Process for the preparation of a petg copolyester
By optimizing the esterification and polycondensation reaction conditions in the PETG synthesis process and using acetate catalysts and germanium dioxide, the problems of thermal degradation and color in PETG synthesis were solved, and a PETG copolyester with high transparency and low color was prepared, thus improving product performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- PETROCHINA CO LTD
- Filing Date
- 2024-12-26
- Publication Date
- 2026-06-26
Smart Images
Figure BDA0005212150850000111 
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of copolyester preparation technology, and relates to a method for preparing PETG copolyester. Background Technology
[0002] PETG copolyester is a copolyester material primarily composed of terephthalic acid (PTA), ethylene glycol (EG), and 1,4-cyclohexanediethanol (CHDM). Compared to traditional PET, PETG, by introducing CHDM comonomers, imparts higher transparency, toughness, and low-melting-point processing characteristics, making it suitable for various complex processing techniques such as extrusion, injection molding, blow molding, and thermoforming.
[0003] PETG, due to its excellent physical properties, environmental characteristics, and biocompatibility, has wide applications in medical devices, food packaging, electronics, and household goods. In recent years, with the increasing promotion of green and sustainable development concepts, PETG has received significant attention due to its recyclability and environmentally friendly production processes. Domestic and international research institutions and companies are committed to continuously improving PETG product performance and reducing production costs by optimizing catalysts, adjusting polymerization processes, and controlling comonomer ratios to meet the growing market demand and the challenges of international competition.
[0004] As is well known, the b-value of polyester materials is an important indicator of polyester quality. A higher b-value indicates a more yellow polyester color, directly affecting a series of properties such as color and hue. Currently, in the synthesis of PETG products, due to the high boiling point of CHDM diol, the removal process often requires high temperature and high vacuum, as well as a long reaction time. Under high temperature and long reaction conditions, thermal degradation of polyester can occur, leading to reduced viscosity, loss of transparency, and the formation of high color intensity. Furthermore, PETG synthesis primarily uses titanium-based catalysts, which significantly impact the product's color. Currently, according to global literature reports, PETG obtained using titanium-based catalyst systems, before adjustment with colorants or masterbatches, has b-values concentrated between 2.0 and 8.0.
[0005] Patent CN114891189B discloses a method for preparing low-color PETG copolyester. The preparation process utilizes one or more esterification catalysts selected from zinc acetate, cobalt acetate, aluminum acetate, magnesium acetate, copper acetate, manganese acetate, and calcium acetate; one or more primary antioxidants selected from 2,6-dimethylphenol, 2,6-di-tert-butylphenol, and 2-tert-butyl-6-methylphenol; and one or more auxiliary antioxidants selected from trimethyl phosphite, triethyl phosphite, triisopropyl phosphite, triphenyl phosphite, and tri-m-toluene phosphite. During the polycondensation process, one or more polymerization catalysts selected from tetraethyl titanate, tetraisopropyl titanate, and tetra-n-butyl titanate are added. The preparation process controls the esterification reaction activity by adding highly efficient acetate-based esterification catalysts and reduces the yellowing phenomenon caused by titanate-based polycondensation catalysts during the polycondensation reaction. Simultaneously, the addition of primary and auxiliary antioxidants helps to reduce the impact of side reactions in the later stages of polycondensation and at high temperatures. However, the titanate polycondensation catalyst added in this preparation method has not reached the minimum level and cannot completely eliminate the yellowing problem. Although the addition of antioxidants and stabilizers can reduce the impact of side reactions in the later stage of polycondensation and at high temperatures, it will cause several adverse effects such as additive migration, thermal degradation by-products, low material compatibility, and decreased processing performance, thereby affecting the post-processing and use value of the product. Summary of the Invention
[0006] To overcome the shortcomings of the prior art, the present invention provides a method for preparing PETG copolyester. The method of the present invention can prepare PETG copolyester products with high viscosity and high transmittance, and low color value, having an intrinsic viscosity of 0.78 dl / g or higher, a light transmittance of 93.00% or higher, an L value of 70 or higher, and a b value of -0.5 or lower.
