Water-based protective coating for corrosion protection of stainless steel cover and preparation method thereof

Abstract

The application discloses a water-based protective coating for corrosion resistance of a stainless steel cover and a preparation method thereof, and belongs to the technical field of coating preparation, and is used for solving the technical problem that the corrosion resistance and ultraviolet aging resistance of the water-based protective coating of the stainless steel cover in the prior art need to be further improved; the silane end group protective resin emulsion, the ultraviolet absorption flexible prepolymer and the hindered amine light stabilizing nanosol are introduced into the coating system in cooperation, a continuous function chain is formed in terms of film structure construction, interface anchoring stability and structure retention in the aging process, the obtained water-based protective coating has high compactness and interface stability, and the protective coating formed after curing of the water-based protective coating can maintain the integrity of the film structure in the ultraviolet aging process.

Description

Technical Field

[0001] This invention relates to the field of coating preparation technology, specifically to a water-based protective coating for corrosion protection of stainless steel covers and its preparation method. Background Technology

[0002] Stainless steel covers are widely used in transportation equipment, infrastructure, and industrial installations. The service environment is often accompanied by multiple factors such as alternating humidity and heat, chloride corrosion, atmospheric pollutant deposition, and continuous ultraviolet radiation, which makes the surface prone to pitting corrosion, interfacial medium penetration, and structural relaxation caused by photoaging. In order to delay the transmission of the above media to the substrate and stabilize the interfacial environment, the industry generally adopts water-based protective coatings to construct barrier films. Traditional water-based systems are mostly based on internally dispersed resin emulsions, which form a continuous phase through the film formation process to provide basic shielding capabilities. They rely on cross-linking structures, particle size distribution control, and additive system optimization to improve density and interfacial bonding stability. At the same time, for the needs of long-term outdoor service, related technical routes often introduce ultraviolet absorbing components, light stabilizers, and inorganic nano-reinforcing materials to reduce the risk of structural degradation under photothermal cycling.

[0003] Currently, water-based protective coatings used in stainless steel covers generally rely on organic emulsions to form a barrier structure. However, the film layer formed after curing still suffers from localized unevenness, high porosity, and insufficient structural continuity at the microscopic level. This allows corrosive media to spread rapidly along defect areas, leading to pitting corrosion initiation and localized instability. Furthermore, due to the limited cross-linking network of water-based systems, the diffusion path inside the film layer is relatively short, and the penetration rate may still be too fast under long-term full immersion conditions. At the same time, some traditional systems cannot ensure surface uniformity during film formation, and tiny defects can easily become corrosion initiation points, thus affecting the overall corrosion resistance.

[0004] On the other hand, traditional water-based systems often exhibit phenomena such as surface structure susceptibility to light energy impact and accelerated aging process under outdoor ultraviolet radiation. The chain segment degradation, microcrack propagation, and surface powdering generated by the coating during photothermal cycling will further weaken the protective effect. In addition, traditional resins rely more on physical adsorption or limited chemical bonding when bonding with metal substrates, resulting in insufficient interfacial anchoring stability. Under humid heat or external force, adhesion is prone to decay. When the coating lacks flexibility and structural balance control, it is more likely to experience interfacial delamination or local damage caused by stress concentration, making it difficult to meet higher levels of protection requirements during long-term use.

[0005] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a water-based protective coating for corrosion protection of stainless steel covers and its preparation method, in order to solve the technical problem that the corrosion resistance and UV aging resistance of water-based protective coatings for stainless steel covers in the prior art need to be further improved.

[0007] The objective of this invention can be achieved through the following technical solution: A water-based protective coating for corrosion protection of stainless steel covers, comprising the following raw materials in parts by weight: 120-150 parts of silane-terminated protective resin emulsion, 20-30 parts of ultraviolet-absorbing flexible prepolymer, 10-20 parts of hindered amine light-stabilized nano-sol, 4-6 parts of dipropylene glycol butyl ether, 2-3 parts of tridecyl polyoxyethylene ether, 1-2 parts of sodium polyacrylate and 1 part of polydimethylsiloxane;

[0008] The preparation method of the silane-terminated protective resin emulsion is as follows: phosphate-modified resin and toluene are added to a reaction vessel, and methanol and 3-propyltrimethoxysilane 3-isocyanate are added under stirring. The reaction vessel is then heated to 50-60℃ and stirred for 2-4 hours. After the reaction vessel is cooled to 30-35℃, a neutralizing agent is added, and emulsification is carried out. After emulsification, the filtrate is collected by filtering with a 150-200 mesh stainless steel filter to obtain the silane-terminated protective resin emulsion.

[0009] The reaction principle for preparing silane-terminated protective resin emulsions is as follows:

[0010] In hydroxyl-containing phosphate ester modified resin systems, the isocyanate groups of 3-propyltrimethoxysilane can be nucleophilically attacked by hydroxyl groups on resin segments, forming an organosilane bond interface linked by a ureane structure. This allows silane groups to be covalently introduced into the resin backbone or side chain structure. Meanwhile, the trimethoxysilane moiety remains hydrolyzable in alcohol solvents, providing a structural basis for the partial hydrolysis and condensation of silane groups during subsequent emulsification. As a result, the resin molecules acquire a hybrid structure with silane end-group characteristics, providing a chemical basis for the formation of a stable emulsion dispersion phase.

