Method for producing polyester resin, and polyester resin

Abstract

The present invention addresses the problem of providing a method for producing a polyester resin having good fluidity, little mold contamination, good mechanical characteristics, and excellent moldability, productivity, and quality. The present invention is a method for producing a polyester resin, the method comprising: a heat treatment [1] step for adding 0.1-5.0 parts by mass of an alkylene glycol to 100 parts by mass of a polyester resin [A] and heating the polyester resin [A] at a temperature exceeding the melting point TmA (DEG C) of the polyester resin [A] to obtain a polyester resin [B]; and a heat treatment [2] step for heating the obtained polyester resin [B] at a temperature equal to or lower than the melting point TmB (DEG C) of the polyester resin [B], the polyester resin [B] containing 0.05-4.76 mass% of an unreacted alkylene glycol.

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 molding processability, and are therefore widely used in various containers, films, electrical and electronic equipment parts, automotive parts, mechanical parts, etc. As specific examples of electrical and electronic equipment parts and automotive parts, they are used as industrial molded products such as connectors, relays, and switches.

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

[0004] In particular, when a polyester resin contains cyclic oligomers mainly composed of cyclic trimers, they exude on the surface of the molded product during molding and adhere to the surface of the mold, thereby causing mold contamination. Such mold contamination causes the surface of the obtained molded product to be rough and whitened, resulting in defective products (non-conforming products). In addition, in order to frequently remove mold contamination, production must be stopped, and there is a problem of reduced productivity. Therefore, a polyester resin with a low oligomer content is required.

[0005] In addition, in recent years, as the transition to a decarbonized society progresses further, the demand for recycling of polyester resins has also been increasing. It is also required to reduce waste by regenerating recycled polyester resins recovered from defective products in the production process and post-consumer waste products into polyester resin products.

[0006] As a method for obtaining a polyester resin with a low oligomer content, a method for producing a high-degree-of-polymerization polybutylene terephthalate resin (Patent Document 1) has been disclosed, which is characterized in that a dicarboxylic acid having terephthalic acid as a main component and / or its alkyl ester derivative and a diol having 1,4-butanediol as a main component are subjected to an esterification reaction or a transesterification reaction, and then melt polymerization is carried out to obtain a low-degree-of-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 is carried out; a method for producing a polyester resin, which is characterized in that in a method for producing a polyester resin having terephthalic acid and ethylene glycol as main components, a prepolymer having a specific limiting viscosity, antimony element concentration, phosphorus element concentration, carboxyl terminal group amount, and hydroxyl terminal group amount is subjected to solid-phase polymerization (Patent Document 2).

[0007] In addition, as a method for recycling polyester resin, the following production method is disclosed (Patent Document 3), which includes: depolymerizing the polyester resin by pressurizing the polyester resin and an alkylene glycol at a temperature above the melting point of the aforementioned polyester resin; and a step of polymerizing the depolymerized product.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2014-181245

[0011] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2002-20473

[0012] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2005-97521 Summary of the Invention

[0013] Problems to be Solved by the Invention

[0014] However, regarding 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. As a result, there is a problem that the fluidity of the resin decreases.

[0015] In addition, regarding the invention disclosed in Patent Document 2, when solid-phase polymerization is carried out in a short time so as not to reduce the fluidity, the reduction of the oligomer content is insufficient, and there is a problem that it is difficult to simultaneously achieve the reduction of the oligomer content and good fluidization.

[0016] In addition, regarding the invention disclosed in Patent Document 3, in order to regenerate the polyester resin, a large amount of alkylene glycol derived from petroleum needs to be added. Since the carbon dioxide emissions from the raw materials and the energy required for heating increase, there is a problem of low efficiency. In addition, the obtained recycled polyester resin has problems such as an increase in acid value and a decrease in hydrolysis resistance due to thermal decomposition during high-temperature melt polymerization.

[0017] 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 also to provide a method for producing a recycled polyester resin that efficiently regenerates a recycled polyester resin and improves its quality.

[0018] Means for Solving the Problems

[0019] To solve the above problems, the present invention provides the following means.

[0020] 1. A method for producing a polyester resin, which includes:

[0021] Heating treatment [1] step: 0.1 to 5.0 parts by mass of an alkylene glycol is added to 100 parts by mass of a polyester resin [A], and heating is performed at a temperature exceeding the melting point T mA (°C) of the polyester resin [A] to obtain a polyester resin [B];

[0022] And heating treatment [2] step: with respect to the melting point T mB (°C) of the polyester resin [B], the obtained polyester resin [B] is heated at a temperature of T mB (°C) or lower,

[0023] The polyester resin [B] contains 0.05% by mass or more and 4.76% by mass or less of unreacted alkylene glycol.

[0024] 2. The method for producing a polyester resin according to item 1, wherein the polyester resin [A] is a recycled polyester resin.

[0025] 3. The method for producing a polyester resin according to item 1 or item 2, wherein the heating treatment [1] step is carried out using an extruder.

[0026] 4. The method for producing a polyester resin according to any one of items 1 to 3, wherein the polyester resin [A] at least contains polybutylene terephthalate.

[0027] 5. The method for producing a polyester resin according to item 4, wherein the alkylene glycol is 1,4-butanediol.

[0028] 6. A polyester resin, the oligomer content of which is less than 0.30% by mass and the intrinsic viscosity of which is 0.70 dL / g or more and 1.00 dL / g or less.

[0029] 7. The polyester resin according to item 6, wherein the polyester resin is polybutylene terephthalate.

[0030] Effects of the invention

[0031] By the present invention, it is possible to provide a polyester resin having good fluidity, suppressing resin decomposition during molding, having less molding defects, less mold contamination caused by oligomers during molding, excellent moldability and productivity, and a method for producing the same. In addition, this production method can be applied not only to the production of virgin resins but also to the production of recycled polyester resins obtained by recycling recycled polyester resins, and can provide recycled polyester resins that are low-cost compared to chemical recycling and of high quality compared to material recycling. Detailed implementation manners

[0032] The method for manufacturing the polyester resin of the present invention includes: a heat treatment [1] step of adding an alkylene glycol to the 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 below the melting point of the polyester resin [B].

[0033] In the heat treatment [1] step, by adding a specified amount of alkylene glycol to the polyester resin [A] and performing the heat treatment [1], the alkylene glycol reacts with the polyester resin [A], increasing the hydroxyl group content while reducing the viscosity of the polyester resin [A], and further enabling the inclusion of a part of the unreacted alkylene glycol. 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, the oligomer content can be efficiently reduced, and a polyester resin with excellent fluidity can be obtained. In addition, only a small amount of the alkylene glycol used in the present invention is required. Furthermore, by heating at a temperature exceeding the melting point of the polyester resin [A], the polyester resin [A] can be rapidly made to contain the alkylene glycol in a short time. Thereby, the amount of alkylene glycol required and the energy consumption in the process can be reduced, and the carbon dioxide emissions can be cut.

[0034] In addition, in the case of a general recycling method, there is a tendency for the oligomer content and acid value of the obtained polyester resin to increase and the intrinsic viscosity to be uneven due to the heat history in the recycling process. In contrast, by applying the recycled polyester resin as the polyester resin [A] and performing the method for manufacturing the polyester resin of the present invention, a recycled polyester resin with a low oligomer content, a low acid value, and little unevenness in intrinsic viscosity can be provided.

