JPH0931178A - Production of polyethylene threphthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a polyethylene terephthalate which contains little oligomer, hardly produces oligomers when molded, and can form a molding with low acetoaldehyde content. SOLUTION: This process for producing a polyethylene terephthalate by the polycondensation of dicarboxylic acids containing terephthalic acid or ester derivatives thereof and diols containing ethylene glycol or ester derivatives thereof in the presence of a polycondensation catalyst, wherein an aliphatic diol ester of an aromatic monocarboxylic acid or its derivative is added to the polycondensation reaction system. It is desirable that the polyethylene terephthalate obtained by the polycondensation be treated with water.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing polyethylene terephthalate, which is less likely to cause mold stains and which can form a molded product having a low acetaldehyde content.

[0002]

TECHNICAL BACKGROUND OF THE INVENTION Polyethylene terephthalate is
It has been used for a wide range of applications such as fibers, bottles, films and sheets. In particular, a bottle made of polyethylene terephthalate is excellent in transparency, mechanical strength, heat resistance and gas barrier property, and is widely used as a beverage filling container (PET bottle) for juice, soft drink, carbonated drink and the like.

Such polyethylene terephthalate is generally obtained by subjecting terephthalic acid and ethylene glycol to an esterification reaction to obtain an esterified product (low-order condensate), and using the low-order condensate as a polycondensation catalyst. It is manufactured through a step of causing a liquid-phase polycondensation reaction in the presence of it and then a step of performing a solid-phase polycondensation reaction of polyethylene terephthalate. Each of the above steps is usually carried out in the presence of a catalyst suitable for each reaction, for example, the polycondensation step is carried out in the presence of a germanium compound.

The PET bottle as described above is usually manufactured by first injection-molding polyethylene terephthalate to produce a preform for a hollow molded body, and then inserting the preform into a mold and blow-molding into a bottle shape. It is manufactured by biaxial stretching or by applying heat treatment (heat setting).

By the way, conventionally, when the polyethylene terephthalate produced as described above is molded, the mold is formed on the vent of the mold of the injection molding machine, the inner surface of the blow molding mold, the gas exhaust port of the mold, the exhaust pipe or the like. There was a problem that dirt was generated. And such mold stains
It causes rough surface and whitening of the obtained bottle. If the bottle becomes white, it must be discarded. For this reason, when molding a bottle using a conventionally known polyethylene terephthalate, it is necessary to frequently remove mold stains, resulting in a serious problem that the productivity of the bottle is significantly reduced.

It is known that the cause of mold stains and the like generated during molding of such polyethylene terephthalate is mainly due to cyclic oligomers such as cyclic trimers.

The oligomers such as the cyclic trimer are produced in the above-mentioned production process, especially in the liquid phase polycondensation process, but they are reduced by the solid phase polycondensation of polyethylene terephthalate, and are usually solid phase polycondensation. The content of polyethylene terephthalate after condensation is about 0.5% by weight. However, at the time of molding, a large amount is newly generated,
It is known that the total amount of oligomers such as cyclic trimers in polyethylene terephthalate increases.
It is presumed that this is because the polycondensation catalyst used during production acts as a cyclization-opening polymerization catalyst of polyethylene terephthalate during molding and produces oligomers such as cyclic trimers.

It is known that the PET bottle manufactured as described above contains acetaldehyde. However, this acetaldehyde deteriorates the taste and aroma of the contents filled in the bottle. In particular, it is desirable that the content of acetaldehyde in bottles used for filling beverages is as low as possible.

[0009]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and provides a molded product having a low content of oligomers, hardly forming oligomers during molding, and having a low content of acetaldehyde. It is an object of the present invention to provide a method for producing polyethylene terephthalate, which can obtain a formable polyethylene terephthalate.

[0010]

SUMMARY OF THE INVENTION A method for producing polyethylene terephthalate according to the present invention comprises: (a) a dicarboxylic acid containing terephthalic acid or an ester derivative thereof and (b) a diol containing ethylene glycol or an ester derivative thereof in a polycondensation catalyst. When a poly (ethylene terephthalate) is produced by a polycondensation reaction in the presence, (c) an ester of an aromatic monocarboxylic acid or its derivative and an aliphatic diol is added to the polycondensation reaction system.

In the present invention, the polyethylene terephthalate obtained by the polycondensation reaction is preferably treated with water.
The ester (c) of the above-mentioned aromatic monocarboxylic acid or its derivative and the aliphatic diol is preferably a monoester of an aliphatic diol.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The method for producing polyethylene terephthalate according to the present invention will be specifically described below.

In the present invention, (a) a dicarboxylic acid containing terephthalic acid or an ester derivative thereof and (b) a diol containing ethylene glycol or an ester derivative thereof are subjected to a polycondensation reaction in the presence of a polycondensation catalyst to form polyethylene. When producing terephthalate, (c) an ester of an aromatic monocarboxylic acid or its derivative and an aliphatic diol is added to the polycondensation reaction system.

