Tin-free weather-resistant hydroxyl polyester resin and preparation method thereof

Abstract

The invention discloses a tin-free weather-resistant hydroxyl polyester resin and a preparation method thereof, and belongs to the technical field of hydroxyl polyester resin, the preparation method comprises the following steps: firstly, carrying out acid pickling and calcining pretreatment on diatomite, then carrying out KH-550 silane coupling agent modification, cerium loading and behenic acid hydrophobic modification to obtain a cerium-loaded hydrophobic modified diatomite catalytic promoter, and finally, carrying out acid pickling and calcining treatment on the cerium-loaded hydrophobic modified diatomite catalytic promoter to obtain the tin-free weather-resistant hydroxyl polyester resin. Then taking polybasic acid and polyhydric alcohol as monomers, adding an ethylene glycol titanium catalyst and a hydrolysis-resistant catalytic promoter, and performing normal-pressure esterification and high-vacuum polycondensation reaction to prepare the tin-free weather-resistant hydroxyl polyester resin; on the basis of tin-free treatment, through synergistic catalysis of the ethylene glycol titanium catalyst and the cerium-loaded hydrophobic modified diatomite catalytic promoter and structural optimization of the rigid monomer, the technical problems that a traditional titanium catalyst is poor in low-temperature dispersity and prone to hydrolysis and deactivation in advance are effectively solved, the stability of a catalytic system and the processing performance of resin are improved, and the service life of the resin is prolonged. The weather-resistant polyester resin is suitable for weather-resistant polyester resin scenes for powder coatings such as high-end outdoor building materials and automobile hubs.

Description

Technical Field

[0001] This invention belongs to the field of hydroxyl polyester resin technology, specifically a tin-free weather-resistant hydroxyl polyester resin and its preparation method. Background Technology

[0002] Hydroxypolyester resin is the core film-forming resin for powder coatings. It is polymerized from polybasic acids and polyols through esterification and condensation reactions. Due to its excellent mechanical properties, decorative properties, and chemical resistance, this type of resin is widely used in high-end home appliances, automobile wheels, outdoor building materials, and other fields. In the industrial synthesis process, the catalyst is the core raw material that controls the reaction rate and ensures the stability of key indicators such as resin molecular weight, viscosity, and acid value. It directly determines the resin's production efficiency, product performance, and environmental compliance. In traditional industrial production, organotin catalysts are often used. Although they have high catalytic activity and good process adaptability, organotin is toxic and bioaccumulative, which does not comply with the EU REACH regulations, China's green product certification, and other environmental requirements. It is also prone to causing high-temperature yellowing and a decrease in weather resistance of the resin, which cannot meet the needs of high-end export products.

[0003] Chinese patent application CN115572376A discloses a high-gloss polyester resin for powder coatings and its preparation method. It uses tetrabutyl titanate as a polymerization catalyst to replace the traditional organotin catalyst, realizing the tin-free and environmentally friendly production of polyester resin. At the same time, it improves the gloss and storage stability of the resin and solves the problems of toxicity and non-compliance with environmental protection requirements of traditional tin-containing catalysts.

[0004] However, the tetrabutyl titanate catalyst used in this scheme has poor hydrolysis resistance. During the esterification stage, it is easily deactivated by hydrolysis due to trace amounts of water in the system, leading to catalytic activity decay, loss of control of the polymerization process, uneven molecular weight distribution of resin, poor batch consistency of products, and insufficient stability of the production process. At the same time, the by-products generated by the hydrolysis of this catalyst will also degrade the color and weather resistance of the resin, making it unable to meet the requirements for long-term outdoor use and difficult to adapt to harsh scenarios such as high-end outdoor building materials and automobile wheels. It is impossible to achieve a synergistic improvement in environmental protection, weather resistance and production stability. Summary of the Invention

[0005] The purpose of this invention is to provide a tin-free weather-resistant hydroxyl polyester resin and its preparation method. Through the synergistic catalysis of titanium glycol catalyst and cerium-supported hydrophobically modified diatomaceous earth catalyst, combined with the structural optimization design of rigid monomer, the technical problems of poor low-temperature dispersibility and easy premature hydrolysis and deactivation of traditional titanium catalysts are effectively improved, ensuring the stability of the catalytic system, improving the resin processing performance and batch consistency, and meeting the requirements of high-end outdoor building materials, automobile wheels and other scenarios for the stability of polyester resin production.

[0006] The objective of this invention can be achieved through the following technical solutions: A tin-free weather-resistant hydroxyl polyester resin, comprising, by weight, the following raw materials: 110-130 parts terephthalic acid, 30-40 parts biphenyl phthalic acid, 15-25 parts isophthalic acid, 80-90 parts neopentyl glycol, 25-35 parts ethylene glycol, 1-1.4 parts titanium glycol catalyst, 0.8-1.2 parts cerium-supported hydrophobically modified diatomaceous earth catalyst, 0.4-0.6 parts antioxidant 1010 and 0.4-0.6 parts antioxidant 168.

