A transparent coating with high hardness and toughness and its preparation method and application

Abstract

This invention relates to a tough and transparent coating capable of withstanding extreme environments, its preparation method, and its applications, belonging to the field of functional material preparation technology. The coating primarily consists of trapezoidal polysilsesquioxanes forming a continuous, dense inorganic network structure. By controlling the hydrolysis and condensation reactions of polysilazanes and aminosilanes in a solution system, a continuous network with trapezoidal polysilsesquioxanes as the main connecting units is constructed in situ, effectively suppressing disordered cross-linking during the hydrolysis-condensation process. This preparation method features mild process conditions and simple operation, suitable for large-area preparation of micron- or submicron-sized transparent coatings using solution methods. The resulting coating maintains high optical transparency while also possessing high surface hardness, good flexibility, and stable adhesion properties. It also maintains stable performance under extreme environmental conditions such as high and low temperature cycling, irradiation, and atomic oxygen, making it suitable for applications in aerospace components, flexible displays, or optical devices.

Description

Technical Field

[0001] This invention belongs to the field of functional material preparation technology, and in particular relates to a tough and transparent coating that can withstand extreme environments, its preparation method and application. Background Technology

[0002] With the development of flexible displays and foldable aerospace components, the application of polymer films and polymer composites is increasing. However, the inherent structural characteristics of polymers make them highly susceptible to performance degradation when faced with extreme environments such as physical wear, high and low temperatures, and radiation. Applying protective coatings to polymer materials is the simplest and most efficient way to solve this problem, but these special application scenarios place extremely high demands on coating performance: while maintaining transparency, the coating must possess both high hardness to resist physical damage and good toughness to maintain structural integrity and optical performance under bending, stretching, and other deformation conditions. In addition, in the aerospace service environment, flexible devices must also withstand extreme environments such as high and low temperature cycling, strong radiation, and atomic oxygen, placing even higher demands on the environmental tolerance and long-term stability of the coating. However, properties such as hardness, toughness, and environmental stability are often mutually restrictive in conventional material systems, making it extremely challenging to achieve all these functions simultaneously in a single coating.

[0003] To further improve the structural stability and service reliability of transparent coatings in extreme environments, researchers have attempted to construct continuous networks dominated by inorganic structures, such as bio-inspired "brick-and-mortar" inorganic structures and perhydropolysilazane (PHPS)-derived silica coatings. However, while "brick-and-mortar" inorganic structures offer advantages in crack deflection, they lack macroscopic flexibility. PHPS-derived silica, although exhibiting high hardness and tolerance to extreme environments, suffers from insufficient toughness due to its rigid framework suppressing network flexibility. Overall, achieving continuous inorganic networks that combine high hardness, good toughness, and ultra-thin processability remains a significant technical challenge in materials science.

[0004] Ladder-shaped polysilsesquioxanes (LPSQs), due to their double-chain silicon-oxygen framework, exhibit a certain balance between structural rigidity and local flexibility, and are considered to have the potential to construct inorganic continuous networks. However, ladder-shaped PPSQs are mainly prepared via the sol-gel method, which requires the hydrolysis and condensation of silane monomers in solution. The reaction conditions are highly sensitive; slight changes in pH, solvent type, water content, temperature, and time can easily lead to the formation of cage-like or three-dimensionally cross-linked insoluble substances, making it difficult to obtain a regular and ordered ladder-shaped structure. Furthermore, the entire process is time-consuming, typically requiring preparation, separation, and purification before coating. During preparation, disordered cross-linking or rapid aggregation easily occurs, forming insoluble or difficult-to-film structures, making it difficult to obtain dense, uniform, and processable transparent coatings. Therefore, how to achieve the controllable construction of continuous networks using ladder-shaped PPSQs remains a key technical problem to be solved for their application in coating construction. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a tough and transparent coating that can withstand extreme environments, as well as its preparation method and application, which solves at least one of the problems in the prior art, such as the difficulty in achieving "hardness-toughness-transparency-resistance to extreme environments-ultra-thinness" in polymer material protective coatings and the long time consumption of the entire process.

[0006] On the one hand, the present invention provides a tough and transparent coating that is resistant to extreme environments. The coating is formed by in-situ hydrolysis-condensation reaction of polysilazane and aminosilane. The in-situ hydrolysis-condensation reaction forms an inorganic network structure mainly composed of ladder-shaped polysilsesquioxane.

[0007] Furthermore, the coating thickness is 100 nanometers to 5 micrometers.

[0008] Further, the aminosilane is selected from one or more of (3-aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, di(3-trimethoxysilylpropyl)amine, N-[3-(trimethoxysilyl)propyl]n-butylamine, and aminoethylaminopropyltrimethoxysilane.

[0009] On the other hand, the present invention provides a method for preparing the transparent coating, comprising the following steps: 1) Mix the polysilazane precursor solution with the aminosilane solution to obtain a mixture; 2) Take the mixture prepared in step 1) and coat it onto a substrate at room temperature to form a thin film; 3) The film prepared in step 2) is cured to obtain the transparent coating. Further, in step 1), the molar ratio of polysilazane in the polysilazane precursor solution and aminosilane in the aminosilane solution in the mixture is 5:1-1:20.

[0010] Further, in step 1), the polysilazane precursor solution is obtained by dissolving polysilazane in solvent A; the mass fraction of polysilazane in the polysilazane precursor solution is 1%-99%.

[0011] Further, in step 1), the aminosilane solution is obtained by dissolving aminosilane in solvent B, and the mass fraction of aminosilane in the aminosilane solution is 1%-99%.

[0012] Further, in step 1), the mixing method is oscillation mixing; the oscillation time is 1h~3h, and the temperature is 18~28℃.

[0013] Further, in step 3), the curing is moisture curing, the temperature of the moisture curing is 50~100℃, the relative humidity is 20%~98%, and the moisture curing time is 1~6h.

[0014] Thirdly, the present invention provides an application of the transparent coating described above or the transparent coating prepared by the preparation method in the fields of aerospace components, flexible displays, or optical devices.

