Method for producing polyester resin

Abstract

Provided is a method for producing a polyester resin, the method comprising: an extrusion step for obtaining a molded body by supplying a depolymerizable solvent to a melt extruder while melting and kneading a raw material polyester using the melt extruder; a crystallization step for crystallizing the molded body to obtain a crystallized molded body; and a solid-phase polymerization step for solid-phase polymerizing the crystallized molded body.

Description

Polyester resin manufacturing method

[0001] This invention relates to a method for producing polyester resin.

[0002] Mechanical recycling is attracting attention as a way to realize horizontal recycling of polyester used in general plastic products. Mechanical recycling is a technology that involves crushing and washing collected used polyester, then removing volatile fractions at high temperatures to obtain pellets or the like. For example, Patent Document 1 discloses a technology in which used plastic bottles are crushed and washed to produce resin flakes, which are then decontaminated at high temperatures, and the resin is melted and extruded to produce a preform using an injection molding machine.

[0003] In the technology described in Patent Document 1, when molten resin is extruded from a decontamination machine, foreign matter in the resin is removed by passing the resin through a filter. In this case, the smaller the mesh size of the filter, the higher the precision of filtering becomes possible, but the pressure of the resin increases, making it difficult to operate the extruder. In other words, the technology described in Patent Document 1 has the problem that foreign matter cannot be sufficiently removed by high-precision filtering.

[0004] Patent Document 1: Japanese Patent Publication No. 2019-514728

[0005] The object of the present invention is to provide a method for producing polyester resin that enables high-precision filtering.

[0006] [1] One aspect of the present invention is a method for producing a polyester resin, comprising: an extrusion step of obtaining a molded article by supplying a depolymerizable solvent to a melt extruder while melting and kneading raw polyester using a melt extruder; a crystallization step of crystallizing the molded article to obtain a crystalline molded article; and a solid-phase polymerization step of solid-phase polymerizing the crystalline molded article.

[0007] [2] Embodiment 2 of the present invention is a method for producing polyester resin according to Embodiment 1, characterized in that in the extrusion step, the molten raw polyester is foamed to obtain a foamed molded body as the molded body.

[0008] [3] Embodiment 3 of the present invention is a method for producing a polyester resin according to Embodiment 1 or 2, wherein the depolymerizable solvent is water, ethylene glycol, or a mixed solvent of water and ethylene glycol.

[0009] [4] Embodiment 4 of the present invention is a method for producing polyester resin according to any of Embodiments 1 to 3, wherein the ratio of the amount of raw material polyester supplied to the amount of depolymerizable solvent supplied in the extrusion step is "1:0.00006 to 1:0.09" in terms of the weight ratio of "raw material polyester:depolymerizable solvent".

[0010] [5] Embodiment 5 of the present invention is a method for producing polyester resin according to any of embodiments 1 to 4, wherein the melt extruder is equipped with a filter with an opening of 50 μm or less.

[0011] [6] Embodiment 6 of the present invention is a method for producing a polyester resin according to any one of embodiments 1 to 5, wherein the raw material polyester is polyethylene terephthalate.

[0012] [7] Embodiment 7 of the present invention is a method for producing a polyester resin according to any one of embodiments 1 to 6, wherein the raw material polyester is recycled polyethylene terephthalate.

[0013] [8] Aspect 8 of the present invention is a foamed molded body having a density of 0.01 g / cm³. ３ ~1.0 g / cm ３ This is a method for producing polyester resin according to any of embodiments 2 to 7.

[0014] According to the present invention, a method for producing polyester resin that enables high-precision filtering is provided.

[0015] Figure 1 is a schematic diagram of a twin-screw extruder 1 used in the extrusion step of the polyester resin manufacturing method according to an embodiment of the present invention.

[0016] <Method for producing polyester resin> The method for producing polyester resin in this embodiment comprises an extrusion step of obtaining a molded body by supplying a depolymerizable solvent to a melt extruder while melting and kneading raw polyester using a melt extruder; a crystallization step of crystallizing the molded body to obtain a crystalline molded body; and a solid-phase polymerization step of solid-phase polymerizing the crystalline molded body.

[0017] <Extrusion Step> The extrusion step is a step of obtaining a molded article by supplying a depolymerizable solvent to a melt extruder while melt-kneating a raw material polyester using the melt extruder. In the present embodiment, by supplying the depolymerizable solvent, a molded article having a molecular weight lower than that of the raw material polyester can be obtained through the extrusion step. Although details will be described later, the molded article obtained by the extrusion step is preferably a foam-molded article.

[0018] The raw material polyester is not particularly limited, and examples thereof include aromatic polyesters, wholly aromatic polyesters, polycarbonates, and aliphatic polyesters, with aromatic polyesters being preferred among these. The aromatic polyester contains a diol unit and a dicarboxylic acid unit. Examples of the diol compound for forming the diol unit include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, 1,6-hexylene glycol, cyclohexanedimethanol, and ethylene oxide adducts of bisphenol A, among which ethylene glycol is preferred. Examples of the dicarboxylic acid compound for forming the dicarboxylic acid unit include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, and furandicarboxylic acid, and derivatives thereof, among which terephthalic acid is preferred. Specific examples of polyesters include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polyethylene furanoate. Among them, polyethylene terephthalate, which is a copolymer of ethylene glycol and terephthalic acid, is preferred. The above-described polyesters are not limited to those derived from petroleum raw materials, and may be polyesters derived from plant raw materials, or may be polyesters obtained by recycling these polyesters derived from petroleum raw materials or plant raw materials. Further, the above polyesters may be used alone or as a mixture.

