A fireproof paint

Abstract

A fire-retardant coating is characterized by comprising the following components in weight percentage: 10-30% vinyl acetate-ethylene copolymer (VAE) emulsion, 10-30% modified urea-formaldehyde resin, 5-20% expandable vermiculite, 10-30% coating additives and other fillers, 10-30% intumescent flame retardant, and 5-30% water; wherein the modified urea-formaldehyde resin is obtained by chemically coating melamine-modified urea-formaldehyde resin with polyacrylate. This fire-retardant coating not only exhibits good expansion properties and excellent fire resistance, but also possesses good water resistance.

Description

Technical Field

[0001] This invention relates to a fire-retardant coating, further comprising a modified urea-formaldehyde resin specifically for fire-retardant materials, wherein the modified urea-formaldehyde resin is obtained by chemically coating melamine-modified urea-formaldehyde resin with polyacrylate. Background Technology

[0002] Intumescent fire retardant coatings are mainly used for fire protection of steel structures. Economic and social development has promoted the development of the construction industry. Large buildings such as exhibition halls, airport terminals, large shopping malls, stadiums, high-end hotels, and industrial plants are increasing and developing towards larger and more aesthetically pleasing designs. Their main load-bearing components are mostly steel structures.

[0003] Therefore, fire protection of steel structures is receiving increasing attention. Although steel is a non-combustible material, its fire resistance is far inferior to that of brick and stone structures and reinforced concrete structures. As temperature rises, the mechanical strength of steel decreases. When the temperature reaches the critical temperature of steel (generally 540℃), its yield stress is only 40% of that at room temperature. Steel has a fire resistance limit of only 15 minutes under direct exposure to high-temperature flames. Using fire-retardant coatings is a relatively ideal method for fire protection of steel structure buildings. Fire-retardant coatings are applied to the surface of steel components, providing fireproof and heat insulation protection, preventing the steel from rapidly heating up and reducing its strength during a fire, and avoiding the collapse of the building due to the loss of structural support.

[0004] Fire-retardant coatings for steel structures can generally be classified into thick-coat, thin-coat, and ultra-thin types. From a development perspective, ultra-thin fire-retardant coatings for steel structures will eventually replace thick-coat and thin-coat fire-retardant materials. Thin or ultra-thin fire-retardant coatings are fire-retardant coatings prepared using water-based resins as film-forming agents and compounded with intumescent flame retardants that can form a coating with the film-forming agent. This type of coating is both decorative and fire-retardant; when exposed to fire, the coating can expand to several tens of times its original thickness, forming a porous charred layer that protects the substrate from combustion and also provides thermal insulation.

[0005] Typical intumescent flame retardants are usually composed of a catalyst containing phosphorus (phosphorus source), a charring agent composed of polyhydroxy organic compounds (carbon source), and a foaming agent composed of nitrogen-containing organic compounds (nitrogen source), and are added in large quantities to the resin. Amino resins (urea-formaldehyde resin, melamine-formaldehyde resin, melamine-urea-formaldehyde resin) contain abundant carbon and nitrogen sources, and act as both charring agents and foaming agents, which can reduce the amount of external flame retardant added. Fire-retardant coatings prepared with amino resins as film-forming materials have good foaming properties.

[0006] Amino resins themselves have a multifunctional structure. After room temperature curing, the coating has a high cross-linking density, resulting in a hard, brittle coating with poor flexibility. The cured coating is prone to cracking shortly after exposure to air. To address these technical problems, CN114250023A discloses a fire-retardant coating and its preparation method. The components used have the following mass fractions: 60%–70% water-based amino resin, 20%–30% intumescent flame retardant, and 5%–10% self-healing microcapsules. A film-forming aid corresponding to the core of the self-healing microcapsules is also added. The water-based amino resin is selected from one or more combinations of urea-formaldehyde resin, melamine-formaldehyde resin, and melamine-urea-formaldehyde resin. The intumescent flame retardant is a mixed-type or reactive intumescent flame retardant. The wall material of the self-healing microcapsules is melamine-urea-formaldehyde resin or urea-formaldehyde resin, and the core is a water-based room temperature self-crosslinking resin. However, this coating preparation process is relatively complex and has poor water resistance.

