Polyester resin, molding, preform, polyester bottle, and mechanically recycled polyester resin

Abstract

To provide a polyester resin capable of suppressing occurrence of staining of a mold during molding.SOLUTION: A polyester resin contains polyester containing a diol unit and a dicarboxylic acid unit as a main component, wherein the polyester resin contains cyclic oligomer containing the diol unit and the dicarboxylic acid unit, and a ratio (C5 / CT) of a peak area of a pentamer oligomer (C5) to a peak area of a trimer oligomer (CT) in the cyclic oligomer measured using liquid chromatography is 0.086 or more.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Polyester resin is a thermoplastic resin having excellent properties such as mechanical stability, chemical stability, transparency, and heat resistance. From the viewpoint of reducing environmental impact, a method of recycling such a polyester resin by solid-phase polymerization and mechanically recycling it is known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

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

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the polyester resin produced by the above technology, BHET remaining as a monomer adheres as dirt to the mold of the manufacturing apparatus during the molding of the polyester resin, and the cost of molding increases in order to remove the dirt.

[0005]

Means for Solving the Problems

[0006] [1] According to Aspect 1 of the present invention, there is provided a polyester resin mainly containing 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 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.

[0007] [2] According to Aspect 2 of the present invention, there is provided the polyester resin according to Aspect 1, 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 measured using liquid chromatography is 0.058 or more.

[0008] [3] According to Aspect 3 of the present invention, there is provided the polyester resin according to Aspect 1, 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 measured using liquid chromatography is 0.031 or more.

[0009] [4] According to Aspect 4 of the present invention, there is provided a molded article made of the polyester resin according to any one of Aspects 1 to 3.

[0010] [5] According to Aspect 5 of the present invention, there is provided a preform made of the polyester resin according to any one of Aspects 1 to 3.

[0011] [6] According to Aspect 6 of the present invention, there is provided a polyester bottle made of the polyester resin according to any one of Aspects 1 to 3.

[0012] [7] According to Aspect 7 of the present invention, there is provided the polyester resin according to any one of Aspects 1 to 3, wherein the polyester resin is a mechanically recycled polyester resin. [Effect of the Invention]

[0013] According to the present invention, it is possible to provide a polyester resin capable of suppressing the generation of mold fouling during molding. [Brief Description of the Drawings]

[0014]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 3

Figure 4

[0015] The polyester resin in the present embodiment mainly contains a polyester containing a diol unit and a dicarboxylic acid unit, and 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.

[0016] The polyesters contained in the polyester resin include aromatic polyesters, wholly aromatic polyesters, polycarbonates, and aliphatic polyesters. Among these, aromatic polyesters are preferred. 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, ethylene oxide adduct of bisphenol A, etc. Among these, ethylene glycol is preferred. Examples of dicarboxylic acid compounds for forming dicarboxylic acid units include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, furandicarboxylic acid, and their derivatives. Among these, terephthalic acid is preferred. Specific examples of polyesters include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene furanoate, etc. Among them, polyethylene terephthalate, which is a copolymer of ethylene glycol and terephthalic acid, is preferred. The above - mentioned polyesters are not limited to those derived from petroleum raw materials, and may be polyesters derived from plant raw materials, or further, polyesters recycled from these polyesters derived from petroleum raw materials or plant raw materials. Also, the above - mentioned polyesters may be used alone or in combination.

[0017] 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.

[0018] Polyethylene terephthalate may contain units consisting of dicarboxylic acids other than terephthalic acid copolymerizable with ethylene glycol and terephthalic acid in all monomer units. Examples of such dicarboxylic acids other than terephthalic acid include, for example, 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, adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, decalin dicarboxylic 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'-diphenylether dicarboxylic acid, 5-sodium sulfoisophthalic acid, phenylendadicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, 9,9'-bis(4-carboxyphenyl)fluorene acid, 2,5-furandicarboxylic acid and their ester derivatives, etc. Among them, 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 all monomer units.

