An environmentally friendly ceramic-graphene composite insulating and protective coating and its preparation method

Abstract

This invention belongs to the field of protective coating technology and discloses an environmentally friendly ceramic-graphene composite insulating protective coating and its preparation method. The coating comprises an aqueous epoxy resin, an inorganic ceramic precursor film-forming component, a core-shell-interface modified insulating graphene functional filler, an aqueous curing agent, and additives. The functional filler includes a graphene core, an Al2O3 insulating shell continuously coated on its surface, and an epoxy reactive organosilicon interface layer grafted onto the outer surface of the Al2O3 insulating shell. By first preparing the functional filler and then compounding it with the aqueous epoxy resin and the inorganic ceramic precursor film-forming component to form a film, the resulting coating possesses excellent insulation, protection, and adhesion stability, making it suitable for insulating and protecting metal substrate surfaces.

Description

Technical Field

[0001] This invention belongs to the field of protective coating technology, specifically relating to an environmentally friendly ceramic-graphene composite insulating protective coating and its preparation method. Background Technology

[0002] With the increasing demands for surface insulation and protection performance in power equipment, metal components, and electronic devices, functional coatings that combine insulation, protection, and environmental friendliness have gradually become a research focus. Existing insulating and protective coatings mostly employ organic resin systems, which, while convenient to apply and with good adhesion, generally suffer from insufficient heat resistance, poor aging resistance, and limited long-term service stability. To improve the corrosion resistance, wear resistance, and density of coatings, graphene and its derivatives, due to their excellent sheet-like barrier and reinforcing effects, have been gradually introduced into coating systems. However, graphene itself has high conductivity; when directly used in insulating and protective coatings, it easily forms conductive pathways, affecting the volume resistivity and insulation stability of the coating, and may even trigger localized electrochemical corrosion risks on the metal substrate surface. On the other hand, ceramic materials possess good insulation, heat resistance, and chemical stability, but when used alone as a coating, they suffer from drawbacks such as high brittleness, easy cracking, and insufficient bonding with organic film-forming systems. While existing technologies have proposed composites of graphene with alumina or inorganic sols, most remain at the level of general composites or surface modifications, failing to effectively address the synergistic issues of graphene insulation, interfacial reactivity, and stable film formation in environmentally friendly aqueous systems. Therefore, there is an urgent need to provide a novel environmentally friendly ceramic-graphene composite insulating and protective coating and its preparation method, which can improve its insulating applicability while ensuring the barrier-reinforcing effect of graphene, and enhance its interfacial bonding with ceramic precursors and epoxy film-forming systems. Summary of the Invention

[0003] To address the shortcomings mentioned in the background art, the present invention aims to provide an environmentally friendly ceramic-graphene composite insulating and protective coating and its preparation method. By constructing a core-shell-interface modified insulating graphene functional filler consisting of a graphene core, a continuous Al2O3 insulating shell, and an outer epoxy reactive organosilicon interface layer, and introducing it into a film-forming system of aqueous epoxy resin and inorganic ceramic precursor, the coating's insulation performance, protective performance, and film-forming stability are synergistically improved.

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] An environmentally friendly ceramic-graphene composite insulating and protective coating comprises, by weight, the following components: 25-55 parts of waterborne epoxy resin, 10-35 parts of inorganic ceramic precursor film-forming component, 0.1-5 parts of core-shell-interface modified insulating graphene functional filler, 8-25 parts of waterborne curing agent, and 0.1-5 parts of additives.

[0006] The core-shell-interface modified insulating graphene functional filler includes a graphene core, an Al2O3 insulating shell continuously coated on the surface of the graphene core, and an epoxy reactive organosilicon interface layer grafted onto the outer surface of the Al2O3 insulating shell.

[0007] More preferably, the inorganic ceramic precursor film-forming component is selected from one or at least two of silica sol, alumina sol, and boehmite sol.

[0008] More preferably, the epoxy reactive organosilicon interface layer is an organosilicon layer formed by hydrolysis and condensation of one or two of γ-glycidoxypropyltrimethoxysilane and γ-glycidoxypropyltriethoxysilane, wherein the organosilicon layer is chemically bonded to the outer surface of the Al2O3 insulating shell, and the side of the organosilicon layer away from the Al2O3 insulating shell contains epoxy groups.

[0009] More preferably, the core-shell-interface modified insulating graphene functional filler is 0.2 to 2 parts, and the average thickness of the Al2O3 insulating shell is 2 to 30 nm.

[0010] More preferably, the core-shell-interface modified insulating graphene functional filler is a functional filler with graphene oxide or few-layer graphene as the core, an aluminum source precursor deposited on its surface to form a coating layer precursor, which is then dried and heat-treated to form a continuous Al2O3 insulating shell layer, and then pre-hydrolyzed epoxy functional silane grafted onto the outer surface of the Al2O3 insulating shell layer.

