Aqueous polyester dispersions and their preparation and use

Abstract

The present application relates to the technical field of paint, in particular to a kind of water-based polyester dispersion and its preparation and application.It includes the following steps: preparation catalyst precursor microspheres;Catalyst precursor microspheres are prepared into natural heterogeneous acid catalyst;Preparation water-based polyester dispersion.The present application uses natural, low-cost waste rice husk and mineral bentonite as raw material, constructs a composite carrier prototype with high specific surface area and stable porous structure, the principle lies in the ingenious use of the characteristics of two kinds of natural materials and composite, powder material is shaped into micron-sized sphere which is easy to handle, and the internal interwoven porous structure is maximally retained, which provides huge surface area and stable support for the subsequent step of loading catalytic active site, thereby affecting the final coating performance of water-based paint, especially improving water resistance, hardness and storage stability.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to an aqueous polyester dispersion and its preparation and application. Background Technology

[0002] Waterborne polyester dispersions are resin systems formed by dispersing polyester resin in an aqueous phase to create a stable system. They combine the excellent mechanical properties, chemical resistance, and decorative properties of traditional polyesters while significantly reducing volatile organic compound emissions. In practical applications, waterborne polyester coatings are widely used in metal decoration, industrial protection, plastic coatings, and wood coatings. However, existing products still face challenges in balancing high performance and environmental safety: on the one hand, it is necessary to improve the hardness, water resistance, and storage stability of the coating film; on the other hand, it is necessary to ensure that the product is non-toxic, free of heavy metal residues, and that the production process is green and low-carbon.

[0003] In the production of waterborne polyester, homogeneous catalysts such as monobutyltin oxide and p-toluenesulfonic acid are commonly used. Although these catalysts have high activity, they have problems such as difficulty in separating them from the product, causing the resin to darken in color, and residues affecting the final coating performance. Heterogeneous catalysts can solve the separation problem, but traditional heterogeneous catalysts often have limitations such as low specific surface area, uneven distribution of acidic sites, and high preparation cost.

[0004] Therefore, developing a novel environmentally friendly preparation process that can ensure the high performance of waterborne polyester dispersions while fundamentally solving the problems of catalyst residue and toxicity has significant theoretical and practical value. By designing novel heterogeneous catalysts and optimizing synthetic routes, it is expected that waterborne polyester products with both excellent comprehensive performance and environmentally friendly characteristics can be obtained to meet the needs of the high-end coatings market. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide an aqueous polyester dispersion and its preparation and application.

[0006] An aqueous polyester dispersion comprising the following raw materials: 30-35 parts by weight of neopentyl glycol, 15-18 parts by weight of tricyclodecanediethanol, 5-8 parts by weight of trimethylolpropane, 40-45 parts by weight of furanyl dicarboxylic acid, 10-12 parts by weight of adipic acid, 0.1-0.3 parts by weight of natural multiphase acid catalyst, 8-10 parts by weight of silane coupling agent, cosolvent and deionized water.

[0007] A method for preparing an aqueous polyester dispersion includes the following steps: S1: Preparation of catalyst precursor microspheres The rice husks are washed with deionized water to remove mud, sand and soluble impurities, dried, and then calcined in a muffle furnace at 600-640℃ for 2-3 hours. After natural cooling, they are ground through a 200-mesh sieve to obtain rice husk ash. Bentonite was ground through a 200-mesh sieve to obtain bentonite powder. Rice husk ash and bentonite powder were mixed at a mass ratio of (3-4):1. Deionized water with a mass of 5-6 times that of rice husk ash and bentonite powder was added. The mixture was stirred at a speed of 50-70 r / min for 20-25 min to obtain a slurry. Vegetable oil cooled to 5-10℃ was added dropwise to the slurry at a rate of 1 mL / s. The amount of vegetable oil added was 1-1.5 times the volume of the slurry. The mixture was stirred for 8-10 min, and the slurry was stirred to form microspheres. After drying, catalyst precursor microspheres were obtained.

[0008] S2: Catalyst precursor microspheres are prepared into natural heterogeneous acid catalysts. The catalyst precursor microspheres were immersed in a 1M citric acid solution for 4-5 hours, filtered and separated, and then dried at 100-110℃ for 12-13 hours. The dried catalyst precursor microspheres were placed in a muffle furnace and calcined at 450-480℃ for 3-4 hours at a heating rate of 5℃ / min. After calcination, the microspheres were cooled to room temperature (22-24℃) with the furnace to obtain a natural heterogeneous acid catalyst.

