JP2012041444A - Method for producing polyester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing polyester that has a low lead element content imposing minimal environmental loads and is excellent in transparency.SOLUTION: In the method for producing polyester, antimony acetate and antimony trioxide used as polycondensation catalysts of the polyester satisfy the following conditions (1) to (3) when the polyester, having not more than 10 ppb lead element in polyethylene terephthalate, are produced by performing polycondensation after performing a transesterification reaction or an esterification reaction of terephthalic acid or an ester-forming derivative thereof and ethylene glycol. (1) The amount of bismuth element relative to the total amount of the antimony acetate and antimony trioxide is 8-105 ppm; (2) the amount of bismuth element in the antimony trioxide is 400 ppm or more; and (3) the total amount of the antimony acetate and antimony trioxide relative to the polyethylene terephthalate is 10-1,000 ppm.

Description

  The present invention relates to a method for producing polyester. Specifically, the present invention relates to a method for producing polyethylene terephthalate, which relates to a method for producing polyethylene terephthalate having a low lead content and excellent transparency.

Polyester, especially polyethylene terephthalate, is widely used for fibers, films and bottles due to its excellent properties.
Industrial production of polyethylene terephthalate includes direct polymerization of terephthalic acid and ethylene glycol, followed by polycondensation, and transesterification of dimethyl terephthalate and ethylene glycol, followed by polycondensation. A transesterification method for carrying out the above is widely adopted.

Conventionally, when producing polyethylene terephthalate, antimony compounds such as antimony trioxide and antimony acetate have been used as polycondensation reaction catalysts.
At this time, it is known that antimony trioxide and antimony acetate can add lead dioxide to improve antimony color tone and transparency (Patent Document 1). However, although this method is an excellent method for improving transparency, it is not preferable in terms of adding lead, which is a heavy metal, to polyethylene terephthalate.
It has been known that the color tone of polyethylene terephthalate is controlled by controlling the bismuth element in antimony trioxide, which is an antimony compound (Patent Documents 2 to 5).

  However, other than Patent Document 1, a method for improving the transparency of polyethylene terephthalate has not been known.

JP-A-49-31793 JP-A-3-215522 Japanese Patent Laid-Open No. 11-60714 JP-A 64-69623 JP-A-1-185355

When lead dioxide is added during the production of polyester as described above, the transparency of polyester can be improved. However, in recent years, the burden on the environment has become a problem, and it is necessary to suppress the content of lead as much as possible. .
An object of the present invention is to provide a method for producing a polyester having a low lead content and excellent transparency in the production of polyester.

The said subject can be achieved by the following manufacturing method of this invention.
(1) When polyester having a lead element in polyethylene terephthalate of 10 ppb or less is produced by subjecting terephthalic acid or its ester-forming derivative and ethylene glycol to transesterification or esterification and then polycondensation, A method for producing polyethylene terephthalate, wherein antimony acetate and antimony trioxide used as a condensation catalyst satisfy the following (1) to (3):
Bismuth element is 8 ppm or more and 105 ppm or less with respect to the total amount of antimony acetate and antimony trioxide (1)
The content of bismuth element in antimony trioxide is 400ppm or more (2)
The total amount of antimony acetate and antimony trioxide is 10 ppm to 1000 ppm with respect to polyethylene terephthalate (3)
(2) The method for producing polyethylene terephthalate according to claim 1, wherein triethyl phosphonoacetate is added before the start of polycondensation.

The method for producing polyethylene terephthalate according to the present invention makes it possible to produce polyethylene terephthalate having excellent transparency and low lead content.

In the polyethylene terephthalate of the present invention, the main carboxylic acid component is a terephthalic acid unit (hereinafter referred to as TPA), and the main glycol unit is an ethylene glycol (hereinafter referred to as EG) unit.
In the production of the polyethylene terephthalate of the present invention, for example, a transesterification method in which dimethyl terephthalate and ethylene glycol are subjected to a transcondensation reaction followed by a polycondensation reaction, or a direct polycondensation reaction in which a terephthalic acid and ethylene glycol are esterified and then subjected to a polycondensation reaction. Any of the legal methods can be employed.

  In addition, in the production of polyethylene terephthalate in the present invention, if it is 20 mol% or less of the carboxylic acid component, it can contain one or more dicarboxylic acid units other than the TPA unit. If it is 20 mol% or less, it can contain 1 type, or 2 or more types of glycol units other than EG unit.

