A gradient functional coating containing hollow glass microspheres and a preparation method and application thereof

Abstract

This invention belongs to the technical field of special protective coating materials, and particularly relates to a gradient functional coating, its preparation method, and its application. Compared with the prior art, the gradient functional coating provided by this invention, through the synergistic effect of cage-like polysilsesquioxane and polycarbonate in the top layer, and the introduction of corundum and silicon carbide, increases the effective long-term protective temperature of the coating from below 600℃ to above 900℃, and reduces the ablation rate by more than 40%. The gradient design effectively matches the thermal expansion coefficients of each layer, and the carbon nanotube bridging in the middle layer and the hard skeleton (corundum, silicon carbide) in the top layer work together to ensure that the coating does not crack after more than 50 cycles in the "quartz lamp heating-liquid nitrogen quenching" cycle test. The innovative intermediate transition layer design and nanomaterial reinforcement enable the interlayer adhesion of the coating to reach level 5B, and the tensile bond strength between the overall coating and the metal substrate is greater than 15MPa, fundamentally solving the problem of peeling off multilayer coatings under thermal cycling.

Description

Technical Field

[0001] This invention belongs to the field of special protective coating materials technology, and particularly relates to a gradient functional coating containing hollow glass microspheres, its preparation method and application. Background Technology

[0002] As aviation technology advances towards higher speeds and greater maneuverability, the outer structure of aircraft faces extremely harsh environments during high-speed flight. These include high temperatures (exceeding 800°C) generated by prolonged aerodynamic heating, enormous thermal stress caused by intense thermal cycling, and erosion from dust, ice crystals, and other particles carried by high-temperature, high-speed airflow. Single heat-resistant or heat-insulating coatings are no longer sufficient to meet the long-term protection requirements under such complex coupled conditions.

[0003] Existing protective coating technologies have the following limitations:

[0004] Single organic coatings (such as silicone and epoxy): The upper limit of temperature resistance is usually below 600°C. At higher temperatures, they will decompose, carbonize, or even burn, losing their protective function.

[0005] Single inorganic / ceramic coating: Although it has extremely high temperature resistance, it is brittle, has poor adhesion to metal or composite substrates, and poor thermal shock resistance. It is prone to cracking and peeling under thermal cycling or mechanical impact.

[0006] Traditional double-layer coatings often employ a simple stacking of an "organic base layer + inorganic top layer," resulting in weak interlayer bonding. Furthermore, the decomposition of the organic base layer at high temperatures can lead to the failure of the entire coating system. In addition, traditional designs typically feature a passive thermal insulation layer, lacking the ability to actively sacrifice protection under extreme heat flux.

[0007] Chinese patent CN116285673B discloses a method for preparing a ceramicizable lightweight organosilicon heat-insulating coating. However, the single ceramic coating results in insufficient resistance to complex stresses. The filler system focuses on lightweight and ceramicization, sacrificing erosion resistance. Its performance cannot be guaranteed in repeated high-temperature and low-temperature environments.

[0008] Although the Chinese patent with publication number CN111534220A, which involves a double-layer ablation-resistant coating, adopts the design concept of "heat insulation layer + temperature-resistant layer", the two layers have relatively independent functions. The interface between the layers is prone to failure under extreme thermal shock. Furthermore, the temperature resistance limit and thermal shock resistance of the outer filler are still insufficient to meet the challenges of ultra-high temperature and particle erosion of the aerospace outer layer.

[0009] Therefore, developing a novel aerospace outer coating with strong interlayer bonding, adaptability to wide temperature gradient changes, and the ability to form a stable ceramic protective layer at ultra-high temperatures is of great engineering significance. Summary of the Invention

[0010] In view of this, the technical problem to be solved by the present invention is to provide a gradient functional coating containing hollow glass microspheres with excellent resistance to ultra-high temperature, thermal shock and ablation, as well as its preparation method and application.

[0011] The present invention provides a gradient functional coating containing hollow glass microspheres, comprising a heat-insulating bottom layer, an intermediate reinforcing layer and a high-temperature resistant and erosion-resistant top layer arranged sequentially.

[0012] The heat insulation substrate comprises cured epoxy-modified silicone resin, silica aerogel powder, modified hollow glass microspheres, nitrogen-based flame retardant, reinforcing fiber, and a first process aid; the mass ratio of the cured epoxy-modified silicone resin, silica aerogel powder, modified hollow glass microspheres, nitrogen-based flame retardant, reinforcing fiber, and process aid is (30~38):(30~50):(15~25):(5~10):(10~20):(2~5); the modified hollow glass microspheres comprise hollow glass microspheres and a cured aluminum dihydrogen phosphate product coated on the surface of the hollow glass microspheres;

[0013] The intermediate reinforcing layer comprises polyimide, silane coupling agent modified glass fiber, coupling agent modified ceramic fiber, and functional nanofiller; the mass ratio of the polyimide, silane coupling agent modified glass fiber, coupling agent modified ceramic fiber, and functional nanofiller is (4~10):(20~30):(10~15):(5~10).

[0014] The high-temperature resistant and erosion-resistant surface layer comprises cured silicone resin, cage-type polysilsesquioxane, polycarbonate, reinforcing filler, and a second process aid; the mass ratio of the cured silicone resin, cage-type polysilsesquioxane, polycarbonate, reinforcing filler, and second process aid is (25~33):(15~25):(8~12):(25~55):(2~6); the reinforcing filler comprises powdered filler, fiber filler, and sheet filler; the mass ratio of the powdered filler, fiber filler, and sheet filler is (15~35):(5~10):(5~10).

[0015] Preferably, the epoxy value of the epoxy-modified silicone resin is 0.02~0.2;

[0016] The polyimide is formed by imidization of polyamic acid; the weight-average molecular weight of the polyamic acid is 50,000~300,000 g / mol.

[0017] The organosilicon resin is selected from one or more of methyl silicone resin, methylphenyl silicone resin, vinyl silicone resin, hydroxyl silicone resin, and alkoxy silicone resin.

[0018] Preferably, the particle size of the silica aerogel powder is 10~20 μm;

[0019] The true density of the modified hollow glass microspheres is 0.2~0.4 g / cm³. 3 The modified hollow glass microspheres have a D90 particle size of 70~110 μm and a compressive strength of 500~4000 psi.

[0020] The nitrogen-based flame retardant comprises ammonium polyphosphate and melamine cyanurate; the mass ratio of ammonium polyphosphate to melamine cyanurate is (2~5):(1~1.5).

[0021] The diameter of the reinforcing fiber is 9~13 μm; the length of the reinforcing fiber is 300~500 μm;

[0022] The modified hollow glass microspheres were prepared according to the following method:

[0023] A1) Hollow glass microspheres were modified with a first silane coupling agent to obtain silane-modified microspheres;

[0024] A2) Silane-modified microspheres were impregnated in aluminum dihydrogen phosphate solution, and then dried and heat-treated to obtain modified hollow glass microspheres.

[0025] Preferably, the solid content of the aluminum dihydrogen phosphate solution is 10% to 20%;

[0026] The mass ratio of the silane-modified microspheres to the aluminum dihydrogen phosphate solution is 1:(1~5).

[0027] The impregnation time is 10-60 min; the drying temperature is 100℃-120℃; the drying time is 2-3 h; the heat treatment temperature is 200℃-300℃; the heat treatment time is 0.5-2 h;

[0028] The reinforcing fiber is selected from silane coupling agent modified basalt fiber.

[0029] Preferably, the diameter of the silane coupling agent modified glass fiber is 5~10 μm; the length of the silane coupling agent modified glass fiber is 100~500 μm.

[0030] The diameter of the coupling agent modified ceramic fiber is 5~10 μm; the length of the coupling agent modified ceramic fiber is 100~500 μm.

[0031] The functional nanofiller is selected from one or more of the following: carbon nanotubes, carboxylated carbon nanotubes, hydroxylated carbon nanotubes, aminated carbon nanotubes, carbon nanofibers, carboxylated carbon nanofibers, hydroxylated carbon nanofibers, aminated carbon nanofibers, silicon carbide whiskers, silicon nitride whiskers, epoxy-functionalized carbon nanotubes, silane coupling agent-grafted carbon nanotubes, surface-modified nano-silica, surface-modified nano-alumina, aminated graphene, and epoxy-functionalized graphene.

[0032] Preferably, the number-average molecular weight of the polycarbonate is 2000-3500;

[0033] The particle size of the powdered filler is 1~20 μm;

[0034] The diameter of the fiber filler is 10~15 μm; the length of the fiber filler is 150~300 μm;

[0035] The sheet-like filler has a sheet diameter of 5~20 μm.

