Method for recovering polyester and method for producing recycled polyester

Abstract

A method for recovering a polyester in which a polyurethane resin is removed by treating a structure containing a polyurethane resin in a lower alcohol at a temperature of 125-185 DEG C in the presence of a catalyst of a first transition metal acetate, said structure containing a fiber mainly composed of a polyester as a base material. Further, preferably, the polyurethane resin is a porous polyurethane, the polyurethane resin is a chemically crosslinked polyurethane, and the first transition metal acetate is manganese acetate, zinc acetate, or cobalt acetate. And a method for producing a recycled polyester in which the polyester obtained by any one of the polyester recovery methods is further depolymerized into an aromatic dicarboxylic acid bis (hydroxyalkyl) ester and then repolymerized.

Description

Technical Field

[0001] This invention relates to a method for recovering polyester from a structure containing polyurethane resin and made primarily of polyester fibers as a substrate, and a method for manufacturing recycled polyester using the recovered polyester. Background Technology

[0002] As a structure containing polyurethane resin in a base material made of polyester fiber, a wide range of products, such as sheet-like artificial leather, synthetic leather, printed fabrics, and bras or shoulder pads using soft polyurethane foam, have been put into practical use.

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

[0004] For example, Patent Document 1 proposes a method for regenerating artificial leather (synthetic leather) with excellent wear resistance and texture, which is mainly composed of fibers and polyurethane resin. However, this invention proposes to easily regenerate artificial leather by replacing the conventional polyurethane resin as the resin with a polyester or polyamide thermoplastic resin emulsion, rather than regenerating the artificial leather or synthetic leather that has been used in the past.

[0005] Furthermore, Patent Document 2 discloses a method for sorting and recycling artificial leather with an epidermal layer. However, although it proposes a technique that uses polyurethane resin as the resin to form a special epidermal layer that is easy to peel off on the artificial leather, it cannot be considered a universal recycling technique.

[0006] On the other hand, an invention has been proposed to regenerate polyester from structures containing used polyester fibers and various resins. However, when using polyester recycled in this way, there is a problem that the recycled polyester polymer is prone to staining and difficult to whiten. Especially in the case of chemical regeneration that attempts to depolymerize and repolymerize the polyester, the hue of the repolymerized polyester tends to be brown, resulting in poor quality.

[0007] As a solution to this coloring problem, Patent Document 3 discloses a method for chemically regenerating waste polyethylene terephthalate (PET) products. The method includes several steps, such as adsorption treatment (contacting the coloring-causing substances with an adsorbent after polyester depolymerization), decomposition treatment (decomposing the coloring-causing substances with a decomposing agent), and reduction treatment (reducing the coloring-causing substances with a reducing agent).

[0008] However, even with such methods, it is difficult to recover the components of polyester fibers with high purity from structures containing polyester fibers and polyurethane resins.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2012-201994

[0012] Patent Document 2: Japanese Patent Application Publication No. 2022-67626

[0013] Patent Document 3: Japanese Patent Application Publication No. 2008-88096 Summary of the Invention

[0014] The object of the present invention is to provide a method for recovering polyester components from a structure containing fibers mainly composed of polyester and polyurethane resin, and a method for manufacturing recycled polyester using the recovered polyester.

[0015] To address the aforementioned issues, the following invention is provided.

[0016] 1. A method for recovering polyester, characterized in that a structure containing polyurethane resin and made primarily of polyester fibers is treated in a lower alcohol at a temperature of 125°C to 185°C in the presence of a catalyst of a first transition metal acetate to remove the polyurethane resin.

[0017] 2. The polyester recycling method according to 1 above, wherein the polyurethane resin is a porous polyurethane.

[0018] 3. The polyester recycling method according to 1 or 2 above, wherein the polyurethane resin is a chemically cross-linked polyurethane.

[0019] 4. The polyester recycling method according to any one of 1 to 3 above, wherein the fiber made of polyester is made of polyester with alkylene terephthalate or alkylene naphthalate as the main repeating unit.

[0020] 5. The method for recovering polyester according to any one of 1 to 4 above, wherein the lower alcohol is selected from 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, glycerol, and benzyl alcohol.

[0021] 6. The method for recovering polyester according to any one of 1 to 5 above, wherein the first transition metal acetate is manganese acetate, zinc acetate, or cobalt acetate.

[0022] 7. The method for recovering polyester according to any one of 1 to 6 above, wherein, after treatment, it is further cleaned with water or an organic solvent.

[0023] Furthermore, this invention includes another invention described below.

[0024] 8. A method for manufacturing recycled polyester, characterized in that the polyester obtained by any one of the methods described in 1 to 7 is further depolymerized into an aromatic dicarboxylic acid bis(hydroxyalkyl) ester, and then the aromatic dicarboxylic acid bis(hydroxyalkyl) ester is repolymerized.

[0025] According to the present invention, a method for recovering polyester from a structure containing fibers mainly composed of polyester and polyurethane resin, and a method for manufacturing polyester using the recovered polyester, can be provided. Attached Figure Description

[0026] Figure 1 The image shows the IR waveform of the fibrous residue (recovered polyester sample) recovered in Example 1.

[0027] Figure 2 The image shows the IR waveform of the fibrous residue (recovered polyester sample) recovered in Example 6.

[0028] Figure 3 The image shows the IR waveform of the fibrous residue (recovered polyester sample) recovered in Example 7.

[0029] Figure 4 The image shows the IR waveform of the fibrous residue (recovered polyester sample) recovered in Example 9. Detailed Implementation

[0030] The present invention will now be described in detail.

[0031] The polyester recycling method of the present invention is a method for recovering polyester from a structure containing polyurethane resin and using fibers mainly composed of polyester as a base material. Here, "mainly" means that among the fibers constituting the base material of the structure, the majority of the fibers are composed of polyester, preferably 50% by mass or more, more preferably 90% by mass or more, and particularly preferably all of the fibers are composed of polyester. Furthermore, based on the total mass of the structure containing the fiber-based base material and the polyurethane resin, it is preferable that 20% to 95% by mass, more preferably 30% to 90% by mass, and more preferably 40% to 80% by mass are composed of polyester fibers. Other fibers besides polyester constituting the base material are preferably fibers that are together with the polyurethane resin constituting the structure or that can be easily separated by other methods.

[0032] Here, the polyester constituting the fiber refers to a condensation polymer synthesized by dehydrating and condensing polycarboxylic acids and polyols to form ester bonds. Moreover, polyester is a polymer containing ester bonds, and polyesters generally classified as aliphatic polyesters, semi-aromatic polyesters, and fully aromatic polyesters can be used.

[0033] As the polycarboxylic acid constituting the polyester, a dicarboxylic acid or its ester-forming derivative is preferred. More preferably, aromatic dicarboxylic acids such as terephthalic acid and 2,6-naphthalenedicarboxylic acid are used primarily as the polycarboxylic acid constituting the polyester used in this invention. Furthermore, while terephthalic acid is primarily used as the polycarboxylic acid, isophthalic acid or similar components are also preferred as copolymerizing agents. More specifically, a polyester obtained by copolymerizing isophthalic acid or sodium isophthalate 5-sulfonate is also preferred.

