Method for producing recycled polyester and method for producing polyester composite material

Abstract

Provided is a production method with which it is possible to produce a recycled polyester having excellent color tone and mechanical strength by a method with little environmental burden. A method for producing a recycled polyester, comprising: a step (A) in which a solvent (X1) containing a phenol-based solvent and / or a chlorine-based organic solvent and one or more solvents (Y1) selected from the group consisting of an aromatic hydrocarbon-based solvent, an aliphatic hydrocarbon-based solvent, a ketone-based solvent, an aldehyde-based solvent, an alcohol-based solvent, an ether-based solvent, and water are mixed to form a cleaning solvent; cleaning the polyester (PEs) composite material; a step (B) for dissolving the PEs in the cleaned PEs composite material in a dissolving solvent containing a solvent (X2) containing a phenol-based solvent and / or a chlorine-based organic solvent, and performing solid-liquid separation to obtain a liquid component (L); a step (C) for obtaining PEs from the liquid component (L) using a poor solvent (PS) having a boiling point of 130 DEG C or less; and a step (D) in which the PEs are dried.

Description

Technical Field

[0001] This invention relates to a method for manufacturing recycled polyester and a method for manufacturing polyester composite materials. Background Technology

[0002] Polyesters (hereinafter, sometimes referred to as "PEs") possess excellent mechanical strength, heat resistance, chemical resistance, and moisture resistance. They are also easy and inexpensive to mold, making them suitable for various applications, including fibers, films, and resin molded products. However, their low cost leads to mass production and consumption, resulting in a short average product lifespan and significant waste disposal through incineration and landfill. Furthermore, their petroleum-based origin poses a significant environmental burden.

[0003] Therefore, there is a need to establish a method for recycling polyester. As methods for polyester recycling, chemical recycling (e.g., Patent Document 1) and material recycling (e.g., Patent Documents 2 and 3) have been proposed. In recent years, the recycling of PET bottles has continued to develop, and products using recycled polyester have also emerged.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2002-60369

[0007] Patent Document 2: Japanese Patent Application Publication No. 11-60795

[0008] Patent Document 3: Japanese Patent No. 6708642 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] However, in recent years, advancements in bottle-to-bottle horizontal recycling technology have made it possible to remanufacture PET bottles from used PET bottles, making it difficult to use used PET bottles as recycled raw materials for other polyester products. Therefore, there is a need to establish technologies for obtaining recycled polyester from polyester composite materials such as clothing fabrics, household goods, automotive interior parts, injection-molded products mixed with other resins, and extruded products.

[0011] On the other hand, the chemical recycling method described in Patent Document 1 can remove impurities and other resins, thus obtaining recycled polyester of the same quality as the original petroleum-derived product. However, chemical recycling involves many processes, and the depolymerization, transesterification, and repolymerization of monomers require a large amount of heat energy, thus posing challenges such as high environmental impact and increased manufacturing costs.

[0012] Material recycling is inexpensive, but on the other hand, if the recycled raw materials contain various impurities, the resulting recycled polyester will also contain impurities, thus deteriorating its quality. For example, in the case of fiber products, since fiber products dyed in various colors may be mixed in, coloring components will be mixed into the recycled polyester, making it highly likely that black recycled polyester will be obtained, and it becomes very difficult to color fiber products made from it to the desired color. In addition, in the case of polyester composites, not only polyester but also other resins are included, making it difficult to recover only polyester through material recycling.

[0013] Patent documents 2 and 3 report the following method: dissolving polyester, separating other fiber raw materials and impurities, and obtaining recycled polyester by using the polyester precipitation solvent.

[0014] However, in Patent Document 2, hexafluoroisopropanol (HFIP) is recommended as a solvent for dissolving polyester. But HFIP is corrosive and therefore unsuitable for industrial application; it is also volatile and highly toxic, thus it cannot be considered the optimal solvent. Furthermore, this method does not adequately address the dyes used to color the fibers or the impurities contained within the fibers. In particular, it is argued that the color tone of recycled polyester deteriorates because a decolorization process is not performed on the dyed fiber products.

[0015] In fact, as shown in Comparative Example 1 described later, the inventors dissolved the polyester fiber product and recovered the recycled polyester without performing a decolorization operation, but were unable to sufficiently remove the coloring components from the fiber.

[0016] Patent document 3 reports the following method: Before dissolving the polyester fiber product, decolorization is performed using the same solvent at a temperature higher than the decolorization temperature to dissolve the polyester, and the solvent is removed by distillation. Cyclic amides were chosen as the dissolving solvent; however, due to the high boiling point of cyclic amides, there is a high possibility of residual cyclic amides in the recycled polyester, and the distillation operation requires a large amount of energy, making it not an optimal process. Furthermore, when removing the solvent from the recycled polyester, the recycled polyester is distilled at high temperatures, which may cause depolymerization of the recycled polyester.

[0017] In fact, as shown in Comparative Example 2 described later, the inventors obtained recycled polyester by the same method as in Patent Document 3, but were unable to remove the coloring components sufficiently. In addition, after long-term drying under high temperature and reduced pressure, a large amount of solvent remained, and the molecular weight was reduced due to the heat load.

[0018] In this situation, there is a need to recover recycled polyester with excellent color and mechanical strength from polyester composites containing polyester, and to reprocess it into polyester composites. The present invention has been made in view of the above situation, and its object is to provide a method for manufacturing recycled polyester that does not require the large number of processes and thermal energy involved in chemical recycling, such as depolymerization, transesterification, and repolymerization, and can obtain recycled polyester with excellent color and mechanical strength in a manner with low environmental impact. Furthermore, the object is to provide a method for manufacturing polyester composites using the obtained recycled polyester to manufacture polyester composites.

[0019] Methods for solving problems

[0020] In order to solve the above-mentioned problems, the inventors conducted in-depth research and found that by cleaning the polyester composite material with a specific cleaning solvent to remove impurities such as colorants and surfactants, the material is dissolved in a solvent that can dissolve polyester. After removing impurities such as fibers, resins, and metals other than polyester by filtration, the material is then brought into contact with a solvent insoluble in polyester, causing the polyester to precipitate. In this way, it is possible to recover recycled polyester with excellent color, mechanical strength, and narrow molecular weight distribution without decomposing it into monomers. Thus, the following invention of a method for manufacturing recycled polyester was completed.

[0021] Furthermore, the inventors discovered that by dissolving the polyester in a polyester composite material in a specific solvent and treating it with a coagulant or a combination of a coagulant and a filter aid to perform solid-liquid separation and precipitate the polyester, it is possible to recover recycled polyester with excellent color, mechanical strength, and narrow molecular weight distribution without decomposing it into monomers. Thus, the following invention of a method for manufacturing recycled polyester was completed.

[0022] That is, the present invention relates to the following invention.

[0023] [1] A method for manufacturing recycled polyester, wherein recycled polyester is manufactured from polyester composite material, the method comprising the following steps (A) to (D),

[0024] Step (A): A step of cleaning polyester composite material using a cleaning solvent (X1) which is a mixture of a solvent (X1) containing phenolic solvents and / or chlorine organic solvents and one or more solvents (Y1) selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, ketone solvents, aldehyde solvents, alcohol solvents, ether solvents and water.

[0025] Step (B): The cleaned polyester composite material is mixed with a solvent (X2) containing a phenolic solvent and / or a chlorine-based organic solvent to obtain a solution of polyester solvent in the polyester composite material. Then, the solution containing the polyester is subjected to solid-liquid separation to obtain a liquid component (L) containing polyester.

[0026] Step (C): The above liquid component (L) is mixed with a poor solvent (PS) with a boiling point below 130°C to precipitate polyester, thereby obtaining a slurry. The slurry is then subjected to solid-liquid separation to obtain solid polyester.

[0027] Process (D): The process of drying the above solid polyester to obtain recycled polyester.

[0028] [2] According to the method for manufacturing recycled polyester described in [1] above, in step (B), the polyester in the above polyester composite material is dissolved in the above dissolving solvent and then mixed with a nonpolar solvent with a dielectric constant of 1 or more and 3 or less to obtain a solution containing the above polyester.

[0029] [3] In the method for manufacturing recycled polyester according to [1] or [2] above, the polyester is one or more selected from the group consisting of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate and copolymers thereof, and copolymers thereof with other resins.

[0030] [4] The method for manufacturing recycled polyester according to any one of [1] to [3] above, wherein the polyester composite material comprises polyester and other components, wherein the other components are selected from one or more of the group consisting of low molecular weight organic compounds, metal compounds, inorganic microparticles, fibers other than polyester and resins other than polyester, and wherein the recycled polyester is polyester from which the other components have been removed.

[0031] [5] According to the method for manufacturing recycled polyester described in [4] above, the low molecular weight organic compound comprises one or more selected from the group consisting of colorant, surfactant, antistatic agent and flame retardant; the metal compound comprises matting agent and / or ultraviolet absorber; the inorganic microparticles comprise pigment; the fiber other than polyester comprises one or more selected from the group consisting of natural fiber, acrylic fiber, rayon fiber, polyurethane fiber, nylon fiber, polyethylene fiber, polypropylene fiber and glass fiber; and the resin other than polyester comprises one or more selected from the group consisting of polyethylene resin, polypropylene resin, polyurethane resin, polystyrene resin, nylon resin, polyvinyl chloride resin and acrylic resin.

[0032] [6] In the method for manufacturing the recycled polyester according to any one of [1] to [5] above, the polyester composite material is a polyester-containing fiber.

[0033] [7] According to the method for manufacturing recycled polyester described in [6] above, the polyester-containing fiber contains at least a colorant, titanium oxide and / or fibers other than polyester, in the above step (A), the polyester-containing fiber is decolored, and in the above step (B), titanium oxide and / or fibers other than polyester are removed.

[0034] [8] In the method for manufacturing the recycled polyester according to any one of [1] to [7] above, the pH of the cleaning solvent is less than 13.0.

[0035] [9] In the method for manufacturing recycled polyester according to any one of [1] to [8] above, the cleaning temperature of the above step (A) is 30°C or higher and 150°C or lower, and the dissolution temperature of the above step (B) is 30°C or higher and 150°C or lower.

[0036]

[10] In the method for manufacturing the recycled polyester according to any one of [1] to [9] above, the boiling point of the solvent (Y1) is below 250°C.

[0037]

[11] In the method for manufacturing recycled polyester according to any one of [1] to

[10] above, the melting temperature of the above step (B) is a higher temperature than the cleaning temperature of the above step (A).

[0038]

[12] In the method for manufacturing recycled polyester according to any one of [1] to

[11] above, the content of solvent (X2) in the dissolving solvent of step (B) is greater than the content of solvent (X1) in the cleaning solvent of step (A).

[0039]

[13] In the method for manufacturing recycled polyester according to any one of [1] to

[12] above, the undesirable solvent (PS) is one or more selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, ketone solvents, aldehyde solvents, alcohol solvents, ether solvents and water.

[0040]

[14] In the method for manufacturing the recycled polyester according to any one of [1] to

[13] above, the solvent (Y1) is one or more selected from the group consisting of toluene, xylene, heptane, hexane, acetone, methanol, ethanol, ethylene glycol, propylene glycol and water, and the undesirable solvent (PS) is one or more selected from the group consisting of acetone, toluene, methanol, ethanol and water.

[0041]

[15] In the method for manufacturing the recycled polyester according to any one of [1] to

[14] above, the Ti content in the polyester composite material is 500 ppm or more, and the Ti content in the recycled polyester is 100 ppm or less.

[0042]

[16] In the method for manufacturing the recycled polyester according to any one of [1] to

[15] above, the N content in the polyester composite material is 400 ppm or more, and the N content in the recycled polyester is 80 ppm or less.

[0043]

[17] In the method for manufacturing recycled polyester according to any one of [1] to

[16] above, before performing the solid-liquid separation in step (B) above, the solution in which the polyester is dissolved is brought into contact with a filter aid.

[0044]

[18] In the method for manufacturing recycled polyester according to any one of [1] to

[17] above, before performing the solid-liquid separation in the above step (B), the solution in which the polyester is dissolved is brought into contact with a coagulant.

[0045]

[19] A method for manufacturing a recycled polyester, wherein the recycled polyester is manufactured from a polyester composite material, the method comprising the following steps (B2), (Z2), (C2), and (D2);

[0046] Step (B2): The process of mixing the above polyester composite material with a solvent (X2) containing a phenolic solvent and / or a chlorine-based organic solvent to obtain a solution in which the polyester in the above polyester composite material is dissolved.

[0047] Process (Z2): After contacting the solution containing the above-mentioned polyester with a coagulant, solid-liquid separation is performed to obtain a liquid component (L2) containing polyester.

[0048] Step (C2): The above liquid component (L2) is mixed with a poor solvent (PS) with a boiling point below 130°C to precipitate polyester and obtain a slurry. The slurry is then subjected to solid-liquid separation to obtain solid polyester.

[0049] Process (D2): The process of drying the above solid polyester to obtain recycled polyester.

[0050]

[20] According to the method for manufacturing recycled polyester described above

[19] , before performing the solid-liquid separation in the above step (Z2), the solution containing the polyester is brought into contact with a filter aid.

[0051]

[21] In the method for manufacturing recycled polyester according to any one of

[18] to

[20] above, the coagulant is one or more selected from the group consisting of inorganic salts other than alkali metals and alkaline earth metals and polymer compounds.

[0052]

[22] In the method of manufacturing the recycled polyester according to any one of

[18] to

[21] above, the coagulant comprises an inorganic salt other than alkali metals and alkaline earth metals.

[0053]

[23] In the method for manufacturing recycled polyester described above

[22] , the inorganic salt other than the alkali metal and alkaline earth metal is selected from one or more of the group consisting of ferric chloride (III), ferrous sulfate (II), ferric sulfate (III), aluminum sulfate and aluminum chloride.

[0054]

[24] According to the method for manufacturing recycled polyester described in

[21] above, after contacting the solution in which the polyester is dissolved with the coagulant containing inorganic salts other than the alkali metal and alkaline earth metal, the solution is then contacted with the coagulant containing the polymer compound.