[0019] Polyethylene terephthalate may contain units consisting of dicarboxylic acids other than terephthalic acid that are copolymerizable with ethylene glycol and terephthalic acid within the total monomer units. Examples of dicarboxylic acids other than terephthalic acid include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedionic acid, eicosanedionic acid, pimelic acid, azelaic acid, methylmalonic acid and 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-sodium sulfoisophthalic acid, phenylendanedicarboxylic acid, anthracenedicarboxylic acid, phenantradicarboxylic acid, 9,9'-bis(4-carboxyphenyl)fluorenic acid, 2,5-franzicarboxylic acid and their ester derivatives, among which isophthalic acid is preferred.

[0020] Polyethylene terephthalate may contain, in all monomer units, a unit composed of a diol other than ethylene glycol that is copolymerizable with ethylene glycol and terephthalic acid. Examples of such diols other than ethylene glycol include propylene glycol, 1,3-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, hexanediol, neopentyl glycol, cyclohexanedimethanol, cyclohexanediethanol, decahydronaphthalenedimethanol, decahydronaphthalenediethanol, norbornanedimethanol, norbornanediethanol, tricyclodecanedimethanol, tricyclodecanediethanol, 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-hydroxycyclopropylpropane), 2,2-bis(4-(2-hydroxyethoxy)cyclohexyl)propane, cyclopentanediol, 3-methyl-1,2-cyclopentanediol, 4-cyclopentene-1,3-diol, adamantanediol, paraxylene glycol, bisphenol A, bisphenol S, styrene glycol, trimethylolpropane, pentaerythritol, diethylene glycol, triethylene glycol, and bis-β-hydroxyethyl terephthalate (BHET). Among these, diethylene glycol is preferred.

[0021] The raw material polyester may be a mixture of two or more of the above resins. Further, the raw material polyester may be a mixture with other plastics such as polyethylene and polypropylene, and fibers such as cotton, nylon, and polyurethane. The raw material polyester may also contain other components such as additives. For example, one or two or more of various additives such as polymerization catalysts, polymerization stabilizers, plasticizers, light stabilizers, antioxidants, ultraviolet absorbers, flame retardants, colorants, pigments, fillers, release agents, antistatic agents, fragrances, foaming agents, antibacterial and antifungal agents may be blended.

[0022] The raw material polyester is preferably recycled polyester. Examples of recycled polyester include those collected after being used once as beverage containers, packaging containers, etc. Recycled polyethylene terephthalate is more preferable as the recycled polyester. Examples of recycled polyethylene terephthalate include recovered PET flakes obtained by collecting and crushing plastic products that were used as PET bottles, or those obtained by further melting and solidifying recovered PET flakes.

[0023] It is preferable that the raw material polyester has undergone a drying treatment. That is, it is preferable to perform a drying process on the raw material polyester before the extrusion process. The drying temperature is preferably 100°C to 170°C, more preferably 130°C to 150°C. Heating is preferably performed under a pressure of 200 Torr or less, under a nitrogen stream, or a combination of these. The heating time is preferably 0.5 hours to 6 hours, more preferably 2 hours to 5 hours. The raw material polyester may contain trace amounts of the same type of compound as the compound used as the depolymerizing solvent described later. On the other hand, this compound can be removed from the raw material polyester by the drying treatment. That is, by performing a drying treatment in advance, it is possible to introduce a raw material polyester into the extruder that substantially does not contain the same type of compound as the depolymerizing solvent during the extrusion process. Therefore, it becomes easier to control the amount of depolymerizing solvent supplied during the extrusion process, and it becomes possible to obtain a stable molded product.

[0024] The depolymerizable solvent is not particularly limited as long as it is a volatile solvent that can depolymerize the raw polyester and can be removed by volatilization in the subsequent solid-phase polymerization step. Examples include water, ethylene glycol, methanol, ethanol, and isopropanol. In particular, water, ethylene glycol, or a mixed solvent of water and ethylene glycol is preferred because the polyester resin obtained after all the steps of the present invention will have properties close to those of the raw polyester. The weight ratio of water to ethylene glycol in the mixed solvent of water and ethylene glycol is preferably 1:99 to 99:1, more preferably 5:95 to 95:5, and even more preferably 10:90 to 90:10. The depolymerizable solvent may contain compounds or additives copolymerizable with polyester. Examples of compounds copolymerizable with polyester that can be contained in the depolymerizable solvent include diethylene glycol, triethylene glycol, trimethylolpropane, pentaerythritol, isophthalic acid, trimellitic acid, and pyromellitic acid. Additives that can be included in the depolymerizable solvent include, for example, polymerization catalysts, polymerization stabilizers, light stabilizers, antioxidants, and colorants. Examples of polymerization catalysts include antimony compounds such as antimony trioxide, antimony triacetate, metallic antimony, and antimony pentoxide, as well as germanium compounds and titanium compounds. The content of other solvents and additives in the depolymerizable solvent is preferably 0.0001% to 1% by weight, more preferably 0.0001% to 0.1% by weight, relative to the total weight of the depolymerizable solvent. It is preferable that the depolymerizable solvent substantially consists only of water, ethylene glycol, or a mixed solvent of water and ethylene glycol.