[0036] Preferably, the powdered filler comprises silane coupling agent modified metal oxide powder, first silane coupling agent modified silicon carbide, and second silane coupling agent modified silicon carbide.

[0037] The particle size of the silane coupling agent modified metal oxide powder is 5~15 μm;

[0038] The particle size of the first silane coupling agent modified silicon carbide is 1~3 μm;

[0039] The particle size of the second silane coupling agent modified silicon carbide is 10~20 μm;

[0040] The total mass ratio of the first silane coupling agent modified silicon carbide and the second silane coupling agent modified silicon carbide to the mass ratio of the silane coupling agent modified metal oxide powder is (5~15):(10~20).

[0041] The mass ratio of the first silane coupling agent modified silicon carbide to the second silane coupling agent modified silicon carbide is 1:(1~3).

[0042] Preferably, the thickness ratio of the heat insulation bottom layer, the intermediate reinforcement layer and the high temperature erosion resistant surface layer is (3~4):(2~3):(5~6).

[0043] The present invention also provides a method for preparing the above-mentioned gradient functional coating containing hollow glass microspheres, comprising the following steps:

[0044] S1) Spray the heat-insulating base coat, heat and pre-cur it to form a semi-cured heat-insulating base coat; the heat-insulating base coat includes epoxy modified silicone resin, silica aerogel powder, modified hollow glass microspheres, nitrogen flame retardant, reinforcing fiber, first process aid and first solvent.

[0045] S2) Spray an intermediate reinforcement layer coating onto the surface of the semi-cured heat insulation substrate and heat-treat it to form an intermediate reinforcement layer; the intermediate reinforcement layer coating includes a polyamic acid solution, silane coupling agent modified glass fiber, coupling agent modified ceramic fiber, functional nanofiller and a second solvent.

[0046] S3) A high-temperature resistant and erosion-resistant surface coating is sprayed onto the surface of the intermediate reinforcing layer and cured by step heating to form a high-temperature resistant and erosion-resistant surface layer; the high-temperature resistant and erosion-resistant surface coating includes organosilicon resin, cage-type polysilsesquioxane, polycarbonate, reinforcing filler, second process aid and third solvent.

[0047] The present invention also provides an aircraft comprising the above-described gradient functional coating containing hollow glass microspheres.

[0048] Compared with the prior art, the gradient functional coating provided by the present invention has the following advantages:

[0049] 1) Breakthrough in temperature resistance and ablation resistance: Through the synergy of surface cage-type polysilsesquioxane and polycarbonate, as well as the introduction of corundum and silicon carbide, the effective long-term protection temperature of the coating is increased from below 600℃ of traditional coatings to above 900℃ (short-term impact of 1200℃), and the ablation rate is reduced by more than 40%.

[0050] 2) Exceptional thermal shock and erosion resistance: The gradient design effectively matches the thermal expansion coefficients of each layer. The carbon nanotube bridging in the middle layer and the hard skeleton (corundum, silicon carbide) in the surface layer work together to ensure that the coating does not crack after more than 50 cycles of "quartz lamp heating-liquid nitrogen quenching" test (ΔT>800℃).

[0051] 3) Excellent interlayer adhesion and service reliability: The innovative intermediate transition layer design and nanomaterial reinforcement enable the interlayer adhesion (cross-cut test) of the coating to reach level 5B, and the tensile bond strength between the overall coating and the metal substrate is greater than 15MPa, which fundamentally solves the problem of peeling off multilayer coatings under thermal cycling. Detailed Implementation

[0052] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0053] This invention provides a gradient functional coating, comprising a heat-insulating underlayer, an intermediate reinforcing layer, and a high-temperature resistant and erosion-resistant top layer arranged sequentially. The heat-insulating underlayer comprises cured epoxy-modified silicone resin, silica aerogel powder, modified hollow glass microspheres, nitrogen-based flame retardant, reinforcing fibers, and a first process aid. The mass ratio of the cured epoxy-modified silicone resin, silica aerogel powder, modified hollow glass microspheres, flame retardant, reinforcing fibers, and process aid is (30~38):(30~50):(15~25):(5~10):(2~5). The modified hollow glass microspheres comprise hollow glass microspheres and a cured aluminum dihydrogen phosphate product coating the surface of the hollow glass microspheres. The intermediate reinforcing layer comprises polyimide, silane coupling agent-modified glass fibers, coupling agent-modified ceramic fibers, and functional... Nanofillers; the mass ratio of the polyimide, silane coupling agent modified glass fiber, coupling agent modified ceramic fiber and functional nanofillers is (4~10):(20~30):(10~15):(5~10); the high-temperature resistant and erosion-resistant surface layer includes cured silicone resin, cage-type polysilsesquioxane, polycarbonate, reinforcing filler and second process aid; the mass ratio of the cured silicone resin, cage-type polysilsesquioxane, polycarbonate, reinforcing filler and second process aid is (25~33):(15~25):(8~12):(25~55):(2~6); the reinforcing fillers include powdered fillers, fiber fillers and sheet fillers; the mass ratio of the powdered fillers, fiber fillers and sheet fillers is (15~35):(5~10):(5~10).

[0054] This invention abandons the simple "heat insulation + temperature resistance" two-layer stacking approach, and constructs a coating system with a continuous gradient change in composition, modulus and function from the bottom layer to the surface layer. This system significantly improves the coating's temperature resistance limit, thermal shock resistance and overall lifespan by introducing a "soft ceramic" precursor and a high-hardness erosion-resistant skeleton in the outer layer, innovatively using multi-level hollow composite fillers in the inner layer, and designing an intermediate transition layer to enhance interlayer interpenetration.

[0055] The gradient functional coating provided by this invention comprises a heat-insulating underlayer, an intermediate reinforcing layer, and a high-temperature erosion-resistant top layer arranged sequentially. The three layers use different resin matrices and functional fillers, and through chemical composition design, they form a strong interfacial bond and functional complementarity during curing and service. The thickness ratio of the heat-insulating underlayer, intermediate reinforcing layer, and high-temperature erosion-resistant top layer is preferably (3~4):(2~3):(5~6). Optionally, the thickness ratio of the heat-insulating underlayer, intermediate reinforcing layer, and high-temperature erosion-resistant top layer is 3:2:5, 4:2:5, 3:3:5, 4:3:5, 3:2:6, 4:2:6, 3:3:6, 4:3:6, or any two of the above ratios.

[0056] The heat insulation layer is in direct contact with the substrate; the substrate is preferably a metal substrate, including but not limited to aluminum alloy, titanium alloy, etc., and the core function of this layer is to minimize the conduction of aerodynamic heat to the substrate.

[0057] In this invention, the heat insulation layer comprises cured epoxy-modified silicone resin, silica aerogel powder, modified hollow glass microspheres, nitrogen-based flame retardant, reinforcing fiber, and a first process aid; the mass ratio of the cured epoxy-modified silicone resin, silica aerogel powder, modified hollow glass microspheres, nitrogen-based flame retardant, reinforcing fiber, and process aid is (30~38):(30~50):(15~25):(5~10):(10~20):(2~5); in the embodiments provided by this invention, the specific mass ratio of the cured epoxy-modified silicone resin, silica aerogel powder, modified hollow glass microspheres, nitrogen-based flame retardant, reinforcing fiber, and process aid is 30:30:15:5:10:2, 35:40:20:8:15:3, or 37.5:50:25:10:20:4, or any two of the above values.

[0058] In this invention, the heat insulation layer uses epoxy-modified silicone resin as the resin matrix, which combines the high adhesion of epoxy resin with the excellent heat resistance of silicone resin and has a high glass transition temperature (Tg). The epoxy value of the epoxy-modified silicone resin is preferably 0.02 to 0.2. Optionally, the epoxy value of the epoxy-modified silicone resin is 0.02, 0.04, 0.06, 0.07, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2 or any two of the above values.

[0059] In one specific embodiment of the present invention, the content of the cured epoxy-modified silicone resin in the heat insulation layer is preferably 30 to 38 parts by weight; optionally, the content of the cured epoxy-modified silicone resin in the heat insulation layer is 30 parts by weight, 32.5 parts by weight, 35 parts by weight, 37.5 parts by weight, or any two of the above values.

[0060] In this invention, the heat insulation filler system in the heat insulation layer adopts a multi-level compounding strategy, including silica aerogel powder and modified hollow glass microspheres; wherein, silica aerogel powder can provide extremely low thermal conductivity; the modified hollow glass microspheres are cured at medium and low temperature (~350℃) to form a high-strength bond, and react with the surface of the microspheres or added Al2O3, SiO2, etc. at higher temperatures (above 800℃) to generate stable ceramic phases such as aluminum phosphate and aluminum silicophosphate, thereby firmly "welding" the microspheres into the ceramic network, playing a key role in strengthening, preventing sintering and heat insulation.

