Light-color high-transparency PETG polyester and preparation method thereof

Abstract

The invention relates to the technical field of high polymer material synthesis, in particular to light-color high-transparency PETG polyester and a preparation method thereof.The preparation method comprises the steps that terephthalic acid, ethylene glycol, polyhydric alcohol and a zinc coordination composite catalyst are mixed in proportion and heated for a polymerization reaction, and an oligomer is obtained; raising the temperature and reducing the pressure to continue the polymerization reaction to obtain a pre-polymerized reactant; and under a nitrogen protection environment, adding a phosphoric acid antioxidant, heating, and continuing the polymerization reaction to prepare the light-color high-transparency PETG polyester. According to the preparation method disclosed by the invention, in the process of synthesizing the PETG by using the zinc coordination composite catalyst, the phosphate ester antioxidant is added, so that the problem of yellowing of the product is effectively solved, and the whiteness and transparency of the PETG are improved; meanwhile, the glass-transition temperature and the barrier property of the product can be improved. The light-color high-transparency PETG prepared by the method disclosed by the invention has excellent comprehensive performance on the premise of not increasing excessive cost.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis technology, and particularly relates to a method for inhibiting yellowing by adding phosphate ester antioxidants during the synthesis of PETG polyester using a zinc-based composite catalyst, and a light-colored, high-transparency PETG polyester obtained by this method. Background Technology

[0002] PETG is a non-crystalline copolyester with excellent overall properties, including high transparency, good toughness, superior processing performance, and chemical resistance. It is widely used in packaging, medical, electronics, and optics industries. Catalysts play a crucial role in the synthesis of PETG. Zinc catalysts are commonly used in PETG synthesis due to their high catalytic activity and relatively low cost. However, in actual production, it has been found that using zinc catalysts in the synthesis of PETG often results in a yellowing of the product. This is mainly because under high-temperature polymerization conditions, the PETG molecular chain is prone to side reactions such as thermal oxidative degradation, producing chromophores with conjugated structures, thus causing the product to turn yellow. The presence of zinc catalysts may, to some extent, promote these side reactions. The yellowing of the product color seriously affects the appearance quality and application range of PETG, especially in high-end application fields with strict color requirements, such as optical lenses and high-end packaging. Yellowed PETG cannot meet the usage requirements. In addition, the glass transition temperature of traditional low melting point polyester fibers is mostly around 70℃. Due to the introduction of CHDM in the molecular chain, the regularity of the molecular chain is reduced, resulting in poor barrier properties against small molecules such as oils and oxygen.

[0003] Currently, there are few studies and solutions to the aforementioned problems in the synthesis of PETG using zinc catalysts. Some existing methods have issues such as poor performance, high cost, or impact on other properties of PETG, which limits their application in high-temperature fields.

[0004] In the prior art, CN1121727A discloses a composite catalyst of manganese diacetate, zinc acetate, titanium isopropoxy, and germanium dioxide for the preparation of PETG. Its main focus is on improving catalytic efficiency and product viscosity, without mentioning the solution to the yellowing problem.

[0005] Patent CN114853991A discloses a method for depolymerizing waste PET polyester raw materials, followed by transesterification with methanol to generate intermediate molecule DMT. After purification, the refined DMT undergoes esterification with 1,4-cyclohexanediethanol and ethylene glycol, finally polymerizing to generate PETG polymer. Its disadvantages include high energy consumption and a complex process; the depolymerization process requires a large amount of methanol, increasing production costs and post-processing complexity.

[0006] Patent CN101121776 discloses a method for preparing polyester using a non-antimony catalyst. It uses a zinc catalyst and phosphite as stabilizers to prepare polyester. Using phosphite as a stabilizer reduces catalyst activity and inhibits yellowing, resulting in a longer polycondensation time. This requires increasing the amount of catalyst. Excessive catalyst addition will affect the thermal degradation of the processing and cause the polyester to yellow.

[0007] Patent US20080064797A1 relates to a method for producing polyethylene terephthalate copolyester from terephthalic acid, isophthalic acid and ethylene glycol. It mainly focuses on process optimization, catalyst dispersibility and activity, synergistic catalyst system and recovery and recycling, but does not solve the problem of yellowing.

[0008] The PETG produced by the aforementioned existing methods all have shortcomings. Therefore, a preparation method is needed to solve the problems of yellowing, complex processes, and thermal degradation during post-processing that exist in the existing technologies. Summary of the Invention

[0009] One objective of this invention is to provide a method for suppressing yellowing during the synthesis of PETG. By adding a specific phosphate ester antioxidant when synthesizing PETG using a zinc-based coordination composite catalyst, the yellowing problem of the product is effectively solved, and the whiteness and transparency of PETG are improved. At the same time, the introduction of the coordination agent helps to improve the glass transition temperature and barrier properties of the product, thus expanding its application areas.