[0009] S3: Preparation of aqueous polyester dispersion Add 30-35 parts by mass of neopentyl glycol, 15-18 parts by mass of tricyclodecanediethanol, 5-8 parts by mass of trimethylolpropane, 40-45 parts by mass of furanyl dicarboxylic acid, 10-12 parts by mass of adipic acid, and 0.1-0.3 parts by mass of natural heterogeneous acid catalyst to a reaction vessel equipped with a fractionating column, condenser, stirrer, thermometer, and nitrogen inlet. Slowly raise the temperature to 180-190℃ and hold for 2-3 hours. Then gradually raise the temperature to 220-230℃ and carry out the esterification reaction at this temperature. Terminate the reaction when the acid value drops to 5-10 mg KOH / g to obtain the condensate. Cool the reaction system containing the condensation polymer to 110-120℃, add 8-10 parts by weight of silane coupling agent dropwise while stirring at 200-300 r / min, keep the temperature at 110-120℃ for 2-3 hours, add 10-15 parts by weight of co-solvent and stir to uniformly cool the system to 80-90℃, slowly add 60-70 parts by weight of deionized water to the reaction system, disperse at high speed at 1000-1100 r / min for 30-40 minutes, add more deionized water to make the volume content of polyester resin 40-45%, filter to remove large molecular particles, and obtain an aqueous polyester dispersion.

[0010] Furthermore, the vegetable oil is any one of soybean oil, peanut oil, or sesame oil.

[0011] Furthermore, the cosolvent is dipropylene glycol methyl ether.

[0012] Furthermore, the silane coupling agent is specifically 3-glycidyl etheroxypropyltrimethoxysilane.

[0013] Furthermore, the filter membrane used during filtration has a pore size of 25 μm.

[0014] An application of an aqueous polyester dispersion, wherein the aqueous polyester dispersion is used in the preparation of aqueous coatings for metal substrates.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: 1. This invention uses natural, low-cost waste rice husks and mineral bentonite as raw materials to construct a prototype composite carrier with high specific surface area and a stable porous structure. The principle lies in the ingenious utilization and composite composition of the properties of these two natural materials. First, after calcining rice husks at 600-640℃, their organic matter is removed, leaving a porous framework structure mainly composed of amorphous silica. This bio-derived silica itself has a high specific surface area and abundant pores. Second, bentonite is a natural nano-clay, whose main component is montmorillonite, possessing excellent swelling properties, adsorption capacity, and a layered structure. Mixing the two materials in a specific ratio and adding water allows the bentonite layers to effectively penetrate and adhere to the porous framework of the rice husk ash, forming a more complex and stable "framework-layer" composite structure. Subsequently, the addition of low-temperature vegetable oil is a crucial step: under low-speed stirring, the oil phase and water phase form microspheres under interfacial tension, while the solid particles in the water phase are encapsulated and fixed at the oil-water interface, ultimately forming solid microspheres as the water evaporates. This process not only shapes the powder material into easily handled micron-sized spheres, but more importantly, it preserves the interwoven porous structure within to the maximum extent possible. This provides a huge surface area and solid support for the loading of catalytic active sites in subsequent steps, thereby affecting the final coating performance of waterborne coatings, especially improving water resistance, hardness, and storage stability.

[0016] 2. This invention modifies the precursor with environmentally friendly citric acid, successfully immobilizing a large number of stable and potent Brønsted acid active sites on a composite support, thus creating a highly efficient, easily separable, and heavy metal-free green catalyst. The principle is a typical "impregnation-calcination" immobilization process. First, the high specific surface area precursor microspheres obtained in S1 are impregnated in a citric acid solution. Citric acid molecules enter and adhere to the inner and outer pores and surface of the microspheres in large quantities through physical adsorption and possible hydrogen bonding. Subsequently, most of the physically adsorbed water is removed during drying at 100-110℃. The most crucial step is calcination at 450-480℃: at this temperature, citric acid undergoes thermal decomposition and carbonization, but its carboxylic acid groups react strongly with silanol groups on the support surface. Through esterification, dehydration, and other reactions, the acidic sites are firmly "anchored" to the surface of the silica and bentonite supports in the form of covalent bonds, forming a stable and non-leaking carbonaceous sulfonic acid-like structure. These immobilized acidic groups can act as proton donors in the subsequent polyester synthesis esterification reaction, efficiently catalyzing the polycondensation reaction between polyols and polyacids. Because the catalyst is prepared in microsphere form, it can be completely separated from the liquid polyester product after the reaction by simple sedimentation or filtration. This combines the high efficiency of homogeneous acid catalysts with the easy separation advantages of heterogeneous catalysts, completely avoiding the toxicity and residue problems that may arise from traditional heavy metal catalysts. This fundamentally ensures the environmental safety and high-quality appearance of the coating products, while also reducing post-processing costs. Attached Figure Description

