JP2583008B2 - Method for producing polyethylene terephthalate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing polyethylene terephthalate used for forming films, sheets and the like, such as bottles, and more specifically, it is possible to obtain polyethylene terephthalate which does not easily cause mold contamination during molding. And a method for producing such polyethylene terephthalate.

[0002]

2. Description of the Related Art Conventionally, various resins have been employed as materials for containers such as seasonings, oils, beverages, cosmetics, and detergents, depending on the type of filling content and the purpose of use.

[0003] Of these, polyethylene terephthalate is excellent in mechanical strength, heat resistance, transparency and gas barrier properties, and is particularly suitable as a material for beverage filling containers such as juices, soft drinks and carbonated drinks.

[0004] Such polyethylene terephthalate comprises terephthalic acid or an ester-forming derivative thereof,
It can be obtained by subjecting ethylene glycol or its ester-forming derivative to esterification in the presence of an esterification catalyst, liquid-phase polycondensation in the presence of a polycondensation catalyst, and then solid-phase polycondensation. The polyethylene terephthalate is supplied to a molding machine such as an injection molding machine to form a preform for a hollow molded body, and the preform is inserted into a mold having a predetermined shape and stretch blow-molded. ) 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 used in a blow mold. Mold contamination is caused by adhering to the inner surface or the gas exhaust port or exhaust pipe of the mold, or the oligomer is adhered to the vent portion of the mold of the injection molding machine as described above, and mold contamination is caused. Had occurred.

[0006] 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 a bottle is molded using a conventionally known polyethylene terephthalate, mold stains must be frequently removed, and there is a serious problem that productivity of the bottle is significantly reduced.

[0007] In view of the above situation, the present inventors have
After extensive research into obtaining polyethylene terephthalate, which is less likely to cause mold stains during molding, the main cause of mold stains during molding is that a large amount of oligomers such as cyclic trimers are formed during polyethylene terephthalate molding. As a result, it has been found that the total amount of oligomers such as cyclic trimers contained in polyethylene terephthalate is increased.

The present inventors have further studied based on the above findings, and found that the polyethylene terephthalate obtained by a series of continuous steps is brought into contact with water to reduce the total amount of oligomers such as cyclic trimers during molding. The inventors have found that the increase can be suppressed, and have completed the present invention.

JP-A-59-25815 discloses that polyethylene terephthalate particles are treated with heated steam at 110 ° C. or more in order to crystallize polyethylene terephthalate prior to solid-phase polycondensation of polyethylene terephthalate. A method for doing so is disclosed.

JP-A-59-219328 discloses that the intrinsic viscosity is at least 0.4 dl / g and the density is 1.3.
14) a step of humidifying a polyester having an ethylene terephthalate unit of 5 g / cm ³ or less as a main repeating unit so that the water content is at least 0.2% by weight or more.
Pre-crystallization at a temperature of 0 ° C. or more, and 180 ° C.
There is disclosed a method for producing a high polymerization degree polyester, which comprises a step of performing solid phase polymerization at a temperature of 240 ° C. or lower and under an inert gas atmosphere or under reduced pressure.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems associated with the prior art as described above, and it is an object of the present invention to provide a polyethylene terephthalate which has a small amount of oligomers formed during molding and is less likely to cause mold contamination. It is an object of the present invention to provide a method for producing polyethylene terephthalate which can be obtained.

[0012]

SUMMARY OF THE INVENTION The method for producing polyethylene terephthalate according to the present invention is obtained by an esterification step of esterifying terephthalic acid or an ester-forming derivative thereof, and ethylene glycol or an ester-forming derivative thereof, and the esterification step. A liquid phase polycondensation step of heating and melting the obtained esterified product in the presence of a polycondensation catalyst, and heating the polycondensation reaction product obtained in the liquid phase polycondensation step to a temperature below the melting point under an inert atmosphere. The solid-phase polycondensation step and the polycondensation reaction product obtained in the solid-phase polycondensation step are brought into contact with water vapor or a gas containing water vapor at a temperature of 70 ° C to 150 ° C for 5 minutes to 10 hours, and contained in polyethylene terephthalate. And a steam treatment step for deactivating the polycondensation catalyst.

