A high-purity fluorine-free trivalent chromium color passivation solution comparable to hexavalent chromium color in color and high resistance to impurities and preparation thereof

Abstract

The present application belongs to the technical field of passivation of galvanized parts, and particularly relates to a high-intolerance fluorine-free trivalent chromium color passivation solution comparable to hexavalent chromium in color and high in impurity resistance and preparation thereof. Main components are main salt, complexing agent, rare earth regulator, color forming agent, color enhancer, auxiliary complexing agent, buffer salt and wetting agent. The main salt includes basic chromium sulfate and chromium acetate, the complexing agent includes modified tartaric acid, gluconic acid and itaconic acid, the rare earth regulator includes lanthanum sulfate and anhydrous cerium nitrate, the color forming agent includes ammonium paratungstate, potassium antimony tartrate and ammonium metatungstate, the color enhancer includes acetylacetone vanadyl and bismuth ammonium citrate, the auxiliary complexing agent includes modified diethylene triamine pentaformyl phosphonic acid, the buffer salt includes citric acid and potassium dihydrogen phosphate, and the wetting agent includes acetylene diol modified siloxane. The prepared trivalent chromium color passivation solution can realize passivation at room temperature, has high impurity resistance, increases the film thickness to the level of hexavalent chromium passivation, and has a full color similar to hexavalent chromium in appearance.

Description

Technical Field

[0001] This invention belongs to the field of passivation technology for zinc-plated parts, and in particular relates to a high-impurity, fluorine-free trivalent chromium colored passivation liquid with a color comparable to hexavalent chromium and its preparation. Background Technology

[0002] The standard process in the electroplating zinc industry is pretreatment → electroplating zinc → passivation → sealing → packaging and shipping. Most domestic zinc plating production lines have completely replaced hexavalent chromium with trivalent chromium for colored passivation. However, the mainstream trivalent chromium passivation solutions contain fluorine and cobalt, which are subject to environmental restrictions and are sensitive to impurities, or they are either fluorine-free and cobalt-free and have a lighter color. Figure 1 and Figure 2 The image shows the appearance of a galvanized part after undergoing trivalent chromium color passivation using existing processes. It can be seen that the passivation film lacks red and purple hues, failing to achieve the vibrant rainbow colors of hexavalent chromium. The trivalent chromium color passivation film thickness is 50nm-150nm, which is insufficient, indicating a deficiency in Fe in the trivalent chromium color passivation solution. 2+ >0.1g / L, Cu 2+ When the concentration is >0.03 g / L, the film layer will turn black and develop a mottled appearance.

[0003] The mechanism of trivalent chromium color passivation for galvanized parts is as follows: During passivation, zinc on the coating surface dissolves to form zinc ions, simultaneously increasing the pH value of the passivation solution on the zinc coating surface. Trivalent chromium reacts directly with zinc ions, hydroxide ions, etc., forming insoluble compounds that precipitate on the zinc coating surface, thus forming a passivation film. The reaction process includes the following: Zinc dissolution process: Zn + O m (Oxidizing agent) → Zn 2+ +O m - Zn+2H + →Zn 2+ +H2; Film formation process: Zn 2+ +xCr 3+ +yH2O→ZnCr x O y +2yH + ; Film dissolution process: ZnCr x O y +2yH + →Zn 2+ +xCr 3+ +yH2O.

[0004] Trivalent chromium passivating agents generally contain the following components: (1) Trivalent chromium (Cr) 3+ The main source of the passivation film is trivalent chromium, which can be obtained from chromium sulfate, chromium nitrate, chromium chloride, chromium acetate, etc.

[0005] (2) Oxidizing agents: These dissolve the zinc plating to produce zinc ions and promote the formation of a passivation film. Suitable oxidizing agents include hydrogen peroxide, nitrates, persulfates, and tetravalent cerium. Oxidizing agents that can oxidize trivalent chromium to hexavalent chromium cannot be used arbitrarily because they do not meet environmental protection requirements.

[0006] (3) Other metal ions: mainly used to adjust appearance, color and corrosion resistance, such as Mn, Ti, Fe, Co and Ni.

[0007] (4) Complexing agents: These affect the stability of the passivation solution, as well as the quality and formation rate of the passivation film. If the complexing ability is too strong, the film formation rate is slow, the film layer is thin, or even no film layer can be formed; if the complexing ability is too weak, the passivation solution has poor stability, and the film layer has no luster. Complexing agents include fluorides, organic carboxylic acids, and mixtures thereof.

[0008] (5) Film-forming accelerators: Adjust the color of the film. Different film-forming accelerators can be selected to form different colors. Organic and inorganic anions can be used, such as NO3. - SO4 2- PO4 3- F - Cl - SiO3 2- SiF6 2- BF4 - 、RCOOH.

