JPH0347830A - Production of polyethylene terephthalate - Google Patents

Abstract

PURPOSE:To obtain the subject polymer having excellent productivity of molded article such as bottle or sheet hardly generating mold dirt in molding by subjecting to esterification, melt polycondensation and solid phase polycondensation and bringing into contact with water. CONSTITUTION:(A) Terephthalic acid (derivative) and (B) ethylene glycol (derivative) are esterfied and (C) polycondensation catalyst such as germanium dioxide of preferably 0.0005-0.2wt.% calculated as a metal, is added, then the system is subjected to melt polycondensation. Next, the resultant polycondensate is granularly formed and (D) subjected to solid phase polycondensation in an inert gas atmosphere such as N2 gas, then (E) brought into contact with water preferably at a temperature from room temperature to 150 deg.C to afford the aimed polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a method for producing polyethylene terephthalate, which is used for forming bottles, films, sheets, etc. The present invention relates to a method for producing polyethylene terephthalate that can yield polyethylene terephthalate.

Technical background of the invention and its problems Various resins have been used as materials for containers for seasonings, oils, beverages, cosmetics, detergents, etc., depending on the type of contents and the purpose of use. .

Among these, polyethylene terephthalate has excellent mechanical strength, heat resistance, transparency, and gas barrier properties, and is therefore particularly suitable as a material for containers for filling beverages such as juices, soft drinks, and carbonated drinks.

Such polyethylene terephthalate is produced by esterifying terephthalic acid or its ester-forming derivative with ethylene glycol or its ester-forming derivative in the presence of an esterification catalyst, and then carrying out liquid phase polycondensation in the presence of a polycondensation catalyst. and then solid-phase polycondensation. This polyethylene terephthalate is then supplied to a molding machine such as an injection molding machine to form a preform for a hollow molded object, and this preform is inserted into a mold of a predetermined shape and stretch blow molded, and then heat treated (heat set). )
It is generally molded into a blow-molded container.

However, the conventionally known polyethylene terephthalate obtained by the above-mentioned production method contains oligomers such as cyclic trimers, and these oligomers such as cyclic trimers are exposed to the inner surface of the blow molding mold and the metal. type gas exhaust port,
The oligomers adhered to exhaust pipes and the like, causing mold stains, or the oligomers adhered to the vent portion of the mold of the injection molding machine as described above, causing mold stains.

Such mold stains cause surface roughness and whitening of the resulting bottle. If the bottle turns white, it must be discarded. For this reason, when molding bottles using conventionally known polyethylene terephthalate, mold stains must be removed frequently, resulting in a major problem in that the productivity of the bottles is significantly reduced.

In view of the above-mentioned current situation, the present inventors conducted intensive research to obtain polyethylene terephthalate that does not easily cause mold stains during molding, and found that the main cause of mold stains during molding is the molding of polyethylene terephthalate. It has been found that sometimes oligomers such as cyclic trimers are produced in large quantities, resulting in an increase in the total amount of oligomers such as cyclic trimers contained in polyethylene terephthalate.

Based on the above findings, the present inventors further investigated and found that by bringing polyethylene terephthalate obtained through a series of continuous steps into contact with water, the increase in the total amount of oligomers such as cyclic trimers during molding can be suppressed. We have discovered that this can be done, and have completed the present invention.

Furthermore, JP-A-59-25815 discloses a method of treating polyethylene terephthalate powder with heated steam at 110° C. or higher in order to crystallize the polyethylene terephthalate prior to solid-phase polycondensation of the polyethylene terephthalate. Disclosed.

In addition, JP-A-59-219328 discloses that the intrinsic viscosity is at least 0.4 dl/g and the density is 1.35 dl/g.
140 g/- or less of polyester having ethylene terephthalate units as the main repeating unit, the moisture content is at least 0.2% by weight or more;
A method for producing a highly polymerized polyester, comprising the steps of preliminary crystallization at a temperature of 180° C. or higher and 240° C. or higher in an inert gas atmosphere or under reduced pressure. is disclosed.

Purpose of the Invention The present invention aims to solve the problems associated with the prior art as described above, and is to obtain polyethylene terephthalate that produces less oligomer during molding and is less likely to cause mold fouling. The purpose of the present invention is to provide a method for producing polyethylene terephthalate.

