Salt-fog-resistant metal protective paint as well as preparation method and application thereof

Abstract

The invention is applicable to the technical field of metal protective coatings, and provides a salt-fog-resistant metal protective coating and a preparation method and application thereof. The coating comprises a coating base solution and a coating working solution which are independently stored; the coating base solution comprises functional silane Tri-VS with a'vinyl-trimethoxy silane-terminal sulfydryl 'structure; the coating working solution comprises water-borne epoxy resin and polyion liquid intelligent microgel, and the microgel is provided with an MOF-rare earth composite inner core and a sulfur ion response type Schiff base shell layer. The invention also discloses a preparation method of the salt-spray-resistant metal protective paint. By constructing a triple synergistic system of a'crystalline mechanical interlocking bottom layer ', a'precise identification-conversion intelligent microgel' and a'interface fusion gradient structure ', the coating disclosed by the invention shows the comprehensive performance of super-strong vulcanization resistance, super-long salt mist resistance and excellent electrical compatibility under the submicron thickness, and can be safely used for long-acting protection of precise devices such as electronic connectors and jewelry.

Description

Technical Field

[0001] This invention belongs to the field of metal protective coating technology, and particularly relates to a salt spray resistant metal protective coating, its preparation method and application. Background Technology

[0002] Metals such as silver, copper, and their alloys are widely used in the electronics, electrical engineering, and jewelry industries due to their excellent electrical conductivity, thermal conductivity, and decorative properties. However, these metals are extremely prone to discoloration (such as silver forming black Ag2S) or corrosion in sulfur- and chlorine-containing atmospheric environments, which seriously affects their appearance, electrical contact reliability, and service life.

[0003] In the prior art, various protective methods have been proposed. For example, patent document CN109053794A discloses a thiol-olefin click preparation of silane coatings, which forms a cross-linked network by reacting vinyl silanes with polythiols. Although this method is environmentally friendly, the resulting network structure is disordered, and under ultra-thin (<1μm) coating conditions, it suffers from high internal stress, poor flexibility, and brittleness, which may lead to microcracks and protective failure with long-term use. Another patent document CN115820080A discloses a polyelectrolyte microgel anticorrosive coating, in which the microgel can release corrosion inhibitors in response to changes in ambient pH or temperature. However, this response mechanism lacks specific corrosion inhibitors (such as sulfur ions). 2- The specific recognition of silane is slow and inefficient, failing to accurately suppress the sulfidation discoloration of silver. Furthermore, none of the aforementioned technologies address the weak interfacial bonding between the silane substrate and the organic main coating, or the uneven distribution of functional components within the coating. This results in limited protective lifespan and makes it difficult to achieve both long-lasting corrosion resistance and excellent electrical properties in extremely thin coatings.

[0004] Some water-based protective agents on the market typically only withstand 3% potassium sulfide for 5-10 minutes and neutral salt spray for less than 100 hours, making it difficult to meet the requirements for long-term reliability.

[0005] Therefore, developing an environmentally friendly metal protective coating that can simultaneously achieve ultra-high resistance to sulfur discoloration, ultra-long salt spray life, excellent electrical compatibility, and strong interfacial adhesion at a submicron thickness has significant industrial application value. Summary of the Invention

[0006] This invention provides a salt spray resistant metal protective coating, its preparation method, and its application, aiming to solve the above-mentioned problems.

[0007] The present invention is achieved as follows: a salt spray resistant metal protective coating, comprising separately stored coating primer and coating working fluid.

