JP4828163B2 - Method for producing polyethylene terephthalate - Google Patents

Description

  The present invention relates to a polyethylene terephthalate produced by producing a low-order condensate from terephthalic acid or an ester-forming derivative thereof and ethylene glycol or an ester-forming derivative thereof and then polycondensing in the presence of a polycondensation catalyst. More particularly, the present invention relates to polyethylene terephthalate that enables bottle molding with good transparency after molding.

  Polyethylene terephthalate is excellent in mechanical strength, heat resistance, transparency and gas barrier properties, and is suitable for use as materials for films, sheets, fibers, as well as materials for beverage filling containers such as juices, soft drinks, and carbonated beverages. Has been.

  Such polyethylene terephthalate is usually produced using a dicarboxylic acid such as terephthalic acid and an aliphatic diol such as ethylene glycol as raw materials. Specifically, first, a low-order condensate (ester low polymer) is formed by an esterification reaction of an aromatic dicarboxylic acid and an aliphatic diol, and then this low-order condensate is formed in the presence of a polycondensation catalyst. It is deglycolized (liquid phase polycondensation) to increase the molecular weight. In some cases, solid state polycondensation is performed to further increase the molecular weight.

In such a method for producing polyethylene terephthalate, an antimony compound, a germanium compound, a titanium compound, or the like has been conventionally used as a polycondensation catalyst.
However, polyethylene terephthalate produced using an antimony compound as a catalyst is inferior to polyethylene terephthalate produced using a germanium compound or a titanium compound as a catalyst in terms of transparency.

  The antimony compound reacts with the phosphorus compound to produce a precipitate that hinders transparency. In order to suppress this, Patent Document 1 proposes a method in which an antimony compound and a phosphorus compound are prevented from contacting each other as much as possible, or a phosphorus compound is diluted with EG.

  Patent Documents 2 and 3 propose a method of heating polyester in an inert gas atmosphere or under reduced pressure in a temperature range from 180 ° C. to the melting point, and also describes that an inert gas contains a glycol component. ing. However, in this technique, the change in the intrinsic viscosity before and after heating is suppressed within ± 0.05 (dl / g) in order to suppress fluctuations in the crystallization rate, and the molecular weight is low (that is, the intrinsic viscosity is low). It cannot be applied to a process in which a polymer is polymerized by solid phase polymerization.

Patent Document 4 proposes a method in which polyester is heated in a temperature range from 180 ° C. to the melting point under an inert gas flow containing a glycol component of 500 ppm or more. However, this technique is aimed at improving the hue (b value), and the pressurization operation is essential, so the equipment burden was heavy. Further, the method of Patent Document 4 cannot be applied to a process of increasing the molecular weight by solid phase polymerization because the viscosity is decreased by heat treatment or the increase in viscosity is small.
US Pat. No. 5,962,625 Japanese Patent Laid-Open No. 2003-160657 JP 2002-173528 JP Japanese Patent No. 3470304

  An object of the present invention is to provide a method for producing a polyethylene terephthalate resin, which is a polyethylene terephthalate containing Sb and is characterized by high transparency after molding. Furthermore, it is an object to provide a polyethylene terephthalate resin that achieves both high productivity during polymerization and high transparency after molding.

As a result of earnest research on the production method of polyethylene terephthalate in view of the above-described conventional technology, the present inventors have found that polyethylene terephthalate produced using an antimony compound as a polycondensation catalyst or additive is contained in an atmosphere containing ethylene glycol. The present invention was completed by finding a method for solid phase polymerization.
That is, the gist of the present invention is as follows.
[1] Polyethylene characterized in that polyethylene terephthalate containing Sb atoms in the range of 100 to 300 ppm is solid-phase polymerized in a gas containing ethylene glycol to increase the intrinsic viscosity by 0.10 [dl / g] or more. A method for producing terephthalate.

Furthermore, it is preferable that the molar ratio of gas to ethylene glycol is in a specific range because the balance between the polymerization activity and the transparency of polyethylene terephthalate becomes good. In addition, the atmospheric gas is preferably an inert gas, and among them, nitrogen is more preferable in terms of cost and handling.
[2] The gas containing ethylene glycol contains ethylene glycol in a molar ratio of 0.2 × 10 ^{−3 to} 2.5 × 10 ⁻³ mol / mol. A method for producing polyethylene terephthalate.
[3] The method for producing polyethylene terephthalate according to [1], wherein the gas containing ethylene glycol is nitrogen.
Is a preferred embodiment of the present invention.

