Preparation method and application of a self-cleaning water-based coating for the exterior wall of high-speed railway

Abstract

The present invention relates to the technical field of coating compositions, and specifically discloses a preparation method and application of a self-cleaning water-based coating for the outer wall of a high-speed railway. The water-based coating comprises, by weight, 20 to 30 parts of modified polyurethane, 20 to 30 parts of hydrophobic silica, 2 to 5 parts of dispersant, 2 to 5 parts of defoamer, 1 to 3 parts of anti-settling agent, 1 to 2 parts of anti-aging agent, and 40 to 80 parts of water. The present invention also provides a preparation method thereof. Compared with the prior art, the water-based coating prepared by the present invention has the advantages of being green and environmentally friendly, having good wear resistance, and having excellent self-cleaning performance.

Description

Technical Field

[0001] The present invention relates to the technical field of coating compositions, and in particular to a preparation method and application of a self-cleaning water-based coating for the outer wall of a high-speed railway. Background Art

[0002] Outdoor coatings on building exterior walls, cars, high-speed railways, etc. are exposed to the external environment for a long time and are easily attached and polluted by pollutants such as dust and oil stains. In order to ensure the beauty and service life of the coating, it is necessary to regularly spend financial and human resources to clean the coating surface. Self-cleaning coatings do not require subsequent maintenance and cleaning, which is more in line with the environmental protection and low-carbon development model of contemporary society, and has a broad market and development prospects. Due to the practicality and significant use effect of the self-cleaning phenomenon, self-cleaning coatings have been widely concerned by researchers in recent years. In view of its huge market potential, the preparation technology of self-cleaning coatings has also made great progress. With the rapid popularization of high-speed railways in my country and its beginning to go global, the high-speed railway industry has ushered in a period of prosperity, and the demand for high-performance high-speed railway self-cleaning coatings has increased sharply.

[0003] Chinese patent 201710041535.7 discloses a highly wear-resistant water-based anti-fouling self-cleaning polyurethane coating, which includes, by weight: 100-200 parts of silicone-modified polyurethane emulsion; 40-80 parts of fluorocarbon emulsion; 20-60 parts of nano-elastic particles; 5-20 parts of silane coupling agent; 10-20 parts of auxiliary film-forming agent; 5-15 parts of additives; 40-100 parts of water. The invention also provides a method for preparing a highly wear-resistant water-based anti-fouling self-cleaning polyurethane coating. The invention reduces the surface energy through the triple effects of silicone-modified polyurethane emulsion, fluorocarbon emulsion and nano-elastic particles, while constructing a rough nanostructure on the surface of the coating, so that the coating has super-hydrophobic properties and anti-fouling self-cleaning effects. At the same time, the introduced nano-elastic particles make the super-hydrophobic coating have high wear resistance.

[0004] Chinese patent 202211234496.X discloses an environmentally friendly self-cleaning modified polyaspartic acid ester coating and a preparation method thereof, wherein the coating comprises modified polyaspartic acid ester, functional additives, dispersants, defoamers, wear resistant agents, anti-settling agents, leveling agents, anti-aging agents, pigments, and water; the above scheme has a simple formula, and the resulting coating has good water resistance and self-cleaning properties. The application also proposes a method for preparing an environmentally friendly self-cleaning modified polyaspartic acid ester coating, comprising mixing modified polyaspartic acid ester, functional additives, dispersants, defoamers, wear resistant agents, anti-settling agents, anti-aging agents, leveling agents, pigments, and water and grinding them to obtain the desired coating; the above method is simple, the preparation cost is low, and the resulting self-cleaning modified polyaspartic acid ester coating has good dispersion stability, greatly reduces the cracking phenomenon of the coating, and optimizes the comprehensive performance of the coating.

[0005] In the prior art, there are relatively few studies on self-cleaning coatings for the outer wall of high-speed railways. Since the outer wall of high-speed railways has a large surface area, the coating does not meet the requirements of green environmental protection. Water-based coatings themselves have problems with poor adhesion, wear resistance, and durability. High-speed railways are often exposed outdoors, so there are certain requirements for the performance of the coating itself. Therefore, the development of a self-cleaning water-based coating for the outer wall of high-speed railways with good durability and wear resistance will have great application prospects. Summary of the invention

[0006] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a self-cleaning coating with good mechanical properties and green environmental protection.

