Method for producing polyester film through chemical recycling and polyester film

Abstract

A polyester film obtained by melting and molding a polyester resin, wherein the polyester film is obtained by polycondensing a raw material containing bis-2-hydroxyethylterephthalate obtained by decomposing a polyester resin using an aluminum compound and a phosphorus compound as catalysts.

Description

Chemically recycled polyester film manufacturing method and polyester film

[0001] The present invention relates to a method for producing a polyester film using a polyester resin obtained by polycondensation of bis-2-hydroxyethyl terephthalate obtained by chemical recycling, and to the polyester film obtained.

[0002] Polyester films are widely used for packaging and industrial materials because they have excellent mechanical strength, chemical stability, heat resistance, and moisture resistance, and can also be made highly transparent, and they are available at low cost and in stable supply.

[0003] General-purpose polyester films are made of polyethylene terephthalate, a polycondensate of terephthalic acid and ethylene glycol. Terephthalic acid and ethylene glycol are produced from petroleum, a fossil fuel. In recent years, recycling of fossil fuel-derived products has progressed to reduce environmental impacts, such as reducing carbon dioxide emissions. For polyesters, not only mechanical recycling, in which products are crushed and remelted for molding, but also chemical recycling, in which polyester is decomposed to the monomer level and then re-polycondensed using the resulting raw material, is becoming practical (see, for example, Patent Document 1).

[0004] In the case of polyester films, in order to reduce the environmental impact, the use of polyethylene terephthalate obtained by chemical recycling from PET beverage bottles, polyester fibers for clothing, etc. is being considered. Such environmentally friendly films are often made into products with a guarantee of the extent to which they have been environmentally friendly, for example, by ensuring that the proportion of chemically recycled raw materials is above a certain level.

[0005] On the other hand, in the production of polyester film, not all of the polyester resin used for production becomes film, due to factors such as portions clamped by tenter clips during transverse stretching and film that is not suitable for shipping until production conditions are stabilized and ready for production. These recycled polyester resins obtained from the film production process are sometimes reused as raw materials for film production, but once melted and placed in a high-temperature environment, they decompose, resulting in a decrease in molecular weight and an increase in terminal carboxyl groups. To stabilize the quality of films made from such recycled polyester resins, it is desirable to always add a constant amount of recycled polyester resin. However, because film production does not always generate a constant amount of recycled polyester resin, nor does it always produce a constant amount, recycled polyester resins are often collected from multiple production lines or from different brands and combined to be reused as recycled polyester resin.

[0006] However, due to the constraints imposed on environmentally friendly films as described above, it is necessary to prevent non-chemical recycled raw materials from being mixed into the recovered polyester resin, which can make it difficult to secure a constant amount of recovered polyester resin.Since a constant amount is not produced continuously, and when there are short-term fluctuations in production volume, it is difficult to avoid fluctuations in the amount of recovered polyester resin added.

[0007] For these reasons, it has become necessary to ensure that the properties of the resulting film made from chemically recycled polyethylene terephthalate do not change significantly even if the amount of recycled polyester film added varies.

[0008] Japanese Patent Application Laid-Open No. 2004-175912

[0009] The present invention has been made in light of the problems of the prior art. That is, the object of the present invention is to provide a polyester film made from chemically recycled polyethylene terephthalate, in which the properties of the resulting film do not change significantly even when the amount of recycled polyester film added varies, and to provide a method for producing the same.

[0010] The present invention has the following configurations. [Item 1] A polyester film comprising a chemically recycled polyethylene terephthalate resin obtained by polycondensing a raw material containing bis-2-hydroxyethyl terephthalate obtained by decomposing a polyester resin, using an aluminum compound and a phosphorus compound as catalysts. [Item 2] The polyester film according to Item 1, in which the raw material containing bis-2-hydroxyethyl terephthalate accounts for 50% by mass or more. [Item 3] The polyester film according to Item 1 or 2, in which the polyester resin comprises a recycled polyester resin obtained from a film production process. [Item 4] The polyester film according to Item 3, in which the recycled polyester resin accounts for 5 to 50% by mass of the total polyester resin constituting the polyester film. [Item 5] The polyester film according to Item 1 or 3, in which the polyester resin constituting the polyester film has an intrinsic viscosity of 0.52 to 0.73 dL / g. [Item 6] The polyester film according to Item 1 or 3, in which the polyester resin constituting the polyester film has an acid value of 5 to 80 dL / g. [Item 7] A method for producing a polyester film, comprising the step of producing a polyester film using a chemically recycled polyethylene terephthalate resin obtained by polycondensation of a raw material containing bis-2-hydroxyethyl terephthalate obtained by decomposing a polyester resin, the method comprising melt-mixing the unused chemically recycled polyethylene terephthalate resin obtained by polycondensation of the raw material containing bis-2-hydroxyethyl terephthalate with a polyethylene terephthalate resin recovered from a molten molding product discharged from the polyester film production step, and molding the mixture into a film. [Item 8] The method for producing a polyester film according to Item 7, wherein the recovered polyethylene terephthalate resin accounts for 5 to 50% by mass of the total amount of the unused chemically recycled polyethylene terephthalate resin and the recovered polyethylene terephthalate resin.[Item 9] The method for producing a polyester film according to Item 7 or 8, wherein the chemically recycled polyethylene terephthalate resin obtained by polycondensation of a raw material containing bis-2-hydroxyethyl terephthalate contains bis-2-hydroxyethyl terephthalate obtained by decomposing a polyester resin in a proportion of 50 mass% or more relative to the total amount of bis-2-hydroxyethyl terephthalate used as a raw material in polycondensation of the resin. [Item 10] The method for producing a polyester film according to Item 7 or 8, wherein the polychemically recycled ethylene terephthalate resin obtained by polycondensation using bis-2-hydroxyethyl terephthalate obtained by decomposing a polyester resin contains an aluminum compound and a phosphorus compound as catalysts. [Item 11] The method for producing a polyester film according to Item 7 or 8, wherein the difference in intrinsic viscosity between the unused chemically recycled polyethylene terephthalate resin and the recovered polyethylene terephthalate resin is 0.1 dL / g or less. [Item 12] The method for producing a polyester film according to Item 7 or 8, wherein a ratio of the intrinsic viscosity of the unused chemically recycled polyethylene terephthalate resin to the intrinsic viscosity of the recovered polyethylene terephthalate resin is 0.85 to 1. [Item 13] The method for producing a polyester film according to Item 7 or 8, wherein a difference in acid value between the unused chemically recycled polyethylene terephthalate resin and the recovered polyethylene terephthalate resin is 22 eq / ton or less.