[0007] This invention also provides a method for preparing a tin-free weather-resistant hydroxyl polyester resin, comprising the following steps: Step 1: Diatomaceous earth powder is successively modified with KH-550 silane coupling agent, cerium loading, and behenic acid hydrophobic modification to obtain cerium-loaded hydrophobic modified diatomaceous earth catalyst.

[0008] Step 2: Using terephthalic acid, biphenyl phthalic acid, and isophthalic acid as polyacid monomers, and neopentyl glycol and ethylene glycol as polyol monomers, titanium glycol catalyst and cerium-supported hydrophobically modified diatomaceous earth catalyst are added. The reaction is carried out under normal pressure esterification and high vacuum polycondensation. After the reaction is completed, antioxidant 1010 and antioxidant 168 are added. After mixing and granulation, tin-free weather-resistant hydroxyl polyester resin is obtained.

[0009] Furthermore, the pre-dispersion temperature is 25-40℃, and the rotation speed is 150-250 r / min.

[0010] Furthermore, the esterification temperature under normal pressure is 180-220℃.

[0011] Furthermore, the high-vacuum polycondensation reaction is carried out at a temperature of 240-250°C and evacuated to a vacuum level of <100Pa.

[0012] Furthermore, the specific preparation steps of the cerium-supported hydrophobically modified diatomaceous earth catalyst are as follows: Cerium-supported silane-modified diatomaceous earth powder and behenic acid anhydrous ethanol solution were added to a reaction vessel and ultrasonically dispersed for 10-20 min. The pH of the system was adjusted to 5-6 using 5wt% dilute acetic acid solution. The mixture was stirred at 70-75℃ and 250-350 r / min for 3.5-4.5 h. After the reaction was completed, the mixture was centrifuged, washed, dried, ground, and passed through a 200-mesh standard sieve to obtain cerium-supported hydrophobic modified diatomaceous earth catalyst.

[0013] Furthermore, the ratio of cerium-supported silane-modified diatomaceous earth powder to behenic acid anhydrous ethanol solution is 4-6:22-26.

[0014] Furthermore, the behenic acid anhydrous ethanol solution is prepared by behenic acid and anhydrous ethanol in a mass ratio of 0.8-1.2:21-25.

[0015] Furthermore, the specific preparation steps of cerium-supported silane-modified diatomaceous earth powder are as follows: Anhydrous ethanol and ethylene glycol were added to a reaction vessel and mixed thoroughly at 20-30℃ and 250-350 r / min. Cerium nitrate hexahydrate was added to the vessel and stirred until dissolved under the same conditions. Then, silane-modified diatomaceous earth powder was added and stirred for another 0.5-1.5 h under the same conditions. The reaction vessel was sealed and the temperature was increased to 175-185℃ at 5℃ / min. The reaction was maintained at this temperature for 11-13 h. After the reaction was completed, the mixture was cooled to room temperature, discharged, washed, and dried to obtain cerium-supported silane-modified diatomaceous earth powder.

[0016] Furthermore, the ratio of anhydrous ethanol, ethylene glycol, cerium nitrate hexahydrate, and silane-modified diatomaceous earth powder is 60-70 mL: 30-35 mL: 0.5-0.7 g: 4-6 g.

[0017] Furthermore, the silane-modified diatomaceous earth powder is obtained by modifying diatomaceous earth powder with the silane coupling agent KH-550.

[0018] The beneficial effects of this invention are: 1. This invention completely abandons traditional toxic organotin catalysts and adopts a synergistic catalytic system of ethylene glycol titanium catalyst and cerium-supported hydrophobically modified diatomaceous earth catalyst. Combined with the structural optimization design of rigid monomers, it effectively improves the technical problem of insufficient hydrolysis resistance of traditional titanium catalysts. To a certain extent, it avoids the phenomena of catalytic activity decay and uneven resin molecular weight distribution caused by catalyst hydrolysis and deactivation, which helps to improve the catalytic stability of the system. It achieves synergistic optimization of environmental protection, catalytic stability and processing performance, and can meet the usage requirements of high-end outdoor building materials, automobile wheels and other scenarios for the stability of polyester resin production.

[0019] 2. In the synergistic catalytic system constructed in this invention, titanium glycol catalyst is the core catalytic component, ensuring the efficient conduct of esterification and polycondensation reactions; the cerium-supported hydrophobically modified diatomaceous earth catalyst promoter plays a synergistic role in multiple aspects: Firstly, diatomaceous earth modified with KH-550 silane coupling agent introduces siloxane groups and amino active groups, which can bond with the carboxyl and hydroxyl groups of polyester monomers, enhancing the interfacial bonding force with the resin matrix, improving component compatibility, and helping to optimize molecular chain regularity and improve resin processing performance. Secondly, the pre-removal of some hydrophilic groups on the surface reduces the adverse effects of moisture in the system on subsequent reactions. At the same time, its porous high specific surface area structure can act as a dispersion carrier to anchor the titanium glycol catalyst. Combined with the modified groups, it reduces the difficulty of dispersion, allowing the catalyst to be rapidly and uniformly dispersed in the system under low-temperature conditions under nitrogen protection without the need for heating to promote dispersion. This avoids premature hydrolysis of the catalyst caused by heating from the source, ensuring stable release of catalytic activity.