In the present invention, polyethylene terephthalate can be produced by applying the conventionally known polycondensation reaction of a dicarboxylic acid and a diol, without any particular limitation, except that the above ester (c) is added. However, the polyethylene terephthalate obtained by the polycondensation reaction is preferably subjected to water treatment as described later.

In the present invention, homopolyethylene terephthalate may be produced using terephthalic acid and ethylene glycol, and dicarboxylic acid containing terephthalic acid and dicarboxylic acid other than terephthalic acid and / or ethylene glycol and ethylene glycol other than ethylene glycol. The copolymerized polyethylene terephthalate can also be produced by using a diol containing the diol.

Specific examples of the dicarboxylic acid other than terephthalic acid used in producing the copolymerized polyethylene terephthalate include phthalic acid (orthophthalic acid), isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid and diphenoxyethanedicarboxylic acid. And aromatic dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid, and decanedicarboxylic acid; and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. These may be used in combination of two or more. Of these, isophthalic acid is preferably used.

It is also possible to use ester derivatives of these dicarboxylic acids. Specific examples of the diol other than ethylene glycol include diethylene glycol, trimethylene glycol (propylene glycol), tetramethylene glycol, neopentyl glycol, hexamethylene glycol, dodecamethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, Aliphatic glycols such as polyethylene glycol, alicyclic glycols such as cyclohexanedimethanol, bisphenols, hydroquinone,
Examples thereof include aromatic diols such as 2,2-bis (4-β-hydroxyethoxyphenyl) propane. These may be used in combination of two or more. Among these, diethylene glycol and cyclohexanedimethanol are preferably used.

It is also possible to use ester derivatives of these diols. Dicarboxylic acid used in the present invention (a)
Is 0 to 10 mol% of dicarboxylic acid other than terephthalic acid
It may be contained in an amount of preferably 0 to 5 mol%, more preferably 0 to 3 mol%, and the diol (b) contains 0 to 10 mol% of a diol other than ethylene glycol, preferably 0 to 5 mol%. , More preferably in an amount of 0 to 3 mol%.

In the present invention, a small amount of a unit derived from a polyfunctional compound such as trimesic acid, trimellitic acid, pyromellitic acid, trimethylolethane, trimethylolpropane, trimethylolmethane and pentaerythritol is contained in a small amount, for example, 2 mol% or less. It is also possible to produce polyethylene terephthalate which is contained in an amount.

In the method for producing polyethylene terephthalate according to the present invention, an aromatic monocarboxylic acid or its derivative and an aliphatic diol are used in the polycondensation reaction of the above-mentioned dicarboxylic acid (a) and diol (b). Esther with
(c) is used. This ester (c) is used as a terminal blocking agent.

The ester (c) used in the present invention may be a monoester of aromatic monocarboxylic acid or its derivative: aliphatic diol (molar ratio) of 1: 1.
It may be a 2: 1 diester.

Examples of the aromatic monocarboxylic acid and its derivative include benzoic acid, methylbenzoic acid, dimethylbenzoic acid, trimethylbenzoic acid, ethylbenzoic acid, propylbenzoic acid, i-propylbenzoic acid, butylbenzoic acid,
Examples thereof include i-butylbenzoic acid and t-butylbenzoic acid.

Of these, benzoic acid is preferred. Examples of the aliphatic diol include alkylene diols having 2 to 20 carbon atoms, such as ethylene glycol,
Propylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,4-butanediol, 2,3-butanediol, 2,3-pentamethylene glycol, neopentyl glycol, Hexamethylene glycol, dodecamethylene glycol, diethylene glycol and the like can be mentioned.

Of these, ethylene glycol is preferred. More specifically, as such ester (c),

[0025]

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Diesters such as Among these, monoesters of benzoic acid and ethylene glycol, diesters of benzoic acid and ethylene glycol,
Diesters of p-benzoic acid and ethylene glycol are preferred.

In the present invention, the ester (c) as described above is used.
Is preferably used in an amount of 0.05 to 2 mol%, preferably 0.1 to 1 mol%, based on 1 mol of the dicarboxylic acid (a). In the present invention, the ester (c) may be used in combination of two or more kinds.

In the present invention, in addition to the above-mentioned ester (c), benzoylbenzoic acid, diphenylsulfone monocarboxylic acid, stearic acid, methoxy polyethylene glycol, phenoxy polyethylene glycol, insofar as the object of the present invention is not impaired. You may use monofunctional compounds, such as.