[0013] The 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 generated during molding, and therefore is less likely to cause mold contamination.

[0014]

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

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,
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, and a contact between the polycondensation reaction product obtained in the solid phase polycondensation step and steam or a gas containing steam. And a steam treatment step.

The process for producing polyethylene terephthalate according to the present invention is carried out using terephthalic acid or an ester-forming derivative thereof and ethylene glycol or an ester-forming derivative thereof as raw materials. The following other dicarboxylic acids and / or other glycols may be copolycondensed.

Examples of the dicarboxylic acid used for 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, and adipic acid. And aliphatic dicarboxylic acids such as sebacic acid, azelaic acid and decanedicarboxylic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid.

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

A raw material containing terephthalic acid or an ester-forming derivative thereof as described above and ethylene glycol or an ester-forming derivative thereof is esterified. Specifically, first, a slurry containing terephthalic acid or an ester-forming derivative thereof and ethylene glycol or an ester-forming derivative thereof is prepared.

Such a slurry contains 1.02 to 1 mole of terephthalic acid or its ester-forming derivative.
〜1.4 mol, preferably 1.03-1.3 mol of ethylene glycol or an ester-forming derivative thereof. This slurry is continuously supplied to the esterification reaction step.

The esterification reaction is carried out by using a device in which at least two esterification reactors are connected in series while removing water produced by the reaction outside the system by a rectification column under the condition that ethylene glycol is refluxed. Will be implemented. The reaction conditions for carrying out the esterification reaction are such that the temperature of the first-stage esterification reaction is usually from 240 to 270 ° C., preferably from 24 to 2 ° C.
65 ° C., the pressure is usually 0.2 to 3 kg / cm ² G, preferably 0.5 to ² kg / cm ² G, and the temperature of the final esterification reaction is usually 250 to 280 ° C., preferably 2 to ² kg / cm ² G.
55-275 ° C. and pressure is usually 0-1.5 kg / cm ²
G is preferably 0 to 1.3 kg / cm ² G.

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

For example, when the esterification reaction is carried out in three stages, the reaction temperature of the second stage esterification reaction is usually 245 to 275 ° C., preferably 250 to 270 ° C., and the pressure is usually 0 to 270 ° C. 2 kg / cm ² G, preferably 0.2 to
1.5 kg / cm ² G. The reaction rates of these esterification reactions are 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 distributed smoothly, and furthermore, the final stage of the esterification In the reaction product, it is usually desirable to reach 90% or more, preferably 93% or more.

An esterified product (low-order condensate) is obtained by these esterification steps, and the number-average molecular weight of the esterified product is usually from 500 to 5,000. Such an esterification reaction can be carried out without adding an additive other than terephthalic acid and ethylene glycol, and can be carried out in the presence of a polycondensation catalyst described later. Tertiary amines such as triethylamine, tri-n-butylamine, and benzyldimethylamine; tetraethylammonium hydroxide;
By adding a small amount of quaternary ammonium hydroxide such as butylammonium and trimethylbenzylammonium hydroxide and a basic compound such as lithium carbonate, sodium carbonate, potassium carbonate and sodium acetate, dioxygen in the main chain of polyethylene terephthalate is reduced. This is preferable because the ratio of the ethylene terephthalate component unit can be maintained at a relatively low level.

Next, the obtained esterified product is heated to a temperature not lower than the melting point of the obtained polyethylene terephthalate under reduced pressure in the presence of a polycondensation catalyst, and the resulting glycol is distilled out of the system to perform polycondensation. To the liquid-phase polycondensation step.

Such a polycondensation reaction in the liquid phase may be carried out in one stage or may be carried out in a plurality of stages. When the reaction is carried out in a plurality of stages, the polycondensation reaction conditions are such that the reaction temperature of the first stage polycondensation is usually from 250 to 290 ° C, preferably from 260 to 280 ° C, and the pressure is usually from 500 to 20 ° C.
Torr, preferably 200 to 30 Torr, the temperature of the final polycondensation reaction is usually 265 to 300 ° C, preferably 270 to 295 ° C, and the pressure is usually 10 to 0.1 Torr.
Preferably it is 5-0.5 Torr.

