JPH0617466B2 - Method for producing high degree of polymerization polyester - Google Patents

Description

The present invention relates to a method for producing a high degree of polymerization polyester, and more particularly to an improvement in a method for producing a high degree of polymerization polyester by solid phase assembly. Its purpose is to produce a high degree of polymerization polyester having a low content of acetaldehyde, and in particular to provide a high degree of polymerization polyester useful for the production of containers used for foods, pharmaceuticals, cosmetics and the like.

In recent years, polyester containers centered on polyethylene terephthalate have been noted for their excellent transparency, outstanding mechanical properties, balanced gas barrier properties and excellent hygiene, and soy sauce, sauce, cooking oil, juice, beer, It has been used in food containers such as carbonated drinks and containers for detergents, cosmetics, pharmaceuticals, etc., and has made remarkable progress. However, the polyester having ethylene terephthalate as a main repeating unit contains acetaldehyde, which is a by-product of thermal decomposition during melt polymerization of polyester, in the pellets, so when the acetaldehyde is molded into a container such as a bottle or a film, the molding is performed. In addition to the newly generated acetoaldehyde, as a result of being sealed in the container material, when the bottle or film container is filled with a liquid food such as a carbonated beverage, edible oil, or juice, acetaldehyde is eluted in these liquid foods to give a taste. This is a major drawback of the polyester container because it has an adverse effect on the smell and smell.

In view of these circumstances, the inventors of the present invention have made extensive studies on a method for producing a polyester resin having a low acetaldehyde content and a method for producing a polyester resin having a low generation of acetaldehyde during molding, and as a result, have reached the present invention. Is. That is, in the present invention, a polyester having an ethylene terephthalate unit as a main repeating unit, which has an intrinsic viscosity of at least 0.4 or more, a density of 1.38 or less, and a diethylene glycol content of 3 mol% or less based on all glycol components, is steamed. Provided is a method for producing a high degree of polymerization polyester, which comprises crystallizing at a temperature of 140 to 180 ° C. in an atmosphere and then performing solid phase polymerization at a temperature of 180 ° C. to 240 ° C. in an inert gas atmosphere or under reduced pressure. To do.

It is well known in the art to solid-state polymerize a low-viscosity (low degree of polymerization) polyester to obtain a high-viscosity (high degree of polymerization) polyester. It is also described in U.S. Pat. No. 4,064,112 and Japanese Patent Laid-Open No. 54-149792 that the acetaldehyde contained in the pellets is reduced at the same time as the solid-state polymerization increases the viscosity.

In the present invention, the solid-phase polymerization method itself uses a method similar to a conventionally known method, but by limiting the properties of the prepolymer to be subjected to the solid-state polymerization and adding specific pretreatment conditions, the known method is known. It was found that the solid-state polymerization method by the above method can reduce the acetaldehyde content in the pellet unexpectedly and effectively.

The high degree of polymerization polyester according to the present invention has a low content of acetaldehyde and a very small content of acetaldehyde in a container material such as a bottle or a film after molding, and is suitable for a packaging material for foods, pharmaceuticals and the like.

The polyester having an ethylene terephthalate unit as a main repeating unit in the present invention is mainly a polyester obtained from terephthalic acid or an ester-forming derivative thereof and ethylene glycol or an ester-forming derivative thereof. It may be a copolymer of other dicarboxylic acid and / or diol components in a proportion of 20 mol% or less.

Examples of the dicarboxylic acid that can be copolymerized include isophthalic acid, orthophthalic acid, diphenyl ether 4,4′-dicarboxylic acid, naphthalenedicarboxylic acid, hexahydroterephthalic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, Examples include aromatic, aliphatic or alicyclic dicarboxylic acids such as 5-sodium sulfoisophthalic acid and ester-forming derivatives of these dicarboxylic acids. or. Examples of the copolymerizable diol component include trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, diethylene glycol, cyclohexanedimethanol and other aliphatic or alicyclic glycols, hydroquinone, resorcinol, 2,2-bis ( Aromatic diols such as 4-hydroxyphenyl) propane and 2,2-bis (4-hydroxyethoxyphenyl) propane are exemplified. Further, a polyester obtained by copolymerizing P-oxybenzoic acid, P-oxyethoxybenzoic acid or an ester-forming derivative thereof as the oxyacid may be used.