In the method for producing polyethylene terephthalate according to the present invention, a dicarboxylic acid containing terephthalic acid or an ester derivative thereof (hereinafter referred to as dicarboxylic acid) (a), a diol containing ethylene glycol or an ester derivative thereof (hereinafter referred to as diol) is used. (b) The ester (c) of an aromatic monocarboxylic acid or its derivative and an aliphatic diol can be used for the following production.

In the present invention, it is preferable to produce polyethylene terephthalate by a process including an esterification step, a liquid phase polycondensation step and a solid phase polycondensation step. Further, it is preferable to treat the polyethylene terephthalate thus produced with water.

In such a process, the ester (c) of the above-mentioned aromatic monocarboxylic acid or its derivative and the aliphatic diol can be added to any reaction step. It is preferable to add it in the latter stage, and more specifically, it is preferable to add it in the final stage of the liquid-phase (melting) polycondensation step performed in multiple stages as described later.

In the esterification step, first, a slurry containing the above dicarboxylic acid and diol is prepared. This slurry is usually continuously fed to the esterification step.

In this slurry, usually 1.02 to 2.0 mol, preferably 1.03, relative to 1 mol of dicarboxylic acid.
~ 1.5 moles of diol are included. Further, other compounds such as polyfunctionalization may be contained in the above slurry, for example, 0.01 to 20 mol%, preferably 0.05 to 5 mol% based on the total amount of the dicarboxylic acid and the diol. 10
It may optionally be contained in an amount of mol%.

The esterification reaction is usually carried out by removing at least two esterification reactors in series with a rectifying column to remove the water and the like produced by the reaction under the condition that the diol is refluxed. While being carried out.

When the esterification reaction is carried out in, for example, two stages, the esterification reaction in the first stage is carried out from 240 to
The second stage (final stage) is preferably performed at a temperature of 270 ° C., preferably 245 to 265 ° C., and a pressure of 0.2 to 3 kg / cm ² G, preferably 0.5 to ² kg / cm ² G. The esterification reaction of the eye is 250 to 280 ° C., preferably 25
It is desirable to carry out at a temperature of 5 to 275 ° C. and a pressure of 0 to 1.5 kg / cm ² G, preferably 0 to 1.3 kg / cm ² G.

When the esterification reaction is carried out in three or more stages, the intermediate stages are carried out under the conditions between the reaction conditions of the first stage and the reaction conditions of the final stage. For example, when the esterification reaction is carried out in three stages, the second stage esterification reaction is usually carried out at a reaction temperature of 245 to 275 ° C., preferably 250 to 270 ° C., a pressure of 0 to ² kg / cm ² G, preferably Is carried out under the conditions of 0.2 to 1.5 kg / cm ² G.

The esterification reaction rate in each of these stages is not particularly limited, but it is preferable that the degree of increase in the esterification reaction rate in each stage is distributed smoothly.
Further, in the final stage esterification reaction product, it is usually desired to reach 90% or more, preferably 93% or more.

An esterification product (low-order condensate) of a dicarboxylic acid and a diol is obtained by the esterification reaction as described above, and usually a low-order condensate having a number average molecular weight of about 500 to 5,000 is obtained.

The esterification reaction as described above can be carried out without adding any additives other than dicarboxylic acid and diol, or can be carried out by adding a polycondensation catalyst described later. However, it is usually desirable to add a small amount of the following basic compound.

Examples of the basic compound include tertiary amines such as triethylamine, tri-n-butylamine and benzyldimethylamine, and tertiary hydroxides such as tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide and trimethylbenzylammonium hydroxide. Quaternary ammonium and lithium carbonate, sodium carbonate, potassium carbonate, sodium acetate and the like can be mentioned.

When the dicarboxylic acid and the diol are subjected to an esterification reaction in the presence of such basification, polyethylene terephthalate having a low content of dioxyethylene terephthalate units (ii) as described below can be produced. it can.

These basic compounds may be added to all of the esterification reactors, or may be added in the first stage or the second stage.
It may be added to a specific reactor after the first stage. The esterified product thus obtained is continuously supplied to the liquid phase polycondensation reactor.

In the liquid phase polycondensation reactor, the polycondensation is carried out by heating under reduced pressure in the presence of a polycondensation catalyst to a temperature not lower than the melting point of the obtained polyester while distilling out the diol produced as a by-product. Let

The polycondensation reaction may be carried out in one stage or in a plurality of stages. For example, when the polycondensation reaction is carried out in two stages, the first stage polycondensation reaction, 250 to
290 ° C., preferably at a temperature of 260-280 ° C., and 5
It is carried out under a pressure of 00 to 20 torr, preferably 200 to 30 torr. The second stage (final stage) polycondensation reaction is 26
5 to 300 ° C., preferably at a temperature of 270 to 295 ° C., 1
It is carried out under a pressure of 0 to 0.1 torr, preferably 5 to 0.5 torr.

