Polyester type powder coating and preparation method thereof

Abstract

The invention discloses a polyester type powder coating and a preparation method thereof, and belongs to the technical field of coating production, firstly, the polyester type powder coating is prepared from the following raw materials in parts by mass: 45 to 55 parts of film forming matter, 15 to 20 parts of curing agent, 5 to 15 parts of pigment, 10 to 15 parts of filler, 0.3 to 0.8 part of benzoin and 0.5 to 1.5 parts of antioxidant. Wherein the film forming substance is prepared by carrying out a self-polycondensation reaction on 2, 2-dimethylolpropionic acid under high-temperature catalysis and nitrogen protection; wherein the curing agent is prepared by the following steps: esterifying 2, 4-dihydroxybenzophenone and trimellitic anhydride in N, N-dimethylformamide, and catalyzing by ion exchange resin to obtain a carboxylic acid-containing intermediate; and carrying out ring-opening reaction with epoxy chloropropane, carrying out ring-closing reaction with NaOH, and introducing a glycidyl ester structure.

Description

Technical Field

[0001] The invention belongs to the technical field of powder coatings, and in particular relates to a polyester powder coating and a preparation method thereof. Background Art

[0002] Polyester-based coatings are widely used, offering full film coverage and excellent mechanical properties. Depending on the type of resin and curing agent, powder coatings can be categorized into epoxy and polyester-epoxy hybrids for indoor applications, as well as pure polyester and polyurethane types for outdoor weathering applications. Polyester-based powder coatings are a key category within this category.

[0003] When used as a weather-resistant outdoor powder coating, polyester powder coatings are susceptible to degradation due to ultraviolet light, which can cause some groups in the coating to degrade. Furthermore, because the coating contains easily hydrolyzed ester bonds, moisture can also cause this hydrolysis, significantly affecting the weatherability of the polyester coating. Traditional polyester-based transparent powder coatings typically have a low hardness and limited abrasion resistance, leading to cracking, wear, and even shedding of the coating.

[0004] Existing methods for improving the performance of polyester powder coatings include cold-blending with organic fluorine and silicone compounds, additive blending, and composite modification with highly weatherable pigments and fillers. However, these methods suffer from limitations such as imperfections on flat surfaces, the tendency to produce surface defects, accelerated aging due to additive failure, and limited improvement in weatherability. Powder coatings primarily use polyester resin as a film-forming agent. Under the action of the curing agent, triglycidyl isocyanurate (TGIC), a ring-opening and cross-linking reaction occurs to form a three-dimensional crosslinked network structure. The selection of the appropriate film-forming agent and curing agent directly impacts the coating's performance. Summary of the Invention

[0005] Existing polyester powder coatings have the following problems: (1) Ultraviolet rays can degrade some groups in the coating, leading to coating aging; (2) The coating has poor adhesion and leveling properties; (3) Traditional polyester powder coatings have low hardness and limited wear resistance, which can easily cause the coating to crack, wear, or even fall off.

[0006] The core improvement of the present invention is as follows: This formula uses a hyperbranched polyester synthesized from 2,2-dihydroxymethylpropionic acid (DMPA) as a film-forming substance, and is combined with a product synthesized from trimellitic anhydride as a curing agent. The hyperbranched polyester has a highly branched structure and a large number of end groups, which can give the coating good adhesion and leveling properties; the polyepoxy groups of the curing agent can efficiently react with the end carboxyl groups of the hyperbranched polyester, thereby increasing the cross-linking density and enhancing the hardness and UV aging resistance of the coating.

[0007] The purpose of the present invention can be achieved through the following technical solutions: A polyester powder coating comprising the following raw materials in parts by weight: 45-55 parts of film-forming substance; 15-20 parts of curing agent; 5-15 parts of pigment; 10-15 parts of filler; 0.3-0.8 parts of benzoin; 0.5-1.5 parts of antioxidant.

