Methods for manufacturing polyester, components, and extruded parts.

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

Polyester production method, composition and molded article

[0001] The present invention relates to a method for producing a polyester, a composition, and a molded article.

[0002] Polyesters made from an aliphatic diol or alicyclic diol and an aliphatic dicarboxylic acid, an alicyclic dicarboxylic acid, or an aromatic dicarboxylic acid as the main raw materials, and polyesters made from an aliphatic oxycarboxylic acid as the main raw material, 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.

[0003] However, during polymerization and melt molding of the polyester, a reaction of cyclization of a portion of the polyester inevitably occurs, resulting in the by-production of cyclic oligomers. As a result, when the polyester is molded into a product, it is known that the cyclic oligomers bleed out onto the surface of the molded product, resulting in a deterioration in the surface appearance, and that productivity is significantly reduced due to the need to clean molds, rolls, etc. that are contaminated during molding.

[0004] To solve the above problems, it is known that after polymerization of a polyester, the polyester is washed by contacting the polyester with pure water, or pure water and alcohol, or pure alcohol at a specific temperature range to prevent deterioration in the appearance of the molded product (see Patent Document 1).It is also known to perform a post-treatment by contacting the polyester with water and a water-soluble organic solvent selected from the group consisting of ketones, ethers, and esters (see Patent Document 2).

[0005] Furthermore, it is known that contacting polyester with a specific ratio of isopropanol / water mixture or ethanol / water mixture can suppress deterioration in the surface appearance of molded articles and decreases in productivity such as mold cleaning (see Patent Documents 3 and 4). Patent Documents 3 and 4 disclose, as methods for contacting polyester with an alcohol / water mixture (contact treatment liquid), a batch treatment method in which pelletized polyester and the contact treatment liquid are placed in a treatment tank and contacted, and the pellets are withdrawn after the contact treatment, and a continuous treatment method in which pellets are continuously supplied to a pipe or treatment tank and the contact treatment liquid is contacted in a cocurrent or countercurrent flow to the flow of the pellets, and the pellets are continuously withdrawn.

[0006] Patent Document 5 discloses a production 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.

[0007] Japanese Patent Laid-Open No. 7-316276 Japanese Patent Laid-Open No. 2004-107457 Japanese Patent Laid-Open No. 2010-195989 Japanese Patent Laid-Open No. 2012-092310 Japanese Patent Laid-Open No. 2005-162891

[0008] Patent Document 5 describes a method for treating and reusing contact-treated oligomers and other components, but the recovered oligomer components are concentrated by evaporating organic solvent components from a used contact treatment solvent, and have not undergone 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 a polyester, there is a problem that the degree of deterioration in color tone of the polymer due to the addition of the recovered oligomers increases. In view of the above problems, a first object of the present invention is to provide a polyester production method 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 solution in the contact treatment process is increased.

[0009] Furthermore, when the oligomer mixture obtained by the above method is reused as a raw material to polymerize a polyester, there are problems such as a slower polymerization rate as the amount added increases, resulting in a lower molecular weight of the polymer achieved per unit time, and a greater degree of color deterioration in the polymer relative to the amount of recovered oligomer component added, resulting in a lower 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 a polyester that can improve polyester productivity and suppress color deterioration.

[0010] As a result of investigations, the present inventors have found that the first problem can be solved by setting the content of cyclic oligomer components in oligomer components contained in a polyester raw material within a specific range, and have completed the present invention.

[0011] That is, a first aspect of the present invention resides in the following [A1] to [A15]. [A1] A method for producing a polyester, comprising a reaction step involving at least one reaction treatment selected from the group consisting of an esterification reaction treatment and a transesterification reaction treatment, in which a polyester raw material is reacted, wherein the polyester raw material comprises a diol component, a dicarboxylic acid component, and an oligomer component, the oligomer component having a cyclic oligomer component content of 35% by mass or more and 100% by mass or less, the cyclic oligomer component comprising structural units derived from the diol component and structural units derived from the dicarboxylic acid component, and the sum of the number of repeating units of the structural units derived from the diol component and the number of repeating units of the structural units derived from the dicarboxylic acid component is 2 to 7. [A2] A method for producing a polyester according to [A1], wherein the diol component comprises at least one selected from the group consisting of 1,4-butanediol and derivatives thereof. [A3] A 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 for producing a polyester according to any one of [A1] to [A3], further comprising 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, and the oligomer component in the treatment liquid is reused as an oligomer component in the polyester raw material in the reaction step. [A5] The method for producing a polyester according to [A4], 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. [A6] The method for producing a polyester according to any one of [A1] to [A5], further comprising a raw material preparation step of preparing the polyester raw material before the reaction step, in which the oligomer component in the contact treatment liquid is supplied to any step between the raw material preparation step and the reaction step. [A7] The method for producing a polyester according to any one of [A1] to [A6], further comprising a drying step of performing a drying treatment to dry the post-contact treatment reaction product.[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 are each independently a divalent hydrocarbon group which may have a substituent; x is 0 to 7; and in formula (2), R ３ and R ４ are each independently a divalent hydrocarbon group which may have a substituent; y is 0 to 7, and x+y is 2 to 7. [A10] The R １ ~R ４ are each independently a divalent hydrocarbon group having 2 to 40 carbon atoms, which may have a substituent. [A11] The method for producing a polyester according to [A9] or [A10], wherein the polyester raw material comprises, as the dicarboxylic acid component, 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, and as the diol component, 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, and the at least one selected from the group consisting of the at least one selected from the group consisting of diols represented by the following formula (C) and at least one selected from the group consisting of diols represented by the following formula (D) is at least one selected from the group consisting of 1,4-butanediol and derivatives thereof. (In formulas (A) to (D), R １ ~R ４ are R in the formula (1), respectively. １ ~R ４[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 batch or semi-batch manner. [A13] A composition comprising a polyester containing constitutional units derived from a diol component and constitutional units 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 are each independently a divalent hydrocarbon group which may have a substituent; x is 0 to 7; and in formula (2), R ３ and R ４ are each independently a divalent hydrocarbon group which may have a substituent; y is 0 to 7, and x + y is 2 to 7. [A14] The composition according to [A13], wherein the polyester contains a structural unit derived from the cyclic oligomer component. [A15] A molded article obtained by molding the composition according to [A13] or [A14].

[0012] Furthermore, as a result of further investigations, the present inventors have investigated a process for purifying a contact treatment solution containing oligomer components obtained by contact treatment in polyester production, and have found that the second problem can be solved by recovering the oligomer components obtained by the process for reuse as part of the raw materials, thereby completing the present invention.

[0013] That is, a second aspect of the present invention resides in the following [B1] to [B8]. [B1] A method for producing a polyester, comprising: a reaction step for 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 for obtaining a contact treatment liquid containing an oligomer component and a post-contact treatment reaction product by contacting the reaction product with a contact treatment liquid; a purification step for purifying the oligomer component in the contact treatment liquid from the oligomer component-containing contact treatment liquid so that the content of cyclic oligomer components in the oligomer component is increased; and a recovery step for recovering the oligomer component obtained in the purification step as part of the raw material. [B2] The method for producing a polyester according to [B1], wherein the purification step comprises a distillation separation treatment for separating a low-boiling liquid from a high-boiling liquid containing the oligomer component. [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 a polyester according to [B3], further comprising a crystallization treatment for further crystallizing the oligomer components separated by the phase separation treatment. [B5] The method for producing a polyester according to [B2], further comprising a crystallization treatment for crystallizing the oligomer components contained in the high-boiling liquid. [B6] The method for producing a polyester according to any one of [B1] to [B5], further comprising 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. [B7] The method for producing a polyester according to any one of [B1] to [B6], further comprising a raw material preparation step for preparing the raw material before the reaction step, and a supply step for supplying, after the recovery step, a melt obtained by melting the recovered oligomer components or a solution obtained by dissolving the oligomer components 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. [B8] The method for producing a polyester according to any one of [B1] to [B7], in which the contact treatment liquid contains an alcohol.[B9] The method for producing a polyester according to any one of [B1] to [B8], further comprising a drying step of carrying out a drying step of drying the reaction product after the contact treatment step. [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 the contact treatment in the contact treatment step and the 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 the contact treatment in the contact treatment step and the drying treatment in the drying step is carried out batchwise or semi-batchwise.

[0014] According to the first aspect of the present invention, it is possible 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 solution in the contact treatment process is increased.

[0015] Furthermore, according to the second aspect of the present invention, it is possible to provide a method for producing a polyester, which can improve the productivity of the polyester and suppress deterioration in color tone. For example, when an oligomer component in a contact treatment solution obtained in the production of a polyester is reused as a raw material for polymerization, even if the amount of recovered oligomer component is increased, the decrease in polymerization reactivity and deterioration in polymer color tone are small, so that production efficiency and raw material consumption rate are improved, and a polyester of good quality can be provided.

[0016] 1 is a schematic diagram showing an embodiment of an esterification reaction treatment; 2 is a schematic diagram showing an embodiment of a polycondensation reaction treatment; 3 is a schematic diagram showing an embodiment of a contact treatment and a separation treatment in a first aspect, or a contact treatment step and a purification step in a second aspect; 4 is a schematic diagram showing an embodiment of a drying step;

[0017] The present invention is not limited to the following description and can be implemented with any modifications within the scope of the gist of the present invention. In this specification, when a numerical value or physical property value is enclosed before and after the "~" symbol, 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 multiple embodiments are described in this specification, various conditions in each embodiment can be applied to each other within the applicable range.

[0018] In this specification, "mass %", "mass ppm", and "parts by mass" have the same meaning as "weight %", "weight ppm", and "parts by weight", respectively.

[0019] <First Aspect> <Method for Producing Polyester> A first aspect of a method for producing a polyester according to one embodiment of the present invention (hereinafter, also simply referred to as "method for producing a polyester" in the section for this first aspect) is 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 a transesterification reaction treatment, in which a polyester raw material is reacted, wherein the polyester raw material comprises a diol component, a dicarboxylic acid component, and an oligomer component, the oligomer component has a content of cyclic oligomer components of 35% by mass or more and 100% by mass or less, the cyclic oligomer component comprises structural units derived from the diol component and structural units derived from the dicarboxylic acid component, and the sum of the number of repeating units of the structural units derived from the diol component and the number of repeating units of the structural units derived from the dicarboxylic acid component is 2 to 7.

[0020] [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.

[0021] (Diol Component) The diol component may be any diol component that is commonly 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.

[0022] Examples of the aliphatic diol component 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 from the viewpoint of the physical properties of the resulting polyester. These aliphatic diol components may or may not be derivatives thereof.

[0023] In particular, since it is possible to use diol components derived from biomass (plant raw materials), it is preferable that the diol component contains at least one selected from the group consisting of 1,4-butanediol and derivatives thereof, that is, the diol component contains at least one selected from the group consisting of 1,4-butanediol and derivatives thereof. The form of the derivative is not particularly limited as long as it can be used to produce a polyester. The polyester raw material may contain a diol component containing at least one selected from the group consisting of 1,4-butanediol and derivatives thereof, as described above, or may contain other diol components.

[0024] 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 thereof.

[0025] The above aliphatic diol compounds and / or aromatic diol compounds may be compounds having a structure in which one or more kinds of compounds are mutually dehydrated and condensed.

[0026] The above aliphatic diol component and / or aromatic diol component may be used alone or in combination of two or more kinds.

[0027] 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, or 45% by mass or more, and may be 70% by mass or less, 60% by mass or less, or 50% by mass or less.

[0028] 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, relative to 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.

[0029] Furthermore, ethylene glycol, 1,3-propanediol, 1,4-butanediol, etc., derived from plant materials can be used.

[0030] (Dicarboxylic acid component) The dicarboxylic acid component may be any dicarboxylic acid typically used as a raw material for polyesters, and 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.

[0031] Examples of aliphatic dicarboxylic acid components 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. Aliphatic dicarboxylic acids having 4 or less carbon atoms, such as succinic acid and succinic anhydride, are particularly preferred. These aliphatic dicarboxylic acid components may or may not be derivatives thereof.

[0032] 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 thereof. For example, derivatives of the aromatic dicarboxylic acid components exemplified above are preferred, and among these, lower alkyl esters having 1 to 4 carbon atoms, acid anhydrides, and the like are mentioned. 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.

[0033] The above aliphatic dicarboxylic acid component and / or aromatic dicarboxylic acid component may be used alone or in combination of two or more kinds.

[0034] 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, or 45% by mass or more, and may be 70% by mass or less, 65% by mass or less, or 60% by mass or less.

[0035] 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, relative to 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.

[0036] Succinic acid, succinic anhydride, adipic acid, and the like derived from plant materials can be used.

