TW202602995A - Polyester resin and its manufacturing method - Google Patents

Abstract

[Topic] To provide a polyester resin with an inherent viscosity sufficient for processing and low antimony impurities, and a method for manufacturing the same. [Solution] A polyester resin comprising ethylene glycol as the main diol component and terephthalic acid as the main dicarboxylic acid component, wherein the antimony impurity content is below 0.1 ppm by mass; and a film. A method for manufacturing the polyester resin comprises the following steps in the following order: [Step 1] 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, a polyester resin with an inherent viscosity of 0.52~0.59 dl/g is produced by melt polymerization. [Step 2] The polyester resin obtained in Step 1 is subjected to solid-state polymerization at 197~225℃ for 5~10 hours to produce a polyester resin with an intrinsic viscosity of 0.59~0.75dl/g.

Description

Polyester resin and its manufacturing method

This invention relates to a polyester resin with low antimony impurities and a method for manufacturing the same.

Polyester resins possess excellent mechanical and chemical properties, and are used in a wide range of fields depending on their properties, such as: fibers for clothing and industrial materials; films and sheets for packaging, magnetic tapes, and optical applications; bottles for hollow molding; protective covers for electrical and electronic components; and other engineering plastic molded products.

Among these applications, optical films and release films, in particular, have seen increased demand in recent years, leading to higher quality requirements. However, while antimony compounds are widely used as polymerization catalysts due to their low cost and excellent polymerization activity, a certain amount of antimony impurities can precipitate into the resin, causing black spots and other impurities. This affects the quality of polyester resins and their processed products. Antimony impurities are composed of metallic antimony.

Regarding catalysts that provide polyester resins without the aforementioned problems, germanium compounds are already being put into practical use. However, they have the problems of being very expensive and the tendency to extract from the reaction system during polymerization, which alters the catalyst concentration and makes polymerization difficult to control.

There is also research into polymerization catalysts that can replace antimony or germanium compounds, and a titanium compound represented by tetraalkoxytitanium ester has been proposed. However, polyester resins made using titanium compounds are prone to thermal degradation during melt molding, or there is a problem of significant coloring of the polyester resin.

Furthermore, regarding novel polymerization catalysts, a catalyst system composed of aluminum and phosphorus compounds has been disclosed and has attracted considerable attention (see, for example, patents 1 and 2). By using this polymerization catalyst, polyester resins with good color, transparency, and thermal stability can be obtained. However, this method suffers from the problem of increased catalyst cost due to the large amount of catalyst added and the high cost of the phosphorus compounds used. [Prior Art Documents] [Patents]

Patent Document 1: International Publication No. 2007/032325; Patent Document 2: Japanese Patent Application Publication No. 2006-169432

[Problem Solved by the Invention] This invention addresses the problems of the prior art described above, providing a polyester resin with an inherent viscosity sufficient for processing and low antimony impurities, as well as a method for manufacturing the same. [Means for Solving the Problems]

As a result of the inventors' dedicated research in order to solve the above-mentioned problems, they discovered that by adjusting the amount of antimony contained in the polyester resin, polymerizing it to a specific viscosity by melt polymerization, and then polymerizing it to the target viscosity by solid-state polymerization, the purpose can be achieved, thus completing the present invention.

This invention comprises the following components.

[1] A polyester resin comprising ethylene glycol as the main diol component, terephthalic acid as the main dicarboxylic acid component, and an antimony compound as the polymerization catalyst, wherein the antimony impurity content is below 0.1 ppm by mass. [2] A method for manufacturing the polyester resin of claim 1, comprising the following steps in the following order: [Step 1] 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, a polyester resin with an intrinsic viscosity of 0.52 to 0.59 dl/g is produced by melt polymerization. [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 with an intrinsic viscosity of 0.59 to 0.75 dl/g. [3] A thin film composed of a polyester resin as described in [1]. [Invention Effect]

According to the present invention, it is a polyester resin obtained by using an antimony compound as the main polymerization catalyst. This polyester resin can suppress the generation of antimony impurities while also reducing catalyst costs. Furthermore, films using the polyester resin of the present invention have fewer antimony impurities and exhibit high quality with excellent transparency.

[Forms for Implementing the Invention] The invention will now be described in detail.

