Process for producing polyester resins and fibers containing recycled bis(2-hydroxyethyl) terephthalate

Abstract

The polyester resin according to the present invention is high purity and contains recycled bis(2-hydroxyethyl) terephthalate containing a controlled amount of diethylene glycol ester below a certain level, and therefore has heat resistance and quality comparable to that of the original resin, despite being a polyester resin regenerated by chemical recycling. In particular, the polyester fiber containing the polyester resin according to the present invention has excellent strength, elongation, and processability, and can therefore be used as an environmentally friendly textile product.

Description

[Technical field]

[0001] The present invention relates to a method for preparing polyester resins and polyester fibers containing recycled bis(2-hydroxyethyl) terephthalate. [Background technology]

[0002] 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. In addition, polyester is widely produced around the world as an industrial material for medical fibers, tire cords, etc. In particular, polyester sheets or polyester plates have good transparency and excellent mechanical strength, and are therefore widely used as raw materials for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior and exterior materials, etc.

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

[0004] In the chemical recycling process, the ester bonds of the waste polyester are broken down to depolymerize it. Reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. Among these, glycolysis is the decomposition of the waste polyester by adding glycols such as ethylene glycol or diethylene glycol at high temperature. The reaction product obtained mainly contains bis(2-hydroxyethyl) terephthalate (BHET). After crystallization or purification, bis(2-hydroxyethyl) terephthalate can be used as a raw material for preparing unsaturated polyester or ester polyols. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Korean Patent No. 1386683 [Patent Document 2] U.S. Patent No. 7,211,193 Summary of the Invention [Problem to be solved by the invention]

[0006] In general, the products of the depolymerization reaction of waste polyester resin contain a large amount of oligomers such as dimers and trimers in addition to bis(2-hydroxyethyl) terephthalate (BHET). Since diethylene glycol (DEG) is formed at high depolymerization temperatures, the formation of side reaction products derived from diethylene glycol is inevitable. For example, diethylene glycol esters (DEG esters) cause a deterioration of physical properties when polymerizing recycled polyester resins, and the degree is even greater in the case of polyester copolymers. In addition, the color of the polymerization raw material becomes dark and yellow, which inevitably limits the use of this raw material.

[0007] As a result of research conducted by the present inventors to solve this problem, it was found that by carrying out the depolymerization reaction in multiple stages while significantly lowering the temperature in the latter stages, thereby reducing the formation of diethylene glycol and impurities derived from diethylene glycol, it was possible to prepare high-purity recycled BHET in which the content of diethylene glycol esters was controlled below a certain level, and using this, it was possible to prepare polyester resins and fibers with excellent heat resistance and quality.

[0008] Therefore, an object of the present invention is to provide a polyester resin and a polyester fiber containing high-purity and high-quality recycled bis(2-hydroxyethyl) terephthalate, and a method for preparing the same. [Means for solving the problem]

[0009] According to the present invention, there is provided a method for preparing a polyester resin, comprising the steps of: (1) depolymerizing waste polyester to prepare recycled bis(2-hydroxyethyl) terephthalate, the recycled bis(2-hydroxyethyl) terephthalate having a total peak area fraction of bis(2-hydroxyethyl) terephthalate of 96% or more and a peak area fraction of diethylene glycol ester of less than 2% when measured by high performance liquid chromatography (HPLC); (2) mixing the recycled bis(2-hydroxyethyl) terephthalate with a solvent to prepare a solution of recycled bis(2-hydroxyethyl) terephthalate; (3) subjecting the recycled bis(2-hydroxyethyl) terephthalate solution to a first polycondensation reaction under a pressure of 200mmHg to 600mmHg to prepare an oligomer; and (4) subjecting the oligomer to a second polycondensation reaction under a pressure of less than 200mmHg to prepare a polyester resin.

[0010] Furthermore, according to the present invention, there is provided a polyester resin prepared by the above method and having an intrinsic viscosity of 0.6 dl / g to 1.2 dl / g.

[0011] Further, according to the present invention, there is provided a polyester fiber containing this polyester resin.

[0012] Further according to the present invention there is provided a method for preparing polyester fibres, comprising the step of spinning a polyester resin to obtain fibres. Effect of the Invention

[0013] The polyester resin according to the present invention is highly pure and contains recycled bis(2-hydroxyethyl) terephthalate with the diethylene glycol ester content adjusted to a certain level or less. Therefore, even though it is a polyester resin regenerated by chemical recycling, it has heat resistance and quality comparable to that of virgin resin.

[0014] In particular, the polyester fiber containing the polyester resin of the present invention has excellent strength, elongation, and processability, and can therefore be used as an environmentally friendly textile product. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention will now be described in more detail.

[0016] In this specification, the terms referring to each component are used to distinguish them from one another and are not intended to limit the scope of the embodiments. Furthermore, in this specification, the singular expressions are to be interpreted as including the plural as well, unless otherwise indicated by the context.

[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 only to distinguish one element from another element.

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

[0019] The method for preparing the polyester resin of the present invention includes the steps of: (1) depolymerizing waste polyester to prepare regenerated bis(2-hydroxyethyl) terephthalate, the regenerated bis(2-hydroxyethyl) terephthalate having a total peak area fraction of bis(2-hydroxyethyl) terephthalate of 96% or more and a peak area fraction of diethylene glycol ester of less than 2% when measured by high performance liquid chromatography (HPLC); (2) mixing the regenerated bis(2-hydroxyethyl) terephthalate with a solvent to prepare a solution of the regenerated bis(2-hydroxyethyl) terephthalate; (3) subjecting the regenerated bis(2-hydroxyethyl) terephthalate solution to a first polycondensation reaction under a pressure of 200mmHg to 600mmHg to prepare an oligomer; and (4) subjecting the oligomer to a second polycondensation reaction under a pressure of less than 200mmHg to prepare a polyester resin.

[0020] Bis(2-hydroxyethyl)terephthalate is an ester of two ethylene glycols and one terephthalic acid. For example, bis(2-hydroxyethyl)terephthalate is a compound formed as an intermediate in the process for preparing polyesters, such as polyethylene terephthalate (PET), via the polymerization of ethylene glycol and terephthalic acid or its esters.

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

[0022] In this specification, bis(2-hydroxyethyl) terephthalate (BHET) 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, but it should be understood as being different from the pure BHET compound.

[0023] Specifically, recycled BHET may contain by-products formed by side reactions with reagents or solvents used in various chemical steps during the depolymerization of waste polyester. These impurities may remain in trace amounts even after several purification steps. Thus, recycled BHET generally contains trace amounts of organic and inorganic impurities in addition to the main component BHET. For this reason, recycled BHET can also be considered as a type of composition containing two or more components, i.e., BHET composition. Recycled BHET can be used as a polymerization raw material for producing polyester resins.

[0024] According to one embodiment, the regenerated bis(2-hydroxyethyl)terephthalate of step (1) can be prepared by a process including: (1a) subjecting waste polyester to depolymerization by a first glycolysis reaction at a temperature of 180°C to 200°C to obtain a first reactant; (1b) subjecting the first reactant to depolymerization by a second glycolysis reaction at a temperature of 150°C to 170°C to obtain a second reactant; (1c) subjecting the second reactant to ion exchange by an ion exchange resin to obtain a third reactant; (1d) removing unreacted glycol from the third reactant by distillation at a temperature of 150°C or less to obtain a fourth reactant; and (1e) subjecting the fourth reactant to distillation to obtain crude bis(2-hydroxyethyl)terephthalate.

[0025] Each step will now be described in detail. Preparation of waste polyester The waste polyester used as the raw material in the present invention can be obtained from polyester material products that have been discarded after use.

[0026] For example, waste polyester can be obtained from products such as beverage bottles, fabrics, films, cases, boxes, dividers, shelves, protective panels, packaging materials, building materials, and interior and exterior materials made from various polyester materials that are discarded after use by consumers.

[0027] The waste polyester material may be pre-treated before being subjected to the depolymerization step.

[0028] First, the waste polyester material is cleaned of other plastics, metals, and contaminants, and then washed and sorted, if necessary, according to specific characteristics such as color.

[0029] The waste polyester material thus selected is put into a crusher and crushed into small flakes. The waste polyester flakes thus obtained may be sieved into a desired particle size or less using a mesh. The size of the mesh may be, for example, 4 mm or less, 3 mm or less, or 2 mm or less.

[0030] The sieved flakes can be washed, dried, such as with hot air, and then subjected to a depolymerization step.

