Silica gel pad with high thermal conductivity and heat resistance and preparation method thereof

Abstract

The invention discloses a silica gel pad with high thermal conductivity and heat resistance and a preparation method thereof, and the method comprises the following steps: preparing a composite thermal conductive filler, mixing boron nitride nanosheets and graphene according to a certain mass ratio, adding a silane coupling agent, carrying out ball milling, adding spherical alumina, and mixing; preparing modified organic silicon resin, wherein methyl vinyl silicone rubber, hydrogen-containing silicone oil, a platinum catalyst and MQ silicon resin react to obtain the modified organic silicon resin; mixing and defoaming the modified organic silicon resin, the composite heat-conducting filler, the flame retardant and the antioxidant to obtain a heat-conducting silica gel mixture; preparing a reinforced base material, carrying out plasma treatment on glass fiber cloth, and then impregnating the glass fiber cloth with vinyl ester resin for pre-curing; and grinding the mixture by three rollers, coating the mixture on a reinforced base material, and heating and curing. The thermal conductivity of the obtained silica gel pad is 2.5-3.5 W / m.K, the volume resistivity is larger than 1012 omega.cm, the long-term heat-resistant temperature reaches 200 DEG C or above, the tensile strength is larger than 5 MPa, the peel strength is larger than 15 N / cm, and the silica gel pad has excellent thermal conductivity, insulativity, heat resistance and mechanical strength.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of silica gel, and particularly relates to a silica gel pad with high thermal conductivity and heat resistance and a preparation method thereof. BACKGROUND

[0002] As an important thermal interface material, the silica gel pad is widely used between electronic components and heat sinks to transfer heat, insulate, dampen and seal. With the development of 5G communication, high-performance computing and power electronic devices towards miniaturization and high power density, the thermal conductivity, heat resistance and process environmental friendliness of the thermal silica gel pad are extremely required.

[0003] At present, the mainstream high-performance thermal silica gel pad on the market is committed to improving the thermal conductivity by filling high-thermal-conductivity fillers. Traditional fillers such as alumina and zinc oxide have limited intrinsic thermal conductivity, and even with high filler content, the thermal conductivity is difficult to break through 2.0 W / (m·K). Therefore, the industry has begun to explore the use of emerging high-thermal-conductivity fillers such as boron nitride, graphene and carbon nanotubes.

[0004] However, the application of such advanced fillers faces a series of new technical challenges: (1) Filler dispersion and interface problem: nano materials such as boron nitride nanosheets and graphene have large specific surface area and high surface energy, and are prone to agglomeration in the silicone matrix, making it difficult to form a uniform and efficient three-dimensional thermal conduction network. At the same time, the interface compatibility between inorganic fillers and organic resin matrix is poor, and there is significant phonon scattering, resulting in actual thermal conductivity gain far lower than the theoretical value.

[0005] (2) Process and curing efficiency contradiction: In order to obtain high thermal conductivity, high filler filling is often required, which leads to a sharp increase in the viscosity of the mixture and poor flowability, making it difficult for subsequent processes such as coating and molding. In addition, in the thick film system with high filling and no light transmission, the traditional thermal curing process faces new challenges, i.e. longer time is needed to ensure complete curing in the deep layer, which seriously restricts the production efficiency; and if the curing is insufficient, it will directly affect the long-term heat resistance reliability and mechanical properties of the product.

[0006] (3) Comprehensive performance balance problem: Simply improving thermal conductivity often comes at the expense of mechanical properties, resulting in increased brittleness and decreased tear resistance. At the same time, in high temperature (such as >180℃) environment, thermal degradation of the organic silicon molecular chain and thermal mismatch of the filler-matrix interface will lead to thermal conductivity decay and shortened service life.

[0007] Therefore, it has become a technical problem to be solved in the field to develop a new type of silica gel pad and a preparation method thereof, which can solve the problems of efficient dispersion and three-dimensional network construction of fillers, interface thermal resistance reduction, and full and efficient curing in a high-filled and non-transparent system while ensuring high insulation. SUMMARY

[0008] The present application aims to overcome the deficiencies of the prior art, and provides a silica gel pad with high thermal conductivity and heat resistance and a preparation method thereof, and the specific content is shown as follows: The preparation method of a silica gel pad with high thermal conductivity and heat resistance comprises the following steps: (1) Preparation of composite thermal conductive filler: mix boron nitride nanosheets and graphene at a mass ratio of (1.5-3):1, add 1-3% of silane coupling agent as a surface treatment agent based on the total mass of the composite thermal conductive filler, and ball mill in a planetary ball mill at a speed of 300-500 r / min under the protection of inert gas for 2-4 hours. After ball milling, add 5-15% of spherical alumina based on the total mass of the composite thermal conductive filler, and mix by high-speed mechanical stirring at a speed of 800-1500 r / min for 10-30 minutes. The particle size of the obtained composite thermal conductive filler is controlled to be 0.1-1 μm; (2) Preparation of modified silicone resin: add 100 parts of methyl vinyl silicone rubber with a vinyl content of 0.1-0.5%, 5-12 parts of hydrogen-containing silicone oil with a hydrogen content of 0.5-1.0% in a reaction kettle, the molar ratio of Si-H bond in the hydrogen-containing silicone oil to vinyl in the methyl vinyl silicone rubber is (1.0-1.2):1, and then add 0.1-0.5 parts of platinum catalyst and 3-8 parts of MQ type silicone resin as a structure reinforcing agent. Stir at a speed of 200-300 r / min at 70-90°C for 1-2 hours to obtain the modified silicone resin; (3) Preparation of thermal conductive silicone mixture: place 100 parts of the modified silicone resin, 35-50 parts of the composite thermal conductive filler, 5-10 parts of flame retardant, and 2-5 parts of antioxidant in a vacuum stirrer, mix and degas at 50-70°C and -0.09 to -0.1 MPa for 30-60 minutes to obtain the thermal conductive silicone mixture; (4) Preparation of reinforced substrate: after the glass fiber cloth with an areal density of 50-100 g / m 2 is treated by plasma, it is immersed in vinyl ester resin and pre-cured at 100-120°C for 10-20 minutes to obtain the reinforced substrate; (5) Coating and composite curing: the thermal conductive silicone mixture is first treated by a three-roll mill at a roll gap of 10-20 μm and a roll speed ratio of 1:2:4 for 2-3 times, and then uniformly coated on the reinforced substrate by a slot coater at a speed of 1-3 m / min, and the coating thickness is controlled to be 0.3-1 mm. Then, it is heated in an oven at 100-120°C for 30-60 minutes to complete the curing, and the silica gel pad is obtained.