[0020] Secondly, the rare earth cerium component supported by the additive can form a synergistic catalytic effect with the titanium glycol catalyst. With its Lewis acidity and strong coordination ability, the cerium ion can help activate the carboxyl group of polybasic acid monomer and the hydroxyl group of polyol monomer, promoting the efficient esterification and polycondensation reaction. On the other hand, its strong coordination ability can stabilize the active center of the catalyst, effectively inhibit the aggregation and deactivation of the titanium catalyst, and further ensure the stability of the catalytic system.

[0021] Third, the bio-based long-chain alkyl groups modified and grafted with behenic acid have excellent compatibility with polyester molecular chains, which can reduce melt friction resistance, further improve component dispersibility, and avoid agglomeration and precipitation. At the same time, the long-chain alkyl groups can form a flexible isolation layer around the catalyst, which helps to strengthen the anchoring effect of the support on the catalyst, ensure the stability of the low-temperature dispersion state, and help the catalyst activity to be released steadily.

[0022] 3. This invention employs polybasic acid monomers composed of terephthalic acid, biphenyl acid, and isophthalic acid, and polyol monomers composed of neopentyl glycol and ethylene glycol. Combined with a nitrogen-protected, atmospheric pressure esterification-high vacuum polycondensation process, the structure and molecular weight distribution of polyester molecular chains can be effectively controlled. In addition, the introduction of the rigid biphenyl acid monomer enhances the rigidity of the molecular chain, reduces melt viscosity, and optimizes leveling. With the temperature and vacuum control of the process stages, the monomers are fully esterified and polycondensed, reducing by-product residues. Finally, a tin-free, weather-resistant hydroxyl polyester resin with uniform molecular weight distribution and excellent processing performance is obtained, taking into account both batch consistency and production stability. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1: A tin-free weather-resistant hydroxyl polyester resin, prepared by the following steps: S1: Place 10g of raw diatomaceous earth in a muffle furnace, heat it to 380℃ at 2℃ / min, keep it at that temperature for 1.5h, cool it down and add 21mL of 10% hydrochloric acid solution. Stir vigorously for 4h at 70℃ and 300r / min. After standing, wash it with deionized water until neutral, dry it at 80℃ for 12h, grind it and pass it through a 200-mesh standard sieve to obtain diatomaceous earth powder.

[0025] 0.6 g of silane coupling agent KH-550 was dissolved in 5 g of anhydrous ethanol to obtain a silane coupling agent KH-550 solution. 6 g of diatomaceous earth powder, 150 g of deionized water, and 150 g of anhydrous ethanol were added to a reaction vessel and dispersed for 30 min at a speed of 800 r / min. The pH of the system was adjusted to 4.2 by adding glacial acetic acid dropwise. 5 g of the silane coupling agent KH-550 solution was slowly added dropwise to the vessel. The reaction was carried out under magnetic stirring at a temperature of 60℃ and a speed of 300 r / min for 4 h. After the reaction was completed, the precipitate was collected by filtration, washed three times with deionized water, and finally dried at 105℃ for 3 h to obtain silane-modified diatomaceous earth powder.

[0026] The diatomaceous earth powder obtained by acid washing and calcination pretreatment is a white or off-white loose powder with no obvious agglomeration. The average particle size is 10-50 μm, retaining the natural porous framework and sufficient silanol activity. Through hydrolysis-condensation reaction, under acid catalysis and heating conditions, the pre-hydrolyzed KH-550 undergoes a condensation reaction with the fully exposed silanol on the surface of the diatomaceous earth powder to form stable Si-O-Si covalent bonds, introducing amino functional groups on the surface of the diatomaceous earth.

[0027] S2: Add 67 mL of anhydrous ethanol and 33 mL of ethylene glycol to the reactor and mix them thoroughly at 25 °C and 300 r / min. Add 0.6 g of cerium nitrate hexahydrate to the reactor and stir until dissolved under the same conditions. Then add 5 g of silane-modified diatomaceous earth powder and continue stirring for 1 h under the same conditions. Seal the reactor and heat it to 180 °C at 5 °C / min. Keep the temperature for 12 h. After the reaction is completed, let the reactor cool to room temperature, discharge the material, and wash it three times repeatedly with deionized water and anhydrous ethanol under ultrasonic assistance. Finally, dry it at 60 °C for 12 h to obtain cerium-supported silane-modified diatomaceous earth powder.

[0028] A solvothermal method was adopted, using anhydrous ethanol and ethylene glycol as mixed solvents, with amino groups on the surface of KH-550 modified diatomaceous earth as coordination sites and cerium ions in cerium nitrate hexahydrate as active components. The two undergo a coordination reaction, and finally, cerium-loaded silane-modified diatomaceous earth powder with uniform cerium component dispersion, strong bonding and retention of porous framework is obtained.

[0029] S3: Add 1g of behenic acid to 23g of anhydrous ethanol, heat and stir until dissolved to obtain behenic acid ethanol solution; add 5g of cerium-supported silane-modified diatomaceous earth powder and 24g of behenic acid anhydrous ethanol solution to the reaction vessel, ultrasonically disperse for 15min to form a uniform suspension, adjust the pH of the system to 5.5 with 5wt% dilute acetic acid solution, stir and react for 4h at 72℃ and 300r / min. After the reaction, centrifuge and wash the mixture with anhydrous ethanol, collect the precipitate, dry at 100℃ for 10h, grind and pass through a 200-mesh standard sieve to finally obtain cerium-supported hydrophobic modified diatomaceous earth catalyst.

