Polyester resin for weather-resistant powder coating and preparation method of polyester resin

Abstract

The invention discloses polyester resin for a weather-resistant powder coating and a preparation method of the polyester resin, and belongs to the technical field of resin preparation. The polyester resin is prepared from polyhydric alcohol, polyatomic acid, a catalyst, an auxiliary agent and modified montmorillonite, wherein the modified montmorillonite is a nano material which is subjected to surface coupling modification by a hydroxyl-terminated cationic waterborne polyurethane intercalation and gamma-aminopropyltriethoxysilane. By optimizing monomers, such as isophthalic acid and 1, 4-cyclohexanedimethanol, and combining a labyrinth barrier structure formed by modified montmorillonite in the resin, the weather resistance and hydrolysis resistance of the material are effectively improved. After the resin is applied to the powder coating, corrosion of water and acidic substances to ester bonds can be remarkably reduced in severe environments such as acid rain, and the service life of the coating is prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of resin preparation and relates to a polyester resin for weather-resistant powder coating and a preparation method thereof. BACKGROUND

[0002] With increasingly stringent environmental regulations and the continuous improvement of people's performance requirements for coatings, powder coatings have been widely used in many fields such as construction, household appliances and automobiles due to their zero VOC emissions, high utilization rate and excellent coating performance. As the main film-forming material for weather-resistant powder coating, polyester resin has become the focus of industry research and application due to its good mechanical properties, chemical resistance and decoration, and plays a key role in improving the overall performance of powder coatings. However, the large number of ester bonds in the molecular structure of polyester resin gives it natural hydrolysis sensitivity. In an acid rain environment, although the coating formed by the powder coating can provide some protection, the coating is not completely dense, and the moisture and acidic substances carried by the acid rain can still slowly penetrate through the small pores, defects or intermolecular gaps of the coating. Once in contact with the polyester resin, the moisture can initiate the ester bond hydrolysis reaction, causing the resin molecular chain to break and the molecular weight to decrease; and the acidic components dissolved in the acid rain can further catalyze the hydrolysis process, accelerating the ester bond breaking speed, severely damaging the stability of the chemical structure of the polyester resin, and thus reducing the weather resistance of the polyester resin. SUMMARY

[0003] The purpose of the present application is to provide a polyester resin for weather-resistant powder coating and a preparation method thereof, which has high weather resistance.

[0004] The purpose of the present application can be achieved by the following technical solutions: In a first aspect, the present application provides a polyester resin for weather-resistant powder coating, comprising the following raw materials in mass percentage: 34-38% polyol, 45-48% polybasic acid, 0.1-0.5% catalyst, 0.2-0.5% additive, 8-10% acidolysis agent, and 5-10% modified montmorillonite. The modified montmorillonite is a montmorillonite modified by a hydroxyl-terminated cationic waterborne polyurethane and gamma-aminopropyl triethoxysilane, the hydroxyl-terminated cationic waterborne polyurethane is intercalated between the layers of the montmorillonite, and the gamma-aminopropyl triethoxysilane is coupled to the surface of the montmorillonite.

[0005] Preferably, the mass ratio of the montmorillonite, the hydroxyl-terminated cationic waterborne polyurethane and the gamma-aminopropyl triethoxysilane is 1: (0.5-1.2): (0.1-0.3).

[0006] Preferably, the particle size of the modified montmorillonite is 0.5-2.0 μm.

[0007] Preferably, the hydroxy-terminated cationic waterborne polyurethane comprises the following raw materials in percentage by mass: 40-45% polybutylene adipate diol 1000, 25-30% isophorone diisocyanate, 5-10% dimethylol propionic acid, 3-8% ethylenediamine, 1-3% triethylamine, and 0.1-0.5% dibutyltin dilaurate.

[0008] Preferably, the preparation steps of the hydroxyl-terminated cationic waterborne polyurethane include: S1, mixing polybutylene adipate diol 1000, isophorone diisocyanate, part of acetone and dibutyltin dilaurate, and then adding dimethylolpropionic acid to obtain a prepolymer containing free isocyanate groups; S2, adding triethylamine to obtain an ionic polyurethane prepolymer solution; S3. Add the remaining acetone, stir, add ethylenediamine dropwise, stir, remove the acetone, and dry to obtain a hydroxyl-terminated cationic waterborne polyurethane.

