A chromium-free surface treatment liquid for color steel plate and a preparation method thereof

Abstract

This invention relates to the field of steel plate surface treatment technology, specifically disclosing a chromium-free surface treatment liquid for color steel plates and its preparation method. The treatment liquid comprises zirconium-titanium composite sol, cerium nitrate, lanthanum nitrate, nano-silica, organosilane coupling agent, potassium fluorozirconate, etc. The preparation method is as follows: first, the silane coupling agent is hydrolyzed and then surface-grafted with nano-silica under cerium ion catalysis; then, the zirconium-titanium sol is coordinated and stabilized with rare earth ions and potassium fluorozirconate; finally, the two are mixed and undergo a co-condensation reaction to form a hybrid network. This invention, through stepwise chemical reactions, utilizes the dual functions of cerium ions (catalysis and bridging) and the controllable complexation of fluoride ions to tightly bind the components through covalent and coordinate bonds, solving the problems of poor component compatibility and wasted reactivity in existing chromium-free technologies. The film formed by this treatment liquid is dense, has strong adhesion, excellent corrosion resistance, and is completely free of hexavalent chromium, making it safe and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of steel plate surface treatment technology, specifically relating to a chromium-free surface treatment liquid for color steel plates and its preparation method. Background Technology

[0002] Color-coated steel sheets are widely used in key sectors such as construction, home appliances, and transportation. The performance of their surface pretreatment layer directly determines the corrosion resistance and service life of the finished sheet. Traditional technology commonly employs hexavalent chromate passivation, generating a self-healing chromate conversion film on the metal surface, exhibiting excellent corrosion resistance and adhesion. However, hexavalent chromium is highly toxic and carcinogenic, and easily leach into the environment during processing and use, seriously violating current environmental regulations. Especially under harsh conditions such as humidity and high salinity, traditional chromate or existing chromium-free passivation layers are prone to penetrating corrosion due to micro-area damage, resulting in a significant decrease in protective effectiveness within a short period.

[0003] In recent years, chromium-free technologies have emerged, such as treatment solutions based on zirconium-titanium inorganic salts, silane coupling agents, or rare earth salts. Most existing technologies employ a simple physical mixing method under acidic conditions. Although these treatment solutions do not contain hexavalent chromium, they still have several significant drawbacks: First, while zirconium-titanium sols form films quickly when used alone, their cross-linking density is low, resulting in a loose and porous film that cannot effectively block the deep penetration of corrosive media such as chloride ions. Second, introduced nanofillers (such as nano-silica) are difficult to stably suspend in the system, easily agglomerating and settling, failing to enhance film density and instead damaging the uniformity of the passivation film. Third, the corrosion inhibition effect of conventionally contained rare earth ions is singular and passive, mostly relying on random embedding into the film after physical mixing, lacking active chemical driving force; once the film is locally damaged, it cannot achieve dynamic self-repair function. Overall, existing technical solutions suffer from core technical bottlenecks such as poor compatibility among multiple components, mutual restraint of passivation reactions, waste of reactivity, and lack of synergistic feedback mechanisms. There is an urgent need to develop a chromium-free treatment technology that features high chemical synergy among the components, mutual feedback and promotion, and long-term self-healing capabilities. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides a chromium-free surface treatment liquid for color steel sheets and its preparation method. This solution innovatively utilizes rare earth cerium ions (Ce) through a unique step-by-step preparation process. 3+The dual function of silane-modified nano-silica (initial catalysis and later bridging) is utilized to tightly bond silane-modified nano-silica with a zirconium-titanium sol network through chemical bonding, constructing a three-dimensional organic-inorganic hybrid network structure with covalent and coordination bonds as nodes. This structure is not a simple stacking of components, but rather generates a novel synergistic protective function through chemical reaction, significantly improving the density, adhesion, and corrosion resistance of the passivation film.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a chromium-free surface treatment liquid for color steel plates, which comprises the following components by weight: 15-30 parts zirconium-titanium composite sol, 0.1-0.8 parts cerium nitrate, 0.05-0.5 parts lanthanum nitrate, 0.5-2 parts nano-silica, 2-6 parts organosilane coupling agent, 0.01-0.1 parts potassium fluorozirconate, 0.5-2 parts film-forming aid, and 55-85 parts deionized water.

