Flame-retardant coating and preparation method thereof

Abstract

The invention discloses a flame-retardant coating and a preparation method thereof, and relates to the technical field of coatings, the flame-retardant coating comprises the following raw materials: 100 parts of epoxy resin, 25-50 parts of hexagonal boron nitride functional modified ammonium polyphosphate, 20-30 parts of cerium-cobalt-iron layered double hydroxide, 10-15 parts of hafnium diboride, 8-16 parts of a fireproof filler, 18-30 parts of a fluxing agent, and 20-25 parts of a curing agent; 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. The cerium-cobalt-iron layered double hydroxide comprises the following raw materials: 3-4 parts of cerium nitrate hexahydrate, 2-4 parts of cobalt nitrate hexahydrate, 16-20 parts of iron nitrate nonahydrate, 80-100 parts of deionized water, 20-30 parts of a sodium hydroxide solution and 60-80 parts of a sodium carbonate solution. The flame retardant provided by the invention has excellent flame retardant property.

Description

Technical Field

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

[0002] With the development of automotive electrification, the safety issues of lithium-ion battery packs have attracted much attention. Battery failures may lead to dangers such as electric leakage and fire, so fire protection is crucial. Currently, common fireproof felt materials (such as mica plates, high-silica oxygen cotton felt, ultra-fine glass wool, etc.) are used as fireproof materials for battery packs, but their adhesion to irregular structures is poor and construction is limited. In contrast, fire retardant coatings have good adhesion to irregular structures, are convenient for construction, can be directly sprayed, and have excellent fireproof performance, and are expected to replace traditional fireproof felt materials.

[0003] Epoxy resin (EP) is a commonly used thermosetting resin. Due to its excellent bonding strength, low curing shrinkage rate, good mechanical properties, and high chemical stability, it is widely used in fields such as coatings. To improve its flame retardancy, flame retardants such as ammonium polyphosphate (APP) are often added. Ammonium polyphosphate is a green and environmentally friendly inorganic flame retardant. As the acid source in the intumescent flame retardant system, it will decompose into ammonia and polyphosphoric acid during combustion, react with the charring agent to form a stable charred structure, thereby playing a flame retardant role.

[0004] However, although a high addition amount of ammonium polyphosphate can improve the flame retardant performance, 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 flame retardant coating provided by the present application adopts the following technical scheme: A flame retardant coating, the raw materials include 100 parts by weight of epoxy resin, 25 - 50 parts by weight of hexagonal boron nitride functionalized ammonium polyphosphate, 20 - 30 parts by weight of cerium cobalt iron layered double hydroxide, 10 - 15 parts by weight of hafnium diboride, 8 - 16 parts by weight of refractory filler, 18 - 30 parts of flux, and 20 - 25 parts of curing agent.

[0007] Preferably, the hexagonal boron nitride functionalized 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.

[0008] 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.

[0009] 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.

[0010] Preferably, the preparation method of the functionalized boron nitride nanosheets comprises the following steps: Add 3-aminopropyltriethoxysilane to the mixed solution of ethanol and water, and ultrasonically hydrolyze 3-aminopropyltriethoxysilane for 20-30 min; then add boron nitride nanosheets to the solution, and stir at 500-600 rpm and 75-85 °C for 6-8 h; wash the product several times with an ethanol aqueous solution, and dry it in a vacuum oven at 60-70 °C to obtain the functionalized boron nitride nanosheets.

[0011] Preferably, the preparation method of the boron nitride nanosheets comprises the following steps: Dissolve D-glucose in water to prepare a D-glucose solution; then add hexagonal boron nitride to the D-glucose solution, ultrasonically treat it for 20-30 min, and transfer it to an agate jar containing spherical grinding beads; perform ball milling on a ball mill at a rotation speed of 400-600 rpm for 12-14 h; after the ball milling is completed, centrifuge the obtained mixture and wash it several times with water, and dry it in a vacuum oven at 60-70 °C to obtain the boron nitride nanosheets.

