Metal surface treatment liquid based on tannic acid as well as preparation method and application of metal surface treatment liquid

Abstract

The invention discloses metal surface treatment liquid based on tannic acid as well as a preparation method and application of the metal surface treatment liquid, and belongs to the technical field of metal surface treatment. The metal surface treatment liquid based on the tannic acid comprises the following components in percentage by mass volume: 3-12% of a composite polyphenol system, 2-6% of a multi-element metal salt system, 2-5% of a slow release system, 5-12% of a composite organic solvent system, 4-10% of a composite additive system, a pH regulator for regulating the pH to 3.5-4.5 and the balance of water, the unit of the mass-volume percent is g / mL; the composite polyphenol system comprises tannic acid and at least one natural polyphenol of which the reducibility is higher than that of the tannic acid; the composite additive system comprises a surfactant, a lamellar nano reinforcing agent and a rheology modifier. The metal surface treatment liquid based on the tannic acid is used for metal surface treatment, is good in film forming property and high in corrosion resistance and has self-repairing capacity.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to a metal surface treatment liquid based on tannic acid, its preparation method, and its application. Background Technology

[0002] In the drawing of metal wire, traditional processes require pickling to remove oxide scale, followed by phosphating and saponification to form a lubricating film. This process is cumbersome and highly polluting (e.g., pickling waste liquid, phosphating slag). In recent years, research has proposed an in-situ oxide scale conversion technology. Through specific chemical or electrochemical treatments, the surface oxide scale is directly converted into a lubricating film (e.g., Fe3O4-based or composite oxide layer), replacing multiple pretreatment steps in one step. This technology not only eliminates the pickling step and reduces waste acid emissions, but also achieves efficient lubrication by controlling the conversion film structure (e.g., porosity, low shear strength), significantly improving drawing efficiency (reducing the coefficient of friction by more than 30%) and aligning with green manufacturing trends. For example, using acidic chelating agents, alkaline oxidants, or low-temperature molten salt treatment can generate a uniform self-lubricating film on the steel wire surface, which can be directly used for drawing, offering both environmental and cost advantages. However, current acidic chelating agents mostly use single-component tannic acid combined with other functional components, resulting in poor film formation, poor corrosion resistance, and no self-healing ability. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a tannic acid-based metal surface treatment liquid, its preparation method, and its application. This solves the problems of poor film formation, poor corrosion resistance, and lack of self-healing ability in current tannic acid-based metal surface treatment liquids.

[0004] This invention uses a special formula and processing technology to form a rapid conversion film layer, replacing the conventional tannic acid conversion, which promotes the direct conversion of oxide scale into a film layer. It adds chelating and slow-release substances and film-forming substances, replacing the conventional acid washing-water washing-phosphating-water washing-saponification process.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] This invention provides a tannic acid-based metal surface treatment liquid, comprising the following components by mass-volume percentage:

[0007] Complex polyphenol system 3-12%

[0008] Multi-metal salt system 2-6%

[0009] Sustained-release system 2-5%

[0010] 5-12% of the compound organic solvent system

[0011] 4-10% of the compound additive system

[0012] Adjust the pH to 3.5-4.5 using a pH adjuster.

[0013] The remainder is water;

[0014] The unit for mass-volume percentage is g / mL;

[0015] The composite polyphenol system includes tannic acid and at least one natural polyphenol with stronger reducing power than tannic acid.

[0016] The composite additive system includes surfactants, layered nano-reinforcing agents, and rheology modifiers.

[0017] Preferably, the natural polyphenols with stronger reducing properties than tannic acid include at least one of gallic acid, catechin, ellagic acid, and caffeic acid.

[0018] Preferably, the mass ratio of tannic acid to natural polyphenols with stronger reducing power than tannic acid in the composite polyphenol system is (2-8):(1-4).

[0019] Preferably, the multi-metal salt system includes at least one of cerium salt and lanthanum salt and a zinc salt.

[0020] More preferably, the mass ratio of the total amount of cerium salt and lanthanum salt to zinc salt in the multi-metal salt system is (1.5-4.5):(0.5-1.5).

[0021] Preferably, the sustained-release system includes a pH-responsive unit and an ion-responsive unit.

[0022] More preferably, the pH-responsive unit is a β-cyclodextrin-benzotriazole inclusion complex.

[0023] More preferably, the preparation method of the β-cyclodextrin-benzotriazole inclusion complex is as follows: benzotriazole is mixed with a β-cyclodextrin solution, heated and ultrasonically treated, cooled and crystallized, filtered, washed and dried to obtain the β-cyclodextrin-benzotriazole inclusion complex.

[0024] More preferably, the ion response unit is a sodium alginate-sodium molybdate microcapsule.

[0025] More preferably, the preparation method of the sodium alginate-sodium molybdate microcapsules is as follows: sodium alginate solution and sodium molybdate solution are mixed and stirred, added dropwise to calcium chloride solution, stirred and solidified, filtered, washed and dried to obtain sodium alginate-sodium molybdate microcapsules.

[0026] More preferably, the mass ratio of the pH-responsive unit to the ion-responsive unit in the sustained-release system is (1-3):(1-2).

[0027] Preferably, the composite organic solvent system includes a penetrant, a coupling agent / stabilizer, and a humectant / film-forming aid.

[0028] More preferably, the penetrant includes at least one of ethanol and isopropanol.

[0029] More preferably, the coupling agent / stabilizer includes at least one of γ-valerolactone and dipropylene glycol methyl ether (DPM).

[0030] More preferably, the humectant / film-forming aid includes at least one of glycerin and polyethylene glycol.

[0031] More preferably, the molecular weight of the polyethylene glycol is 100-2000.

