A modified polysilazane coating having both flexibility and surface hardness and a method for preparing the same

Abstract

The application provides a modified polysilazane coating with flexibility and surface hardness and a preparation method thereof, and belongs to the technical field of coatings. The application is prepared by reacting hydroxyl polydimethylsiloxane with borate triisooctyl ester to obtain borate modified polysiloxane, and removing by-products to reduce the risk of residual small molecules causing pores, which is similar to the structure of organic polysilazane resin, is easy to disperse uniformly, gradually generates active centers containing boron after being affected by moisture, promotes the hydrolysis and condensation of silazane and the rearrangement of the network, forms a dense siloxane network on the surface layer and stabilizes the surface hardening; the double-end silane-terminated polyisobutylene is microphase-separated into flexible and hydrophobic domains during curing, the end groups are hydrolyzed and condensed, and the network is covalently connected and anchored, which reduces migration and stickiness and enhances the barrier; in combination with butyl acetate / isoparaffin mixed solvent, compatible agent, interfacial anchoring agent and water capturing agent, fine dispersion and storage stability are achieved, a gradient structure with hard surface and flexible interior is obtained, and the application is suitable for long-term service and heavy corrosion of marine engineering.

Description

Technical Field

[0001] This invention belongs to the field of coating technology and relates to a modified polysilazane coating that combines flexibility and surface hardness, and its preparation method. Background Technology

[0002] With the rapid development of marine engineering, offshore wind power, and ocean-going vessels, extremely high requirements have been placed on protective coatings for metal substrates. Organopolysilazanes, due to the repeating Si-N bonds in their molecular structure, can transform into a ceramic network similar to quartz glass after curing, exhibiting excellent high-temperature resistance, high hardness, and oxidation resistance, and are considered a potential next-generation high-performance marine heavy-duty anti-corrosion material. However, the application of polysilazanes in large-scale marine engineering equipment still faces core technical bottlenecks such as difficulty in room-temperature curing, the challenge of achieving both hardness and toughness, and microstructural defects leading to anti-corrosion failure.

[0003] First, achieving high density through room-temperature curing is difficult. High-performance polysilazane coatings typically rely on high-temperature baking to achieve high hardness and density; however, large components such as large ships and offshore wind turbine towers cannot be baked at high temperatures. Existing room-temperature catalytic methods often result in low deep-layer conversion rates and porous coatings, failing to achieve ideal protective performance. Second, there is a trade-off between hardness and flexibility. The inorganic network of cured polysilazane is inherently brittle and prone to cracking; while traditional physical blending toughening methods (such as introducing organic resins or plasticizers) not only significantly sacrifice surface hardness and weather resistance but also suffer from migration and precipitation problems due to thermodynamic incompatibility of toughening components, severely affecting long-term stability. Furthermore, long-term barrier properties are insufficient. Microporous channels generated by gas release during coating curing, as well as the hydrophilic instability of intermediate states, easily lead to the penetration of corrosive media. Traditional physical fillers cannot effectively seal these defects at the microscale through chemical bonding, failing to meet the stringent corrosion protection requirements of marine environments. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a modified polysilazane coating that combines flexibility and surface hardness, as well as its preparation method. This application uses hydroxyl polydimethylsiloxane and triisooctyl borate to react and prepare a borate-modified polysiloxane, removing byproducts to reduce the risk of residual small molecules causing pores. Its structure is similar to that of organopolysilazane resins, making it easy to disperse uniformly. Upon exposure to moisture, it gradually generates boron-containing active centers, promoting the hydrolysis and condensation of silazane and network rearrangement, resulting in a dense silicon-oxygen network on the surface and stable surface hardening. During curing, the double-terminated silane-capped polyisobutylene undergoes microphase separation into flexible hydrophobic domains, which are anchored by end-group hydrolysis and condensation and covalent network connection, reducing migration and stickiness and enhancing barrier properties. Combined with a butyl acetate / isoalkane mixed solvent, compatibilizer, interface anchoring agent, and water trapping agent, fine dispersion and storage stability are achieved, resulting in a gradient structure with a hard surface and tough interior, suitable for long-term heavy-duty corrosion protection in marine engineering.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing a modified polysilazane coating that combines flexibility and surface hardness, the method comprising:

[0007] S1: Hydroxypolydimethylsiloxane and triisooctyl borate were pretreated by molecular sieve drying and then filtered through a plate and frame filter to obtain pretreated hydroxypolydimethylsiloxane and pretreated triisooctyl borate; the pretreated hydroxypolydimethylsiloxane was heated under nitrogen protection and pretreated triisooctyl borate was added dropwise to obtain reaction solution A. During the reaction, byproducts generated were continuously removed by micro-purging with nitrogen. After the reaction was completed, the system was depressurized and devolatilized, cooled and filtered to obtain borate-modified polysiloxane.

[0008] S2: Add vinyl-silicon-terminated polyisobutylene to an isoalkane solvent to obtain a polymer solution; add Karstedt catalyst and heat to obtain reaction solution B; add triethoxysilane dropwise to obtain reaction solution C; after heat preservation reaction, use activated carbon adsorption filtration to remove residual catalyst to obtain pretreated solution; remove solvent and excess silane under vacuum to obtain double-terminated silane-terminated polyisobutylene.

