A method for preparing an aqueous aluminum pigment

Abstract

The application discloses a preparation method of water-based aluminum pigment, which comprises the following steps: cleaning aluminum silver paste in a first solvent and hydrogen peroxide to obtain cleaned aluminum pigment; placing the cleaned aluminum pigment in a second solvent, adding sodium silicate aqueous solution, sodium hydroxide and water to obtain a first mixture; adding aminopropyl triethoxysilane and methyl methacrylate trimethoxysilane to the first mixture, and then adding ethanol amine to perform a first reaction to obtain aluminum pigment with free radical polymerizable silane on the surface; and sequentially adding polysiloxane, amino silane coupling agent and phenoxy trimethoxysiloxane to the aluminum pigment with free radical polymerizable silane on the surface to perform a second reaction to obtain water-based aluminum pigment. The application provides a preparation method of water-based aluminum pigment, the prepared water-based aluminum pigment is tightly coated, well dispersed in a water-based system, has excellent gloss performance of a coating layer, excellent alkali resistance, and extremely low hydrogen evolution amount of a prepared paint, and long-term protection stability.

Description

Technical Field

[0001] This invention relates to the field of aluminum pigment technology, and more particularly to a method for preparing a water-based aluminum pigment. Background Technology

[0002] In water-based aluminum pigment systems, aluminum, being a typical amphoteric and reactive material, readily undergoes electrochemical hydrogen evolution corrosion with water molecules and hydroxide ions in alkaline environments. This not only causes slurry swelling and safety hazards during storage but also damages the smooth, mirror-like structure of the aluminum flakes, leading to a series of application defects such as paint film blackening, diminished metallic luster, and a significant decrease in hiding power. To address these defects, the current industry focus is on constructing a continuous and complete inert inorganic barrier film on the surface of aluminum flakes using an inorganic oxide coating method. This effectively blocks the contact between water molecules and hydroxide ions and the aluminum matrix, thereby improving corrosion resistance.

[0003] Currently, patent CN109694592A discloses a method that abandons pure inorganic passivation or single inorganic SiO2 / TiO2 coating. It introduces macromolecular active polysiloxanes to crosslink on the surface of aluminum flakes to form an organosilicon micro-barrier layer, thereby introducing a single-layer organosilicon coating. This results in a denser coating layer for the aluminum pigment, achieving higher corrosion resistance while retaining good gloss. However, single-organosilane coupling barriers have certain limitations. Adding the organosilicon in a single step leads to a rapid self-polymerization of the macromolecular polysiloxane, generating a large number of free silicon particles, causing undesirable phenomena such as rough powder and haze. Strict control of the production process is required during coating and manufacturing, as it is prone to forming pores or defects, or resulting in uneven or insufficient coating, thus losing its corrosion resistance. Furthermore, it is difficult to maintain good stability in complex chemical environments in practical applications, and it is prone to bloating and swelling during long-term storage experiments. Its storage resistance still needs further improvement. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the present invention provides a method for preparing water-based aluminum pigments. The reaction conditions are mild, and by optimizing the surface modification process of aluminum pigments, the prepared water-based aluminum pigments are tightly coated, have higher compatibility, good dispersibility in water-based systems, excellent coating gloss, and superior alkali resistance. The resulting coatings have extremely low hydrogen evolution, long-term protection and stability, and can be stored for a longer period of time.

[0005] To achieve the above objectives, the embodiments of the present invention adopt the following technical solutions: A method for preparing a water-based aluminum pigment includes the following steps: The aluminum silver paste was washed in a first solvent and hydrogen peroxide to obtain the washed aluminum pigment. The cleaned aluminum pigment is placed in a second solvent and mixed, and sodium silicate aqueous solution, sodium hydroxide and water are added and mixed to obtain a first mixture; Add aminopropyltriethoxysilane and trimethoxysilane methacrylate to the first mixture, and then add ethanolamine to carry out the first reaction to obtain an aluminum pigment with a surface-forming free radical polymerizable silane; Polysiloxane, aminosilane coupling agent, and phenoxytrimethoxysiloxane are sequentially added to the aluminum pigment in which free radical polymerizable silane is formed on the surface, followed by a second reaction and post-treatment to obtain an aqueous aluminum pigment.

