Alkaline passivation solution for medium aluminum-zinc-aluminum-magnesium coated steel plate and passivation method

Abstract

The invention discloses an alkaline passivation solution for a medium aluminum-zinc-aluminum-magnesium coated steel plate and a passivation method, and the passivation solution comprises the following components: 2-3% of ethylene-vinyl acetate copolymer, 2-3% of water-resistant acrylic resin monomer, 2-3% of styrene, 0.5-1% of tackifying resin, 0.01-0.05% of plasticizer, 2-4% of emulsifier, 0.5-1.5% of initiator, 0.1-0.2% of auto-polymerization polyphenol, 5-15% of nano titanium dioxide antibacterial sol, and the balance of water. And the balance of water. The method overcomes the defects that a traditional acrylic resin film loses efficacy and is poor in water resistance due to the fact that the traditional acrylic resin film easily absorbs water and swells, zinc and aluminum ions react with an oxidizing agent in an alkaline environment to be converted into a zinc oxide and aluminum oxide passivation film, a persulfate oxidizing agent initiates resin polymerization to form a film, and finally an organic-inorganic composite passivation film is formed on the surface of a plating layer. The alkaline passivation solution does not use heavy metal oxysalt, is green and environment-friendly, and is suitable for industrial large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material surface treatment, and specifically relates to an alkaline passivation solution for a medium aluminum-zinc-aluminum-magnesium coated steel plate and a passivation method. Background Art

[0002] Zn-Al-Mg alloy coating attracted wide attention abroad in the 1980s and became the research focus in the professional field of hot-dip galvanizing and zinc alloy coating. According to the research results of domestic and foreign peers, under the same level of Zn and Al content in the coating, hot-dip Zn-Al-Mg alloy coated steel plates with Mg added have better corrosion resistance, and the processing and application performance (formability, weldability and paintability) of the material is excellent. Due to the excellent corrosion resistance of the punching and cutting parts, it can replace the current corresponding hot-dip galvanized or zinc alloy coated steel plates, and the market demand prospects are very broad.

[0003] Existing hot-dip Zn-Al-Mg alloy coated steel plates can be divided into three types: "low aluminum" (W Al < 5%), "medium aluminum" (5% ≤ W Al < 13%) and "high aluminum" (47% ≤ W Al ≤ 57%). In the field of engineering and construction applications, in order to ensure that the Zn-Al-Mg alloy coated steel plates meet the user's requirements for corrosion resistance and formability, especially the protection performance of punching parts and cut sections, medium aluminum zinc aluminum magnesium coating is usually used.

[0004] Since there are a large number of Al and Mg elements on the surface of the zinc-aluminum-magnesium alloy coating, oxidation and rust are very likely to occur during placement, storage and transportation. In order to improve the corrosion resistance of zinc-aluminum-magnesium alloy coated steel plates, surface passivation treatment is required. The existing zinc-plated surface treatment technology is still mainly based on the acidic system. Under the acidic system, the metal surface is first "activated" to form zinc ions, and then reacts with metal oxygen-containing acid salts such as phosphates, molybdates, chromates, and vanadates in the passivation solution to form the corresponding metal oxygen-containing acid zinc salt passivation film. However, the formed zincate film, such as zinc molybdate, zinc chromate, and vanadate, is easy to dissolve in acidic conditions and produce heavy metal salt residues, polluting the environment. The metal surface treatment solution of the acidic system has the problems that zinc ions are not easy to convert into zinc oxide passivation layers, and the passivation film is easy to dissolve in acidic environments.

[0005] Compared with acidic passivation, passivation under alkaline conditions can form a denser and more complete zinc oxide film or aluminum oxide passivation film, which is more corrosion-resistant than metal oxygen acid salt passivation film. At the same time, alkaline passivation treatment is relatively mild and more suitable for some special applications, such as food processing, medical equipment and other fields, so it is more environmentally friendly. The formula avoids the use of metal oxygen acid salts such as chromium, zirconium, manganese, vanadium, cobalt, nickel acid salts, etc., and the content of heavy metal ions introduced into the passivation solution is less, which is conducive to reducing environmental pollution and harm to human health. For example, the patent with publication number CN102753728B provides a surface composition of alkaline passivated zinc, comprising at least 50ppm trivalent Fe ions, 100ppm phosphate ions, and 100ppm chelating agent; the patent with publication number CN107002247A provides an alkaline cerium-based coating composition for metal surface pretreatment. Although these patented technologies are all alkaline passivators, they all contain heavy metal oxygenates, phosphates or rare earth metal salts. The passivation conversion film takes a long time and the temperature is high, which is not conducive to efficient continuous coated steel plate passivation production lines. Summary of the invention

[0006] To overcome the defects of the prior art, the passivation liquid used in the present invention is an organic-inorganic composite passivation liquid, and the organic substance is mainly composed of styrene-acrylic emulsion-EVA mixed resin as the main film-forming agent, with excellent hydrophobic properties, existing in the emulsion as an oil phase, and water as a continuous phase. The passivation agent is an O / W type emulsion, so there is no need to use volatile and toxic resin solvents such as toluene and xylene, which is more environmentally friendly. Compared with the hydrophilic groups of traditional acrylic resins and polyurethane resins, there are fewer and stronger water resistance. Adding self-polymerizing polyphenol compounds in an alkaline environment, a high adhesion and reductive protective film is formed on the surface of the coating, and the styrene-acrylic emulsion EVA mixed resin film is coordinated to protect the coating. At the same time, persulfate is used in the water-resistant styrene-acrylic emulsion polymerization process, which can promote the double bond polymerization of the resin on the one hand, and as an oxidant, the zinc-aluminum-magnesium coating metal is ionized, and the corresponding metal oxide is generated in situ in an alkaline environment to complete the passivation reaction. The passivation liquid does not contain heavy metals or rare earth metal salts, is not only environmentally friendly, but also has good corrosion resistance, water resistance and good anti-processing performance.

