A colored aluminum pigment based on a metal aluminum substrate and a method for preparing the same

Abstract

This invention provides a colored aluminum pigment based on an aluminum substrate and its preparation method, belonging to the field of effect pigment technology. The colored aluminum pigment based on an aluminum substrate of this invention comprises a metal substrate, a first silicon dioxide layer, a second silicon dioxide layer, an oxide layer, and an iron oxide layer stacked sequentially. The colored aluminum pigment of this invention exhibits high metallic luster, vibrant color, and excellent stability.

Description

Technical Field

[0001] This invention relates to the field of effect pigment technology, and in particular to a colored aluminum pigment based on a metallic aluminum substrate and its preparation method. Background Technology

[0002] Metallic aluminum pigments are widely used in automotive coatings, industrial coatings, plastic coloring, and printing inks due to their unique metallic luster. However, traditional metallic aluminum pigments are only silver-white, offering a limited color range and only capable of producing silver-gray hues, which fails to meet the demands of modern industry for personalized and vibrant colors. Furthermore, their chemically reactive nature makes them highly susceptible to corrosion in aqueous systems or acidic / alkaline environments, leading to a decrease in gloss or even discoloration. To achieve a colored metallic effect, the common practice is to physically blend metallic aluminum pigments with organic or inorganic colored pigments. However, this method has significant drawbacks: the colored pigments can block the reflected light from the aluminum flakes, resulting in a significant reduction in metallic luster, a dull and lifeless color, and a tendency for color differences due to pigment separation.

[0003] To impart color to metallic aluminum pigments and improve their stability, the current mainstream method involves coating the surface of metallic aluminum powder with one or more layers of translucent metal oxides (such as silicon dioxide, iron oxide, etc.), utilizing the principle of thin-film interference to generate brilliant interference colors. However, problems remain, including poor dispersion and coating uniformity, insufficient bonding between different coating layers, oxidation issues, and the complexity and stability of the process. Summary of the Invention

[0004] The purpose of this invention is to provide a colored aluminum pigment based on a metallic aluminum substrate and its preparation method. The colored aluminum pigment has the characteristics of bright color, high metallic luster and good chemical stability, which can meet the demand for coloring metallic aluminum pigments.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a colored aluminum pigment based on a metallic aluminum substrate, comprising a metallic aluminum substrate, a first silicon dioxide layer, a second silicon dioxide layer, an oxide layer, and an iron oxide layer stacked sequentially. The iron oxide layer is a first iron oxide layer, or the iron oxide layer is a first iron oxide layer and a second iron oxide layer stacked together; The metal elements corresponding to the oxides in the oxide layer include aluminum, zirconium, tin, or zinc.

[0006] Preferably, it further includes an outer layer, which comprises an organosilane coupling agent layer.

[0007] Preferably, the aluminum substrate is a sheet-like aluminum sheet; the average particle size of the aluminum substrate is 1~100μm, and the average thickness is 0.01~5μm.

[0008] This invention provides a method for preparing colored aluminum pigments based on a metallic aluminum substrate as described in the above technical solution, comprising the following steps: The first product is a metallic aluminum substrate coated with a first silicon dioxide layer. The first product is mixed with water, soluble silicate and acid, and subjected to a first hydrolysis to form a second silica layer, thereby obtaining the second product; The second product is mixed with water, the water-soluble salt corresponding to the oxide layer, and alkali to undergo a second hydrolysis, forming an oxide layer and obtaining the third product. The third product is mixed with an aqueous solution of ferric chloride and a first alkaline solution to undergo a third hydrolysis, forming a first ferric oxide layer, and thus obtaining the fourth product. The fourth product is mixed with an aqueous solution of ferric nitrate and a second alkaline solution to undergo a fourth hydrolysis, forming a second iron oxide layer, and thus obtaining the fifth product. The fourth or fifth product is calcined under a nitrogen atmosphere to obtain a colored aluminum pigment based on a metallic aluminum substrate.

[0009] Preferably, when an outer layer is also included, the outer layer material is coated on the surface of the calcined product to form an outer layer.

[0010] Preferably, the soluble silicate includes one or more of sodium silicate, potassium silicate, and lithium silicate; The first hydrolysis is performed at a temperature of 70-90℃, a pH value of 5.0-10.0, and a time of 4-6 hours.