[0007] Existing technology CN114213912A discloses a multifunctional water-based coating and its preparation method. The multifunctional water-based coating, based on its total mass of 100%, comprises the following raw material components: 10-30% vinyl acetate-ethylene copolymer emulsion, 10-30% elastic emulsion, 2-5% rust-preventive pigment, 1-2% flash rust inhibitor, 0.3-1% mildew and corrosion inhibitor, 0.5-1.5% silane coupling agent, 30-40% flame-retardant pigments and fillers, 1-10% auxiliary agents, and the balance being water. The multifunctional water-based coating provided in this application simultaneously possesses fire-retardant, waterproof, and corrosion-resistant properties. The applicant, using this patented formulation, discovered that to overcome the problem of weak waterproofing in the vinyl acetate-ethylene copolymer film-forming material, a large amount of elastic emulsion is added to the formulation. While elastic emulsions can improve waterproofing, their ability to promote foam formation and maintain foam stability and integrity is far inferior to that of VAE emulsions and urea-formaldehyde resins. This results in a decrease in the fire resistance of the coating. Therefore, this formula requires the addition of up to 30-40% flame-retardant pigments and fillers composed of pentaerythritol, melamine, ammonium polyphosphate, and titanium dioxide to ensure fire resistance. This significantly increases the cost of the coating and makes it unsuitable for the current highly competitive coating market.

[0008] Urea-formaldehyde resin, especially melamine-modified urea-formaldehyde resin (MUF), is widely used in the woodworking industry for bonding wood or as an adhesive in the production of wood-based materials, such as particleboard, plywood, and various fiberboards. Urea-formaldehyde resin is a reaction product of urea and formaldehyde. Because this type of urea-formaldehyde resin has poor water resistance and strength, it is generally modified with urea-formaldehyde resin modifiers to obtain modified urea-formaldehyde resins, such as the commonly used melamine-modified urea-formaldehyde resin (MUF). This modified urea-formaldehyde resin has significantly higher water resistance and strength than unmodified conventional urea-formaldehyde resin. The urea-formaldehyde resin modifiers typically include melamine, phenol or resorcinol, acrylate copolymer solutions, isocyanates, polyvinyl alcohol, lignin, etc. For example, CN102898604A discloses a method for preparing a modified urea-formaldehyde resin with improved storage stability. The method includes: (1) reacting a first batch of urea, a modifier, and formaldehyde in a first contact reaction until the water-to-mixability ratio is 0.4–1.5, with a molar ratio of formaldehyde to the total amount of the first batch of urea and the modifier being 1–1.7:1; (2) reacting the resulting mixture with a second batch of urea in a second contact reaction at a temperature of 60±15℃ for 1–30 min, with a molar ratio of formaldehyde to the total amount of the first batch of urea, the second batch of urea, and the modifier being 0.6–1.25:1; (3) adjusting the pH of the mixture obtained in step (2) to 8.5–10 and cooling it to below 40℃. The modifier is at least one of melamine, phenol, resorcinol, isocyanate, polyvinyl alcohol, and lignin. The urea-formaldehyde resin is primarily used to improve storage stability and reduce formaldehyde release. The water resistance of the modified urea-formaldehyde resin is improved, but it still cannot compare with that of acrylic resin and cannot meet the water resistance requirements of fire-retardant coatings.

