A chromium-free passivation solution with high curing activity, a preparation method and application thereof

Abstract

This invention discloses a highly curable, chromium-free passivation solution, its preparation method, and its applications, belonging to the field of metal surface treatment technology. The passivation solution comprises: an organic film-forming agent (containing an aqueous epoxy resin and an organic film-forming agent for forming an interpenetrating polymer network (IPN) film-forming polymer emulsion), an inorganic film-forming agent, a latent curing catalyst (metal-amine complex), and a pH adjuster. This invention achieves a balance between room temperature stable storage and low-temperature rapid curing by constructing a multi-component polymer IPN structure and combining it with a latent curing catalyst. This passivation solution can rapidly cure at 90-110℃ for 10-20 seconds. The treated coated steel sheet exhibits a white rust time greater than 96 hours in a neutral salt spray test, demonstrating corrosion resistance that reaches or even surpasses that of traditional chromate passivation. Furthermore, it is completely free of hexavalent chromium, making it environmentally friendly and widely applicable to the surface passivation treatment of galvanized steel sheets, aluminized zinc steel sheets, and zinc-aluminum-magnesium steel sheets.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, specifically to a chromium-free passivation liquid with high curing activity, its preparation method, and its application. Background Technology

[0002] Galvanized steel sheets, aluminized zinc steel sheets, and galvanized aluminum-magnesium steel sheets are widely used in construction, home appliances, automobiles, and transportation due to their excellent corrosion resistance. However, the coating is susceptible to corrosion from humid air, salt spray, and other environmental factors during storage, transportation, and use, resulting in white rust (basic zinc carbonate) corrosion, which affects the product's appearance and service life. Therefore, passivation treatment is usually required for the surface of coated steel sheets.

[0003] Traditional chromate passivation technologies (such as hexavalent chromium passivation) offer advantages such as dense film formation, strong self-healing properties, and good corrosion resistance. However, hexavalent chromium compounds are highly toxic and carcinogenic, posing serious threats to the environment and human health. The EU RoHS Directive, REACH regulations, and relevant domestic environmental standards all impose strict restrictions on the use of chromates. Developing environmentally friendly chromium-free passivation technologies has become an urgent need in the metal surface treatment industry.

[0004] For example, Chinese patent CN110205613A discloses a chromium-free passivation solution containing components such as hydrogen peroxide, metal complexing agent, titanium oxysulfate, tetrabutyl titanate, and sodium silicate. This solution mainly relies on inorganic film-forming agents to form an oxide film layer. However, this solution requires high-temperature curing above 150°C and a curing time of over 60 seconds, which is difficult to meet the rapid thermal curing requirements of continuous galvanizing production lines; moreover, it has poor room temperature storage stability, easily causing precipitation and delamination, limiting its practical application. Chinese patent CN100585004C discloses a chromium-free passivation solution containing molybdate, tungstate, and acrylic acid. Although this solution has salt spray resistance performance close to chromate passivation, the curing temperature still requires 140°C, and the coating hardness and adhesion are insufficient, easily leading to coating defects under high-speed roller coating conditions. In recent years, organic / inorganic composite passivation systems have become a research hotspot.

[0005] Current chromium-free passivation technologies mainly employ composite systems of organic resins (such as acrylic acid and polyurethane) and inorganic salts (such as silicates and molybdates). However, existing technologies still have the following prominent problems: High curing temperature: Most chromium-free passivation solutions require baking and curing at temperatures above 150°C, which consumes a lot of energy and cannot meet the process requirements of high-speed continuous galvanizing production lines (which typically require 90-120°C and 10-20 seconds of rapid curing).

[0006] Poor room temperature stability: Many single-component passivation solutions are prone to precipitation or gelation during storage, resulting in short shelf life and making them difficult to commercialize.

[0007] Insufficient curing activity: Existing waterborne resin systems exhibit slow crosslinking reactions at low temperatures (≤110℃), resulting in incomplete curing of the coating film and poor corrosion resistance.

[0008] Salt spray resistance is not ideal: the white rust appearance time of existing patented chromium-free passivation formulations is generally 48-72 hours, which is difficult to replace the performance level of chromate passivation (white rust time > 96 hours).

[0009] Therefore, developing a chromium-free passivation solution that is stable at room temperature, cures rapidly at low temperatures (90-110℃), and has excellent salt spray resistance (white rust time >96 hours) has significant industrial value and environmental significance. Summary of the Invention

[0010] This invention aims to overcome the shortcomings of existing technologies and provide a chromium-free passivation solution with high curing activity and its applications. This passivation solution achieves a balance between room temperature stable storage and low-temperature rapid curing by constructing a multi-component polymer interpenetrating network (IPN) structure and combining it with a specific latent curing catalyst, resulting in excellent corrosion resistance.

[0011] To achieve the above objectives, the present invention adopts the following technical solution.

[0012] First, the present invention provides a chromium-free passivation liquid with high curing activity, comprising an organic film-forming agent, an inorganic film-forming agent, a latent curing catalyst, and a pH adjuster; The organic film-forming agent comprises an aqueous epoxy resin and a film-forming polymer emulsion. The inorganic film-forming agent is a water-soluble silicate; The latent curing catalyst is a metal-amine complex, formed by the complexation of a metal salt and an amine compound; The pH adjuster adjusts the pH of the passivation solution to 4-5.

