High-perspiration-resistance alkaline chromium-free passivator for metal surface treatment as well as preparation method and application of high-perspiration-resistance alkaline chromium-free passivator

Abstract

The invention relates to the technical field of passivators, in particular to a high-perspiration-resistance alkaline chromium-free passivator for metal surface treatment and a preparation method and application of the high-perspiration-resistance alkaline chromium-free passivator. The invention discloses a high-perspiration-resistance alkaline chromium-free passivator for metal surface treatment. The high-perspiration-resistance alkaline chromium-free passivator is prepared from the following raw materials in parts by mass: 20 to 30 parts of waterborne polyurethane, 0.1 to 0.3 part of titanyl sulfate, 0.05 to 0.15 part of complexing agent, 6 to 12 parts of silica sol, 3 to 7 parts of microcapsule emulsion, 0.5 to 1 part of wetting agent, 0.5 to 1 part of defoaming agent and 40 to 75 parts of deionized water. The microcapsule emulsion contains an oil-in-water microcapsule which is formed by using high-activity isocyanate as a core material and quaternization modified chitosan-sodium alginate as a composite wall material through glutaraldehyde crosslinking and curing. A passivation film formed by the passivator is excellent in salt spray resistance, the artificial sweat test resistance color difference delta E is smaller than or equal to 1.03, the passivator is a single-component system, the storage stability is larger than or equal to 4 months in the environment of 50 DEG C, and the phenomena of gelation, abnormal viscosity rising and the like are avoided.

Description

Technical Field

[0001] This invention relates to the field of passivating agent technology, and in particular to a highly sweat- and alkali-resistant chromium-free passivating agent for metal surface treatment, its preparation method, and its application. Background Technology

[0002] In industries such as machinery manufacturing, automotive parts, and aerospace, corrosion and rust prevention treatment of metal workpiece surfaces is a crucial step in ensuring product quality and service life. In the field of metal surface corrosion prevention, chromium-based passivators have long dominated. While hexavalent chromium passivators possess excellent corrosion resistance and self-healing capabilities, their high toxicity, strong carcinogenicity, and severe environmental pollution have led to strict restrictions or bans under global regulations such as RoHS and REACH. Trivalent chromium passivators, as a transitional solution, have lower toxicity and meet current environmental requirements, but still contain the heavy metal chromium and lack self-healing capabilities, have limited film color, and have limited adaptability to deep drawing. On the other hand, existing acidic chromium-free passivators (such as molybdates and fluorotitanium / zirconate systems) achieve chromium-free operation, but their acidic environment easily causes pitting or hydrogen embrittlement in the metal substrate. The resulting passivation film lacks density and adhesion, easily cracking and peeling off during subsequent deep drawing, bending, and other forming processes. Furthermore, they have poor resistance to artificial sweat and damp heat aging, and still generate acidic waste liquid, limiting their environmental advantages.

[0003] Alkaline passivating agents are gradually replacing traditional acidic chromium-containing processes due to their advantages such as low corrosivity to the substrate and environmental friendliness. Currently, related technologies are mainly divided into chromium-containing two-component systems and chromium-free single-component systems. For example, CN116590701A discloses an AB two-component alkaline zinc plating black passivating agent, wherein component A contains 20-35 parts of trivalent chromium salt, 7-15 parts of complexing agent, 5-15 parts of pH adjuster, 5-15 parts of auxiliary blackening agent, 10-20 parts of oxidant, and 30-40 parts of water, and component B contains 15-25 parts of main blackening agent, 1-10 parts of film-forming promoter, and 70-90 parts of water. In use, components A and B are mixed to form a black passivation film. Although the solution achieves blackening and passivation under alkaline conditions, it still relies on trivalent chromium salts as the core film-forming component, failing to eliminate the use of heavy metals and not conforming to the trend of green manufacturing and chromium-free development. At the same time, the AB two-component design requires on-site preparation, which is cumbersome and difficult to apply to automated continuous production lines. Furthermore, the resulting film is mainly composed of inorganic chromium compounds, which lacks flexibility and is prone to cracking and falling off during subsequent deep drawing or bending processes.

