Polyester recovery methods and recycled polyester production methods

Abstract

The invention relates to a method for recovering polyester, including processing a structure consisting of a matrix composed mainly of polyester fibers and containing polyurethane resin in a low-alcohol environment in the presence of a first-order transition metal acetate salt as a catalyst at temperatures of 125°C or greater and 185°C or less, thereby removing the polyurethane resin. Furthermore, preferably the polyurethane resin is porous polyurethane, the polyurethane resin is chemically cross-linked polyurethane, and the first-order transition metal acetate salt is manganese acetate, zinc acetate, or cobalt acetate. The invention also relates to a method for producing recycled polyester, in which polyester obtained by any of the above polyester recovery methods is depolymerized to aromatic bis(hydroxyalkyl) dicarboxylate and then repolymerized.

Description

Method for recovering polyester and method for producing recycled polyester

[0001] The present invention relates to a method for recovering polyester from a structure having a base material made mainly of polyester fibers and containing a polyurethane resin, and to a method for producing recycled polyester using the recovered polyester.

[0002] Structures containing polyurethane resin in a polyester fiber substrate have been put to practical use in a wide range of products, including sheet-like artificial leather, synthetic leather, and printed clothing, as well as clothing and interior goods such as bras and shoulder pads made with flexible polyurethane foam.

[0003] However, when attempting to reuse these products after use, the properties of polyester fiber and polyurethane resin are significantly different, making effective recycling difficult.

[0004] For example, Patent Document 1 proposes a recyclable artificial leather (synthetic leather) with excellent abrasion resistance and texture as a method for recycling artificial leather or synthetic leather mainly composed of fibers and polyurethane resin. However, this invention proposes an artificial leather that is easy to recycle by replacing the general polyurethane resin with a polyester or polyamide thermoplastic resin emulsion, and does not recycle conventional artificial leather or synthetic leather.

[0005] Patent Document 2 also discloses a method for separating and recovering artificial leather with a surface layer. However, although polyurethane resin is used as the resin, the proposed technology involves forming a special surface layer on the artificial leather that is easily peeled off, and therefore it cannot be said to be a general-purpose recycling technology.

[0006] On the other hand, there have been proposed inventions for recovering and recycling polyester from structures containing used polyester fibers and various resins. However, when using polyester recovered in this way, there has been a problem that the recycled polyester polymer is easily discolored and difficult to whiten. In particular, when chemical recycling is attempted by depolymerizing and repolymerizing polyester, the color of the polyester after repolymerization tends to be brown, resulting in poor quality.

[0007] As a solution to such discoloration problems, for example, Patent Document 3 discloses a method for chemically recycling waste polyethylene terephthalate products. In this method, first, as a step for removing discoloration-causing substances, attempts are made to perform an adsorption treatment in which the discoloration-causing substances are brought into contact with an adsorbent after depolymerization of the polyester, a decomposition treatment in which the discoloration-causing substances are decomposed with a decomposing agent, and a reduction treatment in which the discoloration-causing substances are reduced with a reducing agent.

[0008] However, even with this method, it has been difficult to recover the constituent components of the polyester fiber with high purity from a structure containing the polyester fiber and polyurethane resin.

[0009] JP 2012-201994 A JP 2022-67626 A JP 2008-88096 A

[0010] An object of the present invention is to provide a method for recovering polyester components from a structure containing mainly polyester fibers and a polyurethane resin, and a method for producing recycled polyester using the recovered polyester.

[0011] In order to solve the above problems, the following inventions are provided: 1. A method for recovering polyester, comprising treating a structure having a substrate made mainly of polyester fibers and containing a polyurethane resin in a lower alcohol in the presence of a first transition metal acetate catalyst at a temperature of 125°C to 185°C, thereby removing the polyurethane resin. 2. A method for recovering polyester according to the above 1, wherein the polyurethane resin is a porous polyurethane. 3. A method for recovering polyester according to the above 1 or 2, wherein the polyurethane resin is a chemically crosslinked polyurethane. 4. A method for recovering polyester according to any one of the above 1 to 3, wherein the polyester fibers are made of a polyester having alkylene terephthalate or alkylene naphthalate as the main repeating unit. 5. The method for recovering polyester according to any one of items 1 to 4 above, wherein the lower alcohol is an alcohol selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, diethylene glycol, ethylene glycol, glycerin, and benzyl alcohol. 6. The method for recovering polyester according to any one of items 1 to 5 above, wherein the first transition metal acetate is manganese acetate, zinc acetate, or cobalt acetate. 7. The method for recovering polyester according to any one of items 1 to 6 above, wherein the treatment is followed by further washing with water or an organic solvent. The present invention also encompasses the following other inventions. 8. A method for producing recycled polyester, comprising further depolymerizing the polyester obtained by the method according to any one of items 1 to 7 above into a bis(hydroxyalkyl) aromatic dicarboxylate, and then repolymerizing the bis(hydroxyalkyl) aromatic dicarboxylate.

[0012] According to the present invention, it is possible to provide a method for recovering polyester from a structure containing fibers mainly made of polyester and a polyurethane resin, and a method for producing polyester using the recovered polyester.

[0013] 1 is an IR waveform of the fibrous residue (recovered polyester sample) recovered in Example 1. 2 is an IR waveform of the fibrous residue (recovered polyester sample) recovered in Example 6. 3 is an IR waveform of the fibrous residue (recovered polyester sample) recovered in Example 7. 4 is an IR waveform of the fibrous residue (recovered polyester sample) recovered in Example 9.

[0014] The present invention will be described in detail below.

[0015] The polyester recovery method of the present invention is a method for recovering polyester from a structure containing a polyurethane resin and having a substrate primarily made of polyester fibers. Here, "primarily" means that the majority of the fibers constituting the substrate of the structure are polyester fibers, and it is preferable that the polyester fibers account for at least 50% by weight, even at least 90% by weight, and particularly that all fibers are polyester fibers. Furthermore, based on the total weight of the structure containing the fiber substrate and polyurethane resin, it is preferable that 20% by weight to 95% by weight, preferably 30% by weight to 90% by weight, and more preferably 40% to 80% by weight, of the polyester fibers are polyester fibers. The fibers other than polyester constituting the substrate are preferably fibers that can be easily separated from the polyurethane resin constituting the structure or by other methods.

[0016] The polyester that constitutes the fiber is a polycondensate synthesized by dehydration condensation of a polycarboxylic acid and a polyalcohol to form an ester bond. The polyester is a polymer having an ester bond, and can be generally classified as an aliphatic polyester, a semi-aromatic polyester, a wholly aromatic polyester, or the like.

[0017] As the polycarboxylic acid constituting the polyester, it is preferable to use a dicarboxylic acid or an ester-forming derivative thereof. In particular, it is more preferable to use an aromatic dicarboxylic acid such as terephthalic acid or 2,6-naphthalenedicarboxylic acid as the polycarboxylic acid constituting the polyester used in the present invention. It is also preferable to use terephthalic acid as the polycarboxylic acid as the main component and further use a component such as isophthalic acid as a copolymerization component. More specifically, polyesters copolymerized with isophthalic acid or 5-sodium sulfoisophthalic acid are also preferable.

