A polyester resin for TGIC powder coatings and its preparation method

Abstract

The present invention relates to a polyester resin for powder coatings, specifically a matte, halogen-free flame-retardant polyester resin for TGIC curing system. This polyester resin is polymerized using raw materials including phenylphosphonic dichloride, 2-ethyl-1,3-hexanediol, dimethyl isophthalate, N-methylethanolamine, succinic acid, ethylenediaminetetraacetic acid, 6-amino-1-naphthalenesulfonic acid, and 3-methylglutaric acid. This solution has no added small-molecule flame retardant components, achieving excellent water resistance and flame retardancy of the polyester resin. Finally, after low-temperature curing with TGIC curing agent, the gloss of its coating film is basically between 30% and 45%, with outstanding decorative properties. In the case of not containing non-environmental halogen atoms, the oxygen index of the coating film can reach about 34%, and the flame retardant performance is excellent.

Description

Technical Field

[0001] The present invention relates to the technical field of powder coatings. Specifically, it relates to a polyester resin for TGIC powder coatings, its preparation method, and its application in a powder coating system. Background Art

[0002] Powder coatings have prominent advantages such as environmental protection, no VOC emissions, and recyclability, and have developed rapidly in recent years. Powder coatings are mainly divided into categories such as indoor hybrids and outdoor weather resistance. Outdoor weather-resistant powder coatings are mainly based on the TGIC curing system, and ordinary TGIC powder coatings basically do not have flame retardant properties. Although a polyester resin for TGIC powder coatings was developed in CN202110828226.0, which has a certain flame retardant ability, due to the presence of chlorine atoms in its molecules, it does not meet the requirements of environmentally friendly halogen-free flame retardants. With the popularization of powder coatings, there is also a large demand for various low-gloss decorative powder coatings. Currently, matting is mostly achieved by adding external matting agents. However, after the addition of matting agents, problems such as uneven mixing and poor compatibility often occur, resulting in poor matting stability of the powder coatings. How to stably obtain a relatively low-gloss (30 - 50%) coating film is also a challenge. Summary of the Invention

[0003] Aiming at the problems existing in the current TGIC curing system, the present invention is obtained by polymerization using raw materials including phenylphosphoryl dichloride, 2-ethyl-1,3-hexanediol, dimethyl isophthalate, N-methylethanolamine, succinic acid, ethylenediaminetetraacetic acid, 6-amino-1-naphthalenesulfonic acid, and 3-methylglutaric acid. The resulting polyester resin has a high nitrogen content and phosphate ester content in its chain segment structure, and has an environmentally friendly flame retardant effect; at the same time, the introduction of phosphate esters results in a relatively low softening point of the polyester resin and high terminal carboxyl activity, which can not only achieve low-temperature curing, but also after using a composite capping agent, in addition to carboxyl groups, the end groups of the polyester resin also have an appropriate amount of active amino groups. Finally, due to the speed difference during the curing process, a better matting effect will be produced. Moreover, the special hydrophobic raw materials used in the synthesis of the polyester resin, such as phenylphosphoryl dichloride, 2-ethyl-1,3-hexanediol, 6-amino-1-naphthalenesulfonic acid, and 3-methylglutaric acid, and at the same time without adding external flame retardant components, achieve excellent water resistance of the polyester resin. Finally, after low-temperature curing (160°C / 20 min) with a TGIC curing agent, the gloss of its coating film is basically between 30 - 50%, with excellent decoration. Without containing non-environmentally friendly halogen atoms, the oxygen index of the coating film can reach about 34%, and the flame retardant performance is excellent.

[0004] The present invention relates to a polyester resin for powder coatings, comprising the following raw materials in parts by mole:

[0005]

[0006] The raw materials further include a catalyst, an antioxidant, and an acid-binding agent.

[0007] Among them, there are two kinds of catalysts. Catalyst 1 is sodium tert-butoxide, and its dosage is 0.5-0.8% of the molar amount of dimethyl isophthalate; Catalyst 2 is stannous oxalate, and its dosage is 0.04-0.1% of the total molar amount of the raw materials.

