JP2015067661A - Polyester resin and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently provide a polyester resin having excellent thermal stability and a low content of terminal carboxy groups.SOLUTION: The present invention relates to a polyester resin obtained by containing dicarboxylic acid or dicarboxylic acid alkyl ester and diol as main raw materials, wherein the polyester resin contains a metal halide represented by the following formula (i) and having a purity of higher than 95%, with the formula (i): MX(M: alkali metal or copper, X: bromine or iodine, n=1 or 2).

Description

  The present invention relates to a polyester resin having excellent thermal stability and a low amount of carboxyl end groups, and a method for efficiently producing the same.

  Polyester is one of the most commonly used synthetic resins in the world as fibers, bottles, films, sheets, containers, etc. because it is excellent in mechanical strength, chemical stability and transparency and inexpensive.

  Usually, polyester is remelted and molded after chipping, but if a thermal history of 250 ° C. or higher is applied at this time, the molding machine may become yellowed due to thermal decomposition, molecular weight decreases, or foreign matter occurs due to gelation. There is a problem that undesired phenomena such as increase in the amount of dirt on the base and clogging of the filter in the manufacturing process occur.

  Examples of means for improving the thermal stability of the polyester include addition of a metal halide.

  Patent Document 1 discloses a polyester film containing copper (I) iodide, and describes that thermal stability is improved by containing copper (I) iodide. However, when producing a polyester resin as a raw material for a polyester film, there is a problem that when copper (I) iodide is present, the polymerization time is long and it cannot be produced efficiently.

  Patent Document 2 discloses a biaxially stretched polyester film having at least one of a copper salt and a halide, and describes that a copper salt or iodide is effective for decarboxylation. However, it has been disclosed that the addition of Cu (I) salt as a copper salt results in undesirable coloration, and when copper salt is contained, there is a problem of poor thermal stability such that coloration occurs. There was a need for improvement.

JP-A-62-177057 JP 2010-265459 A

  An object of the present invention is to provide a polyester resin having excellent thermal stability and a low amount of carboxyl end groups, and a method for producing the same.

  As a result of intensive studies to solve the above problems, a polyester resin excellent in thermal stability and having a low carboxyl end group amount and a production method thereof have been found, and the present invention has been achieved.

That is, the present invention is as follows.
(1) A polyester resin obtained using a dicarboxylic acid or an alkyl ester of dicarboxylic acid and a diol as a main raw material and containing a metal halide represented by the following formula (i) and having a purity higher than 95%.
(I) MX _n (M: alkali metal or copper, X: bromine or iodine, n = 1 or 2)
(2) The polyester resin according to (1), which contains 0.1 to 3 mmol of the metal halide per 100 g of the polyester resin.
(3) The polyester resin according to (1) or (2), wherein the dicarboxylic acid or dicarboxylic acid alkyl ester is an aromatic dicarboxylic acid or an aromatic dicarboxylic acid alkyl ester, and the diol is ethylene glycol.
(4) In a method for producing a polyester resin in which dicarboxylic acid or dicarboxylic acid alkyl ester and diol are esterified or transesterified and then polymerized, a metal halogen represented by the following formula (i) and having a purity of more than 95% A method for producing a polyester resin, comprising adding a compound.
(I) MX _n (M: alkali metal or copper, X: bromine or iodine, n: 1 or 2)
(5) The method for producing a polyester resin according to (4), wherein the metal halide is added in an amount of 0.1 to 3 mmol per 100 g of the polyester resin.
(6) The method for producing a polyester resin according to (4) or (5), wherein the metal halide is added at the start of the polymerization reaction.
(7) The method for producing a polyester resin according to any one of (4) to (6), wherein the dicarboxylic acid or the dicarboxylic acid alkyl ester is an aromatic dicarboxylic acid or an aromatic dicarboxylic acid alkyl ester, and the diol is ethylene glycol. .

  According to the present invention, a polyester resin having excellent thermal stability and a low amount of carboxyl end groups can be efficiently obtained.

  The polyester resin of the present invention is obtained from dicarboxylic acid or dicarboxylic acid alkyl ester and diol, and the purity of the metal halide contained in the polyester is higher than 95%. When the purity of the metal halide in the obtained polyester resin is lower than the above range, the polymerization is delayed due to impurities contained in the metal halide, and the polyester resin cannot be obtained efficiently.