[0018] As the polyalcohol, the other component constituting the polyester, it is preferable to use a diol or an ester-forming derivative thereof. More specifically, examples include aliphatic glycols having 2 to 20 carbon atoms, such as ethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, and 1,6-hexanediol. Among these, it is preferable to use ethylene glycol, 1,3-propanediol, or 1,4-butanediol as the alcohol constituting the polyester used in the present invention.

[0019] The polyester of the present invention is a polyester obtained by combining a polycarboxylic acid and a polyalcohol as described above. The polyester is preferably a semi-aromatic polyester, and more preferably a polyalkylene terephthalate or a polyalkylene naphthalate. The polyalkylene terephthalate is preferably any one of polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate. The polyalkylene naphthalate is preferably any one of polyethylene naphthalate, polytrimethylene naphthalate, and polybutylene naphthalate.

[0020] On the other hand, the polyurethane resin contained in the structure is not particularly limited as long as it can be combined with the substrate using the above-mentioned polyester fiber. For example, segmented polyurethane resins or segmented polyurethane urea resins, which form crosslinking points through a physical crosslinking structure based on hydrogen bonds in the hard segment moieties, and polyurethane resins, which form crosslinking points through a chemical crosslinking structure based on covalent bonds in the crosslinking agent, can be used. Among these, the latter crosslinked polyurethane resins can be used in applications such as urethane foams for sponges and cushioning materials, artificial leathers, synthetic leathers, pigment prints for textile products, and adhesive layers for sheet-like materials, and are suitable for utilizing a soft, elastomeric texture. Furthermore, to impart durability, it is also preferable to use polyurethanes having a three-dimensional crosslinking structure at the molecular level. More specifically, the polyol components and polyisocyanate components constituting the polyurethane resin of the present invention are as follows:

[0021] Polyol components that are raw materials for polyurethane resins include aliphatic carboxylic acids such as malonic acid, succinic acid, maleic acid, adipic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid, aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and hexahydroisophthalic acid, and ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,2-dimethyl-1,3-propanediol, 1,6-hexanediol, and 3-methyl-1,5-pentanediol. polyester polyols obtained by polycondensation of aliphatic glycols such as 1,8-octanediol, diethylene glycol, triethylene glycol, dipropanediol, triporpanediol, cyclohexane-1,4-diol, and cyclohexane-1,4-dimethanol; ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,2-dimethyl-1,3-propanediol, 1,6-hexanediol, and 3-methyl-1,5-pentanediol; Glycol components such as 1,8-octanediol, diethylene glycol, triethylene glycol, dipropanediol, tripropanediol, cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol, or ethylene oxide, propylene oxide, butylene oxide, styrene oxide, or ring-opening polymers of two or more of these using the polyester polyol as an initiator, ring-opening polymers of tetrahydrofuran, polyhydric alcohols such as glycerin, pentaerythritol, trimethylolpropane, sorbitol, sucrose, ammonia, ethylenediamine, aliphatic amine compounds such as ethanolamines, aromatic amine compounds such as toluenediamine, diphenylmethane-4,4'-diamine, and / or mixtures thereof to which ethylene oxide, propylene oxide, etc. are added, polyether polyols such as compounds obtained by adding ethylene oxide, propylene oxide, etc. to, polyether polyols and ethylenically unsaturated monomers (e.g., butadiene, acrylonitrile, styrene, etc.) in the presence of a radical polymerization catalyst, polymer polyols, etc., can be used.

[0022] Similarly, examples of polyisocyanate components that serve as raw materials for polyurethane resins include aromatic polyisocyanates such as tolylene diisocyanate (TDI), 4,4'- or 4,2'-diphenylmethane diisocyanate (MDI), naphthalene diisocyanate, and xylylene diisocyanate, alicyclic polyisocyanates such as isophorone diisocyanate and dicyclohexamethane diisocyanate, aliphatic polyisocyanates such as tetramethylene diisocyanate, pentamethylene diisocyanate, and hexamethylene diisocyanate, free isocyanate-containing prepolymers obtained by reacting these polyisocyanates with polyols, modified polyisocyanates such as carbodiimide-modified isocyanates, and mixed polyisocyanates thereof. The polyester recovery method of the present invention is an effective method even when the polyurethane is physically or chemically crosslinked.

[0023] For chemical crosslinking, it is preferable to use the above-mentioned polyol or polyisocyanate having three or more functional groups, especially a polyol having three or more hydroxyl groups as the functional group. However, since too high a degree of crosslinking increases the hardness of the polyurethane, it is preferable to use a polyol or polyisocyanate having five or fewer functional groups. Furthermore, to improve the physical properties of the polyurethane, it is preferable to crosslink not only the main chain of the polyurethane skeleton but also the side chain, and it is also preferable to use the following crosslinking agents.

[0024] Preferred examples of crosslinking agents for polyurethanes used in the present invention include polyhydric alcohols such as ethylene glycol, triethylene glycol, propylene glycol, 1,3-butanediol, glycerin, trimethylolpropane, pentaerythritol, and sorbitol; amines such as ethylenediamine, diethylenetriamine, hexamethylenediamine, hydrazine, diethyltoluenediamine, and diethylenetriamine; aminoalcohols such as diethanolamine and triethanolamine; and compounds obtained by adding ethylene oxide, polypropylene oxide, or the like to these active hydrogen compounds.

[0025] Polyurethane resin is a thermoplastic resin with a urethane bond (-NHCOO-), and is usually composed of a flexible soft segment with a low melting point and a hard segment with a high melting point. The soft segment is composed of a long-chain polyol and a diisocyanate, and the hard segment is composed of a diisocyanate and a short-chain diol (chain extender).

[0026] Polyurethane resins can also be classified by the structure of the soft segment, with the following three main types: polyether-based polyurethane resins that use polyether diols such as polytetramethylene glycol, polypropylene glycol, and polyethylene glycol as the soft segment component; polyester-based polyurethane resins that use polyester polyols such as polycaprolactone polyol, polyethylene adipate, and polypropylene adipate as the soft segment component; and polycarbonate-based polyurethane resins that use polycarbonate polyol as the soft segment component.

[0027] The hard segment is mainly a structure in which an aromatic diisocyanate such as diphenylmethane diisocyanate (MDI) or tolylene diisocyanate (TDI) is bonded to a chain extender such as ethylene glycol, 1,4-butanediol, or ethylenediamine.

[0028] The polyester recovery method of the present invention can be applied to the various polyurethanes described above and is an excellent and practical method. The target structures for recovery in the present invention are structures composed of fibers made of the above-mentioned polyesters and polyurethane resins. More specific examples of such structures include artificial leathers, synthetic leathers, various cushions used in furniture, bedding, and interiors, various clothing pads such as shoulder pads and brassiere pads, and even pigment-printed and polyurethane resin-laminated products on the surface of fiber substrates. Furthermore, structures containing polyurethane resins include not only structures in which polyurethane resin is present inside the substrate, such as by impregnating a fiber substrate with polyurethane resin, but also structures in which polyurethane resin forms a coating layer on the surface, and refer to structures in which polyurethane resin components are present integrally within or on the surface of the structure.

