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

Abstract

To provide a method for producing polyester molding bodies from used polyester products that have excellent chemical decomposition efficiency and are easy to chemically recycle.SOLUTION: The method of producing a molded body from a used polyester product is to prepare a polyester resin having an IV value of 0.50 dL / g or more from the used polyester product, adjust the moisture content of the polyester resin, and then, while the moisture content is more than 1,000 ppm and less than 10,000 ppm, to perform the Melt kneading of the polyester resin is carried out for at least 20 seconds to reduce the IV value to 0.40 dL / g or less, and the polyester resin is discharged from the extruder and quenched to obtain a polyester molding body with a crystallinity correlation parameter (ΔHTc1 / Δ HTm) of 0.50 to 0.75.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Plastic bottles are widely and massively used as containers for various liquid substances such as drinking water, seasonings, edible oils, alcoholic beverages, fuels, and detergents because of their light weight and transparency that allows the contents to be clearly visible. Among them, polyethylene terephthalate bottles (hereinafter sometimes referred to as PET bottles) account for the majority. Used plastic bottles were conventionally disposed of by incineration or landfilling, but in recent years, laws regarding the promotion of separate collection and recycling of containers and packaging have been implemented, and the collection and recycling of PET bottles, as well as the separate collection and recycling of used plastics for containers and packaging, have been initiated.

[0003] As methods for recycling these used plastics, there are material recycling in which used plastics are remanufactured and utilized as raw materials, chemical recycling in which used plastics are decomposed to the monomer level and reused, thermal recycling in which used plastics are reused as energy, and the like.

[0004] Taking used PET bottles as an example, as a chemical recycling method, a method has been developed and is beginning to be put into practical use, in which polyester is chemically decomposed to recover oligomers or monomers and then polyester is polymerized again. For example, a method of washing and pulverizing used PET bottles into flakes, adding methanol to decompose them into dimethyl terephthalate, and then hydrolyzing them again to obtain high-purity terephthalic acid (Patent Document 1, etc.), or adding ethylene glycol to polyethylene terephthalate to decompose it into bis(2-hydroxyethyl) terephthalate, and melt polycondensing bis(2-hydroxyethyl) terephthalate to obtain a polyethylene terephthalate polymer (Patent Document 2), and also a method of reacting polyethylene terephthalate with water in a high-temperature and high-pressure state called supercritical or subcritical to hydrolyze it to obtain terephthalic acid (Patent Document 3) are known. Furthermore, in recent years, a method of hydrolyzing polyethylene terephthalate with an enzyme to obtain terephthalic acid has also been proposed (Patent Document 4).

[0005] Also, as a method of obtaining monomers by hydrolyzing semi-crystalline polyester with an enzyme, it has been proposed that the decomposition efficiency can be improved by melting the polymer at a temperature above the melting point and rapidly cooling it to below the crystallization temperature to make it amorphous (Patent Document 5).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

[0007] The chemical recycling method of decomposing used plastics, especially used polyester products, to the monomer level for reuse can basically be said to be a method of chemically decomposing polymer materials. However, none of the conventionally known methods can be said to have sufficient decomposition efficiency for practical use, and there was room for improvement in practical use.

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

[0009] The inventors remelted used polyester products to produce molded bodies, and in the case of chemically recycling the molded bodies, they obtained the finding that the chemical decomposition efficiency is improved in the molded bodies obtained through specific manufacturing processes. Based on such findings, further studies were conducted, and it was found that by reducing the molecular weight of the polyester in the remelting process and rapidly cooling it so that it does not crystallize during cooling and solidification, the chemical decomposition efficiency of the obtained molded body is dramatically improved. The present invention is based on such findings. That is, the gist of the present invention is as follows.