[0013] This technical solution provides a film-forming base through a film-forming polymer emulsion, provides crosslinking sites through an aqueous epoxy resin, accelerates the curing reaction through a latent curing catalyst, forms an IPN interpenetrating network structure to enhance the mechanical properties of the coating, and improves corrosion resistance through a multi-crosslinking system, achieving a synergistic effect of room temperature stable storage and rapid thermal curing.

[0014] Preferably, the film-forming polymeric emulsion is selected from at least two of cationic or nonionic acrylic emulsions, polyurethane emulsions, polyvinyl alcohol emulsions, phenolic resin emulsions, and amino silicone oil emulsions; using at least two film-forming polymeric emulsions with different structures can form a physical interpenetrating network, in which different polymer chains interpenetrate and entangle with each other during the curing process, significantly improving the density and mechanical properties of the coating film.

[0015] Preferably, the metal salt is selected from one or more of ammonium fluorotitanate, ammonium fluorozirconate, ammonium molybdate, cerium nitrate, and zinc nitrate. These metal salts can form stable complexes with amine compounds, significantly improving curing efficiency as curing catalysts. Furthermore, the titanium and zirconium elements in ammonium fluorotitanate and ammonium fluorozirconate can participate in the formation of inorganic networks, further enhancing coating performance.

[0016] Preferably, the amine compound is one or more selected from polyethyleneimine, polydopamine, triethanolamine, triethylamine, hexamethylenetetramine, hexamethylenediamine, triethylenediamine, tetramethylethylenediamine, diethylenetriamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, monoethanolamine, diethanolamine, ethylenediaminetetraacetic acid, liquid polyamide, imidazole, 2-methylimidazole, and dimethyl-4-ethylimidazole. These ligands can form complexes with metal salts and simultaneously provide amino groups to participate in crosslinking reactions.

[0017] The metal-amine complex of the present invention has three functions: First, it chelates metal ions to improve the stability of resin emulsions in surface treatment solutions; second, the amine complex can be adsorbed on the metal surface to form a nano-protective film, improving corrosion resistance; third, it undergoes protonation in an acidic environment to reduce the room temperature curing activity of amines, improves the stability of coexistence with cationic emulsions, and makes the emulsion stable and prevents demulsification.

[0018] Preferably, the mass ratio of the metal salt to the ligand is 1:1.5 to 1:3. This range ensures the stability and catalytic activity of the complex. Excess ligand ensures complete complexation of the metal ions, avoiding the adverse effects of free metal ions on the emulsion stability. If the ratio is lower than 1:1.5, the metal ion complexation is incomplete, affecting storage stability; if it is higher than 1:3, excessive free ligand may interfere with the crosslinking equilibrium of the curing system.

[0019] Furthermore, the amount of the latent curing catalyst added is 0.25-0.5% of the total volume of the passivation solution. This addition range ensures curing efficiency while avoiding the degradation of coating performance caused by excessive catalyst. When the addition amount is less than 0.25%, the low-temperature curing activity is insufficient; when the addition amount is more than 0.5%, the coating brittleness increases and the adhesion decreases.

[0020] Preferably, the waterborne epoxy resin is ethylene glycol diglycidyl ether or glycerol triglycidyl ether. These low molecular weight epoxy resins have excellent reactivity and water solubility, and can undergo ring-opening crosslinking reactions with the active hydrogen groups on the side chains of film-forming polymers during the curing process.

[0021] Preferably, the amount of the multi-film-forming polymeric emulsion added to the passivation solution is 5-10% of the passivation solution volume, and the amount of the water-based epoxy resin added is 1% of the total passivation solution volume. This addition range ensures film thickness and performance while maintaining the low viscosity of the passivation solution for easy roller coating.

[0022] Preferably, the inorganic film-forming agent is a high-modulus silicate, specifically potassium silicate or lithium silicate with a modulus of 3.3, 4.7, 8, or 12, and its addition amount is 2% of the total volume of the passivation solution. The inorganic film-forming agent provides an inorganic silicon-oxygen network structure, forming an organic-inorganic hybrid system with the organic resin, thereby enhancing the high-temperature resistance and corrosion resistance of the coating. More preferably, the inorganic film-forming agent is potassium silicate with a modulus of 3.3 or lithium silicate with a modulus of 8, as silicates within this modulus range exhibit the best compatibility and synergistic effect with the organic resin. If the modulus is too low, the silicate's reactivity is too high, affecting the storage stability of the passivation solution; if the modulus is too high, the compatibility between the silicate and the resin decreases, affecting the uniformity of film formation.

[0023] Preferably, the pH adjuster is one or more of phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, oxalic acid, citric acid, and acetic acid. The pH adjuster adjusts the pH of the passivation solution to 4-5. This pH range ensures the stability of the film-forming polymer emulsion and the catalytic activity of the metal-amine catalyst. When the pH is below 4, the system is too acidic and may corrode the coating substrate; when the pH is above 5, the stability of the film-forming polymer emulsion decreases, and the latent catalyst is not sufficiently protonated, resulting in a shortened storage period at room temperature.

[0024] Preferably, the solid content of the passivation solution is 15-20%. This solid content range ensures both film-forming performance and coating uniformity and room temperature storage stability. If the solid content is too low, the film thickness per coat will be insufficient, and the corrosion resistance will decrease; if the solid content is too high, the system viscosity will increase, making roller coating difficult and reducing storage stability.

