Biaxially oriented polyester resin film and method for producing the same

Abstract

To provide a biaxially oriented polyester resin film using a resin obtained by polymerization with bis(2-hydroxyethyl) terephthalate (BHET) as a starting raw material, having mechanical properties including transparency, especially excellent flex resistance in low-temperature environments, and further offering superior operability.SOLUTION: A biaxially oriented polyester resin film characterized in that it is a polyester resin film containing 60 mass% or more of a polyester resin A, in which the content of diethylene glycol is 4.0 mol% or less when the total amount of all glycol components is 100 mol%, and the number of pinholes after 200 repeated flex fatigue tests using a Gelbo flex tester under an atmosphere of -10°C is 10 or less per 500 cm2.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyester film using bis-2-hydroxyethyl terephthalate as a starting material and a method for producing the same. [Background technology]

[0002] Polyethylene terephthalate (PET), a typical example of polyester resin, has a high melting point, is chemical resistant, and is relatively low cost, so it is widely used in fibers, films, plastic bottles, and other molded products.

[0003] It has been investigated to obtain PET by polymerizing bis-2-hydroxyethyl terephthalate (BHET) as a starting material (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2005 / 035621 Summary of the Invention [Problem to be solved by the invention]

[0005] However, as in Patent Document 1, polyester resins polymerized using only BHET tend to produce a large amount of diethylene glycol as a by-product. During the stretching process, which is particularly stressful when forming a film using the polyester resin, foreign matter such as diethylene glycol and thermal degradation products generated during polymerization can cause breakage problems, and the resulting stretched film can be inferior in transparency and mechanical properties.

[0006] Therefore, an object of the present invention is to solve the above problems and to provide a biaxially oriented polyester resin film using a resin obtained by polymerization using BHET as a starting material, which film has excellent transparency, mechanical properties such as excellent flex resistance, particularly in low-temperature environments, and excellent operability. [Means for solving the problem]

[0007] The present inventors have conducted extensive research in light of the problems of the prior art and have found that the above-mentioned object can be achieved by a biaxially oriented polyester resin film obtained through a specific process using bis-2-hydroxyethyl terephthalate (BHET), thereby completing the present invention.

[0008] That is, the present invention relates to the following biaxially oriented polyester resin film and a method for producing the same. 1. A polyester resin film containing 60% by mass or more of polyester resin A having a diethylene glycol content of 4.0 mol% or less when the total amount of all glycol components is taken as 100 mol%, and having a pinhole count of 10 / 500cm after 200 repeated bending fatigue tests using a Gelbo flex tester in a -10°C atmosphere. 2 A biaxially stretched polyester resin film characterized by the following: 2. The biaxially stretched polyester resin film according to 1, characterized in that in differential scanning calorimetry (DSC), the film crystallizes at a temperature of 160 to 180°C when heated 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 rate of 40°C / min. 3. The biaxially stretched polyester resin film according to 1 or 2, which has a haze of 10.0% or less. 4. The biaxially stretched polyester resin film according to any one of 1 to 3, having a carboxyl terminal group concentration of 20 to 60 equivalents / t. 5. The biaxially stretched polyester resin film according to any one of 1 to 4, which has a surface crystallinity of 1.1 to 1.4 as determined by attenuated total reflection infrared spectroscopy (ATR-IR). 6. The biaxially stretched polyester resin film according to any one of 1 to 5, which has a thickness of 50 μm or less and a tensile elongation of 100% or more in both the MD and TD directions. 7. The biaxially stretched polyester resin film according to any one of 1 to 6, wherein the b* value is 0 or less. 8. A packaging material comprising the biaxially oriented polyester resin film according to any one of 1 to 7 above. 9. A method for producing a biaxially oriented polyester resin film, comprising: (1) a step of adding bis-2-hydroxyethyl terephthalate to a mixture containing an ethylene terephthalate oligomer and ethylene glycol, and carrying out an esterification reaction under heat treatment conditions of 200 to 280°C to obtain a reaction product; (2) adding a polymerization catalyst to the reaction product and subjecting the mixture to a polycondensation reaction at a temperature of 260 to 285°C under reduced pressure of 1.0 hPa or less to obtain a polyester resin A; (3) producing an unstretched film using a starting material containing the polyester resin A, and then biaxially stretching the unstretched film; 8. The method for producing a biaxially stretched polyester resin film according to any one of 1 to 7, comprising: 10. A method for producing a biaxially oriented polyester resin film, comprising: (4) a step of adding terephthalic acid to bis-2-hydroxyethyl terephthalate and carrying out an esterification reaction under heat treatment conditions of 200 to 250°C to obtain a reaction product; (5) a step of adding a polymerization catalyst to the reaction product and subjecting the mixture to a polycondensation reaction at a temperature of 260 to 285°C under a reduced pressure of 1.0 hPa or less to obtain a polyester resin A; (6) producing an unstretched film using a starting material containing the polyester resin A, and then biaxially stretching the unstretched film; 8. The method for producing a biaxially stretched polyester resin film according to any one of 1 to 7, comprising: [Effects of the Invention]

[0009] According to the present invention, a biaxially stretched film obtained using polyester resin A, which uses bis-2-hydroxyethyl terephthalate as a starting material and has a small amount of foreign matter such as thermal degradation products generated during polymerization and a small amount of diethylene glycol as a by-product, has excellent mechanical properties and processing operability in the film-forming and stretching steps, and exhibits physical properties similar to or superior to those of a biaxially stretched film formed from a virgin polyester resin, and can provide a biaxially stretched polyester resin film having excellent flex resistance, particularly in low-temperature environments.

[0010] In particular, since the biaxially oriented polyester resin film of the present invention contains polyester resin A with a low amount of foreign matter and a low amount of the by-product diethylene glycol, it can be continuously produced over a long period of time at a high stretching speed even when the thickness is 50 μm or less, and has better bending resistance in low-temperature environments than polyester resins that do not contain recycled 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 materials.

[0011] Furthermore, this film has excellent mechanical properties such as tensile strength and tensile modulus, as well as excellent transparency, color tone, wettability, printability, etc., and is therefore particularly suitable for use as a packaging material.

