Low-melting-point polyester and preparation method thereof

Abstract

The invention discloses low-melting-point polyester and a preparation method thereof. The preparation method comprises the following steps: mixing and pulping each monomer and a part of catalyst to prepare slurry, and sequentially performing two-stage esterification reaction and polycondensation reaction to obtain the low-melting-point polyester. Diacid is added into the monomers to serve as a third monomer so as to reduce the regularity of macromolecular chains or improve the flexibility of macromolecules, and then a fourth dihydric alcohol monomer containing a plurality of methylene or ether bonds is added so as to increase the melting entropy of the product. Meanwhile, the titanium catalyst is added step by step, so that after the third monomer and the fourth monomer are added, the esterification reaction activity of the system is greatly reduced, and the reaction activity is enhanced; inactivation of part of the catalyst due to contact with water in the esterification reaction can be avoided to the greatest extent, so that high viscosity is realized; by adopting the accelerant, a macromolecular chain of which the regularity is seriously damaged due to the addition of the third monomer also has certain regularity arrangement capability, so that crystallinity is realized.

Description

Technical Field

[0001] This invention relates to the field of polyester modification and synthesis, specifically to a low-melting-point polyester and its preparation method, and particularly to a low-melting-point polyester with high intrinsic viscosity and certain crystallinity and its preparation method. Background Technology

[0002] Low-melting-point polyester is a type of modified polyester. Depending on the application, its melting point is about 20°C to 170°C lower than that of conventional polyester (PET). Because its macromolecular structure is similar to that of conventional polyester, it has good compatibility with conventional polyester and good melt processing performance. It can be widely used in many fields such as clothing, construction, and coatings. It can be used as a hot melt adhesive or spun into low-melting-point polyester fibers.

[0003] One of the main applications of low-melting-point polyester is the composite spinning of core-sheath composite fibers. These composite fibers can be widely used as thermal bonding fibers in the production of nonwoven fabrics, overcoming the drawbacks of traditional polyester nonwovens that required ES fibers for thermal bonding, such as uneven heat shrinkage and a stiff feel. Polyester wadding made from this composite is softer and fluffier, and can be widely used in the manufacture of medical and industrial nonwoven fabrics. Low-melting-point polyester can also be used in the preparation of color masterbatches. The color masterbatches made from this composite can be colored by injection molding, avoiding the high-temperature, high-pressure dyeing required for conventional polyester fibers and fabrics, which causes significant fiber damage, high energy consumption, wastewater generation, and poor lightfastness and colorfastness. The entire process is simple and the mixing is uniform, resulting in colored fibers with no color difference and high colorfastness. Furthermore, it has low energy consumption and produces no wastewater. In addition, low-melting-point polyester can be widely used in the production of hot-melt cotton wadding, producing spray-bonded cotton with uniform inside and out, high strength, and a good feel; therefore, its application areas are very wide.

[0004] There are many reports on the synthesis of "low melting point polyester" and the preparation of its composite fibers, but the following problems exist: (1) The intrinsic viscosity is generally not high. The intrinsic viscosity of polyester is directly proportional to its molecular weight. A low intrinsic viscosity means that its molecular weight is low, which will lead to low melt strength during melt processing, resulting in poor mechanical properties of the final product; (2) Antimony catalysts are commonly used. Antimony catalysts are the most commonly used catalysts in polyester synthesis, including antimony trioxide, antimony acetate and antimony glycolate, etc. Since antimony is a heavy metal element, as a component of the catalyst, it will remain in the polyester product and will migrate out during long-term use. Antimony is toxic and can cause heart and liver poisoning. It has been listed as a key pollutant and is strictly controlled by regulations. (3) Poor crystallinity. Poor crystallinity will make it difficult to cool and form the product, especially when spinning low melting point polyester fibers. This will lead to problems such as poor yarn doubling and poor yarn cake forming due to poor curing. Summary of the Invention

[0005] The purpose of this invention is to provide a low-melting-point polyester and its preparation method, wherein the low-melting-point polyester has a high intrinsic viscosity and certain crystallinity.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing low-melting-point polyester, wherein the preparation method includes the following steps: Purified terephthalic acid (PTA), ethylene glycol (EG), a third monomer, a fourth monomer, and a portion of a catalyst are mixed and pulped to form a slurry. The slurry is continuously fed into a first esterification reactor for a first esterification reaction. Then it is fed into a second esterification reactor for a second esterification reaction. After the second esterification reaction is completed, a polycondensation reaction is carried out to obtain the low-melting-point polyester. The third monomer is selected from at least one of isophthalic acid (IPA), phthalic acid (PA), adipic acid (AA), azelaic acid (AzA), sebacic acid (SA), dodecanoic acid (DDDA), and 1,4-cyclohexanedicarboxylic acid (CHDA); the fourth monomer is selected from at least one of 1,4-butanediol (BDO), 1,6-hexanediol (HDO), 1,10-decanediol, neopentyl glycol (NPG), diethylene glycol (DEG), triethylene glycol (TEG), polyethylene glycol (PEG, preferably with a molecular weight of 400-1000), polytetrahydrofuran ether glycol (PTMG), 1,4-cyclohexanediol (CHDM), 2-methyl-1,3-propanediol (MPO), and 3-methyl-1,5-pentanediol (MPD); the catalyst is selected from at least one of titanium glycol, tetrabutyl titanate (TBOT), tetraisopropyl titanate (TIPT), tetraethyl titanate (TET), and titanium supported on silica. The second esterification reactor adopts a horizontal three-chamber structure. Additives are added to different chambers to reduce mutual interference between them. A heat stabilizer, colorant, and refluxed ethylene glycol are added to the first chamber; a macromolecular chain regularization promoter is added to the second chamber; and 40%–80% of the total catalyst is added to the third chamber. The catalyst added during the pulping stage accounts for 20%–60% of the total catalyst. The catalyst is added in stages: part of the catalyst is added during the formulation stage, and the other part is added to the third chamber of the second esterification reactor, effectively reducing catalyst hydrolysis. Furthermore, since the addition of a third and fourth monomer during the preparation of the low-melting-point polyester in this invention affects the activity of the esterification reaction, this invention adds a portion of the catalyst during pulping, which facilitates the esterification reaction under this formulation system.

[0007] According to the preparation method of the present invention, preferably, the heat stabilizer is selected from at least one of trimethyl phosphate (TMP), triphenyl phosphite (TPPi), and triethyl phosphate (TEP).

