Polyester resins, molded articles, preforms, polyester bottles, and mechanically recycled polyester resins

Abstract

To provide a polyester resin having an excellent color tone.SOLUTION: A polyester resin contains polyester containing a diol unit and a dicarboxylic acid unit as a main component, wherein a shoulder correlation parameter S, which is derived using a differential molecular weight distribution curve obtained by GPC and is represented by the following expression (1), is more than 0.130 and 0.197 or less. In the expression (1), M is a molecular weight of a polyester resin, f(LogM) represents a differential molecular weight distribution curve of the polyester resin, and g(LogM) represents a primary function in which LogM in f(LogM) is connected at two points data of 3.40 and 3.75.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to polyester resin, molded articles, preforms, and polyester bottles made from this polyester resin, and to mechanically recycled polyester resin. [Background technology]

[0002] Polyester resins are thermoplastic resins with excellent properties such as mechanical stability, chemical stability, transparency, and heat resistance. From the viewpoint of reducing environmental impact, a method of mechanical recycling is known for regenerating such polyester resins by solid-phase polymerization (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] Patent Document 1: Japanese Unexamined Patent Publication No. 2000-219728 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, when the above technology is used to repeatedly perform mechanical recycling of polyester resin, there is a problem in that the yellowing of the polyester resin increases and the color tone deteriorates.

[0005] The object of the present invention is to provide a polyester resin having excellent color tone. [Means for solving the problem]

[0006] [1]According to aspect 1 of the present invention, a polyester resin is provided which mainly comprises a polyester containing diol units and dicarboxylic acid units, characterized in that the shoulder correlation parameter S, which is derived using a differential molecular weight distribution curve obtained by GPC and expressed by the following equation (1), is greater than 0.130 and less than or equal to 0.197. In the above formula (1), M is the molecular weight of the polyester resin, f(LogM) represents the differential molecular weight distribution curve of the polyester resin, and g(LogM) represents a linear function connected by the data of two points where LogM is 3.40 and 3.75 in f(LogM).

[0007] [2] According to Embodiment 2 of the present invention, there is provided a polyester resin according to Embodiment 1, characterized in that the polydispersity Mw / Mn measured using GPC is 2.315 or more and less than 2.500.

[0008] [3] According to Embodiment 3 of the present invention, there is provided a molded body made from the polyester resin according to Embodiment 1 or 2.

[0009] [4] According to Embodiment 4 of the present invention, there is provided a preform made from the polyester resin according to Embodiment 1 or 2.

[0010] [5] According to Embodiment 5 of the present invention, there is provided a polyester bottle made from the polyester resin according to Embodiment 1 or 2.

[0011] [6] According to Embodiment 6 of the present invention, there is provided a polyester resin according to Embodiment 1 or 2, characterized in that the polyester resin is a mechanically recycled polyester resin. [Advantages of the Invention]

[0012] According to the present invention, it is possible to provide a polyester resin having an excellent color tone. [Brief Description of the Drawings]

[0013] [Figure 1] FIG. 1 is a flowchart showing an example of a method for producing a polyester resin in an embodiment of the present invention. [Figure 2A] FIG. 2A is a graph showing the measurement results of the 1H-NMR spectrum in Example 1. [Figure 2B]Figure 2B is a graph showing the measurement results of the 1H-NMR spectrum in Comparative Example 6. [Figure 2C] Figure 2C is a graph showing the measurement results of the 1H-NMR spectrum in virgin isophthalic acid copolymerized polyethylene terephthalate resin. [Figure 3] Figure 3(a) is a graph showing the measurement results of the differential molecular weight distribution curve in Example 1, and Figure 3(b) is an enlarged view of Figure 3(a). [Figure 4] Figure 4(a) is a graph showing the measurement results of the differential molecular weight distribution curve in Comparative Example 6, and Figure 4(b) is an enlarged view of Figure 4(a).

Mode for Carrying Out the Invention

[0014] The polyester resin in the present embodiment mainly contains a polyester containing a diol unit and a dicarboxylic acid unit, is obtained by GPC, and has a shoulder correlation parameter S derived using the differential molecular weight distribution curve represented by the following formula (1) of more than 0.130 and not more than 0.197. TIFF0007900350000002.tif11134 In the above formula (1), M is the molecular weight of the polyester resin, f(LogM) represents the differential molecular weight distribution curve of the polyester resin, and g(LogM) represents a linear function connected by the data of two points where LogM is 3.40 and 3.75 in f(LogM).