[0009] Preferably, the polyol comprises the following raw materials: neopentyl glycol, trimethylolpropane and 1,4-cyclohexanedimethanol.

[0010] Preferably, the polyacid comprises the following raw materials: terephthalic acid, isophthalic acid, adipic acid, and trimellitic anhydride.

[0011] Preferably, the catalyst is dibutyltin oxide.

[0012] Preferably, the auxiliary agent is an antioxidant and a curing accelerator; Preferably, the antioxidant is AT-215, and the curing accelerator is tetrabutylammonium bromide.

[0013] In a second aspect, the present invention provides a method for preparing the weather-resistant polyester resin for powder coatings as described above, comprising the following steps: Y1. Mixing a polyol, a polyacid and a catalyst in proportion, and esterifying the mixture to obtain an esterified product; Y2, adding an acidolysis agent, reacting to obtain an acidolysis product; Y3. Vacuum polycondensation, adding additives and modified montmorillonite, stirring, and obtaining a polyester resin for weather-resistant powder coatings.

[0014] Beneficial effects of the present invention: (1) The present invention effectively improves the weather resistance and hydrolysis resistance of polyester resin in acid rain environment by introducing montmorillonite modified with terminal hydroxyl cationic waterborne polyurethane and γ-aminopropyltriethoxysilane. The modified montmorillonite has a layered structure. After intercalation and surface coupling treatment, it can be evenly dispersed in the polyester matrix to form a dense "maze-like" barrier layer, which prolongs the path for moisture and acidic substances (such as hydrogen ions) in rainwater to penetrate into the resin interior and reduces the probability of ester bond hydrolysis. At the same time, the siloxane group of γ-aminopropyltriethoxysilane introduced on its surface can form hydrogen bonds with the ester bonds in the polyester resin, further inhibiting the hydrolysis reaction, thereby enhancing the overall stability and weather resistance of the resin.

[0015] (2) Weather-resistant monomers such as isophthalic acid and 1,4-cyclohexanedimethanol are used to construct the polyester main chain, thereby improving the resin's resistance to ultraviolet rays and oxidation. The powder coating prepared using the polyester resin of the present invention has high weather resistance. DETAILED DESCRIPTION

[0016] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0017] Example 1 A polyester resin for weather-resistant powder coating includes the following raw materials in percentage by mass, as shown in Table 1.

[0018] Table 1 The modified montmorillonite is a mixture of hydroxyl-terminated cationic waterborne polyurethane and γ-aminopropyltriethoxysilane. The hydroxyl-terminated cationic waterborne polyurethane is intercalated between the montmorillonite layers, while the γ-aminopropyltriethoxysilane is coupled to the montmorillonite surface. The mass ratio of montmorillonite, hydroxyl-terminated cationic waterborne polyurethane, and γ-aminopropyltriethoxysilane is 1:0.8:0.2.

[0019] The hydroxyl-terminated cationic waterborne polyurethane includes the following raw materials in percentage by mass, as shown in Table 2: Table 2 The preparation steps of hydroxyl-terminated cationic waterborne polyurethane are as follows: S1. Add polybutylene adipate diol 1000, isophorone diisocyanate, a portion of acetone (accounting for 15% of the total acetone), and dibutyltin dilaurate to a high-speed stirring reactor according to the mass ratio; then start mechanical stirring at a speed of 500 rpm, heat the reaction system to 60°C, and maintain constant stirring for 1 hour; then, slowly add dimethylolpropionic acid in proportion, and continue stirring at 60°C for 2 hours to obtain a prepolymer containing free isocyanate groups.

[0020] S2. Add triethylamine to the prepolymer according to the mass ratio and continue stirring for 30 minutes to form an ionic polyurethane prepolymer solution. Control the reaction temperature not to exceed 65°C to ensure uniform reaction.

[0021] S3: After the reaction solution is cooled to room temperature, the remaining acetone is slowly added while stirring at a low speed of 100 rpm, and then ethylenediamine is added dropwise in proportion and stirred for 1 hour to allow the chain extension reaction to proceed fully. After the reaction is completed, the mixture is placed in a vacuum drying oven and the acetone is removed by reduced pressure distillation at 60°C. The mixture is dried for 24 hours and crushed to obtain a terminal hydroxyl cationic waterborne polyurethane solid product.