[0009] In summary, the traditional hexavalent chromium passivation process has a long history of application, a long service life, and extremely high acceptance for its appearance, texture, and visual effects. Therefore, developing a trivalent chromium passivation solution that meets both color and quality requirements is an urgent problem to be solved. Summary of the Invention

[0010] To address the problems existing in the prior art, this invention provides a passivation solution of trivalent chromium with high impurity resistance and color comparable to hexavalent chromium, and its preparation process.

[0011] This invention provides a high-impurity, fluorine-free trivalent chromium passivation solution with a color comparable to hexavalent chromium, containing the following components: main salt, complexing agent, rare earth regulator, colorant, color enhancer, auxiliary complexing agent, buffer salt, and wetting agent. The main salts include basic chromium sulfate and chromium acetate, with a mass ratio of 5:2. The main salt content in the passivation solution is 8.0 g / L to 10.5 g / L. The complexing agent includes modified tartaric acid, gluconic acid and itaconic acid, with a mass ratio of 4:3:2. The complexing agent content in the passivation solution is 14.0 g / L to 17.5 g / L. The rare earth modifiers include lanthanum sulfate and anhydrous cerium nitrate in a mass ratio of 2:1, and the content of rare earth modifiers in the passivation solution is 2.0 g / L to 3.5 g / L. The colorant includes ammonium molybdate, potassium antimony tartrate, and ammonium metatungstate, with a mass ratio of 6:2:1. The content of the colorant in the passivation solution is 3.0 g / L to 4.8 g / L. The color enhancer includes vanadium acetylacetonate and bismuth ammonium citrate in a mass ratio of 3:1, and the color enhancer content in the passivation solution is 0.2 g / L to 0.45 g / L. The auxiliary complexing agent includes modified diethylenetriamine pentamethylphosphonic acid, and the content of the auxiliary complexing agent in the passivation solution is 0.6 g / L~1.2 g / L; The buffer salts consist of citric acid and potassium dihydrogen phosphate in a mass ratio of 3:1, and the buffer salt content in the passivation solution is 3.5 g / L to 5.5 g / L. The wetting agent includes acetylenic diol modified siloxane, and the wetting agent content in the passivation solution is 0.2 g / L to 0.5 g / L; The pH of the passivation solution is 2.5 to 2.9, which can be adjusted using dilute sulfuric acid (10% by mass). Passivation can be carried out at room temperature without additional heating, preferably 26℃-32℃.

[0012] This invention discloses a method for preparing a trivalent chromium passivation solution with color comparable to hexavalent chromium, resistant to impurities, and fluorine-free, comprising the following steps: adding a complexing agent and a buffer salt to hot water, and adding the main salt in batches after complete dissolution to form a chromium chelation system; then adding a rare earth regulator and a colorant to allow the coloring ions to complex after complete dissolution; after the solution cools to room temperature, adding a color enhancer, an auxiliary complexing agent, and a wetting agent; mixing well; adjusting the pH; and filtering to obtain a trivalent chromium colored passivation solution, denoted as RTDH555.

[0013] The trivalent chromium passivation solution of this invention has stable performance and does not contain fluorides, nitrates, hydrogen peroxide, cobalt salts, etc., and is effective against Zn. 2+ The tolerance reaches 15 g / L, and it is effective against Fe. 2+ Its tolerance reaches 0.2 g / L, and it is effective against Cu. 2+ The tolerance reaches 0.06 g / L; a smooth, adjustable film thickness, a hexavalent chromium passivation level, high corrosion resistance, and a bright color imitating hexavalent chromium can be prepared on flat, curved, and sharp surfaces of galvanized parts.

[0014] The present invention has the following beneficial effects: 1. Integrated system: Passivation can be achieved with a single set of solutions, eliminating the need for mixing base solution and color-enhancing solution.

[0015] 2. Differentiated Combination: The four conventional color-matching additives, namely fluoride, nitrate, hydrogen peroxide, and cobalt salt, are completely eliminated throughout the process. A brand-new combination of modified tricarboxylic acid, lanthanum and cerium rare earth elements, and molybdenum, antimony, tungsten and bismuth is adopted for coloring.

[0016] 3. Differentiated Mechanism: Abandoning the oxidant oxidation color development mode, it refines the grain size through rare earth elements and improves the refractive index and thickness of the film through multi-metal ion lattice doping. It relies on optical interference to form a complete rainbow color gradation, fundamentally avoiding Cr... 3+ Conversion of Cr 6 + .

[0017] 4. Performance differentiation: The passivation system has advantages such as high impurity tolerance, pH self-buffering, and long bath life. At the same time, it increases the film thickness to the level of hexavalent chromium passivation and achieves equivalent substitution in appearance, with a full color that imitates hexavalent chromium.

