Biaxially oriented polyester resin film and method for manufacturing the same

Abstract

To provide a biaxially oriented polyester resin film having excellent physical properties, particularly excellent flex resistance in a low-temperature environment, equal to or superior to those of biaxially oriented polyester films that do not use recycled raw materials. The present invention provides a compound having the following physical properties (1) to (2): (1) In differential scanning calorimetry (DSC), the temperature is increased from 25°C to 300°C at a rate of 20°C / min, held at 300°C for 10 minutes, and then decreased at a rate of 40°C / min. The crystallization temperature is 160-180°C. (2) After 200 repeated bending fatigue tests using a Gelbo flex tester in a -10°C atmosphere, the number of pinholes is 10 / 500cm. 2 The present invention relates to a biaxially stretched polyester resin film characterized by satisfying all of the following requirements:

Description

[Technical Field]

[0001] The present invention relates to a novel biaxially oriented polyester resin film and a method for producing the same. [Background technology]

[0002] Polyethylene terephthalate (PET), a representative example of polyester resin, is widely used in fibers, films, molded products such as PET bottles, etc., due to its high melting point, chemical resistance, and relatively low cost. However, the generation of waste is unavoidable during the manufacturing or processing of these polyester products, and these products are often disposed of after use. Therefore, there is a need to dispose of large quantities of this polyester waste and used polyester products. However, incinerating these materials generates high heat, severely damaging the incinerator and shortening its lifespan, as well as causing problems such as air pollution and CO2 gas emissions.

[0003] In contrast, if polyester resin is not disposed of by incineration, the problems mentioned above can be avoided, but since polyester resin does not decompose in nature, it will remain almost indefinitely. As a result, polyester products that have been used once, such as discarded polyester containers, flow into the ocean via rivers, and are broken down into microplastics by the action of waves, currents, and ultraviolet rays. In recent years, the accumulation of these microplastics in the bodies of marine organisms and their concentration through the food chain have been recognized as a major cause of plastic pollution in the ocean, negatively impacting marine ecosystems. For these reasons, there is a global movement to reduce the amount of plastics, including polyester resin, used, and to switch to biodegradable plastics.

[0004] For similar reasons, recycling is being carried out in various ways to reuse resources. Regarding polyester products, such as PET, in addition to recycling the polyester waste generated during the manufacturing process, methods are being considered to collect products that have been discarded after entering the market and reuse them as raw materials. In particular, in recent years, products bearing the Eco Mark, which certifies that a certain recycling rate has been achieved, have become widespread.

[0005] Furthermore, various recycling methods have been proposed that use recycled polyester, obtained by recovering polyester waste generated during the manufacturing process or used polyester products, as raw material.

[0006] For example, methods have been proposed such as adding methanol to PET waste to decompose it into dimethylene terephthalate (hereinafter sometimes referred to as "DMT") and ethylene glycol (hereinafter sometimes referred to as "EG") (Patent Document 1), adding EG to PET waste to depolymerize it, and then adding methanol to recover DMT (Patent Document 2), depolymerizing PET waste with EG to obtain an oligomer and using it in a polycondensation reaction (Patent Document 3), or using it in solid-phase polymerization after depolymerization (Patent Documents 4 and 5).

[0007] Incidentally, impurities that become problematic when recycling PET bottles and other products once they have been manufactured include various additives added to the polyester resin, as well as components attached to the bottle itself, such as a) caps (aluminum, polypropylene, polyethylene), b) inner stoppers, c) liners (polypropylene, polyethylene), d) labels (paper, polystyrene or other resins, ink), e) adhesives, and f) printing inks.

[0008] Generally, the pretreatment for the recycling process is carried out using the following procedure. First, the collected PET bottles are passed through a vibrating sieve to remove sand, metal, etc. Then, the PET bottles are washed, colored bottles are separated, and then coarse crushing is performed. Next, labels and other materials are removed by air separation. Furthermore, aluminum fragments derived from caps, etc., are removed, and the PET bottle fragments are finely crushed. High-temperature alkaline washing is performed to remove components such as adhesives, proteins, and mold, and a process is carried out to separate different components such as polypropylene and polyethylene based on differences in specific gravity. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Special Publication No. 42-8855 [Patent Document 2] Japanese Patent Application Publication No. 48-62732 [Patent Document 3] Japanese Patent Application Publication No. 60-248646 [Patent Document 4] Japanese Patent Publication No. 2012-126763 [Patent Document 5] Japanese Patent Publication No. 2012-041463 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, these conventional technologies have problems in the manufacturing process of the resulting polyester resin film, and there is room for further improvement in terms of the physical properties of the resulting polyester resin film.

[0011] For example, the methods described in Patent Documents 1 to 3 involve significant costs for the installation, operation, and maintenance of the recovery device, leaving room for improvement in terms of practicality.

[0012] In addition, the recycled polyester resin obtained by the recycling methods described in Patent Documents 1 to 3 cannot sufficiently remove foreign substances derived from non-polyester resins, and the amount of foreign substances mixed therein cannot be sufficiently reduced. For this reason, contamination of the T-die surface (lip surface) occurs in the film-forming process of the film, and troubles such as breakage of the film frequently occur in the stretching process. As a result, the processing operability becomes extremely poor, and long-term continuous operation becomes difficult. In particular, when manufacturing a thin film, it is necessary to increase the take-up speed during film formation, and therefore, since more tension is applied than in the case of a thick film, the above problem becomes more prominent.

[0013] A film formed from a recycled polyester resin obtained by the method described in Patent Document 4 or 5 does not have sufficient mechanical strength including tensile elongation, and thus breakage also easily occurs in the stretching process when forming a thin film, and there are also problems in operability, and it is inferior in flex resistance under a low-temperature environment.

[0014] Regarding this, generally, if the content ratio of virgin polyester as a film raw material is increased, it becomes possible to obtain a film having better physical properties, but the flex resistance under a low-temperature environment has not been improved. On the other hand, from an environmental perspective, it is desirable that the ratio of recycled raw materials in the film can be increased. For example, for the certification of an eco-mark for a laminate packaging material formed by laminating a film made of a polyester film and other materials, it is required that the recycled raw material ratio is 25% by mass or more. However, it is difficult to manufacture a highly stretched film with a recycle ratio of 35% or more in a thin polyester film with a thickness of 50 μm or less.

[0015] Thus, from the viewpoint of reducing the amount of plastic used, there is a need for a method capable of manufacturing a biaxially stretched polyester resin film that can be continuously operated for a long time even for a thin film with a thickness of 50 μm or less and has excellent physical properties equivalent to or better than those of a biaxially stretched polyester film not using recycled raw materials, but in fact, its development has not yet been achieved.

[0016] Therefore, the main object of the present invention is to provide a biaxially stretched polyester resin film having excellent physical properties equivalent to or better than those of a biaxially stretched polyester film not using recycled raw materials, particularly excellent flex resistance under low temperature environments. Furthermore, another object of the present invention is to provide a manufacturing method capable of long-term continuous operation even when using recycled polyester raw materials or for thin films with a thickness of 50 μm or less.

Means for Solving the Problems

[0017] As a result of intensive research in view of the problems of the prior art, the inventors of the present invention have found that a polyester resin film obtained through specific processes using a recycled polyester raw material obtained by recovering polyester pieces generated in the manufacturing process of used polyester products or polyester products can achieve the above object, and thus have completed the present invention.

[0018] That is, the present invention relates to the following biaxially stretched polyester resin-based film and its manufacturing method. 1. The following physical properties (1) to (2): (1) In differential scanning calorimetry (DSC), when heating from 25°C to 300°C at a heating rate of 20°C / min, holding at 300°C for 10 minutes, and then cooling at a cooling rate of 40°C / min, the crystallization temperature is 160 to 180°C. (2) The number of pinholes after 200 repeated bending fatigue tests using a gelbo flex tester in a -10°C atmosphere is 10 or less per 500 cm 2 as follows. A biaxially stretched polyester resin-based film characterized by satisfying all of the above. 2. The biaxially stretched polyester resin-based film according to item 1 above, characterized in that the haze is 10.0% or less. 3. The biaxially stretched polyester resin-based film according to item 1 above, wherein the carboxyl end group concentration is 20 to 60 equivalents / t. 4. The biaxially oriented polyester resin film described in item 1, wherein the surface crystallinity determined by infrared spectroscopy (ATR-IR) using total internal reflection is 1.1 to 1.4. 5. A biaxially oriented polyester resin film according to item 1, wherein the thickness is 50 μm or less, and the tensile elongation in both the MD direction and the TD direction is 100% or more. 6. A biaxially oriented polyester resin film as described in item 1, wherein the b* value is 0 or less. 7. A packaging material comprising a biaxially oriented polyester resin film as described in any of items 1 to 6 above. 8. A method for producing a biaxially oriented polyester resin film, (A) A step of obtaining a reaction product by subjecting recycled polyester raw material to a depolymerization reaction, (B) A step of filtering the reaction product and recovering the filtrate. (C) A step of obtaining a polyester resin by subjecting the filtrate to a polycondensation reaction at a temperature of 260°C or higher and a pressure of 1.0 hPa or lower in the presence of a polymerization catalyst. (D) A step of producing an unstretched film using the starting material containing the polyester resin, and then biaxially stretching the unstretched film. A method for producing a biaxially oriented polyester resin film, characterized by including the following: 9. A method for producing a biaxially oriented polyester resin film according to item 8, wherein step (A) is carried out in the presence of an ethylene terephthalate oligomer and an ethylene glycol. 10. The method for producing a biaxially oriented polyester resin film according to item 9, wherein step (A) is carried out with all components of the ethylene terephthalate oligomer, ethylene glycol, and recycled polyester raw material in a molar ratio of total glycol component to total acid component within the range of 1.08 to 1.35. 11. The method for producing a biaxially oriented polyester resin film according to item 8, wherein in step (B) above, the filtration is performed using a filter with a particle size of 10 to 25 μm. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a biaxially oriented polyester resin film that has excellent physical properties equivalent to or better than biaxially oriented polyester films that do not use recycled materials, and in particular excellent bending resistance in low-temperature environments.

