Low-dielectric ablation-resistant heat-proof coating and preparation method thereof

Abstract

The invention provides a low-dielectric ablation-resistant heat-proof coating and a preparation method thereof, and the low-dielectric ablation-resistant heat-proof coating is prepared from the following raw materials in parts by weight: 100 parts of silicone rubber, 50-100 parts of a heat insulation medium, 2-8 parts of a curing agent, 0.5-1 part of an organic tin catalyst, 0.5-2 parts of a silane coupling agent and 15-33 parts of a reinforcing filler. The silicone rubber is room temperature vulcanized silicone rubber L7525; the heat insulation medium is hollow glass microspheres or phenolic microspheres; the curing agent is tetraethyl orthosilicate; the organic tin catalyst is dibutyltin dilaurate or octyl stannous; the silane coupling agent is gamma-aminopropyl triethoxy silane, vinyl triethoxy silane or gamma-glycidyl ether oxypropyl trimethoxy silane, and the silane coupling agent is gamma-aminopropyl triethoxy silane, vinyl triethoxy silane or gamma-glycidyl ether oxypropyl trimethoxy silane; the reinforcing filler is one or a combination of more than one of fumed silica, ammonium polyphosphate, glass fiber and mica. According to the thermal protection coating prepared by the method, the dielectric constant fluctuates in the range of 1.7-1.81 within the frequency range of 2-18 GHz, the fluctuation range is small, and the dielectric constant is more stable at a low level.

Description

Technical Field

[0001] This invention belongs to the field of aerospace thermal protection technology, and relates to heat insulation layers, specifically to a low dielectric ablation resistant heat-resistant coating and its preparation method. Background Technology

[0002] The new generation of spacecraft places increasingly stringent demands on the performance of thermal protection materials. Spacecraft flying at high Mach numbers (Ma 2.5-Ma 3.0) within the atmosphere generate intense convective and radiative heat transfer, with surface temperatures reaching 800-1100℃ and internal temperatures exceeding 200℃. To ensure the reliability of instruments and equipment within the spacecraft under prolonged aerodynamic heating conditions and to guarantee thermal stability, highly efficient thermal protection materials must be used to impede heat transfer into the spacecraft's interior. Furthermore, with the accelerating advancement of the global military revolution, the trends of long-range precision, intelligence, stealth, and unmanned weaponry are becoming more pronounced. Wave transmission performance has become a crucial capability for weaponry, placing higher demands on the dielectric properties and impedance matching of materials. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a low-dielectric, ablation-resistant heat-resistant coating and its preparation method, thereby solving the technical problem that the dielectric constant fluctuation range of existing heat-resistant coatings needs to be further reduced while ensuring ablation and dielectric properties.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A low-dielectric, ablation-resistant, and heat-resistant coating is made from the following raw materials in parts by weight: 100 parts silicone rubber, 50-100 parts heat insulation medium, 2-8 parts curing agent, 0.5-1 part organotin catalyst, 0.5-2 parts silane coupling agent, and 15-33 parts reinforcing filler.

[0005] The present invention also has the following technical features: Preferably, the silicone rubber is room temperature vulcanizing silicone rubber L7525; the heat insulation medium is hollow glass microspheres or phenolic microspheres; the curing agent is tetraethyl orthosilicate; the organotin catalyst is dibutyltin dilaurate or octyltin oxide; the silane coupling agent is γ-aminopropyltriethoxysilane, vinyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane; and the reinforcing filler is one or more of fumed silica, ammonium polyphosphate, glass fiber and mica.

[0006] Further preferably, the product is made from the following raw materials in parts by weight: 100 parts silicone rubber, 50 parts heat insulation medium, 5 parts curing agent, 0.8 parts organotin catalyst, 2 parts silane coupling agent, and 33 parts reinforcing filler.