[0011] Furthermore, in the preparation of the silane-terminated protective resin emulsion, the ratio of the phosphate-modified resin, toluene, methanol, propyltrimethoxysilane 3-isocyanate, and neutralizing agent is 5-6g:50-60mL:2-3mL:1-2mL:1mL, wherein the neutralizing agent is dimethylethanolamine. The emulsification operation is as follows: 1.2-1.5 times the volume of deionized water is added dropwise to the reaction vessel in 4-6 portions at a dropping rate of 8-10mL / min. During the dropping process, the stirring speed is maintained at 2000-2500rpm, and the reaction vessel is controlled at 25-35℃. The interval between each water addition is 3-5min. After the deionized water is added, stirring is continued for 20-30min, and then the stirring speed is reduced to 300-500rpm for 10-15min.

[0012] Furthermore, the phosphate-modified resin is prepared by the following method:

[0013] A1. Add bisphenol A diglycidyl ether and N,N-dimethylformamide to a reaction vessel and stir. After dissolving, add a compound dopamine solution and ethylene glycolamine. Heat the reaction vessel to 75-85℃ and stir for 3-5 hours. After the reaction is complete, cool naturally to obtain a catechol-modified epoxy amine resin solution.

[0014] A2. Add the catechol-modified epoxy amine resin solution and dichloromethane to the reaction vessel and stir. Add triethylamine under ice bath conditions. After mixing evenly, add phosphoryl chloride. After the addition is complete, heat the reaction solution to 25-35℃ and keep it at this temperature for 2-4 hours. After the reaction is complete, filter and collect the filtrate. Distill under reduced pressure until no liquid is collected to obtain the phosphate ester modified resin.

[0015] The reaction principle for preparing phosphate-modified resin solutions is as follows:

[0016] In an environment where amines and epoxy structures coexist, the epoxy groups of bisphenol A type epoxy compounds undergo ring-opening reactions due to the attack of nucleophilic sites in ethylene glycol amines and dopamine derivatives. This results in the formation of stable ether bonds and amide-related structures between the phenolic hydroxyl groups, primary amines, and epoxy units, thereby constructing an organic amination resin skeleton with catechol substitution characteristics. When phosphoryl chloride is further introduced, its active acyl chloride group can undergo esterification with the hydroxyl groups on the resin chain. Simultaneously, the generated hydrogen chloride is immediately captured by the organic base, thereby promoting the smooth formation of phosphate ester bonds in the organic phase. The nucleophilic substitution between the acyl chloride and hydroxyl groups leads to the incorporation of phosphoro-oxygen bonds into the resin backbone or side chain structure, causing the resin molecule to exhibit organophosphorus hybrid characteristics with POC bonds as the main linkage mode. Finally, a phosphate ester modified resin system with phosphate ester structural units is obtained.

[0017] Further, in step A1, the ratio of bisphenol A diglycidyl ether, N,N-dimethylformamide, complex dopamine solution and ethylene glycolamine is 7-8g:12-15mL:3-4mL:2-3g, wherein the complex dopamine solution is obtained by mixing dopamine hydrochloride, deionized water and 12wt% sodium hydroxide aqueous solution in a ratio of 8-12g:25mL:10mL;

[0018] Furthermore, in step A2, the ratio of the catechol-modified epoxy amine resin solution, dichloromethane, triethylamine, and phosphoryl chloride is 10-12 mL: 8-12 mL: 2-3 mL: 0.8-1.0 mL.

[0019] Furthermore, the preparation method of the ultraviolet-absorbing flexible prepolymer is as follows: polyethylene glycol diglycidyl ether and N,N-dimethylformamide are added to a reaction vessel. After mixing evenly, a calculated amount of modifier and triethylamine are added. The reaction vessel is then heated to 70-90°C and stirred for 3-5 hours. After distillation under reduced pressure until no liquid is collected, the ultraviolet-absorbing flexible prepolymer is obtained.

[0020] The reaction equation for preparing the ultraviolet-absorbing flexible prepolymer is as follows:

[0021]

[0022] In the formula: .

[0023] The reaction principle for preparing ultraviolet-absorbing flexible prepolymers is as follows:

[0024] Under weakly alkaline conditions, the carboxyl group of allyl alcohol preferentially undergoes ring-opening addition with the epoxy group in the polyethylene glycol diglycidyl ether molecule, gradually transforming the epoxy structure into ester and hydroxyl structures to form a prepolymer framework with flexible segments. Simultaneously, the phenolic hydroxyl group in ethyl 2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]maleate undergoes a nucleophilic ring-opening reaction with the active epoxy group, covalently embedding it into the gradually growing polymer network. The tertiary amine in the system mainly exhibits catalytic characteristics that promote ring-opening addition during the reaction, stabilizing the interconnection of chemical bonds among the multiple components in the solution, thereby obtaining a structurally continuous ultraviolet-absorbing flexible prepolymer.

[0025] Furthermore, in the preparation of the UV-absorbing flexible prepolymer, the ratio of polyethylene glycol diglycidyl ether, N,N-dimethylformamide, and triethylamine is 45-55g:120-150mL:2-3mL. The molar amount of hydroxyl groups in the added modifier is 0.55-0.60 times the molar amount of epoxy groups in the polyethylene glycol diglycidyl ether. The modifier is obtained by mixing allyl alcohol and ethyl 2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]maleate in a ratio of 5-6mL:4-6g.