[0007] The above-mentioned objective of this invention is achieved through the following technical solution:
[0008] A method for preparing PETG copolyester, wherein the raw materials terephthalic acid, ethylene glycol, and CHDM undergo esterification and polycondensation reactions in an esterification catalyst and a polycondensation catalyst system to obtain the polymer PETG copolyester; wherein the molar ratio of the raw materials terephthalic acid, ethylene glycol, and CHDM is 1-1.05:0.9-1.15:0.2-0.52.
[0009] Furthermore, the esterification catalyst in the esterification reaction is any one or a combination of two or more of cobalt acetate, manganese acetate, zinc acetate, magnesium acetate, and copper acetate, and its addition amount is 0 to 199 ppm of the amount of terephthalic acid added.
[0010] Furthermore, the polycondensation catalyst in the polycondensation reaction is germanium dioxide, and its addition amount is 20 to 130 ppm of the amount of terephthalic acid added.
[0011] The specific preparation steps of the above-mentioned PETG copolyester preparation method are as follows:
[0012] S1. Esterification reaction;
[0013] Terephthalic acid, ethylene glycol, and CHDM are added to the esterification reactor at a molar ratio of 1:0.9-1.1:0.2-0.5. At the same time, the esterification catalyst and polycondensation catalyst used in the catalytic stabilization system are added to the esterification reactor. The esterification reactor is stirred at a given stirring rate. When the distillate from the fractionation tower reaches the set value, the esterification reaction is considered to be completed. The connecting valve between the esterification reactor and the polycondensation reactor is opened, and nitrogen gas is introduced to completely transfer the esterified material in the esterification reactor to the polycondensation reactor.
[0014] S2. Condensation polymerization;
[0015] When the temperature inside the polycondensation reactor reaches above 250°C, close the connecting valve between the esterification reactor and the polycondensation reactor. Vacuum the polycondensation reactor containing the esterification material in step S1. At this point, the low-vacuum polycondensation reaction stage begins. After vacuuming at a uniform speed for 10–60 minutes, reduce the pressure inside the polycondensation reactor to 30–90 Pa and then enter the high-vacuum polycondensation reaction stage. Finally, control the polycondensation temperature at 275–280°C. When the stirring power of the polycondensation reactor reaches 0.25–0.30 kW, the reaction is considered complete, and the polymer melt is obtained.
[0016] S3. Dicing
[0017] The polymer melt obtained in step S2 is immersed in a water tank containing cooling water at 20°C and pelletized using a casting strip to finally obtain a PETG copolyester material with high viscosity, high transparency, and low color value.
[0018] Furthermore, in step S1, the stirring rate of the esterification reactor is set to 60–120 r / min.
[0019] Furthermore, in step S1, the esterification reaction is carried out at a temperature of 220–260°C, a pressure of 0.1–0.35 MPa, and a reaction time of 90–178 minutes.
[0020] Furthermore, the esterification reaction is considered complete when the distillate from the fractionation tower reaches a set value, specifically: the esterification reaction is considered complete when the distillate from the fractionation tower reaches 80% to 90% of the theoretical output water. Preferably, the esterification reaction is considered complete when the distillate from the fractionation tower reaches 80% of the theoretical output water.
[0021] Furthermore, in step S2, the polycondensation reaction is in a low-vacuum polycondensation stage, with a reaction temperature of 220–265°C, a reaction pressure of 0–0.1 MPa (gauge pressure), and a reaction time of 10–60 minutes.
[0022] Furthermore, in step S2, the high-vacuum polycondensation reaction stage, the reaction temperature is 250–290°C, the vacuum degree of the reaction system is 30–90 Pa, and the reaction time is 70–180 minutes.
[0023] The PETG copolyester prepared by the above-mentioned method has an intrinsic viscosity of ≥0.78 dl / g, a light transmittance of ≥93.00%, an L value of ≥70, a b value of ≤-0.5, and exhibits characteristics of high viscosity, high transmittance, and low color value.
