High performance multi-component composite bio-based powder coating and method for its preparation

Abstract

The application discloses a kind of high-performance multi-element composite bio-based powder coating and preparation method thereof, it is related to powder coating technical field.The raw materials include carboxyl polyester resin, isocyanuric acid triglycidyl ester, tetrabutylammonium bromide, filler, leveling agent, benzoin, ethylene bis-stearamide, amide wax;The filler includes barium sulfate, air glass bead and mica;Preparation method includes the following steps: using full bio-based raw materials are prepared by step feeding, step temperature control, vacuum polycondensation, low-temperature end-capping, gradient cooling synthesis process carboxyl polyester resin;Using the above carboxyl polyester resin to prepare target powder coating.The carboxyl polyester resin prepared in the application is matched with the ternary filler system, and after curing with TGIC, the impact strength of the coating reaches more than 50 kg·cm, there is no corrosion after neutral salt spray test for more than 1000 hours, the gloss retention is excellent after QUVA artificial accelerated aging for 1000 hours, and the comprehensive performance reaches or even surpasses the petroleum-based similar products.

Description

Technical Field

[0001] This invention relates to the field of powder coating technology, specifically to a high-performance multi-component composite bio-based powder coating and its preparation method. Background Technology

[0002] Powder coatings are solvent-free and environmentally friendly coatings that have been widely used in building materials, home appliances, automobiles, and other fields in recent years. Among them, outdoor weather-resistant powder coatings typically use carboxylated polyester resins with TGIC (triglycidyl isocyanurate) or HAA (β-hydroxyalkylamide) as the curing system.

[0003] The synthesis of traditional carboxylated polyester resins mainly relies on petroleum-based monomers, such as terephthalic acid (PTA), isophthalic acid (IPA), neopentyl glycol (NPG), trimethylolpropane (TMP), and trimellitic anhydride (TMA). These raw materials are derived from non-renewable petroleum resources, resulting in high carbon emissions during the production process, and the products are difficult to degrade at the end of their life cycle.

[0004] With increasing environmental awareness and the advancement of dual-carbon goals, the use of bio-based materials to replace petroleum-based materials has become a research hotspot in the industry. However, the development of bio-based polyester resins in existing technologies still faces many challenges. First, the raw materials exhibit significant differences in activity. Bio-based monomers, such as 2,5-furandicarboxylic acid (FDCA), are highly reactive and easily sublimate, while the secondary hydroxyl group of isosorbide has low reactivity, making it difficult to control the reaction synchronously when the two coexist. Second, process control is challenging. Bio-based monomers are prone to oxidation and discoloration at high temperatures, affecting the coating's appearance; simultaneously, anhydride raw materials are hygroscopic and easily decompose, requiring stringent process conditions. Third, achieving the same performance is difficult. Bio-based monomers are relatively rigid, which can easily lead to increased coating brittleness and decreased impact resistance; furthermore, key properties such as weather resistance and salt spray resistance are difficult to achieve the same level as petroleum-based products.

[0005] Therefore, developing a fully bio-based polyester resin for powder coatings that can completely replace petroleum-based monomers, has controllable processing, and exhibits excellent performance, as well as its preparation method, is of significant practical importance. Summary of the Invention

[0006] The purpose of this invention is to provide a high-performance multi-component bio-based powder coating and its preparation method, which realizes the replacement of powder coating with carboxyl polyester resin as a fully bio-based raw material, while ensuring that the synthesis process is stable and controllable, and the final product performance reaches or even exceeds the level of petroleum-based products.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A high-performance multi-component composite bio-based powder coating, comprising the following raw materials by weight:

[0009] 50-70 parts of carboxylated polyester resin; 3-6 parts of triglycidyl isocyanurate (TGIC); 0.05-0.2 parts of tetrabutylammonium bromide (TBAB); 20-40 parts of filler; 0.5-2 parts of leveling agent; 0.1-0.5 parts of benzoin; 0.3-0.8 parts of ethylene bis-stearamide (EBS); 0.1-0.4 parts of amide wax;

[0010] The filler comprises barium sulfate, air-glass microspheres, and mica, and the mass ratio of barium sulfate, air-glass microspheres, and mica is 1:0.15~0.67:0.1~0.67;

[0011] The carboxylated polyester resin is prepared by melt polycondensation and end-capping reaction of 2,5-furandicarboxylic acid, bio-based isophthalic acid, isosorbide, 1,5-pentanediol, bio-based trimethylolpropane and 2-furan carboxylic anhydride, with a glass transition temperature of 65~72℃ and an acid value of 32~38 mgKOH / g.

[0012] This invention achieves a fully bio-based replacement of carboxylated polyester resins for powder coatings. It utilizes renewable bio-based monomers such as 2,5-furandicarboxylic acid, bio-based isophthalic acid, isosorbide, 1,5-pentanediol, bio-based trimethylolpropane, and 2-furan carboxylic anhydride, completely eliminating petroleum-based raw materials and reducing dependence on fossil fuels at the source. Simultaneously, based on the high rigidity and high glass transition temperature of the fully bio-based carboxylated polyester resin, this invention designs a ternary composite filler system of barium sulfate, air-glass microspheres, and mica, and limits the mass ratio of these three components within a specific range. The fully bio-based resin is then compounded with the above three fillers in a specific ratio and systematically applied to the powder coating system to achieve a comprehensive balance of processing performance, mechanical properties, and weather resistance. Furthermore, the glass transition temperature of the carboxylated polyester resin of the present invention is 65~72℃ and the acid value is 32~38mgKOH / g, which ensures that the resin and the curing agent TGIC have suitable reactivity and form a good process match with the filler compound system. This allows the bio-based resin to maintain its environmental advantages while achieving coating performance that meets or even surpasses that of traditional petroleum-based products.

