Pellets, injection molded products, and extruded products

Abstract

We offer pellets containing PBST, which has excellent blocking resistance. [Solution] A pellet containing PBST having as its main constituent units a constituent unit derived from succinic acid, a constituent unit derived from terephthalic acid, and a constituent unit derived from 1,4-butanediol, wherein the Raman spectrum measured from the pellet is 1680-1780 cm⁻¹ -1 The spectrum in the wavenumber range is 1711±5cm². -1 The first wavenumber range, and 1722±5cm -1 In a Raman spectrum fitted using a Lorentz function with two peaks each having a peak top in the second wavenumber range, the intensity of the peak in the first wavenumber range I 01 And the peak intensity I in the second wavenumber range 02 The intensity ratio (I 01 / I 02 Pellets in which the ratio is 1.00 or higher.

Description

[Technical Field]

[0001] This invention relates to pellets containing polybutylene succinate terephthalate (hereinafter sometimes referred to as "PBST"), and injection-molded and extruded articles obtained using these pellets. More specifically, it relates to pellets containing PBST that are suitable for injection molding and extrusion molding, and injection-molded and extruded articles obtained using resin pellets containing these pellets. [Background technology]

[0002] In modern society, paper, plastics, aluminum foil, and other materials are used in a wide range of applications, including packaging materials for various foods, pharmaceuticals, general merchandise, liquids, powders, and solids, as well as agricultural and construction materials. Plastics, in particular, excel in strength, water resistance, moldability, transparency, and cost, and are widely used as bags and containers. Plastics currently used in these applications include polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate. However, molded products made from the above-mentioned plastics do not biodegrade or hydrolyze in the natural environment, or their decomposition rate is extremely slow. As a result, if buried after use, they may remain in the soil, or if dumped, they may spoil the landscape. Furthermore, even when incinerated, they have problems such as generating harmful gases and damaging incinerators.

[0003] To address these challenges, numerous studies and developments have been conducted on biodegradable resins that are broken down into carbon dioxide and water by microorganisms in soil or water. Representative examples of biodegradable resins include aliphatic polyester resins such as polylactic acid, PBS, and polybutylene succinate adipate (PBSA), and aromatic-aliphatic copolymer polyester resins such as polybutylene adipate terephthalate (PBAT) and polybutylene succinate terephthalate (PBST).

[0004] In particular, PBST has been the subject of various studies because it is a material that can achieve a high level of both biodegradability and mechanical strength and moldability. Patent Document 1 discloses a method for producing aliphatic aromatic polyester with improved crystallinity, addressing the problem of blocking caused by insufficient crystallinity that conventional aliphatic aromatic polyesters such as PBST have. Specifically, it discloses that aliphatic aromatic polyester with a high degree of crystallinity can be obtained by introducing a specific nucleating agent into the reaction system when producing aliphatic aromatic polyester by polycondensation reaction via esterification and / or transesterification reactions. Furthermore, Patent Document 3 discloses a method for producing polyester in which THF and oligomers produced as by-products in the manufacturing process of aliphatic aromatic polyester affect the quality of the polyester, and in order to reduce this, a contact treatment step is disclosed in which aliphatic aromatic polyester pellets are brought into contact with a mixed liquid containing ethanol and water. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2021 / 161846 [Patent Document 2] Japanese Patent Publication No. 2024-049583 [Patent Document 3] Japanese Patent Publication No. 2018-145221 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, according to the inventors' research, PBS produced by the method described in Patent Document 1 Even with pellets containing T, we found that under more severe conditions, specifically when heat or load is applied to the pellets during drying or supplying them to a molding machine, a problem can occur where the pellet particles fuse together and aggregate, known as blocking. This problem is presumed to be due to the fact that PBST has a larger amorphous portion compared to PBS, and blocking can occur even at low temperatures such as 50-60°C. One aspect of the present invention aims to solve the above-mentioned problems and provides pellets containing PBST that are less prone to blocking even when heat and / or pressure is applied, and that can be stably supplied to a molding machine as a feed material for injection molding, extrusion molding, etc. Another aspect of the present invention aims to provide biodegradable injection molded or extruded articles that can be stably manufactured. [Means for solving the problem]

[0007] The gist of this invention is as follows: [1] A pellet containing polybutylene succinate terephthalate having as its main constituent units a constituent unit derived from succinic acid, a constituent unit derived from terephthalic acid, and a constituent unit derived from 1,4-butanediol, The Raman spectrum measured from the pellet shows values ​​between 1680 and 1780 cm⁻¹. -1 The spectrum in the wavenumber range is 1711±5cm². -1 The first wavenumber range, and 1722±5cm -1 In a Raman spectrum fitted using a Lorentz function with two peaks each having a peak top in the second wavenumber range, the intensity of the peak in the first wavenumber range I 01 And the peak intensity I in the second wavenumber range 02 The intensity ratio (I 01 / I 02 Pellets in which the ratio is 1.00 or higher. [2] The pellet according to [1], wherein the strength ratio is 1.00 or more and 2.50 or less. [3] The pellet according to [1] or [2], wherein the content of a cyclic dimer consisting of succinic acid and 1,4-butanediol in the pellet is 2,500 ppm by mass or less. [4] The pellet according to any one of [1] to [3], wherein the intrinsic viscosity (IV) of the pellet is 1.2 dL / g or more and 2.2 dL / g or less. [5] A pellet according to any one of [1] to [4], wherein the molar ratio of constituent units derived from succinic acid to constituent units derived from terephthalic acid (constituent units derived from succinic acid / constituent units derived from terephthalic acid) is 10 / 90 to 90 / 10. [6] The pellet according to [5], wherein the molar ratio is 40 / 60 to 60 / 40. [7] An injection-molded resin pellet containing at least one of the pellets described in [1] to [6]. [8] An extruded resin pellet product containing at least one of the pellets described in [1] to [6]. [Effects of the Invention]

[0008] According to one aspect of the present invention, pellets containing PBST that are less prone to blocking even when heat and / or pressure are applied can be obtained. According to another aspect of the present invention, biodegradable injection-molded or extruded articles that can be manufactured stably can be obtained. [Brief explanation of the drawing]

[0009] [Figure 1] This is a Raman chart (Lorentz-fitted Raman Spectrum) showing the results obtained by fitting the Raman spectrum measured from the pellet according to Example 1 using the Lorentz function. [Figure 2] This is a schematic diagram illustrating one aspect of a part of the pellet manufacturing process (esterification reaction step) related to this disclosure. [Figure 3] This is a schematic diagram illustrating one aspect of a part of the pellet manufacturing process (polycondensation process) related to this disclosure. [Figure 4]Schematic explanatory diagram of one aspect of a part of the pellet manufacturing process according to the present disclosure (solvent contact process / cyclic dimer separation process). [Figure 5] Schematic explanatory diagram of one aspect of a part of the pellet manufacturing process according to the present disclosure (drying process).

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist. In this specification, “mass %” and “weight %” are synonymous, “mass ppm” and “weight ppm” are synonymous, and “parts by mass” and “parts by weight” are synonymous. In this specification, expressions representing numerical ranges, such as “XX or more”, “YY or less”, and “XX to YY”, mean numerical ranges including XX and YY as endpoints, unless otherwise specified. When numerical ranges are described stepwise, any combination of the upper and lower limits of each numerical range is also disclosed. Further, in this specification, for example, a description such as “at least one selected from the group consisting of XX, YY, and ZZ” means any one of only XX, only YY, only ZZ, a combination of XX and YY, a combination of XX and ZZ, a combination of YY and ZZ, or a combination of XX, YY, and ZZ.

[0011] The present inventors conducted further studies to solve the above problems. In the process, PBST prepared by the method described in Patent Document 1 was heated and melted to be transferred from the crystalline state to the amorphous state, and the change in the Raman spectrum of PBST before and after the heating and melting was observed. As a result, in the Raman spectrum of PBST before heating and melting, one peak having a peak top in the wavenumber range of 1711 ± 5 cm -1 was observed, but in the Raman spectrum of PBST after heating and melting, the Raman peak was 1722 ± 5 cm -1We confirmed that it shifts to the wavenumber range (second wavenumber range). In the Raman spectrum of PBST, the above-mentioned 1711±5 cm⁻¹ was observed. -1 and 1722±5cm -1 The peak appearing in the wavenumber range is attributed to the C=O stretching in the succinic acid units of PBST. From this, it is presumed that the peak observed in the first wavenumber range is attributed to the C=O stretching in the succinic acid units of crystalline PBST, and the peak observed in the second wavenumber range is attributed to the C=O stretching in the succinic acid units of amorphous PBST. Furthermore, the Raman peak observed in the Raman spectrum of PBST before heating and melting, which has its peak top in the first wavenumber range, is thought to be a superposition of the peak attributed to the C=O stretching in the succinic acid units of crystalline PBST and the peak attributed to the C=O stretching in the succinic acid units of amorphous PBST. Furthermore, the present inventors have subjected the pellets of PBST prepared by the method described in Patent Document 1 to a specific treatment, specifically, a solvent contact step described later, or both the solvent contact step and the slow cooling step described later, thereby increasing the Raman spectrum measured from the pellets between 1680 and 1780 cm⁻¹. -1 The spectrum in the wavenumber range is 1711±5cm². -1 The first wavenumber range, and 1722±5cm -1 In a Raman spectrum fitted using a Lorentz function with two peaks, each having a peak top in the second wavenumber range, the second wavenumber range (1722±5cm) -1 The intensity of the peak I, which is attributed to the C=O stretching of succinate units in PBST expressed in ) 02 For the first wavenumber range (1711±5cm) -1 The intensity of the peak I, which is attributed to the C=O stretching of succinate units in PBST expressed in ) 01 Ratio I 01 / I 02We discovered that the intensity ratio (hereinafter also simply referred to as "intensity ratio") changes. Specifically, we found that the intensity ratio of pellets that have undergone a specific processing step is significantly higher than the intensity ratio of pellets that have undergone that specific processing step, and that pellets with an intensity ratio above a certain value are less likely to block when heated and / or pressurized. This invention is based on these new findings.

[0012] In other words, a pellet according to one aspect of the present invention contains polybutylene succinate terephthalate (PBST) having as its main constituent units a constituent unit derived from succinic acid, a constituent unit derived from terephthalic acid, and a constituent unit derived from 1,4-butanediol. The Raman spectrum measured from the pellet is 1680-1780 cm⁻¹. -1 The spectrum in the wavenumber range is 1711±5cm². -1 The first wavenumber range, and 1722±5cm -1 In a Raman spectrum fitted using a Lorentz function with two peaks each having a peak top in the second wavenumber range, the intensity of the peak in the first wavenumber range I 01 And the peak intensity I in the second wavenumber range 02 The intensity ratio (I 01 / I 02 ) is 1.00 or higher.

