Highly transparent, high brightness and neutral tone co-polyester and method for making the same

Abstract

This invention relates to the technical field of copolyester preparation, and discloses a highly transparent, high-brightness, and neutral-toned copolyester and its preparation method. The preparation method includes the following steps: esterification reaction of terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol; after complete esterification, addition of a color-correcting agent and other auxiliaries for polycondensation reaction to obtain the copolyester; wherein the color-correcting agent includes color-correcting agent I and color-correcting agent II, color-correcting agent I being one or more of cobalt acetate and cobalt acetate tetrahydrate, and color-correcting agent II being dodecyl sulfate. This invention uses cobalt salt and dodecyl sulfate as a compound color-correcting agent, added together with other auxiliaries in the polycondensation stage. The complexation effect of dodecyl sulfate and cobalt salt can stabilize the catalytic activity of cobalt ions, reducing the b-value of the copolyester chips while maintaining high brightness, thus preparing a highly transparent, high-brightness, and neutral-toned copolyester.

Description

Technical Field

[0001] This invention relates to the technical field of copolyester preparation, and in particular to a highly transparent, high-brightness, and neutral-toned copolyester and its preparation method. Background Technology

[0002] Polyethylene terephthalate-1,4-cyclohexanediethanol (PETG) is a random copolyester obtained by terpolymerization of terephthalic acid (PTA), ethylene glycol (EG), and 1,4-cyclohexanediethanol (CHDM). Compared to traditional polyethylene terephthalate (PET), PETG copolyester contains a third monomer, CHDM, which effectively improves the copolyester's resistance to chemical solvents and transparency, further mitigating stress whitening. The physicochemical properties of PETG copolyester vary with the amount of CHDM added. As the amount of CHDM increases, the melting point of the copolyester decreases, its crystallinity weakens, and its glass transition temperature increases, ultimately forming a non-crystallizable amorphous copolyester.

[0003] PETG possesses high toughness and impact strength, making it a viable alternative to lower-performance polymethyl methacrylate (PMMA). As a heat-shrinkable film, it offers good printability, food safety, and excellent oxygen and carbon dioxide barrier properties. PETG also boasts excellent environmental performance; waste is recyclable, and complete incineration yields water and carbon dioxide. Furthermore, its low molding temperature and short molding cycle allow for processing via injection molding, blow molding, extrusion, and calendering, leading to its widespread application.

[0004] As the usage of PETG increases year by year, downstream markets are also raising their requirements for PETG's transparency, hue, and viscosity. In response to these demands, polyester researchers have offered corresponding solutions from two aspects: the polymerization and blending modification of PETG polyesters.

[0005] Chinese invention patent CN105153651A discloses a method for preparing optical-grade PETG high-transparency plates. Optical-grade PETG is prepared by blending PETG resin with brighteners, ultraviolet absorbers, antioxidants, anti-yellowing agents and other additives. However, it involves secondary processing, and the number of additives is large, which significantly increases the cost.

[0006] Chinese invention patent CN1440993A discloses a method for preparing a copolyester of terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol that exhibits a neutral hue, high transparency, and increased brightness. The method improves the hue of the polyester by adding inorganic or organic toners before the polycondensation stage. However, the addition of toners can severely affect the brightness of PETG. The patent only involves the b-value parameter and lacks data on the brightness (L-value) of the slices.

[0007] Chinese invention patent with publication number CN114891189A discloses a method for preparing low-color PETG copolyester. By introducing an acetate catalyst, the amount of titanium catalyst is reduced, thus reducing the probability of polymer yellowing. However, the introduction of acetate will reduce the brightness and graying of the chips, affecting the gloss of injection molded products and thus affecting the texture of thick-walled PETG products. Summary of the Invention

[0008] To address the technical problems of copolyesters turning yellow and dark after polymerization and becoming yellow and brittle during processing, this invention provides a highly transparent, high-brightness, and neutral-toned copolyester and its preparation method. By using cobalt acetate and dodecyl sulfate as compound colorants, a highly transparent, high-brightness, and neutral-toned copolyester is obtained.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a highly transparent, high-brightness, and neutral-toned copolyester, comprising the following steps: esterifying terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol; after complete esterification, adding a color-correcting agent and other auxiliaries to perform a polycondensation reaction to obtain the copolyester; wherein the color-correcting agent comprises color-correcting agent I and color-correcting agent II, color-correcting agent I being one or more of cobalt acetate and cobalt acetate tetrahydrate, and color-correcting agent II being dodecyl sulfate.