[0022] The preparation steps of modified montmorillonite are as follows: X1. Mix montmorillonite (particle size ≤ 2.0 μm) and the above-prepared hydroxyl-terminated cationic waterborne polyurethane in a mass ratio of 1:0.8, heat to 120°C, and use a disperser to stir at a speed of 3000 rpm for 30 minutes to ensure that the polyurethane is evenly inserted into the montmorillonite layers.

[0023] X2. Add γ-aminopropyltriethoxysilane in proportion, stir at 60°C and 800 rpm for 2 hours to allow the silane coupling agent to chemically bond with the surface of the montmorillonite; finally, place the modified montmorillonite in a vacuum drying oven, dry it at 80°C for 6 hours, crush and sieve it to ensure that the particle size of the modified montmorillonite is 0.5-2.0 μm, thereby obtaining modified montmorillonite for later use.

[0024] The preparation steps of a weather-resistant polyester resin for powder coating are as follows: Y1. Weigh each substance according to the mass ratio of the raw materials of the polyester resin, and place neopentyl glycol, trimethylolpropane, 1,4-cyclohexanedimethanol, terephthalic acid, isophthalic acid, adipic acid, trimellitic anhydride, and dibutyltin oxide (DBTO) into a high-speed stirring reactor. Under nitrogen protection, start stirring, set the speed to 300 rpm, and quickly raise the temperature to 180°C to generate and distill off esterification water. Then, raise the temperature to 240°C at a rate of 10°C per hour and maintain the temperature for reaction. During this period, measure the acid value every 30 minutes. When the acid value reaches 15-18 mgKOH / g, switch to a vacuum state (pressure reduced to -0.09 MPa) and continue the reaction. When the acid value reaches 5-8 mgKOH / g, release the vacuum state to obtain an esterification product. Y2. Under the protection of nitrogen, add the acidolysis agent to the esterification product in proportion, and carry out acidolysis reaction at 240° C. for 2 h to obtain an acidolysis product with an acid value of 57-60 mgKOH / g; Y3. The acidolysis product was subjected to polycondensation reaction under a vacuum degree of 0.096 MPa for 1 hour, and the acid value reached 46-48 mgKOH / g and the hydroxyl value was less than 5 mgKOH / g. The temperature was lowered to 200°C, and modified montmorillonite, AT-215 and tetrabutylammonium bromide were added in proportion. The mixture was stirred at a speed of 300 rpm for 1.5 hours. Finally, the mixture was cooled and solidified and then crushed to obtain finished polyester resin particles.

[0025] The polyester resin prepared in this example has an acid value of 47 mgKOH / g, a hydroxyl value of 3.5 mgKOH / g, and a softening point of 108°C.

[0026] Example 2 A polyester resin for weather-resistant powder coatings includes the following raw materials in percentage by mass, as shown in Table 3.

[0027] Table 3 The modified montmorillonite is a mixture of hydroxyl-terminated cationic waterborne polyurethane and γ-aminopropyltriethoxysilane. The hydroxyl-terminated cationic waterborne polyurethane is intercalated between the montmorillonite layers, while the γ-aminopropyltriethoxysilane is coupled to the montmorillonite surface. The mass ratio of montmorillonite, hydroxyl-terminated cationic waterborne polyurethane, and γ-aminopropyltriethoxysilane is 1:1:0.25.

[0028] The hydroxyl-terminated cationic waterborne polyurethane includes the following raw materials in percentage by mass, as shown in Table 4: Table 4 The preparation steps of hydroxyl-terminated cationic waterborne polyurethane are as follows: S1. Add polybutylene adipate diol 1000, isophorone diisocyanate, a portion of acetone (accounting for 15% of the total acetone), and dibutyltin dilaurate to a high-speed stirring reactor according to the mass ratio; then start mechanical stirring at a speed of 500 rpm, heat the reaction system to 60°C, and maintain constant stirring for 1 hour; then, slowly add dimethylolpropionic acid in proportion, and continue stirring at 60°C for 2 hours to obtain a prepolymer containing free isocyanate groups.

[0029] S2. Add triethylamine to the prepolymer according to the mass ratio and continue stirring for 30 minutes to form an ionic polyurethane prepolymer solution. Control the reaction temperature not to exceed 65°C to ensure uniform reaction.

