Polyester resin for weather-resistant anti-yellowing powder coating as well as preparation method and application of polyester resin

Abstract

The invention provides polyester resin for a weather-resistant anti-yellowing powder coating as well as a preparation method and application of the polyester resin. The polyester resin is prepared from the following raw materials: 30 to 35 percent of dihydric alcohol, 0.01 to 0.9 percent of esterification catalyst, 35 to 50 percent of aromatic polybasic acid, 10 to 20 percent of aliphatic dibasic acid, 0.5 to 2.5 percent of chain extender and 1 to 8 percent of acidolysis agent. The total amount of the raw materials is 100%. Compared with the prior art, the composition of the dihydric alcohol with hydrolysis resistance and different chain lengths and steric hindrances and the raw materials has a synergistic effect on improving the weather resistance and yellowing resistance of the polyester resin, and yellowing and aging of the prepared polyester resin after long-time use under severe conditions can be effectively avoided. Besides, due to the long straight chain structures of hexanediol and adipic acid, the flexibility, proper viscosity and excellent impact resistance of the molecular chain of the polyester resin can be improved, and the introduction of aromatic rings in the synthesis of the polyester resin is reduced, so that the yellowing of the polyester resin caused by the aromatic ring structure is effectively avoided.

Description

Technical Field

[0001] The invention belongs to the field of coatings and polyester resins, and in particular relates to a polyester resin for weather-resistant and yellowing-resistant powder coatings, a preparation method and an application thereof. Background Art

[0002] With the country's restrictions on the use of polluting coatings, powder coatings have received more and more attention due to their excellent properties such as no organic solvents, high raw material utilization rate and green environmental protection. Among them, polyester powder coatings are widely used in the field of automotive coatings due to their relatively low cost, strong weather resistance and high comprehensiveness. However, for engineering vehicles and special transport vehicles operating in long-term harsh outdoor conditions, there are higher requirements for the weather resistance of the powder coatings used.

[0003] As a key part of powder coatings, polyester resin contains unsaturated functional groups such as carbonyl, ketone, benzene ring and double bond in its base resin. It is easily affected by environmental factors such as light, moisture and other media during use, resulting in poor weather resistance such as discoloration, blistering and shedding, which directly affects the use effect of powder coatings. Monomers such as hexanediol, phthalic anhydride and terephthalic acid are mostly used in traditional synthesis processes, which have weak anti-yellowing ability, small steric hindrance and poor hydrolysis resistance.

[0004] In the prior art, the patent with publication number CN 114573820 A published on June 3, 2022 discloses a polyester resin for weather-resistant coatings, including the following raw materials: neopentyl glycol, 1,6-hexanediol, trimethylolpropane, terephthalic acid, hexahydrophthalic anhydride, diamine compounds, catalysts, and stabilizers. Its technical scheme is: first, neopentyl glycol, 1,6-hexanediol, trimethylolpropane, terephthalic acid, and hexahydrophthalic anhydride are used as the main synthetic substrates of the polyester resin, and the polyester prepolymer chain is synthesized by a one-pot method, and the weight of the above-mentioned substrate is controlled so that the obtained polyester prepolymer chain contains a terminal carboxyl group, and then the terminal carboxyl group and the homemade diamine compound are reacted to make the final polyester molecular chain contain a POSS structure and a hindered amine structure, and the high temperature resistance of the POSS structure and the characteristic of hindered amine absorbing free radicals are used to make the obtained polyester resin have excellent weather resistance. However, it is not disclosed that it has an anti-yellowing effect. Summary of the invention

[0005] The object of the present invention is to provide a polyester resin for weather-resistant and yellowing-resistant powder coating and a preparation method thereof. Through the design of raw materials and components, the obtained polyester resin has excellent weather resistance and yellowing resistance.

[0006] Another object of the present invention is to provide an application of a polyester resin for weather-resistant and yellowing-resistant powder coatings, which is used to prepare powder coatings, especially for preparing powder coatings for engineering vehicles and special transport vehicles in the automotive field to meet the needs of use in harsh environments.

