Environmentally friendly passivation solution for galvanized aluminum-magnesium plate and preparation method thereof

Abstract

The invention discloses an environmentally friendly passivation solution for galvanized aluminum-magnesium plates and a preparation method thereof. The environmentally friendly passivation solution is composed of the following components by weight percentage: (A) a silane hydrolysis solution containing at least one divalent silane: 1%-10%; (B) an aqueous dispersion or emulsion of an organic resin: 5%-20%; (C) a water-soluble trivalent chromium salt: 5%-10%; (D) nitric acid or nitrate: 0.5%-5%; (E) nickelate: 0.5%-5%; (F) fluoride: 0.1%-1%; the balance is deionized water. The environmentally friendly passivation solution for galvanized aluminum-magnesium plates of the invention not only retains the advantages of corrosion resistance and low ton consumption of traditional trivalent chromium passivation solutions, but also provides excellent rust resistance and blackening resistance, has fast and uniform film formation, can be quickly dried under medium and low temperature conditions, and meets the requirements of continuous and high-speed production in steel plants.

Description

Technical Field

[0001] The invention belongs to the field of chemical materials, and specifically relates to an environmentally friendly passivation solution for galvanized aluminum-magnesium plates and a preparation method thereof. Background Art

[0002] Zn-Al-Mg is a highly corrosion-resistant zinc alloy hot-dip coated steel sheet. The main elements of the alloy coating, zinc (Zn), aluminum (Al) and magnesium (Mg), form a ternary eutectic structure under a certain composition ratio and process. Due to the effects of Mg and Al, this type of alloy sheet has excellent corrosion resistance, scratch resistance and formability. The trend of replacing hot-dip galvanized or aluminum-zinc coated steel sheets is becoming increasingly obvious. Existing Zn-Al-Mg alloy coated steel sheets can be divided into "medium-low aluminum" with Al content <13% and "high aluminum" alloy steel sheets with Al content of 47%≤Al≤57%, and the Mg content is generally between 0.1%-3%.

[0003] In the prior art, the surface of zinc-aluminum-magnesium plates turns black after being placed in a hot and humid environment for a period of time, which is called "blackening". The mechanism of "blackening" is still under study. Relevant literature shows that the following reasons may cause blackening: the metal magnesium on the alloy surface is electrochemically active and is easily dissolved by chemical or electrochemical means to form corrosion products. When the magnesium alloy is exposed to a hot and humid environment, the carbon dioxide (CO2) in the hot and humid air and the naturally formed magnesium hydroxide (Mg(OH)2) layer on the magnesium alloy plate undergo a "carbonization" reaction to generate "hydromagnesite" (Mg5(CO3)4(OH)2·4H2O). These surface defects not only affect the appearance of the plate, but also affect its subsequent use, especially for zinc-aluminum-magnesium alloy coatings with medium and low aluminum. Existing passivation products are still unable to effectively solve this problem. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the main purpose of the present invention is to provide an environmentally friendly passivation solution for galvanized aluminum-magnesium plates. In addition to retaining the advantages of traditional trivalent chromium passivation solution such as corrosion resistance and low ton consumption, the passivation solution also provides excellent rust resistance and blackening resistance, has fast and uniform film formation, can be quickly dried under medium and low temperature conditions, and meets the requirements of continuous and high-speed production in steel mills.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned environmentally friendly passivation solution for galvanized aluminum-magnesium plates, which has a simple process and is easy to mass produce.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] The present invention provides an environmentally friendly passivation solution for galvanized aluminum-magnesium plates, which is composed of the following components in terms of weight percentage:

[0008] (A) Silane hydrolysis solution containing at least one dipodal silane: 1%–10%;

[0009] (B) Aqueous dispersion or emulsion of organic resin: 5%–20%;

[0010] (C) Water-soluble trivalent chromium salt: 5%–10%;

[0011] (D) Nitric acid or nitrates: 0.5%–5%;

[0012] (E) Nickelate: 0.5%–5%;

[0013] (F) Fluoride: 0.1%–1%;

[0014] The balance was deionized water.

