JP3095166B1 - Polyester production method - Google Patents

Abstract

An object of the present invention is to provide a polyester which is less likely to cause mold stains during molding, and further has good bottle transparency. SOLUTION: In a method for producing polyester in which polyester chips are water-treated in a treatment layer, water treatment is performed while maintaining the sodium content of treated water discharged together with the polyester chips from the treatment tank at 0.001 to 10.0 ppm. A method for producing a polyester, comprising:

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 polyester used for molding bottles, films, sheets and the like. The present invention relates to a method for producing a polyester having excellent controllability.

[0002]

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

[0003] Among them, polyester is excellent in mechanical strength, heat resistance, transparency and gas barrier properties, and is therefore particularly suitable as a material for containers for filling beverages such as juices, soft drinks and carbonated drinks.

[0004] Such polyester 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. Heat treatment (heat set)
Then, it is general that the plug portion of the bottle is heat-treated (the plug portion is crystallized) if necessary.

However, conventional polyesters contain oligomers such as cyclic trimers and the like, and these oligomers adhere to the inner surface of the mold, the gas exhaust port of the mold, and the exhaust pipe. Dirt was easy to occur.

[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, mold contamination must be removed frequently, and there has been a problem that the productivity of the bottle is reduced.

As a solution to these problems, Japanese Patent Laid-Open Publication No.
Japanese Patent No. 4441 discloses a method of treating polyester with water.

However, when this method is carried out industrially, the use of distilled water as treatment water is disadvantageous in terms of cost. It is common to use water. However, when water treatment is performed using industrial water, there is a problem that crystallization during molding is often too early, resulting in a bottle having poor transparency. Further, there is also a problem that shrinkage of the plug portion due to crystallization of the plug portion does not fall within the standard, resulting in poor capping.

According to the study of the present inventors, this is because, at the stage of water treatment, the content of metal-containing substances such as sodium, magnesium, calcium, silicon (silicic acid) and the like contained in industrial water is larger than a certain value. In this case, metal-containing substances such as oxides and hydroxides of these metals float and precipitate in the treated water, and further adhere to the walls of the processing tanks and pipes, which adhere to and penetrate the polyester chips to form It has been found that crystallization at the time is accelerated, resulting in a bottle having poor transparency. Further, problems such as clogging of the piping with the metal-containing substance and making cleaning of the processing tank and the piping difficult are caused. In particular, the content of sodium does not cause generation of scale, but sodium ions penetrate into the chip surface layer, and crystallization proceeds with the sodium ions as nuclei, which has been a major factor in whitening the bottle.

[0010] In particular, the sodium content increases after rain and varies from season to season, often with very high values. Furthermore, the sodium content varied greatly depending on where the industrial water source was sought.

[0011]

In order to achieve the above object, the present invention provides treated water by a method other than distillation.
A method for producing polyester in which polyester chips are subjected to water treatment in a treatment tank by using the obtained water, wherein the sodium content of treated water discharged together with the polyester chips from the treatment tank is maintained at 0.001 to 1.14 ppm. It is characterized by performing water treatment while performing.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art, and to provide a polyester which is less likely to cause mold stains during molding and has a good bottle transparency. It is intended to be.

[0013]

In order to achieve the above object, the present invention relates to a method for producing polyester in which polyester chips are water-treated in a treatment layer, wherein the sodium content of treated water discharged together with the polyester chips from a treatment tank is reduced. Is maintained at 0.005 to 10.0 ppm.

In this case, at least a part of the treatment water discharged from the treatment tank can be returned to the treatment tank and used repeatedly.

In this case, the polyester chips can be continuously supplied to the processing tank.

In this case, the polyester chips can be intermittently supplied to the treatment tank.

In this case, the whole amount of the polyester chips can be filled in the treatment layer, and the whole amount of the polyester chips can be extracted after the completion of the water treatment.

In this case, the discharge of the treated water from the treatment tank and the return of the discharged treated water to the treatment tank can be continued.

In this case, the discharge of the treated water from the treatment tank and the return of the discharged treated water to the treatment tank can be intermittent.

In this case, new treated water to be supplied to the treatment tank can be supplied to the treatment tank after the ion exchange treatment.

