Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/91—Polymers modified by chemical after-treatment
  • C08G63/914—Polymers modified by chemical after-treatment derived from polycarboxylic acids and polyhydroxy compounds
  • C08G63/916—Dicarboxylic acids and dihydroxy compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
  • C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
  • C08G63/16—Dicarboxylic acids and dihydroxy compounds
  • C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
  • C08G63/181—Acids containing aromatic rings
  • C08G63/183—Terephthalic acids
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
  • C08J11/12—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by dry-heat treatment only

Definitions

• the present invention relates to a method for producing polyester resin and to a polyester resin.
• Polyester resins have excellent mechanical properties, insulating properties, heat resistance, and moldability, and are therefore widely used in a variety of containers, films, electrical and electronic equipment parts, automobile parts, machine parts, etc.
• Specific examples of electrical and electronic equipment parts and automobile parts include industrial molded products such as connectors, relays, and switches.
• polyester resins contain cyclic oligomers, the main component of which is a cyclic trimer. These bleed out onto the surface of the molded product during molding and adhere to the surface of the mold, causing mold fouling. Such mold fouling can cause the surface of the resulting molded product to become rough or white, resulting in substandard products (defective products). In addition, production must be stopped frequently to remove the mold fouling, which poses the problem of reduced productivity. For this reason, there is a demand for polyester resins with a low oligomer content.
• a method for producing a high-polymerization polybutylene terephthalate resin which is characterized by esterifying or transesterifying a dicarboxylic acid and/or its alkyl ester derivative, mainly composed of terephthalic acid, with a diol mainly composed of 1,4-butanediol, followed by melt polymerization to obtain a low-polymerization polybutylene terephthalate having a terminal carboxyl group concentration of 10 eq/t or less and an intrinsic viscosity of 0.6 to 0.7 dL/g, and then solid-phase polymerization (Patent Document 1).
• Patent Document 3 a manufacturing method (Patent Document 3) includes a process for depolymerizing polyester resin by pressurizing polyester resin and alkylene glycol at a temperature equal to or higher than the melting point of the polyester resin, and a process for polymerizing the depolymerized product.
• Patent Document 1 had the problem that in order to obtain a polyester resin with a low oligomer content, it was necessary to increase the degree of polymerization of the polyester resin, which resulted in a decrease in the fluidity of the resin.
• Patent Document 2 has the problem that when solid-phase polymerization is carried out for a short period of time to prevent a decrease in fluidity, the reduction in oligomer content is insufficient, making it difficult to achieve both a reduction in oligomer content and good fluidity.
• Patent Document 3 requires the addition of a large amount of petroleum-derived alkylene glycol to regenerate the polyester resin, which is inefficient due to the increased amount of carbon dioxide emissions from the raw materials and the increased amount of energy required for heating.
• the acid value of the resulting recycled polyester resin increases due to thermal decomposition during high-temperature melt polymerization, resulting in reduced hydrolysis resistance and other problems.
• the present invention aims to provide a polyester resin that has excellent fluidity and a reduced oligomer content, and a method for producing the same, and further to provide a method for producing recycled polyester resin that efficiently regenerates recovered polyester resin and improves its quality.
• the polyester resin [B] contains 0.05% by mass or more and 4.76% by mass or less of unreacted alkylene glycol.
• a method for producing polyester resin 2.
• the present invention can provide a polyester resin with excellent moldability and productivity, with good fluidity, suppression of resin decomposition and molding defects during molding, and minimal mold contamination due to oligomers during molding, as well as a manufacturing method thereof. Furthermore, this manufacturing method can be applied not only to the manufacture of virgin resin, but also to the manufacture of recycled polyester resin that reuses recovered polyester resin, making it possible to provide recycled polyester resin that is lower in cost than chemical recycling and higher in quality than material recycling.
• the method for producing a polyester resin of the present invention includes a heat treatment [1] step in which an alkylene glycol is added to a polyester resin [A] and the polyester resin [A] is heated at a temperature above the melting point of the polyester resin [A] to obtain a polyester resin [B], and a heat treatment [2] step in which the obtained polyester resin [B] is heated at a temperature below the melting point of the polyester resin [B].
• heat treatment [1] step a predetermined amount of alkylene glycol is added to the polyester resin [A] and heat treatment [1] is performed, whereby the alkylene glycol reacts with the polyester resin [A], increasing the amount of hydroxyl groups and lowering the viscosity of the polyester resin [A], while also allowing some unreacted alkylene glycol to be contained.
• heat treatment [2] step heat treatment [2] is performed in the presence of unreacted alkylene glycol, which promotes the ring-opening reaction and volatilization of the cyclic oligomers, and allows a polyester resin with excellent fluidity to be obtained while efficiently reducing the oligomer content.