[0015] Polyesters included in polyester resins include aromatic polyesters, fully aromatic polyesters, polycarbonate esters, and aliphatic polyesters, with aromatic polyesters being preferred among these. Aromatic polyesters contain diol units and dicarboxylic acid units. Examples of diol compounds for forming diol units include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, 1,6-hexylene glycol, cyclohexanedimethanol, and ethylene oxide adducts of bisphenol A, with ethylene glycol being preferred among these. Examples of dicarboxylic acid compounds for forming dicarboxylic acid units include aromatic dicarboxylic acids and their derivatives such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, and franguocarboxylic acid, with terephthalic acid being preferred among these. Specific examples of polyesters include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polyethylene furanoate, with polyethylene terephthalate, a copolymer of ethylene glycol and terephthalic acid, being preferred among these. The polyesters mentioned above are not limited to those derived from petroleum raw materials; they may also be derived from plant raw materials, or even recycled polyesters derived from petroleum or plant raw materials. Furthermore, the polyesters mentioned above may be used individually or in mixtures.

[0016] The content of ethylene terephthalate units in polyethylene terephthalate is preferably 70 mol% or more, and more preferably 90 mol% or more, relative to the total monomer units.

[0017] Polyethylene terephthalate may contain units consisting of dicarboxylic acids other than terephthalic acid that are copolymerizable with ethylene glycol and terephthalic acid within the total monomer units. Examples of dicarboxylic acids other than terephthalic acid include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedionic acid, eicosanedionic acid, pimelic acid, azelaic acid, methylmalonic acid and ethylmalonic acid, adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, decalindicarboxylic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodium sulfisoisophthalic acid, phenylendanedicarboxylic acid, anthracenedicarboxylic acid, phenantradicarboxylic acid, 9,9'-bis(4-carboxyphenyl)fluorenic acid, 2,5-franzicarboxylic acid and their ester derivatives, among which isophthalic acid is preferred. The content of units consisting of dicarboxylic acids other than terephthalic acid is preferably 30 mol% or less, and more preferably 10 mol% or less, relative to the total monomer units.

[0018] Polyethylene terephthalate may contain units consisting of diols other than terephthalic acid that can copolymerize with ethylene glycol and terephthalic acid in the total monomer units. Such diols other than ethylene glycol include 1,2-propanediol, 1,3-propanediol, butanediol, 2-methyl-1,3-propanediol, hexanediol, neopentyl glycol, cyclohexanedimethanol, cyclohexanediethanol, decahydronaphthalenedimethanol, decahydronaphthalenediethanol, norbornanediethanol, norbornanediethanol, tricyclodecanediethanol, tricyclodecanediethanol, tetracyclododecanediethanol, tetracyclododecanediethanol, decalindiethanol, decalindiethanol, 5-methylol-5-ethyl-2-(1,1-dimethyl-2-hydroxyethyl Examples include ethylene glycol-1,3-dioxane, cyclohexanediol, bicyclohexyl-4,4'-diol, 2,2-bis(4-hydroxycyclohexylpropane), 2,2-bis(4-(2-hydroxyethoxy)cyclohexyl)propane, cyclopentanediol, 3-methyl-1,2-cyclopentadiol, 4-cyclopentene-1,3-diol, adamandiol, paraxylene glycol, bisphenol A, bisphenol S, styrene glycol, trimethylolpropane, pentaerythritol, diethylene glycol, triethylene glycol, and bis-β-hydroxyethyl terephthalate (BHET), among which diethylene glycol is preferred. The content of units consisting of diols other than ethylene glycol is preferably 30 mol% or less, and more preferably 10 mol% or less, relative to the total monomer units.

[0019] Polyethylene terephthalate may contain other components such as additives. For example, it may contain one or more additives such as plasticizers, light stabilizers, antioxidants, UV absorbers, flame retardants, colorants, pigments, fillers, release agents, antistatic agents, fragrances, foaming agents, and antibacterial / antifungal agents.

