Polyester resin and method for producing the same, and method for determining polyester resin with low coloration resulting from processing involving melt kneading treatment

Abstract

To provide a polyester resin composition exhibiting a reduced degree of coloration when a molded article is produced under strong thermal history, and a method for producing the same, and to provide a method for determining a polyester resin with low coloration resulting from processing involving melt kneading treatment.SOLUTION: A polyester resin composition having an integrated value of chemiluminescence emission intensity, measured every one second from the beginning of measurement up to 2,400 seconds, of 1.35×107 count or less, the polyester resin composition including a plurality of polyester resins, at least one of which is a recycled polyester resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyester resin and a method for producing the same, and also to a method for identifying a polyester resin that is less discolored by processing involving melt-kneading. [Background technology]

[0002] Polyester resins, such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), are excellent in transparency, mechanical properties, and chemical characteristics, and are used in a wide range of fields depending on the properties of each polyester resin, such as fibers for clothing and industrial materials, various films and sheets for packaging and industrial use, and hollow molded articles such as bottles and engineering plastics.

[0003] In recent years, hollow molded articles made from, for example, polyester resins have become indispensable for our daily lives. On the other hand, the increased use of hollow molded articles has led to various problems, such as resource depletion, increased marine litter, and global warming. One method for solving these problems has attracted attention. This involves the collection and regeneration of hollow molded articles, such as polyester bottles, which are then recycled and reused as polyester bottles, fibers, nonwoven fabrics, and other molded articles. This is known as material recycling, and has attracted attention as a recovery and regeneration recycling system.

[0004] However, when used polyester resins using widely used antimony compounds, titanium compounds, or germanium compounds as polymerization catalysts are recovered and recycled, the polyester resin deteriorates, resulting in discoloration and a decrease in molecular weight, and therefore improvements in this area are needed.

[0005] As a method for solving the above problems, a method of adding a catalyst consisting of an aluminum compound and a phosphorus compound containing a hindered phenol structure in the production of a polyester resin is known (Patent Documents 1 and 2). However, no study has been conducted on recycling used polyester resins, particularly used polyester resins using at least one compound selected from antimony compounds, titanium compounds, and germanium compounds as a polymerization catalyst.

[0006] Patent Document 3 proposes a method for producing a polyester resin composition that is resistant to coloration and molecular weight reduction even after multiple recycling (hereinafter referred to as "excellent recyclability") by adding a polyester resin containing an aluminum compound and a phosphorus compound to a recovered polyester resin containing at least one element selected from antimony, titanium, and germanium. However, this method has the problem that the quality of the recycled resin depends on the degree of deterioration of the recovered polyester resin. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2007 / 032325 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-169432 [Patent Document 3] International Publication No. 2022 / 234749 Summary of the Invention [Problem to be solved by the invention]

[0008] It is known that subjecting a polyester resin composition to a thermal history, such as melt-kneading, accelerates degradation of the polyester resin and reduces its intrinsic viscosity. It is also known that the intrinsic viscosity retention before and after thermal history is used as an indicator of polyester resin degradation. However, even when polyester resin compositions with similar intrinsic viscosities and / or intrinsic viscosity retention are melt-molded under the same conditions, the degree of discoloration that occurs during the process varies. In some cases, the degree of discoloration is very low, while in other cases, the degree of discoloration is so high that it is unacceptable for the quality of the molded product. Furthermore, when the melt-kneading temperature is high or the time is long, or when molded products are produced using a severe thermal history, such as repeated melt-kneading, the difference in the degree of discoloration tends to be even greater. This phenomenon is likely to pose a major problem when recovering and reusing polyester resins.

[0009] The present invention aims to provide a polyester resin composition that exhibits a low degree of discoloration when molded articles are produced by subjecting the composition to a strong thermal history, a method for producing the same, and a method for identifying polyester resins that exhibit low discoloration when processed using a melt-kneading process. [Means for solving the problem]

[0010] As a result of extensive research conducted by the inventors to achieve the above-mentioned object, they discovered that polyester resin compositions having an integrated value of chemiluminescence emission intensity within a specific range exhibit low degree of discoloration when subjected to a strong thermal history such as repeated melt-kneading, and have excellent recyclability, thereby arriving at the present invention.