[0035] Each component in the manufacturing method of the present invention will be described in detail.

[0036] [Polyester resin [A]]

[0037] 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 that among all the structural units, at least one residue selected from the group consisting of (1) to (3) has 50 mol% or more, and it is preferable that these residues have 80 mol% or more. Among these, from the aspect of more excellent mechanical properties and heat resistance, a polymer or copolymer having a residue of (1) a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative as a main structural unit is preferable.

[0038] Examples of the dicarboxylic acid or its ester-forming derivative described above 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'-diphenylether dicarboxylic acid, isophthalic acid 5-tetrabutylphosphonium, sodium 5-sulfoisophthalate; 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 their ester-forming derivatives. Two or more of them can be used.

[0039] Examples of the diol or its ester-forming derivative described above include aliphatic or alicyclic diols having 2 to 20 carbon atoms such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, cyclohexanedimethanol, cyclohexanediol, dimer diol; long-chain diols having a molecular weight of 200 to 100,000 such as polyethylene glycol, poly-1,3-propylene glycol, poly-1,4-butanediol; aromatic dioxy compounds such as 4,4'-dihydroxybiphenyl, hydroquinone, tert-butylhydroquinone, bisphenol A, bisphenol S, bisphenol F and their ester-forming derivatives. Two or more of them can be used.

[0040] As polymers or copolymers having dicarboxylic acids or their ester-forming derivatives and diols or their ester-forming derivatives as structural units, for example, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polytrimethylene isophthalate, polybutylene isophthalate, polybutylene naphthalate, polypropylene glycol isophthalate / terephthalate, polybutylene glycol isophthalate / terephthalate, polypropylene glycol terephthalate / naphthalate, polybutylene glycol terephthalate / naphthalate, polybutylene glycol terephthalate / decane dicarboxylate, polytrimethylene terephthalate / 5-sodium sulfoisophthalate, polybutylene terephthalate / 5-sodium sulfoisophthalate, polytrimethylene terephthalate / polyethylene glycol, polybutylene terephthalate / polyethylene glycol, polytrimethylene terephthalate / poly-1,4-butylene glycol, polybutylene terephthalate / poly-1,4-butylene glycol, polypropylene glycol terephthalate / isophthalate / poly-1,4-butylene glycol, polybutylene glycol terephthalate / isophthalate / poly-1,4-butylene glycol, polybutylene glycol terephthalate / succinate, polypropylene glycol terephthalate / adipate, polybutylene glycol terephthalate / adipate, polypropylene glycol terephthalate / sebacate, polybutylene glycol terephthalate / sebacate, polypropylene glycol terephthalate / isophthalate / adipate, polybutylene glycol terephthalate / isophthalate / succinate, polybutylene glycol terephthalate / isophthalate / adipate, polybutylene glycol terephthalate / isophthalate / sebacate and other aromatic polyester resins can be mentioned. These polymers and copolymers can be used alone or in combination of two or more. Here, " / " represents a copolymer containing the polymer components before and after.

[0041] Among these, from the viewpoint of further improving mechanical properties and heat resistance, polymers or copolymers having residues of aromatic dicarboxylic acids or their ester-forming derivatives and residues of aliphatic diols or their ester-forming derivatives as main structural units are more preferable, and polymers or copolymers having residues of terephthalic acid, naphthalic acid or their ester-forming derivatives and residues of aliphatic diols or their ester-forming derivatives selected from propylene glycol and 1,4-butylene glycol as main structural units are further preferable.

[0042] Among them, it is particularly preferably at least one aromatic polyester resin selected from polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polypropylene naphthalate, polybutylene naphthalate, polypropylene glycol isophthalate / terephthalate, polybutylene glycol isophthalate / terephthalate, polypropylene glycol terephthalate / naphthalate, polybutylene glycol adipate / terephthalate, polybutylene glycol terephthalate / sebacate, polybutylene glycol terephthalate / naphthalate, etc., and more preferably at least one selected from polyethylene terephthalate, polybutylene terephthalate, polybutylene glycol isophthalate / terephthalate, polybutylene glycol decanedicarboxylate / terephthalate, polybutylene glycol terephthalate / naphthalate, polybutylene glycol / ethylene glycol terephthalate. In addition, two or more of them can be used in any content. From the aspect of excellent balance between mechanical properties and moldability, polybutylene terephthalate is further preferred.

[0043] From the viewpoints of suppressing the reduction of the mechanical properties of the polyester resin obtained by the present invention and moldability, 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, further preferably 30 eq / t or less, and particularly preferably 20 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 polyester resin [A] dissolved in an o-cresol / chloroform solvent with ethanolic potassium hydroxide.

[0044] Regarding the polyester resin [A] that can be used in the present invention, from the aspect of the ease of granulation of the obtained polyester resin [B], the intrinsic viscosity when measuring its o-chlorophenol solution at 25 °C is preferably 0.30 dL / g or more, more preferably 0.36 dL / g or more. If the polyester resin [B] is granulated, the subsequent heat treatment [2] can be appropriately carried out. In addition, from the aspect of being able to improve fluidity, it is preferably 2.00 dL / g or less, more preferably 1.60 dL / g or less.

[0045] From the aspect of the ease of granulation of the obtained polyester resin [B], the weight average molecular weight of the polyester resin [A] that can be used in the present invention is preferably 9000 or more, more preferably 10000 or more. If the polyester resin [B] is granulated, the subsequent heat treatment [2] can be appropriately carried out. In addition, from the aspect of being able to improve fluidity, it is preferably 40000 or less, more preferably 30000 or less. The weight average molecular weight referred to here is a value calculated by gel permeation chromatography (solvent: hexafluoroisopropanol, standard sample: polymethyl methacrylate).

[0046] As the shape of the polyester resin [A], flakes, powders, pellets, etc. are preferably selected. From the viewpoint of efficiently performing the subsequent heat treatment [1], it is preferable that the particle size is also reduced to a certain extent in advance. 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.

[0047] 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 defective products in the manufacturing process, a post-consumer recycled product obtained by recycling resin products using commercially available polyester resins, etc., a recycled polyester resin [A-2]. One of them can be used, or both can be used in any proportion.

[0048] In the case of using the recycled polyester resin [A-2] in the manufacturing method of the present invention, a high-quality polyester resin can be obtained from a recycled polyester resin of low quality, the uses for which the recycled polyester resin can be used are broadened, and waste and carbon dioxide emissions can be reduced. Therefore, it is preferable to use the recycled polyester resin [A-2].

[0049] [Virgin polyester resin [A-1]]

[0050] The virgin polyester resin [A-1] used in the present invention can be produced by known polycondensation methods, ring-opening polymerization methods, etc. The production method can be either batch polymerization or continuous polymerization, and either transesterification reaction or reaction based on direct polymerization can be applied. From the viewpoint of productivity, continuous polymerization is preferred, and direct polymerization is more preferably used.

[0051] 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, it can be produced by subjecting the dicarboxylic acid or its ester-forming derivative and the diol or its ester-forming derivative to an esterification reaction or a transesterification reaction, and then performing a polycondensation reaction.

