Zinc sheet pigment for zinc-aluminum coating and preparation method of zinc sheet pigment

Abstract

The invention belongs to the technical field of chemical materials, and particularly relates to a zinc sheet pigment for a zinc-aluminum coating and a preparation method of the zinc sheet pigment. The preparation method of the zinc sheet pigment for the zinc-aluminum coating comprises the following steps: (1) adding zinc powder, a ball milling aid, an additive and a solvent into a ball mill, carrying out first-stage ball milling, and after the first-stage ball milling is finished, adding a surface treating agent and water, and carrying out second-stage ball milling; (2) screening a material obtained after ball milling; and (3) carrying out filter pressing on the screened material to obtain a filter cake. And (4) adding an antioxidant and a dispersing agent into the filter cake, and kneading to obtain the product. The zinc sheet pigment prepared by the invention can be uniformly dispersed in water, can stably exist in a coating system for a long time, and does not settle or re-agglomerate; therefore, the use performance of the zinc-aluminum coating paint is greatly improved; the method is especially suitable for corrosion-resistant water-based zinc sheet pigments such as Dacromet, Jimet and water-based zinc-rich coatings.

Description

Technical Field

[0001] This invention belongs to the field of chemical materials technology, specifically relating to a zinc flake pigment for zinc-aluminum coating and its preparation method. Background Technology

[0002] High-performance anti-corrosion zinc-aluminum pigments are produced by grinding spherical zinc or aluminum powder using appropriate methods to transform it into a more regular flake structure, thereby enhancing its shielding ability and covering effect. This product is environmentally friendly and widely used in Dacromet, cyclohexane, and solvent-based long-lasting heavy-duty anti-corrosion coatings. With economic development and improved living standards, people's environmental awareness is gradually increasing, leading to higher demands for coatings. They require not only aesthetically pleasing and high-performance products but also environmentally friendly and pollution-free coatings. Currently, zinc-aluminum coatings on the market, as heavy-duty anti-corrosion coatings, possess superior anti-corrosion performance that is difficult for other coatings to match.

[0003] However, the zinc powder in zinc-aluminum coatings reacts with water, significantly impacting the water-based nature of the coatings. Currently, commercially available water-based zinc-aluminum coatings are typically two-component, with zinc powder and a water-based component mixed temporarily before use. Most current technologies involve ball milling the zinc powder to create a finished product, dispersing it in a suitable solvent, and then treating the zinc powder surface to improve its water resistance. This process is complex, costly, and severely hinders its water-based development. Furthermore, surface modification of the zinc powder after production may alter the surface energy of the zinc flakes, making secondary dispersion in water difficult. This leads to decreased dispersibility of the zinc flake pigments in water and may even cause secondary agglomeration, resulting in easy sedimentation, clumping, unstable storage, uneven coating composition during use, and reduced corrosion resistance.

[0004] Therefore, developing a ready-to-use zinc flake pigment that combines good flake structure, excellent corrosion resistance, water resistance, and outstanding dispersion stability is of great significance for significantly improving the performance of zinc-aluminum coatings. Summary of the Invention

[0005] One objective of this invention is to provide a method for preparing zinc flake pigments for zinc-aluminum coatings. This process directly treats the zinc powder during ball milling, simplifying the process and reducing costs.

[0006] The second objective of this invention is to provide a zinc flake pigment for zinc-aluminum coatings. The zinc flake pigment prepared by this invention can be uniformly dispersed in water and can exist stably in coating systems for a long period without sedimentation or re-agglomeration; thus greatly improving the performance of zinc-aluminum coatings; it is particularly suitable for corrosion-resistant water-based zinc flake pigments for Dacromet, cyclohexane, and water-based zinc-rich coatings.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing zinc flake pigment for zinc-aluminum coating includes the following steps: (1) Add zinc powder, ball milling aid, additives and solvent into the ball mill for the first stage of ball milling. After the first stage of ball milling is completed, add surface treatment agent and water for the second stage of ball milling. (2) Screen the material obtained after ball milling in step (1); (3) The material obtained by screening in step (2) is pressed and filtered to obtain filter cake; (4) Add antioxidant and dispersant to the filter cake from step (3) and knead to obtain slurry zinc flake pigment.