[0030] A liquid-phase surface modification method was adopted, using behenic acid as a hydrophobic modifier. The carboxyl groups of behenic acid were anchored to the surface of cerium-supported diatomite through physical adsorption, salt formation / coordination and other interactions. Its long-chain alkyl groups were arranged outward to form a hydrophobic layer, thereby preparing a cerium-supported hydrophobic modified diatomite catalyst.

[0031] S4: Add 120g terephthalic acid, 35g biphenyl phthalic acid, 20g isophthalic acid, 85g neopentyl glycol, 30g ethylene glycol, 1.2g titanium glycol catalyst, and 1g cerium-supported hydrophobic modified diatomaceous earth catalyst to the reactor. Purge with nitrogen for protection throughout the process. Mix thoroughly at 35℃ and 200r / min to achieve low-temperature pre-dispersion of the titanium glycol catalyst under the support of the cerium-based diatomaceous earth catalyst, preventing premature hydrolysis of the catalyst due to temperature rise. Increase the temperature to 200℃ at 3℃ / min for atmospheric pressure esterification reaction. Collect the distillate water and maintain the temperature until the water output reaches more than 95% of the theoretical output, completing the esterification stage.

[0032] The temperature was then gradually increased to 245℃, while a vacuum was slowly drawn until the vacuum level was <100Pa to carry out the polycondensation reaction. The reaction was maintained at a speed of 150r / min, and the viscosity of the system was monitored in real time. When the viscosity of the system reached 3000Pa·s at 200℃, the vacuum was stopped and nitrogen was introduced to break the vacuum. The system was then cooled to 190℃, and 0.5g of antioxidant 1010 and 0.5g of antioxidant 168 were added. The mixture was stirred and mixed for 20min until completely dissolved. Finally, the molten resin was discharged through a water-cooled belt granulator. After cooling, it was crushed into particles with a particle size of <5mm to obtain tin-free weather-resistant hydroxyl polyester resin.

[0033] This step uses terephthalic acid, biphenyl phthalic acid, and isophthalic acid as polyacid monomers, neopentyl glycol and ethylene glycol as polyol monomers, and titanium glycol as the main catalyst and cerium-supported hydrophobically modified diatomaceous earth as a synergistic catalyst component. After feeding, the materials are first pre-dispersed under low temperature and nitrogen protection to ensure that the titanium glycol is uniformly dispersed under the action of the synergist carrier, thus avoiding hydrolysis and deactivation of the catalyst due to premature heating. Subsequently, esterification under normal pressure and high vacuum polycondensation reaction are carried out to prepare tin-free hydroxyl polyester resin.

[0034] Example 2: A tin-free weather-resistant hydroxyl polyester resin, prepared by the following steps: S1: Place 8g of raw diatomaceous earth in a muffle furnace, heat it to 350℃ at 2℃ / min, keep it at that temperature for 1h, cool it down and add 18mL of 10% hydrochloric acid solution. Stir vigorously for 3.5h at 65℃ and 250r / min. After standing, wash it with deionized water until neutral, dry it at 80℃ for 12h, grind it and pass it through a 200-mesh standard sieve to obtain diatomaceous earth powder.

[0035] 0.5g of silane coupling agent KH-550 was dissolved in 4g of anhydrous ethanol to obtain a silane coupling agent KH-550 solution. 5g of diatomaceous earth powder, 140g of deionized water, and 140g of anhydrous ethanol were added to a reaction vessel and dispersed for 25min at a speed of 700r / min. The pH of the system was adjusted to 4.0 by adding glacial acetic acid dropwise. 4g of the silane coupling agent KH-550 solution was slowly added dropwise to the vessel. The reaction was carried out under magnetic stirring at a temperature of 55℃ and a speed of 250r / min for 3.5h. After the reaction was completed, the precipitate was collected by filtration, washed three times with deionized water, and finally dried at 105℃ for 3h to obtain silane-modified diatomaceous earth powder.

[0036] S2: Add 60 mL of anhydrous ethanol and 30 mL of ethylene glycol to the reactor and mix them thoroughly at 20 °C and 250 r / min. Add 0.5 g of cerium nitrate hexahydrate to the reactor and stir until dissolved under the same conditions. Then add 6 g of silane-modified diatomaceous earth powder and continue stirring for 0.5 h under the same conditions. Seal the reactor and heat it to 175 °C at 5 °C / min. Keep the temperature for 11 h. After the reaction is complete, let the reactor cool to room temperature, discharge the material, and wash it three times repeatedly with deionized water and anhydrous ethanol under ultrasonic assistance. Finally, dry it at 60 °C for 12 h to obtain cerium-supported silane-modified diatomaceous earth powder.