[0015] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. The formation of the ladder-shaped polysilsesquioxane-dominated inorganic continuous network in the transparent coating of this invention is achieved through in-situ controlled hydrolysis-condensation. In-situ formation avoids structural damage or agglomeration during separation and purification, ensuring a dense and uniform coating. Polysilazane and aminosiloxane, as two precursors, act as co-reactants, jointly constructing the ladder-shaped framework. This invention utilizes the synergistic transformation of these two precursors during film formation, rather than a pre-reaction in solution. Using polysilazane and aminosiloxane as precursors, their synergistic effect regulates the hydrolysis-condensation process of aminosilane. The core microstructural feature of the coating of this invention is the ladder-shaped polysilsesquioxane-dominated inorganic continuous network. The inorganic network structure is controllable, and the ladder-shaped polysilsesquioxane constitutes a high proportion. This invention is formed through the in-situ hydrolysis-condensation reaction of polysilazane and aminosilane. The microstructure of the coating of this invention, a ladder-shaped polysilsesquioxane-dominated inorganic network, is the structural basis for simultaneously achieving high hardness, good toughness, and tolerance to extreme environments, as well as ultra-thinness.

[0016] 2. The coating thickness of this invention is 100 nanometers to 5 micrometers. The coating can be prepared into an ultra-thin, continuous, transparent coating to meet the needs of thickness-sensitive applications such as flexible displays and optical devices. Figure 1 SEM images show that the coating is dense and defect-free with uniform thickness, indicating that the structure remains intact within this thickness range.

[0017] 3. This invention provides a key co-reactant—aminosilane—which functions as both a catalyst and a T-unit provider. The aminosilane catalyzes the hydrolysis of polysilazane while simultaneously participating in the construction of a ladder-like double-chain framework as a trifunctional siloxane, forming a synergistic effect with the polysilazane. This is crucial for the controllable construction of the ladder-like network. The aminosilane solution is added in solution form to ensure the uniformity and coatability of the mixture.

[0018] 4. This invention provides another key component – ​​polysilazane, which provides active groups such as Si–H and Si–NH–Si, and synergistically transforms with aminosilane under amino catalysis. The polysilazane precursor solution is made by adding polysilazane in solution form; the mass fraction of polysilazane in the polysilazane precursor solution is 1%-99%, and this concentration range ensures suitable coating viscosity, avoiding excessive concentration leading to gelation or excessively low concentration leading to an excessively thin coating.

[0019] 5. In the coating preparation method of this invention, polysilazane and aminosiloxane are simply mixed without prior hydrolysis and directly coated onto the substrate for curing. During the film formation process after coating, the two raw materials utilize the synergistic hydrolysis and condensation characteristics of their functional groups to transform in situ into a ladder-shaped polysilsesquioxane structure. The amino group in the aminosilane catalyzes the hydrolysis and condensation of the polysilazane, while the amino group itself, as a trifunctional siloxane, participates in the construction of the ladder-shaped double-chain framework. The synergistic transformation of the two achieves in-situ film formation, thereby controlling the in-situ construction of a continuous and dense inorganic network structure dominated by ladder-shaped polysilsesquioxane. This realizes the process of "simple blending followed by direct coating and in-situ formation of a ladder-shaped double-chain structure", which has a short process time.

[0020] 6. The molar ratio of the polysilazane precursor solution and the aminosilane solution in the mixture of the present invention is 5:1-1:20, which can achieve (1) ensuring the controllable construction of the trapezoidal polysilsesquioxane network; (2) the aminosilane and polysilazane form a uniform mixed system in the solution through synergistic hydrolysis-condensation reaction, ensuring the integrity of the film formation and the uniformity of the surface during the coating process, and improving the film-forming properties and density of the coating; (3) within this ratio range, the Si–O–Si network is fully cross-linked, with low thermal weight loss rate, and maintains stable performance in extreme environments such as thermal cycling, irradiation, and atomic oxygen, enhancing the coating's tolerance to extreme environments and environmental tolerance. Moreover, the mixing method and parameters of the present invention ensure that the two components are uniformly mixed at the molecular level, avoiding local concentration unevenness; and limit the key parameter window for moisture curing, which is the process guarantee for the orderly construction of the trapezoidal network.

[0021] 7. The present invention adopts a solution method for preparation, which is simple and controllable and suitable for large-area continuous preparation. The transparent coating prepared by the method of the present invention forms a stable interface bond with the substrate. While maintaining high transparency, it also has high surface hardness, good flexibility and reliable substrate adhesion performance. It can still maintain stable performance under harsh environmental conditions such as high and low temperature cycling, strong radiation and atomic oxygen, and has good engineering application prospects. Attached Figure Description

[0022] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0023] Figure 1 Scanning electron microscope images of the surface and cross-sectional morphology of the transparent coating prepared in Example 5.

[0024] Figure 2 Optical photographs of the transparent coatings prepared in Example 2 and Comparative Example 1.

[0025] Figure 3 Infrared spectra of the transparent coatings prepared in Examples 2-4 and Comparative Examples 1-3.

[0026] Figure 4 Load-displacement curves obtained by nanoindentation testing of the transparent coatings prepared in Examples 1-4.

[0027] Figure 5 Thermogravimetric analysis curves of the transparent coatings prepared in Examples 1-3 and Comparative Examples 1-2 are shown.

[0028] Figure 6 The results of the cross-cut adhesion test on the CPI substrate for the transparent coating prepared in Example 5 are shown.

[0029] Figure 7 The optical transmittance curve of the transparent coating prepared in Example 5.

[0030] Figure 8 This is a schematic diagram of the bending performance of the transparent coating in Example 5.

[0031] Figure 9 The results show the wear resistance test results of the transparent coatings prepared in Example 5 and Comparative Example 4.

[0032] Figure 10 The transmittance curves of the transparent coating prepared in Example 5 after being treated with high and low temperature cycling, ionizing radiation and vacuum ultraviolet irradiation.