[0015] Preferably, the diphenylsilane in component (A) is selected from one or more of 1,2-bis(triethoxysilyl)ethane, 1,2-bis(trimethoxysilyl)ethane, bis(3-trimethoxysilylpropyl)amine, bis[3-(triethoxysilyl)propyl]amine, and 4,4'-bis(triethoxysilyl)-1,1'-biphenyl.

[0016] Preferably, the silane used in the silane hydrolysis solution in the component (A) is a silane coupling agent, selected from one or more of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropyloxy)propyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, ethyl orthosilicate and methyl orthosilicate.

[0017] Preferably, the aqueous dispersion or emulsion of the organic resin in the component (B) is selected from one or more of an acidic aqueous acrylic resin, an aqueous polyurethane resin, an aqueous epoxy resin or an aqueous phenolic resin.

[0018] Preferably, the water-soluble trivalent chromium salt in the component (C) is selected from one or more of chromium phosphate, chromium nitrate, chromium sulfate and chromium chloride.

[0019] Preferably, the nitrate in the component (D) is a water-soluble nitrate selected from one or more of potassium nitrate, cerium nitrate and magnesium nitrate.

[0020] Preferably, the nickelate in component (E) is selected from one or more of nickel sulfate, nickel carbonate and nickel chloride.

[0021] Preferably, the fluoride in the component (F) is selected from one or more of sodium fluoride, potassium fluoride and ammonium fluoride.

[0022] Among the components of the environmentally friendly passivation solution for galvanized aluminum-magnesium plates of the present invention, the role of the diisocyanate is to form a dense passivation film, thereby improving the damage resistance of the passivation film during its processing; the organic resin is also used to improve the density and ductility of the trivalent chromium passivation film; the fluoride can promote the dissolution of the surface zinc layer, improve the activity of the plate surface, and promote the rapid film formation of the passivation film, thereby achieving the purpose of low-temperature film formation; the role of nitric acid or nitrates and nickelates is to inhibit the oxidation of magnesium in the zinc-aluminum-magnesium steel plate, thereby providing excellent blackening resistance.

[0023] The present invention also provides a method for preparing the environmentally friendly passivation solution for the galvanized aluminum-magnesium plate, comprising the following steps:

[0024] (1) weighing at least one dipodal silane, adding it to a mixture of deionized water and / or an alcohol solvent with stirring for hydrolysis, adjusting the pH value of the mixed solution to 4-5 with an acid, and stirring until the solution is clear to obtain a dipodal silane hydrolysis solution; preparing a silane hydrolysis solution in the same manner, mixing the dipodal silane hydrolysis solution and the silane hydrolysis solution in proportion to obtain a silane hydrolysis solution containing at least one dipodal silane;

[0025] (2) weighing a measured amount of trivalent chromium salt, dissolving the trivalent chromium salt with deionized water at 50-70°C, and stirring evenly to form a water-soluble trivalent chromium salt solution;

[0026] (3) adding nitric acid or nitrate, nickelate, or fluoride to the water-soluble trivalent chromium salt solution of step (2), stirring until completely dissolved, and adding deionized water to compensate for the water volatilized during the preparation of the solution;

[0027] (4) cooling to room temperature under stirring, and adding the silane hydrolysis solution containing at least one diphenylsilane described in step (1) to the mixed solution obtained in step (3), and stirring evenly;

[0028] (5) Under stirring conditions, adding the aqueous dispersion or emulsion of the organic resin to the mixed solution obtained in step (4) and stirring evenly.