[0055]

[25] In the method for manufacturing recycled polyester according to

[21] or

[24] above, the polymer compound is one or more selected from the group consisting of polyacrylamide and polyethylene oxide.

[0056]

[26] In the method for manufacturing recycled polyester according to

[17] ,

[18] or

[20] above, the filter aid is selected from one or more of the group consisting of activated carbon, activated clay, diatomaceous earth, silica gel, synthetic adsorbent, bentonite, alumina and zeolite.

[0057]

[27] A method for manufacturing a polyester composite material, comprising: a step of obtaining recycled polyester by any one of the above-described [1] to

[26] methods for manufacturing recycled polyester; and a step of manufacturing a polyester composite material using the obtained recycled polyester.

[0058] Invention Effects

[0059] According to the present invention, a method for manufacturing recycled polyester is provided, which does not require a large number of processes and heat energy, and can obtain recycled polyester with excellent color and mechanical strength with low environmental impact. Attached Figure Description

[0060] [ Figure 1 [This is a flowchart of an example of a method for manufacturing the first recycled polyester (recycled PEs) of the present invention.]

[0061] [ Figure 2 [ ] is a flowchart illustrating step (B) of the method for manufacturing the first recycled polyester of the present invention.

[0062] [ Figure 3 [This is a flowchart illustrating an example of a method for manufacturing the first recycled polyester of the present invention when using polyester-containing fibers (PE fibers) as a polyester composite material (PE composite material).] Detailed Implementation

[0063] The embodiments of the present invention are described in detail below. However, the description of the constituent elements described below is only one example (representative example) of the embodiments of the present invention, and the present invention is not limited to the following content as long as its spirit is not changed. In addition, when expressions such as "~" are used in this specification, they are used to express the numerical values ​​or physical property values ​​that include the values ​​before and after them.

[0064] <Methods for manufacturing recycled polyester>

[0065] (Method for manufacturing first recycled polyester)

[0066] The method for manufacturing the first recycled polyester of the present invention is a method for manufacturing recycled polyester from polyester composite materials (hereinafter, sometimes referred to as "the method for manufacturing the first recycled polyester of the present invention"), comprising the following steps (A) to (D):

[0067] Step (A): A step of cleaning polyester composite material using a cleaning solvent (X1) which is a mixture of a solvent (X1) containing phenolic solvent and / or chlorine organic solvent and one or more solvents (Y1) selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, ketone solvents, aldehyde solvents, alcohol solvents, ether solvents and water.

[0068] Step (B): The above-mentioned polyester composite material after cleaning is mixed with a solvent (X2) containing a phenolic solvent and / or a chlorine-based organic solvent to obtain a solution in which the polyester in the above-mentioned polyester composite material is dissolved (hereinafter, sometimes referred to as "PEs solution"). The above-mentioned PEs solution is then subjected to solid-liquid separation to obtain a liquid component (L) containing dissolved polyester.

[0069] Step (C): The above liquid component (L) is mixed with a poor solvent (PS) with a boiling point below 130°C to precipitate polyester, thereby obtaining a slurry. The slurry is then subjected to solid-liquid separation to obtain solid polyester.

[0070] Process (D): The process of drying the above solid polyester to obtain recycled polyester.

[0071] One feature of the method for manufacturing the first recycled polyester of the present invention is that impurities are removed in multiple steps (i.e., steps (A), (B), and (C)) by utilizing differences in solubility. The inventors have discovered that by washing the polyester composite material with a specific cleaning solvent before dissolving the polyester in the composite material (step (A)), impurities such as low-molecular-weight organic compounds (colorants, surfactants, etc.) that may be present in the polyester composite material can be dissolved and removed. Furthermore, it has been found that after washing the polyester composite material with the specific cleaning solvent, dissolving and filtering the polyester (step (B)) removes fiber, resin, and metal impurities other than polyester. Then, by reprecipitation (step (C)), the polyester is recovered, thus enabling the recovery of recycled polyester with excellent color and mechanical strength without requiring a large number of steps and thermal energy as in chemical recycling. By employing the method for manufacturing the first recycled polyester of the present invention, recycled polyester can be manufactured inexpensively and with low energy without breaking down the polyester into monomers.

[0072] (Method for manufacturing second recycled polyester)

[0073] The method for manufacturing the second recycled polyester of the present invention is a method for manufacturing recycled polyester from polyester composite materials (hereinafter, sometimes referred to as "the method for manufacturing the second recycled polyester of the present invention"), comprising the following steps (B2), (Z2), (C2), and (D2).

[0074] Step (B2): The process of mixing the above polyester composite material with a solvent (X2) containing a phenolic solvent and / or a chlorine-based organic solvent to obtain a solution (PEs solution) in which the polyester in the above polyester composite material is dissolved.

[0075] Process (Z2): After the above PEs solution comes into contact with the coagulant, solid-liquid separation is performed to obtain a liquid component (L2) containing dissolved polyester.

[0076] Step (C2): The above liquid component (L2) is mixed with a poor solvent (PS) with a boiling point below 130°C to precipitate polyester and obtain a slurry. The slurry is then subjected to solid-liquid separation to obtain solid polyester.

[0077] Process (D2): The process of drying the above solid polyester to obtain recycled polyester.

[0078] One feature of the manufacturing method of the second recycled polyester of the present invention is that impurity removal is performed in multiple steps (i.e., steps (B2), (Z2), and (C2)). The inventors conducted research and found that by dissolving the polyester in the polyester composite material in a specific solvent, components insoluble in the solvent (fibers other than polyester, resins, metallic impurities, inorganic particles, etc.) in the polyester composite material can be separated from the polyester. However, although small inorganic particles are insoluble in the solvent, they are not captured as solids during solid-liquid separation and tend to mix into the liquid. Furthermore, it was found that by treating the PEs solution with a coagulant before solid-liquid separation, small inorganic particles can be adsorbed and aggregated, enabling the separation of small inorganic particles during solid-liquid separation. Therefore, in the manufacturing method of the second recycled polyester of the present invention, solid-liquid separation is performed after treating the PEs solution with a coagulant in step (Z2). Furthermore, by recovering the polyester through reprecipitation (step (C)), impurities soluble in unsuitable solvents (PS) can be separated from the polyester.

[0079] In addition, in this application, "the method for manufacturing the first recycled polyester of the present invention" and "the method for manufacturing the second recycled polyester of the present invention" are sometimes described together as "the method for manufacturing the recycled polyester of the present invention".

[0080] <Polyester Composite Materials (PE Composites)>

[0081] The following describes the polyester composite material common to the "method of manufacturing the first recycled polyester of the present invention" and the "method of manufacturing the second recycled polyester of the present invention".

[0082] The polyester composite material used in this invention is waste material containing polyester and other components besides polyester, and is a pre-consumer material or a post-consumer material.

[0083] (Polyester (PEs))

[0084] There is no limitation on the type of polyester contained in polyester composites. Polyesters are polymers or copolymers obtained by dehydrating and condensing dicarboxylic acids with diols to form ester bonds. Polyesters can be homopolymers or copolymers. Examples of polyesters include polyethylene terephthalate (PET), polypropylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and copolymers thereof. Additionally, polyesters can also be copolymers with other resins.

[0085] (Other components besides polyester)

[0086] Other components besides polyester contained in the polyester composite material are impurities that are removed in any step of the method for manufacturing the recycled polyester of the present invention.

[0087] Other components besides polyester include compounds used as additives in the manufacture of various products, fibers other than polyester, resins other than polyester, etc. For example, as a polyester composite material, a composite material containing polyester and one or more other components selected from the group consisting of low-molecular-weight organic compounds, metal compounds, inorganic microparticles, fibers other than polyester, and resins other than polyester can be used. By means of the method for manufacturing recycled polyester of the present invention, other components can be removed, and as a recycled polyester, polyester from which other components have been removed can be obtained. Examples of low-molecular-weight organic compounds include compounds used as colorants, antistatic agents, flame retardants, surfactants, antioxidants, lightfastness agents, etc., and typically have a molecular weight of 2000 or less. Examples of metal compounds include metal oxides and metal salts used as matting agents, ultraviolet absorbers, etc. Examples of inorganic microparticles include pigments such as carbon black. Examples of fibers other than polyester include natural fibers, acrylic fibers, rayon fibers, polyurethane fibers, nylon fibers, polyethylene fibers, polypropylene fibers, acetate fibers, glass fibers, carbon fibers, etc. Examples of resins other than polyester include polyethylene resin, polypropylene resin, polyurethane resin, polystyrene resin, nylon resin, polyvinyl chloride resin, and acrylic resin.

[0088] In the manufacturing method of the first recycled polyester of the present invention, colorants (dyes) can be removed efficiently. Therefore, the manufacturing method of the first recycled polyester of the present invention is more effective for materials that contain at least colorants as components other than polyester.

[0089] Furthermore, the method for manufacturing the second recycled polyester of the present invention can efficiently remove pigments. Therefore, the method for manufacturing the second recycled polyester of the present invention is more effective for materials that contain at least pigments as components other than polyester.

[0090] Polyester composite materials are not particularly limited in form and can be made from fibers, resin molded products, laminates, etc. For example, polyester-containing fibers are composite materials that include natural fibers (cotton, linen, silk, etc.), synthetic fibers (acrylic, rayon, etc.), and various additives (dyes, pigments, titanium dioxide, etc.) in addition to polyester fibers. Furthermore, polyester-containing injection molded products and polyester-containing laminates are composite materials that include resins other than polyester (polypropylene, polyethylene, polyurethane, acrylic, etc.), glass fibers, and various additives in addition to polyester. Additionally, products that incorporate metal loading, dyeing, or surface treatments using organic materials to improve the functionality and design of polyester composite materials are also considered polyester composite materials.

[0091] The polyester content in the polyester composite material is not particularly limited, but it is preferable to use a material containing 10% by mass or more of polyester, and more preferably a material containing 30% by mass or more of polyester. Furthermore, one material or two or more materials can be used as the polyester composite material.

[0092] As a specific polyester composite material, it conforms to waste materials such as those used in polyester fiber products such as clothing, bedding, sofas, curtains, carpets, cushioning pads, mats, automotive interior panels, and aircraft interior panels, blow-molded products such as PET bottles, injection-molded products, and extruded products used in electrical / electronic components and automotive parts.

[0093] The polyester composite material used in this invention is preferably a small-scale material. By refining the use of the polyester composite material, the efficiency of impurity removal is improved, and it is also easier to process in subsequent processes. The polyester composite material can be reduced to small-scale (miniaturized) materials by combining one or more methods such as cutting, crushing, breaking, and slicing, depending on its morphology. The small-scale polyester composite material can be cut, crushed, broken, or sliced.

[0094] The small-sized polyester composite material is preferably 5 cm square or less, more preferably 3 cm square or less, and even more preferably 2 cm square or less. If the size of the polyester composite material is too large, the impurity removal in step (A) will not be sufficient, or the polyester dissolution time in step (B) will be longer, so it is not preferred. It should be noted that 5 cm square or less refers to the size that passes through a sieve with a mesh size of 5 cm, 3 cm square or less refers to the size that passes through a sieve with a mesh size of 3 cm, and 2 cm square or less refers to the size that passes through a sieve with a mesh size of 2 cm. The lower limit is not particularly limited, and is above 1 cm square.

[0095] Small-sized polyester composite materials can be used directly in process (A) or process (B2), but impurities adhering to the surface of the polyester composite material can sometimes be easily removed by washing with water. Therefore, the small-sized polyester composite material can be used in process (A) or process (B2) after washing with water. For example, process (A) or process (B2) can be performed after the process of small-sized polyester composite material and the process of washing the small-sized polyester composite material. As a washing method, for example, a method of immersing the small-sized polyester composite material in water and then removing the water can be mentioned. Considering the boiling point of water, the temperature of the water used for washing is usually below 80°C.

[0096] <Method for manufacturing first-cycle polyester>

[0097] The following describes the method for manufacturing the first recycled polyester of the present invention.

[0098] Figure 1This is a flowchart illustrating an example of a method for manufacturing the first recycled polyester (recycled PEs) of the present invention. Figure 2 This is a flowchart illustrating an example of step (B) of the method for manufacturing the first recycled polyester of the present invention. Hereinafter, refer to... Figure 1 , Figure 2 The method for manufacturing the first recycled polyester of the present invention will be described.

[0099] <Process (A)>

[0100] Step (A) is a step of cleaning polyester composite material using a cleaning solvent (X1) which is a mixture of a solvent (X1) containing phenolic solvents and / or chlorine organic solvents and one or more solvents (Y1) selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, ketone solvents, aldehyde solvents, alcohol solvents, ether solvents and water.

[0101] Step (A) removes impurities (hereinafter sometimes referred to as "impurities (α)") in the polyester composite material that are soluble in the cleaning solvent, resulting in a polyester composite material with impurities (α) removed. The impurities (α) removed in step (A) are components soluble in the cleaning solvent used, including one or more low-molecular-weight organic compounds (e.g., low-molecular-weight organic compounds with a molecular weight of less than 2000) selected from the group consisting of colorants, surfactants, antistatic agents, antioxidants, light retardants, and flame retardants, nylon fibers, thermoplastic polyurethane fibers, nylon resins, thermoplastic polyurethane resins, etc.

[0102] Process (A) efficiently removes colorants from impurities (α), significantly reducing the amount of colorants in polyester composites. Currently, azo dyes and other low-molecular-weight organic compounds containing nitrogen (N) are widely used as colorants, and process (A) is particularly effective in removing these nitrogen-containing low-molecular-weight organic compounds.

[0103] Cleaning of polyester composite materials can be carried out by contacting the polyester composite material with a cleaning solvent for a predetermined time followed by solid-liquid separation. The solid component recovered through solid-liquid separation is the polyester composite material from which impurities (α) have been removed.

[0104] The method of contacting the polyester composite material with the cleaning solvent is not particularly limited, but impregnating the polyester composite material in the cleaning solvent is preferred. The order in which the polyester composite material and the cleaning solvent are supplied to the reaction vessel is not particularly limited; the cleaning solvent can be supplied after the polyester composite material, after the cleaning solvent, or simultaneously. Furthermore, during impregnation, the cleaning solvent can be allowed to stand, but it is preferable to dissolve the impurities (α) while stirring.