[0009] Further, in step (1), part of the boron nitride nanosheet is treated by amination, and the aminated boron nitride nanosheet accounts for 10-30% of the total mass; the graphene is functionalized graphene prepared by an oxidation-reduction method, and the oxygen content of the functionalized graphene is 8-15%. By controlling the amination ratio of boron nitride and the oxygen content of graphene, a moderate active site is established on the surface of the filler, which not only enhances the interfacial bonding force between the filler and the matrix, but also avoids the influence of too many functional groups on the thermal conductivity, so that the interfacial thermal resistance is reduced by more than 25%, while the intrinsic thermal conductivity of the filler is maintained.

[0010] Further, in step (1), the silane coupling agent is γ-aminopropyl triethoxysilane (KH-550) or γ-(2,3-epoxypropoxy) propyl trimethoxysilane (KH-560); the inert gas is nitrogen or argon. By selecting a specific silane coupling agent and performing ball milling under inert gas protection, the structural damage and performance degradation of graphene and boron nitride under mechanical force are effectively prevented, and the integrity retention rate of the filler is more than 95%, while the dispersion stability of the filler in the matrix is significantly improved through surface modification.

[0011] Further, in step (2), the platinum catalyst is isopropanol solution of chloroplatinic acid or platinum-vinylsiloxane complex. By using a suitable platinum catalyst system, the hydrosilylation reaction is efficiently carried out under mild conditions of 70-90°C, with a reaction conversion rate of more than 98%, effectively avoiding the influence of catalyst residues on the long-term thermal stability of the product, and improving the service life of the product at 200°C high temperature environment by more than 15%. Further, in step (2), the mass ratio of M unit to Q unit in the MQ type silicone resin is (0.6-0.8):1. By accurately controlling the structure composition of MQ silicone resin, a moderate rigid-flexible network structure is constructed at the molecular level, so that the material not only maintains excellent flexibility (elongation at break > 150%), but also significantly improves the mechanical strength, with a tensile strength of more than 5 MPa, solving the problem of material embrittlement caused by high thermal conductivity filler.

[0012] Further, in step (3), the flame retardant is surface-modified aluminum hydroxide or ammonium polyphosphate; the antioxidant is a compound of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester and tris[2,4-di-tert-butylphenyl] phosphite with a mass ratio of 1:(0.5-1). By using a synergistic system of surface-modified flame retardant and composite antioxidant, through physical isolation and chemical inhibition mechanisms, excellent flame retardant performance (reaching UL94 V-0 level) of the material is realized, and the anti-aging ability of the material is significantly improved, with a service life of more than 2000 hours at 200°C high temperature environment, and a performance retention rate of more than 85%.

[0013] Further, in step (4), the plasma treatment is performed under the conditions of a power of 300-500 W and an oxygen or argon atmosphere for 30-120 seconds. By optimizing the plasma treatment process parameters, suitable micro-nano structures and active groups are formed on the surface of the glass fiber cloth, the interfacial bonding strength of the fiber cloth and the resin is greatly improved, the interlayer peeling strength reaches 15 N / cm or more, the delamination phenomenon during use is effectively prevented, and the product reliability is improved.

[0014] Further, the silica gel pad further comprises a foamed buffer layer, the foamed buffer layer is prepared by mixing methyl vinyl silicone rubber, insulating and heat-conducting filler and fumed white carbon black at a mass ratio of 60:20:10, adding 2-5 parts of a chemical foaming agent, and foaming at 160-180 DEG C, and the thickness is 0.2-0.5 mm; the foamed buffer layer is compounded with one side of the uncoated silica gel of the reinforced substrate through hot pressing, and a layer of silane interface treatment agent is coated on the composite interface before hot pressing. The foamed buffer layer of the innovative design uses methyl vinyl silicone rubber with excellent heat resistance as the matrix, while maintaining the flexibility of the foamed structure, an independent heat conduction network is established, which not only provides excellent buffer sealing function (compression permanent deformation <10%), but also maintains moderate heat conduction performance (>1.0 W / m·K), which is matched with the long-term heat resistance temperature (more than 200 DEG C) of the silica gel pad as a whole, and realizes the perfect combination of heat conduction and buffer function.

[0015] Further, the chemical foaming agent is azodicarbonamide; the hot pressing conditions are: temperature 120-140 DEG C, pressure 1-3 MPa, time 30-90 seconds; the silane interface treatment agent is gamma-(2,3-epoxypropoxy) propyl trimethoxysilane; and the insulating and heat-conducting filler is spherical aluminum oxide or boron nitride. By optimizing the ratio of foaming agent and interface treatment agent and process parameters, the foamed layer with uniform pore size (50-200 mu m) and stable structure is obtained while ensuring the firm combination of the foamed layer and the substrate (interface peeling strength >=8 N / cm), and the compression resilience is excellent, which provides reliable mechanical protection and thermal management function for electronic products.

[0016] The application also provides a high-thermal-conductivity insulating silica gel pad prepared by the above method, the thermal conductivity of the silica gel pad is 2.5-3.5 W / m·K, the volume resistivity is greater than 10 12 Ω·cm, the long-term heat resistance temperature reaches 200 DEG C or more, the tensile strength is greater than 5 MPa, and the peeling strength is greater than 15 N / cm. The final product realizes breakthroughs in multiple key performance indicators, fully meeting the harsh requirements of 5G communication equipment, high-performance computing and other high-end electronic devices on heat-conducting materials.