[0009] S3: Under a nitrogen atmosphere, butyl acetate and isoparaffin solvent are mixed to obtain a mixed solvent; organopolysilazane resin is mixed with the mixed solvent and dispersed to obtain a resin base liquid; double-terminated silane-capped polyisobutylene and compatibilizer are added sequentially and stirred to obtain dispersion D; borate ester modified polysiloxane is then added to obtain dispersion E; after stirring, interface anchoring agent and carbodiimide type water trapping agent are added; after continuing to stir, the mixture is filtered and sealed and packaged to obtain a modified polysilazane coating that has both flexibility and surface hardness.

[0010] As a preferred technical solution of the present invention, in step S1, the pretreated hydroxyl polydimethylsiloxane is heated to 60-80°C under nitrogen protection. For example, it can be heated to 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0011] In some optional embodiments, the molar ratio of boron atoms in the pretreated triisooctyl borate to hydroxyl atoms in the pretreated hydroxyl polydimethylsiloxane is (0.4-0.7):1, for example, it can be 0.40:1, 0.43:1, 0.46:1, 0.49:1, 0.52:1, 0.55:1, 0.58:1, 0.61:1, 0.64:1, 0.67:1 or 0.70:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0012] In some optional embodiments, the stirring speed of the reaction solution A during reaction is 300-500 rpm, for example, it can be 300 rpm, 320 rpm, 340 rpm, 360 rpm, 380 rpm, 400 rpm, 420 rpm, 440 rpm, 460 rpm, 480 rpm or 500 rpm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0013] In some optional embodiments, the reaction temperature of the reaction solution A is 100-120°C, for example, it can be 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, 112°C, 114°C, 116°C, 118°C or 120°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0014] In some optional embodiments, the reaction time of the reaction solution A is 4-6 hours, for example, it can be 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5.0 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours or 6.0 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0015] In some optional embodiments, the temperature for vacuum devolatilization is 110-130°C, for example, it can be 110°C, 112°C, 114°C, 116°C, 118°C, 120°C, 122°C, 124°C, 126°C, 128°C or 130°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0016] In some optional embodiments, the vacuum degree of the depressurization devolatilization is -0.08 to -0.095 MPa, for example, it can be -0.0950 MPa, -0.0935 MPa, -0.0920 MPa, -0.0905 MPa, -0.0890 MPa, -0.0875 MPa, -0.0860 MPa, -0.0845 MPa, -0.0830 MPa, -0.0815 MPa or -0.0800 MPa, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0017] In some optional embodiments, the decompression and volatilization time is 1-2 hours, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0018] As a preferred technical solution of the present invention, in step S2, the solid content of the polymer solution is 30-50%, for example, it can be 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48% or 50%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] In some optional embodiments, the amount of Karstedt catalyst fed is 10-30 ppm of the mass of vinyl-silicon-terminated polyisobutylene, for example, 10 ppm, 12 ppm, 14 ppm, 16 ppm, 18 ppm, 20 ppm, 22 ppm, 24 ppm, 26 ppm, 28 ppm or 30 ppm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0020] In some optional embodiments, the temperature of the reaction solution B is 70-80°C, for example, it can be 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0021] In some optional embodiments, the molar ratio of the Si-H bond in the triethoxysilane to the carbon-carbon double bond in the vinyl-silicon-terminated polyisobutylene is (1.05-1.30):1, for example, it can be 1.050:1, 1.075:1, 1.100:1, 1.125:1, 1.150:1, 1.175:1, 1.200:1, 1.225:1, 1.250:1, 1.275:1 or 1.300:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0022] In some optional embodiments, the reaction solution C is kept at a constant temperature for 4-8 hours, for example, 4.0 hours, 4.4 hours, 4.8 hours, 5.2 hours, 5.6 hours, 6.0 hours, 6.4 hours, 6.8 hours, 7.2 hours, 7.6 hours, or 8.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0023] In some optional embodiments, the temperature for vacuum solvent removal is 80-100°C, for example, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C or 100°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0024] As a preferred embodiment of the present invention, in step S3, the mass ratio of butyl acetate to isoparaffin solvent in the mixed solvent is (1.5-3.0):1, for example, it can be 1.50:1, 1.65:1, 1.80:1, 1.95:1, 2.10:1, 2.25:1, 2.40:1, 2.55:1, 2.70:1, 2.85:1 or 3.00:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0025] In some optional embodiments, the mass ratio of the organopolysilazane resin to the mixed solvent is 100:(40-80), for example, it can be 100:40, 100:44, 100:48, 100:52, 100:56, 100:60, 100:64, 100:68, 100:72, 100:76 or 100:80, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0026] In some optional embodiments, the dispersion speed of the organopolysilazane resin after mixing with the mixed solvent is 500-1000 rpm, for example, it can be 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, 950 rpm or 1000 rpm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0027] In some optional embodiments, the dispersion time of the organopolysilazane resin after mixing with the mixed solvent is 10-15 min, for example, it can be 10.0 min, 10.5 min, 11.0 min, 11.5 min, 12.0 min, 12.5 min, 13.0 min, 13.5 min, 14.0 min, 14.5 min or 15.0 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0028] In some optional embodiments, the mass ratio of the bi-silane-terminated polyisobutylene to the organopolysilazane resin is (8-15):100, for example, it can be 8.0:100, 8.7:100, 9.4:100, 10.1:100, 10.8:100, 11.5:100, 12.2:100, 12.9:100, 13.6:100, 14.3:100 or 15.0:100, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0029] In some optional embodiments, the amount of compatibilizer added is 0.5%-1% of the mass of the organopolysilazane resin, for example, it can be 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95% or 1.00%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0030] In some optional embodiments, the mass ratio of the borate-modified polysiloxane to the organopolysilazane resin is (3-6):100, for example, it can be 3.0:100, 3.3:100, 3.6:100, 3.9:100, 4.2:100, 4.5:100, 4.8:100, 5.1:100, 5.4:100, 5.7:100 or 6.0:100, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0031] In some optional embodiments, the dispersion E is stirred for 10-20 min, for example, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min or 20 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0032] In some optional embodiments, the amount of the interface anchoring agent is 0.5-1% of the mass of the organopolysilazane resin, for example, it can be 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95% or 1.00%, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0033] In some optional embodiments, the amount of the carbodiimide-type water capture agent is 0.1-0.6% of the mass of the organopolysilazane resin, for example, it can be 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55% or 0.60%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0034] In some optional embodiments, the continued stirring time is 5-10 min, for example, it can be 5.0 min, 5.5 min, 6.0 min, 6.5 min, 7.0 min, 7.5 min, 8.0 min, 8.5 min, 9.0 min, 9.5 min or 10.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0035] Secondly, the present invention provides a modified polysilazane coating that combines flexibility and surface hardness prepared by the preparation method described above.

