Polyester resin, molded body, preform, polyester bottle, and mechanically recycled polyester resin

Abstract

The present invention provides a polyester resin which contains, as a main component, a polyester that includes a diol unit and a dicarboxylic acid unit, and which is characterized in that the shoulder correlation parameter S that is derived using a differential molecular weight distribution curve obtained by GPC and is expressed by formula (1) is 0.160 or less. (In formula (1), M represents 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 connecting data of two points at which LogM in f(LogM) is 3.40 and 3.75.)

Description

Polyester resin, molded body, preform, polyester bottle, and mechanically recycled polyester resin

[0001] The present invention relates to a polyester resin, a molded article, a preform, and a polyester bottle made from the polyester resin, and a mechanically recycled polyester resin.

[0002] Polyester resin is a thermoplastic resin that has excellent properties such as mechanical stability, chemical stability, transparency, heat resistance, etc. From the viewpoint of reducing the environmental load, a method of mechanically recycling such polyester resin by regenerating it through solid-state polymerization is known (for example, Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-219728

[0004] However, in the polyester resin produced by the above-mentioned technique, BHET remaining as a monomer adheres to the mold of the production equipment as a stain during molding of the polyester resin, and there is a problem in that the cost of molding increases in order to remove the stain.

[0005] An object of the present invention is to provide a polyester resin having a reduced BHET content and capable of suppressing the occurrence of mold contamination during molding, and a molded article made from such a polyester resin.

[0006] [1] According to a first aspect of the present invention, there is provided a polyester resin comprising, as a main component, a polyester containing a diol unit and a dicarboxylic acid unit, wherein the polyester resin has a shoulder correlation parameter S of 0.160 or less, which is calculated using a differential molecular weight distribution curve obtained by GPC and is represented by the following formula (1): In the above formula (1), M is the molecular weight of the polyester resin, f(Log M) represents the differential molecular weight distribution curve of the polyester resin, and g(Log M) represents a linear function connecting two data points in f(Log M) where Log M is 3.40 and 3.75.

[0007] [2] According to a second aspect of the present invention, there is provided the polyester resin according to the first aspect, characterized in that the polydispersity index Mw / Mn measured by GPC is 2.470 or more.

[0008] [3] According to a third aspect of the present invention, there is provided a polyester resin comprising, as a main component, a polyester containing a diol unit and a dicarboxylic acid unit, wherein the polyester resin comprises a cyclic oligomer containing the diol unit and the dicarboxylic acid unit, and wherein the ratio (C5 / CT) of the peak area of ​​a pentameric oligomer (C5) to the peak area of ​​a trimer oligomer (CT) in the cyclic oligomer measured by liquid chromatography is 0.086 or more.

[0009] [4] A fourth aspect of the present invention provides the polyester resin according to the third aspect, wherein the ratio (C6 / CT) of the peak area of ​​the hexamer oligomer (C6) to the peak area of ​​the trimer oligomer (CT) in the cyclic oligomer is 0.058 or more, as measured by liquid chromatography.

[0010] [5] A fifth aspect of the present invention provides the polyester resin according to the third or fourth aspect, wherein 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 is 0.031 or more, as measured by liquid chromatography.

[0011] [6] According to a sixth aspect of the present invention, there is provided a polyester resin containing, as a main component, a polyester containing a diol unit and a dicarboxylic acid unit, １ The peak area (A) derived from all dicarboxylic acids measured using H-NMR ａｃｉｄ ) and the peak area (A ７．５ ) ratio (A ７．５ / A ａｃｉｄ ) is 0.00020 or more.

[0012] [7] According to aspect 7 of the present invention, １The peak area (A) derived from all dicarboxylic acids measured using H-NMR ａｃｉｄ ) and the peak area (A ７．８ ) ratio (A ７．８ / A ａｃｉｄ ) is 0.00010 or more.

[0013] [8] According to an eighth aspect of the present invention, there is provided a molded article made from the polyester resin according to any one of the first to seventh aspects.

[0014] [9] According to a ninth aspect of the present invention, there is provided a preform made from the polyester resin according to any one of the first to seventh aspects.

[0015]

[10] According to a tenth aspect of the present invention, there is provided a polyester bottle made from the polyester resin according to any one of the first to seventh aspects.

[0016]

[11] According to an eleventh aspect of the present invention, there is provided the polyester resin according to any one of the first to seventh aspects, wherein the polyester resin is a mechanically recycled polyester resin.

[0017] According to the present invention, it is possible to provide a polyester resin that can suppress the occurrence of mold contamination during molding.

[0018] FIG. 1 is a flowchart showing an example of a method for producing a polyester resin according to an embodiment of the present invention. FIG. 2A is a graph showing the results of 1H-NMR spectrum measurement in Example 6. FIG. 2B is a graph showing the results of 1H-NMR spectrum measurement in Comparative Example 1. FIG. 2C is a graph showing the results of 1H-NMR spectrum measurement for a virgin isophthalic acid-copolymerized polyethylene terephthalate resin. FIG. 3(a) is a graph showing the results of measurement of the differential molecular weight distribution curve in Example 6, and FIG. 3(b) is an enlarged view of FIG. 3(a). FIG. 4(a) is a graph showing the results of measurement of the differential molecular weight distribution curve in Comparative Example 1, and FIG. 4(b) is an enlarged view of FIG. 4(a).

[0019] <<First Embodiment>> A polyester resin in a first embodiment contains, as a main component, a polyester containing a diol unit and a dicarboxylic acid unit, and is characterized in that the polyester resin has a shoulder correlation parameter S of 0.160 or less, which is obtained by GPC and derived using a differential molecular weight distribution curve represented by the following formula (1): In the above formula (1), M is the molecular weight of the polyester resin, f(Log M) represents the differential molecular weight distribution curve of the polyester resin, and g(Log M) represents a linear function connecting two data points in f(Log M) where Log M is 3.40 and 3.75.

