Recycled polyester resin composition and method for producing the same

Abstract

To provide a recycled polyester resin composition which contains particles, contains a waste polyester resin composition containing 10% or more and 90% or less of particles having a particle diameter of more than 0.5 μm with respect to the total amount of the particles in terms of volume as a raw material, and contains little particles having a particle diameter of more than 1.0 μm, and a method for producing the same.SOLUTION: A recycled polyester resin composition contains a waste polyester resin composition containing particles as a raw material, in which in the particles contained in the waste polyester resin composition, particles having a particle diameter of more than 0.5 μm is 10% or more and 90% or less with respect to the total amount of the particles, and the recycled polyester resin composition satisfies (1) and (2). (1) The content of particles is 1 mass ppm or more and less than 10,000 mass ppm. (2) Particles having a particle diameter of more than 1.0 μm among particles contained in the recycled polyester resin composition are 0% or more and 20% or less with respect to the total amount of the particles in terms of volume.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a recycled polyester resin composition derived from a waste polyester resin composition containing particles, and a method for producing the same. [Background technology]

[0002] Polyesters have excellent mechanical properties, thermal properties, chemical resistance, electrical properties, and moldability, and are used in a variety of applications. Among polyesters, polyethylene terephthalate (hereinafter referred to as PET) in particular has excellent transparency and processability, so it is widely used in applications that require high quality, such as optical films and release films. However, in the case of process films such as release films, they are disposed of after use, and in recent years there has been a demand for reducing the environmental impact.

[0003] One way to reduce environmental impact is to use thermal recycling, which involves burning discarded polyester resin to obtain thermal energy. However, thermal recycling generates carbon dioxide and results in a loss of polyester raw materials, so new petroleum-based raw materials must be used to reproduce polyester.

[0004] Another method is to depolymerize and repolymerize discarded polyester resin to improve its quality and reuse it, but the coarse particles contained in the discarded polyester resin can cause foreign matter defects when processed into film, or can cause thread breakage when processed into thread.

[0005] To address these issues, Patent Document 1 discloses a method of depolymerizing scrap PET and obtaining a recycled polyester resin composition using a disk-type centrifugal separator.

[0006] Patent Document 2 discloses a technology relating to a recycled polyester resin composition having a low content of particles with a particle diameter of 17 μm or more, which is obtained by depolymerizing unused polyester generated in the process of manufacturing used polyester products and / or polyester products.

[0007] Patent Document 3 discloses a technology relating to a recycled polyester resin composition obtained by depolymerizing at least one type of used polyester product and unused polyester generated in the process of manufacturing polyester products, and which has a small average rate of increase when passing through a 12 μm filter. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 5-230199 [Patent Document 2] Japanese Patent Application Publication No. 2023-129213 [Patent Document 3] Patent Publication No. 2021-120445 Summary of the Invention [Problem to be solved by the invention]

[0009] Patent Document 1 discloses a method for obtaining a recycled polyester resin composition by depolymerizing scrap PET and removing insoluble particles using a disk-type centrifuge. In the examples, filtration is performed using a 20-mesh wire filter (filtration accuracy of approximately 1 mm), but the filtration accuracy of the filter is so high that insoluble particles are essentially removed only by the centrifuge, which is insufficient for removing particles with a diameter exceeding 1.0 μm.

[0010] Patent Document 2 discloses a technique for depolymerizing used polyester products and / or unused polyester generated in the process of manufacturing polyester products, and filtering the depolymerized polyester through a 10 μm filter to obtain a recycled polyester resin composition with a low content of particles with a particle size of 17 μm or more. However, a 10 μm filter is insufficient to remove particles with a particle size of more than 1.0 μm.

[0011] Patent Document 3 discloses a technique for depolymerizing at least one of used polyester products and unused polyesters generated in the process of manufacturing polyester products, and filtering the depolymerized polyester through a 10-25 μm filter to obtain a recycled polyester resin composition that has a small average rising speed when passing through a 12 μm filter. However, filtration through a 10-25 μm filter is insufficient to remove particles with a particle size exceeding 1.0 μm.

[0012] An object of the present invention is to provide a recycled polyester resin composition containing particles with a particle diameter exceeding 1.0 μm, the composition being made from a waste polyester resin composition in which particles with a particle diameter exceeding 0.5 μm account for 10% to 90% by volume of the total amount of particles, and which contains a small amount of particles with a particle diameter exceeding 1.0 μm, and a method for producing the same. [Means for solving the problem]

[0013] As a result of intensive research to solve the above problems, the present inventors have arrived at a recycled polyester resin composition containing particles with a particle diameter exceeding 1.0 μm, and a method for producing the same, which is made from a waste polyester resin composition containing particles, and in which particles with a particle diameter exceeding 0.5 μm account for 10% to 90% by volume of the total amount of particles.

