Method for producing molded body from used polyester product, and method for recycling used polyester product

Abstract

Provided is a method for producing, from a used polyester product, a polyester molded body that exhibits excellent chemical decomposition efficiency and is easy to chemically recycle. This method comprises: preparing, from a used polyester product, a polyester resin for which the IV value is 0.50 dL / g or more; adjusting the water content of the polyester resin and melt-kneading the polyester resin in an extruder for at least more than 20 seconds in a state in which the water content is more than 1,000 ppm and not more than 10,000 ppm; and discharging a polyester resin for which the IV value has been reduced to 0.40 dL / g or less from the extruder and rapidly cooling the resin to obtain a polyester molded body for which a crystallinity correlation parameter (ΔHTc1 / ΔHTm) is 0.50 to 0.75.

Description

Method for producing molded articles from used polyester products and method for recycling used polyester products

[0001] The present invention relates to a method for producing a molded article from a used polyester product, and more particularly to a method for producing a molded article suitable for recycling from a used polyester product, and a method for recycling used polyester products.

[0002] Plastic bottles are widely used in large quantities as containers for various liquids, such as drinking water, seasonings, cooking oil, alcoholic beverages, fuel, and detergents, due to their light weight and transparency, which allows the contents to be seen clearly. Of these, polyethylene terephthalate bottles (hereinafter sometimes referred to as PET bottles) account for the majority. Used plastic bottles were traditionally disposed of by incineration or landfill, but in recent years, the Act on the Promotion of Separate Collection and Recycling of Containers and Packaging has come into effect, and the separate collection and recycling of used plastic containers and packaging has begun, along with the collection and recycling of PET bottles.

[0003] Methods for recycling these used plastics include material recycling, in which used plastics are remanufactured as raw materials for reuse; chemical recycling, in which used plastics are broken down to the monomer level for reuse; and thermal recycling, in which used plastics are reused as energy.

[0004] Taking used PET bottles as an example, chemical recycling methods have been developed and are beginning to be put into practical use, in which polyester is chemically decomposed to recover oligomers or monomers and then repolymerized into polyester. Examples of known methods include a method in which used PET bottles are washed and crushed into flakes, and methanol is added to decompose them into dimethyl terephthalate, which is then hydrolyzed again to obtain high-purity terephthalic acid (see, for example, Patent Document 1); a method in which ethylene glycol is added to polyethylene terephthalate to decompose it into bis(2-hydroxyethyl) terephthalate, and the bis(2-hydroxyethyl) terephthalate is melt-polycondensed to obtain polyethylene terephthalate polymer (see, for example, Patent Document 2); and a method in which polyethylene terephthalate is reacted with water in a high-temperature, high-pressure state known as supercritical or subcritical, to hydrolyze it and obtain terephthalic acid (see, for example, Patent Document 3). Furthermore, a method in which polyethylene terephthalate is hydrolyzed with an enzyme to obtain terephthalic acid has also been proposed in recent years (see, for example, Patent Document 4).

[0005] Furthermore, a method for obtaining a monomer by enzymatic hydrolysis of a semi-crystalline polyester has been proposed in which the polymer is melted at a temperature equal to or higher than the melting point and then rapidly cooled to a temperature equal to or lower than the crystallization temperature to make it amorphous, thereby improving the decomposition efficiency (Patent Document 5).

[0006] Japanese Patent Application Laid-Open No. 2002-60369 Japanese Patent Application Laid-Open No. 2000-169623 Japanese Patent Application Laid-Open No. 2000-53801 Japanese Patent Application Laid-Open No. 2016-505650 U.S. Patent Publication No. 2019 / 218360

[0007] Chemical recycling methods, in which used plastics, particularly used polyester products, are decomposed to the monomer level for reuse, can basically be considered methods for chemically decomposing polymer materials. However, none of the conventionally known methods have been found to have sufficient decomposition efficiency for practical use, and there is room for improvement in terms of practical application.

[0008] Therefore, a main object of the present invention is to provide a method for producing a polyester molded product from a used polyester product, which has excellent chemical decomposition efficiency and is easy to chemically recycle, when recycling used polyester products. Another object of the present invention is to provide a method for recycling used polyester products using the method.

[0009] The present inventors have discovered that when used polyester products are remelted to produce molded bodies and then chemically recycled, molded bodies obtained through a specific manufacturing process have improved chemical decomposition efficiency. Based on this discovery, they conducted further studies and found that reducing the molecular weight of the polyester in the remelting process and rapidly cooling the polyester to prevent crystallization during cooling and solidification dramatically improves the chemical decomposition efficiency of the resulting molded body. The present invention is based on this discovery. Specifically, the gist of the present invention is as follows.

