WO2013077294A1

WO2013077294A1 - Polyester resin

Info

Publication number: WO2013077294A1
Application number: PCT/JP2012/079982
Authority: WO
Inventors: 北野　善拡; 甲斐　正次郎; 寛明武井; 菊地　淳
Original assignee: 東洋製罐株式会社
Priority date: 2011-11-21
Filing date: 2012-11-19
Publication date: 2013-05-30
Also published as: JP2013107992A

Abstract

The present invention is a polyester resin which comprises ethylene terephthalate units as the main component and which exhibits, in a pelletized state, an intrinsic viscosity of 0.70 to 0.81dL/g, a molecular weight distribution of 3.2 or more in the neighborhood of a pellet surface, and a maximum melting point ending temperature of 280°C or lower in the melting point distribution. The polyester resin exhibits excellent meltability and moldability and a reduced acetaldehyde concentration, and has a characteristic of exhibiting a reduced strain in stretching by virtue of the excellent shapability and thus imparting excellent heat resistance to a molded product.

Description

Polyester resin

The present invention relates to a polyester resin suitable for bottle molding. More specifically, the present invention relates to a polyester resin that has excellent meltability and moldability, has a reduced acetaldehyde concentration, and can impart excellent heat resistance. .

Containers made of a polyester resin typified by polyethylene terephthalate are widely used as containers for beverages, oils, seasonings and the like because of their excellent properties such as transparency and mechanical strength.
Generally, a container made of a polyester resin, particularly a bottle made of a polyester resin mainly composed of ethylene terephthalate units (hereinafter referred to as “PET bottle”) is a polyester resin produced by melt polymerization or solid phase polymerization after melt polymerization. It is used.
The polyester resin produced by melt polymerization contains low molecular weight components such as acetaldehyde and oligomers such as cyclic trimers, and when a container is molded using a polyester resin containing these substances, During molding, oligomers in the polyester resin are deposited and adhere to the mold surface, causing problems such as a decrease in transparency due to rough skin, or frequent cleaning of the mold. In addition, when a large amount of acetaldehyde is present in the molded container, there is also a problem that the content is transferred to the content and the flavor of the content is impaired.

In order to solve such problems, it has been conventionally performed to subject the polyester resin produced by melt polymerization to solid-phase polymerization in order to reduce oligomers such as cyclic trimers and acetaldehyde in the polyester resin. Yes.
However, in the solid-phase polymerization process, molecular weight increase and crystal growth remarkably occur compared to the inside of the pellet due to heat transfer and diffusion on the surface of the polyester resin pellet and its vicinity. In some cases, melting tends to be difficult. As a result, when a preform is molded by injection molding using a polyester resin that has undergone a solid-phase polymerization process, the preform is whitened or hardly melted, so high-temperature molding is required. There is a possibility that the vent of the extruder is clogged or that acetaldehyde is generated at a high concentration.
In addition, in the case of solid-state polymerization, if the increase in the intrinsic viscosity of the pellet surface is significant, in addition to the above-mentioned problems, the shapeability by blow molding may be reduced, or the strain during stretching may be increased. There may be a problem that the heat resistance of the PET bottle is lowered.

In order to solve the problems caused by the difference in intrinsic viscosity and crystallization in the inner and outer layers of the polyester resin pellets that have undergone such solid phase polymerization, the difference in intrinsic viscosity between the inner and outer layers is 0.125 or less and the difference in density is Proposal is made of a chip (Patent Document 1) of 0.0019 or less and a polyester composition (Patent Document 2) in which the ratio of the intrinsic viscosity of the center part to the surface layer part of the solid-phase polymerized polyester chip is 0.70 to 0.95. Has been.

Japanese Patent Laid-Open No. 5-70567 Japanese Patent Laid-Open No. 9-24964

However, as described in Patent Documents 1 and 2 above, controlling the conditions of polymerization to control the increase in the intrinsic viscosity and density of the surface can be done by specializing the formulation or using dedicated equipment. It may be necessary to introduce it, and the processing time may be prolonged, and it has not been fully satisfied in terms of productivity and economy.
Accordingly, an object of the present invention is to provide a polyester resin with improved meltability and moldability and reduced acetaldehyde concentration.
Another object of the present invention is to provide a polyester resin capable of imparting excellent heat resistance to a molded article, in which distortion during stretching is reduced by excellent formability and crystal formation is suppressed. That is.
Still another object of the present invention is to provide a production method capable of producing a polyester resin having the above characteristics with high productivity and economy.

