Oligomer composition and method for producing oligomer composition

Abstract

Provided are a composition obtained by separating and recovering a component, which is derived from PBT, from a raw material containing PBT together with another polymer while suppressing contamination of a component derived from the other polymer, and a method for obtaining such a composition.　This oligomer composition contains a butylene terephthalate (BT) oligomer in which both ends are terminated with 1,4-butanediol (14BD), and does not contain PA or PET, or a decomposition product thereof in an amount detectable by infrared absorption spectroscopy. This production method includes: a first separation step for heating, in 14BD, a raw material mixture at a first temperature equal to or higher than the dissolution start point of PA and lower than the dissolution start point of PBT to isolate an insoluble product; a second separation step for heating, in 14BD, the insoluble product obtained in the first separation step at a second temperature equal to or higher than the dissolution start point of PBT and lower than the dissolution start point of PET to isolate a dissolved and separated component; and a solvent removal step for removing a solvent from the dissolved and separated component obtained in the second separation step.

Description

Oligomer composition and method for producing the oligomer composition

[0001] This disclosure relates to oligomer compositions and methods for producing oligomer compositions.

[0002] Wire harnesses used in automobiles and other vehicles utilize many polymers as insulation for the wires, connector housings, and outer coverings. From the perspective of a circular economy, it is desirable to recover and recycle polymers from discarded wire harnesses. However, since wire harnesses are composed of a wide variety of polymers, it is important to separate these polymers by type in order to effectively carry out recycling.

[0003] One method for separating a specific polymer from a raw material containing multiple types of polymers is to chemically decompose the polymer of interest and elute it into the liquid phase. For example, Patent Document 1 discloses a process comprising the steps of: depolymerizing a first polymer containing polyethylene terephthalate with 1,4-butanediol in the presence of at least one second polymer composed of polyvinyl chloride, polyvinylidene chloride, polyamide, polylactic acid, and combinations thereof to produce a molten mixture; and polymerizing the molten mixture under conditions sufficient for the formation of a modified polybutylene terephthalate copolymer. The resulting modified polybutylene terephthalate copolymer contains polyethylene terephthalate component residues and residues of the second polymer or residues derived from the second polymer.

[0004] Special Publication No. 2012-514111

[0005] Polybutylene terephthalate (PBT) is one of the polymer species widely used in polymer materials that make up wire harnesses and other components, and it is desirable to separate it from other polymer components for recycling. Polyesters such as polybutylene terephthalate (PBT) and polyethylene phthalate (PET) can be depolymerized and eluted into the liquid phase using polyhydric alcohols such as 1,4-butanediol or alkaline aqueous solutions, as described in Patent Document 1. However, methods for separating and recovering PBT from polymers other than polyester, such as polyamides, or from other types of polyester, such as PET, are not common. In Patent Document 1, a PBT copolymer is obtained as the recovered product, but this PBT copolymer uses PET as the ester source, not PBT itself. However, PBT accounts for a large proportion of polymer-based waste, including wire harness waste, and it is expected that being able to separate and recover PBT as is, or in the form of PBT decomposition products, would greatly contribute to the recycling of polymer materials.

[0006] Furthermore, in Patent Document 1, the PBT component is not obtained in the form of a homopolymer or the like, containing only the PBT backbone unit, but rather as a copolymer containing both the PBT component and a second polymer or its derivative, such as polyvinyl chloride or polyamide. However, when the recovered material is reused after further polymerization, it is preferable to recover the polymer component in a state containing only the backbone unit of the target polymer, from the viewpoint of ease of reuse and control of the structure of the reused product. For example, when recovering PBT from waste containing multiple polymers, it is preferable to recover PBT or its derivative alone, minimizing copolymerization or mixing with other polymers or their derivatives.

[0007] In view of the above, the objective is to provide a composition obtained by separating and recovering components derived from polybutylene terephthalate from a raw material containing polybutylene terephthalate together with other polymers, while suppressing the inclusion of components derived from other polymers, and a method for obtaining such a composition.

[0008] The oligomer composition according to this disclosure comprises a butylene terephthalate oligomer terminated at both ends with 1,4-butanediol, and does not contain polyamide, polyethylene terephthalate or its decomposition products in amounts detectable by infrared absorption spectroscopy.

[0009] A method for producing an oligomer composition according to this disclosure includes: a first separation step of heating a raw material mixture containing a polyester containing polybutylene terephthalate and a polyamide in 1,4-butanediol at a first temperature above the temperature at which the polyamide begins to dissolve and below the temperature at which the polybutylene terephthalate begins to dissolve, thereby separating insoluble matter; a second separation step of heating the insoluble matter obtained in the first separation step in 1,4-butanediol at a second temperature above the temperature at which the polybutylene terephthalate begins to dissolve and below the temperature at which polyethylene terephthalate begins to dissolve, thereby separating the dissolved and separated components; and a solvent removal step of removing the solvent from the dissolved and separated components obtained in the second separation step to obtain an oligomer composition containing a butylene terephthalate oligomer.

[0010] The oligomer composition according to this disclosure is obtained by separating and recovering the component derived from polybutylene terephthalate from a raw material containing polybutylene terephthalate together with other polymers, while suppressing the inclusion of components derived from other polymers. Furthermore, the method for producing the oligomer composition according to this disclosure is a method for obtaining such a composition.

[0011] Figure 1 is a flow chart illustrating a method for producing an oligomer composition according to one embodiment of the present disclosure. Figures 2A and 2B illustrate the dissolution mechanisms of PBT and PA in 1,4-butanediol, respectively. Figure 3 shows DSC curves for PA6, PA66, PBT, and PET. Figure 4 shows the IR spectra of the products obtained from the second dissolution separation, along with various polymers as reference samples. Figure 5 shows the molecular weight distribution of the products obtained from the second dissolution separation, along with PBT. Figure 6 shows the IR spectra of the products obtained from the second dissolution separation, along with PBT and alkali-depolymerized oligomers as reference samples. Figures 7A and 7B are micrographs of the gel-like substance obtained in the second separation step, each showing different regions. Figure 7C is a micrograph of carbon-colored PBT as a reference sample. Figure 8A shows the IR spectra of the dissolution separation products obtained in various dissolution separation steps, along with reference samples. Figure 8B shows the IR spectra of various components of the second insoluble substance, along with the reference sample. Figure 9 shows the DSC curves of the dissolved and separated products obtained in various dissolution and separation steps, along with the various reference samples.