[0019] Polyethylene terephthalate may contain units consisting of diols other than terephthalic acid copolymerizable with ethylene glycol and terephthalic acid in all monomer units. 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, cyclohexanedietanol, decahydronaphthalenedimethanol, decahydronaphthalenedietanol, norbornanedimethanol, norbornanedietanol, tricyclodecanedimethanol, tricyclodecanedietanol, tetracyclododecanedimethanol, tetracyclododecanedietanol, decalindimethanol, decalindietanol, 5-methylol-5-ethyl-2-(1,1-dimethyl-2-hydroxyethyl)-1,3-dioxane, cyclohexanediol, bicyclohexyl-4,4'-diol, 2,2-bis(4-hydroxycyclohexyl)propane, 2,2-bis(4-(2-hydroxyethoxy)cyclohexyl)propane, cyclopentanediol, 3-methyl-1,2-cyclopentadiene diol, 4-cyclopentene-1,3-diol, adamantadiol, paraxylene glycol, bisphenol A, bisphenol S, styrene glycol, trimethylolpropane, pentaerythritol, diethylene glycol, triethylene glycol, and bis-β-hydroxyethyl terephthalate (BHET), etc. Among them, diethylene glycol is 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 all monomer units.

[0020] 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, mold release agents, antistatic agents, fragrances, foaming agents, antibacterial and antifungal agents may be blended.

[0021] The polyester resin in this embodiment contains a cyclic oligomer containing a diol unit and a dicarboxylic acid unit. Such a cyclic oligomer is a by-product in the polymerization reaction of the above diol compound and dicarboxylic acid compound. The polyester resin in this embodiment contains, as cyclic oligomers, a trimer oligomer (cyclic trimer; CT) and a pentamer oligomer (C5). For example, the trimer oligomer (CT) contained in a polyester resin containing polyethylene terephthalate as a polyester is composed of three constituent units of polyethylene terephthalate.

[0022] The content of the cyclic oligomer in the polyester resin is preferably 1% by weight or less, more preferably 0.5% by weight or less.

[0023] 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. The polyester resin in this embodiment can reduce the content of BHET and suppress the occurrence of mold fouling during molding because 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. Further, the polyester resin in this embodiment is excellent in light-shielding property, mouth crystallization suitability, and flavor property because the ratio of the peak areas (C5 / CT) is within the above range. 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 ratio of the peak areas of the hexamer oligomer and heptamer oligomer described later.

[0024] 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 by 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 staining during molding of the polyester resin can be further suppressed. In addition, by setting the peak area ratio (C6 / CT) within the above range, the polyester resin can be made more excellent in light blocking properties, mouth crystallization suitability, and flavor properties.

[0025] 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 by 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 staining during molding of the polyester resin can be further suppressed. In addition, by setting the peak area ratio (C7 / CT) within the above range, the polyester resin can be made more excellent in light blocking properties, mouth crystallization suitability, and flavor properties.

[0026] In polyester resin, the peak area (A acid ) for 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 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, and the peak area (A acid The peak area (A) from all dicarboxylic acids is the sum of the peak areas present in all these ranges. acid ) for 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 ) within the above range, the polyester resin can be made more excellent in light-shielding properties, suitability for crystallization at the mouth portion, and flavor properties.

[0027] In polyester resin, the peak area (A acid ) for 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 ) for the peak area (A 7.8 ) ratio (A 7.8 / A acid ) within the above range, It is possible to further suppress the occurrence of mold contamination during molding of polyester resin. In addition, 7.8 / A acid ) within the above range, the polyester resin can be made more excellent in light-shielding properties, suitability for crystallization at the mouth portion, and flavor properties.

[0028] In a polyester resin, the shoulder correlation parameter S, which is derived using the differential molecular weight distribution curve obtained by GPC and is represented by the following 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. TIFF2025084471000001.tif11134In 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 data at two points where LogM is 3.40 and 3.75 in f(LogM). Also, the vertical axis of the differential molecular weight distribution curve is dw / dLogM obtained by differentiating the concentration fraction w(%) with respect to LogM. By setting the shoulder correlation parameter S within the above range, the occurrence of mold fouling during the molding of the polyester resin can be suppressed. Also, by setting the shoulder correlation parameter S within the above range, the polyester resin can be made excellent in light-shielding property, mouth crystallization suitability, and flavor property.