According to the present invention, it is a polyester resin mainly composed of ethylene terephthalate units, and in the pellet state, the intrinsic viscosity is 0.70 to 0.81 dL / g, and the molecular weight distribution (Mw / Mn) in the vicinity of the pellet surface is 3 An ethylene terephthalate-based polyester resin having a melting point distribution of 280 ° C. or lower is provided.
In the ethylene terephthalate-based polyester resin of the present invention, it is preferable that the content of diethylene glycol is less than 2.0 mol%.
According to the present invention, there is also provided an ethylene terephthalate-based polyester resin having an intrinsic viscosity of 0.82 dL / g or more, a maximum peak temperature in a maximum existence ratio of a melting point distribution of 245 ° C. or more, and a maximum melting point end temperature of 281 ° C. or more. There is provided a method for producing an ethylene terephthalate-based polyester resin characterized by hydrolysis.
According to the present invention, there is further provided a molded article characterized in that the acetaldehyde concentration comprising the ethylene terephthalate polyester resin is less than 10 ppm.

In general, the melting point of a polymer depends on the molecular weight. The melting point depends on the thickness of the crystal (lamella) and the surface free energy of the lamella surface from the Gibbs-Thompson relational expression. The thinner the crystal (lamellar), the lower the melting point. The melting point of the ethylene terephthalate polyester resin (hereinafter sometimes simply referred to as “PET resin”) obtained by solid layer polymerization is expressed as a melting point distribution corresponding to the density distribution resulting from the difference in lamellar thickness during solid layer polymerization. .
For reference, regarding the PET resin before hydrolysis used in Example 1, the abundance ratio to the pellet density and the melting point peak temperature (A) and the relationship between the melting point peak temperature and the abundance ratio (B) are shown in FIG.
In the present invention, from such a viewpoint, the intrinsic viscosity of the whole pellet is in the range of 0.70 to 0.81 dL / g, the molecular weight distribution on the pellet surface is large, and the maximum melting point end temperature of the melting point distribution is 280 ° C. It has been found that the following PET resin has excellent meltability and moldability.
That is, as described above, the molecular weight is increasing in the vicinity of the pellet surface by solid phase polymerization, but in the PET resin of the present invention, such a polymer chain is cleaved and has a wide molecular weight distribution. The reason for the maximum melting point end temperature of the melting point distribution is that the maximum melting point end point indicates the temperature necessary for completely melting the PET resin, and is directly related to the meltability and moldability of the PET resin. . Regarding the melting point distribution, the maximum melting point end temperature, and the maximum peak temperature at the maximum abundance ratio, the measuring method will be described in detail in Examples described later. As an example, regarding the PET resin used in Example 1, the melting point end temperature (A) with respect to the existing ratio before and after hydrolysis and the melting point peak temperature (B) with respect to the existing ratio before hydrolysis are shown in FIG.
In the present invention, the vicinity of the pellet surface of the PET resin refers to a portion having a thickness of 0.5 mm from the pellet surface, although it depends on the size of the pellet.

In addition, since the melting point of the PET resin is affected not only by the molecular weight distribution but also by the copolymerization component, in the present invention, the content of diethylene glycol (hereinafter sometimes referred to as “DEG”) is particularly less than 2.0 mol%. It is more preferable that this makes it possible to suppress crystal formation and to lower the melting point.

