Polyester resin, polyester resin composition, and powder coating comprising polyester resin composition

Abstract

Disclosed in the present application are a polyester resin, a polyester resin composition, and a powder coating comprising the polyester resin composition. The polyester resin comprises dicarboxylic acid units and dimethanol units, wherein dicarboxylic acid units derived from 1,2-cyclohexanedicarboxylic acid or 1,2-cyclohexanedicarboxylic anhydride account for a molar percentage of greater than 99% of the total dicarboxylic acid units, and dimethanol units derived from 1,4-cyclohexanedimethanol account for a molar percentage of greater than 99% of the total dimethanol units. The polyester resin of the present application has a main chain mainly composed of dicarboxylic acid units containing a saturated six-membered alicyclic ring and dimethanol units containing a saturated six-membered alicyclic ring. The polyester resin of the present application is used for powder coatings, which can improve the weather resistance of the powder coatings and meet the requirements of green environmental protection at the same time. When used for powder coatings using a β-hydroxyalkylamide curing agent, the polyester resin can also improve the leveling performance of the powder coatings to solve the pinhole problem of powder coating demolding.

Description

Polyester resins, polyester resin compositions, and powder coatings comprising polyester resin compositions Technical Field

[0001] This invention relates to the field of powder coating technology, and more specifically to a polyester resin, a polyester resin composition, and a powder coating comprising the polyester resin composition. Background Technology

[0002] When powder coatings are used in outdoor applications, they are susceptible to aging, loss of gloss, cracking, and peeling due to natural factors such as light, water, and temperature, thus losing their protective and decorative functions. Therefore, the weather resistance of powder coatings is a crucial performance indicator for outdoor applications. The weather resistance of polyester powder coatings primarily depends on the weather resistance of the polyester resin used. Traditional methods typically improve the weather resistance of polyester resin by increasing the ratio of neopentyl glycol to isophthalic acid. However, polyester resins synthesized primarily using neopentyl glycol and isophthalic acid can achieve an average weather resistance of approximately 800 hours (tested according to the GSB AL631 European aluminum profile standard).

[0003] Existing technologies, such as Chinese invention patent document CN201711476169.4, disclose a method for preparing alicyclic weather-resistant powder coatings by adding PVDF fluorocarbon resin to powder coatings; CN201611081678.2 discloses a method for preparing fluorinated carboxyl-terminated polyester resins for powder coatings. Both methods improve the weather resistance of powder coatings by adding fluorinated materials. However, fluorinated coatings often contain chlorofluorocarbons, which are potent carcinogens. Long-term exposure to these substances can cause irreversible harm to the human body. Furthermore, when a building catches fire, the thermal decomposition of fluorinated coatings can produce dozens of harmful compounds such as phosgene and fluoroolefins, which can also be harmful to human health.

[0004] Curing agents are an important component of powder coatings, significantly influencing their production, storage, and application. These influence factors include extrusion temperature, curing temperature, leveling properties, impact resistance and hardness, storage stability, weather resistance, and chemical resistance. Currently, the main weather-resistant curing agents for powder coatings that cure with carboxyl-terminated polyester resins include triglycidyl isocyanate (TGIC) and β-hydroxyalkylamide. TGIC-cured coatings exhibit good performance in all aspects, but they are sensitizing and potentially carcinogenic to humans. β-hydroxyalkylamide, on the other hand, is relatively non-toxic and harmless, making it a popular choice. Technical issues

[0005] Polyester resin end-capping acids generally include a mixture of one or more of isophthalic acid, 1,4-cyclohexanedicarboxylic acid, and adipic acid. When the resulting polyester resin reacts with a β-hydroxyalkylamide curing agent at 180~200℃, the hydroxyl groups in the β-hydroxyalkylamide curing agent become highly active due to the influence of the amide structure. Moreover, this type of curing agent has a high functionality, resulting in a particularly fast reaction rate with the polyester resin. This leads to poor leveling effect in the prepared powder coating and a tendency for pinholes to appear in the coating film. Technical solutions

[0006] This application provides a polyester resin, a polyester resin composition, and a powder coating comprising the polyester resin composition. The polyester resin of this application, when used in powder coating, can significantly improve the weather resistance of the powder coating and is green and pollution-free. When used in powder coatings using β-hydroxyalkylamide as a curing agent, it can also improve the leveling properties and solve the pinhole problem during coating demolding.