[0020] While not particularly limited, the polyester resin in this embodiment may include cyclic oligomers containing diol units and dicarboxylic acid units. Such cyclic oligomers are by-products in the polymerization reactions of the diol and dicarboxylic acid compounds described above. The polyester resin in this embodiment includes trimer oligomers (cyclic trimers; CTs) and pentamer oligomers (C5s) as cyclic oligomers. For example, a trimer oligomer (CT) contained in a polyester resin containing polyethylene terephthalate as the polyester consists of three constituent units of polyethylene terephthalate.

[0021] The content of cyclic oligomers in the polyester resin is preferably 1% by weight or less, and more preferably 0.5% by weight or less.

[0022] In polyester resins, the shoulder correlation parameter S, derived using the differential molecular weight distribution curve obtained by GPC and expressed by equation (1) below, is greater than 0.130 and less than or equal to 0.197, preferably greater than 0.145 and less than or equal to 0.196. TIFF0007900350000003.tif11134 In equation (1) above, M is the molecular weight of the polyester resin, f(LogM) represents the differential molecular weight distribution curve of the polyester resin, and g(LogM) represents a linear function connected by two data points where LogM in f(LogM) is 3.40 and 3.75. The vertical axis of the differential molecular weight distribution curve is dw / dLogM, which is the derivative of the concentration fraction w(%) with respect to LogM. In this embodiment, the polyester resin has suppressed yellowing, excellent color tone, and excellent molding stability because the shoulder correlation parameter S is within the above range.

[0023] In polyester resins, the polydispersity Mw / Mn measured using GPC is preferably 2.315 or more and less than 2.500, and more preferably 2.320 or more and less than 2.490. By keeping the polydispersity Mw / Mn within the above range, the polyester resin can be made to have superior color tone and molding stability.

[0024] While not particularly limited, polyester resins may contain a pentamer oligomer (C5) as a cyclic oligomer. In polyester resins, the ratio of the peak area of ​​the pentamer oligomer (C5) to the peak area of ​​the trimer oligomer (CT) in the cyclic oligomer (C5 / CT), measured using liquid chromatography, is preferably 0.068 or more and less than 0.090, and more preferably 0.070 or more and less than 0.088. By setting the ratio of the peak area of ​​the pentamer oligomer (C5) to the peak area of ​​the trimer oligomer (CT) (C5 / CT) within the above range, the polyester resin can be made to have superior color tone and molding stability. When measuring using liquid chromatography, it is preferable to use a UV / Vis detector or a diode array detector (DAD) as the detector. The same applies when determining the peak area ratios of the hexamer oligomer and heptamer oligomer described later.

[0025] While not particularly limited, the polyester resin may contain a hexameric oligomer (C6) as a cyclic oligomer. In the polyester resin, the ratio of the peak area of ​​the hexameric oligomer (C6) to the peak area of ​​the trimer oligomer (CT) in the cyclic oligomer, as measured by liquid chromatography (C6 / CT), is preferably 0.0482 or more and less than 0.0620, and more preferably 0.0485 or more and less than 0.0600. By setting the peak area ratio (C6 / CT) within the above range, the polyester resin can be made to have better color tone and molding stability.

[0026] Although not particularly limited, the polyester resin may contain a heptamer oligomer (C7) as a cyclic oligomer. In the polyester resin, the ratio (C7 / CT) of the peak area of the heptamer oligomer (C7) to the peak area of the trimer oligomer (CT) in the cyclic oligomer measured using liquid chromatography is preferably 0.0225 or more and less than 0.0330, more preferably 0.0230 or more and less than 0.0320. By setting the ratio of the peak areas (C7 / CT) within the above range, the polyester resin can be made to have superior color tone and molding stability.

[0027] In the polyester resin, the ratio (A acid / A 7.5 ) of the peak area (A 7.5 ) at 7.43 to 7.55 ppm to the peak area (A acid ) derived from all dicarboxylic acids measured using 1H-NMR is preferably less than 0.00060, more preferably less than 0.00040. The peak derived from the dicarboxylic acid is present in the range of 7.60 to 7.75 ppm, 7.90 to 8.55 ppm, and 8.75 to 8.90 ppm, and the peak area (A acid ) derived from all dicarboxylic acids refers to the sum of the peak areas present in all these ranges. By setting the ratio (A acid / A 7.5 ) of the peak area (A 7.5 ) at 7.43 to 7.55 ppm to the peak area (A acid ) derived from all dicarboxylic acids within the above range, the polyester resin can be made to have superior color tone and molding stability.

