Method for storing recycled bis(2-hydroxyethyl) terephthalate and method for preparing polyester resin

Abstract

By mixing and storing the recycled bis(2-hydroxyethyl) terephthalate obtained by the depolymerization of waste polyester with a solvent under specific conditions, the purity and yellowness of the final polyester resin prepared from the recycled bis(2-hydroxyethyl) terephthalate are stably maintained, and the product quality including color is improved.

Description

Technical Field

[0001] The present invention relates to a method for storing recycled bis(2-hydroxyethyl) terephthalate and a method for preparing a polyester resin. Further, the present invention relates to a polyester resin prepared using the above method and an article containing the same.

Background Art

[0002] Polyester is widely used as a material for beverage filling containers, packaging films, audio and video films, etc. because of its excellent mechanical strength, heat resistance, transparency, and gas barrier properties. Further, polyester is widely produced 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, interior and exterior finishing materials, etc.

[0003] As a result, plastic waste such as polyester is generated at an uncollectable level worldwide every year. In recent years, regulations and plans regarding the recycling of waste plastic resources including waste polyester have been established in various countries around the world. For example, there have been attempts to use recycled resin at a certain ratio or more in packaging materials used in various fields. As a method for recycling waste polyester, physical or chemical methods are used, but the physical recycling method cannot guarantee purity and is not widely used.

[0004] In the chemical recycling method, the ester bonds of waste polyester are cleaved to depolymerize it. Reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. Among these, glycolysis is the decomposition of waste polyester by adding a glycol such as ethylene glycol or diethylene glycol at a high temperature. A reaction product mainly containing bis(2-hydroxyethyl) terephthalate (BHET) is obtained. After crystallization or purification, bis(2-hydroxyethyl) terephthalate can be used as a raw material for preparing unsaturated polyester or ester polyol.

[0005] In this regard, Korean Patent No. 1386683 discloses a crystallization method and apparatus for the chemical recycling of waste polyester. US Patent No. 7,211,193 discloses a method for purifying bis(2-hydroxyethyl) terephthalate (BHET), which includes subjecting a solution produced by decomposing a polyester mainly containing polyethylene terephthalate (PET) using ethylene glycol (EG) to crystallization under certain temperature conditions and solid-liquid separation.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The recycled bis(2-hydroxyethyl) terephthalate obtained by the depolymerization of waste polyester may be stored for a certain period after depolymerization and before being used for the polymerization of polyester resin. The quality of recycled BHET may deteriorate during the storage period, and in that case, it may affect the quality of the final polyester resin.

[0008] As a result of the research by the present inventors, when recycled bis(2-hydroxyethyl) terephthalate is mixed with a solvent and stored under specific conditions, the purity and yellowness index can be stably maintained, and thereby, it has been discovered that the quality such as the color of the final polyester resin produced from recycled bis(2-hydroxyethyl) terephthalate can be improved.

[0009] Accordingly, an object of the present invention is to provide a method for stably storing a solution of recycled bis(2-hydroxyethyl) terephthalate and a method for preparing a high-quality polyester resin using the same.

Means for Solving the Problems

[0010] According to the present invention, there is provided a method for storing recycled bis(2-hydroxyethyl) terephthalate, comprising: (1) mixing recycled bis(2-hydroxyethyl) terephthalate obtained by depolymerization of waste polyester with a solvent to prepare a solution of recycled bis(2-hydroxyethyl) terephthalate having a concentration of 95% by weight or less; and (2) storing the solution of recycled bis(2-hydroxyethyl) terephthalate at a temperature of 120° C. or lower to maintain the following defined YID index: YID index = (YID - YID[day 0]) / YID[day 0] (wherein YID[day 0] is the yellowness index of the solution of recycled bis(2-hydroxyethyl) terephthalate 30 minutes after preparation in step (1), and YID is the yellowness index of the solution of recycled bis(2-hydroxyethyl) terephthalate after storage in step (2)) at 2 or less. A method is provided that includes these steps.

[0011] Furthermore, according to the present invention, there is provided a method for preparing a polyester resin, comprising the step of polymerizing a polyester resin using the recycled bis(2-hydroxyethyl) terephthalate stored according to the above method.

[0012] Furthermore, according to the present invention, there is provided a polyester resin containing the regenerated bis(2-hydroxyethyl) terephthalate stored according to the above method.

[0013] Furthermore, according to the present invention, there is provided an article containing this polyester resin.

Effects of the Invention

[0014] According to the present invention, the regenerated bis(2-hydroxyethyl) terephthalate obtained by depolymerization of waste polyester is mixed with a solvent and stored under specific temperature and concentration conditions to suppress a decrease in purity and yellowness index. Thereby, the quality such as the color of the final polyester resin prepared from the regenerated bis(2-hydroxyethyl) terephthalate can be improved.

[0015] Specifically, according to the present invention, since the changes in the purity and yellowness index of the regenerated BHET solution are very small even after storage for a certain period, the color quality of the final polyester resin obtained from the regenerated BHET solution can hardly be deteriorated even when subjected to a polymerization reaction after storage for a certain period.

[0016] Therefore, the regenerated BHET stored according to the present invention and the polyester resin prepared from the regenerated BHET can be used for manufacturing articles made of environmentally friendly materials in various fields.

Modes for Carrying Out the Invention

[0017] [Best Mode for Carrying Out the Invention] Hereinafter, the present invention will be described in more detail.

[0018] In this specification, the terms referring to each component are used to distinguish them from each other and are not intended to limit the scope of the embodiments. Furthermore, in this specification, unless otherwise specified in the context, a singular expression is to be construed as including a plural expression as well.

[0019] In this specification, terms such as first, second, etc. are used to describe various components. However, the components should not be limited by the terms. This term is used for the purpose of distinguishing one element from another.

[0020] In this specification, the term "comprising" is intended to specify a particular characteristic, region, step, method, element, and / or component. Unless otherwise stated, it does not exclude the presence or addition of any other characteristic, region, step, method, element, and / or component. Recycled bis(2-hydroxyethyl) terephthalate Bis(2-hydroxyethyl) terephthalate is an ester of two ethylene glycols and one terephthalic acid. For example, bis(2-hydroxyethyl) terephthalate is a compound formed as an intermediate in the process of preparing polyesters such as polyethylene terephthalate (PET) through the polymerization of ethylene glycol and terephthalic acid or its esters.

[0021] Bis(2-hydroxyethyl) terephthalate (BHET) used as a polymerization raw material for the polyester resin according to the present invention is obtained from waste polyesters having repeating units of ethylene glycol and terephthalic acid, such as polyethylene terephthalate (PET) or glycol-modified polyethylene terephthalate (PETG). For example, it can be obtained by well-known depolymerization methods such as glycolysis, hydrolysis, and methanolysis.

[0022] The bis(2-hydroxyethyl) terephthalate (BHET) obtained by depolymerization of waste polyester as described above is referred to as "recycled bis(2-hydroxyethyl) terephthalate (recycled BHET)", or abbreviated as r-BHET or rBHET, but it should be understood as being different from a pure BHET compound.

[0023] Specifically, the recycled BHET may contain reagents or solvents used in various chemical steps during the depolymerization of waste polyester, or by-products formed by side reactions with them. Therefore, the BHET recycled by a general depolymerization method may contain organic impurities and inorganic impurities in addition to BHET as the main component. For this reason, recycled BHET can also be considered as a kind of composition containing two or more components, that is, a BHET composition. Recycled BHET may be used as a polymerization raw material for producing polyester resin.

[0024] The impurities contained in the recycled BHET may include, for example, diethylene glycol derivatives and unreacted monomers. The total content of impurities contained in the recycled BHET can be 10% by weight or more, 15% by weight or more, or 20% by weight or more, and can be 40% by weight or less, 35% by weight or less, 30% by weight or less, or 25% by weight or less.