[0017] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate embodiments of the present disclosure and, together with the specification, further serve to explain the principles of the present disclosure and enable those skilled in the art to implement and use the present disclosure.

[0018] Figure 1 This is a flowchart illustrating a method for preparing an aqueous polyester dispersion used in an embodiment of the present invention. Detailed Implementation

[0019] The aqueous polyester dispersion and its preparation and application provided by the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, to make the embodiments more detailed, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0020] Example 1:

[0021] A method for preparing an aqueous polyester dispersion, such as Figure 1 As shown, it includes the following steps: S1: Preparation of catalyst precursor microspheres After initial treatment, the rice husks are first washed multiple times with sufficient deionized water, thoroughly agitated to remove impurities such as mud, dust, and soluble inorganic salts adhering to the surface, ensuring the purity of the raw material and preventing the introduction of impurities during subsequent high-temperature processing. The washed rice husks are then placed in an oven and dried at 105℃ to constant weight to completely remove moisture. Subsequently, the dried rice husks are evenly spread in a crucible and transferred to a muffle furnace for high-temperature calcination: the temperature is slowly increased to 600℃ using a programmed temperature control method and held for 2 hours, allowing the organic matter within the rice husks, such as cellulose and hemilignin, to fully decompose and carbonize, ultimately forming white or grayish-white rice husk ash with porous silica as the main component. After calcination, it is allowed to cool naturally to room temperature to avoid rapid cooling that could cause the silica structure to become brittle. Finally, it is finely ground using a mortar and pestle or ball mill and passed through a 200-mesh sieve to obtain rice husk ash powder with uniform particle size, high specific surface area, and high activity, laying the foundation for the subsequent preparation of catalyst supports. Bentonite was ground through a 200-mesh sieve to obtain bentonite powder. Rice husk ash and bentonite powder were mixed in a mass ratio of 3:1. Deionized water with a mass of 5 times that of rice husk ash and bentonite powder was added. The mixture was stirred at 50 r / min for 20 min to obtain a slurry. Soybean oil cooled to 5°C was added dropwise to the slurry at a rate of 1 mL / s. The amount of vegetable oil added was 1 times the volume of the slurry. The mixture was stirred for 8 min, and the slurry was stirred to form microspheres. After drying, catalyst precursor microspheres were obtained.

[0022] S2: Catalyst precursor microspheres are prepared into natural heterogeneous acid catalysts. The obtained catalyst precursor microspheres were completely immersed in a 1 mol / L citric acid solution, ensuring the solution fully penetrated into the pores of the microspheres. Immersion was continued for 4 hours to allow citric acid molecules to be fully adsorbed onto the carrier surface and within the pores. After filtration, excess impregnation solution was removed, and the solid material was collected. The filtered microspheres were placed in a drying oven and heat-treated at 100℃ for 12 hours to completely remove physically adsorbed water and form a preliminarily stable supported structure. Subsequently, the dried microspheres were transferred to a muffle furnace for programmed temperature-controlled calcination: slowly heated to 450℃ at a heating rate of 5℃ / min and held at this temperature for 3 hours. During this process, citric acid underwent pyrolysis and carbonization. Its carboxyl and hydroxyl groups were not completely decomposed but instead anchored to the SiO2 substrate surface of rice husk ash through esterification and condensation, forming a composite layer of amorphous carbon material rich in carboxyl and hydroxyl groups. The carbon layer structure is stable and can provide abundant Brønsted acid active sites, thus achieving efficient solid acid catalysis. After calcination, the cooling method is controlled by slowly cooling the furnace to room temperature of 22°C to avoid the support structure from cracking or loss of active sites due to excessive thermal stress, and finally a natural heterogeneous acid catalyst with high acid content and high stability is obtained.