[0008] Furthermore, the additive is at least one of polyethylene glycol fatty acid ester (which has emulsifying and stabilizing effects, maintaining the physical stability of the product), polyoxyethylene sorbitan fatty acid ester (which has emulsifying and stabilizing effects, maintaining the physical stability of the product, and also has auxiliary lubricating effects), polydimethylsiloxane (which has emulsifying effects and also has a significant coupling effect, effectively increasing the amount of isostearic acid adsorbed on the zinc sheet surface), or polyglycerol-10 stearate (which has compatibilizing effects, reduces system viscosity, and improves grinding efficiency).

[0009] Furthermore, the surface treatment agent is at least one of sodium molybdate, isotridecyl phosphate, sodium silicate, or siloxane.

[0010] The surface treatment agent of this invention forms a transparent protective film on the surface of zinc powder, thereby achieving resistance to acid and alkali corrosion and solving the problem of poor corrosion resistance of water-based zinc flake pigments. Specifically, sodium silicate and siloxane ketones can form a dense organosilicon protective layer on the zinc flake surface through hydrolysis, making the zinc flake's corrosion resistance even more outstanding.

[0011] Further, the mass ratio of zinc powder, ball milling aid, additive, solvent, surface treatment agent and water is (100-150): (3-5): (0.1-1.0): (100-150): (2-4): (30-50).

[0012] Furthermore, the mass ratio of zinc powder, ball milling aid, additive, solvent, surface treatment agent, and water is 100:4:0.4:150:4:40.

[0013] Furthermore, the antioxidant is antioxidant 5057; the dispersant is WELLMIX-1530 dispersant.

[0014] Furthermore, the ball milling aid is isostearic acid; the solvent is propylene glycol or dipropylene glycol methyl ether.

[0015] Of these, isostearic acid possesses saturated bonds and a branched structure, with both a low melting point and freezing point, resulting in excellent lubrication and helping zinc sheets maintain a regular shape. Dipropylene glycol methyl ether, due to its hydrophilicity and low viscosity, is even more beneficial for the flake formation and dispersibility of zinc powder.

[0016] Further, in step (1), the rotation speed of the first ball mill is 35-40 r / min and the ball milling time is 5-7 h; the rotation speed of the second ball mill is 20-25 r / min and the ball milling time is 3-5 h; the ball milling medium used in step (1) is stainless steel balls with a diameter of 3.00-8.00 mm; the zinc powder is spherical zinc powder with a mesh size of 325-500.

[0017] In the first stage of ball milling, isostearic acid is added, and a solvent (propylene glycol or dipropylene glycol methyl ether) is used as the grinding medium. This can effectively make the zinc powder into flakes. At the same time, the addition of additives can make the zinc flake pigment better dispersed in water in the second stage of ball milling. In the second stage of ball milling, a surface treatment agent and water are added. The surface treatment agent hydrolyzes or passivates the zinc flakes, forming a protective film on the zinc flake surface, which can improve the corrosion resistance of the zinc flake pigment. Further, in step (2), the sieving specifically involves passing the material through 100-mesh and 350-mesh sieves in sequence.

[0018] Further, in step (4), the amount of antioxidant added is 0.5-1 wt% of the filter cake; the amount of dispersant added is 1-2 wt% of the filter cake.

[0019] Further, step (4) is replaced by: washing the filter cake from step (3) with n-propanol, filtering by pressure, drying, and mixing to obtain powdered zinc flake pigment.

[0020] A zinc flake pigment for zinc-aluminum coating is prepared using the above-described method.

[0021] Compared with the prior art, the beneficial effects of this invention are as follows: 1. This invention provides a method for preparing zinc flake pigment for zinc-aluminum coating. The zinc flake is surface-treated during ball milling, eliminating the need for ball milling followed by reaction in a reactor. The process is simple and low-cost.

