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

Abstract

According to the present invention, the bis (glycol) terephthalate is prepared by performing ester exchange on the recovered monomer bis (2-hydroxyethyl) terephthalate obtained by depolymerizing waste polyester and a diol having 3 or more carbon atoms and then performing copolymerization, such that the amount of the recovered monomer in the polyester resin can be increased; and the purity is improved by removing impurities during transesterification, thereby improving the quality, such as color, of the final resin.

Description

Technical Field

[0001] The present invention relates to a polyester resin containing terephthalate diol as a recovery monomer and a preparation method thereof. Background Art

[0002] Polyester is widely used as a material for beverage filling containers, packaging films, audio and video films, etc. due to its excellent mechanical strength, heat resistance, transparency and gas barrier properties. In addition, 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, so they are widely used as raw materials for boxes, boxes, partitions, shelves, panels, packaging materials, construction materials, indoor and outdoor materials, etc.

[0003] As a result, the amount of waste plastics such as polyester generated worldwide each year has reached an uncontrollable level. Recently, countries around the world have formulated regulations and plans for the recycling of waste plastic resources, including waste polyester. For example, some people have tried to use recycled resins at a certain ratio or higher in packaging materials used in various fields. Although physical or chemical methods are used as methods for recycling waste polyester, physical recycling methods cannot guarantee purity and are therefore not widely used.

[0004] In the chemical recycling method, the ester bonds of the waste polyester are cleaved to depolymerize it. Reactions such as glycolysis, hydrolysis, methanolysis and aminolysis are used. Among them, glycolysis is the decomposition of waste polyester at high temperature by adding glycols such as ethylene glycol or diethylene glycol. The reaction products obtained mainly include bis(2-hydroxyethyl) terephthalate (BHET). Bis(2-hydroxyethyl) terephthalate can be used as a raw material for the preparation of unsaturated polyesters or ester polyols after crystallization or purification.

[0005] In this regard, Korean Patent No. 1386683 discloses a crystallization method and apparatus for chemical recovery of waste polyester. U.S. Patent No. 7211193 discloses a purification method for bis(2-hydroxyethyl) terephthalate (BHET), which comprises crystallizing a solution produced by decomposing polyester containing polyethylene terephthalate (PET) as a main component using ethylene glycol (EG) under certain temperature conditions and performing solid-liquid separation.

[0006] [Prior art literature]

[0007] (Patent Document 1) Korean Patent No. 1386683

[0008] (Patent Document 2) U.S. Patent No. 7,211,193. Summary of the invention

[0009] Technical issues

[0010] The present inventors attempted to develop a method that can improve the quality of the final product while increasing the content of recycled monomers by recycling BHET obtained by depolymerizing waste PET products into various engineering polyester products or environmentally friendly biodegradable polyester products.

[0011] Meanwhile, due to impurities formed by reagents used in the depolymerization process and side reactions, the recovered BHET usually has low purity, so that a separate process such as ion exchange or recrystallization is required to purify it, resulting in a problem of increased cost. In addition, in addition to BHET, diol monomers (DEG, ISB, CHDM, etc.) must be used to produce copolyester resins, which makes it difficult to increase the content of the recovered monomers in the final resin.

[0012] As a result of studies conducted by the present inventors, it has been found that when the diol used for copolymerization is previously subjected to an ester exchange reaction with BHET to prepare bis(glycol) terephthalate and then subjected to a polymerization reaction, the content of recycled monomers in the polyester resin can be increased; and the purity is improved by removing impurities during the ester exchange reaction, thereby improving the quality of the final resin, such as color.

[0013] Therefore, an object of the present invention is to provide a method for preparing a polyester resin having a high content of recycled monomers (such as bis(2-hydroxyethyl) terephthalate) and excellent final resin quality, and a polyester resin prepared thereby.

[0014] Solution to the problem

[0015] According to the present invention, a method for preparing a polyester resin is provided, which comprises reacting bis(2-hydroxyethyl) terephthalate with a diol having 3 or more carbon atoms to prepare bis(diol) terephthalate; and preparing a copolymer using bis(diol) terephthalate and bis(2-hydroxyethyl) terephthalate.

[0016] According to the present invention, there is provided a polyester resin comprising bis(2-hydroxyethyl)terephthalate and bis(diol)terephthalate as comonomers, wherein the diol has 3 or more carbon atoms.

[0017] Advantageous Effects of the Invention

[0018] According to the present invention, bis(2-hydroxyethyl)terephthalate obtained by depolymerizing waste polyester is subjected to an ester exchange reaction with a glycol having 3 or more carbon atoms to prepare bis(glycol)terephthalate, which is then copolymerized. This can increase the content of recovered monomers in the polyester resin and improve the purity by removing impurities during the ester exchange reaction, thereby improving the quality of the final resin, such as color.

[0019] In addition, according to the present invention, since the diol monomer of the desired copolymerization composition suitable for the polyester resin is previously subjected to an ester exchange reaction with bis(2-hydroxyethyl)terephthalate, the diol by-product formed in the polymerization reaction can be reduced, and even when low-purity bis(2-hydroxyethyl)terephthalate is used, the purity of the recovered monomer can be improved, thereby reducing the raw material and processing costs. Therefore, it can be used to prepare an environmentally friendly polyester product. DETAILED DESCRIPTION

[0020] Best Mode for Carrying Out the Invention

[0021] Hereinafter, the present invention will be described in detail.

[0022] In the present specification, the terms relating to the respective components are used to distinguish them from each other, and are not intended to limit the scope of the embodiments. In addition, in the present specification, unless otherwise specified in the context, singular expressions are interpreted as also covering the plural.

[0023] In this specification, the terms first, second, etc. are used to describe various components. However, these components should not be limited by these terms. These terms are used to distinguish one element from another element.

[0024] In this specification, the term "includes / comprising" is intended to specify specific features, regions, steps, methods, elements and / or components. Unless explicitly stated to the contrary, the existence or addition of any other features, regions, steps, methods, elements and / or components is not excluded.

[0025] The molecular weight of the compound or polymer described in this specification, such as the number average molecular weight or weight average molecular weight, is a well-known relative mass based on carbon- 12. Although its unit is not described, it can be understood as the molar mass (g / mol) of the same numerical value if necessary.

[0026] In the present specification, a "derivative" of a specific compound means a compound obtained by partially converting the compound or combining it with other components through a chemical reaction, thereby containing a main part of the compound.

[0027] In this specification, a unit or group "derived" from a specific component refers to a part of the component included in the final product through a chemical reaction such as a polymerization reaction. It may exist in a form in which a part of it is modified during the reaction or combined with other components. For example, a unit or group derived from at least one monomer is included in the chain constituting a polymer.

[0028] In the present specification, "recycled monomer" may refer to a monomer obtained by decomposing, depolymerizing, reprocessing or repolymerizing waste plastics such as waste polyester by a physical or chemical method, or a polymerization raw material containing the monomer or derived from the monomer.

[0029] As an example, bis(2-hydroxyethyl)terephthalate (BHET) used as a raw material in the process according to the present invention can be a recycled monomer obtained by depolymerization of waste polyester, and bis(glycol)terephthalate (BHDT, BHIT and BHCT) prepared therefrom can also be considered as a recycled monomer.

[0030] As another example, the recycled monomers can also be used as diols having 3 or more carbon atoms for transesterification in the method of the present invention. As a specific example, at least one type of recycled diols can be used, such as recycled 1,4-cyclohexanedimethanol (r-CHDM), recycled diethylene glycol (r-DEG), and recycled isosorbide (r-ISB).