[0007] Polyester resin comprising dicarboxylic acid units and diethanol units, wherein the molar percentage of dicarboxylic acid units derived from 1,2-cyclohexanedicarboxylic acid or 1,2-cyclohexanedicarboxylic anhydride is greater than 99% of the total dicarboxylic acid units, and the molar percentage of diethanol units derived from 1,4-cyclohexanediethanol is greater than 99% of the total diethanol units.

[0008] The polyester resin's main chain consists of dicarboxylic acid units and diethanol units. The polyester resin of this application has a main chain primarily composed of dicarboxylic acid units containing saturated six-membered alicyclic rings and diethanol units containing saturated six-membered alicyclic rings. The dicarboxylic acid units are mainly derived from 1,2-cyclohexanedicarboxylic acid or 1,2-cyclohexanedicarboxylic anhydride, while the diethanol units are mainly derived from 1,4-cyclohexanediethanol. When used in powder coatings, this polyester resin with this main chain structure significantly improves the weather resistance of the powder coatings and is environmentally friendly and pollution-free. Furthermore, when used in powder coatings employing β-hydroxyalkylamide as a curing agent, it improves the leveling properties and solves the pinhole problem during demolding when β-hydroxyalkylamide is used as a curing agent.

[0009] Optionally, the polyester resin satisfies at least one of the following (a) to (f):

[0010] (a) The acid value range is 20-30 mg KOH / g;

[0011] (b) The hydroxyl value ranges from 3 to 10 mg KOH / g;

[0012] (c) The melt viscosity at 200℃ ranges from 1000 to 3500 mPa·s;

[0013] (d) The glass transition temperature range is 40-50℃;

[0014] (e) The number-average molecular weight ranges from 3500 to 7600 g / mol;

[0015] (f) The weight-average mass range is 7000-25000 g / mol.

[0016] Optionally, the polyester resin further includes triethanol units. The triethanolamine units constitute the branches of the polyester resin.

[0017] Optionally, the molar ratio of the triethanolamine unit to the diethanolamine unit is 1:157~162.

[0018] Optionally, the triethanol unit is derived from one or a mixture of several of trimethylolpropane, trimethylolethane, and sac (tris(2-hydroxyethyl)isocyanurate).

[0019] Preferably, the dicarboxylic acid unit is 100% derived from 1,2-cyclohexanedicarboxylic acid or 1,2-cyclohexanedicarboxylic anhydride (hexahydrophthalic anhydride), and the diethanol unit is 100% derived from 1,4-cyclohexanediethanol.

[0020] This application also provides a polyester resin composition comprising the aforementioned polyester resin.

[0021] Optionally, the polyester resin composition may further contain a curing accelerator.

[0022] Optionally, the curing accelerator is selected from one or a mixture of several of triphenylethylphosphine bromide, triphenylbutylphosphine bromide, and tetraphenylphosphine bromide.

[0023] Optionally, the polyester resin composition may further contain an antioxidant.

[0024] Optionally, the antioxidant is selected from one or a mixture of several of tris(2,4-di-tert-butylphenyl) phosphite, phosphorous acid, triphenyl phosphite, and 4,4'-butylidene bis(6-tert-butyl-m-cresol).

[0025] Optionally, the curing accelerator and antioxidant are added in the same amounts as the conventional amounts used for this type of resin.

