Method for producing polyester composition with excellent moisture absorption

Abstract

To provide a method for producing moisture absorptive polyester which has a small foreign matter amount in a polyester resin composition, can prevent reduction in operability such as increase in replacement frequency of a spinning pack at the time of spinning and increase in the number of yarn breakage, and can suppress yellowness and oxidation heat generation after washing treatment.SOLUTION: A method for producing copolymerization polyester includes performing esterification reaction or ester exchange reaction using an aromatic dicarboxylic acid or an ester-forming derivative thereof, and diol or an ester-forming derivative thereof, and reacting an esterification reaction product obtained by the esterification reaction or the ester exchange reaction with 10-50 wt.% of polyethylene glycol having a number average molecular weight of 5,000-20,000, in which an amount of a phosphorus compound in the polyethylene glycol is less than 40 ppm as the amount of a phosphorus atom.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a moisture-absorbing polyester composition. [Background technology]

[0002] Polyester fibers are inexpensive and have excellent mechanical properties and a dry feel, making them widely used in a wide range of applications. However, due to their poor moisture absorption, they have issues that must be resolved in terms of comfort, such as a stuffy feeling during high humidity in summer and static electricity during low humidity in winter.

[0003] In order to overcome the above drawbacks, various methods for imparting moisture absorption to polyester fibers have been proposed. Common methods for imparting moisture absorption include copolymerization of a hydrophilic compound to polyester or addition of a hydrophilic compound, and one example of the hydrophilic compound is polyethylene glycol.

[0004] Furthermore, various methods have been proposed for producing polyester compositions containing polyalkylene glycols, including polyethylene glycol, as constituent components and containing other additives.

[0005] For example, Patent Document 1 proposes splittable polyester fibers using polyester copolymerized with 1 to 20% by weight of polyoxyalkylene glycol.

[0006] Patent Document 2 proposes a core-sheath type polyester fiber in which a polymer copolymerized with hygroscopic polyethylene glycol is used as the core component.

[0007] Patent Document 3 proposes a core-sheath composite fiber using a polyetherester in which 10 to 60 wt% of a polyether having a number average molecular weight of 4,000 to 30,000 g / mol and containing a semi-hindered phenol-based antioxidant is copolymerized, and the diol component is 1,4-butanediol. A high-molecular-weight polyethylene glycol copolymer polyester containing an antioxidant is processed into a fiber by itself to impart moisture absorption to the polyester fiber.

[0008] On the other hand, Patent Document 4 discloses polybutylene terephthalate with a low amount of foreign matter, which is produced by carrying out an esterification reaction while supplying a titanium catalyst and raw materials in a specific mode. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-293024 [Patent Document 2] Japanese Patent Publication No. 2020-117828 [Patent Document 3] Special Publication No. 2019-502036 [Patent Document 4] Japanese Patent Application Laid-Open No. 2004-277719 Summary of the Invention [Problem to be solved by the invention]

[0010] However, although Patent Document 1 discloses, for example, in its examples, copolymerized polyethylene terephthalate in which 10 wt % of polyethylene glycol having a molecular weight of 4000 is copolymerized, there is an increasing demand for even higher levels of moisture absorption.

[0011] On the other hand, the methods described in Patent Documents 2 and 3 can obtain polyethylene glycol copolymer polyesters having excellent moisture absorption properties, but because the polyethylene glycol copolymer polyesters are produced according to known polyester production methods, there are problems such as an increase in the amount of foreign matter in the obtained copolymer polyester, which affects yarn properties such as the occurrence of yarn unevenness, and decreases operability such as yarn breakage during spinning and an increase in the frequency of replacing a spinning pack.

[0012] Therefore, it has been considered to apply a technology to suppress the formation of foreign matter, and Patent Document 4 discloses a method for producing polybutylene terephthalate with a small amount of foreign matter by a continuous polymerization method. However, because it is a continuous polymerization method, it is difficult to apply it to polybutylene terephthalate copolymerized with polyethylene glycol, and there is a problem that the obtained polyester has poor moisture absorption properties.

[0013] Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing a moisture-absorbing polyester composition which can improve the yarn properties and workability during spinning by suppressing the amount of foreign matter in a copolymer polyester, and which can also suppress yellowing and oxidation heat generation after water washing treatment (JIS L0217). [Means for solving the problem]

[0014] In order to solve the above problems, the present invention mainly employs the following means.

[0015] A method for producing a copolymer polyester, comprising carrying out an esterification reaction or an ester exchange reaction using an aromatic dicarboxylic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof, and then reacting an esterification reaction product obtained by the esterification reaction or the ester exchange reaction with 10 to 50% by weight of polyethylene glycol having a number average molecular weight of 5,000 to 20,000, wherein the amount of phosphorus compounds in the polyethylene glycol is 10 to 50% by weight in terms of the amount of phosphorus atoms. The amount of alkali metal compounds is 30 ppm or less, and the amount of alkali metal compounds is 100 ppm or less in terms of the amount of alkali metal atoms. 1. A method for producing a copolymer polyester composition, comprising: [Effects of the Invention]

[0016] The resulting moisture-absorbing polyester fiber has high moisture absorption properties while containing a small amount of foreign matter in the polyester and polyester composition, and therefore can prevent deterioration in operability such as an increase in the frequency of replacing a spinning pack during spinning and an increase in the number of yarn breakages, and can also be inhibited from yellowing and generating heat due to oxidation after washing with water. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below.

[0018] In the present invention, moisture absorption can be expressed as the difference between the moisture absorption rate at a temperature of 30°C and a humidity of 90% RH, which is the assumed temperature and humidity inside the clothing after light exercise, and the moisture absorption rate at an outdoor temperature and humidity of 20°C and a humidity of 65% RH: ΔMR. The larger the ΔMR value, the higher the moisture absorption, and the more comfortable it will be when made into fibers or fabrics. 。

[0019] From the viewpoint of wearing comfort, ΔMR of the polyester composition containing the copolymer polyester obtained by the method for producing a copolymer polyester of the present invention is preferably 2.0 to 25.0%, more preferably 4.0 to 25.0%, even more preferably 8.0 to 25.0%, particularly preferably 15.0 to 25.0%, and most preferably 20.0 to 25.0%. If ΔMR is less than 2.0%, moisture absorption is low and the feeling of stuffiness inside the clothing increases. If ΔMR is more than 25.0%, melt moldability is deteriorated, and the mechanical strength of the molded product may decrease or fluff may occur.

[0020] The method for producing a copolymer polyester of the present invention comprises carrying out an esterification reaction or a transesterification reaction using an aromatic dicarboxylic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof, and reacting the esterification reaction product obtained by the esterification reaction or the transesterification reaction with 10 to 50% by weight of polyethylene glycol having a number average molecular weight of 5,000 to 20,000, wherein the amount of phosphorus compounds in the polyethylene glycol is 10 to 50% by weight in terms of the amount of phosphorus atoms. The amount of alkali metal compounds is 30 ppm or less, and the amount of alkali metal compounds is 100 ppm or less in terms of the amount of alkali metal atoms.This is a method for producing a copolymer polyester.

[0021] In the method for producing the copolymerized polyester of the present invention, the polyester is a polyester comprising a dicarboxylic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof.

[0022] Specific examples of such polyesters include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polycyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate, polyethylene-1,2-bis(2-chlorophenoxy)ethane-4,4'-dicarboxylate, etc. In the production method of the present invention, polybutylene terephthalate is preferred from the viewpoints of excellent crystallinity and excellent cuttability when discharged after polymerization is completed.

[0023] In the method for producing the polyester composition of the present invention, a dicarboxylic acid such as isophthalic acid, naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, cyclohexanedicarboxylic acid, or 5-sulfoisophthalic acid or an ester-forming derivative thereof may be copolymerized as a dicarboxylic acid component in the polyester. The amount of the copolymerized dicarboxylic acid component in the total dicarboxylic acid components is preferably 20 mol % or less, more preferably 10 mol % or less.

[0024] In the method for producing the copolymerized polyester of the present invention, these polyesters may be copolymerized with diol compounds such as ethylene glycol, propylene glycol, butanediol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, cyclohexanedimethanol, neopentyl glycol, and polypropylene glycol, as well as ester-forming derivatives thereof, as diol components. Preferably, butanediol accounts for 80 mol % or more of the total diol components. Diol components other than butanediol can also be copolymerized within a range that does not impair the effects of the present invention.

[0025] Examples of aromatic dicarboxylic acids include isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, bis(p-carboxyphenyl)methane, anthracene dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, and 5-sodium sulfoisophthalic acid.

[0026] In order to efficiently produce a polyester composition having excellent heat resistance, mechanical properties, and dyeability, terephthalic acid preferably accounts for 50 mol% or more of all dicarboxylic acid components, more preferably 90 mol% or more, and most preferably 100 mol%. In another preferred embodiment, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 5-sodium sulfoisophthalic acid are used in combination as aromatic dicarboxylic acid components other than terephthalic acid.

[0027] Examples of diols include aromatic diols, aliphatic diols, alicyclic diols, heterocyclic diols, etc. Two or more of these may be used.

[0028] Examples of the aromatic diol include bisphenol A derivatives to which ethylene oxide has been added, such as polyoxyethylene-(2.0)-2,2-bis(4-hydroxyphenyl)propane, polyoxyethylene-(2.3)-2,2-bis(4-hydroxyphenyl)propane, polyoxyethylene-(2.8)-2,2-bis(4-hydroxyphenyl)propane, and polyoxyethylene-(3.0)-2,2-bis(4-hydroxyphenyl)propane; and bisphenol A derivatives to which propylene oxide has been added, such as polyoxypropylene-(2.0)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene-(2.3)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene-(2.8)-2,2-bis(4-hydroxyphenyl)propane, and polyoxypropylene-(3.0)-2,2-bis(4-hydroxyphenyl)propane.

[0029] Examples of the other aliphatic diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, diethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0030] Examples of the alicyclic diol include cyclopentanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol, and two or more of these may be used.

[0031] Examples of the heterocyclic diol include isosorbide, isomannide, and isoidet.

[0032] From the viewpoint of efficiently producing polybutylene terephthalate having excellent crystallization properties, moldability, heat resistance, and mechanical properties, 1,4-butanediol preferably accounts for 50 mol% or more of all diol components, more preferably 90 mol% or more, and most preferably 100 mol%. In a preferred embodiment, ethylene glycol, 1,3-propanediol, and 1,4-cyclohexanedimethanol are used in combination as diol components other than 1,4-butanediol.

[0033] The method for producing a copolymer polyester of the present invention is a method for producing a copolymer polyester in which polyethylene glycol is copolymerized with polyester. Compared to a method in which polyethylene glycol is kneaded and mixed with polyester, the copolymer polyester in which polyethylene glycol is copolymerized does not leach out of polyethylene glycol during the washing step in the advanced processing step, and can maintain high moisture absorption, and is therefore suitable for use in processed products such as fibers.

[0034] The method for producing a copolymerized polyester of the present invention is a method for obtaining a copolymerized polyester in which polyethylene glycol copolymerized with the polyester has a number average molecular weight of 5000 to 20000 and is copolymerized in an amount of 10 to 50% by weight based on the weight of the copolymerized polyester. Specific methods for measuring the number average molecular weight and copolymerization amount of polyethylene glycol in the copolymerized polyester will be described later, but the copolymerized polyester can be hydrolyzed with an aqueous alkaline solution and then measured by gel permeation chromatography (GPC).

[0035] In the method for producing the copolymerized polyester of the present invention, polyethylene glycol having a specific number-average molecular weight is copolymerized with the polyester, thereby significantly enhancing moisture absorption properties and improving processability. Specifically, moisture absorption performance is significantly enhanced when the number-average molecular weight of the polyethylene glycol copolymerized with the polyester is 5000 or more. While the reason for this is not clear, it is believed that when the number-average molecular weight is 5000 or more, the polyethylene glycol and polyester in the polyester composition of the present invention form a unique structure, resulting in significantly enhanced moisture absorption. The number-average molecular weight of the polyethylene glycol is more preferably 5500 or more, and even more preferably 6000 or more.