[0032] More preferably, the mass ratio of the penetrant, coupling agent / stabilizer and humectant / film-forming aid in the composite organic solvent system is ((2-4):(2-5):(1-3).

[0033] Preferably, the surfactant includes at least one of acetylenic diols and modified organosilicones.

[0034] Preferably, the layered nano-reinforcing agent includes at least one of layered nano-silica and modified montmorillonite (bis(octadecyldimethylammonium chloride) modified montmorillonite).

[0035] Preferably, the rheology modifier includes at least one of a hydrophobically modified alkali-swellable thickener and polyvinylpyrrolidone.

[0036] Preferably, the mass ratio of surfactant, layered nano-reinforcing agent and rheology modifier in the composite additive system is (2-4):(1-3):(1-3).

[0037] Preferably, the pH adjuster includes at least one of citric acid and lactic acid and triethanolamine.

[0038] More preferably, the total concentration of citric acid and lactic acid in the pH adjuster is 1.1-1.5% (w / v, g / mL), and the concentration of triethanolamine is 0.78-1.0% (w / v, g / mL).

[0039] This invention provides a method for preparing the above-mentioned tannic acid-based metal surface treatment liquid, comprising the following steps:

[0040] The composite organic solvent system, surfactant, and some water were mixed, and the composite polyphenol system was added and stirred until completely dissolved. The pH was adjusted to 3.5-4.5 by adding a pH adjuster. The multi-metal salt system was added and stirred. The layered nano-reinforcing agent and the slow-release system were added and stirred. The rheology modifier was added and stirred. The remaining water was added to obtain a metal surface treatment solution based on tannic acid.

[0041] This invention provides an application of the above-mentioned tannic acid-based metal surface treatment liquid or the tannic acid-based metal surface treatment liquid prepared by the above-mentioned preparation method in metal surface treatment.

[0042] Preferably, the metal surface treatment includes the following steps:

[0043] Immerse the carbon steel metal workpiece with oxide scale into a tannic acid-based metal surface treatment solution at 60-75℃ for 15-30 minutes, then remove, wash with water, and dry.

[0044] This invention provides a novel technology to replace traditional processes: polyphenol-iron chelates: tannic acid / natural polyphenols and Fe in oxide scale. 3+ A black tannic acid iron complex is formed. The cyclodextrin corrosion inhibitor complex and sodium alginate-sodium molybdate microcapsules embedded in the film provide long-lasting corrosion inhibition, and the additives enhance film adhesion.

[0045] The advantages of this invention are as follows:

[0046] (1) Intelligent dual self-repair: Innovatively introducing a dual slow-release mechanism of pH response and ion response, it can accurately sense the microenvironmental changes at the corrosion initiation point, target the release of repair agent, and simultaneously inhibit the anodic reaction, realizing the leap from "passive protection" to "active intelligent repair", significantly extending the protection life.

[0047] (2) Synergistically enhanced composite membrane: A dense inorganic-organic hybrid network was constructed through in-situ co-assembly of polyphenol-zinc and rare earth doping. This structure has multiple protection mechanisms, including physical barrier, anodic sacrificial (zinc) and cathodic passivation (cerium / lanthanum), and its corrosion resistance far exceeds that of traditional conversion membranes.

[0048] (3) Combining environmental protection and high efficiency: With natural polyphenols as the core, it completely eliminates the toxic substances in traditional phosphating and chromating processes, which is in line with the trend of green environmental protection. At the same time, its strong chelation and reduction ability ensures efficient one-time treatment of workpieces with oxide scale, eliminating the need for previous pickling and simplifying the process.

[0049] (4) Strong process adaptability: The formulation system has good stability and fast film formation speed. It is suitable for various processes such as soaking and spraying. The film layer has strong bonding force with the substrate and can meet the requirements of subsequent cold heading, drawing and other deformation processing. It has a wide range of applications.

[0050] The beneficial effects of this invention are:

[0051] This invention provides a tannic acid-based metal surface treatment solution for metal surface treatment, which exhibits good film-forming properties, strong corrosion resistance, and self-healing capabilities. Attached Figure Description

[0052] Figure 1 Metallographic images of metal surface treatment liquids used in Examples 1-5 after metal surface treatment.

[0053] Figure 2 Metallographic images of metal surface treatment solutions used in comparative examples 1-5 after metal surface treatment.

[0054] Figure 3 Metallographic images of scratches after metal surface treatment with the metal surface treatment liquids of Examples 1-3 and metallographic images of metal surfaces after being left at room temperature for 24 hours.

[0055] Figure 4 Metallographic images of scratches after metal surface treatment with the metal surface treatment liquid of Examples 4-5 and metallographic images of metal surfaces after being left at room temperature for 24 hours.

[0056] Figure 5 Metallographic images of the metal surface treatment solutions used in Comparative Examples 1-3 after scratching the metal surface and the metallographic images after being left at room temperature for 24 hours.

[0057] Figure 6 Metallographic images of the metal surface treatment liquid used in Comparative Examples 4-5 after scratching the metal surface and after being left at room temperature for 24 hours are shown. Detailed Implementation

[0058] The present invention will be further described below with reference to embodiments.

[0059] The following will clearly and completely describe the concept, specific solutions, and technical effects of the present invention with reference to embodiments, so as to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. The various technical features in the present invention can be combined interactively without contradicting each other.

[0060] This invention provides a tannic acid-based metal surface treatment solution, comprising the following components by mass-volume percentage (g / mL):

[0061] The mixture consists of a complex polyphenol system (3-12%), a multi-metal salt system (2-6%), a sustained-release system (2-5%), a complex organic solvent system (5-12%), a complex additive system (4-10%), and a pH adjuster (adjusting the pH to 3.5-4.5), with the remainder being water.

