Polyester resin containing bis(glycol) terephthalate and method for preparing same

Abstract

Bis(glycol) terephthalate is prepared by transesterification of bis(2-hydroxyethyl) terephthalate, a recycled monomer obtained by depolymerization of waste polyester, with a glycol having at least three carbon atoms, and then copolymerized, thereby increasing the amount of recycled monomer in the polyester resin and improving purity by removing impurities during the transesterification reaction, thereby enhancing the quality of the final resin, such as color.

Description

Detailed Description of the Invention

[0001] [Technical field] The present invention relates to polyester resins containing bis(glycol) terephthalate as a recycled monomer and methods for preparing the same.

[0002] [Background technology] Due to its excellent mechanical strength, heat resistance, transparency, and gas barrier properties, polyester is widely used as a material for beverage containers, packaging films, audio and video films, etc. Furthermore, polyester is widely produced worldwide as an industrial material for medical fibers, tire cords, etc. In particular, polyester sheets or plates have good transparency and excellent mechanical strength, and as a result, are widely used as raw materials for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior and exterior materials, etc.

[0003] As a result, plastic waste, including polyester, is generated at an uncontrollable rate on a global scale every year. Recently, countries around the world have been creating regulations and plans for the reuse of waste plastic resources, including waste polyester. For example, there are attempts to use recycled resins in packaging materials used in various fields above a certain percentage. While physical and chemical methods are used to reuse waste polyester, physical recycling methods cannot guarantee purity and are not widely used.

[0004] In chemical recycling processes, the ester bonds of waste polyesters are broken to depolymerize them. Reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. Among them, glycolysis is the decomposition of waste polyesters by adding glycols such as ethylene glycol or diethylene glycol at high temperatures. The resulting reaction product contains primarily bis(2-hydroxyethyl) terephthalate (BHET). Bis(2-hydroxyethyl) terephthalate may be used as a raw material for preparing unsaturated polyester or ester polyols after their crystallization or purification.

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

[0006] [Prior art document] [Patent Document 1] Korean Patent No. 1386683 [Patent Document 2] U.S. Patent No. 7,211,193

[0007] [DISCLOSURE OF THE INVENTION] [Technical issues] The inventors attempted to develop a method for recycling BHET obtained by depolymerization of waste PET-based products into various engineering polyester products or environmentally friendly biodegradable polyester products, which could increase the content of recycled monomers while improving the quality of the final products.

[0008] However, recycled BHET generally has low purity due to impurities formed from the reagents used in the depolymerization process and side reactions, and therefore requires a separate process such as ion exchange or recrystallization to purify it, thereby causing cost problems. Furthermore, glycol monomers (DEG, ISB, CHDM, etc.) must be used in addition to BHET to produce copolyester resins, making it difficult to increase the content of recycled monomers in the final resin.

[0009] As a result of research conducted by the present inventors, it was discovered that if the glycol to be copolymerized is subjected to a transesterification reaction with BHET prior to preparing bis(glycol) terephthalate, which is then subjected to a polymerization reaction, the content of recycled monomer in the polyester resin can be increased; purity is improved by removing impurities during the transesterification reaction, thereby enhancing qualities such as color of the final resin.

[0010] It is therefore an object of the present invention to provide a method for preparing a polyester resin having a high content of recycled monomers, such as bis(2-hydroxyethyl) terephthalate, and excellent quality of the final resin, and a polyester resin prepared thereby.

[0011] [Solution to the problem] According to the present invention, there is provided a method for preparing a polyester resin, the method comprising the steps of reacting bis(2-hydroxyethyl) terephthalate with a glycol having three or more carbon atoms to prepare bis(glycol) terephthalate, and preparing a copolymer using bis(glycol) terephthalate and bis(2-hydroxyethyl) terephthalate.

[0012] According to the present invention, there is provided a polyester resin comprising bis(2-hydroxyethyl) terephthalate and bis(glycol) terephthalate as comonomers, wherein the glycol has 3 or more carbon atoms.

[0013] [Advantageous effects of the invention] According to the present invention, bis(2-hydroxyethyl) terephthalate obtained by depolymerization of waste polyester is subjected to a transesterification reaction with a glycol having three or more carbon atoms to prepare bis(glycol) terephthalate, which is then subjected to copolymerization, thereby increasing the content of recycled monomers in the polyester resin and improving the purity by removing impurities during the transesterification reaction, thereby enhancing the quality of the final resin, such as color.

[0014] Furthermore, according to the present invention, glycol monomers suitable for the desired copolymerization composition of polyester resins are subjected to a transesterification reaction with bis(2-hydroxyethyl) terephthalate in advance, so that the glycol by-products formed in the polymerization reaction can be reduced, and even when bis(2-hydroxyethyl) terephthalate with low purity is used, the purity of the recycled monomers can be improved, thereby reducing the costs for raw materials and processing. Therefore, it can be applied to the preparation of environmentally friendly polyester articles.

[0015] [Best Mode for Carrying Out the Invention] The invention is described in more detail below.

[0016] As used herein, the terms referring to each component are used to distinguish one from the other and are not intended to limit the scope of the embodiments. Furthermore, as used herein, the singular "a," "an," or "the" is to be construed as including the plural as well, unless the context clearly dictates otherwise.

[0017] 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. The terms are used to distinguish one element from another.

[0018] As used herein, the term "comprise" is intended to specify certain properties, regions, steps, processes, elements and / or components. It does not exclude the presence or addition of any other properties, regions, steps, processes, elements and / or components, unless specifically stated to the contrary.

[0019] The molecular weight of the compounds or polymers described herein, e.g., number average molecular weight or weight average molecular weight, is, as is well known, a relative mass based on carbon 12. Although the units are not given, if necessary, it may be understood as the molecular weight (g / mol) of the same numerical value.

[0020] As used herein, a "derivative" of a particular compound refers to a compound obtained by partially converting the compound by chemical reaction or by combining it with other components, thereby containing the major portion of the compound.

[0021] As used herein, a unit or group "derived from" a particular component refers to a portion of the component that is contained in the final product through a chemical reaction, such as a polymerization reaction. It may be that the portion is modified during the reaction, or it may exist in a form that is combined with other components. For example, a unit or group derived from at least one monomer is contained in the chain that makes up the polymer.

[0022] As used herein, "recycled monomer" may refer to a monomer obtained by decomposing, depolymerizing, reprocessing, or repolymerizing waste plastics, such as waste polyester, by physical or chemical methods, or by polymerizing a feedstock containing or derived from the monomer.

[0023] As an example, bis(2-hydroxyethyl) terephthalate (BHET) used as a starting material in the process according to the invention may be a recycled monomer obtained by depolymerization of waste polyester, and bis(glycol) terephthalates (BHDT, BHIT and BHCT) prepared therefrom may also be considered recycled monomers.

[0024] As another example, recycled monomers may also be used as glycols having 3 or more carbon atoms that are subjected to transesterification in the process of the present invention. As a specific example, at least one type of recycled glycol may be used, such as recycled 1,4-cyclohexanedimethanol (r-CHDM), recycled diethylene glycol (r-DEG), and recycled isosorbide (r-ISB).

[0025] As another example, recycled monomers may also be used as comonomers in the polymerization reaction of polyester resins in the method of the present invention. As a specific example, at least one type selected from recycled dicarboxylic acids and recycled diols may be used. As a more specific example, at least one type of recycled monomer may be used, such as recycled terephthalic acid (r-TPA), recycled isophthalic acid (r-IPA), recycled dimethyl terephthalate (r-DMT), recycled ethylene glycol (r-EG), recycled 1,4-cyclohexanedimethanol (r-CHDM), recycled diethylene glycol (r-DEG), and recycled isosorbide (r-ISB).

[0026] Such recycled monomers may be obtained directly from waste plastics, such as waste polyester, by known methods, or may be purchased and used commercially.

[0027] According to an aspect of the present invention, there is provided a method for preparing a polyester resin, the method comprising the steps of reacting bis(2-hydroxyethyl) terephthalate with a glycol having three or more carbon atoms to prepare bis(glycol) terephthalate, and preparing a copolymer using bis(glycol) terephthalate and bis(2-hydroxyethyl) terephthalate.

[0028] A method for preparing bis(glycol) terephthalate includes feeding a glycol having three or more carbon atoms to a reactor, and feeding bis(2-hydroxyethyl) terephthalate to the reactor and carrying out a transesterification reaction.