[0007] In order to achieve the above-mentioned invention object, the present invention provides an alkaline passivation solution for medium-aluminum-zinc-aluminum-magnesium coated steel plate, wherein the passivation solution comprises the following components by mass content: 2% to 3% ethylene-vinyl acetate copolymer, 2% to 3% water-resistant acrylic resin monomer, 2% to 3% styrene, 0.5% to 1% tackifying resin, 0.01% to 0.05% plasticizer, 2% to 4% emulsifier, 0.5% to 1.5% initiator, 0.1% to 0.2% self-polymerizing polyphenol, 5% to 15% nano titanium dioxide antibacterial sol, and the rest is water.

[0008] Furthermore, the water in the components of the alkaline passivation solution is pure water, and its specific resistance is ≥1 MΩ·cm.

[0009] Furthermore, the ethylene-vinyl acetate (EVA) copolymer in the components of the alkaline passivation solution is one of many brands such as EVA705, EVA707, EVA602, EVA716, EVA905, EVA907, EVA916, EVA960, etc., the mass fraction of ethylene in EVA is 5% to 22%, and the viscosity at 25°C is 500 to 2200 mPa·s.

[0010] Furthermore, the plasticizer in the components of the alkaline passivation solution is one of dioctyl phthalate (DOP), dibutyl phthalate (DBP), and diethyl phthalate (DEP), preferably dibutyl phthalate (DBP).

[0011] Further, the emulsifier in the components of the alkaline passivation solution is an oil-in-water O / W type anionic emulsifier, such as one of sodium dodecylbenzene sulfonate, sodium lauryl sulfate, sodium laurate, sodium oleate, and sodium stearate. Anionic surfactants are used in alkaline environments mainly because they have better solubility and surface activity than cationic surfactants or nonionic surfactants under alkaline conditions.

[0012] Furthermore, the self-polymerizing polyphenol in the components of the alkaline passivation solution is 5,6-dihydroxyindole or 2-(3,4-dihydroxyphenyl)ethylamine. In an alkaline environment, these two monomers can self-polymerize into a high-adhesion and reducing polymer film as an electron donor, providing cathodic protection for the medium-aluminum-zinc-aluminum-magnesium coating and enhancing the corrosion resistance of the coating.

[0013] Furthermore, the nano antibacterial component in the alkaline passivation solution is a nano titanium dioxide sol, which is prepared by hydrolysis of titanium alkoxide, and the titanium alkoxide is one or more of tetraethyl titanate, n-propyl titanate, isopropyl titanate and tetrabutyl titanate. The hydrolysis method is used to prepare nano titanium dioxide, which requires the use of an alkaline environment, which is compatible with the pH environment of the passivation solution finally prepared, and the prepared nano titanium dioxide sol does not need to be separated separately by centrifugal drying or the like, and other components can be directly added to continue to configure the passivation agent.

[0014] Further, the initiator used in the styrene-acrylic emulsion polymerization process in the components of the alkaline passivation solution is a water-soluble inorganic peroxide initiator, including one of ammonium persulfate, sodium persulfate, potassium persulfate, and potassium hydrogen persulfate. Persulfate in the passivation solution can promote resin polymerization on the one hand, and can also oxidize the coating and promote the formation of a passivation film.

[0015] A method for preparing an alkaline passivation solution for the above-mentioned aluminum-zinc-aluminum-magnesium coated steel plate, the preparation method comprising preparing a nano titanium dioxide-EVA emulsion by a sol-gel method, preparing a water-resistant styrene-acrylic emulsion by thermal polymerization, and finally configuring the passivation solution; specifically comprising the following steps

[0016] ① Add 1 to 2 parts by weight of polyethylene glycol to 30 to 40 parts by weight of titanium alkoxide, and mix thoroughly in a water bath at 70° C. to 80° C. to obtain a mixed solution A;

[0017] ② Add the mixed solution A dropwise into 100 parts by weight of ethylene-vinyl acetate copolymer emulsion containing 5 wt% ammonia water within 2 hours, and react under stirring at 500-700 rpm to obtain a nano-titanium dioxide antibacterial sol, which is named as emulsion B for standby use;

[0018] ③ Pre-emulsification: 100 parts by mass of deionized water, 1-2 parts by mass of emulsifier sodium dodecylbenzene sulfonate, 2 parts by mass of sodium bicarbonate, 0.1-0.2 parts by mass of plasticizer dibutyl phthalate, 20 parts by mass of methyl methacrylate, and 15 parts by mass of styrene mixed monomer solution are added into a pre-emulsification kettle, and pre-emulsified at room temperature to obtain a stable pre-emulsified liquid C; at this time, the emulsion monomer is in an unpolymerized state;

[0019] ④ Prepare an initiator solution and a protective colloid solution: add 1 part by mass of sodium persulfate to 100 parts by mass of the emulsion B to prepare an initiator protective colloid solution;

[0020] ⑤ Polymerization: Add 50 parts by weight of the pre-emulsion C into the polymerization kettle, heat to 70°C, add the initiator colloidal solution, and carry out emulsion polymerization at about 80°C; after keeping warm for 10 minutes, start to drop 50 parts by weight of emulsion B, maintain the polymerization reaction temperature at 60°C to 80°C during the dropwise addition, keep warm and continue stirring for 1 hour after the dropwise addition is completed, and naturally cool to room temperature to prepare a water-resistant styrene-acrylic emulsion D containing nano-titanium dioxide antibacterial properties.

