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

Abstract

To provide a polyester resin having an excellent color tone.SOLUTION: A polyester resin contains polyester containing a diol unit and a dicarboxylic acid unit as a main component, wherein 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 0.068 or more and less than 0.090.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polyester resin, a molded article made of this polyester resin, a preform, a polyester bottle, and 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, when the mechanical recycling process of the polyester resin is repeatedly performed by the above technique, there is a problem that the yellowness of the polyester resin increases and the color tone deteriorates.

[0005] An object of the present invention is to provide a polyester resin having an excellent color tone.

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 0.068 or more and less than 0.090.

[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 0.0482 or more and less than 0.0620.

[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 0.0225 or more and less than 0.0330.

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

Advantages of the Invention

[0013] According to the present invention, a polyester resin having excellent color tone can be provided.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 3

Figure 4

Modes for Carrying Out the Invention

[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 by liquid chromatography is 0.068 or more and less than 0.090.

[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, and 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-cyclopentanediol, 4-cyclopenten-1,3-diol, adamantadiol, p-xylene 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 the polyester is composed of three constitutional 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 0.068 or more and less than 0.090, preferably 0.070 or more and less than 0.088. The polyester resin in this embodiment has 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, so that the yellowness is suppressed, the color tone is excellent, and the molding stability is excellent. 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 the 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 0.0482 or more and less than 0.0620, more preferably 0.0485 or more and less than 0.0600. By setting the peak area ratio (C6 / CT) within the above range, the polyester resin can be made more excellent in color tone and molding stability.

[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 0.0225 or more and less than 0.0330, more preferably 0.0230 or more and less than 0.0320. By setting the peak area ratio (C7 / CT) within the above range, the polyester resin can be made more excellent in color tone and molding stability.

[0026] In polyester resin, the peak area (A acid ) for the peak area (A 7.5 ) ratio (A 7.5 / A acid 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) derived from all dicarboxylic acids is preferably less than 0.00060, and more preferably less than 0.00040. 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 / Aacid By setting () within the above range, the polyester resin can be made to have excellent color tone and molding stability.

[0027] In the polyester resin, the peak area (A acid ) derived from all dicarboxylic acids measured using 1H-NMR, with respect to the peak area (A 7.8 ) at 7.75 to 7.85 ppm, the ratio (A 7.8 / A acid ) is preferably less than 0.00030, more preferably less than 0.00020. By setting the ratio (A acid ) derived from all dicarboxylic acids, with respect to the peak area (A 7.8 ) at 7.75 to 7.85 ppm, (A 7.8 / A acid ) within the above range, the polyester resin can be made to have excellent color tone and molding stability.

[0028] In the 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 greater than 0.130 and less than or equal to 0.197, more preferably greater than 0.145 and less than or equal to 0.196. TIFF2025084422000001.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, g(LogM) represents a linear function connected by the data of 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 polyester resin can be made to have excellent color tone and molding stability.

[0029] In the polyester resin, the polydispersity Mw / Mn measured using GPC is preferably 2.315 or more and less than 2.500, more preferably 2.320 or more and less than 2.490. By setting the polydispersity Mw / Mn within the above range, the polyester resin can be made to have better color tone and molding stability.

[0030] The intrinsic viscosity (IV) of the polyester resin in this embodiment is preferably 0.60 to 1.40 dL / g, more preferably 0.70 to 1.00 dL / g.

[0031] The chromaticity b of the polyester resin in this embodiment * is preferably 15.0 or less, more preferably 10.0 or less, in the form of pellets after solid-phase polymerization.

[0032] The cold crystallization peak top temperature Tc1 of the polyester resin in this embodiment is preferably 149°C or more and 162°C or less, more preferably 149°C or more and 153°C or less. By setting the cold crystallization peak top temperature Tc1 of the polyester resin to be not less than the above lower limit, the polyester resin can be made to have better molding stability. However, if the cold crystallization peak top temperature Tc1 of the polyester resin exceeds the above upper limit, it will be difficult to impart heat resistance when molding the polyester resin into a polyester bottle or the like.

[0033] 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 on the polyester containing the above-mentioned diol unit and dicarboxylic acid unit, which includes a first melt extrusion step, a second melt extrusion step, a crystallization step, and a solid-phase polymerization step.

[0034] First, in the first melt extrusion step, the pelletized polyester obtained by polymerizing the above diol compound and dicarboxylic acid is 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 single-screw extruders, twin-screw extruders, multi-screw extruders, etc. 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 30000 kg / h, and more preferably 10 to 10000 kg / h.

[0035] 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 single-screw extruders, twin-screw extruders, multi-screw extruders, etc. Among them, a twin-screw extruder is preferred. In addition, 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.

[0036] 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, under a nitrogen stream, or a combination of these. The heating time is preferably 0.5 to 6 hours, and more preferably 2 to 5 hours.