[0062] In this complex polyphenol system, the main conversion agent accounts for 2-8%, preferably tannic acid, to provide strong chelation and the main film-forming substance. Tannic acid solution has good permeability, allowing it to penetrate into the microcracks and pores of oxide scale (mainly composed of Fe2O3 and Fe3O4) and adsorb onto the surface of both the oxide scale and the base iron. The tannic acid molecule contains a large number of catechol or pyrogallol groups, which are strong chelating groups that can bind with Fe in the oxide scale. 3+ And Fe produced by the dissolution of matrix iron 2+ A strong chelation reaction occurs, forming a stable, insoluble ferric tannate chelate. Tannic acid also has reducing properties, capable of chelating the insoluble ferric iron (Fe3+) in the oxide layer. 3+ (e.g., Fe2O3) is partially reduced to soluble ferrous iron (Fe2O3). 2+ This helps loosen the oxide layer structure, allowing the reaction to proceed deeper, while the generated Fe... 2+ It can also participate in the formation of chelates. The resulting iron tannin chelate is a dense, bluish-black or black precipitate film that adheres tightly to the metal substrate, transforming the reactive metal surface into a corrosion-resistant protective layer.

[0063] The proportion of auxiliary reducing / chelating agents in the complex polyphenol system is 1-4%, preferably gallic acid, catechin, ellagic acid, and caffeic acid (these polyphenols have stronger reducing properties and can more effectively reduce Fe). 3+ Reduced to Fe 2+ It promotes transformation and provides antioxidant properties.

[0064] The main metal salt in the multi-metal salt system accounts for 1.5-4.5%, preferably zinc nitrate hexahydrate (Zn(NO3)2·6H2O); the doped metal ion salt accounts for 0.5-1.5%, preferably cerium nitrate (Ce(NO3)3·6H2O) or lanthanum nitrate (La(NO3)3·6H2O). Rare earth ions have extremely strong cathodic passivation function, which can greatly improve corrosion resistance.

[0065] The sustained-release system employs an intelligent repair system, which includes a pH-responsive unit and an ion-responsive unit.

[0066] The pH-responsive unit comprises 1-3%, preferably a β-cyclodextrin-benzotriazole inclusion complex, to address general corrosion. In a complete coating, the ambient pH is stable, and the BTA corrosion inhibitor is stably encapsulated within the cavities of the β-cyclodextrin, remaining in a "dormant" state. When the coating breaks down and corrosion begins, the pH in the cathodic region at the point of damage increases. The inclusion forces between β-cyclodextrin and BTA molecules (mainly hydrogen bonds and hydrophobic interactions) are weakened or disrupted. Repair effect: BTA molecules are released and rapidly diffuse to the exposed metal surface. The heterocyclic nitrogen atoms of BTA can coordinate with metal atoms (such as Fe, Cu) to form an extremely thin, dense protective film, preferentially adsorbed in the anodic region, inhibiting further metal dissolution and thus terminating the corrosion process.

[0067] The proportion of ion-responsive units is 1-2%, preferably sodium alginate-sodium molybdate microcapsules, with sodium alginate and Ca... 2+ Cross-linking forms an "egg-box" structure, encapsulating molybdate and forming stable, intact microcapsules. Following the corrosion reaction, Fe is generated at the anolyte. 2+ Fe 2+ It is the trigger signal ion. Fe 2+ When combined with the sodium alginate chain, it will bind with Ca. 2+ Competitive cross-linking occurs, forming an unstable and heterogeneous mixed network, leading to instability, swelling, and rupture of the sodium alginate-sodium molybdate microgel structure. Rupture releases molybdate, which reacts with Fe... 2+ The reaction generates a Fe2(MoO4)3 protective film, which inhibits the anodic reaction, thereby achieving precise anodic-directed and highly efficient corrosion suppression. The ion-response unit mainly acts on the anodic region, blocking corrosion by directly inhibiting metal dissolution.

[0068] The combination of pH response unit and ion response unit enables the suppression of the "anode" of the corrosion cell, achieving both symptomatic and root-cause relief, with repair efficiency and reliability far exceeding that of a single mechanism.

[0069] The penetrant in the composite organic solvent system accounts for 2-4%, preferably ethanol or isopropanol, to reduce surface tension and penetrate deep into the micro-crevices of the oxide layer;

[0070] The proportion of coupling agent / stabilizer in the composite organic solvent system is 2-5%, preferably γ-valerol lactone or dipropylene glycol methyl ether (DPM). It is a novel green solvent with excellent solubility for organic and inorganic salts, which can stabilize the precursor solution and prevent premature hydrolysis.

[0071] The proportion of humectant / film-forming aid in the composite organic solvent system is 1-3%, preferably glycerin or polyethylene glycol 400 (PEG-400), to prevent film cracking during drying and make film formation more uniform.

[0072] The surfactant in the composite additive system accounts for 2-4%, preferably acetylenic diol or modified organosilicon, which has low dynamic surface tension, faster penetration, and a wetting effect far superior to traditional TX-10.

[0073] The proportion of layered nano-reinforcing agents in the composite additive system is 1-3%, preferably layered nano-silica or modified montmorillonite. During the film formation process, they are oriented to form a "maze effect", which greatly prolongs the penetration path of corrosive media.

[0074] The rheology modifier in the composite additive system accounts for 1-3%, preferably a hydrophobic modified alkali-swelling thickener or polyvinylpyrrolidone, which provides slight thixotropy, resulting in more uniform liquid coating when the workpiece is lifted from the liquid surface and avoiding dripping.

[0075] The preferred pH adjuster is a buffer pair consisting of citric acid / lactic acid and triethanolamine, which stabilizes the pH in the optimal range of 3.5-4.5.

