JP2001348425A - Method for drying polyester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for drying a polyester into a dried product capable of giving a molding (e.g. bottle) being excellent in transparency and hardly generating the contents to give a foreign taste and/or a foreign odor and less problematic in deposition on a mold without raising a viscosity lowering and a hue change during drying. SOLUTION: Provided is a method for drying a polyester by continuously or intermittently feeding an undried polyester into the upper feed opening 1 of a tower drier and drying the polyester in a heated gas stream while continuously or intermittently discharging the dried polyester from the lower discharge opening 2 of the drier, which method comprises performing the drying by heating a moisture-containing gas fed from the lower gas feed opening 4 of a dried polyester cooling and storing tank 7 directly connected to the drier and discharged from the upper gas discharge opening of the cooling and storing tank after countercurrent contact with the dried polyester to 90-140 deg.C and continuously feeding it from a gas feed opening 5 provided at the intermediate part of the drier and continuously feeding a moisture removing gas heated to below 100-160 deg.C from the gas feed port 3 provided at the lower part of the drier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drying a polyester used for forming a film, a sheet and the like as well as a bottle. Particularly, the economical drying of the polyester which has been subjected to contact treatment with water in order to obtain a polyester having excellent transparency of the obtained molded article, less likely to generate an unpleasant taste and odor, and less likely to cause mold stains during molding. About the method.

[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 by the present inventors, this is because when the content of metal-containing substances such as sodium, magnesium, calcium, and silicon contained in industrial water is larger than a certain value at the stage of water treatment, Metal-containing substances such as metal oxides and hydroxides float and precipitate in the treatment water, and further adhere to the walls of the treatment tank and piping, which adhere to and penetrate the polyester chips, and It was found that crystallization was accelerated, resulting in a bottle with 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.

The content of these metal-containing substances increases after rain, fluctuates depending on the season, and often has a very large value. Furthermore, the location of the industrial water source was greatly different.

Accordingly, in order to obtain a water-treated polyester which gives a molded article having good transparency, the polyester is water-treated using ion-exchanged water obtained by treating industrial water with an ion-exchange treatment apparatus. It is dried after separation, and is subjected to molding. The water content after water treatment is about 0.5 to 1
Because of its high weight percent, when drying using undehumidified air, it is necessary to dry with air at 140 ° C. or less in order to prevent a decrease in intrinsic viscosity. In this case, a time of 10 hours or more is required. is there. In the case of drying using dehumidified air, a decrease in the intrinsic viscosity can be prevented, but there is an economical problem.

[0012]

SUMMARY OF THE INVENTION The present invention solves the problems of the prior art, and it is an object of the present invention to provide a method for drying a polyester which has been subjected to contact treatment with water without lowering the intrinsic viscosity of the polyester upon drying or changing the color tone. Provides a drying method that can be used, and also has excellent transparency from polyester after drying,
It is an object of the present invention to provide an economical drying method for polyester which can produce a molded article which does not easily generate an unpleasant odor and which does not easily cause mold contamination during molding.

[0013]

In order to achieve the above-mentioned object, the present invention relates to a method for drying a undried polyester having a main repeating unit of ethylene terephthalate and having a density of 1.37 g / cm ³ or more in a tower type. A polyester drying method in which the polyester is continuously or intermittently supplied from an upper supply port of the apparatus and dried under a heated gas flow while continuously or intermittently extracting the dried polyester from a lower discharge port of the drying apparatus. In the method, the gas supplied from the cooling gas supply port of the cooling storage tank of the dried polyester directly connected to the drying device, and the gas discharged from the gas discharge port of the cooling storage tank after contact with the dried polyester is heated to a temperature of 90 to 140 ° C. Dehumidified air heated continuously to a temperature of 100 to 160 ° C. The characterized by drying by continuously feeding than established the gas supply port in the lower portion of the drying apparatus.