[0004] On the other hand, CN117867484A discloses an alkaline chromium-free passivating agent with a pH of 8-10, prepared by compounding 8%-15% organic aqueous resin, 5%-10% silane coupling agent, 0.02%-2% molybdate aqueous solution, 0.05%-3% alkaline substance, and 0.02%-2% functional additives. Although this system achieves chromium-free treatment and utilizes silane coupling agent to enhance the organic-inorganic interfacial bonding force, the silane coupling agent is prone to hydrolysis and condensation reactions in the alkaline aqueous phase, leading to a rapid decline in its activity during storage. This, in turn, causes an increase in system viscosity, gelation, or a decrease in film-forming properties, making it difficult to meet the long shelf-life requirements of industrial production. Furthermore, this system lacks an effective cross-linking enhancement mechanism, resulting in limited density of the passivation film, and its protective performance remains insufficient under harsh conditions such as artificial sweat.

[0005] Therefore, existing alkaline passivation technology still fails to effectively meet multiple requirements such as single-component stability, complete chromium-free treatment, high cross-linking density, and high sweat resistance. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned shortcomings of the prior art by providing a highly sweat- and alkali-resistant chromium-free passivating agent for metal surface treatment, its preparation method, and its application.

[0007] The first objective of this invention is to provide a highly sweat-resistant, alkali-resistant, chromium-free passivating agent for metal surface treatment, comprising the following raw materials in parts by weight: 20-30 parts of waterborne polyurethane, 0.1-0.3 parts of titanium oxysulfate, 0.05-0.15-0.05 parts of complexing agent, 6-12 parts of silica sol, 3-7 parts of microcapsule emulsion, 0.5-1 part of wetting agent, 0.5-1 part of defoamer, and 40-75 parts of deionized water; The microcapsule emulsion contains oil-in-water microcapsules formed by cross-linking and curing with glutaraldehyde, using highly active isocyanate as the core material and quaternized modified chitosan-sodium alginate as the composite wall material.

[0008] Furthermore, the microcapsule particle size is 1–5 μm.

[0009] Furthermore, in the microcapsule emulsion, the mass of the microcapsules is 10% to 40%.

[0010] Furthermore, the highly active isocyanate is selected from at least one of isophorone diisocyanate, hexamethylene diisocyanate, and diphenylmethane diisocyanate.

[0011] Furthermore, the specific preparation method of the microcapsule emulsion is as follows: Take deionized water, add emulsifier and stir. Adjust the pH to 9.0-10.0 with ammonia to form an alkaline aqueous phase. Keep stirring and slowly add highly active isocyanate, adjust the speed to 800-1000 rpm, and emulsify at high speed for 20-30 minutes to form an oil-in-water emulsion. Add quaternized modified chitosan and sodium alginate to the emulsion, heat to 55-60℃ and stir until completely dissolved, and keep warm and stir for a period of time. Slowly add the curing agent glutaraldehyde and continue stirring at low speed for 2-2.5 hours, with the speed not exceeding 300 rpm, and maintain the pH at 9.0-10.0 throughout the process to obtain a microcapsule emulsion.

[0012] Furthermore, the silica sol contains 20% SiO2, and the particle size of the SiO2 is 15-25 nm.

[0013] Furthermore, the emulsifier is Tween-80.

[0014] Furthermore, the mass ratio of the sum of the masses of highly active isocyanate, quaternized modified chitosan, and sodium alginate is 1:(0.10-0.40).

[0015] Furthermore, the weight ratio of quaternized modified chitosan to sodium alginate is 5:3, and the amount of glutaraldehyde added is 1% to 2% of the total weight of the microcapsule emulsion.

[0016] A second objective of this invention is to provide a method for preparing the alkaline chromium-free passivating agent as described above, comprising the following steps: Preparation of microcapsule emulsions; The complexing agent is first dissolved in deionized water, then titanium oxysulfate is added and dispersed evenly to prepare a titanium-containing complex solution. The pH is then adjusted to 8-9 with ammonia water to obtain a solution containing titanium oxysulfate-citric acid complex. The mass ratio of complexing agent to titanium oxysulfate is 1:2. Deionized water was slowly added to aqueous polyurethane and stirred until completely dispersed. A solution containing a titanium sulfate-citric acid complex and silica sol were added sequentially and stirred to form a stable inorganic dispersion. The prepared microcapsule emulsion was slowly added and stirred at low speed. Finally, a wetting agent and an antifoaming agent were added and stirred to obtain the alkaline chromium-free passivating agent.