[0026] Furthermore, the preparation method of the hindered amine photostable nanosol is as follows: anhydrous ethanol and deionized water are added to a reaction vessel and stirred. After adjusting the pH of the reaction system to 2-4 with acetic acid, a mixed solution is added, followed by the addition of 4-amino-2,2,6,6-tetramethylpiperidine. The mixture is stirred at room temperature for 6-8 hours. After the reaction is completed, the solid content is adjusted to 30 wt% to obtain the hindered amine photostable nanosol.

[0027] The reaction equation for preparing hindered amine photostable nanosols is as follows:

[0028]

[0029] The reaction principle for preparing hindered amine photostable nanosols is as follows:

[0030] In an acidic ethanol-water system, methyl orthosilicate and silane-containing organic precursors first undergo acid-catalyzed hydrolysis, gradually generating silanol structures, which then form a continuous siloxane framework network through condensation. The succinic anhydride structure introduced into the system can undergo ring-opening reactions with amine compounds, allowing the hindered amine components containing amino groups to covalently bind to the surface or structural units of the gradually growing siloxane polymers. As siloxane bonds accumulate in the sol system, the dispersed phase gradually forms nanoscale inorganic-organic hybrid particles with a certain degree of stability, thus constituting the final hindered amine photostable nanosol system.

[0031] Furthermore, in the preparation of hindered amine photostable nanosols, the ratio of anhydrous ethanol, deionized water, the mixed solution, and 4-amino-2,2,6,6-tetramethylpiperidine is 150-200 mL: 50-70 mL: 30-45 mL: 3-5 g. The mixed solution is obtained by mixing methyl orthosilicate and dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione in a ratio of 2-3 mL: 1 mL.

[0032] This invention also discloses a method for preparing a water-based protective coating for corrosion protection of stainless steel covers, comprising the following steps: adding a silane-terminated protective resin emulsion to a stirred tank, adding a UV-absorbing flexible prepolymer and a hindered amine photostable nanosol sequentially under stirring conditions, stirring until uniform, adding dipropylene glycol butyl ether, tridecyl polyoxyethylene ether, sodium polyacrylate and polydimethylsiloxane, continuing to stir until uniform, adjusting the solid content of the system to 38-42 wt%, stirring at 800-1200 rpm for 20-30 min, filtering through a 150-200 mesh stainless steel filter to collect the filtrate, and obtaining the water-based protective coating.

[0033] The present invention has the following beneficial effects:

[0034] 1. The silane-terminated protective resin emulsion prepared by this invention can form a dense and uniformly distributed silicon-oxygen network after curing, which enables the coating to maintain good continuity and stability in water-soluble media, thereby significantly slowing down the penetration rate of corrosive media into the metal substrate. This type of structure constructs a longer diffusion path inside the coating, reducing the overall penetration rate, so that the metal substrate can still maintain a low degree of corrosion in a full immersion environment. On this basis, the introduced ultraviolet-absorbing flexible prepolymer improves the film integrity of the system during the coating curing process, making the coating surface more uniform, thereby reducing the number of micro-defects that are easy to become corrosion initiation points. The addition of hindered amine photostabilized nanosol further improves the structural balance of the coating, so that the protective layer is not prone to local pitting corrosion due to small and loose areas at the interface during long-term immersion. In addition, the synergistic effect of multiple components makes the coating exhibit a low corrosion rate in the full immersion corrosion test, and the overall protective performance is significantly better than that of conventional water-based coatings that do not use this combination system.

[0035] 2. The UV-absorbing flexible prepolymer prepared by this invention can reduce the direct impact of high-energy UV radiation on the surface structure of the coating under light conditions, making the aging process more gradual and thus delaying the degradation trend of appearance and performance. On this basis, the hindered amine photostabilized nanosol has an inhibitory effect on the degradation factors caused by aging in the long-term light environment, so that the coating maintains higher structural stability in photothermal cycling. At the same time, the silicon-oxygen network formed by the silane-terminated protective resin emulsion can still maintain structural integrity under UV environment, so that the coating is not prone to brittleness or powdering, thus ensuring the continuity of overall performance. The three components complement each other under light conditions, so that the coating still maintains good appearance and stable performance after UV aging.

[0036] 3. The silane-terminated protective resin emulsion prepared by this invention can form a stable interfacial bond on the metal surface after curing, enabling the coating to achieve a high level in the initial adhesion test and maintain good stability under external force or humid heat conditions. The multi-point anchoring structure formed by the resin reduces the possibility of delamination due to uneven stress at the interface. At the same time, the ultraviolet-absorbing flexible prepolymer gives the coating appropriate flexibility, allowing the interface to remain synchronized during the deformation process caused by temperature changes, reducing the risk of local cracking caused by stress concentration. Furthermore, the presence of hindered amine photostabilized nanosol makes the overall structure of the coating more uniform, making the interface area less prone to adhesion attenuation due to minor defects. Finally, the coordination between multiple components ensures that the adhesion not only performs well in the initial test but also remains stable in subsequent test stages, with significantly better interface retention than traditional systems. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] In this application, the sodium polyacrylate used was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with item number 767418; the polydimethylsiloxane used was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with item number P708882; and the polyethylene glycol diglycidyl ether used was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with item number P790564.

