Fireproof coating and preparation method thereof

Abstract

The invention discloses a fireproof coating and a preparation method thereof, and relates to the technical field of coatings. The fireproof coating comprises the following raw materials in parts by weight: 90-110 parts of modified magnesium oxide, 40-50 parts of magnesium chloride, 5-8 parts of magnesium sulfate, 1.5-3 parts of polyvinyl alcohol, 1-2 parts of starch, 0.3-0.8 part of borax, 70-90 parts of deionized water, 3-5 parts of modified melamine, 0.5-1 part of a titanate coupling agent and 2-4 parts of ammonium dihydrogen phosphate. The fireproof coating is scientific in raw material ratio and contains efficient flame-retardant components such as modified magnesium oxide and modified melamine. The modification process improves the synergistic flame retardant efficiency of the inorganic phase, and the titanate coupling agent enhances the compatibility. During preparation, step-by-step feeding, particle size control and grinding are performed to ensure fineness and uniformity. The paste is in a specific wiredrawing state, is free of caking and has good flame retardance and coating performance, raw materials are easy to obtain, and the process is controllable.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a fire-retardant coating and its preparation method. Background Technology

[0002] In fields such as construction, transportation, and power, fire hazards remain a critical issue threatening life and property safety. Fire-retardant coatings, as important fire protection materials, directly affect fire protection effectiveness. Traditional fire-retardant coatings suffer from insufficient flame retardant efficiency, poor coating adhesion, and weak weather resistance, making it difficult to meet the long-term fire protection requirements in complex environments.

[0003] Currently, most fire-retardant coatings on the market rely on a single flame-retardant mechanism. For example, while intumescent coatings can form a heat-insulating char layer, the char layer is prone to cracking and peeling off at high temperatures. Inorganic fire-retardant coatings have long-lasting flame retardancy, but the coating is brittle and prone to powdering and peeling. At the same time, some coatings use halogenated flame retardants, which release toxic gases when burning, causing secondary harm to the environment and human health.

[0004] Furthermore, poor dispersibility and compatibility of coating raw materials lead to poor coating uniformity, affecting the stability of fire resistance performance. Ordinary inorganic flame retardants such as magnesium oxide and melamine, when unmodified, tend to agglomerate in the base material, failing to fully exert their synergistic flame-retardant effect. This results in low flame-retardant efficiency of the coating, requiring large amounts to meet fire resistance standards, increasing coating thickness and cost.

[0005] Existing preparation processes also have shortcomings, such as uneven mixing of raw materials and improper particle size control, resulting in insufficient coating fineness and defects such as sagging and pinholes during application, affecting coating integrity and fire resistance. Therefore, developing a fire-retardant coating that combines high flame retardancy, good mechanical properties, environmental friendliness, and stable processing has become an important issue that urgently needs to be addressed in the field of coating technology. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a fire-retardant coating and its preparation method, which solves the problems of insufficient flame retardant efficiency, poor coating adhesion, poor raw material dispersion compatibility, and insufficient environmental friendliness of traditional coatings.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A fire-retardant coating comprises the following raw materials in parts by weight: 90-110 parts modified magnesium oxide, 40-50 parts magnesium chloride, 5-8 parts magnesium sulfate, 1.5-3 parts polyvinyl alcohol, 1-2 parts starch, 0.3-0.8 parts borax, 70-90 parts deionized water, 3-5 parts modified melamine, 0.5-1 part titanate coupling agent, and 2-4 parts ammonium dihydrogen phosphate.

[0009] Furthermore, the titanate coupling agent is isopropyl tris(dioctyl pyrophosphate) titanate, the starch is hydroxypropyl starch, the polyvinyl alcohol is type 1788, the particle size of the modified magnesium oxide is 1-5 μm, and the particle size of the modified melamine is 2-8 μm.

[0010] Furthermore, the modified magnesium oxide is prepared using the following specific steps:

[0011] A1. Add magnesium oxide powder to a three-necked flask, add a mixture of deionized water and ethanol, place in a 50°C constant temperature water bath, and stir at 350 rpm for 25 min; then add silane coupling agent KH-550, stir for 15 min, and then add 10% dilute nitric acid dropwise to adjust the pH to 5.0, raise the temperature to 65°C, and add 5% nano zinc oxide dispersion in 3 portions, with an interval of 10 min each time, while stirring at 400 rpm for 3.5 h; after the reaction is completed, cool to room temperature, centrifuge to obtain the solid, wash with deionized water and ethanol alternately 3 times, and dry in a vacuum drying oven at 75°C for 3 h;

[0012] Magnesium oxide is initially dispersed in a water-ethanol mixture at 50°C by stirring. Silane coupling agent KH-550 introduces amino groups through the condensation of alkoxy groups with surface hydroxyl groups. Nano zinc oxide is added in batches under acidic conditions and uniformly loaded by electrostatic attraction. Stirring at 65°C promotes the formation of a "magnesium oxide-zinc oxide" composite inorganic layer. The structure is fixed by washing and drying to enhance the inorganic synergistic flame retardancy.

