Silica sol-based hydrophobic coating and method for preparing the same

Abstract

The application relates to the technical field of paint, and discloses a hydrophobic paint based on silica sol and a preparation method thereof; the method comprises the following operation steps: step 1: acidic silica sol is heated to 45-60 DEG C, methyl potassium silicate is added, and stirring is uniformly carried out; basic silica sol is added, and stirring is uniformly carried out; silane modified polyurethane is added, and stirring is uniformly carried out, so that acid / alkali composite silica sol is obtained; step 2: the acid / alkali composite silica sol is added into deionized water and uniformly mixed, modified styrene-acrylic emulsion is added, and stirring is uniformly carried out, so that the hydrophobic paint is obtained. In the scheme, the hydrophobicity of the paint is synergistically improved through the methyl potassium silicate, the silane modified polyurethane and the modification of the styrene-acrylic emulsion.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a hydrophobic coating based on silica sol and its preparation method. Background Technology

[0002] In fields such as construction, electronics, and automobiles, the demand for waterproof, stain-proof, and corrosion-resistant materials is becoming increasingly urgent. Traditional waterproof materials, such as methyl silicates, have poor weather resistance and are too alkaline due to containing only a single hydrophobic group, which limits their application. While fluorine-based superhydrophobic materials have excellent performance, they also pose significant environmental risks.

[0003] Then, as an inorganic nanomaterial, silica sol has advantages such as good weather resistance, high surface activity and good film-forming properties, making it an ideal substrate for preparing functional coatings; however, pure silica sol coatings have defects such as many pores and insufficient density, and water vapor can easily penetrate them, making it difficult to meet the requirements for high-performance waterproofing.

[0004] In conclusion, the preparation of a silica sol-based hydrophobic coating is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a hydrophobic coating based on silica sol and its preparation method, so as to solve the problems raised in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing a hydrophobic coating based on silica sol includes the following steps:

[0008] Step 1: Heat the acidic silica sol to 45~60℃, add potassium methylsilicate and stir until homogeneous; add alkaline silica sol and stir until homogeneous; add silane-modified polyurethane and stir until homogeneous to obtain acid / alkali composite silica sol.

[0009] Step 2: Add the acid / alkali composite silica sol to deionized water and mix evenly. Add the modified styrene-acrylic emulsion and stir evenly to obtain a hydrophobic coating.

[0010] In a more optimized form, the raw materials of the acid / alkali composite silica sol include the following components: by mass parts, 35-40 parts acidic silica sol, 4-6 parts potassium methylsilicate, 20-30 parts alkaline silica sol, and 17-22 parts silane-modified polyurethane.

[0011] In a more optimized form, the raw materials for the hydrophobic coating include the following components: by mass parts, 40-50 parts of acid / alkali composite silica sol, 10-15 parts of modified styrene-acrylic emulsion, and 60-70 parts of deionized water.

[0012] The preparation method of alkaline silica sol in the scheme is as follows: (1) Dilute 60 parts of 25% water glass with 5 times the amount of deionized water, and exchange it with 732 type strong acid cation exchange resin, 711 type anion exchange resin and 732 type strong acid cation exchange resin in sequence to obtain active silicic acid, and control the pH at 2~4; (2) Heat 100 parts of sodium hydroxide solution (the pH of sodium hydroxide solution is 10.5) to 100°C, stir and drop 60 parts of active silicic acid, mix for 1 hour, continue to add 240 parts of active silicic acid and stir for 4 hours. For every 60 parts of active silicic acid added, add 0.05 parts of 3M sodium hydroxide aqueous solution to maintain the pH at about 10~11, age at 90°C for 10 hours, cool to room temperature, filter with a 0.22μm filter membrane to obtain alkaline silica sol; the solid content is 25wt%.

[0013] The method for preparing acidic silica sol in the scheme is as follows: alkaline silica sol is exchanged with 732 type strong acid cation exchange resin, the pH is adjusted to 2~3, and after concentration, acidic silica sol is obtained; the solid content is 25wt%.

