Silica sol-based flame-retardant coating and preparation method thereof

Abstract

The invention relates to the technical field of silica sol coatings, in particular to a silica sol-based flame-retardant coating and a preparation method thereof. The preparation method comprises the following steps: S1, carrying out hydrolytic polycondensation on ethyl orthosilicate and 3-glycidyl ether oxypropyl triethoxy silane to obtain epoxy modified silica sol; s2, enabling DOPO to react with maleic anhydride to obtain carboxyl modified DOPO; s3, carrying out esterification reaction on the epoxy group modified silica sol, glycidyl methacrylate, monoglycidyl ether terminated polydimethylsiloxane and the carboxyl modified DOPO to obtain DOPO modified silica sol containing unsaturated double bonds; and S4, initiating polymerization of the DOPO modified silica sol containing unsaturated double bonds and an acrylate monomer to obtain polyacrylate / DOPO modified silica sol, namely the silica sol-based flame-retardant coating.

Description

Technical Field

[0001] The invention relates to the technical field of silica sol coatings, in particular to a silica sol-based flame retardant coating and a preparation method thereof. Background Art

[0002] As demand for wood materials in the construction and home furnishing sectors grows, the fire hazards caused by its flammability are becoming increasingly prominent. Wood combustion produces large amounts of heat, smoke, and toxic gases. High temperatures accelerate the spread of fire, smoke significantly reduces visibility at the scene, and toxic gases can even cause suffocation and death. Therefore, to eliminate this potential fire hazard, flame retardant treatment of wood is necessary to improve its fire safety.

[0003] Currently, the most common method for treating wood with flame retardant treatment is to apply a flame retardant layer, such as a silica sol layer, to the wood surface. Although silica sol layers have good flame retardant effects, they also have drawbacks such as high brittleness, poor adhesion, and poor water resistance, which to some extent limit their application.

[0004] Based on this, the present invention proposes a silica sol-based flame retardant coating and a preparation method thereof, which is of great significance. Summary of the Invention

[0005] The object of the present invention is to provide a silica sol-based flame retardant coating and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for preparing a silica sol-based flame retardant coating comprises the following steps: S1: Epoxy-modified silica sol is obtained by hydrolysis and polycondensation of tetraethyl orthosilicate and 3-glycidyloxypropyltriethoxysilane; S2: DOPO reacts with maleic anhydride to obtain carboxyl-modified DOPO; S3: Epoxy-modified silica sol, glycidyl methacrylate, monoglycidyl ether-terminated polydimethylsiloxane and carboxyl-modified DOPO undergo esterification reaction to obtain DOPO-modified silica sol containing unsaturated double bonds; S4: DOPO-modified silica sol containing unsaturated double bonds initiates polymerization with acrylate monomer to obtain polyacrylate / DOPO-modified silica sol, i.e., silica sol-based flame retardant coating.

[0007] Furthermore, the preparation method of the silica sol-based flame retardant coating comprises the following steps, specifically: S1: Add ethyl orthosilicate, 3-glycidyloxypropyltriethoxysilane, ethanol, hydrochloric acid, and deionized water into a reaction vessel, stir and heat to 60-80°C, stir and react for 6-12 hours, and terminate the reaction to obtain epoxy-modified silica sol; S2: Under nitrogen protection, DOPO and toluene are added to a reaction vessel and stirred to mix evenly. Maleic anhydride is then added thereto, and the mixture is heated to 90-100°C with stirring for 6-12 hours. The reaction is terminated, and the carboxyl-modified DOPO is obtained by separation and purification. S3: Under nitrogen protection, carboxyl-modified DOPO is added to epoxy-modified silica sol, and the mixture is stirred and mixed evenly. Then, 3,5-diisopropyl chromium salicylate is added thereto, and the mixture is heated to 70-80°C with stirring and reacted for 2-6 hours. Then, monoglycidyl ether-terminated polydimethylsiloxane is added thereto, and the mixture is stirred and reacted for 1-3 hours. Finally, glycidyl methacrylate and a polymerization inhibitor are added thereto, and the mixture is stirred and reacted for 2-4 hours. The reaction is terminated, and the mixture is separated and purified to obtain DOPO-modified silica sol containing unsaturated double bonds. S4: Under nitrogen protection, DOPO-modified silica sol containing unsaturated double bonds, acrylate monomer, alkylphenol polyoxyethylene ether, and deionized water are added to a reaction vessel, stirred for pre-emulsification, then stirred and heated to 70-80°C, and then an ammonium persulfate aqueous solution is added dropwise thereto for 1-2 hours. After the addition is completed, the reaction is continued with stirring for 4-8 hours, and the reaction is terminated. Ammonia water is added to adjust the pH to neutral, and the polyacrylate / DOPO-modified silica sol, i.e., a silica sol-based flame retardant coating, is obtained through separation and purification.

