JPH0714997B2 - Method for producing polyethylene terephthalate - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing polyethylene terephthalate, which is used for forming films and sheets including bottles, and more specifically, polyethylene terephthalate in which mold stains are less likely to occur during molding. And a method for producing polyethylene terephthalate.

TECHNICAL BACKGROUND OF THE INVENTION AND ITS PROBLEMS Conventionally, various resins have been adopted as materials for containers such as seasonings, oils, beverages, cosmetics and detergents according to the type of filling contents and the purpose of use thereof. .

Among these, polyethylene terephthalate is excellent in mechanical strength, heat resistance, transparency and gas barrier property, and is therefore particularly suitable as a material for a beverage filling container such as juice, soft drink, carbonated drink and the like.

Such polyethylene terephthalate is obtained 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 conducting liquid phase polycondensation in the presence of a polycondensation catalyst. And then solid phase polycondensation. Then, this polyethylene terephthalate is supplied to a molding machine such as an injection molding machine to mold a preform for a hollow molded body, and the preform is inserted into a mold of a predetermined shape and stretch blow molded, or further heat treated (heat set). ) And then molded into a hollow molded container.

However, the conventionally known polyethylene terephthalate obtained by the above-mentioned production method contains oligomers such as cyclic trimers, and the oligomers such as cyclic trimers are blow mold inner surfaces and metal molds. Mold gas outlet,
The mold was contaminated by adhering to the exhaust pipe or the like, or the oligomers were adhered to the vent part of the mold of the injection molding machine as described above and the mold was contaminated.

Such mold stains cause the surface roughness 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.

In view of the above-mentioned circumstances, the inventors of the present invention have earnestly studied in order to obtain polyethylene terephthalate that is less likely to cause mold fouling during molding, and the main cause of mold fouling during molding is molding of polyethylene terephthalate. It has been found that a large amount of oligomers such as a cyclic trimer is sometimes produced and the total amount of oligomers such as a cyclic trimer contained in polyethylene terephthalate increases.

The inventors of the present invention further studied based on the above findings, and suppressed the increase in the total amount of oligomers such as cyclic trimers during molding by contacting polyethylene terephthalate obtained by a series of continuous steps with water. They have found that they can do so and have completed the present invention.

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

Further, JP-A-59-219328 discloses that the intrinsic viscosity is at least 0.4 dl / g or more and the density is 1.35 g / cm ³ or less,
A step of adjusting the humidity of a polyester containing polyethylene terephthalate units as the main repeating unit so that the water content is at least 0.2% by weight, a step of pre-crystallization at a temperature of 140 ° C or higher, and a temperature of 180 ° C or higher and 240 ° C or lower. Discloses a method for producing a polyester having a high degree of polymerization, which comprises a step of performing solid phase polymerization under an inert gas atmosphere or under reduced pressure.

An object of the present invention is to solve the problems associated with the prior art as described above, and to obtain polyethylene terephthalate in which the amount of oligomers produced during molding is small and mold stains are less likely to occur. It is an object of the present invention to provide a method for producing polyethylene terephthalate capable of

SUMMARY OF THE INVENTION The method for producing polyethylene terephthalate according to the present invention comprises terephthalic acid or an ester-forming derivative thereof,
An esterification step of esterifying ethylene glycol or an ester-forming derivative thereof, a liquid-phase polycondensation step of heating and melting the esterified product obtained in the esterification step in the presence of a polycondensation catalyst, and the liquid-phase polycondensation step. Solid-phase polycondensation step of heating the polycondensation reaction product obtained in the condensation step to a temperature below the melting point under an inert atmosphere, and the intrinsic viscosity obtained in the solid-phase polycondensation step is 0.54 dl / g. A polycondensation reaction product having a density of 1.37 g / cm ³ or more and an oligomer (cyclic trimer) content of 0.50% by weight or less is brought into contact with water at 70 to 110 ° C for 3 minutes to 5 hours to obtain polyethylene. And a water treatment step of deactivating the polycondensation catalyst contained in terephthalate.

The polyethylene terephthalate obtained by the method for producing polyethylene terephthalate according to the present invention has a small amount of an oligomer such as a cyclic trimer produced at the time of 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 comprises 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 comprises terephthalic acid or an ester-forming derivative thereof,
It is carried out using ethylene glycol or an ester-forming derivative thereof as a raw material, but this polyethylene terephthalate may be copolycondensed with 20 mol% or less of another dicarboxylic acid and / or another glycol.

