Composite flame-retardant coating and preparation method thereof, and flame-retardant hydrogel coating and preparation method thereof

Abstract

The invention relates to the technical field of new materials, and discloses a composite flame-retardant coating and a preparation method thereof, and a flame-retardant hydrogel coating and a preparation method thereof. The method comprises the following steps: (1) in the presence of a reinforcing agent, a cross-linking agent, a photoinitiator and water, carrying out polymerization reaction on a sulfonate monomer containing double bonds and a phosphate monomer containing double bonds to obtain a precursor solution; and (2) performing contact mixing on the precursor solution and a filler to obtain the composite flame-retardant coating. The composite flame-retardant coating prepared by adopting the method for preparing the composite flame-retardant coating provided by the invention has relatively high fire resistance and high temperature resistance, is more excellent in char forming performance compared with common hydrogel coatings and the like, and has the characteristic of high designability.

Description

Technical Field

[0001] The present invention relates to the technical field of new materials, and particularly relates to a composite flame retardant coating and its preparation method, and a flame retardant hydrogel coating and its preparation method. Background Art

[0002] Due to its excellent heat insulation performance, rigid polyurethane foam (RPUF) has been widely used in various industries such as building exterior walls, pipeline insulation, and aerospace. However, it has a porous structure and a large specific surface area, and is very easy to burn. Once ignited, the flame will spread rapidly, and at the same time, a large amount of toxic gases will be generated, posing a significant fire hazard. To solve the fire hazard of RPUF, efforts have been made to develop flame-retardant RPUF. Surface coating flame retardant technology is a promising alternative method, which can inhibit flame spread and provide fire protection by forming a thermally stable carbon layer without affecting the material properties.

[0003] Hydrogel is a cross-linked polymer network that can retain a large amount of water and maintain a 3D layered structure. Hydrogel coatings have high water content, high viscosity, and hydrophilicity, and are considered a green material. When exposed to flame or high temperature, the water vapor in the hydrogel can effectively dissipate a large amount of heat, acting as an oxygen barrier, and can maintain a low temperature on the material surface before the water completely evaporates, hindering the combustion process. This unique property endows hydrogel coatings with great potential as flame retardant coatings. In addition, adding flame retardant materials to the hydrogel can reduce the heat transfer rate when generating coke residues, thereby suppressing fires; at the same time, it can prevent water loss and form a refractory layer on the material surface. Therefore, hydrogel coatings have received increasing attention in polymer flame retardancy, and have been used in rigid polyurethane foam materials and achieved relatively ideal flame retardant effects.

[0004] However, the low thermal stability of the hydrogel and the weak adhesion of the formed protective layer limit its application. Therefore, we need to further improve the thermal stability, carbonization function, and adhesion ability of the hydrogel coating.

[0005] CN 105348427A discloses a preparation method of a polymer sulfonate flame retardant. In this preparation method, an unsaturated sodium sulfonate monomer, an unsaturated potassium sulfonate monomer, and a vinyl monomer are reacted by a free radical polymerization method to form the polymer sulfonate. The vinyl monomer is any one or several selected from C6-C12 aromatic vinyl compounds, (meth)acrylate compounds, vinyl amide compounds, vinyl ether compounds, or cyanated vinyl compounds. This technical solution solves the problems of conventional small molecule sulfonate flame retardants, such as strong hydrophilicity, easy moisture absorption and deliquescence, easy migration of components, and poor compatibility and difficult to disperse evenly. However, it still has the defects of low flame retardancy efficiency and poor smoke suppression effect. Summary of the Invention

[0006] The object of the present invention is to solve the problems of poor adhesion, weak thermal stability and weak charring ability of the hydrogel coating in the prior art.