[0025] The purity of the recycled BHET can be measured using liquid chromatography or the like. Specifically, the purity of the recycled BHET can be calculated by measuring the peak area fraction (%) of BHET with respect to the total peak area in the spectrum obtained using high performance liquid chromatography (HPLC).

[0026] For example, the purity of the recycled BHET can be 99.9% or less, 99% or less, 95% or less, 90% or less, or 85% or less, and can be 60% or more, 65% or more, 70% or more, 75% or more, or 80% or more. Specifically, the purity of the BHET subjected to the transesterification reaction of the present invention can be 60% - 99.9%, more specifically 65% - 99%, or 70% - 99%.

[0027] Furthermore, the recycled bis(2-hydroxyethyl) terephthalate may have a yellowness index (YID) measured with a spectrophotometer in a 25% by weight solution of 3.0 or less. Specifically, the yellowness index can be 2.5 or less, 2.0 or less, 1.5 or less, or 1.0 or less.

[0028] The bis(2-hydroxyethyl) terephthalate used in the present invention may be prepared by a conventional depolymerization method. However, in order to obtain a higher purity by reducing impurities such as diethylene glycol ester, it can be prepared by performing a multi-stage depolymerization reaction. Specifically, bis(2-hydroxyethyl) terephthalate can be obtained by performing the depolymerization reaction in multiple stages while significantly reducing the temperature in the latter stage, and then performing ion exchange and distillation of unreacted glycol after the depolymerization reaction.

[0029] A method for preparing recycled bis(2-hydroxyethyl) terephthalate according to one embodiment may include: (1a) subjecting waste polyester to depolymerization by a first glycolysis reaction at a temperature of 180°C to 200°C to obtain a first reactant; (1b) subjecting the first reactant to depolymerization by a second glycolysis reaction at a temperature of 150°C to 170°C to obtain a second reactant; (1c) subjecting the second reactant to ion exchange with an ion exchange resin to obtain a third reactant; (1d) removing unreacted glycol from the third reactant by distillation at a temperature of 150°C or lower to obtain a fourth reactant; and (1e) subjecting the fourth reactant to distillation to obtain crude bis(2-hydroxyethyl) terephthalate.

[0030] According to a specific embodiment, first, waste polyester is pulverized to a size of 4 mm or less, ethylene glycol is added thereto, and then it is subjected to the first glycolysis reaction in the presence of a zinc acetate catalyst at a temperature of 180°C to 200°C for about 2 hours. Ethylene glycol is further added thereto, and then the second glycolysis reaction is performed at a temperature of 150°C to 170°C for about 2 hours. Thereafter, it is cooled to 120°C or lower using vacuum flash, a small amount of filter aid is added, and then insoluble impurities are separated by filtration through solid-liquid separation and ion exchange is performed by passing it through a column filled with an ion exchange resin. Next, unreacted glycol is recovered at a temperature of 100°C to 130°C, purification is performed by thin-film evaporation at 190°C to 250°C, and finally an adsorption-crystallization step is performed to obtain high-purity and high-quality bis(2-hydroxyethyl) terephthalate.

[0031] By the above method, a two-step glycolysis reaction (i.e., the first glycolysis reaction and the second glycolysis reaction) is carried out. When solvation is promoted in the first glycolysis reaction, in the second glycolysis reaction, the transesterification reaction of waste polyester can be carried out under conditions of lower temperature and shorter reaction time. Therefore, the concentration of diethylene glycol (DEG) naturally formed at the general glycolysis reaction temperature can be significantly reduced, and the content of diethylene glycol ester in the finally prepared bis(2-hydroxyethyl) terephthalate can be significantly reduced.

[0032] Preparation and storage of a solution of recycled bis(2-hydroxyethyl) terephthalate Recycled bis(2-hydroxyethyl) terephthalate (BHET) may be stored for a certain period of time before being used for the polymerization of polyester resin.

[0033] Since recycled BHET is obtained by the depolymerization of waste polyester, compared with newly synthesized high-purity BHET monomers, many side reactions may occur depending on storage conditions such as temperature. As a result, the quality of recycled BHET may decrease depending on the storage conditions before being subjected to the polymerization reaction, and in that case, it may affect the quality of the final polyester resin. When such recycled BHET with reduced quality is used, the quality of the final polyester resin may be impaired.

[0034] According to the present invention, by mixing recycled BHET with a solvent to prepare a solution in a specific concentration range and then storing it in a specific temperature range, the generation of by-products that affect the color quality of the final polyester resin can be suppressed, and storage stability can be ensured. Then, a polymerization reaction is carried out using the recycled BHET solution stored by the above method, thereby ensuring the process stability during the supply of the polyester resin and finally obtaining a high-quality polyester resin.

[0035] First, the recycled BHET is mixed with a solvent to prepare a solution of recycled BHET with a concentration of 95% by weight or less. Within the above concentration range, it is advantageous for maintaining the quality of the recycled BHET solution during the storage period and improving the properties of the polyester resin prepared from the recycled BHET solution. For example, the concentration of the recycled BHET solution may be 90% by weight or less, 85% by weight or less, 80% by weight or less, 75% by weight or less, 70% by weight or less, 65% by weight or less, 60% by weight or less, or 55% by weight or less, and may also be 5% by weight or more, 10% by weight or more, 15% by weight or more, 20% by weight or more, 25% by weight or more, 30% by weight or more, 35% by weight or more, 40% by weight or more, or 45% by weight or more. As a specific example, the concentration of the recycled BHET solution may be 5% by weight to 95% by weight, 5% by weight to 55% by weight, 45% by weight to 95% by weight, or 25% by weight to 95% by weight.

[0036] Examples of the solvent used for preparing the solution of recycled BHET include water, ethylene glycol, methanol, and ethanol. As a specific example, the solvent may contain at least one of water and ethylene glycol. When the solvent contains both water and ethylene glycol at the same time, the mixing weight ratio of water and ethylene glycol may be, for example, 1:5 or 1:2.

[0037] The temperature (dissolution temperature) when mixing the recycled BHET with the solvent may be, for example, 60°C or higher, 65°C or higher, 70°C or higher, or 75°C or higher, and may also be 197°C or lower, 180°C or lower, 165°C or lower, 140°C or lower, 120°C or lower, 100°C or lower, 90°C or lower, or 80°C or lower. According to a specific embodiment, the mixing temperature may be 60°C to 120°C. Within the above preferred temperature range, it is advantageous for maintaining the quality of the recycled BHET solution during the storage period and improving the properties of the polyester resin prepared from the recycled BHET solution.

[0038] In the step of preparing the recycled BHET solution, further addition or evaporation of the solvent may be performed after mixing to adjust the concentration to a desired concentration.

[0039] Thereafter, the solution of recycled bis(2-hydroxyethyl) terephthalate is stored at a temperature of 120°C or lower. Within the above temperature range, it is advantageous for maintaining the quality of the recycled BHET solution during the storage period and improving the properties of the polyester resin prepared from the recycled BHET solution. For example, the storage temperature of the recycled BHET solution may be 120°C or lower, 115°C or lower, 110°C or lower, 105°C or lower, 100°C or lower, 95°C or lower, or 90°C or lower, and may also be 20°C or higher, 25°C or higher, 40°C or higher, 60°C or higher, 70°C or higher, or 80°C or higher. According to one embodiment, the storage temperature of the recycled BHET solution may be 60°C to 120°C.

[0040] As an example, the storage temperature of the recycled BHET solution may be the same as the temperature (dissolution temperature) for preparing the recycled BHET solution. As a specific example, the recycled BHET solution can be prepared at a temperature of 60°C to 120°C and can be stored while maintaining the temperature conditions.