[0012] [Description of Embodiments of the Disclosure] First, embodiments of the Disclosure will be listed and described. The oligomer composition and method for producing the oligomer composition according to the Disclosure have the following configurations.

[0013] [1] The oligomer composition according to the present disclosure comprises a butylene terephthalate oligomer terminated at both ends with 1,4-butanediol, and does not contain polyamide, polyethylene terephthalate or its decomposition products in amounts detectable by infrared absorption spectroscopy.

[0014] The oligomer composition according to this disclosure contains a butylene terephthalate oligomer terminated at both ends with 1,4-butanediol, and does not contain polyamide, polyethylene terephthalate or its decomposition products. Therefore, it can be easily used as a well-controlled butylene terephthalate (BT) oligomer source with minimal contamination from other components. For example, PBT can be obtained by homopolymerizing the oligomer composition as a polymerization raw material. This oligomer composition can be easily obtained by separating PBT from other polymers by performing a two-stage heat treatment using 1,4-butanediol on a raw material containing PBT together with other polymers, such as waste, at a predetermined temperature, as described in the method for producing the oligomer composition according to this disclosure. Therefore, the oligomer composition according to this disclosure allows for the easy separation and recovery of PBT-derived components from a raw material containing multiple types of polymers, while suppressing contamination from components derived from other polymers, and can be used for PBT regeneration.

[0015] [2] In the embodiment of [1] above, the butylene terephthalate oligomer preferably has a number average molecular weight of 1000 or less and a molecular weight polydispersity of 1.5 or less. When the oligomer composition according to this embodiment is produced by heat treatment with 1,4-butanediol on a raw material containing PBT, a BT oligomer with a low degree of polymerization and a well-uniform degree of polymerization is obtained as the depolymerization product of PBT. In other words, a BT oligomer with a low number average molecular weight and a low molecular weight polydispersity is easily obtained as described above. Thus, an oligomer composition containing a BT oligomer with a low degree of polymerization and a well-uniform degree of polymerization is easily usable as a polymerization raw material for PBT, etc.

[0016] [3] In the embodiment of [1] or [2] above, the oligomer composition may further contain at least one of a colorant and glass fibers. Colorants and glass fibers are additives that are often added to polymer materials that constitute wire harnesses, and are easily incorporated into the oligomer composition when it is produced from wire harness waste as a raw material through heat treatment with 1,4-butanediol. Therefore, the presence of at least one of a colorant and glass fibers in the oligomer composition indicates that the oligomer composition was obtained from wire harness waste as a raw material.

[0017] [4] In any of the embodiments of [1] to [3] above, the butylene terephthalate oligomer may be obtained by depolymerizing polybutylene terephthalate with 1,4-butanediol. By heating and depolymerizing PBT in 1,4-butanediol, an oligomer composition containing a BT oligomer can be easily obtained. By appropriately setting the heating temperature, even if a raw material containing other polymers in addition to PBT is used, the PBT can be separated from the other polymer components, selectively depolymerized, and recovered. The BT oligomer obtained by depolymerizing PBT using 1,4-butanediol is terminated at both ends with 1,4-butanediol, and tends to have a relatively low degree of polymerization and a narrow distribution of the degree of polymerization.

[0018] [5] In the embodiment described in [4] above, the oligomer composition may be obtained by heating a raw material derived from wire harness waste containing polybutylene terephthalate in 1,4-butanediol at a temperature above the temperature at which polyamide begins to dissolve and below the temperature at which polybutylene terephthalate begins to dissolve, separating the insoluble material, and then heating the insoluble material in 1,4-butanediol at a temperature above the temperature at which polybutylene terephthalate begins to dissolve and below the temperature at which polyethylene terephthalate begins to dissolve, separating the dissolved components, and then removing the solvent. Wire harness waste often contains polyethylene terephthalate (PET) and polyamide (PA) in addition to PBT. However, as will be explained in detail later, in relation to the dissolution mechanisms and molecular structures of PBT, PET, and PA, the temperatures at which dissolution in 1,4-butanediol begins are, from lowest to highest, PA, PBT, and PET. Therefore, by setting the heating temperature as described above and performing a two-stage heat treatment with 1,4-butanediol on the raw material derived from wire harness waste, the BT oligomer can be separated and recovered from PA and PET as a component dissolved and separated in the second stage. The fact that the oligomer composition obtained in this way is derived from raw material derived from wire harness waste can be confirmed, for example, by the presence of additives added to the polymer material constituting the wire harness, such as colorants and glass fibers.

[0019] [6] A method for producing an oligomer composition according to the present disclosure includes: a first separation step of heating a raw material mixture containing a polyester containing polybutylene terephthalate and a polyamide in 1,4-butanediol at a first temperature above the temperature at which the polyamide begins to dissolve and below the temperature at which the polybutylene terephthalate begins to dissolve, thereby separating insoluble matter; a second separation step of heating the insoluble matter obtained in the first separation step in 1,4-butanediol at a second temperature above the temperature at which the polybutylene terephthalate begins to dissolve and below the temperature at which polyethylene terephthalate begins to dissolve, thereby separating the dissolved and separated components; and a solvent removal step of removing the solvent from the dissolved and separated components obtained in the second separation step to obtain an oligomer composition containing a butylene terephthalate oligomer.

[0020] In the method for producing the oligomer composition according to this disclosure, due to differences in dissolution mechanisms, PA dissolves in 1,4-butanediol at a lower temperature than PBT. Therefore, by going through the first separation step, a composition containing PBT as an insoluble substance but not PA can be obtained. Furthermore, due to differences in molecular structure, PBT dissolves in 1,4-butanediol at a lower temperature than PET. Therefore, by performing the second separation step at a second temperature on the insoluble substance obtained in the first separation step, even if PET is contained in the raw material mixture, a composition can be obtained that contains PBT as a component dissolved and separated in 1,4-butanediol, but not PET or other components that do not dissolve in 1,4-butanediol at the second temperature. In this way, by performing the treatment with 1,4-butanediol in two stages, even if PA or PET is contained in the raw material mixture, an oligomer composition containing BT oligomers can be easily obtained while suppressing the inclusion of polymer components other than PBT.