[0007] The main reason for the poor durability of self-cleaning coatings is that under outdoor conditions, due to the poor adhesion between the coating itself and the substrate, it is very easy to fall off after long-term exposure to wind and sun. In addition, after experiencing wear and tear such as rain and flying sand, it is more likely to cause damage to the coating surface and lose its self-cleaning properties. Self-repairing coatings can effectively solve the problem of coating surface damage, self-healing the damaged surface, thereby restoring the original performance of the surface, and thus ensuring the wear resistance and durability of the coating.

[0008] As a block copolymer containing carbamate groups (-NHCOO-) and urea groups (-NHCONH-), polyurethane has the advantages of high strength, wear resistance, tear resistance, etc., and is widely used in water-based coatings. Since polyurethane is a multi-segment polymer with soft and hard alternating chain units, in which the soft chain is composed of polyols and the hard chain is composed of isocyanates. Through proper molecular chain modulation, polyurethane can easily achieve self-healing, which can not only solve the problems of poor durability and poor wear resistance of current self-cleaning coatings, but also can adjust the toughness of the molecular chain by regulating the chain segment composition to achieve improved mechanical properties. In the present invention, the polyurethane obtained by synthesis has good mechanical properties and substrate adhesion due to its special interlayer hydrogen bonding force, electrostatic interaction and layered molecular stacking structure. The disulfide bond and hydrogen bonding force are also introduced into the structure to achieve a self-healing effect. The component obtained by compounding it with hydrophobically modified silica is added to the water-based coating to play a good self-cleaning effect. The hard segment and soft segment in the polyurethane molecular chain reciprocate to build a good network structure, so that it has good toughness and can withstand a large tensile limit. When the molecular chain is cut off under the action of an external force, the molecular chain can be accelerated to flow by simple heating so as to reassemble and complete self-repair. Its self-repair mechanism not only has self-assembly between molecular chains but also interlayer hydrogen bonds and disulfide bonds. Under the action of multiple mechanisms, the coating only needs to be heated by simple sunlight to complete the repair of the coating surface when it is damaged outdoors. Therefore, the wear resistance and durability of the coating are greatly improved. The interlayer stacking of aromatic groups in the modified polyurethane in the coating can enhance its adhesion, and complexation can occur on the metal surface to further enhance the adhesion effect, which makes the coating itself have better wear resistance and mechanical properties.

[0009] To achieve the above-mentioned purpose, the present invention provides a self-cleaning water-based coating for the outer wall of a high-speed railway, which comprises, by weight, 20 to 30 parts of modified polyurethane, 20 to 30 parts of hydrophobic silica, 2 to 5 parts of dispersant, 2 to 5 parts of defoaming agent, 1 to 3 parts of anti-settling agent, 1 to 2 parts of anti-aging agent, and 40 to 80 parts of water.

[0010] The preparation method of the modified polyurethane comprises the following steps:

[0011] X1: 1.5-4.5 parts by weight of ethylenediaminetetraacetic acid dianhydride and 1-3 parts by weight of 3-amino-1-propanol are added to 5-25 parts by weight of pyridine, heated to 40-55°C and stirred for 1-2 hours, then heated to 110-125°C, and stirred for 3-6 hours. After the stirring is completed, water is added, filtered, and the residue is washed with alcohol and dried to obtain a dihydroxy imide derivative;

[0012] X2: Add 5-15 parts by weight of polytetramethylene ether glycol, 1.1-3.5 parts by weight of naphthalene diisocyanate, 1.5-4.5 parts by weight of 1,8-diisocyanooctane and 0.01-0.05 parts by weight of dibutyltin dilaurate to 25-80 parts by weight of N,N-dimethylformamide, heat to 55-70°C and stir for 1-2h, then add 2-4.5 parts by weight of the dihydroxyimide derivative of step X1 and 1-2.5 parts by weight of 2-hydroxyethyl disulfide, heat to 70-85°C and stir for 4-8h to polymerize, cool to room temperature after stirring, add a large amount of water to dilute, filter after precipitation, wash the residue with water and dry to obtain modified polyurethane.

[0013] Furthermore, the dispersant is one of sodium carboxymethyl cellulose, sodium dodecyl sulfate, and sorbitol ester.

[0014] Furthermore, the defoaming agent is one of the defoaming agents selected from the group consisting of silicone, polyether, and polyether-modified polysiloxane.