[0013] The filler system of this invention is composed of barium sulfate, air-glass microspheres, and mica in a mass ratio of 1:0.15~0.67:0.1~0.67. These three components complement and synergize in terms of morphology, particle size, and function. Barium sulfate, in the form of blocky particles with a particle size of 5~10 μm, acts as a skeletal filler, providing basic hardness and volume filling. Air-glass microspheres, in the form of hollow spheres with a particle size of 20~40 μm, exert a lubricating effect during melt extrusion, reducing melt viscosity, improving processing fluidity, and dispersing impact stress in the cured coating. Mica, in the form of sheet-like structures with a particle size of 10~30 μm, forms a labyrinth effect in the coating by arranging its particles in parallel, effectively extending the penetration path of water vapor and corrosive media, and significantly improving shielding performance. The three components form a three-dimensional graded filler network of spherical-sheet-block structures, resulting in synergistic effects in stress dispersion, enhanced barrier properties, and optimized processing fluidity. Meanwhile, the filler compound system forms a good performance match with the high rigidity bio-based polyester resin of the present invention. Because the resin contains high rigidity units such as 2,5-furandicarboxylic acid and isosorbide, the glass transition temperature is relatively high. When used alone, the coating is prone to brittleness. However, through the stress dispersion of spherical microspheres and the interlayer reinforcement of flaky mica, the brittleness defect caused by the rigidity of the resin is effectively compensated, so that the coating can obtain good impact resistance while maintaining high hardness. The rigid resin and tough coating are unified. Experiments show that the impact strength of the coating using this filler compound system reaches more than 50 kg·cm.

[0014] A method for preparing the high-performance multi-component composite bio-based powder coating includes the following steps:

[0015] S100, 2,5-furandicarboxylic acid, bio-based isophthalic acid, isosorbide, 1,5-pentanediol and catalyst are added to the reactor, and the temperature is raised while stirring under a protective atmosphere to melt the materials;

[0016] S200, continue heating and maintain the temperature until the esterification water output reaches more than 90% of the theoretical value;

[0017] S300, add bio-based trimethylolpropane, heat up, and carry out polycondensation reaction under vacuum until the acid value of the reactants drops to 5~15mgKOH / g;

[0018] S400, cool down, add 2-furan carboxylic anhydride, keep the reaction at the temperature until the acid value reaches 32~38mgKOH / g;

[0019] S500, remove free small molecules, cool down, add antioxidant, stir evenly and discharge, cool using gradient cooling method, crush to obtain carboxylated polyester resin;

[0020] S600. The target powder coating is prepared using the above-mentioned carboxylated polyester resin.

[0021] Existing technologies lack a publicly available method for copolymerizing multiple bio-based monomers with varying properties, including 2,5-furandicarboxylic acid (FDCA), bio-based isophthalic acid (bio-based IPA), isosorbide, 1,5-pentanediol, bio-based trimethylolpropane (bio-based TMP), and 2-furan carboxylic anhydride. Furthermore, no systematic process solution has been disclosed to simultaneously address issues such as the easy sublimation of FDCA, incomplete reaction of isosorbide, easy decomposition of acid anhydrides, and easy oxidation and discoloration of the furan ring. This invention addresses the differences in reactivity, thermal stability, and sublimation characteristics of various bio-based monomers by providing a stepwise feeding—stepped temperature control—vacuum polycondensation—low-temperature end-capping—gradient cooling synthesis process.

[0022] This invention successfully copolymerizes six bio-based monomers with significantly different reactivity characteristics—FDCA, bio-based IPA, isosorbide, 1,5-pentanediol, bio-based TMP, and 2-furan carboxylic anhydride—into high-molecular-weight carboxylated polyester resin through a stepwise feeding and stepped temperature control process. This solves technical challenges such as the easy sublimation of FDCA, the low reactivity of isosorbide, and the easy decomposition of acid anhydrides, enabling the synthesis yield and reproducibility of bio-based polyester to meet the requirements of industrial production. Furthermore, this invention achieves synergistic unity between molecular chain growth and end-group modification through staged temperature control and optimized feeding sequence.

[0023] This invention effectively inhibits the oxidation and discoloration of the furan ring structure at high temperatures through the synergistic effects of nitrogen protection throughout the process, mild catalysis of monobutyltin oxide, antioxidant compound (168 / 1010), and gradient cooling process. The resulting resin has a light yellow to transparent appearance and stable color (B value), which meets the strict requirements of powder coating for appearance quality.

[0024] This invention achieves a precise final resin acid value within the range of 32~38 mgKOH / g and a glass transition temperature within the range of 65~72℃ through multi-point synergy of acid value control during the esterification stage, vacuum degree and temperature control during the polycondensation stage, and anhydride dosage and temperature control during the end-capping stage. This results in a good match with the TGIC curing system in terms of reactivity, while also ensuring the storage stability and melt flowability of the powder coating.

[0025] This invention separates the esterification stage from the polycondensation stage, creating conditions for the subsequent end-capping stage. In the end-capping stage, the high reactivity of 2-furan carboxylic anhydride is utilized to achieve precise acid control, while avoiding the risk of gelation caused by its premature participation in the main chain reaction.

[0026] The carboxylated polyester resin prepared by this invention, when combined with a ternary composite filler system (barium sulfate, air glass microspheres, and mica), achieves an impact strength of over 50 kg·cm, exhibits no corrosion after over 1000 hours of neutral salt spray testing, and demonstrates excellent gloss retention after over 1000 hours of QUVA accelerated aging. Its overall performance meets or surpasses that of similar petroleum-based products.

[0027] Compared with conventional petroleum-based polyester synthesis processes, this invention uses fully bio-based monomers and designs a step-by-step feeding and stepped temperature control process to address the differences in the characteristics of each monomer. Compared with existing bio-based polyester synthesis processes, this invention differs in terms of monomer combination, precise control of end-capping temperature, and gradient cooling method, achieving efficient synthesis and performance optimization of bio-based resins.

[0028] Depending on the specific color requirements, 1 to 10 parts of pigment (by weight) may be added to the formula. Pigments may include titanium dioxide (rutile type), pyrrolopyrrole dione red (DPP red), titanium nickel yellow, phthalocyanine blue, phthalocyanine green, etc.

[0029] Further, by weight, 300-500 parts of 2,5-furandicarboxylic acid; 100-200 parts of bio-based isophthalic acid; 100-200 parts of isosorbide; 300-400 parts of 1,5-pentanediol; 400-500 parts of bio-based trimethylolpropane; 50-100 parts of 2-furan carboxylic anhydride; 0.5-1.0 parts of monobutyltin oxide; and 2-5 parts of antioxidant.

[0030] The antioxidant is prepared by compounding antioxidant 168 and antioxidant 1010 in a mass ratio of 0.5 to 2:1.

[0031] The weight percentages of the carboxylated polyester resin raw materials mentioned above are not equal to the weight percentages of the powder coating raw materials.

[0032] Antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is a hindered phenolic primary antioxidant. It captures free radicals (R·, ROO·) through the phenolic hydroxyl group in its molecule, forming stable phenoxy radicals, thereby terminating the oxidation chain reaction. This antioxidant features high thermal stability, low volatility, and good compatibility with polyesters, primarily providing long-term protection against thermo-oxidative aging.