[0013] The inventors speculate that the reason such pellets exhibit excellent blocking resistance even when heat / pressure is applied is as follows: As described above, in the Raman chart of PBST pellets, the peaks appearing in the first and second wavenumber ranges are attributed to C=O stretching in the succinic acid units of PBST, and the Raman peak with a peak top in the first wavenumber range is considered to be a superposition of a peak attributed to C=O stretching in the succinic acid units of amorphous PBST over a peak attributed to C=O stretching in the succinic acid units of crystalline PBST. Therefore, the intensity of the peak in the first wavenumber range is I 01And the peak intensity I in the second wavenumber range 02 The intensity ratio (I 01 / I 02 This value is considered to be an indicator of the degree of balance between crystalline PBST and amorphous PBST in a pellet containing PBST. And I 01 / I 02 However, PBST pellets with a value of 1.00 or higher are considered to have a higher crystalline state compared to PBST obtained by the method described in Patent Document 1, and are therefore less prone to blocking even when heated or pressurized.

[0014] The intensity ratio of PBST according to the present invention is 1.00 or higher, but more preferably 1.10 or higher. The upper limit of the intensity ratio is not particularly limited, but is preferably 2.50 or lower, more preferably 1.40 or lower, and particularly preferably 1.35 or lower. In other words, the intensity ratio of pellets containing PBST according to the present invention is preferably 1.00 or higher and 2.50 or lower, more preferably 1.10 or higher and 1.40 or lower, and particularly preferably 1.10 or higher and 1.35 or lower. Pellets with an intensity ratio within the above range have a high crystallinity of PBST in the pellet, so blocking can be more reliably prevented when heat or pressure is applied to the pellet.

[0015] The method for measuring the spectrum of pellets containing PBST according to this embodiment by Raman spectroscopy is not particularly limited, but it is preferable to measure it in accordance with, for example, Japanese Industrial Standard (JIS) K0317:2010 (General Rules for Raman Spectroscopic Analysis). More specifically, for example, the Raman spectrum of pellets according to this disclosure can be measured using the following Raman spectrometer and under the following conditions. Raman spectrometer: "RAMAN touch" (product name, manufactured by Nanophoton Corporation) Measurement conditions • Measurement mode: Point • Laser wavelength: 532nm • Laser output: 12mW (Neutral-reducing filter opening: 200 / 255) • Diffraction grating: 1200 gr / mm • Pinhole: 20 μm Exposure time: 100 seconds • Number of cumulative counts: 10 • Objective lens: 100x ·Measurement temperature: 25℃

[0016] The Raman spectrum obtained using the above Raman spectrometer and measurement conditions is attributed to the C=O stretching in the succinic acid unit of PBST, with a range of 1711±5 cm². -1 The peak of the Raman scattering intensity has a peak top in the first wavenumber range and is 1722±5 cm. -1 The Raman scattering intensity peak, which has its peak top in the second wavenumber range, and its two components are fitted using the Lorentz function shown in the following formula (1). In formula (1), A represents the peak intensity and w represents the full width at half maximum of the peak. Furthermore, X0 represents the peak position, which in this disclosure is 1711±5cm. -1 , and 1722±5cm -1 This is the result.

[0017]

number

[0018] Then, in the obtained fitted Raman spectrum (Lorentz-fitted Raman Spectrum), the peak intensity I in the first wavenumber range 01 and the peak intensity I in the second wavenumber range 02 The intensity ratio (I 01 / I 02 Specifically, the peak of the first wavenumber range obtained by fitting (i.e., X0 = 1711 ± 5 cm) is determined. -1 The intensity A (hereinafter also referred to as "A1") obtained by the above formula (1) relating to ), and the peak of the second wavenumber range (i.e., X0 = 1722 ± 5 cm) -1 The ratio (A1 / A2) of the intensity A (hereinafter also referred to as "A2") obtained by the above formula (1) relating to ) is I 01 / I 02 It corresponds to this.

[0019] <Polybutylene succinate terephthalate (PBST)> PBST is an aliphatic aromatic polyester having as its main constituent units a constituent unit derived from succinic acid, a constituent unit derived from terephthalic acid, and a constituent unit derived from 1,4-butanediol. Specifically, for example, PBST according to one aspect of the present invention has as its main constituent units a constituent unit derived from succinic acid represented by the following structural formula (1), a constituent unit derived from terephthalic acid represented by the following structural formula (2), and a constituent unit derived from 1,4-butanediol represented by the following structural formula (3). -OC-CH2-CH2-CO- (1) -OC-C6H4-CO- (2) -O-(CH2)4-O- (3)

[0020] Furthermore, "constituent units derived from succinic acid" refers to the constituent units corresponding to succinic acid, that is, the constituent units formed by the reaction of the two carboxyl groups present in succinic acid. Similarly, "constituent units derived from terephthalic acid" refers to the constituent units corresponding to terephthalic acid, that is, the constituent units formed by the reaction of the two carboxyl groups present in terephthalic acid. Moreover, "constituent units derived from 1,4-butanediol" refers to the constituent units corresponding to 1,4-butanediol, that is, the constituent units formed by the reaction of the two hydroxyl groups present in 1,4-butanediol. Furthermore, in this specification, the constituent units of PBST may be referred to as compound units for the compounds from which each constituent unit is derived. Specifically, for example, a constituent unit derived from succinic acid may be called a "succinic acid unit," and a constituent unit derived from terephthalic acid may be called a "terephthalic acid unit." The constituent units derived from 1,4-butanediol are sometimes called "1,4-butanediol units," the constituent units derived from carboxylic acids are sometimes called "carboxylic acid units," and the constituent units derived from diols are sometimes called "diol units."

[0021] Furthermore, the term "main constituent unit" usually means that the constituent unit accounts for 80 mol% or more of the total number of moles of constituent units in PBST. Specifically, in the PBST according to this embodiment, the total number of moles of succinic acid units, terephthalic acid units, and 1,4-butanediol units is 80 mol% or more of the total number of moles of constituent units that make up PBST. Furthermore, the PBST according to this embodiment may be an aliphatic aromatic polyester in which the total number of moles of succinic acid units, terephthalic acid units, and 1,4-butanediol units is 90% or more of the total number of moles of constituent units constituting the PBST, and may be 95% or more of the total number of moles of constituent units constituting the PBST, and furthermore, in which no constituent units other than succinic acid units, terephthalic acid units, and 1,4-butanediol units are included at all, that is, it consists only of succinic acid units, terephthalic acid units, and 1,4-butanediol units, and the total number of moles of succinic acid units, terephthalic acid units, and 1,4-butanediol units is 100 mol% of the total number of moles of constituent units constituting the PBST. In this specification, when counting the number of moles of constituent units in PBST, the smallest ester unit constituting the PBST is considered to be 1 mole.

[0022] The total ratio of succinic acid units to terephthalic acid units in PBST is preferably 80 mol% or more, more preferably 85 mol% or more, particularly preferably 90 mol% or more, even more preferably 95 mol% or more, and may also be 100 mol% relative to the total number of dicarboxylic acid units in PBST. That is, based on the total number of moles of dicarboxylic acid units in PBST, the ratio of the total number of moles of succinic acid units and terephthalic acid units is preferably 80 to 100 mol%, more preferably 85 to 100 mol%, particularly preferably 90 to 100 mol%, and particularly preferably 95 to 100 mol%. By having the ratio of the total number of moles of succinic acid units and terephthalic acid units relative to the total number of moles of dicarboxylic acid units in PBST within the above range, it is possible to obtain PBST with superior biodegradability and mechanical properties.

[0023] The ratio of succinic acid units to terephthalic acid units in PBST is preferably such that the proportion of succinic acid units is 10 mol% or more, more preferably 40 mol% or more, particularly preferably 50 mol% or more, and preferably 90 mol% or less, and more preferably 60 mol% or less, based on the total number of moles of succinic acid units and terephthalic acid units. In other words, the molar ratio of succinic acid units to terephthalic acid units in PBST is preferably 10 / 90 to 90 / 10, more preferably 40 / 60 to 60 / 40, and particularly preferably 50 / 50 to 60 / 40. By keeping the ratio of succinic acid units to terephthalic acid units within the above range, PBST with excellent biodegradability and mechanical properties can be obtained.

[0024] Other dicarboxylic acids that can constitute the dicarboxylic acid unit in PBST are not particularly limited, but include, for example, aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic anhydride, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecadicarboxylic acid, dodecadicarboxylic acid, and dimer acid; aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, and diphenyldicarboxylic acid; and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. These can be used individually or as a mixture of two or more in addition to the above succinic acid and terephthalic acid. Furthermore, succinic acid, sebacic acid, and adipic acid can be derived from plant materials.

[0025] The proportion of 1,4-butanediol units in PBST is based on the total number of diol units in PBST. As a general rule, the proportion of 1,4-butanediol units is preferably 80 mol% or more, more preferably 85 mol% or more, particularly preferably 90 mol% or more, even more preferably 95 mol% or more, and may also be 100 mol%. That is, based on the total number of moles of diol units in PBST, the proportion of 1,4-butanediol units is preferably 80 to 100 mol%, more preferably 85 to 100 mol%, particularly preferably 90 to 100 mol%, and even more preferably 95 to 100 mol%. By having the proportion of 1,4-diol units within the above range, PBST with excellent heat resistance and mechanical properties can be obtained.

[0026] Examples of diols other than 1,4-butaneol that can constitute the diol unit in PBST include alkylenediols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and neopentyl glycol; oxyalkylenediols such as diethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol; and cycloalkylenediols such as 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol. These can be used individually or as a mixture of two or more in addition to the above-mentioned 1,4-butaneol. Furthermore, ethylene glycol, 1,3-propanediol, and 1,4-butanediol can be derived from plant materials.

