Polyester resin for high-temperature-resistant and flame-retardant powder coating and preparation method of polyester resin

Abstract

The invention relates to polyester resin for a TGIC (triglycidyl isocyanurate) curing system, which is obtained by performing polymerization reaction on raw materials such as enzymatic hydrolysis lignin, epichlorohydrin, 2, 3-dibromopropionic acid, dodecanedioic acid, neopentyl glycol, terephthalic acid, chloromalonic acid and the like. The preparation of the polyester resin fully utilizes the enzymatic hydrolysis lignin, the enzymatic hydrolysis lignin fully reacted with epichlorohydrin can be completely dissolved in a reaction system to participate in a subsequent polymerization reaction, no additional step is needed to filter out insoluble substances, the utilization rate of the enzymatic hydrolysis lignin almost reaches 100%, the cost of the polyester resin is low, and after the polyester resin and TGIC are finally solidified, the polyester resin has good stability. A coating film has excellent hardness, flame retardant property, high temperature resistance and the like, and other conventional properties meet the use requirements of conventional TGIC powder coatings.

Description

Technical Field

[0001] The invention belongs to the technical field of powder coatings, and in particular relates to a polyester resin for high temperature resistant and flame retardant powder coatings, and application of the polyester resin in a TGIC powder coating system. Background Art

[0002] Powder coating is a solid powdered synthetic resin coating composed of solid resin, pigment, filler and additives. Unlike ordinary solvent-based coatings and water-based coatings, it has the advantages of no solvent pollution, 100% film formation and low energy consumption. At present, the most commonly used powder coating is TGIC system powder coating, which is composed of TGIC curing agent and carboxyl polyester resin as the main film-forming material. It has excellent comprehensive properties such as weather resistance and water boiling resistance and is widely used. However, traditional TGIC system powder coatings basically have no flame retardant properties and there is a hidden danger of combustion. Enzymatic lignin is a new type of lignin separated from the residue of microbial enzymatic hydrolysis of corn straw to prepare ethanol, butanol and other energy sources. Due to its relatively large molecular structure and excellent high temperature resistance, enzymatic lignin has multiple active groups and better reaction activity compared with traditional alkali lignin and sulfate lignin. The comprehensive utilization of enzymatic lignin is also a hot topic of research. At present, it has a wide range of applications, such as high temperature resistant adhesives and various resins. Previously, some studies have used enzymatic lignin to prepare polyester resins for powder coatings, such as: (1) CN202110857569.X mainly uses small molecule liquid alcohols such as methyl propanediol and diethylene glycol for high-temperature liquefaction treatment. In fact, it uses the dissolution effect of these liquid alcohols on the enzymatic lignin components at high temperature to achieve comprehensive utilization of the soluble part. The shortcomings are: the small molecule liquid alcohols such as diethylene glycol and methyl propylene glycol are too small in molecule, and the weather resistance and high temperature resistance are poor, so they are not suitable for use in weather-resistant powder coating polyester resins. The TGIC system is a weather-resistant powder coating, and the diols used have poor solubility for enzymatic lignin, making it difficult to use this dissolution method; (2) CN202110857569.X is an indoor 70 / 30 powder coating, which has no requirements for weather resistance. Although it can use small molecule alcohols with poor weather resistance, it is only a high-temperature dissolution effect, and no chemical reaction occurs during the entire dissolution process, resulting in its comprehensive utilization rate for enzymatic lignin is still low. The dissolution rate of high-quality enzymatic lignin is basically 80%, which is difficult to further improve the utilization efficiency, resulting in low resource utilization. How to achieve a higher utilization rate of enzymatic lignin, and give new polyester resins new functions such as high temperature resistance and flame retardancy to meet the application requirements of functional powder coatings.

