JPH11181064A - Polyester resin, sheetlike material, blow molded product and oriented film comprising the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject resin excellent in transparency, gas barrier properties, heat resistance, mechanical characteristics and aroma retaining properties and useful as containers, etc., for foods, etc., by specifying the contents of acetic acid and formic acid. SOLUTION: This polyester resin comprises a main recurring unit composed of ethylene terephthalate and has <=50 ppb content of acetic acid, <=50 ppb content of formic acid and preferably >=0.65 dL/g intrinsic viscosity, >=1.37 g/cm<3> density, <=20 ppm content of free ethylene glycol, <=50 ppm content of (a) free monohydroxyethyl terephthalate, <=70 ppm content of (b) free bishydroxyethyl terephthalate, <=100 ppm sum total of the content of the component (a) and the content of the component (b) and <=200 ppm content of free bishydroxyethyl terephthalate dimer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester resin which is excellent in transparency, gas barrier properties, heat resistance, mechanical properties and fragrance retention and can be advantageously used as a container or packaging material for food or beverages. It is.

[0002]

2. Description of the Related Art Polyethylene terephthalate resin is used as a material for containers of carbonated beverages, juices, mineral water, etc. due to its excellent transparency, mechanical strength, heat resistance, gas barrier properties and the like. Have been. However, a polyester resin containing ethylene terephthalate as a main repeating unit contains a by-product acetaldehyde. When the content of acetaldehyde in the polyester resin is large, the content of acetaldehyde in the material of a container or other packaging formed therefrom also increases, which affects the flavor and odor of the beverage or the like filled in the container or the like. Therefore, various measures have conventionally been taken to reduce the acetaldehyde content in the polyester resin.

[0003] In recent years, containers made of polyester resin, mainly polyethylene terephthalate, have come to be used as containers for low-flavor beverages, such as mineral water and Wurong tea. In the case of such beverages, these beverages are generally heat-filled or sterilized by heating after filling, but the reduction of the acetaldehyde content of the beverage container alone may not improve the flavor and odor of these contents. I understand. In addition, for metal cans for beverages, for the purpose of process simplification, hygiene, pollution prevention, and the like, cans are manufactured using a metal plate whose inner surface is coated with a polyester film having ethylene terephthalate as a main repeating unit. The method of doing it has been adopted. Also in this case, the contents are heat-sterilized at a high temperature after filling, and it has been found that the flavor and odor of the contents are not improved even if a film having a low acetaldehyde content is used.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and is excellent in transparency, gas barrier properties, heat resistance, mechanical properties and fragrance retention, and Another object is to provide a polyester resin that can be advantageously used as a container or packaging material for beverages and the like.

[0005]

Means for Solving the Problems The present inventors have assiduously studied in view of the above problems, and have reached the present invention. To achieve the above object, the polyester resin whose main repeating unit is composed of ethylene terephthalate is a polyester resin having an acetic acid content of 50 ppb or less and a formic acid content of 50 ppb or less. The polyester resin of the present invention has an intrinsic viscosity of 0.65 dl / g.
As described above, the density is 1.37 g / cm ³ or more, the acetic acid content is 50 ppb or less, the formic acid content is 50 ppb or less, the free ethylene glycol content is 20 ppm or less, and the free monohydroxyethyl terephthalate content is 70 ppm. Hereinafter, the content of free bishydroxyethyl terephthalate is 100 ppm or less, the total of free monohydroxyethyl terephthalate content and free bishydroxyethyl terephthalate content is 150 ppm or less, and free bishydroxyethyl terephthalate. Tartrate dimer content is 350p
pm or less.

Further, the polyester resin of the present invention preferably has an acetaldehyde content of 10 ppm or less and a formaldehyde content of 7 ppm or less. The polyester resin of the present invention preferably has a cyclic trimer content of 0.5% by weight or less. Further, in the polyester resin of the present invention, the amount of copolymerized diethylene glycol is preferably from 1.0 to 5.0 mol% of the glycol component. The polyester resin having the above-mentioned properties provides a hollow molded article, a sheet-like material or a stretched film having excellent transparency, heat resistance, mechanical properties and fragrance retention, and a container or a packaging material therefrom.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The polyester resin having a main repeating unit composed of ethylene terephthalate of the present invention is a linear polyester resin containing 85 mol% or more of ethylene terephthalate units, preferably 90 mol% or more, more preferably. Is a linear polyester resin containing 95 mol% or more.