  Examples of the dicarboxylic acid or dicarboxylic acid alkyl ester of the present invention include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl-4,4′-dicarboxylic acid, 5-tetrabutylphosphonium isophthalic acid, and 5-sodium sulfoisophthalic acid. Examples include acids, oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, malonic acid, glutaric acid, dimer acid, or alkyl esters thereof. The dicarboxylic acid alkyl ester referred to in the present invention is the above-described lower alkyl ester, acid anhydride, acyl chloride or the like of dicarboxylic acid, and methyl ester, ethyl ester, hydroxyethyl ester, etc. are preferably used. A more preferable embodiment of the dicarboxylic acid or dicarboxylic acid dialkyl ester of the present invention is terephthalic acid or a dimethyl ester thereof in that a polyester resin having a high melting point and easy to be processed into a fiber or a film can be obtained.

  Examples of the diol of the present invention include ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, decamethylene glycol, 2,2, Examples include 4,4-tetramethyl-1,3-cyclobutanediol, cyclohexanedimethanol, xylylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and bisphenol A-ethylene oxide adduct, among others, fibers and films. Ethylene glycol is preferable in that a polyester resin that can be easily processed into a resin can be obtained.

  The polyester resin of the present invention may be any polyester resin that can be obtained by using a preferred dicarboxylic acid or dicarboxylic acid alkyl ester and using a preferred diol, and each of the dicarboxylic acid or dicarboxylic acid alkyl ester and diol may be used alone. It may be used in combination, or two or more types may be used in combination. Examples of the polyester resin of the present invention include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polycyclohexanedimethylene terephthalate, polyethylene isophthalate, polypropylene isophthalate, polybutylene isophthalate, polycyclohexanedimethylene isophthalate, polyethylene naphthalate, polypropylene. Naphthalate, polybutylene naphthalate, polyethylene isophthalate / terephthalate, polypropylene isophthalate / terephthalate, polybutylene isophthalate / terephthalate, polyethylene terephthalate / naphthalate, polypropylene terephthalate / naphthalate, polybutylene terephthalate / naphthalate, polyethylene terephthalate / 5-sodium sulfoisophthalate, polypropylene terephthalate / 5-sodium sulfoisophthalate, polybutylene terephthalate / 5-sodium sulfoisophthalate, polyethylene terephthalate / polyethylene glycol, polypropylene terephthalate / polyethylene glycol, polybutylene terephthalate / polyethylene glycol, polyethylene terephthalate / Polytetramethylene glycol, polypropylene terephthalate / polytetramethylene glycol, polybutylene terephthalate / polytetramethylene glycol, polyethylene terephthalate / isophthalate / polytetramethylene glycol, polypropylene terephthalate / isophthalate / polytetramethylene glycol, polybutylene Rephthalate / isophthalate / polytetramethylene glycol, polyethylene terephthalate / succinate, polypropylene terephthalate / succinate, polybutylene terephthalate / succinate, polyethylene terephthalate / adipate, polypropylene terephthalate / adipate, polybutylene terephthalate / adipate, polyethylene terephthalate / sebacate, polypropylene terephthalate / Sebacate, polybutylene terephthalate / sebacate, polyethylene oxalate, polypropylene oxalate, polybutylene oxalate, polyethylene succinate, polypropylene succinate, polybutylene succinate, polyethylene adipate, polypropylene adipate, polybutylene adipate, Examples include polyethylene sebacate, polypropylene sebacate, polybutylene sebacate, polyethylene succinate / adipate, polypropylene succinate / adipate, polybutylene succinate / adipate. Here, “/” represents a copolymer. Of these, terephthalic acid or its dimethyl ester, and polyethylene terephthalate obtained using ethylene glycol as the diol component are preferred.

The metal halide of the present invention is a metal halide represented by the following formula (i) and having a purity higher than 95%. Here, purity is measured by a titration method.
(I) MX _n (M: alkali metal or copper, X: bromine or iodine, n = 1 or 2)

  Examples of the metal halide of the present invention include copper (I) iodide, copper (I) bromide, copper (II) bromide, potassium iodide, sodium iodide and the like. From the viewpoint of superiority, any of copper iodide (I), copper bromide (II), potassium iodide, and sodium iodide is preferable, and it is possible to obtain a polyester resin having excellent resistance to moist heat and being less colored. Either copper (I) iodide or sodium iodide is more preferred. In the present invention, one kind of metal halide may be used. However, two or more kinds of metal halides are excellent in that both heat stability and moisture and heat resistance are excellent, and a less colored polyester resin can be efficiently produced. It is preferable to use together.

