Method for producing polyester resin and polyester resin

Abstract

The present invention addresses the problem of providing a method for producing a polyester resin which has satisfactory flowability, causes little mold fouling, has satisfactory mechanical properties, and is excellent in terms of moldability, producibility, and quality.　This method for producing a polyester resin comprises a heating [1] step in which 0.1-5.0 parts by mass of an alkylene glycol is added to 100 parts by mass of a polyester resin [A] and the mixture is heated at a temperature exceeding the melting point TmA (°C) of the polyester resin [A], thereby obtaining a polyester resin [B] and a heating [2] step in which the obtained polyester resin [B] is heated at a temperature not higher than TmB (°C), the TmB (°C) being the melting point of the polyester resin [B], the polyester resin [B] containing the alkylene glycol remaining unreacted in an amount of 0.05-4.76 mass%.

Description

Technical Field

[0001] The present invention relates to a method for producing a polyester resin and a polyester resin.

Background Art

[0002] Polyester resins have excellent mechanical properties, insulation properties, heat resistance, and moldability, and are therefore widely used in various containers, films, electrical and electronic equipment parts, automotive parts, mechanical parts, etc. Specific examples of electrical and electronic equipment parts and automotive parts include industrial molded products such as connectors, relays, and switches.

[0003] However, in recent years, the demand for miniaturization and weight reduction of industrial molded products has been increasing. In particular, polyester resins used in automotive and electrical and electronic equipment applications are desired to improve the fluidity during melting without causing a decrease in mechanical properties or mold contamination during molding.

[0004] In particular, polyester resins contain cyclic oligomers mainly composed of cyclic trimers. During molding, these oligomers bleed out to the surface of the molded product and adhere to the surface of the mold, resulting in mold fouling. Such mold fouling causes surface roughness and whitening of the obtained molded product, resulting in out-of-spec products (defective products). In addition, in order to frequently remove mold fouling, production must be stopped, which poses a problem of reduced productivity. Therefore, there is a demand for polyester resins with a low oligomer content.

[0005] In recent years, the demand for recycling polyester resins for a decarbonized society has also been increasing. It is also required to reduce waste by recycling off-spec products in the production process and recovered polyester resins recovered from consumed and discarded products into polyester resin products again.

[0006] As a method for obtaining a polyester resin with a low oligomer content, a dicarboxylic acid mainly composed of terephthalic acid and / or its alkyl ester derivative and a diol mainly composed of 1,4-butanediol are subjected to an esterification reaction or a transesterification reaction, and then melt-polymerized to obtain a low-polymerization-degree polybutylene terephthalate with a terminal carboxyl group concentration of 10 eq / t or less and an intrinsic viscosity of 0.6 to 0.7 dL / g, followed by solid-phase polymerization (Patent Document 1). Also, in a method for producing a polyester resin mainly composed of terephthalic acid and ethylene glycol, a prepolymer having a specific limiting viscosity, antimony element concentration, phosphorus element concentration, carboxyl terminal group amount, and hydroxy terminal group amount is subjected to solid-phase polymerization (Patent Document 2).

[0007] Further, as a method for recycling a polyester resin, a production method including a step of depolymerizing the polyester resin by pressurizing the polyester resin and an alkylene glycol at a temperature equal to or higher than the melting point of the polyester resin and polymerizing the depolymerized product (Patent Document 3) is disclosed.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, in the invention disclosed in Patent Document 1, in order to obtain a polyester resin with a low oligomer content, it is necessary to increase the degree of polymerization of the polyester resin, resulting in a problem that the fluidity of the resin decreases.

[0010] In addition, in the invention disclosed in Patent Document 2, when solid-phase polymerization is carried out in a short time so as not to reduce fluidity, the reduction of the oligomer content is insufficient, and there is a problem that it is difficult to achieve both a reduction in the oligomer content and good fluidization.

[0011] In addition, in the invention disclosed in Patent Document 3, it is necessary to add a large amount of petroleum-derived alkylene glycol to regenerate the polyester resin, which is inefficient because the carbon dioxide emissions from the raw materials and the amount of energy required for heating increase. In addition, there are problems such that the acid value of the obtained recycled polyester resin increases due to thermal decomposition during high-temperature melt polymerization, and the hydrolysis resistance and the like decrease.

[0012] An object of the present invention is to provide a polyester resin having excellent fluidity and a reduced oligomer content, and a method for producing the same, and further to provide a method for producing a recycled polyester resin that efficiently regenerates a recovered polyester resin and improves its quality.

Means for Solving the Problems

[0013] In order to solve the above problems, the present invention provides the following means. 1. A heat treatment [1] step of adding 0.1 to 5.0 parts by mass of alkylene glycol to 100 parts by mass of polyester resin [A] and heating at a temperature exceeding the melting point T mA (°C) of the polyester resin [A] to obtain a polyester resin [B]; and a heat treatment [2] step of heating the obtained polyester resin [B] at a temperature equal to or lower than T mB (°C) with respect to the melting point T mB (°C) of the polyester resin [B], wherein 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 a polyester resin. 2. The method for producing a polyester resin according to item 1, wherein the polyester resin [A] is a recovered polyester resin. 3. The method for producing a polyester resin according to claim 1 or 2, wherein the heat treatment [1] step is carried out using an extruder. 4. The method for producing a polyester resin according to any one of claims 1 to 3, wherein the polyester resin [A] contains at least polybutylene terephthalate. 5. The method for producing a polyester resin according to claim 4, wherein the alkylene glycol is 1,4 - butanediol. 6. A polyester resin having an oligomer content of less than 0.30% by mass and an intrinsic viscosity of 0.70 dL / g or more and 1.00 dL / g or less. 7. The polyester resin according to claim 6, wherein the polyester resin is polybutylene terephthalate.

Advantages of the Invention

[0014] According to the present invention, it is possible to provide a polyester resin and a method for producing the same, which have good fluidity, suppress resin decomposition and molding defects during molding, have excellent moldability with less mold fouling by oligomers during molding, and have excellent productivity. Further, this production method can be applied not only to the production of virgin resins but also to the production of recycled polyester resins using recycled polyester resins, and can provide recycled polyester resins with low cost compared to chemical recycling and high quality compared to material recycling.

Embodiments for Carrying Out the Invention

[0015] The method for producing a polyester resin of the present invention includes a heat treatment [1] step of adding an alkylene glycol to a polyester resin [A] and heating at a temperature exceeding the melting point of the polyester resin [A] to obtain a polyester resin [B], and a heat treatment [2] step of heating the obtained polyester resin [B] at a temperature not exceeding the melting point of the polyester resin [B].

[0016] In the heat treatment [1] step, by adding a predetermined amount of alkylene glycol to the polyester resin [A] and performing the heat treatment [1], the alkylene glycol reacts with the polyester resin [A], reducing the viscosity of the polyester resin [A] while increasing the amount of hydroxyl groups, and further allowing a part of the unreacted alkylene glycol to be contained. Then, in the heat treatment [2] step, by performing the heat treatment [2] in the presence of the unreacted alkylene glycol, the ring-opening reaction and volatilization of the cyclic oligomer are promoted, and a polyester resin excellent in fluidity can be obtained while efficiently reducing the oligomer content. In addition, a small amount of alkylene glycol is sufficient for use in the present invention, and by performing the heat treatment at a temperature exceeding the melting point of the polyester resin [A], the alkylene glycol can be quickly contained in the polyester resin [A] in a short time. Thereby, the required amount of alkylene glycol and the energy consumption in the process can be reduced, and the carbon dioxide emission can be reduced.

