Flame retardant coating and preparation method thereof

Abstract

The present application discloses a flame retardant coating and a preparation method thereof, relating to the field of coating technology, wherein the flame retardant coating raw materials include 100 parts of epoxy resin, 25-50 parts of hexagonal boron nitride functionalized modified ammonium polyphosphate, 20-30 parts of cerium cobalt iron layered double hydroxide, 10-15 parts of hafnium diboride, 8-16 parts of refractory filler, 18-30 parts of flux, and 20-25 parts of curing agent; the hexagonal boron nitride functionalized modified ammonium polyphosphate raw materials include 1-3 parts of functionalized boron nitride nanosheets, 5-10 parts of ammonium polyphosphate, 70-90 parts of ethanol, and 7-9 parts of water; the cerium cobalt iron layered double hydroxide raw materials include 3-4 parts of cerium nitrate hexahydrate, 2-4 parts of cobalt nitrate hexahydrate, 16-20 parts of ferric nitrate nonahydrate, 80-100 parts of deionized water, 20-30 parts of sodium hydroxide solution, and 60-80 parts of sodium carbonate solution. The flame retardant of the present application has excellent flame retardant properties.

Description

Technical Field

[0001] The present invention relates to the field of coating technology, and in particular to a flame retardant coating and a preparation method thereof. Background Art

[0002] With the increasing adoption of electric vehicles, the safety of lithium-ion battery packs has attracted significant attention. Battery failure can lead to hazards such as leakage and fire, making fire prevention crucial. Currently, fireproofing felt materials (such as mica sheets, high-silica wool felt, and ultra-fine glass wool) are commonly used as fireproofing materials for battery packs. However, these materials exhibit poor adhesion to irregular structures, limiting their application. In contrast, fire-retardant coatings adhere well to irregular structures, are easy to apply, can be sprayed directly, and offer excellent fire-resistant properties, making them a promising alternative to traditional fireproofing felt materials.

[0003] Epoxy resin (EP) is a commonly used thermosetting resin, widely used in coatings and other fields due to its excellent bond strength, low cure shrinkage, superior mechanical properties, and high chemical stability. To enhance its flame retardancy, flame retardants such as ammonium polyphosphate (APP) are often added. APP is a green and environmentally friendly inorganic flame retardant. As the acid source in intumescent flame retardant systems, APP decomposes during combustion to produce ammonia and polyphosphoric acid, which react with carbonizing agents to form a stable carbonized structure, thereby exerting its flame retardant effect.

[0004] However, although a high addition of ammonium polyphosphate can improve flame retardant properties, it often reduces the mechanical properties of epoxy resin, and its compatibility with polymers is poor, which limits its application in epoxy resin flame retardant coatings. Summary of the Invention

[0005] In order to solve the problems in the prior art, the present application provides a flame retardant coating and a preparation method thereof.

[0006] The present application provides a flame retardant coating, which adopts the following technical solution:

[0007] A flame retardant coating comprises, by weight, 100 parts of epoxy resin, 25-50 parts of hexagonal boron nitride functionalized modified ammonium polyphosphate, 20-30 parts of cerium cobalt iron layered double hydroxide, 10-15 parts of hafnium diboride, 8-16 parts of refractory filler, 18-30 parts of flux, and 20-25 parts of curing agent.

[0008] Preferably, the hexagonal boron nitride functionalized modified ammonium polyphosphate is prepared from the following raw materials in parts by weight: 1-3 parts of functionalized boron nitride nanosheets, 5-10 parts of ammonium polyphosphate, 70-90 parts of ethanol, and 7-9 parts of water.

[0009] Preferably, the functionalized boron nitride nanosheets are prepared from the following raw materials in parts by weight: 0.1-0.2 parts of 3-aminopropyltriethoxysilane, 2-4 parts of boron nitride nanosheets, 20-40 parts of ethanol, and 2-4 parts of water.

[0010] Preferably, the boron nitride nanosheets are prepared from the following raw materials in parts by weight: 10-20 parts of D-glucose, 20-30 parts of water, 2-4 parts of hexagonal boron nitride, and 100-200 parts of spherical grinding beads.