[0013] A2. Add the first-modified magnesium oxide to a three-necked flask, add anhydrous ethanol, place in a 50°C constant temperature water bath, and stir at 450 rpm for 30 min to disperse; then add maleic anhydride-grafted polypropylene wax, stir for 20 min, add benzoyl peroxide, heat to 70°C, and stir at 400 rpm for 3 h; after the reaction is complete, cool, filter and separate, wash twice with anhydrous ethanol, and dry in a forced-air environment at 65°C for 2.5 h;

[0014] After the first modified product was dispersed in anhydrous ethanol, maleic anhydride-grafted polypropylene wax was grafted onto the magnesium oxide surface through esterification or amidation reactions initiated by benzoyl peroxide. Stirring at 70°C enhanced the grafting effect, the organic segments improved surface compatibility, reduced coating brittleness, and the organic modified structure was stabilized after washing and drying.

[0015] A3. Add the product after the second modification to a three-necked flask, add deionized water, and stir at 550 r / min for 25 min at room temperature; then add a mixture of silane coupling agent KH-550 and propylene glycol, stir for 15 min, add polyethyleneimine, adjust the speed to 500 r / min, raise the temperature to 50℃ and stir continuously for 4.5 h; after the reaction is completed, let it stand and separate into layers, take the lower precipitate, wash it with deionized water until neutral, and dry it in an oven at 70℃ for 5 h to obtain modified magnesium oxide.

[0016] After the secondary modified product is dispersed at high speed, the surface is further modified by a mixture of silane coupling agent KH-550 and propylene glycol. Polyethyleneimine introduces polar chains through the reaction of amino groups with active groups. Stirring at 50°C promotes bonding and enhances hydrogen bonding with organic base materials, ultimately forming a multilayer structure that improves adhesion and compatibility.

[0017] Furthermore, the ratio of magnesium oxide powder, deionized water, ethanol, silane coupling agent KH-550, dilute nitric acid, and nano zinc oxide dispersion in A1 is 50g:150mL:100mL:3g:5mL:30mL.

[0018] Furthermore, the ratio of anhydrous ethanol, maleic anhydride-grafted polypropylene wax, and benzoyl peroxide in A2 is 200mL:5g:1g.

[0019] Furthermore, the ratio of deionized water, silane coupling agent KH-550, propylene glycol, and polyethyleneimine in A3 is 200mL:2mL:8mL:4g.

[0020] Furthermore, the nano zinc oxide dispersion in A1 is added in three stages, with each stage spaced 10 minutes apart, and stirred at 400 r / min for 3.5 hours at 65°C. By adding the material in stages, the uniform loading of nano zinc oxide on the magnesium oxide surface is controlled, thereby improving the synergistic flame retardant efficiency of the inorganic phase.

[0021] Furthermore, the modified melamine is prepared using the following specific steps:

[0022] B1. Melamine was added to a three-necked flask, deionized water was added, and the flask was placed in a 60°C constant temperature water bath. The mixture was stirred at 250 rpm until it was evenly dispersed. Then, a 37% formaldehyde solution was added and stirred for 10 min. After stirring, a 5% sodium bicarbonate solution was added to adjust the pH to 9.0. The mixture was stirred for another 15 min. The temperature was then raised to 75°C, and urea was added in three portions, with an interval of 20 min between each addition. The mixture was stirred at 200 rpm for 3 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature to obtain the hydroxymethylated melamine preproduct.

[0023] Melamine is dispersed in water at 60°C and then undergoes hydroxymethylation with formaldehyde under alkaline conditions. The temperature is raised to 75°C and urea is added in stages to control the reaction rate and reduce excessive cross-linking, forming a stable hydroxymethylated preproduct, which provides an active basis for subsequent modification.

[0024] B2. Add ethylene glycol monomethyl ether to the first modified product, place it in a 50°C constant temperature water bath, and stir at 300 r / min for 20 min; then add 15% phosphoric acid solution to adjust the pH to 5.5, stir for 10 min, add sodium benzoate, raise the temperature to 80°C, and stir at 350 r / min for 4 h; after cooling, neutralize with 10% sodium hydroxide solution to pH 7.0, let stand for 30 min, and then filter to collect the filtrate;

[0025] The hydroxymethylated product is dispersed in ethylene glycol monomethyl ether, and the etherification reaction is initiated under acidic conditions to form a network structure. Sodium benzoate inhibits side reactions and enhances thermal stability. After neutralization and filtration, impurities are removed, thereby improving the purity and stability of the product.