[0010] Another object of the present invention is to provide a light-colored, high-transparency PETG prepared by the method, which has excellent overall performance.

[0011] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0012] A method for preparing a light-colored, high-transparency PETG polyester includes the following steps:

[0013] S1. Terephthalic acid, ethylene glycol, polyol, and zinc-based coordination composite catalyst are mixed in proportion and heated to carry out a polymerization reaction to obtain oligomers.

[0014] S2. Continue the polymerization reaction by raising the temperature and reducing the pressure to obtain the prepolymer.

[0015] S3. Under nitrogen protection, phosphoric acid antioxidants are added and the temperature is raised to continue the polymerization reaction, resulting in light-colored, high-transparency PETG polyester.

[0016] In some specific embodiments, the polyol mentioned in S1 is one or more of 1,4-cyclohexanediol, neopentyl glycol, isosorbide, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, spirocyclodiol, and phenylethylene glycol, preferably 1,4-cyclohexanediol and neopentyl glycol, and more preferably 1,4-cyclohexanediol;

[0017] Preferably, the molar ratio of the polyol to terephthalic acid is 1.1-1.8, more preferably 1.3-1.5.

[0018] In some specific implementation schemes, the zinc-based coordination composite catalyst described in S1 is selected from one or more of the following: zinc-Citric Acid composite catalyst, zinc-EDTA composite catalyst, zinc-EDTA-2Na composite catalyst, zinc-Sodium Gluconate composite catalyst, and zinc-Tartaric Acid composite catalyst.

[0019] Preferably, the amount of the zinc-based coordination composite catalyst is 30-200 ppm, more preferably 40-100 ppm, based on the mass of terephthalic acid.

[0020] In some specific embodiments, the zinc in the zinc-based coordination composite catalyst in S1 is derived from zinc compounds, preferably one or more of zinc acetate, zinc chloride, zinc sulfate, zinc nitrate, zinc trifluoroacetate, zinc oxide, zinc lactate, zinc trifluoromethanesulfonate, zinc acetylacetonate, nano zinc oxide, and zinc-based MOF, more preferably zinc acetate, zinc chloride, zinc sulfate, and zinc nitrate.

[0021] In some specific embodiments, the ligands of the zinc-based coordination composite catalyst in S1 are citric acid, ethylenediaminetetraacetic acid (EDTA), sodium salt (EDTA-2Na), sodium gluconate, and tartaric acid, preferably one or more of citric acid and ethylenediaminetetraacetic acid (EDTA).

[0022] In some specific implementations, the molar ratio of zinc to ligand is 1-1.5, preferably 1.15-1.25.

[0023] In some specific implementation schemes, the polymerization reaction described in S1 is carried out at a reaction temperature of 220-270°C for 2-6 hours.

[0024] In some specific implementation schemes, the polymerization reaction described in S2 has a reaction temperature of 240-280℃, a reaction time of 0.5-2h, and a vacuum pressure of 5-20KPa.

[0025] In some specific implementations, in S3, the phosphoric acid antioxidant is selected from one or more of phosphoric acid, phosphorous acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, triethyl phosphate, tris(2,4-di-tert-butyl)phosphite (antioxidant 168), and tris(nonylphenol) phosphite (antioxidant TNP), with phosphoric acid being more preferred;

[0026] Preferably, the amount of the phosphoric acid antioxidant is 10ppm-50ppm, based on the mass of terephthalic acid.

[0027] In some specific implementation schemes, in S3, the reaction temperature is 250-290℃, the reaction time is 2.5-5h, and the vacuum pressure is 20-150Pa.

[0028] On the other hand, the present invention provides a light-colored, high-transmittance PETG polyester prepared by the aforementioned method, wherein the PETG polyester has a b-value ≤ 3, a transmittance ≥ 89%, and a permeation rate ≤ 10 mg / (dm³). 2 ·10d.

[0029] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0030] 1) By adjusting the catalyst formulation and using zinc-based coordination composite catalysts, the occurrence of side reactions during PETG synthesis can be effectively reduced, thereby reducing the color value of PETG products, improving their hue, and increasing their transmittance.

[0031] 2) In the zinc-based coordination composite catalyst used in this invention, the introduction of ligands can affect the polyester molecular structure and improve its barrier properties and glass transition temperature.

[0032] 3) The product obtained by this invention has good thermal stability, the synthesis method is simple and the cost is low, and it can be used for practical engineering applications. Detailed Implementation

[0033] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" may be used herein to include any and all combinations of one or more of the associated listed items.

