Low-temperature curing polyester resin powder coating and preparation method thereof

Abstract

A low-temperature curing polyester resin powder coating and a preparation method thereof, relating to the technical field of powder coatings, comprising the following materials in proportion by weight: 180-230 parts of an amino-terminated hyperbranched polyamide resin, 10-15 parts of a reducing agent, and 40-60 parts of a metal salt. The amino-terminated hyperbranched polyamide resin is prepared by using AB-type monomers and AB-type monomers in an aprotic solvent and a catalyst. The amino-terminated hyperbranched polyamide resin is introduced and stirred evenly with the remaining materials, and then the amino-terminated hyperbranched polyamide resin reacts with the metal salt under stirring to replace amino groups with metal ions and achieve the purpose of evenly distributing the metal ions. The metal ions are then reduced to nano-metal particles by the reducing agent, so that the metal particles can be more evenly distributed in the powder.

Description

Technical Field

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

[0002] Since its advent in the 1970s, powder coatings have been increasingly widely used in the coating of housings of household appliances, the automotive industry, office equipment, metal materials, outdoor buildings, etc., because they do not contain organic solvents and are 100% solid. Compared with conventional coatings, they have the advantages of being pollution-free, saving energy and resources, having high mechanical strength of the coating film, and the complete recycling of excess coatings.

[0003] Polyester powder coatings have been a hot topic in coatings R&D in recent years, with a constant stream of new processes emerging. Ultimately, these processes are driven by both the development of new properties for polyester coatings and the need to reduce costs. However, under existing, mature high-temperature curing processes, some substrates are susceptible to high temperatures during the curing process. Therefore, low-temperature curing processes are urgently needed to expand the application range of polyester coatings. Summary of the Invention

[0004] The purpose of the present invention is to solve the above technical difficulties and provide a low-temperature curing polyester resin powder coating and a preparation method and device thereof, which at least partially solve the above problems.

[0005] The technical solution adopted by the present invention is: a low-temperature curing polyester resin powder coating, comprising the following materials in proportion by weight: 180-230 parts of amino-terminated hyperbranched polyamide resin, 10-15 parts of reducing agent, and 40-60 parts of metal salt;

[0006] Wherein, the amino-terminated hyperbranched polyamide resin is prepared by using AB type monomers, The amino-terminated hyperbranched polyamide resin was prepared by using the monomer in an aprotic solvent and a catalyst.

[0007] Furthermore, the AB type monomer is one or more of methyl acrylate, ethyl acrylate and methyl methacrylate;

[0008] described The monomer is one or more of ethylenediamine, diethylenetriamine and triethylenetetramine.

[0009] Furthermore, the aprotic solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, hexamethylphosphoric triamide and dimethylacetamide;

[0010] The catalyst is one or more of hydrochloric acid, toluenesulfonic acid, sulfuric acid, butyl titanate, butyltin laurate, sodium alkoxide, potassium alkoxide, sodium nitride, potassium nitride, butyl lithium and zinc acetate.

[0011] Furthermore, the reducing agent is one or more of catechol, ethylene glycol, sodium borohydride, potassium borohydride and ascorbic acid;

[0012] The metal salt is one or more of tin salt, zinc salt, titanium salt, zirconium salt, cobalt salt or manganese salt.

[0013] Furthermore, the composition further comprises 5800-6400 parts of terephthalic acid, 360-420 parts of ethylene glycol, 2900-3300 parts of neopentyl glycol, 80-110 parts of trimethylolpropane, 690-730 parts of adipic acid, 20-30 parts of antioxidant, 10-15 parts of flame retardant and 8-12 parts of accelerator.