When the polycondensation reaction is carried out in two stages,
The conditions of the polycondensation reaction of the first and second stages are respectively in the above ranges.
The reaction conditions for the polycondensation reaction from the first stage to the last stage before the last stage are those between the above-mentioned first stage reaction conditions and the last stage reaction conditions.

For example, when the polycondensation reaction is carried out in three stages, the reaction temperature of the second stage polycondensation reaction is usually 2
60-295 ° C., preferably 270-285 ° C., and the pressure is usually in the range of 50-2 Torr, preferably 40-5 Torr. The intrinsic viscosity (IV) attained in each of these polycondensation reaction steps is not particularly limited, but it is preferable that the degree of increase in the intrinsic viscosity in each stage is smoothly distributed, and furthermore, the final stage polycondensation Intrinsic viscosity of polyethylene terephthalate obtained from reactor (IV)
Is usually 0.35 to 0.80 dl / g, preferably 0.45 to
0.75 dl / g, more preferably 0.55 to 0.75
It is desirably in the range of dl / g.

[0029] In the present specification, the intrinsic viscosity of polyethylene terephthalate is 1.2 g of o-chlorophenol 15
Calculated from the solution viscosity measured at 25 ° C. after heating and dissolving in cc.

The density of the polyethylene terephthalate is usually desirably 1.33 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 above-mentioned polycondensation reaction is preferably carried out in the presence of a catalyst and a stabilizer. As the catalyst, germanium compounds such as germanium dioxide, germanium tetraethoxide, and germanium tetra n-butoxide, antimony catalysts such as antimony trioxide, and titanium catalysts such as titanium tetrabutoxide can be used. Among these catalysts, it is preferable to use a germanium dioxide compound because the resulting polyethylene terephthalate has excellent hue and transparency. Examples of the stabilizer include phosphates such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, triphenyl phosphate and tricresyl phosphate, triphenyl phosphite, trisdodecyl phosphite, and trisnonyl phenyl. Phosphites such as phosphites, acid phosphates such as methyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, dibutyl phosphate, monobutyl phosphate, dioctyl phosphate, and phosphorus compounds such as phosphoric acid and polyphosphoric acid Is used. The use ratio of these catalysts or stabilizers is usually 0.0005 to 0.2% by weight as the weight of the metal in the catalyst in the case of the catalyst, based on the weight of the mixture of terephthalic acid and ethylene glycol. Is in the range of 0.001 to 0.05% by weight, and in the case of a stabilizer, usually 0.001 to 0.1% by weight, preferably 0.1% by weight of phosphorus atom in the stabilizer.
002 to 0.02% by weight. These catalysts and stabilizers can be supplied at the stage of the esterification reaction step or in the first step of the polycondensation reaction step.
It can also be supplied to the reactor at the stage.

As described above, the polyethylene terephthalate used in the present invention may contain a dicarboxylic acid other than terephthalic acid and a diol other than ethylene glycol in an amount of 20 mol% or less, and particularly preferably used polyethylene. Terephthalate has the general formula [I]

[0033]

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The content of the ethylene terephthalate component unit (a) represented by the formula is in the range of 95.0 to 99.0 mol%, and the general formula [II]

[0035]

Embedded image

It is desirable that the content of the dioxyethylene terephthalate component unit (b) represented by the formula is in the range of 1.0 to 5.0 mol%. In this way, the polyethylene terephthalate obtained from the final polycondensation reactor is:
Usually, it is formed into a granular shape (chip shape) by a melt extrusion molding method.

Such a granular polyethylene terephthalate is usually 2.0 to 5.0 mm, preferably 2.2 to 4.0 mm.
It is desirable to have an average particle size of 0 mm. A solid-phase polycondensation step is added to the granular polyethylene terephthalate that has undergone the liquid-phase polycondensation step in this way.

The granular polyethylene terephthalate supplied to the solid phase polycondensation step is preliminarily crystallized by heating to a temperature lower than the temperature at which solid phase polycondensation is carried out.
It may be supplied to a solid phase polycondensation step.