[0029] Compared with the prior art, the environmentally friendly passivation solution for galvanized aluminum-magnesium plate of the present invention has the following beneficial effects:

[0030] ① It does not contain hexavalent chromium compounds and is an environmentally friendly passivation composition that complies with RoHs and Reach certifications;

[0031] ② Excellent black discoloration resistance, black discoloration resistance color difference △E can be controlled within 3 (traditional trivalent chromium is coated on zinc-aluminum-magnesium plates, and the black discoloration resistance color difference △E is around 10-20);

[0032] ③ Rapid film formation and rapid drying under medium and low temperature conditions (i.e. low temperature curing) to meet the requirements of continuous and high-speed production in steel plants;

[0033] ④Low ton consumption. Compared with similar chromium-free products, the cost is at least reduced by half. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention is clearly and completely described below. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The environmentally friendly passivation solution for galvanized aluminum-magnesium plates provided in the following embodiments is composed of the following components in weight percentage: (A) a silane hydrolysis solution containing at least one dipodal silane: 1%-10%; (B) an aqueous dispersion or emulsion of an organic resin: 5%-20%; (C) a water-soluble trivalent chromium salt: 5%-10%; (D) nitric acid or nitrate: 0.5%-5%; (E) a nickelate: 0.5%-5%; (F) a fluoride: 0.1%-1%; the remainder is deionized water.

[0036] The method for using the environmentally friendly passivation solution for galvanized aluminum-magnesium plates in the following embodiments includes degreasing cleaning and roller coating to evenly distribute the passivation solution on the surface of the galvanized aluminum-magnesium plates. The specific steps are as follows:

[0037] 1) Degreasing to remove organic pollutants on the surface of galvanized aluminum-magnesium plate;

[0038] 2) Rinse with tap water;

[0039] 3) Wash with deionized water and blow dry for later use;

[0040] 4) At room temperature, a certain amount of the environmentally friendly passivation solution for the galvanized aluminum-magnesium plate of the present invention is evenly coated on the surface of the galvanized aluminum-magnesium plate using a stainless steel coating stick;

[0041] 5) putting it into an automatic discharge oven for drying to obtain the galvanized aluminum-magnesium plate passivated by the above passivation solution.

[0042] The performance test of the environmentally friendly passivation solution for galvanized aluminum-magnesium plates in the following examples is as follows:

[0043] (a) Blackening resistance test (excellent blackening resistance): According to the wet heat test (GB / T1740-2007 Determination of wet heat resistance of paint film), the surface color difference △E is tested using a surface colorimeter.

[0044] (b) Drying property (low temperature curing effect): Using an automatic discharge oven, at 240°C hot air drying conditions, the formation of the passivation film on the board surface was observed at different drying times. The drying time when no green color was lost when wiped with a wet tissue at a force of 10N was taken as the complete curing time of the passivation film.

[0045] (c) Salt spray performance (excellent rust resistance): According to the national standard (GB / T10125-2012 Artificial atmosphere corrosion test salt spray test), the salt spray performance is judged by the corrosion area. The salt spray test time is 120 hours.

[0046] The raw material composition and proportion of Examples 1-8 are shown in Table 1. At the same time, a conventional silane-based acidic chromium-free passivation product is used as Comparative Example 1 and a conventional trivalent chromium passivation product is used as Comparative Example 2. The performance test results of the passivation compositions obtained from Examples 1-8, Comparative Example 1 and Comparative Example 2 are shown in Table 2.

[0047] Table 1

[0048]

[0049] In Table 1, the dipodal silane is Hangzhou Jessica KH-170; the acrylic-polyurethane emulsion is Hubei Nuobao AC 014; the trivalent chromium salt is Shanghai Liangren Chemical chromium nitrate; and the nitrate, nickelate and fluoride are provided by Shanghai Jingxuan.