[0008] According to the preparation method of the present invention, adding a macromolecular chain regularization accelerator during the reaction process can improve the crystallization properties and spinnability of low-melting-point polyester. Preferably, the macromolecular chain regularization accelerator is selected from MOFs (preferably nano-sized UiO-66), potassium dimethyl isophthalate-5-sulfonate, sodium dimethyl isophthalate-5-sulfonate, sodium benzoate, sodium p-tert-butylbenzoate, N,N'-ethylenebis(12-hydroxystearamide) (EBH), nano-silica, nano-titanium dioxide, and sodium carbonate, or a composite accelerator composed of two or more of these.

[0009] More preferably, the macromolecular chain regularity promoter is a composite promoter, preferably a combination of nano-sized UiO-66 and nano-sized titanium dioxide, and secondarily a combination of sodium dimethyl isophthalate-5-sulfonate and potassium dimethyl isophthalate-5-sulfonate.

[0010] According to the preparation method of the present invention, preferably, the molar fraction of the third monomer in the total dicarboxylic acid is 0-55%; and the molar fraction of the fourth monomer in the total diol is 0-40%. The total dicarboxylic acid includes purified terephthalic acid and the third monomer, and the total diol includes ethylene glycol and the fourth monomer. The preferred acid-to-alcohol ratio in the polymerized monomers is 1:(1.15-1.3).

[0011] According to the preparation method of the present invention, preferably, based on a theoretical copolyester yield of 100%, the amount of the macromolecular chain regularity promoter added is 0.3wt%~1.0wt%.

[0012] According to the preparation method of the present invention, preferably, the amount of catalyst added is 25~60 ppm, based on a theoretical copolyester yield of 100%.

[0013] According to the preparation method of the present invention, preferably, based on a theoretical copolyester yield of 100%, the amount of heat stabilizer added is 0.005wt%~0.15wt%.

[0014] According to the preparation method of the present invention, preferably, the amount of the colorant added is 2~4 ppm, based on a theoretical copolyester yield of 100%.

[0015] According to the preparation method of the present invention, preferably, the pressure of the first esterification reaction is 0.25~0.35MPa, the temperature is 225~235℃, the material residence time is 1.5~2.0h, and the esterification rate is controlled to be ≥89%.

[0016] More preferably, the first esterification reactor is a vertical reactor with a stirrer, with an internal coil structure for heating the material and an external jacket for insulation.

[0017] According to the preparation method of the present invention, preferably, the pressure of the second esterification reaction is 0.0~0.15MPa, the temperature is 225~235℃, and the esterification rate is controlled to reach more than 95%.

[0018] According to the preparation method of the present invention, preferably, after the second esterification reaction is completed, the material is sequentially fed into the first pre-shrinking reactor, the second pre-shrinking reactor and the final polycondensation reactor for polycondensation reaction; after the viscosity of the material reaches a predetermined value, it is output to obtain the low melting point polyester.

[0019] According to the preparation method of the present invention, preferably, the reaction pressure in the first pre-shrinking reactor is 4~10 kPa, the temperature is 235~245℃, and the material residence time is 40~60 min.

[0020] More preferably, the first pre-shrinking reactor is a vertical reactor with a stirring mechanism, with an internal coil structure for heating materials and an external jacket for insulation.

[0021] According to the preparation method of the present invention, preferably, the reaction pressure in the second pre-shrinking reactor is 1~2 kPa, the temperature is 250~260℃, and the material residence time is 30~50 min.

[0022] More preferably, the second pre-shrinking reactor is a horizontal disc reactor, and the intrinsic viscosity of the obtained prepolymer is about 0.28~0.45 dL / g.

[0023] According to the preparation method of the present invention, preferably, the reaction pressure in the final polycondensation reactor is 50~133 Pa, the temperature is 265~275 °C, and the material residence time is 120~180 min.

[0024] The polycondensation reaction proceeds until the material viscosity reaches a predetermined value, and then the product is output. Preferably, it is processed by water-cooled casting and pelletizing to obtain high-viscosity, crystalline, low-melting-point polyester chips; or the product is output after the material viscosity reaches a predetermined value and directly spun into low-melting-point fibers.

[0025] In a preferred embodiment, such as Figure 1 As shown, the preparation method of the present invention includes the following steps: Purified terephthalic acid (PTA), ethylene glycol (EG), the third monomer, the fourth monomer, and the first part of the catalyst are mixed and pulped to prepare a slurry. The slurry is continuously fed into the first esterification reactor, where a first esterification reaction is carried out at 0.25~0.35MPa and 225~235℃, with a material residence time of 1.5~2.0h, and the esterification rate is controlled to be ≥89%. Then, it enters the second esterification reactor, where a second esterification reaction is carried out at 0.0~0.15MPa and 225~235℃. Once the esterification rate reaches ≥95%, it enters the first pre-shrinking reactor. The second esterification reactor preferably adopts a horizontal three-chamber structure. The heat stabilizer, colorant, and refluxed ethylene glycol are added in the first chamber, the accelerator is added in the second chamber, and the second portion of the catalyst solution is added in the third chamber. The material is held in the first pre-condensation reactor at 4~10 kPa and 235~245℃ for 40~60 min. After the first pre-condensation reaction is completed, the material is fed into the second pre-condensation reactor and held at 1~2 kPa and 250~260℃ for 30~50 min. After the second pre-condensation reaction is completed, the material is fed into the final condensation reactor and held at 50~133 Pa and 265~275℃ for 120~180 min. After the material viscosity reaches the predetermined value, it is output and then cut into pellets by water-cooled casting belt to obtain high-viscosity crystalline low-melting-point polyester chips; or after the material viscosity reaches the predetermined value, it is output and directly spun into low-melting-point fibers.

[0026] In this preferred embodiment, the first esterification reactor is preferably a vertical stirred reactor with an internal coil structure for heating the material and an external jacket for insulation. The second esterification reactor is preferably a horizontal three-chamber structure. The heat stabilizer, colorant, and refluxed ethylene glycol are added in the first chamber, the accelerator is added in the second chamber, and the catalyst solution is added in the third chamber. The catalyst added in this stage accounts for 40% to 80% of the total catalyst added. The first pre-shrinking reactor is a vertical stirred reactor with an internal coil structure for heating the material and an external jacket for insulation. The second pre-shrinking reactor is a horizontal disc reactor, and the resulting prepolymer has an intrinsic viscosity of approximately 0.28 to 0.45 dL / g.

