Method for producing recycled polybutylene terephthalate resin, method for separating polybutylene terephthalate resin from material for recycling, and method for recovering solution that includes at least polybutylene terephthalate

Abstract

Provided are a method for efficiently producing a recycled polybutylene terephthalate resin from a material for recycling that includes polybutylene terephthalate, a method for separating polybutylene terephthalate, and a method for recovering a solution that includes at least polybutylene terephthalate.　This method for producing a recycled polybutylene terephthalate resin from a material for recycling that includes polybutylene terephthalate and a polycarbonate includes step 1, which is a step for placing the material for recycling in a solvent (solvent S1) that has a set swelling rate with regard to polybutylene terephthalate, heating and stirring the result, and separating a solution A and insoluble matter B that includes at least the polybutylene terephthalate.

Description

Method for producing recycled polybutylene terephthalate resin, method for separating polybutylene terephthalate resin from recycling materials, and method for recovering solution containing at least polybutylene terephthalate

[0001] The present disclosure relates to a method for producing recycled polybutylene terephthalate resin, a method for separating polybutylene terephthalate resin from recycling materials, a method for separating polybutylene terephthalate resin, and a method for recovering a solution containing at least polybutylene terephthalate.

[0002] Polybutylene terephthalate (PBT) has excellent mechanical properties, heat resistance, and chemical resistance, and is widely used as an engineering plastic in the fields of electric and electronic, automotive, etc. Since PBT has a relatively low melting point (225°C), it is possible to impart various properties with various additives. Therefore, mechanical properties, flame retardancy, impact resistance, etc. are imparted with compounding agents such as inorganic fillers, flame retardants, and elastomers, or dimensional accuracy is improved by alloying with amorphous resins such as polycarbonate (PC) and styrene resins. On the other hand, from the perspective of recycling, various engineering plastics containing PBT are molded products of resin compositions containing various raw materials as described above, so it is difficult to separate each component. Also, even if various engineering plastics containing PBT are recovered from the market, pulverized, and pelletized, it is difficult to obtain stable physical properties similar to those of new products. At present, the recycling of various engineering plastics containing PBT is limited to thermal recycling, and the material recycling of PBT has not advanced. Patent Document 1 describes a method for recovering PBT by depolymerizing PBT resin and recovering raw materials butanediol and terephthalic acid. Patent Document 2 describes a method for separating PBT from a composite material containing PBT and AS (acrylonitrile styrene) resin, HIPS (high impact polystyrene) resin, etc. using a solvent such as cresol.

[0003] Japanese Patent Application Laid-Open No. 2023-111250 International Publication No. 2024 / 204775

[0004] While chemical recycling methods utilizing the depolymerization of PBT resin, such as those described in Patent Document 1, allow for the recovery of butanediol and terephthalic acid (raw materials) and polymerization from the raw material level, enabling the production of high-quality recycled PBT, the process is complex, requires significant energy for depolymerization and repolymerization, resulting in a large environmental burden and high costs. Furthermore, while the method described in Patent Document 2 is effective for separating PBT from AS resin and HIPS resin, when PBT and PC are mixed, their similar solubility properties in solvents make it difficult to separate and recover individual resins through processes involving dissolution in a solvent. Therefore, there is a need for a method to efficiently produce recycled polybutylene terephthalate resin from composite materials containing multiple resins, such as PBT / PC / ABS (acrylonitrile butadiene styrene) or PBT / PC / ABS / PS, and a method to efficiently separate and recover PBT.

[0005] The object of this disclosure is to provide a method for efficiently producing recycled polybutylene terephthalate resin from recycled materials containing polybutylene terephthalate, a method for separating polybutylene terephthalate resin, and a method for recovering a solution containing at least polybutylene terephthalate.

[0006] This disclosure includes the following aspects: A method for producing recycled polybutylene terephthalate resin from a recyclable material containing polybutylene terephthalate, comprising: Step 1: Adding the recyclable material to a solvent (solvent S1) in which the swelling rate of polybutylene terephthalate, as measured under the following condition 1, is greater than 5%, heating and stirring, and separating solution A from insoluble matter B containing at least the polybutylene terephthalate; <Condition 1> A polybutylene terephthalate film in the shape of 50 × 50 × 0.1 mm is immersed in solvent S1 at 70°C for 1 hour. The percentage increase in the mass of the film removed from solvent S1 after immersion relative to the mass of the film before immersion is calculated as [{(mass of film removed from solvent after immersion) / (mass of film before immersion)} × 100 - 100] (%). A manufacturing method comprising: Step 2: Adding the insoluble matter B to a solvent (solvent S2) capable of dissolving polybutylene terephthalate, heating and stirring, and separating the solution C containing at least the polybutylene terephthalate from the insoluble matter D; Step 3: Precipitating recycled polybutylene terephthalate resin by adding a poor solvent (solvent S3) for polybutylene terephthalate to the solution C, or by removing the solvent S2 from the solution C, and separating and recovering the recycled polybutylene terephthalate resin.

[0007] According to this disclosure, it is possible to provide a method for efficiently producing recycled polybutylene terephthalate resin from recycled materials containing polybutylene terephthalate, a method for separating polybutylene terephthalate resin, and a method for recovering a solution containing at least polybutylene terephthalate.

[0008] This is a flowchart illustrating the method for producing recycled polybutylene terephthalate resin according to this embodiment. This is a flowchart illustrating one embodiment of the method for producing recycled polybutylene terephthalate resin according to this embodiment.

[0009] One embodiment of the present disclosure will be described in detail below, but the scope of the present disclosure is not limited to the embodiment described herein, and various modifications can be made without departing from the spirit of the present disclosure. Each embodiment disclosed herein can be combined with any other features disclosed herein. If multiple upper and lower limits are given for a particular parameter, any combination of these upper and lower limits can be used to create a suitable numerical range. The lower and / or upper limits of the numerical ranges described herein may be replaced with numerical values ​​within that range, as shown in the examples. The expression "X to Y" indicating a numerical range means "X or greater and Y or less". If a particular description given for one embodiment also applies to other embodiments, that description may be omitted in the other embodiments.