[0020] In particular, the biaxially oriented polyester resin film of the present invention is made from recycled raw materials processed in a specific process, resulting in a low amount of foreign matter contamination and containing polyester resin with a specific cooling crystallization temperature range. Therefore, even with a thickness of 50 μm or less, continuous production at a high stretching speed is possible over a long period, and the surface crystallinity of the film is kept low. For this reason, it has superior bending resistance in low-temperature environments compared to polyester resins that do not contain recycled raw materials, and its tensile elongation in the MD and TD directions is as good as that of polyester resin films that do not use recycled raw materials.

[0021] Furthermore, the present invention provides a biaxially oriented polyester resin film with a high recycling rate of 35% or more. This film is excellent in mechanical properties such as tensile strength and tensile modulus, as well as in transparency, color tone, wettability, and printability, making it particularly suitable for use as a packaging material.

[0022] The manufacturing method of the present invention makes it possible to efficiently and reliably produce biaxially oriented polyester resin films with excellent properties such as flexibility, as described above. In other words, the biaxially oriented polyester resin film obtained by the manufacturing method of the present invention can also exhibit the excellent properties described above. [Modes for carrying out the invention]

[0023] 1. Biaxially oriented polyester resin film The biaxially oriented polyester resin film of the present invention (the present invention film) has the following physical properties (1)~(2): (1) In differential scanning calorimetry (DSC), when the temperature is increased from 25°C to 300°C at a heating rate of 20°C / min, held at 300°C for 10 minutes, and then cooled at a cooling rate of 40°C / min, the temperature at which crystallization occurs is 160-180°C. (2) After 200 repeated bending fatigue tests using a gel flex tester in a -10°C atmosphere, the number of pinholes was 10 / 500cm. 2 The following: It is characterized by satisfying all of the following conditions.

[0024] (A) Composition of the film of the present invention The film of the present invention contains a polyester resin, but its content is not particularly limited. In the present invention, the polyester resin content is preferably about 60 to 100% by mass of the film of the present invention, and more preferably 80 to 100% by mass. Therefore, other components may be included as long as they do not hinder the effects of the present invention.

[0025] Other components include, for example, additives commonly found in films, as will be described later. Furthermore, these additives include not only those added for the first time during the manufacturing of the film of the present invention, but also additives and impurities present in the raw materials.

[0026] The polyester resin included in the film of the present invention includes polyethylene terephthalate and polybutylene terephthalate, but in the present invention, it is desirable to include polyethylene terephthalate (PET) because it is easy to use a polyester resin (hereinafter referred to as "recycled polyester resin") that contains a component derived from recycled polyester raw materials in part or all as its raw material. In this case, the proportion of PET in the polyester resin is not particularly limited, but can usually be appropriately set within the range of 70 to 100% by mass, preferably 80 to 100% by mass, and most preferably 90 to 100% by mass.

[0027] PET is usually a polycondensate of ethylene glycol and terephthalic acid, but depending on the raw materials used, it may contain components other than the two components mentioned above. In this case, polyester resins other than PET may be produced by polycondensation reactions, and such embodiments are also included in the present invention. That is, when the film of the present invention contains polyester resins other than PET, it may contain polyester resins copolymerized with components such as those shown below as acid components or glycol components. Furthermore, when it contains polyester resins other than PET, it may contain one or more types of polyester resins.

[0028] Examples of acidic components that make up polyester resins include isophthalic acid, phthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, adipic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, dodecanedioic acid, dimer acids, and also trimellitic anhydride, trimellitic acid, pyromellitic acid, 1,4-cyclohexanedicarboxylic acid, sebacic acid, and dimer acids. These may be present individually or in combination of two or more.

[0029] Furthermore, examples of glycol components constituting the polyester resin include neopentyl glycol, 1,4-butanediol, 1,2-propylene glycol, 1,5-pentanediol, 1,3-propanediol, 1,6-hexamethylenediol, diethylene glycol, 1,4-cyclohexanedimethanol, dimer diol, butylethylpropanediol, (2-methyl-1,3-propanediol, trimethylolpropane, glycerin, pentaerythritol, ethylene oxide adducts of bisphenol A or bisphenol S, etc. These may be present individually or in combination of two or more.

[0030] The carboxyl-terminal group concentration of the film of the present invention is not particularly limited, but is usually preferably around 20 to 60 equivalents / t. In particular, the upper limit is preferably 50 equivalents / t or less, and among those, 45 equivalents / t or less is most preferable. The lower limit is most preferably 30 equivalents / t or more. By setting the carboxyl-terminal group concentration to 60 equivalents / t or less, it is possible to obtain a biaxially oriented film with excellent heat resistance and excellent tensile elongation in the MD and TD directions. On the other hand, by setting the carboxyl-terminal group concentration to 20 equivalents / t or more, even a relatively thin biaxially oriented film of 50 μm or less can be produced continuously over a relatively long period of time, producing a biaxially oriented film with a high stretch ratio that exhibits tensile elongation in the MD and TD directions as excellent as that of polyester resin films that do not use recycled materials.

[0031] Furthermore, in the polyester resin film of the present invention, when the total amount of all glycol components is 100 mol%, the diethylene glycol content is preferably 0.5 to 3.0 mol%, more preferably 1.0 to 3.0 mol%, and most preferably 1.2 to 3.0 mol%. In particular, by using recycled polyester resin as described later, surface (lip surface) contamination of the T-die during film formation can be suppressed, and it becomes possible to obtain a biaxially oriented film that can be continuously produced over a long period of time at a high stretch ratio using polyester resin with a high recycling rate.

[0032] The polyester resin-based film of the present invention may contain one or more additives, such as colorants, fillers, dispersants, antioxidants, UV absorbers, preservatives, antistatic agents, antiblocking agents, and inorganic fine particles, to the extent that they do not adversely affect the performance of the film.

[0033] In particular, the film of the present invention may contain a lubricant for purposes such as improving the slipperiness of the film. Either an inorganic or organic lubricant can be used. Specific examples of lubricants include clay, talc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, magnesium aluminosilicate, glass balloons, carbon black, zinc oxide, antimony trioxide, zeolite, hydrotalcite, layered silicates, and ethylenebisstearamide. Among these, silica is preferred. The lubricant content is not limited, but is usually appropriate in the range of about 0.01 to 0.3% by mass in the polyester resin film.

[0034] On the other hand, in the film of the present invention, from the viewpoint of improving transparency, the content of the impact-resistant modifier is preferably 3% by mass or less, more preferably 2% by mass or less, even more preferably 1% by mass or less, particularly preferably 0.5% by mass or less, and most preferably substantially absent. The impact-resistant modifier is a dispersant (dispersed particles) for suppressing the propagation of cracks due to impact or bending applied to the film. Therefore, any material having such a function is included, for example, materials commercially available under names such as "impact-resistant modifier" or "impact strength modifier," as well as materials commercially available or used under other names.

[0035] In particular, elastomers and rubbers are examples of materials having such functions. More specifically, these include olefin polymers such as (ethylene and / or propylene)-α-olefin copolymers, (ethylene and / or propylene)-α,β-unsaturated carboxylic acid and / or unsaturated carboxylic acid ester) copolymers and ionomer polymers, elastomers such as styrene elastomers, urethane elastomers, fluorine elastomers, vinyl chloride elastomers, polyester elastomers, and polyamide elastomers, and synthetic rubbers such as thiocol rubber, polysulfide rubber, acrylic rubber, silicone rubber, polyether rubber, and epichlorohydrin rubber.

[0036] Adding impact-resistant modifiers improves the flexibility of the film, but the dispersion of these modifier particles within the film reduces its transparency. Therefore, in conventional biaxially oriented polyester resin films, flexibility and transparency are considered mutually exclusive properties, making it difficult to achieve both simultaneously. In contrast, the film of the present invention exhibits excellent flexibility and other properties even without these impact-resistant modifiers, thus ensuring high transparency. In other words, the present invention provides a film that combines excellent flexibility and high transparency.

[0037] The film of the present invention may be subjected to surface treatments such as corona discharge treatment or easy-adhesion treatment, to the extent that it does not impair the effects of the present invention. Furthermore, an easy-adhesion layer, a barrier coat layer, a printed layer, etc., may be provided as needed.

[0038] (B) Structure and characteristics of the film of the present invention The film of the present invention is a biaxially oriented (biaxially stretched) film, and has the following physical properties (1)~(2): (1) In differential scanning calorimetry (DSC), when the temperature is increased from 25°C to 300°C at a heating rate of 20°C / min, held at 300°C for 10 minutes, and then cooled at a cooling rate of 40°C / min, the temperature at which crystallization occurs (cooling crystallization temperature) is 160-180°C, and (2) After 200 repeated bending fatigue tests using a gel flex tester in a -10°C atmosphere, the number of pinholes was 10 / 500cm. 2 The following conditions must be met (flexural resistance): All of the following conditions must be met.

[0039] (1) Cooling crystallization temperature (Tc) The cooling crystallization temperature (Tc) of the film of the present invention must have a lower limit of 160°C or higher, more preferably 163°C or higher, more preferably 165°C or higher, and most preferably 170°C or higher.

