Protective coating for surface layer of steel structure and preparation method of protective coating

Abstract

The invention relates to the field of curing coatings, and particularly discloses a protective coating for a steel structure surface layer and a preparation method of the protective coating. The protective coating for the surface layer of the steel structure comprises a component A and a component B. The component A is prepared from the following raw materials in parts by weight: 20-30 parts of hydroxyl fluorine-containing acrylic emulsion, 20-30 parts of inorganic filler, 5-10 parts of bisphenol A epoxy resin, 1-2 parts of an emulsifier, 0.2-0.5 part of a coalescing agent, 0.2-0.4 part of a flatting agent, 0.1-0.2 part of a defoaming agent, 0.1-0.3 part of a thickening agent, 0-0.05 part of a preservative and 15-25 parts of water. The component B is prepared from the following raw materials: hydrophilic aliphatic polyisocyanate; in the component A and the component B, the ratio of-NCO to-OH is (1.1-1.3): 1. After being cured, the protective coating disclosed by the invention has excellent chloride ion resistance and moisture resistance, and also has good adhesive force, impact resistance and surface hardness.

Description

Technical Field

[0001] The present application relates to the technical field of curing coatings, and in particular to a protective coating for the surface of steel structures and a preparation method thereof. Background Art

[0002] In concrete buildings, in order to improve the stability of the structure, technicians usually add steel bars to the concrete. In order to increase the service life of the steel bars, people usually make coatings on the surface of the steel bars to provide a certain degree of protection for the steel bars. Among the many protective coatings, acrylic-polyurethane coatings have many advantages, mainly because they can resist environmental erosion such as ultraviolet rays, rain, wind and sand, and maintain the gloss and color stability of the coating. They are particularly suitable for outdoor steel structures, building facades and other scenes. Their paint film is relatively tough, wear-resistant and impact-resistant, and is suitable for high-load scenes. At the same time, their water-based system complies with environmental regulations and adopts a low-VOC formula to reduce environmental pollution during the construction process. During construction, acrylic-polyurethane coatings support a variety of construction methods such as spraying, roller coating, and brushing. They have good leveling properties and dry quickly (surface drying ≤ 1 hour). In short, acrylic-polyurethane coatings have become the preferred solution in the field of industrial protection and decorative coatings due to their good weather resistance, mechanical strength, environmental protection and construction flexibility. They are especially suitable for scenes with high durability requirements.

[0003] However, with actual use, people have found that in humid, coastal or saline environments, the protective coating of concrete is easily destroyed by harsh environments and it is difficult to isolate corrosive media such as chloride ions and moisture, which has a great impact on the service life of reinforced concrete. Summary of the Invention

[0004] In order to solve the above technical problems, the present application provides a protective coating for the surface of a steel structure and a preparation method thereof.

[0005] In the first aspect, the present application provides a protective coating for the surface of a steel structure, comprising component A and component B. The raw materials used in component A include the following components in parts by weight: 20-30 parts of a hydroxyl fluorinated acrylic emulsion, 20-30 parts of an inorganic filler, 5-10 parts of a bisphenol A epoxy resin, 1-2 parts of an emulsifier, 0.2-0.5 parts of a film-forming aid, 0.2-0.4 parts of a leveling agent, 0.1-0.2 parts of a defoaming agent, 0.1-0.3 parts of a thickener, 0-0.05 parts of a preservative, and 15-25 parts of water. The raw materials used in component B include a hydrophilic aliphatic polyisocyanate; in component A and component B, -NCO:-OH = (1.1-1.3):1.