[0021] ⑥ Take 0.2 parts by mass of 2-(3,4-dihydroxyphenyl)ethylamine and add it to 100 parts by mass of water, stir and dissolve it, add an alkaline pH adjuster to adjust the pH to 8-9, stir at room temperature for 2 hours, and stop stirring after the solution gradually changes from colorless and transparent to dark brown during the stirring process. At this time, the polyphenol monomer completes self-polymerization, and the solution is named E.

[0022] ⑦ The water-resistant styrene-acrylic emulsion D containing nano titanium dioxide and the self-polymerizing polyphenol solution E are mixed and stirred evenly to obtain an alkaline passivation solution for a medium aluminum-zinc-aluminum-magnesium coated steel plate.

[0023] The above technical solution uses an acrylic adhesive resin containing double bonds as the main film-forming agent, which has high transparency, high toughness, and impact resistance. EVA tackifying resin is used as an auxiliary film-forming agent to overcome the shortcomings of the traditional acrylic resin film main chain, which has a large number of hydrophilic groups, is easy to absorb water and swell, resulting in resin film failure and poor water resistance. The plasticizer increases the flexibility and impact resistance of the film-forming resin and increases the processing formability of the substrate. The emulsifier promotes the dispersion stability of the organic resin in water and the wetting and adhesion to the substrate. 5,6-dihydroxyindole or 2-(3,4-dihydroxyphenyl)ethylamine can self-polymerize into a highly adhesive and highly reducible protective film in an alkaline environment. At the same time, since zinc and aluminum are both amphoteric metals, zinc ions and aluminum ions are generated in an alkaline environment, which react with oxidants in an alkaline environment to further convert into zinc oxide and aluminum oxide passivation films. The persulfate oxidant simultaneously initiates the polymerization of the resin to form an organic-inorganic composite passivation film on the surface of the coating.

[0024] A passivation method using the alkaline passivation solution for the above-mentioned aluminum-zinc-aluminum-magnesium coated steel plate, the passivation method adopts one of the methods such as immersion, roller coating, brush coating, etc.

[0025] When the passivation liquid is used to treat the surface of the zinc-aluminum-magnesium coated steel plate, the passivation liquid is dried by one of the following methods: ultraviolet light curing, hot air drying and curing, electromagnetic induction heating steel plate curing, etc. The drying and curing temperature is 105°C to 120°C. The curing time is 1 to 2 minutes for immersion and brushing, and 5 to 10 seconds for roller coating, depending on the treatment method.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention uses an acrylic adhesive resin containing double bonds as the main film-forming agent, which has high transparency, high toughness, and impact resistance. EVA tackifying resin is used as an auxiliary film-forming agent to overcome the shortcomings of the traditional acrylic resin film main chain, which has a large number of hydrophilic groups, is easy to absorb water and swell, resulting in resin film failure and poor water resistance. The plasticizer increases the flexibility and impact resistance of the film-forming resin and increases the processing formability of the substrate. The emulsifier promotes the dispersion stability of the organic resin in water and the wetting and adhesion to the substrate. 5,6-dihydroxyindole or 2-(3,4-dihydroxyphenyl)ethylamine can self-polymerize into a protective film with high adhesion and high reducibility in an alkaline environment. At the same time, since zinc and aluminum are both amphoteric metals, zinc ions and aluminum ions are generated in an alkaline environment, and react with an oxidant in an alkaline environment to further convert into zinc oxide and aluminum oxide passivation films. The persulfate oxidant simultaneously initiates the polymerization of the resin to form an organic-inorganic composite passivation film on the surface of the coating. The alkaline passivation solution of the present invention does not use heavy metal oxygen acid salts, so it is green and environmentally friendly and is suitable for the needs of aluminum-zinc-aluminum-magnesium coated steel plates in industrial-scale production. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with specific examples, but the present invention is not limited in any way. To avoid redundant description, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0029] The invention discloses an alkaline passivation solution for a medium-aluminum-zinc-aluminum-magnesium coated steel plate, the passivation solution comprising the following components by mass: 2% to 3% of ethylene-vinyl acetate copolymer, 2% to 3% of water-resistant acrylic resin monomer, 2% to 3% of styrene, 0.5% to 1% of tackifying resin, 0.01% to 0.05% of plasticizer, 2% to 4% of emulsifier, 0.5% to 1.5% of initiator, 0.1% to 0.2% of self-polymerizing polyphenol, 5% to 15% of nano titanium dioxide antibacterial sol, and the rest is water.

[0030] The matters not described in the following embodiments are the same as the description of the above specific implementation methods.

[0031] Example 1

[0032] An alkaline passivation solution and passivation method for a medium aluminum-zinc-aluminum-magnesium coated steel plate, the specific process flow is:

[0033] First, the easy hydrolysis property of titanium alkoxide is used to prepare nano-titanium dioxide antibacterial sol, and the specific steps are as follows:

[0034] ① Add 1 part by mass of polyethylene glycol 400 to 30 parts by mass of n-propyl titanate and mix thoroughly in a water bath at 70° C. to prepare a mixed solution A;

[0035] ② Add the mixed solution A dropwise into 100 parts by weight of ethylene-vinyl acetate copolymer emulsion containing 5 wt% ammonia water within 2 hours, and react under stirring at 500 rpm to obtain EVA-nano-titanium dioxide antibacterial sol, which is named as emulsion B for standby use;

[0036] Secondly, water-resistant styrene acrylic emulsion is prepared by emulsion polymerization, and the preparation steps are as follows:

[0037] ③ Pre-emulsification: 100 parts by mass of deionized water, 1 part by mass of emulsifier sodium dodecylbenzene sulfonate, 2 parts by mass of sodium bicarbonate, 0.1 parts by mass of plasticizer dibutyl phthalate, 20 parts by mass of methyl methacrylate, and 15 parts by mass of styrene mixed monomer solution are added into a pre-emulsification kettle, and pre-emulsified at room temperature to obtain a stable pre-emulsion liquid C, at which time the emulsion monomer is in an unpolymerized state;

