JP2001302778A - Method for manufacturing polyester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treating method of a polyester which conducts water treatment with good efficiency to reduce staining of a treating vessel and piping upon the water treatment. SOLUTION: This method for manufacturing a polyester by continuously feeding polyester chips to a treating vessel and feeding treating water to the treating vessel to effect the water treatment of the polyester chips comprises providing at least two treating water feed openings at different positions in height in the treating vessel to feed the treating water to the treating vessel.

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 No. 10-1
No. 14819 discloses a method of treating polyester with water.

However, at the stage of the water treatment, there has been a problem that the water treatment is not sufficient and the effect on the mold stain is insufficient. Fine (resin fine powder) adhering to the polyester chips floats and precipitates in the treated water and adheres to the walls of the processing tanks and pipes, thereby clogging the pipes and making it difficult to clean the processing tanks and pipes. And so on.

Further, fines floating and settled in the treated water and adhering to the walls of the treatment tank and pipes adhere to the polyester chips again, which promotes crystallization during molding, resulting in a bottle with poor transparency, The shrinkage of the plug part in the plug part crystallization causes a problem such as poor capping.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art and to make it difficult to generate mold stains at the time of molding. It is an object of the present invention to provide a polyester which can reduce contamination of piping and piping, and further, can improve the transparency of a bottle and the crystallization of a plug portion.

[0011]

Means for Solving the Problems To achieve the above object, the method for producing polyester according to the present invention comprises the steps of continuously supplying polyester chips to a treatment tank and supplying the treated water to the treatment tank. In the method for producing a polyester to be treated, at least two or more treated water supply ports are provided at different positions in the treatment tank, and the treated water is supplied to the treatment tank.

Although the position of the treated water supply port is not particularly limited, it is preferable that the supply port at the lowest position is located in the lowermost portion when the treatment tank is divided into five parts by height. By providing two or more supply ports having different heights, uneven distribution of the temperature distribution in the treatment tank can be reduced, and the water treatment effect can be made uniform.

In the method for producing a polyester according to the present invention, the temperature of the treated water supplied from the supply port at the higher position is at least one more than the temperature of the treated water supplied from the lower supply port.
It is characterized by being higher than ℃. Usually, when supplying the treated water from one place, when the polyester chips are continuously supplied to the treatment tank, the temperature of the upper treated water is lower than the supplied temperature of the treated water due to the cooling by the supply chips. For this reason, in order to sufficiently exert the effect of the water treatment on the mold contamination, the treatment time has to be lengthened, which leads to a decrease in productivity. On the other hand, two or more supply ports are provided,
By making the temperature of the processing water supplied from the supply port at a higher position higher than the temperature of the processing water supplied from the lower supply port by at least 1 ° C. or more, the processing efficiency can be dramatically improved.

In the method for producing polyester of the present invention, at least a part of the treated water discharged from the treatment tank is supplied to the treatment tank while maintaining the fine amount of the treated water discharged together with the polyester chips from the treatment tank at 1000 ppm or less. It is characterized by being returned and used repeatedly.

Here, the fine is defined by JIS-Z-880.
1 means fine powder of polyester of 20 mesh or less, and the fine amount is JIS from the outlet of treated water in the treatment tank.
-1000 cc of treated water passed through a 20-mesh filter by Z-8801 was collected and used for 1G1 manufactured by Iwaki Glass Co., Ltd.
After filtration through a glass filter, the residue remaining on the filter is dried at 100 ° C. for 2 hours, cooled at room temperature, and then weighed to calculate.

In the method for producing a polyester according to the present invention, a polyester chip is filled in a treatment tank,
In a method for producing polyester in which polyester water is treated by supplying treated water to a treatment tank, the treatment discharged from the treatment tank so that the fine amount of the treated water in the treatment tank at the end of the water treatment is 1000 ppm or less. It is characterized in that at least part of the water is returned to the treatment tank and used repeatedly.

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, the treated water containing fines discharged from the processing tank can be filtered and removed by a filtration device of a belt filter type, then returned to the processing tank and used repeatedly.

