Long-acting anti-oxidation bismuth vanadate pigment for coating and preparation method of long-acting anti-oxidation bismuth vanadate pigment

Abstract

The invention belongs to the field of chemical engineering, and relates to a long-acting anti-oxidation bismuth vanadate pigment for a coating and a preparation method thereof, and the preparation method comprises the following steps: preparing a bismuth vanadate matrix by adopting a sol-gel method; and grafting a tea polyphenol derivative EGCG-COOH on the surface of the bismuth vanadate matrix. According to the long-acting anti-oxidation bismuth vanadate pigment for the coating and the preparation method of the long-acting anti-oxidation bismuth vanadate pigment, the bismuth vanadate matrix is prepared by adopting a sol-gel method, the particle size can be strictly controlled, and excellent optical performance is ensured; rich hydroxyl groups can be formed on the surface of bismuth vanadate prepared by a sol-gel method, so that ester bonds can be formed with carboxyl groups of EGCG-COOH, and the grafting efficiency is improved; eGCG-COOH is used as a bio-based anti-oxidation layer to improve the long-acting anti-oxidation performance of the bismuth vanadate pigment, the release rate of EGCG can be regulated and controlled through carboxyl modification, the anti-oxidation activity is prolonged, and the durability of the anti-oxidation layer is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering, specifically relating to a long-lasting antioxidant bismuth vanadate pigment for coatings and its preparation method. Background Technology

[0002] Bismuth vanadate (BiVO4), due to its unique bright yellow hue, non-toxic and environmentally friendly properties, and excellent chemical stability, has become an important environmentally friendly yellow pigment in modern industry, replacing traditional chromium- and lead-containing pigments. Currently, bismuth vanadate pigments are mainly used in the coatings industry, serving as key colorants for high-end automotive metallic paints and pearlescent paints. Bismuth vanadate pigments impart a vibrant lemon yellow color to coatings while meeting the automotive industry's stringent requirements for weather resistance. Bismuth vanadate can also be used for coloring engineering plastics, packaging materials, outdoor products (such as building materials), toys, and as a mineral pigment in cosmetic products such as eyeshadow and lipstick.

[0003] In many applications, bismuth vanadate pigments are exposed to light, oxygen, and chemical media for extended periods, and their antioxidant properties directly determine the product's lifespan and commercial value. Although bismuth vanadate possesses good initial color development, its antioxidant properties remain significantly limited. Among the four different crystal forms of bismuth vanadate, monoclinic bismuth vanadate exhibits the best heat resistance and a vibrant yellow color, making it the most suitable for use as a yellow pigment. However, monoclinic bismuth vanadate is a narrow bandgap semiconductor and a photocatalyst itself. Under ultraviolet light, it may generate reactive oxygen species (ROS). ROS damages the vanadium-oxygen bonds on the bismuth vanadate surface, causing lattice distortion and oxygen vacancy defects, resulting in pigment yellowing (increased b-value) and decreased gloss. ROS also oxidizes the CH bonds of paint-based resins, causing polymer chain breakage, leading to coating chalking and loss of gloss. Therefore, the performance limitations of bismuth vanadate pigments in highly oxidizing environments restrict their application in the high-end coatings market.

[0004] Existing technologies employ organosilicon coupling agents or traditional antioxidants such as phenolic compounds to improve the antioxidant properties of bismuth vanadate. However, organosilicon coupling agents are prone to decomposition at high temperatures and cannot provide long-lasting antioxidant protection. Phenolic compounds may migrate and precipitate, forming oily exudates on the pigment surface, damaging the interfacial bonding between the pigment and the matrix. Antioxidant migration also leads to a sharp drop in local concentration on the pigment particle surface, resulting in decreased antioxidant efficiency. Furthermore, phenolic antioxidants that migrate to the surface can undergo auto-oxidation under the influence of light and heat, generating toxic byproducts that are difficult to meet the biosafety requirements in fields such as food packaging and children's toys.