[0033] Figure 11 This is a schematic diagram of the internal molecular structure of the polysilsesquioxane transparent coating dominated by the trapezoidal structure of the present invention. Detailed Implementation

[0034] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0035] Ladder-shaped polysilsesquioxanes (LPSQs), due to their double-chain silicon-oxygen framework, exhibit a certain balance between structural rigidity and local flexibility, and are considered to have the potential to construct inorganic continuous networks. However, ladder-shaped PPSQs are mainly prepared via the sol-gel method, which requires the hydrolysis and condensation of silane monomers in solution. The reaction conditions are highly sensitive; slight changes in pH, solvent type, water content, temperature, and time can easily lead to the formation of cage-like or three-dimensionally cross-linked insoluble substances, making it difficult to obtain a regular, ordered linear ladder-shaped structure. Furthermore, the entire process is time-consuming, typically requiring preparation, separation, and purification before coating. During preparation, disordered cross-linking or rapid aggregation easily occurs, forming insoluble or difficult-to-film structures, making it difficult to obtain dense, uniform, and processable transparent coatings. Therefore, how to achieve the controllable construction of continuous networks using ladder-shaped PPSQs remains a key technical problem to be solved for their application in coating construction.

[0036] Therefore, on the one hand, the present invention provides a tough and transparent coating that is resistant to extreme environments. The coating is formed by in-situ hydrolysis-condensation reaction of polysilazane and aminosilane. The in-situ hydrolysis-condensation reaction forms an inorganic network structure mainly composed of ladder-shaped polysilsesquioxane.

[0037] Furthermore, the coating thickness is 100 nanometers to 5 micrometers.

[0038] The coating can be prepared into an ultra-thin, continuous, transparent coating to meet the needs of thickness-sensitive applications such as flexible displays and optical devices. Figure 1 SEM images show that the coating is dense and defect-free with uniform thickness, indicating that the structure remains intact within this thickness range.

[0039] Furthermore, the polysilsesquioxane network is formed in situ through a controlled hydrolysis and condensation process.

[0040] Furthermore, the controlled hydrolysis and condensation process is carried out with the participation of an aminosilane. The aminosilane is selected from one or more of (3-aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, bis(3-trimethoxysilylpropyl)amine, N-[3-(trimethoxysilyl)propyl]n-butylamine, and aminoethylaminopropyltrimethoxysilane.

[0041] Specifically, aminosilanes have the dual functions of catalyst (accelerating the reaction rate) and co-reactant (providing the T-units required for the ladder structure). The amino group in aminosilanes catalyzes the hydrolysis and condensation of polysilazanes, while it itself, as a trifunctional siloxane, participates in the construction of the ladder double-chain framework. The polysilazane and aminosiloxane work together to achieve in-situ film formation, which is fundamentally different from the existing technology that uses them only as catalysts or coupling agents.

[0042] Furthermore, the controlled hydrolysis and condensation process is carried out with the participation of a polysilazane having the formula (I).

[0043]

[0044] (I) In formula (I), R1, R2, R3 and R4 may be the same or different and are independently selected from one of hydrogen, methyl, ethyl, vinyl, phenyl and amino; x and y are selected from integers from 1 to 3000, and the number average molecular weight of the polysilazane is 150 to 440000.

[0045] Preferably, when R1 and R3 are methyl, R2 is vinyl, and R4 is hydrogen, formula (I) is polysilazane (OPZ).

[0046] On the other hand, the present invention provides a method for preparing a tough and transparent coating that can withstand extreme environments, comprising the following steps: 1) Mix the polysilazane precursor solution with the aminosilane solution to obtain a mixture; 2) Take the mixture prepared in step 1) and coat it onto a substrate at room temperature to form a thin film; 3) The film prepared in step 2) is cured to obtain the transparent coating.

[0047] Further, in step 1), the molar ratio of polysilazane in the polysilazane precursor solution and aminosilane in the aminosilane solution in the mixture is 5:1-1:20.

[0048] Specifically, the molar ratio of polysilazane in the polysilazane precursor solution and aminosilane in the aminosilane solution in the mixture is 5:1-1:20, which can achieve (1) ensuring the controllable construction of the ladder-shaped polysilsesquioxane network; (2) aminosilane and polysilazane form a uniform mixed system in the solution through synergistic hydrolysis-condensation reaction, ensuring complete film formation and surface uniformity during the coating process, and improving the film-forming properties and density of the coating; (3) within this ratio range, the Si–O–Si network is fully cross-linked and has a low thermal weight loss rate (e.g., Figure 5As shown in the figure, it maintains stable performance in extreme environments such as thermal cycling, irradiation, and atomic oxygen, enhancing the coating's tolerance to extreme environments and environmental resilience. If the molar ratio of polysilazane in the polysilazane precursor solution and aminosilane in the aminosilane solution in the mixed solution is too large, it cannot effectively catalyze the hydrolysis and condensation reaction of polysilazane, resulting in insufficient cross-linking of the inorganic network, a loose coating structure, and difficulty in forming a continuous and dense ladder structure. If the molar ratio of polysilazane in the polysilazane precursor solution and aminosilane in the aminosilane solution in the mixed solution is too large, the reaction rate is too fast, which can easily lead to disordered cross-linking, destroying the regularity of the ladder structure, and even causing poor film-forming properties and defects in the coating. Therefore, the molar ratio of the polysilazane precursor solution and the aminosilane solution in the mixture is 5:1 to 1:20, and exemplary ratios are 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, and 1:20.

[0049] Further, in step 1), the polysilazane precursor solution is obtained by dissolving polysilazane in solvent A; the mass fraction of polysilazane in the polysilazane precursor solution is 1%-99%, for example 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 99%.

[0050] The polysilazane precursor solution is prepared by adding polysilazane in solution form. The mass fraction of polysilazane in the polysilazane precursor solution is 5%-90%. This concentration range ensures suitable coating viscosity and avoids excessive concentration leading to gelation or excessively low concentration leading to an excessively thin coating. Furthermore, the polysilazane can be linear, cyclic, or a hybrid chain-ring structure. The above formula only lists its structural units and does not represent that the polysilazane is a linear structure.