In such a preliminary crystallization step, the granular polyethylene terephthalate is usually dried in a dry state at a temperature of 120 to 2 μm.
The heating may be carried out by heating at a temperature of 00 ° C., preferably 130 to 180 ° C. for 1 minute to 4 hours, or the granular polyethylene terephthalate is usually heated under a steam atmosphere, under a steam-containing inert gas atmosphere, or under a steam-containing air atmosphere. It may be performed 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 comprises at least one stage, and the polycondensation temperature is usually 190 to 230 ° C., preferably 1 to 230 ° C.
95 to 225 ° C and the pressure is usually 1 kg / cm ² G to 1
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 at 0 Torr, preferably at normal pressure to 100 Torr. Among these inert gases, nitrogen gas is preferred.

The intrinsic viscosity of the polyethylene terephthalate thus obtained is usually at least 0.70 dl / g, preferably at least 0.72 dl / g. 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 1.39 g / cm ³ or more.

The oligomer contained in such polyethylene terephthalate (the following formula:

[0043]

Embedded image

The amount of the cyclic trimer is preferably 0.50% by weight or less, more preferably 0.45% by weight or less, particularly preferably 0.40% by weight or less. In the present specification, the amount of the oligomer contained in polyethylene terephthalate is measured as follows.

That is, a predetermined amount of polyethylene terephthalate is dissolved in o-chlorophenol, reprecipitated with tetrahydrofuran, filtered to remove linear polyethylene terephthalate, and then the obtained filtrate is subjected to liquid chromatography (manufactured by Shimadzu Corporation). LC7A) to determine the amount of oligomers contained in polyethylene terephthalate,
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 particulate polyethylene terephthalate obtained through such a solid-phase polycondensation step is subjected to steam treatment. This steam treatment is performed by converting the particulate polyethylene terephthalate to steam, steam-containing inert gas, steam-containing air, or the like. This is done by contacting with.

The contact between the granular polyethylene terephthalate and water vapor or a gas containing water vapor is usually 70 to 150.
C., preferably 70 to 110.degree. C., steam or steam-containing inert gas or steam-containing air, preferably 0.5 g / kg of granular polyethylene terephthalate.
g or more, or by the presence and contact of particulate polyethylene terephthalate with water vapor.

The contact between the granular polyethylene terephthalate and water vapor is usually performed for 5 minutes to 10 hours. The following is an example of a method for industrially performing the contact treatment between granular polyethylene terephthalate and steam or a gas containing steam, but the method is not limited thereto. The processing method may be either a continuous method or a batch method.

When the granular polyethylene terephthalate is subjected to the contact treatment with steam in a batch system, a silo-type treatment apparatus may be used. That is, the granular polyethylene terephthalate is received in a silo, and a contact treatment is performed by supplying steam or a steam-containing gas in a batch system. Alternatively, it is possible to receive the granular polyethylene terephthalate in a rotary cylinder type contact treatment device and perform the contact treatment while rotating the contact so as to make the contact more efficient.

When the granular polyethylene terephthalate is continuously treated with water vapor, the granular polyethylene terephthalate may be continuously received in a tower-type treatment apparatus from above, and steam may be continuously supplied in cocurrent or countercurrent to be subjected to contact treatment with water vapor. it can. Thereafter, when treated with steam, the granular polyethylene terephthalate is drained with a draining device such as a vibrating sieve or a Simon Carter if necessary, and is transferred to the next drying step.

Drying of the granular polyethylene terephthalate which has been subjected to the contact treatment with water vapor can be carried out by a commonly used drying treatment of polyethylene terephthalate. As a method for continuous drying, a hopper-type through-air dryer that supplies granular polyethylene terephthalate from the upper portion and vents the drying gas from the lower portion is usually used. As a method for reducing the amount of drying gas and drying efficiently, a rotary disk-type continuous dryer is used. Heating steam, heating medium, etc. are supplied to the rotating disk and the outer jacket while passing a small amount of drying gas. The granular polyethylene terephthalate can be indirectly heated and dried.

As a dryer for drying in a batch system, a double cone type rotary dryer is used, and the drying can be performed under vacuum or while passing a small amount of drying gas under 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 preferred from the viewpoint of preventing molecular weight reduction due to hydrolysis of polyethylene terephthalate.

