Method for producing polyester film using recycled polyester resin, and polyester film

Abstract

A method for producing a polyester film, the method comprising a step for mixing a recycled polyester resin (A) and a polyester resin (B) containing an aluminum compound and a phosphorus compound, wherein the polyester resin (A) satisfies (1)-(3). (1) The polyester resin (A) contains at least one element selected from antimony, titanium, and germanium. (2) The total contained amount of antimony elements, titanium elements, and germanium elements in the polyester resin (A) is 2-500 mass ppm. (3) The intrinsic viscosity of the polyester resin (A) is 0.5-0.8 dl / g.

Description

Method for producing polyester film using recycled polyester resin and polyester film

[0001] The present invention relates to a method for producing a polyester film containing recycled polyester resin.

[0002] Polyester resins, typified by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and the like, are excellent in transparency, mechanical properties, and chemical properties, 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, blown molded articles manufactured using, for example, polyester resins have become indispensable for the daily lives of humankind. On the other hand, the increased use of blown 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, namely, a recovery and regeneration recycling system, in which used blown molded articles such as polyester bottles are recovered and reused. In the case of polyester films, various proposals have been made to produce films using such recovered polyester resins as raw materials.

[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. Therefore, improvements in this area are needed. In particular, when film is produced, stretched waste such as selvages generated during film production is often reused as raw material resin, and there has been a demand for recovered polyester resins that are less likely to discolor or decrease in molecular weight due to heat melting.

[0005] As a method for solving the above problems, a method of adding a hindered phenol compound to the production of a polyester resin using an antimony compound, a titanium compound, or a germanium compound as a polymerization catalyst is known (see, for example, Patent Documents 1 and 2).

[0006] The methods described in Patent Documents 1 and 2 improve thermal oxidation stability, but further improvement is required from the viewpoint of suppressing deterioration of physical properties when recycled.

[0007] Meanwhile, the applicant has discovered a catalyst with excellent thermal stability. Specifically, the catalyst is comprised of an aluminum compound and a phosphorus compound containing a hindered phenol structure, as described in Patent Documents 3 and 4. However, no studies have 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, and producing the resins into films.

[0008] International Publication No. WO 2013 / 154042 International Publication No. WO 2013 / 154043 International Publication No. WO 2007 / 032325 JP 2006-169432 A

[0009] The present invention has been made to solve the problems of the prior art, and its object is to provide a method for producing a polyester film that, when produced using a used polyester resin in which at least one compound selected from antimony compounds, titanium compounds, and germanium compounds is used as a polymerization catalyst, results in little decrease in strength due to coloration or molecular weight reduction, and that also results in little deterioration even when film scraps are reused, and a polyester film containing the recovered polyester resin.

[0010] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that 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, and melt-molding the mixture, it is possible to produce a polyester film that is highly recyclable and suffers little discoloration or loss in strength.

[0011] That is, the present invention encompasses the following: [Item 1] A method for producing a polyester film, comprising a step of mixing recovered polyester resin (A) with polyester resin (B) containing an aluminum compound and a phosphorus compound, wherein the polyester resin (A) satisfies the following (1) to (3): (1) The polyester resin (A) contains at least one element selected from antimony, titanium, and germanium, (2) the total content of antimony, titanium, and germanium in the polyester resin (A) is 2 to 500 ppm by mass, and (3) the intrinsic viscosity of the polyester resin (A) is 0.5 to 0.8 dl / g.

[0012] [Item 2] The method for producing a polyester film according to Item 1, wherein the polyester resin (B) satisfies the following (4) and (5): (4) the aluminum content in the polyester resin (B) is 5 to 50 ppm by mass, and (5) the phosphorus content in the polyester resin (B) is 5 to 1,000 ppm by mass.

[0013] [Item 3] The method for producing a polyester film according to Item 1 or 2, further comprising melt-mixing the polyester resin (A) and the polyester resin (B) to obtain the polyester resin composition (C).

[0014] [Item 4] The method for producing a polyester film according to any one of Items 1 to 3, further comprising a step of mixing a polyester resin (D).

[0015] [Item 5] A method for producing a polyester film, comprising a step of mixing a polyester resin composition (C) which is a melt mixture of recovered polyester resin (A) and polyester resin (B) containing an aluminum compound and a phosphorus compound, with a polyester resin (D), wherein the polyester resin (A) satisfies the following (1) to (3): (1) the polyester resin (A) contains at least one element selected from antimony, titanium, and germanium; (2) the total content of antimony, titanium, and germanium in the polyester resin (A) is 2 to 500 ppm by mass; and (3) the intrinsic viscosity of the polyester resin (A) is 0.5 to 0.8 dl / g.

[0016] [Item 6] The method for producing a polyester film according to any one of Items 1 to 5, wherein the polyester resin composition (C) has an intrinsic viscosity retention rate of 89% or more.

[0017] [Item 7] The method for producing a polyester film according to any one of Items 1 to 6, wherein the polyester resin (A) has an intrinsic viscosity retention rate of 92% or less.

[0018] [Item 8] The method for producing a polyester film according to any one of Items 1 to 7, wherein the polyester resin (B) has an intrinsic viscosity retention rate of 93% or more.

[0019] [Item 9] The method for producing a polyester film according to any one of Items 1 to 8, wherein the polyester resin (E) constituting the polyester film has an intrinsic viscosity retention rate of 89% or more.

[0020] [Item 10] The method for producing a polyester film according to any one of Items 1 to 9, wherein the polyester resin (A) is 5 to 95 parts by mass per 100 parts by mass of the total of the polyester resin (A) and the polyester resin (B).

[0021] [Item 11] The method for producing a polyester film according to any one of Items 1 to 10, wherein the polyester resin (D) is 5 to 95 parts by mass per 100 parts by mass of the total of the polyester resins (A), (B), and (D).

[0022] [Item 12] The method for producing a polyester film according to any one of Items 1 to 11, wherein the polyester film is a multilayer polyester film consisting of at least two layers, and at least one surface of the polyester film is a layer that does not contain the polyester resin (A).

[0023] [Item 13] The method for producing a polyester film according to any one of Items 1 to 12, wherein the phosphorus compound has a phosphorus element and a phenol structure in the same molecule.

[0024] [Item 14] The method for producing a polyester film according to any one of Items 1 to 13, wherein the polyester resin (A) contains at least antimony and germanium.

[0025] [Item 15] The method for producing a polyester film according to any one of Items 1 to 14, wherein the polyester resin (A) contains at least isophthalic acid as a copolymerization component.

[0026] [Item 16] The method for producing a polyester film according to Item 4, wherein the polyester resin (D) contains a melt resistivity adjuster.

[0027] [Item 17] A polyester film composed of a recovered polyester resin (A) and a resin (E) containing a polyester resin (B) containing an aluminum compound and a phosphorus compound, wherein the polyester resin (A) satisfies the following (1) to (3): (1) The polyester resin (A) contains at least one element selected from antimony, titanium, and germanium, (2) the total content of antimony, titanium, and germanium in the polyester resin (A) is 2 to 500 ppm by mass, and (3) the intrinsic viscosity of the polyester resin (A) is 0.5 to 0.8 dl / g.

[0028] [Item 18] The polyester film according to Item 17, wherein the polyester resin (B) satisfies the following (4) and (5): (4) the content of aluminum element in the polyester resin (B) is 5 to 50 ppm by mass, and (5) the content of phosphorus element in the polyester resin (B) is 5 to 1000 ppm by mass.

[0029] [Item 19] The polyester film according to item 17 or 18, wherein the polyester resin (E) further contains a polyester resin (D).

[0030] [Item 20] The polyester film according to any one of Items 17 to 19, wherein the polyester resin (E) has an intrinsic viscosity retention rate of 89% or more.

[0031] [Item 21] A polyester film containing at least antimony, germanium, and aluminum elements in a polyester resin constituting the film.

[0032] [Item 22] The polyester film according to Item 21, wherein the polyester resin constituting the film contains isophthalic acid as a copolymerization component.

[0033] According to the present invention, even when recycled polyester is used as a raw material, it is possible to obtain a polyester film with little deterioration of the resin, and with little decrease in molecular weight, coloration, or mechanical strength.

[0034] In the present invention, a polyester film is produced by mixing the recovered polyester resin (A) with a polyester resin (B) containing an aluminum compound and a phosphorus compound. The resulting polyester film has excellent characteristics such as minimal reduction in molecular weight, coloration, and / or mechanical strength.

[0035] [Polyester Resin (A)] The polyester resin (A) is a recycled polyester resin that has been used in some form. Its shape is not limited, but it is preferably in a form that is easily mixed with the polyester resin (B). Examples of the shape include chips, flakes, and powder. The recycled polyester resin (A) is a resin that has been melted to produce a polyester molded product. Examples include PET bottles and trays collected from the streets, fibers and products, waste products before production, B-grade products that were not shipped to the market, edge portions that are gripped during film stretching, slit offcuts, and molded products returned due to complaints. These may be single items with known origins, such as recycled PET bottles or film edge portions, or mixtures of these from different origins.

[0036] The polyester resin (A) preferably contains 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more, of ethylene terephthalate structural units. As the polycarboxylic acid component other than terephthalic acid and the polyhydric alcohol component other than ethylene glycol, the components described below for the polyester resin (B) can be used.

[0037] For quality control, it is preferable to use polyethylene terephthalate resin as the polyester resin (A).In this case, the polyester resin (A) may contain an isophthalic acid component in the copolymerization components, and when the total acid components are 100 mol%, the lower limit of the content of the isophthalic acid component is preferably 0.02 mol%, more preferably 0.05 mol%, even more preferably 0.1 mol%, particularly preferably 0.2 mol%, and most preferably 0.3 mol%.The upper limit is preferably 5.0 mol%, more preferably 4.0 mol%, even more preferably 3.0 mol%, particularly preferably 2.5 mol%, and most preferably 2.0%.

[0038] Diethylene glycol is not only contained in the polyester resin as a by-product of ethylene glycol during polyester polymerization, but may also be added during polymerization to adjust crystallization.The lower limit of the content of the diethylene glycol component in the polyester resin (A) is preferably 0.5 mol%, more preferably 0.8 mol%, even more preferably 1.0 mol%, particularly preferably 1.2 mol%, and most preferably 1.4 mol%, when the total glycol components are taken as 100 mol%.The upper limit is preferably 5.0 mol%, more preferably 4.0 mol%, even more preferably 3.5 mol%, and particularly preferably 3.0 mol%.

[0039] The upper limit of the copolymerization components other than isophthalic acid and diethylene glycol in the polyester resin (A), as acid components and glycol components, is preferably 3.0 mol %, more preferably 2.5 mol %, and even more preferably 2.0 mol %, when the total acidic content is 100 mol % and the total glycol components are 100 mol %.

[0040] The total amount of copolymerization components of polyester resin (A), when the total of all acids and all glycol components is taken as 200 mol%, is the sum of acid components and glycol components. The lower limit is preferably 0.5 mol%, more preferably 1.0 mol%, even more preferably 1.5 mol%, and particularly preferably 2.0 mol%. The upper limit is preferably 7.0 mol%, more preferably 6.0 mol%, even more preferably 5.0 mol%, and particularly preferably 4 mol%. If the upper limit is exceeded, the heat resistance and mechanical strength of the resulting polyester film may be reduced, and in order to prevent this, the amount of recovered polyester resin (A) added may be limited.

[0041] The polyester resin (A) contains at least one element selected from antimony, titanium, and germanium, that is, the polyester resin (A) is preferably produced using a catalytic amount of at least one polymerization catalyst selected from antimony compounds, titanium compounds, and germanium compounds.

[0042] The total content of antimony, titanium, and germanium elements in the polyester resin (A) is 2 to 500 ppm by mass, preferably 5 to 400 ppm by mass, more preferably 10 to 300 ppm by mass, and even more preferably 50 to 250 ppm by mass. If it exceeds 500 ppm by mass, the intrinsic viscosity retention rate of the polyester resin composition (C) described below may become insufficient. In this specification, ppm by mass means 10 ppm by mass. －４ The percentages are expressed as mass %.

[0043] The polyester resin (A) may contain a colorant, lubricant particles, an ultraviolet absorber, a melt resistivity adjuster, an antistatic agent, an antioxidant, a heat stabilizer, and the like, which will be described later.

[0044] The intrinsic viscosity of the polyester resin (A) is preferably 0.5 to 0.8 dl / g, more preferably 0.55 to 0.75 dl / g, and even more preferably 0.57 to 0.73 dl / g. If the intrinsic viscosity of the polyester resin (A) is less than the above range, the mechanical strength and impact resistance of the polyester film produced using the polyester resin (A) may be insufficient. On the other hand, if the intrinsic viscosity of the polyester resin (A) exceeds the above range, localized shear heat may increase when the polyester resin (A) is mixed and melted with the polyester resin (B), resulting in resin deterioration, or the stress during stretching may increase, making film production difficult. Furthermore, there may be stricter restrictions on the intrinsic viscosity and amount of the polyester resin (B) to be mixed.