[0026] Polyester resin is prepared by melt polymerization:

[0027] An esterification reaction is carried out using 1,2-cyclohexanedicarboxylic acid or 1,2-cyclohexanedicarboxylic anhydride (hexahydrophthalic anhydride) as the main dicarboxylic acid and 1,4-cyclohexanediethanol as the main diethanol; wherein the 1,2-cyclohexanedicarboxylic acid or 1,2-cyclohexanedicarboxylic anhydride accounts for more than 99% of the total dicarboxylic acid, and the 1,4-cyclohexanediethanol accounts for more than 99% of the total diethanol.

[0028] Optionally, the raw materials for the esterification reaction may also include a triol; the triol is selected from one or a mixture of several of trimethylolpropane, trimethylolethane, and sac (tris(2-hydroxyethyl)isocyanurate).

[0029] An esterification catalyst is added during the esterification reaction to accelerate the reaction process. Optionally, the esterification catalyst is selected from one or a mixture of several of butyltin, stannous oxalate and titanate.

[0030] After the polyester resin is prepared, it is mixed with a curing accelerator, and then an antioxidant is added and mixed to obtain the polyester resin composition.

[0031] Specifically, one method for preparing a polyester resin composition includes:

[0032] Diformic acid or diformic anhydride, diethanol, and esterification catalyst are added to a reaction apparatus equipped with a distillation column and a condenser. Nitrogen gas is introduced, and the material is heated to complete melting at a rate of 5°C / hour. Stirring is started at a speed of 150 RPM, and then the temperature of the reactants is raised to 250°C at a rate of 10°C / hour and held at that temperature. Nitrogen gas is continuously introduced as a protective gas during this process, and the temperature at the top of the distillation column is controlled to not exceed 102°C. When the temperature at the top of the distillation column drops to about 60°C, a sample is taken to measure the acid value. After the requirement is met, the nitrogen gas is turned off, and the pressure is reduced to -0.1 MPa for about 2-3 hours of distillation. After the acid value reaches the design value, nitrogen gas is introduced to restore the pressure to atmospheric pressure, and the temperature is lowered to 180°C. Then, a curing accelerator is added, or an antioxidant is added further. After stirring evenly, the material is discharged, cooled, and crushed into small particles to obtain the polyester resin composition.

[0033] In the preparation process, in addition to diethanol, a small amount of triol can be added as a branching agent. A preferred formulation for preparing the polyester resin composition, based on the mass percentage of the raw materials, is as follows:

[0034] 50%~55% dicarboxylic acid or dicarboxylic anhydride;

[0035] Dimethylethanol 43%~48%;

[0036] Triols 0~3.5%;

[0037] Esterification catalyst: 0.01%~0.1%;

[0038] Antioxidant 0.2%~1%;

[0039] Curing accelerator: 0.05%~0.2%.

[0040] This application also provides the use of the polyester resin or the polyester resin composition in powder coatings.

[0041] This application also provides a powder coating comprising the aforementioned polyester resin composition.

[0042] Furthermore, the powder coating comprises 60-65% of the polyester resin composition by weight of the raw materials and 2-3% of β-hydroxyalkylamide by weight of the raw materials.

[0043] Optionally, the powder coating may also include conventional components such as leveling agents, benzoin, and titanium dioxide in conventional amounts. Beneficial effects

[0044] (1) The polyester resin prepared by this invention is free of fluorine, making it more environmentally friendly and safe for human health. The high content of saturated six-membered ring structure and high steric carboxyl groups make the ester bonds in the polyester more weather-resistant than ordinary polyester resins. The artificial aging time reaches more than 2800 hours, which is close to that of fluorocarbon coatings.