[0035] A method for preparing a light-colored, high-transparency PETG polyester includes the following steps:

[0036] S1: After purging the reactor with nitrogen, terephthalic acid, ethylene glycol, polyol, and zinc-based coordination composite catalyst are added to the reactor in a certain proportion and mixed. The mixture is heated to carry out the esterification reaction. The timing starts from when the gas phase is extracted. The esterification reaction ends when the extracted water reaches 90% of the theoretical amount, and the esterified product is obtained.

[0037] S2: Continue the pre-condensation reaction by raising the temperature and reducing the pressure to obtain the pre-condensation reactant;

[0038] S3: Under nitrogen protection, add phosphoric acid antioxidants and raise the temperature to carry out the final polycondensation reaction to obtain PETG polyester with ideal molecular weight, which is then cooled in a water bath and pelletized.

[0039] In step S1 of the present invention, the polyol is one or more of 1,4-cyclohexanediol, neopentyl glycol, isosorbide, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, spirocyclodiol, and phenylethylene glycol, preferably 1,4-cyclohexanediol or neopentyl glycol, and more preferably 1,4-cyclohexanediol.

[0040] In step S1 of the present invention, the molar ratio of the added polyol to terephthalic acid is 1.1-1.8, for example, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, etc., more preferably 1.3-1.5.

[0041] In step S1 of this invention, the zinc-based coordination composite catalyst includes one or more of the following: zinc-citric acid composite catalyst, zinc-EDTA composite catalyst, zinc-EDTA-2Na composite catalyst, zinc-Sodium Gluconate composite catalyst, and zinc-Tartaric Acid composite catalyst, preferably zinc-citric acid composite catalyst or zinc-EDTA composite catalyst. The amount of the zinc-based coordination composite catalyst added is 30-2000 ppm, for example, 40 ppm, 50 ppm, 80 ppm, 100 ppm, 200 ppm, 300 ppm, 500 ppm, 800 ppm, 1000 ppm, 1200 ppm, 1500 ppm, 1800 ppm, etc., preferably 40-100 ppm, based on the total mass of terephthalic acid.

[0042] The zinc in the zinc-based coordination composite catalyst is derived from zinc compounds, preferably one or more of zinc acetate, zinc chloride, zinc sulfate, zinc nitrate, zinc trifluoroacetate, zinc oxide, zinc lactate, zinc trifluoromethanesulfonate, zinc acetylacetonate, nano zinc oxide, and zinc-based MOF, preferably zinc acetate, zinc chloride, zinc sulfate, and zinc nitrate, and more preferably zinc acetate.

[0043] The ligands of the zinc-based coordination composite catalyst are citric acid, ethylenediaminetetraacetic acid (EDTA), sodium salt (EDTA-2Na), sodium gluconate, and tartaric acid. d Citric acid and ethylenediaminetetraacetic acid (EDTA) are preferred; EDTA is more preferred.

[0044] The molar ratio of zinc to the ligand compound is 1-1.5, for example 1.1:1, 1.15:1, 1.2:1, 1.25:1, 1.3:1, 1.35:1, 1.4:1, 1.45:1, 1.5:1, etc., preferably 1.15-1.25.

[0045] In this invention, the preparation method of the zinc coordination composite catalyst is not particularly limited. Generally, a zinc compound is mixed with a ligand and stirred thoroughly at a certain temperature. Alternatively, methods from existing technologies can be used. Exemplarily, the preparation method of the zinc coordination composite catalyst includes the following steps:

[0046] (1) Add zinc compounds and ligands to ethylene glycol at a molar ratio of 1:1.2 and mix thoroughly.

[0047] (2) Stir at 50-220℃ for 0.5-10 hours.

[0048] (3) After the stirring reaction is complete, the product is named according to the selected zinc compound and ligand combination, following the rule of "Zinc compound name - ligand English / abbreviation" (if zinc acetate is preferred, it can be directly abbreviated as "Zinc - ligand English / abbreviation"). Specific naming examples are as follows:

[0049] Zinc acetate mixed with citric acid: Zinc-Citric Acid; Zinc acetate mixed with ethylenediaminetetraacetic acid: Zinc-EDTA; Zinc chloride mixed with sodium salt: Zinc chloride-EDTA-2Na; Zinc sulfate mixed with sodium gluconate: Zinc sulfate-Sodium Gluconate; Zinc nitrate combined with tartaric acid: Zinc nitrate-Tartaric Acid d .

[0050] In existing technologies, the core reason for the yellowing of PETG due to the use of zinc-based catalysts is that free Zn... 2+ It readily catalyzes the oxidative degradation of ester bonds to generate unsaturated carbonyl groups, or undergoes a change in its valence state (Zn). 2+ →Zn 0 ) forms colored impurities; in addition, Zn 2+The zinc hydroxyl salt generated by the reaction with trace amounts of water and alcohol in the polymerization system will also exacerbate the color development caused by thermo-oxidative aging.