[0017] Further, in the normal recycling method, the oligomer content and acid value of the polyester resin obtained due to the heat history in the recycling process tend to be high and the intrinsic viscosity tends to vary. On the other hand, by applying the recycled polyester resin as the polyester resin [A] and implementing the method for producing the polyester resin of the present invention, it is possible to provide a recycled polyester resin having a low oligomer content and acid value and a small variation in intrinsic viscosity.

[0018] Details of each component in the production method of the present invention will be described.

[0019] [Polyester resin [A]] 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) a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative, (2) a hydroxycarboxylic acid or its ester-forming derivative, and (3) a lactone as a main structural unit. Here, "as a main structural unit" means having at least one residue selected from the group consisting of (1) to (3) in an amount of 50 mol% or more in all structural units, and a preferred embodiment is having these residues in an amount of 80 mol% or more. Among these, a polymer or copolymer having residues of (1) a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative as a main structural unit is preferred in terms of excellent mechanical properties and heat resistance.

[0020] Examples of the above-mentioned dicarboxylic acid or its ester-forming derivative 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, 5-sodium sulfoisophthalic acid, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, malonic acid, glutaric acid, dimer acid, alicyclic dicarboxylic acids such as 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and ester-forming derivatives thereof. Two or more of these may be used.

[0021] Examples of the diol or its ester-forming derivative 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, dimer diol, etc.; long-chain glycols having a molecular weight of 200 to 100,000 such as polyethylene glycol, poly-1,3-propylene glycol, polytetramethylene glycol, etc.; aromatic dioxy compounds such as 4,4'-dihydroxybiphenyl, hydroquinone, t-butylhydroquinone, bisphenol A, bisphenol S, bisphenol F, etc. and ester-forming derivatives thereof. Two or more of these may be used.

[0022] Examples of the polymer or copolymer having a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative as structural units include aromatic polyester resins such as 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 / decanedicarboxylate, polypropylene terephthalate / 5-sodium sulfoisophthalate, polybutylene terephthalate / 5-sodium sulfoisophthalate, polypropylene terephthalate / polyethylene glycol, polybutylene terephthalate / polyethylene glycol, polypropylene terephthalate / polytetramethylene glycol, polybutylene terephthalate / polytetramethylene glycol, polypropylene terephthalate / isophthalate / polytetramethylene glycol, polybutylene terephthalate / isophthalate / polytetramethylene glycol, polybutylene terephthalate / succinate, polypropylene terephthalate / adipate, polybutylene terephthalate / adipate, polypropylene terephthalate / sebacate, polybutylene terephthalate / sebacate, polypropylene terephthalate / isophthalate / adipate, polybutylene terephthalate / isophthalate / succinate, polybutylene terephthalate / isophthalate / adipate, and polybutylene terephthalate / isophthalate / sebacate. These polymers and copolymers may be used alone or in combination of two or more. Here, " / " represents a copolymer containing the components of the polymers before and after it.

[0023] Among these, from the viewpoint of further improving mechanical properties and heat resistance, a polymer or copolymer having a residue of an aromatic dicarboxylic acid or its ester-forming derivative and a residue of an aliphatic diol or its ester-forming derivative as main structural units is more preferable, and a polymer or copolymer having a residue of terephthalic acid, naphthalenedicarboxylic acid or its ester-forming derivative and a residue of an aliphatic diol selected from propylene glycol and 1,4-butanediol or its ester-forming derivative as main structural units is even more preferable.

[0024] Among them, at least one aromatic polyester resin selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polypropylene naphthalate, polybutylene naphthalate, polypropylene isophthalate / terephthalate, polybutylene isophthalate / terephthalate, polypropylene terephthalate / naphthalate, polybutylene adipate / terephthalate, polybutylene terephthalate / sebacate, and polybutylene terephthalate / naphthalate is particularly preferable, and at least one selected from polyethylene terephthalate, polybutylene terephthalate, polybutylene isophthalate / terephthalate, polybutylene decanedicarboxylate / terephthalate, polybutylene terephthalate / naphthalate, and polybutylene / ethylene terephthalate is more preferable. Also, two or more of these can be used in any content. Polybutylene terephthalate is even more preferable in terms of excellent balance between mechanical properties and moldability.

[0025] 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 viewpoints of suppressing a decrease in the mechanical properties of the polyester resin obtained by the present invention and moldability. The lower limit value of the acid value is 0 eq / t. The acid value referred to here is a value measured by titrating the polyester resin [A] dissolved in an o-cresol / chloroform solvent with ethanolic potassium hydroxide.

[0026] 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 an o-chlorophenol solution at 25°C from the viewpoint of the ease of granulation of the resulting polyester resin [B]. More preferably, it is 0.36 dL / g or more. When the polyester resin [B] is granulated, the subsequent heat treatment [2] can be appropriately carried out. Also, from the viewpoint of improving fluidity, it is preferably 2.00 dL / g or less, and more preferably 1.60 dL / g or less.

[0027] The polyester resin [A] that can be used in the present invention preferably has a weight average molecular weight of 9000 or more, more preferably 10000 or more, from the viewpoint of the ease of granulation of the resulting polyester resin [B]. When the polyester resin [B] is granulated, the subsequent heat treatment [2] can be appropriately carried out. Also, from the viewpoint of improving fluidity, it is preferably 40000 or less, and more preferably 30000 or less. The weight average molecular weight referred to here is a value calculated from gel permeation chromatography (solvent: hexafluoroisopropanol, standard sample: polymethyl methacrylate).

[0028] Preferred examples of the shape of the polyester resin [A] include flakes, powders, pellets, etc. From the viewpoint of efficiently carrying out the subsequent heat treatment [1], it is preferable to make the particle size somewhat small. Therefore, when the shape of the polyester resin [A] is large, it is preferably pulverized to an appropriate size of about 1.5 to 5.0 mm, but it is not limited thereto.

[0029] 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 a pre-consumer recycled product obtained from off-spec products in the manufacturing process, or a post-consumer recycled product such as a resin product using a polyester resin distributed in the market and recovered by recovering the resin product. One or both of them can be mixed and used at an arbitrary ratio.

[0030] When the production method of the present invention uses the recycled polyester resin [A-2], a high-quality polyester resin can be obtained from a low-quality recycled polyester resin, the applicable uses of the recycled polyester resin are expanded, and waste and carbon dioxide emissions can be reduced. Therefore, it is preferable to use the recycled polyester resin [A-2].

[0031] [Virgin polyester resin [A-1]] The virgin polyester resin [A-1] used in the present invention can be produced by known polycondensation methods, ring-opening polycondensation methods, etc. The production method may be either batch polymerization or continuous polymerization, and either an ester exchange reaction or a reaction by direct polymerization can be applied. From the viewpoint of productivity, continuous polymerization is preferable, and direct polymerization is more preferably used.

[0032] When the virgin polyester resin [A-1] used in the present invention is a polymer or copolymer obtained by a condensation reaction mainly composed of a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative, the dicarboxylic acid or its ester-forming derivative and the diol or its ester-forming derivative can be subjected to an esterification reaction or an ester exchange reaction, and then a polycondensation reaction to produce it.