Summary of the Invention The method for producing polyethylene terephthalate according to the present invention includes an esterification step of esterifying terephthalic acid or its ester-forming derivative and ethylene glycol or its ester-forming derivative; A liquid phase polycondensation step in which the esterified product is heated and melted in the presence of a polycondensation catalyst, and a solid phase in which the polycondensation reaction product obtained in the liquid phase polycondensation step is heated to a temperature below the melting point in an inert atmosphere. It is characterized by including a polycondensation step and a water treatment step of bringing the polycondensation reaction product obtained in the solid phase polycondensation step into contact with water.

Such a water treatment step can be carried out, for example, by contacting polyethylene terephthalate with water at 1 to 150°C for 1 minute to 100 hours.

Further, such a water treatment step can be carried out by contacting polyethylene terephthalate with water vapor or water vapor-containing gas at room temperature to 150° C. for 1 minute to 50 hours.

Polyethylene terephthalate obtained by the method for producing polyethylene terephthalate according to the present invention has a small amount of oligomers such as cyclic trimers produced during molding, and therefore mold stains are less likely to occur.

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

The method for producing polyethylene terephthalate according to the present invention includes an esterification step, a liquid phase polycondensation step of heating and melting the esterified product obtained in the esterification step, and a polycondensation reaction product obtained in the liquid phase polycondensation step. It includes a solid phase polycondensation step of heating to a temperature below the melting point, and a water treatment step of bringing the polycondensation reaction product obtained in the solid phase polycondensation step into contact with water.

The method for producing polyethylene terephthalate according to the present invention is carried out using terephthalic acid or its ester-forming derivative, ethylene glycol or its ester-forming property, and a conductor as raw materials. Other dicarboxylic acids and/or other glycols may be copolycondensed.

Examples of dicarboxylic acids used in copolycondensation other than terephthalic acid include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, and diphenoxyethane dicarboxylic acid, adipic acid, and sebacic acid. , azelaic acid, aliphatic dicarboxylic acids such as decanedicarboxylic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid.

Glycols other than ethylene glycol used for copolycondensation include aliphatic glycols such as trimethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, and dodecamethylene glycol, and cyclohexane dimetatool. alicyclic glycols such as bisphenols, hydroquinone, 2.2-bis(4-β-
Examples include aromatic diols such as hydroxyethoxyphenyl)propane.

The raw materials containing terephthalic acid or its ester-forming derivative and ethylene glycol or its ester-forming derivative as described above are esterified.

Specifically, first, a slurry containing terephthalic acid or its ester-forming derivative and ethylene glycol or its ester-forming derivative is prepared.

Such a slurry contains 1.02 to 1.4 moles, preferably 1.03 to 1.3 moles of ethylene glycol or its ester-forming derivative per mole of terephthalic acid or its ester-forming derivative. . This slurry is continuously fed to the esterification reaction step.

The esterification reaction is carried out using an apparatus in which at least two esterification reactors are connected in series, under conditions where ethylene glycol is refluxed, and water produced by the reaction is removed from the system in a rectification column. . The reaction conditions for carrying out the esterification reaction are that the temperature of the first stage esterification reaction is usually 240 to 270°C, preferably 245 to 265°C, and the pressure is usually 0.2 to 3 kg/Cr1G, preferably 0. .5 to 2 kg/car, the temperature of the final stage esterification reaction is usually 250 to 280°C, preferably 255 to 275°C, and the pressure is usually 0 to 1.
5 kg/cnfG preferably 0 to 1.3 kg/cnf
It is G.

Therefore, when the esterification reaction is carried out in two stages, the esterification reaction conditions of the first stage and the second stage are within the above range, and when the esterification reaction is carried out in three or more stages, the esterification reaction conditions of the first stage and the second stage are within the above range. The reaction conditions of the esterification reaction from the first stage to one stage before the final stage are between the reaction conditions of the first stage and the final stage.