[0025] Figure 1 is a schematic diagram of a twin-screw extruder 1 used in the extrusion process of the polyester resin manufacturing method in this embodiment.

[0026] In the extrusion process, a melt extruder is used to melt and knead the raw polyester material and supply a depolymerizable solvent. In this embodiment, the twin-screw extruder 1 shown in Figure 1 is used as the melt extruder. The form of the melt extruder is not particularly limited to this, and a single-screw extruder or a multi-screw extruder may be used, or a twin-screw extruder other than the twin-screw extruder 1 shown in Figure 1 may be used. The twin-screw extruder 1 used in this embodiment includes a plurality of barrels 2a to 2j, a screw 3, a drive unit 4, a pressure measuring unit 5, a breaker plate 6, a die 7, and a filter 8.

[0027] Barrels 2a to 2j are connected to each other in a continuous manner. The first barrel 2a is an open barrel to which raw polyester is supplied. A weight-controlled feeder is connected to barrel 2a, making it possible to supply raw polyester quantitatively. The means for supplying raw polyester to barrel 2a is not particularly limited as long as it is possible to supply raw polyester quantitatively. Also, the barrel to which raw polyester is supplied does not necessarily have to be the first barrel 2a.

[0028] The sixth barrel, 2f, is an open barrel to which the depolymerizable solvent is supplied. A pump (not shown) is connected to the inlet of barrel 2f via a pressure regulating valve, enabling the quantitative supply of the depolymerizable solvent. The connection between the pump and the inlet may also be via a backflow prevention valve. Examples of pumps include well-known diaphragm pumps and plunger pumps, and are not particularly limited. Furthermore, the barrel to which the depolymerizable solvent is supplied does not necessarily have to be the sixth barrel, 2f, but may be located in multiple barrels. It is preferable that the depolymerizable solvent be supplied to a barrel downstream of the barrel to which the raw polyester is supplied. In this embodiment, the other barrels 2b to 2e and barrels 2g to 2j are closed barrels, but as long as the effects of the invention are not impaired, they may be open barrels for the purpose of degassing, pressure adjustment, or internal pressure measurement, as needed. Also, in this embodiment, the twin-screw extruder 1 is equipped with 10 barrels 2a to 2j, but the number of barrels is not particularly limited.

[0029] The screw 3 is connected to the drive unit 4 and is located inside barrels 2a to 2j. In the screw 3, kneading disc sections 3A for mixing and sealing are configured at positions corresponding to the 5th barrel 2e and the 8th barrel 2h. In the screw 3, feed screw-shaped sections 3B for resin transport are configured at positions corresponding to the other barrels 2a to 2d, barrels 2f to 2g, and barrels 2i to 2j. The position of the kneading disc sections 3A is not particularly limited, but it is preferable to provide the kneading disc sections 3A in the barrel located between the barrel to which the raw polyester is supplied and the barrel to which the depolymerizable solvent is supplied, and in the barrel downstream of the barrel to which the depolymerizable solvent is supplied. By providing the kneading disc sections 3A, it is possible to adjust the residence time of the raw polyester in the twin-screw extruder 1 and appropriately control the molecular weight and foaming state of the molded product obtained by the extrusion process.

[0030] The ratio L / D of the screw length L to the screw diameter D of screw 3 is preferably 30 to 100, and more preferably 30 to 80. By setting L / D within the above range, it becomes possible to appropriately control the molecular weight and foaming state of the molded article obtained by the extrusion process.

[0031] At the outlet of the terminal barrel 2j, a pressure measuring unit 5, a breaker plate 6, and a die 7 are arranged in order. A pressure gauge is connected to the pressure measuring unit 5, making it possible to measure the pressure of the molten resin in the twin-screw extruder 1. A filter 8 is located upstream (resin supply side) of the breaker plate 6. In this embodiment, the filter 8 is composed of three wire meshes, but the number of wire meshes constituting the filter 8 is not particularly limited. When the filter 8 is composed of wire meshes, the mesh opening of the filter 8 is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. When the filter 8 is composed of multiple wire meshes, it is preferable that at least one of the wire meshes has a mesh opening of 50 μm or less. From the viewpoint of filtering efficiency, it is more preferable to place a wire mesh with a relatively large mesh opening as the first mesh, and then place wire meshes with a mesh opening of 50 μm or less as the second and subsequent meshes. As the molten resin passes through the filter 8, foreign matter contained in the raw polyester can be filtered and removed. The materials constituting the filter 8 are not particularly limited, and sintered metal, sintered metal nonwoven fabric, etc., may also be used. When sintered metal or metal nonwoven fabric is used, the filtration accuracy (filtration diameter) of the filter 8 is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. The filter 8 may also be constructed by combining sintered metal or metal nonwoven fabric with a wire mesh with a relatively large mesh opening.

