Intumescent fire-retardant coating and preparation method thereof

Abstract

This invention discloses an intumescent fire-retardant coating and its preparation method, belonging to the field of coating technology. The method includes the following steps: Step 1: Preparing expandable graphite; Step 2: Reacting expandable graphite with polymethylene polyphenyl isocyanate to obtain isocyanate graphite; Step 3: Reacting isocyanate graphite with a modifier to obtain modified graphite; Step 4: Mixing modified graphite, acrylic resin emulsion, deionized water, defoamer, and leveling agent to obtain the intumescent fire-retardant coating. This invention effectively improves the overall performance of the coating by using polymethylene polyphenyl isocyanate as a crosslinking bridge group and covalently grafting a self-synthesized modifier onto the surface of expandable graphite.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to an intumescent fire-retardant coating and its preparation method. Background Technology

[0002] Intumescent fire-retardant coatings are a type of functional coating that rapidly expands under flame or high temperatures to form a dense char layer, thereby providing heat insulation and oxygen barrier protection. Expandable graphite, due to its characteristic of rapidly expanding in volume upon heating to form a physical barrier layer, is widely used as a flame-retardant filler in intumescent fire-retardant coatings. However, existing technologies still have significant shortcomings in practical applications: First, the surface of natural expandable graphite is hydrophobic, resulting in poor interfacial compatibility with matrix resins such as water-based acrylic resins. Direct physical blending easily leads to agglomeration and sedimentation, causing interfacial voids and phase separation defects within the coating, severely affecting the mechanical properties and flame-retardant stability of the coating. Second, to achieve ideal fire-retardant effects, a high amount of graphite is often required, but a high filler content disrupts the continuous film-forming properties of the coating, making it brittle, increasing internal stress, and significantly reducing adhesion, flexibility, and impact resistance. Furthermore, existing flame-retardant systems mostly rely on a single graphite expansion mechanism, lacking synergistic design with phosphorus-nitrogen flame retardants, resulting in insufficiently dense char layer structure and limited improvement in fire resistance limits.

[0003] Therefore, how to improve the compatibility between graphite and resin matrix while reducing the amount of graphite and introducing a synergistic flame retardant mechanism to achieve simultaneous optimization of coating mechanical properties and fire resistance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing an intumescent fire-retardant coating.

[0005] The objective of this invention can be achieved through the following technical solutions: A method for preparing an intumescent fire-retardant coating includes the following steps: Step 1: Add natural graphite flakes to the mixed acid and stir at 25°C for 5-8 minutes. Then add potassium permanganate and continue stirring for 150-180 minutes. After the reaction is complete, filter, wash, and dry to obtain expandable graphite. Step 2: Mix expandable graphite, polymethylene polyphenyl isocyanate, and xylene, and stir at 25°C for 30-40 min. Then add dibutyltin dilaurate, and under nitrogen protection, raise the temperature to 80°C and stir for 8-9 h. After the reaction is complete, filter under reduced pressure, wash, and dry to obtain isocyanate graphite. Step 3: Disperse the isocyanate graphite in xylene, add the modifier and dibutyltin dilaurate in sequence, raise the temperature to 80°C under nitrogen protection, stir for 8-9 hours, after the reaction is completed, filter, wash, and dry to obtain modified graphite; Step 4: Add modified graphite, acrylic resin emulsion, and deionized water to the dispersion tank in sequence. First, stir at low speed for 5-10 minutes to make preliminary mixing, then increase the speed and disperse at high speed for 20-30 minutes. Then add defoamer and leveling agent, continue stirring for 5-6 minutes, and filter the material through an 80-120 mesh filter to obtain intumescent fireproof coating.

[0006] In a more optimized manner, the ratio of natural graphite flakes, mixed acid, and potassium permanganate in step 1 is 5g:15mL:1.5g; wherein the mixed acid is a mixed solution of phosphoric acid and nitric acid, with a volume ratio of 7:3.

[0007] In a more optimized manner, the ratio of expandable graphite, polymethylene polyphenyl isocyanate, xylene, and dibutyltin dilaurate in step 2 is 15g:30g:100mL:0.1g.