[0018] 5. Process differentiation: Construction is carried out in the normal temperature range, without the need for high-temperature heating. The entire preparation process is carried out at normal pressure and low temperature, which is compatible with automated rolling and hanging production lines. Attached Figure Description

[0019] Figure 1 The image shows the appearance of a galvanized part after it has undergone trivalent chromium color passivation using existing processes. Figure 2 The image shows the appearance of a galvanized part after it has undergone trivalent chromium color passivation using existing processes. Figure 3 The image shows the appearance of a galvanized part after it has been color passivated with RTDH555 trivalent chromium according to the present invention. Figure 4 The image shows the appearance of a galvanized part after it has been color passivated with RTDH555 trivalent chromium by the second component of this invention. Figure 5 The image shows the appearance of a galvanized part after it has been color passivated with trivalent chromium using the RTDH555 trivalent chromium of this invention. Figure 6 The image shows the appearance of a galvanized part after it has been passivated by the trivalent chromium color passivation method of the fourth component of this invention, RTDH555. Figure 7 The image shows the appearance of a galvanized part after it has been color passivated with RTDH555 trivalent chromium by the fifth component of this invention. Figure 8 The image shows a sample of a galvanized part after being subjected to color passivation with RTDH555 trivalent chromium according to the present invention and after testing. Figure 9 The image shows a sample of a galvanized part after a test of a domestic product following trivalent chromium color passivation. Figure 10 This is a photograph of a test piece of a foreign product after a zinc-plated part underwent trivalent chromium color passivation. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. It should be noted that the embodiments described in this invention are only for further explanation and illustration, and not for limiting their application scope. Based on this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention.

[0021] Example 1 (1) The composition and application process of the trivalent chromium color passivation solution are shown in Table 1.

[0022] Table 1. Formulation and Process Conditions of Trivalent Chromium Color Passivation Solution for Zinc-Plated Parts

[0023] (2) Preparation of trivalent chromium colored passivation solution: S1: Add 650ml of deionized water to the closed reactor, heat to 40℃, and stir at 450r / min; add complexing agent and buffer salt, and stir at constant temperature until the solid is completely dissolved. S2: Add the main salt in 3 to 5 batches, with an interval of 5 minutes between each batch. After the addition is complete, stir at a constant temperature for 25 minutes to build a stable chromium chelation system. S3: Add rare earth regulator (nano-grade lanthanum / cerium salt) and stir for 20 minutes, then add colorant (molybdenum-antimony-tungsten compound) and stir for 30 minutes to complete color ion complexation; S4: Cool to 28℃, add vanadium bismuth colorant, auxiliary complexing agent (also phosphonic acid stabilizer), and wetting agent in sequence, and stir for 15 minutes to mix well; S5: Add water to bring the volume to 1L, adjust the pH with a small amount of dilute sulfuric acid, filter through a 200-mesh filter, and package the finished product.

[0024] (3) Using a certain batch of passivation solution as an example, the stability and passivation effect of the passivation solution are explained: Table 2. Passivation solution formulations used in the tests

[0025] The passivation solution formulations used in the tests are shown in Table 2. The parts passivated with the first group of passivation solution are as follows: Figure 3 As shown, the parts passivated by the group two passivating solution are as follows: Figure 4 As shown, the parts passivated by the group three passivation solution are as follows: Figure 5 As shown, the parts passivated by the group four passivating solution are as follows: Figure 6 As shown, the parts passivated by the group five passivating solution are as follows: Figure 7 As shown in the figure, parts of various shapes and sizes, after being treated with the RTDH555 passivation solution of this invention, all exhibit a beautiful appearance resembling the rainbow color of hexavalent chromium, with a smooth surface and a uniform and complete film thickness.

[0026] The passivation solutions of each group were subjected to stability tests after standing at room temperature. On days 1, 3, 5, and 7, the pH remained essentially unchanged with fluctuations ≤0.01, and no Cr was detected throughout the entire testing period. 6+ The solution remains clear throughout, and the passivation solution exhibits extremely stable performance.

[0027] Different concentrations of Zn were added to each group of passivation solutions. 2+ Fe 2+ Cu 2+ The tolerance of the passivation solution to metallic impurities was tested, and the results were examined after 3 days. Specific tolerance data are shown in Table 3. Overall, the pH fluctuation was small, indicating good tolerance to Zn. 2+ The tolerance reaches 15 g / L, and it is effective against Fe. 2+ Its tolerance reaches 0.2 g / L, and it is effective against Cu. 2+ The tolerance level reached 0.06 g / L.

[0028] Table 3. Stability test of passivation solution to metal impurities

[0029] To compare the corrosion resistance of tri-color passivation films on galvanized parts from different sources, a neutral salt spray test was conducted on five groups of test pieces from different sources, referring to HB5830.12-86. The results of the 96-hour neutral salt spray corrosion resistance test of the passivation film are shown in Table 4. The RTDH555 passivation film after the test... Figure 8 As shown, no white corrosion products were observed; however, a domestic product tested as shown... Figure 9 As shown, white corrosion products were the most abundant; a foreign product tested showed the following... Figure 10 As shown, some of the test pieces showed signs of corrosion.