[0017] Compared with the prior art, the application has the following beneficial effects: I. The present application forms a unique three-dimensional heat conduction framework mainly by sheet lamination and supplemented by spherical alumina particles by scientifically compounding sheet boron nitride, graphene and spherical alumina. Sheet materials are lapped to form the main heat conduction path and establish the basic heat conduction skeleton; spherical alumina particles are precisely filled in the gap of sheet materials and play a key role as a heat conduction bridge, effectively connecting isolated sheet materials and significantly enhancing the connectivity of the heat conduction path. This multi-scale and multi-dimensional heat conduction network design enables rapid multi-stage heat transfer within the material, significantly improves the heat conduction performance from less than 2.0 W / (m·K) of traditional materials to 2.5-3.5 W / (m·K), and improves the heat conduction efficiency by more than 50%.

[0018] II. The present application innovatively uses a two-stage dispersion process of high-speed dispersion + three-roll grinding to solve the problems of viscosity surge and filler agglomeration caused by high filler content (35-50 parts). First, the powerful shear force of high-speed mechanical stirring (800-1500 r / min) breaks the soft agglomeration of fillers and realizes the preliminary dispersion of fillers; then, the three-roll grinding machine is used for precise grinding under specific roll gap and roll speed ratio conditions to further dissociate the hard agglomeration of fillers and promote the directional arrangement of sheet fillers to some extent. This hierarchical dispersion strategy effectively solves the processing problem of high viscosity system, making the mixture have excellent coating process while maintaining high thermal conductivity, and the coating speed can reach 1-3 m / min.

[0019] III. The present application optimizes the thermal curing process parameters in view of the characteristics of high filler content and non-transparent thick film system. The use of 100-120℃ stepwise temperature control combined with 30-60 minutes of sufficient curing time not only avoids surface defects caused by rapid heating, but also ensures that the material can be completely crosslinked from the surface to the inside. This optimized curing scheme effectively solves the common "surface dryness and internal dryness" problem of high filler systems, ensures the mechanical properties and thermal stability of the product, and controls the total production cycle within a reasonable range, achieving the best balance between product quality and production efficiency.

[0020] IV. The present application realizes the synergistic improvement of thermal conductivity, processing performance, mechanical properties and heat resistance through the optimization design of material system and the precise control of process parameters. Not only the heat conduction efficiency is significantly improved, but also the product has good flexibility, mechanical strength and long-term reliability, and all performance indicators are in perfect balance, which can meet the stringent requirements of high-end electronic products for thermal conductive materials. DETAILED DESCRIPTION

[0021] To enable persons skilled in the art to understand the features and effects of the present application, the following will make general explanations and definitions for the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used herein have the usual meanings to those skilled in the art of the present application, and in case of conflict, the definitions in the specification shall prevail.

[0022] The present application will be described below with specific embodiments and examples. It should be understood that these specific embodiments and examples are merely illustrative and are not intended to limit the scope of the present application and its uses.

[0023] The methods, reagents and conditions employed in the following preparation examples, comparative examples and examples are conventional methods, reagents and conditions in the art, unless otherwise specified.

[0024] Unless otherwise specified, in the present application, parts by weight represent the relative mass fraction in the composition, which can be any mass unit, such as but not limited to kilogram, kilogram, gram, etc.

[0025] The specific embodiments are described in detail below, but it should be understood that the scope of protection of the present application is not limited by the specific embodiments. The raw materials and reagents used in the examples are commercially available unless otherwise specified.

[0026] Example 1 (1) Preparation of composite thermal conductive filler: 200 g of boron nitride nanosheet was accurately weighed, of which the nanosheet treated with amino accounted for 20% of the total mass. 100 g of functionalized graphene with an oxygen content of 12% was weighed. The two materials were poured into a mixing tank, and 9 g of KH-560 silane coupling agent was added as a surface treatment agent. The mixture was transferred to a planetary ball mill, nitrogen gas was introduced as a protective gas, and the rotation speed was 400 r / min. Ball milling was carried out for 3 hours. After ball milling, the material was taken out, 45 g of spherical alumina was added, and the high-speed disperser was started at a rotation speed of 1200 r / min for mechanical stirring for 20 minutes to ensure that the components were fully mixed and uniform.

[0027] (2) Preparation of modified silicone resin: In a reaction kettle with stirrer and temperature control, 100 g of methyl vinyl silicone rubber with a vinyl content of 0.3% was added, followed by the addition of 10 g of hydrogen-containing silicone oil with a hydrogen content of 0.8%. The molar ratio of Si-H bond in hydrogen-containing silicone oil to vinyl in methyl vinyl silicone rubber was controlled to be 1.1:1. Then 0.3 g of platinum-vinyl siloxane complex was added as a catalyst, and finally 6 g of MQ type silicone resin with a mass ratio of M unit to Q unit of 0.7:1 was added as a structure enhancer. Start stirring at a speed of 250 r / min, gradually heat to 80°C, and keep the temperature for 1.5 hours to obtain the modified silicone resin.

[0028] (3) Preparation of the heat-conducting silicone mixture: 100 g of the modified silicone resin prepared above was placed in a vacuum stirrer, 42 g of the composite heat-conducting filler, 8 g of the surface-modified aluminum hydroxide flame retardant, and 3.5 g of the antioxidant (a mixture of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester and tris[2,4-di-tert-butylphenyl]phosphite at a mass ratio of 1:0.8) were added. The stirring and heating system was turned on, the temperature was controlled at 60°C, and the mixture was mixed and degassed under a vacuum of -0.095 MPa for 45 minutes to obtain a uniform heat-conducting silicone mixture.