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

The polyethylene terephthalate subjected to the steam treatment as described above has a reduced solid-state polycondensation rate as described above.
The polycondensation rate when the solid phase polycondensation is performed by heating to a temperature of 5 ° C. is 0.0050 dl / g · hour or less, preferably 0.00
40 dl / g · hour or less, particularly preferably 0.0030 dl / g
It is desirably not more than g · hour.

In the present specification, the polycondensation rate at the time of solid-phase polycondensation of polyethylene terephthalate is specifically measured as follows. A cylindrical stainless steel container having an inner diameter of 22 mm and a height of 80 mm is filled with 60 g of granular polyethylene terephthalate and sealed. This container has a nozzle for venting the inert gas at the bottom, and the inert gas is discharged from the top to the outside of the system.

The solid-phase polycondensation is performed by mounting and fixing a sealed stainless steel container filled with granular polyethylene terephthalate in a sand bath (aluminum oxide manufactured by Nippon Parker Zinc Co., Ltd.) having a heating device, and using nitrogen as an inert gas. While ventilating. The nitrogen used at this time has a dew point of -50 ° C.
It is pre-heated so that the temperature is equal to the bath temperature before it is supplied to the stainless steel container. Nitrogen is supplied to the stainless steel container at a rate of 200 Nl / hour (standard condition).

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 a program controller so that the temperature of the bath becomes a predetermined solid-phase polycondensation temperature.

The solid-state polycondensation rate is measured using the above-mentioned apparatus, specifically, by the following method. In a state where the granular polyethylene terephthalate was filled in the above-mentioned cylindrical stainless steel container and hermetically sealed, it was mounted and fixed in a sand bath, and the temperature was raised from room temperature to 170 ° C. for 30 minutes while passing nitrogen at a rate of 200 Nl / h. Then, after maintaining at 170 ° C. for 1 hour, the temperature is raised from 170 ° C. to 215 ° C. for 30 minutes, and further maintained 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 passing nitrogen gas.
Next, the stainless steel container is taken out of the sand bath and the intrinsic viscosity of the solid-phase polycondensed granular polyethylene terephthalate is removed.
Measure dl / g (IV). This IV value is defined as Adl / g.

In the same manner, the holding time at 215 ° C. was 20
IV of granular polyethylene terephthalate as a function of time
Is measured. This IV value is defined as Bdl / g. The solid-state polycondensation rate is calculated by the following equation.

[0062]

(Equation 1)

Here, R is a solid-state polycondensation rate (dl / g · hour), and A and B are IV values (dl / g) after 4 hours and 20 hours, respectively.

In the polyethylene terephthalate subjected to the steam treatment as described above, an increase in oligomers in the subsequent molding process is significantly suppressed. This means
For example, it can be confirmed by measuring the amount of increase in oligomer after heating and melting polyethylene terephthalate to a temperature of 290 ° C. to form a stepped square plate. The polyethylene terephthalate subjected to the steam treatment according to the present invention specifically has an oligomer increase y (% by weight) after heating and melting at a temperature of 290 ° C. to form a stepped square plate, and y ≦ −0.20x
+0.20, preferably y ≦ −0.20x + 0.18
It is more desirable that y ≦ −0.20x + 0.16.

In the above formula, x is the oligomer concentration (% by weight) before forming the stepped square plate. In this specification, the oligomer increase y (% by weight) after the stepped square plate is formed from the granular polyethylene terephthalate is measured as follows.

That is, granular polyethylene terephthalate 2 whose oligomer content was previously measured (measured value X%)
The kg is dried using a tray-type dryer at a temperature of 140 ° C. and a pressure of 10 torr for 16 hours or more to reduce the water content of the granular polyethylene terephthalate to 50 ppm or less.

Next, the dried granular polyethylene terephthalate was sprayed with an M-70A injection molding machine manufactured by Meiki Seisakusho Co., Ltd.
Feed into the screw feeder chute at the rate of 5 normal cubic meters / hour, and set the barrel temperature to 29
0 ° C., and the temperature of the C ₁ / C ₂ / C ₃ / nozzle tip of the molding machine was set to 260/290/290/300 ° C.
Injection molding is performed under the condition of a mold cooling temperature of 15 ° C. to obtain a stepped square plate-like molded product.