[0011] This invention uses cobalt acetate and dodecyl sulfate as compound colorants. By adding them to the polycondensation reaction, a copolyester with high transparency, high brightness and neutral hue can be prepared. Furthermore, the copolyester has good processing performance, and the processed product still maintains high transparency and good hue, with minimal change in intrinsic viscosity.

[0012] Cobalt acetate is a commonly used colorant that can reduce the yellow hue of sections. However, it also makes sections appear darker and grayer by reducing their b-value. Therefore, the amount of cobalt acetate added needs to be strictly controlled.

[0013] Dodecyl sulfate is an organic compound, readily soluble in water, with detergency and emulsifying properties. It is a commonly used anionic surfactant with good biodegradability. Experiments have shown that cobalt acetate and dodecyl sulfate exhibit good solubility in polyester prepolymer melts. Furthermore, dodecyl sulfate and cobalt ions can form cobalt chelates through complexation, stabilizing the catalytic activity and color-correcting effect of cobalt ions, resulting in a better color of the copolyester. This also demonstrates good stability during processing, maintaining the mechanical properties of the processed product while preserving its good color.

[0014] Preferably, the amount of cobalt added in the color-correcting agent I is 2 to 20 ppm of the copolyester mass.

[0015] Preferably, the color-correcting agent II is one or more of sodium dodecyl sulfate and potassium dodecyl sulfate, wherein the amount of the metal element added accounts for 1 to 100 ppm of the copolyester mass.

[0016] Adding excessive amounts of dodecyl sulfate will cause the slices to turn yellow and dark.

[0017] Preferably, the molar ratio of the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol to the molar amount of terephthalic acid is 1.05 to 4:1; and the molar ratio of the 1,4-cyclohexanediethanol to the molar amount of terephthalic acid is 0.3:1.

[0018] The CHDM content in PETG, which has a large commercial demand, is usually around 30%.

[0019] Preferably, the esterification reaction is carried out at 220–260°C and 0–150 kPa nitrogen pressure for 2–4 hours.

[0020] Preferably, the polycondensation reaction is carried out in a vacuum environment at 265–285°C and below 100 Pa for 1–4 hours.

[0021] Preferably, the other additives include catalysts, stabilizers, and antioxidants.

[0022] Preferably, the catalyst is one or more of tetrabutyl titanate, nano-titanium dioxide, and titanium glycol, wherein the amount of titanium added accounts for 4 to 40 ppm of the copolyester mass.

[0023] Preferably, the stabilizer is one or more of phosphoric acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, trimethyl phosphite, triphenyl phosphite, and triethyl phosphonoacetate, wherein the amount of phosphorus added accounts for 5 to 80 ppm of the copolyester mass; the antioxidant is one or more of pentaerythritol tetrakis[-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris[2,4-di-tert-butylphenyl]phosphite, and pentaerythritol dioctadecanyl phosphite, wherein the amount of antioxidant added accounts for 50 to 500 ppm of the copolyester mass.

[0024] Secondly, the present invention also provides a highly transparent, high-brightness, and neutral-toned copolyester prepared by the above-mentioned preparation method.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The complexation of dodecyl sulfate and cobalt salt stabilizes the catalytic activity and color-tuning effect of cobalt ions, and has high brightness while reducing the b value of copolyester chips.

[0027] (2) Under the synergistic effect of dodecyl sulfate, cobalt salt and antioxidant, the processed copolyester still maintains high transparency, high brightness and neutral color tone, low intrinsic viscosity, good heat resistance, which is conducive to maintaining the mechanical properties of the processed products.

[0028] (3) Dodecyl sulfate is non-toxic, harmless, cheap and readily available. When used in combination with cobalt salt, it can reduce the use of fluorescent whitening agents and other related additives, thus mitigating their harm to the human body or the environment. Detailed Implementation

[0029] The technical solution of the present invention is illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0030] Example 1

[0031] Preparation of a PETG copolyester with high transparency, high brightness, and neutral hue:

[0032] (1) Add terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.3 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.3 times the molar equivalent of terephthalic acid) to the esterification vessel, mix evenly, and then esterify for 3.5 h at 230℃ and 150 kPa nitrogen atmosphere to obtain the esterified product; (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, Then, tetrabutyl titanate (10 ppm of titanium by mass of copolyester), cobalt acetate tetrahydrate (20 ppm of cobalt by mass of copolyester), sodium dodecyl sulfate (100 ppm of sodium by mass of copolyester), antioxidant 1010 (300 ppm of copolyester by mass of copolyester) and triethyl phosphate (150 ppm of copolyester by mass of copolyester) are added, and a polycondensation reaction is carried out at 275°C and 60 Pa under vacuum for 2 hours to obtain copolyester.