[0017] A third objective of this invention is to provide an application of the alkaline chromium-free passivating agent as described above in the anti-corrosion treatment of a metal substrate surface, characterized in that the alkaline chromium-free passivating agent is coated or sprayed onto the surface of the metal substrate and then dried at 80–120°C to form a film.

[0018] This invention successfully resolves the fundamental contradiction between the instability of highly active isocyanate crosslinking agents during storage and insufficient film-forming crosslinking in alkaline passivation systems by microencapsulating a highly active isocyanate crosslinking agent under alkaline conditions and combining it with a titanium oxysulfate-citric acid complex and an aqueous polyurethane with a specific glass transition temperature. This achieves a balance between single-component, long-life, and high-performance characteristics. Specific technical effects are as follows: The principle of this invention lies in achieving long-term stable storage and efficient in-situ release of highly active crosslinking agents in a single-component alkaline system through intelligent microcapsule technology and a multi-scale synergistic film-forming mechanism in an alkaline microenvironment, thereby constructing a passivation film with high density, high flexibility, and high corrosion resistance. Specifically, in an alkaline aqueous phase with pH 9.0–10.0, highly active isocyanate is emulsified at high speed to form oil droplets. Quaternized chitosan (positively charged) and sodium alginate (negatively charged) form a composite wall layer on its surface through electrostatic self-assembly, followed by crosslinking and curing with glutaraldehyde to obtain structurally complete and pH-stable microcapsules. During room temperature storage, these microcapsules effectively isolate isocyanate from aqueous components, preventing premature hydrolysis or gelation and ensuring the stability of the system for more than 6 months. During the subsequent drying and film formation process (80~120℃), the microcapsule wall material softens and ruptures upon heating, releasing highly active –NCO groups. These groups rapidly undergo addition reactions with –OH and –NH2 in the waterborne polyurethane, forming a high-density urethane / urea bond crosslinking network, significantly improving the film's density and chemical inertness (e.g., ...). Figure 2 (As shown). After the microcapsule wall material ruptures during the high-temperature film-forming stage (80~120℃), the wall material residue consists of irregular porous polymer particles. The particle size matches the size of the original micropores inside the passivation film, efficiently filling micropores, cracks, and interface defects caused by solvent evaporation and cross-linking shrinkage during film preparation, thus reducing Cl... - SO4² - The permeation rate of corrosive media such as sweat ions is significantly reduced, greatly improving the membrane's resistance to salt spray and artificial sweat. Simultaneously, the wall material residue molecular chains retain a large number of incompletely cross-linked amino (-NH2), hydroxyl (-OH), and quaternary ammonium (-N) groups. +(CH3)3), in which amino and hydroxyl groups can form stable hydrogen bonds with the hydroxyl groups (-OH) on the oxide layer of the metal substrate (such as galvanized sheet, aluminum alloy), improving the adhesion between the coating and the metal substrate. In addition, titanium oxysulfate and citric acid are pre-complexed to form a soluble chelate, which is uniformly decomposed into nano-sized TiO2 or titanium hydroxy oxide during film formation, and embedded in the organic network together with silica to play the role of inorganic skeleton filling and interface reinforcement; flexible polyurethane emulsion is selected to ensure that the film layer is in a highly elastic state at room temperature, and combined with a cross-linking structure with certain dynamic characteristics, the passivation film can extend synchronously with the substrate without cracking during deep drawing or bending deformation. Finally, the dense cross-linking network, nano-inorganic filler, strong interface adhesion and microcapsule quaternized modified chitosan-sodium alginate wall material residue together constitute a multi-layer protective barrier: not only significantly extending Cl - It bypasses the penetration pathways of corrosive media such as H2O, neutralizes the weak acidity of artificial sweat, and inhibits ion migration, thereby achieving excellent resistance to salt spray, sweat, and processing adaptability. This multi-scale, multi-mechanism synergistic design fundamentally solves the technical bottleneck of existing alkaline passivating agents in achieving a balance between stability, activity, and environmental friendliness.

[0019] The passivation film formed by the passivating agent of the present invention has excellent salt spray resistance and a color difference ΔE ≤ 1.03 in artificial sweat resistance test.