[0041] The storage pressure of the recycled BHET solution is, for example, 5 kgf / cm 2 or less, 3 kgf / cm 2 or less, 2 kgf / cm 2 or less, 1.5 kgf / cm 2 or less, or 1 kgf / cm 2 or less, and may also be 0.1 kgf / cm 2 or higher, 0.3 kgf / cm 2 or higher, 0.5 kgf / cm 2 or higher, or 1 kgf / cm 2 or higher. As a specific example, the storage pressure of the recycled BHET solution may be 2 kgf / cm 2 or less. Within the above preferred pressure range, it is advantageous for maintaining the quality of the recycled BHET solution during the storage period and improving the properties of the polyester resin prepared from the recycled BHET solution.

[0042] The storage period of the recycled BHET solution may be, for example, 30 days or less, 20 days or less, 15 days or less, 7 days or less, or 5 days or less, and may also be 1 hour or more, 6 hours or more, 12 hours or more, or 1 day or more, 2 days or more, or 3 days or more. As a specific example, the storage period of the recycled BHET solution may be 7 days or less. Within the above period range, it is advantageous for maintaining the quality during the storage period of the recycled BHET solution and improving the properties of the polyester resin prepared from the recycled BHET solution.

[0043] According to the method of the present invention, the yellowness index is maintained at a certain level during the storage period of the recycled BHET solution. According to one embodiment, when storing the recycled BHET solution, the YID index defined as follows is maintained at 2 or less. YID index = (YID - YID[day 0]) / YID[day 0] In the formula, YID[day 0] is the yellowness index of the solution of recycled bis(2-hydroxyethyl) terephthalate 30 minutes after being prepared in step (1), and YID is the yellowness index of the solution of recycled bis(2-hydroxyethyl) terephthalate after storage in step (2).

[0044] For example, the YID index can be 2 or less, 1.5 or less, 1 or less, 0.7 or less, 0.5 or less, or 0.3 or less. As a specific example, the YID index can be 0 to 2, 0 to 1.5, 0 to 1, or 0 to 0.5.

[0045] According to the present invention, even when the recycled BHET solution is prepared, stored for a certain period, and then subjected to a polymerization reaction, the color quality of the final polyester resin obtained from the recycled BHET solution hardly deteriorates. According to one embodiment, in the method for storing recycled bis(2-hydroxyethyl) terephthalate, the discoloration index according to the following formula is 3 or less. Discoloration index = Col L-b [day 0] - Col L-b In the formula, Col L-b[Day 0] is the value obtained by subtracting the b value from the L value in the Hunter Lab color space of the first polyester resin injection molded product prepared by using bis(2-hydroxyethyl) terephthalate without mixing or storing it with a solvent. Col L-b L-b is the value obtained by subtracting the b value from the L value in the Hunter Lab color space of the second polyester resin injection molded product prepared by using bis(2-hydroxyethyl) terephthalate after mixing and storing it with a solvent in steps (1) and (2). The first and second polyester resin injection molded products are prepared to a thickness of 6 mm under the same polymerization and injection molding conditions except for using their respective bis(2-hydroxyethyl) terephthalates.

[0046] For example, the discoloration index can be 3 or less, 2.5 or less, 2 or less, 1.5 or less, 1 or less, 0.5 or less, or 0.3 or less. As a specific example, the discoloration index can be 0 to 3, 0 to 2, 0 to 1.5, or 0 to 1.

[0047] Furthermore, according to the present invention, during the storage period of the recycled BHET solution, the purity of the recycled BHET is maintained at a certain level. According to one embodiment, the purity of the recycled bis(2-hydroxyethyl) terephthalate used in step (1) can be 60% or more, and the change in purity according to the following formula can be 20% or less. Change in purity = rBHET purity [Day 0] - rBHET purity In the formula, rBHET purity [Day 0] is the purity of the recycled bis(2-hydroxyethyl) terephthalate before mixing with the solvent in step (1), and rBHET purity is the purity of the recycled bis(2-hydroxyethyl) terephthalate obtained by evaporating the solvent in the solution after the solution is stored in step (2).

[0048] For example, the change in purity can be 20% or less, 15% or less, 10% or less, 5% or less, 3% or less, or 1% or less. Specifically, the change in purity can be 0 to 3, 0 to 2, 0 to 1.5, or 0 to 1.

[0049] Method for preparing a polyester resin The solution of recycled bis(2-hydroxyethyl) terephthalate prepared and stored by the above method is used for the polymerization of the polyester resin.

[0050] That is, the method for preparing the polyester resin according to the present invention includes a step of polymerizing the polyester resin using the above-mentioned stored recycled bis(2-hydroxyethyl) terephthalate.

[0051] As an example, the solution of recycled bis(2-hydroxyethyl) terephthalate can be directly used for the polymerization reaction of the polyester, which may be advantageous in terms of uniform supply of raw materials and reaction efficiency. In particular, when used in the polymerization reaction as a solution, recycled BHET can be continuously introduced, enabling a continuous process of uniform polymerization reaction.

[0052] As another example, the solvent in the solution of recycled bis(2-hydroxyethyl) terephthalate may be evaporated to obtain solid-phase recycled bis(2-hydroxyethyl) terephthalate, which may then be used for the polymerization reaction of the polyester resin. In such a case, there is an advantage that the existing methods and apparatuses for introducing solid-phase recycled BHET can be directly used by storing recycled BHET as a solution for thermal stability and then evaporating the solvent and using it for the polymerization reaction.

[0053] In the polymerization, an esterification reaction (the first polymerization reaction step) and a polycondensation reaction (the second polymerization reaction step) may be sequentially carried out.

[0054] The polyester resin according to the present invention can be prepared by further adding terephthalic acid or its derivative and / or ethylene glycol in addition to recycled bis(2-hydroxyethyl) terephthalate. Further, the polyester resin can be prepared as a copolymer by further adding other diacids such as dicarboxylic acids and / or other glycols such as diols as comonomers.

[0055] For example, at least one monomer selected from the group consisting of (a) a dicarboxylic acid, such as terephthalic acid or a derivative thereof, (b) ethylene glycol or diethylene glycol, and (c) another diol component as a comonomer may be further subjected to an esterification reaction.

[0056] The dicarboxylic acid may include at least one selected from terephthalic acid and isophthalic acid.

[0057] The diol component added as a comonomer may include at least one selected from the group consisting of cyclohexanedimethanol, cyclohexanedimethanol derivatives, and isosorbide. The cyclohexanedimethanol derivative may be 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexanemethanol.

[0058] Furthermore, the diol added as a comonomer may further include 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, and 1,4-cyclohexanediol.

[0059] The esterification reaction may be carried out in the presence of an esterification reaction catalyst. For example, a zinc-based compound may be used. Specific examples of the zinc-based catalyst include zinc acetate, zinc acetate hydrate, zinc chloride, zinc sulfate, zinc sulfide, zinc carbonate, zinc citrate, zinc gluconate, or a mixture thereof.

[0060] The esterification reaction is, for example, 0 kgf / cm2 ~10.0 kgf / cm 2 The pressure and the temperature can be 150°C to 300°C. The conditions of the esterification reaction may be appropriately adjusted according to the specific properties of the polyester to be produced, the ratio of each component, or the processing conditions. Specifically, the pressure of the esterification reaction can be 0 kg / cm 2 ~5.0 kg / cm 2 , more specifically 0.1 kg / cm 2 ~3.0 kg / cm 2 It may also be. Furthermore, the temperature of the esterification reaction can be 200°C to 270°C, more specifically 240°C to 260°C.