[0010] <Method for producing recycled polybutylene terephthalate resin> The first embodiment of this disclosure relates to a method for producing recycled polybutylene terephthalate resin from a recycled material containing polybutylene terephthalate, and the manufacturing method includes steps 1 to 3 described below. The inventors have diligently conducted research and have found that the manufacturing method including steps 1 to 3 described below can efficiently separate polybutylene terephthalate from a recycled material containing polybutylene terephthalate, even if other resins such as polycarbonate are also present, thereby enabling the efficient production of recycled polybutylene terephthalate resin, and have completed this disclosure. Furthermore, the manufacturing method of the first embodiment not only enables the production of recycled polybutylene terephthalate resin, but also allows for the reuse of solvents used in each step, making it a superior method from the standpoint of environmental impact and cost. Furthermore, as mentioned above, especially when polycarbonate is included in various engineering plastics used as recycled materials, the similar solubility properties of PBT and PC in solvents make it difficult to separate and recover PBT through processes involving dissolution in a solvent. Confirming whether each recycled material contains PC requires enormous effort and cost. The method disclosed herein enables the efficient production of recycled polybutylene terephthalate resin even if the recycled material contains PC, and is a more cost-effective method. In this specification, "recycled polybutylene terephthalate resin" means polybutylene terephthalate resin separated and recovered from the above-mentioned "recycled materials" by material recycling, and not derived from virgin raw materials. The fact that the separated and recovered resin is polybutylene terephthalate resin can be confirmed, for example, by molecular structure analysis using NMR spectroscopy.

[0011] <Recyclable Materials> In this specification, "recyclable materials" means various articles containing a resin that includes at least polybutylene terephthalate, and includes not only post-consumer materials such as various molded articles, films, and pellets, but also pre-consumer materials such as defective products generated during the manufacturing process of various molded articles, and parts other than the product obtained during injection molding (e.g., runners, sprues, etc.). The polybutylene terephthalate in the recyclable materials may be in the form of a polymer alloy with other polymers, or in the form of a polymer blend. The content of polybutylene terephthalate in the recyclable materials is not particularly limited, but it is preferably 10 to 100% by mass in total, more preferably 30 to 90% by mass, even more preferably 50 to 80% by mass, and even more preferably 60 to 80% by mass in total (100% by mass) of the recyclable materials. The proportions of polybutylene terephthalate and other polymers in a resin containing at least polybutylene terephthalate and other polymers in a recycled material are not particularly limited. For example, with respect to 100 parts by mass of polybutylene terephthalate, the other polymer may be in the range of 10 to 500 parts by mass, 10 to 300 parts by mass, 20 to 200 parts by mass, or 20 to 120 parts by mass. Alternatively, with respect to 100 parts by mass of other polymer, polybutylene terephthalate may be in the range of 10 to 500 parts by mass, 10 to 300 parts by mass, 50 to 200 parts by mass, or 80 to 120 parts by mass.

[0012] (Polybutylene terephthalate) Polybutylene terephthalate (PBT) is at least terephthalic acid or its ester-forming derivative (C １－６This is a type of synthetic resin polyester obtained by polycondensation of a dicarboxylic acid component containing alkyl esters or acid halides (such as 1,4-butanediol) having at least four carbon atoms or an ester-forming derivative thereof (such as an acetylated compound). In one embodiment, the polybutylene terephthalate is not limited to homopolybutylene terephthalate, but may be a copolymer containing 60 mol% or more of butylene terephthalate units. In one embodiment, the intrinsic viscosity (IV) of the polybutylene terephthalate is preferably 0.60 dL / g or more and 1.2 dL / g or less, and more preferably 0.65 dL / g or more and 0.9 dL / g or less.

[0013] (Other components besides polybutylene terephthalate) Other components other than polybutylene terephthalate contained in the recycled material are impurities removed in any step of the manufacturing method of recycled polybutylene terephthalate described herein. Other components other than polybutylene terephthalate include, for example, additives, inorganic fillers, and resins other than polybutylene terephthalate and polycarbonate. Additives include compounds used as colorants, antistatic agents, flame retardants, surfactants, antioxidants, and lightfastness agents. Inorganic fillers include glass fibers, carbon fibers, glass beads, mica, talc, calcium carbonate, titanium dioxide, and carbon black, which are added to improve strength, thermal conductivity, coefficient of thermal expansion, and electrical properties, and to prevent warping of molded products. Resins other than polybutylene terephthalate and polycarbonate include ABS resin, AS resin, polystyrene resin (PS), polyphenylene oxide (PPO), and polycarbonate (PC). The content of components other than polybutylene terephthalate is not particularly limited, but may be 1 to 90% by mass, 2 to 80% by mass, 5 to 60% by mass, 5 to 50% by mass, or 10 to 40% by mass, relative to the total amount (100% by mass) of the recycled material.

[0014] (Polycarbonate) In one embodiment, the recycled material preferably further contains polycarbonate. By further containing polycarbonate in the recycled material, it is possible to produce not only recycled polybutylene terephthalate resin but also recycled polycarbonate resin, as described below.

[0015] Polycarbonate (PC) is a polymer in which dihydroxy compound residues are linked by carbonate ester bonds, and is obtained by the reaction of a dihydroxy compound with a carbonate ester such as phosgene or diphenyl carbonate.

[0016] In one embodiment, the content of polybutylene terephthalate and polycarbonate in the recycled material is not particularly limited, but it is preferably 10 to 100% by mass in total, more preferably 30 to 90% by mass, even more preferably 50 to 80% by mass, and still more preferably 60 to 80% by mass, based on the total amount (100% by mass) of the recycled material. The proportions of polybutylene terephthalate and polycarbonate in the resin containing at least polybutylene terephthalate and polycarbonate in the recycled material are not particularly limited, but the amount of polycarbonate may be 10 to 500 parts by mass, 10 to 300 parts by mass, 250 to 200 parts by mass, or 280 to 120 parts by mass per 100 parts by mass of polybutylene terephthalate, or the amount of polybutylene terephthalate may be 10 to 500 parts by mass, 10 to 300 parts by mass, 50 to 200 parts by mass, or 80 to 120 parts by mass per 100 parts by mass of polycarbonate.

[0017] The recycled material may be used in its post-consumer or pre-consumer form, but it is preferable that the recycled material has a large surface area from the viewpoint of improving the contact between the solvent S1 and the recycled material and improving the separation between solution A and insoluble matter B.

[0018] In one embodiment, it is preferable to prepare a recyclable material having a shape that can pass through a sieve with a nominal mesh size of 20 mm prior to step 1. Methods for preparing a recyclable material having a shape that can pass through a sieve with a nominal mesh size of 20 mm include dividing it into appropriate sizes by cutting, crushing, or pulverizing. The division method such as cutting, crushing, or pulverizing is not particularly limited, and can be used for cutting using a cutting tool; cutting with gas, plasma, laser, etc.; cleaving; shredding using a shredder; coarse crushing to 20 cm or less using a jaw crusher or rotary crusher; medium crushing to 1 cm or less using a rotary crusher, cone crusher, or mill; and pulverizing to 1 mm or less using a mill. These methods may be performed individually or in combination.