[0008] Furthermore, the molar ratio of the ethyl orthosilicate to 3-glycidyloxypropyltriethoxysilane is 4:1.

[0009] Furthermore, the molar ratio of the ethanol, deionized water, hydrochloric acid and n(Si) is 4:4:0.002:1; wherein the hydrochloric acid is a 0.1 mol / L hydrochloric acid solution.

[0010] Furthermore, the molar ratio of DOPO to maleic anhydride is (1-1.05):1.

[0011] Furthermore, the amount of toluene added is 3 times the total mass of DOPO and maleic anhydride.

[0012] Furthermore, the amounts of raw material components required for preparing the DOPO-modified silica sol containing unsaturated double bonds are, by weight, 20 parts of epoxy-modified silica sol, 6-8 parts of carboxyl-modified DOPO, 1.4-2.6 parts of monoglycidyl ether-terminated polydimethylsiloxane, 8 parts of glycidyl methacrylate, 0.3-0.5 parts of 3,5-diisopropyl chromium salicylate, and 0.02-0.03 parts of polymerization inhibitor.

[0013] Furthermore, the polymerization inhibitor is phenothiazine. Since the reaction between epoxy and carboxyl groups requires 3,5-diisopropyl chromium salicylate as a catalyst, if conventional polymerization inhibitors such as hydroquinone and p-hydroxyanisole are used, oxidation side reactions will occur, thereby reducing the reactivity of subsequent glycidyl methacrylate and insufficient grafting amount, thereby affecting the performance of the prepared polyacrylate / DOPO modified silica sol. Therefore, the polymerization inhibitor is preferably phenothiazine.

[0014] Furthermore, the amounts of raw material components required for preparing the polyacrylate / DOPO modified silica sol are, by weight, 30 parts of DOPO containing unsaturated double bonds, 8 to 12 parts of acrylate monomers, 0.1 to 0.3 parts of alkylphenol polyoxyethylene ether, 0.1 to 0.3 parts of ammonium persulfate, and 50 parts of deionized water.

[0015] Furthermore, the acrylate monomer is obtained by mixing acrylic acid, methyl methacrylate, acrylonitrile and styrene in a mass ratio of (1-2):1:(1-2):(1-2).

[0016] Furthermore, the polyacrylate / DOPO modified silica sol prepared by the preparation method of the silica sol-based flame retardant coating.

[0017] Furthermore, the solid content of the polyacrylate / DOPO modified silica sol is 40-50 wt %.

[0018] In the present invention, ethyl orthosilicate and 3-glycidyloxypropyltriethoxysilane are first hydrolyzed and polycondensed to obtain an epoxy-modified silica sol containing epoxy groups. Then, the pH of DOPO is reacted with the double bond of maleic anhydride to obtain a carboxyl-modified DOPO containing carboxyl groups. Subsequently, the carboxyl groups of the carboxyl-modified DOPO are first esterified and grafted with the epoxy groups of the epoxy-modified silica sol. With the carboxyl-modified DOPO as a bridge, monoglycidyl ether-terminated polydimethylsiloxane and glycidyl methacrylate are successively added to the other carboxyl groups of the carboxyl-modified DOPO for esterification and grafting to obtain a DOPO-modified silica sol containing unsaturated double bonds. Finally, the DOPO-modified silica sol containing unsaturated double bonds is polymerized with an acrylate monomer to obtain a polyacrylate / DOPO-modified silica sol.

[0019] In the present invention, monoglycidyl ether-terminated polydimethylsiloxane and glycidyl methacrylate are used in the reaction during the preparation of the DOPO-modified silica sol containing unsaturated double bonds. The amount of monoglycidyl ether-terminated polydimethylsiloxane should not be excessive, both for cost considerations and because excessive polydimethylsiloxane segments can slow the coating's drying speed and even cause stickiness, thus affecting the coating's quality and service life. The amount of glycidyl methacrylate is excessive to ensure complete reaction of the -COOH groups in the reactant, thereby grafting a sufficient amount of polyacrylate segments onto the DOPO-modified silica sol containing unsaturated double bonds.

[0020] Compared with the prior art, the present invention has the following beneficial effects: the polyacrylate / DOPO modified silica sol prepared by the present invention contains polydimethylsiloxane segments, DOPO structures and polyacrylate segments. The role of the polydimethylsiloxane segment is: (1) effectively improving the flexibility of the silica sol after curing and reducing its brittleness; (2) improving the waterproof performance of the subsequent coating layer, preventing water vapor from penetrating into the silica sol coating layer, thereby causing the attenuation of its adhesion, flame retardancy and other properties; (3) promoting the film formation of the coating and making the coating layer quality more uniform. The DOPO structure can further improve the flame retardancy of the coating. As for the role of the polyacrylate segment, it is: (1) further improving the flexibility of the coating layer; (2) effectively improving the adhesion of the coating; (3) also improving the curing speed of the silica sol-based flame retardant coating; (4) the monomers of the polyacrylate segment polymerization contain acrylonitrile and styrene. Acrylonitrile contains nitrogen, which can synergistically enhance the flame retardancy with DOPO. Styrene contains benzene rings, which helps to form carbon and can also promote flame retardancy to a certain extent.