[0036] The borate-modified polysiloxane introduced in this application serves as a latent structure-regulating / conversion-promoting unit in the system. Hydroxydimethylsiloxane and triisooctyl borate introduce boron-containing structures into the polysiloxane chain segments via transesterification or condensation, while continuously removing byproducts to reduce the tendency for coating defects caused by residual small molecules. The resulting borate-modified polysiloxane has two key advantages: firstly, its polysiloxane backbone exhibits good structural similarity to organopolysilazane resins, facilitating uniform distribution in coatings; secondly, its borate structure may undergo hydrolysis and rearrangement upon subsequent contact with moisture, gradually forming boron centers or boron-containing hydroxyl structures with certain Lewis acid characteristics. These structural units, to some extent, promote the hydrolysis-condensation and network rearrangement processes of organopolysilazane resins, making curing easier and leading to the evolution of a silicon-oxygen network with fewer defects and higher connectivity. The borate-modified polysiloxane combines conversion promotion and structural compatibility within the same molecular framework, laying the foundation for subsequent synergistic curing.

[0037] The introduction of bi-silane-terminated polyisobutylene transforms the originally difficult-to-coexist-with inorganic framework flexible segments into reactive soft phases that can participate in network construction and be fixed. After adding vinylsilane-terminated polyisobutylene to an isoalkane solvent, the introduction of a Karstedt catalyst promotes the addition reaction of silane-hydrogen bonds in triethoxysilane to the unsaturated bonds of the end groups, thereby introducing hydrolyzable alkoxysilane end groups into the polyisobutylene chain ends. Bi-silane end-capping makes the polyisobutylene segments, after curing, more like flexible bridge chains bound at both ends, rather than freely diffusing plasticized small molecules: in subsequent humid environments, its end groups can hydrolyze to generate silanols and further condense, forming chemical connections with the surrounding silicon-oxygen network, thus reducing the possibility of soft phase migration to the surface, leading to surface stickiness or decreased scratch resistance. Simultaneously, the low polarity and low permeability of polyisobutylene itself facilitate the formation of a hydrophobic barrier phase within the coating, complementing the dense shielding effect of the silicon-oxygen network, thereby improving the corrosion-resistant shielding effect.

[0038] During the mixing process, the mixed solvent formed by butyl acetate and isoalkane solvent is used to simultaneously meet the dissolution / leveling requirements of organopolysilazane resin and the dispersion requirements of bisilane-terminated polyisobutylene. This ensures that the system is as close as possible to a homogeneous or finely dispersed state in the packaged state, thereby reducing viscosity drift caused by local enrichment in the can. Adding bisilane-terminated polyisobutylene and compatibilizer first is equivalent to pre-setting the interface state of the soft phase before curing: the compatibilizer helps reduce the interfacial tension between the soft phase and the silazane system, weakens the driving force of macroscopic phase separation, and makes the subsequently formed soft phase more likely to remain at a finer scale, reducing the risk of oiling, blooming, or obvious haze. This is crucial for achieving both flexibility and surface hardness, because once the soft phase migrates to the surface, it is detrimental to scratch resistance and stain resistance. Subsequently, borate-modified polysiloxane is added to uniformly embed boron-containing structural units into the system. Finally, an interface anchoring agent and a carbodiimide-type water scavenger are added to improve the engineering usability of the single-component coating from two aspects: interfacial chemical coupling and inhibition of premature hydrolysis during storage. The interface anchoring agent tends to establish a stronger bond with the substrate surface and the coating's silicon-oxygen network after subsequent hydrolysis-condensation, thereby improving adhesion retention under humid, hot, and salt spray conditions. The carbodiimide-type water scavenger is used to consume trace amounts of water in the system, reducing the risk of viscosity increase and gelation caused by premature reaction in the tank. At the same time, with reasonable addition, it usually still retains the possibility of curing triggered by ambient moisture after application.