[0006] According to one aspect of the present invention, the polysiloxane is one or more of the following mixtures: R1 is an alkoxy group, a divalent hydrocarbon group, or a polycyclic aromatic group; R2 is an alkyl, alkenyl, or polycyclic group.

[0007] According to one aspect of the present invention, the mass ratio of the aluminum silver paste to the first solvent is 1:(1.5 to 2.5), and the mass ratio of the aluminum silver paste to the second solvent is 1:(4 to 6).

[0008] According to one aspect of the present invention, the first solvent is propylene glycol methyl ether.

[0009] According to one aspect of the present invention, the mass ratio of the aluminum silver paste to hydrogen peroxide is 1:(0.04 to 0.06).

[0010] According to one aspect of the present invention, the concentration of the sodium silicate aqueous solution is 0.2 to 0.4 mol / L.

[0011] According to one aspect of the present invention, the mass ratio of the aluminum silver paste, sodium silicate aqueous solution, sodium hydroxide and water is 100:0.25-0.35:0.25-0.30:0.85-0.95.

[0012] According to one aspect of the present invention, the mass ratio of the aluminum silver paste, aminopropyltriethoxysilane, trimethoxysilane methacrylate and ethanolamine is 100:0.08-0.12:0.05-0.11:0.12-0.15.

[0013] According to one aspect of the present invention, the mass ratio of the aluminum silver paste, polysiloxane, aminosilane coupling agent and phenoxytrimethoxysiloxane is 100:0.55-0.58:0.15-0.19:0.3-0.4.

[0014] According to one aspect of the present invention, the reaction temperature of the first reaction is 40-50°C and the reaction time is 1.5-2 hours.

[0015] According to one aspect of the present invention, the reaction temperature of the second reaction is 60-80°C, and the reaction time is 4-8 hours.

[0016] According to one aspect of the invention, the aluminum silver paste D50 has a particle size of 20µm.

[0017] According to one aspect of the present invention, the aminosilane coupling agent is a KH-550 coupling agent.

[0018] A water-based aluminum pigment, prepared by the above-described method, comprises aluminum silver paste and a coating layer covering the aluminum silver paste, forming a core-shell structure. The coating layer prevents the aluminum pigment from corroding in the water-based system.

[0019] The aforementioned water-based aluminum pigments can be used in new energy vehicles. Specifically, they can be coated on the body panels, chassis, wheels, interior parts, etc. of the new energy vehicles.

[0020] The beneficial effects of implementing this invention are as follows: 1. The method for preparing the water-based aluminum pigment involves mild reaction conditions. Sodium silicate hydrolysis forms a thin inorganic silica coating layer on the surface of the aluminum sheet, with numerous Si-OH groups attached to the surface as anchoring sites for silane coupling. In the first reaction, small-molecule active silanes act as an intermediate transition layer anchored to the aluminum powder surface. These small-molecule silanes have low molecular weight and high fluidity, enabling them to uniformly adsorb onto all uneven surfaces of the aluminum sheet, filling the micropores in the sodium silicate layer and providing uniform reaction sites for the second crosslinking reaction. Large-molecule organosilanes are added to the system, undergoing both free radical copolymerization and silanol condensation reactions with the amino and acrylic double bonds remaining on the aluminum surface from the first reaction. Multiple siloxane molecules crosslink to form a three-dimensional network of organosilicon polymer film, thus constructing a dense, hydrophobic multilayer coating layer. This results in a tightly coated water-based aluminum pigment that is less prone to flocculation and agglomeration in the aqueous system, exhibiting good dispersibility. Simultaneously, it significantly improves alkali resistance and hydrogen evolution stability, making it suitable for practical applications under strongly alkaline conditions.

[0021] 2. The prepared aluminum pigment exhibits extremely low hydrogen evolution during high-temperature boiling water tests, provides long-lasting protection and stability, and is suitable for use in high-end water-based metal coatings with long shelf life.

[0022] 3. The prepared water-based aluminum pigment, when used to make coatings, exhibits excellent gloss and a pure metallic texture. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 A schematic diagram of the appearance of the water-based aluminum pigment prepared in Example 2.