[0038] ④ Prepare initiator solution and protective colloid solution: add 1 part by mass of sodium persulfate to 100 parts by mass of EVA titanium dioxide nanosol B solution to prepare an initiator protective colloid solution;

[0039] ⑤Polymerization: Add 50 parts by weight of pre-emulsion C into the polymerization kettle, raise the temperature to 70°C, add the initiator colloidal solution, and carry out emulsion polymerization at about 80°C; after keeping warm for 10 minutes, start to drop 50 parts by weight of nano-titanium dioxide colloidal EVA emulsion B, maintain the polymerization reaction temperature at 70°C during the dropwise addition, keep warm and continue stirring for 60 minutes after the dropwise addition, and naturally cool to room temperature to prepare EVA-water-resistant styrene-acrylic emulsion D containing nano-titanium dioxide antibacterial properties.

[0040] Finally, the preparation of the medium aluminum zinc aluminum magnesium passivation solution is completed. The specific steps are as follows:

[0041] ⑥ Take 0.2 parts by mass of 2-(3,4-dihydroxyphenyl)ethylamine and add it to 100 parts by mass of water, stir and dissolve it, add an alkaline pH adjuster to adjust the pH to 8, stir at room temperature for 2 hours, and stop stirring after the solution gradually changes from colorless and transparent to dark brown during the stirring process. At this time, the polyphenol monomer completes self-polymerization, and the solution is named E.

[0042] ⑦ The water-resistant styrene-acrylic emulsion D containing nano titanium dioxide and the self-polymerized polyphenol solution E are mixed and stirred evenly, and the passivating agent solution is prepared.

[0043] The passivation steps on the surface of zinc-aluminum-magnesium coated steel plate are as follows:

[0044] For continuous galvanizing, the passivation liquid is applied on the upper and lower surfaces of the strip by roller coating, the drying and curing temperature is 105℃-110℃, and the heating and curing time is 5s.

[0045] Example 2

[0046] An alkaline passivation solution and passivation method for a medium aluminum-zinc-aluminum-magnesium coated steel plate, the specific process flow is:

[0047] First, the easy hydrolysis property of titanium alkoxide is used to prepare nano-titanium dioxide antibacterial sol, and the specific steps are as follows:

[0048] ① Add 2 parts by mass of polyethylene glycol 400 to 40 parts by mass of tetraethyl titanate and mix thoroughly in a water bath at 80° C. to prepare a mixed solution A.

[0049] ② The mixed solution A was added dropwise to 100 parts by weight of ethylene-vinyl acetate copolymer emulsion containing 5 wt% ammonia water within 2 hours, and reacted under stirring at 700 rpm to obtain a nano-titanium dioxide antibacterial sol, which was named as emulsion B for standby use.

[0050] Secondly, water-resistant styrene acrylic emulsion is prepared by emulsion polymerization, and the preparation steps are as follows:

[0051] ③ Pre-emulsification: 100 parts by mass of deionized water, 2 parts by mass of emulsifier sodium dodecyl sulfonate, 2 parts by mass of sodium bicarbonate, 0.2 parts by mass of plasticizer dimethyl phthalate, 15 parts by mass of butyl acrylate, and 15 parts by mass of styrene mixed monomer solution are added into a pre-emulsification kettle, and pre-emulsified at room temperature to obtain a stable pre-emulsion liquid C, at which time the emulsion monomer is in an unpolymerized state;

[0052] ④ Prepare the initiator solution and protective colloid solution: add 1 part by mass of ammonium persulfate to 100 parts by mass of EVA titanium dioxide nanosol B solution to prepare an initiator protective colloid solution;

[0053] ⑤Polymerization: Add 50 parts by weight of pre-emulsion C into the polymerization kettle, raise the temperature to 60°C, add the initiator colloidal solution, and carry out emulsion polymerization at about 80°C; after keeping warm for 10 minutes, start to drop 50 parts by weight of nano-titanium dioxide colloidal EVA emulsion B, maintain the polymerization reaction temperature at 60°C during the dropwise addition, keep warm and continue stirring for 60 minutes after the dropwise addition, and naturally cool to room temperature to prepare a water-resistant EVA-styrene-acrylic emulsion D containing nano-titanium dioxide antibacterial properties.

[0054] Finally, the preparation of the medium aluminum zinc aluminum magnesium passivation solution is completed. The specific steps are as follows:

[0055] ⑥ Take 0.1 parts by mass of 5,6-dihydroxyindole and add it to 100 parts by mass of water, stir and dissolve it, add an alkaline pH adjuster to adjust the pH to 9, stir at room temperature for 2 hours, and stop stirring after the solution gradually changes from colorless and transparent to dark brown during the stirring process. At this time, the polyphenol monomer completes self-polymerization, and the solution is named E.

[0056] ⑦ The water-resistant styrene-acrylic emulsion D containing nano titanium dioxide and the self-polymerized polyphenol solution E are mixed and stirred evenly, and the passivating agent solution is prepared.

[0057] The passivation steps on the surface of zinc-aluminum-magnesium coated steel plate are as follows:

[0058] For continuous galvanizing, the passivation liquid is applied on the upper and lower surfaces of the strip by roller coating, the drying and curing temperature is 120°C, and the heating and curing time is 5s.

[0059] Example 3

[0060] An alkaline passivation solution and passivation method for a medium aluminum-zinc-aluminum-magnesium coated steel plate, the specific process flow is:

[0061] First, the easy hydrolysis property of titanium alkoxide is used to prepare nano-titanium dioxide antibacterial sol, and the specific steps are as follows:

[0062] ① Add 1 part by mass of polyethylene glycol 400 to 30 parts by mass of tetrabutyl titanate and mix thoroughly in a water bath at 70° C. to prepare a mixed solution A;

[0063] ② Add the mixed solution A dropwise into 100 parts by weight of ethylene-vinyl acetate copolymer emulsion containing 5 wt% ammonia water within 2 hours, and react under stirring at 600 rpm to obtain a nano-titanium dioxide antibacterial sol, which is named as emulsion B for standby use.