[0105] (Contact between polyester composite material and cleaning solvent)

[0106] The cleaning temperature (the temperature of the cleaning solvent when the polyester composite material comes into contact with the cleaning solvent) is preferably 30°C or higher. Furthermore, to weaken the intermolecular interactions of the polyester and allow impurities (α) to dissolve from amorphous regions, it is more preferable to dissolve the impurities (α) while heating. Therefore, cleaning is preferably performed at a temperature of 30°C or higher, and more preferably at 60°C or higher. Heating also facilitates the dissolution of impurities (α) adhering to the surface of the polyester composite material. On the other hand, excessive heating may cause the polyester to dissolve; therefore, cleaning is preferably performed at 150°C or lower, and more preferably at 90°C or lower to avoid using excessive heat energy. For example, the cleaning temperature can be set to 30°C to 150°C or 60°C to 90°C.

[0107] The cleaning time (the contact time between the polyester composite material and the cleaning solvent) is set appropriately according to the cleaning temperature, etc., preferably 5 minutes or more, more preferably 30 minutes or more, preferably within 2 hours, and more preferably within 1 hour. For example, the cleaning time can be set to 5 minutes to 2 hours or 30 minutes to 1 hour.

[0108] The amount of cleaning solvent is not particularly limited. However, if the amount of cleaning solvent is too small, the dissolution of impurities (α) may be insufficient. Therefore, relative to the amount of polyester composite material being processed, the amount of cleaning solvent should preferably be at least 5 times by mass, and more preferably at least 10 times by mass. Furthermore, if the amount of cleaning solvent is too large, a large amount of heat energy will be required during solvent recovery. Therefore, relative to the amount of polyester composite material being processed, the amount of cleaning solvent should preferably be at least 20 times by mass, and more preferably at least 15 times by mass. For example, the amount of cleaning solvent relative to the polyester composite material can be set to at least 5 times and less than 20 times by mass, or at least 10 times and less than 15 times by mass.

[0109] (Cleaning solvent)

[0110] The cleaning solvent is a mixed solvent composed of a solvent (X1) containing phenolic solvents and / or chlorine-based organic solvents and one or more solvents (Y1) selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, ketone solvents, aldehyde solvents, alcohol solvents, ether solvents and water.

[0111] The pH of the cleaning solvent is preferably less than 13.0, more preferably less than 12.5, more preferably less than 12.0, more preferably less than 11.5, and even more preferably less than 11.0.

[0112] In step (A), impurities (α) in the polyester composite material that are soluble in the cleaning solvent are dissolved and removed without substantially dissolving or decomposing the polyester. Therefore, it is preferable not to dissolve the polyester in step (A), and it is generally considered better to use a solvent with low polyester solubility to dissolve the impurities. However, the inventors' research results show that even when using a solvent with low polyester solubility in step (A), it is not possible to sufficiently remove impurities (α) such as colorants and surfactants. This is believed to be because impurities (α) such as colorants and surfactants also enter the intermolecular space of the polyester. Therefore, in order to dissolve the intermolecular impurities (α), it is considered important to weaken the intermolecular interactions of the amorphous sites of the polyester. Research has been conducted, and it has been found that by using phenolic solvents and / or chlorine-based organic solvents with high polyester solubility as part of the cleaning solvent, it is possible to weaken the intermolecular interactions of the amorphous sites without substantially dissolving the polyester, and thus effectively dissolve the intermolecular impurities (α). Thus, the use of a mixed solvent, which is a mixture of a solvent (X1) containing phenolic solvents and / or chlorine-based organic solvents and one or more solvents (Y1) selected from the group consisting of aromatic hydrocarbon solvents, ketone solvents, aldehyde solvents, alcohol solvents, ether solvents and water, as the cleaning solvent in step (A) is also one of the features of the manufacturing method of the first recycled polyester of the present invention.

[0113] The solvent (X1), which includes phenolic solvents and / or chlorine-based organic solvents, is a solvent that weakens the intermolecular interactions of the polyester. By including solvent (X1) in a portion of the cleaning solvent, internal impurities (α) of the polyester are also easily dissolved in the cleaning solvent. Examples of phenolic solvents include phenol, cresol, xylenol, ethylphenol, propylphenol, butylphenol, methoxyphenol, ethoxyphenol, propoxyphenol, butoxyphenol, benzylphenol, phenylphenol, chlorophenol, dichlorophenol, and chloromethylphenol. Examples of chlorine-based organic solvents include dichloromethane, chloroform, chlorohexane, chloropropane, tetrachloroethane, chloropropene, chlorobutene, chloromethoxypropane, dichloroethylene, trichloroethylene, bromochloroethane, chlorobenzene, dichlorobenzene, chlorotoluene, bromochlorobenzene, chloropentane, chloroethoxybenzene, and tetrachloroacetic acid. One or more of these solvents can be selected. The solvent (X1) is preferably one or more selected from the group consisting of phenol, cresol, dichloromethane and chloroform.

[0114] One or more solvents (Y1) selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, ketone solvents, aldehyde solvents, alcohol solvents, ether solvents and water are used as solvents to dissolve impurities (α). Polyester has low solubility. Therefore, by including solvent (Y1) in a part of the cleaning solvent, impurities (α) dissolved in the cleaning solvent can be dissolved without dissolving the polyester. As solvents (Y1), for example, aromatic hydrocarbon solvents such as toluene, xylene, ethylbenzene, diethylbenzene, 1-methylethylbenzene, and mesitylene can be used; aliphatic hydrocarbon solvents such as hexane, heptane, octane, hexene, heptene, octene, cyclopentane, cyclohexane, cycloheptane, cyclohexene, cycloheptene, nonane, decane, and cyclooctane can be used; ketone solvents such as acetone, methyl ethyl ketone, pentanone, hexanone, diethyl ketone, methyl isobutyl ketone, 3-penten-2-one, 2,4-pentanedione, cyclopropanone, cyclobutanone, heptanone, octanone, nonanone, decanone, hexanedione, 3-methyl-3-penten-2-one, cycloheptanone, cyclohexanone, 4-methylcyclohexanone, acetophenone, isophorone, and dimethylacetophenone can be used; propionaldehyde, butyraldehyde, pentanaldehyde, hexanal, vinyl aldehyde, glyoxal, and glyceraldehyde can also be used. Aldehyde solvents such as isobutyraldehyde, succinaldehyde, heptanaldehyde, octanaldehyde, nonanaldehyde, decanaldehyde, benzaldehyde, phenyl acrolein, perylaldehyde, and isopropylbenzaldehyde; alcohol solvents such as methanol, ethanol, propanol, isopropanol, isobutanol, tert-butanol, pentanol, hexanol, pentanediol, hexanediol, 3-ethyl-3-pentanol, ethylene glycol, propylene glycol, 1,4-butanediol, diethylene glycol, cyclohexanol, methylcyclohexanol, and benzyl alcohol; ether solvents such as diethyl ether, 1,4-dioxane, tetrahydrofuran, isopropyl methyl ether, methyl propyl ether, furan, p-dimethoxybenzene, cyclopentyl methyl ether, ethyl isopropyl ether, and tert-butyl propyl ether; ether solvents such as ethylene glycol diethyl ether, methyl phenyl ether, ethyl phenyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl ether, cyclohexyl ethyl ether, dihexyl ether, benzyl ethyl ether, and benzofuran; and water. These solvents can be used in single or multiple forms. Furthermore, the boiling point of solvent (Y1) is preferably below 250°C. From an industrial point of view, to reduce the heat load caused by distillation during solvent recovery, it is more preferably below 145°C. Solvent (Y1) is preferably a solvent capable of dissolving low-molecular-weight organic compounds such as colorants and surfactants, and more preferably one or more selected from the group consisting of toluene, xylene, heptane, hexane, acetone, methanol, ethanol, ethylene glycol, propylene glycol, and water.

[0115] The mixing ratio of solvent (X1) to solvent (Y1) can be adjusted within a range where the polyester is substantially insoluble. For example, when the temperature of the cleaning solvent is high (e.g., above 90°C, 90°C to 150°C), the proportion of solvent (X1) can be reduced; when the temperature of the cleaning solvent is low (e.g., below 50°C, 30°C to 50°C), the proportion of solvent (X1) can be increased. This can be adjusted arbitrarily according to the temperature and time required to dissolve the impurity (α). On the other hand, if the proportion of solvent (X1) is too high, the polyester is easily dissolved; if the proportion of solvent (Y1) is too high, the dissolution of the impurity (α) tends to be insufficient. Therefore, by mass ratio, solvent (X1):solvent (Y1) is preferably about 20:80 to 80:20, and more preferably by mass ratio, solvent (X1):solvent (Y1) is 40:60 to 60:40, 45:55 to 55:45, or 50:50.

[0116] (Solid-liquid separation)

[0117] In step (A), after dissolving the impurities (α) in the polyester composite material in the cleaning solvent, solid-liquid separation is performed to recover the polyester composite material from the cleaning solvent. When recovering the polyester composite material by evaporating the cleaning solvent, the impurities (α) dissolved in the cleaning solvent may precipitate and remain in the solid. Therefore, solid-liquid separation is preferably performed using a method other than evaporating the cleaning solvent. For example, known methods such as filtration and centrifugation, or methods using mesh containers such as cages or baskets, can be used for solid-liquid separation. When filtration is performed, the method is not particularly limited; any of the following can be used: filter paper, centrifugal filtration, cyclone filtration, glass filter, bag filter, candle filter, etc. The mesh size of the filter material is preferably 1 cm or more. When using a mesh container, it is preferable to dissolve the impurities (α) in the polyester composite material in the cleaning solvent in a mesh container installed within the reaction vessel for step (A), then remove the mesh container containing the polyester composite material and transfer it to the reaction apparatus for the next step. Alternatively, when using a mesh container, the mesh container containing the polyester composite material can be installed in the reaction vessel for process (A), or the polyester composite material can be added after the mesh container is installed in the reaction vessel for process (A).

[0118] <Process (A0) (Post-cleaning of Process (A))>

[0119] The polyester composite material recovered through solid-liquid separation can be directly used in process (B). However, since impurities (α) easily remain on the surface of the polyester composite material, it is preferable to further clean the polyester composite material after process (A) (post-cleaning) before using it in process (B). Therefore, a process (A0) for further cleaning the polyester composite material can be performed after process (A). Specifically, the polyester composite material recovered through solid-liquid separation is mixed with a solvent for post-cleaning, stirred, and then the solvent for post-cleaning is removed. This removes the impurities (α) adhering to the surface of the polyester composite material.

[0120] In step (A0), to prevent the polyester composite material from dissolving, it is preferable to use an organic solvent and / or water that does not contain phenolic or chlorine-based solvents. As organic solvents, aromatic hydrocarbon solvents such as toluene and xylene; aliphatic hydrocarbon solvents such as hexane; alcohol solvents such as methanol and ethanol; ketone solvents such as acetone; aldehyde solvents such as propionaldehyde; and ether solvents such as diethyl ether can be used in combination. Furthermore, the organic solvent used as the post-washing solvent preferably has a boiling point of 210°C or lower. From an industrial point of view, to reduce the heat load caused by distillation during solvent recovery, it is more preferably 130°C or lower, and even more preferably 80°C or lower. The post-washing solvent is preferably selected from one or more solvents chosen from the group consisting of acetone, toluene, hexane, methanol, ethanol, and water. The temperature of the solvent during post-washing can be appropriately set according to the boiling point of the solvent used, and is preferably 20–80°C. The amount of post-washing solvent used is preferably at least two times the mass of the polyester composite material, and more preferably at least five times the mass of the composite material.

[0121] Process (A0) can be performed multiple times. When performing multiple processes (A0), the type of solvent, temperature, and amount of solvent used can be set to the same conditions, or the conditions can be different each time. For example, after multiple cleanings using an organic solvent, water can be used for cleaning.

[0122] <Process (B)>

[0123] Step (B) involves mixing the cleaned polyester composite material with a solvent (X2) containing phenolic and / or chlorine-based organic solvents to obtain a PEs solution, and then performing solid-liquid separation on the PEs solution to obtain a liquid component (L) containing dissolved polyester.

[0124] The polyester composite material after step (A) typically contains impurities (hereinafter sometimes referred to as "impurities (β)") that are insoluble in the dissolving solvent used in step (B). These impurities (β) remain in the PE solution in solid form. Therefore, the PE solution is a suspension in which the impurities (β) are dispersed. By performing solid-liquid separation on this PE solution as a suspension, the liquid component containing dissolved polyester can be separated from the solid component containing impurities (β). Impurities (β) are components insoluble in both the cleaning solvent of step (A) and the dissolving solvent of step (B), and include natural fibers such as cotton, linen, and silk; rayon fibers; acrylic fibers; polyethylene fibers; polypropylene fibers; acetate fibers; glass fibers; polyethylene resin; polypropylene resin; polystyrene resin; thermosetting polyurethane resin; polyvinyl chloride resin; acrylic resin; metallic compounds such as titanium dioxide and silicon dioxide; and inorganic particles such as carbon black.

[0125] (Mixing of polyester composite material with solvent)

[0126] There is no particular limitation on the mixing order of the polyester composite material and the dissolving solvent. The dissolving solvent can be supplied to the reaction vessel after the polyester composite material is supplied, or the polyester composite material can be supplied to the reaction vessel after the dissolving solvent is supplied, or the polyester composite material and the dissolving solvent can be supplied simultaneously. Alternatively, the polyester composite material and the dissolving solvent can be mixed and allowed to stand to dissolve the polyester, but it is preferable to stir the liquid to dissolve the polyester.

[0127] The dissolution temperature (the temperature at which the polyester dissolves) is preferably 30°C or higher, more preferably 60°C or higher, and even more preferably 90°C or higher. There is no particular upper limit, but it is preferably carried out at 150°C or lower, and more preferably at 130°C or lower to avoid using excessive heat energy. For example, the melting temperature can be set to 30°C–150°C, 60°C–150°C, or 90°C–130°C. Furthermore, although it also depends on the composition of the cleaning solvent and the dissolving solvent, especially when the compositions of the cleaning solvent and the dissolving solvent are similar, the dissolution temperature of step (B) is preferably a higher temperature than the cleaning temperature of step (A). By carrying out the process at a higher temperature than step (A), the intermolecular interactions of the polyester weaken, making it easier to separate and remove intermolecular impurities in subsequent processes, which is therefore preferable.