[0051] This invention employs a zinc coordination composite catalyst, wherein the ligand and Zn 2+ The strong coordination effect can efficiently lock free zinc ions, forming a stable chelate that effectively reduces Zn. 2+ catalytic activity, reducing free Zn 2+ The catalytic degradation of ester bonds inhibits valence state changes and catalytic oxidation reactions, blocking the oxidation-color development pathway at its source. Experiments revealed that the stable complexes formed by the polydentate ligands and zinc ions affect the structure and properties of the polymerization products. When electron-donating groups are attached to the ligands, the coordination ability of zinc ions with monomers is enhanced, exhibiting a narrow molecular weight distribution, promoting the orderly arrangement of molecular chains, reducing intermolecular gaps, and decreasing free volume, thereby affecting the crystallinity and molecular regularity of the polymer. This further improves its barrier properties, reduces oil and fat permeability, and makes its performance more stable when exposed to more chemicals. Furthermore, the chelating agent ligands have good compatibility with PETG monomers and chain segments, do not introduce new impurities or odors, and the cost increase from ligand dosage is ≤3%, making it suitable for industrial scale-up.

[0052] In step S1 of this invention, the esterification reaction is carried out at a temperature of 220-270℃, such as 225℃, 230℃, 235℃, 240℃, 245℃, 250℃, 255℃, 260℃, 265℃, 270℃, etc., preferably 230-250℃, most preferably 240℃, and at a pressure of 0.2-0.3 MPaG, such as 0.21 MPaG, 0.22 MPaG, 0.23 MPaG, 0.24 MPaG. The reaction time is 2-6 hours, such as 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, etc., preferably 3-4 hours, and most preferably 3.5 hours. The reaction is terminated when the effluent reaches more than 90% of the theoretical value.

[0053] In step S2 of this invention, the pre-condensation reaction is carried out at a temperature of 240-280℃, such as 245℃, 250℃, 255℃, 260℃, 265℃, 270℃, 275℃, 280℃, etc., preferably 250-270℃, most preferably 260℃, at a pressure of 5-20 kPaA, such as 5 kPaA, 6 kPaA, 7 kPaA, 8 kPaA, 9 kPaA, 10 kPaA, 11 kPaA, 12 kPaA, 13 kPaA, 14 kPaA, 15 kPaA, 16 kPaA, 17 kPaA, 18 kPaA, 19 kPaA, etc., preferably 10-15 kPaA, at a time of 0.5-2 h, such as 0.6 h, 0.8 h, 1 h, 1.5 h, 1.8 h, 2 h, etc., preferably 40-60 min.

[0054] In step S3 of the present invention, the phosphoric acid antioxidant is a phosphoric acid compound, preferably one or more of phosphoric acid, phosphorous acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, triethyl phosphoacetate, tris(2,4-di-tert-butyl)phosphite (antioxidant 168), and tris(nonylphenol) phosphite (antioxidant TNP), more preferably phosphoric acid.

[0055] The amount of the phosphoric acid antioxidant is 10ppm-50ppm, such as 15ppm, 20ppm, 25ppm, 30ppm, 35ppm, 40ppm, 45ppm, 50ppm, etc., preferably 15-30ppm, based on the mass of terephthalic acid.

[0056] In step S3 of this invention, the final polycondensation reaction is carried out at a temperature of 250-290℃, such as 250℃, 255℃, 260℃, 265℃, 270℃, 275℃, 280℃, 285℃, etc., preferably 260-270℃; a pressure of 20-150 PaA, such as 30 PaA, 40 PaA, 50 PaA, 60 PaA, 70 PaA, 80 PaA, 90 PaA, 100 PaA, 110 PaA, 120 PaA, 130 PaA, 140 PaA, 150 PaA, etc., preferably 20-100 PaA; and a time of 1.5-5h, such as 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, etc., preferably 3-4h. The PETG resin melt is preferably granulated underwater to obtain PETG resin pellets.

[0057] The PETG polyester obtained in this invention has a weight-average molecular weight of 40,000 or more, for example, 45,000 or more, 50,000 or more, 40,000 to 100,000, preferably 40,000 to 50,000.

[0058] The PETG polyester described in this invention has a melt index of 4-12 g / 10 min at 250℃ and a load of 2.16 kg; an L value ≥ 80; an a value between -0.4 and 0.4; a b value < 3 (L value: brightness; a value: red-green hue; b value: yellow-blue hue); a light transmittance ≥ 89%; and a permeation rate ≤ 10 mg / (dm³). 2 • 10d), Tg temperature ≥ 79℃.