[0011] Preferably, the method for preparing the functionalized boron nitride nanosheets comprises the following steps:

[0012] 3-Aminopropyltriethoxysilane was added to a mixed solution of ethanol and water, and ultrasonication was performed for 20-30 minutes to hydrolyze the 3-aminopropyltriethoxysilane. Boron nitride nanosheets were then added to the solution, and stirred at 500-600 rpm and 75-85°C for 6-8 hours. The product was washed several times with ethanol-water solution and dried in a vacuum oven at 60-70°C to obtain functionalized boron nitride nanosheets.

[0013] Preferably, the method for preparing the boron nitride nanosheets comprises the following steps:

[0014] D-glucose is dissolved in water to prepare a D-glucose solution; hexagonal boron nitride is then added to the D-glucose solution, and after ultrasonic treatment for 20-30 minutes, the solution is transferred to an agate jar containing spherical grinding beads; ball milling is performed on a ball mill at a speed of 400-600 rpm for 12-14 hours; after the ball milling is completed, the resulting mixture is centrifuged and washed with water several times, and dried in a vacuum oven at 60-70°C to obtain boron nitride nanosheets.

[0015] Preferably, the preparation method of the hexagonal boron nitride functionalized modified ammonium polyphosphate comprises the following steps:

[0016] Functionalized boron nitride nanosheets and ammonium polyphosphate are dispersed in a mixed solution of ethanol and water, and stirred at a rotation speed of 1500-2500 rpm to form a suspension; the mixture is then stirred at a rotation speed of 500-600 rpm and a temperature of 60-70°C for 6-8 hours; after the mixture is cooled with ice water, washed several times with ethanol-water solution, and dried in a vacuum oven to obtain hexagonal boron nitride functionalized modified ammonium polyphosphate.

[0017] Preferably, the cerium-cobalt-iron layered double hydroxide is prepared from the following raw materials in parts by weight: 3-4 parts of cerium nitrate hexahydrate, 2-4 parts of cobalt nitrate hexahydrate, 16-20 parts of ferric nitrate nonahydrate, 80-100 parts of deionized water, 20-30 parts of 10% by mass sodium hydroxide solution, and 60-80 parts of 10% by mass sodium carbonate solution.

[0018] Preferably, the preparation method of the cerium-cobalt-iron layered double hydroxide comprises the following steps:

[0019] Cerium nitrate hexahydrate, cobalt nitrate hexahydrate, and ferric nitrate nonahydrate are added to 100 parts of deionized water and stirred to dissolve to obtain a mixed solution; the mixed solution is added dropwise to a 10% by mass sodium carbonate solution, and then a 10% by mass sodium hydroxide solution is added dropwise, and the mixture is stirred at room temperature for 3-5 hours, and then aged at room temperature for 10-14 hours; after suction filtration and washing with water until neutral, the product is freeze-dried for 24-30 hours, and ground to obtain cerium-cobalt-iron layered double hydroxide.

[0020] Preferably, the flux is silicon hexaboride.

[0021] Preferably, the refractory filler is a mixture of one or more of raw vermiculite powder and wollastonite powder.

[0022] This application also provides a method for preparing a flame retardant coating, which adopts the following technical solution:

[0023] A method for preparing a flame retardant coating comprises the following steps:

[0024] Hexagonal boron nitride functionalized modified ammonium polyphosphate, cerium cobalt iron layered double hydroxide, hafnium diboride, refractory filler and flux are added to epoxy resin to obtain a mixed solution; the mixed solution is ground multiple times at a rotation speed of 100-150 rpm for pre-dispersion, and finally a curing agent is added, and the mixture is dispersed with magnetic stirring at 500-600 rpm for 15-25 minutes to obtain a flame retardant coating.

[0025] In summary, this application includes at least one of the following beneficial technical effects:

[0026] 1. By adopting the above technical solution, this application uses epoxy resin as the base resin, hexagonal boron nitride functionalized modified ammonium polyphosphate, cerium cobalt iron layered double hydroxide as a flame retardant, and adds hafnium diboride and other refractory fillers. The resulting coating has excellent flame retardant properties and can withstand flame impact at 1400°C, significantly improving the safety of lithium batteries under extreme conditions, and is suitable for the lithium battery field.