[0031] On the other hand, the waste polyester subjected to the glycolysis reaction may have a controlled particle size. For example, the waste polyester may be pulverized into flakes by the above-mentioned pretreatment step.

[0032] Specifically, the particle size of the waste polyester may be 4 mm or less, 3 mm or less, 2 mm or less, or 1 mm or less. If the particle size is within the above range, the glycolysis reaction can be performed under relatively low temperature conditions. For example, the temperature condition of the first glycolysis reaction may be adjusted to 195°C or less, 190°C or less, 185°C or less, or 180°C, and the temperature condition of the subsequent second glycolysis reaction may be adjusted to 160°C or less or 150°C or less. Furthermore, if the particle size is within the above range, the glycolysis reaction can be performed within a relatively short time. For example, the time of the first and second glycolysis reactions may be 3 hours or less, 2 hours or less, or 1 hour or less from the time when the appropriate temperature is reached.

[0033] Furthermore, the waste polyester may have a fine structure like a fiber. For example, the waste polyester may be waste fiber or fibrous material such as a discarded banner.

[0034] As a specific example, the waste polyester may have a particulate or fibrous form with a particle size of 4 mm or less.

[0035] The fibers may include at least one of monofilament yarns and multifilament yarns. The diameter of the monofilament yarn may be, for example, 0.05 denier to 100 denier, which may correspond to about 0.001 mm to 0.1 mm. Specifically, the monofilament yarn may have a diameter of 0.05 denier to 7 denier, or 7 denier to 100 denier. The diameter of the multifilament yarn may be, for example, 1 denier to 10,000 denier, which may correspond to about 0.01 mm to 1 mm. Specifically, the multifilament yarn may have a diameter of 0.01 denier to 0.2 denier, or 0.2 denier to 1 denier.

[0036] When the particle size or diameter of the waste polyester is adjusted to fall within a specific range and depolymerization is carried out, solvation can be promoted even under conditions of a relatively low temperature and a short reaction time.

[0037] In particular, according to the subject invention, a two-stage glycolysis reaction (i.e., a first glycolysis reaction and a second glycolysis reaction) is carried out. When solvation is promoted in the first glycolysis reaction, a transesterification reaction (ester exchange reaction) of waste polyester can be carried out in the second glycolysis reaction under conditions of lower temperature and shorter reaction time. Therefore, the concentration of diethylene glycol (DEG) naturally formed at a general glycolysis reaction temperature can be significantly reduced, and the content of diethylene glycol ester compounds (DEG esters) in the finally prepared bis(2-hydroxyethyl) terephthalate can be significantly reduced.

[0038] The diethylene glycol ester compound present in bis(2-hydroxyethyl) terephthalate acts as a factor in disrupting the order of the final polymer during the subsequent polymerization of polyesters and polyester copolymers, thereby degrading the heat resistance properties of the final polymer, such as melting point (Tm), glass transition temperature (Tg), etc.

[0039] However, polyester resins and products made using bis(2-hydroxyethyl) terephthalate obtained by the depolymerization method of the present invention can be polymerized into polymers that do not have unwanted structural defects, as occurs when using virgin, non-recycled raw materials. Depolymerization According to the method of the present invention, waste polyester is subjected to pretreatment by pulverization and to a multi-stage depolymerization reaction at a low temperature, so that the content of glycol dimer (diethylene glycol) formed during the depolymerization reaction can be significantly reduced. This has the advantages of improving the purity of the finally obtained bis(2-hydroxyethyl) terephthalate and minimizing the side reaction structure in the subsequent repolymerization to polyester.

[0040] According to one embodiment, the depolymerization comprises subjecting the waste polyester to depolymerization via a first glycolysis reaction at high temperature (180-200°C) to obtain a first reactant, and subjecting the first reactant to depolymerization via a second glycolysis reaction at low temperature (150-170°C) to obtain a second reactant.

[0041] As is well known, glycolysis refers to a chemical reaction in which a polymer chain or the like is broken down by glycol. The glycol may include, for example, at least one selected from the group consisting of ethylene glycol, propylene glycol, and diethylene glycol.

[0042] A catalyst may be used for the glycolysis reaction. The catalyst may be a metal catalyst, such as a metal salt catalyst or a metal organic catalyst. Specifically, the catalyst may be a metal acetate, carbonate, oxide, or hydroxide, and the metal may be an alkali metal, an alkaline earth metal, or a transition metal.

[0043] Specific examples of the catalyst include metal acetates or their anhydrides or hydrides, and more specifically, may be at least one selected from the group consisting of zinc acetate, sodium acetate, cobalt acetate, manganese acetate, or their hydrates or anhydrides.

[0044] The total weight of the glycol to be added may be 1, 2, or 3 times or more, and may be 7, 5, or 4 times or less, of the weight of the waste polyester resin. For example, the weight of the glycol to be added may be 1 to 7 times, specifically 2 to 5 times, and more specifically 3 to 4 times, the weight of the waste polyester resin.

[0045] Furthermore, the weight of the catalyst to be added may be 0.01 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight or more, or 0.3 parts by weight or more, and may be 5 parts by weight or less, 1 part by weight or less, 0.7 parts by weight or less, 0.5 parts by weight or less, or 0.4 parts by weight or less, relative to 100 parts by weight of the waste polyester resin. For example, the weight of the catalyst to be added may be 0.1 parts by weight to 1 part by weight, specifically 0.2 parts by weight to 0.7 parts by weight, relative to 100 parts by weight of the waste polyester resin. More specifically, the catalyst may be used in an amount of 0.2 parts by weight to 0.4 parts by weight relative to 100 parts by weight of the waste polyester.

[0046] The temperature during the first glycolytic reaction may be 170° C. or more, 180° C. or more, or 190° C. or more, and may be 205° C. or less, 200° C. or less, 195° C. or less, or 190° C. or less. For example, the temperature during the first glycolytic reaction may be 180° C. to 200° C., specifically 180° C. to 195° C., and more specifically 180° C. to 190° C.

[0047] Furthermore, the temperature during the second glycolytic reaction may be 140° C. or higher, 150° C. or higher, or 160° C. or higher, and may be 170° C. or lower, or may be 160° C. or lower. For example, the temperature during the second glycolytic reaction may be 150° C. to 170° C., specifically 150° C. to 160° C., and more specifically 150° C. to 155° C.

[0048] The time required for the first and second glycolytic reactions may be 1 hour or more, or 2 hours or more, or 4 hours or less, or 3 hours or less, from the time when the appropriate temperature is reached. For example, the time required for the first and second glycolytic reactions may be 1 hour to 4 hours, specifically 1 hour to 3 hours, and more specifically 1 hour to 2 hours, from the time when the appropriate temperature is reached.

[0049] As a specific example, the first glycolytic reaction may be carried out for 1 to 3 hours at a temperature of 180° C. to 190° C. Furthermore, the second glycolytic reaction may be carried out for 1 to 3 hours at a temperature of 150° C. to 160° C.

[0050] As an example, the first glycolysis reaction may be carried out in the presence of anhydrous zinc acetate catalyst. As a specific example, the first glycolysis reaction may be carried out in the presence of anhydrous zinc acetate catalyst at a temperature of 180°C to 200°C for 1 hour to 3 hours. The anhydrous zinc acetate catalyst may be used in an amount of 0.2 parts by weight to 0.4 parts by weight per 100 parts by weight of waste polyester. Furthermore, the second glycolysis reaction may be carried out at a temperature of 140°C to 160°C for 1 hour to 3 hours without adding a catalyst and by further adding ethylene glycol. Cooling and filtration The second reactant obtained by depolymerization can then be cooled and used in the next step.

[0051] The cooling temperature may be, for example, 150°C or less, 140°C or less, 130°C or less, 120°C or less, 110°C or less, or 100°C or less, or may be 50°C or more, 60°C or more, 70°C or more, 80°C or more, or 90°C or more.

[0052] As an example, cooling may be accomplished by a reduced pressure flash process, in which a vacuum is applied to evaporate ethylene glycol, thereby reducing the temperature of the second reactant.

[0053] For example, the second reactant may be further subjected to a step of cooling to below 120° C. by a vacuum flash prior to the subsequent step. More specifically, the temperature of the second reactant may be reduced to below 110° C. or below 100° C. by a vacuum flash process.

[0054] The pressure condition of the reduced pressure flash process may be, for example, 200 Torr or less, 100 Torr or less, or 50 Torr or less, specifically, 10 Torr to 200 Torr, 10 Torr to 100 Torr, or 10 Torr to 50 Torr.