[0028] In the polyester resin, the ratio (A acid / A 7.8 ) of the peak area (A 7.8 ) at 7.75 to 7.85 ppm to the peak area (A acid ) derived from all dicarboxylic acids measured using 1H-NMR is preferably less than 0.00030, more preferably less than 0.00020. The peak area (A acidPeak area (A) of 7.75-7.85 ppm for ) 7.8 ) ratio (A 7.8 / A acid By setting the above range, the polyester resin can be made to have superior color tone and molding stability.

[0029] The intrinsic viscosity (IV) of the polyester resin in this embodiment is preferably 0.60 to 1.40 dL / g, and more preferably 0.70 to 1.00 dL / g.

[0030] chromaticity b of the polyester resin in this embodiment * The molecular weight in the form of pellets after solid-phase polymerization is preferably 15.0 or less, and more preferably 10.0 or less.

[0031] In this embodiment, the cold crystallization peak top temperature Tc1 of the polyester resin is preferably 149°C to 162°C, and more preferably 149°C to 153°C. By setting the cold crystallization peak top temperature Tc1 of the polyester resin to be above the lower limit, the molding stability of the polyester resin can be improved. However, if the cold crystallization peak top temperature Tc1 of the polyester resin exceeds the upper limit, it becomes difficult to impart heat resistance when molding the polyester resin into polyester bottles or the like.

[0032] Figure 1 is a flowchart showing an example of a method for producing polyester resin in this embodiment. As shown in Figure 1, the polyester resin in this embodiment can be produced by a method that involves a polyester containing the above-mentioned diol units and dicarboxylic acid units, and a thermal history control treatment comprising a first melt extrusion step, a second melt extrusion step, a crystallization step, and a solid-phase polymerization step.

[0033] First, in the first melt extrusion step, the pelletized polyester obtained by polymerizing the above-mentioned diol compound and dicarboxylic acid is first dehumidified in a dehumidifying dryer set to 150°C to reduce its moisture content to 50 ppm or less, and then melt-extruded using an extruder. The extruded molten resin is then air-cooled to form pellets. The extruder is not particularly limited, but examples include single-screw extruders, twin-screw extruders, and multi-screw extruders, with twin-screw extruders being preferred. When using a twin-screw extruder, the extrusion temperature is preferably 0 to 60°C higher than the melting point of the polyester, and in the case of polyethylene terephthalate, it is 260 to 310°C, and more preferably 265 to 300°C. The screw rotation speed of the twin-screw extruder is preferably 50 to 800 rpm, and more preferably 70 to 400 rpm. The discharge rate of the twin-screw extruder is preferably 5 to 30,000 kg / h, and more preferably 10 to 10,000 kg / h.

[0034] Next, in the second melt extrusion step, the pellets obtained in the first melt extrusion step are used to perform melt extrusion again, and the extruded molten resin is air-cooled to form pellets. The extruder is not particularly limited, but examples include single-screw extruders, twin-screw extruders, and multi-screw extruders, with twin-screw extruders being preferred. Furthermore, it is preferable that the extruder used is equipped with a vacuum venting device that can reduce the pressure to below atmospheric pressure. When using a twin-screw extruder equipped with a vacuum venting device in the second melt extrusion step, it is preferable that the melt extrusion conditions are the same as those of the first melt extrusion step, except that the vacuum is maintained at a pressure of 100 Torr or less.

[0035] Next, in the crystallization step, the pellets obtained in the second melt extrusion step are heated to crystallize the resin. The heating temperature is preferably 100 to 170°C, more preferably 130 to 150°C. Heating is preferably carried out under a pressure of 200 Torr or less, under a nitrogen atmosphere, or a combination of these. The heating time is preferably 0.5 to 6 hours, more preferably 2 to 5 hours.

[0036] Next, in the solid-phase polymerization step, the crystallized pellets are heated to carry out solid-phase polymerization of the resin. Solid-phase polymerization is preferably carried out under a pressure of 200 Torr or less, under a nitrogen atmosphere, or a combination of these. The solid-phase polymerization temperature is preferably 200 to 230°C, more preferably 205 to 225°C. The heating time is preferably 2 to 24 hours, more preferably 6 to 20 hours.