[0014] On the other hand, the present invention also provides a method for preparing a low-temperature curing polyester resin powder coating, comprising the following steps:

[0015] Adding amino-terminated hyperbranched polyamide resin, metal salt, terephthalic acid, ethylene glycol, neopentyl glycol, trimethylolpropane, adipic acid, antioxidant, flame retardant and accelerator into a reaction kettle;

[0016] The raw materials in the reactor are stirred at high speed to mix evenly, and at the same time, inert gas is introduced into the reactor to expel the air;

[0017] The reactor is heated and continuously stirred, and the raw materials inside react to obtain pre-cooled material;

[0018] Discharging the cooled material from the reactor onto a cooling device, and cooling the pre-cooled material by the cooling device to obtain a flake material;

[0019] The flake material is put into a crushing device, and the flake material is crushed by the crushing device to obtain a powder coating.

[0020] Furthermore, after the reducing agent is added into the reactor, the reactor is heated, and the temperature in the reactor is adjusted to rise to 260° C.-300° C. until the reaction is complete and then the heating is stopped.

[0021] Furthermore, the heating of the reactor is specifically as follows: first, the reactor is quickly heated to 170°C, and after the temperature inside the reactor reaches 170°C, the heating efficiency of the reactor is reduced, so that the temperature inside the reactor slowly rises to 260°C-300°C until the raw materials in the reactor react completely and then the heating is stopped.

[0022] Furthermore, the preparation method of the amino-terminated hyperbranched polyamide resin comprises the following steps:

[0023] AB monomers and The type monomer is added into the aprotic solvent and the catalyst, mixed evenly, and then placed in an inert gas atmosphere at room temperature and pressure to react;

[0024] The temperature was adjusted to 145-155° C., the reaction was completed, and then cooled to room temperature. Ether was added for precipitation, and then suction filtered, washed, and vacuum dried to obtain an amino-terminated hyperbranched polyamide resin.

[0025] The beneficial effects of the present invention are:

[0026] The present invention introduces an amino-terminated hyperbranched polyamide resin and stirs it evenly with other materials. The amino-terminated hyperbranched polyamide resin reacts with a metal salt under stirring to replace amino groups with metal ions and achieve the purpose of evenly distributing the metal ions. The metal ions are then reduced to nano-metal particles by a reducing agent, so that the metal particles can be distributed more evenly in the powder.

[0027] The hyperbranched polyamide and uniformly distributed nano-metal particles in the final product of the present invention can improve the low-temperature curing ability of the powder coating, so that the polyester resin powder coating can be cured at a low temperature of 120-130°C. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the present invention, the technical solutions of the present invention are further described below with reference to the embodiments.

[0029] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and configurations of specific examples are described below. Of course, these are merely examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numbers and / or reference letters in different examples. This repetition is for the purpose of simplicity and clarity and does not in itself indicate a relationship between the various embodiments and / or configurations discussed. In addition, the present invention provides examples of various specific processes and materials, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0030] The present invention provides a low-temperature curing polyester resin powder coating, comprising the following materials in proportion by weight: 180-230 parts of amino-terminated hyperbranched polyamide resin, 10-15 parts of reducing agent, and 40-60 parts of metal salt;

[0031] Wherein, the amino-terminated hyperbranched polyamide resin is prepared by using AB type monomers, The amino-terminated hyperbranched polyamide resin was prepared by using the monomer in an aprotic solvent and a catalyst.

[0032] It should be noted that due to their unique molecular structure, such as low viscosity, reduced intermolecular entanglement, and high chemical reactivity, hyperbranched polyesters can significantly lower curing temperatures and accelerate curing speeds compared to traditional linear polyesters without compromising storage stability. Furthermore, they can be used as additives to improve the rheological properties and compatibility of conventional polyester resins.

[0033] Hyperbranched polymers are spherical or quasi-spherical macromolecules formed by multiple branches growing outward from a central core. Their molecular structure typically comprises three distinct repeating units: dendritic units, linear units, and terminal units defined by unreacted B functional groups. The degree of branching (DB) of a hyperbranched polymer can be calculated using the formula (D + T) / (D + T + L), where D represents the number of dendritic units, T the number of terminal units, and L the number of linear units. A DB value close to 0.5 indicates the presence of a large number of branching points and terminal functional groups within each molecule.

