Finishing paint for railway vehicle and preparation method of finishing paint

Abstract

The invention is applicable to the technical field of coatings, and provides a finishing coat for railway vehicles and a preparation method thereof, the method comprises the following steps: preparing modified waterborne polyurethane resin, modified nano titanium dioxide, modified silicon carbide and an elastic enhancer; the preparation method comprises the following steps: adding 40-60 parts by weight of modified waterborne polyurethane resin, 15-25 parts by weight of modified nano titanium dioxide, 8-15 parts by weight of modified silicon carbide, 5-10 parts by weight of an elastic reinforcing agent, 3-8 parts by weight of a coalescing agent, 2-5 parts by weight of a dispersing agent, 1-3 parts by weight of a defoaming agent, 0.5-2 parts by weight of a flatting agent and 20-30 parts by weight of deionized water into a stirring kettle, and stirring to obtain mixed slurry; feeding the mixed slurry into a sand mill, and grinding to obtain ground slurry; 1-3 parts of a thickening agent is added into the grinding slurry, stirring is conducted, and the viscosity is adjusted; and filtering the adjusted slurry to obtain the finishing paint for the railway vehicle. According to the method, the comprehensive performance of the finish paint is remarkably improved, and the use requirement of the bullet train under the high-speed running working condition is met.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a topcoat for rail vehicles and its preparation method. Background Technology

[0002] During operation, key components of rail vehicles (especially bullet trains and high-speed trains) such as bogies rotate at high speeds and are exposed to the railway track environment for extended periods, facing complex operating conditions. This requires that the topcoat for rail vehicles not only meet environmental protection requirements and adopt a water-based system to reduce pollution, but also possess excellent comprehensive performance: the dry film thickness must reach more than 400 micrometers to ensure protective effect, while having good adhesion to the primer, maintaining toughness at low temperatures of -40℃, resisting impacts from flying stones and other objects, and preventing problems such as cracking and peeling. In addition, it must have good weather resistance, corrosion resistance, and wear resistance to cope with environmental factors such as outdoor sun and rain, erosion from pollutants around the track, and frictional wear during high-speed operation.

[0003] Existing topcoats for rail vehicles have several shortcomings: some products are solvent-based coatings with poor environmental performance; water-based topcoats generally suffer from insufficient film thickness in a single application, requiring multiple coats and extending the construction cycle; at the same time, there are shortcomings in the synergistic improvement of low-temperature toughness, stone impact resistance, weather resistance, corrosion resistance, and abrasion resistance, making it difficult to simultaneously meet the stringent requirements of rail vehicles. For example, while traditional water-based polyurethane topcoats possess a certain degree of elasticity and adhesion, their weather resistance and corrosion resistance are insufficient, and they are prone to discoloration and chalking after long-term use; topcoats with conventional nanofillers suffer from poor compatibility between the fillers and the resin matrix, resulting in limited coating stability and mechanical properties; conventional silicon carbide fillers are only treated with simple coupling agents, resulting in insufficient surface activity and weak interfacial bonding with the resin, making it difficult to fully exert their reinforcing, toughening, abrasion-resistant, and impact-resistant effects.

[0004] Therefore, in view of the above situation, there is an urgent need to provide a topcoat for rail vehicles and its preparation method to overcome the shortcomings in current practical applications. Summary of the Invention

[0005] The purpose of this invention is to provide a topcoat for rail vehicles and its preparation method, effectively solving the problems in the background art.

[0006] This invention is achieved by a method for preparing a topcoat for rail vehicles, comprising the following steps: Step 1: Preparation of modified waterborne polyurethane resin, modified nano-titanium dioxide, modified silicon carbide, and elastic reinforcing agent; Step 2: By weight, add 40-60 parts of modified waterborne polyurethane resin, 15-25 parts of modified nano titanium dioxide, 8-15 parts of modified silicon carbide, 5-10 parts of elasticity reinforcing agent, 3-8 parts of film-forming aid, 2-5 parts of dispersant, 1-3 parts of defoamer, 0.5-2 parts of leveling agent and 20-30 parts of deionized water to a mixing tank and stir to obtain a mixed slurry; Step 3: Feed the mixed slurry into a sand mill and grind it until the particle size is ≤50μm to obtain the ground slurry; Step 4: Add 1-3 parts of thickener to the grinding slurry and stir to adjust the viscosity to 50-80 seconds; Step 5: Filter the adjusted slurry with a filtration precision of 100-150 mesh to obtain the topcoat for rail vehicles.

[0007] As a further aspect of the present invention: the preparation method of the modified waterborne polyurethane resin is as follows: S11: Add 20-30 parts of polybutylene adipate diol, 10-15 parts of isophorone diisocyanate, and 2-5 parts of fluorinated monomer perfluorooctyl ethyl acrylate to a reactor, purge with nitrogen for protection, and react at 75-85℃ for 2-3 hours. During the reaction, take samples regularly to detect the -NCO group content. When the -NCO content drops to ±5% of the theoretical value, the fluorinated prepolymer is obtained. S12: Add 3-5 parts of dimethylolpropionic acid and 1-3 parts of crosslinking monomer trimethylolpropane to the fluorinated prepolymer, and continue to react at 70-80℃ for 1-2 hours. Take a sample to detect the hydroxyl value. When the hydroxyl value reaches 80-100 mgKOH / g, stop the reaction. Then add 2-4 parts of triethylamine and neutralize for 15-30 minutes, controlling the degree of neutralization at 90-95%. S13: Slowly add the neutralized product to 40-60 parts of deionized water, stir and emulsify for 30-45 minutes to form a stable emulsion, then add dropwise a mixed chain extender of 1-2 parts of ethylenediamine and 0.5-1 parts of diethylenetriamine, and carry out the chain extension reaction at 60-70℃ for 1-1.5 hours. Finally, cool down to below 40℃ and degas under vacuum for 15-20 minutes to obtain a modified waterborne polyurethane resin with a solid content of 35-45%.