[0008] In a more optimized manner, the ratio of isocyanate graphite, xylene, modifier, and dibutyltin dilaurate in step 3 is 15g:100mL:15g:0.1g.

[0009] In a more optimized manner, the ratio of modified graphite, acrylic resin emulsion, deionized water, defoamer, and leveling agent in step 4 is 3-4g: 22-24g: 5-6g: 0.1-0.2g: 0.1-0.2g.

[0010] In a more optimized manner, the preparation process of the modifier is as follows: S1: Mix salicylaldehyde, amino-polyethylene glycol-hydroxyl, and anhydrous ethanol, raise the temperature to 55°C, stir and react for 3-4 hours, then add diethyl phosphite, raise the temperature to 85°C, continue stirring and react for 10-12 hours, after the reaction is completed, remove the ethanol by rotary evaporation to obtain intermediate A. S2: Intermediate A, paraformaldehyde, and 1,4-dioxane were mixed and heated to 110°C. The reaction was carried out for 10-12 hours. After the reaction was completed, the reaction solution was cooled to room temperature and transferred to a separatory funnel. The solution was washed twice with 5% sodium hydroxide aqueous solution and then washed with deionized water until the aqueous phase was neutral. After drying with anhydrous sodium sulfate and filtration, the solvent was removed by rotary evaporation under reduced pressure. The solution was then dried under vacuum at 40°C overnight to obtain the crude product. The crude product was subjected to silica gel column chromatography with a gradient elution using petroleum ether / ethyl acetate as the eluent. The fraction containing the target product was collected, and the solution was rotary evaporated again and dried under vacuum to finally obtain the modifier.

[0011] In this process, the aldehyde group of salicylaldehyde undergoes a Schiff base condensation reaction with the primary amino group of amino-polyethylene glycol-hydroxyl group to generate an intermediate containing an imine bond. The imine double bond of this intermediate undergoes nucleophilic addition with the PH bond of diethyl phosphite, thereby introducing a phosphonate group with flame-retardant function into the molecule while retaining the flexibility and hydrophilicity of the polyethylene glycol segment. Subsequently, the phenolic hydroxyl group of the salicylaldehyde structural unit in the intermediate molecule undergoes a hydroxymethylation reaction with formaldehyde generated from the depolymerization of paraformaldehyde. The generated hydroxymethyl group further undergoes a Mannich condensation reaction with the adjacent amino group to obtain the modifier.

[0012] The synthesis process of the modifier is as follows:

[0013] In a more optimized manner, in step S1, the ratio of salicylaldehyde, amino-polyethylene glycol-hydroxyl, anhydrous ethanol, and diethyl phosphite is 10g:32g:100mL:11g.

[0014] In a more optimized manner, in step S2, the ratio of intermediate A, paraformaldehyde, and 1,4-dioxane is 20 g: 0.8 g: 120 mL.