[0029] In a 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 the molding of the polyester resin can be suppressed. Also, by setting the polydispersity Mw / Mn within the above range, the polyester resin can be made excellent in light-shielding property, mouth crystallization suitability, and flavor property.

[0030] In this embodiment, the acetaldehyde content of the polyester resin is preferably 10 ppm or less, more preferably 5 ppm or less, in the form of pellets after solid-phase polymerization. Further, it is preferable to reduce the increase in acetaldehyde when the polyester resin is formed into a molded article. 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 article when the polyester resin is formed into a molded article can be suppressed, and thus the flavor property can be made excellent.

[0031] In this embodiment, the intrinsic viscosity (IV) of the polyester resin is preferably 0.60 to 1.40 dL / g, more preferably 0.70 to 1.00 dL / g.

[0032] The chromaticity b of the polyester resin in this embodiment * is preferably 15.0 or more, more preferably 27.0 or more, in the form of pellets after solid-phase polymerization. The chromaticity b of the polyester resin * By setting it within the above range, the molded article formed from the polyester resin can be made excellent in light-shielding property.

[0033] In this embodiment, the cold crystallization peak top temperature Tc1 of the polyester resin is preferably 149°C or less. The upper limit of the cold crystallization peak top temperature Tc1 is not particularly limited, but is usually 120°C or more. By setting the cold crystallization peak top temperature Tc1 of the polyester resin within the above range, when the polyester resin is formed into a polyester bottle or the like, crystallization of the mouth part can be easily performed.

[0034] Figure 1 is a flowchart showing an example of the method for producing the polyester resin in this embodiment. As shown in Figure 1, the polyester resin in this embodiment can be produced by a method of performing a heat history control treatment including a first melt extrusion step, a second melt extrusion step, a crystallization step, and a solid-phase polymerization step on the polyester containing the above-mentioned diol unit and dicarboxylic acid unit.

[0035] First, in the first melt extrusion step, the pelletized polyester obtained by polymerizing the above diol compound and dicarboxylic acid is first dried in a dehumidifying dryer set at 150°C in advance to reduce the moisture content to 50 ppm or less, and then melt extruded using an extruder. The discharged molten resin is air-cooled to form pellets. The extruder is not particularly limited, and examples include a single-screw extruder, a twin-screw extruder, and a multi-screw extruder. Among them, a twin-screw extruder is preferred. When using a twin-screw extruder, the extrusion temperature is preferably 0 to 60°C higher than the melting point of the polyester. In particular, 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.

[0036] 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 discharged molten resin is air-cooled to form pellets. The extruder is not particularly limited, and examples include a single-screw extruder, a twin-screw extruder, and a multi-screw extruder. Among them, a twin-screw extruder is preferred. Further, the extruder to be used preferably has a vacuum vent facility capable of reducing the pressure to below atmospheric pressure. In the second melt extrusion step, when using a twin-screw extruder equipped with a vacuum vent facility, the melt extrusion conditions are preferably the same as those in the first melt extrusion step, except that the melt extrusion is performed under a pressure with a vacuum degree of 100 Torr or less.

[0037] Next, in the crystallization step, the pellets obtained in the second melt extrusion step are heated to crystallize the resin. The temperature during heating is preferably 100 to 170°C, and more preferably 130 to 150°C. The heating is preferably performed under a pressure of 200 Torr or less, or under a nitrogen stream and their combined use. The heating time is preferably 0.5 to 6 hours, and more preferably 2 to 5 hours.

[0038] Next, in the solid-phase polymerization step, the pellets that have been subjected to the crystallization treatment are heated to perform solid-phase polymerization of the resin. The solid-phase polymerization is preferably carried out under a pressure of 200 Torr, or under a nitrogen stream and a combination thereof. The temperature of the solid-phase 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.

[0039] As described above, by performing the heat history control treatment consisting of the first melt extrusion step, the second melt extrusion step, the crystallization step, and the solid-phase polymerization step one or more times on the polyester, the polyester resin in the present embodiment can be obtained. The number of times of the heat history control treatment is preferably 4 to 10 times based on so-called virgin polyester that has never been recycled (0 times).

