WO2024204552A1

WO2024204552A1 - Polyester production method, composition, and molded article

Info

Publication number: WO2024204552A1
Application number: PCT/JP2024/012678
Authority: WO
Inventors: 博道奥村; 正樹松原
Original assignee: 三菱ケミカル株式会社
Priority date: 2023-03-29
Filing date: 2024-03-28
Publication date: 2024-10-03

Abstract

A polyester production method having a reaction step that includes at least one reaction treatment selected from the group consisting of an esterification reaction and a transesterification reaction that are for reacting a polyester starting material, wherein the polyester starting material contains a dicarboxylic acid component, an oligomer component, and a diol component that contains at least one substance selected from the group consisting of 1,4-butanediol and derivatives thereof, and the content ratio of a cyclic oligomer component in the oligomer component is 35-100% by mass.

Description

Method for producing polyester, composition and molded article

The present invention relates to a method for producing polyester, a composition, and a molded article.

　Polyesters made primarily from aliphatic diols or alicyclic diols and aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, or aromatic dicarboxylic acids, and polyesters made primarily from aliphatic oxycarboxylic acids, are biodegradable resins with good physical properties and degradability, and are processed and used in products such as agricultural materials, civil engineering materials, and packaging materials.

However, during polymerization and melt molding of the polyester, a reaction in which part of the polyester is cyclized inevitably occurs, producing cyclic oligomers as a by-product. As a result, when the polyester is molded into a product, it is known that problems such as the cyclic oligomers bleeding out onto the surface of the molded product, causing a deterioration in the surface appearance, and a significant decrease in productivity due to the need to clean molds, rolls, etc. that become contaminated during molding can occur.

To solve the above problems, it is known that after polyester polymerization, the polyester is washed by contacting it with pure water, or pure water and alcohol, or pure alcohol at a specific temperature range to prevent deterioration of the appearance of the molded product (see Patent Document 1). It is also known to perform post-treatment by contacting the polyester with a water-soluble organic solvent selected from the group consisting of ketones, ethers, and esters, and water (see Patent Document 2).

Furthermore, it is known that contacting polyester with a specific ratio of isopropanol/water mixture or ethanol/water mixture can suppress deterioration of the surface appearance of the molded body and deterioration of productivity such as mold cleaning (see Patent Documents 3 and 4).

Patent Documents

3 and 4 disclose, as a method of contacting polyester with an alcohol/water mixture (contact treatment liquid), a batch type treatment method in which pelletized polyester is placed in a treatment tank and contacted with the contact treatment liquid, and pellets are removed after contact treatment, and a continuous type treatment method in which pellets are continuously supplied to a pipe or treatment tank, and the contact treatment liquid is brought into contact with the flow of the pellets in a parallel or countercurrent manner, and the pellets are continuously removed.

Patent Document 5 discloses a manufacturing method in which oligomer components contained in aliphatic polyester pellets are separated and recovered, and then the oligomer components are used as raw materials in an amount of 5 parts by weight or less per 100 parts by weight of raw materials other than the aliphatic polyester oligomer.

Japanese Unexamined Patent Publication No. 7-316276 JP 2004-107457 A JP 2010-195989 A JP 2012-092310 A JP 2005-162891 A

Patent Document 5 describes a method for treating and reusing components such as oligomers that have been subjected to contact treatment. However, the recovered oligomer components are concentrated by evaporating organic solvent components from the used contact treatment solvent, and have not been subjected to a step of purifying the oligomer components. Therefore, when the oligomer mixture obtained by the above method is reused as a raw material to polymerize polyester, there is a problem that the addition of the recovered oligomers significantly deteriorates the color tone of the polymer.
In view of the above problems, a first object of the present invention is to provide a method for producing a polyester that can suppress deterioration in color tone of the polyester even when the amount of recycled raw material components recovered from the used contact treatment liquid in the contact treatment process is increased.

Furthermore, when the oligomer mixture obtained by the above method is reused as a raw material to polymerize polyester, there are problems in that the polymerization rate slows down as the amount added increases, resulting in a low molecular weight polymer achieved within a unit time, and that the degree of color deterioration of the polymer increases relative to the amount of recovered oligomer component added, resulting in a decrease in polymer quality, making it difficult to increase the amount of recovered oligomer component.
In view of the above problems, a second object of the present invention is to provide a method for producing polyester that can improve the productivity of polyester and suppress deterioration in color tone.

As a result of their investigations, the inventors discovered that the first problem could be solved by setting the content of cyclic oligomer components in the oligomer components contained in the polyester raw material to a specific range, and thus completed the present invention.

That is, the first aspect of the present invention resides in the following [A1] to [A15].
[A1] A method for producing a polyester, comprising a reaction step including at least one reaction treatment selected from the group consisting of an esterification reaction treatment and an ester exchange reaction treatment, in which a polyester raw material is reacted,
The polyester raw material contains a diol component, a dicarboxylic acid component, and an oligomer component,
The content of a cyclic oligomer component in the oligomer component is 35% by mass or more and 100% by mass or less,
the cyclic oligomer component comprises a constituent unit derived from the diol component and a constituent unit derived from the dicarboxylic acid component, and the total number of repeating units of the constituent units derived from the diol component and the constituent units derived from the dicarboxylic acid component is 2 to 7.
[A2] The method for producing a polyester according to [A1], wherein the diol component contains at least one selected from the group consisting of 1,4-butanediol and derivatives thereof.
[A3] The method for producing a polyester according to [A1] or [A2], wherein the content of the oligomer component in the polyester raw material is 0.1% by mass or more and less than 100% by mass.
[A4] The method further comprises a purification step including a contact treatment in which the reaction product obtained in the reaction step is contacted with a solvent containing water to obtain a contact treatment liquid containing the oligomer component and a post-contact treatment reaction product,
The oligomer component in the treatment liquid is reused as an oligomer component in the polyester raw material in the reaction step.
A method for producing the polyester according to any one of [A1] to [A3].
[A5] The method for producing a polyester according to [A4], further comprising, between the reaction step and the purification step, a pelletizing step of pelletizing the reaction product obtained in the reaction step to obtain pellets.
[A6] The method further includes a raw material preparation step of preparing the polyester raw material before the reaction step,
The method for producing a polyester according to any one of [A1] to [A5], wherein an oligomer component in the contact treatment liquid is supplied to any one of the steps from the raw material preparation step to the reaction step.
[A7] The method further comprises a drying step of drying the reaction product after the contact treatment.
A method for producing the polyester according to any one of [A1] to [A6].
[A8] The method for producing a polyester according to [A7], wherein at least one treatment selected from the group consisting of a contact treatment in the purification step and a drying treatment in the drying step is carried out continuously.
[A9] The method for producing a polyester according to any one of [A1] to [A7], wherein the cyclic oligomer component has a structure represented by the following formula (1) and a structure represented by the following formula (2):

In formula (1), R ¹ and R ² each independently represent a divalent hydrocarbon group which may have a substituent; x is an integer of 0 to 7;
In formula (2), R ³ and R ⁴ each independently represent a divalent hydrocarbon group which may have a substituent; y is an integer of 0 to 7;
x+y is 2 to 7.
[A10] The method for producing a polyester according to [A9], wherein R ¹ to R ⁴ each independently represent a divalent hydrocarbon group having 2 to 40 carbon atoms which may have a substituent.
[A11] The polyester raw material is
The dicarboxylic acid component includes at least one selected from the group consisting of dicarboxylic acids represented by the following formula (A) and derivatives thereof, and at least one selected from the group consisting of dicarboxylic acids represented by the following formula (B) and derivatives thereof:
The diol component includes at least one selected from the group consisting of diols represented by the following formula (C) and derivatives thereof, and at least one selected from the group consisting of diols represented by the following formula (D) and derivatives thereof:
At least one kind selected from the group consisting of at least one kind selected from the group consisting of diols represented by the following formula (C) and at least one kind selected from the group consisting of diols represented by the following formula (D) is at least one kind selected from the group consisting of 1,4-butanediol and derivatives thereof:
A method for producing the polyester according to [A9] or [A10].

(In formulas (A) to (D), R ¹ to R ⁴ have the same meanings as R ¹ to R ⁴ in formula (1), respectively.)
[A12] The method for producing a polyester according to any one of [A1] to [A11], wherein at least one treatment selected from the group consisting of a contact treatment in the purification step and a drying treatment in the drying step is carried out in a batchwise or semi-batchwise manner.
[A13] A composition comprising a polyester containing a constitutional unit derived from a diol component and a constitutional unit derived from a dicarboxylic acid component, and a cyclic oligomer component having a structure represented by the following formula (1) and a structure represented by the following formula (2).

In formula (1), R ¹ and R ² each independently represent a divalent hydrocarbon group which may have a substituent; x is an integer of 0 to 7;
In formula (2), R ³ and R ⁴ each independently represent a divalent hydrocarbon group which may have a substituent; y is an integer of 0 to 7;
x+y is 2 to 7.
[A14] The composition according to [A13], wherein the polyester contains a constitutional unit derived from the cyclic oligomer component.
[A15] A molded article obtained by molding the composition according to [A13] or [A14].

Furthermore, as a result of further investigations, the inventors have investigated a process for purifying a contact treatment liquid containing oligomer components obtained in a contact treatment in the production of polyester, and have found that the second problem can be solved by recovering the oligomer components obtained in the process for reuse as part of the raw material, thus completing the present invention.

That is, the second aspect of the present invention resides in the following [B1] to [B8].
[B1] a reaction step of obtaining a reaction product by a reaction treatment including at least one treatment selected from the group consisting of an esterification reaction treatment and a transesterification reaction treatment of a polyester raw material containing a diol component and a dicarboxylic acid component;
a contact treatment step of contacting the reaction product with a contact treatment liquid to obtain a contact treatment liquid containing an oligomer component and a post-contact treatment reaction product;
a purification step including a treatment for purifying the oligomer components in the contact treatment liquid so that a content ratio of cyclic oligomer components in the oligomer components is increased from the contact treatment liquid containing the oligomer components; and a recovery step for recovering the oligomer components obtained by the purification step as part of the raw material.
A method for producing polyester.
[B2] The method for producing a polyester according to [B1], wherein the purification step includes a distillation separation treatment for separating a low boiling liquid from a high boiling liquid containing the oligomer components.
[B3] The method for producing a polyester according to [B2], further comprising a phase separation treatment for separating the oligomer component from the high-boiling liquid by performing a liquid/liquid phase separation treatment.
[B4] The method for producing the polyester according to [B3], further comprising a crystallization treatment for further crystallizing the oligomer component separated by the phase separation treatment.
[B5] The method for producing the polyester according to [B2], further comprising a crystallization treatment for crystallizing an oligomer component contained in the high boiling liquid.
[B6] The method for producing a polyester according to any one of [B1] to [B5], further comprising, between the reaction step and the contact treatment step, a pelletizing step of pelletizing the reaction product obtained in the reaction step to obtain polyester pellets.
[B7] The method further includes a raw material preparation step of preparing the raw material before the reaction step,
The method further includes a supplying step of supplying, after the recovery step, a melt obtained by melting the recovered oligomer component or a solution obtained by dissolving the oligomer component in a diol component of the polyester raw material to any one of the steps from the raw material preparation step to the reaction step.
A method for producing the polyester according to any one of [B1] to [B6].
[B8] The method for producing a polyester according to any one of [B1] to [B7], wherein the contact treatment liquid contains an alcohol.
[B9] The method for producing a polyester according to any one of [B1] to [B8], further comprising, after the contact treatment step, a drying step of carrying out a drying treatment to dry the reaction product after the contact treatment.
[B10] The method for producing a polyester according to any one of [B1] to [B9], wherein at least one treatment selected from the group consisting of a contact treatment in the contact treatment step and a drying treatment in the drying step is carried out continuously.
[B11] The method for producing a polyester according to any one of [B1] to [B10], wherein at least one treatment selected from the group consisting of a contact treatment in the contact treatment step and a drying treatment in the drying step is carried out in a batchwise or semi-batchwise manner.

The first aspect of the present invention provides a method for producing polyester that can suppress deterioration of the color tone of polyester even when the amount of recycled raw material components recovered from the used contact treatment liquid in the contact treatment process is increased.

The second aspect of the present invention can provide a method for producing polyester that can improve polyester productivity and suppress color deterioration. For example, when oligomer components in a contact treatment solution obtained in polyester production are reused as raw materials for polymerization, even if the amount of recovered oligomer components is increased, there is little decrease in polymerization reactivity and little deterioration in polymer color, so production efficiency and raw material unit consumption are improved, and a polyester of good quality can be provided.

FIG. 1 is a schematic diagram showing one embodiment of an esterification reaction process. FIG. 1 is a schematic diagram illustrating one embodiment of a polycondensation reaction process. FIG. 2 is a schematic diagram showing one embodiment of the contacting treatment and separation treatment in the first aspect, or the contacting treatment step and purification step in the second aspect. FIG. 2 is a schematic diagram showing one embodiment of a drying process.

The present invention is not limited to the following description, and can be modified as desired without departing from the scope of the present invention. In this specification, when "~" is used to express a numerical value or physical property value between the two, the lower limit and upper limit values, which are the endpoints, are included.
In addition, in this specification, the expression "A or B" can be read as "at least one selected from the group consisting of A and B."
In addition, although a number of embodiments are described in this specification, various conditions in each embodiment may be applied to each other to the extent that they are applicable.

In this specification, "mass %", "ppm by mass", and "parts by mass" are synonymous with "weight %", "ppm by weight", and "parts by weight".

<First aspect>
<Production method of polyester>
A first aspect of a method for producing a polyester according to one embodiment of the present invention (hereinafter, in the section on the first aspect, also simply referred to as a "method for producing a polyester") comprises:
A method for producing a polyester, comprising a reaction step including at least one reaction treatment selected from the group consisting of an esterification reaction treatment and an ester exchange reaction treatment, in which a polyester raw material is reacted,
The polyester raw material contains a diol component, a dicarboxylic acid component, and an oligomer component,
The content of a cyclic oligomer component in the oligomer component is 35% by mass or more and 100% by mass or less,
In the method for producing a polyester, the cyclic oligomer component contains a constituent unit derived from the diol component and a constituent unit derived from the dicarboxylic acid component, and the total number of repeating units of the constituent units derived from the diol component and the constituent units derived from the dicarboxylic acid component is 2 to 7.

[Raw material polyester]
The raw material polyester is not particularly limited as long as it contains a diol component, a dicarboxylic acid component, and an oligomer component, and may contain components other than these components.

(Diol component)
The diol component may be any diol component that is usually used as a raw material for polyesters without any particular limitation. The diol component may be an aliphatic diol component or an aromatic diol component.

Examples of aliphatic diol components include alkylene diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, and neopentyl glycol; oxyalkylene diols such as diethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol; and cycloalkylene diols such as 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol. Among these, alkylene diols having 6 or less carbon atoms, such as ethylene glycol or 1,3-propanediol, and cycloalkylene diols having 6 or less carbon atoms, such as 1,4-cyclohexanedimethanol, are preferred in terms of the physical properties of the resulting polyester. These aliphatic diol components may or may not be derivatives.

In particular, since the diol component can be derived from biomass (plant raw material), it is preferable that the diol component contains at least one selected from the group consisting of 1,4-butanediol and its derivatives, that is, the diol component contains at least one selected from the group consisting of 1,4-butanediol and its derivatives. The embodiment of the derivative is not particularly limited as long as it is capable of producing a polyester.
The polyester raw material may contain a diol component containing at least one selected from the group consisting of the above-mentioned 1,4-butanediol and its derivatives, or may contain other diol components.

Examples of aromatic diol components include xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis(4'-hydroxyphenyl)propane, 2,2-bis(4'-β-hydroxyethoxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, bis(4-β-hydroxyethoxyphenyl)sulfonic acid, etc. These aromatic diol components may or may not be derivatives.

The above aliphatic diol compounds and/or aromatic diol compounds may be compounds having a structure in which one or more types are mutually dehydrated and condensed.

The above aliphatic diol component and/or aromatic diol component may be used alone or in combination of two or more types.

The total content of all diol components in the polyester raw material is not particularly limited, and may be, for example, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, and 70% by mass or less, 60% by mass or less, or 50% by mass or less.

When 1,4-butanediol is used, the amount used is preferably 50 mol% or more, more preferably 70 mol% or more, and particularly preferably 90 mol% or more, based on 100 mol% of all diol components in the polyester raw material, from the viewpoints of the melting point (heat resistance), biodegradability, and mechanical properties of the resulting polyester.

Furthermore, ethylene glycol, 1,3-propanediol, 1,4-butanediol, etc., derived from plant materials can be used.

(Dicarboxylic acid component)
The dicarboxylic acid component may be any dicarboxylic acid normally used as a raw material for polyesters without any particular limitation. The type of dicarboxylic acid component is not particularly limited, and examples thereof include the following aliphatic dicarboxylic acid components and aromatic dicarboxylic acid components.