[0027] PBST may have other constitutional units (hereinafter also referred to as "other constitutional units") in addition to the dicarboxylic acid units and the diol units. Examples of copolymerization components that can constitute other constitutional units include oxycarboxylic acids (e.g., lactic acid, glycolic acid, hydroxybutyric acid, hydroxycaproic acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-hydroxyisocaproic acid, malic acid, maleic acid, citric acid, fumaric acid, etc.), esters and lactones of the oxycarboxylic acids, polymers of the oxycarboxylic acids, etc., polyhydric alcohols having three or more functional groups (e.g., glycerin, trimethylolpropane, pentaerythritol, etc.), and at least one component selected from the group consisting of polycarboxylic acids having three or more functional groups or their anhydrides (e.g., propane tricarboxylic acid, pyromellitic acid, trimellitic acid, benzophenone tetracarboxylic acid, and their anhydrides, etc.).

[0028] Among them, by introducing, as other constitutional units, constitutional units derived from at least one polyfunctional compound having three or more functional groups selected from the group consisting of oxycarboxylic acids having three or more functional groups, alcohols having three or more functional groups, and carboxylic acids having three or more functional groups into PBST, it is possible to adjust in the direction of increasing the intrinsic viscosity of PBST described later. As the polyfunctional compound having three or more functional groups, oxycarboxylic acids such as malic acid, citric acid, and fumaric acid, and polyhydric alcohols having three or more functional groups such as glycerin and trimethylolpropane are preferable, and malic acid and trimethylolpropane are particularly preferably used.

[0029] The ratio of the polyfunctional compound units having three or more functional groups to the number of moles of all dicarboxylic acid units of PBST is preferably 0.001 to 5 mol%, and more preferably 0.05 to 0.5 mol%. By setting the ratio of the polyfunctional compound units having three or more functional groups in PBST within the above range, it is possible to more reliably prevent the formation of gels (unmelted substances) in the polyester and more easily adjust the intrinsic viscosity of PBST within a preferable range as described below.

[0030] <Physical properties of PBST> The intrinsic viscosity (IV) of PBST is preferably 1.2 dL / g or more, more preferably 1.4 dL / g. Also, it is preferably 2.2 dL / g or less, more preferably 2.0 dL / g or less. That is, as the intrinsic viscosity of PBST, 1.2 dL / g or more and 2.2 dL / g or less is preferable, and 1.4 dL / g or more and 2.0 dL / g or less is more preferable. By setting the intrinsic viscosity of PBST within the above range, the mechanical strength of the molded product can be further increased, and the viscosity during melting can be adjusted to an appropriate range. As a result, high-quality injection-molded products and extrusion-molded products can be manufactured more easily. Note that the intrinsic viscosity depends on the molecular weight of PBST, and the higher the molecular weight, the higher the intrinsic viscosity can be.

[0031] The intrinsic viscosity can be measured, for example, in accordance with JIS K7367-1:2002 (ISO 1628-1:1998). Specifically, for example, using an Ubbelohde viscometer, and using a mixed solvent of phenol / tetrachloroethane (mass ratio 1:1) as the solvent, at a temperature of 30 °C, measure the dropping seconds of a PBST solution with a concentration of 0.5 g / dL and the dropping seconds of only the mixed solvent, and the intrinsic viscosity can be obtained from the following calculation formula (2). IV = ((1 + 4K H η sp ) 0.5 -1) / (2K H C) ··· (2) However, in formula (2), η SP = η / η0 - 1, where η is the dropping seconds of the sample solution, η0 is the dropping seconds of the solvent, C is the sample solution concentration (g / dL), and K H is the Huggins constant. K H adopts 0.33.

[0032] <Pellets containing PBST> There are no particular restrictions on the shape and size of the pellets containing PBST, and it is preferable that they have a shape and size suitable for being subjected to known plastic processing methods such as injection molding and extrusion molding. Specific examples of the shape include, for example, cylindrical, elliptical columnar, prismatic, disk-shaped, spherical, and the like. Also, as for the size, the size of the pellets may be the generally used size. Specifically, for example, those having a diameter or one side of about 0.7 to 12 mm can be mentioned. Further, when the pellets containing PBST are subjected to the solvent contact step described later, from the viewpoint of the extraction efficiency of the cyclic dimer by the solvent contact step, etc., it is preferable that the mass of one particle of the pellets is 1 to 50 mg, more preferably 3 to 40 mg, and particularly preferably 5 to 30 mg.

[0033] <Cyclic dimer in pellets containing PBST> In the pellets containing PBST, it is preferable that the content of the cyclic dimer is 2,500 mass ppm or less, more preferably 2,000 mass ppm or less, and particularly preferably 1,500 mass ppm or less. By setting the content of the cyclic dimer in the pellets to the above specific amount or less, the blocking resistance when heat / pressure is applied to the pellets can be further improved. Here, the cyclic dimer is a compound that is by-produced when a part of the polyester obtained by reacting a dicarboxylic acid component mainly composed of succinic acid and a diol component mainly composed of 1,4-butanediol is cyclized, and refers to the cyclic dimer composed of succinic acid and 1,4-butanediol. Such a cyclic dimer can be represented, for example, by the following structural formula (4). <00,00304>

Chemical formula

[0035] Regarding the present invention, I 01 / I 02 obtaining pellets containing PBST that are 1.00 or more In the solvent contact step described later, it is important to adjust the content of the cyclic dimer to 2500 ppm or less. That is, the PBST obtained by the method described in Patent Document 1 also achieves a certain degree of crystallization. However, according to the inventors' studies, when the PBST contains a certain amount or more of the cyclic dimer, the cyclic dimer inhibits the crystallization of the PBST, making it difficult to achieve the high crystallization that is considered necessary to prevent blocking when heat / pressure is applied to the pellet containing PBST. Based on these considerations, the inventors' studies have shown that by reducing the content of the cyclic dimer in the solvent contact step described later, 01 / I 02 This study found that it is possible to obtain pellets with a value of 1.00 or higher.

[0036] There is no particular lower limit to the content of cyclic dimers in pellets containing PBST, and it may be 0 ppm by mass. However, limiting the cyclic dimer content to 0 ppm by mass may lead to an increase in the number of steps required to remove cyclic dimers from synthesized PBST, and the need for larger equipment for such removal. From the viewpoint of reducing environmental impact, the inclusion of cyclic dimers in pellets is permissible as long as it does not significantly affect the crystallization of PBST. Specifically, the cyclic dimer content in the pellets can be 1 ppm by mass or more, preferably 50 ppm by mass or more, and more preferably 100 ppm by mass or more. Therefore, from the viewpoint of high crystallization of PBST and reduction of environmental impact, the cyclic dimer content in pellets containing PBST is preferably 1 to 2500 ppm by mass, more preferably 50 to 2000 ppm by mass, and particularly preferably 100 to 1500 ppm by mass. By keeping the cyclic dimer content in pellets containing PBST within the above range, the I 01 / I 02 This can be made easier to achieve a value of 1.00 or higher.

[0037] The method for quantifying cyclic dimers in pellets containing PBST is not particularly limited, but one example is the use of an absolute calibration curve. Specific methods will be explained in the examples. Furthermore, specific methods for adjusting the cyclic dimer content in pellets containing PBST will be described later.

[0038] Pellets containing PBST may contain other components besides PBST. One example of such a component is a mold release agent. Examples of mold release agents include those commonly used in injection molding and extrusion molding. Specifically, examples include ester compounds of polyhydric alcohols and long-chain aliphatic carboxylic acids (e.g., ester compounds of stearic acid or montanic acid with ethylene glycol, glycerin, or pentaerythritol), amide compounds of long-chain aliphatic carboxylic acids (e.g., stearic acid or montanic acid) with stearylamine or ethylenediamine, and silicone compounds. The mixing ratio of the mold release agent is preferably 0.001 to 1% by mass, and more preferably 0.005 to 0.8% by mass, based on the pellets containing PBST, in order to prevent pellet blocking due to excessive bleeding of the mold release agent onto the pellet surface while improving the release properties of the molded product. Furthermore, additives may be included as other components, as long as they do not impair the objectives of the present invention. Examples of additives include reinforcing materials such as talc, kaolin, mica, clay, bentonite, sericite, basic magnesium carbonate, aluminum hydroxide, glass flakes, glass fibers, carbon fibers, asbestos fibers, rock wool, calcium carbonate, silica sand, wollastonite, barium sulfate, glass beads, and titanium dioxide; non-plate-like fillers; antioxidants (phosphorus-based, sulfur-based, etc.); ultraviolet absorbers; heat stabilizers (hindered phenol-based, etc.); transesterification inhibitors; lubricants; antistatic agents; colorants including dyes and pigments; flame retardants (halogen-based, phosphorus-based, etc.); flame retardant enhancers (antimony compounds represented by antimony trioxide, zirconium oxide, molybdenum oxide, etc.); and antibacterial agents. As yet another one of the other components, it may contain other resins other than PBST. In this case, the content ratio of the other resin in the pellet is preferably 20% by mass or less, more preferably 10% by mass or less, particularly preferably 5% by mass or less, based on PBST in the pellet. Also, 0 mass %, that is, the resin component in the pellet may be only PBST.

[0039] <Method for producing a pellet containing PBST> The pellet containing PBST according to the present invention can be produced, for example, through the following steps 1 to 5. (Step 1) A dicarboxylic acid component containing at least one selected from the group consisting of succinic acid and its ester-forming derivatives and at least one selected from the group consisting of terephthalic acid and its ester-forming derivatives, and a diol component containing at least 1,4-butanediol are mixed under stirring in a predetermined ratio to form a raw material slurry. (Step 2) Subsequently to Step 1, the raw material slurry is heated under normal pressure or pressure to cause an esterification reaction to obtain a PBST low polymer. (Step 3) Subsequently to Step 2, the obtained low polymer is gradually depressurized and heated to cause a melt polycondensation reaction under a polycondensation catalyst. ] (Step 4) Next to Step (3), the molten PBST is extruded into strands and cut into pellets to obtain pellets containing PBST. (Step 5) Perform a treatment for controlling I 01 / I 02 in the pellets obtained in Step 4. Note that between Step 4 and Step 5, and / or after Step 5, a step of air classification and sieving of the pellets may be performed.