The PET resin of the present invention maintains the excellent properties of solid-phase polymerization PET, that is, the properties that oligomers such as cyclic trimers and acetaldehyde (hereinafter sometimes referred to as “AA”) are reduced. Because it has better melting characteristics than conventional solid-phase polymerized PET, it can be melted at a lower temperature than conventional solid-phase polymerized PET, has excellent moldability, and reduces strain during stretching. Further, excellent heat resistance can be imparted to the molded body.
Moreover, since the acetaldehyde content in the PET resin is reduced and there is no problem of generation of acetaldehyde due to high temperature molding, a molded article having excellent flavor properties can be provided.
Furthermore, the PET resin of the present invention has the above-mentioned problems that occur when conventional solid-phase polymerization PET is used, that is, whitening of the preform, the vent of the extruder is clogged, or acetaldehyde is generated at a high concentration. Will not cause the problem.
Furthermore, according to the method for producing a PET resin of the present invention, the PET resin of the present invention having the above characteristics can be produced with good productivity and economy.

Such operational effects of the PET resin of the present invention are also apparent from the results of Examples described later. That is, PET resin having a molecular weight distribution (Mw / Mn) of less than 3.2 or PET resin having a maximum melting point end temperature higher than 280 ° C. was injection molded at a standard extrusion temperature of 290 ° C. In some cases, the preform was not sufficiently melted, and the resulting preform was whitened (Comparative Examples 1 and 3). When injection molding was performed at an extrusion temperature of 300 ° C. (high temperature), acetaldehyde was generated and flavor was increased. It was inferior in property (Comparative Example 2).
On the other hand, with the PET resin of the present invention, even when injection molding is performed at an extrusion temperature of 280 ° C. (low temperature), the preform is not whitened and the thermal crystallization of the mouth of the preform can be performed efficiently. It is clear that the film has excellent heat resistance and flavor properties (Example 4). Further, it is apparent that even better heat resistance can be obtained when the DEG content is 2.0 mol% or less (Examples 1 to 4, 6).

It is a reference figure which shows the relationship between the density distribution of PET resin, and melting | fusing point distribution.

(PET resin)
The PET resin of the present invention is mainly composed of ethylene terephthalate units, has an intrinsic viscosity of 0.70 to 0.81 dL / g in a pellet state, and a molecular weight distribution (Mw / Mn) near the pellet surface of 3.2 or more. It is an important feature that the maximum melting point end temperature of the melting point distribution is 280 ° C. or lower.
The PET resin mainly composed of ethylene terephthalate units is one in which 50% or more of the ester repeating units are ethylene terephthalate units, and particularly preferably 80 mol% or more is occupied by ethylene terephthalate units.
In the PET resin of the present invention, as described above, in order to suppress crystal formation, the content of DEG is preferably less than 2.0 mol%, and in particular, homopolyethylene terephthalate is heat resistant. And is particularly suitable.
However, this does not exclude copolyesters containing a very small amount of ester units other than ethylene terephthalate units. Examples of dicarboxylic acids other than terephthalic acid include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; succinic acid, adipic acid, sebacic acid, and dodecanedioic acid. Examples of the diol component other than ethylene glycol include propylene glycol, 1,4-butanediol, diethylene glycol, 1,6-hexylene glycol, and cyclohexanedimethanol. And ethylene oxide adducts of bisphenol A.

(Production method)
The PET resin of the present invention is not necessarily limited to this, but was obtained by subjecting the above-mentioned raw materials mainly composed of the dicarboxylic acid component and the diol component to melt polymerization and solid phase polymerization in the presence of a catalyst. It can be obtained by hydrolyzing solid-phase polymerization PET.
The solid-phase polymerization PET to be subjected to hydrolysis treatment has an intrinsic viscosity of 0.82 dL / g or more, a maximum peak temperature in the maximum abundance ratio of the melting point distribution is 245 ° C. or more, and a maximum melting point end temperature is 280 ° C. or more. A PET resin is desirable.
That is, when the intrinsic viscosity, the maximum peak temperature in the maximum abundance ratio of the melting point distribution, and the maximum melting point end temperature are lower than the above ranges, low molecular weight components such as acetaldehyde and oligomers such as cyclic trimers are obtained by solid phase polymerization. It is not sufficiently reduced, and it is difficult to reduce these even by subsequent processing, and it becomes difficult to obtain a preform that is sufficiently satisfactory in terms of transparency and the like. Moreover, there is a possibility that the copolymer component is contained in a large amount, and there is a possibility that excellent heat resistance cannot be obtained.