[0052] In order to effectively carry out esterification reaction, transesterification reaction and polycondensation reaction, it is preferred to add a polymerization catalyst during these reactions. Specific examples of the polymerization catalyst include organic titanium compounds such as methyl esters, tetra-n-propyl esters, tetra-n-butyl esters, tetra-isopropyl esters, tetra-isobutyl esters, tetra-tert-butyl esters, cyclohexyl esters, phenyl esters, benzyl esters, tolyl esters or their mixed esters of titanic acid, dibutyltin oxide, methylphenyltin oxide, tetraethyltin, hexaethylditin oxide, cyclohexylhexaditin oxide, bis(dodecyl)tin oxide, triethyltin hydroxide, triphenyltin hydroxide, triisobutyltin acetate, dibutyltin diacetate, diphenyltin dilaurate, monobutyltin trichloride, dibutyltin dichloride, tributyltin chloride, dibutyltin sulfide, butylhydroxytin oxide, methyltin acid, ethyltin acid, butyltin acid and other alkyltin acids and other tin compounds, zirconium oxide compounds such as tetra-n-butyl zirconium, antimony compounds such as antimony trioxide and antimony acetate, etc. Two or more of them can be used.

[0053] Among these polymerization catalysts, organic titanium compounds and tin compounds are preferred, and tetra-n-butyl ester of titanic acid is further preferably used. Relative to 100 parts by mass of the virgin polyester resin [A-1], the addition amount of the polymerization catalyst is preferably in the range of 0.01 part by mass or more and 0.2 part by mass or less.

[0054] The polyester resin after polycondensation is taken out from the reaction vessel and cooled to form a solid state. Usually, granulation is carried out by the following methods to obtain pellets: a method of taking out in a wire bundle shape, forming a solidified or semi-solid state in cooling water, and then cutting it with a wire bundle cutting machine; a method of extruding into water while cutting with a cutting machine in water, etc.

[0055] In addition, the virgin polyester resin [A-1] may contain additives such as inorganic particles, fluorescent brighteners, ultraviolet light absorbers, infrared absorbers, heat stabilizers, antioxidants, etc.

[0056] [Recycled polyester resin [A-2]]

[0057] The recycled polyester resin [A-2] used in the present invention is a pre-consumer recycled product obtained from defective products in the manufacturing process, a post-consumer recycled product obtained by recycling resin products using polyester resin in the market. It can reduce waste and carbon dioxide emissions, and obtain a high-quality polyester resin, so it can be suitably used when implementing the manufacturing method of the polyester resin of the present invention.

[0058] Examples of the recycled polyester resin [A-2] include: defective pellets generated during the manufacture of polyester resin or polyester resin composition containing polyester resin; pre-consumer products such as defective products and scraps during the manufacture of resin products such as bottles, films, fibers, injection molded products, etc.; and post-consumer products obtained by recycling products containing polyester resin from the market.

[0059] The recycled polyester resin [A-2] may contain components other than the polyester resin within a range that does not affect the properties of the produced polyester resin. Examples of components other than the 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 the polyester resin.

[0060] [Alkylene glycol]

[0061] The alkylene glycol used in the present invention may be the glycol component exemplified in the above item [Polyester resin [A]]. From the viewpoint of mechanical properties, it is preferably the glycol component constituting the polyester resin [A]. When the polyester resin [A] is polyethylene terephthalate resin, it is preferably ethylene glycol. When the polyester resin [A] is polybutylene terephthalate resin, it is preferably 1,4-butanediol. Considering the balance between mechanical properties and moldability, a combination of polybutylene terephthalate and 1,4-butanediol is further preferred.

[0062] In addition, with respect to the melting point T mA (°C) of the polyester resin [A], the boiling point of the alkylene glycol used in the present invention is preferably in the range of (T mA - 90) °C or higher and (T mA + 20) °C or lower. If the boiling point of the alkylene glycol is (T mA - 90) °C or higher, more preferably (T mA - 60) °C or higher, and further preferably (T mA - 30) °C or higher, then in the heat treatment [1] process, the volatilization of the alkylene glycol can be suppressed less and added to the polyester resin [A] efficiently, and the content of unreacted alkylene glycol in the polyester resin [B] described later can be increased (the details are described later), so it is preferred. In addition, if the boiling point of the alkylene glycol is (T mA + 20) °C or lower, more preferably (T mA + 10) °C or lower, and further preferably T mA (°C) or lower, then in the subsequent heat treatment [2] process, unreacted alkylene glycol and the like are easily volatilized, and the effect of reducing the oligomer content due to volatilization can be obtained, so it is preferred.

[0063] With respect to 100 parts by mass of the polyester resin [A], the addition amount of the alkylene glycol in the present invention is 0.1 to 5.0 parts by mass. When the addition amount of the alkylene glycol is less than 0.1 part by mass, the effects of the decrease in acid value and the decrease in the oligomer content rate brought about by the subsequent heat treatment [2] cannot be exerted. From the viewpoint of reducing the oligomer content rate, 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. In addition, if the addition amount of the alkylene glycol exceeds 5.0 parts by mass, the melt viscosity of the polyester resin [B] is excessively reduced, it is 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 granulation ease of 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.

[0064] [Polyester resin [B]]

[0065] The polyester resin [B] is an intermediate obtained by subjecting the polyester resin [A] to the heat treatment [1] described below.

[0066] 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 a substance that remains in an unreacted state 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 rate decreases during the subsequent heat treatment [2], and mold contamination is suppressed. The upper limit of the content rate of the unreacted alkylene glycol contained in the polyester resin [B] is the same as the upper limit of the alkylene glycol component added in the heat treatment [1], which is 5.0 parts by mass with respect to 100 parts by mass of the polyester resin [B] and 4.76% by mass with respect to 100% by mass of the polyester resin [B]. From the viewpoint of granulation ease, the content rate of the unreacted alkylene glycol is preferably 2.91% by mass or less, more preferably 1.96% by mass or less.

[0067] Regarding the content rate of the unreacted alkylene glycol, after dissolving the polyester resin [B] in a hexafluoroisopropanol / chloroform solvent, acetonitrile is added to precipitate insoluble components, and filtration is carried out using a polytetrafluoroethylene disk filter (0.45 μm). For the filtrate thus obtained, gas chromatography is used for quantification.

[0068] In addition, the polyester resin [B] may contain additives contained in the polyester resin [A].

[0069] Regarding the polyester resin [B] in the present invention, the intrinsic viscosity when measuring its o-chlorophenol solution at 25 °C is preferably 0.30 dL / g or more and less than 0.70 dL / g. 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, in the subsequent heat treatment [2] process, the amount of powdery high-melting polyester resin will not increase, and white foreign matters are not likely to be generated in the molded product, so it is preferred. In addition, if it is less than 0.70 dL / g, the oligomer content rate can be sufficiently reduced within the range where the intrinsic viscosity does not become too high in the heat treatment [2] process, so it is preferred.

[0070] The weight-average molecular weight of the polyester resin [B] in the present invention is preferably 7000 or more and less than 15000. If the weight-average molecular weight is 7000 or more, more preferably 9000 or more, in the subsequent heat treatment [2] process, the increase in the amount of powdery high-melting polyester resin is suppressed, and white foreign matters are not likely to be generated in the molded product, so it is preferred. In addition, if it is less than 15000, more preferably less than 11000, the oligomer content rate can be sufficiently reduced within the range where the intrinsic viscosity does not become too high in the heat treatment [2] process, so it is preferred. The weight-average molecular weight referred to here is a value calculated by gel permeation chromatography (solvent: hexafluoroisopropanol, standard sample: polymethyl methacrylate).