[0039] Example 1

[0040] This embodiment provides a method for preparing a silane-terminated protective resin emulsion, comprising the following steps:

[0041] Step I: Preparation of catechol-modified epoxy amine resin solution

[0042] Weigh out 16.0 g of dopamine hydrochloride, 50.0 mL of deionized water and 20.0 mL of 12 wt% sodium hydroxide and mix them in water to obtain a composite dopamine solution;

[0043] Weigh out 70.0 g of bisphenol A diglycidyl ether and 120.0 mL of N,N-dimethylformamide and add them to the reaction vessel. Stir until dissolved, then add 30.0 mL of compound dopamine solution and 20.0 g of ethylene glycolamine. Heat the reaction vessel to 75 °C and stir for 3 h. After the reaction is complete, allow it to cool naturally to obtain catechol-modified epoxy amine resin solution.

[0044] Step II: Preparation of phosphate ester modified resin

[0045] Weigh 100.0 mL of catechol-modified epoxy amine resin solution and 80.0 mL of dichloromethane and add them to the reaction vessel. Stir and add 20.0 mL of triethylamine under ice bath conditions. After mixing evenly, add 8.0 mL of phosphoric acid chloride. After the addition is complete, heat the reaction solution to 25°C and keep it at this temperature for 2 hours. After the reaction is complete, filter and collect the filtrate. Distill under reduced pressure until no liquid is collected to obtain phosphate ester modified resin.

[0046] Step III: Preparation of silane-terminated protective resin emulsion

[0047] Weigh 50.0 g of phosphate-modified resin and 500.0 mL of toluene and add them to the reactor. Under stirring, add 20.0 mL of methanol and 10.0 mL of propyltrimethoxysilane 3-isocyanate. Then heat the reactor to 50 °C and stir for 2 h. After cooling the reactor to 30 °C, add 10.0 mL of dimethylethanolamine. Then add 1.2 times the volume of deionized water dropwise to the reactor in 4 portions at a dropping rate of 8 mL / min. During the dropping process, maintain a stirring rate of 2000 rpm and control the reactor temperature at 25 °C. Add water 3 min apart each time. After the deionized water is added, continue stirring for 20 min. Then reduce the stirring rate to 300 rpm and stir for 10 min. Filter the solution through a 150-mesh stainless steel filter and collect the filtrate to obtain a silane-terminated protective resin emulsion.

[0048] Example 2

[0049] This embodiment provides a method for preparing a silane-terminated protective resin emulsion, comprising the following steps:

[0050] Step I: Preparation of catechol-modified epoxy amine resin solution

[0051] Weigh out 24.0 g of dopamine hydrochloride, 50.0 mL of deionized water and 20.0 mL of 12 wt% sodium hydroxide and mix them to obtain a composite dopamine solution;

[0052] Weigh out 80.0g of bisphenol A diglycidyl ether and 150.0mL of N,N-dimethylformamide and add them to the reaction vessel. Stir until dissolved, then add 40.0mL of compound dopamine solution and 30.0g of ethylene glycolamine. Heat the reaction vessel to 85℃ and keep it at that temperature for 5 hours. After the reaction is complete, allow it to cool naturally to obtain catechol-modified epoxy amine resin solution.

[0053] Step II: Preparation of phosphate ester modified resin

[0054] Weigh 120.0 mL of catechol-modified epoxyamine resin solution and 120.0 mL of dichloromethane and add them to the reaction vessel. Stir and add 30.0 mL of triethylamine under ice bath conditions. After mixing evenly, add 10.0 mL of phosphoric acid chloride. After the addition is complete, heat the reaction solution to 35°C and keep it at this temperature for 4 hours. After the reaction is complete, filter and collect the filtrate. Distill under reduced pressure until no liquid is collected to obtain phosphate ester modified resin.

[0055] Step III: Preparation of silane-terminated protective resin emulsion

[0056] Weigh 60.0 g of phosphate-modified resin and 600.0 mL of toluene and add them to the reactor. Under stirring, add 30.0 mL of methanol and 20.0 mL of propyltrimethoxysilane 3-isocyanate. Then heat the reactor to 60 °C and stir for 4 h. After cooling the reactor to 35 °C, add 10.0 mL of dimethylethanolamine. Then add 1.5 times the volume of deionized water dropwise to the reactor in 6 portions at a dropping rate of 10 mL / min. During the dropping process, maintain a stirring rate of 2500 rpm and control the reactor temperature at 35 °C. Add water 5 min apart each time. After the deionized water is added, continue stirring for 30 min. Then reduce the stirring rate to 500 rpm and stir for 15 min. Filter the solution through a 200-mesh stainless steel filter and collect the filtrate to obtain a silane-terminated protective resin emulsion.

[0057] Example 3

[0058] This embodiment provides a method for preparing a silane-terminated protective resin emulsion, comprising the following steps:

[0059] Step I: Preparation of catechol-modified epoxy amine resin solution

[0060] Weigh out 20.0 g of dopamine hydrochloride, 50.0 mL of deionized water, and 20.0 mL of 12 wt% sodium hydroxide and mix them in water to obtain a composite dopamine solution;

[0061] Weigh out 75.0 g of bisphenol A diglycidyl ether and 135.0 mL of N,N-dimethylformamide and add them to the reaction vessel. Stir until dissolved, then add 35.0 mL of compound dopamine solution and 25.0 g of ethylene glycolamine. Heat the reaction vessel to 80 °C and keep it at that temperature for 4 hours. After the reaction is complete, allow it to cool naturally to obtain catechol-modified epoxy amine resin solution.