[0022] 2. The zinc flake pigment obtained by this invention is prepared by the combined application of additives and surface treatment agents, which can significantly improve the comprehensive performance of zinc flake pigment. Through physical adsorption, chemical reaction or coating formation, a thin film or modified layer with specific functions is constructed on the surface of zinc flake, thereby giving the material excellent surface properties and solving the problem of poor dispersibility of traditional zinc flake pigment in water-based zinc-rich coating systems.

[0023] 3. Compared with traditional zinc flake pigments, zinc-based coatings prepared using the zinc flake pigments of this invention exhibit superior film stability. Treating the zinc powder surface with a polymer surface treatment agent forms a transparent protective film, effectively improving the buoyancy and dispersibility of the zinc flake pigment in water, and enhancing its antioxidant and acid / alkali resistance; thus allowing the zinc flake pigment to be stored for extended periods in aqueous systems.

[0024] 4. The product obtained by this invention is a powdered or paste-like zinc flake pigment that can be directly dispersed in water and does not require any co-solvents during use.

[0025] 5. The grinding aid used in this invention can improve the hydrophilicity of zinc flake pigments without further processing. Detailed Implementation

[0026] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art are within the scope of protection of this invention. Unless otherwise specified, the raw materials and preparation methods used in this invention are all conventional materials and techniques in the art.

[0027] Example 1 A method for preparing zinc flake pigment for zinc-aluminum coating includes the following steps: (1) Place 150 kg of 325 mesh spherical zinc powder, 5 kg of isostearic acid, 0.4 kg of additive (polyglycerol-10 stearate), and 150 kg of solvent (propylene glycol) into a ball mill (ball mill drum 2.5 m × 1.5 m), select stainless steel balls with a diameter of 6.0 mm as the ball milling medium, and ball mill at 35 r / min for 7 h, then stop the machine; then add 4 kg of surface treatment agent (sodium silicate) and 40 kg of deionized water, and ball mill at 25 r / min for 4 h, then stop the machine; (2) Pass the material after ball milling in step (1) through a 100-mesh sieve and then through a 325-mesh sieve. (3) The material passing through the 325 mesh sieve in step (2) is filtered by pressure to obtain a filter cake with a solid content of 90 wt%. (4) Add antioxidant (antioxidant 5057) and dispersant (WELLMIX-1530 dispersant) to the filter cake obtained after pressing in step (3) and knead it. The amount of antioxidant added is 0.75 wt% of the filter cake; the amount of dispersant added is 1.5 wt% of the filter cake; adjust the solid content to 85 wt% with dipropylene glycol to obtain the paste-like zinc flake pigment.

[0028] This embodiment also provides a method for preparing powdered zinc flake pigment, the specific steps of which are as follows: Steps (1)-(3) are the same as in this embodiment; step (4) is replaced by: putting the filter cake obtained in step (3) into a mixing tank, adding n-propanol with 3 times the weight of the filter cake for washing, pressing and filtering, and then drying in a vacuum drying oven to make the solvent content less than 0.5wt%. The dried product is then put into a mixer for mixing and dispersion to obtain powdered zinc flake pigment.

[0029] Example 2 A method for preparing zinc flake pigment for zinc-aluminum coating includes the following steps: (1) Place 100 kg of 325 mesh spherical zinc powder, 3 kg of ball milling aid (isostearic acid), 0.5 kg of additive (polyethylene glycol fatty acid ester), and 150 kg of solvent (propylene glycol) into a ball mill (ball mill drum 2.5m×1.5m). Select stainless steel balls with a diameter of 6.0 mm as the ball milling medium and ball mill at 35 r / min for 6 h, then stop the machine. Then add 3 kg of surface treatment agent (isotridecyl phosphate) and 40 kg of deionized water, and ball mill at 25 r / min for 4 h, then stop the machine. (2) Pass the material after ball milling in step (1) through a 100-mesh sieve and then through a 325-mesh sieve. (3) The material obtained by screening with a 325-mesh sieve in step (2) is filtered by pressure to obtain a filter cake with a solid content of 90wt%. (4) Add antioxidant (antioxidant 5057) and dispersant (WELLMIX-1530 dispersant) to the filter cake obtained after pressing in step (3) and knead it. The amount of antioxidant added is 0.5 wt% of the filter cake; the amount of dispersant added is 1 wt% of the filter cake. Adjust the solid content to 85 wt% with dipropylene glycol to obtain the paste-like zinc flake pigment.