[0014] In this case, the undried polyester may be one subjected to contact treatment with water. In this case, the dew point of the dehumidifying gas can be −25 ° C. or less. In this case, as the gas used for drying, a gas having a particle size of 0.3 to 5 μm and 1,000,000 particles / cubic foot or less can be used. Also,
In this case, the gas can be any one of gases selected from air, nitrogen, and carbon dioxide.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The polyester whose main repeating unit is ethylene terephthalate used in the present invention is a linear polyester containing 85 mol% or more of ethylene terephthalate units, preferably 90 mol% or more, more preferably 95% or more. .

The dicarboxylic acids used in the copolymerization of the polyester include aromatic dicarboxylic acids such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, diphenoxyethanedicarboxylic acid and the like. Functional derivatives thereof, oxy acids such as p-oxybenzoic acid and oxycaproic acid and their functional derivatives, aliphatic dicarboxylic acids such as adipic acid, sebacic acid, succinic acid and glutaric acid and their functional derivatives, cyclohexanedicarboxylic acid And their functional derivatives.

Examples of the glycol used for copolymerization of 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, pyromellitic acid and the like 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 maintains a substantially linear shape. Further, a monofunctional compound such as benzoic acid or naphthoic acid may be copolymerized.

The above-mentioned polyester is obtained by directly reacting terephthalic acid with ethylene glycol and, if necessary, the above-mentioned copolymerization component to distill water and esterify it, and then selected from Sb compounds, Ge compounds or Ti compounds as polycondensation catalysts. Esterification method in which polycondensation is carried out under reduced pressure using one or more kinds of compounds described above, or dimethyl terephthalate is reacted with ethylene glycol and, if necessary, the copolymerization component in the presence of a transesterification catalyst to obtain methyl alcohol. Is distilled off and transesterified, and then produced by a transesterification method in which polycondensation is carried out mainly under reduced pressure using one or more compounds selected from Sb compounds, Ge compounds and Ti compounds as polycondensation catalysts. You.

The Sb compound used in the present invention includes:
Examples include antimony trioxide, antimony acetate, antimony tartrate, antimony potassium tartrate, antimony oxychloride, antimony glycolate, antimony pentoxide, and triphenylantimony. The Sb compound is added so that the residual amount of Sb in the produced polymer is in the range of 50 to 250 ppm.

The Ge compound used in the present invention includes:
Examples include amorphous germanium dioxide, crystalline germanium dioxide, germanium chloride, germanium tetraethoxide, germanium tetra-n-butoxide, and germanium phosphite. When a Ge compound is used, the amount of the Ge compound used is 5 as the amount of Ge remaining in the polyester.
The amount is from 150 to 150 ppm, preferably from 10 to 100 ppm, more preferably from 15 to 70 ppm.

The Ti compounds used in the present invention include:
Tetraalkyl titanates such as tetraethyl titanate, tetraisopropyl titanate, tetra-n-propyl titanate, tetra-n-butyl titanate and their partial hydrolysates, titanyl oxalate, titanyl ammonium oxalate, sodium titanyl oxalate, potassium titanyl oxalate, titanyl oxalate Examples include calcium, titanyl oxalate compounds such as titanylstrontium oxalate, titanium trimellitate, titanium sulfate, and titanium chloride. The Ti compound is used in an amount of 0.1 to 10 as a residual amount of Ti in the produced polymer.
It is added to be in the range of ppm.

Various P compounds can be used as stabilizers. Examples of the P compound used in the present invention include phosphoric acid, phosphorous acid, phosphonic acid and derivatives thereof. Specific examples include phosphoric acid, trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, monomethyl phosphate, dimethyl phosphate, monobutyl phosphate, dibutyl phosphate, and dibutyl phosphate. Phosphoric acid, Trimethyl phosphite, Triethyl phosphite, Tributyl phosphite, Methylphosphonic acid, Methylphosphonic acid dimethyl ester, Ethylphosphonic acid dimethylester, Phenylphosphonic acid dimethylester, Phenylphosphonic acid diethylester, Phenylphosphonic acid And diphenyl esters and the like. These may be used alone or in combination of two or more. The P compound is added at any stage of the polyester production reaction step so that the residual amount of P in the produced polymer is in the range of 5 to 100 ppm.