[0011] Preferably, the water-soluble salt corresponding to the oxide layer includes aluminum chloride, zirconium chloride, tin chloride, or zinc chloride; the second hydrolysis temperature is 70~90℃, and the time is 0.5h~1.5h; The oxide layer has a coating amount of 0.25 to 10% of the mass of the aluminum substrate.

[0012] Preferably, the mass concentration of the ferric chloride aqueous solution is 5-40%; the temperature of the third hydrolysis is 70-90℃, the pH value is 2.5-4.5, the feeding rate is 0.1-0.5mL / min, and the time is 2-8.5h; The first alkaline solution and the second alkaline solution independently include aqueous solutions of alkali metal hydroxides, aqueous solutions of soluble silicates, aqueous solutions of alkali metal carbonates, aqueous solutions of alkali metal bicarbonates, ammonium carbonate, aqueous solutions of ammonium bicarbonate, or ammonia. Preferably, the mass concentration of the ferric nitrate aqueous solution is 5-45%; the temperature of the fourth hydrolysis is 70-90℃, the pH value is 2.5-4.5, the feeding rate is 0.3-0.7 mL / min, and the time is 1-3 h.

[0013] Preferably, the calcination temperature is 250~450℃ and the time is 0.25~6h.

[0014] The colored aluminum pigment based on an aluminum substrate provided by this invention protects the chemically active aluminum core within a dense and uniform second silica layer. This prevents the aluminum substrate from undergoing hydrogen reaction even in aqueous or acidic / alkaline environments for extended periods, thus avoiding corrosion of the aluminum pigment and preventing a decrease in gloss and loss of metallic sheen. Furthermore, to achieve vibrant colors, an oxide layer is applied after the second silica coating. This improves pigment stability and enhances the optical properties of the outer iron oxide layer. Finally, an iron oxide layer or a stacked first and second iron oxide layer is applied as the outermost layer, achieving a multi-layered, dense coating.

[0015] The colored aluminum pigment based on a metallic aluminum substrate provided by this invention has a certain thickness due to its multi-layer coating, which allows for calcination heat treatment in a nitrogen atmosphere without damaging the aluminum core, thereby improving the pigment's color rendering performance. Further surface treatment (outer layer organosilane coupling agent) of the heat-treated colored aluminum pigment can enhance its weather resistance. Therefore, the colored aluminum pigment prepared by this invention combines vibrant colors, high metallic luster, and excellent chemical stability and weather resistance.

[0016] Aluminum powder particles are fine and prone to agglomeration. The dense iron oxide coating layer of this invention can reduce the direct contact and attraction between aluminum powder particles, thereby preventing self-agglomeration. The iron oxide layer imparts color to the silvery-white aluminum pigment and also changes the surface properties and density of the aluminum powder particles. It can effectively improve the dispersion stability of metallic aluminum powder and can produce colored aluminum pigments with improved color development performance through heat treatment without damaging the metallic aluminum core, while reducing process costs. Attached Figure Description

[0017] Figure 1 SEM image (X7,000) of the red colored aluminum pigment prepared in Example 1; Figure 2 SEM image (X7,000) of the orange-red colored aluminum pigment prepared in Comparative Example 1; Figure 3 SEM image (X20,000) of the red colored aluminum pigment prepared in Example 1; Figure 4 SEM image (X20,000) of the orange-red colored aluminum pigment prepared in Comparative Example 1; Figure 5 A cross-sectional SEM image of the red colored aluminum pigment prepared in Example 1; Figure 6 A cross-sectional SEM image of the orange-red colored aluminum pigment prepared for Comparative Example 1; Figure 7 SEM image (x5000) of the red aluminum pigment prepared in Example 1. Figure 8 Coating cards for the red colored aluminum pigment (right) and the flake-shaped metallic aluminum pigment (left) prepared in Example 1; Figure 9 Coating cards for the gold-colored aluminum pigment (right) and the flake-shaped metallic aluminum pigment (left) prepared in Example 2; Figure 10 Coating cards for the orange colored aluminum pigment (right) and the flake-shaped metallic aluminum pigment (left) prepared in Example 3; Figure 11 This is a comparison coating card of the orange-red aluminum pigment (left) in Comparative Example 1 and the red aluminum pigment (right) in Example 1. Detailed Implementation

[0018] In this invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well known to those skilled in the art.