[0027] 2. By adopting the above technical solution, the layered double hydroxide is a lamellar nanomaterial with good flame retardancy and thermal stability. This application synthesizes cerium-cobalt-iron layered double hydroxide by coprecipitation method, which not only further enhances the flame retardancy of the layered double hydroxide, but also effectively improves the impact resistance of the layered double hydroxide, and further improves the high-temperature stability of the layered double hydroxide.

[0028] 3. By adopting the above-mentioned technical solution, this application uses D-glucose to ball mill and peel off hexagonal boron nitride, and then uses 3-aminopropyltriethoxysilane to functionalize hexagonal boron nitride through a solution blending method, and uses functionalized boron nitride to modify ammonium polyphosphate. This not only effectively improves the temperature resistance and mechanical strength of the ammonium polyphosphate material, but also 3-aminopropyltriethoxysilane acts as a connecting bridge to significantly improve the compatibility of the ammonium polyphosphate material in epoxy resin coatings. DETAILED DESCRIPTION

[0029] The present application is further described in detail below with reference to the embodiments.

[0030] The chemical reagents used in the preparation examples, embodiments and comparative examples provided by the present invention are all commercially available products.

[0031] The epoxy resin used in the examples of the present application is a low molecular weight bisphenol A epoxy resin purchased from Hubei Zhonglong Kangsheng Fine Chemical Co., Ltd.

[0032] The curing agent used was curing agent 593, purchased from Jiangyin Wanqian Chemicals Co., Ltd.

[0033] Ammonium polyphosphate was purchased from Guangzhou Haoyu International Trade Co., Ltd. with purity of (N+P2O5)≥70.0%; P2O5≥48.0%; N≥23.0%.

[0034] Preparation Example 1 Preparation of hexagonal boron nitride functionalized modified ammonium polyphosphate

[0035] Preparation Example 1.1

[0036] S1. Dissolve 10 g of D-glucose in 20 g of water to prepare a D-glucose solution. Then, add 2 g of hexagonal boron nitride to the D-glucose solution. After sonication for 20 min, transfer the solution to an agate jar containing 100 g of spherical grinding beads. Mill the mixture in a planetary ball mill at 400 rpm for 12 h. After milling, centrifuge the resulting mixture, wash it three times with water, and dry it in a vacuum oven at 60°C to obtain boron nitride nanosheets.

[0037] S2. 0.1 g of 3-aminopropyltriethoxysilane was added to a mixed solution of 20 g of ethanol and 2 g of water. The 3-aminopropyltriethoxysilane was hydrolyzed by ultrasonication for 20 min. 2 g of boron nitride nanosheets were then added to the solution and stirred at 500 rpm and 75°C for 6 h. The product was washed three times with an ethanol-water solution and dried in a vacuum oven at 60°C to obtain functionalized boron nitride nanosheets.

[0038] S3. Disperse 1 g of functionalized boron nitride nanosheets and 5 g of ammonium polyphosphate in a mixed solution of 70 g of ethanol and 7 g of water, and stir at a rotation speed of 1500 rpm to form a suspension; then stir the mixture at a rotation speed of 500 rpm and a temperature of 60°C for 6 h; after the suspension, cool with ice water, wash three times with ethanol-water solution, and dry in a vacuum oven at 60°C to obtain hexagonal boron nitride functionalized modified ammonium polyphosphate.

[0039] Preparation Example 1.2

[0040] S1. 15 g of D-glucose was dissolved in 25 g of water to prepare a D-glucose solution. 3 g of hexagonal boron nitride was then added to the D-glucose solution. After ultrasonic treatment for 25 min, the solution was transferred to an agate jar containing 150 g of spherical grinding beads. The mixture was ball-milled at 500 rpm for 13 h on a planetary ball mill. After ball-milling, the resulting mixture was centrifuged, washed three times with water, and dried in a vacuum oven at 65°C to obtain boron nitride nanosheets.

[0041] S2. 0.15 g of 3-aminopropyltriethoxysilane was added to a mixed solution of 30 g of ethanol and 3 g of water. The 3-aminopropyltriethoxysilane was hydrolyzed by ultrasonication for 25 min. 3 g of boron nitride nanosheets were then added to the solution and stirred at 550 rpm and 80°C for 7 h. The product was washed three times with aqueous ethanol and dried in a vacuum oven at 65°C to obtain functionalized boron nitride nanosheets.