[0045] (2) By optimizing the synthetic monomers, all the synthetic monomers can be 1,4-cyclohexanediethanol, 1,2-cyclohexanedicarboxylic acid or hexahydrophthalic anhydride, etc., which have saturated six-membered ring structures, and a small amount of triols can be used to increase the degree of branching. The synthesized polyester resin not only has a relatively high glass transition temperature, which can meet the requirements of powder coating, but also the large steric hindrance carboxyl groups provided by 1,2-cyclohexanedicarboxylic acid can slow down the curing speed of the polyester resin when it reacts with β-hydroxyalkylamide curing agent. The gelation time at 180°C is more than 210 seconds. As a result, the leveling properties of the obtained powder coating are significantly improved compared with those of powder coatings cured by general β-hydroxyalkylamide curing agents. The paint film is also less prone to pinholes, and the number of pinholes when the coating is 120 micrometer thick is 0. Attached Figure Description

[0046] Figure 1 is a preferred synthesis route diagram of the polyester resin of this application. Embodiments of the present invention

[0047] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0049]

[0050] Polyester resin:

[0051] One object of this application is to provide a polyester resin comprising a main chain of diformate units and dimethyl alcohol units as major constituent units. The major constituent unit can be understood as the constituent unit that constitutes the polyester resin in the largest proportion of the constituent units, typically accounting for 50% or more by mass, preferably 60% or more by mass, more preferably 70% or more by mass, further preferably 80% or more by mass, and particularly preferably 90% or more by mass.

[0052] Diformic acid unit:

[0053] The dicarboxylic acid units constituting the polyester resin include dicarboxylic acid units derived from 1,2-cyclohexanedicarboxylic acid or 1,2-cyclohexanedicarboxylic anhydride (hexahydrophthalic anhydride), such dicarboxylic acids containing saturated hexa-membered alicyclic rings. In the dicarboxylic acid units constituting the polyester resin, dicarboxylic acid units containing saturated hexa-membered alicyclic rings account for more than 99% of the total molar percentage of dicarboxylic acid units, preferably 100%.

[0054] Dimethyl alcohol unit:

[0055] The diethanol units constituting the polyester resin include diethanol units derived from 1,4-cyclohexanediethanol, such dicarboxylic acids containing saturated six-membered alicyclic rings. In the diethanol units constituting the polyester resin, diethanol units containing saturated six-membered alicyclic rings account for more than 99% of the total molar percentage of diethanol units, preferably 100%.

[0056] Other polyol units besides the dimethyl alcohol unit:

[0057] Diethanol units are one of the main components constituting the main structure of polyester resin. In some embodiments, a small amount of triol units may also be included, which constitute the branched structure of the polyester resin. The molar ratio of triol units to diol units is controlled at 1:157~162. The triol units can be selected from one or a mixture of several of trimethylolpropane, trimethylolethane, and cyproheptad (tris(2-hydroxyethyl)isocyanurate). When selecting a mixture of several triols, there are no specific requirements for the ratio between each triol, as long as the total amount is controlled within the above-mentioned ratio range.

[0058] Preparation process of polyester resin:

[0059] Polyester resins can be prepared using known methods for preparing polyester resins. Common methods of melt polymerization can be employed, such as esterification and / or transesterification using diformic acid / anhydride and diethanol, followed by polycondensation under reduced pressure.

[0060] Polyester resin is preferably prepared in the presence of an esterification catalyst. As the catalyst, any catalyst suitable for use in the manufacture of polyester can be selected, and metal compounds such as germanium, titanium, zirconium, hafnium, antimony, tin, magnesium, calcium, zinc, aluminum, cobalt, lead, cesium, manganese, lithium, potassium, sodium, copper, barium, and cadmium are suitable. Among these, germanium compounds, titanium compounds, magnesium compounds, tin compounds, zinc compounds, or lead compounds are preferred, with tin compounds or titanium compounds being particularly preferred.

[0061] There are no particular limitations on the titanium compound used as a catalyst. Tetraalkyl titanates are preferred as titanium compounds, such as tetrapropyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetra-tert-butyl titanate, tetraoctyl titanate, tetraphenyl titanate, tetracyclohexyl titanate, tetrabenzyl titanate, and mixed titanates thereof.