The dicarboxylic acids used for the copolymerization of the polyester resin include aromatic acids such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl-4,4'-dicarboxylic acid and diphenoxyethanedicarboxylic acid. Dicarboxylic acids and their functional derivatives, p-oxybenzoic acid, oxyacids such as oxycaproic acid and their functional derivatives, adipic acid, sebacic acid, succinic acid, aliphatic dicarboxylic acids such as glutaric acid and their functional derivatives, Alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid and functional derivatives thereof;

Glycols used for copolymerization of the polyester resin include aliphatic glycols such as diethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, and cyclohexanediol. Examples thereof include alicyclic glycols such as methanol, aromatic glycols such as bisphenol A and alkylene oxide adducts of bisphenol A. Further, examples of other copolymerization components comprising a polyfunctional compound in the polyester resin include trimellitic acid and pyromellitic acid as acid components, and glycerin and pentaerythritol as glycol components. be able to. The amount of the above-mentioned copolymer component to be used must be such that the polyester resin maintains a substantially linear shape.

The intrinsic viscosity of the polyester resin of the present invention is 0.55 to 1.30 dl / g, preferably 0.60 to dl / g.
1.20 dl / g, more preferably 0.65 to 0.9
The range is 0 dl / g. At 0.55 dl / g or less,
The mechanical properties of the obtained molded article are poor. Also, 1.30
When the dl / g exceeds dl / g, the resin temperature rises during melting by a molding machine or the like, and thermal decomposition becomes severe, so that free low-molecular-weight compounds that affect fragrance retention increase or the molded product is colored yellow. And other problems occur.

The polyester resin of the present invention is a polyester resin having an acetic acid content of 50 ppb or less and a formic acid content of 50 ppb or less. The acetic acid content is preferably 30 ppb or less, more preferably 10 ppb.
And the formic acid content is preferably 30 ppb or less, more preferably 10 ppb or less. Both the acetic acid content and the formic acid content of the polyester resin are 50 p
If it exceeds pb, the flavor and aroma of the contents in a container or the like obtained from this polyester resin will be very poor.
These free low molecular weight compounds are eluted in the contents from the material such as a container made of polyester resin, though in a trace amount,
As a result, it is considered that the flavor of the contents is affected.

The polyester resin of the present invention has an intrinsic viscosity of 0.65 dl / g or more, preferably 0.68 dl / g.
/ G or more, more preferably 0.70 dl / g or more, and a density of 1.37 g / cm ³ or more, preferably 1.38 g / cm3.
cm ³ or more, more preferably 1.39 g / cm ³ or more, within the content of acetic acid and formic acid are given above and free Echirenguko - Le is 20ppm or less, preferably 10
ppm or less, more preferably 5 ppm or less, free monohydroxyethyl terephthalate is 50 ppm or less, preferably 30 ppm or less, more preferably 10 ppm or less, and free bishydroxyethyl terephthalate is 70 ppm or less.
ppm or less, preferably 50 ppm or less, more preferably 30 ppm or less, and the total of free monohydroxyethyl terephthalate and free bishydroxyethyl terephthalate is 100 ppm or less, preferably 70 ppm or less,
More preferably 40 ppm or less, and free bishydroxyethyl terephthalate dimer content of 200 ppm
The polyester resin has a content of preferably 100 ppm or less, more preferably 75 ppm or less. When this polyester resin is used for a packaging material, the flavor and the like of the contents are further improved.

The acetaldehyde content of the polyester resin of the present invention is 10 ppm or less, preferably 5 ppm.
The content is more preferably 3 ppm or less, and the formaldehyde content is 7 ppm or less, preferably 4 ppm or less, more preferably 2 ppm or less. Acetaldehyde content is 10 ppm or more, and formaldehyde content is 7 pp
In the case of m or more, the contents such as containers molded from the polyester resin have poor flavor and odor. The acetaldehyde content of the polyester resin of the present invention is 10 ppm
The method for reducing the formaldehyde content to 7 ppm or less is not particularly limited. For example, low-molecular-weight polyester resin is subjected to solid-state polymerization in a temperature range of 195 ° C. to 230 ° C. under reduced pressure or an inert gas atmosphere. Can be mentioned.

The amount of diethylene glycol in the polyester resin of the present invention is from 1.0 to 5.0 mol%, preferably from 1.3 to 4.5 mol%, more preferably from 1.5 to 5.0 mol% of the glycol component. 4.0 mol%. When the amount of diethylene glycol is 5.0 mol% or more, the thermal stability becomes poor,
It is not preferable because the molecular weight is greatly reduced during molding and the acetaldehyde content and the formaldehyde content are increased.