[0042] S3. Disperse 2 g of functionalized boron nitride nanosheets and 7.5 g of ammonium polyphosphate in a mixed solution of 80 g of ethanol and 8 g of water, and stir at a rotation speed of 2000 rpm to form a suspension; then stir the mixture at a rotation speed of 550 rpm and a temperature of 65°C for 7 h; after the suspension, cool with ice water, wash three times with ethanol-water solution, and dry in a vacuum oven at 65°C to obtain hexagonal boron nitride functionalized modified ammonium polyphosphate.

[0043] Preparation Example 1.3

[0044] S1. Dissolve 20 g of D-glucose in 30 g of water to prepare a D-glucose solution. Then, add 4 g of hexagonal boron nitride to the D-glucose solution. After ultrasonic treatment for 30 minutes, transfer the solution to an agate jar containing 200 g of spherical grinding beads. Mill the mixture at 600 rpm for 14 hours on a planetary ball mill. After milling, centrifuge the resulting mixture, wash it three times with water, and dry it in a vacuum oven at 70°C to obtain boron nitride nanosheets.

[0045] S2. 0.2 g of 3-aminopropyltriethoxysilane was added to a mixed solution of 40 g of ethanol and 4 g of water, and the mixture was sonicated for 30 min to hydrolyze the 3-aminopropyltriethoxysilane. 4 g of boron nitride nanosheets were then added to the solution, and the mixture was stirred at 600 rpm and 85°C for 8 h. The product was washed three times with an ethanol-water solution and dried in a vacuum oven at 70°C to obtain functionalized boron nitride nanosheets.

[0046] S3. Disperse 3 g of functionalized boron nitride nanosheets and 10 g of ammonium polyphosphate in a mixed solution of 90 g of ethanol and 9 g of water, and stir at a rotation speed of 2500 rpm to form a suspension; then stir the mixture at a rotation speed of 600 rpm and a temperature of 70°C for 8 h; after the suspension, cool with ice water, wash three times with ethanol-water solution, and dry in a vacuum oven at 70°C to obtain hexagonal boron nitride functionalized modified ammonium polyphosphate.

[0047] Preparation Example 2 Preparation of Cerium-Cobalt-Iron Layered Double Hydroxide

[0048] Preparation Example 2.1

[0049] 3 g of cerium nitrate hexahydrate, 2 g of cobalt nitrate hexahydrate, and 16 g of ferric nitrate nonahydrate were added to 80 g of deionized water and stirred to dissolve to obtain a mixed solution; the mixed solution was added dropwise to 60 g of a 10% by mass sodium carbonate solution, and then 20 g of a 10% by mass sodium hydroxide solution was added dropwise, stirred at room temperature for 3 h, and then aged at room temperature for 10 h; after filtration and washing with water until neutral, the product was freeze-dried for 24 h, and ball-milled on a planetary ball mill at 500 rpm to obtain a cerium-cobalt-iron layered double hydroxide.

[0050] Preparation Example 2.2

[0051] 3.5 g of cerium nitrate hexahydrate, 3 g of cobalt nitrate hexahydrate, and 18 g of ferric nitrate nonahydrate were added to 90 g of deionized water and stirred to dissolve to obtain a mixed solution; the mixed solution was added dropwise to 70 g of a 10% by mass sodium carbonate solution, and then 25 g of a 10% by mass sodium hydroxide solution was added dropwise, stirred at room temperature for 4 h, and then aged at room temperature for 12 h; after filtration and washing with water until neutral, the product was freeze-dried for 27 h, and ball-milled on a planetary ball mill at 550 rpm to obtain a cerium-cobalt-iron layered double hydroxide.