[0008] As a further aspect of the present invention: the preparation method of the modified nano-titanium dioxide is as follows: S21: Add nano-titanium dioxide to a 5-10% hydrochloric acid solution, adjust the solid-liquid ratio to 1:10-1:15 (g / mL), ultrasonically disperse for 30-45 min, then stir and react at 50-60℃ for 1-2 h, filter, wash with deionized water until the pH of the filtrate is 6.5-7.5, vacuum dry at 80-100℃, and pass through a 200-mesh sieve to obtain surface-activated pretreated nano-titanium dioxide; S22: Add 10-15 parts of pretreated nano-titanium dioxide to 80-100 parts of 70-80% ethanol solution, disperse ultrasonically for 15-20 min, then add 3-5 parts of silane coupling agent KH550 and 1-2 parts of stearic acid, heat to 60-70℃, stir and react for 2-3 h, and add 5-10 mL of ethanol solution to the system periodically to maintain the stability of the reaction system concentration. S23: After the reaction is complete, the product is centrifuged and the precipitate is washed with ethanol 3-5 times to remove unreacted coupling agent and stearic acid. It is then vacuum dried at 100-120℃ for 3-4 hours. After drying, it is placed in a planetary ball mill with agate balls as the grinding medium and a ball-to-material ratio of 10:1. The milling is carried out for 30-60 minutes to obtain modified nano-titanium dioxide with a particle size of 20-50nm. S24: Add the ball-milled modified nano-titanium dioxide to 1-3 parts of a 2-5% (w / w) γ-aminopropyltriethoxysilane solution, stir, centrifuge again, and vacuum dry to obtain secondary modified nano-titanium dioxide.

[0009] As a further aspect of the present invention, the method for preparing the modified silicon carbide is as follows: S31: Select silicon carbide particles with a particle size of 5-20μm and subject them to proton irradiation treatment to obtain irradiated silicon carbide with enhanced surface active sites. S32: Add 10-15 parts of irradiated silicon carbide to a sodium hydroxide solution with a mass fraction of 8-12%, adjust the solid-liquid ratio to 1:8-1:12 (g / mL), soak at a constant temperature of 50-60℃ for 2-3 hours, stirring regularly during the soaking process. After soaking, filter and wash with deionized water until the pH of the filtrate is 7.0±0.2. Vacuum dry at 100-120℃ for 2-3 hours to obtain a surface-etched silicon carbide intermediate. S33: Add the silicon carbide intermediate to 80-100 parts of toluene solution, ultrasonically disperse for 20-30 min, then add 2-4 parts of titanate coupling agent NDZ-311, heat to 80-90℃, reflux at 300-400 r / min for 3-4 h, filter after the reaction, wash with toluene 2-3 times, and vacuum dry at 110-130℃ for 3-4 h to obtain coupling modified silicon carbide; S34: Add 10-12 parts of coupling-modified silicon carbide to 50-70 parts of 1-3% cerium nitrate solution, adjust the pH of the system to 4.5-5.5, stir the reaction at 60-70℃ for 1.5-2.5h, and use ultrasonic-assisted dispersion during the reaction. After the reaction is completed, centrifuge the precipitate, wash the precipitate with deionized water until no nitrate ions remain, and vacuum dry to obtain rare earth-doped modified silicon carbide.

[0010] As a further aspect of the present invention: the elastic reinforcing agent is a mixture of polyether-type polyurethane elastomer and nitrile rubber, with a weight ratio of (3-5):1.

[0011] As a further aspect of the present invention: the film-forming aid is one or two of propylene glycol methyl ether acetate and ethylene glycol ethyl ether acetate, mixed in any proportion; The dispersant is a polycarboxylate dispersant; The defoamer is an organosilicon defoamer; The leveling agent is an acrylate leveling agent.

[0012] As a further aspect of the present invention: the thickener is one or two of hydroxyethyl cellulose and polyurethane thickeners mixed in any proportion.

[0013] As a further aspect of the present invention: in S11, the purity of the fluorinated monomer perfluorooctyl ethyl acrylate is ≥98%; In S13, the weight ratio of ethylenediamine to diethylenetriamine in the mixed chain extender is (2-3):1.

[0014] As a further aspect of the present invention: in S21, the temperature of the hydrochloric acid solution is controlled at 25-30°C; In S23, the agate balls used as grinding media in the planetary ball mill have a particle size of 3-5 mm.

[0015] The present invention also provides a topcoat for rail vehicles, which is prepared according to the above-described method for preparing a topcoat for rail vehicles.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention designs the molecular structure of waterborne polyurethane resin, introduces fluorinated monomers and crosslinking monomers, and combines precise control of mixed chain extenders to prepare a modified waterborne polyurethane resin that not only possesses excellent waterborne dispersion stability but also exhibits good elasticity, toughness, weather resistance, and corrosion resistance, laying a core foundation for the comprehensive performance of the topcoat. Simultaneously, it employs an environmentally friendly waterborne system, meeting current environmental requirements, and achieves a dry film thickness of over 400 micrometers with a single coat, significantly shortening the construction cycle.

[0017] The stepwise modification process of nano-titanium dioxide not only solves the problem of agglomeration of nano-titanium dioxide in the coating system, but also significantly improves its compatibility and interfacial bonding with the resin matrix. The synergistic modification of silicon carbide and elastic reinforcing agent enables the topcoat to maintain good toughness at a low temperature of -40℃ and has excellent stone impact resistance, which can effectively resist the impact of splashed stones and prevent cracks and peeling.

[0018] A multi-dimensional modification strategy was implemented for silicon carbide, which enhanced surface activity through proton irradiation, constructed a porous structure through alkaline etching, improved compatibility with resin through coupling agent grafting, and optimized mechanical properties and corrosion resistance through rare earth doping. This significantly improved the reinforcing, toughening, wear resistance, and impact resistance of silicon carbide. In synergy with modified waterborne polyurethane resin and modified nano-titanium dioxide, the weather resistance, corrosion resistance, and wear resistance of the topcoat were greatly improved, enabling it to withstand the complex corrosive factors and frictional wear in the orbital environment for a long time.