Further, solid-state polymerization may be performed to increase the intrinsic viscosity of the polyester and reduce the acetaldehyde content.

The above-mentioned esterification reaction, transesterification reaction, melt polycondensation reaction and solid-state polymerization reaction may be carried out 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. Melt polycondensation and solid phase polymerization may be performed continuously,
It may be performed in a divided manner.

The intrinsic viscosity of the polyester used in the present invention is preferably 0.55 to 0.90 deciliter / gram, more preferably 0.58 to 0.88 deciliter / gram, and still more preferably 0.60 to 0.18 deciliter / gram. It is in the range of 86 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. On the other hand, if it exceeds 0.90 deciliter / gram, the resin temperature rises during melting by a molding machine or the like, and the thermal decomposition becomes severe. Problems such as yellowing occur.

The shape of the polyester chip may be any of a cylinder type, a square type, a flat plate shape and the like, and the size thereof is usually in the range of 1.5 to 4 mm in length, width and height. For example, in the case of a cylinder type, the length is 1.
It is practical that the diameter is about 5 to 4 mm and the diameter is about 1.5 to 4 mm. Further, the weight of the chip is practically in the range of 15 to 30 mg / piece.

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 acetaldehyde content of the polyester used in the present invention is 10 ppm
Hereinafter, the method for reducing the formaldehyde content to 7 ppm or less is not particularly limited. For example, a method for solid-phase polymerization of a low-molecular-weight polyester at a temperature of 170 to 230 ° C. under reduced pressure or an inert gas atmosphere is used. Can be mentioned.

The amount of diethylene glycol copolymerized with the polyester used in the present invention is 1.0 to 5.0 mol%, preferably 1.3 to 4.5 mol%, and more preferably 1.3 to 4.5 mol% of the glycol component constituting the polyester. Preferably 1.5
~ 4.0 mol%. The amount of diethylene glycol is 5.
If it exceeds 0 mol%, the thermal stability will be poor, the molecular weight will decrease during molding, and the acetaldehyde content and the formaldehyde content will increase undesirably. The diethylene glycol content is 1.0 mol%
If it is less than 1, the transparency of the obtained molded article is deteriorated.

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.

Further, the density of the polyester used in the present invention is 1.37 g / cm ³ or more.

In order to prevent mold contamination due to the adhesion of oligomers such as cyclic trimers to the inner surface of the mold, the exhaust port of the mold gas, the exhaust pipe, etc. during molding, the polyester is melted as described above. After the polycondensation or solid-phase polymerization, a contact treatment with water, steam, or a gas containing steam is performed.

Examples of the hot water treatment method include a method of immersing in water and a method of spraying water on a chip with a shower. 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 temperature of water is 20 to 180 ° C, preferably 40 to 150 ° C, and more preferably 50 to 12 ° C.
0 ° C.

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 method of water treatment 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.

In the case of continuously treating polyester chips with water, the polyester chips are continuously or intermittently received in a tower-type treatment tank from the top, and water is continuously supplied in parallel or countercurrent to supply water. Can be processed. The treated polyester chips are continuously or intermittently extracted from the lower portion of the treatment layer.

When water treatment is performed on polyester chips 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.

In this case, the whole amount of the polyester chips is charged and filled into the treatment tank, and the treated water is filled with the treated water. The treated water circulates continuously or intermittently as necessary. Discharge treated water and supply new treated water. After the water treatment, the entire amount of the polyester chips is extracted from the treatment layer.