[0012] The production method of the present invention can efficiently and reliably produce a biaxially oriented polyester resin film having excellent flex resistance and the like in a low-temperature environment as described above. That is, the biaxially oriented polyester resin film obtained by the production method of the present invention can also exhibit the excellent properties described above. DETAILED DESCRIPTION OF THE INVENTION

[0013] The film of the present invention contains 60% by mass or more of polyester resin A having a diethylene glycol content of 4.0 mol% or less when the total amount of all glycol components is 100 mol%, and the content of the polyester resin A is preferably 70% by mass or more, more preferably 75% by mass or more, and particularly preferably 80% by mass or more. Furthermore, when the total amount of all glycol components in the polyester resin A is taken as 100 mol %, the diethylene glycol content is preferably 3.0 mol % or less, and more preferably 2.0 mol % or less. The lower limit of the diethylene glycol content can be, for example, 0.5 mol %, but is not limited thereto.

[0014] Polyester resin A having a diethylene glycol content of 4.0 mol % or less when the total amount of all glycol components is 100 mol %, is not particularly limited, but can be obtained by polymerizing bis-2-hydroxyethyl terephthalate (BHET) through a specific process, as described below.

[0015] The bis-2-hydroxyethyl terephthalate is not particularly limited, and examples thereof include those obtained by crushing used PET products and the like and depolymerizing them with ethylene glycol or the like, those obtained by subjecting terephthalic acid to an esterification reaction with ethylene glycol, and commercially available products. When bis-2-hydroxyethyl terephthalate is obtained by depolymerization of used PET products or the like, it may contain metal components. The metal component content in bis-2-hydroxyethyl terephthalate is preferably 300 ppm or less, more preferably 150 ppm or less, even more preferably 100 ppm or less, and even more preferably 50 ppm or less, in order to further reduce the amount of foreign matter in the resulting polyester resin A and improve various properties. The metal components are, for example, derived from metal catalysts contained in the used PET products that are the raw material, but are not limited thereto.

[0016] When the polyester resin A contains a metal component, the content thereof is preferably 1000 ppm or less, more preferably 500 ppm or less, even more preferably 300 ppm or less, and even more preferably 200 ppm or less, as this provides excellent properties.

[0017] As described below, the polyester resin A used in the film of the present invention uses ethylene glycol as one of its raw materials, which may produce diethylene glycol as a by-product. By containing 60 mass % or more of polyester resin A having a diethylene glycol content of 4.0 mol % or less, the present invention can provide a biaxially stretched polyester resin film with excellent mechanical properties, such as bending resistance, in a low-temperature environment.

[0018] The polyester resin A, which is a part or all of the raw material of the film of the present invention, is preferably composed mainly of polyethylene terephthalate (PET). The content of PET in the polyester resin A is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90 to 100% by mass.

[0019] Usually, PET is obtained as a polycondensation product of ethylene glycol and terephthalic acid, but the following components may be copolymerized as the acid component or glycol component. Two or more of these components may be contained.

[0020] Examples of the acid component constituting the polyester resin A include isophthalic acid, 5-sulfoisophthalic acid, phthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, adipic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, dodecanedioic acid, and other dimer acids, as well as trimellitic anhydride, trimellitic acid, pyromellitic acid, 1,4-cyclohexanedicarboxylic acid, sebacic acid, ε-caprolactone, itaconic acid, and phosphorus-based compounds (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 2-(9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-yl)-methylsuccinic acid bis-(2-hydroxyethyl)-ester, and 2-carboxyethylphenylphosphinic acid).

[0021] Examples of glycol components constituting polyester resin A 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, polyethylene glycol, and ethylene oxide adducts of bisphenol A or bisphenol S.

[0022] The polyester resin A preferably has a carboxyl terminal group concentration of 40 equivalents / t or less, more preferably 30 equivalents / t or less, and even more preferably 20 equivalents / t or less. A carboxyl terminal group concentration of 40 equivalents / t or less can result in polyester resin A with even better heat resistance. The lower limit of the carboxyl terminal group concentration is preferably 10 equivalents / t or more, from the viewpoint of improving mechanical properties such as tensile elongation during film formation.

[0023] The polyester resin A had a foreign matter content of 5,000 particles / m as measured by the method described in the Examples below. 2 It is preferable that the number of particles is 1000 or less per m 2More preferably, it is 500 pieces / m or less. 2 More preferably, it is 300 particles / m or less. 2 It is particularly preferable that the amount of foreign matter is less than 10 ppm. By sufficiently reducing the amount of foreign matter, the properties (haze, mechanical properties) and processing operability of the resulting biaxially stretched polyester resin film are excellent. The lower the lower limit of the amount of foreign matter, the better, and for example, 5 ppm is preferable, and 0 ppm is more preferable.

[0024] The polyester resin A preferably has an average pressure increase rate of 0.6 MPa / h or less, more preferably 0.5 MPa / h or less, and even more preferably 0.4 MPa / h or less, as measured by the following method. The average pressure increase rate in the present invention is an example of an index of the amount of foreign matter, and a lower average pressure increase rate indicates a lower amount of foreign matter mixed in. The lower limit of the average pressure increase rate can be, for example, about 0.01 MPa / h, but is not limited to this.

[0025] The average pressure rise rate was measured using a pressure rise tester including an extruder and a pressure sensor. The filter was set at the tip of the extruder, polyester resin was melted in the extruder at 300°C, and the melt was extruded from the filter at a discharge rate of 29.0 g / min. The pressure value at the start of extrusion was defined as the "initial pressure value (MPa)" and the pressure value at the point when extrusion was continued for 12 hours was defined as the "final pressure value (MPa)." The average pressure rise rate was calculated based on these pressure values ​​using the following formula A: Average pressure rise rate (MPa / h) = (final pressure value - initial pressure value) / 12) A This is the method used.

[0026] The extruder, filter, etc. used in the above measurement may be any known or commercially available product. If necessary, a reinforcing material may be added to the filter within a range that does not substantially affect the measurement results.

[0027] The intrinsic viscosity of the polyester resin A used in the film of the present invention is not particularly limited, but is preferably 0.44 to 0.80, and more preferably 0.55 to 0.70.

[0028] From the viewpoint of improving flex resistance in a low-temperature environment, the content of polyester resin A in the film of the present invention is preferably 60% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more. Therefore, other components may be contained within a range that does not impair the effects of the present invention.

[0029] Examples of other components include additives contained in general films, as described below. The additives include additives that are added for the first time during the production of the film of the present invention, as well as additives and impurities contained in the raw materials.

[0030] Examples of additives include the above-mentioned polymerization catalysts, antioxidants, phosphorus compounds, and the like, as well as colorants, pigments, dispersants, fillers, ultraviolet absorbers, thickeners, antistatic agents, color inhibitors, stabilizers, flame retardants, lubricants, and the like, so long as the additives do not impair the effects of the present invention.