[0014] The object of the present invention is achieved by the following means. (1) A recycled polyester resin composition made from a waste polyester resin composition containing particles, wherein particles having a particle diameter of more than 0.5 μm account for 10% to 90% by volume of the total amount of particles contained in the waste polyester resin composition, and the recycled polyester resin composition satisfies the following conditions (1) and (2): Condition (1) Particle content is 1 mass ppm or more and less than 10,000 mass ppm Condition (2) Among the particles contained in the recycled polyester resin composition, particles having a particle diameter exceeding 1.0 μm account for 0% to 20% by volume of the total amount of particles. (2) A recycled polyester resin composition according to (1), which is made from a waste polyester resin composition containing particles, wherein particles having a particle diameter of more than 1.0 μm account for 21% or more and 90% or less by volume of the total amount of particles contained in the waste polyester resin composition, and the recycled polyester resin composition satisfies the following conditions (3) and (4): Condition (3) Particle content is 10 mass ppm or more and less than 10,000 mass ppm Condition (4) Among the particles contained in the recycled polyester resin composition, particles having a particle diameter exceeding 1.0 μm account for 0% to 20% by volume of the total amount of particles. (3) The recycled polyester resin composition according to (1), wherein particles having a particle diameter exceeding 0.5 μm account for 0% to 20% by volume of the total amount of particles contained in the recycled polyester resin composition. (4) A method for producing a recycled polyester resin composition, comprising steps (a) to (c), using a waste polyester resin composition in which particles having a particle diameter exceeding 1.0 μm account for 21% to 90% by volume of the total amount of particles. Step (a): A step of depolymerizing a waste polyester resin composition containing particles with ethylene glycol to obtain an oligomer. Step (b): A step of filtering the obtained oligomer through a filter having a filtration accuracy of less than 10 μm. Step (c): A step of polymerizing the filtered low polymer to obtain a recycled polyester resin composition. (5) A method for producing a recycled polyester resin composition according to (4), comprising step (a-1) between step (a) and step (b). Step (a-1): A step of removing some of the particles contained in the obtained low polymer using a centrifuge. (6) The method for producing a recycled polyester resin composition according to (5), wherein in step (a-1), the centrifuge is a decanter centrifuge or a cylindrical centrifuge. (7) The method for producing a recycled polyester resin composition according to any one of (4) to (6), which comprises step (a-2) between step (a) and step (b). Step (a-2): A step of filtering the obtained oligomer at least once through a filter with a higher filtration accuracy than the filter used in step (b). (8) A method for producing a recycled polyester resin composition according to any one of (4) to (7), wherein in step (a), ethylene glycol is added in an amount of 0.8 to 6.0 times by mole the dicarboxylic acid component in the polyester to depolymerize. (9) A method for producing a recycled polyester resin composition according to (5) or (6), comprising step (a-2) between step (a) and step (b), and carrying out step (a-1), step (a-2) and step (b) at a temperature of 200°C or higher but lower than 270°C. Step (a-2): A step of filtering the obtained oligomer at least once through a filter with a higher filtration accuracy than the filter used in step (b). [Effects of the Invention]

[0015] The present invention provides a recycled polyester resin composition having excellent transparency and few particles having a particle diameter exceeding 1.0 μm, and a method for producing the same, by recycling a waste polyester resin composition containing particles, in which particles having a particle diameter exceeding 0.5 μm account for 10% to 90% by volume of the total amount of particles. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below. In the present invention, ppm by mass is used to represent a mass ratio. The waste polyester resin composition used in the present invention is a used polyester resin composition and / or a polyester resin composition to be discarded generated in the polyester production process.

[0017] The waste polyester resin composition of the present invention must contain particles, and the particles having a particle diameter of more than 0.5 μm must account for 10% to 90% by volume of the total amount of particles.

[0018] The particle size was determined by observing the surface of the polyester resin composition with a scanning electron microscope (SEM) at a magnification of 2,000x, capturing the particle image in an image analyzer (LUZEX_AP manufactured by Nireco Corporation), and measuring the equivalent circle diameter. The SEM magnification was appropriately selected from 5,000 to 20,000x depending on the particle size. The particle sizes of at least 1,000 particles were measured at various observation locations. The volume fraction of particles with a particle size greater than 1.0 μm was also determined from the resulting volume particle size distribution.

[0019] The recycled polyester resin composition of the present invention must have a particle content of 1 ppm by mass or more and less than 10,000 ppm by mass, and the transparency is preferably 100 ppm by mass or more and less than 1,000 ppm by mass. If the particle content is 10,000 ppm by mass or more, the particle content becomes excessive, resulting in a decrease in the transparency of the recycled polyester resin composition. Furthermore, to achieve a particle content of less than 1 ppm by mass, more advanced separation techniques such as crystallization are required.

