JP3751166B2 - Polyester pellet manufacturing method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing polyester pellets, and more particularly to a method for producing polyester pellets excellent in molded article gas barrier properties, transparency and heat resistance.
[0002]
TECHNICAL BACKGROUND OF THE INVENTION
Saturated polyesters such as polyethylene terephthalate are widely used as containers such as bottles because they are excellent in gas barrier properties, transparency and mechanical strength.
[0003]
In particular, bottles obtained by biaxial stretch blow molding of polyethylene terephthalate are excellent in transparency, mechanical strength, heat resistance, and gas barrier properties. Containers for filling beverages such as juices, soft drinks, carbonated drinks (PET Widely used as a bottle).
[0004]
Such a bottle is generally formed by injection molding a saturated polyester to form a preform having a cap portion and a body portion, and then inserting the preform into a mold having a predetermined shape, followed by stretch blow molding. The bottle portion is manufactured as a bottle having a mouthpiece portion and a drawn barrel portion.
[0005]
In recent years, bottles manufactured from polyester resin (especially polyethylene terephthalate) tend to be smaller, but in the case of such small bottles, the area that contacts the bottle body per unit volume increases, so gas loss or external The influence on the contents due to permeation of oxygen from the water becomes remarkable, and the storage period of the contents is reduced. For this reason, polyester resins are required to have better gas barrier properties than before.
[0006]
As an attempt to improve the heat resistance and gas barrier properties of such a polyester resin, it has been proposed to blend polyethylene terephthalate with polyethylene isophthalate or the like (see, for example, Japanese Patent Publication No. 1-22302). However, in such a blend of polyethylene terephthalate and polyethylene isophthalate, acetaldehyde is generated at the time of melt kneading at a high temperature to improve the compatibility, and the taste of the contents filled in the container decreases, In addition, there are problems such as a decrease in transparency and, further, burnout due to polyethylene isophthalate adhering to the screw and staying for a long time. In addition, when polyethylene isophthalate is amorphous, it is necessary to dry polyethylene terephthalate and polyethylene isophthalate in a dry state after cooling polyethylene terephthalate with an ordinary dryer, and then drying and molding. There were problems such as the cost of equipment until the machine was turned on and the need for a larger space to install the equipment.
[0007]
For this reason, a polyester composed of ethylene glycol and a dicarboxylic acid component containing terephthalic acid as the main component and isophthalic acid has been proposed. Therefore, it is desired to develop a polyester that is more excellent in heat resistance and gas barrier properties and generates less acetaldehyde.
[0008]
OBJECT OF THE INVENTION
The present invention has been made in view of the prior art as described above, and an object thereof is to provide a method for producing polyester pellets that is excellent in gas barrier properties, transparency, and heat resistance, and generates less acetaldehyde. Yes.
[0009]
SUMMARY OF THE INVENTION
The method for producing polyester pellets according to the present invention is as follows.
[A] polyethylene terephthalate before solid phase polymerization having an intrinsic viscosity of 0.3 to 0.8 dl / g; 99 to 20% by weight;
[B] a dicarboxylic acid structural unit derived from a dicarboxylic acid containing terephthalic acid and isophthalic acid, and a diol structural unit derived from a diol containing ethylene glycol and 1,3-bis (2-hydroxyethoxy) benzene A polyethylene isophthalate copolymer before solid phase polymerization having an intrinsic viscosity of 0.3 to 0.9 dl / g; after blending with 1 to 80% by weight, and then solidifying the pelletized polyester,
The melting point (Tm1) measured by a differential scanning calorimeter of the blend before solid phase polymerization and the melting point (Tm2) of the blend after solid phase polymerization are represented by the following formula [I].
Tm1-Tm2 <5 ℃… [I]
It is.
The solid phase polymerization temperature of the blend is preferably 190 ° C. or lower.
The acetaldehyde content of the blend is preferably 8 ppm or less.