[0007] In order to achieve the above object, a first aspect of the present invention provides a method for preparing a composite flame retardant coating, the method comprising:

[0008] (1) In the presence of a reinforcing agent, a crosslinking agent, a photoinitiator and water, a sulfonate monomer containing a double bond and a phosphate monomer containing a double bond are subjected to a polymerization reaction to obtain a precursor solution;

[0009] (2) The precursor solution and a filler are brought into contact and mixed to obtain the composite flame retardant coating;

[0010] Wherein, the weight ratio of the amounts of the sulfonate monomer containing a double bond, the phosphate monomer containing a double bond and the filler is 1: 0.2-10: 0.1-0.5;

[0011] The filler is a fibrous filler and / or a layered filler, and the average diameter of the filler is 300-500 nm.

[0012] A second aspect of the present invention provides a composite flame retardant coating prepared by the method described in the first aspect.

[0013] A third aspect of the present invention provides a flame retardant hydrogel coating, the flame retardant hydrogel coating comprising a substrate and a composite flame retardant coating coated on the upper and lower surfaces of the substrate;

[0014] The composite flame retardant coating is the composite flame retardant coating described in the second aspect.

[0015] A fourth aspect of the present invention provides a method for preparing the flame retardant hydrogel coating described in the third aspect, the method comprising:

[0016] (1) The composite flame retardant coating is coated on the upper and lower surfaces of the substrate to obtain an intermediate;

[0017] (2) The intermediate is subjected to a curing treatment under ultraviolet light irradiation to obtain the flame retardant hydrogel coating.

[0018] By the above technical solutions, the present invention has at least the following advantages:

[0019] (1) The composite flame retardant coating prepared by the method for preparing a composite flame retardant coating provided by the present invention has better charring performance than ordinary hydrogel coatings, and has strong adhesion to the substrate and is not easy to fall off. Therefore, this method not only enhances the strength of the hydrogel coating, ensures the excellent performance of the coating, but also further improves the fire resistance and secondary flame retardancy of the char layer of the composite flame retardant coating.

[0020] (2) The composite flame retardant coating provided by the present invention has fire resistance, high temperature resistance, and has the characteristics of excellent char-forming performance and strong designability, and can be widely applied to fields such as wood, foam, forest fire prevention and extinguishing, etc.

[0021] (3) When the composite flame retardant coating provided by the present invention is applied to a flame retardant hydrogel coating, during the combustion and pyrolysis process of the flame retardant hydrogel coating, water evaporation occurs in the composite flame retardant coating coated on the substrate, which helps to reduce heat and dilute oxygen, thereby forming a carbon layer to prevent the transfer of heat and mass, reduce the surface temperature of the substrate, and improve the fire safety of the material. Therefore, without affecting the mechanical properties, the flame retardant, fire prevention and heat insulation performance of the flame retardant hydrogel coating is remarkable.

[0022] (4) The flame retardant hydrogel coating provided by the present invention has good flame retardant effect, good thermal stability and heat insulation ability, can extend the ignition time of the foam, and has excellent smoke suppression effect. Description of the Drawings

[0023] Figure 1 is the adhesion force data graph of the composite flame retardant coating prepared in Example 1 of the present invention applied to different substrates;

[0024] Figure 2 is the heat release rate curve graph of the flame retardant hydrogel coating prepared from the composite flame retardant coatings of Examples 1-4 of the present invention and the untreated pure rigid polyurethane foam;

[0025] Figure 3 is the total smoke production curve graph of the flame retardant hydrogel coating prepared from the composite flame retardant coatings of Examples 1-4 of the present invention and the untreated pure rigid polyurethane foam;

[0026] Figure 4 is the carbon monoxide production curve graph of the flame retardant hydrogel coating prepared from the composite flame retardant coatings of Examples 1-4 of the present invention and the untreated pure rigid polyurethane foam;

[0027] Figure 5 is the oxygen index and UL-94 level data graph of the flame retardant hydrogel coating prepared from the composite flame retardant coatings of Examples 1-4 of the present invention and the untreated pure rigid polyurethane foam. Detailed Embodiments

[0028] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0029] In the present invention, photoinitiator-1173 refers to 2-hydroxy-2-methyl-1-phenyl-1-propanone; photoinitiator-184 refers to hydroxycyclohexyl phenyl ketone; photoinitiator-2959 refers to 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone.