The molar ratio is represented by ethylene glycol / gas molecules. The molecular weight is ethylene glycol = 62, nitrogen = 28, and the ratio is (62/28) = about 2.2. Therefore, when ethylene glycol / nitrogen is used, 0.2 × 10 ^{−3 to} 2.5 × 10 ⁻³ mol / mol is 0.4 × 10 ^{−3 to} 5.5 × 10 ⁻³ wt / wt by weight ratio.

[4] The method according to [1], wherein the solid-state polymerization temperature is in the range of 190 to 240 ° C., and polyethylene terephthalate produced by the same method.
Thus, polyethylene terephthalate having excellent transparency can be obtained with high productivity.
It is preferable that the temperature of the solid phase polymerization is in the range of 190 to 240 ° C., since the balance between the polymerization activity and the transparency of the obtained polyethylene terephthalate becomes good.
Hereinafter, ethylene glycol may be abbreviated as EG.

  The polyethylene terephthalate obtained by the method of the present invention can be bottle-molded with high productivity and good transparency.

(Method for producing polyethylene terephthalate)
The method for producing polyethylene terephthalate according to the present invention comprises polycondensation of terephthalic acid or an ester-forming derivative thereof with ethylene glycol or an ester-forming derivative thereof in the presence of a catalyst for producing polyethylene terephthalate containing the antimony catalyst. Polyethylene terephthalate is produced. Hereinafter, an example will be described.

(Raw material)
The method for producing polyethylene terephthalate according to the present invention uses terephthalic acid or an ester-forming derivative thereof and ethylene glycol or an ester-forming derivative thereof as raw materials.
In the present invention, together with terephthalic acid, aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid and diphenoxyethanedicarboxylic acid; aliphatics such as adipic acid, sebacic acid, azelaic acid and decanedicarboxylic acid Dicarboxylic acid; alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid can be used as a raw material. The amount used is preferably 10 mol% or less based on terephthalic acid.

In addition to ethylene glycol, aliphatic diols such as ethylene glycol, trimethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, and dodecamethylene glycol; alicyclic glycols such as cyclohexanedimethanol; bisphenol, hydroquinone Aromatic diols such as 2,2-bis (4-β-hydroxyethoxyphenyl) propanes can be used as raw materials.
Furthermore, in this invention, polyfunctional compounds, such as a trimesic acid, a trimethylol ethane, a trimethylol propane, a trimethylol methane, a pentaerythritol, can be used as a raw material.

(Esterification process)
First, when producing polyethylene terephthalate, terephthalic acid or an ester-forming derivative thereof is esterified with ethylene glycol or an ester-forming derivative thereof.
Specifically, a slurry containing terephthalic acid or an ester-forming derivative thereof and ethylene glycol or an ester-forming derivative thereof is prepared.

  In such a slurry, 1.005 to 1.4 mol, preferably 1.01 to 1.3 mol of ethylene glycol or an ester-forming derivative thereof is usually used with respect to 1 mol of terephthalic acid or an ester-forming derivative thereof. included. This slurry is continuously supplied to the esterification reaction step.

  The esterification reaction is preferably carried out under conditions where ethylene glycol is refluxed using an apparatus in which two or more esterification reaction groups are connected in series, while removing water produced by the reaction from the system using a rectification column.

  The esterification reaction step is usually carried out in multiple stages, and the first stage esterification reaction usually has a reaction temperature of 240 to 270 ° C, preferably 245 to 265 ° C, and a pressure of 0.02 to 0.3 MPaG ( 0.2 to 3 kg / cm @ 2 G), preferably 0.05 to 0.2 MPaG (0.5 to 2 kg / cm @ 2 G), and the esterification reaction in the final stage is usually performed at the reaction temperature. Is 250 to 280 ° C., preferably 255 to 275 ° C., and the pressure is 0 to 0.15 MPaG (0 to 1.5 kg / cm 2 G), preferably 0 to 0.13 MPaG (0 to 1.3 kg / cm 2 G). Performed under the conditions of

When the esterification reaction is carried out in two stages, the esterification reaction conditions of the first stage and the second stage are within the above ranges, respectively, and when carried out in three stages or more, the second stage The esterification reaction conditions up to one stage before the final stage may be any conditions between the reaction conditions of the first stage and the final stage.
For example, when the esterification reaction is carried out in three stages, the reaction temperature of the second stage esterification reaction is usually 245 to 275 ° C., preferably 250 to 270 ° C., and the pressure is usually 0 to 0.00. It may be 2 MPaG (0 to 2 kg / cm @ 2 G), preferably 0.02 to 0.15 MPaG (0.2 to 1.5 kg / cm @ 2 G).