[0008] Furthermore, the film-forming material is prepared by the following steps: T1. Dry 2,2-dimethylolpropionic acid (98%; purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) in a vacuum drying oven at 80°C for 4-6 hours to remove adsorbed water. Add the dried 2,2-dimethylolpropionic acid and a catalyst, p-toluenesulfonic acid (99%; purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), to a reactor in an amount of 0.5% to 2% of the total mass of the dried 2,2-dimethylolpropionic acid. Raise the temperature to 140°C under nitrogen protection and react for 1-2 hours. T2. Then, the temperature is raised to 160°C and the reaction is carried out for 2 to 4 hours. The temperature is then raised to 180°C, the nitrogen is turned off, and the reaction system is evacuated to a pressure of ≤100 Pa. The reaction is continued under reduced pressure until no residual water is removed to obtain a light yellow transparent resin, i.e., a film-forming substance.

[0009] Furthermore, the curing agent is prepared by the following steps: A1. Take N,N-dimethylformamide, fill it with nitrogen for protection, then add 2,4-dihydroxybenzophenone and trimellitic anhydride thereto with stirring, stir and mix for 10-30 minutes, then add Amberlyst-15 ion exchange resin thereto with stirring, heat to 65-70°C, and react at constant temperature with stirring for 4-5 hours. After the reaction is completed, filter out the Amberlyst-15 ion exchange resin, collect the filtrate and rotary evaporate to remove the solvent N,N-dimethylformamide, then wash three times with pure water, and then dry at room temperature for 24 hours to obtain an intermediate. In the above reaction process, 2,4-dihydroxybenzophenone and trimellitic anhydride react under the catalytic action of Amberlyst-15 ion exchange resin. The main reaction process is as follows: .

[0010] Furthermore, the usage ratio of N,N-dimethylformamide, 2,4-dihydroxybenzophenone, trimellitic anhydride and Amberlyst-15 ion exchange resin described in A1 is 1L:0.5mol:0.5-0.55mol:80-100g.

[0011] A2. A two-step preparation process is adopted. The intermediate, epichlorohydrin and 3% benzyltriethylammonium chloride (TEBAC) catalyst by weight of the intermediate are added to the reactor, wherein the mass of epichlorohydrin is 4 times the mass of the intermediate. The reactor is placed in a water bath and heated to 45°C. The reaction is carried out under nitrogen protection for 5-6 hours. The temperature is then lowered to 30°C. A 48% NaOH aqueous solution is added dropwise, and the mass of the NaOH aqueous solution is 3.5 times the mass of the intermediate. The addition time is controlled to be 0.5-1 hour. The water bath is then heated to 65°C and kept warm for 3-4 hours. After the reaction is completed, the by-product NaCl is filtered off, the filtrate is collected and washed with water to a pH value of 6.7-7.2, and the excess epichlorohydrin is removed by vacuum distillation. The obtained product is used as a curing agent for the powder coating. During the above reaction process, the intermediate and epichlorohydrin undergo epoxidation reaction. The main reaction process is as follows: .

[0012] Furthermore, the pigment is any one of titanium dioxide and carbon black.

[0013] Furthermore, the filler is any one of barium sulfate and calcium carbonate.

[0014] Furthermore, the antioxidant is any one of antioxidant 1010 and antioxidant 168.

[0015] Furthermore, a method for preparing a polyester powder coating comprises the following steps: S1. Weigh the above raw materials according to mass parts, add the weighed raw materials into a high-speed mixer, and mix them at a speed of 500-1000 r / min for 10-15 minutes to make the components preliminarily dispersed and obtain a premixed material; S2. Use a twin-screw extruder with a screw temperature of 100-120°C to melt and extrude the premixed material. The shearing and conveying action of the screw further promotes uniform dispersion and mixing of the components to form a uniform melt. S3, the extruded melt is rapidly cooled by a cooling device and then pressed into thin sheets for subsequent crushing processing; S4. The cooled flakes are crushed and passed through a 200-mesh sieve to obtain a polyester powder coating.