[0033] Example 2

[0034] Preparation of a PETG copolyester with high transparency, high brightness, and neutral hue:

[0035] (1) Add terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.3 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.3 times the molar equivalent of terephthalic acid) to the esterification vessel, mix evenly, and then esterify for 3.5 h at 230℃ and 150 kPa nitrogen atmosphere to obtain the esterified product; (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, Then, tetrabutyl titanate (10 ppm of titanium by mass of copolyester), cobalt acetate tetrahydrate (20 ppm of cobalt by mass of copolyester), sodium dodecyl sulfate (80 ppm of sodium by mass of copolyester), antioxidant 1010 (300 ppm of copolyester by mass of copolyester) and triethyl phosphate (150 ppm of copolyester by mass of copolyester) are added, and polycondensation reaction is carried out at 275°C and 60 Pa for 2 hours to obtain copolyester.

[0036] Example 3

[0037] Preparation of a PETG copolyester with high transparency, high brightness, and neutral hue:

[0038] (1) Add terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.3 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.3 times the molar equivalent of terephthalic acid) to the esterification vessel, mix evenly, and then esterify for 3.5 h at 230℃ and 150 kPa nitrogen atmosphere to obtain the esterified product; (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, Then, tetrabutyl titanate (with titanium content of 10 ppm of copolyester mass), cobalt acetate tetrahydrate (with cobalt content of 10 ppm of copolyester mass), sodium dodecyl sulfate (with sodium content of 100 ppm of copolyester mass), antioxidant 1010 (with an addition amount of 300 ppm of copolyester mass) and triethyl phosphate (with an addition amount of 150 ppm of copolyester mass) are added, and a polycondensation reaction is carried out under vacuum conditions of 275℃ and 60 Pa for 2 hours to obtain copolyester.

[0039] Example 4

[0040] Preparation of a PETG copolyester with high transparency, high brightness, and neutral hue:

[0041] (1) Add terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.3 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.3 times the molar equivalent of terephthalic acid) to the esterification vessel, mix evenly, and then esterify for 3.5 h at 230℃ and 150 kPa nitrogen atmosphere to obtain the esterified product; (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, Then, tetrabutyl titanate (8 ppm of titanium by mass of copolyester), cobalt acetate tetrahydrate (20 ppm of cobalt by mass of copolyester), sodium dodecyl sulfate (100 ppm of sodium by mass of copolyester), antioxidant 1010 (300 ppm of copolyester by mass of copolyester) and triethyl phosphate (150 ppm of copolyester by mass of copolyester) are added, and polycondensation reaction is carried out at 275°C and 60 Pa for 2 hours to obtain copolyester.

[0042] Example 5

[0043] Preparation of a PETG copolyester with high transparency, high brightness, and neutral hue:

[0044] (1) Add terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.3 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.3 times the molar equivalent of terephthalic acid) to the esterification vessel, mix thoroughly, and then esterify for 3 hours at 250℃ and 150kPa under a nitrogen atmosphere to obtain the esterified product; (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, then... Tetrabutyl titanate (10 ppm of titanium by mass of copolyester), cobalt acetate tetrahydrate (20 ppm of cobalt by mass of copolyester), sodium dodecyl sulfate (100 ppm of sodium by mass of copolyester), antioxidant 1010 (300 ppm of copolyester by mass of copolyester), and triethyl phosphate (150 ppm of copolyester by mass of copolyester) were added, and a polycondensation reaction was carried out at 280 °C and 50 Pa under vacuum for 2 h to obtain the copolyester.

[0045] Example 6

[0046] Preparation of a PETG copolyester with high transparency, high brightness, and neutral hue:

[0047] (1) Add terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.2 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.3 times the molar equivalent of terephthalic acid) to the esterification reactor, mix evenly, and then esterify for 3.5 h at 230℃ and 150 kPa nitrogen atmosphere to obtain the esterified product; (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, Then, tetrabutyl titanate (10 ppm of titanium by mass of copolyester), cobalt acetate tetrahydrate (16 ppm of cobalt by mass of copolyester), sodium dodecyl sulfate (80 ppm of sodium by mass of copolyester), antioxidant 1010 (300 ppm of copolyester by mass of copolyester) and triethyl phosphate (150 ppm of copolyester by mass of copolyester) are added, and polycondensation reaction is carried out at 278°C and 45 Pa under vacuum for 2 hours to obtain copolyester.