[0020] The passivating agent of the present invention is a single-component system, which has a storage stability of ≥4 months at 50°C and does not exhibit gelation, abnormal viscosity increase, or other phenomena. Attached Figure Description

[0021] Figure 1 This is a diagram illustrating the preparation mechanism of microcapsule emulsions. Figure 2 This is a diagram illustrating the crosslinking mechanism of alkaline passivating agents. Detailed Implementation

[0022] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0023] The preparation of alkaline passivating agents includes the following steps: (1) Preparation of microcapsule emulsion Take the prescribed amount of deionized water, add the emulsifier, and stir at 300 rpm for 10 minutes. Adjust the pH to 9.0–10.0 with ammonia to form an alkaline aqueous phase. While stirring, slowly add the highly active isocyanate crosslinking agent, adjust the speed to 800–1000 rpm, and emulsify at high speed for 20–30 minutes to form an oil-in-water emulsion with a particle size of 1–5 μm (maintain pH = 9.0–10.0 throughout the process). Add quaternized modified chitosan and sodium alginate to the emulsion, heat to 55℃–60℃, and stir for 30 minutes until completely dissolved. Keep stirring at this temperature for 1.5 hours to allow the wall material to condense and form a film on the surface of the oil droplets using electrostatic interaction. Slowly add the curing agent glutaraldehyde and continue stirring for 2–2.5 hours to allow the wall material to crosslink and cure, maintaining pH 9.0–10.0 throughout the process to prevent the wall material from dissolving. A 37% microcapsule emulsion is formed.

[0024] Figure 1 The preparation mechanism of emulsion-coated crosslinking agents, such as Figure 1 As shown, the quaternized chitosan molecular chain contains a large number of amino groups (-NH2). The aldehyde group (-CHO) of glutaraldehyde reacts with the amino groups in a Schiff base reaction to form a stable covalent cross-linked structure. The reaction formula is as follows: R1-NH2+OHC-(CH2)3-CHO+H2N-R2→R1-N=CH-(CH2)3-CH=N-R2+2H2O In the formula, R1 and R2 represent the molecular chain segments of modified chitosan. Sodium alginate molecules contain hydroxyl groups (-OH). The aldehyde group of glutaraldehyde undergoes a condensation reaction with the hydroxyl group, further strengthening the cross-linking network of the wall material. The reaction formula is as follows: R3-OH+OHC-(CH2)3-CHO+HO-R4→R3-O-CH-(CH2)3-CH-O-R4+2H2O In the formula, R3 and R4 represent molecular chain segments of sodium alginate. (2) Preparation of a solution containing titanium sulfate-citric acid complex Take 1g of citric acid and 2g of titanium oxysulfate. First, add 1g of citric acid to 97g of deionized water and stir until completely dissolved. Then, add 2g of titanium oxysulfate while stirring continuously. After stirring and dispersing evenly, heat the system to 50℃ and stir at a constant temperature for 30 min. Cool to room temperature to obtain a 3 wt% titanium citrate complex solution. Then, adjust its pH to 8-9 using 25% ammonia water.

[0025] (3) Preparation of alkaline passivating agent Take the prescribed amount of deionized water and place it in a mixing vessel. Slowly add the aqueous polyurethane and stir for 5-10 minutes to ensure complete dispersion of the polyurethane. Add titanium oxysulfate and silica sol in sequence, adjust the speed to 300-350 r / min, and stir for 5-10 minutes to ensure uniform dispersion of the inorganic components and form a stable inorganic dispersion. Slowly add the microcapsule emulsion prepared under alkaline conditions and maintain low-speed stirring for 5-10 minutes to avoid damage to the microcapsule wall material and ensure uniform dispersion. Finally, add the wetting agent and defoamer and stir for 5 minutes to obtain the passivating agent product.

[0026] Example 1 Preparation of microcapsule emulsions Take 63 parts of deionized water and place it in an emulsification vessel. Add 3 parts of emulsifier Tween-80 and stir at 300 rpm for 10 min. Adjust the pH to 9.5 with ammonia. Slowly add 25 parts of isophorone diisocyanate (IPDI) and adjust the stirring speed to 900 rpm. Emulsify at high speed for 25 min to form an oil-in-water emulsion with a particle size of 3 μm. Maintain the pH at 9.5 throughout the process. Add 5 parts of quaternized modified chitosan and 3 parts of sodium alginate. Heat to 58℃ and stir at 300 rpm for 30 min until dissolved. Keep warm and stir for 1.5 h. Add 1 part of glutaraldehyde and continue stirring for 2 h. Maintain the pH at 9.5 to obtain a microcapsule emulsion with a solid content of 37%.