[0037] S3: Add 0.8g of behenic acid to 21g of anhydrous ethanol, heat and stir until dissolved to obtain behenic acid ethanol solution; add 4g of cerium-supported silane-modified diatomaceous earth powder and 22g of behenic acid anhydrous ethanol solution to the reaction vessel, ultrasonically disperse for 10min to form a uniform suspension, adjust the pH of the system to 5 with 5wt% dilute acetic acid solution, stir and react for 3.5h at 70℃ and 250r / min. After the reaction, centrifuge and wash the mixture with anhydrous ethanol, collect the precipitate, dry at 100℃ for 10h, grind and pass through a 200-mesh standard sieve to finally obtain cerium-supported hydrophobic modified diatomaceous earth catalyst.

[0038] S4: Add 110g terephthalic acid, 30g biphenyl phthalic acid, 15g isophthalic acid, 80g neopentyl glycol, 25g ethylene glycol, 1g titanium glycol catalyst, and 0.8g cerium-supported hydrophobically modified diatomaceous earth catalyst to the reactor. Purge with nitrogen for protection throughout the process. Mix evenly at 25℃ and 150r / min to achieve low-temperature pre-dispersion of the titanium glycol catalyst under the support of the cerium-based diatomaceous earth catalyst, avoiding premature hydrolysis of the catalyst due to temperature rise. Increase the temperature to 180℃ at 3℃ / min for atmospheric pressure esterification reaction. Collect the distillate water and keep the reaction at the temperature until the water output reaches more than 95% of the theoretical output, completing the esterification stage.

[0039] The temperature was then gradually increased to 240℃, while a vacuum was slowly drawn until the vacuum level was <100Pa to carry out the polycondensation reaction. The reaction was maintained at a speed of 130r / min, and the viscosity of the system was monitored in real time. When the viscosity of the system reached 2800Pa·s at 200℃, the vacuum was stopped and nitrogen was introduced to break the vacuum. The system was then cooled to 185℃, and 0.4g of antioxidant 1010 and 0.4g of antioxidant 168 were added. The mixture was stirred and mixed for 15min until completely dissolved. Finally, the molten resin was discharged through a water-cooled belt granulator. After cooling, it was crushed into particles with a particle size of <5mm to obtain tin-free weather-resistant hydroxyl polyester resin.

[0040] Example 3: A tin-free weather-resistant hydroxyl polyester resin, prepared by the following steps: S1: Place 12g of raw diatomaceous earth in a muffle furnace, heat it to 400℃ at 2℃ / min, keep it at that temperature for 2h, cool it down and add 24mL of 10% hydrochloric acid solution. Stir vigorously for 4.5h at 75℃ and 350r / min. After standing, wash it with deionized water until neutral, dry it at 80℃ for 12h, grind it and pass it through a 200-mesh standard sieve to obtain diatomaceous earth powder.

[0041] 0.7g of silane coupling agent KH-550 was dissolved in 6g of anhydrous ethanol to obtain a silane coupling agent KH-550 solution. 7g of diatomaceous earth powder, 160g of deionized water, and 160g of anhydrous ethanol were added to a reaction vessel and dispersed for 35min at a speed of 900r / min. The pH of the system was adjusted to 4.5 by adding glacial acetic acid dropwise. 6g of the silane coupling agent KH-550 solution was slowly added dropwise to the vessel. The reaction was carried out under magnetic stirring at a temperature of 65℃ and a speed of 350r / min for 4.5h. After the reaction was completed, the precipitate was collected by filtration, washed three times with deionized water, and finally dried at 105℃ for 3h to obtain silane-modified diatomaceous earth powder.

[0042] S2: Add 70 mL of anhydrous ethanol and 35 mL of ethylene glycol to the reactor and mix them thoroughly at 30 °C and 350 r / min. Add 0.7 g of cerium nitrate hexahydrate to the reactor and stir until dissolved under the same conditions. Then add 6 g of silane-modified diatomaceous earth powder and continue stirring for 1.5 h under the same conditions. Seal the reactor and raise the temperature to 185 °C at 5 °C / min. Maintain the temperature for 13 h. After the reaction is completed, let the reactor cool to room temperature, discharge the material, and wash it three times repeatedly with deionized water and anhydrous ethanol under ultrasonic assistance. Finally, dry it at 60 °C for 12 h to obtain cerium-supported silane-modified diatomaceous earth powder.

[0043] S3: Add 1.2g of behenic acid to 25g of anhydrous ethanol, heat and stir until dissolved to obtain behenic acid ethanol solution; add 6g of cerium-supported silane-modified diatomaceous earth powder and 26g of behenic acid anhydrous ethanol solution to the reaction vessel, ultrasonically disperse for 20min to form a uniform suspension, adjust the pH of the system to 6 with 5wt% dilute acetic acid solution, stir and react for 4.5h at 75℃ and 350r / min. After the reaction, centrifuge and wash the mixture with anhydrous ethanol, collect the precipitate, dry at 100℃ for 10h, grind and pass through a 200-mesh standard sieve to finally obtain cerium-supported hydrophobic modified diatomaceous earth catalyst.