In this case, the treated water discharged from the treatment tank can be subjected to an ion exchange treatment and then returned to the treatment tank for repeated use.

In this case, the polyester is
The polyester having an intrinsic viscosity of 0.55 to 1.30 deciliters / gram in which the main repeating unit is composed of ethylene terephthalate can be used.

According to the method for producing a polyester of the present invention, it is possible to advantageously produce a polyester which is less likely to cause mold stains during molding and which has good bottle transparency.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester used in the present invention is preferably a polyester whose main repeating unit is composed of ethylene terephthalate.
A linear polyester containing at least 95 mol% of ethylene terephthalate units is particularly preferable.

The dicarboxylic acids used by copolymerization in the polyester include aromatic dicarboxylic acids such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl-4,4'-dicarboxylic acid and diphenoxyethanedicarboxylic acid. Acids and their functional derivatives, oxyacids and their functional derivatives such as p-oxybenzoic acid and oxycaproic acid, aliphatic dicarboxylic acids and their functional derivatives such as adipic acid, sebacic acid, succinic acid and glutaric acid, cyclohexane Alicyclic dicarboxylic acids such as dicarboxylic acids and functional derivatives thereof;

Glycols used by copolymerization in the polyester include aliphatic glycols such as diethylene glycol, trimethylene glycol, tetramethylene glycol and neopentyl glycol; alicyclic glycols such as cyclohexane dimethanol; bisphenol A; Aromatic glycols such as an alkylene oxide adduct of bisphenol A and the like can be mentioned.

Further, as other copolymerization components comprising a polyfunctional compound in the polyester, trimellitic acid and pyromellitic acid can be mentioned as acid components, and glycerin and pentaerythritol can be mentioned as glycol components. Can be. The amount of the above-mentioned copolymer component to be used must be such that the polyester resin maintains a substantially linear shape.

The intrinsic viscosity of the polyester used in the present invention, particularly the polyester whose main repeating unit is composed of ethylene terephthalate, is preferably 0.5.
The range is 5 to 1.30 deciliters / gram, more preferably 0.60 to 1.20 deciliters / gram, and even more preferably 0.65 to 0.90 deciliters / gram. If the intrinsic viscosity is less than 0.55 deciliter / gram, the mechanical properties of the obtained molded article and the like are poor. Also,
If it exceeds 1.30 deciliters / gram, the resin temperature rises during melting by a molding machine or the like, and thermal decomposition becomes severe, free low-molecular-weight compounds that affect fragrance retention increase, or the molded product becomes yellow. This causes problems such as coloring.

The shape of the polyester chip may be any of a cylinder type, a square type, a flat plate shape, and the like.
Range. For example, in the case of a cylinder type, it is practical that the length is about 1.5 to 4 mm and the diameter is about 1.5 to 4 mm.

The acetaldehyde content of the polyester used in the present invention is preferably 10 ppm or less, more preferably 8 ppm or less, even more preferably 5 ppm or less, and the formaldehyde content is preferably 7 ppm or less.
More preferably 6 ppm or less, still more preferably 4 ppm
It is as follows. The method for reducing the acetaldehyde content of the polyester used in the present invention to 10 ppm or less and the formaldehyde content to 7 ppm or less is not particularly limited. A method of performing solid phase polymerization at a temperature of 230 ° C. can be mentioned.

The amount of diethylene glycol in the polyester used in the present invention is preferably 1.0 to 5.0 mol% of the glycol component, more preferably 1.3 to 4.0 mol%.
It is 5 mol%, more preferably 1.5 to 4.0 mol%. When the amount of diethylene glycol exceeds 5.0 mol%, the thermal stability deteriorates, the molecular weight decreases during molding, and the acetaldehyde content and the formaldehyde content increase unfavorably.

The content of the cyclic trimer of the polyester used in the present invention is preferably 0.50% by weight or less.
More preferably, it is 0.45% by weight or less, further preferably 0.40% by weight or less. When a heat-resistant hollow molded article or the like is molded from the polyester of the present invention, heat treatment is performed in a heating mold. However, when the content of the cyclic trimer is 0.50% by weight or more, the heating mold is used. The adhesion of oligomers to the surface sharply increases, and the transparency of the obtained hollow molded article or the like becomes extremely poor.

