Recycled polyester resin and method for producing recycled polyester resin

Abstract

To provide a recycled polyester resin small in mixing amount of foreign matter, and excellent in crystallinity and heat resistance, while being a copolymer polyester containing a recycled polyester raw material derived from waste or the like generated from used polyester products or in a process for producing the polyester resin and products at a high rate.SOLUTION: A recycled polyester resin that is a polyester resin containing components derived from recycled polyester raw material and satisfies all the followings (1) to (4). (1) When the total amount of total acid components is set to 100 mol%, 70 mol% or larger is terephthalic acid, (2) when the total amount of all glycol components is set to 100 mol%, 60 to 99 mol% is ethylene glycol, 1 to 20 mol% is an ethylene oxide adduct of bisphenol A, and 4 mol% or smaller is diethylene glycol, (3) the carboxyl terminal group concentration is 30 equivalent / t, and (4) the average step-up speed is 0.6 MPa / h or smaller.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a novel recycled polyester resin and a method for producing the same. In particular, the present invention relates to a recycled polyester resin produced from recycled polyester raw materials derived from used polyester products as well as recycled polyester raw materials derived from unused polyester generated in the process of producing polyester products, which has a low amount of foreign matter mixed in and can be processed into various molded products in the same way as virgin polyester resin, and a method for producing the same. [Background technology]

[0002] Polyethylene terephthalate (hereinafter sometimes abbreviated as PET) has a high melting point, is chemical resistant, and is relatively low cost, so it is widely used in fibers, films, and molded products such as PET bottles. These polyester products inevitably generate waste during the manufacturing and processing stages, and are often disposed of after use, but if they are incinerated, the high heat generated will severely damage the incinerator and shorten its lifespan, while if they are not incinerated, they will remain in the furnace almost indefinitely because they do not decompose. In recent years, plastic containers and other polyester products that have been used and discarded as garbage have been found to be flowing into the ocean via rivers. These microplastics are broken down into small pieces by the action of waves and tidal currents, and accumulate in the bodies of marine organisms. These plastics are concentrated in the food chain, adversely affecting the marine ecosystem, and plastics have become a major cause of marine pollution. This has led to a global movement to reduce the amount of plastic used and to switch to biodegradable plastics.

[0003] From the perspective of reducing the amount of plastic products used and from the perspective of environmental issues, various methods of recycling resources are being used. Regarding polyester products, methods are being considered for recycling polyester waste generated during the manufacturing process and for recovering products that have been discarded after being sold on the market and reusing them as raw materials. In particular, in recent years, textile products that have been awarded the Eco Mark, which is certified as achieving a certain recycling rate, have become popular.

[0004] Various methods have been proposed for recycling recycled polyester raw materials. For example, a method has been proposed in which PET scraps are depolymerized with ethylene glycol (hereinafter sometimes abbreviated as EG) to form oligomers, which are then used in a polycondensation reaction as recycled polyester raw materials (see Patent Document 1). However, the PET obtained by this method contains a large amount of foreign matter derived from the PET scraps, which causes problems such as large variations in quality due to the inclusion of foreign matter in blow-molded products.

[0005] Furthermore, when recycling PET bottles that have already been used as products, problems can arise, such as additives added to the polyester resin and items attached to the bottle itself, such as caps (aluminum, polypropylene, polyethylene), inner stoppers and liners (polypropylene, polyethylene), labels (paper, resins such as polystyrene, ink), adhesives, and printing ink. As a pre-treatment for the recycling process, collected PET bottles are first put through a vibrating sieve to remove sand, metal, etc. The PET bottles are then washed, and colored bottles are separated before being roughly crushed. Labels and other materials are then removed using air separation. Aluminum pieces from caps and other materials are then removed and the PET bottle pieces are finely crushed. Components such as adhesives, proteins, and mold are removed using high-temperature alkaline washing, and heterogeneous components such as polypropylene and polyethylene are separated based on their specific gravity. However, even after these steps, it was difficult to separate non-polyester resins such as polypropylene, polyethylene, and polystyrene from PET resin. Therefore, even if recycled polyester resin was obtained by the recycling method described in Patent Document 1, foreign matter derived from the non-polyester resin could not be sufficiently removed, and the amount of foreign matter mixed in could not be sufficiently reduced, so it was not possible to obtain a product with the same quality as virgin polyester resin.

[0006] The invention described in Patent Document 2 describes a method in which polyester waste is depolymerized with ethylene glycol, filtered through a filter with an average mesh size of 10 to 50 μm, and then repolymerized. It is also shown that the resulting recycled polyester resin contains little foreign matter and is easy to process. However, even with this method, the amount of foreign matter derived from non-polyester resins as described above is not sufficiently removed, and the amount of foreign matter is not sufficiently reduced.

[0007] Furthermore, in general, the production of plastic bottles and the like employs the so-called blow molding method, in which molten plasticized resin is extruded through a die orifice to form a cylindrical parison, which is then sandwiched between molds and air is blown into it, due to its ease of molding, high productivity, and relatively low equipment costs for molding machines, molds, etc. Even in such blow-molded products, the use of recycled polyester resins is being considered from the perspective of environmental issues. Furthermore, since crystallization is likely to occur during blow molding, even if molding is possible, there is a problem in that whitening occurs and transparency becomes insufficient.