[0034] Furthermore, as another component of the polyester, the polyol is preferably a diol or its ester-forming derivative. More specifically, examples include aliphatic diols with 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, ethylene glycol, 1,3-propanediol, and 1,4-butanediol are preferably used as the alcohol constituting the polyester used in this invention.

[0035] Polyesters composed of polycarboxylic acids and polyols as described above can be used as the polyesters of the present invention. Semi-aromatic polyesters are preferred as polyesters, and more preferably polyalkylene terephthalate or polyalkylene naphthalate. In particular, any one of polyethylene terephthalate, polyethylene terephthalate, and polyethylene terephthalate is preferred as the polyalkylene terephthalate. Furthermore, any one of polyethylene naphthalate, polyethylene terephthalate, and polyethylene naphthalate is preferred as the polyalkylene naphthalate.

[0036] On the other hand, there are no particular limitations on the polyurethane resin contained in the structure, as long as it can be combined with the substrate using the aforementioned polyester fibers. For example, segmented polyurethane resins or segmented polyurethane urea resins that form crosslinking points through a physical crosslinking structure based on hydrogen bonds of hard segment portions, or polyurethane resins that form crosslinking points through a chemical crosslinking structure based on covalent bonds of a crosslinking agent, can be used. Among these, the latter type of crosslinked polyurethane resin can be used for applications such as foamed polyurethane foams for sponges and cushioning materials, artificial or synthetic leather, pigment printing for fiber products, and adhesive layers for sheet materials, making it suitable for utilizing the texture of soft elastomers. In addition, for the purpose of imparting durability, polyurethanes with a three-dimensional crosslinking structure at the molecular level are preferred.

[0037] More specifically, the polyol and polyisocyanate components constituting the polyurethane resin of this invention are as follows.

[0038] As a raw material for polyurethane resins, polyols can be composed of aliphatic carboxylic acids such as malonic acid, succinic acid, maleic acid, adipic acid, glutaric acid, pimelic acid, octanoic acid, azelaic acid, and sebacic acid, or aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and hexahydroisophthalic acid, along with ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, and 2,2-dimethyl-1,3-propanediol. Polyester polyols obtained by condensation polymerization of aliphatic diols such as 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,8-octanediol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, cyclohexane-1,4-diol, and cyclohexane-1,4-diethanol, as well as 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... The product contains diols such as 1,5-pentanediol, 1,8-octanediol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, cyclohexane-1,4-diol, and cyclohexane-1,4-diethanol; or ring-opening polymers of ethylene oxide, propylene oxide, butane oxide, and styrene oxide, one or more of these, using the aforementioned polyester polyols as initiators; ring-opening polymers of tetrahydrofuran; glycerol; pentaerythritol; trimethylolpropane; sorbitol; sucrose, etc. Polyether polyols, such as those derived from aliphatic amines like alcohols, ammonia, ethylenediamine, and ethanolamines, aromatic amines like toluenediamine and diphenylmethane-4,4'-diamine, and / or mixtures thereof, by addition to ethylene oxide, propylene oxide, etc., and polymer polyols obtained by reacting polyether polyols with olefinically unsaturated monomers (e.g., butadiene, acrylonitrile, styrene, etc.) in the presence of a free radical polymerization catalyst.

[0039] Similarly, examples of polyisocyanate components that can be used as raw materials for polyurethane resins include aromatic polyisocyanates such as toluene diisocyanate (TDI), 4,4'- or 4,2'-diphenylmethane diisocyanate (MDI), naphthalene diisocyanate, and xylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and dicyclohexane diisocyanate; aliphatic polyisocyanates such as tetramethylene diisocyanate, pentamethylene diisocyanate, and hexamethylene diisocyanate; prepolymers containing free isocyanates obtained by reacting these polyisocyanates with polyols; modified polyisocyanates such as carbodiimide-modified isocyanates; and mixed polyisocyanates thereof.

[0040] Moreover, the polyester recycling method of the present invention is more effective when polyurethane undergoes physical or chemical crosslinking.

[0041] For chemical crosslinking, it is preferable to use the aforementioned polyols or polyisocyanates that are trifunctional or higher, especially those polyols having hydroxyl groups of trifunctional or higher. However, if the crosslinking is too high, the hardness of the polyurethane increases, so it is preferable to use polyols or polyisocyanates with five or fewer functional groups.

[0042] In addition, in order to improve the physical properties of polyurethane, it is preferable not only to crosslink the main chain of the polyurethane skeleton, but also to crosslink the side chains, and it is also preferable to use the crosslinking agent described below.

[0043] As the crosslinking agent for the polyurethane used in this invention, polyols such as ethylene glycol, triethylene glycol, propylene glycol, 1,3-butanediol, glycerol, trimethylolpropane, pentaerythritol, and sorbitol, amines such as ethylenediamine, diethylenetriamine, hexamethylenediamine, hydrazine, diethyltoluenediamine, and diethylenetriamine, amino alcohols such as diethanolamine and triethanolamine, and compounds obtained by adding these active hydrogen compounds to ethylene oxide, polypropylene oxide, etc., are preferred.

[0044] In addition, polyurethane resin is a thermoplastic resin with urethane bonds (-NHCOO-), which is usually composed of soft segments with low melting points and hard segments with high melting points that are flexible. The soft segments are composed of long-chain polyols and diisocyanates, while the hard segments are composed of diisocyanates and short-chain diols (chain extenders).

[0045] As types of polyurethane resins, they can also be classified according to the structure of the soft segments mentioned above, mainly into the following three types.

[0046] Polyether-based polyurethane resins with polyether diols such as polybutanediol, polypropylene glycol, and polyethylene glycol as soft segment components; polyester-based polyurethane resins with polyester polyols such as polycaprolactone polyol, polyethylene adipate, and propylene adipate as soft segment components; and polycarbonate-based polyurethane resins with polycarbonate polyols as soft segment components.

[0047] In addition, the hard segments are mainly composed of aromatic diisocyanates such as diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI) bonded to chain extenders such as ethylene glycol, 1,4-butanediol, and ethylenediamine.

[0048] The polyester recycling method of the present invention can be applied to various polyurethanes as described above, and is an excellent and practical method.

[0049] Furthermore, the structure that is the object of recycling according to this invention is a structure made of polyester fibers and polyurethane resin as described above. More specific examples of such structures include artificial leather or synthetic leather, and furniture. bedding This includes various cushioning pads, shoulder pads, breast pads, and other fabric pads used in interior decoration, as well as pigment-printed products or polyurethane resin laminates applied to the surface of fiber-based substrates. Furthermore, polyurethane resin-containing structures not only include structures in which polyurethane resin is impregnated within a fiber-based substrate, but also structures in which polyurethane resin forms a coating on the surface; that is, structures in which the polyurethane resin component is integrally present within or on the surface of the structure.