[0059] In this invention, a zinc-based coordination composite catalyst is used, and the introduction of ligands can affect the molecular structure of the polymer. Experiments show that zinc ions form coordinate bonds with the O atoms with lone pairs of electrons in the copolyester macromolecular chain. The enhanced physical crosslinking points and intermolecular interactions in the copolyester restrict chain segment movement, making it difficult for chains to slide against each other. More energy is required for chain segments to change their conformation through movement, thus increasing the glass transition temperature of the copolyester to some extent. Adding phosphate ester antioxidants before final shrinkage can decompose the hydroperoxides produced in the oxidation reaction, preventing them from further forming free radicals and thus interrupting the chain reaction of oxidative yellowing. It maintains stability at high temperatures, effectively inhibiting yellowing caused by thermal oxidation, especially in high-temperature processing such as extrusion and injection molding. It improves material stability by reducing oxidative degradation of PETG during long-term storage or use, extending the material's service life and appearance stability. It improves weather resistance by enhancing PETG's resistance to environmental factors such as light and humidity, reducing aging and yellowing problems caused by outdoor exposure or long-term use. It has good compatibility: antioxidants such as phosphate have good compatibility with PETG polyester, are not easily precipitated, and do not affect the material's transparency or processing performance.

[0060] In this invention, the use of zinc-based coordination composite catalysts combined with phosphate ester antioxidants can effectively solve the yellowing problem of PETG and comprehensively improve its stability and practicality.

[0061] Main raw material sources:

[0062] Isosorbide, reagent grade, Aladdin Reagent Co., Ltd.;

[0063] 2,2,4,4-Tetramethyl-1,3-cyclobutanediol, reagent grade, Aladdin Reagent Co., Ltd.;

[0064] Citric acid, reagent grade, Beijing Innocare Technology Co., Ltd.

[0065] Ethylenediaminetetraacetic acid (EDTA), reagent grade, Beijing Innocare Technology Co., Ltd.

[0066] Sodium salt (EDTA-2Na), reagent grade, Beijing Innocare Technology Co., Ltd.

[0067] Sodium gluconate, reagent grade, Sinopharm Chemical Reagent Co., Ltd.

[0068] Tartaric acid, reagent grade, Sinopharm Chemical Reagent Co., Ltd.

[0069] Phosphorous acid, reagent grade, Aladdin Reagent Co., Ltd.;

[0070] Phosphoric acid (85%), reagent grade, Aladdin Reagent Co., Ltd.

[0071] Trimethyl phosphate, reagent grade, Aladdin Reagent Co., Ltd.

[0072] Triethyl phosphate, reagent grade, Aladdin Reagent Co., Ltd.

[0073] Triphenyl phosphate, reagent grade, Aladdin Reagent Co., Ltd.

[0074] Terephthalic acid (PTA), industrial grade, Hengli Petrochemical Co., Ltd.

[0075] Neopentyl glycol (NPG), industrial grade, Wanhua Chemical Group Co., Ltd.

[0076] 1,4-Cyclohexanediethanol (CHDM), industrial grade, Kailin Chemical Co., Ltd.

[0077] Ethylene glycol (EG), industrial grade, China Petroleum & Chemical Corporation.

[0078] Main testing methods:

[0079] Color values: The L, a, b color system was used as the evaluation benchmark. In this system, L is the brightness factor, and a and b are the color measurements. b represents the yellow-blue balance, which is very important for polyester color; the lower the b value, the better the color. The copolyester material was injection molded into a 9cm long × 6cm wide × 3mm thick sample using an injection molding machine (Haitian Plastics Machinery Group Co., Ltd., MA250T). The color values ​​were automatically measured using a BYK Gardner Color35 automatic colorimeter.

[0080] Barrier properties: The permeability test method was adopted according to GB 4806.7-2023 "National Food Safety Standard for Plastic Materials and Products for Food Contact". A certain area of ​​PETG polyester sample was cut and wiped clean with a lint-free cloth. Simulant selection: 10% ethanol was used as the simulated food liquid. The sample was contacted with the 10% ethanol simulated food liquid and soaked at 40℃ for 10 days. After soaking, the ethanol simulated liquid was transferred to an evaporating dish and evaporated to dryness. Then, the mass of the residual substance was weighed, and the total migration amount (also called permeation rate) was calculated according to the formula. Migration amount (also called permeation rate) (mg / dm³) 2= Mass of migrating substance (mg) / Sample contact area (dm²) 2 The limit is ≤10 mg / dm³. 2 .

[0081] NMR: The composition of the copolymer was determined using a Bruker AV 600 NMR spectrometer. 10 mg of copolyester sample was dissolved in 0.7 ml of deuterated chloroform, and the chloroform solvent peak was determined to be 7.28 ppm.