[0016] Beneficial effects of the present invention: The present invention provides a polyester powder coating and a preparation method thereof. The polyester powder coating changes the film-forming material and curing agent of the traditional powder coating, significantly improves the aging resistance and chemical resistance of the powder coating, has good wear resistance, and the coating film is smooth and uniform in color without orange peel, shrinkage cavities, pinholes, etc. The specific analysis is as follows: First, this formulation uses a hyperbranched polyester synthesized from 2,2-dimethylolpropionic acid as a film-forming agent, combined with a glycidyl ester synthesized from trimellitic anhydride as a curing agent, aiming to create a polyester powder coating with excellent overall performance. The hyperbranched polyester has a highly branched structure and a large number of end groups, which impart excellent adhesion and leveling to the coating. The curing agent's polyepoxy groups react efficiently with the hyperbranched polyester's end carboxyl groups, increasing the crosslink density and enhancing the coating's hardness, chemical resistance, and weather resistance. Furthermore, its relatively small number of end groups and the introduction of a rigid benzene ring structure impart excellent thermal stability and mechanical properties to the powder coating. Furthermore, within the crosslinked network, the "flexible segments" of the hyperbranched structure complement the "rigid aromatic rings" introduced by the curing agent, imparting both high hardness and good impact resistance to the coating. The low melt viscosity of the hyperbranched polyester, combined with the curing agent's compatibility, significantly improves leveling, achieving a surface leveling grade of 7-8 according to the PCI standard.

[0017] Finally, the curing agent of the present invention contains a benzophenone structure, which consumes ultraviolet radiation through keto-enol tautomerism, that is, absorbs ultraviolet rays, thereby improving the light aging resistance of the powder coating. DETAILED DESCRIPTION

[0018] Below in conjunction with the embodiment of the present invention, the technical scheme in the embodiment of the present invention is clearly and completely described, it is obvious that described embodiment is only a part of embodiment of the present invention, rather than whole embodiment. Based on the embodiment in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise all fall within the scope of protection of the present invention. Meanwhile, raw materials, reagents or devices used in the following examples, unless otherwise specified, can be obtained from conventional commercial channels, or can be obtained by existing known methods.

[0019] Example 1

[0020] The film-forming material is prepared by the following steps: T1. Dry 2,2-dimethylolpropionic acid (98%; purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) in a vacuum drying oven at 80°C for 4 hours to remove adsorbed water. Add the dried 2,2-dimethylolpropionic acid and p-toluenesulfonic acid (99%; purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) as a catalyst to a reactor. The amount of catalyst added is 0.5% of the total mass of the dried 2,2-dimethylolpropionic acid. Raise the temperature to 140°C under nitrogen protection and react for 1 hour. T2. Then, the temperature is raised to above 160°C and the reaction is carried out for 2 hours. The temperature is then raised to 180°C, the nitrogen is turned off, and the reaction system is evacuated to a pressure of ≤100 Pa. The reaction is continued under reduced pressure until no residual water is removed to obtain a light yellow transparent resin, i.e., a film-forming substance.

[0021] Example 2

[0022] The film-forming material is prepared by the following steps: T1. Dry 2,2-dimethylolpropionic acid (98%; purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) in a vacuum drying oven at 80°C for 5 hours to remove adsorbed water. Add the dried 2,2-dimethylolpropionic acid and p-toluenesulfonic acid (99%; purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) as a catalyst to a reactor, wherein the amount of the catalyst added is 1% of the total mass of the dried 2,2-dimethylolpropionic acid. Raise the temperature to 140°C under nitrogen protection and react for 1.5 hours. T2. Then, the temperature is raised to above 160°C and the reaction is carried out for 3 hours. The temperature is then raised to 180°C, the nitrogen is turned off, and the reaction system is evacuated to a pressure of ≤100 Pa. The reaction is continued under reduced pressure until no residual water is removed to obtain a light yellow transparent resin, i.e., a film-forming substance.

[0023] Example 3

[0024] The film-forming material is prepared by the following steps: T1. Dry 2,2-dimethylolpropionic acid (98%; purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) in a vacuum drying oven at 80°C for 6 hours to remove adsorbed water. Add the dried 2,2-dimethylolpropionic acid and p-toluenesulfonic acid (99%; purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) as a catalyst to a reactor, wherein the amount of the catalyst added is 2% of the total mass of the dried 2,2-dimethylolpropionic acid. Raise the temperature to 140°C under nitrogen protection and react for 2 hours. T2. Then, the temperature is raised to above 160°C and the reaction is carried out for 4 hours. The temperature is then raised to 180°C, the nitrogen is turned off, and the reaction system is evacuated to a pressure of ≤100 Pa. The reaction is continued under reduced pressure until no residual water is removed to obtain a light yellow transparent resin, i.e., a film-forming substance.