[0030] As described above, the first aspect of the present invention provides a method for preparing a composite flame retardant coating, the method comprising:

[0031] (1) Polymerizing a double bond-containing sulfonate monomer and a double bond-containing phosphate monomer in the presence of a reinforcing agent, a crosslinking agent, a photoinitiator and water to obtain a precursor solution;

[0032] (2) Contacting and mixing the precursor solution with a filler to obtain the composite flame retardant coating;

[0033] Wherein, the weight ratio of the amounts of the double bond-containing sulfonate monomer, the double bond-containing phosphate monomer and the filler is 1: 0.2-10: 0.1-0.5;

[0034] The filler is a fibrous filler and / or a layered filler, and the average diameter of the filler is 300-500 nm.

[0035] Preferably, the double bond-containing sulfonate monomer is selected from at least one of sodium vinyl sulfonate, sodium allyl sulfonate, sodium styrene sulfonate, potassium vinyl sulfonate and potassium 3-sulfopropyl methacrylate, preferably at least one of sodium vinyl sulfonate, sodium allyl sulfonate, potassium vinyl sulfonate and potassium 3-sulfopropyl methacrylate. The inventors have found that in this preferred case, the flame retardant and smoke suppression properties of the flame retardant hydrogel coating provided by the technical solution of the present invention are more excellent.

[0036] Preferably, the double bond-containing phosphate monomer is selected from 2-hydroxyethyl methacrylate phosphate, triallyl phosphate, bis[2-(methacryloyloxy)ethyl] phosphate, acrylic acid phosphate FM30 and acrylic acid phosphate FM20, preferably at least one of 2-hydroxyethyl methacrylate phosphate, triallyl phosphate and acrylic acid phosphate FM30. In this preferred case, the flame retardant and smoke suppression properties of the flame retardant hydrogel coating provided by the technical solution of the present invention are more excellent.

[0037] Preferably, the weight ratio of the amounts of the double bond-containing sulfonate monomer, the double bond-containing phosphate monomer and the filler is 1: 0.5-1: 0.25-0.3.

[0038] Preferably, the weight ratio of the double bond-containing phosphate monomer to the enhancer is 1:0.1 - 1, preferably 1:0.1 - 0.2.

[0039] Preferably, the weight ratio of the enhancer, the crosslinking agent, and the photoinitiator is 1:0.1 - 10:0.001 - 1. In this preferred case, the technical solution provided by the present invention can obtain a flame-retardant hydrogel coating with more excellent flame retardancy and smoke suppression.

[0040] Preferably, the weight ratio of the crosslinking agent to the water is 1:200 - 300.

[0041] Preferably, the fibrous filler is selected from at least one of cellulose fiber, silica fiber, alumina fiber, and aramid fiber, preferably cellulose fiber and / or silica fiber.

[0042] Preferably, the layered filler is selected from at least one of black phosphorus flakes, graphene flakes, titanium carbide flakes, boron nitride flakes, and clay, preferably black phosphorus flakes and / or boron nitride flakes.

[0043] Preferably, the enhancer is selected from at least one of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, 2-hydroxyethyl acrylate, and 2-phenoxyethyl acrylate, preferably at least one of acrylamide, acrylic acid, and 2-hydroxyethyl acrylate.

[0044] Preferably, the crosslinking agent is selected from at least one of N,N'-methylenebisacrylamide, ethylene glycol diacrylate, and hexamethylenebisacrylamide, preferably N,N'-methylenebisacrylamide and / or ethylene glycol diacrylate.

[0045] Preferably, the photoinitiator is selected from at least one of photoinitiator-1173, photoinitiator-184, and photoinitiator-2959, preferably photoinitiator-1173 and / or photoinitiator-2959.

[0046] Preferably, in step (1), the conditions of the polymerization reaction include: temperature is 25 - 60 °C, and time is 0.5 - 1 h.