[0055] Thereafter, insoluble impurities can be removed from the cooled second reactant by filtration. As a specific example, before the ion exchange in step (3), a step of cooling the second reactant to 120°C or less, adding a filter aid, and filtering the second reactant may be further performed. As a result, fine particles and insoluble organic matter present in the second reactant can be filtered and removed by solid-liquid separation.

[0056] Known components such as diatomaceous earth, perlite, and asbestos powder can be used as a filter aid. For example, 0.1 to 2.0 parts by weight of the filter aid may be added to 100 parts by weight of the second reactant.

[0057] Since the bis(2-hydroxyethyl) terephthalate (BHET) or oligomer obtained by the depolymerization reaction exists in a solid state at room temperature, it is difficult to separate the impurities at room temperature. Therefore, it is preferable to separate the impurities at a temperature condition of 90°C to 150°C, more specifically, 110°C to 150°C. Furthermore, when the above temperature range is maintained, the fluidity is good, so that insoluble impurities may be easily removed.

[0058] Various methods and devices can be used to remove insoluble impurities by solid-liquid separation. For example, devices such as a pressure filter, a centrifuge, a filter press, a belt press, etc. may be used. However, as long as any method capable of separating impurities is used, it is not limited thereto. Ion exchange The depolymerized, cooled and filtered second reactant is subjected to ion exchange with an ion exchange resin to obtain a third reactant.

[0059] When the second reactant is subjected to ion exchange, ionic impurities present in the second reactant, in particular catalysts and contaminants, can be removed.

[0060] As is well known, an ion exchange resin refers to a resin or polymer that functions as a medium for ion exchange, and can include cation exchange resins, anion exchange resins, amphoteric ion exchange resins, chelating resins, and the like.

[0061] Cation exchange resins contain sulfonic acid groups (-SO 3 The anion exchange resin may include a strongly acidic cation exchange resin having a carboxyl group (-H) and a weakly acidic cation exchange resin having a carboxyl group (-COOH). The anion exchange resin may include a strongly basic anion exchange resin in the form of a quaternary ammonium salt and a weakly basic anion exchange resin having a primary to tertiary amino group.

[0062] As a specific example, the ion exchange resin may include at least one selected from the group consisting of a strong acid cation exchange resin, a weak acid cation exchange resin, and a chelating resin.

[0063] According to one embodiment, the ion exchange is carried out by adding an ion exchange resin to the second reactant.

[0064] The weight of the ion exchange resin added may be 1, 3, or 5 times or more, or may be 20, 15, 10, or 8 times or less, of the weight of the catalyst added in the depolymerization reaction. For example, the weight of the ion exchange resin added may be 1 to 20 times, specifically 3 to 15 times, and more specifically 5 to 8 times, the weight of the catalyst added in the depolymerization reaction.

[0065] Furthermore, the weight of the ion exchange resin to be added may be 1 part by weight or more, 3 parts by weight or more, or 5 parts by weight or more, and may be 50 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 7 parts by weight or less, based on 100 parts by weight of the waste polyester resin used in the depolymerization reaction.

[0066] As a specific example, the ion exchange resin may be used in an amount of 1 part by weight to 20 parts by weight based on 100 parts by weight of the waste polyester.

[0067] According to another embodiment, the ion exchange is carried out using a column containing an ion exchange resin.

[0068] Specifically, a column can be packed with particles of ion exchange resin, and ion exchange can occur while the second reactant is passed through the column.

[0069] The particle size of the ion exchange resin particles may be, for example, 0.3 mm to 1.5 mm, and more specifically, 0.6 mm to 0.9 mm.

[0070] The ion exchange temperature may be, for example, 140°C or less, 130°C or less, 120°C or less, 110°C or less, or 100°C or less, or 50°C or more, 60°C or more, 70°C or more, 80°C or more, or 90°C or more. Removal and recovery of unreacted glycol Unreacted glycol is removed from the third reactant by distillation to obtain a fourth reactant.

[0071] Since unreacted glycol remains in the depolymerization product after its filtration in the previous step, it is necessary to remove the unreacted glycol from the reaction prior to the next step.

[0072] Furthermore, in order to make the depolymerization process economical, it is necessary to carry out a step of recovering the unreacted glycols, i.e., the glycols previously used in the depolymerization and remaining without participating in the glycolysis reaction, such as ethylene glycol, propylene glycol, diethylene glycol, etc., can be recovered and reused.

[0073] The distillation to remove the unreacted glycol can be carried out, for example, by vacuum distillation. For this purpose, a glass distillation apparatus or a rotary evaporator may be used.

[0074] The vacuum distillation for removing the unreacted glycol is carried out at a temperature of 150°C or less, which further reduces the formation of diethylene glycol and impurities derived from diethylene glycol, thereby increasing the purity of BHET. For example, the vacuum distillation for removing the unreacted glycol may be carried out at a temperature of 150°C or less, 130°C or less, or 120°C or less, and 80°C or more, 90°C or more, 100°C or more, or 110°C or more. Specifically, the temperature during the distillation for removing the unreacted glycol may be 80°C to 190°C, or 90°C to 150°C. As a more specific example, the distillation for removing the unreacted glycol may be carried out at a temperature of 100°C to 130°C.

[0075] The pressure during distillation to remove unreacted glycol may be, for example, from 0.1 Torr to 200 Torr, more specifically, from 0.5 Torr to 30 Torr. distillation The fourth reaction product from which the unreacted glycol has been removed is subjected to distillation to obtain crude bis(2-hydroxyethyl) terephthalate.

[0076] Although a variety of methods may be used for distillation, a distillation method that separates the mixture into a thin film to increase the surface area in contact with the heat source can be used.

[0077] For example, the distillation can be carried out by thin film evaporation, falling film evaporation, or short path evaporation. For this purpose, thin film evaporators, falling film evaporators, and short path evaporators, respectively, can be used.

[0078] As a specific example, the distillation for obtaining bis(2-hydroxyethyl) terephthalate may be performed by thin-film evaporation. Specifically, the mixture supplied to the evaporator of the thin-film evaporator forms a thin film on the inner wall of the thin-film evaporator by the wiper rotor. Then, the distillation is performed under appropriate temperature conditions by heating. Furthermore, a cooler for recovering the evaporant may be provided inside the thin-film evaporator.

[0079] Thin film evaporation may be performed by short path evaporation. Such short path and thin film evaporation has a short residence time and allows reduced pressure distillation under high vacuum, making it possible to separate high boiling point or high molecular weight substances that are difficult to separate by other distillation methods while minimizing changes in reactants due to heat. Furthermore, when the pressure inside the thin film evaporator is reduced, the vapor pressure of the substance is lowered, which has the advantage that evaporation can be performed at a temperature lower than the original boiling point.

[0080] In a specific example, the fourth reactant is fed into a short-path and thin-film evaporator, and the wiper for forming the thin film is rotated at 300 rpm or more, so that the evaporated and non-evaporated materials can be separated from each other.

[0081] The internal thin film temperature at the upper part of the thin film evaporator during thin film evaporation may be, for example, 100°C or more, 110°C or more, 120°C or more, or 125°C or more, and may be 250°C or less, 200°C or less, 150°C or less, or 135°C or less, specifically, 150°C to 250°C, 190°C to 250°C, or 180°C to 220°C.

[0082] Furthermore, the internal pressure of the upper part of the thin film evaporator during the thin film evaporation may be, for example, 0.005 Torr to 5.0 Torr, specifically, 0.05 Torr to 5.0 Torr, 0.05 Torr to 1.5 Torr, or 0.05 Torr to 1 Torr. More specifically, the distillation for obtaining crude bis(2-hydroxyethyl) terephthalate may be performed by thin film evaporation under a pressure of 0.05 Torr to 0.4 Torr. Adsorption-Crystallization The crude bis(2-hydroxyethyl) terephthalate is subjected to an adsorption-crystallization step to provide high purity and high quality bis(2-hydroxyethyl) terephthalate.

[0083] For example, adsorption-crystallization may be carried out by adding the adsorbent using water as a solvent, followed by filtration and crystallization.

[0084] Various solvents may be used for the adsorption-crystallization, but preferably a solvent capable of dissolving bis(2-hydroxyethyl) terephthalate is used as the solvent. As a specific example, in order to obtain the final reaction product, water is added as a solvent to the crude bis(2-hydroxyethyl) terephthalate dissolved by heating, and an adsorbent is added thereto, and then the solution obtained by filtration is subjected to cooling-crystallization and final filtration. As a result, high-purity bis(2-hydroxyethyl) terephthalate can be obtained.