[0020] The particles contained in the recycled polyester resin composition of the present invention must have a particle diameter exceeding 1.0 μm of 0% to 20% by volume of the total amount of particles, and from the viewpoint of transparency, it is more preferable that the particle diameter is 10% or less. If the particle diameter exceeds 1.0 μm, the transparency may decrease if the particle diameter exceeds 20%. Furthermore, from the viewpoint of transparency, it is preferable that the particle diameter exceeding 0.5 μm is 0% to 20% by volume of the total amount of particles.

[0021] The method for producing the recycled polyester resin composition of the present invention must include the following steps (a), (b) and (c). Step (a): A step of depolymerizing a waste polyester resin composition containing particles with ethylene glycol to obtain an oligomer. Step (b): A step of filtering the obtained oligomer through a filter having a filtration accuracy of less than 10 μm. Step (c): A step of polymerizing the filtered low polymer to obtain a recycled polyester resin composition.

[0022] In the step (a) of the present invention, a waste polyester resin composition containing particles is depolymerized with ethylene glycol to obtain an oligomer.

[0023] In the method of depolymerizing the waste polyester resin composition of the present invention with ethylene glycol, it is preferable to depolymerize with ethylene glycol in an amount of 0.8 to 6.0 times by mole relative to the dicarboxylic acid component in the waste polyester resin composition, and from the viewpoint of the yield of the recycled polyester resin composition relative to the input raw material, it is preferable to use ethylene glycol in an amount of 0.8 to 1.5 times by mole. In addition, when depolymerization is performed continuously, the reaction time can be shortened by transferring a part of the obtained low polymer to the next step and adding the waste polyester resin composition and ethylene glycol to the remaining low polymer and performing the depolymerization reaction.

[0024] The temperature at which depolymerization is carried out is not particularly limited, but it is preferable to carry out the depolymerization at a final temperature of 200°C or higher and 250°C or lower in terms of reaction efficiency.

[0025] In step (a-2), the low polymer obtained in step (a) is preferably filtered through a filter having a filtration accuracy of 10 μm or more to remove contaminants such as dust.

[0026] The filtration accuracy referred to here is the nominal value set by each filter manufacturer, and is not the absolute filtration accuracy (removal rate of 99.9% or more).

[0027] Before proceeding to step (b), it is preferable to use a centrifuge in step (a-1) to remove some of the particles from the low polymer obtained in step (a) or step (a-2) before proceeding to step (b), in order to extend the filter life of step (b). Furthermore, it is preferable to use a decanter centrifuge as the centrifuge in order to reduce the loss of low polymer entrained in the separated particles. Furthermore, in order to reduce the volumetric ratio of particles exceeding 0.5 μm to 0% to 20% of the total amount of particles, it is preferable to use a cylindrical centrifuge, which has a high particle removal capacity by centrifugation.

[0028] When centrifugal separation is performed using a centrifuge, the temperature is preferably 200° C. or higher and 270° C. or lower. If the temperature is lower than 200° C., the viscosity of the oligomer increases, resulting in a decrease in the efficiency of centrifugal separation.

[0029] In step (b) of the present invention, the low polymer obtained in step (a), step (a-1), or step (a-2) must be filtered through a filter with a filtration accuracy of less than 10 μm, preferably 0.8 μm to 5 μm, and more preferably 0.8 μm to 1.0 μm, from the viewpoint of the efficiency of removing particles having a particle size of more than 1.0 μm. Furthermore, using multiple filters is preferable from the viewpoint of extending the filter life.

[0030] The temperature at which the low polymer obtained in step (a), step (a-1) or step (a-2) is filtered is preferably 200° C. or higher and 270° C. or lower in terms of filterability.

[0031] Step (c) of the present invention is a step of polymerizing the low polymer obtained in step (b) to obtain a recycled polyester resin composition. The polymerization method is not particularly limited, but examples include a method of polymerizing by adding a conventionally known polymerization catalyst compound such as an antimony compound, a titanium compound, an aluminum compound, or a germanium compound, and a method of polymerizing by utilizing a catalyst remaining in the low polymer without adding any additional catalyst. The resulting recycled polyester resin composition may also be solid-phase polymerized. Regarding the polymerization reaction temperature, in order to prevent bumping of the low polymer, it is preferable to gradually increase the temperature from the filtration temperature to the target temperature while reducing the pressure to 1 Torr or less.

[0032] Furthermore, various additives such as antioxidants, heat stabilizers, antistatic agents, copolymerization components, etc. may be added at any stage from before the start of the polymerization reaction to before the end of the polymerization reaction, as long as they do not impair the effects of the present invention.