[0027] According to the preparation method of the present invention, preferably, the catalyst, macromolecular chain regularization promoter, heat stabilizer, and colorant are all prepared into solutions or suspensions using ethylene glycol before being added to the reaction. The concentration of the catalyst solution is preferably 0.05 wt% to 0.15 wt%; the concentration of the macromolecular chain regularization promoter in the suspension is preferably 5 wt% to 10 wt%; the concentration of the heat stabilizer solution is preferably 0.05 wt% to 0.2 wt%; and the concentration of the colorant solution is preferably 0.02 wt% to 0.1 wt%.

[0028] More preferably, the mixing process includes: Preparation of catalyst solution: Ethylene glycol is fed into a catalyst mixing tank, and catalyst is added to prepare a catalyst solution of 0.05wt%~0.15wt%. The catalyst mixing temperature is 50~90℃. Preparation of suspensions of macromolecular chain regularity promoters: Ethylene glycol is fed into an accelerator mixing tank, and the additive is added to prepare a 5wt%~10wt% suspension at room temperature.

[0029] Preparation of heat stabilizer solution: Ethylene glycol is fed into a heat stabilizer mixing tank, and heat stabilizer is added to prepare a heat stabilizer solution of 0.05wt%~0.2wt%. The heat stabilizer mixing temperature is 30~50℃.

[0030] Preparation of toner solution: Ethylene glycol is fed into a colorant mixing tank, and colorant is added to prepare a colorant solution of 0.02wt%~0.1wt%. The colorant mixing temperature is room temperature.

[0031] In another aspect, the present invention provides a low-melting-point polyester obtained by any of the above preparation methods.

[0032] The low-melting-point polyester prepared in this invention uses conventional monomers, purified terephthalic acid and ethylene glycol, with the addition of an appropriate amount of diacid as a third monomer to reduce the regularity of the macromolecular chain or increase its flexibility. An appropriate amount of diol containing multiple methylene or ether bonds is then added as a fourth monomer to increase the melt entropy of the synthesized product. Simultaneously, through improvements to the titanium-based catalyst and its addition process, the system, whose esterification reactivity was significantly reduced after the addition of the third and fourth monomers, exhibits enhanced reactivity. Furthermore, it minimizes the risk of catalyst deactivation due to contact with the byproduct water during esterification, thus ensuring the first objective of this invention: "high viscosity." By employing a "macromolecular chain regularity promoter," especially a composite promoter, the macromolecular chains, whose regularity was severely disrupted by the addition of the third monomer, regain a certain degree of regular arrangement ability, i.e., crystallization ability, which has been proven by DSC test results and spinning practice. This ensures the second objective of this invention: "crystallization."

[0033] The preparation method provided by this invention allows for the convenient preparation of a high-viscosity, crystalline, low-melting-point polyester with an intrinsic viscosity greater than 0.70 dL / g, certain crystallinity, and an adjustable melting point between 105 and 200°C, by adding a third and fourth monomer, along with corresponding catalysts and auxiliaries, during the PTA and EG pulping and esterification stages. Furthermore, the preparation method of this invention can be easily implemented on conventional PET equipment, and the resulting high-viscosity, crystalline, low-melting-point polyester exhibits good spinnability. Attached Figure Description

[0034] Figure 1 This is a schematic flowchart of a preferred embodiment of the present invention for preparing low-melting-point polyester. Detailed Implementation

[0035] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0036] All numerical specifications in this invention (e.g., temperature, time, concentration, and weight, including ranges for each) are generally approximate values ​​that may be changed (+) or (-) in increments of 0.1 or 1.0. All numerical specifications are to be understood as being preceded by the term "about".

[0037] Example 1: A method for preparing a high-viscosity, crystalline, low-melting-point polyester includes the following steps: 1) Pulping: PTA, EG, IPA, AA, DEG, BDO, and TBOT are added to a pulping tank in a certain proportion to make a uniform pulp.

[0038] The molar ratios of the materials are as follows: PTA:IPA:AA=0.45:0.4:0.15, EG:DEG:BDO=0.6:0.05:0.35, and the acid-to-alcohol ratio is 1:1.15; the total amount of TBOT added is 25 ppm of the theoretical yield of low-melting-point polyester, and the amount added in this stage is 20% of the total amount.

[0039] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.25 MPa and a temperature of 225 °C for a residence time of 2.0 h before entering the second esterification reactor. TMP and colorant are added in the first chamber of the esterification reactor, sodium benzoate / titanium dioxide, a compound macromolecular chain regularization accelerator, is added in the second chamber, and the remaining TBOT is added in the third chamber. The amount of colorant added is 2 ppm of the theoretical yield of low-melting-point polyester, the amount of TMP added is 0.005 wt% of the theoretical yield of low-melting-point polyester, and the amount of compound macromolecular chain regularization accelerator added is 0.3 wt% of the theoretical yield of low-melting-point polyester. In the second esterification reactor, esterification continues under the same conditions of temperature and pressure of 0.0 MPa until the esterification rate reaches 97%, at which point the slurry enters the first pre-shrinking reactor.

[0040] 3) Pre-shrinkage: After esterification, the material enters the first pre-shrinking tank and is then held for 40 minutes at a temperature of 245°C and a system pressure of 10 kPa. The material is then pumped into the second pre-shrinking tank by a melt pump. In the second pre-shrinking tank, the material is held for 30 minutes at a temperature of 255°C and a system pressure of 1 kPa. The material is then pumped into the final shrinking tank by a melt pump.

[0041] 4) Final contraction: The material entering the final shrinkage reactor is held at 265℃ and 50Pa for 120 minutes until the viscosity reaches a predetermined value. It is then pumped out by a melt pump and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 105℃, intrinsic viscosity IV = 0.78 dL / g, L value of 79, and b value of 3.2.

[0042] Example 2: A method for preparing a high-viscosity, crystalline, low-melting-point polyester includes the following steps: 1) Pulping: PTA, EG, IPA, sebacic acid, NPG, BDO, and TET are added to a pulping tank in a certain proportion to make a uniform pulp.

[0043] The molar ratios of the materials are as follows: PTA:IPA:Sebacic acid = 0.5:0.4:0.1, EG:NPG:BDO = 0.8:0.15:0.05, and the acid-to-alcohol ratio is 1:1.2; the total amount of TET added is 30 ppm of the theoretical yield of low-melting-point polyester, and the amount added in this stage is 30% of the total amount.