[0024] The beneficial effects of this invention compared to the prior art are:
[0025] This invention provides a method for preparing PETG copolyester, which uses a simpler catalytic stabilization system, reducing the amount of esterification and polycondensation catalysts used. It avoids the use of traditional titanate catalysts, thus preventing the yellowing of the product caused by their addition. Furthermore, it eliminates the need for antioxidants and stabilizers specific to titanate catalysts, preventing the decrease in thermal stability caused by post-processing such as injection molding and extrusion. This effectively avoids several adverse effects resulting from the addition of primary and secondary antioxidants, such as additive migration, thermal degradation byproducts, low material compatibility, and decreased processing performance. It also eliminates the need for secondary color adjustments using colorants, brighteners, and other additives, minimizing the impact of raw materials and additives on the appearance and thermal stability of the chips. The final product exhibits a high viscosity, high transmittance, and low color value, with an intrinsic viscosity above 0.78 dl / g, a light transmittance above 93.00%, an L value above 70, and a b value below -0.5. Attached Figure Description
[0026] Figure 1 This is the NMR spectrum of the PETG copolyester prepared in Example 1 of this invention.
[0027] Figure 2 This is the infrared spectrum of the PETG copolyester prepared in Example 1 of this invention. Detailed Implementation
[0028] The present invention is described in detail below through specific embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used are all available commercially. The stainless steel reaction vessel mentioned in the embodiments is a commercially available product.
[0029] Example 1
[0030] A method for preparing PETG copolyester involves adding 1577 g of terephthalic acid, 417.6 g of 1,4-cyclohexanediethanol (CHDM), 551.8 g of ethylene glycol, 0.19 g of cobalt acetate, 0.05 g of manganese acetate, and 0.15 g of germanium dioxide to a 5L stainless steel reactor equipped with a nitrogen inlet, feed port, discharge port, a fractionating column, two condensers, and a stirrer. The esterification reaction is carried out at a temperature of 220–260 °C, with a final esterification temperature of 258 °C, a reaction pressure of 0.20–0.25 MPa, and a reaction time of 180 minutes. After the esterification reaction, 0.22 g of trimethyl phosphate is added to the system to initiate a polycondensation reaction. The low-vacuum stage polycondensation reaction temperature was 250–260℃, the reaction pressure was 0–0.1 MPa, and the reaction time was 20 minutes. The high-vacuum stage polycondensation reaction temperature was 270–290℃, the final polycondensation temperature was 285℃, the vacuum degree of the reaction system was 50–100 Pa, and the reaction time was 120 minutes. The final product was a PETG copolyester polymer (obtained through…). Figure 1 and Figure 2 (This was confirmed by NMR and IR spectra). The properties of the obtained polymer were determined. The results are shown in Table 1.
[0031] Example 2
[0032] A method for preparing PETG copolyester involves adding 1525.5 g of terephthalic acid, 378.7 g of 1,4-cyclohexanediethanol (CHDM), 521.3 g of ethylene glycol, 0.152 g of cobalt acetate, 0.013 g of manganese acetate, and 0.106 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0033] Example 3
[0034] A method for preparing PETG copolyester involves adding 1522.2 g of terephthalic acid, 401.1 g of 1,4-cyclohexanediethanol (CHDM), 522.5 g of ethylene glycol, 0.162 g of cobalt acetate, 0.017 g of manganese acetate, and 0.115 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0035] Example 4
[0036] A method for preparing PETG copolyester involves adding 1511.2 g of terephthalic acid, 432.6 g of 1,4-cyclohexanediethanol (CHDM), 558.5 g of ethylene glycol, 0.167 g of cobalt acetate, 0.022 g of manganese acetate, and 0.124 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0037] Example 5