[0025] Figure 2 SEM image of the water-based aluminum pigment prepared in Example 2. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] A method for preparing a water-based aluminum pigment includes the following steps: The aluminum silver paste was washed in a first solvent and hydrogen peroxide to obtain the washed aluminum pigment. The cleaned aluminum pigment is placed in a second solvent and mixed, and sodium silicate aqueous solution, sodium hydroxide and water are added and mixed to obtain a first mixture; Add aminopropyltriethoxysilane and trimethoxysilane methacrylate to the first mixture, and then add ethanolamine to carry out the first reaction to obtain an aluminum pigment with a surface-forming free radical polymerizable silane; Polysiloxane, aminosilane coupling agent, and phenoxytrimethoxysiloxane are sequentially added to the aluminum pigment in which free radical polymerizable silane is formed on the surface, followed by a second reaction and post-treatment to obtain an aqueous aluminum pigment.

[0028] In practical applications, both the first solvent and the second solvent are alcohol ether solvents, such as propylene glycol methyl ether.

[0029] In practical applications, hydrogen peroxide can be used to generate a layer of aluminum hydroxide compound anchoring layer rich in hydroxyl active groups on the surface of aluminum sheet in situ.

[0030] In practical applications, the aluminum silver paste D50 has a particle size of 5–100 µm. Preferably, the aluminum silver paste D50 has a particle size of 20 µm.

[0031] In practical applications, the hydrogen peroxide concentration is 20%–30% by mass. The sodium silicate aqueous solution has a concentration of 0.2–0.4 mol / L. The sodium hydroxide concentration is 20%–30% by mass.

[0032] In practical applications, the mass ratio of the aluminum silver paste to the first solvent is 1:(1.5-2.5). The mass ratio of the aluminum silver paste to the second solvent is 1:(4-6). The mass ratio of the aluminum silver paste to hydrogen peroxide is 1:(0.04-0.06).

[0033] In practical applications, the mass ratio of the aluminum silver paste, sodium silicate aqueous solution, sodium hydroxide and water is 100:0.25~0.35:0.25~0.30:0.85~0.95.

[0034] In practical applications, the mass ratio of the aluminum silver paste, aminopropyltriethoxysilane, trimethoxysilane methacrylate, and ethanolamine is 100:0.08-0.12:0.05-0.11:0.12-0.15.

[0035] In practical applications, the mass ratio of the aluminum silver paste, polysiloxane, aminosilane coupling agent and phenoxytrimethoxysiloxane is 100:0.55~0.58:0.15~0.19:0.3~0.4.

[0036] In practical applications, the reaction temperature of the first reaction is 40–50°C, and the reaction time is 1.5–2 hours. The reaction temperature of the second reaction is 60–80°C, and the reaction time is 4–8 hours.

[0037] In practical applications, the polysiloxane is one or more of the following mixtures:

[0038] R1 is an alkoxy group, a divalent hydrocarbon group, or a polycyclic aromatic group. The alkoxy group is either methoxy or ethoxy. The divalent hydrocarbon group is a pure divalent hydrocarbon group without ether bonds or an oxodivalent hydrocarbon group containing ether bonds, with a carbon chain length of C2~C18, preferably C2~C12. The oxygen atom exists only in the form of an ether bond (C−O−C single bond), and oxygen-containing structures such as hydroxyl group -OH, carbonyl group -C=O, and ester group -COO- are not present.

[0039] Preferably, the ether-bonded oxodivalent hydrocarbon group is a monoether straight-chain alkane group, that is, the oxygen atom is embedded between two saturated alkylene segments, and is linear and unbranched.

[0040] Preferably, the polycyclic aromatic group is a linear benzoxene group, with the general structural formula: C 4n+2 H 2n+4(n is the number of benzene rings, n≥2 and n≤6). Preferably, n=2 or 3. When n=2, the polycyclic aromatic group is naphthyl; when n=3, the polycyclic aromatic group is anthraceneyl. When R1 is naphthyl, its linkage site is the α carbon at position 1 of the naphthyl ring. When R1 is anthraceneyl, its linkage site is the median carbon at position 9.

[0041] In practical applications, R2 is an alkyl, alkenyl, or polycyclic group. Specifically, the alkyl group is methyl or ethyl. The alkenyl group is a C2-C8 alkenyl group, preferably with the double bond position of the alkenyl group being a terminal double bond far from the Si atom. Preferably, the alkenyl group is allyl, and the polyoxysilane monomer is methylallylsiloxane.