[0005] Therefore, there is still much room for improvement in the long-term antioxidant properties of current bismuth vanadate pigments used in coatings. Summary of the Invention

[0006] The purpose of this invention is to solve the problems existing in the prior art and to provide a long-lasting antioxidant bismuth vanadate pigment for coatings and its preparation method.

[0007] According to one aspect of the present invention, a method for preparing a long-lasting antioxidant bismuth vanadate pigment for coatings is provided, the method comprising the following steps: (1) Bismuth vanadate matrix was prepared by sol-gel method; (2) Grafting tea polyphenol derivative EGCG-COOH onto the surface of the bismuth vanadate matrix, wherein the molar ratio of tea polyphenol derivative EGCG-COOH to the bismuth vanadate matrix is ​​(1~3):100.

[0008] According to one embodiment of the present invention, the grafting in step (2) includes dispersing the bismuth vanadate matrix in deionized water, adding the tea polyphenol derivative EGCG-COOH, and reacting under a protective atmosphere and a predetermined temperature until the grafting is completed.

[0009] According to one embodiment of the present invention, the predetermined temperature is a single constant temperature selected from 60 to 90°C.

[0010] According to one embodiment of the present invention, the predetermined temperature is a plurality of temperatures that increase in a gradient, and the plurality of temperatures are selected from 60 to 90°C.

[0011] According to one embodiment of the present invention, in step (2), the criterion for determining whether grafting is complete is: The reaction time reaches 2-5 hours; or After testing, the product was found to contain the identifying characteristic of the tea polyphenol derivative EGCG-COOH.

[0012] According to one embodiment of the present invention, the protective atmosphere in step (2) is nitrogen or helium. After adding the tea polyphenol derivative EGCG-COOH, the liquid is stirred at a stirring speed of 250~450 r / min.

[0013] According to an embodiment of the present invention, the preparation of bismuth vanadate matrix by sol-gel method in step (1) includes mixing bismuth salt solution with vanadium salt solution, adding complexing agent, adjusting the pH value of the reaction system, reacting at a constant temperature, collecting the precipitate by centrifugation after the reaction is completed, washing and vacuum drying to obtain the bismuth vanadate matrix.

[0014] According to one embodiment of the present invention, in step (1), the molar ratio of vanadium to bismuth is 1:(1~1.1), the pH value is 5.5~6.5, and the amount of complexing agent is 1%~3% of the total molar number of bismuth and vanadium metal ions.

[0015] According to one embodiment of the present invention, the method further includes composite coating of the surface-grafted tea polyphenol derivative EGCG-COOH obtained in step (2). The composite coating adopts a stepwise coating method, first coating SiO2 and then coating ZrO2, controlling the Si / V molar ratio to be 3.5:1 and the Zr / Si molar ratio to be 1:(2.5~3.5). After coating ZrO2, it is calcined at 550~700℃ for 1~4h.

[0016] According to another aspect of the present invention, a long-lasting antioxidant bismuth vanadate pigment for coatings is provided, the bismuth vanadate pigment being prepared by the method described in any of the above embodiments.

[0017] The present invention relates to a long-lasting antioxidant bismuth vanadate pigment for coatings and its preparation method. First, a bismuth vanadate matrix is ​​prepared using a sol-gel method, which allows for strict control of particle size and ensures excellent optical properties. The bismuth vanadate prepared by the sol-gel method forms abundant hydroxyl groups on its surface, which facilitates the formation of ester bonds with the carboxyl groups of EGCG-COOH, improving grafting efficiency. EGCG-COOH is used as a bio-based antioxidant layer to improve the long-lasting antioxidant properties of the bismuth vanadate pigment, significantly enhancing the durability of the antioxidant layer. Carboxyl modification can also regulate the release rate of EGCG, prolonging antioxidant activity. Attached Figure Description

[0018] Figure 1 A schematic flowchart of a method for preparing a long-lasting antioxidant bismuth vanadate pigment for coatings according to an embodiment of the present invention is shown. Figure 2 A schematic flowchart of a method for preparing a long-lasting antioxidant bismuth vanadate pigment for coatings, including a coating treatment, according to another embodiment of the present invention is shown. Detailed Implementation

[0019] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0020] According to one aspect of the present invention, a method for preparing a long-lasting antioxidant bismuth vanadate pigment for coatings is provided. For example... Figure 1 As shown, the method mainly includes the following steps: Step (1): Bismuth vanadate matrix was prepared by sol-gel method; Step (2): Graft tea polyphenol derivative EGCG-COOH onto the surface of bismuth vanadate matrix, wherein the molar ratio of tea polyphenol derivative EGCG-COOH to bismuth vanadate matrix is ​​(1~3):100.