[0019] This invention provides a colored aluminum pigment based on a metallic aluminum substrate, comprising a metallic aluminum substrate, a first silicon dioxide layer, a second silicon dioxide layer, an oxide layer, and an iron oxide layer stacked sequentially. The iron oxide layer is a first iron oxide layer, or the iron oxide layer is a first iron oxide layer and a second iron oxide layer stacked together; The metal elements corresponding to the oxides in the oxide layer include aluminum, zirconium, tin, or zinc.

[0020] In this invention, the aluminum substrate is a sheet-like aluminum sheet.

[0021] In this invention, the average particle size of the aluminum substrate is preferably 1~100μm, more preferably 5~50μm, and even more preferably 5~30μm, and the average thickness is preferably 0.01~5μm, more preferably 0.02~2μm, and even more preferably 0.05~1μm.

[0022] The present invention uses a metallic aluminum substrate coated with a first silicon dioxide layer as a substrate, and sequentially stacks a second silicon dioxide layer, an oxide layer and an iron oxide layer.

[0023] The aluminum substrate coated with the first silicon dioxide layer described in this invention is a commercially available product, and its specifications are not specifically limited.

[0024] The second silicon dioxide layer in this invention is used to protect the core aluminum pigment and prevent the core aluminum from undergoing a hydrogen reaction under alkaline conditions, which would cause the pigment to lose its luster.

[0025] The present invention does not impose any special limitation on the thickness of the first silicon dioxide layer and the second silicon dioxide layer; the thickness can be adjusted according to actual needs.

[0026] The colored aluminum pigment provided by the present invention includes an oxide layer; the metal element corresponding to the oxide in the oxide layer includes aluminum, zirconium, tin or zinc, more preferably tin.

[0027] The colored aluminum pigment provided by the present invention includes an iron oxide layer; the iron oxide layer is a first iron oxide layer, or the iron oxide layer is a first iron oxide layer and a second iron oxide layer stacked together; the first iron oxide layer is in contact with the oxide layer.

[0028] This invention uses different numbers of iron oxide layers to achieve the desired color of colored aluminum pigments.

[0029] The present invention does not have a special limitation on the thickness of the first iron oxide layer and the second iron oxide layer; it can be adjusted according to the requirements.

[0030] The colored aluminum pigment provided by this invention also includes an outer layer, which comprises an organosilane coupling agent layer. The thickness of the outer layer is not specifically limited in this invention and can be adjusted according to requirements.

[0031] This invention provides a method for preparing colored aluminum pigments based on a metallic aluminum substrate as described in the above technical solution, comprising the following steps: The first product is a metallic aluminum substrate coated with a first silicon dioxide layer. The first product is mixed with water, soluble silicate and acid, and subjected to a first hydrolysis to form a second silica layer, thereby obtaining the second product; The second product is mixed with water, the water-soluble salt corresponding to the oxide layer, and alkali to undergo a second hydrolysis, forming an oxide layer and obtaining the third product. The third product is mixed with an aqueous solution of ferric chloride and a first alkaline solution to undergo a third hydrolysis, forming a first ferric oxide layer, and thus obtaining the fourth product. The fourth product is mixed with an aqueous solution of ferric nitrate and a second alkaline solution to undergo a fourth hydrolysis, forming a second iron oxide layer, and thus obtaining the fifth product. The fourth or fifth product is calcined under a nitrogen atmosphere to obtain a colored aluminum pigment based on a metallic aluminum substrate.

[0032] In this invention, the first product is preferably dispersed in water, the resulting dispersion is heated, acid is added to adjust to the required pH value, and then soluble silicate is added; the concentration of the dispersion is preferably 30~100g / L, more preferably 50~80g / L.

[0033] In this invention, the soluble silicate preferably includes one or more of sodium silicate, potassium silicate and lithium silicate, more preferably sodium silicate; the soluble silicate is preferably used in the form of an aqueous solution, and the concentration of the soluble silicate aqueous solution, based on silicon dioxide, is 25~250gSiO2 / L, preferably 50~200gSiO2 / L, more preferably 90~150gSiO2 / L.

[0034] In this invention, the acid is preferably hydrochloric acid or sulfuric acid, more preferably hydrochloric acid (10% by mass).

[0035] In this invention, the temperature of the first hydrolysis is preferably 70-90℃, more preferably 75-85℃, the pH value is preferably 5.0-10.0, more preferably 6.0-9.0, more preferably 7.2-8.5, and the time is preferably 4-6 hours, more preferably 5 hours. During the first hydrolysis process, hydrochloric acid is used to control and maintain a constant pH value.

