JPH0371455B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing polyester with a high degree of polymerization by solid phase polymerization, which has a low acetaldehyde content and is particularly suitable for foods, pharmaceuticals,
It is an object of the present invention to provide a method for producing a high degree of polymerization polyester suitable for producing containers (including packaging films) for cosmetics and the like. (Prior Art) Polyethylene terephthalate or polyester based on polyethylene terephthalate (hereinafter also simply referred to as polyester) is known for its excellent transparency, outstanding mechanical properties, balanced gas barrier properties, and excellent hygiene. Recently, they have become widely used as food containers for soy sauce, sauces, cooking oil, juice, beer, carbonated drinks, etc., and containers for detergents, cosmetics, pharmaceuticals, etc. However, polyester contains acetaldehyde, which is a by-product due to thermal decomposition during melt polymerization, so when used as a container, acetaldehyde elutes into the contents, which has a negative impact on the taste and odor of the contents. are doing. To overcome this drawback, various methods have been proposed in which polyester chips obtained by melt polymerization are heat-treated under reduced pressure (solid-phase polymerization) to produce polyester with a low acetaldehyde content (for example, JP-A-52-110177, JP-A-54-149793, etc.) (Problems to be solved by the invention) Usually, polyester obtained by melt polymerization method is
Contains a large amount (about 100 to 250 ppm) of acetaldehyde. Even if such polyester chips are treated under normal high vacuum and high temperature conditions, the rate of deacetaldehyde is slow, so the acetaldehyde content must be kept below 3 ppm (according to the measurement method described below), which is sufficient for use as food containers. The problem is that it takes about 50 hours. In addition, when producing thick-walled molded products, polyester chips obtained by heat treatment using conventional methods are
Another problem was that it was difficult to stably obtain transparent molded products. The present invention aims to provide a method for efficiently producing polyester chips that can stably produce molded articles with a low acetaldehyde content and excellent transparency. (Means for Solving the Problems) In order to achieve the above object, the present inventors have made extensive studies and found that if polyester chips are subjected to two-stage solid phase polymerization under specific conditions, it is possible to The present invention was achieved based on the discovery that the acetaldehyde content in chips can be reduced unexpectedly quickly and efficiently. That is, the present invention involves pre-crystallizing chips of polyethylene terephthalate having an intrinsic viscosity of 0.4 or more or polyester mainly composed of polyethylene terephthalate, and then under reduced pressure.
When producing polyester with an intrinsic viscosity of 0.6 or more through solid phase polymerization at 210 to 240°C, the solid phase polymerization is carried out in two stages: the first stage is carried out at a vacuum level of 15 to 50 mmHg for 5 hours or more, and the second stage is 3 with a vacuum level of 10mmHg or less
The gist of the present invention is a method for producing a polyester with a high degree of polymerization, characterized in that the total solid phase polymerization time is 8 to 35 hours. The polyester in the present invention is polyethylene terephthalate or a polyester mainly composed of polyethylene terephthalate. As the polyester mainly composed of polyethylene terephthalate, a copolyester having 80 mol% or more of ethylene terephthalate units is used, and the copolymer components include isophthalic acid,
Orthophthalic acid, diphenyl-4,4'-dicarboxylic acid, naphthalene dicarboxylic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid,
Dicarboxylic acid components such as cyclohexanedicarboxylic acid and 5-sodium sulfoisophthalic acid, trimethylene glycol, tetramethylene glycol,
Hexamethylene glycol, neopentyl glycol, diethylene glycol, cyclohexanedimethanol, hydroquinone, resorcinol, 2,
Diol components such as 2-bis(4-hydroxyethoxyphenyl)propane, p-oxybenzoic acid,
Examples include oxyacid components such as p-oxyethoxybenzoic acid. The polyester chips (referred to as prepolymers) to be subjected to solid-phase polymerization can be produced by a conventional melt polymerization method. Depending on the end use, colorants, UV absorbers,
Additives such as thermal oxidative deterioration inhibitors, antibacterial agents, lubricants, and mold release agents can be added. The prepolymer needs to have an intrinsic viscosity of 0.4 or more; if it is less than 0.4, it will not only be easily damaged when the molten polymer is turned into chips, but also be brittle and powdered during the pre-crystallization stage of solid-state polymerization. occurs in large quantities, which is undesirable. In the present invention, the prepolymer is first pre-crystallized. Pre-crystallization can be carried out by a conventional method, and is usually carried out by heating to a high temperature of 140°C or higher under reduced pressure, in the atmosphere or in an inert gas stream. Note that this preliminary crystallization is preferably carried out under forced stirring to prevent chips from fusing. Forced stirring can be performed by mechanical stirring using a stirring blade, torus disk, screw, etc., stirring by forced air blowing of high-temperature gas, or the like. The polyether chips pre-crystallized in this way are subjected to solid phase polymerization under reduced pressure at a temperature of 210-240°C. Solid phase polymerization must be carried out in two stages: the first stage is carried out at a vacuum level of 15 to 50 mmHg for at least 5 hours, the second stage is carried out at a vacuum level of 10 mmHg or less for at least 3 hours, and the entire solid phase is It is necessary that the polymerization time be between 8 and 35 hours. If the solid phase polymerization temperature is less than 210°C, the rate of desorption of acetaldehyde will not be sufficient, and if it exceeds 240°C, chips will fuse together, which is undesirable. In addition, if the vacuum level of the first stage exceeds 50 mmHg, the desorption rate of acetaldehyde will not be sufficient, and 15 mm
If it is less than Hg, the rate of desorption of acetaldehyde in the second stage will be slow, and the rate of desorption of acetaldehyde as a whole will be slow. A particularly preferable degree of vacuum in the first stage is 20 to 40 mmHg. Furthermore, if the degree of vacuum in the second stage exceeds 10 mmHg, the rate of desorption of acetaldehyde and the rate of solid phase polymerization will become slow. The particularly preferable degree of vacuum in the second stage is 5 mm.
Hg or less. Further, if the total solid phase polymerization time is less than 8 hours, the elimination of acetaldehyde will not be sufficient, and if it exceeds 35 hours, the transparency will be impaired when formed into a molded product. Most preferably, the total solid state polymerization time is 10 to 30 hours. It is necessary to select the intrinsic viscosity of the prepolymer and the solid-state polymerization conditions so that the intrinsic viscosity of the chips after solid-state polymerization is 0.6 or higher.
Preferably, ~1.2 chips are obtained. Chips with an intrinsic viscosity of less than 0.6 do not have good moldability and are not preferred. The polyester chips obtained by the method of the present invention have an acetaldehyde content of 3 ppm or less, have good moldability, and give molded products with excellent transparency, and are useful for manufacturing containers for foods, pharmaceuticals, cosmetics, etc. It is something. (Example) Next, the method of the present invention will be specifically explained with reference to Examples. The method for measuring the characteristic values in the examples is as follows. (1) Intrinsic viscosity Measured at 20°C in a mixed solvent of equal weights of phenol and tetrachloroethane. (2) Acetaldehyde content 2.5 g of polyester chips were sealed in a glass tube with 10 ml of distilled water, extracted at 160°C for 2 hours, cooled to below 5°C, and measured by gas chromatography quantitative method (unit: ppm by weight) (3) Transparency of molded product (base) Polyester chips under vacuum after solid phase polymerization,
After drying at 130℃ for 5 hours, using an injection molding machine PLASTAR S-50 manufactured by Toyo Kikai Metal Co., Ltd., the cylinder temperature was 280℃, the mold temperature was 10℃, and the injection pressure was 80℃.
Kg/cm ² , cooling time 20 seconds, width 60mm x length
Formed into a flat plate of 100mm x 5mm thick and tested with Suga Test Machine.
Baize was measured using a HGM-2D type haze meter manufactured by Co., Ltd. (If the haze is 5% or less, it can be evaluated as a transparent molded product.) Examples and Comparative Examples 100 parts by weight of terephthalic acid and ethylene glycol
A slurry consisting of 45 parts by weight was supplied to a continuous esterification reaction tank, and an esterification reaction was carried out at 250° C. under normal pressure to obtain a reaction product with an esterification reaction rate of 95%. Per 124 parts by weight of this esterification reaction product, 0.016 parts by weight of germanium dioxide was added as a catalyst.
The polymerization reaction was carried out at 280° C. under a reduced pressure of 0.5 mmHg while changing the reaction time, extruded into a strand from a nozzle, cooled, and cut to obtain the prepolymer shown in Table 1. Next, the prepolymer was pre-crystallized in a vacuum dryer at 160°C for 2 hours, and then 400 kg was charged into a vacuum tumbler type solid phase polymerization machine with an internal capacity of 1 m ³ .
A solid phase polymerization reaction was carried out under the conditions shown in Table 1. The results are shown in Table 1. In Comparative Example 2, the chips after solid phase polymerization were fused and it was difficult to take them out.