[0006] By adopting the above technical solution, the hydroxyl fluorinated acrylic emulsion of the present application is an acrylic dispersion containing hydroxyl functional groups. The fluorinated groups introduced into the emulsion can improve the water resistance and acid and alkali resistance of the coating. After curing with the hydrophilic aliphatic polyisocyanate, the resulting coating is hard, anti-adhesive, has good acid and alkali resistance, and has strong anti-yellowing and gloss retention. In addition, the bisphenol A epoxy resin in the system of the present application has good acid and alkali resistance and weather resistance, and the inorganic filler has excellent reinforcing ability. The various substances are blended and coordinated with a series of auxiliary agents such as emulsifiers, film-forming agents, leveling agents, defoamers, thickeners and preservatives to ensure the leveling, construction convenience and environmental performance of the coating. The protective coating finally obtained can have excellent resistance to chloride ions and moisture after curing, and has good adhesion, impact resistance and surface hardness. Experimental data show that the protective coating prepared by the protective coating for the surface of steel structures of the present application has a hardness of more than 3H, an adhesion of more than 4B, and an impact strength of ≥50kg·cm -1 In the electrochemical impedance spectroscopy test, the impedance value of the protective coating after being immersed in a 3.5% sodium chloride solution for 7 days is still not less than 1.95×10 6 Ω·cm -2 .

[0007] In the embodiments of the present application, the emulsifier is sodium lauryl sulfate, the film-forming aid is 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, the leveling agent is a polyether-modified siloxane leveling agent, the defoaming agent is a silicone defoaming agent, and the thickener is hydroxyethyl cellulose. These are merely examples, and those skilled in the art may replace different substances according to actual conditions, and the scope of protection of the present application cannot be limited in sequence.

[0008] Preferably, in the component A and the component B, -NCO:-OH=1.2:1.

[0009] By adopting the above technical solution, the present application optimizes the ratio of -NCO to -OH in components A and B to 1.2:1, which can further improve the curing performance of the protective coating, make the curing reaction more complete, and increase the cross-linking density of the coating, thereby enhancing the chemical corrosion resistance and mechanical strength of the coating. At the same time, the optimization of this ratio can also improve the yellowing resistance and gloss retention of the coating, so that the coating maintains good appearance and performance stability during long-term use.

[0010] Preferably, the raw materials used for component A include the following components in parts by weight: 25 parts of hydroxyl fluorine-containing acrylic emulsion, 25 parts of inorganic filler, 8 parts of bisphenol A epoxy resin, 1.5 parts of emulsifier, 0.4 parts of film-forming aid, 0.3 parts of leveling agent, 0.15 parts of defoaming agent, 0.2 parts of thickener, 0.025 parts of preservative, and 20 parts of water.

[0011] By adopting the above technical solution, the present application optimizes the content of hydroxyl fluorinated acrylic emulsion to 25 parts, which can provide better water resistance and acid and alkali resistance. The coating formed after curing with hydrophilic aliphatic polyisocyanate has stronger anti-adhesion and acid and alkali resistance, and better gloss retention. The content of inorganic filler is optimized to 25 parts, which can further enhance the reinforcement ability of the coating and enhance the mechanical strength and wear resistance of the coating. The content of bisphenol A epoxy resin is optimized to 8 parts, which gives the coating better weather resistance and corrosion resistance. The content of emulsifier is optimized to 1.5 parts. This helps improve the stability of the coating system; the film-forming aid content is optimized to 0.4 parts, which optimizes the film-forming properties of the coating; the leveling agent content is optimized to 0.3 parts, which improves the leveling effect of the coating; the defoamer content is optimized to 0.15 parts, which effectively reduces the problem of bubbles in the coating during application; the thickener content is optimized to 0.2 parts, which adjusts the viscosity of the coating and facilitates construction operations; the preservative content is optimized to 0.025 parts, which enhances the corrosion resistance of the coating; and the water content is optimized to 20 parts as a dispersion medium to ensure uniform mixing of all components. In summary, this preferred solution enables the protective coating to have higher hardness, adhesion, and impact resistance after curing, while significantly enhancing its tolerance to chloride ions and moisture.

[0012] Preferably, the inorganic filler is starch-modified nano-SiO2, which is prepared by the following method: dispersing nano-SiO2 and starch in a weight ratio of 3:(3-7) in water, stirring at a temperature of 20-45°C for 18-22h, then filtering, washing, drying, and grinding to obtain starch-modified nano-SiO2.