[0019] Each raw material component is scientifically proportioned and processed with specific techniques, resulting in good dispersion uniformity, high coating stability, and a smooth and even paint film after application. Its comprehensive performance meets the stringent requirements of rail vehicles (especially EMU bogies) under high-speed operation conditions, and its service life is significantly extended. Attached Figure Description

[0020] Figure 1 This is a photograph of the appearance of Example 1; Figure 2 This is a photograph of the appearance of Example 2; Figure 3 This is a photograph of the appearance of Example 3; Figure 4 This is a photograph of the exterior of Comparative Example 1; Figure 5 This is a photograph of the exterior of Comparative Example 2; Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The present invention will be further explained below with reference to specific embodiments.

[0023] This invention provides a method for preparing a topcoat for rail vehicles, comprising the following steps: Step 1: Preparation of modified waterborne polyurethane resin, modified nano-titanium dioxide, modified silicon carbide, and elastic reinforcing agent; Step 2: By weight, add 40-60 parts of modified waterborne polyurethane resin, 15-25 parts of modified nano titanium dioxide, 8-15 parts of modified silicon carbide, 5-10 parts of elasticity reinforcing agent, 3-8 parts of film-forming aid, 2-5 parts of dispersant, 1-3 parts of defoamer, 0.5-2 parts of leveling agent and 20-30 parts of deionized water to a mixing tank, and stir at 500-800 r / min for 30-60 min to obtain a mixed slurry; Step 3: Feed the mixed slurry into a sand mill and grind it until the particle size is ≤50μm to obtain the ground slurry; Step 4: Add 1-3 parts of thickener to the grinding slurry, stir at 300-500 r / min for 15-30 min, and adjust the viscosity to 50-80 s (Ford Cup 4, 25°C). Step 5: Filter the adjusted slurry with a filtration precision of 100-150 mesh to obtain the topcoat for rail vehicles.

[0024] In a more specific example, the method for preparing the modified waterborne polyurethane resin is as follows: S11: Add 20-30 parts of polybutylene adipate diol, 10-15 parts of isophorone diisocyanate, and 2-5 parts of fluorinated monomer perfluorooctyl ethyl acrylate to a reactor, purge with nitrogen, and react at 75-85℃ for 2-3 hours. During this period, take samples every 30 minutes to detect the -NCO group content. When the -NCO content drops to ±5% of the theoretical value, the fluorinated prepolymer is obtained. S12: Add 3-5 parts of dimethylolpropionic acid and 1-3 parts of crosslinking monomer trimethylolpropane to the fluorinated prepolymer, and continue to react at 70-80℃ for 1-2 hours. Take a sample to detect the hydroxyl value. When the hydroxyl value reaches 80-100 mgKOH / g, stop the reaction. Then add 2-4 parts of triethylamine and neutralize at 300-500 r / min for 15-30 minutes, with the degree of neutralization controlled at 90-95%. S13: Slowly add the neutralized product to 40-60 parts of deionized water, emulsify at 1000-1500 r / min for 30-45 min to form a stable emulsion, then add dropwise a mixed chain extender of 1-2 parts of ethylenediamine and 0.5-1 parts of diethylenetriamine, controlling the dropping rate to 1-2 drops / second, and perform the chain extension reaction at 60-70℃ for 1-1.5 h. Finally, cool down to below 40℃ and degas under vacuum for 15-20 min to obtain a modified waterborne polyurethane resin with a solid content of 35-45%.

[0025] In a more specific example, the method for preparing the modified nano-titanium dioxide is as follows: S21: Add nano-titanium dioxide to a 5-10% hydrochloric acid solution, adjust the solid-liquid ratio to 1:10-1:15 (g / mL), ultrasonically disperse at 300-400W for 30-45 min, then stir and react at 50-60℃ for 1-2 h, filter, wash with deionized water until the pH of the filtrate is 6.5-7.5, vacuum dry at 80-100℃ for 2-3 h, and pass through a 200-mesh sieve to obtain surface-activated pretreated nano-titanium dioxide; S22: Add 10-15 parts of pretreated nano-titanium dioxide to 80-100 parts of 70-80% ethanol solution and ultrasonically disperse for 15-20 min. Then add 3-5 parts of silane coupling agent KH550 and 1-2 parts of stearic acid. Heat to 60-70℃ and stir at 200-300 r / min for 2-3 h. During this period, add 5-10 mL of ethanol solution to the system every 40 min to maintain the stability of the reaction system concentration. S23: After the reaction is complete, the product is centrifuged and the precipitate is washed with ethanol 3-5 times to remove unreacted coupling agent and stearic acid. It is then vacuum dried at 100-120℃ for 3-4 hours. After drying, it is placed in a planetary ball mill with agate balls as the grinding medium and a ball-to-material ratio of 10:1. The milling is carried out at 300-500 r / min for 30-60 min to obtain modified nano-titanium dioxide with a particle size of 20-50 nm. S24: Add the ball-milled modified nano-titanium dioxide to 1-3 parts of a 2-5% (w / w) γ-aminopropyltriethoxysilane solution, stir at 40-50℃ for 30-40 min, centrifuge again, and vacuum dry to obtain secondary modified nano-titanium dioxide.