[0052] Preparation Example 2.3

[0053] 4 g of cerium nitrate hexahydrate, 4 g of cobalt nitrate hexahydrate, and 20 g of ferric nitrate nonahydrate were added to 100 g of deionized water and stirred to dissolve to obtain a mixed solution; the mixed solution was added dropwise to 80 g of a 10% by mass sodium carbonate solution, and then 30 g of a 10% by mass sodium hydroxide solution was added dropwise, and the mixture was stirred at room temperature for 5 h, and then aged at room temperature for 14 h; after filtration and washing with water until neutral, the product was freeze-dried for 30 h, and ball-milled on a planetary ball mill at 700 rpm to obtain a cerium-cobalt-iron layered double hydroxide. Example 1

[0054] 25 g of hexagonal boron nitride functionalized modified ammonium polyphosphate prepared in Preparation Example 1.1, 20 g of cerium cobalt iron layered double hydroxide prepared in Preparation Example 2.1, 10 g of hafnium diboride, 8 g of refractory filler and 18 g of silicon hexaboride were added to 100 g of low molecular weight bisphenol A epoxy resin to obtain a mixed solution; the mixed solution was ground several times at a rotation speed of 100 rpm for pre-dispersion, and finally 20 g of curing agent was added, and the mixture was magnetically stirred and dispersed at 500 rpm for 15 minutes to obtain a flame retardant coating; the refractory filler used in this embodiment is raw vermiculite powder. Example 2

[0055] 25 g of hexagonal boron nitride functionalized modified ammonium polyphosphate prepared in Preparation Example 1.1, 20 g of cerium cobalt iron layered double hydroxide prepared in Preparation Example 2.1, 10 g of hafnium diboride, 12 g of refractory filler and 24 g of silicon hexaboride were added to 100 g of low molecular weight bisphenol A epoxy resin to obtain a mixed solution; the mixed solution was ground several times at a rotation speed of 125 rpm for pre-dispersion, and finally 22.5 g of curing agent was added, and the mixture was magnetically stirred and dispersed at 550 rpm for 20 minutes to obtain a flame retardant coating; the refractory filler used in this embodiment was wollastonite powder. Example 3

[0056] 25 g of hexagonal boron nitride functionalized modified ammonium polyphosphate prepared in Preparation Example 1.1, 20 g of cerium cobalt iron layered double hydroxide prepared in Preparation Example 2.1, 10 g of hafnium diboride, 16 g of refractory filler and 30 g of silicon hexaboride were added to 100 g of low molecular weight bisphenol A epoxy resin to obtain a mixed solution; the mixed solution was ground several times at a rotation speed of 150 rpm for pre-dispersion, and finally 25 g of curing agent was added, and the mixture was magnetically stirred and dispersed at 600 rpm for 25 minutes to obtain a flame retardant coating; the refractory filler used in this embodiment is a mixture of raw vermiculite powder and wollastonite powder, with a mass ratio of 1:1. Example 4

[0057] The difference between Example 4 and Example 1 is that the mass of the hexagonal boron nitride functionalized modified ammonium polyphosphate used in Example 4 is 37.5 g, which comes from Preparation Example 1.1. Example 5

[0058] The difference between Example 5 and Example 1 is that the mass of the hexagonal boron nitride functionalized modified ammonium polyphosphate used in Example 5 is 50 g, which comes from Preparation Example 1.1. Example 6

[0059] The difference between Example 6 and Example 1 is that the mass of the hexagonal boron nitride functionalized modified ammonium polyphosphate used in Example 6 is 25 g, which comes from Preparation Example 1.2. Example 7

[0060] The difference between Example 7 and Example 1 is that the mass of the hexagonal boron nitride functionalized modified ammonium polyphosphate used in Example 7 is 25 g, which comes from Preparation Example 1.3. Example 8

[0061] The difference between Example 8 and Example 1 is that the mass of the cerium-cobalt-iron layered double hydroxide used in Example 8 is 25 g, which comes from Preparation Example 2.1. Example 9

[0062] The difference between Example 9 and Example 1 is that the mass of the cerium-cobalt-iron layered double hydroxide used in Example 9 is 30 g, which comes from Preparation Example 2.1. Example 10

[0063] The difference between Example 10 and Example 1 is that the mass of the cerium-cobalt-iron layered double hydroxide used in Example 10 is 20 g, which comes from Preparation Example 2.2. Example 11

[0064] The difference between Example 11 and Example 1 is that the mass of the cerium-cobalt-iron layered double hydroxide used in Example 11 is 20 g, which comes from Preparation Example 2.3. Example 12

[0065] The difference between Example 12 and Example 1 is that the mass of hafnium diboride used in Example 12 is 12.5 g. Example 13

[0066] The difference between Example 13 and Example 1 is that the mass of hafnium diboride used in Example 13 is 15 g.