[0015] Furthermore, the anti-settling agent is one of bentonite, hydrogenated castor oil and polyolefin wax.

[0016] Furthermore, the anti-aging agent is one of UV-531, UV-292, and antioxidant 1010.

[0017] A method for preparing a self-cleaning water-based coating for a high-speed railway outer wall comprises the following steps:

[0018] S1: Add 5-45 parts by weight of nano-silicon dioxide to 100-500 parts by weight of anhydrous ethanol, then add 10-80 parts by weight of water and 20-85 parts by weight of ammonia water, stir for 2-4 hours, then add 5-35 parts by weight of dodecyltriethoxysilane, heat to 70-85°C, stir for 4-8 hours, then centrifuge and wash with anhydrous ethanol, then dry the lower precipitate to obtain hydrophobic silica;

[0019] S2: Mixing the modified polyurethane, hydrophobic silica, dispersant, defoamer, anti-settling agent, anti-aging agent and water according to the amount in the formula, and stirring evenly at 45-55° C. and 1500-2000 r / min to obtain a premix;

[0020] S3 grinds the premix and filters it, with the filter membrane diameter being less than 10 μm, to obtain the self-cleaning water-based paint.

[0021] The present invention also provides application of the self-cleaning water-based coating in the outer wall of a high-speed railway.

[0022] Beneficial effects of the present invention:

[0023] 1. Compared with the prior art, the coating prepared by the present invention uses water as solvent, is green and environmentally friendly and has low odor.

[0024] 2. The present invention combines modified polyurethane with hydrophobic silica to prepare a water-based coating, which not only has good adhesion to the substrate, but also has an excellent self-cleaning effect. The prepared coating has good wear resistance, and even if the surface is damaged, it can recover its original performance after simple heating. Therefore, it is very suitable for use on the surface of objects exposed outdoors. DETAILED DESCRIPTION

[0025] Nano-silicon dioxide, 400-500nm.

[0026] Polytetramethylene ether glycol, Mw=1000.

[0027] Silicone defoamer, Dow Corning AFE-1410.

[0028] Comparative Example 1

[0029] A method for preparing a self-cleaning water-based coating for a high-speed railway outer wall comprises the following steps:

[0030] S1: Add 250 g of nano-silica to 3.5 L of anhydrous ethanol, then add 500 g of water and 750 g of ammonia water, stir for 3.5 h, then add 180 g of dodecyltriethoxysilane, heat to 80 ° C, stir for 6 h, centrifuge and wash with anhydrous ethanol, then dry the lower precipitate to obtain hydrophobic silica;

[0031] S2: 250 g of modified polyurethane, 250 g of hydrophobic silica, 25 g of sodium dodecyl sulfate, 20 g of silicone defoamer, 15 g of hydrogenated castor oil, 10 g of antioxidant 1010, and 650 g of water are mixed, and stirred at 50° C. and 1800 r / min to obtain a premix;

[0032] S3 grinds the premix and filters it, with the filter membrane diameter being less than 10 μm, to obtain the self-cleaning water-based paint.

[0033] The preparation method of the modified polyurethane comprises the following steps:

[0034] Add 100 g of polytetramethylene ether glycol, 21 g of naphthalene diisocyanate, 19.5 g of 1,8-diisocyanooctane and 0.2 g of dibutyltin dilaurate to 500 mL of N,N-dimethylformamide, heat to 60 ° C and stir for 2 h, then add 15 g of 2-hydroxyethyl disulfide, heat to 80 ° C and stir for 8 h to polymerize, cool to room temperature after stirring, add a large amount of water to dilute, filter after precipitation, wash the residue with water and dry to obtain modified polyurethane.

[0035] Example 1

[0036] A method for preparing a self-cleaning water-based coating for a high-speed railway outer wall comprises the following steps:

[0037] S1: Add 250 g of nano-silica to 3.5 L of anhydrous ethanol, then add 500 g of water and 750 g of ammonia water, stir for 3.5 h, then add 180 g of dodecyltriethoxysilane, heat to 80 ° C, stir for 6 h, centrifuge and wash with anhydrous ethanol, then dry the lower precipitate to obtain hydrophobic silica;

[0038] S2: 250 g of modified polyurethane, 250 g of hydrophobic silica, 25 g of sodium dodecyl sulfate, 20 g of silicone defoamer, 15 g of hydrogenated castor oil, 10 g of antioxidant 1010, and 650 g of water are mixed, and stirred at 50° C. and 1800 r / min to obtain a premix;

[0039] S3 grinds the premix and filters it, with the filter membrane diameter being less than 10 μm, to obtain the self-cleaning water-based paint.