[0040] Furthermore, the upper limit of Tc must be 180°C or less, more preferably 178°C or less, and more preferably 175°C or less. By controlling the cooling crystallization temperature within the above range, excellent tensile elongation and flexibility in low-temperature environments can be achieved. By including a preferred content of 30% by mass or more, and a more preferred content of 40% by mass or more, of the recycled polyester resin described later as a raw material for the film of the present invention, the cooling crystallization temperature (Tc) of the film of the present invention can be set within the above range.

[0041] (2) Flexibility One of the advantages of this invention over conventional polyester resin films (especially virgin polyester films) is its flexibility. The degree of flexibility is indicated by the number of pinholes on the film surface after a specific flexibility test; a lower number of pinholes indicates higher flexibility.

[0042] This test measured the number of pinholes after 200 repeated bending fatigue tests using a Gelboflex tester in a -10°C atmosphere, using a 500cm film. 2 The following is indicated by the number of pinholes per unit. The gel flex tester (device) itself is not particularly limited, and known or commercially available models can be used.

[0043] The number of pinholes in the film of this invention is typically 10 per 500 cm. 2 The following applies, especially 5 pieces / 500cm 2 The following is desirable: Films with such a small number of pinholes have excellent tear resistance when used as packaging, and can be suitably used not only as food containers or food packaging materials for chilled distribution, but also as medical containers such as intravenous fluid bags.

[0044] (3) Other physical properties In addition to the physical properties described in (1) and (2) above, it is desirable that the film of the present invention further possesses at least one of the following physical properties.

[0045] (3-1) Haze (Hz) From the viewpoint of maintaining transparency when used in packaging materials, etc., the haze is usually 10% or less, more preferably 8% or less, and most preferably 7% or less. The lower limit of the haze can be, for example, around 0.1%, but is not limited to this. If transparency is not required for the film of the present invention, the haze may exceed 10%.

[0046] (3-2)Surface crystallinity The surface crystallinity of the film of the present invention is not particularly limited, but it is desirable to set it within the following range. The lower limit is preferably 1.1 or higher, more preferably 1.15 or higher, and most preferably 1.2 or higher. The upper limit is preferably 1.4 or lower, and more preferably 1.35 or lower. By setting the surface crystallinity within this range, it is possible to obtain mechanical strength, and in particular excellent bending resistance.

[0047] (3-3) b* value The film of the present invention has an appearance, b * The value is preferably 0 or less, and more preferably -1 or less. The b* value is an indicator of color tone. A higher b* value indicates a stronger yellow tint in the film, which can suggest deterioration of the packaging material or contents; therefore, a lower b* value is preferred.

[0048] (3-4) Wetting tension In terms of printability when printing on its surface, the film of the present invention preferably has a wet tensile strength of 44 mN / m or more, more preferably 46 mN / m or more, and most preferably 50 mN / m or more.

[0049] (3-5) Tensile elongation The film of the present invention preferably has a tensile elongation of 100% or more in both the MD and TD directions, more preferably 110% or more, even more preferably 115% or more, and most preferably 120% or more. If the tensile elongation is less than 100%, the film is brittle and may break when stretched, making long-term continuous production difficult, and it is unsuitable as a packaging material as it is prone to tearing of the sheet or bag.

[0050] (3-6) Tensile strength The film of the present invention preferably has a tensile strength of 200 MPa or more in both the MD and TD directions, more preferably 210 MPa or more, and most preferably 220 MPa or more.

[0051] (3-7) Tensile modulus The film of the present invention preferably has a tensile modulus of 3.0 GPa or higher in both the MD and TD directions, more preferably 3.5 GPa or higher, and most preferably 3.7 GPa or higher.

[0052] (3-8) Strong piercing The film of the present invention, when used as a packaging material, preferably has a puncture strength of 7.0 N or higher, more preferably 7.5 N or higher, and most preferably 8.0 N or higher, from the viewpoint of suppressing tearing due to contact with protrusions of the contents.

[0053] (3-9) Dry heat shrinkage rate In the present invention, from the viewpoint of suppressing thermal deformation during the processing process, the dry heat shrinkage rate in both the MD and TD directions of the film is preferably 2.0% or less, more preferably 1.5% or less, and most preferably 1.0% or less.

[0054] (3-10) Film thickness From the viewpoint of reducing the amount of plastic used, the thickness of the film of the present invention is preferably 50 μm or less, more preferably 45 μm or less, and most preferably 40 μm or less. Furthermore, from the viewpoint of maintaining mechanical strength, the lower limit is more preferably 5 μm or more, and most preferably 10 μm or more.

[0055] 2. Method for manufacturing biaxially oriented polyester resin film The present invention provides a method for producing a biaxially oriented polyester resin film. (A) A step to obtain a reaction product by subjecting recycled polyester raw material to a depolymerization reaction (depolymerization step), (B) A step of filtering the reaction product and recovering the filtrate (filtration step), (C) A step to obtain a polyester resin by subjecting the filtrate to a polycondensation reaction at a temperature of 260°C or higher and a pressure of 1.0 hPa or lower in the presence of a polymerization catalyst (polycondensation step), (D) After producing an unstretched film using the starting material containing the polyester resin, the process of biaxially stretching the unstretched film (stretching process) It is characterized by including.

[0056] (A) Depolymerization process In the depolymerization process, the reaction product is obtained by subjecting the recycled polyester raw material to a depolymerization reaction.

[0057] In the present invention, recycled polyester raw materials include, for example, used polyester products and polyester scraps generated in the process of manufacturing polyester products.

[0058] Examples of used polyester products include polyester molded products (including fibers and films) that have been on the market and then collected after use. Typical examples include containers or packaging materials such as PET bottles.

[0059] Furthermore, polyester fragments generated during the manufacturing process of polyester products (hereinafter sometimes referred to as "unused polyester resin") are polyesters that did not make it to market. Examples include resin pellets that do not meet specifications, materials that are no longer needed during molding (film edges), fragments that are cut during molding, waste generated during molding or processing (polyester waste), cut pieces of transitional products generated when a brand name is changed, and cut pieces of prototypes or defective products.

[0060] The form of the recycled polyester raw material is not limited and may be the original form of the used polyester product or the unused polyester resin, or it may be in the form of cut fragments, crushed material (powder), etc. obtained by further processing such as cutting and crushing, or in the form of a solid such as a molded body (pellets, etc.) formed by molding these. More specifically, examples include a) pellets obtained by cutting molten polyester waste after cooling, and b) cut fragments obtained by finely cutting polyester molded products such as PET bottles. In addition, it may also be in the form of a liquid (dispersion or solution) obtained by dispersing or dissolving the above-mentioned cut fragments, crushed material (powder), etc. in a solvent. When manufacturing the film of the present invention using these raw materials, they may be melted at a temperature above their melting point and poured into the can as a molten liquid if necessary.

[0061] In the depolymerization process, recycled polyester raw materials are subjected to a depolymerization reaction, thereby obtaining oligomers and other components that make up the raw materials.

[0062] In the depolymerization reaction, recycled polyester raw material can be subjected to the depolymerization reaction alone, but in the present invention, it is desirable to subject the recycled polyester raw material to the depolymerization reaction in the presence of ethylene terephthalate oligomer and ethylene glycol. In conventional methods using recycled polyester raw material, depolymerization is carried out using only the recycled polyester raw material, whereas in the present invention, the depolymerization reaction of the recycled polyester raw material is carried out in the presence of ethylene terephthalate oligomer and ethylene glycol, and it is desirable to add the recycled polyester raw material and carry out the depolymerization reaction so that the molar ratio of "total glycol component / total acid component" in all components of ethylene terephthalate oligomer, ethylene glycol and the recycled polyester raw material is within a specific range. By doing so, not only various inorganic substances but also foreign substances derived from non-polyester resins are efficiently precipitated, so these foreign substances can be effectively removed in the filtration step described later. Then, in the polycondensation step described later, it is possible to obtain a recycled polyester resin in which the diethylene glycol content and carboxyl terminal group concentration are within a specific range, and the amount of foreign substances is relatively small.

[0063] In the manufacturing method of the present invention, it is desirable that the recycled polyester raw material is decomposed to oligomers with approximately 5 to 20 repeating units by the above-mentioned depolymerization reaction, without being decomposed into monomers. By controlling it in this way, not only various inorganic substances but also foreign substances derived from non-polyester resins are efficiently precipitated, making it possible to remove a larger amount of foreign substances.

[0064] Both ethylene terephthalate oligomers and ethylene glycols can be known or commercially available. They can also be produced by known manufacturing methods. In particular, as the ethylene terephthalate oligomer, for example, the esterification reaction product of ethylene glycol and terephthalic acid can be suitably used. The number-average degree of polymerization of the ethylene terephthalate oligomer is not limited, but can be, for example, around 2 to 20.

[0065] While there is no limit to the amount of ethylene terephthalate oligomer and ethylene glycol used, from the above perspective, it is particularly preferable to set the molar ratio of "total glycol component / total acid component" in all components of the ethylene terephthalate oligomer, ethylene glycol, and recycled polyester raw material to 1.08 to 1.35.

[0066] The amount of ethylene terephthalate oligomer used is not particularly limited as long as it can be set to the above molar ratio, but it is preferably about 0.20 to 0.80% by mass of 100% by mass of the polyester resin obtained in the polycondensation step described below (hereinafter also referred to as "recycled polyester resin"), and more preferably 0.30 to 0.70% by mass. If the amount of ethylene terephthalate oligomer is less than the above, when the recycled polyester raw materials are added, the recycled polyester raw materials are more likely to block each other, which may place an excessive load on the stirrer. On the other hand, if the amount of ethylene terephthalate oligomer is greater than the above range, no particular problems occur in the depolymerization reaction, but the recycling ratio of the final recycled polyester resin may be low.