[0037] Next, in the solid-phase polymerization step, the pellets 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 less, under a nitrogen stream, or in a combined use of these. 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.

[0038] 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 1 to 3 times based on a so-called virgin polyester that has never been recycled (0 times).

[0039] 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.

[0040] 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. The molded article produced using the polyester resin in the present embodiment has an excellent color tone.

[0041] As described above, since the polyester resin in this 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 this 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.

[0042] Note that when the second melt extrusion treatment, the crystallization treatment, and the solid-phase polymerization treatment are performed on the molded article, it means that one additional thermal history control treatment has been applied to the polyester resin before molding. Therefore, when the thermal history parameters evaluated by performing the second melt extrusion treatment, the crystallization treatment, and the 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 this 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.

[0043] First, regarding 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 time. 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 adjustment times. Thereafter, the thermal history control treatment is performed on the pellets a plurality of times as necessary, and the thermal history parameters after three or more adjustment times are recorded. In this way, by extrapolating the correlation between the adjustment times and the thermal history parameters, the thermal history parameters corresponding to zero adjustment times are obtained. By evaluating the thermal history parameters corresponding to zero adjustment times, it is possible to confirm whether the thermal history parameters of the polyester resin before molding were within a specific range.

Example

[0044] Next, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[0045] <Example 1> [Production of PET resin pellets and preforms] 30 kg of pellets of isophthalic acid copolymerized polyethylene terephthalate resin (manufactured by Shin-Kosa 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 put 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 shape 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 put 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).

[0046] 15 kg of the obtained pellets were heated at 1 Torr and 150 °C for 5 hours using a stirred vacuum dryer (manufactured by Dalton, 45MV) for crystallization treatment. Subsequently, using the above-mentioned stirred vacuum dryer, the pellets after the crystallization treatment were heated at 1 Torr and 225 °C for 13 hours for solid-phase polymerization treatment to obtain PET resin pellets. In the crystallization treatment and the solid-phase polymerization treatment, the rotation speed of the stirring blade of the stirred vacuum dryer was set to 20 rpm. 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.

[0047] [Cyclic oligomer 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. As the measuring device, 1200 series manufactured by Agilent Technologies was used. The measurement conditions were as follows: As the detector, an Agilent Technologies 1290 Infinity diode array detector (G4212A) was used, the detection wavelength was 254 nm, and the reference wavelength was 500 nm. Also, as the column, an 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. The mobile phase was 0.05 wt% phosphoric acid aqueous solution as solution I and acetonitrile as solution II, with a flow rate of 0.6 mL / min, and 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 of the trimer and pentamer to heptamer (CT, C5, C6, C7) were determined respectively, and C5 / CT, C6 / CT, and C7 / CT were calculated.

[0048]

Table 1

[0049] [NMR history correlation peak] Dissolved PET resin pellets in a mixed solvent of deuterated trifluoroacetic acid and deuterated chloroform (volume ratio 8 / 2), measured the 1H - NMR spectrum with an NMR device (JEOL, 400SS), and obtained the peak area (A acid ) derived from all dicarboxylic acids and the area (A 7.5 ) of NMR history correlation peak 1 and the area (A 7.8) were each determined, and A 7.5 / A acid and A 7.8 / A acid were calculated. Here, the peaks derived from all dicarboxylic acids are 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 is the peak area in the range of 7.43 - 7.55 ppm, and NMR history correlation peak 2 is the peak area in the range of 7.75 - 7.85 ppm. Figure 2A is a graph showing the measurement results of the 1H-NMR spectrum in Example 1, and Figure 2B is a graph showing the measurement results of the 1H-NMR spectrum in Comparative Example 6. Also, for reference, the 1H-NMR spectrum was similarly measured for virgin isophthalic acid copolymerized polyethylene terephthalate resin without the 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.

[0050] [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) to obtain the polydispersity (Mw / Mn). As a sample, a solution in which PET resin pellets were dissolved in a mixed solution of 1,1,1,3,3,3-hexafluoro-2-propanol and chloroform (volume ratio 1 / 49) 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 40 °C. Standard polystyrene (Tosoh, PStQuickMP-M) was used as the molecular weight standard. Also, the shoulder correlation parameter S represented by the above formula (1) was obtained 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 LogM. Figure 3(a) is a graph showing the measurement results of the differential molecular weight distribution curve in Example 1, and Figure 3(b) is an enlarged view of Figure 3(a). Also, Figure 4(a) is a graph showing the measurement results of the differential molecular weight distribution curve in Comparative Example 6, and Figure 4(b) is an enlarged view of Figure 4(a).

[0051] [b * value The b value of PET resin pellets and preforms * was measured by an SM color computer (manufactured by Suga Test Instruments Co., Ltd.). The smaller the value, the better the color tone indicates. * The smaller the value, the better the color tone.

[0052] [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 higher the cold crystallization peak top temperature, the better the molding stability of the PET resin pellets indicates. 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 cold crystallization peak in Step 6.

