Polyimide composite thermal insulation slurry and preparation method thereof

Abstract

The invention relates to the technical field of polyimide slurry preparation, in particular to polyimide composite heat insulation slurry and a preparation method thereof. The problems that a traditional heat insulation material is high in haze and poor in heat aging resistance are solved. The slurry comprises modified hollow mesoporous silicon oxide, a passivated infrared blocking agent and an alicyclic polyimide matrix, precise matching with the refractive index of a matrix is achieved through microsphere surface phenyl modification, and interface scattering is eliminated. An organic-inorganic structure is formed by using surface amino groups to participate in in-situ polymerization, so that microsphere agglomeration and floating are prevented; and in cooperation with dense silicon resin passivation on the surfaces of the nanoparticles, excellent heat insulation performance and extremely high optical transmittance are achieved at the same time on the premise that fluorine is not contained completely, and the fluorine-free heat-insulating film is suitable for high-end display panels such as organic light-emitting diodes and micro light-emitting diodes.

Description

Technical Field

[0001] This invention relates to the field of polyimide slurry preparation technology, specifically to a polyimide composite thermal insulation slurry and its preparation method. Background Technology

[0002] With the rapid development of new display technologies such as organic light-emitting diodes (OLEDs) and micro-LEDs, display panels are evolving towards higher brightness and higher resolution. However, high brightness is often accompanied by high heat generation. If the heat accumulated inside the display module cannot be effectively blocked or managed, it will not only accelerate the aging of organic light-emitting materials, leading to color shift and brightness decay, but also affect the sensitivity of the touch layer. Therefore, introducing heat-insulating materials between the layers of the display panel has become an industry consensus.

[0003] Current thermal insulation materials face significant technological bottlenecks. Firstly, there's a conflict between optical and thermal insulation properties. Traditional materials like porous aerogels and ceramic microspheres, while exhibiting low thermal conductivity, suffer from severe Rayleigh and Mie scattering due to their wide pore size distribution and refractive index mismatch with the matrix. This results in extremely high haze, failing to meet the stringent requirements of display screens for light transmittance and clarity. Secondly, there are environmental compliance issues. To achieve low dielectric strength and low water absorption in highly transparent polyimide matrices, or to reduce the surface energy of thermal insulation fillers for better dispersion, existing technologies heavily utilize fluorinated monomers or surfactants. However, with increasingly stringent global regulations on "permanent chemicals" such as perfluoroalkyl and polyfluoroalkyl groups, developing fluorine-free, environmentally friendly composite materials that combine high light transmittance and high thermal insulation performance has become an urgent need in the display industry.

[0004] Therefore, there is an urgent need to develop a new type of polyimide composite thermal insulation slurry that can achieve both excellent thermal insulation performance and extremely high optical transmittance through precise control of the microstructure without introducing fluorine. Summary of the Invention

[0005] The purpose of this invention is to provide a polyimide composite thermal insulation slurry and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution: Unless otherwise specified, all parts in this invention are parts by weight.

[0007] This invention provides a method for preparing a polyimide composite thermal insulation slurry, the method being as follows: In a reaction vessel equipped with a mechanical stirrer and nitrogen protection, 200 parts of solvent N,N-dimethylacetamide, 3-10 parts of modified hollow mesoporous silica, and 0.1-1 parts of passivating infrared blocking agent are added, and the mixture is sheared and stirred at 2000-3000 rpm for 30 min; 25 parts of diamine monomer are added, and after dissolution, alicyclic dianhydride is added in three batches at 10°C in a mass ratio of 5:4:1. Monomer (16.5 parts in total), with a solid content controlled at 20%, was first reacted at 10℃ for 4 hours, then heated to 25℃ and stirred at 400 rpm for 8-20 hours. During this process, the amino groups on the surface of the hollow mesoporous silica participated in the polymerization and were incorporated into the polyamic acid backbone, resulting in a composite resin liquid with a viscosity of 3000-5000 cps. 0.1 parts of leveling agent BYK-333 were added to the composite resin liquid, stirred evenly, and vacuum degassed for 30 minutes to obtain a polyimide composite thermal insulation slurry. Modified hollow mesoporous silica is prepared by grafting a phenyl silane coupling agent and an amino silane coupling agent onto the surface of hollow mesoporous silica. The passivating infrared blocking agent is prepared from nano-cesium tungsten bronze, tetraethoxysilane and vinyltrimethoxysilane.