[0032] In this embodiment, raw polyester is supplied from barrel 2a, and the resin is extruded from die 7 while being melt-kneaded by screw 3. At this time, a depolymerizable solvent is supplied from barrel 2f while the raw polyester is melt-kneaded. As will be described later, by melt-kneading the raw polyester while supplying a depolymerizable solvent, a decrease in molecular weight occurs, and foaming occurs in the molten resin, and a molded product is obtained by cooling it.

[0033] Raw material polyester discharge volume (supply volume) Q Ｐis preferably 1 kg / h to 50000 kg / h, more preferably 1 kg / h to 10000 kg / h, and still more preferably 1 kg / h to 5000 kg / h.

[0034] Supply amount Q of the depolymerizable solvent ＤＳ is preferably 0.001 g / min to 75000 g / min, more preferably 0.001 g / min to 15000 g / min, and still more preferably 0.001 g / min to 4500 g / min. When supply barrels for the depolymerizable solvent are disposed in a plurality of compartments, the supply amount Q of the depolymerizable solvent ＤＳ is the total amount thereof. When supply barrels for the depolymerizable solvent are disposed in n compartments, the supply amount of the depolymerizable solvent in each barrel may be the same or different from each other, and is preferably (0.001 / n) g / min to (75000 / n) g / min, more preferably (0.001 / n) g / min to (15000 / n) g / min, and still more preferably (0.001 / n) g / min to (4500 / n) g / min. Here, n represents an integer of 1 or greater.

[0035] The set pressure (gauge pressure) of the pressure regulating valve when supplying the depolymerizable solvent is preferably 0 MPa to 20 MPa, more preferably 0 MPa to 10 MPa, and still more preferably 0 MPa to 5 MPa.

[0036] Supply amount Q of the raw material polyester Ｐ and the supply amount Q of the depolymerizable solvent ＤＳ the ratio is "raw material polyester : depolymerizable solvent" (Q ｐ : Q ＤＳThe weight ratio of the raw material polyester to the supply amount of the depolymerizable solvent is preferably 1:0.00006 to 1:0.09, more preferably 1:0.00006 to 1:0.06, even more preferably 1:0.00006 to 1:0.006, particularly preferably 1:0.0004 to 1:0.004, and most preferably 1:0.0015 to 1:0.004. By setting the ratio of the supply amount of raw material polyester to the supply amount of depolymerizable solvent within the above range, as described later, it is possible to appropriately reduce the molecular weight of the raw material polyester by depolymerization, thereby enabling highly accurate filtering, and furthermore, to appropriately control the foaming state and further improve the solid-phase polymerization efficiency in the solid-phase polymerization process.

[0037] Amount of raw polyester supply Q relative to the rotational speed N [rpm] of screw 3 Ｐ Ratio Q Ｐ The value of / N [kg / (h・rpm)] is preferably 0.01 to 0.5, more preferably 0.01 to 0.4, and even more preferably 0.01 to 0.3. Q Ｐ By setting the value of / N within the above range, the residence time of the raw polyester in the twin-screw extruder 1 can be adjusted, and as described later, the molecular weight of the raw polyester can be appropriately reduced by depolymerization, enabling high-precision filtering, and furthermore, the foaming state of the foamed molded product can be appropriately controlled.

[0038] The extrusion temperature in melt extrusion using the twin-screw extruder 1 is preferably between the melting point of the raw polyester + 0°C and the melting point of the raw polyester + 100°C, and more preferably between the melting point of the raw polyester + 10°C and the melting point of the raw polyester + 80°C. By setting the extrusion temperature within the above range, as described later, it is possible to appropriately reduce the molecular weight of the raw polyester by depolymerization, enabling high-precision filtering, and furthermore, to appropriately control the foaming state and further improve the solid-phase polymerization efficiency in the solid-phase polymerization process.

[0039] The resin pressure during melt extrusion by the twin-screw extruder 1 is preferably 100 MPa or less, more preferably 80 MPa or less, and even more preferably 50 MPa or less. By keeping the resin pressure within the above range, the operability of the twin-screw extruder 1 can be improved.

[0040] In this embodiment, the molten resin discharged from the die 7 is cut by a strand-cutting method, which involves cooling and cutting the resin in a water tank. The method of cutting the molten resin is not limited to this, and methods such as a hot-cutting method, an underwater-cutting method, or a sheet-cutting method may also be used.

[0041] While not particularly limited, the cross-sectional area of ​​the flow path from the rear (tip) of the screw 3 to the discharge port of the die 7 is 1 to 100,000 mm², from the viewpoint of obtaining a foamed molded body. ２ Furthermore, the length of the flow path from the rear (tip) of the screw 3 to the discharge port of the die 7 is preferably 10 m or less.