[0039] The synergistic effect of the components in this application is manifested in the curing and structural evolution stages after construction. When the coating is exposed to air moisture, the surface layer is more prone to hydrolysis-condensation and network formation of the organopolysilazane resin. Simultaneously, the borate structure in the borate-modified polysiloxane may gradually hydrolyze under moisture to generate boron-containing active structures. These structural units may lower the kinetic threshold for the transformation of the organopolysilazane resin into a silicon-oxygen network, making the surface layer more prone to forming a dense layer with higher cross-linking and fewer pores. The surface layer entering a glassy or high-modulus state will, to some extent, limit the long-range migration of the soft phase to the surface, providing structural conditions for maintaining surface hardness. Meanwhile, within the coating, as the solvent evaporates and the silicon-oxygen network gradually grows, the double-silane-terminated polyisobutylene, due to its limited thermodynamic compatibility with the inorganic silicon-oxygen network, may undergo microphase separation to form a flexible phase. This flexible phase is not completely free; its end groups can continue to undergo hydrolysis-condensation and connect with the surrounding network, thus being covalently anchored within the network. This forms a synergistic closed loop: borate-modified polysiloxane promotes surface densification; bi-silane-terminated polyisobutylene forms a soft phase internally and is chemically linked during formation; compatibilizers reduce interfacial tension, helping the soft phase remain at a finer scale; interfacial anchoring agents enhance the chemical coupling at the coating-substrate interface; and carbodiimide-type water traps ensure that the single-component storage period is not prematurely triggered by trace amounts of water. This overall synergy makes gradient interpenetrating networks easier to form under ambient temperature and humidity conditions.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] This application prepares borate-modified polysiloxane by reacting hydroxyl polydimethylsiloxane with triisooctyl borate, and removes byproducts during the preparation process to reduce the risk of film defects caused by residual small molecules. Because the structure of the borate-modified polysiloxane is similar to that of organopolysilazane resin, it is easier to distribute uniformly in the system. Moreover, its borate structure can be gradually hydrolyzed and rearranged after contact with moisture to form a boron-containing active structure with certain Lewis acid characteristics. This promotes the hydrolysis-condensation and network rearrangement of organopolysilazane resin to a certain extent, and drives the coating to evolve into a denser and more connected silicon-oxygen network, providing a basis for subsequent synergistic curing.

[0042] This application introduces double-ended silane-terminated polyisobutylene, which enables the flexible polyisobutylene segments to obtain hydrolyzable silane end groups and form chemical connections with the silicon-oxygen network during moisture curing. This anchors the soft phase within the coating, reducing the risk of migration to the surface causing stickiness or decreased scratch resistance. At the same time, the low polarity and low permeability of polyisobutylene are used to form a hydrophobic barrier phase within the coating, further enhancing the corrosion-resistant shielding effect.

[0043] This application utilizes a mixed solvent of butyl acetate / isoalkane to balance the dissolution and leveling of organopolysilazane resin with the fine dispersion control of the flexible phase, reducing viscosity drift in the tank and suppressing soft phase coarsening, oil blooming, or fogging. At the same time, it enhances the bonding between the coating and the substrate through interface anchoring and suppresses premature hydrolysis and gelation during storage through water capture. While maintaining the storage stability of the single component, it still facilitates moisture-triggered curing and performance after construction.

[0044] After construction, under the influence of air humidity, the borate-modified polysiloxane promotes the formation of a silicon-oxygen network on the surface of the organopolysiloxane resin more quickly and densely, thereby inhibiting the migration of the soft phase to the surface and maintaining surface hardening to a certain extent. At the same time, the double-ended silane-terminated polyisobutylene inside the coating undergoes microphase separation to form a flexible phase, which is anchored by covalent connection with the surrounding network through end-group hydrolysis and condensation. Combined with the interfacial tension regulation of the compatibilizer, the interfacial coupling of the interfacial anchoring agent, and the storage stabilization effect of the carbodiimide-type water trap, the coating has a gradient structure with a hard surface and a tough interior. Therefore, it is suitable for heavy-duty corrosion protection under salt spray, humidity, impact and vibration conditions such as marine engineering. Attached Figure Description

[0045] Figure 1 Photograph of the modified polysilazane coating with both flexibility and surface hardness prepared by the preparation method described in Example 1 of this application, coated on a metal specimen and cured under room temperature and humidity conditions;

[0046] Figure 2The modified polysilazane coating with both flexibility and surface hardness prepared by the preparation method described in Example 1 of this application is coated on a metal specimen and cured under room temperature and humidity conditions. The resulting image shows the side view after bending. Detailed Implementation

[0047] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include any obvious substitutions and modifications made to the embodiments described herein.

[0048] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone further purification or processing.

[0049] Vinyl-silicone-terminated polyisobutylene: Kaneka Epion 200A;

[0050] Solvent for isoparaffins: Isopar L;

[0051] Organopolysilazane resin: Durazane® 1800;

[0052] Compatibilizer: Shin-Etsu X-22-2516;

[0053] Interface anchoring agent: Silquest A-1524.

[0054] Example 1

[0055] This embodiment provides a modified polysilazane coating that combines flexibility and surface hardness, and a method for preparing the same. The method for preparing the modified polysilazane coating that combines flexibility and surface hardness specifically includes the following steps:

[0056] S1: Hydroxy-dimethylsiloxane and triisooctyl borate were pretreated by molecular sieve drying and then filtered through a plate and frame filter to obtain pretreated hydroxy-dimethylsiloxane and pretreated triisooctyl borate. The pretreated hydroxy-dimethylsiloxane was heated to 75°C under nitrogen protection, and pretreated triisooctyl borate was added dropwise to obtain reaction solution A, wherein the molar ratio of boron atoms in pretreated triisooctyl borate to hydroxyl atoms in pretreated hydroxy-dimethylsiloxane was 0.6:1. The reaction was carried out at 115°C and 450 rpm for 5.5 h. During the reaction, byproducts were continuously removed by micro-purging with nitrogen. After the reaction, the system was subjected to vacuum devolatilization at 125°C and -0.09 MPa for 1.8 h, and then cooled and filtered to obtain borate-modified polysiloxane.