[0061] In one specific embodiment of the present invention, the particle size of the silica aerogel powder is preferably less than or equal to 50 μm, more preferably 10~20 μm; optionally, the particle size of the silica aerogel powder is 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm or any two of the above values.

[0062] In one specific embodiment of the present invention, the content of silica aerogel powder in the heat insulation layer is preferably 30 to 50 parts by weight; optionally, the content of silica aerogel powder in the heat insulation layer is 30 parts by weight, 35 parts by weight, 40 parts by weight, 45 parts by weight, 50 parts by weight, or any two of the above values.

[0063] In one specific embodiment of the present invention, the true density of the modified hollow glass microspheres is preferably 0.2~0.4 g / cm³. 3 Optionally, the true density of the modified hollow glass microspheres is 0.2 g / cm³. 3 0.25 g / cm 3 0.28g / cm 3 0.3 g / cm 3 0.35 g / cm 3 0.38 g / cm 3 0.4 g / cm 3 Or a range between any two of the above values; the D90 particle size of the modified hollow glass microspheres is preferably 70~110 μm; optionally, the D90 particle size of the modified hollow glass microspheres is 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm or a range between any two of the above values; the pressure resistance of the modified hollow glass microspheres is preferably 500~4000 psi; optionally, the pressure resistance of the modified hollow glass microspheres is 500 psi, 800 psi, 1000 psi, 1200 psi, 1500 psi, 1800 psi, 2000 psi, 2200 psi, 2500 psi, 2800 psi, 3000 psi, 3200 psi, 3500 psi, 3800 psi. psi, 4000psi, or any two of the above values.

[0064] In one specific embodiment of the present invention, the modified hollow glass microspheres comprise hollow glass microspheres and a cured aluminum dihydrogen phosphate product coated on the surface of the hollow glass microspheres; the cured aluminum dihydrogen phosphate product is connected to the hollow glass microspheres via a first silane coupling agent; the first silane coupling agent can be any silane coupling agent well known to those skilled in the art, and there are no special limitations, but is preferably an aminosilane coupling agent and / or an epoxysilane coupling agent; the aminosilane coupling agent includes, but is not limited to, 3-aminopropyltriethoxysilane (KH550), 3-aminopropyltrimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, diethylenetriaminepropyltrimethoxysilane, and bis-[γ-(trimethoxysilyl)propyl] The epoxy silane coupling agent comprises, but is not limited to, one or more of the following: amine (diaminosilane), N-n-butyl-3-aminopropyltrimethoxysilane, N,N-dimethyl-3-aminopropyltrimethoxysilane, and 3-anilinepropyltrimethoxysilane; the epoxy silane coupling agent comprises, but is not limited to, one or more of the following: 3-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560), 3-(2,3-epoxypropoxy)propyltriethoxysilane, 3-(2,3-epoxypropoxy)propylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane.

[0065] In a specific embodiment of the present invention, the modified hollow glass microspheres are preferably prepared by the following method: A1) the hollow glass microspheres are modified with a first silane coupling agent to obtain silane-modified microspheres; A2) the silane-modified microspheres are impregnated in aluminum dihydrogen phosphate solution, and then dried and heat-treated to obtain modified hollow glass microspheres.

[0066] In a specific embodiment of the present invention, step A1) specifically involves: mixing hollow glass microspheres with an alcohol solution of a first silane coupling agent, stirring and mixing evenly, and then drying to obtain silane-modified microspheres; the mass concentration of the coupling agent in the coupling agent solution is preferably 1% to 3%; the mass ratio of the hollow glass microspheres to the coupling agent solution is 1:(5 to 10); the alcohol solvent can be any alcohol solvent well known to those skilled in the art, and there are no special limitations, but ethanol is preferred in the present invention; the modification temperature is preferably 60℃ to 80℃; the modification time is preferably 2 to 8 h to ensure that the silane fully reacts with the hydroxyl groups on the surface of the microspheres; optionally, the modification time is 2 h, 4 h, 6 h, 8 h, or any two of the above values.

[0067] In a specific embodiment of the present invention, step A2) specifically comprises: impregnating silane-modified microspheres in an aluminum dihydrogen phosphate solution, followed by drying and heat treatment to obtain modified hollow glass microspheres; the solid content of the aluminum dihydrogen phosphate solution is preferably 10%~20%; optionally, the solid content of the aluminum dihydrogen phosphate solution is 10%, 12%, 15%, 18%, 20%, or any two of the above values; the mass ratio of the silane-modified microspheres to the aluminum dihydrogen phosphate solution is preferably 1:(5~10); optionally, the mass ratio of the silane-modified microspheres to the aluminum dihydrogen phosphate solution is 1:5, 1:7, 1:8, 1:10, or any two of the above values; the impregnation is preferably carried out at room temperature; the impregnation time is preferably 10~60 min; the drying is preferably forced air drying; the drying temperature is preferably 100℃~120℃; the drying time is preferably 2~3 minutes. h; the heat treatment temperature is preferably 200℃~300℃, more preferably 250℃; the heat treatment time is preferably 0.5~2 h, more preferably 1~2 h.

[0068] In one specific embodiment of the present invention, the content of the modified hollow glass microspheres in the heat insulation layer is preferably 15 to 25 parts by weight; optionally, the content of the modified hollow glass microspheres in the heat insulation layer is 15 parts by weight, 18 parts by weight, 20 parts by weight, 22 parts by weight, 25 parts by weight, or any two of the above values.

[0069] In this invention, the nitrogen-based flame retardant preferably comprises ammonium polyphosphate and melamine cyanurate; when heated, it can promote the carbonization of the bottom resin and react with the upper layer material to enhance the interlayer bonding; the mass ratio of ammonium polyphosphate to melamine cyanurate is preferably (2~5):(1~1.5); optionally, the mass ratio of ammonium polyphosphate to melamine cyanurate is 2:1, 2:1.5, 3:1, 3:1.5, 4:1, 4:1.5, 5:1, 5:1.5 or any two of the above ratios.

[0070] In one specific embodiment of the present invention, the nitrogen-based flame retardant is preferably present in the heat insulation bottom layer at a content of 5 to 10 parts by weight; optionally, the nitrogen-based flame retardant is present in the heat insulation bottom layer at a content of 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, or any two of the above values.

[0071] In one specific embodiment of the present invention, the diameter of the reinforcing fiber is preferably 9-13 μm; optionally, the diameter of the reinforcing fiber is 9 μm, 10 μm, 11 μm, 12 μm, 13 μm or any two of the above values; the length of the reinforcing fiber is 300-500 μm; optionally, the length of the reinforcing fiber is 300 μm, 350 μm, 400 μm, 450 μm, 500 μm or any two of the above values.

[0072] In one specific embodiment of the present invention, the reinforcing fiber is preferably silane coupling agent modified basalt fiber.

[0073] In a specific embodiment of the present invention, the silane coupling agent modified basalt fiber is preferably basalt fiber modified with a second silane coupling agent; the second silane coupling agent is preferably one or more of vinyl silane coupling agents, amino silane coupling agents, and epoxy silane coupling agents; the vinyl silane coupling agent includes, but is not limited to, one or more of vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltri(β-methoxyethoxy)silane; the amino silane coupling agent and epoxy silane coupling agent are the same as described above, and will not be repeated here.

[0074] In a specific embodiment of the present invention, the silane coupling agent modified basalt fiber is preferably prepared by the following method: basalt fiber is added to an alcohol solution of a second silane coupling agent, stirred evenly, fully wetted, and then dried to obtain silane coupling agent modified basalt fiber; the mass concentration of the coupling agent is preferably 1%~3%; the mass ratio of basalt fiber to coupling agent solution is 1:(5~10); the alcohol solvent can be any alcohol solvent well known to those skilled in the art, and there are no special limitations, but ethanol is preferred in the present invention; the drying temperature is preferably 80℃~150℃, more preferably 120℃~150℃; the drying time is preferably 2~3 h; after drying, it is also preferably ball-milled to obtain silane coupling agent modified basalt fiber; the ball-to-material ratio of the ball milling is preferably 1:(1~5), more preferably 1:(2~3); the ball milling speed is preferably 50~100 rpm; the ball milling time is preferably 5~20 min, more preferably 10~15 min.

[0075] In one specific embodiment of the present invention, the content of the reinforcing fiber in the heat insulation layer is preferably 10 to 20 parts by weight; optionally, the content of the reinforcing fiber in the heat insulation layer is 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, or any two of the above values.