Further, the cyclic 3 of the polyester resin of the present invention
Content of the monomer is 0.50% by weight or less, preferably 0.4% by weight or less.
It is at most 5% by weight, more preferably at most 0.40% by weight. When a heat-resistant hollow molded article or the like is molded from the polyester resin of the present invention, heat treatment is performed in a heating mold. However, when the content of the cyclic trimer is 0.50% by weight or more, the heating mold is used. Oligomer attachment to the mold surface increases sharply,
The transparency of the obtained hollow molded article or the like is extremely deteriorated.

The above polyester resin can be produced by a conventionally known production method. That is, it is produced by a direct esterification method in which terephthalic acid and ethylene glycol and / or the third component are directly reacted to esterify while distilling off water, and then subjected to polycondensation under reduced pressure. . Further, solid-state polymerization may be performed to increase the intrinsic viscosity and decrease the acetaldehyde content and the like. The melt polycondensation reaction may be performed in a batch reactor or a continuous reactor. In any of these methods, the melt polycondensation reaction may be performed in one step or may be performed in multiple steps. The solid-state polymerization reaction can be performed in a batch-type apparatus or a continuous-type apparatus as in the melt polycondensation reaction. Melt polycondensation and solid phase polymerization may be performed continuously,
It may be performed in a divided manner.

The polyester resin of the present invention can be produced, for example, by the following method. In other words, melt polycondensation is carried out at a temperature as low as possible in a short time, and after the completion of the melt polycondensation, it is kept in a molten state at a temperature as low as possible and for a short time until it is extruded from the pores to form chips. rear,
Extruded from the pores under a nitrogen atmosphere to form chips. This chip is then subjected to solid-phase polymerization, but it is preferable to carry out the subsequent steps, that is, transporting to the solid-state polymerization step, crystallization, solid-state polymerization, etc., all in a nitrogen atmosphere. The oxygen concentration in the nitrogen used is 20 ppm or less, preferably 10 ppm or less, more preferably 5 ppm or less. It is also desirable to take measures to minimize the content of impurities other than oxygen in nitrogen used during solid phase polymerization.
For example, there is a method in which a solid is completely removed from nitrogen recovered from the solid-phase polymerization step, purification is sufficiently performed, and the resultant is supplied to a solid-phase polymerization vessel together with fresh nitrogen. It is particularly preferable to use fresh nitrogen for all of the nitrogen used in the solid phase polymerization.

As a method for obtaining the polyester resin of the present invention, in addition to the above-mentioned chip formation in a nitrogen atmosphere, a treatment with water, steam, or the like before and / or after the solid-phase polymerization is carried out. It is effective to dry the chips after increasing the moisture content of the chips. As a method of water treatment,
There are a method of immersing in water and a method of applying water on a chip in a shower. The treatment time is 5 minutes to 2 days, preferably 10 minutes to 1 day, more preferably 30 minutes to 10 days.
In time, the temperature of the water is 20 ° C-180 ° C, preferably 40 ° C-150 ° C, more preferably 50 ° C-120 ° C.
° C. The time for the treatment with steam is 5 minutes to 7 days, preferably 10 minutes to 5 days, more preferably 30 minutes to 5 days.
Min-3 days, the steam temperature is 10 ° C.-200
° C, preferably 20 ° C-180 ° C, more preferably 3 ° C.
0 ° C-160 ° C. This water-containing treatment may be performed under reduced pressure and increased pressure. Further, it is preferable that the water-containing treatment and the drying treatment are also performed in a nitrogen atmosphere. Further, it is effective to raise the water content of the chip to 0.05% or more, preferably 0.1% or more, and more preferably 0.2% or more.

The temperature of the polycondensation reaction is from 260 ° C. to 28
5 ° C. is preferable, and the degree of vacuum is 600 to 0.1 Torr. In the case of polycondensation in a batch apparatus, the final stage polycondensation reaction should be completed within 1.5 hours at 260 to 285 ° C and a reduced pressure of 5 to 0.1 Torr. When polycondensation is performed in a continuous apparatus, the final polycondensation reaction is 260 to 2
It is important that the reaction is completed within 2 hours at 85 ° C. and 5 to 0.1 Torr. Further, the holding conditions in the molten state after the completion of the melt polycondensation are as follows: 260 to 285 ° C. within 20 minutes,
It should preferably be within 10 minutes, more preferably within 5 minutes. Perform polycondensation at a high temperature of 285 ° C or higher,
When performing polycondensation for a long time of 2 hours or more, the content of the low molecular compound such as the above-mentioned free monomer becomes the above-mentioned limit or more, and the content of the packaging material from the obtained polyester resin is reduced. The flavor and smell are very bad.