[0021] In the preparation method of the long-lasting antioxidant bismuth vanadate pigment for coatings of the present invention, the bismuth vanadate matrix is ​​first prepared by sol-gel method, and the product is synthesized at low temperature to avoid surface passivation caused by high temperature impurities and high temperature sintering. The resulting product has small particle size, large specific surface area, and high material uniformity. The particle size can be strictly controlled within the range of 150~200nm to ensure excellent optical performance. The bismuth vanadate surface prepared by sol-gel method can form abundant hydroxyl groups, which is conducive to the formation of ester bonds with the carboxyl groups of EGCG-COOH. The obtained nanostructure can also increase grafting sites and improve grafting efficiency.

[0022] The long-lasting antioxidant properties of bismuth vanadate pigments are improved by grafting the tea polyphenol derivative EGCG-COOH onto the surface of a bismuth vanadate matrix as a bio-based antioxidant layer. EGCG-COOH possesses multiple phenolic hydroxyl groups, which are strong reducing agents capable of effectively capturing and neutralizing reactive oxygen free radicals in the environment, thus blocking chain oxidation reactions. EGCG-COOH achieves more stable surface grafting through carboxyl groups, significantly enhancing the durability of the antioxidant layer. Carboxyl modification can also regulate the release rate of EGCG, prolonging antioxidant activity. Furthermore, EGCG-COOH is compatible with a wider range of material surfaces and can be further functionalized, such as by grafting antibacterial groups, expanding its applications in medical coatings, food packaging, and other fields. The modified bismuth vanadate pigments also exhibit excellent biocompatibility, meeting the biosafety requirements of food packaging, children's toys, and other applications.

[0023] In embodiments of the present invention, the molar ratio of tea polyphenol derivative EGCG-COOH to bismuth vanadate matrix is ​​(1~3):100. When the amount of tea polyphenol derivative EGCG-COOH is too low, it only partially covers the active sites on the surface of bismuth vanadate, and the remaining active sites can still react with oxygen, resulting in unsatisfactory antioxidant properties of the pigment. Conversely, when the amount of tea polyphenol derivative EGCG-COOH is too high, it introduces a pale yellow hue, reducing the pigment's brightness.

[0024] In one embodiment of the present invention, the preparation of bismuth vanadate matrix by the sol-gel method may include mixing a bismuth salt solution with a vanadium salt solution, adding a complexing agent, adjusting the pH of the reaction system, reacting at a constant temperature, collecting the precipitate by centrifugation after the reaction is complete, washing, and vacuum drying to obtain the bismuth vanadate matrix. For example, the bismuth salt solution may be a solution of Bi(NO3)3·5H2O dissolved in 15%~20% nitric acid, with a Bi ion concentration of 0.5~1.2 mol / L. The vanadium salt solution may be a solution of NH4VO3 dissolved in 2.5~3.5 mol / L NaOH solution, with a vanadium ion concentration of 0.5~1.2 mol / L. During the mixing of raw materials, the H2O concentration of nitric acid in the reaction system is controlled. + OH with sodium hydroxide - The molar numbers are consistent, and the molar ratio of vanadium to bismuth is 1:(1~1.1). It is understood that the specific selection of the bismuth salt solution and vanadium salt solution described above is merely an illustrative example of the embodiments of this invention. Those skilled in the art, based on the teachings of this invention, can understand and select various other suitable soluble bismuth and vanadium salt raw materials, as well as corresponding solvents or dissolving media, as long as they can provide a sufficient concentration of bismuth and vanadium ion sources and ultimately successfully synthesize bismuth vanadate via the sol-gel method. That is, as long as the requirements of the sol-gel process for precursor solubility, reactivity, and final product formation are met, they all fall within the scope of this invention. Citric acid can be used as the complexing agent, and the amount of complexing agent is 1%~3% of the total molar number of bismuth and vanadium metal ions to ensure product purity. The pH value of the reaction system is controlled at 5.5~6.5 to improve product yield and product color. The reaction pH value can be a constant pH value or a gradient increasing pH value. For example, nitric acid, NaOH, urea, ammonia, etc., can be used to control the reaction pH value. The reaction temperature is at room temperature (e.g., 10~30℃), and the reaction time is 30~70 min. After the reaction is complete, the precipitate is collected by centrifugation, washed with deionized water until neutral, and dried under vacuum at 60℃ to obtain the bismuth vanadate matrix.