[0048] Example 7

[0049] Preparation of a PETG copolyester with high transparency, high brightness, and neutral hue:

[0050] (1) Add terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.3 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.3 times the molar equivalent of terephthalic acid) to the esterification vessel, mix evenly, and then esterify for 3.5 h at 230℃ and 150 kPa nitrogen atmosphere to obtain the esterified product; (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, Then, tetrabutyl titanate (10 ppm of titanium by mass of copolyester), cobalt acetate tetrahydrate (20 ppm of cobalt by mass of copolyester), potassium dodecyl sulfate (80 ppm of potassium by mass of copolyester), antioxidant 1010 (300 ppm of copolyester by mass of copolyester) and triethyl phosphate (150 ppm of copolyester by mass of copolyester) are added, and polycondensation reaction is carried out at 280℃ and 40 Pa under vacuum for 2 hours to obtain copolyester.

[0051] Comparative Example 1

[0052] The difference from Example 1 is that no color-correcting agent is added.

[0053] Preparation of PETG copolyester:

[0054] (1) Add terephthalic acid, ethylene glycol and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.3 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.3 times the molar equivalent of terephthalic acid) to the esterification reactor, mix evenly, and esterify for 3.5 h under a nitrogen atmosphere of 230℃ and 150 kPa to obtain the esterified product; (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, add tetrabutyl titanate (the titanium element accounts for 10 ppm of the copolyester mass), antioxidant 1010 (the amount added accounts for 300 ppm of the copolyester mass) and triethyl phosphate (the amount added accounts for 150 ppm of the copolyester mass), and carry out polycondensation reaction for 2 h under vacuum conditions of 275℃ and 60 Pa to obtain the copolyester.

[0055] Comparative Example 2

[0056] The difference from Example 2 is that color-correcting agent II is not added.

[0057] Preparation of PETG copolyester:

[0058] (1) Add terephthalic acid, ethylene glycol and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.3 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.3 times the molar equivalent of terephthalic acid) to the esterification reactor, mix evenly, and esterify for 3.5 h under a nitrogen atmosphere of 230℃ and 150 kPa to obtain the esterified product; (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, add tetrabutyl titanate (the titanium element accounts for 10 ppm of the copolyester mass), cobalt acetate tetrahydrate (the cobalt element accounts for 20 ppm of the copolyester mass), antioxidant 1010 (the amount added accounts for 300 ppm of the copolyester mass) and triethyl phosphate (the amount added accounts for 150 ppm of the copolyester mass), and carry out a polycondensation reaction for 2 h under vacuum conditions of 275℃ and 60 Pa to obtain the copolyester.

[0059] Comparative Example 3

[0060] The difference from Example 3 is that the type of colorant II is different.

[0061] Preparation of PETG copolyester:

[0062] (1) Add terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.3 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.3 times the molar equivalent of terephthalic acid) to the esterification vessel, mix evenly, and then esterify for 3.5 h at 230℃ and 150 kPa nitrogen atmosphere to obtain the esterified product; (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, Then, tetrabutyl titanate (10 ppm of titanium by mass of copolyester), cobalt acetate tetrahydrate (20 ppm of cobalt by mass of copolyester), sodium dodecyl sulfonate (100 ppm of sodium by mass of copolyester), antioxidant 1010 (300 ppm of copolyester by mass of copolyester) and triethyl phosphate (150 ppm of copolyester by mass of copolyester) are added, and a polycondensation reaction is carried out at 275°C and 60 Pa under vacuum for 2 hours to obtain copolyester.

[0063] Comparative Example 4

[0064] The difference from Example 4 is that the catalyst and additives are added before esterification.

[0065] Preparation of PETG copolyester:

[0066] (1) Add terephthalic acid, ethylene glycol and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.3 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.3 times the molar equivalent of terephthalic acid) to the esterification vessel, then add tetrabutyl titanate (the titanium element accounts for 8 ppm of the copolyester mass), cobalt acetate tetrahydrate (the cobalt element accounts for 20 ppm of the copolyester mass), sodium dodecyl sulfate (the sodium element accounts for 100 ppm of the copolyester mass), antioxidant 1010 (the amount added accounts for 300 ppm of the copolyester mass) and triethyl phosphate (the amount added accounts for 150 ppm of the copolyester mass), mix evenly, and esterify at 230℃ and 150 kPa nitrogen atmosphere for 3.5 h to obtain the esterification product;

[0067] (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, a polycondensation reaction is carried out for 2 hours under vacuum conditions of 275°C and 60Pa to obtain a copolyester.