[0015] The beneficial effects of this invention are: This invention effectively improves the overall performance of the coating by covalently grafting a self-synthesized modifier onto the surface of expandable graphite using polymethylene polyphenyl isocyanate as a crosslinking bridging group, as detailed below: Firstly, the long hydrophilic chains of polyethylene glycol in the modifier change the surface of graphite from hydrophobic to hydrophilic, effectively improving its interfacial compatibility with water-based acrylic resin emulsion. This achieves a monodisperse state and strong interfacial bonding of modified graphite in the coating, eliminating filler agglomeration, interfacial voids and phase separation defects commonly found in traditional physical blending. Secondly, the diethyl phosphite groups introduced in the modifier can decompose at high temperatures to produce strong acids such as phosphoric acid and metaphosphoric acid, which catalyze the dehydration of the substrate into carbon. At the same time, it can release nitrogen-containing non-combustible gases to form a phosphorus-nitrogen synergistic expansion flame retardant system. This system then works synergistically with the intercalation expansion behavior of expandable graphite itself, expanding synchronously and uniformly under flame or high temperature to generate a continuous, dense and thick physical barrier carbon layer, which significantly improves the heat insulation and oxygen barrier capabilities and significantly increases the fire resistance limit of the coating. Thirdly, the flexible polyethylene glycol segments act as "molecular hinges" anchored between the rigid graphite sheets and the acrylic resin matrix. This not only fully utilizes the inherent high modulus reinforcing effect of graphite, improving the coating's hardness and impact resistance, but also avoids brittle fracture through the stress dissipation mechanism of the flexible segments, achieving a mechanical balance between increased rigidity and controllable toughness loss. Furthermore, thanks to the excellent dispersion state of the modified graphite and its higher char-forming efficiency per unit mass, this invention can significantly reduce the actual amount of graphite added without compromising refractoriness. The reduction in graphite content directly weakens its adverse effects on the continuous film formation of the coating, further reducing internal stress and brittleness, resulting in additional improvements in the coating's adhesion, flexibility, and impact resistance. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1: A method for preparing an intumescent fire-retardant coating, comprising the following steps: Step 1: Add 5g of natural graphite flakes to 15mL of mixed acid (a mixed solution of phosphoric acid and nitric acid in a volume ratio of 7:3), stir at 25℃ for 5min, then add 1.5g of potassium permanganate, and continue stirring for 150min. After the reaction is complete, filter, wash, and dry to obtain expandable graphite. Step 2: Mix 15g expandable graphite, 30g polymethylene polyphenyl isocyanate and 100mL xylene, stir at 25℃ for 30min, then add 0.1g dibutyltin dilaurate, raise the temperature to 80℃ under nitrogen protection, stir for 8h, after the reaction is completed, filter under reduced pressure, wash and dry to obtain isocyanate graphite. Step 3: Disperse 15g of isocyanate graphite into 100mL of xylene, add 15g of modifier and 0.1g of dibutyltin dilaurate in sequence, raise the temperature to 80℃ under nitrogen protection, stir for 8h, after the reaction is completed, filter, wash and dry to obtain modified graphite; Step 4: Add 3g of modified graphite, 22g of acrylic resin emulsion, and 5g of deionized water to the dispersion tank in sequence. First, stir at low speed for 5 minutes to make preliminary mixing, then increase the speed and disperse at high speed for 20 minutes. Then add 0.1g of defoamer and 0.1g of leveling agent, continue stirring for 5 minutes, and filter the material through an 80-mesh filter to obtain an intumescent fireproof coating. The preparation process of the modifier is as follows: S1: Mix 10g salicylaldehyde, 32g amino-polyethylene glycol-hydroxy (MW=400) and 100mL anhydrous ethanol, raise the temperature to 55℃, stir and react for 3h, then add 11g diethyl phosphite, raise the temperature to 85℃, continue stirring and react for 10h, after the reaction is completed, remove the ethanol by rotary evaporation to obtain intermediate A. S2: Mix 20g of intermediate A, 0.8g of paraformaldehyde, and 120mL of 1,4-dioxane, raise the temperature to 110℃, and react for 10h. After the reaction is complete, cool the reaction solution to room temperature and transfer it to a separatory funnel. Wash twice with 5% sodium hydroxide aqueous solution, and then wash with deionized water until the aqueous phase is neutral. Dry with anhydrous sodium sulfate, filter, remove the solvent by rotary evaporation under reduced pressure, and dry under vacuum at 40℃ overnight to obtain the crude product. Analyze the crude product by silica gel column chromatography with a gradient elution of petroleum ether / ethyl acetate as eluent. Collect the target product fraction, rotary evaporate again, and dry under vacuum to finally obtain the modifier.