[0033] Antioxidant 168 (tris[2,4-di-tert-butylphenyl]phosphite) is a phosphite-based auxiliary antioxidant that decomposes hydroperoxides (ROOH) into stable alcohols (ROH) through the reducing properties of trivalent phosphorus, preventing hydroperoxides from decomposing into free radicals and thus interrupting the initiation stage of the oxidation chain. This antioxidant primarily provides thermal stability protection during processing.

[0034] The two antioxidants act on different stages of oxidative degradation—antioxidant 1010 captures free radicals during the chain propagation stage, while antioxidant 168 decomposes hydroperoxides during the chain initiation stage. The combined use of these two antioxidants forms a dual protection mechanism of chain termination and peroxide decomposition, exhibiting a superior synergistic effect compared to a single antioxidant. The synergistic effect is most significant when the mass ratio of the two antioxidants is controlled within the range of 0.5 to 2:1, effectively inhibiting thermal oxidative discoloration during processing and ensuring the long-term weather resistance of the coating.

[0035] The bio-based carboxylated polyester resin of this invention contains a large number of 2,5-furandicarboxylic acid (FDCA) units. The furan ring is prone to oxidative ring-opening reactions at high temperatures (>200°C), leading to a darker resin color (increased B value) and even molecular chain degradation. Antioxidant 168, during the melt polycondensation stage (220~240°C), decomposes the hydrogen peroxide generated at high temperatures in the system, inhibiting the initiation of furan ring oxidation. Antioxidant 1010 continuously captures free radicals during subsequent processing and coating applications, protecting the furan ring structure from long-term thermo-oxidative aging damage. The synergistic effect of both allows the resin to maintain a light yellow to transparent appearance even after undergoing multiple thermal processes such as high-temperature synthesis, melt extrusion, and coating curing.

[0036] Further, in step S100, 2,5-furandicarboxylic acid, bio-based isophthalic acid, isosorbide, 1,5-pentanediol and monobutyltin oxide are purged with nitrogen gas and heated to 160~180°C under stirring until the materials melt.

[0037] In S100, FDCA, bio-based IPA, isosorbide, 1,5-pentanediol and catalyst are melted at 160~80℃, so that the reactants are initially mixed evenly at a lower temperature, avoiding the direct sublimation loss of FDCA at high temperature.

[0038] Furthermore, in step S200, the temperature is further increased to 190~210℃, and the reaction is maintained until the amount of water produced by esterification reaches more than 90% of the theoretical value.

[0039] S200 is further heated to 190~210℃ for esterification reaction. At this time, the secondary hydroxyl groups of isosorbide begin to participate in the reaction slowly. By controlling the temperature in a relatively low range, the esterification process is ensured to proceed smoothly, laying the molecular weight basis for subsequent polycondensation.

[0040] Further, in step S300, bio-based trimethylolpropane is added, the temperature is raised to 220~240℃, and a polycondensation reaction is carried out under a vacuum of less than -0.095MPa until the acid value of the reactants drops to 5~15mgKOH / g.

[0041] In S300, the trifunctional structure of TMP introduces branched chains to improve the functionality of the resin. At the same time, the high-temperature vacuum environment forces the secondary hydroxyl groups of isosorbide to react fully, avoiding the impact of incomplete reaction on the performance of subsequent coatings due to low molecular weight or residual hydroxyl groups.

[0042] Further, in step S400, the temperature is lowered to 180~200℃, 2-furan carboxylic anhydride is added, and the reaction is maintained at this temperature for 1~2 hours until the acid value reaches 32~38 mgKOH / g.

[0043] After the S400 polycondensation reaction is completed, the reaction system is cooled to 180-200°C before 2-furan carboxylic anhydride is added for end-capping. Since the polycondensation stage is carried out at a high temperature of 220-240°C, this high temperature is used to force the secondary hydroxyl groups of isosorbide to react fully and increase the molecular weight. However, 2-furan carboxylic anhydride is prone to thermal decomposition above 200°C and has insufficient reactivity below 160°C. This invention precisely controls the end-capping temperature within the range of 180-200°C, allowing the anhydride to complete the end-capping reaction within a suitable temperature window, thus avoiding thermal decomposition losses and ensuring the completeness of end-group modification. Simultaneously, this end-capping temperature is connected to the initial temperature (170-190°C) of the subsequent gradient cooling process, forming a complete thermal history control chain from polycondensation and end-capping to cooling.

[0044] Further, in step S500, free small molecules are removed by vacuuming, the temperature is lowered to 170~190℃, antioxidants are added, the mixture is stirred evenly and then discharged, cooled by gradient cooling, and crushed to obtain carboxylated polyester resin.

[0045] Furthermore, a gradient cooling method is adopted: first, the temperature is rapidly cooled to below 80°C using a cooling medium at 0~5°C, and then slowly cooled to below 40°C using a cooling medium at 15~25°C; wherein, the cooling rate of the rapid cooling stage is ≥10°C / s, and the cooling rate of the slow cooling stage is 1~5°C / min.

[0046] The high molecular weight bio-based polyester obtained through the S300 and S400 reactions contains a large number of rigid FDCA units and isosorbide units, exhibiting a strong tendency to crystallize. If natural cooling or slow cooling alone is used, large spherulites easily form in the resin, leading to a whitening appearance, increased brittleness, and decreased storage stability. If rapid cooling alone is used, although crystallization can be suppressed, excessive internal stress leads to cracking during storage. This invention first rapidly cools the resin through a 0-5°C cooling medium (≥10°C / s), allowing it to quickly pass through the crystallization temperature range, suppressing the formation of large crystals and maintaining high transparency and low brittleness; then it slowly cools it through a 15-25°C cooling medium (1-5°C / min), releasing the internal stress generated by rapid cooling and improving storage stability; finally, it is naturally cooled to room temperature. This gradient cooling method matches the molecular structure characteristics of the resin imparted by S100-S400, achieving a balance between transparency, brittleness, and storage stability.

[0047] Furthermore, step S600 includes the following steps:

[0048] Step 1: Weigh the carboxylated polyester resin, TGIC, tetrabutylammonium bromide, filler, pigment, leveling agent, benzoin, ethylene bis-stearamide, and amide wax according to the specified proportions, and then mix them at 40~60℃ for 5~10 minutes; Step 2: Melt and extrude the mixture, cool and crush it to obtain flakes; Step 3: Grind and sieve the flakes, adding 0.1~0.3% fumed silica during the grinding process to obtain a powder coating with a particle size of 25~35μm.