[0037] (Oligomer Component) In a polyester production process, when a technology for reusing raw material components contained in a contact treatment solution obtained in a contact treatment process after a polymerization reaction is adopted, the contact treatment solution usually contains an oligomer component (ester oligomer component). The oligomer component may contain structural units derived from a diol component constituting the polyester and structural units derived from a polycarboxylic acid component constituting the dicarboxylic acid, but may also be composed only of these structural units. When the contact treatment is performed without any special treatment or when a conventional treatment (e.g., simple solvent distillation) is performed, the oligomer components in the contact treatment solution usually contain a large proportion of oligomer components having a linear or branched structure without a cyclic structure. Specifically, the amount of oligomer components having a linear or branched structure without a cyclic structure relative to the amount of all oligomer components in the contact treatment solution usually exceeds 65% by mass. When a contact treatment solution containing the above oligomer component is reused as a raw material, the production amount of the polymer can be increased, but there is a problem in that the color tone of the final polymer obtained is worse than when it is not reused. As a result of extensive research, the present inventors have found that even when raw material components in a contact treatment solution used in a 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).

[0038] In this specification, the term "cyclic oligomer component" refers to a cyclic ester oligomer component that contains structural units derived from the diol component and structural units derived from the dicarboxylic acid component, and in which the sum of the number of structural units derived from the diol component (the number of repeating units of the structural units) and the number of structural units derived from the dicarboxylic acid component (the number of repeating units of the structural units) is 2 to 7. The cyclic oligomer component is a compound that is produced as a by-product by cyclization of a portion of a polyester obtained through a reaction process that includes at least one reaction process selected from the group consisting of an esterification reaction process and a transesterification reaction process in which a diol component and a dicarboxylic acid component are reacted. The cyclic oligomer component may contain structural units derived from the diol component and structural units derived from the dicarboxylic acid component, but it may also be composed solely of these structural units. An increase in the content of the oligomer component in the reaction product can lead to deterioration in the color tone of the polyester, deterioration in surface appearance, and reduced productivity during molding. However, by setting the amount of the cyclic oligomer component in the polyester raw material within a desired range, the degree of deterioration in the color tone of the polyester, deterioration in surface appearance, and reduced 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 cyclic oligomer components. The cyclic oligomer component may contain the above-mentioned diol component-derived structural units and the above-mentioned dicarboxylic acid component-derived structural units, but may also be composed only of these structural 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).

[0039]

[0040] In formula (1), R １ and R ２ are each independently a divalent hydrocarbon group which may have a substituent; x is 0 to 7; and in formula (2), R ３ and R ４are each independently a divalent hydrocarbon group which may have a substituent; y is 0 to 7; and x+y is 2 to 7.

[0041] R １ and R ２ The form of the divalent hydrocarbon in is not particularly limited, and from the viewpoint of acquisition cost and ease of availability, the number of carbon atoms is independently 1 or more, particularly preferably 2 or more, and is 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.

[0042] R ３ and R ４ The form of the divalent hydrocarbon in is not particularly limited, and from the viewpoint of acquisition cost and ease of availability, the number of carbon atoms is independently 1 or more, particularly preferably 2 or more, and is 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.

[0043] R １ ~R ４ The substituents that R 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, and seleno group. These substituents may be of one type or of two or more types. １ ~R ４ The hydrocarbon group in may not have a substituent.

[0044] The diol component and dicarboxylic acid component constituting the above formulas (1) and (2) may be the diol component and dicarboxylic acid component that are the raw materials for the polyester described above. １ and R ３ may each independently be a structure corresponding to a dicarboxylic acid listed above, and R ２ and R４ may each independently be a structure corresponding to the diols listed above.

[0045] When x is 0 to 7, the solubility in the contact treatment solution is good, and therefore the efficiency of the contact treatment and the recovery of the oligomer component from the polyester pellets are excellent.

[0046] When y is 0 to 7, the solubility in the contact treatment solution is good, and therefore the efficiency of the contact treatment and the recovery of the oligomer component from the polyester pellets are excellent.

[0047] R １ ~R ４ The hydrocarbon group in R may be linear, branched, or may 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 solution, and the polymerization reactivity of the recovered oligomer component. １ ~R ４ The hydrocarbon group in may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group.

[0048] The content of oligomer components 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. It is also 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. If the total content is equal to or greater than the lower limit of the above range, economical production with an increased recovery rate of oligomer components is possible. Furthermore, if the total content is equal to or less than the upper limit of the above range, production can be performed without impairing reactivity while maintaining quality such as color tone.

[0049] 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 obtained 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.

[0050] From the viewpoint of easily suppressing deterioration in color tone of the polyester, the cyclic oligomer component is preferably one produced by a reaction with a diol component and a dicarboxylic acid component contained in the polymer raw material. That is, 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 preferably contains, as the dicarboxylic acid component, 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, and as the diol component, 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 selected from the group consisting of 1,4-butanediol and derivatives thereof, it is preferable that the at least one selected from the group consisting of at least one selected from the group consisting of diols represented by the following formula (C) and at least one selected from the group consisting of diols represented by the following formula (D) is at least one selected from the group consisting of 1,4-butanediol and derivatives thereof.

[0051]

[0052] In formulas (A) to (D), R １ ~R ４ are R in the above formula (1) and formula (2), respectively. １ ~R ４ is synonymous with.

[0053] When the purification step described below is adopted, 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 become 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 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.

[0054] (Other Copolymerization Components) 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. Examples of copolymerization components that can be used in this case include hydroxycarboxylic 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 hydroxycarboxylic acid polymers of these hydroxycarboxylic acids; trifunctional or higher polyhydric alcohols such as glycerin, trimethylolpropane, and pentaerythritol; and trifunctional or higher polyvalent carboxylic acids or anhydrides thereof such as propanetricarboxylic acid, pyromellitic acid, and trimellitic acid, benzophenonetetracarboxylic acid, and anhydrides thereof.

[0055] Furthermore, polyesters with high viscosity can be easily obtained by adding a small amount of a tri- or higher functional hydroxycarboxylic acid, a tri- or higher functional alcohol, or a tri- or higher functional carboxylic acid. Among these, hydroxycarboxylic acids such as malic acid and citric acid are preferred, and malic acid is particularly preferred.

[0056] The content of the tri- or higher functional 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 content exceeds the upper limit of this range, gel (unmelted material) is likely to form in the resulting polyester, while if it is below the lower limit, the advantage of using the multifunctional compound (usually, the advantage of being able to increase the viscosity of the resulting polyester) is difficult to obtain.

[0057] [Physical Properties of Polyester] The intrinsic viscosity (IV, dL / g) of the polyester to be contacted with the contact treatment solution and the intrinsic viscosity of the polyester after contact treatment with the contact treatment solution are preferably 1.4 dL / g or more, particularly preferably 1.6 dL / g or more. Furthermore, the intrinsic viscosity is preferably 2.8 dL / g or less, more preferably 2.5 dL / g or less, 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, making molding difficult.

[0058] The amount of terminal carboxyl groups in the polyester to be contacted 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 will decrease significantly due to hydrolysis, and quality may be significantly impaired.

[0059] [Each step in the polyester production method] Below, each step in the first embodiment of the polyester production method will be described using a continuous production method as an example. However, this is merely an example, and the polyester production method is not limited to this embodiment. In the polyester production method, a continuous production method involves, for example, continuously subjecting a diol component and a dicarboxylic acid component to a reaction step including at least one treatment selected from the group consisting of an esterification reaction treatment and a transesterification reaction treatment, and a polycondensation reaction treatment, using multiple continuous reaction vessels, to obtain a polyester. However, as long as the effects of the present invention are not impaired, the method is not limited to a continuous method, and steps in conventionally known polyester production methods can be adopted. Furthermore, the polyester may be contacted with a contact treatment solution and then dried. When a continuous operation is adopted, from the viewpoint of improving production efficiency and achieving uniformity in the treatment, it is particularly preferable that at least one treatment selected from the group consisting of the contact treatment in the purification step described below and the drying treatment in the drying step described below be performed continuously. In addition, with regard to the batch or semi-batch operation, from the viewpoint of improving production efficiency and uniformity of the treatment, it is particularly preferable 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 be carried out in a batch or semi-batch manner.

[0060] (Raw Material Preparation Step) The method for producing a polyester may further include a raw material preparation step of preparing a polyester raw material before the reaction step described below. The method for preparing the polyester raw material is not particularly limited, and the polyester raw material may be prepared by mixing raw materials produced by synthesis or the like, or by mixing commercially available raw materials.

[0061] (Reaction Step) The method for producing a polyester includes a reaction step of reacting polyester raw materials through at least one reaction treatment selected from the group consisting of an esterification reaction treatment and a transesterification reaction treatment (also referred to herein as "esterification reaction treatment and / or transesterification treatment") to obtain a reaction product. The reaction step may include treatments other than the esterification reaction treatment and / or transesterification reaction treatment.

[0062] (1) Esterification Reaction Treatment / Transesterification Reaction Treatment The reaction process includes an esterification reaction treatment and / or a transesterification reaction treatment in which polyester raw materials are reacted, specifically, an esterification reaction treatment and / or a transesterification reaction treatment in which a diol component and a dicarboxylic acid component are reacted. An esterification reaction is a reaction in which a carboxylic acid is converted into an ester, and a transesterification reaction is a reaction in which an ester and an alcohol are reacted to exchange the main chain moieties. The esterification reaction treatment will be described below, but this description can also be applied to a transesterification reaction to the extent applicable. The esterification reaction treatment and / or transesterification treatment and other subsequent treatments can be carried out in multiple consecutive reaction tanks or in a single reaction tank. However, it is preferable to carry out the treatment in multiple consecutive reaction tanks in order to reduce variation in the physical properties of the resulting polyester.

[0063] The reaction temperature in the esterification reaction treatment is not particularly limited as long as it is a temperature at which the esterification reaction can be carried out. However, in terms of being able 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.

[0064] 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, the decomposition of the diol component and dicarboxylic acid component increases, and the amount of scattered material in the reaction vessel increases, which can easily cause the generation of foreign matter and make the reaction product more likely to become hazy. It is also preferable that the esterification temperature be 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 within ±2°C.

[0065] The reaction atmosphere is not particularly limited, but an inert gas atmosphere such as nitrogen or argon is preferred. The reaction pressure is preferably 50 kPa to 200 kPa, more preferably 60 kPa or more, even more preferably 70 kPa or more, and preferably 130 kPa or less, more preferably 110 kPa or less. If the reaction pressure is below the lower limit of the above range, the amount of flying material in the reaction vessel increases, the haze of the reaction product increases, and this is likely to cause an increase in foreign matter. In addition, the diol component is likely to be distilled out of the reaction system, which is likely to result in a decrease in the polycondensation reaction rate. On the other hand, if the reaction pressure exceeds the upper limit of the above range, the dehydration decomposition of the diol component increases, which is likely to result in a decrease in the polycondensation reaction rate.

[0066] 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.

[0067] 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 the esterified diol component present in the gas phase and the reaction liquid phase of the esterification reaction vessel" to "all dicarboxylic acid components and esterified dicarboxylic acid components present in the gas phase and the reaction liquid phase of the esterification reaction vessel," and does not include the dicarboxylic acid component, the diol component, and their decomposition products that are decomposed in the reaction system and do not contribute to the esterification reaction. For example, when 1,4-butanediol is contained as the diol component, the component that is decomposed and does not contribute to the esterification reaction is the diol component that is formed by decomposing 1,4-butanediol into tetrahydrofuran, and such components that do not contribute are not included in the above molar ratio.

[0068] 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 below the lower limit of the above range, the esterification reaction tends to be insufficient, making it difficult for the subsequent polycondensation reaction to proceed, making it difficult to obtain a polyester with a high degree of polymerization. If the molar ratio exceeds the upper limit of the above range, the decomposition amounts of the diol component and the dicarboxylic acid component tend to increase. To maintain this molar ratio within the preferred range, it is preferable to appropriately replenish the diol component to the esterification reaction system.

[0069] When the reaction step includes a polycondensation reaction treatment described below, 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, while 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 expressed by the following formula: Esterification rate (%) = (saponification value - acid value) / saponification value x 100

[0070] The esterification rate of the esterification reaction product is preferably 85% or more, more preferably 88% or more, and particularly preferably 90% or more. If it is below this lower limit, the polycondensation reactivity, which is a reaction in a subsequent step, will be poor. If it is below this lower limit, more debris will fly during the polycondensation reaction, adhere to the wall surface, and solidify. Furthermore, this debris will fall into the reaction product, causing an increase in haze (generation of foreign matter). The upper limit of the esterification rate is preferably higher for the polycondensation reaction, which is a reaction in a subsequent step, but is usually 99%.