[0029] (4) Preparation of the reinforced substrate: a glass fiber cloth with a surface density of 80 g / m 2 was placed in a plasma treatment device and treated under an argon atmosphere at a power of 400 W for 80 seconds. The treated glass fiber cloth was immersed in the vinyl ester resin, and after ensuring sufficient impregnation, was pre-cured in an oven at 110°C for 15 minutes to obtain a reinforced substrate.

[0030] (5) Coating and composite curing: the heat-conducting silicone mixture was first treated by a three-roll mill, with a roll gap of 15 μm and a roll speed ratio of 1:2:4, and was continuously treated for 3 passes. Then the treated material was transferred to a slot coater and uniformly coated on the reinforced substrate at a speed of 2 m / min, with a coating thickness of 0.5 mm. Finally, the coated material was placed in an oven and cured at 110°C for 45 minutes to obtain a silicone pad product.

[0031] Example 2 (1) Preparation of the composite heat-conducting filler: 150 g of boron nitride nanosheets was accurately weighed, of which the amino-treated nanosheets accounted for 10% of the total mass. 100 g of functionalized graphene with an oxygen content of 8% was weighed. The two materials were poured into a mixing tank, and 7.5 g of KH-550 silane coupling agent was added as a surface treatment agent. The mixture was transferred to a planetary ball mill, argon gas was introduced as a protective gas, and the ball milling was carried out at a speed of 500 r / min for 2 hours. After the ball milling was completed, the material was taken out, 37.5 g of spherical aluminum oxide was added, and the high-speed disperser was started at a speed of 1500 r / min for 10 minutes to ensure that the components were fully mixed and uniform.

[0032] (2) Preparation of modified silicone resin: In a reaction kettle with stirrer and temperature control, 100 g of methyl vinyl silicone rubber with a vinyl content of 0.1% was added, followed by the addition of 5 g of hydrogen-containing silicone oil with a hydrogen content of 0.5%, controlling the molar ratio of Si-H bonds in the hydrogen-containing silicone oil to the vinyl groups in the methyl vinyl silicone rubber to be 1.0:1. Then 0.1 g of chloroplatinic acid isopropyl alcohol solution was added as a catalyst, and finally 3 g of MQ type silicone resin with a mass ratio of M unit to Q unit of 0.6:1 was added as a structure enhancer. Start stirring at 200 r / min, gradually heat to 70°C, and continue to react at this temperature for 2 hours to obtain a modified silicone resin.

[0033] (3) Preparation of thermal conductive silicone mixture: Take 100 g of the modified silicone resin prepared above and place it in a vacuum stirrer, add 35 g of composite thermal conductive filler, 5 g of ammonium polyphosphate flame retardant, and 2 g of antioxidant (a mixture of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester and tris[2,4-di-tert-butylphenyl] phosphite at a mass ratio of 1:0.5). Start stirring and heating system, control the temperature at 50°C, mix and degas under -0.09 MPa vacuum for 60 minutes to obtain a uniform thermal conductive silicone mixture.

[0034] (4) Preparation of reinforced substrate: Take a glass fiber cloth with a surface density of 50 g / m 2 , place it in a plasma treatment device, and treat it under a 300 W power and oxygen atmosphere for 30 seconds. Dip the treated glass fiber cloth in vinyl ester resin, ensure full soaking, and then pre-cure it in a 100°C oven for 20 minutes to obtain a reinforced substrate.

[0035] (5) Coating and composite curing: The thermal conductive silicone mixture is first treated by a three-roll mill, controlling the roll gap to be 10 μm and the roll speed ratio to be 1:2:4, and continuously treated for 2 passes. Then the treated material is transferred to a slot coater and uniformly coated on the reinforced substrate at a speed of 1 m / min, controlling the coating thickness to be 0.3 mm. Finally, the coated material is placed in an oven and cured at 100°C for 60 minutes to obtain a silicone pad product.

[0036] Example 3 (1) Composite thermal conductive filler preparation: accurately weigh 300 g of boron nitride nanosheets, of which the amino-treated nanosheets account for 30% of the total mass. Weigh 100 g of functionalized graphene with an oxygen content of 15%. Pour the two materials into a mixing tank, and add 12 g of KH-560 silane coupling agent as a surface treatment agent. Transfer the mixture into a planetary ball mill, and introduce nitrogen gas as a protective gas. Mill at a speed of 300 r / min for 4 hours. After the ball milling is completed, remove the material, add 60 g of spherical alumina, and transfer it into a high-speed disperser. Mechanically stir at a speed of 800 r / min for 30 minutes to ensure that the components are fully mixed and uniform.

[0037] (2) Preparation of modified silicone resin: In a reaction kettle with a stirrer and temperature control, add 100 g of methyl vinyl silicone rubber with a vinyl content of 0.5%. Then add 12 g of hydrogen-containing silicone oil with a hydrogen content of 1.0%. Control the molar ratio of Si-H bonds in the hydrogen-containing silicone oil to the vinyl groups in the methyl vinyl silicone rubber to be 1.2:1. Add 0.5 g of platinum-vinyl siloxane complex as a catalyst, and finally add 8 g of MQ silicone resin with a mass ratio of M units to Q units of 0.8:1 as a structure enhancer. Start stirring at a speed of 300 r / min, gradually heat to 90°C, and maintain the temperature for 1 hour to obtain the modified silicone resin.

[0038] (3) Preparation of thermal conductive silicone mixture: Take 100 g of the modified silicone resin prepared above and place it in a vacuum stirrer. Add 50 g of composite thermal conductive filler, 10 g of surface-modified aluminum hydroxide flame retardant, and 5 g of antioxidant (a mixture of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester and tris[2,4-di-tert-butylphenyl] phosphite at a mass ratio of 1:1). Start the stirring and heating system, control the temperature at 70°C, and mix and degas under a vacuum of -0.1 MPa for 30 minutes to obtain a uniform thermal conductive silicone mixture.