[0003] In view of the above problems, the present invention uses enzymatic lignin, epichlorohydrin, 2,3-dibromopropionic acid, dodecanedioic acid, neopentyl glycol, terephthalic acid, chloromalonic acid and the like as raw materials for polymerization to obtain a polyester resin for a TGIC curing system. The preparation of the polyester resin makes full use of enzymatic lignin, and the enzymatic lignin after sufficient reaction with epichlorohydrin can be completely dissolved in the reaction system to participate in the subsequent polymerization reaction, and no additional steps are required to filter and remove insoluble matter. The utilization rate of enzymatic lignin is almost 100%, and the cost of the polyester resin is low. After finally being cured with TGIC, the oxygen index of the coating can reach more than 35%, the flame retardant performance is excellent, and the hardness is high, reaching more than 2H, the coating has almost no change at 250°C / 12h, the high temperature resistance is excellent, and other conventional properties also meet the application requirements of conventional TGIC powder coatings. Summary of the invention

[0004] The invention relates to a polyester resin for a TGIC curing system. The polyester resin is obtained by polymerization using enzymatically hydrolyzed lignin, epichlorohydrin, 2,3-dibromopropionic acid, dodecanedioic acid, neopentyl glycol, terephthalic acid, chloromalonic acid and the like as raw materials.

[0005] Enzymatic lignin is a new type of lignin separated from the residue of preparing ethanol, butanol and other energy sources by enzymatic hydrolysis of corn stalks by microorganisms. Due to its relatively large molecular structure and excellent high temperature resistance, compared with traditional alkali lignin and sulfate lignin, enzymatic lignin has multiple active groups and better reaction activity; it is mainly composed of multiple compounds containing phenolic hydroxyl structures, and the phenolic hydroxyl group has good reaction activity with epichlorohydrin. In the present invention, excess epichlorohydrin is used to first undergo a ring-opening reaction with the phenolic hydroxyl group in its molecular structure to achieve reaction modification to obtain an intermediate lignin polychlorinated alcohol compound, so that it can be fully dissolved in the epichlorohydrin system, and then a subsequent polymerization reaction is achieved to obtain a final polyester resin product.

[0006] The present invention relates to a polyester resin for high temperature resistant and flame retardant powder coating, wherein the polyester resin comprises the following raw materials in parts by weight:

[0007] Enzymatic lignin 48-55 parts;

[0008] Epichlorohydrin 75-90 parts;

[0009] 8-11 parts of 2,3-dibromopropionic acid;

[0010] 28-34 parts of dodecanedioic acid;

[0011] Neopentyl glycol 7-10 parts;

[0012] 9-13 parts of terephthalic acid;

[0013] 6-9 parts of chloromalonic acid.

[0014] The raw materials further include catalyst A: triphenylphosphine, the dosage of which is 0.1-0.3% of the mass of epichlorohydrin; catalyst B: monobutyltin oxide, the dosage of which is 0.3-0.5% of the mass of 2,3-dibromopropionic acid.

[0015] The raw material further comprises an antioxidant, for example, antioxidant 1010, namely pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and the amount thereof is 0.1-0.2% of the total mass of the raw material.

[0016] The raw materials are commercially available, such as enzymatic lignin, which can be purchased from Wuhan Jiyesheng Chemical Co., Ltd.

[0017] The method for preparing a polyester resin for a high temperature resistant and flame retardant powder coating as described above comprises the following steps:

[0018] A. Add the formulated amount of epichlorohydrin, enzymatic lignin and catalyst A into the reactor, start stirring, and heat to 110-115°C, then keep warm for a full ring-opening reaction;

[0019] B. Observe the dissolution of the enzymatic lignin. As the enzymatic lignin gradually reacts until it is completely dissolved, continue to keep the temperature at 110-115°C to react again to promote the complete reaction of the enzymatic lignin and epichlorohydrin.

[0020] C. Start the vacuum system and perform vacuum distillation at 110-115°C to remove excess epichlorohydrin;

[0021] D. After no obvious substance is evaporated, the intermediate lignin polychlorinated alcohol compound of the enzymatic lignin and the ring-opening reaction of epichlorohydrin is obtained, and the vacuum system is released at this time, and the catalyst B and the unit acid 2,3-dibromopropionic acid in the formula amount are added to the reactor, and the temperature is raised to 150-155° C., and then the temperature is kept to carry out high-temperature esterification reaction to reduce the functionality of the lignin polychlorinated alcohol compound;