[0051] Further, the solvent A of the polysilazane precursor solution is selected from one or more of hydrocarbon solvents, ether solvents, ketone solvents, benzene derivative solvents, and ester solvents; the hydrocarbon solvent is selected from one or more of n-hexane, n-octane, n-decane, chloroform, dichloromethane, dichloroethylene, petroleum ether, and mineral oil; the ether solvent is selected from one or more of diethyl ether, ethylene glycol dimethyl ether, dibutyl ether, and n-butyl ether; the ketone solvent is selected from one or more of acetone, butanone, methyl ethyl ketone, cyclohexanone, and isophorone; the benzene derivative solvent is selected from one or more of toluene, o-xylene, m-xylene, p-xylene, and chlorobenzene; and the ester solvent is selected from one or more of ethyl acetate, butyl butyrate, amyl acetate, and octyl acetate.

[0052] Further, in step 1), the aminosilane solution is obtained by dissolving aminosilane in solvent B, and the mass fraction of aminosilane in the aminosilane solution is 1%-99%, for example 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 99%.

[0053] Specifically, the aminosilane solution is added in solution form by aminosilane to ensure the uniformity and coatability of the mixture.

[0054] Further, in step 1), the aminosilane is selected from one or more of (3-aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, di(3-trimethoxysilylpropyl)amine, N-[3-(trimethoxysilyl)propyl]n-butylamine, and aminoethylaminopropyltrimethoxysilane.

[0055] Furthermore, the solvent B of the aminosilane solution is selected from one or more of hydrocarbon solvents, ether solvents, ketone solvents, benzene derivative solvents, and ester solvents; the hydrocarbon solvent is selected from one or more of n-hexane, n-octane, n-decane, chloroform, dichloromethane, dichloroethylene, petroleum ether, and mineral oil; the ether solvent is selected from one or more of diethyl ether, ethylene glycol dimethyl ether, and dibutyl ether; the ketone solvent is selected from one or more of acetone, butanone, methyl ethyl ketone, cyclohexanone, and isophorone; the benzene derivative solvent is selected from one or more of toluene, o-xylene, m-xylene, p-xylene, and chlorobenzene; and the ester solvent is selected from one or more of ethyl acetate, butyl butyrate, amyl acetate, and octyl acetate.

[0056] It should be noted that the polysilazane of the present invention is a commercially available product or prepared by existing methods.

[0057] Further, in step 1), the mixing method is oscillation mixing; the oscillation time is 1h~3h, and the temperature is 18~28℃.

[0058] Specifically, step 1) can achieve (1) uniform mixing at the molecular level, avoiding local concentration inconsistencies; oscillation mixing can promote uniform dispersion of the two components at the molecular scale under mild conditions; (2) simple mixing conditions; the temperature of 18~28℃ (preferably 20~25℃) is the room temperature condition, and the mixing conditions are simple and mild; the time of 1~3 h (preferably 2 h) provides sufficient time for uniform dispersion; (3) appropriate time and temperature combination ensures that the precursor mixture is uniformly mixed before coating, ensuring good leveling and complete film formation during coating. If static mixing is used, mass transfer may be limited, local concentration gradients may be large, reactions may be uneven, micro-phase separation may be easily formed, and the density and transparency of the coating may decrease. If the oscillation time is too short or the temperature is too low, the mixing may be insufficient, the subsequent hydrolysis-condensation process may be incomplete, the coating hardness and modulus may decrease, and the tolerance to extreme environments may deteriorate; if the oscillation time is too long or the temperature is too high, gelation may occur, and a uniform film may not be formed. Therefore, the oscillation time is 1h to 3h, for example, the oscillation time is 1h, 1.5h, 2h, 2.5h, 3h; the temperature is 18 to 28℃, for example, the temperature is 18℃, 19℃, 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃.

[0059] Further, in step 2), the mixture prepared in step 1) is transferred and coated onto the substrate at room temperature to form a film. Room temperature coating avoids premature curing. The hydrolysis-condensation reaction rate of polysilazane and aminosilane in the mixture is low at room temperature, and the coating process still maintains low viscosity and good flowability.

[0060] Specifically, two precursors, polysilazane and aminosiloxane, are used as co-reactants to jointly construct a trapezoidal framework. The synergistic transformation of the two during the film formation process is utilized to prepare in-situ films of trapezoidal polysilsesquioxane, rather than pre-reaction film formation in solution.

[0061] Further, in step 2), the coating method is any one of spin coating, spray coating, dip coating, curtain coating or scraping coating.

[0062] Multiple coating methods are available, including common solution coating technologies such as spin coating, spray coating, dip coating, curtain coating, and blade coating. These methods can be flexibly selected according to the shape, area, and production requirements of the substrate, which provides process feasibility for the industrial-scale preparation of coatings.

[0063] Furthermore, in step 2), the substrate can be any one of quartz sheet, glass sheet, polished silicon wafer, aluminum, stainless steel, polyethylene terephthalate (PET), polyimide (PI), or colorless polyimide (CPI). The coating forms a strong interface with different substrates through chemical bonding (such as Si–O–Metal), hydrogen bonding, or van der Waals forces, avoiding engineering problems such as decreased adhesion and coating peeling caused by changes in substrate type, and improving the reliability of the coating under actual service conditions.

[0064] Further, in step 3), the curing is moisture curing, the temperature of the moisture curing is 50~100℃, the relative humidity is 20%~98%, and the moisture curing time is 1~6h.

[0065] Specifically, moisture curing is most conducive to the orderly construction of ladder-like networks. Water molecules act as a mild initiator, promoting the gradual hydrolysis of alkoxy groups in aminosilanes to generate silanol groups (Si–OH). Simultaneously, Si–NH–Si and Si–H groups in polysilazanes are slowly converted to Si–OH under humid conditions. Adjacent Si–OH groups condense to form Si–O–Si bonds, ultimately forming an inorganic network dominated by a ladder-like structure. Heat curing is used when rapid curing is required or the substrate can withstand high temperatures (such as glass, silicon wafers, and metals). Vacuum UV curing is used in applications sensitive to moisture or requiring extremely rapid curing. Moisture curing is preferred because it simulates the "slow condensation" process of siloxanes in nature, which is beneficial for forming regular double-chain ladder-like structures rather than cage-like or three-dimensional cross-linked bodies.