[0030] Table 4 Corrosion Resistance Test of Trivalent Chromium Colored Passivation Film

[0031] The trivalent chromium colored passivation solution formulation and process conditions of the present invention can achieve the above-mentioned effects. It can be seen that the trivalent chromium colored passivation solution RTDH555 of the present invention is stable, has strong resistance to impurity interference, and the passivation film prepared has a color comparable to hexavalent chromium, while also having excellent corrosion resistance.

Claims

1. A high-impurity, fluorine-free trivalent chromium colored passivation solution with a color comparable to hexavalent chromium, characterized in that, The passivation solution contains the following components: main salt, complexing agent, rare earth modifier, colorant, color enhancer, auxiliary complexing agent, buffer salt, and wetting agent; The main salts include basic chromium sulfate and chromium acetate; the complexing agents include modified tartaric acid, gluconic acid, and itaconic acid; the rare earth modifiers include lanthanum sulfate and anhydrous cerium nitrate; the coloring agents include ammonium molybdate, potassium antimony tartrate, and ammonium metatungstate; the color-enhancing agents include vanadium acetylacetonate and bismuth ammonium citrate; the auxiliary complexing agent includes modified diethylenetriamine pentamethylphosphonic acid; the buffer salts include citric acid and potassium dihydrogen phosphate; and the wetting agent includes alkynyldiol modified siloxane.

2. The high-impurity, fluorine-free trivalent chromium colored passivation liquid with a color comparable to hexavalent chromium as described in claim 1, characterized in that, The mass ratio of basic chromium sulfate to chromium acetate in the main salt is 5:2; the mass ratio of modified tartaric acid, gluconic acid, and itaconic acid in the complexing agent is 4:3:2; the mass ratio of lanthanum sulfate to anhydrous cerium nitrate in the rare earth regulator is 2:1; the mass ratio of ammonium molybdate, potassium antimony tartrate, and ammonium metatungstate in the coloring agent is 6:2:1; the mass ratio of vanadium acetylacetonate and bismuth ammonium citrate in the color-enhancing agent is 3:1; and the mass ratio of citric acid to potassium dihydrogen phosphate in the buffer salt is 3:

1.

3. The high-impurity, fluorine-free trivalent chromium colored passivation liquid with a color comparable to hexavalent chromium as described in claim 1, characterized in that, The passivation solution contains a main salt content of 8.0 g / L to 10.5 g / L, a complexing agent content of 14.0 g / L to 17.5 g / L, a rare earth modifier content of 2.0 g / L to 3.5 g / L, a colorant content of 3.0 g / L to 4.8 g / L, a color enhancer content of 0.2 g / L to 0.45 g / L, an auxiliary complexing agent content of 0.6 g / L to 1.2 g / L, a buffer salt content of 3.5 g / L to 5.5 g / L, and a wetting agent content of 0.2 g / L to 0.5 g / L.

4. The high-impurity, fluorine-free trivalent chromium colored passivation liquid with a color comparable to hexavalent chromium as described in claim 1, characterized in that, The passivation solution has a pH of 2.5 to 2.9, which is adjusted using dilute sulfuric acid; passivation is carried out at room temperature without the need for additional heating.

5. The high-impurity, fluorine-free trivalent chromium colored passivation liquid with a color comparable to hexavalent chromium as described in claim 1, characterized in that, The passivation solution for Zn 2+ The tolerance reaches 15 g / L, and it is effective against Fe. 2+ Its tolerance reaches 0.2 g / L, and it is effective against Cu. 2+ The tolerance level reached 0.06 g / L.

6. The high-impurity, fluorine-free trivalent chromium colored passivation liquid with a color comparable to hexavalent chromium as described in claim 1, characterized in that, The passivation solution can produce a smooth, corrosion-resistant passivation film with a hexavalent chromium passivation level on flat, curved, and sharp surfaces of galvanized parts, as well as on surfaces with a bright color that mimics hexavalent chromium.

7. The preparation method of the high-impurity, fluorine-free trivalent chromium colored passivation liquid with a color comparable to hexavalent chromium as described in claim 1, characterized in that, The process includes the following steps: adding a complexing agent and a buffer salt to hot water, adding the main salt in batches after complete dissolution, forming a chromium chelation system after complete dissolution, then adding a rare earth regulator and a colorant, allowing the coloring ions to complex after complete dissolution, and then adding a colorant, an auxiliary complexing agent and a wetting agent after the solution has cooled to room temperature, mixing well, adjusting the pH and filtering to obtain a trivalent chromium colored passivation solution.

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