[0038] A method for preparing PETG copolyester involves adding 1505.5 g of terephthalic acid, 460.7 g of 1,4-cyclohexanediethanol (CHDM), 576.6 g of ethylene glycol, 0.176 g of cobalt acetate, 0.027 g of manganese acetate, and 0.132 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0039] Example 6
[0040] A method for preparing PETG copolyester involves adding 1522.1 g of terephthalic acid, 477.4 g of 1,4-cyclohexanediethanol (CHDM), 592.2 g of ethylene glycol, 0.182 g of cobalt acetate, 0.033 g of manganese acetate, and 0.143 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0041] Example 7
[0042] A method for preparing PETG copolyester involves adding 1533.1 g of terephthalic acid, 504 g of 1,4-cyclohexanediethanol (CHDM), 607.6 g of ethylene glycol, 0.190 g of cobalt acetate, 0.038 g of manganese acetate, and 0.156 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0043] Example 8
[0044] A method for preparing PETG copolyester involves adding 1513.2 g of terephthalic acid, 522.6 g of 1,4-cyclohexanediethanol (CHDM), 608.9 g of ethylene glycol, 0.197 g of cobalt acetate, 0.042 g of manganese acetate, and 0.167 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0045] Example 9
[0046] A method for preparing PETG copolyester involves adding 1515.3 g of terephthalic acid, 560.3 g of 1,4-cyclohexanediethanol (CHDM), 610.3 g of ethylene glycol, 0.202 g of cobalt acetate, 0.046 g of manganese acetate, and 0.175 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0047] Example 10
[0048] A method for preparing PETG copolyester involves adding 1533.5 g of terephthalic acid, 590.1 g of 1,4-cyclohexanediethanol (CHDM), 611.5 g of ethylene glycol, 0.212 g of cobalt acetate, 0.049 g of manganese acetate, and 0.180 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0049] Example 11
[0050] A method for preparing PETG copolyester involves adding 1512.4 g of terephthalic acid, 620.4 g of 1,4-cyclohexanediethanol (CHDM), 612.6 g of ethylene glycol, 0.221 g of cobalt acetate, 0.050 g of manganese acetate, and 0.188 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0051] Example 12
[0052] A method for preparing PETG copolyester involves adding 1507.7 g of terephthalic acid, 650.7 g of 1,4-cyclohexanediethanol (CHDM), 614.5 g of ethylene glycol, 0.231 g of cobalt acetate, 0.052 g of manganese acetate, and 0.196 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0053] Example 13
[0054] A method for preparing PETG copolyester involves adding 1983.15 g of terephthalic acid, 492.31 g of 1,4-cyclohexanediethanol (CHDM), 677.69 g of ethylene glycol, 0.198 g of cobalt acetate, 0.017 g of manganese acetate, and 0.138 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0055] Example 14
[0056] A method for preparing PETG copolyester involves adding 1978.86 g of terephthalic acid, 521.43 g of 1,4-cyclohexanediethanol (CHDM), 679.25 g of ethylene glycol, 0.211 g of cobalt acetate, 0.022 g of manganese acetate, and 0.150 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0057] Example 15
[0058] A method for preparing PETG copolyester involves adding 1964.56 g of terephthalic acid, 562.38 g of 1,4-cyclohexanediethanol (CHDM), 726.05 g of ethylene glycol, 0.217 g of cobalt acetate, 0.029 g of manganese acetate, and 0.161 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0059] Example 16
[0060] A method for preparing PETG copolyester involves adding 1957.15 g of terephthalic acid, 598.91 g of 1,4-cyclohexanediethanol (CHDM), 749.58 g of ethylene glycol, 0.229 g of cobalt acetate, 0.035 g of manganese acetate, and 0.172 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0061] Example 17
[0062] A method for preparing PETG copolyester involves adding 1978.73 g of terephthalic acid, 620.62 g of 1,4-cyclohexanediethanol (CHDM), 769.86 g of ethylene glycol, 0.237 g of cobalt acetate, 0.043 g of manganese acetate, and 0.186 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0063] Example 18