[0014] A more optimized method for preparing the silane-modified polyurethane is as follows: Under nitrogen protection, hydroxyl-terminated polydimethylsiloxane, isophorone diisocyanate, and a portion of dibutyltin dilaurate are added to acetone and mixed uniformly. The mixture is heated to 80-85°C and refluxed for 2-3 hours. The remaining portion of dibutyltin dilaurate, 1,6-hexanediol, and 4,4'-dihydroxydicyclohexane are added and the mixture is stirred for 1-2 hours. The mixture is diluted with acetone, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane is added and the mixture is stirred for 1-3 hours. The mixture is cooled to room temperature, rotary evaporated, and then added back to acetone and mixed to obtain the silane-modified polyurethane.

[0015] In a more optimized form, the raw materials for the silane-modified polyurethane include the following components: by mass parts, 22-27 parts of hydroxyl-terminated polydimethylsiloxane, 17-20 parts of isophorone diisocyanate, 0.17-0.22 parts of dibutyltin dilaurate, 3-5 parts of 1,6-hexanediol, 6-8 parts of 4,4'-dihydroxydicyclohexane, 1-3 parts of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and 10-20 parts of acetone.

[0016] A more optimized method for preparing the modified styrene-acrylic emulsion is as follows: (1) Under nitrogen protection, isophorone diisocyanate and dodecyl alcohol are added to acetone and mixed evenly. A catalyst is added and stirred at 70-80°C for 4-5 hours. The mixture is then cooled to room temperature, and polymerization inhibitor and 2-aminoethyl methacrylate are added. The mixture is stirred for another 1-2 hours, and acetone is removed to obtain an acrylate-based hydrophobic intermediate. (2) Allyloxynonylphenol polyoxyethylene ether ammonium sulfate, sodium bicarbonate, and sodium dodecyl sulfonate are added to deionized water and mixed evenly. The mixture is heated to 60-70°C, and styrene, methyl methacrylate, butyl acrylate, and the acrylate-based hydrophobic intermediate are added. An ammonium persulfate initiator is added and stirred for another 1-2 hours. The mixture is then cooled to room temperature, and the pH is adjusted to 8.5-9.0 to obtain the modified styrene-acrylic emulsion.

[0017] In a more optimized configuration, the molar ratio of isophorone diisocyanate, dodecyl alcohol, and 2-aminoethyl methacrylate is 1:1:1.

[0018] In a more optimized form, the raw materials of the modified styrene-acrylic emulsion include the following components: by mass parts, 0.8-1 parts allyloxynonylphenol polyoxyethylene ether ammonium sulfate, 0.3-0.5 parts sodium bicarbonate, 0.7-1.2 parts sodium dodecyl sulfonate, 15-20 parts styrene, 7-10 parts methyl methacrylate, 20-25 parts butyl acrylate, 12-15 parts acrylate-based hydrophobic intermediate, and 0.5-0.8 parts ammonium persulfate initiator.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] In this scheme, acidic silica sol, alkaline silica sol, and styrene-acrylic emulsion are used as the base materials for hydrophobic coatings;

[0021] Both acidic and alkaline silica sols are aqueous dispersions of nano-silica. During the drying and film formation process of the coating, the two work together to form a continuous inorganic network skeleton structure, which has good chemical stability and water resistance. Meanwhile, the styrene-acrylic emulsion ensures the uniformity of the coating with its good fluidity, and the organic film it forms can fill the gaps in the inorganic silica network, thus optimizing the overall performance of the coating through the organic-inorganic hybrid structure.

[0022] However, when acidic and alkaline silica sols are directly mixed, the violent acid-base neutralization will cause the rapid condensation of silanol groups, resulting in rapid gelation of silica particles. This not only affects the stability of the coating, but also leads to insufficient hydrophobicity and water resistance due to the strong hydrophilicity of the inorganic phase.