In the case of the direct esterification method, compounds of Ge, Sb and Ti are used as a polycondensation catalyst, and a Ge compound is particularly advantageous. Examples of the Ge compound include amorphous germanium dioxide, crystalline germanium dioxide powder or a slurry of ethylene glycol, a solution of crystalline germanium dioxide dissolved in water by heating or a solution prepared by adding ethylene glycol to this solution and heating. In order to obtain the polyester resin of the present invention, it is particularly preferable to use a solution in which germanium dioxide is dissolved in water by heating or a solution in which ethylene glycol is added and heated. These polycondensation catalysts can be added during the esterification step, and it is particularly preferable to add them at an early stage of the esterification step to obtain the polyester resin of the present invention. When a Ge compound is used, the amount of Ge compound used is 20 to 150 ppm, preferably 23 to 100 ppm, more preferably 25 to 7 ppm as the amount of Ge remaining in the polyester resin.
It is 0 ppm.

As the stabilizer, it is preferable to use phosphoric acid, phosphoric acid esters such as polyphosphoric acid and trimethyl phosphate in an amount of 10 to 100 ppm as the amount of residual P metal in the polyester resin. These stabilizers can be added during the esterification reaction step from a terephthalic acid / ethylene glycol slurry blending tank. Particularly, to obtain the polyester resin of the present invention, the slurry blending tank and the middle stage of the esterification reaction are required. It is preferable to add them by no more.

In order to control the DEG content, a basic compound such as triethylamine, tri-
A tertiary amine such as n-butylamine and a quaternary ammonium salt such as tetraethylammonium hydroxide can be added. In addition, a coloring agent, an ultraviolet absorber, an antioxidant, an antistatic agent, a lubricant, a nucleating agent, a release agent, and the like may be added to the polyester resin of the present invention as necessary, as long as the object of the present invention is not impaired. Can be. The polyester resin of the present invention can be preferably used as a hollow molding container, a tray, a packaging material such as a biaxially stretched film, a film for covering a metal can, and the like.

[0023]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples. The method for measuring the main characteristic values will be described below.

1) Intrinsic viscosity (hereinafter referred to as “IV”) of a polyester resin (hereinafter referred to as “PET resin”)
1,2,2-tetrachloroethane / phenol (2: 3
Weight ratio) It was determined from the solution viscosity at 30 ° C. in a mixed solvent.

2) Diethylene glycol content (hereinafter referred to as [D
It was decomposed by methanol, and the amount of DEG was determined by gas chromatography, and expressed as a ratio (mol%) to the total glycol components.

3) Free ethylene glycol content (hereinafter referred to as "EG content") A resin pellet sample was treated with hexafluoroisopropanol /
Dissolve in the chloroform mixture and then homogenize by adding water. EG of the solution obtained by filtering the aqueous phase was determined by gas chromatography.

4) Content of low molecular compounds such as free monomer Resin pellet samples were prepared by using hexafluoroisopropanol /
Dissolve in chloroform mixed solution, further add chloroform and dilute. After adding methanol to precipitate a polymer, the mixture is filtered. The filtrate was evaporated to dryness, made up to a constant volume with dimethylformamide, and quantified by liquid chromatography.

5) Acetaldehyde content (hereinafter referred to as "AA content") A resin pellet sample / distilled water = 1 g / 2 ml was put into a glass ampoule purged with nitrogen, and the upper portion was sealed and heated at 160.degree.
After extraction for a while, acetaldehyde in the extract after cooling was measured by high-sensitivity gas chromatography, and the concentration was determined as pp.
Indicated by m.

6) Formaldehyde content (hereinafter referred to as "FA content") 1 g of a resin pellet sample was put into a glass ampoule together with 2 ml of distilled water, and after replacing with nitrogen, the upper portion was sealed and heated at 160 ° C.
Heated for hours. After cooling, cyclohexane-1,3-
It is converted to a fluorescent derivative with dione and measured by liquid chromatography to determine FA. For details, see Analytical Chemistry, Vol. 3
4, p. 314 (1985).