[0026] B3. Add the filtrate after the second modification to a three-necked flask, stir at 400 r / min for 15 min at room temperature, add ammonium polyphosphate, stir for 10 min, add pentaerythritol, heat to 90℃, and stir at 350 r / min for 3 h; then add methylcellulose and continue stirring for 1.5 h; after the reaction is complete, cool to room temperature, and remove the solvent by vacuum distillation at -0.09 MPa and 60℃ to obtain modified melamine.

[0027] Ammonium polyphosphate (acid source) and pentaerythritol (carbon source) were added to construct an intumescent flame retardant system with modified melamine (gas source); stirring at 90°C promoted the synergistic effect of the flame retardant components, methylcellulose improved dispersibility, and the solvent was removed by vacuum distillation to form a modified product with both intumescent and dispersible functions.

[0028] Furthermore, the ratio of melamine, deionized water, formaldehyde solution, sodium bicarbonate solution, and urea in B1 is 20g:150mL:30mL:5mL:9g.

[0029] Furthermore, the ratio of ethylene glycol monomethyl ether, phosphoric acid solution, and sodium benzoate in B2 is 20 mL: 8 mL: 2 g.

[0030] Furthermore, the ratio of ammonium polyphosphate, pentaerythritol, and methylcellulose in B3 is 6g:4g:2g.

[0031] A method for preparing a fire-retardant coating specifically includes the following steps:

[0032] S1. Heat deionized water to 60℃, then add modified magnesium oxide and stir at 400r / min for 30min to initially disperse the modified magnesium oxide. Then cool down to 40℃ and continue stirring at 350r / min for 30min to fully disperse the modified magnesium oxide, obtaining dispersion A, which is then set aside for later use. Gradient cooling and variable speed stirring are used to achieve uniform dispersion of modified magnesium oxide without agglomeration.

[0033] S2. Take another deionized water and add magnesium chloride, magnesium sulfate, and ammonium dihydrogen phosphate in sequence. After each addition of raw material, stir at 300 r / min for 15 min to ensure that each salt is completely dissolved until the solution is completely transparent to obtain solution B. Adding materials in sequence and stirring to dissolve them avoids precipitation reactions when the salts are mixed, ensuring that the inorganic salts are uniformly dissolved, laying the foundation for subsequent fusion with the organic phase.

[0034] S3. Heat deionized water to 85°C, add polyvinyl alcohol, keep warm and stir at 350 r / min for 40 min until the polyvinyl alcohol is completely dissolved to form a uniform adhesive solution. Then cool down to 40°C and add titanate coupling agent. Stir for 10 min to evenly disperse it in the adhesive solution to obtain adhesive solution C. The high temperature of 85°C ensures that the polyvinyl alcohol is fully dissolved to form a stable adhesive solution. Adding the coupling agent after cooling avoids the high temperature from damaging the active structure of the coupling agent and ensures its compatibility improvement effect.

[0035] S4. Place starch and modified melamine into a mixer and dry mix at 250 r / min for 5 min. Add borax and continue dry mixing for 3 min to ensure that the three dry powder materials are fully and evenly mixed to obtain powder D. Dry mixing pretreatment reduces the risk of agglomeration of dry powder materials in the wet mixing stage and ensures uniform integration with the base material in the subsequent process.

[0036] S5. Slowly pour the adhesive C into the solution B while stirring at 300 r / min to gradually mix the adhesive with the inorganic salt solution. After all the adhesive is added, continue stirring for 15 min to ensure that the two liquid phases are completely mixed to obtain the composite solution E.

[0037] S6. Add dispersion A to composite liquid E in three portions, with a 3-minute interval between each addition. During the first addition, maintain a speed of 200 rpm to prevent splashing. After all the dispersion A has been added, increase the speed to 350 rpm and stir for 20 minutes to ensure thorough mixing of the dispersion and composite liquid, resulting in base material F. Add powder D to base material F in two portions, with a 5-minute interval between each addition. After the first addition, stir at 300 rpm for 10 minutes to initially disperse some of the powder. After the second addition, increase the speed to 450 rpm and stir for 30 minutes until the paste reaches a stringy state, ensuring complete integration of all powder and base material, resulting in preliminary slurry G. Stepwise addition and variable-speed stirring prevent excessively high local concentrations in the system, and speed control promotes thorough material integration.

[0038] S7. Transfer the initial slurry G to the grinding equipment. Use circulating water to cool and control the grinding temperature to ≤50℃. Grind until the particle size reaches 5-10μm to ensure the fineness and uniformity of the coating. Allow it to cool naturally to room temperature to obtain the final fireproof coating product. Low-temperature grinding avoids high temperature damage to the structure of flame-retardant components. Controlling the particle size to 5-10μm improves the smoothness of the coating and the utilization rate of flame-retardant components, ensuring stable construction performance and fireproof effect.

[0039] Furthermore, the "the paste is in a stringy state" in S6 specifically means that when the paste is picked up with a glass rod, it forms a continuous string with a length of 5-8cm, and there is no obvious clumping residue after the string breaks.