[0030] S3: After the reaction solution is cooled to room temperature, the remaining acetone is slowly added while stirring at a low speed of 100 rpm, and then ethylenediamine is added dropwise in proportion and stirred for 1 hour to allow the chain extension reaction to proceed fully. After the reaction is completed, the mixture is placed in a vacuum drying oven and the acetone is removed by reduced pressure distillation at 60°C. The mixture is dried for 24 hours and crushed to obtain a terminal hydroxyl cationic waterborne polyurethane solid product.

[0031] The preparation steps of modified montmorillonite are as follows: X1. Mix montmorillonite (particle size ≤ 2.0 μm) and the above-prepared hydroxyl-terminated cationic waterborne polyurethane in a mass ratio of 1:1, heat to 120°C, and use a disperser to stir at a speed of 3000 rpm for 30 minutes to ensure that the polyurethane is evenly inserted into the montmorillonite layers.

[0032] X2. Add γ-aminopropyltriethoxysilane in proportion, stir at 60°C and 800 rpm for 2 hours to allow the silane coupling agent to chemically bond with the surface of the montmorillonite; finally, place the modified montmorillonite in a vacuum drying oven, dry it at 80°C for 6 hours, crush and sieve it to ensure that the particle size of the modified montmorillonite is 0.5-2.0 μm, thereby obtaining modified montmorillonite for later use.

[0033] The preparation steps of a weather-resistant polyester resin for powder coating are as follows: Y1. Weigh each substance according to the mass ratio of the raw materials of the polyester resin, and place neopentyl glycol, trimethylolpropane, 1,4-cyclohexanedimethanol, terephthalic acid, isophthalic acid, adipic acid, trimellitic anhydride, and dibutyltin oxide (DBTO) into a high-speed stirring reactor. Under nitrogen protection, start stirring, set the speed to 300 rpm, and quickly raise the temperature to 180°C to generate and distill off esterification water. Then, raise the temperature to 240°C at a rate of 10°C per hour and maintain the temperature for reaction. During this period, measure the acid value every 30 minutes. When the acid value reaches 15-18 mgKOH / g, switch to a vacuum state (pressure reduced to -0.09 MPa) and continue the reaction. When the acid value reaches 5-8 mgKOH / g, release the vacuum state to obtain an esterification product. Y2. Under the protection of nitrogen, add the acidolysis agent to the esterification product in proportion, and carry out acidolysis reaction at 240° C. for 2 h to obtain an acidolysis product with an acid value of 57-60 mgKOH / g; Y3. The acidolysis product was subjected to polycondensation reaction under a vacuum degree of 0.096 MPa for 1 hour, and the acid value reached 46-48 mgKOH / g and the hydroxyl value was less than 5 mgKOH / g. The temperature was lowered to 200°C, and modified montmorillonite, AT-215 and tetrabutylammonium bromide were added in proportion. The mixture was stirred at a speed of 300 rpm for 1.5 hours. Finally, the mixture was cooled and solidified and then crushed to obtain finished polyester resin particles.

[0034] The polyester resin prepared in this example has an acid value of 46.5 mgKOH / g, a hydroxyl value of 4.2 mgKOH / g, and a softening point of 111°C.

[0035] Example 3 A polyester resin for weather-resistant powder coatings includes the following raw materials in percentage by mass, as shown in Table 5.

[0036] Table 5 The modified montmorillonite is a mixture of hydroxyl-terminated cationic waterborne polyurethane and γ-aminopropyltriethoxysilane. The hydroxyl-terminated cationic waterborne polyurethane is intercalated between the montmorillonite layers, while the γ-aminopropyltriethoxysilane is coupled to the montmorillonite surface. The mass ratio of montmorillonite, hydroxyl-terminated cationic waterborne polyurethane, and γ-aminopropyltriethoxysilane is 1:0.7:0.15.

[0037] The hydroxyl-terminated cationic waterborne polyurethane includes the following raw materials in percentage by mass, as shown in Table 6: Table 6 The preparation steps of hydroxyl-terminated cationic waterborne polyurethane are as follows: S1. Add polybutylene adipate diol 1000, isophorone diisocyanate, a portion of acetone (accounting for 15% of the total acetone), and dibutyltin dilaurate to a high-speed stirring reactor according to the mass ratio; then start mechanical stirring at a speed of 500 rpm, heat the reaction system to 60°C, and maintain constant stirring for 1 hour; then, slowly add dimethylolpropionic acid in proportion, and continue stirring at 60°C for 2 hours to obtain a prepolymer containing free isocyanate groups.