In this case, the treated water containing fines discharged from the processing tank can be filtered and removed by a bag filter type filtration device, and then returned to the processing tank for repeated use.

In this case, the treated water containing fines discharged from the treatment tank can be filtered and removed by a centrifugal filtration system, 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, dirt in a treatment tank or piping during water treatment is reduced,
Further, it is possible to advantageously produce a polyester which is less likely to cause mold contamination during molding, and furthermore, has good transparency and good crystallization of a plug portion of a bottle.

[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, and more preferably a linear polyester containing at least 85 mol% of ethylene terephthalate units. Particularly preferred is a linear polyester containing 95 mol% or more of ethylene terephthalate units.

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 0.55 to 1.3.
0 deciliter / gram, preferably 0.60 to 1.2
0 deciliter / gram, more preferably 0.65 to
It is in the range of 0.90 deciliter / 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. On the other hand, 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, so that free low-molecular-weight compounds that affect fragrance retention increase, Causes problems such as coloring of yellow.

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 10 ppm or less, preferably 8 ppm.
ppm or less, more preferably 5 ppm or less, the formaldehyde content is 7 ppm or less, preferably 6 ppm or less,
More preferably, it is 4 ppm or less. 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 1.0 to 1.0 of the glycol component.
It is 5.0 mol%, preferably 1.3 to 4.5 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 0.50% by weight or less, preferably 0.45% by weight or less, more preferably 0.40% by weight.
It is as follows. When molding a heat-resistant hollow molded article or the like from the polyester of the present invention, heat treatment is performed in a heating mold,
When the content of the cyclic trimer is 0.50% by weight or more, the adhesion of the oligomer to the surface of the heating mold rapidly increases, and the transparency of the obtained hollow molded article or the like is extremely deteriorated.

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 this solution and performing a heat treatment, 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 used is 20 to 1 as the amount of Ge remaining in the polyester resin.
It is 50 ppm, preferably 23-100 ppm, and more preferably 25-70 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, after the solid phase polymerization, a contact treatment with water is performed. 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.

The following is an example of a method for industrially performing water treatment, but the method is not limited thereto. The processing method is preferably a silo continuous method.

In the present invention, it is necessary to provide two or more treatment water supply ports at different heights. In this case, of course, a plurality of supply ports may be provided at the same height position. However, even at a single height, even if a plurality of supply ports are provided, the flow of the treated water in the treatment tank is often unevenly distributed, and as a result, the water treatment effect on the chips is substantially different. In addition, variations in the effect on mold contamination, that is, variations in quality, occur. In order to eliminate this variation, it is necessary to lengthen the processing time, which causes a decrease in productivity.

The position of the treated water supply ports having different heights is not particularly limited, but it is preferable that the supply port at the lowest position is located at the lowermost portion when the treatment tank is divided into five parts by height. Further, it is preferable that the supply port at the highest position is located in the upper three divided position when the processing tank is divided into five parts by height.

The temperature of the treated water supplied from the higher supply port is preferably at least 1 ° C. higher than the temperature of the treated water supplied from the lower supply port, and more preferably 3 ° C.
C. or higher, more preferably 5 ° C. or higher.

The polyester chips are charged and filled in the treatment tank and filled with treated water, and the treated water is circulated continuously or intermittently (generally, continuously) as necessary. Discharge part of the treated water intermittently and supply new treated water.

When supplying the treated water to a plurality of supply ports having different heights, the fine concentration in the treated water supplied from the lower supply port is made smaller than the fine concentration in the treated water supplied from the upper supply port. Lowering is effective for haze and mouth dimensional stability of the bottle.

At the end of the water treatment, the fine concentration in the water is 1000 ppm or less, preferably 500 pp.
m, more preferably 300 ppm or less.

As a method for reducing the fine amount of the treated water in the treatment tank, the following method can be exemplified.

