JP2002317041A - Method for producing cyclic polyester oligomer, and method for producing polyester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a cyclic polyester oligomer, which gives higher profitability than by conventional known production methods on the production of a high polymerization degree polyester. SOLUTION: The method for producing the cyclic polyester oligomer from a linear polyester oligomer or a linear polyester obtained by subjecting a dicarboxylic acid component and a diol component to an esterification reaction is characterized by controlling the unreacted materials contained in a reaction solvent to <=10 wt.%, when at least a part of the reaction solvent discharged from a reaction vessel for producing the cyclic polyester oligomer is repeatedly returned to the reaction vessel and used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for economically producing a cyclic polyester oligomer using a linear polyester oligomer or a linear polyester, a catalyst and a reaction solvent.

[0002]

2. Description of the Related Art Due to its excellent properties, polyesters are widely used in various fields such as fibers, films, and bottles. Among them, polyalkylene terephthalate is excellent in mechanical strength, chemical properties, dimensional stability and the like, and is preferably used. Among them, for example, fibers for industrial materials are required to have high strength, and a method for improving fiber strength by increasing the molecular weight of polyalkylene terephthalate has been proposed.

Generally, polyalkylene terephthalate is
Manufactured from terephthalic acid or its ester-forming derivative and alkylene glycol.In the commercial process for producing high molecular weight polymers, a method of increasing the degree of polymerization by solid phase polymerization after melt polymerization is widely used. Have been. However, the method of increasing the degree of polymerization by solid-state polymerization has some undesirable characteristics as described below.

For example, solid-state polymerization requires a large increase in equipment cost such as a step of drying polyester chips.
Further, since the residence time of chips is long, it is required to greatly improve the productivity.

In order to solve such a problem, for example, WO96
/ 22319 discloses a polymerization degree of 5 to 3 in a molten state.
5 polyethylene terephthalate prepolymer was added to 12
It is cooled at 0 to 210 ° C. and crystallized at the same time as pelletization, or amorphous polyethylene terephthalate prepolymer in the form of pellets having a degree of polymerization of 5 to 35 is produced at 120 to 210 ° C.
A method has been proposed in which a polyethylene terephthalate prepolymer crystallized by rapidly heating to ℃ is subjected to solid-state polymerization at 230 to 240 ℃. Thus, it has been proposed to reduce the equipment cost by performing the solid-phase polymerization without the melt polycondensation step. However, in order to increase the degree of polymerization of the polyethylene terephthalate prepolymer, a considerable amount of reaction time is required in the solid-state polymerization step, so that it is insufficient to improve the conventional productivity.

On the other hand, a ring-opening polymerization reaction using a cyclic polyester oligomer has attracted attention. For example, Macromolecules (Brunel, 31 (4782), 1998)
(Macromolecules (Daniel J. Brunelle, 31 (4782), 199
Regarding the ring-opening polymerization of the cyclic polyester oligomer described in 8)), it is reported that a polymer having a high degree of polymerization can be obtained in a very short time. In the report,
Cyclic polyester oligomers have been prepared by condensing diol and terephthaloyl chloride as raw materials in the presence of an amine catalyst having no steric hindrance. However, conventional methods using amine catalysts and corrosive acid chlorides such as terephthaloyl chloride require environmentally unfriendly chlorides and require expensive recycle stages involved in the formation of by-product amine salts. Not desirable because it requires.

The macrocyclic polyester oligomer proposed in Japanese Patent Application Laid-Open No. Hei 8-225633 has low viscosity and can be easily impregnated into a dense fibrous preform. ing.
Also, the macrocyclic polyester oligomer melts and polymerizes at a much lower temperature than the resulting polymer,
As melt flow, polymerization and crystallization can occur isothermally,
It states that less time, expense and tools are required for thermal recycling. However, although it is possible to obtain a polymer having a high degree of polymerization by using a cyclic polyester oligomer, the reaction solvent required for synthesizing the cyclic polyester oligomer has a boiling point of a diol by-produced in the reaction step of the cyclic polyester oligomer. It merely discloses that a higher temperature is suitable for improving the yield. Therefore, when producing a more economical polyester, it is not sufficient to improve the economic efficiency and productivity of the prior art using solid-state polymerization by using an expensive reaction solvent as it is.

