A protective coating and a method for its preparation

Abstract

The application discloses a protective coating and a preparation method thereof. The coating comprises modified organic silicone oil, blocked polyurethane prepolymer, phosphate-modified acrylic resin, polyether-modified polysiloxane wetting agent, organic tin catalyst and other components, and an interpenetrating network structure is formed through organic-inorganic hybridization. The coating can be directly cured into a film on the surface of a non-conductive precoating layer, and a secondary protective layer is formed through chemical cross-linking with a hydrophilic precoating layer or an epoxy precoating layer, thereby breaking through the dependence of electrophoresis and anodic oxidation on the conductivity of a base material. After the coating is cured through baking at 140-160 DEG C for 20-30 min, the neutral salt spray resistance is greater than or equal to 1500 h, the bending performance reaches 0T, the corrosion expansion of the cutting edge of a radiator fin and the aluminum-copper multi-metal interface can be effectively blocked, and the coating is suitable for the secondary protection of precoating substrates such as a hydrophilic foil and an epoxy foil.

Description

Technical Field

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

[0002] Currently, radiator fins widely use pre-coated foil materials such as hydrophilic foil or epoxy foil to improve drainage or provide basic corrosion resistance. However, these pre-coatings have significant limitations in practical applications: on the one hand, the protective capability of hydrophilic foil is limited, with neutral salt spray performance typically below 500 hours, making it difficult to meet the requirements of highly corrosive environments such as marine environments (C5 grade); on the other hand, the cut edges, weld points, and multi-metal connection interfaces (such as aluminum fins-copper tubes) after molding lack coating protection, resulting in edge corrosion after about one year of outdoor operation, which spreads along the interior of the fins, leading to functional layer detachment or gap formation. Even more challenging is that traditional electrophoretic coating or anodizing relies on the conductivity of the substrate and cannot form a film on the surface of non-conductive coatings such as hydrophilic foil and epoxy foil; while existing paint systems are difficult to bond well with the original hydrophilic layer (high surface energy) or epoxy layer and fluorocarbon paint (low surface energy), making the interface a weak point for corrosion. Therefore, there is an urgent need for a protective coating that can form a uniform film on a non-conductive surface and is compatible with the original functional layer, so as to achieve corrosion protection of the entire radiator without any dead angles.

[0003] Chinese invention patent application CN106519966A discloses a protective paint for power equipment, comprising 30-40 parts of silicone glass resin, 15-20 parts of polyurethane resin, 15-30 parts of bisphenol A epoxy resin, 10-20 parts of thermosetting phenolic resin, 12-15 parts of ceramic microparticles, 2-3 parts of fumed silica, and 1-2 parts of polyamide wax. This protective paint, through the compounding of various resins, achieves properties such as wear resistance, temperature resistance, weather resistance, and corrosion resistance. However, this technical solution mainly targets the direct coating of metal substrates for power equipment and does not address the issue of secondary film formation on non-conductive surfaces with existing hydrophilic or epoxy coatings. Furthermore, its component design does not consider chemical compatibility with existing hydrophilic / hydrophobic functional layers. If directly coated onto a hydrophilic foil surface, it can easily damage the hydrophilic properties or lead to insufficient interlayer adhesion, failing to solve the problems of edge corrosion and multi-metal interface protection.

[0004] Chinese invention patent application CN116200094B discloses a high-barrier nano-coating, which uses an interpenetrating network formed by crosslinking polymer A (formed from epichlorohydrin and oligomeric silsesquioxane) with modified nano-silica and polyurethane prepolymer, combined with fluorinated emulsion and phenolic resin, to achieve low oxygen permeability and acid and sulfur resistance. However, it also does not optimize for the secondary adhesion of the pre-coated surface, and its preparation process is complex, requiring components to be packaged separately, making it unsuitable for continuous coating of radiator coils and subsequent cutting and stamping processes. In summary, existing technologies have failed to provide a protective coating that can be directly cured on a non-conductive pre-coated surface, provides synergistic protection with the original functional layer, and blocks the propagation of edge and interface corrosion. This invention aims to solve the above problems. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of existing pre-coated foil materials (such as hydrophilic foil and epoxy foil) such as edge corrosion, multi-metal interface corrosion and difficulty in secondary film formation on non-conductive surfaces, and to provide a protective coating and its preparation method that can be directly cured into a film on non-conductive pre-coated surfaces, form chemical cross-links with the original functional layers, and achieve overall protection without dead angles.