[0026] In a more specific example, the method for preparing the modified silicon carbide is as follows: S31: Select silicon carbide particles with a particle size of 5-20μm, and subject them to proton irradiation treatment. The irradiation power is 300-350W, the irradiation time is 1.5-2.5h, and the ambient temperature is controlled at 25-35℃ during the irradiation process to obtain irradiated silicon carbide with enhanced surface active sites. S32: Add 10-15 parts of irradiated silicon carbide to a sodium hydroxide solution with a mass fraction of 8-12%, adjust the solid-liquid ratio to 1:8-1:12 (g / mL), soak at a constant temperature of 50-60℃ for 2-3 hours, stirring for 10 minutes every 30 minutes during the soaking process. After soaking, filter and wash with deionized water until the pH of the filtrate is 7.0±0.2. Vacuum dry at 100-120℃ for 2-3 hours to obtain a surface-etched silicon carbide intermediate. S33: Add the silicon carbide intermediate to 80-100 parts of toluene solution, ultrasonically disperse for 20-30 min, then add 2-4 parts of titanate coupling agent NDZ-311, heat to 80-90℃, reflux at 300-400 r / min for 3-4 h, filter after the reaction, wash with toluene 2-3 times, and vacuum dry at 110-130℃ for 3-4 h to obtain coupling modified silicon carbide; S34: Add 10-12 parts of coupling-modified silicon carbide to 50-70 parts of 1-3% cerium nitrate solution, adjust the pH of the system to 4.5-5.5, stir the reaction at 60-70℃ for 1.5-2.5h, and use ultrasonic-assisted dispersion during the reaction with an ultrasonic power of 200-300W. After the reaction is completed, centrifuge the precipitate and wash it with deionized water until no nitrate ions remain (using sodium diphenylamine sulfonate indicator). Vacuum dry at 120-140℃ for 4-5h to obtain rare earth-doped modified silicon carbide.

[0027] In a more specific example, the elastic reinforcing agent is a mixture of polyether-type polyurethane elastomer and nitrile rubber in a weight ratio of (3-5):1.

[0028] In a more specific example, the film-forming aid is one or a mixture of two of propylene glycol methyl ether acetate and ethylene glycol ethyl ether acetate in any proportion; the dispersant is a polycarboxylate dispersant; the defoamer is a silicone defoamer; and the leveling agent is an acrylate leveling agent.

[0029] In a more specific example, the thickener is one or a mixture of two of hydroxyethyl cellulose and polyurethane thickeners in any proportion.

[0030] In a more specific example, in S11, the purity of the fluorinated monomer perfluorooctyl ethyl acrylate is ≥98%; in S13, the weight ratio of ethylenediamine to diethylenetriamine in the mixed chain extender is (2-3):1.

[0031] In a more specific example, in S21, the temperature of the hydrochloric acid solution is controlled at 25-30°C; in S23, the agate balls used as grinding media in the planetary ball mill have a particle size of 3-5 mm.

[0032] This invention also provides a topcoat for rail vehicles, which is prepared according to the above-described method for preparing a topcoat for rail vehicles.

[0033] Example 1: The preparation method of topcoat for rail vehicles is as follows: Step 1: Preparation of modified waterborne polyurethane resin, modified nano-titanium dioxide, modified silicon carbide, and elastic reinforcing agent; Preparation of modified waterborne polyurethane resin: S11: Add 20 parts of polybutylene adipate diol, 10 parts of isophorone diisocyanate, and 2 parts of perfluorooctyl ethyl acrylate (fluorine-containing monomer with a purity ≥98%) to a reactor, purge with nitrogen, and react at 75°C for 2 hours. During this period, take samples every 30 minutes to detect the -NCO group content. When the -NCO content drops to ±5% of the theoretical value, the fluorine-containing prepolymer is obtained. S12: Add 3 parts of dimethylolpropionic acid and 1 part of crosslinking monomer trimethylolpropane to the fluorinated prepolymer, and continue to react at 70℃ for 1 hour. Take a sample to detect the hydroxyl value. When the hydroxyl value reaches 80-100 mgKOH / g, stop the reaction. Then add 2 parts of triethylamine and neutralize at 300 r / min for 15 minutes. The degree of neutralization is controlled at 90-95%. S13: The neutralized product was slowly added to 40 parts of deionized water and emulsified for 30 min under high-speed stirring at 1000 r / min to form a stable emulsion. Then, a mixed chain extender of 1 part ethylenediamine and 0.5 parts diethylenetriamine (weight ratio 2:1) was added dropwise, with the dropping rate controlled at 1 drop / second. The chain extension reaction was carried out at 60℃ for 1 h. Finally, the temperature was lowered to below 40℃ and vacuum degassing was performed for 15 min to obtain a modified waterborne polyurethane resin with a solid content of 35-45%.

[0034] Preparation of modified nano-titanium dioxide: S21: Add nano-titanium dioxide to a hydrochloric acid solution with a mass fraction of 5% and a temperature of 25℃, adjust the solid-liquid ratio to 1:10 (g / mL), ultrasonically disperse at 300W power for 30min, then stir and react at 50℃ for 1h, filter, wash with deionized water until the pH value of the filtrate is 6.5-7.5, vacuum dry at 80℃ for 2h, and pass through a 200-mesh sieve after drying to obtain surface-activated pretreated nano-titanium dioxide; S22: Add 10 parts of pretreated nano-titanium dioxide to 80 parts of 70% ethanol solution and ultrasonically disperse for 15 min. Then add 3 parts of silane coupling agent KH550 and 1 part of stearic acid. Heat to 60℃ and stir at 200 r / min for 2 h. During this period, add 5 mL of ethanol solution to the system every 40 min to maintain the stability of the reaction system concentration. S23: After the reaction is complete, the product is centrifuged and the precipitate is washed three times with ethanol to remove unreacted coupling agent and stearic acid. It is then vacuum dried at 100℃ for 3 hours. After drying, it is placed in a planetary ball mill with agate balls of 3-5 mm in diameter as the grinding medium and a ball-to-material ratio of 10:1. The mixture is ball-milled at 300 r / min for 30 minutes to obtain modified nano-titanium dioxide with a particle size of 20-50 nm. S24: The ball-milled modified nano-titanium dioxide was added to 1 part by mass of 2% γ-aminopropyltriethoxysilane solution, stirred at 40℃ for 30 min, centrifuged again, and vacuum dried to obtain secondary modified nano-titanium dioxide.