[0025] In one embodiment of the present invention, grafting the tea polyphenol derivative EGCG-COOH onto the surface of a bismuth vanadate matrix may include dispersing the bismuth vanadate matrix in deionized water, adding the tea polyphenol derivative EGCG-COOH, and reacting under a protective atmosphere and at a predetermined temperature until the grafting is complete.

[0026] In one embodiment of the present invention, the grafting operation temperature is a single constant temperature selected from 60~90°C. Setting the grafting temperature to 60~90°C ensures efficient grafting while maintaining the bioactivity of EGCG-COOH and the structural stability of bismuth vanadate. Too low a temperature results in a low grafting rate and low production efficiency. Too high a temperature, because EGCG-COOH is more easily oxidized than ordinary polyphenols, easily triggers side reactions, generating other byproducts, leading to a decrease in free radical scavenging ability. Therefore, the present invention sets the grafting temperature to 60~90°C. This embodiment uses isothermal grafting, which simplifies the production process.

[0027] In one embodiment of the invention, the grafting operation is performed at multiple progressively increasing temperatures, selected from 60 to 90°C. For example, the grafting operation can be controlled by reacting at 60°C for 1-2 hours, at 80°C for 1-2 hours, and at 90°C for 1 hour. The low-temperature stage of around 60°C promotes the penetration of EGCG-COOH molecules into the pores of the BiVO4 surface, forming a physical adsorption layer, while suppressing side reactions. The high-temperature stages of 80°C and 90°C activate EGCG-COOH, rapidly increasing the grafting density and ensuring sufficient grafting.

[0028] In one embodiment of the present invention, the criterion for determining the completion of grafting is: the reaction time reaches 2-5 hours; or, the product is detected, and based on the detection results, it can be determined that the product contains the identifying characteristics of the tea polyphenol derivative EGCG-COOH. For example, the product can be detected by FT-IR at 1720 cm⁻¹. -1 The presence of ester bond characteristic peaks can be used to determine whether grafting is complete.

[0029] In one embodiment of the present invention, the protective atmosphere for the grafting reaction is nitrogen or helium. Since the phenolic hydroxyl groups of EGCG-COOH are readily oxidized at high temperatures, and the variable-valence metal vanadium in bismuth vanadate accelerates this oxidation process in the presence of oxygen, the present invention uses nitrogen or helium to effectively isolate oxygen.

[0030] In one embodiment of the present invention, after adding the tea polyphenol derivative EGCG-COOH to the grafting reaction, the liquid is stirred at a speed of 250-450 r / min. Stirring can promote the contact between EGCG-COOH molecules and BiVO4 surface active sites, and can also prevent grafting dead zones caused by particle agglomeration, so as to ensure that the grafting is fully and uniform.

[0031] In order to further improve the antioxidant properties and chemical stability of bismuth vanadate pigments while maintaining their hiding power and brightness, in some embodiments of the present invention, the grafted bismuth vanadate pigments are subjected to composite coating. Figure 2A schematic flow chart of a method for preparing a long-lasting antioxidant bismuth vanadate pigment for coatings, including a coating treatment, according to another embodiment of the present invention is shown. The method generally includes the following steps: Step (1): Bismuth vanadate matrix was prepared by sol-gel method; Step (2): Grafting the tea polyphenol derivative EGCG-COOH onto the surface of a bismuth vanadate matrix; Step (3): The surface of the bismuth vanadate pigment obtained in step (2) is first coated with a layer of SiO2, then coated with a layer of ZrO2, and then calcined at 550~700℃ for 1~4h.