[0008] The coating primer is prepared from the following raw materials in parts by weight: Functional silane Tri-VS: 3-8 parts; Photoinitiator (2-hydroxy-2-methyl-1-phenyl-1-propanone): 0.1-0.5 parts; Deionized water / anhydrous ethanol mixed solvent (volume ratio 1:1): 91.5-96.9 parts; pH adjuster (acetic acid): Appropriate amount, used to adjust pH to 4.2-4.5; The functional silane Tri-VS is an asymmetric molecule with a trifunctional structure of "vinyl, trimethoxysilyl, and terminal thiol", and its general structural formula is: (CH3O)3Si-(CH2)3-O-CO-C6H4-CO-O-CH2-CH(-S-CH2-CH2-SH)-CH2-O-CO-CH=CH2. It connects the vinyl and thiol groups to the trimethoxysilane terminal via a flexible linking chain containing a benzene ring. Its preparation method includes the following steps: γ-glycidoxypropyltrimethoxysilane (KH-560) was reacted with p-hydroxybenzoic acid at 0-5 °C under the catalysis of N,N'-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP) to generate a silane ester intermediate containing a benzene ring (intermediate I).

[0009] Intermediate I was reacted with acryloyl chloride under triethylamine catalysis to introduce a vinyl group, yielding a silane intermediate (intermediate II) containing a benzene ring and a vinyl group.

[0010] Intermediate II was reacted with excess 1,2-ethylenedithiol at room temperature for 12-24 hours under triphenylphosphine catalysis, causing an addition reaction between the double bond of the acrylate and a thiol group to form a thioether bond, with the other thiol group remaining at the end, to obtain the target product Tri-VS crude product, which was purified by vacuum distillation.

[0011] The coating working fluid is prepared from the following raw materials in parts by weight: Waterborne epoxy resin dispersion (solid content 40%): 40-60 parts; Polyionic liquid intelligent microgel dispersion (solid content 10%): 20-35 parts; Multifunctional thiol crosslinking agent (pentaerythritol tetra-3-mercaptopropionate): 5-10 parts; Flexible epoxy resin (polyethylene glycol diglycidyl ether, molecular weight 400): 5-15 parts; Wetting and leveling agent (polyether modified siloxane): 0.1-0.5 parts; Deionized water: 10-30 parts; the total solids content of the coating working solution is 15-25%.

[0012] The polyionic liquid smart microgel has a core-shell structure, and its preparation method includes the following steps: Preparation of composite core: Cerium nitrate and 8-hydroxyquinoline-5-sulfonic acid were complexed in water to form a rare earth complex solution; this solution was mixed with an ethanol dispersion of ZIF-8 MOF nanoparticles (particle size 50-100nm), and the complex was loaded into the MOF channels by impregnation. After centrifugation, washing and drying, the MOF-rare earth composite core was obtained.

[0013] Preparation of responsive polymer shell: 1-vinyl-3-ethylimidazolium bromide, N-isopropylacrylamide, double-bond functionalized benzotriazole (BTA-Ac, as a corrosion inhibitor precursor) and MOF-rare earth composite core were used as comonomers / fillers. In the presence of crosslinking agent N,N'-methylenebisacrylamide, the mixture was subjected to precipitation polymerization in a water / ethanol mixed solvent and reacted at 70°C for 6 hours to form a microgel encapsulating the composite core. The microgel was then purified by dialysis.

[0014] Schiff base-responsive unit grafting: The microgel dispersion obtained in step 2 was mixed with 0.5 wt% of 4-aminobenzaldehyde and 0.25 wt% of p-toluenesulfonic acid catalyst (equivalent to the mass of the microgel solids), and the mixture was magnetically stirred at 25 ± 2 °C for 24 hours. After the reaction, unreacted raw materials were removed by dialysis to obtain grafted sulfide ions (S... 2- A smart microgel dispersion with responsive Schiff base bonds, with the solid content adjusted to 10%.

[0015] The present invention also provides a method for preparing the above-mentioned salt spray resistant metal protective coating, comprising the following steps: S1. Preparation of coating primer: Dissolve Tri-VS and photoinitiator in a deionized water / ethanol mixed solvent, adjust the pH to 4.2-4.5 with acetic acid, stir evenly to obtain a transparent and uniform coating primer.