[0036] In the method for producing the copolymerized polyester of the present invention, if the number-average molecular weight of the polyethylene glycol copolymerized with the polyester exceeds 20,000, the reactivity with polyethylene terephthalate decreases, resulting in poor dischargeability during polymerization and problems such as the polyethylene glycol dissolving in hot water. From the viewpoint of moldability, particularly spinnability, the number-average molecular weight of the polyethylene glycol copolymerized with the polyester is more preferably 10,000 or less.

[0037] In the method for producing the copolymerized polyester of the present invention, the number-average molecular weight of the polyethylene glycol copolymerized with the polyester can be calculated by the following procedure. Approximately 0.05 g of the copolymerized polyester is placed in a sealable vial, 1 mL of 28 wt % aqueous ammonia is added, and the sample is heated at 120°C for 5 hours to dissolve. After cooling, 1 mL of purified water and 1.5 mL of 6 M hydrochloric acid are added, and the volume is adjusted to 5 mL with purified water. After centrifugation, the mixture is filtered through a 0.45 μm filter, and the number-average molecular weight of the mono-end-capped polyalkylene oxide compound contained in the filtrate is measured by gel permeation chromatography (GPC). Note that the number-average molecular weight of the polyethylene glycol, a copolymerization component in the present invention, refers to the value determined by GPC in terms of standard polyethylene glycol.

[0038] In the method for producing a copolymerized polyester of the present invention, the polyester is a polyester copolymerized with polyethylene glycol, and the copolymerization amount of polyethylene glycol copolymerized with the polyester is 10 to 50 wt % relative to the weight of the copolymerized polyester. If the copolymerization amount of polyethylene glycol is less than 10 wt %, the resulting copolymerized polyester has low moisture absorption, equivalent to that of a polyester not copolymerized with polyethylene glycol, resulting in a stuffy feeling inside the garment. From the viewpoint of achieving high moisture absorption, the copolymerization amount of polyethylene glycol is preferably 10 wt % or more, more preferably 20 wt % or more, even more preferably 30 wt % or more, and particularly preferably 40 wt % or more. Furthermore, from the viewpoints of heat resistance and melt moldability, such as spinnability, the amount of polyethylene glycol added must be 50 wt % or less. If the amount exceeds 50 wt %, the resulting copolymerized polyester may not be able to withstand use in high temperature ranges, or the mechanical strength of molded articles may be reduced.

[0039] In the method for producing the copolymerized polyester of the present invention, the copolymerization amount of polyethylene glycol copolymerized in the polyester can be calculated by the following procedure. Approximately 0.05 g of the copolymerized polyester is placed in a measurement tube of a nuclear magnetic resonance (NMR) spectrometer, and 1 g of deuterated 1,1,1,3,3,3-hexafluoro-2-isopropanol (HFIP) is added and dissolved. The solution is subjected to 1H-NMR measurement, whereby the copolymerization amount of polyethylene glycol copolymerized in the polyester composition can be calculated.

[0040] The copolymer polyester in the method for producing a copolymer polyester of the present invention is a polymer obtained by a condensation reaction of dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative as main components, and therefore can be produced by subjecting a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative to an esterification reaction or an ester exchange reaction, followed by a polycondensation reaction.

[0041] The timing of addition of polyethylene glycol as a copolymerization component may be any stage, such as before the esterification reaction or transesterification reaction, from the time when the esterification reaction or transesterification reaction is substantially completed until the start of the polycondensation reaction, or after the polycondensation reaction is substantially completed. However, from the viewpoint of obtaining a copolymerized polyester with excellent moisture absorption, it is preferable to add polyethylene glycol from the time when the esterification reaction or transesterification reaction is substantially completed until the start of the polycondensation reaction.

[0042] In the method for producing the copolymerized polyester of the present invention, it is preferable to carry out an esterification reaction using an aromatic dicarboxylic acid and a diol containing 50 mol % or more of 1,4-butanediol.

[0043] The method for producing a copolymerized polyester of the present invention involves an esterification reaction or transesterification reaction between an aromatic dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative, followed by transferring the resulting esterification reaction product (oligomer) to a polymerization vessel and carrying out a polycondensation reaction with polyethylene glycol to obtain a copolymerized polyester. In this process, 1,4-butanediol is preferably present in an amount of 50 mol% or more of all diol components, in order to efficiently produce polybutylene terephthalate with excellent crystallization properties, moldability, heat resistance, and mechanical properties. Furthermore, the polyethylene glycol contains less phosphorus compounds in terms of phosphorus atom weight than 40 ppm, in order to reduce the amount of foreign matter in the resulting copolymerized polyester and prevent deterioration in operability, such as increased frequency of spinning pack replacement during spinning and increased number of yarn breakages. From the viewpoints of further suppressing foreign matter formation and reducing pack replacement frequency during spinning, a phosphorus compound content of 30 ppm or less is more preferable, 20 ppm or less is even more preferable, and 10 ppm or less is particularly preferable, and 0 ppm, i.e., no phosphorus compounds, is most preferable. If the amount of phosphorus compounds contained in polyethylene glycol is 40 ppm or more in terms of phosphorus atom weight, the frequency of replacing the spin pack during spinning increases and yarn breakage occurs frequently, resulting in inefficiency.

[0044] In the method for producing the copolymerized polyester of the present invention, the amount of phosphorus atoms in polyethylene glycol can be determined by the following procedure. First, wet decomposition is performed to prepare a solution of the sample. Approximately 0.5 g of polyethylene glycol is placed in a 100 mL Erlenmeyer flask, 10 mL of sulfuric acid is added, and the solution is heated to 250 °C on a sand bath. 1 mL of perchloric acid is added, followed by heating to 300 °C and another 1 mL of perchloric acid. The solution is heated at 350 °C for 10 minutes until the solution becomes colorless and transparent, and then the sulfuric acid is refluxed for 3 minutes. After cooling, the treated solution is transferred to a 250 mL volumetric flask and titrated with 40% NaOH aqueous solution, followed by diluting the volume to 250 mL with pure water. 2 mL of molybdenum blue color-developing solution is added to 10 mL of the resulting neutralized solution, followed by diluting the volume to 20 mL with pure water. After 15 minutes, the absorbance at 720 nm is measured using an absorption spectrophotometer. A calibration curve using phosphoric acid is prepared in advance to calculate the amount of phosphorus in the sample, and then the amount of phosphorus atoms is calculated.

[0045] The method for producing a copolymerized polyester of the present invention is characterized in that the phosphorus atoms in the polyethylene glycol are derived from phosphate. Conventionally, polyethylene glycol has been produced using an alkali metal as a polymerization catalyst and adding phosphoric acid as a catalyst deactivator in the late stage of polymerization, resulting in the presence of phosphate in the polyethylene glycol. However, the inventors have discovered that the phosphate in the polyethylene glycol tends to aggregate upon heating and becomes a foreign substance in the copolymerized polyester made from the polyethylene glycol. Therefore, in order to suppress the formation of foreign substances in the copolymerized polyester, the amount of phosphorus atoms derived from phosphate in the polyethylene glycol is preferably less than 40 ppm, more preferably 30 ppm or less, even more preferably 20 ppm or less, particularly preferably 10 ppm or less, and most preferably 0 ppm, i.e., no phosphate is contained.

[0046] In the method for producing a copolymerized polyester of the present invention, the polyethylene glycol contains an alkali metal compound used during polyethylene glycol polymerization, and the amount of the alkali metal compound is preferably 100 ppm or less in terms of alkali metal atomic weight. The inventors have found that when an antioxidant is kneaded into a copolymerized polyester made from polyethylene glycol, foreign matter originating from the alkali metal compound contained in the polyethylene glycol is formed, resulting in reduced operability, such as an increased frequency of spin pack replacement during spinning and an increased number of yarn breakages. Therefore, from the viewpoint of suppressing the formation of foreign matter in the copolymerized polyester and preventing reduced operability, such as an increased frequency of spin pack replacement during spinning and an increased number of yarn breakages, the amount of the alkali metal compound in the polyethylene glycol is preferably 100 ppm or less, more preferably 70 ppm or less, and particularly preferably 40 ppm or less in terms of alkali metal atomic weight.

[0047] In the method for producing a copolymerized polyester of the present invention, the alkali metal atom refers to an atom belonging to Group 1 of the periodic table, excluding hydrogen, and refers to sodium, potassium, lithium, rubidium, cesium, and francium. Potassium and sodium are preferred, particularly sodium, because they have low basicity as alkali metal compounds and are less active in forming foreign matters, from the viewpoint of suppressing the formation of foreign matters. Regarding the amount of potassium atoms contained in the polyethylene glycol, from the viewpoint of suppressing the formation of foreign matters when an antioxidant is kneaded with a copolymerized polyester made from the polyethylene glycol, the amount of potassium compounds in the polyethylene glycol, expressed as the amount of potassium atoms, is preferably 100 ppm or less, more preferably 60 ppm or less, and particularly preferably 10 ppm or less. Furthermore, regarding the amount of sodium atoms contained in the polyethylene glycol, from the viewpoint of suppressing the formation of foreign matters, the amount of sodium compounds in the polyethylene glycol, expressed as the amount of sodium atoms, is preferably 100 ppm or less, more preferably 70 ppm or less, and particularly preferably 40 ppm or less. Examples of alkali metal compounds include alkali metal hydroxides, acetates, carbonates, and phosphates of alkali metals. Acetate salts are preferred from the viewpoints of low basicity, ability to inhibit the formation of foreign matter, and ability to inhibit hydrolysis of the copolyester made from polyethylene glycol.

[0048] In the method for producing the copolymerized polyester of the present invention, the esterification reaction is preferably carried out under conditions in which the molar ratio of a diol component containing 50 mol % or more of 1,4-butanediol or its ester-forming derivative to terephthalic acid or an ester-forming derivative of terephthalic acid is more than 1.2 and not more than 2.5. The upper limit of the molar ratio is more preferably not more than 1.8, and particularly preferably not more than 1.6, from the viewpoints of suppressing the amount of by-product THF generated by cyclization of 1,4-butanediol, enabling efficient production, and shortening the reaction time of the polycondensation reaction.

[0049] Furthermore, in order to efficiently proceed with the esterification reaction, additional addition of the diol component may be performed. The additional addition of the diol component may be performed after the completion of the esterification reaction or the transesterification reaction and before the start of the polycondensation reaction. However, in order to shorten the polymerization time, it is more preferable to perform the additional addition at any stage after the start of the esterification reaction and before the start of the polycondensation reaction. The additional addition of the diol component may be performed multiple times, but from the viewpoint of operability, it is preferable to perform the additional addition once at any stage after the start of the esterification reaction and before the start of the polycondensation reaction.

[0050] Furthermore, by carrying out an initial polymerization reaction under reduced pressure in the later stage of the esterification reaction after a predetermined esterification reaction time has elapsed, the Mp of the oligomer obtained by the esterification reaction using an aromatic dicarboxylic acid and a diol containing 50 mol% or more of 1,4-butanediol is 1250 or more. The initial polymerization reaction is preferably carried out under reduced pressure at a reaction pressure of 70 kPa or less, more preferably 35 kPa or less, and particularly preferably 10 kPa or less. The reaction time is preferably 30 minutes or more from the viewpoint of increasing the molecular weight of the esterification reaction product (oligomer), and preferably 60 minutes or less from the viewpoint of productivity.

[0051] Furthermore, the esterification reaction is preferably carried out under reduced pressure of 30 kPa or more and 95 kPa or less. When the reaction pressure of the esterification reaction is 30 kPa or more, the strength of the yarn using the obtained polyester can be further improved. From the viewpoint of further improving the strength of the yarn using the obtained polyester, the reaction pressure of the esterification reaction is preferably 60 kPa or more, more preferably 80 kPa or more, and even more preferably 85 kPa or more. On the other hand, when the pressure of the esterification reaction or transesterification reaction is 95 kPa or less, the reaction time of the esterification reaction can be further shortened.