[0021] In summary, the present invention comprehensively prepares a silica sol-based flame retardant coating with a fast curing speed and excellent water resistance, flexibility, adhesion and flame retardancy of the cured coating layer. DETAILED DESCRIPTION

[0022] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0023] It should be noted that the following parts are calculated by weight, and the purchasers of all raw materials involved in the present invention include, without any special restrictions, the following examples: In the following examples, tetraethyl orthosilicate, purity ≥99%; 3-glycidyloxypropyltriethoxysilane, purity ≥97%; glycidyl methacrylate, purity ≥97%; monoglycidyl ether-terminated polydimethylsiloxane, CAS No. 157723-26-7, average molecular weight 5000, product No. 480290; phenothiazine, purity ≥98%; acrylic acid, purity ≥99%; methyl methacrylate, purity ≥99%; acrylonitrile, purity ≥99%; and styrene, purity ≥99% were all purchased from Shanghai MacLean Biochemical Technology Co., Ltd. DOPO, purity ≥99.5%, was purchased from Hubei Yongkuo Technology Co., Ltd.; 3,5-Diisopropyl chromium salicylate, purity ≥98%, purchased from Xi'an Lanhao Additive Factory; the remaining raw materials were purchased from the market; Each weight portion is 50g; Preliminary preparation: Acrylic acid, methyl methacrylate, acrylonitrile, and styrene are mixed in a mass ratio of 1.5:1:1.5:1.5 to obtain an acrylate monomer.

[0024] Example 1: Preparation method of a silica sol-based flame retardant coating: S1: Add 20 parts (about 4.8 mol) of ethyl orthosilicate, 6.682 parts (about 1.2 mol) of 3-glycidoxypropyltriethoxysilane, ethanol, hydrochloric acid, and deionized water into a reaction vessel, stir and heat to 60-80°C, stir and react for 6-12 hours, and terminate the reaction to obtain epoxy-modified silica sol; The molar ratio of ethanol, deionized water, hydrochloric acid and n(Si) is 4:4:0.002:1; S2: Under nitrogen protection, 12 parts (2.776 mol) of DOPO and 52.332 parts of toluene were added to a reaction vessel and stirred to mix evenly. Then, 5.444 parts (2.776 mol) of maleic anhydride were added thereto. The mixture was heated to 95°C with stirring for 8 hours. The reaction was terminated, and the mixture was distilled under reduced pressure, washed, and dried to obtain carboxyl-modified DOPO. S3: Under nitrogen protection, 7 parts of carboxyl-modified DOPO were added to 20 parts of epoxy-modified silica sol, and the mixture was stirred and mixed evenly. Then, 0.4 parts of 3,5-diisopropyl chromium salicylate were added thereto, and the mixture was heated to 75°C with stirring and reacted for 4 hours. Then, 2 parts of monoglycidyl ether-terminated polydimethylsiloxane were added thereto, and the mixture was stirred and reacted for 2 hours. Finally, 8 parts of glycidyl methacrylate and 0.025 parts of phenothiazine were added thereto, and the mixture was stirred and reacted for 3 hours. The reaction was terminated, and the mixture was dialyzed and distilled under reduced pressure to obtain DOPO-modified silica sol containing unsaturated double bonds. S4: Under nitrogen protection, 30 parts of DOPO-modified silica sol containing unsaturated double bonds, 10 parts of acrylate monomer, 0.2 parts of alkylphenol polyoxyethylene ether, and 48 parts of deionized water were added to a reaction vessel, stirred for 40 minutes, pre-emulsified, and then stirred and heated to 75°C. An aqueous solution of ammonium persulfate (prepared by dissolving 0.2 parts of ammonium persulfate in 2 parts of deionized water) was then added dropwise for 1.5 hours. After the addition was completed, the reaction was continued with stirring for 6 hours to terminate the reaction. 10 wt% of ammonia water was added to adjust the pH to neutral. After filtration and blending, a polyacrylate / DOPO-modified silica sol with a solid content of 45 wt% was obtained, i.e., a silica sol-based flame retardant coating.