  Examples of dicarboxylic acid units other than TPA units include aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid; dodecanedioic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid. Examples thereof include aliphatic carboxylic acids such as acids; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; and hydroxycarboxylic acid units such as hydroxybenzoic acid, glycolic acid, and hydroxyethoxybenzoic acid.

Examples of the glycol unit other than the EG unit include propylene glycol, butanediol, diethylene glycol, hexamethylene glycol, p-xylene glycol, 1,4-cyclohexadimethanol, and bisphenol.
Furthermore, a polyester obtained by copolymerizing a trifunctional or higher functional compound may be used as long as the thermoplasticity is not impaired.

The polyester production method of the present invention is characterized in that antimony acetate and antimony trioxide containing a specific amount of bismuth element are used in combination as a catalyst.
The antimony acetate and antimony trioxide may be added as EG slurry or EG solution, respectively, or antimony acetate or antimony trioxide may be added in powder form. When added as a powder, antimony acetate and antimony trioxide may be added separately or mixed and added, but when added as a powder, antimony trioxide does not completely dissolve, Therefore, it is desirable that antimony metal is completely dissolved and generation of coarsening due to aggregation of antimony can be prevented, and as a result, transparency is improved.

In addition, when antimony acetate and antimony trioxide are added before the polycondensation reaction in the direct polymerization method and before the ester exchange reaction in the transesterification method, the antimony metal in polyethylene terephthalate does not aggregate and the transparency is improved. This is desirable.
The total addition amount of antimony acetate and antimony trioxide needs to be 10 ppm or more and 1000 ppm or less with respect to the obtained polyethylene terephthalate. When the addition amount is less than 10 ppm, the polycondensation reaction does not proceed, and it becomes difficult to obtain polyethylene terephthalate having a predetermined intrinsic viscosity. Moreover, when the amount exceeding 1000 ppm is added, the heat resistance of polyethylene terephthalate is lowered, the color tone becomes yellowish, and the dissolved antimony element is insolubilized to deteriorate the transparency. The transparency and color tone of the obtained polyethylene terephthalate are preferably 40 to 500 ppm.
In addition, the amount ratio (antimony acetate weight / antimony trioxide weight) is determined so that the content of bismuth element and the content of bismuth element in antimony trioxide satisfies the specified range with respect to the total amount of antimony acetate and antimony trioxide. 6 or more and 99 or less is desirable. When the amount ratio is 6 or more and 99 or less, the transparency of polyethylene terephthalate is improved, which is preferable.

  The feature of the present invention is obtained by using antimony trioxide containing a specific amount of bismuth element and antimony acetate together, and setting the amount of bismuth element to a specific range with respect to the total amount of antimony acetate and antimony trioxide. The purpose is to improve the transparency of polyethylene terephthalate.

  First, the content of the bismuth element in antimony trioxide must be 400 ppm or more with respect to antimony trioxide. When the amount of bismuth element in antimony trioxide is less than 400 ppm, the transparency of polyethylene terephthalate obtained by using antimony acetate and antimony trioxide in combination is not preferred. In particular, the transparency of a polyester having an amount of bismuth element in antimony trioxide of 400 ppm to 1000 ppm is preferable.

  The transparency of the polyethylene terephthalate obtained by the present invention also depends on the amount of bismuth element relative to the total amount of antimony acetate and antimony trioxide added as a polycondensation catalyst. In the present invention, the bismuth element needs to be in the range of 8 ppm to 105 ppm with respect to the total amount of antimony acetate and antimony trioxide to be added. When the bismuth element is less than 8 ppm, not only the transparency of polyethylene terephthalate cannot achieve the target, but also yellowness (hereinafter referred to as b value) increases. On the other hand, if it exceeds 105 ppm, the whiteness (hereinafter referred to as L value) of polyethylene terephthalate decreases, in addition to insufficient transparency of polyethylene terephthalate. However, if it is 8 ppm or more and 20 ppm or less, the transparency of polyethylene terephthalate is good but the b value is high, and if it is 80 ppm or more and 105 ppm or less, the transparency of polyethylene terephthalate is good but the L value is low. In particular, when the amount of bismuth element with respect to the total amount of antimony acetate and antimony trioxide is 40 ppm or more and 60 ppm or less, the transparency of polyethylene terephthalate is improved, and the color tone of b value and L value is also preferable.

  The reason for the above two points is presumed that the light diffusion can be controlled by controlling the particle size of the antimony metal, but in the case of the present application, the bismuth element in the antimony trioxide is added at a high concentration. Therefore, it is presumed that the antimony metal can be made finer, specifically, the particle size of the antimony metal can be reduced to a visible light wavelength or less.