[0009] In summary, market research revealed that thin-film fire-retardant coatings currently primarily use vinyl acetate-ethylene copolymers and polyacrylate polymers as film-forming materials. Urea-formaldehyde resin, which can function as both a carbon and nitrogen source and a foaming agent, is generally used as an auxiliary resin. This is because even modified phenolic resin is less waterproof than acrylic resin, and its fire-retardant performance is slightly inferior to Wacker 3066 emulsion, which is mainstream in the high-end fire-retardant materials market. Furthermore, it can only be used as an auxiliary film-forming material, and its addition amount cannot be too high. Even with melamine and / or isocyanate-modified urea-formaldehyde resin, although it can increase the stability and other properties of the fire-retardant coating, its waterproof performance still does not meet the requirements of the high-end fire-retardant market. Even with modification using elastic emulsions with better waterproof properties, while waterproof performance is improved, the improvement from physical blending modification is limited. Additionally, excessive amounts of elastic emulsion can inhibit foam formation, thus affecting fire-retardant performance. It is evident that current urea-formaldehyde resins on the market struggle to simultaneously achieve both fire resistance and water resistance. While polyacrylate emulsions offer good water resistance, their fire resistance is poor. VAE emulsions, exemplified by Wacker 3066 emulsion, exhibit excellent fire resistance but poor water resistance. Even when blended, both water resistance and fire resistance decrease. In other words, currently available intumescent fire-retardant coatings using vinyl acetate-ethylene copolymers, polyacrylate polymers, and / or urea-formaldehyde resins as film-forming materials cannot simultaneously possess excellent fire resistance and water resistance. Summary of the Invention

[0010] The purpose of this application is to provide a fire-retardant coating that has both excellent fire-retardant and waterproof properties, characterized in that it comprises the following components in weight percentage: 10-30% vinyl acetate-ethylene copolymer (VAE) emulsion, 10-30% modified urea-formaldehyde resin, 5-20% expandable vermiculite, 10-30% coating additives and other fillers, 10-30% intumescent flame retardant, and 5-30% water;

[0011] The intumescent flame retardant is composed of a low-molecular-weight carbon source, a char-forming catalyst, and a foaming agent. The low-molecular-weight carbon source is pentaerythritol, dipentaerythritol, or tripentaerythritol. The char-forming catalyst is ammonium polyphosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium metaphosphate, ammonium hypophosphite, ammonium phosphite, phosphorous acid, metaphosphoric acid, and / or orthophosphoric acid. The foaming agent is melamine, dicyandiamide, ammonium oxalate, urea, or hexamethylenetetramine. The weight ratio of the low-molecular-weight carbon source, the char-forming catalyst, and the foaming agent is (1-2):(1-2):(0.5-1.5).

[0012] Preferably, the coating additives include defoamers, leveling agents, dispersants, thickeners, and / or wetting agents.

[0013] Preferably, other fillers include titanium dioxide.

[0014] Preferably, other fillers include titanium dioxide, lithopone, or heavy calcium carbonate.

[0015] The vinyl acetate-ethylene copolymer emulsion is selected from at least one of Wacker EZ 3066 and Wacker EZ 3112;

[0016] This application also discloses a manufacturing process for modified urea-formaldehyde resin, which employs an alkali-acid-alkali process, including the following steps:

[0017] (1) Add a certain mass of formaldehyde solution to the reaction vessel, add a certain amount of deionized water, then adjust the pH to 7.5-9.0 with sodium hydroxide aqueous solution, and heat to 40-55℃. Then add the first batch of urea and the first batch of melamine under stirring conditions, raise the temperature to 85-95℃ and keep it at the temperature for 20-40 min or raise the temperature to 70-75℃ and keep it at the temperature for 50-80 min.

[0018] (2) Adjust the pH to 5.0-5.5 with formic acid, raise the temperature to 80-95℃, continue to keep the temperature for a period of time, and finally cool the reactants to 65-75℃, adjust the pH to 7.0-7.5 with sodium hydroxide aqueous solution, add the second batch of urea and the second batch of melamine, stir evenly, and keep the temperature for 20-40 minutes.