[0064] Secondly, water-resistant styrene acrylic emulsion is prepared by emulsion polymerization, and the preparation steps are as follows:

[0065] ③ Pre-emulsification: 100 parts by mass of deionized water, 2 parts by mass of emulsifier sodium dodecyl sulfonate, 2 parts by mass of sodium bicarbonate, 0.1 parts by mass of plasticizer dibutyl phthalate, 15 parts by mass of methyl methacrylate, and 15 parts by mass of styrene mixed monomer solution are added to the pre-emulsification kettle, and pre-emulsified at room temperature to obtain a stable pre-emulsion liquid C, at which time the emulsion monomer is in an unpolymerized state;

[0066] ④ Prepare initiator solution and protective colloid solution: add 1 part by mass of sodium persulfate to 100 parts by mass of EVA titanium dioxide nanosol B solution to prepare an initiator protective colloid solution;

[0067] ⑤Polymerization: Add 50 parts by weight of pre-emulsion C into the polymerization kettle, raise the temperature to 60°C, add the initiator colloidal solution, and carry out emulsion polymerization at about 80°C; after keeping warm for 10 minutes, start to drop 50 parts by weight of nano-titanium dioxide colloidal EVA emulsion B, maintain the polymerization reaction temperature at 80°C during the dropwise addition, keep warm and continue stirring for 60 minutes after the dropwise addition, and naturally cool to room temperature to prepare a water-resistant EVA-styrene-acrylic emulsion D containing nano-titanium dioxide antibacterial properties.

[0068] Finally, the preparation of the medium aluminum zinc aluminum magnesium passivation solution is completed. The specific steps are as follows:

[0069] ⑥ Take 0.2 parts by mass of 2-(3,4-dihydroxyphenyl)ethylamine and add it to 100 parts by mass of water, stir and dissolve it, add an alkaline pH adjuster to adjust the pH to 8.5, stir at room temperature for 2 hours, and stop stirring after the solution gradually changes from colorless and transparent to dark brown during the stirring process. At this time, the polyphenol monomer completes self-polymerization, and the solution is named E.

[0070] ⑦ The water-resistant styrene-acrylic emulsion D containing nano titanium dioxide and the self-polymerized polyphenol solution E are mixed and stirred evenly, and the passivating agent solution is prepared.

[0071] The passivation steps on the surface of zinc-aluminum-magnesium coated steel plate are as follows:

[0072] For continuous galvanizing, the passivation solution was applied to the upper and lower surfaces of the strip by roller coating, with a drying and curing temperature of 105 °C and a heating and curing time of 5 s.

[0073] Comparative Example 1

[0074] An alkaline passivation solution and a passivation method for medium-aluminum-zinc-aluminum-magnesium coated steel plates are provided. The difference from the embodiment is that the synthesis environment of the styrene-acrylic emulsion is acidic rather than alkaline, acetic acid is added to the EVA titanium dioxide nanosol instead of ammonia water, and sodium bicarbonate is not added during the emulsion polymerization process.

[0075] First, the easy hydrolysis property of titanium alkoxide is used to prepare nano-titanium dioxide antibacterial sol, and the specific steps are as follows:

[0076] 1. Add 1 part by mass of polyethylene glycol 400 to 30 parts by mass of n-propyl titanate and mix thoroughly in a water bath at 70°C to prepare a mixed solution A.

[0077] 2. The mixed solution A was added dropwise to 100 parts by weight of ethylene-vinyl acetate copolymer emulsion containing 5 wt% ammonia water within 2 hours, and reacted under stirring at 500 rpm to obtain a nano-titanium dioxide antibacterial sol, which was named as emulsion B for standby use.

[0078] Secondly, water-resistant styrene acrylic emulsion is prepared by emulsion polymerization, and the preparation steps are as follows:

[0079] 1. Pre-emulsification: add 100 parts by mass of deionized water, 1 part by mass of emulsifier sodium dodecylbenzene sulfonate, 0.1 parts by mass of plasticizer dibutyl phthalate, 20 parts by mass of methyl methacrylate, and 15 parts by mass of styrene mixed monomer solution into a pre-emulsification kettle, and perform pre-emulsification at room temperature to obtain a stable pre-emulsion liquid C, at which time the emulsion monomer is in an unpolymerized state;

[0080] 2. Prepare initiator solution and protective colloid solution: add 1 part by mass of sodium persulfate to 100 parts by mass of EVA titanium dioxide nanosol B solution to prepare an initiator protective colloid solution;

[0081] 3. Polymerization: Add 50 parts by weight of pre-emulsion C into the polymerization kettle, heat to 70°C, add initiator colloidal solution, and carry out emulsion polymerization at about 80°C; after keeping warm for 10 minutes, start to drop 50 parts by weight of nano-titanium dioxide colloidal EVA emulsion B, maintain the polymerization reaction temperature at 80°C during the dropwise addition, keep warm and continue stirring for 60 minutes after the dropwise addition, and naturally cool to room temperature to prepare a water-resistant EVA-styrene-acrylic emulsion D containing nano-titanium dioxide antibacterial properties.

[0082] Finally, the preparation of the medium aluminum zinc aluminum magnesium passivation solution is completed. The specific steps are as follows:

[0083] 4. Take 0.2 parts by mass of 2-(3,4-dihydroxyphenyl)ethylamine and add it to 100 parts by mass of water, stir and dissolve it, add an alkaline pH adjuster to adjust the pH to 8, stir at room temperature for 2 hours, and stop stirring after the solution gradually changes from colorless and transparent to dark brown during the stirring process. At this time, the polyphenol monomer completes self-polymerization, and the solution is named Solution E.

