JPH06116377A - Production of polybutylene terephthalate-based polyester - Google Patents

Abstract

PURPOSE:To obtain the subject polymer short in time of polycondensation reaction under reduced pressure, hardly having terminal carboxyl content and having good color tone by adding an organic Co compound to a reactional system at a specific point of time in a process for producing a polyester. CONSTITUTION:A two functional carboxylic acid consisting essentially of terephthalic acid or its lower alkyl ester is made to react with a glycol consisting essentially of 1,4-butane diol to afford a polyester precursor. Then, an organic cobalt compound (preferably a cobalt salt of an organic acid such as cobalt acetate) is added to the polyester precursor, preferably in an amount of 10-45ppm expressed in terms of Co atom based on theoretical polymer yield and the polyester precursor is subjected to polycondensation under reduced pressure. Furthermore, the polycondensation reaction is preferably carried out so that maximum value of reaction temperature may be 245-255 deg.C and the reaction temperature is preferably lowered to 240-245 deg.C when polycondensation reaction is finished.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a polybutylene terephthalate polyester. In detail,
The present invention relates to a method for producing a polybutylene terephthalate-based polyester, which requires a short time for a polycondensation reaction under a reduced pressure, has a small carboxyl group content, and is capable of obtaining a polymer having an excellent color tone.

[0002]

2. Description of the Related Art Polyesters, particularly polyalkylene terephthalates composed of a terephthalic acid component and an alkylene glycol component, have many excellent properties.
Widely used in fibers, films and other molded products. Among the polyalkylene terephthalates, polybutylene terephthalate has excellent crystallization characteristics, low molding temperature and short molding time, so that it can be used for industrial parts such as automobile parts, electric / electronic parts and gears. It is suitable for various purposes and has been widely used in recent years.

Polybutylene terephthalate is generally
It is produced by a direct polymerization method or a transesterification method.
The direct polymerization method is a method in which a polyester precursor is formed by a direct esterification reaction of terephthalic acid and 1,4-butanediol, and then the polyester precursor is polycondensed under reduced pressure to produce polybutylene terephthalate. On the other hand, in the transesterification method, a lower alkyl ester of terephthalic acid and 1,4-butanediol are transesterified to form a polyester precursor, and then the polyester precursor is polycondensed under reduced pressure to produce a polyester. It is a manufacturing method.

[0004]

In the production of polybutylene terephthalate, titanium compounds such as alkyl titanates are widely used as catalysts. However, according to the studies by the present inventors, titanium compounds, especially alkyl titanate catalysts It exhibits excellent performance in the reaction until the polyester precursor is obtained regardless of the direct polymerization method and the transesterification method, but on the other hand, the effect of accelerating the polycondensation reaction under reduced pressure is not so high, and the end of the obtained polyester is It was found that the amount of carboxyl groups increased and the color tone decreased.

Shortening the time required for the polycondensation reaction has been a conventional desire in the production of polybutylene terephthalate, and at the same time, shortening the polycondensation reaction time reduces the terminal carboxyl group content of the finally obtained polybutylene terephthalate. It is also effective in reducing the color tone and improving the color tone. If the content of the terminal carboxyl group of polybutylene terephthalate is high, the hydrolysis resistance and heat resistance of polybutylene terephthalate will be reduced, and the melted product will contaminate the mold and the like due to the decomposed product, and a good molded product can be obtained. It will be difficult to be affected. Further, the improvement of color tone is important in obtaining a polybutylene terephthalate molded product having a good whiteness.

Therefore, an object of the present invention is to promote the polycondensation reaction under reduced pressure when producing a polybutylene terephthalate type polyester by a direct polymerization method or a transesterification method, and further, the content of terminal carboxyl groups is low and the color tone is low. To provide a good polybutylene terephthalate polyester.

[0007]

As a result of continued research by the present inventors from the above points, when a polybutylene terephthalate-based polyester is produced, an organic compound is added to a polyester precursor produced by a direct polymerization method or a transesterification method. When a cobalt compound is added and then a polycondensation reaction under reduced pressure is carried out, the polycondensation reaction under reduced pressure is promoted, and the carboxyl group content in the finally obtained polybutylene terephthalate polyester is reduced, resulting in a color tone. The present invention has been completed by finding that it also improves.