[0050] Table 2

[0051]

[0052] It can be seen from Table 2 that diisopropyl silane, acrylic-polyurethane emulsion and trivalent chromium salt have a promoting effect on salt spray, but the protective effect of blackening resistance on zinc-aluminum-magnesium board is not good. The environmentally friendly passivation composition after adding nitrate and nickelate has excellent blackening resistance, and the blackening resistance color difference △E is within 3 (the blackening resistance color difference △E of traditional trivalent chromium coating on zinc-aluminum-magnesium board is about 10-20). The addition of fluoride can effectively improve the low-temperature curing effect and quickly dry under medium and low temperature conditions to meet the continuous and high-speed production requirements of steel mills.

[0053] The above description of the embodiments is to facilitate the understanding and use of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without having to go through creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the principles of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. An environmentally friendly passivation solution for galvanized aluminum-magnesium plate, characterized in that: The composition is as follows according to weight percentage: (A) Silane hydrolysis solution containing at least one dipodal silane: 1%-10%; (B) Aqueous dispersion or emulsion of organic resin: 5%-20%; (C) Water-soluble trivalent chromium salt: 5%-10%; (D) Nitric acid or nitrate: 0.5%-5%; (E) Nickelate: 0.5%-5%; (F) Fluoride: 0.1%-1%; The balance is deionized water; The dipodal silane in the component (A) is selected from one or more of 1,2-bis(triethoxysilyl)ethane, 1,2-bis(trimethoxysilyl)ethane, bis(3-trimethoxysilylpropyl)amine, bis[3-(triethoxysilyl)propyl]amine, and 4,4'-bis(triethoxysilyl)-1,1'-biphenyl; The silane used in the silane hydrolysis solution in the component (A) is a silane coupling agent, selected from one or more of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropyloxy)propyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, ethyl orthosilicate and methyl orthosilicate; The nitrate is a water-soluble nitrate selected from one or more of potassium nitrate, cerium nitrate and magnesium nitrate; The fluoride is selected from one or more of sodium fluoride, potassium fluoride and ammonium fluoride.

2. The environmentally friendly passivation solution for galvanized aluminum-magnesium plate according to claim 1 is characterized in that: The aqueous dispersion or emulsion of the organic resin is selected from one or more of an acidic aqueous acrylic resin, an aqueous polyurethane resin, an aqueous epoxy resin or an aqueous phenolic resin.

3. The environmentally friendly passivation solution for galvanized aluminum-magnesium plate according to claim 1 is characterized in that: The water-soluble trivalent chromium salt is selected from one or more of chromium phosphate, chromium nitrate, chromium sulfate and chromium chloride.

4. The environmentally friendly passivation solution for galvanized aluminum-magnesium plate according to claim 1 is characterized in that: The nickelate is selected from one or more of nickel sulfate, nickel carbonate and nickel chloride.

5. The method for preparing the environmentally friendly passivation solution for galvanized aluminum-magnesium plate according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) weighing at least one dipodal silane, adding it to a mixture of deionized water and / or an alcohol solvent with stirring for hydrolysis, adjusting the pH value of the mixed solution to 4-5 with an acid, and stirring until the solution is clear to obtain a dipodal silane hydrolysis solution; preparing a silane hydrolysis solution in the same manner, mixing the dipodal silane hydrolysis solution and the silane hydrolysis solution in proportion to obtain a silane hydrolysis solution containing at least one dipodal silane; (2) Weigh a measured amount of trivalent chromium salt, dissolve the trivalent chromium salt in deionized water at 50-70°C, and stir evenly to form a water-soluble trivalent chromium salt solution; (3) adding nitric acid or nitrate, nickelate, and fluoride to the water-soluble trivalent chromium salt solution of step (2), stirring until completely dissolved, and adding deionized water to compensate for the water volatilized during the preparation of the solution; (4) cooling to room temperature under stirring, adding the silane hydrolysis solution containing at least one diphenylsilane described in step (1) to the mixed solution obtained in step (3), and stirring evenly; (5) Under stirring conditions, add the aqueous dispersion or emulsion of the organic resin to the mixed solution obtained in step (4) and stir evenly.

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