[0006] To address the aforementioned challenges, this invention provides a protective coating prepared from the following raw materials in parts by weight: 50-90 parts organic solvent, 18-22 parts modified silicone oil, 22-28 parts blocked polyurethane prepolymer, 12-18 parts bisphenol A epoxy resin, 6-12 parts thermally reactive phenolic resin, 3-6 parts phosphate ester modified acrylic resin, 0.5-1.0 parts polyether modified polysiloxane wetting agent, 3-8 parts modified nano-silica, 2-5 parts silane coupling agent, and 0.1-0.3 parts organotin catalyst. Among them, the modified organosilicon oil is obtained by compounding amino-modified organosilicon oil and epoxy-modified organosilicon oil in a mass ratio of 1-3:1, the modified nano-silica is epoxy-modified nano-silica, and the silane coupling agent contains amino functional groups and / or epoxy functional groups. The protective coating forms an interpenetrating network structure through organic-inorganic hybridization, and is directly cured into a film on the surface of the non-conductive pre-coated layer, forming a chemically cross-linked secondary protective layer with the surface of the non-conductive substrate with a hydrophilic coating or epoxy pre-coated layer.

[0007] The above technical solution introduces amino-modified and epoxy-modified silicone oils, blocked polyurethane prepolymers, and epoxy / phenolic resin systems, combined with epoxy-modified nano-silica and amino / epoxy-containing silane coupling agents, to form an organic-inorganic hybrid interpenetrating network rich in active functional groups. This network can achieve good wetting and spreading on the surface of the non-conductive pre-coating, and can also chemically bond with hydrophilic groups (such as hydroxyl and carboxyl groups) or epoxy groups on the surface of the pre-coating, thereby significantly improving interlayer adhesion, effectively blocking the penetration of corrosive media at cut edges and interfaces, and solving the problem that existing technologies cannot form secondary films on non-conductive pre-coatings and that interfaces are prone to becoming weak corrosion zones.

[0008] Preferably, the organic solvent is prepared by compounding butyl acetate, propylene glycol methyl ether acetate, propylene glycol methyl ether and xylene in a mass ratio of (35-45):(30-40):(10-20):(5-10).

[0009] This compounded organic solvent system exhibits gradient solubility for silicone oil, polyurethane prepolymer, epoxy resin, phenolic resin, and acrylic resin. Utilizing the differences in solubility of each solvent for different types of resins, it ensures that the resin components are fully miscible during the premixing stage, forming a thermodynamically stable homogeneous system and avoiding microscopic defects in the coating caused by phase separation. Simultaneously, the different evaporation rates of butyl acetate, propylene glycol methyl ether acetate, propylene glycol methyl ether, and xylene in this compounded organic solvent system create a reasonable evaporation gradient. This allows the solvent to escape in an orderly manner during the curing process, preventing orange peel, pinholes, or interlayer blistering caused by sudden boiling or solvent residue. This ensures the leveling and film integrity of the coating on the non-conductive pre-coated surface. In other words, this compounded organic solvent system has a moderate evaporation rate and solubility, ensuring that each resin component is fully dissolved and that the coating exhibits good leveling during application, avoiding orange peel or pinholes caused by excessively rapid solvent evaporation, and also avoiding sagging caused by excessively slow evaporation.

[0010] Preferably, the silane coupling agent is obtained by compounding γ-aminopropyltriethoxysilane (KH-550) and γ-glycidoxypropyltrimethoxysilane (KH-560) in a mass ratio of 1:0.8 to 1:1.2.

[0011] The combined use of KH-550 (containing amino groups) and KH-560 (containing epoxy groups) can act as a "bridge" with the epoxy groups and hydroxyl groups on the surface of the pre-coated layer, as well as the epoxy resin and modified silicone oil inside the coating, during the coating curing process. This forms a denser interfacial chemical bond network, further enhancing the interfacial bonding strength. The mass ratio range of 1:0.8 to 1:1.2 ensures that the stoichiometry of the two reactive functional groups, amino and epoxy, at the interface is close to equivalence, avoiding uneven crosslinking density, interfacial stress concentration, or saturation of reaction sites caused by an excess of a single functional group. This significantly improves the chemical bond strength between the secondary protective layer and the pre-coated layer, solving the problem of insufficient adhesion between traditional paint systems and hydrophilic / epoxy layers.