[0025] Preferably, the curing temperature of the passivation solution is 95-110℃, and the curing time is 10-20 seconds. These curing conditions meet the requirements of rapid thermal curing in a continuous galvanizing production line.

[0026] Preferably, the passivation solution further comprises an organic solvent. The organic solvent is selected from ethanol, isopropanol, or propylene glycol butyl ether. The organic solvent comprises 1-2 wt% ethanol, 1-2 wt% isopropanol, and 0.5-1 wt% propylene glycol butyl ether based on the total weight of the passivation solution. Ethanol and isopropanol adjust the viscosity and evaporation rate of the system, while propylene glycol butyl ether improves wettability and leveling. More preferably, the organic solvent comprises 1.5 wt% ethanol, 1.5 wt% isopropanol, and 0.8 wt% propylene glycol butyl ether; this ratio range optimizes the leveling and surface quality of the coating.

[0027] Preferably, the passivation fluid further comprises a self-lubricating agent. The addition of the self-lubricating agent can reduce the coefficient of friction of the coating surface and improve the processing performance of subsequent stamping processes.

[0028] Preferably, the passivation solution further includes an anti-precipitation agent to prevent the precipitation and stratification of inorganic film-forming agents and other solid components, thereby further improving the long-term storage stability of the passivation solution.

[0029] The present invention also provides a method for preparing the chromium-free passivation solution, comprising the following steps: Step S1: Disperse the metal salt in deionized water, add the nitrogen-containing compound ligand under stirring, and react at room temperature to obtain a metal-amine complex or metal-imidazolium complex solution. Step S2: Under stirring conditions, add the cosolvent and high modulus silicate solution to the complex solution obtained in step S1 in sequence, stir evenly to obtain a mixture; Step S3: Add organic solvent, film-forming aid and waterborne epoxy resin to the mixture from step S2, and stir until homogeneous; Step S4: Adjust the pH of the system obtained in step S3 to 4-6 using a pH adjuster; Step S5: Add film-forming polymer emulsion to the system obtained in step S4, adjust the solid content to the target value, and stir evenly to obtain the chromium-free passivation solution.

[0030] This preparation method follows the core principle of "complexation first, hybridization second, and mixing third." Step S1 involves the independent pre-formation of the metal-amine complex before adding the resin, ensuring a complete complexation reaction unaffected by the resin. Step S2 introduces a silicate hybrid precursor, using a co-solvent to promote uniform dispersion of the silicate in the complex solution. Step S3 introduces an aqueous epoxy resin. Step S4 adjusts the pH to ensure the amine groups are in an appropriate protonated state. Step S5 finally adds the film-forming polymer emulsion. Adding the film-forming polymer emulsion last avoids demulsification or localized gelation due to incomplete homogenization of the system. Simultaneously, the silicate and epoxy resin added first provide a stable dispersion medium for the film-forming polymer emulsion. This order of addition is crucial and is a key process feature ensuring the product's room temperature storage stability and coating uniformity.

[0031] Preferably, in step S1, the mass ratio of the metal salt to the nitrogen-containing compound ligand is 1:1.5 to 1:3. An excess of ligand ensures complete complexation of the metal ions, avoiding the adverse effects of free metal ions on the emulsion stability, and simultaneously provides additional amino crosslinking sites for subsequent curing.

[0032] Preferably, in step S1, the room temperature reaction time is 1.5-3 hours. More preferably, the room temperature reaction time is 2 hours.

[0033] Preferably, in step S2, the co-solvent comprises N,N-dimethylformamide and acetylacetone. N,N-dimethylformamide can promote the uniform dispersion of silicates in the complex solution, and acetylacetone can form auxiliary complexes with metal ions, avoiding self-polymerization and precipitation of silicates caused by excessively high local concentrations.

[0034] Preferably, in step S4, the pH adjuster adjusts the pH of the system to 5-6. This pH range ensures that the amine groups are at an appropriate degree of protonation, guaranteeing the stability of the film-forming polymeric emulsion upon subsequent addition.

[0035] Preferably, in step S5, the target solid content is 15-20%. This solid content range ensures coating uniformity and room temperature storage stability while guaranteeing film-forming performance.

[0036] Preferably, in step S5, a self-lubricating agent and / or an anti-settling agent are added before or simultaneously with the addition of the film-forming polymer emulsion. The self-lubricating agent is selected from one or more of amino silicone oil emulsion, cationic polyethylene wax emulsion, and molybdenum disulfide dispersion, and the anti-settling agent is a cationic PVA emulsion.

[0037] Finally, this invention also provides the application of the chromium-free passivation solution in the surface treatment of coated steel sheets. The curing temperature for this application is 90-110℃, and the curing time is 10-20 seconds. The treated coated steel sheet has a coating quality of 1.5-2 g / m², and the white rust time in the neutral salt spray test (NSST) is greater than 96 hours.

[0038] Preferably, the coated steel sheet is a galvanized steel sheet, an aluminized zinc steel sheet, or a galvanized aluminum magnesium steel sheet.

[0039] Compared with the prior art, the present invention has the following beneficial effects: First, it exhibits excellent stability during room temperature storage. Using a latent metal-amine / imidazolium complex as the curing catalyst, it is inert at room temperature and does not undergo cross-linking reactions with the resin system. The passivation solution can be stored for a long period (≥6 months) without gelling or precipitation.