[0011] That is, the present invention comprises the following configurations. Section 1. A method for producing a polyester resin composition, comprising a step of melt-kneading a plurality of types of polyester resins, The plurality of polyester resins includes at least one recycled polyester resin, The integrated value of the chemiluminescence intensity of the obtained polyester resin composition measured every second from the start of measurement to 2,400 seconds was 1.35 × 10 7is less than or equal to count, A method for producing a polyester resin composition. Section 2. The weighted average of the integrated values ​​of the chemiluminescence emission intensity measured every second from the start of measurement to 2,400 seconds for the plurality of polyester resins is 1.15 × 10 7 Item 2. The method for producing a polyester resin composition according to Item 1, wherein the number of carbon atoms in the polyester resin composition is 0.1 or less. Section 3. 3. The method for producing a polyester resin composition according to claim 1 or 2, wherein at least some of the plurality of polyester resins contain one or more metal elements selected from the group consisting of antimony, titanium, germanium, and aluminum, and the total content of the metal elements is 2 to 1000 ppm by mass. Section 4. Item 4. The method for producing a polyester resin composition according to Item 3, wherein at least a part of the metal element is derived from a polymerization catalyst for the polyester resin. Section 5. The integrated value of the chemiluminescence intensity measured every second from the start of measurement to 2,400 seconds is 1.35 × 10 7 is less than or equal to count, The polyester resin composition contains a plurality of types of polyester resins, and at least one of the plurality of types of polyester resins is a recycled polyester resin. Polyester resin composition. Section 6. Item 6. A method for producing a melt-molded product using a polyester resin composition obtained by the production method according to any one of items 1 to 4 and / or the polyester resin composition according to item 5 as a raw material. Section 7. Item 7. The method for producing a melt-molded product according to Item 6, wherein the melt-molded product is a hollow molded product or a solid molded product. Section 8. A method for identifying polyester resins that have little discoloration due to processing involving melt-kneading, based on the integrated value of chemiluminescence. Section 9. Item 9. The method according to item 8, wherein the coloring is evaluated by a color L value and / or a color b value in the Hunter Lab color system. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a polyester resin composition that exhibits a low degree of discoloration when subjected to a strong thermal history such as repeated melt-kneading, and a method for producing the same. It is also possible to provide a polyester resin composition that exhibits a low degree of discoloration when subjected to an increased thermal history through multiple recycling processes, and has excellent recyclability, and a method for producing the same. Furthermore, it is possible to provide a method for identifying polyester resins that exhibit low discoloration due to processing involving melt-kneading. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described in detail below. However, the present invention is not limited to this embodiment, and various modifications can be made within the scope of the description. In addition, in this specification, ppm by mass is 10 -4 The percentages represent mass %.

[0014] The polyester resin composition of the present invention has a chemiluminescence emission intensity measured every second from the start of measurement to 2,400 seconds of 1.35 × 10 7 count or less, and the polyester resin composition may contain multiple types of polyester resins, at least one of which may be a recycled polyester resin, and all of which may be recycled polyester resins. The polyester resin composition of the present invention can be produced by a production method including a step of melt-kneading multiple types of polyester resins.

[0015] The polyester resin composition of the present invention is mainly composed of a polyester resin. Here, "mainly composed of a polyester resin" means that the polyester resin is the component with the largest proportion in the polyester resin composition by mass. The proportion of the polyester resin in the polyester resin composition is preferably 50 mass% or more, more preferably 65 mass% or more, even more preferably 85 mass% or more, particularly preferably 95 mass% or more, and may be 98 mass% or more or 99 mass% or more.

[0016] Recycled polyester refers to, for example, recycled offcuts, scraps, off-spec products, etc. generated in the process of processing polyester resin into shapes such as powder, pellets, films, bottles, fibers, etc., or recycled products processed into shapes such as pellets, films, bottles, fibers, etc. and then used, and / or recycled products that have been processed in some way and / or used, or may be processed by cutting, pulverizing, melt-kneading, pelletizing, etc. The shape of the recycled polyester is not particularly limited, and may be in the form of chips, flakes, powder, etc.

[0017] Chemiluminescence is measured by detecting the weak light generated when molecules in a reaction system change from an excited state to a ground state during a chemical reaction. Chemiluminescence is thought to be able to detect oxidative degradation of polyester resins at a very early stage with high sensitivity. A polyester resin composition with a sufficiently low integrated luminescence intensity is preferred in that it causes little increase in coloration when used as a raw material for melt molding, for example. The integrated luminescence intensity of a polyester resin composition is 1.35 × 10 7 It is preferable that the number of counts is less than 1.15 × 10 7 counts or less, more preferably 1.00 x 10 7 counts or less, particularly preferably 8.50 × 10 6 The lower limit of the integrated luminescence intensity is not particularly limited, but is, for example, 3.95 × 10 6 It may be more than count.

[0018] The polyester resin composition of the present invention can be used as a melt-molding material. The melt-molded product of the present invention may be a hollow or solid molded product, and may contain bubbles inside. The shape of the melt-molded product is not particularly limited, and may be, for example, granular, powdery, film-like, sheet-like, plate-like, pipe-like, tubular, rod-like, fibrous, nonwoven fabric-like, paper-like, or fabric-like. Furthermore, the melt-molded product obtained by melt-molding the polyester resin composition of the present invention may be a solid or hollow molded product, and may contain bubbles. Examples of solid molded products include, but are not limited to, pellets, films, sheets, and fibers. Examples of hollow molded products include, but are not limited to, bottles and boxes.

[0019] The polyester resin composition of the present invention can be used as a melt-extrusion material, and a coating can be formed by coating the polyester resin composition of the present invention on another substrate by melt-extrusion.

[0020] The polyester resin composition of the present invention is, but is not limited to, a polyester resin composition having a weighted average of the integrated values ​​of the chemiluminescence emission intensity measured every second from the start of measurement to 2,400 seconds of 1.15×10 7 The polyester resin composition can be produced by a production method including a step of melt-kneading a plurality of polyester resins having a density of 1000 kJ / cm or less. Here, the term "weighted average of integrated values" refers to a weighted average value obtained by weighting the integrated values ​​of the individual polyester resins by their blending ratios on a mass basis.

[0021] All or a part of the polyester resin used as a raw material may contain one or more metal elements selected from the group consisting of antimony, titanium, germanium, and aluminum, and the total content of the metal elements may be 2 to 1000 ppm by mass.

[0022] The method for melt-kneading multiple polyester resins is not particularly limited. For example, melt-kneading can be performed using a general resin kneading device such as a Banbury mixer, kneader, single-screw extruder, twin-screw extruder, four-screw extruder, or single-screw planetary extruder, with or without dry blending. Among these, it is preferable to use a twin-screw extruder, four-screw extruder, or single-screw planetary extruder that has excellent surface renewal capabilities. Furthermore, it is preferable that the extruder has at least one, preferably two, or more, and more preferably three or more vent ports, and that the vent ports are connected to a vacuum system to suppress deterioration of the polyester resin composition.