[0040] This invention provides a fire-retardant coating and its preparation method, which has the following beneficial effects:

[0041] 1. By subjecting magnesium oxide to three modifications, an inorganic flame-retardant layer is first constructed using silane coupling agent KH-550 and nano-zinc oxide. Then, maleic anhydride-grafted polypropylene wax is used to improve interfacial compatibility. Finally, polyethyleneimine is used to enhance surface activity. Combined with the synergistic effect of modified melamine and ammonium dihydrogen phosphate, a multi-component flame-retardant system is formed. At high temperatures, this system significantly improves the flame-retardant efficiency and fire resistance limit of the coating through multiple mechanisms, including inorganic phase insulation, expanded char layer barrier, and release of flame-retardant gases, thus solving the problem of insufficient effectiveness of traditional coatings with a single flame-retardant mechanism.

[0042] 2. Polyvinyl alcohol (PEA) of type 1788 and hydroxypropyl starch were selected as film-forming substances, and a titanate coupling agent was used to improve the compatibility between inorganic fillers and organic binders. Modified magnesium oxide, after surface organic modification, exhibited enhanced interfacial bonding with the PVA adhesive. The introduction of maleic anhydride-grafted polypropylene wax reduced the coating's brittleness. During the preparation process, controlling the dispersion speed and grinding particle size to 5-10 μm ensured a uniform and stable coating system, ultimately improving coating adhesion, reducing the likelihood of powdering, cracking, or peeling, and extending the service life of the fire-resistant protection.

[0043] 3. During the preparation process, the temperature, rotation speed, and reaction time of each step are strictly controlled to ensure that the raw materials are fully mixed and reacted. The grinding process achieves a coating particle size of 5-10μm, and combined with the "stringy state" quality control standard, the fineness and uniformity of the coating are guaranteed. Problems such as sagging and pinholes are less likely to occur during application, thus improving the integrity of the coating.

[0044] 4. The core flame-retardant system of this invention achieves high-efficiency flame retardancy through the synergistic effect of modified magnesium oxide, modified melamine, and ammonium dihydrogen phosphate. Specifically: the modified magnesium oxide undergoes a three-step modification process to form an inorganic-organic hybrid structure, which insulates against heat at high temperatures through endothermic decomposition and a dense oxide layer; the modified melamine, acting as a gas source, forms an expansion system with ammonium polyphosphate (acid source) and pentaerythritol (carbon source), generating a heat-insulating carbon layer; ammonium dihydrogen phosphate decomposes to produce non-flammable gases such as ammonia and water vapor to dilute oxygen. Magnesium chloride in the system mainly decomposes into magnesium oxide and trace amounts of hydrogen chloride at high temperatures. According to flue gas toxicity tests, its HCl release is less than 0.1%, far below the toxicity threshold of halogenated flame retardants. This invention releases no toxic gases such as dioxins or hydrogen halides during combustion, making it relatively environmentally friendly. Detailed Implementation

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Example 1: Preparation of fire-retardant coating. The specific preparation steps are as follows:

[0047] S1. Take 20 parts of deionized water and heat it to 60°C. Then add 90 parts of modified magnesium oxide and stir at 400 r / min for 30 min to initially disperse the modified magnesium oxide. Then cool it down to 40°C and continue stirring at 350 r / min for 30 min to fully disperse the modified magnesium oxide and obtain dispersion A. Let it stand for later use.

[0048] S2. Add 40 parts magnesium chloride, 5 parts magnesium sulfate, and 2 parts ammonium dihydrogen phosphate to 35 parts of deionized water in sequence. After each addition of raw material, stir at 300 r / min for 15 min to ensure that each salt is completely dissolved until the solution is completely transparent to obtain solution B.

[0049] S3. Take 15 parts of deionized water and heat it to 85°C. Add 1.5 parts of polyvinyl alcohol, keep it warm and stir at 350 r / min for 40 min until the polyvinyl alcohol is completely dissolved to form a uniform adhesive solution. Then cool it down to 40°C and add 0.5 parts of titanate coupling agent. Stir for 10 min to make it evenly dispersed in the adhesive solution to obtain adhesive solution C.

[0050] S4. Place 1 part starch and 3 parts modified melamine into a mixer and dry mix at 250 r / min for 5 min. Add 0.3 parts borax and continue to dry mix for 3 min to ensure that the three dry powder materials are fully mixed and uniform, thus obtaining powder D.

[0051] S5. Slowly pour the adhesive C into the solution B while stirring at 300 r / min to gradually mix the adhesive with the inorganic salt solution. After all the adhesive is added, continue stirring for 15 min to ensure that the two liquid phases are completely mixed to obtain the composite solution E.