[0044] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.3 MPa and a temperature of 230°C for 1.5 hours before entering the second esterification reactor. TPPi and toner are added from the first chamber, while the composite macromolecular chain regularization accelerator EBH / titanium dioxide is added from the second chamber. The remaining TET is added from the third chamber of the second esterification reactor. The amount of toner added is 4 ppm of the theoretical yield of low-melting-point polyester, and the amount of TPPi added is 0.02 wt% of the theoretical yield of low-melting-point polyester. The amount of composite macromolecular regularization accelerator added is 0.4 wt% of the theoretical yield of low-melting-point polyester. Esterification continues in the second esterification reactor at the same temperature and pressure of 0.0 MPa until the esterification rate reaches 98%, at which point the slurry enters the first pre-shrinking reactor.

[0045] 3) Pre-shrinkage: After esterification, the material enters the first pre-shrinking tank and is then held for 50 minutes at a temperature of 243°C and a system pressure of 6 kPa. The material is then pumped into the second pre-shrinking tank by a melt pump. In the second pre-shrinking tank, the material is held for 40 minutes at a temperature of 255°C and a system pressure of 1.0 kPa. The material is then pumped into the final shrinking tank by a melt pump.

[0046] 4) Final shrinkage: The material entering the final shrinkage reactor is held at 265℃ and 120Pa for 150 minutes until the viscosity reaches a predetermined value. It is then pumped out by a melt pump and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 113℃, intrinsic viscosity IV = 0.77 dL / g, L value of 77, and b value of 3.5.

[0047] Example 3: A method for preparing a high-viscosity, crystalline, low-melting-point polyester includes the following steps: 1) Pulping: PTA, EG, IPA, DDDA, DEG, HDO, and titanium glycol are added to a pulping tank in a certain proportion to make a uniform slurry.

[0048] The molar ratios of the materials are as follows: PTA:IPA:DDDA=0.5:0.4:0.1, EG:DEG:HDO=0.7:0.05:0.25, and the acid-to-alcohol ratio is 1:1.25; the total amount of titanium glycol added is 60 ppm of the theoretical yield of low-melting-point polyester, and the amount added in this stage is 40% of the total amount.

[0049] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.35 MPa and a temperature of 235 °C for a residence time of 2.0 h before entering the second esterification reactor. TPPi and toner are added from the first chamber, while the composite macromolecular chain regularization accelerator nano-sized UiO-66 / nano titanium dioxide is added from the second chamber. The remaining titanium glycol is added from the third chamber. The amount of toner added is 4 ppm of the theoretical yield of low-melting-point polyester, the amount of TPPi added is 0.01 wt% of the theoretical yield of low-melting-point polyester, and the amount of composite macromolecular chain regularization accelerator added is 0.4 wt% of the theoretical yield of low-melting-point polyester. In the second esterification reactor, esterification continues under the same conditions of temperature and pressure of 0.15 MPa until the esterification rate reaches 98%, at which point the slurry enters the first pre-shrinking reactor.

[0050] 3) Pre-shrinkage: After esterification, the material enters the first pre-shrinking kettle and is then held for 60 minutes at a temperature of 240°C and a system pressure of 4 kPa. The material is then pumped into the second pre-shrinking kettle by a melt pump. In the second pre-shrinking kettle, the material is held for 40 minutes at a temperature of 260°C and a system pressure of 1.0 kPa. The material is then pumped into the final shrinking kettle by a melt pump.

[0051] 4) Final contraction: The material entering the final shrinkage reactor is held at 275℃ and 133Pa for 180 minutes until the viscosity reaches a predetermined value. It is then pumped out by a melt pump and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 122℃, an intrinsic viscosity IV of 0.78 dL / g, an L value of 75, and a b value of 3.9.

[0052] Example 4: A method for preparing a high-viscosity, crystalline, low-melting-point polyester includes the following steps: 1) Pulping: PTA, EG, IPA, azelaic acid, TEG, NPG, and titanium glycol are added to a pulping tank in a certain proportion to make a uniform pulp.

[0053] The molar ratios of the materials are as follows: PTA:IPA:Azelaic acid = 0.8:0.15:0.05, EG:TEG:NPG = 0.8:0.05:0.15, and the acid-to-alcohol ratio is 1:1.3; the total amount of titanium glycol added is 40 ppm of the theoretical yield of low-melting-point polyester, and the amount added in this stage is 50% of the total amount.

[0054] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.30 MPa and a temperature of 230°C for a residence time of 2.0 h before entering the second esterification reactor. TMP and colorant are added in the first chamber, sodium carbonate / silica, a composite macromolecular regularization accelerator, is added in the second chamber, and the remaining titanium glycolate is added in the third chamber. The amount of colorant added is 3.5 ppm of the theoretical yield of low-melting-point polyester, the amount of TMP added is 0.015 wt% of the theoretical yield of low-melting-point polyester, and the amount of composite macromolecular regularization accelerator added is 1.0 wt% of the theoretical yield of low-melting-point polyester. Esterification continues in the second esterification reactor at the same temperature and a pressure of 0.05 MPa until the esterification rate reaches 97%, at which point the slurry enters the first pre-shrinking reactor.

[0055] 3) Pre-shrinkage: After esterification, the material enters the first pre-shrinking kettle and is then held for 50 minutes at a temperature of 238°C and a system pressure of 8 kPa. The material is then pumped into the second pre-shrinking kettle by a melt pump. In the second pre-shrinking kettle, the material is held for 50 minutes at a temperature of 250°C and a system pressure of 1.5 kPa. The material is then pumped into the final shrinking kettle by a melt pump.

[0056] 4) Final shrinkage: The material entering the final shrinkage reactor is held at 270℃ and 133Pa for 168 minutes. After the material viscosity reaches the predetermined value, it is output by a melt pump and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 138℃, intrinsic viscosity IV = 0.76 dL / g, L value of 77, and b value of 4.1.

[0057] Example 5: A method for preparing a high-viscosity, crystalline, low-melting-point polyester includes the following steps: 1) Pulping: PTA, EG, IPA, PTMG, and titanium glycol are added to a pulping tank in a certain proportion to make a uniform slurry.