[0034] In low-temperature curing polyester resin powder coatings, the use of specific metal ions as catalysts or curing accelerators can achieve good curing results. These metal ions can accelerate the cross-linking reaction between the polyester resin and the curing agent, allowing the coating film to complete the curing process at a lower temperature.

[0035] The reducing agent can reduce the evenly distributed metal salt to nano-metal particles after the metal salt reacts with the amino-terminated hyperbranched polymer to replace the terminal amino group, thereby making the nano-metal particles evenly distributed in the powder coating and achieving a good low-temperature curing effect.

[0036] In a further embodiment of this embodiment, the AB type monomer is one or more of methyl acrylate, ethyl acrylate and methyl methacrylate;

[0037] described The monomer is one or more of ethylenediamine, diethylenetriamine and triethylenetetramine.

[0038] It should be noted that AB type monomers refer to compounds containing two or more reactive groups, one of which is an isocyanate group (-NCO) and the other can be a hydroxyl group (-OH), an amino group (- ) or other reactive groups; refers to a multifunctional monomer containing three or more reactive amino groups.

[0039] During the polymerization process, the -NCO group of the AB type monomer reacts with the C n Type monomer- The groups react to form urea bonds (-NHCONH-) and expose more - As the reaction proceeds, the molecular chain gradually becomes highly branched, eventually forming a hyperbranched polyurethane with abundant terminal amino groups.

[0040] In a further embodiment of this example, the aprotic solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, hexamethylphosphoric triamide and dimethylacetamide;

[0041] The catalyst is one or more of hydrochloric acid, toluenesulfonic acid, sulfuric acid, butyl titanate, butyltin laurate, sodium alkoxide, potassium alkoxide, sodium nitride, potassium nitride, butyl lithium and zinc acetate.

[0042] It should be noted that aprotic solvents refer to solvents that cannot provide protons (i.e., hydrogen ions, H⁺). They have high polarity and good solubility and can effectively promote reactions without interfering with the formation of chemical bonds between reactants.

[0043] Isocyanate groups (-NCO) are very sensitive to moisture and readily undergo hydrolysis in the presence of water, generating amines and carbon dioxide. This not only reduces reaction efficiency but also introduces unwanted byproducts. Aprotic solvents such as dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP) do not contain active hydrogen atoms and therefore do not undergo hydrolysis with isocyanates, thereby ensuring reaction selectivity and yield.

[0044] The use of the above catalyst can accelerate the reaction process, shorten the production cycle, improve production efficiency, have good selectivity, only promote the target reaction, avoid unnecessary side reactions, and ensure product purity.

[0045] In a further embodiment of this example, the reducing agent is one or more of catechol, ethylene glycol, sodium borohydride, potassium borohydride and ascorbic acid;

[0046] The metal salt is one or more of tin salt, zinc salt, titanium salt, zirconium salt, cobalt salt or manganese salt.

[0047] It should be noted that metal hydrides are a very potent class of reducing agents, including lithium aluminum hydride (LiAlH4), sodium borohydride (NaBH4), and potassium borohydride (KBH4). These reducing agents have a complex salt structure of aluminum tetrahydride ions (AlH4⁻) or boron tetrahydride ions (BH4⁻), and can attack the positively charged carbon atoms in polar unsaturated bonds, thereby causing negative ion transfer and reduction. However, while lithium aluminum hydride has a strong reducing property, it has poor monoselectivity and may have a certain degree of side reactions. Therefore, lithium aluminum hydride is not selected as a reducing agent in this scheme.

[0048] Using specific metal ions as catalysts or curing accelerators can achieve good curing effects. Different types of metal ions can also be used in combination to achieve the best curing effect and comprehensive performance.

