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JP-2026514452-A - Recycled polyester resin and film, and methods for producing them.

JP2026514452AJP 2026514452 AJP2026514452 AJP 2026514452AJP-2026514452-A

Abstract

This polyester resin has its cyclic trimer and diethylene glycol content adjusted to a specific range, resulting in excellent heat resistance and processability. It can also improve the strength, elongation, and hydrolysis resistance of polyester films produced from this resin. [Selection Diagram] None

Inventors

  • パク， ジュン‐ヨン
  • キム， ソン‐ギ
  • キム， ジョン‐ギュ
  • キム， ジ‐フン
  • パク， クァン‐ウー
  • パク， ジ ヘ
  • イ， ジュン キ

Assignees

  • エスケー ケミカルズ カンパニー リミテッド

Dates

Publication Date
20260511
Application Date
20240402
Priority Date
20230411

Claims (10)

  1. A polyester resin containing recycled bis(2-hydroxyethyl) terephthalate obtained by depolymerization of waste polyester, wherein the peak area fraction of the cyclic trimer measured by high-performance liquid chromatography (HPLC) is 3,000 ppm or less, and the diethylene glycol (DEG) content measured by gas chromatography (GC) is 1.0% by weight or less.
  2. The polyester resin according to claim 1, having a melting point of 255°C or higher when measured by differential scanning calorimetry (DSC).
  3. The polyester resin according to claim 1, having an intrinsic viscosity (IV) of 0.6 dl/g to 1.2 dl/g at 35°C.
  4. The polyester resin according to claim 1, wherein the recycled bis(2-hydroxyethyl) terephthalate has a total oligomer peak area fraction of 3% or less when measured by high-performance liquid chromatography.
  5. A polyester film comprising the polyester resin described in any one of claims 1 to 4.
  6. The polyester film according to claim 5, wherein when cut into 1.5 cm widths, mounted vertically on clips arranged at 5 cm intervals, and tested at 25°C and a tensile speed of 200 mm/min according to ASTM D882, the tensile strength in the longitudinal direction (MD) is 15 kgf/ mm² or more, and the elongation in the longitudinal direction (MD) is 125% or more.
  7. The following equation (2): (In the formula, S0 is the initial elongation (%) of the polyester film sample, and S1 is the elongation (%) measured after being left at 121°C, 100% R.H., and 2 atmospheres for 96 hours.) The polyester film according to claim 5, having an elongation retention rate (R) of 40% or more, calculated by the method, wherein the elongation is measured by cutting the polyester film into 1.5 cm wide strips, mounting them longitudinally on clips placed at 5 cm intervals, and testing them at a tensile speed of 200 mm/min at 25°C according to ASTM D882.
  8. A method for preparing a polyester film, (1) A step of depolymerizing waste polyester to prepare recycled bis(2-hydroxyethyl) terephthalate, (2) The step of preparing a solution of regenerated bis(2-hydroxyethyl) terephthalate by mixing the regenerated bis(2-hydroxyethyl) terephthalate with a solvent, (3) A step of preparing a polyester resin via a polycondensation reaction using the recycled bis(2-hydroxyethyl) terephthalate solution, (4) The step of melt-extruding the polyester resin and stretching the extruded product, In the aforementioned polyester resin, the peak area fraction of cyclic trimers measured by high-performance liquid chromatography (HPLC) is 3,000 ppm or less, and the diethylene glycol (DEG) content measured by gas chromatography (GC) is 1.0% by weight or less. method.
  9. The method for preparing a polyester resin according to claim 8, wherein the polycondensation reaction comprises the step of (3a) subjecting the regenerated bis(2-hydroxyethyl) terephthalate solution to a first polycondensation reaction under a pressure of 200 mmHg to 600 mmHg to prepare an oligomer.
  10. The method for preparing a polyester resin according to claim 9, wherein the polycondensation reaction includes, after step (3a), step (3b) of subjecting the oligomer to a second polycondensation under a pressure of less than 200 mmHg to prepare a polyester resin.