[0023] To address the issues of intense neutralization reactions between acidic and alkaline silica sols, and poor hydrophobicity, potassium methylsilicate and polyurethane were added. The alkaline groups of potassium methylsilicate can slowly neutralize the hydrogen ions in acidic silica sols, reducing the intensity of localized reactions. The siloxane chains condense with the silanol groups on the silica sol surface to form a buffer layer, delaying gelation. Furthermore, the silanol groups generated by the hydrolysis of potassium methylsilicate can also participate in the formation of a siloxane network, improving water resistance to some extent. However, potassium methylsilicate reduces the compatibility between the inorganic and organic phases (styrene-acrylic emulsion), requiring further optimization. Therefore, silane-modified polyurethane was added.

[0024] In this formulation, hydroxyl-terminated polydimethylsiloxane and isophorone diisocyanate exhibit certain hydrophobicity, which is further enhanced by using 1,6-hexanediol and 4,4'-dihydroxydicyclohexane as chain extenders. Combined with the chemical anchoring of the amino group of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane with isocyanate, silanol is formed in deionized water, improving the compatibility between polyurethane and silica sol, thereby enhancing water resistance. However, when used alone, it cannot buffer acid-base reactions, and the pot life of the coating is relatively short when mixed in high proportions.

[0025] Among them, polyurethane segments can alleviate the difference in interfacial tension between inorganic and organic substances and avoid system delamination; the film structure formed by polyurethane segments in silane-modified polyurethane is dense and has good water resistance. Furthermore, the polyurethane segments are interconnected with styrene-acrylic emulsion and silica sol through chemical bonds and physical interactions, which enhances the density of the entire coating film and prevents water molecules from penetrating.

[0026] However, relying solely on potassium methylsilicate and silane-modified polyurethane has limited effect in improving the hydrophobicity and water resistance of coatings. Therefore, this solution incorporates a modified styrene-acrylic emulsion. The solution is prepared by first using isophorone diisocyanate, dodecyl alcohol, and 2-aminoethyl methacrylate in a 1:1:1 molar ratio under the action of a catalyst. Isophorone diisocyanate provides two -NCO groups, which react with the -OH group of dodecyl alcohol and the -NH2 group of 2-aminoethyl methacrylate, respectively, introducing an alicyclic hydrophobic structure that connects the hydrophobic chain and the acrylate group, resulting in an acrylate-based hydrophobic intermediate. The introduction of isophorone diisocyanate into the polyurethane significantly improves the compatibility between the silane-modified polyurethane and the styrene-acrylic emulsion. This solution requires preparation under a nitrogen atmosphere, and the temperature needs to be lowered when adding 2-aminoethyl methacrylate to prevent self-polymerization at high temperatures.

[0027] Then, an emulsion is prepared by mixing allyloxynonylphenol polyoxyethylene ether ammonium sulfate, sodium bicarbonate, and sodium dodecyl sulfonate. Styrene, methyl methacrylate, butyl acrylate, and acrylate-based hydrophobic intermediates are added, along with an initiator. Under certain conditions, a modified styrene-acrylic emulsion is obtained.

[0028] In this scheme, allyloxynonylphenol polyoxyethylene ether ammonium sulfate and sodium dodecyl sulfonate are compounded to stabilize the emulsion system, allowing the hydrophobic monomers and intermediates to be dispersed in the aqueous phase. The main monomers of the styrene-acrylic emulsion provide film-forming properties, hardness, and flexibility, and copolymerize with the hydrophobic intermediates to form a continuous phase. The polymer film formed by the polymerization of monomers such as styrene, methyl methacrylate, and butyl acrylate in the modified styrene-acrylic emulsion has a certain degree of water resistance. Acrylic polymers themselves have a certain resistance to water, and the introduction of hydrophobic intermediates reduces the channels for water molecules to enter the interior of the polymer film, thereby reducing the swelling and erosion effects of water on the polymer film. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] In the following specific embodiments, "parts" refers to parts by weight. It should be noted that, in this embodiment, there are no special restrictions on the manufacturers of the raw materials involved in this invention; exemplarily, they include:

[0031] The CAS number for isophorone diisocyanate is 4098-71-9; the CAS number for dodecyl alcohol is 112-53-8; the CAS number for 2-aminoethyl methacrylate is 7659-36-1; the CAS number for N-(2-aminoethyl)-3-aminopropyltrimethoxysilane is 1760-24-3; the CAS number for styrene is 100-42-5; and the CAS number for methyl methacrylate is 80-62- 6; CAS number for butyl acrylate is 141-32-2; CAS number for hydroxyl-terminated polydimethylsiloxane is JP-203, molecular weight is 1500; CAS number for dibutyltin dilaurate is 77-58-7; CAS number for 1,6-hexanediol is 629-11-8; CAS number for 4,4'-dihydroxydicyclohexane is 20601-38-1; CAS number for potassium methylsilicate is 31795-24-1.

[0032] Example 1: A method for preparing a hydrophobic coating based on silica sol, comprising the following steps:

[0033] The preparation method of modified styrene-acrylic emulsion is as follows: (1) Isophorone diisocyanate, dodecyl alcohol, and 2-aminoethyl methacrylate are weighed in a molar ratio of 1:1:1; under nitrogen protection, isophorone diisocyanate and dodecyl alcohol are added to acetone and mixed evenly, a catalyst is added, and the mixture is stirred at 75°C for 4 hours. After cooling to room temperature, a polymerization inhibitor (hydroquinone) and 2-aminoethyl methacrylate are added, and the mixture is stirred for 1.5 hours. The acetone is removed to obtain an acrylate-based hydrophobic intermediate; (2) 0.8 parts of allyloxynonylphenol polyoxyethylene ether ammonium sulfate, 0.5 parts of sodium bicarbonate, and 0.7 parts of sodium dodecyl sulfonate are added to deionized water and mixed evenly. The temperature is raised to 65°C, and 15 parts of styrene, 7 parts of methyl methacrylate, 20 parts of butyl acrylate, and 12 parts of the acrylate-based hydrophobic intermediate are added. 0.6 parts of ammonium persulfate initiator are added, and the mixture is stirred for 2 hours. After cooling to room temperature, the pH is adjusted to 9 to obtain the modified styrene-acrylic emulsion;

[0034] The preparation method of silane-modified polyurethane is as follows: Under nitrogen protection, 25 parts of hydroxyl-terminated polydimethylsiloxane, 20 parts of isophorone diisocyanate, and 0.1 parts of dibutyltin dilaurate are added to 10 parts of acetone and mixed evenly. The mixture is heated to 80°C and refluxed for 2 hours. Then, 0.1 parts of dibutyltin dilaurate, 4 parts of 1,6-hexanediol, and 7 parts of 4,4'-dihydroxydicyclohexane are added and the mixture is stirred for another 2 hours. The mixture is diluted with 10 parts of acetone, and 1.2 parts of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane are added and the mixture is stirred for another 2 hours. The mixture is cooled to room temperature, rotary evaporated, and then added back to 15 parts of acetone and mixed to obtain silane-modified polyurethane.

[0035] Step 1: Heat 35 parts of acidic silica sol to 55℃, add 5 parts of potassium methylsilicate, stir for 40 minutes, add 20 parts of alkaline silica sol and mix evenly, add 18 parts of silane-modified polyurethane and continue stirring for 30 minutes to obtain acid / alkali composite silica sol.

[0036] Step 2: Add 40 parts of acid / alkali composite silica sol to 70 parts of deionized water and mix evenly. Add 10 parts of modified styrene-acrylic emulsion and stir for 40 minutes to obtain a hydrophobic coating.