[0045] The intrinsic viscosity retention of the polyester resin (A) is preferably 92% or less, more preferably 91% or less, even more preferably 90% or less, and particularly preferably 89% or less. If the intrinsic viscosity retention of the polyester resin (A) exceeds 92%, the effect of improving recyclability by blending the polyester resin (B) may be insufficient. The method for measuring the intrinsic viscosity retention will be described later. The intrinsic viscosity retention of the polyester resin (A) is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more. If the intrinsic viscosity retention is below 70%, the addition of the polyester resin (B) may not be effective enough, or the amount of polyester resin (A) used may need to be kept low, which may reduce the significance of using recycled polyester.

[0046] When the polyester resin (A) is a PET bottle collected from the street, the amount of CT (cyclic trimer) contained in the polyester resin (A) is preferably 9000 ppm by mass or less, more preferably 8000 ppm by mass or less, and even more preferably 7500 ppm by mass or less. 7000 ppm by mass or less is particularly preferred. The CT content is preferably 4000 ppm by mass or more, more preferably 4500 ppm by mass or more, and even more preferably 5000 ppm by mass or more.

[0047] The polyester resin (A) is preferably composed solely of a polyester resin produced using at least one polymerization catalyst selected from an antimony compound, a titanium compound, and a germanium compound, but may also contain a polyester resin produced using a polymerization catalyst consisting of an aluminum compound and a phosphorus compound. The polyester resin produced using at least one polymerization catalyst selected from an antimony compound, a titanium compound, and a germanium compound in the polyester resin (A) preferably accounts for more than 50 mass%, preferably 70 mass% or more, and more preferably 80 mass% or more.

[0048] The polyester resin (A) may be pelletized by melting recovered molded products, but is preferably in the pulverized state without melting. From the viewpoint of ease of handling, the pulverized product preferably has a shape such that the distance between the longest two points is preferably 3 to 30 mm, more preferably 5 to 20 mm. This value is the average value measured for 100 g of pulverized product and 20 large pulverized products.

[0049] [Polyester Resin (B)] The polyester resin (B) contains an aluminum compound and a phosphorus compound. That is, the polyester resin (B) is preferably produced using a catalytic amount of a polymerization catalyst consisting of an aluminum compound and a phosphorus compound.

[0050] The polyester resin (B) is preferably a polymer formed from at least one selected from polycarboxylic acids and their ester-forming derivatives and at least one selected from polyhydric alcohols and their ester-forming derivatives.

[0051] <Polycarboxylic acid component> The main polycarboxylic acid component constituting the polyester resin (B) 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, and even more preferably 90 mol% or more of dicarboxylic acid. When two or more dicarboxylic acids are used, the total amount thereof is preferably within the above range.

[0052] Examples of dicarboxylic acids include saturated aliphatic dicarboxylic acids such as 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, 1,3-cyclobutanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,5-norbornanedicarboxylic acid, and dimer acid, and ester-forming derivatives thereof; and unsaturated aliphatic dicarboxylic acids such as fumaric acid, maleic acid, and itaconic acid. or ester-forming derivatives thereof; 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, or ester-forming derivatives thereof.

[0053] More preferably, the main polycarboxylic acid component is 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, and ester-forming derivatives thereof.

[0054] 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 or its ester-forming derivative and naphthalenedicarboxylic acid or its ester-forming derivative is more than 50 mol%, preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more of the total polycarboxylic acid components.

[0055] Particularly preferred dicarboxylic acids are terephthalic acid, 2,6-naphthalenedicarboxylic acid, and ester-forming derivatives thereof. If necessary, other dicarboxylic acids may be used as constituent components.

[0056] As polycarboxylic acids other than these dicarboxylic acids, trivalent or higher polycarboxylic acids or hydroxycarboxylic acids may be used in small amounts, with trivalent to tetravalent polycarboxylic acids being preferred. Examples of 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.

[0057] 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 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 hydroxycarboxylic acids are used, the total content is preferably within the above range.

[0058] Examples of the ester-forming derivatives of polycarboxylic acids or hydroxycarboxylic acids include alkyl esters, acid chlorides, and acid anhydrides thereof.

[0059] <Polyhydric alcohol component> The main polyhydric alcohol component constituting the polyester resin (B) is preferably glycol. "The main polyhydric alcohol component is glycol" means that the glycol 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, and even more preferably 90 mol% or more. When two or more glycols are used, the total amount thereof is preferably within the above range.

[0060] Examples of glycols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, triethylene 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, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediethanol, 1,10-decamethylene glycol, and 1,12-dodecanediol. aliphatic glycols exemplified by polyethylene glycol, polytrimethylene glycol, polytetramethylene glycol, and the like; aromatic glycols exemplified by 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, glycols in which ethylene oxide is added to these glycols, and the like.

[0061] Among these glycols, alkylene glycols are preferred, and more preferably ethylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, or 1,4-cyclohexanedimethanol. The alkylene glycols may contain a substituent or an alicyclic structure in the molecular chain, and two or more types may be used simultaneously.

[0062] A small amount of a trihydric or higher polyhydric alcohol may be used in combination with these polyhydric alcohols other than glycols, and trihydric to tetrahydric polyhydric alcohols are preferred. Examples of trihydric or higher polyhydric alcohols include trimethylolmethane, trimethylolethane, trimethylolpropane, pentaerythritol, glycerol, and hexanetriol.

[0063] The content of trihydric or higher polyhydric alcohols relative to the total polyhydric alcohol 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 trihydric or higher polyhydric alcohols are used, the total content thereof is preferably within the above range.

[0064] 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, lactide, etc. Examples of ester-forming derivatives of polyhydric alcohols include esters of polyhydric alcohols with lower aliphatic carboxylic acids such as acetic acid.

[0065] 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.

[0066] The composition of polyester resin (B) may be determined in accordance with the composition of the film to be produced, taking into consideration the composition of polyester resin (A). For example, when polyester resin (A) is mainly made from recycled beverage bottles, the main structural unit of polyester resin (A) is ethylene terephthalate, and therefore, when a polyethylene terephthalate film is to be produced, polyester resin (B) is also polyethylene terephthalate. In this case, polyester resin (B) preferably contains 90% or more, more preferably 95% or more, and even more preferably 97% or more of a component derived from ethylene terephthalate monomer.

[0067] On the other hand, if the film to be produced is a copolymer film such as a heat-shrinkable film or a film for molding, the polyester resin (B) is preferably a copolymer polyester or a polyester resin other than polyethylene terephthalate. Examples include ethylene terephthalate isophthalate copolymer, ethylene butylene terephthalate copolymer, ethylene 2,2-dimethylpropylene terephthalate copolymer (neopentyl glycol added to the glycol component), ethylene 2,2'-oxydiethylene copolymer (diethylene glycol added to the glycol component), ethylene 1,4-cyclohexanedimethylene terephthalate copolymer (1,4-cyclohexanedimethanol added to the glycol component), polyethylene isophthalate, polybutylene terephthalate, poly 2,2-dimethylpropylene terephthalate, 2,2'-oxydiethylene terephthalate, 1,4-cyclohexanedimethylene terephthalate, and the like, as well as copolymers of these with other components.

[0068] The polyester resin (B) is preferably a polymer composed 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 composed of two or more of the above monomers, more preferably polyethylene terephthalate or a copolymer composed of ethylene terephthalate and at least one of the above monomers other than ethylene terephthalate, and particularly preferably polyethylene terephthalate.

[0069] <Polymerization Catalyst> As described above, the polyester resin (B) is preferably produced using a polymerization catalyst comprising an aluminum compound and a phosphorus compound.

[0070] (Aluminum Compound) The aluminum compound constituting the polymerization catalyst for polyester resin (B) is not limited as long as it is soluble in a solvent, and known aluminum compounds can be used without limitation. Examples of the aluminum compound include carboxylates such as aluminum formate, aluminum acetate, basic aluminum acetate, aluminum propionate, aluminum oxalate, aluminum acrylate, aluminum laurate, aluminum stearate, aluminum benzoate, aluminum trichloroacetate, aluminum lactate, aluminum citrate, aluminum tartrate, and aluminum salicylate; inorganic acid salts such as aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride, aluminum nitrate, aluminum sulfate, aluminum carbonate, aluminum phosphate, and aluminum phosphonate; aluminum methoxide, aluminum ethoxide, aluminum n-propoxide, and aluminum aluminum alkoxides such as aluminum isopropoxide, aluminum n-butoxide, and aluminum t-butoxide; chelate compounds such as aluminum acetylacetonate, aluminum ethylacetoacetate, and aluminum ethylacetoacetate di-iso-propoxide; organoaluminum compounds such as trimethylaluminum and triethylaluminum and partial hydrolysates thereof; reaction products of aluminum alkoxides or aluminum chelate compounds with hydroxycarboxylic acids; aluminum oxide, ultrafine aluminum oxide, aluminum silicate, and composite oxides of aluminum with titanium, silicon, zirconium, alkali metals, alkaline earth metals, etc.Of these, at least one selected from carboxylates, inorganic acid salts, and chelate compounds is preferred, and among these, at least one selected from aluminum acetate, basic aluminum acetate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride, and aluminum acetylacetonate is more preferred, at least one selected from aluminum acetate, basic aluminum acetate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride, and aluminum acetylacetonate is even more preferred, at least one selected from aluminum acetate and basic aluminum acetate is particularly preferred, and basic aluminum acetate is most preferred.

[0071] The aluminum compound is preferably an aluminum compound that is soluble in a solvent such as water or glycol. Solvents that can be used in the production of polyester resin (B) include water and alkylene glycols. Examples of alkylene glycols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, trimethylene glycol, ditrimethylene glycol, tetramethylene glycol, ditetramethylene glycol, and neopentyl glycol. Preferably, the solvent is at least one selected from water, ethylene glycol, trimethylene glycol, and tetramethylene glycol, and more preferably water or ethylene glycol.

[0072] The aluminum content in the polyester resin (B) is preferably 5 to 50 ppm by mass, more preferably 7 to 40 ppm by mass, even more preferably 10 to 30 ppm by mass, and particularly preferably 15 to 25 ppm by mass. If the aluminum content is less than 5 ppm by mass, the polymerization activity may not be fully exerted. On the other hand, if the aluminum content exceeds 50 ppm by mass, the amount of aluminum-based foreign matter may increase.

[0073] Furthermore, when cost is a priority, the aluminum content in the polyester resin (B) is preferably 9 to 20 ppm by mass, more preferably 9 to 19 ppm by mass, even more preferably 10 to 17 ppm by mass, and particularly preferably 12 to 17 ppm by mass. If the aluminum content is less than 9 ppm by mass, the polymerization activity may not be fully exerted. On the other hand, if the aluminum content exceeds 20 ppm by mass, the amount of aluminum-based foreign matter may increase in relation to the phosphorus content described below, and in addition, the cost of the catalyst increases.

[0074] (Phosphorus Compound) The phosphorus compound constituting the polymerization catalyst for polyester resin (B) is not particularly limited, but the use of a phosphonic acid-based compound or a phosphinic acid-based compound is preferred because it has a significant effect of improving catalytic activity, and among these, the use of a phosphonic acid-based compound is more preferred because it has a particularly significant effect of improving catalytic activity.

[0075] Among the above phosphorus compounds, phosphorus compounds having a phosphorus element and a phenol structure in the same molecule are preferred. There are no particular limitations on the phosphorus compound as long as it has a phosphorus element and a phenol structure in the same molecule, but using one or more compounds selected from the group consisting of phosphonic acid compounds having a phosphorus element and a phenol structure in the same molecule and phosphinic acid compounds having a phosphorus element and a phenol structure in the same molecule is preferred because it has a significant effect of improving the catalytic activity, and using one or more phosphonic acid compounds having a phosphorus element and a phenol structure in the same molecule is even more preferred because it has a significantly significant effect of improving the catalytic activity.

[0076] Furthermore, examples of phosphorus compounds having a phosphorus element and a phenol structure in the same molecule include P(=O)R 1 (OR 2 ) (OR 3 ) and P(=O)R 1 R 4 (OR 2 ) and the like. 1 represents a hydrocarbon group having 1 to 50 carbon atoms containing a phenol moiety, a hydrocarbon group having 1 to 50 carbon atoms and a phenol structure and a substituent such as a hydroxyl group, a halogen group, an alkoxyl group, or an amino group. 4represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, or a hydrocarbon group having 1 to 50 carbon atoms containing a substituent such as a hydroxyl group, a halogen group, an alkoxyl group, or an amino group. 2 , R 3 R each independently represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, or a hydrocarbon group having 1 to 50 carbon atoms containing a substituent such as a hydroxyl group or an alkoxyl group. However, the hydrocarbon group may contain a branched structure, an alicyclic structure such as cyclohexyl, or an aromatic ring structure such as phenyl or naphthyl. 2 and R 4 The ends of may be bonded together.