[0031] As another example, in the method of the present invention, the recovered monomer can also be used as a comonomer for the polymerization reaction of the polyester resin. As a specific example, at least one selected from the group consisting of recovered dicarboxylic acids and recovered diols can be used. As a more specific example, at least one type of recovered monomer can be used, such as recovered terephthalic acid (r-TPA), recovered isophthalic acid (r-IPA), recovered dimethyl terephthalate (r-DMT), recovered ethylene glycol (r-EG), recovered 1,4-cyclohexanedimethanol (r-CHDM), recovered diethylene glycol (r-DEG) and recovered isosorbide (r-ISB).

[0032] These recycled monomers can be obtained directly from waste plastics (such as waste polyester) by known methods, or can be purchased from the market and used.

[0033] According to one aspect of the present invention, a method for preparing a polyester resin is provided, the method comprising reacting bis(2-hydroxyethyl) terephthalate with a diol having 3 or more carbon atoms to prepare bis(glycol) terephthalate; and preparing a copolymer using bis(glycol) terephthalate and bis(2-hydroxyethyl) terephthalate.

[0034] The method for preparing bis(glycol) terephthalate includes feeding a glycol having 3 or more carbon atoms into a reactor; and feeding bis(2-hydroxyethyl) terephthalate into the reactor and performing an ester exchange reaction.

[0035] The method of the present invention provides a polyester resin having a high content of recycled monomers such as bis(2-hydroxyethyl) terephthalate and excellent final resin quality. Specifically, since the diol monomers of the desired copolymerization composition suitable for the polyester resin are previously subjected to an ester exchange reaction with bis(2-hydroxyethyl) terephthalate, the diol by-products formed in the polymerization reaction can be reduced, and even when low-purity bis(2-hydroxyethyl) terephthalate is used, the purity of the recycled monomers can be improved, thereby reducing the raw material and processing costs. Therefore, it can be used to prepare environmentally friendly polyester products.

[0036] Bis(2-hydroxyethyl) terephthalate

[0037] Bis(2-hydroxyethyl)terephthalate is an ester formed from two ethylene glycols and one terephthalic acid. For example, it is a compound formed as an intermediate in a process for preparing polyesters such as polyethylene terephthalate (PET) by polymerization of ethylene glycol and terephthalic acid or its esters.

[0038] The bis(2-hydroxyethyl) terephthalate used in the present invention can be obtained by the depolymerization of waste polyester. For example, bis(2-hydroxyethyl) terephthalate can be obtained from waste polyesters such as polyethylene terephthalate (PET) or glycol-modified polyethylene terephthalate (PETG) having repeating units of ethylene glycol and terephthalic acid. 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 with ethylene glycol and then purifying it.

[0039] The bis(2-hydroxyethyl)terephthalate obtained by depolymerization of the waste polyester as described above is referred to as "recovered bis(2-hydroxyethyl)terephthalate (recovered BHET)", or simply r-BHET or rBHET, which needs to be understood as different from the pure BHET compound. Specifically, the recovered BHET may contain reagents or solvents used in various chemical steps during the depolymerization of the waste polyester, or by-products formed by side reactions with them. Therefore, the BHET recovered by the ordinary depolymerization method contains organic and inorganic impurities in addition to BHET as the main component; therefore, its purity is not high. Therefore, the recovered BHET can also be regarded as a composition including two or more components, that is, a BHET composition. This recovered BHET can be used as a polymerization raw material for producing polyester resins.

[0040] Impurities contained in the recycled BHET may include diethylene glycol derivatives and unreacted monomers, etc. The total content of impurities contained in the recycled BHET may be 10 wt % or more, 15 wt % or more, or 20 wt % or more, and may be 40 wt % or less, 35 wt % or less, 30 wt % or less, or 25 wt % or less.

[0041] The purity of recovered BHET can be measured using liquid chromatography, etc. Specifically, the purity of recovered BHET can be calculated by measuring the fraction (%) of the peak area of ​​BHET to the total peak area in a spectrum obtained using high performance liquid chromatography (HPLC).

[0042] For example, the purity of the recovered BHET can be 97% or less, 90% or less, 85% or less, or 80% or less, and can be 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 can be 60% to 97%, more specifically, 65% to 90%, 65% to 85%, or 70% to 80%.

[0043] Diol

[0044] The diol used in the transesterification reaction of the present invention undergoes a transesterification reaction with bis(2-hydroxyethyl) terephthalate to form a residue in bis(diol) terephthalate as a product, which constitutes the polymer chain of the final polyester resin polymerized from bis(diol) terephthalate.

[0045] The diol used in the present invention may be a diol having 3 or more carbon atoms, which is used to replace the ethylene glycol residue in the transesterification reaction.

[0046] In particular, the boiling point of the diol is 10° C. or more higher than that of ethylene glycol, which facilitates purification by fractional distillation during the transesterification reaction.

[0047] Specifically, the diol used in the transesterification reaction of the present invention may be a diol monomer other than ethylene glycol (eg, an alkylene glycol having 3 or more carbon atoms) or a polymer diol (eg, polyether).

[0048] As a more specific example, the diol may be at least one selected from a diol monomer having 3 to 20 carbon atoms and a molecular weight of less than 500 and a polymeric diol having a number average molecular weight of 400 to 5,000.

[0049] The number of carbon atoms of the diol 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.

[0050] Specifically, the diol monomer may be an aliphatic diol having 3 to 20 carbon atoms. In addition, the aliphatic diol may be chain-shaped or cyclic.

[0051] As a specific example, the diol having 3 or more carbon atoms may include at least one selected from the group consisting of 1,3-propylene glycol, 1,4-butylene glycol, 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, 1,4-cyclohexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, copolymers of ethylene oxide and tetrahydrofuran, polypropylene glycol added with ethylene oxide, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, poly-1,5-pentanediol and their derivatives.

[0052] As a more specific example, the diol monomer may include at least one selected from the group consisting of diethylene glycol, isosorbide, 1,4-cyclohexanedimethanol and derivatives thereof. Such a diol monomer may be a raw diol.

[0053] As another example, the diol with 3 or more carbon atoms may include at least one recycled diol obtained by depolymerization of waste polyester. As a specific example, the recycled diol may be selected from the group consisting of recycled 1,4-cyclohexanedimethanol, recycled diethylene glycol, and recycled isosorbide. However, the type of recycled diol that can be used in the present invention is not limited thereto. Any recycled diol that can undergo an ester exchange reaction may be used. This recycled diol may be used in an ester exchange reaction to completely replace the original diol. Alternatively, the recycled diol and the original diol may be mixed in a certain ratio and used in an ester exchange reaction. The mixing ratio of the recovered 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, specifically, 1 mol% to 100 mol%, 1 mol% to 99 mol% or 30 mol% to 100 mol%, based on the moles of the total glycol.

[0054] Specific examples of 1,4-cyclohexanedimethanol derivatives may include 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol or a mixture thereof. More specifically, it may be a mixture comprising 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.

[0055] The diol monomer can have a molecular weight of less than 500, less than 400, less than 350, less than 300, or less than 250, for example.

[0056] The polymer diol may be, for example, selected from the group consisting of polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, copolymers of ethylene oxide and tetrahydrofuran, polypropylene glycol added with ethylene oxide, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, and poly-1,5-pentanediol. More specifically, the polymer diol may be at least one selected from the group consisting of polytetramethylene glycol, polycarbonate diol, polypropylene glycol, and polypropylene glycol added with ethylene oxide.

[0057] The number average molecular weight of the polymer diol may be, for example, 400 or more, 500 or more, 600 or more, 700 or more, or 800 or more, or 6000 or less, 5000 or less, 4000 or less, or 3000 or less. As a specific example, the number average molecular weight of the polymer diol may be 400 to 5000. More specifically, from the perspective of reducing phase separation, it may preferably be 1000 to 3000.

