A high-bio-based-content weatherable polyester resin, and a preparation method and application thereof

Abstract

The application discloses a high-bio-based-content weather-resistant polyester resin and a preparation method and application thereof, and the polyester resin comprises the following raw materials in mass fractions: 100-200 parts of bio-based polyols, 150-300 parts of petroleum-based polyols, 400-600 parts of dibasic acids, 40-80 parts of acidolysis agents, and 0.5-2 parts of esterification catalysts; the bio-based polyols comprise bio-based 1,4-butanediol and bio-based vanillyl alcohol derivative diols; the dibasic acids comprise petroleum-based isophthalic acid and bio-based 2,5-furan dicarboxylic acid; and the acidolysis agents comprise bio-based 1,4-succinic acid. The present application adopts random copolymerization of multiple monomers, and the obtained amorphous resin has better transparency and more uniform stress distribution, reduces the concentrated occurrence of photooxidation caused by the interface defects between the crystalline region and the amorphous region, fundamentally solves the problem of poor weather resistance of bio-based polyesters from the molecular design level, and reduces the cost and process complexity.

Description

Technical Field

[0001] This invention belongs to the field of polymer technology, and particularly relates to a weather-resistant polyester resin with high bio-based content, its preparation method, and its application. Background Technology

[0002] Powder coatings, due to their "zero VOC" emissions, high utilization rate, and excellent overall performance, are widely used in building materials, automobiles, home appliances, and other outdoor facilities. Using renewable biomass raw materials to replace traditional petrochemical raw materials in the synthesis of polyester resins has become an important development trend in the powder coating industry. 2,5-furandicarboxylic acid, as an ideal bio-based substitute for terephthalic acid, has been extensively studied. However, in practical applications, polyester resins with high bio-based content often face performance defects, especially in terms of weather resistance, which struggles to meet the requirements for long-term outdoor use.

[0003] Existing technologies for improving the weather resistance of polyester powder coatings mainly include: (1) adding ultraviolet absorbers (UVA) and hindered amine light stabilizers (HALS), such as benzophenones, benzotriazoles, triazine compounds and their complexes with nanoparticles; (2) adding nano-inorganic light shielding agents, such as titanium dioxide, zinc oxide, cerium dioxide, etc.; (3) introducing weather-resistant structures through physical / chemical modification methods such as organosilicon modification, fluorine modification or acrylic resin blending. However, these technical solutions have obvious defects, such as: external additives have problems of migration and precipitation, volatilization loss and insufficient durability, and cannot completely compensate for the decline in resin weather resistance caused by conventional bio-based monomers; nanofillers have poor compatibility with resin matrix and are prone to agglomeration leading to coating defects; physical blending modification has weak interfacial bonding force and is prone to failure after long-term outdoor use; chemical modification process is complex, costly and may introduce side reactions. Summary of the Invention

[0004] In order to overcome at least one of the problems existing in the prior art, one of the objectives of the present invention is to provide a polyester resin that achieves intrinsic weather resistance without adding ultraviolet absorbers or undergoing physical or chemical modification through novel bio-based polyols and specific molecular structure design, while taking into account high biocarbon content and excellent mechanical properties.

[0005] A second objective of this invention is to provide a method for preparing the aforementioned polyester resin.

[0006] The third objective of this invention is to provide a powder coating.

[0007] The fourth objective of this invention is to provide a powder coating.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a polyester resin comprising the following raw materials in parts by weight: 100-200 parts of bio-based polyol, 150-300 parts of petroleum-based polyol, 400-600 parts of diacid, 40-80 parts of acid hydrolysate, and 0.5-2 parts of esterification catalyst; wherein the bio-based polyol comprises bio-based 1,4-butanediol and bio-based vanillyl alcohol derivative diol; wherein the diacid comprises petroleum-based isophthalic acid and bio-based 2,5-furandicarboxylic acid; and wherein the acid hydrolysate comprises bio-based 1,4-succinic acid.

[0009] The core mechanism and monomer function of this invention are as follows: (1) The dicarboxylic acid of the present invention is constructed by synergistic construction of isophthalic acid and 2,5-furandicarboxylic acid. The present invention abandons terephthalic acid, which has poor weather resistance in conventional polyesters, and uses isophthalic acid (IPA) as a weather-resistant monomer. Its meta-structure endows the main chain with extremely strong resistance to ultraviolet degradation. At the same time, 2,5-furandicarboxylic acid is used as a bio-based monomer. Its furan ring not only provides rigid support to replace the aromatic ring, but also greatly increases the bio-carbon content of the resin.

[0010] (2) Introducing bio-based vanillin derivative diol, whose aromatic ring structure can increase the glass transition temperature (Tg) of the resin, while its steric hindrance effect and methoxy group have a shielding effect on the ester group, which provides the coating with core rigidity and significant weather resistance support.