[0071] In the reaction step, 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 being within the above-mentioned ranges. More preferably, the reaction mixture is continuously subjected to a polycondensation reaction described below, whereby a high-quality polyester with low haze and little foreign matter can be efficiently obtained.

[0072] (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 vessels.

[0073] 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 exhibiting sufficient properties for practical use. On the other hand, a production method using ultra-high vacuum polycondensation reaction equipment that keeps the reaction pressure below 0.01 kPa is a preferred embodiment from the viewpoint of improving the polycondensation reaction rate, but requires extremely expensive capital investment, making it economically disadvantageous.

[0074] 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, the polycondensation reaction rate is slow, and not only does it take a long time to produce a polyester with a high degree of polymerization, but it also requires a high-power stirrer, 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 tends to occur, making it difficult to produce a polyester with a high degree of polymerization.

[0075] 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 is insufficient, making it difficult to obtain a polyester with a high degree of polymerization, and the mechanical properties of the molded product tend to be poor. On the other hand, if the reaction time is too long, the molecular weight reduction due to thermal decomposition of the polyester becomes significant, and not only does the mechanical properties of the molded product tend to be poor, but the amount of carboxyl group terminals, which has an adverse effect on the durability of the polyester, may increase due to thermal decomposition.

[0076] By controlling the temperature, time and reaction pressure of the polycondensation reaction within the above ranges, a polyester having a desired intrinsic viscosity can be obtained.

[0077] (3) Reaction Catalyst The esterification reaction and polycondensation reaction are accelerated by using a reaction catalyst. A sufficient reaction rate can be achieved in the esterification reaction even without an esterification catalyst. Furthermore, if an esterification catalyst is present during the esterification reaction, the water produced by the esterification reaction can cause the catalyst to form an insoluble precipitate in the reaction product, which can impair the transparency of the resulting polyester (i.e., increase haze) and can also cause the catalyst to become a foreign substance. Therefore, it is preferable not to add a reaction catalyst during the esterification reaction. Furthermore, adding a catalyst to the gas phase of the reaction vessel can increase the haze of the resulting polyester and can also cause the catalyst to become a foreign substance, so it is preferable to add the catalyst to the reaction liquid.

[0078] In polycondensation reactions, the reaction does not proceed easily without a catalyst, so it is preferable to use a catalyst. As a polycondensation reaction catalyst, a compound containing at least one metal element from Groups 1 to 14 of the periodic table is generally used. 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.

[0079] Furthermore, among the above metals, in order to reduce the polyester terminal concentration, which affects the thermal stability of the polyester, metal elements of Groups 3 to 6 of the periodic table that exhibit Lewis acidity are preferred, specifically scandium, titanium, zirconium, vanadium, molybdenum, or tungsten, with titanium and zirconium being particularly preferred from the viewpoint of availability, and titanium being even more preferred from the viewpoint of reactivity.

[0080] In the present embodiment, as the catalyst, a compound containing an organic group, such as a carboxylate, an alkoxy salt, an organic sulfonate, or a β-diketonate salt, containing the above-mentioned metal element; or an inorganic compound, such as an oxide or halide of the above-mentioned metal element, or a mixture thereof, is preferably used.

[0081] In this embodiment, the catalyst is preferably a liquid during polymerization or a compound that dissolves in the ester oligomer or polyester, because the polymerization rate increases when the catalyst is in a molten or dissolved state during polymerization. Furthermore, the polycondensation reaction is preferably carried out without a solvent. However, a small amount of solvent may be used separately to dissolve the catalyst. Examples of solvents for dissolving the catalyst include alcohols such as methanol, ethanol, isopropanol, or butanol; the aforementioned 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; and mixtures thereof. The amount of solvent used is typically such that the catalyst concentration in the polyester raw material is 0.0001% by mass or more and 99% by mass or less. To dissolve the catalyst, the catalyst can be diluted with a diol such as 1,4-butanediol or ethylene glycol. In this case, the diol can also function as a raw material for the polyester. Therefore, when a diol is used as a solvent for dissolving a catalyst, the amount of the diol component in the raw material is calculated in this specification as including the amount of the diol as the solvent.

[0082] The titanium compound is preferably a tetraalkyl titanate or a hydrolyzate thereof, and specific examples thereof include tetra-n-propyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetra-t-butyl titanate, tetraphenyl titanate, tetracyclohexyl titanate, tetrabenzyl titanate, mixed titanates thereof, and hydrolyzates thereof.

[0083] Furthermore, examples of titanium compounds that are preferably used include titanium (oxy)acetylacetonate, titanium tetraacetylacetonate, titanium (diisoproxide)acetylacetonate, titanium bis(ammonium lactate)dihydroxide, titanium bis(ethylacetoacetate)diisopropoxide, titanium (triethanolaminate)isopropoxide, polyhydroxytitanium stearate, titanium lactate, titanium triethanolaminate, and butyl titanate dimer.

[0084] Furthermore, as the titanium compound, a liquid obtained by mixing an alcohol, a Group 2 metal compound in the long periodic table (Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005) (hereinafter, sometimes referred to as a Group 2 metal compound in the long periodic table), a phosphate ester compound, or a titanium compound may also be used.

[0085] 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 a liquid obtained by mixing alcohols, a Group 2 metal compound in the long periodic table, a phosphate ester compound, and / or a titanium compound are preferred, and tetra-n-butyl titanate, titanium (oxy)acetylacetonate, titanium tetraacetylacetonate, titanium bis(ammonium lactate) dihydroxide, polyhydroxytitanium stearate, titanium lactate, butyl titanate dimer, or a liquid obtained by mixing alcohols, a Group 2 metal compound in the long periodic table, a phosphate ester compound, and / or a titanium compound are preferred. More preferred are tetra-n-butyl titanate, polyhydroxytitanium stearate, titanium lactate, butyl titanate dimer, or a liquid obtained by mixing alcohols, a Group 2 metal compound in the long periodic table, a phosphate ester compound, and / or a titanium compound, and particularly preferred are tetra-n-butyl titanate, polyhydroxytitanium stearate, titanium (oxy)acetylacetonate, titanium tetraacetylacetonate, or a liquid obtained by mixing alcohols, a Group 2 metal compound in the long periodic table, a phosphate ester compound, and / or a titanium compound.

[0086] 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, and mixtures thereof.

[0087] 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, and zirconyl diacetate, zirconium tetraacetate, zirconium acetate hydroxide, zirconium tris(butoxy)stearate, ammonium zirconium oxalate, zirconium tetra-n-propoxide, or zirconium tetra-n-butoxide is more preferred, with zirconium tris(butoxy)stearate being particularly preferred because a polyester with a high degree of polymerization and little coloration can be easily obtained.

[0088] Specific examples of germanium compounds include inorganic germanium compounds such as germanium oxide or germanium chloride, and organic germanium compounds such as tetraalkoxygermanium. In terms of cost and availability, germanium oxide, tetraethoxygermanium, tetrabutoxygermanium, and the like are preferred, with germanium oxide being particularly preferred.

[0089] Examples of iron compounds include inorganic chlorides such as ferric chloride, inorganic oxides such as triiron tetroxide, and organic iron complexes such as ferrocene, etc. Among these, inorganic oxides are preferred.

[0090] Examples of 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 lanthanoid compounds such as cerium chloride, samarium chloride, and ytterbium chloride.

[0091] The amount of the polycondensation reaction catalyst added is not particularly limited, but the lower limit of the metal amount relative to the polyester produced is usually 0.1 mass ppm or more, preferably 0.5 mass ppm or more, and 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 suitable when a metal compound is used as the polycondensation reaction catalyst. Using too much catalyst is not only economically disadvantageous, but can also increase the carboxyl group terminal concentration in the polyester, which can lead to reduced thermal stability and hydrolysis resistance of the polyester due to increased carboxyl group terminal content and residual catalyst concentration. Conversely, if the amount is too small, the polymerization activity will be reduced, which can induce thermal decomposition of the polyester during polyester production, making it difficult to obtain a polyester exhibiting practically useful physical properties.

[0092] The position of the catalyst to be added to the reaction system is not particularly limited as long as it is added before the polycondensation reaction treatment, 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. Therefore, it is preferable to add the catalyst after the esterification reaction treatment.

[0093] (4) Reaction Tank As the esterification reaction tank for carrying out the esterification reaction treatment, known ones can be used, and they may be any of the types such as a vertical stirred complete mixing tank, a vertical thermal convection mixing tank, or a tower-type continuous reaction tank, and may be a single tank or a plurality of tanks of the same or different types connected in series. Among them, a reaction tank having a stirring device is preferred, and as the stirring device, not only a normal type having a power unit, bearings, a shaft, and stirring blades, but also a high-speed rotating type such as a turbine stator type high-speed rotating stirrer, a disk mill type stirrer, or a rotor mill type stirrer can be used.

[0094] There are no limitations on the mode 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 can also be used in which a portion of the reaction liquid is taken out of the reaction tank via piping or the like and stirred with a line mixer or the like to circulate the reaction liquid. 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, Pfaudler blades, full zone blades, and Max Blend blades.

[0095] There are no particular limitations on the type of polycondensation reaction tank, and examples thereof include a vertical stirring polymerization tank, a horizontal stirring polymerization tank, a thin-film evaporation polymerization tank, etc. The polycondensation reaction tank may be a single tank, or a plurality of tanks of the same or different types connected in series, but in the later stage of the polycondensation reaction when the viscosity of the reaction liquid increases, it is preferable to select a horizontal stirring polymerization tank having a thin-film evaporation function that is excellent in interface renewal property, plug flow property, or self-cleaning property.

[0096] 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.

[0097] 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 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.

[0098] (Pelletization Step) 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 polyester production method further includes a pelletization step of pelletizing the reaction product obtained in the reaction step described above to obtain pellets (polyester pellets) after the reaction step described above, particularly between the reaction step described above and the purification step described later.

[0099] The pelletizing method is not particularly limited and can be any known method. For example, a strand cutting method is used in which the molten reaction product is extruded through the nozzle holes of a 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. Alternatively, an underwater hot cutting method is used in which the product is extruded through the nozzle holes into water and immediately cut in a molten state. The underwater hot cutting method is particularly preferred because it produces little chips in the pellets, has a low angle of repose for the resulting pellets, and provides good pellet transport stability and feeding stability to the molding machine during molding. 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.

[0100] 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 circular, elliptical, oblong, rectangular, or star-shaped 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.

[0101] The pellets may be spherical, cylindrical, elliptical, oblong, rectangular, or cocoon-shaped, or may have a flattened shape. In the underwater hot-cut method, spherical, cocoon-shaped, or a flattened shape is preferably used. The size is not particularly limited, but from the viewpoints of the contact treatment efficiency of the oligomer components in the purification step described below, the drying efficiency in the drying step, and the operability of pellet transport, the weight per pellet is 1 to 50 mg, preferably 3 to 40 mg, and more preferably 5 to 30 mg. Furthermore, a larger pellet surface area per mass is preferred from the viewpoint of the contact treatment efficiency in the purification step.

[0102] (Purification Step) The polyester production method 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 oligomer components and a post-contact treatment reaction product. The purification step may include treatments other than the contact treatment. As will be described later, the content of oligomer components in the reaction product can be reduced by performing the contact treatment in the purification step. 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 included 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.

[0103] (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 employed, the pelletizing step) is brought into contact with a contact treatment liquid, thereby bringing oligomer components contained in the reaction product into contact with the contact treatment liquid, thereby making it possible to reduce the content of oligomer components in the reaction product.

[0104] The contact treatment solution 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 from the standpoints of ease of handling, cost, contact treatment efficiency, safety, etc.

[0105] When the polyester production 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.

[0106] (1-1) Composition of Contact Treatment Solution The proportion of water in the entire contact treatment solution to be contacted with the reaction product is not particularly limited, and is typically 10% by mass or more, preferably 20% by mass or more, and more preferably 25% by mass or more. Furthermore, the proportion of water is typically 99% by mass or less, preferably 95% by mass or less, even more preferably 90% by mass or less, and particularly preferably 85% by mass or less. If the water content is below the lower limit of the above range, the quality of the polyester tends to deteriorate due to a decrease in molecular weight caused by alcoholysis. Furthermore, if the proportion of alcohol used is high, the liquid and the gas generated from the liquid may become explosive during use, and therefore, handling with care is required from a safety perspective. On the other hand, if the water content exceeds the upper limit of the above range, oligomer components may not be sufficiently removed, and the content of oligomer components may not be sufficiently reduced, resulting in a polyester of desired quality.