[0020] Examples of polyesters contained in the polyester resin include aromatic polyesters, wholly aromatic polyesters, polycarbonates, and aliphatic polyesters, with aromatic polyesters being preferred. Aromatic polyesters contain diol units and dicarboxylic acid units. Examples of diol compounds for forming the 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. Examples of dicarboxylic acid compounds for forming the dicarboxylic acid units include aromatic dicarboxylic acids and derivatives thereof, such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, and furandicarboxylic acid, with terephthalic acid being preferred. 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. The polyesters mentioned above are not limited to those derived from petroleum raw materials, but may be polyesters derived from plant raw materials, or may be polyesters obtained by recycling these polyesters derived from petroleum raw materials or plant raw materials. The polyesters mentioned above may be used alone or in combination.

[0021] The content of ethylene terephthalate units in polyethylene terephthalate is preferably 70 mol % or more, more preferably 90 mol % or more, based on all monomer units.

[0022] Polyethylene terephthalate may contain, among all the monomer units, units consisting of dicarboxylic acids other than terephthalic acid that are copolymerizable with ethylene glycol and terephthalic acid. Examples of such dicarboxylic acids other than terephthalic acid include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, eicosanedioic 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-sodiumsulfoisophthalic acid, phenylendanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, 9,9'-bis(4-carboxyphenyl)fluorene acid, 2,5-furandicarboxylic acid, and ester derivatives thereof. Among these, isophthalic acid is preferred. The content of units consisting of dicarboxylic acids other than terephthalic acid is preferably 30 mol % or less, more preferably 10 mol % or less, based on the total monomer units.

[0023] Polyethylene terephthalate may contain, among all monomer units, units of a diol other than terephthalic acid that is copolymerizable with ethylene glycol and terephthalic acid. Examples of 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, norbornanedimethanol, norbornanediethanol, tricyclodecanedimethanol, tricyclodecanediethanol, tetracyclododecanedimethanol, tetracyclododecanediethanol, decalindimethanol, decalindiethanol, 5-methylol-5-ethyl-2-(1,1-dimethyl-2-hydroxyethyl) Examples of suitable diols include 2,2-bis(4-hydroxycyclohexyl)propane, 2,2-bis(4-(2-hydroxyethoxy)cyclohexyl)propane, cyclopentanediol, 3-methyl-1,2-cyclopentadiol, 4-cyclopentene-1,3-diol, adamantanediol, paraxylene glycol, bisphenol A, bisphenol S, styrene glycol, trimethylolpropane, pentaerythritol, diethylene glycol, triethylene glycol, and bis-β-hydroxyethyl terephthalate (BHET), with diethylene glycol being preferred. The content of units consisting of diols other than ethylene glycol is preferably 30 mol % or less, more preferably 10 mol % or less, based on the total monomer units.

[0024] Polyethylene terephthalate may contain other components such as additives, for example, one or more of various additives such as plasticizers, light stabilizers, antioxidants, ultraviolet absorbers, flame retardants, colorants, pigments, fillers, release agents, antistatic agents, fragrances, foaming agents, and antibacterial and antifungal agents may be blended.

[0025] The content of polyester contained in the polyester resin is preferably 99% by weight or more, and more preferably 99.5% by weight or more.

[0026] Although not particularly limited, the polyester resin in this embodiment may contain a cyclic oligomer containing a diol unit and a dicarboxylic acid unit. Such a cyclic oligomer is a by-product of the polymerization reaction of the diol compound and the dicarboxylic acid compound. The polyester resin in this embodiment contains a trimer oligomer (cyclic trimer; CT) and a pentamer oligomer (C5) as the cyclic oligomer. For example, the trimer oligomer (CT) contained in a polyester resin containing polyethylene terephthalate as the polyester is composed of three polyethylene terephthalate structural units.

[0027] 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.

[0028] In the polyester resin, the shoulder correlation parameter S, which is calculated using a differential molecular weight distribution curve obtained by GPC and is represented by the following formula (1), is 0.160 or less, preferably 0.145 or less. The lower limit of the shoulder correlation parameter S is not particularly limited, but is usually −0.200 or more. In the above formula (1), M is the molecular weight of the polyester resin, f(Log M) represents the differential molecular weight distribution curve of the polyester resin, and g(Log M) represents a linear function connecting two data points in f(Log M) where Log M is 3.40 and 3.75. The vertical axis of the differential molecular weight distribution curve is dw / dLog M, which is the concentration fraction w (%) differentiated by Log M. In the polyester resin of this embodiment, since the shoulder correlation parameter S is within the above range, the content of BHET can be reduced, and the occurrence of mold contamination during molding can be suppressed. In addition, since the shoulder correlation parameter S is within the above range, the polyester resin of this embodiment has excellent light-blocking properties, mouth crystallization suitability, and flavor.

[0029] In the polyester resin, the polydispersity Mw / Mn measured using GPC is preferably 2.470 or more, more preferably 2.490 or more. The upper limit of the polydispersity Mw / Mn is not particularly limited, but is usually 3.000 or less. By setting the polydispersity Mw / Mn within the above range, the occurrence of mold fouling during molding of the polyester resin can be suppressed. Furthermore, by setting the polydispersity Mw / Mn within the above range, the occurrence of mold fouling during molding can be further suppressed. Furthermore, by setting the polydispersity Mw / Mn within the above range, the polyester resin can be made to have better light-blocking properties, mouth crystallization suitability, and flavor properties.

[0030] Although not particularly limited, the polyester resin may contain a pentamer oligomer (C5) as a cyclic oligomer. In the polyester resin, the ratio (C5 / CT) of the peak area of ​​the pentamer oligomer (C5) to the peak area of ​​the trimer oligomer (CT) in the cyclic oligomer measured using liquid chromatography is preferably 0.086 or more, more preferably 0.088 or more. The upper limit of C5 / CT is not particularly limited, but is usually 0.300 or less. By setting the ratio (C5 / CT) of the peak area of ​​the pentamer oligomer (C5) to the peak area of ​​the trimer oligomer (CT) within the above range, the occurrence of mold fouling during molding of the polyester resin can be further suppressed. Furthermore, by setting the peak area ratio (C5 / CT) within the above range, the polyester resin can be made to have better light-shielding properties, mouth crystallization suitability, and flavor properties.