  In the polyester resin of the present invention, the metal halide may exist in any state, but it is excellent in both thermal stability and wet heat resistance, and efficiently produces a polyester resin with little coloring. It is preferable that the metal component exists in a divalent state in that it can be performed. The state of the metal component can be analyzed by electron spin resonance.

  As the metal halide of the present invention, one having a purity higher than 95% is used in that a polyester resin excellent in thermal stability can be efficiently produced in a short time, and the purity is 96% or more. The purity is more preferably 99% or more, and the purity is more preferably 99.5% or more. The upper limit is 100%. In addition, what kind of thing may exist as an impurity, However, It is preferable that there are few monocarboxylic acids and monoalcohols at the point which can manufacture a polyester resin efficiently.

  The present invention is characterized by containing 0.1 to 3 mmol of metal halide per 100 g of polyester resin. It is preferable that the metal halide is contained in an amount of 0.1 to 2 mmol per 100 g of the polyester resin, and the metal halide is contained in an amount of 0.3 to 1 mmol per 100 g of the polyester resin in that a polyester resin having excellent thermal stability can be efficiently produced. More preferably, the metal halide is more preferably contained in an amount of 0.4 to 0.8 mmol per 100 g of the polyester resin. When the content of the metal halide in the obtained polyester resin is more than the above range, the internal particles in the polyester resin increase to cause problems such as a decrease in transparency, and when it is less, there is no effect of improving thermal stability.

  The method for producing a polyester resin obtained using the dicarboxylic acid or dicarboxylic acid alkyl ester and diol of the present invention as main raw materials comprises the following two-stage processes. That is, it is a first stage process comprising (A) esterification reaction or (B) transesterification reaction, followed by a second stage process comprising (C) polymerization reaction.

  In the method for producing a polyester resin of the present invention, the metal halide may be added at any stage of the step (A) or (B) and the subsequent step (C), but a polyester resin having excellent thermal stability is used. It is preferable to add at the (C) process at the point which can manufacture efficiently, and adding at the time of a polymerization reaction start is especially preferable. The metal halide is added in a state of being mixed with the diol at a weight ratio of 3/100 to 10/100.

  Among the steps of the first step, (A) the esterification reaction step is an esterification reaction of dicarboxylic acid and diol at a predetermined temperature, and a reaction is performed until a predetermined amount of water is distilled off to obtain a low polymer. It is a process. The step (B) transesterification is a step in which a dicarboxylic acid alkyl ester and a diol are transesterified at a predetermined temperature and reacted until a predetermined amount of alcohol is distilled to obtain a low polymer.

  The polymerization reaction (C), which is the second step, is carried out by reducing the pressure in the reactor to which the low polymer obtained by (A) esterification reaction or (B) transesterification reaction is added. (Hereinafter referred to as “the time when the polymerization reaction is started”), the temperature, pressure and stirring speed in the reactor are adjusted to conduct the polymerization reaction. When the stirring torque reaches a predetermined value, that is, the polyester is in a desired state. This is a step of obtaining a high molecular weight polyester by carrying out the polymerization until the viscosity is reached (hereinafter referred to as “the final arrival time of the polymerization reaction”).

  In the method for producing a polyester resin of the present invention, the catalyst used for the esterification reaction may be a compound such as manganese, cobalt, zinc, titanium, calcium, or may be non-catalytic. Moreover, as a catalyst used for transesterification, compounds, such as magnesium, manganese, calcium, cobalt, zinc, lithium, titanium, are used. Moreover, as a catalyst used for the polymerization reaction, compounds such as antimony, titanium, aluminum, tin, and germanium are used.

  Examples of the antimony compound include antimony oxide, antimony carboxylic acid, antimony alkoxide, and the like. Specific examples of the antimony oxide include antimony trioxide, antimony pentoxide, and the like. Antimony carboxylic acid includes acetic acid. Antimony, antimony oxalate, antimony potassium tartrate and the like can be mentioned, and examples of the antimony alkoxide include antimony tri-n-butoxide and antimony triethoxide.