[0107] (1-2) Contact Treatment Temperature The temperature of the contact treatment liquid when the reaction product is brought into contact 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. Setting the contact temperature below the lower limit of the above range not only requires a long treatment time, which is economically disadvantageous, but also reduces the effect of removing oligomer components, making it difficult to obtain a polyester of desired quality. On the other hand, setting the contact temperature above the upper limit of the above range results in a significant decrease in viscosity due to hydrolysis and alcoholysis, which not only impairs quality but also causes operational difficulties, such as fusion between pellets and poor pellet extraction.

[0108] (1-3) Contact Treatment Time The time for contacting the reaction product with the contact treatment solution is not particularly limited and is usually 0.1 hours or more, preferably 1 hour or more, and more preferably 3 hours or more. Furthermore, this time is usually 24 hours or less, preferably 18 hours or less, and more preferably 10 hours or less. If the contact time is below the lower limit of the above range, oligomer components may not be sufficiently removed, and polyester of desired quality may not be obtained. On the other hand, if the contact time exceeds the upper limit of the above range, viscosity may decrease significantly due to hydrolysis and alcoholysis, resulting in a loss of quality.

[0109] (1-4) Ratio of Reaction Product to Contact Treatment Solution The ratio of the reaction product to the contact treatment solution (treatment solution / reaction product ratio), expressed as a mass ratio, is usually 1.0 or more, preferably 1.5 or more, and more preferably 2.0 or more. Furthermore, this ratio, expressed as a mass ratio, is usually 50 or less, preferably 30 or less, and more preferably 20 or less. If the mass ratio of the reaction product to the solution to be contacted is below the lower limit of the above range, the concentration of oligomer components in the contact treatment solution increases during treatment, reducing the effect of removing oligomer components, and polyester of desired quality may not be obtained. On the other hand, if the mass ratio of the pellets to the solution to be contacted exceeds the upper limit of the above range, it is disadvantageous in terms of process and cost, such as increasing the size of the equipment due to the large amount of contact treatment solution used and increasing the cost of the contact treatment solution.

[0110] (1-5) Contact Treatment Method The contact between the reaction product and the contact treatment liquid may be performed in a batchwise manner or a continuous manner, and either manner may be employed. An example of the batchwise manner in this embodiment is a method in which 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 resulting mixture is withdrawn. The contact treatment between the reaction product and the contact treatment liquid may be performed under circulation of the contact treatment liquid, or may be performed without circulation. An example of the continuous manner in this embodiment is a method in which pellets are continuously supplied to a pipe or a treatment tank, and the 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 pellets are continuously withdrawn while maintaining the contact time.

[0111] (2) Separation Treatment From the viewpoint of improving the recycle rate of the contact treatment liquid and reducing costs by improving the recovery efficiency of the cyclic oligomer components, the purification step may include a separation step of separating at least a portion of the cyclic oligomer components in the contact treatment liquid after the contact treatment. Furthermore, after separating at least a portion of the cyclic oligomer components to adjust the content of the cyclic oligomer components in the contact treatment liquid, the resulting liquid can be recycled and reused as the contact treatment liquid in the contact treatment. Furthermore, the cyclic oligomer components containing the separated cyclic oligomer components can be reused as oligomer components in the polyester raw material in the reaction step after being separated from the contact treatment liquid by cooling or after being concentrated. In particular, it is a preferred method to return the separated cyclic oligomer components to the esterification reaction tank where the esterification reaction is performed in the reaction step or to the tank for preparing a slurry of the dicarboxylic acid component and the diol component.

[0112] The contact treatment liquid after the separation treatment can be recycled and reused as it is, or a new contact treatment liquid can be added and reused in an amount corresponding to the amount of the contact treatment liquid extracted together with the separated cyclic oligomer component.

[0113] After the separation treatment, the oligomer component (which may be a mixture of the contact treatment liquid and the oligomer component) separated by distillation concentration and / or cooling, etc., can be recovered as a polyester raw material after being melted or dissolved by heating in the diol component used as a raw material to form a solution. The recovered oligomer component can be fed directly to the esterification reaction tank, or fed to the diol component recycle line (2) or the esterification reaction product withdrawal line (4) shown in Figure 1, or fed to the polycondensation reaction tank (a) shown in Figure 2, or fed to a tank for preparing a slurry of the dicarboxylic acid component and the diol component.

[0114] (Drying Step) The polyester production method may further include a drying step in which the reaction product after the contact treatment is dried. Since the contact-treated reaction product contains the contact treatment liquid, it is preferable to dry it in the drying step to remove this. 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 vertical dryers, and fluidized-bed dryers, which circulate an inert gas such as heated air or heated nitrogen as the drying gas. Dryers other than those using the gas flow method include double-cone rotary vacuum dryers, tumbler rotary vacuum dryers, and microwave dryers.

[0115] These processes can be carried out in a batch, semi-batch, or continuous manner, but for mass production, a continuous process is preferred from the viewpoint of production efficiency. Also, from the viewpoint of avoiding complex equipment, it is preferred to use a moving-bed vertical dryer or a multi-stage continuous dryer.

[0116] The drying temperature is not particularly limited, but is usually 25°C or higher, preferably 30°C or higher, more preferably 35°C or higher, and particularly preferably 40°C or higher, as the gas temperature. The upper limit of the temperature is usually below the melting point of the polyester, preferably below 5°C below the melting point of the polyester, more preferably below 8°C below the melting point of the polyester, and particularly preferably below 10°C below the melting point of the polyester. Setting the drying temperature below the lower limit of the above range requires a long drying time, which is economically disadvantageous. On the other hand, setting the drying temperature above the upper limit of the above range can cause operational difficulties, such as fusion of pellets with each other or poor removal of pellets from the dryer. The drying gas that has passed through the dryer contains components of the contact treatment liquid, and the components of the contact treatment liquid can be reduced by cooling, adsorption, or the like, and reused as the drying gas.

[0117] 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 drying system, 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 alcohol content is too high, the melt viscosity tends to decrease significantly during melt molding of the pellets, resulting in poor moldability. The lower the alcohol content, the better, but an industrially and reasonably achievable concentration is usually 50 ppm by mass or more. The moisture content of the dried pellets is usually lower 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 the reaction product contains a large amount of water, the IV will drop significantly due to hydrolysis when the pellets are melt-molded, resulting in poor moldability and poor physical properties of the molded product.

[0118] [Example of Production Process] A preferred embodiment of a method for producing a polyester using succinic acid as the dicarboxylic acid component, 1,4-butanediol (hereinafter sometimes abbreviated as BG) as the 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.

[0119] A preferred embodiment of the polyester production method will be described below with reference to the accompanying drawings. Fig. 1 is an explanatory diagram of an example of an esterification reaction treatment employed in this embodiment, and Fig. 2 is an explanatory diagram of an example of a polycondensation reaction treatment employed in this embodiment. Note that Fig. 1 can be applied not only to an esterification reaction treatment but also to a transesterification reaction treatment, and in that case, in the following description, the esterification reaction tank will be read as a transesterification reaction tank.

[0120] 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 to the esterification reaction tank (A) in the form of a slurry or liquid from a raw material supply line (1). When a catalyst is added during the esterification reaction, the BG is prepared into a solution in the catalyst in a catalyst preparation tank (not shown), and the catalyst solution is then supplied to a 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 portion of the esterification reaction tank (A).

[0121] The gas distilled from the esterification reaction tank (A) passes through a distillation line (5) and is separated into a high-boiling component and a low-boiling component in a rectification column (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.

[0122] The high-boiling components separated in the rectification column (C) are withdrawn through the withdrawal line (6) and pumped through (D). A portion is circulated through the recycle line (2) to the esterification reaction tank (A), and a portion is returned through the recycle line (7) to the rectification column (C). The excess is withdrawn through the withdrawal line (8) to the outside. On the other hand, the low-boiling components separated in the rectification column (C) are withdrawn through the gas withdrawal 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) is returned to the rectification column (C) through the withdrawal line (11), pump (E), and recycle line (12), and the remainder is withdrawn through the withdrawal line (13) to the outside. 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 withdrawal pump (B) and the esterification reaction product withdrawal line (4).

[0123] 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. In addition, the raw material supply line (1) may be connected to the liquid phase part of the esterification reaction tank (A).

[0124] When a catalyst is added to the esterification reaction product before the polycondensation reaction tank, the catalyst is prepared to a predetermined concentration in a catalyst preparation tank (not shown), and then passed through the catalyst supply line (L7) in FIG. 2 and connected to the raw material supply line (L8), where it is further diluted with BG and then supplied to the esterification reaction product withdrawal line (4).

[0125] Next, the esterification reaction product supplied to the first polycondensation reaction tank (a) via the esterification reaction product withdrawal line (4) and the filter (p) undergoes a polycondensation reaction under reduced pressure to form a polyester low polymer, which is then supplied to the second polycondensation reaction tank (d) via the withdrawal gear pump (c), the withdrawal line (L1), and the filter (q). In the second polycondensation reaction tank (d), the polycondensation reaction typically proceeds further at a pressure lower than that in the first polycondensation reaction tank (a). The resulting polycondensation reaction product is supplied to the third polycondensation reaction tank (k) via the withdrawal gear pump (e), the outlet line (L3), and the filter (r). The third polycondensation reaction tank (k) is a horizontal reaction tank composed of multiple agitator blade blocks and equipped with two self-cleaning agitator 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 therein and is then transferred to a pelletization step.

[0126] In the pelletizing step, the molten reaction product passes through a discharge gear pump (m), a filter (s) serving as an outlet flow path, and a discharge line (L5), and is discharged from a die head (g) in the form of a molten strand into the atmosphere, where it is cooled with water or the like and then cut by a rotary cutter (h) into polyester pellets. Alternatively, the strand may be discharged into water instead of the atmosphere, and then cut by a rotary underwater cutter into pellets.

[0127] In Figure 2, symbols (L2), (L4), and (L6) designate vent lines for 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 together, and can be installed as appropriate, taking into consideration the foreign matter removal effect and operational stability.

[0128] FIG. 3 is an explanatory diagram of an example of the contact treatment and separation treatment that can be employed in this embodiment. The contact treatment liquid is temperature-controlled by a pump (IX) from a circulation tank (I) through a heat exchanger (II) and supplied to a treatment tank (III) through a contact treatment liquid supply line (101). After countercurrent contact with pellets in the treatment tank, the liquid is withdrawn through a withdrawal line (102), passes through a fines remover (IV), and is then recovered in the circulation tank (I) through a separator (XI). The contact treatment liquid supplied to the separator (XI) is separated into cyclic oligomer components, and is supplied to a liquid phase separation tank (XIII) through a high boiling liquid withdrawal line (111). The separated oligomer components are withdrawn to the outside through a withdrawal line (112). A contact treatment liquid in an amount equivalent to the contact treatment liquid withdrawn from the withdrawal line (112) together with the separated cyclic oligomer components is supplied from a supply line (107). The aqueous solution containing the oligomer components in the upper layer of the liquid-phase separation tank (XIII) is supplied to the solid-liquid separation tank (XIV) via the 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 solid oligomer components is supplied to the solid-liquid separator (XV) via the solid-liquid separation tank overflow line (114), and the oligomer components are extracted. The separated water is sent to the activated sludge plant via the drain line (116). As described above, the recovered oligomer components can be reused as part of the raw material, etc. Note that FIG. 3 shows an example of the contact treatment and separation treatment in the first embodiment, and an example of the contact treatment step and purification step (specifically, the distillation separation treatment in the purification step) in the second embodiment described below. The example of the contact treatment and separation treatment in the first embodiment and the example of the contact treatment step and purification step in the second embodiment can both be similarly represented by the process shown in FIG. 3.

[0129] Pellets to be subjected to contact treatment are continuously supplied through a pellet supply line (103), and after contact treatment with the contact treatment liquid for a predetermined time, are continuously withdrawn through 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), passes through a recovery tank (VII), and is returned to a recovery line (106) through 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, passes through a solid-liquid separator (VIII), and is continuously supplied to a drying step.

[0130] FIG. 4 is an explanatory diagram of an example of a drying process that can be employed in this embodiment. The illustration shows an example equipped with two drying towers (I) and (K). Polyester pellets that have undergone the purification process are continuously supplied to the first drying tower (I) via the pellet supply line (201). Heated dry nitrogen gas is continuously introduced into the first drying tower via the supply line (208) and discharged via the dry gas recovery line (207). The discharged gas passes through the condenser (L), is heated in the heat exchanger (N), and is recycled to the first drying tower via the dry gas supply line (208). The contact treatment liquid condensed in the condenser (L) and heat exchanger (M) is discharged via the condensate withdrawal line (210). Fresh dry nitrogen gas is supplied via the new dry gas supply line (209). The pellets are continuously sent from the first drying tower via the rotary valve (O) to the cooling tower (J). Dry air is introduced into the cooling tower via the cooling gas supply line (212) and discharged via the cooling gas withdrawal line (211).