[0033] In order to effectively promote the esterification reaction, transesterification reaction, and polycondensation reaction, it is preferable to add a polymerization reaction catalyst during these reactions. Specific examples of the polymerization reaction catalyst include organic titanium compounds such as methyl esters, tetra-n-propyl esters, tetra-n-butyl esters, tetraisopropyl esters, tetraisobutyl esters, tetra-tert-butyl esters, cyclohexyl esters, phenyl esters, benzyl esters, tolyl esters, or mixed esters thereof; dibutyltin oxide, methylphenyltin oxide, tetraethyltin, hexaethyldistannoxide, cyclohexanehexyldistannoxide, didodecyltin oxide, triethyltin hydroxide, triphenyltin hydroxide, triisobutyltin acetate, dibutyltin diacetate, diphenyltin dilaurate, monobutyltin trichloride, dibutyltin dichloride, tributyltin chloride, dibutyltin sulfide, butylhydroxytin oxide, methylstannonic acid, ethylstannonic acid, butylstannonic acid, and other alkylstannonic acids such as tin compounds; zirconia compounds such as zirconium tetra-n-butoxide; antimony compounds such as antimony trioxide and antimony acetate. Two or more of these may be used.

[0034] Among these polymerization reaction catalysts, organic titanium compounds and tin compounds are preferred, and tetra-n-butyl ester of titanic acid is more preferably used. The addition amount of the polymerization reaction catalyst is preferably in the range of 0.01 part by mass or more and 0.2 part by mass or less with respect to 100 parts by mass of the virgin polyester resin [A-1].

[0035] The polyester resin after polycondensation is taken out from the reaction vessel and cooled to a solid state. Generally, it is granulated into pellets by a method of being taken out in a strand shape, solidified or semi-solidified in cooling water, and then cut with a strand cutter, or a method of cutting with an underwater cutter while extruding into water.

[0036] Furthermore, the virgin polyester resin [A-1] may contain additives such as inorganic particles, optical brighteners, ultraviolet light absorbers, infrared light absorbers, heat stabilizers, and antioxidants.

[0037] [Recycled polyester resin [A-2]] The recycled polyester resin [A-2] used in the present invention is a post-consumer recycled product obtained by collecting pre-consumer recycled products obtained from off-spec products in the manufacturing process or resin products using polyester resin distributed in the market, and can obtain high-quality polyester resin while reducing waste and carbon dioxide emissions. Therefore, it can be suitably used when implementing the method for producing the polyester resin of the present invention.

[0038] Examples of the recycled polyester resin [A-2] include off-spec pellets generated during the production of polyester resin or the production of a polyester resin composition containing polyester resin, off-spec products and scraps during the production of resin products such as bottles, films, fibers, injection-molded products, etc., which are pre-consumer products, and post-consumer products obtained by collecting products containing polyester resin from the market.

[0039] The recycled polyester resin [A-2] may contain components other than polyester resin as long as it does not affect the properties of the polyester resin to be produced. Examples of components other than polyester resin include, for example, stabilizers, weathering agents, lubricants, pigments, dyes, crystal nucleating agents, plasticizers, antistatic agents, flame retardants, anti-coloring agents, inorganic fillers such as fibrous reinforcing materials, and other polymers other than polyester resin.

[0040] [Alkylene glycol] The alkylene glycol used in the present invention may be any diol component exemplified in the section of [Polyester resin [A]] described above, but it 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, ethylene glycol is preferably used. If the polyester resin [A] is a polybutylene terephthalate resin, 1,4-butanediol is preferably used. From the balance between mechanical properties and moldability, a combination of polybutylene terephthalate and 1,4-butanediol is more preferable.

[0041] Further, the boiling point of the alkylene glycol used in the present invention is (T mA (°C) of the polyester resin [A] to (T mA -90)°C or higher and (T mA +20)°C or lower. It is preferable that the boiling point of the alkylene glycol is (T mA -90)°C or higher, more preferably (T mA -60)°C or higher, and even more preferably (T mA -30)°C or higher. In the heat treatment [1] step, the volatilization of the alkylene glycol can be suppressed to a small extent, and it can be efficiently added to the polyester resin [A]. The content of unreacted alkylene glycol in the polyester resin [B] (details will be described later) can be increased, which is preferable. Also, if the boiling point of the alkylene glycol is (T mA +20)°C or lower, more preferably (T mA +10)°C or lower, and even more preferably T mA (°C) or lower, in the subsequent heat treatment [2] step, unreacted alkylene glycol and the like are likely to volatilize, and the effect of reducing the oligomer content due to volatilization can be obtained, which is preferable.

[0042] In the present invention, the addition amount of the alkylene glycol is 0.1 to 5.0 parts by mass with respect to 100 parts by mass of the polyester resin [A]. When the addition amount of the alkylene glycol is less than 0.1 part by mass, the effect of reducing the acid value and the effect of reducing the oligomer content by the subsequent heat treatment [2] cannot be exerted. From the viewpoint of reducing the oligomer content, the lower limit of the addition amount of the alkylene glycol is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more. Further, when the addition amount of the alkylene glycol exceeds 5.0 parts by mass, the melt viscosity of the 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 appropriately carried out. From the viewpoint of the ease of pelletizing the polyester resin [B], the upper limit of the addition amount of the alkylene glycol is preferably 4.0 parts by mass or less, more preferably 3.0 parts by mass or less.

[0043] [Polyester resin [B]] The polyester resin [B] is an intermediate obtained by performing the heat treatment [1] described below on the polyester resin [A].

[0044] The 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 one that remains unreacted among the alkylene glycol components added in the heat treatment [1]. When the content rate of the unreacted alkylene glycol is 0.05% by mass or more, more preferably 0.10% by mass or more, and further preferably 0.20% by mass or more, the oligomer content is reduced during the subsequent heat treatment [2], and mold fouling is suppressed. The upper limit of the content rate of the unreacted alkylene glycol contained in the polyester resin [B] is 5.0 parts by mass with respect to 100 parts by mass of the polyester resin [B], which is 4.76% by mass with respect to 100% by mass of the polyester resin [B], similar to the upper limit of the alkylene glycol component added in the heat treatment [1]. From the viewpoint of the ease of pelletizing, the content rate of the unreacted alkylene glycol is preferably 2.91% by mass or less, more preferably 1.96% by mass or less.

[0045] The content rate of unreacted alkylene glycol is quantified using a gas chromatograph for the filtrate obtained by dissolving the polyester resin [B] in a hexafluoroisopropanol / chloroform solvent, adding acetonitrile to precipitate the insoluble components, and filtering through a polytetrafluoroethylene disk filter (0.45 μm).

[0046] Also, the polyester resin [B] may contain additives that were contained in the polyester resin [A].

[0047] 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, it is preferable because in the subsequent heat treatment [2] step, there will not be many powdery high-melting polyester resins, and white foreign substances are less likely to occur in the molded product. Also, if it is less than 0.70 dL / g, it is preferable because the oligomer content rate can be sufficiently reduced within a range where the intrinsic viscosity does not increase too much during the heat treatment [2] step.

[0048] The polyester resin [B] in the present invention preferably has a weight average molecular weight of 7000 or more and less than 15000. If the weight average molecular weight is 7000 or more, more preferably 9000 or more, it is preferable because it suppresses the increase in the amount of powdery high-melting polyester resin in the subsequent heat treatment [2] step, and white foreign substances are less likely to occur in the molded product. Also, if it is less than 15000, more preferably less than 11000, it is preferable because the oligomer content rate can be sufficiently reduced within a range where the intrinsic viscosity does not increase too much during the heat treatment [2] step. The weight average molecular weight referred to here is a value calculated from a gel permeation chromatograph (solvent: hexafluoroisopropanol, standard sample: polymethyl methacrylate).

