JP3357488B2 - Polyester production method - 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 a polyester, and more particularly, to a polyester which has a small amount of acetaldehyde and hardly increases acetaldehyde during molding, and can simplify the production process. And a method for producing a polyester.

[0002]

BACKGROUND OF THE INVENTION Bottles obtained by biaxially stretching a saturated polyester such as polyethylene terephthalate are excellent in transparency, mechanical strength, heat resistance and gas barrier properties, and are used in juices, soft drinks, carbonated drinks and the like. Are widely used as beverage filling containers (PET bottles).

In order to produce a bottle from such a polyester, for example, it is usual to produce a preform by injection molding the polyester and then to biaxially stretch the preform into a bottle shape by blow molding or the like. It is manufactured by.

[0004] If acetaldehyde remains in the bottle obtained from the polyester as described above, the taste of the contents to be filled is significantly reduced. For this reason, it is desirable that the acetaldehyde content contained in the polyester forming the bottle is as low as possible. In order to reduce the amount of acetaldehyde contained in the polyester forming the bottle, it is necessary to use a polyester that has a small amount of acetaldehyde before molding and that does not easily increase the amount of acetaldehyde even during bottle molding.

By the way, polyester is obtained by subjecting a dicarboxylic acid such as terephthalic acid or an ester derivative thereof to a diol or an ester derivative thereof such as ethylene glycol, and then subjecting the esterified product to a polycondensation reaction in the presence of a polycondensation catalyst. It is manufactured by doing. This polycondensation reaction is performed in a liquid-phase polycondensation step and a solid-phase polycondensation step, and the polyester obtained in the liquid-phase polycondensation step is then subjected to solid-phase polycondensation to obtain a high intrinsic viscosity and acetaldehyde. A polyester having a reduced content is obtained.

As described above, in the method for producing polyester,
A liquid-phase polycondensation step and a solid-phase polycondensation step must be performed. However, this solid-phase polycondensation requires a long time, resulting in an increase in production cost.

If the polyester obtained by liquid-phase polycondensation is to be directly produced into a molded article such as a bottle without omitting the solid-phase polycondensation step, acetaldehyde is generated during molding, and this acetaldehyde is contained in the polyester molded article. There is a problem that it remains.

[0008] Therefore, it is possible to provide a polyester having a very small amount of acetaldehyde and also having a small amount of acetaldehyde during molding of a bottle or the like.
In addition, there is a demand for a polyester production method that can omit the solid-phase polycondensation step.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and has as its object to provide a polyester which has a small amount of acetaldehyde and hardly increases acetaldehyde even when molding a bottle or the like. It is an object of the present invention to provide a method for producing a polyester, which can perform a solid phase polycondensation step.

[0010]

SUMMARY OF THE INVENTION The polyester production process according to the present invention comprises: [A] heating a dicarboxylic acid containing terephthalic acid or an ester derivative thereof and a diol containing ethylene glycol or an ester derivative thereof in the presence of a polycondensation catalyst. A liquid-phase polycondensation step of melting and liquid-phase polycondensation to produce a polyester (a) having an intrinsic viscosity of 0.7 to 1.5 dl / g measured in o-chlorophenol; [B] Polyester (a) obtained in the liquid phase polycondensation step,
In an atmosphere at an elevated temperature of crystallization temperature (Tc ₁ ) to 200 ° C.,
A pre-crystallization step of keeping the mixture for 4 minutes to 4 hours, and [C] a polyester (b) having undergone the above-mentioned pre-crystallization step.
Is heated to a temperature of 160 to 200 ° C. for 1 to 10 hours.
A hot water treatment step of bringing the polyester into contact with hot water at a temperature of about 130 ° C. for 5 minutes to 10 hours. (I) In the steps [B] and [C], the intrinsic viscosity of the polyester is substantially increased. And (ii) the resulting polyester (d) has an acetaldehyde content of 10 ppm or less.

In the above-mentioned production method, the polyester obtained in the step [A] preferably has an intrinsic viscosity of 0.8 to 1.2 dl / g measured in o-chlorophenol.

