A polyester powder coating and a method for its preparation

Abstract

The application discloses polyester type powder coating and a preparation method thereof, and belongs to the technical field of coating production. First, the polyester type powder coating comprises the following raw materials in mass parts: 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 and 0.5-1.5 parts of antioxidant. The film forming substance is prepared by self-condensation reaction of 2,2-dimethylol propionic acid under high-temperature catalysis and nitrogen protection; the curing agent is prepared by esterification of 2,4-dihydroxybenzophenone and trimellitic anhydride in N,N-dimethylformamide, ion exchange resin catalysis, introduction of carboxylic acid intermediate, ring opening of epichlorohydrin, NaOH ring closing reaction and introduction of glycidyl ester structure.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of powder coatings, and particularly relates to a polyester type powder coating and a preparation method thereof. BACKGROUND

[0002] Polyester type coatings are widely used and have full film and excellent mechanical properties. According to the types of resins and curing agents, powder coatings can be divided into indoor epoxy type, polyester-epoxy hybrid type, and outdoor weather-resistant pure polyester type and polyurethane type, and polyester type powder coating is an important type.

[0003] When used as outdoor weather-resistant powder coating, the polyester powder coating is easily degraded under the action of ultraviolet light, and the coating layer will be aged and degraded. At the same time, due to the presence of hydrolyzable ester bonds in the coating layer, water will also promote the hydrolysis of the ester bonds, greatly affecting the weather resistance of the polyester coating. The traditional polyester type transparent powder coating generally has low hardness and limited wear resistance, which causes the coating film to be prone to cracking, wear, and even peeling.

[0004] To improve the performance of polyester type powder coating, existing methods include organic fluorine cold splicing modification, organic silicon cold splicing modification, additive blending modification, high weather-resistant pigment filler composite modification, etc., but these methods have problems such as being unable to be applied to flat powder, being prone to surface defects, additives being prone to failure and accelerating aging, and limited weather resistance improvement. Powder coating mainly uses polyester resin as a film-forming material, which undergoes ring-opening and cross-linking curing reaction under the action of isocyanuric acid triglycidyl ester (TGIC) to generate a three-dimensional cross-linked network structure, and the selection of appropriate film-forming material and curing agent will directly affect the application performance of the coating. SUMMARY

[0005] The existing polyester type powder coating has the following problems: (1) ultraviolet light will cause partial groups in the coating film to degrade, resulting in coating aging; (2) the adhesion and leveling property of the coating are poor; (3) and the traditional polyester type powder coating has low hardness and limited wear resistance, which easily causes the coating film to crack, wear, and even peel off.

[0006] The core improvement point of the present application is that the super-branched polyester synthesized from 2,2-dimethylol propionic acid (DMPA) as a raw material is used as a film-forming material, and the product synthesized from trimellitic anhydride as a raw material is used as a curing agent. The super-branched polyester has a highly branched structure and a large number of end groups, which can give the coating film good adhesion and leveling property; the multiple epoxy groups of the curing agent can efficiently react with the end carboxyl groups of the super-branched polyester, improve the cross-linking density, and enhance the hardness and ultraviolet aging resistance of the coating film.

[0007] The object of the present application can be achieved by the following technical solutions:

[0008] A polyester type powder coating comprises the following raw materials by mass:

[0009] Film forming material 45-55 parts;

[0010] Curing agent 15-20 parts;

[0011] Pigment 5-15 parts;

[0012] Filler 10-15 parts;

[0013] Camphor 0.3-0.8 parts;

[0014] Antioxidant 0.5-1.5 parts.

[0015] Further, the film forming material is prepared by the following steps:

[0016] T1, 2,2-dihydroxymethyl propionic acid (98%, purchased from Shanghai Maikelin Biochemical Technology Co., Ltd.) is dried in a vacuum drying oven at 80°C for 4-6 hours to remove adsorbed water, and the dried 2,2-dihydroxymethyl propionic acid and a catalyst, p-toluenesulfonic acid (99%, purchased from Shanghai Maikelin Biochemical Technology Co., Ltd.), are added to a reactor, the catalyst is added in an amount of 0.5%-2% of the total mass of the dried 2,2-dihydroxymethyl propionic acid, and the temperature is raised to 140°C under nitrogen protection, and the reaction is carried out for 1-2 hours.