The above polyester can be produced by a conventionally known production method. That is, a direct esterification method in which terephthalic acid and ethylene glycol and, if necessary, other copolymerization components are directly reacted to distill off water and esterify, followed by polycondensation under reduced pressure, or dimethyl terephthalate and ethylene glycol It is produced by a transesterification method in which methyl alcohol is distilled off and transesterification is carried out by reacting other copolymerization components if necessary, followed by polycondensation under reduced pressure. Solid-state polymerization may be further performed to increase the intrinsic viscosity and decrease the acetaldehyde content and the like.

The melt polycondensation reaction may be performed in a batch reactor or a continuous reactor. In any of these methods, the melt polycondensation reaction may be performed in one step or may be performed in multiple steps.
The solid-state polymerization reaction can be performed in a batch-type apparatus or a continuous-type apparatus as in the melt polycondensation reaction. The melt polycondensation and the solid phase polymerization may be performed continuously or may be performed separately.

In the case of the direct esterification method, compounds of Ge, Sb and Ti are used as a polycondensation catalyst, and a Ge compound is particularly advantageous. As the Ge compound, amorphous germanium dioxide, crystalline germanium dioxide powder or a slurry of ethylene glycol, a solution obtained by heating and dissolving crystalline germanium dioxide in water, or a solution obtained by adding ethylene glycol to the solution and heat-treating the same are used. In particular, in order to obtain the polyester used in the present invention, it is preferable to use a solution obtained by heating and dissolving germanium dioxide in water or a solution obtained by adding ethylene glycol to this solution and heating. These polycondensation catalysts can be added during the esterification step. When a Ge compound is used, the amount thereof is preferably 20 to 150 ppm, more preferably 23 to 100 ppm, as the amount of Ge remaining in the polyester resin.
pm, more preferably 25 to 70 ppm.

As the stabilizer, it is preferable to use phosphoric acid, polyphosphoric acid, or phosphoric esters such as trimethyl phosphate. These stabilizers can be added during the esterification reaction step from a slurry preparation tank of terephthalic acid and ethylene glycol.

In order to control the DEG content in the polyester, a basic compound such as a tertiary amine such as triethylamine or tri-n-butylamine is used in the esterification step.
A quaternary ammonium salt such as tetraethylammonium hydroxide can be added.

In the present invention, the polyester is used to prevent mold contamination and the like due to the adhesion of oligomers such as cyclic trimers to the inner surface of the mold, the exhaust port of the mold gas, and the exhaust pipe during molding. Then, a contact treatment with water is performed after the solid phase polymerization. As a method of the contact treatment with water, a method of immersing in water may be mentioned. The time for performing the contact treatment with water is 5 minutes to 2 days, preferably 10 minutes to 1 day, more preferably 30 minutes to 10 hours, and the water temperature is 20 to 180 ° C, preferably 40 to 150 ° C. ° C, more preferably 50 to 120 ° C.

In the case of industrially treating polyester chips with water, natural water (industrial water) and wastewater are often reused because the amount of water used for the treatment is large. Normally, this natural water is collected from river water, groundwater, or the like, and refers to water that has been subjected to treatment such as sterilization and removal of foreign substances without changing the shape of water (liquid). Further, natural water generally used for industrial use contains a large amount of metal-containing substances such as sodium, magnesium, calcium, and silicon. When the water treatment is performed using natural water, it adheres to and penetrates the polyester chips to form crystal nuclei, and the transparency of the hollow molded container using such polyester chips becomes extremely poor.

The following is an example of a method for industrially performing water treatment, but the method is not limited thereto. The processing method may be either a continuous method or a batch method, but the continuous method is preferable for industrial use.

Regardless of whether the water treatment method is continuous or batch, if all or most of the treated water discharged from the treatment tank is converted into industrial wastewater, a large amount of new water is required. In addition to the above, there is a concern about the impact on the environment due to increased wastewater. That is, at least a part of the treated water discharged from the treatment tank is returned to the water treatment tank and reused, thereby reducing the required amount of water and reducing the effect on the environment by increasing the amount of wastewater. If the wastewater returned to the water treatment tank maintains a certain temperature, the amount of heating of the treated water can be reduced, so that the treated water discharged from the treatment layer is preferably returned to the water treatment layer and reused. . In addition, by reusing water, the flow rate of the treated water in the treated layer can be increased, and as a result, fines attached to the polyester chips can be washed out, thereby producing a fine removing effect.