For example, when the esterification reaction is carried out in three stages, the reaction temperature of the second stage esterification reaction is usually 245
-275°C, preferably 250-270°C, and the pressure is usually 0-2kg/cnfG, preferably 0.2-1.5k
g/c go G. The reaction rate of these esterification reactions is not particularly limited in each stage, but it is preferable that the increase and degree of esterification reaction rate in each stage is smoothly distributed, and furthermore, in the final stage of esterification. In the reaction product, usually 90% or more, preferably 9
It is desirable to reach 3% or more.

Through these esterification steps, an esterified product (lower condensate) is obtained, and the number average molecular weight of this esterified product is usually 500 to 5,000.

Such an esterification reaction can be carried out without adding any additives other than terephthalic acid and ethylene glycol, or it can also be carried out in the coexistence of a polycondensation catalyst as described below. In addition, tertiary amines such as triethylamine, tri-n-butylamine, benzyldimethylamine, quaternary ammonium hydroxides such as tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide, trimethylbenzylammonium hydroxide, and lithium carbonate, It is preferable to add a small amount of a basic compound such as sodium carbonate, potassium carbonate, or sodium acetate, since this allows the proportion of dioxyethylene terephthalate component units in the main chain of polyethylene terephthalate to be kept at a relatively low level.

Next, the obtained esterified product is heated under reduced pressure in the presence of a polycondensation catalyst to a temperature equal to the melting point of the obtained polyethylene terephthalate, and the glycol produced at this time is distilled out of the system to perform polycondensation. Supplied to the liquid phase polycondensation process.

Such a polycondensation reaction in a liquid phase may be carried out in one step, or may be carried out in multiple steps. When carrying out the polycondensation reaction in multiple stages, the polycondensation reaction conditions are such that the reaction temperature for the first stage polycondensation is usually 250 to 290°C, preferably 260°C.
0 to 280°C, and the pressure is usually 500 to 20To
rr is preferably 200 to 30 Torr, the temperature of the final stage polycondensation reaction is usually 265 to 300°C, preferably 270 to 295°C, and the pressure is usually 10 to 0.1
To+r is preferably 5 to 0.5 Tott.

When the polycondensation reaction is carried out in two stages, the polycondensation reaction conditions for the first stage and the second stage are within the above ranges, and when the polycondensation reaction is carried out in three or more stages, from the second stage The reaction conditions for the polycondensation reaction up to one stage before the final stage are between the reaction conditions for the first stage and the reaction conditions for the final stage.

For example, if the polycondensation reaction is carried out in three stages,
The reaction temperature of the second stage polycondensation reaction is usually 260 to 295
℃ Preferably 270 to 285℃, and the pressure is usually 5
It is in the range of 0 to 2 Torr, preferably 40 to 5 Tor+. There is no particular limit to the intrinsic viscosity (rv) reached in each of these polycondensation reaction steps, but it is preferable that the degree of increase in intrinsic viscosity in each step is distributed smoothly, and that The intrinsic viscosity (IV) of polyethylene terephthalate obtained from a polycondensation reactor is usually 0.35 to 0.80 d
I/g preferably 0.45-0.75dj! /g, more preferably 0.55-0. A range of 75 dl/g is desirable.

In this specification, the intrinsic viscosity is calculated from the solution viscosity measured at 25° C. after heating and dissolving 1.2 g of polyethylene terephthalate in 15 cc of 0-chlorophenol and then cooling the solution.

In addition, the density of this polyethylene terephthalate is usually 1
．． It is desirable that it is 33 to 1.35 g/-.

Herein, the density of polyethylene terephthalate is measured at a temperature of 23° C. in a density gradient tube using a mixed solvent of carbon tetrachloride and heptane.

4. The polycondensation reaction as described above is preferably carried out in the presence of a catalyst and a stabilizer. As the catalyst, germanium compounds such as germanium dioxide, germanium tetraethoxide, germanium tetralobtoxide, antimony catalysts such as antimony trioxide, and titanium catalysts such as titanium tetrabutoxide can be used. Among these catalysts, germanium dioxide compounds are preferred because the produced polyethylene terephthalate has excellent hue and transparency. In addition, as stabilizers, phosphoric acid esters such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, triph, enyl phosphate, tricresyl phosphate, triphenyl phosphite, trisdodecyl phosphite, trisnonyl Phosphite esters such as phenyl phosphite, acidic phosphoric acid esters such as methyl arashido phosphate, isoprobil arashido phosphate, butyl arashido phosphate, dibutyl phosphate, monobutyl phosphate, di5-octyl phosphate, phosphoric acid, polyphosphorus Phosphorus compounds such as acids are used. The proportion of these catalysts or stabilizers used is usually 0.00 as the weight of the metal in the catalyst, based on the weight of the mixture of terephthalic acid and ethylene glycol.
05 to 0.2% by weight, preferably 0.001 to 0.05% by weight, and in the case of a stabilizer, usually 0.001 to 0.1% by weight as the weight of phosphorus atoms in the stabilizer. %
Preferably it is in the range of 0.002 to 0.02% by weight.