In general, the synthesis of PET resin is a method of directly reacting high-purity terephthalic acid (TPA) and ethylene glycol (EG) to synthesize polyethylene terephthalate (PET), which is usually divided into two steps. ) It comprises a step of synthesizing bis-β-hydroxyethyl terephthalate (BHT) oligomer by reacting TPA and EG, and (B) a step of performing polycondensation by distilling off ethylene glycol from the BHT oligomer.

The synthesis of the BHT oligomer can be carried out under conditions known per se. For example, the amount of EG with respect to TPA is 1.0 to 1.5 mole times and heated to a temperature not lower than the boiling point of EG, for example, 240 to 280 ° C. Esterification is performed while distilling water out of the system under a pressure of 1 to 5 kg / cm ² . In this case, since TPA itself becomes a catalyst, a catalyst is usually not necessary, but a known esterification catalyst can also be used.

In the second stage polycondensation step, a known polycondensation catalyst is added to the BHT oligomer obtained in the first stage, and then the pressure is gradually reduced while maintaining the reaction system at 260 to 290 ° C. The mixture is stirred under reduced pressure of 1 to 3 mmHg, and the reaction is allowed to proceed while distilling the produced EG out of the system. The molecular weight is detected based on the viscosity of the reaction system. When the molecular weight reaches a predetermined value, it is discharged out of the system to form a chip after cooling.
As the polycondensation catalyst, conventionally known catalysts such as a germanium compound, a titanium compound, an antimony compound, and an aluminum compound can be used, but it is particularly preferable to use a titanium compound.

Polyesters obtained by melt polymerization generally have an intrinsic viscosity of 0.5 to 0.75 dl / g. Next, the polyester is pelletized to perform solid phase polymerization. Prior to solid phase polymerization, the pellets can be heated to the crystallization temperature of the polyester to cause precrystallization of the polyester.
As the polyester crystallizes, the cyclic trimer contained inside protrudes to the outside, and the cyclic trimer content decreases. In general, the crystallization is suitably performed in the range of 160 to 200 ° C., and the treatment time is suitably 2 to 240 minutes. The heat treatment for crystallization of the polyester pellets can be performed in a fluidized bed or a fixed bed using a heated inert gas such as heated nitrogen gas, or can be performed in a vacuum heating furnace. After precrystallization, the pellets are dried and preheated at a temperature of 180 to 220 ° C. for 30 to 240 minutes, and then subjected to solid phase polymerization.

In the case of solid-phase polymerization, unlike the case of melt polymerization, the cyclic trimer content decreases as the intrinsic viscosity increases. In general, the cyclic trimer content decreases with increasing solid phase polymerization temperature, and the cyclic trimer content decreases with increasing polymerization time. In general, the solid-phase polymerization is desirably performed at a temperature of 200 to 230 ° C. for 8 to 20 hours.
As described above, the intrinsic viscosity of the PET resin obtained by solid phase polymerization is 0.82 dL / g or more, and particularly preferably in the range of 0.83 to 1.0 dl / g. The cyclic trimer content is preferably 0.3 to 0.6 wt% and the acetaldehyde concentration is preferably 1 ppm or less.
Further, the PET resin obtained by solid phase polymerization preferably has a terminal carboxyl group concentration in the range of 15 to 50 eq / ton, particularly 20 to 45 eq / ton. When the terminal carboxyl group concentration is lower than the above range, the intrinsic viscosity cannot be efficiently reduced by the subsequent hydrolysis treatment, whereas when the terminal carboxyl group concentration is higher than the above range, the terminal decomposition is caused. This is not preferable because by-products such as acetaldehyde may be generated.
In order to adjust the terminal carboxyl group concentration within the above range, the terminal carboxyl group concentration can be increased by bringing the EG / TPA ratio (molar ratio) close to 1 in the charge amount in the melt polymerization, and conversely the EG / TPA ratio. By making the value larger than 1, the terminal carboxyl group concentration can be reduced.

In the present invention, the PET resin obtained by solid phase polymerization is subjected to a hydrolysis treatment, so that the intrinsic viscosity is 0.70 to 0.81 dL / g and the molecular weight distribution near the pellet surface is 3 in the pellet state. And a PET resin having a melting point distribution with a maximum melting point end temperature of 280 ° C. or lower.