• alkylene glycol only a small amount is used in the present invention, and by performing heat treatment at a temperature exceeding the melting point of the polyester resin [A], it is possible to quickly incorporate alkylene glycol into the polyester resin [A] in a short period of time. This allows the amount of alkylene glycol required and the amount of energy consumed in the process to be reduced, thereby reducing carbon dioxide emissions.
• the oligomer content and acid value of the polyester resin obtained due to the thermal history in the recycling process tend to be high, and the intrinsic viscosity tends to vary.
• polyester resin [A] by using recovered polyester resin as polyester resin [A] and carrying out the polyester resin manufacturing method of the present invention, it is possible to provide a recycled polyester resin with a low oligomer content and acid value and small variation in intrinsic viscosity.
• the polyester resin [A] that can be used in the present invention is a polymer or copolymer having at least one residue selected from the group consisting of (1) dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative, (2) hydroxycarboxylic acid or its ester-forming derivative, and (3) lactone as the main structural unit.
• “having as the main structural unit” refers to having at least one residue selected from the group consisting of (1) to (3) in 50 mol% or more of all structural units, and a preferred embodiment is having these residues in 80 mol% or more.
• the polymer or copolymer having as the main structural unit (1) residues of dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative is preferred in terms of being more excellent in mechanical properties and heat resistance.
• dicarboxylic acids or their ester-forming derivatives include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, bis(p-carboxyphenyl)methane, 1,4-anthracenedicarboxylic acid, 1,5-anthracenedicarboxylic acid, 1,8-anthracenedicarboxylic acid, 2,6-anthracenedicarboxylic acid, 9,10-anthracenedicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-tetrabutylphosphonium isophthalic acid, and 5-sodium sulfoisophthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid;
• examples of the above diols or their ester-forming derivatives include aliphatic or alicyclic glycols having 2 to 20 carbon atoms, such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, decamethylene glycol, cyclohexanedimethanol, cyclohexanediol, and dimer diol; long-chain glycols having a molecular weight of 200 to 100,000, such as polyethylene glycol, poly-1,3-propylene glycol, and polytetramethylene glycol; aromatic dioxy compounds, such as 4,4'-dihydroxybiphenyl, hydroquinone, t-butylhydroquinone, bisphenol A, bisphenol S, and bisphenol F, and ester-forming derivatives thereof. Two or more of these may be used.
• polymers or copolymers having dicarboxylic acids or their ester-forming derivatives and diols or their ester-forming derivatives as structural units include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polypropylene isophthalate, polybutylene isophthalate, polybutylene naphthalate, polypropylene isophthalate/terephthalate, polybutylene isophthalate/terephthalate, polypropylene terephthalate/naphthalate, polybutylene terephthalate/naphthalate, polybutylene terephthalate/decane dicarboxylate, polypropylene terephthalate/5-sodium sulfoisophthalate, polybutylene terephthalate/5-sodium sulfoisophthalate, polypropylene terephthalate/polyethylene glycol, polybutylene terephthalate/polyethylene
• aromatic polyester
• polymers or copolymers having as their main structural units residues of aromatic dicarboxylic acids or their ester-forming derivatives and residues of aliphatic diols or their ester-forming derivatives are more preferred, and polymers or copolymers having as their main structural units residues of terephthalic acid, naphthalenedicarboxylic acid or their ester-forming derivatives and residues of an aliphatic diol or its ester-forming derivatives selected from propylene glycol and 1,4-butanediol are even more preferred.
• the acid value of the polyester resin [A] that can be used in the present invention is preferably 100 eq/t or less, more preferably 60 eq/t or less, even more preferably 30 eq/t or less, and particularly preferably 20 eq/t or less, from the viewpoint of suppressing deterioration of the mechanical properties of the polyester resin obtained by the present invention and moldability.
• the lower limit of the acid value is 0 eq/t.
• the acid value here is the value measured by dissolving the polyester resin [A] in an o-cresol/chloroform solvent and then titrating with ethanolic potassium hydroxide.
• the polyester resin [A] that can be used in the present invention preferably has an intrinsic viscosity of 0.30 dL/g or more when measured in o-chlorophenol solution at 25°C, from the viewpoint of ease of granulation of the resulting polyester resin [B]. More preferably, it is 0.36 dL/g or more. If the polyester resin [B] is granulated, the subsequent heat treatment [2] can be carried out appropriately. Furthermore, from the viewpoint of improving fluidity, it is preferably 2.00 dL/g or less, and more preferably 1.60 dL/g or less.