[0077] Examples of phosphorus compounds having a phosphorus element and a phenol structure in the same molecule include p-hydroxyphenylphosphonic acid, dimethyl p-hydroxyphenylphosphonate, diethyl p-hydroxyphenylphosphonate, diphenyl p-hydroxyphenylphosphonate, bis(p-hydroxyphenyl)phosphinic acid, methyl bis(p-hydroxyphenyl)phosphinate, phenyl bis(p-hydroxyphenyl)phosphinate, p-hydroxyphenylphosphinic acid, methyl p-hydroxyphenylphosphinate, and phenyl p-hydroxyphenylphosphinate.

[0078] In addition to the above examples, examples of phosphorus compounds having a phosphorus element and a phenol structure in the same molecule include phosphorus compounds having a phosphorus element and a hindered phenol structure (such as a phenol structure in which an alkyl group having a tertiary carbon (preferably an alkyl group having a tertiary carbon at the benzylic position, such as a t-butyl group or a thexyl group; a neopentyl group, etc.) is bonded to one or two ortho-positions of a hydroxyl group) in the same molecule. Phosphorus compounds having a phosphorus element and a structure represented by the following formula A in the same molecule are preferred, and among these, dialkyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate represented by the following formula B is more preferred. The phosphorus compound used in the production of polyester resin (B) is preferably dialkyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate represented by the following formula B, but may also include modified forms of dialkyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate. Details of the modified form will be described later.

[0079]

[0080] (In (Chemical Formula A), * represents a bond.)

[0081]

[0082] (In (Chemical Formula B), X 1 , X 2 respectively represent hydrogen and an alkyl group having 1 to 4 carbon atoms.

[0083] In this specification, a polyester resin in which at least one type of hindered phenol structure can be detected by P-NMR measurement of a solution dissolved in a hexafluoroisopropanol-based solvent is said to "have a hindered phenol structure." In other words, polyester resin (B) is preferably a polyester resin produced using a phosphorus compound having a phosphorus element and a hindered phenol structure in the same molecule as a polymerization catalyst. A method for detecting the hindered phenol structure in polyester resin (B) (P-NMR measurement method) will be described later.

[0084] In the above (Chemical Formula B), X 1 , X 2is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably an alkyl group having 1 to 2 carbon atoms. In particular, an ethyl ester having 2 carbon atoms is preferred because Irganox 1222 (manufactured by BASF) is commercially available and easily available.

[0085] The phosphorus compound is preferably heat-treated in a solvent before use. Details of the heat treatment will be described later. When the phosphorus compound is dialkyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, which is the phosphorus compound represented by the above (Chemical Formula B), the heat treatment causes a partial structural change in the dialkyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, which is the phosphorus compound represented by the above (Chemical Formula B). For example, the change occurs due to elimination of the t-butyl group, hydrolysis of the ethyl ester group, and a hydroxyethyl ester exchange structure (ester exchange structure with ethylene glycol). Therefore, in the present invention, the phosphorus compound includes structurally changed phosphorus compounds in addition to dialkyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate represented by the above (Chemical Formula B). Elimination of the t-butyl group occurs significantly at high temperatures during the polymerization process.

[0086] The following shows nine phosphorus compounds in which the structure of part of 3,5-di-tert-butyl-4-hydroxybenzyl diethyl phosphonate is changed when 3,5-di-tert-butyl-4-hydroxybenzyl diethyl phosphonate is used as the phosphorus compound. The amount of each phosphorus compound whose structure has changed in glycol solution can be quantified by P-NMR measurement.

[0087]

[0088] Therefore, the phosphorus compound in the present invention may include not only dialkyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate but also modified products of dialkyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate represented by the nine chemical formulas above.

[0089] When Irganox 1222 is used as the phosphorus compound, the polyester resin contains residues of the nine phosphorus compounds shown in Table 1 below. When at least one of the nine hindered phenol structures shown in Table 1 is detected by P-NMR measurement, the polyester resin (B) can be said to be a polyester resin produced using a phosphorus compound having a phosphorus element and a hindered phenol structure in the same molecule as a polymerization catalyst. By using a phosphorus compound having a hindered phenol structure, sufficient polymerization activity can be exhibited while reducing catalyst costs.

[0090]

[0091] In the present invention, it is preferable that at least one of the above formulas 1, 4, and 7 is contained.

[0092] The phosphorus content in polyester resin (B) is preferably 5 to 1000 ppm by mass, more preferably 10 to 500 ppm by mass, even more preferably 15 to 200 ppm by mass, particularly preferably 20 to 100 ppm by mass, and most preferably 30 to 50 ppm by mass. If the phosphorus content is less than 5 ppm by mass, there is a risk of a decrease in polymerization activity and an increase in the amount of aluminum-based foreign matter. On the other hand, if the phosphorus content exceeds 1000 ppm by mass, there is a risk of a decrease in polymerization activity and an increase in the amount of phosphorus compound added, which may increase catalyst costs.

[0093] When cost is a major consideration, the phosphorus content in polyester resin (B) is preferably 13 to 31 ppm by mass, more preferably 15 to 29 ppm by mass, and even more preferably 16 to 28 ppm by mass. If the phosphorus content is less than 13 ppm by mass, the polymerization activity may decrease and the amount of aluminum-based foreign matter may increase. On the other hand, if the phosphorus content exceeds 31 ppm by mass, the polymerization activity may decrease and the amount of phosphorus compound added may increase, resulting in increased catalyst costs.

[0094] In the polyester resin (B), the molar ratio of phosphorus to aluminum (hereinafter referred to as the "remaining molar ratio of phosphorus to aluminum" to distinguish it from the "additional molar ratio of phosphorus to aluminum" described below) is preferably 1.00 to 5.00, more preferably 1.10 to 4.00, even more preferably 1.20 to 3.50, and particularly preferably 1.25 to 3.00. As described above, the aluminum and phosphorus in the polyester resin (B) are derived from the aluminum compound and phosphorus compound used as the polymerization catalyst for the polyester resin (B), respectively. By using these aluminum compounds and phosphorus compounds in combination at a specific ratio, a complex having catalytic activity is functionally formed in the polymerization system, thereby enabling sufficient polymerization activity to be exerted. Furthermore, resins produced using a polymerization catalyst composed of an aluminum compound and a phosphorus compound have higher catalyst costs (higher production costs) than polyester resins produced using catalysts such as antimony catalysts. However, by using an aluminum compound and a phosphorus compound in combination at a specific ratio, sufficient polymerization activity can be exerted while reducing catalyst costs. If the residual molar ratio of phosphorus to aluminum is less than 1.00, the thermal stability and thermal oxidation stability may decrease and the amount of aluminum-based foreign matter may increase. On the other hand, if the residual molar ratio of phosphorus to aluminum exceeds 5.00, the amount of phosphorus compound added may become too large, which may increase the catalyst cost. When cost is more important, the residual molar ratio of phosphorus to aluminum is preferably 1.32 to 1.80, more preferably 1.38 to 1.68.

[0095] In addition to the aluminum compounds and phosphorus compounds described above, other polymerization catalysts such as antimony compounds, germanium compounds, and titanium compounds may be used in combination as polymerization catalysts for the production of polyester resin (B) within a range that does not cause problems in the properties, processability, color tone, and other aspects of the polyester resin (B). The content of antimony element in polyester resin (B) is preferably 30 mass ppm or less, the content of germanium element in polyester resin (B) is preferably 10 mass ppm or less, and the content of titanium element in polyester resin (B) is preferably 3 mass ppm or less. However, it is preferable to avoid using the above-mentioned other polycondensation catalysts as much as possible. Note that this does not deny the possibility of trace amounts of other polymerization catalysts being mixed in with residual resin in the polyester resin (B) production equipment.

[0096] The content of aluminum elements in polyester resin (B), which corresponds to aluminum-based foreign matter, is preferably 3000 ppm by mass or less, more preferably 2800 ppm by mass or less, even more preferably 2000 ppm by mass or less, and even more preferably 1500 ppm by mass or less. Aluminum-based foreign matter is caused by the aluminum compound used as a polymerization catalyst and is foreign matter insoluble in polyester resin (B). If the content of aluminum-based foreign matter exceeds the above range, fine foreign matter insoluble in polyester resin (B) may cause deterioration in the quality of the molded product. This also leads to the problem of increased filter clogging during polyester filtration in the polycondensation process and molding process. The preferred lower limit of the content of aluminum elements, which corresponds to aluminum-based foreign matter, is 0 ppm by mass, but due to technical difficulties, it is approximately 300 ppm by mass. As can be seen from the fact that the amount of aluminum element is measured by the measurement method described later in the Examples section of this specification, this index is used to relatively evaluate the amount of aluminum-based foreign matter based on the amount of aluminum element, and does not indicate the absolute value of the amount of aluminum-based foreign matter contained in the polyester resin.

[0097] The intrinsic viscosity of the polyester resin (B) is preferably 0.50 to 0.90 dl / g, more preferably 0.55 to 0.80 dl / g, and even more preferably 0.58 to 0.75 dl / g. If the intrinsic viscosity of the polyester resin (B) is less than the above range, friction between the polyester resin pellets and the pneumatic conveying pipe may result in the generation of a large amount of fine powder (fine). If the intrinsic viscosity of the polyester resin (B) exceeds the above range, localized shear heating may increase when the polyester resin (B) is melt-mixed with the recovered polyester resin (A), resulting in resin deterioration or increased stress during stretching, making film production difficult. The intrinsic viscosity of the polyester resin (B) can be adjusted to match the intrinsic viscosity of the polyester resin (A) so that the intrinsic viscosity of the polyester constituting the film falls within an appropriate range. Note that, when an attempt is made to produce a polyester resin (B) having an intrinsic viscosity exceeding 0.62 dl / g by melt polymerization alone, there is a risk of a decrease in economic efficiency. Therefore, when a polyester resin (B) having an intrinsic viscosity exceeding 0.62 dl / g is required, it is preferable to polymerize the polyester resin (B) obtained by melt polymerization by a solid-state polymerization method.

[0098] When solid-state polymerization is performed, the CT content in the polyester resin (B) is preferably 7000 mass ppm or less, more preferably 6000 mass ppm or less, and even more preferably 5500 mass ppm or less. In reality, the CT content is preferably 2500 mass ppm or more, and more preferably 3000 mass ppm or more.

[0099] The intrinsic viscosity retention of the polyester resin (B) is preferably 93% or more, more preferably 94% or more, and even more preferably 95% or more. If the intrinsic viscosity retention of the polyester resin (B) is less than 93%, the intrinsic viscosity retention of the polyester resin composition (C) will be low, and recyclability may be insufficient. The upper limit of the intrinsic viscosity retention of the polyester resin (B) is preferably 100%, but is approximately 99% due to technical difficulties.

[0100] The method for producing the polyester resin (B) will be described later. The polyester resin (B) is preferably formed into pellets having a longest distance between two points of 2 to 10 mm, more preferably 3 to 6 mm. The shape of the pellets may be spherical, ellipsoidal, round, cubic, or the like.

[0101] The polyester resin (B) may be a resin pelletized after polymerization, or may be a product recovered in the process of molding an article using the polyester resin (B). Examples of the product recovered in the process include products that were not shipped to the market as grade B products, edge portions that are gripped during film stretching, off-cuts from slits, and molded products that have been returned due to complaints, etc. In the case of these recovered products in the process, they are preferably pulverized in the same manner as the polyester resin (A).

[0102] The polyester resin (B) may be used as a master batch (concentrated resin) of additives, like the polyester resin (D) described below.

[0103] [Polyester Resin Composition (C)] In the present invention, a film is produced by mixing polyester resin (A) and polyester resin (B). The mixture of polyester resin (A) and polyester resin (B) is referred to as polyester resin composition (C). In producing the film, polyester resin (A) and polyester resin (B) may be charged into separate inlets of an extruder, or both may be charged into the same inlet, or both may be dry-blended in advance. However, from the viewpoint of handleability, it is also preferable to melt-mix polyester resin (A) and polyester resin (B) to form polyester resin composition (C) and use this for film production. It is preferable to produce polyester resin composition (C) by mixing polyester resin (A) and polyester resin (B) in a mass ratio of 5:95 to 95:5. That is, in polyester resin composition (C), it is preferable that the polyester resin (A) is 5 to 95 parts by mass per 100 parts by mass of the total of polyester resin (A) and polyester resin (B). By keeping the ratio within the above range, coloration and molecular weight reduction of polyester resin composition (C) can be suppressed. In this specification, suppression of coloration refers to suppressing a decrease in the L value (described below) and an increase in the b value (described below) even after repeated recycling (repeated remixing). If the blending ratio of polyester resin (A) exceeds 95 parts by mass, the intrinsic viscosity retention of the polyester resin composition (C) may decrease, resulting in insufficient recyclability. On the other hand, if the blending ratio of polyester resin (A) is less than 5 parts by mass, the coloration suppression effect may saturate and economic efficiency may decrease. Since polyester resin (B) is produced using a polymerization catalyst composed of an aluminum compound and a phosphorus compound, even when the residual molar ratio of phosphorus to aluminum falls within the above-mentioned range, the catalyst cost (production cost) is higher than that of polyester resins produced using catalysts such as antimony catalysts. However, by using polyester resin (A) and polyester resin (B) in combination, production costs can be reduced while also improving recyclability. Increasing the blending ratio of polyester resin (A) can reduce the production cost of the polyester resin composition (C), but the color tone is likely to deteriorate with repeated recycling.On the other hand, if the blending ratio of polyester resin (B) is increased, deterioration in color tone can be suppressed even when the polyester resin composition (C) is recycled many times, but the manufacturing cost may increase. The mass ratio of polyester resin (A) to polyester resin (B) is more preferably 20:80 to 80:20, and even more preferably 25:75 to 75:25.