[0042] In practical applications, the polycyclic group is indenyl or fluorenyl. When the polycyclic group is indenyl, the carbon atom at position 1 of the indenyl ring is directly connected to the silicon atom of the polysiloxane backbone via a C-Si single bond. Preferably, the polyoxysilane monomer is 1-indenylmethyldimethoxysilane.

[0043] In practical applications, when the polycyclic group is fluorene, the Si atom is attached to the C atom at position 9 of the fluorene group. Preferably, the polyoxysilane monomer is 9-fluorenemethyldiethoxysilane.

[0044] In practical applications, the aminosilane coupling agent is KH-550 coupling agent.

[0045] A water-based aluminum pigment is prepared by the above-described method. The water-based aluminum pigment comprises aluminum silver paste and a coating layer covering the aluminum silver paste, forming a core-shell structure. The coating layer prevents the aluminum pigment from corroding in the water-based system.

[0046] The aforementioned water-based aluminum pigments can be used in new energy vehicles. Specifically, they can be coated on the body panels, chassis, wheels, interior parts, etc. of the new energy vehicles.

[0047] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto. It should be pointed out that the following specific embodiments are only applicable to further illustrative purposes and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make non-essential improvements and adjustments to the present application based on the above application content.

[0048] Example 1 A method for preparing a water-based aluminum pigment includes the following steps: S1: Weigh 100g of silver dollar-type aluminum silver paste (aluminum silver paste model: 9606A, D50 particle size: 20µm, manufactured by Zuxing) and wash it in a 500mL beaker with 150g of propylene glycol methyl ether and 4g of hydrogen peroxide with a mass concentration of 20%, and then filter it to obtain the washed aluminum pigment. S2: Place the cleaned aluminum pigment in 400g of propylene glycol methyl ether, stir and heat to 40℃ to obtain a mixed slurry. Mix 0.25g of 0.2mol / L sodium silicate aqueous solution, 0.25g of 20% sodium hydroxide aqueous solution and 0.85g of deionized water and add them to the mixed slurry and stir for 30 minutes. S3: Add 0.08g aminopropyltriethoxysilane and 0.05g trimethoxysilane methacrylate to the mixed slurry, stir for 30 minutes, then add 0.12g ethanolamine and run the reaction for 1.5 hours to carry out free radical polymerization reaction, thereby forming free radical polymerizable silane on the surface of aluminum pigment.

[0049] S4: Continue heating to 60℃, then add 0.65g polysiloxane (structural formula below), 0.15g KH550, and 0.3g phenoxytrimethoxysiloxane in sequence. The reaction polymerization is completed after 4 hours. Then filter the material to obtain water-based aluminum pigment with silica coating.

[0050] Example 2 A method for preparing a water-based aluminum pigment includes the following steps: S1: Weigh 100g of silver dollar-type aluminum silver paste (aluminum silver paste model: 9606A, D50 particle size: 20µm, manufactured by Zuxing) and wash it in a 500mL beaker with 200g of propylene glycol methyl ether and 5g of hydrogen peroxide with a mass concentration of 25%, and then filter it to obtain the washed aluminum pigment. S2: Place the cleaned aluminum pigment in 500g of propylene glycol methyl ether, stir and heat to 50℃ to obtain a mixed slurry. Mix 0.25g of 0.3mol / L sodium silicate aqueous solution, 0.25g of 25% sodium hydroxide aqueous solution and 0.85g of deionized water and add them to the mixed slurry and stir for 30 minutes. S3: Add 0.08g aminopropyltriethoxysilane and 0.05g trimethoxysilane methacrylate to the mixed slurry, stir for 30 minutes, then add 0.12g ethanolamine and run the reaction for 2 hours to carry out free radical polymerization reaction, thereby forming free radical polymerizable silane on the surface of aluminum pigment.

[0051] S4: Continue heating to 80℃, then add 0.55g polysiloxane (structural formula below), 0.15g KH550, and 0.3g phenoxytrimethoxysiloxane in sequence. The reaction polymerization is completed after 8 hours. Then filter the material to obtain water-based aluminum pigment with silica coating. Figure 1 This is a schematic diagram showing the appearance of the water-based aluminum pigment prepared in this embodiment. Figure 2 This is a SEM image of the water-based aluminum pigment prepared in this embodiment.