[0025] Example 4

[0026] The curing agent is prepared by the following steps: A1, 1L of solvent N,N-dimethylformamide (AR; purchased from Sinopharm Chemical Reagent Co., Ltd.) was added to the reactor, and nitrogen was introduced to replace the air in the reactor A, so that the reactor was in a nitrogen atmosphere, and then 0.5 mol of 2,4-dihydroxybenzophenone (99%; purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) and 0.5 mol of trimellitic anhydride (95%; purchased from Anhui Botai Electronic Materials Co., Ltd.) were added to the reactor with stirring, and the mixture was stirred for 10 minutes. Then, 80 g of Amberlyst-15 ion exchange resin (purchased from Shanghai Yuanye Biotechnology Co., Ltd.) was added to the reactor with stirring, and the reactor was heated to 65° C. and stirred at constant temperature for 4 hours. After completion of the reaction, the Amberlyst-15 ion exchange resin was filtered out, the filtrate was collected and the solvent N,N-dimethylformamide was removed by rotary evaporation, and then washed three times with pure water, and then dried at room temperature for 24 hours to obtain an intermediate; A2. Add the intermediate, epichlorohydrin (99%; purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), and triethylbenzyl ammonium chloride (98%; purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) catalyst (3% by weight of the intermediate, wherein the mass of epichlorohydrin is 4 times the mass of the intermediate) to the reactor. Place the reactor in a water bath and heat it to 45°C. React under nitrogen protection for 5 hours. Then cool the reactor to 30°C and add a 48% NaOH aqueous solution dropwise. The mass of the NaOH aqueous solution is 3.5 times the mass of the intermediate. The addition time is controlled to 0.5 hour. Then, heat the water bath to 65°C and keep the reaction for 3 hours. After the reaction is completed, filter out the by-product NaCl, collect the filtrate and wash it with water until the pH is 6.7, and remove the excess epichlorohydrin by distillation under reduced pressure to obtain a curing agent.

[0027] Example 5

[0028] The curing agent is prepared by the following steps: A1. Add 1 L of solvent N,N-dimethylformamide (AR; purchased from Sinopharm Chemical Reagent Co., Ltd.) to the reactor, fill with nitrogen to replace the air in the reactor, and place the reactor in a nitrogen atmosphere. Then, add 0.5 mol of 2,4-dihydroxybenzophenone (99%; purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) and 0.55 mol of trimellitic anhydride (95%; purchased from Anhui Botai Electronic Materials Co., Ltd.) to the reactor with stirring, and stir for 30 minutes. Then, add 100 g of Amberlyst-15 ion exchange resin (purchased from Shanghai Yuanye Biotechnology Co., Ltd.) to the reactor with stirring. The reactor is heated to 68° C. and stirred at this constant temperature for 5 hours. After completion of the reaction, the Amberlyst-15 ion exchange resin is filtered to remove the Amberlyst-15 ion exchange resin, the filtrate is collected and the solvent N,N-dimethylformamide is removed by rotary evaporation, and then washed three times with pure water, and then dried at room temperature for 24 hours to obtain an intermediate. A2. Add the intermediate, epichlorohydrin (99%; purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), and triethylbenzyl ammonium chloride (98%; purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) catalyst (3% by weight of the intermediate, wherein the mass of epichlorohydrin is 4 times the mass of the intermediate) to the reactor. Place the reactor in a water bath and heat it to 45°C. React under nitrogen for 5.5 hours. Then cool the reactor to 30°C and add a 48% NaOH aqueous solution dropwise. The mass of the NaOH aqueous solution is 3.5 times the mass of the intermediate. The addition time is controlled to 0.5 hour. Then, heat the water bath to 65°C and keep the reaction for 3.5 hours. After the reaction is completed, filter out the by-product NaCl, collect the filtrate, wash with water until the pH is 7.0, and remove the excess epichlorohydrin by distillation under reduced pressure to obtain a curing agent.