[0039] (4) Preparation of reinforced substrate: Take a glass fiber cloth with a surface density of 100 g / m 2 , and place it in a plasma treatment device. Treat it under an argon atmosphere at a power of 500 W for 120 seconds. Dip the treated glass fiber cloth in vinyl ester resin, ensure that it is fully soaked, and then pre-cure it in an oven at 120°C for 10 minutes to obtain the reinforced substrate.

[0040] (5) Coating and composite curing: First, process the thermal conductive silicone mixture through a three-roll mill, control the roll gap to be 20 μm, the roll speed ratio to be 1:2:4, and continuously process for 3 passes. Then, transfer the processed material into a slot coater, uniformly coat it on the reinforced substrate at a speed of 3 m / min, and control the coating thickness to be 1.0 mm. Finally, place the coated material in an oven and cure it at 120°C for 30 minutes to obtain the finished silicone pad.

[0041] Example 4 (1) Preparation of composite thermal conductive filler: 200 g of boron nitride nanosheets were accurately weighed, of which the amino-treated nanosheets accounted for 20% of the total mass. 100 g of functionalized graphene with an oxygen content of 12% was weighed. The two materials were poured into a mixing tank, and 9 g of KH-560 silane coupling agent was added as a surface treatment agent. The mixture was transferred to a planetary ball mill, and nitrogen gas was introduced as a protective gas. The ball mill was operated at a speed of 400 r / min for 3 hours. After the ball milling was completed, the material was taken out, 45 g of spherical alumina was added, and the high-speed disperser was operated at a speed of 1200 r / min for 20 minutes to ensure that the components were fully mixed and uniform.

[0042] (2) Preparation of modified silicone resin: In a reaction kettle with a stirrer and temperature control, 100 g of methyl vinyl silicone rubber with a vinyl content of 0.3% was added, followed by the addition of 10 g of hydrogen-containing silicone oil with a hydrogen content of 0.8%. The molar ratio of Si-H bonds in the hydrogen-containing silicone oil to the vinyl groups in the methyl vinyl silicone rubber was controlled to be 1.1:1. Then 0.3 g of platinum-vinyl siloxane complex was added as a catalyst, and finally 6 g of MQ-type silicone resin with a mass ratio of M unit to Q unit of 0.7:1 was added as a structure enhancer. The stirring was started, and the speed was controlled at 250 r / min. The temperature was gradually increased to 80°C, and the reaction was continued at this temperature for 1.5 hours to obtain the modified silicone resin.

[0043] (3) Preparation of thermal conductive silicone mixture: 100 g of the modified silicone resin prepared above was placed in a vacuum stirrer, and 42 g of composite thermal conductive filler, 8 g of surface-modified aluminum hydroxide flame retardant, and 3.5 g of antioxidant (a mixture of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester and tris[2,4-di-tert-butylphenyl]phosphite with a mass ratio of 1:0.8) were added. The stirring and heating system was started, and the temperature was controlled at 60°C. The mixture was mixed and degassed under a vacuum of -0.095 MPa for 45 minutes to obtain a uniform thermal conductive silicone mixture.

[0044] (4) Preparation of reinforced substrate: A glass fiber cloth with a surface density of 80 g / m 2 was placed in a plasma treatment device and treated under an argon atmosphere at a power of 400 W for 80 seconds. The treated glass fiber cloth was immersed in vinyl ester resin, and after ensuring sufficient infiltration, it was pre-cured in an oven at 110°C for 15 minutes to obtain the reinforced substrate.

[0045] (5) Coating and composite curing: The heat-conducting silica gel mixture is first processed by a three-roll grinder, with a nip of 15 μm and a roller speed ratio of 1:2:4, for 3 continuous passes. The processed material is then transferred to a slot coater and uniformly coated on the reinforced substrate at a speed of 2 m / min, with a coating thickness of 0.5 mm. Finally, the coated material is placed in an oven and cured at 110°C for 45 minutes to obtain the silica gel pad substrate.

[0046] (6) Foamed cushion layer preparation and composite: 60 g of methyl vinyl silicone rubber, 20 g of spherical boron nitride insulation and heat-conducting filler, and 10 g of fumed white carbon black are accurately weighed and poured into a mixing tank for thorough mixing. 3 g of azodicarbonamide chemical foaming agent is added, and after uniform mixing, it is transferred into a mold for foaming and molding at 170°C, with a foamed layer thickness of 0.3 mm. A layer of γ-(2,3-epoxypropoxy) propyl trimethoxysilane interface treatment agent is uniformly coated between the foamed cushion layer and the uncoated surface of the silica gel pad reinforced substrate. The two are stacked and placed in a hot press at a temperature of 130°C and a pressure of 2 MPa for 60 seconds, completing the composite and obtaining the final composite silica gel pad product.

[0047] Comparative Example 1 (Traditional Single Filler) (1) Heat-conducting filler preparation: 345 g of ordinary micron-sized aluminum oxide powder is accurately weighed and poured into a mixing tank, and 9 g of KH-560 silane coupling agent, accounting for 2.6% of the total mass, is added as a surface treatment agent. The mixture is transferred to a planetary ball mill, nitrogen gas is introduced as a protective gas, and the ball mill is operated at a speed of 400 r / min for 3 hours to obtain a single-component heat-conducting filler. (The total mass of this filler is the same as that of the composite filler in Example 1, both being 345 g) (2) Silicone resin preparation: In a reaction kettle with a stirrer and temperature control, 100 g of methyl vinyl silicone rubber with a vinyl content of 0.3% is added, followed by the addition of 10 g of hydrogen-containing silicone oil with a hydrogen content of 0.8%. The molar ratio of Si-H bonds in the hydrogen-containing silicone oil to vinyl groups in the methyl vinyl silicone rubber is controlled at 1.1:1. 0.3 g of platinum-vinyl siloxane complex is added as a catalyst. The stirrer is turned on at a speed of 250 r / min, and the temperature is gradually raised to 80°C. The reaction is continued at this temperature for 1.5 hours to obtain the silicone resin (without adding MQ silicone resin reinforcing agent).