Examples of the aliphatic dicarboxylic acid component include aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, succinic anhydride, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecadicarboxylic acid, dodecadicarboxylic acid, maleic acid, fumaric acid, and dimer acid. Among these, aliphatic dicarboxylic acids such as succinic acid, succinic anhydride, adipic acid, and sebacic acid are preferred in terms of the physical properties of the resulting polyester. In particular, aliphatic dicarboxylic acids having 4 or less carbon atoms, such as succinic acid or succinic anhydride, are preferred. These aliphatic dicarboxylic acid components may or may not be derivatives thereof.

Examples of aromatic dicarboxylic acid components include phthalic acid, isophthalic acid, dibromoisophthalic acid, sulfoisophthalic acid, 1,4-phenylenedioxydicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-diphenylketonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, hexahydrophthalic acid, hexahydroisophthalic acid, and hexahydroterephthalic acid. These aromatic dicarboxylic acid components may or may not be derivatives. For example, derivatives of the aromatic dicarboxylic acid components listed above are preferred, and among these, lower alkyl esters having 1 to 4 carbon atoms, or acid anhydrides, etc. are included. Specific examples of derivatives of aromatic dicarboxylic acid compounds include lower alkyl esters such as methyl esters, ethyl esters, propyl esters, and butyl esters of the aromatic dicarboxylic acid components exemplified above; and cyclic acid anhydrides of the aromatic dicarboxylic acid components exemplified above, such as succinic anhydride.

The above aliphatic dicarboxylic acid components and/or aromatic dicarboxylic acid components may be used alone or in combination of two or more types.

The total content of all dicarboxylic acid components in the polyester raw material is not particularly limited, and may be, for example, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, and 70% by mass or less, 65% by mass or less, or 60% by mass or less.

When succinic acid is used as the dicarboxylic acid component, the amount of succinic acid used is preferably 50 mol% or more, more preferably 70 mol% or more, and particularly preferably 90 mol% or more, based on 100 mol% of all dicarboxylic acid components in the polyester raw material, from the viewpoints of the melting point (heat resistance), biodegradability, and mechanical properties of the resulting polyester.

Succinic acid, succinic anhydride, or adipic acid, etc., can be derived from plant materials.

(Oligomer Component)
In the polyester production process, when a technology for reusing raw material components contained in the contact treatment liquid obtained in the contact treatment process after the polymerization reaction is adopted, the contact treatment liquid usually contains an oligomer component (ester oligomer component). The oligomer component may contain a constituent unit derived from a diol component constituting a polyester and a constituent unit derived from a polycarboxylic acid component constituting a dicarboxylic acid, but may be composed of only these constituent units. When the contact treatment is performed without any special treatment or when a conventional treatment (for example, simple distillation of the solvent) is performed, the oligomer components in the contact treatment liquid usually contain more oligomer components having a linear structure or a branched structure without a cyclic structure. Specifically, the amount of oligomer components having a linear structure or a branched structure without a cyclic structure relative to the amount of all oligomer components in the contact treatment liquid usually exceeds 65 mass%.
When the contact treatment liquid containing the above-mentioned oligomer components is reused as a raw material, the production amount of the polymer can be increased, but there arises a problem that the color tone of the final polymer obtained is worse than that when the contact treatment liquid is not reused.
As a result of extensive research, the inventors have found that even when the raw material components in the used contact treatment liquid of the contact treatment process are reused, deterioration in the color tone of the final polyester can be suppressed by setting the conditions of the oligomer components in the recycled polyester raw material within a desired range (the range described above).

In this specification, the cyclic oligomer component is a cyclic ester oligomer component that includes a constituent unit derived from the above-mentioned diol component and a constituent unit derived from the above-mentioned dicarboxylic acid component, and the total number of the constituent units derived from the diol component (the number of repeating units of the constituent unit) and the number of the constituent units derived from the dicarboxylic acid component (the number of repeating units of the constituent unit) is 2 to 7. The cyclic oligomer component is a compound that is produced as a by-product by cyclization of a part of a polyester obtained through a reaction process including at least one reaction process selected from the group consisting of an esterification reaction process and an ester exchange reaction process in which a diol component and a dicarboxylic acid component are reacted. The cyclic oligomer component may include the constituent units derived from the above-mentioned diol component and the constituent units derived from the above-mentioned dicarboxylic acid component, but may be composed of only these constituent units. If the content of the oligomer component in the reaction product increases, the color tone of the polyester will deteriorate, the surface appearance will deteriorate, and the productivity during molding will decrease. However, by setting the amount of the cyclic oligomer component in the polyester raw material to a desired range, the degree of the deterioration of the color tone of the polyester, the deterioration of the surface appearance, and the decrease in the productivity during molding can be reduced. The cyclic oligomer component may be one type or two or more types, and all cyclic ester oligomer components that satisfy the above conditions are included. In other words, when the above cyclic oligomers from dimer to heptamer are included, all of these cyclic oligomers are treated as the cyclic oligomer component.
The cyclic oligomer component may contain a constituent unit derived from the diol component and a constituent unit derived from the dicarboxylic acid component, but may be composed of only these constituent units.
The cyclic oligomer component may have, for example, a structure represented by the following formula (1) and a structure represented by the following formula (2).

In formula (1), R ¹ and R ² each independently represent a divalent hydrocarbon group which may have a substituent; x is an integer of 0 to 7;
In formula (2), R ³ and R ⁴ each independently represent a divalent hydrocarbon group which may have a substituent; y is an integer of 0 to 7;
x+y is 2 to 7.

The embodiment of the divalent hydrocarbon in ^R1 and ^R2 is not particularly limited, and the number of carbon atoms therein is, from the viewpoint of acquisition cost and ease of availability, independently 1 or more, particularly preferably 2 or more, and usually 40 or less, preferably 36 or less, more preferably 30 or less, even more preferably 24 or less, particularly preferably 20 or less, and most particularly preferably 18 or less.

The embodiment of the divalent hydrocarbon in ^R3 and ^R4 is not particularly limited, and the number of carbon atoms therein is, from the viewpoint of acquisition cost and ease of availability, independently 1 or more, particularly preferably 2 or more, and usually 40 or less, preferably 36 or less, more preferably 30 or less, even more preferably 24 or less, particularly preferably 20 or less, and most particularly preferably 18 or less.

The substituents that R ¹ to R ⁴ may have are not particularly limited, and examples thereof include halogen, cyano group, amino group, ester group, alkylcarbonyl group, acetyl group, silyl group, boryl group, nitrile group, thio group, seleno group, etc. These substituents may be of only one type or of two or more types, and the hydrocarbon groups in R ¹ to R ⁴ may not have any substituents.

The diol component and dicarboxylic acid component constituting the above formula (1) and (2) may be the diol component and dicarboxylic acid component that are the raw materials of the above polyester. Therefore, R ¹ and R ³ in the above formula (1) and (2) may each independently be a structure corresponding to the dicarboxylic acid listed in the above dicarboxylic acid, and R ² and R ⁴ may each independently be a structure corresponding to the diol listed in the above diol.

If x is 0 to 7, the solubility in the contact treatment solution is good, and the contact treatment efficiency and recovery of the oligomer components from the polyester pellets are excellent.

If y is 0 to 7, the solubility in the contact treatment solution is good, and the contact treatment efficiency and recovery of the oligomer components from the polyester pellets are excellent.

The hydrocarbon group in R ¹ to R ⁴ may be linear, branched, or have a cyclic structure, but is preferably linear from the viewpoints of the melting point of the oligomer component, the solubility in the contact treatment liquid, and the polymerization reactivity of the recovered oligomer component.
Furthermore, the hydrocarbon groups in R ¹ to R ⁴ may be either aliphatic hydrocarbon groups or aromatic hydrocarbon groups.

The content of oligomer components in the polyester raw material is not particularly limited, but is usually 0.1 mass% or more, preferably 0.5 mass% or more, more preferably 1.0 mass% or more, even more preferably 2.5 mass% or more, and particularly preferably more than 5.0 mass%, and is usually less than 100 mass%, preferably 90 mass% or less, more preferably 80 mass% or less, even more preferably 70 mass% or less, and particularly preferably 60 mass% or less.
When the total content is equal to or higher than the lower limit of the range, it is possible to perform economical production with an increased recovery rate of the oligomer components, while when the total content is equal to or lower than the upper limit of the range, it is possible to perform production without impairing reactivity while maintaining quality such as color tone.

The content (total content) of the cyclic oligomer components having the structure represented by the above formula (1) and the structure represented by the above formula (2) in the oligomer component is not particularly limited as long as it is 35% by mass or more and 100% by mass or less, from the viewpoint of suppressing deterioration in the color tone of the resulting polyester, but is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

From the viewpoint of easily suppressing the deterioration of the color tone of the polyester, the above-mentioned cyclic oligomer component is preferably generated by a reaction with a diol component and a dicarboxylic acid component contained in the polymer raw material. In other words, when the cyclic oligomer component has a structure represented by the above formula (1) and a structure represented by the following formula (2), the polyester raw material is
The dicarboxylic acid component includes at least one selected from the group consisting of dicarboxylic acids represented by the following formula (A) and derivatives thereof, and at least one selected from the group consisting of dicarboxylic acids represented by the following formula (B) and derivatives thereof,
The diol component preferably contains at least one selected from the group consisting of diols represented by the following formula (C) and derivatives thereof, and at least one selected from the group consisting of diols represented by the following formula (D) and derivatives thereof:
In particular, when the diol component contains at least one kind selected from the group consisting of 1,4-butanediol and derivatives thereof, it is preferable that the at least one kind selected from the group consisting of at least one kind selected from the group consisting of diols represented by the following formula (C) and at least one kind selected from the group consisting of diols represented by the following formula (D) is at least one kind selected from the group consisting of 1,4-butanediol and derivatives thereof.

In formulas (A) to (D), R ¹ to R ⁴ have the same meanings as R ¹ to R ⁴ in formulas (1) and (2) above, respectively.

When the purification process described below is employed, the oligomer components obtained by the contact treatment are recovered, and the recovered oligomer components are reused as polyester raw materials, the diol components and dicarboxylic acid components in the polyester raw materials are the same as the oligomer components and dicarboxylic acid components constituting the cyclic oligomer components in the polyester raw materials, and therefore the content of the cyclic oligomer components having the structure represented by the above formula (1) and the structure represented by the above formula (2) in the oligomer components in the polyester raw materials can be increased.

(Other Copolymer Components)
In the method for producing polyester, as long as at least a diol component and a dicarboxylic acid component are used, other components may be copolymerized. Examples of copolymerization components that can be used in this case include oxycarboxylic acids such as lactic acid, glycolic acid, hydroxybutyric acid, hydroxycaproic acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-hydroxyisocaproic acid, malic acid, and citric acid; esters, lactones, and oxycarboxylic acid polymers of these oxycarboxylic acids; trifunctional or higher polyhydric alcohols such as glycerin, trimethylolpropane, and pentaerythritol; and trifunctional or higher polyvalent carboxylic acids or their anhydrides such as propanetricarboxylic acid, pyromellitic acid, and trimellitic acid, benzophenonetetracarboxylic acid, and their anhydrides.

In addition, by adding a small amount of trifunctional or higher oxycarboxylic acid, trifunctional or higher alcohol, or trifunctional or higher carboxylic acid, it is easy to obtain a polyester with high viscosity. Among them, oxycarboxylic acid such as malic acid or citric acid is preferred, and malic acid is particularly preferred.

The amount of the trifunctional or higher polyfunctional compound is preferably 0.001 to 5 mol %, and more preferably 0.05 to 0.5 mol %, relative to 100 mol % of all dicarboxylic acid components in the polyester raw material. If the amount exceeds the upper limit of this range, gel (unmelted material) is likely to form in the resulting polyester, and if it is below the lower limit, the advantage of using a polyfunctional compound (usually the advantage of being able to increase the viscosity of the resulting polyester) is difficult to obtain.

[Physical properties of polyester]
The intrinsic viscosity (IV, dL/g) of the polyester to be contacted with the contact treatment liquid and the intrinsic viscosity of the polyester after contact treatment with the contact treatment liquid are preferably 1.4 dL/g or more, and particularly preferably 1.6 dL/g or more. The intrinsic viscosity is preferably 2.8 dL/g or less, more preferably 2.5 or less, and particularly preferably 2.3 dL/g or less. If the intrinsic viscosity is below the lower limit of the above range, it is difficult to obtain sufficient mechanical strength when molded into a molded product. If the intrinsic viscosity exceeds the upper limit of the above range, the melt viscosity during molding is high and molding is difficult.

The amount of terminal carboxyl groups in the polyester to be brought into contact with the contact treatment solution is usually 80 (equivalents/ton) or less, preferably 60 (equivalents/ton) or less, more preferably 40 (equivalents/ton) or less, and particularly preferably 25 (equivalents/ton) or less. The lower the lower limit, the better the thermal stability and hydrolysis resistance, but it is usually 5 (equivalents/ton) or more. If the upper limit is exceeded, the viscosity reduction due to hydrolysis becomes significant, and the quality may be significantly impaired.

[Each step in the polyester manufacturing method]
Each step in the first embodiment of the method for producing a polyester will be described below using a continuous production method as an example, but this is merely an example, and the method for producing a polyester is not limited to this embodiment.
In the continuous polyester production method, for example, a diol component and a dicarboxylic acid component are continuously subjected to a reaction process including at least one treatment selected from the group consisting of an esterification reaction treatment and an ester exchange reaction treatment, and a polycondensation reaction treatment, using a plurality of continuous reaction tanks to obtain a polyester. However, the method is not limited to the continuous method, and any step in a conventional polyester production method can be adopted, so long as it does not impede the effects of the present invention. Furthermore, the polyester may be subjected to a contact treatment with a contact treatment liquid and then dried.
When a continuous operation is employed, from the viewpoints of production efficiency and uniformity of the treatment, it is particularly preferred that at least one treatment selected from the group consisting of a contact treatment in the purification step described below and a drying treatment in the drying step described below is carried out continuously. Also, with respect to a batch or semi-batch operation, it is particularly preferred that at least one treatment selected from the group consisting of a contact treatment in the purification step described below and a drying treatment in the drying step described below is carried out batch or semi-batch, from the viewpoints of production efficiency and uniformity of the treatment.

(Raw material preparation process)
The method for producing a polyester may further include a raw material preparation step of preparing a polyester raw material prior to the reaction step described below.
The method for preparing the polyester raw material is not particularly limited, and the raw material may be prepared by mixing raw materials produced by synthesis or the like, or the raw materials may be procured commercially and mixed.

(Reaction step)
The method for producing a polyester has a reaction step including at least one reaction treatment selected from the group consisting of an esterification reaction treatment and an ester exchange reaction treatment (also referred to herein as "esterification reaction treatment and/or ester exchange treatment") in which a polyester raw material is reacted to obtain a reaction product. The reaction step may include treatments other than the esterification reaction treatment and/or the ester exchange reaction treatment.

(1) Esterification reaction process/ester exchange reaction process The reaction process includes an esterification reaction process and/or an ester exchange reaction process in which a polyester raw material is reacted, specifically, an esterification reaction process and/or an ester exchange reaction process in which a diol component is reacted with a dicarboxylic acid component. The esterification reaction is a reaction in which a carboxylic acid is converted into an ester, and the ester exchange reaction is a reaction in which an ester is reacted with an alcohol to exchange the main chain portions of these. The esterification reaction process will be described below, but this description can be applied to the ester exchange reaction as well to the extent that it is applicable.
The esterification reaction treatment and/or ester exchange treatment and other subsequent treatments can be carried out in multiple continuous reaction tanks or in a single reaction tank. However, in order to reduce variation in the physical properties of the resulting polyester, it is preferable to carry out the treatments in multiple continuous reaction tanks.

There are no particular limitations on the reaction temperature in the esterification reaction treatment, so long as it is a temperature at which the esterification reaction can be carried out, but in order to increase the reaction rate, it is preferably 200°C or higher, and more preferably 210°C or higher, and in order to prevent discoloration of the polyester, it is preferably 250°C or lower, more preferably 245°C or lower, and particularly preferably 240°C or lower.

If the reaction temperature is too low, the esterification reaction rate is slow, requiring a long reaction time, and undesirable reactions such as dehydration decomposition of the diol component occur frequently. If the reaction temperature is too high, decomposition of the diol component and dicarboxylic acid component increases, and the amount of scattered material in the reaction tank increases, which can easily cause the generation of foreign matter and can easily cause turbidity (haze) in the reaction product. It is also preferable that the esterification temperature is a constant temperature. A constant temperature stabilizes the esterification rate. The constant temperature may be within ±5°C of the set temperature, and is preferably ±2°C.