When the polycondensation reaction step is carried out in three or more stages, the polycondensation reaction in each intermediate stage is carried out under the conditions between the reaction conditions of the first stage and the reaction conditions of the final stage. Done.
For example, when the polycondensation reaction step is carried out in three stages,
The second-stage polycondensation reaction is usually carried out at a reaction temperature of 260 to 29.
5 ° C., preferably 270-285 ° C., pressure 50-2 torr,
It is preferably carried out under the conditions of 40 to 5 torr.

The intrinsic viscosity reached in each stage of the liquid-phase polycondensation reaction carried out in a plurality of stages is not particularly limited except for the final stage, but the degree of increase in the intrinsic viscosity in each stage is smoothly distributed. It is preferable.

In the present invention, it is preferable to add the ester (c) of an aromatic monocarboxylic acid or its derivative and an aliphatic diol to the final stage of this liquid phase polycondensation step. The liquid phase polycondensation reaction as described above is usually carried out in the presence of a polycondensation catalyst.

As the polycondensation catalyst, germanium compounds such as germanium dioxide, germanium tetraethoxide and germanium tetra n-butoxide, and antimony catalysts such as antimony trioxide, antimony acetate and antimony glycoloxide can be used.

Of these polycondensation catalysts, the use of germanium dioxide compounds is preferable because polyesters excellent in hue and transparency can be obtained. The polycondensation catalyst is in a proportion of 0.0005 to 0.2% by weight, preferably 0.001 to 0.05% by weight, calculated as the weight of the metal in the polycondensation catalyst, based on the total weight of the dicarboxylic acid and the diol. It is desirable to be used in.

The polycondensation reaction is preferably carried out in the presence of a phosphorus-based stabilizer. Examples of phosphorus stabilizers include phosphoric acid esters such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, triphenyl phosphate, tricresyl phosphate, and methyl acid phosphate. Acid phosphates such as ethyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, dibutyl phosphate, monobutyl phosphate, dioctyl phosphate and phosphoric acid such as phosphoric acid and polyphosphoric acid, trimethyl phosphite, triethyl Phosphite, triphenyl phosphite, trilauryl phosphite, tridecyl phosphite, triisodecyl phosphite, triisooctyl phosphite Ito, trioctyl phosphite, trioctadecyl phosphite, tristearyl phosphite, tris dodecyl phosphite, tris nonylphenyl phosphite, tris -di- nonylphenyl phosphite,
Tris (2,4-di-tert-butylphenyl) phosphite, trisnonylphenylphosphite, bis (2,6-
Di-tert-butyl-4-methylphenyl) pentaerythritol-di-phosphite and other phosphite esters, dilauryl phosphite, dimethyl phosphite, diethyl phosphite, diphenyl phosphite and other phosphite diesters and Mention may be made of phosphorus compounds such as phosphorous acid.

Of these, trimethyl phosphate, triethyl phosphate, methyl acid phosphate, ethyl acid phosphate, isopropyl acid phosphate and phosphoric acid are preferable.

These phosphorus compounds may be used alone or in combination with a plurality of stabilizers. The phosphorus compound as described above is 0.001 in terms of phosphorus atom weight in the stabilizer with respect to the total weight of the dicarboxylic acid and the diol.
~ 0.1% by weight, preferably 0.002-0.02% by weight
It is desirable to be used in a ratio of.

These polycondensation catalysts and phosphorus compounds may be supplied to the reactor at the first stage of the polycondensation reaction,
It may also be supplied to the esterification reaction as described above. The intrinsic viscosity of the polyethylene terephthalate obtained in the above liquid phase polycondensation step is 0.35 to 0.80 dl / g, preferably 0.45 to 0.75 dl / g.

In this specification, the intrinsic viscosity number is a value calculated from a solution viscosity measured at 25 ° C. after 1.2 g of polyester was dissolved by heating in 15 ml of o-chlorophenol.

The polyethylene terephthalate obtained in this liquid phase polycondensation step is usually formed into particles (chips) by a melt extrusion molding method. This polyethylene terephthalate chip is usually 2.0 to 5.0 mm, preferably 2.2.
It is desirable to have an average particle size of ~ 4.0 mm.

In the present invention, it is preferable that the polyethylene terephthalate obtained in the above liquid phase polycondensation step is further subjected to a solid phase polycondensation step. Further, prior to the solid phase polycondensation, polyethylene terephthalate may be heated at a temperature lower than the solid phase polycondensation temperature for pre-crystallization.

Specifically, the polyethylene terephthalate chips may be pre-crystallized by heating them in a dry state to a temperature of usually 120 to 200 ° C., preferably 130 to 180 ° C. for 1 minute to 4 hours, or polyethylene terephthalate. The chips may be pre-crystallized by heating to a temperature of 120 to 200 ° C. for 1 minute or more in a steam atmosphere, a steam-containing inert gas atmosphere or a steam-containing air atmosphere.

