / or aluminum nitride powder.

7. The method for preparing a low-density weight-reducing thermally conductive silica gel according to claim 1, characterized in that: In step (3), the mass ratio of the silane coupling agent modified boron nitride and / or aluminum nitride powder to the vinyl silicone oil and hydrogen-containing silicone oil is 100:30~80:20~50; the catalyst is chloroplatinic acid or Custer platinum catalyst; the amount of the catalyst is 0.005%~0.02% of the total mass of the reaction materials.

8. The method for preparing a low-density weight-reducing thermally conductive silica gel according to claim 1, characterized in that: The mixing in step (3) refers to first mixing the silane coupling agent modified boron nitride and / or aluminum nitride powder with the vinyl silicone oil and the hydrogen-containing silicone oil in a vacuum kneader at 100-160°C, then cooling to room temperature and adding the catalyst to mix evenly; the temperature of the hot pressing curing molding is 100-150°C and the time is 5-15 minutes.

9. A low-density, weight-reducing, thermally conductive silica gel, characterized in that: It is prepared by the method according to any one of claims 1 to 8.

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