The reaction atmosphere is not particularly limited, but is preferably an inert gas atmosphere such as nitrogen or argon, etc. The reaction pressure is preferably 50 kPa to 200 kPa, more preferably 60 kPa or more, and even more preferably 70 kPa or more, and is preferably 130 kPa or less, and more preferably 110 kPa or less.
If the reaction pressure is less than the lower limit of the above range, the amount of scattered material in the reaction tank increases, the haze of the reaction product increases, and this tends to cause an increase in foreign matter, and the diol component is more likely to be distilled out of the reaction system, which tends to decrease the polycondensation reaction rate.If the reaction pressure is more than the upper limit of the above range, the dehydration decomposition of the diol component increases, which tends to decrease the polycondensation reaction rate.

The reaction time is not particularly limited, but is preferably 1 hour or more, and is preferably 10 hours or less, and more preferably 4 hours or less.

The molar ratio of the diol component to the dicarboxylic acid component undergoing the esterification reaction (diol component/dicarboxylic acid component) represents the molar ratio of the "diol component and esterified diol component present in the gas phase and reaction liquid phase of the esterification reaction vessel" to the "all dicarboxylic acid components and esterified dicarboxylic acid components present in the gas phase and reaction liquid phase of the esterification reaction vessel", and does not include the dicarboxylic acid components, diol components, and their decomposition products that are decomposed in the reaction system and do not contribute to the esterification reaction. For example, in the case where 1,4-butanediol is included as a diol component, the diol component is formed by decomposing 1,4-butanediol into tetrahydrofuran, and such non-contributing components are not included in the above molar ratio.

The molar ratio is usually 1.10 or more, preferably 1.12 or more, more preferably 1.15 or more, and particularly preferably 1.20 or more. The molar ratio is usually 2.00 or less, preferably 1.80 or less, more preferably 1.60 or less, and particularly preferably 1.55 or less.
If the molar ratio is less than the lower limit of the above range, the esterification reaction is likely to be insufficient, and the polycondensation reaction, which is a reaction in a subsequent step, is unlikely to proceed, making it difficult to obtain a polyester with a high degree of polymerization. If the molar ratio is more than the upper limit of the above range, the decomposition amounts of the diol component and the dicarboxylic acid component tend to increase. In order to keep this molar ratio within the preferred range, it is a preferred method to appropriately supply the diol component to the esterification reaction system.

When the reaction step includes a polycondensation reaction treatment described later, it is preferable to subject an esterification reaction product having an esterification rate of 80% or more to the polycondensation reaction treatment. The polycondensation reaction generally refers to a high molecular weight reaction of polyester carried out at a reaction pressure of 50 kPa or less. The esterification reaction is generally carried out at 50 to 200 kPa and is preferably carried out in an esterification reaction tank, and the polycondensation reaction is generally carried out at 50 kPa or less, preferably 10 kPa or less, and is preferably carried out in a polycondensation reaction tank. In this specification, the esterification rate indicates the ratio of esterified dicarboxylic acid components to all dicarboxylic acid components in the polyester raw material and is represented by the following formula.
Esterification rate (%)=(saponification value−acid value)/saponification value×100

The esterification rate of the esterification reaction product is preferably 85% or more, more preferably 88% or more, and particularly preferably 90% or more. Below this lower limit, the polycondensation reactivity, which is the reaction in the subsequent process, is poor. Also, below this lower limit, the amount of flying material during the polycondensation reaction increases, adheres to the wall surfaces and solidifies, and this flying material falls into the reaction product, causing a deterioration in haze (generation of foreign matter). The upper limit of the esterification rate is preferably high for the polycondensation reaction, which is the reaction in the subsequent process, but is usually 99%.

In the reaction process, it is preferable to carry out a continuous reaction in the esterification reaction treatment with the molar ratio of the dicarboxylic acid component to the diol component, the reaction temperature, the reaction pressure, and the reaction rate in the above-mentioned ranges, and more preferably, to continuously subject the reaction to the polycondensation reaction described below, thereby efficiently obtaining a high-quality polyester with low haze and little foreign matter.

(2) Polycondensation Reaction Treatment The reaction step preferably includes a polycondensation reaction treatment in which a polycondensation reaction is carried out following the esterification reaction treatment. The polycondensation reaction can be carried out under reduced pressure using a plurality of continuous reaction tanks.

The reaction pressure in the polycondensation reaction tank (particularly the final polycondensation reaction tank) is not particularly limited, but is usually 0.01 kPa or more, preferably 0.03 kPa or more, and usually 5 kPa or less, preferably 3 kPa or less.
If the pressure during the polycondensation reaction is too high, the polycondensation time becomes long, which leads to a decrease in molecular weight and coloration due to thermal decomposition of the polyester, and it tends to become difficult to produce a polyester that exhibits sufficient properties for practical use.
On the other hand, a production method using an ultra-high vacuum polycondensation reaction facility with a reaction pressure of less than 0.01 kPa is a preferable embodiment from the viewpoint of improving the polycondensation reaction rate, but is economically disadvantageous because it requires an extremely expensive capital investment.

The reaction temperature is not particularly limited, but is usually 215°C or higher, preferably 220°C or higher, and usually 270°C or lower, preferably 260°C or lower. If the reaction temperature is below the lower limit of the above range, not only will the polycondensation reaction rate be slow, and it will take a long time to produce a polyester with a high degree of polymerization, but a high-power mixer will also be required, which is economically disadvantageous. On the other hand, if the reaction temperature exceeds the upper limit of the above range, thermal decomposition of the polyester during production is likely to occur, and it will tend to be difficult to produce a polyester with a high degree of polymerization.

The reaction time is not particularly limited, but is usually 1 hour or more and usually 15 hours or less, preferably 10 hours or less, and more preferably 8 hours or less. If the reaction time is too short, the reaction will be insufficient, making it difficult to obtain a polyester with a high degree of polymerization, and the mechanical properties of the molded product will tend to be poor. On the other hand, if the reaction time is too long, the molecular weight will decrease significantly due to thermal decomposition of the polyester, and not only will the mechanical properties of the molded product tend to be poor, but the amount of carboxyl group terminals, which has a negative effect on the durability of the polyester, may increase due to thermal decomposition.

By controlling the temperature, time, and reaction pressure of the polycondensation reaction within the above ranges, a polyester with the desired intrinsic viscosity can be obtained.

(3) Reaction catalyst The esterification reaction and polycondensation reaction are accelerated by using a reaction catalyst. In the esterification reaction, a sufficient reaction rate can be obtained even without an esterification reaction catalyst. In addition, if an esterification reaction catalyst is present during the esterification reaction, the catalyst may produce insoluble precipitates in the reaction product due to water produced by the esterification reaction, which may impair the transparency of the polyester obtained (i.e., increase the haze) and may become a foreign substance, so it is preferable not to add a reaction catalyst during the esterification reaction. In addition, if a catalyst is added to the gas phase of the reaction tank, the haze of the polyester obtained may increase and the catalyst may become a foreign substance, so it is preferable to add the catalyst to the reaction liquid.

　Polycondensation reactions do not proceed easily without a catalyst, so it is preferable to use a catalyst. Generally, a compound containing at least one of the metal elements of Groups 1 to 14 of the Periodic Table is used as a polycondensation reaction catalyst. Specific examples of metal elements include scandium, yttrium, samarium, titanium, zirconium, vanadium, chromium, molybdenum, tungsten, tin, antimony, cerium, germanium, zinc, cobalt, manganese, iron, aluminum, magnesium, calcium, strontium, sodium, and potassium. Among these, scandium, yttrium, titanium, zirconium, vanadium, molybdenum, tungsten, zinc, iron, and germanium are preferred, and titanium, zirconium, tungsten, iron, and germanium are particularly preferred.

Furthermore, in order to reduce the polyester end concentration that affects the thermal stability of the polyester, among the above metals, metal elements in Groups 3 to 6 of the periodic table that exhibit Lewis acidity are preferred. Specifically, these are scandium, titanium, zirconium, vanadium, molybdenum, or tungsten, with titanium and zirconium being particularly preferred due to their ease of availability, and titanium being even more preferred in terms of reaction activity.

In this embodiment, the catalyst preferably used is a compound containing an organic group, such as a carboxylate, an alkoxy salt, an organic sulfonate, or a β-diketonate salt, containing the above metal element; or an inorganic compound, such as an oxide or halide of the above metal element, or a mixture thereof.

In this embodiment, the catalyst is preferably a compound that is liquid during polymerization or dissolves in the ester oligomer or polyester, because the polymerization rate increases when the catalyst is in a molten or dissolved state during polymerization. In addition, the polycondensation reaction is preferably performed without a solvent, but a small amount of solvent may be used separately to dissolve the catalyst. Examples of the solvent for dissolving the catalyst include alcohols such as methanol, ethanol, isopropanol, or butanol, the above-mentioned diols such as ethylene glycol, butanediol, or pentanediol, ethers such as diethyl ether or tetrahydrofuran, nitriles such as acetonitrile, hydrocarbon compounds such as heptane or toluene, water, or mixtures thereof, and the amount used is such that the catalyst concentration in the polyester raw material is usually 0.0001% by mass or more and 99% by mass or less. In order to dissolve the catalyst, the catalyst can be diluted with diols such as 1,4-butanediol or ethylene glycol, and in this case, the diols can also function as raw materials for polyester. Therefore, when diols are used as a solvent for dissolving the catalyst, the amount of the diol component in the raw material is calculated in this specification as including the amount of the diols as the solvent.

The titanium compound is preferably a tetraalkyl titanate or a hydrolyzate thereof, and specific examples include tetra-n-propyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetra-t-butyl titanate, tetraphenyl titanate, tetracyclohexyl titanate, tetrabenzyl titanate, mixed titanates thereof, or hydrolyzates thereof.

Furthermore, examples of titanium compounds that are preferably used include titanium (oxy)acetylacetonate, titanium tetraacetylacetonate, titanium (diisopropoxide)acetylacetonate, titanium bis(ammonium lactate)dihydroxide, titanium bis(ethylacetoacetate)diisopropoxide, titanium (triethanolamine)isopropoxide, polyhydroxytitanium stearate, titanium lactate, titanium triethanolamine, and butyl titanate dimer.

Also, as titanium compounds, liquids obtained by mixing alcohol, Group 2 metal compounds in the long-form periodic table (Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005) (hereinafter sometimes referred to as Group 2 metal compounds in the long-form periodic table), phosphate compounds, or titanium compounds can also be used.

Among these, tetra-n-propyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, titanium (oxy) acetylacetonate, titanium tetraacetylacetonate, titanium bis(ammonium lactate) dihydroxide, polyhydroxytitanium stearate, titanium lactate, butyl titanate dimer, or liquids obtained by mixing alcohols, Group 2 metal compounds in the long periodic table, phosphate ester compounds, and/or titanium compounds are preferred, and ... More preferred are liquids obtained by mixing cetyl acetonate, polyhydroxy titanium stearate, titanium lactate, butyl titanate dimer, alcohols, a Group 2 metal compound in the long periodic table, a phosphate ester compound, and/or a titanium compound, and particularly preferred are liquids obtained by mixing tetra-n-butyl titanate, polyhydroxy titanium stearate, titanium (oxy) acetylacetonate, titanium tetraacetylacetonate, alcohols, a Group 2 metal compound in the long periodic table, a phosphate ester compound, and/or a titanium compound.

Specific examples of zirconium compounds include zirconium tetraacetate, zirconium acetate hydroxide, zirconium tris(butoxy)stearate, zirconyl diacetate, zirconium oxalate, zirconyl oxalate, potassium zirconium oxalate, polyhydroxyzirconium stearate, zirconium ethoxide, zirconium tetra-n-propoxide, zirconium tetraisopropoxide, zirconium tetra-n-butoxide, zirconium tetra-t-butoxide, zirconium tributoxyacetylacetonate, or mixtures thereof.

Among these, zirconyl diacetate, zirconium tris(butoxy)stearate, zirconium tetraacetate, zirconium acetate hydroxide, ammonium zirconium oxalate, potassium zirconium oxalate, polyhydroxyzirconium stearate, zirconium tetra-n-propoxide, zirconium tetraisopropoxide, zirconium tetra-n-butoxide, and zirconium tetra-t-butoxide are preferred, with zirconyl diacetate, zirconium tetraacetate, zirconium acetate hydroxide, zirconium tris(butoxy)stearate, ammonium zirconium oxalate, zirconium tetra-n-propoxide, and zirconium tetra-n-butoxide being more preferred, and zirconium tris(butoxy)stearate being particularly preferred because it allows for easy production of polyesters with a high degree of polymerization and little coloration.

Specific examples of germanium compounds include inorganic germanium compounds such as germanium oxide or germanium chloride, and organic germanium compounds such as tetraalkoxygermanium. In view of cost and availability, germanium oxide, tetraethoxygermanium, and tetrabutoxygermanium are preferred, with germanium oxide being particularly preferred.

Examples of iron compounds include inorganic chlorides such as ferric chloride, inorganic oxides such as triiron tetroxide, and organic iron complexes such as ferrocene. Of these, inorganic oxides are preferred.

Other metal-containing compounds include scandium compounds such as scandium carbonate, scandium acetate, scandium chloride, and scandium acetylacetonate; yttrium compounds such as yttrium carbonate, yttrium chloride, yttrium acetate, and yttrium acetylacetonate; vanadium compounds such as vanadium chloride, vanadium trichloride oxide, vanadium acetylacetonate, and vanadium acetylacetonate oxide; molybdenum compounds such as molybdenum chloride and molybdenum acetate; tungsten compounds such as tungsten chloride, tungsten acetate, and tungstic acid; and lanthanide compounds such as cerium chloride, samarium chloride, and ytterbium chloride.

The amount of the polycondensation reaction catalyst to be added is not particularly limited, but the lower limit of the amount of metal relative to the polyester produced is usually 0.1 mass ppm or more, preferably 0.5 mass ppm or more, more preferably 1 mass ppm or more, and the upper limit is usually 3000 mass ppm or less, preferably 1000 mass ppm or less, more preferably 250 mass ppm or less, and particularly preferably 130 mass ppm or less. This range is particularly preferably applicable when a metal compound is used as a polycondensation reaction catalyst. If the amount of catalyst used is too large, not only is it economically disadvantageous, but the concentration of carboxyl groups in the polyester may increase, and the thermal stability and hydrolysis resistance of the polyester may decrease due to the increase in the amount of carboxyl groups and the residual catalyst concentration. Conversely, if the amount is too small, the polymerization activity will be low, which will induce thermal decomposition of the polyester during polyester production, making it difficult to obtain a polyester that exhibits practically useful physical properties.

The location of the catalyst added to the reaction system is not particularly limited as long as it is added before the polycondensation reaction process, and it may be added when the raw materials are charged. However, if the catalyst is present in a situation where a large amount of water is present or generated, the catalyst may be deactivated, causing the precipitation of foreign matter and impairing the quality of the product, so it is preferable to add it after the esterification reaction process.

(4) Reactor As the esterification reaction tank for carrying out the esterification reaction treatment, a known one can be used, and it may be any of the types such as a vertical agitated complete mixing tank, a vertical thermal convection mixing tank, or a tower-type continuous reaction tank, and it may be a single tank or a multiple tank of the same or different types connected in series. Among them, a reaction tank having an agitator is preferred, and as the agitator, in addition to a normal type having a power unit, bearings, shaft, and agitator blades, a high-speed rotating type such as a turbine stator type high-speed rotating agitator, a disk mill type agitator, or a rotor mill type agitator can also be used.

There are no limitations on the type of stirring, and in addition to the usual stirring method of directly stirring the reaction liquid in the reaction tank from the top, bottom, or side of the reaction tank, a method of taking part of the reaction liquid outside the reaction tank via piping or the like and stirring it with a line mixer or the like to circulate the reaction liquid can also be used. The type of stirring blade can also be selected from known types, and specific examples include propeller blades, screw blades, turbine blades, fan turbine blades, disk turbine blades, Pfaudle blades, full zone blades, and Max Blend blades.

There are no particular limitations on the type of polycondensation reaction tank, and examples include vertical agitation polymerization tanks, horizontal agitation polymerization tanks, and thin-film evaporation polymerization tanks. The polycondensation reaction tank can be a single tank, or a multiple tank arrangement in which multiple tanks of the same or different types are connected in series. However, in the later stages of the polycondensation reaction when the viscosity of the reaction liquid increases, it is preferable to select a horizontal agitation polymerization machine with a thin-film evaporation function that has excellent interface renewal properties, plug flow properties, or self-cleaning properties.

The content of polyester in the reaction product obtained in the reaction step is not particularly limited, but is usually 90% by mass or more, preferably 92.5% by mass or more, more preferably 95% by mass or more, and even more preferably 97% by mass or more, and is usually 100% by mass or less, preferably 99.5% by mass or less, more preferably 99% by mass or less, and even more preferably 98.5% by mass or less.

The content of the oligomer component in the reaction product obtained in the reaction step is not particularly limited and may be the remainder excluding the above polyester, but is usually 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, and is usually 3% by mass or less, preferably 2.5% by mass or less, more preferably 2% by mass or less, and even more preferably 1.5% by mass or less.