[0011] More preferably, the waterborne epoxy resin is selected from one or two of waterborne bisphenol A type epoxy resin and waterborne bisphenol F type epoxy resin, the waterborne curing agent is selected from one or two of waterborne amine curing agents and waterborne polyamide amine curing agents, and the additives include one or more of dispersants, defoamers and leveling agents.

[0012] A method for preparing an environmentally friendly ceramic-graphene composite insulating and protective coating includes the following steps:

[0013] S1. Graphene oxide or few-layer graphene is dispersed in an alcohol solvent, an aluminum source precursor is added and formed into a continuous coating layer precursor on the graphene surface, and after drying and heat treatment, a graphene intermediate with a continuous Al2O3 insulating shell on the surface is obtained.

[0014] S2. After pre-hydrolyzing the epoxy functional silane, it is reacted with the graphene intermediate to form an epoxy reactive organosilicon interface layer on the outer surface of the Al2O3 insulating shell, thus obtaining a core-shell-interface modified insulating graphene functional filler.

[0015] S3. Mix and disperse the core-shell-interface modified insulating graphene functional filler, waterborne epoxy resin, inorganic ceramic precursor film-forming component, additives and water to obtain component A, and formulate the waterborne curing agent as component B;

[0016] S4. Mix the components A and B, coat the mixture onto the substrate surface, and cure it to obtain an environmentally friendly ceramic-graphene composite insulating and protective coating.

[0017] More preferably, the aluminum source precursor is selected from one or more of aluminum isopropoxide, aluminum sec-butoxide, aluminum nitrate, aluminum chloride, and aluminum acetylacetonate, and the epoxy functional silane is selected from one or two of γ-glycidoxypropyltrimethoxysilane and γ-glycidoxypropyltriethoxysilane.

[0018] More preferably, the epoxy-functionalized silane is pre-hydrolyzed in a mixed system consisting of an alcohol solvent, deionized water, and an acid regulator, wherein the pH of the pre-hydrolyzed system is 3.5–5.5, and the grafting reaction temperature of the epoxy-functionalized silane with the graphene intermediate is 20–60°C.

[0019] More preferably, after mixing components A and B, a wet film is formed by coating, pre-curing at room temperature, and then curing by heating. The room temperature pre-curing time is 12-24 hours, the heating curing temperature is 50-80°C, and the heating curing time is 1-4 hours.

[0020] The beneficial effects of this invention are:

[0021] This invention constructs a core-shell-interface functional filler consisting of a graphene core, a continuous Al2O3 insulating shell, and an outer epoxy reactive organosilicon interface layer. This filler is then introduced into an environmentally friendly ceramic / epoxy composite film-forming system, enabling the coating to achieve insulation, protection, and film stability within the same structure. The graphene core utilizes its layered structure to extend the penetration paths of moisture, oxygen, and corrosive media within the coating, improving its density and shielding performance. The continuously coated Al2O3 insulating shell effectively isolates the conductive surface of the graphene, reducing the risk of conductive pathways formed by direct graphene exposure, thus improving the coating's insulation stability. The epoxy reactive organosilicon interface layer located on the outer surface of the Al2O3 shell can cure and bond with the epoxy film-forming system, while simultaneously improving the interfacial compatibility between the functional filler and the inorganic ceramic precursor. This allows the functional filler to be more stably embedded in the organic-inorganic composite film-forming network, reducing interfacial defects and local porosity. Therefore, the coating obtained by the present invention not only has excellent insulation and protection properties, but also helps to improve adhesion stability, resistance to media penetration and long-term reliability. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1: The environmentally friendly ceramic-graphene composite insulating protective coating comprises the following components: 25 parts of waterborne epoxy resin, 10 parts of inorganic ceramic precursor film-forming component, 0.1 parts of core-shell-interface modified insulating graphene functional filler, 8 parts of waterborne curing agent, and 0.1 parts of additives.

[0024] The preparation steps are as follows:

[0025] S1. Weigh 10g of graphene oxide and add it to 400g of anhydrous ethanol for ultrasonic dispersion for 30min; separately, dissolve 5g of aluminum isopropoxide in 50g of anhydrous ethanol to obtain an aluminum source precursor solution. Add the aluminum source precursor solution to the graphene oxide dispersion and stir for 2h to form a coating layer precursor on the surface of the graphene oxide. After the reaction is complete, remove the solvent to obtain precursor powder; heat-treat the precursor powder at 350℃ for 1h to obtain a graphene intermediate with a continuous Al2O3 insulating shell on the surface, the average thickness of which is 2nm.