• the polyester resin [A] that can be used in the present invention preferably has a weight average molecular weight of 9,000 or more, more preferably 10,000 or more, in terms of ease of granulation of the resulting polyester resin [B]. If the polyester resin [B] is granulated, the subsequent heat treatment [2] can be carried out appropriately. In addition, in terms of improving fluidity, the weight average molecular weight is preferably 40,000 or less, more preferably 30,000 or less.
• the weight average molecular weight here is a value calculated by gel permeation chromatography (solvent: hexafluoroisopropanol, standard sample: polymethyl methacrylate).
• the polyester resin [A] is preferably in the form of flakes, powder, pellets, etc. From the viewpoint of efficiently carrying out the subsequent heat treatment [1], it is preferable to keep the particle size small to a certain extent. Therefore, if the polyester resin [A] is large in shape, it is preferable to crush it to an appropriate size of about 1.5 to 5.0 mm, but this is not limited to this.
• the polyester resin [A] in the present invention may be a virgin polyester resin [A-1] obtained by a polymerization reaction from raw materials, or may be a recycled polyester resin [A-2] such as a pre-consumer recycled product obtained from non-standard products in the manufacturing process or a post-consumer recycled product obtained by recovering resin products using polyester resins distributed in the market. Either one of them or both may be mixed and used in any ratio.
• the manufacturing method of the present invention preferably uses recycled polyester resin [A-2] because, when recycled polyester resin [A-2] is used, a high-quality polyester resin can be obtained from a low-quality recycled polyester resin, the range of applications in which the recycled polyester resin can be used is expanded, and waste and carbon dioxide emissions can be reduced.
• the virgin polyester resin [A-1] used in the present invention can be produced by a known polycondensation method, ring-opening polymerization method, etc.
• the production method may be either batch polymerization or continuous polymerization, and either transesterification or direct polymerization can be applied, but from the viewpoint of productivity, continuous polymerization is preferred, and direct polymerization is more preferred.
• the virgin polyester resin [A-1] used in the present invention is a polymer or copolymer obtained by a condensation reaction of dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative as the main components, it can be produced by subjecting dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative to an esterification reaction or ester exchange reaction, followed by a polycondensation reaction.
• polymerization catalysts include organotitanium compounds such as methyl ester, tetra-n-propyl ester, tetra-n-butyl ester, tetraisopropyl ester, tetraisobutyl ester, tetra-tert-butyl ester, cyclohexyl ester, phenyl ester, benzyl ester, tolyl ester, or mixed esters of these of titanic acid, dibutyltin oxide, methylphenyltin oxide, tetraethyltin, hexaethylditin oxide, cyclohexahexylditin oxide, didodecyltin oxide, triethyltin halide, and the like.
• organotitanium compounds such as methyl ester, tetra-n-propyl ester, tetra-n-butyl ester, tetraiso
• tin compounds include tin hydroxide, triphenyltin hydroxide, triisobutyltin acetate, dibutyltin diacetate, diphenyltin dilaurate, monobutyltin trichloride, dibutyltin dichloride, tributyltin chloride, dibutyltin sulfide, butylhydroxytin oxide, alkylstannoic acids such as methylstannoic acid, ethylstannoic acid, and butylstannoic acid, zirconia compounds such as zirconium tetra-n-butoxide, and antimony compounds such as antimony trioxide and antimony acetate. Two or more of these may be used.
• polymerization catalysts organic titanium compounds and tin compounds are preferred, and tetra-n-butyl ester of titanic acid is even more preferred.
• the amount of polymerization catalyst added is preferably in the range of 0.01 to 0.2 parts by mass per 100 parts by mass of virgin polyester resin [A-1].
• the polyester resin is removed from the reaction vessel and cooled to solidify. Generally, it is granulated into pellets by removing it in the form of strands, solidifying or semi-solidifying it in cooling water, and then cutting it with a strand cutter, or by extruding it into water and cutting it with an underwater cutter.
• the virgin polyester resin [A-1] may contain additives such as inorganic particles, fluorescent whitening agents, ultraviolet inhibitors, infrared absorbers, heat stabilizers, and antioxidants.
• the recycled polyester resin [A-2] used in the present invention is a pre-consumer recycled product obtained from non-standard products during the production process or a post-consumer recycled product obtained by recovering resin products using polyester resins distributed in the market. Since it is possible to obtain a high-quality polyester resin while reducing waste and carbon dioxide emissions, it can be suitably used when carrying out the production method for a polyester resin of the present invention.
• Examples of recycled polyester resin [A-2] include non-standard pellets generated during the production of polyester resin or polyester resin compositions containing polyester resin, pre-consumer products such as non-standard products and scraps generated during the production of resin products such as bottles, films, fibers, and injection molded products, and post-consumer products obtained by collecting products containing polyester resin from the market.