[0104] The polyester resin composition (C) can be produced by dry-blending the polyester resin (A) and the polyester resin (B). Alternatively, the polyester resin (A) and the polyester resin (B) can be kneaded by melt extrusion to produce the polyester resin composition (C). In this case, the polyester resin (A) and the polyester resin (B) can be separately or dry-blended and then melted and kneaded in 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 to produce the polyester resin composition (C). Among these, twin-screw extruders, four-screw extruders, and single-screw planetary extruders with excellent surface renewal capabilities are preferred. Furthermore, the extruder has at least one, preferably two, and more preferably three, vent ports, and the vent ports are preferably connected to a vacuum system to suppress deterioration of the polyester resin composition (C). Alternatively, after the polymerization of the polyester resin (B) is completed and before the polyester resin (B) is cooled and pelletized, the polyester resin (A) may be added to the molten polyester resin (B) and kneaded to obtain the polyester resin composition (C).

[0105] The polyester resin composition (C) may be formed into a film in a molten state, but is preferably formed into pellets in advance. The shape of the pellets is the same as that of the polyester resin (B).

[0106] The intrinsic viscosity of the polyester resin composition (C) is preferably 0.50 to 0.90 dl / g, more preferably 0.55 to 0.80 dl / g, and more preferably 0.58 to 0.75 dl / g. If the intrinsic viscosity of the polyester resin composition (C) is less than the above range, the mechanical strength and impact resistance of the produced polyester film may be insufficient. If the intrinsic viscosity of the polyester resin composition (C) exceeds the above range, economic efficiency may decrease, localized shear heat may increase during melting in an extruder, causing resin deterioration, or stress during stretching may increase, making film production difficult.

[0107] The intrinsic viscosity retention of the polyester resin composition (C) is preferably 89% or more, more preferably 90% or more, even more preferably 92% or more, particularly preferably 93% or more, and most preferably 94% or more. If the intrinsic viscosity retention of the polyester resin composition (C) is less than 89%, recyclability may be insufficient. The upper limit of the intrinsic viscosity retention of the polyester resin composition (C) is preferably 100%, but is set to about 99% due to technical difficulties. Furthermore, the intrinsic viscosity retention of the polyester resin composition (C) is preferably higher than that of the polyester resin (A). In this specification, when the term "intrinsic viscosity retention" is simply used, it refers to the intrinsic viscosity retention of a remixed product that has been remixed only once.

[0108] It is also a preferred embodiment that the CT amount contained in the re-kneaded product obtained by re-kneading the polyester resin composition (C) once is 6600 ppm by mass or less. It is more preferably 6400 ppm by mass or less, and even more preferably 6000 ppm by mass or less. While the lower limit is not limited, it is preferably about 2500 ppm by mass and 3000 ppm by mass or more due to technical difficulties. If the CT amount exceeds 6600 ppm by mass, the amount of CT precipitated on the film surface increases, causing an increase in haze, which is undesirable depending on the application, or the film-forming equipment may become contaminated with CT, requiring increased cleaning frequency. To achieve the above-mentioned or lower CT amount of the polyester resin composition (C), methods such as using a polyester resin (A) with a low CT amount, reducing the CT amount of the polyester resin (B), or reducing the CT amount of the polyester resin composition (C) can be used. Methods for reducing the CT amount of the polyester resin (B) or the polyester resin composition (C) include carrying out solid-state polymerization, and carrying out heat treatment at 190 to 220°C in a sealed container or under an ethylene glycol-containing gas stream.

[0109] The value (ΔCT) obtained by subtracting the CT amount of a re-kneaded product obtained by re-kneading the polyester resin composition (C) once from the CT amount of a re-kneaded product obtained by re-kneading the polyester resin composition (C) three times is preferably 900 mass ppm or less. It is more preferably 700 mass ppm or less, and even more preferably 600 mass ppm or less. The lower limit is preferably 0 mass ppm, but is about 200 mass ppm due to technical difficulties. If ΔCT exceeds 900 mass ppm, the amount of CT precipitated on the film surface may increase, as described above.

[0110] Furthermore, when polyester resin composition (C) contains polyester resin (B) produced using the above-mentioned Irganox 1222 as the phosphorus compound, P-NMR measurement of polyester resin composition (C) detects at least one of the nine types of hindered phenol structures shown in Table 1. The same applies when a phosphorus compound other than Irganox 1222 having a phosphorus element and a hindered phenol structure in the same molecule is used as the polymerization catalyst.

[0111] [Polyester Resin (D)] When producing a film according to the present invention, it is also a preferred embodiment to further add a polyester resin (D) to produce a polyester film. The polyester resin (D) may have various compositions depending on the film to be produced. For example, when producing a polyethylene terephthalate film, the polyester resin (D) preferably contains copolymer components other than the terephthalic acid component and the ethylene glycol component in total of 10 mol % or less, more preferably 7 mol % or less, and particularly preferably 5 mol % or less. For example, when producing a polyester-based heat-shrinkable film, it is preferable that the polyester resin (D) be a copolymer polyester or other than polyethylene terephthalate, so that the final composition of the heat-shrinkable film is achieved by combining it with the polyester resin (A) and the polyester resin (B). For example, when producing a void-containing polyester film, it may be a polyester copolymerized with polyethylene glycol, polytetramethylene glycol, or the like. The carboxylic acid component and glycol component used in the polyester resin (D) are the same as those exemplified for the polyester resin (B).

[0112] The intrinsic viscosity of polyester resin (D) varies depending on the film to be produced, but is preferably 0.50 to 0.90 dl / g, more preferably 0.55 to 0.80 dl / g, and even more preferably 0.58 to 0.75 dl / g. The catalyst used in polyester resin (D) is one of those listed for polyester resin (A). While a higher viscosity retention rate of polyester resin (D) is preferable, the intrinsic viscosity retention rate may be 92% or less, 91% or less, or even 90% or less, and particularly 89% or less. The viscosity retention rate of polyester resin (D) can be increased by reducing the amount of catalyst, deactivating the catalyst, adding a deterioration inhibitor such as a heat stabilizer, or other methods. The lower limit of the viscosity retention rate of polyester resin (D) is the same as that of polyester resin (A).

[0113] In the production of films, colorants, lubricant particles, UV absorbers, melt resistivity adjusters, antistatic agents, antioxidants, heat stabilizers, etc. are often added, and the polyester resin (D) may be a masterbatch (concentrated resin) of these additives. Examples of lubricant particles include inorganic particles such as silica, calcium carbonate, talc, and kaolin, and organic particles such as cross-linked styrene, cross-linked acrylic resin, and melamine resin. The particle size is preferably 10 nm to 5 μm, and more preferably 50 nm to 3 μm. The particle size can be determined by the Coulter Counter method. Examples of melt resistivity adjusters include combinations of metal compounds such as calcium, magnesium, and potassium with phosphorus compounds.

[0114] When the polyester resin (D) is used as a masterbatch of a melt resistivity adjuster, it is preferable to combine at least one of a magnesium compound and a calcium compound with a phosphorus compound to reduce the melt resistivity, and further to combine an alkali metal compound as needed. In particular, the combination of a magnesium compound with an alkali metal compound and a phosphorus compound is preferable. In addition, the combination of a calcium compound with a phosphorus compound is also preferable because the reaction between the calcium and the phosphorus compound can produce internal particles as a lubricant.

[0115] Known compounds can be used as the magnesium compound and calcium compound. Examples include lower fatty acid salts such as acetates and alkoxides such as methoxides. These compounds may be used alone or in combination of two or more. Magnesium acetate and calcium acetate are particularly preferred.

[0116] The amount of magnesium and calcium elements is preferably 400 to 2700 ppm by mass relative to the polyester resin (D). The amount of magnesium and calcium elements is more preferably 450 to 2500 ppm by mass, and even more preferably 450 to 2000 ppm by mass. Note that the amount of magnesium and calcium elements refers to the amount of each element when only a magnesium compound or only a calcium compound is used, and refers to the total amount when both are used.

[0117] Examples of the alkali metal of the alkali metal compound include lithium, sodium, and potassium. Examples of the alkali metal compound include lower fatty acid salts such as lithium acetate and potassium acetate, and alkoxides such as potassium methoxide. These may be used alone or in combination of two or more. Potassium is preferred as the alkali metal, as it has a significant effect of lowering the melt resistivity. Preferred alkali metal compounds are acetates, with potassium acetate being particularly preferred.

[0118] The amount of alkali metal element is preferably 40 to 270 ppm by mass relative to the polyester resin (D). If the amount of alkali metal element is less than 40 ppm by mass, a large amount of polyester resin (D) must be added to improve film formability during film production. If the amount of alkali metal element exceeds 270 ppm by mass, heat resistance decreases and film discoloration becomes severe, which is undesirable. The amount of alkali metal element is preferably 45 to 250 ppm by mass, and more preferably 45 to 200 ppm by mass. If the amount of magnesium metal element, calcium metal element, or alkali metal element is less than the above range, the melt resistivity increases, and a large amount of polyester resin (D) may need to be added to improve film formability during film production. If the amount exceeds the above range, the amount of insoluble foreign matter generated increases and the film may become more strongly discolored.

[0119] Examples of phosphorus compounds include phosphoric acid, phosphorous acid, hypophosphorous acid, phosphonic acid, phosphinic acid, and ester compounds thereof. 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, dimethyl phenylphosphonate, diethyl phenylphosphonate, diphenyl phenylphosphonate, ethyl diethyl phosphonoacetate, phosphinic acid, methylphosphinic acid, dimethylphosphinic acid, phenylphosphinic acid, diphenylphosphinic acid, methyl dimethylphosphinate, and methyl diphenylphosphinate. Among these, it is preferable to use a phosphoric acid triester having an alkyl group having 2 to 4 carbon atoms. Specific examples include triethyl phosphate, tripropyl phosphate, and tributyl phosphate. These compounds may be used alone or in combination of two or more. In particular, triethyl phosphate is preferred because it is believed to form a complex with magnesium or calcium ions that has a moderately strong interaction, and it can produce a polyester resin with low melt resistivity, little foreign matter, and excellent color tone.

[0120] The amount of phosphorus element is preferably 200 to 4000 ppm by mass relative to the polyester resin (D). If the amount of phosphorus element is less than 200 ppm by mass, the amount of insoluble foreign matter produced may increase. Furthermore, the effect of the magnesium and calcium foreign matter in reducing the melt resistivity is weakened. This may also lead to a decrease in heat resistance and increased coloration of the film. If the amount of phosphorus element exceeds 4000 ppm by mass, the excess phosphorus compound may interact with magnesium and calcium ions, resulting in an increase in the melt resistivity. This is not preferred. The amount of phosphorus element is more preferably 300 ppm by mass or more, and even more preferably 350 ppm by mass or more. Furthermore, the amount of phosphorus element is more preferably 3500 ppm by mass or less, even more preferably 3000 ppm by mass or less, particularly preferably 2500 ppm by mass or less, and most preferably 2000 ppm by mass or less.

[0121] In the polyester resin (D), when the amount of magnesium element relative to the dicarboxylic acid component is m (mol %), the amount of alkali metal element is k (mol %), and the amount of phosphorus element is p (mol %), it is preferable that the molar ratios of magnesium element, alkali metal element, and phosphorus element satisfy the following formula, since this reduces foreign matter and coloration and improves the effect of lowering melt resistivity. 1.5≦(m+k / 2) / p≦5 "(m+k / 2) / p" is more preferably 1.8 or more, even more preferably 2.0 or more, and particularly preferably 2.3 or more. "(m+k / 2) / p" is more preferably 4 or less, even more preferably 3.5 or less. Note that k may be 0.

[0122] In polyester resin (D), when the amount of calcium element relative to the dicarboxylic acid component is c (mol %) and the amount of phosphorus element is p (mol %), it is preferable for the molar ratio of calcium element to phosphorus element to satisfy the following formula, since this reduces foreign matter and coloration and has a greater effect of lowering melt resistivity: 0.01≦c / p≦5, where c / p is more preferably 0.05 or more and 4.0 or less, and even more preferably 0.1 or more and 3.0 or less.

[0123] In the production of polyester resin (D), magnesium compounds, calcium compounds, phosphorus compounds, and alkali metal compounds can be added during polyester polymerization. Addition during the esterification step or between the end of the esterification step and the start of the polymerization step is preferred, as this can prevent the acid component of the polyester from forming a salt with calcium ions, magnesium ions, or alkali metal ions, resulting in foreign matter, and also allows for uniform dispersion in the oligomer. In the production of polyester resin (D), antimony compounds, aluminum compounds, germanium compounds, titanium compounds, and the like can be used as polymerization catalysts.