[0026] S2. Take 1g of γ-glycidyl etheroxypropyltrimethoxysilane and add it to a mixed system consisting of 20g of ethanol, 5g of deionized water, and 0.18g of glacial acetic acid. Adjust the pH of the system to 3.5 and stir at room temperature for 30min to pre-hydrolyze it, obtaining a pre-hydrolyzed epoxy functional silane solution. Add the graphene intermediate obtained in step S1 to the pre-hydrolyzed solution and stir at 20℃ for 2h to graft the pre-hydrolyzed epoxy functional silane onto the outer surface of the Al2O3 insulating shell. After the reaction is complete, centrifuge the product, wash it twice with ethanol, and then vacuum dry it at 60℃ for 6h to obtain the core-shell-interface modified insulating graphene functional filler.

[0027] S3. Take 6g of silica sol and 4g of boehmite sol, and stir them evenly before use. Then weigh 25g of waterborne bisphenol A type epoxy resin emulsion (50% solid content), 0.10g of core-shell-interface modified insulating graphene functional filler obtained in step S2, 0.04g of ammonium polyacrylate dispersant, 0.03g of polyether modified silicone defoamer, 0.03g of polyether modified siloxane leveling agent, and 10g of deionized water. First, add the waterborne epoxy resin, silica sol, and boehmite sol to a dispersion container and mix for 10 minutes under stirring. Then add the core-shell-interface modified insulating graphene functional filler, dispersant, defoamer, leveling agent, and deionized water, and continue high-speed dispersion for 20 minutes to obtain a uniform component A. Separately weigh 8g of waterborne polyamide amine curing agent as component B.

[0028] S4. Using a steel plate as the substrate, before coating, perform acetone degreasing, sanding, and deionized water rinsing in sequence, and then dry at 60℃ for later use. Mix component A and component B obtained in step S3, stir evenly, and let stand for 10 minutes to remove bubbles; then evenly coat the resulting coating onto the pretreated steel plate surface to form a wet film. After coating, allow it to stand at room temperature to level, and pre-cur at room temperature for 12 hours; then heat and cure at 50℃ for 1 hour, and after cooling, obtain the environmentally friendly ceramic-graphene composite insulating protective coating.

[0029] Example 2: The environmentally friendly ceramic-graphene composite insulating protective coating comprises the following components: 55 parts of waterborne epoxy resin, 35 parts of inorganic ceramic precursor film-forming component, 5 parts of core-shell-interface modified insulating graphene functional filler, 25 parts of waterborne curing agent, and 5 parts of additives.

[0030] The preparation steps are as follows:

[0031] S1. Take commercially available graphene oxide powder and dry it at 60℃ for 4 hours. Weigh 10g of the dried graphene oxide and add it to 400g of anhydrous ethanol. Disperse it ultrasonically at room temperature for 30 minutes. Separately, take 35g of aluminum isopropoxide and add it to 120g of anhydrous ethanol. Stir at room temperature until completely dissolved, then add 3g of acetylacetone and continue stirring for 20 minutes to obtain an aluminum source precursor solution. Subsequently, slowly add the aluminum source precursor solution dropwise to the graphene oxide dispersion while stirring. The dropwise addition time is controlled at 30 minutes. After the dropwise addition is completed, continue stirring and reacting for 4 hours to form a continuous coating layer precursor on the surface of the graphene oxide. After the reaction is completed, remove the solvent from the resulting slurry under reduced pressure at 80℃ to obtain the precursor powder. Then, place the precursor powder in a furnace and treat it at 450℃ for 2 hours. Allow it to cool naturally to room temperature to obtain a graphene intermediate with a continuous Al2O3 insulating shell on the surface, wherein the average thickness of the Al2O3 insulating shell is controlled at 30nm.

[0032] S2. Take 1.5 g of γ-glycidyl etheroxypropyltrimethoxysilane and add it to a mixed system consisting of 30 g of ethanol, 8 g of deionized water, and 0.25 g of glacial acetic acid. Adjust the pH of the system to 5.5 and stir at room temperature for 30 min to obtain a pre-hydrolyzed epoxy functional silane solution. Add the graphene intermediate obtained in step S1 to the pre-hydrolyzed solution and stir at 60 °C for 2 h. After the reaction is complete, centrifuge the product, wash it twice with ethanol, and then vacuum dry it at 60 °C for 6 h to obtain the core-shell-interface modified insulating graphene functional filler.