[0058] The polymer diol is used in an amount of 5 to 75 wt %, specifically 10 to 60 wt %, more specifically 15 to 50 wt %, based on the weight of the final polyester resin, which is beneficial to obtain a high molecular weight while improving the elasticity of the polyester resin.

[0059] Transesterification

[0060] The diol and bis(2-hydroxyethyl) terephthalate undergo an ester exchange reaction.

[0061] [Reaction Scheme 1]

[0062]

[0063] In Reaction Scheme 1, m is a number ranging from 1 to 10 or 1 to 4, for example.

[0064] In addition, in Reaction Scheme 1, R is a diol group having 3 or more carbon atoms excluding OH groups at both ends. As an 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 through an ether group or a carbonate group. As another example, R may be a monocyclic or polycyclic group having 3 to 20 carbon atoms, wherein the ring may be aliphatic or aromatic, and may further contain one or more heteroatoms (e.g., O, N, and S).

[0065] The transesterification reaction may be carried out in the presence of a catalyst. Thus, when the diol, acid or bis(2-hydroxyethyl)terephthalate is fed to the reactor, the catalyst may be fed together.

[0066] As a catalyst for the transesterification reaction, for example, at least one selected from the group consisting of a zinc-based catalyst, a titanium-based catalyst, a germanium-based catalyst, an antimony-based catalyst, an aluminum-based catalyst, and a tin-based catalyst may be used.

[0067] The example of zinc-based catalyst comprises zinc acetate, zinc acetate hydrate, zinc chloride, zinc sulfate, zinc sulfide, zinc carbonate, zinc citrate, zinc gluconate or its mixture. The example of titanium-based catalyst comprises tetraethyl titanate, acetyl tripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octanediol titanate, triethanolamine titanate, acetylacetonate titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide etc. The example of germanium-based catalyst comprises germanium dioxide, germanium tetrachloride, ethylene glycol germanium oxide, germanium acetate or its combination. Specifically, germanium dioxide can be used as germanium-based catalyst. Both crystalline and amorphous germanium dioxide can be used as germanium dioxide, and germanium dioxide soluble in glycol can also be used.

[0068] The amount of the transesterification catalyst can vary according to the reaction conditions and the catalyst used. As an example, a metal-based catalyst (e.g., titanium-based catalyst, tin-based catalyst) can be used in an amount of 0.0001 to 0.05 parts by weight relative to 100 parts by weight of the diols and bis(2-hydroxyethyl)terephthalate fed into the reactor.

[0069] The transesterification reaction can be carried out batchwise or continuously.

[0070] As an example, when a diol or a diol and an acid are fed into a reactor and the temperature reaches a certain level while the temperature is increased, bis(2-hydroxyethyl)terephthalate may be fed. The feeding of bis(2-hydroxyethyl)terephthalate may be performed, for example, in a nitrogen atmosphere at a temperature of 180° C. to 280° C. while removing ethylene glycol as a by-product.

[0071] Bis(2-hydroxyethyl) terephthalate can be fed all at once to carry out transesterification with diols. As a specific example, bis(2-hydroxyethyl) terephthalate can be prepared in the form of a powder or a BHET aqueous solution, the BHET aqueous solution having a concentration of about 10-20% by weight, dissolved in about 80-100° C. water, and can be fed into the reactor at once.

[0072] Alternatively, terephthalic acid bis (2-hydroxyethyl) ester can be introduced in the transesterification reaction with diol in a batch or continuous manner. According to one embodiment, terephthalic acid bis (2-hydroxyethyl) ester can be introduced in the transesterification reaction with diol in a manner of two or more times. The number of times introduced in batches can be 2 times or more, 3 times or more, 4 times or more or 5 times or more, or 100 times or less, 50 times or less, 30 times or less, 20 times or less, 15 times or less or 10 times or less. As a specific example, the number of times introduced in batches can be 2 to 30 times or 3 to 15 times. The time interval between batch introductions can be determined by dividing the total introduction time by the number of times introduced in batches. The total introduction time can be, for example, 1 hour or longer or 2 hours or longer, and can be 5 hours or shorter or 4 hours or shorter. In addition, the amount introduced once during batch introduction can be determined by dividing the total amount of terephthalic acid bis (2-hydroxyethyl) ester to be introduced into the reaction by the number of times introduced in batches.

[0073] According to another embodiment, bis(2-hydroxyethyl) terephthalate is introduced into the transesterification reaction of diols in a continuous manner. The total time of continuous introduction can be, for example, 1 hour or longer or 2 hours or longer, and can be 5 hours or shorter or 4 hours or shorter. For example, continuous introduction can be to introduce a constant amount of bis(2-hydroxyethyl) terephthalate per hour. The amount introduced per hour can be determined 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 can be prepared in the form of a powder or a BHET aqueous solution, the concentration of which is about 10-20% by weight, dissolved in about 80-100°C water, which can be fed continuously. Continuous introduction can be carried out from the start of the transesterification reaction to 1 hour before the reaction is completed. A dripping funnel can be used at the laboratory level, or a metering feeder can be used at the commercial level to continuously introduce a constant amount per hour.

[0074] When the feeding of bis(2-hydroxyethyl)terephthalate is completed, reaction conditions can be maintained until the transesterification reaction is completed. In addition, the process of collecting and removing ethylene glycol as a by-product can be continued during the transesterification reaction. The collection and removal of ethylene glycol can be carried out by a distillation process, which utilizes the difference in boiling points with other components. The ethylene glycol distilled out like this can be recovered by cooling and reused in other processes.

[0075] The termination point of the transesterification reaction can be determined by considering the theoretical amount of ethylene glycol formed from bis(2-hydroxyethyl)terephthalate by the transesterification reaction, or as the point at which by-products are no longer released.

[0076] The pressure (absolute pressure) during the transesterification reaction may be, for example, 0.5 kgf / cm 2 or more, 0.7kgf / cm 2 or more or 1.0kgf / cm 2 or more, and 2.5kgf / cm 2 or less, 2.0kgf / cm 2 or less or 1.5kgf / cm 2 or less, specifically, 0.5kgf / cm 2 Up to 2.5kgf / cm 2 .

[0077] The temperature during the transesterification 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. In addition, the transesterification reaction may be performed under a nitrogen atmosphere. As a specific example, the transesterification reaction may be performed under a nitrogen atmosphere at 0.5 kgf / cm 2 Up to 2.5kgf / cm 2 The reaction was carried out at a pressure of 100 to 200° C. and a temperature of 180 to 280° C. in a nitrogen atmosphere.

[0078] The pressure and temperature conditions during the transesterification reaction can be appropriately adjusted according to the specific characteristics of the polyester to be produced, the ratio of each component or the process conditions. For example, the transesterification reaction can be carried out at a temperature of 180°C or higher to smoothly remove the by-product ethylene glycol formed during the transesterification reaction. In addition, it can also be carried out at a temperature 10°C lower than the boiling point of the diol to reduce the loss of the diol used for substitution. As a specific example, when 1,4-butanediol is used as the diol, the temperature can be adjusted to 180°C to 220°C. Alternatively, when 1,4-cyclohexanedimethanol is used, the temperature can be adjusted to 200°C to 270°C.

[0079] The products of the transesterification reaction mainly include bis(glycol) terephthalate and its derivatives, wherein the ethylene glycol residues in bis(2-hydroxyethyl) terephthalate are replaced by other glycol residues.

[0080] According to one embodiment, the bis(glycol)terephthalate obtained by the transesterification reaction includes a compound represented by Formula 1 below.

[0081] [Formula 1]

[0082]

[0083] In Formula 1, —OR—OH is a group derived from a diol having 3 or more carbon atoms, and m is a number ranging from 1 to 10 or 1 to 4, for example.