According to the production method of the present invention, it is possible to omit the solid-state polycondensation step when producing polyester, to produce a polyester having a very small amount of acetaldehyde and hardly increasing acetaldehyde during molding. Can be. The polyester obtained in the present invention is suitable as a material for forming a preform and a beverage bottle.

[0013]

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, a method for producing a polyester according to the present invention will be specifically described with reference to a process flow shown in FIG. As shown in FIG. 1, the manufacturing method according to the present invention comprises:

[A] A dicarboxylic acid containing terephthalic acid or an ester derivative thereof and a diol containing ethylene glycol or an ester derivative thereof are heated and melted in the presence of a polycondensation catalyst to undergo liquid phase polycondensation. 0.7-1.5 dl / g intrinsic viscosity measured in chlorophenol
A liquid-phase polycondensation step for producing a polyester (a), and [B] the polyester (a) obtained in the liquid-phase polycondensation step,
In an atmosphere at an elevated temperature of crystallization temperature (Tc ₁ ) to 200 ° C.,
A pre-crystallization step of keeping the mixture for 4 minutes to 4 hours, and [C] a polyester (b) having undergone the above-mentioned pre-crystallization step.
Is heated to a temperature of 160 to 200 ° C. for 1 to 10 hours.
A hot water treatment step of bringing the polyester into contact with hot water of about 130 ° C. for 5 minutes to 10 hours. (I) In the steps [B] and [C], the intrinsic viscosity of the polyester is substantially increased. And (ii) the resulting polyester (d) has an acetaldehyde content of 10 ppm or less. Hereinafter, each step will be described in detail.

[A] Liquid Phase Polycondensation Step In the present invention, first, in the [A] liquid phase polycondensation step, dicarboxylic acid containing terephthalic acid or an ester derivative thereof (for example, lower alkyl ester, phenyl ester, etc.) and ethylene glycol Is heated and melted in the presence of a polycondensation catalyst to form a liquid phase polycondensation with a diol or an ester derivative thereof (eg, a monocarboxylic acid ester) to produce a polyester (a).

In the present invention, homopolyethylene terephthalate may be produced using terephthalic acid and ethylene glycol, or a dicarboxylic acid containing not more than 20 mol% of a dicarboxylic acid other than terephthalic acid in addition to terephthalic acid. The copolymerized polyester can also be produced using a diol containing 20 mol% or less of a diol other than ethylene glycol in addition to ethylene glycol.

Examples of the dicarboxylic acids other than terephthalic acid used in producing the copolymerized polyester include phthalic acid (orthophthalic acid), isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid and the like. An aromatic dicarboxylic acid,
Examples thereof include aliphatic dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid, and decanedicarboxylic acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, and ester derivatives thereof. These may be used in combination of two or more.

Examples of the diol other than ethylene glycol include dimethylene glycol, trimethylene glycol (propylene glycol), tetramethylene glycol, neopentyl glycol, hexamethylene glycol, dodecamethylene glycol, diethylene glycol, and triethylene glycol. , Aliphatic glycols such as tetraethylene glycol and polyethylene glycol, alicyclic glycols such as cyclohexanedimethanol, aromatic diols such as bisphenols, hydroquinone, and 2,2-bis (4-β-hydroxyethoxyphenyl) propane; These ester derivatives are exemplified. These may be used in combination of two or more.

In the present invention, a small amount of a structural unit derived from a polyfunctional compound such as trimesic acid, pyromellitic acid, trimethylolethane, trimethylolpropane, trimethylolmethane, and pentaerythritol, for example, 2 mol% or less. Polyester containing polyester can also be produced. The present invention can be carried out in either a batch system or a continuous system, and the continuous system will be specifically described below.

In the liquid-phase polycondensation step [A], the above-mentioned dicarboxylic acid or its ester derivative (hereinafter referred to as “derivative”) is used.
Polyester is produced by polycondensation of diol or an ester derivative thereof (hereinafter sometimes also referred to simply as diol) with polycarboxylic acid).
In this liquid phase polycondensation step, first, a dicarboxylic acid and a diol are first subjected to an esterification reaction (an esterification reaction step [A-
1]), followed by a liquid phase polycondensation reaction (polycondensation reaction step [A-
2])

Specifically, first, a slurry containing a dicarboxylic acid and a diol is prepared. Such a slurry contains 1.02-2.0 moles, preferably 1.03-1.5 moles of diol per mole of dicarboxylic acid. This slurry is continuously supplied to the esterification reaction step [A-1].