[0036] After the first hydrolysis is completed, the present invention preferably uses hydrochloric acid to adjust to the required pH value, adds a water-soluble salt solution, and uses alkali to control the pH value to carry out the second hydrolysis.

[0037] Because conventional water-based silicon-coated aluminum substrates lack sufficient stability during coating reactions with strong acids and alkalis in aqueous solutions, hydrogen gas is generated, preventing the formation of a dense and uniform metal oxide coating layer. The colored aluminum pigments of this invention have a thin first silica coating layer, insufficient to withstand prolonged exposure to acids and alkalis. Since this application also requires coating with two layers of iron oxide, the aluminum substrate coated with the first silica layer will be exposed to high-temperature, acidic conditions for extended periods. To prevent hydrogen gas reaction upon contact with acidic conditions, this invention utilizes a thick second silica coating layer for protection, completely and uniformly coating the aluminum core within a silica coating layer of a certain thickness, providing long-term protection. Therefore, the second silica layer in this invention is essential for the subsequent coating of the first and second iron oxide layers, and it solves the instability problem of the silicon-coated aluminum substrate.

[0038] In this invention, the water-soluble salt corresponding to the oxide layer preferably includes aluminum chloride, zirconium chloride, tin chloride or zinc chloride, more preferably zirconium tetrachloride or tin tetrachloride, and even more preferably tin tetrachloride.

[0039] The present invention does not have a specific limitation on the concentration of the water-soluble salt solution, which can be adjusted according to the needs. In the example, it is 62.5 g / L.

[0040] In this invention, the temperature of the second hydrolysis is preferably 70~90℃, more preferably 75~85℃, the time is preferably 0.5h~1.5h, more preferably 1h, and the pH value is 1.8~2.1, more preferably 2.0; during the second hydrolysis process, the alkali is preferably an 8% sodium hydroxide solution by mass concentration.

[0041] The present invention does not have a special limitation on the amount of water used for the first and second hydrolysis; it can be adjusted according to the needs.

[0042] In this invention, the coating amount of the oxide layer is preferably 0.25-10% of the mass of the aluminum substrate, more preferably 0.5-5.0%, and even more preferably 1.0-3.0%. The oxide layer is used to better coat the iron oxide layer onto the silicon dioxide layer, so as to form a uniform and dense iron oxide coating layer.

[0043] After the second hydrolysis is completed, the present invention preferably uses a first alkaline solution to adjust the solution to the required pH value, adds an aqueous solution of ferric chloride, performs a third hydrolysis, and maintains the pH value unchanged.

[0044] In this invention, the mass concentration of the ferric chloride aqueous solution is preferably 5-40%, more preferably 7.5-35%, and even more preferably 8.5-20%; the temperature of the third hydrolysis is preferably 70-90℃, more preferably 75-85℃; the pH value is preferably 2.5-4.5, more preferably 3.2; the feeding rate is 0.1-0.5 mL / min, more preferably 0.3-0.4 mL / min; and the time is preferably 2-8.5 h, more preferably 2.5-5 h.

[0045] In this invention, the first alkaline solution and the second alkaline solution preferably independently comprise an aqueous solution of an alkali metal hydroxide, an aqueous solution of a soluble silicate, an aqueous solution of an alkali metal carbonate, an aqueous solution of an alkali metal bicarbonate, ammonium carbonate, an aqueous solution of ammonium bicarbonate, or ammonia; the mass concentration of the first alkaline solution and the second alkaline solution is preferably 5-15%, more preferably 8%.

[0046] In this invention, the aqueous solution of alkali metal hydroxide is preferably an aqueous solution of sodium hydroxide or potassium hydroxide; the aqueous solution of soluble silicate is preferably an aqueous solution of sodium silicate, potassium silicate or lithium silicate; the aqueous solution of alkali metal carbonate is preferably an aqueous solution of sodium carbonate or potassium carbonate; and the aqueous solution of alkali metal bicarbonate is preferably an aqueous solution of sodium bicarbonate or potassium bicarbonate.

[0047] After the third hydrolysis is completed, the present invention preferably raises the temperature to the required temperature, adds an aqueous solution of ferric nitrate, adjusts the solution to the required pH value using a second alkaline solution, performs the fourth hydrolysis, and maintains the pH value unchanged.

[0048] In this invention, the mass concentration of the ferric nitrate aqueous solution is preferably 5-45%, more preferably 7.5-35%, and even more preferably 10-30%.