[0013] By adopting the above-mentioned technical solution, this application introduces starch-modified nano-SiO2 as an inorganic filler into a protective coating. The preparation method, which involves dispersing the nano-SiO2 and starch in a specific weight ratio, followed by stirring, filtering, washing, drying, and grinding, significantly improves the overall performance of the coating. Specifically, it enhances the coating's water resistance and acid and alkali resistance, improves the coating's hardness and adhesion, and improves its impact resistance. Furthermore, the addition of starch-modified nano-SiO2 optimizes the coating's surface properties, imparting superior resistance to chloride ion penetration and moisture barrier properties, thereby effectively extending the service life of steel structures in harsh environments.

[0014] Preferably, the weight ratio of the nano-SiO2 to starch is 3:5.

[0015] By adopting the above technical solution, the present application optimizes the weight ratio of nano-SiO2 to starch to 3:5, further improving the performance of the inorganic filler. Specifically, the starch-modified nano-SiO2 at this ratio exhibits improved dispersibility and stability, thereby enhancing the protective coating's resistance to chloride ion penetration and moisture. Furthermore, this ratio improves the coating's adhesion and mechanical strength, ensuring that the coating maintains excellent protection even in harsh environments.

[0016] Preferably, after nano-SiO2 and starch are dispersed in water, the mixture is stirred at a temperature of 35°C.

[0017] By adopting the above technical solution, the present application strictly controls the temperature. Stirring at this temperature helps to uniformly disperse and fully react between starch and nano-SiO2, thereby improving the modification effect. It can also improve the performance of inorganic fillers and enhance their reinforcement ability in protective coatings, thereby improving the coating's resistance to chloride ions, moisture resistance, and impact resistance.

[0018] Preferably, the preservative includes at least one of fluorocarbon resin, zinc phosphate, benzotriazole and zinc octoate.

[0019] By adopting the above technical solution, the addition of the preservatives in this application enhances the corrosion resistance of the protective coating. Fluorocarbon resin imparts excellent weather and chemical resistance to the coating, zinc phosphate inhibits corrosion of the metal substrate by forming a protective film, benzotriazole effectively prevents copper ion corrosion, and zinc octanoate provides excellent rust prevention. These preservatives ensure superior stability in complex environments, extending the service life of steel structures.

[0020] Preferably, the preservative comprises fluorocarbon resin and zinc phosphate in a weight ratio of 1:(0.5-1).

[0021] By adopting the above technical solution, the preservative of the present application is composed of fluorocarbon resin and zinc phosphate, and the weight ratio of the two is 1:(0.5-1). Because fluorocarbon resin has excellent weather resistance and chemical corrosion resistance, it can effectively resist the erosion of ultraviolet rays and chemicals, thereby enhancing the overall durability of the protective coating; zinc phosphate can form a protective film on the metal surface, providing cathodic protection, further improving the anti-corrosion performance of the coating. Therefore, the synergistic effect of the two not only enhances the anti-corrosion effect of the protective coating, but also ensures its long-term stability in harsh environments.

[0022] In a second aspect, the present application provides a method for preparing a protective coating for the surface of a steel structure, comprising the following steps: S1, blending an emulsifier, a film-forming aid, a leveling agent, a defoaming agent, a thickener, a preservative and water, stirring evenly, adding an inorganic filler, and then adding a hydroxyl fluorinated acrylic emulsion and a bisphenol A epoxy resin, stirring evenly to obtain component A; S2, mixing the component A with the component B, stirring evenly to obtain a protective coating.

[0023] By adopting the above technical solution, the preparation method of the present application can ensure that the components of the protective coating are fully mixed to form a uniform and stable system. Since the present application first blends the emulsifier, film-forming aid, leveling agent, defoamer, thickener, preservative and water, the dispersibility of the subsequently added inorganic filler and other components can be effectively improved, thereby improving the stability and coating performance of the coating. Subsequently, the present application adds the hydroxyl fluorinated acrylic emulsion and bisphenol A epoxy resin in a specific order, which can ensure that the two react fully with the other components in the system to form a coating with excellent chloride ion resistance and moisture resistance. Finally, the present application mixes component A and component B in a ratio of -NCO:-OH=(1.1-1.3):1, ensuring that the coating has good hardness, adhesion and impact resistance after curing, and strong anti-yellowing and gloss retention. The operating conditions of each step in the preparation process of the present application are mild and easy to control, which is conducive to large-scale industrial production while ensuring stable and reliable product quality.