[0047] Preferably, in step (2), the conditions of the contact mixing include: temperature is 25 - 60 °C, and time is 0.5 - 1 h.

[0048] As described above, the second aspect of the present invention provides a composite flame-retardant coating prepared by the method described in the first aspect.

[0049] As described above, the third aspect of the present invention provides a flame-retardant hydrogel coating, which includes a substrate and the composite flame-retardant coatings coated on the upper and lower surfaces of the substrate;

[0050] The composite flame retardant coating is the composite flame retardant coating described in the second aspect.

[0051] As mentioned above, the fourth aspect of the present invention provides a method for preparing the flame retardant hydrogel coating according to the third aspect, the method comprising:

[0052] (1) applying the composite flame retardant coating to the upper and lower surfaces of the substrate to obtain an intermediate;

[0053] (2) curing the intermediate under ultraviolet light to obtain the flame retardant hydrogel coating.

[0054] Preferably, in step (1), the coating thickness is independently 0.1-5 mm / surface.

[0055] Preferably, in step (1), the substrate is a rigid polyurethane foam.

[0056] Preferably, in step (1), the coating method is selected from at least one of a brush coating method, a spray coating method and a dip coating method.

[0057] Preferably, in step (2), the curing treatment conditions include: a light intensity of 50-80 mW / cm 2 , wavelength is 300-400nm, and illumination time is 1-30min.

[0058] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, the drugs and reagents used are all commercially available products.

[0059] Sodium vinyl sulfonate was purchased from Beijing Bailingwei Technology Co., Ltd., CAS No.: 3039-83-6.

[0060] Sodium allyl sulfonate was purchased from Shanghai Myrel Biochemical Technology Co., Ltd., CAS No.: 2495-39-8.

[0061] Sodium styrene sulfonate was purchased from Beijing Inokai Technology Co., Ltd., CAS No.: 2695-37-6.

[0062] Potassium 3-sulfonate propyl methacrylate was purchased from Beijing Yongchang Haoran Biotechnology Co., Ltd., CAS No.: 31098-21-2.

[0063] 2-Methyl-2-acrylic acid-2-hydroxyethyl ester phosphate was purchased from Beijing Xinbaohai Chemical Technology Co., Ltd., CAS No.: 52628-03-2.

[0064] Triallyl phosphate was purchased from Shanghai Jizhi Biochemical Technology Co., Ltd. CAS number: 1623-19-4.

[0065] In the following examples, acrylic phosphate FM30 is a mixture of an acrylic monophosphate ester and an acrylic diphosphate ester. The phosphate ester monomer is synthesized from O-(EO)n>10-CH3, and the active acrylic group is methacrylate; it is purchased from Beijing Baiyuan Chemical Co., Ltd.

[0066] The following examples are used to illustrate the method for preparing the composite flame retardant coating of the present invention

[0067] Example 1

[0068] (1) In the presence of an enhancer, a crosslinking agent, a photoinitiator, and water, a sulfonate monomer containing a double bond and a phosphate ester monomer containing a double bond are stirred evenly to carry out a polymerization reaction (temperature: 25°C, time: 0.5 h) to obtain a precursor solution;

[0069] (2) The precursor solution and the filler are mixed evenly to carry out contact mixing (temperature: 25°C, time: 1 h) to obtain a composite flame retardant coating.

[0070] For the raw materials and their ratios in this example, see Table 1.

[0071] Examples 2 to 4 are all carried out using the same preparation method as Example 1, except that the raw materials and their ratios are different, as specifically shown in Table 1.

[0072] Table 1 (The dosage of the phosphate ester monomer containing a double bond is 2 g, and the weight ratio of the dosages of the enhancer, crosslinking agent, and photoinitiator is 1:0.1:0.025)

[0073]

[0074] Example 5

[0075] This example is carried out using a method similar to that of Example 1. The difference is that the sulfonate monomer containing a double bond in this example is replaced with sodium styrene sulfonate to obtain a composite flame retardant coating.