In the esterification reaction, for example, water or alcohol produced by the reaction is removed outside the system by a rectification column under the condition that the diol is refluxed using a device in which two esterification reactors are connected in series. It can be implemented while.

When the esterification reaction step [A-1] is carried out, for example, in two stages, the first stage of the esterification reaction usually has a reaction temperature of 240 to 270 ° C., preferably 245 to 265 ° C.
Pressure 0.2 to 3 kg / cm ² G, preferably 0.5 to ² kg / cm ²
Under the conditions of G and the second stage of the esterification reaction, the reaction temperature is usually 250 to 280 ° C., preferably 255 to 275 ° C.
° C, pressure 0 to 1.5 kg / cm ² G, preferably 0 to 1.3 kg
/ Cm ² G.

Although the reaction rate of the esterification reaction in each of these stages is not particularly limited, it is preferable that the degree of the increase in the esterification reaction ratio in each stage is smoothly distributed. It is usually desirable for the product to reach 90% or more, preferably 93% or more.

An esterified product (low-order condensate) is obtained by the above esterification step [A-1], and the number-average molecular weight of the low-order condensate is usually 500 to 5,000. Such an esterification reaction can be carried out without adding additives other than dicarboxylic acids and diols, and can be carried out in the presence of a polycondensation catalyst described later. Tertiary amines such as tri-n-butylamine and benzyldimethylamine, quaternary ammoniums such as tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide and trimethylbenzylammonium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, It can be carried out by adding a small amount of a basic compound such as sodium acetate. These basic compounds may be added to all of the esterification reactors, or may be added to the first or second stage specific reactor.

The esterified product thus obtained is
Subsequently, it is continuously supplied to a liquid phase polycondensation reactor. In the liquid-phase polycondensation reactor, the resulting polyester is heated to a temperature not lower than the melting point of the obtained polyester under reduced pressure in the presence of a polycondensation catalyst, and the resulting glycol is distilled out of the system and polycondensed.

In the present invention, the polycondensation reaction step [A-2] comprises:
It may be performed in one stage or may be performed in a plurality of stages.
When the polycondensation reaction step is performed in a plurality of stages, the first
The second stage polycondensation reaction is usually performed at a reaction temperature of 250 to 290 ° C.
The reaction is preferably carried out at a temperature of 260 to 280 ° C. and a pressure of 500 to 20 Torr, preferably 200 to 30 Torr. The reaction is carried out under a condition of 0.1 Torr, preferably 5 to 0.1 Torr, particularly preferably 2 to 0.1 Torr.

When the polycondensation reaction step is carried out in three or more stages, the polycondensation reaction from the second stage to the last stage before the first stage depends on the reaction conditions of the first stage and the final stage. The reaction is performed under the conditions between the reaction conditions. For example, if the polycondensation reaction step is 3
When carried out in stages, the second stage polycondensation reaction is:
Usually, the reaction temperature is 260-295 ° C, preferably 270-2 ° C.
The reaction is carried out at 85 ° C. and at a pressure of 50 to 2 Torr, preferably 40 to 5 Torr.

In the present invention, in the above-mentioned [A] liquid phase polycondensation step, the intrinsic viscosity measured in o-chlorophenol at 25 ° C. is 0.7 to 1.5 dl / g, preferably 0.1 to 0.1 dl / g. A polyester (a) having a weight of 8 to 1.2 dl / g is produced. In addition, the intrinsic viscosity reached in each stage except the last stage of the liquid phase polycondensation reaction step is not particularly limited, but it is preferable that the degree of increase in the intrinsic viscosity in each stage is smoothly distributed.

[A] In the liquid phase polycondensation step, in order to produce the polyester (a) having such an intrinsic viscosity,
The above-mentioned polycondensation reaction step [A-2] is desirably carried out in three or more stages, preferably three stages, and the final stage (third stage)
It is desirable that the intrinsic viscosity of the polyester supplied to the polycondensation reaction in step (d) be 0.4 to 0.7 dl / g.