[0049] In step 2, the extrusion temperature settings are as follows: Zone 1 temperature is 90~100℃, Zone 2 temperature is 100~110℃, and Zone 3 temperature is 110~120℃.

[0050] S600 combines the carboxylated polyester resin prepared by the above method with a specific ternary composite filler system (barium sulfate, air glass microspheres, mica) and additives to prepare powder coatings. This filler system is designed to address the high rigidity and high Tg characteristics of bio-based resins by compensating for the brittleness defects of the resin through the synergistic effect of spherical, sheet-like, and block-shaped fillers.

[0051] Compared with the prior art, the beneficial effects of the present invention are:

[0052] 1. This invention realizes the replacement of carboxylated polyester resin for powder coatings with fully bio-based raw materials. It adopts renewable bio-based monomers such as 2,5-furandicarboxylic acid, bio-based isophthalic acid, isosorbide, 1,5-pentanediol, bio-based trimethylolpropane, and 2-furan carboxylic anhydride, completely eliminating petroleum-based raw materials, reducing dependence on fossil energy from the source, reducing carbon emissions, and meeting the requirements of green environmental protection and sustainable development.

[0053] 2. This invention designs a synthesis process with stepwise feeding, stepped heating, vacuum polycondensation, and low-temperature end-capping, targeting the reaction characteristics of different bio-based monomers. This effectively solves technical problems such as the easy sublimation of FDCA, the low reactivity of isosorbide, and the easy decomposition of acid anhydrides, ensuring the stability and reproducibility of the synthesis process.

[0054] 3. The present invention combines the prepared carboxylated polyester resin with a ternary composite filler system. After curing with TGIC, the coating has an impact strength of over 50 kg·cm, no corrosion after more than 1000 hours of neutral salt spray test, and excellent gloss retention after 1000 hours of QUVA accelerated aging. Its comprehensive performance reaches or even surpasses that of similar petroleum-based products, achieving a unity of environmental protection and high performance.

[0055] 4. The product of this invention can be widely used in outdoor weather-resistant coating fields such as architectural aluminum profiles, automotive parts, and household appliances, and has good market promotion value. Detailed Implementation

[0056] Example 1

[0057] The carboxylated polyester resin comprises the following raw materials: FDCA: 400g; bio-based IPA: 150g; isosorbide 150g; 1,5-pentanediol 350g; bio-based TMP: 450g; 2-furanic anhydride 70g; monobutyltin oxide 0.8g; antioxidant 3.3g;

[0058] The antioxidant is prepared by compounding antioxidant 168 and antioxidant 1010 in a mass ratio of 1.2:1.

[0059] The preparation method of the carboxylated polyester resin includes the following steps:

[0060] S100, FDCA, bio-based IPA, isosorbide, 1,5-pentanediol and monobutyltin oxide are added to the reactor, nitrogen is introduced to purge three times, and the temperature is raised to 170°C under stirring until the materials melt.

[0061] S200, continue heating to 200℃, and maintain the temperature until the esterification water output reaches 92% of the theoretical value.

[0062] Add S300 and bio-based TMP, heat to 230℃, and carry out polycondensation reaction under a vacuum of less than -0.098MPa until the acid value of the reactants drops to 10mgKOH / g.

[0063] S400, cool to 190℃, add 2-furan carboxylic anhydride, keep the reaction at this temperature for 1.5 hours until the acid value reaches 35mgKOH / g.

[0064] S500, vacuum removal of free small molecules, cooling to 180℃, addition of antioxidant, stirring evenly, discharge, cooling, and crushing to obtain carboxylated polyester resin.

[0065] The gradient cooling process includes: first, rapid cooling to 78°C with 3°C cooling water, and then slow cooling to 38°C with 20°C cooling water; wherein, the cooling rate of the rapid cooling stage is 12°C / s, and the cooling rate of the slow cooling stage is 3°C / min.

[0066] Example 2

[0067] The carboxylated polyester resin comprises the following raw materials: FDCA: 300g; bio-based IPA: 100g; isosorbide 100g; 1,5-pentanediol 300g; bio-based TMP: 400g; 2-furan carboxylic anhydride 50g; monobutyltin oxide 0.5g; antioxidant 2g;

[0068] The antioxidant is prepared by compounding antioxidant 168 and antioxidant 1010 in a mass ratio of 0.5:1.

[0069] The preparation method of the carboxylated polyester resin includes the following steps:

[0070] S100, FDCA, bio-based IPA, isosorbide, 1,5-pentanediol and monobutyltin oxide are added to the reactor, nitrogen is introduced to purge three times, and the temperature is raised to 160°C under stirring until the materials melt.

[0071] S200, continue heating to 190℃, and maintain the temperature until the esterification water output reaches 91% of the theoretical value.

[0072] Add S300 and bio-based TMP, heat to 220℃, and carry out polycondensation reaction under vacuum of -0.096MPa until the acid value of the reactants drops to 5mgKOH / g.

[0073] S400, cool to 180℃, add 2-furan carboxylic anhydride, keep the reaction at this temperature for 1 hour until the acid value reaches 32mgKOH / g.

[0074] S500, vacuum removal of free small molecules, cooling to 170℃, addition of antioxidant, stirring evenly, discharge, cooling, and crushing to obtain carboxylated polyester resin.

[0075] Gradient cooling includes: first, rapid cooling to 79°C using a 5°C cooling medium, and then slow cooling to below 39°C using a 25°C cooling medium; wherein, the cooling rate of the rapid cooling stage is 10°C / s, and the cooling rate of the slow cooling stage is 5°C / min.

[0076] Example 3

[0077] The carboxylated polyester resin comprises the following raw materials: FDCA: 500g; bio-based IPA: 200g; isosorbide 200g; 1,5-pentanediol 400g; bio-based TMP: 500g; 2-furanic anhydride 100g; monobutyltin oxide 1.0g; antioxidant 5g;

[0078] The antioxidant is prepared by compounding antioxidant 168 and antioxidant 1010 in a mass ratio of 2:1.

[0079] The preparation method of the carboxylated polyester resin includes the following steps:

[0080] S100, FDCA, bio-based IPA, isosorbide, 1,5-pentanediol and monobutyltin oxide are added to the reactor, nitrogen is introduced to purge three times, and the temperature is raised to 180°C under stirring until the materials melt.