[0032] Steps (1) and (2) in this embodiment can be compared with those in the reference. Figure 1 The steps described are the same or similar, and for the sake of brevity, they will not be explained here again.

[0033] In an embodiment of the present invention, the composite coating in step (3) may include the following operations: dispersing the bismuth vanadate pigment obtained in step (2) in an ethanol-water mixed solvent, first adding tetraethyl orthosilicate (TEOS), controlling the Si / V molar ratio to be 3.5:1, reacting for 1~3h, then adding zirconium oxychloride (ZrOCl2), controlling the Zr / Si molar ratio to be 1:2.5~3.5, adjusting the pH to 8.0~9.0, reacting at room temperature for 4~8h, calcining at 550~700℃ for 1~4h, with a heating rate of 3~7℃ / min, to obtain the final product.

[0034] In embodiments of the present invention, the total thickness of the composite coating layer is controlled to be 10-15 nm, which improves the chemical stability of the pigment without affecting its optical performance.

[0035] The inorganic SiO2 / ZrO2 coating provides a dense physical barrier. The SiO2 coating reduces oxygen and moisture permeability, inhibiting the swelling of the EGCG-COOH hydrophilic layer. The dense ZrO2 lattice not only effectively blocks oxygen diffusion pathways but also forms a more robust coating. Furthermore, the condensation of silanol groups on the SiO2 surface with the carboxyl groups of EGCG-COOH forms Si-OC bonds, inhibiting the shedding of phenolic hydroxyl groups from the bio-based substrate under humid and hot conditions. In addition, the composite coating improves the pigment's acid and alkali resistance and weather resistance, significantly enhancing its durability.

[0036] Another aspect of the present invention provides a long-lasting antioxidant bismuth vanadate pigment for coatings, which is prepared by the method described in any of the above embodiments.

[0037] After testing, the hiding power of the BiVO4 pigment after composite coating is ≥ 95% (tested according to ISO 787-24 standard), the brightness (L value) is ≥ 93.4 (tested according to CIE Lab standard), it has excellent acid resistance, ΔE < 0.8 after being soaked in 5wt% HCl for 72h, excellent antioxidant property, and after 200h of UV aging test, the activity retention rate is ≥ 92%.

[0038] The method of the present invention will be further elaborated and explained below in conjunction with the embodiments.

[0039] The pigments obtained in the following embodiments and comparative examples are tested for product performance by the following methods: The particle size distribution is tested by DLS.

[0040] The hiding power is tested according to ISO 787-24 standard.

[0041] The brightness L value is tested according to CIE Lab standard.

[0042] The acid resistance test is to soak the pigment in 5wt% HCl solution for 72h, measure the color difference ΔE, and ΔE is calculated by the following formula:

[0043] Among them, ΔL, Δa and Δb respectively represent the difference in L value, a value and b value before and after soaking the bismuth vanadate pigment.

[0044] The alkali resistance test is to soak the pigment in 10wt% NaOH solution for 168h and measure the color difference ΔE.