[0035] Preparation of modified silicon carbide: S31: Select silicon carbide particles with a particle size of 5-20μm, and subject them to proton irradiation treatment. The irradiation power is 300W, the irradiation time is 1.5h, and the ambient temperature is controlled at 25-35℃ during the irradiation process to obtain irradiated silicon carbide with enhanced surface active sites. S32: Add 10 parts of irradiated silicon carbide to an 8% sodium hydroxide solution, adjust the solid-liquid ratio to 1:8 (g / mL), soak at 50℃ for 2 hours, stirring for 10 minutes every 30 minutes during the soaking period, filter after soaking, wash with deionized water until the pH of the filtrate is 7.0±0.2, and vacuum dry at 100℃ for 2 hours to obtain a surface-etched silicon carbide intermediate; S33: Add the silicon carbide intermediate to 80 parts of toluene solution, ultrasonically disperse for 20 min, then add 2 parts of titanate coupling agent NDZ-311, heat to 80℃, reflux at 300 r / min for 3 h, filter after the reaction, wash twice with toluene, and vacuum dry at 110℃ for 3 h to obtain coupling modified silicon carbide. S34: Add 10 parts of coupling-modified silicon carbide to 50 parts of 1% cerium nitrate solution, adjust the pH of the system to 4.5-5.5, stir the reaction at 60℃ for 1.5h, and use 200W ultrasonic wave to assist dispersion during the reaction. After the reaction is completed, centrifuge the precipitate and wash it with deionized water until no nitrate ions remain (detected by sodium diphenylamine sulfonate indicator). Dry it under vacuum at 120℃ for 4h to obtain rare earth doped modified silicon carbide.

[0036] Elasticity enhancer: Polyether-type polyurethane elastomer and nitrile rubber are mixed at a weight ratio of 3:1.

[0037] Step 2: By weight, add 40 parts modified waterborne polyurethane resin, 15 parts modified nano titanium dioxide, 8 parts modified silicon carbide, 5 parts elastic reinforcing agent, 3 parts propylene glycol methyl ether acetate, 2 parts polycarboxylate dispersant, 1 part silicone defoamer, 0.5 parts acrylate leveling agent and 20 parts deionized water to a mixing tank, and stir at 500 r / min for 30 min to obtain a mixed slurry; Step 3: Feed the mixed slurry into a sand mill and grind it until the particle size is ≤50μm to obtain the ground slurry; Step 4: Add 1 part hydroxyethyl cellulose to the grinding slurry, stir at 300 r / min for 15 min, and adjust the viscosity to 50 s (Ford-4 cup, 25°C). Step 5: Filter the adjusted slurry through a 100-mesh filter to obtain the topcoat for rail vehicles.

[0038] Example 2: The preparation method of topcoat for rail vehicles is as follows: Step 1: Preparation of modified waterborne polyurethane resin, modified nano-titanium dioxide, modified silicon carbide, and elastic reinforcing agent; Preparation of modified waterborne polyurethane resin: S11: Add 30 parts of polybutylene adipate diol, 15 parts of isophorone diisocyanate, and 5 parts of perfluorooctyl ethyl acrylate (fluorine-containing monomer with a purity ≥98%) to a reactor, purge with nitrogen, and react at 85°C for 3 hours. During this period, take samples every 30 minutes to detect the -NCO group content. When the -NCO content drops to ±5% of the theoretical value, the fluorine-containing prepolymer is obtained. S12: Add 5 parts of dimethylolpropionic acid and 3 parts of crosslinking monomer trimethylolpropane to the fluorinated prepolymer, and continue to react at 80℃ for 2 hours. Take a sample to detect the hydroxyl value. When the hydroxyl value reaches 80-100 mgKOH / g, stop the reaction. Then add 4 parts of triethylamine and neutralize at 500 r / min for 30 minutes. The degree of neutralization is controlled at 90-95%. S13: The neutralized product was slowly added to 60 parts of deionized water and emulsified for 45 min under high-speed stirring at 1500 r / min to form a stable emulsion. Then, a mixed chain extender of 2 parts ethylenediamine and 1 part diethylenetriamine (weight ratio 3:1) was added dropwise, with the dropping rate controlled at 2 drops / second. The chain extension reaction was carried out at 70℃ for 1.5 h. Finally, the temperature was lowered to below 40℃ and vacuum degassing was performed for 20 min to obtain a modified waterborne polyurethane resin with a solid content of 35-45%.

[0039] Preparation of modified nano-titanium dioxide: S21: Add nano-titanium dioxide to a hydrochloric acid solution with a mass fraction of 10% and a temperature of 30℃, adjust the solid-liquid ratio to 1:15 (g / mL), ultrasonically disperse at 400W power for 45min, then stir and react at 60℃ for 2h, filter, wash with deionized water until the pH value of the filtrate is 6.5-7.5, vacuum dry at 100℃ for 3h, and pass through a 200-mesh sieve after drying to obtain surface-activated pretreated nano-titanium dioxide; S22: Add 15 parts of pretreated nano-titanium dioxide to 100 parts of 80% ethanol solution and ultrasonically disperse for 20 min. Then add 5 parts of silane coupling agent KH550 and 2 parts of stearic acid. Heat to 70℃ and stir at 300 r / min for 3 h. During this period, add 10 mL of ethanol solution to the system every 40 min to maintain the stability of the reaction system concentration. S23: After the reaction is complete, the product is centrifuged and the precipitate is washed with ethanol 5 times to remove unreacted coupling agent and stearic acid. It is then vacuum dried at 120℃ for 4 hours. After drying, it is placed in a planetary ball mill with agate balls of 3-5 mm as the grinding medium and a ball-to-material ratio of 10:1. The mill is then ball-milled at 500 r / min for 60 min to obtain modified nano-titanium dioxide with a particle size of 20-50 nm. S24: The ball-milled modified nano-titanium dioxide was added to 3 parts of 5% γ-aminopropyltriethoxysilane solution, stirred at 50℃ for 40 min, centrifuged again, and vacuum dried to obtain secondary modified nano-titanium dioxide.