[0042] The intrinsic viscosity (IV) of the obtained molded article is preferably 0.3 dL / g to 1.0 dL / g, more preferably 0.4 dL / g to 0.9 dL / g, and even more preferably 0.41 dL / g to 0.8 dL / g.

[0043] The density of the resulting molded body, when it is a foamed molded body, varies depending on the type of resin used as the raw material polyester. However, when polyethylene terephthalate is used, the density is preferably 0.01 g / cm³. ３ ~1.0 g / cm ３ More preferably, 0.05 g / cm³ ３ ~1.0 g / cm ３ And more preferably 0.1 g / cm³ ３ ~1.0 g / cm ３ The density of the foamed molded product can be adjusted by controlling the supply amount of raw polyester, the supply amount of depolymerizable solvent, the extrusion temperature, and the residence time, depending on the type of raw polyester.

[0044] <Crystalling Process> The crystallization process involves heating the molded body obtained in the extrusion process to crystallize it and obtain a crystallized molded body. The heating temperature is preferably 100°C to 170°C, more preferably 130°C to 150°C. Heating is preferably carried out under a pressure of 200 Torr or less, under a nitrogen atmosphere, or a combination of these. The heating time is preferably 0.5 hours to 6 hours, more preferably 2 hours to 5 hours.

[0045] <Solid-phase polymerization process> In the solid-phase polymerization process, the crystalline molded body obtained in the crystallization process is heated to carry out solid-phase polymerization of the resin. Solid-phase polymerization is preferably carried out under a pressure of 200 Torr or less, under a nitrogen atmosphere, or in combination thereof. The temperature of solid-phase polymerization is preferably 200°C to 230°C, more preferably 205°C to 225°C. The heating time is preferably 2 hours to 24 hours, more preferably 6 hours to 20 hours.

[0046] The intrinsic viscosity (IV) of the polyester resin obtained by the solid-phase polymerization process is preferably 0.68 dL / g to 1.40 dL / g, and more preferably 0.72 to 1.00 dL / g.

[0047] As described above, polyester resin can be obtained. In the polyester resin manufacturing method of this embodiment, a depolymerizable solvent is supplied while the raw polyester is melt-kneaded during the extrusion process. At this time, a portion of the raw polyester is depolymerized by the depolymerizable solvent, and the molecular weight of the raw polyester decreases. As a result, the viscosity of the raw polyester decreases, so even when using a filter 8 with a relatively small mesh size (high filtration accuracy), the raw polyester can pass through the filter 8 more easily, and the increase in the pressure of the molten resin in the twin-screw extruder 1 can be suppressed. Therefore, with the polyester resin manufacturing method of this embodiment, it is possible to operate using a filter 8 with a relatively small mesh size, and thus high-precision filtering is possible.

[0048] Furthermore, according to the polyester resin manufacturing method of this embodiment, in the extrusion process, a depolymerizable solvent is supplied while the raw polyester is melt-kneaded, and by appropriately controlling conditions such as the amount of raw polyester supplied and the amount of depolymerizable solvent supplied, the molten raw polyester foams up, and a foamed molded article is obtained. The following is considered to be the reason why foaming occurs in the raw polyester. First, as mentioned above, depolymerization of the raw polyester occurs due to the depolymerizable solvent, but at this time, some of the depolymerizable solvent does not contribute to the depolymerization reaction and remains in the raw polyester. In this state, when the molten raw polyester is discharged from the die and the pressure that was on the raw polyester is released, it is thought that the remaining depolymerizable solvent becomes bubbles. The inventors have newly discovered that by making the resin molded article obtained by melt extrusion a foamed molded article, the solid-phase polymerization efficiency in the solid-phase polymerization process can be improved. The reason for this is not certain, but the following is considered to be the reason. By-products such as oligomers generated during solid-phase polymerization inhibit the solid-phase polymerization reaction and become a factor in reducing the solid-phase polymerization efficiency. In contrast, in this embodiment, the resin molded body is foamed, and by-products diffuse to the surface of the resin through the air bubbles contained in the resin. Furthermore, the by-products diffuse from the surface of the resin into the atmosphere. As a result, by-products that inhibit the solid-phase polymerization reaction are removed from inside the resin, and thus the solid-phase polymerization efficiency can be improved.