[0029] More specifically, for example, when the structure is artificial leather or synthetic leather, not only structures in which a fiber substrate is impregnated with a polyurethane resin, but also structures in which a fiber substrate is impregnated with or coated with a polyurethane resin, and structures in which the surface of such structures is further coated with a polyurethane resin, are preferred. Nonwoven fabrics and woven or knitted fabrics can be used as the fiber substrate, but it is preferable to use nonwoven fabrics that have a soft texture. Non-crosslinked wet-coagulated polyurethanes are commonly used as polyurethanes for impregnating the substrate, and the polyurethane forms a porous structure in the fiber substrate, such as nonwoven fabric, resulting in a soft texture. Polyurethanes for coating the surface of the substrate may be non-crosslinked wet-coagulated polyurethanes with porous structures, as well as dry polyurethanes that form solid films or various foamed polyurethanes. These polyurethanes may be used uncrosslinked, or crosslinked to enhance physical properties. Furthermore, crosslinked polyurethanes are preferably used as a binder layer between the substrate and the coating layer to enhance the adhesive strength between the substrate and the coating layer. As such binder polyurethanes, two-component polyurethane resins containing a crosslinking agent are preferably used.

[0030] Furthermore, for various cushions used in furniture, bedding and interiors, and various pads for clothing such as shoulder pads and brassiere pads, a combination of a fiber base material and foamed polyurethane is preferred.

[0031] As the foamed polyurethane, foamed polyurethane obtained by various methods can be suitably used, such as a method of creating voids in the process of removing the incorporated solvent (solvent removal method) like the wet coagulation polyurethane used in the above-mentioned artificial leather, a method utilizing a chemical reaction (chemical reaction gas method), a method using a solvent with a low boiling point (low boiling point solvent method), or a method of incorporating air (mechanical incorporation method).

[0032] Among these, flexible polyurethane foams are preferred. For example, polyurethane foams obtained by known methods such as the one-shot method, in which a polyol and a polyisocyanate are directly reacted in the presence of a blowing agent such as water or a catalyst, or the prepolymer method, in which a polyol and a polyisocyanate are reacted in advance to obtain a prepolymer having an isocyanate group at its terminal, and then a polyol is reacted with this prepolymer in the presence of a blowing agent, a catalyst, or the like, are preferably used. More specifically, polyurethane foams can be obtained by, for example, discharging a mixed and stirred foaming raw material (reaction mixture raw material) onto a belt conveyor, and continuously producing the raw material by natural foaming and curing at room temperature and atmospheric pressure while the belt conveyor is moving, followed by curing (curing) in a drying oven and cutting into a predetermined shape. To improve physical properties, it is preferable that a chemical crosslinking structure is further formed.

[0033] The polyurethane resin contained in the structure of the present invention is preferably a polyurethane foam having internal pores, such as the above-mentioned wet-coagulated polyurethane and soft polyurethane foam. The pores provide a large surface area in contact with the solution, making recovery easier.

[0034] The structure used in the present invention is also preferably a product in which a polyurethane resin containing a pigment or the like as a coloring agent is printed or gravure coated on the surface of a substrate made of fiber, or a product in which a coating layer of polyurethane resin is laminated.

[0035] It is also preferable to chemically crosslink polyurethanes used in such products to improve their physical properties. For binder resins and curable urethane adhesives used in pigment prints, it is preferable to introduce a chemical crosslinking structure after application in the presence of a crosslinking agent or water.

[0036] Typically, polyurethane resins with chemically crosslinked structures such as three-dimensional crosslinks form a mesh-like polymer structure, which makes the crosslinking points difficult to destroy and makes them difficult to dissolve simply with an organic solvent. However, the recovery method of the present invention makes it possible to recover polyester fiber components even from structures containing polyurethane resins with chemically crosslinked structures.

[0037] The polyester recovery method of the present invention is a method for removing polyurethane resin from a structure containing a polyester fiber substrate. More specifically, the method is a method for removing polyurethane resin by treating a structure containing a fiber mainly made of polyester as a substrate and containing polyurethane resin in a lower alcohol at a temperature of 125°C to 185°C in the presence of a first transition metal acetate catalyst.

[0038] Examples of lower alcohols that can be used in the recovery method of the present invention include monohydric alcohols having a linear hydrocarbon group with 5 or less carbon atoms, dihydric alcohols (also called diols or glycols), trihydric alcohols, and benzyl alcohol having an aromatic ring. These alcohols have a relatively low viscosity even at room temperature and easily penetrate polyurethane, making them ideal for the present invention.

[0039] More specific examples include methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, diethylene glycol, glycerin, and benzyl alcohol. Among these, ethylene glycol, diethylene glycol, propanediol, and benzyl alcohol are more preferred, and ethylene glycol is particularly preferred. In the treatment temperature range described below, boiling, evaporation, decomposition, and side reactions are unlikely to occur, and due to their appropriate viscosity, they have good permeability into polyurethane, allowing for more efficient recovery.

[0040] Furthermore, in the polyester recovery method of the present invention, in addition to using the above-mentioned lower alcohol, it is necessary to treat the polyester at a temperature of 125° C. or higher and 185° C. or lower in the presence of a catalyst of a first transition metal acetate.

[0041] Specific examples of the first transition metal preferably used in the present invention include titanium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, with manganese, zinc, and cobalt being particularly preferred. One of the purposes of the present invention is to further depolymerize and repolymerize the recovered polyester to produce chemically recycled polyester, and even if manganese or zinc remains in the separation and recovery process of the polyurethane and polyester, it is unlikely to have an adverse effect on the quality (particularly the hue) of the chemically recycled polyester in the subsequent depolymerization and repolymerization processes.

[0042] The mechanism by which first transition metals produce better results than when other alkali metals or alkaline earth metals are used as catalysts is unclear. However, in the system of the present invention, it is thought that a complex between the urethane bond and the lower alcohol is easily formed, resulting in a faster reaction rate, and that the bond decomposition reaction of polyurethane (addition of the lower alcohol to the urethane group in the form of substitution) occurs in a shorter time at a lower temperature range than the depolymerization reaction of polyester (alcohololysis, glycolysis). The same effect is not observed with alkali metals or alkaline earth metals other than first transition metals, and polyester and polyurethane cannot be separated successfully.

[0043] Furthermore, in the present invention, acetates of first transition metals are used. Although the mechanism behind this is not clear, it is believed that the organic salts have a higher permeability to polyurethane, an organic polymer, than the elemental metals or metal ions, due to the use of lower organic salts.