[0019] <Step 1> Step 1 is a process in which the regeneration material is placed in a solvent (solvent S1) in which the swelling rate of polybutylene terephthalate, as measured under the following condition 1, is greater than 5%, and the mixture is heated and stirred to separate solution A, which contains at least polycarbonate, from insoluble matter B, which contains at least polybutylene terephthalate. <Condition 1> A polybutylene terephthalate film with dimensions of 50 × 50 × 0.1 mm is immersed in solvent S1 at 70°C for 1 hour. The percentage increase in the mass of the film removed from solvent S1 after immersion, relative to the mass of the film before immersion, is calculated as [{(mass of film removed from solvent after immersion) / (mass of film before immersion)} × 100 - 100] (%).

[0020] (Solvent S1) By adding the regenerating material to a solvent (solvent S1) with a swelling rate greater than 5% as measured under condition 1, and then heating and stirring, the polybutylene terephthalate contained in the regenerating material is swelled without dissolving, thereby separating solution A from insoluble matter B which contains at least polybutylene terephthalate. Therefore, it is preferable that solvent S1 is a solvent that swells the polybutylene terephthalate to a swelling rate exceeding 5% without dissolving it, and that can dissolve other resins. When polybutylene terephthalate is added to solvent S1, it swells to a swelling rate exceeding 5%, so solvent S1 easily penetrates into the internal region of the regenerating material. As a result, not only other resins on the surface of the regenerating material but also other resins in the internal region of the regenerating material can be efficiently dissolved. As a result, solution A and insoluble matter B which contains at least polybutylene terephthalate can be efficiently separated.

[0021] Furthermore, once polybutylene terephthalate dissolves, the degree of swelling cannot be measured. Therefore, the upper limit of the degree of swelling is limited to the range in which the degree of swelling can be measured. In one embodiment, from the viewpoint of the separation of solution A and insoluble matter B, the above swelling rate is preferably greater than 7%, more preferably greater than 10%, even more preferably greater than 15%, even more preferably greater than 20%, and particularly preferably greater than 25%.

[0022] In one embodiment, the degree of swelling is preferably more than 5% to 200%, more preferably 6% to 150%, even more preferably 7% to 100%, and particularly preferably 10% to 30%, from the viewpoint of the ease of separation between solution A and insoluble matter B, and from the viewpoint of the boiling point not being too high and the solvent being easily removed thereafter.

[0023] The following solvents (solvent S1) have a swelling rate greater than 5% as measured under condition 1: One or more aromatic solvents selected from benzene, o-xylene, prenitene, thioanisole, 1-methylnaphthalene, tetralin, naphthalene, anisole, diphenylmate, dibenzyl ether, and 1,3-dimethoxybenzene; One or more amide / cyano compounds selected from N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylpropionamide, N-methylpyrrolidone, 1-ethyl-2-pyrrolidone, 1-cyclohexyl-2-pyrrolidone, hexanenitrile, valeronitrile, undecanenitrile, phenylacetonitrile, pyrrolidine-1-carbonitrile, and N,N-dimethylcyanamide; One or more cyclic nitrogen-containing compounds selected from pyridine, 2-cyanopyridine, 2-picoline, 2,6-lutidine, 3,4-lutidine, 2,4,6-collidine, quinoline, pyrimidine, morpholine, piperidine, pyrrolidine, 1-methylimidazole, and 1,4-dimethylpiperazine; one or more ether solvents selected from 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, 2-methoxy-1,3-dioxolane, bis(2-methoxyethyl) ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and cyclopentyl methyl ether; one or more ester solvents selected from methyl acetate, ethyl acetate, n-propyl acetate, butyl acetate, n-propyl formate, methyl valerate, methyl caproate, methyl caprylate, methyl caprate, methyl methacrylate, dimethyl phthalate, di-n-butyl phthalate, diethyl carbonate, and dimethyl sulfite; One or more ketone / aldehyde solvents selected from cyclohexanone, cyclopentanone, 2-methylcyclohexanone, 4-methylcyclohexanone, 2,6-dimethylcyclohexanone, 2-propylcyclohexanone, 2-hexanone, 2-heptanone, 4-heptanone, 2-octanone, acetophenone, methyl ethyl ketone, and nonanal;A solvent comprising one or more selected from the following is preferable: one or more oxygen-containing compounds selected from γ-butyrolactone, γ-valerolactone, acetic anhydride, ethylene glycol monobutyl ether acetate, propylene glycol methyl ether acetate, 2,5-dimethyl isosorbide, and dihydrolevoglucocenone; and one or more carbonate-based solvents selected from dimethyl carbonate, diethyl carbonate, and propylene carbonate.

[0024] Solvent S1 may be of one type or of two or more types. Solvent S1 may contain a small amount of solvent other than solvent S1, in a range where the swelling rate measured under condition 1 is greater than 5%, but the content of the other solvent is preferably more than 0% by mass and 10% by mass or less, more preferably more than 0% by mass and 5% by mass or less, and particularly preferably more than 0% by mass and 0.5% by mass or less, relative to the total amount of solvent S1 (100% by mass).

[0025] In one embodiment, from the viewpoint of high swelling rate measured under condition 1 with respect to polybutylene terephthalate and good separation of solution A and insoluble matter B, it is preferable that solvent S1 contains one or more solvents selected from 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, N-methylpyrrolidone, 1-methylnaphthalene, cyclohexanone, cyclopentanone, 2-methylcyclohexanone, and toluene. In one embodiment, it is preferable that solvent S1 contains one or more solvents selected from 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, cyclohexanone, and cyclopentanone, as it has a low boiling point and makes solvent removal in subsequent processes easier, and it is more preferable that solvent S1 contains 1,3-dioxolane. In one embodiment, the total amount of one or more solvents selected from 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, cyclohexanone, and cyclopentanone in solvent S1 is preferably 60% by mass or more and 100% by mass or less, more preferably 75% by mass or more and 100% by mass or less, even more preferably 90% by mass or more and 100% by mass or less, and particularly preferably 95% by mass or more and 100% by mass or less.