In order to obtain the polyester (a) having such an intrinsic viscosity by a multistage polycondensation reaction, a known liquid phase polycondensation reactor can be used in combination. For example, in the first stage, a vertical reactor is used. In the second stage, a horizontal reactor having a single-screw agitator can be used, and in the third stage, a horizontal reactor having a twin-screw agitator can be used. In this specification, the intrinsic viscosity is obtained by adding 1.2 g of polyester to o-
After heating and dissolving in 15 ml of chlorophenol, the solution is cooled and calculated from the solution viscosity measured at 25 ° C.

The liquid phase polycondensation reaction is performed in the presence of a catalyst. As the catalyst, germanium compounds such as germanium dioxide, germanium tetraethoxide, and germanium tetra n-butoxide, antimony catalysts such as antimony trioxide and antimony acetate, and titanium catalysts such as titanium tetrabutoxide can be used.

The use of a germanium dioxide compound among these catalysts is preferred because a polyester having excellent hue and transparency can be obtained. The polycondensation reaction is preferably performed in the presence of a stabilizer.

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, tris Phosphites such as nonylphenyl phosphite, acid phosphates such as methyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, dibutyl phosphate, monobutyl phosphate, dioctyl phosphate, and phosphoric acid, and polyphosphoric acid. A phosphorus compound is used.

The above-mentioned catalyst is used in an amount of 0.0005 to 0.2% by weight, preferably 0.001 to 0.2% by weight, based on the total weight of dicarboxylic acid and diol, in terms of the weight of metal in the catalyst.
Preferably, it is used in an amount of .about.0.05% by weight.

The stabilizer is converted to the weight of phosphorus atoms in the stabilizer with respect to the total weight of the dicarboxylic acid and the diol.
0.001-0.1% by weight, preferably 0.002-0.
Preferably, it is used in an amount of 02% by weight. These catalysts and stabilizers can be supplied in the esterification reaction step as described above, or can be supplied to the first stage reactor in the polycondensation reaction step. The polyester thus obtained from the final liquid-phase polycondensation reactor
(a) is usually formed into a granular shape (chip shape) by a melt extrusion molding method.

[B] Preliminary Crystallization Step In the present invention, the granular polyester (a) that has been subjected to the liquid phase polycondensation step is preliminarily crystallized. In this preliminary crystallization step, the granular polyester (a) is dried in a dried state at a temperature of a raised crystallization temperature (Tc ₁ ) to 200 ° C., preferably Tc _1.
It is carried out at a temperature of not less than 180 ° C. for 1 minute to 4 hours.

This pre-crystallization step is preferably performed in air or in an inert atmosphere. The polyester (b) after the pre-crystallization preferably has a crystallinity of 20 to 50%.

In the pre-crystallization step, the so-called solid-state polycondensation reaction of the polyester does not proceed, and the intrinsic viscosity of the polyester (b) after the pre-crystallization is obtained in the liquid-phase polycondensation step [A]. About the same as the intrinsic viscosity of the polyester (a). By adding a pre-crystallization step to the polyester in this way, the content of acetaldehyde contained in the polyester can be reduced, and the fusion of the granular polyester (chip) in the heat treatment step or the hot water treatment step can be prevented. can do.

In the method for producing a polyester according to the present invention, the polyester preliminarily crystallized as described above is used.
(b) is subjected to the following [C] heating step and [D] hot water treatment step.

[C] Heat Treatment Step In the production method according to the present invention, the preliminarily crystallized granular polyester (b) is heated at a high temperature. Specifically, the granular polyester is heated to a temperature of 160 to 200 ° C, preferably 170 to 190 ° C for 1 to 10 hours, preferably 2 to 10 hours.
Heat for ~ 6 hours. More specifically, polyester,
What is necessary is just to make it contact with the gas (air, nitrogen gas, etc.) of the flowing state heated to 160-200 degreeC, preferably 170-190 degreeC. For example, when the polyester is polyethylene terephthalate, specifically, 160 to 200 ° C.
Preferably, it may be brought into contact with a flowing gas heated to a temperature of 170 to 190 ° C.