When the polyester chips are continuously treated with water, the polyester chips are continuously treated in a tower-type treatment tank, or the polyester chips are intermittently received from above, and water is continuously supplied in parallel or countercurrent to the water treatment. Can be done. The treated polyester chips are continuously or intermittently extracted from the lower part of the treatment layer.

In the case of treating the polyester chips with water in a batch system, a silo-type treatment tank may be used. That is, the chips of polyester are received in a silo in a batch system and water treatment is performed. Alternatively, it is also possible to receive a polyester chip in a rotating cylindrical processing tank and perform water treatment while rotating the chip, thereby making contact with water more efficient.

Regardless of whether the water treatment method is a continuous method or a batch method, the sodium content in the treated water discharged together with the polyester chips is 0.0
01 to 1.14 ppm, preferably 0.003 to 1.1
4 ppm, more preferably 0.005 to 1.0 ppm,
Particularly preferably, it is 0.01 to 0.5 ppm. In addition,
The treated water discharged together with the polyester chips here is water discharged together with the polyester from the polyester discharge port in the case of a continuous method when discharging the polyester, and the polyester is discharged together with the water from the discharge port in the case of the batch method. When the water is discharged, it is the water, and when the polyester is pulled up or when only the treated water is discharged first, it means water completely attached to the polyester (water at the end of the water treatment). 0.001 of sodium content of treated water
By setting the content to １．１1.14 ppm, a high-quality bottle with high transparency can be obtained.

[0045] Regardless of whether the water treatment method is a continuous method or a batch method, the sodium content in the treated water discharged together with the polyester chips is 0.00%.
01 to 10.0 ppm, preferably 0.003 to 5.0
ppm, more preferably 0.005 to 1.0 ppm, particularly preferably 0.01 to 0.5 ppm. In addition, the treated water discharged together with the polyester chips here is water discharged together with the polyester from the polyester discharge port in the case of the continuous method when discharging the polyester, and the polyester is discharged from the discharge port in the case of the batch method. When it is discharged together with water, it is the water, and when the polyester is pulled up or when only the treated water is discharged first, it means water completely attached to the polyester (water at the end of the water treatment). The sodium content of the treated water is 0.001 to
By adjusting to 10.0 ppm, a high-quality bottle with high transparency can be obtained.

The magnesium content in the treated water discharged together with the polyester chips is preferably 0.001 to 0.5 ppm, more preferably 0.003 to 0.3 ppm, and further preferably 0.005 to 0.3 ppm.
~ 0.1 ppm, preferably with a calcium content of 0.0
01 to 0.5 ppm, more preferably 0.003 to 0.1 ppm.
3 ppm, more preferably 0.005 to 0.1 ppm,
The silicon content is preferably 0.01 to 2.0 ppm, more preferably 0.03 to 1.0 ppm, and still more preferably 0.1 to 2.0 ppm.
It is better to make it 0.5 to 0.5 ppm.

[0047] Regardless of whether the water treatment method is continuous or batchwise, when the sodium content in the treated water is less than 0.001 ppm, distillation or membrane filtration using a reverse osmosis membrane is required. And so on. In this case, the equipment cost increases, and it becomes difficult to perform economical water treatment.

Hereinafter, a method for reducing sodium, magnesium, calcium, and silicon in the treatment water in the treatment tank will be described, but the present invention is not limited thereto.

In order to reduce the amount of sodium, magnesium, calcium and silicon in the treated water in the treatment tank, at least one of the sodium and magnesium is supplied to the treatment tank until the industrial water is sent to the treatment tank for supply to the treatment tank. ,
Install equipment to remove calcium and silicon. Further, in the process until the treated water discharged from the treatment tank is returned to the treatment tank again, an apparatus for removing sodium, magnesium, calcium, and silicon may be provided at at least one or more places. Examples of an apparatus for removing sodium, magnesium, calcium, and silicon include an ion exchange apparatus.

