Polyester resin and method for producing the same

Abstract

To provide: a polyester resin having a sufficient intrinsic viscosity for processing and containing little antimony-based foreign materials; and a method for producing the same.SOLUTION: There is provided a polyester resin and a film, the polyester comprising ethylene glycol as the main diol component and terephthalic acid as the main dicarboxylic acid component, in which the amount of antimony-based foreign materials is 0.1 mass ppm or less in a polyester. Also provided is a method for producing a polyester resin comprising the following steps in this order: [Step 1] a step of producing a polyester resin having an intrinsic viscosity of 0.52 to 0.59 dl / g by melt polymerization by using terephthalic acid as the main dicarboxylic acid component, ethylene glycol as the main diol component and an antimony compound as the main polymerization catalyst; and [Step 2] a step of producing a polyester resin having an intrinsic viscosity of 0.59 to 0.75 dl / g by the solid-phase polymerization of the polyester resin obtained in Step 1 at 197 to 225°C for 5 to 10 hours.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyester resin containing less antimony-based foreign matter and a method for producing the same. [Background technology]

[0002] Polyester resins have excellent mechanical and chemical properties, and depending on the properties of each polyester resin, they are used in a wide range of fields, such as fibers for clothing and industrial materials, films and sheets for packaging, magnetic tape, and optics, hollow molded bottles, casings for electrical and electronic components, and other engineering plastic molded products.

[0003] Among these applications, optical films and release films have recently seen an increase in demand, resulting in the demand for higher quality. Antimony compounds are widely used as polymerization catalysts because they are inexpensive and have excellent polymerization activity, but they also precipitate a certain amount of antimony-based impurities in the resin, causing blackening and other impurities. This affects the quality of polyester resins and their processed products. The antimony-based impurities consist of metallic antimony.

[0004] Germanium compounds have already been put to practical use as catalysts that can produce polyester resins free from the above-mentioned problems, but they have the problems of being very expensive and of being easily distilled out of the reaction system during polymerization, which changes the catalyst concentration in the reaction system and makes it difficult to control the polymerization.

[0005] Studies are also being conducted on polymerization catalysts that can replace antimony compounds or germanium compounds, and titanium compounds, such as tetraalkoxy titanates, have already been proposed. However, polyester resins produced using titanium compounds are susceptible to thermal degradation during melt molding and suffer from significant coloration.

[0006] Furthermore, a catalyst system consisting of an aluminum compound and a phosphorus compound has been disclosed as a new polymerization catalyst and has attracted attention (see, for example, Patent Documents 1 and 2). By using this polymerization catalyst, a polyester resin with good color tone, transparency, and thermal stability can be obtained, but this method has the problem of high catalyst cost required for polymerization because the amount of catalyst added is large and the cost of the phosphorus compound used is also high. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2007 / 032325 Brochure [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-169432 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above-mentioned problems of the prior art, and aims to provide a polyester resin having an intrinsic viscosity sufficient for processing and containing little antimony-based foreign matter, and a method for producing the same. [Means for solving the problem]

[0009] As a result of extensive investigations to solve the above-mentioned problems, the present inventors discovered that the object can be achieved by adjusting the amount of elemental antimony contained in a polyester resin, polymerizing the polyester resin by melt polymerization to a specific viscosity, and then polymerizing the polyester resin by solid-state polymerization to a target viscosity, thereby arriving at the present invention.

[0010] The present invention comprises the following configurations.

[0011] [1] A polyester resin containing ethylene glycol as the main diol component and terephthalic acid as the main dicarboxylic acid component, the polyester being produced using an antimony compound as a polymerization catalyst, in which the amount of antimony-based foreign matter is 0.1 ppm by mass or less. [2] A method for producing the polyester resin described in claim 1, comprising the following steps in this order: [Step 1] A step of producing a polyester resin having an intrinsic viscosity of 0.52 to 0.59 dL / g by melt polymerization using terephthalic acid as the main dicarboxylic acid component, ethylene glycol as the main diol component, and an antimony compound as the main polymerization catalyst. [Step 2] A step of solid-state polymerizing the polyester resin obtained in step 1 at 197 to 225°C for 5 to 10 hours to produce a polyester resin having an intrinsic viscosity of 0.59 to 0.75 dl / g. [3] A film made of the polyester resin described in [1]. [Effects of the Invention]

[0012] According to the present invention, a polyester resin is obtained using an antimony compound as a main polymerization catalyst, and the polyester resin can reduce catalyst costs while suppressing the generation of antimony-based foreign matter. Furthermore, a film using the polyester resin of the present invention has a low content of antimony-based foreign matter and exhibits high quality with good transparency. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below.