[0044] The amount of such a first transition metal acetate to be added to the lower alcohol is preferably determined depending on the amount of the structure containing the polyester fiber and polyurethane resin to be treated, and is preferably within 3 mass % of the weight of the structure. Furthermore, it is preferable to add an amount of 0.05 to 1.5 mass %, particularly 0.1 to 0.5 mass %, of the weight of the structure to the lower alcohol.

[0045] In the recovery method of the present invention, the treatment temperature is in the range of 125°C to 185°C. Below 125°C, the decomposition reaction of polyurethane is minimal, and for example, the lower alcohol in the reaction solution is hardly colored. Above 185°C, the decomposition reaction of polyurethane accelerates, but at the same time, the depolymerization reaction of polyester (alcoholization, glycolysis) also progresses, making it impossible to sufficiently recover the polyester component. Furthermore, the optimal reaction temperature varies depending on the combination of lower alcohol and catalyst used. For example, when ethylene glycol is used, a range of 135 to 183°C, and particularly a range of 155 to 180°C, is preferred. Furthermore, when benzyl alcohol is used, a range of 125 to 145°C is even more preferred. Furthermore, while atmospheric pressure is preferred as the treatment pressure, treatment under pressure is preferred when a solvent with a low boiling point is used.

[0046] The amount of lower alcohol solution used during treatment is preferably 3 to 1000 times the weight of the textile product, which is the structure to be treated. A liquid volume of 5 to 500 times, and particularly 8 to 50 times, is more preferable. During treatment with the solution, in addition to immersion and standing, it is preferable to agitate the solution with a liquid circulation system or a rotating blade, etc.

[0047] In order to improve the speed and purity of separation of the polyester and polyurethane, it is preferable to cut, crush, or granulate the structure to as small a size as possible. This makes it possible to increase the contact surface area between the catalyst-containing lower alcohol and the structure. For example, when the structure is in the form of a sheet, it is preferable to cut it to a size of 50 mm square or less, and more preferably 5 to 30 mm square or less. Furthermore, the thickness is preferably small, and a thickness of 10 mm or less, and more preferably 0.5 to 5 mm, is suitable.

[0048] Furthermore, the recovery method of the present invention is particularly effective when the polyurethane is a foamed polyurethane and has a porous or foamed structure. This increases the contact surface area of ​​the structure with the lower alcohol in the bath. Furthermore, it is preferable when the single fiber fineness of the fibers constituting the substrate is small, when the structure has a nonwoven structure, or when the polyurethane resin in the substrate is finely dispersed. As a result, the surface area in contact with the lower alcohol is increased, making treatment easier.

[0049] Furthermore, even when a coating layer is present, it is preferable that the coating layer be a porous polyurethane having a porous structure or a foam structure. Alternatively, it is preferable that a porous polyurethane is further present between the fibrous substrate and the solid coating layer. In particular, when the solid coating layer is crosslinked, its solubility in lower alcohols decreases. However, when a porous polyurethane with excellent solubility is present between the fibrous substrate and the solid coating layer, it becomes easy to recover only the polyester fiber in the substrate.

[0050] In the recovery method of the present invention, even one draining by filtration after immersion in the solution is effective. Furthermore, to increase the purity of the recovered polyester, it is preferable to wash the recovered polyester after draining with water or an organic solvent and then filter it again. This makes it possible to more effectively remove decomposed or undissolved polyurethane materials that may adhere to the recovered polyester.

[0051] As the organic solvent for washing, those having a high affinity for polyester, such as methanol, ethanol, ethylene glycol, diethylene glycol, acetone, toluene, xylene, and aqueous acetic acid solution, are preferred because they have a high washing efficiency.

[0052] The immersion and draining may be repeated several times. As the draining treatment, various methods such as squeezing, centrifugal separation, and Soxhlet extraction can be used. Furthermore, the weight of the textile product containing the solution after each draining treatment is preferably 300% or less of the dry weight of the textile product, more preferably 150 to 250%, and particularly preferably 180 to 220%.

[0053] The recovered polyester after dewatering and washing must be dried to confirm its yield, and vacuum drying at a temperature of 25° C. to 95° C., particularly 60 to 95° C., is preferred. The degree of vacuum is preferably 12 kPa or less, particularly in the range of 20 to 200 Pa (0.02 to 0.2 kPa). The vacuum is preferably below the flash point or ignition point of the lower alcohol used.

[0054] The polyester obtained by the method for recovering polyester of the present invention has polyurethane components effectively removed, and if the textile product is dyed, the dye is also effectively removed.

[0055] Another method for producing recycled polyester according to the present invention involves depolymerizing the polyester obtained by the above-described polyester recovery method into a bis(hydroxyalkyl) aromatic dicarboxylate, and then repolymerizing the bis(hydroxyalkyl) aromatic dicarboxylate, thereby producing a polyester with low yellowness and high whiteness.

[0056] Furthermore, in this method for producing recycled polyester, a catalyst is preferably used during depolymerization, and a catalyst based on a first transition metal is preferably selected as the catalyst. More specifically, examples of the catalyst include oxides, fatty acid salts, carbonates, acetates, sulfates, phosphates, oxides, hydroxides, halides, and alcoholates of first transition metals, and it is also preferable to combine one or more of these. In the present invention, manganese, zinc, and cobalt are particularly preferred among the first transition metals, and their oxides and acetates are preferred. More specifically, manganese oxide, manganese acetate, zinc oxide, zinc acetate, cobalt oxide, and cobalt acetate are examples of the catalyst. Manganese acetate, zinc acetate, and cobalt acetate are particularly preferred, with manganese acetate being the most preferred.

[0057] The catalyst is preferably dissolved in alkylene glycol in advance and used as a solution. The alkylene glycol (hereinafter sometimes abbreviated as AG) is preferably the same as the diol component forming the backbone structure of the polyester used in the textile product. It is also possible to use a diol that constitutes the final polyester product obtained by repolymerizing an intermediate aromatic dicarboxylate bis(hydroxyalkyl).

[0058] Examples of alkylene glycols that form or can form the backbone structure of polyester include ethylene glycol (EG) when the polyester is polyethylene terephthalate (PET), 1,3-propanediol (trimethylene glycol, C3G) when the polyester is polytrimethylene terephthalate, and 1,4-butanediol (C4G) when the polyester is polybutylene terephthalate. Furthermore, a mixture of the above alkylene glycols may be used as the alkylene glycol depending on the purpose.

[0059] The effects of the present invention are particularly evident in the case of white structures that do not contain coloring substances. For example, depolymerized polyester products often gradually become discolored over time due to storage, but those depolymerized using a manganese catalyst show significantly less discoloration.

[0060] Furthermore, the amount of catalyst used during depolymerization to obtain the recycled polyester of the present invention is preferably 20 to 500 mmol% relative to the polyester. It is even more preferably 30 to 300 mmol%, and particularly preferably 50 to 150 mmol% relative to the polyester. Here, "1 mol%" refers to the ratio of the number of catalyst molecules to the structural units of the polyester, and "1 mmol%" is 1 / 1000 of that ratio. In particular, the use of a manganese-based catalyst makes it possible to keep the amount used low. If the amount of catalyst used is too low below this range, the catalytic activity is insufficient, and if it is too high, the effect of suppressing discoloration is reduced.