[0010]
In the method for producing polyester pellets according to the present invention,
Polyethylene isophthalate copolymer [B]
(i) The structural unit derived from isophthalic acid is 50 to 98 mol%, the structural unit derived from terephthalic acid is 2 to 50 mol% with respect to all dicarboxylic acid structural units,
(ii) 15 to 99 mol% of structural units derived from ethylene glycol and 1 to 85 structural units derived from 1,3-bis (2-hydroxyethoxy) benzene, based on all diol structural units. Preferably, it is mol%.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the polyester pellet and the method for producing the same according to the present invention will be specifically described.
[0012]
[Production method of polyester pellets]
The method for producing polyester pellets according to the present invention is as follows.
[A] polyethylene terephthalate after solid phase polymerization having an intrinsic viscosity of 0.5 to 1.5 dl / g; 99 to 20% by weight;
[B] polyethylene isophthalate copolymer before solid phase polymerization having an intrinsic viscosity of 0.3 to 0.9 dl / g; 1 to 80% by weight,
After blending, the pelletized polyester is solid phase polymerized.
[0013]
[A] Polyethylene terephthalate The polyethylene terephthalate [A] used in the present invention comprises a dicarboxylic acid unit derived from terephthalic acid or an ester derivative thereof and a diol unit derived from ethylene glycol or an ester derivative thereof.
[0014]
The dicarboxylic acid unit of the polyethylene terephthalate [A] desirably contains terephthalic acid units in an amount of 80 mol% or more, preferably 85 to 100 mol%, when the unit is 100 mol%.
[0015]
As other dicarboxylic acids that may be contained in an amount of 20 mol% or less, specifically, isophthalic acid, phthalic acid (orthophthalic acid), 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, Aromatic dicarboxylic acids such as 2,5-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid,
Examples thereof include aliphatic carboxylic acids such as succinic acid, glutaric acid, adipic acid, sebacic acid, azelaic acid and n-dicarboxylic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid.
[0016]
The diol unit of polyethylene terephthalate [A] desirably contains an ethylene glycol unit in an amount of 80 mol% or more, preferably 85 to 100 mol%, when the unit is 100 mol%.
[0017]
Specific examples of other diols that may be contained in an amount of 20 mol% or less include diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylene glycol, propylene glycol, butanediol, pentanediol, neopentyl glycol, Aliphatic glycols such as hexamethylene glycol and dodecamethylene glycol, alicyclic glycols such as cyclohexanedimethanol, 1,2-bis (2-hydroxyethoxy) benzene, 1,4- (2-hydroxyethoxy) benzene, etc. Glycols containing an aromatic group of
Examples thereof include aromatic diols such as bisphenols, hydroquinone, and 2,2-bis (4-β-hydroxyethoxyphenyl) propane. Of these, diethylene glycol and cyclohexanedimethanol are particularly preferable.
[0018]
Furthermore, the polyethylene terephthalate [A] used in the present invention is derived from polyfunctional carboxylic acids having 3 or more carboxyl groups or polyhydric alcohols having 3 or more hydroxy groups, as long as the object of the present invention is not impaired. May contain units such as trimesic acid, pyromellitic anhydride and other polyfunctional carboxylic acids, glycerin, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, 1,1 , Units derived from polyhydric alcohols such as 1-trimethylolmethane and pentaerythritol may be contained.
[0019]
The polyethylene terephthalate [A] used in the present invention is substantially linear, which is confirmed by the dissolution of polyethylene terephthalate [A] in o-chlorophenol.
[0020]
The polyethylene terephthalate [A] used in the present invention has an intrinsic viscosity [η] measured in o-chlorophenol at 25 ° C. of 0.3 to 0.9 dl / g, preferably 0.5 to 0.85 dl / g. Desirably, it may be either before solid phase polymerization or after solid phase polymerization.