[0062] Step II: Preparation of phosphate ester modified resin

[0063] Weigh 120.0 mL of catechol-modified epoxy amine resin solution and 100.0 mL of dichloromethane and add them to the reaction vessel. Stir and add 25.0 mL of triethylamine under ice bath conditions. After mixing evenly, add 9.0 mL of phosphoric acid chloride. After the addition is complete, heat the reaction solution to 30°C and keep it at this temperature for 3 hours. After the reaction is complete, filter and collect the filtrate. Distill under reduced pressure until no liquid is collected to obtain phosphate ester modified resin.

[0064] Step III: Preparation of silane-terminated protective resin emulsion

[0065] Weigh out 55.0 g of phosphate-modified resin and 550.0 mL of toluene and add them to the reactor. Under stirring, add 25.0 mL of methanol and 15.0 mL of 3-propyltrimethoxysilane. Then heat the reactor to 55°C and stir for 3 hours. After cooling the reactor to 35°C, add 10.0 mL of dimethylethanolamine. Then add 1.5 times the volume of deionized water to the reactor in 5 drops at a rate of 9 mL / min. During the addition, maintain the stirring speed at 2400 rpm and control the reactor temperature at 30°C. Add water 4 min apart each time. After the deionized water is added, continue stirring for 25 min. Then reduce the stirring speed to 400 rpm and stir for 12 min. Filter the solution through a 180-mesh stainless steel filter and collect the filtrate to obtain the silane-terminated protective resin emulsion.

[0066] Example 4

[0067] This embodiment provides a method for preparing a water-based protective coating for corrosion protection of stainless steel covers, including the following steps:

[0068] Step 1: Preparation of UV-absorbing flexible prepolymer

[0069] Weigh out 10.0 mL of allyl alcohol and 8.0 g of ethyl 2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]maleate and mix them to obtain the modifier;

[0070] Weigh out 45.0g of polyethylene glycol diglycidyl ether and 120.0mL of N,N-dimethylformamide and add them to the reactor. After mixing evenly, add a modifier with a hydroxyl molar amount equal to 0.55 times the molar amount of epoxy groups in polyethylene glycol diglycidyl ether and 2.0mL of triethylamine. Then heat the reactor to 70℃, keep it at this temperature and stir for 3 hours. After that, reduce the pressure and distill until no liquid is collected to obtain the ultraviolet-absorbing flexible prepolymer.

[0071] Step 2: Preparation of hindered amine photostable nanosols

[0072] Weigh out 30.0 mL of methyl orthosilicate and 15.0 mL of dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione and mix them to obtain a mixture.

[0073] Weigh out 150.0 mL of anhydrous ethanol and 50.0 mL of deionized water and add them to the reaction vessel. Stir and adjust the pH of the reaction system to 2 with acetic acid. Then add 30.0 mL of the mixture and 3.0 g of 4-amino-2,2,6,6-tetramethylpiperidine. Stir at room temperature for 6 h. After the reaction is complete, adjust the solid content to 30 wt% to obtain hindered amine photostable nanosol.

[0074] Step 3: Preparation of water-based protective coating

[0075] Weigh 120 parts by weight of the silane-terminated protective resin emulsion prepared in Example 1 and add it to a stirred tank. Under stirring conditions, add 20 parts of UV-absorbing flexible prepolymer and 10 parts of hindered amine photostable nanosol in sequence. After stirring evenly, add 4 parts of dipropylene glycol butyl ether, 2 parts of tridecyl polyoxyethylene ether, 1 part of sodium polyacrylate and 1 part of polydimethylsiloxane. After stirring evenly, adjust the solid content of the system to 38 wt%, stir at 800 rpm for 20 min, filter through a 150-mesh stainless steel filter and collect the filtrate to obtain the water-based protective coating.

[0076] Example 5

[0077] This embodiment provides a method for preparing a water-based protective coating for corrosion protection of stainless steel covers, including the following steps:

[0078] Step 1: Preparation of UV-absorbing flexible prepolymer

[0079] Weigh out 12.0 mL of allyl alcohol and 12.0 g of ethyl 2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]maleate and mix them to obtain the modifier;

[0080] Weigh out 55.0 g of polyethylene glycol diglycidyl ether and 150.0 mL of N,N-dimethylformamide and add them to the reaction vessel. After mixing evenly, add a modifier with a hydroxyl molar amount equal to 0.60 times the molar amount of epoxy groups in polyethylene glycol diglycidyl ether and 3.0 mL of triethylamine. Then heat the reaction vessel to 90 °C, keep it at that temperature and stir for 5 h, and then distill it under reduced pressure until no liquid is collected to obtain the ultraviolet-absorbing flexible prepolymer.

[0081] Step 2: Preparation of hindered amine photostable nanosols

[0082] Weigh out 45.0 mL of methyl orthosilicate and 15.0 mL of dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione and mix them to obtain a mixture.