[0131] 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.

[0132] The dried polyester pellets are continuously or intermittently withdrawn through the rotary valve (Q) pellet withdrawal line (206) and passed through a storage tank, a fine powder removal machine, a packaging machine, etc. to become the final product. The storage tank can also be used as the second drying tower. The process after the storage tank is not shown in this diagram.

[0133] The content of cyclic oligomer components obtained by contacting polyester pellets with a contact treatment solution is not particularly limited, but the content of cyclic dimers contained in the polyester pellets (100% by mass) after the contact is preferably 1 ppm by mass or more, more preferably 100 ppm by mass or more, even more preferably 500 ppm by mass or more, and particularly preferably 1000 ppm by mass or more. Furthermore, the content of the cyclic oligomer components is usually 3800 ppm by mass or less, preferably 3500 ppm by mass or less, more preferably 3000 ppm by mass or less, and particularly preferably 2500 ppm by mass or less. If the cyclic dimer content is below the lower limit of the above range, the quality is good, but the time required to remove the oligomer components is prolonged, which is economically disadvantageous due to the increased equipment size. If the content exceeds the upper limit of the above range, problems such as clouding (synonymous with bleed-out or whitening) on ​​the surface and loss of surface gloss occur when the polyester is left for a certain period of time after molding.

[0134] <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-described polyester production method. The polyester produced by the above-described polyester production method 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, as needed, a carbodiimide compound, a filler, a plasticizer, or another biodegradable resin. Examples of other biodegradable resins that may be blended include polycaprolactone, polyamide, polyvinyl alcohol, or cellulose ester; fine powders of animal or plant substances such as starch, cellulose, paper, wood flour, chitin / chitosan, coconut shell powder, and walnut shell powder; or mixtures thereof. Furthermore, for the purpose of adjusting the physical properties and processability of the molded article, additives such as heat stabilizers, plasticizers, lubricants, antiblocking agents, nucleating agents, inorganic fillers, colorants, pigments, UV absorbers, or light stabilizers; modifiers; or crosslinking agents.

[0135] The method for producing the polyester composition is not particularly limited, and examples thereof include a method in which raw material chips of the blended polyesters are melt-mixed in the same extruder using the polyester obtained by the above-mentioned production method, a method in which the raw material chips are melted in separate extruders and then mixed, or a method in which the raw material chips are mixed by kneading using a conventional kneader such as a single-screw extruder, a twin-screw extruder, a Banbury mixer, a roll mixer, a Brabender plastograph, or a kneader blender. It is also possible to directly feed the raw material chips into a molding machine to prepare the composition and simultaneously obtain a molded product.

[0136] A composition according to yet another embodiment of the present invention (a polyester composition, also referred to as "aspect B of the polyester composition") is a composition comprising a polyester including a structural unit derived from a diol component and a structural 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).

[0137]

[0138] In formula (1), R １ and R ２ are each independently a divalent hydrocarbon group which may have a substituent; x is 0 to 7; and in formula (2), R ３ and R ４ are each independently a divalent hydrocarbon group which may have a substituent; y is 0 to 7; and x+y is 2 to 7.

[0139] The above formulas (1) and (2) correspond to the formulas (1) and (2) described in the above-mentioned method for producing a polyester, and the conditions of the formulas (1) and (2) described in the above-mentioned method for producing a polyester, including preferred conditions, can be applied.

[0140] The conditions for the diol component and dicarboxylic acid component in the above composition can be similarly applied to the conditions for the diol component and dicarboxylic acid component described in the above-mentioned polyester production method. The composition according to this embodiment may contain the same components that can be blended as described in aspect A of the polyester composition above, and a similar production method can be used. For example, polyester pellets obtained by the above-mentioned polyester production method usually contain the above-mentioned cyclic oligomer component in addition to the polyester, so the composition can be produced by mixing these polyester pellets with any other component.

[0141] The polyester may also contain structural units derived from the cyclic oligomer component. Since the polyester produced by the above-described polyester production method contains the cyclic oligomer component in the polyester raw material used in the production, the polyester usually contains structural units derived from the cyclic oligomer component.

[0142] <Molded Article> Another embodiment of the present invention is a molded article, specifically a molded article obtained by molding a polyester composition according to Aspect A of the polyester composition described above, a molded article obtained by molding a polyester composition according 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 method for producing a polyester described above. The method for producing the molded article is not particularly limited, and can be a known method applied to general-purpose plastics, or a method combining known methods. Examples of the molding method include compression molding (compression molding, laminate molding, stampable molding), injection molding, extrusion molding or co-extrusion molding (film molding by inflation molding or T-die method, laminate molding, pipe molding, electric wire / cable molding, molding of profiled materials), hot press molding, blow molding (various blow moldings), calendar molding, solid molding (uniaxial stretch molding, biaxial stretch molding, roll rolling molding, stretch-oriented nonwoven fabric molding, thermoforming (vacuum forming, pressure forming), plastic processing, powder molding (rotational molding)), various nonwoven fabric moldings (dry method, adhesion method, entanglement method, spunbond method, etc.), etc. Among these, injection molding, extrusion molding, compression molding, or hot press molding, particularly extrusion molding or injection molding, is preferably applied. Specific shapes are preferably applied to sheets, films, and fibers.

[0143] The uses of the molded article are not particularly limited, and it can be used in known applications applicable 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., which are used outdoors, in the soil, underwater, or in wet environments. Specific examples include extrusion-molded products (e.g., 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.

[0144] <Second Aspect> <Method for Producing Polyester> A second aspect of the method for producing a polyester according to one embodiment of the present invention (hereinafter, in the section regarding the second aspect, this may be simply referred to as the "method for producing a polyester") is a method for producing a polyester, comprising: a reaction step of obtaining a reaction product from a polyester raw material (also simply referred to as the "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 a transesterification reaction treatment; a contact treatment step of obtaining a contact treatment liquid containing oligomer components and a post-contact treatment reaction product by contacting the reaction product with a contact treatment liquid; a purification step including a treatment of purifying oligomer components in the contact treatment liquid containing the oligomer components so that the content of cyclic oligomer components in the oligomer components is increased; and a recovery step of recovering the oligomer components obtained in the purification step as part of the raw material.

[0145] The diol component and dicarboxylic acid used as raw materials can be any of those typically used as raw materials for polyesters without any particular limitation, and the diol component can be an aliphatic diol component or an aromatic diol component, and the dicarboxylic acid component can be an aliphatic dicarboxylic acid component or an aromatic dicarboxylic acid component. The conditions for the diol component and the dicarboxylic acid described in the first embodiment of the polyester production method can be applied in the same way.

[0146] 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 other components described in the first embodiment of the polyester production method can be similarly applied to the copolymerization conditions for the copolymerization components that can be used.

[0147] [Each step in the polyester production method] Below, each step in the second embodiment of the polyester production method will be described using a continuous production method as an example, but this is merely an example, and the polyester production method is not limited to this embodiment. In the polyester production method, similar to the first embodiment described above, for example, a dicarboxylic acid component and a diol component are continuously produced through a reaction process including at least one treatment selected from the group consisting of an esterification reaction treatment and a transesterification reaction treatment, and a polycondensation reaction treatment, using multiple continuous reaction vessels. However, as long as the effects of the present invention are not impaired, the method is not limited to a continuous process, and steps in conventional polyester production methods can be adopted. Furthermore, the polyester may be contacted with a contact treatment solution and then dried. When a continuous operation is adopted, from the viewpoint of improving production efficiency and achieving uniformity in the treatment, it is particularly preferable 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 be carried out continuously. Furthermore, with regard to the batch or semi-batch operation, from the viewpoint of improving 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 contact treatment step described below and a drying treatment in the drying step described below be carried out in a batch or semi-batch manner.

[0148] (Raw Material Preparation Step) The method for producing a polyester may further include a raw material preparation step of preparing a polyester raw material before the reaction step described below. The method for preparing the polyester raw material is not particularly limited, and the polyester raw material may be prepared by mixing raw materials produced by synthesis or the like, or by mixing commercially available raw materials.

[0149] (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 a transesterification 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 transesterification reaction.

[0150] (1) Esterification Reaction Treatment / Transesterification Reaction Treatment The reaction process involves an esterification reaction treatment in which a polyester raw material is reacted. Specifically, the polyester is produced through an esterification reaction treatment and / or transesterification reaction in which a raw material containing at least a dicarboxylic acid component and a diol component is reacted. An esterification reaction is a reaction in which a carboxylic acid is converted into an ester, and a transesterification reaction is a reaction in which an ester and an alcohol are reacted to exchange the main chain moieties of the two. The esterification reaction treatment will be described below, but this description can also be applied to transesterification reactions to the extent applicable. Furthermore, at least one reaction treatment selected from the group consisting of an esterification reaction treatment and a transesterification reaction and subsequent other treatments can be carried out in multiple consecutive reaction tanks or in a single reaction tank. However, it is preferable to carry out these treatments in multiple consecutive reaction tanks in order to reduce variation in the physical properties of the resulting polyester.

[0151] The conditions for the esterification reaction treatment / ester exchange reaction treatment in the first embodiment can be similarly applied to the conditions for the esterification reaction treatment / ester exchange reaction treatment.

[0152] (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 vessels.

[0153] The conditions for the polycondensation reaction treatment may be the same as those for the polycondensation reaction treatment in the first embodiment described above.

[0154] (3) Reaction Catalyst The esterification reaction and polycondensation reaction are accelerated by using a reaction catalyst. A sufficient reaction rate can be achieved in the esterification reaction even without an esterification catalyst. Furthermore, if an esterification catalyst is present during the esterification reaction, the water produced by the esterification reaction can cause the catalyst to form an insoluble precipitate in the reaction product, which can impair the transparency of the resulting polyester (i.e., increase haze) and can also cause the catalyst to become a foreign substance. Therefore, it is preferable not to add a reaction catalyst during the esterification reaction. Furthermore, adding a catalyst to the gas phase of the reaction vessel can increase the haze of the resulting polyester and can also cause the catalyst to become a foreign substance, so it is preferable to add the catalyst to the reaction liquid.

[0155] The conditions for the reaction catalyst in the first embodiment can be similarly applied to the conditions for the reaction catalyst.

[0156] (4) Reactor As the esterification reaction vessel for carrying out the esterification reaction treatment, a known vessel can be used, and the conditions for the reaction catalyst in the first embodiment described above can be similarly applied.

[0157] (Pelletization step) From the viewpoint of improving the convenience of molding and improving the efficiency of the contact treatment of the oligomer component by increasing the surface area in the contact treatment step described later, the polyester production method preferably further includes a pelletization step after the reaction step, particularly between the reaction step and the contact treatment step described later, in which the reaction product obtained in the reaction step is pelletized to obtain pellets (polyester pellets). The polyester obtained through the esterification reaction step is pelletized and contact treated in the pellet state with a contact treatment solution.

[0158] The conditions for the pelletizing step in the first embodiment can be similarly applied to the conditions for the pelletizing step.

[0159] (Contact Treatment Step) The polyester production method further includes a contact treatment step in which the reaction product (polyester) obtained in the above reaction step is contacted with a contact treatment solution to obtain a contact treatment solution containing an oligomer component and a post-contact treatment reaction product. The contact treatment is a purification treatment. The contact treatment step may include treatments other than the contact treatment. The contact treatment solution is not particularly limited and may be, for example, a solvent containing water. Reaction products obtained by esterification reactions, transesterification reactions, polymerization reactions, etc. usually contain oligomer components, so the content of oligomer components in the reaction product can be reduced by performing contact treatment. Furthermore, since the contact treatment solution obtained by the contact treatment contains oligomer components, this oligomer component can be recovered for reuse to improve polyester productivity. Specifically, for example, if a raw material preparation step of preparing a polyester raw material is further included before the reaction step, the oligomer component in the contact treatment solution can be reused by supplying it to any of the steps 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.

[0160] In the contact treatment step, a reaction product (polyester) obtained in the reaction step (pelletization step, if a pelletization step is employed) 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.

[0161] Examples of the contact treatment liquid include an embodiment containing an alcohol such as methanol, ethanol, isopropanol, or butanol, and a mixture of these alcohols with water. Among these, a water / ethanol mixture (a mixture of water and ethanol) is particularly preferred from the standpoints of ease of handling, cost, contact treatment efficiency, safety, etc.

[0162] When the polyester production 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.

[0163] 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.

[0164] (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 constituent units derived from the above-mentioned diol component and constituent units derived from the above-mentioned dicarboxylic acid component, or may have constituent units derived from the above-mentioned diol component and constituent units derived from the above-mentioned dicarboxylic acid component, and typically contains, as main constituent units, structural units derived from the diol component and structural units derived from the dicarboxylic acid component used as raw materials.