[0029] The method of the present invention provides polyester resins with a high content of recycled monomers such as bis(2-hydroxyethyl) terephthalate and excellent quality of the final resin. Specifically, because a glycol monomer appropriate for the desired copolymerization composition of the polyester resin is first subjected to a transesterification reaction with bis(2-hydroxyethyl) terephthalate, the glycol by-product formed in the polymerization reaction can be reduced, and the purity of the recycled monomer can be improved even when bis(2-hydroxyethyl) terephthalate with low purity is used, thereby reducing raw material and processing costs. Therefore, it can be applied to the preparation of environmentally friendly polyester articles.

[0030] (bis(2-hydroxyethyl) terephthalate) Bis(2-hydroxyethyl) terephthalate is an ester of two ethylene glycols and one terephthalic acid. It is a compound formed as an intermediate in the process of preparing polyesters, such as polyethylene terephthalate (PET), by the polymerization of ethylene glycol and terephthalic acid or its esters.

[0031] The bis(2-hydroxyethyl) terephthalate used in the present invention can be obtained by depolymerization of waste polyester. For example, bis(2-hydroxyethyl) terephthalate can be obtained from waste polyesters having repeating units of ethylene glycol and terephthalic acid, such as polyethylene terephthalate (PET) or glycol-modified polyethylene terephthalate (PETG). Specifically, it can be obtained by well-known depolymerization methods such as glycolysis, hydrolysis, and methanolysis. In particular, bis(2-hydroxyethyl) terephthalate can be obtained by depolymerizing waste polyethylene terephthalate using ethylene glycol and then purifying it.

[0032] The bis(2-hydroxyethyl) terephthalate obtained by the depolymerization of the above-mentioned waste polyester is referred to as "regenerated bis(2-hydroxyethyl) terephthalate (regenerated BHET)" or abbreviated as r-BHET or rBHET, and should be understood as being distinct from the pure BHET compound. Specifically, regenerated BHET may contain by-products formed by side reactions with reagents or solvents used in various chemical steps during the depolymerization of waste polyester. Thus, BHET regenerated by a conventional depolymerization process contains organic and inorganic impurities in addition to BHET as the main component; therefore, its purity is low. For this reason, regenerated BHET can also be considered a type of composition containing two or more components, i.e., a BHET composition. Such regenerated BHET may be used as a polymerization raw material for producing polyester resins.

[0033] 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 may be 10% by weight or more, 15% by weight or more, or 20% by weight or more, and may be 40% by weight or less, 35% by weight or less, 30% by weight or less, or 25% by weight or less.

[0034] The purity of the regenerated BHET may be evaluated using liquid chromatography, etc. Specifically, the purity of the regenerated BHET may be calculated by measuring the fraction (%) of the peak area of BHET from the total peak area in a spectrum obtained using high-performance liquid chromatography (HPLC).

[0035] For example, the purity of the recycled BHET may be 97% or less, 90% or less, 85% or less, or 80% or less, or 60% or more, 65% or more, or 70% or more. Specifically, the purity of the BHET introduced into the transesterification reaction of the present invention may be 60% to 97%, particularly 65% to 90%, 65% to 85%, or 70% to 80%.

[0036] (glycol) The glycol used in the transesterification reaction of the present invention undergoes a transesterification reaction with bis(2-hydroxyethyl) terephthalate to form residues in bis(glycol) terephthalate as the product, which constitute the polymer chains of the final polyester resin polymerized from bis(glycol) terephthalate.

[0037] The glycols used in the present invention may be glycols having 3 or more carbon atoms that replace the ethylene glycol residue in the transesterification reaction.

[0038] In particular, glycol has a boiling point 10° C. or more higher than that of ethylene glycol, which is advantageous for purification by fractional distillation during the transesterification reaction.

[0039] Specifically, the glycol used in the transesterification reaction of the present invention may be a glycol monomer other than ethylene glycol (eg, an alkylene glycol having 3 or more carbon atoms) or a polymeric glycol (eg, a polyether).

[0040] As a more specific example, the glycol may be at least one selected from glycol monomers having 3 to 20 carbon atoms and a molecular weight of less than 500, and polymeric glycols having a number average molecular weight of 400 to 5,000.

[0041] The number of carbon atoms in the glycol monomer may be, for example, 3 or more, or 4 or more, and may be 20 or less, 15 or less, 12 or less, 10 or less, or 8 or less.

[0042] Specifically, the glycol monomer may be an aliphatic diol having 3 to 20 carbon atoms. Furthermore, the aliphatic diol may be a chain or a ring type.

[0043] Specific examples of glycols having 3 or more carbon atoms include 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, isosorbide, 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, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, The polyisoprene may contain at least one selected from the group consisting of 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, a copolymer of ethylene oxide and tetrahydrofuran, an ethylene oxide-added polypropylene glycol, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, poly-1,5-pentanediol, and derivatives thereof.

[0044] As a more specific example, the glycol monomer may include at least one selected from the group consisting of diethylene glycol, isosorbide, 1,4-cyclohexanedimethanol, and derivatives thereof. Such glycol monomer may be virgin glycol.

[0045] As another example, the glycol having three or more carbon atoms may include at least one type of recycled glycol obtained by depolymerization of waste polyester. As a specific example, the recycled glycol may be selected from the group consisting of recycled 1,4-cyclohexanedimethanol, recycled diethylene glycol, and recycled isosorbide. However, the types of recycled glycols that can be used in the present invention are not limited thereto. Any recycled glycol that can be subjected to a transesterification reaction may be used. Such recycled glycol may be used in the transesterification reaction to completely replace virgin glycol. Alternatively, recycled glycol and virgin glycol may be mixed in a specific ratio and used in the transesterification reaction. The mixing ratio of recycled glycol may be, for example, 0 mol% or more, 1 mol% or more, 10 mol% or more, 20 mol% or more, 30 mol% or more, 50 mol% or more, or 60 mol% or more, and 100 mol% or less, 99 mol% or less, 90 mol% or less, 50 mol% or less, or 40 mol% or less, particularly 1 mol% to 100 mol%, 1 mol% to 99 mol%, or 30 mol% to 100 mol%, based on the number of moles of total glycol.

[0046] Specific examples of the derivative of 1,4-cyclohexanedimethanol may include 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol, or a mixture thereof. More specifically, the derivative may be a mixture containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a molar ratio of 1:1 to 1:5 or 1:2 to 1:4.

[0047] The glycol monomer may have a molecular weight of less than 500, less than 400, less than 350, less than 300, less than 250, for example.

[0048] The polymer glycol may be selected from the group consisting of, for example, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, a copolymer of ethylene oxide and tetrahydrofuran, ethylene oxide-added polypropylene glycol, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, and poly-1,5-pentanediol. More specifically, the polymer glycol may include at least one selected from the group consisting of polytetramethylene glycol, polycarbonate diol, polypropylene glycol, and ethylene oxide-added polypropylene glycol.

[0049] The polymer glycol may have a number average molecular weight of, for example, 400 or more, 500 or more, 600 or more, 700 or more, or 800 or more, and 6,000 or less, 5,000 or less, 4,000 or less, or 3,000 or less. As a specific example, the number average molecular weight of the polymer glycol may be 400 to 5,000. More specifically, it may be preferably 1,000 to 3,000 from the viewpoint of reducing phase separation.

[0050] The polymer glycol is used in an amount of 5% to 75% by weight, preferably 10% to 60% by weight, and especially 15% to 50% by weight, based on the weight of the final polyester resin, which is advantageous for achieving a high molecular weight while improving the elastic modulus of the polyester resin.

[0051] (Transesterification reaction) Glycol and bis(2-hydroxyethyl) terephthalate are subjected to a transesterification reaction. [ka]

[0052] In Reaction Scheme 1, m is, for example, a number ranging from 1 to 10 or 1 to 4.

[0053] Furthermore, in Reaction Scheme 1, R is a glycol group having 3 or more carbon atoms and excluding the OH groups at both ends. For example, R may be an alkylene group having 3 to 20 carbon atoms, or a group in which two or more identical or different alkylene groups having 2 to 10 carbon atoms are connected via an ether group or a carbonate group. As another example, R may be a group of 3 to 20 carbon atoms containing one or more rings, which may be aliphatic or aromatic and may contain one or more heteroatoms (e.g., O, N, and S).