[0052] Example 3 A method for preparing a water-based aluminum pigment includes the following steps: S1: Weigh 100g of silver dollar-type aluminum silver paste (aluminum silver paste model: 9606A, D50 particle size: 20µm, manufactured by Zuxing) and wash it in a 500mL beaker with 250g of propylene glycol methyl ether and 6g of hydrogen peroxide with a mass concentration of 30%, and then filter it to obtain the washed aluminum pigment. S2: Place the cleaned aluminum pigment in 600g of propylene glycol methyl ether, and heat to 40℃ while stirring to obtain a mixed slurry. Mix 0.25g of 0.4 mol / L sodium silicate aqueous solution, 0.25g of 30% sodium hydroxide aqueous solution and 0.85g of deionized water and add them to the mixed slurry and stir for 30 minutes. S3: Add 0.08g aminopropyltriethoxysilane and 0.05g trimethoxysilane methacrylate to the mixed slurry, stir for 30 minutes, then add 0.12g ethanolamine and run the reaction for 1.5 hours to carry out free radical polymerization reaction, thereby forming free radical polymerizable silane on the surface of aluminum pigment.

[0053] S4: Continue heating to 60℃, then add 0.55g polysiloxane (structural formula below), 0.15g KH550, and 0.3g phenoxytrimethoxysiloxane in sequence. The reaction polymerization is completed after 4 hours. Then filter the material to obtain water-based aluminum pigment with silica coating.

[0054] Example 4 A method for preparing a water-based aluminum pigment includes the following steps: S1: Weigh 100g of silver dollar-type aluminum silver paste (aluminum silver paste model: 9606A, D50 particle size: 20µm, manufactured by Zuxing) and wash it in a 500mL beaker with 200g of propylene glycol methyl ether and 5g of hydrogen peroxide with a mass concentration of 28%, and then filter it to obtain the washed aluminum pigment. S2: Place the cleaned aluminum pigment in 500g of propylene glycol methyl ether, stir and heat to 40℃ to obtain a mixed slurry. Mix 0.25g of 0.3 mol / L sodium silicate aqueous solution, 0.25g of 26% sodium hydroxide aqueous solution and 0.85g of deionized water and add them to the mixed slurry and stir for 30 minutes. S3: Add 0.08g aminopropyltriethoxysilane and 0.05g trimethoxysilane methacrylate to the mixed slurry, stir for 30 minutes, then add 0.12g ethanolamine and run the reaction for 1.5 hours to carry out free radical polymerization reaction, thereby forming free radical polymerizable silane on the surface of aluminum pigment.

[0055] S4: Continue heating to 60℃, then add 0.55g polysiloxane (9-fluorenylmethyldiethoxysilane, its structural formula is as follows), 0.15g KH550, and 0.3g phenoxytrimethoxysiloxane in sequence. The reaction polymerization is completed after 4 hours. Then filter the material to obtain water-based aluminum pigment with silica coating.

[0056]

[0057] Comparative Example 1 The difference from Example 1 is that S3 is omitted; all other aspects are the same as in Example 1. Specifically, in Comparative Example 1: A method for preparing a water-based aluminum pigment includes the following steps: S1: Weigh 100g of silver dollar-type aluminum silver paste (aluminum silver paste model: 9606A, D50 particle size: 20µm, manufactured by Zuxing) and wash it in a 500mL beaker with 150g of propylene glycol methyl ether and 4g of hydrogen peroxide with a mass concentration of 20%, and then filter it to obtain the washed aluminum pigment. S2: Place the cleaned aluminum pigment in 400g of propylene glycol methyl ether, and heat to 40℃ while stirring to obtain a mixed slurry. Mix 0.25g of 0.2mol / L sodium silicate aqueous solution, 0.25g of sodium hydroxide and 0.85g of deionized water and add them to the mixed slurry and stir for 30 minutes. S3: Continue heating to 60℃, then add 0.65g polysiloxane (structural formula below), 0.15g KH550, and 0.3g phenoxytrimethoxysiloxane in sequence. The reaction polymerization is completed after 4 hours. Then filter the material to obtain water-based aluminum pigment with silica coating.

[0058] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the reaction polymerization time in S4 is different. The reaction polymerization time in Comparative Example 2 is 6 hours, while the rest are the same as in Example 1.

[0059] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the reaction polymerization time in S4 is different, while the reaction polymerization time in Comparative Example 2 is 10 hours, and the rest are the same.