In the method for producing a macrocyclic polyester oligomer proposed in Japanese Patent Application Laid-Open No. 9-296036, a linear polyester is brought into contact with an organic solvent substantially free of oxygen and water and a depolymerization catalyst. In this way, the linear polyester is depolymerized to be produced. However, although it is environmentally advantageous because a corrosive acid chloride such as a conventionally known amine catalyst and terephthaloyl chloride is not used, the method for obtaining a cyclic polyester oligomer by depolymerizing a linear polyester is not used. As described above, it is not sufficient to improve productivity and economic efficiency only by using an expensive reaction solvent as it is.

[0009] From the above background, there is a demand for economically obtaining a high-polymerized polyester.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks in the synthesis of cyclic polyester oligomers and to provide a production method of a cyclic polyester oligomer with good productivity and economical efficiency.

[0011]

An object of the present invention is to provide a linear polyester oligomer obtained by subjecting a dicarboxylic acid component and a diol component to an esterification reaction, or a method for producing a cyclic polyester oligomer from a linear polyester. When at least a part of the reaction solvent discharged from the reaction tank for producing the cyclic polyester oligomer is returned to the reaction tank and used repeatedly, unreacted substances contained in the reaction solvent are 10% by weight or less. And a method for producing a cyclic polyester oligomer.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester of the present invention is a polymer synthesized from dicarboxylic acid or its ester-forming derivative, and diol or its ester-forming derivative, and is used as a molded article such as a fiber, a film, and a bottle. There is no particular limitation as long as is possible.

Specific examples of such polyesters include, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polycyclohexylene dimethylene terephthalate, polyethylene 2,6-naphthalenedicarboxylate, and polyethylene-1,2-. Bis (2-chlorophenoxy) ethane-4,4'-dicarboxylate and the like can be mentioned. The present invention is particularly suitable for polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, or a polyester copolymer mainly composed of polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate, which are widely used.

The dicarboxylic acids used to obtain these polyesters include, for example, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and 4,4'-diphenyldicarboxylic acid, adipic acid, sebacic acid and the like. Examples thereof include aliphatic dicarboxylic acids such as acids, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. Examples of the diol include ethylene glycol, propane diol, butane diol, neopentyl glycol, hexamethylene glycol, diethylene glycol, polyethylene glycol, polypropylene glycol, cyclohexane dimethanol, and the like.

These polyesters include, as copolymerization components, dicarboxylic acids such as adipic acid, isophthalic acid, sebacic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, and ester-forming derivatives thereof, polyethylene glycol, diethylene glycol. And dioxy compounds such as hexamethylene glycol, neopentyl glycol, and polypropylene glycol; oxycarboxylic acids such as p- (β-oxyethoxy) benzoic acid and lactic acid; and ester-forming derivatives thereof, and the like.

As a method for producing the cyclic polyester oligomer of the present invention, a linear polyester oligomer obtained by an ester reaction between a dicarboxylic acid and a diol is used (Method A), or a linear polyester is used (B) Method) to produce a cyclic polyester oligomer. The linear polyester has a polymer having an intrinsic viscosity [η] of 0.4 or more, and a polymer having a intrinsic viscosity [η] of less than 0.4 is a linear polyester oligomer.