[0085] Water may be added in an amount of 100 to 500 parts by weight, specifically 200 to 400 parts by weight, and more specifically 300 to 350 parts by weight, relative to 100 parts by weight of crude bis(2-hydroxyethyl) terephthalate.

[0086] Furthermore, the dissolution temperature may be from 50°C to 95°C, specifically from 60°C to 85°C, and more specifically from 70°C to 75°C.

[0087] The added adsorbent can act to adsorb and remove other impurities. The adsorbent may be added in an amount of 0.1 to 3 parts by weight per 100 parts by weight of crude bis(2-hydroxyethyl) terephthalate. The type and form of the adsorbent are not particularly limited. For example, activated carbon may be used. Regenerated Bis(2-hydroxyethyl) terephthalate The bis(2-hydroxyethyl) terephthalate, i.e., recycled BHET finally obtained by the above steps, has high purity and has less than a certain level of organic impurities, especially diethylene glycol and by-products derived from diethylene glycol (such as DEG esters), or other oligomers and inorganic substances, and has excellent color quality.

[0088] This can be confirmed by analyzing the final product obtained by the above method by high performance liquid chromatography (HPLC) and calculating the relative ratio between the peak areas for each component. Specifically, the content of each component can be derived by measuring the peak area fraction (%) relative to the total peak area in the spectrum obtained using high performance liquid chromatography.

[0089] For example, the recycled bis(2-hydroxyethyl) terephthalate may have a peak area fraction (i.e., purity) of bis(2-hydroxyethyl) terephthalate of 90% or more, 93% or more, or 95% or more, as measured by HPLC.

[0090] According to one embodiment, the regenerated bis(2-hydroxyethyl) terephthalate may have a peak area fraction of bis(2-hydroxyethyl) terephthalate of 96% or more when measured by HPLC. Specifically, the peak area fraction of bis(2-hydroxyethyl) terephthalate may be 96.5% or more, 97% or more, 97.5% or more, or 98% or more.

[0091] Furthermore, the recycled bis(2-hydroxyethyl) terephthalate may have a peak area fraction of organic impurities of less than 5% in total as measured by HPLC, specifically less than 4%, less than 3%, less than 2%, less than 1%, or less than 0.7%.

[0092] According to one embodiment, the regenerated bis(2-hydroxyethyl) terephthalate may have a total peak area fraction of diethylene glycol ester compounds of less than 2% when measured by HPLC. Specifically, the total peak area fraction of diethylene glycol ester compounds may be less than 1.5%, less than 1.2%, less than 1%, less than 0.9%, less than 0.8%, or less than 0.7%. More specifically, it may be 0% to less than 1.5%, 0% to less than 1%, or 0% to less than 0.8%.

[0093] The diethylene glycol ester compound may be, for example, a condensation product between an aromatic dicarboxylic acid, such as terephthalic acid, and diethylene glycol. As another example, the diethylene glycol ester compound may be a condensation product between an aromatic dicarboxylic acid, such as terephthalic acid, and a glycol (e.g., ethylene glycol) in addition to diethylene glycol. As a specific example, the diethylene glycol ester compound may include at least one of 2-hydroxyethyl [2-(2-hydroxyethoxy)ethyl] terephthalate and bis [2-(2-hydroxyethoxy)ethyl] benzene-1,4-dicarboxylate.

[0094] Furthermore, the recycled bis(2-hydroxyethyl) terephthalate can have a total oligomer peak area fraction of 3% or less as measured by HPLC, which is a significantly superior level in terms of purity and quality compared to the 10-20% range of oligomer substances present in products obtained by depolymerization using conventional methods.

[0095] Specifically, the regenerated bis(2-hydroxyethyl)terephthalate may have a peak area fraction of BHET dimer of less than 3%, less than 2%, less than 1%, or less than 0.7% when measured by HPLC. Furthermore, the regenerated bis(2-hydroxyethyl)terephthalate may have a peak area fraction of BHET trimer of less than 1%, less than 0.5%, less than 0.3%, less than 0.1%, or 0% when measured by HPLC.

[0096] In addition, the final product may further contain impurities having a structure similar to that of bis(2-hydroxyethyl)terephthalate. For example, it may contain at least one selected from the group consisting of monohydroxyethyl terephthalate (MHET), bis(2-hydroxypropyl)terephthalate, and monohydroxyethylethoxyterephthalate. When measured by HPLC, the peak area fraction of the impurity having a structure similar to that of bis(2-hydroxyethyl)terephthalate may be less than 3%, less than 2%, less than 1%, or less than 0.5%.

[0097] Furthermore, the recycled bis(2-hydroxyethyl) terephthalate may have a yellowness index (YID) of 3.0 or less as measured by a spectrophotometer. Specifically, the yellowness index may be 2.5 or less, 2.0 or less, 1.5 or less, or 1.0 or less.

[0098] Furthermore, the recycled bis(2-hydroxyethyl) terephthalate may have a total inorganic matter content of less than 5 ppm as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Specifically, the total inorganic matter content may be less than 3 ppm, less than 1 ppm, or nearly 0 ppm. Preparation of solutions of regenerated bis(2-hydroxyethyl) terephthalate The regenerated bis(2-hydroxyethyl) terephthalate prepared above is mixed with a solvent to prepare a solution of regenerated bis(2-hydroxyethyl) terephthalate.

[0099] Examples of the solvent used to prepare the solution of regenerated BHET include water, ethylene glycol, methanol, and ethanol. As a specific example, the solvent may include at least one of water and ethylene glycol. As a more specific example, the solvent may include water and ethylene glycol at the same time, in which case the mixing weight ratio of water and ethylene glycol may be 1:5 or 1:2.

[0100] The temperature at which the regenerated BHET is mixed with the solvent (dissolution temperature) may be, for example, 60°C or more, 65°C or more, 70°C or more, or 75°C or more, and may be 197°C or less, 180°C or less, 165°C or less, 140°C or less, 120°C or less, 100°C or less, 90°C or less, or 80°C or less.

[0101] According to one embodiment, the temperature at which the regenerated BHET is mixed with water may be 60° C. to 100° C. According to another embodiment, the temperature at which the regenerated BHET is mixed with ethylene glycol may be 60° C. to 197° C. According to one embodiment, the temperature at which the regenerated BHET is mixed with a mixed solvent of water and ethylene glycol may be 60° C. to 197° C. If the temperature is within the preferred range, it is more advantageous for preventing the problem of a decrease in purity due to the formation of diethylene glycol ester caused by thermal decomposition at high temperatures while the regenerated BHET is sufficiently dissolved.

[0102] For example, the concentration of the regenerated BHET solution may be 25% by weight or more, 35% by weight or more, 50% by weight or more, 65% by weight or more, or 75% by weight or more, and may be 99% by weight or less, 95% by weight or less, 90% by weight or less, 85% by weight or less, or 80% by weight or less. As a specific example, the concentration of the regenerated BHET solution may be 25% by weight to 99% by weight, more specifically, 50% by weight to 95% by weight. If it is within the above preferred range, it may be more advantageous to have excellent reaction efficiency and induce a uniform polymerization reaction. The concentration of the regenerated BHET solution can be calculated as a percentage of the weight of the regenerated BHET based on the total weight of the solution (i.e., the total weight of the regenerated BHET and the solvent). Polyester resin polymerization The solution of regenerated bis(2-hydroxyethyl) terephthalate prepared above is used to polymerize a polyester resin.

[0103] The polymerization of the polyester resin of the present invention includes carrying out a polycondensation reaction (first polycondensation reaction) under low vacuum to prepare a low molecular weight oligomer, and subjecting this oligomer to a polycondensation reaction (second polycondensation reaction) under high vacuum to prepare a polyester resin.

[0104] The first polycondensation reaction and the second polycondensation reaction are carried out under reduced pressure conditions, and the solvent contained in the solution of recycled bis(2-hydroxyethyl) terephthalate and the by-products of the polycondensation reaction (glycol, etc.) can be discharged outside the system.

[0105] The pressure during the first polycondensation reaction may be, for example, 700mmHg or less, 600mmHg or less, 500mmHg or less, 400mmHg or less, 350mmHg or less, 300mmHg or less, or 250mmHg or less, or 160mmHg or more, 180mmHg or more, 200mmHg or more, 220mmHg or more, or 240mmHg or more. According to one embodiment, the pressure during the first polycondensation reaction is 200mmHg to 600mmHg. If it is within the above preferred range, it may be more advantageous to sufficiently remove the by-products of the polycondensation reaction under low vacuum while maintaining the degree of vacuum during the polycondensation reaction.

