Closed-cell heat-conducting flame-retardant foamed silica gel material and preparation method thereof

Abstract

The invention discloses a closed-cell heat-conducting flame-retardant foamed silica gel material and a preparation method thereof in the field of organic silicon functional materials. The closed-cell heat-conducting flame-retardant foamed silica gel material is prepared from the following raw materials: basic silica gel, silane modified boron nitride, titanate modified aluminum hydroxide, a foaming agent, a cross-linking agent, a catalyst, an inhibitor and absolute ethyl alcohol. The raw materials are mixed according to a certain mass ratio. Wherein the silane modified boron nitride is prepared by heating, refluxing and reacting boron nitride powder and a silane coupling agent in an ethanol solvent and then drying; the titanate modified aluminum hydroxide is prepared by ultrasonically dispersing aluminum hydroxide powder and a titanate coupling agent in deionized water, adjusting the pH value, reacting and drying. The preparation method comprises the following steps: mixing the basic silica gel with the two modified fillers at a high speed, sequentially adding other raw materials, continuously mixing, transferring into a mold, pressurizing at a certain temperature to complete vulcanization foaming, taking out, washing with water, and drying in vacuum. According to the material, the interface bonding force is improved through the modified filler, and the material has the characteristics of high heat conductivity, high flame retardance and stable closed-cell structure.

Description

Technical Field

[0001] The present invention relates to the technical field of organic silicon functional materials, and in particular to a closed-cell heat-conducting flame-retardant foamed silicone material and a preparation method thereof. Background Art

[0002] Traditional foamed silicone materials are mostly open-pore or semi-open-pore structures, which easily absorb environmental moisture during long-term use, resulting in a decrease in material performance; at the same time, their mechanical strength is generally low, and they are prone to deformation or breakage when subjected to external forces. In addition, conventional foamed silicone has poor thermal conductivity, with a thermal conductivity coefficient often lower than 0.2W / (m·K), which makes it difficult to meet the needs of efficient heat dissipation of electronic devices; flame retardancy mainly relies on halogen flame retardants, which are prone to decomposition and release toxic gases in high-temperature environments, which not only does not meet environmental protection requirements, but also limits the application of materials in fire safety scenarios. These problems make it difficult for traditional foamed silicone to play an effective role in fields such as electronic component packaging and thermal interface materials that have high requirements for thermal conductivity, flame retardancy and stability.

[0003] In order to improve the above-mentioned defects, the prior art attempts to improve performance by adding inorganic thermal conductive fillers (such as boron nitride, aluminum oxide) or flame retardant fillers (such as aluminum hydroxide, magnesium hydroxide). However, the surface polarity of the inorganic filler is quite different from that of the silica gel matrix, and the interfacial bonding force of the two is relatively weak. The filler is prone to agglomeration and cannot be evenly dispersed in the matrix. This agglomeration not only hinders heat transfer and reduces thermal conductivity, but also weakens the mechanical strength of the material, resulting in the actual effect of the filler being unable to be fully exerted. Therefore, how to improve the interfacial bonding force between the inorganic filler and the silica gel matrix has become a key technical bottleneck restricting the performance upgrade of foamed silica gel.

[0004] To address this need, the present invention proposes a closed-cell, thermally conductive, flame-retardant foamed silicone material and its preparation method. By employing silane modification and titanate modification techniques to surface-treat boron nitride and aluminum hydroxide, respectively, this effectively improves the interfacial compatibility between the filler and the silicone matrix, preventing filler agglomeration. Simultaneously, the synergistic effects of components such as the foaming agent and cross-linking agent form a stable closed-cell structure during the vulcanization process. This material not only exhibits high thermal conductivity and flame retardancy, but also maintains the stability of its closed-cell structure, offering a superior performance option for applications such as electronic component packaging and fire-resistant sealing. Summary of the Invention

[0005] The purpose of the present invention is to provide a closed-cell thermally conductive flame-retardant foamed silicone material and a preparation method thereof, which solves the technical problems of traditional foamed silicone due to its open-cell structure, easy water absorption, low mechanical strength, small thermal conductivity, halogen-dependent flame retardancy and environmental pollution, and filler agglomeration affecting performance.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0007] A closed-cell thermally conductive flame-retardant foamed silicone material, the raw materials of which include, by mass percentage:

[0008] Basic silicone: 70-85%;

[0009] Silane-modified boron nitride: 3-8%;

[0010] Titanate modified aluminum hydroxide: 5-12%;

[0011] Foaming agent: 1-3%;

[0012] Cross-linking agent: 2-5%;

[0013] Catalyst: 0.1-0.5%;

[0014] Inhibitor: 0.05-0.2%;

[0015] Anhydrous ethanol: balance;

[0016] The preparation method of silane-modified boron nitride includes: A1, adding boron nitride powder and γ-aminopropyltriethoxysilane to an ethanol solvent, heating to 70-80°C for reflux reaction, and continuously stirring during the reaction; A2, filtering after the reaction is completed, washing the filter cake with ethanol, and placing the filter cake in a vacuum drying oven to constant weight.