[0044] S4: Add 130g terephthalic acid, 40g biphenyl phthalic acid, 25g isophthalic acid, 90g neopentyl glycol, 35g ethylene glycol, 1.4g titanium glycol catalyst, and 1.2g cerium-supported hydrophobic modified diatomaceous earth catalyst to the reactor. Probe nitrogen gas throughout the process and mix thoroughly at 40℃ and 250r / min. This allows the titanium glycol catalyst to achieve low-temperature pre-dispersion under the support of the cerium-based diatomaceous earth catalyst, preventing premature hydrolysis due to temperature increases. Increase the temperature to 220℃ at 3℃ / min for atmospheric pressure esterification. Collect the distillate water and maintain the temperature until the water output reaches more than 95% of the theoretical output, completing the esterification stage.

[0045] The temperature was then gradually increased to 250℃, while a vacuum was slowly drawn until the vacuum level was <100Pa to carry out the polycondensation reaction. The reaction was maintained at a speed of 170r / min, and the viscosity of the system was monitored in real time. When the viscosity of the system reached 3500Pa·s at 200℃, the vacuum was stopped and nitrogen was introduced to break the vacuum. The system was then cooled to 195℃, and 0.6g of antioxidant 1010 and 0.6g of antioxidant 168 were added. The mixture was stirred and mixed for 25min until completely dissolved. Finally, the molten resin was discharged through a water-cooled belt granulator. After cooling, it was crushed into particles with a particle size of <5mm to obtain tin-free weather-resistant hydroxyl polyester resin.

[0046] The raw materials used in Examples 1-3 of this application are all commercially available. Among them, terephthalic acid (purity 99%), biphenyl phthalic acid (purity 99.5%), isophthalic acid (purity 99%, reagent grade) and neopentyl glycol (purity 99%) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; diatomaceous earth (active ingredient content 99%, industrial grade) was purchased from Hubei Xinjiecheng Chemical Technology Co., Ltd.; cerium nitrate hexahydrate (purity ≥99.5%), behenic acid (purity ≥85%, industrial grade) and ethylene glycol (purity ≥99%) were purchased from Shanghai Aladdin Biochemical Co., Ltd.; titanium glycol catalyst and antioxidant 168 were purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.; antioxidant 1010 was purchased from Guangzhou Dayin New Material Co., Ltd.

[0047] Comparative Example 1: Based on Example 1, steps S1, S2, and S3 for preparing the cerium-supported hydrophobic modified diatomaceous earth catalyst were omitted. In step S4, the titanium glycol catalyst was replaced with an equal amount of tetrabutyl titanate. All other steps and parameters remained unchanged, resulting in a tin-free weather-resistant hydroxyl polyester resin.

[0048] Comparative Example 2: Based on Example 1, steps S1, S2, and S3 for preparing the cerium-supported hydrophobic modified diatomite catalyst were omitted. In step S4, only titanium glycol catalyst was added, while all other steps and parameters remained unchanged, resulting in a tin-free weather-resistant hydroxyl polyester resin.

[0049] Comparative Example 3: Based on Example 1, steps S2 and S3 for cerium loading and hydrophobic modification of diatomite were omitted. In step S4, the silane-modified diatomite powder obtained in step S1 was used to replace the cerium-loaded hydrophobic modified diatomite catalyst. All other steps and parameters remained unchanged, resulting in a tin-free weather-resistant hydroxyl polyester resin.

[0050] Comparative Example 4: Based on Example 1, the hydrophobic modification of cerium-supported diatomaceous earth in step S3 was omitted. In step S4, the cerium-supported silane-modified diatomaceous earth powder obtained in step S2 was used to replace the cerium-supported hydrophobic modified diatomaceous earth catalyst. All other steps and parameters remained unchanged, and a tin-free weather-resistant hydroxyl polyester resin was obtained.

[0051] The performance of the tin-free weather-resistant hydroxyl polyester resins prepared in Examples 1-3 and Comparative Examples 1-4 was tested. The appearance was tested by visual inspection, observing the color and state of the resin particles. The whiter and purer the resin appearance, the higher the purity of the resin and the better the processing stability, which can effectively avoid defects such as impurities and yellowing in the coating.

[0052] The tin content is tested using the ICP-MS method to detect the tin metal content in the resin. The lower the tin content, the better the environmental performance of the resin, meeting the environmental protection requirements of no heavy metal residue, and making it suitable for high-end environmentally friendly powder coating systems.

[0053] The acid value test was conducted in accordance with the GB / T 27808-2011 standard. The end carboxyl group content of the resin was determined by titration, and the unit was mgKOH / g. The acid value directly reflects the end hydroxyl content and crosslinking activity of the resin. A suitable acid value (28-35 mgKOH / g) can ensure the balance between the crosslinking density and leveling of the coating.

[0054] The glass transition temperature (Tg) test was conducted in accordance with the GB / T 19466.2-2004 standard. The glass transition temperature (Tg) of the resin was determined by differential scanning calorimetry (DSC), and the unit is ℃. The more stable the Tg value, the better the anti-caking performance of the resin, which can ensure the extrusion processing effect and storage stability of the powder coating.

[0055] Viscosity testing was conducted in accordance with GB / T 9751.1-2008 standard. The viscosity of the resin melt was measured using a rotational viscometer at 200℃, with the unit being Pa·s. Controlling the viscosity between 2500-3500 Pa·s ensures that the powder coating has suitable leveling properties, while also considering the coating gloss and application performance.