[0040] Preparation of modified silicon carbide: S31: Select silicon carbide particles with a particle size of 5-20μm, and subject them to proton irradiation treatment. The irradiation power is 350W, the irradiation time is 2.5h, and the ambient temperature is controlled at 25-35℃ during the irradiation process to obtain irradiated silicon carbide with enhanced surface active sites. S32: Add 15 parts of irradiated silicon carbide to a 12% sodium hydroxide solution, adjust the solid-liquid ratio to 1:12 (g / mL), soak at 60℃ for 3 hours, stirring for 10 minutes every 30 minutes during the soaking period, filter after soaking, wash with deionized water until the pH of the filtrate is 7.0±0.2, and vacuum dry at 120℃ for 3 hours to obtain a surface-etched silicon carbide intermediate; S33: Add the silicon carbide intermediate to 100 parts of toluene solution, sonicate for 30 min, then add 4 parts of titanate coupling agent NDZ-311, heat to 90℃, reflux at 400 r / min for 4 h, filter after the reaction, wash with toluene 3 times, and vacuum dry at 130℃ for 4 h to obtain coupling modified silicon carbide. S34: 12 parts of coupling-modified silicon carbide were added to 70 parts of 3% cerium nitrate solution, the pH of the system was adjusted to 4.5-5.5, and the reaction was stirred at 70℃ for 2.5h. During the reaction, 300W ultrasonic wave was used to assist dispersion. After the reaction was completed, the mixture was centrifuged and the precipitate was washed with deionized water until no nitrate ions remained (detected by sodium diphenylamine sulfonate indicator). The precipitate was then vacuum dried at 140℃ for 5h to obtain rare earth-doped modified silicon carbide.

[0041] Elasticity enhancer: Polyether-type polyurethane elastomer and nitrile rubber are mixed at a weight ratio of 5:1.

[0042] Step 2: By weight, add 60 parts of modified waterborne polyurethane resin, 25 parts of modified nano titanium dioxide, 15 parts of modified silicon carbide, 10 parts of elastic reinforcing agent, 8 parts of ethylene glycol ethyl ether acetate, 5 parts of polycarboxylate dispersant, 3 parts of silicone defoamer, 2 parts of acrylate leveling agent and 30 parts of deionized water to a mixing tank, and stir at 800 r / min for 60 min to obtain a mixed slurry; Step 3: Feed the mixed slurry into a sand mill and grind it until the particle size is ≤50μm to obtain the ground slurry; Step 4: Add 3 parts of polyurethane thickener to the grinding slurry, stir at 500 r / min for 30 min, and adjust the viscosity to 80 s (Ford Cup 4, 25°C). Step 5: Filter the adjusted slurry through a 150-mesh filter to obtain the topcoat for rail vehicles.

[0043] Example 3: The preparation method of topcoat for rail vehicles is as follows: Step 1: Preparation of modified waterborne polyurethane resin, modified nano-titanium dioxide, modified silicon carbide, and elastic reinforcing agent; Preparation of modified waterborne polyurethane resin: S11: Add 25 parts of polybutylene adipate diol, 12 parts of isophorone diisocyanate, and 3 parts of perfluorooctyl ethyl acrylate (fluorine-containing monomer with a purity ≥98%) to a reactor, purge with nitrogen, and react at 80°C for 2.5 h. During this period, take samples every 30 min to detect the -NCO group content. When the -NCO content drops to ±5% of the theoretical value, the fluorine-containing prepolymer is obtained. S12: Add 4 parts of dimethylolpropionic acid and 2 parts of crosslinking monomer trimethylolpropane to the fluorinated prepolymer, and continue to react at 75℃ for 1.5h. Take a sample to detect the hydroxyl value. When the hydroxyl value reaches 80-100mgKOH / g, stop the reaction. Then add 3 parts of triethylamine and neutralize at 400r / min for 20min. The degree of neutralization is controlled at 90-95%. S13: The neutralized product was slowly added to 50 parts of deionized water and emulsified for 35 min under high-speed stirring at 1200 r / min to form a stable emulsion. Then, a mixed chain extender of 1.5 parts of ethylenediamine and 0.8 parts of diethylenetriamine (weight ratio 2.5:1) was added dropwise, with the dropping rate controlled at 1.5 drops / second. The chain extension reaction was carried out at 65℃ for 1.2 h. Finally, the temperature was lowered to below 40℃ and vacuum degassing was performed for 18 min to obtain a modified waterborne polyurethane resin with a solid content of 35-45%.

[0044] Preparation of modified nano-titanium dioxide: S21: Add nano-titanium dioxide to a hydrochloric acid solution with a mass fraction of 8% and a temperature of 28℃, adjust the solid-liquid ratio to 1:12 (g / mL), ultrasonically disperse at 350W power for 40min, then stir and react at 55℃ for 1.5h, filter, wash with deionized water until the pH of the filtrate is 6.5-7.5, vacuum dry at 90℃ for 2.5h, and pass through a 200-mesh sieve after drying to obtain surface-activated pretreated nano-titanium dioxide; S22: Add 12 parts of pretreated nano-titanium dioxide to 90 parts of 75% ethanol solution and ultrasonically disperse for 18 min. Then add 4 parts of silane coupling agent KH550 and 1.5 parts of stearic acid. Heat to 65℃ and stir at 250 r / min for 2.5 h. During this period, add 8 mL of ethanol solution to the system every 40 min to maintain the stability of the reaction system concentration. S23: After the reaction is complete, the product is centrifuged and the precipitate is washed with ethanol 4 times to remove unreacted coupling agent and stearic acid. It is then vacuum dried at 110℃ for 3.5h. After drying, it is placed in a planetary ball mill with agate balls of 3-5mm as the grinding medium and a ball-to-material ratio of 10:1. The mixture is ball-milled at 400r / min for 45min to obtain modified nano-titanium dioxide with a particle size of 20-50nm. S24: The ball-milled modified nano-titanium dioxide was added to 2 parts of a 3% (w / w) γ-aminopropyltriethoxysilane solution, stirred at 45°C for 35 min, centrifuged again, and vacuum dried to obtain secondary modified nano-titanium dioxide.