[0011] (3) Achieving a balance between rigidity and flexibility by utilizing bio-based 1,4-butanediol and bio-based 1,4-succinic acid: To overcome the excessive rigidity of isophthalic acid (IPA) and the brittleness of the coating, this invention cleverly introduces bio-based 1,4-butanediol and bio-based 1,4-succinic acid as flexible segments, with bio-based 1,4-succinic acid serving as an acid hydrolysant. These two bio-based aliphatic monomers not only significantly improve the flexibility of the macromolecular chain and endow the coating with excellent impact toughness (e.g., allowing both positive and negative impacts to pass through 50cm), but also serve as a high-purity biomass source. In synergy with 2,5-furandicarboxylic acid, they enable the final polyester resin to have a stable biocarbon content, for example, which can be stably controlled between 20% and 55%, significantly reducing dependence on petroleum-based resources and achieving a green and low-carbon profile.

[0012] In this invention, "bio-based" raw materials refer to raw materials whose carbon elements originate from modern biomass (containing carbon-14 isotopes) participating in the current carbon cycle, such as renewable resources like corn, sugarcane, straw, lignocellulose, and agricultural and forestry waste, obtained through fermentation, biocatalysis, physical extraction, or chemical conversion. "Petroleum-based" raw materials refer to raw materials whose carbon elements originate from traditional fossil resources buried deep underground (where carbon-14 isotopes have decayed significantly), such as those processed from petroleum, natural gas, and coal. Using bio-based raw materials can significantly reduce dependence on petroleum-based resources, resulting in a green and low-carbon approach.

[0013] In this invention, bio-based vanillin derivative diol refers to a diol synthesized using bio-based vanillin.

[0014] In some embodiments of the present invention, the bio-based vanillin derivative diol is formed by reacting bio-based vanillin, C2-C4 haloallohydrin and a basic compound; further, the reaction temperature is 85-90°C, the reaction time is 4-5 h, and the reaction is carried out in N,N-dimethylformamide solvent.

[0015] Bio-based vanillin is a monohydric alcohol. Since the phenolic hydroxyl group on bio-based vanillin is difficult to react with carboxylic acids, the acidity difference between the phenolic hydroxyl group and the alcoholic hydroxyl group is utilized to achieve selective etherification of the phenolic hydroxyl group through a weak base. Then, it can be reacted with a haloalcohol to produce a bio-based vanillin derivative diol.

[0016] In some embodiments of the present invention, the alkaline compound includes potassium carbonate, sodium carbonate, or a combination thereof; in some specific embodiments of the present invention, the alkaline compound is selected from potassium carbonate.

[0017] In some embodiments of the present invention, the C2-C4 haloalcohol includes at least one of 2-chloroethanol, 2-bromoethanol, 3-chloro-1-propanol or 4-chloro-1-butanol; in some specific embodiments of the present invention, the C2-C4 haloalcohol is selected from 2-chloroethanol.

[0018] In some embodiments of the present invention, the bio-based vanillin derivative diol comprises at least one of 4-(2-hydroxyethoxy)-3-methoxybenzyl alcohol, 4-(3-hydroxypropoxy)-3-methoxybenzyl alcohol, or 4-(4-hydroxybutoxy)-3-methoxybenzyl alcohol; in some specific embodiments of the present invention, the bio-based vanillin derivative diol is selected from 4-(2-hydroxyethoxy)-3-methoxybenzyl alcohol.

[0019] In some embodiments of the present invention, the mass ratio of the bio-based 1,4-butanediol to the bio-based vanillin derivative diol is 1:(0.5~1.5); in some specific embodiments of the present invention, the mass ratio of the bio-based 1,4-butanediol to the bio-based vanillin derivative diol is 1:(0.6~1.2).

[0020] In some embodiments of the present invention, the mass ratio of the petroleum-based isophthalic acid to the bio-based 2,5-furandicarboxylic acid is 1:(0.01~3); in some specific embodiments of the present invention, the mass ratio of the petroleum-based isophthalic acid to the bio-based 2,5-furandicarboxylic acid is 1:(0.05~2).

[0021] In some embodiments of the present invention, the petroleum-based polyol includes petroleum-based neopentyl glycol, petroleum-based trimethylolpropane, or a combination thereof; in some specific embodiments of the present invention, the petroleum-based polyol includes petroleum-based neopentyl glycol and petroleum-based trimethylolpropane.

[0022] In some embodiments of the present invention, the mass ratio of petroleum-based neopentyl glycol to petroleum-based trimethylolpropane is 1:(0.04~0.08); in some specific embodiments of the present invention, the mass ratio of petroleum-based neopentyl glycol to petroleum-based trimethylolpropane is 1:(0.05~0.07).

[0023] In some embodiments of the present invention, the esterification catalyst includes organotitanium catalysts, organotin catalysts, or combinations thereof; in some embodiments of the present invention, the esterification catalyst includes at least one of tetrabutyl titanate, tetraisopropyl titanate, monobutyltin oxide, or stannous oxalate.

[0024] In some embodiments of the present invention, the polyester resin further includes the following raw materials in parts by weight: 0.1 to 1 part of curing accelerator and 0.5 to 2 parts of antioxidant.

[0025] In some embodiments of the present invention, the curing accelerator includes at least one of triphenylethylphosphine bromide, 2-ethyl-4-methylimidazolium, or benzyltrimethylammonium chloride.

[0026] In some embodiments of the present invention, the antioxidant includes at least one of antioxidant 1010, antioxidant 1076, or antioxidant 168; in some specific embodiments of the present invention, the antioxidant includes antioxidant 1010 and antioxidant 168; specifically, the mass ratio of antioxidant 1010 to antioxidant 168 is 1:(0.3~0.7).