[0165] 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 finally obtained polymer, it is preferably a cyclic oligomer component having a structure represented by the following formula (11) or the following formula (12): The cyclic oligomer component can be easily obtained by undergoing this contact treatment step and the recovery step described below.

[0166]

[0167] In formula (11), R １１ and R １２ are each independently a divalent hydrocarbon group which may have a substituent; x １ is 0 to 7, and in formula (12), R １３ and R １４each independently represents a divalent hydrocarbon group which may have a substituent; y １ is 0 to 7, and x １ +y １ is 2 to 7.

[0168] R in formula (11) and formula (12) １１ , R １２ , x １ , y １ The condition is satisfied by the R １ , R ２ , x, y conditions can be applied in a similar manner.

[0169] 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 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. 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.

[0170] The oligomer component may be contained in the raw material. For example, as described in the recovery and supply processes below, the oligomer component obtained in the recovery process can be incorporated into 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. It is also 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 greater than the lower limit of the above range, economical production with an increased recovery rate of the oligomer component is possible. When the total content is equal to or less than the upper limit of the above range, production can be carried out without impairing reactivity while maintaining quality such as color tone.

[0171] When the polyester raw material contains an oligomer component, the content of 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 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.

[0172] From the viewpoint of easily suppressing deterioration in color tone of the polyester, the cyclic oligomer component is preferably one produced by a reaction with a diol component and a dicarboxylic acid component contained in the polymer raw material. That is, the polyester raw material preferably contains, as the dicarboxylic acid component, 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, and as the diol component, 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.

[0173]

[0174] In formulas (A1) to (D1), R １１ ~R １４ are R in the above formulas (11) and (12), respectively. １１ ~R １４ is synonymous with.

[0175] When the contact treatment step 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 material become the same as the oligomer components and dicarboxylic acid components constituting the cyclic oligomer components in the polyester raw material, and therefore the content of 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.

[0176] [Physical Properties of Polyester] The intrinsic viscosity (IV, dL / g) of the polyester to be contacted with the contact treatment solution and the intrinsic viscosity of the polyester after contact treatment with the contact treatment solution are preferably 1.4 dL / g or more, particularly preferably 1.6 dL / g or more. Furthermore, the intrinsic viscosity is preferably 2.8 dL / g or less, more preferably 2.5 dL / g or less, 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, making molding difficult.

[0177] The amount of terminal carboxyl groups in the polyester to be contacted 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 will decrease significantly due to hydrolysis, and quality may be significantly impaired.

[0178] Regarding the conditions for the contact treatment in the second embodiment, the conditions described in the sections (1-1) Composition of the contact treatment solution, (1-2) Contact treatment temperature, (1-3) Contact treatment time, (1-4) Ratio of the reaction product to the contact treatment solution, and (1-5) Contact treatment method in the first embodiment can be similarly applied.

[0179] (Purification step) The method for producing a polyester includes a purification step, which includes a treatment of purifying an oligomer component from a contact treatment solution containing the oligomer component so that the content of cyclic oligomer components in the oligomer component is increased. As mentioned above, the contact treatment step is also a step related to the treatment of purifying a reaction product, but this purification step is a separate step from the contact treatment step. The oligomer component obtained by the purification step or an object containing the oligomer component is also referred to as a "purified product."

[0180] The method for purifying oligomer components from a contact treatment solution containing oligomer components so as to increase the content of cyclic oligomer components in the oligomer components is not particularly limited, and examples thereof include a method including a distillation separation process for separating a low-boiling liquid from a high-boiling liquid containing oligomer components and water. In this specification, the term "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, etc., and the term "low-boiling liquid" refers to a liquid that is more volatile than water, such as ethanol, tetrahydrofuran, or acetone, and is distilled from the top of a distillation column, etc. Furthermore, it is preferable that the low-boiling liquid is substantially free of oligomer components, and more preferably, it is free of them. The distillation separation method is not particularly limited, and can be performed by a known method.

[0181] 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.

[0182] The distillation separation can be carried out either batchwise or continuously, but in view of production efficiency, the continuous method is more preferable.

[0183] In order to efficiently recover the 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 can be carried out either batchwise or continuously, but continuous is more preferable in terms of production efficiency. Crystallization is carried out, for example, by cooling a crystallization tank containing the high-boiling liquid in the distillation separation treatment 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 40°C or less, and even more preferably 35°C or less.

[0184] Furthermore, 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 of liquid / liquid phase separation is not particularly limited, and can be performed either batchwise or continuously, but continuous is more preferable in terms of production efficiency. For example, while visually checking the liquid / liquid interface using a sight glass or the like installed in the tank, the molten oligomer phase (the lower liquid phase, which is thought to contain small amounts of linear oligomers that cause color deterioration) is extracted from the bottom and separated from the aqueous solution phase (the upper phase, purified oligomer components). Furthermore, the liquid / liquid phase separation is preferably performed 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.

[0185] When the phase separation treatment is performed, it is preferable to further include a crystallization treatment for further crystallizing the oligomer component separated by the phase separation treatment. The conditions for the crystallization treatment can be the same as those for the crystallization treatment described above.

[0186] (Recovery Step) The method for producing a polyester includes a recovery step in which the oligomer component obtained in the purification step is recovered as 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 that constitutes part of the polyester together with a diol or a dicarboxylic acid, or it can be a structural unit that constitutes part of the polyester by replacing part of the diol or dicarboxylic acid. The form of the recovered oligomer component 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.

[0187] 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 treatment is performed, and then the crystallized oligomer component is removed 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 treatment or the like can be performed in the above-mentioned reaction step.

[0188] 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, and the resulting product can then be recycled and reused as a contact treatment liquid in the above-mentioned contact treatment step.

[0189] The purified product after the purification step can be recycled and reused as it is, or can be reused by adding a new contact treatment liquid in an amount corresponding to the amount of the contact treatment liquid extracted together with the separated oligomer components.

[0190] After the separation step, the oligomer component (which may be a mixture of the contact treatment liquid and the oligomer component) separated by distillation concentration and / or cooling, etc., can be recovered as a raw material for polyester after being temporarily made into a molten state or after being heated and dissolved in a diol component to be used as a raw material to make a solution.

[0191] The recovery operation can be carried out either batchwise or continuously, and is not particularly limited, but from the viewpoint of efficiency, a continuous system is more preferable.

[0192] (Supplying Step) When the method for producing a polyester includes the raw material preparing step described above, it may further include, after the recovering step, a supplying 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 preparing step to the reaction step.

[0193] The manner in which the oligomer components are supplied is not particularly limited. For example, the recovered oligomer components can be reused by being supplied to the polyester raw material in the reaction step. Specifically, the recovered oligomer components can be supplied to the esterification reaction, transesterification reaction, or polycondensation reaction in the reaction step and used as a polyester raw material. It is particularly preferred to return the recovered oligomer components to the esterification reaction tank for the esterification reaction, the transesterification reaction tank for the transesterification reaction, or the dicarboxylic acid component and diol component slurry tank. More specifically, the recovered oligomer components can be supplied directly to the esterification reaction tank, or to the diol component recycle line (2) or the esterification reaction product withdrawal line (4) shown in FIG. 1, or to the polycondensation reaction tank (a) shown in FIG. 2, or to a dicarboxylic acid component and diol component slurry preparation tank.

[0194] The supply method can be either a batch method or a continuous method, but in view of production efficiency, a continuous method is more preferable.

[0195] (Drying step) The polyester production method may further include a drying step in which the post-contact treatment reaction product (preferably the purified product) is dried after the contact treatment step (preferably the purification step). The post-contact treatment reaction product may be the contact treatment liquid before the purification step or the purified product after the purification step, but it is preferable that at least the purified product is subjected to a drying step. The conditions for the drying step can be the same as those for the drying step in the first embodiment described above.

[0196] [Example of Manufacturing Process] The example of the manufacturing process described in the section "Example of Manufacturing Process" in the first embodiment can be similarly applied as an example of the manufacturing process in the second embodiment.

[0197] <Polyester Composition> A polyester composition according to another embodiment of the present invention is a polyester composition containing a polyester obtained by the polyester production method described above. The polyester produced by the polyester production method described above 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 optionally contain a carbodiimide compound, a filler, a plasticizer, or another biodegradable resin. Examples of other biodegradable resins that may be included include polycaprolactone, polyamide, polyvinyl alcohol, or cellulose ester; fine powders of animal or plant substances such as starch, cellulose, paper, wood flour, chitin / chitosan, coconut shell powder, and walnut shell powder; or mixtures thereof. Furthermore, additives such as heat stabilizers, plasticizers, lubricants, antiblocking agents, nucleating agents, inorganic fillers, colorants, pigments, UV absorbers, or light stabilizers; modifiers; or crosslinking agents may be added to adjust the physical properties and processability of the molded article.

[0198] The method for producing the polyester composition is not particularly limited, and examples thereof include a method in which raw material chips of the blended polyesters are melt-mixed in the same extruder using the polyester obtained by the above-mentioned production method, a method in which the raw material chips are melted in separate extruders and then mixed, or a method in which the raw material chips are mixed by kneading using a conventional kneader such as a single-screw extruder, a twin-screw extruder, a Banbury mixer, a roll mixer, a Brabender plastograph, or a kneader blender. It is also possible to directly feed the raw material chips into a molding machine to prepare the composition and simultaneously obtain a molded product.

[0199] <Molded Article> Another embodiment of the present invention is a molded article, specifically a molded article obtained by molding the polyester composition described above, or a molded article produced by a molded article production method including a step of producing a polyester by the polyester production method described above. The method for producing the molded article 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, laminate 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 profiled materials), heat press molding, blow molding (various blow moldings), calendar molding, solid molding (uniaxial stretch molding, biaxial stretch molding, roll rolling molding, stretch-oriented nonwoven fabric molding, thermoforming (vacuum forming, pressure forming), plastic processing, powder molding (rotational molding)), various nonwoven fabric moldings (dry method, adhesive method, entanglement method, spunbond method, etc.), etc. Among these, injection molding, extrusion molding, compression molding, or hot press molding, particularly extrusion molding or injection molding, is preferably applied. Specific shapes are preferably applied to sheets, films, and fibers.

[0200] The uses of the molded article are not particularly limited, and it can be used in known applications applicable 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., which are used outdoors, in the soil, underwater, or in wet environments. Specific examples include extrusion-molded products (e.g., 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.

[0201] The present invention will be described 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 physical properties and evaluation items used in the following examples are as follows.

[0202] <Characteristics Evaluation> [Intrinsic Viscosity (IV) dL / g] The intrinsic viscosity of the polyester was determined using an Ubbelohde viscometer in the following manner. That is, polyester pellets were dissolved in a mixed solvent of phenol / tetrachloroethane (1 / 1 by mass ratio) 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 calculated using the following formula (1): IV = ((1 + 4K Ｈ η ｓｐ ) ０．５ -1) / (2K Ｈ C) ... (1) where, in equation (1), η ＳＰ = η / η ０ -1, η is the time it takes for the sample solution to fall, η ０ is the number of seconds for the solvent to fall, C is the concentration of the sample solution (g / dL), K Ｈ is Huggins' constant. Ｈ was set to 0.33.

[0203] [Esterification rate (%)] The esterification rate in polyester production was calculated from the sample acid value and saponification value using the following calculation formula (2). The acid value was determined by heating 0.3 g of an esterification reaction product sample in 40 mL of benzyl alcohol at 180°C for 20 minutes, cooling for 10 minutes, and then titrating with a 0.1 mol / L potassium hydroxide / methanol solution. The saponification value was determined by hydrolyzing the oligomer component with a 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)

[0204] [Quantification of the Content of Cyclic Oligomer Components in Polyester Pellets (ppm by Mass)] 0.5 g of polyester pellets were accurately weighed, 10 mL of chloroform was added, and the mixture was dissolved at room temperature. 30 mL of an ethanol / water mixture (volume ratio 4 / 1) was then slowly added dropwise with 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 and evaporated to dryness, after which 2 mL of acetonitrile was added to dissolve the supernatant. After filtration through a 0.45 μm filter, the mixture was subjected to elution using a Shimadzu high-performance liquid chromatography system "Prominence," starting with an acetonitrile / water (volume ratio = 4 / 6) mobile phase and continuously changing the composition to acetonitrile / water (volume ratio = 9 / 1) using 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 structural units derived from the diol component and the number of repeating units of the structural 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, 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.