7) Cyclic trimer content of PET resin A resin pellet sample was prepared by using hexafluoroisopropanol /
Dissolve in chloroform mixed solution, further add chloroform and dilute. After adding methanol to precipitate a polymer, the mixture is filtered. The filtrate was evaporated to dryness, made up to volume with dimethylformamide, and quantified by liquid chromatography.

8) Acetic acid content and formic acid content of PET resin 2 g of resin pellets are put into a glass container, 500 ml of boiling ion-exchanged water is poured, left tight for 10 minutes, cooled to room temperature, and left for 1 day. Quantification was performed by ion chromatography using 1 ml of this liquid.

9) Density: 25 using a density gradient tube of a mixed solvent of carbon tetrachloride / n-heptane.
Measured in ° C.

10) Sensory test A parison is injection-molded at a polymer temperature of 275 ° C. using a 50T type stretch blow molding machine manufactured by Nissei ASB Machine Co., Ltd., and then stretch blown to form a 1.5 L hollow. A molded container was molded. However, the PET resin was dried under nitrogen (oxygen concentration 2 ppm or less), put in a hopper filled with the same nitrogen, and subjected to molding. The body of the container was cut into sections of about 5 mm × 20 mm, and about 100 g of the sections were placed in a 2 L glass container, and 1.5 L of boiling ion-exchanged water was placed therein.
After leaving it at 0 ° C. for 1 day, it was left at 25 ° C. for 1 month, and after opening, tests such as flavor and odor were conducted. As a blank for comparison,
Only ion-exchanged water was placed in a glass container and used in the same manner as in the previous period. The sensory test was carried out by 10 panelists according to the following criteria and compared with the average value. 0: No off-flavor or smell is felt. 1: A slight difference from the blank is felt. 2: Feel the difference from the blank. 3: A considerable difference from the blank is felt. 4: A very large difference from the blank is felt.

Example 1 A PET resin was produced by a continuous polymerization facility in the following manner. A slurry of 865 parts by weight of high-purity terephthalic acid / hour and 580 parts by weight of ethylene glycol is continuously supplied to the first esterification reactor containing the reactants in advance, and the slurry is stirred for about 250 minutes. ° C, 0.
The reaction was carried out at 5 kg / cm ² G for an average residence time of 3 hours.
Further, a catalyst solution obtained by heating and dissolving crystalline germanium dioxide in water, adding ethylene glycol thereto, and heat-treating the solution.
And a solution of phosphoric acid in ethylene glycol
It was continuously fed to the esterification reactor. The reaction was sent to a second esterification reactor and stirred at about 260 ° C.
The reaction was performed at 0.05 kg / cm ² G up to a predetermined reactivity. This esterification reaction product is continuously sent to the first polymerization reactor, and is stirred at about 265 ° C. and 25 torr for 1 hour, and then at about 265 ° C. for 3 tons with stirring in the second polymerization reactor.
orr for 1 hour and further with stirring in a third polymerization reactor for about 2 hours.
Polymerization was performed at 75 ° C. and 0.5 to 1 torr for 1 hour. The polymerization reaction product was sent to the pores at a retention time of about 275 ° C. within 5 minutes, extruded into strands and cut into chips while cooling with water. For cooling and cutting the strands, the oxygen concentration is 2pp
m under a nitrogen gas atmosphere. PET obtained
The IV of the resin was 0.54. This resin is subsequently crystallized at about 155 ° C. in a nitrogen atmosphere having an oxygen concentration of 2 ppm or less, and after preheating to about 200 ° C. in the same nitrogen atmosphere,
Nitrogen atmosphere (oxygen concentration 2pp
m) or less at about 205 ° C. Nitrogen sent to the solid-state polymerization process is about 1/3 of the nitrogen recovered from the solid-state polymerization process.
Was mixed with fresh nitrogen (oxygen concentration of 1 ppm or less). IV of the obtained PET resin is 0.74, D
The EG content was 2.5 mol%, the cyclic trimer content was 0.37% by weight, and the density was 1.399 g / cm ³ . Table 1 shows the results of analysis of acetic acid, formic acid, and the like. This resin was dried under a nitrogen atmosphere (oxygen concentration: 2 ppm or less), and a hollow molded container was obtained by the molding machine described above. Table 1 shows the results of the sensory test. It can be seen that the PET resin of the present invention provides a hollow molded container that does not change the taste of the contents.