[0017] According to a preferred embodiment of the present invention, the basic silica gel is purchased from the Organic Silicon Division of Xin'an Group, and the model is XH-200 (hydroxyl-terminated polydimethylsiloxane, viscosity 2500-3500 mPa·s).

[0018] According to a preferred embodiment of the present invention, the boron nitride powder is purchased from Beijing Xingrong Fine Chemical Co., Ltd., with a model number of BN-510 (particle size 5-10 μm, purity ≥98%).

[0019] According to a preferred embodiment of the present invention, the γ-aminopropyltriethoxysilane is purchased from Nanjing Shuguang Chemical Group Co., Ltd., and the model number is KH550 (γ-aminopropyltriethoxysilane, purity ≥99%).

[0020] According to a preferred embodiment of the present invention, the vacuum drying oven is purchased from Shanghai Keheng Industrial Development Co., Ltd., model DZF-6020 (temperature range: room temperature + 10°C ~ 200°C).

[0021] According to a preferred embodiment of the present invention, the foaming agent is purchased from Shanghai Xiangyang Chemical Plant, and its model is AC-100 (azodicarbonamide, decomposition temperature 160-200° C.).

[0022] According to a preferred embodiment of the present invention, the catalyst is purchased from Guiyan Platinum Co., Ltd., and the model is Pt-Cat-01 (chloroplatinic acid-tetramethylvinylsiloxane complex, platinum content 0.2 wt %).

[0023] According to a preferred embodiment of the present invention, the inhibitor was purchased from Jiangsu Feixiang Chemical Co., Ltd., and the model number was MTBE-01 (3-methyl-1-butyn-3-ol, purity ≥98%).

[0024] According to a preferred embodiment of the present invention, the anhydrous ethanol is purchased from Sichuan Northern Nitrocellulose Co., Ltd., and the model is ETOH-99.5 (analytical grade, moisture ≤ 0.05%).

[0025] The reaction mechanism between the components in the present invention is based on the hydroxyl-terminated polydimethylsiloxane of the basic silica gel as the core skeleton, through the surface functionalization modification of silane-modified boron nitride and titanate-modified aluminum hydroxide, combined with the decomposition and gas production of the foaming agent, the construction of the cross-linking agent network and the dynamic regulation of the catalyst, ultimately forming a stable closed-cell structure with both high thermal conductivity and high flame retardancy.

[0026] According to a preferred embodiment of the present invention, in step A1, the particle size of the boron nitride powder is 5-10 μm; the molar ratio of the boron nitride powder to γ-aminopropyltriethoxysilane is 1:(0.3-0.5); the mass ratio of the boron nitride to ethanol is 1:(10-15); and the reflux reaction time is 4-6 h.

[0027] The improvement in thermal conductivity in the present invention relies on the uniform dispersion of silane-modified boron nitride. Boron nitride (thermal conductivity of approximately 30 W / (m·K)) acts as a highly thermally conductive filler. It covalently bonds with the silica gel matrix through surface amino groups, reducing the interfacial thermal resistance between the filler and the matrix (the interfacial thermal resistance is reduced by approximately 70%). This allows heat to be efficiently transferred through the "filler-interface-matrix" path, ultimately achieving a significant improvement in the overall thermal conductivity of the material.

[0028] According to a preferred embodiment of the present invention, in step A2, the filter cake is washed with ethanol three times; the drying temperature in the vacuum drying oven is 60-65° C., and the drying time is 12-14 h.

[0029] During the preparation of the silane-modified boron nitride of the present invention, the ethoxy group of γ-aminopropyltriethoxysilane undergoes a hydrolysis reaction with trace water in an ethanol solvent under reflux conditions at 70-80°C to generate an intermediate containing a silanol (-Si-OH). Simultaneously, the hydroxyl groups (-OH) or adsorbed water on the surface of the boron nitride powder dissociate into active hydrogen under heating conditions, which reacts with the silanol hydroxyl groups of the silanol to form a -Si-O-Si- covalent bond, bridging the amino group (-NH2) to the surface of the boron nitride via a methylene group (-CH2-). This process not only enhances the interfacial bonding between the boron nitride and the silica gel matrix, but also improves the dispersibility of the filler in the silica gel through the polarity of the amino group. The reflux reaction is performed for 4-6 hours to ensure that the hydrolysis and condensation reactions are fully carried out. Subsequently, three ethanol washes are performed to remove the unreacted silane coupling agent. The surface of the boron nitride is then vacuum-dried at 60-65°C for 12-14 hours to completely remove the moisture, thereby obtaining surface-functionalized silane-modified boron nitride.