[0012] Preferably, the preparation method of the hexagonal boron nitride-functionalized ammonium polyphosphate comprises the following steps: Disperse the functionalized boron nitride nanosheets and ammonium polyphosphate in the mixed solution of ethanol and water, and stir into a suspension at a rotation speed of 1500-2500 rpm; then stir the mixture at a rotation speed of 500-600 rpm and a temperature of 60-70 °C for 6-8 h; after completion, cool it with ice water, wash it several times with an ethanol aqueous solution, and dry it in a vacuum oven to obtain the hexagonal boron nitride-functionalized ammonium polyphosphate.

[0013] 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 iron nitrate nonahydrate, 80-100 parts of deionized water, 20-30 parts of a 10% sodium hydroxide solution, and 60-80 parts of a 10% sodium carbonate solution.

[0014] Preferably, the preparation method of the cerium cobalt iron layered double hydroxide comprises the following steps: Cerium nitrate hexahydrate, cobalt nitrate hexahydrate, and iron nitrate nonahydrate were added to 100 parts of deionized water and stirred until dissolved to obtain a mixed solution; the mixed solution was added dropwise to a 10% sodium carbonate solution, and then a 10% sodium hydroxide solution was added dropwise. After stirring at room temperature for 3 - 5 h, it was aged at room temperature for 10 - 14 h; after suction filtration and washing with water until neutral, the product was freeze-dried for 24 - 30 h, and after grinding treatment, cerium cobalt iron layered double hydroxide was obtained.

[0015] Preferably, the flux is silicon hexaboride.

[0016] Preferably, the refractory filler is one or a mixture of raw vermiculite powder and wollastonite powder.

[0017] This application also provides a preparation method of a flame retardant coating, adopting the following technical solution: A preparation method of a flame retardant coating, comprising the following steps: Hexagonal boron nitride functionalized modified ammonium polyphosphate, cerium cobalt iron layered double hydroxide, hafnium diboride, refractory filler, and flux were added to epoxy resin to obtain a mixed solution; the mixed solution was ground multiple times at a rotation speed of 100 - 150 rpm for pre-dispersion, and finally a curing agent was added, and magnetic stirring dispersion was carried out at 500 - 600 rpm for 15 - 25 min to obtain the flame retardant coating.

[0018] In summary, this application includes at least one of the following beneficial technical effects: 1. By adopting the above technical solution, this application uses epoxy resin as the matrix resin, hexagonal boron nitride functionalized modified ammonium polyphosphate and cerium cobalt iron layered double hydroxide are compounded as flame retardants, and hafnium diboride and other refractory fillers are added. The obtained coating has excellent flame retardant performance, can withstand the flame impact of 1400 °C, significantly improves the safety of lithium batteries under extreme conditions, and is applicable to the field of lithium batteries.

[0019] 2. By adopting the above technical solution, the layered double hydroxide is a lamellar nanomaterial with good flame retardancy and thermal stability. In this application, cerium cobalt iron layered double hydroxide is synthesized by the co-precipitation method, which not only further enhances the flame retardant performance 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.

[0020] 3. By adopting the above technical solution, this application uses D-glucose to ball mill and exfoliate hexagonal boron nitride, and then functionalizes hexagonal boron nitride by the solution blending method using 3-aminopropyltriethoxysilane. The functionalized boron nitride is used to modify ammonium polyphosphate, which not only effectively improves the temperature resistance and mechanical strength of the ammonium polyphosphate material, but also 3-aminopropyltriethoxysilane acts as a connecting bridge, which can significantly improve the compatibility of the ammonium polyphosphate material in the epoxy resin coating. Detailed implementation manners

[0021] The following further elaborates on this application in conjunction with embodiments.

[0022] The chemical reagents used in the preparation examples, embodiment and comparative examples provided by the present invention are all commercially available products. The epoxy resin used in the embodiment of this application is a low-molecular-weight bisphenol A epoxy resin, purchased from Hubei Zhonglong Kangsheng Fine Chemical Co., Ltd.; The curing agent used is curing agent 593, purchased from Jiangyin Wanqian Chemical Co., Ltd.; Ammonium polyphosphate is purchased from Guangzhou Haoyu International Trade Co., Ltd., purity: (N + P2O5) ≥ 70.0%; P2O5 ≥ 48.0%; N ≥ 23.0%.