[0076] Example 6

[0077] This example is carried out using a method similar to that of Example 1. The difference is that the phosphate ester monomer containing a double bond in this example is replaced with bis[2-(methacryloyloxy)ethyl] phosphate to obtain a composite flame retardant coating.

[0078] Example 7

[0079] This example is carried out using a method similar to that of Example 1. The difference is that the dosage of the enhancer in this example remains unchanged, and the weight ratio of the dosages of the enhancer, crosslinking agent, and photoinitiator is adjusted to 1:0.05:0.025 to obtain a composite flame retardant coating.

[0080] Comparative Example 1

[0081] This comparative example was carried out by a method similar to that of Example 1. The difference is that while keeping the amount of the sulfonate monomer containing a double bond in this comparative example unchanged, the weight ratio of the sulfonate monomer containing a double bond, the phosphate ester monomer containing a double bond and the filler was adjusted to 1:0.1:1 to obtain a composite flame retardant coating.

[0082] Test Example

[0083] Under room temperature conditions, the adhesion of the composite flame retardant coating prepared in the examples to different substrates such as polyurethane, glass, nylon (PA), polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) was tested. The peak data of the adhesion test are shown in Table 2.

[0084] Among them, the test method for adhesion is as follows: ① Conduct a lap shear test on the material according to the ASTM F2255-05 (2015) standard. Before each test, carefully wipe off the excess surface moisture with a paper towel; ② Cut the sample into a rectangular specimen of 4 cm (length) × 1.2 cm (width); ③ Place a hydrogel sample with a side length of 1.2 cm and a thickness of 2 mm on one side of the sample surface near the end point; ④ Place another sample on the hydrogel sample to form a square overlapping area with a side length of 1.2 cm; ⑤ Conduct a tensile test, and the force divided by the cross-sectional area is the adhesion.

[0085] Table 2

[0086]

[0087]

[0088] The present invention Figure 1 exemplarily provides an adhesion data graph of the composite flame retardant coating prepared in Example 1 of the present invention applied to different substrates; from Figure 1 it can be seen that the composite flame retardant coating prepared in Example 1 has strong adhesion to substrates such as polyurethane, glass, nylon (PA), polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA).

[0089] The following application examples are used to illustrate the method for preparing the flame retardant hydrogel coating of the present invention

[0090] Application Example 1

[0091] (1) The composite flame retardant coating prepared in Example 1 was uniformly coated on the upper and lower surfaces of the substrate (rigid polyurethane foam) by a brushing method, and the coating thickness was 1 mm / surface to obtain an intermediate product.

[0092] (2) Keep the intermediate horizontal and cure the intermediate under ultraviolet light irradiation (light intensity: 80 mW / cm 2 , wavelength: 365 nm, irradiation time: 1 min) to obtain a flame-retardant hydrogel coating.

[0093] Application Examples 2 to 7

[0094] According to the method of Application Example 1, except that the composite flame-retardant coatings prepared in Examples 2 to 7 are used to replace the composite flame-retardant coating prepared in Example 1, respectively.

[0095] Flame-retardant hydrogel coatings are obtained respectively.

[0096] Comparative Application Examples 1 to 2

[0097] According to the method of Application Example 1, except that the composite flame-retardant coatings prepared in Comparative Examples 1 to 2 are used to replace the composite flame-retardant coating prepared in Example 1, respectively.

[0098] Flame-retardant hydrogel coatings are obtained respectively.

[0099] Application Test Example

[0100] Perform performance tests on the flame-retardant hydrogel coatings prepared in the application examples, including: heat release rate, total smoke production, carbon monoxide production, limiting oxygen index (LOI), and UL-94 rating, and compare the above test results with the test results of untreated pure rigid polyurethane foam. The test results are shown in Table 3.

[0101] Among them, the relevant test methods are as follows:

[0102] Heat release rate, total smoke production, carbon monoxide production: According to ASTM E1354 / ISO 5660 standard, use a cone calorimeter to test and evaluate the combustion performance of materials (Fire Testing Technology, UK). Wrap the standard sample of the material (100×100×3 mm 3 ) with aluminum foil and place it on the sample stage of the calorimeter for combustion test. Usually, the radiant flux is set to 35 kW / m 2 .