[0040] An example of step 2 above for obtaining PBST low polymer is a method using a single esterification reactor or a multi-stage reactor in which multiple esterification reactors are connected in series, in which the water and excess diol components produced in the reaction are removed from the system, and the esterification rate is carried out until the esterification rate reaches 85% or more, which is usually the case for obtaining PBST low polymer. The esterification rate is the proportion of the total carboxyl groups of the starting material dicarboxylic acid component that react with the diol component and are esterified, and is expressed by the following calculation formula (3). Esterification rate (%) = (Saponification value - Acid value) / Saponification value × 100 (3) The reaction temperature in step 2 (esterification reaction step) is not particularly limited as long as it is a temperature at which the esterification reaction can be carried out. However, in order to increase the reaction rate, it is preferably 200°C or higher, more preferably 210°C or higher, and to prevent discoloration of the polyester, it is preferably 250°C or lower, more preferably 245°C or lower, and particularly preferably 240°C or lower. In other words, the reaction temperature is preferably 200 to 250°C, more preferably 210 to 245°C, and particularly preferably 210 to 240°C. By keeping the reaction temperature within the above range, the esterification reaction rate slows down, and the occurrence of dehydration decomposition of the diol component due to the longer reaction time can be more reliably prevented. In addition, the generation of foreign matter caused by the increase in scattered material in the reaction vessel due to the decomposition of the diol and dicarboxylic acid components can be more reliably prevented. From the viewpoint of stabilizing the esterification rate, it is preferable to keep the reaction temperature as constant as possible, for example, within ±5°C of the set temperature, and more preferably within ±2°C of the set temperature. The reaction atmosphere in step 2 is preferably an inert gas atmosphere such as nitrogen or argon. The reaction pressure is preferably 50 kPa to 200 kPa, more preferably 60 kPa or higher, particularly preferably 70 kPa or higher, even more preferably 130 kPa or lower, and particularly preferably 110 kPa or lower. That is, the reaction pressure is preferably 50 to 200 kPa, more preferably 60 to 130 kPa, and particularly preferably 70 to 110 kPa. If the reaction pressure is within the above range, it is possible to more reliably prevent an increase in scattered material in the reaction vessel, a rise in the haze of the reactants, and an increase in foreign matter. Furthermore, it is possible to more reliably prevent a decrease in the polycondensation reaction rate due to a large amount of distillation of the diol component out of the reaction system. In addition, it is possible to more reliably prevent a decrease in the polycondensation reaction rate due to dehydration decomposition of the diol component. Furthermore, the reaction time is not particularly limited, but for example, 1 to 10 hours is preferred, and 1 to 4 hours is particularly preferred. In this process, it is preferable that the esterification rate of the esterified product be 85% or higher. In this disclosure, polycondensation reaction refers to a high molecular weight polyester reaction carried out at a reaction pressure of 50 kPa or less, particularly 10 kPa or less, and esterification reaction refers to a reaction carried out at 50 to 200 kPa. The esterification rate of the esterified product is preferably 85% or higher, more preferably 88% or higher, and more preferably 90% or higher. The upper limit is better if it is higher for the subsequent polycondensation reaction, but it is usually 99%. That is, the esterification rate is preferably 85-99%, more preferably 88-99%, and particularly preferably 90-99%. By keeping the esterification rate within the above range, the polycondensation reactivity in the subsequent polycondensation step can be improved, and scattering during the polycondensation reaction can be suppressed, and the deterioration of haze (generation of foreign matter) can be more reliably prevented.

[0041] An example of step 3, in which a melt polycondensation reaction is carried out, is a multi-stage reactor consisting of, for example, a single melt polycondensation tank or multiple melt polycondensation tanks connected in series, with the first stage being a fully mixed reactor equipped with stirring blades, and the second and third stages being horizontal plug-flow reactors equipped with stirring blades, while distilling the diol produced out of the system under reduced pressure.

[0042] The PBST polycondensation catalyst may be added to the reaction system at any stage of the mixing and preparation of the dicarboxylic acid component and the diol component, at any stage of the process of forming the PBST low polymer, or at an early stage of the melt polycondensation process. In this case, one or more conventionally known metal compounds such as antimony, germanium, and titanium may be used as the PBST polycondensation catalyst.

[0043] Furthermore, to promote the crystallization of PBST, a nucleating agent may be added in step 1, for example. Examples of nucleating agents include hydrocarbon-based nucleating agents such as polyethylene wax and polypropylene wax, aliphatic amide-based nucleating agents, phosphate ester metal salt-based nucleating agents, and inorganic nucleating agents such as anhydrous silica, talc, titanium dioxide, and calcium carbonate. From the viewpoint of affecting the color tone and polymerizability of the resulting PBST, hydrocarbon-based and inorganic nucleating agents are preferred, more preferably polyethylene wax, polypropylene wax, and talc, and even more preferably polyethylene wax and talc. Only one type of nucleating agent may be used, or two or more types may be mixed and used. The nucleating agent is preferably added to PBST in an amount of 100 to 10,000 ppm by mass, more preferably 200 to 5,000 ppm by mass, and particularly preferably 500 to 3,000 ppm by mass. By using the above range for the amount of nucleating agent, the effect of promoting the crystallization of PBST can be obtained more reliably, and it is also advantageous in terms of cost.

[0044] Furthermore, in steps 1 and 2 above, which involve forming a PBST low polymer, and in step 3 above, which involves melt polycondensation, antioxidants and basic compounds can be added to suppress side reactions such as thermal decomposition and dimerization of diols.Specific examples of antioxidants include, for example, "Irganox 1330" (trade name, manufactured by BASF) and "Irganox 1010" (trade name, manufactured by BASF).Examples of basic compounds include, for example, tertiary amines such as triethylamine, tri-n-butylamine, and benzyldimethylamine; quaternary ammonium hydroxides such as tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide, and trimethylbenzylammonium hydroxide; lithium carbonate, sodium carbonate, sodium hydroxide, potassium carbonate, and sodium acetate.

[0045] Examples of the above step 4, which involves cutting the synthesized PBST into pellets, include the strand cutting method, in which molten PBST is extruded from the nozzle hole of a die head using a gear pump or extruder and then cut with a cutter while being cooled with water or the cooled and solidified strand is cut; and the underwater hot cutting method, in which molten PBST is extruded into water from the nozzle hole and immediately cut.

[0046] <Intensity ratio (I 01 / I 02 ) How to adjust > Pellets containing PBST 01 / I 02 For example, the PBST synthesized by solution polycondensation in step 3 above can be prepared by extruding the strand-shaped PBST from a die into a cooling liquid in step 4, cutting it into pellets, and then subjecting it to a step described later, in which it is immersed in a solvent adjusted to a predetermined temperature for a predetermined time (hereinafter also referred to as the "solvent contact step"), or in which it is held at a predetermined temperature for a predetermined time (hereinafter also referred to as the "slow cooling step") and the "solvent contact step".

[0047] <Solvent Contact Process> The solvent contact process is a process to reduce the content of cyclic dimers in the pellets, and also, 01 / I02 This process may also be for adjusting the value of to 1.00 or higher. In other words, by going through this process, the content of the cyclic dimer is adjusted to 2500 ppm or less, and I 01 / I 02 This allows you to obtain pellets containing PBST that have been adjusted to a value of 1.00 or higher. This step includes, for example, contacting the pellet obtained in step 4 above with a solvent capable of dissolving the cyclic dimer, which has been adjusted to a predetermined temperature, for a predetermined time. By going through this step, at least a portion of the cyclic dimer in the pellet can be removed, making it easier to adjust the cyclic dimer content in the pellet to 2500 ppm by mass or less. Furthermore, by going through this step, the amount of cyclic dimer in the pellet that is thought to inhibit the orientation of PBST molecules is reduced, and as a result, by holding the pellet at a predetermined temperature for a predetermined time, the PBST molecules in the pellet can be oriented better, and the I 01 / I 02 It can be controlled to a value of 1.00 or higher.

[0048] The solvent used in this process is preferably one that does not substantially dissolve the PBST even when in contact with the pellets at a predetermined temperature and for a predetermined time, while on the other hand, it can dissolve the cyclic dimer well. Examples of such solvents include C1 to C4 alcohols (methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, etc.). Alternatively, it may be an aqueous solution of at least one alcohol selected from the group consisting of these alcohols. The concentration of the alcohol in such an aqueous alcohol solution is not particularly limited, but for example, from the viewpoint of good solubility of the cyclic dimer, it is preferably 10% by mass or more and less than 100% by mass based on the aqueous alcohol solution.

[0049] Furthermore, the solvent temperature in the solvent contact step is preferably 70°C or lower, more preferably 65°C or lower, and particularly preferably 60°C or lower. As a lower limit, from the viewpoint of better extracting the cyclic dimer and orienting the PBST molecules, it is preferably 30°C or higher, more preferably 35°C or higher, and particularly preferably 40°C or higher. In other words, the solvent temperature range in the solvent contact step is preferably 30 to 70°C, more preferably 35 to 65°C, and particularly preferably 40 to 60°C. Furthermore, as for the processing time, from the viewpoint of better extracting the cyclic dimer and orienting the PBST molecules, it is preferably 0.1 to 10 hours, more preferably 0.5 to 8 hours, and particularly preferably 1 to 5 hours. Furthermore, the mass ratio of the polyester pellets to the solvent (solvent / pellets) is preferably 1.0 or higher, more preferably 1.5 or higher, and even more preferably 2.0 or higher. The mass ratio is also preferably 50.0 or lower, more preferably 30.0 or lower, and particularly preferably 20.0 or lower. In other words, the mass ratio is preferably 1.0 to 50.0, more preferably 1.5 to 30.0, and particularly preferably 2.0 to 20.0. By having the mass ratio within the above range, it is possible to prevent the concentration of cyclic dimers in the solvent from becoming too high, and to remove the cyclic dimers in the pellets more stably. Furthermore, this prevents an excessive amount of solvent from being used relative to the pellets, thus preventing cost increases associated with larger processing equipment.

[0050] Specific methods for the solvent contact process described above include, for example, the methods described in i) and ii) below. i) A method in which pellets obtained through a slow cooling process and a solvent are placed in a processing tank, and after contact at the predetermined temperature range and for the predetermined time, the pellets are recovered from the processing tank (hereinafter also referred to as the "batch method" or "palindrome method"); ii) A method (hereinafter also referred to as the "continuous method") in which pellets obtained through a slow cooling process are continuously supplied to a processing tank, and a solvent adjusted to the above-mentioned predetermined temperature range is flowed in parallel or countercurrent to the flow of pellets, allowing the pellets to be processed and the solvent to come into contact for a predetermined time, and then the processed pellets are continuously collected. The specific methods and apparatus used for the palindromic and continuous processing described above are not particularly limited, but as a method and apparatus for the continuous process that can continuously adjust the content of cyclic dimers in pellets, for example, the method and apparatus described in Patent Document 2 can be suitably used.