[0049] The conditions for obtaining a foamed molded product are not particularly limited, as long as the raw polyester material can be depolymerized during extrusion while a portion of the depolymerizable solvent remains in the raw polyester material. Such conditions include, for example, a condition in which the amount of depolymerizable solvent added per unit time exceeds the amount of depolymerizable solvent consumed per unit time by the depolymerization reaction, and the type of raw polyester material, the type of depolymerizable solvent, the configuration of the extruder, and the raw polyester supply amount Q. Ｐ , supply amount Q of depolymerizable solvent ＤＳ This can be achieved by appropriately selecting conditions such as extrusion temperature and resin pressure. Specifically, preferably, the supply amount Q of the raw material polyester. Ｐ Q is the amount of depolymerizable solvent supplied. ＤＳThe ratio is "raw material polyester: depolymerizable solvent" (Q ｐ : Q ＤＳ The weight ratio of ) is 1:0.0015 to 1:0.004. More preferably, polyethylene terephthalate or recycled polyethylene terephthalate is used as the raw material polyester, water, ethylene glycol, or a mixed solvent of water and ethylene glycol is used as the depolymerizable solvent, the ratio L / D of the screw length L to the screw diameter D of the screw 3 is 30 to 100, and the supply amount Q of the raw material polyester is 30 to 100. Ｐ Q is the amount of depolymerizable solvent supplied. ＤＳ The ratio is "raw material polyester: depolymerizable solvent" (Q ｐ : Q ＤＳ The weight ratio of ) is 1:0.0015 to 1:0.004, and the discharge amount (supply amount) of raw material polyester Q Ｐ The supply rate of the depolymerizable solvent is 1 kg / h to 50,000 kg / h. ＤＳ The supply amount Q of raw polyester is between 0.001 g / min and 75,000 g / min, and the supply amount Q of raw polyester is relative to the rotational speed N [rpm] of screw 3. Ｐ Ratio Q Ｐ The pressure per N [kg / (h·rpm)] is 0.01 to 0.5, the extrusion temperature in melt extrusion is 260°C to 360°C, the resin pressure in melt extrusion is 100 MPa or less, and the cross-sectional area of ​​the flow path from the screw to the discharge port is 1 to 100,000 mm². ２ One characteristic is that the length of the flow path from the screw to the discharge port is 10 m or less.

[0050] As described above, the polyester resin manufacturing method of this embodiment enables high-precision filtering. Furthermore, the polyester resin manufacturing method of this embodiment enables solid-phase polymerization with high efficiency.

[0051] In this embodiment, a foamed molded article can be obtained by appropriately controlling the manufacturing conditions, particularly the supply amount of raw polyester and the supply amount of depolymerizable solvent, during the extrusion process. However, the molded article obtained in the extrusion process does not necessarily have to be foamed. That is, if high-precision filtering is possible in the extrusion process, the molded article can be obtained without foaming the raw polyester during the extrusion process.

[0052] The polyester resin produced by the method for producing polyester resin in this embodiment can be suitably used for processing into molded articles such as preforms and polyester bottles. The preform can be produced by injection molding of the polyester resin. The polyester bottle can be produced by stretch blow molding such a preform.

[0053] The polyester resin produced by the manufacturing method in this embodiment may be processed directly into a molded article, or it may be melted again to form pellets, and then these pellets may be used to process the article. By melting the polyester resin again, air bubbles generated in the resin during the extrusion process can be removed.

[0054] Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

[0055] [Materials Used] PET bottle containers were crushed in a crusher equipped with an 8 mm mesh filter at the outlet, then washed with water and dewatered to obtain polyester resin flakes (raw polyester). The IV of the polyester resin flakes was 0.80. Furthermore, dried flakes were dried in a box-type dehumidifying dryer at 150°C for 5 hours and used in the test.

[0056] [Manufacturing Apparatus for Polyester Resin Molded Articles] For the manufacturing of polyester resin molded articles, a TEM26SS manufactured by Shibaura Machinery Co., Ltd. was used as the twin-screw extruder 1 shown in Figure 1. The screw 3 of the twin-screw extruder 1 had a length L (screw length) / diameter D (screw diameter) of 40. A weight-controlled feeder was installed in the first barrel 2a to allow for the quantitative supply of the aforementioned dried flakes. A plunger pump was connected to the liquid pressure inlet of the sixth barrel 2f via an injection valve to allow for the quantitative supply of the depolymerizable solvent in the desired amount. A strand die with a bore diameter of 5 mm was used as the die 7. The filter 8 was configured as a three-layer structure of plain weave 50 mesh / twill weave 400 mesh / plain weave 50 mesh (Examples 1 to 6, Comparative Example 1) or as a three-layer structure of plain weave 50 mesh / sintered metal nonwoven fabric (filtration accuracy 10 μm) / plain weave 50 mesh (Examples 7 to 12, Comparative Example 2). A water tank set to a temperature of 15 degrees Celsius is placed downstream of die 7, so that the molten resin discharged from die 7 is immediately immersed in the water tank and cooled and solidified.

[0057] [Resin Pressure] In the extrusion process, the resin pressure was measured at the pressure measuring unit 5 10 minutes after the start of extrusion. A lower resin pressure indicates better operability of the twin-screw extruder 1.