[0023] Preparation Example 1 Preparation of hexagonal boron nitride-functionalized modified ammonium polyphosphate Preparation Example 1.1 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, ultrasonically treat for 20 min and transfer it to an agate jar containing 100 g of spherical grinding beads; perform ball milling on a planetary ball mill at a speed of 400 rpm for 12 h; after the ball milling is completed, centrifuge the obtained mixture and wash it with water 3 times, and dry it in a vacuum oven at 60 °C to obtain boron nitride nanosheets; S2. Add 0.1 g of 3-aminopropyltriethoxysilane to a mixed solution of 20 g of ethanol and 2 g of water, and ultrasonically treat for 20 min to hydrolyze 3-aminopropyltriethoxysilane; then add 2 g of boron nitride nanosheets to the solution, and stir at 500 rpm and 75 °C for 6 h; wash the product 3 times with an ethanol aqueous solution, and dry it in a vacuum oven at 60 °C to obtain functionalized boron nitride nanosheets; 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 into a suspension at a speed of 1500 rpm; then stir the mixture at a speed of 500 rpm and a temperature of 60 °C for 6 h; after completion, cool with ice water, wash 3 times with an ethanol aqueous solution, and dry in a vacuum oven at 60 °C to obtain hexagonal boron nitride-functionalized modified ammonium polyphosphate.

[0024] Preparation Example 1.2 S1. Dissolve 15 g of D-glucose in 25 g of water to prepare a D-glucose solution; then add 3 g of hexagonal boron nitride to the D-glucose solution, transfer it to an agate jar containing 150 g of spherical grinding beads after ultrasonic treatment for 25 min; perform ball milling on a planetary ball mill at a speed of 500 rpm for 13 h; after the ball milling is completed, centrifuge the obtained mixture and wash it 3 times with water, and dry it in a vacuum oven at 65 °C to obtain boron nitride nanosheets; S2. Add 0.15 g of 3-aminopropyltriethoxysilane to a mixed solution of 30 g of ethanol and 3 g of water, and ultrasonically hydrolyze 3-aminopropyltriethoxysilane for 25 min; then add 3 g of boron nitride nanosheets to the solution, and stir at 550 rpm and 80 °C for 7 h; wash the product 3 times with an ethanol aqueous solution, and dry it in a vacuum oven at 65 °C to obtain functionalized boron nitride nanosheets; 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 into a suspension at a speed of 2000 rpm; then stir the mixture at a speed of 550 rpm and a temperature of 65 °C for 7 h; after completion, cool it with ice water, wash it 3 times with an ethanol aqueous solution, and dry it in a vacuum oven at 65 °C to obtain hexagonal boron nitride functionalized and modified ammonium polyphosphate.

[0025] Preparation Example 1.3 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, transfer it to an agate jar containing 200 g of spherical grinding beads after ultrasonic treatment for 30 min; perform ball milling on a planetary ball mill at a speed of 600 rpm for 14 h; after the ball milling is completed, centrifuge the obtained mixture and wash it 3 times with water, and dry it in a vacuum oven at 70 °C to obtain boron nitride nanosheets; S2. Add 0.2 g of 3-aminopropyltriethoxysilane to a mixed solution of 40 g of ethanol and 4 g of water, and ultrasonically hydrolyze 3-aminopropyltriethoxysilane for 30 min; then add 4 g of boron nitride nanosheets to the solution, and stir at 600 rpm and 85 °C for 8 h; wash the product 3 times with an ethanol aqueous solution, and dry it in a vacuum oven at 70 °C to obtain functionalized boron nitride nanosheets; 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 into a suspension at a speed of 2500 rpm; then stir the mixture at a speed of 600 rpm and a temperature of 70 °C for 8 h; after completion, cool it with ice water, wash it 3 times with an ethanol aqueous solution, and dry it in a vacuum oven at 70 °C to obtain hexagonal boron nitride functionalized and modified ammonium polyphosphate.