In order to suppress an increase in the fine amount of the treated water in the treatment tank, a device for removing the fine water is installed at at least one place 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. Among them, for continuous operation, belt filter method, centrifugal filtration method,
A bag filter type filtration device is suitable. In the case of a filter device of a belt filter type, as a filter medium,
Examples include paper, metal, cloth, and the like. Further, in order to efficiently remove fines and flow the treated water, the size of the mesh of the filter is 5 to 100 μm, preferably 10 to 70 μm, and more 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 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.

[0051]

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 a mixed solvent of carbon tetrachloride / n-heptane.
Measured in ° C.

(3) Content of Polyester Cyclic Trimer A sample is dissolved in a mixed solution of hexafluoroisopropanol / chloroform, and further diluted by adding 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.

(Evaluation by Biaxial Stretch Molding Container) The polyester resin composition was dried by a dryer using dehumidified air, and a preform was formed at a resin temperature of 290 ° C. by an M-100 injection molding machine manufactured by each machine. Molded. After heating and crystallizing the plug portion of this preform with a home-made plug portion crystallizer, biaxial stretch blow molding was performed using a Corpoplast LB-01 stretch blow molding machine. Heat setting was performed for 10 seconds in the set mold to obtain a 500 cc hollow molded container. Under the same conditions, continuous stretch blow molding was performed, and the stain on the mold was evaluated by the number of moldings until the transparency of the container was impaired by visual inspection. Further, as a sample for haze measurement, a body portion of a container after continuous molding 5,000 times was provided.

(5) Measurement of Plug Shrinkage Rate of Molded Product (%) The height of the plug before the crystallization of the plug of the molded product and the height of the plug after the crystallization of the plug were measured. Obtain from the following formula.

Plug part shrinkage (%) = [(H1-H2) /
H1] × 100

The plug height is the distance from the top of the plug to the lower end of the plug support ring.

H1 and H2 in the above formula are H1: plug height before crystallization (mm) and H2: plug height after crystallization (mm).

(6) Fine amount (p) in the treated water in the treatment tank
pm) 100 ml of treated water that passed through a 20 mesh filter according to JIS-Z-8801 from the treated water discharge port of the treatment tank.
0 cc is collected, filtered through a 1G1 glass filter manufactured by Iwaki Glass Co., Ltd., dried at 100 ° C. for 2 hours, cooled at room temperature, and then weighed to calculate.

A raw material chip supply port (1) at the upper part of the processing tank, an inlet (8, 9) for new ion-exchanged water, an overflow outlet (2) located at the upper limit level of the processing water in the processing tank, and a polyester at the lower part of the processing tank. The drainage of the mixture of chips and treated water (3), the treated water discharged from the overflow discharge port and the treated water discharged through the drainage device (4) for the polyester chips discharged from the discharge port at the bottom of the treatment tank are used as filter media. A pipe (6) for feeding the water treatment tank again through a filtration device (5), which is a 30 μm belt-type filter made of paper, and an internal capacity 320 having an inlet (7) for these finely removed treated water. Using the treatment tank shown in FIG. 1 in the form of a liter tower, the limiting viscosity is 0.75 deciliter / gram, the density is 1.400 g / cm 3, and the cyclic trimer content is 0.33% by weight. In Polyethylene terephthalate (hereinafter, PET abbreviated) and the chip water treatment.

(Example 1) The temperature of the treated water supplied from the supply port (8) was 98 ° C, and the temperature of the treated water supplied from the supply port (9) was 95 ° C.
Continuous charging was started from the upper part (1) of the processing tank at the speed of time. After 4 hours from the start of charging, the PET chips are continuously charged into the water treatment tank and P is fed from the lower part (3) of the water treatment tank.
Withdrawal of the ET chips together with the treated water at a rate of 50 kg / hour was started, and the treated water passed through the draining device (4) was returned to the water treatment tank again through the filtration device (5), and repeated use was started. . PET chips from the drainer (4) and treated water discharged from the discharge port (3) at the lower part of the processing tank were sampled 4, 10, 15, 24, and 72 hours after the start of PET chip extraction.