The hydrolysis treatment is performed by bringing the solid phase polymerization PET pellets into contact with water and hydrolyzing the surface of the solid phase polymerization PET pellets. Specific treatment conditions are pellets, an intrinsic viscosity of 0.70 to 0.81 dL / g, a molecular weight distribution near the pellet surface of 3.2 or more, and a maximum melting point end temperature of the melting point distribution of 280 ° C. or less. Although it is not limited to this as long as it can be prepared as a PET resin, the solid phase polymerization PET pellets are immersed in hot water at 100 to 160 ° C., preferably 120 to 150 ° C. for 1 to 8 hours. It is desirable to do by. Specifically, solid phase polymerization PET pellets are immersed using a water source composed of one or more of tap water, industrial water, and pure water, and predetermined using a heat treatment apparatus such as an autoclave or a retort kettle. After the time treatment, it is returned to a state under atmospheric pressure and subjected to a normal drying process.

After the hydrolysis treatment, the pellets are dehydrated and then dried at a temperature of 80 to 180 ° C. for 0.1 to 24 hours, so that the intrinsic viscosity is 0.70 to 0.00 in the above-described pellet state. The PET resin of the present invention is prepared with 81 dL / g, a molecular weight distribution near the pellet surface of 3.2 or more, and a maximum melting point end temperature of the melting point distribution of 280 ° C. or less.
The PET resin of the present invention is not limited to this, but has a glass transition point (Tg) of 50 to 90 ° C., particularly 55 to 80 ° C., and a melting point (Tm) of 200 to 275 ° C., particularly 220. It is preferable to be at 270 ° C.

(Molded body)
The PET resin of the present invention can be suitably used for bottle molding by direct blow molding, biaxial stretch blow molding or the like, or cup or tray molding by vacuum molding, pressure molding, stretch molding, plug assist molding, or the like. .
Since the PET resin of the present invention can impart excellent heat resistance, it can be suitably used for the production of heat resistant containers. For example, in biaxial stretch blow molding, a preform is used to prevent thermal deformation of the container mouth. In order to prevent thermal deformation and shrinkage deformation of the volume even in thermoforming such as direct blow molding and vacuum forming, or by heat crystallization of the mouth of the film, or after heat forming after stretch forming Although heat setting (heat setting) is performed after the container is molded, it can be efficiently molded by using the PET resin according to the present invention.
The molded product obtained by using the PET resin of the present invention is not only a final molded product such as a bottle, a cup, or a tray, but also a sheet, a blank, a biaxially stretched blow bottle when the container is a cup, a tray, for example. In some cases, precursors such as preforms are included, and these have an acetaldehyde concentration reduced to less than 10 ppm, and are excellent in flavor properties.

When molding a molded body such as a preform or a bottle using the PET resin of the present invention, not only the PET resin of the present invention is used alone, but also solid-phase polymerization PET can be blended and used. In this case, the amount of the PET resin of the present invention is desirably 5% by weight or more.

(Measuring method)
[Intrinsic viscosity (IV)]
0.3000 g of pellets dried at 150 ° C. for 4 hours was weighed. To this, 30 ml of a mixed solvent of 1,1,2,2-tetrachloroethane and phenol (weight ratio 1/1) was added and stirred at 120 ° C. for 20 minutes for complete dissolution. The solution after dissolution was cooled to room temperature, and the intrinsic viscosity was determined using a relative viscometer (Viscotek, Y501) whose temperature was adjusted to 25 ° C.

[Measurement of molecular weight distribution]
The weight ratio of 1,1,1,3,3,3-hexafluoro-2-propanol (manufactured by Central Glass Co., Ltd.) and chloroform (for high performance liquid chromatograph: manufactured by Kishida Chemical Co., Ltd.) is 50 : A 50 mg mixed solvent completely dissolves a 3 mg sample cut from the surface of a pellet of polyethylene terephthalate resin, and then uses gel permeation chromatography (GPC; Integrated System For) equipped with light scattering and a differential refractometer as a detector. The molecular weight distribution (Mw / Mn) was measured using GPC / SEC: Asahi Techneion Co., Ltd., Triple Detector Module TriSEC Model 302: Viscotek).