[0027] In some embodiments of the present invention, the polyester resin comprises the following raw materials in parts by weight: 100-200 parts of bio-based polyol, 150-300 parts of petroleum-based polyol, 400-600 parts of diacid, 40-80 parts of acid hydrolysis agent, 0.5-2 parts of esterification catalyst, 0.1-1 parts of curing accelerator and 0.5-2 parts of antioxidant.

[0028] In some specific embodiments of the present invention, the polyester resin comprises the following raw materials in parts by weight: 60-100 parts of bio-based 1,4-butanediol, 40-100 parts of bio-based vanillin derivative diol, 145-270 parts of petroleum-based neopentyl glycol, 5-30 parts of petroleum-based trimethylolpropane, 150-500 parts of petroleum-based isophthalic acid, 20-350 parts of bio-based 2,5-furandicarboxylic acid, 40-80 parts of bio-based 1,4-succinic acid, 0.5-2 parts of esterification catalyst, 0.1-1 parts of curing accelerator, and 0.5-2 parts of antioxidant.

[0029] In some embodiments of the present invention, the biocarbon content of the polyester resin is 20-55%; in some specific embodiments of the present invention, the biocarbon content of the polyester resin is 21-51%.

[0030] In some embodiments of the present invention, the acid value of the polyester resin is 30~40 mgKOH / g; in some specific embodiments of the present invention, the acid value of the polyester resin is 33~36 mgKOH / g.

[0031] In some embodiments of the present invention, the melt viscosity of the polyester resin at 200°C is 3000~7000 mPa·s; in some specific embodiments of the present invention, the melt viscosity of the polyester resin at 200°C is 5000~7000 mPa·s.

[0032] In some embodiments of the present invention, the glass transition temperature of the polyester resin is 50~65°C; in some specific embodiments of the present invention, the glass transition temperature of the polyester resin is 55~65°C.

[0033] A second aspect of the present invention provides a method for preparing a polyester resin as described in the first aspect of the present invention, comprising the following steps: mixing the bio-based polyol, petroleum-based polyol, diacid and esterification catalyst, and performing a polycondensation reaction to obtain an esterification product; mixing the esterification product with an acid hydrolysate and performing an acid hydrolysate reaction to obtain an acid hydrolysate product; performing a vacuum polycondensation reaction on the acid hydrolysate product to obtain a vacuum polycondensation product; optionally adding a curing accelerator and an antioxidant for mixing to obtain the polyester resin.

[0034] In some embodiments of the present invention, nitrogen is used to fully purge the oxygen in the apparatus before the polycondensation reaction, and the entire reaction process is carried out under a nitrogen protective atmosphere.

[0035] In some embodiments of the present invention, the raw materials are heated and melted before the polycondensation reaction; the heating and melting temperature is 150~160°C and the time is 15~20 min.

[0036] In some embodiments of the present invention, the reaction temperature of the polycondensation reaction is 220~240℃ and the reaction time is 1~6h; in some specific embodiments of the present invention, the reaction temperature of the polycondensation reaction is 228~232℃ and the reaction time is 2~3h.

[0037] In some embodiments of the present invention, the acid value of the esterified product is 9-14 mgKOH / g; in some specific embodiments of the present invention, the acid value of the esterified product is 10-12 mgKOH / g.

[0038] In some embodiments of the present invention, the reaction temperature of the acidolysis reaction is 210~230℃ and the reaction time is 1~8h; in some specific embodiments of the present invention, the reaction temperature of the acidolysis reaction is 215~225℃ and the reaction time is 4~6h.

[0039] In some embodiments of the present invention, the acid value of the acid hydrolysis product is 40-50 mg KOH / g; in some specific embodiments of the present invention, the acid value of the acid hydrolysis product is 46-48 mg KOH / g.

[0040] In some embodiments of the present invention, the reaction temperature of the vacuum polycondensation reaction is 210~230℃ and the reaction time is 1~6h; in some specific embodiments of the present invention, the reaction temperature of the vacuum polycondensation reaction is 215~225℃ and the reaction time is 2~4h.

[0041] In some embodiments of the present invention, the acid value of the vacuum polycondensation product is 30-40 mg KOH / g; in some specific embodiments of the present invention, the acid value of the vacuum polycondensation product is 33-36 mg KOH / g.

[0042] In some embodiments of the present invention, the melt viscosity of the vacuum polycondensation product at 200°C is 4000~7000 Pa·s.

[0043] In some embodiments of the present invention, the system temperature when the curing accelerator and antioxidant are added is 200~210°C; and the mixing time for adding the curing accelerator and antioxidant is 5~10 min.

[0044] A third aspect of the present invention is a powder coating comprising the polyester resin described in the first aspect of the present invention; wherein the polyester resin comprises 50-65% by mass in the powder coating.

[0045] In some embodiments of the present invention, the polyester resin in the powder coating is 53-58% by mass.

[0046] In some embodiments of the present invention, the powder coating further includes a curing agent, filler, and processing aid.

[0047] In some embodiments of the present invention, the powder coating further includes the following components by weight percentage: 4-5% curing agent, 29-42% filler and 1-3% processing aid.