[0023] When it is assumed that the polyester resin composition is used as a raw material for melt molding, the intrinsic viscosity of the polyester resin composition is preferably 0.56 to 0.90 dL / g, more preferably 0.60 to 0.80 dL / g, and even more preferably 0.70 to 0.75 dL / g, but is not limited thereto.

[0024] The intrinsic viscosity retention of the polyester resin composition is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. If the intrinsic viscosity retention of the polyester resin composition is less than 80%, recyclability may be insufficient. The upper limit of the intrinsic viscosity retention of the polyester resin composition is preferably 100%, but due to technical difficulties, it is approximately 99%.

[0025] The polyester resin composition of the present invention can be chipped by, for example, extruding the molten polyester resin composition through a die orifice into water and cutting it underwater, or by extruding strands through a die orifice into air and then cooling with cooling water to form chips. The chips may be cylindrical, angular, spherical, or flat, with flat shapes being particularly preferred. For example, in the case of cylindrical chips, a length of 1.0 to 4 mm and cross-sectional major and minor axes of approximately 1.0 to 4 mm are practical. In the case of spherical particles, a diameter of 1 to 4 mm is practical. The weight per chip is preferably 10 to 50 mg, more preferably 20 to 45 mg, and particularly preferably 25 to 40 mg.

[0026] The polyester resin, which is a raw material for the polyester resin composition, is a polymer having a repeating structure formed by polycondensation of a polycarboxylic acid and a polyhydric alcohol, and can be formed by a polycondensation reaction of at least one selected from polycarboxylic acids and their ester-forming derivatives with at least one selected from polyhydric alcohols and their ester-forming derivatives.

[0027] The polyester resin is preferably, but not limited to, a polymer consisting of only one monomer selected from ethylene terephthalate, butylene terephthalate, propylene terephthalate, 1,4-cyclohexanedimethylene terephthalate, ethylene naphthalate, butylene naphthalate, or propylene naphthalate, or a copolymer consisting of two or more of the above monomers, more preferably polyethylene terephthalate or a copolymer consisting of ethylene terephthalate and at least one of the above monomers other than ethylene terephthalate, and particularly preferably polyethylene terephthalate. The copolymer consisting of ethylene terephthalate and at least one of the above monomers other than ethylene terephthalate preferably contains 70 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more, of a component derived from ethylene terephthalate monomer, and may contain 95 mol% or more or 100 mol%.

[0028] The main polycarboxylic acid component constituting the polyester resin is preferably a dicarboxylic acid. "The main polycarboxylic acid component is a dicarboxylic acid" means that the dicarboxylic acid is contained in an amount of more than 50 mol% of the total polycarboxylic acid components, preferably 70 mol% or more of dicarboxylic acid, more preferably 80 mol% or more of dicarboxylic acid, even more preferably 90 mol% or more of dicarboxylic acid, and may even contain 100 mol% of dicarboxylic acid. When two or more dicarboxylic acids are used, the total amount thereof is preferably within the above range.

[0029] Dicarboxylic acid components that can be used as the main polycarboxylic acid component constituting the polyester resin or as the subsidiary polycarboxylic acid component include saturated aliphatic dicarboxylic acids exemplified by oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, tetradecanedicarboxylic acid, hexadecanedicarboxylic acid, and dimer acid; cycloaliphatic dicarboxylic acids exemplified by 1,3-cyclobutanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and 2,5-norbornanedicarboxylic acid; Examples include dicarboxylic acids having a leucane structure; unsaturated aliphatic dicarboxylic acids exemplified by fumaric acid, maleic acid, and itaconic acid; and aromatic dicarboxylic acids exemplified by orthophthalic acid, isophthalic acid, terephthalic acid, 5-(alkali metal)sulfoisophthalic acid, diphenic acid, 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 4,4'-biphenylsulfonedicarboxylic acid, 4,4'-biphenyletherdicarboxylic acid, 1,2-bis(phenoxy)ethane-p,p'-dicarboxylic acid, pamoic acid, and anthracenedicarboxylic acid.

[0030] The main polycarboxylic acid component constituting the polyester resin is more preferably terephthalic acid or its ester-forming derivative, or naphthalenedicarboxylic acid or its ester-forming derivative. Examples of naphthalenedicarboxylic acid or its ester-forming derivative include 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, or their ester-forming derivatives. Terephthalic acid, 2,6-naphthalenedicarboxylic acid, or their ester-forming derivatives are particularly preferred.

[0031] The phrase "the main polycarboxylic acid component is terephthalic acid or its ester-forming derivative, or naphthalenedicarboxylic acid or its ester-forming derivative" means that the total amount of terephthalic acid components and naphthalenedicarboxylic acid components is greater than 50 mol%, preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and may even be 100 mol%.

[0032] As polycarboxylic acids other than these dicarboxylic acids, trivalent or higher polycarboxylic acids or hydroxycarboxylic acids may be used in small amounts, with trivalent or tetravalent polycarboxylic acids being preferred. Examples of trivalent or higher polycarboxylic acids include ethanetricarboxylic acid, propanetricarboxylic acid, butanetetracarboxylic acid, pyromellitic acid, trimellitic acid, trimesic acid, 3,4,3',4'-biphenyltetracarboxylic acid, and ester-forming derivatives thereof. The trivalent or higher polycarboxylic acid is preferably 20 mol% or less, more preferably 10 mol% or less, and even more preferably 5 mol% or less, of the total polycarboxylic acid components. When two or more trivalent or higher polycarboxylic acids are used, the total amount is preferably within the above range.