[0040] Note that the method for producing the polyester resin in the present embodiment is not particularly limited to the above. For example, by mechanically recycling the polyester used as a polyester bottle or the like, the heat history can be controlled to obtain the polyester resin (mechanically recycled polyester resin) in the present embodiment. As the polyester used for mechanical recycling, for example, a polyester bottle produced from virgin polyester or a polyester bottle produced by performing mechanical recycling one or more times can be used.

[0041] The polyester resin in the present embodiment can be suitably used for processing into molded articles such as preforms and polyester bottles. The preform can be produced by injection molding the polyester resin. Further, the polyester bottle can be produced by performing stretch blow on such a preform.

[0042] As described above, since the polyester resin in the present embodiment is before being processed into a molded article, the ratios of the peak areas of the pentamer, hexamer, and heptamer oligomers (C5 / CT, C6 / CT, C7 / CT) to the peak area of the trimer oligomer (CT) measured by liquid chromatography, 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 1H-NMR, the shoulder correlation parameter S, and the polydispersity Mw / Mn (hereinafter, these are collectively also referred to as "thermal history parameters") cannot be judged in the state of the molded article. The molded article corresponds to the state between the first melt extrusion step and the second melt extrusion step in the flowchart shown in FIG. 1. Therefore, in order to compare the polyester resin constituting the molded article with the polyester resin in the present embodiment, it is necessary to perform a second melt extrusion treatment, a crystallization treatment, and a solid-phase polymerization treatment on the molded article, evaluate the obtained pellets, and judge whether the thermal history parameters are within a specific range.

[0043] Note that when a second melt extrusion treatment, a crystallization treatment, and a solid-phase polymerization treatment are performed on the molded article, it means that the thermal history is additionally applied once for the thermal history control treatment to the polyester resin before molding. Therefore, when the thermal history parameters evaluated by performing a second melt extrusion treatment, a crystallization treatment, and a solid-phase polymerization treatment on a certain molded article are values near the upper limit value and the lower limit value of the specific range defined in the present embodiment, in order to confirm whether the thermal history parameters of the polyester resin before molding were included in the specific range, it is preferable to evaluate according to the following procedure.

[0044] First, for the molded article, the thermal history parameters of the pellets obtained by performing the second melt extrusion treatment, crystallization treatment, and solid-phase polymerization treatment are recorded as the thermal history parameters with one adjustment. Next, a thermal history control treatment is performed on the pellets, and the thermal history parameters of the obtained pellets are recorded as the thermal history parameters with two adjustments. Thereafter, the thermal history control treatment is performed on the pellets a plurality of times as necessary, and the thermal history parameters after three adjustments are recorded. In this way, by extrapolating the correlation between the number of adjustments 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.

Example

[0045] Next, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[0046] <Example 1> [Production of PET resin pellets and preforms] 30 kg of pellets of isophthalic acid copolymerized polyethylene terephthalate resin (manufactured by Shin-Kosa Synthetic Fiber Co., Ltd., isophthalic acid copolymerization ratio 1.8 mol%, IV = 0.83) were prepared and dried using a hopper dryer under the conditions of 150°C for 5 hours. Next, these pellets were charged into a twin-screw extruder (manufactured by 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 a discharge rate of 10 kg / h. The molten resin discharged in a strand form from the extruder was air-cooled while being conveyed by a belt conveyor, and made into pellets using a pelletizer (first melt extrusion treatment). Next, these pellets were charged into the twin-screw extruder again, and melt extrusion was performed under the same conditions as above except that a vacuum vent (9 Torr) was used, and pellets were obtained in the same manner (second melt extrusion treatment).

[0047] The obtained 15 kg of pellets were heated for 5 hours under the conditions of 1 Torr and 150°C using a stirring type vacuum dryer (manufactured by Dalton, 45MV) to perform a crystallization treatment. Subsequently, using the above-mentioned stirring type vacuum dryer, the pellets after the crystallization treatment were heated for 13 hours under the conditions of 1 Torr and 225°C to perform a solid-phase polymerization treatment. In the crystallization treatment and the solid-phase polymerization treatment, the rotation speed of the stirring blade of the stirring type vacuum dryer was set to 20 rpm. For the obtained pellets, the first and second melt extrusion treatments, the crystallization treatment, and the solid-phase polymerization treatment were further repeated 3 times in the same procedure as above to obtain PET resin pellets. That is, the heat history control treatment was performed a total of 4 times on the virgin pellets. Further, a part of the obtained PET resin pellets was supplied to an injection molding machine, the barrel temperature and the hot runner temperature were set to 300°C, the mold temperature was set to 15°C, and the molding cycle was set to 32 seconds to produce a preform for a 500 mL bottle with a weight of 25 g. Each evaluation of the PET resin pellets and the preform for the bottle was performed according to the following procedure. The results are shown in Table 2.