[0061] The esterification reaction may be carried out batchwise or continuously. Furthermore, the raw materials, recycled BHET, dicarboxylic acid component, and diol component, may be introduced into the reactor separately, or may be introduced in a mixed state of two or more raw materials. They may be introduced in the form of a solid, liquid, or slurry. As an example, the dicarboxylic acid component, diol component, and recycled BHET may be added individually or in combination, or may be mixed with a pre-prepared terephthalic acid oligomer. The terephthalic acid oligomer may be prepared, for example, by reacting terephthalic acid with a diol, such as ethylene glycol, cyclohexanedimethanol, and isosorbide. As another example, the dicarboxylic acid component and recycled BHET may be introduced in the form of a slurry mixed with the diol component.

[0062] More specifically, a diol component such as isosorbide, which is solid at room temperature, may be dissolved in water or ethylene glycol and then mixed with a dicarboxylic acid component such as terephthalic acid to prepare a slurry. Alternatively, isosorbide may be melted at 60 °C or higher and then mixed with a dicarboxylic acid component such as terephthalic acid and other diol components to prepare a slurry. Further, water may be additionally added to the mixed slurry to promote an increase in the fluidity of the slurry. Further, in a continuous process, a liquid raw material (for example, a solution of recycled BHET) may be continuously supplied to a reactor using a pump or the like. The supply amount of the raw material per unit time can be determined by dividing the total amount of the supplied raw material by the time until the target production amount per day (for example, 50 t / day) is achieved.

[0063] A mixture of a solution of recycled bis(2-hydroxyethyl) terephthalate and other additive components is left in an esterification reactor for a certain period, for example, 1 hour to 24 hours, or 4 hours to 10 hours, and then transferred to a polycondensation reactor. The polycondensation reaction can produce a polyester resin having a relatively low molecular weight by melt polymerization. Further, after the melt polymerization, a polyester resin having a relatively high molecular weight can be produced by solid-phase polymerization.

[0064] The temperature in the polycondensation reaction may be 150°C to 300°C, specifically 200°C to 290°C, more specifically 260°C to 280°C. Further, the pressure in the polycondensation reaction may be 0.01 mmHg to 600 mmHg, specifically 0.05 mmHg to 200 mmHg, more specifically 0.1 mmHg to 100 mmHg. By adopting a reduced-pressure condition in the polycondensation reaction, glycol, which is a by-product of the polycondensation reaction, can be removed from the system. When the pressure of the polycondensation reaction exceeds the range of 0.01 mmHg to 400 mmHg, the removal of by-products may be insufficient. Further, when the temperature of the polycondensation reaction is less than 150°C, glycol, which is a by-product of the reaction, cannot be effectively removed from the system. Therefore, the intrinsic viscosity of the final reaction product will be low, and the physical properties of the final polyester resin will deteriorate. When the temperature of the polycondensation reaction exceeds 300°C, the possibility of yellowing of the final polyester resin increases. Further, the polycondensation reaction may be carried out for the time required until the intrinsic viscosity of the final reaction product reaches an appropriate level, for example, with an average residence time of 1 hour to 24 hours.

[0065] Furthermore, the polycondensation reaction may be carried out in the presence of a polycondensation catalyst. The polycondensation catalyst may be, for example, a titanium-based compound, a germanium-based compound, an antimony-based compound, an aluminum-based compound, a tin-based compound, or a mixture thereof. Examples of titanium compounds include tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, titanate lactate, triethanolamine titanate, acetylacetonate titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide, and the like. Examples of germanium-based compounds include germanium dioxide, germanium tetrachloride, germanium ethylene glycol oxide, germanium acetate, or a mixture thereof. Preferably, germanium dioxide can be used. Both crystalline and amorphous germanium dioxide may be used, and glycol-soluble germanium dioxide may also be used. The amount of the polycondensation catalyst used may be such that the amount of titanium element relative to the weight of the polyester resin is about 1 ppm to 100 ppm, more preferably about 1 ppm to 50 ppm.

[0066] In addition to the polycondensation catalyst, stabilizers, colorants, crystallization agents, antioxidants, branching agents, etc. may be further used. The timing of adding these additives is not particularly limited, and they may be added at any time during the preparation step of the polyester resin.

[0067] As stabilizers, phosphorus-based compounds such as phosphoric acid, trimethyl phosphate, triethyl phosphate, and triethyl phosphonoacetate can generally be used. The amount of the stabilizer added may be 10 ppm to 200 ppm based on the amount of the element with respect to the weight of the polyester resin. Further, common colorants such as cobalt acetate and cobalt propionate can be exemplified as colorants added to improve the color of the polyester resin. The amount of the colorant added may be 10 ppm to 200 ppm based on the amount of the cobalt element with respect to the weight of the polyester resin. If necessary, anthraquinone-based compounds, perinone-based compounds, azo-based compounds, methine-based compounds, etc. may be used as organic colorants. Commercially available toners such as Polysynthren Blue RLS manufactured by Clarient, or Solvaperm Red BB manufactured by Clarient may be used. The amount of the organic compound colorant added may be adjusted to 0 to 50 ppm based on the weight of the polyester resin. Crystal nucleating agents, ultraviolet absorbers, polyolefin resins, polyamide resins, etc. can be exemplified as crystallization agents. Hindered phenol-based antioxidants, phosphite-based antioxidants, thioether-based antioxidants, or mixtures thereof can be exemplified as antioxidants. Ordinary branching agents having three or more functional groups such as trimellitic anhydride, trimethylolpropane, trimellitic acid, or mixtures thereof can be exemplified as branching agents.

[0068] Composition and Characteristics of Polyester Resin The polyester resin of the present invention is a polyester resin regenerated by chemical recycling of waste polyester.

[0069] The polyester resin according to one embodiment of the present invention contains recycled bis(2-hydroxyethyl) terephthalate preserved by the above method.

[0070] Specifically, since the polyester resin of the present invention is polymerized using recycled BHET, it contains repeating units derived from recycled BHET in the polymer chain.

[0071] The content of recycled BHET in the polyester resin of the present invention may be 1% by weight or more, 5% by weight or more, 10% by weight or more, 30% by weight or more, 50% by weight or more, 70% by weight or more, or 90% by weight or more. Further, the content of recycled BHET may be 100% by weight or less, 99% by weight or less, 80% by weight or less, 60% by weight or less, 40% by weight or less, or 20% by weight or less.

[0072] As an example, recycled bis(2-hydroxyethyl) terephthalate may be used in an amount of 10% to 99% by weight based on the weight of the polyester resin.

[0073] On the other hand, since bis(2-hydroxyethyl) terephthalate has a structure in which two ethylene glycols and one terephthalic acid are bonded, the polyester resin of the present invention may essentially contain repeating units derived from ethylene glycol and terephthalic acid.

[0074] As described above, the polyester resin of the present invention contains a diacid component and a glycol component as monomers constituting the polyester resin. Further, the polyester resin of the present invention may further contain an additional diacid component and an additional glycol component for the polymerization of the polyester.

[0075] In the polyester resin of the present invention, the diacid component may be a dicarboxylic acid or its derivative, and the glycol component may be a diol.

[0076] In particular, the dicarboxylic acid includes terephthalic acid, and the physical properties such as heat resistance, chemical resistance, and weather resistance of the polyester resin can be improved by terephthalic acid. For example, terephthalic acid may be used in an amount of 5 mol% to 100 mol% based on the total number of moles of dicarboxylic acids. Further, the terephthalic acid component may be formed from a terephthalic acid alkyl ester such as dimethyl terephthalate.

[0077] Furthermore, the diol contains ethylene glycol or diethylene glycol, and ethylene glycol or diethylene glycol can contribute to improving the transparency and impact resistance of the polyester resin. For example, ethylene glycol and / or diethylene glycol may be used in an amount of 5 mol% to 100 mol% based on the total number of moles of the diol.

[0078] According to one embodiment, the polyester resin of the present invention may be a copolymer resin containing two or more dicarboxylic acid components and / or two or more diol components.