[0071] Regarding the polyester resin [B] in the present invention, from the viewpoint of reducing the oligomer content rate, the hydroxyl concentration is preferably 50 eq / t or more. More preferably, it is 60 eq / t or more, and further preferably 80 eq / t or more. If the hydroxyl concentration is 50 eq / t or more, a sufficient oligomer content rate reduction effect can be obtained, so it is preferred. The upper limit of the hydroxyl concentration is not particularly limited. In the case of manufacturing and granulating the polyester resin [B], it is preferably 350 eq / t or less, and a sufficient oligomer content rate reduction effect is also exhibited. The hydroxyl concentration is calculated by dissolving the polyester resin [B] in deuterated hexafluoroisopropanol and performing 1 1H-NMR measurement.

[0072] From the viewpoint of suppressing the decrease in the mechanical properties and moldability of the polyester resin produced by the method of the present invention, 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, further preferably 30 eq / t or less, and particularly preferably 20 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 polyester resin [B] dissolved in an o-cresol / chloroform solvent with alcoholic potassium hydroxide.

[0073] [Heat treatment [1] process]

[0074] The method for obtaining the polyester resin [B] by heat-treating the polyester resin [A] of the present invention will be described in detail below.

[0075] In the heating process [1], the polyester resin [A] is heated to a temperature exceeding the melting point T mA The polyester resin [A] is melted at a temperature of (°C), and 0.1 to 5.0 parts by mass of alkylene glycol is added to 100 parts by mass of the obtained polyester resin [A], and shearing is provided 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 "uni-melt" or "dulmage" type screw, a twin screw extruder, a triple screw extruder, a conical extruder, and a kneading machine type mixer, but is not limited thereto. An extruder is more preferred 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.

[0076] In the heat treatment [1] step, the alkylene glycol may be added immediately after the polyester resin [A] is heated or after the polyester resin [A] is melted.

[0077] The upper limit of the temperature of the heat treatment [1] is relative to the melting point T of the polyester resin [A]. mA (℃) is preferably (T mA +40)℃ or less. By making the temperature of the heating treatment [1] exceed T mA (℃) and (T mA +40)°C or less, so that the minimum amount of heat for melting the resin can be provided without deteriorating the properties of the resin.

[0078] 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, the polyester resin [A] can be uniformly contained in the alkylene glycol, which is preferred. If the implementation time is 20 minutes or less, more preferably 10 minutes or less, and even more preferably 5 minutes or less, the unreacted alkylene glycol content of the obtained polyester resin [B] will not be too low, which is preferred. It should be noted that the implementation time of the heat treatment [1] referred to herein refers to the time spent from the addition of the alkylene glycol to the polyester resin [A] until the implementation of the heat treatment [1] is completed.

[0079] When the heat treatment [1] is carried out using an extruder, the alkylene glycol can be added by: providing a liquid adding nozzle midway between the main feed section and the discharge section of the extruder and adding it together with the polyester resin [A] using a plunger pump; or by supplying it from the main feed section using a metering pump.

[0080] In addition, an exhaust section can be provided in the extruder. From the perspective of improving the quality of the pellets, the heating treatment can be carried out by reducing the pressure in the exhaust section to below atmospheric pressure [1]. On the other hand, when the exhaust section is provided on the downstream side of the addition position of the alkylene glycol, the reduction of the pressure in the exhaust section reduces the content rate of the unreacted alkylene glycol. In this case, from the perspective of increasing the content rate of the unreacted alkylene glycol, when the addition amount of the alkylene glycol is 1.5 mass parts or less, it is preferable to carry out the heating treatment with the pressure at the exhaust section being 5000 Pa or more and below atmospheric pressure [1]. When the addition amount of the alkylene glycol exceeds 1.5 mass parts and is 3.0 mass parts or less, it is preferable to carry out the heating treatment with the pressure at the exhaust section being 100 Pa or more and below atmospheric pressure [1]. When the addition amount of the alkylene glycol exceeds 3.0 mass parts, from the perspective of suppressing vent up, it is preferable to carry out the heating treatment with the pressure at the exhaust section being atmospheric pressure [1].

[0081] When carrying out the heating treatment [1] using a polymerization tank equipped with stirring blades, etc. [1], in order to melt the polyester resin [A], the heating time is preferably 5 minutes or more and 90 minutes or less. When it is 5 minutes or more, the polyester resin [A] can be sufficiently melted, so it is preferable. If it is 90 minutes or less, more preferably 60 minutes or less, and further preferably 30 minutes or less, the increase in the acid value due to the thermal decomposition of the obtained polyester resin [B] is small, so it is preferable. In addition, from the aspect that the content rate of the unreacted alkylene glycol contained in the obtained polyester resin [B] becomes high, it is preferable to add it after the polyester resin [A] is melted.

[0082] In order to appropriately carry out the subsequent heating treatment [2], the obtained polyester resin [B] is preferably pelletized. The polyester resin [B] is preferably extruded in a wire harness shape and then cut, or cut while being extruded in water, to produce 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, but the pelletizing 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, during the heating treatment [2], the intrinsic viscosity will not increase excessively in a short time, and the heating treatment [2] can be carried out in an appropriate time, so the effect of reducing the oligomer content rate can be efficiently exerted, so it is preferable. In addition, if 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 part to the surface of the pellets will not be too long, and the oligomers inside the pellets can be efficiently reduced during the heating treatment [2], so it is preferable.

[0083] [Heating treatment [2] process]

[0084] The polyester resin obtained in the present invention is obtained by subjecting the polyester resin [B] to a heat treatment [2]. The heat treatment [2] process in the present invention is carried out under the flow of an inert gas or under high vacuum, and the treatment temperature is set to be relative to the melting point T of the polyester resin [B] mB (°C) is T mB (°C) or lower. By making the temperature of the heat treatment [2] T mB (°C) or lower, it is possible to suppress the increase in the oligomer content rate and the acid value caused by the melting of the polyester resin [B]. In addition, by making the temperature of the heat treatment [2] preferably (T mB -60) °C or higher, more preferably (T mB -40) °C, it is possible to obtain the effect of reducing the acid value and the oligomer content rate brought about by the terminal hydroxyl group and the unreacted alkylene glycol in the polyester resin [B]. When the polyester resin [B] is a polyethylene terephthalate resin, it is preferably carried out 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 preferably carried out under the conditions of 180 to 210 °C, more preferably 185 to 200 °C.

[0085] In the heat treatment [2] process of the present invention, solid-phase polymerization of the polyester resin [B] can also be carried out. The progress of solid-phase polymerization improves the mechanical properties of the obtained polyester resin. On the other hand, it reduces the fluidity. Therefore, the heat treatment [2] is preferably carried out in such a way 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. If the heat treatment [2] is carried out until the intrinsic viscosity of the polyester resin [C] reaches 0.70 dL / g or more, the content rate of the unreacted alkylene glycol will be reduced to 0.03 mass% or less due to consumption and volatilization caused by the reaction with the polyester component. The intrinsic viscosity of the polyester resin represents the value obtained by measuring the o-chlorophenol solution of the polyester resin at 25 °C.