• Recycled polyester resin [A-2] may contain components other than polyester resin as long as they do not affect the properties of the polyester resin produced.
• components other than polyester resin include stabilizers, weathering agents, lubricants, pigments, dyes, crystal nucleating agents, plasticizers, antistatic agents, flame retardants, color inhibitors, inorganic fillers such as fibrous reinforcing materials, and polymers other than polyester resin.
• the alkylene glycol used in the present invention may be any of the diol components exemplified in the section on [Polyester Resin [A]] above, but is preferably a diol component constituting the polyester resin [A] from the viewpoint of mechanical properties. If the polyester resin [A] is a polyethylene terephthalate resin, it is preferably ethylene glycol, and if the polyester resin [A] is a polybutylene terephthalate resin, it is preferably 1,4-butanediol. From the viewpoint of the balance between mechanical properties and moldability, a combination of polybutylene terephthalate and 1,4-butanediol is more preferable.
• the boiling point of the alkylene glycol used in the present invention is preferably within the range of (T mA -90) ° C. or more and (T mA +20) ° C. or less with respect to the melting point T mA (° C.) of the polyester resin [A]. If the boiling point of the alkylene glycol is (T mA -90) ° C. or more, more preferably (T mA -60) ° C. or more, and even more preferably (T mA -30) ° C.
• the alkylene glycol can be efficiently added to the polyester resin [A] while suppressing the volatilization of the alkylene glycol to a small extent in the heat treatment [1] step, and the content of unreacted alkylene glycol in the polyester resin [B] described later (details will be described later) can be increased. Furthermore, if the boiling point of the alkylene glycol is (T + 20) ° C. or lower, more preferably (T + 10) ° C. or lower, and even more preferably T (° C. ) or lower, then unreacted alkylene glycol and the like are easily volatilized in the subsequent heat treatment [2] step, and the effect of reducing the oligomer content due to volatilization is obtained, which is preferable.
• the amount of alkylene glycol added is 0.1 to 5.0 parts by mass per 100 parts by mass of polyester resin [A]. If the amount of alkylene glycol added is less than 0.1 parts by mass, the acid value reduction effect and oligomer content reduction effect of the subsequent heat treatment [2] cannot be achieved. From the viewpoint of reducing the oligomer content, the lower limit of the amount of alkylene glycol added is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more. Furthermore, if the amount of alkylene glycol added exceeds 5.0 parts by mass, the melt viscosity of polyester resin [B] becomes too low, making it difficult to recover the resin in a uniform shape, and the subsequent heat treatment [2] cannot be performed appropriately. From the viewpoint of ease of granulation of polyester resin [B], the upper limit of the amount of alkylene glycol added is preferably 4.0 parts by mass or less, more preferably 3.0 parts by mass or less.
• polyester resin [B] The polyester resin [B] is an intermediate obtained by subjecting the polyester resin [A] to a heat treatment [1] described below.
• Polyester resin [B] contains 0.05% by mass or more and 4.76% by mass or less of unreacted alkylene glycol.
• the unreacted alkylene glycol is the alkylene glycol component added in the heat treatment [1] that remains in an unreacted state.
• the content of unreacted alkylene glycol is 0.05% by mass or more, more preferably 0.10% by mass or more, and even more preferably 0.20% by mass or more, the oligomer content is reduced in the subsequent heat treatment [2], and mold fouling is suppressed.
• the upper limit of the unreacted alkylene glycol content contained in polyester resin [B] is 5.0 parts by mass per 100 parts by mass of polyester resin [B], which is the same as the upper limit of the alkylene glycol component added in the heat treatment [1], and is 4.76% by mass per 100 parts by mass of polyester resin [B].
• the content of unreacted alkylene glycol is preferably 2.91% by mass or less, more preferably 1.96% by mass or less.
• the content of unreacted alkylene glycol is determined by dissolving polyester resin [B] in a hexafluoroisopropanol/chloroform solvent, adding acetonitrile to precipitate the insoluble components, filtering the solution through a polytetrafluoroethylene disc filter (0.45 ⁇ m), and quantifying the filtrate using a gas chromatograph.
• polyester resin [B] may contain additives that were contained in polyester resin [A].
• the polyester resin [B] in the present invention preferably has an intrinsic viscosity of 0.30 dL/g or more and less than 0.70 dL/g when measured in an o-chlorophenol solution at 25°C. More preferably, it is 0.30 dL/g or more and less than 0.60 dL/g. If the intrinsic viscosity is 0.30 dL/g or more, the amount of powdered high-melting-point polyester resin does not increase in the subsequent heat treatment [2] step, and white foreign matter is less likely to occur in the molded product. If the intrinsic viscosity is less than 0.70 dL/g, the oligomer content can be sufficiently reduced without the intrinsic viscosity becoming too high during the heat treatment [2] step.