[0045] The antioxidant property test, weather resistance test, thermal stability test, salt spray resistance test, abrasion resistance test and accelerated aging test all use the color difference ΔE as the main evaluation index to ensure the test accuracy. All tests need to measure ΔE with a spectrophotometer under a standard light source (D65) to ensure data comparability. Among them: The antioxidant property test adopts the following treatment method: place the sample in a constant temperature oxidation oven (100 °C, air atmosphere), take samples regularly, analyze the chemical structure change by XRD or FTIR, and calculate the activity retention rate (%) (compared with the initial optical performance); The thermal stability test adopts the following treatment method: place the sample in a muffle furnace and heat it step by step at an interval of 50 °C (temperature range is 100~800 °C, and keep the temperature for 1h at each temperature point), measure ΔE after the sample cools, record the obvious color change temperature (such as the critical point when ΔE ≥ 3.0), and use this temperature as the temperature for the thermal stability test; The salt spray resistance test adopts the following treatment method: use 5wt% NaCl salt spray, treat it at 35 °C for 96h, clean and dry it, and then test ΔE, and ΔE ≤ 1.5 is qualified; The abrasion resistance test was conducted using the following method: a Taber abrasion tester (CS-10 wheel, 500g load, 100 rpm) was used. The mass difference before and after abrasion was measured, and the weight loss rate (mg / cm²) was calculated. The weight loss was ≤5mg / cm². Temperature and humidity control were required during the test (23°C). + 2℃, 50 + 5%RH); The accelerated aging test adopts the following treatment method: using a QUV accelerated aging instrument (UVA-340 lamp, 60℃ / 4h UV and 50℃ / 4h condensation), the ΔE is tested after 1000h, and ΔE≤2.5 meets the industrial standard.

[0046] The thickness of the coating layer was measured using TEM.

[0047] Example 1 Dissolve 0.1 mol of Bi(NO3)3·5H2O in 200 mL of 15% nitric acid solution. Dissolve 0.1 mol of NH4VO3 in 200 mL of 2.5 mol / L NaOH solution. After mixing the two solutions, add 1% citric acid (relative to the total molar amount of bismuth and vanadium ions) as a complexing agent, and adjust the pH of the reaction system to 5.5 using urea. + The mixture was stirred at 0.1°C for 70 min. The precipitate was collected by centrifugation, washed with deionized water until neutral, and dried under vacuum at 60°C to obtain the bismuth vanadate matrix.

[0048] Bismuth vanadate matrix was dispersed in deionized water, and EGCG-COOH at 1% molar ratio relative to bismuth vanadate was added. The reaction was carried out at 60°C for 5 hours under nitrogen protection. The reaction was confirmed by FT-IR detection at 1720 cm⁻¹. -1 The presence of a characteristic ester bond peak indicates successful grafting. The precipitate was collected by centrifugation and washed with ethanol to obtain the bio-based modified product.

[0049] Product performance characterization: Particle size distribution: 155 + 15nm; Hideout: 95.5%; Luminance L-value: 93.5; Antioxidant properties: Activity retention rate 91.5%.

[0050] Example 2 0.184 mol of Bi(NO3)3·5H2O was dissolved in 200 mL of 18% nitric acid solution. 0.18 mol of NH4VO3 was dissolved in 200 mL of 3 mol / L NaOH solution. After mixing the two solutions, 2% (relative to the total molar amount of bismuth and vanadium ions) of citric acid was added as a complexing agent. The pH of the reaction system was adjusted to 5.8 using urea. +The mixture was stirred at 20°C for 50 min. The precipitate was collected by centrifugation, washed with deionized water until neutral, and dried under vacuum at 60°C to obtain the bismuth vanadate matrix.

[0051] Bismuth vanadate matrix was dispersed in deionized water, and EGCG-COOH at 2% molar ratio relative to bismuth vanadate was added. Under nitrogen protection, the grafting operation was controlled by reacting at 60℃ for 1 h, 80℃ for 2 h, and 90℃ for 1 h, with a total reaction time of 4 h. The precipitate was collected by centrifugation and washed with ethanol to obtain the bio-based modified product.

[0052] Product performance characterization: Particle size distribution: 165 + 15nm; Hideout: 97.5%; Luminance (L-value): 93.9; Antioxidant properties: Activity retention 96.3%; Thermal stability: ΔE=0.75. FT-IR display at 1720cm. -1 The peak intensity was increased by 42% compared to Example 1.

[0053] Example 3 0.24 mol of Bi(NO3)3·5H2O was dissolved in 200 mL of 20% nitric acid solution. 0.22 mol of NH4VO3 was dissolved in 200 mL of 3.5 mol / L NaOH solution. After mixing the two solutions, 3% (relative to the total molar amount of bismuth and vanadium ions) of citric acid was added as a complexing agent. The pH of the reaction system was adjusted using ammonia water to create a gradient, starting at 5.5 and rising to 6.5 after 30 minutes. + The mixture was stirred at 30°C for 35 min. The precipitate was collected by centrifugation, washed with deionized water until neutral, and dried under vacuum at 60°C to obtain the bismuth vanadate matrix.