[0067] The amount of ethylene glycol added is not particularly limited as long as it can be set to the above molar ratio, but from the viewpoint of allowing the depolymerization reaction to proceed sufficiently, it is preferable to add 5 to 15 parts by mass per 100 parts by mass of ethylene terephthalate oligomer, and more preferably 5 to 10 parts by mass. If the amount of ethylene glycol added is too high, the concentration of carboxyl terminal groups in the recycled polyester resin will be low, and if it is too low, the concentration of carboxyl terminal groups will be high, in either case it may deviate from the scope of this application. In particular, if it exceeds 15 parts by mass, the ethylene terephthalate oligomer is likely to solidify in the reactor, and the reaction may not be able to continue thereafter.

[0068] When using ethylene terephthalate oligomer and ethylene glycol in the depolymerization process, the mixing method (order of addition) is not limited, but a method of adding recycled polyester raw material to a mixture containing ethylene terephthalate oligomer and ethylene glycol is particularly preferred. This can reduce unevenness in the progress of the depolymerization reaction.

[0069] Furthermore, when mixing ethylene terephthalate oligomer and ethylene glycol, it is preferable to add ethylene glycol to the ethylene terephthalate oligomer, for example. When adding the glycol, it is preferable to stir the mixture while ensuring a uniform temperature of the contents, in order to prevent the oligomer from solidifying.

[0070] When adding recycled polyester raw materials to the above mixture, it is preferable to do so while stirring under atmospheric pressure, and more preferably while purging with a small amount of inert gas (generally nitrogen gas) before adding the materials. This prevents the incorporation of oxygen and more reliably prevents deterioration of the color tone.

[0071] The recycled polyester raw material preferably has a molar ratio of total glycol component to total acid component of 1.08 to 1.35, more preferably 1.10 to 1.33, and most preferably 1.12 to 1.30. If the molar ratio of total glycol component to total acid component is outside the above range, the resulting recycled polyester resin will not satisfy at least one of the carboxyl terminal group concentration and diethylene glycol content specified in the present invention, and the average pressurization rate may also be high. In other words, if the molar ratio of total glycol component to total acid component during the depolymerization reaction is outside the above range, various inorganic substances and foreign substances derived from non-polyester resins will not precipitate efficiently, and these foreign substances cannot be effectively filtered out in the filtration process. As a result, foreign substances are more likely to precipitate after the polycondensation process, which may result in a recycled polyester resin with a high average pressurization rate.

[0072] In the depolymerization process, the reaction temperature during depolymerization (especially the internal temperature of the reactor) is not limited, but is preferably set in the range of 245 to 280°C, and more preferably in the range of 255 to 275°C. If the reaction temperature during depolymerization is below 245°C, the reactants solidify, operability deteriorates, and even if recycled polyester resin is obtained, the diethylene glycol content or carboxyl end group concentration tends to become too high. If the reaction temperature exceeds 280°C, there is a risk that the diethylene glycol content or carboxyl end group concentration of the obtained recycled polyester resin will become too high.

[0073] Furthermore, the reaction time for the depolymerization reaction (the reaction time from the end of the input of recycled polyester raw materials) should be sufficient to complete the depolymerization reaction and is not particularly limited, but it is usually preferably within 4 hours. In particular, it is more preferable to keep it within 2 hours from the viewpoint of suppressing the amount of diethylene glycol by-product and suppressing deterioration of the polyester's color tone. The lower limit of the reaction time is not limited and can be, for example, around 1 hour.

[0074] The reaction apparatus is not particularly limited, and known or commercially available apparatus can be used. In particular, while the capacity, impeller shape, etc., of the reactor can be those of a commonly used esterification reactor, it is preferable to have a reactor with a distillation column that prevents ethylene glycol from distilling out of the system in order to efficiently advance the depolymerization reaction.

[0075] (B) Filtration process In the filtration step, the reaction product is filtered and the filtrate is recovered. The reaction product obtained in the depolymerization step is a liquid mainly containing the depolymerized recycled polyester raw material (especially the regenerated oligomer). In the filtration step, the reaction product (liquid) is passed through a filter to filter out impurities and the filtrate is recovered.

[0076] In the aforementioned depolymerization process, not only various inorganic substances but also foreign substances derived from non-polyester resins are efficiently precipitated. By passing the material through a filter (preferably a filter with a particle size of about 10-25 μm), the precipitated foreign substances can be filtered out, resulting in a depolymer with a low amount of foreign matter contamination. If a filter with a particle size larger than 25 μm is used, foreign substances in the polymer cannot be sufficiently removed, resulting in a higher amount of foreign matter in the resulting recycled polyester resin. Therefore, when a stretched film is made using such a resin, contamination of the T-die surface (lip surface) may occur, and the film may break during stretching. On the other hand, if a filter with a particle size smaller than 10 μm is used, clogging by foreign matter is likely to occur, shortening the filter life, which is disadvantageous in terms of cost and may also reduce operability.

[0077] While general filters can be used in the filtration process, metal filters are particularly preferred. The material is not particularly limited, but examples include stainless steel. The filter type is also not particularly limited, but examples include screen changer filters, leaf disc filters, and candle-type sintered filters. These can be publicly known or commercially available.

[0078] (C) Polycondensation step In the polycondensation step, the filtrate is subjected to a polycondensation reaction at a temperature of 260°C or higher and a pressure of 1.0 hPa or lower in the presence of a polymerization catalyst to obtain a polyester resin (recycled polyester resin).

[0079] As the polymerization catalyst, although not limited, for example, at least one of a germanium compound, an antimony compound, a titanium compound, a cobalt compound, etc. can be used. Among them, it is particularly preferable to use at least one of a germanium compound and an antimony compound. In particular, when emphasizing the transparency of the resulting recycled polyester resin, it is preferable to use a germanium compound. Examples of each of the above compounds include at least one of oxides, inorganic acid salts, organic acid salts, halides, sulfides, etc. of germanium, antimony, titanium, cobalt, etc.

[0080] The amount of the polymerization catalyst used is not particularly limited. For example, it is preferably 5×10 -5 mol / unit or more per 1 mol of the acid component of the polyester resin to be produced. Among them, it is more preferably 6×10 -5 mol / unit or more. The upper limit of the above usage amount can be, for example, about 1×10 -3 mol / unit, but is not limited thereto.

[0081] [[ID=一三]] In addition, since the polymerization catalyst contained in the recycled polyester raw material may also act as a catalyst during the polycondensation reaction, when adding the polymerization catalyst in the polycondensation step, it is preferable to consider the type and its content of the polymerization catalyst contained in the recycled polyester raw material.

[0082] Also, during the polycondensation reaction, if necessary, in addition to the above polymerization catalyst, for example, a) a fatty acid ester capable of adjusting the melt viscosity, b) a hindered phenol antioxidant, c) a phosphorus compound capable of suppressing the thermal decomposition of the resin, etc. can be added as necessary.

[0083] Examples of fatty acid esters include beeswax (a mixture mainly composed of myricyl palmitate), stearyl stearate, behenyl behenate, stearyl behenate, glycerin monopalmitate, glycerin monostearate, glycerin distearate, glycerin tristearate, pentaerythritol monopalmitate, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, pentaerythritol tetrastearate, and dipentaerythritol hexastearate. Among these, glycerin monostearate, pentaerythritol tetrastearate, and dipentaerythritol hexastearate are preferred. These can be used individually or in combination of two or more.

[0084] Examples of hindered phenol antioxidants include 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 4,4'-butylidenebis-(3-methyl-6-t-butylphenol), and tri Ethylene glycol-bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate], 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1'-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane, etc., are used, but tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane is preferred in terms of effectiveness and cost. These can be used individually or in combination of two or more.

[0085] Examples of phosphorus compounds that can be used include phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl phosphate, tridecyl phosphate, and triphenyl phosphate. These can be used individually or in combination of two or more.

[0086] In the polycondensation reaction, the reaction is carried out at a temperature of 260°C or higher and under reduced pressure of 1.0 hPa or lower. If the polycondensation reaction temperature is below 260°C, or if the pressure during the polycondensation reaction exceeds 1.0 hPa, the reaction time will be prolonged, resulting in lower productivity and an excessively low concentration of carboxyl end groups in the recycled polyester resin.

[0087] The polycondensation reaction temperature is preferably 270°C or higher. On the other hand, if the polycondensation reaction temperature is too high, the polymer will become discolored due to thermal decomposition, resulting in a deterioration of the color tone, and similarly, the concentration of carboxyl terminal groups in the recycled polyester resin will become too high due to thermal decomposition. Therefore, in the present invention, the upper limit of the polycondensation reaction temperature is usually preferably 285°C or lower.

[0088] The pressure is preferably 0.8 hPa or less. The lower limit can be, for example, around 0.1 hPa, but is not limited to this.

[0089] In this way, recycled polyester resin can be obtained by carrying out a polycondensation reaction. The composition or properties of the obtained recycled polyester resin are not particularly limited, but are preferably set as follows.

[0090] In the present invention, the recycled polyester resin is not limited to any particular type, but it is particularly preferable that it is mainly composed of polyethylene terephthalate (PET). The PET content in the recycled polyester resin is preferably 70% by mass or more, more preferably 80% by mass or more, and most preferably 90-100% by mass.