• the polyester resin [B] in the present invention preferably has a weight average molecular weight of 7,000 or more and less than 15,000. If the weight average molecular weight is 7,000 or more, more preferably 9,000 or more, it is preferable because it prevents the powdered high-melting point polyester resin from increasing in the subsequent heat treatment [2] step, and makes it difficult for white foreign matter to occur in the molded product. Also, if it is less than 15,000, more preferably less than 11,000, it is preferable because it is possible to sufficiently reduce the oligomer content without the intrinsic viscosity becoming too high during the heat treatment [2] step.
• the weight average molecular weight here is a value calculated by gel permeation chromatography (solvent: hexafluoroisopropanol, standard sample: polymethyl methacrylate).
• the polyester resin [B] preferably has a hydroxyl group concentration of 50 eq/t or more from the viewpoint of reducing the oligomer content. More preferably, it is 60 eq/t or more, and even more preferably, it is 80 eq/t or more. If the hydroxyl group concentration is 50 eq/t or more, a sufficient oligomer content reduction effect can be obtained, which is preferable. There is no particular upper limit for the hydroxyl group concentration, but when producing a granulated polyester resin [B], it is preferably 350 eq/t or less, and a sufficient oligomer content reduction effect can also be exhibited.
• the hydroxyl group concentration is calculated by dissolving the polyester resin [B] in deuterated hexafluoroisopropanol and performing 1 H-NMR measurement.
• the acid value of the polyester resin [B] in the present invention is preferably 100 eq/t or less, more preferably 60 eq/t or less, even more preferably 30 eq/t or less, and particularly preferably 20 eq/t or less, from the viewpoint of suppressing deterioration of the mechanical properties of the polyester resin produced by the method of the present invention and moldability.
• the lower limit of the acid value is 0 eq/t.
• the acid value here is the value measured by dissolving the polyester resin [B] in an o-cresol/chloroform solvent and then titrating with ethanolic potassium hydroxide.
• the heat treatment [1] step is performed by heating the polyester resin [A] to a temperature exceeding the melting point T mA (°C) of the polyester resin [A] to melt the polyester resin [A], adding 0.1 to 5.0 parts by mass of alkylene glycol to 100 parts by mass of the polyester resin [A], and applying shear for a predetermined time.
• the heat treatment [1] step is preferably performed using a polymerization tank equipped with an agitator, a single-screw extruder equipped with a "Unimelt” or “Dulmage” type screw, a twin-screw extruder, a triple-screw extruder, a conical extruder, a kneader-type kneader, or the like, but is not limited thereto.
• An extruder is more preferable because it can uniformly mix the polyester resin and the alkylene glycol in a short time and can increase the content of unreacted alkylene glycol.
• the alkylene glycol may be added immediately after the start of heating the polyester resin [A], or after the polyester resin [A] has melted.
• the upper limit of the temperature of the heat treatment [1] is preferably equal to or lower than (T mA +40)° C. with respect to the melting point T mA (° C.) of the polyester resin [A].
• the duration of the heat treatment [1] step is preferably 30 seconds or more and 20 minutes or less. A duration of 30 seconds or more is preferable because the alkylene glycol can be uniformly incorporated into the polyester resin [A]. A duration of 20 minutes or less, more preferably 10 minutes or less, and even more preferably 5 minutes or less, is preferable because the content of unreacted alkylene glycol in the resulting polyester resin [B] does not become too low.
• the duration of the heat treatment [1] here refers to the time taken from when the alkylene glycol is added to the polyester resin [A] until the heat treatment [1] is completed.
• the alkylene glycol may be added together with the polyester resin [A] using a plunger pump by installing a liquid addition nozzle midway between the inlet and outlet of the extruder, or may be supplied from the inlet or other location using a metering pump.
• a vent section may be provided in the extruder, and the heat treatment [1] may be performed by reducing the pressure in the vent section to below atmospheric pressure from the viewpoint of improving the quality of the pellets.
• the vent section is provided downstream of the addition position of the alkylene glycol, the reduction in pressure in the vent section reduces the content of unreacted alkylene glycol.
• the heating time for melting the polyester resin [A] is preferably 5 minutes or more and 90 minutes or less. Five minutes or more is preferable because the polyester resin [A] can be sufficiently melted. 90 minutes or less, more preferably 60 minutes or less, and even more preferably 30 minutes or less is preferable because the increase in acid value due to thermal decomposition of the resulting polyester resin [B] is small. In addition, since the content of unreacted alkylene glycol contained in the resulting polyester resin [B] will be high, it is preferable to add it after the polyester resin [A] is melted.