[0048] In some specific embodiments of the present invention, the powder coating further includes the following components by weight percentage: 4-5% curing agent, 35-40% filler and 1-3% processing aid.

[0049] In some embodiments of the present invention, the curing agent includes at least one of triglycidyl isocyanurate, ε-caprolactam-blocked toluene diisocyanate trimer, pyromellitic triglyceride, or β-hydroxyalkylamide; in some specific embodiments of the present invention, the curing agent is triglycidyl isocyanurate.

[0050] In some embodiments of the present invention, the filler is an inorganic filler; the inorganic filler includes titanium dioxide, barium sulfate, or a combination thereof.

[0051] In some embodiments of the present invention, the processing aid includes at least one of a leveling agent, a degassing agent, or a brightening agent; in some embodiments of the present invention, the processing aid includes a leveling agent, a degassing agent, and a brightening agent.

[0052] In some embodiments of the present invention, the leveling agent includes an acrylate leveling agent, such as GLP588.

[0053] In some embodiments of the present invention, the degassing agent includes benzoin.

[0054] In some embodiments of the present invention, the brightening agent includes acrylate copolymers, such as brightening agent 701.

[0055] In some embodiments of the present invention, the powder coating comprises the following components by weight percentage: 50-65% polyester resin, 4-5% curing agent, 29-42% filler, 0.5-1% leveling agent, 0.2-1% degassing agent, and 0.3-1% gloss enhancer.

[0056] In some embodiments of the present invention, the powder coating is prepared by a method comprising the following steps: crushing and mixing the components, melting and extruding them using a twin-screw extruder, pressing, crushing, and sieving to obtain the powder coating.

[0057] In some embodiments of the present invention, the temperature of the first zone of the twin-screw extruder is 85~95°C, the temperature of the second zone is 90~95°C, and the temperature of the third zone is 95~100°C.

[0058] A fourth aspect of the present invention is a powder coating formed by curing the powder coating described in the third aspect of the present invention.

[0059] In some embodiments of the present invention, the thickness of the powder coating is 60~70μm.

[0060] In some embodiments of the present invention, the curing temperature of the powder coating is 190~210℃ and the curing time is 5~15min; in some specific embodiments of the present invention, the curing temperature of the powder coating is 195~205℃ and the curing time is 8~12min.

[0061] The beneficial effects of this invention are: This invention employs random copolymerization of multiple monomers, disrupting the regularity of molecular chains and inhibiting crystallization. The amorphous resin exhibits better transparency and more uniform stress distribution, reducing concentrated photo-oxidation caused by interface defects between crystalline and amorphous regions. No UV absorbers or complex physical or chemical modifications are required during polyester resin preparation. This fundamentally solves the problem of poor weather resistance in bio-based polyesters at the molecular design level, reducing costs and process complexity. The resulting powder coatings and powder coatings possess high bio-carbon content, excellent mechanical toughness, and long-lasting weather resistance. Attached Figure Description

[0062] Figure 1 The DSC curves are for the polyester resins of Examples 1-4 and Comparative Examples 1-2.

[0063] Figure 2 The image shows the weather resistance performance of each powder coating in Application Example 2. Detailed Implementation

[0064] The following specific embodiments further illustrate the content of the present invention in detail. It should also be understood that the following embodiments are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the principles described herein are all within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make selections within a suitable range based on the description herein, and are not intended to be limited to the specific data in the examples below. Unless otherwise specified, the raw materials, reagents, or apparatus used in the following embodiments and comparative examples can be obtained from conventional commercial sources or by existing known methods.

[0065] Unless otherwise specified, all raw materials used in the embodiments and comparative examples of this invention are commercially available industrial-grade products.

[0066] In the embodiments and comparative examples of this invention, the bio-based vanillin derivative diol is 4-(2-hydroxyethoxy)-3-methoxybenzyl alcohol, i.e. Since the phenolic hydroxyl groups on bio-based vanillin react poorly with carboxylic acids, this invention utilizes the acidity difference between the phenolic and alcoholic hydroxyl groups to achieve selective etherification of the phenolic hydroxyl groups through a weak base. The specific synthesis is as follows: 0.1 mol vanillin and 0.02 mol potassium carbonate were added to a reaction vessel and dissolved using N,N-dimethylformamide. Then, 0.12 mol 2-chloroethanol was added dropwise. The reaction mixture was heated to 85-90°C and stirred continuously for 4-5 hours. After cooling, deionized water was added to dissolve the byproduct inorganic salts. The mixture was extracted three times with ethyl acetate, and the organic phases were combined. The organic phases were washed three times with saturated brine to remove N,N-dimethylformamide. After drying with anhydrous sodium sulfate and filtering, the filtrate was evaporated under reduced pressure to obtain 4-(2-hydroxyethoxy)-3-methoxybenzyl alcohol, denoted as bio-based vanillin derivative diol. The chemical formula of the reaction process is as follows: .