[0084] 5. Mix and stir the water-resistant styrene-acrylic emulsion D containing nano titanium dioxide and the self-polymerizing polyphenol solution E evenly, and the passivating agent solution is prepared.

[0085] The passivation steps on the surface of zinc-aluminum-magnesium coated steel plate are as follows:

[0086] For continuous galvanizing, the passivation liquid is applied on the upper and lower surfaces of the strip by roller coating, the drying and curing temperature is 105°C, and the heating and curing time is 5s.

[0087] Comparative Example 2

[0088] An alkaline passivation solution and passivation method for a medium aluminum-zinc-aluminum-magnesium coated steel plate, which differs from the embodiment in that no nano titanium dioxide antibacterial sol is added, and the specific steps are as follows:

[0089] The water-resistant styrene acrylic emulsion is prepared by emulsion polymerization, and the preparation steps are as follows:

[0090] 1. Pre-emulsification: add 100 parts by mass of deionized water, 2 parts by mass of emulsifier sodium dodecyl sulfonate, 2 parts by mass of sodium bicarbonate, 0.2 parts by mass of plasticizer dimethyl phthalate, 15 parts by mass of butyl acrylate, and 15 parts by mass of styrene mixed monomer solution into a pre-emulsification kettle, and perform pre-emulsification at room temperature to obtain a stable pre-emulsion liquid C, at which time the emulsion monomer is in an unpolymerized state;

[0091] 2. Prepare initiator solution and protective colloid solution: add 1 part by mass of ammonium persulfate to 100 parts by mass of EVA emulsion to prepare initiator EVA colloid solution;

[0092] 3. Polymerization: Add 50 parts by weight of pre-emulsion C into the polymerization kettle, heat to 70°C, add initiator colloid solution, and carry out emulsion polymerization at about 80°C; after keeping warm for 10 minutes, start to drop 50 parts by weight of EVA emulsion, maintain the polymerization reaction temperature at 80°C during the dropwise addition, keep warm and continue stirring for 60 minutes after the dropwise addition, and naturally cool to room temperature to prepare a water-resistant EVA-styrene-acrylic emulsion.

[0093] Finally, the preparation of the medium aluminum zinc aluminum magnesium passivation solution is completed. The specific steps are as follows:

[0094] 4. Take 0.1 parts by mass of 5,6-dihydroxyindole and add it to 100 parts by mass of water, stir and dissolve it, add an alkaline pH adjuster to adjust the pH to 9, stir at room temperature for 2 hours, and stop stirring after the solution gradually changes from colorless and transparent to dark brown during the stirring process. At this time, the polyphenol monomer completes self-polymerization.

[0095] 5. The water-resistant styrene-acrylic emulsion and the self-polymerizing polyphenol solution are mixed and stirred evenly to complete the preparation of the passivating agent solution.

[0096] The passivation steps on the surface of zinc-aluminum-magnesium coated steel plate are as follows:

[0097] For continuous galvanizing, the passivation liquid is applied on the upper and lower surfaces of the strip by roller coating, the drying and curing temperature is 105-120℃, and the heating and curing time is 5s.

[0098] Comparative Example 3

[0099] An alkaline passivation solution and a passivation method for medium-aluminum-zinc-aluminum-magnesium coated steel plates, which are different from the embodiments in that polyphenols that self-polymerize in an alkaline environment are not added.

[0100] First, the easy hydrolysis property of titanium alkoxide is used to prepare nano-titanium dioxide antibacterial sol, and the specific steps are as follows:

[0101] 1. Add 1 part by mass of polyethylene glycol 400 to 30 parts by mass of n-propyl titanate and mix thoroughly in a water bath at 70°C to prepare a mixed solution A.

[0102] 2. The mixed solution A was added dropwise to 100 parts by weight of ethylene-vinyl acetate copolymer emulsion containing 5 wt% ammonia water within 2 hours, and reacted under stirring at 500 rpm to obtain a nano-titanium dioxide antibacterial sol, which was named as emulsion B for standby use.

[0103] Secondly, water-resistant styrene acrylic emulsion is prepared by emulsion polymerization, and the preparation steps are as follows:

[0104] 1. Pre-emulsification: add 100 parts by mass of deionized water, 2 parts by mass of emulsifier sodium dodecylbenzene sulfonate, 0.2 parts by mass of plasticizer dibutyl phthalate, 20 parts by mass of methyl methacrylate, and 15 parts by mass of styrene mixed monomer solution into a pre-emulsification kettle, and perform pre-emulsification at room temperature to obtain a stable pre-emulsion liquid C, at which time the emulsion monomer is in an unpolymerized state;

[0105] 2. Prepare initiator solution and protective colloid solution: add 1 part by mass of sodium persulfate to 100 parts by mass of EVA titanium dioxide nanosol B solution to prepare an initiator protective colloid solution;

[0106] 3. Polymerization: Add 50 parts by weight of pre-emulsion C into the polymerization kettle, heat to 70°C, add initiator colloidal solution, and carry out emulsion polymerization at about 80°C; after keeping warm for 10 minutes, start to drop 50 parts by weight of nano titanium dioxide colloidal EVA emulsion B, maintain the polymerization reaction temperature at 80°C during the dropwise addition, keep warm and continue stirring for 60 minutes after the dropwise addition, cool naturally to room temperature, and prepare a water-resistant EVA-styrene acrylic emulsion containing nano titanium dioxide antibacterial properties, completing the preparation of the medium-aluminum-zinc-aluminum-magnesium passivation solution.