First, as the method A, a straight-chain polyester having a molar ratio of diol component / dicarboxylic acid component of 1.0 to 1.6 when the esterification reaction of dicarboxylic acid and diol is carried out. It is preferable to use an oligomer from an economic viewpoint. Here, when the charged molar ratio of the diol component / dicarboxylic acid component is higher than 1.0, the productivity of the esterification reaction is shortened because the time of the esterification reaction is shortened, which is economically preferable. On the other hand, when the charged molar ratio is lower than 1.6, the average degree of polymerization of the linear polyester oligomer obtained by the esterification reaction is higher than 2,
In order to obtain a cyclic polyester oligomer, a step of removing an excess diol component is not required until a desired average degree of polymerization is reached, which is economically preferable. Therefore, it is more preferable that the charged molar ratio of the diol component / dicarboxylic acid component is in the range of 1.1 to 1.5, and still more preferably in the range of 1.25 to 1.40.

For the purpose of the present invention, in order to economically produce a cyclic polyester oligomer, the molar ratio of the diol component / dicarboxylic acid component used in the esterification reaction of the dicarboxylic acid and the diol should be 1.0 to 1.0. In the range of 1.6, it is preferable to use the linear polyester oligomer at the time when the esterification reaction in the continuous polymerization process is completed. Here, the continuous polymerization process includes a conventionally known esterification reaction tank, a pre-polymerization tank, and a final polymerization tank. The continuous polymerization process is performed at the time when the esterification reaction in the continuous polymerization process is completed. To use a linear polyester oligomer,
The reaction may be via an esterification reaction tank where the esterification reaction is substantially completed, or may be via a subsequent prepolymerization tank. Here, the method of the polycondensation reaction in the pre-polymerization tank may be any conventionally known method,
For example, a method in which the temperature of the reactant is raised and the pressure is reduced to remove the diol component and other by-products that are desorbed to increase the degree of polymerization to a predetermined polymerization degree, or an inert gas is blown instead of reducing the pressure of the reaction system For example, a method of increasing the degree of polymerization can be applied.

The esterification reaction in the continuous polymerization process is completed within a range where the charged molar ratio of the diol component / dicarboxylic acid component in performing the esterification reaction between the dicarboxylic acid and the diol is 1.0 to 1.6. The average degree of polymerization of the linear polyester oligomer at the time of
It is preferably 0, more preferably 2 to 10, and even more preferably 2.5 to 4.0. Therefore,
In order to obtain a preferable linear polyester oligomer, it is more preferable to use one that has passed through an esterification reaction tank in a continuous polymerization process. Regarding such a continuous polymerization process, in a conventional continuous polymerization apparatus that performs a melt polycondensation step, a branch pipe is installed in a reactant transfer pipe between an esterification reaction tank and a pre-polymerization tank, and a gear pump or the like is installed. Alternatively, a method of controlling the amount of liquid transfer may be employed, and the esterification reaction may be performed in a continuous polymerization process for a process relating to the production of the cyclic polyester oligomer.

In the present invention, by adding various conventionally known esterification catalysts to the reaction system at any time before the start of the synthesis of the cyclic polyester oligomer, the reaction rate of the esterification reaction can be further improved, and more economical. The esterification reaction can be carried out without adding an esterification catalyst. However, the esterification reaction is not particularly limited because it is economically superior to a conventionally known method for producing a cyclic polyester oligomer. As a specific compound of the esterification catalyst, a tin compound and / or a titanium compound which are known to have an esterification catalyst function are preferable.
The arbitrary point in time before the start of the synthesis of the cyclic polyester oligomer refers to an arbitrary point in time during the preparation of the slurry of the dicarboxylic acid and the diol and in the esterification reaction step.

Examples of the tin compound include dibutyltin oxide, stannous chloride, tin octylate, tin laurate,
Monobutylhydroxytin oxide and the like. These tin compounds may include those in which a plurality of tin compound molecules are associated or oligomerized with a slight change.

