JPS6245250B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing polyester chips with low acetaldehyde content,
More specifically, the purpose is to effectively eliminate acetaldehyde when solid-phase polymerizing polyester chips obtained by melt polycondensation whose main repeating unit is ethylene terephthalate at high temperatures under reduced pressure. . Polyethylene terephthalate, or polyester based on polyethylene terephthalate, has an extremely wide range of uses as molded products such as fibers, films, sheets, and bottles.In recent years, polyester bottles have attracted particular attention as containers for foods, cosmetics, etc. This is what has been done. However, polyester chips manufactured by ordinary melt polycondensation contain acetaldehyde as a by-product, and when used for food packaging containers, especially when the content is 10 ppm or more, the taste of the contents may be affected. There was a problem that it had a negative effect on the fragrance. The inventors of the present invention have conducted extensive research to produce polyester chips containing a small amount of acetaldehyde, and as a result, they have effectively achieved this objective by the method described below. That is, in the present invention, polyester chips having an intrinsic viscosity of 0.3 or more obtained by a melt polycondensation reaction in which the main repeating unit is ethylene terephthalate are subjected to solid phase polymerization in a temperature range of 210°C to 250°C under reduced pressure to obtain polyester chips with an intrinsic viscosity of 0.6 or more. When making polyester chips, after the reaction is completed, the chips are cooled while maintaining reduced pressure, and the reduced pressure is broken after the internal temperature has fallen to 200°C or less. Polyester chips with an acetaldehyde content of 10 ppm or less are This is the manufacturing method. In the present invention, polyester refers to polyethylene terephthalate and polyesters mainly composed of polyethylene terephthalate, including phthalic acid, isophthalic acid, hexahydrophthalic acid, naphthalene dicarboxylic acid, adipic acid, sebacic acid, etc. in an amount of 10 mol% or less of the total acid components. Polyhydric carboxylic acids such as dicarboxylic acids, trimellitic acid and pyromellitic acid, or oxyacids such as P-oxybenzoic acid can be used as the acid component;
Dialcohols such as 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, cyclohexanedimethanol in amounts up to 10 mol%. It is possible to use polyhydric alcohols such as , trimethylolpropane, triethylolpropane, and pentaerythritol as the alcohol component. The polyester chips (referred to as prepolymers) to be subjected to solid phase polymerization in the present invention can be produced by conventional methods. That is, in the case of polyethylene terephthalate, bis-β-hydroxyethyl terephthalate and/or its low polymer is obtained by an esterification reaction between terephthalic acid and ethylene glycol or ethylene oxide or a transesterification reaction between dimethyl terephthalate and ethylene glycol. is melt-polycondensed under reduced pressure in the presence of a polycondensation catalyst to obtain a prepolymer, which is then formed into dice-shaped or cylindrical chips. The prepolymer thus obtained contains a large amount of acetaldehyde, which was produced as a by-product during the polycondensation reaction, but this acetaldehyde has a boiling point of 21
It is generally known that it is a low-volatile substance with a low temperature of ℃ and is desorbed from polymers by heat treatment under reduced pressure, but the rate of desorption is faster at higher temperatures and does not pose a problem as a raw material for food packaging containers. In order to produce polyester chips with a low acetaldehyde content, a high temperature of 210° C. or higher is required in practice, accompanied by a solid phase polymerization reaction. For this purpose, the intrinsic viscosity of the prepolymer used in the present invention is determined by carrying out a solid phase polymerization reaction for the time necessary to reduce acetaldehyde to the desired content.
Intrinsic viscosity that provides the necessary physical properties during molding processing
Prepolymers with an intrinsic viscosity of less than 0.3 are very brittle and difficult to form into chips;
Furthermore, it is difficult to use in practice because powder is easily generated during solid phase polymerization. In this way, the acetaldehyde content in the prepolymer can be reduced by performing solid phase polymerization at a high temperature of 210°C or higher under reduced pressure.
Even if the treatment is carried out for a sufficient time for acetaldehyde to be eliminated, it is difficult to suppress the acetaldehyde content in the final polyester chips to 10 ppm or less. The inventors of the present invention have made extensive efforts to investigate the cause of this problem, and have concluded that this is caused by the formation of acetaldehyde in the polyester at high temperatures of 200° C. or higher. That is, at high temperatures, the rate of desorption of acetaldehyde increases, but on the other hand, acetaldehyde is produced as a by-product.
For this reason, when the vacuum is immediately broken at the end of the solid-phase polymerization reaction according to the conventional method, acetaldehyde is no longer eliminated and only by-products are preferentially produced. To increase. The by-product of acetaldehyde increases as the temperature rises, but it is almost negligible below 200°C. Based on the results of this research, the present invention is designed to reduce the pressure break when the internal temperature is 200°C.
By carrying out the process when the temperature drops below ℃, we were able to effectively suppress the acetaldehyde content to 10 ppm or less. If necessary, solid phase polymerization is carried out under reduced pressure at 210°C to 250°C by a conventional method after preliminary drying at a low temperature of 150°C or lower. Further, as the gas used for the vacuum break, it is preferable to use an inert gas in order to prevent oxidative deterioration of the polymer. Next, the present invention will be specifically explained by showing examples and reference examples. Examples 1 to 3 A slurry consisting of 100 parts of terephthalic acid and 45 parts of ethylene glycol was supplied to a continuous reaction tank, and an esterification reaction was carried out at 250°C under normal pressure to produce bis-β-hydroxy with an esterification reaction rate of 95%. Ethyl terephthalate and its low polymer were prepared, and then 0.016 part of germanium dioxide was added as a catalyst per 124 parts of bis-β-hydroxyethyl terephthalate and its low polymer, and the mixture was heated under a reduced pressure of 0.5 mmHg at 280 °C.
A polycondensation reaction was carried out at °C to prepare a prepolymer with an intrinsic viscosity of 0.52 and an acetaldehyde content of 130 ppm, which was delivered as a strand from a nozzle and cut into chips. The obtained chips were pre-dried under vacuum at 130° C. for 3 hours, and then a solid phase polymerization reaction was carried out using a vacuum tumbler type high temperature dryer with an internal capacity of 1 m ² under the conditions shown in the following table.