[0040] Second, it features rapid low-temperature curing. Under process conditions of 90-110℃ and 10-20 seconds, the catalyst is rapidly activated, driving the formation of the IPN interpenetrating network and multi-component multi-crosslinking reaction, resulting in a curing efficiency significantly higher than that of existing water-based chromium-free passivation solutions.

[0041] Third, the coating is dense and highly corrosion resistant. Through the IPN structure formed by at least two film-forming polymers, combined with the ring-opening crosslinking and carboxyl-amino amidation crosslinking reactions of waterborne epoxy resin, and the filling of high-modulus silicate inorganic network, an organic-inorganic hybrid dense coating is formed. The neutral salt spray white rust time exceeds 96 hours, reaching or even surpassing the level of traditional chromate passivation.

[0042] Fourth, it is environmentally friendly. It contains no hexavalent chromium or other toxic heavy metals, and has low volatile organic compound (VOC) content, meeting environmental protection regulations. Detailed Implementation

[0043] The high-curing-activity chromium-free passivation liquid provided by this invention achieves a synergistic balance between room-temperature storage stability and low-temperature rapid curing through a three-in-one technical architecture consisting of a "latent curing catalytic system + multi-component film-forming polymer interpenetrating network (IPN) + organic-inorganic hybrid," resulting in excellent corrosion resistance. The following provides an overall overview from three dimensions: component system, mechanistic logic, and preparation process.

[0044] I. Component System The passivation solution of this invention consists of four main functional components: (1) Organic film-forming agent: comprising an aqueous epoxy resin and at least two film-forming polymer emulsions with different structures. The film-forming polymer emulsion is selected from at least two of cationic or nonionic acrylic emulsions, polyurethane emulsions, polyvinyl alcohol emulsions, phenolic resin emulsions, and amino silicone oil emulsions. The purpose of using at least two film-forming polymer emulsions is that different polymer segments interpenetrate and entangle with each other during the curing process to form a physical interpenetrating polymer network (IPN), making the coating film significantly more dense, tough, and adhesive than a single resin system. The aqueous epoxy resin (such as ethylene glycol diglycidyl ether or glycerol triglycidyl ether) provides epoxy groups as crosslinking sites, which undergo ring-opening crosslinking reactions with active hydrogen groups (such as amino, hydroxyl, and carboxyl groups) on the side chains of the film-forming polymer during the curing process, transforming the physical IPN structure into a chemical crosslinking network, endowing the coating film with excellent mechanical properties and resistance to media penetration. The total amount of film-forming polymer emulsion added is 5-10% of the total volume of the passivation solution, and the amount of waterborne epoxy resin added is 1%.

[0045] (2) Inorganic film-forming agent: a high-modulus silicate, preferably potassium silicate or lithium silicate with modulus of 3.3, 4.7, 8 or 12, added at 2% of the total volume of the passivation solution. During the curing process, the silicate undergoes dehydration condensation to form a Si-O-Si inorganic network, which interpenetrates and fills the organic IPN network, forming an organic-inorganic hybrid structure. This hybrid structure combines the flexibility of the organic coating with the dense barrier properties of the inorganic coating, which is the structural basis for the coating's salt spray resistance exceeding 96 hours. In addition, the layered / chain structure of the high-modulus silicate can extend the penetration path of the corrosive medium, further improving corrosion resistance.

[0046] (3) Latent curing catalyst: a metal-amine complex, formed by the pre-complexation of a metal salt and an amine compound in solution. The metal salt is selected from one or more of ammonium fluorotitanate, ammonium fluorozirconate, ammonium molybdate, cerium nitrate, and zinc nitrate; the amine compound includes, but is not limited to, polyethyleneimine, polydopamine, hexamethylenetetramine, hexamethylenediamine, triethylenediamine, tetramethylethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, monoethanolamine, diethanolamine, triethanolamine, ethylenediaminetetraacetic acid, liquid polyamide or imidazole, 2-methylimidazole, and dimethyl-4-ethylimidazole. The mass ratio of the metal salt to the ligand is 1:1.5 to 1:3, and the amount of catalyst added is 0.25-0.5% (mass-volume ratio) of the total volume of the passivation solution. This catalyst has three functions: First, under acidic conditions at room temperature, the amine groups are protonated and become inert, preventing cross-linking reactions with the resin and ensuring the passivation solution maintains room temperature storage stability for ≥6 months. Second, under heating conditions of 90-110℃, the protonated amine groups are deprotonated to release free amines, catalyzing multiple curing reactions such as ring-opening cross-linking of epoxy groups and carboxyl-amino amidation cross-linking, achieving rapid curing in 10-20 seconds. Third, metal ions (such as titanium, zirconium, cerium, etc.) in the complex can participate in the formation of inorganic networks or adsorb onto the metal surface to form a nano-protective layer, further enhancing corrosion resistance.

[0047] (4) pH adjuster: selected from one or more of phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, oxalic acid, citric acid, and acetic acid, to adjust the pH of the passivation solution to 4-6. This pH range provides a stable ionic environment for the film-forming polymer emulsion, preventing demulsification; on the other hand, it ensures that the amine groups are at an appropriate degree of protonation. If the pH is too high, the amine groups will not be sufficiently protonated, and the catalyst will have partial activity at room temperature, resulting in a shortened shelf life; if the pH is too low, the amine groups will be over-protonated, requiring a higher activation temperature or a longer activation time during curing.