[0062] The tin compound used as a catalyst is not particularly limited, and can be selected from butyltin-like compounds, stannous oxalate, etc., with butyltin-like compounds, such as monobutyltin oxide, being preferred.

[0063] The acid value can be set at 20-30 mg KOH / g.

[0064] Polyester resin composition:

[0065] After the polycondensation reaction of polyester resin reaches the designed acid value, nitrogen gas is introduced to restore the pressure to normal, the temperature is lowered by 180°C, and then antioxidants and curing accelerators are added. After stirring evenly, the material is discharged, cooled, and crushed into small particles to obtain the polyester resin composition.

[0066] As a curing accelerator, it may be selected from one or a mixture of several of triphenylethylphosphine bromide, triphenylbutylphosphine bromide and tetraphenylphosphine bromide.

[0067] As an antioxidant, conventional antioxidants for this type of resin can be used, such as one or a mixture of several of tris(2,4-di-tert-butylphenyl) phosphite, phosphorous acid, triphenyl phosphite, and 4,4'-butylenebis(6-tert-butyl-m-cresol).

[0068] The amounts of curing accelerator and antioxidant added can be based on the conventional amounts used in the synthesis of this type of resin. After the polyester resin polycondensation reaction is completed, the curing accelerator and antioxidant are directly added and mixed. Therefore, it is more convenient to directly use the reaction raw materials of polyester resin to determine the amount of curing accelerator and antioxidant added.

[0069] A preferred formulation:

[0070] The following is a breakdown by weight percentage of the raw materials:

[0071] 50%~55% dicarboxylic acid or dicarboxylic anhydride;

[0072] Dimethylethanol 43%~48%;

[0073] Triols 0~3.5%;

[0074] Esterification catalyst: 0.01%~0.1%;

[0075] Antioxidant 0.2%~1%;

[0076] Curing accelerator: 0.05%~0.2%.

[0077] Powder coating:

[0078] The polyester resin of this application is used in powder coatings, specifically as a raw material for powder coatings in the form of a polyester resin composition. The polyester resin composition as described above is thoroughly mixed with conventional components for powder coatings, such as curing agents and leveling agents. In a preferred embodiment, the curing agent is a β-hydroxyalkylamide. The polyester resin of this application has a good effect on improving leveling properties and pinhole problems in coating demolding when using β-hydroxyalkylamide as a curing agent. More preferably, the powder coating includes 60-65% of the polyester resin composition by weight of the raw materials and 2-3% of β-hydroxyalkylamide by weight of the raw materials.

[0079] Powder coatings also include conventional components such as leveling agents, benzoin, and titanium dioxide in conventional amounts.

[0080] The leveling agent can be selected from those commonly used in powder coatings. The amount of leveling agent added can be 0.5% to 1.5% of the total mass of the powder coating raw materials.

[0081] The amount of benzoin added can be selected to account for 0.2 to 0.5% of the total mass of the powder coating raw materials.

[0082] The amount of titanium dioxide added can be selected to account for 30-35% of the total mass of powder coating raw materials.

[0083] Parameter determination:

[0084] The acid value was tested according to the GB / T 6743-2008 method.

[0085] The hydroxyl value was determined using the method specified in GB / T 12008.3-2009.

[0086] Melt viscosity was tested according to the GB / T 9751.1-2008 method.

[0087] The glass transition temperature was determined according to the method in GB / T19466.2-2004.

[0088] Number-average molecular weight and weight-average mass were determined by gel permeation chromatography (GPC).

[0089] Gelation time was tested according to GB / T 16995-1997.

[0090] PCI leveling rating is tested using ASTM D 3451-01 method.

[0091] Storage stability was tested using the method specified in GB / T 21782.8-2008.

[0092] Artificial aging time was tested using the GSB AL631 European aluminum profile standard test method.