[0106] Furthermore, the temperature during the first polycondensation reaction may be, for example, 100° C. or more, 130° C. or more, 160° C. or more, 180° C. or more, or 200° C. or more, and may be 300° C. or less, 280° C. or less, 250° C. or less, or 230° C. or less. As a specific example, the first polycondensation reaction may be carried out at a temperature of 180° C. to 250° C. and a pressure of 200 mmHg to 400 mmHg.

[0107] Furthermore, the first polycondensation reaction may be carried out until the number average molecular weight of the low molecular weight oligomer reaches an appropriate level. The time required for the first polycondensation reaction is not particularly limited, but may be, for example, 30 minutes or more, 1 hour or more, 2 hours or more, or 3 hours or more, and may be 15 hours or less, 10 hours or less, 5 hours or less, or 4 hours or less. Specifically, it may be 1 hour to 5 hours.

[0108] The pressure during the second polycondensation reaction may be, for example, less than 200 mmHg, 150 mmHg or less, 100 mmHg or less, 50 mmHg or less, 10 mmHg or less, or 1 mmHg or less, or 0.001 mmHg or more, 0.01 mmHg or more, 0.1 mmHg or more, or 0.5 mmHg or more. According to one embodiment, the pressure during the second polycondensation reaction is less than 200 mmHg. If it is within the above preferred range, it may be more advantageous to sufficiently remove by-products of the polycondensation reaction while maintaining the vacuum degree during the polycondensation reaction.

[0109] Furthermore, the temperature during the second polycondensation reaction may be, for example, 230° C. or higher, 240° C. or higher, 250° C. or higher, or 260° C. or higher, and may be 300° C. or lower, 290° C. or lower, 280° C. or lower, or 270° C. or lower. As a specific example, the second polycondensation reaction may be carried out at a temperature of 250° C. to 300° C. and a pressure of 0.01 mmHg to 150 mmHg. Within the above preferred range, the by-products of the polycondensation reaction can be sufficiently removed while maintaining the degree of vacuum during the polycondensation reaction, which can be further advantageous in suppressing yellowing of the final resin.

[0110] Furthermore, the second polycondensation reaction may be carried out until the number average molecular weight of the polyester resin reaches an appropriate level. The time required for the second polycondensation reaction is not particularly limited, but may be, for example, 30 minutes or more, 1 hour or more, 2 hours or more, or 5 hours or more, and may be 60 hours or less, 48 ​​hours or less, 24 hours or less, or 15 hours or less. Specifically, it may be 1 hour to 24 hours.

[0111] The method for preparing the polyester resin of the present invention may further include steps commonly employed in this field in addition to the steps mentioned above.

[0112] As an example, the method for preparing the polyester resin may further include, after step (4), molding the polyester resin to form pellets.

[0113] As another example, the method for preparing the polyester resin may further include a step of subjecting the polyester resin to solid-state polymerization after step (4). The temperature during the solid-state polymerization may be, for example, 180°C or more, 190°C or more, 200°C or more, or 205°C or more, and may be 260°C or less, 240°C or less, 220°C or less, or 215°C or less. As a specific example, the solid-state polymerization may be performed at a temperature of 200°C to 220°C. Furthermore, the pressure during the solid-state polymerization may be, for example, 10.0 Torr or less, 5.0 Torr or less, 2.0 Torr or less, or 1.0 Torr or less, and may be 0.01 Torr or more, 0.1 Torr or more, 0.2 Torr or more, or 0.5 Torr or more. Specifically, it may be 0.2 Torr to 2.0 Torr. Furthermore, the solid-state polymerization may be performed in an inert gas atmosphere such as nitrogen.

[0114] The polyester resin according to the present invention can be prepared as a copolymerized polyester resin by further adding an additional diacid component in addition to the recycled bis(2-hydroxyethyl) terephthalate. The additional diacid component can be a dicarboxylic acid or a derivative thereof. The dicarboxylic acid can include at least one selected from terephthalic acid and isophthalic acid. For example, a dicarboxylic acid or a derivative thereof can be further added during the first polycondensation reaction.

[0115] Furthermore, the polycondensation reaction may be carried out in the presence of a polycondensation catalyst. The polycondensation catalyst may be selected from the group consisting of titanium-based compounds, germanium-based compounds, antimony-based compounds, and aluminum-based compounds. The amount of polycondensation catalyst used is preferably 0.1 ppm to 500 ppm based on the amount of metal element relative to the weight of the final polyester resin. The amount used may vary depending on the desired color and the stabilizers and colorants used, since the amount used affects the color of the final polyester resin.

[0116] In addition to the polycondensation catalyst, a stabilizer, a colorant, a crystallization agent, an antioxidant, a branching agent, etc. may be further used. The timing of adding these additives is not particularly limited, and they may be added at any time during the preparation step of the polyester resin.

[0117] As the stabilizer, phosphorus compounds such as phosphoric acid, trimethyl phosphate, triethyl phosphate, and triethyl phosphonoacetate can generally be used. The amount of stabilizer added can be 10 to 200 ppm based on the amount of element, based on the weight of the polyester resin. Furthermore, examples of colorants added to improve the color of the polyester resin include common colorants such as cobalt acetate and cobalt propionate. The amount of colorant added can be 10 to 200 ppm based on the amount of cobalt element, based on the weight of the polyester resin. If necessary, anthraquinone compounds, perinone compounds, azo compounds, methine compounds, etc. may be used as organic colorants. Commercially available toners such as Polysynthren Blue RLS manufactured by Clarient or Solvaperm Red BB manufactured by Clarient may be used. The amount of organic compound colorant added can be adjusted to 0 to 50 ppm based on the weight of the polyester resin. Examples of the crystallizing agent include crystal nucleating agents, ultraviolet absorbers, polyolefin resins, polyamide resins, etc. Examples of the antioxidant include hindered phenol-based antioxidants, phosphite-based antioxidants, thioether-based antioxidants, or mixtures thereof. Examples of the branching agent include conventional branching agents having three or more functional groups, such as trimellitic anhydride, trimethylolpropane, trimellitic acid, or mixtures thereof. Composition and properties of polyester resin The polyester resin of the present invention is a polyester resin regenerated by chemical recycling of waste polyester.

[0118] Specifically, the polyester resins of the present invention are polymerized using recycled BHET and therefore contain repeat units derived from recycled BHET in the polymer chain.

[0119] The content of recycled BHET in the polyester resin of the present invention may be 90% by weight or more, or 95% by weight or more, and further, the content of recycled BHET may be 100% by weight or less, 99% by weight or less, or 95% by weight or less.

[0120] As an example, recycled bis(2-hydroxyethyl) terephthalate may be employed in an amount of 90% to 100% by weight based on the weight of the polyester resin.

[0121] On the other hand, since bis(2-hydroxyethyl) terephthalate has a structure in which two ethylene glycols and one terephthalic acid are bonded, the polyester resin of the present invention can essentially contain repeating units derived from ethylene glycol and terephthalic acid.

[0122] Furthermore, the polyester resin of the present invention may be a copolymerized polyester resin. For example, it may further include an additional diacid component as a copolymerization monomer. The additional diacid component may be a dicarboxylic acid or a derivative thereof. The dicarboxylic acid may include at least one selected from terephthalic acid and isophthalic acid. The dicarboxylic acid can improve the physical properties of the polyester resin, such as heat resistance, chemical resistance, and weather resistance.

[0123] As described above, the polyester resin of the present invention contains high-purity, high-quality recycled bis(2-hydroxyethyl) terephthalate, and therefore has few impurities and excellent heat resistance despite being a recycled resin.

[0124] Therefore, the present invention provides a polyester resin prepared by the above-mentioned method, that is, in the polyester resin of the present invention, the peak area fraction of bis(2-hydroxyethyl) terephthalate in total is 96% or more, and the peak area fraction of diethylene glycol (DEG) ester compound is less than 2% when measured by high performance liquid chromatography (HPLC).

[0125] The intrinsic viscosity of the polyester resin of the present invention at 35° C. may be, for example, 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. According to one embodiment, the intrinsic viscosity of the polyester resin at 35° C. may be 0.6 dl / g to 1.2 dl / g. The intrinsic viscosity can be calculated, for example, by dissolving the polyester resin in a solvent such as orthochlorophenol and determining the specific viscosity using an Ubbelohde viscometer or the like.

