JP3536609B2 - Polyester production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyester for producing a polyester having a stable color tone (b value) with little coloring.

[0002]

2. Description of the Related Art Polyethylene terephthalate (hereinafter P)
Polyesters represented by ET) and copolymers thereof have excellent properties and are widely used as fibers for clothing, fibers for industrial materials, films, bottles, and other plastic products. As an industrial production method of polyester, a direct polymerization method in which terephthalic acid (hereinafter, referred to as TPA) and ethylene glycol (hereinafter, referred to as EG) are directly esterified and then subjected to polycondensation is widely used. In the direct polymerization method, in order to obtain good quality in fibers, films, and other plastic products, it is important to reduce coloring of the product polymer, control the color tone in a stable state, and reduce variation.

As a means for reducing the coloring of the polymer and controlling the color tone, there is known a method of increasing the purity of TPA to prevent the polyester from being colored due to contamination with impurities. It is necessary to repeat the process many times, which is disadvantageous industrially and economically. Therefore, conventionally, industrially, a method of reducing the coloring and stabilizing the color tone by optimizing the polyester production conditions by adjusting the reaction temperature or changing the amount of the metal compound added as a catalyst, etc. Has been adopted. However, the method of adjusting the reaction temperature has a problem that the reaction rate fluctuates due to the temperature change and the degree of polymerization becomes unstable, so that it becomes difficult to control the polymerization. Further, in the method in which the amount of the metal compound is changed, when the amount of the metal compound is increased, foreign matter is generated in the polymer due to precipitation of the metal.

In order to solve such a problem, Japanese Patent Laid-Open No.
A proposal such as that of Japanese Patent Application Laid-Open No. 173268/1993 has been made. However, the adjustment of the esterification ratio also causes a change in the rate of the polycondensation reaction, and there is a problem that the polymerization control becomes difficult.

On the other hand, a method for stabilizing the color tone by reducing the coloring of the polymer by limiting the raw materials used within a range not disadvantageous industrially and economically is disclosed in Japanese Patent Laid-Open Publication No. Hei.
No. 56529. This is because 4-carboxybenzaldehyde (hereinafter referred to as 4-CBA), which is a by-product during the synthesis of TPA, is known as an impurity in TPA which is considered to affect the polymer color tone.
That is, the CBA amount is set to a certain amount or less. However, the control of the amount of 4-CBA in TPA alone could not sufficiently stabilize the polymer color tone.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of fluctuations in the degree of polymerization due to fluctuations in the reaction rate and the generation of foreign substances due to the precipitation of metals in the production of polyesters.
An object of the present invention is to provide a method for producing a polyester which produces a polymer having a stable color tone with less coloring.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the relationship between the polymer, the color tone, and the amount of lead element (hereinafter referred to as Pb) in antimony trioxide is reduced. There is a certain relationship, and it has been found that the use of an antimony trioxide polymerization catalyst containing a small amount of Pb can suppress the coloring of the polymer and control the color tone.

The present invention has been made based on this finding. The object of the present invention is to produce a polyester comprising terephthalic acid and / or an ester derivative of terephthalic acid and ethylene glycol with a purity of 99. A method for producing a polyester, characterized in that antimony trioxide containing 0% or more and containing 30 ppm or less of lead element and 60 ppm or less of bismuth element (hereinafter referred to as Bi) as impurities is used as a polymerization catalyst. Can be achieved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In general, antimony trioxide used as a polymerization catalyst for polyester contains metal elements such as arsenic, Pb, iron and Bi as impurities. The present inventors have found that, among various metal elements contained as impurities, Pb has a strong correlation with the polymer color tone. Although the effect of Pb in antimony trioxide used as a polymerization catalyst on the color tone of the polyester, particularly on the b value, varies depending on the type of polyester, it is usually 10 pp.
The range is from -0.1 to -0.5 per m. Further, the b value of the polyester varies depending on the type of the polyester,
It is about -10 to 10. Then, the polymer color tone (b
The amount of Pb in antimony trioxide is set to 30 ppm or more in order to suppress coloring within a range in which the influence of Pb on the value of Pb does not become excessive. When the content is 40 ppm or more, a polymer with further suppressed coloring can be obtained, which is preferable. However, the amount of Pb in antimony trioxide was reduced to 60 ppm.
Doing more will reduce the catalytic activity due to impurities,
The color tone varies, which is not preferable. That is, the range of the Pb content is preferably 30 ppm or more and 60 ppm or less industrially.