[0051] In the solvent contact process, it is preferable to use a fresh solvent from the viewpoint of reducing the concentration of cyclic dimers in the pellets. However, from the viewpoint of reducing environmental impact and effectively utilizing resources, it is preferable to reuse the solvent used in the solvent contact process. In this case, since the solvent that comes into contact with the pellets in the solvent contact process contains cyclic dimers, it is preferable to separate the cyclic dimers according to their concentration and control the concentration of cyclic dimers in the solvent to be low. In particular, when the solvent contact process is continuous and the solvent that has been treated in contact with the pellets is circulated and reused, it is preferable to control the concentration of cyclic dimers in the entire solvent used in the solvent contact process to be low. Since controlling the concentration of cyclic dimers in the entire solvent that comes into contact with the pellets in the solvent contact process makes it easier to reduce the amount of cyclic dimers contained in the resulting pellets, it is preferable to separate the cyclic dimers in the separation process. The method / apparatus (separation apparatus) for separating cyclic dimers from a solution containing cyclic dimers is not particularly limited and includes, for example, a distillation column, a crystallizer, a thin-film evaporator, and a centrifuge. For example, when recycling the solvent used in the solvent contact process, it is conceivable to separate at least a portion of the cyclic dimers contained in the solvent using the separation device described above, adjust (reduce) the concentration of cyclic dimers in the solvent, and then use it again in the solvent contact process. Furthermore, when the solvent contact process is carried out continuously, as shown in Figure 4 described later, the solvent that has come into contact with the pellets in the contact treatment tank (III) in Figure 4 is recovered via the solvent recovery line (106), and the proportion of the recovered solution supplied to the separator (XI) by the solvent supply line (111) is defined as the separation rate. From the viewpoint of achieving a higher level of compatibility between the recyclability of the solvent and the quality of the pellets (low content of cyclic dimers), it is preferable that the separation rate be 20% by mass or more. In particular, it is preferable that the separation rate be 25% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, and even 55% by mass or more, and especially preferable that it be 90% by mass or more. The upper limit of the separation rate is 100% by mass. A separation rate of 100% means that all of the solvent that has come into contact with the pellets is separated through the separator, separating at least a portion of the cyclic dimers contained therein. By achieving a separation rate of 20% by mass or more, the accumulation of cyclic dimers in the solvent can be suppressed, making it easier to obtain pellets of the desired quality. Furthermore, the separated cyclic dimers can be supplied to esterification or polycondensation reaction processes and used as raw materials for polyester. It is a preferred method to return the separated cyclic dimers to the esterification reaction tank in the esterification reaction process or to the slurry tank containing the dicarboxylic acid and diol components. The solvent from which the cyclic dimer has been separated may be used as is in the solvent contact step. If the solvent is lost during the separation of the cyclic dimer, fresh solvent may be added as needed. It can also be replenished and used in solvent contact processes.

[0052] <Slow cooling process> The slow cooling process can be carried out before or during step 4. Specifically, for example, if the slow cooling process is carried out during step 4, the molten PBST obtained in step 3 is extruded from the die into a cooling liquid adjusted to a predetermined temperature in a strand form, and the strand form is held in the cooling liquid for a predetermined time. After that, it is cut to form pellets. Alternatively, the PBST extruded from the die into a cooling liquid adjusted to a predetermined temperature in a strand form is cut in the cooling liquid to form pellets, and the pellets are held in the cooling liquid for a predetermined time. By slowly cooling molten PBST, the orientation of the molecules in the molten PBST is promoted, making it possible to develop the crystalline structure of PBST to a certain extent. However, if molten PBST is extruded into, for example, a room temperature (25°C) environment, the PBST will cool rapidly, and the molecules of PBST will be fixed in a randomly oriented state, so I 01 / I 02 It becomes difficult to make it 1.00 or higher. Note that the step of contacting the pellets with water at a temperature of 30°C for a few seconds as described in the example of Patent Document 1 does not fall under this slow cooling step, and unless the pellets obtained in the example of Patent Document 1 are subjected to the solvent contact step, or both this slow cooling step and the solvent contact step, I 01 / I 02 It is difficult to set it to 1.00 or higher.

[0053] Here, the temperature of the cooling liquid used to extrude the molten PBST into strands is preferably 30 to 60°C, particularly preferably 35 to 55°C, and even more preferably 40 to 50°C. The time for holding the PBST within the above temperature range is I 01 / I 02 While there are no particular restrictions as long as it can be 1.00 or higher, it is preferable to set it to, for example, 1 to 10 minutes, more preferably 1.5 to 5 minutes, and even more preferably 2 to 3 minutes. When the holding time is extended within the above temperature range of the pellet containing PBST, 01 / I 02The value of is generally large. Note that if the temperature of the cooling liquid is set higher within the above range, adjustments such as shortening the holding time may be necessary to achieve the desired I 01 / I 02 This can be done as appropriate depending on the value.

[0054] Furthermore, the type of cooling liquid is not particularly limited as long as it does not react with or dissolve PBST during the above temperature range and holding time. Examples of such cooling liquids include water. Furthermore, regarding this disclosure, I 01 / I 02 In obtaining pellets containing PBST having a ratio of 1.00 or higher, it is particularly preferable to subject the pellets to both the "solvent contact step" and the "slow cooling step." When both the solvent contact step and the slow cooling step are performed, the order is not particularly limited, but it is particularly preferable to subject the pellets obtained in step 4 to the slow cooling step to improve their crystallinity to a certain extent, and then to perform the solvent contact step to extract the cyclic dimer and further develop the crystallinity of PBST.

[0055] As an example of a method for producing pellets according to this disclosure, an example in which the "continuous" method (apparatus) is used in the solvent contact step (cyclic dimer removal step) will be explained with reference to Figures 2 to 5. In the following example, a preferred embodiment of a method for producing polyester pellets using succinic acid as the aliphatic dicarboxylic acid component, terephthalic acid as the aromatic dicarboxylic acid component, 1,4-butanediol as the diol component, and trimethylolpropane as an optional polyfunctional compound as raw materials will be described, but this disclosure is not limited to this embodiment.

[0056] Figure 2 is a schematic diagram illustrating one aspect of a part of the pellet manufacturing process (esterification reaction step) according to this disclosure, and Figure 3 is a diagram illustrating one aspect of a part of the pellet manufacturing process (polycondensation step) according to this disclosure.

[0057] In Figure 2, the raw materials succinic acid and terephthalic acid, along with optional components (e.g., trimethylolpropane), are typically mixed with 1,4-butanediol in a raw material mixing tank (not shown) and supplied to the esterification reactor (A) from the raw material supply line (1) in the form of a slurry or liquid. If a catalyst is added during the esterification reaction, the catalyst solution is prepared in a catalyst preparation tank (not shown) to a solution of 1,4-butanediol, and then supplied to the catalyst supply line (3). Figure 2 shows a configuration in which the catalyst supply line (3) is connected to the 1,4-butanediol recirculation line (2), the two are mixed, and then supplied to the liquid phase of the esterification reactor (A).

[0058] The gas distilled from the esterification reactor (A) is separated into high-boiling and low-boiling components in the rectification column (C) via the distillation line (5). Typically, the main component of the high-boiling component is 1,4-butanediol, and the main components of the low-boiling component are water and tetrahydrofuran (hereinafter sometimes abbreviated as THF), which is a decomposition product of 1,4-butanediol.

[0059] The high-boiling components separated in the rectification column (C) are extracted through the extraction line (6), and via the pump (D), some are recirculated to the esterification reactor (A) via the recirculation line (2), and some are returned to the rectification column (C) via the circulation line (7). The excess is extracted to the outside via the extraction line (8). On the other hand, the low-boiling components separated in the rectification column (C) are extracted through the gas extraction line (9), condensed in the condenser (G), and temporarily stored in the tank (F) via the condensate line (10). Some of the low-boiling components collected in the tank (F) are returned to the rectification column (C) via the extraction line (11), pump (E), and circulation line (12), and the remainder is extracted to the outside via the extraction line (13). The condenser (G) is connected to an exhaust system (not shown) via the vent line (14). The esterified product (low polymer of PBST) generated in the esterification reactor (A) is supplied to the first polycondensation reactor (a) shown in Figure 3 via the extraction pump (B) and the extraction line (4) for the esterified product.

[0060] In the process shown in Figure 2, the catalyst supply line (3) is connected to the recirculation line (2), but the two may be independent. Also, the raw material supply line (1) may be connected to the liquid phase of the esterification reactor (A).

[0061] When adding a catalyst to the esterification reaction product before polycondensation, the catalyst is first prepared to a predetermined concentration in a catalyst preparation tank (not shown), then connected to the raw material supply line (L8) via the catalyst supply line (L7) in Figure 3, further diluted with BG, and then supplied to the esterification reaction product extraction line (4).

[0062] Next, the esterification reaction product, supplied from the esterification reaction product extraction line (4) through the filter (p) to the first polycondensation reactor (a), undergoes polycondensation under reduced pressure and is then supplied to the second polycondensation reactor (d) via the extraction gear pump (c), extraction line (L1), and filter (q). In the second polycondensation reactor (d), the polycondensation reaction proceeds further, usually at a lower pressure than in the first polycondensation reactor (a). The resulting polycondensate is supplied to the third polycondensation reactor (k) via the extraction gear pump (e), the extraction line (L3) which is the outlet channel, and filter (r). The third polycondensation reactor (k) is a horizontal reactor composed of multiple stirring blade blocks and equipped with two self-cleaning type stirring blades. The polycondensation product, introduced from the second polycondensation reactor (d) to the third polycondensation reactor (k) via the extraction line (L3), undergoes further polycondensation reaction there before being transferred to the pelletization process.

[0063] In the pelletizing process, the molten polyester is extracted into the atmosphere in the form of molten strands from the die head (g) via an extraction gear pump (m), an outlet filter (s), and an extraction line (L5), and then cooled with water before being processed by a rotary cutter (h). It is then cut into polyester pellets. Alternatively, it can be extracted in strand form into water without being released into the atmosphere, and then cut into pellets using a rotary underwater cutter.

[0064] In Figure 3, the labels (L2), (L4), and (L6) represent the vent lines for the first polycondensation reactor (a), the second polycondensation reactor (d), and the third polycondensation reactor (k), respectively. Filters (p), (q), (r), and (s) do not necessarily need to be installed in their entirety and can be installed as appropriate, taking into consideration the effectiveness of foreign matter removal and operational stability.