These catalysts and stabilizers can be supplied at the stage of the esterification reaction process, or can be supplied to the first stage reactor of the polycondensation reaction process.

The polyethylene terephthalate used in the present invention includes:
As mentioned above, dicarboxylic acids other than terephthalic acid and diols other than ethylene glycol may be contained in an amount of 20 mol% or less, but particularly preferably used polyethylene terephthalate is ethylene terephthalate represented by the general formula [I] 6 The content of the terephthalate component unit (a) is in the range of 95.0 to 99.0 mol%, and the content of the dioxyethylene terephthalate component unit (b) represented by the general formula [II] is 1.0%. It is desirable that the content be in the range of 5.0 mol %.

The polyethylene terephthalate thus obtained from the final polycondensation reactor is usually molded into granules (chips) by melt extrusion.

Such granular polyethylene terephthalate is usually 2
．． It is desirable to have an average particle size of 0 to 5.0 mm, preferably 2.2 to 4.0 mm.

The granular polyethylene terephthalate that has undergone the liquid phase polycondensation process in this manner is subjected to a solid phase polycondensation process.

The granular polyethylene terephthalate to be supplied to the solid phase polycondensation process is pre-crystallized by heating to a temperature lower than the temperature at which the solid phase polycondensation is performed. Good too.

Such a pre-crystallization step may be carried out by heating the granular polyethylene terephthalate 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 alternatively, the granular polyethylene terephthalate may be Normally, under a water vapor atmosphere, an inert gas atmosphere containing water vapor, or an air atmosphere containing water vapor,
It may be carried out by heating to a temperature of 120 to 200°C for 1 minute or more.

The solid phase polycondensation step in which such granular polyethylene terephthalate is supplied consists of at least one stage, and the polycondensation temperature is usually 190 to 230°C, preferably 195 to 225°C.
℃, and the pressure is usually 1 kg/crlG ~ 10 TO''
r Preferably under conditions of normal pressure to 100 Tour,
The solid phase polycondensation reaction is carried out under an atmosphere of an inert gas such as nitrogen gas, argon gas, or carbon dioxide gas. Among these inert gases, nitrogen gas is preferred.

The intrinsic viscosity of the polyethylene terephthalate thus obtained is usually 0. 50 di 7g or more, preferably 0.54 dI/g or more, more preferably 0.70dj! /g or more, particularly preferably 0.72d
It is desirable that it is 1/g or more.

The density of this polyethylene terephthalate is usually 1.3
7g/- or more, preferably 1.38g/- or more, more preferably 1.39g/cd! The above is desirable.

Further, the amount of oligomer contained in such polyethylene terephthalate is 0.6% by weight or less, preferably 0.5% by weight or less.
It is desirable that the amount is not more than 0.45% by weight, more preferably not more than 0.40% by weight.

In this specification, the amount of oligomer contained in polyethylene terephthalate is measured as follows.

That is, after dissolving a predetermined amount of polyethylene terephthalate in 0-chlorophenol, it was reprecipitated with 90% tetrahydrofuran and filtered to remove linear polyethylene terephthalate, and then the obtained filtrate was subjected to liquid chromatography (Shimadzu Corporation). The amount of oligomers contained in the polyethylene terephthalate is determined by supplying the polyethylene terephthalate to a polyethylene terephthalate (L C7A), and this value is divided by the amount of polyethylene terephthalate used in the measurement to obtain the amount of oligomers contained in the polyethylene terephthalate (% by weight).

The granular polyethylene terephthalate obtained through such a solid phase polycondensation process is subjected to water treatment, which involves treating the granular polyethylene terephthalate with water, steam, an inert gas containing steam, air containing steam, etc. This is done by making contact.