[0045] Preparation of modified silicon carbide: S31: Select silicon carbide particles with a particle size of 5-20μm, and subject them to proton irradiation treatment. The irradiation power is 320W, the irradiation time is 2h, and the ambient temperature is controlled at 25-35℃ during the irradiation process to obtain irradiated silicon carbide with enhanced surface active sites. S32: Add 12 parts of irradiated silicon carbide to a 10% sodium hydroxide solution and adjust the solid-liquid ratio to 1:10 (g / mL). Soak at 55℃ for 2.5 h with stirring for 10 min every 30 min. After soaking, filter and wash with deionized water until the pH of the filtrate is 7.0±0.2. Vacuum dry at 110℃ for 2.5 h to obtain a surface-etched silicon carbide intermediate. S33: Add the silicon carbide intermediate to 90 parts of toluene solution, sonicate for 25 min, then add 3 parts of titanate coupling agent NDZ-311, heat to 85℃, reflux at 350 r / min for 3.5 h, filter after the reaction, wash with toluene 2-3 times, and vacuum dry at 120℃ for 3.5 h to obtain coupling modified silicon carbide; S34: 11 parts of coupling-modified silicon carbide were added to 60 parts of 2% cerium nitrate solution, the pH of the system was adjusted to 4.5-5.5, and the reaction was stirred at 65℃ for 2h. During the reaction, ultrasonic dispersion was used to assist dispersion. After the reaction was completed, the mixture was centrifuged and the precipitate was washed with deionized water until no nitrate ions remained (detected by sodium diphenylamine sulfonate indicator). The precipitate was then vacuum dried at 130℃ for 4.5h to obtain rare earth-doped modified silicon carbide.

[0046] Elasticity enhancer: Polyether-type polyurethane elastomer and nitrile rubber are mixed at a weight ratio of 4:1.

[0047] Step 2: By weight, add 50 parts of modified waterborne polyurethane resin, 20 parts of modified nano titanium dioxide, 12 parts of modified silicon carbide, 8 parts of elastic reinforcing agent, 5 parts of a mixture of propylene glycol methyl ether acetate and ethylene glycol ethyl ether acetate (1:1), 3 parts of polycarboxylate dispersant, 2 parts of silicone defoamer, 1 part of acrylate leveling agent and 25 parts of deionized water to a mixing tank and stir at 650 r / min for 45 min to obtain a mixed slurry; Step 3: Feed the mixed slurry into a sand mill and grind it until the particle size is ≤50μm to obtain the ground slurry; Step 4: Add 2 parts of a mixture of hydroxyethyl cellulose and polyurethane thickener (1:1) to the grinding slurry, stir at 400 r / min for 20 min, and adjust the viscosity to 65 s (Ford-4 cup, 25°C). Step 5: Filter the adjusted slurry through a 120-mesh filter to obtain the topcoat for rail vehicles.

[0048] Comparative Example 1: The difference from Example 3 is that no fluorinated monomer perfluorooctyl ethyl acrylate and crosslinking monomer trimethylolpropane were added in the preparation of the modified waterborne polyurethane resin. Only polybutylene adipate diol and isophorone diisocyanate were used to prepare the conventional waterborne polyurethane resin. Other raw materials and preparation processes were the same as in Example 3.

[0049] Comparative Example 2: The difference from Example 3 is that the modified silicon carbide is simply treated with titanate coupling agent NDZ-311 (without proton irradiation, alkaline etching and rare earth doping steps), while other raw materials and preparation processes are the same as in Example 3.

[0050] The performance of the topcoats for rail vehicles prepared in Examples 1-3 and Comparative Examples 1-2 was tested, and the test results are shown in the table below. Figures 1-5 As shown: Table 1 Performance Test Results

[0051] The test results show that the overall performance of the topcoat in Examples 1-3 is far superior to that in Comparative Examples 1-2: Comparative Example 1, due to the lack of introduction of fluorinated monomers and crosslinking monomers into the waterborne polyurethane resin, resulted in a significant decrease in the weather resistance, corrosion resistance, abrasion resistance, and mechanical properties of the topcoat, as well as severe surface cracking, a xenon lamp aging color difference ΔE of 2.8, localized corrosion in the neutral salt spray test, and a Taber abrasion weight loss of 6.8 mg. Comparative Example 2, due to the lack of multi-dimensional modification of silicon carbide through proton irradiation, alkaline etching and rare earth doping, and only simple coupling agent treatment, has insufficient compatibility and interfacial bonding with the resin matrix. The adhesion, stone impact resistance and wear resistance of the topcoat are significantly worse. The stone impact test shows local peeling and severe surface cracks, and the wear resistance weight loss reaches 5.3 mg. The topcoat of Examples 1-3 can achieve a dry film thickness of over 400μm in a single application. It exhibits excellent performance in terms of adhesion, low-temperature toughness, stone impact resistance, weather resistance, corrosion resistance, stain resistance, and abrasion resistance, fully meeting the stringent requirements for use in rail vehicles.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a topcoat for rail vehicles, characterized in that, Includes the following steps: Step 1: Preparation of modified waterborne polyurethane resin, modified nano-titanium dioxide, modified silicon carbide, and elastic reinforcing agent; Step 2: By weight, add 40-60 parts of modified waterborne polyurethane resin, 15-25 parts of modified nano titanium dioxide, 8-15 parts of modified silicon carbide, 5-10 parts of elasticity reinforcing agent, 3-8 parts of film-forming aid, 2-5 parts of dispersant, 1-3 parts of defoamer, 0.5-2 parts of leveling agent and 20-30 parts of deionized water to a mixing tank and stir to obtain a mixed slurry; Step 3: Feed the mixed slurry into a sand mill and grind it until the particle size is ≤50μm to obtain the ground slurry; Step 4: Add 1-3 parts of thickener to the grinding slurry and stir to adjust the viscosity to 50-80 seconds; Step 5: Filter the adjusted slurry with a filtration precision of 100-150 mesh to obtain the topcoat for rail vehicles.