[0011] According to the present invention, a polyester film can be obtained from chemically recycled polyethylene terephthalate, in which the properties of the resulting film do not change significantly even if the amount of recycled polyester film added varies.This makes it possible to supply film of stable quality even if there are fluctuations in production volume, and further enhances the effect of reducing the burden on the environment.

[0012] In the present invention, polyethylene terephthalate polymerized using bis-2-hydroxyethyl terephthalate obtained by chemical recycling is melted and molded into a polyester film. Note that bis-2-hydroxyethyl terephthalate may be abbreviated as BHET below, and bis-2-hydroxyethyl terephthalate obtained by chemical recycling may be abbreviated as chemically recycled BHET or CR-BHET below.

[0013] Chemically recycled BHET is obtained by heating polyethylene terephthalate in the presence of ethylene glycol to polymerize it. Hereinafter, polyethylene terephthalate may be abbreviated as PET. The original PET is preferably post-consumer PET, such as PET bottles collected from the streets, containers such as trays, fibers and products, waste products before production, B-grade products not shipped to the market, edge portions gripped during film stretching, slit offcuts, and molded products returned due to complaints, etc. The terephthalic acid and ethylene glycol in the original PET may be derived from petroleum or biomass. It may also be a mechanically recycled molded product. It may also be a mixture of these PETs.

[0014] The PET that is the source of these products is generally crushed, washed, and cleaned of foreign matter before being used in the depolymerization process.

[0015] Chemically recycled BHET may contain linear dimers and higher polymers, and may also contain mono-2-hydroxyethyl terephthalate, terephthalic acid, and ethylene glycol.

[0016] The total acid value and hydroxyl value of the chemically recycled BHET is preferably 6,500 eq / ton or more, more preferably 7,000 eq / ton or more, and even more preferably 7,500 eq / ton or more. The upper limit is preferably 9,500 eq / ton, more preferably 9,000 eq / ton, and even more preferably 8,500 eq / ton. By setting the acid value within the above range, productivity can be ensured while maintaining sufficient purity.

[0017] The chemically recycled BHET may contain dicarboxylic acid components other than terephthalic acid components and glycol components other than ethylene glycol. Examples of dicarboxylic acid components other than terephthalic acid components include naphthalenedicarboxylic acid and isophthalic acid, and examples of glycol components other than ethylene glycol include diethylene glycol, neopentyl glycol, cyclohexanedimethanol, trimethylene glycol, tetramethylene glycol, an ethylene glycol or propylene glycol adduct of bisphenol A, and an ethylene glycol or propylene glycol adduct of bisphenol S.

[0018] The amounts of dicarboxylic acid components other than terephthalic acid components and glycol components other than ethylene glycol, when the terephthalic acid component and the ethylene glycol component are each taken as 100 mol%, are each independently preferably 2 mol% or less, more preferably 1.5 mol% or less, even more preferably 1.0 mol% or less, particularly preferably 0.7 mol% or less, and most preferably 0.5 mol% or less. As mentioned above, chemically recycled BHET is preferably obtained by depolymerization of PET, including recycled PET from the market. Although recycled PET from the market may contain components other than PET to adjust crystallinity and physical properties, it is not cost-effective to separate pure PET from the recycled material or to purify BHET to a level where components other than terephthalic acid and ethylene glycol are undetectable. Therefore, the amounts of dicarboxylic acid components other than terephthalic acid components and glycol components other than ethylene glycol may be preferably 0.01 mol% or more, more preferably 0.05 mol% or more.

[0019] Chemically recycled BHET is added with a polycondensation catalyst and heated under reduced pressure to polycondense, producing a chemically recycled polyethylene terephthalate resin. The lower limit of the amount of chemically recycled BHET relative to the total amount of BHET used is preferably 50% by mass, more preferably 60% by mass, even more preferably 70% by mass, particularly preferably 80% by mass, and most preferably 90% by mass. By using a quantity exceeding the above range, environmental friendliness can be improved.

[0020] Furthermore, copolymerization components other than those derived from chemically recycled BHET may be added to the chemically recycled polyethylene terephthalate resin. Representative copolymerizable dicarboxylic acid components and glycol components are the same as those listed above as components that may be contained in chemically recycled BHET. The amount of dicarboxylic acid components other than terephthalic acid components and the amount of glycol components other than ethylene glycol are each independently preferably 20 mol% or less, more preferably 15 mol% or less, even more preferably 10 mol% or less, particularly preferably 7 mol% or less, and most preferably 5 mol% or less, based on the terephthalic acid component and the ethylene glycol component, respectively, being 100 mol%. This amount also includes components other than those derived from chemically recycled BHET.

[0021] Hereinafter, chemically recycled polyethylene terephthalate may be abbreviated as chemically recycled PET or CR-PET.

[0022] Any commonly used catalyst can be used as the catalyst for polycondensation using chemically recycled BHET without any restrictions. Examples include antimony compounds, titanium compounds, germanium compounds, and composite catalysts of aluminum compounds and phosphorus compounds. Among these, antimony compounds and aluminum compounds are preferred because the resulting PET has high thermal stability. A typical example of an antimony compound is antimony trioxide.

[0023] The lower limit of the amount of antimony compound added is preferably 50 ppm by mass, more preferably 80 ppm by mass, and even more preferably 100 ppm by mass, in terms of the content of elemental antimony in the obtained recycled PET. By using an amount equal to or greater than the above, an economical polymerization rate can be ensured. The upper limit of the content of elemental antimony is preferably 330 ppm by mass, more preferably 300 ppm by mass, even more preferably 270 ppm by mass, particularly preferably 250 ppm by mass, and most preferably 230 ppm by mass. By using an amount equal to or less than the above, decomposition of the recovered resin can be suppressed.

[0024] Examples of composite catalysts of aluminum compounds and phosphorus compounds include the following. (Aluminum Compound) The aluminum compound is not limited as long as it is soluble in a solvent, and known aluminum compounds can be used without limitation. Among these, at least one selected from carboxylic acid salts, inorganic acid salts, and chelate compounds is preferred. 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.