The polyester resin of this invention uses ethylene glycol as a diol component and terephthalic acid as a dicarboxylic acid component as the main components, and the antimony impurities relative to the weight of the polyester resin are less than 0.1 ppm.

The polyester resin of the present invention is a polyester resin composed of at least one selected from polycarboxylic acids and their ester-forming derivatives and at least one selected from polyols and their ester-forming derivatives.

With regard to the polyester resin of the present invention, it is preferred to use dicarboxylic acids and their ester-forming derivatives as the main polycarboxylic acids and diols and their ester-forming derivatives as the main polyols.

The present invention primarily comprises a polyester resin of terephthalic acid as its dicarboxylic acid component, but may also contain dicarboxylic acid components other than terephthalic acid. Here, "primarily" means that it contains more than 70 mol% of the total dicarboxylic acid component.

Examples of dicarboxylic acids other than terephthalic acid include: saturated aliphatic dicarboxylic acids or their ester-forming derivatives listed below, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, 1,3-cyclosuccinic acid, 1,3-cyclopentadicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,5-norcamphenic acid, and dimer acids; and unsaturated aliphatic dicarboxylic acids or their ester-forming derivatives listed below. Substances such as fumaric acid, maleic acid, and methylene succinic acid; aromatic dicarboxylic acids, or their ester-forming derivatives, listed below, including phthalic acid, isophthalic acid, 5-(alkali metal)sulfonic acid isophthalic acid, 2,2’-biphenyl dicarboxylic acid, 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4’-biphenyl dicarboxylic acid, 4,4’-diphenyl ether dicarboxylic acid, 1,2-bis(4-carboxyphenoxy)ethane, pamoic acid, anthracene dicarboxylic acid, etc.

The main dicarboxylic acid component is a polyester resin containing terephthalic acid. When the total dicarboxylic acid component is set to 100 mol%, it is preferable to use a polyester resin containing more than 70 mol% terephthalic acid, more preferably ...

The present invention primarily comprises a polyester resin of ethylene glycol, but may also contain other glycol components besides ethylene glycol. Here, "primarily" means that it contains 70 mol% or more of the glycol component.

Other diols besides ethylene glycol include: 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediethanol, 1,10-decanediol, 1,12-cyclohex ... - Dodecanediol, etc.; polyalkylene glycols, diethylene glycol, triethylene glycol, polyethylene glycol, polytrimethylene glycol, polytetramethylene glycol, etc., as exemplified below; aromatic diols, such as hydroquinone, 4,4'-dihydroxybisphenol, 1,4-bis(β-hydroxyethoxy)benzene, 1,4-bis(β-hydroxyethoxyphenyl) monoxide, bis(p-hydroxyphenyl) ether, bis(p-hydroxyphenyl) monoxide, bis(p-hydroxyphenyl)methane, 1,2-bis(p-hydroxyphenyl)ethane, bisphenol A, bisphenol C, 2,5-naphthalenediol, and diols formed by the addition of these diols to ethylene oxide, etc.

The main glycol component is a polyester resin containing ethylene glycol. When the total glycol component is set to 100 mol%, it is preferable to use a polyester resin containing more than 80 mol% ethylene glycol, more preferably ...

The polyester resin of this invention is manufactured using an antimony compound as the primary polymerization catalyst. Here, "primary" means more than 60% by mass of the total catalyst.

Examples of antimony compounds include antimony trioxide, antimony pentoxide, antimony acetate, and antimony salts of aliphatic carboxylic acids. Among these, antimony trioxide is preferred in terms of polymerization reactivity, the color of the resulting polymer, and its availability.

In the method for manufacturing polyester resin of the present invention, in addition to the aforementioned antimony compound, other previously known ester exchange catalysts, polymerization catalysts, co-catalysts, or organic compound-based polymerization catalysts may be used as polymerization catalysts, provided that such use does not cause problems with the properties of the polyester resin obtained by the method of the present invention. The amount of catalyst 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, relative to the total amount of all catalysts.

Furthermore, various compounds and additives can be added to the polyester resin of this invention, within the scope that will not cause problems in achieving the problem of this invention, depending on the use of the polyester resin.