[0091] In the present invention, when the total amount of glycol components in the recycled polyester resin is 100 mol%, the diethylene glycol content is preferably about 0.5 to 4 mol%, more preferably 1 to 3.5 mol%, and most preferably 1.2 to 3 mol%. In particular, in the recycled polyester resin obtained by the manufacturing method of the present invention, if ethylene glycol is used as one of the raw materials, diethylene glycol may be produced as a by-product. The recycled polyester resin in the present invention has a small amount of diethylene glycol produced as a by-product, and by keeping the diethylene glycol content at 4 mol% or less, it is possible to obtain performance with superior thermal stability. Therefore, when forming unstretched sheets or stretched films, surface (lip surface) contamination of the T-die can be suppressed, and high productivity can be obtained.

[0092] Furthermore, the recycled polyester resin preferably has a carboxyl end group concentration of 40 equivalents / t or less, more preferably 30 equivalents / t or less, even more preferably 25 equivalents / t or less, and most preferably 20 equivalents / t or less. By setting the carboxyl end group concentration to 40 equivalents / t or less, it has excellent heat resistance, and it is possible to obtain molded products with excellent heat resistance by various molding methods. The lower limit of the carboxyl end group concentration is preferably 10 equivalents / t or more from the viewpoint of improving mechanical strength such as tensile elongation during film formation.

[0093] The recycled polyester resin has an average pressure increase rate of 0.6 MPa / h or less, preferably 0.5 MPa / h or less, and more preferably 0.4 MPa / h or less, as measured by the following method. In this invention, the average pressure increase rate is an indicator of the amount of foreign matter, such as foreign matter derived from various inorganic materials and foreign matter derived from non-polyester resins, and a smaller average pressure increase rate indicates a smaller amount of foreign matter. An average pressure increase rate of 0.6 MPa / h or less makes it possible to manufacture stretched films with high stretch ratios, such as 10 times or more. The lower limit of the average pressure increase rate can be, for example, around 0.01 MPa / h, but is not limited to this.

[0094] The above method for measuring the average pressure increase rate involves using a pressure test machine including an extruder and a pressure sensor. The filter is set at the tip of the extruder, the polyester resin is melted at 300°C in the extruder, and the molten material is extruded from the filter at a discharge rate of 29.0 g / min. The pressure value applied to the filter at the start of extrusion is defined as the "initial pressure value (MPa)," and the pressure value after 12 hours of continuous extrusion is defined as the "final pressure value (MPa)." Based on these pressure values, the average pressure increase rate is calculated using the following formula A: Average pressure increase rate (MPa / h) = (Final pressure value - Initial pressure value) / 12) ... A

[0095] The extruder, filter, etc. used in the above measurement are not limited as long as they satisfy the provisions of the present invention, and known or commercially available ones may be used as appropriate.

[0096] The intrinsic viscosity of recycled polyester resin is not particularly limited, but is usually preferably around 0.44 to 0.80, and more preferably 0.55 to 0.70. Furthermore, recycled polyester resin can be subjected to a solid-phase polymerization process to achieve a higher degree of polymerization. In this case, the intrinsic viscosity of the resulting recycled polyester resin is usually preferably 0.80 to 1.25.

[0097] The cooling crystallization temperature (Tc) of the recycled polyester resin is preferably 160°C or higher, more preferably 163°C or higher, even more preferably 165°C or higher, and most preferably 170°C or higher.

[0098] Furthermore, the upper limit of Tc is preferably 180°C or less, more preferably 178°C or less, and most preferably 175°C or less. By including a recycled polyester resin in which the cooling crystallization temperature is controlled within the above range, the resulting biaxially oriented polyester resin film exhibits high tensile elongation and excellent bending resistance in low-temperature environments.

[0099] (D) Stretching process In the stretching process, an unstretched film is produced using a starting material containing the polyester resin (recycled polyester resin), and then the unstretched film is biaxially stretched.

[0100] The content of recycled polyester raw materials in the starting materials is not limited, and is usually sufficient if it is around 20% by mass or more (especially 24% by mass or more). However, from an environmental standpoint such as Eco Mark certification, it is preferable to have 25% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, and most preferably 50% by mass or more. If the content is too low, the recycling rate will decrease accordingly. The upper limit of the above content can usually be set to around 80% by mass, but is not limited to this.

[0101] Furthermore, the recycled polyester resin may consist of only one type of recycled polyester resin, a mixture of two or more types of recycled polyester resins, or a mixture of recycled polyester resin and a resin other than recycled polyester resin. In order to define the cooling crystallization temperature of the film of the present invention, the content of recycled polyester resin is usually preferably 30% by mass or more, and more preferably 40% by mass or more. The upper limit may be, for example, 95% by mass or less, even 98% by mass or less, and particularly 100% by mass, but is not limited thereto.

[0102] Examples of resins other than recycled polyester resin include polyester resins that do not use recycled materials (hereinafter sometimes referred to as "virgin polyester resins") and unused polyester resins.

[0103] The starting materials may include unused polyester resins, used polyester products, etc., to increase the recycling rate, as long as it does not impair the effects of the present invention.

[0104] Unused polyester resins are materials that have not yet been commercialized. Examples include unstretched scraps, edge trimming scraps, slitting scraps, and defective products generated during film manufacturing, as mentioned above. These can be added in the form of crushed material (flakes, etc.) or pellets produced by remelting them.

[0105] Used polyester products are products that are intended to be discarded after use following a manufacturing process. After a proper cleaning process, they can be added in the form of pulverized material or pellets produced by remelting them.

[0106] The content of unadopted polyester resin in the starting material is preferably 75% by mass or less, more preferably 65% ​​by mass or less, even more preferably 50% by mass or less, particularly preferably 40% by mass or less, and most preferably 35% by mass or less. If the content of unadopted polyester resin exceeds 75% by mass, the amount of foreign matter or thermally degraded material increases, which tends to cause problems such as cutting during film formation. In addition, the mechanical properties of the film, such as tensile elongation, tend to decrease.

[0107] The film scraps or defective products used as unused polyester resins have varying concentrations of various additives, such as lubricants like silica and antioxidants, depending on the brand of scrap. Therefore, the higher the content of unused polyester resin in the starting material, the greater the variation in the concentration of these additives, which may adversely affect the haze, wettability of the film surface, and printability of the resulting film.

[0108] For the reasons stated above, when the target polyester resin film is composed of multiple layers, the content of unused polyester resin in the surface layer is preferably 50% by mass or less, more preferably 40% by mass or less, and most preferably 35% by mass or less. On the other hand, in the intermediate layer, even if the content of unused polyester resin is high, it does not affect the film surface properties such as wettability and printability, so the content of unused polyester resin can be increased from the viewpoint of increasing the recycling rate. The content of unused polyester resin in the intermediate layer may be 100% by mass.

[0109] Furthermore, regarding the starting materials, a higher recycling rate for the film of the present invention is preferable. More specifically, a recycling rate of 25% by mass or more is generally preferred, 35% by mass or more is more preferred, 40% by mass or more is even more preferred, 50% by mass or more is particularly preferred, and among these, 65% or more is most preferred. The upper limit can be, for example, around 80% by mass, but is not limited thereto. Therefore, it is desirable to adjust the composition of the starting materials so that the recycling rate is as described above. In this invention, the recycling rate R refers to the weight percentage shown by the following formula. R(mass%)=A×B+C (However, A represents the weight percentage (mass%) of recycled polyester raw material in the recycled polyester resin. B represents the weight percentage (mass%) of recycled polyester resin in the film. C represents the weight percentage (mass%) of unused polyester resin in the film.)

[0110] The method for producing the unstretched film is not limited and can be formed by known film-forming methods. For example, it can be obtained by extruding the molten raw material from a T-die and then cooling it with a casting roll. In this case, it is necessary to accurately control the actual temperature of the casting roll surface in order to ensure uniform crystallinity of the unstretched film.

[0111] Next, the obtained unstretched film is biaxially stretched. This allows for the production of a film with excellent tensile elongation in both the MD and TD directions. The biaxial stretching method is not limited to this method; for example, simultaneous biaxial stretching and sequential biaxial stretching can be used. Simultaneous biaxial stretching is preferred from the viewpoint of balancing mechanical properties, minimizing the difference between tensile strength and tensile modulus in the MD and TD directions. Sequential biaxial stretching is preferred from the viewpoint of balancing thermal properties, minimizing the difference between dry heat shrinkage rates in the MD and TD directions, and from the viewpoint of improving puncture strength and impact strength. These methods can be appropriately selected depending on the desired film properties and application.

[0112] The stretching ratio can be appropriately set according to the intended use of the film, desired physical properties, etc., and is not limited to, for example, 2 to 4 times in the MD direction and 2 to 4 times in the TD direction. The stretching temperature is also not limited and can be carried out within the range of, for example, 40 to 220°C. In particular, in the case of sequential stretching, it is preferable to stretch in the MD direction at 40 to 80°C and in the TD direction at 80 to 150°C. In the case of simultaneous biaxial stretching, it is preferable to stretch at 160 to 220°C.

[0113] The resulting biaxially oriented film is preferably subjected to a short heat treatment at a temperature of approximately 220-240°C, if necessary, in order to improve dimensional stability and suppress the rate of hot water shrinkage.

[0114] The deformation and heat applied during the stretching process promote crystallization of the stretched film. By using a recycled polyester resin that exhibits crystallization characteristics such as those expressed by the cooling crystallization temperature within the range of the present invention, it becomes easier to appropriately control the surface crystallinity of the film, resulting in a stretched film with excellent mechanical properties, and in particular, excellent flexural resistance, which is influenced by the crystallization state of the surface.