[0052] S6. Add dispersion A to composite liquid E in 3 portions, with an interval of 3 minutes between each addition. When adding for the first time, maintain a speed of 200 r / min to prevent liquid splashing. After all the liquid has been added, increase the speed to 350 r / min and stir for 20 minutes to ensure that the dispersion and composite liquid are fully mixed to obtain base material F. Add powder D to base material F in 2 portions, with an interval of 5 minutes between each addition. After the first addition, stir at 300 r / min for 10 minutes to allow some powder to be initially dispersed. After the second addition, increase the speed to 450 r / min and stir for 30 minutes until the paste becomes stringy, ensuring that all powder and base material are completely integrated to obtain preliminary slurry G.

[0053] S7. Transfer the initial slurry G to the grinding equipment, control the grinding temperature to ≤50℃ with circulating water cooling, grind until the particle size reaches 5-10μm to ensure the fineness and uniformity of the coating, and allow it to cool naturally to room temperature to obtain the final fireproof coating product.

[0054] Example 2: Preparation of fire-retardant coating. The specific preparation steps are as follows:

[0055] S1. Take 30 parts of deionized water and heat it to 60°C. Then add 110 parts of modified magnesium oxide and stir at 400 r / min for 30 min to initially disperse the modified magnesium oxide. Then cool it down to 40°C and continue stirring at 350 r / min for 30 min to fully disperse the modified magnesium oxide and obtain dispersion A. Let it stand for later use.

[0056] S2. Add 50 parts magnesium chloride, 8 parts magnesium sulfate, and 4 parts ammonium dihydrogen phosphate to 40 parts of deionized water in sequence. After each addition of raw material, stir at 300 r / min for 15 min to ensure that each salt is completely dissolved until the solution is completely transparent to obtain solution B.

[0057] S3. Take 20 parts of deionized water and heat it to 85°C. Add 3 parts of polyvinyl alcohol, keep it warm and stir at 350 r / min for 40 min until the polyvinyl alcohol is completely dissolved to form a uniform solution. Then cool it down to 40°C and add 1 part of titanate coupling agent. Stir for 10 min to make it evenly dispersed in the solution to obtain solution C.

[0058] S4. Place 2 parts starch and 5 parts modified melamine into a mixer and dry mix at 250 r / min for 5 min. Add 0.8 parts borax and continue to dry mix for 3 min to ensure that the three dry powder materials are fully mixed and uniform, thus obtaining powder D.

[0059] S5. Slowly pour the adhesive C into the solution B while stirring at 300 r / min to gradually mix the adhesive with the inorganic salt solution. After all the adhesive is added, continue stirring for 15 min to ensure that the two liquid phases are completely mixed to obtain the composite solution E.

[0060] S6. Add dispersion A to composite liquid E in 3 portions, with an interval of 3 minutes between each addition. When adding for the first time, maintain a speed of 200 r / min to prevent liquid splashing. After all the liquid has been added, increase the speed to 350 r / min and stir for 20 minutes to ensure that the dispersion and composite liquid are fully mixed to obtain base material F. Add powder D to base material F in 2 portions, with an interval of 5 minutes between each addition. After the first addition, stir at 300 r / min for 10 minutes to allow some powder to be initially dispersed. After the second addition, increase the speed to 450 r / min and stir for 30 minutes until the paste becomes stringy, ensuring that all powder and base material are completely integrated to obtain preliminary slurry G.

[0061] S7. Transfer the initial slurry G to the grinding equipment, control the grinding temperature to ≤50℃ with circulating water cooling, grind until the particle size reaches 5-10μm to ensure the fineness and uniformity of the coating, and allow it to cool naturally to room temperature to obtain the final fireproof coating product.

[0062] Example 3: Preparation of fire-retardant coating. The specific preparation steps are as follows:

[0063] S1. Take 25 parts of deionized water and heat it to 60°C. Then add 100 parts of modified magnesium oxide and stir at 400 r / min for 30 min to initially disperse the modified magnesium oxide. Then cool it down to 40°C and continue stirring at 350 r / min for 30 min to fully disperse the modified magnesium oxide and obtain dispersion A. Let it stand for later use.

[0064] S2. Add 45 parts magnesium chloride, 6 parts magnesium sulfate, and 3 parts ammonium dihydrogen phosphate to 37 parts of deionized water in sequence. After each addition of raw material, stir at 300 r / min for 15 min to ensure that each salt is completely dissolved until the solution is completely transparent to obtain solution B.

[0065] S3. Take 17 parts of deionized water and heat it to 85°C. Add 2 parts of polyvinyl alcohol, keep it warm and stir at 350 r / min for 40 min until the polyvinyl alcohol is completely dissolved to form a uniform adhesive solution. Then cool it down to 40°C and add 0.7 parts of titanate coupling agent. Stir for 10 min to make it evenly dispersed in the adhesive solution to obtain adhesive solution C.