[0008] Among them, the molar ratio of 2-ethyl-1,3-hexanediol to phenylphosphoryl dichloride ≥ 2.05.

[0009] Among them, the antioxidant is antioxidant 1076, that is, n-octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and its dosage is 0.3-0.5% of the total molar amount of the raw materials.

[0010] Among them, the acid-binding agent is triethylamine, and its molar amount is 2.2-2.5 times that of phenylphosphoryl dichloride.

[0011] The preparation method of the polyester resin for powder coatings as described above includes the following steps:

[0012] A. Add the formulated amount of anhydrous tetrahydrofuran and phenylphosphoryl dichloride to a mixing tank. After mixing evenly, pump it to a high-level tank for standby;

[0013] B. Add the formulated amount of 2-ethyl-1,3-hexanediol and acid-binding agent to Reactor A. After fully stirring evenly, start the cooling system, cool the mixed solution to 0-5°C and keep it warm. Then open the control valve of the high-level tank and start to dropwise add the tetrahydrofuran solution of phenylphosphoryl dichloride. After the dropping is completed, carry out a holding reaction at 0-5°C;

[0014] C. Take a sample and detect it by gas chromatography. When the conversion rate of phenylphosphoryl dichloride reaches more than 97%, stop the reaction, filter off the insoluble salts, and obtain a reaction-modified phosphoric acid ester diol intermediate solution for standby;

[0015] D. Add the formulated amount of dimethyl isophthalate, N-methylethanolamine, and Catalyst 1 to Reactor B, heat up to 100-110°C for ammonolysis reaction, and collect the by-products obtained from the reaction at the same time;

[0016] E. Take a sample for detection. When the free dimethyl isophthalate is less than 2% and the collected by-products reach more than 90% of the theory, pump the modified phosphoric acid ester diol intermediate solution obtained in step C into Reactor 2, stir evenly, then add the formulated amount of succinic acid and Catalyst 2, and then gradually heat up to 210-220°C for polymerization reaction;

[0017] F. Sample and detect the acid value of the polymer. When the acid value reaches 20 - 30 mgKOH / g, add the formulated amount of ethylenediaminetetraacetic acid for chain extension polymerization reaction, and at the same time, raise the reaction temperature to 225 - 230 °C;

[0018] G. When the acid value of the polymer reaches 22 - 28 mgKOH / g, then add the formulated amount of antioxidant, stir evenly, start the vacuum system, and carry out vacuum polymerization reaction at 225 - 230 °C;

[0019] H. Stop the vacuum system when the acid value of the polymer reaches 8 - 14 mgKOH / g, add the formulated amount of composite end-capping agent 6-amino-1-naphthalenesulfonic acid and 3-methylglutaric acid for end-capping reaction. When the acid value of the polymer reaches 29 - 38 mgKOH / g, stop the reaction, then discharge the material at high temperature, cool the polyester resin, crush and granulate to obtain the product.

[0020] Preferably, in step E, the temperature is gradually raised to 210 - 220 °C at a heating rate of 15 - 18 °C / h for polymerization reaction; during the heating process, small molecule compounds such as tetrahydrofuran, residual triethylamine solvent and esterification water are removed at the same time; in step G, the vacuum degree is controlled at -0.096 Mpa to -0.098 Mpa; in step H, the polyester resin is cooled with a steel belt equipped with a cooling system.

[0021] For example, the preparation method of the above polyester resin for powder coatings includes the following steps:

[0022] A. Add the formulated amount of anhydrous tetrahydrofuran and phenylphosphoryl dichloride to the mixing tank, mix well, and then pump it to the high-level tank for standby;

[0023] B. Add the formulated amount of 2-ethyl-1,3-hexanediol and the acid-binding agent triethylamine to the reaction kettle A, stir well, start the cooling system, cool the mixed solution to 0 - 5 °C and keep it warm, then open the control valve of the high-level tank, start to drip the tetrahydrofuran mixed solution of phenylphosphoryl dichloride, control the dripping time within 1.5 - 2 h, and carry out the insulation reaction at 0 - 5 °C after the dripping is completed;