[0061] In the method for producing recycled polyester of the present invention, after depolymerization using a catalyst, it is preferable to perform crystallization by lowering the temperature in alkylene glycol. The temperature lowering conditions during crystallization are preferably a method of lowering the temperature from a temperature of 60°C or higher to 25°C or lower, and more preferably a method of cooling to 15°C or lower. Furthermore, solid-liquid separation is preferably performed after crystallization, and the alkylene glycol content in the cake after solid-liquid separation is preferably 100% by mass or lower. Furthermore, it is preferable to adjust the alkylene glycol content to 55% by mass or lower, or to a range of 1 to 30% by mass, and particularly to a range of 5 to 25% by mass. Furthermore, it is preferable to use an amount of alkylene glycol that is 2 to 20 times, or even 3 to 10 times, the amount of polyester after recovery treatment. By using a large amount of alkylene glycol during depolymerization and performing crystallization and solid-liquid separation in this way, the production method of the present invention makes it possible to further reduce the amount of depolymerization catalyst and other foreign matter contamination. In particular, when manganese acetate is used as the catalyst, it has high solubility in alkylene glycol, making it possible to more effectively reduce the amount of catalyst remaining in the subsequent steps.

[0062] Furthermore, in the method for producing recycled polyester of the present invention, it is preferable to wash the depolymerized cake with water or alkylene glycol after the crystallization described above. Furthermore, it is preferable to treat the cake using a Nutsche filter while spraying the washing liquid. By performing these treatments, the depolymerization catalyst dissolved in the alkylene glycol and other discoloration-causing substances can be washed away, making it possible to obtain a more highly purified aromatic bis(hydroxyalkyl) dicarboxylate. The solution used for washing preferably has a low viscosity, and from this perspective, water is preferred. The amount of washing liquid is preferably 1 to 100 times, more preferably 1.5 to 10 times, the weight of the cake. The liquid temperature during washing is preferably in the range of 0°C to 40°C. If the temperature is too high, the cake itself will easily dissolve, resulting in a reduced yield. The aromatic bis(hydroxyalkyl) dicarboxylate can then be obtained by drying using a vacuum dryer or the like.

[0063] Furthermore, the obtained bis(hydroxyalkyl) aromatic dicarboxylate may be subjected to an additional treatment of adsorbing foreign matter using an adsorbent such as activated carbon. When the alkylene glycol used in the production method of the present invention is the same as the diol component of the polyester resin after repolymerization, repolymerization without drying as is is also a preferred method for producing a polyester.

[0064] The bis(hydroxyalkyl) aromatic dicarboxylate obtained by such a production process depends on the type of polyester and alkylene glycol used. However, when a polyester (polyalkylene terephthalate) using terephthalic acid primarily as the polycarboxylic acid is used as the raw material, the method is preferably a method for producing bis(hydroxyalkyl) benzenedicarboxylate (hereinafter sometimes referred to as BHAT; bishydroxyalkyl terephthalate). More specifically, when C3G (1,3-propanediol (trimethylene glycol)) is used as the alkylene glycol, BHPT (bishydroxypropyl terephthalate) is produced, and when C4G (1,4-butanediol) is used, BHBT (bishydroxybutyl terephthalate) is produced. In particular, when polyethylene terephthalate, which is primarily composed of terephthalic acid and ethylene glycol, is used as the polyester constituent, it is possible to produce bis(hydroxyethyl) benzenedicarboxylate (BHET; bishydroxyethyl terephthalate).

[0065] Furthermore, such aromatic bis(hydroxyalkyl) dicarboxylates can be repolymerized by a conventionally known method to produce recycled polyester resins that are resistant to coloration and have excellent color hues.

[0066] Next, we will explain the polyester polymer production process in which the bis(hydroxyalkyl) aromatic dicarboxylate obtained by this depolymerization is repolymerized. Known catalysts such as antimony-, germanium-, or titanium-based catalysts can be used as catalysts for repolymerization to obtain polyester resins, with diantimony trioxide being particularly preferred. The polycondensation reaction is preferably carried out while alkylene glycol and other substances generated during the repolymerization reaction are flushed out of the reactor. The amount of catalyst used is preferably in the range of 10 to 1,000 ppm based on the weight of the bis(hydroxyalkyl) aromatic dicarboxylate used. Furthermore, after polycondensation using the catalyst, conventionally known phosphorus-based stabilizers such as orthophosphoric acid and phosphorous acid are preferably used. The amount of phosphorus-based stabilizer used is preferably in the range of 1 to 100 ppm based on the weight of the bis(hydroxyalkyl) aromatic dicarboxylate used.

[0067] The polyester resin obtained in this manner is a resin that is less likely to discolor, such as yellowing, unlike the resins obtained using conventionally known depolymerization catalysts such as magnesium hydroxide, sodium hydroxide, potassium hydroxide, magnesium carbonate, sodium carbonate, and potassium carbonate. This discoloration was only visible even at the stage of the aromatic dicarboxylate bis(hydroxyalkyl). Furthermore, after repolymerization into a resin, the color L ＊ , a ＊ , b ＊ When the value was measured with a colorimeter, ＊ The difference is particularly noticeable in the value of , where polyesters produced under the conditions of the present invention are only -3 or less, more preferably -3.5 or less, while products produced using other catalysts have higher values, and some even have positive values ​​(strong yellowish). The reason for this is not clear, but it is thought that the fact that manganese-based catalysts can depolymerize at low concentrations and are less likely to produce colored by-products, and that they are easily dissociated from the aromatic dicarboxylate bis(hydroxyalkyl) in subsequent crystallization and other processes, making them very unlikely to remain as impurities, etc., are at work.

[0068] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. The values ​​in the examples were determined by the following methods. The unit of "mol %" for the amount of catalyst added relative to the polyester indicates the ratio of the number of catalyst molecules to the constituent units of the polyester.

[0069] (1) Measurement Method 1) Intrinsic Viscosity Number (IV) 0.6 g of polyester was dissolved in 50 cc of o-chlorophenol by heating, and then the solution was cooled. The solution viscosity was measured at a temperature of 35°C using an Ubbelohde viscometer, and the intrinsic viscosity number (IV) was calculated using a separately prepared calibration curve.

[0070] 2) Glass transition point (Tg) and melting point (Tm) 10 mg of the sample was cut and placed in an aluminum pan, and the melting point was measured using a differential scanning calorimeter "DSC Q10" manufactured by TA Instruments-Waters LLC. The measurement conditions were as follows: the sample was first heated from 25°C to 300°C at a heating rate of 20°C / min, and then rapidly cooled and quenched. The quenched sample was then heated from 25°C to 300°C at a heating rate of 20°C / min, and the crystalline melting point was determined.

[0071] 3) Fiber fineness Measured in accordance with JIS L1013:2021 8.3.1 Method A.