[0007] The specific technical solutions of the present invention are as follows:

[0008] A polyester resin for weather-resistant and anti-yellowing powder coating, comprising the following raw materials in percentage by weight:

[0009] 30-35% of diol, 0.01-0.9% of esterification catalyst, 35-50% of aromatic polybasic acid, 10-20% of fatty dibasic acid, 0.5-2.5% of chain extender, 1-8% of acidolysis agent; the total of the above raw materials is 100%.

[0010] The diol preferably contains at least 1,4-cyclohexanediol and hexanediol;

[0011] Further, the diol is 1,4-cyclohexanediol and hexanediol, and other diols, and the other diols include any one or more of neopentyl glycol, 2-ethyl-2-butyl-1,3-propanediol, and hydroxypivalic acid neopentyl glycol monoester;

[0012] Preferably, the diols include 1,4-cyclohexanediol and hexanediol in a mass ratio of 27:8; or, the diols include 1,4-cyclohexanediol, hexanediol and other diols in a mass ratio of 22:8:5; the other diols include any one of neopentyl glycol, 2-ethyl-2-butyl-1,3-propanediol and hydroxypivalic acid neopentyl glycol monoester;

[0013] More preferably, the diols include 1,4-cyclohexanediol, hexanediol and neopentyl glycol in a mass ratio of 22:8:5; or, the diols include 1,4-cyclohexanediol, hexanediol and 2-ethyl-2-butyl-1,3-propanediol in a mass ratio of 22:8:5; or, the diols include 1,4-cyclohexanediol, hexanediol and hydroxypivalic acid neopentyl glycol monoester in a mass ratio of 22:8:5;

[0014] The structural formula of the 1,4-cyclohexanediol is:

[0015] The structural formula of the neopentyl glycol is:

[0016] The structural formula of the 2-ethyl-2-butyl-1,3-propanediol is: The structural formula of the hydroxypivalate neopentyl glycol monoester is

[0017] The esterification catalyst is an organic tin compound; the organic tin compound includes one or a mixture of two or more of dibutyltin dibenzoate, stannous octoate, monobutyltin oxide, and dibutyltin dilaurate, preferably monobutyltin oxide.

[0018] The aromatic polyacid is one of isophthalic acid and terephthalic acid or a mixture of the two, preferably isophthalic acid.

[0019] The fatty dibasic acid is selected from one of 1,4-cyclohexanedicarboxylic acid, adipic acid, and succinic acid, or a mixture of two thereof; preferably, the fatty dibasic acid contains at least adipic acid; more preferably, it is a mixture of 1,4-cyclohexanedicarboxylic acid and adipic acid, and the mass ratio of the two is 0.75:1.

[0020] The raw materials of the polyester resin for weather-resistant and anti-yellowing powder coating contain at least adipic acid and hexanediol.

[0021] The chain extender is one or a mixture of 1,4-butanediol, trimethylolpropane, pentaerythritol, 1,2,3,4,5,6-hexasol, preferably trimethylolpropane.

[0022] The acidolysis agent is one or a mixture of two of isophthalic acid, 1,4-cyclohexanedicarboxylic acid, sebacic acid, and azelaic acid, preferably isophthalic acid and 1,4-cyclohexanedicarboxylic acid.

[0023] The present invention provides a method for preparing a polyester resin for weather-resistant and yellowing-resistant powder coating, which specifically comprises:

[0024] The diol, chain extender and esterification catalyst in the formula are mixed, aromatic polybasic acid and fatty dibasic acid are added after melting, nitrogen is introduced, and the temperature is raised to 240°C for reaction, and the acid value reaches 10-20 mgKOH / g; then an acidolysis agent is added, and the reaction is continued at the temperature until the acid value reaches 30-35 mgKOH / g, and vacuum polycondensation is carried out until the system reaches 25-30 mgKOH / g, and the reaction is stopped to obtain a polyester resin for weather-resistant and anti-yellowing powder coatings.

[0025] The temperature is raised to 240° C. for reaction for 10 hours;

[0026] The continued heat preservation reaction refers to the reaction at 240°C for 3h;

[0027] The vacuum polycondensation refers to making the gas pressure between -0.03MPa and -0.12MPa and polycondensing for 2h.

[0028] The invention provides an application of a polyester resin for weather-resistant and yellowing-resistant powder coating, which is used for preparing powder coatings, especially for preparing powder coatings for engineering vehicles and special transport vehicles in the automotive field.