[0027] Preparation of solutions containing titanium sulfate-citric acid complex Take 1g of citric acid and 2g of titanium oxysulfate. First, add 1g of citric acid to 97g of deionized water and stir until completely dissolved. Then, add 2g of titanium oxysulfate while stirring continuously. After stirring and dispersing evenly, heat the system to 50℃ and stir at a constant temperature for 30 min. Cool to room temperature to obtain a 3 wt% titanium citrate complex solution. Then, adjust its pH to 8-9 using 25% ammonia water.

[0028] Preparation of alkaline passivating agents Take 52 parts of deionized water, add 30 parts of waterborne polyurethane under stirring at 200 rpm, stir for 8 min, add 5 parts of solution containing titanium sulfate-citric acid complex and 8 parts of 20% concentration silica sol, stir at 320 rpm for 8 min; add 4 parts of microcapsule emulsion under low speed stirring, stir for 8 min; add 0.5 parts of wetting agent, add 1 part of organosilicon defoamer (dimethyl silicone oil type), stir for 5 min, and filter to obtain the finished product.

[0029] Example 2 The isophorone diisocyanate (IPDI) used in the preparation of the microcapsule emulsion in Example 1 was replaced with an equal amount of hexamethylene diisocyanate (HDI), and everything else was the same as in Example 1.

[0030] Example 3 The isophorone diisocyanate (IPDI) used in the preparation of the microcapsule emulsion in Example 1 was replaced with an equal amount of diphenylmethane diisocyanate (MDI), and all other aspects were the same as in Example 1.

[0031] Comparative Example 1 Take 55 parts of deionized water, add 30 parts of waterborne polyurethane under stirring at 200 r / min, stir for 8 min, add 5 parts of the solution containing titanium sulfate-citric acid complex prepared in Example 1 and 8 parts of silica sol, stir at 320 r / min for 8 min; add 1 part of isophorone diisocyanate (IPDI) under low speed stirring, stir for 8 min; add 0.5 parts of wetting agent, add 0.5 parts of defoamer, stir for 5 min, and filter to obtain the finished product.

[0032] Comparative Example 2 Take 55 parts of deionized water, add 30 parts of waterborne polyurethane under stirring at 200 r / min, stir for 8 min, add 5 parts of the solution containing titanium sulfate-citric acid complex prepared in Example 1 and 8 parts of silica sol, stir at 320 r / min for 8 min; add 1 part of hexamethylene diisocyanate (HDI) under low speed stirring, stir for 8 min; add 0.5 parts of wetting agent, add 0.5 parts of defoamer, stir for 5 min, and filter to obtain the finished product.

[0033] Comparative Example 3 Take 55 parts of deionized water, add 30 parts of waterborne polyurethane under stirring at 200 r / min, stir for 8 min, add 5 parts of the solution containing titanium sulfate-citric acid complex prepared in Example 1 and 8 parts of silica sol, stir at 320 r / min for 8 min; add 1 part of diphenylmethane diisocyanate (MDI) under low speed stirring, stir for 8 min; add 0.5 parts of wetting agent, add 0.5 parts of defoamer, stir for 5 min, and filter to obtain the finished product.

[0034] Comparative Example 4 This embodiment provides an alkaline passivating agent and its preparation method. The composition and preparation method of the passivating agent are the same as those in Example 1, except that the oxytitanium sulfate-citric acid complex is not added.

[0035] Comparative Example 5 This embodiment provides an alkaline passivating agent and its preparation method. The composition and preparation method of the passivating agent are the same as those in Example 1, except that silica sol is not added.

[0036] Comparative Example 6 This embodiment provides an alkaline passivating agent and its preparation method. The composition and preparation method of the passivating agent are the same as those in Example 2, except that the oxytitanium sulfate-citric acid complex is not added.

[0037] Comparative Example 7 This embodiment provides an alkaline passivating agent and its preparation method. The composition and preparation method of the passivating agent are the same as those in Example 2, except that silica sol is not added.