[0049] In this invention, the temperature of the fourth hydrolysis is preferably 70-90℃, more preferably 75-85℃, and even more preferably 80℃; the pH value is preferably 2.5-4.5, more preferably 2.8-3.8, and even more preferably 3.2-3.6; the feeding rate is 0.3-0.7 mL / min, more preferably 0.4-0.5 mL / min; and the time is preferably 1-3 h, more preferably 2-3 h. Hydrolysis with ferric nitrate aqueous solution can form a denser iron oxide coating layer. After the fourth hydrolysis reaction, stirring is continued for 20-60 min, preferably 30-50 min.

[0050] After the fourth hydrolysis is completed, the present invention preferably filters, washes, dries, and calcines the resulting mixture sequentially. The drying temperature is preferably 105~135℃, more preferably 110~120℃, and the drying time is preferably 3~12h, more preferably 12h.

[0051] In this invention, when the iron oxide layer is a first iron oxide layer, the fourth product is calcined; when the iron oxide layer is a first iron oxide layer and a second iron oxide layer, the fifth product is calcined.

[0052] In this invention, the calcination temperature is preferably 250~450℃, more preferably 300~400℃, and even more preferably 350℃; the calcination time is preferably 0.25~6h, more preferably 0.5~3h, and even more preferably 1~2h; and the atmosphere is preferably nitrogen.

[0053] This invention provides protection for aluminum pigments in subsequent hydrolysis processes through a first hydrolysis, achieves the connection between the first and third hydrolysis products through a second hydrolysis, achieves coloring through the third hydrolysis, and obtains colored aluminum pigments through a fourth hydrolysis.

[0054] In this invention, when an outer layer is also included, the outer layer material is coated on the surface of the calcined product to form an outer layer.

[0055] After calcination, the present invention preferably disperses the calcined colored aluminum pigment in water, adds an organosilane coupling agent to the resulting dispersion for coating, forming an organosilane coupling agent layer, and then filters, washes, and dries the product to obtain the colored aluminum pigment. The concentration of the dispersion is preferably 87.5~137.5 g / L, more preferably 107 g / L~112.5 g / L; the coating temperature is preferably 70~90℃, more preferably 75℃; the coating time is preferably 0.5 h~1.5 h, more preferably 1 h; and the pH value is preferably 3~8, more preferably 4~6.

[0056] In this invention, the organosilane coupling agent preferably includes one or more of methacryloyloxyaminosilane, epoxysilane, isocyanate silane, aminosilane, and alkylsilane, more preferably γ-glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane. When the organosilane coupling agent is two or more of the above, this invention does not have a special limitation on the ratio of different types of organosilane coupling agents, and can be adjusted according to requirements.

[0057] In this invention, the drying temperature is preferably 125~150℃, more preferably 130~140℃, and the drying time is preferably 3~6h, more preferably 4~5h.

[0058] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0059] Unless otherwise specified, the experimental methods described in the various embodiments of this invention are conventional methods; unless otherwise specified, the reagents and raw materials described below are all commercially available.

[0060] Example 1

[0061] Weigh 20g of flake-shaped aluminum substrate (Zuxing Aluminum Pigment SAF-2302) coated with a silica layer and disperse it in 400mL of deionized water to obtain a dispersion with a concentration of 50g / L. Stir and heat to 75℃, then adjust the pH of the dispersion to 7.2 with 10% hydrochloric acid. At this pH, add 150mL of sodium silicate aqueous solution (equivalent to 90g SiO2 / L), while simultaneously controlling and maintaining the pH value with 10% hydrochloric acid. React for 5 hours, then continue stirring for 0.5 hours. Next, lower the pH value to 2.0 with 10% hydrochloric acid, add 3mL of 62.5g / L tin tetrachloride aqueous solution, and maintain the pH value with 8% sodium hydroxide solution, continuing the reaction at 75℃ for 1 hour. After the addition is complete, continue stirring for 0.5 hours. The pH of the solution was adjusted to 3.2 with an 8% sodium hydroxide solution. At this pH, a 20% ferric chloride aqueous solution was added at a feeding rate of 0.3 mL / min. The pH was controlled and maintained constant with the 8% sodium hydroxide solution. The reaction was allowed to proceed for 8 hours until the suspension turned orange. Then, the temperature was raised to 80°C, and a 30% ferric nitrate aqueous solution was added. The pH was adjusted to 3.2 with the 8% sodium hydroxide solution, and the feeding rate was set to 0.4 mL / min. The reaction was allowed to proceed for 3 hours until the suspension turned red. After stirring for another 0.5 hours, the solution was filtered, washed with water, dried at 110°C for 12 hours, and then calcined at 350°C for 0.5 hours under a nitrogen atmosphere to obtain a red aluminum pigment. In this pigment, the tin oxide layer coating amount was 1% of the mass of the aluminum substrate.