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

Specific examples of glycols used for copolycondensation other than ethylene glycol include trimethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, dodecamethylene glycol and other aliphatic glycols, cyclohexanedimethanol and the like. And alicyclic glycols, bisphenols, hydroquinone, and aromatic diols such as 2,2-bis (4-β-hydroxyethoxyphenyl) propane.

The raw material containing the above-mentioned terephthalic acid or its ester-forming derivative and ethylene glycol or its ester-forming derivative is 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 mol, preferably 1.03 to 1.3 mol, of ethylene glycol or its ester-forming derivative with respect to 1 mol of terephthalic acid or its ester-forming derivative. This slurry is continuously supplied to the esterification reaction step.

The esterification reaction is carried out under a condition in which ethylene glycol is refluxed by using a device in which at least two esterification reactors are connected in series, while removing water generated by the reaction from the system in a rectification column. . The reaction conditions for carrying out the esterification reaction are that the temperature of the first step esterification reaction is usually 240 to 270 ° C, preferably 245 to 265 ° C, and the pressure is usually
0.2 to 3 kg / cm ² G, preferably 0.5 to ² kg / cm ² G, 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 / cm ² G and preferably 0~1.3kg / cm ² 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 ranges, respectively, and when carried out in three or more stages, the second stage is carried out. The reaction conditions for the esterification reaction from the first stage to the stage immediately before the final stage are those 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 reaction temperature for the esterification reaction in the second stage is usually 245-2.
75 ℃ is preferably 250 ~ 270 ℃, the pressure is usually 0 ~ 2kg /
cm ² G It is preferably 0.2 to 1.5 kg / cm ² G. The reaction rate of these esterification reactions is not particularly limited in each stage, but it is preferable that the increase and the degree of the esterification reaction rate in each stage be smoothly distributed. 90% for reaction products
Above, it is desirable to reach 93% or more.

An esterified product (low-order condensate) is obtained by these esterification steps, and the number average molecular weight of this esterified product is usually 500 to 5000.

Such an esterification reaction can be carried out without adding an additive other than terephthalic acid and ethylene glycol, and can also be carried out in the coexistence of a polycondensation catalyst described later. Tertiary amines such as triethylamine, tri-n-butylamine and benzyldimethylamine, quaternary ammonium hydroxide such as tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide, trimethylbenzylammonium hydroxide and lithium carbonate, sodium carbonate, It is preferable to add a small amount of a basic compound such as potassium carbonate or sodium acetate, since the ratio of the dioxyethylene terephthalate component unit in the main chain of polyethylene terephthalate can be maintained at a relatively low level.

Then, the obtained esterified product is heated under reduced pressure in the presence of a polycondensation catalyst to a temperature not lower than the melting point of the obtained polyethylene terephthalate, and the glycol produced at this time is distilled out of the system to perform polycondensation. It is supplied to the polycondensation step.

Such a polycondensation reaction in the liquid phase may be carried out in one step or in a plurality of steps. When carried out in a plurality of stages, the polycondensation reaction conditions are such that the reaction temperature of the first stage polycondensation is usually 250 to 290 ° C., preferably 260 to 280 ° C., and the pressure is usually 500 to 20 Torr, preferably 200. ~ 30 Torr
The temperature of the final polycondensation reaction is usually 265 to 3
00 ℃ is preferably 270 ~ 295 ℃, the pressure is usually 10 ~ 0.1T
orr It is preferably 5 to 0.5 Torr.

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

For example, when the polycondensation reaction is carried out in three stages,
The reaction temperature of the second-stage polycondensation reaction is usually 260 to 295 ° C, preferably 270 to 285 ° C, and the pressure is usually 50 to 2 Torr, preferably 40 to 5 Torr. The intrinsic viscosity (IV) reached in each of these polycondensation reaction steps is not particularly limited, but it is preferable that the degree of increase in the intrinsic viscosity at each stage is distributed smoothly. The intrinsic viscosity (IV) of polyethylene terephthalate obtained from the reactor is usually 0.35 to 0.80 dl / g, preferably 0.45 to
It is desirable that the range is 0.75 dl / g, and more preferably 0.55 to 0.75 dl / g.

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

The density of this polyethylene terephthalate is usually 1.
It is preferably 33 to 1.35 g / cm ³ .