[0021] By performing the heat treatment involving the depolymerization of PBT using 1,4-butanediol, unlike when using alkaline aqueous solutions or other alcohols, the BT oligomers formed by the depolymerization of PBT are terminated at both ends with 1,4-butanediol, a component of PBT, and the BT oligomers are composed only of the same unit structures as those contained in PBT. Therefore, the obtained oligomer composition can be suitably used as a polymerization raw material for newly constructing PBT through polymerization. Furthermore, the BT oligomers obtained by the depolymerization of PBT using 1,4-butanediol tend to have a relatively low degree of polymerization and a narrow distribution of the degree of polymerization, which also enhances the suitability of the obtained oligomer composition when used as a new polymerization raw material. Compared to solvents that cause PBT depolymerization by hydrolysis, such as alkaline aqueous solutions, 1,4-butanediol is superior in that it is easy to remove in the solvent removal process and is highly safe.

[0022] [7] In the embodiment of [6] above, the raw material mixture may further contain polyethylene terephthalate as the polyester. As described above, in the method for producing the oligomer composition according to the present disclosure, by performing the second step on the composition from which PA has been removed in the first separation step, the BT oligomer can be recovered by separating it from PET using the difference in the dissolution start temperatures of PBT and PET. In this way, even when a raw material mixture containing both esters, PBT and PET, is used, the two esters can be easily separated.

[0023] [8] In the embodiment of [6] or [7] above, the raw material mixture may be derived from wire harness waste. Wire harness waste contains a large amount of PBT, and by separating and recovering PBT in the form of oligomers, the recycling of wire harness waste can be efficiently promoted. Wire harness waste often contains PA and PET in addition to PBT, but as described above, by performing heat treatment in 1,4-butanediol in two stages, the first separation step and the second separation step, BT oligomers can be separated and recovered from PA and PET.

[0024] [9] In any of the embodiments described in [6] to [8] above, the first temperature is preferably 160°C or more and less than 185°C, and the second temperature is preferably 185°C or more and less than 205°C. Then, after the first separation step and the second separation step, the BT oligomer is separated from PA and PET with high efficiency, and an oligomer composition with reduced contamination of components derived from PA and PET can be easily obtained.

[0025] [Details of Embodiments of the Disclosure] The oligomer composition and the method for producing the oligomer composition according to embodiments of the disclosure will be described below with reference to the drawings.

[0026] [1] Outline of the Oligomer Composition An oligomer composition according to one embodiment of the present disclosure contains a butylene terephthalate oligomer. A butylene terephthalate (BT) oligomer is an oligomer having a structure in which multiple butylene terephthalate units, that is, structural units in which 1,4-butanediol and terephthalic acid are ester-bonded, are linked together via ester bonds. Here, the number of repeating units in the oligomer, that is, the degree of polymerization, is generally recognized to be between 2 and approximately 100, as is typical for oligomers. However, as will be explained in detail later, the degree of polymerization corresponding to a preferred molecular weight range is small within that range, generally 25 or less.

[0027] The BT oligomer constituting the oligomer composition according to this embodiment is terminated at both ends by alcohols. That is, alcohol molecules are bonded to both ends. Preferably, both ends are terminated with 1,4-butanediol. In this case, the structure of the BT oligomer, in which 1,4-butanediol and terephthalic acid are alternately bonded via ester bonds, is closed at both ends by 1,4-butanediol. That is, the functional groups at both ends become 4-hydroxybutoxy groups.

[0028] The oligomer composition according to this embodiment may consist solely of BT oligomers, excluding unavoidable impurities, but may also contain components other than BT oligomers. However, it is preferable that the oligomer composition does not contain polyamide (PA), excluding unavoidable impurities. Furthermore, it is preferable that the oligomer composition does not contain polyethylene terephthalate (PET) and its decomposition products, excluding unavoidable impurities. The absence of a certain polymer species or a component derived from a polymer species, excluding unavoidable impurities, means, for example, that it is not present in an amount detectable by infrared absorption spectroscopy (IR). IR measurement is performed, for example, using powder total internal reflection decay (ATR) at 4 cm². －１ This resolution should be sufficient.

[0029] It is preferable that the oligomer composition does not contain components derived from PA and PET, except for unavoidable impurities, whether as components mixed with BT oligomers or as components that bind to BT oligomers through copolymerization or side chain formation. Similarly, it is preferable that the oligomer composition does not contain components derived from polyvinyl chloride (PVC), or components derived from polyolefins such as polyethylene (PE) and polypropylene (PP), except for unavoidable impurities. On the other hand, the oligomer composition often contains at least one of a colorant and glass fibers, as derived from the manufacturing method described below. Further details of the oligomer composition's composition will be explained after the manufacturing method.

[0030] [2] Method for Producing the Oligomer Composition The above-mentioned oligomer composition can be suitably produced by the method for producing the oligomer composition according to the embodiment of the present disclosure. The method for producing the oligomer composition according to one embodiment of the present disclosure will be described below.

[0031] The flowchart in Figure 1 outlines the method for producing the oligomer composition according to this embodiment. In this production method, as shown in Figure 1, the first separation step, the second separation step, and the solvent removal step are carried out in this order on the raw material mixture to obtain the oligomer composition.

[0032] The raw material mixture used as a raw material for the oligomer composition is composed of a material containing polyester including PBT and PA. The polyester may consist of only PBT, or PBT plus other polyesters; however, it is preferable that polyethylene terephthalate (PET) is included in addition to PBT. A raw material mixture derived from wire harness waste can be suitably used as a polymer mixture containing PBT, PA, and often PET. Wire harnesses consist of electric wires, connectors, and accessories such as tape. During the disposal process, metal materials such as electric wire conductors and connector terminals are removed, and the material is discharged as a mixture of various polymers. It is preferable to crush the discharged material into nugget-like shapes as appropriate and use it as a raw material mixture. In wire harnesses, PBT is frequently used in connector housings, PA in clamps, and PET in nonwoven fabrics as outer coverings. Wire harness waste often contains PVC and polyolefins such as PE and PP, in addition to PBT, PA, and PE as polymers.

[0033] In the manufacturing method according to this embodiment, a first separation step and a second separation step are performed on the above raw material mixture. In both of these separation steps, the material is heated in a polyhydric alcohol such as 1,4-butanediol (14BD), but this heating treatment is carried out in two stages at different heating temperatures. In relation to these heating temperatures, the dissolution of each polymer in 14BD will first be explained.