[0205] The cyclic dimer ((BS)2) was quantitatively determined by an absolute calibration curve method using a pure product of the cyclic dimer ((BS)2). The pure product of the cyclic dimer was obtained as follows. Specifically, 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 treatment 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 form a saturated solution, then slowly cooled, the supernatant was discarded, and the needle-like precipitate was taken out and purified by repeating this recrystallization procedure several times. The needle-like precipitate was １H-NMR analysis and high-performance liquid chromatography analysis confirmed that it was a cyclic dimer. Oligomer components other than the cyclic dimer were identified by LC-MS analysis, and then quantitatively calculated using the relative area value of each oligomer component to the cyclic dimer area value in high-performance liquid chromatography and a factor.

[0206] The cyclic dimer ((BS)2) was quantitatively calculated using the absolute calibration curve based on HPLC area values, using formula (5): (cyclic dimer ((BS)2) quantitative value) = (slope of cyclic dimer ((BS)2) calibration curve) x (cyclic dimer ((BS)2) HPLC 210 nm UV area value) + intercept of cyclic dimer ((BS)2) calibration curve (5). Oligomer components other than the cyclic dimer ((BS)2) that did not contain an aromatic ring were identified by LC-MS analysis, and then quantitatively calculated using formula (6) using the relative area value of each oligomer component to the cyclic dimer ((BS)2) area value in high performance liquid chromatography and a factor. (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)

[0207] The quantity of the aromatic ring-containing oligomer component was determined by preparing an absolute calibration curve using dimethyl terephthalate (DMT) as the standard substance, and after identifying the component by LC-MS analysis in advance, the HPLC area value was used to calculate the DMT equivalent value using the following formula (7): (Quantitative value of aromatic ring-containing oligomer) = Slope of DMT calibration curve × (HPLC 254 nm UV area value) + Intercept of DMT calibration curve (7)

[0208] [Quantitative determination of the amount of terminal carboxyl groups (acid value) equivalents / ton] Polyester pellets were crushed, dried in a hot air dryer at 140°C for 15 minutes, and cooled to room temperature in a desiccator. 0.1 g of the polyester sample was precisely weighed and placed in a test tube. ３ was added and dissolved at 195°C for 3 minutes while blowing in dry nitrogen gas. ３The solution was cooled to room temperature after gradually adding sodium hydroxide and dry nitrogen gas. One to two drops of phenol red indicator were added to the solution, and the titration was completed with 0.1 mol / L sodium hydroxide in benzyl alcohol while stirring. The titration was terminated when the color changed from yellow to red. A blank was also run without adding the polyester sample, and the amount of terminal carboxyl groups (acid value) was calculated using the following formula (3): Amount of terminal carboxyl groups (equivalents / ton) = (a - b) × 0.1 × f / W (3) where a is the amount (μL) of the 0.1 mol / L sodium hydroxide in benzyl alcohol solution required for the titration, b is the amount (μL) of the 0.1 mol / L sodium hydroxide in benzyl alcohol solution required for the blank titration, W is the amount (g) of polyester sample, and f is the titer of the 0.1 mol / L sodium hydroxide in benzyl alcohol solution.

[0209] The potency (f) of a 0.1 mol / L solution of sodium hydroxide in benzyl alcohol was determined by the following method. ３ Add 1-2 drops of phenol red as an indicator to an ethanol solution, and add 0.4 cm of 0.1 mol / L sodium hydroxide solution in benzyl alcohol. ３ Then, titrate to the color change point with 0.2 cm of a 0.1 mol / L aqueous solution of hydrochloric acid with a known titer as the standard solution. ３ The solution was sampled and added, and again titrated with 0.1 mol / L sodium hydroxide in benzyl alcohol to the point of color change (the above operations were carried out under a stream of dry nitrogen gas). The titer (f) was then calculated using the following formula (4): Titer (f) = Titer of 0.1 mol / L hydrochloric acid solution × Amount of 0.1 N hydrochloric acid solution sampled (μL) / Amount of 0.1 mol / L sodium hydroxide in benzyl alcohol titrated (μL) (4)

[0210] <Preparation of Polycondensation Reaction Catalyst> 343.5 parts by weight of magnesium acetate tetrahydrate was placed in a reactor equipped with a stirrer, followed by 1,434 parts by weight of anhydrous ethanol (purity 99% by weight or higher). 218.3 parts by weight of ethyl acid phosphate (monoester:diester weight ratio 45:55) was then added, and the mixture was stirred at 23°C. After confirming that the magnesium acetate was completely dissolved, 410.0 parts by weight of tetra-n-butyl titanate was added. Stirring was continued for an additional 10 minutes, yielding a homogeneous mixed solution. This mixed solution was concentrated under reduced pressure while maintaining a temperature below 60°C. Approximately half of the ethanol added was distilled off, leaving a translucent, viscous liquid. 1,108 parts by weight of 1,4-butanediol was added, and the mixture was further concentrated under reduced pressure while maintaining a temperature below 80°C, yielding a catalyst solution with a titanium atom content of 3.5% by weight.

[0211] <Method for Producing Polyester> [Method for Producing Polybutylene Succinate (PBS)] A polyester was produced as follows by the esterification treatment shown in Fig. 1 and the polycondensation reaction treatment shown in Fig. 2. A slurry at 50°C, prepared by mixing 1.30 mol of 1,4-butanediol and 0.0033 mol of malic acid with 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 that had been previously filled with a low-molecular-weight polyester (esterification reaction product) with an esterification rate of 99% by mass under a nitrogen atmosphere.

[0212] The esterification reaction tank (A) was set to an internal temperature of 230°C and a pressure of 101 kPa, and the produced water, tetrahydrofuran, and excess 1,4-butanediol were distilled through a distillation line (5) and separated into high-boiling components and low-boiling components in a rectification column (C). After the system had stabilized, a portion of the high-boiling components at the bottom of the column was withdrawn to the outside through a withdrawal line (8) so that the liquid level in the rectification column (C) was kept constant. On the other hand, the low-boiling components mainly composed of water and tetrahydrofuran were withdrawn in the form of gas from the top of the column, condensed in a condenser (G), and withdrawn to the outside through a withdrawal line (13) so that the liquid level in the tank (F) was kept constant. At the same time, the entire amount of the bottom component (98% by mass or more of which was 1,4-butanediol) of the 100°C rectification column (C) was fed via the recycle line (2), and 1,4-butanediol in an amount equimolar to the tetrahydrofuran generated in the esterification reaction tank was also fed via the raw material feed line (1), so that the molar ratio of 1,4-butanediol to succinic acid in the esterification reaction tank was adjusted to 1.30. The combined feed rate via the recycle 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 mol per 1.00 mol of succinic acid (THF conversion rate: 9.2 mol% relative to succinic acid).

[0213] 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) shown 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%.

[0214] The catalyst solution previously prepared by the above-mentioned method was diluted with 1,4-butanediol in a catalyst preparation tank so that the titanium atom concentration was 0.12 mass %, and then the catalyst solution was 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 rate was stable throughout the operation period.

[0215] The internal temperature of the first polycondensation reaction vessel (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 withdrawing water, tetrahydrofuran, and 1,4-butanediol from a vent line (L2) connected to a pressure reducer (not shown). The withdrawn reaction liquid was continuously supplied to a 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 withdrawing 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 a third polycondensation reactor (k) via a withdrawal line (L3) using a withdrawal 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 while being cooled with water, it was cut into pellets with a rotary cutter (h). The intrinsic viscosity was 1.80±0.05 dL / g, and the polyester pellets were of stable quality.

[0216] (Contact treatment of polybutylene succinate (PBS) pellets with contact treatment solution) The obtained polyester pellets were contact treated by the contact treatment (contact treatment step) shown in Figure 3. A mixed solution of ethanol and water used as the contact treatment solution was fed from a circulation tank (I) via a heat exchanger (II) by a pump (IX) at a controlled temperature of 70°C 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 solution was 60 mass% water relative to the total contact treatment solution. The mass ratio of the contact treatment solution to the pellets in the treatment tank was 5 (treatment solution / pellet ratio).

[0217] (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 higher (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.

[0218] [Method for Producing 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 3,823 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 previously been charged with a low molecular weight polyester (esterification reaction product) with an esterification rate of 99% by mass under a nitrogen atmosphere. The esterification reaction product sampled at the outlet of the esterification reaction tank (A) had an esterification rate of 92.8%, and the final polyester pellets had an intrinsic viscosity of 1.80±0.05 dL / g, indicating stable quality.

[0219] (Contact treatment of polybutylene succinate adipate (PBSA) pellets with contact treatment solution) The obtained polyester pellets were subjected to a contact treatment (contact treatment step) shown in Fig. 3. The temperature of the ethanol and water mixture used as the contact treatment solution was controlled to 45°C, and the other conditions and operations were the same as those for the contact treatment with PBS.

[0220] (Drying of Polybutylene Succinate Adipate (PBSA) Pellets) Drying was carried out according to the drying process shown in Fig. 4. The drying procedure was the same as that for PBS pellets, except that the gas temperatures in the first drying tower and the second drying tower were set to 65°C.

[0221] [Recovery of Contact Treatment Liquid] The contact treatment liquid was brought into countercurrent contact with the pellets in the treatment tank and then withdrawn through the withdrawal line (102). A portion of the withdrawn treatment liquid was supplied 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 supplied through the supply line (103), brought into contact with the contact treatment liquid for 4 hours, and then continuously withdrawn through 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 then returned to the recovery line (106) via the supply line (105) by the pump (X).

[0222] 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 a heat exchanger (XII) and a line (109). The high boiling liquid containing cyclic oligomer components was extracted into a liquid phase separation tank (XIII) via a line (111). Ethanol and water in amounts corresponding 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) via a supply line (107). The continuously extracted pellets were separated from the entrained contact treatment liquid in a preliminary solid-liquid separator (VI) and then continuously supplied to a drying step from the solid-liquid separator (VIII) via an extraction line (108).

[0223] [Step for recovering oligomer components from high-boiling liquid by phase separation] The high-boiling liquid containing oligomer components and mainly composed of water was supplied to the liquid-phase separation tank (XIII) and separated into an upper layer soluble in water and a lower layer insoluble in water as oil droplets at 100°C, and the molten oligomer components were removed from the lower layer via line (112) into a container. After air-cooling in the container, the oligomer components became almost white lumps in the case of PBS and almost white paste in the case of PBSA. The upper layer overflowed from the liquid-phase separation tank (XIII) and was supplied to the solid-liquid separation tank (XIV) via line (113).

[0224] [Step for recovering oligomer components by crystallization of the upper layer aqueous solution through phase separation treatment] The upper layer aqueous solution 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 components were separated from the aqueous solution in a solid-liquid separator (XV) and discharged into a container. The oligomer components obtained here were an almost white powder in the case of PBS and a nearly white paste in the case of PBSA. The remaining aqueous solution from which the oligomer components had been removed was treated with activated sludge.

[0225] [Composition of Recovered Oligomer Components] The composition of the cyclic oligomer components contained in the recovered oligomer components was quantified using the high-performance liquid chromatograph described above. Tables 1 and 2 below show the results of the composition analysis of the oligomer components of PBS and PBSA. For comparison, Table 1 also shows oligomer components obtained by evaporating the contact treatment solution to dryness without performing liquid-phase separation and solid-liquid separation. Note that the cyclic oligomer components in the recovered oligomer components and oligomer components other than the cyclic oligomer components were all oligomer components produced from the raw materials used as raw materials. That is, when polybutylene succinate (PBS) pellets were used, the cyclic oligomer components were cyclic oligomer components composed of succinic acid-derived constituent units, 1,4-butanediol-derived constituent units, and malic acid-derived constituent units, and when polybutylene succinate adipate (PBSA) was used, the cyclic oligomer components were cyclic oligomer components composed of succinic acid-derived constituent units, adipic acid-derived constituent units, 1,4-butanediol-derived constituent units, and malic acid-derived constituent units.

[0226]

[0227] In Table 1, the cyclic dimer to heptamer were, specifically, as follows, in terms of the composition after liquid / liquid separation and solid / liquid separation: 22.3 wt% cyclic dimer (x=2 in Formula 1, y=0 in Formula 2, x+y=2), 26.3 wt% cyclic trimer (x=3 in Formula 1, y=0 in Formula 2, x+y=3), 20.3 wt% cyclic tetramer (x=4 in Formula 1, y=0 in Formula 2, x+y=4), 7.7 wt% cyclic pentamer (x=5 in Formula 1, y=0 in Formula 2, x+y=5), 2.2 wt% cyclic hexamer (x=6 in Formula 1, y=0 in Formula 2, x+y=6), and 2.2 wt% cyclic heptamer (x=7 in Formula 1, y=0 in Formula 2, x+y=7). The composition after only solvent distillation without purification was 0.3 wt %. The composition was 26 wt % of a cyclic dimer (x = 2 in Formula 1, y = 0 in Formula 2, x + y = 2), 3.6 wt % of a cyclic trimer (x = 3 in Formula 1, y = 0 in Formula 2, x + y = 3), 2 wt % of a cyclic tetramer (x = 4 in Formula 1, y = 0 in Formula 2, x + y = 4), 1.8 wt % of a cyclic pentamer (x = 5 in Formula 1, y = 0 in Formula 2, x + y = 5), 0.7 wt % of a cyclic hexamer (x = 6 in Formula 1, y = 0 in Formula 2, x + y = 6), and 0 wt % of a cyclic heptamer (x = 7 in Formula 1, y = 0 in Formula 2, x + y = 7).