[0065] Figure 4 is a schematic diagram illustrating one aspect of the solvent contact process for pellets and the separation process of cyclic dimers from the solvent that has come into contact with the pellets. The solvent is supplied from a circulation tank (I) to a processing tank (III) via a solvent supply line (101) through a heat exchanger (II) with temperature control by a pump (IX). In the processing tank (III), the solvent comes into contact with the pellets (e.g., countercurrent contact), is then extracted through a solvent extraction line (102), and introduced into a fine particle remover (IV). At least a portion of the solvent introduced into the fine particle remover (IV) is recovered to the circulation tank (I) via a separator (XI), and the remainder is recovered to the circulation tank (I) via an extraction line (110). In the separator (XI), the cyclic oligomer containing the cyclic dimer is separated from the solvent supplied to the separator (XI), and the solution is recovered to the circulation tank (I) via a solution extraction line (113). The cyclic oligomer containing the separated cyclic dimer is extracted to the outside through the cyclic oligomer extraction line (112). The supply line (108) supplies an amount of solvent equivalent to the amount of solvent extracted from the extraction line (112) along with the separated cyclic dimer.

[0066] The pellets to be subjected to contact treatment with the solvent are continuously supplied from the pellet supply line (103), and after being subjected to contact treatment with the solvent for a predetermined time, they are continuously extracted from the pellet extraction line (104) while adjusting the extraction amount with a rotary valve (V). The solvent extracted along with the pellets is separated in the preliminary solid-liquid separator (VI), and after passing through the recovery tank (VII), is returned to the recovery line (106) via the solvent supply line (105) by a pump (X). The continuously extracted pellets are separated from the accompanying solvent in the preliminary solid-liquid separator (VI), and then continuously supplied to the drying process located downstream of the main separation process via the pellet extraction line 109, after passing through the solid-liquid separator (VIII).

[0067] Figure 5 is a schematic diagram illustrating one aspect of the pellet manufacturing process (drying process) according to this disclosure. Here, an apparatus equipped with two drying towers (first drying tower (I) and second drying tower (K)) is used as an example. After the solvent contact process, the pellets are continuously supplied to the first drying tower (I) via the pellet supply line (201), which is connected to the extraction line 109 in Figure 5. In the first drying tower (I), heated and dried dry gas (e.g., nitrogen gas) is continuously introduced from the supply line (208) and discharged from the gas recovery line (207). The discharged nitrogen gas is heated in the heat exchanger (N) via the condenser (L), circulated back to the first drying tower (I) via the supply line (208), and reused. The solvent condensed in the condenser (L) and heat exchanger (M) is extracted from the extraction line (210). New dry gas is supplied from the new dry gas supply line (209). The pellets are continuously sent from the first drying tower (I) to the cooling tower (J) via the rotary valve (O). Dry air is introduced into the cooling tower (J) from the cooling gas supply line (212) and released from the cooling gas extraction line (211).

[0068] Pellets cooled to a temperature lower than the drying temperature of the first drying tower (I) are supplied to the second drying tower (K) via the pellet extraction line (204), rotary valve (P), and pellet supply line (205). Drying gas (usually, for example, air) is supplied to the second drying tower (K) via the heat exchanger (S) and drying gas supply line (214), and also via the extraction line It is discharged from (213).

[0069] The dried pellets are continuously or intermittently extracted through a rotary valve (Q) and a pellet extraction line (206), and then processed through a storage tank, a fine powder removal machine, a packaging machine, etc., to become the final product. In Figure 5, the components after the storage tank are not shown, but the second drying tower (K) can also be used as a storage tank.

[0070] <Application> As described above, I 01 / I 02 However, pellets containing PBST with a PBST content of at least 1.00 and preferably 2500 ppm by mass or less of cyclic dimers are less prone to pellet blocking when subjected to injection molding or extrusion molding. As a result, molded products can be manufactured stably without hindering the supply stability to the molding machine during molding, making them extremely useful as pellets for injection molding and extrusion molding to obtain biodegradable molded products.

[0071] <Molded products (injection molded products, extruded products)> Resin pellets for obtaining injection-molded or extruded articles may consist solely of pellets containing PBST. Alternatively, two or more types of PBST pellets with different molar ratios of succinic acid units, terephthalic acid units, and 1,4-butanediol units may be mixed to form resin pellets.

[0072] The injection-molded products and extrusion-molded products of resin pellets containing pellets containing PBST according to the present disclosure can be obtained by molding using the injection molding method or the extrusion molding method with resin pellets containing pellets containing PBST according to the present disclosure. The molded shape can be any shape as long as it can be molded by the injection molding method or the extrusion molding method. The uses of the injection-molded product or the extrusion-molded product are not limited in any way. Examples of the injection-molded product include cutlery and various containers (cups, cosmetic containers, food containers, detergent containers, bleach containers, etc.). Examples of the extrusion-molded product include packaging materials (packaging films), agricultural films (agricultural mulch films), etc.

Examples

[0073] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. The measurement methods of the physical properties and evaluation items adopted in the following examples are as follows.

[0074] < Intrinsic viscosity (IV) dL / g> It was determined using an Ubbelohde viscometer in the following manner. That is, using a mixed solvent of phenol / tetrachloroethane (mass ratio 1 / 1), at a temperature of 30 °C, the drop times of only the polymer solution with a concentration of 0.5 g / dL and the solvent were measured, and it was determined from the following calculation formula (4). IV = ((1 + 4K H η sp ) 0.5 -1) / (2K H C) ··· (4) However, in the calculation formula (4), η SP = η / η0 - 1, where η is the drop time of the sample solution, η0 is the drop time of the solvent, C is the concentration of the sample solution (g / dL), and K H is the Huggins constant. K H adopted 0.33.

[0075] < Content of cyclic dimer of PBST> 0.5 g of pellet was accurately weighed, 10 mL of chloroform was added, and after dissolving at room temperature, 30 mL of ethanol / water mixture (volume ratio 4 / 1) was slowly added dropwise while stirring to precipitate the polymer components. After 15 minutes, stirring was stopped, and the mixture was allowed to stand for 90 minutes. Next, 2 mL of the supernatant was taken, evaporated to dryness, and then 2 mL of acetonitrile was added to dissolve it. After filtering through a 0.45 μm filter, the mixture was subjected to high-performance liquid chromatography (product name: Prominenc). Using a Shimadzu (e) cell, the mobile phase was started with acetonitrile / water (volume ratio = 4 / 6) and eluted by continuously changing the composition up to acetonitrile / water (volume ratio = 9 / 1) using a high-pressure gradient method. The analysis was performed using an octadecylsilylated silica gel (ODS) column (product name: CAPCELL PAK C-18 TYPE MGII, silica gel particle size: 5 μm, inner diameter: 4.6 mm, length: 150 mm; Osaka Soda Co., Ltd.). A UV detector was used, with detection wavelengths of 210 nm and 254 nm. The obtained results were quantified using an absolute calibration curve method with cyclic dimer pure products. The results were then expressed as mass ppm relative to the pellet.

[0076] The pure cyclic dimer was obtained as follows: A polymer pellet obtained by polymerizing succinic acid and 1,4-butanediol was stirred in acetone at 50°C for 12 hours to extract the oligomer component. After extraction, the pellet was filtered off, and the acetone was evaporated from the acetone solution containing the extracted oligomer component to obtain a solid. This solid was dissolved in acetone at 50°C to form a saturated solution, and then slowly cooled to room temperature (25°C) to precipitate needle-shaped precipitates (crystals) through a recrystallization procedure. The supernatant was then discarded, and the crystals were collected. The obtained crystals were further purified by repeating the above recrystallization procedure several times. These crystals were analyzed by 1H-NMR and high-performance liquid chromatography, confirming that they were cyclic dimers formed from succinic acid and 1,4-butanediol.

[0077] <Raman band intensity ratio ((I 01 / I 02 ))> Using "RAMAN touch" (trade name, manufactured by Nanophoton) as a Raman spectrometer, the Raman spectrum of the pellet was measured. The measurement conditions were as follows. <Measurement conditions> <測定条件> · Measurement mode: Point · Laser wavelength: 532 nm · Laser output: 12 mW (opening degree of the attenuation filter: 200 / 255) · Diffraction grating: 1200 gr / mm · Pinhole: 20 μm · Exposure time: 100 seconds · Number of integrations: 10 times · Objective lens: 100x · Measurement temperature: 25 °C

[0078] For the obtained Raman spectrum, the peak of the Raman scattering intensity having a peak top in the first wavenumber range of 1711 ± 5 cm -1 and the peak of the Raman scattering intensity having a peak top in the second wavenumber range of 1722 ± 5 cm -1 were fitted using the Lorentz function shown in the above formula (1). In the obtained Lorentz-fitted Raman spectrum, the intensity I 01 of the peak in the first wavenumber range and the intensity I 02 of the peak in the second wavenumber range, the intensity ratio (I 01 / I 02 ) was determined. Specifically, from the ratio (A1 / A2) of the intensity A (hereinafter also referred to as "A"1) in the above formula (1) related to the peak in the first wavenumber range obtained by fitting (i.e., X0 = 1711 ± 5 cm -1 ) and the intensity A (hereinafter also referred to as "A2") in the above formula (1) related to the peak in the second wavenumber range (i.e., X0 = 1722 ± 5 cm ), I -1 ) of the peak in the second wavenumber range, I / I<0000x02> / I 02The following was calculated. In this embodiment, the average of three measurements was calculated. Specifically, three samples were taken from the pellet to be measured, and for each sample, the above Raman spectral measurement, fitting, and I were performed. 01 / I 02 The calculation is performed, and I for each measurement sample 01 / I 02 The average value is calculated for each example and each comparative example. 01 / I 02 That's what I decided.

[0079] <Heat fusion test> Place 20g of pellets into a cylindrical container made of stainless steel (SUS) with an inner diameter of 20mm, and then... A weight was placed on the surface of the pellet layer inside the cylindrical container so that a uniform pressure of 180 g per square centimeter was applied. This cylindrical container was heated to 60°C and placed in an inert oven with nitrogen flowing at a rate of 20 liters / minute for 30 minutes, after which it was removed and allowed to return to room temperature (25°C). Next, the pellets were removed from the cylindrical container and the degree of pellet fusion was visually observed. The evaluation criteria were as follows, with rank B or higher being considered a pass. Rank A: There was absolutely no fusion between pellets, and no blocking occurred at all, representing the best possible condition. Rank B: There were 5-10 small clumps, but they crumbled easily when lightly poked with a finger, and no blocking had occurred. Rank C: The pellets were fused together, forming clumps of 10 or more pellets, indicating that blocking had occurred.