[0019] (3) After cooling to a certain temperature, add the third batch of urea, keep the reaction at 70-90℃ for 10-40 minutes, and then adjust the pH value to 8.0-9.0 to obtain the basic modified urea-formaldehyde resin.

[0020] (4) While stirring, add the pre-mixed mixture of isocyanate acrylate, acrylate and ester solvent, and react for 15-25 min; wherein, based on the basic modified urea-formaldehyde resin, the sum of the amounts of isocyanate acrylate and acrylate is 5-10 wt%.

[0021] (5) While stirring, add 5-10 wt% of a mixture of tri(2-hydroxyethyl) isocyanurate triacrylate (THEICTA) and acrylate, with a mass ratio of (2-4):1.

[0022] (6) Add initiator solution and heat to 50-90℃, react for 0.4-3.5 hours to obtain modified urea-formaldehyde resin.

[0023] In steps (1)-(3), the cumulative molar ratio of formaldehyde / (urea + melamine) is 1.05-1.15;

[0024] In step (2), continue the reaction at a constant temperature until the viscosity of the system reaches 16-20 s (for the Forecast cup, 30°C test), and then finally cool the reactants to 65-75°C.

[0025] In step (4), the weight ratio of isocyanate acrylate to acrylate is (3-5):1.

[0026] In step (4), the isocyanate acrylate can be ethyl isocyanate acrylate or ethyl isocyanate methacrylate;

[0027] In step (4), the ester solvents include one or more of ethyl acetate, octyl acetate, and n-butyl acetate.

[0028] In step (4), the acrylate can be methyl methacrylate, ethyl methacrylate, or butyl methacrylate;

[0029] In step (5), the acrylate can be methyl methacrylate, ethyl methacrylate, or butyl methacrylate;

[0030] In step (6), the initiator is one or more of the following: sodium persulfate, azobisisobutyronitrile, benzoyl peroxide, tert-butyl peroxide, di-tert-butyl peroxide, dicumyl peroxide, and di-tert-pentyl peroxide.

[0031] In summary, this application has the following beneficial effects:

[0032] (1) In this application, titanium dioxide is used as a filler for fire-retardant coatings. It not only plays a common coloring role, but also plays a role in catalyzing foaming and improving fire-retardant performance. While using isocyanate to modify urea-formaldehyde resin, it also acts as a functional binder to achieve chemical grafting and coating modification of urea-formaldehyde resin with polyacrylate, thereby improving waterproof performance.

[0033] (2) Among the many types of acrylate monomers, after a large number of experiments, tri(2-hydroxyethyl) isocyanurate triacrylate (THEICTA) was finally selected. It not only achieves waterproof coating of acrylic polymer, but also has the effect of foaming and carbonization. It is speculated that this may be due to its nitrogen content, which avoids the acrylic resin with low nitrogen content around the urea-formaldehyde resin from inhibiting foaming and carbonization.

[0034] (3) In step (4), a mixture of isocyanate acrylate, acrylate, and ester solvent is used to pre-prepare the mixture. This reduces the slow side reaction between isocyanate acrylate and water. Furthermore, by dispersing the isocyanate acrylate in the acrylate and ester solvent, localized high cross-linking between the isocyanate acrylate and urea-formaldehyde resin is avoided, which is beneficial for the uniform coating of the isocyanate acrylate. Finally, the acrylate added together also increases the reaction response rate of the subsequent free radical copolymerization of acrylate and acrylic functional groups in the isocyanate.

[0035] (4) The outer coating uses a compound of tri(2-hydroxyethyl)isocyanurate triacrylate (THEICTA) and acrylate, which avoids the high cross-linking of THEICTA due to its 3-functional groups, which would increase the decomposition temperature and cause a mismatch with the decomposition and dehydration to carbonization temperature of intumescent flame retardants in fireproof materials, and may even inhibit early dehydration and foaming. Some acrylates can significantly reduce the cross-linking density, thus improving the adhesion of the film-forming material while maintaining the effect of improving foaming performance.