The solid phase polycondensation step of polyethylene terephthalate (chips) consists of at least one step, and is usually 19
At a polycondensation temperature of 0 to 230 ° C., preferably 195 to 225 ° C., 1 kg / cm ² G to 10 torr, preferably atmospheric pressure to 10
It is carried out under an atmosphere of an inert gas such as nitrogen gas, argon gas or carbon dioxide gas under a pressure of 0 torr. Among the inert gases, nitrogen gas is preferred.

The production process of polyethylene terephthalate as described above can be carried out by any of batch system, semi-continuous system and continuous system. In the present invention, it is desirable that the polyethylene terephthalate obtained as described above be brought into contact with water for water treatment.

Water treatment of polyethylene terephthalate
Specifically, a polyethylene terephthalate chip, 70
It is carried out by immersing in hot water of ~ 110 ° C for 3 minutes to 5 hours. Particularly preferably, the polyethylene terephthalate chips are immersed in hot water at 80 to 100 ° C. for 5 minutes to 3 hours.

The method of industrially performing the water treatment of polyethylene terephthalate will be illustrated below, but the method is not limited thereto. The processing method may be either a continuous method or a batch method.

When the polyethylene terephthalate is subjected to water treatment in a batch system, the polyethylene terephthalate chips are put into a silo type treatment apparatus, water is supplied in a batch system and brought into contact with water. Alternatively, the water treatment can be carried out more efficiently by placing the polyethylene terephthalate chip in a rotary tube type contact treatment device and bringing it into contact with water while rotating.

In the case of continuously treating polyethylene terephthalate with water, the tower type treatment device continuously receives polyethylene terephthalate chips from the upper part, and continuously supplies water in a cocurrent or countercurrent to continuously perform contact treatment. Can be done.

The polyethylene terephthalate chips thus treated with water are drained by a draining device such as a vibrating screener or Simon Carter, and then subjected to a drying step. When the water treatment is carried out with steam or a steam-containing gas, it can be directly subjected to the drying step.

The polyethylene terephthalate chip can be dried by a known drying method. When polyethylene terephthalate is continuously dried, a hopper type aeration dryer is generally used in which polyethylene terephthalate chips are supplied from the upper part and a dry gas is aerated from the lower part. While venting a small amount of dry gas,
If you use a rotary disk type continuous dryer that heats and dries the polyethylene terephthalate chips indirectly by supplying heating steam, heating medium, etc. to the rotating disk or external jacket, you can dry efficiently with a small amount of dry gas. You can

When the polyethylene terephthalate is dried in a batch system, it can be usually dried by using a double cone type rotary dryer under a vacuum or while a small amount of a drying gas is passed under a vacuum. Alternatively, the drying may be performed while passing a drying gas under atmospheric pressure.

As the dry gas, atmospheric air may be used, but dry nitrogen and dehumidified air are preferable from the viewpoint of preventing a decrease in molecular weight due to hydrolysis of polyethylene terephthalate.

Polyethylene terephthalate treated with water as described above is unlikely to form oligomers such as cyclic trimers during molding. It is considered that this is because the polycondensation catalyst contained in polyethylene terephthalate, such as a germanium catalyst, is deactivated by water treatment and does not act as a depolymerization catalyst for polyethylene terephthalate during molding.

Polyethylene terephthalate The polyethylene terephthalate obtained by the present invention as described above has a unit derived from a dicarboxylic acid containing terephthalic acid and a diol containing ethylene glycol.

The polyethylene terephthalate may be homopolyethylene terephthalate derived from terephthalic acid and ethylene glycol, or a copolymerized polyethylene derived from terephthalic acid and ethylene glycol with other dicarboxylic acid and / or other diol. It may be terephthalate. Specifically, in the polyethylene terephthalate according to the present invention, the unit derived from another dicarboxylic acid is 0 to 10 mol%, preferably 0 to 5 mol%, more preferably when the unit derived from the dicarboxylic acid is 100 mol%. Units derived from other diols, which may be contained in an amount of 0 to 3 mol%,
0 when the unit derived from the diol is 100 mol%
-10 mol%, preferably 0-5 mol%, more preferably 0
It may be contained in an amount of 3 mol%.

The polyethylene terephthalate according to the present invention includes trimesic acid, trimellitic acid, pyromellitic acid, trimethylolethane, trimethylolpropane,
A unit derived from a polyfunctional compound such as trimethylolmethane or pentaerythritol may be contained in a small amount, for example, 2 mol% or less as long as the object of the present invention is not impaired.

The particularly preferred polyethylene terephthalate produced by the present invention preferably contains the ethylene terephthalate unit (i) represented by the following general formula in a proportion of 95.0 to 99.0 mol%.