[0008] Preferred method for preparing modified hollow mesoporous silica is as follows: 10 parts of hollow mesoporous silica are dispersed in 50 parts of toluene and ultrasonically dispersed for 30 min. 2.5-4 parts of phenyltrimethoxysilane (to increase the refractive index to match the polyimide) and 1 part of 3-aminopropyltriethoxysilane (to provide reaction sites) are added. The mixture is refluxed at 60-90℃ for 12 h. After centrifugation and washing with ethanol three times, the mixture is vacuum dried to obtain modified hollow mesoporous silica with phenyl and amino groups on its surface.

[0009] The preferred method for preparing hollow mesoporous silica is as follows: 100 parts of deionized water, 30 parts of anhydrous ethanol, and 2 parts of cationic surfactant cetyltrimethylammonium bromide are mixed, and 6 parts of polystyrene microspheres (purchased from Suzhou Nanomicro Technology Co., Ltd., product code LBWNC-007) are added while stirring at 300 rpm; the temperature is raised to 40℃, and 5 parts of tetraethyl orthosilicate are added dropwise and reacted for 4 hours. The product is centrifuged and calcined at 550℃ for 3 hours to remove the template, thereby obtaining hollow mesoporous silica with a particle size of 80-100 nm.

[0010] The preferred method for preparing the passivating infrared blocking agent is as follows: 0.5 parts of nano-cesium tungsten bronze (Cs) are added... 0.33WO3 (particle size <50nm) was dispersed in 20 parts of isopropanol, deionized water (molar ratio of water to total silane was 3:1) was added, along with 0.1 parts of tetraethoxysilane and 0.1-0.15 parts of vinyltrimethoxysilane. The pH was adjusted to 3.5 with acetic acid, and the mixture was reacted at 60℃ for 6 hours to form a dense, transparent silicone resin coating layer on the surface of the nanoparticles. The solvent was removed by rotary evaporation to obtain a passivated infrared blocking agent.

[0011] Preferably, the alicyclic dianhydride monomer is one of 1,2,3,4-cyclobutanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, or cyclohexanetetracarboxylic dianhydride.

[0012] Preferably, the diamine monomer is bis(3-aminophenyl)phenylphosphine oxide, which is prepared according to the method in the literature "Synthesis and Characterization of Bis(3-aminophenyl)phenylphosphine oxide" (DOI: 10.3969 / j.issn.0258-3283.2010.05.024).

[0013] Another aspect of the present invention provides a polyimide composite thermal insulation slurry, wherein the raw materials for preparing the polyimide composite thermal insulation slurry include hollow mesoporous silica, a passivating infrared blocking agent, a diamine monomer, an alicyclic dianhydride monomer, and a leveling agent; the polyimide composite thermal insulation slurry is prepared by any of the above preparation methods.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention solves the problem of increased optical haze caused by porous heat-insulating fillers, achieving a balance between heat insulation and high light transmittance. By grafting a phenyl-containing silane coupling agent onto the surface of non-fluorinated hollow mesoporous silica, the refractive index of the inorganic filler is effectively controlled, making it highly compatible with the refractive index of the polyimide matrix. This modification significantly suppresses Rayleigh and Mie scattering of light at the inorganic-organic interface. Compared with traditional physically blended hollow microsphere systems, the composite film prepared by the slurry of this invention retains the low thermal conductivity characteristics brought about by the hollow structure while significantly reducing the haze of the material, ensuring extremely high visible light transmittance and meeting the stringent requirements of display panels for high definition.