[0066] Moisture curing is preferred because it can utilize environmental moisture to gradually complete the transformation.

[0067] Specifically, the moisture curing temperature is 50~100℃. Gentle heating promotes the hydrolysis-condensation reaction without causing thermal deformation of the flexible substrate (PET, PI, CPI). Simultaneously, it avoids the direct pyrolysis of polysilazane to SiCN / SiON at high temperatures, preserving the trapezoidal structure. If the moisture curing temperature is too high, it may cause thermal shrinkage or deformation of the flexible substrate (PET, PI, CPI); polysilazane may prematurely pyrolyze, generating non-oxide phases such as Si–C and Si–N, destroying the trapezoidal structure, making the coating brittle, yellowing, and reducing transparency. If the moisture curing temperature is too low, the reaction kinetics may be too slow, resulting in incomplete curing. The coating will retain a large number of Si–H and N–H bonds (obvious infrared peaks), have low hardness (<2H), poor solvent resistance, and be easily damaged by moisture. Therefore, the moisture curing temperature is 50~100℃, preferably 80℃, with exemplary values ​​of 50℃, 60℃, 70℃, 80℃, 90℃, and 100℃.

[0068] A relative humidity of 20%–98% provides sufficient moisture as reactants and catalysts, but excessive humidity (>98%) should be avoided as it can cause condensation to damage the coating surface. At a relative humidity of 90%, moisture diffuses uniformly into the coating in molecular form, promoting the hydrolysis of Si–NH–Si + H2O → Si–OH + NH3 and alkoxy groups, resulting in a stable condensation rate and a dense, non-porous coating. Figure 1 The relative humidity should be 90%, and it should not cause surface whitening or excessive hydrolysis due to excessive moisture. If the relative humidity is too low, there will be insufficient moisture, the hydrolysis reaction will be hindered, and the conversion rate of polysilazane will be low. A large amount of Si-H and N-H will still exist in the coating, the inorganic network will be discontinuous, the hardness will be low, the adhesion will be poor, and it may even be impossible to form a film. If the relative humidity is too high, liquid water will easily condense on the coating surface, leading to uncontrolled hydrolysis-condensation, local formation of silanol gel, or surface whitening and peeling. Excessive hydrolysis may dissolve oligomers, forming pinholes or cracks. Therefore, the relative humidity should be 20%~98%, for example, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 98%.

[0069] The moisture curing time is 1-6 hours, which is sufficient to allow the hydrolysis-condensation reaction to proceed to completion, forming a highly cross-linked inorganic network; at the same time, it avoids excessive curing time, which increases the production cycle. If the moisture curing time is too short, the cross-linking density is insufficient, and the Si-O-Si network transformation is incomplete. The coating is hard and can withstand extreme environmental conditions (high thermal weight loss rate); if the moisture curing time is too long, excessive cross-linking leads to the accumulation of internal stress, increasing the brittleness of the coating, and microcracks or peeling may occur on flexible substrates; at the same time, production efficiency decreases and energy consumption increases. Therefore, the moisture curing time is 1-6 hours, preferably 2 hours, with 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours as examples.

[0070] Furthermore, the coating prepared by the method of the present invention simultaneously exhibits high surface hardness, good elastic deformation capacity, and good adhesion.

[0071] Furthermore, the coating maintains stable performance under thermal cycling, ionizing radiation, vacuum ultraviolet irradiation, or atomic oxygen environment.

[0072] This invention provides a transparent coating that is resistant to extreme environments and possesses both hardness and toughness, as well as its preparation method. The key lies in the use of polysilazane and aminosiloxane as co-reactants to jointly construct a trapezoidal framework; furthermore, this invention utilizes the synergistic transformation of the two during film formation, rather than a pre-reaction in solution. Using polysilazane and aminosiloxane as precursors, the synergistic effect of the two is utilized to regulate the hydrolysis-condensation process of aminosilane. This invention directly mixes the two raw materials, polysilazane and aminosiloxane, without pre-hydrolysis, and directly coats them onto a substrate for curing. During the film formation process after coating, both utilize the synergistic hydrolysis and condensation properties of their own functional groups to transform in situ into a ladder-shaped polysilsesquioxane structure. The amino group in the aminosilane catalyzes the hydrolysis and condensation of the polysilazane. At the same time, as a trifunctional siloxane, it participates in the construction of the ladder-shaped double-chain framework. The synergistic transformation of the two achieves in situ film formation, thereby controlling the in situ construction of a continuous and dense inorganic network structure dominated by ladder-shaped polysilsesquioxane. This realizes the process of "direct coating after simple blending and in situ formation of ladder-shaped double-chain structure". The process time is short, and a transparent coating with high hardness, good toughness and excellent environmental resistance is finally prepared.

[0073] Thirdly, the present invention also provides the use of the transparent coating prepared by the above method in the fields of aerospace components, flexible displays, or optical devices.

[0074] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0075] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0076] The polysilazane (OPZ) structure in the following examples is as follows:

[0077] Formula (I) Formula (I); where x is approximately 1 and y is approximately 4. The preparation method of polysilazane of Formula (I) is as follows: Under an inert atmosphere, methylvinyl dichlorosilane and methyl dichlorohydrosilane in a molar ratio of 0.5:1 are dissolved in anhydrous toluene to obtain a mixture. The mixed solution is cooled to 5°C, and dry ammonia gas is slowly introduced at this temperature to carry out an ammonolysis reaction until the pH of the system reaches 9, at which point the ammonia introduction is stopped. After the reaction is complete, the byproduct ammonium chloride (NH4Cl) is removed by filtration. Finally, the collected filtrate is concentrated under reduced pressure to remove the solvent, thereby obtaining the target product polysilazane (OPZ) with a number average molecular weight of 553.

[0078] Example 1 In step 1), 0.42 g of bis(3-trimethoxysilylpropyl)amine solution with a concentration of 72 wt% and n-butyl ether as the solvent was taken and added to 5 g of polysilazane (OPZ) precursor solution with a concentration of 36 wt% and n-butyl ether as the solvent. The resulting mixed solution was shaken at room temperature for 2.5 h. Step 2): Take the mixture prepared in Step 1) and coat it into a thin film on a substrate at room temperature; the substrate is a glass sheet.