[0026] (Separation Processing Conditions) In step 1, the mass ratio of solvent S1 to the regenerating material to be added to solvent S1 is preferably 1% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 40% by mass or less, even more preferably 1% by mass or more and 30% by mass or less, and particularly preferably 1% by mass or more and 25% by mass or less, based on the total amount of the solution containing the regenerating material.

[0027] In one embodiment, in step 1, the heating temperature is preferably 60°C to 150°C, more preferably 60°C to 120°C, even more preferably 60°C to 100°C, and particularly preferably 60°C to 90°C. A heating temperature within this range results in superior separation between solution A and insoluble matter B.

[0028] In one embodiment, in step 1, the stirring time is preferably 30 minutes to 3 hours, more preferably 30 minutes to 2 hours, even more preferably 45 minutes to 2 hours, and particularly preferably 45 minutes to 1.5 hours. By having the stirring time within the above range, solution A and insoluble matter B can be sufficiently separated in a short time.

[0029] The separation of solution A and insoluble matter B is preferably carried out by filtration. Filtration can be performed using any of the following: filter paper, centrifugal filtration, cyclone filtration, glass filters, bag filters, candle filters, etc., and multiple stages and methods of filtration may be used.

[0030] <Step 2> Step 2 is a process in which insoluble matter B is added to a solvent (solvent S2) capable of dissolving polybutylene terephthalate, heated and stirred, and the solution C containing at least polybutylene terephthalate is separated from the insoluble matter D. A solvent capable of dissolving polybutylene terephthalate means that when polybutylene terephthalate is added to solvent S2 and heated and stirred, no solid material can be visually observed in solvent S2.

[0031] (Solvent S2) In one embodiment, solvent S2 preferably contains a phenolic solvent and / or a halogenated solvent, and more preferably contains a phenolic solvent. Examples of phenolic solvents include phenol, cresol, xylenol, ethylphenol, propylphenol, butylphenol, methoxyphenol, ethoxyphenol, propoxyphenol, butoxyphenol, benzylphenol, phenylphenol, chlorophenol, dichlorophenol, chloromethylphenol, catechol, thymol, carvacrol, etc. One of these solvents may be used, or two or more may be used. The ratio of phenolic solvents in solvent S2 should be such that polybutylene terephthalate can be dissolved, and it is preferable that solvent S2 contains a total of 30% by mass or more and 100% by mass or less, more preferably 35% by mass or more and 100% by mass or less, and even more preferably 40% by mass or more and 100% by mass or less. Examples of halogenated solvents include trifluoromethanesulfonic acid, tetrachloroethane, trifluoroacetic acid, hexafluoroisopropanol, chloroform, and dichloromethane. These solvents may be used individually or in combination of two or more. The ratio of halogenated solvents in solvent S2 should be such that it is possible to dissolve polybutylene terephthalate. Preferably, solvent S2 contains a total of 30% by mass or more of these solvents, more preferably 35% by mass or more, and even more preferably 40% by mass or more. In one embodiment, from the viewpoint of superior solubility of polybutylene terephthalate, solvent S2 preferably contains one or more solvents selected from 1,1,1,3,3,3-hexafluoro-2-propanol, tetrachloroethane, 3,5-bis(trifluoromethyl)phenol, m-cresol, and phenol, and more preferably m-cresol.

[0032] In step 2, the mass ratio of solvent S2 to insoluble material B added to solvent S2 is preferably 1 to 40% by mass, more preferably 1 to 30% by mass, even more preferably 3 to 30% by mass, and particularly preferably 5 to 30% by mass, relative to the total amount of solution containing insoluble material B, from the viewpoint of the solubility of insoluble material B and the yield of recycled polybutylene terephthalate resin.

[0033] In one embodiment, in step 2, the heating temperature is preferably 60°C to 150°C, more preferably 60°C to 120°C, even more preferably 60°C to 100°C, and particularly preferably 60°C to 90°C. A heating temperature within this range results in superior separation between solution C and insoluble matter D.

[0034] In one embodiment, in step 2, the stirring time is preferably 30 minutes to 3 hours, more preferably 30 minutes to 2 hours, even more preferably 45 minutes to 2 hours, and particularly preferably 45 minutes to 1.5 hours. By having the stirring time within the above range, the solution C and the insoluble matter D can be sufficiently separated in a short time.

[0035] The separation of solution C and insoluble matter D is preferably carried out by filtration. Filtration can be performed using any of the following: filter paper, centrifugal filtration, cyclonic filtration, glass filters, bag filters, candle filters, etc., and multiple stages and methods of filtration may be used.

[0036] <Step 3> Step 3 is a process of precipitating recycled polybutylene terephthalate resin by (1) adding a poor solvent (solvent S3) for polybutylene terephthalate to solution C, or (2) removing solvent S2 from solution C, and then separating and recovering the recycled polybutylene terephthalate resin.

[0037] (1) Adding solvent S3) The poor solvent (solvent S3) for polybutylene terephthalate is not particularly limited as long as it can precipitate recycled polybutylene terephthalate resin when added to solution C, but it is preferable that the solvent contains one or more selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, ketone solvents, aldehyde solvents, alcohol solvents, ester solvents, ether solvents, and water. For example, aromatic hydrocarbon solvents such as benzene, toluene, and ethylbenzene; aliphatic hydrocarbon solvents such as hexane, heptane, octane, hexene, heptene, octene, cyclopentane, cyclohexane, cycloheptane, cyclohexene, and cycloheptene; ketone solvents such as acetone, methyl ethyl ketone, pentanone, hexanone, diethyl ketone, diisopropyl ketone, methyl isobutyl ketone, 3-penten-2-one, cyclopropanone, cyclobutanone, and dimethylacetophenone; aldehyde solvents such as propionaldehyde, butyraldehyde, pentanal, hexanal, vinylaldehyde, glyoxal, isobutyraldehyde, and succinaldehyde; and methanol. Examples of solvents include alcoholic solvents such as ethanol, propanol, isopropanol, isobutyl alcohol, and tert-butyl alcohol; esteric solvents such as methyl acetate, ethyl acetate, n-propyl acetate, butyl acetate, n-propyl formate, methyl valerate, methyl caproate, methyl caprylate, methyl caprate, methyl methacrylate, dimethyl phthalate, di-n-butyl phthalate, diethyl carbonate, and dimethyl sulfite; etheric solvents such as diethyl ether, 1,4-dioxane, tetrahydrofuran, isopropyl methyl ether, methyl propyl ether, furan, cyclopentyl methyl ether, ethyl isopropyl ether, and tert-butyl propyl ether; and water. These solvents may be used individually or in combination of two or more. In particular, it is preferable to use one or more solvents selected from the group consisting of acetone, toluene, methanol, ethanol, isopropyl alcohol, and water for solvent S3.Furthermore, if the recycled material contains styrene-based resins such as ABS, PS, and AS, the yield can be increased by using acetone, toluene, ethyl acetate, n-propyl acetate, butyl acetate, diisopropyl ketone, and methyl ethyl ketone. When adding a poor solvent (solvent S3) for polybutylene terephthalate to solution C, it is preferable to add solvent S3 to solution C until the precipitation of recycled polybutylene terephthalate resin no longer increases.