[0023] S3: Preparation of aqueous polyester dispersion 30g neopentyl glycol, 15g tricyclodecanediethanol, 5g trimethylolpropane, 40g furanyl dicarboxylic acid, 10g adipic acid and 0.1g natural multiphase acid catalyst were added to a reactor equipped with a fractionating column, condenser, stirrer, thermometer and nitrogen inlet. Nitrogen gas was introduced for protection, the temperature was slowly raised to 180℃ and held for 2 hours, and then gradually raised to 220℃. Esterification reaction was carried out at this temperature. The reaction was terminated when the acid value dropped to 5mgKOH / g to obtain condensate. The reaction system containing the condensation polymer was cooled to 110°C. 8g of 3-glycidyl etheroxypropyltrimethoxysilane was added dropwise while stirring at 200 rpm. The mixture was kept at 110°C for 2 hours. 10g of the co-solvent dipropylene glycol methyl ether was added and stirred until the system was uniformly cooled to 80°C. 60g of deionized water was slowly added to the reaction system, and the mixture was dispersed at 1000 rpm for 30 minutes. More deionized water was added to bring the volume content of the polyester resin to 40%. The mixture was filtered through a 25μm pore size filter membrane to remove large molecular particles, effectively removing trace amounts of gel particles, impurities, or insufficiently dispersed materials that may have been generated during the preparation process. This ensured that the final product was fine and free of impurities, meeting the requirements of high-end applications, and yielding an aqueous polyester dispersion.

[0024] Example 2:

[0025] A method for preparing an aqueous polyester dispersion, such as Figure 1 As shown, it includes the following steps: S1: Preparation of catalyst precursor microspheres After initial processing, the rice husks are first washed multiple times with sufficient deionized water, thoroughly agitated to remove impurities such as mud, dust, and soluble inorganic salts adhering to the surface, ensuring the purity of the raw material and preventing the introduction of impurities during subsequent high-temperature processing. The washed rice husks are then placed in an oven and dried at 105℃ to constant weight to completely remove moisture. Subsequently, the dried rice husks are evenly spread in a crucible and transferred to a muffle furnace for high-temperature calcination: the temperature is slowly increased to 620℃ using a programmed temperature control method and held for 2.5 hours, allowing the organic matter within the rice husks, such as cellulose and hemilignin, to fully decompose and carbonize, ultimately forming white or grayish-white rice husk ash with porous silica as the main component. After calcination, it is allowed to cool naturally to room temperature to avoid rapid cooling that could cause the silica structure to become brittle. Finally, it is finely ground using a mortar and pestle or ball mill and passed through a 200-mesh sieve to obtain rice husk ash powder with uniform particle size, high specific surface area, and high activity, laying the foundation for the subsequent preparation of catalyst supports. Bentonite was ground through a 200-mesh sieve to obtain bentonite powder. Rice husk ash and bentonite powder were mixed at a mass ratio of 3.5:1. Deionized water with a mass of 5 times that of rice husk ash and bentonite powder was added, and the mixture was stirred at 60 r / min for 22 min to obtain a slurry. Soybean oil cooled to 7°C was added dropwise to the slurry at a rate of 1 mL / s, with the amount of vegetable oil added being 1.2 times the volume of the slurry. The mixture was stirred for 9 min, and the slurry was stirred to form microspheres. After drying, catalyst precursor microspheres were obtained.