[0024] C. Sample and detect by gas chromatography. When the conversion rate of phenylphosphoryl dichloride reaches more than 97%, stop the reaction, filter off the insoluble triethylamine hydrochloride to obtain the reaction-modified phosphoric acid ester diol intermediate solution for standby;

[0025] D. Add the formulated amount of dimethyl isophthalate, N-methylethanolamine and catalyst 1 to the reaction kettle B, raise the temperature to 100 - 110 °C for ammonolysis reaction, and at the same time collect the by-product methanol obtained from the reaction;

[0026] E. Sampling and testing. When the content of free dimethyl isophthalate is lower than 2% and the collected methanol reaches more than 90% of the theoretical value, it indicates that the ammonolysis reaction is basically completed. At this time, pump the modified phosphoric acid ester diol intermediate solution obtained in step C into reactor 2, stir evenly, then add the formulated amount of succinic acid and catalyst 2, and then gradually raise the temperature to 210 - 220 °C at a heating rate of 15 - 18 °C / h for polymerization reaction; during the heating process, simultaneously remove small molecule compounds such as tetrahydrofuran, residual triethylamine solvent and esterification water.

[0027] F. Sampling and testing the acid value of the polymer. When the acid value reaches 20 - 30 mgKOH / g, add the formulated amount of ethylenediaminetetraacetic acid for chain extension polymerization reaction, and at the same time raise the reaction temperature to 225 - 230 °C.

[0028] G. When the acid value of the polymer reaches 22 - 28 mgKOH / g, then add the formulated amount of antioxidant, stir evenly, start the vacuum system, control the vacuum degree at -0.096 Mpa to -0.098 Mpa, and carry out vacuum polymerization reaction at 225 - 230 °C.

[0029] H. When the acid value of the polymer reaches 8 - 14 mgKOH / g, stop the vacuum system, add the formulated amount of composite capping agent 6 - amino - 1 - naphthalenesulfonic acid and 3 - methylglutaric acid for capping reaction. When the acid value of the polymer reaches 29 - 38 mgKOH / g, stop the reaction, then discharge at high temperature, and cool the polyester resin with a steel belt equipped with a cooling system, and crush and granulate to obtain.

[0030] The finally obtained product has a light yellow transparent granular appearance, an acid value of 29 - 38 mgKOH / g, and a softening point of 104 - 114 °C.

[0031] The present invention also relates to the application of the polyester resin for powder coatings as described above in a TGIC curing system. The TGIC transparent powder coating formulation may further include a leveling agent, a brightening agent, benzoin, etc. in addition to the polyester resin and TGIC. The method for preparing the coating layer is as follows: Mix each material according to the powder coating formulation, extrude, press and crush them respectively with a twin - screw extruder, and then pulverize and screen the sheet material to make a powder coating. The powder coating is sprayed on the surface - treated aluminum alloy substrate with an electrostatic spray gun and cured (for example, at 160 °C / 20 min) to obtain the coating layer.

[0032] Beneficial effects:

[0033] Through the creative design of reactants, the polyester resin obtained has a high nitrogen content and phosphate ester content in the chain segment structure, showing an environmentally friendly flame retardant effect. At the same time, the introduction of phosphate ester results in a relatively low softening point of the polyester resin and a high activity of terminal carboxyl groups. It can not only achieve low-temperature curing, but also after using a composite capping agent, in addition to carboxyl groups, the terminal groups of the polyester resin also have an appropriate amount of active amino groups. Eventually, due to the speed difference during the curing process, a good matting effect will be produced. Moreover, the special hydrophobic raw materials used in the synthesis of the polyester resin, such as phenylphosphoryl dichloride, 2-ethyl-1,3-hexanediol, 6-amino-1-naphthalenesulfonic acid, 3-methylglutaric acid, etc., and there is no added small molecule flame retardant component, realizing excellent water resistance and flame retardancy of the polyester resin. Finally, after low-temperature curing (160°C / 20 min) with the TGIC curing agent, the gloss of its coating film is basically between 30% and 50%, with outstanding decorative properties. Without non-environmental halogen atoms, the oxygen index of the coating film can reach about 34%, and the flame retardant performance is excellent. Detailed Embodiments

[0034] The present invention will be further described below in conjunction with embodiments. It should be noted that, without conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be pointed out that unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The "including" or "comprising" and other similar words used in the disclosure of the present invention mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects.