[0081] S200, continue heating to 210℃, and maintain the temperature until the esterification water output reaches 93% of the theoretical value.

[0082] Add S300 and bio-based TMP, heat to 240℃, and carry out polycondensation reaction under vacuum of -0.099MPa until the acid value of the reactants drops to 15mgKOH / g.

[0083] S400, cool to 200℃, add 2-furan carboxylic anhydride, keep the reaction at this temperature for 2 hours until the acid value reaches 38mgKOH / g.

[0084] S500, vacuum removal of free small molecules, cooling to 190℃, addition of antioxidant, stirring evenly, discharge, cooling, and crushing to obtain carboxylated polyester resin.

[0085] Gradient cooling includes: first, rapid cooling to 75°C using a 0°C cooling medium, and then slow cooling to below 35°C using a 15°C cooling medium; wherein, the cooling rate of the rapid cooling stage is 15°C / s, and the cooling rate of the slow cooling stage is 1°C / min.

[0086] Comparative Example 1

[0087] Add TMP in step S100;

[0088] Steps S100 and S300 are replaced with: Continue heating to 200℃ and hold for 2 hours, during which esterification occurs, and TMP participates in the reaction simultaneously. Continue heating to 230℃ and carry out polycondensation under a vacuum below -0.098MPa, holding the reaction until the acid value of the reactants drops to 10mgKOH / g.

[0089] Comparative Example 2

[0090] After cooling the S400 to 220°C, 2-furan carboxylic anhydride was added for end-capping, and the rest was the same as in Example 1.

[0091] Comparative Example 3

[0092] In S500, only 3°C cooling water is used to rapidly cool to 38°C without a slow cooling stage; otherwise, it is the same as in Example 1.

[0093] Comparative Example 4

[0094] In S500, only 20°C cooling water is used to slowly cool to 38°C at a cooling rate of 3°C / min, without a rapid cooling stage. The rest is the same as in Example 1.

[0095] Comparative Example 5

[0096] No antioxidants are added to S500, and everything else is the same as in Example 1.

[0097] Comparative Example 6

[0098] S500 is made with a single antioxidant 1010 at a dosage of 3.3g, without antioxidant 168, and otherwise the same as in Example 1.

[0099] Comparative Example 7

[0100] S500 is made with a single antioxidant 168 at a dosage of 3.3g, without antioxidant 1010, and otherwise the same as in Example 1.

[0101] Comparative Example 8

[0102] The dosage of antioxidant 168 is 0.55g, the dosage of antioxidant 1010 is 2.75g, the mass ratio is 0.2:1, the total dosage is 3.3g, and the rest is the same as in Example 1.

[0103] Comparative Example 9

[0104] The dosage of antioxidant 168 was 2.48g, the dosage of antioxidant 1010 was 0.82g, the mass ratio was 3:1, and the total dosage was 3.3g. The rest was the same as in Example 1.

[0105] Comparative Example 10

[0106] In S100, monobutyltin oxide is replaced with p-toluenesulfonic acid at a dosage of 0.8g, and the rest is the same as in Example 1.

[0107] Comparative Example 11

[0108] S100-S500 are carried out without nitrogen protection and in an air atmosphere, with the rest being the same as in Example 1.

[0109] Comparative Example 12

[0110] All processes from S100 to S400 were carried out at 230°C, without the 170°C melting stage of S100 and the 200°C esterification stage of S200. All raw materials (FDCA, bio-based IPA, isosorbide, 1,5-pentanediol, bio-based TMP, and catalyst) were added at once. The temperature was raised to 230°C and the reaction was carried out until the acid value dropped to 10 mg KOH / g. Then the temperature was lowered to 190°C and the acid anhydride was added for end capping. The rest was the same as in Example 1.

[0111] The performance parameters of the carboxylated polyester resins prepared by the methods in Examples 1-3 and Comparative Examples 1-12 are shown in Table 1.

[0112] Color (B value) was determined using a spectrophotometer in the CIELAB color space according to the method specified in GB / T 39822-2021 "Determination of Yellow Index and Variation Value of Plastics".

[0113] Table 1. Performance parameters of carboxylated polyester resins prepared by the methods in Examples 1-3 and Comparative Examples 1-12.

[0114]

[0115] As shown in Table 1, the carboxylated polyester resins prepared by the methods in Examples 1-3 were all light yellow and transparent, with B values ​​between 7.8 and 8.5; acid values ​​of 32-38 mgKOH / g; Tg of 65-72℃; yields of 95.8-97.2%; and gel times of 175-185 seconds. The agglomeration temperature of all three examples was ≥44℃, and no agglomeration occurred after 30 days of storage at 40℃, indicating that the gradient cooling process effectively released the internal stress of the resin and imparted excellent storage stability.

[0116] In Comparative Example 1, the simultaneous addition of FDCA and TMP resulted in significant sublimation loss of FDCA during the prolonged high-temperature (230℃) reaction, leading to a reduction in the total carboxyl groups and an imbalance in the alcohol-acid molar ratio. Simultaneously, the trifunctional structure of TMP prematurely participated in the reaction, resulting in uncontrollable branching and difficulty in reducing the acid value to the target range of 5-15 mgKOH / g after polycondensation. Ultimately, the acid value after end-capping was only 28 mgKOH / g, far below the required 32-38 mgKOH / g. The resin yield was only 82.3%, and the resin was yellow and opaque with a high B value of 15.6; it also exhibited low storage stability, with a clumping temperature of only 38℃.

[0117] In Comparative Example 2, at 220℃, some of the acid anhydride decomposed and became ineffective, reducing the amount of acid anhydride actually participating in the end-capping reaction. This resulted in incomplete end-capping, with the final acid value reaching as high as 45 mg KOH / g, far exceeding the upper limit of the target range. The resin appeared as a deep yellow, semi-transparent resin with a B value of 18.3.

[0118] Comparative Example 3 involved rapid cooling of the resin to 38°C using only 3°C cooling water after discharge, without a slow cooling stage. Although this process could quickly pass through the crystallization temperature range and suppress the formation of large crystals, maintaining the resin's appearance as a light yellow and translucent (B value 9.8), the internal stress generated by the rapid cooling was not released, resulting in decreased resin storage stability and an agglomeration temperature of only 42°C.