[0058] The molar ratios of the materials are as follows: PTA:IPA=0.85:0.15, EG:PTMG=0.8:0.2, and the acid-to-alcohol ratio is 1:1.2; the total amount of titanium glycol added is 38 ppm of the theoretical yield of low-melting-point polyester, and the amount added in this stage is 60% of the total amount.

[0059] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.30 MPa and a temperature of 230°C for 1.8 hours before entering the second esterification reactor. TEP and colorant are added in the first chamber, sodium carbonate / silica, a composite macromolecular regularization accelerator, is added in the second chamber, and the remaining titanium glycolate is added in the third chamber. The amount of colorant added is 4 ppm of the theoretical yield of low-melting-point polyester, the amount of TEP added is 0.01 wt% of the theoretical yield of low-melting-point polyester, and the amount of composite macromolecular regularization accelerator added is 0.6 wt% of the theoretical yield of low-melting-point polyester. In the second esterification reactor, esterification continues at the same temperature and a pressure of 0.03 MPa until the esterification rate reaches 98%, at which point the slurry enters the first pre-shrinking reactor.

[0060] 3) Pre-shrinkage: After esterification, the material enters the first pre-shrinking kettle and is then held for 55 minutes at a temperature of 245°C and a system pressure of 9 kPa. The material is then pumped into the second pre-shrinking kettle by a melt pump. In the second pre-shrinking kettle, the material is held for 40 minutes at a temperature of 255°C and a system pressure of 1.0 kPa. The material is then pumped into the final shrinking kettle by a melt pump.

[0061] 4) Final shrinkage: The material entering the final shrinkage reactor is held at 270℃ and 122Pa for 180 minutes until the viscosity reaches a predetermined value. It is then pumped out by a melt pump and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 148℃, intrinsic viscosity IV = 0.72 dL / g, L value of 74, and b value of 3.9.

[0062] Example 6: A method for preparing a high-viscosity, crystalline, low-melting-point polyester includes the following steps: 1) Pulping: PTA, EG, IPA, AA, DEG, NPG, and TBOT are added to a pulping tank in a certain proportion to make a uniform pulp.

[0063] The molar ratios of the materials are as follows: PTA:IPA:AA=0.95:0.02:0.03, EG:DEG:NPG=0.8:0.05:0.15, and the acid-to-alcohol ratio is 1:1.15; the amount of TBOT added is 33 ppm of the theoretical yield of low-melting-point polyester, and the amount added in this stage is 35% of the total amount.

[0064] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.33 MPa and a temperature of 232°C for a residence time of 2.0 h before entering the second esterification reactor. TPPi and toner are added in the first chamber, while the composite macromolecular chain regularization accelerator nano-sized UiO-66 / nano titanium dioxide is added in the second chamber. The remaining TBOT is added in the third chamber. The amount of toner added is 2 ppm of the theoretical yield of low-melting-point polyester, the amount of TPPi added is 0.015 wt% of the theoretical yield of low-melting-point polyester, and the amount of composite macromolecular chain regularization accelerator added is 0.3 wt% of the theoretical yield of low-melting-point polyester. Esterification continues in the second esterification reactor at the same temperature and a pressure of 0.0 MPa until the esterification rate reaches 98%, at which point the slurry enters the first pre-shrinking reactor.

[0065] 3) Pre-shrinkage: After esterification, the material enters the first pre-shrinking tank and is held for 45 minutes at a temperature of 240°C and a system pressure of 7 kPa. The material is then pumped into the second pre-shrinking tank by a melt pump. In the second pre-shrinking tank, the material is held for 45 minutes at a temperature of 253°C and a system pressure of 1.5 kPa. The material is then pumped into the final shrinking tank by a melt pump.

[0066] 4) Final shrinkage: The material entering the final shrinkage reactor is held at 270℃ and 133Pa for 170 minutes. After the material viscosity reaches the predetermined value, it is output by a melt pump and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 166℃, intrinsic viscosity IV = 0.72 dL / g, L value of 75, and b value of 3.6.

[0067] Example 7: A method for preparing a high-viscosity, crystalline, low-melting-point polyester includes the following steps: 1) Pulping: PTA, EG, NPG, and titanium glycol are added to a pulping tank in a certain proportion to make a uniform slurry.

[0068] The molar ratios of the materials are as follows: EG:NPG = 0.8:0.2, and the acid-to-alcohol ratio is 1:1.2; the amount of titanium glycol added is 30 ppm of the theoretical yield of low-melting-point polyester, and the amount added in this stage is 45% of the total amount.

[0069] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.35 MPa and a temperature of 235°C for 1.5 hours before entering the second esterification reactor. TPPi and toner are added in the first chamber, while silica, a macromolecular chain regularization accelerator, is added in the second chamber. The remaining titanium glycolate is added in the third chamber. The amount of toner added is 4 ppm of the theoretical yield of low-melting-point polyester, the amount of TPPi added is 0.02 wt% of the theoretical yield of low-melting-point polyester, and the amount of macromolecular regularization accelerator added is 0.35 wt% of the theoretical yield of low-melting-point polyester. Esterification continues in the second esterification reactor at the same temperature and a pressure of 0.06 MPa until the esterification rate reaches 98%, at which point the slurry enters the first pre-shrinking reactor.

[0070] 3) Pre-shrinkage: After esterification, the material enters the first pre-shrinking tank and is then held for 55 minutes at a temperature of 245°C and a system pressure of 10 kPa. The material is then pumped into the second pre-shrinking tank by a melt pump. In the second pre-shrinking tank, the material is held for 40 minutes at a temperature of 255°C and a system pressure of 1.0 kPa. The material is then pumped into the final shrinking tank by a melt pump.

[0071] 4) Final contraction: The material entering the final shrinkage reactor is held at 275℃ and 133Pa for 160 minutes until the viscosity reaches a predetermined value. It is then pumped out by a melt pump and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 185℃, intrinsic viscosity IV = 0.74 dL / g, L value of 76, and b value of 3.7.

[0072] Example 8: A method for preparing a high-viscosity, crystalline, low-melting-point polyester includes the following steps: 1) Pulping: PTA, IPA, azelaic acid, EG, and titanium glycol are added to a pulping tank in a certain proportion to make a uniform pulp.

[0073] The molar ratios of the materials are as follows: PTA:IPA:Azelaic acid = 0.85:0.1:0.05, and the acid-to-alcohol ratio is 1:1.15; the total amount of titanium glycol added is 33 ppm of the theoretical yield of low-melting-point polyester, and the amount added in this stage is 55% of the total amount.