When the treatment is carried out by contacting the polyester chips with steam or a steam-containing gas, 50 to 15
Steam or steam-containing gas or steam-containing air at a temperature of 0 ° C., preferably 50 to 110 ° C., is preferably supplied in an amount of 0.5 g or more as steam per 1 kg of the granular polyester, or is present in the particulate polyester and steam. And contact.

The contact between the polyester chips and water vapor is usually performed for 10 minutes to 2 days, preferably for 20 minutes to
Performed for 10 hours.

The method of industrially carrying out the contact treatment between the granular polyester and steam or a steam-containing gas is exemplified below, but the present invention is not limited thereto. The processing method may be either a continuous method or a batch method.

In the case where the polyester chips are subjected to a contact treatment with steam in a batch system, a silo-type treatment apparatus may be used. That is, a polyester chip is received in a silo, and steam or a steam-containing gas is supplied in a batch system to perform a contact treatment. Alternatively, it is also possible to receive the granular polyester in a rotary cylinder type contact treatment device and perform the contact treatment while rotating the contact polyester, thereby making the contact more efficient.

When the polyester chips are continuously subjected to the contact treatment with steam, the granular polyester is continuously received from above in a tower-type treatment apparatus, and the steam is continuously supplied in cocurrent or countercurrent to carry out the contact treatment with the steam. .

The polyester chips which have been subjected to the contact treatment with water or steam as described above 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, but a continuous drying method is advantageous from the viewpoint of the quality of the polyester. As a method for continuous drying, a tower-type through-air drying apparatus in which undried polyester chips are supplied from the upper portion and a drying gas is passed from the lower portion is usually used.

The moisture content of the undried polyester chips that have been subjected to contact treatment with water or steam and then drained has a water content of about 0.5 to
Very high at 1% by weight. The ventilation type drying apparatus installed in the molding step generally converts a polyester having a moisture content of about 0.1% by weight or less with a gas at 100 to 160 ° C to 0.01% by weight or less, preferably 0.005% by weight in 1 to 3 hours. Designed to dry to less than weight percent. Therefore, it is necessary to dry the water content of the polyester which has been subjected to the contact treatment with water to about 0.1% by weight or less. ,
At 180 ° C., drying for about 5 hours or more is required. However, drying under such conditions may cause a decrease in the intrinsic viscosity of the polyester, and in this case, the transparency of the molded article tends to deteriorate. Further, when air is used as the drying gas, oxidative decomposition of the polyester occurs, and as a result, coloring may occur.

As a result of various investigations to solve such problems, the present invention has been reached. That is, the present invention
An undried polyester whose main repeating unit is ethylene terephthalate and has a density of 1.37 g / cm ³ or more is continuously or intermittently supplied from an upper supply port of a tower-type drying device. In a method for drying polyester under a heated gas flow while continuously or intermittently extracting dried polyester from a lower outlet, a cooling gas supply port of a cooling storage tank for dry polyester directly connected to the drying device. After contact with the dried polyester, the gas discharged from the gas outlet of the cooling storage tank at 90 to 140 ° C., preferably 1 ° C.
It is heated to a temperature of 100 to 135 ° C., more preferably 110 to 130 ° C., and is continuously supplied from a gas supply port provided in an intermediate portion of the drying device, and 100 to 160 ° C., preferably 110 to 150 ° C. More preferably, 120 to 14
This problem is solved by continuously supplying a dehumidified gas at 0 ° C. from a gas supply port provided at a lower portion of the drying device and drying the gas.

When the temperature of the gas discharged from the gas outlet of the cooling storage tank and supplied to the drying device is lower than 90 ° C.,
And when the temperature of the dehumidifying gas is less than 100 ° C., the drying time is prolonged, which is problematic, and the temperature of the gas discharged from the gas outlet of the cooling storage tank and supplied to the drying device exceeds 140 ° C. If the temperature of the dehumidifying gas exceeds 160 ° C., the intrinsic viscosity of the polyester decreases, and the transparency of the molded product deteriorates.