[0010] [1] A method for producing a molded body from used polyester products, comprising: preparing a polyester resin having an IV value of 0.50 dL / g or more from the used polyester products; adjusting the moisture content of the polyester resin, and carrying out melt-kneading of the polyester resin in an extruder for at least more than 20 seconds in a state where the moisture content exceeds 1,000 ppm and is 10,000 ppm or less; discharging the polyester resin with an IV value reduced to 0.40 dL / g or less from the extruder and rapidly cooling it, and the crystallinity correlation parameter (ΔH Tc1 / ΔH Tm) to obtain a polyester molded article having a value of 0.50 to 0.75, A method including this. [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] When the total discharge amount per unit time of the molten polyester resin is Q (kg / hour) and the screw rotation speed of the extruder is N (rpm), the melt-kneading is carried out so that the value of Q / N is in the range of 0.10 to 0.15. The method according to [1]. [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 article is an aggregate of granular bodies having an average particle diameter of 0.5 to 5 mm and / or plate-like bodies having a thickness of 0.1 to 2 mm. [8] The method according to [1], further including pulverizing the polyester molded article to obtain a pulverized product having an average particle diameter (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 the polyester resin.

[11] The method according to

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

[12] Chemically decomposing the polyester molded article 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, A recycling method for a used product composed of polyester, including this.

[13] Chemically decompose the polyester molded article 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, Use the diol component and / or the dicarboxylic acid component as at least a part of the polyester polymerization raw material to polymerize polyester, Manufacture a polyester product from the obtained polyester, A method for recycling used polyester products, which includes this.

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

Embodiments for Carrying Out the Invention

[0012] In one embodiment of the present invention, a method for manufacturing a molded article from a used polyester product is provided. Hereinafter, each step of the method for manufacturing the molded article in one embodiment of the present invention will be described in detail.

[0013] [Polyester Resin Preparation Step] First, a polyester resin having an IV value of 0.50 dL / g or more is prepared from used polyester products. The used polyester products include various items such as containers like bottles, films, sheets, etc., and the product form is not particularly limited. However, among the polyester products, products made of polyester with an IV value of less than 0.50 dL / g are excluded. In polyester products with an IV value of less than 0.50 dL / g, it is considered that even without the present invention, since the molecular weight of the polyester is low, the chemical decomposition efficiency is excellent and it is easy to perform chemical recycling. In other words, products composed of polyester with a molecular weight high enough that the IV value is 0.50 dL / g or more have poor chemical decomposition efficiency and are difficult to chemically recycle. In the present invention, the main object is to provide a method for producing a polyester molded article that is easy to chemically recycle from products composed of such high-molecular-weight polyesters that are inherently inferior 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 polyarylate and liquid crystal polymers; polyester carbonates such as polycarbonate; polylactic acid-based polymers; polybutylene succinate-based polymers; polyethylene adipate-based polymers; polyethylene succinate-based polymers; polycaprolactone-based polymers; aliphatic polyesters such as polyhydroxyalkanoate-based polymers; and aliphatic-aromatic polyesters such as polybutylene adipate terephthalate, polyethylene adipate terephthalate, and polyethylene succinate terephthalate. The polyester constituting the used polyester product is not limited to those derived from petroleum raw materials, and may be a polyester derived from plant raw materials, or further, a polyester recycled from these petroleum raw material-derived or plant raw material-derived polyesters. Also, the above-mentioned polyesters may be used alone or in combination. Among these, polyethylene terephthalate, which is used in a large amount as a material for bottle containers, is particularly useful.

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

[0016] As the copolymerization components of polyethylene terephthalate, examples of the dicarboxylic acid component include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, eicosanedioic acid, pimelic acid, azelaic acid, methylmalonic acid and ethylmalonic acid, adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, decahydro-1,4-naphthalenedicarboxylic 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-sodium sulfoisophthalic acid, phenyleneendodicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, 9,9'-bis(4-carboxyphenyl)fluorene acid, 2,5-furandicarboxylic acid and their ester derivatives, etc.