[0033] The following describes an example of a method for obtaining a recycled polyester resin composition. Process (a) To a waste polyester resin composition containing 600 ppm by mass of calcium carbonate particles, with 50% by volume of particles exceeding 1.0 μm in particle diameter, ethylene glycol was added in an amount 1.0 times the molar ratio of the dicarboxylic acid components in the waste polyester resin composition. After the addition was completed, the mixture was gradually heated to 230°C under total reflux while stirring, taking care not to evaporate the ethylene glycol, to carry out the depolymerization reaction. After reaching 230°C, the mixture was stirred and maintained for 30 minutes to complete the depolymerization reaction, yielding an oligomer. If the amount of ethylene glycol added is large relative to the dicarboxylic acid components in the waste polyester resin composition, the temperature will be difficult to increase due to the heat of vaporization of ethylene glycol, so the depolymerization temperature should be set to approximately 200°C to 210°C.

[0034] After that, in the case where the depolymerization reaction is carried out continuously, a part of the obtained low polymer is transferred to the next step, and the waste polyester resin composition and a predetermined ethylene glycol are added to the remaining low polymer with stirring, and depolymerization can be carried out in the same manner.

[0035] Process (a-2) In order to remove contaminants such as dust from the oligomer obtained in step (a), the oligomer was filtered through a 400 mesh (filtration accuracy: 40 μm) metal filter preheated to 230° C. If the filtration temperature is too low, the oligomer may solidify, so it is recommended to preheat the filter to a temperature equal to or higher than the depolymerization temperature before filtration.

[0036] Process (a-1) The low polymer obtained in step (a-2) is placed in a decanter centrifuge preheated to 230°C, and centrifuged at a centrifugal force of 3,000 G while maintaining the temperature to obtain a low polymer from which some of the particles have been removed. If the centrifugation temperature is too low, the low polymer will solidify, resulting in a significant decrease in yield and possibly damaging the decanter centrifuge. Therefore, it is advisable to preheat the decanter centrifuge to a temperature equal to or higher than the depolymerization temperature before centrifugation.

[0037] If you want to remove more of the loan, it is better to use a cylindrical centrifuge. The centrifugal force should be 20,000 G or more. Cylindrical centrifuges are batch-type, so the yield tends to be lower than that of decanter centrifuges.

[0038] Process (b) The low polymer obtained in step (a-2) is filtered through a metal filter preheated to 230°C and having a filtration accuracy of 1 µm using a liquid-transfer pump preheated to 230°C to obtain a low polymer.

[0039] In this case, the filter life can be extended by using multiple metal filters with different filtration accuracies, for example, filtering through a filter with a filtration accuracy of 3 μm, a filter with a filtration accuracy of 1 μm, and a filter with a filtration accuracy of 0.8 μm in that order can efficiently remove particles with a particle size of 1.0 μm or more. If the filtration temperature is too low, the oligomers may solidify, clogging the filters or damaging the liquid delivery pump, so it is recommended to preheat the filtration to a temperature equal to or higher than the depolymerization temperature.

[0040] Process (c) The low polymer obtained in step (b) was transferred to a polymerization reactor, and antimony trioxide (80 ppm by mass of elemental antimony) was added as a polymerization catalyst to initiate the polymerization reaction. At this time, antioxidants, heat stabilizers, antistatic agents, copolymerization components, etc. may be added as needed. The polymerization temperature is not particularly limited, but for example, the temperature is gradually increased from 230°C, the same as in step (b), while reducing the pressure, to a final temperature of 290°C and 1 Torr or less. When the target degree of polymerization is reached, the mixture is discharged and chipped to obtain a recycled polyester resin composition.

[0041] At this time, if about 200 to 300 mass ppm of antimony element remains as catalyst residue in the waste polyester resin composition, polymerization can be carried out without adding a polymerization catalyst.

[0042] The obtained recycled polyester can be subjected to solid phase polymerization to further increase the degree of polymerization depending on the purpose. [Example]

[0043] The present invention will be described in more detail below with reference to examples. The physical properties in the examples were measured by the following methods.

[0044] (1) Particle size and volume particle size distribution in waste polyester resin composition and recycled polyester resin composition The surface of the polyester resin composition was observed with a scanning electron microscope (SEM) at a magnification of 2,000x to observe particles. The particle image was imported into an image analyzer (LUZEX_AP, manufactured by Nireco Corporation), and the equivalent circle diameter was measured to determine the particle size. The SEM magnification was appropriately selected from 5,000 to 20,000x depending on the particle size. The particle sizes of at least 1,000 particles were measured at various observation locations. The volume fraction of particles with a particle size greater than 1.0 μm and the volume fraction of particles with a particle size greater than 0.5 μm were also determined from the obtained volume particle size distribution.

[0045] (2) Measurement of particle amount in waste polyester resin composition and recycled polyester resin composition The surfaces of the waste polyester resin composition and the recycled polyester resin composition were observed with a scanning electron microscope (SEM) at a magnification of 5,000 to 20,000 times depending on the particle size. The observed particles were observed with SEM-EDX (energy dispersive X-ray spectroscopy) to identify the types of metal elements contained in the particles.