[0025] Example 2: Preparation method of a silica sol-based flame retardant coating: S1: Add 20 parts (about 4.8 mol) of ethyl orthosilicate, 6.682 parts (about 1.2 mol) of 3-glycidoxypropyltriethoxysilane, ethanol, hydrochloric acid, and deionized water into a reaction vessel, stir and heat to 60-80°C, stir and react for 6-12 hours, and terminate the reaction to obtain epoxy-modified silica sol; The molar ratio of ethanol, deionized water, hydrochloric acid and n(Si) is 4:4:0.002:1; S2: Under nitrogen protection, 12 parts (2.776 mol) of DOPO and 52.332 parts of toluene were added to a reaction vessel and stirred to mix evenly. Then, 5.444 parts (2.776 mol) of maleic anhydride were added thereto. The mixture was heated to 95°C with stirring for 8 hours. The reaction was terminated, and the mixture was distilled under reduced pressure, washed, and dried to obtain carboxyl-modified DOPO. S3: Under nitrogen protection, 6 parts of carboxyl-modified DOPO were added to 20 parts of epoxy-modified silica sol, and the mixture was stirred and mixed evenly. Then, 0.4 parts of 3,5-diisopropyl chromium salicylate were added thereto, and the mixture was heated to 75°C with stirring and reacted for 4 hours. Then, 1.4 parts of monoglycidyl ether-terminated polydimethylsiloxane were added thereto, and the mixture was stirred and reacted for 2 hours. Finally, 8 parts of glycidyl methacrylate and 0.025 parts of phenothiazine were added thereto, and the mixture was stirred and reacted for 3 hours. The reaction was terminated, and the mixture was dialyzed and distilled under reduced pressure to obtain DOPO-modified silica sol containing unsaturated double bonds. S4: Under nitrogen protection, 30 parts of DOPO-modified silica sol containing unsaturated double bonds, 10 parts of acrylate monomer, 0.2 parts of alkylphenol polyoxyethylene ether, and 50 parts of deionized water were added to a reaction vessel, stirred for 40 minutes, pre-emulsified, and then stirred and heated to 75°C. An aqueous solution of ammonium persulfate (prepared by dissolving 0.2 parts of ammonium persulfate in 2 parts of deionized water) was then added dropwise for 1.5 hours. After the addition was completed, the reaction was continued with stirring for 6 hours to terminate the reaction. 10 wt% of ammonia water was added to adjust the pH to neutral. After filtration and blending, a polyacrylate / DOPO-modified silica sol with a solid content of 45 wt% was obtained, i.e., a silica sol-based flame retardant coating.

[0026] Example 3: Preparation method of a silica sol-based flame retardant coating: S1: Add 20 parts (about 4.8 mol) of ethyl orthosilicate, 6.682 parts (about 1.2 mol) of 3-glycidoxypropyltriethoxysilane, ethanol, hydrochloric acid, and deionized water into a reaction vessel, stir and heat to 60-80°C, stir and react for 6-12 hours, and terminate the reaction to obtain epoxy-modified silica sol; The molar ratio of ethanol, deionized water, hydrochloric acid and n(Si) is 4:4:0.002:1; S2: Under nitrogen protection, 12 parts (2.776 mol) of DOPO and 52.332 parts of toluene were added to a reaction vessel and stirred to mix evenly. Then, 5.444 parts (2.776 mol) of maleic anhydride were added thereto. The mixture was heated to 95°C with stirring for 8 hours. The reaction was terminated, and the mixture was distilled under reduced pressure, washed, and dried to obtain carboxyl-modified DOPO. S3: Under nitrogen protection, 8 parts of carboxyl-modified DOPO were added to 20 parts of epoxy-modified silica sol, and the mixture was stirred and mixed evenly. Then, 0.4 parts of 3,5-diisopropyl chromium salicylate were added thereto, and the mixture was heated to 75°C with stirring and reacted for 4 hours. Then, 2.6 parts of monoglycidyl ether-terminated polydimethylsiloxane were added thereto, and the mixture was stirred and reacted for 2 hours. Finally, 8 parts of glycidyl methacrylate and 0.025 parts of phenothiazine were added thereto, and the mixture was stirred and reacted for 3 hours. The reaction was terminated, and the mixture was dialyzed and distilled under reduced pressure to obtain DOPO-modified silica sol containing unsaturated double bonds. S4: Under nitrogen protection, 30 parts of DOPO-modified silica sol containing unsaturated double bonds, 10 parts of acrylate monomer, 0.2 parts of alkylphenol polyoxyethylene ether, and 48 parts of deionized water were added to a reaction vessel, stirred for 40 minutes, pre-emulsified, and then stirred and heated to 75°C. An aqueous solution of ammonium persulfate (prepared by dissolving 0.2 parts of ammonium persulfate in 2 parts of deionized water) was then added dropwise for 1.5 hours. After the addition was completed, the reaction was continued with stirring for 6 hours to terminate the reaction. 10 wt% of ammonia water was added to adjust the pH to neutral. After filtration and blending, a polyacrylate / DOPO-modified silica sol with a solid content of 45 wt% was obtained, i.e., a silica sol-based flame retardant coating. The following control experiments are conducted based on Example 1, and comparative examples 1 to 5 are set as follows:

[0027] Comparative Example 1: Comparative Example 1 is based on Example 1, with the following modifications: hydrolysis and polycondensation of ethyl orthosilicate to obtain a silica sol-based flame retardant coating; specifically: a method for preparing a silica sol-based flame retardant coating: S1: Add 25 parts (about 6 mol) of ethyl orthosilicate, ethanol, hydrochloric acid, and deionized water into a reaction vessel, stir and heat to 60-80°C, stir and react for 6-12 hours, terminate the reaction, and blend to obtain a silica sol with a solid content of 45%, which is used as a silica sol-based flame retardant coating; The molar ratio of ethanol, deionized water, hydrochloric acid and n(Si) is 4:4:0.002:1.

[0028] Comparative Example 2: Comparative Example 2 is based on Example 1, with the following adjustments: no carboxyl-modified DOPO is prepared, and other processes remain unchanged. Specifically, a method for preparing a silica sol-based flame retardant coating is as follows: S1: Add 20 parts (about 4.8 mol) of ethyl orthosilicate, 6.682 parts (about 1.2 mol) of 3-glycidoxypropyltriethoxysilane, ethanol, hydrochloric acid, and deionized water into a reaction vessel, stir and heat to 60-80°C, stir and react for 6-12 hours, and terminate the reaction to obtain epoxy-modified silica sol; The molar ratio of ethanol, deionized water, hydrochloric acid and n(Si) is 4:4:0.002:1; S2: Under nitrogen protection, 7 parts of succinic anhydride were added to 20 parts of epoxy-modified silica sol and stirred to mix evenly. Then, 0.4 parts of 3,5-diisopropyl chromium salicylate were added thereto, and the temperature was raised to 75°C with stirring and the reaction was stirred for 4 hours. Then, 2 parts of monoglycidyl ether-terminated polydimethylsiloxane were added thereto, and the temperature was kept stirring and the reaction was continued for 2 hours. Finally, 8 parts of glycidyl methacrylate and 0.025 parts of phenothiazine were added thereto, and the reaction was continued with stirring for 3 hours. The reaction was terminated, and the DOPO-modified silica sol containing unsaturated double bonds was obtained by dialysis and vacuum distillation. S3: Under nitrogen protection, 30 parts of DOPO-modified silica sol containing unsaturated double bonds, 10 parts of acrylate monomer, 0.2 parts of alkylphenol polyoxyethylene ether, and 48 parts of deionized water were added to a reaction vessel, stirred for 40 minutes, pre-emulsified, and then stirred and heated to 75°C. An aqueous solution of ammonium persulfate (prepared by dissolving 0.2 parts of ammonium persulfate in 2 parts of deionized water) was added dropwise thereto for 1.5 hours. After the addition was completed, the reaction was continued with stirring for 6 hours to terminate the reaction. 10 wt% of ammonia water was added to adjust the pH to neutral. After filtration and blending, a polyacrylate / DOPO-modified silica sol with a solid content of 45 wt% was obtained, i.e., a silica sol-based flame retardant coating.

[0029] Comparative Example 3: Comparative Example 3 is based on Example 1, with the following modifications: in S3, monoglycidyl ether-terminated polydimethylsiloxane is not added, and other processes remain unchanged. Specifically, a method for preparing a silica sol-based flame retardant coating is as follows: S1: Add 20 parts (about 4.8 mol) of ethyl orthosilicate, 6.682 parts (about 1.2 mol) of 3-glycidoxypropyltriethoxysilane, ethanol, hydrochloric acid, and deionized water into a reaction vessel, stir and heat to 60-80°C, stir and react for 6-12 hours, and terminate the reaction to obtain epoxy-modified silica sol; The molar ratio of ethanol, deionized water, hydrochloric acid and n(Si) is 4:4:0.002:1; S2: Under nitrogen protection, 12 parts (2.776 mol) of DOPO and 52.332 parts of toluene were added to a reaction vessel and stirred to mix evenly. Then, 5.444 parts (2.776 mol) of maleic anhydride were added thereto. The mixture was heated to 95°C with stirring for 8 hours. The reaction was terminated, and the mixture was distilled under reduced pressure, washed, and dried to obtain carboxyl-modified DOPO. S3: Under nitrogen protection, 7 parts of carboxyl-modified DOPO were added to 20 parts of epoxy-modified silica sol and stirred to mix evenly. Then, 0.4 parts of 3,5-diisopropylchromium salicylate were added thereto, and the temperature was raised to 75°C with stirring and reacted for 4 hours. Then, 8 parts of glycidyl methacrylate and 0.025 parts of phenothiazine were added thereto, and the stirring reaction was continued for 3 hours. The reaction was terminated, and the DOPO-modified silica sol containing unsaturated double bonds was obtained through dialysis and vacuum distillation. S4: Under nitrogen protection, 30 parts of DOPO-modified silica sol containing unsaturated double bonds, 20 parts of acrylate monomer, 0.3 parts of alkylphenol polyoxyethylene ether, and 48 parts of deionized water were added to a reaction vessel, stirred for 40 minutes, pre-emulsified, and then stirred and heated to 75°C. An aqueous solution of ammonium persulfate (prepared by dissolving 0.3 parts of ammonium persulfate in 2 parts of deionized water) was then added dropwise for 1.5 hours. After the addition was completed, the reaction was continued with stirring for 6 hours to terminate the reaction. 10 wt% of ammonia water was added to adjust the pH to neutral. After filtration and blending, a polyacrylate / DOPO-modified silica sol with a solid content of 45 wt% was obtained, i.e., a silica sol-based flame retardant coating.