[0026] S2: Catalyst precursor microspheres are prepared into natural heterogeneous acid catalysts. The obtained catalyst precursor microspheres were completely immersed in a 1 mol / L citric acid solution, ensuring the solution fully penetrated into the internal pores of the microspheres, and soaked for 4.5 hours to allow citric acid molecules to be fully adsorbed onto the surface and pores of the support. Afterwards, filtration was performed to remove excess impregnation solution, and the solid material was collected. The filtered microspheres were placed in a drying oven and heat-treated at 105℃ for 12.5 hours to completely remove physically adsorbed water and form a preliminarily stable supported structure. Subsequently, the dried microspheres were transferred to a muffle furnace for programmed temperature-controlled calcination: slowly heated to 460℃ at a heating rate of 5℃ / min and held at this temperature for 3.5 hours. During this process, citric acid underwent pyrolysis and carbonization. Its carboxyl and hydroxyl groups were not completely decomposed but were anchored to the SiO2 substrate surface of rice husk ash through esterification, condensation, and other processes in the form of chemical bonds, forming a composite layer of amorphous carbon material rich in carboxyl and hydroxyl groups. The carbon layer structure is stable and can provide abundant Brønsted acid active sites, thereby achieving efficient solid acid catalysis. After calcination, the cooling method is controlled by slowly cooling the furnace to room temperature of 23°C to avoid the support structure from cracking or loss of active sites due to excessive thermal stress, and finally obtain a natural heterogeneous acid catalyst with high acid content and high stability.

[0027] S3: Preparation of aqueous polyester dispersion 32g of neopentyl glycol, 17g of tricyclodecanediethanol, 7g of trimethylolpropane, 42g of furanyl dicarboxylic acid, 11g of adipic acid and 0.2g of natural multiphase acid catalyst were added to a reactor equipped with a fractionating column, condenser, stirrer, thermometer and nitrogen inlet. Nitrogen gas was introduced for protection, the temperature was slowly raised to 185℃ and held for 2.5h. Then the temperature was gradually raised to 225℃ and esterification reaction was carried out at this temperature. The reaction was terminated when the acid value dropped to 8mgKOH / g to obtain condensate. The reaction system containing the condensation polymer was cooled to 115°C. 9g of 3-glycidyl etheroxypropyltrimethoxysilane was added dropwise while stirring at 250 rpm. The mixture was kept at 115°C for 2.5 hours. 12g of the co-solvent dipropylene glycol methyl ether was added and stirred until the system was uniformly cooled to 85°C. 65g of deionized water was slowly added to the reaction system, and the mixture was dispersed at 1050 rpm for 35 minutes. More deionized water was added to bring the polyester resin volume content to 42%. The mixture was filtered through a 25μm pore size filter membrane to remove large molecular particles, effectively removing trace amounts of gel particles, impurities, or insufficiently dispersed materials that may have been generated during the preparation process. This ensured that the final product was fine and free of impurities, meeting the requirements of high-end applications, and yielding an aqueous polyester dispersion.

[0028] Example 3:

[0029] A method for preparing an aqueous polyester dispersion, such as Figure 1 As shown, it includes the following steps: S1: Preparation of catalyst precursor microspheres After initial treatment, the rice husks are first washed multiple times with sufficient deionized water, thoroughly agitated to remove impurities such as mud, dust, and soluble inorganic salts adhering to the surface, ensuring the purity of the raw material and preventing the introduction of impurities during subsequent high-temperature processing. The washed rice husks are then placed in an oven and dried at 105℃ to constant weight to completely remove moisture. Subsequently, the dried rice husks are evenly spread in a crucible and transferred to a muffle furnace for high-temperature calcination: the temperature is slowly increased to 640℃ using a programmed temperature control method and held for 3 hours, allowing the organic matter within the rice husks, such as cellulose and hemilignin, to fully decompose and carbonize, ultimately forming white or grayish-white rice husk ash with porous silica as the main component. After calcination, it is allowed to cool naturally to room temperature to avoid rapid cooling that could cause the silica structure to become brittle. Finally, it is finely ground using a mortar and pestle or ball mill and passed through a 200-mesh sieve to obtain rice husk ash powder with uniform particle size, high specific surface area, and high activity, laying the foundation for the subsequent preparation of catalyst supports. Bentonite was ground through a 200-mesh sieve to obtain bentonite powder. Rice husk ash and bentonite powder were mixed at a mass ratio of 4:1. Deionized water with a mass of 6 times that of rice husk ash and bentonite powder was added. The mixture was stirred at 70 r / min for 25 min to obtain a slurry. Soybean oil cooled to 10°C was added dropwise to the slurry at a rate of 1 mL / s. The amount of vegetable oil added was 1.5 times the volume of the slurry. The mixture was stirred for 10 min, and the slurry was stirred to form microspheres. After drying, catalyst precursor microspheres were obtained.