[0029] The inventors have found that in the synthesis of polyester resins, it is necessary to select polyols and polyacid monomers with strong weather resistance, large steric hindrance, and strong hydrolysis resistance, so that the prepared polyester resin has excellent weather resistance. Polyols with strong hydrolysis resistance and large steric hindrance can effectively prevent the prepared polyester resin from yellowing and aging when used under harsh conditions for a long time. This further expands the application range of polyester resins for weather-resistant powder coatings under harsh conditions.

[0030] The present invention aims at the problem that monomers containing carbonyl and benzene ring structures are mostly used in the previous synthesis process, which makes the anti-yellowing performance and weather resistance of polyester resin weak. The diol raw material monomer screening and formula optimization design are carried out, and it is found that under the mixed effect of 1,4-cyclohexanediol in the diol and hydrolysis-resistant diols (neopentyl glycol, 2-ethyl-2-butyl-1,3-propanediol, hydroxypivalic acid neopentyl glycol monoester) with different steric hindrances and chain lengths, the unsaturated groups such as benzene rings, carbonyls, double bonds on the alcohol monomer are reduced, and the yellowing and aging of the polyester resin under long-term harsh conditions are avoided, thereby improving the anti-yellowing performance and weather resistance of the polyester resin. In addition, the present invention adds hexanediol and adipic acid in the synthesis process, and the diol / diacid with a long straight chain structure can improve the flexibility, suitable viscosity and excellent impact resistance of the polyester resin molecular chain, and reduce the introduction of aromatic rings in the synthesis of polyester resin, thereby effectively avoiding the yellowing of polyester resin caused by aromatic ring structure.

[0031] Compared with the prior art, the present invention finds that the compounding of diols with different chain lengths and steric hindrances with hydrolysis resistance and raw material formula design has a synergistic effect in improving the weather resistance and yellowing resistance of polyester resins. The polyols with strong hydrolysis resistance and large steric hindrance can effectively avoid the yellowing and aging of the prepared polyester resins used in harsh conditions for a long time. In addition, hexanediol and adipic acid are added during the synthesis process. The diol / diacid with a long straight chain structure can improve the flexibility, suitable viscosity, and excellent impact resistance of the polyester resin molecular chain, and reduce the introduction of aromatic rings in the synthesis of polyester resins, thereby effectively avoiding the yellowing of polyester resins caused by aromatic ring structures. The polyester resin prepared in the present invention is used for powder coatings to show good weather resistance and yellowing resistance. The weather-resistant and yellowing-resistant powder coatings described in the present invention have broad application prospects for the use of engineering vehicles and special transport vehicles in harsh environments in the automotive field. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0034] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0035] Example 1

[0036] A polyester resin for weather-resistant and anti-yellowing powder coating comprises the following raw materials in percentage by mass: as shown in Table 1.

[0037] The preparation method of the polyester resin for weather-resistant and anti-yellowing powder coating described in this embodiment is as follows:

[0038] In a prepared heated stirring reactor device, diol 1,4-cyclohexanediol and hexanediol, trimethylolpropane and monobutyltin oxide were stirred and mixed, and then isophthalic acid, 1,4-cyclohexanedicarboxylic acid and adipic acid were added after melting. Nitrogen was introduced into the reactor and the temperature was controlled to be raised to 180°C, and esterification water was generated and distilled out. The temperature was then raised and continued to be controlled to 240°C, and maintained at 240°C for 10 hours, and the acid value of the system reached 13 mgKOH / g. The acidolysis agent isophthalic acid was added, and the reaction was continued at 240°C for 3 hours, and the acid value of the system reached 32 mgKOH / g. Finally, vacuum polycondensation was carried out for 2 hours to make the air pressure between -0.03 MPa and -0.12 MPa, and the acid value of the system reached 28 mgKOH / g. The reaction was stopped to obtain a polyester resin for weather-resistant and anti-yellowing powder coatings, which was recorded as resin-1.

[0039] Example 2

[0040] A polyester resin for weather-resistant and anti-yellowing powder coating comprises the following raw materials in percentage by mass: as shown in Table 1.