[0119] Comparative Example 4 involved slow cooling of the resin to 38°C with 20°C cooling water after discharge, at a cooling rate of 3°C / min, without a rapid cooling stage. This process caused the resin to remain in the crystallization temperature range (approximately 120~150°C) for too long, resulting in the formation of large spherulites. The resin appeared milky white and opaque (B value 12.4), and the excessive crystallinity led to increased resin brittleness.

[0120] Comparative Example 5 did not add any antioxidants to S500. The furan ring structure is extremely prone to oxidative ring-opening reaction during high-temperature (220~240℃) synthesis, which leads to a sharp deterioration in resin color, resulting in a dark brown and opaque appearance with a B value as high as 28.5.

[0121] Although the single antioxidant 1010 in Comparative Example 6 can capture free radicals and provide long-term protection against thermal and oxidative aging, it is not capable of decomposing hydrogen peroxide during processing. The resin has a B value of 15.6 and a yellow and semi-transparent appearance.

[0122] In Comparative Example 7, although the single antioxidant 168 could decompose hydroperoxides and provide thermal stability during processing, its ability to capture free radicals from long-term thermo-oxidative aging was insufficient. The resin had a B value of 14.8 and a yellow, semi-transparent appearance. This comparative example, together with Comparative Example 6, demonstrates that a single antioxidant cannot achieve the synergistic effect of a compound system.

[0123] Comparative Example 8 adjusted the mass ratio of antioxidant 168 to 1010 to 0.2:1. At this ratio, the proportion of primary antioxidant 1010 was too high, while the proportion of secondary antioxidant 168 was insufficient. This resulted in incomplete decomposition of hydroperoxides during processing, with some oxidative degradation occurring during the processing stage. The resin had a B value of 12.3 and a light yellow, semi-transparent appearance. While superior to a single antioxidant, this was still significantly higher than the 8.2 of Example 1.

[0124] Comparative Example 9 adjusted the mass ratio of antioxidant 168 to 1010 to 3:1. At this ratio, the proportion of auxiliary antioxidant 168 was too high, and the proportion of primary antioxidant 1010 was insufficient, resulting in a decrease in long-term thermo-oxidative aging protection. The resin's B value was 11.8, and its appearance was light yellow and semi-transparent, higher than the 8.2 of Example 1.

[0125] Comparative Example 10 replaced monobutyltin oxide with p-toluenesulfonic acid (a strong acid catalyst). While p-toluenesulfonic acid accelerated esterification and transesterification reactions, it also triggered side reactions such as etherification and thermal degradation. During the polycondensation stage, the molecular chains degraded, resulting in an abnormally high acid value that was difficult to stabilize at 5-15 mg KOH / g. The reaction system exhibited abnormal viscosity, extremely poor flowability, a resin yield of only 85.3%, a B value of 22.4, and an acid value of 29 mg KOH / g.

[0126] Comparative Example 11 was synthesized entirely under air without nitrogen protection. Oxygen at high temperatures accelerates the oxidation and ring-opening of the furan ring. Although the antioxidant complex system partially inhibits oxidation, the continuous supply of oxygen places an excessive burden on the antioxidant protection. The resin had a B value of 18.6 and a yellowish-brown, semi-transparent appearance. This comparative example demonstrates that the antioxidant complex system and nitrogen protection create a synergistic effect, operating both internally and externally.

[0127] Comparative Example 12 involved adding all raw materials at once and completing esterification and polycondensation at a single temperature of 230°C. FDCA suffered significant sublimation loss at high temperatures, resulting in a yield of only 88.6%. Esterification and polycondensation were not separated, and the generation and removal of small water molecules were asynchronous, leading to incomplete reactions. Increased side reactions at high temperatures resulted in a resin B value of 19.2, a dark yellow and opaque appearance, and an acid value of 31 mgKOH / g, slightly below the lower limit of the target range. This comparative example demonstrates that a stepped temperature control process is crucial for avoiding FDCA sublimation, ensuring complete reaction, and controlling resin color. The simplified process of a single-temperature reaction cannot achieve the target performance in the system of this invention.

[0128] Example 4

[0129] A high-performance multi-component composite bio-based powder coating, comprising the following raw materials:

[0130] Carboxylated polyester resin (prepared by the method in Example 1) 600g; TGIC: 45g; TBAB: 1.2g; filler 300g; titanium nickel yellow 60g; leveling agent (Efka® FL 3740, BASF) 13g; benzoin 3g; EBS: 6g; amide wax 2g;

[0131] The filler comprises barium sulfate, air glass microspheres and mica, and the mass ratio of barium sulfate, air glass microspheres and mica is 1:0.4:0.38;

[0132] A method for preparing the high-performance multi-component composite bio-based powder coating includes the following steps:

[0133] Step 1: Weigh the carboxylated polyester resin, TGIC, TBAB, filler, pigment, leveling agent, benzoin, EBS, and amide wax according to the specified proportions and add them to a high-speed mixer. Mix at 50°C for 8 minutes until homogeneous, ensuring the additives are evenly adsorbed onto the resin surface. Step 2: Feed the above mixture into a twin-screw extruder. Set the extruder zone 1 temperature to 95°C, zone 2 temperature to 105°C, and zone 3 temperature to 115°C, with a screw speed of 400 rpm. After the material is fully mixed and dispersed in a molten state, extrude it, cool it to 26°C using pressure rollers, and crush it to obtain flakes with a particle size of 2-5 mm. Step 3: Feed the flakes into an ACM grinding mill for grinding, using process parameters of a classifying wheel speed of 5000 rpm and an induced draft fan airflow of 2000 m³ / h to control the particle size distribution. During the grinding process, 0.2% of fumed silica by weight of the powder coating is added to the grinding mill as a flow aid to obtain a powder coating with a particle size D50 of 25~35μm.

[0134] Example 5

[0135] A high-performance multi-component composite bio-based powder coating, comprising the following raw materials:

[0136] 500g of carboxylated polyester resin (prepared by the method in Example 1); 30g of TGIC; 0.5g of TBAB; 200g of filler; 10g of titanium dioxide; 5g of leveling agent (Efka® FL 3740, BASF); 1g of benzoin; 3g of EBS; 1g of amide wax;

[0137] The filler comprises barium sulfate, air-glass microspheres, and mica, and the mass ratio of barium sulfate, air-glass microspheres, and mica is 1:0.15:0.1.