[0052] Furthermore, a reaction catalyst can be used in the esterification reaction or transesterification reaction to shorten the reaction time. Examples of the reaction catalyst include a titanium compound and / or a tin compound. In the present invention, it is preferable to use a titanium compound to further shorten the reaction time.

[0053] In the method for producing the copolymerized polyester of the present invention, the titanium compound used as a reaction catalyst during the esterification reaction is preferably a titanate ester or a condensate thereof represented by the general formula (RO)Ti(OR)(4-n) (wherein R and R each independently represent an aliphatic, alicyclic, or aromatic hydrocarbon group having 1 to 10 carbon atoms, and n represents a number from 0 to 4 (including decimals)).

[0054] Specific examples of titanium compounds represented by the above general formula include methyl ester, tetra-n-propyl ester, tetra-n-butyl ester, tetraisopropyl ester, tetraisobutyl ester, tetra-t-butyl ester, cyclohexyl ester, phenyl ester, benzyl ester, and tolyl ester of titanic acid, or mixed esters thereof. Two or more of these may be used. Among these, tetra-n-propyl ester, tetra-n-butyl ester, and tetraisopropyl ester of titanic acid are preferred from the viewpoint of more efficient polyester production, and tetra-n-butyl ester of titanic acid is particularly preferred.

[0055] The amount of these titanium compounds added is preferably in the range of 0.02 to 0.2% by weight based on the polyester produced, in order to enable more efficient production of polyester.

[0056] Specific examples of tin compounds include dibutyltin oxide, methylphenyltin oxide, tetraethyltin oxide, hexaethylditin oxide, cyclohexahexylditin oxide, didodecyltin oxide, triethyltin hydroxide, triphenyltin hydroxide, triisobutyltin acetate, dibutyltin diacetate, diphenyltin dilaurate, monobutyltin trichloride, dibutyltin dichloride, tributyltin chloride, dibutyltin sulfide, and butylhydroxytin oxide. Two or more of these compounds may be used. Among these compounds, monoalkyltin compounds are preferably used because they can produce polybutylene terephthalate more efficiently.

[0057] Other tin compounds that can be used include stannoic acids. For example, alkylstannoic acids such as methylstannoic acid, ethylstannoic acid, and butylstannoic acid are preferably used. Two or more of these may be used.

[0058] The amount of these tin compounds added is preferably in the range of 0.03 to 0.2% by weight based on the polyester produced, in order to enable more efficient production of polyester.

[0059] The timing of adding these reaction catalysts may be any time before the end of the esterification reaction, but it is more preferable to add them before the start of the esterification reaction in order to further shorten the reaction time.

[0060] In the method for producing the copolymerized polyester composition of the present invention, the reaction temperature of the esterification reaction or transesterification reaction is preferably 140° C. or higher, more preferably 150° C. or higher, and even more preferably 160° C. or higher, in order to further shorten the reaction time. The reaction temperature of the esterification reaction is preferably 290° C. or lower, more preferably 280° C. or lower, and even more preferably 240° C. or lower.

[0061] Next, the polycondensation reaction in the present invention will be described.

[0062] In the method for producing the copolymerized polyester of the present invention, a reaction catalyst may be added separately as necessary to effectively promote the polycondensation reaction. For example, an antimony compound such as antimony trioxide or antimony acetate, a zirconia compound such as zirconium tetra-n-butoxide, the above-mentioned titanium compound, or the above-mentioned tin compound is preferably added in an amount of 0.01 to 0.15% by weight based on the copolymerized polyester produced, and the use of a titanium compound is particularly preferred.

[0063] The timing of adding these reaction catalysts may be any time before the end of the polycondensation reaction, but it is preferable to add them after the end of the esterification reaction and before the start of the polycondensation reaction in order to shorten the reaction time.

[0064] In the method for producing a copolymerized polyester of the present invention, the copolymerized polyester is characterized by being a polyester copolymerized with polyethylene glycol. Compared to kneading with polyethylene glycol, polyethylene glycol does not elute during the washing step in the advanced processing step, and high hygroscopicity can be maintained, making it suitable for use in processed products such as fibers.

[0065] In the method for producing the copolymerized polyester of the present invention, it is preferable to charge polyethylene glycol into a polymerization tank in advance and transfer the esterification reaction product (oligomer) when the temperature of the polymerization tank is 210° C. or lower. A temperature of 210° C. or lower is preferred, and 200° C. or lower is more preferred, from the viewpoints of being able to suppress decomposition of polyethylene glycol and not reducing the polycondensation reactivity.

[0066] The temperature of the polymerization vessel when the esterification reaction product is transferred is the same as the temperature of the polyethylene glycol previously charged in the polymerization vessel.

[0067] In the method for producing the copolymerized polyester of the present invention, it is preferable to charge polyethylene glycol in advance into a polymerization tank and melt the polyethylene glycol in air or nitrogen with a moisture content of 0.01% or less. From the viewpoints of being able to suppress decomposition of polyethylene glycol and not reducing polycondensation reactivity, it is preferable to melt the polyethylene glycol in air or nitrogen with a moisture content of 0.01% or less.

[0068] In the method for producing the copolymerized polyester of the present invention, it is preferable to add a phenolic antioxidant during polymerization to reduce the frequency of replacing the spin pack during spinning. The type of phenolic antioxidant is not particularly limited, but from a cost perspective, it is preferable to add pentaerythritol-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenol)propionate) (manufactured by BASF, Irganox® 1010 (IR1010)). The amount of IR1010 added is preferably 0.15 to 0.50 wt% (5.0 to 17.0 mmol / kg), more preferably 0.25 to 0.50 wt% (8.0 to 17.0 mmol / kg), and most preferably 0.35 to 0.50 wt% (11.5 to 17.0 mmol / kg). Addition of less than 0.15 wt% (5.0 mmol / kg) tends to fail to reduce the frequency of replacing the spin pack during spinning. If the amount added is more than 0.50% by weight (17.0 mmol / kg), the yarn obtained in the presence of nitrogen oxides tends to yellow.

[0069] In the method for producing the copolymerized polyester of the present invention, the polycondensation reaction is preferably carried out under reduced pressure conditions of a reaction pressure of 133 Pa or less, since this allows the polycondensation reaction time to be shortened.

[0070] In the polycondensation reaction, polycondensation conditions used in ordinary polyester production, such as a batch method or a continuous method, can be applied as they are. For example, the reaction temperature of the polycondensation reaction is preferably 230°C or higher, more preferably 240°C or higher. In addition, the reaction temperature of the polycondensation reaction is preferably 260°C or lower, more preferably 255°C or lower.

[0071] In the method for producing the copolymerized polyester of the present invention, solid-state polymerization may be further performed to obtain a polyester raw material with a high molecular weight and intrinsic viscosity. Solid-state polymerization is generally performed under reduced pressure or a nitrogen atmosphere, but this is not particularly limited in the present invention. The solid-state polymerization temperature is preferably 180°C or higher, more preferably 185°C or higher, from the standpoints of reaction rate and productivity. On the other hand, from the standpoint of suppressing fusion between polyester chips, it is preferably 240°C or lower, more preferably 230°C or lower. The solid-state polymerization temperature can be set arbitrarily within the above range. Generally, polymerization at a low temperature slows the reaction rate and lengthens the time required to increase the intrinsic viscosity to the desired level, but increases the maximum intrinsic viscosity. Conversely, increasing the polymerization temperature increases the reaction rate, but also promotes degradation, resulting in a lower maximum intrinsic viscosity.

[0072] In the method for producing the copolymer polyester of the present invention, by incorporating a phosphorus compound such as phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, phosphoric triamide, monoammonium phosphate, trimethyl phosphate, dimethyl phosphate, diphenyl phosphate, triphenyl phosphate, diphenyl phosphite, triphenyl phosphite, and dimethylphenyl phosphonate, the color tone of the obtained copolymer polyester can be significantly improved. These phosphorus compounds are preferably added during the polycondensation reaction in the method for producing the copolymer polyester.

[0073] In the method for producing a copolymerized polyester of the present invention, particles may be added to reduce friction with contacting objects such as guides and rollers during the molding process, thereby improving processability, or to adjust the color tone of the product. Any of the conventionally known particles can be used. Specifically, inorganic particles such as silicon dioxide, titanium dioxide, calcium carbonate, barium sulfate, aluminum oxide, and zirconium oxide, as well as organic polymer particles such as cross-linked polystyrene, can be used. Among these particles, titanium dioxide particles are preferred because they have good dispersibility in polymers and are relatively low-cost. Titanium dioxide particles can be produced by various wet and dry methods, and, if necessary, are subjected to pretreatment such as pulverization and classification before being added to the copolymerized polyester reaction system. The particles can be added to the copolymerized polyester reaction system at any stage, but adding them after the esterification reaction or transesterification reaction has essentially been completed is preferred because they provide good dispersibility in the polymer. The amount of particles added to the polymer and the particle size vary depending on the application and are not particularly limited. However, a content of 0.01 to 10% by weight of the copolymerized polyester, an average particle size of 0.05 to 5 μm, and a content of 1,000 particles / 0.4 mg or less of coarse particles with a particle size of 4 μm or more are preferred, as this results in particularly good processability and color tone.

[0074] In the method for producing the copolymerized polyester of the present invention, a color tone adjuster such as a blue adjuster, a red adjuster, or a purple adjuster may be added during polymerization. The color tone adjuster is a dye used in resins, etc. Specific examples of the color tone adjuster, based on the generic names in the Color Index, include blue color tone adjusters such as SOLVENT BLUE 104, SOLVENT BLUE 122, and SOLVENT BLUE 45; red color tone adjusters such as SOLVENT RED 111, SOLVENT RED 179, SOLVENT RED 195, SOLVENT RED 135, PIGMENT RED 263, and VAT RED 41; and purple color tone adjusters such as DESPERSE VIOLET 26, SOLVENT VIOLET 13, SOLVENT VIOLET 37, and SOLVENT VIOLET 49. Among these, SOLVENT BLUE 104, SOLVENT BLUE 45, SOLVENT RED 179, SOLVENT RED 195, SOLVENT RED 135, and SOLVENT VIOLET 49 are preferred because they do not contain halogens, which are a common cause of equipment corrosion, and have relatively good heat resistance at high temperatures and excellent color development. Furthermore, one or more of these color-adjusting agents can be used depending on the purpose. Using one or more blue-based and red-based adjusters is particularly preferred because it allows for fine control of the color tone. Furthermore, in this case, a ratio of blue-based adjusters to the total amount of added color-adjusting agents of 50% by weight or more is preferred, as this results in a particularly good color tone of the resulting copolymerized polyester. Ultimately, the total content of color-adjusting agents relative to the copolymerized polyester is preferably 30 ppm or less. Exceeding 30 ppm can result in reduced transparency of the copolymerized polyester and a dull color development. The content can be calculated from the structural identification of the color tone adjusting agent by nuclear magnetic resonance (NMR) and the proportion of the constituent parts of the color tone adjusting agent.

[0075] The method for producing the copolymerized polyester of the present invention preferably includes a step of adding a phenolic antioxidant represented by the following chemical formula (1) (hereinafter, sometimes abbreviated as phenolic antioxidant) to the copolymerized polyester after obtaining the copolymerized polyester (note that a product to which additives and the like have been added after polymerization is also referred to as a copolymerized polyester composition).

[0076] [ka]

[0077] In the above formula, R1, R2, and R3 represent a hydrocarbon group, a hydroxyl group, or a hydrogen atom.