[0072] 4) Number of filaments of fiber Measured in accordance with JIS L1013:2010 8.4.

[0073] 5) Fiber strength and elongation Measured in accordance with JIS L1013:2010 8.5.1.

[0074] 6) Thickness Measured in accordance with JIS L1913:2010 6.1.1 Method A.

[0075] 7) Basis weight Measured in accordance with JIS L1913:2010 6.2.

[0076] 8) IR Measurement (Infrared Spectroscopy) Infrared spectroscopy was performed on the target sample using an "IRSprint" manufactured by Shimadzu Corporation. The measurement conditions were a wavelength range of 400 to 4000 cm －１ , resolution is 4 cm －１The number of integrations was 20. A peak was confirmed in the obtained waveform. －１ The presence or absence of an absorption peak was used to determine whether or not polyurethane remained in the polyester.

[0077] 9) Polymer Hue The repolymerized polymer (5 g) was pressed between two metal plates to form a plate, which was then heated at 140°C for 2 hours to crystallize the sample. The measurement sample was measured for hue L according to JIS Z8781-4:2013 using a measuring device ("ZE-6cm-1000" manufactured by Nippon Denshoku Industries Co., Ltd.). ＊ , a ＊ , b ＊ The yellowness index (YI) was calculated using the following formula (1), and the whiteness index (W) was calculated using the following formula (2). Yellowness index (YI): 0.34 - 71.7 x a / L + 178.78 x b / L (1) Whiteness index (W): 100 - √{(100 - L) ２ +a ２ +b ２ (2) The higher the value of the yellowness index (YI), the stronger the yellowness, and the higher the value of the whiteness index (W), the higher the whiteness.

[0078] [Example 1] (Polyester recovery process) A polyester waste sack made of polyethylene terephthalate (hereinafter referred to as "PET") short fibers with a basis weight of 220 g / m ２ A needle-punched nonwoven fabric of 412 g / m was used as the substrate. This substrate was impregnated with and coated with a polyether polyester wet polyurethane (hereinafter, polyurethane will be referred to as "PU") to form a nonwoven fabric of 412 g / m ２ The wet PU impregnation coated substrate was prepared. The resin / fiber ratio (R / F) was 47 / 53. The PU in the impregnated substrate and the PU in the coating layer both had porous structures.

[0079] Furthermore, a crosslinked binder PU layer and a surface PU layer were laminated on the substrate to obtain a grain-finished artificial leather. The weight of the binder PU layer was 56 g / m ２ The weight of the surface PU layer is 42 g / m ２Both the binder PU layer and the skin PU layer had a non-porous solid structure. The binder PU layer was a chemically crosslinked PU using a polyisocyanate-based crosslinking agent, and the skin PU layer was a dry-process polyether polyester-based PU.

[0080] The obtained artificial leather (hereinafter referred to as "artificial leather 1") had a thickness of 1.3 mm and a total basis weight of 510 g / m, in which the PET nonwoven fabric accounted for 43% by mass of the total and some of the PU was chemically crosslinked. ２ Furthermore, differential scanning calorimetry (DSC) of this artificial leather confirmed that the polyester fiber used as the base material was PET with a Tg of 70°C and a Tm of 256°C.

[0081] This artificial leather was crushed into pieces measuring approximately 20 mm square or less to prepare 400 g samples. The 400 g samples were then placed in a 5-liter separable flask. Subsequently, 2000 g of ethylene glycol (hereinafter referred to as "EG") was prepared, and 1.5 g (0.375% by mass of the sample) of manganese acetate was dissolved in the resulting mixture as a catalyst. The resulting mixture was then placed in the separable flask. The separable flask was then heated using a mantle heater while adjusting the internal temperature to 160°C, and the mixture was stirred under normal pressure for 4 hours.

[0082] In the separable flask, the PU in the artificial leather gradually became finely dispersed in the EG, and after 4 hours, the PET fibers inside and some of the PU that appeared to be undecomposed were scattered throughout the EG.

[0083] After 4 hours, stirring was stopped, and the entire contents of the separable flask were filtered through a Nutsche filter to remove any undissolved material. Subsequently, the EG and undissolved PU remaining on the PET fiber surface were removed by acetone washing, and the PET fiber was dried in a vacuum dryer at 80°C for 8 hours at a vacuum of 0.3 kPa to recover a white fibrous residue. The mass of the recovered material after treatment was 161 g. IR analysis of the recovered material revealed no absorption at wavelengths considered to be derived from PU, and the absorption spectrum consisted solely of PET, indicating that the PU had been almost completely removed. The melting point and other physical properties of the recovered sample are shown in Table 1, and the IR waveform is shown in Figure 1.

[0084] (Polyester Recycling Step) 300 parts by mass of the recovered material obtained by the same treatment as above were charged into a 2 L separable flask, along with 1,500 parts by mass of ethylene glycol (EG) and 0.38 parts by mass of manganese acetate as a depolymerization catalyst (100 mmol% relative to PET, assuming that all of the recovered material is PET), and the flask was then filled with nitrogen. At this time, the manganese acetate was dissolved in EG before being charged.

[0085] The separable flask containing the sample was then heated to an internal temperature of 220°C using a mantle heater, and depolymerization treatment was carried out at atmospheric pressure for 4 hours while stirring. The depolymerized BHET (bis(hydroxyethyl) benzenedicarboxylate) solution was colorless and transparent, with no visible coloration. The depolymerized solution was then filtered through a 200 μm mesh to remove any remaining solids. The solution was then gradually cooled to 70°C, and the temperature was then lowered from 70°C to 40°C over a period of 0 to 10 minutes, from 40°C to 30°C over a period of 10 to 60 minutes, and from 30°C to 15°C over a period of 60 to 180 minutes while stirring. The internal temperature was then maintained at 15°C for 60 minutes, and the BHET crystals were precipitated (a total of 4 hours) to obtain a BHET / EG slurry.

[0086] The BHET / EG slurry was pressed using a filter press manufactured by Nippon Filter Equipment Co., Ltd., and solid-liquid separation of BHET and EG was carried out. The separated BHET contained 35% by mass of EG based on the weight of the cake recovered from the filter press. After EG separation, the cake was washed with water using a Nutsche filter while spraying it with 25°C pure water in an amount twice the mass of the cake.

[0087] After the solid-liquid separation, the BHET was dissolved in 20 times its mass of hot water (90°C), and 0.25 times its mass of activated carbon was added thereto and stirred for 1 hour. Nutsche filtration was then performed, and the aqueous solution from which the activated carbon had been removed was cooled to precipitate BHET. Nutsche filtration was then performed again to recover the BHET.

[0088] The recovered BHET was dried in a vacuum dryer at 50°C for 8 hours to obtain dried BHET. The obtained BHET was white and free of any foreign matter.