[0007] More preferably, the silicone rubber is room temperature vulcanizing silicone rubber L7525; the heat insulation medium is hollow glass microspheres; the curing agent is tetraethyl orthosilicate; the organotin catalyst is dibutyltin dilaurate; the silane coupling agent is γ-glycidyl etheroxypropyltrimethoxysilane; and the reinforcing filler is a combination of 6 parts fumed silica, 20 parts ammonium polyphosphate, and 7 parts glass fiber.

[0008] Furthermore, the low-dielectric ablation-resistant heat-resistant coating exhibits a dielectric constant that fluctuates between 1.7 and 1.81 within the frequency range of 2–18 GHz, and a dielectric loss tangent value between 0.006 and 0.117.

[0009] Furthermore, the low dielectric ablation-resistant heat-resistant coating has a linear ablation rate of 0.342 mm / s, a thermal conductivity of 0.147 W / mk, a tensile strength of 2.45 MPa, and an elongation at break of 31.35%.

[0010] This invention also protects a method for preparing the low-dielectric, ablation-resistant, and heat-resistant coating as described above, the method comprising the following steps: Step 1: Mix and stir the silicone rubber, heat insulation medium and reinforcing filler until uniform to obtain the first matrix.

[0011] Step 2: Mix the curing agent, organotin catalyst and silane coupling agent and stir until homogeneous to obtain the second matrix.

[0012] Step 3: Mix the first matrix and the second matrix until homogeneous to obtain the third matrix.

[0013] Step four: The third substrate is shaped and cured at room temperature to obtain a fully cured low-dielectric ablation-resistant heat-resistant coating.

[0014] Preferably, the molding process includes compression molding, spray molding, and potting molding.

[0015] Compared with the prior art, the present invention has the following technical effects: (I) The thermal protective coating prepared by the present invention has a dielectric constant that fluctuates between 1.7 and 1.81 in the frequency range of 2 to 18 GHz. The fluctuation range is small and the dielectric constant is more stable at a low level.

[0016] (II) The thermal protective coating prepared by the present invention is easy to conform to complex surface structures and simultaneously meets the requirements of thermal insulation and ablation resistance, low dielectric properties and wave transmission properties. By adjusting the type and quality of the thermal insulation medium and reinforcing filler, the thermal conductivity and mechanical strength of the thermal protective coating can be controlled, and the thermal protective coating can meet the requirements of thermal protection performance and mechanical properties of the coating under different thermal environments.

[0017] (III) The present invention can control the curing rate of the heat-resistant coating by adjusting the curing agent, organotin catalyst and its type and content, and can adapt to different molding process cycles; the heat-resistant coating can be adapted to a variety of molding processes, and can meet the requirements of molding accuracy, quality, batch preparation and high-efficiency molding of the heat-resistant coating. Attached Figure Description

[0018] Figure 1 This is a graph showing the dielectric constant of a low-dielectric, ablation-resistant, and heat-resistant coating.

[0019] Figure 2 This is a graph showing the dielectric loss tangent of a low-dielectric, ablation-resistant, and heat-resistant coating.

[0020] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, all raw materials and processes used in this invention are those known in the prior art.

[0022] Silicone rubber thermal protection materials possess advantages such as high temperature resistance, low thermal conductivity, and ease of molding, making them widely used in the aerospace thermal protection field. Furthermore, silicone rubber itself exhibits excellent dielectric properties, and when combined with fillers possessing low dielectric and high thermal insulation properties, it can greatly meet the high-temperature thermal protection and stealth requirements of aircraft. As spacecraft develop towards more complex and irregular structures, the molding methods, efficiency, and quality of thermal protection coatings need to meet the requirements of simplicity, efficiency, and stable quality. Therefore, developing a high-quality, high-efficiency molding method for thermal protection materials is of great significance for the development of next-generation aircraft.

[0023] In this invention, the low-dielectric ablation-resistant heat-resistant coating is a low-dielectric ablation-resistant heat-resistant coating with a dielectric constant that fluctuates within a small range. Therefore, the "low-dielectric ablation-resistant heat-resistant coating" can also be called the "low-dielectric ablation-resistant heat-resistant coating with a dielectric constant that fluctuates within a small range".