[0010] [1] A method for producing a molded article from a used polyester product, comprising: preparing a polyester resin having an IV value of 0.50 dL / g or more from the used polyester product; adjusting the moisture content of the polyester resin so that the moisture content is more than 1,000 ppm and less than 10,000 ppm; melt-kneading the polyester resin in an extruder for at least 20 seconds; discharging the polyester resin whose IV value has been reduced to 0.40 dL / g or less from the extruder and quenching it; and measuring a crystallinity correlation parameter (ΔH Ｔｃ１ / ΔH Ｔｍand obtaining a polyester molded product having a ratio (Q / N) of 0.50 to 0.75. [2] The method according to [1], wherein the melt-kneading temperature during the melt-kneading is 30 to 70°C higher than the melting point of the polyester resin. [3] The method according to [1], wherein the melt-kneading is carried out at a temperature 30 to 70°C higher than the melting point of the polyester resin for 20 to 65 seconds. [4] The method according to [1], wherein the melt-kneading is carried out so that the value of Q / N is in the range of 0.10 to 0.15, where Q (kg / h) is the total output rate of the molten polyester resin per unit time and N (rpm) is the screw rotation speed of the extruder. [5] The method according to [1], wherein the extruder is a twin-screw extruder equipped with a side vent and a side feeder. [6] The method according to [1], wherein the polyester resin has a flake shape. [7] The method according to [1], wherein the polyester molded body is an aggregate of granules having an average particle size of 0.5 to 5 mm and / or plates having a thickness of 0.1 to 2 mm. [8] The method according to [1], further comprising pulverizing the polyester molded body to obtain a pulverized body having an average particle size (D50) of 300 μm or less. [9] The method according to [1], wherein the used polyester product is a polyethylene terephthalate product.

[10] The method according to [1], wherein the recycling is carried out by chemical decomposition of a polyester resin.

[11] The method according to

[10] , wherein the chemical decomposition is an ester hydrolysis reaction using an enzyme.

[12] A method for recycling used products made of polyester, comprising chemically decomposing a polyester molded body obtained by the method according to any one of [1] to

[11] , to produce a diol component and / or a dicarboxylic acid component from the used polyester product.

[13] A method for recycling used polyester products, comprising: chemically decomposing a polyester molded article obtained by the method according to any one of [1] to

[11] to generate a diol component and / or a dicarboxylic acid component from the used polyester product; polymerizing a polyester using the diol component and / or the dicarboxylic acid component as at least a part of a polyester polymerization raw material; and producing a polyester product from the obtained polyester.

[0011] According to the method of the present invention, polyester molded articles that are excellent in chemical decomposition efficiency and easy to chemically recycle can be obtained from used polyester products.

[0012] In one embodiment of the present invention, there is provided a method for producing a molded article from a used polyester product. Each step of the method for producing a molded article according to one embodiment of the present invention will be described in detail below.

[0013] [Polyester Resin Preparation Process] First, a polyester resin having an IV value of 0.50 dL / g or more is prepared from a used polyester product. Used polyester products include various types of containers such as bottles, films, and sheets, and the product form is not particularly limited. However, among polyester products, products made of polyesters with an IV value of less than 0.50 dL / g are excluded. This is because polyester products with an IV value of less than 0.50 dL / g are considered to have excellent chemical decomposition efficiency and are easy to chemically recycle, even without the present invention, due to the low molecular weight of the polyester. In other words, products made of polyesters with a molecular weight above a certain level, i.e., an IV value of 0.50 dL / g or more, have poor chemical decomposition efficiency and are difficult to chemically recycle. Therefore, the main objective of the present invention is to provide a method for producing a polyester molded product that is easy to chemically recycle from a product made of such a high-molecular-weight polyester, which is inherently poor in chemical decomposition efficiency.

[0014] Examples of polyesters that can be used include aromatic polyesters such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polyethylene furanoate; wholly aromatic polyesters such as polyarylates and liquid crystal polymers; polycarbonates such as polycarbonates; aliphatic polyesters such as polylactic acid polymers, polybutylene succinate polymers, polyethylene adipate polymers, polyethylene succinate polymers, polycaprolactone polymers, and polyhydroxyalkanoate polymers; and aliphatic aromatic polyesters such as polybutylene adipate terephthalate, polyethylene adipate terephthalate, and polyethylene succinate terephthalate. The polyesters that make up used polyester products are not limited to those derived from petroleum-based materials; they may also be polyesters derived from plant-based materials, or polyesters recycled from these petroleum- or plant-based polyesters. The above polyesters may be used alone or in combination. Among these, polyethylene terephthalate, which is widely used as a material for bottle containers, is particularly useful.

[0015] Polyethylene terephthalate is obtained by polycondensation of two main constituent monomers, ethylene glycol and terephthalic acid, but other monomers may be copolymerized as diol or dicarboxylic acid components in addition to these two components.