[0076] In a specific embodiment of the present invention, the first process aid preferably includes, but is not limited to, a third silane coupling agent and a thixotropic agent; the mass ratio of the third silane coupling agent to the thixotropic agent is preferably (1~3):(1~2); optionally, the mass ratio of the third silane coupling agent to the thixotropic agent is 1:1, 1:2, 2:1, 3:1, 3:2 or any two of the above ratios.

[0077] In a specific embodiment of the present invention, the third silane coupling agent is preferably an aminosilane coupling agent and / or an epoxysilane coupling agent; the aminosilane coupling agent and the epoxysilane coupling agent are as described above, and will not be repeated here.

[0078] In one specific embodiment of the present invention, the thixotropic agent is preferably fumed silica; the mesh size of the thixotropic agent is preferably 700-900 mesh; optionally, the mesh size of the thixotropic agent is 700 mesh, 750 mesh, 800 mesh, 850 mesh, 900 mesh or any two of the above values.

[0079] In one specific embodiment of the present invention, optionally, the content of the first process aid in the heat insulation layer is 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, or any two of the above values.

[0080] According to the present invention, an intermediate reinforcing layer is provided on the surface of the heat insulation substrate; this layer is key to the functional gradient transition, the purpose of which is to strengthen the coating and serve as a stress buffer layer, while providing excellent interlayer adhesion; the intermediate reinforcing layer uses polyimide as the base resin; the polyimide is formed by imidization of polyamic acid; the polyamic acid can be imidized at high temperature to form a polyimide with extremely high heat resistance and a modulus between the substrate and the top layer; the weight average molecular weight of the polyamic acid is preferably 50,000~300,000 g / mol, more preferably 80,000~280,000 g / mol, and even more preferably 100,000~250,000 g / mol.

[0081] In one specific embodiment of the present invention, the content of polyimide in the intermediate reinforcing layer is preferably 4 to 10 parts by weight; optionally, the content of polyimide in the intermediate reinforcing layer is 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, or any two of the above values.

[0082] In this invention, the silane coupling agent modified glass fiber, the coupling agent modified ceramic fiber, and the functional nanofiller in the intermediate reinforcing layer together form a gradient reinforcement material.

[0083] In a specific embodiment of the present invention, the diameter of the silane coupling agent modified glass fiber is preferably 5-10 μm; optionally, the diameter of the silane coupling agent modified glass fiber is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any two of the above values; the length of the silane coupling agent modified glass fiber is preferably 100-500 μm; optionally, the length of the silane coupling agent modified glass fiber is 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm or any two of the above values.

[0084] In one specific embodiment of the present invention, the silane coupling agent modified glass fiber is preferably a silane coupling agent modified high-silica glass fiber.

[0085] In a specific embodiment of the present invention, the silane coupling agent modified glass fiber is preferably glass fiber modified with a fourth silane coupling agent; the fourth silane coupling agent is preferably an aminosilane coupling agent and / or an epoxysilane coupling agent; the aminosilane coupling agent and the epoxysilane coupling agent are the same as described above, and will not be repeated here.

[0086] In a specific embodiment of the present invention, the silane coupling agent modified glass fiber is preferably prepared by the following method: glass fiber is added to a solution containing a fourth silane coupling agent, stirred evenly, fully wetted, and then dried to obtain modified glass fiber. The mass concentration of the solution containing the fourth coupling agent is preferably 1% to 3%; the mass ratio of the glass fiber to the solution containing the fourth silane coupling agent is preferably 1:(5 to 10), more preferably 1:(8 to 10), and even more preferably 1:9; the solvent of the solution containing the fourth silane coupling agent is preferably an alcohol solvent; the alcohol solvent can be any alcohol solvent well known to those skilled in the art, and there are no special limitations, but ethanol is preferred in this invention; the drying temperature is preferably 80℃ to 120℃; the drying time is preferably 1 to 3 hours; after drying, a light depolymerization can be carried out using an air jet mill to prevent fiber agglomeration.

[0087] In one specific embodiment of the present invention, the content of the silane coupling agent modified glass fiber in the intermediate reinforcing layer is preferably 20 to 30 parts by weight; optionally, the content of the silane coupling agent modified glass fiber in the intermediate reinforcing layer is 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, 30 parts by weight, or any two of the above values.

[0088] In a specific embodiment of the present invention, the diameter of the coupling agent modified ceramic fiber is preferably 5-10 μm; optionally, the diameter of the coupling agent modified ceramic fiber is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any two of the above values; the length of the coupling agent modified ceramic fiber is preferably 100-500 μm; optionally, the length of the coupling agent modified ceramic fiber is 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm or any two of the above values.

[0089] In one specific embodiment of the present invention, the coupling agent modified ceramic fiber is preferably a coupling agent modified aluminosilicate ceramic fiber.

[0090] In a specific embodiment of the present invention, the silane coupling agent modified ceramic fiber is preferably obtained by using a fifth silane coupling agent modified ceramic fiber; the fifth silane coupling agent is preferably an aminosilane coupling agent and / or an epoxysilane coupling agent; specifically, the preparation method of the coupling agent modified ceramic fiber is the same as the method of silane coupling agent modified glass fiber, except that the type of coupling agent can be the same or different, which will not be repeated here.

[0091] In one specific embodiment of the present invention, the content of the coupling agent modified ceramic fiber in the intermediate reinforcing layer is preferably 10 to 15 parts by weight; optionally, the content of the coupling agent modified ceramic fiber in the intermediate reinforcing layer is 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, or any two of the above values.

[0092] In a specific embodiment of the present invention, the functional nanofiller is preferably one or more of the following: carbon nanotubes, carboxylated carbon nanotubes, hydroxylated carbon nanotubes, aminated carbon nanotubes, carbon nanofibers, carboxylated carbon nanofibers, hydroxylated carbon nanofibers, aminated carbon nanofibers, silicon carbide whiskers, silicon nitride whiskers, epoxy-functionalized carbon nanotubes, silane coupling agent-grafted carbon nanotubes, surface-modified nano-silica, surface-modified nano-alumina, aminated graphene, and epoxy-functionalized graphene. The functional nanofiller has a large aspect ratio and can physically penetrate the upper and lower layer interfaces during the curing process like "needle and thread," and become entangled with the polyimide molecular chains, greatly improving the interlayer bonding strength and the overall toughness of the coating.

[0093] In one specific embodiment of the present invention, the content of the functional nanofiller in the intermediate reinforcing layer is preferably 5 to 10 parts by weight; optionally, the content of the functional nanofiller in the intermediate reinforcing layer is 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, or any two of the above values.

[0094] In this invention, the surface of the intermediate reinforcing layer is provided with a high-temperature resistant and erosion-resistant surface layer. This layer directly faces the high-temperature and high-speed airflow. Its core innovation lies in combining the dual mechanisms of "active heat absorption-ceramic formation" and "passive hard erosion resistance".

[0095] In this invention, the base resin of the high-temperature resistant and erosion-resistant surface layer is an organosilicon resin, which has a high high-temperature carbon residue rate and can be used as a ceramic precursor; the type of organosilicon resin is preferably one or more of methyl silicone resin, methyl phenyl silicone resin, vinyl silicone resin, hydroxyl silicone resin and alkoxy silicone resin, and more preferably methyl phenyl silicone resin.

[0096] In one specific embodiment of the present invention, the content of the cured silicone resin in the high-temperature resistant and erosion-resistant surface layer is preferably 25 to 33 parts by weight; optionally, the content of the cured silicone resin in the high-temperature resistant and erosion-resistant surface layer is 25 parts by weight, 28 parts by weight, 30 parts by weight, 31 parts by weight, 31 parts by weight, 33 parts by weight, or any two of the above values.

[0097] In this invention, the cage-type polysilsesquioxane (POSS) serves as a precursor for soft ceramics. It can be transformed into a silica ceramic phase at high temperatures. This process absorbs a large amount of heat, and the resulting ceramic phase can effectively protect the carbon layer from oxidation.

[0098] In one specific embodiment of the present invention, the content of the cage-type polysilsesquioxane in the high-temperature resistant and erosion-resistant surface layer package is preferably 15 to 25 parts by weight; optionally, the content of the cage-type polysilsesquioxane in the high-temperature resistant and erosion-resistant surface layer package is 15 parts by weight, 17 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 23 parts by weight, 25 parts by weight, or any two of the above values.

[0099] In this invention, polycarbonate can be used as a highly efficient carbon-forming agent to synergistically form a denser carbon-ceramic composite layer with POSS; the number average molecular weight of the polycarbonate is preferably 2000~3500; optionally, the number average molecular weight of the polycarbonate is 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500 or any two of the above values.