[0084] The compound of formula 1 may be a monomer or an oligomer (dimer, trimer, etc.) of bis(glycol) terephthalate.

[0085] In Formula 1, R is a group derived from a diol having 3 or more carbon atoms. As an example, R can 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 by an ether group or a carbonate group. As another example, R can be a group of 3 to 20 carbon atoms comprising a monocyclic or polycyclic ring, wherein the ring can be aliphatic or aromatic, and can also contain one or more heteroatoms (e.g., O, N, and S).

[0086] 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 referred to 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 referred to 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 referred to as BHCT).

[0087]

[0088] The bis(glycol)terephthalate may include two or more compounds represented by Formula 1 or derivatives thereof.

[0089] Because the impurity in terephthalic acid bis (glycol) ester is removed in the process of removing by-products such as the glycol formed in the transesterification reaction, its purity can be improved compared with terephthalic acid bis (2-hydroxyethyl) ester as raw material.For example, the terephthalic acid bis (glycol) ester obtained by transesterification reaction can have a purity of 80% or higher.More specifically, the purity of terephthalic acid bis (glycol) ester can be 85% or higher, 90% or higher or 95% or higher.As a specific example, it can be 80% to 99.9%.

[0090] Preparation of polyester resin

[0091] Thereafter, the polyester resin is prepared by the step of preparing a copolymer using bis(glycol) terephthalate and bis(2-hydroxyethyl) terephthalate.

[0092] In the step of preparing the copolymer, an esterification reaction (first polymerization reaction step) and a polycondensation reaction (second polymerization reaction step) may be performed in sequence.

[0093] For example, the step of preparing the copolymer may include: subjecting a comonomer comprising bis(glycol) terephthalate and bis(2-hydroxyethyl) terephthalate to an esterification reaction to obtain an oligomer; and subjecting the oligomer to a polycondensation reaction to obtain a copolymer.

[0094] Reaction Scheme 2 below schematically shows the copolymerization of polyesters, during which diols may be formed as by-products.

[0095] [Reaction Scheme 2]

[0096]

[0097] In Reaction Scheme 2, R is a group derived from a diol having 3 or more carbon atoms.

[0098] In addition to the recycled monomers, other monomers may be introduced into the esterification reaction. For example, at least one comonomer selected from the group consisting of dicarboxylic acids, dicarboxylic acid derivatives, diols, and diol derivatives may be further introduced into the esterification reaction.

[0099] As a specific example, the dicarboxylic acid may include terephthalic acid or isophthalic acid; the dicarboxylic acid derivative may include dimethyl terephthalate or dimethyl isophthalate; the diol may include diethylene glycol, 1,4-cyclohexanedimethanol, isosorbide, 1,2-propylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propylene glycol, 2-methylene-1,3-propylene glycol, 2-ethyl-1,3-propylene glycol, 2-isopropyl ... diol, 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; diol derivatives may include 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexylcarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol. Such comonomers may be original monomers.

[0100] As another example, at least one comonomer may include a recycled monomer obtained by depolymerization of waste polyester. As a specific example, the at least one comonomer may include at least one recycled monomer selected from the group consisting of: recycled dicarboxylic acid, recycled dicarboxylic acid derivatives, recycled glycols, and recycled glycol derivatives. As a more specific example, 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 type of recycled monomer that can be used as a comonomer in the present invention is not limited thereto. Any recycled monomer that can be used to prepare a polyester resin can be used. This recycled monomer can be used for the polymerization of a polyester resin by completely replacing the original monomer. Alternatively, the recycled monomer and the original monomer can also be mixed in a certain proportion for the polymerization of a polyester resin. The mixing ratio of the recycled monomers can 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, specifically, 1 mol % to 100 mol %, 1 mol % to 99 mol % or 30 mol % to 100 mol %, based on the moles of the total monomers.

[0101] The esterification reaction can be carried out in the presence of an esterification catalyst. For example, a zinc-based compound can 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.

[0102] The esterification reaction can be carried out at, for example, 0 kgf / cm 2Up to 10.0kgf / cm 2 The esterification reaction conditions can be appropriately adjusted according to the specific characteristics of the prepared polyester, the ratio of each component, the process conditions, etc. Specifically, the pressure in the esterification reaction can be 0 kg / cm 2 Up to 5.0kg / cm 2 , more specifically, 0.1 kg / cm 2 Up to 3.0kg / cm 2 In addition, the temperature of the esterification reaction may be 200°C to 270°C, more specifically, 240°C to 260°C.

[0103] Esterification can be carried out in batches or continuously. In addition, the recovery BHET, dicarboxylic acid and glycol as raw materials can be introduced into the reactor respectively, or two or more raw materials can be introduced in a mixed state. They can be introduced in solid, liquid or slurry form. As an example, dicarboxylic acid, glycol and recovery BHET can be introduced alone or in combination, and can be mixed with pre-prepared terephthalic acid oligomers. Terephthalic acid oligomers can be prepared by reacting glycols such as terephthalic acid and ethylene glycol, cyclohexanedimethanol, isosorbide. As another example, they can be introduced in the form of slurry, in which dicarboxylic acid and recovery BHET are mixed with glycol.

[0104] More specifically, a glycol (e.g., isosorbide) that is solid at room temperature can be dissolved in water or ethylene glycol and then mixed with a dicarboxylic acid (e.g., terephthalic acid) to prepare a slurry. Alternatively, isosorbide can be melted at 60°C or higher and then mixed with a dicarboxylic acid (e.g., terephthalic acid) and other glycols to prepare a slurry. In addition, additional water can be added to the mixed slurry to help increase the fluidity of the slurry. In addition, in a continuous process, a pump or the like can be used to continuously feed a liquid raw material (e.g., a solution of recovered BHET) into a reactor. The feed rate per hour can be determined by dividing the total amount of feed by time to achieve a target output per day.

[0105] The mixture of bis(2-hydroxyethyl) terephthalate, bis(glycol) terephthalate and other additive components is placed in the esterification reactor for a certain period of time, such as 1 to 24 hours or 4 to 10 hours, and then transferred to the polycondensation reactor. The polycondensation reaction can produce a polyester resin with a relatively low molecular weight by melt polymerization. In addition, a polyester resin with a relatively high molecular weight can also be produced by solid state polymerization after melt polymerization.

[0106] 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. In addition, 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. Since the polycondensation reaction adopts reduced pressure conditions, the by-product glycol 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, the removal of the by-product may be insufficient. In addition, if the polycondensation reaction temperature is lower than 150°C, the reaction by-product glycol cannot be effectively collected and removed from the system; therefore, the intrinsic viscosity of the final reaction product is low, resulting in a decrease in the physical properties of the final polyester resin. If the temperature of 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 period of time, for example, an average residence time of 1 hour to 24 hours, until the intrinsic viscosity of the final reaction product reaches an appropriate level.

[0107] In addition, the polycondensation reaction can be carried out in the presence of a polycondensation catalyst. The polycondensation catalyst can 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, acetyl tripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octanediol titanate, lactic acid titanate, triethanolamine titanate, acetylacetonate titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide, etc. Examples of germanium-based compounds include germanium dioxide, germanium tetrachloride, ethylene glycol germanium oxide, germanium acetate or a mixture thereof. Preferably, germanium dioxide can be used. Crystalline germanium dioxide and amorphous germanium dioxide can be used, and germanium dioxide soluble in glycol can also be used. The amount of the polycondensation catalyst can be such that the amount of titanium element is about 1 to 100 ppm relative to the weight of the polyester resin, more preferably about 1 to 50 ppm.

[0108] In addition to the polycondensation catalyst, stabilizers, colorants, crystallizing agents, antioxidants, branching agents, etc. may be used. The timing of adding these additives is not particularly limited, and they may be added at any time during the preparation of the polyester resin.