[0038] Comparative Example 8 This embodiment provides an alkaline passivating agent and its preparation method. The composition and preparation method of the passivating agent are the same as those in Example 3, except that the oxytitanium sulfate-citric acid complex is not added.

[0039] Comparative Example 9 This embodiment provides an alkaline passivating agent and its preparation method. The composition and preparation method of the passivating agent are the same as those in Example 3, except that silica sol is not added.

[0040] Comparative Example 10 The amount of microcapsule emulsion added to the alkaline passivating agent in Example 1 was adjusted from 4 parts to 2 parts, and all other aspects were the same as in Example 1.

[0041] Comparative Example 11 The amount of microcapsule emulsion added to the alkaline passivating agent in Example 1 was adjusted from 4 parts to 8 parts, and all other aspects were the same as in Example 1.

[0042] Comparative Example 12 The amount of microcapsule emulsion added to the alkaline passivating agent in Example 2 was adjusted from 4 parts to 2 parts, and all other aspects were the same as in Example 2.

[0043] Comparative Example 13 The amount of microcapsule emulsion added to the alkaline passivating agent in Example 2 was adjusted from 4 parts to 8 parts, and all other aspects were the same as in Example 2.

[0044] Comparative Example 14 The amount of microcapsule emulsion added to the alkaline passivating agent in Example 3 was adjusted from 4 parts to 2 parts, and all other aspects were the same as in Example 3.

[0045] Comparative Example 15 The amount of microcapsule emulsion added to the alkaline passivating agent in Example 2 was adjusted from 4 parts to 8 parts, and all other aspects were the same as in Example 2.

[0046] Performance Tests and Results Test methods Storage stability test Test conditions: The passivating agent samples prepared in each example and comparative example were sealed and placed in a constant temperature oven at 50°C for accelerated aging test.

[0047] Failure determination criteria: Viscosity determination: A rotational viscometer (NDJ-5S type) was used to test the initial viscosity of the sample and the viscosity at different time points during aging at 25℃ in accordance with GB / T 2794-2013 "Determination of viscosity of adhesives". When the viscosity of the sample changes by more than ±50% from the initial viscosity, it is determined that the storage stability has failed. Appearance and film-forming performance assessment: Regularly observe the appearance of the sample. If layering, precipitation, gelation, or clumping occurs and the sample cannot be restored to a uniform and stable state after stirring, it is considered to have failed. At the same time, the aged sample is used to form a film on the surface of a metal substrate using conventional processes. If the salt spray performance of the film layer is greater than 20% after 120h and the sweat resistance performance ΔE is greater than 3, the passivating agent is considered to have failed.

[0048] Test duration: Continue to observe the sample until the above-mentioned failure phenomenon appears, and record the time the sample remains stable; if no failure phenomenon appears within 6 months, stop the test and record the storage stability ≥ 6 months.

[0049] Corrosion resistance test Test standard: The test shall be conducted in accordance with the neutral salt spray test (NSS) method in GB / T 10125-2021 "Civilized Atmosphere Corrosion Test - Salt Spray Test".

[0050] Test sample preparation: The passivating agents of each embodiment and comparative example were uniformly coated onto an aluminized zinc substrate (75mm × 150mm × 6mm). The substrate was then dried at 260℃ (plate temperature 80℃-100℃) for 6 seconds to form a passivation film. The film thickness was controlled at 1.2-1.5 g / m². 3 Test conditions: Salt spray chamber temperature 35℃, salt solution concentration 5% (mass fraction) NaCl solution, continuous spraying, droplet deposition rate 1-2 mL / (80 cm²) h).

[0051] Test duration: 120 hours of continuous testing.

[0052] Evaluation method: After the test, remove the steel sheet, rinse the surface salt with deionized water, blow dry and observe the corrosion of the steel sheet surface, and record the corrosion level: no corrosion (corrosion rate ≤1%), slight corrosion (1% < corrosion rate ≤2%), moderate corrosion (2% < corrosion rate ≤5%), severe corrosion (corrosion rate >5%).

[0053] Sweat resistance test Test standard: The test was conducted in accordance with the artificial sweat formula (ISO 3160-2 Appendix A). The artificial sweat formula is as follows: 20 g / L of analytical grade sodium chloride; 5 g / L of urea (CH4N2O); 2.5 g / L of analytical grade acetic acid; 15 g / L of analytical grade racemic lactic acid; and then an 80 g / L sodium hydroxide solution was added to adjust the pH value to 4.7.