[0033] Examples of hydroxycarboxylic acids include lactic acid, citric acid, malic acid, tartaric acid, hydroxyacetic acid, 3-hydroxybutyric acid, p-hydroxybenzoic acid, p-(2-hydroxyethoxy)benzoic acid, 4-hydroxycyclohexanecarboxylic acid, and ester-forming derivatives thereof. The hydroxycarboxylic acid content of the total polycarboxylic acid components is preferably 20 mol% or less, more preferably 10 mol% or less, and even more preferably 5 mol% or less. When two or more hydroxycarboxylic acids are used, the total content is preferably within the above range.

[0034] The polycarboxylic acid component or hydroxycarboxylic acid component may be used in the form of an ester-forming derivative such as an alkyl ester, an acid chloride, or an acid anhydride.

[0035] The main polyhydric alcohol component constituting the polyester resin is preferably a diol. "The main polyhydric alcohol component is a diol" means that the diol is contained in an amount of more than 50 mol% of the total polyhydric alcohol components, preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, or even 100 mol%. When two or more diols are used, the total amount thereof is preferably within the above range.

[0036] It is preferable to use a diol as the main polyhydric alcohol component constituting the polyester resin and as the secondary polyhydric alcohol component. Preferred diol components include alkylene glycols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,10-decamethylene glycol, and 1,12-dodecanediol; diols having a cycloalkane structure such as 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, and 1,4-cyclohexanediethanol; diethylene glycol, triethylene glycol, and the like. Examples of suitable diols include oligoalkylene ether glycols, such as polyethylene glycol and tetraethylene glycol; polyalkylene ether glycols, such as polyethylene glycol, polytrimethylene glycol, and polytetramethylene glycol; and diols having an aromatic structure, such as hydroquinone, 4,4'-dihydroxybisphenol, 1,4-bis(β-hydroxyethoxy)benzene, 1,4-bis(β-hydroxyethoxyphenyl)sulfone, bis(p-hydroxyphenyl)ether, bis(p-hydroxyphenyl)sulfone, bis(p-hydroxyphenyl)methane, 1,2-bis(p-hydroxyphenyl)ethane, bisphenol A, bisphenol C, 2,5-naphthalenediol, and glycols obtained by adding ethylene oxide to these glycols. The glycols may also contain a substituent in the molecular chain. Two or more of these may also be used in combination.

[0037] The main polyhydric alcohol component constituting the polyester resin is preferably an alkylene glycol, more preferably ethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, or 1,4-cyclohexanedimethanol.

[0038] A small amount of a trihydric or higher polyhydric alcohol may be used in combination with these glycols, and tri- or tetrahydric polyhydric alcohols are preferred. Examples of trihydric or higher polyhydric alcohols include trimethylolmethane, trimethylolethane, trimethylolpropane, pentaerythritol, glycerol, and hexanetriol.

[0039] The trihydric or higher polyhydric alcohol is preferably 20 mol% or less, more preferably 10 mol% or less, and even more preferably 5 mol% or less, of the total polyhydric alcohol components. When two or more trihydric or higher polyhydric alcohols are used, the total amount thereof is preferably within the above range.

[0040] The use of a cyclic ester in combination is also permitted. Examples of cyclic esters include ε-caprolactone, β-propiolactone, β-methyl-β-propiolactone, δ-valerolactone, glycolide, and lactide. Examples of ester-forming derivatives of polyhydric alcohols include esters of polyhydric alcohols with lower aliphatic carboxylic acids such as acetic acid.

[0041] The cyclic ester is preferably 20 mol % or less, more preferably 10 mol % or less, and even more preferably 5 mol % or less, based on the total of all polycarboxylic acid components and all polyhydric alcohol components. When two or more cyclic esters are used, the total amount thereof is preferably within the above range.

[0042] The catalyst for polycondensation used in producing the polyester resin is not particularly limited, but examples thereof include diantimony trioxide, antimony pentoxide, antimony acetate, antimony glycolate, germanium dioxide, organic titanium compounds, and aluminum compounds. Among these, diantimony trioxide, germanium dioxide, aluminum compounds, and titanium compounds are preferred in terms of the transparency of the resulting polyester and ease of availability. These may be used alone or in combination of two or more.

[0043] The total content of antimony, titanium, germanium, and aluminum in the polyester resin is preferably 2 to 1000 ppm by mass, more preferably 5 to 500 ppm by mass, even more preferably 10 to 300 ppm by mass, and particularly preferably 50 to 250 ppm by mass. If it exceeds 500 ppm by mass, the intrinsic viscosity retention of the polyester resin composition described below may be insufficient.

[0044] The polyester composition of the present invention may contain a phosphorus compound as needed. Examples of phosphorus compounds used in the present invention include phosphoric acid, phosphorous acid, phosphonic acid, and derivatives thereof. Specific examples include phosphoric acid, trimethyl phosphate, tributyl phosphate, triphenyl phosphate, monomethyl phosphate, dimethyl phosphate, monobutyl phosphate, dibutyl phosphate, phosphorous acid, trimethyl phosphite, tributyl phosphite, methylphosphonic acid, dimethyl methylphosphonate, dimethyl ethylphosphonate, ethyl diethylphosphonoacetate, dimethyl phenylphosphonate, diethyl phenylphosphonate, and diphenyl phenylphosphonate. The inclusion of a phosphorus compound in the polyester composition can improve heat resistance. These compounds may be used alone or in combination.