[0086] The implementation time of the heat treatment [2] is preferably 5 hours or more and 20 hours or less. When 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 on the molded product can be suppressed, and the oligomer content rate can be efficiently reduced. When the implementation time is 20 hours or less, the intrinsic viscosity of the polyester resin [C] will not be too high, and the fluidity is excellent.

[0087] [Polyester resin [C]]

[0088] The polyester resin [C] obtained by the present invention can be any of the polyester resins disclosed in [Polyester resin [A]]. Considering the excellent balance between mechanical properties and moldability, polybutylene terephthalate is preferred.

[0089] From the viewpoints of suppressing the reduction 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, further preferably 20 eq / t or less, still further preferably 15 eq / t or less, and still further preferably 10 eq / t or less. The lower limit value of the acid value is 0 eq / t. The acid value referred to herein is a value measured by titrating the obtained polyester resin dissolved in an o-cresol / chloroform solvent with alcoholic potassium hydroxide.

[0090] 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, further preferably less than 0.20% by mass, and still further preferably less than 0.15% by mass, the mold contamination during molding can be significantly suppressed, and the frequency of mold cleaning during continuous molding in production can be reduced. The lower limit value of the oligomer content is 0.00% by mass. The oligomer content referred to herein is a value obtained by dissolving the polyester resin [C] in a hexafluoroisopropanol / chloroform solvent (1 / 1, volume ratio), precipitating the high molecular weight component with an acetonitrile solvent, filtering with a polytetrafluoroethylene disk filter (0.45 μm), and quantifying the cyclic trimer in the obtained filtrate using high performance liquid chromatography.

[0091] For the polyester resin [C] of the present invention, the intrinsic viscosity measured for its o-chlorophenol solution at 25°C is 0.70 dL / g or more and 1.00 dL / g or less. When the intrinsic viscosity is 0.70 dL / g or more, more preferably 0.80 dL / g or more, the strength of the molded article can be improved, and in addition, the generation of burrs on the molded article 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 the reduction of the mechanical properties of the molded article and molding defects caused by resin decomposition can be suppressed.

[0092] The weight-average molecular weight of the polyester resin [C] of the present invention is preferably 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 in addition, the generation of burrs on the molded product can be suppressed, so it is preferred. If 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 the reduction of the mechanical properties of the molded product and molding defects caused by resin decomposition can be suppressed, so it is preferred. The weight-average molecular weight referred to here is a value calculated by gel permeation chromatography (solvent: hexafluoroisopropanol, standard sample: polymethyl methacrylate).

[0093] The polyester resin of the present invention can be melt-kneaded with other components as needed to form a polyester resin composition.

[0094] As a method of melt-kneading, for example, a method of premixing the polyester resin and various additives, etc., and supplying them to an extruder, etc. for melt-kneading; or a method of supplying a specified amount of each component to an extruder, etc. using a metering feeder such as a gravimetric feeder for melt-kneading, etc.

[0095] As an example of the above-mentioned premixing, a method of performing dry blending, a method of mixing using a mechanical mixing device such as a drum mixer, a belt mixer, and a Henschel mixer, etc. can be cited. In addition, the fibrous reinforcing material can be added by providing a side feeder midway between the main feeding part and the discharging part of a multi-screw extruder such as a twin-screw extruder. In addition, in the case of a liquid additive, a method of using a liquid addition nozzle provided midway between the main feeding part and the discharging part of a multi-screw extruder such as a twin-screw extruder and adding it using a plunger pump, a method of supplying it from the main feeding part, etc. using a metering pump can be used.

[0096] The above-mentioned composition is preferably subjected to molding processing after granulation. As a granulation method, for example, it is preferably a single-screw extruder, a twin-screw extruder, a triple-screw extruder, a conical extruder, and a kneading type mixer equipped with a "uni-melt" or "dulmage" type screw, etc. The polyester resin and other additives are extruded in a wire bundle shape and then cut, or cut while extruding into water to make pellets with 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.

[0097] By melt-molding the polyester resin composition formed from the polyester resin of the present invention, molded products of various shapes such as films, fibers, and others can be obtained. As a melt-molding method, for example, injection molding, extrusion molding, blow molding, etc. can be cited, and injection molding is particularly preferred.

[0098] As a method of injection molding, in addition to the usual injection molding method, gas-assisted molding, two-color molding, sandwich molding, in-mold molding, insert molding, injection compression molding, etc. are also known, and any molding method can be applied.

[0099] The molded article formed from the polyester resin according to the present invention can be used for various applications such as mechanical mechanism parts, electrical parts, electronic parts, and automotive parts that exhibit excellent mechanical properties and hydrolysis resistance. Specific examples of mechanical mechanism parts, electrical parts, electronic parts, and automotive parts include circuit breakers, electromagnetic switches, focusing boxes, flyback transformers, fixed machine molded articles for copiers and printing presses, housings for general household electrical appliances, OA equipment, etc., variable capacitor housing parts, various terminal boards, transformers, printed wiring boards, housings, wiring boards, bobbins, connectors, relays, disk drive chassis, converters, switch parts, socket parts, motor parts, jacks, plugs, capacitors, various types of housings, resistors, electrical / electronic parts assembled with metal terminals or wires, computer-related parts, voice parts such as audio parts, lighting parts, telecommunications equipment-related parts, telephone equipment-related parts, air conditioner parts, home appliance parts such as VTRs or TVs, copier parts, fax machine parts, optical equipment parts, automotive ignition device parts, automotive connectors, and various automotive electrical parts.

[0100] Examples

[0101] Next, the manufacturing method of the polyester resin of the present invention and the polyester resin will be specifically described by way of examples.

[0102] [Measurement methods for each property]

[0103] In each of the examples and comparative examples, the properties were evaluated using the measurement methods described below.

[0104] 1. Melting point of polyester resin

[0105] Collect about 10 mg of the polyester resin and measure it using a differential scanning calorimeter (DSC7 manufactured by PerkinElmer Co., Ltd.) under a nitrogen atmosphere. After heating the polyester resin to 280 °C at a heating rate of 20 °C / min to form a molten state, cool it to 30 °C at a cooling rate of 20 °C / min, and then heat it at a heating rate of 20 °C / min. The temperature at the apex of the endothermic peak observed at this time is taken as the melting point.

[0106] 2. Acid value of polyester resin

[0107] Dissolve about 2 g of the polyester resin in 50 mL of a chloroform / o-cresol (1 / 2, by volume) adjusting solution. After adding an appropriate amount of bromothymol blue / ethanol solution to this solution, titrate it with a 0.02 N potassium hydroxide ethanol solution, and calculate according to the following formula (unit: eq / t).

[0108] AV = ((V - V 0 ) × C) / (W × 10 -3 )

[0109] 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, by volume) adjusting solution [mL], C: Concentration of the sodium hydroxide / ethanol solution [mol / L], W: Mass of the polyester resin [g].

[0110] 3. Intrinsic viscosity of the polyester resin

[0111] Dissolve the polyester resin in o-chlorophenol to a concentration of 0.5% by mass. Then, using an Ubbelohde viscometer, measure the efflux time of the solution and the efflux time of the solvent at a temperature of 25°C, and calculate according to the following formula.