[0016] S2. Preparation of coating working solution: The aqueous epoxy resin dispersion, multifunctional thiol crosslinking agent, flexible epoxy resin and wetting leveling agent are mixed evenly under stirring. Then, the polyionic liquid intelligent microgel dispersion is slowly added. Finally, deionized water is added to adjust to the target solid content, and the mixture is filtered to obtain the coating working solution.

[0017] The present invention also provides a method for forming a coating on a metal substrate surface using the above-mentioned salt spray resistant metal protective coating, comprising the following steps: (1) Pretreatment of the substrate: The metal workpiece is degreased, pickled and activated, rinsed with deionized water and dried in sequence.

[0018] (2) Electrophoretic deposition of self-assembled underlayer: The pretreated workpiece is used as the cathode and immersed in a coating primer at a temperature of 20-25℃; electrophoretic deposition is performed for 60-90 seconds using a pulsed voltage mode (voltage sequence: 3V for 20s → 5V for 20s → 3V for 20s). Under these conditions, Tri-VS molecules self-assemble to form a crystalline pre-structured layer through π-π stacking of aromatic rings, hydrogen bonding between silanol groups, and electric field orientation. After removal, the layer is dried with nitrogen and immediately exposed to 365nm ultraviolet light (intensity 30mW / cm²). 2 Irradiation for 30 seconds triggers a "thiol-olefin" click reaction, covalently "locking" the crystalline template and forming a partially cured crystalline mechanical interlocking network bottom layer.

[0019] (3) Plasma interface activation: The workpiece after step (2) is placed in a low-temperature plasma treatment device and treated for 10-20 seconds under an argon atmosphere and a power of 15-20W to activate the functional groups on the bottom surface and introduce micro-nano rough structures.

[0020] (4) Gradient spraying of the main layer: using electrostatic spraying equipment, the coating working liquid is sprayed onto the activated bottom surface; during spraying, the spray gun pressure is controlled from 0.3MPa at the initial near workpiece interface to 0.1MPa away from the workpiece surface, forming a coating with a wet film thickness of 8-12μm; this pressure gradient helps the microgel to form a continuous and gradual distribution in the coating thickness direction.

[0021] (5) Gradient curing: Place the sprayed workpiece in an oven and perform programmed temperature curing: First, keep it at 80℃ for 10 minutes to allow the moisture to evaporate and react initially; then raise the temperature to 120℃ and keep it for 20 minutes to allow the terminal thiol groups of the bottom Tri-VS to undergo a "thiol-epoxy" click reaction with the flexible epoxy resin in the main layer, while the microgel shell layer further crosslinks, ultimately forming a gradient coating with a firm interface and integrated structure, with a total dry film thickness of 0.5-1.0μm.

[0022] This invention creatively incorporates "crystalline mechanically interlocked silane substrate" and "S..." 2- The combination of "specifically responsive MOF-rare earth smart microgel" and "plasma interface fusion gradient process" achieves a three-way synergistic protection of the metal substrate through "barrier isolation-precise identification-active elimination", thus achieving unexpected ultra-high corrosion resistance and long-lasting protection at a submicron thickness.

[0023] First, the crystalline mechanically interlocked underlying layer formed by the π-π stacking of Tri-VS molecules provides an extremely ordered and robust physical barrier. Electrochemical impedance spectroscopy tests show that it can prevent corrosive media (Cl) from entering the environment. -The penetration rate of H2O is lower than that of traditional disordered silane coatings; when a very small amount of corrosive agents (such as S) are present, the penetration rate is reduced. 2- After penetrating the dense sublayer, the smart microgels, gradient-distributed in the main layer, immediately activate as a second active defense. The Schiff base bonds grafted onto their shells specifically recognize and capture S. 2- This triggers rapid shrinkage of the microgel, releasing the loaded benzotriazole (BTA) corrosion inhibitor, which promptly repairs micro-defects in the coating; simultaneously, the trapped S... 2- and Cl - Enriched by MOF channels and reacting rapidly with rare earth complexes in the core, stable and harmless substances are generated, fundamentally eliminating the threat of corrosion. Finally, the plasma interface activation process forms a strong interface with covalent bonding and physical interlocking between the bottom layer and the main layer, ensuring the integrity of the coating under harsh environments (such as thermal cycling from -40℃ to 85℃) and avoiding protective failure caused by interlayer peeling. The above-mentioned multi-level synergistic mechanism of "blocking-identification-conversion-repair-stabilization" produces a significant synergistic effect.