[0058] [IV] The polyester resin molded article obtained by the extrusion process was vacuum-dried at 120°C for 2 hours. 0.3 g of the dried polyester resin molded article was weighed and added to a mixed solvent of 1,1,2,2-tetrachloroethane and phenol (weight ratio 1 / 1) to adjust the concentration to 1.00 g / dL. The mixture was stirred at 120°C for 20 minutes to completely dissolve the substance. The solution was cooled to room temperature, and the relative viscosity was determined using a relative viscometer (Malvern Panalytical, Viscotec Y501C) heated to 30°C to measure the intrinsic viscosity (IV before treatment). The intrinsic viscosity (IV after treatment) of the polyester resin molded article obtained through the crystallization process and solid-phase polymerization process was measured using the same procedure. Furthermore, the IV increase rate was calculated according to the following formula. A higher IV increase rate indicates higher solid-phase polymerization efficiency. IV increase rate [%] = (IV after treatment - IV before treatment) / IV before treatment × 100

[0059] <Example 1> The above-mentioned dried flakes, used as raw material polyester, were fed into a twin-screw extruder 1 to produce a polyester resin molded body. The filter consisted of three layers: plain weave 50 mesh / twill weave 400 mesh (mesh opening approximately 40 μm) / plain weave 50 mesh. The temperature of barrel 2a, to which the flakes were supplied, was set to 15°C, and the temperatures of barrels 2b to 2j and die 7 were set to 280°C. The rotational speed N of the screw 3 was 150 rpm, and the discharge volume Q of the dried flakes was set. Ｐ (Q) Ｐ ( / N = 0.067). Water as a depolymerizable solvent, injection amount Q ＤＳ The material was supplied under the condition of 0.2 g / min ("Dry flake discharge volume Q"). Ｐ : Water injection volume Q ＤＳ The weight ratio of the dry flakes was 1:0.0012). Under the above conditions, the dry flakes were melt-extruded, and the molten resin was cooled and solidified by immersion in a water bath to obtain a polyester resin molded body. The polyester resin molded body was foamed and floated in water, indicating a density of 1.0 g / cm³. ３ The following procedure was performed. A polyester resin molded body was cut and weighed into a ground-joint test tube, with 1 g of material placed inside. Next, the ground-joint test tube was connected to a vacuum pump, and the system was subjected to a vacuum atmosphere of 1 Torr. The polyester resin molded body was then immersed in an oil bath set to 150°C for 5 hours to perform crystallization. Furthermore, the oil bath temperature was changed to 205°C and the immersion was continued for 7 hours to perform solid-phase polymerization. Using the above method, the IV of the polyester resin molded body before and after treatment was determined, and the IV increase rate was calculated. The results are shown in Table 1.

[0060] <Example 2> The polyester resin molded article was recovered in the same manner as in Example 1, except that the amount of water injected as the depolymerizable solvent was 0.4 g / min. At that time, the molded article was foamed and floated on water, so its density was 1.0 g / cm³. ３ The results were as follows. In addition, the resin pressure was measured and the IV was measured before and after treatment, as in Example 1, and the IV increase rate was calculated. These results are shown in Table 1.

[0061] <Example 3> The polyester resin molded article was recovered in the same manner as in Example 1, except that the depolymerizable solvent was water / ethylene glycol = 95 / 5 (by weight). The molded article was foamed and floated in water, indicating a density of 1.0 g / cm³. ３ The results were as follows. In addition, the resin pressure was measured and the IV was measured before and after treatment, as in Example 1, and the IV increase rate was calculated. These results are shown in Table 1.

[0062] <Example 4> The polyester resin molded article was recovered in the same manner as in Example 2, except that the depolymerizable solvent was water / ethylene glycol = 95 / 5 (by weight). The molded article was foamed and floated on water, indicating a density of 1.0 g / cm³. ３ The results were as follows. In addition, the resin pressure was measured and the IV was measured before and after treatment, as in Example 1, and the IV increase rate was calculated. These results are shown in Table 1.

[0063] <Example 5> The polyester resin molded article was recovered in the same manner as in Example 1, except that the amount of water injected as the depolymerizable solvent was 0.1 g / min. At that time, the molded article did not foam and sank in the water, so the density was 1.0 g / cm³. ３ The result was excellent. Furthermore, similar to Example 1, the resin pressure was measured, and the IV (infrared temperature) was measured before and after treatment to calculate the IV increase rate. These results are shown in Table 1.

[0064] <Example 6> The polyester resin molded article was recovered in the same manner as in Example 5, except that the depolymerizable solvent was water / ethylene glycol = 95 / 5 (by weight). The molded article did not foam and sank in water, so its density was 1.0 g / cm³. ３ The result was excellent. Furthermore, similar to Example 1, the resin pressure was measured, and the IV (infrared temperature) was measured before and after treatment to calculate the IV increase rate. These results are shown in Table 1.

[0065] <Comparative Example 1> A polyester resin molded article was recovered in the same manner as in Example 1, except that a depolymerizable solvent was not injected. The molded article did not foam and sank in water, indicating a density of 1.0 g / cm³. ３The result was extremely high. Furthermore, the resin pressure was measured in the same manner as in Example 1, and the result was higher than in Examples 1 to 6, indicating poor filtering operability. As a result, IV measurement was not performed. These results are shown in Table 1.