On the other hand, as for antimony acetate, there is no knowledge about the crystal nucleus of antimony in the past, and the interaction between bismuth element and antimony acetate in antimony trioxide of the present invention has not been fully elucidated, but most of them are dissolved. It is assumed that the transparency of polyethylene terephthalate is delicately controlled by controlling the amount of metallic antimony deposited in a minute amount.
By adopting such conditions, it became possible for the first time to reduce the content of lead element to 10 ppm or less with respect to the total amount of antimony acetate and antimony trioxide.

As a method for producing antimony trioxide in the present invention, a conventionally known method for producing antimony trioxide for catalyst or antimony acetate can be applied. For example, there is a method in which antimony trioxide is precipitated by heating and dissolving metal antimony obtained by electrolytic refining antimony ore, then blowing oxygen to perform primary oxidation and sublimation, and further reacting with oxygen. In addition, as a method of adding bismuth element to antimony trioxide, there is a method in which the metal antimony and bismuth metal are heated and dissolved to be sublimated. On the other hand, the antimony acetate in the present invention is obtained by reacting antimony trioxide with acetic anhydride, cooling the obtained reaction mixture, and precipitating antimony acetate.
In the method for producing polyethylene terephthalate of the present invention, conventionally known stabilizers such as phosphorus compounds, lubricants such as silica and titanium dioxide, and the like can be used.

  It is preferable to add triethylphosphonoacetate as the phosphorus compound because the transparency of the resulting polyethylene terephthalate is improved. The reason for this is not clear, but in general, phosphorus compounds deactivate the antimony catalyst. However, triethylphosphonoacetate has a steric hindrance in its molecular structure, so it differs from phosphorus compounds such as phosphoric acid against antimony catalysts. This is presumed to be due to less action. When the amount of phosphorus element is 10 or more and 60 ppm or less, the transparency of polyethylene terephthalate is improved, which is preferable. The phosphorus compound is preferably added before the start of polycondensation. Here, in the transesterification method, after the transesterification reaction and before the start of polycondensation is preferable. However, when added simultaneously with antimony acetate or antimony trioxide, a combined product of antimony and a phosphorus compound may be formed, so it is desirable to avoid simultaneous addition.

A conventionally well-known manufacturing method can be employ | adopted for the manufacturing method of polyester in this invention.
For example, bis-β-hydroxyethyl terephthalate (hereinafter referred to as BHT), which is a reaction product of TPA and EG, is previously stored in a molten state at 255 ° C., and a slurry comprising TPA and EG is provided separately from the reaction vessel. It prepares in a tank, water is distilled off while carrying out fixed quantity supply, maintaining the temperature of a reaction tank, and it is made to esterify. After 4 to 5 hours from the start of the reaction, the esterification is completed, and the reaction product BHT is transferred to a polycondensation reaction tank, and antimony acetate, antimony trioxide and other additives are added. Thereafter, the pressure is reduced until a high vacuum is achieved, and the polycondensation reaction is performed by heating and raising the temperature to about 290 ° C. until the target intrinsic viscosity is reached. After completion of the reaction, the polymer is discharged and cooled in cold water from a polymer discharge nozzle provided at the bottom of the polycondensation reaction tank, and pelletized by a cutter.

The present invention will be described more specifically with reference to the following examples.
In addition, the measuring method of a physical property and the evaluation method of an effect were performed in accordance with the following method.

(1) Method for measuring amounts of bismuth and lead elements in antimony compound The amounts were measured with an ICP emission analyzer (OPTIMA 4300DV, manufactured by Perkin Elmer).

(2) Intrinsic viscosity It measured at 25 degreeC using o-chlorophenol.

(3) Method for measuring the color tone of polyethylene terephthalate The color difference meter (SM color computer (SM-T), manufactured by Suga Test Instruments Co., Ltd.) was used to measure the color tone. The b value (yellowishness) of the obtained color tone is preferably less than 8.0, more preferably less than 6.0.
Further, the L value (whiteness) of the obtained color tone is preferably 45 or more, and more preferably 60 or more.