[0089] Then, 254 parts by mass of the resulting dried BHET was placed in a reaction vessel under atmospheric pressure and nitrogen atmosphere, along with 0.007 parts by mass of a phosphorus-based stabilizer and 0.07 parts by mass of diantimony trioxide as a repolymerization catalyst. The temperature inside the reactor was then raised to 285°C, and the pressure was gradually reduced under the following conditions: atmospheric pressure for 10 minutes, 4 kPa for 10 minutes, and 0.4 kPa for 40 minutes. The polycondensation reaction was carried out while distilling off ethylene glycol and other substances generated during the reaction. The reaction product was then continuously extruded in a strand shape from the discharge port, cooled, and cut to obtain granular pellets of approximately 3 mm. The quality of the final PET polymer is shown in Table 1. A polymer with a melting point comparable to that of the original pre-recycled fiber, a low yellowness index (YI), and a high whiteness index (W) was obtained.

[0090]

[0091] Comparative Example 1 The same treatment as in Example 1 was carried out, except that in the step of stirring in a separable flask under normal pressure for 4 hours in the polyester recovery step in Example 1, the internal temperature was changed from 160°C to 120°C. However, the morphology of the sample did not change even after 4 hours had passed, and no dissolution of PU into the manganese acetate catalyst-containing EG was observed.

[0092] Comparative Example 2 The same treatment as in Example 1 was carried out, except that in the step of stirring in a separable flask under normal pressure for 4 hours in the polyester recovery step in Example 1, the internal temperature was changed from 160°C to 198°C. However, after 4 hours had elapsed, the entire amount of the sample including PET and PU dissolved, making it impossible to recover the polyester by filtration.

[0093] Comparative Example 3 The same treatment as in Example 1 was carried out, except that in the step of stirring in a separable flask under normal pressure for 4 hours in the polyester recovery method of Example 1, manganese acetate as a catalyst was not added and the treatment was carried out using only EG. However, the morphology of the sample did not change even after 4 hours had passed, and no dissolution of PU in EG was observed.

[0094] Comparative Example 4 The same treatment as in Example 1 was carried out, except that in the step of stirring in a separable flask under normal pressure for 4 hours in the polyester recovery method of Example 1, manganese acetate was changed to potassium carbonate as the catalyst. However, the morphology of the sample did not change even after 4 hours had passed, and no dissolution of PU in EG was observed.

[0095] [Example 2] The same treatment as in Example 1 was carried out, except that in the step of stirring in a separable flask at normal pressure for 4 hours in the polyester recovery method of Example 1, manganese acetate was used as the catalyst, instead of zinc acetate. Similar to Example 1, IR measurement of the recovered product after the treatment showed no absorption at wavelengths considered to be due to PU, and showed an absorption spectrum consisting only of PET, confirming that PU had been almost completely removed. The physical properties of the recovered polyester sample, such as the melting point, are shown in Table 1. PET pellets were then obtained using the method described in the polyester recycling process. The quality of the final PET polymer produced is shown in Table 1.

[0096] [Example 3] The same treatment as in Example 1 was carried out, except that in the step of stirring under normal pressure in a separable flask in the polyester recovery method of Example 1, the catalyst was changed from manganese acetate to cobalt acetate and the stirring time was changed from 4 hours to 6 hours. Similar to Example 1, IR measurement of the recovered material after the treatment showed no absorption at wavelengths considered to be due to PU, and showed an absorption spectrum consisting only of PET, confirming that PU had been almost completely removed. The physical properties of the recovered sample, such as the melting point, are shown in Table 1. PET pellets were then obtained using the method described in the polyester recycling process. The quality of the final PET polymer produced is shown in Table 1.

[0097] Example 4 The same process as in Example 1 was carried out, except that in the step of stirring under normal pressure in a separable flask in the polyester recovery method of Example 1, EG was replaced with diethylene glycol and the internal temperature was changed from 160°C to 180°C. Similar to Example 1, IR measurement of the recovered material after the process showed no absorption at wavelengths considered to be derived from PU, and showed an absorption spectrum consisting solely of PET, confirming that PU had been almost completely removed. The physical properties of the recovered sample, such as the melting point, are shown in Table 1. PET pellets were then obtained using the method described in the polyester recycling process. The quality of the final PET polymer produced is shown in Table 1.

[0098] Example 5 The same treatment as in Example 1 was carried out, except that in the step of stirring under normal pressure in a separable flask in the polyester recovery method of Example 1, EG was replaced with 1,3-propanediol and the internal temperature was changed from 160°C to 180°C. Similar to Example 1, IR measurement of the recovered product after treatment revealed no absorption at wavelengths deemed to be derived from PU, and exhibited an absorption spectrum consisting solely of PET, confirming that PU had been almost completely removed. The physical properties of the recovered sample, such as the melting point, are shown in Table 1. PET pellets were then obtained using the method described in the polyester recycling process. The quality of the final PET polymer produced is shown in Table 1.

[0099] [Example 6] In the polyester recovery method of Example 1, the same treatment and recycling as in Example 1 was carried out, except that artificial leather 1 was changed to artificial leather 2, and PET pellets were obtained. Artificial leather 2 had the following properties: PET staple fiber basis weight of 560 g / m ２ The needle-punched nonwoven fabric is used as the base material, and the PU is changed to a polycarbonate-based wet PU, which is then impregnated and coated, resulting in a basis weight of 882 g / m. ２A wet PU impregnation coated substrate with a resin / fiber ratio (R / F) of 37 / 63 was used. Both the PU in the impregnated substrate and the PU in the coating layer had a porous structure. Furthermore, a crosslinked binder PU layer and a surface PU layer were laminated onto the substrate in the same manner as in Artificial Leather 1 to produce a silver-coated artificial leather. However, the surface PU layer was changed from a polyether polyester-based dry PU to a polycarbonate-based dry PU. The resulting artificial leather 2 had a thickness of 2.2 mm and a total basis weight of 980 g / m, with PET nonwoven fabric constituting 57% of the total and some of the PU chemically crosslinked. ２ The melting point and other physical properties of the recovered polyester sample are shown in Table 1, and the IR waveform is shown in Figure 2. The quality of the final PET polymer is shown in Table 1.

[0100] [Example 7] (Polyester Recovery Process) A 400 g sample was prepared, which consisted of 360 g of PET fiber woven fabric and 40 g of chemically crosslinked flexible urethane foam (hereinafter referred to as "foamed PU"). The PET woven fabric had a basis weight of 44 g / m ２ The foamed PU was a urethane polymer of tolylene diisocyanate (TDI), polyoxypropylene triol, and trimethylolpropane as monomers, and had a thickness of 5 mm and a density of 0.055 g / cm. ３ The following was used.

[0101] 400 g of this sample was placed in a 5-liter separable flask. Next, 2000 g of EG was prepared, and 1.5 g (0.375% by mass based on the sample) of manganese acetate was dissolved in the EG as a catalyst. The resulting mixture was then placed in the separable flask. The separable flask was then heated using a mantle heater while adjusting the internal temperature to 160°C, and the mixture was stirred under normal pressure for 4 hours.

[0102] In the separable flask, the foamed PU dissolved in the EG, and the EG gradually became colored. After 4 hours, it was confirmed by visual inspection that the foamed PU had completely dissolved in the EG and no solid foamed PU remained.