  Titanium compounds include titanium complexes, tetra-i-propyl titanate, tetra-n-butyl titanate, tetra-n-butyl titanate tetramer, titanium alkoxides, titanium oxides obtained by hydrolysis of titanium alkoxides, titanium acetylacetonate Etc. Among these, a titanium complex having a polycarboxylic acid and / or a hydroxycarboxylic acid and / or a polyhydric alcohol as a chelating agent is preferable from the viewpoint of the thermal stability of the polymer, the color tone, and the small amount of deposit around the mouthpiece. Examples of the chelating agent for the titanium compound include lactic acid, citric acid, mannitol, tripentaerythritol and the like. In particular, a titanium mannitol chelate complex obtained by the method described in Japanese Patent Application Laid-Open No. 2010-100806 is preferable because generation of foreign particles of the polymer can be suppressed.

  Examples of the aluminum compound include aluminum carboxylate, aluminum alkoxide, aluminum chelate compound, basic aluminum compound, and the like, specifically, aluminum acetate, aluminum hydroxide, aluminum carbonate, aluminum ethoxide, aluminum isopropoxide, aluminum acetyl. Examples include acetonate and basic aluminum acetate.

  Examples of the tin compound include monobutyltin oxide, dibutyltin oxide, methylphenyltin oxide, tetraethyltin oxide, hexaethylditin oxide, triethyltin hydroxide, monobutylhydroxytin oxide, monobutyltin trichloride, and dibutyltin sulfide.

  Examples of germanium compounds include germanium oxides and germanium alkoxides, and specific examples of germanium oxides include germanium dioxide, germanium tetroxide, and germanium alkoxides such as germanium tetraethoxide and germanium tetrabutoxide. It is done.

  Specific examples of the magnesium compound include magnesium oxide, magnesium hydroxide, magnesium alkoxide, magnesium acetate, and magnesium carbonate.

  Specific examples of the manganese compound include manganese chloride, manganese bromide, manganese nitrate, manganese carbonate, manganese acetylacetonate, and manganese acetate.

  Specific examples of the calcium compound include calcium oxide, calcium hydroxide, calcium alkoxide, calcium acetate, and calcium carbonate.

  Specific examples of the cobalt compound include cobalt chloride, cobalt nitrate, cobalt carbonate, cobalt acetylacetonate, cobalt naphthenate, and cobalt acetate tetrahydrate.

  Specific examples of the zinc compound include zinc oxide, zinc alkoxide, and zinc acetate.

  These metal compounds may be hydrates.

  In the method for producing a polyester resin of the present invention, a phosphorus compound is preferably added as a stabilizer. Specifically, phosphoric acid, trimethyl phosphate, ethyl diethylphosphonoacetate and the like are preferable, and 3,9-bis (2,6-di-t-butyl-4-methylphenoxy) -2,4,8,10. -Tetraoxa-3,9-diphosphaspiro [5,5] undecane (PEP-36: manufactured by Asahi Denka) or tetrakis (2,4-di-t-butyl-5-methylphenyl) [1,1-biphenyl]- Trivalent phosphorus compounds such as 4,4′-diylbisphosphonite (GSY-P101: manufactured by Osaki Kogyo Co., Ltd.) are more preferred from the viewpoints of color tone and thermal stability improvement.

  Moreover, the dye used for resin etc. as a color tone regulator may be added as needed. In particular, COLOR INDEX GENERIC NAME gives blue color tone adjusters such as SOLVENT BLUE 104 and SOLVENT BLUE 45, and purple color adjusters such as SOLVENT VIOLET 36, which do not contain halogens that are likely to cause device corrosion. The heat resistance at high temperatures is relatively good and the color developability is excellent, which is preferable. These may be used alone or in combination of two or more.

  Furthermore, you may mix | blend antioxidant, a ultraviolet absorber, a flame retardant, a fluorescent whitening agent, a matting agent, a plasticizer or an antifoamer, or another additive as needed.

  In the present invention, solid phase polymerization may be further performed in order to obtain a higher molecular weight polyester resin. The solid-state polymerization is not particularly limited in apparatus and method, but is carried out by heat treatment under an inert gas atmosphere or under reduced pressure. Any inert gas may be used as long as it is inert to the polyester, and examples thereof include nitrogen, helium, carbon dioxide, etc. Nitrogen is preferably used from the viewpoint of economy. Further, as the reduced pressure, it is advantageous to use a reduced pressure condition because the time required for the solid phase polymerization reaction can be shortened, but it is preferable to maintain 110 Pa or more.