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

  By this esterification step, a low-order condensate (ester low polymer) that is an esterification reaction product of terephthalic acid and ethylene glycol is obtained, and the number-average molecular weight of this low-order condensate is about 500 to 5,000.

  The low-order condensate obtained in the esterification step as described above is then supplied to the polycondensation (liquid phase polycondensation) step.

(Liquid phase polycondensation process)
In the liquid phase polycondensation step, the low-order condensate obtained in the esterification step is heated under reduced pressure to a temperature not lower than the melting point of polyethylene terephthalate (usually 250 to 280 ° C.) in the presence of the above-described catalyst. To polycondense.
This polycondensation reaction is desirably performed while distilling off unreacted ethylene glycol to the outside of the reaction system.

  The polycondensation reaction may be performed in one stage or may be performed in a plurality of stages. For example, when the polycondensation reaction is performed in a plurality of stages, the first stage polycondensation reaction has a reaction temperature of 250 to 290 ° C., preferably 260 to 280 ° C., and a pressure of 0.07 to 0.003 MPa ( 500 to 20 Torr), preferably 0.03 to 0.004 MPa (200 to 30 Torr). The final stage polycondensation reaction is performed at a reaction temperature of 265 to 300 ° C, preferably 270 to 295 ° C, pressure Is carried out under conditions of 1 to 0.01 kPaG (10 to 0.1 Torr), preferably 0.7 to 0.07 kPa (5 to 0.5 Torr).

  When the polycondensation reaction is carried out in three or more stages, the polycondensation reaction between the second stage and the first stage before the last stage is performed between the reaction conditions of the first stage and the reaction conditions of the last stage. It is done in the condition between. For example, when the polycondensation step is performed in three stages, the second stage polycondensation reaction is usually performed at a reaction temperature of 260 to 295 ° C, preferably 270 to 285 ° C, and a pressure of 7 to 0.3 kPa ( 50 to 2 Torr), preferably 5 to 0.7 kPa (40 to 5 Torr).

  As the antimony catalyst, polycondensation can be performed using at least one antimony catalyst such as antimony trioxide, antimony acetate, antimony glycolate and the like. It is desirable to use this in an amount of 0.023 to 0.050 mol% in terms of Sb metal atom, based on the aromatic dicarboxylic acid unit in the low-order condensate. The amount of Sb atoms contained in the obtained polyethylene terephthalate is in the range of 100 to 300 ppm. If the Sb atomic weight is less than 100 ppm, sufficient polymerization activity may not be obtained, and if it exceeds 300 ppm, sufficient transparency may not be obtained.

Phosphorus compounds may be used as the stabilizer, and specifically, phosphate esters such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, triphenyl phosphate;
Phosphites such as triphenyl phosphite, trisdodecyl phosphite, trisnonylphenyl phosphite;
Phosphate esters such as methyl acid phosphate, ethyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, dibutyl phosphate, monobutyl phosphate, dioctyl phosphate;
And phosphorus compounds such as phosphoric acid and polyphosphoric acid.

  The addition amount of such a phosphorus compound is 0.003 to 0.030 mol%, preferably 0.006 to 0.015 mol%, in terms of phosphorus atom in the phosphorus compound, with respect to the aromatic dicarboxylic acid. The amount is desirable.

  You may add a cobalt compound, dye, and a pigment as needed. This only needs to be present during the polycondensation reaction. For this reason, the addition may be performed in any step such as a raw material slurry preparation step, an esterification step, a liquid phase polycondensation step and the like.

  The intrinsic viscosity [IV] of the polyethylene terephthalate obtained in the above liquid phase polycondensation step is 0.40 to 1.0 dl / g, preferably 0.50 to 0.90 dl / g. In addition, although the intrinsic viscosity achieved in each stage excluding the final stage of the liquid phase polycondensation process is not particularly limited, it is preferable that the degree of increase in the intrinsic viscosity in each stage is smoothly distributed.