[0017] As the copolymerization component of polyethylene terephthalate, in the diol component, for example, 1,2-propanediol, 1,3-propanediol, butanediol, 2-methyl-1,3-propanediol, hexanediol, neopentyl glycol, cyclohexanedimethanol, cyclohexanedietanol, decahydronaphthalenedimethanol, decahydronaphthalenedietanol, norbornanedimethanol, norbornanedietanol, tricyclodecanedimethanol, tricyclodecaneethanol, tetracyclododecanedimethanol, tetracyclododecanedietanol, decalindimethanol, decalindietanol, 5-methylol-5-ethyl-2-(1,1-dimethyl-2-hydroxyethyl)-1,3-dioxane, cyclohexanediol, bicyclohexyl-4,4'-diol, 2,2-bis(4-hydroxycyclohexyl)propane, 2,2-bis(4-(2-hydroxyethoxy)cyclohexyl)propane, cyclopentanediol, 3-methyl-1,2-cyclopentanediol, 4-cyclopentene-1,3-diol, adamantadiol, paraxylene glycol, bisphenol A, bisphenol S, styrene glycol, trimethylolpropane, pentaerythritol, and bis-β-hydroxyethyl terephthalate (BHET), etc. may be mentioned.

[0018] The polyester product is composed of the above-mentioned polyester, but other components such as additives may be included. For example, one or more of various additives such as plasticizers, light stabilizers, antioxidants, ultraviolet absorbers, flame retardants, colorants, pigments, fillers, mold release agents, antistatic agents, fragrances, foaming agents, antibacterial and antifungal agents may be blended.

[0019] The form of the used polyester product is not particularly limited. For example, if it is a bottle container, the IV value is about 0.75 to 0.85 dL / g, if it is a film or sheet, etc., it is about 0.70 to 0.80 dL / g, and if it is a fiber, it is about 0.65 to 0.75 dL / g. The IV value can be measured by a standard method in accordance with JIS K7390.

[0020] When remelting used polyester products having various forms as described above to produce a molded body, it is preferable to shape the polyester products into a predetermined shape so that they can be easily remelted by an extruder. Therefore, in the method of the present invention, when preparing the polyester resin obtained from the used polyester product, it is preferable that the polyester resin has a flake shape. For example, select used polyester products recovered from the market and make them into flakes by pulverization or the like. Pulverization can be carried out using a pulverizer such as a single-screw pulverizer, a twin-screw pulverizer, a triple-screw pulverizer, or a cutter mill. The flake shape refers to a thin sheet or flat shape with a thickness of about 2 mm or less.

[0021] In addition, since substances other than polyester may adhere to or be mixed in the pulverized used polyester products, it is preferable to perform water washing or the like after pulverization and then perform water separation or air separation. Water separation is a separation method that utilizes the difference in the density of materials, and it is possible to separate polyester with a specific gravity of 1 g / cm 3 or more and substances or materials with a specific gravity smaller than that of water. Air separation is a separation method that separates pulverized materials by wind force. For example, among the pulverized materials subjected to the airflow generated by the separation device in a separation device capable of generating a rotating airflow inside, those with a large specific gravity or bulk specific gravity that naturally fall by their own weight and those with a small specific gravity or bulk specific gravity that are lifted by the airflow can be separated. Air separation is effective for separating substances with a specific gravity of 1 g / cm 3 or more.

[0022] In addition, the polyester resin (such as flakes) obtained as described above may then be washed by any washing means such as alkali washing or warm water washing. Washing can remove dirt such as residues of the contents remaining on the surface of the pulverized polyester resin and mixed foreign substances, and a polyester molded body with high purity can be obtained.

[0023] [Melting and Kneading Step of Polyester Resin] Next, the polyester resin having an IV value of 0.50 dL / g or more obtained as described above is remelted in an extruder. In the extruder, the melt kneading of the polyester resin is carried out for at least more than 20 seconds in a state where the water content is more than 1,000 ppm and 10,000 ppm or less. By this melt kneading step, the molecular weight of the polyester can be actively reduced. That is, in the step of remelting the polyester, by kneading for a predetermined time with a predetermined amount of water, hydrolysis of the polyester occurs, and the polyester resin with the 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 step is preferably 0.25 to 0.35 dL / g, and more preferably the IV value is reduced to about 0.3 dL / g. In addition, if the IV value of the polyester resin obtained by the melt kneading step becomes too low, it tends to become liquid when discharged from the extruder and it becomes difficult to obtain a molded body.