[0054] Test sample preparation: consistent with the preparation of corrosion resistance test samples, with a passivation film thickness of 1.0-1.5 g / m. 3 .

[0055] Test conditions: The sample was completely immersed in artificial sweat at 40°C for 1 hour, during which the sweat temperature was kept stable.

[0056] Test method: A colorimeter (CR-400 type) was used, and the color difference ΔE before and after immersion was measured according to GB / T 11186.3-1989 "Measurement of paint film color - Part 3: Calculation of color difference" (ΔE=[(ΔL)). )²+(Δa )²+(Δb )²] 1 / 2 Where ΔL is the lightness difference, Δa is the red-green difference, and Δb (The difference between yellow and blue).

[0057] Evaluation criteria: The smaller the ΔE value, the better the sweat resistance of the sample; ΔE≤1.0 is excellent, 1.0<ΔE≤2.0 is good, 2.0<ΔE≤3.0 is acceptable, and ΔE>3.0 is unacceptable.

[0058] Test Results The performance test results of each embodiment and comparative example are shown in Table 1 below: Table 1 Performance Test Results Table 1

[0059] As can be seen from the performance test results of the comparative examples and embodiments above, the technical solution of the present invention, which uses microencapsulated modified isocyanate, functional inorganic filler compounding and alkaline system construction, significantly improves the comprehensive performance of alkaline passivating agent. Compared with the existing technology of directly adding small molecule isocyanate (comparative examples 1-3), it has outstanding inventiveness and practicality.

[0060] Specifically, Examples 1-3 of this invention employ quaternized modified chitosan-sodium alginate microcapsules to encapsulate isocyanates (IPDI, HDI, MDI), effectively addressing the technical pain points of easy hydrolysis and poor storage stability of small molecule isocyanates. This improves the storage stability of the passivating agent at 50°C from 0.5-1 month to 4-7 months, with Example 1 using IPDI as the core material achieving a storage stability of 6 months. Furthermore, the dense film structure formed by the microcapsules on the metal surface enhances the corrosion resistance of the passivating agent from corrosion... Optimization to a corrosion-free state with a rate >20% reduced the perspiration resistance color difference ΔE value from 5.63-6.54 to 0.47-3.45. The combination of titanium oxysulfate-citric acid complex and silica sol exerted a synergistic effect, effectively filling the pores of the passivation film and enhancing the film's density and resistance to media penetration. After removing any one of the fillers (comparative examples 4-5, 6-7, 8-9), the perspiration resistance ΔE value of the passivating agent significantly increased, and slight corrosion occurred in some groups, further confirming the enhancing effect of the two inorganic fillers on the protective performance. This is mainly because the titanium dioxide generated in situ from 20 nm nano-silica and titanium oxysulfate constructs a dense protective structure through a dual mechanism of graded filling and interfacial co-deposition.

[0061] Through performance testing and analysis of Examples 4-9, this invention clarifies the core correlation between the amount of microcapsule emulsion and product performance: When the amount of microcapsule emulsion is 2 parts (Comparative Examples 10, 12, 14), the passivating agent has a storage stability of up to 6 months at 50°C, but the 120-hour neutral salt spray test shows moderate corrosion (2% < corrosion ≤ 5%), and the 48-hour perspiration resistance test ΔE value is 3.24-4.15, indicating only average protective performance; when the amount of microcapsule emulsion is increased to 8 parts (Comparative Examples 11, 13, 15), the storage stability decreases to 1-2 months, but the 120-hour neutral salt spray test shows no corrosion (corrosion ≤ 1%), and the 48-hour perspiration resistance test ΔE value is only 0.34-0.78, indicating a significant improvement in corrosion resistance and perspiration resistance. At low dosages, the system exhibits mild cross-linking and a longer shelf life, but the membrane layer is not dense enough. At high dosages, the membrane layer is fully cross-linked with fewer defects, resulting in superior protective performance. The appropriate microcapsule dosage can be selected based on the storage and protection requirements of the actual application scenario.