[0017] T2, then the temperature is raised to 160°C, and the reaction is carried out for 2-4 hours, then the temperature is raised to 180°C, the nitrogen is turned off, and the reaction system is vacuumed to a pressure ≤100 Pa, and the reaction is continued under reduced pressure until no residual water is released, and a light yellow transparent resin, i.e. the film forming material, is prepared.

[0018] Further, the curing agent is prepared by the following steps:

[0019] A1, N,N-dimethylformamide is filled with nitrogen protection, and then 2,4-dihydroxybenzophenone and trimellitic anhydride are added thereto with stirring, and stirred and mixed for 10-30 min, then Amberlyst-15 ion exchange resin is added thereto with stirring, the temperature is raised to 65-70°C, and constant temperature stirring reaction is carried out for 4-5 h, after the reaction is completed, the Amberlyst-15 ion exchange resin is removed by filtration, the filtrate is collected and rotary evaporation is carried out to remove the solvent N,N-dimethylformamide, then pure water is washed three times, and then it is placed in a room temperature condition for drying for 24 h, to obtain an intermediate, and in the above reaction process, under the catalysis of Amberlyst-15 ion exchange resin, 2,4-dihydroxybenzophenone and trimellitic anhydride react, and the main reaction process is as follows:

[0020] .

[0021] Further, the A1 is N,N-dimethylformamide, 2,4-dihydroxybenzophenone, trimellitic anhydride and Amberlyst-15 ion exchange resin, and the ratio of the amount of use is 1L:0.5mol:0.5-0.55mol:80-100g.

[0022] A2, a two-step preparation process, adding an intermediate, epichlorohydrin and 3% of the mass of the intermediate benzyl triethyl ammonium chloride (TEBAC) catalyst in 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℃, and the reaction is carried out for 5-6 hours under nitrogen protection, then the temperature is lowered to 30℃, 48% NaOH aqueous solution is added dropwise, the mass of NaOH aqueous solution is 3.5 times the mass of the intermediate, the dropwise adding time is controlled in 0.5-1 hour, then the water bath is heated to 65℃ and the reaction is carried out for 3-4 hours, the reaction is completed, NaCl is filtered out, the filtrate is collected and washed with water until the pH value is 6.7-7.2, the excess epichlorohydrin is removed by vacuum distillation, and the obtained product is used as a curing agent for powder coating, in the above reaction process, the intermediate and epichlorohydrin undergo an epoxidation reaction, and the main reaction process is as follows:

[0023] .

[0024] Further, the pigment is any one of titanium dioxide and carbon black.

[0025] Further, the filler is any one of barium sulfate and calcium carbonate.

[0026] Further, the antioxidant is any one of antioxidant 1010 and antioxidant 168.

[0027] Further, a preparation method of a polyester type powder coating, comprising the following steps:

[0028] S1, the above raw materials are weighed according to the mass fraction, and the weighed raw materials are added to a high-speed mixer, mixed at a speed of 500-1000r / min for 10-15 minutes, and uniformly dispersed to obtain a premix;

[0029] S2, a double-screw extruder is used, the screw temperature is set to 100-120℃, the premix is melt-extruded, and the shearing and conveying effects of the screw further promote the uniform dispersion and mixing of the components to form a uniform melt;

[0030] S3, the extruded melt is rapidly cooled by a cooling device, and then pressed into a sheet for subsequent crushing treatment;

[0031] S4, the cooled sheet is crushed and then sieved through a 200-mesh screen to obtain a polyester type powder coating.

[0032] The beneficial effects of the present application are as follows:

[0033] The present application provides a polyester powder coating and a preparation method thereof, which changes the film-forming material and curing agent of 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 flat, uniform in color, and free of orange peel, shrinkage, pinholes and the like, and the specific analysis is as follows:

[0034] Firstly, the hyperbranched polyester synthesized from 2,2-dimethylol propionic acid as raw material is used as the film-forming material, and the glycidyl ester synthesized from trimellitic anhydride as raw material is used as the curing agent, aiming to create a polyester powder coating with excellent comprehensive performance; the hyperbranched polyester has a highly branched structure and a large number of end groups, which can endow the coating film with good adhesion and leveling property; the multi-epoxy groups of the curing agent can react with the end carboxyl groups of the hyperbranched polyester to improve the crosslinking density, enhance the hardness, chemical resistance and weather resistance of the coating film, and at the same time, the relatively small number of end groups and the introduction of rigid benzene ring structure endow the powder coating with excellent thermal stability and mechanical properties; then, in the crosslinking network, the "flexible segment" of the hyperbranched structure and the "rigid aromatic ring" introduced by the curing agent form a complement, so that the coating layer has high hardness and good impact resistance; the low melt viscosity of the hyperbranched polyester combined with the compatibility of the curing agent can significantly improve the leveling property, and the surface leveling property of the coating layer can reach grade 7-8 according to the PCI standard.

[0035] Finally, the curing agent of the present application contains a benzophenone structure, which realizes the ability to consume ultraviolet radiation through the keto-enol tautomerism phenomenon, that is, it realizes the function of absorbing ultraviolet rays, and achieves the purpose of improving the light aging resistance of the powder coating. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application. Meanwhile, the raw materials, reagents or devices used in the following embodiments can be obtained from conventional commercial channels, or can be obtained by existing known methods, unless otherwise specified.

[0037] Example 1

[0038] The film-forming material is prepared by the following steps:

[0039] T1, 2,2-dihydroxymethyl propionic acid (98%; purchased from Shanghai Macklin Biochemical Technology Co., Ltd.) was dried in a vacuum drying oven at 80°C for 4 hours to remove adsorbed water, and the dried 2,2-dihydroxymethyl propionic acid and a catalyst, p-toluenesulfonic acid (99%; purchased from Shanghai Macklin Biochemical Technology Co., Ltd.), were added to a reactor, the catalyst was added in an amount of 0.5% of the total mass of the dried 2,2-dihydroxymethyl propionic acid, and the temperature was raised to 140°C under nitrogen protection, and reacted for 1 hour;

[0040] T2, then the temperature was raised to above 160°C, and reacted for 2 hours, then the temperature was raised to 180°C, the nitrogen was turned off, and the reaction system was vacuumed to a pressure of ≤100 Pa, and the reaction was continued under reduced pressure until no residual water was removed, to obtain a light yellow transparent resin, which was a film-forming material.

[0041] Example 2

[0042] The film-forming material was prepared by the following steps:

[0043] T1, 2,2-dihydroxymethyl propionic acid (98%; purchased from Shanghai Macklin Biochemical Technology Co., Ltd.) was dried in a vacuum drying oven at 80°C for 5 hours to remove adsorbed water, and the dried 2,2-dihydroxymethyl propionic acid and a catalyst, p-toluenesulfonic acid (99%; purchased from Shanghai Macklin Biochemical Technology Co., Ltd.), were added to a reactor, the catalyst was added in an amount of 1% of the total mass of the dried 2,2-dihydroxymethyl propionic acid, and the temperature was raised to 140°C under nitrogen protection, and reacted for 1.5 hours;

[0044] T2, then the temperature was raised to above 160°C, and reacted for 3 hours, then the temperature was raised to 180°C, the nitrogen was turned off, and the reaction system was vacuumed to a pressure of ≤100 Pa, and the reaction was continued under reduced pressure until no residual water was removed, to obtain a light yellow transparent resin, which was a film-forming material.

[0045] Example 3

[0046] The film-forming material was prepared by the following steps:

[0047] T1, 2,2-dihydroxymethyl propionic acid (98%; purchased from Shanghai Macklin Biochemical Technology Co., Ltd.) was dried in a vacuum drying oven at 80°C for 6 hours to remove adsorbed water, and the dried 2,2-dihydroxymethyl propionic acid and a catalyst, p-toluenesulfonic acid (99%; purchased from Shanghai Macklin Biochemical Technology Co., Ltd.), were added to a reactor, the catalyst was added in an amount of 2% of the total mass of the dried 2,2-dihydroxymethyl propionic acid, and the temperature was raised to 140°C under nitrogen protection, and reacted for 2 hours;

[0048] T2, then warmed to 160°C or above, reacted for 4 hours, then warmed to 180°C, closed the nitrogen, and vacuumed the reaction system to a pressure of 100 Pa or less, and continued to react under reduced pressure until no residual water was removed, to produce a light yellow transparent resin, i.e., a film-forming material.