[0025] The amount of aluminum compound added 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, in terms of the aluminum element content in the chemically recycled PET. If the aluminum element content is less than 5 ppm by mass, the polymerization activity may not be fully exerted. On the other hand, if it exceeds 50 ppm by mass, the amount of aluminum-based foreign matter may increase.

[0026] Furthermore, when cost is a priority, the aluminum content in chemically recycled PET 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 due to the relationship with the phosphorus content described below, and in addition, the cost of the catalyst increases.

[0027] (Phosphorus Compound) The phosphorus compound is not particularly limited, but it is preferable to use a phosphonic acid compound or a phosphinic acid compound because it has a significant effect of improving the catalytic activity, and among these, it is more preferable to use a phosphonic acid compound because it has a particularly significant effect of improving the catalytic activity.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032]

[0033] (In (Chemical Formula A), * represents a bond.)

[0034]

[0035] (In (Chemical Formula B), X １ , X ２ respectively represent hydrogen and an alkyl group having 1 to 4 carbon atoms.) 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, it is preferable that the keical recycled PET is a polyester resin produced using, as a polymerization catalyst, a phosphorus compound having a phosphorus element and a hindered phenol structure in the same molecule. The method for detecting hindered phenol structures in PET (P-NMR measurement method) will be described later.

[0036] 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.

[0037] 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.

[0038] The following shows nine phosphorus compounds in which the structure of 3,5-di-tert-butyl-4-hydroxybenzyl diethyl phosphonate has been partially modified. The amount of each structurally modified phosphorus compound in glycol solution can be quantified by P-NMR measurement.

[0039]

[0040] 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.

[0041] 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.

[0042]

[0043] In the present invention, it is preferable that at least one of the above formulas 1, 4, and 7 is contained.

[0044] The phosphorus content in chemically recycled PET 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.

[0045] When cost is a major consideration, the phosphorus content in chemically recycled PET 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, 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 31 ppm by mass, there is a risk of a decrease in polymerization activity and an increase in the amount of phosphorus compound added, resulting in an increase in catalyst costs.

[0046] In chemically recycled PET, the molar ratio of aluminum to phosphorus 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 chemically recycled PET are derived from the aluminum compound and phosphorus compound used as polymerization catalysts, respectively. By using these aluminum and phosphorus compounds in combination at a specific ratio, a catalytically active complex is functionally formed in the polymerization system, enabling sufficient polymerization activity to be achieved. Furthermore, resins produced using a polymerization catalyst composed of an aluminum compound and a phosphorus compound require higher catalyst costs (higher production costs) than polyester resins produced using catalysts such as antimony catalysts. However, by using aluminum and phosphorus compounds in combination at a specific ratio, sufficient polymerization activity can be achieved while reducing catalyst costs. A residual molar ratio of phosphorus to aluminum of less than 1.00 may result in reduced thermal stability and thermal oxidative stability, or an increased amount of aluminum-based foreign matter. On the other hand, if the residual molar ratio of phosphorus element to aluminum element exceeds 5.00, the amount of phosphorus compound added becomes too large, which may increase the catalyst cost.

[0047] When cost is more important, the residual molar ratio of phosphorus element to aluminum element is preferably 1.32 to 1.80, more preferably 1.38 to 1.68.

[0048] Chemically recycled PET is melted, mixed, and formed into film. In the film formation process, not all of the resin input is shipped as a finished product. For example, recycled materials are generated in the process, such as trimmed edges, slit offcuts, and film produced during stable production. These recycled materials are sometimes reused as raw resin rather than discarded, in order to conserve resources and protect the environment, reduce costs, and so on. In particular, in the case of PET film stretched in the width direction by a tenter, a large amount of recycled materials are generated in the process because the clipped portions of the tenter are not stretched.

[0049] In the present invention, such recovered products are preferably mixed with unused chemically recycled PET and reused as raw materials for film production. There are also films that were not shipped because their properties did not meet the specified specifications, and films that were returned due to complaints, and these are also preferably mixed with recovered products and reused. Hereinafter, PET including recovered products may be referred to as recovered PET, and unused chemically recycled PET may be referred to as virgin PET. Note that unused PET does not have a history of being produced, pelletized, remelted, and then solidified.

[0050] Recycled PET may be crushed and fed directly into film production equipment, but in order to ensure a stable input amount and to prevent segregation with virgin PET in the hopper, it is preferable to remelt it and turn it into pellets.

[0051] In the present invention, it is preferable to use, as the raw material PET in the production of the film, virgin PET from chemically recycled PET and recovered PET produced in the film production process of chemically recycled PET.

[0052] The lower limit of the proportion of recycled PET relative to the total raw material resins in film production is preferably 5% by mass, more preferably 10% by mass, and even more preferably 15% by mass. The upper limit of the proportion of recycled PET is preferably 50% by mass, more preferably 40% by mass, and even more preferably 35% by mass. By ensuring the proportion within the above range, stable production and stable quality can be achieved by securing raw materials.

[0053] In the production of films, the raw PET used does not have to be entirely chemically recycled PET, and conventional PET obtained from terephthalic acid and ethylene glycol may also be included. In particular, in the production of films, when lubricant particles, resistivity regulators, pigments, UV absorbers, etc. are added, they may be mixed as a masterbatch, but it is not necessary to use chemically recycled PET for the PET used in the masterbatch; these may be shared with ordinary PET film for economical production.

[0054] In the production of films, the raw material resins do not have to be all PET, and may contain copolymer polyesters or other resins depending on the intended use. Specific copolymer polyesters and other resins will be explained in the examples of use below. In such cases, even if the resin recovered from the film production process contains resins other than PET, it is still considered to be recycled PET.

[0055] The lower limit of the proportion of chemically recycled PET to the total resin constituting the film is preferably 20% by mass, more preferably 30% by mass, even more preferably 50% by mass, particularly preferably 70% by mass, and most preferably 80% by mass. By making it equal to or greater than the above, environmental compatibility can be improved.

[0056] Such recycled PET has a lower molecular weight than virgin PET, and an increased amount of terminal carboxyl groups. As an index of molecular weight, it is preferable to use intrinsic viscosity, abbreviated as IV, the amount of terminal carboxyl groups as AV, and cyclic trimer as CT. Even when the amount of recycled PET added varies for each production lot, it is preferable to set the difference in IV or AV between virgin PET and recycled PET within a specific range in order to minimize quality variations between lots.