[0228]

[0229] In Table 2, the cyclic dimers to heptamers 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%, and BA unit-containing cyclic dimer (x = 0 in Formula 1, y = 2 in Formula 2, x + y = 2) 6.9 wt%.

[0230] <Polymerization of polybutylene succinate (PBS) with added recovered oligomer components> [Example 1] A reaction vessel equipped with a stirrer, a nitrogen inlet, a heater, a thermometer, and a pressure reduction 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 components were added in an amount of 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 purged with nitrogen by vacuum substitution to create a nitrogen atmosphere. Next, the temperature of the system was raised from 160°C to 230°C over 1 hour while stirring, and the reaction was carried out at this temperature for 1 hour.

[0231] To this ester oligomer component, the catalyst solution was added in an amount to give 50 ppm by weight of titanium atoms per polyester obtained, and the mixture was maintained at 230°C for 30 minutes, then heated to 250°C over 30 minutes, and simultaneously heated to 0.07 × 10 ３ The pressure was reduced to 1.78 dL / g or less, and the polycondensation reaction was continued while maintaining the heated and reduced pressure state. The polymerization was terminated when a predetermined viscosity was reached, and the pressure was restored with nitrogen. The polyester obtained had an intrinsic viscosity of 1.78 dL / g and a color b value of 2.8.

[0232] [Example 2] The PBS polymerization procedure was carried out in the same manner as in Example 1, except that the amount of recovered oligomer component added was 10 parts by weight per 100 parts by weight of the polyester product. The intrinsic viscosity of the resulting polyester was 1.71 dL / g, and the color b value of the pellets was 3.6.

[0233] [Example 3] The PBS polymerization procedure was carried out in the same manner as in Example 1, except that the amount of recovered oligomer component added was 20 parts by weight per 100 parts by weight of the polyester product. The intrinsic viscosity of the resulting polyester was 1.78 dL / g, and the color b value of the pellets was 5.9.

[0234] Comparative Example 1 The PBS polymerization procedure was repeated as in Example 1, except that the oligomer component recovered without purification, obtained by only distilling off the solvent, was added in an amount of 5 parts by weight per 100 parts by weight of the polyester product. The intrinsic viscosity of the resulting polyester was 1.72 dL / g, and the color b value of the pellets was 3.4.

[0235] Comparative Example 2 The PBS polymerization procedure was repeated as in Example 1, except that the oligomer component recovered without purification, obtained by only distilling off the solvent, was added in an amount of 10 parts by weight per 100 parts by weight of the polyester product. The intrinsic viscosity of the resulting polyester was 1.75 dL / g, and the color b value of the pellets was 6.3.

[0236] Comparative Example 3 The PBS polymerization procedure was repeated as in Example 1, except that the oligomer component recovered without purification, obtained by only distilling off the solvent, was added in an amount of 20 parts by weight per 100 parts by weight of the polyester product. The intrinsic viscosity of the resulting polyester was 1.73 dL / g, and the color b value of the pellets was 8.6.

[0237]

[0238] Polymerization of polybutylene succinate (PBSA) containing recovered oligomer components added Example 4 A reaction vessel equipped with a stirrer, a nitrogen inlet, a heater, a thermometer, and a pressure reduction 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 components were added in an amount of 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 purged with nitrogen by vacuum substitution to create a nitrogen atmosphere. Next, the temperature of the system was raised from 160°C to 230°C over 1 hour while stirring, and the reaction was carried out at this temperature for 1 hour.

[0239] To this ester oligomer component, the catalyst solution was added in an amount to give 50 ppm by weight of titanium atoms per polyester obtained, and the mixture was maintained at 230°C for 30 minutes, then heated to 250°C over 30 minutes, and simultaneously heated to 0.07 × 10 ３The pressure was reduced to 1.81 dL / g or less, and the polycondensation reaction was continued while maintaining the heated and reduced pressure state. When a predetermined viscosity was reached, the polymerization was terminated, and the pressure was restored with nitrogen. The mixture was then drawn out in the form of a strand into a water bath, cooled with water, and cut into chips to obtain polyester pellets. The resulting polyester had an intrinsic viscosity of 1.81 dL / g and a color b value of 3.0.

[0240] Example 5 The PBSA polymerization procedure was carried out in the same manner as in Example 4, except that the amount of recovered oligomer component added was 10 parts by weight per 100 parts by weight of the polyester product. The intrinsic viscosity of the resulting polyester was 1.81 dL / g, and the color b value of the pellets was 6.6.

[0241] Example 6 The PBSA polymerization procedure was carried out in the same manner as in Example 4, except that the amount of recovered oligomer component added was 20 parts by weight per 100 parts by weight of the polyester product. The intrinsic viscosity of the resulting polyester was 1.84 dL / g, and the color b value of the pellets was 8.5.

[0242]

[0243] 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: Rectification column D: Pump E: Pump F: Tank G: Condenser L1, L3, L5: Polycondensation reaction product withdrawal line L2, L4, L6: Vent line L7: Catalyst supply line L8: Raw material supply line a: First polycondensation reaction tank d: Second polycondensation reaction tank k: Third polycondensation reaction tank c, e, m: Withdrawal gear pump g: Die head h: Rotary cutter p, q, r, s: Filters I: Circulation tank II: Heat exchanger III: Contact treatment vessel 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 vessel XIV: Solid-liquid separation vessel XV: Solid-liquid separator 101: Contact treatment liquid supply line 102: Withdrawal 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 vessel overflow line 114: Solid-liquid separation vessel overflow line 115: Drain 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 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: Cooled gas withdrawal line 212: Cooled gas supply line 213: Dry gas withdrawal line 214: Dry gas supply line

Claims

DEPCT691. A method for the production of polyesters, comprising a reaction procedure which includes at least one reaction treatment allowing a selected polyester feedstock from the group of esterification and ester exchange treatments, in which the polyester feedstock contains a diol component, a dicarboxylic acid component, and an oligomer component, in which the ratio of the cyclic oligomer component to the oligomer component is 35% by mass or more and 100% by mass or less, and in which the cyclic oligomer component contains units derived from the diol component and units derived from the dicarboxylic acid component, in which the total number of repeats of the units derived from the diol component and the total number of repeats of the units derived from the dicarboxylic acid component are 2 to 72. A method for the production of polyesters according to claim 1, in which the diol component contains at least one substance selected from the group of 1.4-Butanediol and its derivatives.

3. Methods for the production of polyesters under claim 1 or 2, where the ratio of the oligomer components present in the polyester raw material is 0.1% by mass or more and less than 100% by mass.

4. Methods for the production of polyesters under claim 1 or 2, which are further incorporated into a purification step which includes contact treatment in which the reaction product is in contact with an aqueous solvent, thus obtaining a contact treatment liquid containing the oligomer components and the reaction product after contact treatment, in which the oligomer components in the treatment liquid are reused as oligomer components in the polyester raw material in the reaction step.

5. Methods for the production of polyesters under claim 4, which are further incorporated, between the reaction step and the purification step, into a pelletizing step of the reaction product, to obtain pellets.

6. Methods for the production of polyesters under claim 4,7. A method for the production of polyesters under claim 4, which includes a drying step for the preparation of polyester raw materials, in which the oligomer components are fed into the contact treatment fluid at any of those steps from the raw material preparation step to the reaction step.

8. A method for the production of polyesters under claim 7, in which at least one treatment is performed from a group consisting of contact treatment in the purification step and drying treatment in the continuous drying step.

9. A method for the production of polyesters under claim 1 or 2, in which the cyclic oligomer components have structures represented by the following formula (1) and structures represented by the following formula (2) (chemical formula) (1) (chemical formula) (2) (in formula (1), R1 and R2 independently represent the divalent hydrocarbons which may be selected to have substituents, and x is 0 to 7; in formula (2),R3 and R4 independently represent selectable divalent hydrocarbon substituents, and y is 0 to 7; and x+y is 2 to 7)10. Method for the production of polyesters according to claim 9, in which R1 to R4 independently represent selectable divalent hydrocarbon substituents; 11. Method for the production of polyesters according to claim 9, in which the polyester raw materials include, as a dicarboxylic acid component, at least one substance selected from the group of dicarboxylic acids represented by the following formulas (A) and their derivatives, and at least one substance selected from the group of dicarboxylic acids represented by the following formulas (B) and their derivatives; and, as a diol component, at least one substance selected from the group of diols represented by the following formulas (C) and their derivatives;and at least one substance selected from the group consisting of diols represented by the following formulas (D) and their derivatives; and where at least one substance selected from the group consisting of: at least one substance selected from the group consisting of diols represented by the following formulas (C); and at least one substance selected from the group consisting of diols represented by the following formulas (D) is at least one substance selected from the group consisting of 1,4-butanediols and their derivatives (chemical formulas)(A)(chemical formulas)(B)(chemical formulas)(C)(chemical formulas)(D)(in formulas (A) to (D), R1 to R4 have the same meaning as R1 to R4 respectively in formula (1) described above).

12. Method for the production of polyesters according to claim 1 or 2,where at least one treatment is performed, selected from a group consisting of contact treatment in the purification phase and drying treatment in the batch or semi-batch drying phase.

13. Compositions which include: polyesters which include units derived from diol components and units derived from dicarboxylic acid components; and cyclic oligomers whose structures are represented by the following formula(1) and the following formula(2) (chemical formulas). (1)(Chemical formula)(2)(In formula(1), R1 and R2 independently represent the divalent hydrocarbon substituents which may be selectively chosen, and x is 0 to 7; in formula(2), R3 and R4 independently represent the divalent hydrocarbon substituents which may be selectively chosen, and y is 0 to 7; and x+y is 2 to 7)14. Composition according to claim 13, in which the polyester is composed of constituent units derived from cyclic oligomers15. Compressed material formed by compression of the constituent unit according to claim 13 or 1416. Method for the production of polyester,This consists of: the reaction step of obtaining reaction products by operation, on polyester raw materials containing diol and dicarboxylic acid components; reaction treatment which includes at least one treatment selected from a group consisting of esterification treatment and ester exchange treatment; the contact treatment step of bringing the reaction products into contact with the contact treatment fluid so that: the contact treatment fluid contains oligomer components; and the reaction products resulting from that contact treatment; the purification step which includes treatment for purification, from the contact treatment fluid containing oligomer components, the oligomer components in the contact treatment fluid in such a way that the ratio of cyclic oligomer components present in the oligomer components is increased; and the recovery step of recovering, from the raw materials, the oligomer components that have passed the purification step.

17. Method for the production of polyesters according to claim 16.Where the purification procedure includes a separation treatment by distillation: high-boiling point liquids containing oligomer components; and low-boiling point liquids.

18. The method for the production of polyesters according to claim 17, which is further included with a phase separation treatment for the liquid / liquid phase separation treatment to separate the oligomer components from the high-boiling point liquids.

19. The method for the production of polyesters according to claim 18, which is further included with a crystallization treatment for the further crystallization of the oligomer components separated in the phase separation treatment.

20. The method for the production of polyesters according to claim 17, which is further included with a crystallization treatment for the crystallization of the oligomer components present in the high-boiling point liquids.

21. The method for the production of polyesters according to claim 16 or 17, which is further included, between the reaction steps and the contact treatment steps, with a pelletizing step of the pelletizing of the reaction products obtained from the reaction steps.

22. Methods for the production of polyesters under claim 16 or 17, which are further incorporated, before the reaction step, with the raw material preparation step, and which are further incorporated, after the separation step, with the feeding step, to any of those steps from the raw material preparation step to the reaction step, a molten substance which melts the separated oligomer components or a solution which dissolves the oligomer components in the diol components of the polyester raw material.

23. Methods for the production of polyesters under claim 16 or 17, in which the contact treatment fluid contains alcohol.

24. Methods for the production of polyesters under claim 16 or 17, which are further incorporated, after the contact treatment step, with the drying step of the drying treatment for drying the reaction product resulting from the contact treatment.

25. Methods for the production of polyesters under claim 24,where at least one treatment selected from the group consisting of contact treatment in the contact treatment step and drying treatment in the continuous drying step is carried out;26. Method for the production of polyester according to claim 24, where at least one treatment selected from the group consisting of contact treatment in the contact treatment step and drying treatment in the batch or semi-batch drying step is carried out;

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