[0082] Transmittance and haze testing: The copolyester material was injection molded into a sample with a length of 9cm × width of 6cm × thickness of 3mm using an injection molding machine (Haitian Plastics Machinery Group Co., Ltd., MA250T). The transmittance / haze tester (Shanghai Precision Instruments Co., Ltd., WGTS) was used for testing.

[0083] Glass transition temperature test: Differential scanning calorimetry was used for the test under a nitrogen atmosphere at a flow rate of 50 mL / min. During the test, the temperature was first increased to 240℃ at a rate of 20℃ / min and held at 240℃ for 2 min to remove the thermal history of the copolyester material. Then, the temperature was cooled to 30℃ at a rate of 20℃ / min and held at 30℃ for 2 min. The temperature was then increased to 240℃ at a rate of 20℃ / min. The glass transition temperature Tg of the copolyester material was calculated from the second heating curve.

[0084] Tensile property test: The copolyester material was injection molded into dumbbell-shaped strips with a width of 10mm and a height of 4mm using an injection molding machine (Haitian Plastics Machinery Group Co., Ltd., MA250T). The test was performed using a universal tensile testing machine, referring to standard ISO 527.

[0085] Intrinsic viscosity test: The intrinsic viscosity of the copolyester material was measured in a mixed solution of phenol and tetrachloroethane (mass ratio 3:2) at 25±0.1℃, referring to standard GB / T-14190-2017.

[0086] Preparation of composite catalysts

[0087] (1) Add zinc compounds and ligands to ethylene glycol at a molar ratio of 1:1.2 and mix thoroughly.

[0088] (2) Stir at 80℃ for 5 hours to obtain the product.

[0089] The product is named according to the selected combination of zinc compounds and ligands. Specific naming examples are as follows:

[0090] Zinc acetate mixed with citric acid: Zinc-Citric Acid; Zinc acetate mixed with ethylenediaminetetraacetic acid: Zinc-EDTA; Zinc chloride mixed with sodium salt: Zinc chloride-EDTA-2Na; Zinc sulfate mixed with sodium gluconate: Zinc sulfate-Sodium Gluconate; Zinc nitrate combined with tartaric acid: Zinc nitrate-Tartaric Acid d .

[0091] Example 1

[0092] In a 5L reactor equipped with a nitrogen pipeline, feed port, stirrer, vapor port, condenser, and thermometer, 27.1 mol of terephthalic acid, 9.14 mol of 1,4-cyclohexanediol, 28.8 mol of ethylene glycol, and 50 ppm of zinc-citric acid composite catalyst were added. Under high-purity nitrogen protection, the temperature was raised to 240°C, and the pressure was controlled at 0.26 MPaG. The esterification reaction was continued for 3 hours. After esterification, the reactor was heated to 260°C and gradually evacuated to 10 kPa for 40 minutes. Then, under nitrogen protection, 20 ppm of phosphoric acid was added, the reactor was heated to 265°C, and gradually evacuated to 40 PaA for polycondensation reaction for 3 hours to obtain polymer melt. After standing for 3 minutes, the melt was pressurized to 0.1 MPaG with nitrogen and pulled out from the bottom of the reactor. The melt was cooled in a water bath filled with room temperature water and then pelletized in a pelletizer to obtain the PETG copolyester material.

[0093] Example 2

[0094] In a 5L reactor equipped with a nitrogen pipeline, feed port, stirrer, vapor port, condenser, and thermometer, 27.1 mol of terephthalic acid, 8.39 mol of 1,4-cyclohexanediol, 26.84 mol of ethylene glycol, and 60 ppm of zinc chloride-EDTA-2Na composite catalyst were added. Under high-purity nitrogen protection, the reactor was heated to 245°C and the pressure was controlled at 0.27 MPaG for 2.9 h of continuous esterification. After esterification, the reactor was heated to 265°C and gradually evacuated to 15 kPa for 50 min. Then, under nitrogen protection, 25 ppm of phosphorous acid was added, the reactor was heated to 260°C, and gradually evacuated to 30 PaA for polycondensation reaction for 2.9 h to obtain polymer melt. After standing for 5 min, the melt was pressurized to 0.1 MPaG with nitrogen and pulled out from the bottom of the reactor. After cooling in a water bath filled with room temperature water, the melt was pelletized in a pelletizer to obtain the copolyester material.