[0031] Although not particularly limited, the polyester resin may contain a hexamer oligomer (C6) as a cyclic oligomer. In the polyester resin, the ratio (C6 / CT) of the peak area of ​​the hexamer oligomer (C6) to the peak area of ​​the trimer oligomer (CT) in the cyclic oligomer measured using liquid chromatography is preferably 0.058 or more, more preferably 0.060 or more. The upper limit of C6 / CT is not particularly limited, but is usually 0.200 or less. By setting the peak area ratio (C6 / CT) within the above range, the occurrence of mold contamination during molding of the polyester resin can be further suppressed. Furthermore, by setting the peak area ratio (C6 / CT) within the above range, the polyester resin can be made to have better light-shielding properties, mouth crystallization suitability, and flavor properties.

[0032] 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 0.031 or more, more preferably 0.032 or more. The upper limit of C7 / CT is not particularly limited, but is usually 0.100 or less. By setting the peak area ratio (C7 / CT) within the above range, the occurrence of mold contamination during molding of the polyester resin can be further suppressed. Furthermore, by setting the peak area ratio (C7 / CT) within the above range, the polyester resin can be made to have better light-shielding properties, mouth crystallization suitability, and flavor properties.

[0033] In polyester resins, １ The peak area (A) derived from all dicarboxylic acids measured using H-NMR ａｃｉｄ ) and the peak area (A ７．５ ) ratio (A ７．５ / A ａｃｉｄ ) is preferably 0.00020 or more, more preferably 0.00040 or more. ７．５ / A ａｃｉｄThe upper limit of the peak area (A) is not particularly limited, but is usually 0.00300 or less. The peaks derived from dicarboxylic acids are present in the ranges of 7.60 to 7.75 ppm, 7.90 to 8.55 ppm, and 8.75 to 8.90 ppm. ａｃｉｄ The peak area (A) derived from all dicarboxylic acids refers to the sum of the peak areas present in all these ranges. ａｃｉｄ ) and the peak area (A ７．５ ) ratio (A ７．５ / A ａｃｉｄ By setting the ratio of peak areas (A) within the above range, it is possible to further suppress the occurrence of mold contamination during molding. ７．５ / A ａｃｉｄ By setting the above range, the polyester resin can be made more excellent in light-blocking properties, suitability for crystallization at the opening, and flavor properties.

[0034] In polyester resins, １ The peak area (A) derived from all dicarboxylic acids measured using H-NMR ａｃｉｄ ) and the peak area (A ７．８ ) ratio (A ７．８ / A ａｃｉｄ ) is preferably 0.00010 or more, more preferably 0.00020 or more. ７．８ / A ａｃｉｄ The upper limit of the peak area (A) derived from all dicarboxylic acids is not particularly limited, but is usually 0.00300 or less. ａｃｉｄ ) and the peak area (A ７．８ ) ratio (A ７．８ / A ａｃｉｄ By setting the peak area ratio (A) within the above range, it is possible to further suppress the occurrence of mold contamination during molding of the polyester resin. ７．８ / A ａｃｉｄ By setting the above range, the polyester resin can be made more excellent in light-blocking properties, suitability for crystallization at the opening, and flavor properties.

[0035] The acetaldehyde content of the polyester resin in this embodiment is preferably 10 ppm or less, more preferably 5 ppm or less, in the form of pellets after solid-state polymerization. Furthermore, it is preferable to reduce the increase in acetaldehyde when the polyester resin is molded into a molded product. By setting the acetaldehyde content within the above range and reducing the increase in acetaldehyde, the influence on the flavor of the contents of the molded product when the polyester resin is molded into a molded product can be reduced, resulting in an excellent flavor.

[0036] 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.

[0037] Chromaticity b of the polyester resin in this embodiment ＊ In the form of pellets after solid-state polymerization, the chromaticity b of the polyester resin is preferably 15.0 or more, and more preferably 27.0 or more. ＊ By setting the value of the thickness of the polyester resin within the above range, it is possible to provide a molded article made from the polyester resin with excellent light-shielding properties.

[0038] The cold crystallization peak top temperature Tc1 of the polyester resin in this embodiment is preferably 149° C. or lower. The upper limit of the cold crystallization peak top temperature Tc1 is not particularly limited, but is usually 120° C. or higher. By setting the cold crystallization peak top temperature Tc1 of the polyester resin within the above range, crystallization of the mouth portion can be easily carried out when the polyester resin is molded into a polyester bottle or the like.

[0039]

[0023] Fig. 1 is a flowchart showing an example of a method for producing a polyester resin according to the present embodiment. As shown in Fig. 1, the polyester resin according to the present embodiment can be produced by a thermal history control process including a first melt-extrusion process, a second melt-extrusion process, a crystallization process, and a solid-state polymerization process for the polyester containing the diol unit and the dicarboxylic acid unit.

[0040] First, in the first melt-extrusion step, the pelletized polyester obtained by polymerizing the diol compound and dicarboxylic acid is melt-extruded using an extruder after the moisture content is reduced to 50 ppm or less in a dehumidifying dryer set at 150°C. The discharged 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, more preferably 265 to 300°C. The screw rotation speed of the twin-screw extruder is preferably 50 to 800 rpm, more preferably 70 to 400 rpm. The output rate of the twin-screw extruder is preferably 5 to 30,000 kg / h, more preferably 10 to 10,000 kg / h.

[0041] Next, in the second melt-extrusion step, the pellets obtained in the first melt-extrusion step are melt-extruded again, and the discharged 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. The extruder used is preferably equipped with a vacuum vent system capable of reducing the pressure to atmospheric pressure or below. When using a twin-screw extruder equipped with a vacuum vent system in the second melt-extrusion step, the melt-extrusion conditions are preferably the same as those in the first melt-extrusion step, except that the vacuum is 100 Torr or less.

[0042] 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 gas flow, or a combination of these. The heating time is preferably 0.5 to 6 hours, more preferably 2 to 5 hours.

[0043] Next, in the solid-state polymerization step, the crystallized pellets are heated to solid-state polymerize the resin. The solid-state polymerization is preferably carried out under a pressure of 200 Torr, under a nitrogen gas flow, or a combination of these. The temperature for the solid-state polymerization 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.

[0044] As described above, the polyester resin of this embodiment can be obtained by subjecting the polyester to the thermal history control treatment, which includes the first melt-extrusion step, the second melt-extrusion step, the crystallization step, and the solid-state polymerization step, once or multiple times. The number of thermal history control treatments is preferably 4 to 10 times, with so-called virgin polyester that has never been recycled being used as the reference (0 times).