[0033] S3. Take 21g of silica sol and 14g of boehmite sol, and stir them evenly before use. Then weigh 55g of waterborne bisphenol F type epoxy resin emulsion (50% solid content), 5g of core-shell-interface modified insulating graphene functional filler, 2g of ammonium polyacrylate dispersant, 1.5g of polyether-modified silicone defoamer, 1.5g of polyether-modified siloxane leveling agent, and 20g of deionized water. First, add the waterborne bisphenol F type epoxy resin emulsion, silica sol, and boehmite sol to a dispersion container and mix for 15 minutes under stirring. Then add the core-shell-interface modified insulating graphene functional filler, ammonium polyacrylate dispersant, polyether-modified silicone defoamer, polyether-modified siloxane leveling agent, and deionized water, and continue high-speed dispersion for 30 minutes to obtain a uniform component A. Separately weigh 25g of waterborne polyamide amine curing agent as component B.

[0034] S4. Using a steel plate as the substrate, before coating, perform acetone degreasing, sanding, and deionized water rinsing in sequence, and then dry at 60℃ for later use. Mix component A and component B obtained in step S3, stir evenly, and let stand for 10 minutes to remove bubbles; then uniformly coat the obtained coating onto the pretreated steel plate surface, controlling the wet film thickness to be 120-140 μm. After coating, allow it to stand at room temperature to level, and pre-cur at room temperature for 24 hours; then heat and cure at 80℃ for 4 hours, and after cooling, the environmentally friendly ceramic-graphene composite insulating protective coating is obtained.

[0035] Example 3: The environmentally friendly ceramic-graphene composite insulating protective coating comprises the following components: 40 parts of waterborne epoxy resin, 22.5 parts of inorganic ceramic precursor film-forming component, 2.55 parts of core-shell-interface modified insulating graphene functional filler, 16.5 parts of waterborne curing agent, and 2.55 parts of additives.

[0036] The preparation steps are as follows:

[0037] S1. Take graphene oxide powder and dry it at 60℃ for 4 hours. Weigh 10g of the dried graphene oxide and add it to 400g of anhydrous ethanol. Disperse it ultrasonically at room temperature for 30 minutes to obtain a uniform graphene oxide dispersion. Separately weigh 20g of aluminum isopropoxide and add it to 85g of anhydrous ethanol. Stir until completely dissolved, then add 1.5g of acetylacetone and continue stirring for 20 minutes to obtain an aluminum source precursor solution. Subsequently, under stirring conditions, slowly add the aluminum source precursor solution to the graphene oxide dispersion. The addition time is controlled at 30 minutes. After the addition is completed, continue stirring for 3 hours. After the reaction is completed, remove the solvent from the resulting slurry under reduced pressure at 80℃ to obtain precursor powder. Then place the precursor powder in a furnace and heat treat it at 400℃ for 1.5 hours. Allow it to cool naturally to room temperature to obtain a graphene intermediate with a continuous Al2O3 insulating shell on the surface, wherein the average thickness of the Al2O3 insulating shell is controlled at 16nm.

[0038] S2. Take 1.25 g of γ-glycidyl etheroxypropyltrimethoxysilane and add it to a mixed system consisting of 25 g of ethanol, 6.5 g of deionized water, and 0.22 g of glacial acetic acid. Adjust the pH of the system to 4.5 and stir at room temperature for 30 min to obtain a pre-hydrolyzed epoxy functional silane solution. Add the graphene intermediate obtained in step S1 to the pre-hydrolyzed solution and stir at 40 °C for 2 h. After the reaction is complete, centrifuge the product, wash it twice with ethanol, and then vacuum dry it at 60 °C for 6 h to obtain the core-shell-interface modified insulating graphene functional filler.

[0039] S3. Take 13.5g of silica sol and 9g of boehmite sol, and stir them evenly before use. Then weigh 40g of waterborne bisphenol A type epoxy resin emulsion (50% solid content), 2.55g of core-shell-interface modified insulating graphene functional filler obtained in step S2, 1.02g of ammonium polyacrylate dispersant, 0.77g of polyether modified silicone defoamer, 0.76g of polyether modified siloxane leveling agent, and 15g of deionized water. First, add the waterborne bisphenol A type epoxy resin emulsion, silica sol, and boehmite sol to a dispersion container and mix for 15 minutes under stirring. Then add the core-shell-interface modified insulating graphene functional filler, ammonium polyacrylate dispersant, polyether modified silicone defoamer, polyether modified siloxane leveling agent, and deionized water, and continue high-speed dispersion for 25 minutes to obtain a uniform component A. Separately weigh 16.5g of waterborne polyamide amine curing agent as component B.