[0030] This embodiment also provides a method for preparing powdered zinc flake pigment, the specific steps of which are as follows: Steps (1)-(3) are the same as in this embodiment; step (4) is replaced by: putting the filter cake obtained in step (3) into a mixing tank, adding n-propanol with 3 times the weight of the filter cake for washing, pressing and filtering, and then drying in a vacuum drying oven to make the solvent content less than 0.5wt%. The dried product is then put into a mixer for mixing and dispersion to obtain powdered zinc flake pigment.

[0031] Example 3 A method for preparing zinc flake pigment for zinc-aluminum coating includes the following steps: (1) Place 120 kg of 500-mesh spherical zinc powder, 4 kg of isostearic acid, 0.5 kg of additive (polydimethylsiloxane), and 150 kg of solvent (dipropylene glycol methyl ether) into a ball mill (ball mill drum 2.5m×1.5m), select stainless steel balls with a diameter of 6.0 mm as the ball milling medium, and ball mill at 35 r / min for 7 h, then stop the machine; then add 3 kg of surface treatment agent (siloxane ketone) and 45 kg of deionized water, and ball mill at 25 r / min for 5 h, then stop the machine; (2) Pass the material after ball milling in step (1) through a 100-mesh sieve and then through a 325-mesh sieve. (3) The material passing through the 325 mesh sieve in step (2) is filtered by pressure to obtain a filter cake with a solid content of 90 wt%. (4) Add antioxidant (antioxidant 5057) and dispersant (WELLMIX-1530 dispersant) to the filter cake obtained after pressing in step (3) according to product requirements, and knead it. The amount of antioxidant added is 1 wt% of the filter cake; the amount of dispersant added is 2 wt% of the filter cake. Adjust the solid content to 80 wt% with dipropylene glycol to obtain slurry zinc flake pigment.

[0032] This embodiment also provides a method for preparing powdered zinc flake pigment, the specific steps of which are as follows: Steps (1)-(3) are the same as in this embodiment; step (4) is replaced by: putting the filter cake obtained in step (3) into a mixing tank, adding n-propanol with 3 times the weight of the filter cake for washing, pressing and filtering, and then drying in a vacuum drying oven to make the solvent content less than 0.5wt%. The dried product is then put into a mixer for mixing and dispersion to obtain powdered zinc flake pigment.

[0033] Example 4 A method for preparing zinc flake pigment for zinc-aluminum coating includes the following steps: (1) Place 120 kg of 500-mesh spherical zinc powder, 4 kg of isostearic acid, 0.4 kg of additive (polyoxyethylene sorbitan fatty acid ester), and 150 kg of solvent (dipropylene glycol methyl ether) into a ball mill (ball mill drum 2.5m×1.5m), select stainless steel balls with a diameter of 6.0 mm as the ball milling medium, and ball mill at 35 r / min for 7 h, then stop the machine; then add surface treatment agent (1 kg of sodium molybdate and 3 kg of siloxane ketone), 45 kg of deionized water, and ball mill at 25 r / min for 5 h, then stop the machine; (2) Pass the material after ball milling in step (1) through a 100-mesh sieve and then through a 325-mesh sieve. (3) The material passing through the 325 mesh sieve in step (2) is filtered by pressure to obtain a filter cake with a solid content of 90 wt%. (4) Add antioxidant (antioxidant 5057) and dispersant (WELLMIX-1530 dispersant) to the filter cake obtained after pressing and filtering in step (3) according to product requirements, and knead it. The amount of antioxidant added is 0.5 wt% of the filter cake; the amount of dispersant added is 2 wt% of the filter cake. Adjust the solid content to 85 wt% with dipropylene glycol to obtain paste-like zinc flake pigment.