[0038] (2) Removal of solvent S2 When removing solvent S2 from solution C to precipitate recycled polybutylene terephthalate resin, the removal method is not limited. For example, it can be done by distillation using an evaporator. Also, if the molecular weight of the recycled polybutylene terephthalate resin is below a certain level, a method of removing solvent S2 by heating can be used, in which case the solid-phase polymerization process can be carried out directly after solvent removal. When removing solvent S2 from solution C, it is preferable to remove solvent S2 until the precipitation of recycled polybutylene terephthalate resin no longer increases.

[0039] The specific temperature during the precipitation operation of recycled polybutylene terephthalate resin is preferably 0°C to 80°C, more preferably 5°C to 60°C, and even more preferably 10°C to 50°C. When removing the solvent by heating, the temperature is preferably above the boiling point of the solvent S2, and in the subsequent solid-phase polymerization step, it is preferable to treat at 150°C to 230°C.

[0040] (Step 4) In one embodiment, the method for producing recycled polybutylene terephthalate resin of this embodiment is preferably further comprising the following Step 4, where the recycled material further contains polycarbonate. Step 4: A step of precipitating recycled polycarbonate resin by adding a poor solvent (S) of polycarbonate resin to solution A, or by removing solvent S1 from solution A, and then separating and recovering the recycled polycarbonate resin. By further comprising the recycled material further containing polycarbonate and Step 4, it is possible to produce not only recycled polybutylene terephthalate resin but also recycled polycarbonate resin from the recycled material. In this specification, "recycled polycarbonate resin" means polycarbonate resin separated and recovered from the above-mentioned "recycled material". The fact that the separated and recovered resin is polycarbonate resin can be confirmed, for example, by molecular structure analysis using NMR spectroscopy.

[0041] When adding a poor solvent (solvent S) for polycarbonate to solution A, it is preferable to add solvent S to solution A until the precipitation of recycled polycarbonate resin no longer increases. Furthermore, when removing solvent S1 from solution A, the removal method is not limited. For example, it can be done by distillation using an evaporator. Also, if the molecular weight of the recycled polycarbonate resin is below a certain level, a method of removing solvent S1 by heating can be used, in which case the process can proceed directly to the solid-phase polymerization step after solvent removal. Continuous processing from solvent removal by heating to solid-phase polymerization is preferable in that the process can be advanced efficiently. When removing solvent S1 from solution A, it is preferable to remove solvent S1 until the precipitation of recycled polycarbonate resin no longer increases. When performing solvent removal by heating, the temperature is preferably above the boiling point of solvent S1, and in the subsequent solid-phase polymerization step, it is preferable to process at 180°C to 250°C.

[0042] (Solvent S) In one embodiment, the solvent S preferably contains one or more solvents selected from diethyl ether, ethylbenzene, methyl methacrylate, propyl acetate, and acetone. When the recycling material contains styrenic resins such as PS and ABS in addition to PC, by containing one or more solvents selected from these, only PC can be precipitated from the solution A containing the styrenic resin, and PC and the styrenic resin can be separated and recovered, enabling the more efficient production of recycled polycarbonate resin.

[0043] (Step 5) In one embodiment, when the recycling material further contains an inorganic filler, the method for producing the recycled polybutylene terephthalate resin of this embodiment preferably further includes the following Step 5. Step 5: A step of recovering the inorganic filler from the insoluble matter D By further including Step 5, the inorganic filler can be recovered from the recycling material, and the recovered inorganic filler can be reused. The content of the inorganic filler is not particularly limited, and examples are those described in the section on the above recycling material. The content of the inorganic filler is preferably 1 to 90% by mass, more preferably 2 to 80% by mass, still more preferably 5 to 60% by mass, and even more preferably 10 to 40% in the total amount (100% by mass) of the recycling material. In one embodiment, the inorganic filler preferably contains glass fibers. The recovered inorganic filler containing glass fibers can be reused.

[0044] (Reuse of Solvent) Each solvent used in each step may be separated from impurities by distillation, recovered, and reused. For example, since the liquid separated from recycled PBT by separation in Step 3 contains Solvent S3 and Solvent S2, they can be recovered by distillation respectively and reused in Step 2 or Step 3.

[0045] (Uses of Solution A and Solution C) Solutions A and C obtained in steps 1 and 2 of this disclosure can be used not only in the manufacture of recycled polymer resins, but also effectively utilized in various fields as solutions containing each resin. For example, solution A obtained from PC-containing recycled materials can be used as a binder for coating paints and adhesives with excellent heat resistance and transparency. Furthermore, by adding additives such as UV absorbers, dispersants, and lubricants to solutions A and C as needed, the functionality can be further improved according to each application. The concentration of recycled polycarbonate resin and recycled polybutylene terephthalate resin is about 10 to 30% by mass of the total mass of the paint (100% by mass) for paint applications, and about 20 to 40% by mass of the total mass of the binder for binder applications. In addition to solvents S1 and S2, solvents can be added as needed, and if there is an excess of solvent, the concentration can be adjusted using an evaporator or the like. The main applications are listed below. [Uses of Solution A] Solution A can be utilized in the following applications, taking advantage of the properties of the separated resin. In particular, solution A obtained from recycled materials containing polycarbonate can be used as a binder for conductive pastes or as an optical material, taking advantage of its unique solvent solubility and transparency. • Binder for conductive pastes: Solution A can be used as a binder for pastes containing conductive materials in the manufacture of electronic substrates and sensors. • Optical material: Polycarbonate has high transparency, so it can be used as an optical film or lens coating material. Furthermore, durability can be improved by adding an ultraviolet absorber to the solution. • Binder for batteries: Solution A can be used as a binder for bonding electrode materials in lithium-ion batteries due to the heat resistance and electrolyte resistance of polycarbonate. [Applications of Solution C] Solution C containing polybutylene terephthalate can be used in the following applications: • Coating material: Polybutylene terephthalate has high heat resistance and chemical resistance, and can be used as an electronic device, industrial paint, or corrosion-resistant coating material. • Adhesive binder: It can be used as a binder material for bonding dissimilar materials such as metals, resins, and ceramics in high-temperature environments.・ It can be used as a binder for paints as an insulating material for electronic components and circuit boards.