[0040] S4. Using a steel plate as the substrate, before coating, perform acetone degreasing, sanding, and deionized water rinsing in sequence, and then dry at 60℃ for later use. Mix component A and component B obtained in step S3, stir evenly, and let stand for 10 minutes to remove bubbles; then uniformly coat the resulting coating onto the pretreated steel plate surface, controlling the wet film thickness to be 100-120 μm. After coating, allow it to stand at room temperature to level, and pre-cur at room temperature for 18 hours; then heat and cure at 65℃ for 2.5 hours. After cooling, the environmentally friendly ceramic-graphene composite insulating protective coating is obtained.

[0041] Comparative Example 1: The environmentally friendly ceramic-graphene composite insulating protective coating comprises the following components: 40 parts of waterborne epoxy resin, 22.5 parts of inorganic ceramic precursor film-forming component, 2.55 parts of graphene filler with a continuous Al2O3 insulating shell on the surface, 16.5 parts of waterborne curing agent, and 2.55 parts of additives.

[0042] The preparation steps are as follows:

[0043] S1. Take graphene oxide powder and dry it at 60℃ for 4 hours. Weigh 10g of the dried graphene oxide and add it to 400g of anhydrous ethanol. Disperse it ultrasonically at room temperature for 30 minutes to obtain a uniform graphene oxide dispersion. Separately weigh 20g of aluminum isopropoxide and add it to 85g of anhydrous ethanol. Stir until completely dissolved, then add 1.5g of acetylacetone and continue stirring for 20 minutes to obtain an aluminum source precursor solution. Subsequently, under stirring conditions, slowly add the aluminum source precursor solution to the graphene oxide dispersion. The addition time is controlled at 30 minutes. After the addition is completed, continue stirring for 3 hours. After the reaction is completed, remove the solvent from the resulting slurry under reduced pressure at 80℃ to obtain precursor powder. Then place the precursor powder in a furnace and heat treat it at 400℃ for 1.5 hours. Allow it to cool naturally to room temperature to obtain a graphene intermediate with a continuous Al2O3 insulating shell on the surface, wherein the average thickness of the Al2O3 insulating shell is controlled at 16nm.

[0044] S2. The graphene intermediate with a continuous Al2O3 insulating shell obtained in step S1 is used directly as a filler without further pre-hydrolysis grafting treatment of epoxy functional silane.

[0045] S3. Take 13.5g of silica sol and 9g of boehmite sol, and stir them evenly before use. Then weigh 40g of waterborne bisphenol A type epoxy resin emulsion (50% solid content), 2.55g of the comparative filler obtained in step S2, 1.02g of ammonium polyacrylate dispersant, 0.77g of polyether-modified silicone defoamer, 0.76g of polyether-modified siloxane leveling agent, and 15g of deionized water. First, add the waterborne bisphenol A type epoxy resin emulsion, silica sol, and boehmite sol to a dispersion container and mix for 15 minutes under stirring. Then add the comparative filler, ammonium polyacrylate dispersant, polyether-modified silicone defoamer, polyether-modified siloxane leveling agent, and deionized water, and continue high-speed dispersion for 25 minutes to obtain a uniform component A. Separately weigh 16.5g of waterborne polyamide amine curing agent as component B.

[0046] S4. Using a steel plate as the substrate, before coating, the plate is first degreased with acetone, sanded, rinsed with deionized water, and then dried at 60°C. Component A and component B obtained in step S3 are mixed, stirred evenly, and allowed to stand for 10 minutes to remove bubbles. The resulting coating is then evenly applied to the pretreated steel plate surface, controlling the wet film thickness to be 100–120 μm. After coating, the plate is allowed to stand at room temperature to level, and then pre-cured at room temperature for 18 hours. It is then heated and cured at 65°C for 2.5 hours. After cooling, the environmentally friendly ceramic-graphene composite insulating protective coating described in Comparative Example 1 is obtained.

[0047] Comparative Example 2: The environmentally friendly ceramic-graphene composite insulating and protective coating comprises the following components: 40 parts of waterborne epoxy resin, 22.5 parts of inorganic ceramic precursor film-forming component, 2.55 parts of epoxy functional silane modified graphene filler, 16.5 parts of waterborne curing agent, and 2.55 parts of additives.

[0048] The preparation steps are as follows:

[0049] S1. Take graphene oxide powder and dry it in a vacuum drying oven at 60℃ for 4 hours to remove adsorbed water; weigh 10g of the dried graphene oxide and add it to 400g of anhydrous ethanol, then ultrasonically disperse it at room temperature for 30 minutes to obtain a uniform graphene oxide dispersion. No aluminum source precursor was added in this comparative example, and no Al2O3 insulating shell construction treatment was performed.