[0048] In addition, the passivation solution may selectively contain the following auxiliary components: organic solvents (such as ethanol, isopropanol, propylene glycol butyl ether) to adjust the viscosity and evaporation rate of the system; self-lubricating agents to reduce the coefficient of friction of the coating surface and improve the subsequent stamping and forming performance; and anti-settling agents to prevent the sedimentation and stratification of inorganic film-forming agents and extend the shelf life.

[0049] II. Mechanism Logic The synergistic mechanism by which this invention achieves the triple technical effects of "room temperature stability + rapid low-temperature curing + high corrosion resistance" is as follows: (1) Room temperature storage stage: The passivation solution is in an acidic environment with a pH of 4-6, and the amine groups in the latent solidification catalyst exist in the form of protonated ammonium salts (-NH3). + The metal ions lose their nucleophilic ability to attack epoxy groups, thus allowing epoxy resins and multi-component film-forming polymers to coexist for extended periods without cross-linking. Simultaneously, the metal ions are "locked in" through complexation with amine ligands, preventing them from being released and causing ionic cross-linking or salting-out effects in the resin. This fundamentally solves the common problem of existing single-component aqueous passivation solutions being prone to gelation and precipitation at room temperature.

[0050] (2) Heating and curing stage: When the passivation solution is applied to the surface of the coated steel plate and heated to 90-110℃, the heat drives two parallel physicochemical processes: First, the protonated amine groups undergo a deprotonation reaction (-NH3). + → -NH3+ H + First, the physical IPN releases free amines with curing catalytic activity. Second, the amine group catalyzes the ring-opening of the epoxy group, and the epoxy group undergoes cross-linking reactions with the hydroxyl, carboxyl, and amino groups on the polymer side chain. At the same time, metal ions (such as titanium and zirconium) and silicates synergistically form a Si-OM inorganic network. The segment entanglement of the physical IPN and the covalent bonds of the chemical cross-linking occur simultaneously, and the coating is fully cured within 10-20 seconds.

[0051] (3) Service Stage: The cured coating forms a bicontinuous phase structure of "organic IPN network + inorganic silicon-oxygen network". The organic phase provides flexibility and adhesion, while the inorganic phase provides hardness and barrier properties. Corrosive media (Cl... - During the infiltration process, H2O and O2 are doubly blocked by the hydrophobic segments of the organic phase and the dense layer of the inorganic phase, significantly prolonging the infiltration path. Furthermore, the nano-adsorption layer formed by amine complexes at the metal interface further inhibits the initiation of interfacial corrosion. The synergistic effect of these three factors allows NSST white rust to persist for over 96 hours.

[0052] III. Preparation Process The preparation method of this invention follows the core principle of "complexation first, hybridization second, and mixing third," and the order of addition has a crucial impact on product performance. The overall process flow is as follows: Step S1 – Pre-formation of the metal-amine complex: A metal salt is dispersed in deionized water, and a nitrogen-containing compound ligand is added under stirring. The mass ratio of metal salt to ligand is 1:1.5 to 1:3 (ligand excess). The mixture is stirred at room temperature for 1.5-3 hours (preferably 2 hours) to obtain a metal-amine complex or metal-imidazolium complex solution. This step is performed independently before the addition of resin to ensure a complete complexation reaction without resin interference. The excess ligand not only ensures complete metal ion complexation but also provides additional amino crosslinking sites for subsequent curing.

[0053] Step S2 – Introduction of the silicate hybrid precursor: Under stirring conditions, a co-solvent (N,N-dimethylformamide and acetylacetone) and a high-modulus silicate solution are added sequentially to the complex solution from step S1, and the mixture is stirred until homogeneous. The co-solvent serves to promote uniform dispersion of silicate in the complex solution and prevent silicate self-polymerization and precipitation caused by excessively high local concentrations.

[0054] Step S3 – Introduction of epoxy resin: Add an organic solvent (such as ethanol), a film-forming aid (such as ethylene glycol butyl ether), and an aqueous epoxy resin to the mixture from step S2, and stir until homogeneous. The film-forming aid lowers the film-forming temperature of the system and improves the leveling and surface quality of the coating.

[0055] Step S4 – pH Adjustment: Adjust the pH of the system to 4-6 (preferably 5-6) using a pH adjuster to ensure that the amine groups are in a proper protonated state, thus ensuring the stability of the system when film-forming polymer emulsions are subsequently added.

[0056] Step S5 – Final addition of film-forming polymer emulsion and adjustment of solid content: Add the multi-component film-forming polymer emulsion (and optional self-lubricating agents and / or anti-settling agents) to the system of step S4, adjust the solid content to 15-20%, and stir evenly (preferably continue stirring for 20-40 minutes) to obtain the chromium-free passivation solution. The reason for adding the film-forming polymer emulsion last is that if the film-forming polymer emulsion is added before the silicate or epoxy resin, the film-forming polymer emulsion may demulsify or locally gel because the system is not completely homogenized; at the same time, the silicate and epoxy resin added first can be evenly dispersed under stirring, providing a stable dispersion medium for the film-forming polymer emulsion.

[0057] The order of adding materials in this preparation method cannot be reversed. If the order of adding materials is changed (for example, mixing all the resins first and then adding the catalyst), the pre-formation of the metal-amine complex and the uniform dispersion of the silicate cannot be achieved, and the room temperature storage stability and coating uniformity of the final product will be significantly deteriorated.