Description

Detailed description of the invention [Technical field] The embodiments relate to recycled polyester resin, films, and methods for preparing them. [Background technology] Due to its excellent mechanical strength, heat resistance, transparency, and gas barrier properties, polyester is widely used as a material for beverage filling containers, packaging films, audio and video films, and other applications. Furthermore, polyester is widely manufactured worldwide as an industrial material such as medical fibers and tire cords. In particular, polyester sheets or plates have good transparency and excellent mechanical strength, and are therefore widely used as raw materials for cases, boxes, partitions, shelves, panels, packaging materials, building materials, and interior and exterior materials. As a result, plastic waste, including polyester, is generated globally every year at an unmanageable level. In recent years, regulations and plans for the recycling of waste plastic resources, including waste polyester, have been developed in various countries around the world. For example, there are attempts to use recycled resin at a certain percentage or higher in packaging materials used in various fields. While physical and chemical methods are used for recycling waste polyester, physical recycling methods cannot guarantee purity and, consequently, are not widely used. In chemical recycling, the ester bonds in waste polyester are cleaved and then depolymerized. Reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. Among these, glycolysis involves adding glycols such as ethylene glycol or diethylene glycol at high temperatures to decompose the waste polyester. The reaction product mainly contains bis(2-hydroxyethyl) terephthalate (BHET). After crystallization or purification, bis(2-hydroxyethyl) terephthalate can be used as a raw material for preparing unsaturated polyesters or ester polyols. [Prior art documents] [Patent Documents] [Patent Document 1] Korean Patent No. 1386683 [Patent Document 2] U.S. Patent No. 7211193 [Summary of the Invention] [Problems that the invention aims to solve] Generally, the depolymerization products of waste polyester resins contain large amounts of oligomers, such as dimers and trimers, in addition to bis(2-hydroxyethyl) terephthalate (BHET). The presence of by-reactants, such as diethylene glycol (DEG), formed at high depolymerization temperatures, is unavoidable. In particular, oligomers are always present in a constant amount at equilibrium concentrations with the polymer during the preparation process, making it difficult to control and reduce their content. These substances cause a decrease in the appearance, performance, and processability of the final product. Therefore, the inventors controlled the recycled raw materials and polycondensation method to produce recycled polyester resins in which the content of cyclic trimers and diethylene glycol was adjusted to a specific range. It was confirmed that the heat resistance, processability, and mechanical properties of the polyester films produced from these resins were improved. Therefore, the object of the present invention is to provide polyester films having the above compositions, polyester films containing them and having excellent properties, and methods for preparing them. [Means for solving the problem] The present invention provides a polyester resin containing recycled bis(2-hydroxyethyl) terephthalate obtained by depolymerization of waste polyester, wherein the peak area fraction of the cyclic trimer measured by high-performance liquid chromatography (HPLC) is 3,000 ppm or less, and the diethylene glycol (DEG) content measured by gas chromatography (GC) is 1.0% by weight or less. Furthermore, the present invention provides a polyester film containing this polyester resin. Furthermore, the present invention provides a method for preparing a polyester film, comprising the steps of: (1) depolymerizing waste polyester to prepare recycled bis(2-hydroxyethyl) terephthalate; (2) mixing the recycled bis(2-hydroxyethyl) terephthalate with a solvent to prepare a solution of recycled bis(2-hydroxyethyl) terephthalate; (3) using the recycled bis(2-hydroxyethyl) terephthalate solution to prepare a polyester resin via a polycondensation reaction; and (4) melt-extruding the polyester resin to stretch the extruded product, wherein the polyester resin has a peak area fraction of cyclic trimers measured by high-performance liquid chromatography (HPLC) of 3,000 ppm or less, and a diethylene glycol (DEG) content measured by gas chromatography (GC) of 1.0% by weight or less. [Advantageous effects of the invention] In the polyester resin according to the present invention, the content of cyclic trimers and diethylene glycol is adjusted to a specific range. As a result, it is possible to improve the heat resistance, processability, and mechanical properties of the polyester film produced from these. Furthermore, in t