[0115] 3. Use of the film of the present invention The film of the present invention may be composed of a single layer, or it may be a film composed of multiple layers formed by simultaneous melt extrusion or lamination.

[0116] For example, in addition to a two-layer configuration consisting of a biaxially oriented polyester resin film containing recycled polyester resin and a biaxially oriented polyester resin film containing unused polyester resin, a two-layer configuration consisting of a biaxially oriented polyester resin film containing unused polyester resin can also be used. With a polyester resin film having a layer configuration that allows for an intermediate layer to be sandwiched, such as a two-layer configuration, the intermediate layer film does not constitute the surface of the film composed of multiple layers, so its impact on the overall flexibility, strength, surface crystallinity, etc. of the film is minimal, and the content of unused polyester resin can be increased.

[0117] Furthermore, the film of the present invention can be used on its own, or it can be used as a laminated film together with other layers (sealant layer, printed layer, gas barrier layer, etc.).

[0118] Furthermore, a predetermined bag can be constructed using the film of the present invention or a laminated film thereof. The shape of the bag is not limited, and various types of bags can be manufactured, such as two-sided bags, three-sided bags, three-sided bags with zippers, gusseted bags, bottom gusseted bags, and stand-up pouches. Accordingly, a packaging bag can be constructed by laminating a sealant layer such as polyolefin with the film of the present invention using known methods such as dry lamination or extrusion lamination, forming a laminated film, and then heat-sealing the sealant layers together.

[0119] When used as packaging material (packaging bags, containers, etc.), it is not limited to its contents and can be widely used as packaging material for food, pharmaceuticals, medical devices, cosmetics, chemicals, general merchandise, electronic components, and more. [Examples]

[0120] The present invention will be specifically described below with reference to embodiments, but the present invention is not limited thereto.

[0121] 1. Materials used The raw materials used in the following examples and comparative examples are as follows: <Recycled polyester resin A-1> A slurry of terephthalic acid (TPA) and ethylene glycol (EG) (TPA / EG molar ratio = 1 / 1.6) was supplied to an esterification reactor and reacted under conditions of 250°C and 50 hPa to obtain ethylene terephthalate oligomer (number average degree of polymerization: 5) with an esterification reaction rate of 95%. 45.0 parts by mass of ethylene terephthalate oligomer were placed in an esterification reactor, and then 7.0 parts by mass of ethylene glycol were added while the reactor's stirrer was running. Once the internal temperature of the esterification reactor (hereinafter referred to as "ES can") stopped decreasing, 55.0 parts by mass of recycled polyester raw material (pellets of polyester waste generated in the process of manufacturing polyester resin) were added quantitatively via a rotary valve over approximately 2 hours. At this time, the molar ratio of total glycol components to total acid components (hereinafter referred to as "G / A") was 1.16. Subsequently, the depolymerization reaction was carried out under heat treatment conditions of 270°C for 1 hour. Next, the resulting depolymer was pumped into the polycondensation reactor (hereinafter referred to as the PC can) through a 20 μm mesh candle filter placed between the ES can and the polycondensation reactor, and then 1.0 × 10⁻¹⁶ antimony trioxide was added as a polymerization catalyst. -4 A titanium dioxide EG slurry was added at a concentration of mol / unit to a total of 0.20 mass%, and after reducing the pressure in the PC can for 60 minutes, a melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 275°C for 4 hours to obtain recycled polyester resin A-1 (intrinsic viscosity: 0.64, carboxyl end group concentration: 27 equivalents / t, cooling crystallization temperature: 170°C).

[0122] <Recycled polyester resin A-2> In the same manner as in A-1, an ethylene terephthalate oligomer with an esterification reaction rate of 95% (number-average degree of polymerization: 5) was obtained. 30.0 parts by mass of ethylene terephthalate oligomer were placed in an ES can, and then 7.0 parts by mass of ethylene glycol were added while the stirrer in the ES can was running. Once the internal temperature of the ES can stopped decreasing, 70.0 parts by mass of recycled polyester raw material (the same as in Example 1) were added quantitatively through a rotary valve over approximately 2 hours. At this time, the G / A ratio was 1.10. Subsequently, the depolymerization reaction was carried out under heat treatment conditions of 270°C for 1 hour. The resulting depolymer was then pumped into the PC can through a candle filter with a mesh size of 20 μm placed between the ES can and the PC can, and then 1.0 × 10⁻⁶ antimony trioxide was added as a polymerization catalyst. -4 After adding the material to a concentration of mol / unit, the PC can was reduced in pressure for 60 minutes, and then a melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 275°C for 5 hours to obtain recycled polyester resin A-2 (intrinsic viscosity: 0.65, carboxyl end group concentration: 38 equivalents / t, cooling crystallization temperature: 170°C).

[0123] <Recycled polyester resin A-3> In the same manner as in A-1, an ethylene terephthalate oligomer with an esterification reaction rate of 95% (number-average degree of polymerization: 5) was obtained. 45.0 parts by mass of ethylene terephthalate oligomer were placed in an ES can, and then 10.0 parts by mass of ethylene glycol were added while the stirrer in the ES can was running. Once the internal temperature of the ES can stopped decreasing, 55.0 parts by mass of recycled polyester raw material (pellets of polyester waste generated in the process of manufacturing polyester resin) were added via a rotary valve over approximately 2 hours, so that the molar ratio of total glycol components to total acid components (hereinafter referred to as "G / A") was 1.20, and the depolymerization reaction was carried out under heat treatment conditions of 270°C for 1 hour. The resulting depolymer was then pumped into the polycondensation reactor (hereinafter referred to as "PC can") through a candle filter with a mesh size of 20 μm placed between the ES can and the polycondensation reactor, and then 1.0 × 10⁻⁶ antimony trioxide was added as a polymerization catalyst. -4A titanium dioxide EG slurry was added at a concentration of mol / unit to a total of 0.20 mass%, and after reducing the pressure in the PC can for 60 minutes, a melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 260°C for 7 hours to obtain recycled polyester resin A-3 (intrinsic viscosity: 0.64, carboxyl end group concentration: 13 equivalents / t, cooling crystallization temperature: 170°C).

[0124] <Recycled polyester resin A-4> In a rotary dryer, 10 parts by mass of ethylene glycol per unit time was added to 100 parts by mass of recycled polyester raw material over a period of 6 hours and mixed. The process was carried out under a nitrogen environment at 220°C. Furthermore, solid-phase polymerization was performed at 0.5 mmHg and 230°C for 10 hours to obtain recycled polyester resin A-4 (intrinsic viscosity 0.65, carboxyl end group concentration 5 equivalents / t, cooling crystallization temperature 144°C).

[0125] <Recycled polyester resin A-5> Recycled polyester resin A-5 (intrinsic viscosity 0.66, carboxyl end group concentration 9 equivalents / t, cooling crystallization temperature 144°C) was obtained in the same manner as A-4, except that 5 parts by mass of ethylene glycol per unit time was added and mixed in a rotary dryer for 6 hours to 100 parts by mass of recycled polyester raw material.

[0126] <Polyester resin not used> Film waste generated during the manufacture of polyethylene terephthalate resin film was crushed, remelted at 250-290°C, and pelletized. It was then dried to produce an unadopted polyester resin (cooling crystallization temperature 179°C) for use in polyester resin film.

[0127] <Virgin polyester resin B-1> Polyethylene terephthalate resin UT-CBR (cooling crystallization temperature 177°C) manufactured by Nippon Ester Co., Ltd. was used.

[0128] <Virgin polyester resin B-2> In an esterification reactor, terephthalic acid was esterified with ethylene glycol to obtain an esterified product. The obtained esterified product was transferred to a polycondensation reactor, where germanium dioxide was added as a catalyst to carry out a polycondensation reaction, followed by chip formation. The obtained polyester chips were further dried and crystallized under a nitrogen atmosphere at 170°C for 2 hours. Subsequently, solid-phase polymerization was carried out in a batch-type solid-phase polymerization apparatus at 230°C for 6 hours under a nitrogen stream. The solid-phase polymerized polyester was immersed in 95°C hot water for 4 hours, treated with water, dehydrated, and dried at 120°C for 2 hours under a nitrogen atmosphere to obtain a polyester resin (intrinsic viscosity 0.65, cooling crystallization temperature 180°C).

[0129] <Virgin polyester resin B-3> Korikisha KH2650A (lowering crystallization temperature 155℃)

[0130] <Silica-containing polyester resin (Silica Master)> GS-BR-MG, manufactured by Nippon Ester Co., Ltd., which contains 1.5% by mass of silica with an average particle size of 2.3 μm in virgin polyethylene terephthalate resin, was used.

[0131] Example 1 93.5% by mass of recycled polyester resin A-1 and 6.5% by mass of silica master were mixed and melt-kneaded in an extruder, supplied to a T-die and extruded in sheet form. This sheet was then wound onto a metal drum heated to 20°C, cooled, and wound up to obtain a single-layer unstretched sheet with a thickness of approximately 120 μm. Next, the ends of this unstretched sheet were held with clips from a tenter-type simultaneous biaxial stretching apparatus, and simultaneously biaxially stretched at 180°C with a stretch ratio of 3.0 times in the MD direction and 3.3 times in the TD direction. After that, a heat treatment was performed at 215°C for 4 seconds with a relaxation rate of 5% in the TD direction, and after slow cooling to room temperature, corona discharge treatment was performed on one side to obtain a biaxially oriented polyester resin film with a thickness of 12 μm. The recycling rate in the film was 51.4%.