[0046] The second embodiment of the present disclosure relates to a method for separating polybutylene terephthalate resin from a recycled material containing polybutylene terephthalate, the method including the above-described steps 1 to 3. By the method including the above-described steps 1 to 3, the polybutylene terephthalate resin can be separated from the recycled material containing polybutylene terephthalate with a high yield and high purity, that is, efficiently. In one embodiment, the recycled material may further contain polycarbonate and may further include the above-described step 4 and may further include the above-described step 5.

[0047] The third embodiment of the present disclosure relates to a method for recovering a solution (solution C) containing at least polybutylene terephthalate from a recycled material containing polybutylene terephthalate, the method including the above-described steps 1 and 2. By the method including the above-described steps 1 and 2, the solution (solution C) containing at least polybutylene terephthalate can be recovered from the recycled material containing polybutylene terephthalate with a high yield and high purity, that is, efficiently. When the method of the third embodiment further includes step 3, it becomes a method for separating polybutylene terephthalate resin from a recycled material containing the method for producing recycled polybutylene terephthalate resin of the first embodiment and polybutylene terephthalate of the second embodiment. However, step 3 is not essential for the purpose of recovering the solution (solution C) containing at least polybutylene terephthalate that can be used for various applications as described above.

[0048] A non-limiting list of exemplary embodiments and combinations of exemplary embodiments of the present disclosure is disclosed below. [1] A method for producing recycled polybutylene terephthalate resin from a recyclable material containing polybutylene terephthalate, comprising: Step 1: Adding the recyclable material to a solvent (solvent S1) having a swelling rate of more than 5% for polybutylene terephthalate as measured under the following condition 1, heating and stirring to separate solution A from insoluble matter B containing at least the polybutylene terephthalate; <Condition 1> A film of polybutylene terephthalate in the shape of 50 × 50 × 0.1 mm is immersed in solvent S1 at 70°C for 1 hour. The percentage increase in the mass of the film removed from solvent S1 after immersion relative to the mass of the film before immersion is calculated as [{(mass of film removed from solvent after immersion) / (mass of film before immersion)} × 100 - 100] (%). A manufacturing method comprising: Step 2: Adding the insoluble matter B to a solvent (solvent S2) capable of dissolving polybutylene terephthalate, heating and stirring to separate the solution C containing at least the polybutylene terephthalate from the insoluble matter D; Step 3: Precipitating recycled polybutylene terephthalate resin by adding a poor solvent (solvent S3) for polybutylene terephthalate to the solution C, or by removing the solvent S2 from the solution C, and separating and recovering the recycled polybutylene terephthalate resin; [2] The manufacturing method according to [1], wherein the solvent S1 comprises one or more solvents selected from 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, N-methylpyrrolidone, 1-methylnaphthalene, cyclohexanone, cyclopentanone, 2-methylcyclohexanone, and toluene. [3] The manufacturing method according to [1] or [2], wherein the solvent S1 comprises one or more solvents selected from 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, cyclohexanone, and cyclopentanone. [4] The manufacturing method according to any one of [1] to [3], wherein in step 1, the heating temperature is 60°C or higher and 150°C or lower. [5] The manufacturing method according to any one of [1] to [4], wherein in step 1, the stirring time is 30 minutes or higher and 3 hours or lower.[6] The manufacturing method according to any one of [1] to [5], wherein the swelling rate of the solvent S1 is greater than 10%. [7] The manufacturing method according to any one of [1] to [6], wherein the solvent S2 comprises a phenolic solvent and / or a halogenated solvent. [8] The manufacturing method according to any one of [1] to [7], wherein the solvent S2 comprises one or more solvents selected from 1,1,1,3,3,3-hexafluoro-2-propanol, tetrachloroethane, 3,5-bis(trifluoromethyl)phenol, m-cresol, and phenol. [9] The manufacturing method according to any one of [1] to [8], wherein in step 2, the heating temperature is 60°C or more and 150°C or less.

[10] The manufacturing method according to any one of [1] to [9], wherein in step 2, the stirring time is 30 minutes or more and 3 hours or less.

[11] The manufacturing method according to any one of [1] to

[10] , comprising preparing the regenerative material having a shape that can pass through a sieve with a nominal mesh opening of 20 mm prior to step 1.

[12] The manufacturing method according to any one of [1] to

[11] , wherein the recycled material further comprises polycarbonate, and further comprises step 4: adding a poor solvent (S) of polycarbonate resin to the solution A, or removing the solvent S1 from the solution A to precipitate recycled polycarbonate resin, and separating and recovering the recycled polycarbonate resin.

[13] The manufacturing method according to any one of [1] to

[12] , wherein the recycled material further comprises an inorganic filler, and further comprises step 5: recovering the inorganic filler from the insoluble matter D.

[14] The manufacturing method according to

[13] , wherein the inorganic filler comprises glass fiber.

[15] A method for separating polybutylene terephthalate resin from a recyclable material containing polybutylene terephthalate, comprising: Step 1: A step of separating solution A and insoluble matter B containing at least the polybutylene terephthalate by placing the recyclable material in a solvent (solvent S1) in which the swelling rate of polybutylene terephthalate measured under the following condition 1 is greater than 5%, heating and stirring; <Condition 1> A film of polybutylene terephthalate in the shape of 50 × 50 × 0.1 mm is immersed in solvent S1 at 70°C for 1 hour.A method comprising: Step 1: Calculate the percentage increase in the mass of the film removed from solvent S1 after immersion relative to the mass of the film before immersion [{(mass of film removed from solvent after immersion) / (mass of film before immersion)} × 100 - 100] (%). Step 2: Add the insoluble matter B to a solvent (solvent S2) capable of dissolving polybutylene terephthalate, heat and stir, and separate the solution C containing at least the polybutylene terephthalate from the insoluble matter D; Step 3: Precipitate the polybutylene terephthalate resin by adding a poor solvent (solvent S3) for polybutylene terephthalate to the solution C, or by removing the solvent S2 from the solution C, and separate the polybutylene terephthalate resin.