Therefore, according to the present invention, after a bifunctional carboxylic acid mainly containing terephthalic acid or a lower alkyl ester thereof is reacted with a glycol mainly containing 1,4-butanediol to produce a polyester precursor, A method for producing a polybutylene terephthalate-based polyester, comprising adding an organic cobalt compound to the polyester precursor, and then subjecting the polyester precursor to a polycondensation reaction under reduced pressure.

In the present invention, a bifunctional carboxylic acid having terephthalic acid as a main component or a lower alkyl ester thereof can be used as a bifunctional carboxylic acid component in the production of the polyester precursor. The manufacturing method includes both a direct polymerization method and a transesterification method.

The "bifunctional carboxylic acid mainly containing terephthalic acid or its lower alkyl ester" in the present invention means that 50 mol% or more of the difunctional carboxylic acid or its lower alkyl ester is terephthalic acid or its lower alkyl ester. It is meant to consist of a lower alkyl ester. It is preferable that 70 mol% or more of the difunctional carboxylic acid or its lower alkyl ester consists of terephthalic acid or its lower alkyl ester, so that the proportion of the other difunctional carboxylic acid or its lower alkyl ester is 30 mol%. The following is preferable.

Other difunctional carboxylic acids or lower alkyl esters thereof include, for example, isophthalic acid, 2,6
-Naphthalenedicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, azelaic acid, adipic acid, hexahydroterephthalic acid or a lower alkyl ester thereof, and the like, and these difunctional carboxylic acids or a lower alkyl ester thereof are One type or two or more types can be used in combination with terephthalic acid or a lower alkyl ester thereof. Further, the above-mentioned "lower alkyl ester" usually refers to an alkyl ester having 1 to 4 carbon atoms,
Particularly preferred is methyl ester.

The "glycol containing 1,4-butanediol as a main component" in the present invention means that 50 mol% or more of the glycol is composed of 1,4-butanediol. 70% by mole or more of 1,4-butanediol, that is, 1,
Glycols other than 4-butanediol are preferably 30 mol% or less. Examples of other glycols include ethylene glycol, neopentyl glycol, 1,4-cyclohexanediol, 1,6-hexanediol, and the like. One or more of these glycols are 1,4-butanediol. It can be used together with.

Further, if the amount is such that the thermoplasticity of the obtained polyester is not substantially impaired, a trifunctional or higher polyfunctional compound such as trimellitic acid or pentaerythritol may be used in a small amount, if necessary. Good.

In the case of the direct polymerization method, the above-mentioned difunctional carboxylic acid mainly containing terephthalic acid and glycol mainly containing 1,4-butanediol and, if necessary, a small amount of a polyfunctional compound are added to the reaction vessel. The polyester precursor is first produced by an esterification reaction in.

In that case, the molar ratio of the bifunctional carboxylic acid: glycol is preferably 1: 1.3 to 1: 2.5. It is effective that the amount of glycol used per mol of the bifunctional carboxylic acid is 1.3 mol or more in order to increase the degree of polymerization of the polyester finally obtained, while it is 2.5 mol or less. Is effective in reducing the amount of tetrahydrofuran by-product that adversely affects the polymerization reaction.

In this direct polymerization method, any polycondensation catalyst usually used in the direct polymerization method of polyester can be appropriately used if necessary, and preferable examples of the catalyst are tetrabutyl titanate and tetraisopropyl titanate. Examples thereof include organic titanium compounds such as titanates and their hydrolysates. The catalyst may be added before or after the esterification.

The esterification reaction is usually preferably carried out at a temperature in the range of about 190 to 240 ° C. under a pressure condition near atmospheric pressure. When the reaction temperature is about 190 ° C. or higher, the esterification reaction can be easily progressed sufficiently and the subsequent polycondensation reaction can be promoted. On the other hand, about 240
When the temperature is below ℃, it is effective to reduce the amount of tetrahydrofuran by-product. The target of stopping the esterification reaction is preferably when the esterification rate reaches about 90% or more. This makes it possible to shorten the time required to obtain a polyester having a desired degree of polymerization in the subsequent polycondensation reaction.