[0030] According to a preferred embodiment of the present invention, the preparation method of the titanate-modified aluminum hydroxide includes: B1, adding aluminum hydroxide powder and isopropyl tris (dioctyl pyrophosphate acyloxy) titanate to deionized water, and ultrasonically dispersing the powder to uniformly disperse it; adjusting the pH of the system to 8-9 with ammonia water, heating it to 60-65°C and reacting at a constant temperature; B2, filtering after the reaction is completed, washing the filter cake with deionized water to a pH of 6.5-7.5, and placing the filter cake in a vacuum drying oven to dry to constant weight.

[0031] According to a preferred embodiment of the present invention, the aluminum hydroxide powder is purchased from China Aluminum Shandong Co., Ltd., model AH-100 (particle size 3-5 μm, purity ≥99.5%).

[0032] According to a preferred embodiment of the present invention, the isopropyl tris(dioctyl pyrophosphate) titanate is purchased from Nanjing Shuguang Chemical Group Co., Ltd., model number NDZ-201 (titanate coupling agent, purity ≥98%).

[0033] According to a preferred embodiment of the present invention, the deionized water was purchased from Shanghai Chunchao Environmental Protection Technology Co., Ltd., model DW-10 (resistivity ≥ 10 MΩ·cm, conductivity ≤ 0.1 μS / cm).

[0034] According to a preferred embodiment of the present invention, the ammonia water is purchased from Jiangsu Runfeng Synthetic Technology Co., Ltd., and the model is NH3·H2O-25 (concentration 25±2%, impurity content ≤0.01%).

[0035] According to a preferred embodiment of the present invention, in step B1, the particle size of the aluminum hydroxide powder is 3-5 μm; the molar ratio of the aluminum hydroxide powder to isopropyl tri(dioctyl pyrophosphate) titanate is 1:(0.2-0.4); the mass ratio of the aluminum hydroxide to deionized water is 1:(8-12); the ultrasonic dispersion time is 30-40 min; and the constant temperature reaction time is 2-3 h.

[0036] According to a preferred embodiment of the present invention, in step B2, the vacuum drying temperature is 80-90° C., and the drying time is 10-12 h.

[0037] In the preparation of titanate-modified aluminum hydroxide in the present invention, the titanium-oxygen bond (-Ti-O-) of isopropyl tris(dioctyl pyrophosphate) titanate is uniformly adsorbed on the surface of 3-5 μm aluminum hydroxide powder under ultrasonic dispersion conditions (30-40 minutes); after adding ammonia water to adjust the pH to 8-9, the alkoxy group (-OR) of the titanate is hydrolyzed to form titanium alcohol (-Ti-OH), which undergoes a condensation reaction with the hydroxyl group (-OH) on the surface of the aluminum hydroxide to form a -Ti-O-Al- chemical bond, thereby introducing the long carbon chain (isopropyl and dioctyl pyrophosphate) of the titanate onto the surface of the aluminum hydroxide. The role of ultrasonic dispersion is to break the agglomeration of aluminum hydroxide particles and allow titanate to fully contact its surface; constant temperature reaction at 60-65℃ for 2-3 hours promotes complete hydrolysis and condensation reactions, and drying at 80-90℃ for 10-12 hours removes moisture and stabilizes the modified layer structure, ultimately obtaining titanate-modified aluminum hydroxide with a hydrophobic long carbon chain on the surface. Its surface energy is reduced and its compatibility with the silica gel matrix is ​​significantly improved.

[0038] The present invention also provides a method for preparing the closed-cell thermally conductive flame-retardant foamed silica gel material, comprising the following steps:

[0039] S1. Add basic silica gel, silane-modified boron nitride, and titanate-modified aluminum hydroxide into a high-speed mixer and mix them evenly at 40-50°C. Add a blowing agent, a cross-linking agent, a catalyst, and an inhibitor to the mixed system in sequence. Continue mixing and control the temperature to not exceed 60°C to avoid premature decomposition of the blowing agent.

[0040] S2. Transfer the mixed material into a mold, place it in a flat vulcanizer at 120-150°C, apply pressure, and maintain the vulcanization and foaming reaction;

[0041] S3. After the reaction is completed, the sample is taken out, washed with deionized water to remove unreacted cross-linking agent and catalyst residue, and placed in a vacuum drying oven to dry.

[0042] According to a preferred embodiment of the present invention, in step S1, the mixing speed is 1000-1500 rpm, the mixing time is 15-20 min, and the mixing time is continued for 10-15 min.

[0043] According to a preferred embodiment of the present invention, in step S2, the mold thickness is 2-10 mm, the applied pressure is 0.1-0.3 MPa, and the holding time is 5-10 min.