2. The method for preparing the topcoat for rail vehicles according to claim 1, characterized in that, The preparation method of the modified waterborne polyurethane resin is as follows: S11: Add 20-30 parts of polybutylene adipate diol, 10-15 parts of isophorone diisocyanate, and 2-5 parts of fluorinated monomer perfluorooctyl ethyl acrylate to a reactor, purge with nitrogen for protection, and react at 75-85℃ for 2-3 hours. During the reaction, take samples regularly to detect the -NCO group content. When the -NCO content drops to ±5% of the theoretical value, the fluorinated prepolymer is obtained. S12: Add 3-5 parts of dimethylolpropionic acid and 1-3 parts of crosslinking monomer trimethylolpropane to the fluorinated prepolymer, and continue to react at 70-80℃ for 1-2 hours. Take a sample to detect the hydroxyl value. When the hydroxyl value reaches 80-100 mgKOH / g, stop the reaction. Then add 2-4 parts of triethylamine and neutralize for 15-30 minutes, controlling the degree of neutralization at 90-95%. S13: Slowly add the neutralized product to 40-60 parts of deionized water, stir and emulsify for 30-45 minutes to form a stable emulsion, then add dropwise a mixed chain extender of 1-2 parts of ethylenediamine and 0.5-1 parts of diethylenetriamine, and carry out the chain extension reaction at 60-70℃ for 1-1.5 hours. Finally, cool down to below 40℃ and degas under vacuum for 15-20 minutes to obtain a modified waterborne polyurethane resin with a solid content of 35-45%.

3. The method for preparing the topcoat for rail vehicles according to claim 1, characterized in that, The method for preparing the modified nano-titanium dioxide is as follows: S21: Add nano-titanium dioxide to a 5-10% hydrochloric acid solution, adjust the solid-liquid ratio to 1:10-1:15 (g / mL), ultrasonically disperse for 30-45 min, then stir and react at 50-60℃ for 1-2 h, filter, wash with deionized water until the pH of the filtrate is 6.5-7.5, vacuum dry at 80-100℃, and pass through a 200-mesh sieve to obtain surface-activated pretreated nano-titanium dioxide; S22: Add 10-15 parts of pretreated nano-titanium dioxide to 80-100 parts of 70-80% ethanol solution, disperse ultrasonically for 15-20 min, then add 3-5 parts of silane coupling agent KH550 and 1-2 parts of stearic acid, heat to 60-70℃, stir and react for 2-3 h, and add 5-10 mL of ethanol solution to the system periodically to maintain the stability of the reaction system concentration. S23: After the reaction is complete, the product is centrifuged and the precipitate is washed with ethanol 3-5 times to remove unreacted coupling agent and stearic acid. It is then vacuum dried at 100-120℃ for 3-4 hours. After drying, it is placed in a planetary ball mill with agate balls as the grinding medium and a ball-to-material ratio of 10:

1. The milling is carried out for 30-60 minutes to obtain modified nano-titanium dioxide with a particle size of 20-50nm. S24: Add the ball-milled modified nano-titanium dioxide to 1-3 parts of a 2-5% (w / w) γ-aminopropyltriethoxysilane solution, stir, centrifuge again, and vacuum dry to obtain secondary modified nano-titanium dioxide.

4. The method for preparing the topcoat for rail vehicles according to claim 1, characterized in that, The method for preparing the modified silicon carbide is as follows: S31: Select silicon carbide particles with a particle size of 5-20μm and subject them to proton irradiation treatment to obtain irradiated silicon carbide with enhanced surface active sites. S32: Add 10-15 parts of irradiated silicon carbide to a sodium hydroxide solution with a mass fraction of 8-12%, adjust the solid-liquid ratio to 1:8-1:12 (g / mL), soak at a constant temperature of 50-60℃ for 2-3 hours, stirring regularly during the soaking process. After soaking, filter and wash with deionized water until the pH of the filtrate is 7.0±0.

2. Vacuum dry at 100-120℃ for 2-3 hours to obtain a surface-etched silicon carbide intermediate. S33: Add the silicon carbide intermediate to 80-100 parts of toluene solution, ultrasonically disperse for 20-30 min, then add 2-4 parts of titanate coupling agent NDZ-311, heat to 80-90℃, reflux at 300-400 r / min for 3-4 h, filter after the reaction, wash with toluene 2-3 times, and vacuum dry at 110-130℃ for 3-4 h to obtain coupling modified silicon carbide; S34: Add 10-12 parts of coupling-modified silicon carbide to 50-70 parts of 1-3% cerium nitrate solution, adjust the pH of the system to 4.5-5.5, stir the reaction at 60-70℃ for 1.5-2.5h, and use ultrasonic-assisted dispersion during the reaction. After the reaction is completed, centrifuge the precipitate, wash the precipitate with deionized water until no nitrate ions remain, and vacuum dry to obtain rare earth-doped modified silicon carbide.

5. The method for preparing the topcoat for rail vehicles according to claim 1, characterized in that, The elastic reinforcing agent is a mixture of polyether-type polyurethane elastomer and nitrile rubber, with a weight ratio of (3-5):

1.

6. The method for preparing the topcoat for rail vehicles according to claim 1, characterized in that, The film-forming aid is one or two of propylene glycol methyl ether acetate and ethylene glycol ethyl ether acetate, mixed in any proportion. The dispersant is a polycarboxylate dispersant; The defoamer is an organosilicon defoamer; The leveling agent is an acrylate leveling agent.

7. The method for preparing the topcoat for rail vehicles according to claim 1, characterized in that, The thickener is one or a mixture of two of hydroxyethyl cellulose and polyurethane thickeners in any proportion.

8. The method for preparing the topcoat for rail vehicles according to claim 2, characterized in that, In S11, the purity of the fluorinated monomer perfluorooctyl ethyl acrylate is ≥98%; In S13, the weight ratio of ethylenediamine to diethylenetriamine in the mixed chain extender is (2-3):

1.

9. The method for preparing the topcoat for rail vehicles according to claim 3, characterized in that, In S21, the temperature of the hydrochloric acid solution is controlled at 25-30℃; In S23, the agate balls used as grinding media in the planetary ball mill have a particle size of 3-5 mm.

10. A topcoat for rail vehicles, characterized in that, It is prepared by the method for preparing the topcoat for rail vehicles according to any one of claims 1-9.

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