[0008] Therefore, in order to improve transparency, polyester resins have been proposed in which polyethylene terephthalate is copolymerized with other monomer components (see, for example, Patent Documents 3 and 4). By using a copolymer polyester resin, crystallization can be suppressed and molded products with excellent transparency can be obtained. However, a copolymer polyester resin using recycled polyester raw materials, which can be sufficiently freed of not only various inorganic substances but also foreign matter derived from non-polyester resins, and which makes it possible to obtain various high-quality products similar to those produced from virgin polyester resins, has not yet been obtained. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 60-248646 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-171138 [Patent Document 3] Japanese Patent Application Publication No. 9-296031 [Patent Document 4] Patent No. 6297351 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to solve the above problems and to provide a recycled polyester resin that contains recycled polyester raw materials derived from used polyester products or recycled polyester raw materials derived from scraps generated in the process of manufacturing polyester resins and products, but that has a low level of foreign matter contamination and can be used to produce high-quality molded products with good productivity. The present invention also aims to provide a production method by which such recycled polyester resin of the present invention can be obtained. [Means for solving the problem]

[0011] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention. That is, the present invention is summarized as follows (i) to (iii). (i) A polyester resin containing a component derived from at least one recycled polyester raw material, which is a) a used polyester product and b) unused polyester generated in the process of manufacturing a polyester product, and which satisfies all of the following (1) to (4): (1) When the total amount of all acid components constituting the polyester is 100 mol %, 70 mol % or more is terephthalic acid, (2) When the total amount of all glycol components is 100 mol%, 60 to 99 mol% is ethylene glycol, 1 to 20 mol% is an ethylene oxide adduct of bisphenol A, and 4 mol% or less is diethylene glycol; (3) The carboxyl end group concentration is 30 equivalents / t; (4) The average pressure rise rate is 0.6 MPa / h or less (wherein the average pressure rise rate is a value calculated by the following procedure: a pressure rise tester including an extruder and a pressure sensor is used, a stainless steel filter (nominal mesh size: 1400 mesh, weave: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical wire diameter: 0.07 mm, horizontal wire diameter: 0.04 mm, filtration particle size: 12 μm) is set at the tip of the extruder, polyester resin is melted in the extruder at 300°C, and the melt is extruded from the filter at a discharge rate of 29.0 g / min. The pressure value at the start of extrusion is defined as the "initial pressure value (MPa)," and the pressure value at the point when extrusion has been continued for 12 hours thereafter is defined as the "final pressure value (MPa)." Based on these pressure values, the average pressure rise rate is calculated using the following formula A: Average pressure rise rate (MPa / h) = (final pressure value - initial pressure value) / 12) A) (ii) A blow-molded product containing the recycled polyester resin described in (i).

[0012] (c) A method for producing a recycled polyester resin using at least one recycled polyester raw material, which is a) a used polyester product and b) unused polyester generated in the process of producing a polyester product, and which is characterized by comprising the following steps (1) to (3): (1) a step of adding a recycled polyester raw material to a mixture containing an ethylene terephthalate oligomer, ethylene glycol, and an ethylene oxide adduct of bisphenol A so that the molar ratio of total glycol components / total acid components becomes 1.2 to 1.45, and performing depolymerization under heat treatment conditions of 245 to 280°C to obtain a reaction product containing a depolymerization product; (2) passing the reaction product through a filter having a filtration particle size of 10 to 25 μm to recover the filtrate; (3) adding a polymerization catalyst to the filtrate and carrying out a polycondensation reaction of the depolymerization product at a temperature of 250°C or higher and a reduced pressure of 1.0 hPa or lower; A method for producing a recycled polyester resin, comprising: [Effects of the Invention]

[0013] The recycled polyester resin of the present invention contains at least one recycled polyester raw material, including a) used polyester products and b) unused polyesters generated during the manufacturing process of polyester products. However, the amount of foreign matter mixed in is low, and the carboxyl end group concentration and the content of ethylene oxide adducts of diethylene glycol and bisphenol A satisfy specific ranges, resulting in excellent crystallinity and heat resistance. This allows for an optimal crystallization rate during the blow molding process, enabling long-term continuous operation and high-quality products to be produced with high productivity. In particular, direct blow molding can be carried out with high productivity, resulting in products with excellent appearance, transparency, and strength similar to those produced using virgin polyester resin. Furthermore, according to the method for producing a recycled polyester resin of the present invention, it is possible to efficiently obtain a recycled polyester resin that is low in the amount of foreign matter as described above and has excellent crystallinity and heat resistance. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below. The recycled polyester resin of the present invention (the resin of the present invention) is a polyester resin containing components derived from at least one recycled polyester raw material, i.e., a) used polyester products and b) unused polyester generated in the process of manufacturing polyester products. These components constitute a part of the polyester constituting the resin of the present invention.

[0015] Examples of used polyester products in the above category a) include polyester molded products (including fibers) that were once on the market and then collected after use. Typical examples include containers such as PET bottles and packaging materials. The unadopted polyester generated in the manufacturing process of polyester products mentioned in b) above is polyester that did not reach the stage of commercialization. Examples include resin pellets that do not meet specifications, materials that are no longer needed during molding, fragments cut during molding, scraps generated during molding or processing, cut-off pieces of transitional products generated when changing brands, and cut-off pieces of prototypes or defective products.

[0016] The above a) and b) are not limited in their form, and may be pelletized by further processing such as pulverization or cutting as necessary, or may be melted and pelletized. The above a) and b) may be used alone or as a mixture of the two. The recycled polyester raw materials a) and b) above may be either crystalline or amorphous. Therefore, for example, pellets of amorphous polyester waste that have not been heat-treated, crystalline pellets that have been heat-treated, or a mixture of crystalline and amorphous pellets can be used. In the present invention, it is preferable to use crystalline recycled polyester raw materials, particularly for the purpose of preventing fusion between pellets during charging into the reactor or during the depolymerization reaction. Therefore, materials a) or b) above that have been crystallized by heat treatment (crystallized pellets, etc.) can be preferably used. The properties of the recycled polyester raw materials in a) and b) above are not limited, and may be in the form of a) and b) above, or may be in the form of cut pieces, crushed material (powders), etc. obtained by further processing such as cutting and crushing, as well as solid forms such as molded bodies (pellets, etc.) obtained by molding these. More specifically, examples include pellets obtained by cooling and cutting melted polyester waste, and cut pieces obtained by finely cutting polyester molded products such as PET bottles. Alternatively, the recycled polyester raw materials may be in the form of a liquid obtained by dispersing or dissolving the cut pieces, crushed material (powders), etc. in a solvent. When producing polyester products using these raw materials, they can be melted at a temperature above their melting point and charged into a can as a melt, if necessary.