Examples of the titanium compound include tetrabutyl titanate, tetraisopropyl titanate, tetrastearyl titanate, potassium titanyl oxalate, lithium titanyl oxalate and the like. Among them, a composite oxide containing a titanium compound as a main metal element and a chelating agent-containing compound containing a titanium compound as a main metal element are particularly preferable. Here, a composite oxide containing a titanium compound as a main metal element is, for example, a titanium alkoxide compound and a alkoxide compound such as silicon, aluminum, zirconium, and germanium, which is produced by a coordination chemical sol-gel method, but is not particularly limited. It is not something to be done. The chelating agent-containing compound containing a titanium compound as a main metal element includes, for example, ethylenediaminetetraacetic acid,
A titanium compound containing a chelating agent such as hydroxyethylimino diacetic acid, diethylene triamine pentaacetic acid, triethylene tetramine hexaacetic acid, citric acid, maleic acid, or a mixture thereof, but is not particularly limited.

The amount of the esterification catalyst is from 0.0001% by weight to the obtained polymer in terms of metal weight.
The content is preferably 0.2% by weight in view of the reaction rate of the esterification reaction and the color tone of the finally obtained polymer, and more preferably 0.0005% by weight to 0.1% by weight.

On the other hand, as the method B, a linear polyester may be produced by a conventionally known method, or a recovered polyester may be used.

In the present invention, if the above-mentioned linear polyester oligomer or linear polyester is used, the method for producing the cyclic polyester oligomer may be a conventionally known method. At least a part of the reaction solvent discharged from the tank needs to be returned to the reaction tank and used repeatedly. At this time, the unreacted substance contained in the reaction solvent was 10% by weight.
The following is required from the viewpoint of the yield of the cyclic polyester oligomer and the economic efficiency. More preferably 5% by weight
Or less, more preferably 3% by weight or less. The unreacted substance contained in the reaction solvent refers to raw materials such as a dicarboxylic acid component, a diol component and their by-products, and a linear polyester oligomer.

Here, regarding the reaction solvent and cyclization catalyst used in the production of the cyclic polyester oligomer, for example, Polymer Letters (Humb, 5 (1057), 19
67) (Polymer Letters (F. Lynn Hamb, 5 (1057), 196
In the method for synthesizing a cyclic polyester oligomer described in 7)), it is reported that 1-methylnaphthalene is used as a reaction solvent and tetraisopropyl titanate is used as a cyclization catalyst. Also, JP-A-8-2256
No. 33 discloses that a hydrocarbon compound such as ortho-, meta- or para-terphenyl is used as a reaction solvent, and an organotin compound and / or a tetraalkoxy titanate such as tetrabutyl titanate is used as a cyclization catalyst. Has been proposed.

Accordingly, the reaction solvent used in the present invention preferably has a temperature higher than the boiling point of the diol by-produced in the reaction step of the cyclic polyester oligomer, which is suitable for improving the yield. It is preferable that the compound is 6 or more. More preferably, it has 10 carbon atoms.
The above compounds, specifically, 1-methylnaphthalene, 2-methylnaphthalene, 1,4-dimethylnaphthalene, 1,7-dimethylnaphthalene, 2,6-dimethylnaphthalene, 2,7-dimethylnaphthalene, ortho -Terphenyl, meta-terphenyl, para-terphenyl,
A hydrocarbon compound such as hexadecane and a mixture thereof may be used.

As the cyclization catalyst, an organotin compound,
And / or tetraalkoxy titanate may be used, and is not particularly limited. Further, the addition amount of the cyclization catalyst is 0.01% by weight to 2% by weight based on the metal weight based on the cyclic polyester oligomer to be produced,
It is preferable from the viewpoint of the reaction rate and economical efficiency of the cyclization reaction.
More preferably, it is 1% by weight to 1% by weight.

As for the method for producing the cyclic polyester oligomer, the reactant produced from the method A or the method B is sent to a reaction vessel for synthesizing the cyclic polyester oligomer,
The above reaction solvent and cyclization catalyst may be used, and the synthesis is performed by a batch polymerization process or a continuous polymerization process. The average residence time of the reaction tank is preferably 0.5 to 2 hours, and the obtained reaction product is sent to a solvent removal tank to remove the reaction solvent, and then sent to a solid precipitation tank, and hexane or the like is used. By adding the above hydrocarbon compound, a reactant contained in the solvent may be precipitated. Further, the obtained mixture is separated from a hydrocarbon compound such as hexane by passing through a centrifugal separation / fluidized bed dryer, whereby a cyclic polyester oligomer can be obtained. Here, when the unreacted substance contained in the reaction solvent is 10% by weight or less, the removed reaction solvent is returned to the reaction tank as it is, and used repeatedly, or by passing through a rectification column. The unreacted material contained in the reaction solvent is reduced to 10% by weight or less, returned to the reaction tank, and used repeatedly. However, a new reaction solvent may be used in the reaction tank in addition to the above-mentioned recovered reaction solvent.