[0112] [η] = 0.25 × (t / t 0 - 1 + 3 × ln(t / t 0 )) / c

[0113] [η]: Intrinsic viscosity [dL / g],

[0114] t: Efflux time of the polyester resin solution [s],

[0115] t 0 : Efflux time of o-chlorophenol [s],

[0116] c: Solution concentration [g / cm 3 .

[0117] 4. Oligomer content of the polyester resin

[0118] After dissolving the polyester resin in a hexafluoroisopropanol / chloroform solvent (1 / 1, volume ratio), the high molecular weight component was precipitated using an acetonitrile solvent, and the mixture was filtered using a polytetrafluoroethylene disk filter (0.45 μm). The obtained filtrate was analyzed using a high performance liquid chromatography (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: UV 242 mm). Acetonitrile solutions of cyclic trimers of various concentrations were prepared, and a standard curve was prepared using the above-mentioned chromatograph, thereby quantifying the cyclic trimers contained in the polyester resin to obtain the oligomer content (unit: mass %).

[0119] 5. Unreacted alkylene glycol content of polyester resin

[0120] After dissolving the polyester resin in a hexafluoroisopropanol / chloroform solvent (1 / 1, volume ratio), the high molecular weight component was precipitated with an acetonitrile solvent, and filtered with a polytetrafluoroethylene disk filter (0.45 μm). The obtained filtrate was analyzed using a gas chromatograph (GC-2010 manufactured by Shimadzu Corporation, column: DB-5, column temperature: 80-300° C., heating rate: 6° C. / min, vaporizer temperature: 300° C., mobile phase: helium, detector: FID). Acetonitrile solutions of alkylene glycols of various concentrations were prepared, and a calibration curve was prepared using the above-mentioned chromatograph to quantify the alkylene glycols and obtain the alkylene glycol content (unit: mass %).

[0121] 6. Whether there is mold contamination

[0122] Regarding polyester resin [C], using an injection molding machine (NEX1000 manufactured by Nissei Plastic Industrial Co., Ltd.), when polyester resin [C] is polybutylene terephthalate, it is molded into a square plate with a width of 80 mm × a length of 80 mm × a thickness of 2 mm under the conditions of a molding temperature of 280 °C, a mold temperature of 80 °C, and a cooling time of 10 seconds; when polyester resin [C] is polyethylene terephthalate, it is molded into a square plate with a width of 80 mm × a length of 80 mm × a thickness of 2 mm under the conditions of a molding temperature of 280 °C, a mold temperature of 120 °C, and a cooling time of 10 seconds; when polyester resin [C] is a polyester elastomer, it is molded into a square plate with a width of 80 mm × a length of 80 mm × a thickness of 2 mm under the conditions of a molding temperature of 280 °C, a mold temperature of 60 °C, and a cooling time of 10 seconds. By visually observing the mold after continuously molding 10,000 square plates, the case where there is no mold contamination caused by the precipitation of oligomers is evaluated as A, the case where a thin layer adheres to a part of the mold is evaluated as B, the case where a thin layer adheres to the entire mold is evaluated as C, the case where the entire mold becomes cloudy and white foreign matters can be clearly seen in a part is evaluated as D, and A and B are judged to have excellent mold contamination inhibition.

[0123] 7. Fluidity of Polyester Resin

[0124] Using a mold for a long strip-shaped molded product with a thickness of 1 mm and a width of 10 mm, it is judged by the flow length during injection molding. Regarding the injection molding conditions, when polyester resin [C] is polybutylene terephthalate, the barrel 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 polyester resin [C] is polyethylene terephthalate, the barrel 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 polyester resin [C] is a polyester elastomer, the barrel temperature is 250 °C, the mold temperature is 60 °C, the injection pressure is 30 MPa, and the injection speed is 100 mm / s. The resin with a flow length of 100 mm or more is judged to have excellent fluidity. 110 mm or more is more excellent, 120 mm or more is further excellent, and 140 mm or more is particularly excellent.

[0125] 8. Mechanical Properties of Polyester Resin

[0126] 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 thickness of 4 mm were obtained. When the polyester resin [C] was polybutylene terephthalate, molding was carried out under the molding cycle conditions of a barrel temperature of 250 °C, a mold temperature of 80 °C, an injection speed of 50 mm / s, a total injection time and holding pressure time of 10 seconds, and a cooling time of 10 seconds. When the polyester resin [C] was polyethylene terephthalate, molding was carried out under the molding cycle conditions of a barrel temperature of 280 °C, a mold temperature of 80 °C, an injection speed of 50 mm / s, a total injection time and holding pressure time of 10 seconds, and a cooling time of 10 seconds. When the polyester resin [C] was a polyester elastomer, molding was carried out under the molding cycle conditions of a barrel temperature of 250 °C, a mold temperature of 60 °C, an injection speed of 50 mm / s, a total injection time and holding pressure time of 10 seconds, and a cooling time of 10 seconds. In addition, 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 set as the average of three measured values.

[0127] 9. Hydrolysis resistance of polyester resin

[0128] 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 thickness of 4 mm were obtained. The obtained ISO-1A dumbbells were put into a highly accelerated life test device (EHS-411 manufactured by ESPEC Corporation) set at a temperature and humidity of 121 °C × 100% RH for 50 hours for damp heat treatment. For the molded products after damp heat treatment, the tensile strength was measured under the same conditions as the tensile test in item 8, and the three measured values were taken as the average. Based on the following formula, the value of the tensile strength after damp heat treatment relative to the tensile strength without damp heat treatment was expressed as a percentage, and the obtained value was used as the tensile strength retention rate.

[0129] (Tensile strength after damp heat treatment / Tensile strength without damp heat treatment) × 100 = Tensile strength retention rate (%)

[0130] A resin with a tensile strength retention rate of less than 70% was judged to have poor hydrolysis resistance, and a material with a large value of the tensile strength retention rate was judged to be excellent. A value of 80% or more was judged to be more excellent, 90% or more was judged to be further excellent, and 99% or more was judged to be particularly excellent.

[0131] <Materials used in Examples and Comparative Examples>

[0132] (1) Polyester resin [A]

[0133] Virgin polyester resin [A-1]

[0134] · PBT1

[0135] 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

[0136] · PBT2

[0137] 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

[0138] · PET1

[0139] 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

[0140] · TPEE

[0141] Polyester elastomer, melting point 201 °C, “Hytrel” (registered trademark) 5556 manufactured by Celanese, intrinsic viscosity 1.46 dL / g.

[0142] Recycled polyester resin [A-2]

[0143] · PBT3

[0144] Recycled defective pellets during the manufacture 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

[0145] · PBT4

[0146] Recycled molding scraps during the injection molding of a resin composition containing polybutylene terephthalate resin, melting point 220 °C, acid value 70 eq / t, intrinsic viscosity 0.53 dL / g, weight average molecular weight 11,900.

[0147] · PBT6

[0148] Recycled molding scraps during the injection molding of a resin composition containing polybutylene terephthalate resin, melting point 223 °C, acid value 56 eq / t, intrinsic viscosity 0.61 dL / g, weight average molecular weight 12,800.

[0149] (2) Alkylene glycol

[0150] · 1,4-Butanediol (BDO, boiling point 228 °C, manufactured by Mitsubishi Chemical Corporation)

[0151] · Ethylene glycol (EG, boiling point 198 °C, manufactured by Mitsubishi Chemical Corporation).