[0057] The lower limit of the IV difference between virgin PET and recycled PET is preferably 0.01 dL / g, more preferably 0.02 dL / g, and the upper limit of the IV difference between virgin PET and recycled PET is preferably 0.1 dL / g, more preferably 0.08 dL / g, even more preferably 0.07 dL / g, particularly preferably 0.065 dL / g, and most preferably 0.06 dL / g.

[0058] The lower limit of the ratio of the IV of recycled PET to the IV of virgin PET, i.e., the IV of recycled PET / the IV of virgin PET, is preferably 0.85, more preferably 0.87, even more preferably 0.88, particularly preferably 0.89, and most preferably 0.9. In practical terms, the upper limit of the IV of recycled PET / the IV of virgin PET is preferably 0.99, more preferably 0.98.

[0059] In practice, the AV difference between virgin PET and recycled PET is preferably 3 eq / ton, more preferably 4 eq / ton, and even more preferably 5 eq / ton. The upper limit of the AV difference between virgin PET and recycled PET is preferably 22 eq / ton, more preferably 20 eq / ton, even more preferably 17 eq / ton, particularly preferably 15 eq / ton, and most preferably 13 eq / ton.

[0060] By keeping the IV difference between virgin PET and recycled PET, the IV of recycled PET / IV of virgin PET, and the AV difference between virgin PET and recycled PET within the above ranges, it is possible to ensure stable product quality even if the amount of recycled resin added varies for each production batch. Note that "practically" in the above means that the recycled PET is not subjected to solid-state polymerization or remelted and subjected to dehydration polymerization under reduced pressure, and even if this is done, strict control is not required, and furthermore, it is possible to carry out this method economically and simply without resorting to complicated measures such as separating recycled PET into those with different IVs and selecting those that match the IV of virgin PET.

[0061] CT in PET is an equilibrium reaction, and its amount is largely determined by the resin temperature. Therefore, if solid-state polymerization is not performed on both virgin PET and recycled PET, the CT content will be roughly the same. In this case, the upper limit of the difference in CT content between virgin PET and recycled PET is preferably 0.1% by mass, more preferably 0.08% by mass.

[0062] On the other hand, when virgin PET undergoes solid-state polymerization, the CT content decreases. In this case, recycled PET may also undergo solid-state polymerization, and the lower limit of the CT content difference between virgin PET and recycled PET is preferably 0% by mass, more preferably 0.02% by mass, and even more preferably 0.05% by mass. The upper limit of the CT content difference between virgin PET and recycled PET is preferably 0.4% by mass, more preferably 0.3% by mass, even more preferably 0.2% by mass, and particularly preferably 0.15% by mass.

[0063] In order to ensure that the differences in IV, AV and CT contents between virgin PET and recycled PET fall within the above ranges, it is preferable that the IV, AV and CT contents of virgin PET fall within specific ranges.

[0064] The lower limit of the IV of virgin PET is preferably 0.54 dL / g, more preferably 0.56 dL / g, even more preferably 0.57 dL / g, and particularly preferably 0.58 dL / g. By setting it at or above the above levels, the mechanical properties of the obtained film can be ensured, and the differences in IV and AV between virgin PET and recycled PET can be easily reduced, making it easier to suppress fluctuations in the mechanical properties and ensure film formation stability.

[0065] The upper limit of the IV of virgin PET is preferably 0.75 dL / g, more preferably 0.70 dL / g, even more preferably 0.68 dL / g, particularly preferably 0.66 dL / g, and most preferably 0.65 dL / g. By setting it to the above or lower limit, film formation stability is ensured, deterioration of the recycled resin is easily suppressed, and the difference in IV and AV between virgin PET and recycled PET can be easily reduced. Furthermore, at 0.68 dL / g or lower, melt polymerization alone is possible, which is economically advantageous.

[0066] The lower limit of AV for virgin PET is preferably 1 eq / ton, more preferably 3 eq / ton, and even more preferably 5 eq / ton, from the viewpoint of productivity. When PET is produced by melt polymerization alone, the lower limit is preferably 10 eq / ton, more preferably 15 eq / ton. At 10 eq / ton or higher, melt polymerization alone is possible, which is economically advantageous.

[0067] The upper limit of AV of virgin PET is preferably 70 eq / ton, more preferably 60 eq / ton, even more preferably 55 eq / ton, and particularly preferably 50 eq / ton. By keeping it at or below the above level, deterioration of the recovered resin can be easily suppressed.

[0068] From the viewpoint of productivity, the lower limit of the CT amount of virgin PET is preferably 0.3% by mass, more preferably 0.5% by mass, even more preferably 0.7% by mass, and particularly preferably 0.8% by mass. The upper limit of the CT amount of virgin PET is preferably 1.1% by mass, more preferably 1.05% by mass, and even more preferably 1% by mass. This can be achieved by keeping it below the above range. When PET is produced only by melt polymerization, the CT amount is about 0.9 to 1.0% by mass.

[0069] The lower limit of the IV of the recycled PET is preferably 0.5 dL / g, more preferably 0.51 dL / g, and even more preferably 0.52 dL / g. By setting it to above the above range, the mechanical properties of the obtained film can be ensured, and the difference in IV between the virgin PET and the recycled PET can be easily reduced, making it easier to suppress fluctuations in the mechanical properties and ensure film formation stability.

[0070] The upper limit of the IV of the recycled PET is preferably 0.72 dL / g, more preferably 0.68 dL / g, even more preferably 0.66 dL / g, particularly preferably 0.64 dL / g, and most preferably 0.63. By setting it at or below the above range, film formation stability can be ensured and the differences in IV and AV between virgin PET and recycled PET can be easily reduced. Furthermore, at or below the above range, solid-state polymerization of the recycled PET is not performed, or if it is performed, it can be performed in a short time, which is advantageous in terms of cost.

[0071] The lower limit of the AV of the recycled PET is preferably 3 eq / ton, more preferably 5 eq / ton, even more preferably 10 eq / ton, particularly preferably 15 eq / ton, and most preferably 20 eq / ton. If it is above the above range, there is no need to perform solid-state polymerization on the recycled PET, or even if solid-state polymerization is performed, it can be performed in a short time, which is advantageous in terms of cost. The upper limit of the AV of the recycled PET is preferably 85 eq / ton, more preferably 80 eq / ton, even more preferably 75 eq / ton, particularly preferably 70 eq / ton, and most preferably 65 eq / ton. By setting it to the above range or less, deterioration of the resin can be suppressed when a film is produced by adding the recycled resin.