[0049] The polyester resin [B] in the present invention 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 still 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. Although there is no particular upper limit for the hydroxyl group concentration, when producing the granulated polyester resin [B], it is preferably 350 eq / t or less, and a sufficient oligomer content reduction effect is also exhibited. The hydroxyl group concentration is calculated by dissolving the polyester resin [B] in hexafluoroisopropanol and 1 performing 1H-NMR measurement.

[0050] 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, still more preferably 30 eq / t or less, and particularly preferably 20 eq / t or less, from the viewpoints of suppressing a decrease in the mechanical properties of the polyester resin produced by the method of the present invention and moldability. The lower limit value of the acid value is 0 eq / t. The acid value herein is a value measured by titrating with alcoholic potassium hydroxide after dissolving the polyester resin [B] in an o-cresol / chloroform solvent.

[0051] [Heat treatment [1] step] Hereinafter, details of a method for obtaining the polyester resin [B] by heat-treating the polyester resin [A] of the present invention will be described.

[0052] The heat treatment [1] step is the melting point T of the polyester resin [A] mAWhile heating to a temperature exceeding (°C) to melt the polyester resin [A], 0.1 to 5.0 parts by mass of alkylene glycol is added to 100 parts by mass of the polyester resin [A], and shear is applied for a predetermined time. The heat treatment [1] step is preferably carried out using a polymerization tank equipped with a stirring blade, a single-screw extruder equipped with a "Unimelt" or "Dalmage" type screw, a twin-screw extruder, a triple-screw extruder, a conical extruder, a kneader of the kneader type, etc., but is not limited thereto. The extruder can uniformly mix the polyester resin and alkylene glycol in a short time and can increase the content rate of unreacted alkylene glycol, so it is more preferable.

[0053] In the heat treatment [1] step, the alkylene glycol may be added immediately after the start of heating of the polyester resin [A], or may be added after the polyester resin [A] has melted.

[0054] The upper limit of the temperature of the heat treatment [1] is preferably (T mA (°C) or less than (T mA +40)°C. By setting the temperature of the heat treatment [1] to exceed T mA (°C) and be (T mA +40)°C or less, it is possible to give the minimum amount of heat for melting the resin without deteriorating the properties of the resin.

[0055] The implementation time of the heat treatment [1] step is preferably 30 seconds or more and 20 minutes or less. If the implementation time is 30 seconds or more, it is preferable because the alkylene glycol can be uniformly contained in the polyester resin [A]. If the implementation time is 20 minutes or less, more preferably 10 minutes or less, and still more preferably 5 minutes or less, the content rate of unreacted alkylene glycol in the obtained polyester resin [B] does not become too low, so it is preferable. Here, the implementation time of the heat treatment [1] refers to the time taken from when the alkylene glycol is added to the polyester resin [A] until the implementation of the heat treatment [1] is completed.

[0056] When performing the heat treatment [1] with an extruder, the addition of alkylene glycol may be carried out by installing a liquid addition nozzle in the middle of the charging section and the discharge section of the extruder together with the polyester resin [A] and using a plunger pump for addition, or by supplying it with a metering pump from the charging section or the like.

[0057] Also, a vent section may be installed in the extruder, and the heat treatment [1] may be carried out with the vent section depressurized to below atmospheric pressure from the viewpoint of improving the quality of the pellets. On the other hand, when installing a vent section downstream of the addition position of alkylene glycol, the decompression of the vent section reduces the content rate of unreacted alkylene glycol. In that case, from the viewpoint of increasing the content rate of unreacted alkylene glycol, when the addition amount of alkylene glycol is 1.5 parts by mass or less, it is preferable to carry out the heat treatment [1] with the pressure in the vent section being 5000 Pa or more and below atmospheric pressure, and when the addition amount of alkylene glycol exceeds 1.5 parts by mass and is 3.0 parts by mass or less, it is preferable to carry out the heat treatment [1] with the pressure in the vent section being 100 Pa or more and below atmospheric pressure. When the addition amount of alkylene glycol exceeds 3.0 parts by mass, from the viewpoint of suppressing vent up, it is preferable to carry out the heat treatment [1] with the pressure in the vent section being atmospheric pressure.

[0058] When performing the heat treatment [1] in a polymerization tank or the like equipped with stirring blades, the heating time for melting the polyester resin [A] is preferably 5 minutes or more and 90 minutes or less. If it is 5 minutes or more, it is preferable because the polyester resin [A] can be sufficiently melted. If it is 90 minutes or less, more preferably 60 minutes or less, and still more preferably 30 minutes or less, it is preferable because the increase in acid value due to thermal decomposition of the obtained polyester resin [B] is small. Also, since the content rate of unreacted alkylene glycol contained in the obtained polyester resin [B] increases, it is preferable to add it after the polyester resin [A] has melted.

[0059] The resulting polyester resin [B] is preferably granulated in order to appropriately perform the subsequent heat treatment [2]. The polyester resin [B] is preferably cut after being extruded in a strand shape or cut while being extruded in water to form pellets having a length of 1.00 mm or more and 5.00 mm or less and a diameter of 1.00 mm or more and 5.00 mm or less. However, the granulation method is not limited to these. When the length and diameter of the pellets are 1.00 mm or more, more preferably 1.50 mm or more, the intrinsic viscosity does not increase too much in a short time during the heat treatment [2], and the heat treatment [2] can be appropriately performed. Therefore, the effect of reducing the oligomer content is preferably exerted efficiently. Further, when the length and diameter of the pellets are 5.00 mm or less, more preferably 3.70 mm or less, the distance from the center to the surface of the pellets does not become too long, and the oligomers inside the pellets are efficiently reduced during the heat treatment [2], which is preferable.

[0060] [Heat treatment [2] step] The polyester resin obtained in the present invention is obtained by performing a heat treatment [2] on the polyester resin [B]. The heat treatment [2] step in the present invention is carried out under an inert gas flow or under high vacuum, and the treatment temperature is the melting point T of the polyester resin [B] mB (°C) with respect to T mB (°C) or less. By setting the temperature of the heat treatment [2] to T mB (°C) or less, it is possible to suppress an increase in the oligomer content and an increase in the acid value due to the melting of the polyester resin [B]. Further, the temperature of the heat treatment [2] is preferably (T mB -60)°C or more, more preferably (T mBBy setting the temperature to -40°C, it is possible to obtain the effect of reducing the acid value and the effect of reducing the oligomer content due to the terminal hydroxyl groups and unreacted alkylene glycol in the polyester resin [B]. When the polyester resin [B] is a polyethylene terephthalate resin, it is preferable to carry out the heat treatment [2] under the conditions of 190 to 250°C, more preferably 195 to 240°C. When the polyester resin [B] is a polybutylene terephthalate resin, it is preferable to carry out the heat treatment [2] under the conditions of 180 to 210°C, more preferably 185 to 200°C.

[0061] During the heat treatment [2] process in the present invention, solid-phase polymerization of the polyester resin [B] may proceed. The progress of solid-phase polymerization improves the mechanical properties of the obtained polyester resin while reducing the fluidity. Therefore, it is preferable to carry out the heat treatment [2] so that the intrinsic viscosity of the finally obtained polyester resin (hereinafter sometimes referred to as polyester resin [C]) is in the range of 0.70 dL / g or more and 1.00 dL / g or less. When the heat treatment [2] is carried out until the intrinsic viscosity of the polyester resin [C] becomes 0.70 dL / g or more, the content of unreacted alkylene glycol decreases to 0.03 mass% or less due to consumption by reaction with the polyester component and volatilization. The intrinsic viscosity of the polyester resin indicates the value obtained by measuring an o-chlorophenol solution of the polyester resin at 25°C.