[0018] Example 2: A method for preparing an intumescent fire-retardant coating, comprising the following steps: Step 1: Add 5g of natural graphite flakes to 15mL of mixed acid (a mixed solution of phosphoric acid and nitric acid, with a volume ratio of 7:3), stir at 25℃ for 8min, then add 1.5g of potassium permanganate, and continue stirring for 180min. After the reaction is complete, filter, wash, and dry to obtain expandable graphite. Step 2: Mix 15g expandable graphite, 30g polymethylene polyphenyl isocyanate and 100mL xylene, stir at 25℃ for 40min, then add 0.1g dibutyltin dilaurate, raise the temperature to 80℃ under nitrogen protection, stir for 9h, after the reaction is completed, filter under reduced pressure, wash and dry to obtain isocyanate graphite. Step 3: Disperse 15g of isocyanate graphite into 100mL of xylene, add 15g of modifier and 0.1g of dibutyltin dilaurate in sequence, raise the temperature to 80℃ under nitrogen protection, stir for 9h, after the reaction is completed, filter, wash and dry to obtain modified graphite; Step 4: Add 4g of modified graphite, 24g of acrylic resin emulsion, and 6g of deionized water to the dispersion tank in sequence. First, stir at low speed for 10 minutes to make it initially mixed. Then, increase the speed and disperse at high speed for 30 minutes. After that, add 0.2g of defoamer and 0.2g of leveling agent, continue stirring for 6 minutes, and filter the material through a 120-mesh filter to obtain an intumescent fireproof coating. The preparation process of the modifier is as follows: S1: Mix 10g salicylaldehyde, 32g amino-polyethylene glycol-hydroxy (MW=400) and 100mL anhydrous ethanol, raise the temperature to 55℃, stir and react for 4h, then add 11g diethyl phosphite, raise the temperature to 85℃, continue stirring and react for 12h, after the reaction is completed, remove the ethanol by rotary evaporation to obtain intermediate A. S2: Mix 20g of intermediate A, 0.8g of paraformaldehyde, and 120mL of 1,4-dioxane, raise the temperature to 110℃, and react for 12h. After the reaction is complete, cool the reaction solution to room temperature and transfer it to a separatory funnel. Wash twice with 5% sodium hydroxide aqueous solution, and then wash with deionized water until the aqueous phase is neutral. Dry with anhydrous sodium sulfate, filter, remove the solvent by rotary evaporation under reduced pressure, and dry under vacuum at 40℃ overnight to obtain the crude product. Analyze the crude product by silica gel column chromatography with a gradient elution of petroleum ether / ethyl acetate as eluent. Collect the target product fraction, rotary evaporate again, and dry under vacuum to finally obtain the modifier.

[0019] Example 3: A method for preparing an intumescent fire-retardant coating, comprising the following steps: Step 1: Add 5g of natural graphite flakes to 15mL of mixed acid (a mixed solution of phosphoric acid and nitric acid in a volume ratio of 7:3), stir at 25℃ for 6.5min, then add 1.5g of potassium permanganate, and continue stirring for 165min. After the reaction is complete, filter, wash, and dry to obtain expandable graphite. Step 2: Mix 15g expandable graphite, 30g polymethylene polyphenyl isocyanate and 100mL xylene, stir at 25℃ for 35min, then add 0.1g dibutyltin dilaurate, raise the temperature to 80℃ under nitrogen protection, stir for 8.5h, after the reaction is completed, filter under reduced pressure, wash and dry to obtain isocyanate graphite. Step 3: Disperse 15g of isocyanate graphite into 100mL of xylene, add 15g of modifier and 0.1g of dibutyltin dilaurate in sequence, raise the temperature to 80℃ under nitrogen protection, stir for 8.5h, after the reaction is completed, filter, wash and dry to obtain modified graphite; Step 4: Add 3.5g of modified graphite, 23g of acrylic resin emulsion, and 5.5g of deionized water to the dispersion tank in sequence. First, stir at low speed for 7.5 minutes to make preliminary mixing, then increase the speed and disperse at high speed for 25 minutes. Then add 0.15g of defoamer and 0.15g of leveling agent, continue stirring for 5.5 minutes, filter the material through a 100-mesh filter to obtain an intumescent fireproof coating. The preparation process of the modifier is as follows: S1: Mix 10g salicylaldehyde, 32g amino-polyethylene glycol-hydroxy (MW=400) and 100mL anhydrous ethanol, raise the temperature to 55℃, stir and react for 3.5h, then add 11g diethyl phosphite, raise the temperature to 85℃, continue stirring and react for 11h, after the reaction is completed, remove the ethanol by rotary evaporation to obtain intermediate A. S2: Mix 20g of intermediate A, 0.8g of paraformaldehyde, and 120mL of 1,4-dioxane. Raise the temperature to 110℃ and react for 11h. After the reaction is complete, cool the reaction solution to room temperature and transfer it to a separatory funnel. Wash twice with 5% sodium hydroxide aqueous solution, then wash with deionized water until the aqueous phase is neutral. Dry with anhydrous sodium sulfate, filter, remove the solvent by rotary evaporation under reduced pressure, and dry under vacuum at 40℃ overnight to obtain the crude product. Analyze the crude product by silica gel column chromatography with a gradient elution of petroleum ether / ethyl acetate. Collect the target product fraction, rotary evaporate again, and dry under vacuum to finally obtain the modifier.