[0037] Example 2: A method for preparing a hydrophobic coating based on silica sol, comprising the following steps:

[0038] The preparation method of modified styrene-acrylic emulsion is as follows: (1) Isophorone diisocyanate, dodecyl alcohol, and 2-aminoethyl methacrylate are weighed in a molar ratio of 1:1:1; under nitrogen protection, isophorone diisocyanate and dodecyl alcohol are added to acetone and mixed evenly, a catalyst is added, and the mixture is stirred at 75°C for 4 hours. After cooling to room temperature, a polymerization inhibitor (hydroquinone) and 2-aminoethyl methacrylate are added, and the mixture is stirred for 1.5 hours. The acetone is removed to obtain an acrylate-based hydrophobic intermediate; (2) 0.8 parts of allyloxynonylphenol polyoxyethylene ether ammonium sulfate, 0.5 parts of sodium bicarbonate, and 0.7 parts of sodium dodecyl sulfonate are added to deionized water and mixed evenly. The temperature is raised to 65°C, and 15 parts of styrene, 7 parts of methyl methacrylate, 20 parts of butyl acrylate, and 12 parts of the acrylate-based hydrophobic intermediate are added. 0.6 parts of ammonium persulfate initiator are added, and the mixture is stirred for 2 hours. After cooling to room temperature, the pH is adjusted to 9 to obtain the modified styrene-acrylic emulsion;

[0039] The preparation method of silane-modified polyurethane is as follows: Under nitrogen protection, 25 parts of hydroxyl-terminated polydimethylsiloxane, 20 parts of isophorone diisocyanate, and 0.1 parts of dibutyltin dilaurate are added to 10 parts of acetone and mixed evenly. The mixture is heated to 80°C and refluxed for 2 hours. Then, 0.1 parts of dibutyltin dilaurate, 4 parts of 1,6-hexanediol, and 7 parts of 4,4'-dihydroxydicyclohexane are added and the mixture is stirred for another 2 hours. The mixture is diluted with 10 parts of acetone, and 1.2 parts of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane are added and the mixture is stirred for another 2 hours. The mixture is cooled to room temperature, rotary evaporated, and then added back to 15 parts of acetone and mixed to obtain silane-modified polyurethane.

[0040] Step 1: Heat 35 parts of acidic silica sol to 55℃, add 5 parts of potassium methylsilicate, stir for 40 minutes, add 20 parts of alkaline silica sol and mix evenly, add 20 parts of silane-modified polyurethane and continue stirring for 30 minutes to obtain acid / alkali composite silica sol.

[0041] Step 2: Add 40 parts of acid / alkali composite silica sol to 70 parts of deionized water and mix evenly. Add 12 parts of modified styrene-acrylic emulsion and stir for 40 minutes to obtain a hydrophobic coating.

[0042] Example 3: A method for preparing a hydrophobic coating based on silica sol, comprising the following steps:

[0043] The preparation method of modified styrene-acrylic emulsion is as follows: (1) Isophorone diisocyanate, dodecyl alcohol, and 2-aminoethyl methacrylate are weighed in a molar ratio of 1:1:1; under nitrogen protection, isophorone diisocyanate and dodecyl alcohol are added to acetone and mixed evenly, a catalyst is added, and the mixture is stirred at 75°C for 4 hours. After cooling to room temperature, a polymerization inhibitor (hydroquinone) and 2-aminoethyl methacrylate are added, and the mixture is stirred for 1.5 hours. The acetone is removed to obtain an acrylate-based hydrophobic intermediate; (2) 0.8 parts of allyloxynonylphenol polyoxyethylene ether ammonium sulfate, 0.5 parts of sodium bicarbonate, and 0.7 parts of sodium dodecyl sulfonate are added to deionized water and mixed evenly. The temperature is raised to 65°C, and 15 parts of styrene, 7 parts of methyl methacrylate, 20 parts of butyl acrylate, and 12 parts of the acrylate-based hydrophobic intermediate are added. 0.6 parts of ammonium persulfate initiator are added, and the mixture is stirred for 2 hours. After cooling to room temperature, the pH is adjusted to 9 to obtain the modified styrene-acrylic emulsion;