[0045] The method for producing the polyester resin in this embodiment is not particularly limited to the above. For example, the polyester resin in this embodiment (mechanically recycled polyester resin) may be obtained by controlling the thermal history through mechanical recycling of polyester used as a polyester bottle or the like. The polyester used for mechanical recycling may be, for example, a polyester bottle produced from virgin polyester or a polyester bottle produced by one or more mechanical recycling processes.

[0046] The polyester resin of this embodiment can be suitably used for processing into molded articles such as preforms and polyester bottles. Preforms can be produced by injection molding the polyester resin. Polyester bottles can be produced by stretch-blowing such preforms.

[0047] As described above, since the polyester resin in this embodiment is a product prior to being processed into a molded body, the ratios of the peak area of ​​pentamer, hexamer, and heptamer oligomers to the peak area of ​​trimer oligomer (CT) measured by liquid chromatography (C5 / CT, C6 / CT, C7 / CT), the ratios of the peak areas at 7.43 to 7.55 ppm and 7.75 to 7.85 ppm to the peak area derived from all dicarboxylic acids measured using H-NMR, the shoulder correlation parameter S, and the polydispersity index Mw / Mn (hereinafter, collectively referred to as "thermal history parameters") cannot be determined in the molded body state. In the flowchart shown in FIG. 1, the molded body corresponds to the state between the first melt extrusion step and the second melt extrusion step. Therefore, to compare the polyester resin constituting the molded body with the polyester resin in this embodiment, it is necessary to subject the molded body to a second melt extrusion treatment, a crystallization treatment, and a solid-state polymerization treatment, and then evaluate the resulting pellets to determine whether the thermal history parameters are within a specific range.

[0048] In addition, when the molded body is subjected to the second melt extrusion treatment, crystallization treatment, and solid-state polymerization treatment, an additional thermal history equivalent to one thermal history control treatment is added to the polyester resin before molding. Therefore, when the thermal history parameters evaluated after the second melt extrusion treatment, crystallization treatment, and solid-state polymerization treatment for a certain molded body are values ​​close to the upper and lower limits of the specific range specified in this embodiment, it is preferable to evaluate the thermal history parameters of the polyester resin before molding by the following procedure in order to confirm whether they were within the specific range.

[0049] First, the thermal history parameters of the pellets obtained by subjecting the molded body to a second melt extrusion process, a crystallization process, and a solid-state polymerization process are recorded as thermal history parameters for one adjustment. Next, the pellets are subjected to a thermal history control process, and the thermal history parameters of the resulting pellets are recorded as thermal history parameters for two adjustments. Thereafter, the pellets are subjected to a thermal history control process multiple times as necessary, and thermal history parameters for three or more adjustments are recorded. In this way, by removing and interpolating the correlation between the adjustment count and the thermal history parameters, the thermal history parameters corresponding to zero adjustments are obtained. By evaluating the thermal history parameters corresponding to zero adjustments, it is possible to confirm whether the thermal history parameters of the polyester resin before molding were within a specific range.

[0050] <<Second Embodiment>> A polyester resin according to a second embodiment includes, as a main component, a polyester containing a diol unit and a dicarboxylic acid unit, and has a cyclic oligomer in which the ratio (C5 / CT) of the peak area of ​​a pentamer oligomer (C5) to the peak area of ​​a trimer oligomer (CT) measured by liquid chromatography is 0.086 or more.

[0051] The polyester contained in the polyester resin can be the same as that in the first embodiment. The content of the polyester in the polyester resin is preferably 99% by weight or more, and more preferably 99.5% by weight or more.

[0052] The polyester resin in this embodiment contains a cyclic oligomer containing a diol unit and a dicarboxylic acid unit, and the cyclic oligomer in this embodiment contains a trimer oligomer (CT) and a pentamer oligomer (C5).

[0053] 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.

[0054] In the polyester resin of this embodiment, the ratio (C5 / CT) of the peak area of ​​the pentamer oligomer (C5) to the peak area of ​​the trimer oligomer (CT) in the cyclic oligomer measured using liquid chromatography is 0.086 or more, preferably 0.088 or more. The upper limit of C5 / CT is not particularly limited, but is usually 0.300 or less. In the polyester resin of this embodiment, the ratio (C5 / CT) of the peak area of ​​the pentamer oligomer (C5) to the peak area of ​​the trimer oligomer (CT) is within the above range, thereby reducing the content of BHET and suppressing the occurrence of mold fouling during molding. Furthermore, in the polyester resin of this embodiment, the peak area ratio (C5 / CT) is within the above range, resulting in excellent light-blocking properties, mouth crystallization suitability, and flavor.

[0055] Although not particularly limited, the polyester resin may contain a hexamer oligomer (C6) as a cyclic oligomer. In the polyester resin, the ratio (C6 / CT) of the peak area of ​​the hexamer oligomer (C6) to the peak area of ​​the trimer oligomer (CT) in the cyclic oligomer measured using liquid chromatography is preferably 0.058 or more, more preferably 0.060 or more. The upper limit of C6 / CT is not particularly limited, but is usually 0.200 or less. By setting the peak area ratio (C6 / CT) within the above range, the occurrence of mold contamination during molding of the polyester resin can be further suppressed. Furthermore, by setting the peak area ratio (C6 / CT) within the above range, the polyester resin can be made to have better light-shielding properties, mouth crystallization suitability, and flavor properties.

[0056] 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 0.031 or more, more preferably 0.032 or more. The upper limit of C7 / CT is not particularly limited, but is usually 0.100 or less. By setting the peak area ratio (C7 / CT) within the above range, the occurrence of mold contamination during molding of the polyester resin can be further suppressed. Furthermore, by setting the peak area ratio (C7 / CT) within the above range, the polyester resin can be made to have better light-shielding properties, mouth crystallization suitability, and flavor properties.