[0049] Example 4

[0050] The curing agent was prepared by the following steps:

[0051] A1, 1L of solvent N,N-dimethylformamide (AR; purchased from China National Pharmaceutical Group Chemical Reagent Co., Ltd.) was added to the reactor, nitrogen was filled 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 Maikelin Biotechnology Co., Ltd.) and 0.5 mol of trimellitic anhydride (95%; purchased from Anhui Botai Electronic Material Co., Ltd.) were added to the reactor with stirring, mixed for 10 min, and then 80 g of Amberlyst-15 ion exchange resin (purchased from Shanghai Yuan Ye Biotechnology Co., Ltd.) was added to the reactor with stirring. The reactor was warmed to 65°C and stirred at constant temperature for 4 h. After the reaction was completed, the Amberlyst-15 ion exchange resin was removed by filtration, the filtrate was collected and rotary evaporated to remove the solvent N,N-dimethylformamide, then washed with pure water three times, and then dried at room temperature for 24 h to obtain an intermediate;

[0052] A2, the intermediate, epichlorohydrin (99%; purchased from Shanghai Maikelin Biotechnology Co., Ltd.) and 3% of triethylbenzylammonium chloride (98%; purchased from Shanghai Maikelin Biotechnology Co., Ltd.) catalyst by mass of the intermediate were added to the reactor. The reactor was placed in a water bath and heated to 45°C under nitrogen protection for 5 hours. Then cooled to 30°C, and 48% NaOH aqueous solution was added dropwise, the mass of the NaOH aqueous solution was 3.5 times the mass of the intermediate, the dropwise time was controlled within 0.5 hours, and then the water bath was warmed to 65°C for 3 hours. After the reaction was completed, NaCl was filtered off, the filtrate was collected and washed with water until the pH value was 6.7, and the excess epichlorohydrin was removed by vacuum distillation to obtain the curing agent.

[0053] Example 5

[0054] The curing agent was prepared by the following steps:

[0055] A1, 1 L of solvent N,N-dimethylformamide (AR; purchased from China National Pharmaceutical Group Chemical Reagent Co., Ltd.) was added into a reactor, nitrogen was filled to replace the air in the reactor, so that the reactor was in a nitrogen atmosphere, then 0.5 mol of 2,4-dihydroxybenzophenone (99%; purchased from Shanghai Macklin Biochemical Technology Co., Ltd.) and 0.55 mol of trimellitic anhydride (95%; purchased from Anhui Botai Electronic Material Co., Ltd.) were added into the reactor with stirring and mixed for 30 min, then 100 g of Amberlyst-15 ion exchange resin (purchased from Shanghai Yuan Ye Biological Technology Co., Ltd.) was added into the reactor with stirring, the reactor was heated to 68°C, and constant temperature stirring was carried out for 5 h, after the reaction was completed, the Amberlyst-15 ion exchange resin was removed by filtration, the filtrate was collected and rotary evaporation was carried out to remove the solvent N,N-dimethylformamide, then pure water was used for washing three times, and then it was placed in a room temperature condition for drying for 24 h, to obtain an intermediate;

[0056] A2, the intermediate, epichlorohydrin (99%; purchased from Shanghai Macklin Biochemical Technology Co., Ltd.) and 3% of triethylbenzylammonium chloride (98%; purchased from Shanghai Macklin Biochemical Technology Co., Ltd.) catalyst were added into a reactor, wherein the mass of epichlorohydrin was 4 times the mass of the intermediate, the reactor was placed in a water bath and heated to 45°C, and reacted for 5.5 hours under nitrogen protection; then the temperature was lowered to 30°C, 48% NaOH aqueous solution was added dropwise, the mass of the NaOH aqueous solution was 3.5 times the mass of the intermediate, the dropwise addition time was controlled within 0.5 hours, then the water bath was heated to 65°C and reacted for 3.5 hours, after the reaction was completed, NaCl was removed by filtration, the filtrate was collected and washed with water until the pH value was 7.0, excess epichlorohydrin was removed by distillation under reduced pressure, to obtain a curing agent.