[0079] Specifically, the dicarboxylic acid component may further contain an aromatic dicarboxylic acid component other than terephthalic acid, an aliphatic dicarboxylic acid component, or a mixture thereof. The dicarboxylic acid other than terephthalic acid may be used in an amount of 1 mol% to 30 mol% based on the weight of the total dicarboxylic acid component.

[0080] The aromatic dicarboxylic acid component may be an aromatic dicarboxylic acid having 8 to 20 carbon atoms, preferably 8 to 14 carbon atoms, or a mixture thereof. Examples of the aromatic dicarboxylic acid include, but are not limited to, isophthalic acid, naphthalenedicarboxylic acid such as 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, 4,4'-stilbenedicarboxylic acid, 2,5-furandicarboxylic acid, 2,5-thiophenedicarboxylic acid, etc.

[0081] The aliphatic dicarboxylic acid component may be an aliphatic dicarboxylic acid having 4 to 20 carbon atoms, preferably 4 to 12 carbon atoms, or a mixture thereof. Examples of the aliphatic dicarboxylic acid include, but are not limited to, linear, branched or cyclic aliphatic dicarboxylic acid components such as cyclohexanedicarboxylic acid such as 1,4-cyclohexanedicarboxylic acid and 1,3-cyclohexanedicarboxylic acid, phthalic acid, sebacic acid, succinic acid, isodecyl succinic acid, maleic acid, fumaric acid, adipic acid, glutaric acid, azelaic acid, etc.

[0082] Furthermore, the diol component may further contain a comonomer other than ethylene glycol or diethylene glycol. The comonomer may include, for example, at least one selected from the group consisting of cyclohexanedimethanol, cyclohexanedimethanol derivatives, and isosorbide.

[0083] Cyclohexanedimethanol (e.g., 1,2 - cyclohexanedimethanol, 1,3 - cyclohexanedimethanol, and 1,4 - cyclohexanedimethanol) can contribute to improving the transparency and impact resistance of the polyester resin to be produced. For example, cyclohexanedimethanol may be used in an amount of 5 mol% to 90 mol% based on the total number of moles of diol. The cyclohexanedimethanol derivative may be 4 - (hydroxymethyl) cyclohexylmethyl - 4 - (hydroxymethyl) cyclohexanecarboxylate or 4 - (4 - (hydroxymethyl) cyclohexylmethoxymethyl) cyclohexylmethanol. The cyclohexanedimethanol derivative may be used in an amount of 0.1 mol% to 25 mol% based on the total number of moles of diol.

[0084] Isosorbide can improve the processability of the final polyester resin. The transparency and impact resistance of the polyester resin are improved by the diol components of cyclohexanedimethanol and ethylene glycol. However, for processability, the shear flow characteristics should be improved and the crystallization rate should be delayed. However, it is difficult to achieve this effect with only cyclohexanedimethanol and ethylene glycol. Therefore, when isosorbide is used as the diol component, the shear flow characteristics can be improved while maintaining the transparency and impact resistance, and the crystallization rate is delayed, thereby improving the processability of the polyester resin produced. Preferably, isosorbide may be used in an amount of 0.1 mol% to 50 mol% based on the total number of moles of diol.

[0085] As a specific example, the polyester resin contains a diacid component and a glycol component. The diacid component may contain at least one selected from the group consisting of terephthalic acid, isophthalic acid, dimethyl isophthalate, phthalic acid, dimethyl phthalate, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, dimethyl 2,6-naphthalenedicarboxylate, diphenyldicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, dimethyl 1,4-cyclohexanedicarboxylate, dimethyl 1,3-cyclohexanedicarboxylate, sebacic acid, succinic acid, isodecyl succinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid, and azelaic acid. The glycol component may contain at least one selected from the group consisting of isosorbide, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol.

[0086] According to one embodiment, in addition to bis(2-hydroxyethyl) terephthalate, the polyester resin may further contain at least one monomer selected from the group consisting of (a) a dicarboxylic acid or its derivative, (b) ethylene glycol or diethylene glycol, and (c) a diol comonomer. The dicarboxylic acid may include at least one selected from terephthalic acid and isophthalic acid. Further, the diol comonomer may include at least one selected from the group consisting of cyclohexanedimethanol, cyclohexanedimethanol derivatives, and isosorbide. The cyclohexanedimethanol derivative may be 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexanedimethanol. The diol comonomer may further include 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, and 1,4-cyclohexanediol.

[0087] The polyester resin may also contain a catalyst used in the polymerization reaction for its preparation. For example, the polyester resin may contain at least one catalyst selected from metal oxides and acetates. The metal contained in the catalyst may be selected from the group consisting of antimony (Sb), titanium (Ti), germanium (Ge), manganese (Mn), cobalt (Co), tin (Sn), and calcium (Ca).

[0088] When measuring the Hunter Lab color space, the value obtained by subtracting the b value from the L value of the polyester resin can be 85 or more. For example, the L - b value can be 85 or more, 86 or more, 87 or more, 88 or more, 89 or more, 90 or more, or 91 or more. Furthermore, the upper limit of the L - b value is not particularly limited. However, for example, it may be 100 or less, 99 or less, 98 or less, 97 or less, or 95 or less. The measurement of the Hunter Lab color space can be performed by preparing a test piece with a thickness of 6 mm from the polyester resin.

[0089] The intrinsic viscosity of the polyester resin according to the present invention at 35°C may be 0.5 dl / g or more, 0.6 dl / g or more, or 0.7 dl / g or more, and may also be 1.2 dl / g or less, 1.1 dl / g or less, 1.0 dl / g or less, or 0.9 dl / g or less. For example, the intrinsic viscosity of the polyester resin at 35°C may be 0.5 dl / g to 1.2 dl / g. Specifically, the intrinsic viscosity of the polyester resin at 35°C may be 0.5 dl / g to 0.9 dl / g.

[0090] Due to its excellent color, mechanical strength, heat resistance, transparency, and gas barrier properties, the polyester resin according to the present invention can be used as a material for beverage filling containers, packaging films, audio and video films, etc. Furthermore, the polyester sheet or polyester plate prepared from the polyester resin according to the present invention has good transparency and excellent mechanical strength, and thus can be used as a raw material for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior and exterior finishing materials, etc. Furthermore, the polyester resin according to the present invention can also be used as industrial materials such as medical fibers and tire cords.

[0091] Accordingly, the present invention provides an article comprising a polyester resin. As an example, the article can be a film, a sheet, or a profile. Specific examples of the film include a shrink film and an inflation film. The profile refers to a continuous extrusion molded product of plastic excluding sheets and films. The profile can be manufactured by a general extrusion molding method and can be, for example, tubular or channel-shaped.

[0092] [Aspects of the Invention] Hereinafter, the present invention will be described in more detail with reference to embodiments. However, these examples are provided for illustrative purposes only, and the present invention is not limited thereto.

[0093] Preparation of Recycled Bis(2-hydroxyethyl) terephthalate Recycled BHET (rBHET) of various purities was prepared by depolymerizing waste polyester resin by a known method or purchased as a commercial product. The following table shows the peak area fraction (%) of BHET, that is, the purity, in the HPLC results of each recycled BHET (rBHET) measured using HPLC.

[0094] [Table 1]

[0095] Example 1 Step A: Preparation and storage of a solution of r-BHET The rBHET#1 prepared above as recycled bis(2-hydroxyethyl) terephthalate was dissolved in ethylene glycol (EG) as a solvent at 120 °C to obtain a solution with a concentration of 25% by weight. The solution of recycled bis(2-hydroxyethyl) terephthalate was stored at the same temperature (120 °C) and a pressure of 1 kgf / cm 2 for 7 days and used as it was in the next step.