The method for manufacturing the polyester resin of the present invention comprises the following steps in the following order: [Step 1] Using terephthalic acid as the main dicarboxylic acid component, ethylene glycol as the main glycol component, and an antimony compound as the main polymerization catalyst, a polyester resin with an intrinsic viscosity of 0.52~0.59 dl/g is produced by melt polymerization. [Step 2] The polyester resin obtained in Step 1 is subjected to solid-state polymerization at 197~225°C for 5~10 hours to produce a polyester resin with an intrinsic viscosity of 0.59~0.75 dl/g.

Melt polymerization can be either batch polymerization or continuous polymerization. While esterification or transesterification reactions can be carried out in one stage in either method, it is preferable to proceed in multiple stages. In melt polymerization, the number and size of the reactors, as well as the manufacturing conditions of each step, can be appropriately selected without limitation. It can be carried out in one stage, or in multiple stages, preferably 2 to 5 stages, more preferably 3 to 4 stages, and even more preferably 3 stages. The above-mentioned melt polymerization reaction is preferably carried out in a continuous reaction apparatus. A continuous reaction apparatus is a system in which reaction vessels for esterification or transesterification are connected to a melt polymerization reaction vessel via piping, allowing for the continuous feeding of raw materials without emptying the reaction vessels, the transfer of materials to the melt polymerization reaction vessel via piping, and the extraction of resin from the melt polymerization reaction vessel.

The steps for continuous polymerization are as follows.

1) Slurry Preparation Steps: A slurry is prepared by introducing dicarboxylic acid and diol components into a slurry preparation tank. The proportions of these components in the slurry are not particularly limited, as long as the slurry has sufficient flowability to be transported to the esterification reaction tank. Furthermore, it is preferable from an economic point of view to reuse the material recovered in the polymerization step as a slurry feedstock for the diol component. In addition, recycled raw materials such as dicarboxylic acid and diol components obtained through chemical decomposition and recovery methods can also be used in this invention.

2) Esterification reaction step: The slurry obtained above is fed into two or more esterification reaction tanks connected in series to carry out the esterification reaction, resulting in an oligomer compound formed by the condensation of diol onto the two terminal carboxyl groups of the dicarboxylic acid component. Preferably, the esterification reaction is carried out while the water produced by the reaction is discharged from the system using a distillation column.

The number and size of the reaction tanks in the esterification reaction step can be appropriately selected without limitation. Furthermore, the manufacturing conditions for each step can be appropriately selected based on the type and amount of the polymerization catalyst and the additives used to improve electrostatic adhesion, as well as the number and size of the reaction tanks. For example, in the case of a three-tank esterification reaction, the temperature of the first esterification reaction tank is set to 240~270°C, the pressure (measured by a gauge) is set to 100~160 kPa, and the average residence time is set to 2~5 hours. The temperature of the second and third esterification reaction tanks is set to 250~280°C, the pressure (measured by a gauge) is set to 0~100 kPa, and the average residence time is set to 0.1~2.5 hours. The final esterification rate is desired to be above 60%, preferably above 70%. Furthermore, the aforementioned esterification reaction tank can also be a multi-stage reactor with an internal weir or similar structure.

In the esterification step, it is preferable to add the glycol component after the second esterification reaction tank. When the entire amount of glycol component supplied is used for esterification in the preparation of the slurry, problems such as changes in the glycol composition of the polyester resin and a decrease in the esterification reaction rate may occur during long-term continuous production. By adding the glycol component after the second esterification reaction tank, these problems can be suppressed.

The polyester resin of this invention is suitable for film molding. To impart electrostatic adhesion during film formation, phosphorus compounds, alkali metals, alkaline earth metals, etc., can also be added. The addition can be made at any time from before the esterification reaction to the start of the polymerization condensation reaction. In continuous polymerization, it is preferred to add it after the third esterification reaction tank.

In the case of manufacturing the polyester resin of the present invention by batch polymerization and continuous polymerization, the antimony compound can be added in the form of powder, ethylene glycol slurry, or ethylene glycol solution, with the addition in the form of ethylene glycol solution being preferred. The addition can be made at any time before the esterification and transesterification reactions, or at any point between the end of the transesterification and esterification reactions and the start of the polymerization condensation reaction.