[0066] S4. Place 1.5 parts of starch and 4 parts of modified melamine into a mixer and dry mix at 250 r / min for 5 min. Add 0.5 parts of borax and continue to dry mix for 3 min to ensure that the three dry powder materials are fully mixed and uniform, thus obtaining powder D.

[0067] S5. Slowly pour the adhesive C into the solution B while stirring at 300 r / min to gradually mix the adhesive with the inorganic salt solution. After all the adhesive is added, continue stirring for 15 min to ensure that the two liquid phases are completely mixed to obtain the composite solution E.

[0068] S6. Add dispersion A to composite liquid E in 3 portions, with an interval of 3 minutes between each addition. When adding for the first time, maintain a speed of 200 r / min to prevent liquid splashing. After all the liquid has been added, increase the speed to 350 r / min and stir for 20 minutes to ensure that the dispersion and composite liquid are fully mixed to obtain base material F. Add powder D to base material F in 2 portions, with an interval of 5 minutes between each addition. After the first addition, stir at 300 r / min for 10 minutes to allow some powder to be initially dispersed. After the second addition, increase the speed to 450 r / min and stir for 30 minutes until the paste becomes stringy, ensuring that all powder and base material are completely integrated to obtain preliminary slurry G.

[0069] S7. Transfer the initial slurry G to the grinding equipment, control the grinding temperature to ≤50℃ with circulating water cooling, grind until the particle size reaches 5-10μm to ensure the fineness and uniformity of the coating, and allow it to cool naturally to room temperature to obtain the final fireproof coating product.

[0070] Example 4: Preparation of modified magnesium oxide. The specific preparation steps are as follows:

[0071] A1. Take 50g of magnesium oxide powder and add it to a three-necked flask. Add a mixture of 150mL of deionized water and 100mL of ethanol. Place the flask in a 50℃ constant temperature water bath and stir at 350r / min for 25min. Then add 3g of silane coupling agent KH-550 and stir for 15min. Add 5mL of 10% dilute nitric acid dropwise to adjust the pH to 5.0. Raise the temperature to 65℃ and add 30mL of 5% nano zinc oxide dispersion in three portions, with an interval of 10min between each addition. Stir at 400r / min for 3.5h. After the reaction is complete, cool to room temperature, centrifuge to obtain the solid, wash it three times alternately with deionized water and ethanol, and dry it in a vacuum drying oven at 75℃ for 3h.

[0072] A2. Add the first-modified magnesium oxide to a three-necked flask, add 200 mL of anhydrous ethanol, place in a 50°C constant temperature water bath, and stir at 450 r / min for 30 min; then add 5 g of maleic anhydride-grafted polypropylene wax, stir for 20 min, add 1 g of benzoyl peroxide, heat to 70°C, and stir at 400 r / min for 3 h; after the reaction is complete, cool, filter and separate, wash twice with anhydrous ethanol, and dry at 65°C for 2.5 h.

[0073] A3. Add the product after the second modification to a three-necked flask, add 200 mL of deionized water, and stir at 550 r / min for 25 min at room temperature; then add 2 mL of a mixture of silane coupling agent KH-550 and 8 mL of propylene glycol, stir for 15 min, then add 4 g of polyethyleneimine, adjust the speed to 500 r / min, raise the temperature to 50 °C and continue stirring for 4.5 h; after the reaction is completed, let it stand and separate into layers, take the lower precipitate and wash it with deionized water until neutral, and dry it in an oven at 70 °C for 5 h to obtain modified magnesium oxide.

[0074] Example 5: Preparation of modified melamine. The specific preparation steps are as follows:

[0075] B1. Add 20g of melamine to a three-necked flask, add 150mL of deionized water, place in a 60℃ constant temperature water bath, and stir at 250r / min until evenly dispersed; then add 30mL of 37% formaldehyde solution, stir for 10min, then add 5mL of 5% sodium bicarbonate solution to adjust the pH to 9.0, continue stirring for 15min, then raise the temperature to 75℃, add 9g of urea in 3 portions, 20min apart each time, and maintain stirring at 200r / min for 3h; after the reaction is complete, cool naturally to room temperature to obtain the hydroxymethylated melamine preproduct;

[0076] B2. Add 20 mL of ethylene glycol monomethyl ether to the first modified product, place it in a 50°C constant temperature water bath, and stir at 300 r / min for 20 min; then add 8 mL of 15% phosphoric acid solution to adjust the pH to 5.5, stir for 10 min, add 2 g of sodium benzoate, raise the temperature to 80°C, and stir at 350 r / min for 4 h; after cooling, neutralize with 10% sodium hydroxide solution to pH 7.0, let stand for 30 min, and then filter to collect the filtrate;

[0077] B3. Add the filtrate after the second modification to a three-necked flask, stir at 400 r / min for 15 min at room temperature, add 6 g of ammonium polyphosphate, stir for 10 min, then add 4 g of pentaerythritol, heat to 90 °C, and stir at 350 r / min for 3 h; then add 2 g of methylcellulose and continue stirring for 1.5 h; after the reaction is complete, cool to room temperature, and remove the solvent by vacuum distillation at -0.09 MPa and 60 °C to obtain modified melamine.