[0031] In particular, a coloring inhibitor can be preferably used. For example, phosphorus compounds such as phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl phosphate, tridecyl phosphate, and triphenyl phosphate can be used. These phosphorus compounds can be used alone or in combination of two or more.

[0032] In addition, in order to suppress coloration due to thermal decomposition of the polyester resin, additives such as cobalt compounds such as cobalt acetate, manganese compounds such as manganese acetate, anthraquinone dye compounds, copper phthalocyanine compounds, etc. may be contained.

[0033] The carboxyl end group concentration of the film of the present invention is not particularly limited, but is usually preferably about 20 to 60 equivalents / t. In particular, the upper limit is preferably 50 equivalents / t or less, and most preferably 45 equivalents / t or less. Furthermore, the lower limit is most preferably 30 equivalents / t or more. By setting the carboxyl end group concentration to 60 equivalents / t or less, it becomes possible to obtain a biaxially stretched film that has excellent heat resistance and excellent tensile elongation in the MD and TD directions. On the other hand, by setting the carboxyl end group concentration to 20 equivalents / t or more, it becomes possible to continuously produce biaxially stretched films with excellent tensile elongation in the MD and TD directions at a high stretch ratio over a relatively long period of time, even if the biaxially stretched film is relatively thin, i.e., 50 μm or less.

[0034] Furthermore, in the polyester resin film of the present invention, when the total amount of all glycol components is taken as 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 polyester resin A described below, contamination of the T-die surface (lip surface) during film formation can be suppressed, and it becomes possible to obtain a biaxially stretched film that can be continuously produced at a high draw ratio over a long period of time.

[0035] The polyester resin film of the present invention may contain one or more additives, such as colorants, fillers, dispersants, antioxidants, ultraviolet absorbers, preservatives, antistatic agents, antiblocking agents, and inorganic fine particles, within the range that does not adversely affect the performance of the film.

[0036] In particular, the film of the present invention may contain a lubricant for the purpose of improving the slip properties of the film. The lubricant may be either inorganic or organic. 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 ethylene bisstearic acid amide. Among these, silica is preferred. The content of the lubricant is not limited, but is typically within the range of about 0.01 to 0.3% by mass in the polyester resin film.

[0037] On the other hand, in the film of the present invention, from the viewpoint of improving transparency, the content of the impact 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 none. The impact modifier is a dispersed material (dispersed particles) that suppresses the development of cracks due to impact or bending applied to the film. Therefore, as long as the material has such a function, it includes, for example, materials commercially available under names such as "impact modifier" or "impact strength modifier," as well as materials commercially available or used under other names.

[0038] In particular, materials having such functions include elastomers and rubbers. 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 thiokol rubber, polysulfide rubber, acrylic rubber, silicone rubber, polyether rubber, and epichlorohydrin rubber.

[0039] Although the inclusion of an impact modifier improves the flex resistance of the film, the dispersion of impact modifier particles in the film reduces transparency. Therefore, in conventional biaxially oriented polyester resin films, flex resistance and transparency are considered to be mutually contradictory properties, making it difficult to achieve both. In contrast, the film of the present invention can exhibit excellent flex resistance and the like even without containing these impact modifiers, and therefore can also ensure high transparency. That is, the present invention can provide a film that combines excellent flex resistance and the like with high transparency.

[0040] The film of the present invention may be subjected to surface treatment such as corona discharge treatment or adhesion enhancing treatment, as long as the effects of the present invention are not impaired. Furthermore, an adhesion enhancing layer, a barrier coat layer, a printed layer, etc. may be provided as needed.

[0041] The film of the present invention is a biaxially stretched (biaxially oriented) film, and after 200 repeated bending fatigue tests using a Gelbo flex tester in an atmosphere of -10°C, the number of pinholes is 10 / 500cm. 2 The following (flexibility) is satisfied.

[0042] <Bending resistance> One of the features of the present invention that makes it superior to conventional polyester resin films (particularly virgin polyester films) is its flex resistance in low-temperature environments. The flex resistance is measured by the number of pinholes on the film surface after a specific flex resistance test, and the fewer the number of pinholes, the higher the flex resistance.

[0043] In this test, the number of pinholes was measured after 200 repeated bending fatigue tests using a Gelbo flex tester in an atmosphere of -10°C. 2 The Gelbo flex tester (device) itself is not particularly limited, and known or commercially available devices can be used.

[0044] The number of pinholes in the film of the present invention is usually 10 per 500 cm 2 Less than 5 pieces / 500cm 2 That is, a film having such a small number of pinholes has excellent resistance to tearing when used as a package, and can be suitably used particularly for food containers or food packaging materials for refrigerated distribution, as well as medical containers such as infusion bags.

[0045] <Other physical properties> In addition to the above-mentioned flex resistance, the film of the present invention preferably further has at least one of the following physical properties.

[0046] <Cooling crystallization temperature (Tc)> The lower limit of the cooling crystallization temperature (Tc) of the film of the present invention is preferably 160°C or higher, more preferably 163°C or higher, particularly preferably 165°C or higher, and most preferably 170°C or higher.

[0047] 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 controlling the cooling crystallization temperature within the above range, excellent tensile elongation and flex resistance in low-temperature environments can be exhibited. The cooling crystallization temperature (Tc) of the film of the present invention can be set within the above range by containing, as a raw material for the film of the present invention, 60% by mass or more of a polyester resin containing 4.0 mol% or less of diethylene glycol obtained by polymerizing BHET as a starting material.

[0048] <Haze (Hz)> From the viewpoint of maintaining transparency when used as a packaging material, 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, about 0.1%, but is not limited thereto. Note that if transparency is not required for the film of the present invention, the haze may exceed 10%.

[0049] <Surface crystallinity> The surface crystallinity of the film of the present invention is not particularly limited, but it is preferably set within the following range. The lower limit value is preferably 1.1 or more, more preferably 1.15 or more, and most preferably 1.2 or more. As the upper limit value, it is preferably 1.4 or less, and more preferably 1.35 or less. By setting the surface crystallinity within this range, it becomes possible to obtain mechanical properties, particularly excellent flex resistance.

[0050] <b* value> In terms of appearance, the b* value of the film of the present invention is preferably 0 or less, and more preferably -1 or less. The b* value is an index indicating the color tone. The higher the b* value, the stronger the yellowish color of the film, which may be associated with the deterioration of the packaging material or the contents. Therefore, a lower b* is preferred.