[0100] In this invention, a composite of powdered filler, fiber filler, and sheet filler is used as the erosion-resistant skeleton reinforcement filler for the high-temperature erosion-resistant surface layer; the preferred mass ratio of the powdered filler, fiber filler, and sheet filler is (15~35):(5~10):(5~10); in some embodiments provided by this invention, the mass ratio of the powdered filler, fiber filler, and sheet filler is 15:5:5, 25:8:8, or 35:10:10.

[0101] In a specific embodiment of the present invention, the powdered filler comprises silane coupling agent modified metal oxide powder, first silane coupling agent modified silicon carbide, and second silane coupling agent modified silicon carbide; wherein, the silane coupling agent modified metal oxide powder is preferably silane coupling agent modified alumina, more preferably silane coupling agent modified corundum powder, and even more preferably silane coupling agent modified fused corundum powder; the metal oxide powder has extremely high hardness and chemical inertness, and is the main framework resisting particle erosion. Surface modification with a silane coupling agent is required to ensure a firm bond with the organosilicon resin and prevent particles from falling off under erosion. Silicon carbide can form a SiO2 glass layer after oxidation at extreme high temperatures, which can flow, seal cracks, and has oxidation resistance and a certain degree of crack self-healing ability.

[0102] In a specific embodiment of the present invention, the preferred mass ratio of the total mass of the first silane coupling agent modified silicon carbide and the second silane coupling agent modified silicon carbide to the mass of the silane coupling agent modified metal oxide powder is (5~15):(10~20); optionally, the mass ratio of the total mass of the first silane coupling agent modified silicon carbide and the second silane coupling agent modified silicon carbide to the mass of the silane coupling agent modified metal oxide powder is 5:10, 5:12, 5:15, 5:18, 5:20, 8:10, 8:12, 8:15, 8:18, 8:20, 10:10, 10:12, 10:15, 10:18, 12:10, 12:15, 12:18, 12:20, 15:10, 15:12, 15:18, 15:20, or any two of the above ratios.

[0103] In one specific embodiment of the present invention, the particle size of the silane coupling agent modified metal oxide powder is preferably 5 to 15 μm; optionally, the particle size of the silane coupling agent modified metal oxide powder is 5 μm, 8 μm, 11 μm, 15 μm or any two of the above values.

[0104] In a specific embodiment of the present invention, the particle size of the first silane coupling agent modified silicon carbide is preferably 1-3 μm; optionally, the particle size of the first silane coupling agent modified silicon carbide is 1 μm, 2 μm, 3 μm, or any two of the above values; the particle size of the second silane coupling agent modified silicon carbide is preferably 10-20 μm; optionally, the particle size of the second silane coupling agent modified silicon carbide is 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any two of the above values. Coarse particles of 10-20 μm provide rigid support, while fine powder fills the pores and increases density; furthermore, in the ablation-resistant composite material, 1-3 μm powder can form a denser oxide layer.

[0105] In a specific embodiment of the present invention, the mass ratio of the first silane coupling agent modified silicon carbide to the second silane coupling agent modified silicon carbide is preferably 1:(1~3); the optimal comprehensive performance can be obtained by compounding coarse and fine particles in proportion; optionally, the mass ratio of the first silane coupling agent modified silicon carbide to the second silane coupling agent modified silicon carbide is 1:1, 1:2, 1:3 or any two of the above ratios.

[0106] In a specific embodiment of the present invention, the silane coupling agent modified metal oxide powder is preferably obtained by using a sixth silane coupling agent modified metal oxide powder; the sixth silane coupling agent is preferably an aminosilane coupling agent and / or an epoxysilane coupling agent; the aminosilane coupling agent and the epoxysilane coupling agent are the same as described above, and will not be repeated here.

[0107] In a specific embodiment of the present invention, the silane coupling agent modified metal oxide powder is preferably prepared by the following method: the metal oxide and the sixth silane coupling agent solution are stirred and then dried to obtain the modified metal oxide; the mass concentration of the sixth coupling agent in the sixth silane coupling agent solution is preferably 1% to 3%; the mass ratio of the metal oxide to the sixth silane coupling agent solution is 1:(8 to 12); the solvent in the sixth silane coupling agent solution is preferably an alcohol solvent; the alcohol solvent can be any alcohol solvent known to those skilled in the art and is not particularly limited, but ethanol is preferred in the present invention; the drying temperature is preferably 60°C to 90°C; and the drying time is preferably 6 to 8 hours.

[0108] In one specific embodiment of the present invention, the content of the silane coupling agent modified metal oxide powder in the high-temperature resistant and erosion-resistant surface layer is preferably 10 to 20 parts by weight; optionally, the content of the silane coupling agent modified metal oxide powder in the high-temperature resistant and erosion-resistant surface layer is 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, or any two of the above values.

[0109] In a specific embodiment of the present invention, the preparation methods of the first silane coupling agent modified silicon carbide and the second silane coupling agent modified silicon carbide are the same as the preparation methods of silane coupling agent modified metal oxide powder, except that the types of silane coupling agents can be the same or different, and there are no special restrictions.

[0110] In a specific embodiment of the present invention, the total amount of the first silane coupling agent modified silicon carbide and the second silane coupling agent modified silicon carbide in the high-temperature resistant and erosion-resistant surface layer is preferably 5 to 15 parts by weight; optionally, the total amount of the first silane coupling agent modified silicon carbide and the second silane coupling agent modified silicon carbide in the high-temperature resistant and erosion-resistant surface layer is 5 parts by weight, 7 parts by weight, 9 parts by weight, 11 parts by weight, 13 parts by weight, 15 parts by weight, or any two of the above values.

[0111] In this invention, the fiber filler acts as a toughening fiber in the high-impact layer, especially in the middle of the high-erosion particles, which can absorb impact energy and prevent the coating from peeling off.

[0112] In one specific embodiment of the present invention, the diameter of the fiber filler is preferably 10-15 μm; optionally, the diameter of the fiber filler is 10 μm, 12 μm, 14 μm, 15 μm or any two of the above values; the length of the fiber filler is preferably 150-300 μm; optionally, the length of the fiber filler is 150 μm, 180 μm, 200 μm, 220 μm, 250 μm, 280 μm, 300 μm or any two of the above values.

[0113] In one specific embodiment of the present invention, the fiber filler is preferably glass fiber, and more preferably high-silica glass fiber.

[0114] In one specific embodiment of the present invention, the content of the fiber filler in the high-temperature resistant and erosion-resistant surface layer is preferably 5 to 10 parts by weight; optionally, the content of the fiber filler in the high-temperature resistant and erosion-resistant surface layer is 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, or any two of the above values.

[0115] In this invention, the sheet-like filler is arranged parallel to the coating surface, providing excellent airtightness and resistance to the penetration of oxidizing media.

[0116] In one specific embodiment of the present invention, the sheet diameter of the sheet packing is preferably 5 to 20 μm; optionally, the sheet diameter of the sheet packing is 5 μm, 10 μm, 15 μm, 20 μm or any two of the above values.

[0117] In one specific embodiment of the present invention, the sheet-like filler is preferably one or more of the following sheet-like reinforcing fillers: flake graphene, hexagonal boron nitride (h-BN), montmorillonite (MMT), kaolin, mica powder (1500 mesh or larger), micron-sized sheet-like alumina, and sheet-like glass powder.

[0118] In one specific embodiment of the present invention, the content of the sheet filler in the high-temperature resistant and erosion-resistant surface layer is preferably 5 to 10 parts by weight; optionally, the content of the sheet filler in the high-temperature resistant and erosion-resistant surface layer is 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, or any two of the above values.

[0119] In a specific embodiment of the present invention, the second process aid preferably includes a wetting and dispersing agent and a defoamer; the mass ratio of the wetting and dispersing agent to the defoamer is preferably (2~4):(1~2); optionally, the mass ratio of the wetting and dispersing agent to the defoamer is 2:1, 2:2, 3:1, 3:2, 4:1 or any two of the above ratios; the wetting and dispersing agent includes, but is not limited to, one or more of BYK-161, BYK-163, BYK-306 and BYK-2150; the defoamer includes, but is not limited to, one or more of silicone defoamers, polyether defoamers and polyether-modified silicone defoamers.

[0120] In one specific embodiment of the present invention, the content of the second process aid in the high-temperature resistant and erosion-resistant surface layer is preferably 2 to 6 parts by weight; optionally, the content of the second process aid in the high-temperature resistant and erosion-resistant surface layer is 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, or any two of the above values.

[0121] In one specific embodiment of the present invention, the thickness of the gradient functional coating is preferably 0.3 to 3 mm; optionally, the thickness of the gradient functional coating is 0.3 mm, 0.5 mm, 1 mm, 2 mm, 3 mm or any two of the above values.