[0012] Preferably, the modified nano-silica has a particle size of 10-50 nm. Using modified nano-silica within this particle size range allows for two advantages: firstly, the small size and surface effects of nanoparticles effectively fill the micropores within the coating, increasing its density and hardness without significantly increasing viscosity; secondly, epoxy-modified nano-silica can participate in the resin cross-linking reaction, forming an organic-inorganic interpenetrating network, thus enhancing the coating's reinforcement and toughening effects while improving its density and barrier properties, effectively blocking the penetration pathways of corrosive media. If the particle size is too large, it is prone to sedimentation and weakens the reinforcing effect; if it is too small, dispersion becomes difficult and costs increase.

[0013] Preferably, the bisphenol A type epoxy resin is selected from at least one of E-44 or E-51.

[0014] E-44 and E-51 epoxy resins have suitable epoxy values ​​and viscosities, and can form highly cross-linked dense networks with blocked polyurethane prepolymers and thermally reactive phenolic resins under heating conditions, providing excellent adhesion and chemical resistance.

[0015] Preferably, the organotin catalyst is selected from at least one of dibutyltin dilaurate or stannous octoate.

[0016] Dibutyltin dilaurate or stannous octoate exhibits highly efficient and selective catalytic activity for the condensation reaction of silanol groups (Si-OH) and the deblocking reaction of blocked isocyanates. It can precisely control the crosslinking reaction rate within a curing temperature window of 140-160℃, avoiding coating embrittlement caused by excessive local crosslinking or a decrease in media resistance caused by insufficient crosslinking, and ensuring that the coating's resistance to neutral salt spray reaches ≥1500 h.

[0017] A method for preparing a protective coating, used in the aforementioned protective coating, comprising the following steps: S1. Resin premixing: Under stirring at 400-600 rpm, add modified silicone oil, blocked polyurethane prepolymer, bisphenol A epoxy resin and thermally reactive phenolic resin to an organic solvent, heat to 50-60℃ and stir until homogeneous to obtain a resin mixture. S2. Introduction of functional resin: After the resin mixture cools down to below 30°C, add phosphate ester modified acrylic resin and polyether modified polysiloxane wetting agent, and continue stirring for 10-20 minutes. S3, Nano-dispersion: Add modified nano-silica, disperse at high speed of 3000-5000 rpm for 10-20 min, and grind until the fineness of the system is ≤10μm; S4. Interface modification: Add silane coupling agent and stir at 700-900 rpm for 15-25 min; S5. Catalytic curing: Add catalyst and stir evenly at 300-500 rpm to obtain the protective coating.

[0018] The above preparation method achieves the orderly mixing of different reactive components through stepwise feeding and temperature control: first, the main resin is dissolved at 50-60℃ to ensure complete miscibility; then, the temperature is lowered to below 30℃ before adding a phosphate-modified acrylic resin with a high acid value and a wetting agent to avoid side reactions at high temperatures; high-speed dispersion and grinding ensure that the nano-silica is fully deagglomerated; finally, a silane coupling agent and a catalyst are added to prevent premature contact with moisture or active groups, which could lead to failure. This process is simple, easy to industrialize, and the resulting coating has good storage stability, making it suitable for continuous roll coating.

[0019] Preferably, the heating and stirring process in step S1 is accompanied by inert gas protection to prevent the resin from oxidizing and discoloring at high temperatures.

[0020] Inert gas (such as nitrogen) protection can effectively inhibit the oxidation reaction of phenolic resin, epoxy resin and modified silicone oil under heating conditions, avoid yellowing of coating or decrease in thermal stability, and thus ensure the appearance stability and protective performance of coating under long-term high-temperature service environment.

[0021] Preferably, in step S3, the grinding is carried out using a three-roll mill or a horizontal sand mill, and the particle size of the zirconium beads in the grinding medium is controlled to be 0.3-0.5 mm to ensure the deagglomeration effect of the nano-silica.