[0024] In summary, this application has the following beneficial technical effects: 1. The coating formed by curing the hydroxyl fluorinated acrylic emulsion and hydrophilic aliphatic polyisocyanate of the present application has excellent acid and alkali resistance and anti-yellowing and gloss retention properties, and can effectively resist corrosive media in humid, coastal or salty environments, thereby improving the durability of the coating; 2. The introduction of the bisphenol A epoxy resin in this application enhances the weather resistance and acid and alkali resistance of the coating. Combined with the reinforcing ability of the inorganic filler, the coating has good adhesion and impact resistance. 3. The protective coating of the present application has a hardness of more than 3H and an adhesion of more than 4B after curing. At the same time, the impedance value after immersion in a 3.5% sodium chloride solution for 7 days is still not less than 1.95×10 6 Ω·cm -2 , showing excellent resistance to chloride ions and moisture. DETAILED DESCRIPTION

[0025] Material Source Unless otherwise specified, the raw materials used in this application are all commercially available products, specifically: Nano-SiO2 aqueous dispersion was purchased from Xuancheng Jingrui New Materials Co., Ltd., with a nano-SiO2 content of 20 wt%; Starch was purchased from Jining Linghua Group Co., Ltd., Shandong Province; Hydroxylated fluorinated acrylic emulsion was purchased from Shanghai Xunda New Material Technology Co., Ltd., with the brand name HD 827, solid content 45% ± 1%, fluorine content 9%-10%, hydroxyl content 2.7%, viscosity 500-3000 mPa·s, and pH = 7.5; Bisphenol A epoxy resin was purchased from Baling Petrochemical, with the brand name CYDW-100 and a viscosity of 500-3000 mPa·s; Hydrophilic aliphatic polyisocyanate was purchased from Covestro with the brand name Bayhydur 305, NCO content of 16.2% ± 0.4%, viscosity (23 ° C) of 6500 ± 1500 mPa·s, and density of 1.16 g / cm 3 ; Sodium lauryl sulfate was purchased from Tianjin Hedong Hongyan Reagent Factory; 2,2,4-Trimethyl-1,3-pentanediol monoisobutyrate was purchased from Shanghai Jieshikai Biotechnology Co., Ltd.; Polyether modified siloxane leveling agent was purchased from Guangzhou Lai Ke Bao New Material Technology Co., Ltd., brand ATS-4033; The organosilicon defoamer was purchased from Guangzhou Chengjian Trading Co., Ltd., brand A-3060; Hydroxyethyl cellulose was purchased from Jining Tangyi Chemical Co., Ltd. with the brand name TT-935; Zinc 2-ethylhexanoate was purchased from Jiangsu Haolong Chemical Co., Ltd.; Benzotriazole was purchased from Jining Tangyi Chemical Co., Ltd.; Fluorocarbon resin was purchased from Jinbaolai; Zinc phosphate was purchased from Guangdong Jiaming New Materials Co., Ltd.

[0026] The present application is further described in detail below with reference to the following examples and comparative examples.

[0027] Preparation Example 1.1 The preparation method of starch-modified nano-SiO2 comprises the following steps: 1.5 kg of nano-SiO2 aqueous dispersion and 0.3 kg of starch were dispersed in 5 L of water, ultrasonically treated in an ultrasonic instrument for 30 min, then stirred at a temperature of 45°C for 18 h, and then filtered, washed, dried, and ground to obtain starch-modified nano-SiO2.

[0028] Preparation Example 1.2 The preparation method of starch-modified nano-SiO2 comprises the following steps: 1.5 kg of nano-SiO2 aqueous dispersion and 0.7 kg of starch were dispersed in 5 L of water, ultrasonically treated in an ultrasonic instrument for 30 min, then stirred at a temperature of 20°C for 22 h, and then filtered, washed, dried, and ground to obtain starch-modified nano-SiO2.