[0072] The lower limit of the CT amount of recycled PET is preferably 0.5% by mass, more preferably 0.7% by mass, and even more preferably 0.8% by mass. The upper limit of the CT amount of recycled PET is preferably 1.1% by mass, more preferably 1.05% by mass, and even more preferably 1% by mass. When PET produced only by melt polymerization is made into a film and used as recycled PET, the CT amount is about 0.9 to 1.0% by mass.

[0073] The lower limit of the proportion of recycled PET in the total raw PET used to produce the film is preferably 5% by mass, more preferably 10% by mass, and even more preferably 15% by mass. The upper limit of the recycled PET proportion is preferably 50% by mass, more preferably 40% by mass, and even more preferably 35% by mass. By ensuring the above range, stable production with secured recycled raw materials and stable quality of the resulting film can be ensured.

[0074] In film production, it is preferable to minimize the decomposition of PET by, for example, reducing the water content of the PET used as a raw material, lowering the resin temperature during melt mixing, and shortening the time the resin is in a molten state, as detailed below.

[0075] The lower limit of the moisture content of both virgin PET and recovered TET used as raw materials during film production is preferably 1 ppm by mass, more preferably 5 ppm by mass, and even more preferably 10 ppm by mass. The upper limit of the moisture content during film production is preferably 150 ppm by mass, more preferably 100 ppm by mass, even more preferably 70 ppm by mass, particularly preferably 50 ppm by mass, and most preferably 30 ppm by mass. By keeping the moisture content at or below the above levels, decomposition of the resin during the film production process can be suppressed, and deterioration of the recovered resin can be suppressed.

[0076] The lower limit of the melting temperature of the resin during film production is the temperature at the location where the temperature is highest, and is preferably 270°C, more preferably 275°C. By setting the temperature above the above range, productivity can be increased. The upper limit of the melting temperature is preferably 290°C, more preferably 288°C, even more preferably 286°C, and particularly preferably 285°C. By setting the temperature below the above range, decomposition of the resin during the film production process can be suppressed, and deterioration of the recovered resin can be suppressed. Generally, during film production, the resin temperature is highest in the latter half of the extruder, and can be detected by the value on a thermometer attached to the extruder.

[0077] The lower limit of the melting time of the resin during film production is preferably 2 minutes, more preferably 3 minutes. The upper limit of the melting time of the resin during film production is preferably 20 minutes, more preferably 15 minutes, even more preferably 10 minutes, particularly preferably 10 minutes, and most preferably 10 minutes. By keeping the melting time within the above range or less, deterioration of the recovered resin can be suppressed.

[0078] It is also important to suppress the decomposition of PET during the process of pelletizing recycled PET.

[0079] The lower limit of the moisture content of the recycled PET during pelletization is preferably 1 ppm by mass, more preferably 5 ppm by mass, and even more preferably 10 ppm by mass. The upper limit of the moisture content of the recycled PET during pelletization is preferably 150 ppm by mass, more preferably 100 ppm by mass, even more preferably 70 ppm by mass, particularly preferably 50 ppm by mass, and most preferably 30 ppm by mass. By keeping the moisture content at or below the above levels, deterioration of the recycled PET can be suppressed.

[0080] In addition, when the recycled PET is the edge portion from the production of a film, it is also preferable to cut off the edge portion and then immediately pelletize it.

[0081] The lower limit of the melting temperature during pelletization of recycled PET is the temperature at the location where the temperature is highest, and is preferably 270°C, more preferably 275°C. By setting it above the above limit, productivity can be increased. The upper limit of the melting temperature during pelletization of recycled PET is preferably 290°C, more preferably 288°C, even more preferably 286°C, and particularly preferably 285°C. By setting it below the above limit, deterioration of the recycled resin can be suppressed. Generally, the resin temperature is highest in the latter half of the extruder, and this can be detected by the value on a thermometer attached to the extruder.

[0082] The lower limit of the melting time during pelletization of the recovered PET is preferably 1 minute, more preferably 2 minutes. The upper limit of the melting time during pelletization of the recovered PET is preferably 15 minutes, more preferably 10 minutes. By keeping the melting time within the above range, deterioration of the recovered resin can be suppressed.

[0083] It is also a preferred method to use a vented extruder to pelletize the recycled PET and melt-knead it under reduced pressure.

[0084] Although the reduced molecular weight can be increased by solid-state polymerizing recycled PET, from an economical standpoint, solid-state polymerizing recycled PET is not necessarily preferable unless the objective is to obtain a film with a high IV, low AV, and low CT that cannot be obtained with melt-polymerized PET.

[0085] In the production of a film, it is preferable to extrude a molten resin into a sheet, cool it, and then stretch the resulting unstretched sheet in at least one direction. For stretching, it is preferable to use a roll stretching method when stretching in the machine direction of the film, and a tenter stretching method when stretching in the transverse direction. Simultaneous biaxial stretching in the machine direction and the transverse direction may also be performed using a tenter.

[0086] The stretching temperature is preferably 80 to 130° C., more preferably 85 to 120° C., both longitudinally and transversely, and can be adjusted within this temperature range depending on the required properties.

[0087] The stretching ratio in at least one of the longitudinal and transverse directions, which are the main stretching directions, is preferably 3 to 8 times, more preferably 3.3 to 7 times, and can be adjusted within this range depending on the required properties. The other stretching ratio can also be adjusted depending on the properties required for the film to be produced.

[0088] The lower limit of the IV of the film is preferably 0.52 dL / g, more preferably 0.54 dL / g, even more preferably 0.55 dL / g, and particularly preferably 0.56 dL / g. The upper limit of the IV of the film is preferably 0.73 dL / g, more preferably 0.70 dL / g, even more preferably 0.67 dL / g, particularly preferably 0.65 dL / g, and most preferably 0.63 dL / g. By setting the IV within the above range, the mechanical properties can be improved, film formability can be improved, and decomposition of the recycled PET can be suppressed.

[0089] The lower limit of the AV of the film is preferably 5 eq / ton, more preferably 10 eq / ton. The upper limit of the AV of the film is preferably 80 eq / ton, more preferably 75 eq / ton, even more preferably 70 eq / ton, particularly preferably 65 eq / ton, and most preferably 60 eq / ton. By keeping it at or below the above levels, decomposition of the recycled PET can be suppressed.