[0062] The implementation time of the heat treatment [2] is preferably 5 hours or more and 20 hours or less. If the implementation time is 5 hours or more, more preferably 10 hours or more, the intrinsic viscosity of the polyester resin [C] will not become too low, the strength of the molded product can be improved, the generation of burrs in the molded product can be suppressed, and the oligomer content can be efficiently reduced. If the implementation time is 20 hours or less, the intrinsic viscosity of the polyester resin [C] will not become too high and it will have excellent fluidity.

[0063] [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 excellent balance between mechanical properties and moldability.

[0064] From the viewpoints of suppressing the deterioration of mechanical properties and moldability, the acid value of the polyester resin [C] obtained by the present invention is preferably 50 eq / t or less, more preferably 30 eq / t or less, still more preferably 20 eq / t or less, still more preferably 15 eq / t or less, and still more preferably 10 eq / t or less. The lower limit value of the acid value is 0 eq / t. The acid value referred to here is a value measured by titrating the obtained polyester resin dissolved in an o-cresol / chloroform solvent with ethanolic potassium hydroxide.

[0065] The oligomer content of the polyester resin [C] obtained by the present invention is preferably less than 0.30% by mass. When the oligomer content is less than 0.30% by mass, more preferably less than 0.25% by mass, still more preferably less than 0.20% by mass, and still more preferably less than 0.15% by mass, mold fouling during molding is greatly suppressed, and the frequency of mold cleaning in continuous molding during production is reduced. The lower limit value of the oligomer content is 0.00% by mass. The oligomer content referred to here is a value obtained by dissolving the polyester resin [C] in a hexafluoroisopropanol / chloroform solvent (1 / 1, volume ratio), precipitating high molecular weight components with an acetonitrile solvent, and quantifying cyclic trimers in the filtrate obtained by filtering through a polytetrafluoroethylene disk filter (0.45 μm) using high performance liquid chromatography.

[0066] 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 an o-chlorophenol solution at 25°C. When 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 generation of burrs on the molded product can be suppressed. When the intrinsic viscosity is 1.00 dL / g or less, more preferably 0.90 dL / g or less, the fluidity during extrusion and molding is good, and a decrease in the mechanical properties of the molded product due to resin decomposition, molding defects, etc. are suppressed.

[0067] The polyester resin [C] of the present invention preferably has a weight average molecular weight of 13,000 or more and 18,000 or less. When the weight average molecular weight is 13,000 or more, more preferably 15,000 or more, the strength of the molded product can be improved, and the generation of burrs on the molded product can be suppressed, which is preferable. When the weight average molecular weight is 18,000 or less, more preferably 16,000 or less, the fluidity during extrusion and molding is good, and a decrease in the mechanical properties of the molded product due to resin decomposition, molding defects, etc. are suppressed, which is preferable. The weight average molecular weight referred to here is a value calculated from gel permeation chromatography (solvent: hexafluoroisopropanol, standard sample: polymethyl methacrylate).

[0068] The polyester resin of the present invention can be made into a polyester resin composition by melt-kneading other components as necessary.

[0069] Examples of the melt-kneading method include a method in which the polyester resin and various additives are preliminarily mixed and then supplied to an extruder or the like for melt-kneading, or a method in which each component is supplied to an extruder or the like in a predetermined amount using a metering feeder such as a gravimetric feeder for melt-kneading.

[0070] Examples of the above preliminary mixing include methods of dry blending and methods of mixing using mechanical mixing devices such as tumblers, ribbon mixers, and Henschel mixers. Further, the fibrous reinforcing material may be added by installing a side feeder midway between the charging section and the discharging section of a multi-screw extruder such as a twin-screw extruder. Also, in the case of a liquid additive, methods such as installing a liquid addition nozzle midway between the charging section and the discharging section of a multi-screw extruder such as a twin-screw extruder and adding it using a plunger pump, or supplying it from the charging section or the like using a metering pump may be used.

[0071] The above composition is preferably granulated and then subjected to a forming process. As a granulation method, polyester resin and other additives are extruded into strands using, for example, a single-screw extruder, twin-screw extruder, triple-screw extruder, conical extruder, and kneader-type kneader equipped with a screw of the "Unimelt" or "Damage" type, and then cut, or cut while extruding in water, and it is preferable to form pellets having a length of about 1.5 to 5.0 mm and a diameter of about 1.5 to 5.0 mm, but the granulation method is not limited to these.

[0072] By melt-molding the polyester resin composition comprising the polyester resin according to the present invention, films, fibers, and molded articles of various other shapes can be obtained. Examples of the melt-molding method include injection molding, extrusion molding, and blow molding, and injection molding is particularly preferably used.

[0073] As methods of injection molding, in addition to the normal injection molding method, gas-assisted molding, two-color molding, sandwich molding, in-mold molding, insert molding, and injection press molding are known, and any of these molding methods can be applied.

[0074] The molded article made of the polyester resin according to the present invention can be used in various applications such as mechanical mechanism parts, electrical parts, electronic parts, and automotive parts, taking advantage of its excellent mechanical properties and hydrolysis resistance. Specific examples of mechanical mechanism parts, electrical parts, electronic parts, and automotive parts include breakers, electromagnetic switches, focus cases, flyback transformers, molded articles for fixing devices of copiers and printers, housings of general household appliances and OA equipment, varicon case parts, various terminal boards, transformers, printed wiring boards, housings, terminal blocks, coil bobbins, connectors, relays, disk drive chassis, transformers, switch parts, outlet parts, motor parts, sockets, plugs, capacitors, various cases, resistors, electrical and electronic parts incorporating metal terminals and conducting wires, computer-related parts, sound parts such as acoustic parts, lighting parts, telecommunications equipment-related parts, telephone equipment-related parts, air conditioner parts, home appliance parts such as VTRs and TVs, parts for copiers, parts for facsimiles, parts for optical equipment, automotive ignition device parts, automotive connectors, and various automotive electrical parts, etc.

Examples

[0075] Next, the manufacturing method of the polyester resin of the present invention and the polyester resin will be specifically described by way of examples.

[0076] [Measurement methods for each property] In each of the examples and comparative examples, the properties were evaluated by the measurement methods described below.

[0077] 1. Melting point of polyester resin Approximately 10 mg of the polyester resin was sampled and measured using a differential scanning calorimeter (DSC7 manufactured by PerkinElmer Co., Ltd.) under a nitrogen atmosphere. The polyester resin was heated to 280°C at a heating rate of 20°C / min to be in a molten state, then cooled to 30°C at a cooling rate of 20°C / min, and the temperature at the peak of the endothermic peak observed when heated at a heating rate of 20°C / min thereafter was taken as the melting point.

[0078] 2. Acid value of polyester resin Approximately 2 g of the polyester resin was dissolved in 50 mL of a chloroform / o-cresol (1 / 2, volume ratio) adjusting solution. After adding an appropriate amount of bromothymol blue / ethanol solution to this solution, it was titrated with a 0.02 N ethanol solution of potassium hydroxide and calculated from the following formula (unit: eq / t). AV=((V-V 0 )×C) / (W×10 -3 ) AV: Acid value [eq / t], V: Titration volume of the polyester resin solution [mL], V 0 : Titration volume of the chloroform / o-cresol (1 / 2, volume ratio) adjusting solution [mL], C: Concentration of the sodium hydroxide / ethanol solution [mol / L], W: Mass of the polyester resin [g].