[0016] As copolymerization components of polyethylene terephthalate, examples of dicarboxylic acid components include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, eicosanedioic acid, pimelic acid, azelaic acid, methylmalonic acid, ethylmalonic acid, adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, decalindicarboxylic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodiumsulfoisophthalic acid, phenylendanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, 9,9'-bis(4-carboxyphenyl)fluorene acid, 2,5-furandicarboxylic acid, and ester derivatives thereof.

[0017] Examples of copolymerization components for polyethylene terephthalate include diol components such as 1,2-propanediol, 1,3-propanediol, butanediol, 2-methyl-1,3-propanediol, hexanediol, neopentyl glycol, cyclohexanedimethanol, cyclohexanediethanol, decahydronaphthalenedimethanol, decahydronaphthalenediethanol, norbornanedimethanol, norbornanediethanol, tricyclodecanedimethanol, tricyclodecaneethanol, tetracyclododecanedimethanol, tetracyclododecanediethanol, decalindimethanol, decalindiethanol, 5-methylol-5 -ethyl-2-(1,1-dimethyl-2-hydroxyethyl)-1,3-dioxane, cyclohexanediol, bicyclohexyl-4,4'-diol, 2,2-bis(4-hydroxycyclohexylpropane), 2,2-bis(4-(2-hydroxyethoxy)cyclohexyl)propane, cyclopentanediol, 3-methyl-1,2-cyclopentadiol, 4-cyclopentene-1,3-diol, adamantanediol, paraxylene glycol, bisphenol A, bisphenol S, styrene glycol, trimethylolpropane, pentaerythritol, and bis-β-hydroxyethyl terephthalate (BHET).

[0018] Although polyester products are composed of the above-mentioned polyesters, they may contain other components such as additives, for example, one or more of various additives such as plasticizers, light stabilizers, antioxidants, ultraviolet absorbers, flame retardants, colorants, pigments, fillers, release agents, antistatic agents, fragrances, foaming agents, antibacterial and antifungal agents, etc.

[0019] The form of used polyester products is not particularly limited, but for example, the IV value is about 0.75 to 0.85 dL / g for bottle containers, about 0.70 to 0.80 dL / g for films or sheets, and about 0.65 to 0.75 dL / g for fibers. The IV value can be measured by a standard method in accordance with JIS K7390.

[0020] When remelting used polyester products having various shapes as described above to produce molded articles, it is preferable to form the polyester products into a predetermined shape so that they can be easily remelted in an extruder. Therefore, in the method of the present invention, when preparing a polyester resin obtained from used polyester products, it is preferable that the polyester resin be in a flake shape. For example, used polyester products collected from the market are sorted and pulverized into flakes. The pulverization can be carried out using a pulverizer such as a single-shaft pulverizer, a biaxial pulverizer, a triaxial pulverizer, or a cutter mill. The flake shape refers to a thin or flat shape with a thickness of approximately 2 mm or less.

[0021] In addition, since crushed used polyester products may contain or be contaminated with substances other than polyester, it is preferable to wash the crushed products with water and then carry out water separation or air separation. Water separation is a separation method that utilizes the difference in density of materials, and is used when the specific gravity is less than 1 g / cm. ３ It is possible to separate polyesters having a specific gravity of 1 g / cm or more from substances or materials having a specific gravity lower than that of water. Also, winnowing is a separation method for separating pulverized materials by wind power. For example, in a separator capable of generating a rotating air current inside, pulverized materials hit by the air current generated by the separator can be separated into those with a high specific gravity or bulk specific gravity that fall naturally under their own weight, and those with a low specific gravity or bulk specific gravity that are blown up by the air current. Winnowing is a method for separating pulverized materials having a specific gravity of 1 g / cm or less that fall naturally under their own weight, and those with a low specific gravity or bulk specific gravity that are blown up by the air current. ３ It is effective for separating substances that are

[0022] The polyester resin (e.g., flakes) obtained as described above may then be washed by any washing means such as alkali washing, hot water washing, etc. Washing can remove contaminants such as residues of the contents remaining on the surface of the pulverized polyester resin and contaminated foreign matter, thereby producing a polyester molded product with high purity.

[0023] [Polyester Resin Melt-Kneading Process] Next, the polyester resin obtained as described above, having an IV value of 0.50 dL / g or more, is remelted in an extruder. The polyester resin is melt-kneaded in the extruder for at least 20 seconds while maintaining a water content of more than 1,000 ppm and less than 10,000 ppm. This melt-kneading process actively reduces the molecular weight of the polyester. That is, in the polyester remelting process, kneading is performed for a predetermined time with a predetermined water content, causing hydrolysis of the polyester, and a polyester resin with an IV value reduced to 0.40 dL / g or less can be discharged from the extruder. The IV value of the polyester resin obtained by the melt-kneading process is preferably 0.25 to 0.35 dL / g, and more preferably reduced to approximately 0.3 dL / g. Note that if the IV value of the polyester resin obtained by the melt-kneading process is too low, it tends to become liquid when discharged from the extruder, making it difficult to obtain a molded product.