In the present invention, the cyclic polyester oligomer produced from Method A or Method B is substantially pure, but in many cases, has a purity of 60% or more, preferably 70% or more.
% Or more, more preferably 80% or more. Further, the obtained cyclic polyester oligomer has 1
It contains 0% or less linear polyester oligomer, preferably 5% or less, more preferably 2% or less linear polyester oligomer. The average degree of polymerization of the obtained cyclic polyester oligomer is 2 to
It is preferably 10 and more preferably 2 to 5.

The linear polyester oligomer or the linear polyester includes a cyclic polyester oligomer without any limitation.

In the present invention, the production of a polyester by ring-opening polymerization using a cyclic polyester oligomer may be carried out by a conventionally known method as long as the cyclic polyester oligomer is brought into contact with a catalyst for a cyclic polyester oligomer. Not done.

For example, various organotin compounds and titanate esters described in US Pat. Nos. 5,039,783, 5,214,158 and 5,231,161 may be used as catalysts for cyclic polyester oligomers. No. 253573, di- (1-butyl) -2,2-dimethylpropane-1,3-dioxytitanate, bis (2,2-
Dimethyl-1,3-propylene) titanate or 1-
A cyclic titanium catalyst such as (1-butoxy) -4-methyl-2,6,7-trioxa-1-titanacyclo [2.2.2] octane may be used as a catalyst for the cyclic polyester oligomer. Macromolecules (Yoke, 33 (3594), 2000) (Macromolecules (J
The antimony compounds and bismuth compounds described in i H. Youk, 33 (3594), 2000)) may be used as the catalyst for the cyclic polyester oligomer, and are not particularly limited.

The amount of the catalyst for the cyclic polyester oligomer to be added is 0.0001% by weight to 1% by weight based on the weight of the metal used for the cyclic polyester oligomer. 0.001% by weight to 0.3% by weight
Is more preferable. When the amount added is less than 0.0001% by weight, these catalysts are sensitive to impurities contained in the cyclic polyester oligomer, in particular water, hydroxy compounds and acidic impurities which may contain carboxylic acids and their anhydrides. Therefore, when such impurities are present, the catalyst is partially deactivated, and as a result, the ring-opening polymerization may be incomplete or a polymer having a low degree of polymerization may be obtained. If the addition amount is more than 1% by weight, the catalyst becomes a part of the polymer terminal group, which inhibits the growth reaction in the ring-opening polymerization of the cyclic polyester oligomer, so that a polymer having a low polymerization degree may be obtained. .

In the present invention, the contact between the cyclic polyester oligomer and the catalyst for the cyclic polyester oligomer may be carried out at a temperature within the range of 160 to 320 ° C., and the molten state is obtained in order to enhance the solubility of the cyclic polyester oligomer. The polymerization may be carried out by mixing with a thermoplastic polymer. As the thermoplastic polymer, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinylidene chloride, fluororesin, which are addition polymerization systems,
Examples include polycondensation-based polyamides, polyesters, polycarbonates, polyphenylene oxides, and polyaddition-based polyurethanes, and ring-opening polymerization-based polyacetals, and the like. Among them, polyesters are preferable. Among them, particularly preferred are polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate, which are widely used, and polyester copolymers mainly composed of polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate.