[0062] Example 2

[0063] Weigh 20g of flake-shaped aluminum substrate (Zuxing aluminum pigment SAF-2302) coated with a silica layer and disperse it in 400mL of deionized water to obtain a dispersion with a concentration of 50g / L. Stir and heat to 75℃, and adjust the pH of the dispersion to 7.2 with 10% hydrochloric acid. At this pH, add 150mL of sodium silicate aqueous solution (equivalent to 90g SiO2 / L), while controlling and maintaining the pH value with 10% hydrochloric acid. Continue stirring for 0.5h after the addition is complete. Then, lower the pH value to 2.0 with 10% hydrochloric acid, add 3mL of 62.5g / L tin tetrachloride aqueous solution, and then add 8% sodium hydroxide solution. The solution pH was kept constant for 1 hour. After the addition was complete, stirring was continued for 0.5 hours. The pH was then adjusted to 3.2 with 8% sodium hydroxide solution. At this pH, a 20% ferric chloride aqueous solution was added at a rate of 0.4 mL / min. The pH was controlled and maintained constant with 8% sodium hydroxide solution. The reaction was allowed to continue for 2.5 hours until the suspension turned golden. After stirring for another 0.5 hours, the solution was filtered, washed, dried at 110°C for 12 hours, and then calcined at 350°C for 0.5 hours under a nitrogen atmosphere to obtain a golden colored aluminum pigment. The amount of tin oxide coating in this pigment was 1% of the mass of the aluminum substrate.

[0064] Example 3

[0065] Weigh 20g of flake-shaped aluminum substrate (Zuxing aluminum pigment SAF-2302) coated with a silica layer and disperse it in 400mL of deionized water to obtain a dispersion with a concentration of 50g / L. Stir and heat to 75℃, and adjust the pH of the dispersion to 7.2 with 10% hydrochloric acid. At this pH, add 150mL of sodium silicate aqueous solution (equivalent to 90g SiO2 / L), while controlling and maintaining the pH value with 10% hydrochloric acid. Continue stirring for 0.5h after the addition is complete. Then, lower the pH value to 2.0 with 10% hydrochloric acid, add 3mL of 62.5g / L tin tetrachloride aqueous solution, and then add 8% sodium hydroxide solution. The solution pH was kept constant for 1 hour. After the addition was complete, stirring was continued for 0.5 hours. The pH was then adjusted to 3.2 with 8% sodium hydroxide solution. At this pH, a 20% ferric chloride aqueous solution was added at a feeding rate of 0.4 mL / min. The pH was controlled and maintained constant with 8% sodium hydroxide solution. The reaction was allowed to proceed for 8.5 hours until the suspension turned orange. Stirring was continued for another 0.5 hours. The solution was then filtered, washed, dried at 110°C for 12 hours, and then calcined at 350°C for 0.5 hours under a nitrogen atmosphere to obtain an orange colored aluminum pigment. The amount of tin oxide coating in this pigment was 1% of the mass of the aluminum substrate.

[0066] Comparative Example 1

[0067] 20g of sheet-like aluminum substrate coated with a silica layer was weighed and added to 400mL of deionized water to obtain a dispersion with a concentration of 50g / L. The mixture was stirred and heated to 75℃, and the pH was adjusted to 7.2 with 10% hydrochloric acid. At this pH, 150mL of sodium silicate solution (equivalent to 90g SiO2 / L) was added, while the pH was controlled and maintained constant with 10% hydrochloric acid. After the addition was complete, stirring was continued for 0.5h. Then, the pH was lowered to 2.0 with 10% hydrochloric acid, and 3mL of 62.5g / L tin tetrachloride aqueous solution was added. The pH of the solution was maintained constant with 8% sodium hydroxide solution, and the reaction time was 1h. After stirring for 0.5 h following the reaction, the pH of the solution was adjusted to 3.2 with 8% sodium hydroxide solution. At this pH, a 20% ferric chloride aqueous solution was added at a feeding rate of 0.4 mL / min, while the pH was controlled and maintained constant with 8% sodium hydroxide solution. The reaction was allowed to proceed for 8.5 h until the suspension turned orange. Subsequently, the temperature was raised to 80℃, and another 20% ferric chloride aqueous solution was added, with the pH adjusted to 3.2 with 8% sodium hydroxide solution at a feeding rate of 0.3 mL / min. After reacting for 4 h, the suspension turned orange-red. After stirring for another 0.5 h, the solution was filtered, washed, dried at 110℃ for 12 h, and calcined at 300℃ for 0.5 h under a nitrogen atmosphere to obtain an orange-red colored aluminum pigment.