[16] A method for recovering a solution (solution C) containing at least polybutylene terephthalate from a recyclable material containing polybutylene terephthalate, comprising: Step 1: Adding the recyclable material to a solvent (solvent S1) in which the swelling rate of polybutylene terephthalate measured under the following condition 1 is greater than 5%, heating and stirring to separate solution A and insoluble matter B containing at least the polybutylene terephthalate; <Condition 1> A polybutylene terephthalate film in the shape of 50 × 50 × 0.1 mm is immersed in solvent S1 at 70°C for 1 hour. The percentage increase in the mass of the film removed from solvent S1 after immersion relative to the mass of the film before immersion is calculated as [{(mass of film removed from solvent after immersion) / (mass of film before immersion)} × 100 - 100] (%). A method comprising the steps of: step 2: adding the insoluble matter B to a solvent (solvent S2) capable of dissolving polybutylene terephthalate, heating and stirring, and separating the solution C containing at least the polybutylene terephthalate from the insoluble matter D; and steps 2 and 3. the insoluble matter B, in a solvent (solvent S2) capable of dissolving polybutylene terephthalate, in a solvent (solvent S2),

[0049] The present disclosure will be further illustrated by the following examples, but these examples will not limit the interpretation of the present disclosure.

[0050] (Preparation of Recycled Material) The following materials were mixed in the mass ratios shown below, and then extruded using a twin-screw compounding extruder (manufactured by Japan Steel Works Ltd., "TEX-30") at a cylinder temperature of 260°C, a discharge rate of 15 kg / h, and a screw rotation speed of 130 rpm to obtain resin composition pellets (pellet length: approximately 5 mm) (hereinafter referred to as "recycled material"). • Polybutylene terephthalate resin (manufactured by Polyplastics Co., Ltd., intrinsic viscosity IV: 0.70 dl / g): 100 parts by mass • Polycarbonate resin (manufactured by Teijin Limited, "Panlite L-1225"): 75 parts by mass • Glass fiber (manufactured by Nippon Electric Glass Co., Ltd., "ECS03T-187"): 75 parts by mass

[0051] (Example 1) The regenerative material was processed according to the following procedure. (1) In a 500 mL flask, 1,3-dioxolane (solvent S1) and the regenerative material were added so that the regenerative material amounted to 10% by mass. The mixture was heated to 70°C and stirred for 1 hour while maintaining the temperature at 70°C. It was visually confirmed that a portion of the regenerative material had dissolved. (2) (1) was separated into solution A and insoluble matter B using a vacuum filtration apparatus (manufactured by Shibata Chemical Co., Ltd.). (3) Insoluble matter B was vacuum dried at 100°C and then weighed. (4) When methanol (solvent S) was added to solution A, it was visually confirmed that insoluble matter was produced by reprecipitation. The insoluble matter was recovered by filtration, vacuum dried at 100°C and then weighed. The insoluble material was measured using 1H NMR (BRUKER, "AVANCE III 400 with CryoProbe") and it was confirmed that the insoluble material was polycarbonate resin (i.e., recycled polycarbonate resin). (5) In a 500 mL flask, phenol (solvent S2) and insoluble material B were added so that insoluble material B was 5% by weight, and the mixture was heated to 70°C and stirred for 1 hour while maintaining the temperature at 70°C. It was visually confirmed that a portion of insoluble material B had dissolved. (6) Solution C and insoluble material D were separated from (5) using a vacuum filtration apparatus (Shibata Chemical Co., Ltd.). (7) Insoluble material D was vacuum dried at 100°C and then weighed. (8) When methanol (solvent S3) was added to solution C, it was visually confirmed that insoluble material was formed by reprecipitation. The insoluble material was recovered by filtration, vacuum dried at 100°C, and then weighed. The insoluble material was measured using 1H NMR (BRUKER, "AVANCE III 400 with CryoProbe"), and it was confirmed that the insoluble material was polybutylene terephthalate resin (i.e., recycled polybutylene terephthalate resin). (9) The insoluble material D was vacuum dried at 100°C and weighed. Examination of the insoluble material D with an optical microscope revealed that it was glass fiber.

[0052] (Comparative Example 1) The regenerative material was processed according to the following procedure. (1) In a 500 mL flask, phenol and the regenerative material were added so that the regenerative material amounted to 10% by mass, and the mixture was heated to 70°C and stirred for 1 hour while maintaining the temperature at 70°C. It was visually confirmed that all of the regenerative material had dissolved. (2) When methanol was added to (1), it was visually confirmed that insoluble matter had been formed by reprecipitation. (3) Solution X and insoluble matter Y were separated from (2) using a vacuum filtration apparatus (manufactured by Shibata Chemical Co., Ltd.). (4) After vacuum drying of insoluble matter Y at 100°C, its weight was measured. When insoluble matter Y was examined under an optical microscope, it was found to be glass fiber. (5) When the solvent was removed from solution X using a rotary evaporator, it was visually confirmed that insoluble matter Z had been formed by reprecipitation. Insoluble matter Z was recovered by filtration, vacuum dried at 100°C, and its weight was measured. Analysis of the insoluble material using 1H NMR (BRUKER, "AVANCE III 400 with CryoProbe") confirmed that the insoluble material Z is a mixture of polycarbonate and polybutylene terephthalate.

[0053] In Example 1, the recovery rate and PBT purity of recycled polybutylene terephthalate resin, the recovery rate and PC purity of recycled polycarbonate resin, and the recovery rate of glass fibers were calculated. In Comparative Example 1, the recovery rate of glass fibers, the PBT purity of insoluble material Z, and the PBT purity were also calculated. The results are shown in Table 1. In Table 1, "Recovery rate (%)" means [(dry weight of each recovered component) / (weight of each component in the recycled material) × 100] (%), and "Purity (%)" means the purity obtained by quantitative NMR measurement using 1H NMR.

[0054]

[0055] As shown in Table 1, the method of Example 1 enabled the efficient production of recycled polybutylene terephthalate resin from a recycled material containing polybutylene terephthalate, with high yield and high purity, and furthermore, recycled polycarbonate resin could be produced. In other words, the method of Example 1 enabled the efficient separation of polybutylene terephthalate resin and polycarbonate resin from a recycled material containing polybutylene terephthalate, with high yield and high purity. Furthermore, the method of Example 1 allowed for the efficient production of solution C containing at least polybutylene terephthalate, and solution A containing at least polycarbonate, with high yield and high purity. On the other hand, the method of Comparative Example 1 yielded a mixture of polybutylene terephthalate and polycarbonate from a recycled material containing polybutylene terephthalate, but it was not possible to separate the polybutylene terephthalate. That is, the method of Comparative Example 1 could not produce recycled polybutylene terephthalate resin.