The contact of the granular polyethylene terephthalate with water is carried out by immersing the polyethylene terephthalate in water at room temperature to 150° C. for 1 minute to 100 hours or more, preferably 1 minute to 20 hours, particularly preferably 5 minutes to 10 hours. Desirably, the granular polyethylene terephthalate is immersed in hot water at 50 to 150°C for 1 minute to 10 hours. More preferably, the granular polyethylene terephthalate is immersed in hot water at 70 to 110°C for 3 minutes to 5 hours.

Particularly preferably, granular polyethylene terephthalate is
This is carried out by immersion in hot water at 0 to 100°C for 5 minutes to 3 hours.

In addition, contact between granular polyethylene terephthalate and water vapor or water vapor-containing gas is usually carried out at room temperature to 150°C.
Preferably 50-150°C, more preferably 70-1
The granular polyethylene terephthalate and the water vapor are brought into contact by supplying or in the presence of water vapor or a water vapor-containing inert gas or water vapor-containing air at a temperature of 10° C., preferably in an amount of 0.5 g or more per kg of granular polyethylene terephthalate. This is done by

The contact between the granular polyethylene terephthalate and water vapor is usually carried out for 1 minute to 50 hours, preferably for 5 minutes to 10 hours.

By treating polyethylene terephthalate with 1 part of water as described above, the solid phase polycondensation rate of polyethylene terephthalate is reduced, and after heating and melting the polyethylene terephthalate at a temperature of 290°C to form a stepped square plate, It is possible to suppress the increase in the amount of oligomers.

Polyethylene terephthalate treated with water in this way has a reduced solid phase polycondensation rate as described above, but it can be heated to a temperature of 215°C in an inert gas atmosphere to undergo solid phase polycondensation. The actual polycondensation rate was 0.0055 d
Preferably less than //g・hour L< is 0.005 dl/g・
Hours or less, more preferably 0. 004 dl! /g・
Especially preferably 0.003 dl! /g·hour or less is desirable.

In this specification, the polycondensation rate upon solid-phase polycondensation of polyethylene terephthalate is specifically measured as follows.

60g of granular polyethylene terephthalate with an inner diameter of 22In
Fill a cylindrical stainless steel container with a height of In1 of 80 mm,
Seal tightly. This container has a nozzle for venting inert gas 2 at the bottom, and the inert gas is discharged from the top to the outside of the system.

Solid-phase polycondensation is carried out by fixing a sealed stainless steel container filled with granular polyethylene terephthalate in a sand bath equipped with a heating device (manufactured by Nihon Parkerizing Zinc Corporation, aluminum oxide), and then blowing nitrogen as an inert gas. implement.

The nitrogen to be removed has a dew point of 150° C. or less and an oxygen concentration of 20 ppm or less, and is preheated to the same temperature as the bath temperature before being supplied to the stainless steel container. Nitrogen is supplied to the stainless steel vessel at a rate of 20 ONl per hour (standard conditions).

The sand bath is kept in a fluidized state by air, so that the temperature of the sand bath is uniform and there is no temperature distribution.

The sand bath heater is controlled by a program controller so that the temperature of the bath reaches a predetermined solid phase polycondensation moisture content.

The solid-phase polycondensation rate is measured using the device described above.
Specifically, it will be quantified using the following method. The granular polyethylene terephthalate was filled into a cylindrical stainless steel container as described above, sealed and fixed in a sand bath, and the temperature was raised from room temperature to 170°C in 30 minutes while nitrogen was aerated at a rate of 20ONl per hour. Next, after holding at 170°C for 1 hour, the temperature was raised from 170°C to 215°C over 30 minutes, and further held at 215°C for 4 hours to perform a solid phase polycondensation reaction.

After the solid phase polycondensation reaction, the heating was stopped and the temperature in the sand bath was lowered to 70°C while nitrogen was still being aerated.Then, the stainless steel container was taken out from the sand bath and the intrinsic viscosity g of the solid phase polycondensed granular polyethylene terephthalate was measured. /dI (
IV). Let this IV value be AdI/g.