[0044] The preparation method of silane-modified polyurethane is as follows: Under nitrogen protection, 25 parts of hydroxyl-terminated polydimethylsiloxane, 20 parts of isophorone diisocyanate, and 0.1 parts of dibutyltin dilaurate are added to 10 parts of acetone and mixed evenly. The mixture is heated to 80°C and refluxed for 2 hours. Then, 0.1 parts of dibutyltin dilaurate, 4 parts of 1,6-hexanediol, and 7 parts of 4,4'-dihydroxydicyclohexane are added and the mixture is stirred for another 2 hours. The mixture is diluted with 10 parts of acetone, and 1.2 parts of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane are added and the mixture is stirred for another 2 hours. The mixture is cooled to room temperature, rotary evaporated, and then added back to 15 parts of acetone and mixed to obtain silane-modified polyurethane.

[0045] Step 1: Heat 35 parts of acidic silica sol to 55°C, add 5 parts of potassium methylsilicate, stir for 40 minutes, add 20 parts of alkaline silica sol and mix evenly, add 22 parts of silane-modified polyurethane and continue stirring for 30 minutes to obtain acid / alkali composite silica sol.

[0046] Step 2: Add 40 parts of acid / alkali composite silica sol to 70 parts of deionized water and mix evenly. Add 15 parts of modified styrene-acrylic emulsion and stir for 40 minutes to obtain a hydrophobic coating.

[0047] Comparative Example 1 is based on Example 3, but without the addition of potassium methylsilicate; the remaining operating steps remain unchanged;

[0048] Step 1: Heat 35 parts of acidic silica sol to 55°C, add 22 parts of silane-modified polyurethane and stir for 40 minutes, then add 20 parts of alkaline silica sol and mix evenly to obtain acid / alkali composite silica sol.

[0049] Step 2: Add 40 parts of acid / alkali composite silica sol to 70 parts of deionized water and mix evenly. Add 15 parts of modified styrene-acrylic emulsion and stir for 40 minutes to obtain a hydrophobic coating.

[0050] Comparative Example 2 is based on Example 3, but without the addition of an acrylate-based hydrophobic intermediate; the remaining operating steps remain unchanged.

[0051] The modified styrene-acrylic emulsion is prepared as follows: 0.8 parts of allyloxynonylphenol polyoxyethylene ether ammonium sulfate, 0.5 parts of sodium bicarbonate, and 0.7 parts of sodium dodecyl sulfonate are added to deionized water and mixed evenly. The mixture is heated to 65°C, and 15 parts of styrene, 7 parts of methyl methacrylate, 20 parts of butyl acrylate, and 0.6 parts of ammonium persulfate initiator are added. The mixture is stirred for 2 hours, cooled to room temperature, and the pH is adjusted to 9 to obtain the modified styrene-acrylic emulsion.

[0052] Step 1: Heat 35 parts of acidic silica sol to 55°C, add 5 parts of potassium methylsilicate, stir for 40 minutes, add 20 parts of alkaline silica sol and mix evenly, add 22 parts of silane-modified polyurethane and continue stirring for 30 minutes to obtain acid / alkali composite silica sol.

[0053] Step 2: Add 40 parts of acid / alkali composite silica sol to 70 parts of deionized water and mix evenly. Add 15 parts of modified styrene-acrylic emulsion and stir for 40 minutes to obtain a hydrophobic coating.

[0054] Comparative Example 3 was based on Example 3, but without the addition of 4,4'-dihydroxydicyclohexane; the remaining operating steps remained unchanged.