[0024] Compared with the prior art, the embodiments of this application have the following main advantages: Superior resistance to sulfide discoloration: Silver products treated with the coating of this invention can maintain their shine for 20-30 minutes when tested in a 3% potassium sulfide solution at 25°C.

[0025] Superior salt spray resistance: The coating significantly extends the salt spray resistance time of the base metal. For example, the treated silver-plated copper parts show the first corrosion point after more than 240 hours in a neutral salt spray test.

[0026] Extremely low electrical performance impact: The ultra-thin coating (<1μm) has a minimal impact on metal contact resistance (increase rate <1.5%) and does not affect soldering performance at all.

[0027] Intelligent Response and Active Protection: Microgels can specifically recognize S 2- It responds quickly, releases corrosion inhibitors, and efficiently converts harmful ions through the MOF confinement effect, thus possessing active protection capabilities.

[0028] Excellent coating adhesion and durability: Through crystalline mechanical interlocking network design and plasma interface fusion process, the coating has strong adhesion to the substrate and good resistance to thermal cycling and mechanical friction.

[0029] Safe and environmentally friendly: Water is the main solvent, it does not contain heavy metals such as chromium and lead, has low VOC content, is safe to operate, and the coating formed is non-toxic and non-irritating. Attached Figure Description

[0030] Figure 1 This is a flowchart of the preparation method of the salt spray resistant metal protective coating provided by the present invention.

[0031] Figure 2 This is a flowchart of the preparation method of the functional silane Tri-VS provided by the present invention.

[0032] Figure 3 This is a flowchart of the preparation method of the polyionic liquid smart microgel provided by the present invention.

[0033] Figure 4 This is a flowchart of the method for forming a protective layer on the surface of a metal substrate provided by the present invention. Detailed Implementation

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings of this application are used to distinguish different objects, not to describe a particular order.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] Example 1: Optimal Formulation and Process I. Raw Material Preparation and Characterization Synthesis and characterization of functional silanes Tri-VS: Under ice bath and nitrogen protection, 10.0 g KH-560, 1.5 g p-hydroxybenzoic acid, 2.3 g DCC, and 0.1 g DMAP were added to a three-necked flask containing a magnetic stir bar and dissolved in 50 mL anhydrous dichloromethane. The reaction was carried out at 0 °C for 12 hours. The solid was removed by filtration, and the filtrate was distilled under reduced pressure to obtain intermediate I. Intermediate I was dissolved in 30 mL tetrahydrofuran, and 2.8 g triethylamine was added. 2.2 g acryloyl chloride was slowly added dropwise under ice bath, and the reaction was carried out at room temperature for 4 hours. The mixture was filtered, and the filtrate was distilled under reduced pressure to obtain intermediate II. Intermediate II was mixed with 10 g 1,2-ethylenedithiol and 0.3 g triphenylphosphine, and the mixture was stirred at room temperature for 18 hours. Excess ethylenedithiol was removed by reduced pressure distillation to obtain a pale yellow oily liquid, Tri-VS, in approximately 78% yield.