[0030] S2: Catalyst precursor microspheres are prepared into natural heterogeneous acid catalysts. The obtained catalyst precursor microspheres were completely immersed in a 1 mol / L citric acid solution, ensuring the solution fully penetrated into the pores of the microspheres. Immersion was continued for 5 hours to allow citric acid molecules to be fully adsorbed onto the carrier surface and within the pores. After filtration, excess impregnation solution was removed, and the solid material was collected. The filtered microspheres were placed in a drying oven and heat-treated at 110℃ for 13 hours to completely remove physically adsorbed water and form a preliminarily stable supported structure. Subsequently, the dried microspheres were transferred to a muffle furnace for programmed temperature-controlled calcination: slowly heated to 480℃ at a heating rate of 5℃ / min and held at this temperature for 4 hours. During this process, citric acid underwent pyrolysis and carbonization. Its carboxyl and hydroxyl groups were not completely decomposed but instead anchored to the SiO2 substrate surface of rice husk ash through esterification and condensation, forming an amorphous carbon composite layer rich in carboxyl and hydroxyl groups. The carbon layer structure is stable and can provide abundant Brønsted acid active sites, thus achieving efficient solid acid catalysis. After calcination, the cooling method is controlled by slowly cooling the furnace to room temperature of 24°C to avoid the support structure from cracking or loss of active sites due to excessive thermal stress, and finally obtain a natural heterogeneous acid catalyst with high acid content and high stability.

[0031] S3: Preparation of aqueous polyester dispersion 35g of neopentyl glycol, 18g of tricyclodecanediethanol, 8g of trimethylolpropane, 45g of furanyl dicarboxylic acid, 12g of adipic acid and 0.3g of natural heterogeneous acid catalyst were added to a reactor equipped with a fractionating column, condenser, stirrer, thermometer and nitrogen inlet. Nitrogen gas was introduced for protection, the temperature was slowly raised to 190℃ and held for 3 hours. Then the temperature was gradually raised to 230℃ and esterification reaction was carried out at this temperature. The reaction was terminated when the acid value dropped to 10mgKOH / g to obtain condensate. The reaction system containing the condensation polymer was cooled to 120°C. 8g of 3-glycidyl etheroxypropyltrimethoxysilane was added dropwise while stirring at 300 rpm. The mixture was kept at 120°C for 3 hours. 15g of the co-solvent dipropylene glycol methyl ether was added and stirred until the system was uniformly cooled to 90°C. 70g of deionized water was slowly added to the reaction system, and the mixture was dispersed at 1100 rpm for 40 minutes. More deionized water was added to bring the volume content of the polyester resin to 45%. The mixture was filtered through a 25μm pore size membrane to remove large molecular particles, effectively removing trace amounts of gel particles, impurities, or insufficiently dispersed materials that may have been generated during the preparation process. This ensured that the final product was fine and free of impurities, meeting the requirements of high-end applications, and yielding an aqueous polyester dispersion.

[0032] Comparative Example 1: Compared with Example 1, Comparative Example 1 is a commercially available water-based polyester coating, specifically a polyester nano-anti-corrosion coating sold by Yunnan Longxin Kunfa Trading Co., Ltd., CAS No.: LX713.

[0033] Comparative Example 2: Compared with Example 1, the difference in Comparative Example 2 is that the catalyst prepared in the example was not added when preparing the aqueous polyester dispersion. Specifically: 30g neopentyl glycol, 15g tricyclodecanediethanol, 5g trimethylolpropane, 40g furanyl dicarboxylic acid, 10g adipic acid and 0.1g natural multiphase acid catalyst were added to a reactor equipped with a fractionating column, condenser, stirrer, thermometer and nitrogen inlet. Nitrogen gas was introduced for protection, the temperature was slowly raised to 180℃ and held for 2 hours, and then gradually raised to 220℃. Esterification reaction was carried out at this temperature. The reaction was terminated when the acid value dropped to 5mgKOH / g to obtain condensate. The reaction system containing the condensation polymer was cooled to 110°C. 8g of 3-glycidyl etheroxypropyltrimethoxysilane was added dropwise while stirring at 200 rpm. The mixture was kept at 110°C for 2 hours. 10g of the co-solvent dipropylene glycol methyl ether was added and stirred until the system was uniformly cooled to 80°C. 60g of deionized water was slowly added to the reaction system, and the mixture was dispersed at 1000 rpm for 30 minutes. More deionized water was added to bring the polyester resin content to 40%. The mixture was filtered through a 25μm pore size filter membrane to remove large molecular particles, effectively removing trace amounts of gel particles, impurities, or insufficiently dispersed materials that may have been generated during the preparation process. This ensured that the final product was fine and free of impurities, meeting the requirements of high-end applications, and yielding an aqueous polyester dispersion.