[0058] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, but this does not limit the present invention in any way. Any modifications or improvements made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0059] The processes, conditions, reagents, and experimental methods used in implementing this invention, except as specifically mentioned below, are all common knowledge and general knowledge in the field, and this invention does not have any particular limitations. Experimental methods in the embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer.

[0060] Unless otherwise stated, all technical terms and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. However, in the event of any conflict, the specification containing the definitions shall prevail.

[0061] The following is some information about the source of raw materials in the examples: Nonionic waterborne polyurethane emulsion: Anda Huatai Polyurethane 1704B; Cationic aqueous acrylic resin emulsion: Ingenic 007; Epoxy 669: CAS: 26403-72-5, Maclean's Reagent Website; Waterborne phenolic resin: Shengquan Group PF-2436; Amino silicone oil emulsion: Qingdao Xingye Organosilicon New Materials Co., Ltd.; Cationic polyethylene wax emulsion: Nanjing Tianshi New Material Technology Co., Ltd.; Cationic polyvinyl alcohol (PVA) emulsion: prepared according to the method described in the paper "Performance characterization of cationic polyvinyl alcohol acrylate copolymer emulsion dry strengthening agent": polyvinyl alcohol and glycidyltrimethylammonium chloride were reacted under alkaline conditions at 65°C for 2 h.

[0062] Example 1 Preparation of metal-amine complex: 0.1 g of zinc nitrate was dispersed in 60 ml of deionized water, and 0.3 g of hexamethylenetetramine (urotropine) was slowly added dropwise. The mixture was stirred at room temperature for 2 hours to obtain complex solution A.

[0063] Preparation of passivation solution: While stirring complex solution A at 200 rpm, add 3 ml of N,N-dimethylformamide, 3 ml of acetylacetone, and 2 ml of sodium silicate aqueous solution with a modulus of 3.3, and stir until homogeneous. Add 3 ml of ethanol, 3 ml of ethylene glycol butyl ether, and 1 ml of aqueous epoxy resin (epoxy 669), and stir until homogeneous. Adjust the pH to 5-6 with nitric acid and oxalic acid. Finally, add 5 ml of aqueous polyurethane emulsion and 5 ml of cationic aqueous acrylic resin, and add deionized water to a final volume of 100 ml. Stir for 30 minutes until homogeneous.

[0064] Example 2 Preparation of metal-amine complex: 0.1 g of ammonium fluorotitanate was dispersed in 60 ml of deionized water, and 0.3 g of triethylenetetramine (TETA) was slowly added dropwise. The mixture was stirred at room temperature for 2 hours to obtain complex solution A.

[0065] Preparation of passivation solution: While stirring complex solution A at 200 rpm, add 3 ml of N,N-dimethylformamide, 3 ml of acetylacetone, and 2 ml of lithium silicate aqueous solution with a modulus of 8, and stir until homogeneous. Add 3 ml of ethanol, 3 ml of ethylene glycol butyl ether, and 1 ml of aqueous epoxy resin (epoxy 669), and stir until homogeneous. Adjust the pH to 5-6 with nitric acid and oxalic acid. Finally, add 3 ml of aqueous phenolic resin and 6 ml of cationic aqueous acrylic resin, add deionized water to a final volume of 100 ml, and stir for 30 minutes until homogeneous. Example 3 Preparation of metal-amine complex: 0.1 g of zinc nitrate and 0.1 g of cerium nitrate were dispersed in 60 ml of deionized water, and 0.5 g of polyethyleneimine (PEI) was slowly added dropwise. The mixture was stirred at room temperature for 2 hours to obtain complex solution A.

[0066] Preparation of passivation solution: While stirring complex solution A at 200 rpm, add 3 ml of N,N-dimethylformamide, 3 ml of acetylacetone, and 2 ml of sodium silicate aqueous solution with a modulus of 3.3, and stir until homogeneous. Add 3 ml of ethanol, 3 ml of ethylene glycol butyl ether, and 1 ml of aqueous epoxy resin (epoxy 669), and stir until homogeneous. Adjust the pH to 5-6 with nitric acid and sulfuric acid. Finally, add 9 ml of aqueous polyurethane and 1 ml of amino silicone oil emulsion, and stir for 30 minutes until homogeneous.

[0067] Example 4 Preparation of metal-amine complex: 0.1 g of ammonium fluorozirconate was dispersed in 60 ml of deionized water, and 0.2 g of tetraethylenepentamine (TEPA) was slowly added dropwise. The mixture was stirred at room temperature for 2 hours to obtain complex solution A.

[0068] Preparation of passivation solution: While stirring complex solution A at 200 rpm, add 3 ml of N,N-dimethylformamide, 3 ml of acetylacetone, and 2 ml of sodium silicate aqueous solution with a modulus of 3.3, and stir until homogeneous. Add 3 ml of ethanol, 3 ml of ethylene glycol butyl ether, and 1 ml of aqueous epoxy resin (epoxy 669), and stir until homogeneous. Adjust the pH to 5-6 with oxalic acid and citric acid. Finally, add 4 ml of aqueous phenolic resin and 1 ml of amino silicone oil emulsion, and stir for 30 minutes until homogeneous.

[0069] Example 5 Preparation of metal-amine complex: 0.1 g of ammonium fluorozirconate was dispersed in 60 ml of deionized water, and 0.15 g of hexamethylenediamine (HMDA) was slowly added dropwise. The mixture was stirred at room temperature for 2 hours to obtain complex solution A.