[0034] This embodiment also provides a method for preparing powdered zinc flake pigment, the specific steps of which are as follows: Steps (1)-(3) are the same as in this embodiment; step (4) is replaced by: putting the filter cake obtained in step (3) into a mixing tank, adding n-propanol with 3 times the weight of the filter cake for washing, pressing and filtering, and then drying in a vacuum drying oven to make the solvent content less than 0.5wt%. The dried product is then put into a mixer for mixing and dispersion to obtain powdered zinc flake pigment.

[0035] Example 5 A method for preparing zinc flake pigment for zinc-aluminum coating includes the following steps: (1) Place 100 kg of 500-mesh spherical zinc powder, 4 kg of isostearic acid, 0.4 kg of additive (polydimethylsiloxane), and 150 kg of solvent (dipropylene glycol methyl ether) into a ball mill (ball mill drum 2.5 m × 1.5 m), select stainless steel balls with a diameter of 6.0 mm as the ball milling medium, and ball mill at 35 r / min for 7 h, then stop the machine; then add 4 kg of surface treatment agent (sodium silicate) and 40 kg of deionized water, and ball mill at 25 r / min for 5 h, then stop the machine; (2) Pass the material after ball milling in step (1) through a 100-mesh sieve and then through a 325-mesh sieve. (3) The material passing through the 325 mesh sieve in step (2) is filtered by pressure to obtain a filter cake with a solid content of 90 wt%. (4) Add antioxidant (antioxidant 5057) and dispersant (WELLMIX-1530 dispersant) to the filter cake obtained after pressing in step (3) according to product requirements, and knead it. The amount of antioxidant added is 1 wt% of the filter cake; the amount of dispersant added is 2 wt% of the filter cake. Adjust the solid content to 80 wt% with dipropylene glycol to obtain slurry zinc flake pigment.

[0036] This embodiment also provides a method for preparing powdered zinc flake pigment, the specific steps of which are as follows: Steps (1)-(3) are the same as in this embodiment; step (4) is replaced by: putting the filter cake obtained in step (3) into a mixing tank, adding n-propanol with 3 times the weight of the filter cake for washing, pressing and filtering, and then drying in a vacuum drying oven to make the solvent content less than 0.5wt%. The dried product is then put into a mixer for mixing and dispersion to obtain powdered zinc flake pigment.

[0037] Comparative Example 1 Comparative Example 1 and Example 5 are basically the same, except that the solvent (dipropylene glycol methyl ether) in step (1) is replaced with an aromatic solvent (model H150). Everything else is the same as in Example 5, and a paste-like zinc flake pigment is prepared.

[0038] Comparative Example 2 Comparative Example 2 is basically the same as Example 5, except that the amount of the ball milling aid isostearic acid is reduced to 2 kg, while everything else is the same as in Example 5, and a paste-like zinc flake pigment is prepared.

[0039] Comparative Example 3 Comparative Example 3 and Example 5 are basically the same, except that the additive (polydimethylsiloxane) is replaced with sodium stearate during the ball milling process. Everything else is the same as in Example 5, and a paste-like zinc flake pigment is prepared.

[0040] Comparative Example 4 Comparative Example 4 and Example 5 are basically the same, except that the surface treatment agent (sodium silicate) is replaced with phosphate ester during the ball milling process. Everything else is the same as in Example 5, and a paste-like zinc flake pigment is prepared.

[0041] Comparative Example 5 Comparative Example 5 is basically the same as Example 5, except that no antioxidant is added during the kneading process. Everything else is the same as in Example 5, and a paste-like zinc flake pigment is prepared.