The injection molding of the stepped square plate-like molded product is performed by measuring 12
The dried granular polyethylene terephthalate is supplied from a hopper to an injection molding machine such that the injection time is 60 seconds and the injection time is 60 seconds. The residence time of the molten resin in the molding machine is about 72 seconds. The weight per one stepped square plate-shaped molded product is 75 g, and the oligomer measurement sample is performed using any one of eleventh to fifteenth samples after the start of injection molding.

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

Next, the formed plate-shaped product having a thickness of 4 mm is cut into chips to obtain a sample for oligomer measurement. The oligomer content of polyethylene terephthalate constituting the stepped square plate is measured by the same method as described above.

By subjecting polyethylene terephthalate to steam treatment as described above, it is possible to reduce the solid-phase polycondensation rate and to suppress the increase in oligomers such as cyclic trimers contained in polyethylene terephthalate during molding. By subjecting terephthalate to steam treatment, the polycondensation catalyst, such as a germanium catalyst, contained in polyethylene terephthalate is deactivated, and therefore, even if heated during molding, the decomposition reaction or transesterification reaction hardly proceeds, and the resulting cyclic The amount of oligomers such as trimers is reduced.

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 generated during molding, and is therefore supplied to a molding machine such as an injection molding machine. When a preform for a hollow molded article is molded, the preform is inserted into a mold having a predetermined shape, stretch-blow molded, and then heat-set to form a hollow molded container. Mold contamination due to adhesion to the mold is less likely to occur.

[0073]

The method for producing polyethylene terephthalate according to the present invention includes a steam treatment step in which the polyethylene terephthalate is brought into contact with steam or a steam-containing gas. Oligomers such as oligomers,
Moreover, since 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 does not require frequent washing when producing a molded article, and the productivity of molded articles such as bottles, films and sheets is reduced. Can be improved, and the resulting bottle, film, and sheet can be prevented from being whitened.

[0075]

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

[0076]

Example 1 A continuous polycondensation apparatus in which the first, second, third, fourth and fifth reactors are tank-type and the sixth reactor is a biaxial rotary horizontal reactor. Using this, continuous polymerization was carried out by the following procedure to produce polyethylene terephthalate.

3750 parts by weight of the reaction solution was previously retained, and was stirred at 255 ° C. under a nitrogen atmosphere at 1.7 kg / cm ^2.
In the first reactor maintained under the conditions of G, 1437 parts by weight of high-purity terephthalic acid and 64
The slurry prepared by mixing 5 parts by weight was continuously supplied, and the first-stage esterification reaction was performed. In the first-stage esterification reaction, a mixed solution of 203 parts by weight of water and 3 parts by weight of ethylene glycol was distilled off. The first-stage esterification reaction product is controlled so that the average residence time is 2.0 hours, and is continuously stirred.
The solution was led to a second reactor maintained at 60 ° C. under a condition of 0.8 kg / cm ² G.

In this reactor 2, a uniform 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 by weight of The mixed solution with ethylene glycol was continuously distilled off, and the second-stage esterification reaction was continued. The second esterification reaction product was controlled so that the average residence time was 2.0 hours, and the third reactor was continuously stirred at 265 ° C. and maintained at normal pressure. Led to.

In the third reactor, 1.23 / h
A homogeneous solution in which 3 parts by weight of trimethyl phosphate and 22 parts by weight of ethylene glycol are mixed is continuously supplied, and a mixed solution of 21 parts by weight of water and 38 parts by weight of ethylene glycol is continuously distilled per hour. And the third-stage esterification reaction was continued.

This third-stage esterification reaction product was also controlled so that the average residence time was 2.0 hours, and was led to a fourth reactor maintained at 275 ° C. and 70 mmHg with continuous stirring. . In the fourth reactor, a mixture of 62 parts by weight of ethylene glycol and 6 parts by weight of water per hour was continuously distilled off to carry out the first stage polycondensation reaction. Also,
The first stage polycondensation reaction product had an average residence time of 1.0
The time was controlled and the mixture was led under continuous stirring to a fifth reactor maintained at 280 ° C. and 5 mmHg.