[0122] In this invention, the unit weight parts of each material in the heat insulation bottom layer, the intermediate reinforcement layer and the high temperature erosion resistant surface layer can be the same or different, and there are no special restrictions, but the unit weight parts of each material in the same layer are the same.

[0123] The present invention also provides a method for preparing the above-mentioned gradient functional coating, comprising the following steps: S1) spraying a heat-insulating underlayer coating and pre-curing it by heating to form a semi-cured heat-insulating underlayer; the heat-insulating underlayer coating comprises epoxy-modified silicone resin, silica aerogel powder, modified hollow glass microspheres, nitrogen-based flame retardant, reinforcing fiber, a first process aid, and a first solvent; S2) spraying an intermediate reinforcing layer coating on the surface of the semi-cured heat-insulating underlayer and pre-curing it by heating to form an intermediate reinforcing layer; the intermediate reinforcing layer coating comprises polyamic acid solution, silane coupling agent modified glass fiber, coupling agent modified ceramic fiber, functional nanofiller, and a second solvent; S3) spraying a high-temperature resistant and erosion-resistant topcoat coating on the surface of the intermediate reinforcing layer and curing it by step heating to form a high-temperature resistant and erosion-resistant topcoat; the high-temperature resistant and erosion-resistant topcoat coating comprises silicone resin, cage-type polysilsesquioxane, polycarbonate, reinforcing filler, a second process aid, and a third solvent.

[0124] In this invention, there are no special restrictions on the source of any raw materials; commercially available materials are acceptable. The types and amounts of each component in the heat-insulating bottom layer, intermediate reinforcing layer, and high-temperature resistant and erosion-resistant top layer are the same as described above and will not be repeated here.

[0125] In this invention, the heat-insulating base coating, the intermediate reinforcing layer coating, and the high-temperature erosion-resistant top coating can all be prepared according to methods well known to those skilled in the art, without any special limitations. Specifically, each component can be placed in a high-speed disperser, fully dispersed and uniformly under inert gas protection, and then vacuum degassing can be performed.

[0126] In a specific embodiment of the present invention, the first solvent and the third solvent can both be organic solvents well known to those skilled in the art, and there are no special limitations, including but not limited to one or more of ethyl acetate, butyl acetate, butanone, acetone and xylene; the first solvent and the third solvent can be the same or different, and there are no special limitations.

[0127] In a specific embodiment of the present invention, the solid content of the epoxy-modified silicone resin is preferably 40%~70%, more preferably 50%~60%, and even more preferably 50%~55%; the mass ratio of the first solvent to the epoxy-modified silicone resin is preferably (40~50):(60~75); optionally, the mass ratio of the first solvent to the epoxy-modified silicone resin is 40:60, 40:70, 40:75, 45:60, 45:70, 45:75, 50:60, 50:70, 50:75 or any two of the above ratios.

[0128] A heat-insulating undercoat is sprayed onto the substrate surface and pre-cured by heating to form a semi-cured heat-insulating undercoat; the pre-curing temperature is preferably 80℃~100℃; the pre-curing time is preferably 20~40 min, more preferably 25~35 min, and even more preferably 30 min.

[0129] A middle reinforcing layer coating is sprayed onto the surface of the semi-cured heat-insulating base layer; partial miscibility is achieved by utilizing the slight dissolving effect of the solvent in the middle reinforcing layer coating on the base layer surface; the solid content of the polyamic acid solution is preferably 10%~20%; the solvent in the polyamic acid solution is preferably one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), etc., more preferably N-methylpyrrolidone (NMP); the type of the second solvent is the same as the solvent in the polyamic acid solution, specifically N-methylpyrrolidone; the mass ratio of the polyamic acid solution to the second solvent is preferably (40~50):(30~40); optionally, the mass ratio of the polyamic acid solution to the second solvent is 40:30:40:35:40:40, 45:30, 45:35:45:40, 50:30, 50:35:50:40 or any two of the above ratios;

[0130] After spraying the intermediate reinforcing layer coating, heat treatment is performed to form the intermediate reinforcing layer; the preferred temperature for the heat treatment is 120℃~140℃; the preferred time for the heat treatment is 1~2 h; the heat treatment can partially imidize the polyamic acid and form an inter-transfer network with the underlying layer.

[0131] In a specific embodiment of the present invention, the solid content of the organosilicon resin is preferably 40%~70%, more preferably 50%~60%, and even more preferably 50%~55%; the mass ratio of the third solvent to the organosilicon resin is preferably (35~50):(50~65); optionally, the mass ratio of the third solvent to the organosilicon resin is 35:50, 35:55, 35:60, 35:65, 40:50, 40:55, 40:60, 40:65, 45:50, 45:55, 45:60, 45:65, 50:50, 50:55, 50:60, 50:65, or any two of the above ratios.

[0132] After spraying a high-temperature resistant and erosion-resistant topcoat, the coating is cured by step-heating to form a high-temperature resistant and erosion-resistant topcoat. Step-heating curing ensures complete curing of each resin layer while simultaneously inducing complete imidization of the intermediate polyimide layer. The step-heating curing includes a first-stage curing, a second-stage curing, and a third-stage curing. The preferred temperature for the first-stage curing is 140℃~160℃; the preferred curing time for the first-stage curing is 1~2 hours. The preferred temperature for the second-stage curing is 180℃~220℃; the preferred curing time for the second-stage curing is 2~4 hours. The preferred temperature for the third-stage curing is 240℃~260℃; the preferred curing time for the third-stage curing is 1~2 hours.

[0133] The present invention also provides an aircraft comprising the aforementioned gradient functional coating.

[0134] In this invention, the aircraft can be an airplane (hypersonic vehicle); the gradient functional coating can be applied to the outer layers of an aircraft (including hypersonic vehicles), such as the skin, engine nacelle, and wing leading edge.

[0135] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a gradient functional coating containing hollow glass microspheres, its preparation method, and its application.

[0136] The epoxy-modified silicone resin used in the examples was sourced from Hubei Longsheng Sihai New Materials Co., Ltd. (SH-023-7); the hollow glass microspheres were sourced from Shenglait Hollow Microsphere New Materials Co., Ltd. (HL25); ammonium polyphosphate and polycyanuric acid cyanate were purchased from Puyang Chengke Chemical Technology Co., Ltd. (CK-APP103, CK-MCA); the APP / MCA compound flame retardant had a mass ratio of 3:1, and short-cut basalt fibers (diameter 10 μm, length approximately 300 μm) were used.

[0137] Silica aerogel (Aibiaihe New Materials Co., Ltd., KSL6 PD-SH);

[0138] Fumed silica (Hubei Huifu Nanomaterials Co., Ltd., HL-200);

[0139] Polyamic acid solution (Changzhou Guangda Electronic Materials Co., Ltd., solid content 15%)

[0140] Aminated carbon nanotubes were obtained from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd. (101178, purity greater than 95%, diameter 1~2 nm).

[0141] High silica glass fiber (6 μm in diameter, approximately 150 μm in length).

[0142] Alumina silicate ceramic fiber (8 μm in diameter, approximately 180 μm in length).

[0143] Methylphenyl silicone resin was purchased from Hubei Longsheng Sihai New Materials Co., Ltd. (SH-9607).

[0144] Methacryloxypropyl POSS was purchased from Xi'an Qiyue Biotechnology Co., Ltd. (molecular weight 1418, purity 99%).

[0145] The polycarbonate was purchased from Cangzhou Dahua Co., Ltd. (CH8200).

[0146] Silicon carbide micro powder (Zhengzhou Haixu Abrasives Co., Ltd., W3, W14); the mass ratio of W3 to W14 is 2:1;

[0147] Fused corundum powder (Zhengzhou Haixu Abrasives Co., Ltd., HXTA09);

[0148] Flake mica powder (Guangdong Yufeng Powder Materials Co., Ltd., Model 1500);

[0149] The defoamer is BYK-066N from BYK Chemicals (Germany), and the dispersant is BYK-306 from BYK Chemicals (Germany).

[0150] Modified hollow glass microspheres: Hollow glass microspheres were added to a silane coupling agent solution at a mass ratio of 1:10, stirred thoroughly, and dried at 80℃ for 4 hours. The coupling agent was KH-550 with a mass fraction of 2%, and the solvent was ethanol. Subsequently, aluminum dihydrogen phosphate solution was added at a mass ratio of 1:8. The aluminum dihydrogen phosphate solvent was deionized water with a mass fraction of 15%. The mixture was slowly stirred at room temperature for 30 minutes, dried in a forced-air dryer at 120℃ for 3 hours, and then heated to 250℃ for 1 hour to obtain modified hollow glass microspheres.