[0029] Preparation Example 2.1 The preparation method of starch-modified nano-SiO2 is different from that of Preparation Example 1.1 in that the amount of starch used is 0.4 kg, and the rest is the same as Preparation Example 1.1.

[0030] Preparation Example 2.2 The preparation method of starch-modified nano-SiO2 is different from that of Preparation Example 1.1 in that the amount of starch used is 0.5 kg, and the rest is the same as Preparation Example 1.1.

[0031] Preparation Example 2.3 The preparation method of starch-modified nano-SiO2 is different from that of Preparation Example 1.1 in that the amount of starch used is 0.6 kg, and the rest is the same as Preparation Example 1.1.

[0032] Preparation Example 3.1 The preparation method of starch-modified nano-SiO2 is different from that of Preparation Example 2.2 in that the stirring temperature is 25°C, and the rest is the same as Preparation Example 2.2.

[0033] Preparation Example 3.2 The preparation method of starch-modified nano-SiO2 is different from that of Preparation Example 2.2 in that the stirring temperature is 30°C, and the rest is the same as Preparation Example 2.2.

[0034] Preparation Example 3.3 The preparation method of starch-modified nano-SiO2 is different from that of Preparation Example 2.2 in that the stirring temperature is 35°C, and the rest is the same as Preparation Example 2.2.

[0035] Preparation Example 3.4 The preparation method of starch-modified nano-SiO2 is different from that of Preparation Example 2.2 in that the stirring temperature is 40°C, and the rest is the same as Preparation Example 2.2.

[0036] Example 1.1 A method for preparing a protective coating for the surface of a steel structure comprises the following steps: S1. Blend 100 g of an emulsifier (sodium lauryl sulfate), 50 g of a film-forming aid (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), 20 g of a leveling agent (polyether-modified siloxane leveling agent), 20 g of a defoamer (organic silicone defoamer), 10 g of a thickener (hydroxyethyl cellulose), 5 g of a preservative (zinc isooctanoate), and 1.5 kg of water. After stirring evenly, add 3 kg of an inorganic filler (starch-modified nano-SiO2 obtained in Preparation Example 1.1), and then add 2 kg of a hydroxyl fluorinated acrylic emulsion and 1 kg of a bisphenol A epoxy resin. Stir evenly to obtain component A. S2. Component A and component B (hydrophilic aliphatic polyisocyanate) are mixed according to the ratio of -NCO:-OH=1.1:1, and stirred evenly to obtain a protective coating.

[0037] Example 1.2 A method for preparing a protective coating for the surface of a steel structure comprises the following steps: S1. 200 g of an emulsifier (sodium lauryl sulfate), 20 g of a film-forming aid (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), 40 g of a leveling agent (polyether-modified siloxane leveling agent), 10 g of a defoamer (organic silicone defoamer), 30 g of a thickener (hydroxyethyl cellulose), and 2.5 kg of water were mixed and stirred uniformly. 2 kg of an inorganic filler (starch-modified nano-SiO2 obtained in Preparation Example 1.2) was added, followed by 3 kg of a hydroxyl fluorinated acrylic emulsion and 0.5 kg of a bisphenol A epoxy resin. The mixture was stirred uniformly to obtain component A. S2. Component A and component B (hydrophilic aliphatic polyisocyanate) are mixed according to the ratio of -NCO:-OH=1.3:1, and stirred evenly to obtain a protective coating.

[0038] Example 1.3 A method for preparing a protective coating for the surface of a steel structure comprises the following steps: S1. Blend 100 g of an emulsifier (sodium lauryl sulfate), 50 g of a film-forming aid (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), 20 g of a leveling agent (polyether-modified siloxane leveling agent), 20 g of a defoamer (organic silicone defoamer), 10 g of a thickener (hydroxyethyl cellulose), 5 g of a preservative (zinc isooctanoate), and 1.5 kg of water. After stirring evenly, add 3 kg of an inorganic filler (starch-modified nano-SiO2 obtained in Preparation Example 1.1), and then add 2 kg of a hydroxyl fluorinated acrylic emulsion and 1 kg of a bisphenol A epoxy resin. Stir evenly to obtain component A. S2. Component A and component B (hydrophilic aliphatic polyisocyanate) are mixed according to the ratio of -NCO:-OH=1.2:1, and stirred evenly to obtain a protective coating.