[0037] As described above, the polyester resin of this embodiment can be obtained by performing a thermal history control treatment consisting of a first melt extrusion step, a second melt extrusion step, a crystallization step, and a solid-phase polymerization step on the polyester once or multiple times. The number of thermal history control treatments is preferably 1 to 3 times, with so-called virgin polyester that has never been recycled being used as the baseline (0 times).

[0038] The method for producing the polyester resin in this embodiment is not limited to the above. For example, the polyester resin in this embodiment (mechanically recycled polyester resin) may be obtained by mechanically recycling polyester that has been used as polyester bottles, etc., thereby controlling the thermal history. As the polyester used for mechanical recycling, for example, polyester bottles manufactured from virgin polyester or polyester bottles manufactured after one or more mechanical recyclings can be used.

[0039] The polyester resin in this embodiment can be suitably used for processing into molded articles such as preforms and polyester bottles. The preform can be manufactured by injection molding of the polyester resin. The polyester bottle can be manufactured by stretch blow molding such a preform. Molded articles manufactured using the polyester resin in this embodiment have excellent color tones.

[0040] As described above, since the polyester resin in this embodiment is in its pre-processed state as a molded article, the ratio of the peak areas of 5, 6, and 7-mer oligomers (C5 / CT, C6 / CT, C7 / CT) to the peak area of ​​the trimer oligomer (CT) measured by liquid chromatography, the ratio of the peak areas of 7.43-7.55 ppm and 7.75-7.85 ppm to the peak area derived from the total dicarboxylic acid measured using 1H-NMR, the shoulder correlation parameter S, and the polydispersity Mw / Mn (hereinafter collectively referred to as "thermal history parameters") cannot be determined in the state of the molded article. The molded article corresponds to the state between the first melt extrusion process and the second melt extrusion process in the flowchart shown in Figure 1. Therefore, in order to compare the polyester resin constituting the molded article with the polyester resin in this embodiment, it is necessary to perform the second melt extrusion treatment, crystallization treatment, and solid-phase polymerization treatment on the molded article, evaluate the resulting pellets, and determine whether the thermal history parameters are within a specific range.

[0041] Furthermore, when a molded body undergoes a second melt extrusion treatment, crystallization treatment, and solid-phase polymerization treatment, an additional thermal history equivalent to one thermal history control treatment is added to the polyester resin before molding. Therefore, if the thermal history parameters evaluated after performing the second melt extrusion treatment, crystallization treatment, and solid-phase polymerization treatment on a molded body are near the upper and lower limits of the specific range defined in this embodiment, it is preferable to evaluate whether the thermal history parameters of the polyester resin before molding were within that specific range using the following procedure.

[0042] First, the thermal history parameters of the pellets obtained by performing a second melt extrusion treatment, crystallization treatment, and solid-phase polymerization treatment on the molded body are recorded as thermal history parameters for adjustment count 1. Next, thermal history control treatment is performed on the pellets, and the resulting thermal history parameters are recorded as thermal history parameters for adjustment count 2. Subsequently, thermal history control treatment is performed on the pellets multiple times as needed, and the thermal history parameters for adjustment count 3 and beyond are recorded. In this way, by decoupling the correlation between the number of adjustment counts and the thermal history parameters, thermal history parameters corresponding to adjustment count 0 are obtained. By evaluating the thermal history parameters corresponding to adjustment count 0, it is possible to confirm whether the thermal history parameters of the polyester resin before molding fell within a specific range. [Examples]

[0043] Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

[0044] <Example 1> [Preparation of PET resin pellets and preforms] 30 kg of isophthalic acid copolymerized polyethylene terephthalate resin (manufactured by Shinko Synthetic Fiber Co., Ltd., isophthalic acid copolymerization ratio 1.8 mol%, IV=0.83) pellets were prepared and dried using a hopper dryer at 150°C for 5 hours. Next, these pellets were fed into a twin-screw extruder (manufactured by Toshiba Machine Co., Ltd., TEM26SS) and melt extrusion was performed at an extrusion temperature of 290°C, a screw rotation speed of 100 rpm, and a discharge rate of 10 kg / h. The molten resin discharged from the extruder in strand form was air-cooled while being transported by a belt conveyor and then pelletized using a pelletizer (first melt extrusion treatment). Next, these pellets were fed back into the twin-screw extruder and melt extrusion was performed under the same conditions as above, except that a vacuum vent (9 Torr) was used, to obtain pellets in the same manner (second melt extrusion treatment).