[0034] As will be shown in detail in later examples, Figure 3 shows the DSC curves obtained when differential scanning calorimetry (DSC) was performed on two types of PA, nylon 6 (PA6) and nylon 6,6 (PA66), PBT, and PET in a sealed aluminum pan while heating in 14BD. In the DSC curve, the peak appearing in the negative direction represents endothermic activity, which corresponds to the dissolution of the polymer in 14BD. In Figure 3, the temperature at which dissolution begins (dissolution initiation point) is indicated by arrows. According to Figure 3, the dissolution initiation point differs depending on the polymer type: 125°C for PA6, 158°C for PA66, 185°C for PBT, and 205°C for PET. The two types of PA begin to dissolve at relatively low temperatures, and then gradually dissolve as the temperature rises, whereas the polyesters PBT and PET begin to dissolve at higher temperatures than the PAs, and dissolution proceeds rapidly as the temperature rises.

[0035] Such differences in the dissolution start point and the subsequent form of dissolution progress are due to differences in the dissolution mechanism. The dissolution mechanisms of PBT and PA are schematically shown in FIGS. 2A and 2B, respectively. First, for PA shown in FIG. 2B, dissolution in an alcohol such as 14BD proceeds by solvation without decomposition (depolymerization) of the polymer chains. In the process of solvation, the hydrogen bonds formed between the polymer chains are replaced by hydrogen bonds between the amide bond portions of each polymer chain and the alcohol molecules, and the crystal structure of the polymer chains is eliminated. Thus, dissolution without depolymerization proceeds from a relatively low temperature. Also, it proceeds gently over a wide temperature range. On the other hand, for PBT shown in FIG. 2A, dissolution in an alcohol such as 14BD proceeds with decomposition of the polymer chains by depolymerization. Depolymerization occurs by transesterification between the ester bonds in the polymer chains and the alcohol molecules. By depolymerization, the molecular weight of PBT decreases and BT oligomers are produced. The produced BT oligomers dissolve in the alcohol. Thus, dissolution with depolymerization does not start unless heated to a relatively high temperature, and also proceeds rapidly within a narrow temperature range. PET also dissolves with a mechanism involving the same depolymerization as PBT. However, the dissolution start points of PBT and PET are different corresponding to the differences in their molecular structures. Specifically, PET has a higher glass transition temperature than PBT, and the dissolution start point due to depolymerization is also higher.

[0036] As described above, the dissolution start temperature when heated in a polyhydric alcohol is in the order of PA, PBT, and PET from the lowest. PVC and polyolefins such as PP and PE hardly dissolve in polyhydric alcohols at least at a temperature at which PET dissolves. By utilizing such differences in the dissolution start points, polymers can be separated by type.

[0037] As shown in Fig. 1, first, in the first separation step, the raw material mixture is heated in a polyhydric alcohol at the first temperature. The first temperature is set to be not lower than the dissolution start point of PA and lower than the dissolution start point of PBT. When 1,4-butanediol (1,4-BD) is used as the polyhydric alcohol, the first temperature may be not lower than 160°C and lower than 185°C. More preferably, it may be not lower than 170°C and lower than 180°C. Since the first temperature is not lower than the dissolution start point of PA, in the first separation step, PA in the raw material mixture dissolves in the polyhydric alcohol and is incorporated into the liquid phase. On the other hand, since the first temperature is lower than the dissolution start point of PBT, PBT and PET in the raw material mixture do not dissolve in the polyhydric alcohol and remain as insoluble substances. Therefore, in the first separation step, after the dissolution of PA has sufficiently proceeded, it is separated from the liquid phase (which may be in a gel form) to separate and collect the insoluble substances. Thereby, a material containing PBT from which PA has been separated and removed can be obtained. This insoluble substance is referred to as the first insoluble substance.

[0038] As a specific operation in the first separation step, the raw material mixture and the polyhydric alcohol may be mixed and heated with stirring at the first temperature. The heating and stirring time can be exemplified as about 5 minutes to 30 minutes. After heating and stirring, a liquid such as water may be appropriately added, and then filtration may be performed to separate and collect the insoluble substances. The first dissolution-separated product, which is a component of the liquid phase separated by dissolution from the insoluble substances, is not used in the production of the oligomer composition thereafter, but contains PA at a high concentration.

[0039] Next, in the second separation step, the first insoluble material obtained in the first separation step is heated in a polyhydric alcohol at a second temperature higher than the first temperature. The second temperature is set to be above the dissolution start point of PBT and below the dissolution start point of PET. When 14BD is used as the polyhydric alcohol, the second temperature should be 185°C or higher and less than 205°C. More preferably, it should be 190°C or higher and less than 200°C. Because the second temperature is above the dissolution start point of PBT, in the second separation step, the PBT in the first insoluble material dissolves in the polyhydric alcohol and is incorporated into the liquid phase. On the other hand, because the second temperature is below the dissolution start point of PET, the PET in the first insoluble material does not dissolve in the polyhydric alcohol and remains as an insoluble material. Therefore, in the second separation step, after sufficient dissolution of PBT has proceeded, it is separated from the insoluble material, and the dissolved and separated components of the liquid phase (which may also be gel-like) are separated. This makes it possible to obtain a dissolved and separated product in which PET has been separated and PBT has dissolved. This dissolved and separated product will be referred to as the second dissolved and separated product.

[0040] In the second separation step, the specific procedure is the same as in the first separation step: the first insoluble substance and the polyhydric alcohol are mixed and heated and stirred at the second temperature. The heating and stirring time can be exemplified as 5 to 30 minutes. After heating and stirring, water or other liquid can be added as needed, and then the dissolved separated product can be separated by filtration.

[0041] As shown in Figure 2A, the PBT component dissolved in the polyhydric alcohol as the second dissolution separation product undergoes depolymerization, i.e., transesterification and demolecularization, upon dissolution, resulting in a BT oligomer. In this process, the BT oligomer produced by depolymerization in the polyhydric alcohol has alcohol termini at both ends and, excluding unavoidable impurities, does not have carboxylic acid termini. When 14BD is used as the polyhydric alcohol, both ends are terminated with 14BD. In other words, the functional groups at both ends are 4-hydroxybutoxy groups. The second insoluble product, which is the insoluble material separated from the second dissolution separation product, is not used in the subsequent production of the oligomer composition, but in addition to PET, it appropriately contains components that do not dissolve at least at the second temperature, such as PVC and polyolefins.

[0042] In the manufacturing method according to this embodiment, a solvent removal step is performed last. In the solvent removal step, the solvent is removed from the second dissolved separated product obtained in the second separation step. The solvent can be removed, for example, by vacuum distillation. By removing the solvent, the BT oligomer that was separated as the second dissolved separated product is recovered as a solid (powdered) oligomer composition.