[0093] The number of pinholes in the 120-micron thick coating was detected by visual inspection.

[0094] All raw materials used in the following examples are commercially available.

[0095] Examples 1-3

[0096] Preparation process of polyester resin composition:

[0097] Polyol, hexahydrophthalic anhydride, and esterification catalyst were added to a reaction apparatus equipped with a distillation column and a condenser. Nitrogen gas was introduced, and the material was heated to complete melting at a rate of 5°C / hour. Stirring was started at a rate of 150 RPM, and the temperature of the reactants was raised to 250°C at a rate of 10°C / hour and held. During this period, nitrogen gas was introduced as a protective gas, and the temperature at the top of the distillation column was controlled to not exceed 102°C. When the temperature at the top of the distillation column dropped to about 60°C, a sample was taken to measure the acid value. After the requirement was met, the nitrogen gas was turned off, and the pressure was reduced to -0.1 MPa for about 2-3 hours for distillation. After the acid value reached the design value, nitrogen gas was introduced to restore the pressure to atmospheric pressure. The viscosity, glass transition temperature, hydroxyl value, number-average molecular weight, and weight-average molecular weight of the polyester resin were measured. The synthesis route diagram is shown in Figure 1. The temperature was lowered to 180°C, and then antioxidants and curing accelerators were added. After stirring evenly, the material was discharged, cooled, and crushed into small particles to form a polyester resin composition.

[0098] Referring to the preparation method described above, the material amounts of each component in Examples 1-9 and the relevant properties of the polyester resin compositions prepared in each example are shown in Table 1:

[0099] Table 1

[0100]

[0101]

[0102] Examples 10-18

[0103] Raw materials for powder coatings:

[0104] By mass percentage: 62.4% polyester resin prepared in Examples 1-9 and Comparative Example 1, 2.6% β-hydroxyalkylamide, 1% leveling agent (leveling agent GLP588 (Ningbo Nanhai Chemical)), 0.4% benzoin (benzoin (Ningbo Nanhai Chemical)), 33.6% titanium dioxide (R982 (Sichuan Longmang)), see Table 2.

[0105] Table 2

[0106]

[0107] Preparation of powder coatings:

[0108] a. Weigh and mix the polyester resin compositions prepared in Examples 1-9 and Comparative Example 1 with β-hydroxyalkylamide, leveling agent, benzoin and titanium dioxide.

[0109] b. The premixed mixture is melt-extruded through a twin-screw extruder for powder coating at 90℃-115℃ (the extrusion temperature is set to 100℃ in this embodiment);

[0110] c. Cooling and pressing;

[0111] d. Crush the flakes in a coffee mill and sieve them through a 180-mesh screen to obtain a powder coating with a certain particle size distribution (10-100μm), and pack it for later use.

[0112] Electrostatic spraying: The powder coating prepared according to the formula in Table 2 is sprayed onto the pretreated steel plate using an electrostatic spray gun, with a voltage of 60~80KV (usually 70KV, which can be adjusted according to the actual situation).

[0113] Baking: Place the sprayed plate in an oven and bake at 190℃ for 15 minutes. After baking, the powder coatings of Examples 10 to 18 are labeled A, B, C, D, E, F, G, H, and I, respectively, and the powder coating of Comparative Example 2 is labeled J. After the plate cools down, the relevant properties can be tested, and the results are shown in Table 3.

[0114] Table 3

[0115]

[0116] Results analysis:

[0117] The results from Tables 1 and 3 show that:

[0118] (1) When the molar percentage of dicarboxylic acid units from 1,2-cyclohexanedicarboxylic acid or 1,2-cyclohexanedicarboxylic anhydride is greater than 99% of the total dicarboxylic acid units, and the molar percentage of dimethanol units from 1,4-cyclohexanediethanol is greater than 99% of the total dimethanol units, the polyester resin composition prepared can be used for powder coatings, and the aging time of the powder coatings can reach more than 2800h. However, when triol units are added to form the branch chain of polyester resin, the glass transition temperature of the polyester resin composition can be increased. The increase of glass transition temperature is the key factor to improve storage stability. Therefore, polyester resin compositions containing triol units have better storage stability.