[0073]

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The content of the dioxyethylene terephthalate component unit (ii) represented by the following formula is preferably 5.0 mol% or less.

[0075]

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In the polyethylene terephthalate obtained in the present invention as described above, 10 to 100%, preferably 50 to 90%, of all molecular terminals have an ester group (c) of an aromatic monocarboxylic acid or its derivative and an aliphatic diol. It is desirable that it is sealed with a group derived from

It is considered that such an ester (c) caps the molecular end by transesterification (alcoholization reaction) with the terminal hydroxyl group of the polymer chain (for example, ethylene terephthalate unit (i) chain). Ester for example
When a monoester is used as (c), the following (1)
It is considered that one molecular end group of the polymer chain (i) is blocked as described above.

[0078]

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When a diester is used as the ester (c), it is considered that two molecular end groups of the polymer chain (i) are blocked as shown in (2) below.

[0080]

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In the present invention, other molecular end groups are monofunctional compounds such as benzoylbenzoic acid, diphenylsulfone monocarboxylic acid, stearic acid, methoxypolyethylene glycol and phenoxypolyethylene glycol within the range not impairing the object of the present invention. May be sealed with a group derived from

The intrinsic viscosity of polyethylene terephthalate as measured above in o-chlorophenol is 0.7.
0 to 1.50 dl / g, preferably 0.75 to 1.20 dl / g
It is desirable that

In the present specification, the intrinsic viscosity of polyethylene terephthalate is polyethylene terephthalate 1.
After heating and dissolving 2 g in 15 cc of o-chlorophenol,
It can be calculated from the melt viscosity measured at 25 ° C. after cooling.

The polyethylene terephthalate obtained in the present invention preferably has an oligomer content of 0.40% by weight or less, preferably 0.30% by weight or less.
This oligomer is considered to be a cyclic trimer of ethylene terephthalate unit (i) represented by the above general formula.

In the present specification, the amount of oligomer contained in this polyethylene terephthalate is measured as follows. After dissolving a predetermined amount of polyethylene terephthalate in o-chlorophenol, precipitating with tetrahydrofuran and removing the linear polyethylene terephthalate by filtration, the filtrate is subjected to liquid chromatography (Shimadzu LC7A) to measure the amount of oligomer. To do. This value is divided by the amount of polyethylene terephthalate used in the measurement to obtain the amount of oligomer (% by weight) contained in polyethylene terephthalate.

The density of the polyethylene terephthalate according to the present invention as described above is usually 1.37 to 1.420 g / cm.
³ It is desirable that the amount is preferably 1.38 to 1.415 g / cm ^{3, and} more preferably 1.39 to 1.410 g / cm ³ .

As described above, in the method for producing polyethylene terephthalate according to the present invention, at least a part of the molecular end is sealed with a specific ester. Such polyethylene terephthalate obtained by the present invention,
The content of oligomers such as cyclic trimers is low, and the amount of oligomers generated during molding is low. Therefore, when it is supplied to a molding machine such as an injection molding machine to mold a preform for a hollow molded body, the preform is inserted into a mold of a predetermined shape, stretch blow molded, and then heat set to mold a hollow molded container. In addition, die contamination due to attachment of oligomers such as cyclic trimer to the die is less likely to occur. Further, from this polyethylene terephthalate, a molded product having a low acetaldehyde content can be obtained.

The polyethylene terephthalate obtained in the present invention can be molded into various shapes by molding methods such as injection molding, blow molding and extrusion molding. Preferably.

The molded product of polyethylene terephthalate obtained in the present invention has an oligomer content of 0.45% by weight or less, preferably 0.35% by weight or less, and more preferably 0.30% by weight or less. The acetaldehyde content is 15 ppm or less, preferably 9 ppm or less.

[0090]

INDUSTRIAL APPLICABILITY As described above, in the present invention, polyethylene terephthalate is produced by using a specific ester as the terminal blocking agent. The polyethylene terephthalate obtained in the present invention has a low oligomer content and a low oligomer content during molding.

Therefore, when the polyethylene terephthalate obtained in the present invention is used, stains on the injection molding machine due to oligomers, stains on the molding machine such as blow mold stains are less likely to occur, and polyethylene terephthalate moldings can be produced with good productivity. it can.

Further, the molded product formed from the polyethylene terephthalate obtained in the present invention has an extremely low acetaldehyde content, and is particularly suitable for use in foods such as containers for filling beverages such as water and food packaging.