[0079] 3. Intrinsic viscosity of the polyester resin The polyester resin was dissolved in o-chlorophenol to a concentration of 0.5% by mass. Then, using an Ubbelohde viscometer, the efflux time of the solution and the efflux time of the solvent were measured at a temperature of 25°C and calculated from the following formula. [η]=0.25×(t / t 0 -1+3×ln(t / t 0 )) / c [η]: Intrinsic viscosity [dL / g], t: Efflux time of the polyester resin solution [s], t 0 : Efflux time of o-chlorophenol [s], c: Solution concentration [g / cm 3 .

[0080] 4. Oligomer content of the polyester resin The polyester resin was dissolved in a hexafluoroisopropanol / chloroform solvent (1 / 1, volume ratio), and then the high molecular weight components were precipitated with an acetonitrile solvent. The filtrate obtained by filtering with a polytetrafluoroethylene disk filter (0.45 μm) was analyzed using a high performance liquid chromatograph (LC-10A manufactured by Shimadzu Corporation, column: Inertsil OSD-3V, column temperature: 45 °C, mobile phase: water / acetonitrile (1 / 4, volume ratio), flow rate 1.5 mL / min, detection wavelength: UV242 nm). Acetonitrile solutions of cyclic trimers with various concentrations were prepared, and a calibration curve was created with the above chromatograph to quantify the cyclic trimers contained in the polyester resin and obtain the oligomer content (unit: mass%).

[0081] 5. Unreacted alkylene glycol content in the polyester resin The polyester resin was dissolved in a hexafluoroisopropanol / chloroform solvent (1 / 1, volume ratio), and then the high molecular weight components were precipitated with an acetonitrile solvent. The filtrate obtained by filtering with a polytetrafluoroethylene disk filter (0.45 μm) was analyzed using a gas chromatograph (GC-2010 manufactured by Shimadzu Corporation, column: DB-5, column temperature: 80 - 300 °C, temperature increase rate: 6 °C / min, vaporization chamber temperature: 300 °C, mobile phase: helium, detector: FID). Acetonitrile solutions of alkylene glycol with various concentrations were prepared, and a calibration curve was created with the above chromatograph to quantify the alkylene glycol and obtain the alkylene glycol content (unit: mass%).

[0082] 6. Presence or absence of mold fouling Using an injection molding machine (NEX1000 manufactured by Nissei Plastic Industrial Co., Ltd.) for the polyester resin [C], when the polyester resin [C] is polybutylene terephthalate, under the conditions of a molding temperature of 280 °C, a mold temperature of 80 °C, and a cooling time of 10 seconds; when the polyester resin [C] is polyethylene terephthalate, under the conditions of a molding temperature of 280 °C, a mold temperature of 120 °C, and a cooling time of 10 seconds; when the polyester resin [C] is a polyester elastomer, under the conditions of a molding temperature of 280 °C, a mold temperature of 60 °C, and a cooling time of 10 seconds, a square plate with a width of 80 mm × a length of 80 mm × a thickness of 2 mm was molded. After continuously molding 10,000 square plates, the mold was visually observed. Those with no mold fouling due to the precipitation of oligomers were rated as A, those with a thin adhesion on a part of the mold were rated as B, those with a thin adhesion on the entire mold were rated as C, and those with the entire mold being white and turbid and white foreign matters being clearly visible in part were rated as D. A and B were judged to be excellent in suppressing mold fouling.

[0083] 7. Fluidity of Polyester Resin Using a mold for a strip-shaped molded product with a thickness of 1 mm and a width of 10 mm, it was judged by the flow length during injection molding. 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. When 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, and the injection speed is 100 mm / s. When 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, and 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.

[0084] 8. Mechanical Properties of Polyester Resin Using an injection molding machine (NEX1000 manufactured by Nissei Plastic Industrial Co., Ltd.), test pieces for evaluating the tensile properties of ISO-1A dumbbells with a test piece thickness of 4 mm were obtained. When the polyester resin [C] is polybutylene terephthalate, it was molded under the molding cycle conditions of a cylinder temperature of 250 °C, a mold temperature of 80 °C, an injection speed of 50 mm / s, an injection time and a holding pressure time combined of 10 seconds, and a cooling time of 10 seconds. When the polyester resin [C] is polyethylene terephthalate, it was molded under the molding cycle conditions of a cylinder temperature of 280 °C, a mold temperature of 80 °C, an injection speed of 50 mm / s, an injection time and a holding pressure time combined of 10 seconds, and a cooling time of 10 seconds. When the polyester resin [C] is a polyester elastomer, it was molded under the molding cycle conditions of a cylinder temperature of 250 °C, a mold temperature of 60 °C, an injection speed of 50 mm / s, an injection time and a holding pressure time combined of 10 seconds, and a cooling time of 10 seconds. Also, for the obtained test pieces for evaluating tensile properties, in accordance with ISO527-1,2 (2012), using a tensile testing machine (Autograph AG-50kNXPlus manufactured by Shimadzu Corporation), the maximum tensile point strength (tensile strength) was measured. The value was the average value of three measured values.

[0085] 9. Hydrolysis resistance of polyester resin Using an injection molding machine (NEX1000 manufactured by Nissei Plastic Industrial Co., Ltd.), under the same injection molding conditions as in item 8, test pieces for evaluating the tensile properties of ISO-1A dumbbells with a test piece thickness of 4 mm were obtained. The obtained ISO-1A dumbbells were put into an accelerated life test device for high temperature and humidity (EHS-411 manufactured by Espec Corporation) set at a temperature and humidity of 121 °C × 100% RH for 50 hours for hydrothermal treatment. The tensile strength of the molded product after hydrothermal treatment was measured under the same conditions as the tensile test in item 8, and the average value of three measured values was taken. The value expressed as a percentage of the tensile strength after hydrothermal treatment to the tensile strength before hydrothermal treatment according to the following formula was defined as the tensile strength retention rate. (Tensile strength after hydrothermal treatment / Tensile strength before hydrothermal treatment) × 100 = Tensile strength retention rate (%) Resins with a tensile strength retention rate of less than 70% were judged to be inferior in hydrolysis resistance, and materials with larger values of the tensile strength retention rate were judged to be excellent. It was judged that those with 80% or more were more excellent, those with 90% or more were even more excellent, and those with 99% or more were particularly excellent.

[0086] <Materials Used in Examples and Comparative Examples> (1) Polyester Resin [A] Virgin Polyester Resin [A-1] · PBT1 Polybutylene terephthalate, melting point 225 °C, manufactured by Toray Industries, Inc., acid value 20 eq / t, intrinsic viscosity 0.88 dL / g, weight average molecular weight 16,100 · 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, "Hytrel" (registered trademark) 5556 manufactured by Celanese, intrinsic viscosity 1.46 dL / g.

[0087] Recycled Polyester Resin [A-2] · PBT3 Off-specification pellet recovered product during the production of polybutylene terephthalate resin, melting point 223 °C, acid value 20 eq / t, intrinsic viscosity 1.08 dL / g, weight average molecular weight 19,100 · PBT4 Molding scrap recovered product during injection molding of a resin composition composed 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.

[0088] · PBT6 Molding scrap recovered product during injection molding of a resin composition composed 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.

[0089] (2) 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).