[0022] E. Sampling and testing the acid value of the polymer in the reactor, when the acid value is lower than 2 mgKOH / g, adding the formulated amount of dodecanedioic acid to carry out a chain extension reaction, and gradually raising the temperature to 200-210° C. and keeping the temperature to carry out the chain extension polymerization reaction;

[0023] F. Sampling and testing. When the acid value of the polymer reaches 20-30 mgKOH / g, add the formulated amount of neopentyl glycol and terephthalic acid, raise the temperature to 225-230°C, and keep warm for secondary high-temperature chain extension polymerization reaction;

[0024] G. When the acid value of the polymer reaches 35-43 mgKOH / g, add the formulated amount of antioxidant and start the vacuum system to carry out vacuum polycondensation reaction;

[0025] H. When the acid value of the polymer reaches 10-17 mgKOH / g, release the vacuum system, add the formulated amount of chloromalonic acid and continue the carboxyl end-capping reaction at 225-230°C. When the acid value reaches 29-35 mgKOH / g, stop the reaction, discharge the material while hot, cool the polyester resin, and then crush and granulate it to obtain the polyester resin.

[0026] Preferably, in step B, the insulation reaction time is 1-1.5h; in step C, the vacuum degree of the vacuum system is controlled at -0.09 to -0.095Mpa; in step D, the standard for no obvious substance to be evaporated is less than 1 drop within 20s, indicating that the epichlorohydrin is basically distilled completely; in step E, the temperature is gradually increased at a heating rate of 12-15°C / h; in step G, the vacuum degree is controlled at -0.097Mpa to -0.098Mpa; in step H, the polyester resin is cooled with a steel belt with cooling water.

[0027] For example, the method for preparing the polyester resin for high temperature resistant and flame retardant powder coating comprises the following steps:

[0028] A. Add the formulated amount of epichlorohydrin, enzymatic lignin and catalyst A into the reactor, start stirring, and heat to 110-115°C, then keep warm for a full ring-opening reaction;

[0029] B. Observe the dissolution of the enzymatic lignin. As the enzymatic lignin gradually reacts until it is completely dissolved (no obvious insoluble matter is observed), continue to keep the temperature at 110-115°C for another 1-1.5h to promote the complete reaction of the enzymatic lignin and epichlorohydrin.

[0030] C. Start the vacuum system and perform reduced pressure distillation at 110-115°C to remove excess epichlorohydrin. The vacuum degree is controlled at -0.09 to -0.095Mpa;

[0031] D. When no obvious substance is evaporated (less than 1 drop within 20 seconds), it means that the epichlorohydrin is basically distilled completely, and the intermediate lignin polychlorohydrin compound of the enzymatic lignin and the ring-opening reaction of epichlorohydrin is obtained. At this time, the vacuum system is released, and the catalyst B and the unit acid 2,3-dibromopropionic acid in the formula amount are added to the reactor, and the temperature is raised to 150-155°C, and then the temperature is kept to carry out high-temperature esterification reaction to reduce the functionality of the lignin polychlorohydrin compound;

[0032] E. Take samples to detect the acid value of the polymer in the reactor. When the acid value is lower than 2 mgKOH / g, it means that the basic reaction of 2,3-dibromopropionic acid is completed. At this time, add the formula amount of dodecanedioic acid to carry out a chain extension reaction, and gradually increase the temperature to 200-210°C at a heating rate of 12-15°C / h, and keep the temperature to carry out chain extension polymerization reaction;

[0033] F. Take samples for testing. When the acid value of the polymer reaches 20-30 mgKOH / g, it means that the primary chain extension reaction basically meets the requirements. At this time, add the formulated amount of neopentyl glycol and terephthalic acid, raise the temperature to 225-230°C, and keep warm for secondary high-temperature chain extension polymerization reaction;

[0034] G. When the acid value of the polymer reaches 35-43 mgKOH / g, add the formulated amount of antioxidant, start the vacuum system for vacuum polycondensation reaction, and control the vacuum degree at -0.097 MPa to -0.098 MPa;

[0035] H. When the acid value of the polymer reaches 10-17 mgKOH / g, release the vacuum system, add the formulated amount of chloromalonic acid and continue the carboxyl end-capping reaction at 225-230°C. When the acid value reaches 29-35 mgKOH / g, stop the reaction, discharge the material while hot, cool the polyester resin with a steel belt with cooling water, and then crush and granulate it to obtain the polyester resin.