In a similar manner, the IV of granular polyethylene terephthalate is measured when the holding time at 215°C is 20 hours.

Let this IV value be Bai/g.

The solid phase polycondensation rate is calculated by the following formula.

4-A-1, R is the solid phase polycondensation rate (dl/g/hour),
A and B are the IV values after 4 and 20 hours, respectively (
dll/g).

Furthermore, polyethylene terephthalate subjected to the water treatment as described above is significantly inhibited from increasing oligomers during the subsequent molding process. This can be confirmed, for example, by measuring the amount of oligomer increase after heating and melting polyethylene terephthalate at a temperature of 290° C. to form a stepped square plate. Specifically, the water-treated polyethylene terephthalate according to the present invention has an oligomer increase amount y (% by weight) after heating and melting at a temperature of 290°C to form a stepped square plate such that y≦−0, 20x+0. 20 Preferably y≦−〇,
20x+0.18 More preferably y≦-0,20
It is desirable that x+0.16.

5 Oligomer concentration (% by weight) in the above formula or before forming a stepped square plate.

In this specification, oligomer increase amount y (wt%) after forming a stepped square plate from granular polyethylene terephthalate
) is measured as follows.

That is, the oligomer content was measured in advance (measured value
%) 2 kg of granular polyethylene terephthalate at a temperature of 14
The granular polyethylene terephthalate is dried under the conditions of 0° C. and pressure IQ tour for 16 hours using an upper rack type dryer to reduce the moisture content of the granular polyethylene terephthalate to 50 ppm or less.

Next, the dried granular polyethylene terephthalate is injection molded using an M-70A injection molding machine manufactured by Meiki Seisakusho under conditions of a cylinder temperature of 290°C and a mold cooling water temperature of 15°C to form a stepped square plate shape. get something

Injection molding of stepped rectangular plate-shaped moldings takes 12 seconds for measurement and 60 seconds for injection.
The dried granular polyethylene terephthalate was supplied from a hopper to an injection molding machine in a manner that the molding process was carried out within 6 seconds. Further, the residence time of the molten resin in the molding machine is approximately 72 seconds. The weight of each stepped rectangular plate-shaped molded product is 75 g, and any one of the 11th to 15th molded products after the start of injection molding is used as the sample for oligomer measurement.

The stepped rectangular plate-shaped molded product 1 has a shape as shown in FIG. The thickness is approximately 4 mm. Using this 0 part, the amount of oligomer increase in the molded product is examined.

Next, the molded plate-shaped product with a thickness of 4 mm is cut into chips to be used as samples for oligomer measurement.

Note that the oligomer content of polyethylene terephthalate constituting the stepped square plate is measured by the same method as above.

By subjecting polyethylene terephthalate to water treatment in this way, it is possible to reduce the solid phase polycondensation rate and suppress the increase in oligomers such as cyclic trimers contained in polyethylene terephthalate during molding. By adding water treatment to polyethylene terephthalate, the polycondensation catalyst, such as germanium catalyst, contained in polyethylene terephthalate is deactivated, so that even if heated during molding, the decomposition reaction or transesterification reaction hardly progresses, and the resulting cyclic It is thought that the amount of oligomers such as trimers decreases.

As described above, the polyethylene terephthalate obtained by the production method according to the present invention has a small amount of oligomers such as cyclic trimers produced during molding, and therefore can be fed to a molding machine such as an injection molding machine to form a hollow molded product. When a preform is molded, this preform is inserted into a mold of a predetermined shape, stretched and blow molded, and then heat set to form a blow molded container, oligomers such as cyclic trimers adhere to the mold. mold contamination is less likely to occur.

Effects of the Invention The method for producing polyethylene terephthalate according to the present invention includes a water treatment step in which polyethylene terephthalate is brought into contact with water. Since the amount of oligomers such as cyclic trimers is small, and the total amount of oligomers such as cyclic trimers contained in polyethylene terephthalate during molding is small, mold stains are less likely to occur during molding.

Therefore, polyethylene terephthalate obtained by the method for producing polyethylene terephthalate according to the present invention is
There is no need for frequent cleaning when manufacturing molded products,
The productivity of molded products such as bottles, films, and sheets can be improved, and the resulting bottles, films,
Whitening of the sheet can be prevented.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 A continuous polycondensation apparatus was used, in which the first, second, third, fourth, and fifth reactors were horizontal, and the sixth reactor was a biaxially rotating horizontal reactor. Polyethylene terephthalate was produced by performing continuous polymerization as follows.