[0074] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.32 MPa and a temperature of 232 °C for 2 hours before entering the second esterification reactor. TMP and colorant are added in the first chamber, while the composite macromolecular regularization accelerator sodium dimethyl isophthalate-5-sulfonate / potassium dimethyl isophthalate is added in the second chamber. The remaining catalyst is added in the third chamber. The amount of colorant added is 2 ppm of the theoretical yield of low-melting-point polyester, the amount of TMP added is 0.15 wt% of the theoretical yield of low-melting-point polyester, and the amount of composite macromolecular regularization accelerator added is 0.8 wt% of the theoretical yield of low-melting-point polyester. In the second esterification reactor, esterification continues under the same conditions of temperature and pressure of 0.0 MPa until the esterification rate reaches 96%, at which point the slurry enters the first pre-shrinking reactor.

[0075] 3) Pre-shrinkage: After esterification, the material enters the first pre-shrinking tank and is then held for 60 minutes at a temperature of 245°C and a system pressure of 5 kPa. The material is then pumped into the second pre-shrinking tank by a melt pump. In the second pre-shrinking tank, the material is held for 50 minutes at a temperature of 252°C and a system pressure of 1.0 kPa. The material is then pumped into the final shrinking tank by a melt pump.

[0076] 4) Final contraction: The material entering the final shrinkage reactor is held at 270℃ and 100Pa for 175 minutes until the viscosity reaches a predetermined value. It is then pumped out by a melt pump and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 200℃, intrinsic viscosity IV = 0.75 dL / g, L value of 79, and b value of 3.1.

[0077] Comparative Example 1: The formulation, additives, and process are the same as in Example 6, except that the catalyst is replaced with an antimony-based catalyst.

[0078] 1) Pulping: PTA, EG, IPA, AA, DEG, NPG, and antimony glycol are added to a mixing tank in a certain proportion to make a uniform slurry.

[0079] The molar ratios of the materials are as follows: PTA:IPA:AA=0.95:0.02:0.03, EG:DEG:NPG=0.8:0.05:0.15, and the acid-to-alcohol ratio is 1:1.15; the amount of TBOT added is 33ppm of the theoretical yield of low-melting-point polyester, and the amount added in this stage is 35% of the total amount.

[0080] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.33 MPa and a temperature of 232°C for a residence time of 2.0 h before entering the second esterification reactor. TPPi and toner are added in the first chamber, while nano-sized UiO-66 / / nano-titanium dioxide, a complex macromolecular chain regularization promoter, is added in the second chamber. The remaining catalyst is added in the third chamber. The amount of toner added is 2 ppm of the theoretical yield of low-melting-point polyester, the amount of TPPi added is 0.015 wt% of the theoretical yield of low-melting-point polyester, and the amount of the complex macromolecular chain regularization promoter added is 0.3 wt% of the theoretical yield of low-melting-point polyester. Esterification continues in the second esterification reactor at the same temperature and a pressure of 0.0 MPa until the esterification rate reaches 98%, at which point the slurry enters the first pre-shrinking reactor.

[0081] 3) Pre-shrinkage: After esterification, the material enters the first pre-shrinking tank and is held for 45 minutes at a temperature of 240°C and a system pressure of 7 kPa. The material is then pumped into the second pre-shrinking tank by a melt pump. In the second pre-shrinking tank, the material is held for 45 minutes at a temperature of 253°C and a system pressure of 1.5 kPa. The material is then pumped into the final shrinking tank by a melt pump.

[0082] 4) Final contraction: The material entering the final shrinkage reactor is held at 270℃ and 133Pa for 170 minutes until the viscosity reaches a predetermined value. It is then pumped out by a melt pump and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 165℃, intrinsic viscosity IV = 0.66 dL / g, L value of 78, and b value of 3.1.

[0083] Compared with Example 6, when using an antimony-based catalyst, the intrinsic viscosity of the final product decreased by 0.06 dL / g compared with the titanium-based catalyst used in this application. This indicates that the non-antimony catalyst used in this application plays a beneficial role in improving the intrinsic viscosity of the obtained low-melting-point polyester, and can yield a high-viscosity, low-melting-point polyester.

[0084] Comparative Example 2: Except for the absence of the compound accelerator, the other formulations and processes are the same as in Example 3.

[0085] 1) Pulping: PTA, EG, IPA, DDDA, DEG, HDO, and titanium glycol are added to a pulping tank in a certain proportion to make a uniform slurry.

[0086] The molar ratios of the materials are as follows: PTA:IPA:DDDA=0.5:0.4:0.1, EG:DEG:HDO=0.7:0.05:0.25, and the acid-to-alcohol ratio is 1:1.25; the total amount of titanium glycol added is 60 ppm of the theoretical yield of low-melting-point polyester, and the amount added in this stage is 40% of the total amount.

[0087] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.35 MPa and a temperature of 235 °C for a residence time of 2.0 h before entering the second esterification reactor. TPPi and toner are added in the first chamber, and the remaining titanium glycolate is added in the third chamber. The amount of toner added is 4 ppm of the theoretical yield of low-melting-point polyester, and the amount of TPPi added is 0.01 wt% of the theoretical yield of low-melting-point polyester. In the second esterification reactor, esterification continues under the same conditions of temperature and pressure of 0.15 MPa until the esterification rate reaches 98%, at which point the slurry enters the first pre-shrinking reactor.

[0088] 3) Pre-shrinkage: After esterification, the material enters the first pre-shrinking kettle and is then held for 60 minutes at a temperature of 240°C and a system pressure of 4 kPa. The material is then pumped into the second pre-shrinking kettle by a melt pump. In the second pre-shrinking kettle, the material is held for 40 minutes at a temperature of 260°C and a system pressure of 1.0 kPa. The material is then pumped into the final shrinking kettle by a melt pump.

[0089] 4) Final contraction: The material entering the final shrinkage reactor is held at 275℃ and 133Pa for 180 minutes until the viscosity reaches a predetermined value. It is then pumped out by a melt pump and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 123℃, intrinsic viscosity IV = 0.77 dL / g, L value of 76, and b value of 3.7.