[0128] The time for dissolving the polyester is preferably 30 minutes or more, more preferably 1 hour or more, preferably 4 hours or less, and even more preferably 2 hours or less. For example, the dissolution time can be set to 30 minutes to 4 hours or 1 hour to 2 hours.

[0129] There is no particular limitation on the amount of solvent added, but if the amount of solvent is too small, the dissolution of the polyester will take time. Therefore, relative to the amount of polyester composite material processed, the amount of solvent added is preferably 5 times or more by mass, more preferably 10 times or more by mass. Furthermore, if the amount of solvent is too large, a large amount of heat energy will be required during solvent recovery. Therefore, relative to the amount of polyester composite material processed, the amount of solvent added is preferably 30 times or less by mass, more preferably 20 times or less by mass. For example, relative to the amount of polyester composite material processed, the amount of solvent added can be set to 5 times or more but less than 30 times by mass, or 10 times or more but less than 20 times by mass.

[0130] (Dissolving solvent)

[0131] The dissolving solvent is a solvent (X2) containing a phenolic solvent and / or a chlorinated organic solvent. Examples of phenolic solvents include phenol, cresol, xylenol, ethylphenol, propylphenol, butylphenol, methoxyphenol, ethoxyphenol, propoxyphenol, butoxyphenol, benzylphenol, phenylphenol, chlorophenol, dichlorophenol, and chloromethylphenol. Examples of chlorinated organic solvents include dichloromethane, chloroform, chlorohexane, chloropropane, tetrachloroethane, chloropropene, chlorobutene, chloromethoxypropane, dichloroethylene, trichloroethylene, bromochloroethane, chlorobenzene, dichlorobenzene, chlorotoluene, bromochlorobenzene, chloropentane, chloroethoxybenzene, and tetrachloroacetic acid. One or more of these solvents may be selected. Preferably, the solvent (X2) is selected from one or more of the group consisting of phenol, cresol, dichloromethane, and chloroform. The solvent (X2) in the dissolving solvent can be the same solvent as the solvent (X1) in the cleaning solvent, or it can be a different solvent. In addition, the dissolving solvent can contain solvent (X2) as long as it can dissolve the polyester, or it can contain other solvents besides solvent (X2) (hereinafter referred to as "solvent (Y2)").

[0132] When the dissolving solvent includes solvent (Y2) (a solvent other than solvent (X2)), the boiling point of solvent (Y2) is preferably below 250°C, and more preferably below 145°C from the viewpoint of solvent recovery. For example, if the polyester dissolves, the viscosity of the solution increases; therefore, in order to improve the fluidity of the polyester dissolving solvent, solvent (Y2) can be added to solvent (X2). Examples of solvent (Y2) include aromatic hydrocarbon solvents such as toluene and xylene; aliphatic hydrocarbons such as hexane; ketone solvents such as acetone; aldehyde solvents such as propionaldehyde; alcohol solvents such as methanol, ethanol, ethylene glycol, and propylene glycol; and ether solvents such as diethyl ether. Preferably, it is selected from one or more solvents in the group consisting of toluene, xylene, hexane, ethanol, ethylene glycol, and propylene glycol, and more preferably toluene.

[0133] It should be noted that when the solvent includes solvent (Y2) in addition to solvent (X2), there is no particular limitation on the mixing order with the polyester composite material. The polyester composite material, solvent (X2), and solvent (Y2) can be mixed in parallel to dissolve the polyester. Alternatively, a mixture of solvent (X2) and solvent (Y2) can be mixed with the polyester composite material to dissolve the polyester. Alternatively, the polyester composite material can be mixed with solvent (X2) to dissolve the polyester to a certain extent, and then solvent (Y2), or a mixture of solvent (X2) and solvent (Y2), can be mixed.

[0134] While it also depends on factors such as dissolution temperature, the polyester needs to be dissolved in step (B). Therefore, regarding the dissolving solvent, the content of solvent (X2) in the dissolving solvent is generally greater than or equal to the content of solvent (X1) in the cleaning solvent used in step (A), and preferably more than the content of solvent (X1) in the cleaning solvent used in step (A). It should be noted that the contents of solvent (X1) and solvent (X2) refer to the total content of phenolic solvents and chlorinated organic solvents. When only phenolic solvents are included, the content is the same as that of phenolic solvents; when only chlorinated organic solvents are included, the content is the same as that of chlorinated organic solvents.

[0135] Furthermore, if the proportion of solvent (X2) in the dissolving solvent is too low, it is difficult to dissolve the polyester, or high temperature is required. Therefore, the content of solvent (X2) in the dissolving solvent is preferably more than the content of solvent (X1) in the cleaning solvent used in step (A) and is 60% by mass or more. To improve the solubility of the polyester, it is preferable to increase the content of solvent (X2) in the dissolving solvent to 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, or 95% by mass or more.

[0136] like Figure 2 As shown, the liquid obtained by dissolving the polyester in the polyester composite material in a dissolving solvent can be used as a PEs solution, or the liquid obtained by washing with water, mixing with a non-polar solvent, etc., can be used as a PEs solution.

[0137] (Washing after polyester dissolution)

[0138] By washing with water after dissolving polyester in a solvent, the removal efficiency of impurities such as titanium oxide, alkali metals, and alkaline earth metals can be improved. Specifically, the washing process involves dissolving the polyester in the polyester composite material in a solvent, mixing it with water, stirring for a predetermined time, and then allowing it to stand to separate the two phases. The aqueous phase is removed, yielding a PE solution as the organic phase. Typically, the stirring time is 10 minutes or more, and the standing time is 10 minutes or more. Furthermore, if the amount of water is too large, polyester may precipitate; if it is too small, the impurity removal effect decreases. Therefore, the water mass is preferably 0.1 times to 0.5 times the mass of the solvent. The washing process can be repeated 3 times or more.

[0139] (Mixed with nonpolar solvents)

[0140] Metal compounds that can be used as UV absorbers and matting agents are small in size and may not be captured by filter materials during filtration. However, by mixing with a nonpolar solvent with a dielectric constant of 1 to 3, the metal compounds can be agglomerated into a size that is easily removed by solid-liquid separation. Therefore, it is preferable to use a liquid obtained by dissolving polyester in a dissolving solvent and then mixing it with a nonpolar solvent with a dielectric constant of 1 to 3 as the PE solution. Examples of nonpolar solvents with a dielectric constant of 1 to 3 include toluene, xylene, hexane, cyclohexane, octane, styrene, benzene, biphenyl, 1,4-dioxane, 1,3-cyclohexadiene, and naphthalene, with toluene and / or xylene being preferred. The mixing temperature is preferably 50 to 130°C, which can be the same as the dissolution temperature or a different temperature. Furthermore, it is preferable to stir for 10 minutes to 1 hour after mixing with the nonpolar solvent. If the amount of nonpolar solvent is too small, there is almost no agglomeration effect; if it is too large, the polyester may precipitate. Therefore, the lower limit of the mass of the nonpolar solvent is preferably 0.5 times or more of the mass of the dissolving solvent, more preferably 1 time or more, and even more preferably 1.5 times or more. Furthermore, the upper limit is preferably 5 times or less of the mass of the dissolving solvent, more preferably 4 times or less, and even more preferably 3 times or less, but can be 2.5 times or less or 2 times or less. For example, the mass of the nonpolar solvent relative to the mass of the dissolving solvent can be set to 0.5 to 5 times, 1 to 4 times, or 2 to 3 times.

[0141] (Contact with filter aids and / or flocculants)

[0142] In addition, during or after the preparation of the PEs solution, there may be a step (Z) of treatment with a filter aid and / or a coagulant.

[0143] When the particle size of impurities (β) that are insoluble in the solvent used in step (B) is small, even though they are solids, they cannot be captured during solid-liquid separation, and there is a tendency for impurities (β) to remain in the liquid component (L). In particular, there is a tendency for pigments with small particle sizes, such as carbon black, to remain. Therefore, in order to improve the removal efficiency of impurities with small particle sizes, such as pigments, it is preferable to contact the PEs solution with a filter aid and / or a coagulant before the solid-liquid separation in step (B). By contacting the PEs solution with the filter aid and / or coagulant before the solid-liquid separation in step (B), the coloring components, such as pigments, adsorb or agglomerate with each other, thereby forming a state that is easily captured by filtration or the like.

[0144] As for the method of contacting the PEs solution with the filter aid and / or coagulant, there is no particular limitation as long as the filter aid and / or coagulant are in contact with the PEs solution. Examples include: adding the filter aid and / or coagulant to a reactor containing the PEs solution after obtaining the PEs solution and mixing them; loading the filter aid into a column and allowing the PEs solution to flow through it; adding the filter aid and / or coagulant while obtaining the PEs solution and mixing them, etc. These methods can also be combined.

[0145] Examples of filter aids include activated carbon, activated clay, bentonite, diatomaceous earth, alumina, silica gel, zeolite, and synthetic adsorbents. When the amount of filter aid added during mixing in the reactor is small, the adsorption of pigments and the like cannot be sufficient. Therefore, relative to the mass of the polyester composite material, it is preferable to add at least 1% by mass of the filter aid, more preferably at least 5% by mass, and even more preferably at least 15% by mass. Insufficient addition results in inadequate adsorption. On the other hand, if the amount of filter aid added is large, leakage may occur, for example, during solid-liquid separation filtration in step (B). Therefore, relative to the mass of the polyester composite material, the amount of filter aid added is preferably 500% by mass or less, and even more preferably 250% by mass or less. For example, the amount of filter aid relative to the polyester composite material can be set to 1% to 500% by mass, 5% to 500% by mass, or 15% to 250% by mass.

[0146] The minimum amount of coagulant added is such that a small amount is sufficient to achieve the desired effect. Therefore, the amount of coagulant added relative to the mass of the polyester composite material is preferably 0.1% by mass or more, more preferably 0.5% by mass or more. On the other hand, if too much coagulant is added, impurities from the coagulant will remain in the PEs solution, potentially deteriorating the color and mechanical strength of the final recycled polyester. Therefore, the amount of coagulant added relative to the mass of the polyester composite material is preferably 20% by mass or less, more preferably 10% by mass or less. For example, the amount of coagulant relative to the polyester composite material can be set to 0.1% to 20% by mass or 0.5% to 10% by mass.

[0147] Coagulants neutralize the charge of impurities such as pigments dispersed in PE solutions, promoting the adsorption and aggregation of these impurities and increasing the particle size to a level that can be captured through solid-liquid separation. Examples of usable coagulants include at least one inorganic salt other than alkali metal and alkaline earth metal salts used in polyester decomposition, and polymeric compounds. Examples of inorganic salts other than alkali metal and alkaline earth metal salts include ferric chloride (III), ferrous sulfate (II), ferric sulfate (III), aluminum chloride, aluminum sulfate, titanium dioxide, cuprous sulfate (I), copper sulfate (II), cuprous chloride (I), copper chloride (II), and zinc sulfate, with at least one preferably selected from the group consisting of ferric chloride (III), ferrous sulfate (II), ferric sulfate (III), aluminum sulfate, and aluminum chloride. Alternatively, mixtures of commercially available inorganic salts can also be used as coagulants. Especially when promoting the adsorption and aggregation of pigments such as carbon black with small particle sizes, using inorganic salts with similar molecular sizes makes adsorption and aggregation easier.

[0148] Inorganic salts can neutralize charges, but when the particle size of the agglomerated particles is small, it is preferable to add polymeric compounds such as anionic polymeric compounds, cationic polymeric compounds, and nonionic polymeric compounds. That is, it is preferable to contact the PEs solution with a coagulant containing inorganic salts other than alkali metal salts and alkaline earth metal salts, and then with a coagulant containing polymeric compounds. Particles dispersed in the PEs solution adhere to the polymer chains, increasing the particle size. As can be seen from the above, when removing impurities with small particle sizes such as pigments, by initially adding an inorganic salt followed by a polymeric coagulant, it is possible to effectively increase the particle size to a level that can be captured by the solid-liquid separation in step (B). Representative examples of polymeric compounds include polyacrylamide and polyethylene oxide.

[0149] Preferably, a filter aid and a coagulant are used together. Preferably, the PEs solution is contacted with the filter aid and then with the coagulant before the solid-liquid separation in step (B). When using both filter aid and coagulant, the PEs solution can be treated with the filter aid followed by the coagulant, or the coagulant can be treated first and then the filter aid, or both can be used simultaneously. Furthermore, the methods for contacting the PEs solution with the filter aid and with the coagulant can be different.

[0150] Regarding the contact time, if the time is too short, adsorption and coagulation cannot proceed sufficiently; therefore, 20 minutes or more is preferred, and 30 minutes or more is even more preferred. On the other hand, if the time is too long, impurities will dissolve from the added filter aids and coagulants; therefore, 180 minutes or less is preferred, and 120 minutes or less is even more preferred. For example, the contact time can be set to 20 to 180 minutes or 30 to 120 minutes.

[0151] In addition to step (A), in step (B), impurities that cannot be removed in step (A) can be fully removed by treatment with filter aids and / or coagulants.

[0152] (Solid-liquid separation)

[0153] The method for solid-liquid separation is not particularly limited, and known methods such as filtration and centrifugation can be cited, with filtration being preferred. The method for filtering the PEs solution is not particularly limited, and any of the following can be used: filter paper, centrifugal filtration, cyclone filtration, glass filter, bag filter, candle filter, etc. Furthermore, the filter can utilize multiple stages and multiple methods. The smallest mesh size of the filter material is preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less. Additionally, the smallest mesh size of the filter material is preferably 0.1 μm or more, more preferably 0.5 μm or more. If the mesh size is too large, the removal of foreign matter becomes insufficient; if it is too small, the filtration performance tends to deteriorate.