[0024] The IV value refers to a value measured at 25° C. using a relative viscometer to prepare a solution by dissolving a polyester test piece in a phenol:tetrachloroethane=1:1 solvent. The water content refers to a value measured using a Karl Fischer reagent, and specifically can be measured using a Karl Fischer moisture meter (for example, CA-310 manufactured by Nitto Seiko Analytech Co., Ltd.).

[0025] The extruder used in the present invention comprises at least a cylinder equipped with a hopper into which polyester resin is introduced, and a screw located within the cylinder that compresses and melts the polyester resin supplied from the hopper into the cylinder while transporting it to the cylinder outlet. The hopper is located at the most upstream side of the cylinder, and the polyester resin supplied from there is transported within the cylinder toward the downstream side (extrusion port side) by the screw. The extrusion port of the extruder is the part from which the molten resin is extruded from the cylinder, and the extrusion port may be equipped with an appropriate screen changer or gear pump. This allows the extrusion amount of the re-melted resin to be adjusted.

[0026] The polyester resin fed from the hopper is compressed and heated while being transported through the cylinder by the screw toward the extrusion port, during which the polyester resin partially melts, becoming a mixture of solid and molten resin. After being transported a certain distance, the entire resin becomes molten. In the present invention, it is preferable to use a twin-screw extruder in which a pair of parallel screws driven by a drive source such as a motor are interposed within the cylinder. The use of a twin-screw extruder makes it easier to adjust the melt-kneading time than an extruder equipped with a single screw.

[0027] The cylinder inner diameter D (mm) of the extruder is not particularly limited, but when the screw length is L (mm), L / D is preferably 30 to 60, more preferably 40 to 60. If L / D is less than 30, the residence time in the extruder is short, the polyester is not sufficiently hydrolyzed, and the IV value may not be reduced to 0.40 dL / g or less. On the other hand, if L / D exceeds 60, the polyester itself may be denatured or decomposed, which is undesirable.

[0028] In the present invention, the extruder used preferably has a side feeder capable of injecting water into a region where the polyester resin introduced into the cylinder from the hopper is not completely melted, i.e., where the polyester resin is a mixture of solid and molten resin, or where the polyester resin is completely melted. In the present invention, the polyester resin is melt-kneaded at a moisture content of more than 1,000 ppm and not more than 10,000 ppm to actively promote hydrolysis of the polyester. While the moisture content may be adjusted by simultaneously adding water when introducing the polyester resin into the hopper, adding a dried polyester resin to the hopper makes it easier to adjust the moisture content. Therefore, it is preferable to introduce a dried polyester resin from the hopper and then inject water into the side feeder to adjust the moisture content. The extruder may also have a side vent (vacuum vent) between the side feeder and the hopper. Even for polyester resins with high moisture content, the polyester can be dried by removing the moisture through the vacuum vent, allowing the moisture content to be adjusted via the side feeder. The moisture content can be calculated from the amount of polyester resin fed per hour and the amount of water fed from the side feeder.

[0029] Melt-kneading in the cylinder of the extruder is preferably carried out at a temperature 30 to 70°C higher than the melting point of the polyester resin. While higher melt-kneading temperatures are thought to promote hydrolysis of the polyester, melt-kneading temperatures that are too high are undesirable because they can denature or decompose the polyester itself. For example, polyethylene terephthalate, the most commonly used polyester, has a melting point of approximately 260°C, so melt-kneading in a temperature range of 290 to 330°C is preferred. It is not necessary to maintain the entire cylinder at the same temperature; for example, the region from the hopper to the side feeder (i.e., the region where the solid resin and molten resin are mixed) can be 240 to 270°C, and the region where melt-kneading is performed at a predetermined water content (the region from the side feeder to the extrusion port) can be 290 to 330°C. The melting point of the polyester resin refers to the peak-top temperature (°C) of the melting peak observed on the highest temperature side during the heating process, measured using a differential scanning calorimeter (DSC) under the following measurement conditions: <DSC measurement conditions> Atmosphere: Nitrogen atmosphere Measurement temperature range: 40 to 290°C Heating rate: 10°C / min Sample weight: 8 mg

[0030] The melt-kneading time in the extruder is more than 20 seconds, preferably more than 20 seconds and not more than 65 seconds. It is believed that the longer the melt-kneading time, the more the hydrolysis of the polyester will proceed. However, if the melt-kneading time is too long, the polyester itself will be denatured or decomposed, which is not preferable.

[0031] The melt-kneading time may be adjusted so that the value of Q / N is in the range of 0.10 to 0.15, where Q (kg / hour) is the total output amount of the molten polyester resin per unit time and N (rpm) is the screw rotation speed of the extruder. If the value of Q / N is too low, there is a high possibility that the melt-kneading time in the extruder cannot be secured. On the other hand, if the value of Q / N is too high, there is a possibility that the polyester resin will be oversupplied and will not be able to be fully introduced into the cylinder from the hopper.