[0050] More specifically, for example, when the structure is artificial leather or synthetic leather, it is not only a structure formed by impregnating a fiber substrate with polyurethane resin, but also preferably a structure impregnated with polyurethane resin. Structures formed by coating a fibrous substrate, or by further coating the surface of such structures with polyurethane resin, etc. Nonwoven fabrics and woven textiles can be used as the fibrous substrate, but soft nonwoven fabrics are preferred. Non-crosslinked wet-cured polyurethane is widely used for impregnation of the substrate, forming a porous structure within the fibrous substrate such as the nonwoven fabric, resulting in a soft texture. In addition to the aforementioned porous non-crosslinked wet-cured polyurethane, dry polyurethane forming a solid film or various foamed polyurethanes can be used as the polyurethane coating on the substrate surface. These polyurethanes are naturally used non-crosslinked, but crosslinking is preferred to improve their physical properties. Furthermore, as a method of using crosslinked polyurethane, to improve the adhesion between the substrate and the coating, it is preferable to use crosslinked polyurethane as an adhesive layer between the substrate and the coating. A two-component polyurethane resin containing a crosslinking agent is preferred as such an adhesive.

[0051] Additionally, as a furniture bedding Various cushioning pads, shoulder pads, chest pads, and other fabric pads for interior decoration are preferably made of polyurethane foam combined with a fiber-based substrate.

[0052] As for foamed polyurethane, it is preferable to use foamed polyurethane obtained by various methods, such as the method of forming voids in the process of removing the contained solvent, which is similar to the wet-cured polyurethane used in the above-mentioned artificial leather, etc. (solvent removal method), the method of using chemical reaction (chemical reaction gas utilization method), the method of using a solvent with a low boiling point (low boiling point solvent utilization method), the method of mixing in air (mechanical mixing method), etc.

[0053] Of these, flexible polyurethane foam is preferred as the foamed polyurethane. For example, it is preferably obtained by a one-step method in which a polyol and a polyisocyanate are directly reacted in the presence of a foaming agent and catalyst such as water, or by a prepolymer method in which a polyol and a polyisocyanate are pre-reacted to obtain a prepolymer with isocyanate groups at the ends, and the polyol is then reacted with the prepolymer in the presence of a foaming agent and catalyst. As a more specific manufacturing method, for example, polyurethane foam obtained by the following method can be used: a mixed and stirred foaming raw material (reaction mixture) is discharged onto a belt conveyor, and during the movement of the belt conveyor, the raw material naturally foams and cures at room temperature and atmospheric pressure, thereby continuously manufacturing the foam. Then, after curing in a drying oven, it is cut into a specified shape. To improve physical properties, it is preferable to further form a chemically cross-linked structure.

[0054] The polyurethane resin contained in the structure of the present invention is preferably a porous foamed polyurethane. Examples include the aforementioned wet-cured polyurethane and flexible polyurethane foam, which, due to their porous nature, have a large surface area in contact with the solution, making them easier to recycle.

[0055] Furthermore, the structure used in this invention is preferably a product obtained by printing polyurethane resin containing pigments as colorants onto the surface of a fiber-based substrate, a product obtained by gravure coating, or a product obtained by laminating a polyurethane resin coating.

[0056] As for polyurethane used in such articles, chemical cross-linking is also preferred to improve its physical properties. In the preferred pigment-printing adhesive resins and curable polyurethane adhesives, it is preferable to introduce a chemically cross-linked structure after coating in the presence of a cross-linking agent and water.

[0057] Typically, polyurethane resins with chemically cross-linked structures, such as three-dimensional cross-linking, form a network polymer structure, making the cross-linking points difficult to destroy and impossible to dissolve using only organic solvents. However, in the recycling method of the present invention, polyester fiber components can be recovered even from structures containing polyurethane resin with chemically cross-linked structures.

[0058] The polyester recycling method of the present invention is characterized by removing polyurethane resin from a structure containing polyurethane resin in the aforementioned polyester fiber substrate. More specifically, it is a method for removing polyurethane resin by treating a structure containing polyurethane resin and using a fiber mainly composed of polyester as a substrate in a lower alcohol at a temperature of 125°C to 185°C in the presence of a catalyst of a first transition metal acetate.

[0059] Examples of lower alcohols used in the recycling method of this invention include monohydric alcohols, dihydric alcohols (also called diols or glycols), trihydric alcohols, and benzyl alcohols with aromatic rings, all of which have a straight-chain hydrocarbon group with 5 or fewer carbon atoms. These have low viscosity even at room temperature and can easily penetrate polyurethane, making them most suitable for this invention.

[0060] More specifically, 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, glycerol, and benzyl alcohol. Among these, ethylene glycol, diethylene glycol, propylene glycol, and benzyl alcohol are more preferred, and ethylene glycol is particularly preferred. Within the processing temperature range described later, boiling, evaporation, decomposition, and side reactions are less likely to occur. Due to its suitable viscosity, it has good permeability to polyurethane, enabling more effective recycling.

[0061] Furthermore, in the polyester recycling method of the present invention, in addition to the use of the aforementioned lower alcohol, it is also necessary to process the product at a temperature of 125°C to 185°C in the presence of a catalyst of a first transition metal acetate.

[0062] Specific examples of preferred first transition metals used in this invention include titanium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, with manganese, zinc, and cobalt being particularly preferred. One purpose of the recycled polyester in this invention is to further depolymerize and repolymerize it to produce chemically recycled polyester. Even if manganese and zinc remain in the separation and recycling process of the polyurethane and polyester, they are unlikely to have an adverse effect on the quality (especially the hue) of the chemically recycled polyester in the subsequent depolymerization and repolymerization processes.

[0063] It should be noted that the mechanism by which the first transition metal yields better results compared to other alkali metals, alkaline earth metals, etc., as catalysts is not yet clear. However, it is believed that in the system of the present invention, complexes of urethane bonds and lower alcohols are readily formed, resulting in a faster reaction rate. Compared to the depolymerization reaction (alcohololysis, diollysis) of polyester, the polyurethane bonding decomposition reaction (lower alcohols adding to urethane groups in a substituted manner) occurs in a shorter time in the low-temperature region.

[0064] It should be noted that the same effect was not observed in alkali metals and alkaline earth metals other than the first transition metal, and polyester could not be well separated from polyurethane.

[0065] Furthermore, the present invention uses an acetate of a first transition metal. The mechanism is not fully understood, but it is believed to be due to the following reason: because a low-grade organic salt is used, compared to a simple metal element or metal ion state, the organic salt improves the permeability to polyurethane, which is an organic polymer.

[0066] Furthermore, the amount of such first transition metal acetate added to the lower alcohol is preferably determined based on the amount of the structure containing polyester fiber and polyurethane resin as the material being treated, and is preferably an amount of up to 3% by mass of the structure. Moreover, it is preferable to add 0.05 to 1.5% by mass, particularly 0.1 to 0.5% by mass of the structure to the lower alcohol.

[0067] Furthermore, in the recycling method of the present invention, the processing temperature is in the range of 125°C to 185°C. If the temperature is below 125°C, the decomposition reaction of polyurethane is minimal, for example, the lower alcohols in the reaction solution are hardly colored. If the temperature exceeds 185°C, the decomposition reaction of polyurethane becomes faster, but at the same time, the depolymerization reaction of polyester (alcohololysis, diollysis) also occurs, making it impossible to fully recover the polyester component. Furthermore, the optimal reaction temperature varies depending on the combination of the lower alcohol and the catalyst used; for example, when using ethylene glycol, a range of 135°C to 183°C is preferred, and a range of 155°C to 180°C is particularly preferred. Additionally, when using benzyl alcohol, a range of 125°C to 145°C is more preferred.