[0024] Note that the IV value means a value measured at a temperature of 25°C using a relative viscometer by preparing a solution in which a test piece of polyester is dissolved in a solvent of phenol:tetrachloroethane = 1:1. The water content means a value measured using a Karl Fischer reagent, and specifically, it can be measured using a Karl Fischer moisture meter (for example, manufactured by Nitto Seiko Analytic Co., Ltd., CA-310, etc.).

[0025] The extruder used in the present invention includes at least a cylinder provided with a hopper into which a polyester resin is charged, and a screw located in the cylinder that compresses and melts the polyester resin supplied from the hopper and transfers it to the cylinder outlet. The hopper is provided on the most upstream side of the cylinder, and the polyester resin supplied from there is transferred in the cylinder toward the downstream side (extrusion port side) by the screw. The extrusion port of the extruder is the part where the molten resin is extruded from the cylinder, and the extrusion port may be provided with an appropriate screen changer or a gear pump. Thereby, the extrusion amount of the remelted resin can be adjusted.

[0026] The polyester resin fed from the hopper is transferred by the screw toward the extrusion port within the cylinder while being compressed and heated. During this process, the polyester resin partially melts and becomes a mixture of solid resin and molten resin. Then, at a stage where it has been transferred a certain distance, it becomes a completely molten resin. In the present invention, it is preferable to use a twin-screw extruder in which a pair of screws parallel to each other and rotationally driven by a drive source such as a motor are installed within the cylinder. By using a twin-screw extruder rather than an extruder equipped with a single-screw, it becomes easier to adjust the melt-kneading time.

[0027] The inner diameter D (mm) of the cylinder 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, and the polyester may not be sufficiently hydrolyzed, and there may be a case where the IV value cannot be reduced to 0.40 dL / g or less. On the other hand, if L / D exceeds 60, it is not preferable because the polyester itself will be denatured or decomposed.

[0028] In the present invention, the extruder to be 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 in the cylinder, that is, a region where the polyester resin is a mixture of solid resin and molten resin, or a region where the polyester resin is completely melted. In the present invention, by melt-kneading the polyester resin in a state where the water content is more than 1,000 ppm and not more than 10,000 ppm, the hydrolysis of the polyester is actively promoted. The water content may be adjusted by simultaneously injecting water when the polyester resin is introduced into the hopper, but it is easier to adjust the water content by introducing the dried polyester resin into the hopper. Therefore, it is preferable to introduce the dried polyester resin from the hopper and inject water from the side feeder to adjust the water content. Further, the extruder may be provided with a side vent (vacuum vent port) between the side feeder and the hopper. Even for a polyester resin with a high water content, the polyester can be dried by removing water from the vacuum vent port, and then the water content can be adjusted from the side feeder. The water content can be calculated from the input amount of the polyester resin per unit time and the amount of water input from the side feeder.

[0029] Melting and 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. Although it is considered that hydrolysis of the polyester proceeds more readily at higher melting and kneading temperatures, if the melting and kneading temperature is too high, the polyester itself will be denatured or decomposed, which is not preferable. For example, polyethylene terephthalate, which is the most common polyester, has a melting point of about 260 °C, so it is preferable to carry out melting and kneading in the temperature range of 290 °C to 330 °C. It is not necessary to set the entire cylinder to the same temperature. For example, the region from the hopper to the side feeder (i.e., the region where the mixture of solid resin and molten resin is present) can be set to 240 to 270 °C, and the region for melting and kneading at a predetermined moisture content (the region from the side feeder to the extrusion die) can be set to 290 to 330 °C. The melting point of the polyester resin shall refer to the peak top temperature (°C) of the melting peak observed on the highest temperature side in the heating process measured under the following measurement conditions using a differential scanning calorimeter (DSC). <DSC Measurement Conditions> · Atmosphere: Nitrogen atmosphere · Measurement temperature range: 40 to 290 °C · Heating rate: 10 °C / min · Sample weight: 8 mg

[0030] The melting and kneading time in the extruder is more than 20 seconds, preferably more than 20 seconds and 65 seconds or less. Although it is considered that hydrolysis of the polyester proceeds more readily with a longer melting and kneading time, if the melting and kneading time is too long, the polyester itself will be denatured or decomposed, which is not preferable.