[0032] In addition, the extruder used in the present invention is preferably equipped with a side vent in the region from the side feeder to the extrusion port. In the present invention, since the polyester is actively hydrolyzed in the melt-kneading step as described above, there is a risk that vaporized water will be contained when the molten polyester is discharged from the extrusion port, causing foaming. Therefore, it is preferable to remove the vaporized excess water under reduced pressure through the side vent (vacuum vent port).

[0033] [Quenching and Solidification Process] After melt-kneading the polyester resin as described above, the molten polyester is discharged from the extrusion port of the extruder and rapidly cooled. In the present invention, the polyester is melt-kneaded at a predetermined water content in the extruder, and the molecular weight is reduced by hydrolysis, resulting in the IV value of the polyester discharged from the extruder being 0.40 dL / g or less. Therefore, compared to polyesters with a normal IV value of 0.50 dL / g or more, oriented crystallization and spherulitization may occur. It is known that the lower the molecular weight (the lower the IV value), the easier it is to crush the molded product, and that producing a crushed product with an increased surface area increases the chemical decomposition efficiency of the polyester resin. However, the present inventors have discovered that even when the molecular weight of the polyester is reduced and the surface area is increased, the chemical decomposition efficiency of the crystallized portions of the polyester is reduced. Therefore, the present inventors have discovered that by rapidly cooling a molten polyester with a low IV value (0.40 dL / g or less) to obtain a polyester molded product with a crystallinity correlation parameter of 0.50 to 0.75, the chemical decomposition efficiency of the resulting molded product is dramatically improved.

[0034] Crystallinity correlation parameter (ΔH Ｔｃ１ / ΔH Ｔｍ There is no particular limitation on the means for quenching so that ΔH ) becomes 0.50 to 0.75, but by quenching while minimizing the application of elongation stress to the molten polyester, it is possible to reduce ΔH Ｔｃ１ / ΔH ＴｍExamples of devices capable of rapidly cooling molten polyester while minimizing the application of elongation stress include underwater cut and water slider type pelletizers, in which polyester discharged from an extruder is immediately immersed in or brought into contact with water to cool and solidify, and molded (pelletized) into a predetermined shape, and molding devices such as steel belt coolers and drum flakers, in which polyester is clamped between or brought into contact with metal plates having excellent thermal conductivity to rapidly cool the polyester, and molded into a predetermined shape (for example, flake shape).

[0035] Here, the crystallinity correlation parameter is an index for determining the degree of crystallization of a polymer, and is the crystallization enthalpy (ΔH) during heating obtained from a melting endothermic curve measured using a differential scanning calorimeter (DSC). Ｔｃ１ ) and crystalline melting enthalpy (ΔH Ｔｍ This value is negatively correlated with the degree of crystallinity measured by a density gradient method or the like. Crystallinity correlation parameter (X) = ΔH Ｔｃ１ / ΔH Ｔｍ <Measurement conditions> Atmosphere: Nitrogen atmosphere Measurement temperature range: 40 to 290°C Heating rate: 10°C / min Sample weight: 8 mg

[0036] In the present invention, from the viewpoint of obtaining a polyester molded article having a small amount of crystalline portions and excellent chemical decomposition efficiency, the crystallinity correlation parameter is preferably in the range of 0.60 to 0.73.

[0037] The molded product obtained by rapidly solidifying the polyester melt using the above-mentioned pelletizer or the like is preferably an aggregate of granules having an average particle size of 0.5 to 5 mm and / or plates having a thickness of 0.1 to 2 mm. These granules or plates may be subjected to chemical recycling as is, but to further improve the chemical decomposition efficiency, the molded product may be pulverized to reduce the particle size. By producing pulverized products having an average particle size (D50) of 300 μm or less, the surface area can be increased as described above, thereby further improving the chemical decomposition efficiency.

[0038] The compact can be pulverized using a conventionally known wet or dry pulverizer, and it is preferable to use a pulverizer such as a hammer mill, disk mill, pin mill, cutter mill, roller mill, jet mill, bead mill, or ball mill. Furthermore, two or more of the above-mentioned pulverizers may be combined to improve pulverization efficiency. By using such a pulverizer, the above-mentioned granular pulverized product having an average particle size of 300 μm or less can be easily and simply obtained.

[0039] [Method for recycling used polyester products] By using the molded body obtained by the method of the present invention, it is possible to efficiently recycle used polyester resin products. For example, by chemically decomposing the pulverized molded body produced from the used polyester resin product as described above using a conventionally known method, it is possible to obtain monomers or oligomers that constitute the polyester from the used polyester resin product. By polymerizing the obtained monomers or oligomers, it is possible to produce polyester resin products again from the used polyester resin product.

