JPS6360058B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing polyester chips with a low acetaldehyde content, and more specifically, the present invention relates to a method for producing polyester chips having a low acetaldehyde content. The purpose is to effectively eliminate acetaldehyde in a method of solid phase polymerization at high temperatures. Polyethylene terephthalate, or polyester based on polyethylene terephthalate, has an extremely wide range of uses as molded products such as fibers, films, sheets, and bolts, and polyester bottles have recently attracted particular attention as containers for foods, cosmetics, etc. This is what has been done. However, polyester chips manufactured by ordinary melt polycondensation reactions contain acetaldehyde as a by-product, and when used for food packaging containers, the content is particularly low at 10 ppm.
In the above cases, there was a problem that the taste and aroma of the contents were adversely affected. The present inventors have arrived at the present invention as a result of intensive research aimed at producing polyester chips with a low acetaldehyde content. That is, the present invention reduces the acetaldehyde content
This provides a method for producing polyester chips with a concentration of 10 ppm or less, in which polyester chips with an intrinsic viscosity of 0.3 or more obtained by a melt polycondensation reaction in which the main repeating unit is ethylene terephthalate are heated from 210°C to 250°C under reduced pressure or inert gas flow. When producing polyester chips with an intrinsic viscosity of 0.6 or higher by performing solid phase polymerization in the temperature range of ℃, an inert gas is passed through so that the average chip temperature becomes 200℃ or less within 1 hour after the completion of the reaction. It is characterized by cooling. In the present invention, polyester means polyethylene terephthalate and polyester mainly composed of polyethylene terephthalate, and in an amount of 10 mol% or less of the total acid components, phthalic acid, isophthalic acid, hexahydrophthalic acid,
Dicarboxylic acids such as naphthalene dicarboxylic acid, adipic acid, and sebacic acid, polyhydric carboxylic acids such as trimellitic acid and pyromellitic acid, or oxyacids such as P-oxybenzoic acid can be used as the acid component, and total alcohol 1,2-propanediol in an amount not more than 10 mol% of the ingredients;
13-propanediol, 1.4-butanediol,
Dialcohols such as 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, and cyclohexanedimethanol, polyhydric alcohols such as trimethylolpropane, triethylolpropane, and pentaerythritol can be used 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-volatility substance with a temperature of 1.5 °C and is desorbed from polymers by high-temperature treatment under reduced pressure or inert gas flow. In order to produce polyester chips with a low acetaldehyde content that does not cause any problems, a high temperature of 210° C. or higher is practically required to accompany the solid phase polymerization reaction. For this purpose, the intrinsic viscosity of the prepolymer used in the present invention is determined to be 0.6 or more, which allows the inherent polymerization reaction to occur for the time necessary to reduce acetaldehyde to the desired content, and to obtain the required physical properties during molding. Although it is selected so that it can be made into polyester chips, prepolymers with an intrinsic viscosity of less than 0.3 are extremely brittle and difficult to mold into chips, and furthermore, they tend to produce powder during solid state polymerization, making them difficult to use in practice. It is. 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 or inert gas flow, but for a sufficient time for acetaldehyde to be eliminated. Even after several treatments, the final acetaldehyde content in polyester chips cannot be reduced.
It is difficult to keep it below 10ppm. As a result of our earnest efforts to investigate the cause of this, the inventors found that this
It was concluded that this was caused by the formation of acetaldehyde in the polyester at high temperatures above 200°C. 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 solid phase polymerization reaction is stopped by immediately breaking the reduced pressure or stopping the flow of inert gas at the end of the solid phase polymerization reaction according to the conventional method, acetaldehyde is not eliminated and only the by-products are prioritized. After that, on the contrary, the amount of acetaldehyde in the polyester system increases. The by-product of acetaldehyde increases as the temperature increases, but it is almost negligible at temperatures below 200°C. Based on these research results, the present invention aims to reduce the average chip temperature to below 200°C within one hour immediately after the completion of the reaction. The acetaldehyde content can be effectively reduced by cooling the polyester chips by passing an inert gas through them.
We have succeeded in keeping the amount below 10ppm. For solid state polymerization, the prepolymer is heated to 150°C if necessary.
After pre-drying at a low temperature below, 210℃ using a conventional method.
Carry out at ~250°C under reduced pressure or inert gas flow. Cooling of the chips after the reaction may be performed in a solid-phase polymerization reactor, but productivity can be increased by providing a separate cooling tank, discharging the chips immediately after the reaction is completed, and cooling the chips in the cooling tank. be able to. Cooling is performed by circulating an inert gas, but cooling from the wall using a refrigerant may also be used. However, it is difficult to uniformly and quickly cool the chip only by cooling from the wall surface, and cooling by inert gas flow is an essential requirement in the present invention. Dehumidified nitrogen gas is normally used as the inert gas, and is used by circulation. It is desirable to provide equipment for removing volatile components from polyester in the inert gas circulation system. An example of an apparatus used to carry out the present invention is shown in FIG. In Figure 1, 1 is a tumbler type high temperature dryer (solid phase polymerization reactor), 2 is a cold air blowing type cooling tank, 3 is an inert gas blowing valve, 4 is an N ₂ gas discharge valve, and 5 is an ejector valve. , 6 is the ejector,
7 is a heater for N ₂ gas, 8 is a blower, and 9 is a cooler for cold air, and the tumbler type high temperature dryer can be used either in a vacuum or under N ₂ gas flow. Further, HTO is a heat medium for heating the tumbler, and M is a drive motor for rotating the tumbler. Next, the present invention will be specifically explained by showing examples and reference examples. Examples 1 and 2 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-hydroxyethyl with an esterification reaction rate of 95%. Terephthalate and its low polymer were prepared, and then 0.016 parts 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 at 280 °C under a reduced pressure of 0.5 mmHg.
A polycondensation reaction was carried out at °C to prepare a prepolymer with an intrinsic viscosity of 0.54 and an acetaldehyde content of 125 ppm.
The strand was discharged from the nozzle and cut into chips. After pre-drying the obtained chips under vacuum at 130° C. for 3 hours, a solid phase polymerization reaction was carried out using a vacuum tumbler type high temperature dryer 1 with an internal capacity of 1 m ² in the apparatus as illustrated in FIG. . After the reaction, the chips are placed in a cooling tank 2 under a vacuum tumbler type high temperature dryer.
The chip was cooled using cold air of nitrogen (N ₂ ) gas. The conditions and results obtained are shown in Table 1. 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 2.5 ml of crushed chips that can pass through a 5-mesh sieve.
g in a glass tube with 10 ml of distilled water,
After extraction at 160°C for 2 hours, the sample solution was cooled to below 5°C, 1 ml of the sample solution was taken, and quantified using gas chromatography equipped with a PEG-20M column.