[0041] The preparation method of the polyester resin for weather-resistant and anti-yellowing powder coating described in this embodiment is as follows:

[0042] In a prepared heated stirring reactor device, diols (1,4-cyclohexanediol, hexanediol and neopentyl glycol), trimethylolpropane and monobutyltin oxide were stirred and mixed, and after melting, isophthalic acid, 1,4-cyclohexanedicarboxylic acid and adipic acid were added, nitrogen was introduced into the reactor, and the temperature was controlled to be 180°C, and esterification water was generated and distilled out; then the temperature was raised and continued to be controlled to 240°C, and maintained at 240°C for 10 hours, and the acid value of the system reached 11 mgKOH / g; acidolysis agent isophthalic acid was added, and the reaction was continued at 240°C for 3 hours, and the acid value of the system reached 31 mgKOH / g, and finally vacuum polycondensation was carried out for 2 hours to make the air pressure between -0.03MPa and -0.12MPa, and the acid value of the system reached 25mgKOH / g, and the reaction was stopped to obtain a polyester resin for weather-resistant and anti-yellowing powder coatings, recorded as resin-2.

[0043] Example 3

[0044] A polyester resin for weather-resistant and anti-yellowing powder coating comprises the following raw materials in percentage by mass: as shown in Table 1.

[0045] The preparation method of the polyester resin for weather-resistant and anti-yellowing powder coating described in this embodiment is as follows:

[0046] In a prepared heated stirring reactor device, diols (1,4-cyclohexanediol, hexanediol and 2-ethyl-2-butyl-1,3-propanediol), trimethylolpropane and monobutyl tin oxide were stirred and mixed, and after melting, isophthalic acid, 1,4-cyclohexanedicarboxylic acid and adipic acid were added, nitrogen was introduced into the reactor, and the temperature was controlled to be 180°C, and esterification water was generated and distilled out; then the temperature was raised and continued to be controlled to 240°C, and maintained at 240°C for 10 hours, and the acid value of the system reached 13 mgKOH / g; acidolysis agent isophthalic acid was added, and the reaction was continued at 240°C for 3 hours, and the acid value of the system reached 33 mgKOH / g, and finally vacuum polycondensation was carried out for 2 hours to make the air pressure between -0.03 MPa and -0.12 MPa, and the acid value of the system reached 25 mgKOH / g, and the reaction was stopped to obtain a polyester resin for weather-resistant and anti-yellowing powder coatings, recorded as resin-3.

[0047] Example 4

[0048] A polyester resin for weather-resistant and anti-yellowing powder coating comprises the following raw materials in percentage by mass: as shown in Table 1.

[0049] The preparation method of the polyester resin for weather-resistant and anti-yellowing powder coating described in this embodiment is as follows:

[0050] In a prepared heated stirring reactor device, diols (1,4-cyclohexanediol, hexanediol and hydroxypivalic acid neopentyl glycol monoester), trimethylolpropane and monobutyl tin oxide were stirred and mixed, and after melting, isophthalic acid, 1,4-cyclohexanedicarboxylic acid and adipic acid were added, nitrogen was introduced into the reactor, and the temperature was controlled to be 180°C, and esterification water was generated and distilled out; then the temperature was raised, and the heating rate was continued to be controlled to 240°C, and the temperature was maintained at 240°C for 10 hours, and the acid value of the system reached 15 mgKOH / g; acidolysis agent isophthalic acid was added, and the reaction was continued at 240°C for 3 hours, and the acid value of the system reached 32 mgKOH / g, and finally vacuum polycondensation was carried out for 2 hours to make the air pressure between -0.03MPa and -0.12MPa, and the acid value of the system reached 26mgKOH / g, and the reaction was stopped to obtain a polyester resin for weather-resistant and anti-yellowing powder coatings, recorded as resin-4.

[0051] Comparative Example 1

[0052] A polyester resin comprises the following raw materials in percentage by weight: as shown in Table 1.