[0022] Using zirconium beads within this particle size range, high shear forces can achieve thorough dispersion and deagglomeration of nano-silica while avoiding damage to the epoxy groups on the nanoparticle surface. This prevents agglomerates from becoming corrosion initiation points, thereby improving the uniformity and long-term corrosion resistance of the coating, making it particularly suitable for the high protection requirements of C5-level marine atmospheric environments. If the zirconium beads are too large, the excessive shear force may damage the particle surface modification layer; if the zirconium beads are too small, the dispersion efficiency is low, making it difficult to achieve the required fineness.

[0023] Preferably, step S5 further includes adjusting the viscosity of the system so that the viscosity of the coating at 25°C is 15-25 s in the Forecast-4 cup, to suit spraying and curtain coating processes. Controlling the viscosity at 15-25 s in the Forecast-4 cup ensures good atomization and prevents clogging of the spray gun during spraying, while also avoiding sagging or excessively thin coatings during curtain coating. This results in a uniform coating thickness on complex structural surfaces such as radiator fins, thus ensuring corrosion resistance without compromising heat dissipation efficiency.

[0024] A radiator protection structure, comprising: The substrate has a pre-coated surface with a hydrophilic coating or an epoxy coating to form a pre-coating. The aforementioned protective coating is cured and formed on the surface of the substrate, and the coating thickness is 1-35 μm; In this process, the protective coating forms a chemical bond with the pre-coating.

[0025] Preferably, the substrate is a heat sink fin or copper pipe, the protective coating is cured by baking at 140-160℃ for 20-30 minutes, and the neutral salt spray resistance is ≥1500h, and the bending performance is 0T.

[0026] The beneficial effects are: 1. Overcoming the limitations of film formation on non-conductive surfaces: No conductive substrate is required. It can be directly wetted, spread and cured on pre-coated surfaces such as hydrophilic foil and epoxy foil, solving the problem that electrophoresis and anodizing cannot be applied.

[0027] 2. Strong interfacial chemical bonding: Through the reaction of amino / epoxy active groups with the hydroxyl and epoxy groups on the pre-coated surface, a strong chemical cross-link is formed, resulting in excellent interlayer adhesion and no corrosion propagation at the cut edges and interfaces.

[0028] 3. Excellent overall corrosion resistance: Neutral salt spray test ≥1500h, and bending performance reaches 0T (no cracks), meeting the requirements of radiator fin stamping and bending processing.

[0029] 4. Good process compatibility: The viscosity of the coating is adjustable, adapting to various coating methods such as spraying, curtain coating, and dip coating, and is suitable for existing coil coating production lines. Attached Figure Description

[0030] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 Comparative images of the surfaces of hydrophilic aluminum foil substrates coated with and uncoated with the coating of Example 2 of the present invention, after undergoing a 1500-hour neutral salt spray test; Figure 2 Comparative images of epoxy pre-coated aluminum foil substrates coated with and uncoated with the coating of Example 2 of the present invention, after 1500h of neutral salt spray testing; Figure 3 The images show a comparison of the surfaces of epoxy pre-coated aluminum foil substrates after the cut edges were coated with and uncoated with the coating of Example 2 of this invention, and after a 1500-hour neutral salt spray test. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention.

[0032] The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. All other embodiments obtained by those skilled in the art based on the specific embodiments of the invention without inventive effort are within the protection scope of the invention. The technical solutions of the various embodiments can be combined with each other, but only on the basis that those skilled in the art can implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope claimed by the invention.

[0033] In the embodiments and comparative examples of this invention, the "parts" used for all components refer to parts by mass, reflecting only the relative mass ratio of each raw material. Unless otherwise specified, all raw materials used are commercially available products familiar to those skilled in the art and can be used directly without additional pretreatment. In the embodiments of this invention, unless specifically indicated, the technical means used are all conventional means familiar to those skilled in the art. Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0034] It is worth noting that the Coat-4 cup is a general-purpose viscosity measuring tool designed by the domestic coatings industry according to the national standard GB / T 1723-93. It characterizes conditional viscosity by measuring the time (in seconds) it takes for 100ml of paint to flow out of a standard orifice. Coat-4 cup measurements must be performed in a standard constant temperature environment of 25±1℃. Before measurement, ensure the nozzle is clean and the viscosity cup is level. Two repeated measurements should have a deviation of less than 3% of the average value for the result to meet accuracy requirements. A Coat-4 cup viscosity of 15-25 seconds meets the flowability requirements of spray painting, preventing the paint from being too thick and clogging the spray gun, or too thin and causing sagging, ensuring a uniform coating.