[0076] This invention provides a method for preparing a metal surface treatment liquid based on tannic acid, comprising the following steps:

[0077] (1) pH Response Unit: Preparation of β-Cyclodextrin-Benzotriazole (β-CD-BTA) Inclusion Complex

[0078] Dissolution: Weigh a certain amount of β-cyclodextrin (β-CD), dissolve it in warm water at 60℃ to prepare a 10% (w / v, g / mL) clear solution, and stir magnetically to ensure complete dissolution.

[0079] Inclusion: Weigh BTA at a molar ratio of 1:1 for β-CD to benzotriazole (BTA) and add it to the above β-CD solution. Place the mixture in a 60°C water bath and sonicate (300W) for 40 minutes.

[0080] Crystallization and maturation: Stop heating and allow the solution to cool naturally to room temperature. Continue stirring at room temperature for 15 hours to allow the inclusion complex to fully crystallize and precipitate.

[0081] Post-processing: The resulting white precipitate was collected by vacuum filtration and washed three times with anhydrous ethanol to remove the physically adsorbed BTA on the surface. The filter cake was dried in a vacuum drying oven at 40°C for 5 hours, and then ground to obtain a white powdery β-CD-BTA inclusion complex, which was sealed and stored for later use.

[0082] (2) Ion Response Unit: Preparation of Sodium Alginate-Sodium Molybdate Microcapsules

[0083] Solution preparation: Weigh sodium alginate (SA), dissolve it in deionized water to prepare a 2% (w / v, g / mL) solution, and stir magnetically overnight to allow it to fully swell and dissolve. Separately, weigh excess sodium molybdate (Na2MoO4), dissolve it in water, and prepare a saturated solution.

[0084] Loading and Crosslinking: A sodium alginate solution and a saturated sodium molybdate solution were mixed at a volume ratio of 5:1 and homogenized at high speed for 5 minutes to form a suspension. This suspension was then added dropwise to a crosslinking solution containing 5% (w / v, g / mL) calcium chloride (CaCl2). Upon contact with CaCl2, the sodium alginate droplets... 2+ Instantaneous ionic cross-linking and gelation occur, encapsulating molybdate within to form microcapsules.

[0085] Solidification and Collection: After the addition is complete, continue stirring at low speed for 1 hour to solidify. Then, filter and collect the microcapsules, repeatedly washing them with deionized water to remove residual chloride ions and unencapsulated molybdates from the surface. The wet capsules are then vacuum-dried at 40°C for 24 hours to obtain a light yellow granular solid, which is then ground and sieved for later use.

[0086] (3) Preparation of solutions of multi-metal salt systems

[0087] Accurately weigh zinc nitrate hexahydrate and cerium nitrate, and dissolve them together in the calculated amount of aqueous solvent. Sonicate for 30 minutes to ensure complete dissolution of the metal salts, yielding a clear and transparent multi-metal salt stock solution. Prepare and use immediately.

[0088] (4) Synthesis of main treatment solution

[0089] Dissolving polyphenols: In a reaction vessel, add deionized water, ethanol, γ-valerol, glycerol, and surfactant, and preheat to 40°C. Start stirring, and add tannic acid and gallic acid (or other auxiliary polyphenols) sequentially until completely dissolved.

[0090] Chelation assembly: Adjust the pH of the system to 3.5-4.5 using a citrate / triethanolamine buffer solution. While stirring at a constant speed, slowly add the multi-metal salt solution. After the addition is complete, continue the reaction for 30 minutes, during which the solution gradually turns dark.

[0091] Add functional components: Keep the temperature at 40℃, add layered nano-silica and two slow-release system powders (pH response and ion response units) in sequence, and stir and disperse at low speed for 40 minutes to avoid high-speed shearing damage to microcapsules.

[0092] Adjust to a final volume: Finally, add the rheology modifier (HASE or PVP) and stir for 1 hour until the system is homogeneous and stable. Adjust the volume to the final volume with deionized water to obtain the final treated solution.

[0093] This invention provides an application of a tannic acid-based metal surface treatment solution in metal surface treatment, comprising the following steps:

[0094] Immerse the oxide-coated metal workpiece in the above treatment solution at 60-75℃ for 15-30 minutes. After removal, rinse with water and dry at 80℃ for 10 minutes to form a dense, self-healing black conversion film on the surface. Applications: Metal workpieces containing oxide scale, such as carbon steel and alloy steel, specifically 22A, 08Al, SCM435, 40Cr, etc. Wire diameters can range from 1.5mm to 25mm. Subsequent processes include direct drawing and cold heading.

[0095] The processing steps are as follows: workpieces containing oxide scale -- soaking -- drying -- drawing -- cold heading finished product.

[0096] The following are the performance tests of the wires after soaking and drying treatments in the examples and comparative examples:

[0097] (1) Corrosion resistance verification: Salt spray test.

[0098] Testing standards: in accordance with ASTM B117.

[0099] Method: The treated sample was placed in a salt spray test chamber and continuously sprayed with 5wt% NaCl solution. The temperature inside the chamber was kept constant at 35℃.

[0100] Evaluation indicators:

[0101] Time of red rust appearance: Record the time when red rust, caused by corrosion of the base iron, first appears on the sample surface.

[0102] (2) Self-healing ability verification: scratch test + room temperature observation method.

[0103] Use a sharp blade to make a clear cross-shaped scratch on the surface of the treated sample. The scratch must penetrate the film to expose the underlying metal.

[0104] The scratched sample was left at room temperature for 24 hours, and the morphology of the scratches was observed.

[0105] Evaluation indicators:

[0106] Repair effect: Observe whether there is a repair film layer at the scratch.