[0067] Example 1 A weather-resistant polyester resin with high bio-based content is prepared as follows: According to the dosages in Table 1, add petroleum-based neopentyl glycol, petroleum-based trimethylolpropane, bio-based 1,4-butanediol, bio-based vanillin derivative diol, petroleum-based isophthalic acid, bio-based 2,5-furandicarboxylic acid, and monobutyltin oxide to a 2L glass reactor. After purging with nitrogen for 5 minutes, start heating to 160°C. Once the materials are completely melted, start stirring at a rate of 200 rpm. Maintain this temperature for 15 minutes. After the esterification water begins to appear at 180°C, monitor the column top temperature closely (do not exceed 98°C). Then, slowly and gradually increase the temperature to 230°C, maintaining a nitrogen atmosphere and normal pressure throughout the reaction. Hold at 230°C for 2-3 hours until the esterification water content reaches [value missing]. When the effluent reaches 95% of the theoretical effluent value and meets the theoretical acid value of the esterification stage, and the esterification stage sampling is clear with an acid value of 10-12 mgKOH / g, the acidolysis stage begins. Bio-based 1,4-succinic acid is added, and the temperature is lowered to 220℃ for 4-6 hours, resulting in an acid value of 46-48 mgKOH / g. The nitrogen gas is then turned off, and the vacuum pump is connected, reducing the vacuum to -0.1 MPa. The reaction continues for 2-4 hours to remove oligomers and moisture, increasing the degree of reaction and molecular weight. When the acid value reaches 33-36 mgKOH / g, the temperature is lowered to 205℃, and a curing accelerator and antioxidant are added. The mixture is stirred for 10 minutes, discharged, and cooled to obtain a high-bio-based content weather-resistant polyester resin, designated Bio-PR1.

[0068] Example 2 A weather-resistant polyester resin with high bio-based content is prepared as follows: According to the dosages in Table 1, add petroleum-based neopentyl glycol, petroleum-based trimethylolpropane, bio-based 1,4-butanediol, bio-based vanillin derivative diol, petroleum-based isophthalic acid, bio-based 2,5-furandicarboxylic acid, and monobutyltin oxide to a 2L glass reactor. After purging with nitrogen for 5 minutes, start heating to 160°C. Once the materials are completely melted, start stirring at a rate of 200 rpm. Maintain this temperature for 15 minutes. After the temperature rises to 178°C and esterification water begins to appear, closely monitor the column top temperature (do not exceed 98°C). Then, slowly and gradually increase the temperature to 230°C, maintaining a nitrogen atmosphere and normal pressure throughout the reaction. Maintain this temperature at 230°C for 2-3 hours until the esterification water content reaches [value missing]. The theoretical effluent water value was 95% of the theoretical acid value required for the esterification stage. Clear samples were taken during the esterification stage, with an acid value of 10-12 mg KOH / g. The process then proceeded to the acidolysis stage, where bio-based 1,4-succinic acid was added. The mixture was cooled to 220℃ and reacted for 4-6 hours, reaching an acid value of 46-48 mg KOH / g. Nitrogen gas was then turned off, and a vacuum pump was connected, reducing the vacuum to -0.098 MPa. The reaction continued for 2-4 hours to remove oligomers and moisture, increasing the reaction rate and molecular weight. Once the acid value reached 33-36 mg KOH / g, the temperature was lowered to 205℃, and a curing accelerator and antioxidant were added. After stirring for 10 minutes, the mixture was discharged and cooled to obtain a high-bio-based, weather-resistant polyester resin, designated Bio-PR2.

[0069] Example 3 A weather-resistant polyester resin with high bio-based content is prepared as follows: According to the dosages in Table 1, add petroleum-based neopentyl glycol, petroleum-based trimethylolpropane, bio-based 1,4-butanediol, bio-based vanillin derivative diol, petroleum-based isophthalic acid, bio-based 2,5-furandicarboxylic acid, and monobutyltin oxide to a 2L glass reactor. After purging with nitrogen for 5 minutes, start heating to 160°C. Once the materials are completely melted, start stirring at a rate of 200 rpm. Maintain this temperature for 15 minutes. After the temperature rises to 178°C and esterification water begins to appear, monitor the column top temperature closely (do not exceed 98°C). Then, slowly and gradually increase the temperature to 230°C, maintaining a nitrogen atmosphere and normal pressure throughout the reaction. Maintain this temperature at 230°C for 2-3 hours until the esterification water content reaches [value missing]. When the effluent reaches 95% of the theoretical effluent value and meets the theoretical acid value of the esterification stage, and the esterification stage sampling is clear with an acid value of 10-12 mgKOH / g, the acidolysis stage begins. Bio-based 1,4-succinic acid is added, and the temperature is lowered to 220℃ for 4-6 hours, resulting in an acid value of 46-48 mgKOH / g. Nitrogen gas is then turned off, and a vacuum pump is connected, reducing the vacuum to -0.1 MPa. The reaction continues for 2-4 hours to remove oligomers and moisture, increasing the degree of reaction and molecular weight. When the acid value reaches 33-36 mgKOH / g, the temperature is lowered to 205℃, and a curing accelerator and antioxidant are added. After stirring for 10 minutes, the material is discharged and cooled to obtain a high bio-based content weather-resistant polyester resin, designated Bio-PR3.