[0093]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited to these examples. [Oligomer] A predetermined amount of polyethylene terephthalate
After dissolving in o-chlorophenol, reprecipitation with tetrahydrofuran and removing linear polyethylene terephthalate by filtration, the filtrate was supplied to a liquid chromatograph (LC-7A manufactured by Shimadzu Corporation) and contained in polyethylene terephthalate. The amount of oligomer (amount of cyclic trimer and total amount of oligomer) was determined. [Measurement of content of acetaldehyde] About 2 g of a test piece was sampled from a polyethylene terephthalate molded product and freeze-ground with a SPEX freeze-grinding machine. 1 g of the obtained polyethylene terephthalate powder was placed in a vial bottle and distilled water 2
Add ml and mix water and polyethylene terephthalate powder well. After capping the vial bottle at 120 ° C 1
Heat for hours. After heating, cool in ice water and clear the supernatant to 5μ.
1 was measured with a gas chromatograph (GC-6A, manufactured by Shimadzu Corporation).

[0094]

[Example 1] 332 g of high-purity terephthalic acid, 143 g of ethylene glycol, and 3.4 g of a monoester of benzoic acid and ethylene glycol were charged into an autoclave, and the pressure was 1.7 kg / cm ² , under a nitrogen atmosphere at 255 ° C for 2 hours. , Reacted with stirring.

Then, the heating temperature was set to 250 ° C. and the reaction was carried out for 6 hours. Water generated by this reaction was always distilled out of the system. Next, 0.042 g of germanium dioxide and 0.080 g of phosphoric acid were added to the reaction system, and the temperature was raised to 280 ° C. over 1 hour while the pressure inside the system was reduced to 1 torr. The reaction was further continued for 3 hours, and unreacted ethylene glycol was distilled out of the system. After completion of the reaction, the reaction product was taken out of the reactor in a strand shape, immersed in water, cooled, and then cut into a chip shape by a strand cutter.

The intrinsic viscosity of polyethylene terephthalate obtained by the above liquid phase polymerization was 0.56 dl / g. Further, polyethylene terephthalate obtained by liquid phase polymerization was pre-crystallized at 170 ° C. for 2 hours and then solid-phase polymerized at 205 ° C. for 15 hours in a nitrogen atmosphere.

The polyethylene terephthalate thus obtained had an intrinsic viscosity of 0.80 dl / g and a density of 1.40 g / cm ³ . The content of cyclic trimer oligomer of this polyethylene terephthalate was 0.28% by weight, and the total oligomer was 0.29% by weight.

Using 10 kg of the polyethylene terephthalate thus obtained, a bottle forming preform (outer diameter of the mouth portion: 28 mmφ) was molded. Using a famous machine M100A molding machine, molding was performed under the conditions that the set temperature was 275 ° C., the mold temperature was 10 ° C., and the hopper atmosphere was dry air.

The cyclic trimer oligomer content in the mouth of the obtained preform was 0.29% by weight, and the total amount of oligomers was 0.30% by weight. The acetaldehyde content was 6 ppm.

[0100]

[Example 2] 332 g of high-purity terephthalic acid and 143 g of ethylene glycol were charged into an autoclave, and the pressure was 1.
The reaction was carried out under a nitrogen atmosphere of 7 kg / cm ² and 255 ° C. for 2 hours while stirring.

Then, the heating temperature was raised to 250 ° C. and the reaction was carried out for 6 hours. Water generated by this reaction was always distilled out of the system. Next, 0.46 g of a mixed solution of germanium dioxide and ethylene glycol in a weight ratio of 1:10 and 0.080 g of phosphoric acid were added to the reaction system, and the pressure in the system was reduced to 1 torr while the temperature was reduced to 280 ° C. over 1 hour. The temperature was raised.
It was further heated, and unreacted ethylene glycol was distilled out of the system.

After 1.5 hours from the completion of heating, 3.4 parts by weight of a monoester of benzoic acid and ethylene glycol was added to the system, and the mixture was heated for another hour. After completion of the reaction, the reaction product was taken out of the reactor in a strand shape, immersed in water, cooled, and then cut into a chip shape by a strand cutter.

The intrinsic viscosity of polyethylene terephthalate obtained by the above liquid phase polymerization was 0.56 dl / g. The germanium content of polyethylene terephthalate measured by atomic absorption spectrometry was 50 ppm, and the germanium residual ratio was 66%.

Further, the polyethylene terephthalate obtained by liquid phase polymerization was pre-crystallized at 170 ° C. for 2 hours and then solid-phase polymerized at 205 ° C. for 15 hours in a nitrogen atmosphere. The polyethylene terephthalate thus obtained has an intrinsic viscosity of 0.80 dl / g and a density of 1.40 g.
It was / cm ³ . The content of cyclic trimer oligomer of polyethylene terephthalate is 0.26% by weight,
The total oligomer was 0.27% by weight.

Using the polyethylene terephthalate thus obtained, a preform (outer diameter of the mouth portion: 28 mmφ) was molded in the same manner as in Example 1. The content of cyclic trimer oligomer at the mouth of the obtained preform was 0.27% by weight, and the total amount of oligomer was 0.28% by weight. The acetaldehyde content was 5 ppm.