3) Polycondensation reaction step: The oligomer compound that has undergone esterification reaction is further fed into the polycondensation reaction tank to carry out the polycondensation reaction.

The number and size of the reaction tanks in the polycondensation reaction step can be appropriately selected without limitation. Furthermore, the manufacturing conditions for each step can be appropriately selected according to the type and amount of the polycondensation catalyst and additives, as well as the number and size of the reaction tanks, as mentioned above. For example, in the case of a three-tank polycondensation reaction, the temperature of the first polycondensation reaction tank is set to 260~290°C, the pressure to 2~8 kPa, and the average residence time to 0.1~1.5 hours. The temperature of the second polycondensation reaction tank is set to 270~290°C, the pressure to 0.5~1.5 kPa, and the average residence time to 0.1~2 hours. The temperature of the third polymerization condensation reaction tank is set to 270~290℃, the pressure to 0.01~0.5kPa, and the average residence time to 0.1~2 hours. The degree of increase in intrinsic viscosity reached in these polymerization condensation reaction steps is preferably distributed smoothly.

Since diols are distilled off during the polymerization reaction, it is preferable to recover, purify, and reuse them. This recovery and purification can be carried out in the same manner as the esterification reaction, using a distillation column.

The polyester resin produced by melt polymerization in this invention preferably has an intrinsic viscosity of 0.52~0.59 dl/g, more preferably 0.52~0.55 dl/g. If the intrinsic viscosity of the polyester resin is within the above range, it has good impurity suppression effect and color tone.

The polyester resin of the present invention, as a method to suppress the generation of antimony impurities, preferably improves the intrinsic viscosity of the polyester resin produced by melt polymerization through solid-phase polymerization.

Solid-state polymerization is performed on polyester resins that are produced in granular form. Granular form refers to fragments, particles, flakes, or powder, preferably granular.

Solid-state polymerization is carried out by heating granular polyester resin at a temperature below its melting point under an inert gas atmosphere or under reduced pressure. The solid-state polymerization is preferably carried out under reduced pressure. The solid-state polymerization step can be carried out in one stage, or it can be divided into multiple stages. The granular polyester resin supplied to the solid-state polymerization step is preferably heated to a temperature lower than the temperature at which the solid-state polymerization is initially carried out and then crystallized before being supplied to the solid-state polymerization step.

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

The present invention's method for manufacturing polyester resin is characterized by solid-state polymerization of the polyester resin produced by melt polymerization at 197-225°C for 5-10 hours. Prior to 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, an inherent viscosity suitable for the application of the polyester resin can be achieved.

The intrinsic viscosity of polyester resin produced by solid-state polymerization is preferably 0.59~0.75 dl/g, more preferably 0.60~0.70 dl/g. If the intrinsic viscosity of the polyester resin is within the above range, the film formability and recyclability are improved.

This invention achieves the ability to suppress antimony impurities through the aforementioned melt polymerization and solid-phase polymerization steps.

Antimony impurities mainly refer to metallic antimony present in polyester resins. Metallic antimony is believed to be generated by the thermal decomposition of antimony compounds in polymerization catalysts at high temperatures. These metallic antimony impurities are insoluble in solvents; they can be separated and quantified from polyester resins by dissolving them in a specific solvent and then filtering.

The quantitative method for antimony impurities is as follows: Polyester resin particles are dissolved in a mixed solution of p-chlorophenol/tetrachloroethane, and the antimony impurities are captured by filtration of the solution through a membrane filter. Next, antimony is dissolved from the membrane filter using hydrochloric acid, and the mass of antimony in the dissolved solution is quantified by ICP emission spectrometry. This quantified antimony mass is then divided by the mass of the polyester resin particles to obtain the antimony impurity mass (unit: ppm).

The antimony impurities quantified by the above method are preferably below 0.1 ppm, and more preferably below 0.05 ppm. If the antimony impurities are below 0.1 ppm, the product will have good color tone and will not impair the quality of the processed polyester resin products.

This invention relates to a low-impurity polyester resin derived from a polymerization catalyst and a method for manufacturing the same. The aforementioned polyester resin is suitable for various applications such as films, fibers, and molded products. In particular, polyester films using the polyester resin of this invention can be used for high-quality films such as optical films and release films. Therefore, the polyester resin of this invention is suitable for film manufacturing.