[0017] The recycled polyester resin of the present invention preferably contains 40% by mass or more, and more preferably 50% by mass or more, of recycled polyester raw materials, which are at least one of the above a) and b). If the content of recycled polyester raw materials is less than 40% by mass, the objective of considering environmental issues cannot be achieved. Although there is no particular upper limit to the content of recycled polyester raw materials, according to the production method of the present invention described below, it is possible to easily obtain a recycled polyester resin with a recycled polyester raw material content of 40 to 80% by mass.

[0018] In the resin of the present invention, when the total amount of all acid components constituting the polyester is taken as 100 mol %, terephthalic acid accounts for 70 mol % or more, and preferably 85 mol % or more. If the proportion of terephthalic acid is less than 70 mol %, the crystallinity and heat resistance of the resulting polyester resin will be poor. Examples of acid components other than terephthalic acid contained in the recycled polyester resin include phthalic acid, isophthalic acid, 5-sodium sulfoisophthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, adipic acid, sebacic acid, and dimer acid. Two or more of these may be used in combination, and ester-forming derivatives of these acids may also be used.

[0019] When the total amount of all glycol components is taken as 100 mol %, the resin of the present invention contains 60 to 99 mol % ethylene glycol, 1 to 20 mol % an ethylene oxide adduct of bisphenol A, and 4 mol % or less diethylene glycol. In other words, the resin contains ethylene glycol as the main component, and the ethylene oxide adduct of bisphenol A and diethylene glycol as copolymerization components.

[0020] The content (copolymerization amount) of the ethylene oxide adduct of bisphenol A is 1 to 20 mol % of the total glycol component, preferably 3 to 15 mol %, and more preferably 3 to 12 mol %. By copolymerizing an appropriate amount of the ethylene oxide adduct of bisphenol A, the crystallization rate of the polyester resin can be adjusted to one suitable for blow molding, and crystallization during blow molding can be prevented.

[0021] If the content of the ethylene oxide adduct of bisphenol A is less than 1 mol%, the resin composition will crystallize too quickly, resulting in crystallization and whitening of the resulting blow-molded article. On the other hand, if the content exceeds 20 mol%, the resin composition will become amorphous, making high-temperature drying and solid-state polymerization difficult. Furthermore, blocking is likely to occur during high-temperature drying and solid-state polymerization, which is undesirable.

[0022] Ethylene glycol accounts for 60 to 99 mol % of the total glycol components, preferably 70 to 90 mol %. If the ethylene glycol content is less than 60 mol %, the resulting polyester resin will have poor crystallinity and heat resistance. On the other hand, if it exceeds 99 mol %, the proportion of ethylene oxide adduct of bisphenol A will be low, making it difficult to adjust the crystallization rate and resulting in poor effectiveness in preventing whitening due to crystallization during blow molding. The total amount of ethylene glycol and ethylene oxide adduct of bisphenol A is preferably 70 mol % or more, and more preferably 80 mol % or more, of the total glycol components.

[0023] Furthermore, when the total amount of all glycol components in the resin of the present invention is taken as 100 mol %, the diethylene glycol content is preferably 4 mol % or less, and more preferably 3.5 mol % or less. In particular, the resin of the present invention obtained by the production method of the present invention uses ethylene glycol as one of the raw materials, and diethylene glycol may be generated as a by-product during this process. The resin of the present invention has a small amount of diethylene glycol as a by-product, and since the diethylene glycol content is 4 mol % or less, it has excellent crystallinity. This makes it possible to produce molded products such as fibers, injection-molded articles, various blow-molded articles, sheets, and films with good productivity. The lower limit of the diethylene glycol content can be, for example, about 0.5 mol %, but is not limited to this.

[0024] Furthermore, examples of diol components that can be used other than ethylene glycol and the ethylene oxide adduct of bisphenol A include neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, dimer diol, and the ethylene oxide adduct of bisphenol S.

[0025] The resin of the present invention has the following characteristic values. (a) Carboxyl end group concentration is 30 equivalents / t or less (b) The average pressure rise rate measured by a pressure rise tester is 0.6 MPa / h or less. The resin of the present invention having these characteristic values can be obtained by the production method of the present invention described below.

[0026] First, the resin of the present invention has the characteristic value (a) of a carboxyl terminal group concentration of 30 equivalents / t or less, preferably 25 equivalents / t or less, and more preferably 20 equivalents / t or less. The resin of the present invention has a carboxyl terminal group concentration of 30 equivalents / t or less, and therefore has excellent heat resistance, making it possible to obtain molded products with excellent heat resistance by various molding methods.

[0027] Furthermore, as a characteristic value of the resin of the present invention, the intrinsic viscosity (IV) is preferably 0.4 to 1.3, and particularly, when used for direct blow molding, it is preferably 0.8 to 1.25. The intrinsic viscosity (IV) is measured at a temperature of 20°C using a mixture of equal masses of phenol and tetrachloroethane as a solvent.

[0028] If the intrinsic viscosity is less than 0.4, the resin viscosity is low, resulting in significant drawdown of the parison during blow molding, making molding itself difficult. In particular, if the intrinsic viscosity is less than 0.8 during direct blow molding, parison drawdown becomes significant, making molding difficult. On the other hand, if the intrinsic viscosity exceeds 1.3, the molding temperature must be increased, which can result in poor color and transparency in the resulting molded product. Furthermore, increasing the molding temperature promotes thermal decomposition of the resin, resulting in significant drawdown of the parison, making molding difficult and resulting in uneven thickness in the molded product.

[0029] The resin of the present invention has a characteristic value (b) of an average pressure increase rate of 0.6 MPa / h or less, preferably 0.5 MPa / h or less, and more preferably 0.4 MPa / h or less, as measured by the following method. The average pressure increase rate in the present invention is an indicator of the amount of foreign matter derived from various inorganic substances and foreign matter derived from non-polyester resins, with a lower average pressure increase rate indicating a lower amount of foreign matter. By having an average pressure increase rate of 0.6 MPa / h or less, it becomes possible to produce fibers having a single fiber fineness of 0.6 decitex or less, for example, by melt spinning. The lower limit of the average pressure increase rate can be, for example, about 0.01 MPa / h, but is not limited to this.