[0079] Step 3): The film prepared in step 2) is cured at 80℃ / 80%RH for 2 hours to obtain the transparent coating.

[0080] Example 2 Step 1): Take 4g of bis(3-trimethoxysilylpropyl)amine solution with a concentration of 48wt%, wherein the solvent is n-butyl ether; add it to 4g of polysilazane (OPZ) precursor solution with an OPZ concentration of 48wt%, wherein the solvent is dichloromethane. Shake the resulting mixed solution at room temperature for 3 h. Step 2): Take the mixture prepared in Step 1) and coat it into a thin film on a substrate at room temperature; the substrate is a polished silicon wafer.

[0081] Step 3): The film prepared in Step 2) is cured at 76℃ / 88%RH for 4 hours to obtain the transparent coating.

[0082] Example 3 Step 1): Take 6g of bis(3-trimethoxysilylpropyl)amine solution with a concentration of 75wt%, wherein the solvent is n-butyl ether; add it to 1g of polysilazane (OPZ) precursor solution with a concentration of 72wt%, wherein the solvent is diethyl ether. Shake the resulting mixed solution at room temperature for 2.6 h. Step 2): Take the mixture prepared in Step 1) and coat it into a thin film on a substrate at room temperature; the substrate is a polished silicon wafer.

[0083] Step 3): The film prepared in Step 2) is cured at 85℃ / 86%RH for 5 hours to obtain the transparent coating.

[0084] Example 4 Step 1): Take 4.3 g of bis(3-trimethoxysilylpropyl)amine solution with a concentration of 78 wt%, wherein the solvent is n-butyl ether; add it to 0.61 g of polysilazane (OPZ) precursor solution with a concentration of 55 wt%, wherein the solvent is dichloromethane. Shake the resulting mixed solution at room temperature for 2.8 h. Step 2): Take the mixture prepared in Step 1) and coat it into a thin film on a substrate at room temperature; the substrate is a polished silicon wafer.

[0085] Step 3): The film prepared in Step 2) is cured at 70℃ / 90%RH for 4.5h to obtain the transparent coating.

[0086] Example 5 Step 1): Take 5.5 g of bis(3-trimethoxysilylpropyl)amine solution with a concentration of 53 wt%, using methyl ethyl ketone as the solvent; add it to 0.58 g of polysilazane (OPZ) precursor solution with a concentration of 50 wt%, using dichloromethane as the solvent. Shake the resulting mixture at room temperature for 3 h. Step 2): Take the mixture prepared in Step 1) and coat it into a thin film on a substrate at room temperature. The substrate is CPI.

[0087] Step 3): The film prepared in Step 2) is cured at 95℃ / 80%RH for 2 hours to obtain the transparent coating.

[0088] Example 6 The difference from Example 3 is that in step (1), the polysilazane is replaced with the structure of formula (III), as shown below:

[0089] Equation (II) Formula (II); where x is approximately 4 and y is approximately 9. The preparation method of polysilazane of formula (II) is as follows: Under an inert atmosphere, methylvinyldichlorosilane and methyltrichlorosilane in a molar ratio of 0.5:1 are dissolved in anhydrous toluene to obtain a mixture. The mixture is cooled to 5°C, and dry ammonia gas is slowly introduced at this temperature to carry out an ammonolysis reaction until the pH of the system reaches 9, at which point the ammonia introduction is stopped. After the reaction is complete, the byproduct ammonium chloride (NH4Cl) is removed by filtration. Finally, the collected filtrate is concentrated under reduced pressure to remove the solvent, thereby obtaining the target product with a number average molecular weight of 1001.

[0090] Example 7 The difference from Example 3 is that in step (1), bis(3-trimethoxysilylpropyl)amine is replaced with (3-aminopropyl)trimethoxysilane.

[0091] Example 8 The difference from Example 3 is that in step (1), bis(3-trimethoxysilylpropyl)amine is replaced with (3-aminopropyl)triethoxysilane.

[0092] Example 9 The difference from Example 3 is that in step (1), di(3-trimethoxysilylpropyl)amine is replaced with N-[3-(trimethoxysilyl)propyl]n-butylamine.

[0093] Example 10 The difference from Example 3 is that in step (1), di(3-trimethoxysilylpropyl)amine is replaced with aminoethylaminopropyltrimethoxysilane.

[0094] Comparative Example 1 The difference from Example 1 is that in step 1), only 0.3 g of bis(3-trimethoxysilylpropyl)amine solution with a concentration of 60 wt% is used, wherein the solvent is n-butyl ether. The rest is the same as in Example 1.

[0095] Comparative Example 2 The difference from Example 1 is that in step 1), only 0.3g of polysilazane (OPZ) precursor solution with a concentration of 60wt% is used, and the solvent is n-butyl ether. The rest is the same as in Example 1.

[0096] Comparative Example 3 The difference from Example 2 is that in step 1): 0.5 g of bis(3-trimethoxysilylpropyl)amine solution with a concentration of 60 wt% is taken and the solvent is n-butyl ether; it is added to 5 g of polysilazane (OPZ) precursor solution with an OPZ concentration of 60 wt%. The rest is the same as in Example 2.

[0097] Comparative Example 4 The comparative example is an unmodified CPI-based film, and the rest is the same as in Example 2.

[0098] Comparative Example 5 The difference from Example 2 is that the moisture curing temperature is 40°C. Everything else is the same as in Example 2.

[0099] Comparative Example 6 The difference from Example 2 is that the relative humidity for moisture curing is 10%. The rest is the same as in Example 2.

[0100] Comparative Example 7 The difference from Example 2 is that the moisture curing time is 0.5 hours. The rest is the same as in Example 2.

[0101] Experimental Example 1 The performance of the transparent coatings of Examples 1-10 and Comparative Examples 1-7 was tested. The test methods and test results are shown in Table 1 below.