[0036] The obtained product is light yellow transparent particles with an acid value of 29-35 mgKOH / g and a softening point of 112-124°C.

[0037] The present invention also relates to the use of the polyester resin for high temperature resistant and flame retardant powder coating as described above or the polyester resin for high temperature resistant and flame retardant powder coating prepared by the preparation method in TGIC curing system powder coating.

[0038] The formula includes polyester resin, TGIC, titanium dioxide, barium sulfate, brightener, leveling agent, benzoin, etc.; the materials are mixed according to the formula, extruded, tableted, and crushed by a twin-screw extruder, and then the tablets are crushed and sieved to form a powder coating (for example, a particle size of 160-180 mesh). The powder coating is sprayed on the tinplate substrate after surface treatment by an electrostatic spray gun, for example, the film thickness is 80 μm, and cured (for example, at 200° C. / 10 min) to obtain a coating.

[0039] Beneficial effects:

[0040] The polyester resin for the TGIC curing system of the present invention is obtained by polymerization using enzymatic lignin, epichlorohydrin, 2,3-dibromopropionic acid, dodecanedioic acid, neopentyl glycol, terephthalic acid, chloromalonic acid and the like as raw materials. The reaction principle is as follows: first, an excess of epichlorohydrin is fully reacted with enzymatic lignin under the catalysis of a catalyst, and the active phenolic hydroxyl groups on the enzymatic lignin are subjected to a ring-opening reaction with epichlorohydrin to obtain an intermediate of a lignin polychlorinated alcohol compound. However, since the alcohol hydroxyl functionality of the intermediate is too high, it will affect the toughness of the subsequent polyester resin. At this time, monofunctional 2,3-dibromopropionic acid is used for partial end-capping reaction to obtain an intermediate for subsequent reactions. The intermediate contains a lignin structure, and relatively high content of flame-retardant elements chlorine and bromine are introduced with the help of epichlorohydrin, 2,3-dibromopropionic acid and malonic acid. Then, the intermediate undergoes a chain extension reaction with a flexible dibasic acid segment, dodecanedioic acid. After the first chain extension is completed, it undergoes a secondary chain extension polymerization with neopentyl glycol and terephthalic acid. Finally, a flexible small molecule dibasic acid malonic acid is used for end-capping reaction to obtain the final polyester resin. The preparation of the polyester resin makes full use of enzymatic lignin. After being fully reacted with epichlorohydrin, the enzymatic lignin can be completely dissolved in the reaction system to participate in the subsequent polymerization reaction. No additional steps are required to filter out insoluble matter. The utilization rate of the enzymatic lignin is almost 100%. The cost of the polyester resin is low. After finally being cured with TGIC, the oxygen index of the coating can reach more than 35%, the flame retardant property is excellent, and the hardness is high, reaching more than 2H. The coating has almost no change at 250°C / 12h, the high temperature resistance is excellent, and other conventional properties also meet the application requirements of conventional TGIC powder coatings.

[0041] The present invention has been described in detail above, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples. DETAILED DESCRIPTION

[0042] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[0043] Unless otherwise specified, the raw materials and reagents used in the examples are all conventional raw materials and reagents in the art. The raw materials are commercially available, such as enzymatic lignin, purchased from Wuhan Jiyesheng Chemical Co., Ltd.

[0044] Preparation Example 1

[0045] A polyester resin for high temperature resistant and flame retardant powder coating, the polyester resin comprising the following raw materials in parts by weight:

[0046]

[0047] Catalyst A: triphenylphosphine, the amount used is 0.3% of the mass of epichlorohydrin;

[0048] Catalyst B: monobutyltin oxide, the amount used is 0.3% of the mass of 2,3-dibromopropionic acid.

[0049] Antioxidant 1010: The dosage is 0.2% of the total mass of raw materials.