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

The polycondensation reaction as described above is preferably carried out in the presence of a catalyst and a stabilizer. As the catalyst, a germanium compound such as germanium dioxide, germanium tetraethoxide, germanium tetra n-butoxide, an antimony catalyst such as antimony trioxide, and a titanium catalyst such as titanium tetrabutoxide can be used. Among these catalysts, the use of a germanium dioxide compound is preferable because the produced polyethylene terephthalate has excellent hue and transparency. Examples of stabilizers include phosphoric acid esters such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, triphenyl phosphate, tricresyl phosphate, tolphenyl phosphite, trisdodecyl phosphate, trisnonylphenyl. Phosphite such as phosphite, acidic phosphoric acid ester such as methyl acid phosphate, isopropyl azido phosphate, butyl acid phosphate, dibutyl phosphate, monobutyl phosphate, dioctyl phosphate and phosphorus compound such as phosphoric acid, polyphosphoric acid Is used. The proportion of these catalysts or stabilizers used is usually 0.0005 to 0.2% by weight, as the weight of the metal in the catalyst in the case of the catalyst, relative to the weight of the mixture of terephthalic acid and ethylene glycol.
It is in the range of 0.001 to 0.05% by weight, and in the case of a stabilizer, it is usually 0.001 to 0.1 as the weight of phosphorus atom in the stabilizer.
% By weight It is preferably in the range of 0.002 to 0.02% by weight. The catalyst and the stabilizer may be supplied at the stage of the esterification reaction step or may be supplied to the reactor at the first stage of the polycondensation reaction step.

The polyethylene terephthalate used in the present invention includes
As described 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 polyethylene terephthalate which is particularly preferably used is represented by the general formula [I] The content of the ethylene terephthalate component unit (a) represented by the formula (I) is in the range of 95.0 to 99.0 mol%,
I] The content of the dioxyethylene terephthalate component unit (b) represented by is preferably in the range of 1.0 to 5. mol%.

In this way, the polyethylene terephthalate obtained from the final polycondensation reactor is usually formed into particles (chip shape) by a melt extrusion molding method.

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

A solid phase polycondensation step is added to the granular polyethylene terephthalate that has undergone the liquid phase polycondensation step in this manner.

The granular polyethylene terephthalate supplied to the solid-phase polycondensation step may be supplied to the solid-phase polycondensation step after being preliminarily crystallized by heating to a temperature lower than the temperature in the case of performing the solid-phase polycondensation in advance. .

In such a pre-crystallization step, granular polyethylene terephthalate is usually dried at 120 to 200 ° C, preferably 130 ° C.
It may be carried out by heating to a temperature of ˜180 ° C. for 1 minute to 4 hours, or granular polyethylene terephthalate is usually heated at 120 to 200 ° C. under a steam atmosphere or a steam-containing inert gas atmosphere or a steam-containing air atmosphere.
You may perform it by heating at the temperature of 1 minute or more.

The solid phase polycondensation step in which such granular polyethylene terephthalate is supplied comprises at least one stage, the polycondensation temperature is usually 190 to 230 ° C., preferably 195 to 225 ° C., and the pressure is usually 1 kg / cm ² G ~ 10 Torr, preferably normal pressure to 100T
The solid-phase polycondensation reaction is carried out under an orr condition in an atmosphere of an inert gas such as nitrogen gas, argon gas or carbon dioxide gas. Of these inert gases, nitrogen gas is preferred.

The intrinsic viscosity of the polyethylene terephthalate thus obtained is usually 0.54 dl / g or more, preferably 0.70 dl / g or more, and particularly preferably 0.72 dl / g or more.

The density of this polyethylene terephthalate is usually 1.37 g /
cm ³ or more, preferably 1.38 g / cm ³ or more, more preferably
It is preferably 1.39 g / cm ³ or more.

Further, an oligomer contained in such a polyethylene terephthalate [formula Is 0.5% by weight or less, preferably 0.45% by weight or less, particularly preferably 0.40% by weight or less.

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

That is, a predetermined amount of polyethylene terephthalate was dissolved in o-chlorophenol, reprecipitated with tetrahydrofuran and filtered to remove linear polyethylene terephthalate, and then the obtained filtrate was subjected to liquid chromatography (Shimadzu LC7A). The amount of oligomer contained in the polyethylene terephthalate supplied is determined, and this value is divided by the amount of polyethylene terephthalate used for the measurement to obtain the amount of oligomer (% by weight) contained in the polyethylene terephthalate.