[0035] All the raw materials described in the present invention are commercially available.

[0036] Preparation Example 1

[0037] A polyester resin for powder coatings, comprising the following raw materials in mole parts:

[0038]

[0039] Catalyst 1 is sodium tert-butoxide, and the dosage is 0.8% of the molar amount of dimethyl isophthalate;

[0040] Catalyst 2 is stannous oxalate, and the dosage is 0.1% of the total molar amount of the raw materials;

[0041] The antioxidant is antioxidant 1076, and the dosage is 0.5% of the total molar amount of the raw materials;

[0042] The acid-binding agent is triethylamine, and the molar amount is 2.5 times the molar amount of phenylphosphoryl dichloride.

[0043] The preparation method of the polyester resin for powder coatings includes the following steps:

[0044] A. Add the formulated amount of anhydrous tetrahydrofuran and phenylphosphonic dichloride into a mixing tank. After fully mixing evenly, pump it to a high-level tank for standby.

[0045] B. Add the formulated amount of 2-ethyl-1,3-hexanediol and the acid-binding agent triethylamine into Reactor A. After fully stirring evenly, start the cooling system. Cool the mixed solution to 0 °C and keep it warm. Then open the control valve of the high-level tank and start dropping the tetrahydrofuran mixed solution of phenylphosphonic dichloride. Control the dropping time within 1.5 - 2 h. After the dropping is completed, carry out a holding reaction at 0 °C.

[0046] C. Take a sample for gas chromatography detection. When the conversion rate of phenylphosphonic dichloride reaches more than 97%, stop the reaction. Filter off the insoluble triethylamine hydrochloride to obtain a reaction-modified phosphoric acid ester diol intermediate solution for standby.

[0047] D. Add the formulated amount of dimethyl isophthalate, N-methylethanolamine and Catalyst 1 into Reactor B. Heat up to 100 °C for ammonolysis reaction, and simultaneously collect the by-product methanol obtained from the reaction.

[0048] E. Take a sample for detection. When the free dimethyl isophthalate is less than 2% and the collected methanol reaches more than 90% of the theory, it indicates that the ammonolysis reaction is basically completed. At this time, pump the modified phosphoric acid ester diol intermediate solution obtained in step C into Reactor 2. After stirring evenly, add the formulated amount of succinic acid and Catalyst 2, and then gradually heat up to 210 °C at a heating rate of 16 °C / h for polymerization reaction; during the heating process, simultaneously remove small molecular compounds such as tetrahydrofuran, residual triethylamine solvent and esterification water.

[0049] F. Take a sample to detect the acid value of the polymer. When the acid value reaches 25 mgKOH / g, add the formulated amount of ethylenediaminetetraacetic acid for chain extension polymerization reaction, and at the same time raise the reaction temperature to 225 °C.

[0050] G. When the acid value of the polymer reaches 28 mgKOH / g, then add the formulated amount of antioxidant. After stirring evenly, start the vacuum system. Control the vacuum degree at -0.096 Mpa and carry out vacuum polymerization reaction at 230 °C.

[0051] H. When the acid value of the polymer reaches 12 mgKOH / g, stop the vacuum system. Add the formulated amount of composite capping agent 6-amino-1-naphthalenesulfonic acid and 3-methylglutaric acid for capping reaction. When the acid value of the polymer reaches the expected value, stop the reaction, then discharge the material at high temperature, and cool the polyester resin with a steel belt equipped with a cooling system, and crush and granulate to obtain the product.

[0052] The obtained product has a light yellow transparent granular appearance, an acid value of 32 mgKOH / g, and a softening point of 108 °C.