[0078] Comparative Example 1: Fire-retardant coating was prepared. The specific preparation steps are as follows:

[0079] The remaining steps remain the same, except that the modified magnesium oxide in Example 3 is replaced with untreated magnesium oxide to prepare a fire-retardant coating.

[0080] Comparative Example 2: Fire-retardant coating was prepared. The specific preparation steps are as follows:

[0081] The remaining steps remain the same, except that the modified melamine in Example 3 is replaced with untreated melamine to prepare a fire-retardant coating.

[0082] Performance testing

[0083]

[0084] According to the performance test results, the fire-retardant coatings of Examples 1-3 of this invention showed excellent performance in terms of fire resistance limit (2.1-2.5h), coating adhesion (0-1 level), flame retardant performance (oxygen index 38%-42%), coating water resistance (96-110h without blistering or peeling), and high-temperature char layer integrity (dense and without cracking). In contrast, the comparative examples 1-2, which used unmodified magnesium oxide or melamine, showed a significant decrease in all performance aspects, fully demonstrating the role of modified raw materials in improving coating performance.

[0085] 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 fire-retardant coating, characterized in that: It contains the following raw materials in parts by weight: 90-110 parts modified magnesium oxide, 40-50 parts magnesium chloride, 5-8 parts magnesium sulfate, 1.5-3 parts polyvinyl alcohol, 1-2 parts starch, 0.3-0.8 parts borax, 70-90 parts deionized water, 3-5 parts modified melamine, 0.5-1 part titanate coupling agent, and 2-4 parts ammonium dihydrogen phosphate.

2. The fire-retardant coating according to claim 1, characterized in that: The titanate coupling agent is isopropyltris(dioctylpyrophosphate) titanate, the starch is hydroxypropyl starch, the polyvinyl alcohol is type 1788, the particle size of the modified magnesium oxide is 1-5 μm, and the particle size of the modified melamine is 2-8 μm.

3. The fire-retardant coating according to claim 1, characterized in that: The modified magnesium oxide is prepared by the following steps: A1. Add magnesium oxide powder to a three-necked flask, add a mixture of deionized water and ethanol, place in a 50°C constant temperature water bath, and stir at 350 rpm for 25 min; then add silane coupling agent KH-550, stir for 15 min, and then add 10% dilute nitric acid dropwise to adjust the pH to 5.0, raise the temperature to 65°C, and add 5% nano zinc oxide dispersion in 3 portions, with an interval of 10 min each time, while stirring at 400 rpm for 3.5 h; after the reaction is completed, cool to room temperature, centrifuge to obtain the solid, wash with deionized water and ethanol alternately 3 times, and dry in a vacuum drying oven at 75°C for 3 h; A2. Add the first-modified magnesium oxide to a three-necked flask, add anhydrous ethanol, place in a 50°C constant temperature water bath, and stir at 450 rpm for 30 min to disperse; then add maleic anhydride-grafted polypropylene wax, stir for 20 min, add benzoyl peroxide, heat to 70°C, and stir at 400 rpm for 3 h; after the reaction is complete, cool, filter and separate, wash twice with anhydrous ethanol, and dry in a forced-air environment at 65°C for 2.5 h; A3. Add the product after the second modification to a three-necked flask, add deionized water, and stir at 550 r / min for 25 min at room temperature; then add a mixture of silane coupling agent KH-550 and propylene glycol, stir for 15 min, add polyethyleneimine, adjust the speed to 500 r / min, raise the temperature to 50℃ and stir continuously for 4.5 h; after the reaction is completed, let it stand and separate into layers, take the lower precipitate, wash it with deionized water until neutral, and dry it in an oven at 70℃ for 5 h to obtain modified magnesium oxide.

4. The fire-retardant coating according to claim 3, characterized in that: The ratio of magnesium oxide powder, deionized water, ethanol, silane coupling agent KH-550, dilute nitric acid, and nano zinc oxide dispersion in A1 is 50g:150mL:100mL:3g:5mL:30mL. The ratio of anhydrous ethanol, maleic anhydride-grafted polypropylene wax, and benzoyl peroxide in A2 is 200mL:5g:1g. The ratio of deionized water, silane coupling agent KH-550, propylene glycol, and polyethyleneimine in A3 is 200mL:2mL:8mL:4g.

5. A fire-retardant coating according to claim 3, characterized in that: The nano zinc oxide dispersion in A1 was added in three stages, with each stage spaced 10 minutes apart, and stirred at 400 r / min for 3.5 hours at 65°C. By adding the material in stages, the uniform loading of nano zinc oxide on the magnesium oxide surface was controlled, thereby improving the synergistic flame retardant efficiency of the inorganic phase.