In the present invention, the total residence time of the polyester in the drying apparatus is about 3 to about 5 hours, and the polyester is discharged from the gas discharge port of the cooling storage tank and supplied from the gas supply port supplied to the drying apparatus. The feed port is installed so that the residence time of the polyester present at the top corresponds to about 25 to about 40% of the total residence time.

The temperature at the outlet of the drying device of the polyester dried after the contact treatment with water is almost the same as the drying temperature. If this is stored in air for a long time, it will be oxidized and colored. Therefore, a method is employed in which the dried polyester is brought into contact with a low-temperature gas in a cooling storage tank to cool the mixture to approximately room temperature. As the cooling gas, a dehumidified gas or a non-dehumidified gas can be used.

The gas used to cool the dried polyester is maintained at about 50-70 ° C. at the outlet of the cooling storage tank.
In the present invention, the water-containing gas is used for the initial drying of the polyester which has been subjected to the contact treatment with water, thereby reducing the energy cost. In addition, it is preferable that the cooling storage tank introduces a cooling gas from the lower part, cools the polyester in a counter current, and exhausts the polyester from the upper part.

The dew point of the dehumidified gas used for drying in the present invention is -25 ° C or lower, preferably -28 ° C or lower, more preferably -30 ° C or lower. When the dew point exceeds -25 ° C, the intrinsic viscosity of the dried polyester decreases, which is problematic.

In the present invention, the gas used for drying and cooling is particles having a particle size of 0.3 to 5 μm.
00000 pieces / cubic foot or less, preferably 5000
00 pieces / cubic foot or less, more preferably 1000
It must be less than 00 / cubic foot of gas. As a gas for drying and cooling, a particle size of 0.3 to 5 μm
If a gas containing more than 1,000,000 particles / cubic foot is introduced from the outside of the system and used, the molded product obtained from the dried polyester chips, particularly a large-sized large-sized molded product, has poor transparency.

Hereinafter, a method of controlling the number of particles having a particle size of 0.3 to 5 μm in a gas used for drying and cooling to 1,000,000 particles / cubic foot or less will be described, but the present invention is not limited to this. Absent.

As a method for reducing the number of particles having a particle size of 0.3 to 5 μm to 1,000,000 particles / cubic foot or less in the gas used for drying and cooling, the gas is supplied to the cooling storage tank or the drying device. A cleaning device for removing the particles is installed at at least one place in the steps up to the step.

When the gas is air near the processing equipment, JIS B is applied during the process until the air introduced from the air intake port by the blower comes into contact with the polyester chip.
9908 (1991), a gas cleaning apparatus equipped with a type 1 and / or type 2 filter unit is installed, and the number of particles having a particle size of 0.3 to 5 μm in the air is reduced to 100.
It is preferred to be less than 0000 cubic feet.
Also, JIS B 9908 (19)
It is possible to extend the life of the filter unit by installing a gas purifier equipped with a type 3 filter unit specified in 91) and using it together with the gas purifier equipped with the filter unit. .

JIS B 99 for removing particles in gas
As a material of an ultra-high performance filter (hereinafter abbreviated as a HEPA filter) unit of the type 1 specified in JP 08 (1991), a filter paper made of glass fiber is cited.

Further, JIS B 9908 (1991)
Examples of the material of the high-performance filter unit of the type 2 defined in the above include a filter made of polypropylene fiber and a filter made of a laminate of Teflon (registered trademark) film and PET fiber cloth. Generally, an electrostatic filter made of polypropylene fiber is used.

Further, JIS B 9908 (1991)
Examples of the material of the low-performance filter unit of the type 3 defined by the above include a nonwoven fabric made of PET or polypropylene.

Further, the gas may be any one of gases selected from air, nitrogen and carbon dioxide.

Next, the cooled polyester is filled in a storage or transport container through a sieving step or the like.