By heating under such conditions,
Acetaldehyde contained in the polyester is removed, and a polyester (c) containing only a small amount of acetaldehyde is obtained. In this [C] heating step, the polycondensation reaction of the polyester hardly proceeds, and the intrinsic viscosity of the polyester (c) obtained after the heat treatment depends on the intrinsic viscosity of the polyester (a) obtained in the liquid phase polycondensation step. It is almost the same as viscosity.

[D] Hot Water Treatment Step In the production method according to the present invention, the polyester (c) that has undergone the heating step is subjected to a hot water treatment. , Water vapor, an inert gas containing water vapor, air containing water vapor, or the like.

The contact between the granular polyester (c) and hot water is as follows:
Desirably, the polyester is immersed in hot water heated to a temperature of usually 60 to 130 ° C, preferably 80 to 100 ° C. The contact between the granular polyester (c) and hot water is usually performed for 5 minutes to 10 hours, preferably for 30 minutes to 5 hours. When the granular polyester (c) is brought into contact with steam, the steam or the inert gas containing steam or air containing steam at a temperature of usually 60 to 130 ° C., preferably 80 to 100 ° C.
Granular polyester supplied in an amount of 0.5 g or more per kg
This is performed by bringing (c) into contact with steam. The contact between the granular polyester and water vapor is usually 5 minutes to
The reaction is performed for 10 hours, preferably for 1 to 8 hours.

The granular polyester immediately after the hot water treatment contains water in an amount of 5,000 to 10,000 ppm. By subjecting the polyester (c) to the hydrothermal treatment as described above, it is possible to suppress an increase in acetaldehyde during molding. By subjecting the polyester to the hydrothermal treatment as described above, the increase in acetaldehyde contained in the polyester at the time of molding can be suppressed because the polycondensation catalyst contained in the polyester, such as a germanium catalyst, is added by subjecting the polyester to the hydrothermal treatment. It is considered that the decomposition reaction or the transesterification reaction hardly proceeds even when heated during molding, and therefore the amount of acetaldehyde generated is considered to be reduced.

Polyester thus treated with hot water
(d) is preferably dried at a low temperature.
At a temperature of 10 to 150 ° C, preferably 120 to 140 ° C,
It is desirable to dry for 30 minutes to 6 hours, preferably 1 hour to 4 hours. Thus, the polyester (d) from which the moisture has been removed by the low-temperature drying is prevented from being hydrolyzed by the moisture.

In the method for producing a polyester according to the present invention, as described above, the [B] pre-crystallization step and the [C]
Since the heating step is performed at a lower temperature than the so-called solid-state polymerization step, the polycondensation reaction of the polyester does not substantially proceed, and the intrinsic viscosity of the polyester does not substantially increase in these steps.

The polyester produced according to the present invention has (i) an intrinsic viscosity of 0.4 in o-chlorophenol.
7 to 1.5 dl / g, preferably 0.8 to 1.1 dl
/ G, particularly preferably 0.8 to 1.0 dl / g. The polyester produced in the present invention has (ii) an acetaldehyde content of 10 ppm or less, preferably 5 ppm or less. Further, the crystallinity of the polyester produced in the present invention is desirably 30 to 50%.

As described above, the polyester obtained by the production method according to the present invention not only has a low content of acetaldehyde, but also does not easily increase acetaldehyde during molding.
Specifically, the polyester produced in the present invention is injection-molded at a molding temperature of 270 to 310 ° C., for example, 290 ° C. In a molded article such as a preform obtained, the acetaldehyde content is usually 20 ppm or less, preferably Is 1
It is 5 ppm or less.

A bottle obtained by supplying such a polyester to a molding machine such as an injection molding machine to form a preform for a hollow molded article, inserting the preform into a mold having a predetermined shape, and stretch blow molding. Hollow molded containers such as
It does not change the taste of the contents.

The polyester produced in the present invention is suitably used particularly as a material for forming a beverage bottle and a preform material for forming the bottle.

[0052]

The polyester obtained by the process for producing a polyester according to the present invention not only has a low acetaldehyde content but also a small amount of acetaldehyde which increases during molding. The container does not change the taste of the contents.

Further, in the method for producing a polyester according to the present invention, there is no need to perform a solid-phase polycondensation step on the polyester, which is excellent in productivity and economy. Thus, the polyester obtained by the method for producing a polyester according to the present invention is suitable as a material for a preform or a beverage bottle.