[Measurement of pellet density]
Make a 1.400 g / ml solution using n-heptane and carbon tetrachloride in a 1000 ml graduated cylinder and place 50 g of pellets in it. Carbon tetrachloride is added to this solution to adjust the density to 0.001 g / ml. Collect pellets floating after standing after density adjustment. Density adjustment by adding carbon tetrachloride and collection of pellets were repeated, and pellets of each density were collected. The density distribution curve of the pellet was obtained by counting the collected pellets, and the pellet having the maximum density in the density distribution curve was determined.

[Measurement of melting point and end of melting temperature]
About the sample (8 mg) of the pellet which the density in a density distribution curve becomes the maximum value, DSC measurement was performed using the differential scanning calorimeter (DSC7 by PERKIN ELMER). The sample was used by cutting from the pellet cut surface and the pellet surface of the side portion.
The sample temperature is
1. Hold at 20 ° C. for 3 minutes 2. Scan the temperature from 2.20 ° C. to 300 ° C. in the order of 30 ° C./min. did. When a plurality of melting peaks appeared, the first peak was taken as the melting point.

[DEG amount]
The freeze-pulverized pellet was dissolved in a mixed solvent of deuterated trifluoroacetic acid / deuterated chloroform (1/1) (weight ratio), and 1H-NMR spectrum was measured with an NMR apparatus (EX270: JEOL Datum Co., Ltd.). Of the obtained spectrum, the content ratio of DEG was calculated from the ratio of the integrated values of the peaks derived from the DEG site (4.27 ppm) and the terephthalic acid site (8.22 ppm).

(Evaluation methods)
[Preform molding]
A polyester resin dried at 150 ° C. for 4 hours was supplied to a hopper, and a 28 g 500 ml heat-resistant preform was prepared using an injection molding machine set to a predetermined molding temperature. At this time, the mold temperature was set to 20 ° C., and the molding cycle was set to 30 seconds. The temperature of the injection machine and the hot runner was set to the same temperature, and this temperature was used as the molding temperature. 290 ° C. is a standard molding temperature.

[Evaluation of whitening of preforms]
The preform created above was seen through the light, and the whitening state around the trunk and the gate was observed. The case where the preform was entirely whitened was evaluated as “×”, the case where it was partially whitened as “Δ”, and the case where there was no whitening as “◯”.

[Acetaldehyde content]
1.0 g of the crushed sample of the preform crushed by the freeze pulverizer was weighed into a glass bottle, and 5 ml of pure water was added and sealed. The suspension was heated in an oven adjusted to a temperature of 120 ° C. for 60 minutes and then cooled in ice water. 3.0 ml of the supernatant of the suspension was collected, and 0.6 ml of a 2,4-dinitrophenylhydrazine / phosphoric acid solution having a concentration of 0.1% was added thereto, and the mixture was allowed to stand for 30 minutes. The supernatant after standing was filtered through a membrane filter having a pore diameter of 0.45 μm, and the filtrate was measured by high performance liquid chromatography. At the same time, a standard solution of acetaldehyde was measured, and the content in the preform was calculated from the obtained calibration curve.

[Heat-resistant]
Using a preform crystallized at the mouth using a heat crystallization apparatus, biaxial stretch blow molding is performed at 150 ° C. for 0.7 seconds by a one-stage blow molding method, and a full capacity of 520 ml Ten heat-resistant PET bottles were prepared. The produced bottle was stored in a constant temperature and humidity box at 30 ° C. and 80% for 7 days. Ten bottles were filled with 87 ° C. hot water so that the head space was 15 ml, and the caps were closed. Thereafter, it was laid down for 1 minute, erected for 4 minutes, then passed through a shower at 77 ° C. for 5 minutes and cooled with 20 ° C. water. The bottles were observed for unevenness on the 6 sides of the bottle. “○” when there was no unevenness, “△” when there was unevenness that did not impair the product value within 2 surfaces, and 3 or more unevenness occurred. The evaluation of the case was “x”.