When the cyclic polyester oligomer and the thermoplastic polymer in the molten state are mixed, the reaction tank and the ring-opening polymerization reaction tank are used for the polymer that has passed through the prepolymerization tank or the final polymerization tank in the continuous polymerization process. A static mixing device may be installed in the reactant transfer pipe between the two, and a cyclic polyester oligomer may be supplied through a branch pipe immediately before the device. Further, the thermoplastic polymer chipped or the existing thermoplastic polymer chipped and the cyclic polyester oligomer may be melt-mixed by an extruder via a final polymerization tank in the continuous polymerization process. Here, the extruder is not particularly limited, and examples of conventionally known extruders include a single-screw kneader, a twin-screw kneader, and a kneader with a vent.

In the present invention, when the cyclic polyester oligomer is mixed with the thermoplastic polymer in a molten state, the intrinsic viscosity of the obtained polyester is preferably 0.65 or more, more preferably 0.70 or more. Highly polymerized polyester.

In the present invention, a conventionally known phosphorus compound or cobalt compound may be added to the finally obtained polyester at an arbitrary time point for the purpose of improving heat resistance and color tone. In the present invention, known compounds, for example, inorganic particles for matting, antioxidants, heat insulating materials, antistatic agents, ultraviolet absorbers, and the like may be added and contained as necessary.

As described above, the present invention relates to a method for producing a cyclic polyester oligomer, wherein at least a part of the reaction solvent discharged from the reaction tank is returned to the reaction tank and is used repeatedly. To 10% by weight or less to produce a cyclic polyester oligomer, it is possible to obtain a polyester having a higher degree of polymerization more economically than conventionally known solid-state polymerization processes and ring-opening polymerization processes.

[0040]

The present invention will be described in more detail with reference to the following examples. The physical properties in the examples were measured by the methods described below. (1) Intrinsic viscosity [η] of polymer Measured at 25 ° C. using orthochlorophenol as a solvent. (2) Quantification of Unreacted Substance in Reaction Solvent Calculated from the ratio of low polymer peak areas of each degree of polymerization identified in advance (UV absorption basis:%) in a liquid chromatograph. (3) Purity and Average Degree of Polymerization of Cyclic Polyester Oligomer Calculated from the ratio of the low polymer peak area of each degree of polymerization previously identified (UV absorption standard:%) in a liquid chromatograph.

Example 1 In a continuous polymerization apparatus consisting mainly of three reaction tanks, a first esterification reaction tank, a second esterification reaction tank and a polycondensation reaction tank, 16.6 parts by weight of terephthalic acid and 8.18 g of ethylene glycol were previously prepared. 2 parts by weight were stirred and the prepared slurry was mixed with 2 parts by weight.
It was fed to the first esterification reactor at a feed rate of 3.8 parts by weight / hour. The average residence time in the first esterification reactor is 3
Time 50 minutes, reaction temperature 250 ° C, reaction pressure 1.013 ×
10 ⁵ Pa, and the average degree of polymerization of the obtained reaction product was 3.
It was 0. The step of producing this linear polyester oligomer is referred to as step 1.

This reaction product was continuously withdrawn and sent to a reactor for the synthesis of a cyclic polyester oligomer. In this reaction tank, recovered α-methylnaphthalene containing 2.5% by weight of an unreacted substance was used as a reaction solvent, and tetraisopropyl titanate was used as a catalyst. The average residence time in the reactor was 50 minutes. The obtained reaction product is sent to a solvent removal tank to remove α-methylnaphthalene, and then sent to a solid deposition tank, and hexane is added to precipitate a reaction product contained in the solvent. Was. The resulting mixture is
Separation from hexane by passing through a centrifugal separator / fluidized bed drier gave a cyclic polyester oligomer. The step of producing this cyclic polyester oligomer is referred to as step 2. Note that α-methylnaphthalene used as a reaction solvent was recovered and returned to the reaction tank.