[0044] During the vulcanization and foaming stage of the present invention, the hydroxyl groups (-OH) of the base silica gel (hydroxyl-terminated polydimethylsiloxane) and the hydrogen (-H) of the hydrogen-containing silicone oil undergo a hydrogen transfer condensation reaction catalyzed by a chloroplatinic acid-tetramethylvinylsiloxane complex (platinum content 0.1-0.3 wt%). The -Si-OH groups of the silica gel and the -Si-H groups of the hydrogen-containing silicone oil, catalyzed by platinum, form -Si-O-Si crosslinks and release H2. (This side reaction is suppressed by the inhibitor 3-methyl-1-butyn-3-ol, preventing premature bubble formation.) Simultaneously, azodicarbonamide (the blowing agent) decomposes upon heating at 120-150°C, releasing nitrogen (N2): NH2-CO-N=N-CO-NH2→2N2↑+2CO↑+2H2O↑. The generated nitrogen is trapped in the three-dimensional network formed by crosslinking, forming initial bubbles. The inhibitor captures free radicals (such as nitrogen radicals generated by decomposition) or suppresses the chain reaction rate, allowing the bubbles to grow uniformly without bursting.

[0045] The crosslinking sites provided by the crosslinking agent (hydrogen-containing silicone oil) in the present invention work synergistically with the reaction rate regulated by the catalyst to ensure that the bubbles are fixed in the network during their growth, ultimately forming a closed-cell structure with no connecting channels between the bubbles and no gas escape, thereby stabilizing the closed-cell morphology.

[0046] During the flame retardant process of the present invention, the titanate-modified aluminum hydroxide begins to decompose above 200°C, following the reaction formula: 2Al(OH)₃→Al₂O₃+3H₂O↑. This decomposition process absorbs a significant amount of heat (approximately 1967 J / g), lowering the system temperature. Simultaneously, the released water vapor dilutes the oxygen concentration (from 21% by volume to below 15%), inhibiting the continued combustion reaction. The presence of long carbon chains on the surface of the modified aluminum hydroxide significantly enhances its dispersibility, allowing it to be evenly distributed within the silica gel matrix, avoiding localized hot spots and further enhancing the flame retardant effect.

[0047] According to a preferred embodiment of the present invention, in step S3, the number of deionized water washings is 2-3 times; the drying temperature is 60-80° C.; the drying time is 4-6 hours; and the pressure is ≤-0.09 MPa.

[0048] The beneficial effects of the present invention are:

[0049] Traditional foamed silicone rubber has an open or semi-open porous structure, and the interface bonding between the filler and the matrix is ​​weak, resulting in low thermal conductivity, insufficient flame retardancy, and easy water absorption. The present invention effectively solves this problem through the synergistic effect of silane-modified boron nitride and titanate-modified aluminum hydroxide. The amino groups on the surface of the silane-modified boron nitride undergo a condensation reaction with the hydroxyl groups of the silica gel, which enhances the interface bonding between the filler and the matrix, avoids filler agglomeration, and enables the highly thermally conductive boron nitride to be evenly dispersed in the silica gel network, significantly improving the thermal conductivity efficiency of the material; the titanium oxygen bonds on the surface of the titanate-modified aluminum hydroxide form chemical bonds with the silicon oxygen bonds of the silica gel, improving the dispersibility of the flame retardant filler, and fully utilizing its characteristics of absorbing heat and releasing water vapor when decomposing. The two work together to enable the material to have thermal conductivity and flame retardancy far exceeding that of traditional foamed silicone rubber while maintaining its elasticity.

[0050] The flame retardancy of traditional foamed silicone mostly relies on halogen flame retardants. This type of substance easily decomposes and releases toxic gases at high temperatures, which not only does not meet environmental protection requirements, but also limits its application in fire safety scenarios. The present invention adopts a halogen-free flame retardant system and achieves high-efficiency flame retardancy through the synergistic effect of titanate-modified aluminum hydroxide. The modified aluminum hydroxide decomposes when heated, absorbs a large amount of heat and releases water vapor, diluting the surrounding oxygen concentration and effectively inhibiting the combustion reaction; at the same time, the high porosity of the closed-cell structure further delays heat transfer, so that the flame retardant performance of the material reaches a higher standard, and no harmful gases are released, which is more suitable for electronic component packaging, fireproof sealing and other fields with strict safety requirements.

[0051] Traditional foamed silica gel easily absorbs water due to its open-pore structure, which leads to a decrease in the mechanical strength of the material and a shortened service life; however, the present invention fixes the gas generated by foaming through a vulcanization reaction, forming a stable closed-pore structure, which significantly reduces the water absorption rate of the material. At the same time, the introduction of modified fillers enhances the bonding force between the filler and the matrix, avoids the influence of filler agglomeration on the mechanical properties, and effectively improves the compressive strength and weather resistance of the material. This closed-pore structure also gives the material excellent dimensional stability, allowing it to maintain consistent performance under different environmental conditions. In summary, the material of the present invention has high thermal conductivity, high flame retardancy, low water absorption and a stable closed-pore structure, providing a functional material option with better comprehensive performance for the fields of electronic component packaging, thermal interface materials, fireproof sealing, etc. DETAILED DESCRIPTION

[0052] The following specific implementation methods are only used to further illustrate the present application and should not be understood as limiting the scope of protection of the present application. Technicians in this field may make some non-essential improvements and adjustments to the present application based on the above application content.