[0057] In polyester resins, １ The peak area (A) derived from all dicarboxylic acids measured using H-NMR ａｃｉｄ ) and the peak area (A ７．５ ) ratio (A ７．５ / A ａｃｉｄ ) is preferably 0.00020 or more, more preferably 0.00040 or more. ７．５ / A ａｃｉｄ The upper limit of the peak area (A) derived from all dicarboxylic acids is not particularly limited, but is usually 0.00300 or less. ａｃｉｄ ) and the peak area (A ７．５ ) ratio (A ７．５ / A ａｃｉｄ By setting the peak area ratio (A) within the above range, it is possible to further suppress the occurrence of mold contamination during molding of the polyester resin. ７．５ / A ａｃｉｄ By setting the above range, the polyester resin can be made more excellent in light-blocking properties, suitability for crystallization at the opening, and flavor properties.

[0058] In polyester resins, １ The peak area (A) derived from all dicarboxylic acids measured using H-NMR ａｃｉｄ) and the peak area (A ７．８ ) ratio (A ７．８ / A ａｃｉｄ ) is preferably 0.00010 or more, more preferably 0.00020 or more. ７．８ / A ａｃｉｄ The upper limit of the peak area (A) derived from all dicarboxylic acids is not particularly limited, but is usually 0.00300 or less. ａｃｉｄ ) and the peak area (A ７．８ ) ratio (A ７．８ / A ａｃｉｄ By setting the peak area ratio (A) within the above range, it is possible to further suppress the occurrence of mold contamination during molding of the polyester resin. ７．８ / A ａｃｉｄ By setting the above range, the polyester resin can be made more excellent in light-blocking properties, suitability for crystallization at the opening, and flavor properties.

[0059] In the polyester resin, the shoulder correlation parameter S, which is derived using a differential molecular weight distribution curve obtained by GPC and is represented by the above formula (1), is preferably 0.160 or less, more preferably 0.145 or less. The lower limit of the shoulder correlation parameter S is not particularly limited, but is usually -0.200 or more. By setting the shoulder correlation parameter S within the above range, it is possible to suppress the occurrence of mold contamination during molding of the polyester resin. Furthermore, by setting the shoulder correlation parameter S within the above range, it is possible to make the polyester resin more excellent in light blocking properties, mouth crystallization suitability, and flavor properties.

[0060] In the polyester resin, the polydispersity Mw / Mn measured using GPC is preferably 2.470 or more, more preferably 2.490 or more. The upper limit of the polydispersity Mw / Mn is not particularly limited, but is usually 3.000 or less. By setting the polydispersity Mw / Mn within the above range, the occurrence of mold contamination during molding of the polyester resin can be suppressed. Furthermore, by setting the polydispersity Mw / Mn within the above range, the polyester resin can be made to have better light-blocking properties, mouth crystallization suitability, and flavor properties.

[0061] Acetaldehyde content, intrinsic viscosity (IV), and color b of the polyester resin in this embodiment ＊ and the cold crystallization peak top temperature Tc1 may be the same as in the first embodiment.

[0062] The polyester resin of this embodiment can be produced by the same method as in the first embodiment. That is, as shown in Figure 1, the polyester resin of this embodiment can be produced by a method in which a polyester containing the above-mentioned diol units and dicarboxylic acid units is subjected to a thermal history control treatment including a first melt extrusion step, a second melt extrusion step, a crystallization step, and a solid-state polymerization step. Alternatively, the polyester resin may be produced by mechanically recycling polyester used as a polyester bottle or the like.

[0063] The polyester resin of this embodiment can be suitably used for processing into molded articles such as preforms and polyester bottles. Preforms can be produced by injection molding the polyester resin. Polyester bottles can be produced by stretch-blowing such preforms.

[0064] As described above, the polyester resin in this embodiment is one before it is processed into a molded body, so the thermal history parameters cannot be determined in the molded body state. The molded body corresponds to the state between the first melt extrusion process and the second melt extrusion process in the flowchart shown in FIG. 1 . Therefore, to compare the polyester resin constituting the molded body with the polyester resin in this embodiment, it is necessary to subject the molded body to the second melt extrusion process, crystallization process, and solid-state polymerization process, and evaluate the resulting pellets to determine whether the thermal history parameters are within a specific range. Whether the thermal history parameters of the polyester resin before molding are within a specific range can be determined using the same method as in the first embodiment.

[0065] <<Third Embodiment>> A polyester resin according to a third embodiment includes, as a main component, a polyester containing a diol unit and a dicarboxylic acid unit, １ The peak area (A) derived from all dicarboxylic acids measured using H-NMR ａｃｉｄ ) and the peak area (A ７．５ ) ratio (A ７．５ / A ａｃｉｄ ) is 0.00020 or more.

[0066] The polyester contained in the polyester resin can be the same as that in the first and second embodiments. The content of the polyester in the polyester resin is preferably 99% by weight or more, and more preferably 99.5% by weight or more.

[0067] Although not particularly limited, the polyester resin in this embodiment may contain a cyclic oligomer containing a diol unit and a dicarboxylic acid unit. The content of the cyclic oligomer in the polyester resin is preferably 1% by weight or less, and more preferably 0.5% by weight or less.

[0068] In polyester resins, １ The peak area (A) derived from all dicarboxylic acids measured using H-NMR ａｃｉｄ ) and the peak area (A７．５ ) ratio (A ７．５ / A ａｃｉｄ ) is 0.00020 or more, preferably 0.00040 or more. ７．５ / A ａｃｉｄ The upper limit of the peak area (A ａｃｉｄ ) and the peak area (A ７．５ ) ratio (A ７．５ / A ａｃｉｄ When the ratio of peak areas (A ) is within the above range, the content of BHET is reduced, and the occurrence of mold contamination during molding can be suppressed. ７．５ / A ａｃｉｄ ) is within the above range, the product has excellent light-shielding properties, suitability for crystallization at the mouth, and flavor.

[0069] In polyester resins, １ The peak area (A) derived from all dicarboxylic acids measured using H-NMR ａｃｉｄ ) and the peak area (A ７．８ ) ratio (A ７．８ / A ａｃｉｄ ) is preferably 0.00010 or more, more preferably 0.00020 or more. ７．８ / A ａｃｉｄ The upper limit of the peak area (A) derived from all dicarboxylic acids is not particularly limited, but is usually 0.00300 or less. ａｃｉｄ ) and the peak area (A ７．８ ) ratio (A ７．８ / A ａｃｉｄ By setting the peak area ratio (A) within the above range, it is possible to further suppress the occurrence of mold contamination during molding of the polyester resin. ７．８ / A ａｃｉｄ By setting the above range, the polyester resin can be made more excellent in light-blocking properties, suitability for crystallization at the opening, and flavor properties.