[0154] Solid-liquid separation can be carried out at room temperature or under heating conditions. Filtration can be carried out at room temperature or under heating, but heating filtration is preferred to prevent polyester precipitation. The temperature of the filtrate is preferably maintained at or above 50°C, more preferably at or above 80°C. In addition, to prevent polyester degradation due to heat load, the upper limit is preferably below 110°C, and even more preferably below 100°C. For example, the temperature of the filtrate during solid-liquid separation can be set to 50°C to 110°C or 80°C to 100°C.

[0155] <Process (C)>

[0156] Process (C) involves mixing the liquid component (L) with a poor solvent (PS) with a boiling point below 130°C to precipitate polyester and obtain a slurry. The slurry is then subjected to solid-liquid separation to obtain solid polyester.

[0157] By mixing with a poor solvent (PS), the polyester precipitates in solid form, while impurities dissolved in the poor solvent (PS) remain dissolved and do not precipitate. By appropriately selecting the poor solvent (PS), it is possible to keep impurities dissolved in the liquid component (L) while precipitating the polyester, and to remove the impurities dissolved in the poor solvent (PS) through solid-liquid separation. The impurities that remain dissolved and can be removed in step (C) are impurities such as acrylic fibers and acrylic resins (β), which are slightly dissolved in step (B) and cannot be completely removed, and impurities (α), which cannot be completely removed in step (A).

[0158] Furthermore, by ensuring that the boiling point of the undesirable solvent (PS) is below 130°C, the solvent can be easily removed in process (D), which, from an industrial point of view, reduces the heat load caused by distillation during solvent recovery. The boiling point of the undesirable solvent (PS) is preferably below 100°C.

[0159] (Poor solvent)

[0160] The unsuitable solvent (PS) used in step (C) is a solvent with a boiling point below 130°C and low solubility in polyester. There are no particular limitations on the unsuitable solvent (PS) as long as it has a boiling point below 130°C and can precipitate the polyester. Generally, solvents with a boiling point below 130°C other than phenolic solvents and chlorinated organic solvents are used. Preferably, it is selected from one or more solvents grouped together with aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, ketone solvents, aldehyde solvents, alcohol solvents, ether solvents, and water. Examples of unsuitable solvents (PS) include: aromatic hydrocarbon solvents such as toluene; aliphatic hydrocarbon solvents such as hexane, heptane, octane, hexene, heptene, octene, cyclopentane, cyclohexane, cycloheptane, cyclohexene, and cycloheptene; ketone solvents such as acetone, methyl ethyl ketone, pentanone, hexanone, diethyl ketone, methyl isobutyl ketone, 3-penten-2-one, cyclopropanone, cyclobutanone, and dimethyl acetophenone; propionaldehyde; aldehyde solvents such as butyraldehyde, pentanaldehyde, hexanal, vinyl aldehyde, glyoxal, isobutyraldehyde, and succinaldehyde; alcohol solvents such as methanol, ethanol, propanol, isopropanol, isobutanol, and tert-butyl alcohol; ether solvents such as diethyl ether, 1,4-dioxane, tetrahydrofuran, isopropyl methyl ether, methyl propyl ether, furan, cyclopentyl methyl ether, ethyl isopropyl ether, and tert-butyl propyl ether; and water. Only one of these solvents may be used, or two or more may be used. The preferred solvent (PS) is one or more selected from the group consisting of acetone, toluene, methanol, ethanol and water.

[0161] The mixing ratio of the liquid component (L) and the undesirable solvent (PS) is not particularly limited as long as it allows the polyester to precipitate. However, whether the undesirable solvent is too little or too much relative to the solvent (X2) in the liquid component (L), the polyester cannot be fully precipitated. Therefore, by mass ratio, the solvent (X2):undesirable solvent ratio in the liquid component (L) is preferably 1:0.5 to 1:10, more preferably 1:1 to 1:5. The content of solvent (X2) in the liquid component (L) is the same as that of solvent (X2) in the dissolving solvent. Therefore, the amount of undesirable solvent (PS) can be appropriately set according to the amount of solvent (X2) in the dissolving solvent. The mass ratio of undesirable solvent (PS) to solvent (X2) in the dissolving solvent is preferably 0.5 to 10, more preferably 1 to 5.

[0162] (Precipitation of polyester)

[0163] In step (C), the liquid component (L) is typically mixed with a poor solvent (PS), and the mixture is stirred for a predetermined time, thereby causing polyester to precipitate and obtaining a slurry. The precipitated polyester is usually at least partially composed of polyester crystals with a crystalline structure. The method of mixing the liquid component (L) and the poor solvent (PS) is not particularly limited; either the poor solvent (PS) can be supplied to the liquid component (L), or the poor solvent (PS) can be supplied to the liquid component (L). From the viewpoint of enabling slow precipitation of polyester and minimizing the entry of impurities into the polyester, the method of supplying the poor solvent (PS) to the liquid component (L) is preferred, and the method of supplying the poor solvent (PS) dropwise to the liquid component (L) is more preferred. When supplying two or more poor solvents (PS) to the liquid component (L), the two or more poor solvents (PS) can be supplied mixedly or separately.

[0164] As polyester precipitates, the proportion of solid (polyester) to liquid increases, thus tending to gradually decrease the stirring efficiency. To suppress the decrease in stirring efficiency accompanying the precipitation of polyester, it is preferable to mix the liquid component (L) and the undesirable solvent (PS) while controlling the temperature, so that the polyester precipitates slowly and the particle size of each solid particle becomes uniform. More preferably, mixing is carried out by dropwise addition while controlling the temperature.

[0165] To allow the polyester to slowly precipitate, the mixing of the liquid component (L) and the unsuitable solvent (PS) is preferably performed with the liquid temperature in the reaction vessel of step (C) set to above 20°C and below 100°C. When supplying the liquid component (L) with the unsuitable solvent (PS), the temperature of the unsuitable solvent (PS) also depends on the boiling points of the unsuitable solvent (PS) and the liquid component (L), preferably above 20°C, more preferably above 30°C, and even more preferably above 50°C. Furthermore, to suppress the deterioration of the polyester, the lower limit is preferably below 100°C, more preferably below 80°C. Additionally, when supplying the unsuitable solvent (PS) with the liquid component (L), the temperature of the liquid component (L) also depends on the boiling points of the unsuitable solvent (PS) and the liquid component (L), preferably above 50°C and below 100°C, and even more preferably above 60°C and below 80°C.

[0166] The supply rate can be appropriately set within the range not exceeding the aforementioned temperature, depending on the size of the reaction vessel and the liquid volume, preferably at a rate that can supply the entire quantity within 2 hours. Furthermore, if the supply rate is too fast, the growth of solid particles will proceed rapidly, and impurities will easily enter; therefore, it is preferable to set a rate that can supply the entire quantity in 0.25 hours or more. That is, the supply time is preferably 0.25 to 2 hours, more preferably 0.5 to 1.5 hours. It should be noted that, regarding the supply time, when supplying liquid component (L) to undesirable solvent (PS), it refers to the time required to supply the entire quantity of liquid component (L); when supplying undesirable solvent (PS) to liquid component (L), it refers to the time required to supply the entire quantity of undesirable solvent (PS).

[0167] In step (C), it is preferable to mix the liquid component (L) with the undesirable solvent (PS), cool the mixture to a predetermined curing temperature of 20°C or lower, and maintain the curing temperature to allow the polyester to precipitate. The curing temperature is preferably 20°C or lower, more preferably 10°C or lower. The cooling rate is preferably 5°C / min or lower, more preferably 3°C / min or lower, and even more preferably 1°C / min or lower. If the time for maintaining the curing temperature (curing time) is too short, the polyester will not precipitate sufficiently, potentially worsening the yield of recycled polyester; therefore, it is preferably 0.5 hours or more, more preferably 1.5 hours or more. Furthermore, beyond a certain time, the increase in polyester precipitation is small; therefore, the upper limit of the curing time is typically 3 hours or less.

[0168] (Separation of polyester)

[0169] In step (C), after obtaining the slurry from which polyester has precipitated, the slurry undergoes solid-liquid separation to recover the solid polyester. Solid-liquid separation of the slurry can be carried out by known methods such as filtration and centrifugation, with filtration being preferred. Polyester composite materials often contain low-molecular-weight polyester, but filtration can preferentially remove these low-molecular-weight polyesters, resulting in recycled polyester with a small molecular weight distribution. Filtration can be performed using any of the following: filter paper, centrifugal filtration, cyclone filtration, glass filter, bag filter, candle filter, etc. Furthermore, multiple stages and methods can be used for filtration. If the mesh size of the filter material is too large, the removal of foreign matter becomes insufficient; if it is too small, the filtration performance tends to deteriorate. Therefore, the minimum mesh size of the filter material is preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. Additionally, the minimum mesh size of the filter material is preferably 1 μm or more, more preferably 3 μm or more.

[0170] <Process (C0) (Post-cleaning of Process (C))>

[0171] The solid polyester recovered through solid-liquid separation can be directly dried in step (D). However, since impurities may adhere to the surface of the polyester, it is preferable to further clean the polyester (post-cleaning) before drying it in step (D). Therefore, a further cleaning step (C0) can be performed after step (C). Specifically, in step (C0), the solid polyester recovered through solid-liquid separation is mixed with a solvent for post-cleaning, stirred, and then the solvent is removed. This removes impurities adhering to the surface of the polyester.

[0172] The solvent used for post-washing can be a solvent that can be used as the undesirable solvent (PS) in step (C), preferably one or more selected from the group consisting of acetone, toluene, methanol, ethanol, and water. The solvent used for post-washing can be the same as or different from the undesirable solvent (PS) in step (C). In order to facilitate solvent removal in step (D), the boiling point of the solvent used for post-washing is preferably below 100°C, more preferably below 60°C. The temperature of the solvent used for post-washing can be appropriately set according to the boiling point of the solvent used, etc., preferably 25 to 80°C. The amount of solvent used for post-washing is preferably more than 2 times by mass relative to the amount of solid polyester, more preferably more than 5 times by mass. In addition, step (C0) can be performed multiple times. When performing multiple steps (C0), the type of solvent, temperature, amount of solvent, etc. used can be set to the same conditions, or the conditions can be set to be different each time.

[0173] <Process (D)>

[0174] Step (D) is the process of drying solid polyester to obtain recycled polyester. There are no particular limitations on the drying method; known methods can be used, such as vacuum drying or drying under normal pressure. The drying temperature and time can be appropriately determined; for example, drying can be carried out at 50–120°C for 2–15 hours.

[0175] Solvent Recycling

[0176] In the case of obtaining recycled polyester on an industrial scale, the solvents used in each process can be recovered and reused by separating them from impurities through distillation. For example, the cleaning solvent used in process (A) can be separated from the solvent by distillation, and the recovered solvent can be reused in process (A). Similarly, the liquid separated from the polyester by solid-liquid separation in process (C) also contains dissolved solvents and undesirable solvents (PS), which can therefore be recovered by distillation and reused in processes (B) and (C).

[0177] <Recycled polyester is made from polyester-containing fibers>

[0178] Figure 3 This is a flowchart illustrating an example of a method for manufacturing the first recycled polyester (recycled PEs) of the present invention when using polyester-containing fibers (PE-containing fibers) as a polyester composite material. Figure 3 The manufacturing method shown includes: a step of cleaning polyester-containing fibers with a cleaning solvent (S10); a step of post-cleaning polyester-containing fibers (S20); a step of dissolving polyester in polyester-containing fibers in a dissolving solvent (S30); a step of mixing the liquid containing polyester with a nonpolar solvent with a dielectric constant of 1 or higher and 3 or lower (S31); a step of performing solid-liquid separation on the PEs solution mixed with the nonpolar solvent to obtain a liquid component (L) containing polyester (S32); a step of mixing the liquid component (L) with a poor solvent (PS) to precipitate polyester, and then obtaining polyester by solid-liquid separation (S40); a step of post-cleaning polyester (S50); and a step of drying polyester (S60).

[0179] Most polyester fibers are dyed and colored with dyes and pigments. Additionally, additives include antistatic agents, UV absorbers, matting agents, flame retardants, surfactants, antioxidants, and lightfastness agents. As UV absorbers and matting agents, metal oxides, especially titanium dioxide, are often mixed into the fibers. When manufacturing recycled polyester from polyester-containing fibers, decolorization (removal of colorants) and removal of metal oxides are particularly important. When recycled polyester is colored, more dye is needed than before to process it to the target color; therefore, the recycled polyester needs thorough decolorization to remove the dye. Furthermore, when recycled polyester contains metal oxides, especially titanium dioxide, these metal oxides act as nucleating agents, readily crystallizing and becoming a major cause of deterioration in mechanical strength; therefore, thorough removal of metal oxides is necessary. The inventors have discovered that by treating the dyed polyester-containing fibers with the aforementioned specific cleaning solvent before dissolving the polyester, dyes can be efficiently removed and decolorization achieved. Furthermore, the inventors have discovered that by dissolving the polyester in polyester-containing fibers in the aforementioned specific solvent and then mixing it with a nonpolar solvent with a dielectric constant of 1 or higher and 3 or lower, metal oxides can be agglomerated to form a size that is easily captured by filtration. Based on these insights, it is preferable to manufacture recycled polyester from polyester-containing fibers. Figure 3 The manufacturing method shown.

[0180] (S10)

[0181] S10 is a step of cleaning polyester-containing fibers with a cleaning solvent. S10 is step (A) of the first recycled polyester manufacturing method of the present invention, and can be carried out by the same method as step (A) described above. The polyester-containing fibers can be polyester fiber monomers, or can include polyester fibers and fibers other than polyester, preferably using cut materials cut by a cutting machine. In S10, impurities (α) such as colorants, antistatic agents, flame retardants, surfactants, antioxidants, lightfastness agents, nylon fibers, and polyurethane fibers can be dissolved and removed by the cleaning solvent.

[0182] In particular, to remove the colorant more efficiently, in S10, it is preferable to heat the cleaning solvent, more preferably to set the cleaning temperature to 30–150°C, and even more preferably to set the cleaning temperature to 60–90°C. Polyester has high crystallinity; therefore, dispersion dyeing is commonly used for dyeing fibers. This method involves heating the fiber to weaken the intermolecular forces of the non-crystalline polyester, allowing the colorant to flow in, and then using a carrier or applying pressure to diffuse the dye within the fiber for dyeing. Similarly, in the removal (decolorization) of the colorant, heating the fiber can also make the polyester substantially insoluble, weakening the intermolecular interactions and creating a state where the colorant molecules can easily dissolve from the amorphous regions.