[0068] In addition, atmospheric pressure is preferred as the pressure during processing, but when using solvents with low boiling points, it is preferable to process under pressure.

[0069] Furthermore, the amount of lower alcohol solution used in the treatment is preferably 3 to 1000 times the weight of the structure to be treated, i.e., the fiber product. More preferably, it is 5 to 500 times the weight, and particularly preferably 8 to 50 times the weight. In addition, when using the solution for treatment, besides immersion and settling, it is preferable to agitate the solution through liquid circulation, rotating blades, or the like.

[0070] It should be noted that, in order to improve the speed and purity of the separation of polyester and polyurethane, the structure is preferably cut into small sizes or pulverized or granulated. This can further increase the contact surface area between the lower alcohol containing the catalyst and the structure. For example, when the structure is in sheet form, it is preferable to cut it into sizes of 50 mm square or less, and further to 5 to 30 mm square or less. In addition, the thinner the thickness, the better; an appropriate thickness is 10 mm or less, and further to 0.5 to 5 mm.

[0071] Furthermore, in the recycling method of the present invention, it is particularly effective that the polyurethane is foamed polyurethane and adopts a porous or foamed structure. In the bath, the contact surface area of ​​the structure with the lower alcohol increases. Additionally, it is preferable when the single yarn fineness of the fibers constituting the substrate is small, when a non-woven fabric structure is adopted, or when the polyurethane resin in the substrate is relatively dispersed. As a result, the surface area in contact with the lower alcohol increases, making it easier to process.

[0072] Furthermore, when a coating is present, the coating is preferably a porous polyurethane with a porous or foamed structure. Alternatively, it is preferable that a porous polyurethane is further present between the fibrous substrate and the solid coating. In particular, when the solid coating is cross-linked, the solubility of lower alcohols decreases, but when a porous polyurethane with excellent solubility is present between the fibrous substrate and the solid coating, it is easy to recover only the polyester fibers in the substrate.

[0073] In the recycling method of the present invention, the immersion treatment with the solution followed by filtration and desolvation is effective with only one step. Furthermore, in order to improve the purity of the recycled polyester, it is preferable to temporarily wash the recycled polyester after desolvation with water or an organic solvent and then filter it again. This can more effectively remove decomposition products or undissolved substances of polyurethane that sometimes adhere to the recycled polyester.

[0074] As organic solvents used for cleaning at this time, methanol, ethanol, ethylene glycol, diethylene glycol, acetone, toluene, xylene, and aqueous acetic acid solutions, which have high affinity for polyester, have high cleaning efficiency and are therefore preferred.

[0075] Furthermore, the soaking and dehydration can be repeated multiple times. Various methods can be used for dehydration, such as pressing, centrifugation, and Soxhlet extraction. Additionally, the weight of the fiber product containing the solution after each dehydration treatment is preferably 300% or less of the dry weight of the fiber product, and more preferably 150-250%, particularly 180-220%, of the dehydration treatment.

[0076] For the recovered polyester after dehydration and washing, drying is required to confirm the yield. Vacuum drying at 25°C to 95°C, particularly 60°C to 95°C, is sufficient. The vacuum level is preferably below 12 kPa, and particularly preferably in the range of 20 to 200 Pa (0.02 to 0.2 kPa). It should be noted that the flash point and ignition point of the lower alcohol used are preferably below these values.

[0077] The polyester obtained by the polyester recycling method of the present invention can effectively remove polyurethane components. Furthermore, in the case of dyed fiber products, the dye can also be effectively removed.

[0078] Furthermore, another method for manufacturing the recycled polyester according to the present invention is a method for manufacturing recycled polyester by depolymerizing the polyester obtained by the polyester recycling method described above into an aromatic dicarboxylic acid bis(hydroxyalkyl) ester, and then repolymerizing the aromatic dicarboxylic acid bis(hydroxyalkyl) ester. This method can then produce a polyester with low yellowness and high whiteness.

[0079] Furthermore, in the method for manufacturing this recycled polyester, a catalyst is used during depolymerization, and preferably, a catalyst of the first transition metal system is selected. More specifically, examples include oxides or fatty acid salts, carbonates, acetates, sulfates, phosphates, oxides, hydroxides, halides, alkoxides, etc., of the first transition metal system, and combinations of one or more of them are also preferred. In this invention, manganese, zinc, or cobalt are particularly preferred among the first transition metals, and their oxides or acetates are preferred. More specifically, manganese oxide, manganese acetate, zinc oxide, zinc acetate, cobalt oxide, or cobalt acetate can be cited, with manganese acetate, zinc acetate, or cobalt acetate being particularly preferred, and manganese acetate being the most preferred.

[0080] Furthermore, the catalyst used is preferably pre-dissolved in an alkylene glycol and used in solution form. As the alkylene glycol (hereinafter, sometimes abbreviated as AG), it is preferable to use an alkylene glycol with the same diol composition as the polyester that forms the backbone structure for fibrous products. Alternatively, a diol constituting the polyester ultimately obtained as a product by repolymerizing an aromatic dicarboxylic acid bis(hydroxyalkyl) ester of an intermediate may also be used.

[0081] As alkylene glycols that form or are capable of forming the backbone structure of polyester, examples include ethylene glycol (EG) in the case of polyethylene terephthalate (PET), 1,3-propanediol (trimethylene glycol, C3G) in the case of polyethylene terephthalate, and 1,4-butanediol (C4G) in the case of polyethylene terephthalate. Furthermore, mixtures of the above-mentioned alkylene glycols can be used as alkylene glycols depending on the purpose.

[0082] It should be noted that the effects of the present invention are particularly significant in the case of white structures that do not contain coloring substances. For example, most depolymerized polyesters gradually change color due to prolonged storage, but substances obtained by depolymerization using manganese-based catalysts show significantly less color change.

[0083] Furthermore, the amount of catalyst used for depolymerizing the recycled polyester of the present invention is preferably 20 to 500 mmol% relative to the polyester. More preferably, it is 30 to 300 mmol% relative to the polyester, and particularly preferably 50 to 150 mmol%. Here, "1 mol%" represents the ratio of the number of catalyst molecules to the constituent units of the polyester, and "1 mmol%" is 1 / 1000 of that ratio. In particular, by using a manganese-based catalyst, it is possible to suppress the use of low amounts. If the amount of catalyst used is too small compared to the above range, the catalyst activity is insufficient; if it is too large, the effect of suppressing discoloration is reduced.