[0070] Although not particularly limited, the polyester resin may contain a pentamer oligomer (C5) as a cyclic oligomer. In the polyester resin, the ratio (C5 / CT) of the peak area of ​​the pentamer oligomer (C5) to the peak area of ​​the trimer oligomer (CT) in the cyclic oligomer measured using liquid chromatography is preferably 0.086 or more, more preferably 0.088 or more. The upper limit of C5 / CT is not particularly limited, but is usually 0.300 or less. By setting the ratio (C5 / CT) of the peak area of ​​the pentamer oligomer (C5) to the peak area of ​​the trimer oligomer (CT) within the above range, the occurrence of mold fouling during molding of the polyester resin can be further suppressed. Furthermore, by setting the peak area ratio (C5 / CT) within the above range, the polyester resin can be made to have better light-shielding properties, mouth crystallization suitability, and flavor properties.

[0071] Although not particularly limited, the polyester resin may contain a hexamer oligomer (C6) as a cyclic oligomer. In the polyester resin, the ratio (C6 / CT) of the peak area of ​​the hexamer oligomer (C6) to the peak area of ​​the trimer oligomer (CT) in the cyclic oligomer measured using liquid chromatography is preferably 0.058 or more, more preferably 0.060 or more. The upper limit of C6 / CT is not particularly limited, but is usually 0.200 or less. By setting the peak area ratio (C6 / CT) within the above range, the occurrence of mold contamination during molding of the polyester resin can be further suppressed. Furthermore, by setting the peak area ratio (C6 / CT) within the above range, the polyester resin can be made to have better light-shielding properties, mouth crystallization suitability, and flavor properties.

[0072] 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 0.031 or more, more preferably 0.032 or more. The upper limit of C7 / CT is not particularly limited, but is usually 0.100 or less. By setting the peak area ratio (C7 / CT) within the above range, the occurrence of mold contamination during molding of the polyester resin can be further suppressed. Furthermore, by setting the peak area ratio (C7 / CT) within the above range, the polyester resin can be made to have better light-shielding properties, mouth crystallization suitability, and flavor properties.

[0073] In the polyester resin, the shoulder correlation parameter S, which is derived using a differential molecular weight distribution curve obtained by GPC and is represented by the above formula (1), is preferably 0.160 or less, more preferably 0.145 or less. The lower limit of the shoulder correlation parameter S is not particularly limited, but is usually -0.200 or more. By setting the shoulder correlation parameter S within the above range, it is possible to suppress the occurrence of mold contamination during molding of the polyester resin. Furthermore, by setting the shoulder correlation parameter S within the above range, it is possible to make the polyester resin more excellent in light blocking properties, mouth crystallization suitability, and flavor properties.

[0074] In the polyester resin, the polydispersity Mw / Mn measured using GPC is preferably 2.470 or more, more preferably 2.490 or more. The upper limit of the polydispersity Mw / Mn is not particularly limited, but is usually 3.000 or less. By setting the polydispersity Mw / Mn within the above range, the occurrence of mold contamination during molding of the polyester resin can be suppressed. Furthermore, by setting the polydispersity Mw / Mn within the above range, the polyester resin can be made to have better light-blocking properties, mouth crystallization suitability, and flavor properties.

[0075] Acetaldehyde content, intrinsic viscosity (IV), and color b of the polyester resin in this embodiment ＊ and the cold crystallization peak top temperature Tc1 may be the same as in the first embodiment.

[0076] The polyester resin of this embodiment can be produced by the same method as in the first and second embodiments. That is, as shown in Figure 1, the polyester resin of this embodiment can be produced by a method in which a polyester containing the above-mentioned diol units and dicarboxylic acid units is subjected to a thermal history control treatment including a first melt extrusion step, a second melt extrusion step, a crystallization step, and a solid-state polymerization step. Alternatively, the polyester resin may be produced by mechanically recycling polyester used as a polyester bottle or the like.

[0077] The polyester resin of this embodiment can be suitably used for processing into molded articles such as preforms and polyester bottles. Preforms can be produced by injection molding the polyester resin. Polyester bottles can be produced by stretch-blowing such preforms.

[0078] As described above, the polyester resin in this embodiment is one before it is processed into a molded body, so the thermal history parameters cannot be determined in the molded body state. The molded body corresponds to the state between the first melt extrusion process and the second melt extrusion process in the flowchart shown in FIG. 1 . Therefore, to compare the polyester resin constituting the molded body with the polyester resin in this embodiment, it is necessary to subject the molded body to the second melt extrusion process, crystallization process, and solid-state polymerization process, and evaluate the resulting pellets to determine whether the thermal history parameters are within a specific range. Whether the thermal history parameters of the polyester resin before molding are within a specific range can be determined using the same method as in the first and second embodiments.

[0079] Next, the present invention will be specifically explained by way of examples, but the present invention is not limited to these examples.

[0080] Example 1 Preparation of PET Resin Pellets and Preforms 30 kg of pellets of isophthalic acid copolymerized polyethylene terephthalate resin (manufactured by Shinko Synthetic Fibers Co., Ltd., isophthalic acid copolymerization ratio 1.8 mol%, IV = 0.83) were prepared and dried using a hopper dryer at 150 °C for 5 hours. The pellets were then loaded into a twin-screw extruder (manufactured by Toshiba Machine Co., Ltd., TEM26SS) and melt-extruded 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 extruded in strand form from the extruder was air-cooled while being conveyed on a belt conveyor and pelletized using a pelletizer (first melt-extrusion process). The pellets were then loaded back into the twin-screw extruder and melt-extruded 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 process).