There are no particular limitations on the method for making thin films, and known methods can be used. For example, polyester resin can be melted at a temperature above its melting point, extruded to obtain a polyester resin sheet, and then stretched to obtain a polyester resin film. More specifically, a method for obtaining a polyester resin film can be described as follows: polyester resin is melted and extruded into a film at 250~320°C, then cured to form an amorphous sheet, and then stretched sequentially in the longitudinal and transverse directions at 70°C~140°C, or simultaneously biaxially, or uniaxially in the longitudinal or transverse directions, and then heat-treated at 160~240°C. Typically, the stretching temperature is preferably 80~140℃, and the stretch ratio can be selected from 1.1 to 10 times in the longitudinal and transverse directions, respectively. The thickness of the polyester resin film is usually around 1~300μm. Using the polyester resin film obtained above as a component in a display is also preferable. [Example]

The present invention will now be illustrated by examples, but the present invention is not limited to these examples. The evaluation methods used in each example and comparative example are described below.

(1) Determination of the intrinsic viscosity of polyester resin: The polyester resin was dissolved in a mixture of p-chlorophenol/tetrachloroethane (3/1: weight ratio) and the viscosity was measured at 30°C using an Oswald viscometer.

(2) Impurity determination method: Weigh 10g of polyester resin particles and place them together with 80ml of a chlorophenol/tetrachloroethane (3:1 weight ratio) mixed solution into an Erlenmeyer flask. After capping, stir and dissolve at 135℃ for 2 hours. Use a polytetrafluoroethylene (PTFE) membrane filter (Advantec PTFE membrane filter, product number: T050A430A) with a diameter of 47mm and a pore size of 0.5μm to filter the entire volume of the mixed solution under reduced pressure. After filtration, clean the membrane filter with 10ml of chloroform and then dry it at 80℃ for 1 hour. The obtained membrane filter was immersed in 20 ml of 1.2N hydrochloric acid and heated for 3 hours. After cooling, the resulting eluent was introduced into an ICP emission spectrometer (Hitachi High-Tech Science Co., Ltd., SPECTROBLUE) to quantify the total amount of antimony in the solution, which was then divided by the mass of polyester resin particles and expressed in ppm.

The evaluation criteria for antimony impurities are as follows: ○: The amount of antimony remaining in the filter after filtration is less than 0.1 ppm. △: The amount of antimony remaining in the filter after filtration is greater than 0.1 ppm but less than 0.2 ppm. ×: The amount of antimony remaining in the filter after filtration is greater than 0.2 ppm.

(Example 1) <Manufacturing of polyester resin (melt polymerization)> (slurry blending) In a slurry preparation tank, 0.71 parts by mass of ethylene glycol are continuously supplied relative to 1 part by mass of terephthalic acid while stirring under nitrogen flow to produce slurry.

(Esterification Reaction) A continuous esterification reaction apparatus consisting of a fully mixing tank with three sections—a stirring device, a distillation column, a feed inlet, and a product outlet—is used as the esterification reaction apparatus. The prepared terephthalic acid glycol slurry, along with an antimony trioxide ethylene glycol solution (antimony concentration: 12 g/L), is fed into the first esterification reaction tank, where the esterification reaction is carried out under pressure. The reaction liquid is removed from the first esterification reaction tank while maintaining a constant liquid level and transferred to the second esterification reaction tank. Ethylene glycol is continuously added from another inlet of the second esterification reaction tank, and the esterification reaction is further carried out under atmospheric pressure. The reaction liquid is removed from the second esterification reaction tank while maintaining a constant liquid level and transferred to the third esterification reaction tank. In the third esterification reaction tank, equal amounts of magnesium acetate, sodium acetate, and trimethyl phosphate in ethylene glycol solution are added through another inlet and stirred under normal pressure.