[0064] A method for preparing PETG copolyester involves adding 1993.03 g of terephthalic acid, 655.20 g of 1,4-cyclohexanediethanol (CHDM), 789.88 g of ethylene glycol, 0.247 g of cobalt acetate, 0.049 g of manganese acetate, and 0.203 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0065] Example 19
[0066] A method for preparing PETG copolyester involves adding 1967.16 g of terephthalic acid, 679.38 g of 1,4-cyclohexanediethanol (CHDM), 791.57 g of ethylene glycol, 0.256 g of cobalt acetate, 0.055 g of manganese acetate, and 0.217 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0067] Example 20
[0068] A method for preparing PETG copolyester involves adding 1969.89 g of terephthalic acid, 728.39 g of 1,4-cyclohexanediethanol (CHDM), 793.39 g of ethylene glycol, 0.263 g of cobalt acetate, 0.060 g of manganese acetate, and 0.228 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0069] Example 21
[0070] A method for preparing PETG copolyester involves adding 1993.55 g of terephthalic acid, 767.13 g of 1,4-cyclohexanediethanol (CHDM), 793.39 g of ethylene glycol, 0.276 g of cobalt acetate, 0.064 g of manganese acetate, and 0.234 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0071] Example 22
[0072] A method for preparing PETG copolyester involves adding 1966.12 g of terephthalic acid, 796.38 g of 1,4-cyclohexanediethanol (CHDM), 806.52 g of ethylene glycol, 0.287 g of cobalt acetate, 0.065 g of manganese acetate, and 0.244 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0073] Example 23
[0074] A method for preparing PETG copolyester involves adding 1960.01 g of terephthalic acid, 845.91 g of 1,4-cyclohexanediethanol (CHDM), 798.85 g of ethylene glycol, 0.300 g of cobalt acetate, 0.068 g of manganese acetate, and 0.255 g of germanium dioxide to a stainless steel reactor. Other steps are the same as in Example 1. The properties of the obtained polymer were measured. The results are shown in Table 1.
[0075] Comparative Example 1
[0076] 3.32 kg of terephthalic acid, 1.40 kg of ethylene glycol, and 1.08 kg of CHDM (total glycol excess 50 mol%) were added to an esterification reactor. 1.0 g of manganese acetate and 0.6 g of calcium acetate were added. After nitrogen purging, the temperature was raised to 240 °C, and timing was started. The pressure was controlled at 0–0.5 MPaA, and the stirring speed at 200 rpm. After 1 hour of reaction, the output was 600 g. The reaction solution was transferred to a pre-polymerization reactor via a gear pump, and 0.2 g of tetrabutyl titanate was added simultaneously. The temperature was controlled at 220–230 °C, the pressure at 40–50 kPaA, and the stirring speed at 50 rpm. After 2 hours of reaction, the output was 500 g. The reaction solution was transferred to a post-condensation packed tower via a gear pump, and simultaneously 0.45 g of a mixture of triphenyl phosphate and triethyl phosphate, 0.3 g of 2,6-dimethylphenol, and 0.2 g of trimethyl phosphite were added. The temperature was controlled at 270–290 °C, the pressure at 30–90 Pa, and the reaction time at 0.5 h. The final product was discharged via a gear pump, transferred to water for rapid cooling, and pelletized. Infrared and nuclear magnetic resonance (NMR) analysis confirmed the product to be PETG polyester, with an intrinsic viscosity of 0.77 dL / g and a colorimetric b-value of -0.99. The results are shown in Table 1.
[0077] Table 1 Performance Indicators of Comparative Examples and Embodiments
[0078]
[0079]
[0080] The intrinsic viscosity of the copolyester chips prepared in Comparative Example 1 is lower than that of the copolyester chips prepared in Examples 1-23 of this invention. The b-value of the copolyester chips prepared in this invention can reach as low as -1.5, showing significantly superior performance. Examples 1-23 use a catalytic stabilization system with simpler components than Comparative Example 1, and no antioxidants, stabilizers, or titanate condensation catalysts are added. The L-value and transmittance of the copolyester chips prepared in this invention are significantly better than those of the comparative examples and existing technologies.
[0081] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.