[0102] Infrared spectroscopy was performed using a Bruker ALPHA II microscope, and microstructure was observed using a Hitachi SU8020 scanning electron microscope. Thickness was measured using a JAWoollam alpha-SE elliptic polarization spectrometer. Hardness and modulus were determined using a nanoindenter (G200, Agilent) in continuous stiffness mode. Pencil hardness was tested using a portable pencil hardness tester according to ASTM D3363. Thermogravimetric behavior was evaluated using a Hitachi STA 7300 thermogravimetric analyzer. Transmittance was measured using a Lambda 1050+ UV-Vis-NIR spectrophotometer. Unless otherwise specified, all coatings were applied to glass slides (with the slides as the test background), and the data listed in the table are at a wavelength of 550 nm. Adhesion was tested using the cross-cut test according to ASTM D3359.

[0103] Thermal cycling test: A rapid temperature change test involving 100 cycles of alternating exposure of the sample to extreme temperatures of 200°C and -196°C. Each cycle consists of heating at 200°C in an oven for 20 min, followed immediately by immersion in liquid nitrogen (-196°C) for 20 min, with a transfer interval of less than 1 min.

[0104] Ionizing radiation testing: Ionizing radiation testing was conducted using a 60Co gamma-ray source (GB X200). Coated samples were tested at 8 × 10⁻⁶ mm. 4 Gy h -1 Dose rate irradiation, with a total cumulative dose of 2.4 × 10⁻⁶. 6 Gy.

[0105] Vacuum UV irradiation: UV irradiation experiments were conducted using a mercury lamp system (BZZ250GS-ZK185) equipped with dual characteristic wavelengths of 185 and 254 nm. The sample was irradiated at an average UV intensity of approximately 15 mW / cm². -2 Vacuum ultraviolet irradiation is performed under a continuously flowing argon atmosphere.

[0106] Table 1 shows the test results of Examples 1-11 and Comparative Examples 1-6.

[0107] As can be seen from Table 1, the coating thickness of Examples 1-10 of the present invention is 1.1-2.3 μm, the coating modulus is 5.9-7.8 GPa, the coating hardness is 0.73-0.9 GPa, the coating pencil hardness is 2H-7H, the transmittance is 94-101.76%, and the residual weight at 1050℃ is between 60-80%.

[0108] Figure 2 Optical photographs of the transparent coatings prepared in Example 2 and Comparative Example 1. Figure 2 It can be seen that the coating formed in Example 2 has a complete film and a uniform surface, while the coating prepared in Comparative Example 1 has obvious unevenness and shrinkage defects, indicating that the introduction of the polysilazane precursor is beneficial to improving the film-forming properties of the coating. The coating modulus of Comparative Example 2 is smaller than that of Examples 1-10, and the coating hardness is lower, indicating that polysilazane and aminosilane are indispensable. The two work together to construct an inorganic network dominated by trapezoidal polysilsesquioxane, which is the fundamental reason why the coating achieves both hardness and toughness. In Comparative Example 3, the molar ratio of aminosilane in the polysilazane and aminosilane solution does not meet the protection scope of this invention, the inorganic network crosslinking is insufficient, the coating structure is loose, and it is difficult to form a continuous and dense trapezoidal structure. The CPI substrate of Comparative Example 4 is not coated, and the surface hardness is low. The moisture curing temperature of Comparative Example 5 is too low, the curing is incomplete, and the hardness is low. The relative humidity of moisture curing in Comparative Example 6 is too low, and the hardness of the coating is low. The moisture curing time of Comparative Example 7 is too short, resulting in low coating hardness. The H / E* ratio and elastic recovery rate (We) are considered important parameters for characterizing the mechanical properties of flexible hard coatings. When H / E* ≥ 0.1 and We ≥ 60%, the material can simultaneously possess high hardness, toughness, and elastic recovery capability. Examples 1-10 all meet the above requirements.

[0109] Figure 5 Thermogravimetric analysis curves of the transparent coatings prepared in Examples 1-3 and Comparative Examples 1-2 are shown. Figure 5 It can be seen that at 1050℃, Comparative Example 1 had the highest percentage of thermal weight loss and the lowest residual weight, followed by Example 1, while Comparative Example 2 had the lowest percentage of thermal weight loss and the highest residual weight. Combined with the data in Table 1, this indicates that the introduction of the polysilazane precursor helps improve the tolerance of the transparent coating to extreme environments. The cross-cut adhesion test results of the prepared transparent coating on CPI substrate are shown below. Figure 6 The results show that no coating peeling or cracking occurred at the edges of the gridded areas, and the adhesion level reached the highest level 5B, indicating that the transparent coating has excellent interfacial bonding performance with the CPI substrate.

[0110] Depend on Figure 8It can be seen that after 1000 cycles of rubbing with 0000# steel wool and 1N load, no obvious scratches were observed on the surface of the transparent coating of Example 5; while after 50 cycles of rubbing with the same conditions, the surface of the sample of Comparative Example 4 showed obvious damage, indicating that the coating of Example 5 has significantly improved wear resistance.

[0111] Figure 10 The transmittance curves of the transparent coating prepared in Example 5 after treatment with high and low temperature cycling, ionizing radiation, and vacuum ultraviolet irradiation are shown. Figure 10 As can be seen, after being subjected to the above extreme conditions, the transmittance of the coating remained basically unchanged and did not decrease significantly, indicating that the transparent coating has excellent stability in extreme environments. The test results show that the prepared transparent coating simultaneously possesses properties of hardness, toughness, transparency, tolerance to extreme environments, ultrathinness, and wear resistance.

[0112] Figure 1 Scanning electron microscope images of the surface and cross-sectional morphology of the transparent coating prepared in Example 5. Figure 1 It can be seen that the prepared transparent coating continuously covers the substrate surface, with a uniform and dense structure, and no obvious pores or defects were observed.

[0113] Figure 2 Optical photographs of the transparent coatings prepared in Example 2 and Comparative Example 1. Figure 2 It can be seen that the coating formed in Example 2 has a complete film and a uniform surface, while the coating prepared in Comparative Example 1 has obvious unevenness and is accompanied by shrinkage defects, indicating that the introduction of polysilazane precursor is beneficial to improving the film-forming properties of the coating.