[0103] Limiting oxygen index (LOI): The limiting oxygen index (LOI) is measured by an HC-2 oxygen index meter (Jiangning Analytical Instrument Factory). The sample size is 100 mm×6.5 mm×3.2 mm, and the test standard is based on ASTM D2863.

[0104] UL-94 rating: The vertical burning test (UL-94) was carried out on a CFZ-2 horizontal and vertical burning tester (Jiangning Analytical Instrument Factory). The dimensions of the test specimens were 130.0 mm × 13.0 mm × 3.2 mm and 130.0 mm × 13.0 mm × 1.6 mm. The test standard was based on ASTM D3801.

[0105] Table 3

[0106]

[0107]

[0108] The present invention Figure 2 exemplarily provides the heat release rate curves of the flame-retardant hydrogel coatings prepared from the composite flame-retardant coatings of Examples 1-4 of the present invention and the untreated pure rigid polyurethane foam. Among them, the pure foam refers to the pure rigid polyurethane foam; from Figure 2 it can be seen that the peak heat release rate of the flame-retardant hydrogel coatings prepared in Application Examples 1-4 is between 200 - 300 kW / m 2 while the peak heat release rate of the untreated pure rigid polyurethane foam is around 450 kW / m 2 . This shows that the flame-retardant hydrogel coatings provided by the present invention exhibit good flame-retardant performance.

[0109] The present invention Figure 3 exemplarily provides the total smoke production curves of the flame-retardant hydrogel coatings prepared from the composite flame-retardant coatings of Examples 1-4 of the present invention and the untreated pure rigid polyurethane foam. Among them, the pure foam refers to the pure rigid polyurethane foam; from Figure 3 it can be seen that the total smoke production of the flame-retardant hydrogel coatings prepared in Application Examples 1-4 is between 4 - 5 m 2 while the total smoke production of the untreated pure rigid polyurethane foam is nearly 8 m 2 . This shows that the flame-retardant hydrogel coatings provided by the present invention exhibit good smoke suppression performance.

[0110] The present invention Figure 4 exemplarily provides the carbon monoxide production curves of the flame-retardant hydrogel coatings prepared from the composite flame-retardant coatings of Examples 1-4 of the present invention and the untreated pure rigid polyurethane foam. Among them, the pure foam refers to the pure rigid polyurethane foam; from Figure 4 it can be seen that the carbon monoxide production of the flame-retardant hydrogel coatings prepared in Application Examples 1-4 is between 0.004 - 0.005 g / s, while the carbon monoxide production of the pure rigid polyurethane foam exceeds 0.008 g / s. This shows that the flame-retardant hydrogel coatings provided by the present invention exhibit good smoke suppression and toxicity reduction performance.

[0111] The present inventionFigure 5 Figure 1 provides the oxygen index and UL-94 rating data graphs of the flame-retardant hydrogel coatings prepared from the composite flame-retardant coatings of Examples 1-4 of the present invention and untreated pure rigid polyurethane foam. Among them, the pure foam refers to pure rigid polyurethane foam; Figure 5 It can be seen that the flame-retardant hydrogel coatings prepared in Application Examples 1-4 all reach the UL-94 V0 rating, and the oxygen index exceeds 34%. While the pure rigid polyurethane foam has no rating in the UL-94 test and the oxygen index does not exceed 20%. This shows that the flame-retardant hydrogel coating provided by the present invention exhibits good flame-retardant and smoke-suppressing properties.