Further, the reaction product was continuously withdrawn,
Separately manufactured polyethylene terephthalate chips were mixed so that the mixing ratio was oligomer / polymer = 80/20.
It was fed to a screw extruder. Note that tetraisopropyl titanate was added as a ring-opening polymerization catalyst to the twin-screw extruder. The average residence time of this twin-screw extruder was 10 minutes, and the intrinsic viscosity of the obtained polyethylene terephthalate was 1.31. The step of producing a polyester by this ring-opening polymerization is referred to as step 3.

The average residence time required after the step 2 was 1 hour, and a polyester having a high degree of polymerization could be produced economically.

Example 2 In place of the synthesis of the linear polyester oligomer in Step 1 of Example 1, a cyclic polyester oligomer was synthesized using polyethylene terephthalate as a raw material.
3.9% by weight of unreacted material was used as a reaction solvent in step 2.
Using the contained m-terphenyl, the polymer was polymerized in the same manner as in Example 1 except that the oligomer / polymer mixing ratio in step 3 and the types of the polymer and the catalyst were changed.

The intrinsic viscosity of the obtained polymer is 1.01,
The average residence time required after step 2 was 1 hour and 50 minutes, and the polymer could be produced within a time period excellent in economy.

Example 3 A polymer was polymerized in the same manner as in Example 1 except that polybutylene terephthalate was used as a starting material and the reaction solvent, catalyst and the like were changed.

The intrinsic viscosity of the obtained polymer is 1.12,
The average residence time required after step 2 was 2 hours, and the polymer could be produced within a time period excellent in economy.

Example 4 A polymer was polymerized in the same manner as in Example 1 except that propylene glycol and terephthalic acid were used as starting materials and the reaction solvent, catalyst and the like were changed.

The intrinsic viscosity of the obtained polymer is 1.05,
The average residence time required after step 2 was 1 hour and 10 minutes, and the polymer could be produced within a time period excellent in economy.

Comparative Example Since a cyclic oligomer was synthesized using a reaction solvent containing an unreacted substance outside the present invention, the degree of polymerization of the polymer finally obtained was low.

[0052]

[Table 1]

[0053]

According to the method for producing a cyclic polyester oligomer of the present invention, a polyester having a high degree of polymerization can be obtained more economically as compared with a conventionally known production method.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J029 AA03 AB04 AC01 AC02 AC04 BA02 BA03 BA04 BA05 BA08 BA09 BA10 BD07 BF09 BF25 CA02 CA06 CB05 CB06 CB10 CC05 CD00 JB023 JB043 JF251 JF371 KE03 KE07 LA02 LA05

Claims (8)

[Claims] When producing a cyclic polyester oligomer from a linear polyester oligomer or a linear polyester obtained by subjecting a dicarboxylic acid component and a diol component to an esterification reaction, the cyclic polyester oligomer is discharged from a reactor for producing the cyclic polyester oligomer. A method for producing a cyclic polyester oligomer, wherein the unreacted substance contained in the reaction solvent is 10% by weight or less when at least a part of the reaction solvent is returned to the reaction tank and used repeatedly. 2. A linear polyester oligomer obtained by subjecting a dicarboxylic acid component and a diol component to an esterification reaction at a charged molar ratio (diol component / dicarboxylic acid component) of 1.0 to 1.6. The method for producing a cyclic polyester oligomer according to claim 1. 3. The process for producing a cyclic polyester oligomer according to claim 1, wherein the dicarboxylic acid component and the diol component are esterified by a continuous polymerization process. 4. The method for producing a cyclic polyester oligomer according to claim 1, wherein a linear polyester is used. 5. The method for producing a cyclic polyester oligomer according to claim 1, wherein the reaction solvent is a compound having 6 or more carbon atoms. 6. The method for producing a cyclic polyester oligomer according to claim 1, wherein the average degree of polymerization of the cyclic polyester oligomer is 2 to 10. 7. A process for producing a polyester by contacting the cyclic polyester oligomer according to any one of claims 1 to 6 with a catalyst for a cyclic polyester oligomer and subjecting it to ring-opening polymerization. 8. The method according to claim 7, wherein the polyester is polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate or a copolymer thereof.