[0014] The polyester resin of the present invention is mainly composed of ethylene glycol as a diol component and terephthalic acid as a dicarboxylic acid component, and contains antimony-based foreign matter in an amount of 0.1 ppm or less based on the weight of the polyester resin.

[0015] The polyester resin of the present invention is a polyester resin comprising at least one selected from polycarboxylic acids and their ester-forming derivatives, and at least one selected from polyhydric alcohols and their ester-forming derivatives.

[0016] The polyester resin of the present invention preferably contains a dicarboxylic acid or an ester-forming derivative thereof as the main polycarboxylic acid, and a diol or an ester-forming derivative thereof as the main polyhydric alcohol.

[0017] The present invention relates to a polyester resin in which the main dicarboxylic acid component is terephthalic acid, and which may contain a dicarboxylic acid component other than terephthalic acid, where "mainly" means that the dicarboxylic acid component accounts for 70 mol% or more of the total dicarboxylic acid components.

[0018] Examples of dicarboxylic acid components other than terephthalic acid include saturated aliphatic dicarboxylic acids or ester-forming derivatives thereof, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, tetradecanedicarboxylic acid, hexadecanedicarboxylic acid, 1,3-cyclobutanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,5-norbornanedicarboxylic acid, and dimer acid; and unsaturated aliphatic dicarboxylic acids, such as fumaric acid, maleic acid, and itaconic acid. aliphatic dicarboxylic acids or ester-forming derivatives thereof; aromatic dicarboxylic acids such as orthophthalic acid, isophthalic acid, 5-(alkali metal)sulfoisophthalic acid, diphenic acid, 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 4,4'-biphenylsulfonedicarboxylic acid, 4,4'-biphenyletherdicarboxylic acid, 1,2-bis(phenoxy)ethane-p,p'-dicarboxylic acid, pamoic acid, and anthracenedicarboxylic acid, or ester-forming derivatives thereof.

[0019] The polyester resin in which the main dicarboxylic acid component is terephthalic acid is preferably a polyester resin containing 70 mol% or more of the terephthalic acid component, more preferably 80 mol% or more, and even more preferably 90 mol% or more, when the total dicarboxylic acid components are taken as 100 mol%.

[0020] The present invention relates to a polyester resin in which the main diol component is ethylene glycol, and may contain a diol component other than ethylene glycol, where "mainly" means that the diol component is contained in an amount of 70 mol % or more.

[0021] Examples of diol components other than ethylene glycol include alkylene glycols such as 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediethanol, 1,10-decamethylene glycol, and 1,12-dodecanediol; polyalkylene glycols exemplified by glycol, triethylene glycol, polyethylene glycol, polytrimethylene glycol, polytetramethylene glycol, and the like; aromatic diols exemplified by hydroquinone, 4,4'-dihydroxybisphenol, 1,4-bis(β-hydroxyethoxy)benzene, 1,4-bis(β-hydroxyethoxyphenyl)sulfone, bis(p-hydroxyphenyl)ether, bis(p-hydroxyphenyl)sulfone, bis(p-hydroxyphenyl)methane, 1,2-bis(p-hydroxyphenyl)ethane, bisphenol A, bisphenol C, 2,5-naphthalenediol, glycols in which ethylene oxide is added to these glycols, and the like.

[0022] The polyester resin having ethylene glycol as the main diol component is preferably a polyester resin containing 80 mol % or more of ethylene glycol, more preferably 90 mol % or more, and even more preferably 95 mol % or more, when the total diol components are taken as 100 mol %.

[0023] The polyester resin of the present invention is produced using an antimony compound as the main polymerization catalyst, where "main" means 60% by mass or more of the total catalyst amount.

[0024] Examples of antimony compounds include antimony trioxide, antimony pentoxide, antimony acetate, and antimony salts of aliphatic carboxylic acids. Among these, antimony trioxide is preferably used in view of its polycondensation reactivity, the color tone of the resulting polymer, and its inexpensive availability.

[0025] In the method for producing a polyester resin of the present invention, in addition to the antimony compound described above as a polymerization catalyst, conventionally known transesterification catalysts, polymerization catalysts, co-catalysts, such as germanium compounds and titanium compounds, or organic compound-based polymerization catalysts may be used in combination within a range that does not adversely affect the properties of the polyester resin obtained by the production method of the present invention. The amount of catalysts other than the antimony compound is preferably 40% by mass or less, more preferably 20% by mass or less, and even more preferably 5% by mass or less, based on the total amount of all catalysts.