[0053] The preparation method of the polyester resin described in this comparative example is:

[0054] In a prepared heated stirring reactor device, diols (1,4-cyclohexanediol, hexanediol and ethylene glycol), trimethylolpropane and monobutyltin oxide were stirred and mixed, and after melting, isophthalic acid, 1,4-cyclohexanedicarboxylic acid and adipic acid were added, nitrogen was introduced into the reactor, and the temperature was controlled to be 180°C, and esterification water was generated and distilled out; the temperature was then raised and continued to be controlled to 240°C, and maintained at 240°C for 10 hours, and the acid value of the system reached 15 mgKOH / g; acidolysis agent isophthalic acid was added, and the reaction was continued at 240°C for 3 hours, and the acid value of the system reached 30 mgKOH / g, and finally vacuum polycondensation was carried out for 2 hours to make the air pressure between -0.03 MPa and -0.12 MPa, and the acid value of the system reached 25 mgKOH / g, and the reaction was stopped to obtain a polyester resin for weather-resistant and anti-yellowing powder coatings, which was recorded as comparative resin-1.

[0055] Comparative Example 2

[0056] A polyester resin comprises the following raw materials in percentage by weight: as shown in Table 1.

[0057] The preparation method of the polyester resin described in this comparative example is:

[0058] In a prepared heated stirring reactor device, diols (1,4-cyclohexanediol, hexanediol and pentanediol), trimethylolpropane and monobutyltin oxide were stirred and mixed, and after melting, isophthalic acid, 1,4-cyclohexanedicarboxylic acid and adipic acid were added, nitrogen was introduced into the reactor, and the temperature was controlled to be 180°C, and esterification water was generated and distilled out; then the temperature was raised, and the heating rate was continued to be controlled to 240°C, and the temperature was maintained at 240°C for 10 hours, and the acid value of the system reached 17 mgKOH / g; acidolysis agent isophthalic acid was added, and the reaction was continued at 240°C for 3 hours, and the acid value of the system reached 34 mgKOH / g, and finally vacuum polycondensation was carried out for 2 hours to make the air pressure between -0.03MPa and -0.12MPa, and the acid value of the system reached 27mgKOH / g, and the reaction was stopped to obtain a polyester resin for weather-resistant and anti-yellowing powder coatings, which was recorded as comparative resin-2.

[0059] Comparative Example 3

[0060] A polyester resin comprises the following raw materials in percentage by weight: as shown in Table 1.

[0061] The preparation method of the polyester resin described in this comparative example is:

[0062] In a prepared heated stirring reactor device, 1,4-cyclohexanediol, trimethylolpropane and monobutyltin oxide were stirred and mixed, and then isophthalic acid and 1,4-cyclohexanedicarboxylic acid were added after melting. Nitrogen was introduced into the reactor and the temperature was controlled to be raised to 180°C, and esterification water was generated and distilled out. The temperature was then raised and continued to be controlled to 240°C, and maintained at 240°C for 10 hours, and the acid value of the system reached 12 mgKOH / g. The acidolysis agent isophthalic acid was added, and the reaction was continued at 240°C for 3 hours, and the acid value of the system reached 31 mgKOH / g. Finally, vacuum polycondensation was carried out for 2 hours to make the air pressure between -0.03 MPa and -0.12 MPa, and the acid value of the system reached 29 mgKOH / g. The reaction was stopped to obtain a polyester resin for weather-resistant and anti-yellowing powder coatings, which was recorded as comparative resin-3.

[0063] Table 1 Ratio of raw materials in each embodiment and comparative example

[0064]

[0065] The polyester resins prepared in the above examples and comparative examples are used for powder coating preparation:

[0066] Different polyester resins (resin 1-resin 4, comparative resin 1-comparative resin 3) prepared according to the examples and comparative examples, curing agent (triglycidyl isocyanurate), titanium dioxide, barium sulfate, leveling agent 588, and benzoin are added to a batching container according to a given formula, first fully stirred, melt-extruded, crushed, and sieved through an extruder, and finally powder coatings of different polyester resins can be obtained. The dosage ratio is based on mass parts: 100 parts of polyester resin, 10 parts of curing agent (triglycidyl isocyanurate), 35 parts of titanium dioxide, 30 parts of barium sulfate, 1 part of leveling agent, and 0.5 part of benzoin.

[0067] Performance testing:

[0068] The impact resistance test of the prepared coating examples and comparative examples was carried out in accordance with the provisions of the national standard GB / T 1732-2020. The specific results are shown in Table 2.

[0069] According to the provisions of the national standard GB / T 14522-2008, the prepared coating examples and comparative examples were subjected to weathering aging tests. The specific results are shown in Table 2.