[0183] (S20)

[0184] S20 is a post-cleaning process for the polyester-containing fibers. S20 is step (A0) of the method for manufacturing the first recycled polyester of the present invention, and can be implemented by the same method as step (A0) described above.

[0185] (S30~S32)

[0186] S30 is a step of dissolving polyester in polyester-containing fibers in a dissolving solvent; S31 is a step of mixing the liquid containing dissolved polyester with a nonpolar solvent with a dielectric constant of 1 or higher and 3 or lower; and S32 is a step of performing solid-liquid separation on the PEs solution mixed with the nonpolar solvent to obtain a liquid component (L) containing dissolved polyester. S30 to S32 are steps (B) of the method for manufacturing the first recycled polyester of the present invention, and can be implemented by the same method as the corresponding stage of step (B) described above.

[0187] By performing steps S30 to S32, impurities (β) such as natural fibers, rayon fibers, acrylic fibers, polyethylene fibers, polypropylene fibers, and metal compounds can be removed. In particular, titanium oxide can be removed by performing steps S30 to S32. As mentioned above, polyester-containing fibers often contain metal oxides, especially titanium oxide. Due to the small particle size of these metal oxides, when a liquid formed by dissolving polyester in a solvent is directly filtered, the metal oxides may pass through the filter material and become mixed into the liquid component (L). Figure 3 In the manufacturing method, in S31, the liquid containing dissolved polyester is mixed with a nonpolar solvent with a dielectric constant of 1 or higher and 3 or lower, and the metal oxide is condensed. Then, solid-liquid separation is carried out in S32, thereby further reducing the mixing of metal oxide, especially titanium oxide, into the liquid component (L).

[0188] (S40)

[0189] S40 is a process in which a liquid component (L) is mixed with a poor solvent (PS) to precipitate solid polyester, and then polyester is obtained by solid-liquid separation. S40 is step (C) of the first recycled polyester manufacturing method of the present invention, and can be implemented by the same method as step (C) described above.

[0190] (S50)

[0191] S50 is a post-cleaning process for the polyester. S50 is a step (C0) in the method for manufacturing the first recycled polyester of the present invention, and can be implemented by the same method as step (C0) described above.

[0192] (S60)

[0193] S60 is a step of drying the polyester. S60 is step (D) of the method for manufacturing the first recycled polyester of the present invention, and can be implemented by the same method as step (D) described above.

[0194] in particular, Figure 3 The manufacturing method shown is suitable for cases where polyester-containing fibers include colorants and fibers other than titanium dioxide and / or polyester. Furthermore, as mentioned above, since low-molecular-weight organic compounds containing nitrogen (N) are widely used as colorants, therefore... Figure 3 The manufacturing method shown is more suitable for cases where polyester fibers contain low-molecular-weight organic compounds containing nitrogen and fibers other than titanium dioxide and / or polyester. By setting... Figure 3 The manufacturing method shown allows for the decolorization (removal of colorant) of polyester-containing fibers in S10, and the removal of titanium oxide and / or fibers other than polyester in S30 to S32. From the viewpoint of the hue and mechanical strength of the obtained recycled polyester, it is preferable that the recycled polyester has sufficiently reduced colorant and titanium oxide. As will be described later, decolorization can be indicated by the N content of the recycled polyester, and the removal of titanium oxide can be indicated by the Ti (titanium) content of the recycled polyester.

[0195] in addition, Figure 3 The manufacturing method shown is one example of a method for manufacturing recycled polyester from polyester-containing fibers, but the method for manufacturing recycled polyester from polyester-containing fibers is not limited to this.

[0196] <Method for manufacturing second-cycle polyester>

[0197] The following describes the method for manufacturing the second recycled polyester of the present invention.

[0198] In the second recycled polyester manufacturing method of the present invention, step (A) of the first recycled polyester manufacturing method is not performed. Instead, the polyester composite material is contacted with a coagulant when or after dissolving in a specific solvent.

[0199] <Process (B2)>

[0200] Step (B2) is a process of mixing the polyester composite material with a solvent (X2) containing a phenolic solvent and / or a chlorine-based organic solvent to obtain a PEs solution. Step (B2) is similar to the preparation of the PEs solution in step (B) of the first recycled polyester manufacturing method of the present invention, except that step (A) is omitted and the polyester composite material is used. The preferred method is also the same.

[0201] <Process (Z2)>

[0202] Process (Z2) involves contacting the PEs solution with a coagulant and then performing solid-liquid separation to obtain a liquid component (L2) containing dissolved polyester.

[0203] The contact method, type of coagulant, and contact conditions between the PE solution and the coagulant are the same as those described in process (B) regarding the coagulant, and the preferred method is also the same.

[0204] By performing steps (B2) and (Z2), components insoluble in the dissolving solvent can be removed. These insoluble components include natural fibers such as cotton, linen, and silk; rayon fibers; acrylic fibers; polyethylene fibers; polypropylene fibers; acetate fibers; glass fibers; polyethylene resin; polypropylene resin; polystyrene resin; thermosetting polyurethane resin; polyvinyl chloride resin; acrylic resin; metallic compounds such as titanium dioxide and silicon dioxide; and inorganic particles such as carbon black. In particular, steps (B2) and (Z2) effectively separate small inorganic particles such as pigments.

[0205] Furthermore, in the manufacturing method of the second recycled polyester, it is preferable to contact the PE solution with a filter aid before the solid-liquid separation in step (Z2). By using both a coagulant and a filter aid, impurities can be removed more efficiently. The contact between the PE solution and the filter aid can be performed simultaneously with, before, or after the contact between the PE solution and the coagulant. The method of contacting the PE solution with the filter aid, the type of filter aid, the contact conditions, etc., are the same as those described regarding the filter aid in step (B), and the preferred method is also the same.

[0206] <Process (C2)>

[0207] Step (C2) involves mixing the liquid component (L2) with a poor solvent (PS) with a boiling point below 130°C to precipitate the polyester, thereby obtaining a slurry. The slurry is then subjected to solid-liquid separation to obtain solid polyester. Step (C2) is identical to step (C) of the first recycled polyester manufacturing method of the present invention, except that liquid component (L2) is used instead of liquid component (L), and the preferred embodiment is also the same.

[0208] Impurities dissolved in the solvent of step (B2) remain in the liquid component (L2). These impurities may include one or more low-molecular-weight organic compounds (e.g., low-molecular-weight organic compounds with a molecular weight below 2000) selected from the group consisting of colorants, surfactants, antistatic agents, antioxidants, lightfasts, and flame retardants; nylon fibers; thermoplastic polyurethane fibers; acrylic fibers; nylon resins; thermoplastic polyurethane resins; acrylic resins; etc. These impurities do not precipitate as solids even with the addition of a poor solvent (PS), and therefore can be removed by separation from the polyester in step (C2).

[0209] Furthermore, the surface of the polyester recovered through solid-liquid separation in step (C2) may be contaminated with impurities. Therefore, it is preferable to further clean the polyester (post-cleaning) and dry it in step (D2). The post-cleaning in step (C2) (step (C0)) can be performed in the same manner as the post-cleaning in step (C) of the method for manufacturing the first recycled polyester of the present invention.

[0210] <Process (D2)>

[0211] Step (D2) is a process of drying solid polyester to obtain recycled polyester. Step (D2) is the same as step (D) of the first recycled polyester manufacturing method of the present invention, except that the polyester obtained in step (C2) can be used directly or after post-washing.

[0212] <Recycled Polyester (Recycled PEs)>

[0213] The recycled polyester obtained by the method of manufacturing recycled polyester of the present invention is a polyester recycled from polyester composite materials through material recycling. The weight-average molecular weight of the recycled polyester is the same as that of the raw materials and the original product, and its molecular weight distribution is lower than that of the raw materials and the original product. It has excellent color and mechanical strength.

[0214] The weight-average molecular weight difference between the recycled polyester and the polyester in the polyester composite material is preferably less than 1000. The weight-average molecular weight of the recycled polyester is 10000 to 12000.

[0215] The molecular weight distribution of the recycled polyester is the same as or lower than that of the raw materials and the original product, preferably 1.8 or higher and 2.5 or lower. It should be noted that the lower the molecular weight distribution value, the less deviation in molecular weight, which is preferred, for example, when using recycled polyester to regenerate fibers, etc.

[0216] The hue of the recycled polyester is preferably the same as that of the virgin polyester, and the color difference between the recycled polyester and the virgin polyester, as measured by a colorimeter, is preferably 10 or less. The color b value of the recycled polyester, as measured by a colorimeter, is preferably 5 or less.

[0217] Furthermore, in order to ensure that the hue of the recycled polyester is identical to that of the virgin polyester, it is preferable to have a low content of nitrogen-containing compounds widely used as colorants, which can be indicated by nitrogen content. The nitrogen content in the recycled polyester is preferably 80 ppm or less, more preferably 50 ppm or less, and even more preferably 5 ppm or less. The nitrogen content can be determined using the method described in the examples.

[0218] Therefore, in the preferred method for manufacturing the recycled polyester of the present invention, the N content in the polyester composite material is 400 ppm or more, and the N content in the recycled polyester is 80 ppm or less.

[0219] From the viewpoint of the mechanical strength of recycled polyester, the content of metal compounds in recycled polyester is preferably low. Most polyester composite materials contain metal compounds as additives; if the content of metal compounds is high, there is a tendency for mechanical strength to deteriorate. For example, the Ti (titanium) content in recycled polyester is preferably 100 ppm or less, and more preferably 50 ppm or less.

[0220] Therefore, in the preferred method for manufacturing the recycled polyester of the present invention, the Ti content in the polyester composite material is 500 ppm or more, and the Ti content in the recycled polyester is 100 ppm or less.

[0221] As described later in the examples, the recycled polyester preferably exhibits a crystallization peak between 120°C and 170°C in DSC measurements. Furthermore, the exothermic reaction of the crystallization peak between 120°C and 170°C is preferably 50% or more, more preferably 80% or more, of the molten heat of the original polyester.

[0222] <Manufacturing Method of Polyester Composite Materials>

[0223] In addition, the present invention relates to a method for manufacturing a polyester composite material (hereinafter, sometimes referred to as "method for manufacturing a polyester composite material of the present invention"), comprising: a step of manufacturing a recycled polyester by the method for manufacturing recycled polyester of the present invention; and a step of manufacturing a polyester composite material using the obtained recycled polyester.

[0224] The process for manufacturing recycled polyester is as described above. The process for manufacturing polyester composite materials, besides using recycled polyester as a raw material, can be carried out using known manufacturing methods. Examples of methods for manufacturing polyester composite materials include: methods for processing polyester fiber products by spinning using a spinneret; and methods for molding various polyester products such as polyester films and polyester molded products by melt extrusion, injection molding using a mold, etc.

[0225] In addition, in the process of manufacturing polyester composite materials, the raw material polyester can include recycled polyester. It is possible to use only recycled polyester or to use both recycled polyester and virgin polyester.

[0226] The form of the manufactured polyester composite material is not particularly limited, and polyester-containing fibers, polyester-containing molded articles, polyester-containing laminates, etc. can be manufactured by the polyester composite material manufacturing method of the present invention.

[0227] Example

[0228] The present invention will be described in more detail below through embodiments, but the present invention is not limited to the following embodiments as long as its spirit is not changed.

[0229] <Analytical Methods>

[0230] =Molecular weight determination=

[0231] The sample was dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), filtered through a 0.45 μm injection filter, and determined by size exclusion chromatography under the following conditions.

[0232] • Device: Waters "ACQUITY"

[0233] • Mobile phase: HFIP with 0.01M sodium trifluoroacetate added

[0234] • Flow rate: 0.2 mL / min

[0235] ·Column: ACQUITY APC XT900+XT450+XT125

[0236] Column temperature: 50℃

[0237] Injection volume: 10μL

[0238] • Detector: Differential refractometer

[0239] • Molecular weight calculation: Polymethyl methacrylate (PMMA) conversion

[0240] =Analysis of N content in samples before and after recycling=

[0241] Whether decolorization has been performed is determined by analyzing the nitrogen content. The recycled polyester is burned in an argon and oxygen atmosphere, and the resulting combustion gases are measured using a micro-nitrogen analyzer (TN-2100H, manufactured by Nitto Seiko Analytical Technology Co., Ltd.) employing reduced-pressure chemiluminescence. A sample obtained by dissolving aniline in toluene is used as the standard sample.

[0242] =Color Determination of Recycled Polyester=

[0243] The L, a, and b values ​​of the recycled polyester were measured using a colorimeter (Nippon Denshoku Kogyo Co., Ltd., "ZE-6000"). Additionally, the original polyester (Mitsubishi Chemical Engineering Plastics Co., Ltd., "GG 500D") was also measured. L1, a1, and b1 were set as the L, a, and b values ​​of the recycled polyester, respectively, and L0, a0, and b0 were set as the L, a, and b values ​​of the original polyester, respectively. The color difference ΔEa*b* was calculated using the following formula.

[0244] [Number 1]

[0245]

[0246] =Analysis of Ti content in samples before and after recycling=

[0247] Sulfuric acid was added to the recycled polyester, and after white fume treatment on a hot plate, it was dry-ashed at 650°C using an electric furnace (Yamato Corporation's "Muffle Furnace FP410"). Pure water and sulfuric acid were added to the residual ash, and white fume treatment was performed to dissolve it. The ash was then brought to a final volume with pure water. The Ti content in the recycled polyester was then quantified using an ICP-based luminescence analyzer (Agilent Technologies Corporation's "5800ICP-OES").

[0248] =Molding Test=

[0249] 3g of recycled polyester was melted at 290 degrees Celsius and hot-pressed to form a shape of 7cm in length × 7cm in width × 0.5mm in thickness. Depending on the sample, some samples were so brittle that they cracked immediately after molding. Therefore, the following evaluation of the molded products was conducted.