[0045] The intrinsic viscosity of the polyester resin is preferably 0.56 to 0.90 dL / g, more preferably 0.60 to 0.80 dL / g, and even more preferably 0.65 to 0.75 dL / g. If the intrinsic viscosity of the polyester resin is less than 0.56 dL / g, friction between the polyester resin pellets and the pneumatic transport piping may result in the generation of a large amount of fines during pneumatic transport of the polyester resin. Furthermore, if an attempt is made to produce a polyester resin with an intrinsic viscosity exceeding 0.62 dL / g by melt polymerization alone, the economic viability may be reduced. Therefore, when a polyester resin exceeding 0.62 dL / g is required, it is preferable to polymerize the polyester resin obtained by melt polymerization using a solid-state polymerization method.

[0046] The polyester resin can be produced, for example, through an esterification step (or transesterification step) in which a polycarboxylic acid component and a polyhydric alcohol component are transferred to an esterification reaction tank and subjected to an esterification reaction, followed by a melt polycondensation step in which the obtained low molecular weight material is transferred to a polycondensation reaction tank and subjected to a melt polycondensation reaction, and further, if necessary, a heat treatment step such as solid-state polymerization.

[0047] The esterification step is carried out, for example, using one or more esterification reaction vessels under stirring. When a single esterification reaction vessel is used, the reaction temperature is usually 240 to 280°C, and the pressure relative to atmospheric pressure is usually 0 to 400 kPa (0 to 4 kg / cm). 2 G), the reaction time is usually 1 to 10 hours. The esterification reaction product obtained in the esterification step preferably has an esterification reaction rate of 95% or more.

[0048] The melt polycondensation step can be carried out, for example, by a continuous or batch system using one or more polycondensation reaction vessels, and is carried out while gradually reducing the pressure from normal pressure and distilling out the polyhydric alcohol such as ethylene glycol produced under heating and stirring. For example, in the case of a batch system using a single polycondensation reaction vessel, the reaction temperature is usually 250 to 290°C, the final absolute pressure, which is gradually reduced from normal pressure, is usually 1.3 to 0.013 kPa (10 to 0.1 Torr), and the reaction time is usually 1 to 20 hours.

[0049] The intrinsic viscosity of the polyester resin can be adjusted by using the stirring torque of the polymer as an indicator of the end point of polymerization. When the stirring torque is high, the melt viscosity of the polymer increases, and the intrinsic viscosity also increases. The stirring torque for determining the end point of the polymerization apparatus can be set to achieve the target intrinsic viscosity.

[0050] The resulting polyester resin is discharged in the form of strands from the bottom of the polymerization apparatus and cut with a cutter while being cooled with water. The chip shape can be controlled by adjusting the cutting conditions, so polyester chips with a desired bulk density can be obtained. It is also preferable to filter the polyester resin before discharging it. A filter with a mesh size of about 3 to 20 μm may be used for such filtration.

[0051] In the method for producing a polyester resin, the timing of adding the polymerization catalyst is not particularly limited. That is, the polymerization catalyst may be added at an early stage of the esterification reaction or later. In addition, when the esterification reaction is performed via the polymerization catalyst, the polymerization catalyst is preferably added after the esterification reaction rate reaches 95% or more, more preferably 97% or more.

[0052] In the method for producing a polyester resin, the polymerization catalyst is preferably added as an ethylene glycol solution from the viewpoint of supply accuracy.

[0053] The temperature inside the esterification reactor (reaction system) is usually 240 to 280°C, preferably 255 to 265°C. A temperature below 240°C is undesirable because the oligomer tends to solidify and the reaction rate decreases, while a temperature above 280°C is undesirable because the amount of by-product condensation products of polyhydric glycol components such as diethylene glycol increases and the color of the polyester resin tends to deteriorate. From the viewpoint of polyester production efficiency, it is preferable to limit the number of esterification reactors to five or less.

[0054] The polycondensation reaction of the polyester resin is carried out by melt polycondensation, and may further include a heat treatment step such as solid-state polymerization, if necessary. The solid-state polymerization is preferably carried out by converting the polyester resin obtained by melt polycondensation into a powder or granular form. The powder or granular form refers to pellets, chips, flakes, or powdered polyester, and pellets or chips are preferred.

[0055] The solid-state polymerization is carried out by heating the granular polyester resin at a temperature below the melting point of the polyester resin in an inert gas stream or under reduced pressure. The solid-state polymerization process may be carried out in one stage or in multiple stages.

[0056] The particulate polyester resin to be supplied to the solid-phase polymerization step may be pre-crystallized by heating it to a temperature lower than the temperature at which the solid-phase polymerization is carried out, and then supplied to the solid-phase polymerization step.

[0057] Such a pre-crystallization step may be carried out by heating the granular polyester resin in a dry state at a temperature of usually 120 to 200°C, preferably 130 to 180°C, for 1 minute to 4 hours, or by heating the granular polyester resin in a water vapor atmosphere, a water vapor-containing inert gas atmosphere, or a water vapor-containing air atmosphere at a temperature of usually 120 to 200°C for 1 minute or more.