  Moreover, the polyester resin obtained by this invention can also be recycled. Specifically, when the polyester resin is polyethylene terephthalate, the waste is used as a raw material, and a depolymerization reaction is performed with a glycol component to obtain bis (hydroxyethyl) terephthalate. This may be polymerized again, but is preferably further transesterified with methanol or ethanol to give dimethyl terephthalate or diethyl terephthalate. These terephthalic acid dialkyl esters are preferred because they can be purified to high purity by distillation. The terephthalic acid dialkyl ester thus obtained can be used for polymerization again.

  The polyester resin of the present invention can be produced by batch polymerization, semi-continuous polymerization, or continuous polymerization.

  The polyester resin obtained in the present invention can be molded by a known processing method, and can be processed into various products such as fibers, films, bottles, and injection molded products.

  For example, a normal melt spinning-drawing process can be applied to a method of processing a polyester resin into fibers. Specifically, after the polyester resin was heated to the melting point or higher and melted, it was discharged from the pores, cooled and solidified with cooling air, applied with an oil agent, taken up by the take-up roller, and disposed after the take-up roller. Undrawn yarn can be collected by winding with a winding device.

  The undrawn yarn wound in this way becomes a fiber to which physical properties such as mechanical properties according to the application are given by drawing with a pair of heated rollers or more and finally applying tension or relaxation heat treatment. In addition, in this extending process, it can carry out continuously, without winding once after taking up in the above-mentioned melt spinning process, and it is preferable to set it as continuous extending | stretching from industrial viewpoints, such as productivity. Here, in performing this stretching-heat treatment, the draw ratio, the stretching temperature, and the heat treatment conditions can be appropriately selected depending on the target fiber fineness, strength, elongation, shrinkage rate, and the like.

  When processing the polyester resin of the present invention into various products, various additives such as colorants including pigments and dyes, lubricants, antistatic agents, flame retardants, ultraviolet absorbers, as long as the effects of the present invention are not impaired. One or more additives such as an antibacterial agent, a nucleating agent, a plasticizer, and a release agent may be added.

  The polyester resin of the present invention can be used as various products such as fibers, films, bottles, injection-molded products, taking advantage of excellent thermal stability and low carboxyl end group content. It is useful for agricultural materials, horticultural materials, fishery materials, civil engineering / architectural materials, stationery, medical supplies, automotive parts, electrical / electronic components or other applications.

Hereinafter, the present invention will be described in more detail with reference to examples. The raw materials used in the examples are as follows.
・ Terephthalic acid manufactured by Mitsui Chemicals, Inc., hereinafter referred to as TPA.
-Dimethyl terephthalate manufactured by SK Chemical Co., hereinafter this may be referred to as DMT.
-Nippon Shokubai Co., Ltd. ethylene glycol, hereinafter this may be referred to as EG.
-Copper iodide (I) manufactured by Wako Pure Chemical Industries, Ltd., purity 99.5%
-Copper (I) bromide manufactured by Wako Pure Chemical Industries, Ltd., purity 99.9%
-Copper (II) bromide manufactured by Wako Pure Chemical Industries, Ltd., purity 99.9%
-Potassium iodide manufactured by Wako Pure Chemical Industries, Ltd., purity 99.5%
-Sodium iodide manufactured by Wako Pure Chemical Industries, Ltd., purity 99.5%
-Copper iodide (I) manufactured by Wako Pure Chemical Industries, Ltd., purity 95%
-Wako Pure Chemical Industries, Ltd. copper (I) chloride, purity 99.9%

  In addition, the physical-property value in an Example was measured by the method described below.

(1) Intrinsic viscosity of polyester ([η], unit: dl / g)
Using orthochlorophenol (OCP) as a solvent, a 7% solution was prepared and measured at 25 ° C.

(2) Carboxyl terminal group amount of polyester (unit: eq / t)
Orthocresol was used as a solvent, a 0.02 N NaOH aqueous solution was adjusted at 25 ° C., and measured with an automatic titrator (COM-550, manufactured by Hiranuma Sangyo Co., Ltd.).