[0026] Furthermore, various compounds and additives may be added to the polyester resin of the present invention depending on the intended use of the polyester resin, within the range that does not cause any problems in achieving the objects of the present invention.

[0027] The method for producing a polyester resin of the present invention includes the following steps in this order: [Step 1] A step of producing a polyester resin having an intrinsic viscosity of 0.52 to 0.59 dl / g by melt polymerization using terephthalic acid as the dicarboxylic acid component, ethylene glycol as the diol component as the main components, and an antimony compound as the main polymerization catalyst. [Step 2] A step of solid-state polymerizing the polyester resin obtained in step 1 at 197 to 225°C for 5 to 10 hours to produce a polyester resin having an intrinsic viscosity of 0.59 to 0.75 dl / g.

[0028] The melt polymerization may be a batch polymerization method or a continuous polymerization method. In either method, the esterification reaction or transesterification reaction may be carried out in one stage, but is preferably carried out in multiple stages. In the melt polymerization reaction, the number and size of reactors and the production conditions for each step can be selected as appropriate without any limitations. The melt polymerization reaction may be carried out in one stage or in multiple stages, preferably in two to five stages, more preferably in three to four stages, and even more preferably in three stages. The melt polymerization reaction is preferably carried out in a continuous reactor. A continuous reactor is a method in which a reaction vessel for the esterification reaction or transesterification reaction and a melt polymerization reaction vessel are connected by piping, and raw materials are continuously introduced into each reaction vessel without emptying, transferred to the melt polymerization reaction vessel via the piping, and the resin is withdrawn from the melt polymerization reaction vessel.

[0029] The steps of the continuous polymerization method are as follows.

[0030] 1) Slurry preparation process A dicarboxylic acid component and a diol component are introduced into a slurry preparation tank to prepare a slurry. The content ratio of these components in the slurry is not particularly limited as long as the slurry has sufficient fluidity to be transported to an esterification reaction tank. From an economical viewpoint, it is preferable to reuse the diol component recovered in the polycondensation step as a slurry raw material. In the present invention, recycled raw materials such as dicarboxylic acid components and diol components obtained by chemical decomposition and recovery methods may also be used.

[0031] 2) Esterification reaction process The slurry obtained above is introduced into two or more esterification reaction vessels connected in series and subjected to an esterification reaction to obtain an oligomer compound in which a diol is condensed with both terminal carboxyl groups of a dicarboxylic acid component. The esterification reaction is preferably carried out while removing water produced by the reaction from the system using a distillation column.

[0032] The number and size of the reaction vessels in the esterification reaction step can be appropriately selected without any limitations. The production conditions for each step can be appropriately selected depending on the type and amount of the polycondensation catalyst and the additive for improving electrostatic adhesion, the number and size of the reaction vessels, etc. For example, in the case of a system having three esterification reaction tanks, the temperature of the first esterification reaction tank is 240 to 270°C, the pressure is 100 to 160 kPa (gauge pressure), and the average residence time is 2 to 5 hours. The temperature of the second and third esterification reaction tanks is 250 to 280°C, the pressure is 0 to 100 kPa (gauge pressure), and the average residence time is 0.1 to 2.5 hours. It is desirable that the final esterification reaction rate reaches 60% or more, preferably 70% or more. Furthermore, the esterification reaction tank may be a multi-stage reaction tank provided with a weir or the like inside.

[0033] In the esterification step, it is preferable to additionally supply the diol component after the second esterification reaction tank. If the entire amount of the supplied diol component is used for esterification using the diol component used for preparing the slurry, problems may arise in that the diol component composition in the polyester resin fluctuates or the esterification reaction rate decreases during long-term continuous production. These problems can be prevented by additionally supplying the diol component after the second esterification reaction tank.

[0034] The polyester resin of the present invention is a polyester resin suitable for film molding, and may contain a phosphorus compound, an alkali metal, an alkaline earth metal, or the like to impart electrostatic adhesion during film formation. The timing of addition may be any time from before the esterification reaction to the start of the polycondensation reaction, but in the case of a continuous polymerization method, addition is preferably made after the third esterification reaction tank.

[0035] When the polyester resin of the present invention is produced by a batch polymerization method or a continuous polymerization method, the antimony compound may be added in the form of a powder, an ethylene glycol slurry, an ethylene glycol solution, etc., but it is preferably added as an ethylene glycol solution. The timing of addition may be either before the esterification reaction and the ester exchange reaction, or between the end of the ester exchange reaction and the esterification reaction and the start of the polycondensation reaction.