[0107] Excellent self-healing coating makes scratches virtually invisible, completely covers the metal, and prevents corrosion.

[0108] With a good self-healing film, scratches become significantly shallower and narrower, and most areas are covered. Slight traces may be visible in some areas, but there is no corrosion.

[0109] Typical self-healing film scratches show signs of partial closure, but still have obvious grooves and exposed metal, possibly accompanied by minor corrosion spots.

[0110] Example 1

[0111] A tannic acid-based metal surface treatment solution comprises the following components by mass-volume percentage (g / mL):

[0112] Tannic acid: 5%

[0113] Gallic acid: 2%

[0114] Zinc nitrate hexahydrate: 3%

[0115] Cerium nitrate: 0.6%

[0116] β-CD-BTA inclusion complex: 1.5%

[0117] SA-Mo microcapsules: 1%

[0118] Ethanol: 3%

[0119] γ-Velolactone: 3%

[0120] Glycerin: 2%

[0121] Alkyne diol surfactants (CAS No.: 126-86-3): 2%

[0122] Layered nano-silica: 1.5%

[0123] HASE thickener: 1%

[0124] Citric acid / triethanolamine buffer pair: Adjust pH to 4.0

[0125] Deionized water: Balance.

[0126] The metal surface treatment liquid in this embodiment is a general-purpose treatment liquid suitable for carbon steel wire.

[0127] The above-mentioned method for preparing the tannic acid-based metal surface treatment solution includes the following steps:

[0128] (1) pH Response Unit: Preparation of β-Cyclodextrin-Benzotriazole (β-CD-BTA) Inclusion Complex

[0129] Dissolution: Weigh a certain amount of β-cyclodextrin (β-CD), dissolve it in warm water at 60℃ to prepare a 10% (w / v, g / mL) clear solution, and stir magnetically to ensure complete dissolution.

[0130] Inclusion: Weigh BTA at a molar ratio of 1:1 for β-CD to benzotriazole (BTA) and add it to the above β-CD solution. Place the mixture in a 60°C water bath and sonicate (300W) for 40 minutes.

[0131] Crystallization and maturation: Stop heating and allow the solution to cool naturally to room temperature. Continue stirring at room temperature for 15 hours to allow the inclusion complex to fully crystallize and precipitate.

[0132] Post-processing: The resulting white precipitate was collected by vacuum filtration and washed three times with anhydrous ethanol to remove the physically adsorbed BTA on the surface. The filter cake was dried in a vacuum drying oven at 40°C for 5 hours, and then ground to obtain a white powdery β-CD-BTA inclusion complex, which was sealed and stored for later use.

[0133] (2) Ion Response Unit: Preparation of Sodium Alginate-Sodium Molybdate Microcapsules

[0134] Solution preparation: Weigh sodium alginate (SA), dissolve it in deionized water to prepare a 2% (w / v, g / mL) solution, and stir magnetically overnight to allow it to fully swell and dissolve. Separately, weigh excess sodium molybdate (Na2MoO4), dissolve it in water, and prepare a saturated solution.

[0135] Loading and Crosslinking: A sodium alginate solution and a saturated sodium molybdate solution were mixed at a volume ratio of 5:1 and homogenized at high speed for 5 minutes to form a suspension. This suspension was then added dropwise to a crosslinking solution containing 5% (w / v, g / mL) calcium chloride (CaCl2). Upon contact with CaCl2, the sodium alginate droplets... 2+ Instantaneous ionic cross-linking and gelation occur, encapsulating molybdate within to form microcapsules.

[0136] Solidification and Collection: After the addition is complete, continue stirring at low speed for 1 hour to solidify. Then, filter and collect the microcapsules, repeatedly washing them with deionized water to remove residual chloride ions and unencapsulated molybdates from the surface. The wet capsules are then vacuum-dried at 40°C for 24 hours to obtain a light yellow granular solid, which is then ground and sieved for later use.

[0137] (3) Preparation of multi-metal salt precursor solution

[0138] Accurately weigh zinc nitrate hexahydrate and cerium nitrate, and dissolve them together in the calculated amount of aqueous solvent. Sonicate for 30 minutes to ensure complete dissolution of the metal salts, yielding a clear and transparent multi-metal salt precursor stock solution. Prepare and use immediately.

[0139] (4) Synthesis of main treatment solution

[0140] Dissolving polyphenols: In a reaction vessel, add deionized water, ethanol, γ-valerol, glycerol, and acetylacetonate surfactant, and preheat to 40°C. Start stirring, and add tannic acid and gallic acid (or other auxiliary polyphenols) sequentially until completely dissolved.

[0141] Chelation assembly: The pH of the system was adjusted to 4.0 using a citric acid / triethanolamine buffer solution (11g citric acid + 7.8g triethanolamine, dissolved and stirred to 1L solution). The multi-metal salt precursor solution prepared in step (3) was slowly added under uniform stirring. After the addition was complete, the reaction continued for 30 minutes, and the solution gradually turned dark.

[0142] Add functional components: Keep the temperature at 40℃, and add layered nano-silica and two slow-release system powders in sequence (pH-responsive unit β-CD-BTA inclusion complex and ion-responsive unit SA-Mo microcapsule). Stir and disperse at low speed for 40 minutes to avoid high-speed shearing damage to the microcapsules.

[0143] Adjusting to a final volume: Finally, add the rheology modifier (HASE thickener) and stir for 1 hour until the system is homogeneous and stable. Adjust the volume to the final volume with deionized water to obtain the final treated solution.