An ordinary polymerization method is applied to the prepolymer for solid phase polymerization produced by melt polymerization. Although polyethylene terephthalate will be described as an example, a copolymerized polyester can be produced in the same manner. Bis (β-hydroxyethyl) terephthalate and / or its oligomer are formed by esterification or transesterification using terephthalic acid or its ester-forming derivative and ethylene glycol, and then polycondensation of germanium compound, antimony compound, etc. Polycondensation is performed under reduced pressure at high temperature using a catalyst to produce a prepolymer having an intrinsic viscosity of 0.4 or more.

As the catalyst for esterification or transesterification, sodium, alkali metal salts such as lithium, magnesium,
Alkaline earth metal salts such as calcium and metal compounds such as zinc and manganese are preferably used. Further, as a catalyst for polycondensation, a germanium compound, an antimony compound,
A compound soluble in the reaction system such as a titanium compound or a tin compound is used. Further, depending on the end use, a colorant, an ultraviolet absorber, a thermal oxidative deterioration inhibitor, an antibacterial agent, an antistatic agent, a lubricant, a release agent, a nucleating agent, etc. may be added during or after the polymerization of the prepolymer. .

The properties of the prepolymer to be subjected to solid-phase polymerization are as follows: the amount of diethylene glycol in the polymer main chain is 3 relative to the total glycol components in order to accelerate desorption of acetaldehyde and to suppress the production of acetaldehyde during solid-phase polymerization. Mol% or less, and the terminal carboxylic acid concentration is polymer 1
It is preferable that the amount is 10 equivalents or more and 40 equivalents or less in 0 ⁶ g.

When the content of diethylene glycol is 3 mol% or more, the elimination of acetaldehyde during solid-state polymerization becomes extremely slow.
Further, if the concentration of the terminal carboxylic acid is less than 10 equivalents, the rate of increasing the degree of polymerization by solid-state polymerization is slow, and if it exceeds 40 equivalents, not only is acetaldehyde released slowly, but surprisingly, after a certain period of time, acetaldehyde is removed. On the contrary, the content tends to increase. This suggests that terminal decomposition occurs due to polymer properties even during solid-phase polymerization to generate acetaldehyde, which is an important finding as a method for producing a polyester having a low acetaldehyde content of the present invention.

The intrinsic viscosity of the prepolymer must be at least 0.4 or more, and if it is less than 0.4, not only is it easily broken during melt pelletizing, but also it is brittle and a large amount of powder is generated during the pre-crystallization step of solid phase polymerization, which is not preferable. The upper limit is not particularly limited, but is usually up to about 0.7. Further, in the present invention, the density of the prepolymer needs to be usually 1.38 or less, particularly preferably 1.35 or less. If the density exceeds 1.38, the crystallinity will be close to 50%. Probably because acetaldehyde cannot be desorbed efficiently even if a step of treating in a steam atmosphere is added, the object of the present invention can no longer be achieved.

As a method of crystallizing a prepolymer having an intrinsic viscosity of 0.4 or more and a density of 1.38 or less in a steam atmosphere, a chip is put in a pressure pot and treated with pressurized steam, a method of contacting with superheated steam under atmospheric pressure. However, it is preferable to treat the prepolymer for as short a time as possible because exposure to water vapor for a long time causes the prepolymer to be hydrolyzed to reduce the degree of polymerization. Even if the prepolymer is hydrolyzed at the time of crystallization and the degree of polymerization is reduced, the desorption efficiency of acetaldehyde is not hindered, but the solid phase polymerization time is unavoidably lengthened. Therefore, as preferable crystallization conditions, the temperature is 140 ° C. or higher and 180 ° C. or lower, and the treatment time is 10 minutes or shorter. Under this condition, a crystallinity of about 50% can be obtained. At a temperature below 140 ° C, the crystallization rate is slow and the deacetaldehyde rate is slow. At a temperature above 180 ° C, it is easily hydrolyzed. The shorter the crystallization time is, the better, but it is necessary to obtain a crystallinity of about 50%, and therefore 5 minutes is necessary if the temperature rising time is included.

Since the polymer thus crystallized is moistened with water vapor and contains water in the resin, it is usually added to 0.01% by weight under dry air or an inert gas atmosphere or under reduced pressure at the same temperature as the crystallization temperature for 2 to 4 hours. The following, particularly preferably 0.005
After drying to a moisture content of less than 80% by weight, 180 ° C or more, 2
Solid phase polymerization is carried out by a conventional method at a temperature of 40 ° C. or lower under an inert gas atmosphere or under reduced pressure. If the temperature is lower than 180 ° C, the desorption of acetaldehyde and the solid-state polymerization rate are insufficient,
On the other hand, if the temperature exceeds 240 ° C., the polymers are fused together, which is not preferable. The solid phase polymerization time is usually about 5 to 40 hours, preferably 8 to 15 hours, although it varies depending on the temperature, the properties of the prepolymer and the desired degree of polymerization. Thus, a polyester having an intrinsic viscosity of about 0.6 to 1.3 is produced. Further, a polyester having an acetaldehyde content of 3 ppm or less can be easily obtained.