[0021]
Such polyethylene terephthalate can be produced by a conventionally known method. For example, after directly diesterifying the dicarboxylic acid and diol, a germanium compound such as germanium dioxide, antimony trioxide, antimony acetate, etc. Or polycondensation in the presence of a polycondensation catalyst such as titanium compounds such as antimony compounds and titanium tetraalkoxides, or dicarboxylic acid esters and diols with titanium alkoxides such as titanium isopropoxide and titanium tetrabutoxide. Transesterification is carried out in the presence of a transesterification catalyst such as cobalt acetate, zinc acetate, manganese acetate, and metal acetates such as calcium acetate. As the transesterification catalyst, titanium tetrabutoxide or zinc acetate is desirable. Then, it undergoes melt polycondensation in the presence of a polycondensation catalyst such as a germanium compound such as germanium dioxide, an antimony compound such as antimony trioxide or antimony acetate, or a titanium compound such as titanium tetraalkoxide, followed by solid phase polymerization. Can be manufactured. The solid state polymerization is performed by heating the melt polycondensate at a temperature of usually 180 to 230 ° C, preferably 190 to 220 ° C. In the solid phase polymerization, it is desirable that the melt polycondensate is dried. For this reason, the melt polycondensate may be previously dried at 80 to 180 ° C.
[0022]
Polyethylene isophthalate copolymer [B]
The polyethylene isophthalate copolymer [B] used in the present invention comprises a dicarboxylic acid structural unit derived from a dicarboxylic acid containing terephthalic acid and isophthalic acid, ethylene glycol and 1,3-bis (2-hydroxyethoxy) It consists of a diol structural unit derived from a diol containing benzene.
[0023]
The dicarboxylic acid structural unit is based on all dicarboxylic acid structural units.
The structural unit derived from isophthalic acid is in the range of 50 to 98 mol%, preferably 60 to 95 mol%,
It is preferable that the structural unit derived from terephthalic acid is contained in the range of 2 to 50 mol%, preferably 5 to 40 mol%.
[0024]
Further, such a polyethylene isophthalate copolymer [B] contains dicarboxylic acid structural units other than isophthalic acid and terephthalic acid in an amount of less than 15 mol%, as long as the object of the present invention is not impaired. May be.
[0025]
Specific examples of other dicarboxylic acids that may be contained in an amount of less than 15 mol% include phthalic acid (orthophthalic acid), 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 2, Aromatic dicarboxylic acids such as 5-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid, aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid, cyclohexane And alicyclic dicarboxylic acids such as dicarboxylic acids.
[0026]
These dicarboxylic acids may be ester derivatives thereof or a combination of two or more.
Also, the diol structural unit is based on all diol structural units.
The structural unit derived from ethylene glycol is in the range of 15 to 99 mol%, preferably 15 to 90 mol%, more preferably 20 to 88 mol%,
1 to 85 mol%, preferably 10 to 85 mol%, more preferably 12 to 80 mol% of a structural unit derived from 1,3-bis (2-hydroxyethoxy) benzene Is preferred.
[0027]
Furthermore, the polyethylene isophthalate copolymer [B] used in the present invention is a diol other than ethylene glycol and 1,3-bis (2-hydroxyethoxy) benzene as long as the object of the present invention is not impaired. The structural unit may be contained in an amount of less than 15 mol%.
[0028]
Specific examples of other diols that may be contained in an amount of less than 15 mol% include diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylene glycol, propylene glycol, butanediol, pentanediol, and neopentyl glycol. , Aliphatic glycols such as hexamethylene glycol and dodecamethylene glycol, alicyclic glycols such as cyclohexanedimethanol, 1,2-bis (2-hydroxyethoxy) benzene, 1,4- (2-hydroxyethoxy) benzene Examples thereof include aromatic diols such as glycols containing an aromatic group such as bisphenols, hydroquinone and 2,2-bis (4-β-hydroxyethoxyphenyl) propane.
[0029]
These diols may be ester derivatives thereof or a combination of two or more.
Of these, diethylene glycol is preferred as the other diols.
[0030]
Further, the polyethylene isophthalate copolymer [B] used in the present invention is a polyfunctional group having three or more carboxyl groups as shown in the polyethylene terephthalate [A] as long as the object of the present invention is not impaired. A unit derived from a carboxylic acid or a polyhydric alcohol having 3 or more hydroxy groups may be contained, specifically, a unit derived from a polyfunctional carboxylic acid and / or a polyhydric alcohol. The unit may be independently contained in an amount of 0.05 to 0.4 mol%, preferably 0.1 to 0.35 mol%, more preferably 0.2 to 0.35 mol%, based on 100 mol% of the dicarboxylic acid unit.