[0080] <Esterification rate (%)> The acid value and saponification value of the sample were calculated using the following formula (5). The acid value was determined by heating 0.3 g of the esterification reaction product sample in 40 mL of benzyl alcohol at 180 °C for 20 minutes, cooling for 10 minutes, and then titrating with a 0.1 mol / L potassium hydroxide / methanol solution. The saponification value was determined by hydrolyzing the oligomer with a 0.5 mol / L potassium hydroxide / ethanol solution and then titrating with 0.5 mol / L hydrochloric acid. Esterification rate (%) = (Saponification value - Acid value) / Saponification value × 100 ... (5)

[0081] (Example 1) This embodiment is an example in which the solvent contact process is carried out in a batch manner. [Preparation of catalyst for polycondensation] 343.5 parts by mass of magnesium acetate tetrahydrate were added to a reactor equipped with a stirrer, followed by 1434 parts by mass of anhydrous ethanol (purity 99% or higher). Then, 218.3 parts by mass of ethyl acid phosphate (monoester and diester mixed in a weight ratio of 45:55) were added, and the mixture was stirred at 23°C. After confirming that the magnesium acetate was completely dissolved, 410.0 parts by mass of tetra-n-butyl titanate were added. Stirring was continued for another 10 minutes to obtain a homogeneous mixed solution. This mixed solution was concentrated under reduced pressure at a controlled temperature of 60°C or lower. Approximately half the amount of ethanol was distilled off, leaving a translucent, viscous liquid in the reactor. To this, 1108 parts by mass of 1,4-butanediol were added, and the mixture was further concentrated under reduced pressure at a controlled temperature of 80°C or lower to obtain a catalyst solution with a titanium atom content of 3.5% by mass.

[0082] [Manufacturing of pellets containing PBST] In a reaction vessel equipped with a stirrer, nitrogen inlet, heater, thermometer, and vacuum port, 33.6 parts by mass of succinic acid, 38.6 parts by mass of terephthalic acid, 69.7 parts by mass of 1,4-butanediol, 0.138 parts by mass of trimethylolpropane, 0.10 parts by mass of polyethylene wax (trade name: ACumist B6, manufactured by Honeywell, melting point: 124°C), and 0.0017 parts by mass of sodium hydroxide (NaOH) were added as raw materials. Tetra-n-butyl titanate was then added so that the titanium atoms content was 30 ppm by mass per unit of PBST obtained. The contents of the reaction vessel were stirred, nitrogen gas was introduced into the reaction vessel, and the system was subjected to a nitrogen atmosphere by vacuum displacement. Next, while stirring the contents of the reaction vessel, the temperature was raised from 160°C to 230°C over 1 hour, and the reaction was carried out at 230°C for 3 hours to obtain an ester oligomer (low polymer of PBST).

[0083] To the obtained ester oligomer, the previously prepared catalyst solution is added in an amount equal to 70 ppm by mass of titanium atoms per polyester obtained, and the temperature is raised to 250°C over 45 minutes, while simultaneously, 0.07 × 10⁻¹⁶ is added over 1 hour and 20 minutes. 3 The pressure was reduced to below Pa. Then, polycondensation was continued while maintaining the heated and reduced pressure state, and polymerization occurred when the desired viscosity was reached. After completing the process, the obtained polyester copolymer was cut into pellets using an underwater cutter (product name: EUP10, manufactured by ECON, cooling water temperature: 14-28°C), and the pellets immediately after cutting were cooled in 30°C hot water for about 1 minute (slow cooling process). After that, the pellets were recovered by centrifugal dewatering. Table 1 shows the content of cyclic dimers in the pellets at this point (before the solvent contact process).

[0084] In a container equipped with a stirrer, nitrogen inlet, heating device, and thermometer, 25 parts by mass of the pellets obtained above and a mixture of 40 parts by mass of ethanol and 60 parts by mass of water were placed. While stirring the contents of the container, nitrogen gas was introduced into the container, and the pellets were brought into contact with the solvent at a temperature of 60°C for 2 hours (solvent contact step). The pellets that had undergone this solvent contact step were dried in a nitrogen atmosphere at a temperature of 50°C to obtain pellets. The molar ratio of constituent units derived from succinic acid to constituent units derived from terephthalic acid in the obtained pellets (constituent units derived from succinic acid / constituent units derived from terephthalic acid) was 55 / 45. The intrinsic viscosity and strength ratio (I) of the pellets thus obtained (final product) were determined according to the method described above. 01 / I 02 The content of ), and the cyclic dimer were measured. The samples were also subjected to the aforementioned heat fusion test. Figure 1 shows the Raman spectrum measured from the pellet according to this embodiment, and the fitted Raman spectrum obtained by fitting with two peaks having peak tops in the first wavenumber range and the second wavenumber range. In Figure 1, P is the Raman spectrum measured from the pellet, P01 and P02 are Raman spectra obtained by curve fitting using the Lorentz function to the peaks in the first wavenumber range and the second wavenumber range, respectively, and PS is the spectrum obtained by combining the waveform related to P01 and the waveform related to P02.

[0085] (Example 2) Pellets were prepared in the same manner as in Example 1, except that the solvent contact step time was changed from 2 hours to 4 hours. The pellets thus obtained were then subjected to the same procedure as in Example 1, determining the intrinsic viscosity and strength ratio (I 01 / I 02 The content of ), and cyclic dimers was measured, and the samples were subjected to a heat fusion test.

[0086] (Comparative Example 1) Pellets were obtained in the same manner as in Example 1, except that the solvent contact step was omitted. The pellets thus obtained were then subjected to the same procedure as in Example 1, determining the intrinsic viscosity and strength ratio (I 01 / I 02 The content of ), and cyclic dimers was measured, and the samples were subjected to a heat fusion test. (Comparative Example 2) Pellets were obtained in the same manner as in Comparative Example 1, except that the pellets immediately after cutting were cooled for a few seconds in warm water at 30°C. The pellets obtained in this manner were then subjected to the same procedure as in Example 1, determining the intrinsic viscosity and strength ratio (I 01 / I 02 The content of ), and cyclic dimers was measured, and the samples were subjected to a heat fusion test.

[0087] Table 1 shows the measurement results for each pellet related to Examples 1-2 and Comparative Examples 1-2, as well as the results of the heat fusion test. Note that for Comparative Examples 1-2, since the solvent contact process was not performed in these comparative examples, the cyclic dimer content of the final product pellets obtained in Comparative Examples 1-2 is equivalent to the cyclic dimer content of the pellets before the solvent contact process. Therefore, the column for the cyclic dimer content of the pellets before the solvent contact process in Table 1 is left blank.

[0088] [Table 1]

[0089] From Table 1, the intensity ratio of the Raman band (I 01 / I 02 Pellets containing PBST with a PBST ratio of 1.00 or higher were found to exhibit good blocking resistance even under heating and pressurization. This indicates that pellets containing PBST can be supplied stably to injection molding machines and extrusion molding machines, enabling the stable production of injection molded and extruded products.

[0090] (Example 3) This embodiment is an example in which the solvent contact process and the separation process of the cyclic dimer from the solvent to which the pellets were contacted were carried out in a continuous manner. [Preparation of catalyst for polycondensation] 100 parts by mass of magnesium acetate tetrahydrate were placed in a glass pear-shaped flask equipped with a stirring device, and 1500 parts by mass of anhydrous ethanol (purity 99% by mass or higher) were added. Then, 65.3 parts by mass of ethyl acid phosphate (mixture mass ratio of monoester and diester: 45:55) was added, and the mixture was stirred at 23°C. After 15 minutes, it was confirmed that the magnesium acetate was completely dissolved, and then 122 parts by mass of tetra-n-butyl titanate was added. Stirring was continued for another 10 minutes to obtain a homogeneous mixed solution. This mixed solution was transferred to a pear-shaped flask and concentrated under reduced pressure using an evaporator in an oil bath at 60°C. After 1 hour, most of the ethanol had evaporated, yielding a translucent, viscous liquid. The oil bath temperature was further increased to 80°C, and the solution was further concentrated under reduced pressure of 5 Torr to obtain a viscous liquid. This liquid catalyst was dissolved in 1,4-butanediol to prepare a solution with a titanium atom content of 3.36% by mass. The catalyst solution exhibited good storage stability in 1,4-butanediol; no precipitate formation was observed in the catalyst solution stored under a nitrogen atmosphere at 40°C for at least 40 days. The pH of this catalyst solution was 6.3.

[0091] [PBST manufacturing] PBST was produced as follows by the esterification process shown in Figure 2 and the polycondensation process shown in Figure 3. First, a slurry at 50°C was prepared by mixing succinic acid and terephthalic acid in amounts of 55 mol% and 45 mol% respectively, with 0.20 mol% trimethylolpropane, 1.5 times the molar amount of 1,4-butanediol, and tetra-n-butyl titanate containing 0.012 mol% Ti. This slurry was then fed from a slurry preparation tank (not shown) through a raw material supply line (1)... Therefore, under a nitrogen atmosphere, the low molecular weight product (esterification reaction product) with an esterification rate of 99% by mass was continuously supplied at a rate of 45.5 kg / hour to an esterification reaction vessel (A) equipped with a stirrer and filled with the product.

[0092] The esterification reactor (A) was set to an internal temperature of 230°C and a pressure of 101 kPa. The resulting water, tetrahydrofuran, and excess 1,4-butanediol were distilled off through the distillation line (5) and separated into high-boiling and low-boiling components in the rectification column (C). After the system stabilized, a portion of the high-boiling component at the bottom of the column was extracted to the outside through the extraction line (8) to maintain a constant liquid level in the rectification column (C). Meanwhile, the low-boiling component, mainly water and tetrahydrofuran, was extracted in gaseous form from the top of the column, condensed in a condenser (G), and then extracted to the outside through the extraction line (13) to maintain a constant liquid level in the tank (F). Simultaneously, the entire amount of the bottom component (98% or more by mass of 1,4-butanediol) from the rectification column (C) at a temperature of 100°C was supplied from the recirculation line (2), and tetrahydrofuran and an equimolar amount of 1,4-butanediol generated in the esterification reactor were supplied from the raw material supply line (1), adjusting the molar ratio of 1,4-butanediol to succinic acid and terephthalic acid in the esterification reactor to 1.50.