In the case of the transesterification method, first, the above-mentioned lower alkyl ester of a bifunctional carboxylic acid mainly containing terephthalic acid and a glycol mainly containing 1,4-butanediol, and a small amount of a small amount thereof may be added if necessary. A polyester precursor is produced by transesterifying a polyfunctional compound in a reaction tank. This transesterification reaction is preferably carried out in the presence of a catalyst. When using a catalyst, any of the catalysts commonly used for this type of transesterification reaction may be used. Preferred examples of the catalyst include organic titanium compounds such as tetrabutyl titanate, tetraisopropyl titanate, and hydrolyzates thereof.

The lower alkyl ester of difunctional carboxylic acid: glycol is used in a molar ratio of 1: 1.05.
-1: 1.50 is preferable, and 1: 1.10-1: 1.
A value of 1.30 is particularly preferable. When the amount of glycol used is 1.05 mol or more per mol of the lower alkyl ester of difunctional carboxylic acid, it is effective to increase the polymerization degree of the finally obtained polyester, while 1.
When the amount is 50 mol or less, it is effective in reducing the amount of tetrahydrofuran by-produced.

The transesterification reaction is preferably carried out at a temperature in the range of about 140 to 240 ° C. under a pressure condition near atmospheric pressure. When the reaction temperature is set to about 140 ° C or higher, the transesterification reaction can be easily progressed sufficiently and is effective in promoting the next polycondensation reaction. It is possible to reduce the amount of raw material.

From the viewpoints of the time required for the transesterification reaction, the time required for the subsequent polycondensation reaction under reduced pressure, the suppression of the by-product amount of tetrahydrofuran, and the physical properties of the polyester finally obtained, the transesterification rate is It is desirable to stop the transesterification reaction when it is in the range of about 70 to 90%.

In the present invention, it is important to carry out the polycondensation reaction under reduced pressure after adding the organic cobalt compound to the polyester precursor produced by the above esterification reaction or transesterification reaction. That is, in the present invention, the organic cobalt compound is added to the reaction system after the production of the polyester precursor and before shifting to the polycondensation reaction under reduced pressure.

If the addition timing of the organic cobalt compound is before or during the production of the polyester precursor, the reaction after the addition is delayed, which is not desirable. On the other hand, when the organic cobalt compound is added during the polycondensation reaction, it may not be possible to shorten the polycondensation reaction time.
Further, the polyester finally obtained may have a low degree of polymerization, which is not preferable. Further, when added after the completion of the polycondensation reaction, the acceleration of the polycondensation reaction, which is one of the objects of the present invention, cannot be achieved.

Preferable examples of the organic cobalt compound include cobalt salts of organic acids such as cobalt acetate. The amount of the organic cobalt compound added is 5 to 5 in terms of cobalt atom based on the theoretical polymer yield.
It is preferably 0 ppm, more preferably 10 to 45 ppm. If the addition amount of the organic cobalt compound is too small, it becomes difficult to shorten the polycondensation reaction time, reduce the carboxyl group content in the obtained polyester, and improve the color tone, while the addition amount of the organic cobalt compound is large. If it is too much, the color tone of the resulting polybutylene terephthalate (hereinafter referred to as "PBT") type polyester deteriorates.

The method of adding the organic cobalt compound to the reaction system is not particularly limited. For example, the organic cobalt compound may be added to the polyester precursor directly in the form of powder or by heating and melting, or a small amount of 1,4-. It may be dissolved in butanediol or another glycol and added to the polyester precursor.

The polyester precursor to which the organic cobalt compound has been added is then subjected to a polycondensation reaction under reduced pressure to produce the desired PBT polyester. The method and reaction conditions of the polycondensation reaction under reduced pressure are not particularly limited, and any of the method and conditions of the polycondensation reaction under reduced pressure that are usually adopted when producing a PBT-based polyester can be adopted. , The maximum reaction temperature of the polycondensation reaction is 240-260 ° C
It is preferable to carry out under heating conditions such that it falls within the range of
More preferably, the maximum value is in the range of 245 to 255 ° C. This is because the higher the maximum reaction temperature is, the shorter the time required for the polycondensation reaction tends to be. However, if the maximum reaction temperature is too high, the resulting PBT-based polyester may be more colored.