[0060] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the reaction temperature in S4 was set to 60°C, while all other conditions were the same.

[0061] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the reaction temperature in S4 was set to 70°C, while all other conditions were the same.

[0062] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that the reaction temperature in S4 was set to 90°C, while all other conditions were the same.

[0063] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that the amount of sodium silicate aqueous solution added in reaction step S2 is 0.35g, while the rest are the same.

[0064] Comparative Example 8 The difference between Comparative Example 8 and Example 1 is that the amount of sodium silicate aqueous solution added in reaction step S2 is 0.40g, while the rest are the same.

[0065] Comparative Example 9 The difference between Comparative Example 9 and Example 1 is that the amount of polysiloxane added in step S4 is 0.55g, while the rest are the same.

[0066] Comparative Example 10 The difference between Comparative Example 10 and Example 1 is that the amount of polysiloxane added in step S4 is 0.60g, while the rest are the same.

[0067] Comparative Example 11 The difference between Comparative Example 11 and Example 1 is that the amount of polysiloxane added in step S4 is 0.70g, while the rest are the same.

[0068] Comparative Example 12 The difference between Comparative Example 12 and Example 2 is that the amount of polysiloxane added in step S4 is 0.75g, while the rest are the same.

[0069] Performance testing: The water-based aluminum pigments prepared in Examples 1, 2, 3, 4, and Comparative Examples 1-12 were subjected to the following performance tests. The specific testing methods for each performance are as follows: I. Dispersion Test: The dispersion test was conducted according to the "Chemical Industry Standard of the People's Republic of China - Aluminum Pigments for Coatings Part 5: Water-based Aluminum Powder Paste: HG / T 2456.5-2016". The specific test methods include: Weigh approximately 1.0 g of water-based aluminum pigment and place it in a beaker. Add 3.0 g of propylene glycol methyl ether for pre-dispersion, then add 10 ml of water. Stir thoroughly with a glass rod and observe whether flocculation or agglomeration occurs in the mixed dispersion system. If no flocculation or agglomeration occurs, the dispersibility grade is considered good; if obvious flocculated particles appear, the dispersibility grade is considered average.

[0070] II. Alkali resistance test: Accurately weigh 1g of water-based aluminum pigment and place it in a beaker. Use a graduated cylinder to measure 20ml of pre-prepared 0.5% NaOH solution to soak the pigment. Observe the bubbling phenomenon and record the bubbling time with a stopwatch.

[0071] III. Hydrogen Evolution Test: The hydrogen evolution amount was tested according to the section on hydrogen evolution amount measurement in the "Chemical Industry Standard of the People's Republic of China - Aluminum Pigments for Coatings Part 5: Waterborne Aluminum Powder Paste: HG / T2456.5-2016".

[0072] IV. Gloss Test: Weigh 8g of water-based acrylic resin into a beaker using a balance, then weigh 0.5g of water-based aluminum pigment and add it to the resin, stirring continuously with a glass rod. After even dispersion, spray the mixture onto a plastic substrate, and then use a BYK single-angle colorimeter to measure the gloss of the aluminum pigment coating.

[0073] V. Stability Test: Referring to the storage stability test method in "Chemical Industry Standard of the People's Republic of China - Aluminum Pigments for Coatings Part 5: Waterborne Aluminum Powder Paste: HG / T 2456.5-2016", 3 g of waterborne aluminum pigment was weighed and stored in a constant temperature drying oven at 50℃ for 30 days. An equal amount of sample was stored at room temperature (25℃) for 30 days. After the storage period, both groups of samples were prepared into coatings according to the same formula and applied to standard test plates to obtain coating samples. Visual comparison was performed according to the coating appearance evaluation method in HG / T 2456.5-2016. If the appearance of the coating after storage at 50℃ is not significantly different from that of the sample stored at room temperature, and the coating surface shows no particles, no agglomeration, and no significant changes in gloss or color, then the storage stability of the waterborne aluminum pigment is deemed qualified. If the coating surface shows obvious particles, agglomeration, or significant deterioration in gloss or color, then it is deemed unqualified.

[0074] The performance test results are shown in Table 1 below.