[0042] Comparative Example 6 Comparative Example 6 is basically the same as Example 5, except that no dispersant is added during the kneading process. Everything else is the same as in Example 5, and a paste-like zinc flake pigment is prepared.

[0043] Comparative Example 7 Comparative Example 7 is basically the same as Example 5, except that: step (1) is as follows: 100 kg of 500-mesh spherical zinc powder, 4 kg of isostearic acid, 0.4 kg of additive (polydimethylsiloxane), 150 kg of solvent (dipropylene glycol methyl ether), 4 kg of surface treatment agent (sodium silicate), and 40 kg of deionized water are placed in a ball mill (ball mill drum 2.5m × 1.5m), and stainless steel balls with a diameter of 6.0 mm are selected as the ball milling medium. The ball mill is run at 35 r / min for 12 h, and then stopped. Everything else is the same as in Example 5, and a paste-like zinc flake pigment is prepared.

[0044] Comparative Example 8 Comparative Example 8 is basically the same as Example 5, except that step (1) is adjusted as follows: 100 kg of 500-mesh spherical zinc powder, 4 kg of isostearic acid, 4 kg of surface treatment agent (sodium silicate), and 150 kg of solvent (dipropylene glycol methyl ether) are placed in a ball mill (ball mill drum 2.5m × 1.5m), and stainless steel balls with a diameter of 6.0 mm are selected as the ball milling medium. The ball milling is carried out at 35 r / min for 7 h, and then the machine is stopped; then 0.4 kg of additive (polydimethylsiloxane) and 40 kg of deionized water are added, and the ball milling is carried out at 25 r / min for 5 h, and then the machine is stopped. Everything else is the same as in Example 5, and a paste-like zinc flake pigment is prepared.

[0045] Comparative Example 9 Comparative Example 9 is basically the same as Example 5, except that step (1) is adjusted as follows: 100 kg of 500-mesh spherical zinc powder, 4 kg of isostearic acid, 0.4 kg of additive (polydimethylsiloxane), and 150 kg of solvent (dipropylene glycol methyl ether) are placed in a ball mill (ball mill drum 2.5m × 1.5m), and stainless steel balls with a diameter of 6.0 mm are selected as the ball milling medium. The ball milling is carried out at 25 r / min for 5 h, and then the machine is stopped; then 4 kg of surface treatment agent (sodium silicate) and 40 kg of deionized water are added, and the ball milling is carried out at 35 r / min for 7 h, and then the machine is stopped. Everything else is the same as in Example 5, and a paste-like zinc flake pigment is prepared.

[0046] Experimental Example 1 To characterize the properties of the zinc flake pigments obtained in Examples 1-5 and Comparative Examples 1-9, the following tests were conducted: 1. The method for determining water dispersibility is as follows: Add 200g of water to a beaker, add 100g of slurry zinc flake pigment while stirring, stir at 300rpm / min for 20min, pass through a 100-mesh sieve, dry the zinc flake pigment remaining on the sieve after filtration, weigh (m1), and the water dispersibility is: (1-m1 / 100)×100%.

[0047] 2. The storage stability test method is as follows: Take 100g of the paste-like zinc flake pigment product, put it into an iron can and seal it. Place the iron can in a constant temperature and humidity chamber with a temperature of 50℃ and a humidity of 60%. Check the dispersion of the zinc flake pigment every day and record the time when clumping occurs.

[0048] 3. The corrosion resistance test method is as follows: Prepare a coating solution from the slurry zinc flake pigment. The specific method is as follows: Under stirring, slowly add 50g of deionized water, 10g of ethanol, 0.5g of dispersant, and 1.5g of thickener to a container and mix thoroughly. Slowly add chromic acid to the above mixture. This process is exothermic, so the addition rate needs to be controlled and continuous cooling and stirring should be performed to prevent the temperature from becoming too high. Under high-speed stirring, slowly and in batches add 30g of the slurry zinc flake pigment obtained in Examples 1-5 and Comparative Examples 1-9 of this application and 8g of aluminum powder to the chromic acid solution (i.e., Example 1 group uses the slurry zinc flake pigment obtained in Example 1); continue high-speed stirring for 4 hours until a uniform, fine, and particle-free coating solution is formed. Seal and let the prepared coating solution stand (mature) for 24 hours to allow the components to fully react and stabilize, reaching the optimal coating state. Dip the coating solution onto a tinplate and then place it in a neutral salt spray tester to perform a 5% sodium hydroxide salt spray test, observing the rust phenomenon on the paint film surface every 24 hours.