[0124] A plurality of types of polyester resin (D) may be used. The content of polyester resin (D) is preferably 90 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 70 parts by mass or less, particularly preferably 60 parts by mass or less, and most preferably 50 parts by mass or less, when the total amount of polyester resin (A), polyester resin (B), and polyester resin (D) is 100 parts by mass. If the content exceeds the above range, the economic and environmental significance of using recycled polyester resin is weakened.

[0125] [Polyester Resin Composition (E)] The polyester film can be produced by melt-mixing the polyester resin (A) and the polyester resin (B), or the polyester resin composition (C), as raw polyester resins, and, if necessary, the polyester resin (D), and forming the resulting film according to a conventional method.

[0126] In this way, the polyester resin constituting the film is referred to as polyester resin composition (E). In the case of a multi-layer polyester film described later, the polyester resin constituting the layer containing polyester resin (A) and polyester resin (B) is referred to as polyester resin composition (E). In addition, when polyester resin (D) is not used, polyester resin composition (C) becomes polyester resin composition (E). The composition and intrinsic viscosity of polyester resin composition (E) are the same as those described for polyester resin (D).

[0127] The amount of antimony element in the polyester resin composition (E) is preferably 10 ppm by mass or more, more preferably 15 ppm by mass or more, and even more preferably 20 ppm by mass or more. The amount of antimony element in the polyester resin composition (E) is preferably 250 ppm by mass or less, more preferably 200 ppm by mass or less, and even more preferably 180 ppm by mass or less. By setting the amount within the above range, it is possible to obtain a film that is less prone to deterioration, has high transparency, and has low haze while ensuring economic efficiency.

[0128] The amount of germanium element in the polyester resin composition (E) is preferably 0.1 mass ppm or more, more preferably 0.15 mass ppm or more, and even more preferably 0.20 mass ppm or more. The amount of germanium element in the polyester resin composition (E) is preferably 5 mass ppm or less, more preferably 4 ppm or less, and even more preferably 3 ppm or less. By setting it in the above range, it is possible to ensure economic efficiency and prevent deterioration of the film.

[0129] The amount of aluminum element in the polyester resin composition (E) is preferably 1 mass ppm or more, more preferably 3 mass ppm or more, and even more preferably 5 mass ppm or more. The amount of aluminum element in the polyester resin composition (E) is preferably 20 mass ppm or less, more preferably 17 ppm or less, and even more preferably 15 ppm or less. By setting the amount in the above range, it is possible to obtain a film that is less susceptible to deterioration while ensuring economic efficiency.

[0130] The CT amount in the polyester resin composition (E) is preferably 6600 mass ppm or less, more preferably 6400 mass ppm or less, and even more preferably 6000 mass ppm or less. The CT amount in the polyester resin composition (E) is preferably 3000 mass ppm or more, and more preferably 4000 mass ppm or more.

[0131] The ratio of the amount of antimony element to the amount of aluminum element in the polyester resin composition (E) (Sb amount / Al amount) is preferably 1 or more, more preferably 5 or more, even more preferably 18 or more, and particularly preferably 10 or more. The Sb amount / Al amount in the polyester resin composition (E) is preferably 200 or less, more preferably 170 or less, even more preferably 150 or less, and particularly preferably 130 or less. By setting the ratio within the above range, it is possible to obtain a film that is less prone to deterioration, has high transparency, and has low haze while ensuring economic efficiency.

[0132] In the film production process, in order to stably adhere the molten resin onto the cooling roll using static electricity, the polyester composition (E) must have a melt resistivity of 0.05 × 10８ ~10 x 10 ８ The melt resistivity is preferably 0.1×10 ８ More preferably, 5×10 ８ More preferably, 1×10 or less ８ The following is more preferred. The melt resistivity can be adjusted by the amount and composition of the polyester composition (D) used as a masterbatch of the melt resistivity adjuster. For example, if the polyester resin (A) is derived from PET bottles, it generally does not contain a melt resistivity adjuster, so the amount of polyester resin (D) can be increased, whereas if the polyester resin (A) is derived from recycled film and contains a melt resistivity adjuster, the amount of polyester resin (D) can be decreased. Furthermore, polyester resin (A) may contain a phosphorus compound as a catalyst aid or stabilizer, and if this phosphorus compound acts as a melt resistivity adjuster, the amount of the phosphorus compound in polyester resin (D) may be decreased.

[0133] Specifically, the amount of magnesium element in the polyester composition (E) is preferably adjusted to 15 to 150 ppm by mass, more preferably 20 to 120 ppm by mass. Furthermore, the amount of alkali metal element is preferably adjusted to 1.5 to 15 ppm by mass, more preferably 2 to 12 ppm by mass. In this case, a calcium compound may not be contained. Furthermore, when a calcium compound is contained, the amount of calcium element is preferably 15 to 350 ppm by mass, more preferably 20 to 300 ppm by mass, with the upper limit being 250 ppm by mass, 200 ppm by mass, or 150 ppm by mass. In this case, a magnesium compound may not be contained. Note that these values ​​exclude those derived from lubricant particles such as calcium carbonate.

[0134] The amount of phosphorus element in polyester composition (E) includes phosphorus element derived from polyester resin (A) or polyester resin (B), but since these phosphorus elements may have little contribution to adjusting the melt resistivity, a preferred amount of phosphorus element in polyester composition (E) is not specified, and it is preferable that the amount be an amount that falls within the range of an appropriate melt resistivity, taking into consideration the amount of phosphorus element contained in polyester resin (A) or polyester resin (B). For example, it is preferably 10 to 400 ppm by mass, more preferably 15 to 300 ppm by mass, and the upper limit may be any of 250 ppm by mass, 200 ppm by mass, or 150 ppm by mass.

[0135] The intrinsic viscosity retention of the polyester resin composition (E) is preferably 89% or more, more preferably 90% or more, even more preferably 91% or more, particularly preferably 92% or more, and most preferably 93% or more. The intrinsic viscosity retention of the polyester resin composition (E) is preferably 100%, but in reality, it is preferably 99% or less, and more preferably 98% or less.

[0136] The various properties of the polyester resin composition (E) are the same as those described for the polyester resin composition (C).

[0137] The film may contain various additives other than the polyester resin depending on its intended use and required properties. In addition to the various additives listed for the polyester resin (D), resins such as polyamide, polyimide, polycarbonate, polyurethane, polyether, polyphenylene sulfide, polyphenylene sulfide, polyetherimide, and polyphenylene oxide may also be added as additives. In the case of a void-containing polyester film, a void-containing agent such as polystyrene or polyolefin may also be added. The amount of these resins other than polyesters added is preferably 1 to 30% by mass, more preferably 2 to 20% by mass, based on the total amount of the polyester resin composition (E) and the resins other than the polyester resin composition (E).

[0138] [Polyester Film] When the polyester film is an unstretched film, it can be melt-kneaded in an extruder and then extruded into a thin film form from a die onto a cooling roll to form a film. Alternatively, the film may be formed by a calendaring method. When a stretched film is to be formed, the unstretched film obtained as described above can be stretched in the length direction or width direction to form a uniaxially or biaxially stretched polyester film.

[0139] As for the stretching method, for example, in the case of longitudinal stretching, stretching can be performed between rolls with different peripheral speeds. Stretching in the width direction can be performed, for example, by gripping both ends of the film width with running clips or the like, leading the film to a tenter, and then widening the running rail width of the clips. In the case of sequential biaxial stretching, either direction may be performed first, but stretching in the length direction is generally performed first. Alternatively, stretching in the length direction and width direction may be performed simultaneously or in any order using a simultaneous biaxial stretching machine. Stretching may be performed in multiple stages, and in the case of multiple stages, stretching in the length direction and width direction may be performed alternately.

[0140] The stretching temperature is preferably in the range of glass transition temperature (Tg) of the polyester resin composition (E) + 5 to Tg + 70°C, more preferably in the range of Tg + 10 to Tg + 60°C. The stretching ratio is preferably 10 times or less, more preferably 8 times or less, and particularly preferably 6 times or less in at least one direction. In order to impart strong orientation, the stretching ratio is preferably 2 times or more, more preferably 2.5 times or more, and particularly preferably 2.8 times or more. Even if biaxial stretching is used, if a film with strong uniaxiality is to be obtained, the stretching ratio in the direction perpendicular to the main stretching direction may be less than the above ratio.

[0141] After stretching, the polyester film is preferably heat-set at a temperature equal to or lower than the crystalline melting point (mp) of the polyester resin composition (E). The heat-setting temperature is preferably mp-10°C or lower, more preferably mp-20°C or lower. The lower limit of the heat-setting temperature depends on the composition of the polyester resin composition (E) and the heat resistance desired to be imparted to the film, but is generally preferably 100°C or higher, more preferably 130°C or higher. For example, if the polyester resin composition (E) is a polyethylene terephthalate film, the heat-setting temperature is preferably 170 to 250°C, more preferably 180 to 240°C.

[0142] Heat setting is preferably carried out while maintaining the stretch ratio, but in order to reduce the heat shrinkage of the polyester film, a relaxation step may be added by shrinking the film by about 1 to 5% from the stretched state between heat setting and cooling. The relaxation step is preferably carried out at 100°C to the heat setting temperature - 5°C, more preferably at 120°C to the heat setting temperature - 10°C. The relaxation rate is more preferably 1.5 to 4%.

[0143] The polyester film may be a single layer or a multilayer. In the case of a multilayer film, at least one layer must be made of the polyester resin composition (E). Multiple or all layers may be made of the polyester resin composition (E), and in this case, the compositions and ratios of the polyester resins (A), (B), and (D) may differ depending on the layer. Furthermore, in the case of a multilayer film, it is also preferable to have a three-layer or more structure, with the intermediate layer being a layer of the polyester resin composition (E), and the outermost layer not containing recycled polyester resin A, particularly polyester resin A recycled from the streets. In the case of a multilayer film, the thickness of the layer of the polyester resin composition (E) is preferably 30% or more of the total thickness of the film, more preferably 50% or more, even more preferably 60% or more, and particularly preferably 70% or more. If it is less than the above, the significance of using recycled polyester (A) is diminished.

[0144] The thickness of the polyester film is preferably 1 to 2000 μm, more preferably 2 to 1000 μm. The thickness can be adjusted to an appropriate range depending on the application. For example, typical thicknesses are 20 to 150 μm for optical applications, 10 to 100 μm for transfer or release films, 5 to 50 μm for general packaging films, and 200 to 1000 μm for thick products such as trays.

[0145] <Surface Treatment of Polyester Film> The polyester film is preferably surface-treated to improve adhesion to adhesives, coating materials, inks, etc. Examples of surface treatments include corona treatment, plasma treatment, and flame treatment.

[0146] The polyester film may be provided with an easy-adhesion layer. Examples of resins used in the easy-adhesion layer include polyester resins, polyurethane resins, polycarbonate resins, and acrylic resins, with polyester resins, polyester polyurethane resins, polycarbonate polyurethane resins, and acrylic resins being preferred. The easy-adhesion layer is preferably crosslinked. Examples of crosslinking agents include isocyanate compounds, melamine compounds, epoxy resins, and oxazoline compounds. Adding a water-soluble resin such as polyvinyl alcohol is also a useful means for improving adhesion to the polarizer.

[0147] The easy-adhesion layer can be formed by applying and drying a water-based coating containing these resins and, if necessary, a crosslinking agent, particles, etc., to a polyester film. Examples of particles include those used for the polyester film described above. The easy-adhesion layer may be formed offline on a stretched film, but is preferably formed in-line during the film-forming process. When formed in-line, it may be formed either before longitudinal stretching or transverse stretching, but it is preferably coated just before transverse stretching, and then dried and crosslinked in a preheating, heating, and heat treatment process using a tenter. When in-line coating is performed just before longitudinal stretching using rolls, it is preferable to dry the coated film in a vertical dryer after coating and then introduce it into the stretching rolls. The coating amount of the easy-adhesion layer is 0.01 to 1.0 g / m ２ is preferable, and more preferably 0.03 to 0.5 g / m ２ is preferred.

[0148] The polyester film produced by the present invention can be used in a variety of applications without limitation. Examples include substrate films for prisms and lens sheets, hard coat films, electrode substrate films for touch panels, shatterproof films, anti-reflection films, polarizer protective films, polarizing plate protective films, surface protective films for displays and circuits, release films for ceramic green sheets, polarizing plate release films, transfer films, in-mold transfer films, in-mold molding films, aluminum or inorganic oxide vapor-deposited barrier films, solar cell backsheets, circuit substrate films, flat cable substrate films, magnetic recording medium substrate films, ink ribbons, image-receiving films, films for labels, tags, and cards, films for packaging bags, heat-shrinkable films, trays, and cover tapes. Depending on the application, additives can be added to the film, or post-processing can be performed to impart functionality to the film.