[0084] In the method for manufacturing recycled polyester of the present invention, it is preferable to perform crystallization by cooling in alkylene glycol after depolymerization using a catalyst. As the cooling conditions for crystallization, it is preferable to cool from a temperature of 60°C or higher to 25°C or lower, and more preferably to a temperature of 15°C or lower. Furthermore, it is preferable to perform solid-liquid separation after crystallization, and the alkylene glycol content in the filter cake after solid-liquid separation is preferably 100% by mass or less. Furthermore, it is preferable to keep the alkylene glycol content at 55% by mass or less, or to adjust it to a range of 1 to 30% by mass, particularly a range of 5 to 25% by mass. In addition, the amount of alkylene glycol used in the initial depolymerization is preferably 2 to 20 times, and further 3 to 10 times, the amount of recycled polyester. Thus, by using a larger amount of alkylene glycol during depolymerization and performing crystallization and solid-liquid separation, the amount of depolymerization catalyst and other foreign matter mixed in can be further reduced in the manufacturing method of the present invention. In addition, especially when manganese acetate is used as a catalyst, its high solubility with alkylene glycols can more effectively reduce the amount of catalyst residue in subsequent processes.

[0085] Furthermore, in the method for manufacturing the recycled polyester of the present invention, it is preferable to wash the depolymerized filter cake with water or with alkylene glycol after crystallization as described above. Furthermore, it is preferable to process the filter cake using a Knocking filter while spraying the cleaning solution. By performing these treatments, the depolymerization catalyst and other coloring agents dissolved in the alkylene glycol can be washed away, resulting in a more purified aromatic dicarboxylic acid bis(hydroxyalkyl) ester. As the cleaning solution, a low-viscosity solution is preferred; from this viewpoint, water is preferred. As the amount of cleaning solution, it is preferably 1 to 100 times the weight of the filter cake, more preferably 1.5 to 10 times. As the cleaning temperature, it is preferably in the range of 0°C to 40°C. If the temperature is too high, the filter cake itself easily dissolves, reducing the yield. Then, by drying using a vacuum dryer or the like, the aromatic dicarboxylic acid bis(hydroxyalkyl) ester can be obtained.

[0086] Alternatively, the obtained aromatic dicarboxylic acid bis(hydroxyalkyl) ester can be further subjected to adsorption treatment to remove foreign matter, etc. It should be noted that when the alkylene glycol used in the manufacturing method of the present invention has the same diol composition as the repolymerized polyester resin, directly repolymerizing without drying is also a preferred method for manufacturing polyester.

[0087] As for the aromatic dicarboxylic acid bis(hydroxyalkyl) esters obtained through such a manufacturing process, although it depends on the type of polyester and alkylene glycol used, when using a polyester (polyalkylene terephthalate) that mainly uses terephthalic acid as a polycarboxylic acid as a raw material, the method for manufacturing di(hydroxyalkyl) terephthalic acid bis(hydroxyalkyl) esters (hereinafter, BHAT; sometimes referred to as dihydroxyalkyl terephthalate) is preferred. More specifically, when using C3G (1,3-propanediol (trimethylene glycol)) as an alkylene glycol, BHPT (dihydroxypropyl terephthalate) is manufactured, and when using C4G (1,4-butanediol), BHBT (dihydroxybutyl terephthalate) is manufactured. In particular, when using polyethylene terephthalate, which is mainly composed of terephthalic acid and ethylene glycol, as a component constituting the polyester, di(hydroxyethyl) terephthalic acid bis(hydroxyethyl) esters (BHET; dihydroxyethyl terephthalate) can be manufactured.

[0088] Furthermore, such aromatic dicarboxylic acid bis(hydroxyalkyl) esters are recycled polyester resins with excellent hue and are not easily colored by repolymerization using conventionally known methods.

[0089] Next, the manufacturing process of the polyester polymer by repolymerizing the aromatic dicarboxylic acid bis(hydroxyalkyl) ester obtained by this depolymerization will be described.

[0090] As a catalyst for the repolymerization of the polyester resin, known catalysts such as antimony-based, germanium-based, or titanium-based catalysts can be used, with antimony trioxide being particularly preferred. Alkyl glycols and the like generated during the repolymerization reaction are preferably discharged from the reactor while undergoing polycondensation. The amount of catalyst used is preferably in the range of 10 to 1000 ppm relative to the weight of the aromatic dicarboxylic acid bis(hydroxyalkyl) ester used. Furthermore, after polycondensation using the catalyst, conventionally known phosphoric acid stabilizers such as orthophosphoric acid or phosphorous acid are preferably used. The amount of phosphoric acid stabilizer used is preferably in the range of 1 to 100 ppm relative to the weight of the aromatic dicarboxylic acid bis(hydroxyalkyl) ester used.

[0091] The polyester resin obtained in this manner differs from that obtained using conventional depolymerization catalysts such as magnesium hydroxide, sodium hydroxide, potassium hydroxide, magnesium carbonate, sodium carbonate, and potassium carbonate, resulting in a resin with minimal discoloration, including yellowing. This level of discoloration can be visually confirmed even during the intermediate stage of obtaining the aromatic dicarboxylic acid bis(hydroxyalkyl) ester. Furthermore, after repolymerization into resin, the hue L is measured using a colorimeter. * a * b * Values, results, especially b *The value of is significant; the polyester produced using the conditions of the present invention has a value of -3 or less, more preferably only -3.5 or less. In contrast, substances produced using other catalysts have values ​​higher than 3, and some even achieve positive values ​​(yellow tone). The reason for this is not yet clear, but it is believed that manganese-based catalysts can depolymerize at low concentrations and are less likely to produce coloring byproducts. Furthermore, they are easily dissociated from aromatic dicarboxylic acid bis(hydroxyalkyl) esters even in subsequent crystallization processes, and are extremely unlikely to remain as impurities. These aspects are considered to be effective.

[0092] Example

[0093] The present invention will be further described in detail below through embodiments, but the present invention is not limited thereto. It should be noted that the values ​​in the embodiments were obtained by the following methods.

[0094] In addition, the amount of catalyst added, expressed in "mol%" of catalyst relative to polyester, indicates the ratio of the number of catalyst molecules to the constituent units of polyester.

[0095] (1) Measurement method

[0096] 1) Intrinsic viscosity number (IV)

[0097] After dissolving 0.6g of polyester in 50cc of o-chlorophenol by heating, the solution was temporarily cooled and the viscosity was calculated using a separately prepared calibration curve based on the solution viscosity measured by an Ubbelohde viscometer at 35°C.

[0098] 2) Glass transition temperature (Tg), melting point (Tm)

[0099] A 10 mg sample was cut and filled into an aluminum disk. The melting point was determined using a differential scanning calorimeter (DSC) device Q10 manufactured by TA Instruments-Waters LLC. As part of the determination, the sample was first temporarily heated from 25 °C to 300 °C at a heating rate of 20 °C / min, followed by quenching. Then, the quenched sample was heated from 25 °C to 300 °C at a rate of 20 °C / min to determine the crystal melting point.

[0100] 3) Fiber fineness

[0101] The determination was performed according to JIS L1013:2021 8.3.1 A method.

[0102] 4) Number of fiber filaments

[0103] The determination was carried out in accordance with JIS L1013:2010 8.4.

[0104] 5) Fiber strength and elongation

[0105] The determination was carried out in accordance with JIS L1013:2010 8.5.1.