(Pelletizing process)
From the viewpoint of improving the convenience of molding and improving the efficiency of contact treatment of oligomer components by increasing the surface area in the contact treatment in the purification step described later, it is preferable that the production method for polyester further includes a pelletizing step of pelletizing the reaction product obtained in the above reaction step to obtain pellets (polyester pellets) after the above reaction step, particularly between the above reaction step and the purification step described later.

The pelletizing method is not particularly limited and known methods can be used. For example, a strand cutting method is used in which the molten reaction product is extruded from the nozzle hole of the die head using a gear pump or extruder, and the strands are cut with a cutter while being cooled with water or the like, or the cooled and solidified strands are cut with a cutter, or an underwater hot cutting method is used in which the product is extruded from the nozzle hole into water and immediately cut in a molten state. In particular, the underwater hot cutting method is preferably used because there is little cutting waste in the pellets, the angle of repose of the resulting pellets is low, and the pellets are transported stably and the feeding stability to the molding machine during molding is good. The cooling water temperature in the underwater cutting method is not particularly limited, but is usually preferably 10°C or higher, more preferably 20°C or higher, and preferably 70°C or lower, more preferably 60°C or lower, and even more preferably 50°C or lower.

The size of the nozzle hole is not particularly limited, but a hole diameter of 1 mm to 30 mm is usually used. The shape of the opening is also not particularly limited, but shapes such as circle, ellipse, oblong, square, or star are used. The discharge rate per opening is usually 5 to 100 kg/hour, preferably 10 to 70 kg/hour, and more preferably 20 to 50 kg/hour.

The pellets may be spherical, cylindrical, elliptical, oblong, rectangular, or cocoon-shaped, or may have a flattened shape. In the underwater hot-cut method, a spherical or cocoon-shaped shape or a flattened shape is preferably used. There are no particular restrictions on the size, but from the viewpoints of the contact treatment efficiency of the oligomer components in the purification process described below, the drying efficiency in the drying process, and the ease of pellet transport, the weight of each pellet is 1 to 50 mg, preferably 3 to 40 mg, and more preferably 5 to 30 mg. Also, a larger pellet surface area per mass is preferable in terms of the contact treatment efficiency in the purification process.

(Refining process)
The method for producing a polyester preferably further includes a purification step including a contact treatment in which the reaction product obtained in the above reaction step is contacted with a solvent containing water to obtain a treatment liquid containing an oligomer component and a post-contact treatment reaction product. The purification step may include treatments other than the contact treatment.
As described later, the content of oligomer components in the reaction product can be reduced by performing contact treatment in the purification step, and furthermore, since the contact treatment liquid obtained by the contact treatment contains oligomer components, this oligomer component can be reused. Specifically, for example, the oligomer components in the contact treatment liquid can be reused as oligomer components in the polyester raw material in the reaction step. More specifically, when a raw material preparation step for preparing a polyester raw material is further provided before the reaction step, the oligomer components in the contact treatment liquid can be reused by supplying them to any of the steps from the raw material preparation step to the reaction step.

(1) Contact Treatment In the purification step, a contact treatment is carried out in which the reaction product obtained in the reaction step (when a pelletizing step is adopted, the pelletizing step) is brought into contact with a contact treatment liquid, whereby oligomer components contained in the reaction product are brought into contact with the contact treatment liquid, thereby making it possible to reduce the content of oligomer components in the reaction product.

The contact treatment liquid is not particularly limited as long as it is a solvent containing water, and examples thereof include a mixture of water and an alcohol such as methanol, ethanol, isopropanol, or butanol. Among these, a water/ethanol mixture (a mixture of water and ethanol) is particularly preferred in terms of ease of handling, cost, contact treatment efficiency, and safety.

If the polyester manufacturing method includes the above-mentioned pelletizing step, the contact treatment is usually carried out immediately after pelletizing, but the contact treatment may also be carried out after temporarily storing the obtained pellets in a storage tank.

(1-1) Composition of the contact treatment liquid The proportion of water in the entire contact treatment liquid to be contacted with the reaction product is not particularly limited, and is usually 10% by mass or more, preferably 20% by mass or more, more preferably 25% by mass or more. The proportion of water is usually 99% by mass or less, preferably 95% by mass or less, further preferably 90% by mass or less, and particularly preferably 85% by mass or less.
If the mixing ratio of the water is less than the lower limit of the above range, the quality of the polyester tends to deteriorate due to a decrease in molecular weight caused by alcohol decomposition. In addition, if the alcohol content is increased, the liquid and the gas generated from the liquid during use may become explosive, and therefore care must be taken in handling from the viewpoint of safety. On the other hand, if the mixing ratio of the water exceeds the upper limit of the above range, the oligomer components may not be sufficiently removed, and the content of the oligomer components may not be sufficiently reduced, resulting in a polyester of desired quality.

(1-2) Contact Treatment Temperature The temperature of the contact treatment liquid when the reaction product is contacted with the contact treatment liquid is not particularly limited, and is preferably 25°C or higher, more preferably 30°C or higher, even more preferably 35°C or higher, and particularly preferably 40°C or higher. The upper limit of the temperature is usually below the melting point of the polyester, preferably 95°C or lower, more preferably 90°C or lower, and particularly preferably 85°C or lower. If the contact temperature is below the lower limit of the above range, not only will a long treatment time be required, which is economically disadvantageous, but also a polyester of desired quality may not be obtained due to a decrease in the effect of removing oligomer components. On the other hand, if the contact temperature exceeds the upper limit of the above range, the viscosity will decrease significantly due to hydrolysis and alcoholysis, which will not only impair the quality, but will also cause difficulties in operation, such as fusion between pellets and poor pellet extraction.

(1-3) Contact Treatment Time The time for contacting the reaction product with the contact treatment liquid is not particularly limited, and is usually 0.1 hours or more, preferably 1 hour or more, and more preferably 3 hours or more. The time is usually 24 hours or less, preferably 18 hours or less, and more preferably 10 hours or less. If the contact time is less than the lower limit of the above range, the oligomer components may not be sufficiently removed, and a polyester of desired quality may not be obtained. On the other hand, if the contact time exceeds the upper limit of the above range, the viscosity may decrease significantly due to hydrolysis and alcoholysis, and the quality may be impaired.

(1-4) Ratio of reaction product to contact treatment liquid The ratio of the reaction product to the contact treatment liquid (treatment liquid/reaction product ratio) is usually 1.0 or more, preferably 1.5 or more, and more preferably 2.0 or more, in terms of mass ratio. Moreover, the ratio is usually 50 or less, preferably 30 or less, and more preferably 20 or less, in terms of mass ratio. If the mass ratio of the reaction product to be contacted to the liquid is less than the lower limit of the above range, the effect of removing the oligomer component may decrease due to an increase in the concentration of the oligomer component in the contact treatment liquid during treatment, and a polyester of desired quality may not be obtained. On the other hand, if the mass ratio of the pellets to be contacted to the liquid exceeds the upper limit of the above range, it is disadvantageous in terms of process and cost, such as an increase in the size of the equipment due to a large amount of contact treatment liquid used and an increase in the cost of the contact treatment liquid.

(1-5) Contact Treatment Method The reaction product may be contacted with the contact treatment liquid by a batch method or a continuous method, and either method may be employed.
In the embodiment of the batch system, the reaction product and the contact treatment liquid are placed in a treatment tank, and the reaction product and the contact treatment liquid are subjected to contact treatment at a predetermined temperature for a predetermined time, and then the reaction product and the contact treatment liquid are discharged. The contact treatment between the reaction product and the contact treatment liquid can be performed with or without circulation of the contact treatment liquid.
An example of a continuous mode in this embodiment is a method in which pellets are continuously supplied to a pipe or treatment tank, and a contact treatment liquid at a predetermined temperature is brought into contact with the flow of the reaction product in a cocurrent or countercurrent manner, and the contact time is maintained for a predetermined time, while the pellets are continuously withdrawn.

(2) Separation treatment From the viewpoint of cost reduction by improving the recycling rate of the contact treatment liquid and improving the recovery efficiency of the cyclic oligomer component, the purification step may include a separation treatment for separating at least a part of the cyclic oligomer component in the contact treatment liquid after the contact treatment. In addition, after separating at least a part of the cyclic oligomer component to adjust the content of the cyclic oligomer component in the contact treatment liquid, it can be recycled and reused as the contact treatment liquid in the contact treatment. Furthermore, the cyclic oligomer component containing the separated cyclic oligomer component can be reused as an oligomer component in the polyester raw material in the reaction step after being separated from the contact treatment liquid by cooling or the like, or after being concentrated. In particular, it is a preferred method to return the separated cyclic oligomer component to the esterification reaction tank in which the esterification reaction is performed in the reaction step, or to the slurry preparation tank for the dicarboxylic acid component and the diol component.

The contact treatment liquid after the separation process can be recycled as is, or it can be reused by adding new contact treatment liquid in an amount equivalent to the amount of contact treatment liquid extracted along with the separated cyclic oligomer components.

After the separation process, the oligomer component (which may be a mixture of the contact treatment liquid and the oligomer component) separated by distillation concentration and/or cooling can be recovered as a polyester raw material after being melted or heated and dissolved in the diol component used as a raw material to form a solution. The recovered oligomer component can be directly supplied to the esterification reaction tank, or can be supplied to the diol component recycle line (2) or the esterification reaction product withdrawal line (4) shown in Figure 1, or can be supplied to the polycondensation reaction tank (a) shown in Figure 2, or can be supplied to a slurry preparation tank for the dicarboxylic acid component and the diol component.

(Drying process)
The method for producing a polyester may further include a drying step in which a drying treatment is performed to dry the reaction product after the contact treatment. Since the reaction product after the contact treatment contains the contact treatment liquid, it is preferable to dry it in the drying step in order to remove the contact treatment liquid.
Dryers used in the drying step include tray-type dryers, band dryers, horizontal cylindrical rotary dryers, horizontal dryers with rotary blades, vertical dryers with rotary blades (so-called hopper dryer type dryers), moving bed type vertical dryers, fluidized bed dryers, etc., which circulate an inert gas such as heated air or heated nitrogen as a drying gas. Dryers different from the above gas circulation type include double-cone type rotary vacuum dryers, tumbler type rotary vacuum dryers, microwave dryers, etc.

These processes can be carried out in a batch, semi-batch, or continuous manner, but for mass production, a continuous method is preferable from the viewpoint of production efficiency. Also, from the viewpoint of keeping the equipment complex, it is preferable to use a moving bed vertical dryer or a multiple-stage continuous dryer.

The drying temperature is not particularly limited, but the gas temperature is usually 25°C or higher, preferably 30°C or higher, more preferably 35°C or higher, and particularly preferably 40°C or higher. The upper limit of the temperature is usually below the melting point of the polyester, preferably below the melting point of the polyester minus 5°C, more preferably below the melting point of the polyester minus 8°C, and particularly preferably below the melting point of the polyester minus 10°C. If the drying temperature is below the lower limit of the above range, a long drying time is required, which is economically disadvantageous. On the other hand, if the drying temperature exceeds the upper limit of the above range, it may cause operational difficulties such as fusion of pellets and poor removal when removing the pellets from the dryer. The drying gas that has passed through the dryer contains contact treatment liquid components, and the contact treatment liquid components can be reduced by cooling or adsorption of the drying gas, and reused as drying gas.

The drying time is not particularly limited, but is usually 0.1 to 100 hours, preferably 1 to 80 hours, and more preferably 5 to 50 hours. In the case of a moving bed type, the flow rate of the drying gas is usually 0.05 to 1.0 m/s (superficial velocity). The alcohol content in the reaction product after drying is usually 1000 ppm by mass or less, preferably 800 ppm by mass or less, and more preferably 500 ppm by mass or less. If the content of alcohol is large, the melt viscosity of the pellets tends to decrease significantly during melt molding, resulting in poor moldability. The lower the alcohol content, the better, but an industrially and rationally obtainable concentration is usually 50 ppm by mass or more. The moisture content of the pellets after drying is usually less than the alcohol content. The moisture content in the reaction product is usually 1000 ppm by mass or less, preferably 500 ppm by mass or less, and more preferably 250 ppm by mass or less. If there is a large amount of moisture in the reaction product, the IV will drop significantly due to hydrolysis when the pellets are melt molded, leading to poor moldability and reduced physical properties of the molded product.

[Manufacturing process example]
A preferred embodiment of a method for producing a polyester using succinic acid as a dicarboxylic acid component, 1,4-butanediol (hereinafter sometimes abbreviated as BG) as a diol component, and malic acid as another copolymerization component (polyfunctional compound) as raw materials will be described below as an example, but the present invention is not limited thereto.

Below, a preferred embodiment of the polyester manufacturing method will be described with reference to the attached drawings. Fig. 1 is an explanatory diagram of an example of an esterification reaction process employed in this embodiment, and Fig. 2 is an explanatory diagram of an example of a polycondensation reaction process employed in this embodiment. Note that Fig. 1 can be applied not only to an esterification reaction process but also to an ester exchange reaction process, in which case, in the following description, the esterification reaction tank will be read as an ester exchange reaction tank.

In Figure 1, the raw materials succinic acid and malic acid are usually mixed with BG in a raw material mixing tank (not shown) and supplied in the form of a slurry or liquid from the raw material supply line (1) to the esterification reaction tank (A). If a catalyst is added during the esterification reaction, it is made into a BG solution in a catalyst preparation tank (not shown) and the catalyst solution is supplied to the catalyst supply line (3). Figure 1 shows an embodiment in which the catalyst supply line (3) is connected to the recycle line (2) for recycle 1,4-butanediol, and the two are mixed and then supplied to the liquid phase of the esterification reaction tank (A).

The gas distilled from the esterification reaction tank (A) passes through the distillation line (5) and is separated into high-boiling and low-boiling components in the fractionator (C). Usually, the main component of the high-boiling component is 1,4-butanediol, and the main component of the low-boiling component is water and tetrahydrofuran (hereinafter sometimes abbreviated as THF), which is a decomposition product of BG.

The high boiling components separated in the distillation tower (C) are extracted through the extraction line (6) and pump (D), some of which is circulated through the recirculation line (2) to the esterification reaction tank (A), and some of which is returned through the circulation line (7) to the distillation tower (C). The surplus is extracted to the outside through the extraction line (8). On the other hand, the low boiling components separated in the distillation tower (C) are extracted through the gas extraction line (9), condensed in the condenser (G), and temporarily stored in the tank (F) through the condensate line (10). A portion of the low boiling components collected in the tank (F) are returned to the distillation tower (C) through the extraction line (11), pump (E), and circulation line (12), and the remainder is extracted to the outside through the extraction line (13). The condenser (G) is connected to an exhaust device (not shown) through a vent line (14). The esterification reaction product produced in the esterification reaction tank (A) is supplied to the first polycondensation reaction tank (a) shown in FIG. 2 via the discharge pump (B) and the discharge line (4) for the esterification reaction product.

In the process shown in FIG. 1, the catalyst supply line (3) is connected to the recirculation line (2), but the two may be independent. Also, the raw material supply line (1) may be connected to the liquid phase of the esterification reaction tank (A).

When a catalyst is added to the esterification reaction product before the polycondensation reaction tank, it is prepared to a predetermined concentration in a catalyst preparation tank (not shown), then passed through the catalyst supply line (L7) in Figure 2, connected to the raw material supply line (L8), further diluted with BG, and supplied to the esterification reaction product withdrawal line (4).

Next, the esterification reaction product supplied to the first polycondensation reaction tank (a) through the esterification reaction product discharge line (4) and the filter (p) undergoes a polycondensation reaction under reduced pressure to become a polyester low polymer, which is then supplied to the second polycondensation reaction tank (d) through the discharge gear pump (c), the discharge line (L1), and the filter (q). In the second polycondensation reaction tank (d), the polycondensation reaction usually proceeds further at a lower pressure than in the first polycondensation reaction tank (a). The obtained polycondensation reaction product is supplied to the third polycondensation reaction tank (k) through the discharge gear pump (e), the discharge line (L3) which is the outlet flow path, and the filter (r). The third polycondensation reaction tank (k) is a horizontal reaction tank composed of multiple stirring blade blocks and equipped with two-shaft self-cleaning type stirring blades. The polycondensation reaction product introduced from the second polycondensation reaction tank (d) to the third polycondensation reaction tank (k) through the withdrawal line (L3) undergoes further polycondensation reaction here and is then transferred to the pelletization process.

In the pelletizing process, the molten reaction product passes through an extraction gear pump (m), an outlet flow path filter (s), and an extraction line (L5) and is extracted from a die head (g) in the form of molten strands into the atmosphere, where it is cooled with water or the like and then cut by a rotary cutter (h) to become polyester pellets. It is also possible to extract the strands into water instead of into the atmosphere and cut them into pellets by a rotary underwater cutter.