[0138] A method for preparing the high-performance multi-component composite bio-based powder coating includes the following steps:

[0139] Step 1: Weigh the carboxylated polyester resin, TGIC, TBAB, filler, pigment, leveling agent, benzoin, EBS, and amide wax according to the specified proportions and add them to a high-speed mixer. Mix at 40°C for 5 minutes until homogeneous, ensuring the additives are evenly adsorbed onto the resin surface. Step 2: Feed the above mixture into a twin-screw extruder. Set the extruder zone 1 temperature to 90°C, zone 2 temperature to 100°C, and zone 3 temperature to 110°C, with a screw speed of 300 rpm. After the material is fully mixed and dispersed in a molten state, extrude it, cool it to 29°C using pressure rollers, and crush it to obtain flakes with a particle size of 2-5 mm. Step 3: Feed the flakes into an ACM grinding mill for grinding, using process parameters of a classifying wheel speed of 4000 rpm and an induced draft fan airflow of 1500 m³ / h to control the particle size distribution. During the grinding process, 0.1% of fumed silica by weight of the powder coating is added to the grinding mill as a flow aid to obtain a powder coating with a particle size D50 of 25~35μm.

[0140] Example 6

[0141] A high-performance multi-component composite bio-based powder coating, comprising the following raw materials:

[0142] 700g of carboxylated polyester resin (prepared by the method in Example 1); 60g of TGIC; 2g of TBAB; 400g of filler; 100g of phthalocyanine blue; 20g of leveling agent (Efka® FL 3740, BASF); 5g of benzoin; 8g of EBS; 4g of amide wax;

[0143] The filler comprises barium sulfate, air-glass microspheres, and mica, and the mass ratio of barium sulfate, air-glass microspheres, and mica is 1:0.67:0.67.

[0144] A method for preparing the high-performance multi-component composite bio-based powder coating includes the following steps:

[0145] Step 1: Weigh the carboxylated polyester resin, TGIC, TBAB, filler, pigment, leveling agent, benzoin, EBS, and amide wax according to the specified proportions and add them to a high-speed mixer. Mix at 60°C for 10 minutes until homogeneous, ensuring the additives are evenly adsorbed onto the resin surface. Step 2: Feed the mixture into a twin-screw extruder. Set the extruder zone 1 temperature to 100°C, zone 2 to 110°C, and zone 3 to 120°C, with a screw speed of 500 rpm. After the material is fully mixed and dispersed in a molten state, extrude it, cool it to 25°C using pressure rollers, and crush it to obtain flakes with a particle size of 2-5 mm. Step 3: Feed the flakes into an ACM mill for grinding, using process parameters of a classifying wheel speed of 6000 rpm and an induced draft fan airflow of 2500 m³ / h to control the particle size distribution. During the grinding process, 0.3% of fumed silica by weight of the powder coating is added to the grinding mill as a flow aid to obtain a powder coating with a particle size D50 of 25~35μm.

[0146] Comparative Example 13

[0147] The mass ratio of barium sulfate, air glass microspheres, and mica in the filler was adjusted to 1:1:1, while the total amount of filler remained unchanged. The rest was the same as in Example 4.

[0148] Comparative Example 14

[0149] The filler used was barium sulfate, with the total amount remaining the same, and the rest was the same as in Example 4.

[0150] Comparative Example 15

[0151] The filler used is only mica, the total amount remains the same, and the rest is the same as in Example 4.

[0152] Comparative Example 16

[0153] The filler material uses only air glass microspheres, with the total amount remaining the same, and the rest is the same as in Example 4.

[0154] Comparative Example 17

[0155] In step 1, no premixing is performed. All raw materials are directly put into a high-speed mixer and mixed at room temperature for 8 minutes. The rest is the same as in Example 4.

[0156] Comparative Example 18

[0157] In step 2, the temperature of each section of the extruder is uniformly set to 115℃ (without stepped temperature control), and the rest is the same as in Example 4.

[0158] Comparative Example 19

[0159] In step 3, no fumed silica is added during the grinding process; otherwise, it is the same as in Example 4.

[0160] Comparative Example 20

[0161] The filler is composed only of barium sulfate and air glass microspheres in a mass ratio of 1:0.4, without adding mica, and the total amount of filler remains unchanged. The rest is the same as in Example 4.

[0162] Comparative Example 21

[0163] The filler is composed only of barium sulfate and mica in a mass ratio of 1:0.38, without the addition of air glass microspheres. The total amount of filler remains unchanged, and the rest is the same as in Example 4.

[0164] Comparative Example 22

[0165] The filler is composed only of air glass microspheres and mica in a mass ratio of 0.4:0.38, without the addition of barium sulfate, and the total amount of filler remains unchanged. The rest is the same as in Example 4.

[0166] Comparative Example 23

[0167] The carboxylated polyester resin was replaced with commercially available petroleum-based carboxylated polyester resin (model: LT-4ET) (acid value 30~36mgKOH / g, Tg≥65℃), and the rest was the same as in Example 4.

[0168] Comparative Example 24

[0169] The carboxylated polyester resin was replaced with commercially available petroleum-based carboxylated polyester resin (model: LT-4ET), and the powder coating preparation method was changed to mixing the raw materials evenly; melt dispersing and extruding at an extrusion temperature of 115℃ and a screw speed of 400rpm; cooling and crushing into 2~5mm flakes; grinding into a product with a particle size of 30±5μm, and the rest is the same as in Example 4.

[0170] The powder coatings prepared by the methods in Examples 4-6 and Comparative Examples 13-24 were electrostatically sprayed and cured at 200°C for 10 minutes to create samples. The coating thickness of the cured samples was 50-70 micrometers.

[0171] The performance of the powder coatings prepared by the methods in Examples 4-6 and Comparative Examples 13-24 after electrostatic spraying and curing is shown in Table 2.

[0172] Table 2. Performance of powder coatings prepared by the methods of Examples 4-6 and Comparative Examples 13-24 after electrostatic spraying and curing.

[0173]

[0174] As shown in Table 2, Examples 4-6 all performed excellently in the 1000-hour salt spray test, confirming the significant synergistic effect of the ternary filler compound system designed for the high rigidity and high Tg characteristics of bio-based resins in this invention. Specifically, the sheet-like structure of mica creates a labyrinth effect in the coating, effectively extending the penetration paths of chloride ions and water vapor; the cavity structure of air-glass microspheres disrupts the continuous penetration channels of corrosive media; and the chemical inertness of barium sulfate maintains the stability of the coating-filler interface. The three components, compounded in a specific ratio, form a three-dimensional graded filling network of spherical-sheet-block structures, enabling the corrosion resistance of the fully bio-based coating to reach the level of petroleum-based products. Furthermore, Examples 4-6 exhibited an impact strength of 48-52 kg·cm, a gloss retention rate of 83-86% after 1000 hours of QUVA aging, and a gloss level of 88-92%, demonstrating excellent overall performance.