[0030] Comparative Example 4: Comparative Example 4 is based on Example 1, with the following adjustments: in S3, the amount of monoglycidyl ether-terminated polydimethylsiloxane is increased, and other processes remain unchanged. Specifically, a method for preparing a silica sol-based flame retardant coating is as follows: S1: Add 20 parts (about 4.8 mol) of ethyl orthosilicate, 6.682 parts (about 1.2 mol) of 3-glycidoxypropyltriethoxysilane, ethanol, hydrochloric acid, and deionized water into a reaction vessel, stir and heat to 60-80°C, stir and react for 6-12 hours, and terminate the reaction to obtain epoxy-modified silica sol; The molar ratio of ethanol, deionized water, hydrochloric acid and n(Si) is 4:4:0.002:1; S2: Under nitrogen protection, 12 parts (2.776 mol) of DOPO and 52.332 parts of toluene were added to a reaction vessel and stirred to mix evenly. Then, 5.444 parts (2.776 mol) of maleic anhydride were added thereto. The mixture was heated to 95°C with stirring for 8 hours. The reaction was terminated, and the mixture was distilled under reduced pressure, washed, and dried to obtain carboxyl-modified DOPO. S3: Under nitrogen protection, 7 parts of carboxyl-modified DOPO were added to 20 parts of epoxy-modified silica sol, and the mixture was stirred and mixed evenly. Then, 0.4 parts of 3,5-diisopropylchromium salicylate were added thereto, and the mixture was heated to 75°C with stirring and reacted for 4 hours. Then, 4 parts of monoglycidyl ether-terminated polydimethylsiloxane were added thereto, and the mixture was stirred and reacted for 2 hours. Finally, 8 parts of glycidyl methacrylate and 0.025 parts of phenothiazine were added thereto, and the mixture was stirred and reacted for 3 hours. The reaction was terminated, and the mixture was dialyzed and distilled under reduced pressure to obtain DOPO-modified silica sol containing unsaturated double bonds. S4: Under nitrogen protection, 30 parts of DOPO-modified silica sol containing unsaturated double bonds, 10 parts of acrylate monomer, 0.2 parts of alkylphenol polyoxyethylene ether, and 48 parts of deionized water were added to a reaction vessel, stirred for 40 minutes, pre-emulsified, and then stirred and heated to 75°C. An aqueous solution of ammonium persulfate (prepared by dissolving 0.2 parts of ammonium persulfate in 2 parts of deionized water) was then added dropwise for 1.5 hours. After the addition was completed, the reaction was continued with stirring for 6 hours to terminate the reaction. 10 wt% of ammonia water was added to adjust the pH to neutral. After filtration and blending, a polyacrylate / DOPO-modified silica sol with a solid content of 45 wt% was obtained, i.e., a silica sol-based flame retardant coating.