[0051] <Wetting tension> From the viewpoint of printing suitability when printing on the surface of the film of the present invention, the wetting tension is preferably 44 mN / m or more, more preferably 46 mN / m or more, and most preferably 50 mN / m or more.

[0052] <Tensile elongation> For the film of the present invention, the tensile elongations in both the MD and TD directions are preferably 100% or more, more preferably 110% or more, further 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 during stretching, making long-term continuous production difficult, and it is also unsuitable as a packaging material because the sheet or bag body is likely to break.

[0053] <Tensile strength> For the film of the present invention, the tensile strengths in both the MD and TD directions are preferably 200 MPa or more, more preferably 210 MPa or more, and most preferably 220 MPa or more.

[0054] <Tensile modulus> The film of the present invention preferably has a tensile modulus in both the MD and TD directions of 3.0 GPa or more, more preferably 3.5 GPa or more, and most preferably 3.7 GPa or more.

[0055] <Powerful piercing> In order to prevent the film of the present invention from tearing due to contact with protrusions on the contents when used as a packaging material, the puncture strength is preferably 7.0 N or more, more preferably 7.5 N or more, and most preferably 8.0 N or more.

[0056] <Dry heat shrinkage rate> In order to suppress thermal deformation during processing, the film of the present invention preferably has a dry heat shrinkage rate in both the MD and TD directions of 2.0% or less, more preferably 1.5% or less, and most preferably 1.0% or less.

[0057] <Film thickness> 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, from the viewpoint of reducing the amount of plastic used. The lower limit is more preferably 5 μm or more, and most preferably 10 μm or more, from the viewpoint of maintaining mechanical strength.

[0058] Two methods for producing the biaxially stretched polyester resin film of the present invention will be described below.

[0059] The first method for producing a biaxially stretched polyester resin film of the present invention includes the following steps (1) to (3). (1) A process of adding bis-2-hydroxyethyl terephthalate (BHET) to a mixture containing ethylene terephthalate oligomer and ethylene glycol, and carrying out an esterification reaction under heat treatment conditions of 200 to 280°C to obtain a reaction product. (2) A step of adding a polymerization catalyst to the reaction product and subjecting it to a polycondensation reaction at a temperature of 260 to 285°C under reduced pressure of 1.0 hPa or less to obtain a polyester resin A. (3) A step of producing an unstretched film using a starting material containing the polyester resin, and then biaxially stretching the unstretched film.

[0060] In step (1), it is important to use ethylene terephthalate oligomer and ethylene glycol in addition to BHET as a starting material. By using BHET, the reaction temperature can be lowered to suppress the generation of foreign matter, and by using ethylene terephthalate oligomer and ethylene glycol, the amount of diethylene glycol as a by-product can be reduced. In other words, a polyester resin A can be obtained in which both the diethylene glycol content and the amount of foreign matter are sufficiently reduced.

[0061] The ethylene terephthalate oligomer and ethylene glycol used may be known or commercially available products, or may be produced by known production methods. In particular, as the ethylene terephthalate oligomer, for example, an esterification reaction product of ethylene glycol and terephthalic acid can be suitably used. In the present invention, the number average degree of polymerization of the ethylene terephthalate oligomer is preferably 2 to 20.

[0062] From the viewpoint of allowing the reaction to proceed sufficiently, the amounts of ethylene glycol and ethylene terephthalate oligomer used are preferably 5 to 15 parts by mass, and more preferably 10 to 15 parts by mass, per 100 parts by mass of ethylene terephthalate oligomer. If the amount of ethylene glycol added exceeds 15 parts by mass, the ethylene terephthalate oligomer tends to solidify in the reactor, and the subsequent reaction may not be able to continue.

[0063] Although there are no particular limitations on the mixing of the ethylene terephthalate oligomer and ethylene glycol, it is preferable to add ethylene glycol to the ethylene terephthalate oligomer, for example. Furthermore, when adding, it is preferable to make the temperature of the contents uniform while rotating a stirrer in order to prevent solidification of the oligomer.

[0064] In step (1), the amounts (mass ratio) of the raw materials used are preferably (ethylene terephthalate oligomer) / (bis-2-hydroxyethyl terephthalate)=80 / 20 to 20 / 80, more preferably 70 / 30 to 30 / 70, and even more preferably 60 / 40 to 40 / 60. If the former is greater than the above range, the reaction temperatures in steps (1) and (2) may not be adjusted to low levels, which may result in a large amount of foreign matter in the resulting polyester resin. If the latter is greater than the above range, it may be impossible to reduce the molar ratio (G / A) of (total glycol components) / (total acid components) described below, and as a result, the diethylene glycol content tends to be high. Furthermore, when a polyester resin is obtained using BHET obtained from used PET or the like, the amount of metal residue derived from the raw materials may be large, and as a result, the amount of foreign matter may be large.

[0065] When the raw materials are added, it is preferable to do so under normal pressure with stirring, and it is more preferable to add them while purging with a small amount of inert gas (generally nitrogen gas), which prevents oxygen from being mixed in and more reliably prevents deterioration of color tone.

[0066] The method for adding bis-2-hydroxyethyl terephthalate is not particularly limited. For example, it may be added to the reaction vessel in a solid state such as flake form, or it may be heated and melted and then added to the reaction vessel in a molten state.

[0067] In step (1), all components including the oligomer, ethylene glycol, and bis-2-hydroxyethyl terephthalate are preferably used so that the molar ratio (G / A) of (total glycol components) / (total acid components) is 1.1 to 2.5, more preferably 1.1 to 1.8, and even more preferably 1.1 to 1.5. By setting the molar ratio to 1.1 or more, the esterification reaction proceeds sufficiently, making it easier to obtain a reaction product. By setting the ratio to 2.5 or less, the content of diethylene glycol in polyester resin A can be reduced to fall within a specific range.

[0068] In step (1), the reaction temperature (particularly the internal temperature of the reactor) is preferably set in the range of 200 to 280°C, more preferably in the range of 220 to 270°C. If the temperature is below 200°C, the reaction time will be long, which may result in poor productivity. In addition, the reaction product may solidify, which may worsen operability or prevent the esterification reaction from proceeding. On the other hand, if the temperature exceeds 280°C, the amount of diethylene glycol produced as a by-product will increase, and the amount of foreign matter due to thermal decomposition will increase.