[0053] Preparation Example 2

[0054] A polyester resin for powder coatings, comprising the following raw materials in parts by mole:

[0055]

[0056] Catalyst 1 is sodium tert-butoxide, and the dosage is 0.8% of the molar amount of dimethyl isophthalate;

[0057] Catalyst 2 is stannous oxalate, and the dosage is 0.1% of the total molar amount of the raw materials;

[0058] The antioxidant is antioxidant 1076, and the dosage is 0.5% of the total molar amount of the raw materials;

[0059] The acid-binding agent is triethylamine, and the molar amount is 2.5 times the molar amount of phenylphosphoryl dichloride.

[0060] The preparation method is the same as that of Preparation Example 1.

[0061] The obtained product has a light yellow transparent granular appearance, acid value: 35 mgKOH / g, softening point: 106 °C.

[0062] Preparation Example 3

[0063] A polyester resin for powder coatings, comprising the following raw materials in parts by mole:

[0064]

[0065]

[0066] Catalyst 1 is sodium tert-butoxide, and the dosage is 0.8% of the molar amount of dimethyl isophthalate;

[0067] Catalyst 2 is stannous oxalate, and the dosage is 0.1% of the total molar amount of the raw materials;

[0068] The antioxidant is antioxidant 1076, and the dosage is 0.5% of the total molar amount of the raw materials;

[0069] The acid-binding agent is triethylamine, and the molar amount is 2.5 times the molar amount of phenylphosphoryl dichloride.

[0070] The preparation method is the same as that of Preparation Example 1.

[0071] The obtained product has a light yellow transparent granular appearance, acid value of 33 mgKOH / g, and softening point of 111 °C.

[0072] Preparation Example 4

[0073] A polyester resin for powder coatings, comprising the following raw materials in parts by mole:

[0074]

[0075]

[0076] Catalyst 1 is sodium tert-butoxide, and its dosage is 0.6% of the molar amount of dimethyl isophthalate;

[0077] Catalyst 2 is stannous oxalate, and its dosage is 0.1% of the total molar amount of raw materials;

[0078] The antioxidant is antioxidant 1076, and its dosage is 0.5% of the total molar amount of raw materials;

[0079] The acid-binding agent is triethylamine, and its molar amount is 2.5 times that of phenylphosphoryl dichloride.

[0080] The preparation method is the same as that of Preparation Example 1.

[0081] The obtained product has a light yellow transparent granular appearance, an acid value of 35 mgKOH / g, and a softening point of 109 °C.

[0082] Examples 1-4 (the polyester resins are respectively obtained from the above Preparation Examples 1-4):

[0083] TGIC transparent powder coating formulation: 558 parts of polyester resin, 42 parts of TGIC, 10 parts of leveling agent, 8 parts of brightening agent, and 3 parts of benzoin.

[0084] Preparation of the coating film: Mix the various materials according to the above powder coating formulation, extrude, press into tablets, and crush them respectively with a twin-screw extruder, and then crush the tablet materials and sieve them to make a powder coating. The powder coating is sprayed on the surface-treated aluminum alloy substrate with an electrostatic spray gun and cured at 160 °C for 20 min to obtain the coating film.

[0085] Comparative Example 1: Use a commercially available ordinary TGIC polyester resin, model SJ9000, Huangshan Shenjian New Materials Co., Ltd.;

[0086] Comparative Example 2: The same as Comparative Example 1, except that the curing conditions are adjusted from 160 °C / 20 min to 185 °C / 15 min;

[0087] Basis for detecting the coating film index: GB / T 21776-2008 "Test Standard Guide for Powder Coatings and Their Coatings"; The flame retardant performance of the coating film is tested according to GB / T2406-93 "Test Method for Combustion Performance of Materials - Oxygen Index Method".

[0088] After the polyester resins prepared in the above examples and comparative examples are made into coatings according to the coating formulation provided by the present invention, the coating film properties are tested and the results are shown in Table 1 below.