[0078] Specific examples of the phenolic antioxidant to be added in the production method of the copolymerized polyester of the present invention include 2,6-di-t-butyl-p-cresol, butylhydroxyanisole, 2,6-di-t-butyl-4-ethylphenol, stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol), 3,9-bis{1,1-dimethyl-2-{β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}ethyl}2,4,8,10-tetraoxaspiro{5,5}undecane, 1,1,3-tris(2-methyl-4 Examples of suitable phenolic compounds include, but are not limited to, 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, bis{3,3'-bis-(4'-hydroxy-3'-t-butylphenyl)butyric acid}glycol ester, tocopherol, pentaerythritol-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenol)propionate), bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylenebis(oxyethylene)], and 1,3,5-tris[[4-(1,1-dimethylethyl)-3-hydroxy-2,6-dimethylphenyl]methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione. These phenolic compounds may be used alone or in combination of two or more.From the viewpoint of highly inhibiting oxidative decomposition, reducing the amount of yellow quinone compounds generated during washing with water, and highly inhibiting yellowing, bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylenebis(oxyethylene)] (IRGANOX® 245, manufactured by BASF), 3,9-bis{1,1-dimethyl-2-{β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}ethyl}2,4,8,10-tetraoxaspiro{5,5}undecane (ADK STAB® AO-80, manufactured by ADEKA), and 1,3,5-tris[[4-(1,1-dimethylethyl)-3-hydroxy-2,6-dimethylphenyl]methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (THANOX1790, manufactured by RIANINLON CORPORATION) can be preferably used.

[0079] The type of phenolic antioxidant contained in the copolymer polyester composition obtained by the production method of the present invention can be identified by the following procedure. Approximately 1 g of the copolymer polyester composition is dissolved in 20 mL of HFIP, and 40 mL of toluene is added. 60 mL of methanol is then added to precipitate the mixture. The prepared solution is filtered through a 0.45 μm filter, and the solvent is removed from the filtrate using an evaporator to obtain the antioxidant. The obtained antioxidant is placed in an NMR measurement tube, and 1 g of deuterated HFIP is added and dissolved. The structure of the phenolic antioxidant contained in the polyester composition can be determined by 1H-NMR measurement of this solution, allowing the type to be identified.

[0080] In the method for producing the copolymerized polyester of the present invention, the phenolic antioxidant is preferably added in an amount of 10.0 to 200.0 mmol / kg (0.5 to 8.0 wt%). If the amount of the phenolic antioxidant added is less than 10 mmol / kg (0.5 wt%), the oxidation heat generation resistance of the composite fiber made using the copolymerized polyester composition obtained by the present invention after water washing treatment (JIS L0217-1995) will decrease, and oxidation heat generation will occur in less than 90 hours. If the amount of the phenolic antioxidant added is more than 200.0 mmol / kg (8.0 wt%), the orientation of the fiber made using the copolymerized polyester composition will be suppressed, resulting in reduced fiber strength, frequent yarn breakage during knitting and weaving processes, and reduced quality due to fuzz generation during use. From the viewpoint of oxidation heat resistance and fiber strength, the amount of the phenolic antioxidant added is more preferably 70.0 to 200.0 mmol / kg (3.0 to 8.0 wt %), and particularly preferably 120.0 to 200.0 mmol / kg (5.0 to 8.0 wt %).

[0081] The oxidation heat generation resistance test for composite fibers made using the copolymer polyester composition is carried out according to the following procedure. Samples that have been subjected to a water washing treatment (JIS L0217-1995) are stacked in a cylindrical container to a depth of 25 mm, and a thermocouple is installed in the center. Further stacked samples are packed into the cylindrical container without gaps. The cylindrical container filled with samples is placed in a thermostatic dryer set at 150°C, and the time until oxidation heat generation begins is measured. A time of 100 hours or more is considered pass, 90 hours or more is good, and less than 90 hours is considered fail.

[0082] The content of the phenolic antioxidant contained in the copolymerized polyester composition obtained by the production method of the present invention can be calculated by the following procedure. Approximately 1 g of copolymerized polyester is dissolved in 20 mL of HFIP, and then 40 mL of toluene is added. 60 mL of methanol is then added to cause precipitation. The prepared solution is filtered through a 0.45 μm filter, and the resulting filtrate is used as a measurement sample and subjected to HPLC analysis, allowing the content of the phenolic antioxidant contained in the polyester composition to be calculated.

[0083] The method for producing a copolymerized polyester of the present invention preferably further comprises the step of adding a phosphorus-based antioxidant. The addition of the phosphorus-based antioxidant suppresses the deactivation of phenol by hypochlorite bleaches used in water washing treatments (JIS L0217-1995), and the polyester exhibits high oxidation heat resistance even after water washing treatments. The phosphorus-based antioxidant to be added in the method for producing a polyester composition of the present invention is not particularly limited as long as it is a compound containing a phosphorus element. Specific examples include triphenyl phosphite, tris(2,4-t-butylphenyl) phosphite, bis[2,4 bis(1,1-dimethylethyl)-6-methylphenyl]ethyl ester phosphorous acid, bis(2,4-t-butylphenyl)pentaerythritol diphosphite, tetrakis(2,4-di-t-butylphenyl)[1,1 biphenyl]-4,4'-diyl bisphosphonite, tetra(C12 to C15 alkyl)-4,4'-isopropylidene diphenyl diphosphite, 3,9-bis(2,6-t-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5 undecane], 1,1'-biphenyl-4,4'-diylbis[bis(2,4-di-t-butylphenyl)]phosphonite, and tri(C12 to C18 alkyl) phosphite. These phosphorus-based antioxidants may be used alone or in combination of two or more.Among these, tris(2,4-t-butylphenyl)phosphite (manufactured by BASF, IRGAFOS® 168), 3,9-bis(2,6-t-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5 undecane] (manufactured by ADEKA, Adekastab® PEP-36), tetra(C12-C15 alkyl)-4,4'-isopropylidenediphenyl diphosphite (manufactured by Johoku Chemical, JA-805), 1,1'-biphenyl-4,4'-diylbis[bis(2,4-di-t-butylphenyl)phosphonite] (manufactured by Clariant Chemicals, HOSTANOX®) P-EPQ), trioleyl phosphite (JP-318-O, manufactured by Johoku Chemical Industry Co., Ltd.), and tristearyl phosphite (JP-318E, manufactured by Johoku Chemical Industry Co., Ltd.) are preferably used because they have good resistance to oxidative decomposition after washing with water, and P-EPQ, PEP-36, JP-318-O, and JP-318E are more preferred from the viewpoint of suppressing yellowing after washing with water. PEP-36 and JP-318E are particularly preferred from the viewpoint of suppressing bleed-out during chip drying before spinning and suppressing the formation of foreign matter derived from phosphorus-based antioxidants, as will be described later, and preventing decreases in operability such as increased frequency of spin pack replacement during spinning and increased number of yarn breakages.

[0084] The type of phosphorus-based antioxidant contained in the copolymer polyester composition obtained by the production method of the present invention can be identified by the following procedure. Approximately 1 g of the copolymer polyester composition is dissolved in 20 mL of HFIP, and 40 mL of toluene is added. 60 mL of methanol is then added to precipitate the mixture. The prepared solution is filtered through a 0.45 μm filter, and the solvent is removed from the filtrate using an evaporator to obtain the antioxidant. The obtained antioxidant is placed in an NMR measurement tube, and 1 g of deuterated HFIP is added and dissolved. 1H-NMR measurement of this solution reveals the structure of the phosphorus-based antioxidant contained in the copolymer polyester composition, allowing the type to be identified.

[0085] In the method for producing the copolymer polyester of the present invention, it is preferable to add a phosphorus-based antioxidant with a phosphorus content of 15.0 to 75.0 mmol / kg (0.10 to 0.25 wt % based on the weight of the copolymer polyester). If the phosphorus content of the phosphorus-based antioxidant is less than 15.0 mmol / kg (0.10 wt %), yellowing may occur after washing with water (JIS L0217-1995), oxidation heat resistance may decrease, and oxidation heat generation may occur in less than 90 hours. If the phosphorus content of the phosphorus-based antioxidant is more than 75.0 mmol / kg (0.25 wt %), the orientation of the fiber made using the copolymer polyester composition may be suppressed, resulting in reduced fiber strength, frequent yarn breakage during knitting and weaving processes, and reduced quality due to fuzz generation during use. From the viewpoints of inhibiting yellowing after washing with water, resistance to oxidation heat generation, and fiber strength, the phosphorus content of the phosphorus-based antioxidant is more preferably 35.0 to 65.0 mmol / kg (0.15 to 0.25% by weight), and particularly preferably 35.0 to 50.0 mmol / kg (0.15 to 0.20% by weight).

[0086] The phosphorus content of the phosphorus-based antioxidant contained in the copolymer polyester composition obtained by the production method of the present invention can be calculated by the following procedure. 10 mL of sulfuric acid is added to approximately 1 g of copolymer polyester, and the mixture is decomposed on a sand bath at 250°C. 1.0 mL of perchloric acid is added, and the mixture is further decomposed at 300°C. When the sample becomes colorless and transparent, it is decomposed at 350°C and refluxed with sulfuric acid. After cooling, the mixture is neutralized with a 20% aqueous sodium hydroxide solution. The absorbance at 720 nm of the obtained solution and the sample solution is measured using a spectrophotometer, and the phosphorus content can be calculated.

[0087] In the method for producing the copolymerized polyester of the present invention, the phosphorus-based antioxidant added is characterized in that it has a 5% weight loss temperature of 170°C or higher when evaluated for heat loss using a thermogravimetric differential thermal analyzer (TG-DTA) at a heating rate of 10°C / min under a nitrogen atmosphere. If the 5% weight loss temperature is lower than 170°C, the antioxidant may decompose and / or volatilize during kneading or spinning, resulting in a decrease in the oxidation heat resistance and yellowing suppression effect of the resulting fiber. From the viewpoint of achieving oxidation heat resistance and yellowing suppression effect, the 5% weight loss temperature is preferably 170°C or higher, more preferably 180°C or higher, even more preferably 200°C or higher, and particularly preferably 220°C or higher.

[0088] In the method for producing a copolymerized polyester of the present invention, the phosphorus-based antioxidant to be added preferably has a molecular structure containing two or more phosphorus atoms per molecule. If a phosphorus-based antioxidant with a molecular structure containing one phosphorus atom per molecule is used, it will volatilize during kneading or spinning, resulting in a decrease in the oxidation heat resistance and yellowing suppression effect of the resulting fiber. From the viewpoint of achieving oxidation heat resistance and yellowing suppression effect, the phosphorus-based antioxidant preferably has a molecular structure containing two or more phosphorus atoms per molecule.

[0089] In the method for producing a copolymerized polyester of the present invention, the phosphorus-based antioxidant to be added must have a melting point of 80°C or higher. If the melting point of the phosphorus-based antioxidant is lower than 80°C, it may decompose and / or volatilize during kneading or spinning, and the resulting fiber may tend to have reduced oxidation heat resistance and yellowing suppression effects. From the viewpoint of exhibiting oxidation heat resistance and yellowing suppression effects, the melting point is preferably 80°C or higher, more preferably 100°C or higher, even more preferably 150°C or higher, particularly preferably 180°C or higher, and most preferably 200°C or higher.

[0090] In the method for producing the copolymerized polyester of the present invention, the phosphorus-based antioxidant to be added preferably has a molecular structure represented by the following chemical formula (2), (3), or (4).

[0091] [ka]

[0092] In the above formula (2), R represents a hydrocarbon group.

[0093] [ka]

[0094] In the above formula (3), R represents a hydrocarbon group.

[0095] [ka]

[0096] In the above formula (4), R represents a hydrocarbon group.

[0097] An example of a phosphorus-based antioxidant having a molecular structure represented by chemical formula (2) is HOSTANOX P-EPQ manufactured by Clariant Chemicals.

[0098] An example of a phosphorus-based antioxidant having a molecular structure represented by chemical formula (3) is Adeka STAB (registered trademark) PEP-36 manufactured by ADEKA.

[0099] An example of a phosphorus-based antioxidant having a molecular structure represented by chemical formula (4) is JP-318E manufactured by Johoku Chemical Industry Co., Ltd.