Claims
1. A method for preparing PETG copolyester, characterized in that, The raw materials terephthalic acid, ethylene glycol, and CHDM undergo esterification and polycondensation reactions in an esterification catalyst and a polycondensation catalyst system to obtain the polymer PETG copolyester; wherein the molar ratio of the raw materials terephthalic acid, ethylene glycol, and CHDM is 1~1.05:0.9~1.15:0.2~0.
52.
2. The method for preparing PETG copolyester as described in claim 1, characterized in that, The esterification catalyst in the esterification reaction is any one or a combination of two or more of cobalt acetate, manganese acetate, zinc acetate, magnesium acetate, and copper acetate, and its addition amount is 0 to 199 ppm of the amount of terephthalic acid added.
3. The method for preparing PETG copolyester as described in claim 1, characterized in that, The polycondensation catalyst in the polycondensation reaction is germanium dioxide, and its addition amount is 20 to 130 ppm of the amount of terephthalic acid added.
4. The method for preparing PETG copolyester as described in claim 1, characterized in that, The specific preparation steps are as follows: S1. Esterification reaction; Terephthalic acid, ethylene glycol, and CHDM are added to the esterification reactor at a molar ratio of 1:0.9-1.1:0.2-0.
5. At the same time, the esterification catalyst and polycondensation catalyst used in the catalytic stabilization system are added to the esterification reactor. The esterification reactor is stirred at a given stirring rate. When the distillate from the fractionation tower reaches the set value, the esterification reaction is considered to be completed. The connecting valve between the esterification reactor and the polycondensation reactor is opened, and nitrogen gas is introduced to completely transfer the esterified material in the esterification reactor to the polycondensation reactor. S2. Condensation polymerization; When the temperature inside the polycondensation reactor reaches above 250°C, close the connecting valve between the esterification reactor and the polycondensation reactor. Vacuum the polycondensation reactor containing the esterification material in step S1. At this point, the low-vacuum polycondensation reaction stage begins. After vacuuming at a uniform speed for 10–60 minutes, reduce the pressure inside the polycondensation reactor to 30–90 Pa and then enter the high-vacuum polycondensation reaction stage. Finally, control the polycondensation temperature at 275–280°C. When the stirring power of the polycondensation reactor reaches 0.25–0.30 kW, the reaction is considered complete, and the polymer melt is obtained. S3. Dicing The polymer melt obtained in step S2 is immersed in a water bath containing 20°C cooling water and pelletized using a casting strip to finally obtain a high-viscosity, high-transparency, and low-color-value PETG copolyester material.
5. The method for preparing PETG copolyester as described in claim 4, characterized in that, In step S1, the stirring rate of the esterification reactor is 60–120 r / min.
6. The method for preparing PETG copolyester as described in claim 4, characterized in that, In step S1, the esterification reaction is carried out at a temperature of 220–260 °C and a pressure of 0.1–0.35 MPa.
7. The method for preparing PETG copolyester as described in claim 4, characterized in that, In step S1, the esterification reaction takes 90 to 178 minutes.
8. The method for preparing PETG copolyester as described in claim 4, characterized in that, In step S2, the polycondensation reaction is in a low-vacuum polycondensation stage, with a reaction temperature of 220–265°C and a reaction pressure of 0–0.1 MPa.
9. The method for preparing PETG copolyester as described in claim 4, characterized in that, In step S2, the polycondensation reaction is a low-vacuum polycondensation reaction stage, and the reaction time is 10 to 60 minutes.
10. The method for preparing PETG copolyester as described in claim 4, characterized in that, In step S2, the high-vacuum polycondensation reaction stage, the reaction temperature is 250–290℃, the vacuum degree of the reaction system is 30–90 Pa, and the reaction time is 70–180 minutes.
11. A method for preparing PETG copolyester according to any one of claims 1-10, characterized in that, The PETG copolyester prepared by the preparation method has an intrinsic viscosity of ≥0.78 dl / g, a light transmittance of ≥93.00%, an L value of ≥70, and a b value of ≤0.5.