[0089] Table 1 Application properties of the coating film

[0090]

[0091] As can be seen from the above table, the product of the present invention can achieve sufficient curing under the condition of low-temperature curing (160°C / 20 min) through a special raw material formula and process combination. The appearance and impact of the coating film can meet the requirements. Due to the presence of active amino groups, there is an obvious difference in the curing speed between them and the terminal carboxyl groups when curing with the epoxy groups of TGIC, resulting in an obvious matting effect. The gloss is basically between 30% and 45%, and the aesthetics and decorativeness are good. At the same time, due to the presence of the environmentally friendly flame-retardant components phosphate ester and nitrogen element, the flame-retardant performance of the final coating film is good, and the oxygen index is basically between 32% and 35%, meeting the requirements of excellent halogen-free flame retardancy. Moreover, the product of the present invention is synthesized with special hydrophobic raw materials, and the hydrophobicity of the polyester chain segments is excellent, with basically no obvious change after boiling in water for 3 h. However, in Comparative Example 1, the coating film performance is poor because effective curing cannot be achieved at 160°C / 20 min. In Comparative Example 2, after conventional high-temperature curing, the coating film performance is good, but compared with the present invention, its gloss is higher and there is no matting effect. Since it does not contain flame-retardant components, the coating film has no flame-retardant effect and is slightly inferior to the product of the present invention in terms of boiling water resistance (3 h).

[0092] Only some exemplary embodiments of the present invention have been described by way of illustration above. Undoubtedly, for those of ordinary skill in the art, the described embodiments can be modified in various different ways without departing from the spirit and scope of the present invention. Therefore, the above description is illustrative in nature and should not be construed as a limitation on the protection scope of the claims of the present invention.

Claims

1. A polyester resin for powder coatings, characterized in that, Comprising the following raw materials in parts by mole: Phenylphosphonic dichloride 10 - 12 parts; 2 - Ethyl - 1,3 - hexanediol 22 - 25 parts; Dimethyl isophthalate 8 - 12 parts; N - Methylethanolamine 10 - 15 parts; Succinic acid 8 - 11 parts; Ethylenediaminetetraacetic acid 3 - 5 parts; 6 - Amino - 1 - naphthalenesulfonic acid 4 - 5 parts; 3 - Methylglutaric acid 8 - 10 parts; Anhydrous tetrahydrofuran 35 - 40 parts; The raw materials further include a catalyst, an antioxidant, and an acid - binding agent; The preparation method of the polyester resin for powder coatings comprises the following steps: A. Add the formulated amount of anhydrous tetrahydrofuran and phenylphosphonic dichloride into a mixing tank. After mixing evenly, pump it to a high - level tank for standby; B. Add the formulated amount of 2 - ethyl - 1,3 - hexanediol and an acid - binding agent into reaction kettle A. After fully stirring evenly, start the cooling system, cool the mixed solution to 0 - 5°C and keep it warm. Then open the control valve of the high - level tank, start to dropwise add the tetrahydrofuran solution of phenylphosphonic dichloride. After the dropping is completed, carry out a holding reaction at 0 - 5°C; C. Take a sample and detect it by gas chromatography. When the conversion rate of phenylphosphonic dichloride reaches more than 97%, stop the reaction, filter off the insoluble salts by suction to obtain a reaction - modified phosphoric acid ester diol intermediate solution for standby; D. Add the formulated amount of dimethyl isophthalate, N - methylethanolamine and catalyst 1 into reaction kettle B, heat up to 100 - 110°C for ammonolysis reaction, and collect the by - products obtained from the reaction at the same time; E. Take a sample for detection. When the free dimethyl isophthalate is less than 2% and the collected by - products reach more than 90% of the theory, pump the modified phosphoric acid ester diol intermediate solution obtained in step C into reaction kettle B, stir evenly, then add the formulated amount of succinic acid and catalyst 2, and then gradually heat up to 210 - 220°C for polymerization reaction; F. Take a sample to detect the acid value of the polymer. When the acid value reaches 20 - 30mgKOH / g, add the formulated amount of ethylenediaminetetraacetic acid for chain - extension polymerization reaction, and at the same time, raise the reaction temperature to 225 - 230°C; G. When the acid value of the polymer reaches 22 - 28mgKOH / g, then add the formulated amount of antioxidant, stir evenly, start the vacuum system, and carry out vacuum polymerization reaction at 225 - 230°C; H. When the acid value of the polymer reaches 8 - 14mgKOH / g, stop the vacuum system, add the formulated amount of composite capping agents 6 - amino - 1 - naphthalenesulfonic acid and 3 - methylglutaric acid for capping reaction. When the acid value of the polymer reaches 29 - 38mgKOH / g, stop the reaction, then discharge the material at high temperature, cool the polyester resin, and crush and granulate to obtain; The catalyst includes two kinds. Catalyst 1 is sodium tert - butoxide, and its dosage is 0.5 - 0.8% of the molar amount of dimethyl isophthalate; Catalyst 2 is stannous oxalate, and its dosage is 0.04 - 0.1% of the total molar amount of the raw materials; The antioxidant is antioxidant 1076, and its dosage is 0.3 - 0.5% of the total molar amount of the raw materials; The acid - binding agent is triethylamine, and its molar amount is 2.2 - 2.5 times the molar amount of phenylphosphonic dichloride.