[0132] Example 2 A biaxially oriented polyester resin film with a thickness of 12 μm was obtained in the same manner as in Example 1, except that unused polyester resin was mixed in and the content of recycled polyester resin A-1 and silica master was changed as shown in Table 1. The recycling ratio in the film was 60.2%.

[0133] Example 3 The unstretched film obtained in the same manner as in Example 2 was stretched 3.5 times in the MD direction at 85°C using a roll stretcher, and then, with the ends held by clips, it was successively biaxially stretched at a stretching ratio of 3.6 times in the TD direction at 120°C. After that, it was heat-treated at 230°C for 3 seconds with a relaxation rate of 2% in the TD direction, slowly cooled to room temperature, and corona discharge treatment was performed on one side to obtain a biaxially oriented polyester resin film with a thickness of 12 μm. The recycling rate in the film was 60.2%.

[0134] Example 4 Except for changing to recycled polyester resin A-2 and changing the content of recycled polyester resin, unused polyester resin, and silica master as shown in Table 1, a biaxially oriented polyester resin film with a thickness of 12 μm was obtained by sequential biaxial stretching in the same manner as in Example 3. The recycling ratio in the film was 69.6%.

[0135] Example 5 A biaxially oriented polyester resin film with a thickness of 12 μm was obtained by sequential biaxial stretching in the same manner as in Example 3, except that recycled polyester resin A-3 was used and the content of recycled polyester resin, unused polyester resin, and silica master was changed as shown in Table 1. The recycling ratio in the film was 60.2%.

[0136] Example 6 A biaxially oriented polyester resin film was obtained by sequential biaxial stretching in the same manner as in Example 4, except that the take-up speed from the T-die to the sheet was adjusted to change the thickness of the stretched film to 25 μm, the temperature of the roll stretcher was set to 83°C, and the relaxation in the TD direction was set to 228°C for 6 seconds. The recycling rate in the film was 69.6%.

[0137] Example 7 A biaxially oriented polyester resin film with a thickness of 12 μm was obtained in the same manner as in Example 3, except that the content of recycled polyester resin A-1, unused polyester resin, virgin polyester resin B-1, and silica master was changed as shown in Table 1. The recycling ratio in the film was 42.6%.

[0138] Example 8 A biaxially oriented polyester resin film with a thickness of 12 μm was obtained by sequential biaxial stretching in the same manner as in Example 3, except that the recycled polyester resin was changed to A-2, and the content of the unused polyester resin, virgin polyester resin B-1, and silica master was changed as shown in Table 1. The recycling ratio in the film was 43.3%.

[0139] Example 9 A biaxially oriented polyester resin film with a thickness of 12 μm was obtained by sequential biaxial stretching in the same manner as in Example 3, except that the recycled polyester resin was changed to A-3, and the content of the unused polyester resin, virgin polyester resin B-1, and silica master was changed as shown in Table 1. The recycling ratio in the film was 42.6%.

[0140] Comparative Example 1 The polyester resin film was prepared using a composition of 46.7% by mass of virgin polyester resin B-1, 50.0% by mass of unused polyester resin, and 3.3% by mass of silica master. Simultaneous biaxial stretching was performed in the same manner as in Example 1 to obtain a biaxially oriented polyester resin film with a thickness of 12 μm. The recycling rate in the film was 50.0%.

[0141] Comparative Example 2 The unstretched film obtained in the same manner as in Comparative Example 1 was sequentially biaxially stretched under the same conditions as in Example 3 to obtain a biaxially oriented polyester resin film with a thickness of 12 μm. The recycling rate in the film was 50.0%.

[0142] Comparative Example 3 A biaxially oriented polyester resin film with a thickness of 12 μm was obtained in the same manner as in Example 3, except that the recycled polyester resin was changed to A-4, and the virgin polyester resin B-1 and silica master content were changed as shown in Table 1. The recycling ratio in the film was 50.0%.

[0143] Comparative Example 4 A biaxially oriented polyester resin film with a thickness of 12 μm was obtained in the same manner as in Example 7, except that the recycled polyester resin was changed to A-4. The recycling ratio in the film was 62.8%.

[0144] Comparative Example 5 A biaxially oriented polyester resin film with a thickness of 12 μm was obtained in the same manner as in Example 7, except that the recycled polyester resin was changed to A-5. The recycling ratio in the film was 62.8%.

[0145] Comparative Example 6 A biaxially oriented polyester resin film was obtained by sequential biaxial stretching in the same manner as in Comparative Example 4, except that the take-up speed from the T-die to the sheet was adjusted to change the thickness of the stretched film to 25 μm, and the relaxation in the TD direction was set to 8 seconds at 213°C. The recycling rate in the film was 62.8%.

[0146] Comparative Example 7 A biaxially oriented polyester resin film with a thickness of 12 μm was obtained by simultaneous biaxial stretching in the same manner as in Example 1, except that the composition of the polyester resin film consisted of 93.5% by mass of virgin polyester resin B-1 and 6.5% by mass of silica master. The recycling rate in the film was 0.0%.

[0147] Comparative Example 8 The polyester resin film was composed of 76.7% by mass of virgin polyester resin B-1, 18.0% by mass of unused polyester resin, and 5.3% by mass of silica master. Except for these components, the film was sequentially biaxially stretched under the same conditions as in Example 3 to obtain a biaxially oriented polyester resin film with a thickness of 12 μm. The recycling rate in the film was 18.0%.

[0148] Comparative Example 9 A biaxially oriented polyester resin film was obtained by sequential biaxial stretching in the same manner as in Comparative Example 4, except that the take-up speed from the T-die to the sheet was adjusted to change the thickness of the stretched film to 60 μm, the temperature of the roll stretcher was set to 81°C, and the relaxation in the TD direction was set to 228°C for 10 seconds. The recycling rate in the film was 50.0%.

[0149] Comparative Example 10 An unstretched film obtained in the same manner as in Comparative Example 7, except that virgin polyester resin B-2 was used, was sequentially biaxially stretched under the same conditions as in Example 3 to obtain a biaxially oriented polyester resin film with a thickness of 12 μm. The recycling rate in the film was 0.0%.

[0150] Comparative Example 11 An unstretched film obtained in the same manner as in Comparative Example 7, except that virgin polyester resin B-3 was used, was sequentially biaxially stretched under the same conditions as in Example 3 to obtain a biaxially oriented polyester resin film with a thickness of 12 μm. The recycling rate in the film was 0.0%.

[0151] Reference example 1 A 15 μm biaxially oriented polyester resin film was obtained in the same manner as in Example 1, except that it consisted of 91.5% virgin polyester resin B-1, 6.5% by mass of silica master, and 3.5% by mass of Mitsubishi Chemical's "Modic GQ131" (polyester elastomer) added as an impact resistance modifier. The recycling rate in the film was 0.0%.

[0152] Test Example 1 The following physical properties were evaluated for the films obtained in each example, comparative example, and reference example. The results are shown in Tables 1 and 2. For each measurement, samples were left in an environment of 23°C and 50% RH for at least 2 hours, and measurements were taken in an environment of 23°C and 50% RH.

[0153] (1) Intrinsic viscosity The measurements were taken at 20°C using an equal mass mixture of phenol and tetrachloroethane as the solvent.

[0154] (2) Carboxylate terminal group concentration The obtained polyester resin film was dissolved in 10 ml of benzyl alcohol, 10 ml of chloroform was added to this solution, and then the result was obtained by titration with a 1 / 10 N potassium hydroxide benzyl alcohol solution.

[0155] (3) Composition of polyester resin The obtained recycled polyester resin or polyester resin film is dissolved in a mixed solvent of deuterated hexafluoroisopropanol and deuterated chloroform in a volume ratio of 1:20, and then analyzed using a JEOL LA-400 NMR spectrometer. 1 1H-NMR was measured, and the type and content of copolymer components were determined from the integrated intensity of the proton peaks of each component in the resulting chart.

[0156] (4) Tensile strength (MPa) Tensile strength was measured using an autograph manufactured by Shimadzu Corporation in accordance with Japanese Industrial Standard JIS K7127. Samples were taken from the center of the polyester resin film obtained in the Examples, Comparative Examples, and Reference Examples, cut into strips 10 mm wide and 150 mm long in the MD and TD directions, respectively. Measurements were performed under conditions of a measurement length of 100 mm and a tensile speed of 500 mm / min, and the strength was calculated using the following formula. Tensile strength (MPa) = Tensile load at fracture (N) / Original average cross-sectional area of ​​the sample (mm²) 2 )

[0157] (5) Tensile elongation (%) Tensile elongation was measured using an autograph manufactured by Shimadzu Corporation in accordance with Japanese Industrial Standard JIS K7127. Samples were prepared by cutting 10 mm wide and 150 mm long sections from the central part in the TD direction of the polyester resin film obtained in the examples, comparative examples, and reference examples, in both the MD and TD directions. Measurements were performed under conditions of a measurement length of 100 mm (distance between grips) and a tensile speed of 500 mm / min, and the tensile elongation was calculated using the following formula. Tensile elongation (%) = Distance traveled by the grip at the time of fracture (mm) / Original distance between grips (100 mm) × 100

[0158] (6) Tensile modulus (GPa) The tensile modulus was measured using an autograph manufactured by Shimadzu Corporation in accordance with the Japanese Industrial Standard JIS K7127. Samples were taken from the center of the polyester resin film obtained in the Examples, Comparative Examples, and Reference Examples, cut into strips 10 mm wide and 150 mm long in the MD and TD directions, respectively. Measurements were performed under conditions of a measurement length of 100 mm (distance between grips) and a tensile speed of 20 mm / min, and the modulus was calculated using the following formula. Tensile modulus (GPa) = F / A × ΔL(1mm) / L(100mm) × 9.807 × 10 -3 F: Stress at 1% elongation (kgf) A: Initial cross-sectional area of ​​the test specimen (mm²) 2 ) ΔL: Length of the test specimen at 1% elongation (mm) L: Distance between gripping parts (100mm)

[0159] (7) Strong piercing (N) The polyester resin films obtained in the examples, comparative examples, and reference examples were cut to 50 mm x 50 mm centered on the TD direction, attached to a dedicated fixing plate having a 30 mm diameter circular hole in the center, and measured for puncture strength using a Shimadzu Autograph with a semicircular needle with a diameter of 1.0 mm and a tip radius of 0.5 mm at a test speed of 50 mm / min.