[0054] The transesterification reaction may be carried out in the presence of a catalyst, so when glycol, acid, or bis(2-hydroxyethyl) terephthalate is fed to the reactor, the catalyst may be fed along with it.

[0055] As a catalyst for the transesterification reaction, for example, at least one selected from the group consisting of zinc-based catalysts, titanium-based catalysts, germanium-based catalysts, antimony-based catalysts, aluminum-based catalysts, and tin-based catalysts may be used.

[0056] Examples of zinc-based catalysts include zinc acetate, zinc acetate hydrate, zinc chloride, zinc sulfate, zinc sulfide, zinc carbonate, zinc citrate, zinc gluconate, or mixtures thereof. Examples of titanium-based catalysts include tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, triethanolamine titanate, acetylacetonato titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide, etc. Examples of germanium-based catalysts include germanium dioxide, germanium tetrachloride, germanium ethylene glycol oxide, germanium acetate, or combinations thereof. Specifically, germanium dioxide can be used as the germanium-based catalyst. Both crystalline and amorphous germanium dioxide can be used, and glycol-soluble germanium dioxide can also be used.

[0057] The amount of transesterification catalyst used can vary depending on the reaction conditions and the catalyst used. For example, a metal-based catalyst (e.g., a titanium-based catalyst, a tin-based catalyst) may be used in an amount of 0.0001 to 0.05 parts by weight per 100 parts by weight of glycol and bis(2-hydroxyethyl) terephthalate fed to the reactor.

[0058] The transesterification reaction may be carried out batchwise or continuously.

[0059] For example, glycol, or glycol together with acid, may be fed to the reactor, and the temperature may be increased until a certain temperature level is reached, at which point bis(2-hydroxyethyl) terephthalate may be fed. The feeding of bis(2-hydroxyethyl) terephthalate may be carried out at a temperature of, for example, 180°C to 280°C in a nitrogen atmosphere, while ethylene glycol is removed as a by-product.

[0060] Bis(2-hydroxyethyl) terephthalate may be supplied all at once and subjected to the transesterification reaction with glycol. As a specific example, bis(2-hydroxyethyl) terephthalate may be prepared in powder form or in an aqueous BHET solution having a concentration of about 10 to 20 wt % dissolved in water at about 80 to 100°C, and then supplied all at once to the reactor.

[0061] Alternatively, bis(2-hydroxyethyl) terephthalate may be introduced into the transesterification reaction with glycol in a divided or continuous manner. According to one embodiment, bis(2-hydroxyethyl) terephthalate may be introduced into the transesterification reaction with glycol in two or more divided portions. The number of divided introductions may be two or more, three or more, four or more, or five or more, and may be 100 or less, 50 or less, 30 or less, 20 or less, 15 or less, or 10 or less. As a specific example, the number of divided introductions may be 2 to 30 or 3 to 15. The time interval between divided introductions may be determined by dividing the total introduction time by the number of divided introductions. The total introduction time may be, for example, 1 hour or more, 2 hours or more, and 5 hours or less, or 4 hours or less. Furthermore, the amount introduced at one time during divided introduction may be determined by dividing the total amount of bis(2-hydroxyethyl) terephthalate introduced into the reaction by the number of divided introductions.

[0062] According to another embodiment, bis(2-hydroxyethyl) terephthalate is continuously introduced into the transesterification reaction with glycol. The total time for continuous introduction may be, for example, 1 hour or more, or 2 hours or more, and 5 hours or less, or 4 hours or less. For example, continuous introduction may involve introducing a fixed amount of bis(2-hydroxyethyl) terephthalate per hour. The amount introduced per hour may be calculated by dividing the total amount of bis(2-hydroxyethyl) terephthalate introduced into the reaction by the total introduction time. As a specific example, bis(2-hydroxyethyl) terephthalate may be prepared in powder form or dissolved in water at about 80 to 100°C to form an aqueous BHET solution having a concentration of about 10 to 20% by weight, and may be continuously introduced. Continuous introduction may be carried out from the beginning of the transesterification reaction until 1 hour before the completion of the reaction. A dropping funnel may be used at the laboratory level, or at a commercial level, a metered feeder may be used for continuous introduction of a fixed amount per hour.

[0063] Once the supply of bis(2-hydroxyethyl) terephthalate is complete, the reaction conditions may be maintained until the transesterification reaction is complete. Furthermore, the process of collecting and removing ethylene glycol as a by-product may be continued during the transesterification reaction. The collection and removal of ethylene glycol may be carried out by a distillation process using the difference in boiling point from the other components. The distilled ethylene glycol may be recovered by cooling and reused in other processes.

[0064] The end point of the transesterification reaction may be determined by taking into account the theoretical amount of ethylene glycol formed from bis(2-hydroxyethyl) terephthalate by the transesterification reaction, or as the point at which no more by-products are released.

[0065] The pressure (absolute pressure) during the transesterification reaction is, for example, 0.5 kgf / cm 2 More than 0.7kgf / cm 2 or more, or 1.0 kgf / cm 2 or more, and 2.5kgf / cm 2 Below, 2.0kgf / cm 2 or less, or 1.5kgf / cm 2 Below, especially 0.5kgf / cm 2 ~2.5kgf / cm 2 may be.

[0066] The temperature during the ester exchange reaction may be 140°C or higher, 160°C or higher, 180°C or higher, or 200°C or higher, and may be 300°C or lower, 280°C or lower, 270°C or lower, 250°C or lower, or 220°C or lower. Furthermore, the ester exchange reaction may be carried out under a nitrogen atmosphere. As a specific example, the ester exchange reaction may be carried out under a nitrogen atmosphere of 0.5 kgf / cm. 2 ~2.5kgf / cm 2 The reaction may be carried out at a pressure of 1000 kJ / cm 2 and a temperature of 180° C. to 280° C. under a nitrogen atmosphere.

[0067] The pressure and temperature conditions during the transesterification reaction may be appropriately adjusted depending on the specific properties of the polyester to be produced, the ratio of each component, or the process conditions. For example, the transesterification reaction may be carried out at a temperature of 180°C or higher to facilitate the removal of ethylene glycol, a by-product formed during the transesterification reaction. Furthermore, the transesterification reaction may be carried out at a temperature 10°C lower than the boiling point of the glycol to reduce the loss of glycol during the transesterification reaction. As a specific example, when 1,4-butanediol is used as the glycol, the temperature may be adjusted to 180°C to 220°C. Alternatively, when 1,4-cyclohexanedimethanol is used, the temperature may be adjusted to 200°C to 270°C.

[0068] The products of the transesterification reaction primarily include bis(glycol) terephthalate and its derivatives, where the ethylene glycol residues in bis(2-hydroxyethyl) terephthalate are replaced with other glycol residues.

[0069] According to one embodiment, the bis(glycol) terephthalate obtained by the transesterification reaction comprises a compound represented by the following formula 1: [ka]

[0070] In formula 1, —OR—OH is a group derived from a glycol having 3 or more carbon atoms, and m is a number ranging from 1 to 10 or 1 to 4, for example.

[0071] The compound of Formula 1 may be a monomer or oligomer (dimer, trimer, etc.) of bis(glycol) terephthalate.

[0072] In Formula 1, R is a group derived from a glycol having three or more carbon atoms. For example, R may be an alkylene group having 3 to 20 carbon atoms, or a group in which two or more identical or different alkylene groups having 2 to 10 carbon atoms are connected via an ether group or a carbonate group. As another example, R may be a group of 3 to 20 carbon atoms containing a single or multiple rings, where the rings may be aliphatic or aromatic and may contain one or more heteroatoms (e.g., O, N, and S).

[0073] As a specific example, Formula 1 may be a compound in which R is a group derived from diethylene glycol and m is 1, i.e., bis(diethylene glycol) terephthalate (hereinafter abbreviated as BHDT). As another specific example, Formula 1 may be a compound in which R is a group derived from isosorbide and m is 1, i.e., bis(isosorbide) terephthalate (hereinafter abbreviated as BHIT). As another specific example, Formula 1 may be a compound in which R is a group derived from 1,4-cyclohexanedimethanol and m is 1, i.e., bis(1,4-cyclohexanedimethanol) terephthalate (hereinafter abbreviated as BHCT). [ka]

[0074] The bis(glycol) terephthalate may comprise two or more compounds represented by Formula 1 or derivatives thereof.