[0096] Step B: Polymerization of the polyester resin Into the esterification reactor, a solution of recycled bis(2-hydroxyethyl) terephthalate obtained in the previous step (weight of rBHET#1: 19,051.9 kg), terephthalic acid (TPA, 29,052.9 kg), ethylene glycol (EG, 6,665.7 kg), 1,4-cyclohexanedimethanol (CHDM, 4,320.4 kg), isosorbide (ISB, 1,460.1 kg), diethylene glycol (DEG, 265.0 kg), Ge catalyst (64.0 kg), phosphoric acid (50.0 kg), blue toner (0.050 kg), and red toner (0.025 kg) were charged. Subsequently, nitrogen was injected into the esterification reactor, and the reactor was pressurized 2.0 kgf / cm 2 higher than the standard pressure (absolute pressure: 2,231.1 mmHg). Then, the temperature of the esterification reactor was raised to 220°C over 90 minutes, held at 220°C for 2 hours, and then raised again to 260°C over 2 hours. The mixture in the esterification reactor was stored at 260°C for about 7 hours and then transferred to the polycondensation reactor, and the by-products formed during the reaction were discharged through a column and a cooler. Then, the pressure of the esterification reactor was reduced from the standard pressure to 5 Torr (absolute pressure: 5 mmHg) over 30 minutes. At the same time, the temperature of the polycondensation reactor was raised to 280°C over 1 hour, and the polycondensation reaction was then carried out while maintaining the pressure of the polycondensation reactor at 1 Torr (absolute pressure: 1 mmHg) or less. At the start of the polycondensation reaction, the stirring speed may be set high. As the polycondensation reaction proceeds, if the viscosity of the reactants increases and the stirring force weakens, or if the temperature of the reactants exceeds the set temperature, the stirring speed may be appropriately adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.70 dl / g.

[0097] When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged out of the reactor to form pellets, solidified with a coolant, and then granulated so that the average weight was about 12 - 14 mg. The granules were left at 150 °C for 1 hour for crystallization and then fed into a solid-state polymerization reactor. While flowing nitrogen at a rate of 50 L / min, the temperature of the reactor was raised from room temperature to 190 °C at a rate of 40 °C / hour. While maintaining this, solid-state polymerization was carried out until the intrinsic viscosity (IV) of the granules in the reactor reached 1.20 dl / g, and about 50 tons of polyester resin (copolymer) was obtained.

[0098] Example 2 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), provided that in Step A, r-BHET#2 was used as recycled bis(2-hydroxyethyl) terephthalate, water was used as the solvent, the concentration was 25 wt%, the dissolution and storage temperature was 100 °C, and the storage pressure was 2 kgf / cm 2 and that in Step B, a solution of recycled bis(2-hydroxyethyl) terephthalate (weight of rBHET#2: 64,677.1 kg), ethylene glycol (EG, 263.1 kg), 1,4-cyclohexanedimethanol (CHDM, 1,833.4 kg), isosorbide (ISB, 495.7 kg), diethylene glycol (DEG, 539.8 kg), Ge catalyst (32.0 kg), blue toner (0.150 kg), and red toner (0.075 kg) was charged into the reactor, except that the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (molten substance) in the reactor reached 0.60 dl / g, and the solid-state polymerization was carried out until the intrinsic viscosity (IV) of the granules in the reactor reached 0.85 dl / g.

[0099] Example 3 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), provided that in Step A, r-BHET#3 was used as recycled bis(2-hydroxyethyl) terephthalate, water was used as the solvent, the concentration was 70 wt%, the dissolution and storage temperature was 90 °C, and the storage pressure was 1 kgf / cm 2That it was, and in Step B, a solution of recycled bis(2-hydroxyethyl) terephthalate (rBHET#3 weight: 48,636.6 kg), terephthalic acid (TPA, 10,595.4 kg), ethylene glycol (EG, 474.9 kg), 1,4-cyclohexanedimethanol (CHDM, 735.3 kg), diethylene glycol (DEG, 1,353.1 kg), Ge catalyst (32.0 kg), Ti catalyst (4.5 kg), phosphoric acid (5.0 kg), blue toner (0.200 kg), and red toner (0.050 kg) were charged into the reactor, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (molten substance) in the reactor reached 0.70 dl / g, except that solid-phase polymerization was not carried out.

[0100] Example 4 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), provided that in Step A, r-BHET#4 was used as recycled bis(2-hydroxyethyl) terephthalate, ethylene glycol (EG) was used as the solvent, the concentration was 90% by weight, the dissolution and storage temperature was 120 °C, and the storage pressure was 1 kgf / cm 2 That it was, and in Step B, a solution of recycled bis(2-hydroxyethyl) terephthalate (rBHET#4 weight: 6,392.2 kg), terephthalic acid (TPA, 37,598.1 kg), ethylene glycol (EG, 13,106.5 kg), 1,4-cyclohexanedimethanol (CHDM, 2,174.4 kg), diethylene glycol (DEG, 1,333.8 kg), Ti catalyst (2.2 kg), and phosphoric acid (10.0 kg) were charged into the reactor, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (molten substance) in the reactor reached 0.60 dl / g, except that solid-phase polymerization was carried out until the intrinsic viscosity (IV) of the granules in the reactor reached 1.00 dl / g.

[0101] Example 5 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), provided that in Step A, r-BHET#5 was used as recycled bis(2-hydroxyethyl) terephthalate, water was used as the solvent, the concentration was 95 wt%, the dissolution and storage temperature was 100 °C, and the storage pressure was 1.5 kgf / cm 2 and that in Step B, a solution of recycled bis(2-hydroxyethyl) terephthalate (weight of rBHET#5: 49,166.5 kg), terephthalic acid (TPA, 5,670.4 kg), ethylene glycol (EG, 706.0 kg), 1,4-cyclohexanedimethanol (CHDM, 10,493.7 kg), CHDM derivatives (4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a molar ratio of 1:3, containing 997.4 kg), Ge catalyst (64.0 kg), Ti catalyst (4.5 kg), phosphoric acid (5.0 kg), cobalt acetate (6.3 kg), blue toner (0.030 kg), and red toner (0.010 kg) were charged into the reactor, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (molten material) in the reactor reached 0.78 dl / g, except that solid-phase polymerization was not carried out.

[0102] Example 6 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), provided that in Step A, r-BHET#6 was used as recycled bis(2-hydroxyethyl) terephthalate, ethylene glycol (EG) was used as the solvent, the concentration was 85 wt%, the dissolution and storage temperature was 120 °C, and the storage pressure was 1 kgf / cm 2That it was so, and in Step B, a solution of recycled bis(2-hydroxyethyl) terephthalate (rBHET#6 weight: 13,403.4 kg), terephthalic acid (TPA, 26,279.1 kg), 1,4-cyclohexanedimethanol (CHDM, 19,756.8 kg), isosorbide (ISB, 6,163.5 kg), diethylene glycol (DEG, 2,237.4 kg), Ge catalyst (320.2 kg), phosphoric acid (1.0 kg), blue toner (0.150 kg), and red toner (0.050 kg) were charged into the reactor, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (molten substance) in the reactor reached 0.70 dl / g, except that solid-phase polymerization was not carried out.

[0103] Example 7 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), provided that in Step A, r-BHET#7 was used as recycled bis(2-hydroxyethyl) terephthalate, ethylene glycol (EG) was used as the solvent, the concentration was 50% by weight, the dissolution and storage temperature was 120 °C, and the storage pressure was 1 kgf / cm 2 That it was so, and in Step B, a solution of recycled bis(2-hydroxyethyl) terephthalate (rBHET#7 weight: 31,552.1 kg), terephthalic acid (TPA, 16,871.4 kg), isophthalic acid (IPA, 20,620.7 kg), ethylene glycol (EG, 2,660.6 kg), 1,4-cyclohexanedimethanol (CHDM, 10,082.2 kg), diethylene glycol (DEG, 2,394.1 kg), Ti catalyst (0.9 kg), phosphoric acid (10.0 kg), and cobalt acetate (13.7 kg) were charged into the reactor, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (molten substance) in the reactor reached 0.82 dl / g, except that solid-phase polymerization was not carried out.