[0020] Comparative example: Polyethylene glycol was used instead of the modifier, as follows: Step 1: Add 5g of natural graphite flakes to 15mL of mixed acid (a mixed solution of phosphoric acid and nitric acid in a volume ratio of 7:3), stir at 25℃ for 6.5min, then add 1.5g of potassium permanganate, and continue stirring for 165min. After the reaction is complete, filter, wash, and dry to obtain expandable graphite. Step 2: Mix 15g expandable graphite, 30g polymethylene polyphenyl isocyanate and 100mL xylene, stir at 25℃ for 35min, then add 0.1g dibutyltin dilaurate, raise the temperature to 80℃ under nitrogen protection, stir for 8.5h, after the reaction is completed, filter under reduced pressure, wash and dry to obtain isocyanate graphite. Step 3: Disperse 15g of isocyanate graphite into 100mL of xylene, add 15g of polyethylene glycol (MW=500) and 0.1g of dibutyltin dilaurate in sequence, raise the temperature to 80℃ under nitrogen protection, stir for 8.5h, filter, wash and dry to obtain modified graphite; Step 4: Add 3.5g of modified graphite, 23g of acrylic resin emulsion, and 5.5g of deionized water to the dispersion tank in sequence. First, stir at low speed for 7.5 minutes to make preliminary mixing, then increase the speed and disperse at high speed for 25 minutes. Then add 0.15g of defoamer and 0.15g of leveling agent, and continue stirring for 5.5 minutes. Filter the material through a 100-mesh filter to obtain the intumescent fireproof coating.

[0021] Comparative Example 2: No modifications were made to the expandable graphite, as follows: Step 1: Add 5g of natural graphite flakes to 15mL of mixed acid (a mixed solution of phosphoric acid and nitric acid in a volume ratio of 7:3), stir at 25℃ for 6.5min, then add 1.5g of potassium permanganate, and continue stirring for 165min. After the reaction is complete, filter, wash, and dry to obtain expandable graphite. Step 2: Add 3.5g of expandable graphite, 23g of acrylic resin emulsion, and 5.5g of deionized water to a dispersion tank in sequence. First, stir at low speed for 7.5 minutes to make preliminary mixing, then increase the speed and disperse at high speed for 25 minutes. Then add 0.15g of defoamer and 0.15g of leveling agent, and continue stirring for 5.5 minutes. Filter the material through a 100-mesh filter to obtain an intumescent fireproof coating.

[0022] Testing and experimentation: The intumescent fire-retardant coatings obtained in the examples and comparative examples were poured onto a soda-lime glass plate coated with beeswax and allowed to dry naturally at room temperature for 24 hours. They were then transferred to a 60°C convection oven for further drying for 12 hours to obtain a dried coating film. The following tests were then conducted: (1) The elongation at break and tensile modulus of the coating were tested according to the standard ASTM D638; (2) The limiting oxygen index of the coating was tested according to the standard ASTM D2863; The obtained data is shown in the table below:

[0023] Conclusion: Based on the above test results, it can be seen that the present invention fundamentally improves the dispersion state and interfacial bonding of expandable graphite in the coating by covalently grafting a phosphorus-nitrogen-containing modifier, thereby achieving a comprehensive improvement in mechanical and flame-retardant properties with similar graphite addition amounts.

[0024] Specifically, the tensile modulus of the embodiment reached 230.6-240.6 MPa, which is much higher than the 55.5 MPa of Comparative Example 2, while the elongation at break remained at 130.7%-139.6%, which not only retained sufficient flexibility, but also avoided the brittle defects caused by filler agglomeration in the physical blend system. Regarding flame retardancy, the limiting oxygen index of the examples reached 28.5%-29.5%, significantly better than 21.6% in Comparative Example 2 and 23.7% in Comparative Example 1. This fully demonstrates the synergistic effect between the phosphorus-nitrogen synergistic structure in the modifier and the expansion behavior of expandable graphite intercalation. Even without increasing the amount of graphite, or even reducing it, the density and heat insulation capacity of the char layer were significantly improved. In contrast, Comparative Example 1 was modified only with polyethylene glycol, which improved compatibility but lacked flame-retardant functional groups. It could neither form an effective expandable char layer nor maintain high fire resistance at low addition levels.