At the end of this polycondensation reaction, that is, when the system is subjected to atmospheric pressure or its vicinity or under a pressure condition of pressurization, if the temperature is too high, P formed after the polycondensation reaction is completed.
When the BT-based polyester is taken out from the polymerization tank, the degree of polymerization of the polyester (that is, the intrinsic viscosity [η]) decreases with the lapse of the taking-out time. When the temperature at the end of the polycondensation reaction is too low, the melt viscosity of the PBT polyester becomes abnormally high and it becomes difficult to take it out from the polymerization tank. Therefore, at the end of the polycondensation reaction, the reaction temperature is set to 240 to 245.
It is preferable to lower the temperature to ℃. As a method of lowering the reaction temperature to 240 to 245 ° C. at the end of the polycondensation reaction, a method of rapidly cooling the polymerization tank immediately before the end of the polycondensation reaction to lower the reaction temperature, and gradually decreasing toward the end of the polycondensation reaction A method of lowering the reaction temperature can be adopted.

The polycondensation reaction is usually carried out under reduced pressure of 5 mmHg or less. Thereby, the time required for the polycondensation reaction can be shortened, and a polyester having a high degree of polymerization can be easily obtained. The system pressure should be gradually lowered as the polycondensation reaction proceeds.

The above-mentioned esterification reaction, transesterification reaction and polycondensation reaction may be carried out, if necessary, for example with phosphoric acid, phosphorous acid, trimethyl phosphate, dimethyl phosphate,
Phosphorus compounds such as triphenyl phosphate; n-octadecyl 3- (4-hydroxy-3,5-di-t-butylphenyl) propionate, tetrakis [methylene (3,5-di-t-butyl-4-hydroxy) Phenylpropionate)] Sterically hindered phenolic compounds such as methane; arbitrary additives such as talc, silica, kaolinite, carbon black, glass fibers, fillers such as metal powder, and the like can be appropriately added.

[0030]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. In the following examples and the like, parts represent parts by weight. The degree of polymerization of PBT is represented by the intrinsic viscosity [η] (dl / g). The intrinsic viscosity [η] is based on the solution viscosity measured at 30 ° C. by dissolving the PBT obtained in each example in a mixed solvent of phenol / tetrachloroethane (1: 1 weight ratio). The carboxyl group content [COOH amount] in PBT was determined by dissolving PBT in benzyl alcohol and titrating with 0.01N sodium hydroxide aqueous solution. Furthermore,
The color tone (b value and L value) of PBT was measured using an SM color computer manufactured by Suga Test Instruments Co., Ltd. The b value is preferably around 0, and as it becomes larger than 0, yellow tends to become stronger, and as it becomes smaller than 0, blue tends to become stronger. Also, the L value is preferably close to 100, and as it becomes smaller than 100, the dark color tends to become stronger.

Example 1 Dimethyl terephthalate 10
0 parts, 60 parts of 1,4-butanediol and 0.04 parts of tetraisopropyl titanate were charged into a reaction tank and heated under a normal pressure while gradually increasing the temperature from 145 ° C. to 230 ° C. to carry out a transesterification reaction, The transesterification reaction was stopped when 28 parts of methanol was distilled. The time required from the start of the distillation of methanol to the termination of the transesterification reaction by the distillation of 28 parts of methanol (hereinafter referred to as “transesterification reaction time”) was 120 minutes. Immediately after stopping the transesterification reaction, 0.007 part of powder of cobalt acetate tetrahydrate (15 ppm of theoretical amount of PBT finally obtained in terms of cobalt atom) was added, and then the system was subjected to polycondensation under reduced pressure. It was transferred to the reaction system. That is, about 3
It took 0 minutes to raise the reaction temperature from 230 ° C. to 250 ° C. and reduce the pressure from atmospheric pressure to a pressure of 0.3 mmHg. After maintaining the reaction temperature and pressure for about 10 minutes, the reaction temperature was gradually lowered to 240 ° C. at a pressure of 0.3 mmHg for about 50 minutes. Then, the polycondensation reaction was stopped by supplying nitrogen gas to the reaction tank and returning the system to normal pressure (total polycondensation reaction time = 90 minutes). The reaction tank was pressurized with nitrogen gas, and PBT generated from the bottom of the reaction tank was extruded out of the tank and taken out. The intrinsic viscosity [η] of the obtained PBT, the amount of terminal carboxyl groups and the color tone (b value, L
Value) was measured by the method described above. The results are shown in Table 1 below.