[0068] Characterization and performance testing

[0069] 1) Observation using scanning electron microscopy (SEM):

[0070] Figure 1 SEM image (X7,000) of the red colored aluminum pigment prepared in Example 1; Figure 2 SEM image (X7,000) of the orange-red colored aluminum pigment prepared in Comparative Example 1; Figure 3 SEM image (X20,000) of the red colored aluminum pigment prepared in Example 1; Figure 4 SEM image (X20,000) of the orange-red colored aluminum pigment prepared in Comparative Example 1; from Figures 1-4 As can be seen from the SEM images, the sample surface of Example 1 of this invention has a significantly more uniform and denser iron oxide layer compared to Comparative Example 1, thus enhancing the red hue; from Figure 11 It is even more obvious that Comparative Example 1 has less red hue compared to Example 1, and is generally orange-red, failing to achieve the desired red hue.

[0071] 2) Using a common coating and scraping method, 0.25g of pigment from the samples prepared in Example 1 and Comparative Example 1 were added to 4.5g of polyurethane leather resin system (Zhejiang Huafeng Synthetic Resin Co., Ltd., JE-S-8080 resin, methyl ethyl ketone, and N,N-dimethylformamide in a mass ratio of 10:5:0.08) and 0.6g of alcohol. After stirring evenly, the mixture was coated onto a scraping card, and the color and hue were tested using a BYK-mac colorimeter. The color measurement results are shown in Table 1, where L represents the brightness of the color; a represents the color bias on the red-green axis; b represents the color bias on the yellow-blue axis; C represents the vividness and purity of the color; and h represents the angle of the color on the color wheel, determining whether it belongs to red, orange, yellow, green, blue, or purple.

[0072] Table 1 shows the results of color measurement using BYK-mac.

[0073] In Table 1, Example 1 is the sample of the present invention, a A high value indicates a strong red hue, as shown in Comparative Example 1 (b). A high h value indicates a pronounced yellow hue. The h value (hue angle) of Example 1 is significantly lower than that of Comparative Example 1, indicating that the sample of the present invention clearly exhibits a red hue.

[0074] 3) Figure 5 A cross-sectional SEM image of the red colored aluminum pigment prepared in Example 1; Figure 6 The image shows a cross-sectional SEM image of the orange-red colored aluminum pigment prepared in Comparative Example 1; where a-sheet aluminum substrate; b-silica layer (layer 1); c-silica layer (layer 2); d-tin dioxide layer; e-iron oxide layer (layer 1); f-iron oxide layer (layer 2); from Figures 5-6 It can be seen that the colored aluminum pigment is regularly coated on the surface of the aluminum pigment in a specific number of layers. Through... Figures 5-6 As can be seen, the b-layer coating is as thin as a cicada's wing compared to the subsequent c, d, e, and f layers. This makes conventional silver-white aluminum pigments extremely prone to hydrogen evolution and corrosion in aqueous systems or acidic / alkaline environments, resulting in a decrease in gloss or even discoloration.

[0075] Figure 7 SEM image (x5000) of the red aluminum pigment prepared in Example 1; as Figure 7 As shown, the aluminum pigment coating layer is a dense shell that completely covers the surface of each aluminum sheet, which can improve the stability of the aluminum pigment.

[0076] Furthermore, stability and durability are generally proportional to the thickness of the cladding layer, and only a cladding layer of uniform thickness can provide a long-lasting and reliable physical barrier for the aluminum sheet, resisting external acids and alkalis. Figure 5 , Figure 6The thickness of the coating can be seen. Figure 7 The uniformity and density of the coating layer can be observed. From... Figures 5-7 It can also be seen that the coating layer is tightly bonded to the aluminum substrate without gaps or peeling, indicating strong adhesion between the two. Such a coating layer is not easy to peel off from the aluminum sheet when subjected to mechanical processing (such as paint mixing and spraying) or thermal expansion and contraction, and can maintain its appearance, color and function stability for a long time, with good stability and durability.