[0152] (3) Dicarboxylic acid

[0153] · Terephthalic acid (manufactured by Mitsui Chemicals, Inc.).

[0154] (4) Transesterification catalyst

[0155] · Tetra-n-butyl orthotitanate (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0156] (5) Masterbatch for black coloring

[0157] · MB-9811BLACK (polybutylene terephthalate, pigment concentration 20%, manufactured by Kotobuki Kasei Kogyo Co., Ltd.).

[0158] <Preparation of low-viscosity polyester resin [A] (PBT5, PET2)>

[0159] · PBT5 (Comparative Examples 3 and 4)

[0160] 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 was added (mass ratio of terephthalic acid / tetra-n-butyl titanate = 1 / 0.0005), and the transesterification reaction was started at a temperature of 190 °C under a nitrogen stream. Then, the temperature was gradually raised, and the transesterification reaction was carried out for 3 hours under the condition of a final temperature of 240 °C. Antimony trioxide as a polycondensation reaction catalyst (1.0×10 -4 moles relative to 100 g of the produced polyester resin) was added to the obtained reactant, and the polymerization reaction was carried out for 2 hours under the conditions of a temperature of 250 °C and a pressure of 100 Pa, and then discharged in a wire bundle form, passed through a cooling bath, and granulated using a wire bundle cutter while adjusting the pulling speed so as to obtain granules having the pellet size described in Table 3, thereby obtaining granules of a polybutylene terephthalate prepolymer (PBT5, acid value 26 eq / t, intrinsic viscosity 0.58 dL / g). The obtained granules were dried for 6 hours using a hot air dryer at a temperature of 110 °C.

[0161] · PET2 (Comparative Examples 6 and 7)

[0162] 1,4-Butanediol was changed to ethylene glycol, and the temperature of the polymerization reaction was changed to 280 °C. Otherwise, the same operation as in the preparation of PBT5 was carried out to obtain granules of a polyethylene terephthalate prepolymer (PET2, acid value 20 eq / t, intrinsic viscosity 0.50 dL / g). The obtained granules were dried for 6 hours using a hot air dryer at a temperature of 110 °C.

[0163] [Examples 1 - 20, Comparative Examples 1 - 14]

[0164] For each polyester resin [A] corresponding to each example shown in Tables 1 - 3, heat treatment [1] and heat treatment [2] were carried out. 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 polyester resin [B] was used as polyester resin [C], and the evaluation of each property was directly carried out. For Comparative Examples 9 and 11, heat treatments [1] and [2] were not carried out, and polyester resin [A] was used as polyester resin [C], and the evaluation of each property was directly carried out.

[0165] <Heat treatment [1] in Examples 1 - 6, 9 - 20, Comparative Examples 5, 8, 13, 14>

[0166] In Examples 1 - 6, 9 - 20, Comparative Examples 5, 8, 13, 14, heat treatment [1] based on an extruder was carried out. Using a co - rotating twin - screw extruder with an exhaust port (manufactured by Japan Steel Works, TEX - 30α) having a screw diameter of 30 mm and an L / D of 35, the polyester resin [A] and the alkylene glycol were added from the main 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, heat treatment [1] was carried out with the exhaust section at atmospheric pressure, and in Examples 19, 20 and Comparative Example 14, heat treatment [1] was carried out with the exhaust section in a reduced - pressure state. It should be noted that the alkylene glycol was supplied using a metering pump. Further, when the polyester resin [A] was polybutylene terephthalate, melt - kneading was carried out under the extrusion conditions of a kneading temperature of 250°C and a screw speed of 200 rpm; when it was polyethylene terephthalate, melt - kneading was carried out under the extrusion conditions of a kneading temperature of 280°C and a screw speed of 200 rpm; when it was a polyester elastomer, melt - kneading was carried out under the extrusion conditions of a kneading temperature of 250°C and a screw speed of 200 rpm, discharged in a wire - harness shape, passed through a cooling bath, and granulated using a wire - harness cutter by adjusting the traction speed to obtain granules of polyester resin [B] (Table 1). The obtained granules were dried for 6 hours using a hot - air dryer at a temperature of 110°C.

[0167] Note that when preparing polyester resin [B], 3 parts by mass of the black masterbatch MB-9811BLACK for coloring is added to 100 parts by mass of polyester resin [A] from the main feed section of the extruder. Starting from the time point of addition, the time is measured. After confirming the black color from the black masterbatch for coloring in the resin discharged from the discharge port, the measurement of time ends at the time point when the black color can no longer be confirmed. The time elapsed from the start to the end of the measurement is used as the heat treatment time in this example (Table 1). This operation is carried out after obtaining the amount of polyester resin [B] required for the subsequent heat treatment [2] process, and the polyester resin obtained by adding the black masterbatch for coloring is not used in the subsequent processes.

[0168] In Comparative Example 5, the melt viscosity of the polyester resin [B] after the heat treatment [1] is low, and it is difficult to discharge it in a wire harness shape, so the subsequent operations cannot be carried out.

[0169] <Heat treatment [1] in Comparative Examples 1, 2, 10, and 12>

[0170] In Comparative Examples 1, 2, 10, and 12, no alkylene glycol is added, and only polyester resin [A] is passed through the extruder. Other than that, the operations are the same as in Examples 1-6 and Comparative Example 5, and the heat treatment [1] is carried out.

[0171] <Heat treatment [1] in Example 7>

[0172] In Example 7, the heat treatment [1] based on the polymerization tank is carried out. 1000 g of PBT1 is put into a 5 L polymerization tank with stirring blades, and under a nitrogen stream, the temperature is raised to 250 °C and stirred for 30 minutes. After confirming that PBT1 has melted, 10 g of 1,4-butanediol is added and stirred for 1 minute. After confirming that the viscosity of the melt is stable, it is discharged in a wire harness shape from the discharge port, passed through the cooling bath, and granulated using a wire harness cutter to adjust the drawing speed so as to obtain pellets of polyester resin [B] having the pellet size described in Table 1 (Table 1). The obtained pellets are dried for 6 hours using a hot air dryer at a temperature of 110 °C.

[0173] Note that the time from adding the alkylene glycol to polyester resin [A] until the start of discharge is set as t 1 , and the time from adding the alkylene glycol until the end of discharge is set as t 2 , and the heat treatment time t is calculated using the following formula.

[0174] t = (t 1 + t 2 ) / 2... (Formula).

[0175] <Heat treatment [1] in Example 8>

[0176] In Example 8, a heat treatment based on an aggregation tank [1] was carried out. 1000 g of PBT1 was put into a 5 L aggregation tank with stirring blades, heated to 250°C under a nitrogen stream, 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 wire harness shape from the discharge port, passed through a cooling bath, and granulated using a wire harness cutter while adjusting the pulling speed so as to obtain pellets having the pellet size described in Table 1, thereby obtaining pellets of polyester resin [B] (Table 1). The obtained pellets were dried for 6 hours using a hot air dryer at a temperature of 110°C.

[0177] It should be noted that the heat treatment time was calculated in the same manner as the heat treatment time in the heat treatment [1] of Example 7.