[0067] Comparative Example 1

[0068] The difference between Comparative Example 1 and Example 1 is that the mass of the hexagonal boron nitride functionalized modified ammonium polyphosphate used in Comparative Example 1 is 15 g, which comes from Preparation Example 1.1.

[0069] Comparative Example 2

[0070] The difference between Comparative Example 2 and Example 1 is that the mass of the hexagonal boron nitride functionalized modified ammonium polyphosphate used in Comparative Example 2 is 60 g, which comes from Preparation Example 1.1.

[0071] Comparative Example 3

[0072] The difference between Comparative Example 3 and Example 1 is that in Comparative Example 3, an equal amount of ammonium polyphosphate is used instead of the hexagonal boron nitride functionalized modified ammonium polyphosphate.

[0073] Comparative Example 4

[0074] The difference between Comparative Example 4 and Example 1 is that the mass of the medium-cerium-cobalt-iron layered double hydroxide used in Comparative Example 4 is 15 g, which is from Preparation Example 2.1.

[0075] Comparative Example 5

[0076] The difference between Comparative Example 5 and Example 1 is that the mass of the cerium-cobalt-iron layered double hydroxide used in Comparative Example 5 is 35 g, which comes from Preparation Example 2.1.

[0077] Comparative Example 6

[0078] The difference between Comparative Example 6 and Example 1 is that in Comparative Example 6, cerium-cobalt-iron layered double hydroxide is not added.

[0079] Comparative Example 7

[0080] The difference between Comparative Example 7 and Example 1 is that the mass of hafnium diboride used in Comparative Example 7 is 5 g.

[0081] Comparative Example 8

[0082] The difference between Comparative Example 8 and Example 1 is that the mass of hafnium diboride used in Comparative Example 8 is 20 g.

[0083] Performance testing

[0084] The coatings prepared in Examples 1-13 and Comparative Examples 1-8 were evenly applied to steel plates to form a 1 mm thick coating, baked in an oven at 80°C for 30 min, and allowed to stand at room temperature for 24 h before testing.

[0085] (1) Flame retardancy: The flame retardancy of the coating was tested with reference to the UL94 Flame Retardancy Test Method and Standard. The results are shown in Table 1.

[0086] (2) Adhesion: The adhesion grade of the coating was tested with reference to GB / T 9286-2021 "Paints and varnishes - cross-cut test". The results are shown in Table 1.

[0087] (3) 1400℃ flame impact resistance: Use a 1400℃ flame spray gun to burn the middle of the sample for 5 minutes; observe whether the expanded carbon layer is complete. The results are shown in Table 1.

[0088] (4) 1400℃ flame impact back temperature: A 1400℃ flame spray gun was aimed at the middle of the front side of the sample and burned for 5 min. The back side temperature of the steel plate was recorded by an infrared thermometer. The results are shown in Table 1.

[0089] The specific test results are as follows:

[0090] Table 1 Performance test results

[0091]

[0092] It can be seen from the test results in Table 1 that the flame retardant coating provided in this application has a flame retardant grade of V0 and an adhesion of 0. Under the impact of a flame at 1400°C, the carbon layer can still remain intact and undamaged, and the back temperature is lower than 280°C, indicating that the coating provided in this application has good flame retardant properties and good adhesion.