Example 2 The temperature of the solid-state polymerization was changed to about 210 ° C.
A PET resin was produced under substantially the same reaction conditions as in Example 1 except that a gas mixed with fresh nitrogen was used.
The IV of the obtained PET resin was 0.73, the DEG content was 2.1 mol%, and the density was 1.402 g / cm ³ .
Table 1 shows the results of analysis of acetic acid, formic acid, and the like. This resin was dried under the same conditions as in Example 1 to obtain a container for hollow molding. Table 1 shows the results of the sensory test. It can be seen that the PET resin of the present invention provides a hollow molded container that does not change the taste of the contents.

(Example 3) Cooling and cutting of a melt-polymerized PET resin strand, storage of these resins, transportation to a solid-phase polymerization step, crystallization and other pre-solid-state polymerization steps were performed at an oxygen concentration of 1%.
The reaction was carried out under a nitrogen gas atmosphere of not more than 1 ppm, and the whole amount was replaced with fresh nitrogen (containing oxygen concentration of 1 pp) as a gas for solid phase polymerization.
m or less) and changing the solid-state polymerization temperature to about 210 ° C. under the same reaction conditions as in Example 1 with PET.
A resin was manufactured. IV of the obtained PET resin is 0.7
6, DEG content is 2.0 mol%, cyclic trimer content is
The density was 0.30% by weight and the density was 1.405 g / cm ³ . Table 1 shows the results of analysis of acetic acid, formic acid, and the like. This resin was dried under a nitrogen atmosphere (oxygen concentration: 1 ppm or less), and a hollow molded container was obtained using the molding machine described above. Table 1 shows the results of the sensory test. It can be seen that the PET resin of the present invention provides a hollow molded container that does not change the taste of the contents.

Example 4 A PET resin was manufactured under substantially the same conditions as in Example 1 except that the cooling and cutting of the melt-polymerized PET resin strand were performed in an air atmosphere.
The obtained PET resin had an IV of 0.73, a DEG content of 2.1 mol%, a cyclic trimer content of 0.39% by weight, and a density of 1.398 g / cm ³ . Table 1 shows the results of analysis of acetic acid, formic acid, and the like. This resin was dried under a nitrogen atmosphere (oxygen concentration: 2 ppm or less), and a hollow molded container was obtained using the molding machine described above. Table 1 shows the results of the sensory test. It can be seen that the PET resin of the present invention provides a hollow molded container that does not change the taste of the contents.

Example 5 Using a high-purity terephthalic acid and isophthalic acid in a quantitative ratio such that the content of isophthalic acid in the acid component of the obtained resin becomes 2% by weight, the temperature and melting temperature of the third polymerization reactor The residence temperature of the resin after polymerization is 270.
Polymerization was carried out under substantially the same conditions as in Example 2 except that the temperature and the solid phase polymerization temperature were changed to 203 ° C., to obtain a polyester resin in which isophthalic acid was copolymerized as an acid component at 2 mol%. PE obtained
The IV of the T resin was 0.74, the DEG content was 1.8 mol%, the cyclic trimer content was 0.35 wt%, and the density was 1.3.
97 g / cm ³ . Table 1 shows the results of analysis of acetic acid, formic acid, and the like. Put this resin in a nitrogen atmosphere (oxygen concentration 2ppm)
The mixture was dried under the following conditions), and a hollow molded container was obtained using the above molding machine. Table 1 shows the results of the sensory test. It can be seen that the PET resin of the present invention provides a hollow molded container that does not change the taste of the contents.

Example 6 Fifty kg of pellets obtained by performing melt polymerization in the same manner as in Example 1 were kept in a stainless steel tank at 30 ° C. and 95% relative humidity for 72 hours. The moisture content of the pellet was 0.43%. The pellets were pre-crystallized in a vacuum dryer at 160 ° C. for 2 hours, followed by solid phase polymerization at 205 ° C. under a reduced pressure of 0.05 mmHg for 16 hours. The humidity control and the preliminary crystallization were performed in a nitrogen atmosphere (oxygen concentration: 0.2 ppm), and the solid-phase polymerization was performed while blowing fresh nitrogen (oxygen concentration: 0.2 ppm) heated to 205 ° C. Thus, until the target PET pellets are finally obtained from the polymerization, exposure to an atmosphere in which the oxygen concentration exceeds 0.2 ppm is prevented. PE obtained
The T resin has an IV of 0.75, a DEG content of 2.5 mol%,
The cyclic trimer content is 0.35% by weight, and the density is 1.398 g.
/ Cm ³ . Table 1 shows the results of analysis of acetic acid, formic acid, and the like. This resin was dried under a nitrogen atmosphere (oxygen concentration: 2 ppm or less), and a hollow molded container was obtained by the molding machine described above. Table 1 shows the results of the sensory test. It can be seen that the PET resin of the present invention provides a hollow molded container that does not change the taste of the contents.