On the other hand, the fluctuation range of the polymer color tone (b value) required for industrially used polyesters such as fibers, films, bottles, and other molding materials varies depending on the application and the type of polyester. 0.5 to ± 2.5. Therefore, in order to stabilize the color tone (b value) of the polymer, the fluctuation range of the amount of Pb in antimony trioxide should be 3
It is preferable that the concentration be 0 (± 15) ppm or less. Further P
If the fluctuation range of the amount b is 20 (± 10) ppm or less,
It is suitable for use in fibers, transparent films, bottles, and the like that require a small change in product color tone.

From the above points, antimony trioxide used in the present invention is antimony trioxide having a Pb content of 30 ppm to 60 ppm.

For better coloring and stabilizing the color tone of the polymer, better results can be obtained by controlling the amount of Bi contained in antimony trioxide in combination. B
If the i content is more than 5 ppm, the bluishness of the polymer will increase significantly, causing a decrease in the b value. Therefore, in order to obtain stable quality without fluctuation of polymer color tone, 5p
pm or less, and more preferably 3 ppm or less.

If the purity of antimony trioxide is lower than 99.0%, the catalytic activity is lowered, and the polymerization reaction is undesirably delayed. Further, as a result of a longer polymerization reaction time, the polymer color tone is deteriorated. Further, the color tone of the polymer deteriorates due to the influence of impurities, which is not preferable.

In the present invention, P in antimony trioxide
The amounts of b and Bi are measured by a fluorescent X-ray method, an atomic absorption method, an ICP emission spectroscopic method, or the like.

In the process for producing the polyester of the present invention, terephthalic acid is used as a direct starting material, and TPA and EG, which are widely used as an industrial production process, are directly esterified and then subjected to polycondensation. It is legal. In addition, any method of batch polymerization or continuous polymerization may be used.

The polyester of the present invention is not particularly limited, but the main component of the dicarboxylic acid unit is a TPA unit, the main component of the glycol unit is an ethylene glycol (hereinafter referred to as EG) unit, and the TPA unit is a dicarboxylic acid unit of 4%.
It is suitable when the EG unit occupies 5 to 100 mol% and the EG unit occupies 45 to 100 mol% of the glycol unit. The polyester in the present invention has 45 mol% of the total structural units.
To the extent of the following, it may contain one or more dicarboxylic acid units other than terephthalic acid units, and may also contain one or more glycol units other than EG units. As dicarboxylic acid units other than TPA, for example, aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid; dodecandioic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid, Aliphatic carboxylic acids such as cyclohexanedicarboxylic acid; and hydroxycarboxylic acids such as hydroxybenzoic acid, glycolic acid and hydroxyethoxybenzoic acid. Also,
As glycol units other than EG units, propylene glycol, butanediol, diethylene glycol, hexamethylene glycol, p-xylene glycol,
Examples thereof include 1,4-cyclohexadimethanol and bisphenol. Further, a polyester obtained by copolymerizing a trifunctional or higher polyfunctional compound may be used as long as the thermoplasticity is not impaired.

In the production of the polyester of the present invention, conventionally known conditions can be used for the esterification reaction and the polycondensation reaction. For example, a known stabilizer such as a phosphorus compound and a lubricant such as silica and titanium dioxide can be used.

[0019]

The present invention will be described in more detail with reference to the following examples.