[0040] As an example of chemical recycling of polyester resin products, polyester resin obtained by crushing used PET bottles is remelted to produce a molded product of the present invention, and the molded product is then immersed in a solvent such as methanol or ethylene glycol, an alkaline solution, or a medium containing an enzyme, whereby polyethylene terephthalate is depolymerized to obtain ethylene glycol and terephthalic acid.

[0041] Hydrolysis of PET can be carried out using, for example, a raw material composition containing a molded article, a microorganism capable of expressing and excreting a degrading enzyme, water, etc. Alternatively, instead of a microorganism, a purified enzyme produced by the microorganism may be used as the degrading enzyme. A buffer may be added to the raw material composition to stabilize the pH. The pH of the raw material composition is preferably 5 to 11 from the viewpoint of enzyme activity.

[0042] The depolymerization treatment time is preferably 1 to 24 hours, more preferably 4 to 16 hours.

[0043] To isolate the monomer from the recovered active ingredient, the monomer (terephthalic acid) may be extracted with an organic solvent in which the monomer is soluble, and the monomer constituting the polyester may be isolated from the extracted monomer solution by distillation, crystallization, etc. Alternatively, the monomer solution may be subjected to crystallization or distillation as is. Alternatively, the monomer solution may be subjected to ion exchange treatment or the like, followed by extraction, distillation, crystallization, etc.

[0044] In the above-mentioned chemical recycling, the use of a medium containing an enzyme for depolymerization eliminates the need for solvent recovery equipment and the like, compared with the use of a solvent such as methanol or ethylene glycol, and therefore allows chemical recycling to be performed more efficiently and at lower cost.

[0045] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0046] <Raw Materials Used> A polyester resin (in flake form) prepared from used PET bottles was used, having a weight average molecular weight of 54,000, an IV value of 0.83, and a melting point of 250° C. The melting point, weight average molecular weight, and IV value were measured as follows.

[0047] The melting point of the polyester resin was measured using a differential scanning calorimeter (PerkinElmer, DSC8500) by sealing approximately 8 mg of a sample piece of the polyester resin in an aluminum pan (PerkinElmer). The measurement conditions were a temperature rise rate of 10°C / min and a measurement temperature range of 40 to 290°C. The peak top temperature of the melting peak observed on the highest temperature side during the temperature rise process was taken as the melting point.

[0048] The weight-average molecular weight was measured by first dissolving a polyester resin test piece in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) to prepare a solution, and then measuring the weight-average molecular weight using a high-performance GPC system (HLC-8320GPC, manufactured by Tosoh Corporation) at 40°C. Chloroform was used as the mobile phase, and a TSKgel Super HM-H column manufactured by Tosoh Corporation was used. TSKgel standard polystyrene manufactured by Tosoh Corporation was used as the molecular weight standard.

[0049] The IV value was measured by preparing a solution by dissolving a polyester resin test piece in a phenol:tetrachloroethane = 1:1 solvent, and adjusting the temperature to 25°C using a relative viscometer (Viscotec Y501C, manufactured by Malvern Panalytical).

[0050] [Production Example 1] First, the polyester resin was allowed to stand for at least one week under conditions of 30°C temperature and 80% RH, thereby adjusting the moisture content to 5,000 ppm. The moisture content was measured using a Karl Fischer moisture meter (CA-310, manufactured by Nitto Seiko Analytech Co., Ltd.). Next, the polyester resin with the adjusted moisture content was supplied to a twin-screw extruder (ULTNano 05-20AG, manufactured by Technovel Co., Ltd.) and melted at a barrel temperature of 300°C. The screw rotation speed N [rpm] was changed to adjust the residence time of the molten resin in the twin-screw extruder to 38 seconds. At this time, the resin discharge rate Q [kg / hr] was also changed to maintain a constant Q / Ns (resin filling rate) (0.13). The molten resin discharged from the die of the twin-screw extruder in this manner was sampled. The weight average molecular weight and IV value of the sampled resin were measured in the same manner as described above. The measurement results were as shown in Table 1 below.

[0051] [Production Example 2] The molten resin was sampled and the weight average molecular weight and IV value were measured in the same manner as in Production Example 1, except that the residence time of the molten resin in the twin-screw extruder was changed to 15 seconds.

[0052] [Production Example 3] The molten resin was sampled and the weight average molecular weight and IV value were measured in the same manner as in Production Example 1, except that the residence time of the molten resin in the twin-screw extruder was changed to 20 seconds.

[0053] [Production Example 4] A polyester resin was allowed to stand for one week or more under conditions of a temperature of 25°C and a humidity of 50% RH, thereby adjusting the moisture content to 1,000 ppm. The molten resin was sampled in the same manner as in Production Example 1, except that the polyester resin with the moisture content adjusted as described above was used, and the weight average molecular weight and IV value were measured.