9 3,750 parts by weight of the reaction solution was retained in advance, and 1.7 kg/Cr was heated at 255°C under nitrogen atmosphere with stirring.
1437 parts by weight of high purity terephthalic acid and 6 parts by weight of ethylene glycol were added per hour to the first reactor maintained under conditions of 1G.
A slurry prepared by mixing 45 parts by weight was continuously fed to perform the first esterification reaction. In this first stage esterification reaction, 203 parts by weight of water and 3 parts by weight of water were used.
Part by weight of the mixture with ethylene glycol was distilled off.

The esterification reaction product in the first stage was controlled to have an average residence time of 2.0 hours, and the esterification reaction product was continuously stirred at 260°C and maintained at 0.8 kg/cJG. 2 reactors.

In this reactor 2, a homogeneous solution of 0.35 parts by weight of germanium dioxide and 32 parts by weight of ethylene glycol is continuously supplied per hour, and at the same time, a uniform solution of 0.35 parts by weight of germanium dioxide and 32 parts by weight of ethylene glycol is supplied per hour. The mixed liquid was continuously distilled off to continue the second stage esterification reaction. In addition, the esterification reaction product in the second stage was controlled so that the average residence time was 2.0 hours, and the esterification reaction product was continuously stirred for 2 hours.
It was led to a third reactor maintained at 65° C. and under atmospheric pressure conditions.

In this third reactor, a homogeneous solution in which 1.23 parts by weight of trimethyl phosphate and 22 parts by weight of ethylene glycol were mixed is continuously supplied per hour, and at the same time, 21 parts by weight of water and 38 parts by weight are supplied per hour. The mixture with ethylene glycol was continuously distilled off, and the third stage esterification reaction was continued.

This third stage esterification reaction product also has an average residence time of 2.
275°C under continuous stirring for 0 hours.
into a fourth reactor maintained at 70 mmHg. In this fourth reactor, a mixture of 62 parts by weight of ethylene glycol and 6 parts by weight of water was continuously distilled off per hour to carry out the first stage polycondensation reaction. The polycondensation reaction product in the first stage was controlled to have an average residence time of 1.0 hours, and was heated to 5 mmH at 280°C with continuous stirring.
to a fifth reactor maintained at g.

1 In this fifth reactor, a liquid mixture of 26 parts by weight of ethylene glycol and 3 parts by weight of water was continuously distilled off per hour to continue the second stage polycondensation reaction. In addition, the second stage polycondensation reaction product was controlled to have an average residence time of 1.0 hours, and was continuously heated at 282°C to 285°C and 1.8mmHg to 2.5mmHg. The reactor was then led to the sixth reactor, which was a maintained horizontal twin-screw rotating reactor.

In this sixth reactor, the reaction solution of 12 parts by weight of ethylene glycol and 1 part by weight of water was continuously distilled off per hour to continue the third stage polycondensation reaction. The polycondensation reaction product in the third stage is controlled to have an average residence time of 2.5 hours, and is continuously extracted in the form of a strand out of the reactor by a polyester extractor and immersed in water. After being soaked and cooled, it was cut into chips using a strand cutter. The intrinsic viscosity IV of polyethylene terephthalate obtained by the above liquid phase polymerization measured in 0-chlorophenol at 25°C is (L, 5
7 dA/g, and the content of the dioxyethylene terephthalate component was 2.50 mol%.

Furthermore, the polyethylene terephthalate obtained by liquid phase polymerization is dried at about 140° C. for about 15 hours in a nitrogen atmosphere and crystallized, and then loaded into a basic solid phase polymerization vessel.
Solid phase polymerization was performed at 205° C. for 15 hours under a nitrogen atmosphere. 0 of the polyethylene terephthalate thus obtained
-Intrinsic viscosity measured in chlorophenol at 25°C is 0.
80dl/g, density is 1.40g/all
The oligomer content is 0.31% by weight, and the content of dioxyethylene terephthalate component is 2.
．． It was 53 mol%.