[0038] S2. Add triethylamine to the prepolymer according to the mass ratio and continue stirring for 30 minutes to form an ionic polyurethane prepolymer solution. Control the reaction temperature not to exceed 65°C to ensure uniform reaction.

[0039] S3: After the reaction solution is cooled to room temperature, the remaining acetone is slowly added while stirring at a low speed of 100 rpm, and then ethylenediamine is added dropwise in proportion and stirred for 1 hour to allow the chain extension reaction to proceed fully. After the reaction is completed, the mixture is placed in a vacuum drying oven and the acetone is removed by reduced pressure distillation at 60°C. The mixture is dried for 24 hours and crushed to obtain a terminal hydroxyl cationic waterborne polyurethane solid product.

[0040] The preparation steps of modified montmorillonite are as follows: X1. Mix montmorillonite (particle size ≤ 2.0 μm) and the above-prepared hydroxyl-terminated cationic waterborne polyurethane in a mass ratio of 1:0.7, heat to 120°C, and use a disperser to stir at a speed of 3000 rpm for 30 minutes to ensure that the polyurethane is evenly inserted into the montmorillonite layers.

[0041] X2. Add γ-aminopropyltriethoxysilane in proportion, stir at 60°C and 800 rpm for 2 hours to allow the silane coupling agent to chemically bond with the surface of the montmorillonite; finally, place the modified montmorillonite in a vacuum drying oven, dry it at 80°C for 6 hours, crush and sieve it to ensure that the particle size of the modified montmorillonite is 0.5-2.0 μm, thereby obtaining modified montmorillonite for later use.

[0042] The preparation steps of a weather-resistant polyester resin for powder coating are as follows: Y1, each material was weighed according to the raw material mass ratio of polyester resin, neopentyl glycol, trimethylolpropane, 1, 4-cyclohexane dimethanol, terephthalic acid, isophthalic acid, adipic acid, trimellitic anhydride and dibutyl tin oxide (DBTO) were put into a high-speed stirring reaction kettle, under the protection of nitrogen, the stirring was started, the speed was set to 300 rpm, the temperature was quickly raised to 180℃, the esterification water was generated and distilled out, then the temperature was raised to 240℃ at the rate of 10℃ per hour, the temperature was maintained, the acid value was measured every 30 minutes during the reaction, when the acid value reached 15-18 mgKOH / g, the vacuum state was switched (the pressure was reduced to-0.09 MPa), the reaction was continued, when the acid value reached 5-8 mgKOH / g, the vacuum was released, and the esterification product was obtained; Y2, under the protection of nitrogen, the acidolysis agent was added to the esterification product in proportion, and the acidolysis reaction was carried out at 240℃ for 2h, and the acidolysis product was obtained, and the acid value reached 57-60 mgKOH / g; Y3, the acidolysis product was subjected to polycondensation reaction under the vacuum degree of 0.096 MPa for 1h, the acid value reached 46-48 mgKOH / g, the hydroxyl value was less than 5 mgKOH / g, the temperature was reduced to 200℃, the modified montmorillonite, AT-215 and tetrabutylammonium bromide were added in proportion, the stirring was carried out at the speed of 300 rpm for 1.5 hours, finally, the product polyester resin particles were obtained after cooling, solidification and crushing.

[0043] The acid value of the polyester resin prepared in this example was 47.8 mgKOH / g, the hydroxyl value was 2.9 mgKOH / g, and the softening point was 113℃.

[0044] Comparative Example 1 The difference from Example 1 is that no modified montmorillonite is added in the preparation process of the polyester resin for weather-resistant powder coating.

[0045] Comparative Example 2 The difference from Example 1 is that an equal amount of montmorillonite (particle size ≤2.0 μm) is used to replace the modified montmorillonite in the preparation process of the polyester resin for weather-resistant powder coating.

[0046] Preparation Example 500g of the polyester resin prepared in Examples 1-3 and Comparative Examples 1-2 was mixed with 20g of TGIC, 125g of calcium carbonate, 5g of phthalocyanine blue, 7g of leveling agent 588, 2g of benzoin, and 1.5g of antioxidant 1010, respectively, and then fed into a twin-screw extruder. The screw speed of the twin-screw extruder was set at 200 r / min, and the temperatures of each zone were set to 80°C in Zone 1, 100°C in Zone 2, 120°C in Zone 3, and 140°C in Zone 4, allowing the materials to be fully melt-blended in the extruder. The extrudate was water-cooled and stretched into strands, then cut into uniform pellets using a pelletizer. The pellets were then pulverized in a pulverizer until the particle size reached 100 mesh. Finally, the extruder was screened using a vibrating screen to remove coarse particles and fine powder that did not meet the particle size requirements, thereby obtaining a powder coating.