[0046] The amounts of the identified metal elements contained in the waste polyester resin composition and the recycled polyester resin composition were quantified using a fluorescent X-ray analyzer (model number: 3270) manufactured by Rigaku Denki Co., Ltd., and calculated using the following formula, and the total was taken as the particle amount. Ca (mass ppm) × 2.50 = calcium carbonate particle amount (mass ppm) (1) Ti (mass ppm) × 1.65 = titanium oxide particle amount (mass ppm) (2) Ba (mass ppm) × 1.70 = barium sulfate particle amount (mass ppm) (3) Al (mass ppm) × 1.59 = aluminum oxide particle amount (mass ppm) (4) Si (mass ppm) × 2.14 = silicon dioxide particle amount (mass ppm) (5)

[0047] (3) Quantitative determination of dicarboxylic acid components in waste polyester resin compositions The content of copolymerization components in the waste polyester resin composition was determined by NMR. After sampling the waste polyester resin composition, it was dissolved in hexafluoroisopropanol (HFIP) / d-chloroform (volume ratio 1 / 1) and quantified using 1H-NMR. After quantification, the content of dicarboxylic acid components was calculated.

[0048] (4) Yield of recycled polyester resin composition The weight of the waste polyester resin composition used was taken as 100%, and the weight of the resulting recycled polyester resin composition was calculated as a percentage.

[0049] (5) Solution haze (optical properties) 2 g of the recycled polyester resin composition was dissolved in 20 mL of a 3 / 2 (volume ratio) mixed solution of orthochlorophenol / 1,1,2,2-tetrachloroethane, and the haze was measured by integrating sphere photoelectric photometry using a cell with an optical path length of 20 mm and a haze meter (HZ-1 manufactured by Suga Test Instruments Co., Ltd.).

[0050] The solution haze is an index that indicates that the lower the value, the more excellent the transparency, and a value of 10.0% or less (◯, △) was considered to be acceptable. 10.0% or less ○ 10.1% or more and 20.0% or less △ 20.1% or more ×

[0051] The waste polyester used is shown in Table 1.

[0052] [Table 1]

[0053] [Example 1] Process (a) 150 parts by weight of waste polyester resin composition A and 50 parts by weight of ethylene glycol (1.0 times the molar ratio of the dicarboxylic acid component) were charged into a reactor and stirring was started. The mixture was refluxed to prevent ethylene glycol from distilling out of the reaction system, and the temperature was raised to 230°C. After reaching 230°C, the mixture was stirred for 30 minutes to complete the depolymerization reaction and obtain an oligomer.

[0054] Process (a-2) The oligomer obtained in step (a) was filtered through a 400 mesh (filtration accuracy: 40 μm) metal filter preheated to 230°C.

[0055] Process (a-1) The low polymer obtained in step (a-2) was placed in a decanter centrifuge preheated to 230°C, and centrifuged at a centrifugal force of 3,000 G while maintaining the temperature to obtain a low polymer.

[0056] Process (b) The low polymer obtained in step (a-2) was filtered through a metal filter preheated to 230°C and having a filtration accuracy of 1 µm using a liquid-transfer pump preheated to 230°C to obtain a low polymer.

[0057] Process (c) The low polymer obtained in step (b) was transferred to a polymerization reactor, and 0.03 parts by weight of antimony trioxide (equivalent to 80 ppm by mass of elemental antimony) was added as a polymerization catalyst to initiate the polymerization reaction. The temperature was gradually increased from 230°C while reducing the pressure, and finally to 290°C and 1 Torr or less. When the target degree of polymerization was reached, the mixture was discharged and chipped to obtain a recycled polyester resin composition. The results are shown in Table 2.

[0058] [Table 2-1]

[0059] [Table 2-2]

[0060] [Table 2-3]

[0061] The obtained recycled polyester resin composition had a particle size of more than 1.0 μm of 10% by volume of the total particle amount, that is, a particle amount of 200 ppm by mass, a yield of the recycled polyester resin composition of 90%, and a solution haze, which is an index of transparency, of 10% or less, and thus had sufficient quality as a recycled polyester resin composition.

[0062] [Examples 2 to 12, Comparative Examples 1 to 4] A recycled polyester resin composition was obtained in the same manner as in Example 1, except that the raw materials used, the amount of ethylene glycol added, the filtration conditions, and the centrifugation conditions were changed. The results are shown in Table 2.

[0063] In Example 2, a recycled polyester resin composition was obtained in the same manner as in Example 1, except that filters with filtration accuracies of 3 μm, 1 μm, and 0.8 μm were used in step (b), and filtration was performed in order from the filter with the highest filtration accuracy. As a result, although the yield tended to decrease, more particles could be removed, and the recycled polyester resin composition had sufficient quality.