[0049] 4. The buoyancy test method is as follows: refer to section 6.7 of HG / T2456.1-2013 for determination.

[0050] 5. The floating stability test method is as follows: Add 1g of slurry zinc flake pigment to 10g of dipropylene glycol, disperse it evenly, let it stand, observe the changes in the floating layer, and record the time when the floating layer disappears.

[0051] 6. The particle size of the products obtained in Examples 1-5 and Comparative Examples 1-9 of this invention was tested using a BT-9300S laser particle size analyzer. The test results are recorded in Table 1.

[0052] Table 1 As shown in Table 1, the zinc flake pigment products prepared in Examples 1-5 of this invention have high water dispersibility and buoyancy, good storage stability and high corrosion resistance.

[0053] In Comparative Example 1, the solvent (dipropylene glycol methyl ether) was replaced with a common aromatic solvent. Due to the poor compatibility between aromatic solvents and water, and the poor passivation and coating function of surface treatment aids on the product surface in aromatic solvents, the dispersion performance of the product in water decreased significantly.

[0054] In Comparative Example 2, the amount of isostearic acid, a ball milling aid, was reduced, resulting in poorer product buoyancy and floating stability, and finer particle size.

[0055] In Comparative Example 3, replacing polydimethylsiloxane with sodium stearate resulted in a decrease in the product's water dispersibility, storage stability, buoyancy, and floating stability. This is because the additive polydimethylsiloxane introduced in this invention has both emulsifying and coupling effects, which can enhance the binding force between zinc flakes and isostearic acid.

[0056] In Comparative Example 4, replacing the surface treatment agent (sodium silicate) with phosphate ester during ball milling resulted in decreased corrosion resistance and water dispersibility of the product. This is because the surface treatment agent of this invention can form a passivation film on the zinc sheet surface, protecting the zinc sheet from rapid corrosion when it comes into contact with water.

[0057] In Comparative Example 5, no antioxidant was added during the kneading process; in Comparative Example 6, no dispersant was added during the kneading process. Storage stability, buoyancy, and floating stability all deteriorated. This is because the dispersant and antioxidant of this invention both wet and protect the pigment from oxidation upon contact with air, leading to the re-aggregation of pigment particles in the system and the formation of a rough structure.

[0058] In Comparative Example 7, when ball milling was performed in one step, various properties changed compared to Example 5. Compared to Example 5, its water dispersibility was poor, the particle size was finer, and its storage stability and corrosion resistance were worse. This is because when all solvents and additives are added at the same time for ball milling, the ball milling additives cannot fully protect the surface of the product, and the zinc sheet will be quickly broken.

[0059] In Comparative Example 8, the order of addition of additives and surface treatment agents was adjusted, and the various properties changed compared to Example 5. The reason for the decrease in performance compared to Example 5 is that the surface treatment agent was added first, and during the grinding process, the surface treatment agent would be adsorbed onto the surface of the zinc sheet. When water and additives were added subsequently, the surface treatment agent underwent a hydrolysis reaction on the zinc sheet surface, causing multiple pigment particles to cross-link and form large particles, which in turn affected the various properties.

[0060] In Comparative Example 9, compared to Example 5, its water dispersibility deteriorated and its flocculation value decreased. The specific reason for this was that the rapid grinding in the second stage, which increased the grinding time, was not conducive to the coating of the zinc sheet by the surface treatment agent and would also damage the isostearic acid adsorption layer.