[0048] [Cyclic oligomer content and BHET content] Weighed 0.2 g of PET resin pellets and preforms for bottles, added 1 mL of a mixed solvent of 1,1,1,3,3,3 - hexafluoro - 2 - propanol and chloroform (weight ratio 1 / 1) thereto, and completely dissolved them. After adding 4 mL of chloroform to the solution, 5 mL of acetonitrile was gradually added, and the mixture was left standing for 3 hours to precipitate the PET polymer. 1 mL of the supernatant of this suspension was taken out, filtered through a membrane filter with a pore size of 0.20 μm, and the filtrate was measured by high - performance liquid chromatography. At the same time, the measurement of the BHET standard solution was also carried out, and the BHET content in the pellets and preforms for bottles was calculated based on the obtained calibration curve. As the measuring device, 1200 series manufactured by Agilent Technologies was used. The measurement conditions were as follows: As the detector, Agilent Technologies 1290 Infinity diode array detector (G4212A) was used, the detection wavelength was 254 nm, and the reference wavelength was 500 nm. As the column, Agilent Technologies ZORBAX Eclipse Plus C18 (Rapid Resolution HD 2.1×150 mm 1.8 Micron) was used, and the column temperature was 40 °C. Also, as the mobile phase, 0.05 wt% phosphoric acid aqueous solution was used as solution I, and acetonitrile was used as solution II. The flow rate was 0.6 mL / min, and it was flowed under the gradient conditions shown in Table 1 below. The injection volume was 2 μL. Regarding the cyclic oligomers in the pellets, the peak areas from the trimer to the heptamer (CT, C5, C6, C7) were determined respectively, and C5 / CT, C6 / CT, and C7 / CT were calculated. Regarding the BHET content in the preforms for bottles, the numerical value normalized with the BHET content in the preforms made from virgin pellets as 1 is shown.

[0049]

Table 1

[0050] [NMR history correlation peak] Dissolve PET resin pellets in a mixed solvent of heavy trifluoroacetic acid and heavy chloroform (volume ratio 8 / 2), measure the 1H-NMR spectrum with an NMR apparatus (JEOL, 400SS), and determine the peak area (A acid ) derived from all dicarboxylic acids, the area (A 7.5 ) of NMR history correlation peak 1, and the area (A 7.8 ) of NMR history correlation peak 2, and calculate A 7.5 / A acid and A 7.8 / A acid . Here, the peak derived from all dicarboxylic acids is the total peak area in the range of 7.60 - 7.75 ppm, 7.90 - 8.55 ppm, and 8.75 - 8.90 ppm. NMR history correlation peak 1 refers to the peak area in the range of 7.43 - 7.55 ppm, and NMR history correlation peak 2 refers to 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 6, and Figure 2B is a graph showing the measurement results of the 1H-NMR spectrum in Comparative Example 1. Also, for reference, the 1H-NMR spectrum was similarly measured for virgin isophthalic acid copolymerized polyethylene terephthalate resin without heat history control treatment. Figure 2C is a graph showing the measurement results of the 1H-NMR spectrum in virgin isophthalic acid copolymerized polyethylene terephthalate resin.

[0051] [Polydispersity (Mw / Mn) and Shoulder Correlation Parameter S] The differential molecular weight distribution curve was measured using a high-speed GPC device (Tosoh, HLC-8320GPC), and the polydispersity (Mw / Mn) was determined. As a sample, 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. 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 set at 40 °C. Standard polystyrene (Tosoh, PStQuickMP-M) was used as the molecular weight standard. Also, the shoulder correlation parameter S represented by the above equation (1) was determined from the differential molecular weight distribution curve. The vertical axis of the differential molecular weight distribution curve was set as dw / dLogM obtained by differentiating the concentration fraction w (%) with respect to 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). Also, 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).