[0090] The lower limit of the CT amount of the film is preferably 0.5 mass%, more preferably 0.7 mass%, and even more preferably 0.8 mass%, and the upper limit of the CT amount of the film is preferably 1.1 mass%, more preferably 1.05 mass%.

[0091] The film may contain colorants, lubricant particles, ultraviolet absorbers, melt resistivity adjusters, antistatic agents, antioxidants, heat stabilizers, and the like.

[0092] The film may have a single layer structure or a multi-layer structure obtained by coextrusion. In the case of a multi-layer structure, each layer may have a different composition, such as adding an ultraviolet absorber only to the middle layer or adding a lubricant only to the surface layer. Furthermore, each layer may have a different IV, AV, and CT value. In the case of a multi-layer structure, the IV, AV, and CT values ​​of the film are values ​​measured for the entire film without separating the layers.

[0093] 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.

[0094] The polyester film may be provided with an easy-adhesion layer.

[0095] The resin used in the adhesion layer is a polyester resin, a polyurethane resin, a polycarbonate resin, an acrylic resin, or the like, and a polyester resin, a polyester polyurethane resin, a polycarbonate polyurethane resin, or an acrylic resin is preferred. The adhesion layer is preferably crosslinked. Examples of crosslinking agents include an isocyanate compound, a melamine compound, an epoxy resin, and an oxazoline compound. Adding a water-soluble resin such as polyvinyl alcohol is also a useful means for improving adhesion to the polarizer.

[0096] The adhesive layer can be formed by applying a water-based coating containing these resins and, if necessary, adding a crosslinking agent, particles, etc., to the polyester film and drying the coating. Examples of particles include those used for the substrates described above.

[0097] The easy-adhesion layer may be provided on the stretched film offline, but is preferably provided in-line during the film-forming process. When provided in-line, it may be provided either before longitudinal stretching or transverse stretching, but is preferably coated just before transverse stretching, and 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.

[0098] The coating amount of the easy-adhesion layer is 0.01 to 1.0 g / m２ is preferable, and more preferably 0.03 to 0.5 g / m ２ is preferred.

[0099] Polyester films can be used in a variety of applications, such as those exemplified below: Process release films: for example, ceramic green sheets, resin solution film casting, etc. Transfer films: for example, metal foils, printed pattern layers, liquid crystal compound retardation layers, liquid crystal compound polarizers, etc.

[0100] Release films and transfer films may be provided with a release layer made of fluorine-based resins, silicone-based resins, long-chain alkyl group-containing acrylics, polyolefins, etc. Protective films: for example, polarizing plate protective films, surface protective films for image display devices, back surface protective films, solar cell backsheets, etc.

[0101] In these applications, a pressure-sensitive adhesive layer may be provided. The protective film may be provided with a pressure-sensitive adhesive layer, such as a rubber-based, acrylic-based, silicone-based, or urethane-based adhesive layer. Furthermore, in the case of permanent protective films such as solar cell backsheets, they may be attached to the object with an adhesive. Optical films: for example, lens sheet substrates, prism sheet substrates, nanoimprint film substrates, diffusion sheet substrates, shatterproof films, polarizer protective films, transparent conductive film substrates, etc.

[0102] In the case of lenses, prism sheets, and nanoimprinting, a layer of an acrylic compound provided on a polyester film can be brought into contact with a mold and cured to form a pattern.

[0103] Surface protection films for image display devices and polarizer protection films may be provided with a hard coat layer, an anti-reflection layer, a reflection-reducing layer, an anti-glare layer, etc. Transparent conductive films may be provided with a hard coat layer, a refractive index adjustment layer, etc. Examples of conductive layers in transparent conductive films include ITO films, metal etching or conductive paste meshes, and metal whisker coating layers. Electrical, electronic, and communication films: For example, flexible circuit substrates, coverlay films, carrier tape covers, electronic tag substrates, IC cards, motor insulating films, etc. Printing substrate films: For example, electrical product labels, advertising labels, campaign labels, etc. Barrier films: For example, metal vapor deposition films, metal oxide vapor deposition films, barrier coat films, etc.

[0104] Examples of metal vapor deposition include aluminum, examples of metal oxides include aluminum oxide, silicon dioxide, and aluminum oxide-silicon composite oxide, and examples of barrier coatings include sol-gel coatings, inorganic layered compound particle-containing coatings, polyvinyl alcohol coatings, ethylene-vinyl alcohol copolymer coatings, and vinyl chloride coatings. ・Packaging laminate films: Laminates with nylon film, polypropylene film, etc. ・Heat-sealable films: Laminates with a heat-seal layer of polyethylene, polypropylene, copolymer polyester, etc.

[0105] In these laminates, adhesives such as isocyanate-curing, epoxy-curing, and radiation-curing types can be used.Heat-shrinkable polyester film: beverage bottle labels, beverage can labels, cap seals, packaging for lidded containers, bundling packaging, etc.

[0106] In these applications, it is preferable to blend other polyesters or copolymer polyester resins into the film to adjust the heat shrinkage properties. Examples of other polyesters include tetramethylene terephthalate and trimethylene terephthalate. Examples of copolymer polyesters 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), and ethylene 1,4-cyclohexanedimethylene terephthalate copolymer (1,4-cyclohexanedimethanol added to the glycol component), as well as copolymers of these with other components. The copolymerization and blending amounts can be determined so that, assuming the total acidic content and total glycol components in the film are 100 mol%, the total content of copolymerization components other than the terephthalic acid component and the ethylene glycol component is preferably 5 to 70 mol%, more preferably 8 to 50 mol%, and even more preferably 10 to 40 mol%.

[0107] The polyester film may be a void-containing film obtained by blending a polyester resin with an incompatible resin such as polypropylene, polymethylpentene, or polystyrene and stretching the blend. In this case, the incompatible resin preferably accounts for 3 to 30% by mass, more preferably 5 to 20% by mass, of the total resin content of the film.

[0108] Various pigments, such as titanium oxide, barium sulfate, and carbon, may also be added to produce films in white, black, or other colors. These films are suitable for use in labels, printing films as a paper substitute, light-reflecting films, circuit substrates, cards, tags, and the like.