[0151] Modified silicon carbide: Silicon carbide micro powder was added to a 2% KH560-ethanol solution and stirred until homogeneous. The mass ratio of silicon carbide to coupling agent solution was 1:10. The mixture was dried at 80℃ for 6 hours to obtain modified silicon carbide micro powder.

[0152] Modified fused alumina powder: Add fused alumina powder to a 3% KH560-ethanol solution, stir and mix evenly, the mass ratio of fused alumina powder to coupling agent solution is 1:8, dry at 80℃ for 6h to obtain modified fused alumina powder.

[0153] Modified chopped basalt fiber: Chopped basalt fiber was added to a 2% KH550-ethanol solution and stirred until homogeneous. The mass ratio of chopped basalt fiber to coupling agent solvent was 1:8. The mixture was dried at 120℃ for 3 hours. Then, grinding balls with a diameter of 3 mm were added at a ratio of 1:3 and the mixture was ball-milled at 50 rpm for 10 minutes to obtain modified chopped basalt fiber.

[0154] Modified high-silica glass fiber: The high-silica glass fiber was heat-treated at 300℃ for 2 hours, and then added to a 3% KH550-ethanol solution at a mass ratio of 1:9 and stirred until homogeneous. The mixture was then dried at 120℃ for 3 hours to obtain the modified high-silica glass fiber.

[0155] Modified aluminosilicate ceramic fiber: The aluminosilicate ceramic fiber was immersed in a 5% (w / w) dilute hydrochloric acid solution and stirred at room temperature for 1 hour. Then, it was added to a 1% (w / w) KH550-ethanol solution at a mass ratio of 1:10 and stirred at 80°C for 2 hours. The fiber was then placed in an air jet mill and treated at 200 rpm for 5 minutes for mild depolymerization. Finally, it was dried at 100°C for 3 hours to obtain the modified aluminosilicate ceramic fiber.

[0156] Example 1

[0157] Preparation of the heat-insulating bottom layer slurry: Weigh 60 parts of epoxy-modified silicone resin, add 40 parts of mixed solvent (butyl acetate: xylene = 1:1), and under high-speed dispersion, add 1 part of KH-560, 30 parts of silica aerogel powder, 15 parts of modified hollow glass microspheres, 5 parts of APP / MCA compound flame retardant, 10 parts of modified short-cut basalt fiber, and 1 part of fumed silica. After uniform dispersion, degas under vacuum.

[0158] Preparation of intermediate reinforcing layer slurry: Weigh 40 parts of polyamic acid solution, add 30 parts of N-methylpyrrolidone, then add 20 parts of modified high silica glass fiber, 10 parts of modified aluminosilicate ceramic fiber, and 5 parts of aminated carbon nanotubes in sequence, and ultrasonically disperse for 2 hours before use.

[0159] Preparation of high-temperature resistant and erosion-resistant surface layer slurry: Weigh 50 parts of methylphenyl silicone resin, add 35 parts of xylene, and under high-speed dispersion, add 15 parts of methacryloxyPOSS, 8 parts of polycarbonate, 5 parts of modified high-silica glass fiber, 5 parts of modified silicon carbide micro powder, 10 parts of modified fused alumina powder, 5 parts of flake mica powder, 1 part of defoamer, and 2 parts of dispersant. Stir evenly and then defoam.

[0160] Coating Application and Curing: The aluminum alloy sheet underwent surface treatment. First, a base coat was sprayed to a dry film thickness of approximately 120 μm and baked at 90℃ for 30 min. Then, an intermediate coat was sprayed to a dry film thickness of approximately 60 μm and baked at 130℃ for 1 h. Finally, a top coat was sprayed to a dry film thickness of approximately 180 μm, with a programmed temperature rise: 150℃ / 1h + 200℃ / 2h + 250℃ / 1h. After natural cooling, a gradient functional coating with a total thickness of approximately 360 μm was obtained.

[0161] Example 2

[0162] Preparation of the thermal insulation underlayer slurry: Weigh 70 parts of epoxy-modified silicone resin, add 40 parts of mixed solvent (butyl acetate: xylene = 1:1), and sequentially add 1.5 parts of KH-560, 40 parts of silica aerogel powder, 20 parts of modified hollow glass microspheres, 8 parts of APP / MCA compound flame retardant, 15 parts of modified short-cut basalt fiber, and 1.5 parts of fumed silica under high-speed dispersion. After uniform dispersion, degas under vacuum.

[0163] Preparation of intermediate reinforcing layer slurry: Weigh 45 parts of polyamic acid solution, add 35 parts of N-methylpyrrolidone, then add 25 parts of modified high silica glass fiber, 15 parts of modified aluminosilicate ceramic fiber, and 8 parts of aminated carbon nanotubes in sequence, and ultrasonically disperse for 2 hours before use.

[0164] Preparation of high-temperature resistant and erosion-resistant surface layer slurry: Weigh 55 parts of methylphenyl silicone resin, add 40 parts of xylene, add 3 parts of BYK-163, and under high-speed dispersion, add 20 parts of methacryloxyPOSS, 10 parts of polycarbonate, 8 parts of modified high-silica glass fiber, 10 parts of modified silicon carbide micro powder, 15 parts of modified fused alumina powder, 8 parts of flake mica powder, and 1.5 parts of defoamer. After uniform dispersion, defoaming is performed.

[0165] A gradient functional coating was obtained by applying and curing the coating as described in Example 1.

[0166] Example 3

[0167] Preparation of the thermal insulation underlayer slurry: Weigh 75 parts of epoxy-modified silicone resin, add 50 parts of mixed solvent (butyl acetate: xylene = 1:1), and sequentially add 2 parts of KH-560, 50 parts of silica aerogel powder, 25 parts of modified hollow glass microspheres, 10 parts of APP / MCA compound flame retardant, 20 parts of modified short-cut basalt fiber, and 2 parts of fumed silica under high-speed dispersion. After uniform dispersion, degas under vacuum.

[0168] Preparation of intermediate reinforcing layer slurry: Weigh 50 parts of polyamic acid solution, add 40 parts of N-methylpyrrolidone, then add 30 parts of modified high-silica glass fiber, 15 parts of modified aluminosilicate ceramic fiber, and 10 parts of aminated carbon nanotubes in sequence, and then ultrasonically disperse for 2 hours for later use.

[0169] Preparation of high-temperature resistant and erosion-resistant surface slurry: Weigh 60 parts of methylphenyl silicone resin, add 50 parts of xylene, add 4 parts of BYK-163, and under high-speed dispersion, add 25 parts of methacryloxyPOSS, 12 parts of polycarbonate, 10 parts of modified high-silica glass fiber, 15 parts of modified silicon carbide micro powder, 20 parts of modified fused alumina powder, 10 parts of flake mica powder, and 2 parts of defoamer. After uniform dispersion, defoaming is performed.

[0170] A gradient functional coating was obtained by applying and curing the coating as described in Example 1.

[0171] Comparative Example 1

[0172] Preparation of the heat-insulating underlayer slurry: Weigh 70 parts of epoxy-modified silicone resin, add 40 parts of mixed solvent (butyl acetate: xylene = 1:1), and sequentially add 1.5 parts of KH-560, 60 parts of silica aerogel powder, 8 parts of APP / MCA compound flame retardant, 15 parts of modified short-cut basalt fiber, and 1.5 parts of fumed silica under high-speed dispersion. After uniform dispersion, degas under vacuum.

[0173] Preparation of intermediate reinforcement layer slurry: Same as in Example 2.

[0174] Preparation of high-temperature resistant and erosion-resistant surface slurry: Same as in Example 2.

[0175] A gradient functional coating was obtained by applying and curing the coating as described in Example 1.

[0176] Comparative Example 2

[0177] Preparation of the heat insulation base layer slurry: Same as in Example 2.

[0178] Preparation of intermediate reinforcement layer slurry: Weigh 53 parts of polyamic acid solution, add 40 parts of N-methylpyrrolidone, then add 25 parts of modified high silica glass fiber and 15 parts of modified aluminosilicate ceramic fiber in sequence, and ultrasonically disperse for 2 hours before use.

[0179] Preparation of high-temperature resistant and erosion-resistant surface slurry: Same as in Example 2.

[0180] A gradient functional coating was obtained by applying and curing the coating as described in Example 1.

[0181] Comparative Example 3

[0182] Preparation of the heat insulation base layer slurry: Same as in Example 2.

[0183] Preparation of intermediate reinforcement layer slurry: Same as in Example 2.

[0184] Preparation of high-temperature resistant and erosion-resistant surface slurry: Weigh 85 parts of methylphenyl silicone resin, add 50 parts of xylene, add 3 parts of BYK-163, then add 8 parts of modified high-silica glass fiber, 10 parts of modified silicon carbide micro powder, 15 parts of modified fused alumina powder, 8 parts of flake mica powder, and 1.5 parts of defoamer in sequence. After uniform dispersion, defoam.