• the polyester resin [B] obtained is preferably granulated in order to perform the subsequent heat treatment [2] appropriately.
• the polyester resin [B] is preferably extruded into a strand shape and then cut, or cut while extruding in water to form pellets with a length of 1.00 mm to 5.00 mm and a diameter of 1.00 mm to 5.00 mm, but the granulation method is not limited to these. If the length and diameter of the pellets are 1.00 mm or more, more preferably 1.50 mm or more, the inherent viscosity does not increase too much in a short time during the heat treatment [2], and the heat treatment [2] can be performed for an appropriate time, so that the effect of reducing the oligomer content is efficiently exerted.
• polyester resin [B] is a polyethylene terephthalate resin
• heat treatment [2] is preferably carried out under conditions of 190 to 250°C, more preferably 195 to 240°C.
• the polyester resin [B] is a polybutylene terephthalate resin
• the heat treatment [2] is preferably carried out under conditions of 180 to 210°C, more preferably 185 to 200°C.
• polyester resin [C] the intrinsic viscosity of the polyester resin finally obtained (hereinafter, sometimes referred to as polyester resin [C]) is in the range of 0.70 dL/g to 1.00 dL/g.
• polyester resin [C] The polyester resin [C] obtained by the present invention is selected from any of the polyester resins disclosed in [Polyester resin [A]], but polybutylene terephthalate is preferred in terms of an excellent balance between mechanical properties and moldability.
• the polyester resin [C] of the present invention has an intrinsic viscosity of 0.70 dL/g or more and 1.00 dL/g or less when measured in o-chlorophenol solution at 25°C. If the intrinsic viscosity is 0.70 dL/g or more, more preferably 0.80 dL/g or more, the strength of the molded product can be improved and the occurrence of burrs in the molded product can be suppressed. If the intrinsic viscosity is 1.00 dL/g or less, more preferably 0.90 dL/g or less, the flowability during extrusion and molding is good, and deterioration of the mechanical properties of the molded product and molding defects due to resin decomposition are suppressed.
• polyester resin [C] was molded into a square plate having a width of 80 mm, a length of 80 mm, and a thickness of 2 mm under the following conditions: when polyester resin [C] was polybutylene terephthalate, the molding temperature was 280° C., the mold temperature was 80° C., and the cooling time was 10 seconds; when polyester resin [C] was polyethylene terephthalate, the molding temperature was 280° C., the mold temperature was 120° C., and the cooling time was 10 seconds; when polyester resin [C] was polyester elastomer, the molding temperature was 280° C., the mold temperature was 60° C., and the cooling time was 10 seconds.
• NEX1000 manufactured by Nissei Plastics Co., Ltd.
• the fluidity was judged by the flow length during injection molding using a mold for a rectangular molded product with a thickness of 1 mm and a width of 10 mm.
• the injection molding conditions are as follows: when the polyester resin [C] is polybutylene terephthalate, the cylinder temperature is 250°C, the mold temperature is 80°C, the injection pressure is 30 MPa, and the injection speed is 100 mm/s.
• the polyester resin [C] is polyethylene terephthalate
• the cylinder temperature is 280°C
• the mold temperature is 40°C
• the injection pressure is 30 MPa
• the injection speed is 100 mm/s.
• the polyester resin [C] is a polyester elastomer
• the cylinder temperature is 250°C
• the mold temperature is 60°C
• the injection pressure is 30 MPa
• the injection speed is 100 mm/s.
• Resins with a flow length of 100 mm or more were judged to have excellent fluidity. 110 mm or more is more excellent, 120 mm or more is even more excellent, and 140 mm or more is particularly excellent.
• polyester resin [C] was polybutylene terephthalate
• molding was performed under molding cycle conditions of cylinder temperature 250°C, mold temperature 80°C, injection speed 50 mm/s, injection time and pressure holding time total 10 seconds, and cooling time 10 seconds.
• the polyester resin [C] was polyethylene terephthalate
• molding was performed under molding cycle conditions of cylinder temperature 280°C, mold temperature 80°C, injection speed 50 mm/s, injection time and pressure holding time total 10 seconds, and cooling time 10 seconds.
• Polyester resin [A] Virgin polyester resin [A-1] PBT1 Polybutylene terephthalate, melting point 225°C, manufactured by Toray Industries, Inc., acid value 20eq/t, intrinsic viscosity 0.88dL/g, weight average molecular weight 16100 ⁇ PBT2 Polybutylene terephthalate, melting point 222°C, manufactured by Toray Industries, Inc., acid value 30 eq/t, intrinsic viscosity 1.30 dL/g, weight average molecular weight 23,000 PET1 Polyethylene terephthalate, melting point 260°C, manufactured by Toray Industries, Inc., acid value 20 eq/t, intrinsic viscosity 0.80 dL/g, weight average molecular weight 15,000 ⁇ TPEE Polyester elastomer, melting point 201° C., Celanese “Hytrel” (registered trademark) 5556, inherent viscosity 1.46 dL/g.