[0036] (5) The amount of isocyanate acrylate should be appropriate. If too little is used, the coating effect will be poor, and the effect of improving waterproof and fireproof performance will be insufficient. If too much is used, the isocyanate will consume a large amount of the amino and even hydroxyl groups inside the urea-formaldehyde resin, and the hydroxyl content determines the dehydration and foaming rate of the urea-formaldehyde resin. Therefore, the amount of isocyanate acrylate should be appropriate. Example

[0037] Example 1 Preparation of Modified Urea-Formaldehyde Resin A

[0038] Modified urea-formaldehyde resin is produced using an alkali-acid-alkali process, which includes the following steps:

[0039] (1) Add a certain mass of 4.05 kg (48.6 mol) of formaldehyde solution (36%) to the reactor, add a certain amount of deionized water, then adjust the pH to 8.0 with 30% sodium hydroxide aqueous solution, heat to 50°C, and then add the first batch of urea 0.8 kg and the first batch of melamine 0.315 kg under stirring conditions, raise the temperature to 95°C and keep it at the temperature for 30 min;

[0040] (2) Adjust the pH to 5.0 with 10% by weight formic acid, raise the temperature to 95°C, and continue the reaction until the viscosity of the system reaches 18s (tested at 30°C in Cup 4). Finally, cool the reactants to 70°C, adjust the pH to 7.0 with sodium hydroxide aqueous solution, add 1.0 kg of the second batch of urea and 0.315 kg of the second batch of melamine, stir evenly, and keep the reaction at 30 min.

[0041] (3) After cooling to a certain temperature, add 0.6 kg of the third batch of urea, keep the reaction at 70℃ for 20 min, cool to 40℃, and then adjust the pH value to 8.0 to obtain the basic modified urea-formaldehyde resin.

[0042] (4) While stirring, add 0.354 kg of a mixture of 5 wt% isocyanate ethyl acrylate and ethyl acrylate and 0.708 kg of ethyl acetate, with a mass ratio of 4:1.

[0043] (5) Add tri(2-hydroxyethyl)isocyanurate triacrylate (THEICTA) and ethyl acrylate (0.354 kg) in a mass ratio of 2:1.

[0044] (6) Add initiator solution and heat to 70°C. React for 2 hours to obtain modified urea-formaldehyde resin.

[0045] Example 2 Preparation of modified urea-formaldehyde resin B

[0046] Based on Example 1, in step (5), the mixture of tri(2-hydroxyethyl) isocyanurate triacrylate (THEICTA) and ethyl acrylate in a mass ratio of 2:1 was completely replaced with ethyl acrylate, and the other preparation steps were the same to obtain modified urea-formaldehyde resin B.

[0047] Example 3 Preparation of modified urea-formaldehyde resin C

[0048] Based on Example 1, in step (5), the mixture of tri(2-hydroxyethyl) isocyanurate triacrylate (THEICTA) and ethyl acrylate in a mass ratio of 2:1 was completely replaced with THEICTA, and the other preparation steps were the same to obtain modified urea-formaldehyde resin C.

[0049] Example 4 Preparation of modified urea-formaldehyde resin D

[0050] Based on Example 1, in step (4), 0.354 kg of the mixture of ethyl isocyanate acrylate and ethyl acrylate and ethyl acetate were completely replaced with 0.354 kg of ethyl isocyanate acrylate. The other preparation steps were the same, and modified urea-formaldehyde resin D was obtained.

[0051] Example 5 Preparation of modified urea-formaldehyde resin E

[0052] Based on Example 1, steps (4)-(6) are omitted. Meanwhile, 3.54 kg of acrylic resin elastic emulsion (solid content 20%) is added to the basic modified urea-formaldehyde resin, and the mixture is stirred at high speed for 20 minutes to obtain modified urea-formaldehyde resin E.