[0149] [Method for Producing Polyester Resin (B)] Next, a method for producing polyester resin (B) will be described. The method for producing polyester resin (B) can be carried out by a method including known steps except for using a polyester polymerization catalyst comprising an aluminum compound and a phosphorus compound as the catalyst. However, it is preferable to add the polymerization catalyst so as to satisfy the following (4) and (5), and it is even more preferable to add the polymerization catalyst so as to satisfy the following (6) in addition to the following (4) and (5). Note that the preferred numerical ranges for the following (4) to (6) are described above. (4) The content of aluminum element in the polyester resin (B) is 5 to 50 ppm by mass. (5) The content of phosphorus element in the polyester resin (B) is 5 to 1000 ppm by mass. (6) The residual molar ratio of phosphorus element to aluminum element in the polyester resin (B) is 1.00 or more and 5.00 or less.

[0150] The method for producing the polyester resin (B) preferably comprises a first step of synthesizing a polyester or an oligomer thereof, which is a polycondensate (low-order condensate) as an intermediate, and a second step of further polycondensing the intermediate.

[0151] Furthermore, it is preferable to add a solution S in which an aluminum compound is dissolved and a solution T in which a phosphorus compound is dissolved to the intermediate after the first step and before the second step so as to satisfy the following (7) to (9): The polycarboxylic acids and their ester-forming derivatives, the hydroxycarboxylic acids and their ester-forming derivatives which may be added in small amounts, and the cyclic esters which may be added in small amounts, which are used in the production of polyester resin (B), are not distilled out of the reaction system during polymerization, and almost 100% of the amount initially added to the system as a catalyst remains in the polyester resin (B) produced by polymerization, and the mass of the "polyester resin to be produced" can be calculated from the amounts charged. (7) The amount of aluminum added to the polyester resin (B) to be produced is 5 to 50 ppm by mass (more preferably 7 to 40 ppm by mass, even more preferably 10 to 30 ppm by mass, and particularly preferably 15 to 25 ppm by mass). (8) The amount of phosphorus added to the polyester resin (B) to be produced is 5 to 1500 ppm by mass (more preferably 10 to 500 ppm by mass, even more preferably 20 to 200 ppm by mass, and particularly preferably 30 to 100 ppm by mass). (9) The molar ratio of the amount of phosphorus added in (8) to the amount of aluminum added in (7) (hereinafter referred to as "molar ratio of phosphorus added to aluminum") is 1.00 or more and 7.00 or less (more preferably 1.50 to 6.00, and even more preferably 2.00 to 5.00).

[0152] There are no particular limitations on the method for producing the polyester or its oligomer, which is the low-order condensate (low polymer) synthesized in the first step.

[0153] The polyester resin (B) can be produced by a method including conventionally known steps, except that a polyester polymerization catalyst composed of an aluminum compound and a phosphorus compound is used as the catalyst and the amount of polyester polymerization catalyst added is carefully considered. For example, polyethylene terephthalate can be produced by a direct esterification method in which terephthalic acid and ethylene glycol, and optionally other copolymerization components, are directly reacted, water is distilled off, esterification is performed, and polycondensation is then performed under normal or reduced pressure. Alternatively, dimethyl terephthalate and ethylene glycol, and optionally other copolymerization components, are reacted, methyl alcohol is distilled off, transesterification is performed, and polycondensation is then performed under normal or reduced pressure. If necessary, solid-state polymerization can be performed to increase the intrinsic viscosity. The amount (mass) of the resulting polyester resin (B) can be calculated from the amount (mass) of polycarboxylic acids, including dicarboxylic acids, used as raw materials.

[0154] In any of these methods, the esterification reaction or transesterification reaction may be carried out in one step or in multiple steps.

[0155] Alternatively, a polyester resin produced by melt polymerization may be additionally polymerized by solid-state polymerization. The solid-state polymerization reaction can be carried out in a continuous apparatus, similar to the melt polycondensation reaction.

[0156] In the case of a continuous polycondensation apparatus consisting of three or more reactors (a three-stage polymerization method consisting of an initial stage, a middle stage, and a later stage), it is preferable that the first stage is the initial stage, the final stage is the later stage, and the stages from the second stage to the stage just before the final stage are the intermediate stages, and the reaction conditions for the polymerization reaction in the intermediate stage are between those in the initial stage and those in the final stage. It is preferable that the degree of increase in intrinsic viscosity achieved in each of these polymerization reaction steps is smoothly distributed.

[0157] (Solid-state polymerization method) In order to increase the intrinsic viscosity, the polyester resin produced by the melt polymerization method may be subjected to solid-state polymerization. The solid-state polymerization may be a batch polymerization method or a continuous polymerization method, but it is preferable that the solid-state polymerization is carried out in a continuous apparatus, as in the melt polymerization.

[0158] In order to reduce the CT amount of polyester resin (B), it is preferable to additionally polymerize the polyester resin produced by melt polymerization using solid-state polymerization. The solid-state polymerization is carried out by converting the polyester obtained in the second step (melt polymerization) into a powder or granular form. The powder or granular form refers to polyester in chip, pellet, flake, or powder form, and chip or pellet form is preferred.

[0159] The solid-state polymerization is carried out by heating the granular polyester at a temperature below the melting point of the polyester 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.

[0160] The particulate polyester 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.

[0161] Such a pre-crystallization step may be carried out by heating the granular polyester 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 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.

[0162] The polyester melt-polymerized as described above is, for example, chipped and then 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, air, the surface of the melt-polymerized polyester chips is subjected to a large impact force when it collides with the pipeline, resulting in the generation of a large amount of fines and film-like substances. These fines and film-like substances have the effect of promoting the crystallization of the polyester, and if present in large quantities, the transparency of the resulting molded product will be significantly reduced. Therefore, adding a process for removing these fines and film-like substances is one preferred embodiment.

[0163] 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.

[0164] When an aluminum compound and a phosphorus compound are used as catalysts, they are preferably added in the form of a slurry or a solution, more preferably in a solvent such as water or glycol, still more preferably in water and / or glycol, and most preferably in ethylene glycol.

[0165] It is preferable to add the solution S in which an aluminum compound is dissolved and the solution T in which a phosphorus compound is dissolved at any stage before the start of the polymerization reaction in the production process of the polyester resin (B) so that the contents (residual amounts) in the polyester resin (B) fall within the ranges that satisfy the above (4) to (6).

[0166] By adding the solution S containing an aluminum compound and the solution T containing a phosphorus compound so that their contents (residual amounts) in the polyester resin (B) satisfy the above (4) to (6), a catalytically active complex is functionally formed in the polymerization system, thereby achieving sufficient polymerization activity and suppressing the generation of aluminum-based foreign matter.

[0167] Incidentally, even if the polyester resin is polymerized under a reduced pressure, almost 100% of the aluminum atoms in the aluminum compound that functions as a catalyst initially added to the system remain in the polyester resin (B) produced by polymerization. That is, since the amount of aluminum compound remains almost unchanged before and after polymerization, when the amount of aluminum atoms added to the intermediate is 5 to 50 ppm by mass, the content of aluminum atoms in the polyester resin (B) will also be 5 to 50 ppm by mass.

[0168] Furthermore, when the phosphorus compound, which functions as a catalyst together with the aluminum compound, is placed in a reduced pressure environment during polymerization of the polyester resin, a portion (about 10 to 40%) of the amount initially added to the system as a catalyst is removed from the system, but this removal rate varies depending on the molar ratio of phosphorus atoms to aluminum atoms added, the basicity or acidity of the solution in which the aluminum compound or phosphorus compound is dissolved, the method of adding the aluminum-containing solution or the phosphorus-containing solution (whether they are added as a single solution or added separately), etc. Therefore, it is preferable to appropriately set the amount of phosphorus compound added in the polyester resin (B) that becomes the final product so as to satisfy the above (5).

[0169] It is preferable to simultaneously add the solution S having the aluminum compound dissolved therein and the solution T having the phosphorus compound dissolved therein, and it is a more preferable embodiment to previously prepare a mixed solution by mixing the solution S having the aluminum compound dissolved therein and the solution T having the phosphorus compound dissolved therein in the ratio to be added to the intermediate, and then add the one-component mixed solution to the intermediate. Examples of the method for previously preparing the one-component solution include a method in which the respective solutions are mixed in a tank, and a method in which the solutions are mixed by merging the pipes for adding the catalyst midway.

[0170] When adding the catalyst solution to a reaction vessel, it is preferable to vigorously stir the reaction vessel. When adding the catalyst solution to a pipe between reaction vessels, it is preferable to install an in-line mixer or the like so that the added catalyst solution is quickly and uniformly mixed.

[0171] When solution S in which an aluminum compound is dissolved and solution T in which a phosphorus compound is dissolved are added separately, a large amount of foreign matter caused by the aluminum compound is likely to be generated, which may result in a lower temperature-rising crystallization temperature or a higher temperature-falling crystallization temperature, making it impossible to obtain sufficient catalytic activity. By adding the aluminum compound and the phosphorus compound simultaneously, a complex of the aluminum compound and the phosphorus compound that brings about polymerization activity can be produced quickly and efficiently, but when they are added separately, the production of the complex of the aluminum compound and the phosphorus compound is insufficient, and further, the aluminum compound that was not able to form a complex with the phosphorus compound may precipitate as foreign matter.

[0172] Furthermore, it is preferable that the solution S having the aluminum compound dissolved therein and the solution T having the phosphorus compound dissolved therein are added before the start of the polymerization reaction and after the completion of the esterification reaction or the transesterification reaction, and it is more preferable that the solution S having the aluminum compound dissolved therein and the solution T having the phosphorus compound dissolved therein are added to the intermediate after the first step and before the second step. If they are added before the completion of the esterification reaction or the transesterification reaction, the amount of aluminum-based foreign matter may increase.

[0173] When the polyester resin (B) is composed of at least one selected from polycarboxylic acids and their ester-forming derivatives and at least one selected from polyhydric alcohols and their ester-forming derivatives, the solution S in which the aluminum compound is dissolved is preferably a glycol solution in which the aluminum compound is dissolved, and the solution T in which the phosphorus compound is dissolved is preferably a glycol solution in which the phosphorus compound is dissolved.

[0174] <Heat treatment of phosphorus compound> The phosphorus compound used in the production of polyester resin (B) is preferably heat-treated in a solvent. The solvent used is not limited as long as it is at least one selected from the group consisting of water and alkylene glycol, but it is preferable to use a solvent that dissolves the phosphorus compound as the alkylene glycol, and it is more preferable to use a glycol that is a constituent component of polyester resin (B), such as ethylene glycol. The heat treatment in the solvent is preferably carried out after dissolving the phosphorus compound, but it is not necessary for the phosphorus compound to be completely dissolved.

[0175] The heat treatment conditions are that the heat treatment temperature is preferably 170 to 196° C., more preferably 175 to 185° C., and even more preferably 175 to 180° C. The heat treatment time is preferably 30 to 240 minutes, and more preferably 50 to 210 minutes.

[0176] The concentration of the phosphorus compound during the heat treatment is preferably 3 to 10% by mass.

[0177] The heat treatment described above can maintain the acidity of the phosphorus compound contained in the glycol solution constant, improve the polymerization activity by using the phosphorus compound in combination with the aluminum compound, reduce the amount of aluminum-based foreign matter produced by the polymerization catalyst, and suppress the amount of phosphorus compound distilled off during the polymerization step, thereby improving economy. Therefore, the heat treatment described above is preferred.

[0178] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The evaluation methods used in each example and comparative example are as follows.

[0179] [Evaluation Method] (1) Intrinsic Viscosity (IV) Approximately 3 g of a sample was freeze-pulverized and dried at 140°C for 15 minutes, and then 0.20 g was weighed out and added to 20 ml of a mixed solvent of 1,1,2,2-tetrachloroethane and p-chlorophenol in a 1:3 (mass ratio) mixture at 100°C for 60 minutes, followed by stirring to completely dissolve the solution. The solution was then cooled to room temperature and passed through a glass filter to obtain a sample. The falling time of the sample and solvent was measured using an Ubbelohde viscometer (manufactured by Rigo Co., Ltd.) controlled to 30°C, and the intrinsic viscosity [η] was calculated using the following formula: [η] = (-1 + √(1 + 4K'ηSp)) / 2K'C ηSp = (τ - τ0) τ0 where, [η]: intrinsic viscosity (dl / g) ηSp: specific viscosity (-) K': Huggins' constant (= 0.33) C: concentration (= 1 g / dl) τ: sample drop time (sec) τ0: solvent drop time (sec)

[0180] (2) Content of specified metal elements in polyester resin A polyester resin described below was weighed into a platinum crucible, carbonized on an electric stove, and then incinerated in a muffle furnace at 550°C for 8 hours. The incinerated sample was dissolved in 1.2 M hydrochloric acid to prepare a sample solution. The prepared sample solution was measured under the following conditions, and the concentrations of antimony, germanium, titanium, and aluminum in the polyester resin were determined by high-frequency inductively coupled plasma atomic emission spectrometry. Apparatus: CIROS-120 manufactured by SPECTRO Corporation Plasma output: 1400 W Plasma gas: 13.0 L / min Auxiliary gas: 2.0 L / min Nebulizer: Cross-flow nebulizer Chamber: Cyclone chamber Measurement wavelength: 167.078 nm

[0181] (3) Phosphorus Content in Polyester Resin Polyester Film Polyester resin was subjected to wet decomposition with sulfuric acid, nitric acid, and perchloric acid, and then neutralized with ammonia water. Ammonium molybdate and hydrazine sulfate were added to the prepared solution, and the absorbance at a wavelength of 830 nm was measured using an ultraviolet-visible absorption spectrophotometer (Shimadzu Corporation, UV-1700). The phosphorus concentration in the polyester resin was determined from a previously prepared calibration curve.