[0058] Polyester resin may be transported through a transport pipeline to a storage silo or a solid-state polymerization process. If such chips are transported using a forced low-density transport method, for example, using air, the surface of the polyester resin chips may be subjected to a large impact force when they collide with the pipeline, resulting in the generation of a large amount of fine particles or film-like material. Such fine particles and film-like material have the effect of promoting the crystallization of the polyester resin, and if present in large quantities, the transparency of the resulting molded product may be significantly reduced. Therefore, a process for removing such fine particles and film-like material may be added. The method for removing the fines and film-like substances is not limited, but examples thereof include a method of treating the fines and film-like substances using a vibrating sieve process, an air current classification process using an air current, a gravity classification process, etc., which are separately installed as an intermediate process between the solid-state polymerization process and a subsequent process installed after the solid-state polymerization process.

[0059] A stretched film made from the polyester resin composition of the present invention can be improved in properties such as mechanical strength by stretching the sheet-like product obtained by injection molding or extrusion molding. Examples of stretching methods include uniaxial stretching, sequential biaxial stretching, and simultaneous biaxial stretching. Furthermore, a stretched film or sheet-like product made from the polyester resin composition of the present invention can be formed into a cup or tray shape by pressure forming or vacuum forming.

[0060] The present invention includes a method for estimating and distinguishing polyester resins with little discoloration due to processing involving melt-kneading based on the integrated value of chemiluminescence. Since there is a correlation between the integrated value of chemiluminescence and the degree of discoloration due to processing involving melt-kneading, as long as the correlation can be grasped in advance, it is possible to predict the degree of discoloration due to processing involving melt-kneading based on the integrated value of chemiluminescence, even without performing melt-kneading each time. Therefore, it is possible to estimate and distinguish a polyester resin composition with little discoloration due to processing involving melt-kneading based on the integrated value of chemiluminescence, even if the melt-kneading processing is not performed each time.

[0061] If there are multiple polyester resin compositions with known integrated chemiluminescence values, the order of the degree of coloration due to processing involving kneading can be estimated based on the order of the integrated chemiluminescence values. Alternatively, a reference value can be set in advance, and if the integrated chemiluminescence value is below the reference value, it can be determined that the composition is usable as is for processing involving melt-kneading, and if it is equal to or greater than the reference value, it can be determined that the composition is inappropriate for use as is. Furthermore, in the latter case, the composition may be mixed with a polyester resin composition with a lower integrated chemiluminescence value, and processed to reduce the integrated chemiluminescence value, thereby regenerating the composition into a polyester resin composition usable for processing involving melt-kneading. Alternatively, the composition may be diverted to applications where a high degree of coloration is acceptable even when processing involves melt-kneading, such as for melt-molded products containing dyes and / or pigments. Alternatively, the composition may be diverted to applications other than processing involving melt-kneading, such as for use as a chemically recycled raw material.

[0062] The reference value may vary depending on the operating conditions such as temperature and time in the processing involving melt-kneading, the required properties of the product obtained by the processing involving melt-kneading, etc. The reference value may be set in accordance with the required properties of the product obtained by the processing involving melt-kneading, by creating a correlation equation in advance between the integrated value of chemiluminescence and the degree of coloration due to the processing involving melt-kneading.

[0063] The method for evaluating the degree of coloration is not particularly limited, but for example, the color L value and / or color b value in the Hunter Lab color system can be used. [Example]

[0064] [Evaluation method] (1) Intrinsic viscosity (IV) For the IV measurement, the polyester resin was dissolved in a mixed solvent of 1,1,2,2-tetrachloroethane and p-chlorophenol = 1:3 (mass ratio), and the IV was measured using an Ostwald viscometer at 30°C. The intrinsic viscosity retention was calculated using the following formula. Intrinsic viscosity retention rate (%) = 100 × intrinsic viscosity after remixing / intrinsic viscosity before remixing

[0065] (2) The content of specified aluminum and titanium elements in the sample The sample was weighed into a platinum crucible and pre-carbonized on a hot plate up to 400°C. It was then incinerated for 8 hours at 550°C using a Yamato Scientific FO610 electric furnace. After incineration, small amounts of 6.0N hydrochloric acid and hydrofluoric acid were added, and the sample was decomposed on a hot plate and heated until the acid had completely evaporated. After completion of the acid decomposition, the sample was diluted to volume with 20 mL of 1.2N hydrochloric acid, and the resulting solution was used as the measurement solution. Elements contained in an amount of 1 mass ppm or less are omitted. Equipment: SPECTROBLUE manufactured by Hitachi High-Tech Science Corporation Plasma power: 1400W Plasma gas: 13.0 L / min Auxiliary gas: 1.0L / min Nebulizer: Crossflow nebulizer Chamber: Scott Chamber Measurement wavelength: Aluminum 396.152nm, Titanium 334.941nm

[0066] (3) The content of specified antimony and germanium elements in the sample The sample was weighed into a platinum crucible, 5 mL of a 5% yttrium nitrate ethanol solution was added, and the sample was pre-carbonized on a hot plate to 400 °C. The sample was then ashed for 8 hours at 550 °C using a Yamato Scientific FO610 electric furnace. After ashing, 20 mL of 1.2 N hydrochloric acid was added to dissolve the nitrate, creating a measurement solution. The element concentrations in the resulting measurement solution were measured using a high-frequency inductively coupled plasma emission spectrometer under the following conditions, and the element contents in the sample were calculated. Elements present at a concentration of 1 ppm by mass or less were omitted. Equipment: SPECTROBLUE manufactured by Hitachi High-Tech Science Corporation Plasma power: 1400W Plasma gas: 13.0 L / min Auxiliary gas: 1.0L / min Nebulizer: Crossflow nebulizer Chamber: Scott Chamber Measurement wavelength: Antimony 217.581nm, Germanium 265.118nm

[0067] (4) Moisture content measurement Using a Karl Fischer moisture meter (CA-200, manufactured by Mitsubishi Chemical Analytech Co., Ltd.), 0.6 g of sample was measured at 230°C for 5 minutes under a nitrogen gas flow of 250 mL / min, which is a coulometric titration method.