[0107] 4. Take 0.1 parts by mass of 5,6-dihydroxyindole and add it to 100 parts by mass of water, stir and dissolve it, add an alkaline pH adjuster to adjust the pH to 8, stir at room temperature for 2 hours, and stop stirring after the solution gradually changes from colorless and transparent to dark brown during the stirring process. At this time, the polyphenol monomer completes self-polymerization.

[0108] 5. Mix the pure acrylic emulsion and the self-polymerizing polyphenol solution and stir them evenly to complete the preparation of the passivating agent solution.

[0109] The surface passivation steps of zinc-aluminum-magnesium coated steel plate are as follows:

[0110] For continuous galvanizing, the passivation liquid is applied on the upper and lower surfaces of the strip by roller coating, the drying and curing temperature is 110°C, and the heating and curing time is 5s.

[0111] Comparative Example 4

[0112] An alkaline passivation solution and passivation method for a medium aluminum-zinc-aluminum-magnesium coated steel plate, which is different from the embodiment in that the film-forming resin uses a pure acrylic emulsion instead of a styrene-free styrene-containing styrene-acrylic emulsion, and the specific steps are as follows:

[0113] First, the easy hydrolysis property of titanium alkoxide is used to prepare nano-titanium dioxide antibacterial sol, and the specific steps are as follows:

[0114] 1. Add 1 part by mass of polyethylene glycol 400 to 30 parts by mass of n-propyl titanate and mix thoroughly in a water bath at 70° C. to prepare a mixed solution A;

[0115] 2. The mixed solution A was added dropwise to 100 parts by weight of ethylene-vinyl acetate copolymer emulsion containing 5 wt% ammonia water within 2 hours, and reacted under stirring at 600 rpm to obtain a nano-titanium dioxide antibacterial sol, which was named as emulsion B for standby use.

[0116] Secondly, pure acrylic emulsion is prepared by emulsion polymerization, and the preparation steps are as follows:

[0117] 1. Pre-emulsification: add 100 parts by mass of deionized water, 1 part by mass of emulsifier sodium dodecyl sulfonate, 2 parts by mass of sodium bicarbonate, 0.1 parts by mass of plasticizer dimethyl phthalate, 15 parts by mass of acrylic acid, and 15 parts by mass of ethyl methacrylate monomer solution into a pre-emulsification kettle, and perform pre-emulsification at room temperature to obtain a stable pre-emulsion liquid C, at which time the emulsion monomer is in an unpolymerized state;

[0118] 2. Polymerization: Add 50 parts by weight of pre-emulsion C into the polymerization kettle, heat to 70°C, add initiator colloid solution, and carry out emulsion polymerization at about 80°C; after keeping warm for 10 minutes, start to drop 50 parts by weight of EVA emulsion, maintain the polymerization reaction temperature at 80°C during the dropwise addition, keep warm and continue stirring for 60 minutes after the dropwise addition, and naturally cool to room temperature to prepare EVA-pure acrylic emulsion.

[0119] Finally, the preparation of the medium aluminum zinc aluminum magnesium passivation solution is completed. The specific steps are as follows:

[0120] 1. Take 0.1 parts by mass of 5,6-dihydroxyindole and add it to 100 parts by mass of water, stir and dissolve it, add an alkaline pH adjuster to adjust the pH to 8, stir at room temperature for 2 hours, and stop stirring after the solution gradually changes from colorless and transparent to dark brown during the stirring process. At this time, the polyphenol monomer completes self-polymerization.

[0121] 2. Mix the pure acrylic emulsion and the self-polymerizing polyphenol solution and stir them evenly to complete the preparation of the passivating agent solution.

[0122] The passivation steps on the surface of zinc-aluminum-magnesium coated steel plate are as follows:

[0123] For continuous galvanizing, the passivation liquid is applied on the upper and lower surfaces of the strip by roller coating. The drying and curing temperature is 105℃~110℃, and the heating and curing time is 5s.

[0124] The corrosion resistance, blackening resistance, fingerprint resistance, water resistance and heat resistance of the surface coating of the alkaline zinc-aluminum-magnesium alloy coated steel plate surface treatment liquid were determined by testing the examples and comparative examples. The results are shown in Table 1.

[0125] Among them, the corrosion resistance is tested according to the methods and conditions specified in GB / T10125, and then the corrosion results are evaluated according to the provisions of GB12335-90 (expressed as the percentage of the corrosion area after 72h and 120h to the total area); the smaller the corrosion area, the better (currently the NSST / 72h corrosion area is generally required to be ≤5%). The blackening resistance is tested according to the color difference before and after the NSST / 120h test. If there is no obvious color change on the surface, that is, the color difference value is ≤2, the blackening resistance is good.

[0126] Fingerprint resistance is determined by the change in color difference before and after Vaseline is applied to the sample surface: if the change in color difference is less than 1, it is grade A; if the change in color difference is greater than 1 and less than 2, it is grade B; if the change in color difference is greater than 2 and less than 4, it is grade C; if the change in color difference is greater than 4, it is grade D. Water resistance is determined by dropping 100°C deionized water on the sample: if there is no water mark on the sample, it is grade A; if there is a slight water mark, it is grade B; if there is a clear water mark, it is grade C.

[0127] The heat resistance is determined by the change in color difference before and after the sample is baked at 350°C for 30 minutes: if the change in color difference is less than 2, it is grade A; if the change in color difference is greater than 2 and less than 4, it is grade B; if the change in color difference is greater than 4 and less than 8, it is grade C; if the change in color difference is greater than 8, it is grade D.