[0030] The average pressure rise rate was measured using a pressure rise tester including an extruder and a pressure sensor. A stainless steel filter (nominal mesh size: 1400 mesh, weave: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical wire diameter: 0.07 mm, horizontal wire diameter: 0.04 mm, filtration particle size: 12 μm) was attached to the tip of the extruder. The polyester resin was melted in the extruder at 300°C, and the melt was extruded from the filter at a discharge rate of 29.0 g / min. The pressure value at the start of extrusion was defined as the "initial pressure value (MPa)," and the pressure value at the end of 12 continuous hours of extrusion was defined as the "final pressure value (MPa)." The average pressure rise rate was calculated based on these pressure values using the following formula A. Average pressure rise rate (MPa / h) = (final pressure value - initial pressure value) / 12) A)

[0031] By employing the production method described below, the amount of foreign matter derived from various inorganic substances and foreign matter derived from non-polyester resins can be reduced in the resin of the present invention, and therefore the average pressure increase rate measured by a pressure increase tester, which is the characteristic value of (b), can be reduced to 0.6 MPa / h or less.

[0032] Next, a method for producing the resin of the present invention will be described. In the production method of the present invention, it is important to carry out the steps (1) to (3) in this order. (1) a step of adding recycled polyester raw material to a mixture containing ethylene terephthalate oligomer, ethylene glycol, and an ethylene oxide adduct of bisphenol A so that the molar ratio of total glycol components / total acid components becomes 1.2 to 1.45, and performing depolymerization under heat treatment conditions of 245 to 280°C to obtain a reaction product containing a depolymerization product; (2) passing the reaction product through a filter having a filtration particle size of 10 to 25 μm to recover the filtrate; (3) A step of adding a polymerization catalyst to the filtrate and carrying out a polycondensation reaction at a temperature of 250°C or higher and under reduced pressure of 1.0 hPa or lower.

[0033] First, in step (1), as a preliminary step to depolymerizing the recycled polyester raw material, a slurry of ethylene glycol and terephthalic acid is added to obtain an esterification reaction product (ethylene terephthalate oligomer). The amount of ethylene terephthalate oligomer is preferably 0.20 to 0.80 mass% and more preferably 0.30 to 0.70 mass% based on 100 mass% of the finally obtained recycled polyester resin. If the amount of ethylene terephthalate oligomer is less than the above range, the recycled polyester raw material is likely to block with itself when the recycled polyester raw material is added, which is undesirable because it places an excessive load on the mixer. On the other hand, if the amount of ethylene terephthalate oligomer is greater than the above range, no particular problems will arise in the depolymerization reaction, but the recycling rate of the finally obtained recycled polyester resin will be undesirably low.

[0034] In order to sufficiently advance the depolymerization reaction, the amount of ethylene glycol added in step (1) is preferably 1 to 15 mass % relative to 100 mass % of the ethylene terephthalate oligomer, and more preferably 5 to 10 mass %. If the amount of ethylene glycol added exceeds 15 mass %, the ethylene terephthalate oligomer tends to solidify in the reactor, which may make it impossible to continue the subsequent reaction, and this is not preferable. When adding ethylene glycol to the ethylene terephthalate oligomer, it is preferable to make the temperature of the contents uniform while rotating the stirrer before adding the ethylene glycol, in order to prevent the oligomer from solidifying.

[0035] The amount of the ethylene oxide adduct of bisphenol A added in step (1) is 1 to 20 mol % of the total glycol component, preferably 3 to 15 mol %, and more preferably 3 to 12 mol %. When the ethylene oxide adduct of bisphenol A is added to the oligomer, it is preferable to uniformize the temperature of the contents while rotating the stirrer before adding the adduct, in order to prevent the oligomer from solidifying.

[0036] In step (1), the recycled polyester raw material is charged and stirred so that the molar ratio of total glycol components / total acid components becomes 1.2 to 1.45, and depolymerization is carried out under heat treatment conditions of 245 to 280°C. This step is important in the production method of the present invention. In other words, while conventional methods using recycled polyester raw materials involve depolymerization using only the recycled polyester raw material, the present invention involves depolymerizing the recycled polyester raw material in the presence of ethylene terephthalate oligomer and ethylene glycol, and depolymerizing all components of the oligomer, ethylene glycol, and recycled polyester raw material by adding the recycled polyester raw material so that the molar ratio of total glycol components to total acid components is 1.2 to 1.45. The molar ratio of total glycol components to total acid components is preferably 1.22 to 1.43, and more preferably 1.25 to 1.40.

[0037] By carrying out the above-described step (1), not only various inorganic substances but also foreign substances derived from non-polyester resins are efficiently precipitated, and these foreign substances can be completely filtered out in step (2). Then, in the polycondensation reaction in step (3), it becomes possible to obtain a recycled polyester resin having the characteristic values of the present invention, such as the diethylene glycol content (copolymerization amount) and the carboxyl terminal group concentration, which are not more than specific amounts, and which contains only a small amount of foreign substances.

[0038] If the molar ratio of total glycol components / total acid components during the depolymerization reaction is outside the above range, the resulting recycled polyester resin will not satisfy at least one of the carboxyl terminal group concentration and diethylene glycol content specified in the present invention, and will also have a high average pressure rise rate. This is because, when the molar ratio of total glycol components / total acid components during the depolymerization reaction is outside the above range, precipitation of various inorganic substances and non-polyester resin-derived foreign matter does not occur efficiently, making it impossible to filter out these foreign matters completely in step (2), and foreign matter precipitates after the polycondensation reaction in step (3), resulting in a recycled polyester resin with a high average pressure rise rate.

[0039] The reactor used in the production method of the present invention may be a commonly used esterification reactor with no particular problem in terms of volume or shape of stirring blades. However, in order to efficiently proceed with the depolymerization reaction, it is preferable that the reactor has a structure equipped with a distillation column that prevents ethylene glycol from being distilled out of the system. When the recycled polyester raw material is charged, it is preferably stirred under normal pressure, and more preferably charged in a state purged with a small amount of inert gas (generally nitrogen gas).