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. The height of the plug portion of the obtained preform was measured. Next, the plug part of this preform was heated by a home-made plug crystallizer of a near-infrared heater type to crystallize the plug part. The height of the plug portion of the preform was measured again to determine the change in height due to crystallization of the plug portion. Next, the 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 by using an LB-01E molding machine manufactured by COPOPLAST to form a container having a capacity of 1500 cc. The stretching temperature was controlled at 100 ° C.

The fine amount contained in the sampled treated water was determined.

Table 1 shows the evaluation results.

[0067]

[Table 1]

As is clear from Table 1, when the fine amount in the treatment water of the treatment tank of the present invention is set to 1000 ppm or less, the obtained molded product maintains excellent transparency and shrinks the plug portion. The rate is also maintaining good.

(Comparative Example 1) The same operation as in Example 1 was carried out except that the fine water removing device used in Example 1 was removed, and that part was changed to a direct connection pipe. As shown in Table 1, the fine amount of the treated water continued to increase, the transparency of the molded product obtained by the treatment gradually deteriorated, and the shrinkage of the plug part increased.

(Examples 2, 3, 4 and Comparative Example 2) The temperature of the treated water supplied from the supply ports (8) and (9) and the time until the treated PET chips were taken out were changed as shown in Table 1. A PET chip was processed in the same manner as in Example 1 except for the above, and the chip taken out was evaluated. Table 2 shows the results of the haze of the molded container.

[0071]

[Table 2]

As is clear from Table 2, in Comparative Example 1, the haze of the molded product exceeded 5%, and the product did not meet the requirements. Further, in Comparative Example 3 in which the processing time was lengthened, the demand as a product could be endured, but it was clearly inferior to that of the example, and the productivity was poor.

[0073]

According to the present invention, by supplying treated water from a plurality of supply ports having different heights when supplying treated water to the treatment tank, the water treatment is efficiently performed and the transparency of the bottle is improved. Can be advantageously used as the resulting polyester. Further, the present invention is a method in which the polyester chips are supplied to a water treatment tank, a part of the treated water discharged from the treatment tank is returned to the treatment tank again and used repeatedly, and the fine amount of the treated water is 1000 ppm. Since it is the following, it is possible to reduce the contamination of the treatment tank and piping during water treatment, furthermore, it is difficult to generate mold contamination during molding, and furthermore, the transparency of the bottle and the crystallization of the plug portion are good. Can be advantageously used as a polyester.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw material chip supply port 2 Overflow discharge port 3 Discharge port of polyester chip and treated water 4 Drainer 5 Fine removal device 6 Pipe 7 Treated water inlet 8, 9 Ion exchange water inlet

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J029 AA03 AB04 AC01 AD01 AE01 AE03 BA03 BD06A BF09 BF17 CA02 CA04 CA05 CA06 CB05A CB06A CC06A KD03 KJ06 LB07

Claims (6)

[Claims] 1. A method for producing a polyester in which polyester chips are water-treated by continuously supplying polyester chips to a treatment tank and supplying treated water to a treatment tank.
A method for producing polyester, comprising providing at least two or more treated water supply ports at different positions in a treatment tank and supplying treated water to the treatment tank. 2. The process for producing polyester according to claim 1, wherein the temperature of the treated water supplied from the supply port at a higher position is at least 1 ° C. higher than the temperature of the treated water supplied from the lower supply port. . 3. The method for producing a polyester according to claim 1, wherein discharge of the treated water from the treatment tank and return of the discharged treated water to the treatment tank are continuous. 4. The method for producing a polyester according to claim 1, wherein discharge of the treated water from the treatment tank and return of the discharged treated water to the treatment tank are intermittent. 5. The method 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 while maintaining the fine amount of the treated water discharged together with the polyester chips at 1000 ppm or less. 1,
5. The method for producing a polyester according to 2, 3, or 4. 6. A polyester having an intrinsic viscosity of 0.55 to 0.55.
The method for producing a polyester according to claim 1, wherein the main repeating unit of 1.30 deciliter / gram is a polyester composed of ethylene terephthalate.