[0029] Example 6

[0030] The curing agent is prepared by the following steps: A1, 1L of solvent N,N-dimethylformamide (AR; purchased from Sinopharm Chemical Reagent Co., Ltd.) was added to the reactor, and nitrogen was introduced to replace the air in the reactor A, so that the reactor A was in a nitrogen atmosphere, and then 0.5 mol of 2,4-dihydroxybenzophenone (99%; purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) and 0.55 mol of trimellitic anhydride (95%; purchased from Anhui Botai Electronic Materials Co., Ltd.) were added to the reactor with stirring, and the mixture was stirred for 30 minutes. Then, 100 g of Amberlyst-15 ion exchange resin (purchased from Shanghai Yuanye Biotechnology Co., Ltd.) was added to the reactor with stirring, and the reactor was heated to 70° C. and stirred at constant temperature for 5 hours. After completion of the reaction, the Amberlyst-15 ion exchange resin was filtered out, the filtrate was collected and the solvent N,N-dimethylformamide was removed by rotary evaporation, and then washed three times with pure water, and then dried at room temperature for 24 hours to obtain an intermediate; A2. Add the intermediate, epichlorohydrin (99%; purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), and triethylbenzyl ammonium chloride (98%; purchased from Shanghai Maclean Biochemical Technology Co., Ltd.) catalyst (3% by weight of the intermediate, wherein the mass of epichlorohydrin is 4 times the mass of the intermediate) to the reactor. Place the reactor in a water bath and heat it to 45°C. React under nitrogen for 6 hours. Then cool the reactor to 30°C and add a 48% NaOH aqueous solution dropwise. The mass of the NaOH aqueous solution is 3.5 times the mass of the intermediate. The addition time is controlled to 0.5 hour. Then, heat the water bath to 65°C and keep the reaction for 3.5 hours. After the reaction is completed, filter out the by-product NaCl, collect the filtrate and wash it with water until the pH is 7.2, and remove the excess epichlorohydrin by distillation under reduced pressure to obtain a curing agent.

[0031] Example 7

[0032] Preparation of polyester powder coatings: First, the polyester powder coating includes the following raw materials in parts by weight: 45 parts of the film-forming material prepared in Example 1; 15 parts of the curing agent prepared in Example 4; 5 parts of titanium dioxide; 10 parts of barium sulfate; 0.3 parts of benzoin; 0.5 parts of antioxidant 1010.

[0033] Then, the preparation method of the above polyester powder coating comprises the following steps: S1. Weigh the above raw materials according to mass parts, add the weighed raw materials into a high-speed mixer, and mix them at a speed of 500 r / min for 10 minutes to make the components preliminarily dispersed and obtain a premixed material; S2. Use a twin-screw extruder with a screw temperature of 100°C to melt and extrude the premixed material. The shearing and conveying action of the screw further promotes the uniform dispersion and mixing of the components to form a uniform melt. S3, the extruded melt is rapidly cooled by a cooling device and then pressed into thin sheets for subsequent crushing processing; S4. The cooled flakes are crushed and passed through a 200-mesh sieve to obtain a polyester powder coating.

[0034] Example 8

[0035] Preparation of polyester powder coatings: 50 parts of the film-forming material prepared in Example 2; 17 parts of the curing agent prepared in Example 5; 10 parts of carbon black; 12 parts of calcium carbonate; 0.5 parts of benzoin; 1 part of antioxidant 1010.

[0036] Then, the preparation method of the above polyester powder coating comprises the following steps: S1. Weigh the above raw materials according to mass parts, add the weighed raw materials into a high-speed mixer, and mix them at a speed of 750 r / min for 10 minutes to make the components preliminarily dispersed and obtain a premixed material; S2. Use a twin-screw extruder with a screw temperature of 110°C to melt and extrude the premixed material. The shearing and conveying action of the screw further promotes the uniform dispersion and mixing of the components to form a uniform melt. S3, the extruded melt is rapidly cooled by a cooling device and then pressed into thin sheets for subsequent crushing processing; S4. The cooled flakes are crushed and passed through a 200-mesh sieve to obtain a polyester powder coating.