[0026] Preparation Example 2 Preparation of Cerium Cobalt Iron Layered Double Hydroxide Preparation Example 2.1 Dissolve 3 g of cerium nitrate hexahydrate, 2 g of cobalt nitrate hexahydrate, and 16 g of iron nitrate nonahydrate in 80 g of deionized water with stirring to obtain a mixed solution; add the mixed solution dropwise to 60 g of a 10% sodium carbonate solution by mass, then add 20 g of a 10% sodium hydroxide solution by mass. After stirring at room temperature for 3 h, age at room temperature for 10 h; after suction filtration and washing with water until neutral, freeze-dry the product for 24 h, and then perform ball milling treatment on a planetary ball mill at a rotation speed of 500 rpm to obtain cerium cobalt iron layered double hydroxide.

[0027] Preparation Example 2.2 Dissolve 3.5 g of cerium nitrate hexahydrate, 3 g of cobalt nitrate hexahydrate, and 18 g of iron nitrate nonahydrate in 90 g of deionized water with stirring to obtain a mixed solution; add the mixed solution dropwise to 70 g of a 10% sodium carbonate solution by mass, then add 25 g of a 10% sodium hydroxide solution by mass. After stirring at room temperature for 4 h, age at room temperature for 12 h; after suction filtration and washing with water until neutral, freeze-dry the product for 27 h, and then perform ball milling treatment on a planetary ball mill at a rotation speed of 550 rpm to obtain cerium cobalt iron layered double hydroxide.

[0028] Preparation Example 2.3 Dissolve 4 g of cerium nitrate hexahydrate, 4 g of cobalt nitrate hexahydrate, and 20 g of iron nitrate nonahydrate in 100 g of deionized water with stirring to obtain a mixed solution; add the mixed solution dropwise to 80 g of a 10% sodium carbonate solution by mass, then add 30 g of a 10% sodium hydroxide solution by mass. After stirring at room temperature for 5 h, age at room temperature for 14 h; after suction filtration and washing with water until neutral, freeze-dry the product for 30 h, and then perform ball milling treatment on a planetary ball mill at a rotation speed of 700 rpm to obtain cerium cobalt iron layered double hydroxide. Example 1

[0029] Add 25 g of hexagonal boron nitride functionalized and 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 to 100 g of low molecular weight bisphenol A epoxy resin to obtain a mixed solution; grind the mixed solution multiple times at a rotation speed of 100 rpm for pre-dispersion, and finally add 20 g of curing agent, and stir and disperse magnetically at 500 rpm for 15 min to prepare a flame retardant coating; the refractory filler used in this example is raw vermiculite powder. Example 2

[0030] Add 25 g of the hexagonal boron nitride functionalized and modified ammonium polyphosphate prepared in Preparation Example 1.1, 20 g of the 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 to 100 g of low molecular weight bisphenol A epoxy resin to obtain a mixed solution; grind the mixed solution multiple times at a rotation speed of 125 rpm for pre-dispersion, and finally add 22.5 g of curing agent, and magnetically stir and disperse at 550 rpm for 20 min to obtain a flame retardant coating; the refractory filler used in this example is wollastonite powder. Example 3

[0031] Add 25 g of the hexagonal boron nitride functionalized and modified ammonium polyphosphate prepared in Preparation Example 1.1, 20 g of the 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 to 100 g of low molecular weight bisphenol A epoxy resin to obtain a mixed solution; grind the mixed solution multiple times at a rotation speed of 150 rpm for pre-dispersion, and finally add 25 g of curing agent, and magnetically stir and disperse at 600 rpm for 25 min to obtain a flame retardant coating; the refractory filler used in this example is a mixture of raw vermiculite powder and wollastonite powder, and the mass ratio is 1:1. Example 4

[0032] The difference between Example 4 and Example 1 is that the mass of the hexagonal boron nitride functionalized and modified ammonium polyphosphate used in Example 4 is 37.5 g, which is from Preparation Example 1.1. Example 5

[0033] The difference between Example 5 and Example 1 is that the mass of the hexagonal boron nitride functionalized and modified ammonium polyphosphate used in Example 5 is 50 g, which is from Preparation Example 1.1. Example 6

[0034] The difference between Example 6 and Example 1 is that the mass of the hexagonal boron nitride functionalized and modified ammonium polyphosphate used in Example 6 is 25 g, which is from Preparation Example 1.2. Example 7