[0040] The preparation method of the modified polyurethane comprises the following steps:

[0041] X1: Add 25 g of ethylenediaminetetraacetic acid dianhydride and 15 g of 3-amino-1-propanol to 100 mL of pyridine, heat to 50°C and stir for 2 h, then raise the temperature to 115°C and continue stirring for 4 h. After stirring, add water, filter, wash the residue with alcohol and dry to obtain a dihydroxy imide derivative;

[0042] X2: 100 g of polytetramethylene ether glycol, 21 g of naphthalene diisocyanate, 19.5 g of 1,8-diisocyanooctane and 0.2 g of dibutyltin dilaurate are added to 500 mL of N,N-dimethylformamide, heated to 60°C and stirred for 2 h, then 30 g of the dihydroxyimide derivative of step X1 and 15 g of 2-hydroxyethyl disulfide are added, the temperature is raised to 80°C and stirred for 8 h to polymerize, after the stirring is completed, the mixture is cooled to room temperature and a large amount of water is added to dilute it, and the precipitate is filtered, and the residue is washed with water and dried to obtain a modified polyurethane.

[0043] Example 2

[0044] A method for preparing a self-cleaning water-based coating for a high-speed railway outer wall comprises the following steps:

[0045] S1: Add 250 g of nano-silica to 3.5 L of anhydrous ethanol, then add 500 g of water and 750 g of ammonia water, stir for 3.5 h, then add 180 g of dodecyltriethoxysilane, heat to 80 ° C, stir for 6 h, centrifuge and wash with anhydrous ethanol, then dry the lower precipitate to obtain hydrophobic silica;

[0046] S2: 250 g of hydrophobic silica, 25 g of sodium dodecyl sulfate, 20 g of an organosilicon defoamer, 15 g of hydrogenated castor oil, 10 g of an antioxidant 1010, and 650 g of water were mixed, and stirred at 50° C. and a speed of 1800 r / min to obtain a premix;

[0047] S3 grinds the premix and filters it, with the filter membrane diameter being less than 10 μm, to obtain the self-cleaning water-based paint.

[0048] Example 3

[0049] A method for preparing a self-cleaning water-based coating for a high-speed railway outer wall comprises the following steps:

[0050] S1: Add 250 g of nano-silica to 3.5 L of anhydrous ethanol, then add 500 g of water and 750 g of ammonia water, stir for 3.5 h, then add 180 g of dodecyltriethoxysilane, heat to 80 ° C, stir for 6 h, centrifuge and wash with anhydrous ethanol, then dry the lower precipitate to obtain hydrophobic silica;

[0051] S2: 200 g of modified polyurethane, 250 g of hydrophobic silica, 25 g of sodium dodecyl sulfate, 20 g of silicone defoamer, 15 g of hydrogenated castor oil, 10 g of antioxidant 1010, and 650 g of water were mixed, and stirred at 50° C. and 1800 r / min to obtain a premix;

[0052] S3 grinds the premix and filters it, with the filter membrane diameter being less than 10 μm, to obtain the self-cleaning water-based paint.

[0053] The preparation method of the modified polyurethane comprises the following steps:

[0054] X1: Add 25 g of ethylenediaminetetraacetic acid dianhydride and 15 g of 3-amino-1-propanol to 100 mL of pyridine, heat to 50°C and stir for 2 h, then raise the temperature to 115°C and continue stirring for 4 h. After stirring, add water, filter, wash the residue with alcohol and dry to obtain a dihydroxy imide derivative;

[0055] X2: 100 g of polytetramethylene ether glycol, 21 g of naphthalene diisocyanate, 19.5 g of 1,8-diisocyanooctane and 0.2 g of dibutyltin dilaurate are added to 500 mL of N,N-dimethylformamide, heated to 60°C and stirred for 2 h, then 30 g of the dihydroxyimide derivative of step X1 and 15 g of 2-hydroxyethyl disulfide are added, the temperature is raised to 80°C and stirred for 8 h to polymerize, after the stirring is completed, the mixture is cooled to room temperature and a large amount of water is added to dilute it, and the precipitate is filtered, and the residue is washed with water and dried to obtain a modified polyurethane.