[0144] The above-mentioned tannic acid-based metal surface treatment solution is used for metal surface treatment, including the following steps:

[0145] Immerse the oxide-coated metal workpiece in the above treatment solution at 70°C for 20 minutes. After removal, rinse with water and dry at 80°C for 10 minutes to form a dense black conversion film with intelligent self-healing function on the surface.

[0146] Application Results: Treating 22A steel wire at 70℃ for 20 minutes forms a uniform blackish-gray film. The film is dense, showing no red rust after 96 hours of salt spray testing, and exhibits good lubrication during subsequent drawing with no film peeling.

[0147] Example 2

[0148] A tannic acid-based metal surface treatment solution comprises the following components by mass-volume percentage (g / mL):

[0149] Tannic acid: 7%

[0150] EGCG (Gastrointestinal catechin): 3%

[0151] Zinc nitrate hexahydrate: 2.5%

[0152] Lanthanum nitrate: 1%

[0153] β-CD-BTA inclusion complex: 2%

[0154] SA-Mo microcapsules: 1.5%

[0155] Isopropanol: 4%

[0156] DPM: 4%

[0157] PEG-400: 2%

[0158] Modified silicone surfactant (CAS No.: 27306-78-1): 3%

[0159] Modified montmorillonite (CAS No.: 1318-93-0, modified with dioctadecyldimethylammonium chloride): 2%

[0160] PVP K90: 2%

[0161] Lactic acid / triethanolamine buffer pair (dissolve 11g lactic acid + 7.8g triethanolamine in water and stir to a final volume of 1L): Adjust pH to 3.5.

[0162] Deionized water: Balance.

[0163] The metal surface treatment solution in this embodiment is a high-penetration treatment solution suitable for workpieces with thick oxide scale.

[0164] The preparation method of the above metal surface treatment liquid is the same as that in Example 1.

[0165] The method of using the above-mentioned metal surface treatment liquid for metal surface treatment is the same as in Example 1, except that the metal workpiece and the immersion temperature and time are different.

[0166] Application Results: For 40Cr steel forgings (with thick oxide scale), treatment at 75℃ for 30 minutes effectively penetrates and transforms the thick oxide scale, forming a complete film with strong adhesion to the substrate and a salt spray resistance time exceeding 88 hours.

[0167] Example 3

[0168] A tannic acid-based metal surface treatment solution comprises the following components by mass-volume percentage (g / mL):

[0169] Formula: Tannins: 4%

[0170] Caffeic acid: 1.5%

[0171] Zinc nitrate hexahydrate: 4%

[0172] Cerium nitrate: 0.5%

[0173] β-CD-BTA inclusion complex: 1%

[0174] SA-Mo microcapsules: 0.8%

[0175] Ethanol: 2%

[0176] Isopropanol: 2%

[0177] γ-Velolactone: 2%

[0178] Glycerin: 1%

[0179] Acetylene diol surfactant (CAS No.: 126-86-3): 2.5%

[0180] Layered nano-silica: 1%

[0181] HASE thickener: 0.5%

[0182] Citric acid / triethanolamine buffer pair (dissolve 11g citric acid + 7.8g triethanolamine in water and stir to a final volume of 1L): Adjust pH to 4.5.

[0183] Deionized water: Balance

[0184] The metal surface treatment liquid in this embodiment is a rapid film-forming liquid suitable for high-speed production.

[0185] The preparation method of the above metal surface treatment liquid is the same as that in Example 1.

[0186] The method of using the above-mentioned metal surface treatment liquid for metal surface treatment is the same as in Example 1, except that the metal workpiece and the immersion temperature and time are different.

[0187] Application Results: Designed for continuous production lines of SCM435 wire, film can be formed after treatment at 65℃ for 15 minutes. The film has uniform color, fast drying speed, meets the requirements of high-speed production, salt spray resistance for 90 hours, and rust prevention period meets the requirements of transit storage.

[0188] Example 4

[0189] A tannic acid-based metal surface treatment solution comprises the following components by mass-volume percentage (g / mL):

[0190] Tannic acid: 8%

[0191] Ellagic acid: 2%

[0192] Zinc nitrate hexahydrate: 1.5%

[0193] Cerium nitrate: 1.2%

[0194] β-CD-BTA inclusion complex: 2.5%

[0195] SA-Mo microcapsules: 1.8%

[0196] DPM: 5%

[0197] Glycerin: 3%

[0198] Modified silicone surfactant (CAS No.: 27306-78-1): 3.5%

[0199] Layered nano-silica: 2.5%

[0200] PVP K90: 2.5%

[0201] Citric acid / triethanolamine buffer pair (dissolve 11g citric acid + 7.8g triethanolamine in water and stir to a final volume of 1L): Adjust pH to 4.2.

[0202] Deionized water: Balance

[0203] The metal surface treatment liquid in this embodiment is suitable for applications requiring high corrosion resistance and self-healing properties.

[0204] The preparation method of the above metal surface treatment liquid is the same as that in Example 1.

[0205] The method of using the above-mentioned metal surface treatment liquid for metal surface treatment is the same as in Example 1, except that the metal workpiece and the immersion temperature and time are different.

[0206] Application results: Suitable for automotive fasteners requiring extremely high corrosion resistance; treated at 70℃ for 25 minutes. Excellent salt spray resistance, up to 95 hours.

[0207] Example 5

[0208] A tannic acid-based metal surface treatment solution comprises the following components by mass-volume percentage (g / mL):

[0209] Tannic acid: 6%

[0210] Gallic acid: 1%

[0211] Zinc nitrate hexahydrate: 3.5%

[0212] Cerium nitrate: 0.8%

[0213] β-CD-BTA inclusion complex: 1.2%

[0214] SA-Mo microcapsules: 0.8%

[0215] Ethanol: 3%

[0216] DPM: 2%

[0217] PEG-400: 1%

[0218] Alkyne diol surfactants (CAS No.: 126-86-3): 2%

[0219] Modified montmorillonite (CAS No.: 1318-93-0, modified with dioctadecyldimethylammonium chloride): 1%

[0220] HASE thickener: 1.2%

[0221] Lactic acid / triethanolamine buffer pair (dissolve 11g lactic acid + 7.8g triethanolamine in water and stir to a final volume of 1L): Adjust pH to 4.3.