The treated water discharged from the treatment tank in the water treatment includes fines already adhered to the polyester chips at the stage of receiving the polyester chips in the treatment tank, and the polyester chips or the walls of the treatment tank during the water treatment. Contains fines of polyester generated by friction with. Therefore, at least one or more devices for removing fines are installed in the process until the treated water discharged from the treatment tank is returned to the treatment tank again. Examples of the device for removing fines include a filter filtration device, a membrane filtration device, a sedimentation tank, a centrifugal separator, and a foam entrainer. For example, in the case of a filter filtration device, a filtration device such as a belt filter system, a bag filter system, a cartridge filter system, and a centrifugal filtration system may be used. Above all, a belt filter system, a centrifugal filtration system, and a bag filter system are suitable for continuous operation. In the case of a filter device of a belt filter type, examples of the filter medium include paper, metal, cloth, and the like. In order to efficiently remove fines and flow treated water, the mesh size of the filter is preferably 5 to 100 μm, more preferably 10 to 70 μm, and further preferably 15 to 40 μm.

The water-treated polyester chips are drained by a draining device such as a vibrating sieve or a Simon Carter and transferred to a drying step. Naturally, the water separated from the polyester chips by the draining device is sent to the above-mentioned fine removing device, and can be used again for water treatment.

For drying the polyester chips, a commonly used drying treatment of the polyester chips can be used. As a method for continuous drying, a hopper-type through-air dryer that supplies a polyester chip from the upper portion and allows a drying gas to flow from the lower portion is usually used. As a method of reducing the amount of drying gas and drying efficiently, a rotating disk type continuous dryer is selected, and heating steam, heating medium, etc. are supplied to the rotating disk and the outer jacket while passing a small amount of drying gas. The dried granular polyester chips can be dried indirectly.

As a dryer for drying in a batch system, a double cone type rotary dryer is used, and 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 or thermal oxidative decomposition of polyester.

[0055]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. In addition, the measuring method of the main characteristic value in this specification is demonstrated below.

(1) Intrinsic viscosity of polyester (IV) It was determined from the solution viscosity at 30 ° C. in a 1,1,2,2-tetrachloroethane / phenol (2: 3 weight ratio) mixed solvent.

(2) Density: 25 using a density gradient tube of carbon tetrachloride / n-heptane mixed solvent.
Measured in ° C.

(3) Content of cyclic trimer of polyester A sample is dissolved in a mixed solution of hexafluoroisopropanol / chloroform, and further diluted with chloroform. After adding methanol to precipitate a polymer, the mixture is filtered. The filtrate was evaporated to dryness, made up to a constant volume with dimethylformamide, and a cyclic trimer composed of ethylene terephthalate units was quantified by liquid chromatography.

(4) Haze (% haze) A sample was cut from the body (thickness: about 0.4 mm) of the hollow molded article and measured with a haze meter manufactured by Toyo Seisakusho.

(5) Metal content (p
pm) Treated water was collected from the outlet of the treated water in the treatment tank, filtered through a 1G1 glass filter manufactured by Iwaki Glass Co., Ltd., and the filtrate was measured with an inductively coupled plasma emission analyzer manufactured by Shimadzu Corporation.

(Example 1) Raw material chip supply port (1) at the top of treatment tank, water inlet (8) through ion exchange device (10) for removing sodium from industrial water (9), treatment of treatment tank Overflow discharge port (2) located at the upper limit level of water, discharge port (3) of a mixture of polyester chips and treated water at the bottom of the treatment tank, treated water discharged from the overflow discharge port, and discharge from the discharge port at the bottom of the treatment tank The treated water that has passed through the draining device (4) for the removed polyester chips is sent again to the water treatment tank through the filtering device (5), which is a 30-μm belt-type filter made of paper, and the piping (6). A polyethylene terephthalate (hereinafter abbreviated as PET) chip is treated with water using a treatment tank shown in FIG. 1 having a capacity of 320 liters and having an inlet (7) for treated water after fine removal. It was.