[0075] Since impurities in bis(glycol) terephthalate are removed in the process of removing by-products such as glycol formed during the transesterification reaction, its purity can be increased compared to that of the starting material, bis(2-hydroxyethyl) terephthalate. For example, the bis(glycol) terephthalate obtained by the transesterification reaction may have a purity of 80% or more. More specifically, the purity of bis(glycol) terephthalate may be 85% or more, 90% or more, or 95% or more. As a specific example, it may be 80% to 99.9%.

[0076] (Preparation of Polyester Resin) A polyester resin is then prepared by preparing a copolymer using bis(glycol) terephthalate and bis(2-hydroxyethyl) terephthalate.

[0077] In the step of preparing the copolymer, the esterification reaction (first polymerization reaction step) and the polycondensation reaction (second polymerization reaction step) may be carried out sequentially.

[0078] For example, preparing the copolymer may include subjecting comonomers including bis(glycol) terephthalate and bis(2-hydroxyethyl) terephthalate to an esterification reaction to obtain an oligomer, and subjecting the oligomer to polycondensation to obtain the copolymer.

[0079] Reaction Scheme 2 below illustrates schematically the copolymerization reaction of polyesters in which glycols may be formed as by-products. [ka]

[0080] In Reaction Scheme 2, R is a group derived from a glycol having 3 or more carbon atoms.

[0081] Additional monomers may be introduced into the esterification reaction in addition to the recycled monomers, for example, at least one comonomer selected from the group consisting of dicarboxylic acids, dicarboxylic acid derivatives, diols, and diol derivatives.

[0082] As specific examples, the dicarboxylic acid may include terephthalic acid or isophthalic acid; the dicarboxylic acid derivative may include dimethyl terephthalate or dimethyl isophthalate; the glycol may include diethylene glycol, 1,4-cyclohexanedimethanol, isosorbide, 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 The diol derivative may include 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol. Such comonomers may be virgin monomers.

[0083] In another example, the at least one comonomer may include recycled monomers obtained by depolymerization of waste polyester. Specifically, the at least one comonomer may include at least one recycled monomer selected from the group consisting of recycled dicarboxylic acids, recycled dicarboxylic acid derivatives, recycled diols, and recycled diol derivatives. More specifically, the recycled monomer may be selected from the group consisting of recycled ethylene glycol, recycled 1,4-cyclohexanedimethanol, recycled diethylene glycol, recycled isosorbide, recycled terephthalic acid, recycled dimethyl terephthalate, recycled isophthalic acid, and recycled dimethyl isophthalate. However, the types of recycled monomers that can be used as comonomers in the present invention are not limited thereto. Any recycled monomers that can be used in the preparation of polyester resins can also be used. Such recycled monomers may be used in the polymerization of polyester resins by completely replacing virgin monomers. Alternatively, recycled and virgin monomers may be mixed in a specific ratio and used in the polymerization of polyester resins. The mixing ratio of the recycled monomer may be, for example, 0 mol% or more, 1 mol% or more, 10 mol% or more, 20 mol% or more, 30 mol% or more, 50 mol% or more, or 60 mol% or more, and 100 mol% or less, 99 mol% or less, 90 mol% or less, 50 mol% or less, or 40 mol% or less, particularly 1 mol% to 100 mol%, 1 mol% to 99 mol%, or 30 mol% to 100 mol%, based on the number of moles of the total monomers.

[0084] The esterification reaction may be carried out in the presence of an esterification catalyst. For example, a zinc-based compound may be used. Specific examples of zinc-based catalysts include zinc acetate, zinc acetate hydrate, zinc chloride, zinc sulfate, zinc sulfide, zinc carbonate, zinc citrate, zinc gluconate, or a mixture thereof.

[0085] The esterification reaction can be carried out at a pressure of, for example, 0 kgf / cm 2 ~10.0kgf / cm 2The esterification reaction may be carried out at a pressure of 0.01 to 0.15 kg / cm and a temperature of 150 to 300°C. The esterification reaction conditions may be suitably adjusted depending on the specific properties of the polyester to be produced, the ratio of each component, or the process conditions. Specifically, the pressure in the esterification reaction may be adjusted to 0.01 to 0.15 kg / cm. 2 ~5.0kg / cm 2 , especially 0.1 kg / cm 2 ~3.0kg / cm 2 Furthermore, the temperature in the esterification reaction may be 200°C to 270°C, particularly 240°C to 260°C.

[0086] The esterification reaction may be carried out batchwise or continuously. Furthermore, the raw materials, recycled BHET, dicarboxylic acid, and diol, may be introduced into the reactor separately, or two or more raw materials may be introduced in a mixed state. They may be introduced in solid, liquid, or slurry form. For example, the dicarboxylic acid, diol, and recycled BHET may be added individually or in combination, or may be mixed with pre-prepared terephthalic acid oligomers. Terephthalic acid oligomers may be prepared, for example, by reacting terephthalic acid with a diol such as ethylene glycol, cyclohexanedimethanol, and isosorbide. In another example, they may be introduced in the form of a slurry in which the dicarboxylic acid and recycled BHET are mixed with the diol.

[0087] More specifically, a diol such as isosorbide, which is solid at room temperature, may be dissolved in water or ethylene glycol and then mixed with a dicarboxylic acid 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 such as terephthalic acid and another diol to prepare a slurry. Furthermore, water may be added to the mixed slurry to help increase the fluidity of the slurry. Furthermore, in a continuous system, a liquid feedstock (e.g., a solution of recycled BHET) may be continuously fed to the reactor using a pump or the like. To achieve a target daily production volume, the hourly feed rate of the feedstock can be calculated by dividing the total amount of the feedstock by the time.

[0088] The mixture of bis(2-hydroxyethyl) terephthalate, bis(glycol) terephthalate, and other additive components is left in the esterification reactor for a certain period of time, 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. Furthermore, a polyester resin having a relatively high molecular weight can be produced by solid-state polymerization after melt polymerization.

[0089] The temperature in the polycondensation reaction may be 150°C to 300°C, preferably 200°C to 290°C, and especially 260°C to 280°C. Furthermore, the pressure in the polycondensation reaction may be 0.01 mmHg to 600 mmHg, preferably 0.05 mmHg to 200 mmHg, and especially 0.1 mmHg to 100 mmHg. When reduced pressure conditions are used in the polycondensation reaction, glycol, a by-product of the polycondensation reaction, can be collected and removed from the system. If the pressure in the polycondensation reaction exceeds the range of 0.01 mmHg to 400 mmHg, removal of the by-product may be insufficient. Furthermore, if the temperature in the polycondensation reaction is lower than 150°C, glycol, a by-product of the reaction, cannot be effectively collected and removed from the system; therefore, the intrinsic viscosity of the final reaction product is low, resulting in reduced physical properties of the final polyester resin. If the temperature in the polycondensation reaction exceeds 300° C., the possibility of yellowing of the final polyester resin increases. Furthermore, the polycondensation reaction may be carried out for a required time, for example, an average residence time of 1 hour to 24 hours, until the intrinsic viscosity of the final reaction product reaches a suitable level.

[0090] 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-based compounds include tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, lactate titanate, triethanolamine titanate, acetylacetonato titanate, ethyl acetoacetate titanate, isostearyl titanate, and titanium dioxide. Examples of germanium-based compounds include germanium dioxide, germanium tetrachloride, germanium ethylene glycol oxide, germanium acetate, or a mixture thereof. Preferably, germanium dioxide is used. Both crystalline and amorphous germanium dioxide may be used, and glycol-soluble germanium dioxide may also be used. The amount of polycondensation catalyst used may be such that the amount of elemental titanium is about 1 ppm to 100 ppm, more preferably about 1 ppm to 50 ppm, based on the weight of the polyester resin.

[0091] In addition to the polycondensation catalyst, a stabilizer, a pigment, a crystallizing agent, an antioxidant, a branching agent, etc. may also be 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.