[0035] Raw material source: Propylene glycol methyl ether acetate (PMA), CAS No. 108-65-6, industrial grade, purity ≥99%, provided by Baichuan Chemical Co., Ltd. Propylene glycol methyl ether (PM), CAS No. 107-98-2, industrial grade, purity ≥99%, provided by Dena Tianyin (Jiangsu) Chemical Co., Ltd. Modified silicone oil, brand: Shin-Etsu Chemical, model: X-22-9409 (amino modified silicone oil) and X-22-163 (epoxy modified silicone oil) are used in combination. Both models of modified silicone oil are supplied by Shin-Etsu Chemical Industry Co., Ltd. Closed-cell polyurethane prepolymer, brand: Covestro (formerly Bayer), model: Desmocap® 14 CNB, provided by Covestro Polymers (China) Co., Ltd. Bisphenol A type epoxy resin, all branded as Phoenix, models E-44 (viscosity 10000-16000 m·Pas) and E-51 (viscosity 10000-18000 m·Pas), were provided by Henan Shuizhihuan Industrial Co., Ltd. Thermo-reactive phenolic resin, brand: Guangzhou Liben, model: HY-203 (octylphenol thermoplastic resin, softening point 85-105℃), provided by Guangzhou Liben Chemical Co., Ltd. Phosphate ester modified acrylic resin, brand: Shanghai Juncai, model: phosphate ester modified acrylic resin, provided by Shanghai Juncai Materials Technology Co., Ltd. Polyether-modified polysiloxane wetting agent, brand: BYK, model: BYK-346 (52% active ingredient, solvent: dipropylene glycol monomethyl ether), provided by BYK. Epoxy-modified nano-silica, particle size 10-30 nm, brand: Hubei Huifu, provided by Hubei Huifu Nanomaterials Co., Ltd. All other raw and auxiliary materials are commercially available.

[0036] Example 1 This application provides a method for preparing a protective coating, comprising the following steps: S1. Solvent preparation: Mix butyl acetate, propylene glycol methyl ether acetate, propylene glycol methyl ether and xylene in a mass ratio of 35:30:10:5 to obtain an organic solvent.

[0037] S2. Resin premixing: Nitrogen protective gas is introduced into the reaction vessel and the stirring device is turned on, maintaining a stirring speed of 400 rpm. According to the mass parts, 50 parts of the above organic solvent, 18 parts of modified organosilicon oil (obtained by compounding amino-modified organosilicon oil and epoxy-modified organosilicon oil in a mass ratio of 1:1), 22 parts of blocked polyurethane prepolymer, 12 parts of bisphenol A type epoxy resin E-44 and 6 parts of thermally reactive phenolic resin are added to the reaction vessel. The temperature is raised to 50°C and stirred until homogeneous to obtain a resin mixture.

[0038] S3. Introduction of functional resin: After the above resin mixture cools down to below 30°C, add 3 parts of phosphate ester modified acrylic resin and 0.5 parts of polyether modified polysiloxane wetting agent, and continue stirring for 10 minutes.

[0039] S4. Nano-dispersion: Add 3 parts of epoxy-modified nano-silica with a particle size of 10-50 nm, disperse at high speed of 3000 rpm for 10 min, and grind with a three-roll mill until the fineness of the system is ≤10 μm. The zirconium beads of the grinding medium have a particle size of 0.3 mm.

[0040] S5. Interface modification: Add 2 parts of silane coupling agent (KH-550 to KH-560 mass ratio of 1:0.8) and stir at 700 rpm for 15 min.

[0041] S6. Catalytic curing: Add 0.1 parts of dibutyltin dilaurate and stir evenly at 300 rpm to obtain the protective coating; adjust the viscosity of the system with the remaining organic solvent so that the viscosity of the protective coating at 25°C is 15s in the Forecast cup 4.

[0042] Example 2 This application provides a method for preparing a protective coating, comprising the following steps: S1. Solvent preparation: The organic solvent is prepared by mixing butyl acetate, propylene glycol methyl ether acetate, propylene glycol methyl ether and xylene in a mass ratio of 40:35:15:7.5.