[0031] When the total discharge amount per unit time of the molten polyester resin is Q (kg / h) and the screw rotation speed of the extruder is N (rpm), the value of Q / N may be adjusted to be in the range of 0.10 to 0.15 for the above-mentioned melting and kneading time. If the value of Q / N is too low, it is highly likely that the melting and kneading time in the extruder cannot be ensured. Also, if the value of Q / N is too high, it may result in overfeeding and there is a possibility that the polyester resin cannot be completely fed from the hopper into the cylinder.

[0032] In addition, the extruder used in the present invention preferably has a side vent in the region from the side feeder to the extrusion port. In the present invention, since the hydrolysis of polyester is actively carried out in the melt-kneading step as described above, there is a risk that the water volatilized when discharging the molten polyester from the extrusion port will be contained and cause foaming. Therefore, it is preferable to remove the volatilized excess water by decompression from the side vent (vacuum vent port).

[0033] [Quenching and solidification step] After melt-kneading the polyester resin as described above, the molten polyester is discharged from the extrusion port of the extruder and quenched. In the present invention, the polyester is melt-kneaded at a predetermined moisture content in the extruder, the molecular weight is reduced by hydrolysis, and the IV value of the polyester discharged from the extruder is 0.40 dL / g or less. Therefore, compared with polyester having a normal IV value of 0.50 dL / g or more, orientation crystallization or spherulitization may occur. It is known that the lower the molecular weight (the lower the IV value), the easier it is to pulverize the molded body, and by making it a pulverized product with an increased surface area, the chemical decomposition efficiency of the polyester resin increases. However, the present inventors have found that even when the molecular weight of polyester is reduced to obtain a pulverized product with an increased surface area, the crystallized portion of the polyester has a low chemical decomposition efficiency. Therefore, it has been found that by quenching the molten polyester with a low IV value (0.40 dL / g or less) to obtain a polyester molded body having a crystallinity correlation parameter of 0.50 to 0.75, the chemical decomposition efficiency of the obtained molded body is dramatically improved.

[0034] Crystallinity correlation parameter (ΔH Tc1 / ΔH Tm ) is quenched so as to be 0.50 to 0.75, there is no particular limitation, but by quenching so that as little elongation stress as possible is applied to the molten polyester, ΔH Tc1 / ΔH TmA polyester molded article within the above range can be obtained. As an apparatus capable of rapidly cooling the molten polyester so that as little elongation stress as possible is applied thereto, for example, an underwater cutter or a water slider type pelletizer apparatus that immediately puts the polyester discharged from an extruder into water or brings it into contact with water for cooling and solidification to form it into a predetermined shape (pelletization), or a forming apparatus such as a steel belt cooler or a drum flaker that sandwiches or contacts it with a metal plate having excellent thermal conductivity for rapid cooling and forms it into a predetermined shape (for example, a flake shape).

[0035] Here, the crystallinity correlation parameter is an index for knowing the degree of crystallization of a polymer, and is the value calculated from the following formula using the crystallization enthalpy (ΔH Tc1 ) and the crystal melting enthalpy (ΔH Tm ) obtained from the melting endotherm curve measured using a differential scanning calorimeter (DSC). This value has a negative correlation with the 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 crystal portion and excellent chemical decomposition efficiency, the crystallinity correlation parameter is preferably in the range of 0.60 to 0.73.