[0050] S2. Take 1.25 g of γ-glycidyl etheroxypropyltrimethoxysilane and add it to a mixed system consisting of 25 g of ethanol, 6.5 g of deionized water, and 0.22 g of glacial acetic acid. Adjust the pH of the system to 4.5 and stir at room temperature for 30 min to pre-hydrolyze it, obtaining a pre-hydrolyzed epoxy-functionalized silane solution. Add the pre-hydrolyzed solution to the graphene oxide dispersion obtained in step S1 and stir at 40 °C for 2 h to graft the pre-hydrolyzed epoxy-functionalized silane onto the graphene oxide surface. After the reaction is complete, centrifuge the product, wash it twice with ethanol, and then vacuum dry it at 60 °C for 6 h to obtain epoxy-functionalized silane-modified graphene filler. The filler obtained in this comparative example does not have a continuous Al2O3 insulating shell.

[0051] S3. Take 13.5g of silica sol and 9g of boehmite sol, and stir them evenly before use. Then weigh 40g of waterborne bisphenol A type epoxy resin emulsion (50% solid content), 2.55g of epoxy functionalized silane-modified graphene filler obtained in step S2, 1.02g of ammonium polyacrylate dispersant, 0.77g of polyether-modified silicone defoamer, 0.76g of polyether-modified siloxane leveling agent, and 15g of deionized water. First, add the waterborne bisphenol A type epoxy resin emulsion, silica sol, and boehmite sol to a dispersion container and mix for 15 minutes under stirring. Then add the epoxy functionalized silane-modified graphene filler, ammonium polyacrylate dispersant, polyether-modified silicone defoamer, polyether-modified siloxane leveling agent, and deionized water, and continue high-speed dispersion for 25 minutes to obtain a uniform component A. Separately weigh 16.5g of waterborne polyamide amine curing agent as component B.

[0052] S4. Using a steel plate as the substrate, before coating, the plate is first degreased with acetone, sanded, rinsed with deionized water, and then dried at 60°C. Component A and component B obtained in step S3 are mixed, stirred evenly, and allowed to stand for 10 minutes to remove bubbles. The resulting coating is then evenly applied to the pretreated steel plate surface, controlling the wet film thickness to be 100–120 μm. After coating, the plate is allowed to stand at room temperature to level, and then pre-cured at room temperature for 18 hours. It is then heated and cured at 65°C for 2.5 hours. After cooling, the environmentally friendly ceramic-graphene composite insulating protective coating described in Comparative Example 2 is obtained.

[0053] Performance testing

[0054] 1. Electrical insulation performance test

[0055] Volume resistivity was tested according to GB / T 31838.2—2019, and surface resistivity was tested according to GB / T 31838.3—2019. The coatings obtained in each example and comparative example were made into free films or coated onto insulating substrates. The sample thickness was controlled at 100±10 μm, and the samples were placed at 23±2℃ and 50±5% relative humidity for 24 hours before testing. Volume resistivity and surface resistivity were measured using a high-resistivity meter. Breakdown field strength was tested according to GB / T 1408.1—2016 using a power frequency breakdown tester. Under standard electrode conditions, the voltage was gradually increased, and the sample breakdown voltage was recorded and converted into breakdown field strength. Each group of samples was tested 5 times, and the average value was taken. The results are shown in Table 1 below.

[0056] Table 1 Electrical insulation performance

[0057] sample Volume resistivity (Ω·cm) Surface resistivity (Ω / □) <![CDATA[Dielectric strength (kV·mm -1 )]]> Example 1 <![CDATA[3.5×10 14 ]]> <![CDATA[8.0×10 15 ]]> 18 Example 2 <![CDATA[4.2×10 14 ]]> <![CDATA[9.5×10 15 ]]> 20 Example 3 <![CDATA[1.1×10 15 ]]> <![CDATA[2.4×10 16 ]]> 28 Comparative Example 1 <![CDATA[2.8×10 14 ]]> <![CDATA[6.0×10 15 ]]> 16 Comparative Example 2 <![CDATA[6.5×10 9 ]]> <![CDATA[1.8×10 10 ]]> 6

[0058] As shown in Table 1, the volume resistivity, surface resistivity, and dielectric strength of Examples 1-3 are significantly higher than those of Comparative Examples 1 and 2, indicating that the core-shell-interface modified insulating graphene functional filler used in this invention can significantly improve the electrical insulation performance of the coating. Among them, the volume resistivity of Example 3 reaches 1.1 × 10⁻⁶. 15 Ω·cm, surface resistivity reaches 2.4×10 16 Ω / □, dielectric strength reaches 28kV·mm -1 The values ​​were the highest among all groups, indicating that under intermediate ratio conditions, the sheet-like effect of the graphene core, the isolation effect of the continuous Al2O3 insulating shell, and the interfacial synergistic effect of the outer epoxy reactive organosilicon interface layer could be effectively combined. Although Comparative Example 1 had a continuous Al2O3 insulating shell, the lack of an outer epoxy reactive organosilicon interface layer resulted in weaker interfacial bonding between the filler and the film-forming system, leading to lower insulation performance than Example 3. Comparative Example 2, lacking a continuous Al2O3 insulating shell, had a more easily exposed graphene conductive surface, resulting in a significant decrease in volume resistivity, surface resistivity, and dielectric strength. This demonstrates that the continuous Al2O3 insulating shell plays a crucial role in suppressing the formation of conductive pathways and improving the insulation stability of the coating.