[0034] The aqueous polyester dispersions, dispersant, defoamer and titanium dioxide prepared in Examples 1-3 and Comparative Example 2 were mixed at a mass ratio of 70:1:0.5:15 under stirring at 300 r / min. The mixture was then filtered through a 200 mesh sieve, allowed to stand for 30 min to mature, and coated onto a carbon steel plate with a thickness of 1 mm.

[0035] The parameters of the water-based coating prepared in Example 1 are as follows: pH value 7.5, viscosity 372 mPa·s, particle size 80-150 nm, and acid value 6.2 mg / KOH.

[0036] The water resistance was tested using the method in GB / T5209-1985 "Determination of water resistance of paints and varnishes - Immersion method", as shown in Table 1. The pencil hardness, i.e. physical hardness, was tested using the method in GB / T6739-2022 "Determination of Hardness of Paints and Varnishes by Pencil Method", as shown in Table 2. The initial viscosity and pH value of the waterborne polyester coatings of Examples 1-3 and Comparative Examples 1-2 were recorded. After being stored at 50°C for 30 days, the viscosity and pH value were tested again, as shown in Table 3, to evaluate their storage stability.

[0037] Table 1

[0038] Table 2

[0039] Table 3

[0040] As can be seen from Tables 1 and 2, the paint films obtained in Examples 1-3 showed no blistering or peeling after 48 hours of immersion in water. In contrast, the commercially available water-based polyester coating in Comparative Example 1 and the uncatalyzed Comparative Example 2 showed slight blistering and edge peeling, indicating that the water resistance of Examples 1-3 was significantly better than that of the commercially available product and the product without catalyst. The pencil hardness of Examples 1-3 was 2H, while that of Comparative Examples 1 and 2 was only HB, indicating that the hardness of the paint film of Examples 1-3 was significantly higher than that of commercially available products and products without catalysts.

[0041] As can be seen from Table 3, the viscosity of Examples 1-3 changed by no more than 20% after 30 days of storage at 50°C, while the changes in Comparative Examples 1 and 2 were much larger, far exceeding 20%, indicating that their storage stability was not as good as that of the Examples. The pH value of Examples 1-3 also changed relatively stably, not exceeding 0.5, while the pH value changes in Comparative Examples 1 and 2 were 0.8 and 1, respectively, which were far less stable than those of the Examples.

[0042] In summary, the waterborne polyester dispersion prepared using the aforementioned natural multiphase acid catalyst outperforms traditional commercially available waterborne polyester coatings in both key properties, namely water resistance and hardness, thus verifying the feasibility and advantages of this process.

[0043] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An application of an aqueous polyester dispersion, characterized in that, It is used in the preparation of water-based coatings for metal substrates; The aqueous polyester dispersion comprises the following raw materials: 30-35 parts by weight of neopentyl glycol, 15-18 parts by weight of tricyclodecanediethanol, 5-8 parts by weight of trimethylolpropane, 40-45 parts by weight of furanyl dicarboxylic acid, 10-12 parts by weight of adipic acid, 0.1-0.3 parts by weight of natural heterogeneous acid catalyst, 8-10 parts by weight of silane coupling agent, cosolvent and deionized water; The method for preparing the aqueous polyester dispersion includes the following steps: S1: Preparation of catalyst precursor microspheres Rice husks are washed with deionized water to remove mud, sand and soluble impurities, dried, calcined and ground and sieved to obtain rice husk ash. Bentonite is ground and sieved to obtain bentonite powder. Rice husk ash and bentonite powder are mixed, deionized water is added and stirred to obtain slurry. Vegetable oil is added dropwise to the slurry to form microspheres. After drying, catalyst precursor microspheres are obtained. S2: Catalyst precursor microspheres are prepared into natural heterogeneous acid catalysts. The catalyst precursor microspheres were immersed in citric acid solution, filtered and separated, and then dried. The dried catalyst precursor microspheres were calcined to obtain a natural heterogeneous acid catalyst. S3: Preparation of aqueous polyester dispersion Neopentyl glycol, tricyclodecanediethanol, trimethylolpropane, furanyl dicarboxylic acid, adipic acid, and a natural multiphase acid catalyst were added to a reactor, and nitrogen gas was introduced for protection. The reaction was heated to obtain a condensate. The reaction system containing the condensate was cooled, and 3-glycidyl etheroxypropyltrimethoxysilane was added dropwise with stirring. The system was kept at a constant temperature, and a co-solvent was added and stirred to cool the system uniformly. Deionized water was added to the reaction system and dispersed at high speed. More deionized water was added to make the volume content of polyester resin 40-45%. Macromolecular particles were removed by filtration to obtain an aqueous polyester dispersion.