In Figure 2, symbols (L2), (L4), and (L6) are the vent lines of the first polycondensation reaction tank (a), the second polycondensation reaction tank (d), and the third polycondensation reaction tank (k), respectively. Filters (p), (q), (r), and (s) do not necessarily need to be installed all at once, and can be installed as appropriate, taking into consideration the foreign matter removal effect and operational stability.

FIG. 3 is an explanatory diagram of an example of the contact treatment and separation treatment that can be adopted in this embodiment. The contact treatment liquid is temperature-controlled from the circulation tank (I) through the heat exchanger (II) by the pump (IX) and supplied to the treatment tank (III) through the contact treatment liquid supply line (101). After being countercurrently contacted with the pellets in the treatment tank, it is withdrawn through the withdrawal line (102), passed through the fine powder remover (IV), and then recovered in the circulation tank (I) through the separator (XI). The contact treatment liquid supplied to the separator (XI) is separated into cyclic oligomer components, and is supplied to the liquid phase separation tank (XIII) through the high boiling liquid withdrawal line (111). The separated oligomer components are withdrawn to the outside through the withdrawal line (112). From the supply line (107), the contact treatment liquid is supplied in an amount equivalent to the contact treatment liquid withdrawn from the withdrawal line (112) together with the separated cyclic oligomer components. The aqueous solution containing the oligomer components in the upper layer of the liquid phase separation tank (XIII) is supplied to a solid-liquid separation tank (XIV) via a liquid phase separation tank overflow line (113). The aqueous solution supplied to the solid-liquid separation tank (XIV) is cooled by adding water to crystallize the oligomer components. The suspension containing the solidified oligomer components is supplied to a solid-liquid separator (XV) via a solid-liquid separation tank overflow line (114), and the oligomer components are extracted. The separated water is sent to an activated sludge facility via a drainage line (116). As described above, the recovered oligomer components can be reused as part of the raw material, etc.
3 shows an example of the contact treatment and separation treatment in the first embodiment, and shows an example of the contact treatment step and the purification step (specifically, the distillation separation treatment in the purification step) in the second embodiment described later. An example of the contact treatment and separation treatment in the first embodiment and an example of the contact treatment step and the purification step in the second embodiment can both be similarly represented by the process shown in FIG.

The pellets to be subjected to contact treatment are continuously supplied from a pellet supply line (103) and, after being in contact with the contact treatment liquid for a predetermined time, are continuously withdrawn from a withdrawal line (104) while adjusting the withdrawal amount with a rotary valve (V). The contact treatment liquid withdrawn together with the pellets is separated in a preliminary solid-liquid separator (VI) and, after passing through a recovery tank (VII), is returned to the recovery line (106) via a supply line (105) by a pump (X). The continuously withdrawn pellets are separated from the entrained contact treatment liquid in the preliminary solid-liquid separator, and then passed through a solid-liquid separator (VIII) and continuously supplied to the drying process.

4 is an explanatory diagram of an example of a drying process that can be adopted in this embodiment. The illustrated example has two drying towers (I) and (K).
The polyester pellets after the purification process are continuously supplied to the first drying tower (I) through the pellet supply line (201). Heated dry nitrogen gas is continuously introduced into the first drying tower through the supply line (208) and discharged through the dry gas recovery line (207). The discharged gas is heated in the heat exchanger (N) through the condenser (L) and circulated to the first drying tower through the dry gas supply line (208). The contact treatment liquid condensed in the condenser (L) and heat exchanger (M) is discharged through the condensate discharge line (210). New dry nitrogen gas is supplied through the new dry gas supply line (209). The pellets are continuously sent from the first drying tower to the cooling tower (J) through the rotary valve (O). Dry air is introduced into the cooling tower through the cooling gas supply line (212) and discharged through the cooling gas discharge line (211).

The pellets cooled to a temperature lower than the drying temperature of the first drying tower are supplied to the second drying tower (K) via a pellet discharge line (204), a rotary valve (P) and a pellet supply line (205). A dry gas (usually air) is supplied to the second drying tower via a heat exchanger (S) and a dry gas supply line (214) and discharged from a dry gas discharge line (213).
The temperature of the air supplied to the second drying tower is usually lower than the temperature of the nitrogen gas supplied to the first drying tower, for example, the nitrogen gas temperature is 80°C and the air temperature is 50°C.

After drying, the polyester pellets are extracted continuously or intermittently through the rotary valve (Q) pellet extraction line (206), and become the finished product after passing through a storage tank, fine powder removal machine, packaging machine, etc. The storage tank can also be used as the second drying tower. This diagram does not show the process after the storage tank.

The content of the cyclic oligomer component obtained by contacting the polyester pellets with the contact treatment liquid is not particularly limited, but the content of the cyclic dimer contained in the polyester pellets (100 mass%) after the contact is preferably 1 mass ppm or more, more preferably 100 mass ppm or more, even more preferably 500 mass ppm or more, and particularly preferably 1000 mass ppm or more. The content of the cyclic oligomer component is usually 3800 mass ppm or less, preferably 3500 mass ppm or less, even more preferably 3000 mass ppm or less, and particularly preferably 2500 mass ppm or less. If the content of the cyclic dimer is less than the lower limit of the above range, the quality is good, but it is economically disadvantageous because the time required to remove the oligomer component is extended, which requires large-scale equipment. If the content exceeds the upper limit of the above range, when the polyester is left for a certain period of time after molding, the surface becomes cloudy (synonymous with bleed-out or whitening phenomenon), causing problems such as loss of surface gloss.

<Polyester Composition>
A polyester composition according to another embodiment of the present invention (also referred to as "aspect A of the polyester composition") is a polyester composition containing a polyester obtained by the above-mentioned method for producing a polyester. The polyester produced by the above-mentioned method for producing a polyester may be an aliphatic polyester or an aromatic-aliphatic copolymer polyester.
The polyester composition may further contain an aliphatic oxycarboxylic acid or the like. Furthermore, the polyester composition may contain a carbodiimide compound, a filler, a plasticizer, or other biodegradable resins that are used as necessary. Examples of other biodegradable resins include polycaprolactone, polyamide, polyvinyl alcohol, or cellulose ester, or starch, cellulose, paper, wood flour, chitin/chitosan, coconut shell powder, walnut shell powder, or other animal/plant material fine powders, or mixtures thereof. Furthermore, in order to adjust the physical properties and processability of the molded body, additives such as heat stabilizers, plasticizers, lubricants, antiblocking agents, nucleating agents, inorganic fillers, colorants, pigments, ultraviolet absorbers, or light stabilizers, modifiers, crosslinking agents, or the like may be contained.

The method for producing the polyester composition is not particularly limited, but examples include a method in which the polyester obtained by the above-mentioned production method is used to melt-mix the blended polyester raw material chips in the same extruder, a method in which each is melted in a separate extruder and then mixed, or a method in which the raw material chips are mixed by kneading using a normal kneading machine such as a single-screw extruder, twin-screw extruder, Banbury mixer, roll mixer, Brabender plastograph, or kneader blender. It is also possible to directly feed each raw material chip into a molding machine to prepare the composition and simultaneously obtain a molded body.

A composition according to yet another embodiment of the present invention (a polyester composition, also referred to as "polyester composition aspect B") is a composition that includes a polyester containing a constituent unit derived from a diol component and a constituent unit derived from a dicarboxylic acid component, and a cyclic oligomer component having a structure represented by the following formula (1) and a structure represented by the following formula (2).

The above formulas (1) and (2) correspond similarly to the formulas (1) and (2) described in the above-mentioned method for producing polyester, and the conditions of the formulas (1) and (2) described in the above-mentioned method for producing polyester, including the preferred conditions, can be applied.

The conditions for the diol component and the dicarboxylic acid component in the above composition can be similarly applied to the conditions for the diol component and the dicarboxylic acid component explained in the above-mentioned method for producing polyester.
The composition according to this embodiment may contain the same components as those described in the polyester composition aspect A, and the same manufacturing method can be used. For example, the polyester pellets obtained by the above-mentioned polyester manufacturing method usually contain the above-mentioned cyclic oligomer component in addition to the polyester, and therefore the composition can be manufactured by mixing the polyester pellets with any other component.

The polyester may also contain structural units derived from the cyclic oligomer component. If the polyester is produced by the above-mentioned polyester production method, the polyester raw material used in the production contains the above-mentioned cyclic oligomer component, and therefore the polyester usually has structural units derived from the above-mentioned cyclic oligomer component.

<Molded body>
Another embodiment of the present invention is a molded article, specifically, a molded article obtained by molding the polyester composition related to aspect A of the polyester composition described above, a molded article obtained by molding the polyester composition related to aspect B of the polyester composition described above, or a molded article produced by a method for producing a molded article including a step of producing a polyester by the above-mentioned method for producing a polyester.
The method for producing the molded body is not particularly limited, and can be a known method applied to general-purpose plastics, or a combination of known methods. Examples of the molding method include compression molding (compression molding, lamination molding, stampable molding), injection molding, extrusion molding or co-extrusion molding (film molding by inflation method or T-die method, laminate molding, pipe molding, electric wire/cable molding, molding of profile material), heat press molding, hollow molding (various blow moldings), calendar molding, solid molding (uniaxial stretch molding, biaxial stretch molding, roll rolling molding, stretch-oriented nonwoven fabric molding, thermoforming (vacuum molding, pressure molding), plastic processing, powder molding (rotational molding)), various nonwoven fabric molding (dry method, adhesion method, entanglement method, spunbond method, etc.), etc. Among them, injection molding, extrusion molding, compression molding, or heat press molding, especially extrusion molding or injection molding, are preferably applied. As specific shapes, application to sheets, films, and fibers is preferable.

The uses of the molded body are not particularly limited, and it can be used in known applications that are applied to general-purpose plastics. In particular, when it is biodegradable, it is particularly suitable for use in agricultural and forestry materials, fishing materials, civil engineering materials, etc. that are used outdoors, in the soil, underwater, or in wet environments. Specific examples include extrusion molded products (for example, film products such as agricultural mulch films, mushroom cultivation films, and tree protection films, sheet products such as water-retaining sheets, and textile products such as fishing lines, fishing nets, aquaculture nets, vegetation nets, and ropes), and injection molded products (stakes, seedling pots, or mushroom bed cultivation containers). It is also suitable for use in compost bags and garbage bags that are expected to be stored for a certain period of time at home or in a business.

<Second aspect>
<Production method of polyester>
A second aspect of the method for producing a polyester according to one embodiment of the present invention (hereinafter, in the section on the second aspect, also simply referred to as a "method for producing a polyester") is
A reaction step of obtaining a reaction product from a polyester raw material (also simply referred to as "raw material") containing a diol and a dicarboxylic acid by a reaction treatment including at least one treatment selected from the group consisting of an esterification reaction treatment and an ester exchange reaction treatment;
a contact treatment step of contacting the reaction product with a contact treatment liquid to obtain a contact treatment liquid containing an oligomer component and a post-contact treatment reaction product;
a purification step including a treatment for purifying the oligomer components in the contact treatment liquid so that a content ratio of cyclic oligomer components in the oligomer components is increased from the contact treatment liquid containing the oligomer components; and a recovery step for recovering the oligomer components obtained by the purification step as part of the raw material.
A method for producing polyester.

As the diol component and dicarboxylic acid used as raw materials, those usually used as raw materials for polyesters can be used without any particular limitation. As the diol component, an aliphatic diol component or an aromatic diol component may be used, and as the dicarboxylic acid component, an aliphatic dicarboxylic acid component or an aromatic dicarboxylic acid component may be used.
As the conditions for these diol components and dicarboxylic acids, the conditions for the diol components and dicarboxylic acids explained in the first embodiment of the above-mentioned method for producing polyester can be similarly applied.

In addition, in the polyester production method, as long as at least a diol component and a dicarboxylic acid component are used, other components may be copolymerized. In this case, the conditions for the copolymerization components that can be used can be the same as those for the other components described in the first embodiment of the polyester production method described above.

[Each step in the production of polyester]
Each step in the second embodiment of the method for producing a polyester will be described below using a continuous production method as an example, but this is merely an example, and the method for producing a polyester is not limited to this embodiment.
In the continuous polyester production method, as in the first embodiment described above, for example, a dicarboxylic acid component and a diol component are continuously subjected to a reaction process including at least one treatment selected from the group consisting of an esterification reaction treatment and an ester exchange reaction treatment, and a polycondensation reaction treatment, using a plurality of continuous reaction tanks to obtain a polyester. However, as long as the effects of the present invention are not hindered, the method is not limited to the continuous method, and steps in the conventional polyester production methods can be adopted. Furthermore, the polyester may be subjected to a contact treatment with a contact treatment liquid and then dried.
When a continuous operation is employed, from the viewpoints of production efficiency and uniformity of the treatment, it is particularly preferred that at least one treatment selected from the group consisting of the contact treatment in the contact treatment step described below and the drying treatment in the drying step described below is carried out in a continuous manner. Also, when a batch or semi-batch operation is employed, it is particularly preferred that at least one treatment selected from the group consisting of the contact treatment in the contact treatment step described below and the drying treatment in the drying step described below is carried out in a batch or semi-batch manner from the viewpoints of production efficiency and uniformity of the treatment.

(Raw material preparation process)
The method for producing a polyester may further include a raw material preparation step of preparing a polyester raw material prior to the reaction step described below.
The method for preparing the polyester raw material is not particularly limited, and the raw material may be prepared by mixing raw materials produced by synthesis or the like, or the raw materials may be procured as commercially available products and mixed to prepare the polyester raw material.

(Reaction step)
The method for producing a polyester includes a reaction step of subjecting a polyester raw material containing a diol and a dicarboxylic acid to a reaction treatment including at least one treatment selected from the group consisting of an esterification reaction treatment and an ester exchange reaction treatment to obtain a reaction product containing a polyester. The reaction treatment is preferably carried out in the presence of a catalyst. The reaction step may include treatments other than the esterification reaction treatment and the ester exchange reaction.

(1) Esterification reaction process/ester exchange reaction process The reaction process is an esterification reaction process in which a polyester raw material is reacted, specifically, an esterification reaction process in which a raw material containing at least a dicarboxylic acid component and a diol component is reacted, and/or an ester exchange reaction is carried out to produce the polyester. The esterification reaction is a reaction in which a carboxylic acid is converted into an ester, and the ester exchange reaction is a reaction in which an ester and an alcohol are reacted to exchange the main chain portions of these. The esterification reaction process will be described below, but this description can be applied to the ester exchange reaction as well to the extent that it is applicable.
In addition, at least one reaction process selected from the group consisting of an esterification reaction process and an ester exchange reaction and the subsequent other processes can be carried out in a plurality of continuous reaction tanks or in a single reaction tank. However, in order to reduce variation in the physical properties of the resulting polyester, it is preferable to carry out the processes in a plurality of continuous reaction tanks.

The conditions for the esterification reaction process/ester exchange reaction process can be the same as those for the esterification reaction process/ester exchange reaction process in the first embodiment described above.

The polycondensation reaction conditions can be the same as those in the first embodiment described above.

The reaction catalyst conditions can be the same as those in the first embodiment described above.

(4) Reactor As the esterification reaction tank for carrying out the esterification reaction treatment, a known esterification reaction tank can be used, and the reaction catalyst conditions in the first embodiment described above can be similarly applied.

(Pelletizing process)
From the viewpoint of improving the convenience of molding and improving the efficiency of the contact treatment of the oligomer component by expanding the surface area in the contact treatment step described later, the method for producing polyester preferably further includes a pelletizing step of pelletizing the reaction product obtained in the above reaction step to obtain pellets (polyester pellets) after the above reaction step, particularly between the above reaction step and the contact treatment step described later. The polyester obtained through the esterification reaction step is pelletized, and contact treatment is performed in the form of pellets with a contact treatment liquid.

The conditions for the pelletizing process can be the same as those for the first embodiment described above.

(Contact treatment step)
The method for producing polyester further includes a contact treatment step in which the reaction product (polyester) obtained by the above reaction step is contacted with a contact treatment liquid to obtain a contact treatment liquid containing an oligomer component and a post-contact treatment reaction product. The contact treatment is a treatment for purification. The contact treatment step may include treatments other than the contact treatment. The contact treatment liquid is not particularly limited and may be, for example, a solvent containing water.
Since a reaction product obtained by an esterification reaction, an ester exchange reaction, a polymerization reaction, or the like usually contains an oligomer component, the content of the oligomer component in the reaction product can be reduced by performing a contact treatment, and further, since the contact treatment liquid obtained by the contact treatment contains an oligomer component, the oligomer component can be recovered for reuse to improve the productivity of polyester. Specifically, for example, when a raw material preparation step for preparing a polyester raw material is further provided before the reaction step, the oligomer component in the contact treatment liquid can be reused by supplying it to any step from the raw material preparation step to the reaction step.
Furthermore, the present inventors have found that a polyester obtained by reusing as a raw material the oligomer component recovered through this contact treatment step exhibits less deterioration in color tone than a polyester obtained by reusing as a raw material the oligomer component recovered without being subjected to a purification treatment, or a polyester obtained by reusing as a raw material the oligomer component obtained by a conventional purification treatment.