[0037] Example 9

[0038] Preparation of polyester powder coatings: 55 parts of the film-forming material prepared in Example 3; 20 parts of the curing agent prepared in Example 6; 15 parts of carbon black; 15 parts of calcium carbonate; 0.8 parts of benzoin; 1.5 parts of antioxidant 168.

[0039] Then, the preparation method of the above polyester powder coating comprises the following steps: S1. Weigh the above raw materials according to mass parts, add the weighed raw materials into a high-speed mixer, and mix them at a speed of 1000 r / min for 10 minutes to make the components preliminarily dispersed and obtain a premixed material; S2. Use a twin-screw extruder with a screw temperature of 120°C to melt and extrude the premixed material. The shearing and conveying action of the screw further promotes the uniform dispersion and mixing of the components to form a uniform melt. S3, the extruded melt is rapidly cooled by a cooling device and then pressed into thin sheets for subsequent crushing processing; S4. The cooled flakes are crushed and passed through a 200-mesh sieve to obtain a polyester powder coating.

[0040] Comparative Example 1 Comparative Example 1 is the control group of Example 8, except that the raw material film-forming substance in Example 8 is replaced with polyester resin P2706 (purchased from Huangshan Jiajie New Materials Co., Ltd.), and the remaining raw materials, raw material amounts and preparation methods remain the same as in Example 8, and finally a polyester powder coating is obtained.

[0041] Comparative Example 2 Comparative Example 2 is the control group of Example 8, except that the raw material curing agent in Example 8 is replaced with triglycidyl isocyanurate (purchased from Shanghai MacLean Biochemical Technology Co., Ltd.), and the remaining raw materials, raw material amounts and preparation methods remain the same as in Example 8, and finally a polyester powder coating is obtained.

[0042] Comparative Example 3 Comparative Example 3 is the control group of Example 8, except that the raw material film-forming substance in Example 8 is replaced by polyester resin P2706 (purchased from Huangshan Jiajie New Materials Co., Ltd.), and the curing agent is replaced by triglycidyl isocyanurate (purchased from Shanghai MacLean Biochemical Technology Co., Ltd.). The remaining raw materials, raw material amounts and preparation methods remain the same as in Example 8, and a polyester powder coating is finally obtained.

[0043] The polyester powder coatings prepared in Examples 7 to 9 and Comparative Examples 1 to 3 were tested for adhesion, leveling, hardness, and UV aging resistance. The performance test process is as follows, and the test results are shown in Table 1: Adhesion performance test: The adhesion of the paint film is tested according to GB / T9286-2021; Leveling performance test: Leveling rating is carried out according to the leveling effect rating standard board of PCI in the United States; Hardness performance test: The pencil hardness of the paint film is tested according to GB / T6739-2006; The UV aging resistance is tested according to the provisions of GB / T23987-2009. Specifically: Light stage: UVB-313 lamp, irradiance 0.71W / (m 2 ·nm), blackboard temperature 60℃, 2h; water spraying stage: water temperature 20-30℃, water spraying 18min, (total cycle 2h18min, repeated); aging time is 2000h. After aging, △E is tested with a spectrocolorimeter; Table 1 Test results project Example 7 Example 8 Example 9 Comparative Example 1 Comparative Example 2 Comparative Example 3 Adhesion (grade) 1.5 1.2 1.4 3.0 1.7 3.1 Leveling (grade) 8 8 7 4 6 4 hardness 5H 6H 5H 3H 2H 2H △E 1.3 1.2 1.3 3.5 3.3 4.5 By comparing the data of Example 8 and Comparative Example 1, it can be seen that using hyperbranched polyester as a film-forming substance can give the coating excellent adhesion; By comparing the data of Example 8 and Comparative Example 1, it can be seen that using hyperbranched polyester as a film-forming substance can give the coating excellent leveling properties; Comparing the data of Example 8 and Comparative Example 2, it can be seen that the addition of the curing agent prepared in Example 5 of the present invention helps to improve the hardness of the coating compared to the existing curing agent triglycidyl isocyanurate; By comparing the data of Example 8 and Comparative Example 2, it can be seen that adding the curing agent prepared in Example 5 of the present invention can significantly improve the UV aging resistance of the powder coating.