[0106]

Example 3 Polyethylene terephthalate was prepared in the same manner as in Example 1 except that 6.5 g of a diester of p-methylbenzoic acid and ethylene glycol was added instead of the monoester of benzoic acid and ethylene glycol. Obtained.

The intrinsic viscosity of the liquid phase polymer (polyethylene terephthalate) was 0.57 dl / g, and the intrinsic viscosity of the solid phase polymer was 0.80 dl / g. The amount of the obtained cyclic oligomer of polyethylene terephthalate was 0.27% by weight, and the total amount of the oligomer was 0.28% by weight.

Using the obtained polyethylene terephthalate, a preform (outer diameter of the mouth portion;
28 mmφ) was molded. After injection molding, the amount of cyclic trimer oligomer at the mouth of the preform was 0.28% by weight, the total amount of oligomer was 0.29% by weight, and the acetaldehyde content was 7 ppm.

[0109]

Example 4 Polyethylene terephthalate was obtained in the same manner as in Example 1 except that 5.5 g of a diester of benzoic acid and ethylene glycol was added instead of the monoester of benzoic acid and ethylene glycol.

The intrinsic viscosity of the liquid phase polymerized product is 0.57 dl / g,
The intrinsic viscosity of the solid-phase polymerized product was 0.79 dl / g. The obtained polyethylene terephthalate cyclic trimer oligomer content was 0.27% by weight, and the total oligomer content was 0.28% by weight.
Met.

Using the obtained polyethylene terephthalate, a preform (outer diameter of the mouth portion;
28 mmφ) was molded. After injection molding, the amount of cyclic trimer oligomer at the mouth of the preform was 0.28% by weight, the total amount of oligomer was 0.29% by weight, and the acetaldehyde content was 6 ppm.

[0112]

Example 5 10 kg of polyethylene terephthalate after the solid phase polymerization obtained in Example 1 was converted into distilled water 13 at 90 ° C.
Water treatment was carried out by immersing in kg for 4 hours. Then dehydrated,
It was dried at 140 ° C. in dry air for 14 hours.

Using the polyethylene terephthalate thus treated, a preform (outer diameter of the mouth portion: 28 mmφ) was molded in the same manner as in Example 1. After injection molding, the amount of cyclic trimer oligomer at the mouth of the preform was 0.28% by weight, the total amount of oligomer was 0.29% by weight, and the acetaldehyde content was 5 ppm.

[0114]

Comparative Example 1 Polyethylene terephthalate was obtained in the same manner as in Example 1 except that the monoester of benzoic acid and ethylene glycol was not added.

The intrinsic viscosity of the liquid-phase polymerized product is 0.56 dl / g,
The intrinsic viscosity of the solid-state polymerized product was 0.81 dl / g. The resulting polyethylene terephthalate cyclic trimer oligomer content was 0.30% by weight, and the total oligomer content was 0.32% by weight.
Met.

Using the obtained polyethylene terephthalate, a preform (outer diameter of the mouth portion;
28 mmφ) was molded. After injection molding, the amount of cyclic trimer oligomer in the mouth of the preform was 0.45% by weight, the total amount of oligomer was 0.50% by weight, and the acetaldehyde content was 15 ppm.

[0117]

Comparative Example 2 Polyethylene terephthalate was obtained in the same manner as in Example 1 except that 2.5 g of benzoic acid was added instead of the monoester of benzoic acid and ethylene glycol.

The intrinsic viscosity of the liquid phase polymerized product is 0.56 dl / g,
The intrinsic viscosity of the solid-phase polymerized product was 0.79 dl / g. The amount of the obtained polyethylene terephthalate cyclic trimer oligomer was 0.29% by weight, and the total amount of the oligomer was 0.30% by weight.
Met.

After injection molding, the amount of cyclic trimer oligomer at the mouth of the preform was 0.31% by weight, the total amount of oligomer was 0.33% by weight, and the acetaldehyde content was 10 p.
It was pm.

Claims (3)

[Claims] 1. A polyethylene terephthalate is obtained by subjecting (a) a dicarboxylic acid containing terephthalic acid or an ester derivative thereof to (b) a diol containing ethylene glycol or an ester derivative thereof in a polycondensation reaction in the presence of a polycondensation catalyst. A method for producing polyethylene terephthalate, characterized in that (c) an ester of an aromatic monocarboxylic acid or its derivative and an aliphatic diol is added to a polycondensation reaction system during production. 2. The method for producing polyethylene terephthalate according to claim 1, wherein the polyethylene terephthalate obtained by the polycondensation reaction is treated with water. 3. The method for producing polyethylene terephthalate according to claim 1, wherein the ester (c) of an aromatic monocarboxylic acid or its derivative and an aliphatic diol is a monoester of an aliphatic diol.