[0056] The method for producing recycled polybutylene terephthalate resin according to this embodiment can efficiently produce recycled polybutylene terephthalate resin from recycled materials containing polybutylene terephthalate, and therefore can be suitably used in the production of recycled polybutylene terephthalate resin, thus having industrial applicability. The method for separating polybutylene terephthalate resin according to this embodiment can efficiently separate polybutylene terephthalate resin from recycled materials containing polybutylene terephthalate, and therefore can be suitably used in recycling processes for various engineering plastics including PBT, thus having industrial applicability. The method for recovering a solution containing at least polybutylene terephthalate according to this embodiment can efficiently recover a solution containing at least polybutylene terephthalate from recycled materials containing polybutylene terephthalate, and therefore the recovered solution can be suitably used in the production of coatings, adhesives, and other binders, thus having industrial applicability.

Claims

1. A method for producing recycled polybutylene terephthalate resin from a recyclable material containing polybutylene terephthalate, comprising: Step 1: A step of separating solution A and insoluble matter B containing at least the polybutylene terephthalate by placing the recyclable material in a solvent (solvent S1) in which the swelling rate of polybutylene terephthalate measured under the following condition 1 is greater than 5%, heating and stirring; <Condition 1> A polybutylene terephthalate film in the shape of 50 × 50 × 0.1 mm is immersed in solvent S1 at 70°C for 1 hour. The percentage increase in mass of the film removed from solvent S1 after immersion relative to the mass of the film before immersion is calculated as [{(mass of film removed from solvent after immersion) / (mass of film before immersion)} × 100 - 100] (%). A manufacturing method comprising: Step 2: Adding the insoluble matter B to a solvent (solvent S2) capable of dissolving polybutylene terephthalate, heating and stirring, and separating the solution C containing at least the polybutylene terephthalate from the insoluble matter D; Step 3: Precipitating recycled polybutylene terephthalate resin by adding a poor solvent (solvent S3) for polybutylene terephthalate to the solution C, or by removing the solvent S2 from the solution C, and separating and recovering the recycled polybutylene terephthalate resin.

2. The production method according to claim 1, wherein the solvent S1 comprises one or more solvents selected from 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, N-methylpyrrolidone, 1-methylnaphthalene, cyclohexanone, cyclopentanone, 2-methylcyclohexanone, and toluene.

3. The manufacturing method according to claim 1 or 2, wherein the solvent S1 comprises one or more solvents selected from 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, cyclohexanone, and cyclopentanone.

4. The manufacturing method according to claim 1 or 2, wherein in step 1, the heating temperature is 60°C or higher and 150°C or lower.

5. The manufacturing method according to claim 1 or 2, wherein the stirring time in step 1 is 30 minutes or more and 3 hours or less.

6. The manufacturing method according to claim 1 or 2, wherein the swelling rate of the solvent S1 is greater than 10%.

7. The manufacturing method according to claim 1 or 2, wherein the solvent S2 includes a phenolic solvent and / or a halogenated solvent.

8. The production method according to claim 1 or 2, wherein the solvent S2 comprises one or more solvents selected from 1,1,1,3,3,3-hexafluoro-2-propanol, tetrachloroethane, 3,5-bis(trifluoromethyl)phenol, m-cresol, and phenol.

9. The manufacturing method according to claim 1 or 2, wherein in step 2, the heating temperature is 60°C or higher and 150°C or lower.

10. The manufacturing method according to claim 1 or 2, wherein the stirring time in step 2 is 30 minutes or more and 3 hours or less.

11. The manufacturing method according to claim 1 or 2, further comprising preparing the recycled material having a shape that allows it to pass through a sieve with a nominal mesh opening of 20 mm prior to step 1.

12. The manufacturing method according to claim 1 or 2, wherein the recycled material further comprises polycarbonate, and further comprises step 4: adding a poor solvent (S) of polycarbonate resin to solution A, or removing the solvent S1 from solution A to precipitate recycled polycarbonate resin, and separating and recovering the recycled polycarbonate resin.

13. The manufacturing method according to claim 1 or 2, wherein the recycled material further comprises an inorganic filler, and further comprises step 5: a step of recovering the inorganic filler from the insoluble matter D.

14. The manufacturing method according to claim 13, wherein the inorganic filler includes glass fibers.

15. A method for separating polybutylene terephthalate resin from a recyclable material containing polybutylene terephthalate, comprising: Step 1: The recyclable material is placed in a solvent (solvent S1) in which the swelling rate of polybutylene terephthalate, as measured under the following condition 1, is greater than 5%, and the mixture is heated and stirred to separate solution A from insoluble matter B containing at least the polybutylene terephthalate; <Condition 1> A polybutylene terephthalate film in the shape of 50 × 50 × 0.1 mm is immersed in solvent S1 at 70°C for 1 hour. The percentage increase in the mass of the film removed from solvent S1 after immersion relative to the mass of the film before immersion is calculated as [{(mass of film removed from solvent after immersion) / (mass of film before immersion)} × 100 - 100] (%). A method comprising: Step 2: Adding the insoluble matter B to a solvent (solvent S2) capable of dissolving polybutylene terephthalate, heating and stirring, and separating the solution C containing at least the polybutylene terephthalate from the insoluble matter D; Step 3: Precipitating the polybutylene terephthalate resin by adding a poor solvent (solvent S3) for polybutylene terephthalate to the solution C, or by removing the solvent S2 from the solution C, and separating the polybutylene terephthalate resin.

16. A method for recovering a solution (Solution C) containing at least polybutylene terephthalate from a recyclable material containing polybutylene terephthalate, comprising: Step 1: The recyclable material is placed in a solvent (solvent S1) in which the swelling rate of polybutylene terephthalate, as measured under the following condition 1, is greater than 5%, and the mixture is heated and stirred to separate Solution A from insoluble matter B containing at least the polybutylene terephthalate; <Condition 1> A polybutylene terephthalate film in the shape of 50 × 50 × 0.1 mm is immersed in solvent S1 at 70°C for 1 hour. The percentage increase in the mass of the film removed from solvent S1 after immersion relative to the mass of the film before immersion is calculated as [{(Mass of film removed from solvent after immersion) / (Mass of film before immersion)} × 100 - 100] (%). A method comprising: step 2: adding the insoluble matter B to a solvent (solvent S2) capable of dissolving polybutylene terephthalate, heating and stirring, and separating the solution C containing at least the polybutylene terephthalate from the insoluble matter D;

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