[0047] The powder coatings prepared in Examples 1-3 and Comparative Examples 1-2 correspond to Preparation Examples 1-3 and Comparative Preparation Examples 1-2, respectively.

[0048] Performance testing: The powder coatings of Preparation Examples 1-5 were sprayed onto aluminum plates by electrostatic spraying, and cured in an oven at 200°C for 15 minutes. The samples were then taken out and the coating properties were tested after the samples cooled to room temperature. The test standards are as follows: (1) Accelerated aging test Test standard: GB / T 1865-2017.

[0049] Test method: artificial accelerated aging test was conducted using fluorescent ultraviolet lamp (UVA-340). Test conditions were: light intensity 0.55W / (m 2 ·nm) @340nm, blackboard temperature 60±3℃, condensation cycle 4h / illumination cycle 4h, circulation cycle 8h, test period is 2000 hours.

[0050] Evaluation indicators: record the gloss retention rate, chalking level (0-5), and cracking of the coating after aging.

[0051] Hydrolysis resistance test Test standard: GB / T 1733.1-1993.

[0052] Test method: Immerse the cured coating sample in boiling water (95±2℃) for 72 hours. After taking it out, cool it to room temperature and observe whether there is blistering, peeling or loss of gloss on the coating surface.

[0053] Evaluation indicators: water contact angle (°), coating gloss loss rate (%), adhesion grade (determined by the cross-cut method of GB / T 9286-1998).

[0054] (3) Acid and alkali resistance test Test standard: GB / T 9274-1988.

[0055] Test method: After curing, the coating sample was immersed in hydrochloric acid solution (pH = 2) and sodium hydroxide solution (pH = 12) respectively, the temperature was (23 ± 2) ℃, and the sample was taken out after 72 hours of immersion, washed with water and dried, and the surface change of the coating was observed.

[0056] Evaluation index: adhesion grade after acid and alkali immersion, color change ΔE value (determined by color difference meter).

[0057] (4) Adhesion test Test standard: GB / T 9286-1998 (crosshatch method) Test method: A knife was used to draw a vertical and horizontal grid on the surface of the coating with a spacing of 1 mm, and then the adhesive tape was quickly removed after being pasted, and the coating shedding was observed.

[0058] Evaluation index: adhesion grade (0-5 grade, 0 grade for no shedding).

[0059] (5) Hardness test Test standard: GB / T 6739-2006 Test method: The pencil hardness of the coating was determined by a pendulum hardness tester.

[0060] Evaluation index: pencil hardness (such as 2H, 3H, etc.).

[0061] The test data is shown in Table 7.

[0062] Table 7 From Table 7, it can be seen that: Accelerated aging performance: the gloss retention rate of the coatings of Examples 1-3 was all above 83%, the powdering grade was 1 grade and no cracking occurred; while the gloss retention rate of Comparative Examples 1 (without modified montmorillonite) and 2 (without modified montmorillonite) was 62% and 70% respectively, the powdering grade reached 3-4 grade, and slight cracking occurred. It shows that the introduction of modified montmorillonite significantly improves the ultraviolet aging resistance of the coating, and the "labyrinth" barrier structure effectively delays the degradation of the resin molecular chain.

[0063] Hydrolysis resistance: the water contact angle of Examples 1-3 was all above 91°, the gloss loss rate was less than 9%, and the adhesion grade was 0 grade (no shedding); the water contact angle of Comparative Examples 1-2 decreased to 58°-72°, the gloss loss rate reached 25%-35%, and the adhesion grade was 1 grade (slight shedding). It shows that the modified montmorillonite can inhibit the hydrolysis reaction of ester bond, and the unmodified montmorillonite has limited hydrolysis resistance due to insufficient dispersion and interfacial bonding force.

[0064] Acid and alkali resistance: After acid and alkali immersion, the adhesion of Examples 1-3 is still level 0, and the color difference ΔE is less than 1. The adhesion level of Comparative Examples 1-2 is reduced to level 1, and the color difference ΔE reaches 1.6-2.5, which proves that the modified montmorillonite enhances the resin's resistance to acid and alkali corrosion, and the chemical bonding between the silane coupling agent and the polyester on its surface effectively prevents the penetration of corrosive ions.