[0092] Phosphorus-based compounds, such as phosphoric acid, trimethyl phosphate, triethyl phosphate, and triethyl phosphonoacetate, are commonly used as stabilizers. Their added amount may be about 10 ppm to 200 ppm based on the amount of elemental cobalt relative to the weight of the polyester resin. Furthermore, common pigments such as cobalt acetate and cobalt propionate may be added to enhance the color of the polyester resin. Their added amount may be about 10 ppm to 200 ppm based on the amount of elemental cobalt relative to the weight of the polyester resin. If necessary, anthraquinone-based compounds, perinone-based compounds, azo-based compounds, methine-based compounds, and the like may be used as organic pigments. Commercially available toners, such as Polysynthren Blue RLS from Clarient or Solvaperm Red BB from Clarient, may also be used. The amount of organic pigment 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, and the like may also be used as crystallization agents. Examples of the antioxidant include a hindered phenol antioxidant, a phosphite antioxidant, a thioether antioxidant, or a mixture thereof. Examples of the branching agent include a conventional branching agent having three or more functional groups, such as trimellitic anhydride, trimethylolpropane, trimellitic acid, or a mixture thereof.

[0093] (polyester resin) According to another aspect of the present invention, there is provided a polyester resin prepared by the above process.

[0094] The polyester resin of the present invention is a polyester resin regenerated by chemical recycling of waste polyester.

[0095] That is, the polyester resin is prepared by copolymerization of monomers including bis(2-hydroxyethyl) terephthalate and bis(glycol) terephthalate. Thus, the polyester resin contains bis(2-hydroxyethyl) terephthalate and bis(glycol) terephthalate as comonomers, where the glycol has three or more carbon atoms.

[0096] As mentioned above, bis(glycol) terephthalate may be the transesterification reaction product between bis(2-hydroxyethyl) terephthalate and a glycol having three or more carbon atoms.

[0097] Here, the glycol has 3 or more carbon atoms, and specific types thereof are as exemplified above.

[0098] As a specific example, the bis(glycol) terephthalate may be selected from the group consisting of bis(diethylene glycol) terephthalate, bis(isosorbide) terephthalate, bis(1,4-cyclohexanedimethanol) terephthalate, and derivatives thereof.

[0099] The total recycled monomer content in the polyester resin of the present invention may be 1 wt% or more, 5 wt% or more, 10 wt% or more, 30 wt% or more, 50 wt% or more, 70 wt% or more, or 90 wt% or more. Furthermore, the total recycled monomer content may be 100 wt% or less, 99 wt% or less, 80 wt% or less, 60 wt% or less, 40 wt% or less, or 20 wt% or less. As a specific example, the polyester resin may contain bis(2-hydroxyethyl) terephthalate and bis(glycol) terephthalate in a combined amount of 30 wt% or more based on the weight of the polyester resin.

[0100] Generally, the monomers (i.e., unused monomers) used in the polymerization of polyester resins, such as at least one selected from the group consisting of the above-mentioned dicarboxylic acids, dicarboxylic acid derivatives, diols, and diol derivatives, are used in addition to recycled monomers in the preparation of polyester resins, and therefore the polyester resins may further contain these comonomers.

[0101] The bis(2-hydroxyethyl) terephthalate used in preparing the polyester resin of the present invention has a structure in which two ethylene glycols and one terephthalic acid are bonded, so the polyester resin of the present invention can contain repeating units derived from ethylene glycol and terephthalic acid. Furthermore, since bis(glycol) terephthalate has a structure in which two ethylene glycols and one terephthalic acid, each having three or more carbon atoms, are bonded, the polyester resin of the present invention can further contain repeating units derived from a glycol having three or more carbon atoms.

[0102] As described above, the polyester resin of the present invention contains a dicarboxylic acid component and a glycol component as monomer components (polymer building block units) that constitute the polyester resin. These components may be derived from bis(2-hydroxyethyl) terephthalate and a glycol having 3 or more carbon atoms that were initially introduced for the preparation of the polyester resin, or from recycled bis(glycol) terephthalate prepared therefrom, and further comonomers that were introduced.

[0103] Thus, the polyester resin of the present invention may be a copolymerized resin containing two or more dicarboxylic acid components and / or two or more diol components.

[0104] According to one embodiment, the diol component may further include a diol component other than ethylene glycol as a comonomer, such as at least one selected from the group consisting of diethylene glycol, cyclohexanedimethanol, cyclohexanedimethanol derivatives, and isosorbide.

[0105] Diethylene glycol can contribute to enhancing the transparency and impact resistance of the polyester resin. For example, diethylene glycol may be used in an amount of 0.1 mol % to 50 mol % based on the total number of moles of diols.

[0106] Cyclohexanedimethanol (e.g., 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol) can contribute to enhancing the transparency and impact resistance of the resulting polyester resin. For example, cyclohexanedimethanol may be used in an amount of 5 mol % to 90 mol % based on the total number of moles of the diol component. 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 the diol component.

[0107] Isosorbide can improve the processability of the final polyester resin. The transparency and impact resistance of polyester resins are enhanced by the diol components cyclohexanedimethanol and ethylene glycol, but the shear thinning properties must be improved and the crystallization rate must be slowed for processability; however, it is difficult to achieve this effect with cyclohexanedimethanol and ethylene glycol alone. Therefore, when isosorbide is used as the diol component, the shear thinning properties are improved and the crystallization rate is slowed, while the transparency and impact resistance are maintained, thereby improving the processability of the resulting polyester resin. Preferably, isosorbide may be used in an amount of 0.1 mol% to 70 mol% based on the total moles of the diol component.

[0108] The polyester resin may contain terephthalic acid as a dicarboxylic acid component. 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. Furthermore, the terephthalic acid component may be formed from a terephthalic acid alkyl ester such as dimethyl terephthalate.

[0109] Furthermore, 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 total weight of the dicarboxylic acid component.

[0110] 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 aromatic dicarboxylic acids include, but are not limited to, isophthalic acid, naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, 4,4'-stilbene dicarboxylic acid, 2,5-furandicarboxylic acid, 2,5-thiophenedicarboxylic acid, and the like.

[0111] 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 aliphatic dicarboxylic acids include, but are not limited to, linear, branched, or cyclic aliphatic dicarboxylic acid components, for example, cyclohexanedicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and 1,3-cyclohexanedicarboxylic acid, phthalic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, fumaric acid, adipic acid, glutaric acid, azelaic acid, etc.

[0112] 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).

[0113] When the Hunter Lab color space is measured, the polyester resin may have a value obtained by subtracting the b value from the L value of 88 or more, 89 or more, 90 or more, 91 or more, 92 or more, or 93 or more. Furthermore, the upper limit of the Lb value is not particularly limited. However, it may be, for example, 100 or less, 99 or less, 98 or less, 97 or less, or 95 or less. Measurement of the Hunter Lab color space may be performed by making a test piece having a thickness of 6 mm using the polyester resin. As a specific example, when the Hunter Lab color space is measured, the polyester resin may have a value obtained by subtracting the b value from the L value of 88 or more under a thickness condition of 6 mm.

[0114] The intrinsic viscosity of the polyester resin 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 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 polyester resin may have an intrinsic viscosity of 0.5 dl / g to 1.2 dl / g at 35°C. Specifically, the polyester resin may have an intrinsic viscosity of 0.5 dl / g to 0.9 dl / g at 35°C.

[0115] 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 containers, packaging films, audio and video films, etc. Furthermore, polyester sheets or plates prepared from the polyester resin according to the present invention have good transparency and excellent mechanical strength, and as a result, can be used as raw materials for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior and exterior materials, etc. Furthermore, the polyester resin according to the present invention can be used as industrial materials, for example, medical fibers and tire cords.

[0116] Thus, the present invention provides an article comprising a polyester resin. For example, the article may be a film, a sheet, or a profile. Specific examples of films include heat-shrinkable films and blown films. A profile refers to a continuously extruded plastic article, excluding sheets and films. It may be fabricated by a typical extrusion method and may have the shape of, for example, a tube or a conduit.

[0117] [Embodiments of the present invention] Hereinafter, the present invention will be described in more detail with reference to embodiments, but these examples are provided for illustrative purposes only and the present invention is not limited thereto.

[0118] In the examples below, it should be understood that for glycols used in transesterification reactions and dicarboxylic acids or diols used as comonomers in the polymerization of polyester resins, virgin monomer was used unless it is indicated as recycled monomer (e.g., terephthalic acid, ethylene glycol, etc.).