(4) Transparency measurement method The obtained polyethylene terephthalate is dried at 170 ° C. for 4 hours using a dryer, and then molded using an injection molding machine at a cylinder set temperature of 275 ° C. and a residence time of 60 seconds. A plate was obtained. A portion having a thickness of 4 mm of the obtained plate was measured with a haze meter (NDH-20D, manufactured by Nippon Denshoku Co., Ltd.).
With respect to the obtained transparency, those with less than 1.1% are very good, those with 1.1 or more and less than 1.5% are good, those with 1.5 or more and less than 2.4% are acceptable, and 2. 4% or more was rejected.

(5) Amount of lead element in polyethylene terephthalate The amount of lead element in the obtained polyethylene terephthalate was calculated from the content of lead element in the additive during production. The lead element content passed less than 10 ppb, and rejected 10 ppb or more.

[Example 1]
46.4 parts by weight of bis-β-hydroxyethyl terephthalate (hereinafter referred to as “BHT”), which is a reaction product of terephthalic acid and ethylene glycol, consisting of 41.1 parts by weight of terephthalic acid was previously stored in a molten state at 255 ° C. A slurry consisting of 45.3 parts by weight of acid and 19.5 parts by weight of ethylene glycol was prepared in a separate mixing tank, and water was distilled off while conducting a constant amount supply while maintaining the temperature of the reaction tank to cause esterification. After 4 hours and 40 minutes from the start of the reaction, the esterification was completed, BHT as this reaction product was transferred to a polycondensation reaction tank, and 0.0218 parts by weight of triethylphosphonoacetate was added. Subsequently, 0.06 parts by weight of magnesium acetate, 0.0006 parts by weight of calcium hydroxide, 237 ppm of antimony acetate, and 23 ppm of antimony trioxide containing 500 ppm of bismuth element were added (in this case, the total amount of antimony acetate and antimony trioxide) The amount of bismuth element was 45 ppm and the amount of lead element was 1 ppm or less), and the pressure was reduced until 40 minutes in a high vacuum, and the mixture was heated to 290 ° C. and heated to perform a polycondensation reaction. It was carried out until it reached. After the reaction was completed, the strands were discharged into cold water from the die at the bottom of the polycondensation reaction tank, and formed into a cylindrical pellet by an extrusion cutter. The obtained polyethylene terephthalate was 100 parts by weight, and as shown in Table 2, the polymer characteristics were all good.

[Examples 2 to 15]
The content of bismuth element in the antimony trioxide to be added, the amount of bismuth element with respect to the total amount of antimony acetate and antimony trioxide, and the addition amount of antimony acetate and antimony trioxide are the same as in Example 1, except that Table 1 shows. The method was carried out. As shown in Table 2, the polymer characteristics were all good.

[Example 16]
The same procedure as in Example 1 was performed except that antimony acetate and antimony trioxide were added in a slurry. As shown in Table 2, the polymer characteristics were all good.
[Example 17]
The same procedure as in Example 1 was performed except that a slurry of antimony acetate and antimony trioxide was heated at 150 ° C. and added as a solution. As shown in Table 2, the polymer characteristics were all good.

[Examples 18 to 20]
The same procedure as in Example 1 was carried out except that the amount of triethylphosphonoacetate was changed to Table 1. As shown in Table 2, the polymer characteristics were all good.

[Examples 21 to 28]
The phosphorus compound to be added is phosphoric acid, the bismuth element content in the antimony trioxide to be added, the bismuth element amount with respect to the total amount of antimony acetate and antimony trioxide, and the addition amounts of antimony acetate and antimony trioxide are shown in Table 1. The same method as in Example 1 was carried out except that. As shown in Table 2, the polymer characteristics were all good.

[Example 29]
Total amount of antimony trioxide containing 101 parts by weight of dimethyl terephthalate and 50 parts by weight of ethylene glycol in a transesterification reaction vessel, containing 0.06 parts by weight of magnesium acetate, 0.006 parts by weight of calcium hydroxide, 237 ppm of antimony acetate, and 500 ppm of bismuth element 23 ppm was added. At this time, the amount of bismuth element was 45 ppm and the amount of lead element was 1 ppm or less with respect to the total amount of antimony acetate and antimony trioxide. Thereafter, the temperature was gradually raised from 140 to 235 ° C. over 3.5 hours, and the methanol produced was cooled with a condenser and distilled to complete the transesterification reaction. Then, 0.0218 parts by weight of triethyl phosphonoacetate was added to the reaction product BHT. Subsequently, a polymer having good characteristics shown in Table 2 was obtained by polycondensation reaction in the same manner as in Example 1.