[0054]

[0055] As is clear from the evaluation results in Table 1, even when a polyester resin with a weight-average molecular weight of 54,000 and an IV value of 0.83 was used as a raw material, melt-kneading for more than 20 seconds at a water content of more than 1,000 ppm and less than 10,000 ppm produced a polyester with a weight-average molecular weight of 21,000 and an IV value of 0.40 dL / g (Production Example 1). The reduced weight-average molecular weight and IV increase the brittleness of PET, improving the efficiency of the subsequent crushing process, increasing the surface area of ​​the crushed product, and improving recyclability. On the other hand, a water content of 1,000 ppm did not sufficiently reduce the weight-average molecular weight and IV value, preventing the production of a polyester with an IV value of 0.40 dL / g or less (Production Example 4). It is believed that a water content of more than 10,000 ppm could result in excess water being ejected with the molten resin during extrusion, potentially impairing moldability. Furthermore, it is clear that if the melt-kneading time is 20 seconds or less, the weight-average molecular weight and IV value do not decrease sufficiently, and a polyester with an IV value of 0.40 dL / g or less cannot be obtained (Production Examples 2 and 3). Note that if the melt-kneading time is longer than necessary, the thermal decomposition of the polyester will proceed, generating a large amount of foreign matter such as burnt matter, which is thought to reduce the recyclability.

[0056] [Example 1] In the same manner as in Production Example 1, a resin was extruded in the form of a strand from the die of an extruder and solidified by being poured into cold water at 20°C to obtain a polyester pellet-shaped product having a diameter of approximately 3 mm. The time from extrusion from the die to being poured into the cold water was 0.5 seconds.

[0057] The crystallinity correlation parameters were measured for the polyester molded article obtained as described above. Specifically, the measurement was carried out as follows. First, approximately 8 mg of the polyester molded article was sealed in an aluminum pan (manufactured by PerkinElmer) and subjected to measurement using a differential scanning calorimeter (manufactured by PerkinElmer, DSC8500). The measurement was carried out under the condition of a temperature rise rate of 10°C / min. The analysis software "Pyris" manufactured by PerkinElmer was used for data analysis. From the heat flow profile obtained from the measurement, the crystallization enthalpy (ΔH Ｔｃ１) and crystalline melting enthalpy (ΔH Ｔｍ The calculation range was set appropriately depending on the peak shape. Ｔｃ１ and ΔH Ｔｍ The crystallinity correlation parameter (X) was calculated from the following formula: X = ΔH Ｔｃ１ / ΔH Ｔｍ This value has a negative correlation with the crystallinity measured by a density gradient method or the like, and a value of about 0.50 to 0.75 is considered to indicate a small amount of crystalline material. The measurement results are shown in Table 2 below.

[0058] The polyester molded body obtained as described above was pulverized using a freeze-pulverizing device (6770, manufactured by SPEX Sample Prep) to obtain a pulverized product. The average particle size was measured in a dry free-fall mode using a laser diffraction particle size distribution analyzer (SALD-3100, manufactured by Shimadzu Corporation).

[0059] 10.5 mg of the resulting pulverized material was immersed in a buffer solution containing the enzyme for 24 hours. The decomposition product concentration was measured to confirm the chemical decomposition efficiency. The decomposition product concentrations, terephthalic acid and MHET (monohydroxyethyl terephthalate), were measured using a high-performance liquid chromatograph (manufactured by JASCO Corporation). The measurement results of the decomposition product concentrations are shown in Table 2 below. The theoretical value of the decomposition product concentration when all the decomposition products are terephthalic acid and MHET, is 109 mM.

[0060] Example 2: The resin strand extruded from the die was sandwiched between a pair of steel plates cooled with 25°C cold water to solidify the resin and obtain a polyester molded body in the form of a plate approximately 1 mm thick. The molded body was then pulverized and the decomposition product concentration was measured in the same manner as in Example 1. The weight-average molecular weight and IV value of the resin sample extruded from the die were measured, as were the crystallinity correlation parameter of the molded body and the average particle size of the pulverized molded body. The measurement results are shown in Table 2 below.

[0061] Comparative Example 1 A polyester molded article was obtained in the same manner as in Example 1, except that the resin was solidified by air cooling. The obtained molded article was then pulverized, and the concentration of decomposition products was measured. Furthermore, the weight-average molecular weight and IV value of the resin sample discharged from the die were measured, as well as the crystallinity correlation parameter of the molded article and the average particle size of the pulverized molded article, all in the same manner as above. The measurement results are shown in Table 2 below.

[0062] Comparative Example 2 The molten resin was discharged from the extruder die in the same manner as in Production Example 4, except that the residence time of the molten resin in the twin-screw extruder was changed to 15 seconds, and after cooling and pulverization in the same manner as in Example 1, the decomposition product concentration was measured. Furthermore, the weight average molecular weight and IV value of the resin sample discharged from the die were measured, as well as the crystallinity correlation parameter of the molded body and the average particle size of the pulverized molded body, all in the same manner as above. The measurement results are shown in Table 2 below.