[0048] (3) Preparation of the heat-conducting silicone mixture: 100 g of the above-prepared silicone resin was placed in a vacuum stirrer, 42 g of single-component heat-conducting filler, 8 g of surface-modified aluminum hydroxide flame retardant, and 3.5 g of antioxidant (tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester and tri[2,4-di-tert-butylphenyl] phosphite in a mass ratio of 1:0.8) were added. The stirring and heating system was turned on, the temperature was controlled at 60°C, and the mixture was mixed and degassed under a vacuum of-0.095 MPa for 45 minutes to obtain the heat-conducting silicone mixture.

[0049] (4) Preparation of the reinforced substrate: a glass fiber cloth with a surface density of 80 g / m 2 was directly immersed in the vinyl ester resin without plasma treatment and was pre-cured in an oven at 110°C for 15 minutes to obtain the reinforced substrate.

[0050] (5) Coating and composite curing: the heat-conducting silicone mixture was directly transferred to a slot coater (without three-roll grinding treatment) and uniformly coated on the reinforced substrate at a speed of 2 m / min, with the coating thickness controlled at 0.5 mm. The coated material was placed in an oven and cured at 110°C for 45 minutes to obtain the silicone pad finished product.

[0051] Comparative Example 2 (simplified dispersion process) (1) Preparation of the composite heat-conducting filler: 200 g of boron nitride nanosheets, of which the nanosheets treated with amino accounted for 20% of the total mass, and 100 g of functionalized graphene with an oxygen content of 12% were weighed. The two materials were poured into a mixing tank, and 9 g of KH-560 silane coupling agent was added as a surface treatment agent. The mixture was transferred to a planetary ball mill, nitrogen was introduced as a protective gas, and the ball milling was carried out at a speed of 400 r / min for 3 hours. After the ball milling was completed, the material was taken out, 45 g of spherical aluminum oxide was added, and the high-speed dispersion machine was started at a speed of 1200 r / min for mechanical stirring for 20 minutes to ensure that the components were fully mixed and uniform.

[0052] (2) Preparation of the modified silicone resin: exactly the same as in Example 1.

[0053] (3) Preparation of the heat-conducting silicone mixture: 100 g of the above-prepared modified silicone resin was placed in a vacuum stirrer, 42 g of the composite heat-conducting filler, 8 g of surface-modified aluminum hydroxide flame retardant, and 3.5 g of antioxidant were added. The stirring and heating system was turned on, the temperature was controlled at 60°C, and the mixture was mixed and degassed under a vacuum of-0.095 MPa for 45 minutes to obtain the heat-conducting silicone mixture (without three-roll grinding treatment).

[0054] (4) Preparation of the reinforced substrate: exactly the same as in Example 1.

[0055] (5) Coating and composite curing: The heat-conducting silica gel mixture is directly transferred into a slot coater (without three-roll grinding treatment), and uniformly coated on the reinforced substrate at a speed of 2 m / min, with the coating thickness controlled at 0.5 mm. The coated material is placed in an oven and cured at 110°C for 45 minutes to obtain the silica gel pad product.

[0056] Comparative Example 3 (insufficient curing process) Steps (1) to (4) are exactly the same as in Example 1.

[0057] (5) Coating and composite curing: The heat-conducting silica gel mixture is first treated by a three-roll grinder, with the gap controlled at 15 μm and the roller speed ratio at 1:2:4, for continuous treatment of 3 times. Then the treated material is transferred into a slot coater, and uniformly coated on the reinforced substrate at a speed of 2 m / min, with the coating thickness controlled at 0.5 mm. Finally, the coated material is placed in an oven and cured at 110°C for 15 minutes (30 minutes shorter than in Example 1), to obtain the silica gel pad product.

[0058] Comparative Example 4 (use of conductive filler) (1) Preparation of composite heat-conducting filler: 200 g of boron nitride nanosheets is accurately weighed, of which the nanosheets treated with amino account for 20% of the total mass. 100 g of unoxidized conductive graphene (oxygen content <2%) is weighed. The two materials are poured into a mixing tank, and 9 g of KH-560 silane coupling agent is added as a surface treatment agent. The mixture is transferred into a planetary ball mill, and nitrogen gas is introduced as a protective gas, with a rotation speed of 400 r / min for 3 hours. After ball milling, the material is taken out, 45 g of spherical alumina is added, and the high-speed disperser is started at a rotation speed of 1200 r / min for mechanical stirring for 20 minutes, to ensure that the components are fully mixed and uniform.

[0059] Steps (2) to (5) are exactly the same as in Example 1.

[0060] Comparative Example 5 (use of conductive filler in foaming layer) According to the complete steps of Example 4, but in the preparation of the foaming buffer layer, the spherical boron nitride insulating heat-conducting filler is replaced with an equal amount of conductive carbon black, and all other raw material ratios and process parameters remain exactly the same as in Example 4.

[0061] Comparative Example 6 (single boron nitride nanosheet filler) (1) Preparation of the thermal conductive filler: 345 g of boron nitride nanosheets was accurately weighed, of which the amino-treated nanosheets accounted for 20% of the total mass. 9 g of KH-560 silane coupling agent accounting for about 2.6% of the total mass was added as a surface treatment agent. The mixture was transferred into a planetary ball mill, nitrogen was introduced as a protective gas, and the ball milling was carried out at a speed of 400 r / min for 3 hours to obtain a single-component thermal conductive filler. (The total mass of this filler is the same as that of the composite filler in Example 1, both being 345 g) Steps (2) to (5) are the same as in Example 1.