[0035] The difference between Example 7 and Example 1 is that the mass of the hexagonal boron nitride functionalized and modified ammonium polyphosphate used in Example 7 is 25 g, which is from Preparation Example 1.3. Example 8

[0036] 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 is from Preparation Example 2.1. Example 9

[0037] Example 9 is different from Example 1 in that the mass of the cerium cobalt iron layered double hydroxide used in Example 9 is 30 g, which is from Preparation Example 2.1. Example 10

[0038] Example 10 is different from Example 1 in that the mass of the cerium cobalt iron layered double hydroxide used in Example 10 is 20 g, which is from Preparation Example 2.2. Example 11

[0039] Example 11 is different from Example 1 in that the mass of the cerium cobalt iron layered double hydroxide used in Example 11 is 20 g, which is from Preparation Example 2.3. Example 12

[0040] Example 12 is different from Example 1 in that the mass of hafnium diboride used in Example 12 is 12.5 g. Example 13

[0041] Example 13 is different from Example 1 in that the mass of hafnium diboride used in Example 13 is 15 g.

[0042] Comparative Example 1 Comparative Example 1 is different from Example 1 in that the mass of the hexagonal boron nitride functionalized ammonium polyphosphate used in Comparative Example 1 is 15 g, which is from Preparation Example 1.1.

[0043] Comparative Example 2 Comparative Example 2 is different from Example 1 in that the mass of the hexagonal boron nitride functionalized ammonium polyphosphate used in Comparative Example 2 is 60 g, which is from Preparation Example 1.1.

[0044] Comparative Example 3 Comparative Example 3 is different from Example 1 in that an equal amount of ammonium polyphosphate is used in Comparative Example 3 to replace the hexagonal boron nitride functionalized ammonium polyphosphate.

[0045] Comparative Example 4 Comparative Example 4 is different from Example 1 in that the mass of the cerium cobalt iron layered double hydroxide used in Comparative Example 4 is 15 g, which is from Preparation Example 2.1.

[0046] Comparative Example 5 Comparative Example 5 is different from Example 1 in that the mass of the cerium cobalt iron layered double hydroxide used in Comparative Example 5 is 35 g, which is from Preparation Example 2.1.

[0047] Comparative Example 6 Comparative Example 6 is different from Example 1 in that no cerium cobalt iron layered double hydroxide is added in Comparative Example 6.

[0048] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that the mass of hafnium diboride used in Comparative Example 7 is 5 g.

[0049] Comparative Example 8 The difference between Comparative Example 8 and Example 1 is that the mass of hafnium diboride used in Comparative Example 8 is 20 g.

[0050] Performance Detection Test The coatings prepared in Examples 1 - 13 and Comparative Examples 1 - 8 were evenly coated on steel plates to form a 1 - mm - thick coating, baked in an oven at 80 °C for 30 min, and left to stand at room temperature for 24 h before testing; (1) Flame retardancy: The flame retardancy of the coating was detected with reference to the "UL94 Flame Retardancy Test Method and Standard", and the results are shown in Table 1.

[0051] (2) Adhesion: The adhesion grade of the coating was tested with reference to GB / T 9286 - 2021 "Paints and Varnishes - Cross - cut Test", and the results are shown in Table 1.

[0052] (3) Flame impact resistance at 1400 °C: A 1400 °C flame spray gun was aimed at the middle of the sample and burned for 5 min; observe whether the expanded carbon layer is intact, and the results are shown in Table 1.

[0053] (4) Back - side temperature under 1400 °C flame impact: A 1400 °C flame spray gun was aimed at the middle of the front of the sample and burned for 5 min, and the temperature on the back of the steel plate was recorded by an infrared thermometer, and the results are shown in Table 1.

[0054] The specific detection results are as follows: Table 1 Performance Detection Results

[0055] It can be seen from the detection results in Table 1 that the flame - retardant coating provided by this application has a flame - retardant grade reaching V0, an adhesion reaching grade 0. Under the flame impact at 1400 °C, the carbon layer can still remain intact without damage, and the back - side temperature is lower than 280 °C, indicating that the coating provided by this application has good flame - retardant properties and good adhesion.

[0056] This specific embodiment is only an interpretation of this application, and it does not limit this application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as they are within the scope of the claims of this application, they are protected by the patent law.