[0182] (4) Amount of Aluminum-Based Foreign Matter in Polyester Resin 30 g of polyester resin and 250 mL of a mixed solution of p-chlorophenol / tetrachloroethane (3 / 1: mass ratio) were placed in a 500 mL Erlenmeyer flask containing a stirrer and heated to 100-105°C for 1.5 hours using a hot stirrer to dissolve the mixture. The solution was filtered to remove foreign matter using a polytetrafluoroethylene membrane filter (PTFE membrane filter manufactured by Advantec, product name: T100A047A) with a diameter of 47 mm and a pore size of 1.0 μm. The effective filtration diameter was 37.5 mm. After filtration, the filter was subsequently washed with 50 mL of chloroform and then dried.

[0183] The aluminum element content of the filtration surface of the membrane filter was quantified using a scanning X-ray fluorescence analyzer (RIGAKU Corporation, ZSX100e, Rh line bulb 4.0 kW). Quantification was performed on a central 30 mm diameter portion of the membrane filter. The calibration curve for the X-ray fluorescence analysis was obtained using polyethylene terephthalate resin with a known aluminum element content, and the apparent aluminum element content was expressed in ppm. Measurements were performed using an X-ray output of 50 kV-70 mA, pentaerythritol as the analyzing crystal, and a PC (proportional counter) as the detector, by measuring the Al-Kα line intensity under conditions of PHA (pulse height analyzer) 100-300. The aluminum element content in the polyethylene terephthalate resin for the calibration curve was quantified using high-frequency inductively coupled plasma atomic emission spectrometry.

[0184] (5) Confirmation of the Presence of Hindered Phenol Structures or Their Decomposition Residues in the Sample: 420 mg of sample was dissolved in 2.7 mL of a mixed solvent of hexafluoroisopropanol and deuterated benzene in a 1:1 (mass ratio), and 10 μL of a 25% phosphoric acid solution in deuterated acetone was added and centrifuged. Subsequently, 100-150 mg of trifluoroacetic acid was added to the supernatant, and P-NMR measurement was immediately performed under the following conditions: Apparatus: Fourier Transform Nuclear Magnetic Resonance Spectrometer (Bruker, AVANCE 500); P Resonance Frequency: 202.456 MHz; Lock Solvent: Deuterated Benzene; Detection Pulse Flip Angle: 65°; Data Acquisition Time: 1.5 seconds; Delay Time: 0.5 seconds; Proton Decoupling: Full Decoupling; Measurement Temperature: 25-35°C; Number of Accumulations: Approximately 20,000-30,000; The peak wavelengths of the formula number residues shown in Table 1 are shown below. When these peak wavelengths were detected, it was determined that the sample contained a hindered phenol structure. Chemical formula 1: 34.5 ppm, chemical formula 4: 30.5 ppm, chemical formula 7: 53.6 ppm, chemical formula 2: 33.8 ppm, chemical formula 5: 30.1 ppm, chemical formula 8: 53.0 ppm, chemical formula 3: 31.9 ppm, chemical formula 6: 28.7 ppm, chemical formula 9: 51.3 ppm

[0185] (6) Quantitative Determination of Cyclic Trimer The sample was frozen, crushed, or fragmented, and 100 mg of the sample was weighed out. This was dissolved in 3 mL of a hexafluoroisopropanol / chloroform mixture (volume ratio = 2 / 3), and then diluted with 20 mL of chloroform. 10 mL of methanol was added to this to precipitate the polymer, which was then filtered. The filtrate was evaporated to dryness and made up to a constant volume with 10 mL of dimethylformamide. The amount of cyclic trimer in the polyester resin or blown molded article was then quantified using the following high-performance liquid chromatography method. The above procedure was repeated five times, and the average value was taken as the CT content. Apparatus: L-7000 (Hitachi) Column: μ-Bondasphere C18 5μ 100 Å 3.9 mm × 15 cm (Waters) Solvent: Eluent A: 2% acetic acid / water (v / v) Eluent B: acetonitrile Gradient B%: 10 → 100% (0 → 55 min) Flow rate: 0.8 mL / min Temperature: 30°C Detector: UV-259 nm

[0186] (7) Intrinsic Viscosity Retention Rate of Sample The sample was dried in a vacuum at 140°C for 16 hours to reduce the moisture content to 150 ppm or less. In the case of a film, the film was cut into pieces of approximately 1 cm square, and in the case of resin pellets, the pellets were used as they were. Using this dried polyester, a re-kneading treatment was carried out once in a twin-screw extruder under the following conditions, and the intrinsic viscosity of the re-kneaded product was measured, and the intrinsic viscosity retention rate was calculated using the following formula. In addition, using the above dried polyester resin, a re-kneading treatment was carried out three times in a twin-screw extruder under the following conditions, and the intrinsic viscosity of the re-kneaded product was measured, and the intrinsic viscosity retention rate was calculated using the following formula. The method for measuring the intrinsic viscosity was as described in (1) above. Twin-screw extruder: KZW15TW-45 / 60MG-NH (-2200) manufactured by Technobel Co., Ltd. Set temperature: 260°C (actual temperature 268 to 270°C) Screw rotation speed: 200 rpm Discharge rate 1.7 to 2.0 kg / h Intrinsic viscosity retention (%) = 100 × intrinsic viscosity of re-kneaded product / intrinsic viscosity of sample The moisture content was measured using a Karl Fischer moisture meter (CA-200 manufactured by Mitsubishi Chemical Analytech Corporation) using a coulometric titration method, with a 0.6 g sample at 230°C for 5 minutes in a nitrogen stream of 250 mL / min.

[0187] (8) 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 1:9 (volume ratio) mixture, followed by centrifugation. The supernatant was then collected and subjected to H-NMR measurement under the following conditions: Apparatus: Fourier transform nuclear magnetic resonance apparatus (manufactured by BRUKER, AVANCE NEO600) H resonance frequency: 600.13 MHz Lock solvent: deuterated chloroform Flip angle: 30° Data acquisition time: 4 seconds Delay time: 1 second Measurement temperature: 30°C Number of accumulations: 128

[0188] The preparation of the aluminum-containing ethylene glycol solution and the phosphorus-containing ethylene glycol solution will be described below.

[0189] <Preparation of Aluminum-Containing Ethylene Glycol Solution s> A 20 g / L aqueous solution of basic aluminum acetate and an equal amount (volume ratio) of ethylene glycol were charged into a blending tank and stirred at room temperature (23°C) for several hours. After that, water was distilled off from the system while stirring under reduced pressure (3 kPa) at 50 to 90°C for several hours, to prepare an aluminum-containing ethylene glycol solution s containing 20 g / L of an aluminum compound.

[0190] <Preparation of phosphorus-containing ethylene glycol solution t> Irganox 1222 (manufactured by BASF Co., Ltd.) as a phosphorus compound was charged into a blending tank together with ethylene glycol, and the mixture was heat-treated at 175°C for 150 minutes while stirring under nitrogen substitution to prepare a phosphorus-containing ethylene glycol solution t containing 50 g / L of the phosphorus compound.

[0191] [Production of Polyester Resin] <Polyester Resin (B1)> A 10-liter stainless steel autoclave equipped with a stirrer was charged with a polyester oligomer having an esterification rate of approximately 95% and consisting of high-purity terephthalic acid and ethylene glycol. An esterification reaction was carried out at 260°C to obtain an oligomer mixture. The resulting oligomer mixture had an acid end group concentration of 750 eq / ton and a hydroxyl end group ratio (OH%) of 59 mol%. A one-component mixture of the aluminum-containing ethylene glycol solution S and the phosphorus-containing ethylene glycol solution T prepared by the above method was added to the resulting oligomer mixture. The mixture was prepared so that the aluminum and phosphorus contents were 21 ppm by mass and 58 ppm by mass, respectively, relative to the mass of the oligomer mixture. The molar ratio of added phosphorus to aluminum was 2.41. The amount of polyester resin produced can be calculated from the amount of terephthalic acid added. In this example, the mixed solution was added so that the aluminum and phosphorus contents were 21 ppm by mass and 58 ppm by mass, respectively, relative to the polyester resin produced. The system temperature was then raised to 280°C over 1 hour, during which time the system pressure was gradually reduced to 0.15 kPa. A polycondensation reaction was carried out under these conditions to obtain a polyester resin with an IV of 0.60 dl / g. The resulting polyester resin was then extruded into strands and cut into 2.5 x 3 x 4 mm pellets. Then, using a batch-type solid-state polymerization apparatus, solid-state polymerization was carried out at 230°C under reduced pressure for 7 hours to obtain a polyester resin (B1) with an intrinsic viscosity of 0.75 dl / g and a CT content of 4700 ppm by mass. The residual aluminum content in the polyester resin (B1) was 21 ppm by mass, the residual phosphorus content was 45 ppm by mass, and the residual molar ratio of phosphorus to aluminum was 1.87. The content of aluminum element in polyester resin (B1), which corresponds to aluminum-based foreign matter, was 710 ppm by mass, and the L value of polyester resin (B-1) was 58.7, confirming that polyester resin (B1) had a hindered phenol structure. DEG was 1.5 mol%. The intrinsic viscosity retention was 98% in the first remixing and 88% in the third remixing.

[0192] Polyester Resin (B2) A polyester resin (B2) having an intrinsic viscosity of 0.75 dl / g and a CT content of 4700 ppm by mass was obtained in the same manner as polyester resin (B1), except that the amounts of aluminum and phosphorus added were different. The residual amount of aluminum in polyester resin (B2) was 16 ppm by mass, the residual amount of phosphorus was 26 ppm by mass, and the residual molar ratio of phosphorus to aluminum was 1.42. The content of aluminum in polyester resin (B2), which corresponds to aluminum-based foreign matter, was 2000 ppm by mass, and the L value of polyester resin (B2) was 58.5, confirming that polyester resin (B2) contained a hindered phenol structure. The intrinsic viscosity retention was 97% after the first remixing and 87% after the third remixing.

[0193] Polyester Resin (B3) A polyester resin (B3) having an intrinsic viscosity of 0.75 dl / g and a CT content of 4700 ppm by mass was obtained in the same manner as polyester resin (B1), except that the amounts of aluminum and phosphorus added were different. The residual amount of aluminum in polyester resin (B3) was 10 ppm by mass, the residual amount of phosphorus was 16 ppm by mass, and the residual molar ratio of phosphorus to aluminum was 1.39. The content of aluminum in polyester resin (B3), which corresponds to aluminum-based foreign matter, was 2300 ppm by mass, and the L value of polyester resin (B3) was 56.6, confirming that polyester resin (B3) contained a hindered phenol structure. The intrinsic viscosity retention was 96% after the first remix and 86% after the third remix.

[0194] Polyester Resin (B4) Polyester resin (B1) and silica particles having an average particle size of 2.5 μm were charged into a twin-screw extruder and kneaded at 285° C. to prepare masterbatch pellets containing 10,000 ppm of silica particles.

[0195] Polyester resin (D1): Polyethylene terephthalate pellets catalyzed by antimony trioxide (antimony element content: 230 ppm by mass, phosphorus element content: 50 ppm by mass, intrinsic viscosity: 0.75 dl / g)

[0196] Polyester Resin (D2) Polyester resin (D1) and silica particles having an average particle size of 2.5 μm were charged into a twin-screw extruder and kneaded at 285° C. to prepare masterbatch pellets containing 6000 ppm of silica particles.

[0197] Polyester resin (D3) To an oligomer prepared from terephthalic acid and ethylene glycol according to a conventional method, basic aluminum acetate, magnesium acetate dihydrate, potassium acetate, and triethyl phosphate were added so that the aluminum content, magnesium content, potassium content, and phosphorus content were 60 ppm, 1000 ppm, 100 ppm, and 500 ppm, respectively, relative to the polyester resin after production. The temperature of the system was raised to 280°C over 1 hour, during which the pressure of the system was gradually reduced to 0.15 kPa. Under these conditions, polycondensation reaction was carried out for 80 minutes to obtain pellets of polyester resin (D3). The intrinsic viscosity of polyester resin (D3) was 0.67 dl / g. The aluminum content, magnesium content, potassium content, and phosphorus content of polyester resin (D3) were determined by the following methods.

[0198] Measurement of the amount of each element in polyester resin (D3) A sample piece was prepared by heating and melting a polyester resin at 280°C in a stainless steel circular ring having a thickness of 5 mm and an inner diameter of 50 mm, and the amount of elements was determined by X-ray fluorescence analysis and expressed in ppm (by mass). Note that, for quantification, a calibration curve previously obtained from samples with known amounts of each element was used.