[0053] 1. Implementation

[0054] Example 1

[0055] The raw materials were weighed by mass: basic silica gel (Xynacosilicon Division of Xinan Group, model XH-200, hydroxyl-terminated polydimethylsiloxane, viscosity 2500-3500 mPa·s) 80 g, silane-modified boron nitride (homemade) 5 g, titanate-modified aluminum hydroxide (homemade) 8 g, foaming agent (Shanghai Xiangyang Chemical Plant, model AC-100, azodicarbonamide) 2 g, cross-linking agent (hydrogen-containing silicone oil, hydrogen content 0.3 wt%) 3 g, catalyst (Guiyan Platinum Co., Ltd., model Pt-Cat-01, chloroplatinic acid-tetramethylvinylsiloxane complex, platinum content 0.2 wt%) 0.3 g, inhibitor (Jiangsu Feixiang Chemical Co., Ltd., model MTBE-01, 3-methyl-1-butyn-3-ol) 0.1 g, anhydrous ethanol (Sichuan Northern Nitrocellulose Co., Ltd., model ETOH-99.5, analytical grade) 3.6 g (balance).

[0056] Pretreatment of silane-modified boron nitride: 5 g of boron nitride powder (Beijing Xingrong Fine Chemical Co., Ltd., model BN-510, purity ≥98%) with a particle size of 5-10 μm was placed in a 100 ml beaker, and 3.75 g of ethanol solvent (mass ratio of boron nitride to ethanol 1:7.5) was added and ultrasonically dispersed for 10 min (frequency 40 kHz) until the powder was evenly dispersed without agglomeration; 2.5 g of γ-aminopropyltriethoxysilane (Nanjing Shuguang Chemical Group Co., Ltd., model KH550, purity ≥99%) (molar ratio with boron nitride 1:0.3) was taken and slowly added dropwise to the dispersion, and the temperature was raised to 70 ° C (controlled in an oil bath with an accuracy of ±1 ° C). ), install a reflux condenser (circulating water in the condenser tube), and react with magnetic stirring (speed 300 rpm) for 4 hours; after the reaction is completed, filter while hot (suction filtration device, filter paper pore size 10-15 μm) to collect the filter cake; wash the filter cake with ethanol (20 ml each time) for 3 times until the filtrate is clear (no silane coupling agent residue); transfer the filter cake to a vacuum drying oven (Shanghai Keheng Industrial Development Co., Ltd., model DZF-6020, temperature range room temperature + 10 ° C ~ 200 ° C), set the temperature to 60 ° C, vacuum degree ≤ -0.09 MPa, and dry for 12 hours (weigh every 2 hours, and the weight no longer changes is constant weight) to obtain silane-modified boron nitride.

[0057] Titanate modified aluminum hydroxide pretreatment: 8 g of aluminum hydroxide powder (China Aluminum Shandong Co., Ltd., model AH-100, purity ≥99.5%) with a particle size of 3-5 μm was placed in a 250 ml beaker, and 64 g of deionized water (Shanghai Chunchao Environmental Protection Technology Co., Ltd., model DW-10, resistivity ≥10 MΩ·cm) was added (the mass ratio of aluminum hydroxide to deionized water was 1:8), and ultrasonic dispersion (frequency 40 kHz) was performed for 30 min until uniform; 2.4 g of isopropyl tris (dioctyl pyrophosphate) titanate (Nanjing Shuguang Chemical Group Co., Ltd., model NDZ-201, purity ≥98%) was taken (molarized with aluminum hydroxide) The mixture was slowly added dropwise to the dispersion (with a pH of 1:0.2) and ammonia water (Jiangsu Runfeng Synthetic Technology Co., Ltd., model NH3·H2O-25, concentration 25±2%) was used to adjust the pH to 8 (measured after calibration with a pH meter). The temperature was raised to 60°C (controlled in a water bath) and the reaction was carried out at a constant temperature for 2 hours (magnetic stirring speed 200 rpm). After the reaction was completed, the mixture was filtered (suction filtration device) and the filter cake was collected. The filter cake was washed with deionized water (50 ml each time) to a pH of 6.5 (detected with a pH meter), and the mixture was transferred to a vacuum drying oven (same as above) with a temperature set at 80°C and a vacuum degree ≤-0.09 MPa. The mixture was dried for 10 hours (constant weight) to obtain titanate-modified aluminum hydroxide.

[0058] Material preparation: basic silica gel, silane-modified boron nitride, and titanate-modified aluminum hydroxide were added to a high-speed mixer (Shanghai Keheng Industrial Development Co., Ltd., model DZF-6020), set the temperature to 40°C, the speed to 1000 rpm, and mixed for 15 minutes (no lumps were observed through the observation window); foaming agent, cross-linking agent, catalyst, and inhibitor were added in sequence and mixed for 10 minutes (mixing for 5 minutes after each addition of a raw material, temperature ≤ 60°C); the mixture was transferred to a 2 mm thick stainless steel mold (size 100 mm × 100 mm × 2 mm) and placed on a flat plate. A vulcanizing machine (model XL-100, pressure sensor accuracy 0.01 MPa) was set at a temperature of 120°C (±2°C), and a pressure of 0.1 MPa was applied for 5 minutes to complete vulcanization and foaming (the vulcanization was completed when no continuous bubbling occurred on the surface of the material). After taking out the sample, it was immediately washed twice with deionized water (room temperature) (immersing for 10 minutes each time, with magnetic stirring at low speed), transferred to a vacuum drying oven (same as before), set at a temperature of 60°C, a vacuum degree of ≤-0.09 MPa, and dried for 4 hours (the sample was completed when it was not sticky when gently pinched by hand) to obtain a closed-cell thermally conductive flame-retardant foamed silicone material.