[0015] 2. Existing technologies often utilize fluorinated monomers to suppress the formation of charge-transfer complexes within polyimide molecules to achieve transparency, but this does not comply with increasingly stringent environmental regulations. This invention overcomes the dependence of high-transmittance polyimides on fluorinated monomers, achieving environmental compliance while maintaining high transparency by ensuring the entire formulation is free of perfluoroalkyl and polyfluoroalkyl substances. By employing a synergistic system of alicyclic dianhydrides and phosphine-containing diamines: the alicyclic structure fundamentally suppresses yellowing caused by charge-transfer complexes by disrupting the coplanarity of the molecular chains; the phosphine-containing groups impart excellent heat resistance to the matrix. This solution successfully balances optical transparency and environmental friendliness without introducing any perfluoro or polyfluoroalkyl substances, meeting green manufacturing standards.

[0016] 3. The organic-inorganic network constructed in this invention solves the problem of nanofiller agglomeration. Through in-situ polymerization, the amino groups on the filler surface react chemically with acid anhydrides during the polymerization stage, locking the hollow microspheres in the polyimide molecular chain network in a covalent bond form. This chemically bonded structure not only effectively prevents agglomeration, floating, or stratification of the slurry due to differences in filler specific gravity during standing and coating curing, ensuring the uniformity of the thermal insulation layer, but also enhances the interfacial bonding force between the inorganic and organic phases, avoiding microcracks caused by interfacial peeling after film formation.

[0017] 4. This invention achieves full-band thermal management and improves spectral stability during high-temperature processes. By introducing nano-cesium tungsten bronze, passivated and coated with fluorine-free silicone resin, a synergistic effect is formed with the hollow microspheres, simultaneously cutting off the heat conduction path and blocking thermal radiation energy. The silicone resin shell effectively isolates the cesium tungsten bronze lattice from the corrosion of oxygen and moisture during high-temperature imidization, preventing the attenuation of near-infrared blocking ability and color deterioration caused by the oxidation failure of nanoparticles. This allows the composite film prepared from the slurry to maintain stable spectral selectivity and efficient heat insulation capability even after high-temperature processes and long-term use, effectively reducing the surface temperature of the display module. Attached Figure Description

[0018] Figure 1 The figures show the test results of thermal insulation performance of Examples 1-4 and Comparative Examples 1 and 3-7 of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1This invention provides a polyimide composite thermal insulation slurry and its preparation method, the technical solution of which is as follows: Example 1 100 parts of deionized water, 30 parts of anhydrous ethanol, and 2 parts of cationic surfactant cetyltrimethylammonium bromide were mixed, and 6 parts of polystyrene microspheres were added under stirring at 300 rpm. The mixture was heated to 40 °C, and 5 parts of tetraethyl orthosilicate were added dropwise for 4 h. The product was centrifuged, calcined at 550 °C for 3 h to remove the template, and hollow mesoporous silica was obtained. 10 parts of hollow mesoporous silica were dispersed in 50 parts of toluene and ultrasonically dispersed for 30 min. 2.5 parts of phenyltrimethoxysilane and 1 part of 3-aminopropyltriethoxysilane were added, and the mixture was refluxed at 60 °C for 12 h. After centrifugation and washing with ethanol three times, the mixture was vacuum dried to obtain modified hollow mesoporous silica with phenyl and amino groups on the surface.

[0021] 0.5 parts of nano-cesium tungsten bronze were dispersed in 20 parts of isopropanol, deionized water (molar ratio of water to total silane was 3:1) was added, along with 0.1 parts of tetraethoxysilane and 0.1 parts of vinyltrimethoxysilane. The pH was adjusted to 3.5 with acetic acid, and the mixture was reacted at 60°C for 6 hours. The solvent was removed by rotary evaporation to obtain the passivated infrared blocking agent.