[0090] In this comparative example, except for the absence of a composite accelerator, the formulation and process were the same as in Example 3. The low-melting-point polyester samples obtained were subjected to DSC testing after being subjected to wet heat treatment for 30 minutes, and melt spinning experiments were conducted on a small melt spinning test machine. The spinning and forming results are compared in Table 1 below: Table 1

[0091] As can be seen from the results of Comparative Example 2, the crystallinity of low-melting-point polyester was effectively improved after the addition of the accelerator, which was directly reflected in the DSC test results and verified by the forming effect in the melt spinning experiment.

[0092] Comparative Example 3: Compared with Example 6, the catalyst was added entirely during the prepolymerization reaction.

[0093] 1) Pulping: PTA, EG, IPA, AA, DEG, and NPG are added to a pulping tank in a certain proportion to make a uniform pulp.

[0094] The molar ratios of the materials are as follows: PTA:IPA:AA=0.95:0.02:0.03, EG:DEG:NPG=0.8:0.05:0.15, and the acid-to-alcohol ratio is 1:1.15.

[0095] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.33 MPa and a temperature of 232°C for a residence time of 2.0 h before entering the second esterification reactor. TPPi and toner are added from the first chamber, while the composite macromolecular chain regularization accelerator nano-sized UiO-66 / nano titanium dioxide is added from the second chamber. The amount of toner added is 2 ppm of the theoretical yield of low-melting-point polyester, the amount of TPPi added is 0.015 wt% of the theoretical yield of low-melting-point polyester, and the amount of composite macromolecular chain regularization accelerator added is 0.3 wt% of the theoretical yield of low-melting-point polyester. Esterification continues in the second esterification reactor at the same temperature and a pressure of 0.0 MPa until the esterification rate reaches 98%, at which point the slurry enters the first pre-shrinking reactor.

[0096] 3) Pre-shrinkage: After esterification, the material and catalyst are fed into the first pre-shrinking reactor. The catalyst TBOT is added to the pipeline leading to the first pre-shrinking reactor at a rate of 33 ppm, which is equivalent to the theoretical yield of low-melting-point polyester. The material is then held at 240°C and 7 kPa for 45 minutes, and then pumped into the second pre-shrinking reactor by a melt pump. In the second pre-shrinking reactor, the material is held at 253°C and 1.5 kPa for 45 minutes, and then pumped into the final shrinking reactor by a melt pump.

[0097] 4) Final contraction: The material entering the final shrinkage reactor is held at 270℃ and 133Pa for 170 minutes. The material is then pumped out and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 165℃, intrinsic viscosity IV = 0.70 dL / g, L value of 71, and b value of 5.1.

[0098] The effects of Comparative Example 3 and Example 6 are compared in Table 2.

[0099] Table 2

[0100] As can be seen from the comparative data in Table 2, when the catalyst is added in the manner described in this invention (i.e., as shown in Example 6) compared to the comparative example where the catalyst is added all at once before pre-shrinking, under the same conditions, the intrinsic viscosity of the product obtained by the process adopted in this invention is higher, by 0.02 dL / g, which is about 2.9% higher; the L value is increased by 4, which is about 5.6% higher; and the b value is decreased by 1.5, which is about 29.4% lower, that is, the yellowness value is lower and the hue is better.

[0101] Comparative Example 4: Compared with Example 5, the catalyst was added entirely during the pulping stage.

[0102] 1) Pulping: PTA, EG, IPA, PTMG, and titanium glycol are added to a pulping tank in a certain proportion to make a uniform slurry.

[0103] The molar ratios of the materials are as follows: PTA:IPA=0.85:0.15, EG:PTMG=0.8:0.2, and the acid-to-alcohol ratio is 1:1.2; the total amount of titanium glycol added is 38 ppm of the theoretical yield of low-melting-point polyester.

[0104] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.30 MPa and a temperature of 230°C for 1.8 hours before entering the second esterification reactor. TEP and colorant are added from the first chamber, while the composite macromolecular regularization accelerator sodium carbonate / silica is added from the second chamber. The amount of colorant added is 4 ppm of the theoretical yield of low-melting-point polyester, the amount of TEP added is 0.01 wt% of the theoretical yield of low-melting-point polyester, and the amount of composite macromolecular regularization accelerator added is 0.6 wt% of the theoretical yield of low-melting-point polyester. In the second esterification reactor, esterification continues at the same temperature and a pressure of 0.03 MPa until the esterification rate reaches 98%, at which point the slurry enters the first pre-shrinking reactor.

[0105] 3) Pre-shrinkage: After esterification, the material enters the first pre-shrinking kettle and is then held for 55 minutes at a temperature of 245°C and a system pressure of 9 kPa. The material is then pumped into the second pre-shrinking kettle by a melt pump. In the second pre-shrinking kettle, the material is held for 40 minutes at a temperature of 255°C and a system pressure of 1.0 kPa. The material is then pumped into the final shrinking kettle by a melt pump.

[0106] 4) Final contraction: The material entering the final shrinkage reactor is held at 270℃ and 122Pa for 180 minutes until the viscosity reaches a predetermined value. It is then pumped out by a melt pump and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 150℃, intrinsic viscosity IV = 0.68 dL / g, L value of 72, and b value of 4.8.

[0107] The effects of Comparative Example 4 and Example 5 are compared in Table 3.

[0108] Table 3

[0109] As can be seen from the comparative data in Table 3, when the catalyst is added in the manner described in this invention (i.e., as shown in Example 5) compared to the comparative example where the catalyst is added all at once during slurry preparation (before esterification), under the same conditions, the intrinsic viscosity of the product obtained by the process used in this aspect is higher, increasing by 0.04 dL / g, which is about 5.9%; the L value increases by 2, which is about 2.8%; and the b value decreases by 1.1, which is about 22.9%, meaning that the yellowness value is lower and the hue is better.

[0110] Comparative Example 5: Compared with Example 7, all catalysts were added in the third chamber of the second esterification reactor.

[0111] 1) Pulping: PTA, EG, and NPG are added to a pulping tank in a certain proportion to make a uniform pulp.

[0112] The molar ratios of the materials are as follows: EG:NPG = 0.8:0.2, and the acid-to-alcohol ratio is 1:1.2.