[0050] The method for preparing the polyester resin for high temperature resistant and flame retardant powder coating comprises the following steps:

[0051] A. Add the formulated amount of epichlorohydrin, enzymatic lignin and catalyst A into the reactor, start stirring, raise the temperature to 115°C, and then keep warm for a full ring-opening reaction;

[0052] B. Observe the dissolution of the enzymatic lignin. As the enzymatic lignin gradually reacts until it is completely dissolved (no obvious insoluble matter is observed), continue to keep the temperature at 115°C for another 1.5h to promote the complete reaction of the enzymatic lignin and epichlorohydrin.

[0053] C. Start the vacuum system and perform reduced pressure distillation at 115°C to remove excess epichlorohydrin. The vacuum degree is controlled at -0.09 to -0.095Mpa;

[0054] D. When no obvious substance is evaporated (less than 1 drop in 20 seconds), it means that the epichlorohydrin is basically distilled completely, and the intermediate lignin polychlorohydrin compound of the enzymatic lignin and the ring-opening reaction of epichlorohydrin is obtained. At this time, the vacuum system is released, and the catalyst B and the unit acid 2,3-dibromopropionic acid in the formula amount are added to the reactor, and the temperature is raised to 155°C, and then the temperature is kept to carry out high-temperature esterification reaction to reduce the functionality of the lignin polychlorohydrin compound;

[0055] E. Take samples to detect the acid value of the polymer in the reactor. When the acid value is lower than 2 mgKOH / g, it means that the basic reaction of 2,3-dibromopropionic acid is completed. At this time, add the formula amount of dodecanedioic acid to carry out a chain extension reaction, and gradually increase the temperature to 210°C at a heating rate of 15°C / h, and keep the temperature to carry out chain extension polymerization reaction;

[0056] F. Take samples for testing. When the acid value of the polymer reaches 20-30 mgKOH / g, it means that the primary chain extension reaction basically meets the requirements. At this time, add the formulated amount of neopentyl glycol and terephthalic acid, raise the temperature to 230°C, and keep the temperature to carry out the secondary high-temperature chain extension polymerization reaction;

[0057] G. When the acid value of the polymer reaches 35-43 mgKOH / g, add the formulated amount of antioxidant, start the vacuum system for vacuum polycondensation reaction, and control the vacuum degree at -0.097 MPa to -0.098 MPa;

[0058] H. When the acid value of the polymer reaches 10-17 mgKOH / g, release the vacuum system, add the formulated amount of chloromalonic acid and continue the carboxyl end-capping reaction at 230°C. When the acid value reaches the expected value, stop the reaction, discharge the material while hot, cool the polyester resin with a steel belt with cooling water, and then crush and granulate it to obtain the polyester resin.

[0059] The obtained product is light yellow transparent particles, the acid value of the polyester resin is 30 mgKOH / g, and the softening point is 122°C.

[0060] Example 2

[0061] A polyester resin for high temperature resistant and flame retardant powder coating, the polyester resin comprising the following raw materials in parts by weight:

[0062]

[0063]

[0064] Catalyst A: triphenylphosphine, the amount used is 0.2% of the mass of epichlorohydrin;

[0065] Catalyst B: monobutyltin oxide, the amount used is 0.5% of the mass of 2,3-dibromopropionic acid.

[0066] Antioxidant 1010: The dosage is 0.2% of the total mass of raw materials.

[0067] The method is the same as Preparation Example 1.

[0068] The obtained product is light yellow transparent particles with an acid value of 34 mgKOH / g and a softening point of 116°C.

[0069] Preparation Example 3

[0070] A polyester resin for high temperature resistant and flame retardant powder coating, the polyester resin comprising the following raw materials in parts by weight:

[0071]

[0072] Catalyst A: triphenylphosphine, the amount used is 0.3% of the mass of epichlorohydrin;

[0073] Catalyst B: monobutyltin oxide, the amount used is 0.4% of the mass of 2,3-dibromopropionic acid.

[0074] Antioxidant 1010: The dosage is 0.2% of the total mass of raw materials.

[0075] The method is the same as Preparation Example 1.

[0076] The obtained product is light yellow transparent particles with an acid value of 32 mgKOH / g and a softening point of 119°C.