[0178] <Heat treatment [2]>

[0179] For the pellets of the polyester resin obtained in the foregoing process, when the polyester resin [A] used was polyethylene terephthalate, a heat treatment [2] was carried out under the conditions of a temperature of 230°C and a pressure of 100 Pa; when it was polybutylene terephthalate, a heat treatment [2] was carried out under the conditions of a temperature of 170 to 210°C and a pressure of 100 Pa; when it was a polyester elastomer, a heat treatment [2] was carried out under the conditions of a temperature of 180°C and a pressure of 100 Pa, thereby obtaining polyester resin [C] (Table 1). It should be noted that for Comparative Example 13, the heat treatment [2] was carried out at 240°C which exceeded the melting point of polyester resin [B].

[0180] For Examples 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 the suppression of die contamination was excellent. On the other hand, for 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 the suppression of die contamination was poor.

[0181] For Comparative Examples 1, 2, 10, and 12 in which the heat treatment [2] was carried out after the heat treatment [1] without adding alkylene glycol, the effect of reducing the oligomer content brought about by the unreacted alkylene glycol could not be obtained, and thus it was impossible to simultaneously achieve a reduction in the oligomer content and fluidity.

[0182] For Comparative Example 5 in which 6 mass parts of alkylene glycol was added, the melt viscosity of polyester resin [B] after the heat treatment [1] became too low, it could not be discharged in a wire harness shape, it was difficult to recover in a uniform shape, and the granulation property was significantly poor.

[0183] Regarding Comparative Examples 3, 4, 6, and 7 in which the polyester resin [A] with a low intrinsic viscosity is not subjected to heat treatment [1] but directly subjected to heat treatment [2], if the implementation time of heat treatment [2] is short, the mold contamination inhibition is poor, and if the implementation time of heat treatment [2] is long, the fluidity is poor.

[0184] Regarding Comparative Example 8 in which each property is directly evaluated without performing heat treatment [2], compared with Example 3 in which heat treatment [2] was performed, there is more mold contamination and the hydrolysis resistance is also poor.

[0185] Regarding Comparative Example 13 in which heat treatment [2] is performed at a temperature exceeding the melting point of the polyester resin [B], the oligomer content rate is not reduced due to heat treatment [2], and the mold contamination inhibition is poor.

[0186] Regarding Examples 5, 6, and 17 using recycled polyester resin, the oligomer content rate is low, the fluidity is excellent, and in addition, the acid value can be significantly reduced compared with the time of recycling. Compared with Examples 1-4, 7-16, and 18-20 using virgin polyester resin, it is also at a comparable level. It can be seen that by applying the present invention to recycled polyester resin, waste can be reduced, the alkylene glycol and heat energy required for recycling can be reduced, and the carbon dioxide emission can be reduced.

[0187] On the other hand, regarding Comparative Examples 10 and 12 in which heat treatment [1] is performed on the recycled polyester resin without adding alkylene glycol, and Comparative Examples 9 and 11 in which each property is directly evaluated without performing heat treatment [1] and [2] on the recycled polyester resin, the mold contamination inhibition is poor.

[0188] Regarding Examples 1-3, 5, and 6 in which heat treatment [1] is performed using an extruder, compared with Examples 7 and 8 in which a polymerization tank is used in heat treatment [1], heat treatment can be performed in a shorter time. Therefore, the alkylene glycol volatilized and consumed in the transesterification reaction is less, and the unreacted alkylene glycol content rate of the polyester resin [B] becomes a high value. Therefore, the oligomer content rate reduction effect of Examples 1-3, 5, and 6 is higher, and the mold contamination inhibition is more excellent.

[0189] When Example 7 in which heat treatment [1] is performed using a polymerization tank is compared with Example 8, the volatilization of alkylene glycol and the transesterification reaction with polyester are less in Example 7 with a shorter heat treatment time from the addition of alkylene glycol. The alkylene glycol content rate of the polyester resin [B] becomes higher, and the oligomer content rate of the polyester resin [C] becomes a low value.

[0190] For Examples 1-3, 5, and 6 in which polyester resin [A] is polybutylene terephthalate and 1,4-butanediol is used as the alkylene glycol and passed through the extruder, compared with Example 4 in which polyester resin [A] is polyethylene terephthalate and ethylene glycol is used as the alkylene glycol, since the melting point of the polyester resin is low and the boiling point of the alkylene glycol is high, in the implementation of the heat treatment [1] using the extruder, less alkylene glycol is volatilized and consumed in the transesterification reaction, and the unreacted alkylene glycol content of polyester resin [B] becomes a high value. Therefore, the oligomer content reduction effect in Examples 1-3, 5, and 6 is higher, and the mold contamination inhibition is more excellent.

[0191] Compared with Example 1, the increase in intrinsic viscosity due to the heat treatment [2] is greater in Examples 9 and 10 with smaller pellet sizes (diameters), especially significantly in Example 10 with a pellet diameter of less than 1.00 mm, and the treatment is completed in a short time. Therefore, compared with Example 1 and Example 10 which completes the treatment in a short time, the oligomer content reduction effect is higher, and the mold contamination inhibition is more excellent.

[0192] Compared with Example 1, Examples 11 and 12 with larger pellet sizes (diameters), the distance from the center to the surface of the pellet is shorter, and the oligomers inside the pellet can be more efficiently reduced during the heat treatment [2]. Especially compared with Example 12 with a pellet diameter greater than 5.00 mm, this tendency is significant. Therefore, compared with Example 12, the mold contamination inhibition in Example 1 is more excellent.

[0193] Compared with Example 1, in Example 13 where the heat treatment [2] is carried out at a low temperature, there is a tendency for the increase in intrinsic viscosity during the heat treatment [2] to become smaller.

[0194] Compared with Example 1, in Example 14 where the heat treatment [2] is carried out at a high temperature, there is a tendency for the increase in intrinsic viscosity during the heat treatment [2] to become larger, and the treatment is completed in a short time. Therefore, compared with Example 14 which completes the treatment in a short time, the oligomer content reduction effect in Example 1 is large, and the mold contamination inhibition is excellent.

[0195] Compared with Example 1, in Example 15 where the heat treatment [2] is completed in a short time, there is a tendency for the intrinsic viscosity to be low and the oligomer content to be high.

[0196] Compared with Example 1, in Example 16 where the heat treatment [2] is carried out for a long time, there is a tendency for the intrinsic viscosity to be high and the oligomer content to be low.

[0197] For Examples 1-3, 5, and 6 in which polyester resin [A] is polybutylene terephthalate, compared with Example 18 in which polyester resin [A] is a polyester elastomer, cyclic oligomers can be more efficiently reduced, and therefore the mold contamination inhibition is more excellent.

[0198] [Table 1]

[0199]

[0200] [Table 2]

[0201]

[0202] [Table 3]

[0203]

Claims

1. Method for manufacturing a polyester resin, which comprises: Heating treatment [1] process, 0.1 to 5.0 parts by mass of an alkylene glycol is added to 100 parts by mass of polyester resin [A], and heating is carried out at a temperature exceeding the melting point T mA (°C) of the polyester resin [A] to obtain polyester resin [B]; and a heat treatment [2] step, at a temperature below T mB (°C) with respect to the melting point T of the polyester resin [B], heat the obtained polyester resin [B] mB (°C). The polyester resin [B] contains 0.05% by mass or more and 4.76% by mass or less of unreacted alkylene glycol.

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

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

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

6. A polyester resin, the oligomer content rate of which is less than 0.30% by mass, and the intrinsic viscosity is 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.

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