Examples 1 to 3 and Comparative Examples 1 to 3 PET was polymerized using the continuous polymerization equipment shown in the flow sheet of FIG.

The pure EG content in the mixture of the distillate EG generated from the process, the raw material EG supplied through the control valve 17 and the EG additionally added to the circulation EG storage tank 14 is always 13.8.
The mixture was controlled to be 3 parts by weight / hour and supplied to the slurry mixer 1 together with 31.1 parts by weight / hour of TPA to form a slurry, and then supplied to the esterification reactor 3 via the pump 2. Then, an esterification reaction and a polymerization reaction were performed under the conditions shown in Table 1. In addition, antimony trioxide of the quality shown in Table 2 0.01 parts by weight / hour and phosphoric acid 0.005 parts by weight / hour,
0.15 parts by weight / hour of titanium dioxide was continuously supplied to the esterification reactor 4. Table 2 shows the obtained PET qualities.

[0022]

[Table 1]

[Table 2] [Examples 4, 5, Comparative Example 4] TPA1730 parts by weight and EG77 having the quality shown in Table 3
An esterification reaction and then a polymerization reaction were carried out using 5 parts by weight.

First, the total amount of TPA and EG was charged into a reaction vessel equipped with a rectification column, and the esterification reaction was started at 200 ° C. under a pressure of 150 kPa. Thereafter, the temperature was gradually increased, and the reaction pressure was changed to normal pressure during the reaction. Further, with the progress of the reaction, generated water was distilled off via a rectification column. After 3 hours and 56 minutes from the start of the esterification reaction (temperature at this time: 250 ° C.), the esterification reaction was terminated. At this time, the reaction rate was 98.3%.

The reaction product bis (ω-hydroxyethyl) terephthalate and its low polymer (BHE)
T) (temperature: 240 ° C.) was transferred to a polymerization reactor, and 0.7 parts by weight of antimony trioxide, 1.4 parts by weight of calcium acetate,
0.3 parts by weight of phosphoric acid was dissolved and added to 10 parts by weight of EG. After that, the pressure was reduced from normal pressure to high vacuum over 30 minutes,
At the same time, the mixture was heated to 290 ° C. and heated to carry out a polycondensation reaction. 3 hours and 12 minutes after the start of the reaction, the melt viscosity 2
A polycondensation reaction was performed up to 000 ps, and the reaction was terminated.

The obtained polymer was discharged from a die having 58 circular small holes having a diameter of 9 mm at the bottom of a polymerization reactor pressurized to 200 kPa, and was taken off by a nip roller while being rapidly cooled in a cold water shower and a water bath. The strand was taken out at a rate of 75 m / sec, and the discharged strand was cut into chips. Table 3 shows the obtained PET qualities.

[0026]

[Table 3]

[0027]

EFFECTS OF THE INVENTION By adopting the polyester production method of the present invention, a stable color tone (b value) with little coloring can be obtained without excessive purification of TPA, and without changing the reaction temperature or the amount of metal compound added. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an apparatus for producing polyester used in Example 1.

[Explanation of symbols]

1: Slurry mixer 2: Slurry supply pump 3-4: Esterification reactor 5: Rectification tower 6: Distilled EG storage tank 7-9: polycondensation reaction device 10-12: Wet condenser 13-14: Circulating EG storage tank 15: Distillation EG extraction pump 16: Distillation EG supply pump 17: Control valve 18: Automatic densitometer 19: Distillation EG filter 20: Distillation EG separation processor

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08G 63/00-63/91

Claims (1)

(57) [Claims] 1. A method for producing a polyester by subjecting mainly a terephthalic acid and ethylene glycol to an esterification reaction followed by polycondensation, wherein the purity is 99.0% or more and the lead element contained as an impurity is 30 ppm or more. A method for producing a polyester, comprising using, as a polymerization catalyst, antimony trioxide containing 60 ppm or less and bismuth element of 5 ppm or less.