[0119] Preparation Example 1: Regenerated bis(2-hydroxyethyl) terephthalate Recycled BHET of various purities was prepared by depolymerization of waste polyester resin by known methods or purchased commercially. The table below shows the peak area fraction (%) of BHET alone in the HPLC results of each recycled BHET, i.e., purity, as measured using HPLC. [Table 1]

[0120] Preparation Example 2: Preparation of bis(glycol) terephthalate by transesterification A 1-liter reactor for ester exchange reaction, equipped with a column and a condenser that can be cooled with water, was charged with 1,4-cyclohexanedimethanol as a glycol (CHDM, 641 g) and zinc acetate as a reaction catalyst (0.003 parts by weight per 100 parts by weight of the monomer mixture in the reactor). The pressure in the reactor was then reduced to standard pressure (1.0 kg / cm) with flowing nitrogen. 2 ), and the temperature was increased while maintaining the pressure and stirring. When the temperature in the reactor reached approximately 200°C, the temperature was increased to 220°C over 3 hours, while bis(2-hydroxyethyl) terephthalate (BHET, 254 g) was fed to carry out the transesterification reaction. Glycol, a by-product, was discharged through a column and a condenser during the reaction. Even after the addition of BHET was completed, the transesterification reaction was continued while maintaining the temperature at 220°C until the discharge of glycol stopped. Upon completion of the transesterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to standard pressure to obtain bis(1,4-cyclohexanedimethanol) terephthalate.

[0121] Example 1: Preparation of polyester resin Step A: Preparation of bis(glycol) terephthalate by transesterification Bis(2-hydroxyethyl) terephthalate (BHET #1) was subjected to transesterification with diethylene glycol (DEG), isosorbide (ISB), and 1,4-cyclohexanedimethanol (CHDM), respectively, according to the method of Preparation Example 2 above, to give bis(diethylene glycol) terephthalate (BHDT), bis(isosorbide) terephthalate (BHIT), and bis(1,4-cyclohexanedimethanol) terephthalate (BHCT), respectively.

[0122] Step B: Preparation of polyester resin by polycondensation reaction An esterification reactor was charged with bis(2-hydroxyethyl) terephthalate (BHET #1, 3,570.2 g), bis(diethylene glycol) terephthalate (BHDT, 69.7 g), bis(isosorbide) terephthalate (BHIT, 42.2 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT, 212.9 g), terephthalic acid (TPA, 913.0 g), ethylene glycol (EG, 46.3 g), isosorbide (ISB, 9.9 g), Ge catalyst (2.6 g), blue toner (0.012 g), and red toner (0.006 g).

[0123] Subsequently, nitrogen was injected into the esterification reactor, and the reactor was heated to a pressure of 2.0 kgf / cm 2 above standard pressure. 2 The mixture was pressurized to a high pressure (absolute pressure: 2,231.1 mmHg). The temperature of the esterification reactor was then increased to 220°C over 90 minutes, maintained at 220°C for 2 hours, and then increased 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 a polycondensation reactor, and the by-products formed during the reaction were discharged through a column and a condenser.

[0124] The pressure in the polycondensation reactor was then reduced from standard pressure to 5 Torr (absolute pressure: 5 mmHg) over 30 minutes. Simultaneously, the temperature of the polycondensation reactor was increased to 280°C over 1 hour, and the polycondensation reaction was then carried out while maintaining the pressure in the polycondensation reactor at 1 Torr (absolute pressure: 1 mmHg) or less. At the beginning of the polycondensation reaction, the stirring speed was set high. As the polycondensation reaction progressed, if the stirring power weakened due to an increase in the viscosity of the reactants or if the temperature of the reactants exceeded the set temperature, the stirring speed was adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.60 dL / g. The mixture was then discharged outside the reactor to form pellets, which were solidified using a cooling liquid and then granulated to an average weight of approximately 12-14 mg to prepare approximately 4 kg of polyester resin (copolymer).

[0125] Example 2: Preparation of polyester resin In step A, bis(2-hydroxyethyl) terephthalate (BHET #2) was subjected to a transesterification reaction with diethylene glycol (DEG) to produce bis(diethylene glycol) terephthalate (BHDT); in step B, a reactor was charged with bis(2-hydroxyethyl) terephthalate (BHET #2, 2,594.0 g), bis(diethylene glycol) terephthalate (BHDT, 174.6 g), terephthalic acid (TPA, 1,610.5 g), ethylene glycol (EG, 671.2 g), 1,4-cyclohexanedimethanol (CHDM, 58.8 g), Ge catalyst (2.6 g), Ti catalyst (0.4 g), phosphoric acid (0.4 g), blue toner (0.016 g), and red toner (0.004 g) and maintained at 0.5 kgf / cm above standard pressure. 2The same procedure as in Example 1 was repeated to obtain polyester granules, except that the esterification reaction was carried out at high pressure and a temperature of 260°C, and the polycondensation reaction was carried out at a temperature of 275°C until the intrinsic viscosity (IV) reached 0.70 dL / g. The granules were left to crystallize at 150°C for 1 hour 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 increased from room temperature to 200°C at a rate of 40°C / hr. While maintaining this temperature, solid-state polymerization was carried out until the intrinsic viscosity (IV) of the granules in the reactor reached 0.90 dL / g, yielding approximately 4 kg of polyester resin (copolymer).

[0126] Example 3: Preparation of polyester resin In step A, bis(2-hydroxyethyl) terephthalate (BHET #3) is subjected to a transesterification reaction with 1,4-cyclohexanedimethanol (CHDM) to produce bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); in step B, the reactor is charged with bis(2-hydroxyethyl) terephthalate (BHET #3, 3,941.2 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT, 1,144.6 g), ethylene glycol (EG, 34.0 g), 1,4-cyclohexanedimethanol (CHDM, 52.6 g), diethylene glycol (DEG, 38.7 g), CHDM derivative (4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a 1:3 molar ratio, 80.0 kg), Ge catalyst (5.1 g), Ti catalyst (0.4 g), phosphoric acid (0.4 g), blue toner (0.010 g), and red toner (0.002 g) were loaded into the 1000-kJ / kg sieve, and the pressure was increased by 2.0 kgf / cm above standard pressure. 2 The same procedure as in Example 1 was repeated, except that the esterification reaction was carried out at high pressure and a temperature of 255°C, and the polycondensation reaction was carried out at a temperature of 285°C until the intrinsic viscosity (IV) reached 0.78 dL / g, to obtain about 4 kg of polyester resin (copolymer).

[0127] Example 4: Preparation of polyester resin In step A, bis(2-hydroxyethyl) terephthalate (BHET #4) is subjected to a transesterification reaction with 1,4-cyclohexanedimethanol (CHDM) to produce bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); in step B, the reactor is charged with bis(2-hydroxyethyl) terephthalate (BHET #4, 2,782.0 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT, 763.1 g), terephthalic acid (TPA, 909.1 g), ethylene glycol (EG, 147.1 g), 1,4-cyclohexanedimethanol (CHDM, 315.4 g), diethylene glycol (DEG, 38.7 g), CHDM derivative (4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a 1:3 molar ratio, 80.0 kg), Ge catalyst (5.1 g), Ti catalyst (0.4 g), phosphoric acid (0.4 g), cobalt acetate (0.5 g), blue toner (0.002 g), and red toner (0.001 g) were charged, and the pressure was 2.0 kgf / cm above standard pressure. 2 The same procedure as in Example 1 was repeated, except that the esterification reaction was carried out at high pressure and a temperature of 255°C, and the polycondensation reaction was carried out at a temperature of 285°C until the intrinsic viscosity (IV) reached 0.78 dL / g, to obtain about 4 kg of polyester resin (copolymer).

[0128] Example 5: Preparation of polyester resin In step A, bis(2-hydroxyethyl) terephthalate (BHET #5) was subjected to a transesterification reaction with 1,4-cyclohexanedimethanol (CHDM) to produce bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); in step B, a reactor was charged with bis(2-hydroxyethyl) terephthalate (BHET #5, 907.1 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT, 2,596.3 g), terephthalic acid (TPA, 953.7 g), ethylene glycol (EG, 134.8 g), Ti catalyst (0.1 g), phosphoric acid (0.8 g), blue toner (0.002 g), and red toner (0.001 g) and pressurized at 1.5 kgf / cm above standard pressure. 2 The same procedure as in Example 1 was repeated, except that the esterification reaction was carried out at high pressure and a temperature of 250°C, and the polycondensation reaction was carried out at a temperature of 270°C until the intrinsic viscosity (IV) reached 0.82 dL / g, to obtain about 4 kg of polyester resin (copolymer).