[0007] Furthermore, the zirconium-titanium composite sol is prepared by co-hydrolyzing zirconium oxychloride and tetrabutyl titanate under acidic conditions. The preparation method is as follows: zirconium oxychloride and tetrabutyl titanate are dissolved in a mixed solvent of ethanol and water with a volume ratio of 1:1 at a Zr:Ti molar ratio of 1.5:1. Under vigorous stirring, 0.5 mol / L nitric acid solution is slowly added dropwise until the pH of the system reaches 3. The reaction is first refluxed at 75°C for 3 hours, and then aged at 60°C for 24 hours to obtain a clear and stable zirconium-titanium composite sol.

[0008] Furthermore, the organosilane coupling agent is γ-aminopropyltriethoxysilane or γ-glycidyl etheroxypropyltrimethoxysilane.

[0009] Furthermore, the film-forming aid is polyethylene glycol 400 or triethylene glycol monobutyl ether.

[0010] This invention also provides a method for preparing a chromium-free surface treatment liquid for color steel sheets, specifically including the following steps:

[0011] S1. Add the organosilane coupling agent to 3-6 times its weight of deionized water, adjust the pH to 3-4 with glacial acetic acid, and hydrolyze at 40-50℃ for 1-2 hours to obtain a silane hydrolysate. Then, add nano-silica and 40-60% cerium nitrate, raise the temperature to 60-70℃, and disperse under high-speed shear for 2-3 hours. During this process, cerium ions (Ce)... 3+ Through its coordination unsaturation properties, it coordinates and activates the silanol groups on the surface of nano-silica, lowering the reaction energy barrier for dehydration condensation between silanol groups, thereby promoting the dehydration condensation reaction between -Si-OH in the silane hydrolysate and the silanol groups on the surface of nano-silica; simultaneously, some Ce... 3+By anchoring silane molecules to the surface of nanoparticles through coordination bonds, silane molecules are stably grafted onto the surface of nanoparticles through the dual effects of covalent bonds (Si-O-Si) and coordination bonds, resulting in a cerium-silane modified nano silica dispersion.

[0012] S2. Mix the zirconium-titanium composite sol with the remaining deionized water, and add lanthanum nitrate, the remaining cerium nitrate, and potassium fluorozirconate while stirring. Heat to 45-55℃ and stir for 1.5-2.5 hours. Under acidic sol conditions, trace amounts of potassium fluorozirconate dissociate to release F... - Priority with Zr 4+ The formation of a moderate complex inhibits the spontaneous condensation tendency of zirconium-titanium sol particles and maintains the density of highly reactive metal hydroxyl groups on their surface. At the same time, cerium and lanthanum rare earth ions coordinate with the metal hydroxyl groups on the surface of zirconium-titanium sol particles to obtain rare earth-zirconium-titanium coordination sol with high reactivity and catalytic potential.

[0013] S3. Under stirring at 35-40℃ and 500rpm, slowly add the cerium-silane modified nano-silica dispersion prepared in step S1 to the rare earth-zirconium-titanium coordination sol obtained in step S2. During the addition process, the Ce2-silica pre-anchored on the nano-silica... 3+ With Ce in solution 3+ La 3+ Through coordination interactions, the -Si-OH on the surface of the nanoparticles and the Zr / Ti-OH in the zirconium-titanium sol network jointly promote the co-condensation reaction, rapidly forming a dense and highly cross-linked Ti-O-Si and Zr-O-Si covalent network. Simultaneously, nano-silica acts as a cross-linking node, forming an interpenetrating structure with organosilanes and inorganic zirconium-titanium oxide networks. After the addition is complete, a film-forming aid is added, and stirring is continued for 0.5-1 hour. Then, the pH of the system is adjusted to 3.8-4.5 with ammonia. Finally, the solution is filtered through a 1.0 μm filter to obtain the treatment solution.