[0031] Comparative Example 5: Comparative Example 5 is based on Example 1, with the following adjustments: In S3, the polymerization inhibitor is hydroquinone, and other processes remain unchanged. Specifically, a method for preparing a silica sol-based flame retardant coating is as follows: S1: Add 20 parts (about 4.8 mol) of ethyl orthosilicate, 6.682 parts (about 1.2 mol) of 3-glycidoxypropyltriethoxysilane, ethanol, hydrochloric acid, and deionized water into a reaction vessel, stir and heat to 60-80°C, stir and react for 6-12 hours, and terminate the reaction to obtain epoxy-modified silica sol; The molar ratio of ethanol, deionized water, hydrochloric acid and n(Si) is 4:4:0.002:1; S2: Under nitrogen protection, 12 parts (2.776 mol) of DOPO and 52.332 parts of toluene were added to a reaction vessel and stirred to mix evenly. Then, 5.444 parts (2.776 mol) of maleic anhydride were added thereto. The mixture was heated to 95°C with stirring for 8 hours. The reaction was terminated, and the mixture was distilled under reduced pressure, washed, and dried to obtain carboxyl-modified DOPO. S3: Under nitrogen protection, 7 parts of carboxyl-modified DOPO were added to 20 parts of epoxy-modified silica sol, and the mixture was stirred and mixed evenly. Then, 0.4 parts of 3,5-diisopropyl chromium salicylate were added thereto, and the mixture was heated to 75°C with stirring and reacted for 4 hours. Then, 2 parts of monoglycidyl ether-terminated polydimethylsiloxane were added thereto, and the mixture was stirred and reacted for 2 hours. Finally, 8 parts of glycidyl methacrylate and 0.025 parts of hydroquinone were added thereto, and the mixture was stirred and reacted for 3 hours. The reaction was terminated, and the mixture was dialyzed and distilled under reduced pressure to obtain DOPO-modified silica sol containing unsaturated double bonds. S4: Under nitrogen protection, 30 parts of DOPO-modified silica sol containing unsaturated double bonds, 10 parts of acrylate monomer, 0.2 parts of alkylphenol polyoxyethylene ether, and 48 parts of deionized water were added to a reaction vessel, stirred for 40 minutes, pre-emulsified, and then stirred and heated to 75°C. An aqueous solution of ammonium persulfate (prepared by dissolving 0.2 parts of ammonium persulfate in 2 parts of deionized water) was then added dropwise for 1.5 hours. After the addition was completed, the reaction was continued with stirring for 6 hours to terminate the reaction. 10 wt% of ammonia water was added to adjust the pH to neutral. After filtration and blending, a polyacrylate / DOPO-modified silica sol with a solid content of 45 wt% was obtained, i.e., a silica sol-based flame retardant coating.

[0032] Performance test: The silica sol-based flame retardant coatings prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were respectively applied to the surface of a 20 cm × 20 cm × 1 cm wooden board using a 40 μm wire rod coater, and the following relevant performance tests were performed: (1) Surface drying time test: According to the standard of GB / T 1728-2020, the surface drying time is tested at a temperature of 23°C and a relative humidity of 50%. After the surface is dried, subsequent performance tests are carried out. In subsequent tests, the wood board obtained after the silica sol-based flame retardant coating is dried is called "coated wood board"; (2) Adhesion performance test: According to the standard of GB / T 4893.4-2023, at a temperature of 23°C and a relative humidity of 50%, use a grid knife to cut 6 parallel cutting lines in the horizontal and vertical directions on the surface of the coated wood board, with the spacing between the cuts of each parallel cutting line being 2 mm. Then observe the surface appearance of each cross-cut area and rate it according to the shedding area; (3) Water resistance test: According to the standard of GB / T 1733-1993, immerse 2 / 3 of the coated wood board in water at a temperature of 23°C. After 24 hours, take it out and observe whether there is blistering, wrinkling, or shedding on the surface; (4) Flame retardant performance test: According to GB / T 16172-2007 and ISO 5660-1:2015 standards, the flame retardant and smoke suppression performance of the coated wood board was tested using a cone calorimeter at a temperature of 23°C and a relative humidity of 50%. The radiation power was 50kW / m 2 .

[0033] The data results of the above test items are shown in Table 1 below: Table 1 sample Surface drying time (min) Attachment level (grade) Surface state Ignition time (s) <![CDATA[Peak heat release rate (Kw / m 2 )]]> <![CDATA[Peak smoke release rate (m 2 / s)]]> Example 1 47 0 No significant changes 68 73.2 0.015 Example 2 43 0 No significant changes 59 81.4 0.019 Example 3 56 0 No significant changes 75 69.2 0.013 Comparative Example 1 156 5 Falling off 12 226.3 0.068 Comparative Example 2 49 0 No significant changes 36 168.6 0.048 Comparative Example 3 55 2 wrinkles 48 104.5 0.028 Comparative Example 4 84 0 No significant changes 41 117.4 0.033 Comparative Example 5 73 1 foaming 60 77.7 0.018 Result analysis: By comparing the data results of the embodiment and the comparative example in Table 1 above, it can be seen that the present invention comprehensively prepares a silica sol-based flame retardant coating with a fast curing speed and excellent comprehensive performance of the cured coating layer.