[0126] Furthermore, the polyester resin of the present invention may have a melting point (Tm), for example, of 240° C. or more, 245° C. or more, 250° C. or more, or 255° C. or more, and may be 270° C. or less, 265° C. or less, or 260° C. or less. According to one embodiment, the melting point of the polyester resin may be 255° C. or more. The melting point may be measured, for example, by a method including placing the polyester resin in a differential scanning calorimeter (DSC) and increasing the temperature from room temperature to 280° C. at a constant rate.

[0127] Furthermore, the polyester resin may have a diethylene glycol concentration of, for example, 2.5% by weight or less, 1.5% by weight or less, 1.2% by weight or less, 1.0% by weight or less, or 0.9% by weight or less, as measured by gas chromatography. As a specific example, the polyester resin may have a diethylene glycol concentration of 0.8% by weight or less, as measured by gas chromatography. Polyester fiber and method for preparing same The polyester resins, when spun into fibers as described above, have excellent strength, elongation, and processability and can be used to prepare polyester fibers.

[0128] Therefore, the present invention provides a polyester fiber containing the polyester resin prepared by the above-mentioned method. That is, the polyester fiber of the present invention is prepared from a polyester resin containing recycled bis(2-hydroxyethyl) terephthalate, in which the peak area fraction of bis(2-hydroxyethyl) terephthalate in total is 96% or more and the peak area fraction of diethylene glycol (DEG) ester compound is less than 2% when measured by high performance liquid chromatography (HPLC).

[0129] A method for preparing a polyester fiber according to one embodiment of the present invention includes the steps of: (1) depolymerizing waste polyester to prepare regenerated bis(2-hydroxyethyl) terephthalate, the regenerated bis(2-hydroxyethyl) terephthalate having a total peak area fraction of bis(2-hydroxyethyl) terephthalate of 96% or more and a peak area fraction of diethylene glycol ester of less than 2% when measured by high performance liquid chromatography (HPLC); (2) mixing the regenerated bis(2-hydroxyethyl) terephthalate with a solvent to prepare a solution of the regenerated bis(2-hydroxyethyl) terephthalate; (3) subjecting the regenerated bis(2-hydroxyethyl) terephthalate solution to a first polycondensation under a pressure of 200 mmHg to 600 mmHg to prepare an oligomer; (4) subjecting the oligomer to a second polycondensation under a pressure of less than 200 mmHg to prepare a polyester resin; and (5) spinning the polyester resin to obtain a fiber.

[0130] Steps (1) to (4) can be carried out in the same manner and under the same conditions as described in the method for preparing the polyester resin.

[0131] The spinning of the polyester resin in step (5) may include (5a) drying the polyester resin, (5b) melt spinning the dried polyester resin to obtain an undrawn yarn, and (5c) drawing the undrawn yarn. It may further include (5d) heat treating the drawn yarn. Alternatively, it may include melt spinning the dried polyester resin to obtain a heat treated drawn yarn, i.e., steps (5b), (5c), and (5d) may be carried out simultaneously to obtain a drawn polyester yarn.

[0132] Specifically, the spinning step can be carried out by melt spinning the polyester resin composition, which may be carried out using a conventional melt spinning device, for example, a single-screw or twin-screw extruder type spinning machine.

[0133] The temperature of the spinning step is preferably as low as possible while being sufficient to melt the polyester resin from the viewpoint of suppressing gelation. For example, the spinning step may be performed under conditions in which the temperature of the polyester resin discharged from the spinneret is 275°C to 300°C, or may be performed under a nitrogen atmosphere.

[0134] A spinneret commonly used in melt spinning can be used as the spinneret. For example, a spinneret with a nozzle diameter of 0.1 mmφ to 1.0 mmφ and a nozzle length of about 0.1 mm to 5.0 mm can be used. The cross-sectional shape of the fiber to be spun is not particularly limited, but may be a conventional one such as a circular cross section, a triangular cross section, a rectangular cross section, a Y-shaped cross section, a cross-shaped cross section, a C-shaped cross section, a hollow cross section, or a lattice cross section.

[0135] The fibers discharged from the spinneret are generally cooled by exposure to wind at a speed of 5 m / min to 100 m / min, and then wound up. In this procedure, an oiling agent may be added as a bundling agent. The winding speed may be 300 m / min to 5,000 m / min.

[0136] This method can be carried out by spinning the polyester resin composition at a low speed to obtain an undrawn yarn (UDY) or spinning the polyester resin composition at a high speed to obtain a semi-drawn yarn (POY), winding the undrawn yarn or the semi-drawn yarn, and drawing the wound undrawn yarn or the semi-drawn yarn to obtain a drawn yarn (FDY). Alternatively, the method can be carried out by feeding the wound undrawn yarn, the semi-drawn yarn, or the drawn yarn to a twisting machine and twisting and drawing the yarn to obtain a draw-textured yarn.

[0137] Alternatively, the spinning step may be carried out by directly spinning and drawing the polyester resin composition to obtain a spin-drawn yarn (SDY) in one step.

[0138] Further, the method may include spinning a polyester resin composition to obtain undrawn fibers, drawing the undrawn fibers, subjecting the drawn fibers to serrated crimp, and cutting the crimped continuous fibers to obtain staple fibers.

[0139] The staple fiber may have an average single filament diameter of 0.5 denier to 5 denier. It is possible to obtain crimped continuous fibers having a sawtooth crimp with a crimp frequency (i.e., repeated bending) of 50 or less times per centimeter in the longitudinal direction of the fiber.

[0140] Furthermore, the polyester resin composition is melt-spun through a spinneret to form a filament, which is then cooled and solidified by a water-cooling type cooling device and an air-cooling type cooling device installed directly below the spinneret, stretched in a warm water bath at a temperature higher than Tg, and then heat-set to obtain a monofilament in one step using one machine.

[0141] The monofilament fiber is different from the multifilament fiber and refers to a fiber formed of one filament. The average diameter of the monofilament fiber is about 800 denier to about 1,000 denier, but it may have a different average diameter depending on the application. For example, the average diameter may be about 200 denier for wig thread applications, about 800 denier to about 1,000 denier for cable sleeve applications, and about 2,500 denier to about 4,000 denier for papermaking fabric (PMC) applications.

[0142] The drying in step (5a) may be carried out in an inert gas atmosphere such as nitrogen. For example, it may include preliminary crystallization carried out at a temperature of 100° C. to 150° C. for 2 to 5 hours and main drying carried out at a temperature of 140° C. or higher for 5 hours or more. The drying may be carried out until the moisture content in the polyester resin is 200 ppm or less, specifically 50 ppm or less.

[0143] The melt spinning in step (5b) can be carried out using an extruder equipped with a nozzle, and the melt spinning temperature condition can be, for example, 275° C. to 300° C. The diameter of the obtained undrawn yarn can be, for example, 1,000 denier or less, or 500 denier or less, and 30 denier or more.

[0144] The drawing in step (5c) may be carried out using a heated drum drawing device or the like, and may be carried out, for example, at a draw ratio of 1.05 to 5.0 and at a temperature of 70° C. to 180° C. The diameter of the obtained drawn yarn may be, for example, 200 denier or less, or 150 denier or less, and 30 denier or more.

[0145] The heat treatment in step (5d) may be carried out, for example, at 100° C. to 180° C. for 1 minute to 60 minutes.

[0146] The polyester fibers according to the present invention may have a tenacity of 3.0 g / denier or more, 3.5 g / denier or more, 4.0 g / denier or more, 4.5 g / denier or more, 5.0 g / denier or more, 5.3 g / denier or more, or 5.4 g / denier or more, and 9.0 g / denier or less, 8.0 g / denier or less, 7.0 g / denier or less, or 6.0 g / denier or less, when measured according to ASTM D638 at 25° C. at a speed of 5 mm / min.

[0147] As a specific example, the polyester fibers may have a tenacity of 3.5 g / denier or greater, more specifically 4.8 g / denier to 9.0 g / denier, when measured according to ASTM D638 at 25° C. and a speed of 5 mm / min.

[0148] Further, the polyester fibers may have an elongation at break of 15% or more, 20% or more, 25% or more, 30% or more, 32% or more, or 34% or more, and may be 70% or less, 60% or less, 50% or less, 45% or less, or 40% or less, when measured at 25° C. at a speed of 5 mm / min according to ASTM D638.

[0149] As a specific example, the polyester fiber may have an elongation at break of 20% or more, more specifically 30% to 50%, when measured according to ASTM D638 at 25° C. at a rate of 5 mm / min.