[0031]
The intrinsic viscosity [η] measured in o-chlorophenol at 25 ° C. of the polyethylene isophthalate copolymer [B] used in the present invention is 0.3 to 0.9 dl / g, preferably 0.35 to 0.85 dl / g. It is desirable that it is after completion of liquid phase polymerization and before solid phase polymerization.
[0032]
The glass transition temperature of the polyethylene isophthalate copolymer measured by a differential scanning calorimeter (DSC, heating rate 10 ° C./min) is usually 40 to 120 ° C., preferably 50 to 100 ° C. .
[0033]
The polyethylene isophthalate copolymer [B] used in the present invention may be pre-crystallized as necessary, like the polyethylene terephthalate [A].
Such a polyethylene isophthalate copolymer can be produced by a conventionally known method. For example, after directly diesterifying the dicarboxylic acid and the diol, a germanium compound such as germanium dioxide, antimony trioxide, Melt polycondensation in the presence of a polycondensation catalyst such as an antimony compound such as antimony acetate and a titanium compound such as titanium tetraalkoxide, or an ester of a dicarboxylic acid and a diol can be used such as titanium isopropoxide or titanium tetrabutoxide. The transesterification reaction is performed in the presence of a transesterification catalyst such as titanium alkoxide, cobalt acetate, zinc acetate, manganese acetate, calcium acetate, and other metal acetates. As the transesterification catalyst, titanium tetrabutoxide or zinc acetate is desirable. Then, it can be manufactured by melt polycondensation in the presence of a polycondensation catalyst such as germanium compounds such as germanium dioxide, antimony compounds such as antimony trioxide and antimony acetate, and titanium compounds such as titanium tetraalkoxide. it can.
[0034]
Blend of polyester In the production method according to the present invention, the above polyethylene terephthalate [A]; 99 to 20 wt%, preferably 99 to 40 wt%, more preferably 98 to 50 wt%,
The polyethylene isophthalate copolymer [B] is blended in an amount of 1 to 80% by weight, preferably 1 to 60% by weight, more preferably 2 to 50% by weight.
[0035]
Blending is performed by blending polyethylene terephthalate [A] and polyethylene isophthalate copolymer [B] so as to have the above composition, and then melt-kneading at 260 to 310 ° C. for 30 to 300 seconds. The blended material after kneading is pelletized by an extruder or the like. The average particle size of the pellets is preferably 2.0 to 5.0 mm.
[0036]
When blending the polyethylene terephthalate [A] and the polyethylene isophthalate copolymer [B] as described above, if necessary, an ester exchange catalyst, a lubricant, etc. may be added as in the production method (1). Good.
[0037]
The intrinsic viscosity of the obtained blend measured in o-chlorophenol at 25 ° C. is 0.3 to 0.9 dl / g, preferably 0.35 to 0.85 dl / g.
The temperature rise crystallization temperature (Tcc) of the obtained blend is 170 ° C. or lower, preferably 160 ° C. or lower, more preferably 100 to 155 ° C.
[0038]
Crystallization of the blend The pellets of the blend thus obtained are then crystallized.
Crystallization is to maintain the blend in a dry state at a temperature between the glass transition temperature (Tg) and the melting point, preferably 20 ° C. above Tg and below 190 ° C. for 1 to 300 minutes, preferably 5 to 200 minutes. Is done by. Specifically, it is carried out by heating to 80 to 190 ° C, preferably 100 to 170 ° C. Such crystallization can be performed in air or in an inert atmosphere.
[0039]
It is desirable that the crystallized polyester blend has a crystallinity of 20 to 50%.
In such crystallization, the so-called polyester solid-phase polymerization reaction does not proceed, and the intrinsic viscosity of the polyester after crystallization is almost the same as the intrinsic viscosity of the polyester before crystallization. The difference between the intrinsic viscosity of the polyester and the intrinsic viscosity of the polyester before crystallization is usually 0.06 dl / g or less.
[0040]
Solid phase polymerization of blend In the present invention, the polyester blend is crystallized and then subjected to solid phase polymerization. The solid phase polymerization is usually carried out at 140 to 190 ° C, preferably 150 to 190 ° C. In the solid phase polymerization, the pellets of the blended product are desirably dried. For this reason, the pellets of the blended product may be dried at 80 to 170 ° C. in advance.