[0109] As a stabilizer, phosphorus-based compounds such as phosphoric acid, trimethyl phosphate, triethyl phosphate and triethyl phosphonoacetate can generally be used. Based on the amount of the element, relative to the weight of the polyester resin, its addition amount can be 10 to 200ppm. In addition, common colorants, such as cobalt acetate and cobalt propionate, can also be used as colorants to increase the color of the polyester resin. Based on the amount of the cobalt element, relative to the weight of the polyester resin, its addition amount can be 10 to 200ppm. If necessary, anthraquinone compounds, perinone compounds, azo compounds, methine compounds, etc. can be used as organic colorants. Commercially available toners can be used, such as Polysynthren Blue RLS from Clariant or Solvaperm Red BB from Clariant. Based on the weight of the polyester resin, the addition amount of the organic compound colorant can be adjusted to 0 to 50ppm. The crystallizer can be a crystal nucleating agent, an ultraviolet absorber, a polyolefin resin, a polyamide resin, etc. The antioxidant may be a hindered phenol antioxidant, a phosphite antioxidant, a thioether antioxidant or a mixture thereof. The branching agent may be a conventional branching agent having three or more functional groups, such as trimellitic anhydride, trimethylolpropane, trimellitic acid or a mixture thereof.

[0110] Polyester resin

[0111] According to another aspect of the present invention, a polyester resin prepared by the above method is provided.

[0112] The polyester resin of the present invention is a polyester resin regenerated by chemically recovering waste polyester.

[0113] That is, the polyester resin is prepared by copolymerizing monomers comprising bis(2-hydroxyethyl) terephthalate and bis(glycol) terephthalate. Therefore, the polyester resin comprises bis(2-hydroxyethyl) terephthalate and bis(glycol) terephthalate as comonomers. Here, the glycol has 3 or more carbon atoms.

[0114] As described above, the bis(glycol) terephthalate may be a transesterification product between bis(2-hydroxyethyl) terephthalate and a glycol having 3 or more carbon atoms.

[0115] Here, the diol has 3 or more carbon atoms, and its specific types are as described above.

[0116] 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.

[0117] The total content of recovered monomers in the polyester resin of the present invention can 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. In addition, the total content of recovered monomers can 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. As a specific example, based on the weight of the polyester resin, the polyester resin can contain a total amount of 30% by weight or more of bis(2-hydroxyethyl) terephthalate and bis(glycol) terephthalate.

[0118] In the preparation of the polyester resin, in addition to the recycled monomers, monomers commonly used for polymerization of polyester resins (i.e., original monomers) are used, for example, at least one selected from the group consisting of dicarboxylic acids, dicarboxylic acid derivatives, diols and diol derivatives as described above, and thus the polyester resin may further contain these comonomers.

[0119] Since the bis(2-hydroxyethyl)terephthalate used to prepare the polyester resin of the present invention has a structure in which two ethylene glycols and one terephthalic acid are bonded, the polyester resin of the present invention may contain a repeating unit derived from ethylene glycol and terephthalic acid. In addition, since the structure of the bis(glycol)terephthalate is formed by bonding two ethylene glycols each having 3 or more carbon atoms and one terephthalic acid, the polyester resin of the present invention may further contain a repeating unit derived from a glycol having 3 or more carbon atoms.

[0120] As described above, the polyester resin of the present invention contains a dicarboxylic acid component and a diol component as monomer components (polymer constituent units) constituting it. These may be derived from bis(2-hydroxyethyl)terephthalate and a diol having 3 or more carbon atoms initially introduced for the preparation of the polyester resin, or recycled bis(diol)terephthalate prepared therefrom and a comonomer introduced additionally.

[0121] Therefore, the polyester resin of the present invention may be a copolymerized resin comprising two or more dicarboxylic acid components and / or two or more diol components.

[0122] According to one embodiment, the diol component may further include a diol component other than ethylene glycol as a comonomer. The comonomer may include, for example, at least one selected from the group consisting of diethylene glycol, cyclohexanedimethanol, cyclohexanedimethanol derivatives, and isosorbide.

[0123] Diethylene glycol can help enhance the transparency and impact resistance of the polyester resin. For example, diethylene glycol can be used in an amount of 0.1 mol % to 50 mol % based on the moles of all diols.

[0124] Cyclohexanedimethanol (e.g., 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol) can help improve the transparency and impact resistance of the produced polyester resin. For example, cyclohexanedimethanol can be used in an amount of 5 mol % to 90 mol % based on the moles of all diol components. The cyclohexanedimethanol derivative can be 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol. The cyclohexanedimethanol derivative can be used in an amount of 0.1 mol % to 25 mol % based on the moles of all diol components.

[0125] Isosorbide can improve the processing properties of the final polyester resin. Although the diol components in cyclohexanedimethanol and ethylene glycol can improve the transparency and impact resistance of the polyester resin, the shear fluidization characteristics should also be improved and the crystallization rate should be delayed to improve the processing properties; however, it is difficult to achieve this effect by relying solely on cyclohexanedimethanol and ethylene glycol. Therefore, if isosorbide is used as a diol component, the shear fluidization characteristics can be improved, the crystallization rate can be delayed, and the transparency and impact resistance can be maintained, thereby improving the processing properties of the polyester resin. Preferably, isosorbide can be used in an amount of 0.1 mol% to 70 mol% based on the molar number of all diol components.

[0126] 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 moles of all dicarboxylic acids. In addition, the terephthalic acid component may be formed from an alkyl terephthalate (such as dimethyl terephthalate).

[0127] In addition, the dicarboxylic acid component may include an aromatic dicarboxylic acid component, an aliphatic dicarboxylic acid component or a mixed component thereof in addition to terephthalic acid. The dicarboxylic acid in addition to terephthalic acid may be used in an amount of 1 mol% to 30 mol% based on the weight of all dicarboxylic acid components.

[0128] The aromatic dicarboxylic acid component may be an aromatic dicarboxylic acid or a mixture thereof having 8 to 20 carbon atoms, preferably 8 to 14 carbon atoms. Examples of aromatic dicarboxylic acids include isophthalic acid, naphthalene dicarboxylic acid (e.g., 2,6-naphthalene dicarboxylic acid), diphenyl dicarboxylic acid, 4,4'-stilbene dicarboxylic acid, 2,5-furan dicarboxylic acid, 2,5-thiophene dicarboxylic acid, etc., but are not limited thereto.

[0129] The aliphatic dicarboxylic acid component may be an aliphatic dicarboxylic acid or mixture thereof having 4 to 20 carbon atoms, preferably 4 to 12 carbon atoms. Examples of aliphatic dicarboxylic acids include linear, branched or cyclic aliphatic dicarboxylic acid components such as cyclohexanedicarboxylic acids (e.g., 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., but are not limited thereto.

[0130] The polyester resin may also contain a catalyst for the polymerization reaction used in 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).

[0131] When the Hunter Lab color space is measured, the value obtained by subtracting the b value from the L value of the polyester resin may be 88 or greater, 89 or greater, 90 or greater, 91 or greater, 92 or greater, or 93 or greater. In addition, the upper limit of the L-b value is not particularly limited. However, it may also be, for example, 100 or less, 99 or less, 98 or less, 97 or less, or 95 or less. The measurement of the HunterLab color space can be performed by making a sample with a thickness of 6 mm using a polyester resin. As a specific example, when the Hunter Lab color space is measured, under the condition of a thickness of 6 mm, the value obtained by subtracting the b value from the L value of the polyester resin may be 88 or greater.

[0132] 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 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.