[0043] In the manufacturing method according to this embodiment, as described above, by utilizing the difference in the dissolution start temperature of each polymer species in polyhydric alcohol, PBT can be separated and recovered from a raw material mixture containing multiple polymer species, separate from other polymers such as PA and PET. This allows PBT to be recovered from a raw material mixture derived from wire harness waste and used for recycling. In this case, since PBT is recovered in the form of BT oligomers, it can be reused by, for example, polymerizing it again to produce PBT. In the manufacturing method according to this embodiment, the separation and recovery of PBT can be performed in just two steps: heating the material in a polyhydric alcohol and separating the product. After removing the solvent, an oligomer composition containing BT oligomers can be easily obtained while suppressing the contamination of components derived from polymer species other than PBT. Polyhydric alcohols such as 14BD are also excellent in terms of handling safety and ease of removal from the product. Depolymerization of PBT can also be performed by hydrolysis using an alkaline aqueous solution, but in that case, handling the alkaline aqueous solution may be dangerous, and separation from the product is also time-consuming. Furthermore, the polyhydric alcohols used in the two separation steps can be reused by recovering them through distillation as needed.

[0044] [Details of the Oligomer Composition to be Produced] As already described, the oligomer composition according to one embodiment of the present disclosure contains a BT oligomer and has a distinctive structure because it is obtained by a production method that includes a first separation step and a second separation step by heating in a polyhydric alcohol. First, since the PBT in the mixed raw materials is recovered in the form of a BT oligomer directly formed by depolymerization using a polyhydric alcohol, the PBT-derived recovered product does not contain unit structures derived from components other than PBT, except for the bonding of the polyhydric alcohol to the terminal part of the oligomer. Therefore, the recovered BT oligomer composition can be used simply and with high controllability as a raw material for a new product containing BT units. In particular, when 14BD is used as the polyhydric alcohol, both ends of the BT oligomer are terminated with 14BD, and the oligomer chain does not contain any elements other than the same unit structures that constitute PBT. Therefore, the obtained oligomer composition can be suitably used for the regeneration of PBT by polymerization.

[0045] Furthermore, the BT oligomers constituting the oligomer composition according to this embodiment are obtained by the depolymerization of PBT with polyhydric alcohols, and are therefore relatively low molecular weight oligomers. Specifically, the number average molecular weight (Mn) tends to be 5000 or less, and particularly 1000 or less. The formula weight of the structural unit in PBT, i.e., the BT unit, is 220, and the above number average molecular weight corresponds to a degree of polymerization of approximately 22 or less, and particularly approximately 5 or less. There is no particular lower limit set for the number average molecular weight, but it is generally 400 or more. In addition, the obtained BT oligomers have a narrow molecular weight distribution. Specifically, the polydispersity of molecular weight (Mw / Mn) tends to be 2.0 or less, and particularly 1.5 or less. Here, the polydispersity (Mw / Mn) is determined as the ratio of the weight-average molecular weight (Mw) to the number average molecular weight (Mn), and a larger value indicates a wider molecular weight distribution. There is no particular lower limit set for the polydispersity, but a value closer to 1.0 is preferable. Thus, the relatively low molecular weight of the resulting BT oligomers increases their convenience when used as raw materials for repolymerization. Furthermore, the narrow molecular weight distribution enhances the uniformity of the oligomer composition's physical properties and reactivity, making it easier to control the structure of recycled products obtained through repolymerization. Polymeric waste, such as that derived from wire harnesses, may contain various PBTs with different degrees of polymerization. Even in such cases, a BT oligomer with a narrow molecular weight distribution can be obtained as an oligomer composition, thereby significantly increasing its suitability as a raw material for repolymerization.

[0046] Furthermore, in the above manufacturing method, PBT is selectively dissolved and separated by utilizing the differences in the dissolution initiation points of each polymer species in polyhydric alcohol. Therefore, in the resulting oligomer composition, the inclusion of other polymers, including PA and PET, as well as decomposition products and other components derived from these other polymers, into the BT oligomer can be minimized. As shown in later examples, it is also possible to obtain a BT oligomer that does not contain PA, PET, or PET decomposition products, except for unavoidable impurities. In this way, by suppressing the inclusion of components derived from polymers other than PBT, when the obtained oligomer composition is recycled by repolymerization or the like, the influence of components derived from other polymers can be suppressed, and a well-controlled product can be obtained.

[0047] When materials derived from wire harness waste are used as raw materials for the production of oligomer compositions, fine solid additives that were added to the wire harness components may be incorporated into the oligomer composition without being completely separated or removed. Examples of such additives include colorants (pigments) such as carbon colorants, reinforcing fillers such as glass fibers, and stabilizers such as hydrotalcite. Reinforcing fillers such as glass fibers are large in size and can be easily removed as needed, but colorants such as carbon are small in particle size and are difficult to remove, and tend to remain in the oligomer composition. If additives such as colorants remain in the oligomer composition, the oligomer composition may appear colored rather than white. However, the effects of these components are limited, especially when the oligomer composition is reused as a raw material for wire harnesses.

[0048] Examples are shown below. The present invention is not limited to these examples. Unless otherwise specified, sample preparation and evaluation were carried out at room temperature in air.

[0049] [1] Confirmation of the dissolution initiation point of various polymer components First, as basic information for setting the manufacturing conditions of BT oligomers, the dissolution initiation point of various polymers when dissolved in 14BD was confirmed.

[0050] <Test Method> 5 mg each of four polymers, PA6, PA66, PBT, and PET, were prepared in the form of resin pieces and sealed in a lidded aluminum pan with 5 μL of 14BD, and heated. Differential scanning calorimetry (DSC) was performed using a differential scanning calorimeter while heating. The heating rate was set to 10°C / min.

[0051] <Test Results> Figure 3 shows the DSC curves obtained for each polymer. Endothermic peaks appeared for all polymers, and these endothermic peaks correspond to dissolution in 14BD. In the figure, the dissolution initiation point is indicated by an arrow, which represents the temperature at which the endothermic peak begins to appear (the temperature at which the DSC curve begins to rise in the endothermic direction).

[0052] The dissolution initiation points are 125°C for PA6, 158°C for PA66, 185°C for PBT, and 205°C for PET, with PA6 and PA66 showing significantly lower initiation points than PBT and PET. Furthermore, in PA6 and PA66, endothermic reactions proceed gradually, whereas in PBT and PET, endothermic reactions proceed rapidly after passing the dissolution initiation point. These differences in dissolution initiation points and the shapes of the endothermic peaks corresponding to dissolution correspond, as explained above, to the fact that dissolution to 14BD proceeds by solvation without decomposition of polymer chains in the case of PA, while in the case of PBT and PET, it proceeds with depolymerization by 14BD.