[0053] Example 6 Preparation of modified urea-formaldehyde resin F

[0054] Based on Example 1, steps (4)-(6) are omitted, and the basic modified urea-formaldehyde resin F is obtained directly.

[0055] Example 7 Preparation of fire-retardant coating

[0056] Fire-retardant coatings were prepared by mixing 6% expandable vermiculite, 12% coating additives and fillers, 24% intumescent flame retardant, 20% vinyl acetate-ethylene copolymer (VAE) emulsion, 20% modified urea-formaldehyde resin, and 18% tap water in a high-speed disperser at 1000 rpm, according to weight percentage. Fire-retardant coatings A, B, C, D, E, and F were obtained by using the fire-retardant coatings A, B, C, D, E, and F prepared in Examples 1-6. The VAE emulsion was EZ 3066, and the composition included 0.4% defoamer, 0.3% leveling agent, 0.3% thickener, 0.5% dispersant, 0.5% preservative, and 10% titanium dioxide. The intumescent flame retardant included 6% pentaerythritol, 12% ammonium polyphosphate, and 6% melamine.

[0057] Fire resistance performance test

[0058] The water-based fire-retardant coating for steel structures prepared in Example 7 was sprayed onto a steel plate, resulting in a coating thickness of 3 ± 0.1 mm. After 12 hours of surface drying, the fire resistance limit of the coating was tested according to the test method for thermal insulation efficiency deviation described in GB 14907-2018. The fire resistance limit of the water-based fire-retardant coating for steel structures prepared in Example 7 was tested, and the test results are shown in Table 1. The coating of this example was tested according to the standard GB 14907-2018 "Fire-retardant Coatings for Steel Structures", and the results are shown in Table 1.

[0059] Water resistance test

[0060] According to GB14907-2018 standard, the sample edges are sealed with a molten mixture of paraffin and rosin (mass ratio 1:1), with a sealing width of not less than 5 mm. After the mixture has completely solidified, continue curing for 24 hours. During testing, the entire sample is immersed in a container filled with tap water. The appearance of the fire-retardant coating on the sample surface should be observed and recorded during the experiment until the specified test time (24 hours) is reached. At the same time, to compare the differences in water resistance of different coatings, the time elapsed when delamination, blistering, and peeling of the coating occur should be recorded.

[0061] Table 1 Fire resistance and water resistance tests of fire-retardant coatings

[0062] coating Fire resistance time / min Water resistance (24-hour water immersion test: no peeling, bubbling, or flaking of the coating) Evaluation of the strength, uniformity and adhesion of the carbon foam layer Fire-retardant coating A 152 Pass (28h) High strength and uniformity Fire retardant coating B 122 Pass (28h) High strength and uniformity Fire retardant coating C 131 Pass (28h) High strength and uniformity Fire retardant coating D 135 Pass (27h) High strength and uniformity Fire retardant coating E 102 The coating began to peel off after 24 hours (12 hours). The strength is average and uneven, and it is easy to fall off. Fire retardant coating F 121 The coating began to peel off after 24 hours (8 hours). The strength is average and uneven, and it is easy to fall off.

[0063] As can be seen from Table 1, the water-based ultra-thin intumescent fireproof coating for steel structures of the present invention has good fire resistance and water resistance.