• Recycled polyester resin [A-2] ⁇ PBT3 Non-standard pellets recovered during polybutylene terephthalate resin production. Melting point: 223°C, acid value: 20 eq/t, intrinsic viscosity: 1.08 dL/g, weight average molecular weight: 19100 ⁇ PBT4 Recovered molding waste from injection molding of a resin composition made of polybutylene terephthalate resin. Melting point: 220° C.; acid value: 70 eq/t; intrinsic viscosity: 0.53 dL/g; weight average molecular weight: 11,900.
• PBT6 Recovered molding waste from injection molding of a resin composition made of polybutylene terephthalate resin. Melting point: 223° C.; acid value: 56 eq/t; intrinsic viscosity: 0.61 dL/g; weight average molecular weight: 12,800.
• Alkylene glycol 1,4-butanediol (BDO, boiling point 228°C, manufactured by Mitsubishi Chemical Corporation) Ethylene glycol (EG, boiling point 198°C, manufactured by Mitsubishi Chemical Corporation).
• MB-9811 BLACK polybutylene terephthalate, pigment concentration 20%, manufactured by Koshigaya Chemical Industry Co., Ltd.
• the product was then extruded in the form of a strand, passed through a cooling bath, and granulated to the pellet size shown in Table 3 by adjusting the take-up speed with a strand cutter, to obtain pellets of polybutylene terephthalate prepolymer (PBT5, acid value 26 eq/t, intrinsic viscosity 0.58 dL/g).
• PBT5 polybutylene terephthalate prepolymer
• the pellets were then dried for 6 hours in a hot air dryer at a temperature of 110° C.
• PET2 Polyethylene terephthalate prepolymer
• acid value 20 eq/t, 1,4-butanediol was replaced with ethylene glycol and the polymerization temperature was changed to 280° C.
• the pellets were dried in a hot air dryer at 110° C. for 6 hours.
• the alkylene glycol was supplied by a metering pump. Further, when the polyester resin [A] was polybutylene terephthalate, the extrusion conditions were 250° C. kneading temperature and 200 rpm screw rotation, when the polyester resin [A] was polyethylene terephthalate, 280° C. kneading temperature and 200 rpm screw rotation, and when the polyester elastomer was polyester elastomer, the extrusion conditions were 250° C.
• polyester resin [B] 3 parts by mass of black coloring master batch MB-9811 BLACK was added to 100 parts by mass of polyester resin [A] from the input section of the extruder, and time measurement was started from the time of addition. After the black color originating from the black coloring master batch was confirmed in the resin discharged from the discharge port, the time measurement was stopped when the black color was no longer confirmed, and the time taken from the start to the end of measurement was regarded as the heat treatment time in this example (Table 1). This operation was carried out after obtaining the amount of polyester resin [B] required for the subsequent heat treatment [2] step, and the polyester resin obtained by adding the black coloring master batch was not used in the subsequent step.
• Example 7 ⁇ Heat treatment in Example 7 [1]>
• the heat treatment [1] was carried out in a polymerization tank. 1000 g of PBT1 was added to a 5 L polymerization tank equipped with an agitator, and the tank was heated to 250°C under nitrogen flow and stirred for 30 minutes. After confirming that PBT1 had melted, 10 g of 1,4-butanediol was added and stirred for 1 minute. After confirming that the viscosity of the melt was stable, the melt was discharged in the form of strands from the discharge port, passed through a cooling bath, and granulated to the pellet size shown in Table 1 by adjusting the take-up speed with a strand cutter to obtain pellets of polyester resin [B] (Table 1). The obtained pellets were dried for 6 hours in a hot air dryer at a temperature of 110°C.
• Example 8 ⁇ Heat treatment in Example 8 [1]>
• the heat treatment [1] was carried out in a polymerization tank. 1000 g of PBT1 was added to a 5 L polymerization tank equipped with an agitator, and the tank was heated to 250°C under nitrogen flow and stirred for 30 minutes. After confirming that PBT1 had melted, 10 g of 1,4-butanediol was added and stirred for 5 minutes. After confirming that the viscosity of the melt was stable, the melt was discharged in the form of strands from the discharge port, passed through a cooling bath, and granulated to the pellet size shown in Table 1 by adjusting the take-up speed with a strand cutter to obtain pellets of polyester resin [B] (Table 1). The obtained pellets were dried for 6 hours in a hot air dryer at a temperature of 110°C.