Further, the terminal COOH concentration at this time is 20 to 70 eq / ton, preferably 30 to 60 eq / ton.
The amount of DEG (diethylene glycol) is 0.8 to 2.5 wt%, preferably 1.0 to 2.0 wt%.

The polyethylene terephthalate obtained in this polycondensation step is usually melt extruded and formed into granules (chips).
(Solid phase polycondensation process)
The method of the present invention is carried out by solid-phase polymerization of granular polyethylene terephthalate obtained at the time when such a liquid weight process is completed in an EG / nitrogen mixed gas.

  The granular polyethylene terephthalate supplied to the solid phase polycondensation step may be preliminarily crystallized by heating to a temperature lower than the temperature for solid phase polycondensation before being supplied to the solid phase polycondensation step. Good.

  Such a precrystallization step can be performed by heating granular polyethylene terephthalate in a dry state to a temperature of usually 120 to 200 ° C., preferably 130 to 180 ° C. for 1 minute to 4 hours. Such precrystallization can also be performed by heating granular polyethylene terephthalate at a temperature of 120 to 200 ° C. for 1 minute or more in a steam atmosphere, a steam-containing inert gas atmosphere, or a steam-containing air atmosphere. .

The precrystallized polyethylene terephthalate desirably has a crystallinity of 20 to 50%.
By this precrystallization treatment, the so-called polyethylene terephthalate solid-phase polycondensation reaction does not proceed, and the intrinsic viscosity of the precrystallized polyethylene terephthalate is almost the same as the intrinsic viscosity of polyethylene terephthalate after liquid-phase polycondensation. The difference between the intrinsic viscosity of pre-crystallized polyethylene terephthalate and the intrinsic viscosity of polyethylene terephthalate before pre-crystallization is usually 0.06 dl / g or less.

  The solid phase polycondensation step comprises at least one stage, the temperature is 190 to 240 ° C., preferably 200 to 235 ° C., and the pressure is 0.2 to 0.001 MPa (1 kg / cm 2 G to 10 Torr), preferably normal The pressure is 0.01 MPa (100 Torr) under the pressure, and the reaction is performed in a mixed gas atmosphere of EG and gas, preferably EG and nitrogen. A temperature of 200 to 235 ° C. is preferable because the vapor pressure of EG becomes appropriate as the scope of the present invention.

The atmospheric gas for solid phase polycondensation preferably contains ethylene glycol in a molar ratio of EG / gas molecule = 0.2 × 10 ^{−3 to} 2.5 × 10 ⁻³ mol / mol. When nitrogen is used as the atmospheric gas, EG / nitrogen is 0.4 × 10 ^{−3 to} 5.5 × 10 ⁻³ wt / wt by weight.
The EG may be supplied in nitrogen before being supplied to the solid weight process or directly to the solid weight process. Further, the EG / nitrogen weight ratio may be adjusted by adjusting the flow rate of nitrogen supplied to the solid phase polycondensation to adjust the weight ratio of EG and nitrogen produced in the solid tower. In the case of continuous solid phase polymerization, the average value of the EG / nitrogen weight ratio in the solid phase polymerization reactor may be within the above range.

  The intrinsic viscosity [IV] of the polyethylene terephthalate obtained by the solid phase polycondensation step as described above is 0.6 to 1.2 dl / g, preferably 0.7 to 1.0 dl / g. The intrinsic viscosity increase amount of polyethylene terephthalate in the solid phase polycondensation step is usually 0.1 dl / g or more, preferably 0.2 to 0.5 dl / g.

The production process of polyethylene terephthalate including the esterification process and the polycondensation process as described above can be performed in any of batch, semi-continuous and continuous processes.
The polyethylene terephthalate produced in this way may be added with conventionally known additives, for example, colorants such as stabilizers, mold release agents, antistatic agents, dispersants, dyes and pigments, etc. These additives may be added at any stage during the production of polyethylene terephthalate, or may be added by a master batch before molding.

  The polyethylene terephthalate obtained by the present invention can be used as a raw material for various molded products. For example, it is melt-molded and used for hollow molded products such as bottles, sheets, films, fibers, etc. Is preferred.

As a method for molding a bottle, a sheet, a film, a fiber or the like from the polyethylene terephthalate obtained by the present invention, a conventionally known method can be employed.
For example, when molding a bottle,
A method of producing a hollow molded body by extruding the polyethylene terephthalate from a die in a molten state to form a tubular parison, then blowing the air after holding the parison in a mold having a desired shape, and mounting the mold on the mold,
A preform is manufactured from the above polyethylene terephthalate by injection molding, the preform is heated to an appropriate stretching temperature, and then the preform is held in a mold having a desired shape, and then blown in air to be fitted into the mold. There is a method for producing a molded body.