[0077] Preparation Example 4

[0078] A polyester resin for high temperature resistant and flame retardant powder coating, the polyester resin comprising the following raw materials in parts by weight:

[0079]

[0080]

[0081] Catalyst A: triphenylphosphine, the amount used is 0.2% of the mass of epichlorohydrin;

[0082] Catalyst B: monobutyltin oxide, the amount used is 0.3% of the mass of 2,3-dibromopropionic acid.

[0083] Antioxidant 1010: The dosage is 0.2% of the total mass of raw materials.

[0084] The method is the same as Preparation Example 1.

[0085] The obtained product is light yellow transparent particles with an acid value of 33 mgKOH / g and a softening point of 120°C.

[0086] Comparative Preparation Example 1

[0087] The commercially available common TGIC system polyester resin was used, model SJ4301, Anhui Shenjian New Materials Co., Ltd.

[0088] Examples 1-4 and Comparative Example 1:

[0089] The polyester resins of the above-mentioned Preparation Examples 1-4 and Comparative Preparation Example 1 are respectively used and mixed with the following other components to obtain the polyester resins.

[0090] TGIC powder coating formula (mass parts):

[0091] 558 parts of polyester resin (obtained from Preparation Examples 1-4 and Comparative Preparation Example 1);

[0092]

[0093] Preparation of coating: Mix all materials according to the above powder coating formula, extrude, tablet and crush them by twin screw extruder, crush the tablets, and then sieve them to make powder coating (particle size 160-180 mesh). The powder coating is sprayed on the surface treated tinplate substrate by electrostatic spray gun, with a film thickness of 80μm, and cured at 200℃ / 10min to obtain the coating.

[0094] The coating index test is based on: GB / T 21776-2008 "Guide to the Testing Standards of Powder Coatings and Their Coatings"; the coating film hardness test is based on GB / T 6739-2006 "Determination of Film Hardness of Paints and Varnishes by Pencil Method"; the flame retardant performance of the coating film is tested in accordance with GB / T2406-93 "Test Method for Combustion Performance of Materials - Oxygen Index Method".

[0095] The polyester resins prepared in the above examples and comparative examples were used to prepare coatings according to the coating formulations provided by the present invention. The coating properties were tested and the results are shown in Table 1 below.

[0096] Table 1 Powder coating film properties

[0097]

[0098] As can be seen from the above table, the product of the present invention adopts a specific raw material and process combination to achieve full utilization of high-dosage enzymatic lignin without the need for additional separation steps. At the same time, it is matched with a unit acid 2,3-dibromopropionic acid to carry out a functionalization reduction reaction, and then the high-toughness dodecanedioic acid and other raw materials are used to carry out two chain extension polymerization reactions to obtain the prepared polyester resin. The prepared polyester resin is used to prepare TGIC powder coatings, and after high-temperature curing (200°C / 10min), the coating surface is flat and smooth, and the gloss is basically above 93%. In terms of impact resistance, it can pass 50cm positive and negative impacts; at the same time, in terms of high temperature resistance, the sample is baked at 250°C / 12h for a long time, and the surface of the coating is almost unchanged, and no cracking or yellowing occurs; at the same time, the hardness of the coating is basically above 2H, and the hardness is relatively high. In terms of flame retardancy, the oxygen index is basically above 35%, the flame retardancy is relatively good, and the coating is almost unchanged after being boiled in boiling water for 2h. Comparative Example 1 uses common commercially available TGIC polyester resin, and the powder coating film prepared therefrom has good appearance, gloss and impact resistance, but its high temperature resistance, hardness and flame retardancy are lower than those of the product of the present invention.

[0099] It can be seen that the present invention not only prepares a polyester resin product with excellent high temperature resistance, flame retardancy and apparent hardness, but also adopts a specific preparation method to achieve full utilization of enzymatic lignin in the polyester resin synthesis process, which not only reduces the cost of polyester resin, but also provides a method for high value-added comprehensive utilization of enzymatic lignin, and has better economic value.