[0106] 6) Thickness

[0107] The determination was performed according to JIS L1913:2010 6.1.1 A method.

[0108] 7) Weight per unit area

[0109] The determination was carried out in accordance with JIS L1913:2010 6.2.

[0110] 8) IR measurement (infrared spectroscopy)

[0111] Infrared spectroscopy of the sample was performed using an "IRSprint" instrument manufactured by Shimadzu Corporation. The measurement conditions were a wavelength range of 400–4000 cm⁻¹. －1 Resolution is 4cm －1 The cumulative number of iterations was 20. The obtained waveforms were used to confirm the peak. The peak at 3290 cm⁻¹ was determined based on the presence or absence of urethane bonds. －1 The absorption peaks are used to determine whether there is any polyurethane residue in the polyester.

[0112] 9) The hue of the polymer

[0113] The polymer (5g) obtained by pressing and repolymerizing two metal plates was formed into a plate and then heated at 140℃ for 2 hours to crystallize the sample. The hue L of this sample was determined using a measuring apparatus (Nippon Denshoku Kogyo Co., Ltd. "ZE-6cm-1000") according to JIS Z8781-4:2013. * a * b * The value of .

[0114] Yellowness (YI) is calculated using the following formula (1), and whiteness (W) is calculated using the following formula (2).

[0115] Yellowness (YI): 0.34―71.7×a / L+178.78×b / L (1)

[0116] Whiteness (W): 100 - √ {(100 - L)} 2 +a 2 +b 2} (2)

[0117] The higher the yellowness (YI) value, the stronger the yellow tone; the higher the whiteness (W) value, the higher the whiteness.

[0118] [Example 1]

[0119] (Polyester recycling process)

[0120] The unit area weight of the fiber is 220 g / m², which is composed of polyethylene terephthalate (hereinafter referred to as "PET") short fibers. 2 Needle-punched nonwoven fabric was used as the substrate. A polyether polyester-based wet polyurethane (hereinafter, polyurethane is referred to as "PU") was impregnated and coated onto the substrate to produce a product with a unit area weight of 412 g / m². 2 The substrate is wet-processed with impregnated PU. The resin / fiber ratio (R / F) is 47 / 53. Both the impregnated PU and the coated PU in the substrate have a porous structure.

[0121] Furthermore, a cross-linked adhesive PU layer and a surface PU layer are laminated onto the substrate through a lamination process to create artificial leather with silver accents. The unit area weight of the adhesive PU layer is 56 g / m². 2 The unit area weight of the PU skin layer is 42g / m². 2 Both the adhesive PU layer and the outer PU layer are non-porous solid structures. Furthermore, the adhesive PU layer is a chemically cross-linked PU using a polyisocyanate-based cross-linking agent, while the outer PU layer is a dry-processed PU based on a polyether polyester.

[0122] The resulting artificial leather (hereinafter referred to as "artificial leather 1") is composed of 43% by mass of PET nonwoven fabric, a portion of chemically cross-linked PU with a thickness of 1.3 mm, and a total unit area weight of 510 g / m². 2 The artificial leather. Furthermore, differential scanning calorimetry (DSC) analysis of the artificial leather confirmed that the polyester fiber used as the substrate is PET with Tg = 70℃ and Tm = 256℃.

[0123] The artificial leather was broken into pieces approximately 20 mm square or smaller, yielding a 400 g sample. This 400 g sample was then placed into a 5-liter separable flask. Next, 2000 g of ethylene glycol (hereinafter referred to as "EG") was prepared, and 1.5 g of manganese acetate (0.375% by mass relative to the sample) was dissolved and added to the separable flask. The separable flask was then heated to an internal temperature of 160°C using a heating mantle, and stirred at atmospheric pressure for 4 hours.

[0124] In a separable flask, the PU in the artificial leather is slowly and finely dispersed in the EG. After 4 hours, the PET fibers inside are visible, and some undecomposed PU is scattered randomly in the EG.

[0125] After 4 hours, stop stirring and use a Nutchi filter to remove the undissolved contents from the total volume of the contents in the separable flask.

[0126] Then, undissolved EG and PU residues on the PET fiber surface were removed by acetone washing. The residue was then dried in a vacuum dryer at 80°C for 8 hours at a vacuum degree of 0.3 kPa to recover the white fibrous residue. The mass of the recovered material was 161 g. IR spectroscopy of the recovered material showed no absorption at wavelengths identified as originating from PU, exhibiting an absorption spectrum composed solely of PET, indicating that PU was almost completely removed.

[0127] The melting point and other physical properties of the recovered samples are shown in Table 1, and the IR waveforms are shown in Table 2. Figure 1 .

[0128] (Polyester recycling process)

[0129] Relative to 300 parts by mass of the recovered material obtained through the same treatment as described above, 1500 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 all recovered material is PET) were added to a 2 L separable flask and nitrogen-sealed. The manganese acetate was pre-dissolved in the EG before being added.

[0130] Then, the separable flask containing the sample was heated using a heating mantle at an internal temperature of 220°C, and depolymerization was carried out for 4 hours under normal pressure while stirring. The depolymerized BHET (bis(hydroxyethyl) diphenylcarboxylate) solution was colorless and transparent with no visible coloring. The depolymerized solution was then filtered through a 200 μm sieve to remove any remaining solid components. After slow cooling to 70°C, the solution was stirred and cooled in stages: 70°C → 40°C over 0–10 minutes, 40°C → 30°C over 10–60 minutes, and 30°C → 15°C over 60–180 minutes. The mixture was then stirred for 60 minutes while maintaining an internal temperature of 15°C to further reduce the internal temperature and allow BHET crystals to precipitate (totaling 4 hours), yielding the BHET / EG slurry.

[0131] The BHET / EG slurry was press-pressed using a filter press manufactured by Nippon Filtration Equipment Co., Ltd. to separate BHET from EG. The separated BHET contained 35% by mass of EG relative to the weight of the recovered filter cake after pressing. The filter cake after this EG separation was then washed with water using a Nutchi filter while being sprayed with twice its mass of 25°C pure water.

[0132] After solid-liquid separation, BHET was dissolved in 20 times its mass of hot water (90°C), and then 0.25 times its mass of activated carbon was added and stirred for 1 hour. Then, a Nooch filtration was performed, and the aqueous solution with the activated carbon removed was cooled to precipitate BHET. This was followed by another Nooch filtration to recover BHET.

[0133] The recovered BHET was dried at 50°C for 8 hours using a vacuum dryer to obtain dried BHET. The obtained BHET was white, and no foreign matter was observed to be mixed in.

[0134] Then, the obtained dried BHET254 parts by mass, along with 0.007 parts by mass of phosphorus-based stabilizer and 0.07 parts by mass of antimony trioxide as a repolymerization catalyst, were loaded into a reaction vessel under a nitrogen atmosphere and atmospheric pressure. Next, the temperature inside the reactor was set to 285°C, and the pressure was reduced in stages: 10 minutes at atmospheric pressure, 10 minutes at 4 kPa, and then 40 minutes at 0.4 kPa. While distilling off ethylene glycol and other substances produced during the reaction, the polycondensation reaction continued. The reactants in the system were then continuously extruded from the discharge section into filaments, cooled, and cut to obtain granular particles of approximately 3 mm. The quality of the final PET polymer is shown in Table 1. A polymer with a melting point equivalent to that of the initially recycled fiber, low yellowness (YI), and high whiteness (W) was obtained.