[0049] In a further embodiment of this embodiment, the composition further comprises 5800-6400 parts of terephthalic acid, 360-420 parts of ethylene glycol, 2900-3300 parts of neopentyl glycol, 80-110 parts of trimethylolpropane, 690-730 parts of adipic acid, 20-30 parts of antioxidant, 10-15 parts of flame retardant and 8-12 parts of accelerator.

[0050] On the other hand, the present invention also provides a method for preparing a low-temperature curing polyester resin powder coating, comprising the following steps:

[0051] Adding amino-terminated hyperbranched polyamide resin, metal salt, terephthalic acid, ethylene glycol, neopentyl glycol, trimethylolpropane, adipic acid, antioxidant, flame retardant and accelerator into a reaction kettle;

[0052] The raw materials in the reactor are stirred at high speed to mix evenly, and at the same time, inert gas is introduced into the reactor to expel the air;

[0053] The reactor is heated and continuously stirred, and the raw materials inside react to obtain pre-cooled material;

[0054] Discharging the cooled material from the reactor onto a cooling device, and cooling the pre-cooled material by the cooling device to obtain a flake material;

[0055] The flake material is put into a crushing device, and the flake material is crushed by the crushing device to obtain a powder coating.

[0056] In a further embodiment of this example, after the reducing agent is added into the reactor, the reactor is heated, and the temperature in the reactor is adjusted to rise to 260° C.-300° C. until the reaction is complete and then the heating is stopped.

[0057] In a further implementation of this embodiment, the heating of the reactor is specifically as follows: the reactor is first quickly heated to 170°C, and after the temperature inside the reactor reaches 170°C, the heating efficiency of the reactor is reduced, and the temperature inside the reactor is slowly increased to 260°C-300°C until the raw materials in the reactor react completely and the heating is stopped.

[0058] In a further embodiment of this embodiment, the preparation method of the amino-terminated hyperbranched polyamide resin comprises the following steps:

[0059] AB monomers and The type monomer is added into the aprotic solvent and the catalyst, mixed evenly, and then placed in an inert gas atmosphere at room temperature and pressure to react;

[0060] The temperature was adjusted to 145-155° C., the reaction was completed, and then cooled to room temperature. Ether was added for precipitation, and then suction filtered, washed, and vacuum dried to obtain an amino-terminated hyperbranched polyamide resin.

[0061] The present invention is further illustrated below through several specific embodiments. These embodiments are only for illustration and are not intended to be limiting.

[0062] Example 1

[0063] Methyl methacrylate and diethylenetriamine were added to dimethylacetamide and hydrochloric acid in a mass ratio of 1.2:1, mixed evenly, and then placed in an argon atmosphere at room temperature and pressure to react for 3 hours;

[0064] The temperature was adjusted to 145-155° C., the reaction was completed, and then cooled to room temperature. Ether was added for precipitation, and then suction filtered, washed, and vacuum dried to obtain an amino-terminated hyperbranched polyamide resin.

[0065] 180 parts of amino-terminated hyperbranched polyamide resin, 40 parts of metal salt, 5800 parts of terephthalic acid, 360 parts of ethylene glycol, 2900 parts of neopentyl glycol, 80 parts of trimethylolpropane, 690 parts of adipic acid, 20 parts of antioxidant, 10 parts of flame retardant and 8 parts of accelerator were put into a reactor;

[0066] The raw materials in the reactor are stirred at high speed to mix evenly, and at the same time, inert gas is introduced into the reactor to expel the air;

[0067] After 10 parts of a reducing agent is added to a reactor, the reactor is first quickly heated to 170° C. After the temperature in the reactor reaches 170° C., the heating efficiency of the reactor is reduced, and the temperature in the reactor is slowly increased to 260° C.-300° C. until the raw materials in the reactor are completely reacted. After that, the heating is stopped and the reactor is continuously stirred. The raw materials inside react to obtain a pre-cooled material;

[0068] Discharging the cooled material from the reactor onto a cooling device, and cooling the pre-cooled material by the cooling device to obtain a flake material;

[0069] The flake material is put into a crushing device, and the flake material is crushed by the crushing device to obtain a powder coating.