[0083] Weigh out 200.0 mL of anhydrous ethanol and 70.0 mL of deionized water and add them to the reaction vessel. Stir and adjust the pH of the reaction system to 4 with acetic acid. Then add 45.0 mL of the mixture and 5.0 g of 4-amino-2,2,6,6-tetramethylpiperidine. Stir at room temperature for 8 h. After the reaction is complete, adjust the solid content to 30 wt% to obtain hindered amine photostable nanosol.

[0084] Step 3: Preparation of water-based protective coating

[0085] Weigh 150 parts by weight of the silane-terminated protective resin emulsion prepared in Example 2 and add it to a stirred tank. Under stirring conditions, add 30 parts of UV-absorbing flexible prepolymer and 20 parts of hindered amine photostable nanosol in sequence. After stirring evenly, add 6 parts of dipropylene glycol butyl ether, 3 parts of tridecyl polyoxyethylene ether, 2 parts of sodium polyacrylate and 1 part of polydimethylsiloxane. After stirring evenly again, adjust the solid content of the system to 42wt%, stir at 1200rpm for 30min, filter through a 200-mesh stainless steel filter and collect the filtrate to obtain the water-based protective coating.

[0086] Example 6

[0087] This embodiment provides a method for preparing a water-based protective coating for corrosion protection of stainless steel covers, including the following steps:

[0088] Step 1: Preparation of UV-absorbing flexible prepolymer

[0089] Weigh out 11.0 mL of allyl alcohol and 10.0 g of ethyl 2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]maleate and mix them to obtain the modifier;

[0090] Weigh out 55.0g of polyethylene glycol diglycidyl ether and 135.0mL of N,N-dimethylformamide and add them to the reactor. After mixing evenly, add a modifier with a hydroxyl molar amount equal to 0.58 times the molar amount of epoxy groups in polyethylene glycol diglycidyl ether and 2.5mL of triethylamine. Then heat the reactor to 80℃, keep it at this temperature and stir for 4 hours. After that, reduce the pressure and distill until no liquid is collected to obtain the ultraviolet-absorbing flexible prepolymer.

[0091] Step 2: Preparation of hindered amine photostable nanosols

[0092] Weigh out 35.0 mL of methyl orthosilicate and 15.0 mL of dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione and mix them to obtain a mixture.

[0093] Weigh out 180.0 mL of anhydrous ethanol and 60.0 mL of deionized water and add them to the reaction vessel. Stir and adjust the pH of the reaction system to 3 with acetic acid. Then add 40.0 mL of the mixture, followed by 4.0 g of 4-amino-2,2,6,6-tetramethylpiperidine. Stir at room temperature for 7 h. After the reaction is complete, adjust the solid content to 30 wt% to obtain hindered amine photostable nanosol.

[0094] Step 3: Preparation of water-based protective coating

[0095] Weigh out 135 parts by weight of the silane-terminated protective resin emulsion prepared in Example 3 and add it to a stirred tank. Under stirring conditions, add 25 parts of UV-absorbing flexible prepolymer and 15 parts of hindered amine photostabilized nanosol in sequence. After stirring evenly, add 5 parts of dipropylene glycol butyl ether, 3 parts of tridecyl polyoxyethylene ether, 2 parts of sodium polyacrylate and 1 part of polydimethylsiloxane. After stirring evenly again, adjust the solid content of the system to 40 wt%, stir at 1000 rpm for 25 min, filter through a 180-mesh stainless steel filter and collect the filtrate to obtain the water-based protective coating.

[0096] Comparative Example 1

[0097] The difference between this comparative example and Example 6 is that the use of the ultraviolet-absorbing flexible prepolymer is omitted in step three.

[0098] Comparative Example 2

[0099] The difference between this comparative example and Example 6 is that the hindered amine photostable nanosol is omitted in step three.

[0100] Comparative Example 3

[0101] The difference between this comparative example and Example 6 is that the silane-terminated protective resin emulsion used in step 3 is prepared without the addition of 3-propyl isocyanatetrimethoxysilane in step III.

[0102] Performance testing:

[0103] The water-based protective coatings prepared in Examples 4-6 and Comparative Examples 1-3 were placed in a coating spraying machine and sprayed onto a clean stainless steel surface. The coating thickness was 200 μm. After spraying, the coating was left to stand at room temperature for 4 hours. After standing, the coating was placed in a drying oven at 60°C for 40 minutes to obtain a protective coating.

[0104] The corrosion resistance of the protective coatings obtained after curing the water-based protective coatings prepared in Examples 4-6 and Comparative Examples 1-3 was tested in accordance with the standard JB / T 6073-1992 "Laboratory Total Immersion Corrosion Test of Metal Coatings".

[0105] The adhesion grades of the protective coatings obtained after curing the water-based protective coatings prepared in Examples 4-6 and Comparative Examples 1-3 were tested in accordance with the standard GB / T 31586.2-2015 "Evaluation and Acceptance Criteria of Adhesion / Cohesion (Breaking Strength) of Protective Coating Systems for Corrosion Protection of Steel Structures Part 2: Cross-cut Test and Cross-cut Test".

[0106] According to the standard GB / T 23987-2009 "Artificial weathering exposure of paint and varnish coatings, exposure to fluorescent ultraviolet light and water", the protective coatings obtained after curing of the water-based protective coatings prepared in Examples 4-6 and Comparative Examples 1-3 were subjected to ultraviolet aging. The corrosion resistance and adhesion grade of the coatings were tested twice, and the performance data of the coatings after aging were obtained. The specific data are shown in Table 1.