Water treatment is added to the granular polyethylene terephthalate obtained through such a solid phase polycondensation step, and this water treatment is performed by bringing the granular polyethylene terephthalate into contact with water.

To contact granular polyethylene terephthalate with water, add granular polyethylene terephthalate to hot water at 70-110 ° C for 3 hours.
It is performed by soaking for 5 minutes to 5 hours. Particularly preferably, it is carried out by immersing the granular polyethylene terephthalate in hot water at 80 to 100 ° C. for 5 minutes to 3 hours.

The method for industrially carrying out the contact treatment between the granular polyethylene terephthalate and water will be illustrated below, but the method is not limited thereto. Further, the treatment method may be either a continuous method or a batch method.

When the granular polyethylene terephthalate is subjected to contact treatment with water by a batch method, a silo type treatment device is used. That is, granular polyethylene terephthalate is received in a silo, and water is supplied in a batch method to perform contact treatment. Alternatively, the granular polyethylene terephthalate may be received in a rotating tube type contact treatment device, and the contact treatment may be performed while rotating to make the contact more efficient.

When the granular polyethylene terephthalate is continuously treated with water, the tower type treatment device can continuously receive the granular polyethylene terephthalate from the upper portion, and the water can be continuously supplied in a cocurrent or a countercurrent to perform the contact treatment with water. Then, when treated with water, the granular polyethylene terephthalate is drained by a draining device such as a vibrating screener or Simon Carter, and transferred to the next drying step. When treated with steam or a steam-containing gas, it can be directly transferred to the drying step.

For drying the granular polyethylene terephthalate which has been contact-treated with water, a commonly used drying treatment of polyethylene terephthalate can be used. As a method for continuously drying, supply granular polyethylene terephthalate from the top,
A hopper type ventilating dryer which ventilates dry gas from the bottom is usually used. As a method of reducing the amount of dry gas and efficiently drying, a rotating disk type continuous dryer is selected, and while supplying a small amount of dry gas, heating steam and heating medium are supplied to the rotating disk and the outer jacket. The granular polyethylene terephthalate can be indirectly dried by heating.

A double-cone rotary dryer is used as a dryer for batch-type drying, and can be dried under a vacuum or under a vacuum while a small amount of dry gas is passed through. Alternatively, it may be dried under atmospheric pressure while aerating a dry gas.

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

By subjecting polyethylene terephthalate to water treatment as described above, the solid phase polycondensation rate of polyethylene terephthalate is reduced, and the oligomer after polyethylene terephthalate is heated and melted at a temperature of 290 ° C. to form a stepped rectangular plate. The amount of increase can be suppressed.

Polyethylene terephthalate thus treated with water has a reduced solid phase polycondensation rate as described above, but is heated to a temperature of 215 ° C. under an inert gas atmosphere to undergo solid phase polycondensation. The polycondensation rate in this case is 0.0050 dl / g-hour or less, preferably 0.0040 dl / g-hour or less, particularly preferably 0.
0030 dl / g · hour or less is desirable.

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

Granular polyethylene terephthalate 60 g, inner diameter 22 mm, height 8
Fill a 0 mm cylindrical stainless steel container and seal. This container has a nozzle for venting an inert gas at the bottom, and the inert gas is discharged from the upper part to the outside of the system.

Solid-phase polycondensation is carried out by mounting and fixing a stainless steel container in which granular polyethylene terephthalate is filled and sealed in a sand bath (aluminum oxide manufactured by Nippon Parkerizing Co., Ltd.) having a heating device, and nitrogen is passed as an inert gas. carry out. The nitrogen used at this time has a dew point of −50 ° C. or lower and an oxygen concentration of 20 ppm or lower, and is preheated to the same bath temperature before being supplied to the stainless steel container. Nitrogen is supplied to the stainless steel container in an amount of 200 N (standard condition) per hour.

The sand bath is made to flow by air so that the temperature of the sand bath is uniform and there is no temperature distribution. The heater of the sand bath is controlled by the program controller so that the bath temperature reaches a predetermined solid-phase polycondensation temperature.