[0070] Example 2

[0071] Methyl methacrylate and diethylenetriamine were added to dimethylacetamide and hydrochloric acid in a mass ratio of 1.2:1, mixed evenly, and then placed in an argon atmosphere at room temperature and pressure to react for 3 hours;

[0072] The temperature was adjusted to 145-155° C., the reaction was completed, and then cooled to room temperature. Ether was added for precipitation, and then suction filtered, washed, and vacuum dried to obtain an amino-terminated hyperbranched polyamide resin.

[0073] 190 parts of amino-terminated hyperbranched polyamide resin, 44 parts of metal salt, 5900 parts of terephthalic acid, 370 parts of ethylene glycol, 3000 parts of neopentyl glycol, 86 parts of trimethylolpropane, 700 parts of adipic acid, 22 parts of antioxidant, 11 parts of flame retardant and 9 parts of accelerator were put into a reactor;

[0074] The raw materials in the reactor are stirred at high speed to mix evenly, and at the same time, inert gas is introduced into the reactor to expel the air;

[0075] After 11 parts of reducing agent are added into the reactor, the reactor is first quickly heated to 170°C. After the temperature in the reactor reaches 170°C, the heating efficiency of the reactor is reduced, and the temperature in the reactor is slowly increased to 260°C-300°C until the raw materials in the reactor are completely reacted. After that, the heating is stopped and the reactor is continuously stirred. The raw materials inside react to obtain pre-cooled material;

[0076] Discharging the cooled material from the reactor onto a cooling device, and cooling the pre-cooled material by the cooling device to obtain a flake material;

[0077] The flake material is put into a crushing device, and the flake material is crushed by the crushing device to obtain a powder coating.

[0078] Example 3

[0079] Methyl methacrylate and diethylenetriamine were added to dimethylacetamide and hydrochloric acid in a mass ratio of 1.2:1, mixed evenly, and then placed in an argon atmosphere at room temperature and pressure to react for 3 hours;

[0080] The temperature was adjusted to 145-155° C., the reaction was completed, and then cooled to room temperature. Ether was added for precipitation, and then suction filtered, washed, and vacuum dried to obtain an amino-terminated hyperbranched polyamide resin.

[0081] 200 parts of amino-terminated hyperbranched polyamide resin, 48 parts of metal salt, 6000 parts of terephthalic acid, 380 parts of ethylene glycol, 3100 parts of neopentyl glycol, 92 parts of trimethylolpropane, 710 parts of adipic acid, 24 parts of antioxidant, 12 parts of flame retardant and 10 parts of accelerator were put into a reactor;

[0082] The raw materials in the reactor are stirred at high speed to mix evenly, and at the same time, inert gas is introduced into the reactor to expel the air;

[0083] After 12 parts of a reducing agent is added to a reactor, the reactor is first quickly heated to 170° C. After the temperature in the reactor reaches 170° C., the heating efficiency of the reactor is reduced, and the temperature in the reactor is slowly increased to 260° C.-300° C. until the raw materials in the reactor are completely reacted, and then the heating is stopped and the reactor is continuously stirred, and the raw materials inside react to obtain a pre-cooled material;

[0084] Discharging the cooled material from the reactor onto a cooling device, and cooling the pre-cooled material by the cooling device to obtain a flake material;

[0085] The flake material is put into a crushing device, and the flake material is crushed by the crushing device to obtain a powder coating.