[0066] <Example 7> The polyester resin molded body was recovered in the same manner as in Example 1, except that the filter configuration was 50 mesh plain weave / sintered metal nonwoven fabric (filtration accuracy 10 μm) / 50 mesh plain weave, and the amount of water injected as a depolymerizable solvent was 0.3 g / min. At that time, the molded body was foamed and floated on water, so its density was 1.0 g / cm³. ３ The results were as follows. In addition, the resin pressure was measured and the IV was measured before and after treatment, as in Example 1, and the IV increase rate was calculated. These results are shown in Table 2. <Example 8> The polyester resin molded article was recovered in the same manner as in Example 7, except that ethylene glycol was used as the depolymerizable solvent. At that time, the molded article was foamed and floated on water, so the density was 1.0 g / cm³ ３ The results were as follows. In addition, the resin pressure was measured and the IV was measured before and after treatment, as in Example 1, and the IV increase rate was calculated. These results are shown in Table 2. <Example 9> The polyester resin molded article was recovered in the same manner as in Example 7, except that the amount of water injected as the depolymerizable solvent was 0.2 g / min. At that time, the molded article did not foam and sank in water, so the density was 1.0 g / cm³ ３ The result was excellent. In addition, the resin pressure was measured and the IV was measured before and after treatment, as in Example 1, and the IV increase rate was calculated. These results are shown in Table 2. <Example 10> The polyester resin molded article was recovered in the same manner as in Example 9, except that the depolymerizable solvent was water / ethylene glycol = 50 / 50 (weight ratio). At that time, the molded article did not foam and sank in water, so the density was 1.0 g / cm³ ３ The result was excellent. In addition, the resin pressure was measured and the IV was measured before and after treatment, as in Example 1, and the IV increase rate was calculated. These results are shown in Table 2. <Example 11> The polyester resin molded article was recovered in the same manner as in Example 9, except that ethylene glycol was used as the depolymerizable solvent. At that time, the molded article did not foam and sank in water, so the density was 1.0 g / cm³３ The result was excellent. In addition, the resin pressure was measured and the IV was measured before and after treatment, as in Example 1, and the IV increase rate was calculated. These results are shown in Table 2. <Example 12> The polyester resin molded article was recovered in the same manner as in Example 11, except that the amount of ethylene glycol injected as the depolymerizable solvent was 0.1 g / min. At that time, the molded article did not foam and sank in water, so the density was 1.0 g / cm³ ３ The result was excellent. In addition, the resin pressure was measured and the IV was measured before and after treatment, as in Example 1, and the IV increase rate was calculated. These results are shown in Table 2. <Comparative Example 2> The polyester resin molded article was recovered in the same manner as in Example 7, except that a depolymerizable solvent was not injected. At that time, the molded article did not foam and sank in water, so the density was 1.0 g / cm³ ３ The result was extremely high. Furthermore, the resin pressure was measured in the same manner as in Example 1, and the result was higher than in Examples 7-12, indicating poor filtering operability. As a result, IV measurement was not performed. These results are shown in Table 2.

[0067]

[0068]

[0069] As shown in Tables 1 and 2, in Examples 1-6 and 7-12, where a depolymerizable solvent was supplied while melt-kneading the raw polyester material during the extrusion process, the resin pressure during melt extrusion was kept lower and filtering operation was better compared to the case where no depolymerizable solvent was supplied. Furthermore, in Examples 1-4, 7, and 8, the resulting molded articles were foamed, resulting in a high rate of increase in IV during the subsequent solid-phase polymerization treatment. On the other hand, in Comparative Examples 1 and 2, where no depolymerizable solvent was injected, the resin pressure during melt extrusion was high and filtering operation was poor.

[0070] 1...Twin-screw extruder 2a-2j...Barrel 3...Screw 3A...Kneading disc section 3B...Feed screw section 4...Drive section 5...Pressure measuring section 6...Breaker plate 7...Die 8...Filter

Claims

1. A method for producing a polyester resin, comprising: an extrusion step of obtaining a molded article by supplying a depolymerizable solvent to a melt extruder while melting and kneading raw polyester using the melt extruder; a crystallization step of crystallizing the molded article to obtain a crystalline molded article; and a solid-phase polymerization step of solid-phase polymerizing the crystalline molded article.

2. The method for producing polyester resin according to claim 1, characterized in that, in the extrusion step, the molten raw polyester is foamed to obtain a foamed molded body as the molded body.

3. The method for producing a polyester resin according to claim 1 or 2, wherein the depolymerizable solvent is water, ethylene glycol, or a mixed solvent of water and ethylene glycol.

4. A method for producing a polyester resin according to any one of claims 1 to 3, wherein the ratio of the amount of raw material polyester supplied to the amount of depolymerizable solvent supplied in the extrusion step is "1:0.00006 to 1:0.09" in terms of the weight ratio of "raw material polyester:depolymerizable solvent".

5. The method for producing polyester resin according to any one of claims 1 to 4, wherein the melt extruder is equipped with a filter with a mesh opening of 50 μm or less.

6. A method for producing a polyester resin according to any one of claims 1 to 5, wherein the raw material polyester is polyethylene terephthalate.

7. A method for producing a polyester resin according to any one of claims 1 to 6, wherein the raw material polyester is recycled polyethylene terephthalate.

8. The density of the foamed molded body is 0.01 g / cm³. ３ ~1.0 g / cm ３ The method for producing a polyester resin according to claim 2.

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