The present invention will be described below with reference to examples. The characteristic values in the examples were measured and obtained by the following methods.

(1) Intrinsic viscosity of polyester Measured at 30 ° C. in a mixed solvent of phenol / tetrachloroethane (6/4 weight ratio).

(2) 10 g of acetaldehyde pellets in polyester pellets and molded articles were weighed, placed in a stainless steel container with a screw stopper, 20 ml of water was added, and the vessel was tightly capped and then extracted in an oil bath at 160 ° C. for 2 hours. After cooling the container in a refrigerator, the container was opened and measured by a gas chromatograph by a conventional method. In the case of a molded product, the molded product was cut into pellets and then measured in the same manner as the pellets. The unit is ppm.

(3) Acid value 0.1 g of the polymer was dissolved in 20 ml of benzyl alcohol under heating, and titrated with 0.02 N potassium spirit using phenolphthalein as an indicator.

Units are given in gram equivalents / 10 ⁶ g polymer.

(4) Moisture content MICRO KAISEI KOGYO CO., LTD. Trace moisture analyzer VA-01, CA
It was measured using a -02 model.

(5) Density The density was measured at 30 ° C. using a density gradient tube of a mixed solvent of carbon tetrachloride and heptane.

Examples 1 to 3 398 kg of dimethyl terephthalate, 280 kg of ethylene glycol and 250 g of manganese acetate tetrahydrate were transesterified in a reaction vessel of 1 m ³ , and then 40 g of germanium dioxide and 150 g of phosphoric acid were added to carry out a melt polycondensation reaction to obtain an intrinsic viscosity.
360 kg of polyethylene terephthalate pellets of 0.52 were obtained. The polyethylene terephthalate obtained by this melt polymerization had a terminal acid value of 25 geq / 10 ⁶ g polymer, a diethylene glycol unit content of 2.3 mol%, an acetaldehyde content of 120 ppm and a density of 1.338. The melt-polymerized pellets were steamed at 160 ° C. for 10 minutes in Example 1, 180 ° C. for 10 minutes in Example 2, and 180 ° C. for 3 minutes in Example 3.
Heat treatment was performed for 0 minutes. The prepolymer densities after treatment are 1.380, 1.382, and 1.383, respectively, with a crystallinity of 50%.
Is almost equal to. The pellets were dried in a dry air atmosphere at 160 ° C. for 4 hours, then placed in a blender 10 and solid-state polymerized at an internal temperature of 210 ° C. under a reduced pressure of 0.05 mmHg for 16 hours. Sampling was performed every 4 hours on the way to quantify acetaldehyde. The results of each are summarized in Table 1. From Table 1, the content of acetaldehyde after solid state polymerization of pellets crystallized in a steam atmosphere is 3 ppm in all cases.
It was below.

In addition, in all Examples 3, the IV after solid phase polymerization is low probably because the crystallization time is long.

Comparative Example 1 The prepolymer obtained in Example 1 was preliminarily crystallized in a vacuum dryer at 160 ° C. for 2 hours, then placed in a blender at 10 ° C., and the internal temperature was 210 ° C. under a reduced pressure of 0.05 mmHg.
Solid-state polymerization was carried out for a period of time. The results are shown in Table 1. When the solid phase polymerization was performed by performing the crystallization treatment in the air, the deacetaldehyde rate was slower than that in Examples 1 to 3 in which the solid phase polymerization was performed after the crystallization under the steam.

The acetaldehyde content of the hollow container obtained by injection-molding the parison using the solid-state polymerization pellets obtained in Example 1 by a conventional method and then biaxially stretch-blow molding is 50% as compared with Comparative Example 1. It was below.

Claims (1)

[Claims] 1. An intrinsic viscosity of at least 0.4 or more,
After crystallization of a polyester having a density of 1.38 or less and a content of diethylene glycol of 3 mol% or less based on all glycol components and having ethylene terephthalate units as a main repeating unit at a temperature of 140 to 180 ° C. under a steam atmosphere, A method for producing a polyester having a high degree of polymerization, which comprises performing solid phase polymerization at a temperature of 180 ° C. or higher and 240 ° C. or lower under an inert gas atmosphere or under reduced pressure.