[0070] Preparation of passivation solution: While stirring complex solution A at 200 rpm, add 3 ml of N,N-dimethylformamide, 3 ml of acetylacetone, and 2 ml of potassium silicate aqueous solution with a modulus of 3.7, and stir until homogeneous. Add 3 ml of ethanol, 3 ml of ethylene glycol butyl ether, and 1 ml of aqueous epoxy resin (epoxy 669), and stir until homogeneous. Adjust the pH to 5-6 with nitric acid and acetic acid. Finally, add 3 ml of cationic aqueous acrylic resin emulsion and 4 ml of cationic polyvinyl alcohol (PVA) emulsion, and stir for 30 minutes until homogeneous.

[0071] Example 6 Preparation of metal-amine complex: 0.1 g of zinc nitrate was dispersed in 60 ml of deionized water, and 0.3 g of ethylenediaminetetraacetic acid (EDTA) was slowly added dropwise. The mixture was stirred at room temperature for 2 hours to obtain complex solution A.

[0072] Preparation of passivation solution: While stirring complex solution A at 200 rpm, add 3 ml of N,N-dimethylformamide, 3 ml of acetylacetone, and 2 ml of lithium silicate aqueous solution with a modulus of 8, and stir until homogeneous. Add 3 ml of ethanol, 3 ml of ethylene glycol butyl ether, and 1 ml of aqueous epoxy resin (epoxy 669), and stir until homogeneous. Adjust the pH to 5-6 with oxalic acid and sulfuric acid. Finally, add 6 ml of nonionic aqueous polyurethane emulsion and 3 ml of cationic polyvinyl alcohol (PVA) emulsion dropwise, and stir for 30 minutes until homogeneous.

[0073] Comparative Example 1 The difference from Example 1 is that no metal salt was added, that is, the amine compound did not form a complex with the metal salt, and the other conditions were the same as in Example 1.

[0074] Comparative Example 2 The difference from Example 1 is that no film-forming polymer emulsion was added, while the other conditions were the same as in Example 1.

[0075] Comparative Example 3 The difference from Example 1 is that no metal salts and amine compounds were added to prepare the metal-complex, while the other conditions were the same as in Example 1.

[0076] Comparative Example 4 Passivation solution preparation: Same as in Example 1, except that only nonionic aqueous polyurethane emulsion is used as the film-forming polymer emulsion, with an addition amount of 10 ml, and the pH is adjusted to 5-6 with nitric acid and oxalic acid.

[0077] Comparative Example 5 The difference from Example 1 is that no pH adjuster was added to adjust the pH, while the other conditions are the same as in Example 1.

[0078] Comparative Example 6 The difference from Example 1 is that no amine compound was added, that is, the metal salt did not form a complex with the amine compound, and the other conditions were the same as in Example 1.

[0079] Performance testing Salt spray resistance test method: The prepared metal surface treatment solution is evenly applied to the surface of the galvanized sheet using a No. 4 wire rod. After baking in a 120℃ oven for 10 seconds, it is removed. The liquid coating amount is 10-20 g / m², and the dry film weight is 1-2 g / m². The steel sheet coated with the passivation solution is placed in a neutral salt spray test chamber containing 3.5% sodium chloride for corrosion resistance testing. The time it takes for the white rust area to reach 5% is recorded.

[0080] Table 1. Examples and Comparative Examples: Formulations and Salt Spray Performance

[0081] The neutral salt spray time (NSST) of Examples 1-6 all reached over 72 hours, with Examples 1, 2, 3, and 6 achieving an excellent level of 96 hours. This indicates that the metal surface treatment liquid provided by the present invention forms a dense, complete, and stable composite passivation film on the surface of the galvanized sheet, giving the substrate excellent corrosion resistance.

[0082] The neutral salt spray time (NSST) of Comparative Examples 1-6 was significantly lower than that of the Example Group, ranging from only 24 to 72 hours. Specifically, the NSST of Comparative Example 2 (lacking film-forming agent) and Comparative Example 5 (lacking pH adjuster) was only 24 hours. This result indicates that all components in the present invention (metal-amine complex, compounded film-forming polymer emulsion, pH adjuster) are indispensable, and there is a significant synergistic effect among them.

[0083] When the metal salt was completely omitted (Comparative Example 1), the NSST dropped sharply from 96 hours to 48 hours, a decrease of 50%. When both the metal salt and amine ligand were omitted (Comparative Example 3), the NSST was also only 48 hours. When the amine ligand was omitted (Comparative Example 6), the NSST was also only 48 hours. This indicates that the metal salt and amine ligand must coexist in the passivation solution and form a complex to exert their core anti-corrosion effect. Using either the metal salt or the amine ligand alone cannot achieve the excellent results of this invention. This complex is considered a key functional anchor point for subsequent cross-linking reactions with polymeric film-forming agents, silicates, and other components to form a dense, continuous passivation film.