[0054]

EXAMPLES Next, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. In this specification, acetaldehyde concentration (ppm)
Is measured for a stepped square plate-like molded product as shown in FIG. 2 which is injection molded from a polyester chip as follows. The stepped square plate-like molded product has a thickness of 2 mm for the portion A, a thickness of 4 mm for the portion B, a thickness of 6 mm for the portion C, a thickness of 3 mm for the portion D, a thickness of 5 mm for the portion E, and a thickness of 7 mm for the portion F. It is. Using this part E, the acetaldehyde concentration of the molded article is measured.

The polyester chips obtained by forming and drying the stepped rectangular plate-like molded product were obtained from Miki Seisakusho Co., Ltd.
Dew point is -70 ° C during molding by -70A injection molding machine
Is fed to the upper portion of the hopper and the screw feeder chute at a rate of 5 Nm ³ / hour, and the barrel temperature is 290 ° C. and the temperature of the C1 / C2 / C3 / nozzle tip of the molding machine is 260 ° C./280° C./280. Injection molding was performed at a temperature of 15 ° C. at a temperature of 15 ° C. at a temperature of 300 ° C./300° C. to obtain a stepped square plate-shaped molded product as shown in FIG. Injection molding of the stepped square plate-like molded product is performed by supplying a polyester chip, which has been dried so that the measurement time is 12 seconds and the injection time is 60 seconds, from a hopper to an injection molding machine. The residence time of the molten resin in the molding machine is about 72 seconds. In addition, the weight per one stepped square plate-shaped molded product is about 75 g.

The acetaldehyde concentration of the square plate-like molded article with acetaldehyde measurement step was determined by crushing the sample with a freezer mill, extracting the acetaldehyde in the sample with hot water, and using gas chromatography to determine the acetaldehyde concentration by the internal standard method. I do. The intrinsic viscosity and the intrinsic viscosity (dl / g) of the polyester were determined by dissolving a sample in o-chlorophenol (OCP) by heating, determining the solution viscosity with a capillary viscometer, and using the value and an empirical formula prepared in advance.

Measurement of Temperature-Increasing Crystallization Temperature Using a DSC-2 type differential scanning calorimeter manufactured by Perkin Elmer, a sample from the center of a polyester chip dried at about 140 ° C. under a pressure of about 5 mmHg for about 5 hours or more. 10mm
g in a liquid aluminum pan under a nitrogen atmosphere. The measurement conditions were as follows: first, the temperature was rapidly raised from room temperature, melted and maintained at 290 ° C. for 10 minutes, then rapidly cooled to room temperature, and then the peak temperature of the exothermic peak detected when the temperature was raised at a rate of 10 ° C./minute Ask for.

[0058]

Example 1 100 parts by weight of terephthalic acid and 46.8 parts by weight of ethylene glycol and germanium dioxide 0.0
31 parts by weight were added, and an esterification reaction was carried out by a conventional method. The liquid temperature at the end of the reaction was 240 ° C. Next, 0.030 parts by weight of trimethyl phosphate was added, and a polycondensation reaction was performed in three stages. In the final stage, a polycondensation reaction is performed at a reaction temperature of 270 ° C. and a reaction pressure of 1 Torr, and the intrinsic viscosity is 0.83 dl.
/ G of polyester was obtained. The acetaldehyde concentration of the polyester chip was 53 ppm, and the heating crystallization temperature was 159.0 ° C.

Next, the polyester chips were pre-crystallized at 170 ° C. for 2 hours under nitrogen flow, heated at 180 ° C. for 3 hours, and immersed in 95 ° C. hot water for 3 hours. Thereafter, it was further dried at 130 ° C. for 2 hours at low temperature. Table 1 shows the intrinsic viscosity, acetaldehyde concentration, and water content of the polyester chip in each processing step.

[0060]

[Table 1]

Further, the polyester chip was dried at 160 ° C. for 3 hours under a nitrogen flow to reduce the water content in the chip to 40 pp.
m. At this time, the chips had an intrinsic viscosity of 0.81 dl / g and an acetaldehyde concentration of 1.7 ppm. Then, it was heated and melted at a temperature of 290 ° C. to form a stepped square plate. The molded product had an acetaldehyde concentration of 12 ppm.