[0057] S2: Vinylsilane-terminated polyisobutylene was added to an isoalkane solvent to obtain a polymer solution with a solid content of 45%; Karstedt catalyst was added, wherein the amount of Karstedt catalyst added was 25 ppm of the mass of vinylsilane-terminated polyisobutylene, and the temperature was raised to 78°C to obtain reaction solution B; triethoxysilane was added dropwise to obtain reaction solution C, wherein the molar ratio of Si-H bond in triethoxysilane to carbon-carbon double bond in vinylsilane-terminated polyisobutylene was 1.2:1, and the reaction was kept at the temperature for 7 h. The residual catalyst was removed by activated carbon adsorption filtration to obtain a pretreated solution, and the solvent and excess silane were removed under vacuum at 95°C to obtain double-terminated silane-terminated polyisobutylene.

[0058] S3: Under a nitrogen atmosphere, butyl acetate and isoparaffin solvent are mixed at a mass ratio of 2.5:1 to obtain a mixed solvent; organopolysilazane resin is mixed with the mixed solvent at a mass ratio of 100:70 and dispersed at 800 rpm for 14 min to obtain a resin base liquid; bisilane-terminated polyisobutylene and compatibilizer are added sequentially and stirred to obtain dispersion D, wherein the mass ratio of bisilane-terminated polyisobutylene to organopolysilazane resin is 12:100, and the amount of compatibilizer added is 0.8% of the mass of organopolysilazane resin; Subsequently, borate-modified polysiloxane was added to obtain dispersion E. The mass ratio of borate-modified polysiloxane to organopolysilazane resin was 5:100. After stirring for 18 minutes, an interface anchoring agent and a carbodiimide-type water scavenger were added. The amount of interface anchoring agent added was 0.9% of the mass of organopolysilazane resin, and the amount of carbodiimide-type water scavenger added was 0.5% of the mass of organopolysilazane resin. After stirring for another 8 minutes, the mixture was filtered, discharged, and sealed in packaging to obtain a modified polysilazane coating that combines flexibility and surface hardness. Figure 1 The image shows a modified polysilazane coating with both flexibility and surface hardness prepared by the preparation method described in Example 1 of this application. The coating was applied to a metal sample and cured under normal temperature and humidity conditions. The coating surface is continuous and smooth, and the overall color and gloss are relatively uniform. No obvious macroscopic defects such as shrinkage cavities or sagging are observed. Figure 2The modified polysilazane coating, which combines flexibility and surface hardness, prepared by the preparation method described in Example 1 of this application, is coated on a metal test piece and cured under room temperature and humidity conditions. The side view of the curved area is shown in the photo. The coating still maintains continuous coverage in the curved area, and no obvious cracks or peeling are observed in the appearance, indicating that the coating has a certain degree of flexibility and adaptability.

[0059] Example 2

[0060] This embodiment provides a modified polysilazane coating that combines flexibility and surface hardness, and a method for preparing the same. The method for preparing the modified polysilazane coating that combines flexibility and surface hardness specifically includes the following steps:

[0061] S1: Hydroxy-dimethylsiloxane and triisooctyl borate were pretreated by molecular sieve drying and then filtered through a plate and frame filter to obtain pretreated hydroxy-dimethylsiloxane and pretreated triisooctyl borate. The pretreated hydroxy-dimethylsiloxane was heated to 60°C under nitrogen protection, and pretreated triisooctyl borate was added dropwise to obtain reaction solution A, wherein the molar ratio of boron atoms in pretreated triisooctyl borate to hydroxyl atoms in pretreated hydroxy-dimethylsiloxane was 0.4:1. The reaction was carried out at 100°C and 300 rpm for 4 h. During the reaction, byproducts were continuously removed by nitrogen micro-purging. After the reaction, the system was de-idered at 110°C and vacuum degree -0.08 MPa for 1 h, cooled and filtered to obtain borate-modified polysiloxane.

[0062] S2: Vinyl silane-terminated polyisobutylene is added to an isoalkane solvent to obtain a polymer solution with a solid content of 30%; Karstedt catalyst is added, wherein the amount of Karstedt catalyst added is 10 ppm of the mass of vinyl silane-terminated polyisobutylene, and the temperature is raised to 70°C to obtain reaction solution B; triethoxysilane is added dropwise to obtain reaction solution C, wherein the molar ratio of Si-H bond in triethoxysilane to carbon-carbon double bond in vinyl silane-terminated polyisobutylene is 1.05:1, and the reaction is maintained at the temperature for 4 h. The residual catalyst is removed by activated carbon adsorption filtration to obtain a pretreated solution. The solvent and excess silane are removed under vacuum at 80°C to obtain double-terminated silane-terminated polyisobutylene.

[0063] S3: Under a nitrogen atmosphere, butyl acetate and isoparaffin solvent were mixed at a mass ratio of 1.5:1 to obtain a mixed solvent; organopolysilazane resin was mixed with the mixed solvent at a mass ratio of 100:40 and dispersed at 500 rpm for 10 min to obtain a resin base liquid; bisilane-terminated polyisobutylene and a compatibilizer were added sequentially, and the mixture was stirred to obtain dispersion D, wherein the mass ratio of bisilane-terminated polyisobutylene to organopolysilazane resin was 8:100, and the amount of compatibilizer added was 0.5% of the mass of organopolysilazane resin; Then, borate-modified polysiloxane was added to obtain dispersion E. The mass ratio of borate-modified polysiloxane to organopolysilazane resin was 3:100. After stirring for 10 minutes, an interface anchoring agent and a carbodiimide-type water scavenger were added. The amount of interface anchoring agent was 0.5% of the mass of organopolysilazane resin, and the amount of carbodiimide-type water scavenger was 0.1% of the mass of organopolysilazane resin. After stirring for another 5 minutes, the mixture was filtered, discharged, and sealed in packaging to obtain a modified polysilazane coating that has both flexibility and surface hardness.