[Hydrolysis]
Using an autoclave, the hydrolysis treatment was performed at 150 ° C. for the time described in each example and comparative example.
The hydrolysis treatment conditions were as follows.
1. Heat treatment was started from a liquid temperature of 20 ° C.
2. After 15 minutes, time proportional control was performed so that the liquid temperature became the set temperature and the predetermined pressure.
3. After the set time treatment, the liquid temperature was controlled to 20 ° C. and the internal pressure to atmospheric pressure in 15 minutes.

Example 1
Polyethylene terephthalate having IV of 0.85 dL / g, molecular weight distribution Mw / Mn = 3.1, maximum peak temperature of 255 ° C., maximum melting point end temperature of 292 ° C. and DEG of 1.2 mol% is hydrolyzed using an autoclave. This was carried out for 120 minutes to obtain polyethylene terephthalate having IV = 0.78 dL / g, Mw / Mn = 3.4, and a maximum melting point end temperature of 277 ° C.
After cooling the pellet with cold water, the pellet was sufficiently drained and dried at 150 ° C. for 4 hours. The dried pellets were preformed at a molding temperature of 290 ° C. The whitening of the molded preform was observed and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

(Example 2)
The treatment was conducted in the same manner as in Example 1 except that the hydrolysis time was 60 minutes to obtain polyethylene terephthalate having IV = 0.81 dL / g, Mw / Mn = 3.2, and a maximum melting point end temperature of 280 ° C.
The dried pellets were preformed at a molding temperature of 290 ° C. in the same manner as in Example 1. The whitening of the molded preform was observed and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

(Example 3)
The same treatment as in Example 1 was carried out except that the hydrolysis time was 210 minutes, to obtain polyethylene terephthalate having IV = 0.71 dL / g, Mw / Mn = 3.8, and a maximum melting point end temperature of 272 ° C.
The dried pellets were preformed at a molding temperature of 290 ° C. in the same manner as in Example 1. The whitening of the molded preform was observed and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

(Example 4)
Hydrolysis treatment was carried out in Example 1, and the obtained pellets of IV = 0.78 dL / g, Mw / Mn = 3.4, maximum melting point end temperature 277 ° C. were formed at a molding temperature of 280 ° C. Except for the preform molding, whitening of the preform molded in the same manner as in Example 1 was observed, and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

(Example 5)
Polyethylene terephthalate having an IV of 0.85 dL / g, a molecular weight distribution Mw / Mn = 3.1, a maximum peak temperature of 256 ° C., a maximum melting point end temperature of 285 ° C., and a DEG of 2.1 mol% is hydrolyzed using an autoclave. This was carried out for 120 minutes to obtain polyethylene terephthalate having IV = 0.78 dL / g, Mw / Mn = 3.4, and a maximum melting point end temperature of 274 ° C.
After cooling the pellet with cold water, the pellet was sufficiently drained and dried at 150 ° C. for 4 hours. The dried pellets were preformed at a molding temperature of 290 ° C. The whitening of the molded preform was observed and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

(Example 6)
Polyethylene terephthalate having IV of 0.82 dL / g, molecular weight distribution Mw / Mn = 2.9, maximum peak temperature 245 ° C., maximum melting point end temperature 280 ° C. and DEG 1.8 mol% is hydrolyzed using an autoclave. This was carried out for 60 minutes to obtain polyethylene terephthalate having IV = 0.77 dL / g, Mw / Mn = 3.2, and a maximum melting point end temperature of 277 ° C.
After cooling the pellet with cold water, the pellet was sufficiently drained and dried at 150 ° C. for 4 hours. The dried pellets were preformed at a molding temperature of 290 ° C. The whitening of the molded preform was observed and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

(Comparative Example 1)
Polyethylene terephthalate having an IV of 0.85 dL / g, a molecular weight distribution Mw / Mn = 3.1, a maximum peak temperature of 255 ° C., a maximum melting point end temperature of 292 ° C., and a DEG of 1.2 mol% used in Example 1, Used without hydrolysis.
The pellet was dried at 150 ° C. for 4 hours. The dried pellets were preformed at a molding temperature of 290 ° C. The whitening of the molded preform was observed and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