The limiting viscosity is 0.75 deciliter / gram.
With a density of 1.400 g / cm ^ThreeAnd the cyclic 3 quantity
PET chips with a body content of 0.33% by weight
50kg / h into a water treatment tank controlled at 95 ° C
Water from the upper part of the treatment tank (1)
After 5 hours, the PET chip was discharged
Process water at 50 kg / hour
I started. After 72 hours of continuous operation from the drainer (4)
PET chips and discharged from the outlet (3) at the bottom of the treatment tank
Sampled treated water.

The sampled PET chips were dried under reduced pressure, and preformed bottles were molded using an M-100 injection molding machine manufactured by Meiki Seisakusho. Injection molding temperature is 295
° C. Next, this preformed body was biaxially stretched and blown at a magnification of about 2.5 times in the vertical direction and about 5 times in the circumferential direction using an LB-01E molding machine manufactured by COPOPLAST, and the capacity was 1500 c.
The container of c was molded. The stretching temperature was controlled at 100 ° C.

The properties of the polyester container obtained in Example 1 and the sodium content in the treated water are shown in Table 1 together with Comparative Examples.

(Examples 2 and 3) Water treatment was performed in the same manner as in Example 1 except that the capacity of the ion exchange device and the type of ion exchange resin were changed, and a container was obtained using the obtained chips. Table 1 shows the results.

[0066]

[Table 1]

As is clear from Table 1, the sodium content in the treated water of the treatment tank of the present invention was 0.001 to 10.0.
By setting the content to ppm, the obtained molded article has excellent transparency.

(Comparative Example 1) An ion exchange apparatus for removing sodium used in industrial water used in Example 1 was removed, and the part was changed to a direct connection pipe. As shown in Table 1, the sodium content of the treated water was large, and the transparency of the molded product obtained by the treatment was poor.

[0069]

According to the present invention, there is provided a method in which polyester chips are supplied to a water treatment tank, and a part of the treatment water discharged from the treatment tank is returned to the treatment tank again for repeated use.
The sodium content of the treated water is 0.001 to 10.0 pp
m, it is difficult to generate mold stains during molding,
Further, it can be advantageously used as a polyester having good bottle transparency.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of an apparatus used in a method for producing a polyester of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Raw material chip supply port 2 Overflow discharge port 3 Polyester chip and treated water discharge port 4 Drainer 5 Fine removal device 6 Piping 7 Treated water inlet 8 Metal-removed water inlet 9 Industrial water inlet 10 Underwater Equipment for removing metal-containing substances

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-174441 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29B 13/00 C08G 63/80-63 / 90

Claims (10)

(57) [Claims] (1) Processed water is obtained by a method other than distillation.
A method for producing polyester in which polyester chips are subjected to water treatment in a treatment tank by using the obtained water, wherein the sodium content of treated water discharged together with the polyester chips from the treatment tank is maintained at 0.001 to 1.14 ppm. A method for producing a polyester, wherein water treatment is performed while treating. 2. The method for producing polyester according to claim 1, wherein at least a part of the treated water discharged from the treatment tank is returned to the treatment tank and used repeatedly. 3. The method according to claim 1, wherein the polyester chips are continuously supplied to the treatment tank. 4. The method for producing polyester according to claim 1, wherein the polyester chips are intermittently supplied to the treatment tank. 5. The method for producing polyester according to claim 1, wherein the whole amount of the polyester chips is filled in the treatment layer, and the whole amount of the polyester chips is extracted after the water treatment. And discharge of treated water from wherein the processing tank, a method of producing a polyester of any crab claimed in claims 1 to 5, characterized in that return to the treatment tank discharge the treated water is continuously . 7. The method for producing a polyester according to claim 1, wherein the discharge of the treated water from the treatment tank and the return of the discharged treated water to the treatment tank are intermittent. . 8. The method for producing a polyester according to claim 1, wherein fresh treated water supplied to the treatment tank is subjected to ion exchange treatment and then supplied to the treatment tank. 9. The method for producing a polyester according to claim 1, wherein the treated water discharged from the treatment tank is subjected to ion exchange treatment, returned to the treatment tank, and used repeatedly. 10. The polyester has an intrinsic viscosity of 0.55 to 0.55.
The polyester production method according to any one of claims 1 to 9, wherein a main repeating unit of 1.30 deciliter / gram is a polyester composed of ethylene terephthalate.