[0024] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0025] Example 1: This embodiment provides a low dielectric ablation resistant heat-resistant coating, which is made from the following raw materials by weight: 100 parts silicone rubber, 50 parts heat insulation medium, 5 parts curing agent, 0.8 parts organotin catalyst, 2 parts silane coupling agent, and 33 parts reinforcing filler.

[0026] The silicone rubber is room temperature vulcanizing silicone rubber L7525.

[0027] The heat insulation medium is hollow glass microspheres.

[0028] The curing agent is tetraethyl orthosilicate.

[0029] The organotin catalyst is dibutyltin dilaurate.

[0030] The silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0031] The reinforcing filler is a combination of fumed silica (6 parts), ammonium polyphosphate (20 parts), and glass fiber (7 parts).

[0032] The method for preparing the low-dielectric, ablation-resistant, and heat-resistant coating in this embodiment includes the following steps: Step 1: Mix and stir the silicone rubber, heat insulation medium and reinforcing filler until uniform to obtain the first matrix.

[0033] Step 2: Mix the curing agent, organotin catalyst and silane coupling agent and stir until homogeneous to obtain the second matrix.

[0034] Step 3: Mix the first matrix and the second matrix until homogeneous to obtain the third matrix.

[0035] Step four: The third substrate is shaped and cured at room temperature to obtain a low dielectric ablation resistant heat-resistant coating.

[0036] In the preparation method of this embodiment, the molding process adopts compression molding. The third substrate of the heat insulation coating is soft and easily deformable, which can fully meet the molding requirements of various molds, and the molding pressure is low, the molding time is short, and the process is simple. In the compression molding process, the mold can only be demolded after the coating has completely cured.

[0037] Specifically, in this embodiment, the third substrate is placed in a molding die, pressurized and shaped, and cured at room temperature. A heat-resistant coating preform can be obtained within 1 hour, a heat-resistant coating with a curing degree of more than 90% can be obtained after 24 hours, and a fully cured low-dielectric ablation-resistant heat-resistant coating can be obtained after 120 hours.

[0038] Performance testing: Figure 1 This is a dielectric constant data diagram of the low-dielectric, ablation-resistant, and heat-resistant coating in this embodiment. Figure 1 As can be seen from the data, the dielectric constant of the low dielectric ablation-resistant heat-resistant coating in this embodiment fluctuates between 1.7 and 1.81 in the frequency range of 2 to 18 GHz. Figure 2 This is a graph showing the dielectric loss tangent of the low-dielectric, ablation-resistant, and heat-resistant coating in this embodiment. Figure 2 It can be seen that the dielectric loss tangent of the low dielectric ablation resistant heat-resistant coating in this embodiment is between 0.006 and 0.117.

[0039] In existing technologies, within the 300GHz frequency range, the suitable dielectric constant value for excellent wave-transparent materials is 1–4, and the tanδ value is 10. -3 ~10 -2 In terms of magnitude, the dielectric constant of known low-dielectric silicone rubber-based heat-resistant coatings in the prior art fluctuates between 1.5 and 2.7, and the dielectric loss tangent is around 0.025. In contrast, the dielectric constant of the low-dielectric ablation-resistant heat-resistant coating in this embodiment is between 1.7 and 1.81 in the frequency range of 2 to 18 GHz, and the dielectric loss tangent is between 0.006 and 0.117. The comparison shows that the dielectric constant of the heat-resistant coating prepared in this embodiment has a smaller fluctuation range and is more stable at low levels.

[0040] Table 1 Performance data of the low dielectric ablation resistant heat-resistant coating of Example 1

[0041] Table 1 shows the performance data of the low-dielectric ablation-resistant heat-resistant coating of this embodiment. As can be seen from Table 1, the linear ablation rate of this embodiment is also at an excellent level. In addition, it also has a low thermal conductivity and excellent mechanical properties. In summary, the coating of this embodiment has the advantages of heat insulation and ablation resistance, low dielectric properties, and wave transmission properties.