[0022] In a reactor equipped with a mechanical stirrer and nitrogen protection, 200 parts of solvent N,N-dimethylacetamide, 3 parts of modified hollow mesoporous silica, and 0.1 parts of passivating infrared blocking agent were added, and the mixture was sheared and stirred at 2000 rpm for 30 min. Then, 25 parts of the diamine monomer bis(3-aminophenyl)phenylphosphine oxide were added and dissolved. At 10°C, 8.25 parts of the alicyclic dianhydride monomer cyclopentanetetracarboxylic acid dianhydride were added first, and the stirring speed was increased to 700 rpm for 60 min. Next, 6.6 parts of the alicyclic dianhydride monomer were added, and the mixture was stirred... The reaction was accelerated to 450 rpm for 60 min. Finally, the remaining 1.65 parts of alicyclic dianhydride monomer were dissolved in N,N-dimethylacetamide to prepare a 20% concentration solution. This solution was added dropwise, with the solid content controlled at 20%. The reaction was first carried out at 10℃ for 4 h, and then the temperature was raised to 25℃ and stirred at 400 rpm for 8 h to obtain a composite resin liquid with a viscosity of 3000 cps. 0.1 parts of leveling agent BYK-333 were added to the composite resin liquid, stirred evenly, and vacuum degassed for 30 min to obtain a polyimide composite thermal insulation slurry.

[0023] Example 2 Referring to the preparation method and parameters of Example 1, the differences are as follows: when preparing modified hollow mesoporous silica, the amount of phenyltrimethoxysilane is 3 parts, and the reflux reaction temperature is 70°C; when preparing the passivating infrared blocking agent, the amount of vinyltrimethoxysilane is 0.12 parts; when preparing the polyimide composite heat insulation slurry, the amount of modified hollow mesoporous silica is 5 parts, the amount of passivating infrared blocking agent is 0.4 parts, the mixture is sheared and stirred at 2300 rpm for 30 min, the alicyclic dianhydride monomer is cyclohexanetetracarboxylic acid dianhydride, the temperature is raised to 25°C, and the reaction is stirred at 400 rpm for 12 h, resulting in a composite resin liquid viscosity of 3500 cps.

[0024] Example 3 Referring to the preparation method and parameters of Example 1, the differences are as follows: when preparing modified hollow mesoporous silica, the amount of phenyltrimethoxysilane is 3.5 parts, and the reflux reaction temperature is 80°C; when preparing the passivating infrared blocking agent, the amount of vinyltrimethoxysilane is 0.13 parts; when preparing the polyimide composite heat insulation slurry, the amount of modified hollow mesoporous silica is 7 parts, the amount of passivating infrared blocking agent is 0.6 parts, the mixture is sheared and stirred at 2600 rpm for 30 min, the alicyclic dianhydride monomer is 1,2,3,4-cyclobutanetetracarboxylic dianhydride, the temperature is raised to 25°C, and the reaction is stirred at 400 rpm for 15 h, resulting in a composite resin solution viscosity of 4000 cps.

[0025] Example 4 Referring to the preparation method and parameters of Example 1, the differences are as follows: when preparing modified hollow mesoporous silica, the amount of phenyltrimethoxysilane is 4 parts, and the reflux reaction temperature is 90°C; when preparing the passivating infrared blocking agent, the amount of vinyltrimethoxysilane is 0.15 parts; when preparing the polyimide composite heat insulation slurry, the amount of modified hollow mesoporous silica is 10 parts, the amount of passivating infrared blocking agent is 1 part, the mixture is sheared and stirred at 3000 rpm for 30 min, the alicyclic dianhydride monomer is 1,2,3,4-cyclobutanetetracarboxylic dianhydride, the temperature is raised to 25°C, and the reaction is stirred at 400 rpm for 20 h, with a composite resin solution viscosity of 5000 cps.