[0133] The polyester resin according to the present invention can be used as materials such as beverage filling containers, packaging films, audio and video films, etc. due to its excellent color, mechanical strength, heat resistance, transparency and gas barrier properties. In addition, the polyester sheet or plate prepared from the polyester resin according to the present invention has good transparency and excellent mechanical strength, and can be used as a raw material for boxes, boxes, partitions, shelves, panels, packaging materials, building materials, indoor and outdoor materials, etc. In addition, the polyester resin according to the present invention can be used as an industrial material such as medical fiber and tire cord.

[0134] Therefore, the present invention provides a product comprising the polyester resin. As an example, the product can be a film, a sheet or a profile. Specific examples of films include heat shrinkable films and blown films. Profiles refer to plastic products formed by continuous extrusion, excluding sheets and films. It can be manufactured by conventional extrusion molding methods, for example, it can be tubular or grooved.

[0135] Invention Mode

[0136] The present invention will be described in more detail below in conjunction with the embodiments. However, these embodiments are provided only for illustrative purposes, and the present invention is not limited thereto.

[0137] In the following examples, in the diols used in the transesterification reaction and the dicarboxylic acids or diols used as comonomers in the polymerization of the polyester resin, unless recycled monomers (e.g., terephthalic acid, ethylene glycol, etc.) are indicated, it should be understood that virgin monomers are used.

[0138] Preparation Example 1: Recovery of bis(2-hydroxyethyl) terephthalate

[0139] Recovered BHET of various purities was prepared by depolymerization of waste polyester resins purchased by a known method or commercially. The following table shows the peak area fraction (%) of only BHET in the HPLC results of each recovered BHET measured using HPLC, that is, the purity.

[0140]

Table 1

[0141]

[0142] Preparation Example 2: Preparation of terephthalic acid bis (glycol) ester by ester exchange reaction

[0143] To a 1-liter reactor for transesterification reactor equipped with a tower and a condenser which can be cooled with water, 1,4-cyclohexanedimethanol (CHDM, 641 g) as a diol and zinc acetate (0.003 parts by weight relative to 100 parts by weight of the monomer mixture in the reactor) as a reaction catalyst were added. Then, the pressure in the reactor was adjusted to normal pressure (1.0 kg / cm 2 ), and the temperature is raised while maintaining the pressure under stirring. When the temperature in the reactor reaches about 200°C, the temperature is raised to 220°C within 3 hours, and bis(2-hydroxyethyl)terephthalate (BHET, 254g) is fed to carry out an ester exchange reaction. During the reaction, the by-product glycol is discharged through the tower and the condenser. Even after the addition of BHET is completed, the ester exchange reaction continues while the temperature is maintained at 220°C until the glycol stops being discharged. After the ester exchange reaction is completed, the nitrogen in the pressurized reactor is released to the outside, and the pressure in the reactor is reduced to normal pressure to obtain bis(1,4-cyclohexanedimethanol)terephthalate.

[0144] Example 1: Preparation of polyester resin

[0145] Step A: Preparation of terephthalic acid bis(glycol) esters by transesterification

[0146] According to the method of Preparation Example 2 above, bis(2-hydroxyethyl) terephthalate (BHET#1) was subjected to transesterification reaction with diethylene glycol (DEG), isosorbide (ISB) and 1,4-cyclohexanedimethanol (CHDM) to obtain bis(diethylene glycol) terephthalate (BHDT), bis(isosorbide) terephthalate (BHIT) and bis(1,4-cyclohexanedimethanol) terephthalate (BHCT), respectively.

[0147] Step B: Preparation of polyester resin by polycondensation reaction

[0148] To the esterification reactor were added bis(2-hydroxyethyl) terephthalate (BHET#1, 3570.2 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).

[0149] Then, nitrogen was injected into the esterification reactor to increase the pressure of the reactor by 2.0 kgf / cm2 above the atmospheric pressure (absolute pressure: 2231.1 mmHg). 2 Then, the temperature of the esterification reactor was increased to 220°C within 90 minutes and maintained at 220°C for 2 hours, and then the temperature was increased again to 260°C within 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 the column and condenser.

[0150] Then, the pressure of the polycondensation reactor is reduced from normal pressure to 5 Torr (absolute pressure: 5 mmHg) within 30 minutes. At the same time, the temperature of the polycondensation reactor is raised to 280°C within 1 hour, and then the polycondensation reaction is carried out, while the pressure of the polycondensation reactor is maintained at 1 Torr (absolute pressure: 1 mmHg) or less. At the beginning of the polycondensation reaction, the stirring speed is set very high. As the polycondensation reaction proceeds, when the stirring ability weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed is appropriately adjusted accordingly. The polycondensation reaction is carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.60 dl / g. Thereafter, the mixture is discharged to the outside of the reactor to form pellets, solidified with a coolant, and then granulated to have an average weight of about 12 to 14 mg to prepare about 4 kg of polyester resin (copolymer).

[0151] Example 2: Preparation of polyester resin

[0152] The same steps as in Example 1 were repeated to obtain polyester particles, except that in step A, bis(2-hydroxyethyl) terephthalate (BHET#2) and diethylene glycol (DEG) were subjected to an ester exchange reaction to obtain bis(diethylene glycol) terephthalate (BHDT); and in step B, bis(2-hydroxyethyl) terephthalate (BHET#2, 2594.0 g), bis(diethylene glycol) terephthalate (BHDT, 174.6 g), terephthalic acid (TPA, 1610.5 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) were added into the reactor. The esterification reaction is carried out at a pressure 0.5 kgf / cm higher than normal pressure. 2 The condensation reaction was carried out at a pressure of 200 ° C. 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 particles were placed at 150 ° C. for 1 hour to crystallize, and then fed into a solid polymerization reactor. When nitrogen was flowed 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. / hour. While maintaining this state, solid-state polymerization was carried out until the intrinsic viscosity (IV) of the particles in the reactor reached 0.90 dl / g, and about 4 kg of polyester resin (copolymer) was obtained.

[0153] Example 3: Preparation of polyester resin

[0154] The same steps as in Example 1 were repeated to obtain about 4 kg of polyester resin (copolymer), except that in step A, bis(2-hydroxyethyl) terephthalate (BHET#3) and 1,4-cyclohexanedimethanol (CHDM) were subjected to an ester exchange reaction to obtain bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); and in step B, bis(2-hydroxyethyl) terephthalate (BHET#3, 3941.2 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT, 1144.2 g) were added to the reactor. 6g), ethylene glycol (EG, 34.0g), 1,4-cyclohexanedimethanol (CHDM, 52.6g), diethylene glycol (DEG, 38.7g), CHDM derivative (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol, molar ratio of 1:3, 80.0kg), Ge catalyst (5.1g), Ti catalyst (0.4g), phosphoric acid (0.4g), blue toner (0.010g) and red toner (0.002g). The esterification reaction was carried out at a pressure 2.0kgf / cm higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 1000 ℃ and a temperature of 255 ℃, and the polycondensation reaction was carried out at a temperature of 285 ℃ until the intrinsic viscosity (IV) reached 0.78 dl / g.

[0155] Example 4: Preparation of polyester resin

[0156] The same steps as in Example 1 were repeated to obtain about 4 kg of polyester resin (copolymer), except that in step A, bis(2-hydroxyethyl) terephthalate (BHET#4) and 1,4-cyclohexanedimethanol (CHDM) were subjected to an ester exchange reaction to obtain bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); and in step B, bis(2-hydroxyethyl) terephthalate (BHET#4, 2782.0 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT, 763.1 g), terephthalic acid (TPA, 90 9.1g), ethylene glycol (EG, 147.1g), 1,4-cyclohexanedimethanol (CHDM, 315.4g), diethylene glycol (DEG, 38.7g), CHDM derivative (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol, molar ratio of 1:3, 80.0kg), Ge catalyst (5.1g), Ti catalyst (0.4g), phosphoric acid (0.4g), cobalt acetate (0.5g), blue toner (0.002g) and red toner (0.001g). The esterification reaction was carried out at a pressure 2.0kgf / cm higher than normal pressure. 2The polycondensation reaction was carried out at a pressure of 1000 ℃ and a temperature of 255 ℃, and the polycondensation reaction was carried out at a temperature of 285 ℃ until the intrinsic viscosity (IV) reached 0.78 dl / g.