The contact treatment step is a step in which the reaction product (polyester) obtained in the reaction step (pelletization step, if a pelletization step is adopted) is brought into contact with a contact treatment liquid, thereby contacting the oligomer components contained in the reaction product with the contact treatment liquid, thereby reducing the content of oligomer components in the reaction product.

Contact treatment liquids include, for example, alcohols such as methanol, ethanol, isopropanol, or butanol, and mixtures of these alcohols with water. Among these, water/ethanol mixtures (mixtures of water and ethanol) are particularly preferred in terms of ease of handling, cost, contact treatment efficiency, and safety.

(Oligomer Component)
The structure of the oligomer component is not particularly limited, and may have at least one constituent unit selected from the group consisting of the constituent units derived from the diol component and the constituent units derived from the dicarboxylic acid component, or may have the constituent units derived from the diol component and the constituent units derived from the dicarboxylic acid component, and usually contains, as main constituent units, a structural unit derived from the diol component and a structural unit derived from the dicarboxylic acid component used as raw materials.

The oligomer component may have a linear structure, a branched structure, or a cyclic structure, but from the viewpoint of easily suppressing deterioration in the color tone of the final polymer obtained, it is preferable that the oligomer component is a cyclic oligomer component having a structure represented by the following formula (11) or a structure represented by the following formula (12). The cyclic oligomer component can be easily obtained by going through this contact treatment step and the recovery step described below.

In formula (11), R ¹¹ and R ¹² each independently represent a divalent hydrocarbon group which may have a substituent; x ¹ is an integer of 0 to 7;
In formula (12), R ¹³ and R ¹⁴ each independently represent a divalent hydrocarbon group which may have a substituent; y ¹ is an integer of 0 to 7;
^x1 + ^y1 is an integer from 2 to 7.

The conditions for R ¹¹ , R ¹² , x ¹ , and y ¹ in formulas (11) and (12) can be similarly applied to the conditions for R ¹ , R ² , x, and y in formulas (1) and (2) in the first aspect described above.

The content of the oligomer component in the reaction product obtained in the reaction step is not particularly limited and may be the remainder excluding the above-mentioned polyester, but is usually 0.1 mass% or more, preferably 0.2 mass% or more, more preferably 0.3 mass% or more, and even more preferably 0.5 mass% or more, and is usually 3 mass% or less, preferably 2.5 mass% or less, more preferably 2 mass% or less, and even more preferably 1.5 mass% or less.
In the reaction product obtained in the reaction step, the content of the above-mentioned cyclic oligomer component relative to 100% by mass of the oligomer component is not particularly limited, but is usually 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, and is usually 3% by mass or less, preferably 2.5% by mass or less, more preferably 2% by mass or less, and even more preferably 1.5% by mass or less.

The oligomer component may be contained in the raw material, and for example, as described in the recovery step and the supply step described later, the oligomer component obtained in the recovery step can be contained in the polyester raw material. When the polyester raw material contains the oligomer component, the content of the oligomer component in the polyester raw material is not particularly limited, but is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 1.0% by mass or more, even more preferably 2.5% by mass or more, and particularly preferably more than 5.0% by mass, and is usually less than 100% by mass, preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 60% by mass or less.
When the total content is equal to or higher than the lower limit of the above range, it is possible to perform economical production with an increased recovery rate of the oligomer components, while when the total content is equal to or lower than the upper limit of the above range, it is possible to perform production without impairing reactivity while maintaining quality such as color tone.

When the polyester raw material contains an oligomer component, the content of the cyclic oligomer component having the structure represented by the above formula (1) and the structure represented by the above formula (2) in the oligomer component contained in the polyester raw material is preferably 35% by mass or more and 100% by mass or less, more preferably 40% by mass or more, even more preferably 50% by mass or more, particularly preferably 60% by mass or more, and most particularly preferably 70% by mass or more, from the viewpoint of being able to easily suppress deterioration in the color tone of the resulting polyester.

From the viewpoint of easily suppressing deterioration in color tone of the polyester, the above-mentioned cyclic oligomer component is preferably generated by a reaction with a diol component and a dicarboxylic acid component contained in the polymer raw material.
The dicarboxylic acid component includes at least one selected from the group consisting of dicarboxylic acids represented by the following formula (A1) and derivatives thereof, and at least one selected from the group consisting of dicarboxylic acids represented by the following formula (B1) and derivatives thereof,
The diol component preferably contains at least one selected from the group consisting of diols represented by the following formula (C1) and derivatives thereof, and at least one selected from the group consisting of diols represented by the following formula (D1) and derivatives thereof:

In the formulae (A1) to (D1), R ¹¹ to R ¹⁴ have the same meanings as R ¹¹ to R ¹⁴ in the above formulae (11) and (12), respectively.

When the contact treatment process described below is employed, the oligomer components obtained by the contact treatment are recovered, and the recovered oligomer components are reused in the polyester raw material, the diol components and dicarboxylic acid components in the polyester raw material become the same as the oligomer components and dicarboxylic acid components constituting the cyclic oligomer components in the polyester raw material, so that the content of the cyclic oligomer components having the structure represented by the above formula (11) and the structure represented by the above formula (12) in the oligomer components in the polyester raw material can be increased.

The conditions for the contact treatment in the second embodiment can be the same as those described in the first embodiment above, in terms of (1-1) the composition of the contact treatment liquid, (1-2) the contact treatment temperature, (1-3) the contact treatment time, (1-4) the ratio of the reaction product to the contact treatment liquid, and (1-5) the contact treatment method.

(Refining process)
The method for producing a polyester includes a purification step including a process for purifying an oligomer component from a contact treatment solution containing the oligomer component so that the content ratio of cyclic oligomer components in the oligomer component is increased. As described above, the above-mentioned contact treatment step is also a process for purifying a reaction product, but this purification step is a different process from the above-mentioned contact treatment step. The oligomer component obtained by the purification step or a target containing the oligomer component is also referred to as a "purified product".

The method of purifying the oligomer component from the contact treatment liquid containing the oligomer component so that the content ratio of cyclic oligomer components in the oligomer component is increased is not particularly limited, and examples thereof include a method having a distillation separation process for separating a low boiling liquid from a high boiling liquid containing oligomer components and water. In this specification, the high boiling liquid refers to a liquid that is mainly composed of water containing low volatility components such as oligomer components and is extracted from the bottom of a distillation column or the like, and the low boiling liquid refers to a liquid that is more volatile than water and is distilled from the top of a distillation column or the like, such as ethanol, tetrahydrofuran, and acetone. In addition, it is preferable that the low boiling liquid does not substantially contain oligomer components, and it is more preferable that it does not contain any oligomer components.
The method for distillation separation is not particularly limited, and can be carried out by a known method.

The temperature for distillation separation is not particularly limited, and is usually 80°C or higher, preferably 85°C or higher, more preferably 90°C or higher, and even more preferably 95°C or higher, and is usually 120°C or lower, preferably 115°C or lower, more preferably 110°C or lower, and even more preferably 105°C or lower.

Distillation separation can be carried out either batchwise or continuously, but continuous separation is more preferable in terms of production efficiency.

In order to efficiently recover cyclic oligomer components from the high boiling liquid in the distillation separation treatment, the purification step preferably further includes a crystallization step of crystallizing the oligomer components contained in the high boiling liquid after the distillation separation treatment.
The crystallization method is not particularly limited, and may be carried out in either a batch or continuous manner, but in terms of production efficiency, a continuous manner is more preferable.
Crystallization is carried out, for example, by cooling a crystallization tank containing a high boiling liquid in a distillation separation process to a predetermined temperature and separating oligomer components such as cyclic oligomer components precipitated in particulate or paste form from the aqueous solution phase. Crystallization is preferably carried out at a temperature of 50° C. or less, more preferably at a temperature of 40° C. or less, and even more preferably at a temperature of 35° C. or less.

In addition, in order to efficiently separate many cyclic oligomer components from the high-temperature high-boiling liquid after the distillation separation treatment into the aqueous solution phase, the purification step preferably further includes a phase separation treatment in which a liquid/liquid phase separation treatment is performed after the distillation separation treatment to separate the oligomer components from the high-boiling liquid.
The method for liquid/liquid phase separation is not particularly limited, and may be carried out in a batch or continuous manner, but in terms of production efficiency, a continuous manner is more preferable.
The liquid/liquid phase separation is carried out, for example, by extracting the molten oligomer phase (the lower liquid phase, which is believed to contain a small amount of linear oligomers that cause color deterioration) from the bottom while visually checking the liquid/liquid interface using a sight glass or the like provided in the tank, and separating it from the aqueous solution phase (the upper phase, purified oligomer components). The liquid/liquid phase separation is preferably carried out at a temperature of 85° C. or higher, more preferably at a temperature of 90° C. or higher, and even more preferably at a temperature of 95° C. or higher.

When a phase separation process is performed, it is preferable to further include a crystallization process in which the oligomer components separated by the phase separation process are further crystallized. The conditions for this crystallization process can be the same as those for the crystallization process described above.

(Recovery process)
The method for producing a polyester includes a recovery step of recovering the oligomer component obtained in the purification step as a part of the raw material. The oligomer component can be used as a raw material for the polyester, specifically, it can be a structural unit constituting a part of the polyester together with a diol or a dicarboxylic acid, or it can be a structural unit constituting a part of the polyester by replacing a part of the diol or a dicarboxylic acid.
The form of the oligomer component to be recovered is not particularly limited, and may be, for example, the oligomer component alone (including crystals), a liquid containing the oligomer component, or a solid containing the oligomer component.

The recovery step is not particularly limited as long as it can recover a purified product (the target product after purification or a liquid or solid containing the target product), and may be, for example, a recovery step in which the above-mentioned crystallization process is performed, and then the crystallized oligomer component is taken out and recovered as part of the raw material. In this case, the recovered oligomer component can be supplied as a raw material in the supply step described below, and an esterification reaction process or the like can be performed in the above-mentioned reaction step.

In addition, in the recovery step, at least a portion of the oligomer components in the purified product may be separated to adjust the content of the oligomer components in the purified product, which can then be recycled and reused as the contact treatment liquid in the above-mentioned contact treatment step.

The purified product after the purification process can be recycled as is, or it can be reused by adding new contact treatment liquid in an amount equivalent to the amount of contact treatment liquid extracted along with the separated oligomer components.

After the separation step, the oligomer components (which may be a mixture of the contact treatment liquid and the oligomer components) separated by distillation concentration and/or cooling can be recovered as a polyester raw material after being temporarily melted or after being heated and dissolved in the diol component used as a raw material to form a solution.

The recovery operation can be performed either batchwise or continuously, and there are no particular restrictions, but from the perspective of efficiency, a continuous system is more preferable.

(Supply process)
When the method for producing a polyester has the above-mentioned raw material preparation step, it may further have, after the recovery step, a supply step of supplying at least one of a melt obtained by melting the recovered oligomer component and a solution obtained by dissolving the oligomer component in a diol component of the polyester raw material to any step from the raw material preparation step to the reaction step.

The manner of supplying the oligomer components is not particularly limited, but for example, the recovered oligomer components can be supplied to the polyester raw material in the reaction process and reused. Specifically, the recovered oligomer components can be supplied to the esterification reaction process, the ester exchange reaction process, and the polycondensation reaction process in the reaction process and used as a raw material for polyester. In particular, it is a preferred method to return the recovered oligomer components to the esterification reaction tank for the esterification reaction process, the ester exchange reaction tank for the ester exchange reaction process, or the slurry tank for the dicarboxylic acid component and the diol component. More specifically, the recovered oligomer components can be directly supplied to the esterification reaction tank, or can be supplied to the diol component recycle line (2) or the esterification reaction product withdrawal line (4) illustrated in FIG. 1, or can be supplied to the polycondensation reaction tank (a) illustrated in FIG. 2, or can be supplied to a slurry preparation tank for the dicarboxylic acid component and the diol component.

The supply method can be either batch or continuous, but continuous is more preferable in terms of production efficiency.

(Drying process)
The method for producing a polyester may further include a drying step in which the reaction product after the contact treatment (preferably the purification step) is dried after the contact treatment step (preferably the purification step). The reaction product after the contact treatment may be the contact treatment liquid before the purification step or may be the purified product after the purification step, but it is preferable that at least the purified product is dried. The conditions for the drying step may be the same as those for the drying step in the first embodiment described above.

[Manufacturing process example]
The example of the manufacturing process described in the section "Example of Manufacturing Process" in the above-mentioned first embodiment can be similarly applied as an example of the manufacturing process in the second embodiment.

<Polyester Composition>
A polyester composition according to another embodiment of the present invention is a polyester composition containing a polyester obtained by the above-mentioned method for producing a polyester. The polyester produced by the above-mentioned method for producing a polyester may be an aliphatic polyester or an aromatic-aliphatic copolymer polyester.
The polyester composition may further contain an aliphatic oxycarboxylic acid or the like. Furthermore, the polyester composition may contain a carbodiimide compound, a filler, a plasticizer, or other biodegradable resins that are used as necessary. Examples of other biodegradable resins include polycaprolactone, polyamide, polyvinyl alcohol, or cellulose ester, or starch, cellulose, paper, wood flour, chitin/chitosan, coconut shell powder, walnut shell powder, or other animal/plant material fine powders, or mixtures thereof. Furthermore, in order to adjust the physical properties and processability of the molded body, additives such as heat stabilizers, plasticizers, lubricants, antiblocking agents, nucleating agents, inorganic fillers, colorants, pigments, ultraviolet absorbers, or light stabilizers, modifiers, crosslinking agents, or the like may be contained.

<Molded body>
Another embodiment of the present invention is a molded article, specifically, a molded article obtained by molding the above-mentioned polyester composition, or a molded article produced by a method for producing a molded article including a step of producing a polyester by the above-mentioned method for producing a polyester.
The method for producing the molded body is not particularly limited, and can be a known method applied to general-purpose plastics, or a combination of known methods. Examples of the molding method include compression molding (compression molding, lamination molding, stampable molding), injection molding, extrusion molding or co-extrusion molding (film molding by inflation method or T-die method, laminate molding, pipe molding, electric wire/cable molding, molding of profile material), heat press molding, hollow molding (various blow moldings), calendar molding, solid molding (uniaxial stretch molding, biaxial stretch molding, roll rolling molding, stretch-oriented nonwoven fabric molding, thermoforming (vacuum molding, pressure molding), plastic processing, powder molding (rotational molding)), various nonwoven fabric molding (dry method, adhesion method, entanglement method, spunbond method, etc.), etc. Among them, injection molding, extrusion molding, compression molding, or heat press molding, especially extrusion molding or injection molding, are preferably applied. As specific shapes, application to sheets, films, and fibers is preferable.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. The methods for measuring the physical properties and evaluation items used in the following examples are as follows.

<Characteristics evaluation>
[Intrinsic viscosity (IV) dL/g]
The intrinsic viscosity of the polyester was determined using an Ubbelohde viscometer in the following manner: Polyester pellets were dissolved in a mixed solvent of phenol/tetrachloroethane (mass ratio 1/1) to prepare a polymer solution with a concentration of 0.5 g/dL, and the number of seconds it took for the polymer solution and the solvent alone to fall at 30° C. was measured, and the intrinsic viscosity was determined from the following formula (1).
IV=((1+4K _H η _sp ) ^0.5 -1)/(2K _H C)...(1)
In formula (1), η _SP =η/η ₀ -1, η is the number of seconds it takes for the sample solution to drop, η ₀ is the number of seconds it takes for the solvent to drop, C is the concentration of the sample solution (g/dL), and K _H is Huggins' constant. K _H was set to 0.33.

[Esterification rate (%)]
The esterification rate in the production of polyester was calculated from the sample acid value and saponification value by the following calculation formula (2). The acid value was determined by heating 0.3 g of the esterification reaction product sample in 40 mL of benzyl alcohol at 180° C. for 20 minutes, cooling for 10 minutes, and then titrating with 0.1 mol/L potassium hydroxide/methanol solution. The saponification value was determined by hydrolyzing the oligomer component with 0.5 mol/L potassium hydroxide/ethanol solution, and titrating with 0.5 mol/L hydrochloric acid.
Esterification rate (%)=(saponification value−acid value)/saponification value×100 (2)

[Quantitative determination of cyclic oligomer content in polyester pellets (ppm by mass)]
0.5 g of polyester pellets were weighed out, 10 mL of chloroform was added, and the mixture was dissolved at room temperature. 30 mL of ethanol/water mixture (volume ratio 4/1) was slowly dropped under stirring to precipitate the polymer component. After 15 minutes, stirring was stopped and the mixture was allowed to stand for 90 minutes for separation. Next, 2 mL of the supernatant was collected, evaporated to dryness, and then 2 mL of acetonitrile was added to dissolve the mixture. After filtration with a filter having a diameter of 0.45 μm, a high-performance liquid chromatography system "Prominence" manufactured by Shimadzu Corporation was used, and the mobile phase was started with acetonitrile/water (volume ratio = 4/6) and eluted by continuously changing the composition to acetonitrile/water (volume ratio = 9/1) by a high-pressure gradient method. The amount of cyclic oligomer components (cyclic ester oligomer components in which the total number of repeating units of the constitutional units derived from the diol component and the number of repeating units of the constitutional units derived from the dicarboxylic acid component is 2 to 7) was quantified using "CAPCELL PAK C-18 TYPE MGII" manufactured by Osaka Soda Co., Ltd. and expressed as ppm by mass relative to the pellet. A UV detector was used as the detector, and the detection wavelength for oligomers not containing an aromatic ring was 210 nm, and the detection wavelength for oligomers containing an aromatic ring was 254 nm.