The solid-phase polycondensation rate is measured using the above-mentioned device,
Specifically, it is quantified by the following method. Granular polyethylene terephthalate was filled and sealed in the cylindrical stainless steel container as described above, fixed and mounted in a sand bath, and nitrogen was ventilated at an amount of 200 N per hour, and the temperature was raised from room temperature to 17
After raising the temperature to 0 ° C in 30 minutes and then holding it at 170 ° C for 1 hour, raise the temperature from 170 ° C to 215 ° C in 30 minutes and then
Hold at 4 ° C for 4 hours to carry out solid phase polycondensation reaction.

After the solid phase polycondensation reaction, the heating was stopped, the temperature in the sand bath was lowered to 70 ° C with nitrogen aeration, then the stainless container was taken out from the sand bath, and the intrinsic viscosity dl of the solid phase polycondensed granular polyethylene terephthalate dl / g (IV) is measured. Let this IV value be A dl / g.

In the same manner, IV of granular polyethylene terephthalate is measured when the holding time at 215 ° C. is 20 hours. This IV
Let the value be B dl / g.

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

Where R is the solid phase polycondensation rate (dl / g · hour), and A
IV values (dl / g) after 4 and 20 hours, respectively.
Is.

Further, in the polyethylene terephthalate treated with water as described above, the increase of oligomers in the subsequent molding process is significantly suppressed. This can be confirmed, for example, by measuring the amount of increase in oligomers after heating and melting polyethylene terephthalate at a temperature of 290 ° C. to form a stepped rectangular plate. The water-treated polyethylene terephthalate according to the present invention is, specifically, an oligomer increase amount y after heating and melting at a temperature of 290 ° C. to form a step angle.
It is desirable that (% by weight) be y ≦ −0.20x + 0.20, preferably y ≦ −0.20x + 0.18, and more preferably y ≦ −0.20x + 0.16.

In the above formula, x is the oligomer concentration (% by weight) before forming the stepped rectangular plate.

In the present specification, the oligomer increase amount y (% by weight) after molding a stepped rectangular plate from granular polyethylene terephthalate is measured as follows.

That is, the oligomer content was measured in advance (measured value X
%) 2 kg of granular polyethylene terephthalate at a temperature of 140 ° C,
Dry at a pressure of 10 Torr for 16 hours or more using a tray dryer to remove the moisture content of granular polyethylene terephthalate by 50%.
Keep it below ppm.

Next, the dried granular polyethylene terephthalate was molded by an M-70A injection molding machine manufactured by Meiki Seisakusho Co., Ltd. at the time of molding with nitrogen having a dew point of −70 ° C. in the hopper upper part and the screw feeder chute part at 5 normal cubic meters / hour each. Feed in proportion, barrel set temperature 290 ℃, molding machine C
₁ / C ₂ / C ₃ / The nozzle tip temperature is set to 260/290/290/300 ° C, and injection molding is performed under the condition that the mold cooling temperature is 15 ° C. To get

Injection molding of a stepped rectangular plate-shaped molded product is performed by supplying dried granulated polyethylene terephthalate from a hopper to an injection molding machine at a metering time of 12 seconds and an injection time of 60 seconds. The residence time of the molten resin in the molding machine is about 72 seconds. The weight of each stepped rectangular plate-shaped molded product is 75 g, and any one of the 11th to 15th oligomer measurement samples is used after the start of injection molding.

The stepped rectangular plate-shaped molded product 1 has a shape as shown in FIG. 1, the thickness of the A portion is about 6.5 mm, and the thickness of the B portion is about 5 mm.
mm, and the thickness of part C is about 4 mm. Using this part C, the amount of increase in the oligomer of the molded product is examined.

Next, the molded plate-shaped product having a thickness of 4 mm is cut into chips and used as a sample for oligomer measurement.

The content of the oligomer of polyethylene terephthalate forming the stepped rectangular 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 of oligomers such as cyclic trimers contained in polyethylene terephthalate during molding. By adding processing
The polycondensation catalyst contained in polyethylene terephthalate, such as the germanium catalyst, is deactivated, so that the decomposition reaction or transesterification reaction hardly progresses even when heated during molding, and therefore the amount of oligomers such as cyclic trimers produced. Is less.

As described above, the polyethylene terephthalate obtained by the production method according to the present invention has a small amount of oligomers such as a cyclic trimer produced at the time of molding, and therefore is supplied to a molding machine such as an injection molding machine to obtain a hollow molding. When molding a preform for molding, inserting this preform into a mold of a predetermined shape and stretch blow molding, and then heat setting to mold a hollow molding container, oligomers such as cyclic trimers are attached to the mold. Stain does not easily occur in the mold.