[0041]
In the present invention, the melting point (Tm1) measured by a differential scanning calorimeter of the polyester blend before solid phase polymerization and the melting point (Tm2) of the blend after solid phase polymerization are expressed by the following formula [I].
Tm1-Tm2 <5 ℃… [I]
It is preferable that
When Tm1-Tm2 is 5 ° C. or higher, it indicates that transesterification of polyethylene terephthalate [A] and polyethylene isophthalate copolymer [B] proceeds during solid phase polymerization. Tm1-Tm2 <5 ° C. is preferable because the gas barrier property does not deteriorate.
[0042]
The polyester pellet thus obtained preferably has an acetaldehyde content of 8 ppm or less, and more preferably 6 ppm or less.
[0043]
The polyester pellets thus obtained may be subjected to hot water treatment in the same manner as in the production method (1). The hot water treatment is performed by immersing the obtained solid-phase polymer in hot water at 70 to 120 ° C. for 1 to 360 minutes.
[0044]
The polyester pellets obtained by the production method according to the present invention are additives, which are usually added to polyester as necessary, for example, colorants, antioxidants, oxygen absorbers, ultraviolet absorbers, antistatic agents, flame retardants. May be contained.
[0045]
The polyester pellets obtained by the production method according to the present invention can be used as materials for various molded products such as preforms, bottles, (stretched) films, sheets and the like.
[0046]
Bottles made from such polyester pellets are excellent in gas barrier properties, transparency and heat resistance. Moreover, since there is little generation | occurrence | production of acetaldehyde, the taste of contents, such as juice, does not fall.
[0047]
【The invention's effect】
When using the polyester pellets of the present invention, not only can the raw material drying supply line up to injection molding machine and extruder introduction be greatly simplified, the cost related to equipment can be greatly reduced, It is possible to greatly reduce the burnt burn that occurs in the molded product. Moreover, the obtained molded product is excellent not only in gas barrier properties, transparency and heat resistance, but also has a low amount of acetaldehyde, is excellent in bottle strength, and does not easily cause delamination even when a knife is put in the bottle.
[0048]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these Examples.
[0049]
In the examples, each characteristic was measured as follows.
Intrinsic viscosity
Prepare a 1 g / dl sample solution using o-chlorophenol solvent, measure the solution viscosity using an Ubbelohde capillary viscometer at 25 ° C, and then gradually add o-chlorophenol to the low concentration side. The solution viscosity was measured and extrapolated to 0% concentration from these data.
[0050]
Carbon dioxide permeability coefficient ( gas barrier property )
Measurement was performed using a gas permeability measuring device GPM-250 manufactured by GL Science Co., Ltd. under conditions of 23 ° C. and relative humidity 60%.
[0051]
The film used for the measurement was produced as follows.
Stretched film: A 0.3 mm-thick film was produced using a press molding machine having a mold temperature of 290 ° C., and this film was rapidly cooled at a cooling mold temperature of 0 ° C. to obtain an amorphous film. Next, this amorphous film was subjected to simultaneous biaxial stretching 3 × 3 times at a temperature 15 ° C. higher than the glass transition temperature (Tg) to obtain a stretched film.
[0052]
Acetaldehyde content rate About 2 g of a test piece is collected from a sample molding, and freeze-pulverized by a freeze pulverizer manufactured by SPEX. 1 g of the obtained sample powder is put in a vial, 2 ml of distilled water is added, and water and the sample powder are mixed well. After capping, the vial is heated at 120 ° C for 1 hour. After heating, the mixture was cooled in ice water, and 5 μl of the supernatant was measured with a gas chromatograph (GC-6A, manufactured by Shimadzu Corporation).
[0053]
Melting point Measured using a differential calorimeter (DSC) manufactured by PerkinElmer.
10 mg of the sample was weighed in a sample pan, held at 30 ° C. for 10 minutes in a nitrogen stream, and then the peak temperature of the melting point that appeared when the temperature was raised to 290 ° C. at a rate of 10 ° C./min was measured.