[0045] 15 kg of the obtained pellets were heated in a stirring vacuum dryer (Dalton, 45 MV) at 1 Torr and 150°C for 5 hours to undergo crystallization. Next, the crystallized pellets were heated in the same stirring vacuum dryer at 1 Torr and 225°C for 13 hours to undergo solid-phase polymerization to obtain PET resin pellets. In both the crystallization and solid-phase polymerization processes, the rotation speed of the stirring blades in the stirring vacuum dryer was set to 20 rpm. In addition, a portion of the obtained PET resin pellets was supplied to an injection molding machine, and a 25 g preform for a 500 mL bottle was produced by setting the barrel temperature and hot runner temperature to 300°C, the mold temperature to 15°C, and the molding cycle to 32 seconds. The PET resin pellets and bottle preform were evaluated according to the following procedure. The results are shown in Table 2.

[0046] [Cyclic oligomer content] 0.2 g of PET resin pellets and bottle preforms were weighed, and 1 mL of a mixed solvent of 1,1,1,3,3,3,-hexafluoro-2-propanol and chloroform (weight ratio 1 / 1) was added to completely dissolve them. After adding 4 mL of chloroform to the solution, 5 mL of acetonitrile was gradually added, and the mixture was allowed to stand for 3 hours to precipitate the PET polymer. 1 mL of the supernatant of this suspension was taken and filtered through a 0.20 μm pore size membrane filter, and the filtrate was measured by high-performance liquid chromatography. An Agilent Technologies 1200 series was used as the measurement instrument. The measurement conditions were as follows: an Agilent Technologies 1290 Infinity diode array detector (G4212A) was used as the detector, with a detection wavelength of 254 nm and a reference wavelength of 500 nm. Furthermore, an Agilent Technologies ZORBAX Eclipse Plus C18 column (Rapid Resolution HD 2.1×150 mm 1.8 Micron) was used, and the column temperature was set to 40°C. The mobile phase consisted of a 0.05 wt% phosphoric acid aqueous solution as solution I and acetonitrile as solution II, flowed at a flow rate of 0.6 mL / min under the gradient conditions shown in Table 1 below. The injection volume was 2 μL. For the cyclic oligomers in the pellet, the peak areas for the trimer and pentamers up to the heptamer (CT, C5, C6, C7) were determined, and the C5 / CT, C6 / CT, and C7 / CT ratios were calculated.

[0047] [Table 1]

[0048] [NMR history correlation peaks] PET resin pellets were dissolved in a mixed solvent of deuterated trifluoroacetic acid and deuterated chloroform (volume ratio 8 / 2), and the 1H-NMR spectrum was measured using an NMR spectrometer (JEOL, 400SS). The peak area (A) derived from all dicarboxylic acids was then determined. acid ) and the area of ​​NMR history correlation peak 1 (A 7.5 ) and the area of ​​NMR history correlation peak 2 (A 7.8Find the values ​​for each of them, and A 7.5 / A acid and A 7.8 / A acid The following was calculated. Here, the peaks derived from all dicarboxylic acids are defined as the sum of the peak areas in the ranges of 7.60-7.75 ppm, 7.90-8.55 ppm, and 8.75-8.90 ppm, the NMR history correlation peak 1 is defined as the peak area in the range of 7.43-7.55 ppm, and the NMR history correlation peak 2 is defined as the peak area in the range of 7.75-7.85 ppm. Figure 2A is a graph showing the measurement results of the 1H-NMR spectrum in Example 1, and Figure 2B is a graph showing the measurement results of the 1H-NMR spectrum in Comparative Example 6. For reference, the 1H-NMR spectrum was also measured in the same manner for virgin isophthalic acid copolymer polyethylene terephthalate resin that had not undergone thermal history control treatment. Figure 2C is a graph showing the measurement results of the 1H-NMR spectrum for virgin isophthalic acid copolymer polyethylene terephthalate resin.