[0039] Example 1.4 A method for preparing a protective coating for the surface of a steel structure comprises the following steps: S1. Blend 150 g of an emulsifier (sodium lauryl sulfate), 40 g of a film-forming aid (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), 30 g of a leveling agent (polyether-modified siloxane leveling agent), 15 g of a defoamer (organic silicone defoamer), 20 g of a thickener (hydroxyethyl cellulose), 2.5 g of a preservative (benzotriazole), and 2 kg of water. After stirring evenly, add 2.5 kg of an inorganic filler (starch-modified nano-SiO2 obtained in Preparation Example 1.1), and then add 2.5 kg of a hydroxyl fluorinated acrylic emulsion and 0.8 kg of a bisphenol A epoxy resin. Stir evenly to obtain component A. S2. Component A and component B (hydrophilic aliphatic polyisocyanate) are mixed according to the ratio of -NCO:-OH=1.2:1, and stirred evenly to obtain a protective coating.

[0040] Examples 2.1-2.3 A method for preparing a protective coating for the surface of a steel structure, which differs from Example 1.4 in that the starch-modified nano-SiO2 prepared in Preparation Example 1.1 is replaced by the starch-modified nano-SiO2 prepared in Preparation Examples 2.1-2.3 respectively, and the rest is the same as Example 1.4.

[0041] Examples 3.1-3.4 A method for preparing a protective coating for the surface of a steel structure, which differs from Example 2.2 in that the starch-modified nano-SiO2 prepared in Preparation Example 2.2 is replaced by the starch-modified nano-SiO2 prepared in Preparation Examples 3.1-3.4 respectively, and the rest is the same as Example 2.2.

[0042] Example 4.1 A method for preparing a protective coating for the surface of a steel structure, which differs from Example 1.4 in that 2.5 g of benzotriazole is replaced with 1.67 g of fluorocarbon resin and 0.83 g of zinc phosphate, and the rest is the same as Example 1.4.

[0043] Example 4.2 A method for preparing a protective coating for the surface of a steel structure, which differs from Example 1.4 in that 2.5 g of benzotriazole is replaced with 1.25 g of fluorocarbon resin and 1.25 g of zinc phosphate, and the rest is the same as Example 1.4.

[0044] Example 4.3 A method for preparing a protective coating for the surface of a steel structure, which differs from Example 1.4 in that 2.5 g of benzotriazole is replaced with 1.67 g of fluorocarbon resin and 0.83 g of benzotriazole, and the rest is the same as Example 1.4.

[0045] Example 4.4 A method for preparing a protective coating for the surface of a steel structure, which differs from Example 1.4 in that 2.5 g of benzotriazole is replaced with 1.67 g of zinc isooctanoate and 0.83 g of zinc phosphate, and the rest is the same as Example 1.4.

[0046] Comparative Example 1.1 The difference from Example 1.4 is that in step S2, component A and component B are mixed according to the ratio of -NCO:-OH=1:1, and the rest are the same as Example 1.4.

[0047] Comparative Example 1.2 The difference from Example 1.4 is that in step S2, component A and component B are mixed according to the ratio of -NCO:-OH=1:4, and the rest are the same as Example 1.4.

[0048] Comparative Example 2 The difference from Example 1.4 is that in step S1, the bisphenol A epoxy resin is removed, and the amount of hydroxyl fluorinated acrylic emulsion used is 3.3 kg. The rest is the same as Example 1.4.