[0062] Comparative Example 7 (single graphene filler) (1) Preparation of the thermal conductive filler: 345 g of functionalized graphene with an oxygen content of 12% was accurately weighed, and 9 g of KH-560 silane coupling agent accounting for about 2.6% of the total mass was added as a surface treatment agent. The mixture was transferred into a planetary ball mill, nitrogen was introduced as a protective gas, and the ball milling was carried out at a speed of 400 r / min for 3 hours to obtain a single-component thermal conductive filler. (The total mass of this filler is the same as that of the composite filler in Example 1, both being 345 g) Steps (2) to (5) are the same as in Example 1.

[0063] Comparative tests were conducted on Examples 1-4 and Comparative Examples 1-7, and the test methods were as follows: Thermal conductivity test: ASTM D5470 standard heat flow meter method was used, and LW-9389 thermal conductivity tester was used to measure at a temperature of 50°C and a pressure of 0.5 MPa.

[0064] Volume resistivity test: According to GB / T 1410 standard, ZC-90G high insulation resistance measuring instrument was used to test at a direct current voltage of 500 V.

[0065] Thermal aging test: The sample was placed in a constant temperature oven at 200°C and continuously heated for 500 hours, and the performance change before and after the test was tested.

[0066] Tensile strength test: According to GB / T 528 standard, UTM2103 electronic universal testing machine was used, and the tensile speed was 500 mm / min.

[0067] Peeling strength test: According to GB / T 2792 standard, 90° peeling test method was used, and the peeling speed was 100 mm / min.

[0068] Flame retardant grade test: According to UL94 vertical burning standard.

[0069] The test results are shown in the following table: From the analysis of the table data: 1. Thermal conductivity comparison analysis The thermal conductivities of Examples 1-4 are in the range of 2.6-3.4 W / m·K, which are significantly higher than 1.8 W / m·K of Comparative Example 1, which has the lowest thermal conductivity, proving the effectiveness of the composite thermal conductive filler system. The thermal conductivity of Comparative Example 2, which has a simplified dispersion process, decreases significantly, indicating the key role of three-roll grinding in filler dispersion. Although the thermal conductivity of Comparative Example 4 is relatively high (3.0 W / m·K), its insulation performance is seriously substandard.

[0070] Under the premise that the total mass of the composite thermal conductive filler is completely the same (345 g), the thermal conductivity of Example 1 (BNNS / graphene / alumina complex) is significantly higher than that of Comparative Example 6 (2.3 W / m·K) using only boron nitride nanosheets and Comparative Example 7 (2.7 W / m·K) using only graphene. This fully proves the scientificity and synergistic effect of the three-dimensional thermal conduction architecture proposed in the present application, which is "mainly sheet lapping and auxiliary spherical filling". Spherical alumina effectively fills the gaps between sheet-like fillers and plays a key role as a "thermal conduction bridge", which cannot be achieved by a single filler.

[0071] 2. Insulation performance comparison analysis The volume resistivity of all examples is >10 12 Ω·cm, meeting the high insulation requirement. Comparative Example 4 and Comparative Example 5 use conductive fillers, and the volume resistivity is only 10 8 Ω·cm level, which decreases by 4 orders of magnitude. This result highlights the importance of strictly controlling the insulation properties of the filler.

[0072] Comparative Example 6 (using only BNNS) exhibits the best insulation but average thermal conductivity; Comparative Example 7 (using only graphene) has good thermal conductivity but significantly decreased insulation. Example 1, by complexing the three, maintains excellent insulation while achieving the highest thermal conductivity, achieving the best balance of performance.

[0073] 3. Heat resistance comparison analysis After 500 hours of aging at 200℃, the thermal retention rate of the examples is >87%, and the retention rate of Comparative Example 1 is only 78%, proving the necessity of the composite system and sufficient curing. The retention rate of Comparative Example 3 (insufficient curing) is 82%, indicating the influence of sufficient curing on long-term reliability.

[0074] 4. Mechanical property comparison analysis The tensile strength (5.1-6.2 MPa) and peel strength (14-18 N / cm) of the examples are significantly better than those of the comparative examples, and the mechanical properties of Comparative Example 1 are the worst, proving the importance of MQ silicone resin reinforcement and plasma treatment. The mechanical properties of Comparative Example 2 decrease due to uneven dispersion.

[0075] The mechanical properties of Example 1 are also superior to Comparative Examples 6 and 7, indicating that the combination of multiple shapes and sizes of fillers, in conjunction with the MQ resin, is more conducive to forming a stable reinforcing network.

[0076] 5. Process performance comparison All examples have good appearance quality, while Comparative Examples 1 and 2 have surface defects, which proves the importance of the complete process route (including three-roll milling, plasma treatment, etc.) to product quality.

[0077] Through systematic comparison tests and analysis, the following comprehensive conclusions can be clearly drawn: the technical scheme of the present application, by innovatively designing a composite heat-conducting filler system, combines flaky boron nitride, graphene, and spherical aluminum oxide in a scientific ratio to build a unique three-dimensional heat-conducting network, cooperates with a secondary dispersion process of high-speed dispersion and three-roll milling to effectively solve the agglomeration and processing problems caused by high filler content, and then through an optimized thermal curing process to ensure the full crosslinking and long-term reliability of the product, finally successfully realizes the synergistic improvement of the heat-conducting performance (2.6-3.4 W / m·K), insulation performance (volume resistivity > 10 12 Ω·cm), mechanical performance (tensile strength 5.1-6.2 MPa, peel strength 14-18 N / cm), and heat resistance (heat-conducting retention rate > 87% after 500 hours of aging at 200℃) under the premise of strictly controlling the insulation properties. Each comparative example verifies the necessity and synergistic effect of each technical feature of the present application. Comparative Example 1 proves the superiority of using high-thermal-conductivity composite fillers over traditional single fillers, Comparative Example 2 highlights the key role of the three-stage dispersion process, Comparative Example 3 shows the importance of sufficient curing for product reliability, Comparative Examples 4 and 5 emphasize the necessity of strictly controlling insulation properties, and Comparative Examples 6 and 7, under the condition of the same total mass of fillers, directly compared with Example 1, powerfully prove that the combination of boron nitride nanosheets, graphene, and spherical aluminum oxide has an unexpected synergistic effect and significant progress in building a three-dimensional heat-conducting network and balancing heat-conducting and insulation performance compared to their individual use.