[0185] A gradient functional coating was obtained by applying and curing the coating as described in Example 1.

[0186] The gradient functional coatings obtained in Examples 1-3 and Comparative Examples 1-3 were placed at room temperature and atmospheric pressure for 24 h, and relevant performance tests were conducted. The results are shown in Table 1.

[0187] Table 1 Performance Test Results

[0188]

[0189] As shown in Table 1:

[0190] Comparative Example 1: Inner layer modified hollow glass microspheres omitted. The results showed that the thermal conductivity of the coating increased significantly, the density increased, and the thermal shock resistance decreased, proving that the synergistic effect of hollow glass microspheres as lightweight porous aggregate and aerogel powder is indispensable.

[0191] Comparative Example 2: Aminated carbon nanotubes in the intermediate layer were omitted. The results showed that the interlayer adhesion decreased from 5B to 3B, and the tensile strength decreased by more than 30%, proving that the nano-bridging effect of carbon nanotubes is the key to ensuring the integrity of the coating.

[0192] Comparative Example 3: The surface layer POSS and polycarbonate were omitted. The results showed that the linear ablation rate increased from 0.15 mm / s to over 0.30 mm / s, and a dense ceramic layer could not be formed at high temperatures, proving that the synergistic ceramicization mechanism of POSS and polycarbonate is the core of achieving ultra-high temperature protection.

[0193] The above results show that the gradient functional coating provided by the present invention is significantly superior to traditional single-layer or double-layer coatings in all key performance aspects, and is particularly suitable for applications in extreme environments such as aircraft outer layers.

[0194] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A gradient functional coating containing hollow glass microspheres, characterized in that, It includes a heat-insulating base layer, an intermediate reinforcing layer, and a high-temperature resistant and erosion-resistant surface layer arranged in sequence; The heat insulation substrate comprises cured epoxy-modified silicone resin, silica aerogel powder, modified hollow glass microspheres, nitrogen-based flame retardant, reinforcing fiber, and a first process aid; the mass ratio of the cured epoxy-modified silicone resin, silica aerogel powder, modified hollow glass microspheres, nitrogen-based flame retardant, reinforcing fiber, and process aid is (30~38):(30~50):(15~25):(5~10):(10~20):(2~5); the modified hollow glass microspheres comprise hollow glass microspheres and a cured aluminum dihydrogen phosphate product coated on the surface of the hollow glass microspheres; The intermediate reinforcing layer comprises polyimide, silane coupling agent modified glass fiber, coupling agent modified ceramic fiber, and functional nanofiller; the mass ratio of the polyimide, silane coupling agent modified glass fiber, coupling agent modified ceramic fiber, and functional nanofiller is (4~10):(20~30):(10~15):(5~10). The high-temperature resistant and erosion-resistant surface layer comprises cured silicone resin, cage-type polysilsesquioxane, polycarbonate, reinforcing filler, and a second process aid; the mass ratio of the cured silicone resin, cage-type polysilsesquioxane, polycarbonate, reinforcing filler, and second process aid is (25~33):(15~25):(8~12):(25~55):(2~6); the reinforcing filler comprises powdered filler, fiber filler, and sheet filler; the mass ratio of the powdered filler, fiber filler, and sheet filler is (15~35):(5~10):(5~10).

2. The gradient functional coating according to claim 1, characterized in that, The epoxy value of the epoxy-modified silicone resin is 0.02~0.2; The polyimide is formed by imidization of polyamic acid; the weight-average molecular weight of the polyamic acid is 50,000~300,000 g / mol. The organosilicon resin is selected from one or more of methyl silicone resin, methylphenyl silicone resin, vinyl silicone resin, hydroxyl silicone resin, and alkoxy silicone resin.

3. The gradient functional coating according to claim 1, characterized in that, The particle size of the silica aerogel powder is 10~20 μm; The true density of the modified hollow glass microspheres is 0.2~0.4 g / cm³. 3 ; The modified hollow glass microspheres have a D90 particle size of 70~110 μm and a compressive strength of 500~4000 psi. The nitrogen-based flame retardant comprises ammonium polyphosphate and melamine cyanurate; the mass ratio of ammonium polyphosphate to melamine cyanurate is (2~5):(1~1.5). The diameter of the reinforcing fiber is 9~13 μm; the length of the reinforcing fiber is 300~500 μm; The modified hollow glass microspheres were prepared according to the following method: A1) Hollow glass microspheres were modified with a first silane coupling agent to obtain silane-modified microspheres; A2) Silane-modified microspheres were impregnated in aluminum dihydrogen phosphate solution, and then dried and heat-treated to obtain modified hollow glass microspheres.

4. The gradient functional coating according to claim 3, characterized in that, The solid content of the aluminum dihydrogen phosphate solution is 10%~20%; The mass ratio of the silane-modified microspheres to the aluminum dihydrogen phosphate solution is 1:(1~5). The impregnation time is 10-60 min; the drying temperature is 100℃-120℃; the drying time is 2-3 h; the heat treatment temperature is 200℃-300℃; the heat treatment time is 0.5-2 h; The reinforcing fiber is selected from silane coupling agent modified basalt fiber.

5. The gradient functional coating according to claim 1, characterized in that, The diameter of the silane coupling agent modified glass fiber is 5~10 μm; the length of the silane coupling agent modified glass fiber is 100~500 μm. The diameter of the coupling agent modified ceramic fiber is 5~10 μm; the length of the coupling agent modified ceramic fiber is 100~500 μm. The functional nanofiller is selected from one or more of the following: carbon nanotubes, carboxylated carbon nanotubes, hydroxylated carbon nanotubes, aminated carbon nanotubes, carbon nanofibers, carboxylated carbon nanofibers, hydroxylated carbon nanofibers, aminated carbon nanofibers, silicon carbide whiskers, silicon nitride whiskers, epoxy-functionalized carbon nanotubes, silane coupling agent-grafted carbon nanotubes, surface-modified nano-silica, surface-modified nano-alumina, aminated graphene, and epoxy-functionalized graphene.

6. The gradient functional coating according to claim 1, characterized in that, The number average molecular weight of the polycarbonate is 2000~3500; The particle size of the powdered filler is 1~20 μm; The diameter of the fiber filler is 10~15 μm; the length of the fiber filler is 150~300 μm; The sheet-like filler has a sheet diameter of 5~20 μm.

7. The gradient functional coating according to claim 6, characterized in that, The powdered filler includes silane coupling agent modified metal oxide powder, first silane coupling agent modified silicon carbide and second silane coupling agent modified silicon carbide. The particle size of the silane coupling agent modified metal oxide powder is 5~15 μm; The particle size of the first silane coupling agent modified silicon carbide is 1~3 μm; The particle size of the second silane coupling agent modified silicon carbide is 10~20 μm; The total mass ratio of the first silane coupling agent modified silicon carbide and the second silane coupling agent modified silicon carbide to the mass ratio of the silane coupling agent modified metal oxide powder is (5~15):(10~20). The mass ratio of the first silane coupling agent modified silicon carbide to the second silane coupling agent modified silicon carbide is 1:(1~3).

8. The gradient functional coating according to claim 1, characterized in that, The thickness ratio of the heat insulation bottom layer, the intermediate reinforcement layer and the high temperature erosion resistant surface layer is (3~4):(2~3):(5~6).

9. The method for preparing the gradient functional coating containing hollow glass microspheres according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1) Spray the heat-insulating base coat, heat and pre-cur it to form a semi-cured heat-insulating base coat; the heat-insulating base coat includes epoxy modified silicone resin, silica aerogel powder, modified hollow glass microspheres, nitrogen flame retardant, reinforcing fiber, first process aid and first solvent. S2) Spray an intermediate reinforcement layer coating onto the surface of the semi-cured heat insulation substrate and heat-treat it to form an intermediate reinforcement layer; the intermediate reinforcement layer coating includes a polyamic acid solution, silane coupling agent modified glass fiber, coupling agent modified ceramic fiber, functional nanofiller and a second solvent. S3) A high-temperature resistant and erosion-resistant surface coating is sprayed onto the surface of the intermediate reinforcing layer and cured by step heating to form a high-temperature resistant and erosion-resistant surface layer; the high-temperature resistant and erosion-resistant surface coating includes organosilicon resin, cage-type polysilsesquioxane, polycarbonate, reinforcing filler, second process aid and third solvent.

10. An aircraft, characterized in that, This includes the gradient functional coating containing hollow glass microspheres as described in any one of claims 1 to 8, or the gradient functional coating containing hollow glass microspheres prepared by the preparation method described in claim 9.

Images