[0040] The reaction temperature during depolymerization in step (1) is preferably set at an internal reactor temperature in the range of 245 to 280°C, and more preferably at an internal temperature in the range of 255 to 280°C. If the reaction temperature during depolymerization is less than 245°C, the reaction product solidifies, resulting in poor operability. Even if a recycled polyester resin is obtained, the diethylene glycol content and carboxyl terminal group concentration will be too high. If the reaction temperature exceeds 280°C, the diethylene glycol content and carboxyl terminal group concentration of the resulting recycled polyester resin will be too high. The depolymerization reaction time (the reaction time from the end of the addition of the recycled polyester raw material) is preferably within 4 hours, and more preferably within 2 hours from the viewpoints of suppressing the amount of diethylene glycol by-products and suppressing deterioration in the color tone of the polyester.

[0041] In step (2), the reaction product containing the depolymerized polymer from step (1) is passed through a filter with a filtration size of 10 to 25 μm to filter out foreign matter. As described above, by carrying out the depolymerization reaction under the conditions of step (1), not only various inorganic substances but also foreign matter derived from non-polyester resins is efficiently precipitated. Therefore, by passing the resultant mixture through a filter with a filtration size of 10 to 25 μm, the precipitated foreign matter can be filtered out, and a filtrate containing little foreign matter can be obtained. If a filter with a filtration particle size larger than 25 μm is used, foreign matter in the polymer cannot be sufficiently removed, resulting in a large amount of foreign matter in the resulting recycled polyester resin. Therefore, when such a resin is used for spinning, pressure buildup in the nozzle pack and broken threads occur. On the other hand, if a filter with a filtration particle size smaller than 10 μm is used, it is prone to clogging with foreign matter, shortening the filter life, resulting in cost disadvantages and a deterioration in operability.

[0042] Furthermore, filters that can be used in step (2) of the present invention may be any ordinary type, and examples thereof include screen changer type filters, leaf disc filters, and candle-type sintered filters.

[0043] In the production method of the present invention, a polymerization catalyst is added to the filtrate obtained through step (2) above, and a polycondensation reaction is carried out at a temperature of 250°C or higher and a reduced pressure of 1.0 hPa or lower. As the polymerization catalyst, for example, one or more of germanium, antimony, titanium, and cobalt compounds can be used, but germanium or antimony compounds are preferred. Furthermore, when the transparency of the resulting recycled polyester resin is important, it is preferable to use a germanium compound. Examples of germanium or antimony compounds include their oxides, inorganic acid salts, organic acid salts, halides, and sulfides. These polycondensation catalysts are used in an amount of 5 × 10 per mole of the acid component of the resulting polyester resin. -5 It is preferable to set the concentration to 6×10 moles / unit or more. -5 It is more preferable to set it to mol / unit or more. In addition, since the polymerization catalyst contained in the recycled polyester raw material may also act as a catalyst during the polycondensation reaction, when adding the polymerization catalyst in step (3), it is preferable to take into consideration the amount and type of polymerization catalyst contained in the recycled polyester raw material.

[0044] Furthermore, during the polycondensation reaction, a fatty acid ester, a hindered phenol-based antioxidant, or a phosphorus compound may be added in addition to the above-mentioned polymerization catalyst. Specific examples of fatty acid esters include beeswax (a mixture containing myricyl palmitate as a main component), stearyl stearate, behenyl behenate, stearyl behenate, glycerin monopalmitate, glycerin monostearate, glycerin distearate, glycerin tristearate, pentaerythritol monopalmitate, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, pentaerythritol tetrastearate, dipentaerythritol hexastearate, etc. Among these, glycerin monostearate, pentaerythritol tetrastearate, and dipentaerythritol hexastearate are preferred.

[0045] Hindered phenol antioxidants include 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 4,4'-butylidenebis-(3-methyl-6-t-butylphenol), triethylenediamine, methyl ... Examples of suitable ethylene glycol bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate] and 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1'-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane are used, but tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane is preferred from the standpoints of effectiveness and cost.

[0046] Examples of phosphorus compounds that can be used include phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl phosphate, tridecyl phosphate, and triphenyl phosphate.

[0047] Then, in the polycondensation reaction tank, the polycondensation reaction is carried out at a temperature of 250°C or higher and under a reduced pressure of 1.0 hPa or lower. If the polycondensation reaction temperature is lower than 250°C or the pressure during the polycondensation reaction exceeds 1.0 hPa, the polycondensation reaction time becomes long, resulting in poor productivity. The polycondensation reaction temperature is more preferably 270°C or higher. However, if the polycondensation reaction temperature is too high, the polymer will be colored due to thermal decomposition, resulting in a deterioration in color tone, and the amount of terminal groups (COOH) will also increase due to thermal decomposition. Therefore, in the present invention, the upper limit of the polycondensation reaction temperature is preferably 285°C or lower. The intrinsic viscosity of the recycled polyester (prepolymer) obtained here is preferably 0.44 to 0.80.

[0048] The resin of the present invention may contain various additives other than the above-mentioned additives such as polymerization catalyst, antioxidant, phosphorus compound, etc., as long as the effects of the resin are not impaired. As various additives, for example, phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl phosphate, tridecyl phosphate, triphenyl phosphate, and other phosphorus compounds can be used as coloration inhibitors, and these phosphorus compounds may be used alone or in combination of two or more. Furthermore, in order to suppress coloration due to thermal decomposition of the polyester resin, additives such as cobalt compounds such as cobalt acetate, manganese compounds such as manganese acetate, anthraquinone dye compounds, and copper phthalocyanine compounds may also be contained.

[0049] The prepolymer obtained by the melt polymerization reaction is then cut into chips of any desired shape, such as dice or cylinders. The polyester chips are continuously fed into a crystallizer and crystallized at 150-190°C. After that, the chips are fed into a dryer and dried at 190°C or less for 4-16 hours. The chips are then fed into a preheater and heated to the solid-state polymerization temperature described below for 2-5 hours. The resulting mixture is then continuously fed into a solid-state polymerization reactor to undergo solid-state polymerization, yielding a polyester resin with the desired intrinsic viscosity. Solid-state polymerization is preferably carried out under an inert gas, such as nitrogen gas. Solid-state polymerization is typically carried out at a temperature between 170 and 230°C, preferably between 180 and 220°C. The polymerization time is typically between 20 and 80 hours, with the reaction occurring in the solid-state polymerization reactor.