[0250] ◎: Samples that maintained their strength without breaking during all 10 molding processes.

[0251] 〇: Samples that maintained their strength without breaking during 7 to 9 out of 10 molding cycles.

[0252] △: Samples that maintained their strength without breaking during 3 to 6 out of 10 molding cycles.

[0253] ×: Samples that maintained their strength without breaking in 2 or fewer out of 10 molding cycles.

[0254] =Crystallization Determination=

[0255] To confirm the thermal history of the samples obtained in the above molding tests during molding, crystallinity was measured. Crystallinity was measured using a DSC (Hitachi High Technology Co., Ltd. "EXSTAR 6000"). 8 mg of molded articles made from recycled polyester were taken and heated from 30°C to 360°C at a rate of 10°C / min.

[0256] Polyester is characterized by its slow crystallization rate, which results in molded articles with excellent transparency and mechanical strength. Therefore, when performing DSC measurements on a large number of molded articles, a crystallization peak was identified between 120°C and 170°C. However, if impurities are present in the molded article, they act as nucleating agents, thus accelerating the crystallization rate. As a result, the crystallinity of the molded article increases, while its mechanical strength decreases. When performing DSC measurements on such molded articles, no crystallization peak was identified between 120°C and 170°C. Therefore, in this invention, measurements were performed to confirm the crystallization rate of the recycled polyester molded articles obtained in the above molding tests. Ten measurements were taken on the original molded articles, and the average heat of melt at 260°C was calculated. This average was compared with the heat of release of each crystallization peak of the recycled polyester molded articles obtained in the above molding tests, and the following evaluation was conducted.

[0257] ◎: The crystallization peak was confirmed between 120℃ and 170℃, and its heat release was 80 to 100% of the heat of fusion of the original product.

[0258] 〇: The crystallization peak was confirmed between 120℃ and 170℃, and its heat release was 50% to 80% of that of the original product.

[0259] △: The crystallization peak was confirmed between 120℃ and 170℃, and its heat release was less than 50% of that of the original product.

[0260] ×: No crystallization peak was detected between 120℃ and 170℃.

[0261] =Determination of the melting point of raw materials=

[0262] To identify the type of polyester in the polyester composite material, melting point determination was performed using a DSC (Hitachi High Technology Co., Ltd. "EXSTAR 6000") to determine the polyester type. In the case of polyethylene terephthalate (PET), a melting peak was observed around 260°C, and in the case of polybutylene terephthalate (PET), a melting peak was observed around 220°C, thus confirming the polyester type.

[0263] <Ingredients>

[0264] Use the following raw materials A through E.

[0265] Raw material A: 100% polyester clothing (1)

[0266] Raw material B: 100% polyester clothing (2)

[0267] Raw material C: 100% polyester clothing (3)

[0268] Material D: Polyester and cotton blend clothing (1)

[0269] Material E: Polyester and cotton blend clothing (2)

[0270] Raw material F: Automotive interior fiber

[0271] Raw material G: Polybutylene terephthalate resin containing 30% glass fiber (GF) (containing carbon black (CB))

[0272] The raw materials were pre-cut into 2cm × 2cm sizes using a cutting machine. Additionally, Table 1 shows the polyester content, polyester type, color, weight-average molecular weight Mw, number-average molecular weight Mn, Mw / Mn, N content, and Ti content of raw materials A through G.

[0273] [Table 1]

[0274]

[0275] [Example 1]

[0276] (Process A)

[0277] 300g of the cut sample A was added to a 5L detachable flask, along with 3000g of a solution containing toluene and phenol adjusted to a 50:50 (mass ratio) as a cleaning solvent. The mixture was heated at 80°C for 1 hour under a nitrogen atmosphere with stirring to decolorize the fibers and remove other impurities. The solution was then removed by filtration, yielding the decolorized sample A.

[0278] (Process (A0))

[0279] Add 2000g of toluene heated to 80℃, stir, and perform two operations to remove the toluene, thereby cleaning and removing colorants and other substances adhering to the fibers.

[0280] (Process (B))

[0281] Next, 3000g of phenol was added as a solvent, and the mixture was heated at 110°C under a nitrogen atmosphere with stirring for 1 hour to dissolve the polyester fibers. The solution was then filtered through 0.5μm filter paper to remove impurities, yielding a filtrate containing dissolved polyester fibers.

[0282] (Process (C))

[0283] While maintaining the filtrate at 50°C, 3000g of acetone (PS) as a poor solvent was added dropwise to the filtrate at a temperature not exceeding 50°C, causing PET to precipitate. After adding all the acetone, the temperature was lowered to 20°C over 30 minutes, and then stirred at 20°C for 1 hour. The filtrate was then filtered using 7μm filter paper, and the filtrate (PET) was recovered.

[0284] (Process (C0))

[0285] Add 2000g of acetone to the filter material (PET), wash, and filter again. Repeat this process three times to remove impurities and obtain a wet filter cake (washed PET).

[0286] (Process (D))

[0287] The wet filter cake obtained is dried under reduced pressure and at 80°C using an evaporator to obtain recycled polyester.

[0288] The obtained recycled polyester was evaluated according to the steps described above. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results. The polyester recovery rate was calculated relative to the polyester content in the feedstock.

[0289] [Example 2]

[0290] In a 5L detachable flask, 300g of chopped sample B was added instead of chopped sample A. Otherwise, recycled polyester was obtained using the same method as in Example 1, and various evaluations were performed. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results.

[0291] [Example 3]

[0292] In a 5L detachable flask, 300g of chopped sample C was added instead of chopped sample A. Otherwise, recycled polyester was obtained using the same method as in Example 1, and various evaluations were performed. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results.

[0293] [Example 4]

[0294] In a 5L detachable flask, 300g of chopped sample D was added instead of chopped sample A. Otherwise, recycled polyester was obtained using the same method as in Example 1, and various evaluations were performed. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results.

[0295] [Example 5]

[0296] In a 5L detachable flask, 300g of chopped sample E was added instead of chopped sample A. Otherwise, recycled polyester was obtained using the same method as in Example 1, and various evaluations were performed. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results.

[0297] [Example 6]

[0298] (Process A)

[0299] 300g of the cut sample A was added to a 5L detachable flask, along with 3000g of a solution containing toluene and dichloromethane adjusted to a 50:50 (mass ratio) as a cleaning solvent. The mixture was stirred under a nitrogen atmosphere and heated at 40°C for 1 hour to decolorize the fibers and remove other impurities. The solution was then removed by filtration to obtain the decolorized sample A.

[0300] (Process (A0))

[0301] Add 2000g of room temperature toluene, stir, remove the toluene, and repeat this operation twice to clean and remove colorants and other substances adhering to the fibers.

[0302] (Process (B))

[0303] Next, 600g of phenol and 2400g of dichloromethane were added as solvents, and the mixture was heated at 45°C under a nitrogen atmosphere with stirring for 1 hour to dissolve the polyester fibers. The solution was then filtered through 0.5μm filter paper to remove impurities, yielding a filtrate containing dissolved polyester fibers.

[0304] (Process (C))

[0305] While maintaining the filtrate at 40°C, 3000g of acetone (PS) as a poor solvent was added dropwise to the filtrate at a temperature not exceeding the controlled temperature of 40°C, causing PET to precipitate. After adding all the acetone, the temperature was lowered to 20°C over 30 minutes, and then stirred at 20°C for 1 hour. The filtrate was then filtered using 7μm filter paper, and the filtrate (PET) was recovered.

[0306] (Process (C0))

[0307] Add 2000g of acetone to the filter material (PET), wash, and filter again. Repeat this process three times to remove impurities and obtain a wet filter cake (washed PET).

[0308] (Process (D))

[0309] The wet filter cake obtained is dried under reduced pressure and at 80°C using an evaporator to obtain recycled polyester.

[0310] The obtained recycled polyester was evaluated according to the steps described above. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results. The polyester recovery rate was calculated relative to the polyester content in the feedstock.

[0311] [Example 7]

[0312] Step (B) was set as follows: "Add 3000g of phenol as a dissolving solvent, heat at 110°C for 1 hour to dissolve the polyester fibers, then add 4500g of toluene, stir for 30 minutes, and filter using 0.5μm filter paper to obtain the filtrate." Otherwise, recycled polyester was obtained using the same method as in Example 1, and various evaluations were performed. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results.

[0313] [Example 8]

[0314] In a 5L detachable flask, 300g of chopped sample B was added instead of chopped sample A. Otherwise, recycled polyester was obtained using the same method as in Example 7, and various evaluations were performed. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results.

[0315] [Example 9]

[0316] In a 5L detachable flask, 300g of chopped sample C was added instead of chopped sample A. Otherwise, recycled polyester was obtained using the same method as in Example 7, and various evaluations were performed. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results.

[0317] [Example 10]

[0318] In a 5L detachable flask, 300g of cut sample D was added instead of cut sample A. Otherwise, recycled polyester was obtained using the same method as in Example 7, and various evaluations were performed. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results.

[0319] [Example 11]

[0320] In a 5L detachable flask, 300g of chopped sample E was added instead of chopped sample A. Otherwise, recycled polyester was obtained using the same method as in Example 7, and various evaluations were performed. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results.

[0321] [Example 12]

[0322] The PET was precipitated using water, and otherwise recycled polyester was obtained using the same method as in Example 7. Evaluations were then conducted. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results.

[0323] [Example 13]

[0324] (Process A)

[0325] 100g of the cut sample D was added to a 5L detachable flask, along with 1000g of a solution containing toluene and phenol adjusted to a 50:50 (mass ratio) as a cleaning solvent. The mixture was stirred under a nitrogen atmosphere and heated at 80°C for 1 hour to decolorize the fibers and remove other impurities. The solution was then removed by filtration to obtain the decolorized sample A.

[0326] (Process (A0))

[0327] Add 700g of room temperature toluene, stir, remove the toluene, and repeat this operation twice to clean and remove colorants and other substances adhering to the fibers.

[0328] (Process (B))

[0329] Next, 1000g of phenol was added as a solvent, and the mixture was heated at 110°C under a nitrogen atmosphere with stirring for 1 hour to dissolve the polyester fibers. After dissolution, 10g of activated carbon was added, and the mixture was stirred for 60 minutes. The solution was then filtered through 0.5μm filter paper to remove impurities, yielding a filtrate containing dissolved polyester fibers.

[0330] (Process (C))

[0331] While maintaining the filtrate at 40°C, 1000g of acetone (PS) as a poor solvent was added dropwise to the filtrate at a temperature not exceeding the controlled temperature of 40°C, causing PET to precipitate. After adding all the acetone, the temperature was lowered to 20°C over 30 minutes, and then stirred at 20°C for 1 hour. The filtrate was then filtered using 7μm filter paper, and the filtrate (PET) was recovered.

[0332] (Process (C0))

[0333] Add 700g of acetone to the filter material (PET) for washing, and filter again. Repeat this process three times to remove impurities and obtain a wet filter cake (washed PET).

[0334] (Process (D))

[0335] The wet filter cake obtained is dried under reduced pressure and at 80°C using an evaporator to obtain recycled polyester.

[0336] The obtained recycled polyester was evaluated according to the steps described above. Table 2 shows the experimental conditions, and Table 4 shows the evaluation results. The polyester recovery rate was calculated relative to the polyester content in the feedstock.

[0337] [Example 14]

[0338] In step (B), after dissolving the polyester fibers, 5g of activated carbon and 3g of ferrous sulfate (II) were added to replace 10g of activated carbon. Otherwise, recycled polyester was obtained using the same method as in Example 13, and various evaluations were performed. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results.

[0339] [Example 15]

[0340] In a 5L detachable flask, 300g of chopped sample F was added instead of chopped sample A. Otherwise, recycled polyester was obtained using the same method as in Example 7, and various evaluations were performed. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results.

[0341] [Example 16]

[0342] In a 5L detachable flask, instead of the cut sample A, 300g of the cut sample F was added. Step (B) was set as follows: "Add 3000g of phenol as a dissolving solvent, heat at 110°C for 1 hour to dissolve the polyester fibers, then add 30g of activated carbon and 10g of ferrous(II) sulfate, stir at 80°C for 60 minutes, and filter using 0.5μm filter paper to obtain the filtrate." Otherwise, recycled polyester was obtained using the same method as in Example 1, and various evaluations were performed. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results.

[0343] [Example 17]

[0344] In a 5L detachable flask, instead of the cut sample A, 300g of the cut sample F was added. Step (B) was set as follows: "Add 3000g of phenol as a dissolving solvent, heat at 110°C for 1 hour to dissolve the polyester fibers, then add 4500g of toluene, stir for 30 minutes, add 30g of ferric chloride (III), stir at 80°C for 60 minutes, and filter using 0.5μm filter paper to obtain the filtrate." Otherwise, recycled polyester was obtained using the same method as in Example 7, and various evaluations were performed. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results.

[0345] [Example 18]

[0346] In a 5L detachable flask, 300g of chopped sample G was added instead of chopped sample A. Otherwise, recycled polyester (PBT) was obtained using the same method as in Example 1, and various evaluations were performed. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results.

[0347] [Example 19]

[0348] In a 5L detachable flask, instead of the cut sample A, 300g of the cut sample G was added. Step (B) was set as follows: "Add 3000g of phenol as a dissolving solvent, heat at 90°C for 1 hour to dissolve the polyester fibers, add 15g of ferric chloride (III), stir at 80°C for 60 minutes, and filter using 0.5μm filter paper to obtain the filtrate." Otherwise, recycled polyester (PBT) was obtained using the same method as in Example 1, and various evaluations were performed. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results.

[0349] [Example 20]

[0350] In a 5L detachable flask, instead of the cut sample A, 300g of the cut sample G was added. Step (B) was set as follows: "Add 3000g of phenol as a dissolving solvent, heat at 100°C for 1 hour to dissolve the polyester fibers, then add 30g of activated clay and 15g of ferric sulfate (III), stir at 80°C for 60 minutes, and filter using 0.5μm filter paper to obtain the filtrate." Otherwise, recycled polyester (PBT) was obtained using the same method as in Example 1, and various evaluations were performed. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results.