[0064] In Example 3, a recycled polyester resin composition was obtained in the same manner as in Example 2, except that steps (a-1) and (a-2) were not performed and filters with filtration accuracies of 7 μm, 1 μm, and 0.8 μm were used in step (b). By not performing steps (a-1) and (a-2), the number of particles and the volume fraction of particles with a particle size of more than 1.0 μm increased, and the solution haze tended to increase, but the recycled polyester resin composition had sufficient quality.

[0065] In Example 4, a recycled polyester resin composition was obtained in the same manner as in Example 3, except that filtration using a filter with a filtration accuracy of 10 μm was performed in step (a-2). As a result, the volume fraction of particles having a particle size of more than 1.0 μm tended to decrease, and the recycled polyester resin composition had sufficient quality.

[0066] In Example 5, a recycled polyester resin composition was obtained in the same manner as in Example 2, except that a disc centrifuge was used in step (a-1). Although the use of the disc centrifuge resulted in a decrease in the yield of the recycled polyester resin composition, which was thought to be due to an increase in the amount of low polymers entrained in the separated particles, the recycled polyester resin composition had sufficient quality.

[0067] In Example 6, the raw material was changed to waste polyester resin composition B, and a recycled polyester resin was obtained in the same manner as in Example 2, except that the filtration accuracy of the filter in step (b) was increased. The volume fraction and particle amount of particles having a particle diameter of 1.0 μm or more tended to increase, which is thought to be due to the large amount of particles contained in the raw material waste polyester resin composition B, and the solution haze also tended to increase, but the recycled polyester resin composition had sufficient quality.

[0068] In Example 7, compared to Example 2, the amount of ethylene glycol added in step (a) was changed, and the depolymerization temperature and the temperatures in steps (a-1), (a-2), and (b) were changed by 200°C. Furthermore, in step (c), after adding antimony trioxide, the temperature was raised to 230°C, and the excess ethylene glycol was distilled off before starting the polymerization reaction. The resulting recycled polyester resin composition tended to have a reduced particle amount and an improved yield, and was of sufficient quality as a recycled polyester resin composition. This is thought to be because the viscosity of the low polymer decreased as the amount of ethylene glycol added increased, allowing the centrifugation in step (a-1) to be carried out more efficiently.

[0069] In Example 8, a recycled polyester resin composition was obtained in the same manner as in Example 2, except that the amount of ethylene glycol added in step (a) was reduced. Although the volume fraction of particles with a particle size of more than 1.0 μm tended to increase and the yield also tended to decrease, the recycled polyester resin composition had sufficient quality. This is thought to be due to the fact that the reduced amount of ethylene glycol added increased the viscosity of the low polymer, reducing the efficiency of the centrifugation in step (b), and increasing the amount of low polymer entrained in the separated particles.

[0070] In Example 9, a recycled polyester resin composition was obtained in the same manner as in Example 2, except that the amount of ethylene glycol added in step (a) was increased and the depolymerization temperature and the temperatures in steps (a-1), (a-2), and (b) were changed to 220°C. As a result, the quality was almost the same as in Example 2, and the recycled polyester resin composition had sufficient quality. This is thought to be because the effects of the decrease in viscosity of the low polymer due to the increase in ethylene glycol and the increase in viscosity due to lowering the temperature of the low polymer to 220°C were offset.

[0071] In Comparative Example 1, a test recycled polyester resin composition was obtained in the same manner as in Example 1, except that step (a-1) and step (b) were not performed. As a result, there was almost no change in the volume fraction and particle amount of particles having a particle diameter of 1.0 μm or more, and the target value for solution haze was not achieved, resulting in an insufficient quality as a recycled polyester resin composition.

[0072] In Comparative Example 2, a recycled polyester resin composition was obtained in the same manner as in Example 1, except that the raw materials and the centrifugal force in (a-1) were changed and step (a-1) was not performed. As a result, the volume fraction and particle amount of particles having a particle size of more than 1.0 μm were not sufficiently improved, and the target value for solution haze was not achieved, resulting in an insufficient quality as a recycled polyester resin composition.

[0073] In Comparative Example 3, a recycled polyester resin composition was obtained in the same manner as in Example 1 except for changing the raw materials. As a result, the improvement in the volume fraction of particles having a particle diameter of more than 1.0 μm was insufficient, and the target for solution haze was not achieved, resulting in an insufficient quality as a recycled polyester resin composition. This is thought to be because the volume fraction of particles having a particle diameter of more than 1.0 μm among the particles contained in waste polyester resin composition F was too high, and they could not be completely removed using only a filter with a filtration accuracy of 1.0 μm.

[0074] In Comparative Example 4, a recycled polyester resin composition was obtained in the same manner as in Example 1 except for changing the raw materials. As a result, the particle amount was large, and the target solution haze was not achieved, resulting in an insufficient quality as a recycled polyester resin composition. This is thought to be because the volume fraction of particles with a particle diameter of more than 1.0 μm contained in the waste polyester resin composition G was low, so most of the particles passed through a filter with a filtration accuracy of 1.0 μm, resulting in a decrease in solution haze.