For the quantitative determination of the cyclic dimer ((BS)2), an absolute calibration curve method using a pure product of the cyclic dimer ((BS)2) was employed. The pure product of the cyclic dimer was obtained as follows. That is, polymer pellets obtained by polymerizing succinic acid and 1,4-butanediol were stirred in acetone at 50°C for 12 hours to contact-treat the oligomer components. After the contact-treat was completed, the pellets were filtered off, and the acetone was volatilized from the acetone solution in which the oligomer components had been contact-treated to obtain a solid. This solid was dissolved in acetone at 50°C to obtain a saturated solution, and then slowly cooled, the supernatant was discarded, and the needle-shaped precipitate was taken out. This recrystallization procedure was repeated several times for purification. This needle-shaped precipitate was confirmed to be the cyclic dimer by ^1H -NMR analysis and high-performance liquid chromatography analysis. Oligomer components other than the cyclic dimer were identified by LC-MS analysis, and then quantitatively calculated using the relative area value and factor of each oligomer component to the area value of the cyclic dimer in high performance liquid chromatography.

The amount of the cyclic dimer ((BS)2) was determined by calculation using the formula (5) based on an absolute calibration curve using HPLC area values.
(Quantitative value of cyclic dimer ((BS)2)) = (slope of cyclic dimer ((BS)2) calibration curve) x (HPLC 210 nm UV area value of cyclic dimer ((BS)2)) + intercept of cyclic dimer ((BS)2) calibration curve ... (5)
Oligomer components not containing an aromatic ring other than the cyclic dimer ((BS)2) were identified by LC-MS analysis, and then quantified using the relative area value of each oligomer component to the area value of the cyclic dimer ((BS)2) in high performance liquid chromatography and a factor, according to formula (6).
(Quantitative value of oligomers other than cyclic dimer ((BS)2))=(Factor of oligomers other than cyclic dimer ((BS)2))×Quantitative value of cyclic dimer ((BS)2)×(HPLC 210 nm UV area value of oligomers other than cyclic dimer ((BS)2))/(HPLC 210 nm UV area value of cyclic dimer ((BS)2))...(6)

The amount of the aromatic ring-containing oligomer component was determined by preparing an absolute calibration curve using dimethyl terephthalate (DMT) as a standard substance, and after identifying the component by LC-MS analysis in advance, the amount of the aromatic ring-containing oligomer component was calculated using the HPLC area value as a DMT equivalent value according to the formula (7).
(Quantitative value of oligomer containing aromatic ring) = slope of DMT calibration curve × (HPLC 254 nm UV area value) + intercept of DMT calibration curve ... (7)

[Terminal carboxyl group amount (acid value) equivalent/ton]
After crushing the polyester pellets, the polyester sample was dried at 140°C for 15 minutes in a hot air dryer and cooled to room temperature in a desiccator. 0.1 g was precisely weighed and collected in a test tube, and 3 cm ³ of benzyl alcohol was added and dissolved at 195°C for 3 minutes while blowing in dry nitrogen gas. Then, 5 cm ³ of chloroform was gradually added and cooled to room temperature. 1 to 2 drops of phenol red indicator were added to this solution, and titration was performed with a 0.1 mol/L benzyl alcohol solution of sodium hydroxide while stirring while blowing in dry nitrogen gas, and the titration was completed when the color changed from yellow to red. In addition, the same operation was performed without adding the polyester sample as a blank, and the amount of terminal carboxyl groups (acid value) was calculated by the following formula (3).
Amount of terminal carboxyl groups (equivalents/ton)=(a−b)×0.1×f/W (3)
Here, a is the amount (μL) of 0.1 mol/L sodium hydroxide solution in benzyl alcohol required for titration, b is the amount (μL) of 0.1 mol/L sodium hydroxide solution in benzyl alcohol required for titration of a blank, W is the amount (g) of the polyester sample, and f is the titer of the 0.1 mol/L sodium hydroxide solution in benzyl alcohol.

The potency (f) of 0.1 mol/L sodium hydroxide in benzyl alcohol was determined by the following method. 5 ^cm3 of methanol was collected in a test tube, 1-2 drops of phenol red in ethanol solution were added as an indicator, and titrated to the color change point with 0.4 ^cm3 of 0.1 mol/L sodium hydroxide in benzyl alcohol. Next, 0.2 ^cm3 of 0.1 mol/L hydrochloric acid solution with a known potency was collected and added as a standard solution, and titrated again to the color change point with 0.1 mol/L sodium hydroxide in benzyl alcohol (the above operations were performed under blowing in dry nitrogen gas). The potency (f) was calculated by the following formula (4).
Titer (f) = Titer of 0.1 mol/L hydrochloric acid solution × Amount of 0.1 N hydrochloric acid solution collected (μL) / Titer amount of 0.1 mol/L sodium hydroxide benzyl alcohol solution (μL) ... (4)

<Preparation of catalyst for polycondensation reaction>
In a reactor equipped with a stirrer, 343.5 parts by weight of magnesium acetate tetrahydrate was placed, and 1434 parts by weight of anhydrous ethanol (purity 99% by weight or more) was added. 218.3 parts by weight of ethyl acid phosphate (mixture weight ratio of monoester and diester is 45:55) was added, and stirring was performed at 23°C. After confirming that magnesium acetate was completely dissolved, 410.0 parts by weight of tetra-n-butyl titanate was added. Stirring was continued for another 10 minutes to obtain a homogeneous mixed solution. This mixed solution was concentrated under reduced pressure while controlling the temperature at 60°C or less. Approximately half of the amount of ethanol added was distilled off, leaving a translucent viscous liquid. 1108 parts by weight of 1,4-butanediol was added thereto, and further concentration was performed under reduced pressure while controlling the temperature at 80°C or less to obtain a catalyst solution with a titanium atom content of 3.5% by weight.

<Production method of polyester>
[Production method of polybutylene succinate (PBS)]
A polyester was produced as follows by the esterification process shown in Fig. 1 and the polycondensation reaction process shown in Fig. 2. A slurry at 50°C, in which 1.30 mol of 1,4-butanediol and 0.0033 mol of malic acid were mixed relative to 1.00 mol of succinic acid, was continuously supplied at a flow rate of 3721 kg/h from a slurry preparation tank (not shown) through a raw material supply line (1) to an esterification reaction tank (A) equipped with a stirrer which had been previously packed with a low molecular weight polyester (esterification reaction product) having an esterification rate of 99% by mass under a nitrogen atmosphere.

The esterification reaction tank (A) had an internal temperature of 230°C and a pressure of 101 kPa, and the water, tetrahydrofuran, and excess 1,4-butanediol produced were distilled through the distillation line (5) and separated into high-boiling and low-boiling components in the distillation tower (C). After the system had stabilized, a portion of the high-boiling components at the bottom of the tower were withdrawn to the outside through the withdrawal line (8) so that the liquid level in the distillation tower (C) would be constant. Meanwhile, the low-boiling components, mainly water and tetrahydrofuran, were withdrawn in gas form from the top of the tower, condensed in the condenser (G), and withdrawn to the outside through the withdrawal line (13) so that the liquid level in the tank (F) would be constant. At the same time, the entire amount of the bottom component (98% by mass or more of 1,4-butanediol) of the 100°C rectification column (C) was fed from the recirculation line (2), and an equal mole of 1,4-butanediol to the tetrahydrofuran generated in the esterification reaction tank was fed from the raw material feed line (1), and the molar ratio of 1,4-butanediol to succinic acid in the esterification reaction tank was adjusted to 1.30. The total feed amount from the recirculation line (2) and the raw material feed line (1) was 133.1 kg/h. The amount of 1,4-butanediol converted to tetrahydrofuran was 0.092 moles per 1.00 mole of succinic acid (THF conversion rate of 9.2 moles per 1 mole of succinic acid).

The esterification reaction product produced in the esterification reaction tank (A) was continuously withdrawn from the esterification reaction product withdrawal line (4) using a pump (B), and the liquid level was controlled so that the average residence time of the liquid in the esterification reaction tank (A) was 3 hours in terms of succinic acid units. The esterification reaction product withdrawn from the withdrawal line (4) was continuously supplied to the first polycondensation reaction tank (a) in Figure 2. After the system stabilized, the esterification rate of the esterification reaction product collected at the outlet of the esterification reaction tank (A) was 92.8%.

The catalyst solution previously prepared by the method described above was diluted with 1,4-butanediol in a catalyst preparation tank so that the titanium atom concentration was 0.12 mass%, and the catalyst solution was then continuously supplied to the esterification reaction product withdrawal line (4) through the supply line (L8) at a rate of 125.6 kg/h (the catalyst was added to the liquid phase of the reaction liquid). The supply amount was stable throughout the operation period.

The internal temperature of the first polycondensation reaction tank (a) was set to 240°C, the pressure to 2.7 kPa, and the liquid level was controlled so that the residence time was 120 minutes. An initial polycondensation reaction was carried out while extracting water, tetrahydrofuran, and 1,4-butanediol from a vent line (L2) connected to a pressure reducer (not shown). The extracted reaction liquid was continuously supplied to the second polycondensation reactor (d). The internal temperature of the second polycondensation reactor (d) was set to 240°C, the pressure to 400 Pa, and the liquid level was controlled so that the residence time was 120 minutes. The polycondensation reaction was further carried out while extracting water, tetrahydrofuran, and 1,4-butanediol from a vent line (L4) connected to a pressure reducer (not shown). The obtained polyester was continuously supplied to the third polycondensation reactor (k) via the extraction line (L3) by the extraction gear pump (e). The internal temperature of the third polycondensation reactor (k) was 240°C, the pressure was 130 Pa, and the residence time was 120 minutes, and the polycondensation reaction was further carried out. The obtained polyester was continuously extracted in the form of a strand from the die head (g) and cooled with water, while being cut into pellets by a rotary cutter (h). The intrinsic viscosity was 1.80±0.05 dL/g, and the polyester pellets were of stable quality.

(Contact treatment of polybutylene succinate (PBS) pellets with contact treatment solution)
The obtained polyester pellets were subjected to contact treatment by the contact treatment (contact treatment step) shown in Fig. 3. A mixed liquid of ethanol and water used as a contact treatment liquid was controlled to 70°C from a circulation tank (I) via a heat exchanger (II) by a pump (IX) and supplied to a contact treatment tank (III) via a supply line (101). The ratio of ethanol (hereinafter sometimes abbreviated as EtOH) to water in the contact treatment liquid was 60 mass% of water relative to the entire contact treatment liquid. The mass ratio of the contact treatment liquid to the pellets in the treatment tank was 5 (treatment liquid/pellet ratio).

Drying of Polybutylene Succinate (PBS) Pellets
Drying was performed according to the drying process shown in Fig. 4. The dry nitrogen gas in the first drying tower had a purity of 99% or more (dew point -40°C), a gas temperature of 80°C, a gas (superficial) velocity of 0.125 m/sec, and a pellet residence time of 15 hours, while the dry air in the second drying tower (dew point -40°C) had a temperature of 80°C, a gas (superficial) velocity of 0.125 m/sec, and a pellet residence time of 24 hours.

[Production method of polybutylene succinate adipate (PBSA)]
A polyester was produced as follows by the esterification reaction treatment (esterification step) shown in FIG. 1 and the polycondensation reaction treatment shown in FIG. 2. A 50° C. slurry containing 0.74 mol of succinic acid, 0.26 mol of adipic acid, 1.30 mol of 1,4-butanediol, and 0.0033 mol of malic acid was continuously supplied at a flow rate of 3823 kg/h from a slurry preparation tank (not shown) through a raw material supply line (1) to an esterification reaction tank (A) having a stirrer previously filled with a low molecular weight polyester (esterification reaction product) having an esterification rate of 99% by mass under a nitrogen atmosphere. The other operations were the same as those in the production method of PBS. The esterification rate of the esterification reaction product collected at the outlet of the esterification reaction tank (A) was 92.8%, and the intrinsic viscosity of the finally obtained polyester pellets was 1.80±0.05 dL/g, and the quality was stable.

(Contact treatment of polybutylene succinate adipate (PBSA) pellets with contact treatment solution)
The obtained polyester pellets were subjected to a contact treatment by the contact treatment (contact treatment step) shown in Fig. 3. The temperature of the mixture of ethanol and water used as the contact treatment liquid was controlled to 45°C, and other conditions and operations were the same as those of the contact treatment with PBS.

Drying of Polybutylene Succinate Adipate (PBSA) Pellets
Drying was carried out according to the drying process shown in Fig. 4. The drying process was carried out in the same manner as for the PBS pellets, except that the gas temperatures in the first drying tower and the second drying tower were set to 65°C.

[Recovery of contact treatment liquid]
The contact treatment liquid was contacted with the pellets in the treatment tank in a countercurrent manner and then withdrawn from the withdrawal line (102). A part of the withdrawn treatment liquid was fed to the separator (XI) via the fine powder remover (IV), and the remainder was recovered in the circulation tank (I). The pellets to be subjected to the contact treatment were continuously fed from the supply line (103), contacted with the contact treatment liquid for 4 hours, and then continuously withdrawn from the withdrawal line (104) via the rotary valve (V). The contact treatment liquid withdrawn together with the pellets was separated in the preliminary solid-liquid separator (VI), passed through the recovery tank (VII), and returned to the recovery line (106) via the supply line (105) by the pump (X).

The contact treatment liquid supplied to the separator (XI) was separated into a low boiling liquid not containing oligomer components and a high boiling liquid containing oligomer components in the distillation column (XI). The low boiling liquid was supplied to the circulation tank (I) via the heat exchanger (XII) and line (109). The high boiling liquid containing cyclic oligomer components was extracted to the liquid phase separation tank (XIII) via line (111). Ethanol and water in an amount equivalent to the contact treatment liquid extracted from the extraction line (111) entrained with the high boiling liquid containing cyclic oligomer components were supplied to the circulation tank (I) from the supply line (107). The continuously extracted pellets were separated from the entrained contact treatment liquid in the preliminary solid-liquid separator (VI) and then continuously supplied to the drying process from the solid-liquid separator (VIII) via the extraction line (108).

[Recovery process of oligomer components from high boiling liquid by phase separation treatment]
The high boiling liquid containing oligomer components and mainly composed of water, which was supplied to the liquid phase separation tank (XIII), was separated into an upper layer that dissolved in water and a lower layer that was insoluble in water and formed oil droplets at 100°C, in which the oligomer components were in a molten state, and the molten oligomer components in the lower layer were taken out of the container through the line (112). After air cooling in the container, the oligomer components became almost white lumps in the case of PBS, and in the case of PBSA, they were in a paste state close to white. The upper layer was allowed to overflow from the liquid phase separation tank (XIII) and was supplied to the solid-liquid separation tank (XIV) through the line (113).

[Step for recovering oligomer components by crystallization of the upper layer aqueous solution through phase separation treatment]
The aqueous solution in the upper layer of the separation tank (XIII) supplied to the solid-liquid separation tank (XIV) was cooled to 30°C by adding water, and the precipitated solid oligomer component was separated from the aqueous solution in a solid-liquid separator (XV) and taken out into a container. The oligomer component obtained here was an almost white powder in the case of PBS, and a paste-like substance close to white in the case of PBSA. The aqueous solution remaining after the oligomer component was removed was treated with activated sludge.

[Composition of Recovered Oligomer Component]
The composition of the cyclic oligomer components contained in the recovered oligomer components was quantified using the above-mentioned high performance liquid chromatograph. The results of the composition analysis of the oligomer components of PBS and PBSA are shown in the following Tables 1 and 2. For comparison, Table 1 also shows oligomer components obtained by evaporating the contact treatment liquid to dryness without performing liquid-phase separation and solid-liquid separation.
The cyclic oligomer components in the recovered oligomer components and the oligomer components other than the cyclic oligomer components were all only oligomer components generated from the raw materials used as the raw materials. That is, the cyclic oligomer components in the case where polybutylene succinate (PBS) pellets were used were cyclic oligomer components composed of constitutional units derived from succinic acid, constitutional units derived from 1,4-butanediol, and constitutional units derived from malic acid, and the cyclic oligomer components in the case where polybutylene succinate adipate (PBSA) was used were cyclic oligomer components composed of constitutional units derived from succinic acid, constitutional units derived from adipic acid, constitutional units derived from 1,4-butanediol, and constitutional units derived from malic acid.