[0056] Example 4

[0057] A method for preparing a self-cleaning water-based coating for a high-speed railway outer wall comprises the following steps:

[0058] S1: Add 250 g of nano-silica to 3.5 L of anhydrous ethanol, then add 500 g of water and 750 g of ammonia water, stir for 3.5 h, then add 180 g of dodecyltriethoxysilane, heat to 80 ° C, stir for 6 h, centrifuge and wash with anhydrous ethanol, then dry the lower precipitate to obtain hydrophobic silica;

[0059] S2: 250 g of modified polyurethane, 300 g of hydrophobic silica, 25 g of sodium dodecyl sulfate, 20 g of silicone defoamer, 15 g of hydrogenated castor oil, 10 g of antioxidant 1010, and 650 g of water were mixed, and stirred at 50° C. at a speed of 1800 r / min to obtain a premix;

[0060] S3 grinds the premix and filters it, with the filter membrane diameter being less than 10 μm, to obtain the self-cleaning water-based paint.

[0061] The preparation method of the modified polyurethane comprises the following steps:

[0062] X1: Add 25 g of ethylenediaminetetraacetic acid dianhydride and 15 g of 3-amino-1-propanol to 100 mL of pyridine, heat to 50°C and stir for 2 h, then raise the temperature to 115°C and continue stirring for 4 h. After stirring, add water, filter, wash the residue with alcohol and dry to obtain a dihydroxy imide derivative;

[0063] X2: 100 g of polytetramethylene ether glycol, 21 g of naphthalene diisocyanate, 19.5 g of 1,8-diisocyanooctane and 0.2 g of dibutyltin dilaurate are added to 500 mL of N,N-dimethylformamide, heated to 60°C and stirred for 2 h, then 30 g of the dihydroxyimide derivative of step X1 and 15 g of 2-hydroxyethyl disulfide are added, the temperature is raised to 80°C and stirred for 8 h to polymerize, after the stirring is completed, the mixture is cooled to room temperature and a large amount of water is added to dilute it, and the precipitate is filtered, and the residue is washed with water and dried to obtain a modified polyurethane.

[0064] Test Example 1

[0065] The coating prepared in the control example and the embodiment was sprayed on the surface of the aluminum alloy specimen to obtain a coating with a thickness of 100 μm, and the water contact angle and self-cleaning performance of the coating were tested, wherein the contact angle was referenced to GB / T 30447-2013 "Nanofilm Contact Angle Measurement Method", and the self-cleaning performance was referenced to DL / T 627-2018 "Room Temperature Curing Silicone Rubber Anti-Flashover Coating for Insulators".

[0066] Table 1 Self-cleaning performance test of self-cleaning water-based coatings

[0067]

[0068]

[0069] From the contact angle test and the self-cleaning test, it can be seen that the coating prepared by the coating of the present invention has good hydrophobicity and excellent self-cleaning effect. Applying it to the outer wall of the high-speed railway can not only reduce the maintenance cost but also keep the exterior clean. Since the hydrophobic silica surface in the coating has a hydrophobic alkyl chain, it can reduce the surface energy, and the micro-nano structure formed on the surface of the coating enables it to have good self-cleaning properties.

[0070] Test Example 2

[0071] The coating was prepared by referring to the method in Test Example 1, and abrasion resistance test, impact resistance test and self-repair test were performed on it. The abrasion resistance test was based on GB / T 6739-2022 "Determination of film hardness by pencil method for paints and varnishes", and the impact resistance test was based on GB / T 1732-2020 "Determination of impact resistance of paint films". The self-repair test was to scratch the coating on the surface of the test piece with a knife to make the surface coating obviously separated and then heated. After heating the sample at different temperatures for 6 hours, the surface was observed and its hydrophobicity was verified to see whether self-repair was completed, and the self-repair temperature was recorded.