[0100] Furthermore, it is more preferable that the phosphorus-based antioxidant has a molecular structure represented by chemical formula (3) and / or (4). The inventors have found that the phosphorus-based antioxidant undergoes a transesterification reaction with the copolymer polyester to form foreign matter, which reduces operability, such as increasing the frequency of spin pack replacements and the number of yarn breakages during spinning. For this reason, it is preferable that the added phosphorus-based antioxidant has low transesterification reactivity. As a result of extensive research, the inventors have found that a phosphorus-based antioxidant having a molecular structure represented by chemical formula (3) and / or (4) has low transesterification reactivity with the copolymer polyester and can suppress the formation of foreign matter, thereby suppressing the reduction in operability, such as increasing the frequency of spin pack replacements and the number of yarn breakages during spinning. For this reason, it is preferable that the phosphorus-based antioxidant has a molecular structure represented by chemical formula (3) and / or (4) because it has low transesterification reactivity with hydroxyl groups and can suppress the formation of foreign matter after kneading. Furthermore, if the number of carbon atoms contained in R in the molecular structure represented by (4) is less than 12, the compound may decompose and / or volatilize during kneading or spinning, and the resulting fiber may tend to have reduced oxidation heat resistance and yellowing suppression effects. Therefore, from the viewpoint of achieving oxidation heat resistance and yellowing suppression effects, the number of carbon atoms in R is preferably 12 or more, more preferably 15 or more, and particularly preferably 18 or more.

[0101] In the method for producing the copolymerized polyester of the present invention, the method for adding the phenolic antioxidant and the phosphorus-based antioxidant to the copolymerized polyester is not particularly limited as long as the requirements of the present invention are satisfied. However, a method in which the phenolic antioxidant and the phosphorus-based antioxidant are uniformly melt-kneaded into the copolymerized polyester using a single-screw or twin-screw extruder as a kneader is preferred, and a method in which the phenolic antioxidant and the phosphorus-based antioxidant are uniformly kneaded with the copolymerized polyester using a twin-screw extruder is particularly preferred because it gives fibers having excellent mechanical properties.

[0102] In an embodiment of the present invention, when melt-kneading, the components may be added by, for example, using an extruder having two input ports and feeding the copolymer polyester, which is the main component of the copolymer polyester composition, the phenolic antioxidant, the phosphorus-based antioxidant, and other components as required, through the main input port located at the base of the screw; or by feeding the copolymer polyester, which is the main component of the polyester composition, and other components through the main input port, and feeding the phenolic antioxidant and phosphorus-based antioxidant through a side input port located between the main input port and the tip of the extruder, and melt-mixing the components. Of these, the method of feeding the copolymer polyester, which is the main component of the polyester composition, the phenolic antioxidant, the phosphorus-based antioxidant, and other components as required through the main input port is preferred in terms of excellent mechanical properties and production stability.

[0103] Particles may be added to the copolymer polyester composition for the purposes of reducing friction with contacting objects such as guides and rollers during the molding process, thereby improving processability, or adjusting the color tone of the product. Any of the conventionally known particles can be used. Specifically, inorganic particles such as silicon dioxide, titanium dioxide, calcium carbonate, barium sulfate, aluminum oxide, and zirconium oxide, as well as organic polymer particles such as cross-linked polystyrene, can be used. Among these particles, titanium dioxide particles are preferred because of their good dispersibility in polymers and their relatively low cost. Titanium dioxide particles can be produced by various wet and dry methods, and, if necessary, are subjected to pretreatment such as pulverization and classification before being added to the copolymer polyester reaction system. The particles can be added to the copolymer polyester reaction system at any stage, but adding them after the esterification reaction or transesterification reaction has essentially been completed is preferred because they provide good dispersibility in the polymer. The amount of particles added to the polymer and the particle size vary depending on the application and are not particularly limited. However, a content of 0.01 to 10% by weight of the copolymerized polyester, an average particle size of 0.05 to 5 μm, and a content of 1,000 particles / 0.4 mg or less of coarse particles with a particle size of 4 μm or more are preferred, as this results in particularly good processability and color tone.

[0104] Furthermore, after polymerization, a blue-tone adjuster, a red-tone adjuster, or a purple-tone adjuster may be added as a color tone adjuster. The color tone adjusters are as exemplified above, and one or more types can be used depending on the purpose. Using one or more blue-tone adjusters and one or more red-tone adjusters is particularly preferable because it allows for fine control of the color tone. Furthermore, in this case, it is preferable that the ratio of the blue-tone adjuster to the total amount of added color tone adjusters is 50% by weight or more, as this results in a particularly good color tone of the resulting copolymerized polyester. Ultimately, the total amount of color tone adjusters added to the copolymerized polyester is preferably 30 ppm or less. Exceeding 30 ppm may result in a decrease in the transparency of the copolymerized polyester or a dull color. The amount added can be calculated from the structural characteristics of the color tone adjuster and the proportion of its constituent parts using nuclear magnetic resonance (NMR) analysis.

[0105] Other additives to be added after polymerization include, in addition to the above-mentioned particles and color tone adjusters, pigments such as carbon black, surfactants such as alkylbenzenesulfonic acid, conventionally known antioxidants, color inhibitors, light fasteners, antistatic agents, compatibilizers, plasticizers, fluorescent brighteners, release agents, antibacterial agents, nucleating agents, adjusters, matting agents, antifoaming agents, preservatives, gelling agents, latex, fillers, inks, colorants, fragrances, etc. These other additives may be used alone or in combination of two or more.

[0106] In the method for producing the polyester composition of the present invention, the melt-kneading temperature when producing the polyester composition is preferably 110 to 360°C, more preferably 210 to 320°C, and particularly preferably 240 to 280°C, in terms of excellent mechanical properties.

[0107] The copolymerized polyester composition obtained by the production method of the present invention preferably has an intrinsic viscosity (IV) of 1.50 dL / g or more, more preferably 1.55 dL / g or more, even more preferably 1.60 dL / g or more, and particularly preferably 1.63 dL / g or more, when measured at 25°C using o-chlorophenol as a solvent. The upper limit is preferably 2.20 dL / g or less, more preferably 2.15 dL / g or less, and even more preferably 2.10 dL / g or less. When the IV is within this range, the copolymerized polyester can produce high-strength fibers with a high degree of polymerization.

[0108] By using the copolymerized polyester composition obtained by the production method of the present invention as a constituent component of a conjugated fiber, it is possible to obtain a conjugated fiber that exhibits unprecedented moisture absorption properties and does not impair the fiber properties.

[0109] Specific examples of the composite fiber are described below.

[0110] Examples of fiber configurations include sheath-core composite fibers, sheath-core composite hollow fibers, and islands-in-sea composite fibers. The polyester composition obtained by the production method of the present invention can be used as a constituent component in any ratio. For example, in the case of sheath-core composite fibers and sheath-core composite hollow fibers, the composite ratio (wt%) of the polyester composition in the core portion is preferably core / sheath = 10 / 90 to 90 / 10, more preferably 15 / 85 to 50 / 50, and particularly preferably 20 / 80 to 40 / 60. The lower limit of the composite ratio in the core portion is set to impart sufficient moisture absorption, while the upper limit of the composite fiber ratio is set to prevent deterioration of spinnability and fiber properties. In the case of islands-in-sea composite fibers, the composite ratio (wt%) of the polyester composition in the island portion is preferably islands / sea = 10 / 90 to 90 / 10, more preferably 15 / 85 to 50 / 50, and particularly preferably 20 / 80 to 40 / 60. The lower limit of the island portion conjugation ratio is set for the purpose of imparting sufficient moisture absorption, and the upper limit of the conjugated fiber ratio is set from the viewpoint of preventing deterioration of spinnability and fiber properties.

[0111] Conjugate fibers using the copolymerized polyester composition obtained by the production method of the present invention and other polyesters can be produced by conventional methods. A representative method for producing islands-in-sea composite fibers is described below. In the case of islands-in-sea composite fibers, the copolymerized polyester composition (island portions) obtained by the production method of the present invention and the polyester (sea portion) are separately melted and introduced into a spinning pack, forming a sea-island composite flow in a spinneret device and spun out from an extrusion hole. The spun filament yarn is taken up at a predetermined speed and temporarily wound up on a package, and the resulting undrawn yarn is drawn in a conventional drawing machine. Drawing may be carried out continuously after taking up the spun yarn without winding, or it may be drawn up at a high speed of 4000 m / min or more to achieve the desired fiber properties in one go without substantial drawing. Examples of direct spinning and drawing methods include taking up the spun yarn at 1000 to 5000 m / min, followed by drawing and heat setting at 3000 to 6000 m / min. The filamentary form of the fiber may be either a filament or a staple, and may be appropriately selected depending on the intended use. The fabric form may be woven, knitted, nonwoven, or the like, and may be appropriately selected depending on the intended use. [Example]

[0112] The present invention will be described in more detail below with reference to examples. The characteristic values ​​in the examples were determined by the following methods.

[0113] A. Extraction of polyethylene glycol from copolymer polyester The polyethylene glycol in the copolymer polyester was extracted according to the following procedure, and the molecular weight of the polyethylene glycol was measured by gel permeation chromatography (GPC).

[0114] The procedure for extracting polyethylene glycol from a copolymer polyester is shown below.

[0115] 0.05 g of the obtained copolymer polyester was sampled and dissolved in 1 mL of 28% aqueous ammonia at 120°C for 5 hours by heating. After cooling, 1 mL of purified water and 1.5 mL of 6 M hydrochloric acid were added, and the volume was adjusted to 5 mL with purified water. After centrifugation, the mixture was filtered through a 0.45 μm filter, and the filtrate was used for GPC measurement.

[0116] B. Number average molecular weight of polyethylene glycol The molecular weight of polyethylene glycol in the copolymerized polyester was analyzed by gel permeation chromatography (GPC) of the extracted filtrate. Detector: Waters 2410 refractive index detector, sensitivity 128x Column: Tosoh TSKgel G3000PWXLI Solvent: 0.1M sodium chloride aqueous solution Flow rate: 0.8mL / min Injection volume: 200μL Column temperature: 40℃ Standard substance: polyethylene glycol (Mw 106-10100, manufactured by AML Co., Ltd.).

[0117] C. Amount of copolymerization of polyethylene glycol The copolymerization amount of polyethylene glycol in the copolymerized polyester was analyzed using a nuclear magnetic resonance (NMR) spectrometer. Equipment: JEOL Ltd. AL-400 Deuterated solvent: deuterated 1,1,1,3,3,3-hexafluoro-2-isopropanol (HFIP) Number of times accumulated: 128 Sample concentration: 0.05 g of sample / 1 mL of deuterated solvent.

[0118] D. Phosphorus atom content in polyethylene glycol or copolymer polyester composition Approximately 0.5 g of sample was placed in a 100 mL Erlenmeyer flask, 10 mL of sulfuric acid was added, and the mixture was heated to 250 °C on a sand bath. 1 mL of perchloric acid was added, followed by heating to 300 °C and another 1 mL of perchloric acid. The solution was heated at 350 °C for 10 minutes until the solution became colorless and transparent, and then refluxed with sulfuric acid for 3 minutes. After cooling, the treated solution was transferred to a 250 mL volumetric flask and titrated with 40% NaOH aqueous solution, followed by diluting the volume to 250 mL with purified water. 2 mL of molybdenum blue color-developing solution was added to 10 mL of the resulting neutralized solution, followed by diluting the volume to 20 mL with purified water. After 15 minutes, the absorbance at 720 nm was measured using an absorption spectrophotometer. A calibration curve using potassium dihydrogen phosphate was prepared in advance to calculate the amount of phosphate in the sample, and then the amount of phosphorus atoms was calculated. Equipment: Hitachi High-Tech Science U-3310 Measurement wavelength: 720nm.

[0119] E. Structural analysis of phosphorus compounds in polyethylene glycol The following equipment was used to perform structural analysis of phosphorus compounds in polyethylene glycol. Equipment: Bruker FT-IR LUMOS Light source: Silicon carbide rod heating element (glo bar) Detector: 250μm Narrow MCT Detection wave number range: 4000 to 600 cm -1 Resolution: 4cm -1 Accumulation count: 256 or more times.