[0061] Experimental Example 2 Referring to the preparation method of the coating liquid in the corrosion resistance test method of Example 1, the slurry zinc flake pigment obtained in Example 5 of this application was used to prepare a coating liquid, and the sedimentation stability and viscosity stability of the coating liquid were tested. Then, the coating liquid was dipped onto a tinplate, and the appearance and uniformity of the cured paint film were observed, and the adhesion was tested. A comparison was made with a coating liquid prepared from zinc flake pigment obtained by existing methods (zinc powder prepared by dry grinding). Specific testing methods and standards are shown in Table 2 below, and experimental results are shown in Table 3.

[0062] Table 2 Table 3 Compared with zinc flake pigments prepared by existing methods, the coating solution prepared using the zinc flake pigment of this invention exhibits excellent sedimentation stability and can be easily restored to a homogeneous state by stirring. The viscosity stability of the coating obtained by this invention is far superior to that of existing methods, and the cured paint film has a uniform, smooth, and defect-free surface. The paint film obtained by existing methods shows a drop in adhesion to grade 3 after 15 days, while the paint film cured by this invention still maintains grade 1 adhesion after 15 days, indicating that the paint film obtained by this invention has excellent stability.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing zinc flake pigment for zinc-aluminum coating, characterized in that, Includes the following steps: (1) Add zinc powder, ball milling aid, additives and solvent into the ball mill for the first stage of ball milling. After the first stage of ball milling is completed, add surface treatment agent and water for the second stage of ball milling. (2) Screen the material obtained after ball milling in step (1); (3) The material obtained by screening in step (2) is pressed and filtered to obtain filter cake; (4) Add antioxidant and dispersant to the filter cake from step (3) and knead to obtain a paste-like zinc flake pigment.

2. The method for preparing zinc flake pigment for zinc-aluminum coating according to claim 1, characterized in that, The additive is at least one of polyethylene glycol fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polydimethylsiloxane, or polyglycerol-10 stearate.

3. The method for preparing zinc flake pigment for zinc-aluminum coating according to claim 1, characterized in that, The surface treatment agent is at least one of sodium molybdate, isotridecyl phosphate, sodium silicate, or siloxane.

4. The method for preparing zinc flake pigment for zinc-aluminum coating according to claim 1, characterized in that, The mass ratio of zinc powder, ball milling aid, additive, solvent, surface treatment agent and water is (100-150): (3-5): (0.1-1.0): (100-150): (2-4): (30-50).

5. The method for preparing zinc flake pigment for zinc-aluminum coating according to claim 1, characterized in that, The ball milling aid is isostearic acid; the solvent is propylene glycol or dipropylene glycol methyl ether; the antioxidant is antioxidant 5057; and the dispersant is WELLMIX-1530 dispersant.

6. The method for preparing zinc flake pigment for zinc-aluminum coating according to claim 1, characterized in that, In step (1), the rotation speed of the first ball mill is 35-40 r / min and the milling time is 5-7 h; the rotation speed of the second ball mill is 20-25 r / min and the milling time is 3-5 h; the ball milling medium used in step (1) is stainless steel balls with a diameter of 3.00-8.00 mm; the zinc powder is spherical zinc powder with a mesh size of 325-500.

7. The method for preparing zinc flake pigment for zinc-aluminum coating according to claim 1, characterized in that, In step (2), the sieving specifically involves passing the material through 100-mesh and 350-mesh sieves in sequence.

8. The method for preparing zinc flake pigment for zinc-aluminum coating according to claim 1, characterized in that, In step (4), the amount of antioxidant added is 0.5-1 wt% of the filter cake; the amount of dispersant added is 1-2 wt% of the filter cake.

9. The method for preparing zinc flake pigment for zinc-aluminum coating according to claim 1, characterized in that, Replace step (4) with: wash the filter cake from step (3) with n-propanol, filter by pressure, dry and mix to obtain powdered zinc flake pigment.

10. A zinc flake pigment for zinc-aluminum coating, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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