　In Table 1, the composition of the cyclic dimer to heptamer after liquid/liquid separation and solid/liquid separation is as follows: cyclic dimer (x=2 in formula 1, y=0 in formula 2, x+y=2) 22.3 wt%, cyclic trimer (x=3 in formula 1, y=0 in formula 2, x+y=3) 26.3 wt%, cyclic tetramer (x=4 in formula 1, y=0 in formula 2, x+y=4) 20.3 wt%, cyclic pentamer (x=5 in formula 1, y=0 in formula 2, x+y=5) 7.7 wt%, cyclic hexamer (x=6 in formula 1, y=0 in formula 2, x+y=6) 2.2 wt%, cyclic heptamer (x=7 in formula 1, y=0 in formula 2, x+y=6) 2.2 wt%, The composition after only solvent distillation and no purification was as follows: cyclic dimer (x=2 in formula 1, y=0 in formula 2, x+y=2) 26 wt%, cyclic trimer (x=3 in formula 1, y=0 in formula 2, x+y=3) 3.6 wt%, cyclic tetramer (x=4 in formula 1, y=0 in formula 2, x+y=4) 2 wt%, cyclic pentamers (x=5 in formula 1, y=0 in formula 2, x+y=5) 1.8 wt%, cyclic hexamers (x=6 in formula 1, y=0 in formula 2, x+y=6) 0.7 wt%, and cyclic heptamers (x=7 in formula 1, y=0 in formula 2, x+y=7) 0 wt%.

In Table 2, the cyclic dimer to heptamer are specifically: homocyclic dimer (x=2 in formula 1, y=0 in formula 2, x+y=2) 10.1 wt%, homocyclic trimer (x=3 in formula 1, y=0 in formula 2, x+y=3) 11.6 wt%, homocyclic tetramer (x=4 in formula 1, y=0 in formula 2, x+y=4) 5.4 wt%, homocyclic pentamer (x=5 in formula 1, y=0 in formula 2, x+y=5) 7.0 wt%, homocyclic hexamer (x=6 in formula 1, y=0 in formula 2, x+y=6) 2.0 wt% %, homocyclic heptamer (x=7 in formula 1, y=0 in formula 2, x+y=7) 3.0 wt%, BA unit-containing cyclic dimer (x=1 in formula 1, y=1 in formula 2, x+y=2) 15.1 wt%, BA unit-containing cyclic trimer (x=2 in formula 1, y=1 in formula 2, x+y=3) 14.4 wt%, BA unit-containing cyclic tetramer (x=3 in formula 1, y=1 in formula 2, x+y=4) 5.7 wt%, BA unit-containing cyclic dimer (x=0 in formula 1, y=2 in formula 2, x+y=2) 6.9 wt%.

<Polymerization of polybutylene succinate (PBS) containing recovered oligomer components>
[Example 1]
A reaction vessel equipped with a stirrer, a nitrogen inlet, a heater, a thermometer, and a pressure reducing port was charged with 65.2 parts by weight of succinic acid, 64.5 parts by weight of 1,4-butanediol, and 0.257 parts by weight of malic acid as raw materials, and the recovered oligomer component was added so that it was 5 parts by weight per 100 parts by weight of the product polyester. Nitrogen gas was introduced into the vessel while stirring the contents, and the system was placed under a nitrogen atmosphere by vacuum replacement. Next, the temperature in the system was raised from 160°C to 230°C over one hour while stirring, and the reaction was carried out at this temperature for one hour.

The catalyst solution was added to this ester oligomer component in an amount of 50 ppm by weight of titanium atom per polyester obtained, and the mixture was kept at 230°C for 30 minutes, then heated to 250°C over 30 minutes, and simultaneously reduced in pressure to 0.07 x ¹⁰³ Pa or less over 2 hours. The polycondensation reaction was continued while maintaining the heated and reduced pressure state, and polymerization was terminated when a predetermined viscosity was reached. The pressure was restored with nitrogen, and the mixture was drawn out in the form of a strand into a water bath, cooled with water, and then cut into chips to obtain polyester pellets. The intrinsic viscosity of the obtained polyester was 1.78 dL/g, and the color b value of the pellets was 2.8.

[Example 2]
The PBS polymerization was carried out in the same manner as in Example 1, except that the amount of the recovered oligomer component added was 10 parts by weight per 100 parts by weight of the product polyester. The intrinsic viscosity of the resulting polyester was 1.71 dL/g, and the color b value of the pellets was 3.6.

[Example 3]
The PBS polymerization was carried out in the same manner as in Example 1, except that the amount of the recovered oligomer component added was 20 parts by weight per 100 parts by weight of the product polyester. The intrinsic viscosity of the resulting polyester was 1.78 dL/g, and the color b value of the pellets was 5.9.

[Comparative Example 1]
The PBS polymerization was carried out in the same manner as in Example 1, except that the oligomer component recovered without purification by only distilling off the solvent was added in an amount of 5 parts by weight per 100 parts by weight of the product polyester. The intrinsic viscosity of the resulting polyester was 1.72 dL/g, and the color b value of the pellets was 3.4.

[Comparative Example 2]
The PBS polymerization was carried out in the same manner as in Example 1, except that the oligomer component recovered without purification by only distilling off the solvent was added in an amount of 10 parts by weight per 100 parts by weight of the product polyester. The intrinsic viscosity of the resulting polyester was 1.75 dL/g, and the color b value of the pellets was 6.3.

[Comparative Example 3]
The PBS polymerization was carried out in the same manner as in Example 1, except that the oligomer component recovered without purification by only distilling off the solvent was added in an amount of 20 parts by weight per 100 parts by weight of the product polyester. The intrinsic viscosity of the resulting polyester was 1.73 dL/g, and the color b value of the pellets was 8.6.

<Polymerization of polybutylene succinate (PBSA) containing recovered oligomer components>
[Example 4]
A reaction vessel equipped with a stirrer, a nitrogen inlet, a heater, a thermometer, and a pressure reducing port was charged with 48.6 parts by weight of succinic acid, 21.2 parts by weight of adipic acid, 65.1 parts by weight of 1,4-butanediol, and 0.239 parts by weight of malic acid as raw materials, and the recovered oligomer component was added so that it was 5 parts by weight per 100 parts by weight of the polyester product. Nitrogen gas was introduced into the vessel while stirring the contents, and the system was placed under a nitrogen atmosphere by vacuum replacement. Next, the temperature in the system was raised from 160°C to 230°C over one hour while stirring, and the reaction was carried out at this temperature for one hour.

The catalyst solution was added to this ester oligomer component in an amount of 50 ppm by weight of titanium atom per polyester obtained, and the mixture was kept at 230°C for 30 minutes, then heated to 250°C over 30 minutes, and simultaneously reduced in pressure to 0.07 x ¹⁰³ Pa or less over 2 hours. The polycondensation reaction was continued while maintaining the heated and reduced pressure state, and polymerization was terminated when a predetermined viscosity was reached. The pressure was restored with nitrogen, and the mixture was drawn out in the form of a strand into a water bath, cooled with water, and then cut into chips to obtain polyester pellets. The intrinsic viscosity of the obtained polyester was 1.81 dL/g, and the color b value of the pellets was 3.0.

[Example 5]
The PBSA polymerization was carried out in the same manner as in Example 4, except that the amount of the recovered oligomer component added was 10 parts by weight per 100 parts by weight of the product polyester. The intrinsic viscosity of the resulting polyester was 1.81 dL/g, and the color b value of the pellets was 6.6.

[Example 6]
The PBSA polymerization was carried out in the same manner as in Example 4, except that the amount of the recovered oligomer component added was 20 parts by weight per 100 parts by weight of the product polyester. The intrinsic viscosity of the resulting polyester was 1.84 dL/g, and the color b value of the pellets was 8.5.

1: Raw material supply line 2: Recirculation line 3: Catalyst supply line 4: Esterification reaction product withdrawal line 5: Distillation line 6: Withdrawal line 7: Circulation line 8: Withdrawal line 9: Gas withdrawal line 10: Condensate line 11: Withdrawal line 12: Circulation line 13: Withdrawal line 14: Vent line 15: Supply line A: Esterification reaction tank B: Withdrawal pump C: Distillation column D: Pump E: Pump F: Tank G: Condenser L1, L3, L5: Polycondensation reaction product withdrawal lines L2, L4, L6: Vent line L7: Catalyst supply line L 8: Raw material supply line a: First polycondensation reaction tank d: Second polycondensation reaction tank k: Third polycondensation reaction tank c, e, m: Discharge gear pump g: Die head h: Rotary cutter p, q, r, s: Filter I: Circulation tank II: Heat exchanger III: Contact treatment tank IV: Fine powder remover V: Rotary valve VI: Spare solid-liquid separator VII: Recovery tank VIII: Solid-liquid separator IX: Pump X: Pump XI: Distillation column XII: Heat exchanger XIII: Liquid phase separation tank XIV: Solid-liquid separation tank XV: Solid-liquid separator 101: Contact treatment liquid supply line 102: Discharge Line 103: Pellet supply line 104: Withdrawal line 105: Supply line 106: Recovery line 107: Supply line 108: Withdrawal line 109: Low boiling liquid withdrawal line 110: Contact treatment liquid supply line 111: High boiling liquid withdrawal line 112: Oligomer component recovery line 113: Liquid phase separation tank overflow line 114: Solid-liquid separation tank overflow line 115: Drainage line 116: Drainage line 117: Oligomer component recovery line I: First drying tower J: Cooling tower K: Second drying tower L: Condenser M: Heat exchanger N: Heat exchanger Heat exchanger O: rotary valve P: rotary valve Q: rotary valve R: blower S: heat exchanger 201: pellet supply line 202: pellet withdrawal line 203: pellet supply line 204: pellet withdrawal line 205: pellet supply line 206: pellet withdrawal line 207: dry gas recovery line 208: dry gas supply line 209: new dry gas supply line 210: condensate withdrawal line 211: cooling gas withdrawal line 212: cooling gas supply line 213: dry gas withdrawal line 214: dry gas supply line

Claims

A method for producing a polyester, comprising a reaction step including at least one reaction treatment selected from the group consisting of an esterification reaction treatment and an ester exchange reaction treatment, in which a polyester raw material is reacted,
The polyester raw material contains a diol component, a dicarboxylic acid component, and an oligomer component,
The content of a cyclic oligomer component in the oligomer component is 35% by mass or more and 100% by mass or less,
the cyclic oligomer component comprises a constituent unit derived from the diol component and a constituent unit derived from the dicarboxylic acid component, and the total number of repeating units of the constituent units derived from the diol component and the constituent units derived from the dicarboxylic acid component is 2 to 7.
The method for producing polyester according to claim 1, wherein the diol component includes at least one selected from the group consisting of 1,4-butanediol and its derivatives.
The method for producing polyester according to claim 1 or 2, wherein the content of the oligomer component in the polyester raw material is 0.1% by mass or more and less than 100% by mass.
The method further comprises a purification step including a contact treatment in which the reaction product obtained in the reaction step is contacted with a solvent containing water to obtain a contact treatment liquid containing the oligomer component and a post-contact treatment reaction product,
The oligomer component in the treatment liquid is reused as an oligomer component in the polyester raw material in the reaction step.
A method for producing the polyester according to claim 1 or 2.
The method for producing polyester according to claim 4, further comprising a pelletizing step between the reaction step and the purification step, in which the reaction product obtained in the reaction step is pelletized to obtain pellets.
The method further includes a raw material preparation step of preparing the polyester raw material before the reaction step,
The method for producing a polyester according to claim 4 , wherein the oligomer component in the contact treatment liquid is supplied to any one of the steps from the raw material preparation step to the reaction step.
The method for producing polyester according to claim 4 further comprises a drying step in which the reaction product is dried after the contact treatment.
The method for producing polyester according to claim 7, wherein at least one treatment selected from the group consisting of a contact treatment in the purification step and a drying treatment in the drying step is carried out continuously.
The method for producing a polyester according to claim 1 or 2, wherein the cyclic oligomer component has a structure represented by the following formula (1) and a structure represented by the following formula (2):

In formula (1), R 1 and R 2 each independently represent a divalent hydrocarbon group which may have a substituent; x is an integer of 0 to 7;
In formula (2), R 3 and R 4 each independently represent a divalent hydrocarbon group which may have a substituent; y is an integer of 0 to 7;
x+y is 2 to 7.
10. The method for producing a polyester according to claim 9, wherein R 1 to R 4 are each independently a divalent hydrocarbon group having 2 to 40 carbon atoms which may have a substituent.
The polyester raw material is
The dicarboxylic acid component includes at least one selected from the group consisting of dicarboxylic acids represented by the following formula (A) and derivatives thereof, and at least one selected from the group consisting of dicarboxylic acids represented by the following formula (B) and derivatives thereof:
The diol component includes at least one selected from the group consisting of diols represented by the following formula (C) and derivatives thereof, and at least one selected from the group consisting of diols represented by the following formula (D) and derivatives thereof:
At least one kind selected from the group consisting of at least one kind selected from the group consisting of diols represented by the following formula (C) and at least one kind selected from the group consisting of diols represented by the following formula (D) is at least one kind selected from the group consisting of 1,4-butanediol and derivatives thereof:
A method for producing the polyester according to claim 9.

(In formulas (A) to (D), R 1 to R 4 have the same meanings as R 1 to R 4 in formula (1), respectively.)
The method for producing polyester according to claim 1 or 2, wherein at least one treatment selected from the group consisting of the contact treatment in the purification step and the drying treatment in the drying step is carried out in a batch or semi-batch manner.
A composition comprising a polyester including a constitutional unit derived from a diol component and a constitutional unit derived from a dicarboxylic acid component, and a cyclic oligomer component having a structure represented by the following formula (1) and a structure represented by the following formula (2):

In formula (1), R 1 and R 2 each independently represent a divalent hydrocarbon group which may have a substituent; x is an integer of 0 to 7;
In formula (2), R 3 and R 4 each independently represent a divalent hydrocarbon group which may have a substituent; y is an integer of 0 to 7;
x+y is 2 to 7.
The composition of claim 13, wherein the polyester comprises constitutional units derived from the cyclic oligomer component.
A molded article obtained by molding the composition according to claim 13 or 14.
a reaction step of obtaining a reaction product by subjecting a polyester raw material containing a diol component and a dicarboxylic acid component to a reaction treatment including at least one treatment selected from the group consisting of an esterification reaction treatment and an ester exchange reaction treatment;
a contact treatment step of contacting the reaction product with a contact treatment liquid to obtain a contact treatment liquid containing an oligomer component and a post-contact treatment reaction product;
a purification step including a treatment for purifying the oligomer components in the contact treatment liquid so that a content ratio of cyclic oligomer components in the oligomer components is increased from the contact treatment liquid containing the oligomer components; and a recovery step for recovering the oligomer components obtained by the purification step as part of the raw material.
A method for producing polyester.
The method for producing polyester according to claim 16, wherein the purification step includes a distillation separation process for separating the oligomer component into a high boiling liquid and a low boiling liquid.
The method for producing polyester according to claim 17 further comprises a phase separation process for performing a liquid/liquid phase separation process to separate the oligomer component from the high boiling liquid.
The method for producing polyester according to claim 18, further comprising a crystallization process for further crystallizing the oligomer components separated in the phase separation process.
The method for producing polyester according to claim 17, further comprising a crystallization process for crystallizing oligomer components contained in the high boiling liquid.
The method for producing polyester according to claim 16 or 17 further comprises a pelletizing step between the reaction step and the contact treatment step, in which the reaction product obtained in the reaction step is pelletized to obtain polyester pellets.
The method further includes a raw material preparation step of preparing the raw material before the reaction step,
The method further includes a supplying step of supplying, after the recovery step, a melt obtained by melting the recovered oligomer component or a solution obtained by dissolving the oligomer component in a diol component of the polyester raw material to any one of the steps from the raw material preparation step to the reaction step.
A method for producing the polyester according to claim 16 or 17.
The method for producing polyester according to claim 16 or 17, wherein the contact treatment liquid contains alcohol.
The method for producing polyester according to claim 16 or 17 further comprises a drying step of drying the reaction product after the contact treatment step.
The method for producing polyester according to claim 24, wherein at least one treatment selected from the group consisting of the contact treatment in the contact treatment step and the drying treatment in the drying step is carried out continuously.
The method for producing polyester according to claim 24, wherein at least one treatment selected from the group consisting of the contact treatment in the contact treatment step and the drying treatment in the drying step is carried out in a batch or semi-batch manner.