[0109] Furthermore, polyimide, polyamideimide, polyamide, polyphenylene sulfide, polyphenylene sulfone, polyphenylene ether, etc. may be added to form a modified polyester film. In this case, the modifying resin other than polyester is preferably 0.5 to 20 mass% of the total resin amount constituting the film, more preferably 1 to 15 mass%, and even more preferably 2 to 10 mass%.

[0110] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. (1) Intrinsic Viscosity (IV) Approximately 3 g of a sample was freeze-pulverized and dried at 140°C for 15 minutes. 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 times of the sample and solvent were measured using an Ubbelohde viscometer (manufactured by Rigo Co., Ltd.) thermostated at 30°C, and the intrinsic viscosity [η] was calculated using the following equation:

[0111] [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)

[0112] (2) Content of specified metal elements in the sample Polyester resin 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 and aluminum elements in the polyester resin were determined by high-frequency inductively coupled plasma atomic emission spectrometry.

[0113] Apparatus: CIROS-120 manufactured by SPECTRO Plasma output: 1400 W Plasma gas: 13.0 L / min Auxiliary gas: 2.0 L / min Nebulizer: Crossflow nebulizer Chamber: Cyclone chamber Measurement wavelength: 167.078 nm

[0114] (3) Phosphorus Content in Polyester Resin 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.

[0115] (4) Acid Value The film and raw polyester resin were measured using the following method. Sample Preparation: The film or raw polyester resin was pulverized and vacuum-dried at 70°C for 24 hours, and then weighed to within 0.20±0.0005 g using a balance. When measuring the acid value of each layer, each layer was extruded as a single layer to prepare a sample. The mass at that time was designated W (g). 10 ml of benzyl alcohol and a weighed sample were added to a test tube, and the test tube was immersed in a benzyl alcohol bath heated to 205°C. The sample was dissolved while stirring with a glass rod. Samples obtained after dissolution times of 3, 5, and 7 minutes were designated A, B, and C, respectively. Next, a new test tube was prepared, and only benzyl alcohol was added. The same procedure was repeated. Samples obtained after dissolution times of 3, 5, and 7 minutes were designated A, B, and C, respectively.

[0116] Titration: Titrate using a 0.04 mol / l potassium hydroxide solution (ethanol solution) whose factor is known in advance. Phenol red is used as the indicator, and the end point is when the color changes from yellow-green to pale pink, and the titer (ml) of the potassium hydroxide solution is determined. The titer volumes of samples A, B, and C are designated XA, XB, and XC (ml). The titer volumes of samples a, b, and c are designated Xa, Xb, and Xc (ml).

[0117] Using the titer amounts XA, XB, and XC for each dissolution time, the titer amount V (ml) at 0 minute dissolution time is calculated by the least squares method. Similarly, using Xa, Xb, and Xc, the titer amount V0 (ml) is calculated. Next, the acid value is calculated using the following formula: Carboxyl terminal concentration (eq / ton) = [(V-V0) x 0.04 x NF x 1000] / W, where NF is the factor of 0.04 mol / l potassium hydroxide solution.

[0118] (5) Quantitative Determination of Cyclic Trimer The sample was frozen, crushed, or fragmented, and 100 mg of 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.

[0119] 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

[0120] (6) Breaking elongation (TE) was measured in accordance with JIS-C-2318-19975.3.31 (tensile strength and elongation). Film test pieces 10 mm wide and 190 mm long were sampled from the MD direction (longitudinal direction, film winding direction) and the TD direction (transverse direction, direction perpendicular to the MD direction). The film test pieces were set in a tensile tester (Tensilon RTC-125A, manufactured by ORIENTEC Co., Ltd.) and elongated at a chuck distance of 100 mm and a take-up speed of 200 mm / min under an environment of a temperature of 23°C and a humidity of 65% RH. The stress required for breaking and the elongation of the film were measured, and the breaking elongation (%) was calculated.

[0121] The reduction rate of elongation at break is a value obtained by dividing the measured value by the elongation at break of the film of Reference Example made only from virgin PET.

[0122] Preparation of PET resins Chemically recycled PET (A1, A2) Chemically recycled BHET was obtained by depolymerizing recovered PET bottles, PET fibers, etc. in the presence of ethylene glycol, and was then polycondensed using a composite catalyst of basic aluminum acetate and Irganox 1222 (manufactured by BASF). The properties are shown in Table 2.

[0123] The total acid value and hydroxyl value of the chemically recycled BHET used was 8,100 eq / ton. Measurement was performed as follows. (Measurement of BHET acid value (AV)) 1.00 g of a sample pulverized in a handy mill (pulverizer) was precisely weighed, and 20 ml of pyridine was added. A few grains of zeolite were added, and the mixture was boiled under reflux for 15 minutes to dissolve. Immediately after boiling under reflux, 10 ml of pure water was added, and the mixture was allowed to cool to room temperature. Titration was performed with N / 10-NaOH using phenolphthalein as an indicator. The same procedure was also performed on a blank without the sample. If the oligomer did not dissolve in pyridine, it was measured in benzyl alcohol. AV (eq / ton) was calculated according to the following formula:

[0124] AV = (A - B) x 0.1 x f x 1000 / W (A = titration constant (ml), B = titration constant of blank (ml), f = N / 10 - NaOH factor, W = sample weight (g))

[0125] (Measurement of hydroxyl value (OHV)) 0.50 g of a sample pulverized in a handy mill (pulverizer) was precisely weighed, 10 ml of an acetylating agent (0.5 mol / L solution of pyridine acetic anhydride) was added, and the sample was immersed in a water bath at 95°C or higher for 90 minutes. Immediately after removing from the water bath, 10 ml of pure water was added and the sample was allowed to cool to room temperature. ３ The same procedure was carried out for a blank without adding the sample. In advance, 20 ml of N / 10-HCl was titrated with N / 5-NaOH-CH ３ The solution is titrated with OH solution, and the factor (F) of the solution is calculated according to the following formula.

[0126] F = 0.1 x f x 20 / a (f = N / 10 - hydrochloric acid factor, a = titration constant (ml)) Calculate the OHV (eq / ton) according to the following formula.

[0127] OHVo = {(B - A) x F x 1000 / W} + AV (A = titration constant (ml), B = titration constant of blank (ml), F = N / 5-NaOH-CH ３ OHOH solution factor, W = sample weight (g)

[0128] Chemically recycled PET (A3, A4) These were obtained by polycondensation of the same chemically recycled BHET used in A1 with antimony trioxide as a catalyst. The properties are shown in Table 2.