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, and the second stage polycondensation reaction was continued.
The second-stage polycondensation reaction product is controlled so that the average residence time becomes 1.0 hour, and continuously from 282 ° C.
The mixture was led to a sixth reactor, which is a horizontal twin-screw rotary reaction tank maintained at 285 ° C. and 1.8 mmHg to 2.5 mmHg.

In the sixth reactor, a reaction solution of 12 parts by weight of ethylene glycol and 1 part by weight of water was continuously distilled off, and the third stage polycondensation reaction was continued.
The third-stage polycondensation reaction product is controlled so that the average residence time is 2.5 hours, and is continuously withdrawn in a strand form outside the reactor by a polyester withdrawing device, and is taken into water. After being immersed and cooled, it was cut into chips by a strand cutter. The intrinsic viscosity IV of the polyethylene terephthalate obtained by the above liquid phase polymerization measured at 25 ° C. in o-chlorophenol was 0.57 dl / g, and the content of the dioxyethylene terephthalate component was 2.50 mol%. Met.

Further, the polyethylene terephthalate obtained by the liquid phase polymerization was dried at about 140 ° C. for about 15 hours in a nitrogen atmosphere and crystallized, and then charged into a column-type solid-state polymerization vessel, and then heated at 205 ° C. in a nitrogen atmosphere. For 15 hours. The intrinsic viscosity of the thus obtained polyethylene terephthalate measured at 25 ° C. in o-chlorophenol was 0.80 dl / g, and the density was 1.40 g / cm ^3.
The oligomer content was 0.31% by weight and the content of the dioxyethylene terephthalate component was 2.53% by mole.

5 kg of the polyethylene terephthalate (A) thus obtained was filled in a stainless steel container, and steam treatment was carried out by passing steam at about 100 ° C. at a rate of 0.5 kg / hour for 30 minutes.

Next, polyethylene terephthalate was added to 14
Dried in nitrogen at 0 ° C. for 14 hours. The polycondensation rate of the solid-phase polycondensation treatment by heating the dried polyethylene terephthalate to a temperature of 215 ° C. under a nitrogen gas atmosphere as described above was 0.0052 dl / g · hour.

The oligomer content of the stepped rectangular plate-like molded product obtained by molding the polyethylene terephthalate (M-70A manufactured by Meiki Seisakusho Co., Ltd.) at 290 ° C. was 0.40% by weight, The oligomer increase was 0.09% by weight.

[0087]

EXAMPLE 2 In Example 1, 5 kg of polyethylene terephthalate (A) was filled into a pressurized stainless steel container, and 0.43 kg / cm ² of steam (saturation temperature: 110 ° C.) was added at a rate of 0.5 kg / hour. It carried out similarly to Example 1 except having passed through for 30 minutes and performing water treatment.

After drying in the same manner as in Example 1, the solid-state polymerization rate was measured to be 0.0048 dl / g · hr. The oligomer content of the molded product molded in the same manner as in Example 1 was 0.37% by weight, and the amount of increased oligomer was 0.06% by weight.

[0089]

Comparative Example 1 The polyethylene terephthalate obtained in Example 1 without performing steam treatment was treated at 140 ° C. for 1 hour.
After drying in nitrogen gas for 4 hours, 215 under nitrogen atmosphere
Polycondensation rate of solid phase polycondensation treatment by heating to a temperature of ° C.,
It was 0.0067 dl / g-hour.

Further, the polyethylene terephthalate is
The oligomer content of the molded article molded at 0 ° C. was 0.50% by weight, and the increase in oligomer was 0.19% by weight.

[Brief description of the drawings]

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

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Claims (1)

(57) [Claims] 1. An esterification step of esterifying terephthalic acid or an ester-forming derivative thereof and ethylene glycol or an ester-forming derivative thereof, and the esterified product obtained in the esterification step is reacted with a polycondensation catalyst in the presence of a polycondensation catalyst. A liquid-phase polycondensation step of heating and melting at a temperature; a solid-phase polycondensation step of heating the polycondensation reaction product obtained in the liquid-phase polycondensation step to a temperature equal to or lower than a melting point under an inert atmosphere; The polycondensation reaction product obtained in the condensation step
A process of contacting with steam or a gas containing steam at a temperature of 150 ° C. for 5 minutes to 10 hours to deactivate a polycondensation catalyst contained in polyethylene terephthalate.