[0057] Example 6

[0058] The curing agent was prepared by the following steps:

[0059] A1, add 1 L of solvent N, N-dimethylformamide (AR; purchased from the national pharmaceutical group chemical reagent co., LTD.) to the reactor, replace the air in the reactor A with nitrogen, make the reactor A in a nitrogen atmosphere, then add 0.5 mol of 2,4-dihydroxybenzophenone (99%; purchased from Shanghai Maikelin biochemical technology co., LTD.) and 0.55 mol of trimellitic anhydride (95%; purchased from Anhui Botai electronic material co., LTD.) to the reactor under stirring, stir and mix for 30 min, then add 100 g of amberlyst-15 ion exchange resin (purchased from Shanghai Yuan Ye biological technology co., LTD.) to the reactor under stirring, heat the reactor to 70℃, and stir at constant temperature for 5 h. After the reaction is completed, remove the amberlyst-15 ion exchange resin by filtration, collect the filtrate and rotary evaporate to remove the solvent N, N-dimethylformamide, then wash with pure water three times, and dry at room temperature for 24 h to obtain an intermediate;

[0060] A2, add the intermediate, epichlorohydrin (99%; purchased from Shanghai Maikelin biochemical technology co., LTD.) and 3% of triethylbenzylammonium chloride (98%; purchased from Shanghai Maikelin biochemical technology co., LTD.) catalyst of the mass of the intermediate to the reactor, wherein the mass of epichlorohydrin is 4 times the mass of the intermediate, heat the reactor to 45℃ in a water bath, and react for 6 hours under nitrogen protection; then cool to 30℃, add 48% NaOH aqueous solution, the mass of NaOH aqueous solution is 3.5 times the mass of the intermediate, the dropwise adding time is controlled within 0.5 h, then heat the water bath to 65℃ and keep for 3.5 h after reaction, filter out the by-product NaCl, collect the filtrate and wash with water until the pH value is 7.2, remove the excess epichlorohydrin by distillation under reduced pressure, and obtain a curing agent.

[0061] Example 7

[0062] Preparation of polyester powder coating:

[0063] First, the polyester powder coating includes the following mass parts of raw materials:

[0064] 45 parts of the film-forming material prepared in example 1;

[0065] 15 parts of the curing agent prepared in example 4;

[0066] 5 parts of titanium white;

[0067] 10 parts of barium sulfate;

[0068] 0.3 parts of benzoin;

[0069] 0.5 parts of antioxidant 1010.

[0070] Then, the preparation method of the above polyester powder coating includes the following steps:

[0071] S1, the above raw materials are weighed according to the mass fraction, and the weighed raw materials are added into a high-speed mixer, mixed at a speed of 500 r / min for 10 minutes, so that each component is uniformly dispersed, and a premix material is obtained;

[0072] S2, a double screw extruder is used, the screw temperature is set to 100℃, the premix material is melt-extruded, and the shearing and conveying effects of the screw further promote the uniform dispersion and mixing of each component to form a uniform melt;

[0073] S3, the extruded melt is rapidly cooled by a cooling device, and then pressed into a sheet for subsequent crushing treatment;

[0074] S4, the cooled sheet is crushed and sieved through a 200 mesh screen to obtain a polyester powder coating.

[0075] Example 8

[0076] Preparation of polyester powder coating:

[0077] 50 parts of the film-forming material prepared in Example 2;

[0078] 17 parts of the curing agent prepared in Example 5;

[0079] 10 parts of carbon black;

[0080] 12 parts of calcium carbonate;

[0081] 0.5 parts of benzoin;

[0082] 1 part of antioxidant 1010.

[0083] Then, the preparation method of the polyester powder coating includes the following steps:

[0084] S1, the above raw materials are weighed according to the mass fraction, and the weighed raw materials are added into a high-speed mixer, mixed at a speed of 750 r / min for 10 minutes, so that each component is uniformly dispersed, and a premix material is obtained;

[0085] S2, a double screw extruder is used, the screw temperature is set to 110℃, the premix material is melt-extruded, and the shearing and conveying effects of the screw further promote the uniform dispersion and mixing of each component to form a uniform melt;

[0086] S3, the extruded melt is rapidly cooled by a cooling device, and then pressed into a sheet for subsequent crushing treatment;

[0087] S4, the cooled sheet is crushed and sieved through a 200 mesh screen to obtain a polyester powder coating.