The polyester dried by the method of the present invention can be preferably used as a hollow molding, a tray, a packaging material such as a biaxially stretched film, a film for covering a metal can, and the like. Further, the polyester of the present invention can also be used as one constituent layer of a multilayer molded article, a multilayer film, or the like.

[0063]

EXAMPLES The present invention will be described below in more detail 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 of Polyester The density was measured at 30 ° C. with a density gradient tube of a calcium nitrate / water mixed solution.

(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 molded article (wall thickness: 5 mm) of the following (6) and the body (wall thickness: about 0.45 mm) of the hollow molded container, and the haze was changed to Nippon Denshoku ( Measured by a haze meter manufactured by Co., Ltd.

(5) Color b value of polyester (hereinafter referred to as “Co-b”) The color b value was measured as follows using a color difference meter TC1500MC88 manufactured by Tokyo Denshoku. The chips were placed in a glass cell with the glossy side down, and inserted until the eighth minute of the cell. After further shaking the cell lightly and packing it tightly, resin was added until the lid was formed, and the lid was closed. The cell filled with the resin was placed on a sample table and measured. The measurement is about 12 for each measurement of the cell.
The measurement was performed three times at 0 degree, that is, at 120 degrees in three directions, and the average was obtained.

(6) Molding of Stepped Molded Plate The dried polyester was prepared using M-150C (D
M) Molding is performed by an injection molding machine at a cylinder temperature of 290 ° C. using a stepped flat mold cooled to 10 ° C. The resulting stepped plates were 2, 3, 4, 5, 6, 7, 8,
A plate of about 3 cm x about 5 cm square with a thickness of 9, 10 and 11 mm is provided in a stepwise manner, and the weight of one piece is about 146
g. A plate having a thickness of 5 mm is used for measuring haze (% haze).

(7) Measurement of the number of particles in the gas that comes into contact with the chip The gas that is sent by a blower or the like for forcedly sending the gas and that has passed through the gas cleaning device branches off into the main gas stream before coming into contact with the chip. Into a particle meter to measure. The measurement is repeated five times, the average value is calculated, and the number per cubic foot of gas is calculated. As a particle measuring device, a light scattering type particle measuring device manufactured by Rion Co., Ltd., KC-01B, was used.

Example 1 The intrinsic viscosity was 0.725 deciliter / gram, Co-b was 0.8, and the density was 1.
A polyethylene terephthalate (hereinafter abbreviated as PET) chip having 430 g / cm ³ and a cyclic trimer content of 0.30% by weight was charged into a continuous water treatment apparatus, and continuously treated at a treated water temperature of 95 ° C. for 4 hours. Was subjected to water treatment. Using the drying apparatus of FIG. 1, the moisture-containing air discharged from the upper gas discharge port of the cooling storage tank was heated to 125 ° C., and dehumidified air heated to 135 ° C. from another line (dew point −30). C.) to dry the water-treated PET. In addition, a filter unit made of a PET non-woven fabric of JIS B 9908 (1991) type 3 was installed as the air that comes into contact with PET water-treated in the process up to the drying device after the draining process and the two types of drying air. Air filtered with an air purifier and an air purifier equipped with an HEPA filter unit having a particle collection rate of 99% or more of JIS B 9908 (1991) type 1 (particle size: 0.3 to 5 μm)
(The number of particles was about 510 particles / cubic foot).

The intrinsic viscosity after drying was 0.724 deciliter / gram, Co-b was unchanged at 0.8, and the water content was 0.035% by weight. The total residence time in the drying apparatus was 4 hours, and the drying time of PET remaining above the undehumidified air supply port was about 1.5 hours.