[0050] As described above, the resin of the present invention is suitable for blow molding. However, even if injection molding or drawing methods are employed, molded articles (injection molded articles, sheets, films, etc.) excellent in color tone and transparency can be obtained, and it is also possible to obtain fibers by melt spinning.

[0051] The blow-molded article of the present invention is made of the resin of the present invention. The blow-molded article of the present invention can be produced using a general-purpose direct blow molding machine or stretch blow molding machine, and the temperature of each part of the cylinder and the nozzle of the molding machine is preferably in the range of 230 to 280°C. [Example]

[0052] The present invention will now be described in detail with reference to examples, in which the measurement and evaluation methods for various properties and the like are as follows. (a) Intrinsic viscosity The obtained recycled polyester resin is used, and the measurement is carried out at a temperature of 20°C using an equal mass mixture of phenol and tetrachloroethane as a solvent. (b) Composition of polyester resin The obtained polyester resin was dissolved in a mixed solvent of deuterated hexafluoroisopropanol and deuterated chloroform in a volume ratio of 1 / 20, and 1H-NMR was measured using a JEOL LA-400 NMR apparatus. The type and content of copolymerized components were determined from the integrated intensity of the proton peak of each component in the obtained chart. (c) Carboxyl end group concentration 0.1 g of the resulting recycled polyester resin was dissolved in 10 ml of benzyl alcohol, and 10 ml of chloroform was added to the solution, followed by titration with a 1 / 10 N potassium hydroxide benzyl alcohol solution to determine the content. (d) Average pressure rise rate measured by a pressure rise tester The obtained recycled polyester resin was melted at 300°C in an extruder, and a stainless steel twill weave filter (nominal mesh size: 1400 mesh, weaving method: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical wire diameter: 0.07 mm, horizontal wire diameter: 0.04 mm, filtration particle size: 12 μm, viscous resistance coefficient (m -1 ): 2.60 x 10 7A filter (Kamijo Seiki Co., Ltd., inertial resistance coefficient: 5.14 × 10) was set in place, and a reinforcing material (stainless steel plain weave wire mesh (nominal mesh size: 40 mesh, weave: plain weave, wire diameter: 0.21 mm, Kamijo Seiki Co., Ltd.) was layered on the back (downstream side) of the filter. The polymer discharge rate was set to 29.0 g / min, and the filter pressure was measured using a pressure rise tester (ASAHI GAGE MES-Y44D type detector). The pressure rise test using the pressure rise tester was performed continuously for 12 hours, and the average pressure rise rate was calculated using the following formula from the initial pressure value (MPa) at the start of the pressure rise test (the minimum pressure value between 5 and 10 minutes after the polyester resin began to pass through the filter was defined as the initial pressure) and the final pressure value (MPa) after 12 hours had elapsed. Average pressure rise rate (MPa / h) = (final pressure value - initial pressure value) / 12

[0053] (e) Formability The thickness of the body of the resulting containers (100 samples) was measured, and those with a difference in thickness between the thickest and thinnest parts of up to 0.30 mm were deemed to have passed. If 90 or more samples passed, the moldability was evaluated as good. (f) Haze Sample pieces (20 pieces) were cut out from the resulting container, and the turbidity was measured using a turbidity meter, Model 1001DP, manufactured by Nippon Denshoku Industries Co., Ltd. (air: haze 0%), and the average value was calculated for 20 samples. The smaller this value, the better the transparency, and a value of 6% or less was judged to be excellent transparency. (g) Impact resistance (e) Molded products (100 samples) that passed the moldability evaluation were filled with 340 ml of tap water and dropped once on a P tile from a height of 200 cm, with the bottom and side facing downwards. If 90 or more molded products did not break, the impact resistance was evaluated as good.

[0054] Example 1 [Recycled polyester resin] A slurry of terephthalic acid (TPA) and ethylene glycol (EG) (TPA / EG molar ratio = 1 / 1.6) was supplied to an esterification reactor and reacted at a temperature of 250°C and a pressure of 50 hPa to obtain ethylene terephthalate oligomer (number average degree of polymerization: 5) with an esterification reaction rate of 95%. 45.0 parts by mass of ethylene terephthalate oligomer was charged into the esterification reactor, followed by 6.5 parts by mass of ethylene glycol while the esterification reactor's agitator was running. When the internal temperature of the esterification reactor (hereafter referred to as the ES can) bottomed out, 10 parts by mole of bisphenol A ethylene oxide adduct (hereafter referred to as BAEO) was added. Then, 55 parts by mass of recycled polyester raw material (pelletized polyester waste generated in the polyester resin manufacturing process) was added via a rotary valve over a period of approximately 2 hours. At this time, the recycled polyester raw material was charged so that the molar ratio of total glycol components to total acid components (hereinafter sometimes referred to as G / A) was 1.25. Thereafter, a depolymerization reaction was carried out for 1 hour under heat treatment conditions at 260°C. The resulting depolymerized polymer was then pressure-fed to a polycondensation reactor (hereinafter referred to as a PC can) through a candle filter with a mesh size of 20 μm set between the esterification reactor and the polycondensation reactor. Then, 1.0 × 10 antimony trioxide was added as a polymerization catalyst. -4 The PC can was then decompressed for 60 minutes, and the melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 280°C for 4 hours to obtain a prepolymer of recycled polyester resin. The intrinsic viscosity of this prepolymer was 0.66. The prepolymer was then continuously fed to a crystallizer and crystallized at 150°C, then fed to a dryer and dried at 130°C for 10 hours, then sent to a preheater and heated to 180°C, and then fed to a solid-state polymerization reactor where a solid-state polymerization reaction was carried out at 190°C for 50 hours under nitrogen gas, yielding a recycled polyester resin with an intrinsic viscosity of 1.14. [Blow molded products] The recycled polyester resin was chipped and dried, and then extruded at 280°C using a direct blow molding machine (manufactured by Tahara) to form a cylindrical parison. While the parison was still softened, it was clamped in a mold to form a bottom, and then blown into a bottle. At this time, the bottom was formed when the parison reached a diameter of 3 cm and a length of 25 cm, and then blow-molded to obtain a 350 ml hollow container (direct blow-molded product).