[0120] F. Alkali metal content in polyethylene glycol 0.1 g of polyethylene glycol was weighed into a Teflon (registered trademark) container, sulfuric acid, nitric acid, hydrofluoric acid, and perchloric acid were added, and the mixture was heated and decomposed on a hot plate. The mixture was then concentrated until white sulfuric acid smoke was generated, and the solution was dissolved in dilute nitric acid to prepare a constant volume solution. The metal content of the polyethylene glycol was measured using an ICP mass spectrometer (Agilent 8800, manufactured by Agilent Tschologies), and the sum of the detected alkali metal atomic weights was calculated as the alkali metal content in the polyethylene glycol. G. Extraction of phenolic antioxidants from copolyesters or copolyester compositions The phenolic antioxidant in the copolymer polyester or copolymer polyester composition was extracted according to the following procedure, and the structure of the phenolic antioxidant was analyzed using a nuclear magnetic resonance (NMR) spectrometer.

[0121] The extraction procedure for the phenolic antioxidant in the copolyester is shown below.

[0122] Approximately 1 g of the obtained copolymer polyester or copolymer polyester composition was dissolved in 20 mL of HFIP, and 40 mL of toluene was added. 60 mL of methanol was then added to precipitate the product. The precipitate was removed using a 0.45 μm filter, and the filtrate was concentrated using an evaporator to obtain a dry product. This dry product was used for 1H-NMR measurement or high-performance liquid chromatography (HPLC) measurement.

[0123] H. Structural analysis of phenolic groups and phenolic antioxidants in copolyesters or copolyester compositions The structural formula of the phenol group and the structure of the phenolic antioxidant in the copolyester or the copolyester composition were analyzed using a nuclear magnetic resonance (NMR) spectrometer. Equipment: JEOL Ltd. AL-400 Deuterated solvent: Deuterated HFIP Number of times accumulated: 128 Sample concentration: 0.05 g of sample / 1 mL of deuterated solvent.

[0124] I. Analysis of phenol group content in copolyester or copolyester composition The copolymerized polyester or fiber obtained in the examples was used as a sample. 0.01 g of the sample was decomposed in 4 mL of 10% hydrochloric acid in methanol at 80°C. After cooling, 1 mL of hydrochloric acid in methanol was added, and the precipitate was filtered. HPLC measurement was performed using the filtrate. Standard solutions were prepared by dissolving IRGANOX® 1010, methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid in chloroform / acetonitrile solvent, respectively. A calibration curve was created, and the phenol group content (mmol / kg) in the copolymerized polyester or fiber obtained in the examples was calculated. Column: Inertsil ODS-3 (3 x 150 mm, 5 μm) Detector: Shimadzu LC-20A Mobile phase: A. 0.1 vol% formic acid aqueous solution, B. acetonitrile Program: 0.0min → 10.0min B25% → 100% 10.0min → 20min B100% Flow rate: 0.8mL / min Injection volume: 20μL Column temperature: 50℃ Detection wavelength: PDA 260~280nm.

[0125] J. Content Analysis of Phenolic Antioxidants in Copolyesters or Copolyester Compositions The content of the phenolic antioxidant in the copolymer polyester or copolymer polyester composition was analyzed by HPLC measurement using the precipitate described in Section G. The content of the phenolic antioxidant contained in the HPLC measurement sample was quantified using a calibration curve of a standard substance (1,4-diphenylbenzene) prepared in advance. The measurement was performed five times per sample, and the average value was used. Column: YMC-Pack ODS-A (inner diameter 4.6 mm, length 150 mm, particle diameter 5 nm) Detector: Shimadzu SPD-10AVVP Mobile phase: methanol (solvent A), water (solvent B), solvent A:solvent B = 88:12 Flow rate: 1.3mL / min Injection volume: 1μL Column temperature: 40℃ Standard substance: 1,4-diphenylbenzene.

[0126] K. Structural analysis of phosphorus-based antioxidants Using the precipitate obtained by the method described in Section G, structural analysis of the phosphorus-based antioxidant contained in the copolymer polyester composition was carried out by nuclear magnetic resonance (NMR) spectroscopy. Equipment: JEOL Ltd. AL-400 Deuterated solvent: Deuterated HFIP Number of times accumulated: 128 Sample concentration: 0.05 g of sample / 1 mL of deuterated solvent.

[0127] L. Fineness 100 m of the fiber obtained in the examples was reeled out using an INTEC electric measuring machine under an environment of 20°C temperature and 65% RH. The weight of the reel was measured, and the fineness (dtex) was calculated using the following formula. The measurement was performed five times for each sample, and the average value was taken as the fineness.

[0128] Fineness (dtex) = weight (g) of 100m of fiber x 100.

[0129] M. Strength, elongation Tenacity and elongation were calculated in accordance with JIS L1013:2010 (Testing Methods for Chemical Fiber Filament Yarns) 8.5.1 using the fibers obtained in the examples as samples. Tensile tests were conducted using an Orientec Tensilon UTM-III-100 under conditions of 20°C temperature and 65% RH humidity, with an initial sample length of 20 cm and a tensile speed of 20 cm / min. The stress (cN) at the point showing the maximum load was divided by the fineness (dtex) to calculate strength (cN / dtex). The elongation (L1) at the point showing the maximum load and the initial sample length (L0) were used to calculate elongation (%) according to the following formula. Ten measurements were performed per sample, and the average values ​​were used to calculate strength and elongation. A strength of 2.0 cN / dtex or higher was considered good, and a strength of 2.3 cN / dtex or higher was considered even better. Elongation (%)={(L1-L0) / L0}×100.

[0130] N. Difference in moisture absorption rate of sample (△MR) (1) ΔMR of fabric The resulting fiber was used as a sample to knit approximately 2 g of tubular fabric using an Eiko Sangyo NCR-BL circular knitting machine (3.5 inch (8.9 cm) diameter, 27 gauge), and then placed in an aqueous solution containing 1 g / L sodium carbonate and Meisei Chemical Industry's Grand Up US-20 surfactant. The knitted fabric was then scoured at 80°C for 20 minutes and dried in a hot air dryer at 60°C for 60 minutes to obtain the tubular fabric after scouring. The tubular fabric after scouring was then treated with hot water at a bath ratio of 1:100, at a treatment temperature of 130°C, and for 60 minutes, and then dried in a hot air dryer at 60°C for 60 minutes to obtain the tubular fabric after hot water treatment.

[0131] The moisture absorption rate (%) was calculated in accordance with moisture content 8.10 of JIS L1096:2010 (Fabric testing methods for woven and knitted fabrics) using the tubular knitted fabrics after scouring and hot water treatment as samples. First, the tubular knitted fabric was hot-air dried at 60°C for 30 minutes, then left to stand for 24 hours in an Espec thermo-hygrostat LHU-123 conditioned at a temperature of 20°C and a humidity of 65%RH, and the weight (W1) of the tubular knitted fabric was measured. The tubular knitted fabric was then left to stand for 24 hours in an Espec thermo-hygrostat conditioned at a temperature of 30°C and a humidity of 90%RH, and the weight (W2) of the tubular knitted fabric was measured. The tubular knitted fabric was then hot-air dried at 105°C for 2 hours, and the weight (W3) of the tubular knitted fabric after bone-drying was measured. The weights of the cylindrical knitted fabric, W1 and W3, were used to calculate the moisture absorption rate MR1 (%) when the fabric was left standing from an absolutely dry state in an atmosphere at a temperature of 20°C and a humidity of 65% RH for 24 hours, using the formula below. The weights of the cylindrical knitted fabric, W2 and W3, were used to calculate the moisture absorption rate MR2 (%) when the fabric was left standing from an absolutely dry state in an atmosphere at a temperature of 30°C and a humidity of 90% RH for 24 hours, using the formula below. The moisture absorption rate difference (ΔMR) was then calculated using the formula below. Measurements were made five times per sample, and the average value was taken as the moisture absorption rate difference (ΔMR). A ΔMR of 2.0% or higher was considered to be moisture absorbent, and a ΔMR of 3.0% or higher was considered to be even better. MR1(%)={(W1-W3) / W3}×100 MR2(%)={(W2-W3) / W3}×100 Moisture absorption rate difference (△MR) (%) = MR2-MR1.

[0132] (2) Chip ΔMR 3 g of the resulting chips were freeze-pulverized and used as a measurement sample. After 30 minutes of hot air drying at 60°C, the sample was placed in an Espec thermo-hygrostat LHU-123 (controlled at 20°C and 65%RH) for 24 hours, and the weight of the sample (W1) was measured. The sample was then placed in a thermo-hygrostat controlled at 30°C and 90%RH for 24 hours, and the weight of the tubular knit (W2) was measured. The sample was then hot air-dried at 105°C for 2 hours, and the weight of the sample after drying (W3) was measured. The moisture absorption rate MR1 (%) was calculated using the sample weights W1 and W3 according to the above formula when the sample was left standing from an absolutely dry state in an atmosphere at a temperature of 20°C and a humidity of 65% RH for 24 hours, and the moisture absorption rate MR2 (%) was calculated using the sample weights W2 and W3 according to the above formula when the sample was left standing from an absolutely dry state in an atmosphere at a temperature of 30°C and a humidity of 90% RH for 24 hours, and then the moisture absorption rate difference (ΔMR) was calculated according to the above formula.

[0133] O. Evaluation of yellowing prevention after washing with water The test was conducted in accordance with Method 103 of JIS L0217:1995 (Symbols and methods of labeling for handling textile products). Kao Corporation's detergent "Attack" and 2.3 ml / L of Kao Corporation's bleach "Haiter" were added, and the laundry was washed 10 times. This was followed by a 30-minute drying cycle at 60°C in a tumble dryer. This cycle was repeated 10 times. The color tone measurement described below evaluated the yellowing inhibition after washing in water, with a b* value of less than 10 being graded as A, a b* value of 10 to 15 being graded as B, and a b* value of greater than 15 being graded as C.

[0134] P. Oxidation heat generation test (oxidation heat generation start time) The samples prepared in the above step O and washed with water were stacked to a depth of 25 mm in a cylindrical container, and a thermocouple was placed in the center. The samples were further stacked to fill the cylindrical container without any gaps. The cylindrical container filled with the samples was placed in a thermostatic oven set to 150°C for 200 hours, and the time when oxidation heat generation began was measured. "No oxidation heat generation occurred even after 150 hours" was rated S, "No oxidation heat generation occurred even after 100 hours" was rated A, "Oxidation heat generation began after 90 hours" was rated B, and "Oxidation heat generation began in less than 90 hours" was rated C, with S and A being considered pass.

[0135] Q. Fastness to nitrogen oxides The test was carried out in accordance with the weak test (one-cycle test) of JIS L0855:2005 (Testing method for color fastness to nitrogen oxides). The tubular knitted fabric after scouring prepared in section N(1) was used as a sample, exposed to nitrogen oxides, and then post-treated with a buffered urea solution. The degree of discoloration of the sample was graded using the gray scale for discoloration specified in JIS L0804:2004 to evaluate the fastness to nitrogen oxides.

[0136] R. Spinnability Evaluation (1) Pack replacement frequency Spinnability was evaluated by the pack replacement frequency when undrawn yarn of 92 dtex-72 f was spun from a sea-island composite spinneret using a filter with a 5 μm mesh size, with the polymer to be evaluated as the island component. "Replacement period of 3 days or more" was rated as S, "replacement period of 1 day or more but less than 3 days" as A, "replacement period of 12 hours or more but less than 24 hours" as B, and "replacement period of less than 12 hours" as C.

[0137] (2) Number of thread breaks Spinnability was evaluated by using the polymer to be evaluated as an island component and spinning an undrawn 92 dtex-72 f yarn from a sea-island composite spinneret using a filter with a mesh size of 5 μm. S was given for "2 or fewer yarn breakages / t," A for "3 or fewer yarn breakages / t," B for "5 or fewer yarn breakages / t," and C for "6 or more yarn breakages / t."