Comparative Example 1 A PBT was produced in the same manner as in Example 1 except that cobalt acetate tetrahydrate was not added at all. In Comparative Example 1, the transesterification reaction time was 120 minutes, and the total polycondensation reaction time was 110 minutes. Table 1 shows the intrinsic viscosity [η], the amount of terminal carboxyl groups and the color tone (b value, L value) of the obtained PBT.

Comparative Example 2 Cobalt acetate 4 was added not before the termination of the transesterification reaction but before the initiation of the transesterification reaction.
PBT was produced in the same manner as in Example 1 except that 0.007 parts of hydrate powder was added. In Comparative Example 2, the transesterification reaction time was 150 minutes, and the total polycondensation reaction time was 9 minutes.
It was 0 minutes. Table 1 shows the intrinsic viscosity [η], the amount of terminal carboxyl groups and the color tone (b value, L value) of the obtained PBT.

Comparative Example 3 Cobalt acetate tetrahydrate powder 0.0 30 minutes after the start of the polycondensation reaction under reduced pressure (30 minutes after the start of reduced pressure), not immediately after the termination of the transesterification reaction.
A PBT was produced in the same manner as in Example 1 except that 07 parts were added. In this comparative example 2, the transesterification reaction time is 12
It was 0 minutes, and the total polycondensation reaction time was 110 minutes. Table 1 shows the intrinsic viscosity [η], the amount of terminal carboxyl groups and the color tone (b value, L value) of the obtained PBT.

[0035]

[Table 1]

From the results in Table 1 above, in the case of Example 1 in which cobalt acetate was added after the completion of the transesterification reaction and before the polycondensation reaction, the time required for the transesterification reaction and the polycondensation reaction was short. The PBT that can be obtained
Has a low carboxyl group content and ab value of 0,
It can be seen that the L value is close to 100 and the color tone is good. On the other hand, in Comparative Example 1 in which cobalt acetate was not added, the polycondensation reaction took a long time and the obtained PBT
It can be seen that has a large amount of carboxyl groups and a high b value and is colored in yellow, resulting in poor color tone. Further, in Comparative Example 2 in which cobalt acetate is added before the start of the transesterification reaction, it can be seen that although the physical properties of the obtained PBT are good, the transesterification reaction requires a long time. Furthermore, in Comparative Example 3 in which cobalt acetate was added after the start of the polycondensation reaction, the polycondensation reaction could not be shortened, and the obtained PBT had a large amount of carboxyl groups, a high b value, and a low L value. It can be seen that the color tone is inferior.

Example 2 The cobalt acetate tetrahydrate powder was added immediately after the transesterification reaction and in the polycondensation reaction by changing the addition amount of the cobalt acetate tetrahydrate powder as shown in Table 2 below. In addition to immediately before, in the same manner as in Example 1, P
When BT was manufactured, the results shown in Table 2 were obtained.

[0038]

[Table 2]

[0039]

EFFECT OF THE INVENTION In the production of PBT-based polyester, transesterification is carried out by the method of the present invention in which the organic cobalt compound is added to the reaction system after the production of the polyester precursor and before the initiation of the polycondensation reaction. The reaction or esterification reaction and polycondensation reaction can be carried out in a short time, and the obtained PBT polyester has a low content of carboxyl groups and a good color tone.

Claims (1)

[Claims] 1. A polyester precursor is produced by reacting a difunctional carboxylic acid mainly containing terephthalic acid or a lower alkyl ester thereof with a glycol mainly containing 1,4-butanediol, and then producing the polyester precursor. A method for producing a polybutylene terephthalate-based polyester, which comprises adding an organic cobalt compound to, and then subjecting the polyester precursor to a polycondensation reaction under reduced pressure.