[0069] The reaction time in step (1) (the reaction time from the end of the introduction of the raw materials) is not particularly limited, but is usually preferably within 4 hours, and more preferably within 2 hours, particularly from the viewpoints of suppressing the amount of diethylene glycol by-product and suppressing deterioration in the color tone of the polyester. The lower limit of the reaction time is not particularly limited, but is, for example, 1 hour.

[0070] The internal pressure in step (1) may be normal pressure, or the reaction may be carried out under pressure as needed. The internal pressure of the reactor is preferably 0 to 0.5 MPa, more preferably 0.05 to 0.3 MPa.

[0071] The reaction apparatus used in the production method of the present invention is not particularly limited, and known or commercially available apparatuses can be used. In particular, although there are no particular problems with the volume, shape of the stirring blades, etc. of the reactor, a commonly used esterification reactor can be used, and in order to efficiently proceed with the depolymerization reaction, it is preferable to use a reactor having a structure equipped with a distillation column that does not distill ethylene glycol out of the system.

[0072] The reaction product obtained in step (1) is a liquid and may be subjected to a filtration step. Filters that can be used for filtration include, for example, metal filters such as stainless steel filters. The filter type is not particularly limited, and examples include screen changer filters, leaf disc filters, candle-type sintered filters, etc. The filtration particle size of the filter is preferably 10 to 25 μm.

[0073] In step (2), a polycondensation catalyst is added to the reaction product, and the reaction product is subjected to a polycondensation reaction at a temperature of 260 to 285° C. under a reduced pressure of 1.0 hPa or less, thereby obtaining polyester resin A.

[0074] The polycondensation catalyst is not particularly limited, and for example, at least one of a germanium compound, an antimony compound, a titanium compound, a cobalt compound, etc. Alternatively, an organic sulfonic acid compound such as 2-sulfobenzoic anhydride, o-sulfobenzoic acid, m-sulfobenzoic acid, p-sulfobenzoic acid, 5-sulfosalicylic acid, benzenesulfonic acid, o-aminobenzenesulfonic acid, m-aminobenzenesulfonic acid, p-aminobenzenesulfonic acid, p-toluenesulfonic acid, methyl p-toluenesulfonate, 5-sulfoisophthalic acid, or a salt thereof may be used as the polycondensation catalyst.

[0075] The amount of the polycondensation catalyst used is not particularly limited, but for example, it is 5 × 10 -5 It is preferable to set the concentration to 6×10 moles / unit or more. -5The upper limit of the amount used is, for example, 1 × 10 -3 It can be, but is not limited to, moles / unit.

[0076] When BHET obtained by depolymerizing used PET products is used as a raw material, the polymerization catalyst residue contained in this raw material may also act as a catalyst during the polycondensation reaction. Therefore, it is preferable to adjust the amount of polycondensation catalyst used taking into account the type and content of the polymerization catalyst contained in the raw material BHET.

[0077] During the polycondensation reaction, if necessary, a fatty acid ester capable of adjusting the melt viscosity, a hindered phenol-based antioxidant, or a phosphorus compound capable of suppressing thermal decomposition of the resin can also be added in addition to the polycondensation catalyst.

[0078] 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 alone or in combination of two or more.

[0079] 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), ... Examples of suitable compounds include ethylene glycol-bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate] and 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1'-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane, but tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane is preferred from the standpoint of effectiveness and cost. These compounds can be used alone or in combination of two or more.

[0080] Examples of phosphorus compounds that can be used include phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl phosphate, tridecyl phosphate, triphenyl phosphate, etc. These compounds can be used alone or in combination of two or more.

[0081] In step (2), the polycondensation reaction is carried out at a temperature of 260 to 285°C under reduced pressure of 1.0 hPa or less. If the polycondensation reaction temperature is lower than 260°C or the pressure during the polycondensation reaction exceeds 1.0 hPa, the polycondensation reaction time becomes longer, resulting in poor productivity. Furthermore, the reaction time becomes longer, and the amount of diethylene glycol increases due to thermal history, which may increase the amount of foreign matter. Among these, the polycondensation reaction temperature is more preferably 270°C or higher, as this facilitates the progress of the polycondensation reaction. On the other hand, if the polycondensation reaction temperature is too high, the polymer may become discolored due to thermal decomposition, resulting in a deterioration in color tone, and the amount of diethylene glycol and foreign matter may also increase due to thermal decomposition. Therefore, the upper limit of the polycondensation reaction temperature is preferably 285°C or lower.

[0082] If necessary, the polyester resin A obtained above may be further subjected to a crystallization step, thereby increasing the crystallinity of the polyester resin A. The crystallization conditions are not particularly limited, but can be carried out, for example, by heat treatment at the crystallization temperature of the polyester resin A used or a temperature higher. For example, when the polyester resin A is PET, the crystallization temperature of PET is usually about 130°C, so the heat treatment can be carried out at a temperature of 135°C or higher (preferably 140 to 180°C). The heat treatment time can be changed depending on the heat treatment temperature, etc., and can be, for example, about 30 minutes to 20 hours.

[0083] In the present invention, if necessary, the resin obtained in the polycondensation step or the crystallization step can be further subjected to a solid-state polymerization reaction, thereby further increasing the degree of polymerization of the polyester resin A, thereby making it possible to obtain physical properties more suitable for molding.

[0084] The conditions for the solid-state polymerization reaction are not particularly limited, but it is preferable to carry out the heat treatment so that the intrinsic viscosity of the resulting polyester resin A is 0.80 to 1.25 (particularly 0.82 to 1.24). More specifically, for example, the heat treatment can be carried out by heat treating the resulting polyester resin A in an inert gas atmosphere at about 180 to 240°C. The heat treatment time depends on the heat treatment temperature, etc., but is usually about 5 to 50 hours.

[0085] In the step (3), an unstretched film is produced using a starting material containing the polyester resin A obtained in the step (2), and the unstretched film is biaxially stretched.

[0086] The starting material may contain a resin other than the polyester resin A, provided that the effects of the present invention are not impaired. Examples of resins other than polyester resin A include polyester resins not polymerized from BHET (hereinafter sometimes referred to as "virgin polyester resins"), unused polyester resins, used polyester products, and the like.

[0087] Unused polyester resins are materials that have not yet been commercialized. Examples include unstretched waste, edge trimming waste, slit waste, and defective products generated during film production, as mentioned above. These can be added in the form of pulverized material (flakes, etc.) or pellets made by remelting them.

[0088] The post-consumer polyester product is a product that is to be disposed of after use. After an appropriate washing process, it can be added in the form of a pulverized product or pellets prepared by remelting the pulverized product.