[0053] Since the dissolution initiation points of PA, PBT, and PET appear at sufficiently distant temperatures in this order from low temperatures, it is shown that PBT can be separated and recovered from PA and PET by mixing a raw material mixture containing PA, PBT, and PET with 14BD and heating it while controlling the temperature. Specifically, it is shown that the PBT depolymerization product can be separated from PA and PET by heating the raw material mixture with 14BD at a first temperature of 160°C to less than 185°C, which is above the dissolution initiation point of PA and below the dissolution initiation point of PBT, separating the insoluble material, and then heating that insoluble material with 14BD at a second temperature of 185°C to less than 205°C, which is above the dissolution initiation point of PBT and below the dissolution initiation point of PET, and separating the dissolved and separated material.

[0054] [2] Identification of product species Next, in the method for producing the oligomer composition according to the embodiment of the present disclosure described above, the product obtained from the second dissolved and separated product was identified.

[0055] <Test Method> (1) Implementation of Manufacturing Process As described in detail above, the method for producing an oligomer composition according to the embodiment of the present disclosure, including the first separation step, the second separation step, and the solvent removal step, was carried out. In this case, 20 g of resin nuggets obtained by crushing wire harness waste after removing the metal material was used as the raw material mixture. The first and second separation steps were carried out using 14BD. The heating temperature in the first separation step (first temperature) was set to 175°C, and the heating temperature in the second separation step (second temperature) was set to 195°C. In both the first and second separation steps, the solid material was mixed with 60 mL of 14BD and heated and stirred at the above-specified temperature for 15 minutes. After the heating and stirring of the second separation step was completed, a gel-like substance was obtained. The gel-like substance was added to an excess amount of pure water, stirred, and then filtered to obtain the second dissolved separation product as a filtrate. Furthermore, the filtrate was subjected to a solvent removal step by vacuum distillation to remove 14BD. The obtained product was dried to obtain a light gray powder. This powder was used as the product for analysis.

[0056] (2) Analysis of the product The product obtained above was measured by infrared absorption spectroscopy (IR). The IR measurement was performed using powder total reflection decay method (ATR method) and Fourier transform infrared spectroscopy (FT-IR). The measurement resolution was 4 cm. －１ The same measurements were also performed on individual samples of PBT, PET, PVC, PP, and PA66 as reference samples. In subsequent tests, IR measurements were performed using the same method as described above.

[0057] The molecular weight distribution of the products obtained above and PBT as a reference sample was evaluated. The molecular weight distribution was evaluated by dissolving each sample substance in hexafluoro-2-propanol (HFIP) and performing gel permeation chromatography (GPC).

[0058] <Test Results> Figure 4 shows the IR spectra of the product obtained from the second dissolution separation and each reference sample. The spectrum of the product was obtained at 1700 cm⁻¹. －１ A clear peak (peak A) corresponding to the C=O stretching of the ester bond is shown nearby, indicating that the product has an ester as its basic structure. Furthermore, the 1270 cm⁻¹ peak corresponds to the C-O stretching vibration. －１ The characteristic shape of the nearby peak (peak B), as well as the overall peak positions and shapes of the spectrum, are very similar to those of PBT alone. This indicates that the product has the same basic structure as PBT. However, the spectrum of the product contains peaks between 3500 and 3100 cm⁻¹, which are almost not seen in the spectrum of PBT alone. －１ A gentle peak (peak C) appears in the vicinity. This peak can be correlated with the O-H stretching vibration of the alcohol. The appearance of this peak in the product is thought to be due to the depolymerization of the product by 14BD, which increased the proportion of 14BD at the ends of the molecular chain. Based on the above IR measurement results, it can be said that the product is based on the depolymerization product of PBT.

[0059] Furthermore, the 1300 cm⁻¹ spectrum, which is unique to the PET spectrum, is also observed. －１ The sharp peak in the vicinity (peak D) does not appear in the product spectrum. Furthermore, the product spectrum does not show a peak at 3300 cm⁻¹. －１ Nearby N-H stretching vibration peaks, and 1650-1550 cm －１ The product spectrum does not contain any of the characteristic peaks seen in the PA66 spectrum alone, such as the two peaks referred to as amide I and amide II. Similarly, the product spectrum does not contain any of the characteristic peaks found in the PVC spectrum alone or the PP spectrum alone. From these findings, it can be concluded that the product does not contain PET, PA, PVC, PP, or derivatives with the same basic structure as these, at least in levels detectable by IR spectroscopy.

[0060] Next, Figure 5 shows the molecular weight distribution (differential molecular weight distribution curve) for the product and the reference sample PBT. Table 1 below shows the parameters derived from this molecular weight distribution.

[0061]

[0062] As shown in Figure 5, the product has a distribution in the low molecular weight region compared to PBT. Furthermore, the molecular weight distribution of the product is narrower. This is confirmed by the fact that the number-average molecular weight (Mn) and polydispersity (Mw / Mn) values ​​in Table 1 are significantly smaller in the product compared to PBT. Converting the number-average molecular weight of the product to a degree of polymerization yields approximately 2. In other words, it is confirmed that the depolymerization product of PBT takes the form of an oligomer with a low molecular weight and a small molecular weight distribution.

[0063] From the results of the IR measurements and molecular weight distribution measurements described above, it can be seen that the product obtained from the second dissolved separation product mainly consists of BT oligomers generated by the depolymerization of PBT. In other words, the product is an oligomer composition mainly composed of BT oligomers. Furthermore, it can be confirmed that the BT oligomers have a low degree of polymerization and a narrow distribution of the degree of polymerization. In addition, it can be confirmed that the oligomer composition does not contain any polymer species other than PBT, such as PET, PA, PVC, PP, or derivatives with a similar skeleton to these polymer species, such as PET decomposition products, at least at levels detectable by IR spectroscopy.

[0064] [3] End structure of butylene terephthalate oligomer Next, the end structure of the BT oligomer, which was confirmed to constitute the product obtained from the second dissolved separation in the test in [2] above, was further examined.