[0042] Example 2: This embodiment provides a low dielectric, ablation-resistant, and heat-resistant coating. The formulation of this embodiment is basically the same as that of Example 1, except that in this embodiment, an equal amount of phenolic microspheres are used instead of hollow glass microspheres; an equal amount of octyl tin oxide is used instead of dibutyltin dilaurate; an equal amount of γ-aminopropyltriethoxysilane is used instead of γ-glycidoxypropyltrimethoxysilane; and an equal amount of mica is used instead of glass fiber.

[0043] The preparation method of the low-dielectric ablation-resistant heat-resistant coating in this embodiment is basically the same as that given in Example 1, except that the forming process in this embodiment is a spray coating process. The spray coating process can be specifically divided into air spraying, airless spraying, brushing, and scraping. The third substrate of the heat-insulating coating is soluble in various diluents, including but not limited to ethyl acetate, 120... # Solvent oil. By adding a thinner, the viscosity of the coating can be adjusted to meet the requirements of various spray coating processes.

[0044] Specifically, in this embodiment, the third matrix prepared in this embodiment is thoroughly mixed with 220 parts of ethyl acetate for 30 minutes. Then, the coating is placed into the material tank of the spraying system. The spraying distance is adjusted to 15-20 cm, the outlet pressure to 0.4 MPa, and the spray gun movement speed to 10 cm / s. Spraying begins, with each coat approximately 0.3 mm thick. The spraying interval is 10-15 minutes. After reaching the designed thickness, the coating is cured at room temperature for 5-7 days to obtain a low-dielectric, ablation-resistant, and heat-resistant coating. Specifically, the Shore hardness of the low-dielectric, ablation-resistant, and heat-resistant coating obtained by spraying is approximately 65.

[0045] The performance test results of this embodiment are basically the same as those of Embodiment 1.

[0046] Example 3: This embodiment provides a low dielectric ablation resistant and heat-resistant coating. The formulation of this embodiment is basically the same as that of Example 1, except that in this embodiment, an equal amount of vinyltriethoxysilane is used to replace γ-glycidyl etheroxypropyltrimethoxysilane; the reinforcing filler is fumed silica.

[0047] The preparation method of the low-dielectric ablation-resistant heat-resistant coating in this embodiment is basically the same as that given in Example 1. The only difference is that the molding process in this embodiment adopts a potting molding process. The potting molding process can adjust the viscosity of the third substrate of the heat-insulating coating by adding a small amount of diluent, and is suitable for potting processes of different molds and products. The product can be statically cured for 5 to 7 days, during which the solvent can slowly evaporate to complete the curing process. Gas evaporation pores should be reserved in the potting area entering the coating molding area.

[0048] Specifically, in this embodiment, the third matrix prepared in this embodiment is thoroughly mixed with 100 parts of ethyl acetate for 30 minutes, and can be potted into the coating forming area. The ethyl acetate evaporates completely in 24 hours, and the coating can be completely cured in 5-7 days.

[0049] The performance test results of this embodiment are basically the same as those of Embodiment 1.

[0050] Example 4: This embodiment provides a low dielectric ablation resistant heat-resistant coating. The formulation of this embodiment is basically the same as that of Embodiment 1, except that in this embodiment, the silicone rubber is 100 parts, the heat insulation medium is 80 parts, the curing agent is 2 parts, the organotin catalyst is 0.5 parts, the silane coupling agent is 1 part, and the reinforcing filler is 15 parts.

[0051] The preparation method of the low dielectric ablation-resistant heat-resistant coating in this embodiment is basically the same as the preparation method of the low dielectric ablation-resistant heat-resistant coating given in Example 1.

[0052] The performance test results of this embodiment are basically the same as those of Embodiment 1.