[0054]
[Example 1]
Polyethylene terephthalate (A-1)
A slurry consisting of 332 g of high-purity terephthalic acid and 143 g of ethylene glycol was prepared, and 0.042 g of germanium dioxide and 0.080 g of phosphoric acid were added thereto. This slurry was heated to a temperature of 255 ° C. under pressure (absolute pressure 1.7 kg / cm ² ), and an esterification reaction was carried out until the esterification rate reached 95% to produce a low polymer. Subsequently, the low polymer was melt polymerized at a temperature of 280 ° C. under a reduced pressure of 1 torr to produce a polyethylene terephthalate (A-1) prepolymer having an intrinsic viscosity of 0.660 dl / g. It was extruded into a strand shape and cut into cylindrical pellets having a diameter of 2.5 mm and a height of 3.5 mm.
[0055]
Polyethylene isophthalate copolymer (B-1)
A slurry composed of 299 g of isophthalic acid, 33 g of terephthalic acid, 122 g of ethylene glycol and 21 g of 1,3-bis (2-hydroxyethoxy) benzene was prepared, and 0.042 g of germanium dioxide and 0.080 g of phosphoric acid were added thereto. The slurry was heated under pressure (absolute pressure 1.7 kg / cm ² ) to a temperature of 255 ° C. and subjected to esterification until the esterification rate reached 95% to produce a low polymer. Subsequently, the low polymer was melt polymerized at a temperature of 280 ° C. under a reduced pressure of 1 torr, and a prepolymer (isophthalic acid: isophthalic acid: B) having an intrinsic viscosity of 0.856 dl / g. Terephthalic acid (molar ratio) = 90:10, ethylene glycol: 1,3-bis (2-hydroxyethoxy) benzene (molar ratio) = 85:15), and this was extruded into a strand from a nozzle and cut. A cylindrical pellet having a diameter of 2.5 mm and a height of 3.5 mm was obtained.
[0056]
Blend Next, 90 parts by weight of the above polyethylene terephthalate (A-1) is dry blended so that the polyethylene isophthalate copolymer (B-1) is 10 parts by weight, manufactured by Thermo Corporation. The mixture was melt-kneaded at a molding temperature of 275 ° C. using a 20 mmφ single-screw extrusion molding apparatus, extruded from a nozzle in a strand shape, and cut into a cylindrical pellet (C-1) having a diameter of 2.5 mm and a height of 3.5 mm. This prepolymer had a melting point of 255 ° C. and an acetaldehyde content of 25 ppm.
[0057]
Solid phase polymerization Next, the pellet (C-1) obtained above was pre-crystallized at 150 ° C for 2 hours in a nitrogen stream, and then solid phase polymerization was performed at 180 ° C for 70 hours in a nitrogen atmosphere. went.
[0058]
The intrinsic viscosity of the polyester thus obtained is 0.710 dl / g, the melting point is 252 ° C., the content of acetaldehyde is 3.0 ppm, and the difference in melting point before and after solid phase polymerization (Tm1-Tm2 =) there were.
The stretched film obtained from this polyester had a carbon dioxide gas permeability coefficient of 10.5 cc · mm / m ² · day · atm, and an acetaldehyde content of 11 ppm.
[0059]
[Example 2]
Polyethylene terephthalate (A-2)
Polyethylene terephthalate (A-1) produced as in Example 1 was pre-crystallized at 170 ° C. for 2 hours in a nitrogen stream, and then subjected to solid state polymerization at 210 ° C. for 6 hours in a nitrogen atmosphere. The intrinsic viscosity of the polyethylene terephthalate (A-2) thus obtained was 0.801 dl / g.
[0060]
Blend Next, 90 parts by weight of the above polyethylene terephthalate (A-2) was dry blended so that the polyethylene isophthalate copolymer (B-1) was 10 parts by weight, manufactured by Thermo Corporation. The mixture was melt-kneaded at a molding temperature of 275 ° C. using a 20 mmφ single-screw extrusion molding apparatus, extruded into a strand form from a nozzle and cut to form cylindrical pellets (C-2) having a diameter of 2.5 mm and a height of 3.5 mm. The melting point of this prepolymer was 254 ° C., and the content of acetaldehyde was 19 ppm.