[0351] [Example 21]

[0352] Without performing steps (A) and (A0), the same method as in Example 16 was performed, thereby carrying out steps (B2), (Z2), (C2), (C0), and (D2) to obtain recycled polyester. The obtained recycled polyester was evaluated. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results.

[0353] [Example 22]

[0354] In a 5L detachable flask, instead of the cut sample A, 300g of the cut sample G was added. Steps (A) and (A0) were omitted. Step (B) was set as follows: "Add 3000g of phenol as a dissolving solvent, heat at 80°C for 1 hour to dissolve the polyester fibers, then add 15g of activated carbon and 15g of ferrous(II) sulfate, stir at 60°C for 60 minutes, and filter using 0.5μm filter paper to obtain the filtrate." Otherwise, the same method as in Example 1 was performed, thus proceeding to steps (B2), (Z2), (C2), (C0), and (D2) to obtain recycled polyester (PBT). The obtained recycled polyester was evaluated. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results.

[0355] [Comparative Example 1]

[0356] 10g of chopped sample A was added to a 500mL round-bottom flask without decolorization (step (A)). 100g of hexafluoroisopropanol (HFIP) was added, and the polyester fibers were dissolved at room temperature for 1 hour. The solution was filtered through 0.5μm filter paper to remove impurities, yielding a filtrate (corresponding to step (B)). The filtrate was added dropwise to 100g of water to precipitate PET. The filtrate was then filtered through 7μm filter paper, and the filtrate (PET) was recovered (corresponding to step (C)). 70g of water was added to the filtrate for washing, followed by filtration. This process was repeated three times to remove impurities, yielding a wet filter cake (washed PET) (corresponding to step (C0)). The wet filter cake was dried to obtain recycled polyester (corresponding to step (D)). The recycled polyester was evaluated according to the above steps. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results.

[0357] [Comparative Example 2]

[0358] 50g of the cut sample A was placed in a 1L detachable flask, and 500g of 1,3-dimethyl-2-imidazolinone (DMI) was added. The mixture was heated at 120°C for 1 hour under a nitrogen atmosphere to decolorize the fibers. The solution was then removed, yielding the decolorized sample A (corresponding to step (A)). 350g of 1,3-dimethyl-2-imidazolinone heated to 120°C was added, and the mixture was stirred. This process was repeated twice to remove the coloring components adhering to the fibers (corresponding to step (A0)). Next, 500g of 1,3-dimethyl-2-imidazolinone was added, and the mixture was heated at 170°C for 1 hour to dissolve the polyester fibers. The solution was filtered through 0.5μm filter paper to remove impurities, yielding the filtrate (corresponding to step (B)). The filtrate was added dropwise to 500g of ethanol to precipitate PET. The filter was filtered using 7 μm pore size filter paper, and the filtered material (PET) was recovered (corresponding to step (C)). 350 g of ethanol was added to the filter material for washing, and the mixture was filtered again. This process was repeated three times to remove impurities, resulting in a wet filter cake (washed PET) (corresponding to step (C0)). The obtained wet filter cake was dried under reduced pressure at 80°C for 3 hours, but it was not completely dried. Therefore, the temperature was increased to 120°C, and the mixture was dried further under reduced pressure of 3 kPa for 3 hours. However, solvent residue remained on the flask wall, and the solvent could not be completely removed from the recycled polyester (corresponding to step (D)). The recycled polyester was recovered while still containing solvent, and the evaluations were performed according to the above steps. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results. The evaluation results shown in Table 5 indicate that DMI is a nitrogen-containing solvent, therefore the nitrogen content was higher than before treatment, and DMI could not be completely removed.

[0359] [Comparative Example 3]

[0360] Add 300g of the cut sample A to a 5L detachable flask without decolorization (step (A)). Add 3000g of phenol and heat at 110°C for 1 hour to dissolve the polyester fibers. Filter the solution using 0.5μm filter paper to remove impurities, obtaining the filtrate (corresponding to step (B)). Recover the filtrate and, while maintaining it at 50°C, add it dropwise to 3000g of acetone at a temperature not exceeding 50°C, allowing PET to precipitate. After adding all the acetone, lower the temperature to 20°C over 30 minutes and stir at 20°C for 1 hour. Filter the solution using 7μm filter paper and recover the filtrate (PET) (corresponding to step (C)). Add 2000g of acetone to the filtrate, wash, and filter again. Repeat this process three times to remove impurities, obtaining a wet filter cake (washed PET) (corresponding to step (C0)). The resulting wet filter cake was dried under reduced pressure at 80°C using an evaporator to obtain recycled polyester (corresponding to step (D)). The obtained recycled polyester was evaluated according to the steps described above. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results.

[0361] [Comparative Example 4]

[0362] Add 300g of the cut sample G to a 5L detachable flask without decolorization (step (A)). Add 3000g of phenol and heat at 110°C for 1 hour. Filter the flask using 0.5μm filter paper to remove impurities, obtaining the filtrate (corresponding to step (B)). Recover the filtrate and, while maintaining it at 50°C, add it dropwise to 3000g of acetone at a temperature not exceeding 50°C, allowing PBT to precipitate. After adding all the acetone, lower the temperature to 20°C over 30 minutes and stir at 20°C for 1 hour. Filter the filtrate using 7μm filter paper and recover the filtrate (PBT) (corresponding to step (C)). Add 2000g of acetone to the filtrate, wash, and filter again. Repeat this process three times to remove impurities, obtaining a wet filter cake (washed PET) (corresponding to step (C0)). The resulting wet filter cake was dried under reduced pressure at 80°C using an evaporator to obtain recycled polyester (corresponding to step (D)). The obtained recycled polyester was evaluated according to the steps described above. Table 3 shows the experimental conditions, and Table 5 shows the evaluation results.

[0363] Table 4 shows the evaluation results for Examples 1 to 13, and Table 5 shows the evaluation results for Examples 15 to 22 and Comparative Examples 1 to 4. Items not evaluated are shown as NT. From the results of Examples 1 to 20 and Comparative Examples 1 to 4, it can be seen that by following the process of step (A) (cleaning with a cleaning solvent), step (B) (polyester dissolution and filtration), and step (C) (polyester reprecipitation), a recycled polyester with a molecular weight distribution of approximately 1.85 to 2.1 and excellent color tone can be obtained without chemically decomposing the polyester. In particular, it can be seen that in step (B), by performing a titanium dioxide coagulation operation, a recycled polyester with excellent color tone and mechanical strength can be obtained. Furthermore, from the results of Examples 21 and 22 and Comparative Examples 1 to 4, it can be seen that even without performing step (A), a recycled polyester with excellent color tone and mechanical strength can be obtained by using a coagulant and / or a filter aid (performing step (Z2)).

[0364] [Table 2]

[0365]

[0366] [Table 3]

[0367]

[0368] [Table 4]

[0369]

[0370] [Table 5]

[0371]

Claims

1. A method for manufacturing recycled polyester, comprising steps (A) to (D) of a polyester composite material. Step (A): A step of cleaning polyester composite material using a cleaning solvent (X1) which is a mixture of a solvent (X1) containing phenolic solvents and / or chlorine organic solvents and one or more solvents (Y1) selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, ketone solvents, aldehyde solvents, alcohol solvents, ether solvents and water. Step (B): The cleaned polyester composite material is mixed with a solvent (X2) containing a phenolic solvent and / or a chlorine-based organic solvent to obtain a solution in which the polyester in the polyester composite material is dissolved. Then, the solution containing the polyester is subjected to solid-liquid separation to obtain a liquid component (L) containing the polyester. Step (C): The liquid component (L) is mixed with a poor solvent (PS) with a boiling point below 130°C to precipitate polyester, thereby obtaining a slurry. The slurry is then subjected to solid-liquid separation to obtain solid polyester. Process (D): Drying the solid polyester to obtain recycled polyester.

2. The method for manufacturing recycled polyester according to claim 1, in step (B), after the polyester in the polyester composite material is dissolved in the dissolving solvent, it is mixed with a nonpolar solvent with a dielectric constant of 1 or more and 3 or less to obtain a solution containing the polyester.

3. The method for manufacturing recycled polyester according to claim 1 or 2, wherein the polyester is one or more selected from the group consisting of polyethylene terephthalate, polyethylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, polyethylene naphthalate and copolymers thereof, and copolymers thereof with other resins.

4. The method for manufacturing recycled polyester according to claim 1 or 2, wherein the polyester composite material comprises polyester and other components, wherein the other components are one or more selected from the group consisting of low-molecular-weight organic compounds, metal compounds, inorganic microparticles, fibers other than polyester, and resins other than polyester. The recycled polyester is a polyester from which the other components have been removed.

5. The method for manufacturing recycled polyester according to claim 4, wherein the low-molecular-weight organic compound comprises one or more selected from the group consisting of colorants, surfactants, antistatic agents, and flame retardants. The metal compound contains a matting agent and / or an ultraviolet absorber. The inorganic particles contain pigments. The fibers other than polyester include one or more selected from the group consisting of natural fibers, acrylic fibers, rayon fibers, polyurethane fibers, nylon fibers, polyethylene fibers, polypropylene fibers, and glass fibers. The resin other than polyester comprises one or more selected from the group consisting of polyethylene resin, polypropylene resin, polyurethane resin, polystyrene resin, nylon resin, polyvinyl chloride resin and acrylic resin.

6. The method for manufacturing recycled polyester according to claim 1 or 2, wherein the polyester composite material is a polyester-containing fiber.

7. The method for manufacturing recycled polyester according to claim 6, wherein the polyester-containing fiber comprises at least a colorant, and titanium dioxide and / or fibers other than polyester. In step (A), the polyester-containing fibers are decolorized. In step (B), titanium oxide and / or fibers other than the polyester are removed.

8. The method for manufacturing recycled polyester according to claim 1 or 2, wherein the pH of the cleaning solvent is less than 13.

0.

9. The method for manufacturing recycled polyester according to claim 1 or 2, wherein the cleaning temperature of step (A) is above 30°C and below 150°C, and the dissolution temperature of step (B) is above 30°C and below 150°C.

10. The method for manufacturing recycled polyester according to claim 1 or 2, wherein the solvent (Y1) has a boiling point below 250°C.

11. The method for manufacturing recycled polyester according to claim 9, wherein the dissolution temperature of step (B) is higher than the cleaning temperature of step (A).

12. The method for manufacturing recycled polyester according to claim 1 or 2, wherein the content of solvent (X2) in the dissolving solvent of step (B) is greater than the content of solvent (X1) in the cleaning solvent of step (A).

13. The method for manufacturing recycled polyester according to claim 1 or 2, wherein the undesirable solvent (PS) is one or more selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, ketone solvents, aldehyde solvents, alcohol solvents, ether solvents and water.

14. The method for manufacturing recycled polyester according to claim 1 or 2, wherein the solvent (Y1) is one or more selected from the group consisting of toluene, xylene, heptane, hexane, acetone, methanol, ethanol, ethylene glycol, propylene glycol, and water. The undesirable solvent (PS) is one or more selected from the group consisting of acetone, toluene, methanol, ethanol and water.

15. The method for manufacturing recycled polyester according to claim 1 or 2, wherein the Ti content in the polyester composite material is 500 ppm or more, and the Ti content in the recycled polyester is 100 ppm or less.

16. The method for manufacturing recycled polyester according to claim 1 or 2, wherein the N content in the polyester composite material is 400 ppm or more, and the N content in the recycled polyester is 80 ppm or less.

17. The method for manufacturing recycled polyester according to claim 1, wherein before performing the solid-liquid separation in step (B), the solution containing the polyester is contacted with a filter aid.

18. The method for manufacturing recycled polyester according to claim 1 or 17, wherein the solution containing the polyester is contacted with a coagulant before the solid-liquid separation in step (B).

19. A method for manufacturing recycled polyester, comprising manufacturing recycled polyester from polyester composite materials, the method comprising the following steps (B2), (Z2), (C2), and (D2). Step (B2): The step of mixing the polyester composite material with a solvent (X2) containing a phenolic solvent and / or a chlorine-based organic solvent to obtain a solution in which the polyester in the polyester composite material is dissolved. Step (Z2): A step in which a solution containing the polyester is brought into contact with a coagulant and then solid-liquid separation is performed to obtain a liquid component (L2) containing the polyester. Step (C2): The liquid component (L2) is mixed with a poor solvent (PS) with a boiling point below 130°C to precipitate polyester, thereby obtaining a slurry. The slurry is then subjected to solid-liquid separation to obtain solid polyester. Process (D2): The process of drying the solid polyester to obtain recycled polyester.

20. The method for manufacturing recycled polyester according to claim 19, wherein before the solid-liquid separation of step (Z2), the solution containing the polyester is contacted with a filter aid.

21. The method for manufacturing recycled polyester according to claim 19, wherein the coagulant is one or more selected from the group consisting of inorganic salts other than alkali metals and alkaline earth metals and polymeric compounds.

22. The method for manufacturing recycled polyester according to claim 19 or 20, wherein the coagulant comprises an inorganic salt other than alkali metals and alkaline earth metals.

23. The method for manufacturing recycled polyester according to claim 22, wherein the inorganic salt other than alkali metal and alkaline earth metal is selected from one or more of the group consisting of ferric chloride (III), ferrous sulfate (II), ferric sulfate (III), aluminum sulfate and aluminum chloride.

24. The method for manufacturing recycled polyester according to claim 21, wherein a solution containing the polyester is contacted with the coagulant containing an inorganic salt other than the alkali metal and alkaline earth metal, and then contacted with the coagulant containing the polymer compound.

25. The method for manufacturing recycled polyester according to claim 21 or 24, wherein the polymer compound is one or more selected from the group consisting of polyacrylamide and polyethylene oxide.

26. The method for manufacturing recycled polyester according to claim 17 or 20, wherein the filter aid is one or more selected from the group consisting of activated carbon, activated clay, diatomaceous earth, silica gel, synthetic adsorbents, bentonite, alumina and zeolite.

27. A method for manufacturing a polyester composite material, comprising: a step of obtaining recycled polyester by a method for manufacturing recycled polyester selected from any one of claims 1, 2, 17, 19, 20, 21 and 24; and a step of using the obtained recycled polyester to manufacture a polyester composite material.

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