[0036] 3) Polycondensation reaction process The oligomer compound that has undergone the esterification reaction is subsequently transferred to a polycondensation reaction vessel where the polycondensation reaction is carried out.

[0037] The number and size of the reaction vessels in the polycondensation reaction step can be appropriately selected without any limitations. The production conditions for each step can be appropriately selected depending on the types and amounts of the polycondensation catalyst and additives, the number and size of the reaction vessels, etc. For example, in the case of a system having three polycondensation reaction tanks, the temperature of the first polycondensation reaction tank is 260 to 290°C, the pressure is 2 to 8 kPa, and the average residence time is 0.1 to 1.5 hours. The temperature of the second polycondensation reaction tank is 270 to 290°C, the pressure is 0.5 to 1.5 kPa, and the average residence time is 0.1 to 2 hours. The temperature of the third polycondensation reaction tank is 270 to 290°C, the pressure is 0.01 to 0.5 kPa, and the average residence time is 0.1 to 2 hours. It is preferable that the degree of increase in intrinsic viscosity achieved in each of these polycondensation reaction steps is smoothly distributed.

[0038] In the polycondensation reaction step, the diol component is distilled, and it is preferable to recover, purify, and reuse the diol component. This recovery and purification can be carried out in a distillation column, as in the esterification reaction step.

[0039] The intrinsic viscosity of the polyester resin produced by melt polymerization of the present invention is preferably 0.52 to 0.59 dL / g, more preferably 0.52 to 0.55 dL / g. When the intrinsic viscosity of the polyester resin is within the above range, the effect of suppressing foreign matter and the color tone are good.

[0040] In order to suppress the generation of antimony-based foreign matters in the polyester resin of the present invention, it is preferable to increase the intrinsic viscosity of the polyester resin produced by melt polymerization by solid-phase polymerization.

[0041] The solid-state polymerization is carried out on a polyester resin in the form of granules, which may be chips, pellets, flakes, or powder, with pellets being preferred.

[0042] The solid-state polymerization is carried out by heating the granular polyester resin at a temperature below the melting point of the polyester resin in an inert gas flow or under reduced pressure. The solid-state polymerization is preferably carried out under reduced pressure. The solid-state polymerization process may be carried out in one stage or in multiple stages. The particulate polyester resin to be supplied to the solid-state polymerization step is preferably crystallized by heating it to a temperature lower than the temperature at which solid-state polymerization is carried out, and then supplied to the solid-state polymerization step.

[0043] The crystallization step is preferably carried out by heating the granular polyester at a temperature of 70 to 90°C for 3 to 5 hours to dry it, and then heating it at a temperature of usually 120 to 200°C, preferably 130 to 150°C, for 1 to 4 hours.

[0044] The method for producing a polyester resin of the present invention is characterized in that a polyester resin produced by melt polymerization is subjected to solid-state polymerization at 197 to 225°C for 5 to 10 hours. Prior to the solid-state polymerization, it is preferable to dry and crystallize the polyester resin produced by melt polymerization. By carrying out solid-state polymerization within the above range, it is possible to achieve an intrinsic viscosity suitable for the intended use of the polyester resin.

[0045] The intrinsic viscosity of the polyester resin produced by solid-state polymerization is preferably 0.59 to 0.75 dL / g, more preferably 0.60 to 0.70 dL / g. When the intrinsic viscosity of the polyester resin is within the above range, film formability and recyclability are improved.

[0046] The present invention makes it possible to suppress antimony-based foreign matter by undergoing the above-mentioned melt polymerization step and solid-state polymerization step.

[0047] Antimony-based contaminants primarily refer to metallic antimony present in polyester resins, which is thought to be generated by the thermal decomposition of antimony compounds in the polymerization catalyst at high temperatures. The metallic antimony is insoluble in solvents, and can be isolated from the polyester resin by dissolving the polyester resin in a specific solvent and filtering it, and then quantitatively determined.

[0048] The method for quantifying antimony-based foreign matter is as follows. The polyester resin pellets were dissolved in a p-chlorophenol / tetrachloroethane mixed solution, and the solution was filtered through a membrane filter to capture antimony-based contaminants. Antimony was then eluted from the membrane filter using hydrochloric acid, and the mass of antimony element contained in the eluted solution was quantified using an ICP emission spectrometer. This was then divided by the mass of the polyester resin pellets to obtain the amount of antimony-based contaminants (unit: mass ppm).