2. The polyester resin for powder coatings according to claim 1, wherein The molar ratio of 2-ethyl-1,3-hexanediol to phenylphosphoryl dichloride is ≥ 2.

05.

3. A method for preparing the polyester resin for powder coatings according to any one of claims 1-2, characterized in that, It includes the following steps: A. Add the formulated amount of anhydrous tetrahydrofuran and phenylphosphoryl dichloride into a mixing tank. After mixing evenly, pump it to a high-level tank for standby; B. Add the formulated amount of 2-ethyl-1,3-hexanediol and an acid-binding agent into Reactor A. After fully stirring evenly, start the cooling system, cool the mixed solution to 0 - 5 °C and keep it warm. Then open the control valve of the high-level tank and start to dropwise add the tetrahydrofuran solution of phenylphosphoryl dichloride. After the dropping is completed, carry out a holding reaction at 0 - 5 °C; C. Take a sample and detect it by gas chromatography. When the conversion rate of phenylphosphoryl dichloride reaches more than 97%, stop the reaction, filter off the insoluble salts by suction to obtain a reaction-modified phosphoric acid ester diol intermediate solution for standby; D. Add the formulated amount of dimethyl isophthalate, N-methylethanolamine and Catalyst 1 into Reactor B, heat up to 100 - 110 °C for an ammonolysis reaction, and collect the by-products obtained from the reaction at the same time; E. Take a sample for detection. When the free dimethyl isophthalate is less than 2% and the collected by-products reach more than 90% of the theory, pump the modified phosphoric acid ester diol intermediate solution obtained in step C into Reactor B, stir evenly, then add the formulated amount of succinic acid and Catalyst 2, and then gradually heat up to 210 - 220 °C for a polymerization reaction; F. Take a sample to detect the acid value of the polymer. When the acid value reaches 20 - 30 mgKOH / g, add the formulated amount of ethylenediaminetetraacetic acid for a chain extension polymerization reaction, and at the same time raise the reaction temperature to 225 - 230 °C; G. When the acid value of the polymer reaches 22 - 28 mgKOH / g, then add the formulated amount of antioxidant, stir evenly, start the vacuum system, and carry out a vacuum polymerization reaction at 225 - 230 °C; H. When the acid value of the polymer reaches 8 - 14 mgKOH / g, stop the vacuum system, add the formulated amount of composite capping agent 6-amino-1-naphthalenesulfonic acid and 3-methylglutaric acid for a capping reaction. When the acid value of the polymer reaches 29 - 38 mgKOH / g, stop the reaction, then discharge the material at high temperature, cool the polyester resin, crush and granulate to obtain it.

4. A method for preparing the polyester resin for powder coatings according to claim 3, characterized in that, In step G, the vacuum degree is controlled at -0.096 Mpa to -0.098 Mpa.

5. A method for preparing a polyester resin for powder coatings according to claim 3, characterized in that, In step H, the polyester resin is cooled with a steel belt equipped with a cooling system.

6. The application of the polyester resin for powder coatings as described in any one of claims 1 - 2 in a TGIC curing system.

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