[0114] Figure 3 Infrared spectra of the transparent coatings prepared in Examples 2-4 and Comparative Examples 1-3. Figure 3 It can be seen that in Examples 2-4, the location is at 3381 cm. -1 and 2160 cm -1 At 1114 cm⁻¹, the characteristic absorption peaks attributable to N-H and Si-H vibrations, respectively, essentially disappeared; however, in Comparative Examples 2-3, obvious N-H and Si-H absorption peaks were still observed, indicating that the presence of aminosilane can promote the conversion of polysilazane precursors to Si-O bonds. Meanwhile, at 1114 cm⁻¹... -1 and 1034 cm -1 Two strong absorption peaks appear at the point, which correspond to the asymmetric stretching vibrations of siloxane bonds in the horizontal direction (—Si—O—Si—) and the vertical direction (—Si—O—Si—R), respectively. These characteristic peaks are typical fingerprint peaks of high molecular weight ladder-like polysilsesquioxane structures.

[0115] Figure 4Load-displacement curves obtained from nanoindentation tests of the transparent coatings prepared in Examples 1-4. Figure 4 It can be seen that each sample exhibits minimal hysteresis during unloading, demonstrating good elasticity. The H / E* ratio and elastic recovery rate (We) are considered important parameters for characterizing the mechanical properties of flexible hard coatings. When H / E* ≥ 0.1 and We ≥ 60%, the material can simultaneously possess high hardness, toughness, and elastic recovery capability. Examples 1-11 all meet the above requirements.

[0116] Figure 5 Thermogravimetric analysis curves of the transparent coatings prepared in Examples 1-3 and Comparative Examples 1-2 are shown. Figure 5 It can be seen that the percentage of thermal weight loss of Comparative Example 1 is the largest, followed by Example 1, while the percentage of thermal weight loss of Comparative Example 2 is the smallest, indicating that the introduction of the polysilazane precursor helps to improve the ability of the transparent coating to withstand extreme environments.

[0117] Figure 6 The results of the cross-cut adhesion test on a CPI substrate for the transparent coating prepared in Example 5 are shown. Figure 6 As can be seen, no coating peeling or cracking occurred at the edges of the gridded areas, and its adhesion level reached the highest level, 5B, indicating that the transparent coating has excellent interfacial bonding performance with the CPI substrate. A schematic diagram of the internal molecular structure of the trapezoidal-dominated polysilsesquioxane transparent coating prepared in Example 5 is shown below. Figure 11 As shown.

[0118] Figure 7 This is a schematic diagram illustrating the bending properties of the transparent coating prepared in Example 5. Figure 7 It can be seen that under small bending radius conditions, the coating did not show cracks or peeling, indicating that it has good flexibility.

[0119] Figure 8 The results show the abrasion resistance test results of the transparent coatings prepared in Example 5 and Comparative Example 4. Figure 8 It can be seen that after 1000 cycles of rubbing with 0000# steel wool and 1N load, no obvious scratches were observed on the surface of the transparent coating of Example 5; while after 50 cycles of rubbing with the same conditions, the surface of the sample of Comparative Example 4 showed obvious damage, indicating that the coating of Example 5 has significantly improved wear resistance.

[0120] Figure 9 The optical transmittance curves are for the transparent coatings prepared in Example 5 and Comparative Example 4. Figure 9 It can be seen that the transmittance of Example 5 in the visible light band is significantly higher than that of the comparative sample, indicating that it has good optical transmittance performance.

[0121] Figure 10The transmittance curves of the transparent coating prepared in Example 5 after treatment with high and low temperature cycling, ionizing radiation, and vacuum ultraviolet irradiation are shown. Figure 10 As can be seen, after the above extreme conditions, the transmittance of the coating remained basically unchanged and did not decrease significantly, indicating that the transparent coating has excellent environmental stability.

[0122] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A tough and transparent coating that is resistant to extreme environments, characterized in that, The coating is formed by in-situ hydrolysis-condensation reaction of polysilazane and aminosilane, and the in-situ hydrolysis-condensation reaction forms an inorganic network structure mainly composed of ladder-shaped polysilsesquioxane.

2. The transparent coating according to claim 1, characterized in that, The coating thickness is 100 nanometers to 5 micrometers.

3. The transparent coating according to claim 1 or 2, characterized in that, The aminosilane is selected from one or more of (3-aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, di(3-trimethoxysilylpropyl)amine, N-[3-(trimethoxysilyl)propyl]n-butylamine, and aminoethylaminopropyltrimethoxysilane.

4. A method for preparing the transparent coating according to any one of claims 1-3, characterized in that, Includes the following steps: 1) Mix the polysilazane precursor solution with the aminosilane solution to obtain a mixture; 2) Take the mixture prepared in step 1) and coat it onto a substrate at room temperature to form a thin film; 3) The film prepared in step 2) is cured to obtain the transparent coating.

5. The preparation method according to claim 4, characterized in that, In step 1), the molar ratio of polysilazane in the polysilazane precursor solution to aminosilane in the aminosilane solution is 5:1-1:

20.

6. The preparation method according to claim 5, characterized in that, In step 1), the polysilazane precursor solution is obtained by dissolving polysilazane in solvent A; the mass fraction of polysilazane in the polysilazane precursor solution is 1%-99%.

7. The preparation method according to claim 5, characterized in that, In step 1), the aminosilane solution is obtained by dissolving aminosilane in solvent B, and the mass fraction of aminosilane in the aminosilane solution is 1%-99%.

8. The preparation method according to claim 5, characterized in that, In step 1), the mixing method is oscillation mixing; the oscillation time is 1h~3h, and the temperature is 18~28℃.

9. The preparation method according to any one of claims 5-8, characterized in that, In step 3), the curing is moisture curing, the temperature of moisture curing is 50~100℃, the relative humidity is 20%~98%, and the time of moisture curing is 1~6h.

10. The application of a transparent coating according to any one of claims 1-3 or a transparent coating prepared by the preparation method according to any one of claims 4-9 in the fields of aerospace components, flexible displays, or optical devices.

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