[0059] Example 2

[0060] The preparation method is the same as that of Example 1, except that the raw material mass is: basic silica gel 75g, silane-modified boron nitride 8g, titanate-modified aluminum hydroxide 12g, foaming agent 3g, cross-linking agent 5g, catalyst 0.5g, inhibitor 0.2g, and anhydrous ethanol (balance) 3.8g. Preparation method: basic silica gel, silane-modified boron nitride, and titanate-modified aluminum hydroxide are added to a high-speed mixer and mixed at 40°C and 1500rpm for 20 minutes. The foaming agent, cross-linking agent, catalyst, and inhibitor are added in sequence and mixed for 15 minutes (temperature ≤ 60°C). The mixture is transferred to a 10mm thick mold and placed in a flat vulcanizer at 150°C (pressure 0.3MPa) for 10 minutes to complete vulcanization and foaming. The sample is removed and rinsed with deionized water three times and vacuum dried at 80°C (pressure ≤ -0.09MPa) for 6 hours.

[0061] Example 3

[0062] The preparation method is the same as that of Example 1, except that the raw material mass is: basic silica gel 85g, silane-modified boron nitride 3g, titanate-modified aluminum hydroxide 5g, foaming agent 1g, cross-linking agent 2g, catalyst 0.1g, inhibitor 0.05g, and anhydrous ethanol (balance) 3.85g. Preparation method: basic silica gel, silane-modified boron nitride, and titanate-modified aluminum hydroxide are added to a high-speed mixer and mixed at 50°C and 1200rpm for 18 minutes. The foaming agent, cross-linking agent, catalyst, and inhibitor are added in sequence and mixed for another 12 minutes (temperature ≤ 60°C). The mixture is transferred to a 5mm thick mold and placed in a flat vulcanizer at 130°C (pressure 0.2MPa) for 8 minutes to complete vulcanization and foaming. The sample is removed and rinsed twice with deionized water and vacuum dried at 70°C (pressure ≤ -0.09MPa) for 5 hours.

[0063] Comparative Example 1

[0064] The preparation method is the same as that of Example 1, except that the raw material mass is: basic silica gel 80g, unmodified boron nitride 5g (not silane modified), titanate-modified aluminum hydroxide 8g, foaming agent 2g, cross-linking agent 3g, catalyst 0.3g, inhibitor 0.1g, and anhydrous ethanol 3.6g.

[0065] Comparative Example 2

[0066] The preparation method is the same as that of Example 1, except that the raw material mass is: basic silica gel 80g, silane-modified boron nitride 5g, unmodified aluminum hydroxide 8g (not titanate-modified), foaming agent 2g, cross-linking agent 3g, catalyst 0.3g, inhibitor 0.1g, and anhydrous ethanol 3.6g.

[0067] Comparative Example 3

[0068] The preparation method is the same as that of Example 1, except that the raw material mass is: basic silica gel 80g, silane-modified boron nitride 5g, titanate-modified aluminum hydroxide 8g, foaming agent 4g, cross-linking agent 3g, catalyst 0.3g, inhibitor 0.1g, and anhydrous ethanol 3.6g.

[0069] 2. Performance Testing

[0070] The materials prepared in Examples 1-3 and Comparative Examples 1-3 were tested for performance according to the following method:

[0071] 1. Thermal conductivity test

[0072] Equipment: Laser flash thermal conductivity tester (model: LFA-447NanoFlash, accuracy ±2%). Sample preparation: Cut the material into regular blocks of 20mm×20mm×2mm (5 parallel samples), polish the surface with sandpaper until it is flat, clean it with alcohol and dry it to constant weight. Test conditions: Test temperature 25℃, heat flow direction perpendicular to the material surface, pulse energy 10mJ, data acquisition time 2000μs. Test steps: Place the sample in the test chamber, start the instrument, record the thermal diffusion coefficient, and calculate the thermal conductivity by the formula λ=α·ρ·Cp (λ: thermal conductivity, α: thermal diffusion coefficient, ρ: density, Cp: specific heat capacity).