Example 7 50 kg of solid-phase-polymerized pellets obtained in the same manner as in Example 1 were passed through a stainless steel tank at 110 ° C. with steam at a rate of 3 kg / hour for 2 hours to perform a water-containing treatment. The water content of the pellets was 0.24%. Thereafter, vacuum drying was performed at 160 ° C. for 3 hours. The humidity control and the preliminary crystallization were performed under a nitrogen atmosphere (oxygen concentration 0.2
(ppm) until the target PET pellets were finally obtained from the polymerization, so as not to be exposed to an atmosphere having an oxygen concentration exceeding 0.2 ppm. The obtained PET resin had an IV of 0.74, a DEG content of 2.5 mol%, a cyclic trimer content of 0.30 wt%, and a density of 1.399 g / cm ^3.
Met. The results of analysis of acetic acid, formic acid and the like are shown in Table 2. This resin was dried under a nitrogen atmosphere (oxygen concentration: 2 ppm or less), and a hollow molded container was obtained by the molding machine described above. Table 2 shows the results of the sensory tests. It can be seen that the PET resin of the present invention provides a hollow molded container that does not change the taste of the contents.

(Example 8) 50 kg of pellets obtained by melt polymerization in the same manner as in Example 1 were immersed in water at 50 ° C in a stainless steel tank and held for 2 hours. The moisture content of the pellet was 0.3%. The pellets were pre-crystallized in a vacuum dryer at 160 ° C. for 2 hours.
Solid phase polymerization was carried out at a temperature of 0.05 ° C. and a reduced pressure of 0.05 mmHg for 16 hours.
The humidity control and the preliminary crystallization were performed under a nitrogen atmosphere (oxygen concentration: 0.1%).
2 ppm) and the solid-phase polymerization was performed while blowing in fresh nitrogen (oxygen concentration 0.2 ppm) heated to 205 ° C. Thus, until the target PET pellets are finally obtained from the polymerization, exposure to an atmosphere in which the oxygen concentration exceeds 0.2 ppm is prevented. The obtained PET resin had an IV of 0.75, a DEG content of 2.5 mol%, a cyclic trimer content of 0.33 wt%, and a density of 1.400 g / cm ^3.
Met. The results of analysis of acetic acid, formic acid and the like are shown in Table 2. This resin was dried under a nitrogen atmosphere (oxygen concentration: 2 ppm or less), and a hollow molded container was obtained by the molding machine described above. Table 2 shows the results of the sensory tests. It can be seen that the PET resin of the present invention provides a hollow molded container that does not change the taste of the contents.

(Embodiment 9) Obtained in the same manner as in Embodiment 1.
50 kg of pellets after solid phase polymerization
For 5 hours in water at 90 ° C. to perform a water-containing treatment. This page
The water content of the let was 0.44%. After this, 160 ° C
For 3 hours under vacuum. In addition, humidity control and pre-crystallization
Polymerization under nitrogen atmosphere (oxygen concentration 0.2ppm)
Until the desired PET pellets are finally obtained.
Avoid exposure to atmospheres with a temperature exceeding 0.2 ppm
I made it. IV of the obtained PET resin is 0.75, DEG
Content is 2.5 mol%, cyclic trimer content is 0.31 weight
%, Density 1.399 g / cm ^ThreeMet. Acetic acid, formic acid
Table 2 shows the analysis results. Place this resin in a nitrogen atmosphere
(Oxygen concentration 2 ppm or less) and dried by the molding machine.
A hollow molded container was obtained. Table 2 shows the results of the sensory tests.
The PET resin of the present invention can change the taste of the contents.
It can be seen that there is no hollow molded container.