[0112] From the above results, it can be seen that the composite flame-retardant coating prepared by the method for preparing a composite flame-retardant coating provided by the present invention has strong fire resistance, high temperature resistance, and better char-forming performance than ordinary hydrogel coatings, etc., and has the characteristics of strong designability;

[0113] At the same time, the composite flame-retardant coating has strong adhesion to the substrate, ensuring the excellent performance of the flame-retardant hydrogel coating, enhancing the strength of the flame-retardant hydrogel coating, further improving the fire resistance and secondary flame-retardant properties of the char layer, so that the flame-retardant hydrogel coating can be widely used in fields such as wood, foam, and forest fire prevention and extinguishing.

[0114] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite flame retardant coating, characterized in that, The method includes: (1) Performing a polymerization reaction on a sulfonate monomer containing a double bond and a phosphate ester monomer containing a double bond in the presence of a reinforcing agent, a crosslinking agent, a photoinitiator, and water to obtain a precursor solution; (2) Contacting and mixing the precursor solution with a filler to obtain the composite flame retardant coating; wherein, the weight ratio of the amounts of the sulfonate monomer containing a double bond, the phosphate ester monomer containing a double bond, and the filler is 1: 0.2 - 10: 0.1 - 0.5; the filler is a fibrous filler and / or a layered filler, and the average diameter of the filler is 300 - 500 nm.

2. The method according to claim 1, wherein The sulfonate monomer containing a double bond is selected from at least one of sodium vinyl sulfonate, sodium allyl sulfonate, sodium styrene sulfonate, potassium vinyl sulfonate, and potassium 3 - sulfopropyl methacrylate.

3. The method according to claim 1, wherein, The phosphate monomer containing a double bond is selected from 2-hydroxyethyl 2-methylacrylate phosphate, triallyl phosphate, bis[2-(methacryloyloxy)ethyl] phosphate, and acrylic acid phosphate FM30 and acrylic acid phosphate at least one of FM20.

4. The method according to any one of claims 1-3, wherein, The weight ratio of the amounts of the phosphate ester monomer containing a double bond and the reinforcing agent is 1: 0.1 - 1; and / or, the weight ratio of the amounts of the reinforcing agent, the crosslinking agent, and the photoinitiator is 1: 0.1 - 10: 0.001 - 1; and / or, the weight ratio of the amounts of the crosslinking agent and the water is 1: 200 - 300.

5. The method according to any one of claims 1 to 3, wherein The fibrous filler is selected from at least one of cellulose fiber, silica fiber, alumina fiber, and aramid fiber; and / or, the layered filler is selected from at least one of black phosphorus flakes, graphene flakes, titanium carbide flakes, boron nitride flakes, and clay; and / or, the reinforcing agent is selected from at least one of acrylamide, 2 - acrylamido - 2 - methylpropanesulfonic acid, acrylic acid, 2 - hydroxyethyl acrylate, and 2 - phenoxyethyl acrylate; and / or, the crosslinking agent is selected from at least one of N,N'-methylenebisacrylamide, ethylene glycol diacrylate, and hexamethylenebisacrylamide; and / or, the photoinitiator is selected from at least one of photoinitiator - 1173, photoinitiator - 184, and photoinitiator - 2959.

6. A composite flame retardant coating prepared by the method according to any one of claims 1 - 5.

7. A flame-retardant hydrogel coating, characterized in that, The flame retardant hydrogel coating includes a substrate and the composite flame retardant coating coated on the upper and lower surfaces of the substrate; the composite flame retardant coating is the composite flame retardant coating according to claim 6.

8. A method for preparing the flame-retardant hydrogel coating according to claim 7, characterized in that, The method includes: (1) Coating the composite flame retardant coating on the upper and lower surfaces of a substrate to obtain an intermediate; (2) Curing the intermediate under ultraviolet light irradiation to obtain the flame retardant hydrogel coating.

9. The method according to claim 8, wherein, In step (1), the coating thickness is independently 0.1 - 5 mm per surface; and / or, the substrate is a rigid polyurethane foam.

10. The method according to claim 8 or 9, wherein In step (2), the conditions for the curing treatment include: the light intensity is 50 - 80 mW / cm 2 , the wavelength is 300 - 400 nm, and the light irradiation time is 1 - 30 min.

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