[0088] Example 9

[0089] The polyester powder coating is prepared by the following steps:

[0090] The film-forming material prepared in Example 3 is 55 parts;

[0091] The curing agent prepared in Example 6 is 20 parts;

[0092] Carbon black is 15 parts;

[0093] Calcium carbonate is 15 parts;

[0094] Camphor is 0.8 parts;

[0095] Antioxidant 168 is 1.5 parts.

[0096] Then, the polyester powder coating is prepared by the following steps:

[0097] S1, the above raw materials are weighed according to the mass parts, and the weighed raw materials are added to a high-speed mixer and mixed at a speed of 1000 r / min for 10 minutes to make the components preliminarily uniformly dispersed to obtain a premix;

[0098] S2, a double-screw extruder is used, the screw temperature is set to 120°C, and the premix is melt-extruded, and the shearing and conveying effects of the screw further promote the uniform dispersion and mixing of the components to form a uniform melt;

[0099] S3, the extruded melt is rapidly cooled by a cooling device and then pressed into a sheet for subsequent crushing treatment;

[0100] S4, the cooled sheet is crushed and then sieved through a 200-mesh sieve to obtain the polyester powder coating.

[0101] Comparative Example 1

[0102] Comparative Example 1 is a control group of Example 8, the film-forming material in Example 8 is replaced with polyester resin P2706 (purchased from Huangshan Jiajie New Material Co., Ltd.), and the rest of the raw materials, the amount of the raw materials, and the preparation method remain the same as in Example 8. Finally, a polyester powder coating is obtained.

[0103] Comparative Example 2

[0104] Comparative Example 2 is a control group of Example 8, the curing agent in Example 8 is replaced with isocyanuric acid triglycidyl ester (purchased from Shanghai Maikelin Biochemical Technology Co., Ltd.), and the rest of the raw materials, the amount of the raw materials, and the preparation method remain the same as in Example 8. Finally, a polyester powder coating is obtained.

[0105] Comparative Example 3

[0106] Comparative Example 3 is a control group of Example 8, in which the raw material film-forming substance in Example 8 is replaced with polyester resin P2706 (purchased from Huangshan Jiajie New Material Co., Ltd.), the curing agent is replaced with isocyanuric acid triglycidyl ester (purchased from Shanghai Maikelin Biochemical Technology Co., Ltd.), and the rest of the raw materials, the amount of the raw materials, and the preparation method are kept consistent with those in Example 8, and finally a polyester powder coating is obtained.

[0107] The polyester powder coatings prepared in Examples 7-9 and Comparative Examples 1-3 are respectively subjected to adhesion, leveling, hardness, and ultraviolet light aging resistance performance tests, and the performance test process is as follows, and the test results are shown in Table 1.

[0108] The adhesion performance test detects the adhesion of the paint film according to GB / T9286-2021;

[0109] The leveling performance test is performed according to the leveling effect rating standard plate of American PCI;

[0110] The hardness performance test detects the pencil hardness of the paint film according to GB / T6739-2006;

[0111] The ultraviolet light aging resistance is performed according to the provisions in GB / T23987-2009. Specifically: the light stage: UVB-313 lamp, irradiance 0.71 W / (m 2 ·nm), blackboard temperature 60℃, 2h; water spraying stage: water temperature 20-30℃, water spraying 18min, (total cycle 2h18min, repeat); aging time is 2000h, after aging, test ΔE with a spectrophotometer;

[0112] Table 1 Test results

[0113] Item 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

[0114] Comparing the data of Comparative Example 8 and Comparative Example 1, it can be seen that using a hyperbranched polyester as a film-forming substance can impart excellent adhesion to the coating;

[0115] Comparing the data of Comparative Example 8 and Comparative Example 1, it can be seen that using a hyperbranched polyester as a film-forming substance can impart excellent leveling to the coating;

[0116] Comparing the data of Comparative Example 8 and Comparative Example 2, it can be seen that adding the curing agent prepared in Example 5 of the present application can help to improve the hardness of the coating compared with the existing curing agent isocyanuric acid triglycidyl ester;

[0117] Comparing the data of Comparative Example 8 and Comparative Example 2, it can be seen that adding the curing agent prepared in Example 5 of the present application can significantly improve the ultraviolet light aging resistance of the powder coating.