[0043] S2. Resin premixing: Nitrogen protective gas is introduced into the reaction vessel and the stirring device is turned on, maintaining a stirring speed of 500 rpm. According to the mass parts, 70 parts of the above organic solvent, 20 parts of modified organosilicon oil (obtained by compounding amino-modified organosilicon oil and epoxy-modified organosilicon oil in a mass ratio of 2:1), 25 parts of blocked polyurethane prepolymer, 15 parts of bisphenol A type epoxy resin E-51 and 9 parts of thermally reactive phenolic resin are added to the reaction vessel. The temperature is raised to 55°C and stirred until homogeneous to obtain a resin mixture.

[0044] S3. Introduction of functional resin: After the above resin mixture cools down to below 30°C, add 4.5 parts of phosphate ester modified acrylic resin and 0.75 parts of polyether modified polysiloxane wetting agent, and continue stirring for 15 minutes.

[0045] S4. Nano-dispersion: Add 5.5 parts of epoxy-modified nano-silica with a particle size of 10-50 nm, disperse at high speed of 4000 rpm for 15 min, and grind with a horizontal sand mill until the fineness of the system is ≤10 μm. The zirconium beads of the grinding medium have a particle size of 0.4 mm.

[0046] S5. Interface modification: Add 3.5 parts of silane coupling agent (KH-550 and KH-560 in a mass ratio of 1:1) and stir at 800 rpm for 20 min.

[0047] S6. Catalytic curing: Add 0.2 parts of stannous octoate and stir evenly at 400 rpm to obtain the protective coating; adjust the viscosity of the system with the remaining organic solvent so that the viscosity of the protective coating at 25°C is 20s in the Forecast-4 cup.

[0048] Example 3 This application provides a method for preparing a protective coating, comprising the following steps: S1. Solvent preparation: The organic solvent is prepared by mixing butyl acetate, propylene glycol methyl ether acetate, propylene glycol methyl ether and xylene in a mass ratio of 45:40:20:10.

[0049] S2. Resin premixing: Nitrogen protective gas is introduced into the reaction vessel and the stirring device is turned on, maintaining a stirring speed of 400 rpm. According to the mass parts, 90 parts of the above organic solvent, 22 parts of modified organosilicon oil (obtained by compounding amino-modified organosilicon oil and epoxy-modified organosilicon oil in a mass ratio of 3:1), 28 parts of blocked polyurethane prepolymer, 18 parts of E-44 bisphenol A type epoxy resin and 12 parts of thermally reactive phenolic resin are added to the reaction vessel. The temperature is raised to 60°C and stirred until homogeneous to obtain a resin mixture.

[0050] S3. Introduction of functional resin: After the above resin mixture cools down to below 30°C, add 6 parts of phosphate ester modified acrylic resin and 1 part of polyether modified polysiloxane wetting agent, and continue stirring for 20 minutes.

[0051] S4. Nano-dispersion: Add 8 parts of epoxy-modified nano-silica with a particle size of 10-50 nm, disperse at 5000 rpm for 20 min, and grind with a horizontal sand mill until the fineness of the system is ≤10 μm. The zirconium beads of the grinding medium have a particle size of 0.5 mm.

[0052] S5. Interface modification: Add 5 parts of silane coupling agent (KH-550 to KH-560 in a mass ratio of 1:1.2) and stir at 900 rpm for 25 min.

[0053] S6. Catalytic curing: Add 0.3 parts of dibutyltin dilaurate and stir evenly at 500 rpm to obtain the protective coating; adjust the viscosity of the system with the remaining organic solvent so that the viscosity of the protective coating at 25°C is 25s in the Forecast cup 4.

[0054] Comparative Example 1 The only difference between this comparative example and Example 2 is that the modified silicone oil is replaced with an equal mass fraction of polydimethylsiloxane. All other process parameters and operating steps are the same as in Example 2.

[0055] Comparative Example 2 The only difference between this comparative example and Example 2 is that no phosphate-modified acrylic resin was added; its mass fraction was made up by an equal amount of organic solvent. All other process parameters and operating steps remain the same as in Example 2.

[0056] Comparative Example 3 The only difference between this comparative example and Example 2 is that the mass ratio of KH-550 to KH-560 in the silane coupling agent is 3:0.5. All other process parameters and operating steps are the same as in Example 2.