[0081] 15 kg of the obtained pellets were heated for 5 hours at 1 Torr and 150 ° C using an agitator vacuum dryer (Dalton, 45MV) to undergo crystallization. Next, using the above-mentioned agitator vacuum dryer, the pellets after crystallization were heated for 13 hours at 1 Torr and 225 ° C to undergo solid-state polymerization. In the crystallization and solid-state polymerization treatments, the rotation speed of the agitator blade of the agitator vacuum dryer was 20 rpm. The obtained pellets were subjected to the first and second melt extrusion treatments, crystallization treatment, and solid-state polymerization treatment three more times in the same manner as above to obtain PET resin pellets. That is, the thermal history control treatment was performed a total of four times on the virgin pellets. In addition, a portion of the obtained PET resin pellets was fed into an injection molding machine, and the barrel temperature and hot runner temperature were set to 300 ° C, the mold temperature to 15 ° C, and the molding cycle was set to 32 seconds. A 500 mL bottle preform weighing 25 g was produced. The PET resin pellets and bottle preforms were evaluated according to the following procedures. The results are shown in Table 2.

[0082] [Cyclic Oligomer Content and BHET 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 (1 / 1 by weight) was added to completely dissolve the pellets. 4 mL of chloroform was added to the solution, and then 5 mL of acetonitrile was gradually added. The solution was left for 3 hours to precipitate the PET polymer. 1 mL of the supernatant of this suspension was removed and filtered through a membrane filter with a pore size of 0.20 μm, and the filtrate was measured by high-performance liquid chromatography. A BHET standard solution was also measured at the same time, and the BHET content in the pellets and bottle preforms was calculated based on the obtained calibration curve. An Agilent Technologies 1200 series analyzer was used as the measuring device. 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. An Agilent Technologies ZORBAX Eclipse Plus C18 (Rapid Resolution HD 2.1 x 150 mm 1.8 Micron) was used as the column, with the column temperature set to 40 ° C. The mobile phase consisted of a 0.05 wt% aqueous phosphoric acid solution as Solution I and acetonitrile as Solution II, with a flow rate of 0.6 mL / min and gradient conditions as shown in Table 1 below. The injection volume was 2 μL. For the cyclic oligomers in the pellets, the peak areas of the trimer and pentamer to heptamer (CT, C5, C6, C7) were determined, and C5 / CT, C6 / CT, and C7 / CT were calculated. The BHET content in the bottle preforms is shown as a normalized value, with the BHET content in a preform made from virgin pellets set at 1.

[0083]

[0084] [NMR History Correlation Peak] 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 apparatus (JEOL, 400SS). The peak area (Aａｃｉｄ ) and the area of ​​NMR hysteresis correlation peak 1 (A ７．５ ) and the area of ​​NMR hysteresis correlation peak 2 (A ７．８ ) respectively, and A ７．５ / A ａｃｉｄ and A ７．８ / A ａｃｉｄ was calculated. Here, the peaks derived from all dicarboxylic acids refer to the sum of the peak areas in the ranges of 7.60 to 7.75 ppm, 7.90 to 8.55 ppm, and 8.75 to 8.90 ppm, NMR history correlation peak 1 refers to the peak area in the range of 7.43 to 7.55 ppm, and NMR history correlation peak 2 refers to the peak area in the range of 7.75 to 7.85 ppm. FIG. 2A is a graph showing the results of measurement of the 1H-NMR spectrum in Example 6, and FIG. 2B is a graph showing the results of measurement of the 1H-NMR spectrum in Comparative Example 1. Furthermore, for reference, the 1H-NMR spectrum was similarly measured for virgin isophthalic acid-copolymerized polyethylene terephthalate resin that had not been subjected to thermal history control treatment. FIG. 2C is a graph showing the results of measurement of the 1H-NMR spectrum for virgin isophthalic acid-copolymerized polyethylene terephthalate resin.

[0085] [Polydispersity (Mw / Mn) and Shoulder Correlation Parameter S] The differential molecular weight distribution curve was measured using a high-speed GPC apparatus (Tosoh Corporation, HLC-8320GPC) to determine the polydispersity (Mw / Mn). A solution prepared by dissolving PET resin pellets in a mixed solution of 1,1,1,3,3,3-hexafluoro-2-propanol and chloroform (volume ratio 1 / 49) was used as the sample. Chloroform was used as the mobile phase, and a TSKgel SuperMultipore HZ-M column manufactured by Tosoh Corporation was used as the column. The measurement temperature was 40°C. Standard polystyrene (Tosoh Corporation, PStQuickMP-M) was used as the molecular weight standard. Furthermore, the shoulder correlation parameter S, expressed by the above formula (1), was determined from the differential molecular weight distribution curve. The vertical axis of the differential molecular weight distribution curve was dw / dLogM, which was obtained by differentiating the concentration fraction w (%) with LogM. Fig. 3(a) is a graph showing the measurement results of the differential molecular weight distribution curve in Example 6, and Fig. 3(b) is an enlarged view of Fig. 3(a). Fig. 4(a) is a graph showing the measurement results of the differential molecular weight distribution curve in Comparative Example 1, and Fig. 4(b) is an enlarged view of Fig. 4(a).

[0086] [b ＊ Value] b of PET resin pellets and preforms ＊ The value was measured using an SM color computer (manufactured by Suga Test Instruments Co., Ltd.). ＊ The larger the value, the better the light-blocking property.

[0087] [Cold Crystallization Peak Top Temperature Tc1] Using 5 mg of PET resin pellets as a sample, the cold crystallization peak top temperature Tc1 was measured using a differential scanning calorimeter (PerkinElmer, Diamond DSC). A lower cold crystallization peak top temperature indicates better suitability for neck crystallization when the PET resin pellets are molded into a molded article. The measurement conditions were as follows: Step 1: Hold at 20°C for 5 minutes; Step 2: Heat from 20°C to 290°C at 10°C / min; Step 3: Hold at 290°C for 5 minutes; Step 4: Cool from 290°C to 20°C at 300°C / min; Step 5: Hold at 20°C for 10 minutes; Step 6: Heat from 20°C to 290°C at 10°C / min; Tc1 was calculated from the peak top temperature (°C) of the cold crystallization peak in Step 6.