[0150] Furthermore, the diameter of the polyester fibers may be 200 denier or less, or 150 denier or less, or 30 denier or more. EXAMPLES

[0151] The present invention will be described in more detail below with reference to embodiments. However, these examples are provided for illustrative purposes only and the present invention is not limited thereto. Example 1 Step 1: Preparation of regenerated bis(2-hydroxyethyl) terephthalate 2,000 g of waste polyester resin pulverized to a particle size of 4 mm or less, 4,000 g of ethylene glycol, and 7.0 g of anhydrous zinc acetate were charged into a first reactor made of stainless steel (SUS). The temperature inside the reactor was raised to 180°C, and depolymerization (first glycolysis reaction) was carried out over two hours. The resulting reactant (first reactant) was transferred to a second reactor and cooled to 150°C. 2,000 g of ethylene glycol was further added thereto, and depolymerization (second glycolysis reaction) was carried out for two hours while maintaining the reactor temperature at 150°C.

[0152] The resulting reaction product (second reaction product) was cooled to 120°C by vacuum flashing, 16 g of a filter aid was added thereto, and then pressure filtration was performed to separate the solid and liquid. The separated liquid reaction product was passed through a column packed with an ion exchange resin (Bonlite BC107(H)) to remove ionic impurities, and a mixture containing bis(2-hydroxyethyl) terephthalate and ethylene glycol (third reaction product) was obtained.

[0153] This mixture (third reactant) was transferred to a 10-liter distillation apparatus and vacuum distilled at 130° C. to recover unreacted ethylene glycol. The reactant from which ethylene glycol had been removed (fourth reactant) was thin-film evaporated in a thin-film evaporator (VTA VKL70-4S) at 220° C. and 0.08 Torr to obtain 1,040 g of a product from which dimers and higher oligomers had been removed.

[0154] Then, for adsorption-crystallization, 1,040g of the above product and 3,120g of distilled water were charged into a 20-liter glass reactor and dissolved at a temperature of 70°C, and then 5.2g of activated carbon was added thereto, followed by stirring for 30 minutes and filtering. The filtrate was cooled to room temperature for crystallization, filtered, and dried in a vacuum oven. As a result, 1,980g of the final product containing regenerated bis(2-hydroxyethyl) terephthalate was obtained.

[0155] Step 2: Preparation of a solution of regenerated bis(2-hydroxyethyl) terephthalate 1,980 g of regenerated bis(2-hydroxyethyl) terephthalate (r-BHET), 312 g of water, and 483 g of ethylene glycol (EG) were mixed uniformly at 70° C. to prepare a r-BHET solution (concentration: 71.4 wt %).

[0156] Step 3: Polycondensation reaction under low vacuum A 7-liter reactor capable of reaction under vacuum was charged with 2,775 g of the regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) solution prepared above, 0.8 g of antimony trioxide as catalyst, 0.6 g of triethyl phosphate as stabilizer, and 0.4 g of cobalt acetate as colorant. The temperature of the reactor was raised to 190°C over a period of 2 hours. Once the temperature reached 190°C, the pressure of the reactor was reduced from standard pressure to 200 Torr (absolute pressure: 200 mmHg) over a period of 30 minutes. The polycondensation reaction was carried out under low vacuum for 1 hour while maintaining the reactor pressure at 200 Torr (absolute pressure: 200 mmHg).

[0157] Step 4: Polycondensation reaction under high vacuum The reactor pressure was reduced from 200 Torr (absolute pressure: 200 mmHg) to 5 Torr (absolute pressure: 5 mmHg) over 30 minutes. At the same time, the reactor temperature was increased to 280°C over 1 hour, and the polycondensation reaction was carried out under high vacuum while maintaining the reactor pressure at 1 Torr (absolute pressure: 1 mmHg) or less. At the start of the polycondensation reaction under high vacuum, the stirring speed may be set high. As the polycondensation reaction proceeds under high vacuum, if the viscosity of the reactants increases and the stirring power becomes weak, or if the temperature of the reactants exceeds the set temperature, the stirring speed may be appropriately adjusted accordingly. The polycondensation reaction was carried out under high vacuum until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.64 dl / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was then discharged out of the reactor to form strands, which were solidified with a cooling liquid and then granulated to an average weight of about 12 to 14 mg.

[0158] The granules were left at 150°C for 1 hour to crystallize, and then fed into a 20-liter reactor for solid-state polymerization. Nitrogen was then flowed into the reactor at a rate of 50 liters / min. During this, the temperature of the reactor was increased from room temperature to 140°C at a rate of 40°C / hr, maintained at 140°C for 3 hours, then increased to 220°C at a rate of 40°C / hr, and maintained at 220°C. The solid-state polymerization reaction was carried out until the intrinsic viscosity (IV) of the granules in the reactor reached 0.78-0.82 dl / g, and a polyester resin was prepared.

[0159] Example 2 A polyester resin was prepared in the same manner as in Example 1, except that in step 2, 1,980 g of recycled bis(2-hydroxyethyl) terephthalate (r-BHET) and 312 g of water were uniformly mixed at 70°C to prepare a r-BHET solution (concentration: 86.4 wt%).

[0160] Example 3 A polyester resin was prepared in the same manner as in Example 1, except that in step 1, the first glycolysis reaction was carried out at 180° C. for 1 hour.

[0161] Example 4 A polyester resin was prepared in the same manner as in Example 1, except that in step 1, 2,000 g of waste fibers was used as the waste polyester raw material.

[0162] Example 5 A polyester resin was prepared in the same manner as in Example 1, except that in step 1, 2,000 g of discarded banners were used as the waste polyester raw material.

[0163] Example 6 A polyester resin was prepared in the same manner as in Example 1, except that in step 1, the adsorption-crystallization was not carried out after the thin film evaporation.

[0164] Comparative Example 1 2,000g of waste polyester resin, 8,000g of ethylene glycol, and 7.0g of anhydrous zinc acetate were charged into a stainless steel (SUS) reactor. The temperature inside the reactor was raised to 196°C, and depolymerization (glycolysis reaction) was carried out over 4 hours. The resulting reaction product was cooled to 30°C, and crystallization of bis(2-hydroxyethyl) terephthalate was carried out over 2 hours. The resulting slurry of bis(2-hydroxyethyl) terephthalate and ethylene glycol was subjected to solid-liquid separation using a centrifuge. The bis(2-hydroxyethyl) terephthalate obtained by centrifugation was washed twice with sufficient distilled water, and the residual solvent was removed in an oven to obtain approximately 2,020g of a final product containing bis(2-hydroxyethyl) terephthalate.

[0165] A polyester resin was prepared in the same manner as in Example 1 using the bis(2-hydroxyethyl) terephthalate thus obtained.

[0166] Comparative Example 2 A polyester resin was prepared in the same manner as in Comparative Example 1, except that in step 1, depolymerization (glycolysis reaction) was carried out at 210°C.

[0167] Comparative Example 3 A polyester resin was prepared in the same manner as in Comparative Example 1, except that in step 1, depolymerization (glycolysis reaction) was carried out at 196° C. and adsorption-crystallization was not carried out.

[0168] Test Example 1: Evaluation of Regenerated Bis(2-hydroxyethyl)terephthalate 1A. Analysis of r-BHET components - HPLC The components of the regenerated bis(2-hydroxyethyl) terephthalate (BHET) were analyzed by high performance liquid chromatography (HPLC). About 0.01 g of the sample was diluted in about 20 ml of methanol and then measured by HPLC. Model:Waters e2695 Column: C18 (4.6 x 250 mm), 5 μm UV detector: 242 nm Injection volume: 10μl Eluent (gradient) A:H 2 O+H 3 PO 4 , B: acetonitrile Measured components: Bis(2-hydroxyethyl) terephthalate (BHET), mono(2-hydroxyethyl) terephthalate (MHET), 2-hydroxyethyl [2-(2-hydroxyethoxy)ethyl] terephthalate (DEG ester 1), bis[2-(2-hydroxyethoxy)ethyl] benzene-1,4-dicarboxylate (DEG ester 2), dimer, trimer, etc. 2B.Residual solvent-GC The content of residual ethylene glycol (EG) in the regenerated bis(2-hydroxyethyl) terephthalate (BHET) was measured by gas chromatography (GC). Approximately 0.1 g of sample was dissolved in CHCl 3 It was diluted to about 10 ml, filtered through a 0.45 μm filter, and then measured by GC. Model: Agilent 7890B Column: DB-624 (30m x 0.25mm x 1.4μm) Oven temperature: 60℃(2min)-10℃ / min-200℃(0min)-20℃ / min-260℃(5min) Injection temperature: 250℃ Detector temperature: 250℃ Flow rate: 1.5ml / min(N 2 ), split ratio: 1 / 50 1C. Melting Temperature, Glass Transition Temperature, and Crystallization Temperature - DSC Differential scanning calorimetry (DSC, Q20 model, TA equipment) was used. Each sample was filled into an aluminum pan, heated to 280°C at 10°C / min, held at 280°C for 5 minutes, and then cooled to 30°C at -300°C / min. The glass transition temperature (Tg) and melting temperature (Tm) were calculated from the heat flow obtained when the temperature was then raised to 280°C at 10°C / min. The temperature at the apex of the exothermic curve when the temperature was then held at 280°C for 5 minutes and lowered to 30°C at -10°C / min was taken as the cooling crystallization temperature (Tmc). 1D.Inorganic substances-ICP-AES Approximately 0.3 g of each sample was pretreated by ultrasound and diluted with ultrapure water. The inorganic components were analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES, 5100, Agilent) (detection limit: 5 ppm).