[0089] The content of unused polyester resin in the starting material is usually 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 unused polyester resin exceeds 75% by mass, foreign matter or heat-degraded products tend to increase, which tends to cause problems such as breakage during film formation. In addition, the mechanical properties of the film, such as tensile elongation, tend to deteriorate.

[0090] The film scraps or defective products used as unused polyester resins have different concentrations of additives, such as lubricants such as silica, as well as antioxidants, depending on the brand of the scrap. Therefore, the greater the content of unused polyester resin in the starting material, the greater the variation in the additive concentrations, which may adversely affect the haze of the resulting film, the wetting tension of the film surface, printability, etc.

[0091] For the above reasons, 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 wet tension and printability, so the content of unused polyester resin can be increased from the perspective of increasing the recycling rate. The content of unused polyester resin in the intermediate layer may be 100% by mass.

[0092] The method for producing the unstretched film is not limited, and it can be formed by a known film-forming method. For example, it can be obtained by extruding the melt of the raw material through a T-die and then cooling it with a casting roll. In this case, it is necessary to precisely control the actual temperature of the casting roll surface in order to ensure a uniform crystallinity of the unstretched film.

[0093] The unstretched film is then 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, and examples include simultaneous biaxial stretching and sequential biaxial stretching. From the viewpoint of achieving a balance between mechanical properties, i.e., minimizing the difference between tensile strength and tensile modulus in the MD and TD directions, simultaneous biaxial stretching is preferred. From the viewpoint of achieving a balance between thermal properties, i.e., minimizing the difference between dry heat shrinkage in the MD and TD directions, and improving puncture strength and impact strength, sequential biaxial stretching is preferred. These methods can be selected appropriately depending on the desired film properties and application.

[0094] The stretching ratio can be appropriately set depending on, for example, the application of the film, the desired physical properties, etc., and can be, for example, 2 to 4 times in the MD direction and 2 to 4 times in the TD direction, but is not limited thereto. The stretching temperature is also not limited, and can be, for example, within a range of 40 to 220°C. In particular, in the case of sequential stretching, it is preferable that the stretching temperature in the MD direction is 40 to 80°C and the stretching temperature in the TD direction is 80 to 150°C. In addition, in the case of simultaneous biaxial stretching, it is preferable that the temperature is 160 to 220°C.

[0095] The obtained biaxially stretched film is preferably subjected to a short-time heat treatment at a temperature of about 220 to 240° C. as needed in order to improve dimensional stability and suppress hot water shrinkage.

[0096] The deformation and heat imparted during the stretching process cause the stretched film to undergo crystallization. By using polyester resin A, which has crystallization characteristics that are expressed by a specific range of cooling crystallization temperature, it becomes easier to appropriately control the surface crystallization of the film, and it is possible to obtain a stretched film with excellent mechanical properties, especially excellent flex resistance, which is affected by the state of surface crystallization.

[0097] The second method for producing the polyester resin film of the present invention includes the following steps (4) to (6). (4) A step of adding terephthalic acid to bis-2-hydroxyethyl terephthalate and carrying out an esterification reaction under heat treatment conditions of 200 to 250°C to obtain a reaction product. (5) A step of adding a polymerization catalyst to the reaction product and subjecting it to a polycondensation reaction at a temperature of 260 to 285°C under a reduced pressure of 1.0 hPa or less to obtain a polyester resin A. (6) A step of producing an unstretched film using a starting material containing the polyester resin A, and then biaxially stretching the unstretched film.

[0098] In step (4), it is important to use terephthalic acid in addition to BHET as a starting material. By using BHET, the reaction temperature can be lowered to suppress the generation of foreign matter, and by using terephthalic acid, the amount of diethylene glycol, a by-product, can be reduced. In other words, a polyester resin A can be obtained in which both the diethylene glycol content and the amount of foreign matter are sufficiently reduced.

[0099] The terephthalic acid used may be any known or commercially available product, or may be produced by a known production method.

[0100] In step (4), the amounts (mass ratio) of the raw materials used are preferably (terephthalic acid) / (bis-2-hydroxyethyl terephthalate)=40 / 60 to 1 / 99, more preferably 30 / 70 to 10 / 90. If the former is greater than the above range, the esterification reaction time in steps (4) and (5) may become longer, or the reaction temperature may not be able to be adjusted low, resulting in a higher amount of foreign matter in the resulting polyester resin. If the latter is greater than the above range, it may be impossible to reduce the molar ratio (G / A) of (total glycol components) / (total acid components) described below, and as a result, the diethylene glycol content tends to be high. Furthermore, when a polyester resin is obtained using BHET obtained from used PET or the like, the amount of metal residue derived from the raw materials may be large, and as a result, the amount of foreign matter may be large.

[0101] When the raw materials are added, it is preferable to do so under normal pressure with stirring, and it is more preferable to add them while purging with a small amount of inert gas (generally nitrogen gas), which prevents oxygen from being mixed in and more reliably prevents deterioration of color tone.

[0102] The method for adding bis-2-hydroxyethyl terephthalate is not particularly limited. For example, it may be added to the reaction vessel in a solid state such as flakes, or may be heated and melted and added to the reaction vessel in a molten state.

[0103] In step (4), all components including terephthalic acid and bis-2-hydroxyethyl terephthalate are preferably used so that the molar ratio (G / A) of (total glycol components) / (total acid components) is 1.1 to 2.5, more preferably 1.1 to 1.8, and even more preferably 1.1 to 1.5. By setting the molar ratio to 1.1 or more, the esterification reaction proceeds sufficiently, making it easier to obtain a reaction product. By setting the ratio to 2.5 or less, the content of diethylene glycol in polyester resin A can be reduced to fall within a specific range.

[0104] In step (4), the reaction temperature (particularly the internal temperature of the reactor) is preferably set in the range of 200 to 250°C, more preferably in the range of 220 to 240°C. If the temperature is below 200°C, the reaction time will be long, which may result in poor productivity. In addition, the reaction product may solidify, which may worsen operability or prevent the esterification reaction from proceeding. On the other hand, if the temperature exceeds 250°C, the amount of diethylene glycol produced as a by-product will increase, and the amount of foreign matter due to thermal decomposition will increase.