[0157] Example 5: Preparation of polyester resin

[0158] The same steps as in Example 1 were repeated to obtain about 4 kg of polyester resin (copolymer), except that in step A, bis(2-hydroxyethyl) terephthalate (BHET#5) and 1,4-cyclohexanedimethanol (CHDM) were subjected to an ester exchange reaction to obtain bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); and in step B, bis(2-hydroxyethyl) terephthalate (BHET#5, 907.1 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT, 2596.3 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) were added to the reactor. The esterification reaction was carried out at a pressure 1.5 kgf / cm higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 250°C and a temperature of 270°C until the intrinsic viscosity (IV) reached 0.82 dl / g.

[0159] Example 6: Preparation of polyester resin

[0160] The same steps as in Example 1 were repeated to obtain about 4 kg of polyester resin (copolymer), except that in step A, bis(2-hydroxyethyl) terephthalate (BHET#6) was subjected to an ester exchange reaction with diethylene glycol (DEG) and 1,4-cyclohexanedimethanol (CHDM) to obtain bis(diethylene glycol) terephthalate (BHDT) and bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); and in step B, bis(2-hydroxyethyl) terephthalate (BHET#6, 1 376.8g), bis(diethylene glycol) terephthalate (BHDT, 278.1g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT, 1132.9g), terephthalic acid (TPA, 1514.7g), ethylene glycol (EG, 784.2g), 1,4-cyclohexanedimethanol (CHDM, 26.0g), Ti catalyst (0.1g), phosphoric acid (0.8g), cobalt acetate (1.1g), blue toner (0.002g) and red toner (0.001g). The esterification reaction was carried out at a pressure 1.5kgf / cm higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 250°C and a temperature of 270°C until the intrinsic viscosity (IV) reached 0.82 dl / g.

[0161] Example 7: Preparation of polyester resin

[0162] The same steps as in Example 1 were repeated to obtain about 4 kg of polyester resin (copolymer), except that in step A, bis(2-hydroxyethyl) terephthalate (BHET#7) was subjected to an ester exchange reaction with isosorbide (ISB) and 1,4-cyclohexanedimethanol (CHDM) to obtain bis(isosorbide) terephthalate (BHIT) and bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); and in step B, bis(2-hydroxyethyl) terephthalate (BHET#7, 1072.3 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT) were added to the reactor. The esterification reaction was carried out at a pressure 1.0 kgf / cm2 higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 100°C 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.

[0163] Example 8: Preparation of polyester resin

[0164] The same steps as in Example 1 were repeated to obtain about 4 kg of polyester resin (copolymer), except that in step A, bis(2-hydroxyethyl) terephthalate (BHET#8) was subjected to an ester exchange reaction with diethylene glycol (DEG) and 1,4-cyclohexanedimethanol (CHDM) to obtain bis(diethylene glycol) terephthalate (BHDT) and bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); and in step B, bis(2-hydroxyethyl) terephthalate (BHET#8, 483.4 g), bis(diethylene glycol) terephthalate (BHDT, 358.0 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT) were added to the reactor. The esterification reaction was carried out at a pressure of 0.5 kgf / cm2 higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 100°C 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.

[0165] Example 9: Preparation of polyester resin

[0166] The same steps as in Example 1 were repeated to obtain polyester particles, except that in step A, bis(2-hydroxyethyl) terephthalate (BHET#9) and 1,4-cyclohexanedimethanol (CHDM) were subjected to an ester exchange reaction to obtain bis(1,4-cyclohexanedimethanol) terephthalate (BHCT); and in step B, bis(2-hydroxyethyl) terephthalate (BHET#9, 3621.9 g), bis(1,4-cyclohexanedimethanol) terephthalate (BHCT) were added to the reactor. HCT, 212.9g), recovered terephthalic acid (r-TPA, 929.9g), isophthalic acid (IPA, 2451.6g), ethylene glycol (EG, 21.0g), isosorbide (ISB, 39.7g), recovered diethylene glycol (r-DEG, 21.6g), diethylene glycol (DEG, 21.6g), Ti catalyst (0.4g), phosphoric acid (8.0g), cobalt acetate (0.7g), blue toner (0.020g) and red toner (0.008g). The esterification reaction was carried out at a pressure 3.0kgf / cm higher than normal pressure. 2The condensation polymerization reaction was carried out at a temperature of 280°C until the intrinsic viscosity (IV) reached 0.60 dl / g. The particles were placed at 150°C for 1 hour to crystallize, and then fed into a solid polymerization reactor. While nitrogen was flowing 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 state, solid-state polymerization was carried out until the intrinsic viscosity (IV) of the particles in the reactor reached 1.10 dl / g, and about 4 kg of a polyester resin (copolymer) was obtained.

[0167] Comparative Example 1: Preparation of polyester resin

[0168] The same steps as in Example 3 were repeated to obtain about 4 kg of polyester resin (copolymer), except that step A was not performed; and in step B, bis(2-hydroxyethyl)terephthalate (BHET#3a, 4636.7 g), ethylene glycol (EG, 56.6 g), 1,4-cyclohexanedimethanol (CHDM, 841.2 g), a CHDM derivative (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol, in a molar ratio of 1:3, 80.0 kg), a Ge catalyst (5.1 g), a Ti catalyst (0.4 g), phosphoric acid (0.4 g), a blue toner (0.010 g) and a red toner (0.002 g) were added to the reactor. The esterification reaction was carried out at a pressure 2.0 kgf / cm higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 1000 ℃ and a temperature of 255 ℃, and the polycondensation reaction was carried out at a temperature of 285 ℃ until the intrinsic viscosity (IV) reached 0.78 dl / g.

[0169] Comparative Example 2: Preparation of polyester resin

[0170] The same steps as in Example 1 were repeated to obtain about 4 kg of a polyester resin (copolymer), except that step A was not performed; and in step B, bis(2-hydroxyethyl)terephthalate (BHET#4a, 3709.4 g), terephthalic acid (TPA, 606.1 g), ethylene glycol (EG, 56.6 g), 1,4-cyclohexanedimethanol (CHDM, 841.2 g), a CHDM derivative (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a molar ratio of 1:3, 80.0 kg), a Ge catalyst (5.1 g), a Ti catalyst (0.4 g), phosphoric acid (0.4 g), cobalt acetate (0.5 g), a blue toner (0.002 g), and a red toner (0.001 g) were added to the reactor. The esterification reaction is 2.0kgf / cm higher than the normal pressure. 2The polycondensation reaction was carried out at a pressure of 200°C 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.

[0171] Comparative Example 3: Preparation of polyester resin

[0172] The same steps as in Example 1 were repeated to obtain about 4 kg of polyester resin (copolymer), except that step A was not performed; and in step B, bis(2-hydroxyethyl) terephthalate (BHET#7a, 1072.3 g), terephthalic acid (TPA, 2102.3 g), ethylene glycol (EG, 83.8 g), 1,4-cyclohexanedimethanol (CHDM, 1580.5 g), recovered 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) were added to the reactor. The esterification reaction was carried out at a pressure 1.0 kgf / cm higher than normal pressure. 2 The polycondensation reaction was carried out at a pressure of 100°C 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.