[0104] Comparative Example 1 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), provided that in Step A, r-BHET#5-1 was used as recycled bis(2-hydroxyethyl) terephthalate, without mixing with a solvent, at 160 °C, and 1.5 kgf / cm 2 and stored for 7 days, and in Step B, a solution of recycled bis(2-hydroxyethyl) terephthalate (weight of rBHET#5-1: 49,166.5 kg), terephthalic acid (TPA, 5,670.4 kg), ethylene glycol (EG, 706.0 kg), 1,4-cyclohexanedimethanol (CHDM, 10,493.7 kg), CHDM derivatives (4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a molar ratio of 1:3, 997.4 kg in total), Ge catalyst (64.0 kg), Ti catalyst (4.5 kg), phosphoric acid (5.0 kg), cobalt acetate (6.3 kg), blue toner (0.030 kg), and red toner (0.010 kg) were charged, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (molten substance) in the reactor reached 0.78 dl / g, except that solid-state polymerization was not carried out.

[0105] Comparative Example 2 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), provided that in Step A, r-BHET#1-1 was used as recycled bis(2-hydroxyethyl) terephthalate, ethylene glycol (EG) was used as a solvent, the concentration was 98 wt%, the dissolution and storage temperature was 180 °C, and the storage pressure was 1.8 kgf / cm 2That it was so, and in Step B, a solution of recycled bis(2-hydroxyethyl) terephthalate (rBHET#1-1 weight: 19,051.9 kg), terephthalic acid (TPA, 29,052.9 kg), ethylene glycol (EG, 6,665.7 kg), 1,4-cyclohexanedimethanol (CHDM, 4,320.4 kg), isosorbide (ISB, 1,460.1 kg), diethylene glycol (DEG, 265.0 kg), Ge catalyst (64.0 kg), phosphoric acid (50.0 kg), blue toner (0.050 kg), and red toner (0.025 kg) were charged into the reactor, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (molten substance) in the reactor reached 0.70 dl / g, and the solid-phase polymerization was carried out until the intrinsic viscosity (IV) of the granules in the reactor reached 1.20 dl / g are excluded.

[0106] Comparative Example 3 The same procedure as in Example 1 was repeated to obtain about 50 tons of polyester resin (copolymer), provided that in Step A, r-BHET#7-1 was used as recycled bis(2-hydroxyethyl) terephthalate, stored at 120 °C and 1 kgf / cm 2 for 7 days without mixing with a solvent, and in Step B, a solution of recycled bis(2-hydroxyethyl) terephthalate (rBHET#7-1 weight: 31,552.1 kg), terephthalic acid (TPA, 16,871.4 kg), ethylene glycol (EG, 2,660.6 kg), 1,4-cyclohexanedimethanol (CHDM, 10,082.2 kg), diethylene glycol (DEG, 2,394.1 kg), Ti catalyst (0.9 kg), phosphoric acid (10.0 kg), and cobalt acetate (13.7 kg) were charged into the reactor, and the polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (molten substance) in the reactor reached 0.78 dl / g, and the solid-phase polymerization was not carried out are excluded.

[0107] Test Example 1: Evaluation of Recycled BHET Solution The evaluation of the recycled BHET solution was carried out as follows.

[0108] (1)YID Measurement method: The transmittance data of this solution was obtained using a Hunter Lab Color Flex EZ at an observer angle of 2° with illuminant D65. The yellow index (YID) value was calculated using the software's color analyzer.

[0109] Measurement of YID [Day 0]: The yellow index was measured 30 minutes after the preparation of the recycled BHET solution (0-day storage) in Step A of Examples 1 to 7 and Comparative Examples 1 to 3. In Comparative Examples 1 and 3 where the solution was not prepared, recycled BHET was dissolved in ethylene glycol (EG) at 120°C at a concentration of 25% by weight, and the yellow index was measured after 30 minutes.

[0110] Measurement of YID [Day 1] and YID [Day 7]: The yellow index was measured in the same manner as above after storing the recycled BHET solution for 1 day and 7 days under the storage conditions of Step A of Examples 1 to 7 and Comparative Examples 1 to 3.

[0111] The YID index was calculated according to the following formula. YID index = (YID [Day 7] - YID [Day 0]) / YID [Day 0] In the formula, YID [Day 0] is the yellow index at the time when 30 minutes have elapsed since the preparation of the recycled BHET solution, and YID [Day 7] is the yellow index of the recycled BHET solution after 7-day storage.

[0112] (2) HPLC Analysis method: Approximately 0.01 g of the recycled BHET sample was diluted with approximately 20 ml of methanol and analyzed by high performance liquid chromatography (HPLC) (Model: Waters e2695, Column: C18 (4.6 × 250 mm), 5 μm, UV detector: 242 nm, Injection volume: 10 μl, Eluent (gradient) A: H2O + H3PO4, B: Acetonitrile) Measurement of rBHET purity [Day 0]: The recycled BHET used in Step A of Examples 1 to 7 and Comparative Examples 1 to 3 was analyzed by HPLC before mixing with the solvent respectively, and the peak area fraction of BHET among the total peak areas was measured.

[0113] Measurement of rBHET purity [Day 1], rBHET purity [Day 3], rBHET purity [Day 5], and rBHET purity [Day 7]: Under the storage conditions of Step A in Examples 1 to 7 and Comparative Examples 1 to 3, each recycled BHET solution was stored for 1, 3, 5, and 7 days, then the solvent was evaporated, and analyzed by HPLC in the same manner as above. In Comparative Examples 1 and 3 where recycled BHET was not mixed with the solvent, recycled BHET was stored in a solid state, and then the yellowness index was measured.

[0114] The change in purity was calculated according to the following formula. Change in purity = rBHET purity [Day 0] - rBHET purity [Day 7] In the formula, rBHET purity [Day 0] is the purity of recycled bis(2-hydroxyethyl) terephthalate before mixing with the solvent, and rBHET purity [Day 7] is the purity of recycled bis(2-hydroxyethyl) terephthalate obtained by evaporating the solvent in the solution after storage for 7 days.

[0115] Tables 2 and 3 below show the preparation and storage conditions of the recycled BHET solutions and the test results in the examples and comparative examples.

[0116]

Table 2

[0117]

Table 3

[0118] As can be seen from Tables 2 and 3 above, the recycled BHET solutions prepared and stored under the preferred concentration and temperature conditions in Examples 1 to 7 maintained a high purity with a YID index of 2 or less after 7 days, indicating that a polyester resin of good quality can be produced from this recycled BHET solution.

[0119] In contrast, in Comparative Examples 1 to 3, the recycled BHET solutions prepared and stored under conditions deviating from the preferred concentration and temperature showed a YID index exceeding 2 after 7 days, indicating a significant decrease in purity, and demonstrating that a polyester resin of poor quality was produced from this recycled BHET solution.

[0120] <Preparation and Evaluation of Polyester Resin> The preparation and evaluation of the polyester resin were carried out as follows.

[0121] (0) Preparation of Polyester Resin <Test Group> Each polyester resin was prepared according to the procedures of Examples 1 to 7 and Comparative Examples 1 to 3 (i.e., a recycled BHET solution was prepared, stored for 7 days, and then subjected to a polymerization reaction to prepare a polyester resin).

[0122] <Reference Group> The procedures of Examples 1 to 7 and Comparative Examples 1 to 3 were carried out, except that the step of mixing recycled BHET with a solvent or the step of storing under specific temperature and pressure conditions (i.e., Step A) was not performed, but Step B was performed to prepare a polyester resin.