[0057] Comparative Example 4 The only difference between this comparative example and Example 2 is that the epoxy-modified nano-silica is replaced with an equal mass fraction of hydrophilic fumed silica. All other process parameters and operating steps are the same as in Example 2.

[0058] Comparative Example 5 The only difference between this comparative example and Example 2 is that in step S1, butyl acetate, propylene glycol methyl ether acetate, propylene glycol methyl ether, and xylene were mixed in a mass ratio of 55:30:10:5 to obtain 100 parts of organic solvent. All other process parameters and operating steps are the same as in Example 2.

[0059] Test Example 1 Experimental subjects: Coating samples prepared in Examples 1-3 and Comparative Examples 1-5 Hydrophilic aluminum foil substrate was selected, and its surface was treated by dust removal, degreasing and drying. The coating samples provided in Examples 1-3 and Comparative Examples 1-5 were uniformly sprayed onto the surface of the aluminum-based hydrophilic foil, and the coating was cured by baking at 140℃ for 30 minutes to form a coating with a thickness of 1μm.

[0060] Neutral salt spray resistance test: Performed in accordance with GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test"; Cyclic corrosion test: The test was conducted according to the C5-M cyclic corrosion testing method for highly corrosive marine environments in ISO 12944-9:2018 "Paints and varnishes — Protective coating systems for corrosion protection of steel structures — Part 9: Protective coating systems for offshore facilities and associated structures and laboratory testing methods". The total test duration was 4200 hours (25 weeks), with a single cycle of 7 days. The complete cycle process was: 3 days of continuous neutral salt spray (5wt% NaCl solution, 35℃, salt spray deposition rate 1~2mL / 80cm). 2 • 1 day in a dry environment (60℃, relative humidity ≤30%) + 2 days in a humid environment (40℃, relative humidity ≥95%) + 1 day in a natural environment (23℃, relative humidity 50%). After completing 25 complete cycles, observe the coating appearance and interface condition.

[0061] Coating T-bend test: Performed according to ASTM D4145-10 (2022) "Standard Test Method for Flexibility of Pre-coated Sheet Coatings". This test evaluates the flexibility of the coating by folding a painted sample in half and inserting shims of different thicknesses. The results are expressed as T-values ​​(e.g., 0T, 1T, 2T, etc.). The smaller the T-value, the stronger the coating's ability to not crack under severe bending, i.e., the better the flexibility. 0T indicates no cracks after bending. Adhesion test: The test was conducted in accordance with GB / T 9286-2021 "Cross-cut test for paint and varnish film". The test results are shown in Table 1.

[0062] Table 1 shows the test results of aluminum-based hydrophilic foil. Test Example 2 Experimental subjects: Coating samples prepared in Examples 1-3 and Comparative Examples 1-5 Epoxy pre-coated aluminum foil substrates were selected. After dust removal, degreasing, and drying treatment, the coating samples provided in Examples 1-3 and Comparative Examples 1-5 were uniformly coated onto the epoxy pre-coated foil surface. After removal, the coatings were baked at 160℃ for 20 minutes to cure, forming a coating with a thickness of 20 μm. The standards for neutral salt spray resistance test, coating T-bending test, and adhesion test were the same as those in Test Example 1, and will not be repeated here. The test results are shown in Table 2.

[0063] Table 2 shows the test results for epoxy pre-coated aluminum foil substrates. Test Example 3 Experimental subjects: Coating samples prepared in Examples 1-3 and Comparative Examples 1-5 Aluminum fins and copper tube structural components were selected as the substrate and were dipped into the coating samples provided in Examples 1-3 and Comparative Examples 1-5. After removal, the coating was cured at 160°C for 20 minutes using infrared technology to form a coating with a thickness of 35 μm. The standards for neutral salt spray resistance, coating T-bend test, and adhesion test were the same as those in Test Example 1 and will not be repeated here. The test results are shown in Table 3.