[0073] 2. Vertical burning level test

[0074] Equipment: Vertical combustion test machine (model: CZF-5400, in compliance with GB / T 2408-2021). Sample preparation: Cut the material into 125mm×13mm×3mm strip specimens (5 parallel specimens), secure the edges with tape, and hang them in the test machine fixture. Test conditions: Ambient temperature 23±2°C, humidity 50±5%, oxygen flow rate (volume fraction) 21%, nitrogen flow rate 0%. Test steps: Hold the lower end of the specimen 10mm from the flame of the alcohol lamp (height 20mm). After ignition, record the burning time and whether there are any drips that ignite the cotton. Determine the grade according to GB / T 2408-2021 (V-0: Self-extinguishes within 10 seconds after removal from the fire and no dripping; V-1: Self-extinguishes within 30 seconds after removal from the fire and no dripping; V-2: Self-extinguishes within 30 seconds after removal from the fire but there are drips that ignite the cotton).

[0075] 3. Closed cell rate test

[0076] Equipment: Mercury intrusion porosimeter (Model: Micromeritics AutoPore IV 9500, accuracy ±1%). Sample preparation: The material was cut into discs with a diameter of 25 mm and a thickness of 2 mm (3 parallel samples), coated with a gold film (thickness 5 nm) to enhance conductivity, and vacuum dried to constant weight (≤0.09 MPa, 4 h). Test conditions: Vacuum degree ≤-0.09 MPa, mercury temperature 20°C, maximum pressure 360 ​​MPa. Test steps: The sample was placed in the sample chamber, and mercury was injected after vacuuming. The mercury intrusion volume at different pressures was recorded, and the closed pore volume ratio was calculated by the formula (closed pore ratio = closed pore volume / total volume × 100%).

[0077] 4. Water absorption test

[0078] Equipment: Electronic balance (model: FA2004B, accuracy ±0.0001g), constant temperature and humidity chamber (model: DHG-9070A, temperature 23±2°C, humidity 50±5%). Sample preparation: Cut the material into 50mm×50mm×2mm blocks (3 parallel samples), clean the surface with alcohol, and dry to constant weight (recorded as m0). Test steps: Place the sample in a constant temperature and humidity chamber. After 24 hours, remove the sample and absorb the surface moisture with filter paper. Weigh the wet weight (m1). Water absorption rate = (m1-m0) / m0×100%.

[0079] 5. Density test

[0080] Equipment: Electronic density meter (model: DH-300, accuracy ±0.01g / cm 3 ). Sample preparation: Cut the material into 10mm×10mm×2mm blocks (5 parallel samples), clean the surface with alcohol and dry to constant weight. Test steps: Place the sample in the sample chamber of the density meter and measure the volume (V) and mass (m). Density = m / V (g / cm 3 ).

[0081] Corrosion inhibition efficiency results:

[0082] Table 1: Corrosion inhibition efficiency results of various examples and comparative examples

[0083]

[0084]

[0085] As can be seen from Table 1, the embodiments of the present invention solve the technical problems of traditional foamed silica gel through the following mechanism: traditional foamed silica gel is easy to absorb water due to its open-pore structure, while the water absorption rate of Examples 1-3 of the present invention is only 0.7-0.9% (much lower than 2.3-3.8% of Comparative Examples 1-3). Thanks to the surface modification of silane-modified boron nitride and titanate-modified aluminum hydroxide, the former condenses with the hydroxyl group of silica gel through amino groups, and the latter bonds with the silane-oxygen bond of silica gel through titanium-oxygen bonds, thereby enhancing the interfacial bonding force between the filler and the matrix, avoiding the loose structure caused by filler agglomeration, and thus reducing the water absorption rate. The thermal conductivity of traditional foamed silica gel is low (usually <0.2W / (m·K)), while the thermal conductivity of Examples 1-3 reaches 1.1-1.3W / (m·K) (much higher than the 0.4-0.6W / (m·K) of Comparative Examples 1-3). This is mainly because silane-modified boron nitride is used as a high thermal conductivity filler (thermal conductivity of approximately 30W / (m·K)), and the amino groups on its surface form covalent bonds with the silica gel matrix, reducing the interfacial thermal resistance between the filler and the matrix (the interfacial thermal resistance is reduced by approximately 70%). Heat can be efficiently transferred through the "filler-interface-matrix" path. Traditional foamed silicone relies on halogens for flame retardancy, and releases toxic gases when burned. However, Examples 1-3 have a vertical combustion rating of V-0 (no dripping, self-extinguishing within 10 seconds), and no halogen is added. This is due to the decomposition characteristics of titanate-modified aluminum hydroxide, which decomposes above 200°C to absorb heat (decomposition heat of approximately 1967 J / g) and releases water vapor to dilute oxygen. At the same time, the modified aluminum hydroxide has improved dispersibility (reduced agglomeration) and significantly improved flame retardant efficiency. Comparative Examples 1 (unmodified boron nitride) and 2 (unmodified aluminum hydroxide) have poor filler dispersibility, and their flame retardant ratings are reduced to V-1. Comparative Example 3 (excessive foaming agent) has an unstable bubble structure, and its flame retardant rating is only V-2. Traditional foamed silica gel has low mechanical strength due to filler agglomeration, while the closed-cell rate of Examples 1-3 is stable at 48-55% (much higher than 28-40% of Comparative Examples 1-3). The closed-cell structure fixes bubbles through vulcanization reaction, avoiding stress concentration caused by open holes. At the same time, the modified filler has a strong bonding force with the matrix, which inhibits filler agglomeration and improves the overall mechanical properties of the material. The comparative example has a low closed-cell rate, loose structure, and decreased mechanical strength due to unmodified fillers or excessive foaming agent.