[Table] The dryer uses a heat medium heating method. After a predetermined solid phase polymerization reaction time has passed, the heat medium is cooled through a heat exchanger while maintaining reduced pressure to lower the chip temperature and reduce the internal temperature. When the temperature reached 200°C, nitrogen gas was introduced and a vacuum break was performed. However, the intrinsic viscosity in Table 1 is the value measured at 20°C in a mixed solvent of equal weight of phenol/tetrachloroethane, and the acetaldehyde content is measured using 2.5 g of polyester chips that have been crushed to the extent that they can pass through a 5-mesh sieve. It was weighed and sealed in a glass tube with 10 ml of distilled water, extracted at 160°C for 2 hours, cooled to below 5°C, 1 ml of the sample solution was taken, and quantified using gas chromatography equipped with a PEG-20M column. . Comparative Examples 1 and 2 In the same manner as Examples 1 to 3, however, immediately after the predetermined solid phase polymerization reaction time had elapsed, nitrogen gas was introduced, a vacuum break was performed, and cooling was performed. The results are shown in Table-2.

[Table] As is clear from the comparison between Examples and Comparative Examples,
The method of the present invention is an extremely effective method for producing polyester chips suitable for food packaging containers with a low acetaldehyde content.

Claims (1)

[Claims] 1 Intrinsic viscosity obtained by melt polycondensation reaction in which the main repeating unit is ethylene terephthalate
Polyester chips with a viscosity of 0.3 or higher are subjected to solid phase polymerization under reduced pressure at a temperature range of 210℃ to 250℃ to determine the intrinsic viscosity.
When making polyester chips of 0.6 or higher, after the reaction is complete, cool while maintaining reduced pressure until the internal temperature reaches 200℃.
A method for manufacturing a polyester chip, characterized in that a vacuum break occurs after the temperature drops below ℃.