[0052] [b * value] The b * values of PET resin pellets and preforms were measured using an SM color computer (manufactured by Suga Test Instruments Co., Ltd.). * The larger the value, the better the light-shielding property.

[0053] [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). The lower the cold crystallization peak top temperature, the better the suitability for mouth crystallization when the PET resin pellets are used as a molded body. 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 a rate of 10 °C / min Step 3: Hold at 290 °C for 5 minutes Step 4: Cool from 290 °C to 20 °C at a rate of 300 °C / min Step 5: Hold at 20°C for 10 minutes Step 6: Heat from 20°C to 290°C at a rate of 10°C / min Tc1 was determined from the peak top temperature (°C) of the crystallization peak in Step 6.

[0054] [Measurement of Acetaldehyde (AA)] A 1.0 g sample of the PET resin pellets and preforms crushed by a cryogenic grinding device was weighed into a glass bottle, 5.0 mL of pure water was added, and the bottle was sealed. This suspension was heated in an oven maintained at a temperature of 120°C for 60 minutes and then cooled in ice water. 1.0 mL of the supernatant of the suspension was collected, 0.2 mL of a 2,4-dinitrophenylhydrazine·phosphoric acid solution with a concentration of 0.1% was added thereto, and the mixture was left standing for 30 minutes. The supernatant after standing was filtered through a membrane filter with a pore size of 0.20 μm, and the filtrate was measured by high performance liquid chromatography. At the same time, a standard solution of acetaldehyde was also measured, and the acetaldehyde content in the PET resin pellets and preforms was calculated based on the obtained calibration curve. The change (ΔAA) in the acetaldehyde content 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 the acetaldehyde content, the smaller the increase in acetaldehyde when the PET resin pellets are used as a molded body, the influence on the flavor of the contents of the molded body is suppressed, and it indicates excellent flavor properties.

[0055] <Examples 2 to 7> PET resin pellets and preforms were obtained in the same manner as in Example 1 except that the total number of heat history control treatments for the pellets was changed to 5 to 10 times, and the evaluation was performed in the same manner.

[0056] <Comparative Examples 1 to 3> PET resin pellets were obtained in the same manner as in Example 1 except that the total number of heat history control treatments for the pellets was 1 to 3 times, and the evaluation was performed in the same manner. For Comparative Example 1, preforms were further produced using the PET resin pellets, and the evaluation was performed in the same manner as in Example 1.

[0057] <Comparative Example 4> Pellets of isophthalic acid copolymerized polyethylene terephthalate resin that had never undergone heat history control treatment were evaluated in the same manner as in Example 1. Also, preforms were obtained using pellets that had not undergone heat history control treatment and were evaluated in the same manner as in Example 1.

[0058]

Table 2

[0059] As shown in Table 2, the PET resin pellets of Examples 1 to 7 and the preforms molded using them, 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 using liquid chromatography was 0.086 or more, had a low BHET content and were able to suppress the occurrence of mold fouling during molding. Also, the PET resin pellets and preforms of Examples 1 to 7 were excellent in light shielding properties because the b * value was large, excellent in mouth crystallization suitability because Tc1 was low, and excellent in flavor properties because ΔAA was small. On the other hand, the PET resin pellets of Comparative Examples 1 to 4 and the preforms molded using them, in which C5 / CT was less than 0.086, were all inferior in terms of the occurrence of mold fouling, light shielding properties, mouth crystallization suitability, and flavor properties.

Claims

1. A polyester resin mainly containing 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 a polyester resin characterized in that 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.

2. The polyester resin according to claim 1, 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.

3. The polyester resin according to claim 1, 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.

4. A molded article made of the polyester resin according to any one of claims 1 to 3.

5. A preform made of the polyester resin according to any one of claims 1 to 3.

6. A polyester bottle made of the polyester resin according to any one of claims 1 to 3.

7. The polyester resin according to any one of claims 1 to 3, characterized in that the polyester resin is a mechanically recycled polyester resin.

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