[0135] [Table 1]

[0136]

[0137] [Comparative Example 1]

[0138] In the polyester recycling process of Example 1, during the stirring process at atmospheric pressure in a separable flask for 4 hours, the internal temperature was set from 160°C to 120°C. Otherwise, the same treatment as in Example 1 was performed. After 4 hours, the morphology of the sample did not change, and no dissolution of PU in EG containing manganese acetate catalyst was observed.

[0139] [Comparative Example 2]

[0140] In the polyester recovery process of Example 1, during the stirring process at atmospheric pressure in a separable flask for 4 hours, the internal temperature was set from 160°C to 198°C. Otherwise, the same treatment as in Example 1 was performed. After 4 hours, the total amount of sample containing PET and PU dissolved, and polyester could not be recovered by filtration.

[0141] [Comparative Example 3]

[0142] In the polyester recovery method of Example 1, during the step of stirring at atmospheric pressure in a separable flask for 4 hours, manganese acetate was not added as a catalyst and only EG was used for treatment. Otherwise, the same treatment as in Example 1 was performed. After 4 hours, the morphology of the sample did not change and no dissolution of PU in EG was observed.

[0143] [Comparative Example 4]

[0144] In the polyester recovery method of Example 1, during the step of stirring at atmospheric pressure for 4 hours in a separable flask, the manganese acetate catalyst was changed to potassium carbonate. Otherwise, the same treatment as in Example 1 was performed. After 4 hours, the morphology of the sample did not change, and no dissolution of PU in EG was observed.

[0145] [Example 2]

[0146] In the polyester recovery method of Example 1, during the step of stirring at atmospheric pressure for 4 hours in a separable flask, the manganese acetate catalyst was changed to zinc acetate. Otherwise, the same treatment as in Example 1 was performed. Based on the IR measurement of the recovered material after treatment, no absorption of wavelengths determined to be from PU was observed, and an absorption spectrum consisting only of PET was observed, confirming that PU was almost completely removed.

[0147] The melting point and other physical properties of the recycled polyester samples are shown in Table 1.

[0148] Then, PET pellets are obtained using the method described in the polyester recycling process. The quality of the final PET polymer is shown in Table 1.

[0149] [Example 3]

[0150] In the polyester recovery method of Example 1, during the stirring process in a separable flask at atmospheric pressure, the manganese acetate catalyst was changed to cobalt acetate and the stirring time was changed from 4 hours to 6 hours. Otherwise, the same treatment as in Example 1 was performed. Based on the IR measurement of the recovered material after treatment, no absorption of wavelengths determined to be from PU was observed, and an absorption spectrum consisting only of PET was observed, confirming that PU was almost completely removed.

[0151] The melting point and other physical properties of the recovered samples are shown in Table 1.

[0152] Then, PET pellets are obtained using the method described in the polyester recycling process. The quality of the final PET polymer is shown in Table 1.

[0153] [Example 4]

[0154] In the polyester recovery method of Example 1, during the stirring process in the separable flask at atmospheric pressure, EG was replaced with diethylene glycol and the internal temperature was changed from 160°C to 180°C. Otherwise, the same treatment as in Example 1 was performed. Based on the IR measurement of the recovered material after treatment, no absorption of wavelengths determined to be from PU was observed. Instead, an absorption spectrum consisting only of PET was observed, confirming that PU was almost completely removed.

[0155] The melting point and other physical properties of the recovered samples are shown in Table 1.

[0156] Then, PET pellets are obtained using the method described in the polyester recycling process. The quality of the final PET polymer is shown in Table 1.

[0157] [Example 5]

[0158] In the polyester recovery method of Example 1, during the stirring process in a separable flask at atmospheric pressure, EG was replaced with 1,3-propanediol and the internal temperature was changed from 160°C to 180°C. Otherwise, the same treatment as in Example 1 was performed. Based on the IR measurement of the recovered material after treatment, no absorption of wavelengths determined to be from PU was observed, and an absorption spectrum consisting only of PET was observed, confirming that PU was almost completely removed.

[0159] The melting point and other physical properties of the recovered samples are shown in Table 1.

[0160] Then, PET pellets are obtained using the method described in the polyester recycling process. The quality of the final PET polymer is shown in Table 1.

[0161] [Example 6]

[0162] In the polyester recycling method of Example 1, artificial leather 1 is replaced with artificial leather 2. Otherwise, the processing and recycling are carried out in the same manner as in Example 1 to obtain PET pellets.

[0163] Artificial leather 2 is the leather described below.

[0164] With a unit area weight of 560g / m² for PET staple fiber 2 Using needle-punched nonwoven fabric as the base material, the PU was changed to a polycarbonate-based wet PU and impregnated and coated to produce a product with a unit area weight of 882 g / m². 2 The substrate is a wet-process PU impregnation-coated substrate with a resin / fiber ratio (R / F) of 37 / 63. Both the PU in the impregnated substrate and the PU in the coating have a porous structure.

[0165] Furthermore, similar to artificial leather 1, a cross-linked adhesive PU layer and an outer PU layer are laminated onto the substrate through a lamination process to produce artificial leather with silver. The outer PU layer is changed from a polyether polyester-based dry PU to a polycarbonate-based dry PU.

[0166] The resulting artificial leather 2 is composed of 57% by mass of PET nonwoven fabric and a portion of chemically cross-linked PU with a thickness of 2.2 mm and a total unit area weight of 980 g / m². 2 Artificial leather.

[0167] The melting point and other physical properties of the recycled polyester samples are shown in Table 1, and the IR waveforms are shown in Table 2. Figure 2 .

[0168] The quality of the final PET polymer is shown in Table 1.

[0169] [Example 7]

[0170] (Polyester recycling process)

[0171] A 400g sample was prepared, consisting of 360g of PET fiber fabric and 40g of chemically cross-linked soft polyurethane foam (hereinafter referred to as "blown PU"). The PET fabric has a basis weight of 44g / m². 2 PET fabric with IV of 0.60 dl / g, Tg = 70℃, and Tm = 255℃. Foamed PU uses toluene diisocyanate (TDI) as monomer, polypropylene triol, and trimethylolpropane as monomers, polymerized via polyurethane polymerization, with a thickness of 5 mm and a density of 0.055 g / cm³. 3 Foamed PU.

[0172] 400g of the sample was added to a 5-liter separable flask. Next, 2000g of EG was prepared, and 1.5g of manganese acetate (0.375% by mass relative to the sample) was dissolved and added to the separable flask. Then, the separable flask was heated to an internal temperature of 160°C using a heating mantle, and stirred at atmospheric pressure for 4 hours.

[0173] In a separable flask, the foamed PU dissolved in EG, and the EG gradually changed color. After 4 hours, the foamed PU was completely dissolved in EG, and it was confirmed by visual inspection that no solid foamed PU remained.