Claims

1. A fire-retardant coating, characterized in that, It comprises the following components by weight percentage: 10-30% vinyl acetate-ethylene copolymer (VAE) emulsion, 10-30% modified urea-formaldehyde resin, 5-20% expandable vermiculite, 10-30% coating additives and other fillers, 10-30% intumescent flame retardant, and 5-30% water; wherein, the modified urea-formaldehyde resin is obtained by chemically coating melamine-modified urea-formaldehyde resin with polyacrylate. The intumescent flame retardant consists of a low-molecular-weight carbon source, a char-forming catalyst, and a foaming agent. The low-molecular-weight carbon source is pentaerythritol, dipentaerythritol, or tripentaerythritol. The char-forming catalyst is ammonium polyphosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium metaphosphate, ammonium hypophosphite, ammonium phosphite, phosphorous acid, metaphosphoric acid, and / or orthophosphoric acid. The foaming agent is melamine, dicyandiamide, ammonium oxalate, urea, or hexamethylenetetramine. The weight ratio of the low-molecular-weight carbon source, char-forming catalyst, and foaming agent is (1-2):(1-2):(0.5-1.5). Coating additives include defoamers, leveling agents, dispersants, thickeners, and / or wetting agents. Other fillers include titanium dioxide. The modified urea-formaldehyde resin is manufactured using an alkali-acid-alkali process, specifically including the following steps: (1) Add a certain mass of formaldehyde solution to the reaction vessel, add a certain amount of deionized water, then adjust the pH to 7.5-9.0 with sodium hydroxide aqueous solution, and heat to 40-55℃. Then add the first batch of urea and the first batch of melamine under stirring conditions, raise the temperature to 85-95℃ and keep it at the temperature for 20-40 min or raise the temperature to 70-75℃ and keep it at the temperature for 50-80 min; (2) Adjust the pH to 5.0-5.5 with formic acid, raise the temperature to 80-95℃, continue to keep it at the temperature for a period of time, and finally cool the reactants to 65-75℃, adjust the pH to 7.0-7.5 with sodium hydroxide aqueous solution, add the second batch of urea and the second batch of melamine, stir evenly, and keep it at the temperature for 20-40 min; (3) After cooling to a certain temperature, add the third batch of urea, keep it at 70-90℃ and keep it at the temperature for 10-40 min, and then adjust the pH to 8.0-9.0 to obtain the basic modified urea-formaldehyde resin; (4) While stirring, add the pre-mixed mixture of isocyanate acrylate, acrylate and ester solvent, and react for 15-25 min; wherein, based on the basic modified urea-formaldehyde resin, the sum of the amounts of isocyanate acrylate and acrylate is 5-10 wt%; (5) While stirring, add 5-10 wt% of the mixture of tris(2-hydroxyethyl) isocyanurate triacrylate (THEICTA) and acrylate based on the basic modified urea-formaldehyde resin, with a mass ratio of (2-4):1; (6) Add the initiator solution and heat to 50-90℃, and react for 0.4-3.5 hours; to obtain the modified urea-formaldehyde resin.

2. The fire-retardant coating according to claim 1, characterized in that, In steps (1)-(3), the cumulative molar ratio of formaldehyde / (urea + melamine) is 1.05-1.

15.

3. The fire-retardant coating according to claim 1, characterized in that, In step (2), the reaction is kept at a constant temperature until the viscosity of the system reaches 16-20s. Finally, the reactants are cooled to 65-75℃. The test conditions are 30℃, and the Forte 4 cup is used for testing.

4. The fire-retardant coating according to claim 1, characterized in that, In step (4), the weight ratio of isocyanate acrylate to acrylate is (3-5):

1.

5. The fire-retardant coating according to claim 1, characterized in that, Isocyanate acrylates are ethyl isocyanate acrylates or ethyl isocyanate methacrylates.

6. The fire-retardant coating according to claim 1, characterized in that, In step (4), the ester solvents include one or more of ethyl acetate, octyl acetate, and n-butyl acetate.

7. The fire-retardant coating according to claim 1, characterized in that, In step (4), the acrylates are methyl methacrylate, ethyl methacrylate, and butyl methacrylate.

8. The fire-retardant coating according to claim 1, characterized in that, In step (5), the acrylates are methyl methacrylate, ethyl methacrylate, and butyl methacrylate.

9. The fire-retardant coating according to claim 1, characterized in that, In step (6), the initiator is one or more of sodium persulfate, azobisisobutyronitrile, benzoyl peroxide, tert-butyl peroxide, di-tert-butyl peroxide, diisopropylbenzene peroxide, and di-tert-pentyl peroxide.