[0055] Example 2 A prepolymer of recycled polyester resin was obtained in the same manner as in Example 1, except that the copolymerization amount of BAEO and the G / A value were changed to those shown in Table 1. Then, using the obtained prepolymer, solid-state polymerization was carried out in the same manner as in Example 1, except that the drying conditions in the dryer were changed to 160°C for 8 hours, the heating temperature in the pre-dryer to 190°C, and the solid-state reaction time was changed to 60 hours, to obtain a recycled polyester resin with an intrinsic viscosity of 1.23. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0056] Example 3 A prepolymer for recycled polyester resin was obtained in the same manner as in Example 1, except that the composition was changed so that the copolymerization amount of BAEO and the G / A value were as shown in Table 1. Then, using the obtained prepolymer, solid-state polymerization was carried out in the same manner as in Example 1, except that the drying conditions in the dryer were 160°C for 8 hours and the heating temperature in the pre-dryer was 190°C, to obtain a recycled polyester resin with an intrinsic viscosity of 1.10. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0057] Example 4 A prepolymer for recycled polyester resin was obtained in the same manner as in Example 1, except that the composition was changed so that the copolymerization amount of BAEO and the G / A value were as shown in Table 1. Then, using the obtained prepolymer, solid-state polymerization was carried out in the same manner as in Example 1, except that the drying conditions in the dryer were changed to 120°C for 18 hours and the heating temperature in the pre-dryer was changed to 175°C, to obtain a recycled polyester resin with an intrinsic viscosity of 1.12. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0058] Example 5 A prepolymer for recycled polyester resin was obtained in the same manner as in Example 1, except that the composition was changed so that the copolymerization amount of BAEO and the G / A value were as shown in Table 1. Then, using the obtained prepolymer, solid-state polymerization was carried out in the same manner as in Example 1, except that the drying conditions in the dryer were changed to 110°C for 24 hours, the heating temperature in the pre-dryer to 170°C, and the solid-state reaction time was changed to 60 hours, to obtain a recycled polyester resin with an intrinsic viscosity of 1.26. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0059] Example 6 A prepolymer for recycled polyester resin was obtained in the same manner as in Example 1, except that the composition was changed so that the amount of BAEO copolymerized, the amount of recycled polyester added, and the G / A value were as shown in Table 1. Then, using the obtained prepolymer, a solid-state polymerization reaction was carried out in the same manner as in Example 2, except that the solid-state polymerization reaction was carried out for 15 hours, to obtain a recycled polyester resin with an intrinsic viscosity of 0.75. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0060] Example 7 A prepolymer for recycled polyester resin was obtained in the same manner as in Example 1, except that the composition was changed so that the amount of BAEO copolymerized, the amount of recycled polyester added, and the G / A value were as shown in Table 1. Then, using the obtained prepolymer, a solid-state polymerization reaction was carried out in the same manner as in Example 2, except that the solid-state polymerization reaction was carried out for 35 hours, to obtain a recycled polyester resin with an intrinsic viscosity of 1.04. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0061] Examples 8 and 9 A prepolymer of recycled polyester resin was obtained in the same manner as in Example 1, except that the melt polymerization reaction step was carried out at the temperature shown in Table 1. Then, using the obtained prepolymer, a solid-state polymerization reaction was carried out in the same manner as in Example 1, except that the solid-state polymerization reaction time was changed to 35 hours, to obtain recycled polyester resins with intrinsic viscosities of 1.17 and 1.19. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0062] Examples 10 to 12 A prepolymer of recycled polyester resin was obtained in the same manner as in Example 1, except that a candle filter with the mesh size shown in Table 1 was used. The obtained prepolymer was then used to carry out a solid-state polymerization reaction in the same manner as in Example 1, to obtain recycled polyester resins with mesh sizes of 1.05, 1.01, and 0.98. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0063] Example 13 A prepolymer of recycled polyester resin was obtained in the same manner as in Example 1, except that the heat treatment step was carried out at the temperature shown in Table 1. Then, using the obtained prepolymer, a solid-state polymerization reaction was carried out in the same manner as in Example 1, except that the solid-state polymerization reaction time was changed to 35 hours, to obtain a recycled polyester resin with an intrinsic viscosity of 1.06. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0064] Comparative Example 1 A prepolymer of recycled polyester resin was obtained in the same manner as in Example 1, except that the composition was changed so that the amount of recycled polyester added and the G / A value were as shown in Table 1. Then, using the obtained prepolymer, a solid-state polymerization reaction was carried out in the same manner as in Example 2, except that the solid-state polymerization reaction was carried out for 35 hours, to obtain a recycled polyester resin with an intrinsic viscosity of 0.99. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0065] Comparative Example 2 A prepolymer for recycled polyester resin was obtained in the same manner as in Example 1, except that the composition was changed so that the amount of BAEO copolymerized, the amount of recycled polyester added, and the G / A value were as shown in Table 1. Then, using the obtained prepolymer, a solid-state polymerization reaction was carried out in the same manner as in Example 4, except that the solid-state polymerization reaction was carried out for 80 hours, to obtain a recycled polyester resin with an intrinsic viscosity of 1.29. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0066] Comparative Example 3 A prepolymer of recycled polyester resin was obtained in the same manner as in Example 1, except that the heat treatment step was carried out at the temperature shown in Table 1. Then, using the obtained prepolymer, a solid-state polymerization reaction was carried out in the same manner as in Example 1, except that the solid-state polymerization reaction time was changed to 80 hours, to obtain a recycled polyester resin with an intrinsic viscosity of 1.31. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0067] Comparative Example 4 A prepolymer of recycled polyester resin was obtained in the same manner as in Example 1, except that a candle filter with the mesh size shown in Table 1 was used. The obtained prepolymer was then used to carry out a solid-state polymerization reaction in the same manner as in Example 1, to obtain a recycled polyester resin with an intrinsic viscosity of 1.15. A hollow container was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0068] Comparative Example 5 A recycled polyester resin prepolymer with an intrinsic viscosity of 0.65 was obtained in the same manner as in Example 1, except that the composition was changed so that the amount of BAEO copolymerized and the G / A value were as shown in Table 1. Solid-state polymerization was then attempted, but fusion of the resin occurred, making solid-state polymerization impossible.