[0065] Basic mechanical properties: The adhesion grade of all samples is 0, and the pencil hardness is 2H, indicating that the addition of modified montmorillonite has no negative impact on the mechanical strength of the coating, and its uniform dispersion ensures the structural stability of the resin matrix.

[0066] In summary, the present invention, through the synergistic effect of hydroxyl-terminated cationic waterborne polyurethane intercalation and silane coupling agent-modified montmorillonite, constructs a dense "maze-like" barrier network within the polyester resin. Furthermore, chemical bonding enhances interfacial compatibility, significantly improving the resin's weathering, hydrolysis, and chemical corrosion resistance. Compared to unmodified montmorillonite or a blank sample, the polyester resin incorporating the modified montmorillonite exhibits superior long-term stability in harsh environments such as acid rain.

[0067] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A polyester resin for weather-resistant powder coating, characterized in that: The method comprises the following raw materials in the following mass percentages: 34-38% of polyol, 45-48% of polyacid, 0.1-0.5% of catalyst, 0.2-0.5% of additive, 8-10% of acidolysis agent, and 5-10% of modified montmorillonite; The modified montmorillonite is montmorillonite modified by terminal hydroxyl cationic waterborne polyurethane and γ-aminopropyltriethoxysilane, the terminal hydroxyl cationic waterborne polyurethane is intercalated between the montmorillonite layers, and the γ-aminopropyltriethoxysilane is coupled to the surface of the montmorillonite.

2. The weather-resistant polyester resin for powder coating according to claim 1, characterized in that: The mass ratio of the montmorillonite, the terminal hydroxyl cationic waterborne polyurethane and the gamma-aminopropyltriethoxysilane is 1: (0.5-1.2): (0.1-0.3).

3. The weather-resistant polyester resin for powder coating according to claim 1, characterized in that: The particle size of the modified montmorillonite is 0.5-2.0 μm.

4. The weather-resistant polyester resin for powder coating according to claim 1, characterized in that: The hydroxyl-terminated cationic waterborne polyurethane comprises the following raw materials in percentage by mass: 40-45% of polybutylene adipate diol 1000, 25-30% of isophorone diisocyanate, 5-10% of dimethylol propionic acid, 3-8% of ethylenediamine, 1-3% of triethylamine, 0.1-0.5% of dibutyltin dilaurate, and the balance is acetone.

5. The polyester resin for weather-resistant powder coating according to claim 4, characterized in that: The preparation steps of the hydroxyl-terminated cationic waterborne polyurethane include: S1, mixing polybutylene adipate diol 1000, isophorone diisocyanate, part of acetone and dibutyltin dilaurate, and then adding dimethylolpropionic acid to obtain a prepolymer containing free isocyanate groups; S2, adding triethylamine to obtain an ionic polyurethane prepolymer solution; S3. Add the remaining acetone, stir, add ethylenediamine dropwise, stir, remove the acetone, and dry to obtain a hydroxyl-terminated cationic waterborne polyurethane.

6. The polyester resin for weather-resistant powder coating according to claim 1, characterized in that: The polyols include neopentyl glycol, trimethylolpropane and 1,4-cyclohexanedimethanol.

7. The weather-resistant polyester resin for powder coating according to claim 1, characterized in that: The polyacid includes the following raw materials: terephthalic acid, isophthalic acid, adipic acid and trimellitic anhydride.

8. The weather-resistant polyester resin for powder coating according to claim 1, characterized in that: The catalyst is dibutyltin oxide.

9. The polyester resin for weather-resistant powder coating according to claim 1, characterized in that: The auxiliary agents are antioxidants and curing accelerators; Preferably, the antioxidant is AT-215, and the curing accelerator is tetrabutylammonium bromide.

10. The method for preparing a weather-resistant polyester resin for powder coating according to any one of claims 1 to 9, characterized in that: The following steps are involved: Y1. Mixing a polyol, a polyacid and a catalyst in proportion, and esterifying the mixture to obtain an esterified product; Y2, adding an acidolysis agent, reacting to obtain an acidolysis product; Y3. Vacuum polycondensation, adding additives and modified montmorillonite, stirring, and obtaining a polyester resin for weather-resistant powder coatings.

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