[0037] The molded article obtained by rapidly cooling and solidifying the polyester melt using the above-described pelletizer device or the like is preferably an aggregate of granular bodies having an average particle size of 0.5 to 5 mm and / or plate-like bodies having a thickness of 0.1 to 2 mm. These granular bodies and plate-like bodies may be directly subjected to chemical recycling, but in order to further improve the chemical decomposition efficiency, the molded article may be pulverized to reduce the particle size. By making the pulverized product have an average particle size (D50) of 300 μm or less, the surface area can be increased as described above, and the chemical decomposition efficiency can be further improved.

[0038] For pulverizing the molded article, conventionally known wet pulverizers or dry pulverizers can be used. For example, it is preferable to pulverize using a pulverizer such as a hammer mill, a disk mill, a pin mill, a cutter mill, a roller mill, a jet mill, a bead mill, a ball mill, etc. Further, in order to enhance the pulverization efficiency, two or more of the above-described pulverizers may be combined. By using such a pulverizer, a granular pulverized product having an average particle size of 300 μm or less as described above can be obtained simply and conveniently.

[0039] [Recycling method for used polyester products] By using the molded article obtained by the method of the present invention, it becomes possible to efficiently recycle used polyester resin products. For example, by chemically decomposing the pulverized product of the molded article produced as described above from a used polyester resin product by a conventionally known method, monomers or oligomers that constituted the polyester can be obtained from the used polyester resin product. By polymerizing the obtained monomers or oligomers, polyester resin products can be produced again from the used polyester resin products.

[0040] As an example of the chemical recycling of polyester resin products, the polyester resin obtained by pulverizing used PET bottles is remelted to produce the molded body of the present invention, and it is 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] The hydrolysis of PET can be carried out, for example, using a raw material composition containing a molded body, a microorganism capable of expressing and discharging a degrading enzyme, water, and the like. Further, instead of the microorganism, an enzyme produced by the microorganism that has been purified may be used as the degrading enzyme. A buffer may be added to the raw material composition in order to stabilize the pH. The pH of the raw material composition is preferably 5 to 11 from the viewpoint of the activity of the enzyme.

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

[0043] In order to isolate the monomer from the recovered active ingredient, the monomer (terephthalic acid) may be extracted with an organic solvent in which the monomer dissolves, and the monomer constituting the polyester may be isolated from the extracted monomer solution by distillation, crystallization, etc., or crystallization or distillation may be carried out as it is. Further, the monomer solution may be subjected to ion exchange treatment, etc., and then extraction, distillation, crystallization, etc. may be carried out.

[0044] In the above chemical recycling, using a medium containing an enzyme rather than using a solvent such as methanol or ethylene glycol for depolymerization eliminates the need for solvent recovery equipment, etc., so that chemical recycling can be carried out more efficiently and inexpensively.

Examples

[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 the form of flakes) having a weight average molecular weight of 54,000, an IV value of 0.83, and a melting point of 250 °C, prepared from used PET bottle containers, was used. 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 (DSC8500, manufactured by PerkinElmer). Approximately 8 mg of a sample piece of the polyester resin was sealed in an aluminum pan (manufactured by PerkinElmer). The measurement conditions were a heating 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 heating process was taken as the melting point.

[0048] For the measurement of the weight average molecular weight, first, a solution was prepared by dissolving a test piece of the polyester resin in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). The measurement was carried out at 40 °C using a high-speed GPC device (HLC-8320GPC, manufactured by Tosoh Corporation). Chloroform was used as the mobile phase, and a TSKgel SuperHM-H column manufactured by Tosoh Corporation was used as the column. 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 test piece of the polyester resin in a solvent of phenol:tetrachloroethane = 1:1, 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 under the conditions of a temperature of 30 °C and a humidity of 80% RH for more than one week to adjust the water content to 5,000 ppm. The water content was measured using a Karl Fischer moisture meter (CA-310, manufactured by Nitto Seiko Analytic). Next, a polyester resin with adjusted water content was supplied to a twin-screw extruder (ULTNano 05-20AG manufactured by TechnoBel) and melted at a barrel temperature of 300°C. By changing the screw rotation speed N [rpm], the residence time of the molten resin in the twin-screw extruder was adjusted to 38 seconds. At this time, by also changing the resin discharge rate Q [kg / hour], Q / Ns indicating the resin filling rate was made constant (0.13). In this way, the molten resin discharged from the die of the twin-screw extruder was sampled. The weight-average molecular weight and IV value of the sampled resin were measured in the same manner as 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] The water content was adjusted to 1,000 ppm by allowing the polyester resin to stand under the conditions of a temperature of 25°C and a humidity of 50% RH for one week or more. 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 polyester resin with adjusted water content as described above was used.