[0026] Comparative Example 1 The preparation method and parameters of Example 1 are the same, except that the hollow mesoporous silica is replaced with solid silica microspheres. That is, in the first step of silica preparation, polystyrene microspheres are not added as pore-forming templates, while the subsequent modification steps remain unchanged.

[0027] Comparative Example 2 The preparation method and parameters of Example 1 are the same, except that phenyltrimethoxysilane was not added when preparing the modified hollow mesoporous silica.

[0028] Comparative Example 3 The preparation method and parameters of Example 1 are the same, except that 3-aminopropyltriethoxysilane was not added when preparing the modified hollow mesoporous silica.

[0029] Comparative Example 4 The preparation method and parameters of Example 1 are the same, except that the order of feeding is changed from in-situ polymerization to physical blending. That is, the modified hollow mesoporous silica is not added first, and the polymerization reaction of diamine and dianhydride is carried out directly to obtain pure polyimide resin liquid. After the reaction is completed, 3 parts of modified hollow mesoporous silica are added to the resin liquid and physically mixed and stirred.

[0030] Comparative Example 5 The preparation method and parameters are the same as in Example 1, except that modified hollow mesoporous silica is not added to the polyimide composite thermal insulation slurry.

[0031] Comparative Example 6 The preparation method and parameters of Example 1 are the same, except that unpassivated nano-cesium tungsten bronze is used. Specifically, 0.1 parts of pure nano-cesium tungsten bronze powder that has not been coated with tetraethoxysilane / vinylsilane is directly added during slurry preparation.

[0032] Comparative Example 7 The preparation method and parameters are the same as in Example 1, except that no passivating infrared blocking agent is added to the polyimide composite heat insulation slurry.

[0033] Comparative Example 8 The preparation method and parameters are the same as in Example 1, except that the alicyclic dianhydride is replaced with the aromatic dianhydride pyromellitic dianhydride.

[0034] Comparative Example 9 The preparation method and parameters of Example 1 were used, except that after dissolving the diamine, all 16.5 parts of the alicyclic dianhydride monomer were added at once.

[0035] Experiment Example 1: Thermal Insulation Performance Test The slurries prepared in the examples and comparative examples were coated onto glass substrates and subjected to gradient curing: first, the substrates were treated at 80°C and -0.05 MPa for 30 min to remove the solvent; then, they were treated at 150°C for 30 min to release the molecular chain stress; finally, the temperature was increased to 280°C at a rate of 2°C / min and kept at the temperature for 60 min to complete imidization; after natural cooling, the polyimide composite heat insulation film was peeled off and its performance was tested.

[0036] Thermal conductivity: Tested using a steady-state heat flow thermal conductivity meter according to ASTM D5470 standard; Infrared blocking rate: The transmittance T of the membrane material at a wavelength of 1000 nm was measured using a UV-Vis-NIR spectrophotometer. 1000And calculate the infrared blocking rate; Infrared blocking rate = 100% - T 1000 ; The results are shown in Table 1 and Figure 1 As shown.

[0037] Table 1 Thermal insulation performance tests of Examples 1-4 and Comparative Examples 1 and 3-7 From Table 1 and Figure 1 As can be seen from Examples 1-4, this application first utilizes the nanoscale air pocket structure sealed inside the modified hollow mesoporous silica to effectively reduce the mean free path of phonons and enhance the phonon scattering effect, thus significantly cutting off the heat conduction path from a physical perspective. Secondly, by introducing nano-cesium tungsten bronze protected by core-shell passivation technology, the material is endowed with excellent spectral selectivity, which can efficiently absorb and block near-infrared thermal radiation. This synergistic effect of "internal resistance to conduction and external radiation blocking" can effectively prevent the accumulation and diffusion of heat inside the display module, reduce the surface temperature of the device, and the thermal conductivity of the prepared slurry after curing into a film is 0.060-0.085 W / (m·K), and the infrared blocking rate is 90.5%-93.7%.