[0175] Comparative Examples 14-16 demonstrate that no single filler can simultaneously meet the comprehensive requirements of impact, hardness, and salt spray resistance. Comparative Examples 20-22 demonstrate that the absence of any type of filler leads to a significant decrease in impact or salt spray resistance performance. Comparative Example 13 demonstrates that even with all three fillers present, deviations from the scope of this invention in their proportions weaken the synergistic effect. Example 4 demonstrates that only when the three fillers are compounded in a specific proportion can a complete spherical-plate-block three-dimensional graded filling network be formed, achieving comprehensive synergy in stress dispersion, shielding enhancement, and skeletal support.

[0176] Comparative Examples 17-19 demonstrate the necessity of the preparation process of this invention tailored to the characteristics of bio-based resins. The absence of process features such as premixing, stepped melt extrusion, and fumed silica surface modification leads to a 4-13% decrease in impact strength and a 5-9% decrease in gloss retention after aging. These process features are matched with the thermal stability and surface polarity of bio-based resins and are key to ensuring resin processing stability and coating quality.

[0177] Comparative Example 23 shows that even using the same filler system and preparation process, the impact strength and aging resistance of the petroleum-based resin are slightly inferior to those of the bio-based resin of this invention, proving that there is a specific synergistic effect between the bio-based resin and the ternary filler compound system, overcoming the technical prejudice that bio-based performance is inferior to that of petroleum-based resin. Comparative Example 24 shows that this invention achieves full bio-based substitution while reaching or even surpassing the overall performance level of conventional petroleum-based products.

[0178] This invention achieves a comprehensive balance in corrosion resistance, aging resistance, mechanical properties, and processing performance of fully bio-based powder coatings.

Claims

1. A high-performance multi-component composite bio-based powder coating, characterized in that, By weight, it includes the following ingredients: 50-70 parts of carboxylated polyester resin; 3-6 parts of triglycidyl isocyanurate; 0.05-0.2 parts of tetrabutylammonium bromide; 20-40 parts filler; 0.5-2 parts leveling agent; 0.1-0.5 parts benzoin; 0.3-0.8 parts ethylene bis-stearamide; 0.1-0.4 parts amide wax; The filler comprises barium sulfate, air-glass microspheres, and mica, and the mass ratio of barium sulfate, air-glass microspheres, and mica is 1:0.15~0.67:0.1~0.67; The carboxylated polyester resin is prepared by melt polycondensation and end-capping reaction of 2,5-furandicarboxylic acid, bio-based isophthalic acid, isosorbide, 1,5-pentanediol, bio-based trimethylolpropane and 2-furan carboxylic anhydride, with a glass transition temperature of 65~72℃ and an acid value of 32~38mgKOH / g. A method for preparing carboxylated polyester resin includes the following steps: S100, 2,5-furandicarboxylic acid, bio-based isophthalic acid, isosorbide, 1,5-pentanediol and monobutyltin oxide are purged with nitrogen gas and heated to 160~180℃ while stirring to melt the materials; S200, continue heating to 190~210℃, and maintain the temperature until the esterification water output reaches more than 90% of the theoretical value; S300, add bio-based trimethylolpropane, heat to 220~240℃, carry out polycondensation reaction under vacuum until the acid value of the reactants drops to 5~15mgKOH / g; S400, cool to 180~200℃, add 2-furan carboxylic anhydride, keep the reaction at the temperature until the acid value reaches 32~38mgKOH / g; S500, remove free small molecules, cool down, add antioxidant, stir evenly and discharge, cool using gradient cooling method, crush to obtain carboxylated polyester resin; The antioxidant is prepared by compounding antioxidant 168 and antioxidant 1010 in a mass ratio of 0.5 to 2:

1. Gradient cooling method: First, the temperature is rapidly cooled to below 80°C by a cooling medium at 0~5°C, and then slowly cooled to below 40°C by a cooling medium at 15~25°C.

2. A method for preparing a high-performance multi-component composite bio-based powder coating as described in claim 1, characterized in that, The preparation of the target powder coating using the above-mentioned carboxylated polyester resin includes the following steps: Step 1: Weigh the carboxylated polyester resin, triglycidyl isocyanurate, tetrabutylammonium bromide, filler, leveling agent, benzoin, ethylene bis-stearamide, and amide wax according to the specified proportions, and mix them at 40-60℃ for 5-10 minutes. Step 2: Melt and extrude the mixture, then cool and crush it to obtain flakes; Step 3: Grind and sieve the sheet material, adding 0.1~0.3% fumed silica during the grinding process to obtain a powder coating with a particle size of 25~35μm.

3. The preparation method according to claim 2, characterized in that, By weight, 300-500 parts of 2,5-furandicarboxylic acid; 100-200 parts of bio-based isophthalic acid; 100-200 parts of isosorbide; 1,5-Pentanediol 300-400 parts; bio-based trimethylolpropane 400-500 parts; 2-furanic anhydride 50-100 parts; Monobutyltin oxide 0.5~1.0 parts; antioxidant 2~5 parts.

4. The preparation method according to claim 2, characterized in that, In step S300, a polycondensation reaction is carried out under a vacuum of less than -0.095 MPa until the acid value of the reactants drops to 5~15 mg KOH / g.

5. The preparation method according to claim 2, characterized in that, In step S400, 2-furan carboxylic anhydride is added, and the reaction is maintained at a certain temperature for 1 to 2 hours until the acid value reaches 32 to 38 mg KOH / g.

6. The preparation method according to claim 2, characterized in that, In step S500, free small molecules are removed by vacuuming, the temperature is lowered to 170~190℃, antioxidants are added, the mixture is stirred evenly, discharged, cooled, and crushed to obtain carboxylated polyester resin.

7. The preparation method according to claim 2, characterized in that, The cooling rate during the rapid cooling stage is ≥10℃ / s, and the cooling rate during the slow cooling stage is 1~5℃ / min.

8. The preparation method according to claim 2, characterized in that, In step 2, the extrusion temperature is set to 90~100℃ for zone 1, 100~110℃ for zone 2, and 110~120℃ for zone 3.

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