[0173] The monomer compositions of the Examples and Comparative Examples are summarized in Tables 2 and 3 below.

[0174]

Table 2

[0175]

[0176]

Table 3

[0177]

[0178]

[0179] Test Case

[0180] The raw materials and the tests of the final resins used in the Examples and Comparative Examples are as follows.

[0181] (1) Addition amount of recycled BHET

[0182] The mole number of bis(2-hydroxyethyl)terephthalate (BHET) added is calculated as a percentage (mol %) based on the total mole number of dicarboxylic acids and their derivatives (TPA, BHET, BHDT, BHIT and BHCT) added to prepare the polyester resin.

[0183] (2) Purity of recovered BHET (HPLC)

[0184] About 0.01 g of recovered bis(2-hydroxyethyl)terephthalate was diluted in about 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). Thereafter, the fraction (%) of the BHET peak area alone in the total peak area of ​​HPLC was obtained.

[0185] (3) Content of recovered monomer in resin

[0186] Based on the total weight of the monomers (BHET, BHDT, BHIT, BHCT, TPA, IPA, EG, CHDM, ISB, DEG, r-EG, r-CHDM, r-DEG, r-TPA, r-IPA, etc.) added to prepare the polyester resin, the percentage (wt %) of the total weight of only recycled monomers (BHET, BHDT, BHIT, BHCT, r-EG, r-CHDM, r-DEG, r-TPA and r-IPA) is calculated.

[0187] (4) Copolymer composition (NMR)

[0188] Each polyester resin was dissolved in CDCl3 solvent at a concentration of 3 mg / mL, and its molecular weight was obtained at 25°C using a nuclear magnetic resonance device (JEOL, 600 MHz FT-NMR). 1 H-NMR spectrum. By analyzing the above spectrum, the residue contents (mol %) derived from diethylene glycol (DEG), isosorbide (ISB), cyclohexanedimethanol (CHDM) and their derivatives were calculated respectively, and the contents were based on the total molar number of residues derived from all diols (EG, DEG, ISB, CHDM, etc.).

[0189] As a result, it was confirmed that the copolymerization compositions of the polyester resins of Examples and Comparative Examples were different. Specifically, it was confirmed that the content of the residue derived from diol (DEG, ISB, CHDM, etc.) and its derivatives was different in each polyester resin.

[0190] However, some polyester resins have the same composition. Specifically, the copolymer compositions of Comparative Example 1 and Example 3, Comparative Example 2 and Example 4, and Comparative Example 3 and Example 7 were confirmed to be the same.

[0191] (5) Color (Hunter Lab)

[0192] The chromaticity and brightness of polyester resin were measured using a Varian Cary 5UV / Vis / NIR spectrophotometer equipped with a diffuse reflectance accessory. For a polyester resin sample with a thickness of 6 mm prepared by injection molding at 250°C, transmittance data was obtained with illuminant D65 at an observer angle of 2° and processed using a color analyzer in Grams / 32 software to calculate Hunter Lab values. The value of subtracting the b value from the L value (L–b) was calculated.

[0193] The test results are shown in Tables 4 and 5 below.

[0194]

Table 4

[0195]

[0196]

Table 5

[0197]

[0198] As can be seen from Tables 4 and 5 above, in Examples 1 to 9, part of BHET is used as a recycled monomer to undergo an ester exchange reaction with other diols (DEG, ISB, CHDM) to obtain BHDT, BHIT and BHCT, which are then added to the polymerization reaction to obtain a polyester resin, and the color quality of the polyester resin is excellent, while the total content of the recycled monomer is increased. In particular, in Examples 7 to 9, additional recycled diols (r-EG, r-DEG, r-CHDM or r-ISB) and recycled carboxylic acids (r-TPA) are further used to increase the total content of the recycled monomer.

[0199] In contrast, the copolymerization composition of Comparative Example 1 is the same as that of Example 3, and only BHET is used as a recycled monomer, which reduces the content of recycled monomers in the resin, and due to the low purity of BHET, the color of the final polyester resin is poor. In addition, in Comparative Example 2, only BHET is used as a recycled monomer, and the purity cannot be improved by transesterification reaction with diol; therefore, the color of the final polyester resin is poor compared with Example 1 using BHET of the same purity. In addition, in Comparative Example 3, which has almost the same amount of BHET and r-ISB as Example 3, no other recycled monomers are used, which reduces the total content of recycled monomers and the color of the final polyester resin is poor.

Claims

1. A method for preparing a polyester resin, comprising: reacting bis(2-hydroxyethyl)terephthalate with a diol having 3 or more carbon atoms to prepare bis(diol)terephthalate; as well as The copolymer was prepared using bis(glycol) terephthalate and bis(2-hydroxyethyl) terephthalate.

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. The method for preparing a polyester resin according to claim 1, wherein the step of preparing bis(glycol) terephthalate comprises: feeding a diol having 3 or more carbon atoms into a reactor; as well as Bis(2-hydroxyethyl)terephthalate was fed into the reactor and subjected to transesterification reaction.

4. The method for preparing a polyester resin according to claim 1, wherein the diol having 3 or more carbon atoms comprises at least one selected from the group consisting of 1,3-propylene glycol, 1,4-butylene glycol, 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, diol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyhexamethylene glycol, copolymers of ethylene oxide and tetrahydrofuran, polypropylene glycol added with ethylene oxide, polycarbonate diol, polyneopentyl glycol, poly-3-methylpentanediol, poly-1,5-pentanediol and their derivatives. 5 . The method for preparing a polyester resin according to claim 1 , wherein the diol having 3 or more carbon atoms comprises at least one recycled diol obtained by depolymerization of waste polyester.

6. The method for preparing a polyester resin according to claim 5, wherein the recycled diol is selected from the group consisting of recycled ethylene glycol, recycled 1,4-cyclohexanedimethanol, recycled diethylene glycol and recycled isosorbide. 7 . The method for preparing a polyester resin according to claim 1 , wherein the purity of the bis(2-hydroxyethyl) terephthalate is 60% to 97%.

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

9. The method for preparing a polyester resin according to claim 1, wherein the step of preparing the copolymer comprises: esterifying comonomers comprising bis(glycol) terephthalate and bis(2-hydroxyethyl) terephthalate to obtain an oligomer; as well as The oligomers are subjected to polycondensation to obtain copolymers.

10. The method for preparing a polyester resin according to 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 method for preparing a polyester resin according to claim 10, wherein the dicarboxylic acid comprises terephthalic acid or isophthalic acid; The dicarboxylic acid derivatives include dimethyl terephthalate or dimethyl isophthalate; The diol includes diethylene glycol, 1,4-cyclohexanedimethanol, isosorbide, 1,2-propylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propylene glycol, 2-methylene-1,3-propylene glycol, 2-ethyl-1,3-propylene glycol, 2-isopropyl-1,3-propylene glycol, 2,2-dimethyl-1,3-propylene glycol, 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; and The diol derivatives include 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol.

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

14. A polyester resin comprising bis(2-hydroxyethyl)terephthalate and bis(diol)terephthalate as comonomers, wherein the diol has 3 or more carbon atoms.

15. The polyester resin according to claim 14, wherein the polyester resin comprises bis(2-hydroxyethyl)terephthalate and bis(glycol)terephthalate in a total amount of 30 wt% or more based on the weight of the polyester resin. 16 . The polyester resin according to claim 14 , wherein when a Hunter Lab color space is measured, the polyester resin has a value obtained by subtracting a b value from an L value of 88 or more under a condition of a thickness of 6 mm.

17. The polyester resin according to claim 14, wherein the bis(glycol)terephthalate is an ester exchange product between bis(2-hydroxyethyl)terephthalate and a glycol having 3 or more carbon atoms.

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