[0055] The preparation method of silane-modified polyurethane is as follows: Under nitrogen protection, 25 parts of hydroxyl-terminated polydimethylsiloxane, 20 parts of isophorone diisocyanate, and 0.1 parts of dibutyltin dilaurate are added to 10 parts of acetone and mixed evenly. The mixture is heated to 80°C and refluxed for 2 hours. Then, 0.1 parts of dibutyltin dilaurate and 4 parts of 1,6-hexanediol are added and the mixture is stirred for another 2 hours. The mixture is diluted with 10 parts of acetone, and 1.2 parts of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane are added and the mixture is stirred for another 2 hours. The mixture is cooled to room temperature, rotary evaporated, and then added back to 15 parts of acetone and mixed to obtain silane-modified polyurethane.

[0056] Step 1: Heat 35 parts of acidic silica sol to 55°C, add 5 parts of potassium methylsilicate, stir for 40 minutes, add 20 parts of alkaline silica sol and mix evenly, add 22 parts of silane-modified polyurethane and continue stirring for 30 minutes to obtain acid / alkali composite silica sol.

[0057] Step 2: Add 40 parts of acid / alkali composite silica sol to 70 parts of deionized water and mix evenly. Add 15 parts of modified styrene-acrylic emulsion and stir for 40 minutes to obtain a hydrophobic coating.

[0058] Comparative Example 4 is based on Example 3, but without the addition of alkaline silica sol; the remaining operating steps remain unchanged;

[0059] Step 1: Heat 35 parts of acidic silica sol to 55°C, add 5 parts of potassium methylsilicate, stir for 40 minutes, add 22 parts of silane-modified polyurethane and continue stirring for 30 minutes to obtain composite silica sol.

[0060] Step 2: Add 40 parts of composite silica sol to 70 parts of deionized water and mix evenly. Add 15 parts of modified styrene-acrylic emulsion and stir for 40 minutes to obtain a hydrophobic coating.

[0061] Testing: The hydrophobic coatings prepared in Examples 1-3 and Comparative Examples 1-4 were applied to stone products and dried to form hydrophobic coatings; then the water contact angles were measured; and the coatings were soaked in deionized water for 72 hours to test the adhesion of the hydrophobic coatings.

[0062] Table 1

[0063] water contact angle adhesion (MPa) example 1 128.7 3.92 example 2 132.4 4.14 example 3 134.2 4.35 comparative example 1 126.5 4.01 comparative example 2 118.4 3.53 comparative example 3 123.3 3.84 comparative example 4 114.6 3.37

[0064] Conclusions: Comparative Example 1 was based on Example 3 but without potassium methylsilicate. Potassium methylsilicate is an aqueous hydrophobic agent that can form a stable hydrophobic structure with silica sol, enhancing the density of the coating. Its absence led to a decrease in the performance of Comparative Example 1. Comparative Example 2 was based on Example 3 but without the acrylate-based hydrophobic intermediate. The acrylate-based hydrophobic intermediate contains a long-chain alkyl group (dodecyl alcohol) and a hydrophobic isophorone structure, which is key to modifying the hydrophobicity of the styrene-acrylic emulsion. Its absence led to a decrease in the performance of Comparative Example 2. Comparative Example 3 was based on Example 3 but without 4,4'-dihydroxydicyclohexane. Rigid chain extenders help form a more rigid network structure, improving the mechanical interlocking and chemical bonding between the coating and the substrate. Their absence led to a decrease in the performance of Comparative Example 3.

[0065] Comparative Example 4 is based on Example 3, but without the addition of alkaline silica sol. Because acid / alkali composite silica sol can form a denser silicon network, the pH of alkaline silica sol is similar to that of styrene-acrylic emulsion, and the two have good compatibility. The absence of alkaline silica sol leads to insufficient cross-linking, which reduces the compatibility between acidic silica sol and styrene-acrylic emulsion, thus causing a decrease in the performance of Comparative Example 4.