[0054]

Table 1

[0055] As is clear from the evaluation results in Table 1, even when using a polyester resin with a weight average molecular weight of 54,000 and an IV value of 0.83 as a raw material, by performing melt kneading for more than 20 seconds in a state where the water content exceeds 1,000 ppm and is 10,000 ppm or less, it can be seen that a polyester with a weight average molecular weight of 21,000 and an IV value of 0.40 dL / g or less can be obtained (Production Example 1). Since the brittleness of PET increases as the weight average molecular weight and IV decrease, it is considered that the efficiency in the subsequent grinding process is improved, the surface area of the ground product becomes larger, and the recyclability is improved. On the other hand, when the water content is 1,000 ppm, it can be seen that the weight average molecular weight and the IV value do not sufficiently decrease, and a polyester with an IV value of 0.40 dL / g or less cannot be obtained (Production Example 4). In addition, when the water content exceeds 10,000 ppm, it is considered that there is a risk of hindering the moldability, such as excess moisture being ejected together with the molten resin during ejection. Also, when the melt kneading time is 20 seconds or less, it can be seen that the weight average molecular weight and the IV value do not sufficiently decrease, and a polyester with an IV value of 0.40 dL / g or less cannot be obtained (Production Examples 2 and 3). In addition, if the melt kneading is made longer than necessary, thermal decomposition of the polyester progresses, and a large amount of foreign substances such as cokes are generated, which is considered to deteriorate the recyclability.

[0056] [Example 1] In the same manner as in Production Example 1, the resin was discharged in the form of strands from the die of the extruder and solidified by being put into cold water at 20°C to obtain a pellet-shaped polyester molded body with a diameter of about 3 mm. The time from discharge from the die to input into the cold water was 0.5 seconds.

[0057] For the polyester molded body obtained as described above, the crystallinity correlation parameter was measured. Specifically, it was measured as follows. First, about 8 mg of the polyester molded body was enclosed in an aluminum pan (manufactured by PerkinElmer) and subjected to measurement using a differential scanning calorimeter (DSC8500, manufactured by PerkinElmer). The measurement conditions were a heating rate of 10 °C / min. For data analysis, the analysis software "Pyris" manufactured by PerkinElmer was used. From the heat flow profile obtained from the measurement, the crystallization enthalpy (ΔH Tc1 ) and the crystal melting enthalpy (ΔH Tm ) were calculated. Regarding the calculation range, it was appropriately set according to the peak shape. The obtained ΔH Tc1 and ΔH Tm were used to calculate the crystallinity correlation parameter (X) by the following formula. X = ΔH Tc1 / ΔH Tm This value has a negative correlation with the crystallinity measured by the density gradient method or the like, and when the value is about 0.50 to 0.75, it is determined that the crystal part is small. The measurement results were as shown in Table 2 below.

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

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

[0060] [Example 2] A plate-shaped polyester molded body with a thickness of about 1 mm was obtained by sandwiching the resin strand discharged from the die and solidifying the resin while cooling a pair of steel plates with cold water at 25°C. Except for this, in the same manner as in Example 1, after pulverizing the molded body, the concentration of the decomposition product was measured. Also, the weight-average molecular weight and IV value of the resin sample discharged from the die were measured, and the crystallinity correlation parameter of the molded body and the average particle diameter of the pulverized product of the molded body were measured in the same manner as above. The measurement results were as shown in Table 2 below.