6. The fire-retardant coating according to claim 1, characterized in that: The modified melamine is prepared using the following specific steps: B1. Melamine was added to a three-necked flask, deionized water was added, and the flask was placed in a 60°C constant temperature water bath. The mixture was stirred at 250 rpm until it was evenly dispersed. Then, a 37% formaldehyde solution was added and stirred for 10 min. After stirring, a 5% sodium bicarbonate solution was added to adjust the pH to 9.

0. The mixture was stirred for another 15 min. The temperature was then raised to 75°C, and urea was added in three portions, with an interval of 20 min between each addition. The mixture was stirred at 200 rpm for 3 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature to obtain the hydroxymethylated melamine preproduct. B2. Add ethylene glycol monomethyl ether to the first modified product, place it in a 50°C constant temperature water bath, and stir at 300 r / min for 20 min; then add 15% phosphoric acid solution to adjust the pH to 5.5, stir for 10 min, add sodium benzoate, raise the temperature to 80°C, and stir at 350 r / min for 4 h; after cooling, neutralize with 10% sodium hydroxide solution to pH 7.0, let stand for 30 min, and then filter to collect the filtrate; B3. Add the filtrate after the second modification to a three-necked flask, stir at 400 r / min for 15 min at room temperature, add ammonium polyphosphate, stir for 10 min, add pentaerythritol, heat to 90℃, and stir at 350 r / min for 3 h; then add methylcellulose and continue stirring for 1.5 h; after the reaction is complete, cool to room temperature, and remove the solvent by vacuum distillation at -0.09 MPa and 60℃ to obtain modified melamine.

7. A fire-retardant coating according to claim 6, characterized in that: The ratio of melamine, deionized water, formaldehyde solution, sodium bicarbonate solution, and urea in B1 is 20g:150mL:30mL:5mL:9g; The ratio of ethylene glycol monomethyl ether, phosphoric acid solution, and sodium benzoate in B2 is 20 mL: 8 mL: 2 g; The ratio of ammonium polyphosphate, pentaerythritol, and methylcellulose in B3 is 6g:4g:2g.

8. A method for preparing a fire-retardant coating, characterized in that: Specifically, it includes the following steps: S1. Heat deionized water to 60°C, then add modified magnesium oxide and stir at 400 r / min for 30 min to initially disperse the modified magnesium oxide. Then cool down to 40°C and continue stirring at 350 r / min for 30 min to fully disperse the modified magnesium oxide and obtain dispersion A. Let stand for later use. S2. Take another deionized water and add magnesium chloride, magnesium sulfate and ammonium dihydrogen phosphate in sequence. After each addition of raw material, stir at 300 r / min for 15 min to ensure that each salt is completely dissolved until the solution is completely transparent to obtain solution B. S3. Heat deionized water to 85°C, add polyvinyl alcohol, keep warm and stir at 350 r / min for 40 min until the polyvinyl alcohol is completely dissolved to form a uniform solution. Then cool down to 40°C and add titanate coupling agent. Stir for 10 min to make it evenly dispersed in the solution to obtain solution C. S4. Place starch and modified melamine into a mixer and dry mix at 250 r / min for 5 min. Add borax and continue dry mixing for 3 min to ensure that the three dry powder materials are fully mixed and uniform, thus obtaining powder D. S5. Slowly pour the adhesive C into the solution B while stirring at 300 r / min to gradually mix the adhesive with the inorganic salt solution. After all the adhesive is added, continue stirring for 15 min to ensure that the two liquid phases are completely mixed to obtain the composite solution E. S6. Add dispersion A to composite liquid E in 3 portions, with an interval of 3 minutes between each addition. When adding for the first time, maintain a speed of 200 r / min to prevent liquid splashing. After all the liquid has been added, increase the speed to 350 r / min and stir for 20 minutes to ensure that the dispersion and composite liquid are fully mixed to obtain base material F. Add powder D to base material F in two batches, with a 5-minute interval between each batch. After the first addition, stir at 300 rpm for 10 minutes to allow some powder to be initially dispersed. After the second addition, increase the stirring speed to 450 rpm for 30 minutes until the paste becomes stringy, so that all powder and base material are completely blended to obtain the initial slurry G. S7. Transfer the initial slurry G to the grinding equipment, control the grinding temperature to ≤50℃ with circulating water cooling, grind until the particle size reaches 5-10μm to ensure the fineness and uniformity of the coating, and allow it to cool naturally to room temperature to obtain the final fireproof coating product.

9. The method for preparing a fire-retardant coating according to claim 8, characterized in that: The phrase "the paste is in a stringy state" in S6 specifically means that when the paste is lifted with a glass rod, it forms a continuous string with a length of 5-8cm, and there is no obvious clumping residue after the string breaks.

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