The dried PET chips were further vacuum-dried, and evaluated using a molded plate and a biaxially stretched bottle. The haze of the formed plate (5 mm thick) was 2.5%, which was no problem. In addition, a preform of the bottle was molded by an M-150 (DM) injection molding machine manufactured by Meiki Seisakusho. The injection molding temperature was 295 ° C. Next, the plug was crystallized from the preform using a home-made plug crystallization apparatus using a far-infrared heater. 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 using an LB-01E molding machine manufactured by COPOPLAST, and the capacity was 2000 cc.
(With a body thickness of 0.45 mm). The stretching temperature was controlled at 100 ° C. The haze of the obtained polyester container was as good as 0.6%. Note that, in the schematic diagram of the drying apparatus in FIG. 1, a rotary feeder for transporting polyester and the like, which is installed between the devices, is omitted.

Comparative Example 1 The same conditions as in Example 1 were used except that the temperature of the non-dehumidified air was changed to 150 ° C. and the temperature of the dehumidified air was changed to 180 ° C. using the PET and the drying apparatus used in Example 1. Dried. The intrinsic viscosity after drying is 0.70
0 deciliters / gram and Co-b is reduced to 5.
8 was worse. The water content was 0.009% by weight. The dried PET chips are further vacuum dried,
Evaluation was performed using a molded plate and a biaxially stretched molded bottle.
The haze of the molded plate (5 mm thickness) was as poor as 10.5%, and the haze of the obtained polyester container was as high as 4.6%.

[0075]

According to the polyester drying method of the present invention, it is possible to dry the polyester which has been subjected to the contact treatment with water without lowering the intrinsic viscosity of the polyester during drying and without changing the color tone. It is possible to provide a molded article which is excellent in transparency from the polyester and has no unpleasant taste and odor in the contents.

[Brief description of the drawings]

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

[Explanation of symbols]

1 After the water treatment, the supply port of the polyester from the draining device 2 The discharge port of the polyester from the cooling storage tank 3 The supply line of the filtered dehumidified air 4 The supply line of the filtered air 5 The supply line of the moisture-containing air 6 The drying tower 7 Cooling storage tank 8 Filter for water containing air discharged from cooling storage tank 9 Heater

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshitaka Eto 20F term of 248 Takagi, Shiga-cho, Shiga-gun, Shiga Prefecture (reference) 3L113 AA07 AB03 AC01 AC45 AC46 AC52 AC53 AC67 BA19 CA08 CB01 CB40 DA24 4J029 AA03 AB04 AE01 AE03 BA02 BA03 BA10 BB13A BD03A CA04 CA05 CA06 CB05A CB10A CC06A CD03 EB05A KH06 LB05

Claims (5)

[Claims] An undried polyester whose main repeating unit is ethylene terephthalate and has a density of 1.37 g / cm ³ or more is continuously or intermittently supplied from an upper supply port of a tower type drying apparatus. A method for drying polyester under a heated gas flow while continuously or intermittently extracting the dried polyester from a lower outlet of the drying device, wherein the cooling storage tank of the dried polyester directly connected to the drying device. The gas supplied from a cooling gas supply port, and after contact with the dried polyester, is discharged from a gas discharge port of the cooling storage tank to a temperature of 90 to 140 ° C., and is supplied to a gas supply installed in an intermediate portion of the drying device. The dehumidified gas is supplied continuously from a gas outlet and heated to a temperature of 100 to 160 ° C. or lower continuously from a gas supply port provided at a lower portion of the drying device. Drying a polyester, which comprises drying by supplying. 2. The method for drying a polyester according to claim 1, wherein the undried polyester has been subjected to a contact treatment with water. 3. The method according to claim 1, wherein the dehumidifying gas has a dew point of -25 ° C. or lower. 4. The gas used for drying has a particle size of 0.3.
The method for drying polyester according to any one of claims 1 to 3, wherein a gas having a particle size of 1 to 5 µm is used in an amount of 1,000,000 particles / cubic foot or less. 5. The method for drying a polyester according to claim 1, wherein the gas is one selected from the group consisting of air, nitrogen, and carbon dioxide.