[0107] Table 1 - Performance Test Data for Each Sample

[0108] Data Analysis:

[0109] Comparative analysis of the data in Table 1 reveals that the water-based protective coating prepared in this invention exhibits a corrosion rate of 1.8% and an adhesion grade of 0 after curing. Furthermore, the protective coating after UV aging has a corrosion rate of 3.2% and an adhesion grade of 1. All these data are superior to the comparative example, indicating that:

[0110] In Comparative Example 1, the lack of introduction of a UV-absorbing flexible prepolymer in step three resulted in the coating losing its role in regulating local fluidity and chain segment synergy within the system during the film-forming stage. This led to an uneven phase evolution during the film-forming process. Due to the lack of buffer regulation on resin network shrinkage behavior and interfacial stress, the coating was more prone to forming micropores, local density fluctuations, and discontinuous areas on the surface after curing. These structural weaknesses became the preferred points of failure under immersion or mechanical disturbance conditions, allowing corrosive media to penetrate more quickly along weak paths. The interfacial bonding area was also more prone to stress concentration and local delamination. As a result, the coating exhibited an increased corrosion rate and decreased adhesion interface stability in the comprehensive performance test, reflecting the importance of this component in the system of the example for the equalization of the film structure.

[0111] In Comparative Example 2, the hindered amine light-stabilized nanosol was not added in step three, resulting in a lack of internal regulation mechanism for aging-induced structural disturbances in the coating system during its service life. Due to the absence of this regulation mechanism, the coating is more prone to accumulating micro-degradation points under photothermal cycling and environmental fluctuations, leading to a decrease in the overall uniformity of the polymer network and an imbalance in the activity of local chain segments in the film layer. As the structural weakening gradually amplifies in local areas, the continuity of the coating and the density of the interface region are weakened, allowing subsequent corrosive media to penetrate more quickly along the degradation path. The adhesion interface also shows a tendency to desorb due to the propagation of microcracks. Ultimately, in the comprehensive performance test after aging, the coating showed significant deterioration. The root cause lies in the lack of a network stability regulation mechanism, which undermines the system's long-term structural maintenance ability.

[0112] In Comparative Example 3, 3-propyltrimethoxysilane was not added in step III, which prevented the resin emulsion from forming silane end-group structures. As a result, the silicon-oxygen crosslinking network present in the examples could not be established during the coating curing process. The lack of this network weakened the spatial grid support capacity of the film, significantly reduced the film density and structural coherence, and simultaneously reduced the diffusion resistance of water vapor and corrosive media. At the same time, since the interface did not form multi-point anchoring connections, the bonding mode of the resin to the metal substrate tended to be simple, and the interface was more susceptible to damage under humid heat and mechanical disturbance. As the accumulated structural loosening and microcracks increased during the service life, the coating showed a significant decrease in both immersion corrosion test and adhesion test. This phenomenon verifies from the opposite perspective that the silane end groups play a structural framework and interface stability support role in the system of the examples.

[0113] In conclusion, the overall performance of the coating system of this invention stems from the synergistic achievement of three action pathways: film structure construction, interface synergistic regulation, and long-term stability maintenance. Comparative Example 1 lacked regulatory factors for chain segment movement and interface shrinkage behavior during the film formation stage, leading to an imbalance in the film densification process and a decrease in initial structural uniformity. Comparative Example 2 lacked an intrinsic suppression mechanism for photothermal-induced structural disturbances during long-term service, allowing the aging accumulation effect to be amplified in the film, resulting in a significant decrease in structural stability after aging. Comparative Example 3 failed to form a silicon-oxygen structural framework due to the resin system, resulting in limited spatial network support and interface anchoring modes, causing a decrease in the overall structural integrity of the coating. The declining trends of these three aspects collectively indicate that each component in the system of the examples plays a role in structure construction, film formation regulation, and stability maintenance, respectively. The absence of any one of these links will disrupt the continuous synergistic chain of the system, thereby significantly weakening the overall performance.

[0114] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A water-based protective coating for corrosion protection of stainless steel covers, characterized in that, The raw materials consist of the following parts by weight: 120-150 parts silane-terminated protective resin emulsion, 20-30 parts UV-absorbing flexible prepolymer, 10-20 parts hindered amine light-stabilized nanosol, 4-6 parts dipropylene glycol butyl ether, 2-3 parts tridecyl polyoxyethylene ether, 1-2 parts sodium polyacrylate and 1 part polydimethylsiloxane; The preparation method of the silane-terminated protective resin emulsion is as follows: phosphate-modified resin and toluene are added to a reaction vessel, and methanol and 3-propyltrimethoxysilane 3-isocyanate are added under stirring. The reaction vessel is then heated to 50-60℃ and stirred for 2-4 hours. After the reaction vessel is cooled to 30-35℃, a neutralizing agent is added, and emulsification is carried out. After emulsification, the filtrate is collected by filtering with a 150-200 mesh stainless steel filter to obtain the silane-terminated protective resin emulsion.