[0063] [Reference Example 1] 10.5 mg of polyester resin (average particle size: approximately 2,000 μm) used as a raw material was immersed in a buffer solution containing an enzyme for 24 hours, and the concentration of decomposition products was measured in the same manner as above. The measurement results of the decomposition product concentration are shown in Table 2 below.

[0064]

[0065] As is clear from the evaluation results in Table 2, even in the case of polyesters in which crystallization is facilitated by reducing the IV value to 0.4 dL / g or less, a molded article with a high crystallinity correlation parameter (i.e., a large amount of amorphous portion) can be obtained by rapid cooling using a cooled medium, and it is clear that this polyester molded article has excellent chemical decomposition efficiency and is easy to chemically recycle (Examples 1 and 2).

[0066] On the other hand, even if the average particle size of the pulverized material is similar to that of Examples 1 and 2, it is clear that the chemical decomposition efficiency is insufficient in polyester molded articles with a high degree of crystallinity (Comparative Example 1).

[0067] Furthermore, polyester resins melt-kneaded for 20 seconds or less at a low water content did not have an IV value of 0.4 or less, and polyester molded articles rapidly solidified at a high IV value had a high crystallinity correlation parameter (i.e., many amorphous portions), but it was difficult to obtain fine powder even after pulverization, and as a result, it was found that the chemical decomposition efficiency was insufficient (Comparative Example 2).

[0068] As shown in the evaluation results of Production Examples, Examples, and Comparative Examples, a polyester resin having an IV value of 0.50 dL / g or more was prepared, the water content of the polyester resin was adjusted, and the polyester resin was melt-kneaded in an extruder for at least 20 seconds while the water content was between 1,000 ppm and 10,000 ppm. The polyester resin, whose IV value had been reduced to 0.40 dL / g or less, was then discharged from the extruder and quenched, and the crystallinity correlation parameter (ΔH Ｔｃ１ / Δ ＨＴｍ By making the polyester molding into one having a % % saturation ratio of 0.50 to 0.75, the chemical decomposition efficiency can be improved, and the chemical recycling of used polyester products can be carried out easily and efficiently.

Claims

1. A method for producing a molded article from a used polyester product, comprising: preparing a polyester resin having an IV value of 0.50 dL / g or more from the used polyester product; adjusting the moisture content of the polyester resin; melt-kneading the polyester resin in an extruder for at least 20 seconds in a state in which the moisture content is more than 1,000 ppm and less than 10,000 ppm; discharging the polyester resin with an IV value of 0.40 dL / g or less from the extruder and quenching it; and measuring the crystallinity correlation parameter (ΔH Ｔｃ１ / ΔH Ｔｍ obtaining a polyester molding having a molecular weight of 0.50 to 0.

75.

2. The method according to claim 1, wherein the melt-kneading temperature is 30 to 70° C. higher than the melting point of the polyester resin.

3. The method according to claim 1, wherein the melt-kneading is carried out at a temperature 30 to 70° C. higher than the melting point of the polyester resin for 20 to 65 seconds.

4. The method according to claim 1, wherein the melt kneading is carried out so that the value of Q / N is in the range of 0.10 to 0.15, where Q is a total output amount of the molten polyester resin per unit time (kg / hour) and N is a screw rotation speed of the extruder (rpm).

5. The method of claim 1, wherein the extruder is a twin screw extruder equipped with a side vent and a side feeder.

6. The method of claim 1, wherein the polyester resin has a flake shape.

7. The method according to claim 1, wherein the polyester molded body is an aggregate of granules having an average particle size of 0.5 to 5 mm and / or platelets having a thickness of 0.1 to 2 mm.

8. The method according to claim 1, further comprising pulverizing the polyester molding to obtain a pulverized product having an average particle size (D50) of 300 μm or less.

9. The method of claim 1, wherein said post-consumer polyester product is a polyethylene terephthalate product.

10. The method of claim 1, wherein said recycling is carried out by chemical decomposition of the polyester resin.

11. The method according to claim 10, wherein the chemical degradation is an enzymatic ester hydrolysis reaction.

12. A method for recycling used products made of polyester, comprising chemically decomposing a polyester molded article obtained by the method according to any one of claims 1 to 11 to generate a diol component and / or a dicarboxylic acid component from the used polyester product.

13. A method for recycling used polyester products, comprising: chemically decomposing a polyester molded body obtained by the method according to any one of claims 1 to 11 to generate a diol component and / or a dicarboxylic acid component from the used polyester product; polymerizing a polyester using the diol component and / or the dicarboxylic acid component as at least a part of a polyester polymerization raw material; and producing a polyester product from the obtained polyester.

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