[0068] (5) Color measurement The sample pellets (approximately 50 g) were packed into the measurement cell and the measurement was carried out while rotating. Equipment: Tokyo Denshokusha precision spectrophotometer colorimeter TC-1500SX Measurement method: JIS Z8722 0°-d method Light source: Halogen lamp 12V 50W 2000H Spectral method: grating method 400~700nm / 10nm interval Detector element: Diode array Measurement area: Reflected light 25mmφ Field of view selection: 2 degree field of view Standard light: C Measurement cell: φ35mm, height 25mm, rotating type (pellet) Color system: Hunter Lab color system

[0069] (6) Composition analysis of polyester resin 20 mg of polyester resin was dissolved in 0.6 ml of a mixed solvent of deuterated hexafluoroisopropanol and deuterated chloroform in a volume ratio of 1:9, and the solution was centrifuged. The supernatant was then collected and subjected to H-NMR measurement under the following conditions. Equipment: Fourier transform nuclear magnetic resonance spectrometer (BRUKER, AVANCENEO 600) 1 H resonance frequency: 600.13MHz Lock solvent: deuterated chloroform Flip angle: 30° Data acquisition time: 4 seconds Delay time: 1 second Measurement temperature: 30℃ Number of times accumulated: 128

[0070] (7) Chemiluminescence measurement After drying at 140°C for 16 hours under vacuum, the pellets were stored in a desiccator for one week and then subjected to chemiluminescence measurement under the following conditions. Since the luminescence intensity does not stabilize for several minutes after the start of measurement, the start point of measurement (0 seconds) was set to the point when the luminescence intensity fell below 1000 cps. Sample amount: approx. 200 mg Equipment: Tohoku Electronics Industries Co., Ltd. Chemiluminescence analyzer CLA-FS5, sample chamber CLS-SH2 Measurement temperature: 50~210℃ Heating rate: 20°C / min Measurement time: 2400 seconds (50 to 210°C heating time: 480 seconds, 210°C holding time: 1920 seconds) Measurement atmosphere: Nitrogen gas Gas flow rate: 100 ml / min Measurement wavelength: 300~650nm

[0071] Raw resin used <Polyester resin (A-1)> Recycled polyester resin pellets were used as the polyester resin (A-1). Composition analysis of the recycled polyester resin pellets confirmed that they contained 97 mol% or more of ethylene terephthalate structural units. The recycled polyester resin pellets had an intrinsic viscosity of 0.74 dl / g. The recycled polyester resin pellets also contained 170 ppm by mass of antimony and 2.7 ppm by mass of germanium. Since the aluminum and titanium contents were very small, less than 1 ppm by mass, the aluminum and titanium contents were omitted from Table 1.

[0072] <Polyester resin (A-2)> Recycled polyester resin pellets were used as polyester resin (A-2). Composition analysis of the recycled polyester resin pellets confirmed that they contained 97 mol% or more of ethylene terephthalate structural units. The recycled polyester resin pellets had an intrinsic viscosity of 0.79 dl / g. The recycled polyester resin pellets also contained 175 ppm by mass of antimony and 4.7 ppm by mass of germanium. Since the aluminum and titanium contents were very small, less than 1 ppm by mass, the aluminum and titanium contents were omitted from Table 1.

[0073] <Polyester resin (A-3)> The polyester resin (A-3) was prepared by melt-kneading and extruding the recycled polyester resin pellets (A-1). The sample was vacuum-dried at 140°C for 16 hours to produce a dried polyester with a moisture content of 150 ppm or less. This dried polyester was melted, extruded, and pelletized in a twin-screw extruder under the following conditions. Twin-screw extruder: Technovel KZW15TW-45 / 60MG-NH (-2200) Set temperature: 260℃ (actual temperature 268-270℃) Screw rotation speed: 200 rpm Discharge amount 1.6~2.0kg / h Composition analysis of the polyester resin pellets confirmed that they contained 97 mol% or more of ethylene terephthalate structural units. The intrinsic viscosity of the polyester resin pellets was 0.68 dL / g. The antimony content in the polyester resin pellets was 170 ppm by mass, and the germanium content was 2.7 ppm by mass. Since the aluminum and titanium content was very small, at 1 ppm by mass or less, the aluminum and titanium content is omitted in Table 1.

[0074] <Polyester resin (A-4)> Recycled polyester resin pellets were used as polyester resin (A-4). Composition analysis of the recycled polyester resin pellets confirmed that they contained 97 mol% or more of ethylene terephthalate structural units. The recycled polyester resin pellets had an intrinsic viscosity of 0.75 dl / g. The recycled polyester resin pellets also contained 180 ppm by mass of antimony and 4.4 ppm by mass of germanium. Since the aluminum and titanium contents were very small, less than 1 ppm by mass, the aluminum and titanium contents were omitted from Table 1.