2. The water-based protective coating for corrosion protection of stainless steel covers according to claim 1, characterized in that, In the preparation of the silane-terminated protective resin emulsion, the ratio of the phosphate-modified resin, toluene, methanol, propyltrimethoxysilane 3-isocyanate, and neutralizing agent is 5-6g:50-60mL:2-3mL:1-2mL:1mL, wherein the neutralizing agent is dimethylethanolamine. The emulsification operation is as follows: 1.2-1.5 times the volume of deionized water is added dropwise to the reaction vessel in 4-6 portions at a dropping rate of 8-10mL / min. During the dropping process, the stirring speed is maintained at 2000-2500rpm, and the reaction vessel temperature is controlled at 25-35℃. The interval between each water addition is 3-5min. After the deionized water is added, stirring is continued for 20-30min, and then the stirring speed is reduced to 300-500rpm for 10-15min.

3. The water-based protective coating for corrosion protection of stainless steel covers according to claim 1, characterized in that, The phosphate-modified resin is prepared by the following method: A1. Add bisphenol A diglycidyl ether and N,N-dimethylformamide to a reaction vessel and stir. After dissolving, add a compound dopamine solution and ethylene glycolamine. Heat the reaction vessel to 75-85℃ and stir for 3-5 hours. After the reaction is complete, cool naturally to obtain a catechol-modified epoxy amine resin solution. A2. Add the catechol-modified epoxy amine resin solution and dichloromethane to the reaction vessel and stir. Add triethylamine under ice bath conditions. After mixing evenly, add phosphoryl chloride. After the addition is complete, heat the reaction solution to 25-35℃ and keep it at this temperature for 2-4 hours. After the reaction is complete, filter and collect the filtrate. Distill under reduced pressure until no liquid is collected to obtain the phosphate ester modified resin.

4. The water-based protective coating for corrosion protection of stainless steel covers according to claim 3, characterized in that, In step A1, the ratio of bisphenol A diglycidyl ether, N,N-dimethylformamide, complex dopamine solution, and ethylene glycolamine is 7-8g:12-15mL:3-4mL:2-3g, wherein the complex dopamine solution is obtained by mixing dopamine hydrochloride, deionized water, and 12wt% sodium hydroxide aqueous solution in a ratio of 8-12g:25mL:10mL; in step A2, the ratio of catechol-modified epoxy amine resin solution, dichloromethane, triethylamine, and phosphoryl chloride is 10-12mL:8-12mL:2-3mL:0.8-1.0mL.

5. The water-based protective coating for corrosion protection of stainless steel covers according to claim 1, characterized in that, The preparation method of the ultraviolet-absorbing flexible prepolymer is as follows: polyethylene glycol diglycidyl ether and N,N-dimethylformamide are added to a reaction vessel. After the mixture is uniform, a calculated amount of modifier and triethylamine are added. The reaction vessel is then heated to 70-90°C and stirred for 3-5 hours. After the mixture is depressurized and distilled until no liquid is collected, the ultraviolet-absorbing flexible prepolymer is obtained.

6. The water-based protective coating for corrosion protection of stainless steel covers according to claim 5, characterized in that, In the preparation of the UV-absorbing flexible prepolymer, the ratio of polyethylene glycol diglycidyl ether, N,N-dimethylformamide, and triethylamine is 45-55g:120-150mL:2-3mL. The molar amount of hydroxyl groups in the added modifier is 0.55-0.60 times the molar amount of epoxy groups in polyethylene glycol diglycidyl ether. The modifier is obtained by mixing allyl alcohol and ethyl 2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]maleate in a ratio of 5-6mL:4-6g.

7. The water-based protective coating for corrosion protection of stainless steel covers according to claim 1, characterized in that, The hindered amine photostable nanosol is prepared by adding anhydrous ethanol and deionized water into a reaction vessel and stirring. After adjusting the pH of the reaction system to 2-4 with acetic acid, a mixed solution is added, followed by the addition of 4-amino-2,2,6,6-tetramethylpiperidine. The mixture is stirred at room temperature for 6-8 hours. After the reaction is completed, the solid content is adjusted to 30 wt% to obtain the hindered amine photostable nanosol.

8. The water-based protective coating for corrosion protection of stainless steel covers according to claim 7, characterized in that, In the preparation of hindered amine photostable nanosols, the ratio of anhydrous ethanol, deionized water, mixed solution and 4-amino-2,2,6,6-tetramethylpiperidine is 150-200 mL: 50-70 mL: 30-45 mL: 3-5 g. The mixed solution is obtained by mixing methyl orthosilicate and dihydro-3-[3-(triethoxysilyl)propyl]furan-2,5-dione in a ratio of 2-3 mL: 1 mL.

9. The method for preparing the water-based protective coating for corrosion protection of stainless steel covers as described in any one of claims 1-8, characterized in that, Includes the following steps: The silane-terminated protective resin emulsion was added to a stirred tank. Under stirring conditions, the UV-absorbing flexible prepolymer and the hindered amine photostable nanosol were added sequentially. After stirring evenly, dipropylene glycol butyl ether, tridecyl polyoxyethylene ether, sodium polyacrylate and polydimethylsiloxane were added. After stirring evenly again, the solid content of the system was adjusted to 38-42 wt%. The mixture was stirred at 800-1200 rpm for 20-30 min. The filtrate was collected by filtering through a 150-200 mesh stainless steel filter to obtain the water-based protective coating.

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