[0095] Example 3

[0096] In a 5L reactor equipped with a nitrogen pipeline, feed port, stirrer, vapor port, condenser, and thermometer, 27.1 mol of terephthalic acid, 9.69 mol of neopentyl glycol, 30.96 mol of ethylene glycol, and 30 ppm of zinc-EDTA composite catalyst were added. Under high-purity nitrogen protection, the temperature was raised to 250°C, and the pressure was controlled at 0.29 MPaG. The esterification reaction was continued for 3.5 h. After esterification, the reactor was heated to 262°C and gradually evacuated to 20 kPa for 50 min. Then, under nitrogen protection, 10 ppm of trimethyl phosphate was added, the reactor was heated to 270°C, and gradually evacuated to 20 PaA for polycondensation reaction for 3.5 h to obtain polymer melt. After standing for 5 min, the melt was pressurized to 0.1 MPaG with nitrogen and pulled out from the bottom of the reactor. It was cooled in a water bath filled with room temperature water and then pelletized in a pelletizer to obtain the copolyester material.

[0097] Example 4

[0098] In a 5L reactor equipped with a nitrogen pipeline, feed port, stirrer, vapor port, condenser, and thermometer, 27.1 mol of terephthalic acid, 7.75 mol of neopentyl glycol, 24.77 mol of ethylene glycol, and 80 ppm of zinc sulfate-Sodium Gluconate composite catalyst were added. Under high-purity nitrogen protection, the temperature was raised to 235°C, and the pressure was controlled at 0.28 MPaG. The esterification reaction was continued for 2.8 h. After esterification, the reactor was heated to 258°C and gradually evacuated to 5 kPa for 40 min. Then, under nitrogen protection, 25 ppm of triethyl phosphate was added, the reactor was heated to 265°C, and gradually evacuated to 80 PaA for polycondensation reaction for 3 h to obtain polymer melt. After standing for 5 min, the melt was pressurized to 0.1 MPaG with nitrogen and pulled out from the bottom of the reactor. It was cooled in a water bath filled with room temperature water and then pelletized in a pelletizer to obtain the copolyester material.

[0099] Example 5

[0100] In a 5L reactor equipped with a nitrogen pipeline, feed port, stirrer, vapor port, condenser, and thermometer, 27.1 mol of terephthalic acid, 10.3 mol of isosorbide, 33.03 mol of ethylene glycol, and 100 ppm of zinc nitrate-tartaric acid composite catalyst were added. Under high-purity nitrogen protection, the reactor was heated to 260°C and the pressure was controlled at 0.25 MPaG for 2.5 h of continuous esterification. After esterification, the reactor was heated to 255°C and gradually evacuated to 10 kPa for 35 min. Then, under nitrogen protection, 30 ppm of phosphoric acid was added, the reactor was heated to 255°C, and gradually evacuated to 100 PaA for polycondensation reaction for 2.8 h to obtain polymer melt. After standing for 5 min, the melt was pressurized to 0.1 MPaG with nitrogen and pulled out from the bottom of the reactor. After cooling in a water bath filled with room temperature water, the melt was pelletized in a pelletizer to obtain the copolyester material.

[0101] Example 6

[0102] In a 5L reactor equipped with a nitrogen line, feed port, stirrer, vapor inlet, condenser, and thermometer, add 27.1 mol terephthalic acid, 9.14 mol 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 28.8 mol ethylene glycol, and 40 ppm zinc-citric acid. The acid composite catalyst was heated to 255°C under high-purity nitrogen protection, and the pressure was controlled at 0.26 MPaG for continuous esterification reaction for 3 hours. After esterification, the reactor was heated to 270°C and gradually evacuated to 10 kPa for 45 minutes. Then, 20 ppm of triphenyl phosphate was added under nitrogen protection, the reactor was heated to 270°C, and gradually evacuated to 90 PaA for polycondensation reaction for 3.2 hours to obtain polymer melt. After standing for 5 minutes, the melt was pressed with nitrogen to 0.1 MPaG and pulled out from the bottom of the reactor. It was cooled in a water tank filled with room temperature water and then entered a pelletizer for pelletizing to obtain the copolyester material.

[0103] Comparative Example 1

[0104] Compared with Example 1, the difference is that no zinc-based composite catalyst is added to the system, but antimony glycol is used for catalysis.

[0105] Comparative Example 2

[0106] Compared with Example 1, the difference is that no zinc-based composite catalyst is added to the system, but tetrabutyl titanate is used for catalysis.

[0107] Comparative Example 3

[0108] Compared with Example 1, the difference is that no zinc-based composite catalyst is added to the system, but dibutyltin oxide is used for catalysis.

[0109] Comparative Example 4

[0110] Compared with Example 1, the difference is that instead of adding a zinc-based composite catalyst to the system, germanium dioxide is used for catalysis.

[0111] Comparative Example 5

[0112] Compared with Example 1, the difference is that no zinc-based composite catalyst is added to the system, but only zinc acetate is used for catalysis.