[0222] Deionized water: Balance

[0223] The metal surface treatment liquid in this embodiment is an economical and highly leveling treatment liquid.

[0224] The preparation method of the above metal surface treatment liquid is the same as that in Example 1.

[0225] The method of using the above-mentioned metal surface treatment liquid for metal surface treatment is the same as in Example 1, except that the metal workpiece and the immersion temperature and time are different.

[0226] Application Results: Optimizes cost while ensuring basic performance. When treating 08Al steel plates, treat at 65℃ for 20 minutes. The film layer exhibits good leveling properties, no color difference, and a uniform appearance, suitable for general applications requiring both appearance and rust prevention. It withstands salt spray for 92 hours.

[0227] Comparative Example 1

[0228] A tannic acid-based metal surface treatment solution (without rare earth ion doping).

[0229] Formula: Basically the same as in Example 1, but cerium nitrate (Ce(NO3)3·6H2O) is completely omitted. The original proportion of cerium nitrate is replaced with an equal amount of zinc nitrate hexahydrate.

[0230] The preparation method and application are the same as in Example 1.

[0231] Comparison of effects: The film appearance is similar to that of Example 1, but the corrosion resistance, especially the salt spray resistance, is significantly reduced. A large amount of red rust appears after only 50 hours of salt spray testing. This is because the film loses the key protective mechanism of cathodic passivation provided by rare earth ions, relying solely on the anodic sacrificial protection of zinc, resulting in a single and unsustainable protective effect. This comparison demonstrates the decisive role of rare earth doping in improving corrosion resistance.

[0232] Comparative Example 2

[0233] A tannic acid-based metal surface treatment liquid (without a smart sustained-release system)

[0234] Formulation: Essentially the same as in Example 2, but with the β-CD-BTA inclusion complex and SA-Mo microcapsules completely omitted. This portion is filled with an equal amount of layered nano-silica.

[0235] The preparation method and application are the same as in Example 2.

[0236] Performance comparison: Initial corrosion resistance is acceptable, with a salt spray test time of 48 hours. This film is a passive protective coating; it fails once damaged.

[0237] Comparative Example 3

[0238] A metal surface treatment liquid based on tannic acid (without a composite polyphenol system, using only tannic acid).

[0239] Formula: Basically the same as in Example 3, but the auxiliary reducing agent caffeic acid is completely omitted. The amount of tannic acid is increased to 5.5% to keep the total polyphenol content roughly the same.

[0240] The preparation method and application are the same as in Example 3.

[0241] Comparison of effects: When treating workpieces with oxide scale, the conversion rate slowed down, the uniformity of the film decreased, and mottled patterns appeared. For thicker oxide scale, the conversion was incomplete, resulting in poor adhesion between the film and the substrate. This is because although tannic acid alone can chelate and reduce, its reducing power is not as strong as that of small molecule polyphenols such as catechins and caffeic acid, and it cannot quickly and effectively loosen the oxide scale structure. The salt spray time was reduced to 10 hours. This comparison demonstrates the advantages of the "primary conversion-secondary reduction" synergistic strategy in the composite polyphenol system.

[0242] Comparative Example 4

[0243] A metal surface treatment liquid based on tannic acid (without layered nano-reinforcing agents)

[0244] Formulation: Basically the same as in Example 4, but the layered nano-silica is completely omitted. This portion is replaced with an equal amount of deionized water.

[0245] The preparation method and application are the same as in Example 4.

[0246] Comparison of effects: The physical barrier effect of the membrane is weakened. Although chemical corrosion protection and self-healing functions remain, corrosive media (water, oxygen, chloride ions) can penetrate the membrane more easily. Its salt spray resistance time will be significantly shorter than that of Example 4, decreasing by 30%-50%. The salt spray time is 55 hours. This comparison demonstrates the key contribution of nanosheet materials to extending the penetration path through the "maze effect," thus improving the overall protective lifespan.

[0247] Comparative Example 5

[0248] A metal surface treatment liquid based on tannic acid (no composite solvent system, only water and ethanol)

[0249] Formulation: Basically the same as in Example 5, but the coupling agent / stabilizer DPM and film-forming aid PEG-400 are completely omitted. The amount of ethanol is increased accordingly.

[0250] The preparation method and application are the same as in Example 5.

[0251] Comparison of effects: Solution stability deteriorated, and metal salt precursors may hydrolyze or precipitate during storage. Film formation was poor during treatment, with films prone to sagging, cracking, or unevenness, severely affecting the consistency of appearance and protective performance. Salt spray time was shortened to 15 hours. This comparison demonstrates the importance of composite solvent systems for stabilizing formulations and ensuring film quality, proving that simple solvents cannot replace them.

[0252] The metal surface treatment liquid formulations of Examples 1-5 and Comparative Examples 1-5 are shown in Table 1.

[0253] Table 1:

[0254]

[0255] The performance of the metal surface treatment solutions of Examples 1-5 and Comparative Examples 1-5 after metal surface treatment is shown in Table 2. Metallographic images of the metal surface treated are shown below. Figure 1 and Figure 2 Metallographic images of metal surfaces after scratching following surface treatment and metallographic images after being left at room temperature for 24 hours, such as... Figures 3-6 .