[0064] Example 3

[0065] This embodiment provides a modified polysilazane coating that combines flexibility and surface hardness, and a method for preparing the same. The method for preparing the modified polysilazane coating that combines flexibility and surface hardness specifically includes the following steps:

[0066] S1: Hydroxy-dimethylsiloxane and triisooctyl borate were pretreated by molecular sieve drying and then filtered through a plate and frame filter to obtain pretreated hydroxy-dimethylsiloxane and pretreated triisooctyl borate. The pretreated hydroxy-dimethylsiloxane was heated to 65°C under nitrogen protection, and pretreated triisooctyl borate was added dropwise to obtain reaction solution A, wherein the molar ratio of boron atoms in pretreated triisooctyl borate to hydroxyl atoms in pretreated hydroxy-dimethylsiloxane was 0.5:1. The reaction was carried out at 105°C and 350 rpm for 4.5 h. During the reaction, byproducts were continuously removed by nitrogen micro-purging. After the reaction, the system was degassed under reduced pressure at 115°C and a vacuum degree of -0.085 MPa for 1.2 h, cooled and filtered to obtain borate-modified polysiloxane.

[0067] S2: Vinyl silane-terminated polyisobutylene was added to an isoalkane solvent to obtain a polymer solution with a solid content of 35%; Karstedt catalyst was added, wherein the amount of Karstedt catalyst added was 15 ppm of the mass of vinyl silane-terminated polyisobutylene, and the temperature was raised to 72°C to obtain reaction solution B; triethoxysilane was added dropwise to obtain reaction solution C, wherein the molar ratio of Si-H bond in triethoxysilane to carbon-carbon double bond in vinyl silane-terminated polyisobutylene was 1.1:1, and after reacting at this temperature for 5 h, the residual catalyst was removed by activated carbon adsorption filtration to obtain a pretreated solution, and the solvent and excess silane were removed under vacuum at 85°C to obtain double-terminated silane-terminated polyisobutylene;

[0068] S3: Under a nitrogen atmosphere, butyl acetate and isoparaffin solvent were mixed at a mass ratio of 2.0:1 to obtain a mixed solvent; organopolysilazane resin was mixed with the mixed solvent at a mass ratio of 100:50 and dispersed at 600 rpm for 11 min to obtain a resin base liquid; bisilane-terminated polyisobutylene and a compatibilizer were added sequentially, and the mixture was stirred to obtain dispersion D, wherein the mass ratio of bisilane-terminated polyisobutylene to organopolysilazane resin was 10:100, and the amount of compatibilizer added was 1% of the mass of organopolysilazane resin; Then, borate-modified polysiloxane was added to obtain dispersion E. The mass ratio of borate-modified polysiloxane to organopolysilazane resin was 4:100. After stirring for 12 minutes, an interface anchoring agent and a carbodiimide-type water scavenger were added. The amount of interface anchoring agent was 0.6% of the mass of organopolysilazane resin, and the amount of carbodiimide-type water scavenger was 0.3% of the mass of organopolysilazane resin. After stirring for another 6 minutes, the mixture was filtered, discharged, and sealed in packaging to obtain a modified polysilazane coating that has both flexibility and surface hardness.

[0069] Example 4

[0070] This embodiment provides a modified polysilazane coating that combines flexibility and surface hardness, and a method for preparing the same. The method for preparing the modified polysilazane coating that combines flexibility and surface hardness specifically includes the following steps:

[0071] S1: Hydroxy-dimethylsiloxane and triisooctyl borate were pretreated by molecular sieve drying and then filtered through a plate and frame filter to obtain pretreated hydroxy-dimethylsiloxane and pretreated triisooctyl borate. The pretreated hydroxy-dimethylsiloxane was heated to 80°C under nitrogen protection, and pretreated triisooctyl borate was added dropwise to obtain reaction solution A, wherein the molar ratio of boron atoms in pretreated triisooctyl borate to hydroxyl atoms in pretreated hydroxy-dimethylsiloxane was 0.7:1. The reaction was carried out at 120°C and 500 rpm for 6 h. During the reaction, byproducts were continuously removed by nitrogen micro-purging. After the reaction, the system was de-idered at 130°C and vacuum degree -0.095 MPa for 2 h, and then cooled and filtered to obtain borate-modified polysiloxane.

[0072] S2: Vinylsilane-terminated polyisobutylene is added to an isoalkane solvent to obtain a polymer solution with a solid content of 50%; Karstedt catalyst is added, wherein the amount of Karstedt catalyst added is 30 ppm of the mass of vinylsilane-terminated polyisobutylene, and the temperature is raised to 80℃ to obtain reaction solution B; triethoxysilane is added dropwise to obtain reaction solution C, wherein the molar ratio of Si-H bond in triethoxysilane to carbon-carbon double bond in vinylsilane-terminated polyisobutylene is 1.30:1, and the reaction is kept at the temperature for 8 hours. The residual catalyst is removed by activated carbon adsorption filtration to obtain a pretreated solution. The solvent and excess silane are removed under vacuum at 100℃ to obtain double-terminated silane-terminated polyisobutylene.