[0105] The reaction time in step (4) (the reaction time from the end of the introduction of the raw materials) is preferably set to the same range as that in step (1) in order to suppress the amount of diethylene glycol by-product and the deterioration of color tone. The internal pressure in step (4) may be normal pressure, or the reaction may be carried out under pressure as necessary. The internal pressure of the reactor is preferably 0 to 0.5 MPa, more preferably 0.05 to 0.3 MPa.

[0106] The reaction apparatus used in the second production method is not particularly limited, as in the first production method, and known or commercially available apparatuses can be used. In particular, although there are no particular problems with the volume, shape of the stirring blades, etc. of the reactor, a commonly used esterification reactor is preferred, in order to efficiently proceed with the depolymerization reaction, but the reactor is preferably structured so as to be equipped with a distillation column that does not distill ethylene glycol out of the system.

[0107] The reaction product obtained in step (4) is a liquid and may be subjected to a filtration step. Filters that can be used for filtration include those exemplified in step (1) of the first method above.

[0108] In step (5), a polycondensation catalyst is added to the reaction product obtained in step (4), and the reaction product is subjected to a polycondensation reaction at a temperature of 260 to 285°C under a reduced pressure of 1.0 hPa or less, which is the same process as step (2) in the first production method. The polyester resin obtained by this method may also be referred to as polyester resin A.

[0109] In step (5), the polycondensation reaction is carried out at a temperature of 260 to 285°C under reduced pressure of 1.0 hPa or less. If the polycondensation reaction temperature is lower than 260°C or the pressure during the polycondensation reaction exceeds 1.0 hPa, the polycondensation reaction time becomes longer, resulting in poor productivity. Furthermore, the reaction time becomes longer, and the amount of diethylene glycol increases due to thermal history, which may increase the amount of foreign matter. Among these, the polycondensation reaction temperature is more preferably 270°C or higher, as this facilitates the progress of the polycondensation reaction. On the other hand, if the polycondensation reaction temperature is too high, the polymer may become discolored due to thermal decomposition, resulting in a deterioration in color tone, and the amount of diethylene glycol and foreign matter may also increase due to thermal decomposition, so the upper limit of the polycondensation reaction temperature is preferably 285°C or lower.

[0110] In step (5), the type and amount of the polymerization catalyst used can be the same as in step (2) above.

[0111] In step (6), an unstretched film is produced using a starting material containing polyester resin A obtained in step (5), and the unstretched film is biaxially stretched, which is a process similar to step (3) of the first manufacturing method described above.

[0112] The film of the present invention may be in the form of a single layer, or may be a film formed by simultaneous melt extrusion or lamination and composed of multiple layers.

[0113] For example, in addition to a two-type, two-layer structure in which a biaxially oriented polyester resin film containing polyester resin A is laminated with a biaxially oriented polyester resin film containing an unadopted polyester resin, a two-type, three-layer structure in which a biaxially oriented polyester resin film containing an unadopted polyester resin is sandwiched between biaxially oriented polyester resin films containing polyester resin A may also be used. In the case of a polyester resin film having a layer structure in which an intermediate layer can be sandwiched, such as a two-type, three-layer structure, the intermediate layer film does not constitute the surface of a film composed of multiple layers, so that the effect on the bending resistance, strength, surface crystallinity, etc. of the entire film is slight, and the content of the unadopted polyester resin can be increased.

[0114] The film of the present invention can be used alone as it is, or can be used as a laminate film together with other layers (sealant layer, print layer, gas barrier layer, etc.).

[0115] 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 also not limited, and various types of bags can be manufactured, such as two-sided bags, three-sided bags, three-sided bags with zippers, palm-seamed bags, gusset bags, bottom gusset bags, and stand-up bags. Therefore, a packaging bag can be constructed by laminating a sealant layer such as a polyolefin or the like with the film of the present invention to form a laminated film using a known method such as dry lamination or extrusion lamination, and then heat-sealing the sealant layers together.

[0116] When used as a packaging material (packaging bags, containers, etc.), there are no restrictions on the contents, and it can be used for a wide range of items, including food, pharmaceuticals, medical devices, cosmetics, chemicals, miscellaneous goods, and electronic components. [Example]

[0117] The features of the present invention will be described in more detail below with reference to examples and comparative examples. However, the scope of the present invention is not limited to these examples. In each measurement where the temperature and humidity are not specified, samples were left in an environment of 23°C temperature and 50% RH for 2 hours or more, and measurements were performed in an environment of 23°C temperature and 50% RH.

[0118] intrinsic viscosity The measurement was carried out at 20°C using an equal weight mixture of phenol and tetrachloroethane as a solvent.

[0119] Metal content in BHET and resin (ppm) The contents of metal components (Sb, Ge) were determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0120] Diethylene glycol content (mol%) The obtained polyester resin was dissolved in a mixed solvent of deuterated hexafluoroisopropanol and deuterated chloroform in a volume ratio of 1:20, and analyzed using a JEOL "LA-400 NMR" apparatus. 1 H-NMR was measured, and the diethylene glycol content was determined from the integrated intensity of the proton peak of each component in the obtained chart.

[0121] Melting point Tm (℃) Using a differential scanning calorimeter DSC-7 manufactured by PerkinElmer, measurements were carried out in a nitrogen stream at a temperature range of 25 to 280°C and a heating rate of 20°C / min.

[0122] Amount of foreign matter (pieces / m 2 ) The number of foreign matters in the obtained resin was measured as follows: A sheet having a thickness of 0.1 mm was produced using a fisheye counter (gel counter) manufactured by Optical Control Systems under the conditions of an extruder temperature of 260 to 290°C, a rotation speed of 50 rpm, a winder temperature of 50°C, and a rotation speed of 5 m / min. 2 The number of foreign particles with a particle size of 25 μm or more per unit area was detected and counted.

[0123] Carboxyl end group concentration (equivalents / t) 0.1 g of the obtained polyester resin film was dissolved in 10 ml of benzyl alcohol, and 10 ml of chloroform was added to the solution, followed by titration with a 1 / 10 N potassium hydroxide benzyl alcohol solution to determine the viscosity.

[0124] Polyester Resin Composition The obtained polyester resin or polyester resin film was dissolved in a mixed solvent of deuterated hexafluoroisopropanol and deuterated chloroform in a volume ratio of 1:20, and 1H-NMR was measured using a JEOL "LA-400 NMR" apparatus. The type and content of copolymerized components were determined from the integrated intensity of the proton peak of each component in the obtained chart.