[0128] As can be seen from Table 1, the passivation solutions of the embodiments all have good corrosion resistance. Comparative Example 1 is an acidic environment, and the stability and emulsification effect of the styrene-acrylic emulsion are worse than those of the alkaline environment; Comparative Example 2 does not have titanium dioxide added nanomaterials, and the hydrophobic effect is worse, and the corrosion resistance, water resistance, fingerprint resistance and stability of the passivation film are worse than those of the embodiments. Comparative Example 3 does not add self-polymerizing polyphenols, and the dispersibility, stability and corrosion resistance of the emulsion are worse than those of the embodiments. Comparative Example 4 uses pure acrylic emulsion, which has higher cost but is not as good as styrene-acrylic emulsion in water resistance, heat resistance, curing speed and alkali resistance.

[0129] Table 1 Performance of passivation solution obtained in Examples and Comparative Examples

[0130]

[0131] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0132] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0133] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. An alkaline passivation solution for medium aluminum-zinc-aluminum-magnesium coated steel sheet, characterized in that: The passivation solution comprises the following components by mass content: 2% to 3% of ethylene-vinyl acetate copolymer, 2% to 3% of water-resistant acrylic resin monomer, 2% to 3% of styrene, 0.5% to 1% of tackifying resin, 0.01% to 0.05% of plasticizer, 2% to 4% of emulsifier, 0.5% to 1.5% of initiator, 0.1% to 0.2% of self-polymerizing polyphenol, 5% to 15% of nano titanium dioxide antibacterial sol, and the rest is water.

2. The alkaline passivation solution according to claim 1, characterized in that The water in the alkaline passivation solution is pure water, and its specific resistance is ≥1MΩ·cm; the mass fraction of ethylene in the ethylene-vinyl acetate copolymer is 5% to 22%, and the viscosity at 25°C is 500 to 2200mPa·s.

3. The alkaline passivation solution according to claim 1, characterized in that The plasticizer in the components of the alkaline passivation solution is one of dioctyl phthalate, dibutyl phthalate, and diethyl phthalate; the emulsifier is an oil-in-water (O / W) type anionic emulsifier, which is one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, sodium laurate, sodium oleate, and sodium stearate.

4. The alkaline passivation solution according to claim 1, characterized in that The self-polymerizing polyphenol in the components of the alkaline passivation solution is 5,6-dihydroxyindole or 2-(3,4-dihydroxyphenyl)ethylamine; the nano titanium dioxide antibacterial sol is prepared by hydrolysis of titanium alcohol salt.

5. The alkaline passivation solution according to claim 4, characterized in that: The initiator in the components of the alkaline passivation solution is a water-soluble inorganic peroxide initiator, which is one of ammonium persulfate, sodium persulfate, potassium persulfate, and potassium hydrogen persulfate.

6. A method for preparing an alkaline passivation solution for a medium aluminum-zinc-aluminum-magnesium coated steel sheet as claimed in claim 1, characterized in that: The preparation method comprises preparing a nano titanium dioxide-EVA emulsion by a sol-gel method, preparing a water-resistant styrene-acrylic emulsion by thermal polymerization, and finally preparing a passivation solution; the specific steps are as follows: ① Add 1 to 2 parts by weight of polyethylene glycol to 30 to 40 parts by weight of titanium alkoxide, and mix thoroughly in a water bath at 70° C. to 80° C. to obtain a mixed solution A; ② Add the mixed solution A dropwise into 100 parts by weight of ethylene-vinyl acetate copolymer emulsion containing 5 wt% ammonia water within 2 hours, and react under stirring at 500-700 rpm to obtain a nano-titanium dioxide antibacterial sol, which is named as emulsion B for standby use; ③ Pre-emulsification: add 100 parts by mass of deionized water, 1-2 parts by mass of emulsifier, 2 parts by mass of sodium bicarbonate, 0.1-0.2 parts by mass of plasticizer, 20 parts by mass of methyl methacrylate, and 15 parts by mass of styrene mixed monomer solution into a pre-emulsification kettle, and perform pre-emulsification at room temperature to obtain a stable pre-emulsified liquid C; ④ Prepare an initiator solution and a protective colloid solution: add 1 part by mass of sodium persulfate to 100 parts by mass of the emulsion B to prepare an initiator protective colloid solution; ⑤ Polymerization: Add 50 parts by weight of the pre-emulsion C into the polymerization kettle, heat to 70°C, add the initiator colloidal solution, and perform emulsion polymerization at 80°C; after keeping warm for 10 minutes, start dripping 50 parts by weight of the emulsion B, maintain the polymerization reaction temperature at 60°C to 80°C during the dripping, keep warm and continue stirring for 1 hour after the dripping is completed, and naturally cool to room temperature to prepare a water-resistant styrene-acrylic emulsion D containing nano-titanium dioxide antibacterial properties; ⑥ Take 0.2 parts by mass of 2-(3,4-dihydroxyphenyl)ethylamine and add it to 100 parts by mass of water, stir and dissolve it, add an alkaline pH regulator to adjust the pH to 8-9, stir at room temperature for 2 hours, and stop stirring after the solution gradually changes from colorless and transparent to dark brown during the stirring process. At this time, the polyphenol monomer completes self-polymerization, and the solution is named E; ⑦ The water-resistant styrene-acrylic emulsion D containing nano titanium dioxide and the self-polymerizing polyphenol solution E are mixed and stirred evenly to obtain an alkaline passivation solution for a medium aluminum-zinc-aluminum-magnesium coated steel plate.

7. A passivation method for an alkaline passivation solution for a medium aluminum-zinc-aluminum-magnesium coated steel sheet as claimed in claim 1, characterized in that: The passivation method adopts one of immersion, roller coating and brush coating; the drying and curing method of the passivation liquid is one of ultraviolet light curing, hot air drying and curing, and electromagnetic induction heating steel plate curing, the drying and curing temperature is 105°C to 120°C, the immersion and brushing surface passivation curing time is 1 to 2 minutes, and the roller coating passivation time is 5 to 10 seconds.

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