[0075] Table 1

[0076] The beneficial effects of implementing this invention are as follows: 1. The method for preparing the water-based aluminum pigment involves mild reaction conditions. Sodium silicate hydrolysis forms a thin inorganic silica coating layer on the surface of the aluminum sheet, with numerous Si-OH groups attached to the surface as anchoring sites for silane coupling. In the first reaction, small-molecule active silanes act as an intermediate transition layer anchored to the aluminum powder surface. These small-molecule silanes have low molecular weight and high fluidity, enabling them to uniformly adsorb onto all uneven surfaces of the aluminum sheet, filling the micropores in the sodium silicate layer and providing uniform reaction sites for the second crosslinking reaction. Large-molecule organosilanes are added to the system, undergoing both free radical copolymerization and silanol condensation reactions with the amino and acrylic double bonds remaining on the aluminum surface from the first reaction. Multiple siloxane molecules crosslink to form a three-dimensional network of organosilicon polymer film, thus constructing a dense, hydrophobic multilayer coating layer. This results in a tightly coated water-based aluminum pigment that is less prone to flocculation and agglomeration in the aqueous system, exhibiting good dispersibility. Simultaneously, it significantly improves alkali resistance and hydrogen evolution stability, making it suitable for practical applications under strongly alkaline conditions.

[0077] 2. The prepared aluminum pigment exhibits extremely low hydrogen evolution during high-temperature boiling water tests, provides long-lasting protection and stability, and is suitable for use in high-end water-based metal coatings with long shelf life.

[0078] 3. The prepared water-based aluminum pigment, when used to make coatings, exhibits excellent gloss and a pure metallic texture.

[0079] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a water-based aluminum pigment, characterized in that, The steps include the following: The aluminum silver paste was washed in a first solvent and hydrogen peroxide to obtain the washed aluminum pigment. The cleaned aluminum pigment is placed in a second solvent and mixed, and sodium silicate aqueous solution, sodium hydroxide and water are added and mixed to obtain a first mixture; Add aminopropyltriethoxysilane and trimethoxysilane methacrylate to the first mixture, and then add ethanolamine to carry out the first reaction to obtain an aluminum pigment with a surface-forming free radical polymerizable silane; Polysiloxane, aminosilane coupling agent, and phenoxytrimethoxysiloxane are sequentially added to the aluminum pigment in which free radical polymerizable silane is formed on the surface, and a second reaction is carried out to obtain water-based aluminum pigment.

2. The method for preparing a water-based aluminum pigment according to claim 1, characterized in that, The polysiloxane is one or more of the following mixtures: R1 is an alkoxy group, a divalent hydrocarbon group, or a polycyclic aromatic group; R2 is an alkyl group, an alkenyl group, or a polycyclic group.

3. The method for preparing a water-based aluminum pigment according to claim 1, characterized in that, The mass ratio of the aluminum silver paste to the first solvent is 1:(1.5-2.5), and the mass ratio of the aluminum silver paste to the second solvent is 1:(4-6).

4. The method for preparing a water-based aluminum pigment according to claim 1, characterized in that, The concentration of the sodium silicate aqueous solution is 0.2–0.4 mol / L.

5. The method for preparing a water-based aluminum pigment according to claim 1, characterized in that, The mass ratio of the aluminum silver paste, sodium silicate aqueous solution, sodium hydroxide and water is 100:0.25~0.35:0.25~0.30:0.85~0.

95.

6. The method for preparing a water-based aluminum pigment according to claim 1, characterized in that, The mass ratio of the aluminum silver paste, aminopropyltriethoxysilane, trimethoxysilane methacrylate, and ethanolamine is 100:0.08-0.12:0.05-0.11:0.12-0.

15.

7. The method for preparing a water-based aluminum pigment according to claim 1, characterized in that, The mass ratio of the aluminum silver paste, polysiloxane, aminosilane coupling agent and phenoxytrimethoxysiloxane is 100:0.55-0.58:0.15-0.19:0.3-0.

4.

8. The method for preparing a water-based aluminum pigment according to claim 1, characterized in that, The reaction temperature of the first reaction is 40-50℃, and the reaction time is 1.5-2h.

9. The method for preparing a water-based aluminum pigment according to claim 1, characterized in that, The reaction temperature of the second reaction is 60-80℃, and the reaction time is 4-8h.

10. The method for preparing a water-based aluminum pigment according to claim 1, characterized in that, The aminosilane coupling agent is KH-550 coupling agent.

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