[0090] (3) Dicarboxylic acid · Terephthalic acid (manufactured by Mitsui Chemicals, Inc.).

[0091] (4) Transesterification catalyst · Tetra-n-butyl orthotitanate (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0092] (5) Masterbatch for black coloring · MB-9811 BLACK (polybutylene terephthalate, pigment concentration 20%, manufactured by Koshigaya Chemical Industry Co., Ltd.).

[0093] <Preparation of low-viscosity polyester resin [A] (PBT5, PET2)> · PBT5 (Comparative Examples 3, 4) To a slurry of 2000 g of terephthalic acid and 1627 g of 1,4-butanediol (molar ratio of terephthalic acid / 1,4-butanediol = 1 / 1.5), tetra-n-butyl titanate (mass ratio of terephthalic acid / tetra-n-butyl titanate = 1 / 0.0005) was added, and the transesterification reaction was started at a temperature of 190°C under a nitrogen stream. Then, the temperature was gradually raised, and finally the transesterification reaction was carried out for 3 hours under the condition of a temperature of 240°C. To the obtained reaction product, antimony trioxide (1.0×10 -4 mol with respect to 100 g of the polyester resin to be produced) was added, and the polymerization reaction was carried out at a temperature of 250°C and a pressure of 100 Pa for 2 hours. Then, it was extruded in a strand shape, passed through a cooling bath, and the take-up speed was adjusted by a strand cutter to granulate it into the pellet size shown in Table 3 to obtain pellets of polybutylene terephthalate prepolymer (PBT5, acid value 26 eq / t, intrinsic viscosity 0.58 dL / g). The obtained pellets were dried in a hot air dryer at a temperature of 110°C for 6 hours.

[0094] · PET2 (Comparative Examples 6, 7) Except for changing 1,4 - butanediol to ethylene glycol and changing the temperature of the polymerization reaction to 280 °C, pellets of a prepolymer of polyethylene terephthalate (PET2, acid value 20 eq / t, intrinsic viscosity 0.50 dL / g) were obtained in the same manner as the preparation of PBT5. The obtained pellets were dried in a hot air dryer at a temperature of 110 °C for 6 hours.

[0095] [Examples 1 - 20, Comparative Examples 1 - 14] Heat treatment [1] and heat treatment [2] were carried out on each polyester resin [A] corresponding to each example shown in Tables 1 - 3. For Comparative Examples 3, 4, 6, and 7, heat treatment [1] was not carried out, and heat treatment [2] was directly carried out on the polyester resin [A]. For Comparative Example 8, heat treatment [2] was not carried out, and the evaluation of each property was carried out as it was assuming that the polyester resin [B] was the polyester resin [C]. For Comparative Examples 9 and 11, heat treatments [1] and [2] were not carried out, and the evaluation of each property was carried out as it was assuming that the polyester resin [A] was the polyester resin [C].

[0096] <Heat treatment [1] in Examples 1 - 6, 9 - 20, Comparative Examples 5, 8, 13, 14> In Examples 1-6, 9-20, and Comparative Examples 5, 8, 13, and 14, heat treatment [1] was carried out using an extruder. Using a twin-screw extruder with a screw diameter of 30 mm and an L / D of 35 and a co-rotating vent (manufactured by Nippon Steel Works, TEX-30α), the polyester resin [A] and alkylene glycol were added from the feed section of the twin-screw extruder in the composition shown in Table 1. In Examples 1-6, 9-18 and Comparative Examples 5, 8, 13, the vent section was at atmospheric pressure, and in Examples 19, 20 and Comparative Example 14, heat treatment [1] was carried out with the vent section under reduced pressure. The alkylene glycol was supplied by a metering pump. Further, when the polyester resin [A] was polybutylene terephthalate, the kneading temperature was 250°C, the screw rotation speed was 200 rpm; when it was polyethylene terephthalate, the kneading temperature was 280°C, the screw rotation speed was 200 rpm; when it was a polyester elastomer, the kneading temperature was 250°C, and the screw rotation speed was 200 rpm. Melt kneading was carried out under these extrusion conditions, extruded in a strand shape, passed through a cooling bath, and the take-up speed was adjusted by a strand cutter to granulate to the pellet size described in Table 1 to obtain pellets of the polyester resin [B] (Table 1). The obtained pellets were dried in a hot air dryer at a temperature of 110°C for 6 hours.

[0097] Note that when preparing the polyester resin [B], 3 parts by mass of the masterbatch MB-9811 BLACK for black coloring was added to 100 parts by mass of the polyester resin [A] from the feed section of the extruder, and the measurement of time was started from the time of addition. After black color derived from the masterbatch for black coloring was confirmed in the resin discharged from the discharge port, the measurement of time was terminated when the black color was no longer confirmed, and the time taken from the start to the end of the measurement was defined as the heat treatment time in this example (Table 1). This operation was carried out after obtaining the amount of the polyester resin [B] required for the subsequent heat treatment [2] process, and the polyester resin obtained by adding the masterbatch for black coloring was not used in the subsequent process.

[0098] In Comparative Example 5, the melt viscosity of the polyester resin [B] after heat treatment [1] was low, and it was difficult to discharge it in a strand shape, so the subsequent operations could not be carried out.

[0099] <Heat treatment [1] in Comparative Examples 1, 2, 10, and 12> In Comparative Examples 1, 2, 10, and 12, no alkylene glycol was added, and only the polyester resin [A] was passed through the extruder. Otherwise, heat treatment [1] was carried out in the same manner as in Examples 1 - 6 and Comparative Example 5.

[0100] <Heat treatment [1] in Example 7> In Example 7, heat treatment [1] was carried out in a polymerization tank. 1000 g of PBT1 was dropped into a 5 L polymerization tank equipped with a stirring blade, the temperature was raised to 250 °C under a nitrogen stream, and it was 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, it was discharged in a strand shape from the discharge port, passed through a cooling bath, and granulated by adjusting the take - up speed with a strand cutter to obtain pellets of polyester resin [B] with the pellet size shown in Table 1 (Table 1). The obtained pellets were dried in a hot air dryer at a temperature of 110 °C for 6 hours.

[0101] Note that the time from adding alkylene glycol to the polyester resin [A] until the start of discharge is t 1 , and the time from adding alkylene glycol to the polyester resin [A] until the end of discharge is t 2 . The heat treatment time t was calculated by the following formula. t=(t 1 + t 2 ) / 2 …(formula).

[0102] <Heat treatment [1] in Example 8> In Example 8, heat treatment [1] was carried out in a polymerization tank. 1000 g of PBT1 was dropped into a 5 L polymerization tank equipped with a stirring blade, and the temperature was raised to 250 °C under a nitrogen fluidized state 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, it was discharged in a strand form from the discharge port, passed through a cooling bath, and the take-up speed was adjusted by a strand cutter to granulate it into the pellet size shown in Table 1 to obtain pellets of polyester resin [B] (Table 1). The obtained pellets were dried in a hot air dryer at a temperature of 110 °C for 6 hours.

[0103] Note that the heat treatment time was calculated in the same manner as in the heat treatment [1] of Example 7.

[0104] <Heat treatment [2]> The pellets of the polyester resin obtained in the previous step were heat-treated [2] under the conditions of a temperature of 230 °C and a pressure of 100 Pa when the used polyester resin [A] was polyethylene terephthalate, a temperature of 170 - 210 °C and a pressure of 100 Pa when it was polybutylene terephthalate, and a temperature of 180 °C and a pressure of 100 Pa when it was a polyester elastomer to obtain polyester resin [C] (Table 1). Note that Comparative Example 13 carried out heat treatment [2] at 240 °C, which exceeded the melting point of polyester resin [B].