[0049] Performance testing The coatings obtained in the examples and comparative examples were added to a spray gun and sprayed. The spray gun was kept about 20 cm away from the sample and the coating was applied evenly to ensure that the dry film thickness was consistent. The sample was naturally dried to obtain a coating. The base steel plate used in the experiment was a tinplate plate with a specification of 150 mm × 70 mm × 2 mm. The sample was surface treated before the experiment and polished to 500 mesh with sandpaper. The iron filings on the surface were wiped off with absorbent cotton, and then the surface was wiped clean with anhydrous ethanol and acetone, and placed in a vacuum drying oven to dry.

[0050] 1. The adhesion and impact strength of the protective coating formed after curing of the protective coating of this application are measured according to the description of GB / T 1732-2020 "Determination of impact resistance of paint films"; 2. The hardness of the protective coating formed after curing of the protective coating of this application is measured according to the description of GB / T 6739-2022 "Determination of Pencil Hardness of Paint Films"; 3. Use the sample as the working electrode, exposing an area of ​​1cm 2 , saturated calomel electrode as reference electrode, platinum electrode as counter electrode, electrochemical impedance spectroscopy amplitude of 10mV, frequency of 10 5 -10 -2 Hz, the measurement system is 3.5% sodium chloride solution at room temperature, and the immersion time is 7 days.

[0051] Table 1 Performance test table Data Analysis: As can be seen from Table 1, the coatings obtained after curing of the coatings of Examples 1.1-1.4 have a hardness of 3H, an adhesion of 4B, and a viscosity of 50.6-52.7 kg·cm -1 The impact strength and corrosion resistance after 7 days are still as high as 1.95×10 6 -2.10×10 6 Ω·cm -2 The impedance value proves that the hydroxyl fluorinated acrylic emulsion of the present application is an acrylic dispersion containing hydroxyl functional groups. The fluorinated groups introduced into the emulsion can improve the water resistance and acid and alkali resistance of the coating. After curing with the hydrophilic aliphatic polyisocyanate, the formed coating is hard, anti-adhesive, has good acid and alkali resistance, and has strong anti-yellowing and gloss retention. In addition, the bisphenol A epoxy resin in the system of the present application has good acid and alkali resistance and weather resistance, and the inorganic filler has excellent reinforcing ability. The blending of multiple substances and a series of auxiliary agents such as emulsifiers, film-forming agents, leveling agents, defoaming agents, thickeners and preservatives ensure the leveling, construction convenience and environmental protection performance of the coating. The protective coating finally obtained can have excellent resistance to chloride ions and moisture after curing, and at the same time has good adhesion, impact resistance and surface hardness.

[0052] In Examples 2.1-2.3, the present application adjusted the amount of starch used in preparing the inorganic filler. The results showed that after curing the coating of Example 2.2, all indicators of the resulting coating were significantly improved. This demonstrates that optimizing the weight ratio of nano-SiO2 to starch to 3:5 can further optimize the performance of the inorganic filler. Specifically, this ratio improves the dispersibility and stability of the starch-modified nano-SiO2, thereby enhancing the protective coating's resistance to chloride ion penetration and moisture. Furthermore, this ratio improves the coating's adhesion and mechanical strength, ensuring that the coating maintains its protective effect even in harsh environments.

[0053] In Examples 3.1-3.4, the present application adjusted the blending temperature during the preparation of the inorganic filler. The results showed that the impact strength and post-corrosion impedance value of the coating obtained after curing of the coating of Example 3.3 were significantly improved, demonstrating that the strictly controlled temperature in the present application facilitated the uniform dispersion and sufficient reaction between starch and nano-SiO2, thereby enhancing the modification effect. It also improved the performance of the inorganic filler and enhanced its reinforcement ability in the protective coating, thereby improving the coating's chloride ion resistance, moisture resistance, adhesion, and impact resistance.

[0054] In Examples 4.1-4.4, the present application adjusted the components of the preservative. The results showed that the impact resistance and post-corrosion impedance value of the coating obtained after the coating of Examples 4.1-4.2 was significantly improved, proving that the preservative of the present application is composed of fluorocarbon resin and zinc phosphate, and the weight ratio of the two is 1: (0.5-1), which can produce a significant synergistic effect, not only improving the anti-corrosion effect of the protective coating, but also ensuring its long-term stability in harsh environments.