[0053] Example 5: This embodiment provides a low dielectric resistant ablation heat-insulating coating. The formulation of this embodiment is basically the same as that of Example 1, except that in this embodiment, the silicone rubber is 100 parts, the heat insulation medium is 100 parts, the curing agent is 8 parts, the organotin catalyst is 1 part, the silane coupling agent is 0.5 parts, and the reinforcing filler is 25 parts.

[0054] The preparation method of the low dielectric ablation-resistant heat-resistant coating in this embodiment is basically the same as the preparation method of the low dielectric ablation-resistant heat-resistant coating given in Example 1.

[0055] The performance test results of this embodiment are basically the same as those of Embodiment 1.

Claims

1. A low-dielectric, ablation-resistant, and heat-resistant coating, characterized in that, It is made from the following raw materials in parts by weight: 100 parts silicone rubber, 50-100 parts heat insulation medium, 2-8 parts curing agent, 0.5-1 part organotin catalyst, 0.5-2 parts silane coupling agent, and 15-33 parts reinforcing filler.

2. The low-dielectric, ablation-resistant, and heat-resistant coating as described in claim 1, characterized in that, The silicone rubber is room temperature vulcanizing silicone rubber L7525; the heat insulation medium is hollow glass microspheres or phenolic microspheres; the curing agent is tetraethyl orthosilicate; the organotin catalyst is dibutyltin dilaurate or octyltin oxide; the silane coupling agent is γ-aminopropyltriethoxysilane, vinyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane; the reinforcing filler is one or more of fumed silica, ammonium polyphosphate, glass fiber and mica.

3. The low-dielectric, ablation-resistant, and heat-resistant coating as described in claim 1, characterized in that, It is made from the following raw materials in parts by weight: 100 parts silicone rubber, 50 parts heat insulation medium, 5 parts curing agent, 0.8 parts organotin catalyst, 2 parts silane coupling agent, and 33 parts reinforcing filler.

4. The low-dielectric, ablation-resistant, and heat-resistant coating as described in claim 3, characterized in that, The silicone rubber is room temperature vulcanizing silicone rubber L7525; the heat insulation medium is hollow glass microspheres; the curing agent is tetraethyl orthosilicate; the organotin catalyst is dibutyltin dilaurate; the silane coupling agent is γ-glycidyl etheroxypropyltrimethoxysilane; and the reinforcing filler is a combination of 6 parts fumed silica, 20 parts ammonium polyphosphate, and 7 parts glass fiber.

5. The low-dielectric, ablation-resistant, and heat-resistant coating as described in claim 4, characterized in that, The low-dielectric ablation-resistant heat-resistant coating exhibits a dielectric constant ranging from 1.7 to 1.81 within the frequency range of 2 to 18 GHz, and a dielectric loss tangent between 0.006 and 0.

117.

6. The low-dielectric, ablation-resistant, and heat-resistant coating as described in claim 4, characterized in that, The low dielectric ablation-resistant heat-resistant coating has a linear ablation rate of 0.342 mm / s, a thermal conductivity of 0.147 W / mk, a tensile strength of 2.45 MPa, and an elongation at break of 31.35%.

7. A method for preparing a low-dielectric, ablation-resistant, and heat-resistant coating as described in any one of claims 1 to 6, characterized in that, The method includes the following steps: Step 1: Mix and stir the silicone rubber, heat insulation medium and reinforcing filler until homogeneous to obtain the first matrix; Step 2: Mix the curing agent, organotin catalyst, and silane coupling agent and stir until homogeneous to obtain the second matrix; Step 3: Mix the first matrix and the second matrix until homogeneous to obtain the third matrix; Step four: The third substrate is shaped and cured at room temperature to obtain a fully cured low-dielectric ablation-resistant heat-resistant coating.

8. The method for preparing the low-dielectric, ablation-resistant, and heat-resistant coating as described in claim 7, characterized in that, The molding process includes compression molding, spray molding, and potting molding.

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