[0014] Compared with the prior art, the beneficial effects of the present invention are:

[0015] (1) This invention utilizes a stepwise chemical reaction to tightly bind nano-silica, silane, zirconium titanium sol, and rare earth ions through coordination and covalent bonds, forming a three-dimensional organic-inorganic hybrid interpenetrating network interwoven at the molecular level. This network eliminates phase separation defects between the organic and inorganic phases, possesses extremely high chemical stability and structural compactness, and can effectively block Cl... - The penetration of corrosive media such as H2O significantly improves the corrosion resistance of the film.

[0016] (2) Conventional highly active zirconium-titanium sols are prone to spontaneous condensation polymerization, leading to gel deactivation. However, in the preparation process of this invention, a reversible complex is formed between trace amounts of fluoride ions and zirconium ions, which inhibits the spontaneous condensation tendency of zirconium-titanium sol particles and maintains the high density of reactive hydroxyl groups on their surface. When subsequently mixed with cerium-silane modified nano-silica, cerium ions anchored on the surface of the nanoparticles can compete with fluoride ions for coordination, releasing the excessive complexation of zirconium ions by fluoride ions and releasing active zirconium ions to participate in the co-condensation reaction. This mechanism ensures the long-term storage stability of the treatment solution and achieves efficient cross-linking during the film formation process, avoiding the problem of catalyst deactivation due to network encapsulation.

[0017] (3) The organic functional groups (amino or epoxy groups) of the silane coupling agent used in this invention form coordination bonds with the metal atoms on the surface of the color steel plate during film formation, while the silicon-oxygen-metal covalent bonds at the other end firmly anchor the inorganic hybrid network to the substrate surface. This "chemical double anchoring" structure creates a strong interfacial bonding force between the film layer and the substrate that far exceeds physical adsorption or simple chemical transformation, effectively preventing blistering and peeling of the film layer under harsh environments.

[0018] (4) Rare earth cerium and lanthanum ions not only act as catalysts for polycondensation reactions, lowering the energy barrier of crosslinking reactions and enabling rapid curing of the film at room temperature or low temperature, but also retain their inherent corrosion inhibition properties. When the film is locally damaged, forming corrosion micro-zones, trivalent cerium ions can be converted into tetravalent cerium ions and deposit insoluble hydroxides, effectively sealing corrosion micropores and endowing the film with dynamic self-repairing passivation capabilities. At the same time, this invention is completely free of hexavalent chromium, making it safe and environmentally friendly. The prepared treatment solution has good stability, and the dense network film formed significantly improves the service life of color steel plates in acidic, salt spray, and humid heat environments. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0021] Unless otherwise specified, all materials used in the following implementation are new materials purchased from the market, including glacial acetic acid, ammonia, and ethanol, which are all analytical grade reagents.

[0022] Example 1: This example provides a chromium-free surface treatment liquid for color steel plates, which, by weight, includes the following raw materials: 15 parts zirconium-titanium composite sol, 0.1 parts cerium nitrate, 0.05 parts lanthanum nitrate, 0.5 parts nano silica, 2 parts γ-aminopropyltriethoxysilane, 0.01 parts potassium fluorozirconate, 0.5 parts polyethylene glycol 400, and 85 parts deionized water.

[0023] The zirconium-titanium composite sol is prepared as follows: 10g of zirconium oxychloride and 7.1g of tetrabutyl titanate are dissolved in 100mL of a mixed solvent of ethanol and water with a volume ratio of 1:1. Under vigorous stirring, 0.5mol / L nitric acid solution is slowly added dropwise until the pH of the system reaches 3. The mixture is first refluxed at 75℃ for 3 hours, and then aged at 60℃ for 24 hours to obtain a clear and stable zirconium-titanium composite sol.