(Comparative Example 2)
As in Comparative Example 1, the resin used in Example 1 was used without being subjected to hydrolysis treatment.
The pellet was dried at 150 ° C. for 4 hours. The dried pellets were preformed at a molding temperature of 300 ° C. The whitening of the molded preform was observed and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

(Comparative Example 3)
The treatment was conducted in the same manner as in Example 1 except that the hydrolysis time was 45 minutes to obtain polyethylene terephthalate having IV = 0.82 dL / g, Mw / Mn = 3.2, and a maximum melting point end temperature of 281 ° C.
The dried pellets were preformed at a molding temperature of 290 ° C. in the same manner as in Example 1. The whitening of the molded preform was observed and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

(Comparative Example 4)
The same treatment as in Example 1 was carried out except that the hydrolysis time was 240 minutes, to obtain polyethylene terephthalate having IV = 0.82 dL / g, Mw / Mn = 3.2, and a maximum melting point end temperature of 281 ° C.
The dried pellets were preformed at a molding temperature of 290 ° C. in the same manner as in Example 1. The whitening of the molded preform was observed and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

(Comparative Example 5)
Polyethylene terephthalate having an IV of 0.85 dL / g, a molecular weight distribution Mw / Mn = 3.1, a maximum peak temperature of 256 ° C., a maximum melting point end temperature of 285 ° C., and a DEG of 2.1 mol% used in Example 5, Used without hydrolysis.
The pellet was dried at 150 ° C. for 4 hours. The dried pellets were preformed at a molding temperature of 290 ° C. The whitening of the molded preform was observed and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

(Comparative Example 6)
Polyethylene terephthalate having an IV of 0.82 dL / g, a molecular weight distribution Mw / Mn = 2.9, a maximum peak temperature of 245 ° C., a maximum melting point end temperature of 280 ° C., and a DEG of 1.8 mol% used in Example 6. Used without hydrolysis.
The pellet was dried at 150 ° C. for 4 hours. The dried pellets were preformed at a molding temperature of 290 ° C. The whitening of the molded preform was observed and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

(Comparative Example 7)
The treatment was conducted in the same manner as in Example 6 except that the hydrolysis time was 30 minutes to obtain polyethylene terephthalate having IV = 0.79 dL / g, Mw / Mn = 3.1, and a maximum melting point end temperature of 279 ° C.
The dried pellets were preformed at a molding temperature of 290 ° C. in the same manner as in Example 1. The whitening of the molded preform was observed and the AA concentration was measured. Moreover, after producing a bottle, heat resistance evaluation was performed.

The PET resin of the present invention has excellent meltability as compared with conventional solid-phase polymerized PET while maintaining the excellent properties of solid-phase polymerized PET. It can be suitably used for packaging containers such as cups and trays.
In addition, the PET resin of the present invention is excellent in heat resistance and can be suitably used for molding a heat-resistant container because strain at the time of stretching can be reduced due to excellent shapeability.
Further, the content of acetaldehyde is 10 ppm or less, and the flavor property is excellent, and it can be suitably used as an aseptic container as well as a heat resistant container.

Claims

Polyester resin mainly composed of ethylene terephthalate units, in the pellet state, the intrinsic viscosity is 0.70 to 0.81 dL / g, the molecular weight distribution near the pellet surface is 3.2 or more, and the maximum melting point of the melting point distribution An ethylene terephthalate polyester resin having an end temperature of 280 ° C. or lower.
The ethylene terephthalate polyester resin according to claim 1, wherein the content of diethylene glycol is less than 2.0 mol%.
A molded article characterized in that the acetaldehyde concentration of the ethylene terephthalate-based polyester resin according to claim 1 or 2 is less than 10 ppm.
An ethylene terephthalate-based polyester resin having an intrinsic viscosity of 0.82 dL / g or more, a maximum peak temperature in a maximum abundance ratio of a melting point distribution of 245 ° C. or more and a maximum melting point end temperature of 281 ° C. or more is hydrolyzed A process for producing an ethylene terephthalate-based polyester resin.