[0129] Example 6: Preparation of polyester resin In step A, bis(2-hydroxyethyl) terephthalate (BHET #6) is subjected to a transesterification reaction with diethylene glycol (DEG) and 1,4-cyclohexanedimethanol (CHDM) to produce bis(diethylene glycol) terephthalate (BHDT) and bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); in step B, a reactor is charged with bis(2-hydroxyethyl) terephthalate (BHET #6, 1,376.8 g), bis(diethylene glycol) terephthalate (BHDT, 278.1 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT, 1,132.9 g), terephthalic acid (TPA, 1,514.7 g), ethylene glycol (EG, 784.2 g), 1,4-cyclohexanedimethanol (CHDM, 26.0 g), Ti catalyst (0.1 g), phosphoric acid (0.8 g), cobalt acetate (1.1 g), blue toner (0.002 g), and red toner (0.001 g) were charged, and the pressure was increased by 1.5 kgf / cm from the standard pressure. 2The same procedure as in Example 1 was repeated, except that the esterification reaction was carried out at high pressure and a temperature of 250°C, and the polycondensation reaction was carried out at a temperature of 270°C until the intrinsic viscosity (IV) reached 0.82 dL / g, to obtain about 4 kg of polyester resin (copolymer).

[0130] Example 7: Preparation of polyester resin In step A, bis(2-hydroxyethyl) terephthalate (BHET #7) is subjected to a transesterification reaction with isosorbide (ISB) and 1,4-cyclohexanedimethanol (CHDM) to produce bis(isosorbide) terephthalate (BHIT) and bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); in step B, a reactor is charged with bis(2-hydroxyethyl) terephthalate (BHET #7, 1,072.3 g), bis(isosorbide) terephthalate (BHIT, 629.2 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT, 2,258.7 g), terephthalic acid (TPA, 953.1 g), ethylene glycol (EG, 83.8 g), 1,4-cyclohexanedimethanol (CHDM, 24.3 g), regenerated isosorbide (r-ISB, 49.3 g), diethylene glycol (DEG, 35.8 g), Ge catalyst (25.6 g), phosphoric acid (0.08 g), blue toner (0.012 g), and red toner (0.004 g) were loaded, and the pressure was increased by 1.0 kgf / cm from the standard pressure. 2 The same procedure as in Example 1 was repeated, except that the esterification reaction was carried out at high pressure and a temperature of 265°C, and the polycondensation reaction was carried out at a temperature of 275°C until the intrinsic viscosity (IV) reached 0.70 dL / g, to obtain about 4 kg of polyester resin (copolymer).

[0131] Example 8: Preparation of polyester resin In step A, bis(2-hydroxyethyl) terephthalate (BHET #8) is subjected to a transesterification reaction with diethylene glycol (DEG) and 1,4-cyclohexanedimethanol (CHDM) to produce bis(diethylene glycol) terephthalate (BHDT) and bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); in step B, a reactor is charged with bis(2-hydroxyethyl) terephthalate (BHET #8, 483.4 g), bis(diethylene glycol) terephthalate (BHDT, 358.0 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT, 556.9 g), terephthalic acid (TPA, 2,448.4 g), recycled ethylene glycol (r-EG, 684.4 g), recycled 1,4-cyclohexanedimethanol (r-CHDM, 13.7 g), diethylene glycol (DEG, 10.1 g), CDM. The M derivative (166.7 kg containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a molar ratio of 1:3), Ge catalyst (2.6 g), phosphoric acid (0.4 g), blue toner (0.020 g), and red toner (0.008 g) were loaded, and the pressure was increased to 0.5 kgf / cm above standard pressure. 2 The same procedure as in Example 1 was repeated, except that the esterification reaction was carried out at high pressure and a temperature of 260°C, and the polycondensation reaction was carried out at a temperature of 275°C until the intrinsic viscosity (IV) reached 0.75 dL / g, to obtain about 4 kg of polyester resin (copolymer).

[0132] Example 9: Preparation of polyester resin In step A, bis(2-hydroxyethyl) terephthalate (BHET #9) is subjected to a transesterification reaction with 1,4-cyclohexanedimethanol (CHDM) to produce bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); in step B, the reactor is charged with bis(2-hydroxyethyl) terephthalate (BHET #9, 3,621.9 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT, 212.9 g), recycled terephthalic acid (r-TPA, 929.9 g), isophthalic acid (IPA, 2,451.6 g), ethylene glycol (EG, 21.0 g), isosorbide (ISB, 39.7 g), recycled diethylene glycol (r-DEG, 21.6 g), diethylene glycol (DEG, 21.6 g), Ti catalyst (0.4 g), phosphoric acid (8.0 g), cobalt acetate (0.7 g), blue toner (0.020 g), and red toner (0.008 g) were loaded, and the pressure was increased by 3.0 kgf / cm from the standard pressure. 2 The same procedure as in Example 1 was repeated to obtain polyester granules, except that the esterification reaction was carried out at high pressure and a temperature of 280°C, and the polycondensation reaction was carried out at 280°C until the intrinsic viscosity (IV) reached 0.60 dL / g. The granules were left to crystallize at 150°C for 1 hour 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 increased from room temperature to 190°C at a rate of 40°C / hr. While maintaining this temperature, solid-state polymerization was carried out until the intrinsic viscosity (IV) of the granules in the reactor reached 1.10 dL / g, yielding approximately 4 kg of polyester resin (copolymer).

[0133] Comparative Example 1: Preparation of polyester resin Step A was not performed; in Step B, the reactor was charged with bis(2-hydroxyethyl) terephthalate (BHET #3a, 4,636.7 g), ethylene glycol (EG, 56.6 g), 1,4-cyclohexanedimethanol (CHDM, 841.2 g), CHDM derivative (4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a 1:3 molar ratio, 80.0 kg), Ge catalyst (5.1 g), Ti catalyst (0.4 g), phosphoric acid (0.4 g), blue toner (0.010 g), and red toner (0.002 g), and the pressure was increased to 2.0 kgf / cm above standard pressure. 2 The same procedure as in Example 3 was repeated, except that the esterification reaction was carried out at high pressure and a temperature of 255°C, and the polycondensation reaction was carried out at a temperature of 285°C until the intrinsic viscosity (IV) reached 0.78 dL / g, to obtain about 4 kg of polyester resin (copolymer).

[0134] Comparative Example 2: Preparation of polyester resin Step A was not performed; in Step B, a reactor was charged with bis(2-hydroxyethyl) terephthalate (BHET #4a, 3,709.4 g), terephthalic acid (TPA, 606.1 g), ethylene glycol (EG, 56.6 g), 1,4-cyclohexanedimethanol (CHDM, 841.2 g), CHDM derivative (4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a 1:3 molar ratio, 80.0 kg), Ge catalyst (5.1 g), Ti catalyst (0.4 g), phosphoric acid (0.4 g), cobalt acetate (0.5 g), blue toner (0.002 g), and red toner (0.001 g), and the reactor was pressurized at 2.0 kgf / cm above standard pressure. 2The same procedure as in Example 1 was repeated, except that the esterification reaction was carried out at high pressure and a temperature of 255°C, and the polycondensation reaction was carried out at a temperature of 285°C until the intrinsic viscosity (IV) reached 0.80 dL / g, to obtain about 4 kg of polyester resin (copolymer).

[0135] Comparative Example 3: Preparation of polyester resin Step A was not performed; in Step B, the reactor was charged with bis(2-hydroxyethyl) terephthalate (BHET #7a, 1,072.3 g), terephthalic acid (TPA, 2,102.3 g), ethylene glycol (EG, 83.8 g), 1,4-cyclohexanedimethanol (CHDM, 1,580.5 g), regenerated isosorbide (r-ISB, 493.1 g), diethylene glycol (DEG, 35.8 g), Ge catalyst (25.6 g), phosphoric acid (0.08 g), blue toner (0.012 g), and red toner (0.004 g) and pressurized to 1.0 kgf / cm above standard pressure. 2 The same procedure as in Example 1 was repeated, except that the esterification reaction was carried out at high pressure and a temperature of 265°C, and the polycondensation reaction was carried out at a temperature of 275°C until the intrinsic viscosity (IV) reached 0.70 dL / g, to obtain about 4 kg of polyester resin (copolymer).