[0059] 2. Protective performance test

[0060] The coatings obtained from each embodiment and comparative example were applied to pretreated steel plates, with a dry film thickness controlled at 100±10 μm, and placed at 23±2℃ and 50±5% relative humidity for 24 h. Electrochemical impedance spectroscopy was performed according to ISO 16773 series, and the 0.01Hz low-frequency impedance modulus |Z| was determined in 3.5wt% NaCl solution. Neutral salt spray test was conducted according to ASTM B117, and the blistering, corrosion, and gloss loss of the coating surface were observed after 500 h of continuous spraying. Water absorption rate was tested according to ASTM D570, and the mass water absorption rate was calculated by immersing the coating in deionized water for 24 h. Each group was tested in parallel for 5 times, and the average value was taken. The results are shown in Table 2 below.

[0061] Table 2 Protective performance results

[0062] sample 0.01Hz low-frequency impedance |Z| (Ω·cm²) Surface condition after 500 hours of salt spray Water absorption rate (%) Example 1 <![CDATA[6.5×10 9 ]]> Slight loss of gloss, no bubbling, no rust. 2.8 Example 2 <![CDATA[1.1×10 10 ]]> There was virtually no loss of gloss, no blistering, and no corrosion. 2.1 Example 3 <![CDATA[2.8×10 10 ]]> The surface is intact, with no loss of gloss, no blistering, and no rust. 1.3 Comparative Example 1 <![CDATA[4.2×10 8 ]]> Slight localized blistering, with no obvious rust at the edges. 3.4 Comparative Example 2 <![CDATA[9.0×10 6 ]]> Severe blistering, obvious corrosion, and localized loss of gloss and peeling of the coating. 5.9

[0063] As shown in Table 2, the protective performance of Examples 1 to 3 is superior to that of Comparative Examples 1 and 2, with Example 3 exhibiting the best performance, achieving a low-frequency impedance of 2.8 × 10⁻⁶ at 0.01 Hz. 10 The surface remained intact after 500 hours of salt spray (Ω·cm²), with the lowest water absorption rate of only 1.3%. Although Comparative Example 1 had a continuous Al₂O₃ insulating shell, the lack of an outer epoxy reactive silicone interface layer resulted in relatively insufficient interfacial bonding and film integrity, leading to lower protective performance than Example 3. Comparative Example 2, lacking a continuous Al₂O₃ insulating shell, had exposed graphene, resulting in a significantly increased coating water absorption rate, a significant decrease in low-frequency impedance, and severe blistering and corrosion after salt spray.

[0064] 3. Adhesion performance test

[0065] The coatings obtained in each embodiment and comparative example were uniformly applied to the pretreated steel plate surface, with the dry film thickness controlled at 100±10μm. The plates were then placed in a standard environment of 23±2℃ and 50±5% relative humidity for 24 hours to ensure complete curing before adhesion testing. Adhesion was evaluated using both the cross-cut test and the pull-off test. The cross-cut test was performed according to ISO 2409 standard (grade 0 being the optimal grade), and the pull-off test was performed according to ISO 4624 standard. Each sample was tested in parallel five times, and the average value was taken as the final test result. Specific test results are shown in Table 3.

[0066] Table 3 Coating Adhesion

[0067] sample Cross-grain adhesion (grade) Pull-off adhesion (MPa) Example 1 1 5.8 Example 2 1 6.5 Example 3 1 7.6 Comparative Example 1 2 4.9 Comparative Example 2 3 3.2

[0068] As shown in Table 3, the adhesion of Examples 1-3 is significantly better than that of Comparative Examples 1 and 2, indicating that the core-shell-interface modified insulating graphene functional filler used in this invention can effectively improve the interfacial bonding performance between the coating and the substrate and the film-forming system. Among them, Example 3 has a cross-cut adhesion grade of 1 and a pull-off adhesion of 7.6 MPa, showing the best overall adhesion performance. This indicates that under intermediate ratio conditions, the continuous Al2O3 insulating shell layer and the outer epoxy reactive organosilicon interface layer can achieve a good synergistic effect, allowing the functional filler to be more stably embedded in the composite film-forming network formed by the waterborne epoxy resin and the inorganic ceramic precursor.