[0086] Example 4

[0087] Methyl methacrylate and diethylenetriamine were added to dimethylacetamide and hydrochloric acid in a mass ratio of 1.2:1, mixed evenly, and then placed in an argon atmosphere at room temperature and pressure to react for 3 hours;

[0088] The temperature was adjusted to 145-155° C., the reaction was completed, and then cooled to room temperature. Ether was added for precipitation, and then suction filtered, washed, and vacuum dried to obtain an amino-terminated hyperbranched polyamide resin.

[0089] 210 parts of amino-terminated hyperbranched polyamide resin, 52 parts of metal salt, 6100 parts of terephthalic acid, 400 parts of ethylene glycol, 3200 parts of neopentyl glycol, 100 parts of trimethylolpropane, 720 parts of adipic acid, 27 parts of antioxidant, 13.5 parts of flame retardant and 11 parts of accelerator were put into a reactor;

[0090] The raw materials in the reactor are stirred at high speed to mix evenly, and at the same time, inert gas is introduced into the reactor to expel the air;

[0091] After 13 parts of a reducing agent is added to a reactor, the reactor is first quickly heated to 170° C. After the temperature in the reactor reaches 170° C., the heating efficiency of the reactor is reduced, and the temperature in the reactor is slowly increased to 260° C.-300° C. until the raw materials in the reactor are completely reacted, and then the heating is stopped and the reactor is continuously stirred, and the raw materials inside react to obtain a pre-cooled material;

[0092] Discharging the cooled material from the reactor onto a cooling device, and cooling the pre-cooled material by the cooling device to obtain a flake material;

[0093] The flake material is put into a crushing device, and the flake material is crushed by the crushing device to obtain a powder coating.

[0094] Example 5

[0095] Methyl methacrylate and diethylenetriamine were added to dimethylacetamide and hydrochloric acid in a mass ratio of 1.2:1, mixed evenly, and then placed in an argon atmosphere at room temperature and pressure to react for 3 hours;

[0096] The temperature was adjusted to 145-155° C., the reaction was completed, and then cooled to room temperature. Ether was added for precipitation, and then suction filtered, washed, and vacuum dried to obtain an amino-terminated hyperbranched polyamide resin.

[0097] 230 parts of amino-terminated hyperbranched polyamide resin, 60 parts of metal salt, 6400 parts of terephthalic acid, 420 parts of ethylene glycol, 3300 parts of neopentyl glycol, 110 parts of trimethylolpropane, 730 parts of adipic acid, 20 parts of antioxidant, 15 parts of flame retardant and 12 parts of accelerator were put into a reactor;

[0098] The raw materials in the reactor are stirred at high speed to mix evenly, and at the same time, inert gas is introduced into the reactor to expel the air;

[0099] After 15 parts of a reducing agent is added to a reactor, the reactor is first quickly heated to 170° C. After the temperature in the reactor reaches 170° C., the heating efficiency of the reactor is reduced, and the temperature in the reactor is slowly increased to 260° C.-300° C. until the raw materials in the reactor are completely reacted, and then the heating is stopped and the reactor is continuously stirred, and the raw materials inside react to obtain a pre-cooled material;

[0100] Discharging the cooled material from the reactor onto a cooling device, and cooling the pre-cooled material by the cooling device to obtain a flake material;

[0101] The flake material is put into a crushing device, and the flake material is crushed by the crushing device to obtain a powder coating.

[0102] The curing temperatures of the polyester resin powder coatings prepared in Examples 1 to 5 were tested, and the results are shown in Table 1 below:

[0103] Table 1: Curing temperatures of Examples 1 to 5

[0104]

[0105] In summary, the low-temperature curing temperature of the polyester resin powder coating prepared by this solution is lower than the temperature of 140° C. in the prior art, and the time required for curing is also shorter.