[0072] Table 2 Mechanical properties and self-repair test of self-cleaning coatings

[0073] Experimental protocol Pencil hardness Impact resistance / kg / cm Self-repairing temperature / ℃ Comparative Example 1 3H 43 110 Example 1 5H 65 70 Example 2 2H 27 / Example 3 3H 46 70 Example 4 4H 58 70

[0074] By comparing Control Example 1 with Example 1, it can be found that the dihydroxyimide derivative added to the modified polyurethane is crucial to the mechanical properties and self-healing temperature of the coating. This may be because dihydroxyimide can form special interlayer hydrogen bonds with naphthalene rings. This force caused by strong electrostatic attraction and layered molecular stacking can not only help it repair faster under damage, but also bring good surface adhesion, so the coating exhibits good wear resistance and impact resistance. From Examples 3 to 4, it can be seen that the ratio of polyurethane to hydrophobic silica in the coating can also affect the mechanical properties of the coating. This may be because the difference in the amount of the two will directly affect the surface structure of the coating, thereby showing performance differences. And the self-healing test shows that when the dihydroxyimide structure does not exist in the polyurethane, its self-healing temperature is higher, which is due to the high energy barrier of the disulfide bond. Therefore, when there is only this kind of self-healing mechanism in the structure, the temperature required is naturally higher, and such high temperature conditions are difficult to achieve in the home. In Example 1, the interaction between the naphthalene ring and the imide depends on the electrostatic force and the interlayer hydrogen bond. When these effects disappear, the self-assembly effect of self-repair only requires a lower energy barrier to complete the healing between the molecular chains, so the self-repair temperature is relatively low.

[0075] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A self-cleaning water-based paint for the outer wall of a high-speed railway, characterized in that: In parts by weight, it comprises 20 to 30 parts of modified polyurethane, 20 to 30 parts of hydrophobic silica, 2 to 5 parts of dispersant, 2 to 5 parts of defoamer, 1 to 3 parts of anti-settling agent, 1 to 2 parts of anti-aging agent, and 40 to 80 parts of water; The preparation method of the modified polyurethane comprises the following steps: X1: 1.5-4.5 parts by weight of ethylenediaminetetraacetic acid dianhydride and 1-3 parts by weight of 3-amino-1-propanol are added to 5-25 parts by weight of pyridine, heated to 40-55°C and stirred for 1-2 hours, then heated to 110-125°C, and stirred for 3-6 hours. After the stirring is completed, water is added, filtered, and the residue is washed with alcohol and dried to obtain a dihydroxy imide derivative; X2: Add 5-15 parts by weight of polytetramethylene ether glycol, 1.1-3.5 parts by weight of naphthalene diisocyanate, 1.5-4.5 parts by weight of 1,8-diisocyanooctane and 0.01-0.05 parts by weight of dibutyltin dilaurate to 25-80 parts by weight of N,N-dimethylformamide, heat to 55-70°C and stir for 1-2h, then add 2-4.5 parts by weight of the dihydroxyimide derivative of step X1 and 1-2.5 parts by weight of 2-hydroxyethyl disulfide, heat to 70-85°C and stir for 4-8h to polymerize, cool to room temperature after stirring, add a large amount of water to dilute, filter after precipitation, wash the residue with water and dry to obtain modified polyurethane.

2. The water-based paint according to claim 1, characterized in that: The dispersant is one of sodium carboxymethyl cellulose, sodium dodecyl sulfate and sorbitol ester.

3. The water-based paint according to claim 1, characterized in that: The defoaming agent is one of the organic silicon type, polyether type, and polyether modified polysiloxane type defoaming agents.

4. The water-based paint according to claim 1, characterized in that: The anti-settling agent is one of bentonite, hydrogenated castor oil and polyolefin wax.

5. The water-based paint according to claim 1, characterized in that: The anti-aging agent is one of UV-531, UV-292 and antioxidant 1010.

6. A method for preparing a water-based coating as claimed in any one of claims 1 to 5, characterized in that: The steps include: S1: Add nano-silica to anhydrous ethanol, then add water and ammonia water, stir for 2-4 hours, then add dodecyltriethoxysilane, heat to 70-85°C, stir for 4-8 hours, then centrifuge and wash with anhydrous ethanol, then dry the lower precipitate to obtain hydrophobic silica; S2: Mixing the modified polyurethane, hydrophobic silica, dispersant, defoamer, anti-settling agent, anti-aging agent and water according to the amount in the formula, and stirring evenly at 45-55° C. and 1500-2000 r / min to obtain a premix; S3 grinds the premix and filters it, with the filter membrane diameter being less than 10 μm, to obtain the self-cleaning water-based paint.

7. Application of the water-based paint as described in any one of claims 1 to 5 on the outer wall of high-speed railway.

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