[0123] (1) Intrinsic Viscosity (IV) The polyester resin was dissolved in orthochlorophenol (OCP) at 150 °C at a concentration of 0.12% to obtain a solution, and the intrinsic viscosity was measured using an Ubbelohde viscometer in a constant temperature bath at 35 °C. Specifically, the temperature of the viscosity tube was maintained at 35 °C, and the time required for the solvent to pass through a specific part inside the viscosity tube (flow-down time) and the time required for the solution to pass through to obtain a specific viscosity were used to calculate the intrinsic viscosity.

[0124] The intrinsic viscosities measured after the melt polymerization of the polyester resins (i.e., melt IV) and the intrinsic viscosities measured after the solid-phase polymerization following the melt polymerization (i.e., solid-phase IV) in Examples 1 to 7 and Comparative Examples 1 to 3 are shown in the following table.

[0125] (2) Composition Each polyester resin was dissolved in a CDCl3 solvent at a concentration of 3 mg / ml, and 1H-NMR spectra were obtained at 25 °C using a nuclear magnetic resonance apparatus (JEOL, 600 MHz FT-NMR). 1 The contents (mol %) of diethylene glycol (DEG), isosorbide (ISB), and cyclohexanedimethanol (CHDM) residues with respect to the total number of moles of residues derived from all glycols (EG, DEG, BD, PDO, PTMG, PO3G, EO-PPG, etc.) were calculated by analyzing the above spectra, respectively.

[0126] Composition tests were conducted on the polyester resins of the test group (polymerization was carried out after preparing a recycled BHET solution and storing it for 7 days) and the reference group (polymerization was carried out using recycled BHET as it is without mixing with a solvent or storing).

[0127] (3) Color The chromaticity and lightness of the samples were measured using a Varian Cary 5 UV / Vis / NIR spectrophotometer equipped with a diffuse reflection accessory. A polyester resin test piece with a thickness of 6 mm was prepared by injection molding at 250 °C, and transmission data of illuminant D65 were obtained at an observer angle of 2°, processed using the color analyzer of Grams / 32 software, and Hunter Lab values were calculated. The value obtained by subtracting the b value from the L value (L - b) was calculated.

[0128] Color tests were conducted on the polyester resins of the test group (polymerization was carried out after preparing a recycled BHET solution and storing it for 7 days) and the reference group (polymerization was carried out using recycled BHET as it is without mixing with a solvent or storing).

[0129] The test results are shown in Tables 4 and 5 below.

[0130]

Table 4

[0131]

Table 5

[0132] As can be seen from Tables 4 and 5 above, the polyester resins of Examples 1 to 7 were prepared from recycled BHET stored for a certain period (7 days), but there was no change in the composition (DEG, ISB, and CHDM contents) compared with the polyester prepared from recycled BHET not stored for a certain period (stored for 0 days). In particular, the discoloration index (change in Hunter L-b value) was very small, and it was confirmed that there was almost no deterioration in the quality related to color.

[0133] On the other hand, although there was no change in the composition of the polyester resins of Comparative Examples 1 to 3, it was confirmed that the discoloration index (change in Hunter L-b value) exceeded 3 and the color quality was significantly deteriorated.

Claims

1. A method for storing recycled bis(2-hydroxyethyl) terephthalate, comprising: (1) mixing the recycled bis(2-hydroxyethyl) terephthalate obtained by depolymerization of waste polyester with a solvent to prepare a solution of recycled bis(2-hydroxyethyl) terephthalate having a concentration of 95% by weight or less; (2) storing the solution of the recycled bis(2-hydroxyethyl) terephthalate at a temperature of 120° C. or lower, and maintaining the YID index defined below: YID index = (YID - YID[day 0]) / YID[day 0] wherein YID[day 0] is the yellowness index of the solution of recycled bis(2-hydroxyethyl) terephthalate 30 minutes after preparation in step (1), and YID is the yellowness index of the solution of recycled bis(2-hydroxyethyl) terephthalate after storage in step (2)) at 2 or less; and the method includes this step.

2. The following formula: Color Rendering Index = Col Ｌ－ｂ [Day 0] - Col Ｌ－ｂ (wherein, Col Ｌ－ｂ [Day 0] is the value obtained by subtracting the b value from the L value in the Hunter Lab color space of the first polyester resin injection molded product prepared by using regenerated bis(2-hydroxyethyl) terephthalate as it is without mixing or storing it with a solvent, Col Ｌ－ｂ is a value obtained by subtracting the b value from the L value in the Hunter Lab color space of a second polyester resin injection molded product prepared using recycled bis(2-hydroxyethyl) terephthalate after being mixed with a solvent and stored in steps (1) and (2). The first and second polyester resin injection molded articles are prepared to a thickness of 6 mm under the same polymerization and injection molding conditions except that each uses bis(2-hydroxyethyl) terephthalate) The method for storing recycled bis(2-hydroxyethyl) terephthalate according to claim 1, wherein the discoloration index according to is 3 or less.

3. The purity of the recycled bis(2-hydroxyethyl) terephthalate used in step (1) is 60% or more, and the following formula: Change in purity = rBHEt purity[day 0] - rBHEt purity wherein rBHEt purity[day 0] is the purity of the recycled bis(2-hydroxyethyl) terephthalate before mixing with the solvent in step (1), and rBHEt purity is the purity of the recycled bis(2-hydroxyethyl) terephthalate obtained by evaporating the solvent in the solution after the solution is stored in step (2)) The method for storing recycled bis(2-hydroxyethyl) terephthalate according to claim 1, wherein the change in purity according to is 20% or less.

4. The method for storing recycled bis(2-hydroxyethyl) terephthalate according to claim 1, wherein the solvent contains at least one of water and ethylene glycol.

5. The method for storing recycled bis(2-hydroxyethyl) terephthalate according to claim 1, wherein the mixing temperature in step (1) is 60° C. to 120° C.

6. The storage pressure in step (2) is 2 kgf / cm ２ The method for storing regenerated bis(2-hydroxyethyl) terephthalate according to claim 1, wherein the storage pressure is 2 kgf / cm or less.

7. The method for storing recycled bis(2-hydroxyethyl) terephthalate according to claim 1, wherein the storage period in step (2) is 7 days or less.

8. A method for preparing a polyester resin, comprising the step of polymerizing a polyester resin using recycled bis(2-hydroxyethyl) terephthalate stored according to the method of claim 1.

9. A polyester resin comprising recycled bis(2-hydroxyethyl) terephthalate stored according to the method of claim 1.

10. The polyester resin according to claim 9, wherein the content of the recycled bis(2-hydroxyethyl) terephthalate in the polyester resin is 10% by weight to 99% by weight.

11. The polyester resin according to claim 9, comprising at least one catalyst selected from metal oxides and acetates, wherein the metal is selected from the group consisting of antimony (Sb), titanium (Ti), germanium (Ge), manganese (Mn), cobalt (Co), tin (Sn), and calcium (Ca).

12. The polyester resin contains a diacid component and a glycol component, The diacid component contains at least one selected from the group consisting of terephthalic acid, isophthalic acid, dimethyl isophthalate, phthalic acid, dimethyl phthalate, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, dimethyl 2,6-naphthalenedicarboxylate, diphenyldicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, dimethyl 1,4-cyclohexanedicarboxylate, dimethyl 1,3-cyclohexanedicarboxylate, sebacic acid, succinic acid, isodecyl succinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid, and azelaic acid. The glycol component contains at least one selected from the group consisting of isosorbide, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol. The polyester resin according to claim 9.

13. The polyester resin according to claim 9, having an intrinsic viscosity (IV) at 35 °C of 0.5 dl / g to 1.2 dl / g.

14. An article comprising the polyester resin according to any one of claims 9 to 13.

15. The article according to claim 14, which is a film, a sheet, or a profiled material.

Images