[0038] In Comparative Example 1, replacing the hollow mesoporous silica with solid silica microspheres resulted in a significant increase in thermal conductivity due to the much higher thermal conductivity of solid silica compared to air, leading to a substantial decrease in insulation performance. This demonstrated the crucial role of the hollow structure in reducing heat conduction. In Comparative Example 3, the absence of 3-aminopropyltriethoxysilane during the preparation of the modified hollow mesoporous silica resulted in the loss of anchoring points, filler agglomeration, and the formation of thermal bridges, further reducing insulation performance. In Comparative Example 4, changing the feeding sequence from in-situ polymerization to physical blending resulted in uneven macroscopic dispersion of the filler and unstable insulation performance. In Comparative Example 5, the polyimide composite insulation slurry, lacking modified hollow mesoporous silica, exhibited a thermal conductivity close to that of pure polyimide resin, thus losing its ability to block heat conduction. In Comparative Example 6, the use of unpassivated nano-cesium tungsten bronze led to easy oxidation of the unprotected cesium tungsten bronze during the high-temperature imidization curing process of polyimide, ultimately resulting in a decrease in the near-infrared blocking rate of the final membrane and severe color changes. In Comparative Example 7, no passivating infrared blocking agent was added to the polyimide composite thermal insulation slurry. At this time, only hollow microspheres blocked heat conduction. Although the thermal conductivity was low, it lacked the ability to block heat radiation, resulting in poor overall thermal insulation effect, which demonstrated the necessity of material synergy.

[0039] Experiment Example 2: Optical Performance Testing Visible light transmittance and haze: According to ASTM D1003 standard, a haze meter was used to test and record the transmittance data at a wavelength of 550nm; the results are shown in Table 2.

[0040] Table 2 Optical performance tests of Examples 1-4 and Comparative Examples 2-4, 6, and 8-9 As shown in Table 2, in Examples 1-4, this application eliminates Rayleigh scattering at the inorganic-organic phase interface by grafting phenylsilanes onto the surface of the inorganic filler and controlling its refractive index to achieve a high degree of matching with the polyimide matrix. Furthermore, by employing a unique in-situ polymerization process and a low-temperature gradient feeding strategy, the microspheres are uniformly dispersed in the polymer network through chemical bonding, solving the optical haze and defects caused by nanoagglomeration. In addition, the use of alicyclic dianhydrides disrupts the coplanarity of the molecular chains and inhibits charge transfer complexes. The formation of the film avoids yellowing of the matrix under the premise of being completely free of perfluoroalkyl and polyfluoroalkyl substances. After the prepared slurry is cured into a film, the visible light transmittance is 91.2%-92.6%, the haze is 0.60%-0.85%, and the film material is colorless and transparent. In Examples 1-3, the haze is reduced due to the optimization of the phenylsilane grafting density and the improvement of the dispersion process. However, in Example 4, the filler content reaches 10 parts, and the distance between the microspheres becomes very close, which inevitably leads to microscopic secondary aggregation, causing the haze to start to rise again.