[0069] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. An environmentally friendly ceramic-graphene composite insulating and protective coating, characterized in that, By weight, it includes the following components: 25-55 parts of waterborne epoxy resin, 10-35 parts of inorganic ceramic precursor film-forming component, 0.1-5 parts of core-shell-interface modified insulating graphene functional filler, 8-25 parts of waterborne curing agent, and 0.1-5 parts of additives. The core-shell-interface modified insulating graphene functional filler includes a graphene core, an Al2O3 insulating shell continuously coated on the surface of the graphene core, and an epoxy reactive organosilicon interface layer grafted onto the outer surface of the Al2O3 insulating shell.

2. The environmentally friendly ceramic-graphene composite insulating and protective coating according to claim 1, characterized in that, The inorganic ceramic precursor film-forming component is selected from one or at least two of silica sol, alumina sol, and boehmite sol.

3. The environmentally friendly ceramic-graphene composite insulating and protective coating according to claim 1, characterized in that, The epoxy reactive organosilicon interface layer is an organosilicon layer formed by hydrolysis and condensation of one or two of γ-glycidoxypropyltrimethoxysilane and γ-glycidoxypropyltriethoxysilane. The organosilicon layer is chemically bonded to the outer surface of the Al2O3 insulating shell, and the side of the organosilicon layer away from the Al2O3 insulating shell contains epoxy groups.

4. The environmentally friendly ceramic-graphene composite insulating and protective coating according to claim 1, characterized in that, The core-shell-interface modified insulating graphene functional filler is 0.2 to 2 parts, and the average thickness of the Al2O3 insulating shell is 2 to 30 nm.

5. The environmentally friendly ceramic-graphene composite insulating and protective coating according to claim 1, characterized in that, The core-shell-interface modified insulating graphene functional filler is a functional filler obtained by depositing an aluminum source precursor on the surface of graphene oxide or few-layer graphene as the core, forming a coating layer precursor, drying and heat treatment to form a continuous Al2O3 insulating shell, and then grafting pre-hydrolyzed epoxy functional silane onto the outer surface of the Al2O3 insulating shell.

6. The environmentally friendly ceramic-graphene composite insulating and protective coating according to claim 1, characterized in that, The waterborne epoxy resin is selected from one or two of waterborne bisphenol A type epoxy resin and waterborne bisphenol F type epoxy resin; the waterborne curing agent is selected from one or two of waterborne amine curing agent and waterborne polyamide amine curing agent; and the additives include one or more of dispersants, defoamers and leveling agents.

7. A method for preparing the environmentally friendly ceramic-graphene composite insulating and protective coating according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Graphene oxide or few-layer graphene is dispersed in an alcohol solvent, an aluminum source precursor is added and formed into a continuous coating layer precursor on the graphene surface, and after drying and heat treatment, a graphene intermediate with a continuous Al2O3 insulating shell on the surface is obtained. S2. After pre-hydrolyzing the epoxy functional silane, it is reacted with the graphene intermediate to form an epoxy reactive organosilicon interface layer on the outer surface of the Al2O3 insulating shell, thus obtaining a core-shell-interface modified insulating graphene functional filler. S3. Mix and disperse the core-shell-interface modified insulating graphene functional filler, waterborne epoxy resin, inorganic ceramic precursor film-forming component, additives and water to obtain component A, and formulate the waterborne curing agent as component B; S4. Mix the components A and B, coat the mixture onto the substrate surface, and cure it to obtain an environmentally friendly ceramic-graphene composite insulating and protective coating.

8. The preparation method according to claim 7, characterized in that, The aluminum source precursor is selected from one or more of aluminum isopropoxide, aluminum sec-butoxide, aluminum nitrate, aluminum chloride, and aluminum acetylacetone, and the epoxy functional silane is selected from one or two of γ-glycidoxypropyltrimethoxysilane and γ-glycidoxypropyltriethoxysilane.

9. The preparation method according to claim 7, characterized in that, The epoxy-functionalized silane is pre-hydrolyzed in a mixed system consisting of an alcohol solvent, deionized water, and an acid regulator, wherein the pH of the pre-hydrolyzed system is 3.5–5.5, and the grafting reaction temperature of the epoxy-functionalized silane with the graphene intermediate is 20–60°C.

10. The preparation method according to claim 7, characterized in that, After mixing components A and B, a wet film is formed by coating. The film is pre-cured at room temperature and then cured by heating. The pre-curing time at room temperature is 12-24 hours, the curing temperature is 50-80℃, and the curing time is 1-4 hours.