[0160] (8) Dry heat shrinkage rate (%) The polyester resin films obtained in the examples, comparative examples, and reference examples were cut from the central part in the TD direction to a width of 10 mm and a length of 150 mm in the MD direction and the TD direction, respectively. Gauge marks of 100 mm length were marked, and the films were treated in hot air at 160°C for 15 minutes. The distance between the gauge marks (mm) after treatment was read and calculated using the following formula. Hydrothermal shrinkage rate (%) = (gauge length before treatment - gauge length after treatment) / gauge length before treatment × 100

[0161] (9) Haze (%) Using a haze meter (NDH4000) manufactured by Nippon Denshoku Industries Co., Ltd., the central portion in the TD direction of the polyester resin films obtained in the examples, comparative examples, and reference examples was measured in accordance with the Japanese Industrial Standard JIS K7136.

[0162] (10)b * value Using a spectrophotometer NF555 manufactured by Nippon Denshoku Industries Ltd., measurements were taken by stacking 30 polyester resin films obtained in the examples, comparative examples, and reference examples, under reflection conditions of light source D65 and field of view 2°, in accordance with Japanese Industrial Standard JIS K7373. A white board with tristimulus values ​​X / Y / Z = 84.3 / 89.0 / 93.5 was used as a backing plate. A positive value indicates a yellow hue, and a negative value indicates a blue hue.

[0163] (11) Wetting tension (mN / m) In accordance with Japanese Industrial Standard JIS K6768, the corona-treated surfaces of polyester resin films obtained in the examples, comparative examples, and reference examples were measured using wet tensile strength test mixture No. 36.0~54.0 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Measurements were taken at five locations in the TD direction, at 200 mm intervals from the center outwards to both ends. These measurements were then taken every 1 m in the MD direction, for a total of 50 measurements. Table 2 shows the minimum and maximum wet tensile strength measurements for the 50 locations. A wet tensile strength of 44 mN / m or higher is practical, and 46 mN / m or higher is particularly preferable.

[0164] (12) Ink adhesion (printability) [Printing process] The printing ink was prepared by mixing Rio Alpha R39 blue (manufactured by TOYOINK) with the diluent NKFS102 (TOYOINK), and adjusting the viscosity to 15 seconds using a Zahn cup #3. The printing roll film was prepared by slitting the polyester resin film obtained in the examples, comparative examples, and reference examples at positions 500 mm to the left and right of the center in the TD direction. After applying the ink to the film using a gradation-changing plate engraved in the MD direction in the order of 10%, 20%, 30%, 40%, and 100% gradation, it was dried at 50°C for 10 seconds and then wound up to produce the printing film. [Evaluation Method] A sheet of cellophane tape (18mm wide) was carefully applied from edge to edge in the TD direction to the 40% grayscale printed area of ​​the prepared printed film, taking care not to introduce air bubbles. The evaluation area was defined as a 100mm wide area to the left and right of the center of the applied area, and the tape was lightly rubbed 20 times over this area. Next, the cellophane tape was rapidly peeled off the film at a peeling angle of 180°, and the degree of ink peeling in the evaluation area was visually observed and evaluated on a three-point scale according to the following criteria. (Evaluation Criteria) ◎...Excellent (ink dots do not come off) ○...Good (Slight ink dots are missing) ×...Defective (More than half of the ink dots are missing)

[0165] (13) Continuous productivity The following criteria were used to evaluate the continuous production of polyester film. ◎; We were able to operate continuously for more than 48 hours. ○; Although continuous operation was possible for more than 24 hours, the continuous operation time was less than 48 hours due to issues such as filter pressure increase, contamination of the T-die lip surface, film breakage, and roll contamination, which prevented film production. ×; During 24 hours of continuous operation, the production of film became impossible due to issues such as increased filter pressure, contamination of the T-die lip surface, film breakage, and roll contamination.

[0166] (14) Cooling temperature of the film (recrystallization temperature) In accordance with Japanese Industrial Standard JIS K7121, 10 mg of the resin film obtained in the examples, comparative examples, and reference examples was weighed and measured as a sample using a PerkinElmer differential scanning calorimeter (input-compensated DSC8000). The measurement conditions were as follows: heating from 25°C to 300°C at a heating rate of 20°C / min, holding at 300°C for 10 minutes, and then cooling to 100°C at a cooling rate of 40°C / min. The peak top temperature at which crystallization occurred during cooling was defined as the cooling crystallization temperature Tc.

[0167] (15) Surface crystallinity of the film Using a JASCO infrared spectrophotometer (FT / IR-6100), the reflection method (ATR method) was measured at 1340 cm². -1 Nearby crystal absorption bands and 1410 cm -1 Absorbance ratio with the nearby correction band (1340 cm) -1 / 1410cm -1 The surface crystallinity was determined by ). In this invention, a horizontal prism ATR610RS was used, with diamond as the prism element, and measurements were taken at an incident angle of 45° and with 64 cumulative measurements.

[0168] (16) Flexural resistance in low-temperature environments The obtained polyester resin film was left for 2 hours in an environmental test chamber adjusted to 5°C and 65%RH, then left to stand for another 5 minutes in a -10°C environment, and then subjected to a 200-cycle flex fatigue test (torsion angle 440°) using a Gelboflex tester (Tester Industries Co., Ltd., BE-1005) in a -10°C environment. The flex fatigue resistance test was performed in accordance with the ASTM F392 standard, and the number of pinholes in the film sample (chuck distance 178 mm, diameter 89 mm) was determined by measuring the number of ink permeation points on filter paper. Measurements were performed with 3 samples, covering 500 cm². 2 The average number of pinholes per unit was calculated.

[0169] [Table 1]

[0170] [Table 2]

[0171] The biaxially oriented polyester resin films of Examples 1 to 9 contain polyester resin (recycled polyester resin) in which part or all of the film raw materials are derived from recycled polyester raw materials, and the cooling crystallization temperature is within the range specified in the present invention. Therefore, even thin films with a thickness of less than 50 μm can be produced continuously for a long period of time, have excellent bending resistance in low temperature environments of -10°C, and furthermore, the tensile elongation in both the MD and TD directions is 100% or more, and the film has a high recycling ratio of 35% or more.

[0172] On the other hand, while Comparative Examples 1 and 2 had a high recycling ratio of 50% in the film, they did not contain recycled polyester resin and only contained unused polyester resin. As a result, cutting problems occurred during the stretching process, leading to poor long-term continuous productivity. The resulting biaxially oriented polyester resin film had poor bending resistance in low-temperature environments and produced many pinholes. Furthermore, it had low tensile elongation, high haze, and a yellowish color.

[0173] Comparative Examples 3-6 did not contain ethylene terephthalate oligomer in the raw materials of the recycled polyester resin used, and therefore the cooling crystallization temperature did not meet the range specified in the present invention. Furthermore, the tensile elongation was low, cutting problems occurred during the stretching process, resulting in poor long-term continuous productivity. The resulting biaxially oriented polyester film had poor bending resistance in low-temperature environments and produced many pinholes.

[0174] Comparative Example 9 had a thicker film thickness compared to Comparative Examples 3-6, resulting in improved long-term continuous productivity and tensile elongation. However, its cooling crystallization temperature did not meet the range specified in the present invention, resulting in poor bending resistance at low temperatures and high haze.

[0175] Comparative Examples 7, 8, 10, and 11 did not contain recycled polyester resin and therefore exhibited poor bending resistance in low-temperature environments. In particular, Comparative Examples 10 and 11 did not meet the range of cooling crystallization temperatures specified in the present invention, resulting in poor bending resistance in low-temperature environments and the formation of many pinholes.

Claims

1. The following physical properties (1) to (4): (1) In differential scanning calorimetry (DSC), when the temperature is increased from 25°C to 300°C at a heating rate of 20°C / min, held at 300°C for 10 minutes, and then cooled at a cooling rate of 40°C / min, the temperature at which crystallization occurs is 160 to 180°C. (2) After 200 repeated bending fatigue tests using a Gelboflex tester in a -10°C atmosphere, the number of pinholes was 10 / 500cm. ２ The following: (3) The carboxyl terminal group concentration is 20 to 60 equivalents / t. (4) The surface crystallinity determined by infrared spectroscopy (ATR-IR) using total internal reflection measurement is 1.1 to 1.

4. All of the following conditions must be met, and Polyester resin containing components derived from recycled polyester raw materials, A biaxially oriented polyester resin-based film characterized by the above.

2. A biaxially oriented polyester resin-based film according to claim 1, wherein the haze is 10.0% or less.

3. A biaxially oriented polyester resin film according to claim 1, wherein the thickness is 50 μm or less, and the tensile elongation in both the MD direction and the TD direction is 100% or more.

4. A biaxially oriented polyester resin-based film according to claim 1, wherein the b* value is 0 or less.

5. A packaging material comprising a biaxially oriented polyester resin film according to any one of claims 1 to 4.

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