[0138] [Reference example 1] A slurry of 82.5 kg of high-purity terephthalic acid (manufactured by Mitsui Chemicals, Inc.) and 35.4 kg of ethylene glycol (manufactured by Nippon Shokubai Co., Ltd.) was sequentially fed over 4 hours into an esterification reaction tank that had been previously charged with 100 kg of bis(hydroxyethyl) terephthalate and maintained at a temperature of 250°C. After the feed was completed, the esterification reaction was continued for another hour, and the resulting esterification reaction product (101.5 kg) was transferred to a polycondensation tank.

[0139] To this esterification reaction product, 25.3 g of trimethyl phosphate was added, followed 10 minutes later by the addition of 20.3 g of cobalt acetate tetrahydrate and 25.3 g of antimony trioxide. Five minutes later, an ethylene glycol slurry of titanium oxide particles was added at 0.3 mass% of the polymer in terms of titanium oxide particles. Five minutes later, the reaction system was depressurized to initiate the reaction. The temperature inside the reactor was gradually increased from 250°C to 290°C, while the pressure was reduced to 40 Pa. The time required to reach the final temperature and pressure was 60 minutes. When the desired stirring torque was reached, the reaction system was purged with nitrogen and returned to normal pressure to terminate the polycondensation reaction. The extrusion was performed as a strand from a die, cooled in a water bath, and cut to obtain polyethylene terephthalate (PET) pellets. The resulting PET had an intrinsic viscosity of 0.65.

[0140] (Example 1) Phosphorus content: 27 ppm, alkali metal content: 31.0 ppm (potassium content: 1.0 ppm) A slurry of 51.9 kg of high-purity terephthalic acid (manufactured by Mitsui Chemicals, Inc.) and 23.3 kg of ethylene glycol (manufactured by Nippon Shokubai Co., Ltd.) was sequentially fed over 4 hours into an esterification reaction tank that had been previously charged with 100 kg of bis(hydroxyethyl) terephthalate and maintained at a temperature of 250°C. After the feed was completed, the esterification reaction was continued for another hour, and 60 kg of the resulting esterification reaction product was transferred to a polycondensation tank.

[0141] 60.0 kg of polyethylene glycol having a number average molecular weight of 8,300 g / mol, a phosphorus content of 27 ppm, a potassium content of 0.7 ppm, and a sodium content of 30.0 ppm, and 600 g of an antioxidant: pentaerythritol-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenol)propionate) (manufactured by BASF, IRGANOX (registered trademark) 1010) were charged into a polymerization tank, and when the temperature of the polymerization tank reached 180°C or higher, the reaction product obtained in the ES reaction tank was transferred thereto.

[0142] 30.0 g of trimethyl phosphate was added, followed 10 minutes later by 20.4 g of cobalt acetate tetrahydrate and 48.0 g of antimony trioxide. Five minutes later, an ethylene glycol slurry containing titanium oxide particles was added at 0.3 mass% titanium oxide particle equivalent to the polymer. Five minutes later, the reaction system was depressurized to initiate the reaction. The temperature inside the reactor was gradually increased from 250°C to 290°C, while the pressure was reduced to 40 Pa. The time required to reach the final temperature and pressure was 60 minutes. When the desired stirring torque was reached, the reaction system was purged with nitrogen and returned to normal pressure to terminate the polycondensation reaction. The pellets were extruded in the form of strands from a nozzle, cooled in a water bath, and cut to obtain pellets of polyethylene glycol-co-polyethylene terephthalate (PET). However, there was some variation in thickness and thinning during extrusion, making the cuttability poor.

[0143] (Example 2) Phosphorus content: 40 ppm, alkali metal content: 31.0 ppm (potassium content: 1.0 ppm) 1.0 kg of butanediol (BDO) was heated to 100° C., and then mixed with 250 g of titanium catalyst: tetra-n-butoxytitanate (TBT) (Tokyo Chemical Industry Co., Ltd.) to obtain a catalyst solution.

[0144] 45.3 kg of terephthalic acid (TPA) (Tokyo Chemical Industry Co., Ltd.) as a dicarboxylic acid component, 44.2 kg of butanediol (BDO) (Tokyo Chemical Industry Co., Ltd.) as a diol component, and 135 g of the catalyst solution obtained by the above method as an esterification reaction catalyst were charged into an ES reactor equipped with a distillation column. After the esterification reaction was initiated at a temperature of 160°C and a reduced pressure of 93 kPa, the temperature was gradually increased, and the esterification reaction was continued for 270 minutes at a final temperature of 235°C. After the esterification reaction was completed, initial polymerization (500 torr x 60 minutes) was carried out.

[0145] 60.0 kg of polyethylene glycol with a number average molecular weight of 8,300 g / mol, a phosphorus content of 27 ppm, a potassium content of 0.7 ppm, and a sodium content of 30.0 ppm, and 480 g of an antioxidant, pentaerythritol-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenol)propionate) (BASF, IRGANOX® 1010), were charged into a polymerization vessel. When the temperature of the polymerization vessel reached 180°C or higher, the reaction product obtained in the ES reactor was transferred. After the temperature of the polymerization vessel reached 250°C, 300 g of the catalyst solution obtained by the above method was added as a polycondensation reaction catalyst. The polycondensation reaction was carried out at a temperature of 250°C and a pressure of 100 Pa. When the predetermined stirring torque was reached, the reaction system was purged with nitrogen and returned to normal pressure to terminate the polycondensation reaction. The product was then extruded into strand form from a spinneret, cooled in a water bath, and cut to obtain pellets of polyethylene glycol copolymerized polybutylene terephthalate. There were no problems with the polymerization and discharging. The intrinsic viscosity of the obtained copolymer polyester was 2.00.

[0146] Subsequently, the obtained polyethylene glycol copolymerized polybutylene terephthalate was mixed with 6.0% by weight of 2,2'-dimethyl-2,2'-(2,4,8,10-tetraoxaspiro[5,5]undecane-3,9-diyl)dipropane-1,1'-diyl bis[3-(3-t-butyl-4-hydroxy5-methylphenyl)propanoate] (ADEKA CORPORATION, ADK STAB® AO-80) as a phenolic antioxidant and 1,1'-biphenyl-4,4'-diylbis[phosphonite bis(2,4-di-t-butylphenyl)] (Clariant Chemicals, HOSTANOX®) as a phosphorus-based antioxidant. The antioxidant was melt-kneaded using a twin-screw extruder with at least two vent holes and an L / D ratio of 45 (L is the screw length, D is the screw diameter) at a cylinder temperature of 250°C, a rotation speed of 200 rpm, and a discharge rate of 30 kg / h.

[0147] The resulting polyester composition was used as an island component, and the polyester obtained in Reference Example 1 was used as a sea component. After drying each component until its moisture content reached 300 ppm or less, the island component and sea component were fed to an extruder-type multi-component spinning machine at a blending ratio of 20% by mass and 80% by mass, respectively, and melted separately. The melts were then fed into a spinning pack (filter opening: 5 μm) equipped with a sea-island composite spinneret at a spinning temperature of 285°C to obtain a 92 dtex-72 f undrawn yarn. The undrawn yarn was then draw-twisted at 1.4 times the heater temperature of 140°C using a draw-twisting machine (twisting section: friction disk type, heater section: contact type) to obtain a 66 dtex-72 f undrawn island-sea composite yarn. During the drying preparation before spinning, there were no problems such as bleed-out.

[0148] The polymer properties of the obtained copolymer polyester, and the fiber properties and fabric properties of the fiber are shown in Tables 1, 2, and 3. The fiber strength was 2.6 cN / dtex. The pack replacement frequency at this time was "S," and the number of thread breakages was "B." The moisture absorption rate difference (△MR) after hot water treatment was 3.9%. The yellowing inhibition after water washing treatment was "A," and the oxidation heat generation after water washing treatment was "S," which were good results. In addition, the nitrogen oxide fastness test results were grade 4-5.

[0149] (Example 3) Phosphorus content: 20 ppm, alkali metal content: 30.6 ppm (potassium content: 0.6 ppm) The same procedure as in Example 2 was carried out, except that 60.0 kg of polyethylene glycol having a number average molecular weight of 8300 g / mol, a phosphorus content of 20 ppm, a potassium content of 0.7 ppm, and a sodium content of 30.0 ppm was used.

[0150] There were no problems with polymerization discharge, and the resulting fiber strength was 2.7 cN / dtex. The pack replacement frequency evaluation result was "S," and the number of thread breakages was "A." The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A," and the oxidation heat generation after water washing treatment was good, with an "S" rating. The nitrogen oxide fastness test result was also grade 4-5.

[0151] (Example 4) Phosphorus content: 10 ppm, alkali metal content: 30.4 ppm (potassium content: 0.4 ppm) The same procedure as in Example 2 was carried out, except that 60.0 kg of polyethylene glycol having a number average molecular weight of 8300 g / mol, a phosphorus content of 10 ppm, a potassium content of 0.4 ppm, and a sodium content of 30.0 ppm was used.

[0152] There were no problems with polymerization discharge, and the resulting fiber strength was 2.7 cN / dtex. The pack replacement frequency evaluation result was "S", and the number of yarn breakages was "S". The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A", and the oxidation heat generation after water washing treatment was "S", which was good. In addition, the nitrogen oxide fastness test result was grade 4-5.

[0153] (Example 5) Phosphorus content: 0 ppm, alkali metal content: 30.2 ppm (potassium content: 0.2 ppm) The same procedure as in Example 2 was carried out, except that 60.0 kg of polyethylene glycol having a number average molecular weight of 8300 g / mol, a phosphorus content of 0 ppm, a potassium content of 0.2 ppm, and a sodium content of 30.0 ppm was used.

[0154] There were no problems with polymerization discharge, and the resulting fiber strength was 2.6 cN / dtex. The pack replacement frequency evaluation result was "S", and the number of yarn breakages was "S". The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A", and the oxidation heat generation after water washing treatment was "S", which was good. In addition, the nitrogen oxide fastness test result was grade 4-5.

[0155] (Example 6) Phosphorus content: 0 ppm, alkali metal content: 30.2 ppm (potassium content: 0.2 ppm) Example 5 was repeated except that the phosphorus-based antioxidant added during kneading was changed to 3,9-bis(2,6-t-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5-undecane] (ADEKA, ADK STAB (registered trademark) PEP-36) in an amount of 1.4 wt %.

[0156] There were no problems with polymerization discharge, and the resulting fiber strength was 2.6 cN / dtex. The pack replacement frequency evaluation result was "S", and the number of yarn breakages was "S". The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A", and the oxidation heat generation after water washing treatment was "S", which was good. In addition, the nitrogen oxide fastness test result was grade 4-5.

[0157] (Example 7) Phosphorus content: 0 ppm, alkali metal content: 35.0 ppm (potassium content: 5.0 ppm) The same procedure as in Example 2 was carried out, except that 60.0 kg of polyethylene glycol having a number average molecular weight of 8300 g / mol, a phosphorus content of 0 ppm, a potassium content of 5.0 ppm, and a sodium content of 30.0 ppm was used.

[0158] There were no problems with polymerization discharge, and the resulting fiber strength was 2.7 cN / dtex. The pack replacement frequency evaluation result was "S", and the number of yarn breakages was "S". The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A", and the oxidation heat generation after water washing treatment was "S", which was good. In addition, the nitrogen oxide fastness test result was grade 4-5.

[0159] (Example 8) Phosphorus content: 0 ppm, alkali metal content: 45.0 ppm (potassium content: 15.0 ppm) The same procedure as in Example 2 was carried out, except that 60.0 kg of polyethylene glycol having a number average molecular weight of 8300 g / mol, a phosphorus content of 0 ppm, a potassium content of 15.0 ppm, and a sodium content of 30.0 ppm was used.

[0160] There were no problems with polymerization discharge, and the resulting fiber strength was 2.7 cN / dtex. The pack replacement frequency evaluation result was "A," and the number of yarn breakages was "S." The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A," and the oxidation heat generation after water washing treatment was "S," showing good results. In addition, the nitrogen oxide fastness test result was grade 4-5.