[0100] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and essence of the claims of the present invention; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A polyester resin for high temperature resistant and flame retardant powder coating, characterized in that: The polyester resin comprises the following raw materials in parts by weight:

2. A polyester resin for high temperature resistant and flame retardant powder coating as claimed in claim 1, further characterized in that the raw materials further include catalyst A: triphenylphosphine, the amount of which is 0.1-0.3% of the mass of epichlorohydrin; catalyst B: monobutyl tin oxide, the amount of which is 0.3-0.5% of the mass of 2,3-dibromopropionic acid.

3. A polyester resin for high temperature resistant and flame retardant powder coatings as claimed in claim 1 or 2, further characterized in that the raw material further comprises an antioxidant in an amount of 0.1-0.2% of the total mass of the raw material.

4. A method for preparing a polyester resin for high temperature resistant and flame retardant powder coating according to any one of claims 1 to 3, characterized in that: The following steps are involved: A. Add the formulated amount of epichlorohydrin, enzymatic lignin and catalyst A into the reactor, start stirring, and heat to 110-115°C, then keep warm for a full ring-opening reaction; B. Observe the dissolution of the enzymatic lignin. As the enzymatic lignin gradually reacts until it is completely dissolved, continue to keep the temperature at 110-115°C to react again to promote the complete reaction of the enzymatic lignin and epichlorohydrin. C. Start the vacuum system and perform vacuum distillation at 110-115°C to remove excess epichlorohydrin; D. After no obvious substance is evaporated, the intermediate lignin polychlorinated alcohol compound of the enzymatic lignin and the ring-opening reaction of epichlorohydrin is obtained, and the vacuum system is released at this time, and the catalyst B and the unit acid 2,3-dibromopropionic acid in the formula amount are added to the reactor, and the temperature is raised to 150-155° C., and then the temperature is kept to carry out high-temperature esterification reaction to reduce the functionality of the lignin polychlorinated alcohol compound; E. Sampling and testing the acid value of the polymer in the reactor. When the acid value is lower than 2 mgKOH / g, adding the formulated amount of dodecanedioic acid to carry out a chain extension reaction, and gradually raising the temperature to 200-210° C. and keeping the temperature to carry out a chain extension polymerization reaction; F. Sampling and testing. When the acid value of the polymer reaches 20-30 mgKOH / g, add the formulated amount of neopentyl glycol and terephthalic acid, raise the temperature to 225-230°C, and keep warm for secondary high-temperature chain extension polymerization reaction; G. When the acid value of the polymer reaches 35-43 mgKOH / g, add the formulated amount of antioxidant and start the vacuum system to carry out vacuum polycondensation reaction; H. When the acid value of the polymer reaches 10-17 mgKOH / g, release the vacuum system, add the formulated amount of chloromalonic acid and continue the carboxyl end-capping reaction at 225-230°C. When the acid value reaches 29-35 mgKOH / g, stop the reaction, discharge the material while hot, cool the polyester resin, and then crush and granulate it to obtain the polyester resin.

5. The method for preparing a polyester resin for high temperature resistant and flame retardant powder coating according to claim 4, further characterized in that in step B, the heat preservation reaction time is 1-1.5 hours.

6. A method for preparing a polyester resin for a high temperature resistant and flame retardant powder coating as claimed in claim 4, further characterized in that the vacuum degree of the vacuum system in step C is controlled at -0.09 to -0.095 MPa; in step D, the standard for no obvious substance to be evaporated is less than 1 drop within 20 seconds, indicating that the epichlorohydrin is basically distilled completely.

7. The method for preparing a polyester resin for high temperature resistant and flame retardant powder coating according to claim 4, further characterized in that in step E, the temperature is gradually increased at a heating rate of 12-15°C / h.

8. The method for preparing a polyester resin for high temperature resistant and flame retardant powder coating according to claim 4, further characterized in that in step G, the vacuum degree is controlled at -0.097 MPa to -0.098 MPa.

9. The method for preparing a polyester resin for a high temperature resistant and flame retardant powder coating according to claim 4, further characterized in that in step H, the polyester resin is cooled by a steel belt with cooling water.

10. Use of the polyester resin for high temperature resistant and flame retardant powder coatings according to any one of claims 1 to 3 or the polyester resin for high temperature resistant and flame retardant powder coatings prepared by the preparation method according to any one of claims 4 to 9 in TGIC curing system powder coatings.

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