[0066] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a hydrophobic coating based on silica sol, characterized in that: The following steps are included: Step 1: Heat the acidic silica sol to 45~60℃, add potassium methylsilicate and stir until homogeneous; add alkaline silica sol and stir until homogeneous; add silane-modified polyurethane and stir until homogeneous to obtain acid / alkali composite silica sol. Step 2: Add the acid / alkali composite silica sol to deionized water and mix evenly. Add the modified styrene-acrylic emulsion and stir evenly to obtain a hydrophobic coating. The preparation method of the silane-modified polyurethane is as follows: Under nitrogen protection, hydroxyl-terminated polydimethylsiloxane, isophorone diisocyanate, and part of dibutyltin dilaurate are added to acetone and mixed evenly. The mixture is heated to 80-85°C and refluxed for 2-3 hours. The remaining part of dibutyltin dilaurate, 1,6-hexanediol, and 4,4'-dihydroxydicyclohexane are added and the mixture is stirred for 1-2 hours. The mixture is diluted with acetone, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane is added and the mixture is stirred for 1-3 hours. The mixture is cooled to room temperature, rotary evaporated, and then added back to acetone and mixed to obtain the silane-modified polyurethane. The modified styrene-acrylic emulsion is prepared as follows: (1) Under nitrogen protection, isophorone diisocyanate and dodecyl alcohol are added to acetone and mixed evenly. Dibutyltin dilaurate is added and stirred at 70-80°C for 4-5 hours. After cooling to room temperature, polymerization inhibitor and 2-aminoethyl methacrylate are added and stirred for 1-2 hours. Acetone is removed to obtain acrylate-based hydrophobic intermediate. (2) Allyloxynonylphenol polyoxyethylene ether ammonium sulfate, sodium bicarbonate and sodium dodecyl sulfonate are added to deionized water and mixed evenly. The temperature is raised to 60-70°C and styrene, methyl methacrylate, butyl acrylate and acrylate-based hydrophobic intermediate are added. Ammonium persulfate initiator is added and stirred for 1-2 hours. After cooling to room temperature, the pH is adjusted to 8.5-9.0 to obtain modified styrene-acrylic emulsion.

2. The method for preparing a hydrophobic coating based on silica sol according to claim 1, characterized in that: The raw materials of the acid / alkali composite silica sol include the following components: by mass, 35-40 parts acidic silica sol, 4-6 parts potassium methylsilicate, 20-30 parts alkaline silica sol, and 17-22 parts silane-modified polyurethane.

3. The method for preparing a hydrophobic coating based on silica sol according to claim 1, characterized in that: The raw materials for the hydrophobic coating include the following components: by mass, 40-50 parts acid / alkali composite silica sol, 10-15 parts modified styrene-acrylic emulsion, and 60-70 parts deionized water.

4. The method for preparing a hydrophobic coating based on silica sol according to claim 1, characterized in that: The raw materials for the silane-modified polyurethane include the following components by mass: 22-27 parts of hydroxyl-terminated polydimethylsiloxane, 17-20 parts of isophorone diisocyanate, 0.17-0.22 parts of dibutyltin dilaurate, 3-5 parts of 1,6-hexanediol, 6-8 parts of 4,4'-dihydroxydicyclohexane, 1-3 parts of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and 10-20 parts of acetone.

5. The method for preparing a hydrophobic coating based on silica sol according to claim 1, characterized in that: In step (1) of the method for preparing the modified styrene-acrylic emulsion, the molar ratio of isophorone diisocyanate, dodecanol, and 2-aminoethyl methacrylate is 1:1:

1.

6. The method for preparing a hydrophobic coating based on silica sol according to claim 1, characterized in that: The modified styrene-acrylic emulsion comprises the following components by mass: 0.8-1 parts allyloxynonylphenol polyoxyethylene ether ammonium sulfate, 0.3-0.5 parts sodium bicarbonate, 0.7-1.2 parts sodium dodecyl sulfonate, 15-20 parts styrene, 7-10 parts methyl methacrylate, 20-25 parts butyl acrylate, 12-15 parts acrylate-based hydrophobic intermediate, and 0.5-0.8 parts ammonium persulfate initiator.

7. A hydrophobic coating is prepared by a method for preparing a silica sol-based hydrophobic coating according to any one of claims 1 to 6.