EFFECT OF THE INVENTION Since the method for producing polyethylene terephthalate according to the present invention includes a water treatment step in which it is brought into contact with water,
The polyethylene terephthalate obtained by this production method has a small amount of oligomers such as cyclic trimers formed during molding, 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, the polyethylene terephthalate obtained by the method for producing polyethylene terephthalate according to the present invention,
There is no need for frequent cleaning when manufacturing molded products,
It is possible to improve the productivity of molded products such as bottles, films and sheets, and obtain bottles and films,
It is possible to prevent whitening of the sheet.

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Using a continuous polycondensation device in which the first, second, third, fourth and fifth reactors are tank type, and the sixth reactor is a biaxial rotation type horizontal reactor A polyethylene terephthalate was produced by carrying out continuous polymerization by operating as follows.

3750 parts by weight of the reaction solution has been accumulated in advance, and it is stirred up to 255
The slurry prepared by continuously mixing 1437 parts by weight of high-purity terephthalic acid and 645 parts by weight of ethylene glycol into the first reactor maintained at 1.7 ° C. under nitrogen atmosphere at 1.7 kg / cm ² G continuously. And the first stage esterification reaction was carried out. In this first-stage esterification reaction, 20
A mixed solution of 3 parts by weight of water and 3 parts by weight of ethylene glycol was distilled off. Further, the esterification reaction product of the first stage is controlled so that the average residence time is 2.0 hours,
It was continuously introduced into a second reactor which was maintained under stirring at 260 ° C. under the conditions of 0.8 kg / cm ² G.

In this reactor 2, a homogeneous solution of 0.35 parts by weight of germanium dioxide and 32 parts by weight of ethylene glycol was continuously supplied, and 84 parts by weight of water and 7 parts of water were continuously supplied.
The mixed liquid with parts by weight of ethylene glycol was continuously distilled off, and the second stage esterification reaction was continued. The second-stage esterification reaction product was controlled so that the average residence time was 2.0 hours, and continuously stirred at 265 ° C.
To a third reactor maintained under normal pressure conditions.

In this third reactor, a homogeneous solution of 1.23 parts by weight of trimethyl phosphate and 22 parts by weight of ethylene glycol was continuously fed at an hourly rate and
A mixed solution of 21 parts by weight of water and 38 parts by weight of ethylene glycol was continuously distilled off, and the third stage esterification reaction was continued.

The average residence time of this esterification reaction product of the third stage is also 2.0.
Controlled for a time, 70m at 275 ℃ with continuous stirring
It was led to a fourth reactor maintained at mHg. In this fourth reactor, 62 parts by weight of ethylene glycol and 6
The mixture with part by weight of water was continuously distilled off to carry out the first stage polycondensation reaction. The polycondensation reaction product of the first stage was controlled so that the average residence time was 1.0 hour, and was continuously introduced into the fifth reactor maintained at 5 mmHg at 280 ° C. under stirring.

In the fifth reactor, a mixed solution of 26 parts by weight of ethylene glycol and 3 parts by weight of water was continuously distilled off to continue the second-stage polycondensation reaction. Also, this second
The polycondensation reaction product of the second stage is controlled so that the average residence time is 1.0 hour, and continuously 1.8 mmHg-2.5 at 282 ° C-285 ° C.
It was introduced into the sixth reactor, which was a horizontal twin-screw rotary reaction tank maintained under the condition of mmHg.

In the sixth reactor, the reaction solution of 12 parts by weight of ethylene glycol and 1 part by weight of water was distilled off continuously every hour to continue the polycondensation reaction in the third stage. Also, this third
The polycondensation reaction product in the second stage was controlled so that the average residence time was 2.5 hours, continuously extracted by a polyester extraction device in a strand form outside the reactor, immersed in water and cooled. It was cut into chips by a strand cutter. Polyethylene terephthalate obtained by the above liquid phase polymerization had an intrinsic viscosity of 1V measured at 25 ° C. in o-chlorophenol of 0.57 dl / g, and the content of dioxyethylene terephthalate component was 2.50 mol%. .