[0049] The antimony-based contaminants quantified by the above method are preferably 0.1 ppm or less, more preferably 0.05 ppm or less. When the antimony-based contaminants are 0.1 ppm or less, the color tone is good and the quality of processed polyester resin products is not impaired.

[0050] The present invention relates to a polyester resin containing little foreign matter derived from a polymerization catalyst, and a method for producing the same. The polyester resin can be suitably used for various applications such as films, fibers, and molded articles. In particular, polyester films using the polyester resin of the present invention can be used for films that require high quality, such as optical films and release films. Therefore, the polyester resin of the present invention is suitable for being formed into a film.

[0051] The method for forming the film is not particularly limited, and any known method can be used. For example, a polyester resin is melted at a temperature equal to or higher than the melting point of the polyester resin, and then extruded to obtain a polyester resin sheet, which is then stretched to obtain a polyester resin film. More specifically, a method for obtaining a polyester resin film includes melt-extruding a polyester resin into a film at 250 to 320°C, solidifying the film to form an amorphous sheet, sequentially or simultaneously biaxially stretching the film in the longitudinal and transverse directions at 70 to 140°C, or uniaxially stretching the film in the longitudinal or transverse direction, and then heat-treating the film at 160 to 240°C. Typically, the stretching temperature is preferably 80 to 140°C, and the stretching ratio is selected from the range of 1.1 to 10 times in both the longitudinal and transverse directions. The thickness of the polyester resin film is typically about 1 to 300 μm. The polyester resin film obtained above is also preferably used as a member in a display. [Example]

[0052] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The evaluation methods used in each example and comparative example are as follows.

[0053] (1) Measurement of intrinsic viscosity of polyester resin The polyester resin was dissolved in a mixed solvent of p-chlorophenol / tetrachloroethane (3 / 1: weight ratio), and the viscosity was measured at 30°C using an Ostwald viscometer.

[0054] (2)Measurement method for amount of foreign matter Ten grams of polyester resin pellets were weighed and placed in an Erlenmeyer flask with 80 ml of a p-chlorophenol / tetrachloroethane (3:1 by weight) mixed solution. The flask was then capped and stirred at 135°C for 2 hours to dissolve the mixture. The entire mixed solution was filtered under reduced pressure using a 47 mm diameter / 0.5 μm pore size polytetrafluoroethylene (PTFE) membrane filter (Advantec PTFE membrane filter, part number: T050A430A). After filtration, the membrane filter was washed with 10 ml of chloroform and then dried at 80°C for 1 hour. The resulting membrane filter was immersed in 20 ml of 1.2 N hydrochloric acid and heated for 3 hours. The resulting eluate was cooled and then introduced into an ICP optical emission spectrometer (Hitachi High-Tech Science Corporation, SPECTROBLUE) to quantify the total antimony content in the solution. This was then divided by the mass of the polyester resin pellets and expressed in ppm.

[0055] The evaluation criteria for the amount of antimony-based foreign matter were as follows: 〇: The amount of antimony remaining on the filter after filtration is 0.1 mass ppm or less △: The amount of antimony element remaining on the filter after filtration is more than 0.1 mass ppm and less than 0.2 ppm ×: The amount of antimony element remaining on the filter after filtration is 0.2 mass ppm or more

[0056] Example 1 <Production of polyester resin (melt polymerization)> (Slurry preparation) A slurry was prepared by continuously feeding 0.71 parts by mass of ethylene glycol per 1 part by mass of terephthalic acid into a slurry preparation tank while stirring under a nitrogen flow.

[0057] (Esterification reaction) The esterification reaction apparatus used was a continuous esterification reaction apparatus consisting of a three-stage complete mixing vessel equipped with a stirrer, a distillation column, a raw material inlet, and a product outlet. The glycol slurry of terephthalic acid prepared above and an ethylene glycol solution of antimony trioxide (antimony concentration: 12 g / L) were supplied to the first esterification reaction vessel, and the esterification reaction was carried out under pressure. The reaction liquid was removed from the first esterification reactor so that the liquid level in the first esterification reactor was kept constant, and then the liquid was introduced into the second esterification reactor. Ethylene glycol was continuously introduced into the second esterification reactor through another inlet, and the esterification reaction was further carried out under atmospheric pressure. The reaction liquid was removed so that the liquid level in the second esterification reactor was constant, and then poured into the third esterification reactor. In the third esterification reactor, equal amounts of magnesium acetate, sodium acetate, and ethylene glycol solution of trimethyl phosphate were each poured into separate inlets, and the mixture was stirred under normal pressure.