[0070] Example 4 A weather-resistant polyester resin with high bio-based content is prepared as follows: According to the dosages in Table 1, add petroleum-based neopentyl glycol, petroleum-based trimethylolpropane, bio-based 1,4-butanediol, bio-based vanillin derivative diol, petroleum-based isophthalic acid, bio-based 2,5-furandicarboxylic acid, and monobutyltin oxide to a 2L glass reactor. After purging with nitrogen for 5 minutes, start heating to 160°C. Once the materials are completely melted, start stirring at a rate of 200 rpm. Maintain this temperature for 15 minutes. After the temperature rises to 176°C and esterification water begins to appear, monitor the column top temperature closely (do not exceed 98°C). Then, slowly and gradually increase the temperature to 230°C, maintaining a nitrogen atmosphere and normal pressure throughout the reaction. Maintain this temperature at 230°C for 2-3 hours until the esterification water content reaches [value missing]. The theoretical effluent water value was 95% of the theoretical acid value required for the esterification stage. Clear samples were taken during the esterification stage, with an acid value of 10-12 mg KOH / g. The process then proceeded to the acidolysis stage, where bio-based 1,4-succinic acid was added. The mixture was cooled to 220℃ and reacted for 4-6 hours, reaching an acid value of 46-48 mg KOH / g. Nitrogen gas was then turned off, and a vacuum pump was connected, reducing the vacuum to -0.098 MPa. The reaction continued for 2-4 hours to remove oligomers and moisture, increasing the reaction rate and molecular weight. Once the acid value reached 33-36 mg KOH / g, the temperature was lowered to 205℃, and a curing accelerator and antioxidant were added. After stirring for 10 minutes, the mixture was discharged and cooled to obtain a high-bio-based, weather-resistant polyester resin, designated Bio-PR4.

[0071] Comparative Example 1 A weather-resistant polyester resin with high bio-based content, differing from Example 1 in that: this example does not contain bio-based 1,4-butanediol; the specific preparation method is as follows: According to the dosages in Table 1, add petroleum-based neopentyl glycol, petroleum-based trimethylolpropane, bio-based vanillin derivative diol, petroleum-based isophthalic acid, bio-based 2,5-furandicarboxylic acid, and monobutyltin oxide to a 2L glass reactor. After purging with nitrogen for 5 minutes, start heating to 160°C. Once the materials are completely melted, start stirring at a rate of 200 rpm. Maintain this temperature for 15 minutes. After the esterification water begins to appear at 180°C, monitor the column top temperature closely (do not exceed 98°C). Then, slowly and gradually increase the temperature to 230°C, maintaining a nitrogen atmosphere and normal pressure throughout the reaction. Maintain this temperature at 230°C for 2-3 hours until the esterification water content reaches the theoretical target. The water content was 95% and the theoretical acid value met the requirements of the esterification stage. The esterification stage samples were clear, with an acid value of 10-12 mgKOH / g. The acidolysis stage was then initiated, with the addition of bio-based 1,4-succinic acid. The temperature was lowered to 220℃ and the reaction proceeded for 4-6 hours, reaching an acid value of 46-48 mgKOH / g. Nitrogen gas was then turned off, and a vacuum pump was connected, reducing the vacuum to -0.1 MPa. The reaction continued for 2-4 hours to remove oligomers and moisture, increasing the reaction rate and molecular weight. Once the acid value reached 33-36 mgKOH / g, the temperature was lowered to 205℃, and a curing accelerator and antioxidant were added. After stirring for 10 minutes, the material was discharged and cooled to obtain a high-bio-based content weather-resistant polyester resin, designated C-PR1.

[0072] Comparative Example 2 A high-bio-based, weather-resistant polyester resin differs from Example 1 in that it does not contain bio-based vanillin alcohol derivative diol; the specific preparation method is as follows. According to the dosages in Table 1, add petroleum-based neopentyl glycol, petroleum-based trimethylolpropane, bio-based 1,4-butanediol, petroleum-based isophthalic acid, bio-based 2,5-furandicarboxylic acid, and monobutyltin oxide to a 2L glass reactor. After purging with nitrogen for 5 minutes, start heating to 160℃. Once the materials are completely melted, start stirring at a rate of 200 rpm. Maintain this temperature for 15 minutes. After the esterification water begins to appear at 182℃, monitor the column top temperature closely (do not exceed 98℃). Then, slowly and gradually increase the temperature to 230℃, maintaining a nitrogen atmosphere and normal pressure throughout the reaction. Maintain this temperature at 230℃ for 2-3 hours until the esterification water content reaches the theoretical value. The theoretical acid value of the esterification stage was 95% and met the requirements. The esterification stage samples were clear, and the acid value was 10-12 mgKOH / g. The acid hydrolysis stage could then be entered. Bio-based 1,4-succinic acid was added, and the temperature was lowered to 220℃ for 4-6 hours. The acid value reached 46-48 mgKOH / g. The nitrogen gas was turned off and the vacuum pump was connected. The vacuum degree was reduced to -0.098 MPa, and the reaction continued for 2-4 hours to remove oligomers and moisture, increase the degree of reaction and increase the molecular weight. After the acid value reached 33-36 mgKOH / g, the temperature was lowered to 205℃, and a curing accelerator and antioxidant were added. The mixture was stirred for 10 minutes, discharged, and cooled to obtain a high bio-based content weather-resistant polyester resin, denoted as C-PR2.

[0073] The specific raw materials and dosages used in the preparation of polyester resins in Examples 1-4 and Comparative Examples 1-2 are shown in Table 1.