[0062] Considering the three key indicators of storage stability, corrosion resistance, and perspiration resistance, Example 1 is the optimal formulation. Through the synergistic effect of microencapsulated emulsion, titanium sulfate oxychloride-citric acid complex, and silica sol, a stable passivating agent system is formed in an alkaline system with pH=9.5. The storage stability reaches 6 months, the corrosion resistance is non-corrosive, and the perspiration resistance ΔE is only 0.47. The overall protective performance is optimal, fully demonstrating the significant advantages of the technical solution of this invention in improving the stability and protective effect of the passivating agent.

[0063] For any points not covered above, existing technologies shall apply.

[0064] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A highly sweat- and alkali-resistant chromium-free passivating agent for metal surface treatment, characterized in that, The raw materials include the following parts by weight: 20-30 parts of waterborne polyurethane, 0.1-0.3 parts of titanium oxysulfate, 0.05-0.15 parts of complexing agent, 6-12 parts of silica sol, 3-7 parts of microcapsule emulsion, 0.5-1 part of wetting agent, 0.5-1 part of defoamer, and 40-75 parts of deionized water; The microcapsule emulsion contains oil-in-water microcapsules formed by cross-linking and curing with glutaraldehyde, using highly active isocyanate as the core material and quaternized modified chitosan-sodium alginate as the composite wall material.

2. The alkaline chromium-free passivating agent as described in claim 1, characterized in that, The microcapsule particle size is 1–5 μm.

3. The alkaline chromium-free passivating agent as described in claim 1, characterized in that, In the microcapsule emulsion, the mass of the microcapsules is 10-40%.

4. The alkaline chromium-free passivating agent as described in claim 1, characterized in that, The highly active isocyanate is selected from at least one of isophorone diisocyanate, hexamethylene diisocyanate, and diphenylmethane diisocyanate.

5. The alkaline chromium-free passivating agent as described in claim 1, characterized in that, The specific preparation method of the microcapsule emulsion is as follows: Take deionized water, add emulsifier and stir. Adjust the pH to 9.0-10.0 with ammonia to form an alkaline aqueous phase. Keep stirring and slowly add highly active isocyanate, adjust the speed to 800-1000 rpm, and emulsify at high speed for 20-30 minutes to form an oil-in-water emulsion. Add quaternized modified chitosan and sodium alginate to the emulsion, heat to 55-60℃ and stir until completely dissolved, and keep warm and stir for a period of time. Slowly add the curing agent glutaraldehyde and continue stirring at low speed for 2-2.5 hours, with the speed not exceeding 300 rpm, and maintain the pH at 9.0-10.0 throughout the process to obtain a microcapsule emulsion.

6. The alkaline chromium-free passivating agent as described in claim 5, characterized in that, The silica sol contains 20% SiO2, and the particle size of SiO2 is 15-25 nm.

7. The alkaline chromium-free passivating agent as described in claim 5, characterized in that, The mass ratio of the sum of the masses of highly active isocyanate, quaternized modified chitosan, and sodium alginate is 1:(0.1~0.4).

8. The alkaline chromium-free passivating agent as described in claim 5, characterized in that, The weight ratio of quaternized modified chitosan to sodium alginate is 5:3, and the amount of glutaraldehyde added is 1% to 2% of the total weight of the microcapsule emulsion.

9. A method for preparing an alkaline chromium-free passivating agent as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Preparation of microcapsule emulsions; The complexing agent is first dissolved in deionized water, then titanium oxysulfate is added and dispersed evenly to prepare a titanium-containing complex solution. The pH is then adjusted to 8-9 with ammonia water to obtain a solution containing titanium oxysulfate-citric acid complex. The mass ratio of complexing agent to titanium oxysulfate is 1:

2. Deionized water was slowly added to aqueous polyurethane and stirred until completely dispersed. A solution containing a titanium sulfate-citric acid complex and silica sol were added sequentially and stirred to form a stable inorganic dispersion. The prepared microcapsule emulsion was slowly added and stirred at low speed. Finally, a wetting agent and an antifoaming agent were added and stirred to obtain the alkaline chromium-free passivating agent.

10. The application of an alkaline chromium-free passivating agent as described in any one of claims 1-8 in the anti-corrosion treatment of a metal substrate surface, characterized in that, An alkaline chromium-free passivating agent is coated or sprayed onto the surface of the metal substrate, and then dried at 80–120°C to form a film.

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