[0093] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A flame retardant coating, characterized in that: The raw materials include, by weight, 100 parts of epoxy resin, 25-50 parts of hexagonal boron nitride functionalized modified ammonium polyphosphate, 20-30 parts of cerium cobalt iron layered double hydroxide, 10-15 parts of hafnium diboride, 8-16 parts of refractory filler, 18-30 parts of flux, and 20-25 parts of curing agent; The cerium-cobalt-iron layered double hydroxide is prepared from the following raw materials in parts by weight: 3-4 parts of cerium nitrate hexahydrate, 2-4 parts of cobalt nitrate hexahydrate, 16-20 parts of ferric nitrate nonahydrate, 80-100 parts of deionized water, 20-30 parts of 10% by mass sodium hydroxide solution, and 60-80 parts of 10% by mass sodium carbonate solution; The preparation method of the cerium-cobalt-iron layered double hydroxide comprises the following steps: adding cerium nitrate hexahydrate, cobalt nitrate hexahydrate, and ferric nitrate nonahydrate into deionized water and stirring to dissolve to obtain a mixed solution; adding the mixed solution dropwise into a 10% by mass sodium carbonate solution, and then adding dropwise a 10% by mass sodium hydroxide solution, stirring at room temperature for 3-5 hours, and then aging at room temperature for 10-14 hours; filtering and washing with water until neutral, freeze-drying the product for 24-30 hours, and grinding to obtain a cerium-cobalt-iron layered double hydroxide; The flux is silicon hexaboride; The refractory filler is wollastonite powder.

2. The flame retardant coating according to claim 1, characterized in that: The hexagonal boron nitride functionalized modified ammonium polyphosphate is prepared from the following raw materials in parts by weight: 1-3 parts of functionalized boron nitride nanosheets, 5-10 parts of ammonium polyphosphate, 70-90 parts of ethanol, and 7-9 parts of water.

3. The flame retardant coating according to claim 2, characterized in that: The functionalized boron nitride nanosheets are prepared from the following raw materials in parts by weight: 0.1-0.2 parts of 3-aminopropyltriethoxysilane, 2-4 parts of boron nitride nanosheets, 20-40 parts of ethanol, and 2-4 parts of water; The boron nitride nanosheets are prepared from the following raw materials in parts by weight: 10-20 parts of D-glucose, 20-30 parts of water, 2-4 parts of hexagonal boron nitride, and 100-200 parts of spherical grinding beads.

4. The flame retardant coating according to claim 3, characterized in that: The preparation method of the functionalized boron nitride nanosheets comprises the following steps: 3-aminopropyltriethoxysilane was added to a mixed solution of ethanol and water, and the solution was sonicated for 20-30 minutes to hydrolyze the 3-aminopropyltriethoxysilane. Boron nitride nanosheets were then added to the solution, and stirred at 500-600 rpm and 75-85°C for 6-8 hours. The product was washed several times with ethanol and water, and dried in a vacuum oven at 60-70°C to obtain functionalized boron nitride nanosheets. The method for preparing the boron nitride nanosheets comprises the following steps: D-glucose is dissolved in water to prepare a D-glucose solution; hexagonal boron nitride is then added to the D-glucose solution, and after ultrasonic treatment for 20-30 minutes, the solution is transferred to an agate jar containing spherical grinding beads; ball milling is performed on a ball mill at a speed of 400-600 rpm for 12-14 hours; after the ball milling is completed, the resulting mixture is centrifuged and washed with water several times, and dried in a vacuum oven at 60-70°C to obtain boron nitride nanosheets.

5. The flame retardant coating according to claim 2, characterized in that: The preparation method of the hexagonal boron nitride functionalized modified ammonium polyphosphate comprises the following steps: Functionalized boron nitride nanosheets and ammonium polyphosphate are dispersed in a mixed solution of ethanol and water, and stirred at a rotation speed of 1500-2500 rpm to form a suspension; the mixture is then stirred at a rotation speed of 500-600 rpm and a temperature of 60-70°C for 6-8 hours; after the mixture is cooled with ice water, washed several times with ethanol-water solution, and dried in a vacuum oven to obtain hexagonal boron nitride functionalized modified ammonium polyphosphate.

6. The method for preparing a flame retardant coating according to any one of claims 1 to 5, characterized in that: The following steps are involved: Hexagonal boron nitride functionalized modified ammonium polyphosphate, cerium cobalt iron layered double hydroxide, hafnium diboride, refractory filler and flux are added to epoxy resin to obtain a mixed solution; the mixed solution is ground multiple times at a rotation speed of 100-150 rpm for pre-dispersion, and finally a curing agent is added, and the mixture is dispersed with magnetic stirring at 500-600 rpm for 15-25 minutes to obtain a flame retardant coating.

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