[0256] Table 2:

[0257]

[0258] From Table 2, Figures 1-6 It can be seen that:

[0259] The metal surface treatment solutions in Examples 1-5 produce uniform film layers, long salt spray resistance, and excellent self-healing ability after metal surface treatment.

[0260] The metal surface treatment solution of Comparative Example 1 is free of rare earth ion doping. After being used for metal surface treatment, it has a short salt spray resistance time and poor self-healing ability compared with Example 1.

[0261] The metal surface treatment liquid in Comparative Example 2 lacks an intelligent slow-release system, resulting in short salt spray resistance time and no self-healing ability after metal surface treatment.

[0262] The metal surface treatment liquid in Comparative Example 3 lacks a composite polyphenol system. After being used for metal surface treatment, the film layer shows mottled patterns and has a short salt spray resistance time.

[0263] The metal surface treatment liquid in Comparative Example 4 lacks layered nano-reinforcing agents, resulting in an uneven film layer and short salt spray resistance time after metal surface treatment.

[0264] The metal surface treatment liquid in Comparative Example 5, which has no composite solvent system, results in an uneven film layer and short salt spray resistance time after metal surface treatment.

[0265] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of the present invention.

Claims

1. A tannin acid-based metal surface treatment liquid, characterized by, The following components are included by mass volume percentage: A complex polyphenol system 3-12% A multi-metal salt system 2-6% A slow-release system 2-5% A complex organic solvent system 5-12% A complex additive system 4-10% A pH adjuster to adjust the pH to 3.5-4.5 The remainder is water; The unit of mass volume percentage is g / mL; The complex polyphenol system includes tannic acid and at least one natural polyphenol that is more reducing than tannic acid; The complex additive system includes a surfactant, a lamellar nano-enhancing agent, and a rheological modifier.

2. The tannin acid-based metal surface treatment liquid according to claim 1, characterized by, The natural polyphenol that is more reducing than tannic acid includes at least one of gallic acid, catechin, ellagic acid, and coffee acid; The mass ratio of tannic acid and the natural polyphenol that is more reducing than tannic acid in the complex polyphenol system is (2-8):(1-4).

3. The tannin-based metal surface treatment liquid according to claim 1, characterized by, The multi-metal salt system includes at least one of a cerium salt and a lanthanum salt and a zinc salt; The mass ratio of the total amount of cerium salt and lanthanum salt and the zinc salt in the multi-metal salt system is (1.5-4.5):(0.5-1.5).

4. The tannin-based metal surface treatment liquid according to claim 1, characterized by, The slow-release system includes a pH-responsive unit and an ion-responsive unit; The pH-responsive unit is a β-cyclodextrin-benzotriazole inclusion compound; The ion-responsive unit is a sodium alginate-sodium molybdate microcapsule; The mass ratio of the pH-responsive unit and the ion-responsive unit in the slow-release system is (1-3):(1-2).

5. The tannin-based metal surface treatment liquid according to claim 4, characterized by, The preparation method of the β-cyclodextrin-benzotriazole inclusion compound is to mix benzotriazole with a β-cyclodextrin solution, heat and ultrasonic treatment, cool crystallization, filtration, washing, and drying to obtain the β-cyclodextrin-benzotriazole inclusion compound; The preparation method of the sodium alginate-sodium molybdate microcapsule is to mix a sodium alginate solution and a sodium molybdate solution, stir, drop a calcium chloride solution, stir and solidify, filter, wash, and dry to obtain the sodium alginate-sodium molybdate microcapsule.

6. The tannin-based metal surface treatment liquid according to claim 1, characterized by, The complex organic solvent system includes a penetrant, a coupling agent / stabilizer, and a humectant / film-forming aid; The penetrant includes at least one of ethanol and isopropyl alcohol; The coupling agent / stabilizer includes at least one of γ-valerolactone and dipropylene glycol methyl ether; The humectant / film-forming aid includes at least one of glycerol and polyethylene glycol; The mass ratio of the penetrant, the coupling agent / stabilizer, and the humectant / film-forming aid in the complex organic solvent system is ((2-4):(2-5):(1-3).

7. The tannin-based metal surface treatment liquid according to claim 1, characterized by, The surfactant includes at least one of acetylenic diols and modified silicones; The lamellar nano-enhancing agent includes at least one of lamellar nano-silicon dioxide and modified montmorillonite; The rheological modifier includes at least one of a hydrophobically modified alkali-swellable thickener and polyvinylpyrrolidone; The mass ratio of the surfactant, the lamellar nano-enhancing agent, and the rheological modifier in the complex additive system is (2-4):(1-3):(1-3); The pH adjuster includes at least one of citric acid and lactic acid and triethanolamine.

8. The method for producing a tannin acid-based metal surface treatment liquid according to any one of claims 1 to 7, characterized by, The following steps are included: The composite organic solvent system, the surfactant and part of the water are mixed, the composite polyphenol system is added and stirred until completely dissolved; the pH regulator is added to adjust the pH to 3.5-4.5; the polybasic metal salt system is added and stirred; the lamellar nano-enhancing agent and the slow-release system are added and stirred; the rheological regulator is added and stirred; the remaining water is added to obtain the tannic acid-based metal surface treatment liquid.

9. The use of the tannic acid-based metal surface treatment liquid according to any one of claims 1-7 or the tannic acid-based metal surface treatment liquid prepared by the preparation method of claim 8 in metal surface treatment.

10. Use according to claim 9, characterized in that, The method comprises the following steps: The carbon steel metal workpiece with the oxide skin to be treated is immersed in the tannic acid-based metal surface treatment liquid, soaked at 60-75℃ for 15-30 minutes, and then taken out, washed with water and dried.

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