[0113] The copolyester materials provided in Examples 1-6 and Comparative Examples 1-4, as well as the copolyesters contained therein, were tested according to the above method. The test results are shown in Table 1 below:

[0114] Table 1 Performance parameters of PETG copolyester

[0115]

[0116]

[0117] As shown in Table 1, the test data of the embodiments indicate that the light-colored, high-transparency PETG copolyester material prepared by the present invention has a TG temperature ≥ 79℃ and a permeability ≤ 10 mg / (dm³). 2 The product exhibits excellent transparency (≥49 MPa, ≥89% light transmittance, ≤1% haze), meeting the requirements of various applications. Compared to PETG products catalyzed by conventional catalysts, the light-colored, high-transparency PETG copolyester material of this application produces products with lower chroma, maintaining high transparency and brightness while meeting the requirements for food contact materials, making it safer and more environmentally friendly. The product prepared by this invention exhibits a clear and transparent appearance, along with higher Tg temperature, barrier properties, strong chemical resistance, and excellent impact resistance, increasing product competitiveness.

[0118] The applicant declares that the copolyester material, its preparation method, and its application are illustrated by the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a light-colored, high-transparency PETG polyester, characterized in that, Includes the following steps: S1. Terephthalic acid, ethylene glycol, polyol, and zinc-based coordination composite catalyst are mixed in proportion and heated to carry out a polymerization reaction to obtain oligomers. S2. Continue the polymerization reaction by raising the temperature and reducing the pressure to obtain the prepolymer. S3. Under nitrogen protection, phosphoric acid antioxidants are added and the temperature is raised to continue the polymerization reaction, resulting in light-colored, high-transparency PETG polyester.

2. The preparation method according to claim 1, characterized in that, The polyol mentioned in S1 is one or more of 1,4-cyclohexanediol, neopentyl glycol, isosorbide, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, spirocyclodiol, and phenylethylene glycol, preferably 1,4-cyclohexanediol and neopentyl glycol, and more preferably 1,4-cyclohexanediol. Preferably, the molar ratio of the polyol to terephthalic acid is 1.1-1.8, more preferably 1.3-1.

5.

3. The preparation method according to claim 1, characterized in that, The zinc-based coordination composite catalyst described in S1 is selected from one or more of the following: zinc-Citric Acid composite catalyst, zinc-EDTA composite catalyst, zinc-EDTA-2Na composite catalyst, zinc-SodiumGluconate composite catalyst, and zinc-Tartaric Acid composite catalyst. Preferably, the amount of the zinc-based coordination composite catalyst is 30-200 ppm, more preferably 40-100 ppm, based on the mass of terephthalic acid.

4. The preparation method according to claim 3, characterized in that, The zinc in the zinc-based coordination composite catalyst in S1 is derived from zinc compounds, preferably one or more of zinc acetate, zinc chloride, zinc sulfate, zinc nitrate, zinc trifluoroacetate, zinc oxide, zinc lactate, zinc trifluoromethanesulfonate, zinc acetylacetone, nano zinc oxide, and zinc-based MOF, and more preferably zinc acetate, zinc chloride, zinc sulfate, and zinc nitrate.

5. The preparation method according to claim 3 or 4, characterized in that, The ligands of the zinc-based coordination composite catalyst in S1 are citric acid, ethylenediaminetetraacetic acid (EDTA), sodium salt (EDTA-2Na), sodium gluconate, and tartaric acid, preferably one or more of citric acid and ethylenediaminetetraacetic acid (EDTA).

6. The preparation method according to any one of claims 3-5, characterized in that, The molar ratio of zinc to ligand is 1-1.5, preferably 1.15-1.

25.

7. The preparation method according to claim 1, characterized in that, The polymerization reaction described in S1 has a reaction temperature of 220-270℃ and a reaction time of 2-6h.

8. The preparation method according to claim 1, characterized in that, The polymerization reaction described in S2 has a reaction temperature of 240-280℃, a reaction time of 0.5-2h, and a vacuum pressure of 5-20KPa.

9. The preparation method according to claim 1, characterized in that, In S3, the phosphoric acid antioxidant is selected from one or more of phosphoric acid, phosphorous acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, triethyl phosphoacetate, tris(2,4-di-tert-butyl)phosphite (antioxidant 168), and tris(nonylphenol) phosphite (antioxidant TNP), with phosphoric acid being more preferred; Preferably, the amount of the phosphoric acid antioxidant is 10ppm-50ppm, based on the mass of terephthalic acid; More preferably, in S3, the reaction temperature is 250-290℃, the reaction time is 2.5-5h, and the vacuum pressure is 20-150Pa.

10. The light-colored, high-transparency PETG polyester prepared by the method according to any one of claims 1-9, characterized in that, The PETG polyester has a b-value ≤ 3, light transmittance ≥ 89%, and permeation rate ≤ 10 mg / (dm³). 2 ·10d).

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