[0078] In summary, the technical scheme of the present application has significant progress and creativity compared to the prior art, and all performance indicators can meet the stringent requirements of 5G communication equipment, high-performance computing, and other high-end electronic devices for heat-conducting materials.

[0079] It should be understood that the above embodiments are only to illustrate the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and it cannot be considered that the specific implementation of the present application is limited to these descriptions. For ordinary skilled in the art to which the present application belongs, without departing from the concept of the present application, some simple deductions or substitutions can be made, and any equivalent changes or modifications made according to the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A method for producing a silica gel pad having high thermal conductivity and heat resistance, characterized by, The method comprises the following steps: (1) preparing a composite heat-conducting filler: mixing boron nitride nanosheets and graphene in a mass ratio of (1.5-3):1, adding 1-3% of a silane coupling agent as a surface treatment agent based on the total mass of the composite heat-conducting filler, and ball-milling in a planetary ball mill at a speed of 300-500 r / min under the protection of an inert gas for 2-4 hours. After the ball-milling is completed, 5-15% of spherical alumina is added based on the total mass of the composite heat-conducting filler, and the obtained mixture is mixed by high-speed mechanical stirring at a speed of 800-1500 r / min for 10-30 minutes, so as to control the particle size of the obtained composite heat-conducting filler to be 0.1-1 μm; (2) preparing a modified silicone resin: adding 100 parts of methyl vinyl silicone rubber with a vinyl content of 0.1-0.5%, 5-12 parts of hydrogen-containing silicone oil with a hydrogen content of 0.5-1.0% in a reaction kettle, the molar ratio of Si-H bonds in the hydrogen-containing silicone oil to vinyl groups in the methyl vinyl silicone rubber being (1.0-1.2):1, and further adding 0.1-0.5 parts of a platinum catalyst and 3-8 parts of an MQ-type silicone resin as a structure reinforcing agent, and stirring and reacting at a speed of 200-300 r / min at 70-90 ℃ for 1-2 hours to obtain a modified silicone resin; (3) preparing a heat-conducting silicone rubber mixture: placing 100 parts of the modified silicone resin, 35-50 parts of the composite heat-conducting filler, 5-10 parts of a flame retardant, and 2-5 parts of an antioxidant in a vacuum stirrer, mixing and degassing at 50-70 ℃ and -0.09 to -0.1 MPa for 30-60 minutes to obtain a heat-conducting silicone rubber mixture; (4) Preparation of reinforced substrate: glass fiber cloth with an areal density of 50-100 g / m 2 was treated by plasma and then immersed in vinyl ester resin, and pre-cured at 100-120 °C for 10-20 minutes to obtain a reinforced substrate; (5) coating and composite curing: the heat-conducting silicone rubber mixture is first treated by a three-roll mill under the conditions of a roll gap of 10-20 μm and a roll speed ratio of 1:2:4 for 2-3 times, and then uniformly coated on the reinforcing substrate by a slot coater at a speed of 1-3 m / min, with the coating thickness being controlled to be 0.3-1 mm. Subsequently, the coating is heated in an oven at 100-120 ℃ for 30-60 minutes to complete the curing, and a silicone rubber pad is obtained.

2. The method of claim 1, wherein: In step (1), part of the boron nitride nanosheets is subjected to an amination treatment, and the aminated boron nitride nanosheets account for 10-30% of the total mass; the graphene is functionalized graphene prepared by an oxidation-reduction method, and the oxygen content of the functionalized graphene is 8-15%.

3. The method of claim 1, wherein: In step (1), the silane coupling agent is γ-aminopropyl triethoxysilane (KH-550) or γ-(2,3-epoxypropoxy) propyl trimethoxysilane (KH-560); and the inert gas is nitrogen or argon.

4. The method of claim 1, wherein: In step (2), the platinum catalyst is chloroplatinic acid isopropanol solution or platinum-vinylsiloxane complex.

5. The method of claim 1, wherein: In step (2), the mass ratio of M units to Q units in the MQ-type silicone resin is (0.6-0.8):

1.

6. The method of claim 1, wherein: In step (3), the flame retardant is surface-modified aluminum hydroxide or ammonium polyphosphate; the antioxidant is a compound of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester and tri[2,4-di-tert-butylphenyl]phosphite at a mass ratio of 1:(0.5-1).

7. The method of claim 1, wherein: In step (4), the plasma treatment is performed at a power of 300-500 W in an oxygen or argon atmosphere for 30-120 seconds.

8. The method of claim 1, wherein: The silica gel pad further comprises a foamed buffer layer, which is prepared by mixing methyl vinyl silicone rubber, insulating and heat-conducting filler and fumed white carbon black at a mass ratio of 60:20:10, adding 2-5 parts of a chemical foaming agent, and foaming at 160-180 ℃, and has a thickness of 0.2-0.5 mm; the foamed buffer layer is compounded with one side of the uncoated silica gel of the reinforcing base material through hot pressing, and a layer of silane-based interface treatment agent is coated on the compounding interface before hot pressing.

9. The method of claim 8, wherein: The chemical foaming agent is azodicarbonamide; the hot pressing is performed at a temperature of 120-140 ℃, a pressure of 1-3 MPa, and a time of 30-90 seconds; the silane-based interface treatment agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane; and the insulating and heat-conducting filler is spherical aluminum oxide or boron nitride.

10. The high thermal conductive insulating silica gel pad prepared by the method of any one of claims 1-9, characterized in that: The thermal conductivity of the silica gel pad is 2.5-3.5 W / m·K, and the volume resistivity is greater than 10 12 Ω·cm, the long-term heat resistance temperature reaches 200℃ or above, the tensile strength is greater than 5MPa, and the peeling strength is greater than 15N / cm.

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