[0103] After 4 hours, stirring was stopped, and the fibrous solid residue was removed from the separable flask and squeezed to remove excess treatment solution. Coloration was observed in the treatment solution, and the weight of the slightly decolorized solid residue after squeezing was 652 g.

[0104] The solid residue was then washed with water to remove any remaining treatment solution, and the residue was dried in a vacuum dryer at 80°C for 8 hours to recover a white fibrous residue. The mass of the recovered product after treatment was 344g, and IR measurement of the recovered product showed no absorption at wavelengths considered to be due to PU, and the absorption spectrum was composed solely of PET, confirming that PU had been almost completely removed. The melting point and other physical properties of the recovered polyester sample are shown in Table 1, and the IR waveform is shown in Figure 3.

[0105] (Polyester Recycling Process) Granular pellets of PET were obtained in the same manner as in Example 1. The quality of the finally produced polyethylene terephthalate polymer is shown in Table 1.

[0106] [Example 8] The same treatment as in Example 7 was carried out, except that in the step of stirring in a separable flask under normal pressure for 4 hours in the polyester recovery method of Example 7, EG was changed to benzyl alcohol (hereinafter referred to as "BA"), the internal temperature was changed from 160°C to 130°C, and the treatment time was changed from 4 hours to 6 hours.

[0107] As in Example 7, IR measurement of the recovered material after treatment showed no absorption at wavelengths believed to be derived from the foamed PU, and instead showed an absorption spectrum consisting solely of PET, confirming that the foamed PU had been almost completely removed. The physical properties of the recovered polyester sample, such as the melting point, are shown in Table 1. PET pellets were then obtained using the method described for polyester recycling. The quality of the final PET polymer is shown in Table 1.

[0108] Comparative Example 5 The same treatment as in Example 7 was carried out, except that in the step of stirring in a separable flask under normal pressure for 6 hours in the method for recovering polyester in Example 8, manganese acetate as a catalyst was not added and treatment was carried out using only BA. However, the morphology of the sample did not change even after 6 hours had passed, and the foamed PU was not found to dissolve in BA.

[0109] [Example 9] A 400 g sample of a woven fabric was prepared, in which PET fibers were printed with a urethane resin. The PET fabric had a basis weight of 44 g / m ２ The print area was made of a resin containing a dry binder polyurethane consisting mainly of polytetramethylene glycol (PTMG), isophorone diisocyanate, 1,6-hexanediamine, and triethylamine, and mainly composed of crosslinked PU, at a concentration of 56 g / m. ２ It was attached.

[0110] 400 g of this sample was placed in a 5-liter separable flask. Next, 2000 g of EG was prepared, and 1.5 g (0.375% by mass based on the sample) of manganese acetate was dissolved in the EG as a catalyst. The resulting mixture was then placed in the separable flask. The separable flask was then heated using a mantle heater while adjusting the internal temperature to 160°C, and the mixture was stirred under normal pressure for 4 hours.

[0111] In the separable flask, the printed area was dissolved in the EG, and the contained pigment was observed to diffuse into the EG. After 4 hours, stirring was stopped, and the fabric-like solid residue was removed from the separable flask and squeezed to remove excess treatment solution. Coloration, likely due to the pigment and decomposition products, was observed in the treatment solution, and the mass of the solid residue after squeezing was 296 g.

[0112] The solid residue was then washed with water to remove any remaining treatment solution, and the solid residue was dried in a vacuum dryer at 80°C for 8 hours to recover a fabric-like residue. The mass of the recovered product after treatment was 168 g. The physical properties of the recovered polyester sample, such as the melting point, are shown in Table 1, and its IR waveform is shown in Figure 4.

[0113] (Polyester Recycling Process) Granular pellets of PET were obtained in the same manner as in Example 1. The quality of the finally produced polyethylene terephthalate polymer is shown in Table 1.

[0114] [Example 10] In the polyester recovery method of Example 1, artificial leather 1 was replaced with artificial leather 3, ethylene glycol was replaced with benzyl alcohol, and the treatment temperature was changed from 160°C to 130°C. The sample after acetone washing was found to have white fibrous residue, and it was visually confirmed that the PU component had been removed. Artificial leather 3 was as follows:

[0115] As with the artificial leather 1 of Example 1, the weight of the PET short fiber was 220 g / m ２ The base material is a needle-punched nonwoven fabric, which is impregnated and coated with PU and has a basis weight of 412 g / m ２ The wet PU impregnation coated substrate had a resin / fiber ratio (R / F) of 47 / 53.

[0116] However, instead of laminating the crosslinked binder PU layer of artificial leather 1, gravure coating of PU was performed. Specifically, a coating solution was prepared by mixing polyetherester polyurethane (solid content concentration 25%) / methyl ethyl ketone / dimethylformamide in a ratio of 100 / 40 / 160, and this coating solution was applied three times to the surface of the wet-PU impregnated coated substrate using a #110 gravure roll, followed by drying. The total PU coating amount in the gravure coating was 4 g / m2 in solid content. ２ In the obtained artificial leather 3, the PET nonwoven fabric constituted 52 mass % of the whole, and all the used PU was non-crosslinked and had a total basis weight of 416 g / m ２ It was artificial leather.

[0117] The method of the present invention for recovering polyester from a structure that uses a fiber mainly made of polyester as a base material and contains a polyurethane resin, and the method of producing recycled polyester by depolymerizing the polyester recovered from the structure and then repolymerizing it, make it possible to separate and recover only polyester from structures such as artificial leather, which have traditionally been disposed of only by incineration or landfill due to the difficulty of separation and removal, and further enable chemical recycling.

Claims

1. A method for recovering polyester, comprising treating a structure having a base material made mainly of polyester fibers and containing polyurethane resin in a lower alcohol in the presence of a catalyst of a first transition metal acetate at a temperature of 125°C to 185°C, thereby removing the polyurethane resin.

2. The method for recovering polyester according to claim 1, wherein the polyurethane resin is a porous polyurethane.

3. The method for recovering polyester according to claim 1, wherein the polyurethane resin is a chemically crosslinked polyurethane.

4. The method for recovering polyester according to claim 1, wherein the polyester fiber is made of a polyester having alkylene terephthalate or alkylene naphthalate as a main repeating unit.

5. The method for recovering polyester according to claim 1, wherein the lower alcohol is an alcohol selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, diethylene glycol, ethylene glycol, glycerin and benzyl alcohol.

6. The method for recovering polyester according to claim 1, wherein the first transition metal acetate is manganese acetate, zinc acetate or cobalt acetate.

7. The method for recovering polyester according to claim 1, wherein the treatment is followed by washing with water or an organic solvent.

8. A method for producing recycled polyester, comprising the steps of: depolymerizing the polyester obtained by the method according to any one of claims 1 to 7 into a bis(hydroxyalkyl) aromatic dicarboxylate; and then repolymerizing the bis(hydroxyalkyl) aromatic dicarboxylate.