[0086] In summary, the present invention systematically solves the problems of open-pore water absorption, low thermal conductivity, flame retardancy and environmental pollution, and filler agglomeration of traditional foamed silica gel by surface-modifying fillers to enhance interfacial bonding, controlling the foaming reaction to form a stable closed-cell structure, and using halogen-free flame retardants.

[0087] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A closed-cell thermally conductive flame-retardant foamed silicone material, characterized in that: In terms of mass percentage, the raw materials include: Basic silicone: 70-85%; Silane-modified boron nitride: 3-8%; Titanate modified aluminum hydroxide: 5-12%; Foaming agent: 1-3%; Cross-linking agent: 2-5%; Catalyst: 0.1-0.5%; Inhibitor: 0.05-0.2%; Anhydrous ethanol: balance; The preparation method of silane-modified boron nitride includes: A1, adding boron nitride powder and γ-aminopropyltriethoxysilane to an ethanol solvent, heating to 70-80°C for reflux reaction, and continuously stirring during the reaction; A2, filtering after the reaction is completed, washing the filter cake with ethanol, and placing the filter cake in a vacuum drying oven to constant weight.

2. The closed-cell thermally conductive flame-retardant silicone foam material according to claim 1, characterized in that: In step A1, the particle size of the boron nitride powder is 5-10 μm; the molar ratio of the boron nitride powder to γ-aminopropyltriethoxysilane is 1:(0.3-0.5); the mass ratio of the boron nitride to ethanol is 1:(10-15); and the reflux reaction time is 4-6 hours.

3. The closed-cell thermally conductive flame-retardant silicone foam material according to claim 1, characterized in that: In step A2, the filter cake is washed with ethanol three times; the drying temperature in the vacuum drying oven is 60-65° C., and the drying time is 12-14 h.

4. The closed-cell thermally conductive flame-retardant silicone foam material according to claim 1, characterized in that: The preparation method of the titanate-modified aluminum hydroxide comprises the following steps: B1, adding aluminum hydroxide powder and isopropyl tri(dioctyl pyrophosphate) titanate to deionized water, and uniformly dispersing the powder through ultrasonic dispersion; adjusting the pH of the system to 8-9 with aqueous ammonia, heating the system to 60-65° C., and reacting at a constant temperature; B2, filtering after the reaction, washing the filter cake with deionized water until the pH reaches 6.5-7.5, and drying the filter cake in a vacuum drying oven to a constant weight.

5. The closed-cell thermally conductive flame-retardant silicone foam material according to claim 1, characterized in that: In step B1, the particle size of the aluminum hydroxide powder is 3-5 μm; the molar ratio of the aluminum hydroxide powder to isopropyl tri(dioctyl pyrophosphate) titanate is 1:(0.2-0.4); the mass ratio of the aluminum hydroxide to deionized water is 1:(8-12); the ultrasonic dispersion time is 30-40 min; and the constant temperature reaction time is 2-3 h.

6. The closed-cell thermally conductive flame-retardant silicone foam material according to claim 1, characterized in that: In step B2, the vacuum drying temperature is 80-90° C., and the drying time is 10-12 h.

7. A method for preparing a closed-cell thermally conductive flame-retardant foamed silicone material according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Add basic silica gel, silane-modified boron nitride, and titanate-modified aluminum hydroxide into a high-speed mixer and mix them evenly at 40-50°C. Add a blowing agent, a cross-linking agent, a catalyst, and an inhibitor to the mixed system in sequence. Continue mixing and control the temperature to not exceed 60°C to avoid premature decomposition of the blowing agent. S2. Transfer the mixed material into a mold, place it in a flat vulcanizer at 120-150°C, apply pressure, and maintain the vulcanization and foaming reaction; S3. After the reaction is completed, the sample is taken out, washed with deionized water to remove unreacted cross-linking agent and catalyst residue, and placed in a vacuum drying oven to dry.

8. The preparation method according to claim 7, characterized in that In step S1, the mixing speed is 1000-1500 rpm, the mixing time is 15-20 min, and the mixing time is continued for 10-15 min.

9. The preparation method according to claim 7, characterized in that In step S2, the mold thickness is 2-10 mm, the applied pressure is 0.1-0.3 MPa, and the holding time is 5-10 min.

10. The preparation method according to claim 7, characterized in that In step S3, the number of times of deionized water washing is 2-3 times; the drying temperature is 60-80° C.; the drying time is 4-6 hours; and the pressure is ≤-0.09 MPa.

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