[0174] After 4 hours, stirring was stopped, and the fibrous solid residue was removed from the separable flask and pressed to remove excess treatment liquid. Coloration was observed in the treatment liquid, and the mass of the slightly decolorized solid residue after pressing was 652 g.

[0175] Then, the residue was washed with water to remove the treatment liquid remaining in the solid residue. It was then dried in a vacuum dryer at 80°C for 8 hours to recover the white fibrous residue. The mass of the recovered material was 344g. IR spectroscopy of the recovered material showed no absorption at wavelengths identified as originating from PU, exhibiting an absorption spectrum consisting only of PET, thus confirming that PU was almost completely removed.

[0176] The melting point and other physical properties of the recycled polyester samples are shown in Table 1, and the IR waveforms are shown in Table 2. Figure 3 .

[0177] (Polyester recycling process)

[0178] PET granules were obtained in the same manner as in Example 1. The quality of the final polyethylene terephthalate polymer is shown in Table 1.

[0179] [Example 8]

[0180] In the polyester recycling method of Example 7, the step of stirring at atmospheric pressure in a separable flask for 4 hours was performed, except that EG was replaced with benzyl alcohol (hereinafter referred to as "BA"), the internal temperature was changed from 160°C to 130°C, and the processing time was changed from 4 hours to 6 hours. Otherwise, the same treatment as in Example 7 was performed.

[0181] Similar to Example 7, based on the IR measurement of the treated recycled material, no absorption of wavelengths judged to be from foamed PU was observed, and an absorption spectrum consisting only of PET was observed, confirming that the foamed PU was almost completely removed.

[0182] The melting point and other physical properties of the recycled polyester samples are shown in Table 1.

[0183] Then, PET pellets are obtained using the method described in the polyester recycling process. The quality of the final PET polymer is shown in Table 1.

[0184] [Comparative Example 5]

[0185] In the polyester recycling method of Example 8, during the step of stirring at atmospheric pressure in a separable flask for 6 hours, manganese acetate was not added as a catalyst and only BA was used for treatment. Otherwise, the same treatment as in Example 7 was performed. After 6 hours, the morphology of the sample did not change and no foamed PU was observed to dissolve in BA.

[0186] [Example 9]

[0187] Prepare 400g of fabric samples printed with polyurethane resin on PET fibers.

[0188] The area weight of PET fabric is 44 g / m². 2IV is 0.60 dl / g, Tg = 70℃, Tm = 255℃. The printed portion uses a dry adhesive composed of polybutadiene glycol (PTMG), isophorone diisocyanate, 1,6-hexanediamine, and triethylamine, with polyurethane as the main component, and is coated with 56 g / m... 2 It is mainly composed of cross-linked PU resin.

[0189] 400g of the sample was added to a 5-liter separable flask. Next, 2000g of EG was prepared, and 1.5g of manganese acetate (0.375% by mass relative to the sample) was dissolved and added to the separable flask. Then, the separable flask was heated to an internal temperature of 160°C using a heating mantle, and stirred at atmospheric pressure for 4 hours.

[0190] In a separable flask, it was confirmed that the printed portion dissolved in EG, and the contained pigment gradually diffused into the EG. After 4 hours, stirring was stopped, and a cloth-like solid residue was removed from the separable flask and pressed to remove excess treatment liquid. Coloration, which was considered to be due to the influence of pigment and decomposition products, was observed in the treatment liquid. The mass of the pressed solid residue was 296 g.

[0191] Then, the residue was washed with water to remove the treatment liquid remaining in the solid residue, and dried under vacuum at 80°C for 8 hours in a vacuum dryer to recover the fabric-like residue. The mass of the recovered material after treatment was 168g.

[0192] The melting point and other physical properties of the recycled polyester samples are shown in Table 1, and the IR waveforms are shown in Table 2. Figure 4 .

[0193] (Polyester recycling process)

[0194] PET granules were obtained in the same manner as in Example 1. The quality of the final polyethylene terephthalate polymer is shown in Table 1.

[0195] [Example 10]

[0196] In the polyester recycling method of Example 1, artificial leather 1 was replaced with artificial leather 3, ethylene glycol was replaced with benzyl alcohol, and the processing temperature was changed from 160°C to 130°C. Otherwise, the treatment was carried out in the same manner as in Example 1. Visual inspection confirmed that the sample after acetone washing was a white fibrous residue and that the PU component had been removed.

[0197] Artificial leather 3 is the following type of leather.

[0198] Similar to the artificial leather 1 in Example 1, the basis weight of PET staple fiber is 220 g / m². 2Using needle-punched nonwoven fabric as the base material, impregnating and coating with PU, a product with a unit area weight of 412g / m² is produced. 2 The wet PU impregnation coating substrate has a resin / fiber ratio (R / F) of 47 / 53.

[0199] In this process, gravure coating of PU replaces the lamination of the PU layer using a crosslinked adhesive in the case of artificial leather 1. Specifically, a coating solution is prepared by mixing polyether ester-based polyurethane (25% solids concentration) / methyl ethyl ketone / dimethylformamide in a ratio of 100 / 40 / 160. This coating solution is then applied three times to the surface of a wet PU impregnation coating substrate using a #110 gravure roller and dried. The total PU coating amount using gravure coating, based on solids, is 4 g / m³. 2 .

[0200] The resulting artificial leather 3 is composed of 52% by mass of PET nonwoven fabric and all PU used is non-crosslinked, with a total unit area weight of 416 g / m². 2 Artificial leather.

[0201] Industrial availability

[0202] By means of the present invention, a method for recovering polyester from a structure containing polyurethane resin and made primarily of polyester fibers as a substrate, and a method for manufacturing recycled polyester obtained by depolymerizing and repolymerizing the polyester recovered from the structure, it is possible to separate and recover polyester from structures such as artificial leather that have been treated by incineration or landfill due to difficulty in separation and removal, and further perform chemical regeneration.

Claims

1. A method for recycling polyester, characterized in that, The polyurethane resin-containing structure, which is based on a fiber mainly composed of polyester, is treated in a lower alcohol at a temperature of 125°C to 185°C in the presence of a catalyst of a first transition metal acetate to remove the polyurethane resin.

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

3. The polyester recycling method according to claim 1, wherein, Polyurethane resin is a chemically cross-linked polyurethane.

4. The method for recycling polyester according to claim 1, wherein, Fibers made of polyester are composed of polyesters with alkylene terephthalate or alkylene naphthalate as the main repeating unit.

5. The polyester recycling method according to claim 1, wherein, Lower alcohols are selected from 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, glycerol, and benzyl alcohol.

6. The method for recycling polyester according to claim 1, wherein, The first transition metal acetates are manganese acetate, zinc acetate, or cobalt acetate.

7. The method for recycling polyester according to claim 1, wherein, After treatment, further cleaning is carried out using water or organic solvents.

8. A method for manufacturing recycled polyester, characterized in that, The polyester obtained by the method described in any one of claims 1 to 7 is further depolymerized into an aromatic dicarboxylic acid bis(hydroxyalkyl) ester, and then the aromatic dicarboxylic acid bis(hydroxyalkyl) ester is repolymerized.

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