[Table] Example 3 Same as Example 1, except that when performing solid phase polymerization, 0.2 Nm ³ /min was supplied from the N ₂ gas blowing valve 3 installed in the tumbler type high temperature dryer 1 illustrated in FIG. Heated N ₂ gas was blown out at _an air volume of When the chip was cooled with N ₂ gas at 15Nm ³ /min at 150°C, the chip temperature reached 200°C after 0.5 hours. The final chips obtained were a colorless product with an intrinsic viscosity of 0.72 and an acetaldehyde content of 7 ppm. Comparative Examples 1 and 2 The results shown in Table 2 were obtained in the same manner as in Example 1, but by changing the cooling conditions after the predetermined solid phase polymerization reaction time had elapsed. 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 low acetaldehyde content.

【table】 [Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of an apparatus used for carrying out the present invention. 1...Tumbler type high temperature dryer (solid phase polymerization reactor), 2...Cold air blowing type cooling tank.

Claims (1)

[Claims] 1. Intrinsic viscosity obtained by melt polycondensation reaction in which the main repeating unit is ethylene terephthalate
When producing polyester chips with an intrinsic viscosity of 0.6 or more by solid-phase polymerizing polyester chips with an intrinsic viscosity of 0.3 or more at a temperature range of 210℃ to 250℃ under reduced pressure or inert gas flow, it is possible to perform solid phase polymerization within 1 hour immediately after the completion of the reaction. A method for producing polyester chips characterized by cooling by flowing an inert gas so that the average chip temperature is 200°C or less. 2. The method for producing polyester chips according to claim 1, wherein cooling is performed in a cooling tank provided separately from the solid phase polymerization reactor.