[0037] Characterization:1 H NMR (CDCl3, 400 MHz): δ 7.85 (d, J=8.4 Hz, 2H, Ar-H), 7.45 (d, J=8.4Hz, 2H, Ar-H), 6.35 (dd, J=17.2, 10.4 Hz, 1H, CH=CH2), 6.15 (d, J=17.2 Hz, 1H, CH=CH2), 5.85 (d, J=10.4 Hz, 1H, CH=CH2), 3.55 (s, 9H, Si-OCH3), 2.85 (t, J=7.6 Hz, 2H, -CH2-SH). FT-IR (cm -1 ): 2950 (CH), 2550 (SH), 1710 (C=O), 1600, 1500 (Ar), 1080 (Si-OC).

[0038] Preparation and characterization of polyionic liquid smart microgels: a) Composite Core: Dissolve 0.5 g of cerium nitrate octahydrate in 20 mL of water, add 0.4 g of 8-hydroxyquinoline-5-sulfonic acid, and stir to dissolve; add 1.0 g of ZIF-8 nanoparticles, ultrasonically disperse, and stir at room temperature for 12 hours. Centrifuge, wash, and vacuum dry at 60 °C to obtain a light yellow composite core powder; b) Microgel synthesis: 1.0 g of 1-vinyl-3-ethylimidazolium bromide, 0.3 g of N-isopropylacrylamide, 0.2 g of BTA-Ac, 0.2 g of the composite core, and 0.03 g of N,N'-methylenebisacrylamide were dissolved in 30 mL of a water / ethanol (1:1) mixed solvent and purged with nitrogen to remove oxygen; 0.02 g of AIBA was added, and the reaction was carried out at 70 °C for 6 hours; the mixture was purified by dialysis to obtain microgel dispersion A; c) Schiff base grafting: Take 10g of dispersion A (solid content about 8%), add 0.04g of 4-aminobenzaldehyde and 0.02g of p-toluenesulfonic acid, stir and react at 25℃ for 24 hours; dialyze to obtain intelligent microgel dispersion, and adjust the solid content to 10%.

[0039] Characterization: TEM showed that the microgels were spherical with an average particle size of about 100 nm and a visible core-shell structure; DLS measured the hydrated particle size to be 115 nm and the polydispersity index (PDI) to be 0.15; the zeta potential was +35 mV.

[0040] II. Coating Preparation and Application Paint primer: Take 5 parts Tri-VS and 0.3 parts photoinitiator Irgacure 2959, dissolve them in 94.2 parts (deionized water / ethanol = 1:1) mixed solvent, adjust the pH to 4.3 with acetic acid, and stir well.

[0041] Coating working solution: Take 50 parts of waterborne epoxy resin dispersion, 7 parts of pentaerythritol tetra-3-mercaptopropionate, 10 parts of polyethylene glycol diglycidyl ether (PEGDGE, M=400), and 0.3 parts of BYK-346, and stir to mix evenly; slowly add 25 parts of the above intelligent microgel dispersion (solid content 10%), and stir for 30 minutes. Add deionized water to adjust the total solid content to 20%, and filter.

[0042] Coating and curing: a) The substrate is a pure silver sheet (20mm×20mm×0.3mm), which is degreased, activated with 5% dilute nitric acid, washed with water, dehydrated with ethanol, and then dried.

[0043] b) Electrophoretic deposition: A silver sheet was used as the cathode. Electrophoresis was performed in a 22°C substrate at a pulsed 3V-5V-3V mode for 75 seconds. After drying, the sample was subjected to ultraviolet light (365nm, 30mW / cm²). 2 Irradiate for 30 seconds.

[0044] c) Plasma activation: Argon atmosphere, power 18W, treatment for 15 seconds.

[0045] d) Gradient spraying: electrostatic spraying, with the spray gun pressure gradually changing from 0.3MPa to 0.1MPa, and the wet film thickness is about 10μm.

[0046] e) Curing process: 80℃ / 10min + 120℃ / 20min.

[0047] Coating characterization: The dry film thickness was measured to be 0.82 μm using an ellipsometry. SEM cross-sectional images showed that the coating was uniform and dense, with the interface between the bottom layer and the substrate fused together. EPMA line scans showed that the Si signal was strongest near the substrate, while the Ce signal (representing microgels) was most enriched in the lower part of the coating, exhibiting a gradient distribution.