[0088] [Measurement of Acetaldehyde (AA)] 1.0 g of PET resin pellets and preforms crushed using a freeze-pulverizer were weighed into a glass bottle, and 5.0 mL of pure water was added and sealed. This suspension was heated for 60 minutes in an oven controlled at 120°C and then cooled in ice water. 1.0 mL of the supernatant of the suspension was sampled, and 0.2 mL of a 0.1% 2,4-dinitrophenylhydrazine / phosphate solution was added thereto and allowed to stand for 30 minutes. After standing, the supernatant was filtered through a membrane filter with a pore size of 0.20 μm, and the filtrate was measured by high-performance liquid chromatography. A standard solution of acetaldehyde was also measured at the same time, and the acetaldehyde content in the PET resin pellets and preforms was calculated based on the obtained calibration curve. The change in acetaldehyde content (ΔAA) before and after injection molding was determined by subtracting the acetaldehyde content in the PET resin pellets from the acetaldehyde content in the preforms. The smaller the change in acetaldehyde content, the smaller the increase in acetaldehyde when the PET resin pellets are molded into a molded product, which reduces the effect on the flavor of the contents of the molded product and indicates excellent flavor properties.

[0089] Examples 2 to 7 PET resin pellets and preforms were obtained in the same manner as in Example 1, except that the number of times the pellets were subjected to the thermal history control treatment was changed to a total of 5 to 10 times, and evaluations were similarly carried out.

[0090] Comparative Examples 1 to 3 PET resin pellets were obtained and evaluated in the same manner as in Example 1, except that the pellets were subjected to the thermal history control treatment a total of 1 to 3 times. For Comparative Example 1, a preform was further produced using the PET resin pellets, and evaluated in the same manner as in Example 1.

[0091] Comparative Example 4 Pellets of isophthalic acid copolymerized polyethylene terephthalate resin that had never been subjected to thermal history control treatment were evaluated in the same manner as in Example 1. In addition, a preform was obtained using pellets that had not been subjected to thermal history control treatment, and was evaluated in the same manner as in Example 1.

[0092]

[0093] As shown in Table 2, the PET resin pellets of Examples 1 to 7, which have a shoulder correlation parameter S of 0.160 or less, and the preforms molded using the pellets, have a low BHET content and can suppress the occurrence of mold contamination during molding. ＊ The large value indicated excellent light-shielding properties, the low Tc1 indicated excellent suitability for neck crystallization, and the small ΔAA indicated excellent flavor. On the other hand, the PET resin pellets of Comparative Examples 1 to 4, in which the shoulder correlation parameter S exceeded 0.160, and the preforms molded therefrom were inferior in all respects of mold contamination, light-shielding properties, neck crystallization suitability, and flavor.

[0094] Furthermore, the PET resin pellets of Examples 1 to 7, in which the ratio (C5 / CT) of the peak area of ​​the pentamer oligomer (C5) to the peak area of ​​the trimer oligomer (CT) in the cyclic oligomer measured by liquid chromatography was 0.086 or more, and the preforms molded using these had a low BHET content and were able to suppress the occurrence of mold fouling during molding. On the other hand, the PET resin pellets of Comparative Examples 1 to 4, in which the C5 / CT was less than 0.086, and the preforms molded using these were inferior in all respects of the occurrence of mold fouling, light-shielding properties, suitability for crystallization at the mouth, and flavor properties.

[0095] Also, １ The peak area (A) derived from all dicarboxylic acids measured using H-NMR ａｃｉｄ ) and the peak area (A ７．５ ) ratio (A ７．５ / A ａｃｉｄ The PET resin pellets of Examples 1 to 7, in which the BHET content was 0.00020 or more, and the preforms molded using the pellets, had a low BHET content and were able to suppress the occurrence of mold contamination during molding. ７．５ / A ａｃｉｄ The PET resin pellets of Comparative Examples 1 to 4, which had a value of less than 0.00020, and the preforms molded using the pellets were inferior in terms of mold contamination, light blocking properties, mouth crystallization suitability, and flavor properties.

Claims

1. A polyester resin comprising as a main component a polyester containing diol units and dicarboxylic acid units, characterized in that the shoulder correlation parameter S, calculated using a differential molecular weight distribution curve obtained by GPC and represented by the following formula (1), is 0.160 or less. (In the above formula (1), M is the molecular weight of the polyester resin, f(Log M) represents the differential molecular weight distribution curve of the polyester resin, and g(Log M) represents a linear function connecting two data points in f(Log M) where Log M is 3.40 and 3.75.) 2. The polyester resin according to claim 1, characterized in that the polydispersity Mw / Mn measured by GPC is 2.470 or more.

3. A polyester resin comprising, as a main component, a polyester containing diol units and dicarboxylic acid units, wherein the polyester resin contains a cyclic oligomer containing the diol units and the dicarboxylic acid units, and wherein the ratio (C5 / CT) of the peak area of ​​a pentamer oligomer (C5) to the peak area of ​​a trimer oligomer (CT) in the cyclic oligomer measured using liquid chromatography is 0.086 or more.

4. A polyester resin as described in claim 3, characterized in that the ratio (C6 / CT) of the peak area of ​​the hexamer oligomer (C6) to the peak area of ​​the trimer oligomer (CT) in the cyclic oligomer measured using liquid chromatography is 0.058 or more.

5. A polyester resin as described in claim 3 or 4, characterized in that 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 0.031 or more.

6. A polyester resin containing, as a main component, a polyester containing a diol unit and a dicarboxylic acid unit, １ The peak area (A) derived from all dicarboxylic acids measured using H-NMR ａｃｉｄ ) and the peak area (A ７．５ ) ratio (A ７．５ / A ａｃｉｄ ) is 0.00020 or more.

7. １ The peak area (A) derived from all dicarboxylic acids measured using H-NMR ａｃｉｄ ) for the peak area at 7.75 to 7.86 ppm (A ７．８ ) ratio (A ７．８ / A ａｃｉｄ 7. The polyester resin according to claim 6, wherein the σ is 0.00010 or more.

8. A molded article made from the polyester resin according to any one of claims 1 to 7.

9. A preform made from the polyester resin according to any one of claims 1 to 7.

10. A polyester bottle made from the polyester resin according to any one of claims 1 to 7.

11. The polyester resin according to any one of claims 1 to 7, characterized in that the polyester resin is a mechanically recycled polyester resin.

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