[0054] Bismuth vanadate matrix was dispersed in deionized water, and EGCG-COOH at 3% molar ratio relative to bismuth vanadate was added. The reaction was carried out at 85°C for 2.5 h under nitrogen protection. The reaction was confirmed by FT-IR detection at 1720 cm⁻¹. -1 The presence of a characteristic ester bond peak indicates successful grafting. The precipitate was collected by centrifugation and washed with ethanol to obtain the bio-based modified product.

[0055] Product performance characterization: Particle size distribution: 180 + 15nm; Hideout: 96.2%; Luminance L-value: 93.6; Antioxidant properties: Activity retention rate 94.1%.

[0056] Example 4 This embodiment describes the composite coating of the bismuth vanadate pigment obtained in Example 2.

[0057] The bismuth vanadate pigment obtained in Example 2 was dispersed in an ethanol-water mixed solvent. Tetraethyl orthosilicate (TEOS) was added first, and the Si / V molar ratio was controlled at 3.5:1. After reacting for 1 hour, zirconium oxychloride (ZrOCl2) was added, and the Zr / Si molar ratio was controlled at 1:2.5. The pH was adjusted to 8.0, and the reaction was carried out at room temperature for 4 hours. Then, it was calcined at 550°C for 4 hours with a heating rate of 4°C / min to obtain the final product.

[0058] Product performance characterization: Coating thickness: inner layer 7nm, outer layer 5nm; Opacity: 96.8%; Brightness L value: 93.7; Antioxidant properties: activity retention rate 96.8%; Acid resistance: ΔE=0.62; Alkali resistance: ΔE=0.85; Salt spray resistance: ΔE=0.93; Abrasion resistance: weight loss only 0.95mg; Accelerated aging test: ΔE=1.32.

[0059] Example 5 This embodiment describes the composite coating of the bismuth vanadate pigment obtained in Example 2.

[0060] The bismuth vanadate pigment obtained in Example 2 was dispersed in an ethanol-water mixed solvent. Tetraethyl orthosilicate (TEOS) was added first, and the Si / V molar ratio was controlled at 3.5:1. After reacting for 2 hours, zirconium oxychloride (ZrOCl2) was added, and the Zr / Si molar ratio was controlled at 1:3. The pH was adjusted to 8.5, and the reaction was carried out at room temperature for 6 hours. The mixture was then calcined at 630°C for 2 hours with a heating rate of 5°C / min to obtain the final product.

[0061] Product performance characterization: Coating thickness: inner layer 7nm, outer layer 6nm; Opacity: 96.3%; Brightness L value: 93.6; Antioxidant properties: activity retention rate 96.9%; Acid resistance: ΔE=0.58; Alkali resistance: ΔE=0.78; Salt spray resistance: ΔE=0.91; Abrasion resistance: weight loss only 0.87mg; Accelerated aging test: ΔE=1.30.

[0062] Example 6 This embodiment describes the composite coating of the bismuth vanadate pigment obtained in Example 2.

[0063] The bismuth vanadate pigment obtained in Example 2 was dispersed in an ethanol-water mixed solvent. Tetraethyl orthosilicate (TEOS) was added first, and the Si / V molar ratio was controlled at 3.5:1. After reacting for 3 hours, zirconium oxychloride (ZrOCl2) was added, and the Zr / Si molar ratio was controlled at 1:3.5. The pH was adjusted to 9.0, and the reaction was carried out at room temperature for 8 hours. The mixture was then calcined at 700°C for 1 hour with a heating rate of 7°C / min to obtain the final product.