(Polycondensation Reaction) The reaction liquid is removed from the third esterification reaction tank while maintaining a constant liquid level, and transferred to the first polycondensation reaction tank. The first polycondensation reaction is carried out under reduced pressure of 5.6 kPa. The reaction liquid is then removed from the first polycondensation reaction tank while maintaining a constant liquid level, and transferred to the second polycondensation reaction tank. The second polycondensation reaction is carried out under reduced pressure of 0.75 kPa. The reaction liquid is then removed from the second polycondensation reaction tank while maintaining a constant liquid level, and transferred to the third polycondensation reaction tank. The vacuum (pressure) is adjusted to achieve an average intrinsic viscosity of 0.53 dl/g for the reaction products. The pressure is in the range of 0.08~0.15 kPa.

(Granulation) The polyester resin obtained above is extruded into strips, cooled in water, and then cut into granules.

<Production of Polyester Resin (Solid-State Polymerization)> The polyester resin obtained from melt polymerization is fed into a solid-state polymerization apparatus. After drying at 90°C for 3.5 hours, it is crystallized at 130°C for 4.5 hours. Next, the temperature is slowly increased from 197°C to 220°C, and solid-state polymerization is carried out at a pressure of 40 Pa for 7 hours to obtain a polyester resin with an intrinsic viscosity of 0.617 dl/g.

(Example 2) Except that the solid-state polymerization time is set to 9 hours, the polyester resin is obtained in the same way as in Example 1.

(Examples 3-4, Comparative Examples 2-4) Except for the polyester resin obtained by granulating the polyester resin produced by melt polymerization when the viscosity reaches the stage recorded in Table 1, and performing solid-state polymerization at the solid-state polymerization time recorded in Table 1, the polyester resin was obtained by the same method as in Example 1.

(Comparative Example 1) Instead of solid-state polymerization, the polyester resin produced by melt polymerization was granulated when its viscosity reached the level recorded in Table 1 to obtain the polyester resin.

Table 1 Melt polymerization solid-phase polymerization Resin quality viscosity Processing time viscosity Impurities unit dl/g hr dl/g - Implementation Example 1 0.534 7 0.617 〇 Implementation Example 2 0.534 9 0.647 〇 Implementation Example 3 0.566 9 0.691 〇 Implementation Example 4 0.588 5 0.639 〇 Comparative example 1 0.616 without × Comparative example 2 0.596 7 0.690 △ Comparative example 3 0.616 20 0.940 ×

The polyester resins of Examples 1-4, through a combination of melt polymerization and solid-state polymerization, can achieve an inherent viscosity sufficient for film fabrication and bring the antimony impurity content within the target range. In Comparative Example 1, solid-state polymerization was not performed; solution polymerization alone achieved the target viscosity of the present invention after solid-state polymerization. The antimony impurity content was greater than 0.1 ppm, resulting in a deterioration in quality. In Comparative Example 2, the viscosity produced by melt polymerization was higher than 0.59 dl/g, exceeding the range of the present invention [Step 1], and it was then solid-state polymerized within the range of the present invention [Step 2]. The antimony impurity content was greater than 0.1 ppm, resulting in a deterioration in quality. Comparative Example 3, produced by melt polymerization, not only exceeded the limits of this invention in terms of viscosity and solid-state polymerization time, but also had impurity levels greater than 0.1 ppm, and the intrinsic viscosity after solid-state polymerization was far higher than 0.75 dl/g, resulting in significantly poorer processability and quality. [Industrial Applicability]

The polyester resin of this invention has an inherent viscosity sufficient to handle processing and low antimony impurities, thus it is suitable for applications requiring high quality, such as optical films and release films.

without.

Claims (3)

A polyester resin comprising ethylene glycol as the main diol component, terephthalic acid as the main dicarboxylic acid component, and antimony compound as the polymerization catalyst, wherein the antimony impurity content is below 0.1 ppm by mass. A method for manufacturing a polyester resin as claimed in claim 1 comprises the following steps in the following order: [Step 1] using terephthalic acid as the main dicarboxylic acid component, ethylene glycol as the main glycol component, and an antimony compound as the main polymerization catalyst to melt polymerize a polyester resin with an intrinsic viscosity of 0.52 to 0.59 dl/g; [Step 2] subjecting the polyester resin obtained in step 1 to solid-state polymerization at 197 to 225°C for 5 to 10 hours to produce a polyester resin with an intrinsic viscosity of 0.59 to 0.75 dl/g. A film comprising a polyester resin as claimed in claim 1.