Polyethylene terephthalate thus obtained (
A) 5 kg was immersed in 6.5 kg of distilled water in a stainless steel container.

Next, a stainless steel container containing polyethylene terephthalate and distilled water was heated from the outside, the internal temperature was controlled at 90°C, and the water was treated by holding it for 4 hours. After that, it was dehydrated and heated to 140°C for 14 hours with nitrogen. It dried inside.

Dry polyethylene terephthalate was subjected to solid-state polycondensation by heating to a temperature of 215° C. under a nitrogen gas atmosphere as described herein, and the polycondensation rate was 0. 0
026 dl/g·hour.

In addition, the polyethylene terephthalate (M made by Meiki Seisakusho)
-7OA) was molded at 290°C using an injection molding machine, and the oligomer content of the stepped square plate-shaped molded product was 0.35% by weight.
The increase in oligomer was 0.04% by weight.

Example 2 In Example 1, polyethylene terephthalate (A)
Fill a stainless steel container with 5 kg of
．． The same procedure as in Example 1 was carried out except that 5 kg of the material was steamed for 30 minutes and water treatment was performed.

After drying in the same manner as in Example 1, the solid phase polycondensation rate was measured to be 0.0052 dA'/g·hr.

Furthermore, the oligomer content of molded product 4 molded in the same manner as in Example 1 was 0.40% by weight, and the increase in oligomer amount was 0.09% by weight.

Example 3 In Example 1, polyethylene terephthalate (A)
Fill a pressurized stainless steel container with 5 kg of
．． The same procedure as in Example 1 was carried out, except that water treatment was carried out by passing 43 kg/ci of steam (saturation temperature 110° C.) at a rate of 0.5 kg/hour for 30 minutes.

After drying in the same manner as in Example 1, the solid phase polymerization rate was measured to be 0.0048 dl/g·hr.

Furthermore, the oligomer content of the molded product molded in the same manner as in Example 1 was 0.37% by weight, and the increase in oligomer amount was 0.06% by weight.

Example 4 In Example 1, polyethylene terephthalate (A)
The same procedure as in Example 1 was carried out except that the water treatment was performed by immersing the sample in distilled water at 18° C. for 30 minutes.

After drying in the same manner as in Example 1, the solid phase polymerization rate was measured to be 0.0042 dl/g·hr.

Furthermore, the oligomer content of the molded product molded in the same manner as in Example 1 was 0.39% by weight, and the increase in oligomer amount was 0.08% by weight.

Comparative Example 1 The polyethylene terephthalate obtained without hydrothermal treatment in Example 1 was dried in nitrogen gas at 140'C for 14 hours, and then heated to a temperature of 215°C in a nitrogen atmosphere to reduce the solid phase weight. The polycondensation rate of the condensation treatment was 0.0o6
It was 7 dl/g·hr.

Further, the oligomer content of the molded product obtained by molding the polyethylene terephthalate at 29000 was 0.50% by weight, and the increase in oligomer amount was 0.19% by weight.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a stepped square plate-shaped molded product.

Claims (3)

[Claims] (1) An esterification step of esterifying terephthalic acid or its ester-forming derivative with ethylene glycol or its ester-forming derivative, and heating the esterified product obtained in the above esterification step in the presence of a polycondensation catalyst. a liquid phase polycondensation step in which the polycondensation reaction product obtained in the liquid phase polycondensation step is melted; a solid phase polycondensation step in which the polycondensation reaction product obtained in the liquid phase polycondensation step is heated to a temperature below the melting point in an inert atmosphere; and the above solid phase polycondensation step A method for producing polyethylene terephthalate, comprising a water treatment step of bringing the polycondensation reaction product obtained in step 1 into contact with water. (2) The above water treatment, polyethylene terephthalate 1
The method for producing polyethylene terephthalate according to claim 1, characterized in that the process is carried out by immersing the polyethylene terephthalate in water at a temperature of -150°C for 1 minute - 100 hours. (3) The above water treatment is performed by adding polyethylene terephthalate to water vapor or water vapor-containing gas at a temperature of room temperature to 150°C.
Claim 1 characterized in that the contact is carried out for 50 minutes to 50 hours.
The method for producing polyethylene terephthalate as described.