• the heat treatment time was calculated in the same manner as for heat treatment [1] in Example 7.
• ⁇ Heat treatment [2]> The polyester resin pellets obtained in the previous step were subjected to a heat treatment [2] at a temperature of 230°C and a pressure of 100 Pa when the polyester resin [A] used was polyethylene terephthalate, at a temperature of 170 to 210°C and a pressure of 100 Pa when the polyester resin [A] used was polybutylene terephthalate, or at a temperature of 180°C and a pressure of 100 Pa when the polyester resin was a polyester elastomer, to obtain a polyester resin [C] (Table 1).
• the heat treatment [2] was performed at 240°C, which is above the melting point of the polyester resin [B].
• Example 1-20 in which the unreacted alkylene glycol content of polyester resin [B] was 0.05 mass% or more, the oligomer content of polyester resin [C] was low and mold fouling inhibition was excellent.
• Comparative Examples 1, 2, 10, 12, and 14 in which the unreacted alkylene glycol content of polyester resin [B] was less than 0.05 mass%, the oligomer content of polyester resin [C] was high and mold fouling inhibition was poor.
• Comparative Example 8 in which the properties were evaluated without carrying out the heat treatment [2], showed more mold fouling and inferior hydrolysis resistance compared to Example 3, in which the heat treatment [2] was carried out.
• Comparative Examples 10 and 12 in which the recovered polyester resin was subjected to heat treatment [1] without adding alkylene glycol, and Comparative Examples 9 and 11, in which the recovered polyester resin was evaluated for each characteristic without being subjected to heat treatments [1] and [2], were inferior in suppressing mold fouling.
• Examples 7 and 8 in which a polymerization tank was used for the heat treatment [1].
• Example 7 Comparing Example 7 and Example 8, in which the heat treatment [1] was carried out in a polymerization tank, Example 7, in which the heat treatment time after the addition of alkylene glycol was shorter, showed less evaporation of alkylene glycol and less ester exchange reaction with polyester, a higher alkylene glycol content in polyester resin [B], and a lower oligomer content in polyester resin [C].
• Examples 1-3, 5, and 6 in which the polyester resin [A] was polybutylene terephthalate and 1,4-butanediol was used as the alkylene glycol and extruded, compared to Example 4, in which the polyester resin [A] was polyethylene terephthalate and ethylene glycol was used as the alkylene glycol, the melting point of the polyester resin was low and the boiling point of the alkylene glycol was high. As a result, less alkylene glycol was consumed in volatilization and transesterification during the heat treatment [1] in the extruder, and the unreacted alkylene glycol content of the polyester resin [B] was high. Therefore, Examples 1-3, 5, and 6 had a greater effect on reducing the oligomer content and were better at suppressing mold fouling.
• Example 1 Compared to Example 1, Examples 9 and 10, which have smaller pellet sizes (diameters), showed a large increase in intrinsic viscosity due to the heat treatment [2], and this was particularly noticeable in Example 10, which had a pellet diameter of less than 1.00 mm, and the treatment was completed in a short time. Therefore, Example 1 had a greater effect in reducing the oligomer content and was more effective at suppressing mold fouling than Example 10, which completed the treatment in a short time.
• Example 1 Compared to Examples 11 and 12, which have larger pellet sizes (diameters), Example 1 has a shorter distance from the center of the pellet to the surface, and was able to more efficiently reduce oligomers inside the pellet during heat treatment [2]. This tendency was particularly notable compared to Example 12, where the pellet diameter exceeded 5.00 mm. Therefore, Example 1 was better at suppressing mold fouling than Example 12.
• Example 13 in which heat treatment [2] was performed at a lower temperature, showed a tendency for the increase in intrinsic viscosity during heat treatment [2] to be smaller.
• Example 14 in which heat treatment [2] was performed at a high temperature, tended to have a greater increase in intrinsic viscosity during heat treatment [2], and the treatment was completed in a short time. Therefore, Example 1 had a greater effect in reducing the oligomer content and was excellent in suppressing mold fouling compared to Example 14, in which the treatment was completed in a short time.
• Example 15 which completed the heat treatment [2] in a short time, had a lower intrinsic viscosity and a tendency for the oligomer content to be higher.
• Example 16 which underwent heat treatment [2] for a long period of time, had a tendency to have a higher intrinsic viscosity and a lower oligomer content.
• Example 1-3, 5, and 6 in which the polyester resin [A] was polybutylene terephthalate, cyclic oligomers were more efficiently reduced, and therefore mold fouling was more effectively suppressed, compared to Example 18, in which the polyester resin [A] was a polyester elastomer.

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