[0061] [Comparative Example 1] A polyester molded body was obtained in the same manner as in Example 1, except that the resin was solidified by air cooling. Next, after pulverizing the obtained molded body, the concentration of the decomposition product was measured. Also, the weight-average molecular weight and IV value of the resin sample discharged from the die were measured, and the crystallinity correlation parameter of the molded body and the average particle diameter of the pulverized product of the molded body were measured in the same manner as above. The measurement results were as shown in Table 2 below.

[0062] [Comparative Example 2] The molten resin was discharged from the die of the extruder 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. After cooling and pulverizing in the same manner as in Example 1, the concentration of the decomposition product was measured. Also, the weight-average molecular weight and IV value of the resin sample discharged from the die were measured, and the crystallinity correlation parameter of the molded body and the average particle diameter of the pulverized product of the molded body were measured in the same manner as above. The measurement results were as shown in Table 2 below.

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

[0064]

Table 2

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

[0066] On the other hand, it can be seen that even when the average particle diameter of the pulverized product is similar to that in Examples 1 and 2, the chemical decomposition efficiency is not sufficient in a polyester molded article with a high degree of crystallinity (Comparative Example 1).

[0067] Also, in the case of a polyester resin in which melt kneading was carried out for 20 seconds or less in a state with a low moisture content, the IV value did not become 0.4 or less. In a polyester molded article that was rapidly cooled and solidified in a state with a high IV value, although it is a molded article with a high crystallinity correlation parameter (i.e., a large amount of amorphous portion), it is difficult to obtain fine powder even when pulverized. As a result, it can be seen that the chemical decomposition efficiency is not sufficient (Comparative Example 2).

[0068] As shown in the evaluation results of the production examples, examples, and comparative examples, a polyester resin with an IV value of 0.50 dL / g or more was prepared, the moisture content of the polyester resin was adjusted, and in a state where the moisture content exceeded 1,000 ppm and was 10,000 ppm or less, melt kneading of the polyester resin was carried out in an extruder for at least more than 20 seconds, and the polyester resin with the IV value reduced to 0.40 dL / g or less was discharged from the extruder and rapidly cooled to obtain a polyester molded article with a crystallinity correlation parameter (ΔH Tc1 / Δ HTm ) of 0.50 to 0.75, thereby improving the chemical decomposition efficiency and enabling easy and efficient chemical recycling of used polyester products.

Claims

1. A method for manufacturing a molded article from a used polyester product, 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, and performing melt-kneading of the polyester resin in an extruder for at least more than 20 seconds in a state where the moisture content is more than 1,000 ppm and 10,000 ppm or less, discharging the polyester resin having the IV value reduced to 0.40 dL / g or less from the extruder and rapidly cooling it to obtain a polyester molded article having a crystallinity correlation parameter (ΔH Ｔｃ１ / ΔH Ｔｍ ) of 0.50 to 0.

75. A method including this.

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

4. When the total discharge amount per unit time of the molten polyester resin is Q (kg / h) and the screw rotation speed of the extruder is N (rpm), the melt-kneading is performed so that the value of Q / N is in the range of 0.10 to 0.

15. The method according to claim 1.

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

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

7. The polyester molded article is an aggregate of granular bodies having an average particle size of 0.5 to 5 mm and / or plate-like bodies having a thickness of 0.1 to 2 mm. The method according to claim 1.

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

9. The method according to claim 1, wherein the used polyester product is a polyethylene terephthalate product.

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

11. The method according to claim 10, wherein the chemical decomposition is an ester hydrolysis reaction using an enzyme.

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

13. Chemically decomposing the polyester molded article obtained by the method according to any one of claims 1 to 11 to produce a diol component and / or a dicarboxylic acid component from the used polyester product. Using the diol component and / or the dicarboxylic acid component as at least a part of the polyester polymerization raw material to polymerize polyester. Manufacturing a polyester product from the obtained polyester. A method for recycling a used polyester product, comprising this.

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