[0058] (Polycondensation reaction) The reaction liquid was removed so that the liquid level in the third esterification reaction tank remained constant, and then poured into the first polycondensation reaction tank, where the first polycondensation reaction was carried out under a reduced pressure of 5.6 kpa. The reaction liquid was removed from the first polycondensation reaction tank so that the liquid level in the first polycondensation reaction tank was kept constant, and then poured into the second polycondensation reaction tank. The second polycondensation reaction was carried out under a reduced pressure of 0.75 kPa. The reaction liquid was removed so that the liquid level of the second polycondensation product remained constant, and then poured into the third polycondensation reactor. The degree of vacuum (pressure) was adjusted so that the average intrinsic viscosity of the reaction product was 0.53 dL / g. The pressure was in the range of 0.08 to 0.15 kPa.

[0059] (pelletization) The polyester resin obtained through the above process was extruded into a strand shape, cooled in water, and then cut into pellets.

[0060] <Production of polyester resin (solid-state polymerization)> The polyester resin obtained by melt polymerization was placed in a solid-state polymerization apparatus. After drying at 90°C for 3.5 hours, it was crystallized at 130°C for 4.5 hours. The temperature was then gradually increased from 197°C to 220°C, and solid-state polymerization was carried out at a pressure of 40 Pa for 7 hours, yielding a polyester resin with an intrinsic viscosity of 0.617 dL / g.

[0061] Example 2 A polyester resin was obtained in the same manner as in Example 1, except that the solid-phase polymerization time was changed to 9 hours.

[0062] (Examples 3 to 4, Comparative Examples 2 to 4) A polyester resin was obtained in the same manner as in Example 1, except that the polyester resin was pelletized when the viscosity of the polyester resin produced by melt polymerization reached the viscosity shown in Table 1, and the pelletized polyester resin was subjected to solid-state polymerization for the solid-state polymerization time shown in Table 1.

[0063] (Comparative Example 1) When the viscosity of the polyester resin produced by melt polymerization without solid-state polymerization reached the viscosity shown in Table 1, the polyester resin was pelletized to obtain the polyester resin.

[0064] [Table 1]

[0065] The polyester resins of Examples 1 to 4 were obtained by combining melt polymerization and solid-phase polymerization, and thus had an intrinsic viscosity sufficient for film formation, and it was possible to achieve an antimony-based foreign matter content within the target range. In Comparative Example 1, the target viscosity after solid-state polymerization of the present invention was achieved by solution polymerization alone, without solid-state polymerization. The amount of antimony-based foreign matter exceeded 0.1 ppm, resulting in poor quality. In Comparative Example 2, the viscosity of the product produced by melt polymerization was higher than 0.59 dL / g, which was outside the range of [Step 1] of the present invention, and this was then solid-state polymerized within the range of [Step 2] of the present invention. The amount of antimony-based impurities exceeded 0.1 ppm, resulting in poor quality. In Comparative Example 3, both the viscosity produced by melt polymerization and the time of solid-state polymerization were outside the ranges of the present invention, the amount of foreign matter exceeded 0.1 ppm, and the intrinsic viscosity after solid-state polymerization was much higher than 0.75 dL / g, resulting in significantly poor processability and quality. [Industrial Applicability]

[0066] The polyester resin of the present invention has an intrinsic viscosity sufficient for processing and contains little antimony-based foreign matter, and therefore can be suitably used in applications requiring particularly high quality, such as optical films and release films.

Claims

1. A polyester resin containing ethylene glycol as a main diol component, terephthalic acid as a main dicarboxylic acid component, and an antimony compound as a polymerization catalyst, the polyester resin having an antimony-based foreign matter content of 0.1 ppm by mass or less.

2. 2. A method for producing the polyester resin according to claim 1, comprising the following steps in this order: [Step 1] A step of producing a polyester resin having an intrinsic viscosity of 0.52 to 0.59 dL / g by melt polymerization using terephthalic acid as a dicarboxylic acid component as a main component, ethylene glycol as a diol component as a main component, and an antimony compound as a main polymerization catalyst. [Step 2] The polyester resin obtained in Step 1 is subjected to solid-state polymerization at 197 to 225°C for 5 to 10 hours to produce a polyester resin having an intrinsic viscosity of 0.59 to 0.75 dl / g.

3. A film comprising the polyester resin according to claim 1.

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