(3) Gelation rate (unit:%)
1 g of polyester was pulverized with a freeze pulverizer (Splex CertiPerp, 6750-115) to form a powder having a diameter of 300 μm or less, and then vacuum-dried (Tokyo Rika Kikai Co., Ltd., VOS-451SD). It was vacuum-dried at ° C for 12 hours. Then, what was heat-processed for 6 hours at 300 degreeC in oxygen 1% atmosphere in oven (the Yamato Scientific company make, DN410I) was dissolved in 50 ml OCP at the temperature of 150 degreeC for 0.5 hour. Subsequently, it is filtered with a Buchner type glass filter (maximum pore size 20-30 μm), washed and vacuum dried. The weight of the OCP insoluble matter remaining on the filter was calculated from the increase in the weight of the filter before and after filtration, and the weight fraction of the OCP insoluble matter relative to the weight of the polyester resin (1 g) was determined to obtain the gelation rate (%).

Example 1
After melting 0.05 mg of magnesium acetate in terms of magnesium atom in 100% by weight of DMT and 60 parts by weight of EG and 100 g of the obtained polymer in a nitrogen atmosphere at 150 ° C., the temperature was raised to 240 ° C. over 4 hours with stirring. Then, methanol was distilled off and transesterification was performed to obtain bis (hydroxyethyl) terephthalate (BHT).

  After BHT was put into a test tube and kept in a molten state at 250 ° C., 0.2 mmol of antimony trioxide in terms of antimony atoms per 100 g of the obtained polymer, and 0.1 mmol of phosphoric acid in terms of phosphorus atoms per 100 g of the resulting polymer Trimethyl, 0.26 mmol of 99.5% pure copper (I) iodide in terms of copper atom was added per 100 g of the resulting polymer. In addition, copper iodide (I) was mixed with EG at a weight ratio of 7/100 30 minutes before addition, and stirred at room temperature for 30 minutes, and then the mixture was added. The reaction was started after 5 minutes had passed since each compound was added. While gradually raising the temperature in the reactor from 250 ° C. to 290 ° C. over 60 minutes, the pressure was reduced from normal pressure to 40 Pa over 60 minutes, and a polymerization reaction was performed at 290 ° C. and 40 Pa for a predetermined time. After the completion of the polymerization reaction, the melt was discharged in a strand form, cooled, and immediately cut to obtain pellets. Using the obtained pellets, the intrinsic viscosity, the amount of carboxyl end groups, and the gelation rate were measured. The results are shown in Table 1.

Example 2
Example 1 was repeated except that the amount of copper (I) iodide added was changed.

Examples 3-6
The procedure was the same as Example 1 except that the additive was changed from copper (I) iodide to that shown in Table 1.

Comparative Example 1
The procedure was the same as Example 1 except that copper (I) iodide was not added.

Comparative Examples 2 and 3
The procedure was the same as Example 1 except that the additive was changed from copper (I) iodide to that shown in Table 1.

  In Examples 1 to 6 of the present invention, a polymer can be efficiently obtained in a short time as compared with Comparative Examples 1 to 3, and both the carboxyl end group amount and the gelation rate were low. In Examples 1 and 2, both the carboxyl end group amount and the gelation rate showed particularly low values.

Claims (7)

A polyester resin obtained using a dicarboxylic acid or an alkyl ester of dicarboxylic acid and a diol as a main raw material and containing a metal halide represented by the following formula (i) and having a purity higher than 95%.
(I) MX _n (M: alkali metal or copper, X: bromine or iodine, n = 1 or 2) The polyester resin according to claim 1, comprising 0.1 to 3 mmol of the metal halide per 100 g of the polyester resin. The polyester resin according to claim 1 or 2, wherein the dicarboxylic acid or dicarboxylic acid alkyl ester is an aromatic dicarboxylic acid or an aromatic dicarboxylic acid alkyl ester, and the diol is ethylene glycol. In a method for producing a polyester resin in which dicarboxylic acid or dicarboxylic acid alkyl ester and diol are esterified or transesterified and then polymerized, a metal halide represented by the following formula (i) and having a purity higher than 95% is added. A method for producing a polyester resin, comprising:
(I) MX _n (M: alkali metal or copper, X: bromine or iodine, n: 1 or 2) The method for producing a polyester resin according to claim 4, wherein the metal halide is added so as to be 0.1 to 3 mmol per 100 g of the polyester resin. 6. The method for producing a polyester resin according to claim 4, wherein the metal halide is added at the start of the polymerization reaction. The method for producing a polyester resin according to any one of claims 4 to 6, wherein the dicarboxylic acid or the dicarboxylic acid alkyl ester is an aromatic dicarboxylic acid or an aromatic dicarboxylic acid alkyl ester, and the diol is ethylene glycol.