[0024] This embodiment also provides a method for preparing a chromium-free surface treatment liquid for color steel sheets, including the following steps:

[0025] S1. Add 2 parts of γ-aminopropyltriethoxysilane to 6 parts of deionized water, adjust the pH to 3 with glacial acetic acid, and hydrolyze at 40°C for 2 hours to obtain silane hydrolysate. Then, add 0.5 parts of nano silica and 0.04 parts of cerium nitrate to it, heat to 60°C, and disperse by high-speed shearing for 3 hours to obtain cerium-silane modified nano silica dispersion.

[0026] S2. Mix 15 parts of zirconium-titanium composite sol with the remaining deionized water, add 0.05 parts of lanthanum nitrate, 0.06 parts of the remaining cerium nitrate and 0.01 parts of potassium fluorozirconate while stirring at 300 rpm, heat to 45℃ and stir for 2.5 hours to obtain rare earth-zirconium-titanium coordination sol.

[0027] S3. Under stirring at 35℃ and 500rpm, slowly add the cerium-silane modified nano silica dispersion prepared in step S1 to the rare earth-zirconium-titanium coordination sol obtained in step S2. After the addition is complete, add 0.5 parts of polyethylene glycol 400 and continue stirring for 1 hour. Then adjust the pH of the system to 3.8 with ammonia water. Finally, filter through a 1.0μm filter to obtain the treatment solution.

[0028] Example 2: This example provides a chromium-free surface treatment liquid for color steel plates. The treatment liquid comprises the following components by weight: 22 parts zirconium-titanium composite sol, 0.45 parts cerium nitrate, 0.25 parts lanthanum nitrate, 1.2 parts nano silica, 4 parts γ-glycidyl etheroxypropyltrimethoxysilane, 0.05 parts potassium fluorozirconate, 1.2 parts triethylene glycol monobutyl ether, and 70.85 parts deionized water.

[0029] The preparation method of the zirconium-titanium composite sol is the same as in Example 1.

[0030] This embodiment also provides a method for preparing a chromium-free surface treatment liquid for color steel sheets, specifically including the following steps:

[0031] S1. Add 4 parts of γ-glycidyl etheroxypropyltrimethoxysilane to 18 parts of deionized water, adjust the pH to 3.5 with glacial acetic acid, and hydrolyze at 45°C for 1.5 hours to obtain silane hydrolysate. Then, add 1.2 parts of nano silica and 0.225 parts of cerium nitrate to it, heat to 65°C, and disperse by high-speed shearing for 2.5 hours to obtain cerium-silane modified nano silica dispersion.

[0032] S2. Mix 22 parts of zirconium-titanium composite sol with the remaining deionized water, add 0.25 parts of lanthanum nitrate, 0.225 parts of the remaining cerium nitrate and 0.05 parts of potassium fluorozirconate under stirring, heat to 50°C, stir and react for 2 hours to obtain rare earth-zirconium-titanium coordination sol with high reactivity and catalytic potential.

[0033] S3. Under stirring at 38℃ and 500rpm, slowly add the cerium-silane modified nano silica dispersion prepared in step S1 to the rare earth-zirconium-titanium coordination sol obtained in step S2. After the addition is complete, add 1.2 parts of triethylene glycol monobutyl ether and continue stirring for 0.8 hours. Then adjust the pH of the system to 4.2 with ammonia water. Finally, filter through a 1.0μm filter to obtain the treatment solution.

[0034] Example 3: This example provides a chromium-free surface treatment liquid for color steel plates. The treatment liquid comprises the following components by weight: 30 parts zirconium-titanium composite sol, 0.8 parts cerium nitrate, 0.5 parts lanthanum nitrate, 2 parts nano silica, 6 parts γ-aminopropyltriethoxysilane, 0.1 parts potassium fluorozirconate, 2 parts polyethylene glycol 400, and 55 parts deionized water.

[0035] The preparation method of the zirconium-titanium composite sol is the same as in Example 1.

[0036] This embodiment also provides a method for preparing a chromium-free surface treatment liquid for color steel sheets, specifically including the following steps:

[0037] S1. Add 6 parts of γ-aminopropyltriethoxysilane to 36 parts of deionized water, adjust the pH to 4 with glacial acetic acid, and hydrolyze at 50°C for 1 hour to obtain silane hydrolysate. Then, add 2 parts of nano silica and 0.48 parts of cerium nitrate to it, heat to 70°C, and disperse by high-speed shearing for 2 hours to obtain cerium-silane modified nano silica dispersion.