【table】

[Table] The relationship between solid phase polymerization time and acetaldehyde content under the conditions of Example 5 and Comparative Example 5 was shown in curves 1 and 2 in FIG. 1 in a graph. As is clear from the results of the Examples and Comparative Orders,
According to the method of the present invention, the rate of desorption of acetaldehyde is extremely high, and it is possible to easily obtain polyester chips with an acetaldehyde content of 3 ppm or less, and the molded products made from the same have good transparency. I understand. (Effects of the Invention) According to the present invention, by appropriately selecting solid-phase polymerization conditions, a high degree of polymerization polyester can be produced in a relatively short period of time to produce a molded product with a low acetaldehyde content and excellent transparency. It can be easily manufactured without causing any trouble.

[Brief explanation of drawings]

FIG. 1 is a graph showing a specific example of the relationship between the acetaldehyde content of a polyester chip and the solid phase polymerization time. Curve 1: Example of the present invention, Curve 2: Comparative example.

Claims (1)

[Claims] 1. When producing polyester with an intrinsic viscosity of 0.6 or more by pre-crystallizing chips of polyethylene terephthalate or a polyester mainly composed of polyethylene terephthalate with an intrinsic viscosity of 0.4 or more, solid-phase polymerization is performed at 210 to 240°C under reduced pressure to produce a polyester with an intrinsic viscosity of 0.6 or more. is carried out in two stages, the first stage is at a vacuum level of 15 to 50 mmHg for 5 hours or more, the second stage is at a vacuum level of 10 mmHg or less for at least 3 hours, and the total solid phase polymerization time is 8 to 35 hours. A method for producing a high degree of polymerization polyester.