[0119] (2) Compared with the powder coating J of traditional ultra-weather-resistant polyester resin containing aromatic rings, the powder coating AC of alicyclic long-term weather-resistant polyester resin, when combined with β-hydroxyalkylamide curing agent, delays the curing time, making the curing time more moderate, and the leveling and degassing properties of the powder coating are better. Since the traditional aromatic polybasic acid is not used in the polyester resin synthesis process, but 1,4-cyclohexanediethanol and hexahydrophthalic anhydride are used, the weather resistance of the powder coating is much greater than that of traditional ultra-weather-resistant powder coatings.

[0120] (3) The weather resistance of powder coating DI is far inferior to that of powder coating AC. The artificial aging performance of powder coating AC reaches more than 2800 hours. The key is that when synthesizing polyester resin, 1,4-cyclohexanediethanol must account for more than 99% of the molar percentage of diethanol; hexahydrophthalic anhydride or 1,2-cyclohexanedicarboxylic acid must account for more than 99% of the molar percentage of dicarboxylic acid. If the molar percentage exceeds 1%, a small amount of other diethanol or dicarboxylic acid will change the molecular chain structure and fail to meet the designed weather resistance requirements.

[0121] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A polyester resin, characterized in that, It includes dicarboxylic acid units and diethanol units, wherein the molar percentage of dicarboxylic acid units derived from 1,2-cyclohexanedicarboxylic acid or 1,2-cyclohexanedicarboxylic anhydride is greater than 99% of the total dicarboxylic acid units, and the molar percentage of diethanol units derived from 1,4-cyclohexanediethanol is greater than 99% of the total diethanol units.

2. The polyester resin according to claim 1, characterized in that, The polyester resin satisfies at least one of the following (a) to (f): (a) The acid value range is 20-30 mg KOH / g; (b) The hydroxyl value ranges from 3 to 10 mg KOH / g; (c) The melt viscosity at 200℃ ranges from 1000 to 3500 mPa·s; (d) The glass transition temperature range is 40-50℃; (e) The number-average molecular weight ranges from 3500 to 7600 g / mol; (f) The weight-average mass range is 7000-25000 g / mol.

3. The polyester resin according to claim 1, characterized in that, It also includes the triethanol unit.

4. The polyester resin according to claim 3, characterized in that, The molar ratio of the triethanolamine unit to the diethanolamine unit is 1:157~162.

5. The polyester resin according to claim 1, characterized in that, The triethanolamine unit is derived from one or a mixture of trimethylolpropane, trimethylolethane, and cyproheptad.

6. The polyester resin according to claim 1, characterized in that, The dicarboxylic acid unit is 100% derived from 1,2-cyclohexanedicarboxylic acid or 1,2-cyclohexanedicarboxylic anhydride; the diethanol unit is 100% derived from 1,4-cyclohexanediethanol.

7. A polyester resin composition, characterized in that, It contains the polyester resin as described in any one of claims 1 to 6.

8. The polyester resin composition according to claim 7, characterized in that, The polyester resin composition also contains a curing accelerator.

9. The polyester resin composition according to claim 7, characterized in that, The polyester resin composition also contains an antioxidant.

10. The use of the polyester resin as claimed in any one of claims 1 to 6 or the polyester resin composition as claimed in any one of claims 7 to 9 in powder coatings.

11. A powder coating, characterized in that, Includes the polyester resin composition as described in any one of claims 7 to 9.

12. The powder coating according to claim 11, characterized in that, The composition comprises 60-65% of the total mass of the powder coating raw materials and 2-3% of the total mass of the raw materials, including the polyester resin composition and β-hydroxyalkylamide.

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