[0038] S2. Mix 30 parts of zirconium-titanium composite sol with the remaining deionized water, add 0.5 parts of lanthanum nitrate, 0.32 parts of the remaining cerium nitrate and 0.1 parts of potassium fluorozirconate under stirring, heat to 55°C, and stir for 1.5 hours to obtain rare earth-zirconium-titanium coordination sol with high reactivity and catalytic potential.

[0039] S3. Under stirring at 40℃ and 500rpm, slowly add the cerium-silane modified nano silica dispersion prepared in step S1 to the rare earth-zirconium-titanium coordination sol obtained in step S2. After the addition is complete, add 2 parts of polyethylene glycol 400 and continue stirring for 0.5 hours. Then adjust the pH of the system to 4.5 with ammonia water. Finally, filter through a 1.0μm filter to obtain the treatment solution.

[0040] Comparative Example 1: This comparative example provides a comparative treatment solution with the same raw material composition as Example 2. The difference is that the preparation method is a simple physical mixing, that is: all raw materials are added to the reaction vessel and stirred at 500 rpm for 2 hours at room temperature. Then, the pH is adjusted to 4.2 with ammonia water and then filtered through a 1.0 μm filter to obtain the comparative treatment solution.

[0041] Comparative Example 2: This comparative example provides a comparative treatment solution, which differs from Example 2 in that: cerium nitrate and lanthanum nitrate are not added to the raw materials, and the steps of adding cerium nitrate and lanthanum nitrate are omitted in preparation steps S1 and S2 respectively; the rest is the same as Example 2.

[0042] Comparative Example 3: This comparative example provides a comparative treatment solution, which differs from Example 2 in that potassium fluorozirconate is not added to the raw materials, and the step of adding potassium fluorozirconate is omitted in preparation step S2; the rest is the same as Example 2.

[0043] Comparative Example 4: This comparative example provides a comparative treatment solution, which differs from Example 2 only in that step S1 in the preparation method is modified. Specifically, step S1 is modified to: directly mixing organosilane coupling agent, nano-silica, cerium nitrate and water and then performing high-speed shear dispersion, without pre-hydrolysis and cerium ion-catalyzed grafting reaction.

[0044] Performance Testing: To verify the performance of the treatment solution prepared in this invention, the products obtained in Examples 1-3 and Comparative Examples 1-4 were subjected to uniform testing. The test substrate was a commercially available ordinary color steel plate that had been degreased with an alkaline degreasing agent, washed with water, and dried. The treatment solution was then uniformly coated onto the surface of the color steel plate at a coating amount of 3 g / m². 2 Then dry and cure at 80°C for 30 seconds.

[0045] 1. Corrosion resistance test: Referring to standard GB / T 10125-2021, the coated sample was cross-scratched and placed in a salt spray chamber for continuous spraying. The time when the first corrosion point appeared on the sample was recorded. The test result was the average of three parallel samples. The results are shown in Table 1.

[0046] 2. Adhesion Test: Referring to standard GB / T 9286-2021, 100 1mm×1mm squares were drawn on the coating using a cross-cutting tool. After adhering the squares with 3M 600 tape, the tape was wiped with an eraser to remove air bubbles. After standing for 1 minute, the tape was quickly peeled off, and the coating peeling was observed. Grade 0 was the best, characterized by completely smooth cut edges and no peeling within the grid. Grade 1 showed only minor peeling (≤5% area). Grade 2 showed 5-15% peeling. Grade 3 showed 15-35% peeling. Grade 4 showed 35-65% peeling. Grade 5 was the worst, with more than 65% peeling. The test results are shown in Table 1.