[0077] Figures 8-10 The red, gold, and orange colored aluminum pigments coated in Examples 1-3 are examples of examples 1-3. Figures 8-10 (middle right) and the pigment on the pre-coated flake-shaped aluminum substrate ( Figures 8-10 A comparison of the left and right sides of the image clearly shows that the colored aluminum pigments coated by this invention have bright colors and a full metallic luster.

[0078] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A colored aluminum pigment based on an aluminum substrate, characterized in that, It includes a metal aluminum substrate, a first silicon dioxide layer, a second silicon dioxide layer, an oxide layer and an iron oxide layer stacked sequentially; The iron oxide layer is a first iron oxide layer, or the iron oxide layer is a first iron oxide layer and a second iron oxide layer stacked together; The metal elements corresponding to the oxides in the oxide layer include aluminum, zirconium, tin, or zinc.

2. The colored aluminum pigment according to claim 1, characterized in that, It also includes an outer layer, which comprises an organosilane coupling agent layer.

3. The colored aluminum pigment according to claim 1, characterized in that, The aluminum substrate is a sheet-like aluminum sheet; the average particle size of the aluminum substrate is 1~100μm, and the average thickness is 0.01~5μm.

4. The method for preparing colored aluminum pigment based on a metallic aluminum substrate according to any one of claims 1 to 3, characterized in that, Includes the following steps: The first product is a metallic aluminum substrate coated with a first silicon dioxide layer. The first product is mixed with water, soluble silicate and acid, and subjected to a first hydrolysis to form a second silica layer, thereby obtaining the second product; The second product is mixed with water, the water-soluble salt corresponding to the oxide layer, and alkali to undergo a second hydrolysis, forming an oxide layer and obtaining the third product. The third product is mixed with an aqueous solution of ferric chloride and a first alkaline solution to undergo a third hydrolysis, forming a first ferric oxide layer, and thus obtaining the fourth product. The fourth product is mixed with an aqueous solution of ferric nitrate and a second alkaline solution to undergo a fourth hydrolysis, forming a second iron oxide layer, and thus obtaining the fifth product. The fourth or fifth product is calcined under a nitrogen atmosphere to obtain a colored aluminum pigment based on a metallic aluminum substrate.

5. The preparation method according to claim 4, characterized in that, When an outer layer is also included, it also includes coating the surface of the calcined product with an outer layer of raw material to form an outer layer.

6. The preparation method according to claim 4 or 5, characterized in that, The soluble silicate includes one or more of sodium silicate, potassium silicate, and lithium silicate; The first hydrolysis is performed at a temperature of 70-90℃, a pH value of 5.0-10.0, and a time of 4-6 hours.

7. The preparation method according to claim 4 or 5, characterized in that, The water-soluble salt corresponding to the oxide layer includes aluminum chloride, zirconium chloride, tin chloride, or zinc chloride; the second hydrolysis temperature is 70~90℃, and the time is 0.5h~1.5h; The oxide layer has a coating amount of 0.25 to 10% of the mass of the aluminum substrate.

8. The preparation method according to claim 4 or 5, characterized in that, The mass concentration of the ferric chloride aqueous solution is 5-40%; the temperature of the third hydrolysis is 70-90℃, the pH value is 2.5-4.5, the feeding rate is 0.1-0.5mL / min, and the time is 2-8.5h. The first alkaline solution and the second alkaline solution independently include aqueous solutions of alkali metal hydroxides, aqueous solutions of soluble silicates, aqueous solutions of alkali metal carbonates, aqueous solutions of alkali metal bicarbonates, ammonium carbonate, aqueous solutions of ammonium bicarbonate, or ammonia.

9. The preparation method according to claim 4 or 5, characterized in that, The mass concentration of the ferric nitrate aqueous solution is 5-45%; the temperature of the fourth hydrolysis is 70-90℃, the pH value is 2.5-4.5, the feeding rate is 0.3-0.7 mL / min, and the time is 1-3 h.

10. The preparation method according to claim 4 or 5, characterized in that, The calcination temperature is 250~450℃, and the time is 0.25~6h.

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