[0199] [Recovered Polyester Resin] <Polyester Resin (A1)> Recovered polyester resin flakes provided by Kyoei Sangyo Co., Ltd. were used as the polyester resin (A1). Composition analysis of the recovered polyester resin flakes revealed that they contained 1.7 mol% isophthalic acid components and 2.1 mol% diethylene glycol components, with a CT content of 4,900 ppm. The flake size was 8.6 mm. The recovered polyester resin flakes had an intrinsic viscosity of 0.750 dl / g. The recovered polyester resin flakes also contained an antimony content of 190 ppm by mass and a germanium content of 1.6 ppm by mass. Because the titanium content was very low, at less than 1 ppm by mass, the titanium content was omitted from Tables 2 and 3. The contents of antimony, germanium, and titanium confirmed that the recovered polyester resin flakes were mainly composed of hollow molded articles made of polyester resin produced using an antimony catalyst. The IV retention rate of polyester resin A1 after the first remix was 88%, and the IV retention rate after the third remix was 77%.

[0200] (Examples, Comparative Examples, Reference Examples) Each polyester resin was fed into a single-screw extruder at the blending ratio (parts by mass) shown in Table 2 and melted at 290 ° C. The molten polymer was filtered through a stainless steel sintered filter medium (nominal filtration accuracy 20 μm particle 95% cut), formed into a sheet from a die, extruded onto a casting drum with a surface temperature of 30 ° C., and then cooled and solidified to produce an unstretched film. Note that when feeding the polyester resin, small amounts were mixed and added to the hopper to prevent segregation. This unstretched film was stretched 3.3 times in the longitudinal direction at 95 ° C. using rolls with different peripheral speeds.

[0201] Subsequently, this uniaxially stretched film was introduced into a tenter stretching machine, and while the film's edges were held with clips, it was introduced into a hot air zone at 125°C and stretched 3.5 times in the width direction. Next, while maintaining the stretched width in the width direction, it was heat-set at 220°C for 10 seconds and further relaxed by 3.0%. Thereafter, both ends (edges) of the film cooled to 120°C were cut with a shear blade to obtain a biaxially stretched PET film with a film thickness of 75 μm. The film was then wound around a cardboard tube.

[0202] Evaluation of film recovery and reusability The recycled edges of the films prepared in the Examples and Comparative Examples were cut, and the cut film pieces were fed into a twin-screw extruder and melt-kneaded at 290°C to produce pellets. The resulting pellets were then melt-kneaded again at 290°C to produce pellets. A film was similarly produced using the second pellets obtained, and the film was wound around a paper tube to produce a remelted resin film. The side of the wound film was observed to check for differences in color tone. ○: No difference in color tone was observed. △: The remelted resin film was slightly yellowish. ×: The remelted resin film was clearly yellowish.

[0203]

[0204] Examples 12 to 15: The polyester resin for the intermediate layer shown in Table 3 was fed to Extruder 1, and the polyester resin for the surface layer was fed to Extruder 2 and melted at 285°C. A two-kind, three-layer die was used to produce biaxially stretched PET films, except that the thickness of the surface layer / intermediate layer / surface layer was 1 / 8 / 1. For evaluation of the recovery and reusability of the film, a single-layer structure similar to that of Example 1 was used.

[0205] Examples 16 and 17: Recycled flakes of edge portions obtained from another polyester film production line (IV = 0.61 dl / g, Sb content: 140 ppm, trace amounts of lubricant particles) were prepared as polyester resin A2, and polyester resin B5 was prepared by melt polymerization in the same manner as polyester resin B1 to an intrinsic viscosity of 0.67 dl / g by melt polymerization alone. Films were produced using the polyester resins shown in Table 4 in the same manner as in Example 1. After stretching in the machine direction, an easy-adhesion coating material having the following composition was applied to both sides of the film, which was then introduced into a tenter to produce biaxially stretched PET having easy-adhesion layers on both sides.

[0206] (Preparation of easy-adhesion coating paint) By carrying out a transesterification reaction and a polycondensation reaction by a conventional method, the dicarboxylic acid component (relative to the total dicarboxylic acid component) was 46 mol% terephthalic acid, 46 mol% isophthalic acid, and 8 mol% sodium 5-sulfonatoisophthalate, and the glycol component (relative to the total glycol component) was 50 mol% ethylene glycol and 50 mol% neopentyl glycol to prepare a water-dispersible sulfonate metal base-containing copolymer polyester resin. Then, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of a nonionic surfactant were mixed, and the mixture was heated and stirred. When the temperature reached 77 ° C., 5 parts by mass of the water-dispersible sulfonate metal base-containing copolymer polyester resin was added, and the mixture was stirred until no lumps of resin remained, and then the resin aqueous dispersion was cooled to room temperature to obtain a uniform water-dispersible copolymer polyester resin solution with a solids concentration of 5.0% by mass. Furthermore, 3 parts by mass of aggregated silica particles (Sylysia 310, manufactured by Fuji Silysia Co., Ltd.) were dispersed in 50 parts by mass of water, and then 0.54 parts by mass of an aqueous dispersion of Sylysia 310 was added to 99.46 parts by mass of the water-dispersible copolymer polyester resin liquid, and 20 parts by mass of water was added while stirring to obtain an easy-adhesion coating paint.

[0207]

[0208] As shown in Table 2, in Examples 1 to 6, the intrinsic viscosity retention rate tended to decrease as the amount of polyester resin B1 decreased, but the intrinsic viscosity retention rate was higher than in Comparative Examples 1 and 2 and the Reference Example. As in Examples 7 to 12, even when polyester resins B2 and B3 were used, which had low aluminum and phosphorus contents to reduce costs, the intrinsic viscosity retention rate was high. Discoloration of the roll end surface after re-filming was not a problem in the Examples.

[0209] Examples 12 to 15 in Table 3 are examples in which recycled polyester resin A1 was used for the intermediate layer. Discoloration of the roll end surface after re-filming was not a problem in these examples. Examples 16 and 17 in Table 4 are examples in which recycled polyester resin from the film manufacturing process was used. In these examples as well, discoloration of the roll end surface after re-filming was not a problem.

[0210] Example 18: Polyester resin (A1), polyester resin (B1), polyester resin (D2), and polyester resin (D3) were fed into a single-screw extruder in a blending ratio (parts by mass) of 50:40:5:5, and a biaxially stretched PET film was obtained in the same manner. Adhesion to the casting drum was performed by electrostatic adhesion using a wire electrode. Even when the casting speed was increased, adhesion to the drum was stable without air entrapment, allowing for stable casting. The intrinsic viscosity retention was 94% after one remixing and 84% after three remixings, and no difference in color tone was observed at the edge of the film using the remelted resin.

[0211] The casting sheet of the polyester resin composition constituting the film of Example 18 was pulverized, and the amount of each element was measured using the same method as for measuring the amount of each element in polyester resin (D3). The amount of antimony was 105 ppm by mass, the amount of aluminum was 10 ppm by mass, the amount of magnesium was 50 ppm by mass, the amount of potassium was 5 ppm by mass, and the amount of phosphorus was 53 ppm by mass.

[0212] The melt resistivity of the polyester resin composition constituting the film of Example 18, measured by the following method, was 0.22 × 10 ８The melt resistivity was Ω·cm. Method for Measuring Melt Resistivity Two electrodes (stainless steel wires with a diameter of 0.6 mm) were placed on both ends of a polyester composition melted at 275°C, and the polyester composition was sandwiched between two quartz plates with a width of 2 cm to form a uniform layer of the molten polyester composition with a width of 2 cm and a thickness of 0.6 mm. A DC voltage of 120 V was applied, and the current (io) was measured. This was then applied to the following equation to determine the melt resistivity ρi (Ω·cm): ρi (Ω·cm) = (A / L) × (V / io) [A: electrode area (cm2), L: distance between electrodes (cm), V: voltage (V)] A (cm2) = [width of the molten polyester composition layer] × [thickness] = 2 (cm) × 0.06 (cm), and V = 120 (V). L was measured without including the diameter of the electrodes.

[0213] By mixing the polyester resin (B) containing an aluminum compound and a phosphorus compound with the recovered polyester resin (A) to produce a polyester film, it is possible to suppress discoloration and a decrease in molecular weight of the polyester film and to obtain a polyester film with excellent recyclability. The present invention can contribute to solving various problems, such as preventing resource depletion, reducing marine litter, and mitigating global warming.

Claims

1. A method for producing a polyester film, comprising a step of mixing recovered polyester resin (A) with polyester resin (B) containing an aluminum compound and a phosphorus compound, wherein the polyester resin (A) satisfies the following (1) to (3): (1) The polyester resin (A) contains at least one element selected from antimony, titanium, and germanium. (2) The total content of antimony, titanium, and germanium in the polyester resin (A) is 2 to 500 ppm by mass. (3) The intrinsic viscosity of the polyester resin (A) is 0.5 to 0.8 dl / g.

2. 2. The method for producing a polyester film according to claim 1, wherein the polyester resin (B) satisfies the following (4) and (5): (4) The content of aluminum element in the polyester resin (B) is 5 to 50 mass ppm. (5) The content of phosphorus element in the polyester resin (B) is 5 to 1000 mass ppm.

3. The method for producing a polyester film according to claim 1 or 2, wherein the step comprises melt-mixing the polyester resin (A) and the polyester resin (B) to obtain a polyester resin composition (C).

4. The method for producing a polyester film according to claim 1 or 2, further comprising a step of mixing a polyester resin (D).

5. A method for producing a polyester film, comprising: mixing a polyester resin composition (C) which is a melt mixture of the recovered polyester resin (A) and a polyester resin (B) containing an aluminum compound and a phosphorus compound, with a polyester resin (D), wherein the polyester resin (A) satisfies the following (1) to (3): (1) The polyester resin (A) contains at least one element selected from antimony, titanium, and germanium. (2) The total content of antimony, titanium, and germanium in the polyester resin (A) is 2 to 500 ppm by mass. (3) The intrinsic viscosity of the polyester resin (A) is 0.5 to 0.8 dl / g.

6. The method for producing a polyester film according to claim 5, wherein the polyester resin composition (C) has an intrinsic viscosity retention rate of 89% or more.

7. 6. The method for producing a polyester film according to claim 1, 2, or 5, wherein the polyester resin (A) has an intrinsic viscosity retention rate of 92% or less.

8. 6. The method for producing a polyester film according to claim 1, wherein the polyester resin (B) has an intrinsic viscosity retention rate of 93% or more.

9. 6. The method for producing a polyester film according to claim 1, wherein the polyester resin (E) constituting the polyester film has an intrinsic viscosity retention rate of 89% or more.

10. 6. The method for producing a polyester film according to claim 1, wherein the amount of the polyester resin (A) is 5 to 95 parts by mass per 100 parts by mass of the total of the polyester resin (A) and the polyester resin (B).

11. 6. The method for producing a polyester film according to claim 5, wherein the polyester resin (D) is 5 to 95 parts by mass per 100 parts by mass of the total of the polyester resins (A), (B), and (D).

12. 6. The method for producing a polyester film according to claim 1, 2 or 5, wherein the polyester film is a multi-layer polyester film consisting of at least two layers, at least one of the surfaces of which is a layer that does not contain the polyester resin (A).

13. The method for producing a polyester film according to claim 1 , 2 or 5 , wherein the phosphorus compound has a phosphorus element and a phenol structure in the same molecule.

14. A method for producing a polyester film described in claim 1, 2, or 5, wherein the polyester resin (A) contains at least antimony and germanium elements.

15. A method for producing a polyester film described in claim 1, 2, or 5, wherein the polyester resin (A) contains at least isophthalic acid as a copolymerization component.

16. A method for producing a polyester film as described in Claim 4, wherein the polyester resin (D) contains a melt resistivity adjuster.

17. A polyester film composed of a recovered polyester resin (A) and a resin (E) containing a polyester resin (B) containing an aluminum compound and a phosphorus compound, wherein the polyester resin (A) satisfies the following (1) to (3): (1) The polyester resin (A) contains at least one element selected from antimony, titanium, and germanium. (2) The total content of antimony, titanium, and germanium in the polyester resin (A) is 2 to 500 ppm by mass. (3) The intrinsic viscosity of the polyester resin (A) is 0.5 to 0.8 dl / g.

18. The polyester film according to claim 17, wherein the polyester resin (B) satisfies the following (4) and (5): (4) The content of aluminum element in the polyester resin (B) is 5 to 50 mass ppm. (5) The content of phosphorus element in the polyester resin (B) is 5 to 1000 mass ppm.

19. The polyester film according to claim 17 or 18, further comprising a polyester resin (D) in the resin (E).

20. 19. The polyester film according to claim 17, wherein the resin (E) has an intrinsic viscosity retention rate of 89% or more.

21. A polyester film containing at least antimony, germanium, and aluminum elements in the polyester resin that constitutes the polyester film.

22. A polyester film as described in claim 21, wherein the polyester resin constituting the polyester film contains isophthalic acid as a copolymerization component.

23. A polyester film as described in Claim 19, wherein the polyester resin (D) contains a melt resistivity adjuster.