(Example)
EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these Examples. Each analysis and molding method is shown below.
(Measurement of IV)
A sample of 0.09 to 0.095 g is adjusted to a concentration of 0.5 g / dl in a mixed solvent of phenol / 1,1,2,2-tetrachloroethane = 1/1 weight ratio. A sample was put into this solution and dissolved at 135 ° C. for 40 minutes, then cooled and calculated from the solution viscosity ηsp measured at 25 ° C.
(Analysis of Sb, P, Co)
The intensity | strength of the fluorescent X-ray peculiar to the element of the press sheet | seat melt-molded using the Philips (PHILIPS) company's fluorescent X-ray analyzer (PW-2400) was measured, and the density | concentration was calculated | required.

(Formation of stepped square plate)
Using a vacuum dryer, polyethylene terephthalate pellets were dried at 140 ° C. for 16 hours or more at 1 mmHg. This was molded at 275 ° C. with an injection molding machine (Miki Seisakusho M-70B) to obtain a stepped square plate. The stepped square plate-like molded body has a shape as shown in FIG. 1, and the thickness of A part is about 6 mm, the thickness of B part is about 4 mm, and the thickness of C part is about 2 mm. The thickness of the D portion is about 7 mm, the thickness of the E portion is about 5 mm, and the thickness of the F portion is 3 mm.
(Measurement of haze)
The thickness 5mm and 6mm part of said stepped square plate was measured using the haze meter HGM-2DP of a Suga test device.
(Quantification of terminal COOH group)
The sample was dissolved by heating with o-cresol, chloroform was added, and titration was performed with a 1/50 N NaOH standard solution using a potentiometric titrator to quantify the terminal COOH group (eq / ton).

(Production example)
Polyethylene terephthalate having a ratio of terephthalic acid to isophthalic acid of 98/2 mol%, IV of 0.59 dl / g, Sb of 230 ppm, P of 12 ppm, Co of 8 ppm, and terminal COOH group of 50 eq / ton at 170 ° C. in nitrogen Crystallized for 2 h under air flow.
Thereafter, solid phase polymerization was performed for 9 to 12 hours in a mixed gas of EG and nitrogen heated to 215 ° C. At this time, the flow rate of nitrogen was set to 315 mm / sec with respect to the stationary pellet.

  Table 1 shows the haze results of polyethylene terephthalate obtained by adjusting the EG / nitrogen weight ratio of the production example to 0.0011.

  Table 1 shows the haze results of polyethylene terephthalate obtained by adjusting the EG / nitrogen weight ratio of the production example to 0.0023.

  Table 1 shows the haze results of polyethylene terephthalate obtained by adjusting the EG / nitrogen weight ratio of the production example to 0.0036.

Table 1 shows the haze results of polyethylene terephthalate obtained by adjusting the EG / nitrogen weight ratio of the production example to 0.0050.
(Comparative Example 1)

Table 1 shows the haze results of polyethylene terephthalate obtained by adjusting the EG / nitrogen weight ratio of the production example to 0.
(Comparative Example 2)

Table 1 shows the haze results of polyethylene terephthalate obtained by adjusting the EG / nitrogen weight ratio of the production example to 0.0002.
(Comparative Example 3)

  Although the solid phase polymerization was carried out by adjusting the EG / nitrogen weight ratio of the production example to 0.0072, the solid phase polymerization rate was greatly reduced, the IV after the solid phase polymerization was low, and good haze was not obtained.

It is a perspective view of the stepped square plate-shaped molded object used for the measurement of haze.

Claims (3)

Solid phase polymerization of polyethylene terephthalate containing Sb atoms in a range of 100 to 300 ppm in a gas containing ethylene glycol in a molar ratio of 0.2 × 10 ^{−3 to} 2.5 × 10 ⁻³ mol / mol. And a method for producing polyethylene terephthalate, wherein the intrinsic viscosity is increased by 0.10 [dl / g] or more.   The method for producing polyethylene terephthalate according to claim 1, wherein the gas containing ethylene glycol is nitrogen. The method for producing polyethylene terephthalate according to claim 1 or 2, wherein the temperature of the solid phase polymerization is in a range of 190 to 240 ° C.

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