[0161] (Example 9) Phosphorus content: 0 ppm, alkali metal content: 90.0 ppm (potassium content: 60.0 ppm) The same procedure as in Example 2 was carried out, except that 60.0 kg of polyethylene glycol having a number average molecular weight of 8300 g / mol, a phosphorus content of 0 ppm, a potassium content of 60.0 ppm, and a sodium content of 30 ppm was used.

[0162] There were no problems with polymerization discharge, and the resulting fiber strength was 2.7 cN / dtex. The pack replacement frequency evaluation result was "B," and the number of thread breakages was "A." The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A," and the oxidation heat generation after water washing treatment was good, with an "S" rating. The nitrogen oxide fastness test result was also grade 4-5.

[0163] (Example 10) Phosphorus content: 0 ppm, alkali metal content: 90.0 ppm (potassium content: 0.2 ppm) The same procedure as in Example 2 was carried out, except that 60.0 kg of polyethylene glycol having a number average molecular weight of 8300 g / mol, a phosphorus content of 0 ppm, a potassium content of 0.2 ppm, and a sodium content of 89.8 ppm was used.

[0164] There were no problems with polymerization discharge, and the resulting fiber strength was 2.7 cN / dtex. The pack replacement frequency evaluation result was "A," and the number of thread breakages was "A." The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A," and the oxidation heat generation after water washing treatment was good, with an "S" rating. The nitrogen oxide fastness test result was also grade 4-5.

[0165] (Example 11) Alkali metal content: 150.0 ppm (potassium content: 120.0 ppm) The same procedure as in Example 2 was carried out, except that 60.0 kg of polyethylene glycol having a number average molecular weight of 8300 g / mol, a phosphorus content of 0 ppm, a potassium content of 120.0 ppm, and a sodium content of 30.0 ppm was used.

[0166] There were no problems with polymerization discharge, and the resulting fiber strength was 2.6 cN / dtex. The pack replacement frequency evaluation result at this time was "C," and the number of thread breakages was "B." The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A," and the oxidation heat generation after water washing treatment was "S," which was good. In addition, the nitrogen oxide fastness test result was grade 4-5.

[0167] (Example 12) Alkali metal content: 45.0 ppm (potassium content: 15.0 ppm) Example 8 was repeated except that the phosphorus-based antioxidant added during kneading was changed to 3,9-bis(2,6-t-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5-undecane] (ADEKA, ADK STAB (registered trademark) PEP-36) in an amount of 1.4 wt %.

[0168] There were no problems with polymerization discharge, and the resulting fiber strength was 2.6 cN / dtex. The pack replacement frequency evaluation result was "S", and the number of yarn breakages was "S". The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A", and the oxidation heat generation after water washing treatment was "S", which was good. In addition, the nitrogen oxide fastness test result was grade 4-5.

[0169] (Example 13) Alkali metal content: 45.0 ppm (potassium content: 15.0 ppm) Example 8 was carried out in the same manner as in Example 8, except that the amount of 1,1'-biphenyl-4,4'-diylbis[bis(2,4-di-t-butylphenyl)phosphonite] (manufactured by Clariant Chemicals, HOSTANOX (registered trademark) P-EPQ) added during kneading was 1.5 mass%.

[0170] There were no problems with polymerization discharge, and the resulting fiber strength was 2.6 cN / dtex. The pack replacement frequency evaluation result was "S", and the number of yarn breakages was "S". The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A", and the oxidation heat generation after water washing treatment was "S", which was good. In addition, the nitrogen oxide fastness test result was grade 4-5.

[0171] (Example 14) Alkali metal content: 45.0 ppm (potassium content: 15.0 ppm) Example 12 was carried out in the same manner as in Example 12, except that the amount of 3,9-bis(2,6-t-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5 undecane] (ADEKA, Adekastab (registered trademark) PEP-36) added during kneading was 0.9 mass%.

[0172] There were no problems with polymerization discharge, and the resulting fiber strength was 2.6 cN / dtex. The pack replacement frequency evaluation result was "S," and the number of yarn breakages was "S." The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "B," and the oxidation heat generation after water washing treatment was "A," which were good results. In addition, the nitrogen oxide fastness test result was grade 3-4.

[0173] (Example 15) Alkali metal content: 45.0 ppm (potassium content: 15.0 ppm) The same procedure as in Example 8 was carried out, except that the phosphorus-based antioxidant added during kneading was tristearyl phosphite (JP-318E, manufactured by Johoku Chemical Co., Ltd.) in an amount of 3.7 mass %.

[0174] There were no problems with polymerization discharge, and the resulting fiber strength was 2.7 cN / dtex. The pack replacement frequency evaluation result was "S", and the number of yarn breakages was "S". The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A", and the oxidation heat generation after water washing treatment was "S", which was good. In addition, the nitrogen oxide fastness test result was grade 4-5.

[0175] (Example 16) Alkali metal content: 150.0 ppm (potassium content: 120.0 ppm) Example 11 was carried out in the same manner as in Example 11, except that the phosphorus-based antioxidant added during kneading was tristearyl phosphite (JP-318E, manufactured by Johoku Chemical Co., Ltd.) in an amount of 3.7 mass%.

[0176] There were no problems with polymerization discharge, and the resulting fiber strength was 2.7 cN / dtex. The pack replacement frequency evaluation result was "B," and the number of thread breakages was "A." The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A," and the oxidation heat generation after water washing treatment was good, with an "S" rating. The nitrogen oxide fastness test result was also grade 4-5.

[0177] (Example 17) Alkali metal content: 150.0 ppm (potassium content: 120.0 ppm) Example 16 was carried out in the same manner as in Example 16, except that the amount of tristearyl phosphite (JP-318E, manufactured by Johoku Chemical Co., Ltd.) added during kneading was 2.4 mass %.

[0178] There were no problems with polymerization discharge, and the resulting fiber strength was 2.6 cN / dtex. The pack replacement frequency evaluation result was "A," and the number of thread breakages was "A." The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A," and the oxidation heat generation after water washing treatment was good, with an "S" rating. The nitrogen oxide fastness test result was grade 4-5.

[0179] (Example 18) Alkali metal content: 90.0 ppm (potassium content: 0.2 ppm) Example 10 was carried out in the same manner as in Example 10, except that the phosphorus-based antioxidant added during kneading was tristearyl phosphite (JP-318E, manufactured by Johoku Chemical Co., Ltd.) in an amount of 3.7 mass %.

[0180] There were no problems with polymerization discharge, and the resulting fiber strength was 2.7 cN / dtex. The pack replacement frequency evaluation result was "A," and the number of yarn breakages was "S." The moisture absorption rate difference after hot water treatment (△MR) was 4.0%. The yellowing inhibition after water washing treatment was "A," and the oxidation heat generation after water washing treatment was "S," showing good results. In addition, the nitrogen oxide fastness test result was grade 4-5.

[0181] (Example 19) Alkali metal content: 45.0 ppm (potassium content: 15.0 ppm) An esterification reaction was carried out in the same manner as in Example 2, except that the amounts of terephthalic acid (TPA) (Tokyo Chemical Industry Co., Ltd.) and butanediol (BDO) (Tokyo Chemical Industry Co., Ltd.) used in the esterification reaction were 63.4 kg, 61.9 kg, and 189 g of the esterification reaction catalyst solution, respectively.

[0182] The polycondensation reaction was carried out in the same manner as in Example 2, except that the polyethylene glycol used was 36.0 kg of polyethylene glycol having a number average molecular weight of 8,300 g / mol, a phosphorus content of 0 ppm, a potassium content of 15.0 ppm, and a sodium content of 30.0 ppm. There were no problems with the polymerization discharge.

[0183] The kneading and spinning were carried out in the same manner as in Example 2, and the resulting fiber strength was 2.8 cN / dtex. The pack replacement frequency was evaluated as "S" and the number of yarn breakages was evaluated as "S." The difference in moisture absorption rate (ΔMR) after hot water treatment was 2.0%. The yellowing inhibition after water washing treatment was evaluated as "A," and the oxidation heat generation after water washing treatment was evaluated as "S," which were good results. The nitrogen oxide fastness test result was grade 4-5.

[0184] (Example 20) Alkali metal content: 45.0 ppm (potassium content: 15.0 ppm) Example 19 was carried out in the same manner as in Example 19, except that the phosphorus-based antioxidant added during kneading was tristearyl phosphite (JP-318E, manufactured by Johoku Chemical Co., Ltd.) in an amount of 3.7 mass %.

[0185] There were no problems with polymerization discharge, and the resulting fiber strength was 2.8 cN / dtex. The pack replacement frequency evaluation result was "S", and the number of yarn breakages was "S". The moisture absorption rate difference after hot water treatment (△MR) was 2.0%. The yellowing inhibition after water washing treatment was "A", and the oxidation heat generation after water washing treatment was "S", which was good. In addition, the nitrogen oxide fastness test result was grade 4-5.

[0186] (Comparative Example 1) The same procedures as in Example 2 were carried out except that prepolymerization was not performed, PEG was not added during polymerization, and the phenol-based antioxidant and phosphorus-based antioxidant were not added during kneading.

[0187] There were no problems with polymerization discharge, and the resulting fiber strength was 3.0 cN / dtex. The pack replacement frequency evaluation result was "S", and the number of yarn breakages was "S". The moisture absorption rate difference after hot water treatment (△MR) was 0.1%. The yellowing inhibition after water washing treatment was "A", and the oxidation heat generation after water washing treatment was "S". In addition, the nitrogen oxide fastness test result was grade 5.

[0188] (Comparative Example 2) An experiment was carried out in the same manner as in Example 2, except that the number average molecular weight was 8,300 g / mol, the phosphorus content was 40 ppm, the potassium content was 1.0 ppm, and the sodium content was 30.0 ppm (60.0 kg), and the antioxidant was 180 g of pentaerythritol-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenol)propionate) (manufactured by BASF, IRGANOX (registered trademark) 1010).

[0189] There were no problems with polymerization discharge, and the resulting fiber strength was 2.5 cN / dtex. The pack replacement frequency evaluation result at this time was "C," and the number of yarn breakages was "C." The moisture absorption rate difference after hot water treatment (△MR) was 4.1%. The yellowing inhibition after water washing treatment was "A," and the oxidation heat generation after water washing treatment was "S." The nitrogen oxide fastness test result was grade 4-5.

[0190] [Table 1]

[0191] [Table 2]

[0192] [Table 3]

[0193] The chemical structural formulas of the phenolic compounds (phenolic antioxidants) and phosphorus-based antioxidants used in the examples and comparative examples are shown in Table 4.

[0194] [Table 4] [Industrial Applicability]

[0195] The method for producing a polyester resin composition of the present invention can prevent deterioration in operability, such as an increase in the frequency of spin pack replacement during spinning or an increase in the number of yarn breakages, and can provide a polyester composition that has high moisture absorption, suppresses yellowing after washing with water, and suppresses oxidation heat generation. Because of these characteristics, the polyester composition obtained by the present invention can be suitably used in applications requiring comfort and quality. Specific examples include general clothing applications, sportswear applications, bedding applications, interior applications, and materials applications.

Claims

1. A method for producing a copolymerized polyester, comprising carrying out an esterification reaction or a transesterification reaction using an aromatic dicarboxylic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof, and then reacting an esterification reaction product obtained by the esterification reaction or the transesterification reaction with 10 to 50% by weight of polyethylene glycol having a number average molecular weight of 5,000 to 20,000, wherein the amount of phosphorus compounds in the polyethylene glycol is 30 ppm or less in terms of the amount of phosphorus atoms, and the amount of alkali metal compounds is 100 ppm or less in terms of the amount of alkali metal atoms.

2. 2. The method for producing a copolymer polyester according to claim 1, wherein the esterification reaction or transesterification reaction is carried out using a diol containing 50 mol % or more of 1,4-butanediol or an ester-forming derivative thereof.

3. 3. The method for producing a copolyester according to claim 1, wherein the phosphorus atom in the polyethylene glycol is derived from a phosphate.

4. The method for producing a copolyester according to any one of claims 1 to 3, characterized in that the polyethylene glycol has a number average molecular weight of 5,500 to 20,000.

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