Comparative Example 1 The amounts of the polycondensation catalyst and phosphoric acid were changed, and the temperature of the third polycondensation reactor was set to about 288 ° C.
The polycondensation was carried out under substantially the same reaction conditions as in Example 1 except that the reaction product was changed to 295 ° C., and sent to the pores at a retention time of about 295 ° C. for about 35 minutes. Cut into pieces. The cooling cutting of the strand was performed under an air atmosphere. IV of the obtained prepolymer =
It was 0.57 dl / g. The resin was sent by air to a prepolymer storage tank under an air atmosphere and left for about 10 days. This prepolymer was placed in a nitrogen atmosphere (oxygen concentration about 300
After crystallization at about 155 ° C under the same nitrogen atmosphere and further preheating to about 200 ° C under the same nitrogen atmosphere, it was sent to a continuous solid-state polymerization reactor, and then heated at about
For solid-phase polymerization. About 1% of nitrogen recovered from solid-state polymerization process
A mixture of / 10 fresh nitrogen was used. The obtained PET resin had an IV of 0.73, a DEG content of 3.5 mol%, a cyclic trimer content of 0.55% by weight, and a density of 1.
It was 397 g / cm ³ . The results of analysis of acetic acid, formic acid and the like are shown in Table 2. The resin was dried under a nitrogen atmosphere, and a hollow molded container was obtained using the molding machine described above. Table 2 shows the results of the sensory test.

Comparative Example 2 Example 1 was repeated except that the esterification reaction conditions were changed to change the DEG content, the temperature of the third polymerization reactor was changed to about 287 ° C., and the degree of vacuum was changed to 3 to 5 torr. Polymerization was carried out under almost the same reaction conditions, and this reaction product was sent to the pores at about 295 ° C. for about 30 minutes, and formed into chips as in Example 4. IV of the obtained PET resin was 0.55. This resin was subjected to solid-state polymerization under the same conditions as in Example 1 except that the solid-state polymerization temperature was set to 200 ° C. IV of the obtained PET resin is 0.75,
DEG was 7.4 mol%, cyclic trimer content was 0.53 wt%, and density was 1.399 g / cm ³ . The results of analysis of acetic acid, formic acid and the like are shown in Table 2. This resin was dried under the same conditions as in Example 1 to obtain a container for hollow molding. Table 2 shows the results of the sensory test.

Comparative Example 3 The temperature of the third polymerization reactor was set to about 2
Melt polymerization was carried out under the same reaction conditions as in Example 1 except that the temperature was reduced to 80 ° C. and the degree of vacuum was changed to 2 to 4 torr, and the reaction product was sent to the pores at about 283 ° C. for about 25 minutes. 1
A chip was formed in the same manner as described above. I of the obtained prepolymer
V = 0.56 dl / g. This prepolymer was subjected to solid-state polymerization under substantially the same conditions as in Example 1. The results of analysis of acetic acid, formic acid and the like are shown in Table 2. The obtained PET resin had an IV of 0.76, a DEG of 3.6 mol%, a cyclic trimer content of 0.45% by weight, and a density of 1.397 g / cm ³ . This resin was dried under the same conditions as in Example 1 to obtain a container for hollow molding. Table 2 shows the results of the sensory test.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

The polyester resin of the present invention has transparency,
It has excellent gas barrier properties, heat resistance, mechanical properties and fragrance retention properties, and can be advantageously used as containers and packaging materials for foods and beverages.

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Claims (8)

[Claims] 1. A polyester resin whose main repeating unit is composed of ethylene terephthalate, wherein the acetic acid content is not more than 50 ppb and the formic acid content is not more than 50 ppb. 2. A polyester resin whose main repeating unit is composed of ethylene terephthalate, having an intrinsic viscosity of 0.65 dl / g or more and a density of 1.37 g / cm.
³ or more and free ethylene glycol content is 20p
pm or less, free monohydroxyethyl terephthalate content of 50 ppm or less, free bishydroxyethyl terephthalate content of 70 ppm or less, free monohydroxyethyl terephthalate content and free bishydroxyethyl terephthalate Total of the content is 100 ppm or less,
2. The polyester resin according to claim 1, wherein the content of free bishydroxyethyl terephthalate dimer is 200 ppm or less. 3. The polyester resin according to claim 1, which has an acetaldehyde content of 10 ppm or less and a formaldehyde content of 7 ppm or less. 4. The polyester resin according to claim 1, wherein the content of the cyclic trimer is 0.5% by weight or less. 5. The amount of diethylene glycol copolymerized is 1.0 to 5.0 mol% of the glycol component.
The polyester resin according to claim 4. 6. A sheet-like product obtained by extruding the polyester resin according to claim 1. 7. A hollow molded article comprising the polyester resin according to claim 1. 8. A stretched film obtained by stretching the sheet material according to claim 6 in at least one direction.