[0049] [Multivariance (Mw / Mn) and shoulder correlation parameter S] The differential molecular weight distribution curve was measured using a high-speed GPC instrument (Tosoh, HLC-8320GPC) to determine the polydispersity (Mw / Mn). As a sample, a solution was used in which PET resin pellets were dissolved in a mixed solution of 1,1,1,3,3,3,-hexafluoro-2-propanol and chloroform (volume ratio 1 / 49). Chloroform was used as the mobile phase, and a TSKgel SuperMultiporeHZ-M column manufactured by Tosoh Corporation was used. The measurement temperature was 40°C. Standard polystyrene (Tosoh, PStQuickMP-M) was used as the molecular weight standard. In addition, the shoulder correlation parameter S, expressed by equation (1) above, was determined from the differential molecular weight distribution curve. The vertical axis of the differential molecular weight distribution curve was dw / dLogM, obtained by differentiating the concentration fraction w (%) with respect to LogM. Figure 3(a) is a graph showing the measurement results of the differential molecular weight distribution curve in Example 1, and Figure 3(b) is an enlarged view of Figure 3(a). Furthermore, Figure 4(a) is a graph showing the measurement results of the differential molecular weight distribution curve in Comparative Example 6, and Figure 4(b) is an enlarged view of Figure 4(a).

[0050] [b * value] b of PET resin pellets and preforms * The values ​​were measured using an SM color computer (manufactured by Suga Test Instruments Co., Ltd.). * A smaller value indicates better color tone.

[0051] [Cold crystallization peak top temperature Tc1] The cold crystallization peak top temperature Tc1 was measured using a differential scanning calorimetry system (PerkinElmer, Diamond DSC) with a 5 mg PET resin pellet as the sample. A higher cold crystallization peak top temperature indicates superior molding stability of the PET resin pellet. The measurement conditions were as follows. Step 1: Hold at 20°C for 5 minutes. Step 2: Increase temperature from 20°C to 290°C at a rate of 10°C / min. Step 3: Hold at 290°C for 5 minutes. Step 4: Cool down from 290°C to 20°C at a rate of 300°C / min. Step 5: Hold at 20°C for 10 minutes Step 6: Increase temperature from 20°C to 290°C at a rate of 10°C / min. Tc1 was determined from the peak top temperature (°C) of the cold crystallization peak in Step 6.

[0052] [Intrinsic viscosity recovery ΔIV] PET resin pellets were fed into a twin-screw extruder (Toshiba Machine Co., Ltd., TEM26SS), and melt extrusion was performed under the conditions of an extrusion temperature of 290°C, a screw rotation speed of 100 rpm, and an extrusion rate of 10 kg / h. The molten resin extruded in strand form from the extruder was air-cooled while being transported by a belt conveyor, and then formed into pellets using a pelletizer. Next, these pellets were fed back into the twin-screw extruder, and melt extrusion was performed under the same conditions as above, except that a vacuum vent (9 Torr) was used, to obtain pellet A. Pellet A was vacuum-dried at 120°C for 2 hours, weighed to 0.3 g, and added to a mixed solvent of 1,1,2,2-tetrachloroethane and phenol (weight ratio 1 / 1) to adjust the concentration to 1.00 g / dL, and stirred at 120°C for 20 minutes to completely dissolve. The dissolved solution was cooled to room temperature, and the relative viscosity was determined using a relative viscometer (Malvern Panalytical, Viscotec Y501C) heated to 30°C to determine the intrinsic viscosity A of pellet A.

[0053] Next, the above-mentioned pellet A was heated for 5 hours at 1 Torr and 150°C using a stirring vacuum dryer (Dalton, 45 MV) to perform a crystallization treatment. Then, the crystallized pellet was heated for 13 hours at 1 Torr and 225°C using the same stirring vacuum dryer to perform a solid-phase polymerization treatment to obtain pellet B. The relative viscosity of pellet B was determined using the same procedure as for pellet A, and the intrinsic viscosity B of pellet B was determined. Using intrinsic viscosities A and B, the intrinsic viscosity recovery ΔIV [dL / g] was calculated based on the following formula. A larger intrinsic viscosity recovery ΔIV indicates higher solid-phase polymerization efficiency when recovering and recycling molded products obtained from PET resin pellets, and that PET resin pellets are suitable for recycling. Intrinsic viscosity recovery ΔIV = Intrinsic viscosity B - Intrinsic viscosity A