[0048] Example 2: High Microgel Content Formulation The process was essentially the same as in Example 1, except that the amount of intelligent microgel dispersion added to the coating working solution was 32 parts, the amount of PEGDGE was 13 parts, and the total solid content was adjusted to 22%. The electrophoresis voltage was constant at 4V for 70 seconds; the final dry film thickness was approximately 0.95μm.

[0049] Example 3: Low Tri-VS Content Formulation The experiment was essentially the same as in Example 1, except that the amount of Tri-VS in the primer was 3 parts, and the solvent was increased accordingly. The electrophoresis time was extended to 90 seconds; the final dry film thickness was approximately 0.68 μm.

[0050] Example 4: Control without flexible epoxy component The process is basically the same as in Example 1, except that: PEGDGE (flexible epoxy resin) is not added to the coating working solution, and the amount of pentaerythritol tetra-3-mercaptopropionate (polythiol) is increased to 12 parts; the curing conditions of the main layer are only 120°C / 30 min.

[0051] Comparative Example 1: Conventional silane substrate The process is basically the same as in Example 1, except that Tri-VS in the coating primer is replaced with an equal amount of γ-aminopropyltriethoxysilane (KH-550); the coating is applied directly after electrophoretic deposition without a plasma activation step.

[0052] Comparative Example 2: Non-smart microgels The process is basically the same as in Example 1, except that the smart microgel in the coating working fluid is replaced with a common thermosensitive microgel with an equal solids content, consisting only of poly(1-vinyl-3-ethylimidazolium bromide-co-N-isopropylacrylamide) and without Schiff base response units and MOF-rare earth composite core.

[0053] Comparative Example 3: Simplified Coating Process The process is basically the same as in Example 1, except that the plasma interface activation step is omitted in the coating process, and a constant pressure of 0.2 MPa is used during spraying.

[0054] Comparative Example 4: Existing Technical Solution Referring to the polyelectrolyte microgel anticorrosive coating formulation and process disclosed in Example 1 of patent CN115820080A, the coating was prepared and applied to the same silver sheet, and the film thickness after curing was approximately 1.0 μm.

[0055] Comparative Example 5: Untreated silver sheet.

[0056] Performance Tests and Results Performance tests were conducted on all the above samples according to the following standards: Potassium sulfide resistance test: Refer to Appendix A of GB / T 15519-2018 and record the time when obvious discoloration or spots appear on the surface of the sample in 3% potassium sulfide solution at 25℃.

[0057] Neutral salt spray test: Refer to GB / T 10125-2021 and record the time when the first corrosion point appears on the sample surface under the conditions of 35℃ and 5% NaCl spray.

[0058] Contact resistance: Measured using a four-terminal micro-ohmmeter under the same pressure, and the percentage increase in resistance before and after coating treatment was calculated.

[0059] Solderability: Refer to GB / T 11364-2008, measure the spreading area of ​​solder on the sample surface, and obtain the spreading rate by comparing it with the spreading area of ​​untreated smooth silver sheet.

[0060] Adhesion: Cross-cut test (1mm spacing) was conducted in accordance with GB / T 9286-2021, with evaluation grades (0 being the best and 5 being the worst).

[0061] Thermal cycling resistance: Cycle the sample between -40℃ (30 min) and 85℃ (30 min) 100 times and observe whether the coating surface cracks or peels off.

[0062] Results analysis: Examples 1-3 demonstrate the superior performance of the present invention under different parameters, with a sulfur resistance time far exceeding that of the comparative example and the prior art (comparative example 4), a salt spray resistance time exceeding 200 hours, and minimal electrical impact.

[0063] Comparative Example 1 (with the replacement substrate) showed a significant overall decline in performance, particularly in salt spray resistance and adhesion, demonstrating that the “crystalline mechanical interlocking network” formed by Tri-VS is crucial for building a strong and dense substrate.