[0056] The tin-free weather-resistant hydroxyl polyester resins prepared in Examples 1-3 and Comparative Examples 1-4 were used to prepare test coatings. The specific steps are as follows: Take 70g of the tin-free weather-resistant hydroxyl polyester resin prepared in the examples / comparative examples, 4.5g of TGIC curing agent (Huangshan Youyi Nanhai New Material Co., Ltd., white powder, average particle size D50: 8-10μm), and 0.8g of acrylate leveling agent (Zhanxin Resin, Modaflow). ® 9200), 0.2g of silicone leveling agent BYK-333, 0.3g of brightener polyethylene wax (BASF Luwax OA2, average particle size D50: 6μm) and 25g of powder coating-specific rutile titanium dioxide (Shanghai Yuanjiang Chemical Co., Ltd., R216) were mixed evenly at high speed and then fed into a twin-screw extruder. The mixture was melt-extruded at 100℃, cooled and pulverized, and passed through a 200-mesh sieve to obtain a powder coating. The powder coating was electrostatically sprayed onto a phosphated cold-rolled steel plate and cured at 200℃ for 15 minutes to obtain a test coating with a thickness of 60-80μm.

[0057] The coatings prepared in each embodiment and comparative example were subjected to performance tests. The gloss test was conducted in accordance with the GB / T 9754-2007 standard. The gloss of the coating was measured using a 60° gloss meter, and the unit is %. The higher the gloss, the better the mirror effect of the coating, which can meet the appearance requirements of high-end high-gloss powder coatings.

[0058] Weather resistance testing was conducted in accordance with GB / T 14522-2008 standard. The cured coating was subjected to a 1000-hour accelerated aging test using a QUV ultraviolet aging test chamber. The color difference value ΔE and gloss retention rate were measured. The smaller the ΔE value and the higher the gloss retention rate, the better the weather resistance performance of the coating, which can meet the weather resistance requirements for long-term outdoor use.

[0059] The results are shown in Table 1: Table 1 Performance test results of various hydroxyl polyester resins and coatings As shown in Table 1, the tin-free weather-resistant hydroxyl polyester resins prepared in Examples 1-3 of this invention, through the introduction of cerium-supported hydrophobically modified diatomaceous earth catalyst and titanium glycol synergistic catalytic system, have achieved optimization of key properties such as appearance, acid value, glass transition temperature, melt viscosity, gloss and weather resistance. This system effectively improves the weather resistance and catalytic efficiency while ensuring the processing stability and application performance of the resin, thus achieving synergistic optimization of environmental protection and performance.

[0060] Comparative Example 1 omitted the preparation of the cerium-supported hydrophobically modified diatomaceous earth catalyst and replaced the titanium glycolate catalyst with an equal amount of tetrabutyl titanate. The results in the table show that the resin's appearance was slightly yellow, and its gloss and weather resistance were inferior to those of Example 1. This may be because tetrabutyl titanate has poor hydrolysis resistance and is easily deactivated by the hydrolysis of trace amounts of water in the system during the esterification stage, which can easily cause the resin to yellow. In addition, the lack of the weather-enhancing effect of the cerium-based additive led to a significant decrease in the resin's UV aging resistance. This result indicates that the synergistic system of titanium glycolate and cerium-supported hydrophobically modified diatomaceous earth catalyst is a necessary condition for this resin to achieve high gloss, high weather resistance, and stable color.

[0061] Comparative Example 2 omitted the preparation of the cerium-supported hydrophobically modified diatomaceous earth catalyst and only added titanium glycol catalyst. The results showed that its key properties, such as weather resistance, were inferior to those of Example 1. This may be due to the lack of the weather-enhancing effect of the cerium-based diatomaceous earth catalyst and the absence of the auxiliary stabilizing effect of the hydrophobic structure of the catalyst on the reaction system. Although titanium glycol itself has a certain degree of stability, it may be difficult to completely avoid the slight influence of trace moisture or other factors on the reaction process during resin synthesis and subsequent applications. This may lead to a slight deficiency in the regularity of the resin molecular chain, ultimately preventing further improvement in the resin's UV aging resistance. These results indicate that the introduction of the cerium-supported hydrophobically modified diatomaceous earth catalyst has a positive significance in assisting to improve the stability of the catalytic system and the weather resistance of the resin.

[0062] Comparative Example 3 omitted the cerium loading and hydrophobic modification of diatomaceous earth, and only used silane-modified diatomaceous earth powder to replace the cerium-loaded hydrophobic modified diatomaceous earth catalyst. The performance test results showed that its gloss and weather resistance were significantly reduced. This was attributed to the absence of the cerium active component and the hydrophobic modification layer, which prevented the cerium from exerting its ultraviolet shielding and hydrophobic protection effects, resulting in limited improvement in the resin's weather resistance. This result strongly confirms that cerium loading and hydrophobic modification are the core structures for cerium-based diatomaceous earth additives to exert their weather resistance enhancement effect, and are beneficial components for obtaining high weather-resistant tin-free hydroxyl polyester resins.