[0118] It has to be noted that, as used herein, such terms as "including", "including a", "having", "comprising", "containing", or any other similar words, are intended to be used inclusively, so that a process, method, article, or apparatus that includes a list of elements is not limited to those elements, but can include other elements not expressly listed or even inherent to such process, method, article, or apparatus.

[0119] While embodiments of the application have been shown and described, it is to be understood that the application is not limited to the details of the embodiments described, since various modifications can be made by those skilled in the art, without departing from the spirit and scope of the application, which are defined by the appended claims and their equivalents.

Claims

1. A polyester-based powder coating, characterized in that, By weight, it includes the following raw materials: 45-55 parts of film-forming substance; 15-20 parts of curing agent; 5-15 parts pigment; 10-15 parts of filler; Benzoin 0.3–0.8 parts; Antioxidant 0.5–1.5 parts; The film-forming substance is prepared by the following steps: T1. Dry 2,2-dimethylolpropionic acid in a vacuum drying oven at 80°C for 4-6 hours. Add the dried 2,2-dimethylolpropionic acid and p-toluenesulfonic acid to a reactor. The amount of p-toluenesulfonic acid added is 0.5%-2% of the mass of the dried 2,2-dimethylolpropionic acid. Under nitrogen protection, heat to 140°C and react for 1-2 hours. T2. Then heat to above 160℃ and react for 2 to 4 hours. Then heat to 180℃, turn off the nitrogen gas, and evacuate the reaction system to make the pressure ≤100Pa. Continue the reaction under reduced pressure until no residual water is removed, and the resin, i.e. the film-forming substance, is obtained. The curing agent is prepared by the following steps: A1. Take N,N-dimethylformamide, purge with nitrogen for protection, then add 2,4-dihydroxybenzophenone and trimellitic anhydride to it while stirring, stir and mix for 10-30 min, then add Amberlyst-15 ion exchange resin while stirring, heat to 65-70℃, and stir at a constant temperature for 4-5 h. After the reaction is complete, filter to remove Amberlyst-15 ion exchange resin, collect the filtrate and remove the solvent N,N-dimethylformamide by rotary evaporation, then wash three times with pure water, and then dry at room temperature for 24 h to obtain the 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 under nitrogen protection for 5–6 hours, then cool it to 30°C. Add a 48% NaOH aqueous solution dropwise, with the mass of the NaOH aqueous solution being 3.5 times the mass of the intermediate. Control the addition time to 0.5–1 hour. Then, raise the water bath temperature to 65°C and maintain the temperature for 3–4 hours. After the reaction is complete, filter out the by-product NaCl, collect the filtrate, and wash it with water until the pH value is 6.7–7.

2. Remove excess epichlorohydrin by vacuum distillation. The obtained product is used as a curing agent for powder coatings.

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

3. The polyester powder coating according to claim 1, characterized in that, The mass of epichlorohydrin described in A2 is four times the mass of the intermediate.

4. The polyester powder coating according to claim 1, characterized in that, The mass of benzyltriethylammonium chloride mentioned in A2 is 3% of the mass of the intermediate.

5. The polyester powder coating according to claim 1, characterized in that, The pigment is either titanium dioxide or carbon black.

6. The polyester powder coating according to claim 1, characterized in that, The filler is either barium sulfate or calcium carbonate.

7. The polyester powder coating according to claim 1, characterized in that, The antioxidant is either antioxidant 1010 or antioxidant 168.

8. A method for preparing a polyester-based powder coating according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Weigh the above raw materials according to the mass fraction, add the weighed raw materials into a high-speed mixer, and mix at a speed of 500-1000 r / min for 10-15 minutes to obtain the premixed material; S2. A twin-screw extruder is used, with the screw temperature set to 100-120℃, to melt and extrude the premixed material to form a melt. S3. The extruded melt is rapidly cooled by a cooling device and then pressed into sheets; S4. After cooling, the sheet is crushed and passed through a 200-mesh sieve to obtain a polyester powder coating.