2. The application of the aqueous polyester dispersion according to claim 1, characterized in that, Step S1, preparing catalyst precursor microspheres, includes the following steps: The rice husks are washed with deionized water to remove mud, sand and soluble impurities, dried, and then calcined in a muffle furnace at 600-640℃ for 2-3 hours. After natural cooling, they are ground through a 200-mesh sieve to obtain rice husk ash. Bentonite was ground through a 200-mesh sieve to obtain bentonite powder. Rice husk ash and bentonite powder were mixed at a mass ratio of (3-4):

1. Deionized water with a mass of 5-6 times that of rice husk ash and bentonite powder was added. The mixture was stirred at a speed of 50-70 r / min for 20-25 min to obtain a slurry. Vegetable oil cooled to 5-10℃ was added dropwise to the slurry at a rate of 1 mL / s. The amount of vegetable oil added was 1-1.5 times the volume of the slurry. The mixture was stirred for 8-10 min, and the slurry was stirred to form microspheres. After drying, catalyst precursor microspheres were obtained.

3. The application of the aqueous polyester dispersion according to claim 2, characterized in that, Step S2 involves preparing the catalyst precursor microspheres into a natural heterogeneous acid catalyst, including the following steps: The catalyst precursor microspheres were immersed in a 1M citric acid solution for 4-5 hours, filtered and separated, and then dried at 100-110℃ for 12-13 hours. The dried catalyst precursor microspheres were placed in a muffle furnace and calcined at 450-480℃ for 3-4 hours at a heating rate of 5℃ / min. After calcination, the microspheres were cooled to room temperature (22-24℃) with the furnace to obtain a natural heterogeneous acid catalyst.

4. The application of the aqueous polyester dispersion according to claim 3, characterized in that, Step S3, preparing the aqueous polyester dispersion, includes the following steps: Add 30-35 parts by mass of neopentyl glycol, 15-18 parts by mass of tricyclodecanediethanol, 5-8 parts by mass of trimethylolpropane, 40-45 parts by mass of furanyl dicarboxylic acid, 10-12 parts by mass of adipic acid, and 0.1-0.3 parts by mass of natural heterogeneous acid catalyst to a reaction vessel equipped with a fractionating column, condenser, stirrer, thermometer, and nitrogen inlet. Slowly raise the temperature to 180-190℃ and hold for 2-3 hours. Then gradually raise the temperature to 220-230℃ and carry out the esterification reaction at this temperature. Terminate the reaction when the acid value drops to 5-10 mg KOH / g to obtain the condensate. Cool the reaction system containing the condensation polymer to 110-120℃, and add 8-10 parts by weight of silane coupling agent 3-glycidyl etheroxypropyltrimethoxysilane dropwise while stirring at 200-300 r / min. Keep the system at 110-120℃ for 2-3 hours, add 10-15 parts by weight of co-solvent and stir to uniformly cool the system to 80-90℃. Slowly add 60-70 parts by weight of deionized water to the reaction system and disperse at 1000-1100 r / min for 30-40 minutes. Add more deionized water to make the volume content of polyester resin 40-45%. Filter to remove macromolecular particles to obtain an aqueous polyester dispersion.

5. The application of the aqueous polyester dispersion according to claim 2, characterized in that, The vegetable oil is any one of soybean oil, peanut oil, or sesame oil.

6. The application of the aqueous polyester dispersion according to claim 4, characterized in that, The cosolvent is dipropylene glycol methyl ether.

7. The application of the aqueous polyester dispersion according to claim 4, characterized in that, The filter membrane used for filtration has a pore size of 25 μm.

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