[0063] Comparative Example 4 omitted the hydrophobic modification of cerium-supported diatomaceous earth and replaced the cerium-supported hydrophobic modified diatomaceous earth catalyst with cerium-supported silane-modified diatomaceous earth powder. The results showed that its weather resistance was slightly lower than that of Example 1. This may be due to the lack of protection from the behenic acid hydrophobic layer. The cerium active component is easily deactivated by water erosion and cannot continue to play a weather-enhancing role. This result shows that the hydrophobic modification layer is an important structure to ensure the long-term effect of cerium-based additives and improve the weather resistance stability of resin.

[0064] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A tin-free, weather-resistant hydroxyl polyester resin, characterized in that, By weight, it includes the following raw materials: 110-130 parts of terephthalic acid; 30-40 parts of biphenyl dicarboxylic acid; 15-25 parts of isophthalic acid; 80-90 parts of neopentyl glycol; 25-35 parts of ethylene glycol; 1-1.4 parts of titanium glycol catalyst; 0.8-1.2 parts of cerium-supported hydrophobically modified diatomaceous earth catalyst; Antioxidant 1010: 0.4-0.6 parts; Antioxidant 168, 0.4-0.6 parts; The cerium-supported hydrophobically modified diatomite catalyst was prepared by sequentially loading cerium and hydrophobically modifying behenic acid onto silane-modified diatomite powder.

2. The method for preparing a tin-free weather-resistant hydroxyl polyester resin according to claim 1, characterized in that, The specific preparation steps of the cerium-supported hydrophobic modified diatomite catalyst are as follows: Cerium-supported silane-modified diatomaceous earth powder and behenic acid anhydrous ethanol solution were added to a reaction vessel and ultrasonically dispersed for 10-20 min. The pH of the system was adjusted to 5-6 using 5wt% dilute acetic acid solution. The mixture was stirred at 70-75℃ and 250-350 r / min for 3.5-4.5 h. After the reaction was completed, the mixture was centrifuged, washed, dried, ground, and passed through a 200-mesh standard sieve to obtain cerium-supported hydrophobic modified diatomaceous earth catalyst.

3. The method for preparing a tin-free weather-resistant hydroxyl polyester resin according to claim 2, characterized in that, The ratio of cerium-supported silane-modified diatomaceous earth powder to behenic acid anhydrous ethanol solution is 4-6:22-26.

4. The method for preparing a tin-free weather-resistant hydroxyl polyester resin according to claim 2, characterized in that, The behenic acid anhydrous ethanol solution is prepared by behenic acid and anhydrous ethanol in a mass ratio of 0.8-1.2:21-25.

5. The method for preparing a tin-free weather-resistant hydroxyl polyester resin according to claim 2, characterized in that, The specific preparation steps of the cerium-supported silane-modified diatomaceous earth powder are as follows: Anhydrous ethanol and ethylene glycol were added to a reaction vessel and mixed thoroughly at 20-30℃ and 250-350 r / min. Cerium nitrate hexahydrate was added to the vessel and stirred until dissolved under the same conditions. Then, silane-modified diatomaceous earth powder was added and stirred for another 0.5-1.5 h under the same conditions. The reaction vessel was sealed and the temperature was increased to 175-185℃ at 5℃ / min. The reaction was maintained at this temperature for 11-13 h. After the reaction was completed, the mixture was cooled to room temperature, discharged, washed, and dried to obtain cerium-supported silane-modified diatomaceous earth powder.

6. The method for preparing a tin-free weather-resistant hydroxyl polyester resin according to claim 5, characterized in that, The ratio of anhydrous ethanol, ethylene glycol, cerium nitrate hexahydrate, and silane-modified diatomaceous earth powder is 60-70 mL: 30-35 mL: 0.5-0.7 g: 4-6 g.

7. The method for preparing a tin-free weather-resistant hydroxyl polyester resin according to claim 5, characterized in that, The silane-modified diatomaceous earth powder is obtained by modifying diatomaceous earth powder with alkane coupling agent KH-550.

8. The method for preparing a tin-free weather-resistant hydroxyl polyester resin according to claim 1, characterized in that, Includes the following steps: Using terephthalic acid, biphenyl phthalic acid, and isophthalic acid as polyacid monomers, and neopentyl glycol and ethylene glycol as polyol monomers, a titanium glycol catalyst and a cerium-supported hydrophobically modified diatomaceous earth catalyst were added for pre-dispersion. The mixture underwent atmospheric pressure esterification and high vacuum polycondensation. After the reaction was completed, antioxidant 1010 and antioxidant 168 were added, and the mixture was mixed and granulated to obtain a tin-free weather-resistant hydroxyl polyester resin.

9. The method for preparing a tin-free weather-resistant hydroxyl polyester resin according to claim 8, characterized in that, The pre-dispersion temperature is 25-40℃, and the rotation speed is 150-250 r / min.

10. The method for preparing a tin-free weather-resistant hydroxyl polyester resin according to claim 8, characterized in that, The atmospheric pressure esterification temperature is 180-220℃; the high vacuum polycondensation reaction temperature is 240-250℃, and the vacuum is evacuated to a vacuum degree of <100Pa.

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