[0074] Table 1. Raw materials and amounts used in the preparation of polyester resins for Examples 1-4 and Comparative Examples 1-2 (amount in g).

[0075] Application Example 1 A series of powder coatings were prepared using the polyester resins in Examples 1-4 and Comparative Examples 1-2 as raw materials. Each polyester resin was weighed and mixed with curing agent triglycidyl isocyanate, titanium dioxide, 8000 barium, leveling agent GLP588, degassing agent benzoin, and brightening agent 701 in the proportions shown in Table 2. The mixture was then melt-extruded, sheeted, and crushed using a screw extruder. The temperature of the first zone of the twin-screw extruder was 90°C, the second zone was 90-95°C, and the third zone was 95-100°C. After sieving, the powder coatings were obtained and designated as Bio-PR1 coating, Bio-PR2 coating, Bio-PR3 coating, Bio-PR4 coating, C-PR1 coating, and C-PR2 coating, respectively.

[0076] Table 2. Components and dosage of each powder coating in Application Example 1 (dosage unit is g).

[0077] Application Example 2 A series of powder coatings were prepared by electrostatically spraying each of the powder coatings (Bio-PR1 coating, Bio-PR2 coating, Bio-PR3 coating, Bio-PR4 coating, C-PR1 coating, and C-PR2 coating) from Application Example 1 onto a surface-treated iron plate and curing them at 200°C for 10 minutes to obtain powder coatings with a thickness of 60~70μm, which were respectively denoted as Bio-PR1 coating, Bio-PR2 coating, Bio-PR3 coating, Bio-PR4 coating, C-PR1 coating, and C-PR2 coating.

[0078] Performance testing (1) Resin acid value: The test was conducted in accordance with GB / T 6743-2008 "Determination of acid value and total acid value of polyester resin for plastics, paint and varnish".

[0079] (2) Glass transition temperature of resin (Tg): The temperature was measured using a differential scanning calorimeter (DSC) at a heating rate of 10℃ / min.

[0080] (3) Biocarbon content: The proportion of C14 in the resin was determined according to ASTM D6866-22 standard.

[0081] (4) Impact resistance of coating: Tested according to GBT1732-2020 "Test Method for Impact Resistance of Coating Film".

[0082] (5) Weather resistance of coating: Accelerated aging test was conducted using UVB-313 fluorescent ultraviolet lamps in accordance with GB / T 14522-2008. The time (in hours) required for the gloss level to drop to 50% of the initial value (i.e., the gloss retention rate to be 50%) was used as the criterion for weather resistance failure assessment.

[0083] Table 3 Performance test results of polyester resins in Examples 1-4 and Comparative Examples 1-2

[0084] Table 4 Performance test results of each powder coating in Application Example 2

[0085] Figure 1 The DSC curves are for the polyester resins of Examples 1-4 and Comparative Examples 1-2. Figure 2 The image shows the weather resistance performance of each powder coating in Application Example 2.

[0086] analyze Figures 1-2 As shown in Tables 3-4, the glass transition temperature (TVT) of the polyester resin determines the room temperature storage stability of the powder coating. The furan ring in 2,5-furandicarboxylic acid imparts rigidity to the main chain. In Examples 1-4, as the amount of isophthalic acid decreased while the amount of 2,5-furandicarboxylic acid increased, the TVT increased to 64.7℃. Simultaneously, the benzene ring of the bio-based vanillin derivative diol also imparts rigidity to the main chain. In Comparative Example 2, the complete removal of the bio-based vanillin derivative diol resulted in a Tg of 45.9℃, directly leading to agglomeration of the powder coating during storage. Generally, the excessive use of isophthalic acid can easily cause the coating to become brittle. However, all examples of this invention passed the 50 kg·cm impact test. This is attributed to the effective relief of stress concentration by the flexible segments of the bio-based 1,4-butanediol, achieving a balance between rigidity and flexibility. The C-PR1 obtained in Comparative Example 1, lacking this flexible monomer, failed in the impact test, fully demonstrating the necessity of this molecular design.

[0087] The intrinsic weather resistance of polyester resins is highly dependent on the synergistic effect of the meta-structure of isophthalic acid and the methoxy shielding effect of the bio-based vanillin derivative diol, which creates excellent weather resistance. Compared with Bio-PR1 in Example 1, C-PR2 in Comparative Example 2 lacks the bio-based vanillin derivative diol, and its gloss retention rate drops from 63.3% to 47.4%.

[0088] Generally, the ether bonds on the furan ring are relatively susceptible to damage from ultraviolet light. As the amount of 2,5-furandicarboxylic acid increases, the weather resistance of high-bio-based polyester resins inevitably weakens; that is, weather resistance decreases with increasing 2,5-furandicarboxylic acid content and with increasing biochar content. However, the embodiments of this invention successfully solve this problem through precise control: while maintaining a high biochar content of 20%~32%, the gloss retention rate after 500 hours of UVB irradiation can still reach 55.2%~63.3%; even when the biochar content climbs to 40.4%, the aging failure time is still around 478 hours, achieving a deep balance between green low-carbon and long-lasting weather resistance.