[0073] S3: Under a nitrogen atmosphere, butyl acetate and isoparaffin solvent were mixed at a mass ratio of 3.0:1 to obtain a mixed solvent; organopolysilazane resin was mixed with the mixed solvent at a mass ratio of 100:80 and dispersed at 1000 rpm for 15 min to obtain a resin base liquid; bisilane-terminated polyisobutylene and a compatibilizer were added sequentially, and the mixture was stirred to obtain dispersion D, wherein the mass ratio of bisilane-terminated polyisobutylene to organopolysilazane resin was 15:100, and the amount of compatibilizer added was 0.7% of the mass of organopolysilazane resin. Subsequently, borate-modified polysiloxane was added to obtain dispersion E. The mass ratio of borate-modified polysiloxane to organopolysilazane resin was 6:100. After stirring for 20 minutes, an interface anchoring agent and a carbodiimide-type water scavenger were added. The amount of interface anchoring agent was 1% of the mass of organopolysilazane resin, and the amount of carbodiimide-type water scavenger was 0.6% of the mass of organopolysilazane resin. After stirring for another 10 minutes, the mixture was filtered, discharged, and sealed in packaging to obtain a modified polysilazane coating that combines flexibility and surface hardness.

[0074] Comparative Example 1

[0075] This comparative example provides a modified polysilazane coating that combines flexibility and surface hardness, and its preparation method. The difference from Example 1 is that no borate ester modified polysiloxane is added, while the other operation steps and process parameters are exactly the same as in Example 1.

[0076] Comparative Example 2

[0077] This comparative example provides a modified polysilazane coating that combines flexibility and surface hardness, and its preparation method. The difference from Example 1 is that triisooctyl borate is used instead of borate ester to modify polysiloxane. Other operating steps and process parameters are exactly the same as in Example 1.

[0078] Comparative Example 3

[0079] This comparative example provides a modified polysilazane coating that combines flexibility and surface hardness, and its preparation method. The difference from Example 1 is that no double-terminated silane-capped polyisobutylene is added, while the other operation steps and process parameters are exactly the same as in Example 1.

[0080] Comparative Example 4

[0081] This comparative example provides a modified polysilazane coating that combines flexibility and surface hardness, and its preparation method. The difference from Example 1 is that polyisobutylene is used instead of double-terminated silane-capped polyisobutylene. Other operating steps and process parameters are exactly the same as in Example 1.

[0082] The modified polysilazane coatings of Examples 1-4 and Comparative Examples 1-4, which combine flexibility and surface hardness, were subjected to performance tests. The specific process is as follows:

[0083] According to GB / T 1728-2020, the drying time of the sample after coating at room temperature was tested;

[0084] The hardness of the coating was tested according to GB / T 6739-2022;

[0085] The adhesion of the coating was tested according to GB / T 5210-2006;

[0086] The flexibility of the coating was tested according to GB / T 1731-2020;

[0087] The corrosion resistance of the coating was tested according to GB / T 10125-2021 (1000h).

[0088] The test results are shown in Table 1.

[0089] Table 1. Performance test results of modified polysilazane coatings with both flexibility and surface hardness in Examples 1-4 and Comparative Examples 1-4.

[0090]

[0091] As shown in Table 1, the test results of Example 1 and Comparative Example 1 reveal that without the addition of borate-modified polysiloxane, the conversion-promoting and densifying effects of the borate-modified polysiloxane are lacking. This results in a slower conversion of the organosilazane resin to the silicon-oxygen network during room temperature and humidity curing, leading to insufficient surface network rearrangement and thus prolonged surface drying and hard drying times. Due to the decreased connectivity and density of the surface silicon-oxygen network, the paint film is more prone to retaining micropores / microdefects, resulting in decreased hardness. Simultaneously, the effective interfacial load-bearing capacity and anti-permeation ability weaken, leading to decreased adhesion. Furthermore, the reduced cross-linking constraint makes the material more susceptible to deformation, manifesting as increased flexibility. However, due to the insufficient density of the shielding layer and the increased penetration channels, corrosive media can more easily reach the substrate, thus reducing corrosion resistance and making failure phenomena such as blistering or rust more likely.

[0092] As shown in Table 1, the test results of Example 1 and Comparative Example 2 indicate that using triisooctyl borate instead of borate esters to modify polysiloxanes, and considering that triisooctyl borate is a small molecule borate ester, is more prone to rapid hydrolysis under moisture, thus promoting early reaction initiation and shortening both surface drying and complete drying times. However, due to its lack of a polysiloxane backbone similar in structure to organopolysilazane resins, uneven distribution, excessively rapid local reactions, or accumulation of volatilization / micro-defects are more likely to occur in the system, resulting in insufficient surface densification stability and a decrease in hardness. Poor structural continuity near the interface also reduces adhesion. Simultaneously, accelerated early reactions and increased defect sensitivity reduce flexural tolerance, manifesting as decreased flexibility. In salt spray environments, pinhole defects are more likely to become penetration points, thus reducing corrosion resistance and making failures such as blistering or pitting more likely.

[0093] As shown in Table 1, the test results of Example 1 and Comparative Example 3 indicate that without the addition of silane-terminated polyisobutylene, the conversion-promoting effect of borate-modified polysiloxane is still retained, resulting in minimal changes in surface drying time and actual drying time. Due to the lack of buffering and dissipation from the internal flexible-to-hardened network, the system as a whole leans towards a high-modulus inorganic structure, making it easier to achieve a higher level of scratch resistance, thus increasing hardness; however, due to increased brittleness, it is more prone to cracking or splitting during bending, leading to a decrease in flexibility. In a salt spray environment, the propagation of microcracks or defects provides channels for media penetration, reducing corrosion resistance; adhesion remains largely unchanged.