[Comparative Examples 1-8]
The content of bismuth element in the antimony trioxide to be added, the amount of bismuth element with respect to the total amount of antimony acetate and antimony trioxide, and the addition amount of antimony acetate and antimony trioxide are the same as in Example 1, except that Table 3 shows. The polymer properties obtained by the method were poor as shown in Table 4.

[Comparative Examples 9 to 10]
The same procedure as in Example 1 was performed except that the amount of triethylphosphonoacetate was changed to Table 3. The polymer properties obtained were poor as shown in Table 4.

[Comparative Examples 11-14]
It was obtained in the same manner as in Example 1 except that 260 ppm of antimony trioxide or antimony acetate shown in Table 3 was added alone. The polymer was poor as shown in Table 4.

[Comparative Example 15]
An antimony acetate was not added, and 260 ppm of antimony trioxide and 0.000015 parts by weight of lead dioxide shown in Table 3 were added, and the same method as in Example 1 was performed. The obtained polyethylene terephthalate has good transparency as shown in Table 4, but contains 145 ppb of lead element.

[Comparative Example 16]
970 parts by weight of dimethyl terephthalate and 620 parts by weight of ethylene glycol were charged into a reactor, and when the temperature of the reactor reached 155 to 160 ° C. by heating, 0.50 parts by weight of manganese acetate was added in an ethylene glycol solution. After the addition, while removing by-product methanol out of the system, when the internal temperature of the reactor reached 220 ° C., 0.02 part by weight of phosphorous acid and 0.05 part by weight of lead dioxide were added to the ethylene glycol solution. The mixture was heated until the internal temperature reached 240 ° C., and excess ethylene glycol was removed from the system. Next, the obtained reaction product was charged into a polycondensation reaction kettle, 417 ppm of antimony trioxide containing 45 ppm of bismuth element and 0.05 part by weight of lead dioxide were added in an ethylene glycol solution, and the temperature was gradually raised from 240 ° C. The initial 30 minutes is normal pressure, and then the ethylene glycol generated under reduced pressure is removed from the system. Finally, the internal temperature is 280 ° C and the final vacuum is 0.20 mmHg or less. went. The obtained polyethylene terephthalate has excellent transparency as shown in Table 4, but contains 527 ppb of lead element.

[Comparative Example 17]
A transesterification reaction and a polycondensation reaction were performed in the same manner as in Comparative Example 16 except that the amount of lead dioxide added was 0.005 parts by weight. The obtained polyethylene terephthalate has excellent transparency as shown in Table 4, but contains 53 ppb of lead element.

[Comparative Example 18]
Instead of manganese acetate, 0.70 part by weight of calcium acetate was used, 0.08 part by weight of lead dioxide was added, and a transesterification reaction and a polycondensation reaction were performed under the same conditions as in Comparative Example 16. The obtained polyethylene terephthalate has excellent transparency as shown in Table 4, but contains 842 ppb of lead element.

[Comparative Example 19]
Instead of 970 parts by weight of dimethyl terephthalate in Comparative Example 16, 920 parts by weight of dimethyl terephthalate and 50 parts by weight of dimethyl isophthalate were used as acid components, and 0.08 part by weight of lead dioxide was added. A transesterification reaction and a polycondensation reaction were carried out under the same conditions. The obtained polyethylene terephthalate has excellent transparency as shown in Table 4, but contains 842 ppb of lead element.

[Comparative Example 20]
Instead of phosphorous acid of Comparative Example 16, 0.03 part by weight of trimethyl phosphite was used, 0.08 part by weight of lead dioxide was added, and transesterification and polycondensation reactions were performed under the same conditions as in Comparative Example 16. It was. The obtained polyethylene terephthalate has excellent transparency as shown in Table 4, but contains 842 ppb of lead element.

Claims (2)

As a polyester polycondensation catalyst, when terephthalic acid or its ester-forming derivative and ethylene glycol are transesterified or esterified, and then polycondensed to produce a polyester in which the lead element in polyethylene terephthalate is 10 ppb or less, A method for producing polyethylene terephthalate, wherein the antimony acetate and antimony trioxide used satisfy the following (1) to (3):
Bismuth element is 8 ppm or more and 105 ppm or less with respect to the total amount of antimony acetate and antimony trioxide (1)
The content of bismuth element in antimony trioxide is 400ppm or more (2)
The total amount of antimony acetate and antimony trioxide is 10 ppm to 1000 ppm with respect to polyethylene terephthalate (3) 2. The method for producing polyethylene terephthalate according to claim 1, wherein triethyl phosphonoacetate is added before the start of polycondensation.