Furthermore, the polyethylene terephthalate produced by the liquid phase polymerization was dried at about 140 ° C. for about 15 hours in a nitrogen atmosphere and crystallized, and then loaded into a tower-type solid-state polymerizer and kept at 205 ° C. for 15 hours under a nitrogen atmosphere. Solid phase polymerization was performed. The polyethylene terephthalate thus obtained has an intrinsic viscosity of 0.80 dl / g, a density of 1.40 g / cm ³ and an oligomer content of 0.31 measured at 25 ° C. in o-chlorophenol.
%, And the content of the dioxyethylene terephthalate component was 2.53 mol%.

5 kg of the polyethylene terephthalate (A) thus obtained 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, the water treatment was carried out by holding for 4 hours, and then dehydration was performed at 140 ° C in nitrogen for 14 hours. Dried in.

The polycondensation rate of dried poly (ethylene terephthalate), which was heated to a temperature of 215 ° C. under a nitrogen gas atmosphere and solid-phase polycondensed as described above, was 0.0026 dl / g.
・ It was time.

The polyethylene terephthalate is manufactured by Meiki Seisakusho Co., Ltd.
The oligomer content of the stepped rectangular plate-shaped molded product molded at 290 ° C by the M-70A injection molding machine is 0.35% by weight,
The amount of increase in oligomer was 0.04% by weight.

Comparative Example 1 Polyethylene terephthalate obtained in Example 1 without hot water treatment 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 perform solid phase polycondensation. The treated polycondensation rate was 0.0067 dl / g · hour.

The molded product obtained by molding the polyethylene terephthalate at 290 ° C. had an oligomer content of 0.50% by weight and an increased amount of oligomer of 0.19% by weight.

Example 2 The granular polyethylene terephthalate used in Example 1 was treated with hot water in the same manner as in Example 1, dehydrated and dried, and then dried under reduced pressure.
After drying at ℃ for about 16 hours, under nitrogen atmosphere, Meiki Seisakusho Co., Ltd.
Barrel set temperature of 28 using M-100A-SJ type injection molding machine
Injection molding was performed at a molding pressure of 700 kg / cm ² G in a preform mold that was melted at 0 ° C and cooled to 10 ° C.
A pleome having a thickness of 64 mm and a body thickness of 4.5 mm and a weight of 64 g was prepared in a molding cycle of 60 seconds.

The oligomer in the preform was 0.35% by weight.

Then, only the mouth plug was crystallized in an oil bath at 160 ° C to prepare a preform. This mouthpiece crystallized preform is a biaxial stretch blow molding machine [CORPOPLA
ST) LB010], using a blowing pressure of about 20 kg / cm ² ,
Preform heating time of about 60 seconds, stretching temperature of 105 ℃ biaxially stretched 2.2 times in the longitudinal direction and 3.0 times in the transverse direction, and further 160 times
After holding for 60 seconds in a mold having a surface temperature of ℃, heat setting was performed by cooling the mold with water for 20 seconds. ,
A biaxially stretched bottle having a bottom-up bottom was prepared.

The heating (heat setting) for 60 seconds after stretching is for accelerating the whitening of the bottle for evaluation, and the heating (heat setting) time during the production of the bottle is 0.1 to 30 seconds.

Although 500 bottles were molded, all transparent bottles were obtained.

Comparative Example 2 The polyethylene terephthalate used in Example 1 was dried and molded in the same manner as in Example 1 without heat treatment and in the same manner as in Example 1.

Although 500 bottles were molded in the same manner as in Example 2, bottles with a cloudy pattern were generated from around the 400th bottle.

The oligomer in the obtained preform was 0.46% by weight.

[Brief description of drawings]

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

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Claims (1)

[Claims] 1. An esterification step of esterifying terephthalic acid or its ester-forming derivative with ethylene glycol or its ester-forming derivative; and the esterified product obtained in the above esterification step in the presence of a polycondensation catalyst. And a solid-phase polycondensation step of heating the polycondensation reaction product obtained in the liquid-phase polycondensation step to a temperature below the melting point in an inert atmosphere, The polycondensation reaction product having an intrinsic viscosity of 0.54 dl / g and a density of 1.37 g / cm ³ or more and an oligomer (cyclic trimer) content of 0.50 wt% or less is 70 to A method for producing polyethylene terephthalate, which comprises a step of contacting with water at 110 ° C. for 3 minutes to 5 hours to deactivate the polycondensation catalyst contained in polyethylene terephthalate.