[0105] In Examples 1 - 20 where 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 it was excellent in suppressing mold fouling. On the other hand, in Comparative Examples 1, 2, 10, 12, and 14 where 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 it was inferior in suppressing mold fouling.

[0106] In Comparative Examples 1, 2, 10, and 12 where heat treatment [2] was carried out after heat treatment [1] without adding alkylene glycol, the effect of reducing the oligomer content by unreacted alkylene glycol was not obtained, so it was impossible to achieve both reduction of the oligomer content and fluidity.

[0107] In Comparative Example 5 where 6 parts by mass of alkylene glycol was added, the melt viscosity of the polyester resin [B] after heat treatment [1] became too low, and it was impossible to discharge it in a strand shape, making it difficult to recover in a uniform shape and resulting in extremely poor granulation properties.

[0108] In Comparative Examples 3, 4, 6, and 7 where heat treatment [2] was carried out directly on the polyester resin [A] with a low intrinsic viscosity without carrying out heat treatment [1], when the implementation time of heat treatment [2] was short, it was inferior in suppressing mold fouling, and when the implementation time of heat treatment [2] was long, it was inferior in fluidity.

[0109] In Comparative Example 8 where each property was evaluated without carrying out heat treatment [2], there was more mold fouling compared to Example 3 where heat treatment [2] was carried out, and it was also inferior in hydrolysis resistance.

[0110] In Comparative Example 13 where heat treatment [2] was carried out at a temperature exceeding the melting point of the polyester resin [B], the oligomer content was not reduced by heat treatment [2], and it was inferior in suppressing mold fouling.

[0111] In Examples 5, 6, and 17 using recycled polyester resin, the oligomer content was low, the fluidity was excellent, and the acid value could also be significantly reduced compared to the time of recovery. It was also comparable to Examples 1 - 4, 7 - 16, and 18 - 20 using virgin polyester resin. By applying the present invention to recycled polyester resin, it was found that waste reduction was possible, less alkylene glycol and thermal energy required for recycling were needed, and carbon dioxide emissions could be reduced.

[0112] On the other hand, Comparative Examples 10 and 12, in which heat treatment [1] was carried out without adding alkylene glycol to the recycled polyester resin, and Comparative Examples 9 and 11, in which each property was evaluated as it was without carrying out heat treatments [1] and [2] on the recycled polyester resin, were inferior in mold stain suppression.

[0113] In Examples 1-3, 5, and 6 where heat treatment [1] was carried out using an extruder, compared with Examples 7 and 8 where a polymerization tank was used for heat treatment [1], since the heat treatment could be carried out in a short time, less alkylene glycol was consumed in volatilization and transesterification reactions, and the unreacted alkylene glycol content of polyester resin [B] was at a high value. Therefore, Examples 1-3, 5, and 6 had a greater effect of reducing the oligomer content and were superior in mold stain suppression.

[0114] Comparing Example 7 and Example 8 where heat treatment [1] was carried out in a polymerization tank, Example 7 with a shorter heat treatment time after adding alkylene glycol had less volatilization of alkylene glycol and transesterification reaction with polyester, the alkylene glycol content of polyester resin [B] was high, and the oligomer content of polyester resin [C] was at a low value.

[0115] In Examples 1-3, 5, and 6 where polyester resin [A] was polybutylene terephthalate and 1,4-butanediol was used as the alkylene glycol and passed through an extruder, compared with Example 4 where polyester resin [A] was polyethylene terephthalate and ethylene glycol was used as the alkylene glycol, since the melting point of the polyester resin was low and the boiling point of the alkylene glycol was high, less alkylene glycol was consumed in volatilization and transesterification reactions during the implementation of heat treatment [1] in the extruder, and the unreacted alkylene glycol content of polyester resin [B] was at a high value. Therefore, Examples 1-3, 5, and 6 had a greater effect of reducing the oligomer content and were superior in mold stain suppression.

[0116] Examples 9 and 10, which have smaller pellet sizes (diameters) compared to Example 1, showed a large increase in intrinsic viscosity due to heat treatment [2]. In particular, Example 10 with a pellet diameter of less than 1.00 mm was remarkable and the treatment was completed in a short time. Therefore, compared with Example 10 which completed the treatment in a short time, Example 1 had a greater effect of reducing the oligomer content and was superior in suppressing mold fouling.

[0117] Compared with Examples 11 and 12 which have larger pellet sizes (diameters), Example 1 had a shorter distance from the center to the surface of the pellet, and oligomers inside the pellet could be more efficiently reduced during heat treatment [2]. In particular, this tendency was remarkable compared with Example 12 with a pellet diameter exceeding 5.00 mm. Therefore, Example 1 was superior in suppressing mold fouling compared with Example 12.

[0118] In Example 13 where heat treatment [2] was carried out at a lower temperature compared to Example 1, the increase in intrinsic viscosity during heat treatment [2] tended to be small.

[0119] In Example 14 where heat treatment [2] was carried out at a higher temperature compared to Example 1, the increase in intrinsic viscosity during heat treatment [2] tended to be large and the treatment was completed in a short time. Therefore, compared with Example 14 which completed the treatment in a short time, Example 1 had a greater effect of reducing the oligomer content and was superior in suppressing mold fouling.

[0120] In Example 15 where heat treatment [2] was completed in a shorter time compared to Example 1, the intrinsic viscosity tended to be low and the oligomer content tended to be high.

[0121] In Example 16 where heat treatment [2] was carried out for a longer time compared to Example 1, the intrinsic viscosity tended to be high and the oligomer content tended to be low.

[0122] Examples 1 - 3, 5, and 6 where the polyester resin [A] was polybutylene terephthalate were superior in suppressing mold fouling because cyclic oligomers were more efficiently reduced compared to Example 18 where the polyester resin [A] was a polyester elastomer.

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Table 1

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Table 2

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Table 3

Claims

1. 0.1 to 5.0 parts by mass of an alkylene glycol is added to 100 parts by mass of the polyester resin [A], and the polyester resin [A] is heated at a temperature exceeding the melting point T ｍＡ (°C) to obtain the polyester resin [B] in the heat treatment [1] step, and heating the obtained polyester resin [B] at a temperature of T ｍＢ (°C) or lower with respect to the melting point T ｍＢ (°C) of the polyester resin [B] in a heat treatment [2] step The polyester resin [B] contains 0.05% by mass or more and 4.76% by mass or less of unreacted alkylene glycol whose boiling point is in the range of (Tm A - 90) °C or higher and (Tm A + 20) °C or lower with respect to the melting point Tm A (°C) of the polyester resin [A]. A method for producing a polyester resin.

2. The method for producing a polyester resin according to claim 1, wherein the polyester resin [A] is a recycled polyester resin.

3. The method for producing a polyester resin according to claim 1 or 2, wherein the heat treatment [1] step is carried out using an extruder.

4. The method for producing a polyester resin according to claim 1 or 2, wherein the polyester resin [A] contains at least polybutylene terephthalate.

5. The method for producing a polyester resin according to claim 4, wherein the alkylene glycol is 1,4 - butanediol.

6. Polybutylene terephthalate containing recycled polyester resin as a raw material, having a cyclic trimer content of less than 0.20% by mass and an intrinsic viscosity of 0.70 dL / g or more and 1.00 dL / g or less.

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