[0068] Comparative Example 5

[0069] The difference from Example 1 is that no antioxidants and stabilizers are added.

[0070] Preparation of PETG copolyester:

[0071] (1) Add terephthalic acid, ethylene glycol and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.3 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.3 times the molar equivalent of terephthalic acid) to the esterification reactor, mix evenly, and esterify for 3.5 h under a nitrogen atmosphere of 230℃ and 150 kPa to obtain the esterified product; (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, add tetrabutyl titanate (the titanium element accounts for 10 ppm of the copolyester mass), cobalt acetate tetrahydrate (the cobalt element accounts for 20 ppm of the copolyester mass) and sodium dodecyl sulfate (the sodium element accounts for 100 ppm of the copolyester mass), and perform polycondensation reaction for 2 h under vacuum conditions of 275℃ and 60 Pa to obtain the copolyester.

[0072] Comparative Example 6

[0073] The difference from Example 1 is that the molar amount of 1,4-cyclohexanediethanol is different.

[0074] Preparation of PETG copolyester:

[0075] (1) Add terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol (the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol is 1.3 times the molar equivalent of terephthalic acid, and the molar amount of 1,4-cyclohexanediethanol is 0.5 times the molar equivalent of terephthalic acid) to the esterification vessel, mix evenly, and then esterify for 3.5 h at 230℃ and 150 kPa nitrogen atmosphere to obtain the esterified product; (2) When the esterification rate of the esterification reaction in step (1) is greater than 90%, Then, tetrabutyl titanate (10 ppm of titanium by mass of copolyester), cobalt acetate tetrahydrate (20 ppm of cobalt by mass of copolyester), sodium dodecyl sulfate (100 ppm of sodium by mass of copolyester), antioxidant 1010 (300 ppm of copolyester by mass of copolyester) and triethyl phosphate (150 ppm of copolyester by mass of copolyester) are added, and a polycondensation reaction is carried out at 275°C and 60 Pa under vacuum for 2 hours to obtain copolyester.

[0076] Performance testing

[0077] The intrinsic viscosity (η), color value (L / a / b), and transparency of the copolyesters prepared in Examples 1-7 and Comparative Examples 1-6 were tested respectively, and the results are shown in Table 1.

[0078] The intrinsic viscosity and color value were tested according to GB / T 14190-2017; the intrinsic viscosity and color value of the copolyester chips before processing were obtained, and the intrinsic viscosity and color value of the injection-molded sample obtained after processing were obtained from the copolyester chips.

[0079] The transparency of the injection-molded sample obtained after injection molding of copolyester chips is tested according to GB / T 2410-2008.

[0080] Table 1. PETG copolyester before and after processing: [η], L / a / b values, viscosity decrease Δη, and transparency after processing.

[0081]

[0082] As shown in Table 1:

[0083] (1) Comparing Comparative Example 1 and Example 1, the slices of Comparative Example 1, which only added tetrabutyl titanate catalyst, had a larger b value, a transparency of less than 90%, a larger viscosity drop before and after processing, and a yellower slice after processing; while the slices of Example 1 had a b value of less than 0, a transparency of more than 90%, and an intrinsic viscosity slightly lower than that of the slices of Comparative Example 1. This indicates that color-adjusting agents I and II have a strong ability to control the color of the slices, and the b value of the slices also affects the transparency of the product. The processing stability is good, but it will slightly inhibit polymerization.

[0084] (2) Comparing Comparative Example 2 and Example 2, the L value of the slices in Comparative Example 2 without the addition of color-adjusting agent II was low and the slices were yellow with a transparency of less than 90%. The yellow color of the slices after processing was deepened. The b value of the slices in Example 2 was close to 0 and the transparency was greater than 90%, indicating that color-adjusting agent II played an effective role in regulating the L value and b value of the slices.

[0085] (3) Comparing Comparative Example 3 and Example 3, the intrinsic viscosity of the slices in Comparative Example 3 was less than 0.75 dL / g, the L value was as low as 65, the b value was greater than 5, the transparency was less than 90%, and the hue of the slices was poor. The b value of the slices in Example 3 was less than 3, and the transparency was greater than 90%, indicating that the complexation effect of dodecyl sulfonate with cobalt ions was not obvious and could not play a role in adjusting the hue of the slices. Moreover, the polymerization inhibition effect of dodecyl sulfonate was very obvious.