[0075] <Polyester resin (B-1)> Polyester resin B-1: N1 manufactured by Indorama (antimony element content: 260 mass ppm, intrinsic viscosity: 0.79 dL / g)

[0076] Examples 1 to 5, Comparative Examples 1 to 4, Reference Example 1 The polyester resin composition was subjected to a re-kneading treatment, and the physical properties before and after the treatment were evaluated. The results are shown in Table 1. The re-kneading treatment was carried out under the following conditions: Re-mixing processing conditions; The sample was vacuum dried at 140°C for 16 hours to produce a dried polyester with a moisture content of 150 ppm or less. This dried polyester was subjected to a first re-kneading treatment in a twin-screw extruder under the following conditions, and various physical properties were measured. A second re-kneading treatment was then performed, and various physical properties were measured. Twin-screw extruder: Technovel KZW15TW-45 / 60MG-NH (-2200) Set temperature: 260℃ (actual temperature 268-270℃) Screw rotation speed: 200 rpm Discharge amount 1.6~2.0kg / h

[0077] In Reference Example 1 and Comparative Examples 1, 2, and 3, polyester resins B-1, A-1, A-3, and A-4 were used as samples as they were. In Examples 1 to 5 and Comparative Example 4, polyester resin compositions obtained by melt-kneading and pelletizing the blending types and blending ratios shown in Table 1 were used as samples. Prior to melt-kneading, the polyester resins were vacuum-dried at 140°C for 16 hours to produce dried polyesters with a moisture content of 150 ppm or less. This dried polyester was melt-kneaded in a twin-screw extruder under the following conditions to obtain the polyester resin compositions of Examples 1 to 5 and Comparative Example 4. Melt-mixing conditions; Twin-screw extruder: Technovel KZW15TW-45 / 60MG-NH (-2200) Set temperature: 260℃ (actual temperature 268-270℃) Screw rotation speed: 200 rpm Discharge amount 1.6~2.0kg / h

[0078] [Table 1]

[0079] In Examples 1 to 5, by using recycled polyester resin (A) and polyester resin (B) with low average values ​​of chemiluminescence integrated light emission and low average values ​​of chemiluminescence integrated light emission when melt-mixed, polyester resin compositions were obtained that maintained low color L values, which are a measure of brightness, and color b values, which are a measure of yellowness, even after multiple recycling. Note that if the color L value of the pellets is 49.0 or less and the color b value is 8.5 or more, the color of the molded product will be extremely poor.

[0080] On the other hand, in Comparative Examples 1 to 3, by using recovered polyester resin (A) and polyester resin (B) with high average values ​​of the integrated chemiluminescence light emission amount or high average values ​​of the integrated chemiluminescence light emission amount when melt-mixed, a polyester resin composition with a high color b value was obtained when recycled multiple times, although the intrinsic viscosity retention rate was similar to that of the Examples.

[0081] As mentioned above, the increase in the b value due to increased thermal history or early resin deterioration cannot be predicted using intrinsic viscosity, but chemiluminescence can reveal the degree of resin deterioration in the very early stages, so the integrated light intensity is 1.35 x 10 7 The weighted average of the integrated light emission of polyester resin composition or raw material is 1.15 × 10 count or less. 7 It was found that by melt molding a polyester resin composition having a chemiluminescence integrated value of 0.1 or less, a polyester resin composition with a low color b value can be obtained even when subjected to a strong thermal history. It was also found that by selecting a polyester resin composition with a low integrated value of chemiluminescence, a polyester resin composition with a low degree of discoloration due to processing involving a melt-kneading treatment can be selected, that is, a polyester resin composition with a low degree of discoloration due to processing involving a melt-kneading treatment can be identified. [Industrial Applicability]

[0082] As is clear from the above explanation, the present invention can provide a polyester resin composition that exhibits a low degree of discoloration when subjected to an extended thermal history and has excellent recyclability, a method for producing the same, and a method for identifying a polyester resin composition that exhibits a low degree of discoloration due to processing involving melt-kneading.

Claims

1. A method for producing a polyester resin composition, comprising a step of melt-kneading a plurality of types of polyester resins, the plurality of polyester resins includes at least one recycled polyester resin; The integrated value of the chemiluminescence emission intensity of the obtained polyester resin composition measured every second from the start of measurement to 2,400 seconds was 1.35 × 10 ７ is less than or equal to count, A method for producing a polyester resin composition.

2. The weighted average of the integrated values ​​of the chemiluminescence emission intensity measured every second from the start of measurement to 2,400 seconds for the plurality of polyester resins is 1.15 × 10 ７ The method for producing a polyester resin composition according to claim 1, wherein the total weight of the polyester resin composition is 1000 kJ / kg or less.

3. 3. The method for producing a polyester resin composition according to claim 1 or 2, wherein at least some of the plurality of polyester resins contain one or more metal elements selected from the group consisting of antimony, titanium, germanium, and aluminum, and the total content of the metal elements is 2 to 1,000 ppm by mass.

4. The method for producing a polyester resin composition according to claim 3 , wherein at least a part of the metal element is derived from a polymerization catalyst for the polyester resin.

5. The integrated value of the chemiluminescence intensity measured every second from the start of measurement to 2,400 seconds was 1.35 × 10 ７ is less than or equal to count, The polyester resin composition contains a plurality of types of polyester resins, and at least one of the plurality of types of polyester resins is a recycled polyester resin. Polyester resin composition.

6. A method for producing a melt-molded product, using as a raw material a polyester resin composition obtained by the production method according to any one of claims 1 to 4 and / or a polyester resin composition according to claim 5.

7. The method for producing a melt-molded product according to claim 6, wherein the melt-molded product is a hollow molded product or a solid molded product.

8. A method for identifying polyester resins that have little discoloration due to processing involving melt-kneading, based on the integrated value of chemiluminescence.

9. 9. The method of claim 8, wherein the coloration is evaluated by the color L value and / or the color b value in the Hunter Lab color system.

Images