[0034] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a silica sol-based flame retardant coating, characterized in that: The following steps are involved: S1: Epoxy-modified silica sol is obtained by hydrolysis and polycondensation of tetraethyl orthosilicate and 3-glycidyloxypropyltriethoxysilane; S2: DOPO reacts with maleic anhydride to obtain carboxyl-modified DOPO; S3: Epoxy-modified silica sol, glycidyl methacrylate, monoglycidyl ether-terminated polydimethylsiloxane and carboxyl-modified DOPO undergo esterification reaction to obtain DOPO-modified silica sol containing unsaturated double bonds; S4: DOPO-modified silica sol containing unsaturated double bonds initiates polymerization with acrylate monomer to obtain polyacrylate / DOPO-modified silica sol, i.e., silica sol-based flame retardant coating.

2. The method for preparing a silica sol-based flame retardant coating according to claim 1, wherein: The process includes the following steps, specifically: S1: Add ethyl orthosilicate, 3-glycidyloxypropyltriethoxysilane, ethanol, hydrochloric acid, and deionized water into a reaction vessel, stir and heat to 60-80°C, stir and react for 6-12 hours, and terminate the reaction to obtain epoxy-modified silica sol; S2: Under nitrogen protection, DOPO and toluene are added to a reaction vessel and stirred to mix evenly. Maleic anhydride is then added thereto, and the mixture is heated to 90-100°C with stirring for 6-12 hours. The reaction is terminated, and the carboxyl-modified DOPO is obtained by separation and purification. S3: Under nitrogen protection, carboxyl-modified DOPO is added to epoxy-modified silica sol, and the mixture is stirred and mixed evenly. Then, 3,5-diisopropyl chromium salicylate is added thereto, and the mixture is heated to 70-80°C with stirring and reacted for 2-6 hours. Then, monoglycidyl ether-terminated polydimethylsiloxane is added thereto, and the mixture is stirred and reacted for 1-3 hours. Finally, glycidyl methacrylate and a polymerization inhibitor are added thereto, and the mixture is stirred and reacted for 2-4 hours. The reaction is terminated, and the mixture is separated and purified to obtain DOPO-modified silica sol containing unsaturated double bonds. S4: Under nitrogen protection, DOPO-modified silica sol containing unsaturated double bonds, acrylate monomer, alkylphenol polyoxyethylene ether, and deionized water are added to a reaction vessel, stirred for pre-emulsification, then stirred and heated to 70-80°C, and then an ammonium persulfate aqueous solution is added dropwise thereto for 1-2 hours. After the addition is completed, the reaction is continued with stirring for 4-8 hours, and the reaction is terminated. Ammonia water is added to adjust the pH to neutral, and the polyacrylate / DOPO-modified silica sol, i.e., a silica sol-based flame retardant coating, is obtained through separation and purification.

3. The method for preparing a silica sol-based flame retardant coating according to claim 2, wherein: In S1, the molar ratio of the tetraethyl orthosilicate and 3-glycidyloxypropyltriethoxysilane is 4:1; The molar ratio of the ethanol, deionized water, hydrochloric acid and n(Si) is 4:4:0.002:1; wherein the hydrochloric acid is a 0.1 mol / L hydrochloric acid solution.

4. The method for preparing a silica sol-based flame retardant coating according to claim 2, wherein: In S2, the molar ratio of DOPO to maleic anhydride is (1-1.05):1; The amount of toluene added is 3 times the total mass of DOPO and maleic anhydride.

5. The method for preparing a silica sol-based flame retardant coating according to claim 2, characterized in that: In S3, the amounts of raw material components required for preparing the DOPO-modified silica sol containing unsaturated double bonds are, by weight, 20 parts of epoxy-modified silica sol, 6-8 parts of carboxyl-modified DOPO, 1.4-2.6 parts of monoglycidyl ether-terminated polydimethylsiloxane, 8 parts of glycidyl methacrylate, 0.3-0.5 parts of 3,5-diisopropyl chromium salicylate, and 0.02-0.03 parts of polymerization inhibitor.

6. The method for preparing a silica sol-based flame retardant coating according to claim 2, characterized in that: In S4, the amounts of raw material components required for preparing the polyacrylate / DOPO modified silica sol are, by weight, 30 parts of DOPO containing unsaturated double bonds, 8-12 parts of acrylate monomer, 0.1-0.3 parts of alkylphenol polyoxyethylene ether, 0.1-0.3 parts of ammonium persulfate, and 50 parts of deionized water.

7. The method for preparing a silica sol-based flame retardant coating according to claim 5, characterized in that: The polymerization inhibitor is phenothiazine.

8. The method for preparing a silica sol-based flame retardant coating according to claim 6, characterized in that: The acrylate monomer is obtained by mixing acrylic acid, methyl methacrylate, acrylonitrile and styrene in a mass ratio of (1-2):1:(1-2):(1-2).

9. The polyacrylate / DOPO modified silica sol prepared by the method for preparing a silica sol-based flame retardant coating according to any one of claims 1 to 8, characterized in that: The solid content of the polyacrylate / DOPO modified silica sol is 40-50 wt%.