The chip was used as a molding machine M manufactured by Meiki Seisakusho Co., Ltd.
It was molded at -100A to obtain a bottle preform. At this time, the molding temperature was 270 ° C., the nozzle temperature was 310 ° C., the mold temperature was 10 ° C., and the acetaldehyde concentration in the preform was 8 ppm.

[0063]

Comparative Example 1 Preliminary crystallization was performed at 170 ° C. for 2 hours under the flow of nitrogen using the same raw material chips as in Example 1;
C. for 3 hours, and further dried at 130.degree. C. for 2 hours. After the treatment, the obtained polyester chips had an intrinsic viscosity of 0.82 dl / g and an acetaldehyde concentration of 1.5 ppm. Next, after drying at 160 ° C. for 3 hours, it was heated and melted at a temperature of 290 ° C. to form a stepped square plate. The molded product had an acetaldehyde concentration of 27 ppm. A preform was molded in the same manner as in Example 1, and the concentration of acetaldehyde in the preform was measured.

[0064]

Example 2 Using the same raw materials as in Example 1, the polyester chips were treated in the same manner as in Example 1.
After performing the heat treatment at 170 ° C. for 4 hours, it was immersed in hot water at 95 ° C. for 3 hours. Thereafter, it was further dried at 130 ° C. for 2 hours at low temperature. Table 2 shows the intrinsic viscosity of the chip, the acetaldehyde concentration, and the water content in the chip in each step.

[0065]

[Table 2]

After further drying at 160 ° C. for 3 hours,
It was heated and melted at 0 ° C. to form a stepped square plate. The acetaldehyde concentration of the molded product was 13 ppm. A preform was formed in the same manner as in Example 1, and the concentration of acetaldehyde in the preform was 9 ppm.

[Brief description of the drawings]

FIG. 1 is a process flow showing a method for producing a polyester according to the present invention.

FIG. 2 is a perspective view of a stepped square plate formed in the example.

Claims (7)

(57) [Claims] [A] A dicarboxylic acid containing terephthalic acid or its ester derivative and a diol containing ethylene glycol or its ester derivative are heated and melted in the presence of a polycondensation catalyst to cause liquid phase polycondensation. 0.7-1.5 dl / g intrinsic viscosity measured in o-chlorophenol
A liquid-phase polycondensation step for producing a polyester (a), and [B] the polyester (a) obtained in the liquid-phase polycondensation step,
In an atmosphere at an elevated temperature of crystallization temperature (Tc ₁ ) to 200 ° C.,
A pre-crystallization step of keeping the mixture for 4 minutes to 4 hours, and [C] a polyester (b) having undergone the above-mentioned pre-crystallization step.
Is heated to a temperature of 160 to 200 ° C. for 1 to 10 hours.
A hot water treatment step of bringing the polyester into contact with hot water at a temperature of about 130 ° C. for 5 minutes to 10 hours. (I) In the steps [B] and [C], the intrinsic viscosity of the polyester is substantially increased. And (ii) the polyester (d) obtained has an acetaldehyde content of 10 ppm or less. 2. The polyester (a) obtained in the liquid phase polycondensation step [A] has an intrinsic viscosity of 0.8 to 1.2 dl / g measured in o-chlorophenol. The method for producing a polyester according to claim 1. 3. The liquid-phase polycondensation step [A] comprises an esterification reaction step [A-1] and a polycondensation reaction step [A-2], and the polycondensation reaction step [A-2]. The method for producing a polyester according to claim 1, wherein the method comprises a polycondensation reaction of three or more stages. 4. In the above polycondensation reaction step [A-2], the intrinsic viscosity of the polyester supplied to the final polycondensation reaction is 0.4 to 0.7 dl / g. The method for producing a polyester according to claim 2. 5. The polyester according to claim 1, wherein the polyester (b) after pre-crystallization obtained in the pre-crystallization step [B] has a crystallinity of 20 to 50%. Method. 6. The polyester (d) has a crystallinity of 30-5.
Method for producing a polyester according to claim 1, characterized in that 0%. 7. The method according to claim 1, wherein the acetaldehyde content in the polyester (d) is 5 ppm or less.