[0136] Tables 2 and 3 below summarize the monomer compositions of the Examples and Comparative Examples. [Table 2] [Table 3]

[0137] Test Example The raw materials and final resins used in the examples and comparative examples were tested as follows.

[0138] (1) Amount of recycled BHET added The number of moles of bis(2-hydroxyethyl) terephthalate (BHET) added was calculated as a percentage (mol%) based on the total number of moles of dicarboxylic acid and its derivatives (TPA, BHET, BHDT, BHIT, and BHCT) added to prepare the polyester resin.

[0139] (2) Purity of regenerated BHET (HPLC) Approximately 0.01 g of regenerated bis(2-hydroxyethyl) terephthalate was diluted in 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: HO + HPO, B: acetonitrile). The fraction (%) of the BHET peak area was then calculated from the total HPLC peak area.

[0140] (3) Recycled monomer content in resin The total weight (percent (wt%)) of recycled monomers only (BHET, BHDT, BHIT, BHCT, r-EG, r-CHDM, r-DEG, r-TPA, and r-IPA) was calculated based on the total weight of monomers (BHET, BHDT, BHIT, BHCT, TPA, IPA, EG, CHDM, ISB, DEG, r-EG, r-CHDM, r-DEG, r-TPA, r-IPA, etc.) added for the preparation of polyester resin.

[0141] (4) Copolymer composition (NMR) Each polyester resin was dissolved in CDCl3 solvent at a concentration of 3 mg / ml. 1 H-NMR spectra were obtained using a nuclear magnetic resonance spectrometer (JEOL, 600 MHz FT-NMR) at 25° C. Based on the total number of moles of residues derived from all glycols (EG, DEG, ISB, CHDM, etc.), the contents (mol %) of residues derived from diethylene glycol (DEG), isosorbide (ISB), cyclohexanedimethanol (CHDM), and their derivatives were calculated by analyzing each of the above spectra.

[0142] As a result, it was confirmed that the copolymer compositions of the polyester resins of Examples and Comparative Examples were different, specifically, the contents of residues derived from glycols (DEG, ISB, CHDM, etc.) and their derivatives were different in each polyester resin.

[0143] However, some of the polyester resins had the same composition. Specifically, it was confirmed that the copolymer compositions of Comparative Example 1 and Example 3, Comparative Example 2 and Example 4, and Comparative Example 3 and Example 7 were the same.

[0144] (5) Color (Hunter Lab) The color and brightness of polyester resins were measured using a Varian Cary 5 UV / Vis / NIR spectrophotometer equipped with a diffuse reflectance attachment. Polyester resin specimens with a thickness of 6 mm were prepared by injection molding at 250°C, and their transmittance data were obtained using illuminant D65 at an observer angle of 2°. The data was processed using the color analyzer with Grams / 32 software to calculate Hunter Lab values. The L value minus the b value (Lb) was calculated.

[0145] The test results are shown in Tables 4 and 5 below. [Table 4] [Table 5]

[0146] As can be seen from Tables 4 and 5 above, in Examples 1 to 9, in which a portion of the recycled monomer BHET was transesterified with other glycols (DEG, ISB, CHDM) to obtain BHDT, BHIT, and BHCT, which were then added to the polymerization reaction to obtain polyester resins, the color quality of the polyester resins was excellent, but the total recycled monomer content increased. In particular, in Examples 7 to 9, additional recycled glycols (r-EG, r-DEG, r-CHDM, or r-ISB) and recycled carboxylic acid (r-TPA) were further used to increase the total recycled monomer content.

[0147] In contrast, in Comparative Example 1, which had the same copolymerization composition as Example 3, BHET was used alone as the recycled monomer, which reduced the recycled monomer content in the resin, and the color of the final polyester resin was insufficient due to the low purity of BHET. Furthermore, in Comparative Example 2, which used BHET alone as the recycled monomer, no increase in purity was achieved by transesterification with glycol; therefore, the color of the final polyester resin was insufficient compared to Example 1, which used BHET of the same purity. Furthermore, in Comparative Example 3, which had almost the same amounts of BHET and r-ISB as those in Example 3, no other recycled monomers were used, which reduced the total recycled monomer content, and the color of the final polyester resin was insufficient.

Claims

1. reacting bis(2-hydroxyethyl) terephthalate with a glycol having three or more carbon atoms to prepare bis(glycol) terephthalate; preparing a copolymer using the bis(glycol) terephthalate and bis(2-hydroxyethyl) terephthalate; 1. A method for preparing a polyester resin, comprising:

2. 2. The method for preparing a polyester resin according to claim 1, wherein the bis(2-hydroxyethyl) terephthalate is obtained by depolymerization of waste polyester.

3. preparing the bis(glycol) terephthalate comprises: feeding a glycol having three or more carbon atoms to a reactor; feeding bis(2-hydroxyethyl) terephthalate to the reactor and carrying out a transesterification reaction; 10. A method for preparing the polyester resin of claim 1, comprising:

4. The glycol having three or more carbon atoms is preferably 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, isosorbide, 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, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 2. The method for preparing the polyester resin according to claim 1, wherein the polyester resin comprises at least one selected from the group consisting of olefins, 1,4-cyclohexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, copolymers of ethylene oxide and tetrahydrofuran, ethylene oxide-added polypropylene glycol, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, poly-1,5-pentanediol, and derivatives thereof.

5. 10. The method for preparing a polyester resin according to claim 1, wherein the glycol having three or more carbon atoms comprises at least one type of recycled glycol obtained by depolymerization of waste polyester.

6. 6. The method for preparing a polyester resin according to claim 5, wherein the recycled glycol is selected from the group consisting of recycled 1,4-cyclohexanedimethanol, recycled diethylene glycol, and recycled isosorbide.

7. 2. The method for preparing a polyester resin according to claim 1, wherein the bis(2-hydroxyethyl) terephthalate has a purity of 60% to 97%.

8. 10. The method for preparing a polyester resin according to claim 1, wherein the bis(glycol) terephthalate has a purity of 80% or greater.

9. preparing the copolymer comprises: subjecting the comonomers comprising bis(glycol) terephthalate and bis(2-hydroxyethyl) terephthalate to an esterification reaction to obtain an oligomer; subjecting said oligomer to a polycondensation reaction to obtain said copolymer; 10. A method for preparing the polyester resin of claim 1, comprising:

10. 6. The method for preparing the polyester resin of claim 5, wherein at least one comonomer selected from the group consisting of dicarboxylic acids, dicarboxylic acid derivatives, diols, and diol derivatives is further introduced into the esterification reaction.

11. the dicarboxylic acid comprises terephthalic acid or isophthalic acid; the dicarboxylic acid derivative comprises dimethyl terephthalate or dimethyl isophthalate; the glycol comprises diethylene glycol, 1,4-cyclohexanedimethanol, isosorbide, 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, or 1,4-cyclohexanediol; the diol derivative comprises 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol; A method for preparing the polyester resin of claim 10.

12. 11. The method for preparing a polyester resin according to claim 10, wherein the at least one comonomer comprises a recycled monomer obtained by depolymerization of waste polyester.

13. 13. The method for preparing the polyester resin of claim 12, wherein the recycled monomer is selected from the group consisting of recycled ethylene glycol, recycled 1,4-cyclohexanedimethanol, recycled diethylene glycol, recycled isosorbide, recycled terephthalic acid, recycled dimethyl terephthalate, recycled isophthalic acid, and recycled dimethyl isophthalate.

14. A polyester resin comprising bis(2-hydroxyethyl) terephthalate and bis(glycol) terephthalate as comonomers, said glycol having 3 or more carbon atoms.

15. 15. The polyester resin according to claim 14, wherein the polyester resin comprises the bis(2-hydroxyethyl) terephthalate and bis(glycol) terephthalate in a combined amount of 30% by weight or more, based on the weight of the polyester resin.

16. 15. The polyester resin according to claim 14, wherein the polyester resin has an L value minus b value of 88 or more under a thickness of 6 mm when measured in a Hunter Lab color space.

17. 15. The polyester resin of claim 14, wherein the bis(glycol) terephthalate is a transesterification reaction product between bis(2-hydroxyethyl) terephthalate and a glycol having 3 or more carbon atoms.

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