[0065] <Test Method> IR measurements were performed on the product obtained from the second dissolved and separated product in the test described in [2] above, as well as on PBT and the alkali-depolymerized oligomer as reference samples. The alkali-depolymerized oligomer was obtained by heating PBT in a 2.5 mol / L aqueous sodium hydroxide solution at 90°C for 2 hours under reflux, neutralizing with hydrochloric acid, and then washing with water and filtering.

[0066] <Test Results> The IR spectra obtained for the product and two reference samples are shown in FIG. 6. Here, the spectra of only the product and PBT are the same as those shown in FIG. 4. In the spectrum of the alkali depolymerized oligomer, a peak (peak E) derived from the carboxyl group of the associated carboxylic acid is observed in the region of approximately 2700 to 2500 cm －１ . This is associated with the fact that during the alkali depolymerization process, hydrolysis by water molecules proceeded, resulting in the formation of BT oligomers terminated with carboxyl groups at the ends.

[0067] In contrast, in the spectrum of the product, as also explained in the test of [2] above, a gentle peak (peak C) in the region of 3500 to 3100 cm －１ corresponding to the O-H stretching vibration appears specifically. From this, it is suggested that the ends of the BT oligomers constituting the product are alcohol ends. On the other hand, the peak (peak E) in the region of 2700 to 2500 cm －１ corresponding to the terminal carboxyl group characteristically observed in the alkali depolymerized oligomer is not seen in the spectrum of the product. That is, it can be said that the PBT oligomers constituting the product do not have carboxyl ends, at least at a level detectable by IR spectrum. From the above results, it is confirmed that in the product obtained from the second dissolution separation product through the depolymerization of PBT using 1,4-butanediol, which is a polyhydric alcohol, both ends of the BT oligomers are alcohol ends rather than carboxyl ends. This corresponds to the fact that the depolymerization of PBT proceeds by transesterification with 1,4-butanediol.

[0068] [4] Additives Contained in the Product In the test of [2] above, since the product obtained from the second dissolution separation product was colored light gray, it is suggested that additives are incorporated into the product in addition to the BT oligomers. Therefore, an attempt was made to identify those additives.

[0069] <Test Method> In the test described in [2] above, the gel-like substance obtained after heating and stirring in the second separation step was collected as a sample before mixing with pure water and filtration. The gel-like substance exhibits a darker black color than the final product obtained as a powder, contains higher concentrations of the additives that will be included in the final product, and is easier to identify than the final product. The collected gel-like substance was dissolved in hexafluoro-2-propanol (HFIP) and observed using a transmission light microscope. Observations were performed in multiple regions. In addition, as a reference sample, PBT was colored black by adding a carbon colorant, and similarly dissolved in HFIP and observed under a microscope.

[0070] <Test Results> Figures 7A and 7B show microscopic images of the HFIP solution of the gel-like substance obtained in the second separation step. Figures 7A and 7B show observations of different regions of the same sample. Figure 7C shows a microscopic image of the HFIP solution of carbon-doped PBT, which is the reference sample.

[0071] In Figure 7A, a rod-shaped substance extending horizontally is observed near the center of the image in the vertical direction. Such a rod-shaped, translucent image is characteristic of glass fibers, and it is highly likely that glass fibers are being observed here as well. In other words, the gel-like substance can be said to contain glass fibers.

[0072] Figure 7B, which shows an observation of a different region, reveals numerous tiny black dots. Comparing the observation image in Figure 7B with the observation image of carbon-doped PBT in Figure 7C, both images show scattered tiny black dots. Therefore, it is highly likely that the black dots observed in the gel-like substance of the sample in Figure 7B are due to the carbon coloring agent.

[0073] Based on the above observations, it is considered that the gel-like substance obtained in the second separation step contains glass fibers and carbon colorants. Furthermore, it is highly probable that the powdered product obtained by processing this gel-like substance also contains similar glass fibers and carbon colorants, albeit in smaller quantities than the gel-like substance. Glass fibers and carbon colorants are commonly added as additives to polymer materials that constitute wire harnesses.

[0074] [5] Identification of polymers separated in each step Up to this point, in the method for producing an oligomer composition according to the embodiments of this disclosure, it has been confirmed that the product obtained from the second dissolved separation product is an oligomer composition containing a small amount of glass fiber and carbon colorant in a BT oligomer having an alcohol terminus. Finally, it was confirmed what polymers are contained in the components separated in each step of the above production method, in addition to the second dissolved separation product.

[0075] <Test Method> In the test described in [2] above, the polymers contained in the substances separated at each step during the process of carrying out the method for producing oligomer materials according to the embodiment of this disclosure were identified. Specifically, in the first and second separation steps, after heating and stirring were completed, the dissolved and insoluble products were separated. In detail, the gel-like substance obtained in each separation step was added to an excess amount of pure water, stirred, and then filtered to obtain the first dissolved product and the second dissolved product, respectively, as filtrates. Furthermore, a solvent removal step by vacuum distillation was performed on each filtrate to remove 14BD. Then, powder samples were obtained by drying the obtained products. The powder material obtained from the first dissolved product was light brown, and the powder material obtained from the second dissolved product was light gray. The powder material obtained from the second dissolved product corresponds to the "product" analyzed in the tests described in [2] to [4] above. Furthermore, in the second separation step, the insoluble material remaining after filtration was recovered, washed with water, and dried to obtain the second insoluble material. The resulting second insoluble material contained three types of insoluble material with different morphologies. These were separated manually and labeled as insoluble material 1, insoluble material 2, and insoluble material 3.

[0076] IR measurements were performed on the powder materials obtained from the first and second dissolved and separated products, as well as on the insoluble products 1, 2, and 3 obtained from the second insoluble product. In addition, the same measurements were performed on individual PBT, PET, PVC, PP, and PA66 as reference samples. Furthermore, IR measurements were also performed on a one-step dissolved and separated product as another reference sample. Here, a one-step dissolved and separated product refers to a dissolved and separated product obtained by performing a separation process equivalent to the second separation process (heating at the second temperature in one step) on the raw material mixture without performing the first separation process. Measurements were performed on the powder material obtained by performing the same process as the first and second dissolved and separated products described above.

[0077] Furthermore, DSC measurements were performed on the powder materials obtained from the first and second dissolved and separated products described above. Specifically, 5 mg of each powder material obtained from the first and second dissolved and separated products was placed in an aluminum pan, heated in the range of 50 to 300°C, and DSC measurements were performed. The heating rate was set to 10°C / min. The endothermic peaks obtained from this DSC measurement correspond to the melting of the polymer. In addition, DSC measurements were similarly performed on the raw material mixture before treatment and the one-step dissolved and separated product described above as reference samples. From these DSC measurements, information regarding polymer mixing and the presence or absence of a low degree of polymerization can be obtained from the number and temperature of endothermic peaks.