[0064] Although Comparative Example 2 (replacing ordinary microgel) showed improved sulfur resistance and salt spray resistance (mainly due to the superior substrate), it was significantly lower than Example 1, demonstrating the "S" of the smart microgel. 2- The "specific recognition" and "MOF-rare earth high-efficiency conversion" mechanisms are the core of achieving super strong sulfur resistance and long-term protection, which is incomparable to ordinary responsive microgels.

[0065] The performance of Comparative Example 3 (simplified process) is between that of Example 1 and Comparative Example 1 / 2, indicating that the "plasma interface activation" and "gradient spraying" processes play an irreplaceable role in strengthening interface bonding, optimizing functional phase distribution, and thus giving full play to the synergistic effect of the underlying layer and microgel.

[0066] Example 4 (without flexible epoxy) showed a slightly greater increase in contact resistance and a slight decrease in resistance to thermal cycling, demonstrating the positive role of the flexible epoxy component (PEGDGE) in stress relief, maintaining coating integrity, and electrical properties.

[0067] In summary, this invention, through the deep synergy of unique molecular design (Tri-VS), smart material construction (MOF-rare earth microgel), and innovative process (interface fusion gradient construction), has successfully solved the industry problem of simultaneously achieving resistance to sulfurization, salt spray resistance, and electrical properties in submicron-level ultrathin coatings, achieving unexpected technical effects and possessing outstanding substantive characteristics and significant progress.

[0068] It should be noted that, for the sake of simplicity, the foregoing embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0069] It should be understood that the disclosed apparatus can be implemented in other ways, as illustrated in the embodiments provided in this application. For example, the apparatus embodiments described above are merely illustrative; the division of units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or communication connections shown or discussed may be through some interfaces; the indirect coupling or communication connections between devices or units may be telecommunications or other forms.

[0070] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0071] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still combine, add, delete, or otherwise adjust the features of the various embodiments of the present invention according to the circumstances without conflict or creative effort, thereby obtaining different technical solutions that do not fundamentally depart from the concept of the present invention. These technical solutions also fall within the scope of protection of the present invention.

Claims

1. A salt spray resistant metal protective coating, characterized in that, This includes separately stored paint primer and paint working solution; The coating primer is made from the following raw materials in parts by weight: 3-8 parts of functional silane Tri-VS, 0.1-0.5 parts of photoinitiator, 91.5-96.9 parts of mixed solvent formed by mixing deionized water and anhydrous ethanol in a volume ratio of 1:1, and a pH adjuster for adjusting the pH to 4.2-4.5; the functional silane Tri-VS is a trifunctional molecule having vinyl, trimethoxysilyl and terminal mercapto groups, and containing a benzene ring linking unit; The coating working solution is made from the following raw materials in parts by weight: 40-60 parts of aqueous epoxy resin dispersion, 20-35 parts of polyionic liquid intelligent microgel dispersion, 5-10 parts of multifunctional thiol crosslinking agent, 5-15 parts of flexible epoxy resin, 0.1-0.5 parts of wetting and leveling agent, and 10-30 parts of deionized water; the total solids content of the coating working solution is 15-25%. The polyionic liquid smart microgel has a core-shell structure. Its core is a ZIF-8 metal-organic framework loaded with rare earth complexes, and its shell is a poly(1-vinyl-3-ethylimidazolium bromide-co-N-isopropylacrylamide) copolymer network grafted with sulfide ion-responsive Schiff base groups. The shell network is loaded with benzotriazole corrosion inhibitor.

2. The salt spray resistant metal protective coating as described in claim 1, characterized in that, The photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone; the multifunctional thiol crosslinking agent is pentaerythritol tetra-3-mercaptopropionate; the flexible epoxy resin is polyethylene glycol diglycidyl ether with a molecular weight of 400; and the wetting and leveling agent is polyether-modified siloxane.