[0041] In Comparative Example 2, phenyltrimethoxysilane was not added during the preparation of modified hollow mesoporous silica. The refractive index of the hollow microspheres was lower than that of the polyimide matrix, resulting in strong interfacial scattering, a sharp increase in haze, and a decrease in transmittance. This demonstrates the crucial role of phenyl modification in adjusting the refractive index for optical performance. In Comparative Example 3, 3-aminopropyltriethoxysilane was not added during the preparation of modified hollow mesoporous silica. The microspheres lacked reactive sites on their surface and could not participate in subsequent polymerization. During coating and curing, the microspheres easily agglomerated or floated, leading to a decrease in transmittance. In Comparative Example 4, the feeding sequence was changed from in-situ polymerization to physical blending. The filler failed to be chemically bonded to the molecular chain, resulting only in physical doping. The slurry exhibited poor storage stability, was prone to sedimentation, and suffered from severe micro-agglomeration, leading to high haze after film formation. This demonstrates the necessity of the in-situ polymerization process. In Comparative Example 6, unpassivated nano-cesium tungsten bronze was used. High-temperature curing caused oxidation of the nano-cesium tungsten bronze, resulting in a grayish appearance. In Comparative Example 8, alicyclic dianhydrides were replaced with aromatic dianhydrides, specifically pyromellitic dianhydrides. Because aromatic structures readily form charge-transfer complexes, the membrane material exhibited a deep yellow or brown color in the absence of fluorine, resulting in a significant reduction in light transmittance. This demonstrates the irreplaceable nature of alicyclic monomers in fluorine-free high-transmittance systems. In Comparative Example 9, after dissolving the diamine, all 16.5 parts of the alicyclic dianhydride monomer were added at once. Due to the presence of amino groups on the filler surface, the initially excessively high anhydride concentration easily triggered localized polymerization or gelation, or resulted in an excessively wide molecular weight distribution. Ultimately, insoluble microgel particles appeared in the slurry, leading to a significant increase in the optical haze of the membrane material and a deterioration in surface smoothness.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polyimide composite thermal insulation slurry, characterized in that: The preparation method is as follows: N,N-dimethylacetamide is added to a reaction vessel, followed by the addition of modified hollow mesoporous silica and passivating infrared blocking agent, and the mixture is sheared and stirred; after the diamine monomer is dissolved, alicyclic dianhydride monomer is added in three batches and stirred to react, thereby obtaining a composite resin liquid; a leveling agent is added to the composite resin liquid and stirred evenly, followed by vacuum degassing to obtain the polyimide composite heat insulation slurry; The modified hollow mesoporous silica is prepared by grafting a phenyl silane coupling agent and an amino silane coupling agent onto the surface of hollow mesoporous silica. The passivating infrared blocking agent is prepared from nano-cesium tungsten bronze, tetraethoxysilane and vinyltrimethoxysilane.

2. The method for preparing a polyimide composite thermal insulation slurry according to claim 1, characterized in that: The modified hollow mesoporous silica is prepared as follows: the hollow mesoporous silica is dispersed in toluene, ultrasonically dispersed, phenyltrimethoxysilane and 3-aminopropyltriethoxysilane are added, refluxed, centrifuged, washed with ethanol, and vacuum dried to obtain the modified hollow mesoporous silica.

3. The method for preparing a polyimide composite thermal insulation slurry according to claim 2, characterized in that: The hollow mesoporous silica is prepared as follows: deionized water, anhydrous ethanol and cationic surfactant are mixed, and polystyrene microspheres are added under stirring; after heating, tetraethyl orthosilicate is added dropwise to react, the product is separated by centrifugation, and the template is removed by calcination to obtain the hollow mesoporous silica.

4. The method for preparing a polyimide composite thermal insulation slurry according to claim 1, characterized in that: The passivated infrared blocking agent is prepared as follows: the nano-cesium tungsten bronze is dispersed in isopropanol, deionized water is added, tetraethoxysilane and vinyltrimethoxysilane are added, the pH value is adjusted with acetic acid, and the solvent is removed by rotary evaporation after the reaction is completed to obtain the passivated infrared blocking agent.

5. The method for preparing a polyimide composite thermal insulation slurry according to claim 1, characterized in that: The alicyclic dianhydride monomer is one of 1,2,3,4-cyclobutanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, or cyclohexanetetracarboxylic dianhydride.

6. The method for preparing a polyimide composite thermal insulation slurry according to claim 1, characterized in that: The diamine monomer is bis(3-aminophenyl)phenylphosphine oxide.

7. A polyimide composite thermal insulation mortar, characterized in that: The raw materials for preparing the polyimide composite thermal insulation slurry include hollow mesoporous silica, passivating infrared blocking agent, diamine monomer, alicyclic dianhydride monomer and leveling agent; the polyimide composite thermal insulation slurry is prepared by the preparation method according to any one of claims 1-6.

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