[0025] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0026] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for preparing an intumescent fire-retardant coating, characterized in that, Includes the following steps: Step 1: Add natural graphite flakes to the mixed acid and stir at 25°C for 5-8 minutes. Then add potassium permanganate and continue stirring for 150-180 minutes. After the reaction is complete, filter, wash, and dry to obtain expandable graphite. Step 2: Mix expandable graphite, polymethylene polyphenyl isocyanate, and xylene, and stir at 25°C for 30-40 min. Then add dibutyltin dilaurate, and under nitrogen protection, raise the temperature to 80°C and stir for 8-9 h. After the reaction is complete, filter under reduced pressure, wash, and dry to obtain isocyanate graphite. Step 3: Disperse the isocyanate graphite in xylene, add the modifier and dibutyltin dilaurate in sequence, raise the temperature to 80°C under nitrogen protection, stir for 8-9 hours, after the reaction is completed, filter, wash, and dry to obtain modified graphite; Step 4: Add modified graphite, acrylic resin emulsion, and deionized water to the dispersion tank in sequence. First, stir at low speed for 5-10 minutes to make preliminary mixing, then increase the speed and disperse at high speed for 20-30 minutes. Then add defoamer and leveling agent, continue stirring for 5-6 minutes, and filter the material through an 80-120 mesh filter to obtain intumescent fireproof coating.

2. The method for preparing an intumescent fire-retardant coating according to claim 1, characterized in that, In step 1, the ratio of natural graphite flakes, mixed acid, and potassium permanganate is 5g:15mL:1.5g; the mixed acid is a mixed solution of phosphoric acid and nitric acid, with a volume ratio of 7:

3.

3. The method for preparing an intumescent fire-retardant coating according to claim 1, characterized in that, In step 2, the ratio of expandable graphite, polymethylene polyphenyl isocyanate, xylene, and dibutyltin dilaurate is 15g:30g:100mL:0.1g.

4. The method for preparing an intumescent fire-retardant coating according to claim 1, characterized in that, In step 3, the ratio of isocyanate graphite, xylene, modifier, and dibutyltin dilaurate is 15g:100mL:15g:0.1g.

5. The method for preparing an intumescent fire-retardant coating according to claim 1, characterized in that, In step 4, the ratio of modified graphite, acrylic resin emulsion, deionized water, defoamer, and leveling agent is 3-4g: 22-24g: 5-6g: 0.1-0.2g: 0.1-0.2g.

6. The method for preparing an intumescent fire-retardant coating according to claim 1, characterized in that, The preparation process of the modifier is as follows: S1: Mix salicylaldehyde, amino-polyethylene glycol-hydroxyl, and anhydrous ethanol, raise the temperature to 55°C, stir and react for 3-4 hours, then add diethyl phosphite, raise the temperature to 85°C, continue stirring and react for 10-12 hours, after the reaction is completed, remove the ethanol by rotary evaporation to obtain intermediate A. S2: Mix intermediate A, paraformaldehyde, and 1,4-dioxane, raise the temperature to 110℃, and react for 10-12 hours. After the reaction is complete, perform post-processing and purification to obtain the modifier.

7. The method for preparing an intumescent fire-retardant coating according to claim 6, characterized in that, In step S1, the ratio of salicylaldehyde, amino-polyethylene glycol-hydroxyl, anhydrous ethanol, and diethyl phosphite is 10g:32g:100mL:11g.

8. The method for preparing an intumescent fire-retardant coating according to claim 6, characterized in that, In step S2, the ratio of intermediate A, paraformaldehyde, and 1,4-dioxane is 20g:0.8g:120mL.

9. An intumescent fire-retardant coating obtained by the preparation method of an intumescent fire-retardant coating according to any one of claims 1-8.

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