[0129] Non-chemically recycled PET (B1) was obtained by polycondensation of terephthalic acid and ethylene glycol using antimony trioxide as a catalyst, and had an IV of 0.62 dL / g, an AV of 34 eq / ton, and a CT content of 0.92% by mass. The properties are shown in Table 2.

[0130]

[0131] Preparation of recycled PET pellets Dried virgin pellets were fed into the film manufacturing equipment used in the examples, and extruded into a sheet using a die onto a cooling roll under the conditions shown in Table 2, and then wound into a roll without stretching.

[0132] The rolled sheet was crushed in a crusher, placed in a flexible container bag, and left in an unair-conditioned room for at least one week. The crushed resin was then dried under reduced pressure and fed into a twin-screw kneader. It was melted under the conditions listed in Table 2, extruded into strands, cooled with water, and chipped to obtain pellets of the recovered resin. The melting time in Table 2 is the average time from the region of the extruder set above the melting point of the film to the die exit, and is calculated by dividing the total amount of resin in the extruder calculated by simulation and the amount from the piping to the die exit by the volume of resin fed per unit time.

[0133] The properties of the recovered resin are shown in Table 3.

[0134]

[0135] Virgin PET pellets and recycled PET pellets were mixed and dried under reduced pressure, then placed in a hopper of a film production facility and extruded into a sheet on a cooling roll under the conditions shown in Table 3. The resulting sheet was stretched 3.4 times in the longitudinal direction at 90°C using rolls with different circumferences. Subsequently, it was stretched 3.8 times in the transverse direction in a tenter heated to 120°C and then heat-set at 230°C to obtain a biaxially stretched polyester film with a thickness of 40 μm.

[0136] Each reference example was produced using only virgin resin.

[0137] In Examples 1 and 2, even when the amount of recovered resin increased, the difference in IV and AV of the film was small compared to Reference Example, and the decrease in physical properties (breaking strength) was also small. In particular, in Examples 1 to 6, which used an Al-based catalyst, the difference in IV, AV, and film physical properties was small, and there was almost no risk of problems occurring even when the amount of recovered resin added changed significantly.

[0138] On the other hand, in the comparative examples, in Comparative Example 1, in which 10% by mass of recycled resin was used, the difference in IV and AV of the film was small compared to the Reference Example, and there was no decrease in physical properties (breaking strength). However, when the recycled resin was increased to 35%, a decrease in IV, an increase in AV, and a decrease in physical properties were observed. In order to produce a film with the same properties, there was a limit to the amount of recycled resin that could be added. Furthermore, if the amount of recycled resin added was large, there was a concern that the film would be more susceptible to deterioration if exposed to humid and hot conditions for a long period of time, and it was difficult to obtain a film of stable quality in terms of durability.

[0139]

[0140] According to the present invention, it is possible to obtain a polyester film made from chemically recycled polyethylene terephthalate, in which the properties of the resulting film do not change significantly even if the amount of recovered polyester film added varies.This makes it possible to supply a film that is highly effective in reducing the burden on the environment and has stable quality even if there are fluctuations in production volume, making a significant contribution to industry.

Claims

1. A polyester film containing a chemically recycled polyethylene terephthalate resin obtained by polycondensing a raw material containing bis-2-hydroxyethyl terephthalate, obtained by decomposing polyester resin, using an aluminum compound and a phosphorus compound as catalysts.

2. The polyester film according to claim 1, wherein the proportion of the raw material containing bis-2-hydroxyethyl terephthalate is 50% by mass or more.

3. The polyester film according to claim 1, wherein the polyester resin includes recovered polyester resin obtained from the film manufacturing process.

4. The polyester film according to claim 3, wherein the proportion of recovered polyester resin is 5 to 50% by mass of the total polyester resin constituting the polyester film.

5. The polyester film according to claim 1 or 3, wherein the intrinsic viscosity of the polyester resin constituting the polyester film is 0.52 to 0.73 dL / g.

6. The polyester film according to claim 1 or 3, wherein the acid value of the polyester resin constituting the polyester film is 5 to 80 dL / g.

7. A method for producing a polyester film, characterized by comprising the step of melting and mixing unused chemically recycled polyethylene terephthalate resin obtained by polycondensing raw materials containing bis-2-hydroxyethyl terephthalate obtained by decomposing polyester resin, and polyethylene terephthalate resin recovered from molten molded product discharged from the process of producing the polyester film, and forming it into a film.

8. The method for producing a polyester film according to claim 7, wherein the recovered polyethylene terephthalate resin is 5 to 50% by mass of the total amount of the unused chemically recycled polyethylene terephthalate resin and the recovered polyethylene terephthalate resin.

9. A method for producing a polyester film according to claim 7 or 8, wherein the proportion of bis-2-hydroxyethyl terephthalate obtained by decomposing the polyester resin is 50% by mass or more of the total amount of bis-2-hydroxyethyl terephthalate used as a raw material when polycondensing the unused chemically recycled polyethylene terephthalate resin.

10. A method for producing a polyester film according to claim 7 or 8, wherein the chemically recycled polyethylene terephthalate resin obtained by polycondensation of a raw material containing bis-2-hydroxyethyl terephthalate obtained by decomposing the polyester resin contains an aluminum compound and a phosphorus compound as catalysts.

11. A method for producing a polyester film according to claim 7 or 8, wherein the absolute value of the difference between the intrinsic viscosity of the unused chemically recycled polyethylene terephthalate resin and the intrinsic viscosity of the recovered polyethylene terephthalate resin is 0.1 dL / g or less.

12. A method for producing a polyester film according to claim 7 or 8, wherein the ratio of the intrinsic viscosity of the unused chemically recycled polyethylene terephthalate resin to the intrinsic viscosity of the recovered polyethylene terephthalate resin (intrinsic viscosity of the recovered polyethylene terephthalate resin / intrinsic viscosity of the unused chemically recycled polyethylene terephthalate resin) is 0.85 to 1.

13. A method for producing a polyester film according to claim 7 or 8, wherein the absolute value of the difference between the acid value of the unused chemically recycled polyethylene terephthalate resin and the acid value of the recovered polyethylene terephthalate resin is 22 eq / ton or less.