[0078] <Test Results> Figure 8A shows the IR spectra for the first dissolved and separated product, the second dissolved and separated product, the one-step dissolved and separated product, and each of the reference samples. Figure 8B shows the IR spectra for insoluble products 1, 2, and 3, and each of the reference samples.

[0079] The spectrum of the first dissolved separation in Figure 8A is close to that of PA66 alone. 3300 cm⁻¹ －１ The peak of N-H stretching vibration in the vicinity (peak F), and 1650-1550 cm －１Characteristic peaks of PA are also observed, including two distinctive peaks (peak G) in the vicinity, referred to as amide I and amide II. From this, it is confirmed that PA is separated as a dissolved product in the first separation step. The spectrum of the second dissolved product is the same as that of test [2] shown in Figure 4, and as explained for test [2], comparison with the reference spectrum shows that PBT is separated as the second dissolved product. This PBT is a BT oligomer with alcohol terminus at both ends. In the one-step dissolved product, both the characteristic peaks of PA and the characteristic peaks of PBT appear, indicating that it is a mixture of PA and PBT.

[0080] Next, looking at the spectra of insoluble substances 1, 2, and 3 in Figure 8B, the spectrum of insoluble substance 1 is at 600 cm⁻¹. －１ The spectrum is similar to that of PVC alone, with a peak (peak H) of C-Cl stretching vibration visible in the vicinity. The spectrum of insoluble material 2 is at 1700 cm⁻¹. －１ Nearby are the peaks of C=O stretching of ester bonds (Peak A) and 1300 cm, which corresponds to the C-O stretching vibration. －１ The spectrum is similar to that of PET alone, with a sharp peak (peak D) visible in the vicinity. The spectrum of insoluble material 3 is from 3000 to 2800 cm⁻¹. －１ The peak of the C-H stretching vibration is strongly visible in the vicinity, at 1470 cm. －１ and 1380 cm －１ The spectrum is similar to that of PP alone, as evidenced by the presence of a C-H bending vibration peak (peak I). These results indicate that the second insoluble material contains polyolefins such as PVC, PET, and PP.

[0081] Finally, looking at the DSC curve shown in Figure 9, the first dissolved product yields only peaks of almost the same temperature and shape as the reference sample containing only PA66. In other words, the first dissolved product contains PA as a polymer alone and without undergoing depolymerization. The second dissolved product yields a single peak in a temperature range lower than that of PBT alone and PA66 alone. This indicates that PBT has a lower melting point in the second dissolved product, which is consistent with PBT becoming an oligomer through depolymerization.

[0082] When measurements were taken directly on the raw material mixture before processing, the results showed complex peaks, reflecting the fact that the raw material mixture is a mixture of various polymers. The one-stage dissolved and separated product also showed complex peaks, although less pronounced than those of the raw material mixture. A closer examination of the measurement results for the one-stage dissolved product revealed peaks similar to those found in the case of PA66 alone, and peaks similar to those found in the second-stage dissolved and separated product, i.e., peaks corresponding to BT oligomers. This indicates that in the one-stage dissolved product, PA and BT oligomers are mixed together without being separated.

[0083] Based on the combined results of IR and DSC measurements, it can be seen that the polymer components separated in each step of the method for producing the oligomer composition according to the embodiment of this disclosure are as follows: In the first separation step, PA that has not undergone depolymerization is separated as a dissolved product. In the second separation step, PBT is depolymerized and separated as a dissolved product, yielding a BT oligomer. The second insoluble product remaining after the second separation step includes polyolefins such as PVC, PET, and PP. Furthermore, if only a single separation step corresponding to the second separation step is performed without carrying out the first separation step, it is not possible to separate and recover PBT from PA. From this, it can be said that two separation steps are necessary to separate PBT from PA and other types of polymers and recover it.

[0084] Although embodiments of the present disclosure have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention.

Claims

It contains a butylene terephthalate oligomer terminated at both ends with 1,4-butanediol, An oligomer composition that does not contain polyamide, polyethylene terephthalate, or its decomposition products in amounts detectable by infrared absorption spectroscopy. 　 The oligomer composition according to claim 1, wherein the butylene terephthalate oligomer has a number average molecular weight of 1000 or less and a molecular weight polydispersity of 1.5 or less. 　 The oligomer composition according to claim 1 or claim 2, further comprising at least one of a colorant and glass fibers. 　 The oligomer composition according to claim 1 or claim 2, wherein the butylene terephthalate oligomer is obtained by depolymerizing polybutylene terephthalate with 1,4-butanediol. 　 For raw materials derived from wire harness waste containing polybutylene terephthalate, the material is heated in 1,4-butanediol at a temperature above the dissolution temperature of polyamide but below the dissolution temperature of polybutylene terephthalate, and the insoluble material is separated. The oligomer composition according to claim 4, wherein the insoluble substance is heated in 1,4-butanediol at a temperature above the temperature at which polybutylene terephthalate begins to dissolve and below the temperature at which polyethylene terephthalate begins to dissolve, and the solvent is removed from the dissolved and separated components. 　 A first separation step involves heating a raw material mixture containing a polyester containing polybutylene terephthalate and a polyamide in 1,4-butanediol at a first temperature above the temperature at which the polyamide begins to dissolve and below the temperature at which the polybutylene terephthalate begins to dissolve, thereby separating the insoluble material. The insoluble material obtained in the first separation step is heated in 1,4-butanediol at a second temperature above the temperature at which polybutylene terephthalate begins to dissolve and below the temperature at which polyethylene terephthalate begins to dissolve, and the dissolved and separated components are separated in a second separation step. A method for producing an oligomer composition, comprising: a solvent removal step, which involves removing the solvent from the dissolved and separated components obtained in the second separation step to obtain an oligomer composition containing a butylene terephthalate oligomer. 　 The method for producing the oligomer composition according to claim 6, wherein the raw material mixture further comprises polyethylene terephthalate as the polyester. 　 A method for producing the oligomer composition according to claim 6 or claim 7, wherein the raw material mixture is derived from wire harness waste. 　 The first temperature is 160°C or higher and less than 185°C. A method for producing an oligomer composition according to claim 6 or claim 7, wherein the second temperature is 185°C or higher and less than 205°C.

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