[0064] Table 3 shows the test results for aluminum finned and copper tube structural components. like Figure 1 As shown, these are surface comparison images of hydrophilic aluminum foil substrates coated with and uncoated with the coating of Example 2 of this invention, after undergoing a 1500-hour neutral salt spray test; Figure 2 As shown, these are surface comparison images of epoxy pre-coated aluminum foil substrates coated with and uncoated with the coating of Example 2 of this invention, after undergoing a 1500-hour neutral salt spray test; Figure 3 As shown, the three images are comparison pictures of the cut edges of epoxy pre-coated aluminum foil substrates coated with and uncoated with the coating of Example 2 of the present invention, after a 1500-hour neutral salt spray test; the three comparison pictures can further prove the excellent performance of the coating of the present invention.

[0065] The above are merely embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A protective coating, characterized in that, The composition includes the following components by weight: 50-90 parts organic solvent, 18-22 parts modified silicone oil, 22-28 parts blocked polyurethane prepolymer, 12-18 parts bisphenol A epoxy resin, 6-12 parts thermally reactive phenolic resin, 3-6 parts phosphate ester modified acrylic resin, 0.5-1.0 parts polyether modified polysiloxane wetting agent, 3-8 parts modified nano silica, 2-5 parts silane coupling agent, and 0.1-0.3 parts organotin catalyst. The modified silicone oil is obtained by compounding amino-modified silicone oil and epoxy-modified silicone oil, the modified nano-silica is epoxy-modified nano-silica, and the silane coupling agent contains amino functional groups and / or epoxy functional groups.

2. The protective coating according to claim 1, characterized in that, The organic solvent is prepared by compounding butyl acetate, propylene glycol methyl ether acetate, propylene glycol methyl ether and xylene in a mass ratio of 35-45:30-40:10-20:5-10; the silane coupling agent is prepared by compounding KH-550 and KH-560 in a mass ratio of 1:0.8 to 1:1.2; the modified organosilicon oil is prepared by compounding amino-modified organosilicon oil and epoxy-modified organosilicon oil in a mass ratio of 1-3:

1.

3. The protective coating according to claim 1, characterized in that, The modified nano-silica has a particle size of 10-50 nm.

4. The protective coating according to claim 1, characterized in that, The bisphenol A type epoxy resin is selected from at least one of E-44 or E-51; the organotin catalyst is selected from at least one of dibutyltin dilaurate or stannous octoate.

5. A method for preparing a protective coating, characterized in that, The preparation of the protective coating according to any one of claims 1 to 4 comprises the following steps: S1. Resin premixing: Under stirring at 400-600 rpm, the modified silicone oil, blocked polyurethane prepolymer, bisphenol A epoxy resin and thermally reactive phenolic resin are added to an organic solvent, heated to 50-60℃ and stirred until homogeneous to obtain a resin mixture. S2. Introduction of functional resin: After the resin mixture cools down to below 30°C, add the phosphate ester modified acrylic resin and polyether modified polysiloxane wetting agent, and continue stirring for 10-20 minutes. S3, Nano-dispersion: Add the modified nano-silica and disperse at a high speed of 3000-5000 rpm for 10-20 min, and grind until the fineness of the system is ≤10μm; S4. Interface modification: Add the silane coupling agent and stir at 700-900 rpm for 15-25 min. S5. Catalytic curing: Add the organotin catalyst and stir at 300-500 rpm until homogeneous to obtain the protective coating.

6. The preparation method according to claim 5, characterized in that, The heating and stirring process described in step S1 is accompanied by inert gas protection.

7. The preparation method according to claim 5, characterized in that, The grinding in step S3 is performed using a three-roll mill or a horizontal sand mill, and the particle size of the zirconium beads used in the grinding media is controlled to be 0.3-0.5 mm.

8. The preparation method according to claim 5, characterized in that, Step S5 also includes adjusting the viscosity of the system so that the viscosity of the coating at 25°C is 15-25s in the Forecast cup 4.

9. A radiator protection structure, characterized in that, include: The substrate has a pre-coated surface with a hydrophilic coating or an epoxy coating to form a pre-coating. The protective coating as described in any one of claims 1 to 4 is cured onto the surface of the substrate, and the coating thickness is 1-35 μm; The protective coating forms a chemical bond with the pre-coating.

10. The radiator protection structure according to claim 9, characterized in that, The substrate is a heat sink fin or a copper tube. The protective coating is cured by baking at 140-160℃ for 20-30 minutes and has a neutral salt spray resistance of ≥1500h and a bending performance of 0T.

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