[0086] (4) Comparing Comparative Example 4 and Example 4, the intrinsic viscosity of the slices in Comparative Example 4 was as low as 0.65 dL / g and the transparency was less than 90%, indicating that tetrabutyl titanate is easily hydrolyzed. Adding tetrabutyl titanate before esterification will reduce the transesterification activity in the polycondensation stage, thereby reducing the intrinsic viscosity of the slices.

[0087] (5) Comparing Comparative Example 5 and Example 1, the b value of the slices in Comparative Example 5 is larger and the viscosity decreases more before and after processing. This indicates that without the addition of antioxidants and stabilizers, the side reactions and thermo-oxidative degradation will be more obvious, the processing stability of the slices will be worse, and the color of the product will be worse.

[0088] (6) Comparing Comparative Example 6 and Example 1, Comparative Example 6 has a higher intrinsic viscosity, but the viscosity decreases significantly before and after, and the transmittance is less than 90%. This indicates that increasing the molar amount of 1,4-cyclohexanediethanol will increase the CHDM content on the PETG chain segment, resulting in an increase in the intrinsic viscosity of the slice. However, with the improvement of crystallization ability, the transmittance of the slice is reduced.

[0089] Using the method of this invention, the hue of the chips can be controlled by adjusting the amount of color-adjusting additives, and the amount of catalyst can be controlled to prepare copolyesters with controllable intrinsic viscosity, high transparency, high brightness, and neutral hue.

[0090] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a copolyester with high transparency, high brightness, and neutral hue, characterized in that, The process includes the following steps: esterification of terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol; after complete esterification, addition of colorant and other auxiliaries to carry out polycondensation reaction to obtain a copolyester; The molar ratio of 1,4-cyclohexanediethanol to terephthalic acid is 0.3:1; the color-tuning aid includes color-tuning aid I and color-tuning aid II, color-tuning aid I is one or more of cobalt acetate and cobalt acetate tetrahydrate, and color-tuning aid II is dodecyl sulfate; the amount of cobalt added in color-tuning aid I is 2 to 20 ppm of the copolyester mass; the amount of metal added in color-tuning aid II is 1 to 100 ppm of the copolyester mass; the other aids include catalysts, stabilizers and antioxidants.

2. The method for preparing the highly transparent, high-brightness, and neutral-toned copolyester as described in claim 1, characterized in that, The amount of cobalt added in the color-correcting agent I is 20 ppm of the copolyester mass.

3. The method for preparing the highly transparent, high-brightness, and neutral-toned copolyester as described in claim 1, characterized in that, The color-correcting agent II is one or more of sodium dodecyl sulfate and potassium dodecyl sulfate.

4. The method for preparing the highly transparent, high-brightness, and neutral-toned copolyester as described in claim 1, characterized in that, The ratio of the total molar amount of ethylene glycol and 1,4-cyclohexanediethanol to the molar amount of terephthalic acid is 1.05 to 4:

1.

5. The method of claim 1-4 for preparing a copolyester which is highly transparent, highly bright and has a neutral color tone, characterized in that, The esterification reaction is carried out at 220~260℃ and 0~150 kPa nitrogen pressure for 2~4 h.

6. The method for preparing the highly transparent, high-brightness, and neutral-toned copolyester as described in any one of claims 1-4, characterized in that, The polycondensation reaction is carried out in a vacuum environment at 265~285 °C and below 100 Pa for 1~4 hours.

7. The method for preparing the highly transparent, high-brightness, and neutral-toned copolyester as described in claim 1, characterized in that, The catalyst is one or more of tetrabutyl titanate, nano titanium dioxide, and titanium glycol, wherein the amount of titanium added accounts for 4 to 40 ppm of the copolyester mass.

8. The method for preparing a highly transparent, high-brightness, and neutral-toned copolyester as described in claim 1 or 7, characterized in that, The stabilizer is one or more of phosphoric acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, trimethyl phosphite, triphenyl phosphite, and triethyl phosphonoacetate, wherein the amount of phosphorus added is 5-80 ppm of the copolyester mass; the antioxidant is one or more of pentaerythritol tetrakis[-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris[2,4-di-tert-butylphenyl]phosphite, and pentaerythritol dioctadecyl phosphite, wherein the amount of antioxidant added is 50-500 ppm of the copolyester mass.

9. A highly transparent, high-brightness, and neutral-toned copolyester prepared by the preparation method according to any one of claims 1-8.

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