[0084] When the polymer emulsion was completely omitted (Comparative Example 2), the NSST dropped sharply from 96 hours to 24 hours, a decrease of 75%, making it the single variable with the greatest impact among all components. This indicates that the film-forming polymer is the core skeletal structure for forming a physical barrier film and resisting the penetration of corrosive media. When only a single nonionic aqueous polyurethane emulsion was used (Comparative Example 4), the NSST was 72 hours, which was better than Comparative Example 2, but still significantly lower than Example 1 (96 hours). This invention does not simply provide a film-forming polymer; its key lies in the use of at least two polymer emulsions with different properties or ionic types for compounding (such as "nonionic aqueous polyurethane + cationic aqueous acrylic resin", "aqueous cationic phenolic resin + cationic acrylic emulsion", etc.). This compounding method can utilize the complementary advantages of different polymers in terms of crosslinking density, flexibility, adhesion, etc., to form a composite organic film with a denser structure, fewer defects, and better overall performance, demonstrating a synergistic effect of "1+1>2".

[0085] When the pH adjuster is omitted, i.e., the passivation solution pH is not adjusted to the acidic range of 5-6 (Comparative Example 5), the NSST drops sharply from 96 hours to 24 hours, which is comparable to the effect of Comparative Example 2, where all film-forming agents are omitted. This indicates that precisely controlling the pH value within the weakly acidic range of 5-6 is a necessary process condition for this technical solution, rather than a simple conventional choice. Only under such a pH environment can the metal-amine complex, silicate, and polymer emulsion coexist stably, react fully, and crosslink effectively in the most suitable state, thereby forming a uniform, dense, and strongly adherent passivation film. Once this step is skipped, the entire system will fail.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high solidification activity chromium-free passivation liquid, characterized by, It contains organic film-forming agents, inorganic film-forming agents, latent curing catalysts, and pH adjusters; The organic film-forming agent comprises an aqueous epoxy resin and a film-forming polymer emulsion, wherein the film-forming polymer emulsion is selected from at least two of cationic or nonionic acrylic emulsions, polyurethane emulsions, polyvinyl alcohol emulsions, phenolic resin emulsions, and amino silicone oil emulsions. The inorganic film-forming agent is a water-soluble silicate; The latent curing catalyst is a metal-amine complex, formed by the complexation of a metal salt and an amine compound; The pH adjuster adjusts the pH of the passivation solution to 4-6.

2. The chromium-free passivation solution according to claim 1, characterized in that, The metal salt is selected from one or more of ammonium fluorotitanate, ammonium fluorozirconate, ammonium molybdate, cerium nitrate, and zinc nitrate; The amine compound is one or more of the following: polyethyleneimine, polydopamine, triethanolamine, triethylamine, hexamethylenetetramine, hexamethylenediamine, triethylenediamine, tetramethylethylenediamine, diethylenetriamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, monoethanolamine, diethanolamine, ethylenediaminetetraacetic acid, liquid polyamide, imidazole, 2-methylimidazole, or dimethyl-4-ethylimidazole.

3. The chromium-free passivation solution according to claim 1, wherein The mass ratio of the metal salt to the amine compound is 1:1.5 to 1:3, and the amount of the latent curing catalyst added is 0.25-0.5% of the total volume of the passivation solution.

4. The chromium-free passivation solution according to claim 1, wherein The aqueous epoxy resin is ethylene glycol diglycidyl ether or glycerol triglycidyl ether; the amount of film-forming polymer emulsion added to the passivation solution is 5-10% of the total volume of the passivation solution, and the amount of aqueous epoxy resin added is 1% of the total volume of the passivation solution.

5. The chromium-free passivation solution according to claim 1, wherein The inorganic film-forming agent is potassium silicate or lithium silicate with a modulus of 3.3, 4.7, 8 or 12, and its addition amount is 2% of the total volume of the passivation solution.

6. The chromium-free passivation solution according to claim 1, wherein The passivation solution has a solid content of 15-20%; the pH adjuster is one or more of phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, oxalic acid, citric acid, and acetic acid.

7. The chromium-free passivation solution according to claim 1, wherein The passivation solution further comprises at least one of an organic solvent, a self-lubricating agent, and an anti-precipitation agent; the organic solvent is selected from ethanol, isopropanol, or propylene glycol butyl ether.

8. A method for preparing the chromium-free passivation solution according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step S1: Disperse the metal salt in deionized water, add the nitrogen-containing compound ligand under stirring, and react at room temperature to obtain a metal-amine complex or metal-imidazolium complex solution, wherein the mass ratio of the metal salt to the nitrogen-containing compound ligand is 1:1.5 to 1:

3. Step S2: Under stirring conditions, add the cosolvent and high modulus silicate solution to the complex solution obtained in step S1 in sequence, stir evenly to obtain a mixture; Step S3: Add organic solvent, film-forming aid and waterborne epoxy resin to the mixture from step S2, and stir until homogeneous; Step S4: Adjust the pH of the system obtained in step S3 to 4-6 using a pH adjuster; Step S5: Add film-forming polymer emulsion to the system obtained in step S4, adjust the solid content to 15-20%, and stir evenly to obtain the chromium-free passivation solution.

9. The production method according to claim 8, characterized by, In step S2, the cosolvent comprises N,N-dimethylformamide and acetylacetone.

10. Use of the chromium-free passivation solution according to any one of claims 1 to 7 or produced by the production method according to claim 8 or 9 for the surface treatment of plated steel sheets, characterized in that, The curing temperature is 90-110℃, and the curing time is 10-20 seconds; the coated steel sheet after treatment has a coating quality of 1.5-2 g / m², and the white rust time in the neutral salt spray test is greater than 96 hours; the coated steel sheet is a galvanized steel sheet, an aluminized zinc steel sheet, or a galvanized aluminum magnesium steel sheet.

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