[0064] Product performance characterization: Coating thickness: inner layer 8nm, outer layer 7nm; Opacity: 96.1%; Brightness L value: 93.5; Antioxidant properties: activity retention rate 97.2%; Acid resistance: ΔE=0.53; Alkali resistance: ΔE=0.68; Salt spray resistance: ΔE=0.90; Abrasion resistance: weight loss only 0.75mg; Accelerated aging test: ΔE=1.28.

[0065] Comparative Example 1 Comparative Example 1 uses the commercial L1100 product, which is a benchmark product in the industry. Its coverage is 95%; luminance L value is 91.8; oxidation resistance is 78%; acid resistance is ΔE=2.1; alkali resistance is ΔE=2.8.

[0066] The comparison shows that the BiVO4 pigment prepared by the method of the present invention has significantly higher long-lasting antioxidant properties compared with commercial products, and its hiding power and brightness are not reduced.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Any modifications or equivalent substitutions made to the present invention without departing from the spirit and scope thereof should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a long-lasting antioxidant bismuth vanadate pigment for coatings, characterized in that, Includes the following steps: (1) Bismuth vanadate matrix was prepared by sol-gel method; (2) Grafting tea polyphenol derivative EGCG-COOH onto the surface of the bismuth vanadate matrix, wherein the molar ratio of tea polyphenol derivative EGCG-COOH to the bismuth vanadate matrix is ​​(1~3):

100.

2. The method for preparing long-lasting antioxidant bismuth vanadate pigment for coatings according to claim 1, characterized in that, The grafting in step (2) involves dispersing the bismuth vanadate matrix in deionized water, adding the tea polyphenol derivative EGCG-COOH, and reacting under a protective atmosphere and at a predetermined temperature until the grafting is complete.

3. The method for preparing long-lasting antioxidant bismuth vanadate pigment for coatings according to claim 2, characterized in that, The predetermined temperature is a single constant temperature selected from 60 to 90°C.

4. The method for preparing long-lasting antioxidant bismuth vanadate pigment for coatings according to claim 2, characterized in that, The predetermined temperature is a plurality of temperatures that increase in a gradient, and the plurality of temperatures are selected from 60 to 90°C.

5. The method for preparing the long-lasting antioxidant bismuth vanadate pigment for coatings according to claim 2, characterized in that, In step (2), the criteria for determining whether grafting is complete are as follows: The reaction time reaches 2-5 hours; or After testing, the product was found to contain the identifying characteristic of the tea polyphenol derivative EGCG-COOH.

6. The method for preparing long-lasting antioxidant bismuth vanadate pigment for coatings according to claim 2, characterized in that, The protective atmosphere in step (2) is nitrogen or helium. After adding the tea polyphenol derivative EGCG-COOH, the liquid is stirred at a speed of 250~450 r / min.

7. The method for preparing long-lasting antioxidant bismuth vanadate pigment for coatings according to claim 1, characterized in that, The preparation of bismuth vanadate matrix in step (1) using the sol-gel method includes mixing bismuth salt solution with vanadium salt solution, adding a complexing agent, adjusting the pH value of the reaction system, reacting at a constant temperature, collecting the precipitate by centrifugation after the reaction is completed, washing and vacuum drying to obtain the bismuth vanadate matrix.

8. The method for preparing a long-lasting antioxidant bismuth vanadate pigment for coatings according to claim 7, characterized in that, In step (1), the molar ratio of vanadium to bismuth is 1:(1~1.1), the pH value is 5.5~6.5, and the amount of complexing agent is 1%~3% of the total molar number of bismuth and vanadium metal ions.

9. The method for preparing a long-lasting antioxidant bismuth vanadate pigment for coatings according to claim 1, characterized in that, The method further includes composite coating of the surface-grafted tea polyphenol derivative EGCG-COOH obtained in step (2). The composite coating adopts a stepwise coating method, first coating SiO2 and then coating ZrO2, controlling the Si / V molar ratio to be 3.5:1 and the Zr / Si molar ratio to be 1:(2.5~3.5). After coating ZrO2, it is calcined at 550~700℃ for 1~4h.

10. A long-lasting antioxidant bismuth vanadate pigment for coatings, characterized in that, The bismuth vanadate pigment is prepared by the method according to any one of claims 1-9.

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