Claims

1. A flame retardant coating, characterized in that: The raw materials include 100 parts by weight of epoxy resin, 25 - 50 parts by weight of hexagonal boron nitride functionalized modified ammonium polyphosphate, 20 - 30 parts by weight of cerium cobalt iron layered double hydroxide, 10 - 15 parts by weight of hafnium diboride, 8 - 16 parts by weight of refractory filler, 18 - 30 parts by weight of flux, and 20 - 25 parts by weight of curing agent.

2. A 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, wherein: 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. A flame retardant coating according to claim 3, characterized in that: The preparation method of the functionalized boron nitride nanosheets includes the following steps: Add 3 - aminopropyltriethoxysilane to the mixed solution of ethanol and water, and ultrasonically hydrolyze 3 - aminopropyltriethoxysilane for 20 - 30 min; then add boron nitride nanosheets to the solution, and stir at 500 - 600 rpm and 75 - 85 °C for 6 - 8 h; wash the product several times with an ethanol - aqueous solution, and dry it in a vacuum oven at 60 - 70 °C to obtain functionalized boron nitride nanosheets; The preparation method of the boron nitride nanosheets includes the following steps: Dissolve D - glucose in water to prepare a D - glucose solution; then add hexagonal boron nitride to the D - glucose solution, ultrasonically treat it for 20 - 30 min, and transfer it to an agate jar containing spherical grinding beads; ball - mill at a speed of 400 - 600 rpm on a ball mill for 12 - 14 h; after ball - milling, centrifuge the obtained mixture and wash it several times with water, and dry it in a vacuum oven at 60 - 70 °C to obtain boron nitride nanosheets.

5. The flame-retardant coating according to claim 2, wherein: The preparation method of the hexagonal boron nitride functionalized modified ammonium polyphosphate includes the following steps: Disperse the functionalized boron nitride nanosheets and ammonium polyphosphate in the mixed solution of ethanol and water, and stir into a suspension at a speed of 1500 - 2500 rpm; then stir the mixture at a speed of 500 - 600 rpm and a temperature of 60 - 70 °C for 6 - 8 h; after completion, cool it with ice - water, wash it several times with an ethanol - aqueous solution, and dry it in a vacuum oven to obtain hexagonal boron nitride functionalized modified ammonium polyphosphate.

6. A flame retardant coating according to claim 1, wherein: 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 iron nitrate nonahydrate, 80 - 100 parts of deionized water, 20 - 30 parts of 10% sodium hydroxide solution by mass, and 60 - 80 parts of 10% sodium carbonate solution by mass.

7. A flame retardant coating according to claim 6, characterized in that: The preparation method of the cerium cobalt iron layered double hydroxide includes the following steps: Cerium nitrate hexahydrate, cobalt nitrate hexahydrate, and iron nitrate nonahydrate were added to 100 parts of deionized water and stirred until dissolved to obtain a mixed solution; the mixed solution was dropped into a 10% sodium carbonate solution by mass fraction, and then a 10% sodium hydroxide solution by mass fraction was dropped. After stirring at room temperature for 3 - 5 h, it was aged at room temperature for 10 - 14 h; after suction filtration and washing with water until neutral, the product was freeze-dried for 24 - 30 h, and after grinding treatment, cerium-cobalt-iron layered double hydroxide was obtained.

8. A flame retardant coating according to claim 1, characterized in that: The flux is silicon hexaboride.

9. A flame retardant coating according to claim 1, wherein: The refractory filler is one or a mixture of one or more of raw vermiculite powder and wollastonite powder.

10. The preparation method of a flame retardant coating according to any one of claims 1-9, characterized in that: It includes the following steps: Hexagonal boron nitride-functionalized ammonium polyphosphate, cerium-cobalt-iron layered double hydroxide, hafnium diboride, refractory filler, and flux were added to epoxy resin to obtain a mixed solution; the mixed solution was ground multiple times at a rotation speed of 100 - 150 rpm for pre-dispersion, and finally a curing agent was added, and it was magnetically stirred and dispersed at 500 - 600 rpm for 15 - 25 min to prepare the flame-retardant coating.

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