[0061]
Solid-phase polymerization Next, the pellet (C-2) obtained above was pre-crystallized at 150 ° C for 2 hours under a nitrogen stream, followed by solid-phase polymerization at 180 ° C for 40 hours under a nitrogen atmosphere. went.
[0062]
The polyester thus obtained has an intrinsic viscosity of 0.807 dl / g, a melting point of 252 ° C., and an acetaldehyde content of 2.9 ppm. there were.
The stretched film obtained from this polyester had a carbon dioxide gas permeability coefficient of 10.9 cc · mm / m ² · day · atm, and an acetaldehyde content of 12 ppm.
[0063]
[Example 3]
Blend: 60 parts by weight of the polyethylene terephthalate (A-2) produced in Example 2 was dry blended so that the polyethylene isophthalate copolymer (B-1) was 40 parts by weight. , Melt-kneaded at a molding temperature of 275 ° C using a Thermo 20mmφ single-screw extrusion molding device, extruded into strands from a nozzle and cut, and cylindrical pellets (C-3) with a diameter of 2.5mm and a height of 3.5mm did.
[0064]
The melting point of this prepolymer was 235 ° C., and the content of acetaldehyde was 19 ppm.
[0065]
Solid phase polymerization Next, the pellet (C-3) obtained above was pre-crystallized at 140 ° C for 2 hours in a nitrogen stream, and then solid phase polymerization was performed at 170 ° C for 40 hours in a nitrogen atmosphere. went.
[0066]
The intrinsic viscosity of the polyester thus obtained is 0.811 dl / g, the melting point is 232 ° C., the content of acetaldehyde is 2.9 ppm, and the difference in melting point before and after solid phase polymerization (Tm1-Tm2 =) is 3 ° C. there were.
The stretched film obtained from the polyester had a carbon dioxide gas permeability coefficient of 6.3 cc · mm / m ² · day · atm, and an acetaldehyde content of 13 ppm.
[0067]
[Comparative Example 1]
The blend (C-1) obtained in Example 1 was precrystallized in a nitrogen stream at 170 ° C. for 2 hours, and then subjected to solid state polymerization at 210 ° C. for 5 hours in a nitrogen atmosphere.
The intrinsic viscosity of the polyester thus obtained is 0.721 dl / g, the melting point is 246 ° C., the content of acetaldehyde is 3.2 ppm, and the difference in melting point before and after solid phase polymerization (Tm1-Tm2 =) is 6 ° C. there were.
The stretched film obtained from this polyester had a carbon dioxide gas permeability coefficient of 12.2 cc · mm / m ² · day · atm and was inferior in gas barrier properties. The acetaldehyde content was 13 ppm.
[0068]
[Comparative Example 2]
The blend (C-2) obtained in Example 2 was molded as it was (the acetaldehyde content was 19 ppm). The stretched film had a good carbon dioxide permeability coefficient of 9.5, but the acetaldehyde content was as high as 28 ppm.

Claims (3)

[A] polyethylene terephthalate having an intrinsic viscosity of 0.3 to 0.8 dl / g; 99 to 20 % by weight, [B] a dicarboxylic acid structural unit derived from a dicarboxylic acid containing terephthalic acid and isophthalic acid, and ethylene glycol Polyethylene isophthalate copolymer consisting of diol structural units derived from a diol containing 1,3-bis (2-hydroxyethoxy) benzene and having an intrinsic viscosity of 0.3 to 0.9 dl / g; 1 to 80 % by weight When the pelletized polyester is subjected to solid phase polymerization, the melting point (Tm1) measured by a differential scanning calorimeter of the blend before solid phase polymerization and the melting point (Tm2) of the blend after solid phase polymerization are expressed by the following formula [ I]
Tm1-Tm2 <5 ℃ ・ ・ ・ [I]
The manufacturing method of the polyester pellet characterized by these . 2. The method for producing polyester pellets according to claim 1, wherein the solid phase polymerization temperature is 190 ° C. or lower . 3. The method for producing polyester pellets according to claim 1, wherein the content of acetaldehyde is 8 ppm or less .