[0075] In Example 10, a recycled polyester resin composition was obtained in the same manner as in Example 2, except that the raw materials were changed. As a result, the amount of particles tended to increase, but the recycled polyester resin composition had sufficient quality. This is thought to be because the amount of particles contained in the waste polyester resin composition C was large and the volume fraction of particles with a particle diameter of more than 1.0 μm was low, so the amount of particles that could be removed relative to the total amount of particles was small.

[0076] In Example 11, a recycled polyester resin composition was obtained in the same manner as in Example 2 except for changing the raw materials. As a result, the amount of particles tended to increase, but the recycled polyester resin composition had sufficient quality. This is thought to be because the amount of particles contained in the waste polyester resin composition D was large, resulting in an increase in the amount of remaining particles.

[0077] In Example 12, a recycled polyester resin composition was obtained in the same manner as in Example 2 except for changing the raw materials. As a result, the amount of particles tended to increase, but the recycled polyester resin composition had sufficient quality. This is thought to be because the volume fraction of particles with a particle diameter of more than 1.0 μm contained in the waste polyester resin composition C was low, and therefore the amount of particles that could be removed relative to the total amount of particles was small.

[0078] [Example 13] A recycled polyester resin composition was obtained in the same manner as in Example 1, except that a cylindrical centrifuge was used as the centrifuge in step (a-1) and centrifugation was carried out at a centrifugal force of 20,000 G.

[0079] The obtained recycled polyester resin composition had 0% by volume of particles with a particle size exceeding 1.0 μm relative to the total particle amount, 10% by volume of particles with a particle size exceeding 0.5 μm relative to the total particle amount, and a particle amount of 10 ppm by mass, and the yield of the recycled polyester resin composition was 85%, and the solution haze, which is an index of transparency, was also 10% or less. Compared to Example 1, the yield of the recycled polyester resin composition tended to decrease, but both the coarse particles and the particle amount were significantly reduced, and the recycled polyester resin composition had sufficient quality.

[0080] [Example 14] A recycled polyester resin composition was obtained in the same manner as in Example 13, except that the centrifugal force and the filter were changed.

[0081] The obtained recycled polyester resin composition contained 0% by volume of particles having a particle diameter exceeding 1.0 μm relative to the total particle amount, 0% by volume of particles having a particle diameter exceeding 0.5 μm relative to the total particle amount, and the particle amount was 2 ppm by mass.The yield of the recycled polyester resin composition was 85%, and the solution haze, which is an index of transparency, was 10% or less.

[0082] Comparative Example 5 A recycled polyester resin composition was obtained in the same manner as in Example 13, except that waste polyester resin composition H was used and the centrifugal force was changed.

[0083] The resulting recycled polyester resin composition had a particle amount as large as 12,000 ppm by mass and a solution haze exceeding 20%, and was of insufficient quality as a recycled polyester resin composition.

[0084] This is thought to be because the ratio of particles with a particle size of less than 0.5 μm contained in the waste polyester resin composition H used as the raw material was high and could not be sufficiently removed.

[0085] [Example 15] A recycled polyester resin composition was obtained in the same manner as in Example 10, except that a cylindrical centrifuge was used as the centrifuge and the centrifugation was carried out at a centrifugal force of 20,000 G.

[0086] The obtained recycled polyester resin composition had 0% by volume of particles with a particle diameter exceeding 1.0 μm relative to the total particle amount, 0% by volume of particles with a particle diameter exceeding 0.5 μm relative to the total particle amount, and a particle amount of 20 ppm by mass, and the recycled polyester resin composition yield was 83%, and the solution haze, which is an index of transparency, was 10% or less. Compared to Example 10, the yield of the recycled polyester resin composition tended to decrease, but both the coarse particles and the particle amount were reduced, and the recycled polyester resin composition had sufficient quality.

[0087] [Example 16] A recycled polyester resin composition was obtained in the same manner as in Example 11, except that a cylindrical centrifuge was used as the centrifuge and the centrifugation was carried out at a centrifugal force of 20,000 G.

[0088] The obtained recycled polyester resin composition had 0% by volume of particles with a particle diameter exceeding 1.0 μm relative to the total particle amount, 0% by volume of particles with a particle diameter exceeding 0.5 μm relative to the total particle amount, and a particle amount of 15 mass ppm. The recycled polyester resin composition yield was 83%, and the solution haze, which is an index of transparency, was 10% or less. Compared to Example 11, the yield of the recycled polyester resin composition tended to decrease, but both the coarse particles and the particle amount were reduced, and the recycled polyester resin composition had sufficient quality.