[0094] As shown in Table 1, the test results of Example 1 and Comparative Example 4 reveal that when polyisobutylene is used instead of silane-terminated polyisobutylene, the polyisobutylene lacks hydrolyzable condensation end groups. This makes it difficult for the soft phase to form covalent bonds with the silicon-oxygen network during curing, leading to phase separation, coarsening, or migration, which interferes with film formation and network construction, thus prolonging surface drying and hardness. Soft phase migration and network weakening reduce surface load-bearing capacity and scratch resistance, resulting in decreased hardness. Disruption of interfacial continuity and effective cross-linking also leads to decreased adhesion. Although the introduction of rubber segments may bring some softening, the lack of anchoring of the soft phase and more pronounced defects and phase separation make it more prone to cracking or debonding during bending, resulting in decreased flexibility. In salt spray environments, phase separation defects and migration channels accelerate media penetration, reducing corrosion resistance and making significant blistering and rusting more likely.

[0095] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a modified polysilazane coating that combines flexibility and surface hardness, characterized in that, The preparation method includes: S1: Hydroxypolydimethylsiloxane and triisooctyl borate were pretreated by molecular sieve drying and then filtered through a plate and frame filter to obtain pretreated hydroxypolydimethylsiloxane and pretreated triisooctyl borate; the pretreated hydroxypolydimethylsiloxane was heated under nitrogen protection and pretreated triisooctyl borate was added dropwise to obtain reaction solution A. During the reaction, byproducts generated were continuously removed by micro-purging with nitrogen. After the reaction was completed, the system was depressurized and devolatilized, cooled and filtered to obtain borate-modified polysiloxane. S2: Add vinyl-silicon-terminated polyisobutylene to an isoalkane solvent to obtain a polymer solution; add Karstedt catalyst and heat to obtain reaction solution B; add triethoxysilane dropwise to obtain reaction solution C; after heat preservation reaction, use activated carbon adsorption filtration to remove residual catalyst to obtain pretreated solution; remove solvent and excess silane under vacuum to obtain double-terminated silane-terminated polyisobutylene. S3: Under a nitrogen atmosphere, butyl acetate and isoparaffin solvent are mixed to obtain a mixed solvent; organopolysilazane resin is mixed with the mixed solvent and dispersed to obtain a resin base liquid; double-terminated silane-capped polyisobutylene and compatibilizer are added sequentially and stirred to obtain dispersion D; borate ester modified polysiloxane is then added to obtain dispersion E; after stirring, interface anchoring agent and carbodiimide type water trapping agent are added; after continuing to stir, the mixture is filtered and sealed and packaged to obtain a modified polysilazane coating that has both flexibility and surface hardness.

2. The method for preparing a modified polysilazane coating possessing both flexibility and surface hardness according to claim 1, characterized in that, In S1: The pretreated hydroxyl polydimethylsiloxane was heated to 60-80°C under nitrogen protection; The molar ratio of boron atoms in the pretreated triisooctyl borate to hydroxyl atoms in the pretreated hydroxyl polydimethylsiloxane is (0.4-0.7):

1.

3. The method for preparing a modified polysilazane coating possessing both flexibility and surface hardness according to claim 1, characterized in that, In S1: The reaction temperature of reaction solution A is 100-120℃; The temperature for vacuum devolatilization is 110-130℃.

4. The method for preparing a modified polysilazane coating possessing both flexibility and surface hardness according to claim 1, characterized in that, In S2: The solid content of the polymer solution is 30-50%; The amount of Karstedt catalyst fed is 10-30 ppm of the mass of vinyl-silicon-terminated polyisobutylene.

5. The method for preparing a modified polysilazane coating possessing both flexibility and surface hardness according to claim 1, characterized in that, In S2: The temperature of the reaction solution B is 70-80℃; The molar ratio of the Si-H bond in the triethoxysilane to the carbon-carbon double bond in the vinyl-silicon-terminated polyisobutylene is (1.05-1.30):

1.

6. The method for preparing a modified polysilazane coating possessing both flexibility and surface hardness according to claim 1, characterized in that, In S3: The mass ratio of butyl acetate to isoparaffin solvent in the mixed solvent is (1.5-3.0):1; The mass ratio of the organopolysilazane resin to the mixed solvent is 100:(40-80).

7. The method for preparing a modified polysilazane coating possessing both flexibility and surface hardness according to claim 1, characterized in that, In S3: The mass ratio of the double-terminated silane-capped polyisobutylene to the organopolysilazane resin is (8-15):

100. The amount of compatibilizer added is 0.5%-1% of the mass of the organopolysilazane resin.

8. The method for preparing a modified polysilazane coating possessing both flexibility and surface hardness according to claim 1, characterized in that, In S3: The mass ratio of the borate-modified polysiloxane to the organopolysilazane resin is (3-6):

100. The dispersion E is stirred for 10-20 minutes.

9. The method for preparing a modified polysilazane coating possessing both flexibility and surface hardness according to claim 1, characterized in that, In S3: The amount of the interface anchoring agent added is 0.5-1% of the mass of the organopolysilazane resin; The amount of the carbodiimide-type water capture agent is 0.1-0.6% of the mass of the organopolysilazane resin.

10. A modified polysilazane coating with both flexibility and surface hardness prepared by the preparation method according to any one of claims 1-9.

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