[0044] It should be noted that, in this document, terms such as "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0045] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A polyester powder coating, characterized in that: Calculated by mass, it includes the following raw materials: 45-55 parts of film-forming substance; 15-20 parts of curing agent; 5-15 parts of pigment; 10-15 parts of filler; 0.3-0.8 parts of benzoin; 0.5-1.5 parts of antioxidant.

2. A polyester powder coating according to claim 1, characterized in that: The film-forming material is prepared by the following steps: T1, drying 2,2-dimethylol propionic acid in a vacuum drying oven at 80 ° C for 4 to 6 hours, adding the dried 2,2-dimethylol propionic acid and p-toluenesulfonic acid to a reactor, wherein the amount of p-toluenesulfonic acid added is 0.5% to 2% of the mass of the dried 2,2-dimethylol propionic acid, heating to 140 ° C under nitrogen protection, and reacting for 1 to 2 hours; T2. Then, the temperature is raised to above 160°C and the reaction is carried out for 2 to 4 hours. The temperature is then raised to 180°C, the nitrogen is turned off, and the reaction system is evacuated to a pressure of ≤100 Pa. The reaction is continued under reduced pressure until no residual water is removed to obtain a resin, i.e., a film-forming material.

3. A polyester powder coating according to claim 1, characterized in that: The curing agent is prepared by the following steps: A1. Take N,N-dimethylformamide, fill it with nitrogen for protection, then add 2,4-dihydroxybenzophenone and trimellitic anhydride thereto with stirring, stir and mix for 10 to 30 minutes, then add Amberlyst-15 ion exchange resin thereto with stirring, heat to 65 to 70°C, and stir and react at this temperature for 4 to 5 hours. After the reaction is completed, filter out the Amberlyst-15 ion exchange resin, collect the filtrate, and evaporate to remove the solvent N,N-dimethylformamide, then wash three times with pure water, and then dry at room temperature for 24 hours to obtain an intermediate; A2. Add the intermediate, epichlorohydrin and benzyltriethylammonium chloride catalyst to the reactor, place the reactor in a water bath and heat it to 45°C. React for 5 to 6 hours under nitrogen protection, then cool to 30°C, add dropwise a 48% NaOH aqueous solution with a mass fraction of 3.5 times the mass of the intermediate, and control the addition time to be 0.5 to 1 hour. Then raise the water bath temperature to 65°C and keep the reaction for 3 to 4 hours. After the reaction is completed, filter out the by-product NaCl, collect the filtrate and wash with water until the pH value is 6.7 to 7.2, and remove the excess epichlorohydrin by distillation under reduced pressure. The obtained product is used as a curing agent for powder coatings.

4. A polyester powder coating according to claim 3, characterized in that: The usage ratio of N,N-dimethylformamide, 2,4-dihydroxybenzophenone, trimellitic anhydride and Amberlyst-15 ion exchange resin in A1 is 1 L: 0.5 mol: 0.5-0.55 mol: 80-100 g.

5. The polyester powder coating according to claim 3, characterized in that: The mass of epichlorohydrin described in A2 is 4 times the mass of the intermediate.

6. The polyester powder coating according to claim 3, characterized in that: The mass of benzyltriethylammonium chloride described in A2 is 3% of the mass of the intermediate.

7. The polyester powder coating according to claim 1, characterized in that: The pigment is any one of titanium dioxide and carbon black.

8. The polyester powder coating according to claim 1, characterized in that: The filler is any one of barium sulfate and calcium carbonate.

9. The polyester powder coating according to claim 1, characterized in that: The antioxidant is any one of antioxidant 1010 and antioxidant 168.

10. A method for preparing a polyester powder coating according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. Weigh the above raw materials according to mass parts, add the weighed raw materials into a high-speed mixer, and mix them at a speed of 500-1000 r / min for 10-15 minutes to obtain a premixed material; S2. Using a twin-screw extruder, setting the screw temperature to 100-120°C, melt-extrude the premixed material to form a melt; S3, the extruded melt is rapidly cooled by a cooling device and then pressed into a sheet; S4. The cooled sheet is crushed and passed through a 200-mesh sieve to obtain a polyester powder coating.