[0169] Test Example 2: Evaluation of polyester resin 2A. Melting point - DSC The melting point of each polyester resin was measured using DSC in the same manner as in 1C above. 2B. Intrinsic viscosity (IV) Each polyester resin was dissolved in orthochlorophenol (OCP) at 150° C. at a concentration of 1.2 g / dl to obtain a solution, and the intrinsic viscosity was measured using an Ubbelohde viscometer. Specifically, the temperature of the viscosity tube was maintained at 35° C., and the time required for the solvent to pass through a specific part inside the viscosity tube (flow time) and the time required for the solution to pass through and obtain a specific viscosity were used to calculate the intrinsic viscosity. 2C.DEG content - GC Each polyester resin was finely pulverized in a grinder, and 2 g of the resin was subjected to aminolysis with hydrazine hydrate, and then the diethylene glycol (DEG) content (wt %) was measured by gas chromatography (GC). Test Example 3: Evaluation of polyester fiber 3A. Preparation of Polyester Fibers Each polyester resin prepared in the examples and comparative examples was dried for a long time in a nitrogen atmosphere to adjust the moisture content to 50 ppm or less. The dried polyester resin was melt-spun through an extruder equipped with a 36-hole nozzle at the tip of the extruder to prepare an undrawn yarn of 300 denier. The undrawn yarn was drawn with a heated drum drawing device to obtain a drawn yarn of 60 to 85 denier, which was then heat-treated at 180°C. 3B. Tenacity and Elongation at Break The polyester fibers were measured for tenacity and elongation at break according to ASTM D638 using a Zwick Z010 at 25° C. with a measurement speed of 5 mm / min. 3C. Processability Evaluation The number of yarn breaks was measured over a 5-hour spinning process, and the processability was evaluated according to the following criteria: ◎Number of thread breaks: 0 ○Number of thread breaks: 1 △ Number of thread breaks: 2-3 × Number of thread breaks: 4 or more The results of the test examples are shown in the table below.

[0170] [Table 1]

[0171] [Table 2] As can be seen from the above table, the recycled bis(2-hydroxyethyl) terephthalate (rBHET) prepared in step 1 of Examples 1 to 6 had high purity, low contents of impurities such as diethylene glycol ester (DEG ester) and dimer, and no inorganic impurities were observed. As a result, the polyester resins prepared in Examples 1 to 6 each had a low content of diethylene glycol (DEG), a high melting point, and excellent structural regularity, and therefore had both excellent tenacity and processability when spun into fibers.

[0172] In particular, Example 1, in which ethylene glycol was further added during the preparation of the regenerated bis(2-hydroxyethyl) terephthalate solution in step (2), exhibited better properties than Example 2, in which ethylene glycol was not further added.

[0173] In contrast, the recycled bis(2-hydroxyethyl) terephthalate (rBHET) prepared in step 1 of Comparative Examples 1 and 3 contained a large amount of dimer or diethylene glycol ester (DEG ester), and therefore the polyester resins prepared therefrom had a high diethylene glycol (DEG) content, a low melting point, and poor structural regularity, resulting in poor tenacity and processability during fiber spinning.

Claims

1. 1. A process for preparing a polyester resin comprising the steps of: (1) a step of preparing recycled bis(2-hydroxyethyl) terephthalate by depolymerizing waste polyester, the recycled bis(2-hydroxyethyl) terephthalate having a peak area fraction of bis(2-hydroxyethyl) terephthalate of 96% or more and a peak area fraction of diethylene glycol ester of less than 2% in total, when measured by high performance liquid chromatography (HPLC); (2) mixing the regenerated bis(2-hydroxyethyl) terephthalate with a solvent to prepare a solution of regenerated bis(2-hydroxyethyl) terephthalate; (3) subjecting the solution of regenerated bis(2-hydroxyethyl) terephthalate to a first polycondensation reaction under a pressure of 200 mmHg to 600 mmHg to prepare an oligomer; (4) subjecting the oligomer to a second polycondensation reaction under a pressure of less than 200 mmHg to prepare a polyester resin; A method comprising:

2. The regenerated bis(2-hydroxyethyl) terephthalate of step (1) is (1a) subjecting the waste polyester to depolymerization by a first glycolysis reaction at a temperature of 180° C. to 200° C. to obtain a first reactant; (1b) subjecting the first reactant to depolymerization by a second glycolysis reaction at a temperature of 150° C. to 170° C. to obtain a second reactant; (1c) subjecting the second reactant to ion exchange with an ion exchange resin to obtain a third reactant; (1d) removing unreacted glycol from the third reactant by distillation at a temperature of 150° C. or less to obtain a fourth reactant; (1e) subjecting the fourth reactant to distillation to obtain crude bis(2-hydroxyethyl) terephthalate; 2. A process for preparing the polyester resin of claim 1, which is prepared by a process comprising:

3. 2. The method for preparing a polyester resin according to claim 1, wherein the peak area fraction of oligomers of the recycled bis(2-hydroxyethyl) terephthalate in step (1) is 3% or less in total, as measured by high performance liquid chromatography.

4. 2. The method for preparing a polyester resin according to claim 1, wherein the concentration of the solution of recycled BHET in step (2) is 50% by weight to 95% by weight.

5. 10. The method for preparing a polyester resin according to claim 1, wherein the solvent comprises at least one of water and ethylene glycol.

6. 2. The method for preparing a polyester resin according to claim 1, wherein the first polycondensation reaction of step (3) is carried out at a temperature of 180° C. to 250° C. and a pressure of 200 mmHg to 400 mmHg.

7. 2. The method for preparing a polyester resin according to claim 1, wherein the second polycondensation reaction of step (4) is carried out at a temperature of 250° C. to 300° C. and a pressure of 0.01 mmHg to 150 mmHg.

8. 10. The method for preparing the polyester resin of claim 1, further comprising, after step (4), subjecting the polyester resin to solid state polymerization.

9. The process for preparing a polyester resin according to claim 8, wherein the solid state polymerization is carried out at a temperature of 200°C to 220°C.

10. 10. A polyester resin prepared by the method of claim 1, having an intrinsic viscosity of 0.6 dl / g to 1.2 dl / g.

11. 11. The polyester resin according to claim 10, having a diethylene glycol concentration of 0.8% by weight or less as measured by gas chromatography.

12. A polyester fiber comprising the polyester resin of claim 10.

13. 13. The polyester fiber of claim 12, having a tenacity of 3.0 g / denier or greater when measured according to ASTM D638 at 25° C. and a speed of 5 mm / min.

14. 13. The polyester fiber of claim 12, having an elongation at break of 20% or more when measured according to ASTM D638 at 25°C at a speed of 5 mm / min.

15. 1. A method for preparing polyester fibers, comprising the steps of: (1) a step of preparing recycled bis(2-hydroxyethyl) terephthalate by depolymerizing waste polyester, the recycled bis(2-hydroxyethyl) terephthalate having a peak area fraction of bis(2-hydroxyethyl) terephthalate of 96% or more and a peak area fraction of diethylene glycol ester of less than 2% in total, when measured by high performance liquid chromatography (HPLC); (2) mixing the regenerated bis(2-hydroxyethyl) terephthalate with a solvent to prepare a solution of regenerated bis(2-hydroxyethyl) terephthalate; (3) subjecting the solution of regenerated bis(2-hydroxyethyl) terephthalate to a first polycondensation under a pressure of 200 mmHg to 600 mmHg to prepare an oligomer; (4) subjecting the oligomer to a second polycondensation under a pressure of less than 200 mmHg to prepare a polyester resin; (5) spinning the polyester resin to obtain fibers; A method comprising:

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