[0089] The polyester resin provided in this embodiment of the invention has excellent overall weather resistance. When the bio-carbon content of the polyester resin is in the range of 20% to 40%, the UVB accelerated aging failure time of the coating can reach about 470 to 530 hours. Under the requirement of high bio-based (bio-carbon content of 40% to 50%), the aging failure time can still be maintained at an excellent level of 220 to 470 hours.

[0090] The polyester resin provided in this invention can achieve a balance between mechanical and thermal properties, without the need for toughening additives. The coating can pass the 50 kg·cm test for both positive and negative impacts, and has excellent toughness. At the same time, the glass transition temperature (Tg) of the resin is maintained between 55℃ and 65℃, ensuring the excellent storage stability of the powder coating at room temperature.

[0091] In summary, this invention employs random copolymerization of multiple monomers, disrupting the regularity of the molecular chains and inhibiting crystallization. The amorphous resin exhibits better transparency and a more uniform stress distribution, reducing concentrated photo-oxidation caused by interface defects between crystalline and amorphous regions. The polyester resin preparation process eliminates the need for adding UV absorbers and complex physical or chemical modifications, fundamentally solving the problem of poor weather resistance in bio-based polyesters at the molecular design level. This reduces costs and process complexity, resulting in powder coatings and powder coating layers that combine high bio-carbon content, excellent mechanical toughness, and long-lasting weather resistance.

Claims

1. A polyester resin, characterized in that, The polyester resin comprises the following raw materials in parts by weight: 100-200 parts of bio-based polyol, 150-300 parts of petroleum-based polyol, 400-600 parts of diacid, 40-80 parts of acid hydrolysis agent, and 0.5-2 parts of esterification catalyst; the bio-based polyol includes bio-based 1,4-butanediol and bio-based vanillyl alcohol derivative diol; the diacid includes petroleum-based isophthalic acid and bio-based 2,5-furandicarboxylic acid; and the acid hydrolysis agent includes bio-based 1,4-succinic acid.

2. The polyester resin according to claim 1, characterized in that, The bio-based vanillin derivative diol is formed by the reaction of bio-based vanillin, C2-C4 halogenated fatty alcohols and basic compounds; And / or, the mass ratio of the bio-based 1,4-butanediol to the bio-based vanillyl alcohol derivative diol is 1:(0.5~1.5). And / or, the mass ratio of the petroleum-based isophthalic acid to the bio-based 2,5-furandicarboxylic acid is 1:(0.01~3).

3. The polyester resin according to claim 1, characterized in that, The bio-based vanillin derivative diol includes at least one of 4-(2-hydroxyethoxy)-3-methoxybenzyl alcohol, 4-(3-hydroxypropoxy)-3-methoxybenzyl alcohol, or 4-(4-hydroxybutoxy)-3-methoxybenzyl alcohol. And / or, the petroleum-based polyols include petroleum-based neopentyl glycol, petroleum-based trimethylolpropane, or combinations thereof; And / or, the esterification catalyst includes organotitanium catalysts, organotin catalysts, or combinations thereof.

4. The polyester resin according to claim 1, characterized in that, The polyester resin also includes the following raw materials in parts by weight: 0.1 to 1 part curing accelerator and 0.5 to 2 parts antioxidant.

5. The polyester resin according to claim 4, characterized in that, The curing accelerator includes at least one of triphenylethylphosphine bromide, 2-ethyl-4-methylimidazolium or benzyltrimethylammonium chloride; And / or, the antioxidant includes at least one of antioxidant 1010, antioxidant 1076, or antioxidant 168.

6. A method for preparing a polyester resin according to any one of claims 1 to 5, characterized in that, Includes the following steps: The bio-based polyol, petroleum-based polyol, diacid, and esterification catalyst are mixed and subjected to a polycondensation reaction to obtain an esterified product; the esterified product is mixed with an acid hydrolysate and subjected to an acid hydrolysate reaction to obtain an acid hydrolysate; the acid hydrolysate is subjected to a vacuum polycondensation reaction to obtain a vacuum polycondensation product; optionally, a curing accelerator and an antioxidant are added and mixed to obtain the polyester resin.

7. The preparation method according to claim 6, characterized in that, The reaction temperature of the polycondensation reaction is 220~240℃, and the reaction time is 1~6h; And / or, the acid value of the esterified product is 9~14 mgKOH / g; And / or, the acidolysis reaction is carried out at a temperature of 210~230℃ for 1~8h. And / or, the acid value of the acid hydrolysis product is 40~50 mgKOH / g; And / or, the reaction temperature of the vacuum polycondensation reaction is 210~230℃, and the reaction time is 1~6h; And / or, the acid value of the vacuum polycondensation product is 30~40 mgKOH / g; And / or, the system temperature when the curing accelerator and antioxidant are added is 200~210℃.

8. A powder coating, characterized in that, The powder coating comprises the polyester resin according to any one of claims 1 to 5; wherein the polyester resin in the powder coating has a mass percentage of 50 to 65%.

9. The powder coating according to claim 8, characterized in that, The powder coating also includes the following components by weight percentage: 4-5% curing agent, 29-42% filler and 1-3% processing aid.

10. A powder coating, characterized in that, The powder coating is formed by curing the powder coating as described in claim 8 or 9; the thickness of the powder coating is 60~70μm.

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