[0053] [Intrinsic viscosity recovery ΔIV] PET resin pellets were fed into a twin-screw extruder (manufactured by Toshiba Machine Co., Ltd., TEM26SS), and melt extrusion was carried out 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 then pelletized using a pelletizer. Next, these pellets were fed into the twin-screw extruder again, and melt extrusion was carried out under the same conditions as above except that a vacuum vent (9 Torr) was used, and pellet A was obtained. Pellet A was vacuum-dried at 120 °C for 2 hours, weighed 0.3 g, added to a mixed solvent of 1,1,2,2-tetrachloroethane and phenol (weight ratio 1 / 1), adjusted to a concentration of 1.00 g / dL, and stirred at 120 °C for 20 minutes to be completely dissolved. The solution after dissolution was cooled to room temperature, and the relative viscosity was determined using a relative viscometer (Malvern Panalytical, Viscotec Y501C) thermostatically controlled at 30 °C, and the intrinsic viscosity A of pellet A was determined.

[0054] Next, for the above pellet A, crystallization treatment was carried out by heating at 1 Torr and 150 °C for 5 hours using a stirring vacuum dryer (manufactured by Dalton, 45MV). Then, using the above stirring vacuum dryer, the pellets after crystallization treatment were heated at 1 Torr and 225 °C for 13 hours to carry out solid-phase polymerization treatment, and pellet B was obtained. For pellet B, the relative viscosity was determined in the same procedure as for pellet A, and the intrinsic viscosity B of pellet B was determined. Using the intrinsic viscosity A and the intrinsic viscosity B, the intrinsic viscosity recovery ΔIV [dL / g] was determined based on the following formula. The larger the intrinsic viscosity recovery ΔIV, the higher the solid-phase polymerization efficiency when the molded product obtained from the PET resin pellets is recovered and recycled, indicating that the PET resin pellets are suitable for recycling. Intrinsic viscosity recovery ΔIV = Intrinsic viscosity B - Intrinsic viscosity A

[0055] Note that since pellet A is obtained by performing the first melt extrusion treatment and the second melt extrusion treatment on PET resin pellets, pellet A corresponds to pellets produced by collecting a molded product (after the first melt extrusion treatment) obtained from PET resin pellets and performing extrusion molding (the second melt extrusion treatment). On the other hand, since pellet B is a pellet obtained by performing a crystallization treatment and a solid-phase polymerization treatment on pellet A, it corresponds to pellets obtained by mechanically recycling a molded product obtained from PET resin pellets.

[0056] <Example 2> PET resin pellets of Example 1 were obtained in the same manner as in Example 1 and evaluated in the same manner, except that the first melt extrusion treatment, the second melt extrusion treatment, the crystallization treatment, and the solid-phase polymerization treatment were each additionally performed once. That is, the PET resin pellets of Example 2 are those in which the heat history control treatment was performed a total of 2 times on virgin pellets.

[0057] <Example 3> PET resin pellets were obtained in the same manner as in Example 1 and evaluated in the same manner, except that the total number of heat history control treatments on the pellets was set to 3 times.

[0058] <Comparative Examples 1 to 7> PET resin pellets were obtained in the same manner as in Example 1 and evaluated in the same manner, except that the total number of heat history control treatments on the pellets was set to 4 to 10 times, respectively. In Comparative Example 2 and Comparative Example 7, preforms were further produced using the obtained PET resin pellets, and the preforms were evaluated in the same manner as in Example 1.

[0059] <Reference Example> Pellets of isophthalic acid copolymerized polyethylene terephthalate resin that had not undergone any 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 evaluated in the same manner as in Example 1.

[0060]

Table 2

[0061] As shown in Table 2, 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 0.068 or more and less than 0.090. The PET resin pellets of Examples 1 to 3 and the preforms molded using the same have a small b * value, suppressed yellowness, and excellent color tone. Further, the PET resin pellets and preforms of Examples 1 to 3 had excellent molding stability because Tc1 was high. On the other hand, the PET resin pellets of Comparative Examples 1 to 7 in which C5 / CT was 0.090 or more and the preforms molded using the same were inferior in color tone and molding stability.

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 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 0.068 or more and less than 0.

090. The polyester resin is characterized by this.

2. The polyester resin according to claim 1, wherein a ratio (C6 / CT) of a peak area of a hexamer oligomer (C6) to a peak area of the trimer oligomer (CT) in the cyclic oligomer measured using liquid chromatography is 0.0482 or more and less than 0.0620.

3. The polyester resin according to claim 1, wherein a ratio (C7 / CT) of a peak area of a heptamer oligomer (C7) to a peak area of the trimer oligomer (CT) in the cyclic oligomer measured using liquid chromatography is 0.0225 or more and less than 0.0330.

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

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

6. A polyester bottle made from 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, wherein the polyester resin is a mechanically recycled polyester resin.

Images