[0070] The aging and weather resistance tests were performed on the prepared coating examples and comparative examples according to the national standard GB / T 1771-2007. The specific results are shown in Table 2.

[0071] Table 2 Comparison of properties of polyester resin powder coatings

[0072]

[0073]

[0074] Result analysis: According to the discussion of the powder coating test results in Table 2, the impact resistance, gloss retention, color difference and salt spray resistance of the powder coating in the example are significantly better than those in the comparative example. The results show that the selection of diols that are resistant to hydrolysis, have large steric hindrance and have long chains has a synergistic effect on improving the anti-yellowing and weather resistance of powder coatings for polyester resins. The coordinated use of diol monomers in the raw material formula in the synthesis of polyester resins is crucial. In addition, during the synthesis process, hexanediol and adipic acid are added, and the diol / diacid with a long straight chain structure can improve the flexibility, suitable viscosity and excellent impact resistance of the polyester resin molecular chain, and reduce the introduction of aromatic rings in the synthesis of polyester resins, thereby effectively avoiding the yellowing of polyester resins caused by aromatic ring structures. It also shows that the powder coating prepared from the polyester resin described in the present invention has excellent weather resistance and anti-yellowing properties.

[0075] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A polyester resin for weather-resistant and anti-yellowing powder coating, characterized in that: The polyester resin for weather-resistant and anti-yellowing powder coating comprises the following raw materials in percentage by weight: 30-35% of diol, 0.01-0.9% of esterification catalyst, 35-50% of aromatic polybasic acid, 10-20% of fatty dibasic acid, 0.5-2.5% of chain extender, 1-8% of acidolysis agent; the total of the above raw materials is 100%.

2. The polyester resin for weather-resistant and anti-yellowing powder coating according to claim 1, characterized in that: The diol contains at least 1,4-cyclohexanediol and hexanediol.

3. The polyester resin for weather-resistant and anti-yellowing powder coating according to claim 1 or 2, characterized in that: The diols are 1,4-cyclohexanediol and hexanediol, and other diols, and the other diols include any one or more of neopentyl glycol, 2-ethyl-2-butyl-1,3-propanediol, and hydroxypivalic acid neopentyl glycol monoester.

4. The polyester resin for weather-resistant and anti-yellowing powder coating according to claim 1, characterized in that: The fatty dibasic acid is selected from one of 1,4-cyclohexanedicarboxylic acid, adipic acid, and succinic acid, or a mixture of two of them.

5. The polyester resin for weather-resistant and anti-yellowing powder coating according to any one of claims 1 to 4, characterized in that: The fatty dibasic acid contains at least adipic acid.

6. The polyester resin for weather-resistant and anti-yellowing powder coating according to any one of claims 1 to 5, characterized in that: The aromatic polyacid is one of isophthalic acid and terephthalic acid or a mixture of the two.

7. The polyester resin for weather-resistant and anti-yellowing powder coating according to claim 1, characterized in that: The chain extender is one or a mixture of two of 1,4-butanediol, trimethylolpropane, pentaerythritol, and 1,2,3,4,5,6-hexasol.

8. A method for preparing the polyester resin for weather-resistant and anti-yellowing powder coating according to any one of claims 1 to 7, characterized in that: The preparation method is specifically as follows: mixing a formula amount of diol, a chain extender and an esterification catalyst, adding aromatic polyacid and fatty dibasic acid after melting, introducing nitrogen, heating to 240°C for reaction, and the acid value reaches 10-20 mgKOH / g; then adding an acidolysis agent, continuing the heat preservation reaction, the acid value reaches 30-35 mgKOH / g, performing vacuum polycondensation, the system reaches 25-30 mgKOH / g, stopping the reaction, and obtaining a polyester resin for weather-resistant and anti-yellowing powder coatings.

9. The preparation method according to claim 8, characterized in that: The temperature is raised to 240°C for reaction for 10 hours; the continued heat preservation reaction refers to the reaction at 240°C for 3 hours; the vacuum polycondensation refers to the vacuum polycondensation for 2 hours at a pressure between -0.03MPa and -0.12MPa.

10. An application of the polyester resin for weather-resistant and anti-yellowing powder coating according to any one of claims 1 to 7, characterized in that: Used to prepare powder coatings.

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