[0047] 3. Stability test: Each treatment solution sample was placed in a 50mL stoppered transparent glass bottle and placed in a constant temperature drying oven at 50℃ for accelerated storage test. After 7 days, the sample was taken out, cooled to room temperature, and the sample state (whether it was layered, precipitated, gelled, etc.) was observed. The corrosion resistance was retested according to the above method, and the corrosion resistance retention rate was calculated. The results are shown in Table 1.

[0048] Table 1 Performance Test Results

[0049]

[0050] As can be seen from the data in Table 1, Examples 1-3 all exhibited excellent corrosion resistance and adhesion, and good storage stability. However, Comparative Example 1 showed a sharp decline in performance, demonstrating that the chemical reaction assembly process of this invention is indispensable. Comparative Example 2 had a salt spray time of only 144 hours, proving that Ce... 3+ / La 3+ The catalytic bridging effect is crucial. The salt spray time of Comparative Example 3 was 216 h, significantly lower than that of Example 2, demonstrating that F... - For Zr 4+ The necessity of appropriate complexation to control sol activity. Comparative Example 4 showed a decrease in storage stability after 168 hours of salt spraying, demonstrating that silane pre-hydrolysis and cerium ion catalytic grafting are prerequisites for the formation of a stable hybrid network.

[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0052] The present invention and its embodiments have been described above. This description is not restrictive, and practical applications are not limited thereto. In conclusion, if those skilled in the art are inspired by this description and, without departing from the spirit of the invention, design similar methods and embodiments to this technical solution without creative effort, all such designs should fall within the protection scope of the present invention.

Claims

1. A chromium-free surface treatment liquid for a color steel sheet, characterized by comprising: The treatment solution comprises the following components by weight: 15-30 parts zirconium-titanium composite sol, 0.1-0.8 parts cerium nitrate, 0.05-0.5 parts lanthanum nitrate, 0.5-2 parts nano-silica, 2-6 parts organosilane coupling agent, 0.01-0.1 parts potassium fluorozirconate, 0.5-2 parts film-forming aid, and 55-85 parts deionized water; the zirconium-titanium composite sol is prepared by co-hydrolyzing zirconium oxychloride and tetrabutyl titanate under acidic conditions. The method for preparing the treatment solution includes the following steps: S1. Add organosilane coupling agent to 3-6 times its weight of deionized water, adjust the pH to 3-4 with glacial acetic acid, hydrolyze to obtain silane hydrolysate, then add nano silica and some cerium nitrate to it, heat and shear dispersion to obtain cerium-silane modified nano silica dispersion. S2. Mix the zirconium-titanium composite sol with the remaining deionized water, then add lanthanum nitrate, the remaining cerium nitrate and potassium fluorozirconate, heat and stir to react and obtain rare earth-zirconium-titanium coordination sol. S3. Add cerium-silane modified nano silica dispersion dropwise to rare earth-zirconium-titanium coordination sol. After the addition is complete, add film-forming aid, adjust pH, and filter to obtain the treatment solution.

2. The chromium-free surface treatment solution for a color steel plate according to claim 1, characterized in that, The zirconium-titanium composite sol is prepared by dissolving zirconium oxychloride and tetrabutyl titanate in a mixed solvent of ethanol and water, then adding nitric acid solution dropwise until the pH of the system is 3, refluxing the reaction and then aging it to obtain the zirconium-titanium composite sol.

3. The chromium-free surface treatment solution for a color steel plate according to claim 2, characterized in that, The molar ratio of Zr to Ti in the zirconium oxychloride and tetrabutyl titanate is 1.5:1; the volume ratio of ethanol to water is 1:

1.

4. The chromium-free surface treatment solution for color steel sheets according to claim 1, characterized in that, The organosilane coupling agent is γ-aminopropyltriethoxysilane or γ-glycidyl etheroxypropyltrimethoxysilane.

5. The chromium-free surface treatment solution for color-coated steel sheets according to claim 1, characterized in that, The film-forming aid is polyethylene glycol 400 or triethylene glycol monobutyl ether.

6. The chromium-free surface treatment solution for color coated steel sheets according to claim 1, wherein The amount of cerium nitrate used in step S1 is 40%-60% of the total amount of cerium nitrate.

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