3. A method for preparing a salt spray resistant metal protective coating as described in claim 1 or 2, characterized in that, Includes the following steps: S1. Preparation of coating primer: Dissolve functional silane Tri-VS and photoinitiator in a mixed solvent, adjust the pH to 4.2-4.5 with a pH adjuster, stir evenly to obtain the coating primer; S2. Preparation of coating working solution: The aqueous epoxy resin dispersion, multifunctional thiol crosslinking agent, flexible epoxy resin and wetting leveling agent are mixed evenly, polyionic liquid intelligent microgel dispersion is added, and deionized water is added to adjust the solid content. After filtration, the coating working solution is obtained.

4. The method for preparing the salt spray resistant metal protective coating as described in claim 3, characterized in that, The preparation method of the functional silane Tri-VS includes: (1) γ-glycidoxypropyltrimethoxysilane was reacted with p-hydroxybenzoic acid at 0-5°C under DCC and DMAP catalysis to obtain intermediate I containing a benzene ring. (2) Intermediate I was reacted with acryloyl chloride under triethylamine catalysis to obtain intermediate II containing benzene ring and vinyl group; (3) Intermediate II was reacted with excess 1,2-ethylenedithiol at room temperature for 12-24 hours under triphenylphosphine catalysis, and the resulting product was purified to obtain functional silane Tri-VS.

5. The method for preparing the salt spray resistant metal protective coating as described in claim 3, characterized in that, The preparation method of the polyionic liquid smart microgel includes: (1) Cerium nitrate was complexed with 8-hydroxyquinoline-5-sulfonic acid and then mixed with ZIF-8 for loading to obtain MOF-rare earth composite core; (2) 1-vinyl-3-ethylimidazolium bromide, N-isopropylacrylamide, double-bond functionalized benzotriazole, the composite core and crosslinking agent are subjected to precipitation polymerization to obtain microgels; (3) The microgel was reacted with 4-aminobenzaldehyde at 25°C for 24 hours under the catalysis of p-toluenesulfonic acid to graft Schiff base groups and obtain polyionic liquid smart microgel.

6. A method for forming a protective layer on the surface of a metal substrate, characterized in that, Using the metal protective coating according to claim 1 or 2 includes the following steps: (1) Pretreatment of the substrate: The metal substrate is subjected to degreasing, pickling and activation, deionized water rinsing and drying in sequence; (2) Underlayer formation: The pretreated substrate is used as the cathode and immersed in the coating primer. Electrophoretic deposition is carried out at 20-25°C and pulse voltage mode for 60-90 seconds. After removal, it is dried and cured by ultraviolet light irradiation. (3) Interface activation: The substrate with the bottom layer is subjected to low-temperature plasma treatment; (4) Main layer spraying: The coating working liquid is sprayed onto the activated bottom layer surface using a gradient pressure spraying method, and the wet film thickness is 8-12μm; (5) Curing by temperature program: First, maintain the temperature at 80℃ for 10 minutes, then raise the temperature to 120℃ and maintain it for 20 minutes to obtain a protective layer with a dry film thickness of 0.5-1.0μm.

7. The forming method as described in claim 6, characterized in that, The pulse voltage mode in step (2) is: 3V held for 20s → 5V held for 20s → 3V held for 20s.

8. The forming method as described in claim 6, characterized in that, The conditions for the low-temperature plasma treatment in step (3) are: argon atmosphere, power 15-20 W, and treatment time 10-20 seconds.

9. The forming method as described in claim 6, characterized in that, The gradient pressure spraying in step (4) is as follows: the spray gun pressure gradually changes from 0.3 MPa near the substrate interface to 0.1 MPa away from the substrate surface.

10. Use of the metal protective coating as described in claim 1 or 2 in the preparation of protective layers for electronic connectors, electrical contacts, jewelry, ornaments or metal utensils.

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