[0069] Comparative Example 6 The same procedure as in Example 1 was carried out except that the polycondensation reaction temperature was set at the temperature shown in Table 1, but a prepolymer of recycled polyester resin could not be obtained.

[0070] Comparative Example 7 The same procedure as in Example 1 was carried out except that the heat treatment step was carried out at the temperature shown in Table 1, but the contents in the reactor solidified, making it impossible to continue the reaction thereafter.

[0071] The properties and evaluation results of the recycled polyester resins and hollow containers obtained in Examples 1 to 13 and Comparative Examples 1 to 4 are shown in Table 1.

[0072] [Table 1]

[0073] As is clear from Table 1, the recycled polyester resins obtained in Examples 1 to 13 had the BAEO copolymerization amount, intrinsic viscosity, carboxyl terminal group amount, diethylene glycol content, and average pressure rise rate within the ranges specified in the present invention, so they had low levels of foreign matter contamination and excellent thermal stability.As a result, the problem of whitening due to crystallization during blow molding did not occur, and hollow containers with excellent transparency and impact resistance could be easily obtained.

[0074] On the other hand, in Comparative Example 1, the G / A ratio during the depolymerization reaction was low, so the resulting recycled polyester resin had a high carboxyl end group concentration and a high average pressure rise rate. Furthermore, because the carboxyl end group concentration was high, thermal decomposition of the recycled polyester resin occurred during molding, resulting in poor haze in the resulting molded product, as well as poor moldability and impact resistance. In Comparative Example 2, the G / A ratio during the depolymerization reaction was high, so the resulting recycled polyester resin had a high diethylene glycol content and a high average pressure rise rate. Furthermore, the high diethylene glycol content caused thermal decomposition of the recycled polyester resin during molding, resulting in poor haze and poor moldability and impact resistance in the resulting molded product. In Comparative Example 3, the depolymerization in step (1) was carried out under heat treatment conditions at 290°C, so the resulting recycled polyester resin had a high carboxyl terminal group concentration and a high diethylene glycol content. Furthermore, because both the carboxyl terminal group concentration and the diethylene glycol content were high, thermal decomposition of the recycled polyester resin occurred during molding, and the resulting molded product had poor haze and also deteriorated in moldability and impact resistance. In Comparative Example 4, the filtration particle size of the candle filter placed between the ES can and the PC can was 30 μm, so the recycled polyester resin obtained contained a large amount of foreign matter and had a high average pressure rise rate, resulting in a blow-molded product with high haze and poor transparency. In Comparative Example 5, the amount of copolymerized BAEO was too high, which caused fusion during solid-state polymerization, making it impossible to carry out the solid-state polymerization reaction. As a result, the resulting recycled polyester resin had a low intrinsic viscosity, making it impossible to carry out direct blow molding. In Comparative Example 6, the polycondensation reaction temperature in step (3) was 240° C., so the polymerization rate was slow and a recycled polyester resin could not be obtained. In Comparative Example 7, the depolymerization in step (1) was carried out under heat treatment conditions at 230°C, so that the contents in the reactor solidified, making it impossible to continue the reaction thereafter.

Claims

1. A blow-molded article containing a recycled polyester resin that contains a component derived from at least one recycled polyester raw material, which is a) a used polyester product and b) an unused polyester generated in the process of manufacturing the polyester product, and satisfies all of the following (1) to (4): (1) When the total amount of all acid components constituting the polyester is 100 mol %, 70 mol % or more is terephthalic acid, (2) When the total amount of all glycol components is taken as 100 mol%, 60 to 96.22 mol% is ethylene glycol, 1 to 20 mol% is an ethylene oxide adduct of bisphenol A, and 0.5 to 4 mol% is diethylene glycol; (3) The carboxyl terminal group concentration is 30 equivalents / t; (4) The average pressure rise rate is 0.6 MPa / h or less (wherein the average pressure rise rate is a value calculated by the following procedure: a pressure rise tester including an extruder and a pressure sensor is used, a stainless steel filter (nominal mesh size: 1400 mesh, weave: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical wire diameter: 0.07 mm, horizontal wire diameter: 0.04 mm, filtration particle size: 12 μm) is set at the tip of the extruder, a polyester resin is melted in the extruder at 300° C., and the melt is extruded from the filter at a discharge rate of 29.0 g / min. The pressure value at the start of extrusion is defined as the “initial pressure value (MPa),” and the pressure value at the time of subsequent continuous extrusion for 12 hours is defined as the “final pressure value (MPa).” The average pressure rise rate is calculated based on these pressure values using the following calculation formula A: Average pressure increase rate (MPa / h) = (final pressure value - initial pressure value) / 12) ... A)

2. A method for producing the recycled polyester resin contained in the blow-molded article according to claim 1, comprising the steps of: (1) producing a recycled polyester resin from at least one recycled polyester raw material selected from a) used polyester products and b) unused polyesters generated in the process of producing polyester products; and (3) comprising the steps of: (1) a step of adding a recycled polyester raw material to a mixture containing an ethylene terephthalate oligomer, ethylene glycol, and an ethylene oxide adduct of bisphenol A so that the molar ratio of total glycol components / total acid components becomes 1.2 to 1.45, and performing depolymerization under heat treatment conditions of 245 to 280°C to obtain a reaction product containing a depolymerization product; (2) passing the reaction product through a filter having a filtration particle size of 10 to 25 μm to recover the filtrate; (3) adding a polymerization catalyst to the filtrate and carrying out a polycondensation reaction of the depolymerization at a temperature of 250°C or higher and a reduced pressure of 1.0 hPa or lower;

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