[0113] 2) Esterification: The slurry is continuously pumped into the first esterification reactor by a plunger pump and esterified at a pressure of 0.35 MPa and a temperature of 235°C for 1.5 hours before entering the second esterification reactor. TPPi and toner are added in the first chamber; the amount of toner added is 4 ppm of the theoretical yield of low-melting-point polyester, and the amount of TPPi added is 0.02 wt% of the theoretical yield of low-melting-point polyester. Silica, a macromolecular chain regularization promoter, is added in the second chamber at an amount of 0.35 wt% of the theoretical yield of low-melting-point polyester. Titanium glycol catalyst is added in the third chamber at an amount of 30 ppm of the theoretical yield of low-melting-point polyester. Esterification continues in the second esterification reactor at the same temperature and a pressure of 0.06 MPa until the esterification rate reaches 98%, at which point the slurry enters the first pre-shrinking reactor.

[0114] 3) Pre-shrinkage: After esterification, the material enters the first pre-shrinking tank and is then held for 55 minutes at a temperature of 245°C and a system pressure of 10 kPa. The material is then pumped into the second pre-shrinking tank by a melt pump. In the second pre-shrinking tank, the material is held for 40 minutes at a temperature of 255°C and a system pressure of 1.0 kPa. The material is then pumped into the final shrinking tank by a melt pump.

[0115] 4) Final contraction: The material entering the final shrinkage reactor is held at 275℃ and 133Pa for 160 minutes until the viscosity reaches a predetermined value. It is then pumped out by a melt pump and granulated by a water-cooled casting belt to obtain low-melting-point polyester chips. The resulting chips have a melting point of 186℃, intrinsic viscosity IV = 0.73 dL / g, L value of 74, and b value of 4.0.

[0116] The effects of Comparative Example 5 and Example 7 are compared in Table 4 below.

[0117] Table 4

[0118] As can be seen from the comparative data in Table 4, when the catalyst is added in the manner described in this invention (i.e., as shown in Example 7) compared with the catalyst added in the third chamber of the second esterification reactor in the comparative example in a single step, under the same conditions, the intrinsic viscosity of the product obtained by the process adopted in this invention is higher, by 0.01 dL / g, which is about 1.4% higher; the L value is increased by 2, which is about 2.7% higher; and the b value is decreased by 0.3, which is about 7.5% lower, that is, the yellowness value is lower and the hue is better.

[0119] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A process for the preparation of a low melting point polyester, wherein, The preparation method comprises the following steps: The p-diphthalic acid, ethylene glycol, the third monomer, the fourth monomer and part of the catalyst are mixed to be beaten into pulp to form pulp; the pulp is continuously beaten into a first esterification reactor to perform a first esterification reaction; then, it is put into a second esterification reactor to perform a second esterification reaction; after the second esterification reaction is completed, a polycondensation reaction is performed to obtain the low-melting-point polyester; The third monomer is selected from at least one of isophthalic acid, phthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid and 1,4-cyclohexane dicarboxylic acid; the fourth monomer is selected from at least one of 1,4-butanediol, 1,6-hexanediol, 1,10-decanediol, neopentyl glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polytetrahydrofuran ether glycol, 1,4-cyclohexane dimethanol, 2-methyl-1,3-propanediol and 3-methyl-1,5-pentanediol; and the catalyst is selected from at least one of titanium glycol, tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate and silicon dioxide supported titanium. The second esterification reactor adopts a horizontal three-chamber structure; the first chamber is added with a thermal stabilizer, a toner and refluxed and reused ethylene glycol, the second chamber is added with a macromolecular chain regularity promoter, and the third chamber is added with 40% to 80% of the total amount of catalyst.

2. The production method according to claim 1, wherein The thermal stabilizer is selected from at least one of trimethyl phosphate, triphenyl phosphite and triethyl phosphate.

3. The production method according to claim 1, wherein, The macromolecular chain regularity promoter is selected from one or more than two composite promoters composed of MOFs, dimethyl isophthalate-5-sodium sulfonate, dimethyl isophthalate-5-sodium sulfonate, sodium benzoate, sodium p-tert-butylbenzoate, N,N'-ethylene bis (12-hydroxystearamide), nano silicon dioxide, nano titanium dioxide and sodium carbonate.

4. The production method according to claim 1, wherein The macromolecular chain regularity promoter is a composite promoter, which is a combination of nano UiO-66 and nano titanium dioxide or a combination of dimethyl isophthalate-5-sodium sulfonate and dimethyl isophthalate-5-potassium sulfonate.

5. The production method according to claim 1, wherein The mole fraction of the third monomer in total diacid is 0% to 55%, and the mole fraction of the fourth monomer in total dihydric alcohol is 0% to 40%.

6. The production method according to claim 1, wherein The addition amount of the macromolecular chain regularity promoter is 0.3wt% to 1.0wt% based on 100% of the theoretical yield of the copolyester.

7. The production method according to claim 1, wherein The addition amount of the catalyst is 25ppm to 60ppm based on 100% of the theoretical yield of the copolyester.

8. The production method according to claim 1, wherein The addition amount of the thermal stabilizer is 0.005wt% to 0.15wt% based on 100% of the theoretical yield of the copolyester.

9. The production method according to claim 1, wherein The addition amount of the toner is 2ppm to 4ppm based on 100% of the theoretical yield of the copolyester.

10. The production method according to claim 1, wherein, The pressure of the first esterification reaction is 0.25MPa to 0.35MPa, the temperature is 225℃ to 235℃, the material residence time is 1.5h to 2.0h, and the esterification rate is controlled to be greater than or equal to 89%.

11. The production method according to claim 10, wherein The pressure of the second esterification reaction is 0.0MPa to 0.15MPa, the temperature is 225℃ to 235℃, and the esterification rate is controlled to be greater than or equal to 95%.

12. The method of producing according to claim 1, wherein, After the second esterification reaction is completed, the material is sequentially introduced into a first pre-shrinking reactor, a second pre-shrinking reactor and a final polycondensation reactor for polycondensation reaction; and the material is outputted after the viscosity reaches a predetermined value, thereby obtaining the low-melting-point polyester.

13. The production method according to claim 12, wherein The reaction pressure in the first pre-shrinking reactor is 4-10 kPa, the temperature is 235-245℃, and the residence time of the material is 40-60 min.

14. The method of making according to claim 12, wherein, The reaction pressure in the second pre-shrinking reactor is 1-2 kPa, the temperature is 250-260℃, and the residence time of the material is 30-50 min.

15. The method of making according to claim 12, wherein, The reaction pressure in the final polycondensation reactor is 50-133 Pa, the temperature is 265-275℃, and the residence time of the material is 120-180 min.

16. A low-melting-point polyester obtained by the preparation method of any one of claims 1-15.

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