[0054] Pellet A is obtained by performing a first melt extrusion treatment and a second melt extrusion treatment on PET resin pellets. Therefore, pellet A corresponds to pellets manufactured by recovering molded products (after the first melt extrusion treatment) obtained from PET resin pellets and extruding them (second melt extrusion treatment). On the other hand, pellet B is obtained by performing a crystallization treatment and a solid-phase polymerization treatment on pellet A. Therefore, pellet B corresponds to pellets obtained by mechanically recycling molded products obtained from PET resin pellets.

[0055] <Example 2> PET resin pellets were obtained in the same manner as in Example 1, except that the PET resin pellets of Example 1 were subjected to one additional first melt extrusion treatment, one additional second melt extrusion treatment, one crystallization treatment, and one additional solid-phase polymerization treatment. The evaluation was performed in the same manner. In other words, the PET resin pellets of Example 2 were obtained by subjecting virgin pellets to a total of two thermal history control treatments.

[0056] <Example 3> PET resin pellets were obtained and evaluated in the same manner as in Example 1, except that the total number of thermal history control treatments for the pellets was set to three.

[0057] <Comparative Examples 1-7> PET resin pellets were obtained and evaluated in the same manner as in Example 1, except that the total number of thermal history control treatments for the pellets was set to 4 to 10 times. In Comparative Examples 2 and 7, preforms were further manufactured using the obtained PET resin pellets, and the preforms were evaluated in the same manner as in Example 1.

[0058] <Reference example> Pellets of isophthalic acid copolymerized polyethylene terephthalate resin that had never undergone thermal history control treatment were evaluated in the same manner as in Example 1. Furthermore, preforms were obtained using these untreated pellets and evaluated in the same manner as in Example 1.

[0059] [Table 2]

[0060] As shown in Table 2, the PET resin pellets of Examples 1-3 and the preforms molded using them, for which the shoulder correlation parameter S is greater than 0.130 and less than or equal to 0.197, are b * The values ​​were low, the yellow tint was suppressed, and the color tone was excellent. Furthermore, the PET resin pellets and preforms of Examples 1 to 3 had high Tc1 values, resulting in excellent molding stability. On the other hand, the PET resin pellets of Comparative Examples 1 to 7, and the preforms molded using them, which had shoulder correlation parameters S of 0.130 or less, were inferior in color tone and molding stability.

Claims

1. A polyester resin containing diol units and dicarboxylic acid units, and containing 70 mol% or more of ethylene terephthalate units, The polydispersity Mw / Mn measured using GPC is 2.315 or higher and less than 2.

500. A polyester resin characterized in that the shoulder correlation parameter S, derived using the differential molecular weight distribution curve obtained by GPC and expressed by the following equation (1), is greater than 0.145 and less than or equal to 0.

197. (In equation (1) above, M is the molecular weight in the differential molecular weight distribution curve, f(LogM) represents the differential molecular weight distribution curve of the polyester resin, and g(LogM) represents a linear function connected by two data points in f(LogM) where LogM is 3.40 and 3.75.)

2. A molded article made from the polyester resin described in claim 1.

3. A preform made from the polyester resin described in claim 1.

4. A polyester bottle made from the polyester resin described in claim 1.

5. The polyester resin according to claim 1, characterized in that the polyester resin is a mechanically recycled polyester resin.

6. A method for producing a polyester resin according to claim 1, A method for producing a polyester resin comprising a first melt extrusion step, a second melt extrusion step, a crystallization step, and a solid-phase polymerization step, in which a polyester containing the diol units and the dicarboxylic acid units and containing 70 mol% or more of the ethylene terephthalate units is subjected to thermal history control treatment.

7. A method for producing a polyester resin according to claim 6, A method for producing polyester resin, comprising performing the aforementioned thermal history control treatment one to three times.

8. A method for producing a polyester resin according to claim 6 or 7, A method for producing a polyester resin, using a polyester having an intrinsic viscosity of 0.70 or higher.

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