[0055] In Comparative Examples 1.1-1.2, the present application adjusted the ratio of -NCO:-OH in step S2. The results showed that the various indicators of the coating obtained after the coating of Comparative Examples 1.1-1.2 was cured were significantly reduced, proving that the ratio of -NCO to -OH in the present application can further improve the curing performance of the protective coating, the curing reaction is more complete, and the cross-linking density of the coating is increased, thereby enhancing the chemical corrosion resistance and mechanical strength of the coating. At the same time, this ratio can also improve the yellowing resistance and gloss retention of the coating, so that the coating maintains good appearance and performance stability during long-term use.

[0056] In Comparative Example 2, the present application removed the bisphenol A epoxy resin. The results showed that the various indicators of the coating obtained after the coating of Comparative Example 2 was cured were significantly reduced, proving that the bisphenol A epoxy resin of the present application has good acid and alkali resistance and weather resistance, and gives the coating better weather resistance and corrosion resistance.

[0057] The embodiments of this specific implementation method are all preferred embodiments of the present application and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A protective coating for the surface of a steel structure, characterized in that: The invention comprises a component A and a component B. The raw materials used in the component A include the following components in parts by weight: 20-30 parts of a hydroxyl fluorine-containing acrylic emulsion, 20-30 parts of an inorganic filler, 5-10 parts of a bisphenol A epoxy resin, 1-2 parts of an emulsifier, 0.2-0.5 parts of a film-forming aid, 0.2-0.4 parts of a leveling agent, 0.1-0.2 parts of a defoaming agent, 0.1-0.3 parts of a thickener, 0-0.05 parts of a preservative, and 15-25 parts of water. The raw materials used in the component B include a hydrophilic aliphatic polyisocyanate. In the components A and B, the ratio of -NCO:-OH is (1.1-1.3):

1.

2. The protective coating for the surface of a steel structure according to claim 1, characterized in that: In the component A and the component B, -NCO:-OH=1.2:

1.

3. The protective coating for the surface of a steel structure according to claim 1, characterized in that: The raw materials used for component A include the following components in parts by weight: 25 parts of hydroxy fluorine-containing acrylic emulsion, 25 parts of inorganic filler, 8 parts of bisphenol A epoxy resin, 1.5 parts of emulsifier, 0.4 parts of film-forming aid, 0.3 parts of leveling agent, 0.15 parts of defoaming agent, 0.2 parts of thickener, 0.025 parts of preservative, and 20 parts of water.

4. The protective coating for the surface of a steel structure according to claim 1, characterized in that: The inorganic filler is starch-modified nano-SiO2, which is prepared by the following method: dispersing nano-SiO2 and starch in a weight ratio of 3:(3-7) in water, stirring at a temperature of 20-45°C for 18-22 hours, and then filtering, washing, drying, and grinding to obtain starch-modified nano-SiO2.

5. The protective coating for the surface of a steel structure according to claim 4, characterized in that: The weight ratio of the nano-SiO2 to starch is 3:

5.

6. The protective coating for the surface of a steel structure according to claim 4, characterized in that: After dispersing nano-SiO2 and starch in water, stir at a temperature of 35°C.

7. The protective coating for the surface of a steel structure according to claim 1, characterized in that: The preservative includes at least one of fluorocarbon resin, zinc phosphate, benzotriazole and zinc ethyl octanoate.

8. The protective coating for the surface of a steel structure according to claim 7, characterized in that: The preservative includes fluorocarbon resin and zinc phosphate in a weight ratio of 1:(0.5-1).

9. A method for preparing the protective coating for the surface of a steel structure according to claims 1 to 8, characterized in that: The following steps are involved: S1. Blending an emulsifier, a film-forming aid, a leveling agent, a defoamer, a thickener, a preservative, and water, stirring uniformly, adding an inorganic filler, and subsequently adding a hydroxyl fluorinated acrylic emulsion and a bisphenol A epoxy resin, stirring uniformly, to obtain component A; S2. Mix the component A and the component B, and stir them evenly to obtain a protective coating.

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