[0089] [Example 17] A recycled polyester resin composition was obtained in the same manner as in Example 12, except that a cylindrical centrifuge was used as the centrifuge and the centrifugation was carried out at a centrifugal force of 20,000 G.

[0090] The obtained recycled polyester resin composition had 0% by volume of particles with a particle diameter exceeding 1.0 μm relative to the total particle amount, 0% by volume of particles with a particle diameter exceeding 0.5 μm relative to the total particle amount, and a particle amount of 20 ppm by mass, and the recycled polyester resin composition yield was 83%, and the solution haze, which is an index of transparency, was 10% or less. Compared to Example 12, the yield of the recycled polyester resin composition tended to decrease, but both the coarse particles and the particle amount were reduced, and the recycled polyester resin composition had sufficient quality.

[0091] [Example 18] A recycled polyester resin composition was obtained in the same manner as in Example 8, except that a cylindrical centrifuge was used as the centrifuge and the centrifugation was carried out at a centrifugal force of 20,000 G.

[0092] The obtained recycled polyester resin composition had 0% by volume of particles with a particle diameter exceeding 1.0 μm relative to the total particle amount, 10% by volume of particles with a particle diameter exceeding 0.5 μm relative to the total particle amount, and a particle amount of 12 ppm by mass, and the yield of the recycled polyester resin composition was 73%, and the solution haze, which is an index of transparency, was also 10% or less. Compared to Example 12, the yield of the recycled polyester resin composition tended to decrease, but both the coarse particles and the particle amount were reduced, and the recycled polyester resin composition had sufficient quality. [Industrial Applicability]

[0093] The recycled polyester resin composition thus obtained is useful for optical applications, agricultural materials, horticultural materials, fishing materials, civil engineering and construction materials, stationery, medical supplies, automotive parts, electrical and electronic parts, and other applications.

Claims

1. A recycled polyester resin composition made from a waste polyester resin composition containing particles, wherein particles having a particle diameter of more than 0.5 μm account for 10% to 90% by volume of the total amount of particles contained in the waste polyester resin composition, and the recycled polyester resin composition satisfies the following conditions (1) and (2): Condition (1) Particle content is 1 mass ppm or more and less than 10,000 mass ppm Condition (2) Among the particles contained in the recycled polyester resin composition, particles having a particle diameter exceeding 1.0 μm account for 0% to 20% by volume of the total amount of particles.

2. 2. A recycled polyester resin composition according to claim 1, wherein the recycled polyester resin composition is made from a waste polyester resin composition containing particles, and the particles contained in the waste polyester resin composition have a particle diameter of more than 1.0 μm, which accounts for 21% to 90% by volume of the total amount of particles, and the recycled polyester resin composition satisfies the following conditions (3) and (4): Condition (3) Particle content is 10 mass ppm or more and less than 10,000 mass ppm Condition (4) Among the particles contained in the recycled polyester resin composition, particles having a particle diameter exceeding 1.0 μm account for 0% to 20% by volume of the total amount of particles.

3. 2. The recycled polyester resin composition according to claim 1, wherein particles having a particle diameter exceeding 0.5 μm account for 0% to 20% by volume of the total amount of particles contained in the recycled polyester resin composition.

4. A method for producing a recycled polyester resin composition, comprising steps (a) to (c), using a waste polyester resin composition in which particles having a particle diameter of more than 1.0 μm account for 21% to 90% by volume of the total amount of particles. Step (a): A step of depolymerizing a waste polyester resin composition containing particles with ethylene glycol to obtain a low polymer. Step (b): A step of filtering the obtained low polymer through a filter having a filtration accuracy of less than 10 μm. Step (c): A step of polymerizing the filtered low polymer to obtain a recycled polyester resin composition.

5. The method for producing a recycled polyester resin composition according to claim 4, comprising step (a-1) between step (a) and step (b). Step (a-1): A step of removing a portion of the particles contained in the obtained low polymer using a centrifuge.

6. The method for producing a recycled polyester resin composition according to claim 5, wherein in the step (a-1), the centrifuge is a decanter centrifuge or a cylindrical centrifuge.

7. The method for producing a recycled polyester resin composition according to claim 4, comprising step (a-2) between step (a) and step (b). Step (a-2): A step of filtering the obtained low polymer at least once through a filter having a higher filtering accuracy than the filter used in step (b).

8. 5. The method for producing a recycled polyester resin composition according to claim 4, wherein in step (a), ethylene glycol is added in an amount of 0.8 to 6.0 times by mole the acid component in the polyester to depolymerize it.

9. The method for producing a recycled polyester resin composition according to claim 5 or 6, comprising step (a-2) between step (a) and step (b), and carrying out step (a-1), step (a-2) and step (b) at a temperature of 200°C or higher and lower than 270°C. Step (a-2): A step of filtering the obtained low polymer at least once through a filter having a higher filtering accuracy than the filter used in step (b).

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