[0093] The esterified product generated in the esterification reactor (A) was continuously withdrawn from the esterification product withdrawal line (4) using a pump (B), and the liquid level was controlled so that the average residence time of the liquid in the esterification reactor (A) was 3 hours. The esterified product withdrawn from the withdrawal line (4) was continuously supplied to the first polycondensation reactor (a) in Figure 3. After the system stabilized, the esterification rate of the esterified product collected at the outlet of the esterification reactor (A) was 96.5%.

[0094] The previously prepared catalyst solution was diluted with 1,4-butanediol in a catalyst preparation tank to a titanium atom concentration of 0.10% by mass. This catalyst solution was then continuously supplied at a rate of 2.1 kg / h to the esterification product extraction line (4) via the supply line (L8) (the catalyst was added to the liquid phase of the reaction solution). The supply rate remained stable throughout the operation.

[0095] The internal temperature of the first polycondensation reactor (a) was set to 240°C and the pressure to 2.0 kPa, and the liquid level was controlled so that the residence time was 120 minutes. The initial polycondensation reaction was carried out while water, tetrahydrofuran, and 1,4-butanediol were withdrawn from a vent line (L2) connected to a vacuum pump (not shown). The withdrawn reaction solution was continuously supplied to the second polycondensation reactor (d). The internal temperature of the second polycondensation reactor (d) was set to 240°C and the pressure to 450 Pa. The liquid level was controlled to ensure a residence time of 120 minutes. Water, tetrahydrofuran, and 1,4-butanediol were withdrawn from a vent line (L4) connected to a vacuum pump (not shown) while the polycondensation reaction continued. The resulting polyester was continuously supplied to the third polycondensation reactor (k) via an extraction gear pump (e) through an extraction line (L3). The internal temperature of the third polycondensation reactor (k) was set to 240°C and the pressure to 200 Pa. The residence time was 120 minutes, and the polycondensation reaction continued. The resulting polyester was continuously drawn out in strand form from a die head (g), water-cooled, and cut into pellets using a rotary cutter (h). The esterification and polycondensation reactions were carried out continuously for 7 days. Samples were taken every 8 hours starting 16 hours after the start of the reaction, and the properties of the resulting polyester were measured. The average value and range for each sample are shown. The intrinsic viscosity was 1.50 ± 0.05 dL / g, and the pellets contained stable quality PBST with a pellet weight of 15 ± 1 mg / pellet. The cyclic dimer content of the pellets at this point is shown in Table 2 as the pellet properties before contact treatment.

[0096] [Contact treatment of pellets with solvents] The obtained pellets were subjected to a solvent-based extraction process to extract the cyclic dimer from the solvent, as shown in Figure 4. The mixture of ethanol and water used as the solvent in the solvent contact process was controlled to 70°C via a heat exchanger (II) through a pump (IX) from a circulation tank (I). The solvent was supplied from supply line (101) to treatment tank (III). The ratio of ethanol (hereinafter sometimes abbreviated as EtOH) to water in the solvent was 60% by mass of water relative to the total solvent. The mass ratio of solvent to pellets in the treatment tank was 5 (treatment liquid / pellet ratio).

[0097] The solvent was brought into countercurrent contact with pellets (not shown) in a processing tank (III), and then withdrawn from the withdrawal line (102). The entire amount (100% by mass) of the withdrawn solvent was supplied to the separator (XI) via a fine particle remover (IV). The pellets to be used in the solvent contact process were continuously supplied from the supply line (103), and after being in contact with the solvent for 4 hours, they were continuously withdrawn from the withdrawal line (104) by a rotary valve (V). The solvent withdrawn along with the pellets was separated in a preliminary solid-liquid separator (VI), and after passing through a recovery tank (VII), was returned to the recovery line (106) via the supply line (105) by a pump (X).

[0098] The solvent supplied to the separator (XI) separated the cyclic dimers in the circulating tank (I) so that the concentration of cyclic dimers in the solvent was 0 ppm by mass, and the cyclic dimers were extracted to the outside through the extraction line (112). A distillation column was used as the separator (XI). From the solvent supply line (108), an amount of new solvent (ethanol aqueous solution) equivalent to the amount of solvent extracted from the extraction line (112) along with the cyclic dimers was supplied to the circulating tank (I). The continuously extracted pellets were separated from the accompanying solvent in the preliminary solid-liquid separator (IV), and then continuously supplied to the drying process via the extraction line (109) from the solid-liquid separator (VIII).

[0099] [Drying the pellets] The pellets that had undergone the solvent contact process were dried by the drying process shown in Figure 5. For the first drying tower (I), nitrogen gas with a purity of 99% or higher (dew point -40°C) was used as the drying gas, with a gas temperature of 50°C, a gas (empty tower) velocity of 0.125 m / sec, and a pellet residence time of 24 hours. For the second drying tower, air (dew point -40°C) was used as the drying gas, with a temperature of 50°C, a gas (empty tower) velocity of 0.125 m / sec, and a pellet residence time of 48 hours. The PBST pellets obtained in this way were used as the final product, and the cyclic dimer content was measured and the Raman band intensity ratio calculated according to the method described above. Furthermore, these pellets were subjected to the heat fusion test described above. Table 2 shows the cyclic dimer content, Raman band intensity ratio, and evaluation rank from the heat fusion test of the final product.

[0100] (Reference example) 21% by mass (separation rate: 21% by mass) of the solvent that was in countercurrent contact with the pellets, which was withdrawn from the processing tank (III), was supplied to the separator (XI) via the fine particle remover (IV), and the remainder was recovered into the circulation tank (I). The solvent supplied to the separator (XI) separated the cyclic dimers, and the cyclic dimers were withdrawn to the outside through the extraction line (112). In this way, the concentration of cyclic dimers in the solvent in the circulation tank (I) was adjusted as shown in Table 2. Otherwise, pellets as the final product were manufactured in the same manner as in Example 3. The cyclic dimer content of the obtained pellets was measured according to the method described above. The measurement results are shown in Table 2.

[0101] (Comparative Example 3) Of the solvent extracted from the processing tank (III) and brought into countercurrent contact with the pellets, 1% (1% separation rate) of the solvent was supplied to the separator (XI), and the remainder was recovered into the circulation tank (I). In this way, the concentration of cyclic dimers in the solvent in the circulation tank (I) was adjusted as shown in Table 2. Otherwise, the pellets as the final product were manufactured in the same manner as in Example 3. The cyclic dimer content of the obtained pellets was measured according to the method described above, and the Raman band intensity ratio was calculated. Furthermore, these pellets were subjected to the heat fusion test described above. The cyclic dimer content, Raman band intensity ratio, and evaluation rank from the heat fusion test of the final product are shown in Table 2. This will be shown.

[0102] [Table 2]

[0103] As shown in Table 2, when the solvent contact process was carried out continuously, and the cyclic dimer content of the solvent used to extract the cyclic dimers contained in the pellets was set to 3000 ppm by mass (Comparative Example 3), the cyclic dimer content in the resulting pellets was high, resulting in poor pellet quality. On the other hand, from Example 3, by setting the concentration of cyclic dimers in the solvent used in the continuous solvent contact process to zero, the cyclic dimer content was low, and as a result, the Raman band intensity ratio (I 01 / I 02 This allowed for more efficient production of pellets containing PBST adjusted to 1.00 or higher. [Explanation of Symbols]

[0104] 1: Raw material supply line 2: Recirculation line 3: Catalyst supply line 4: Esterification reaction product extraction line 5: Dilution line 6: Extraction line 7: Circulation line 8: Extraction line 9: Gas extraction line 10: Condenser line 11: Extraction line 12: Circulation line 13: Extraction line 14: Ventline 15: Supply Line A: Esterification reactor B: Extraction pump C: Rectification tower D: Pump E: Pump F: Tank G: Capacitor L1, L3, L5: Polycondensation reaction product extraction lines L2, L4, L6: Vent lines L7: Catalyst supply line L8: Raw material supply line a: First polycondensation reactor d: Second double condensation reactor Q: Rotary valve R: Blower S: Heat exchanger 101, 105, 108: Solvent supply lines 102, 110, 113: Solvent extraction lines 103: Pellet supply line 104, 109: Pellet extraction line 106: Solvent recovery line 111: Solvent supply line 112: Circular oligomer extraction line I: Circulation tank II: Heat exchanger III: Treatment tank IV: Fine powder removal machine V: Rotary valve VI: Preliminary solid-liquid separator VII: Recovery Tank VIII: Solid-liquid separator IX, X: Pump XI: Separator 201: Pellet supply line 202: Pellet extraction line 203: Pellet supply line 204: Pellet extraction line 205: Pellet supply line 206: Pellet extraction line 207: Dry gas recovery line 208: Dry gas supply line 209: New dry gas supply line 210: Condensate extraction line 211: Cooling gas extraction line 212: Cooling gas supply line 213: Dry gas extraction line 214: Dry gas supply line

Claims

1. A pellet containing polybutylene succinate terephthalate having as its main constituent units a constituent unit derived from succinic acid, a constituent unit derived from terephthalic acid, and a constituent unit derived from 1,4-butanediol, The Raman spectrum measured from the pellet shows values ​​of 1680–1780 cm⁻¹. －１ The spectrum in the wavenumber range is 1711±5 cm⁻¹. －１ The first wavenumber range, and 1722±5 cm －１ In a Raman spectrum fitted using a Lorentz function with two peaks each having a peak top in the second wavenumber range, the intensity of the peak in the first wavenumber range I ０１ And the peak intensity I in the second wavenumber range ０２ The intensity ratio (I ０１ / I ０２ Pellets in which the ratio is 1.00 or higher.

2. The pellet according to claim 1, wherein the strength ratio is 1.00 or more and 2.50 or less.

3. The pellet according to claim 1, wherein the content of a cyclic dimer consisting of succinic acid and 1,4-butanediol in the pellet is 2,500 ppm by mass or less.

4. The pellet according to claim 1, wherein the intrinsic viscosity (IV) of the pellet is 1.2 dL / g or more and 2.2 dL / g or less.

5. The pellet according to claim 1, wherein the molar ratio of constituent units derived from succinic acid to constituent units derived from terephthalic acid (constituent units derived from succinic acid / constituent units derived from terephthalic acid) is 10 / 90 to 90 / 10.

6. The pellet according to claim 5, wherein the molar ratio is 40 / 60 to 60 / 40.

7. An injection-molded resin pellet article comprising at least one of the pellets described in any one of claims 1 to 6.

8. An extruded resin pellet article comprising at least one of the pellets described in any one of claims 1 to 6.

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