[0106] The above are merely embodiments of the present invention. Common knowledge such as the well-known specific structures and characteristics in the scheme are not described in detail here. Ordinary technicians in the relevant field are aware of all common technical knowledge in the technical field of the invention before the application date or priority date, can obtain all existing technologies in the field, and have the ability to apply conventional experimental means before that date. Ordinary technicians in the relevant field can improve and implement this scheme based on their own abilities under the inspiration given by this application. Some typical well-known structures or well-known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for technicians in this field, without departing from the structure of the present invention, they can also make several variations and improvements, which should also be regarded as the scope of protection of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. A low-temperature curing polyester resin powder coating, characterized in that: The invention comprises the following materials in proportions by weight: 180-230 parts of amino-terminated hyperbranched polyamide resin, 10-15 parts of reducing agent, 40-60 parts of metal salt, 5800-6400 parts of terephthalic acid, 360-420 parts of ethylene glycol, 2900-3300 parts of neopentyl glycol, 80-110 parts of trimethylolpropane, 690-730 parts of adipic acid, 20-30 parts of antioxidant, 10-15 parts of flame retardant and 8-12 parts of accelerator; Wherein, the amino-terminated hyperbranched polyamide resin is prepared by using AB type monomers, The amino-terminated hyperbranched polyamide resin is prepared by using an AB-type monomer in an aprotic solvent and a catalyst; the AB-type monomer is one or more of methyl acrylate, ethyl acrylate and methyl methacrylate; the The monomer is one or more of ethylenediamine, diethylenetriamine and triethylenetetramine; the aprotic solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, hexamethylphosphoric triamide and dimethylacetamide; the catalyst is one or more of hydrochloric acid, methylbenzenesulfonic acid, sulfuric acid, butyl titanate, butyltin laurate, sodium alkoxide, potassium alkoxide, sodium nitrile, potassium nitrile, butyl lithium and zinc acetate; The preparation method of the amino-terminated hyperbranched polyamide resin comprises the following steps: AB monomers and The type monomer is added into the aprotic solvent and the catalyst, mixed evenly, and then placed in an inert gas atmosphere at room temperature and pressure to react; The temperature was adjusted to 145-155° C., the reaction was completed, and then cooled to room temperature. Ether was added for precipitation, and then suction filtered, washed, and vacuum dried to obtain an amino-terminated hyperbranched polyamide resin.

2. The low-temperature curing polyester resin powder coating according to claim 1, characterized in that: The reducing agent is one or more of catechol, ethylene glycol, sodium borohydride, potassium borohydride and ascorbic acid; The metal salt is one or more of tin salt, zinc salt, titanium salt, zirconium salt, cobalt salt or manganese salt.

3. A method for preparing a low-temperature curing polyester resin powder coating according to claim 1 or 2, characterized in that: The following steps are involved: Adding amino-terminated hyperbranched polyamide resin, metal salt, terephthalic acid, ethylene glycol, neopentyl glycol, trimethylolpropane, adipic acid, antioxidant, flame retardant and accelerator into a reaction kettle; The raw materials in the reactor are stirred at high speed to mix evenly, and at the same time, inert gas is introduced into the reactor to expel the air; After the reducing agent is added into the reactor, the reactor is heated and continuously stirred, and the raw materials inside react to obtain a pre-cooled material; Discharging the cooled material from the reactor onto a cooling device, and cooling the pre-cooled material by the cooling device to obtain a flake material; The flake material is put into a crushing device, and the flake material is crushed by the crushing device to obtain a powder coating.

4. The method for preparing a low-temperature curing polyester resin powder coating according to claim 3, wherein: After the reducing agent is added into the reactor, the reactor is heated, and the temperature in the reactor is adjusted to rise to 260° C.-300° C. until the reaction is complete and then the heating is stopped.

5. The method for preparing a low-temperature curing polyester resin powder coating according to claim 4, characterized in that: The heating of the reactor is specifically as follows: first, the reactor is quickly heated to 170°C, and after the temperature inside the reactor reaches 170°C, the heating efficiency of the reactor is reduced, so that the temperature inside the reactor slowly rises to 260°C-300°C until the raw materials in the reactor react completely, and then the heating is stopped.

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