[0125] Tensile strength (MPa) Tensile strength was measured using an autograph manufactured by Shimadzu Corporation in accordance with Japanese Industrial Standard JIS K7127. The polyester resin films obtained in the Examples and Comparative Examples were cut from the center in the TD direction to a width of 10 mm and a length of 150 mm in the MD and TD directions, respectively, to prepare samples. Measurements were carried out under conditions of a measurement length of 100 mm and a pulling speed of 500 mm / min, and the tensile strength was calculated using the following formula: Tensile strength (MPa) = tensile load at break (N) / average original cross-sectional area of ​​the measurement sample (mm 2 )

[0126] Tensile elongation (%) Tensile elongation was measured using an autograph manufactured by Shimadzu Corporation in accordance with Japanese Industrial Standard JIS K7127. Samples of 10 mm width and 150 mm length were cut out from the center of the TD direction of the polyester resin films obtained in the Examples and Comparative Examples in both the MD and TD directions. Measurements were carried out under conditions of a measurement length of 100 mm (distance between grippers) and a pulling speed of 500 mm / min, and the elongation was calculated using the following formula: Tensile elongation (%) = Distance traveled by gripper at break (mm) / Distance between original grippers (100 mm) x 100

[0127] Tensile modulus (GPa) The tensile modulus was measured using an autograph manufactured by Shimadzu Corporation in accordance with Japanese Industrial Standard JIS K7127. The polyester resin films obtained in the Examples and Comparative Examples were cut from the center of the TD direction to a width of 10 mm and a length of 150 mm in both the MD and TD directions to form samples. Measurements were carried out at a measurement length of 100 mm (distance between grippers) and a pulling speed of 20 mm / min, and the modulus was calculated using the following formula: Tensile modulus (GPa) = F / A × ΔL (1 mm) / L (100 mm) × 9.807 × 10 -3 F: Stress at 1% elongation (kgf) A: Initial cross-sectional area of ​​the test piece (mm 2 ) ΔL: Length of test piece at 1% elongation (mm) L: Distance between grippers (100 mm)

[0128] Piercing strength (N) The polyester resin films obtained in the examples and comparative examples were cut into 50 mm x 50 mm pieces centered on the central part in the TD direction, and attached to a special fixing plate with a 30 mm diameter circular hole in the center.The puncture strength was measured using an autograph manufactured by Shimadzu Corporation, using 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.

[0129] Dry heat shrinkage rate (%) The central portion in the TD direction of the polyester resin films obtained in the Examples and Comparative Examples was cut into a width of 10 mm and a length of 150 mm in the MD and TD directions, respectively, and a 100 mm long gauge was marked. The film was treated in hot air at 160°C for 15 minutes, and the gauge length (mm) after treatment was read and calculated using the following formula. Hot water shrinkage rate (%) = (gauge length before treatment - gauge length after treatment) / gauge length before treatment x 100

[0130] Haze (%) Using a haze meter (NDH4000) manufactured by Nippon Denshoku Industries Co., Ltd., the central part in the TD direction of the polyester resin films obtained in the examples and comparative examples was measured in accordance with Japanese Industrial Standard JIS K7136.

[0131] b * value Using a spectrophotometric color difference meter NF555 manufactured by Nippon Denshoku Industries Co., Ltd., measurements were carried out by stacking 30 sheets of the polyester resin films obtained in the Examples and Comparative Examples under reflective conditions of light source D65 and a viewing angle of 2° in accordance with Japanese Industrial Standard JISK 7373. A white board with tristimulus values ​​X / Y / Z = 84.3 / 89.0 / 93.5 was used as the backing plate. A positive value indicates a yellow hue, and a negative value indicates a blue hue.

[0132] Wetting tension (mN / m) In accordance with Japanese Industrial Standard JIS K6768, the corona-treated surfaces of the polyester resin films obtained in the Examples and Comparative Examples were measured using wet tension test mixtures No. 36.0 to 54.0 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The wet tension was measured at five locations at 200 mm intervals from the center toward both ends in the TD direction. Measurements were repeated every 1 m in the MD direction, for a total of 50 locations. The minimum and maximum wet tension values ​​measured at the 50 locations are shown in Table 2. A practical wet tension is 44 mN / m or higher, with 46 mN / m or higher being particularly preferred.

[0133] Ink adhesion (printability) [Printing process] The printing ink was Rio Alpha R39 indigo (manufactured by TOYOINK) mixed with diluent NKFS102 (manufactured by TOYOINK) and adjusted to a viscosity of 15 seconds using a Zahn cup #3. The printing roll film was prepared by slitting the polyester resin film obtained in the Examples and Comparative Examples at positions 500 mm to the left and right of the center in the TD direction. The ink was applied to the film using a gradation-changing plate engraved in the MD direction in the order of 10%, 20%, 30%, 40%, and 100% gradation, followed by drying at 50°C for 10 seconds and winding up to produce the printed film. [Evaluation method] Cellophane tape (18 mm wide) was applied from end to end in the TD direction to the 40% gradation printed area of ​​the prepared printed film, taking care not to trap air bubbles, and the evaluation area was an area 100 mm to the left and right of the center of the applied area, which was lightly rubbed 20 times from above. Next, the cellophane tape was quickly peeled off at an angle of 180° to the film, and the degree of ink peeling in the evaluation area was visually observed and rated on a three-point scale according to the following criteria. (Evaluation criteria) ◎...Very good (ink dots do not come off) ○...Good (slight ink dots come off) ×... Poor (more than half of the ink dots are removed)

[0134] Continuous Productivity The polyester film was continuously produced and evaluated according to the following criteria. ◎: Operation was possible for more than 48 hours continuously. ○: Continuous operation was possible for more than 24 hours, but due to pressure buildup in the filter, contamination of the lip surface of the T-die, film breakage, roll contamination, etc., film could not be produced, and the continuous operation time was less than 48 hours. ×: During 24 hours of continuous operation, the film could not be produced due to pressure buildup in the filter, contamination of the lip surface of the T-die, film breakage, roll contamination, etc.

[0135] Film crystallization temperature Tc (℃) In accordance with Japanese Industrial Standard JIS K7121, 10 mg of the resin films obtained in the examples and comparative examples were measured as samples using a differential scanning calorimeter (power compensation type DSC8000) manufactured by PerkinElmer Co., Ltd. The measurement conditions were as follows: the temperature was increased from 25°C to 300°C at a rate of 20°C / min, held at 300°C for 10 minutes, and then cooled to 100°C at a rate of 40°C / min; the peak top temperature at which crystallization occurred during cooling was taken as the cooling crystallization temperature Tc.

[0136] Surface crystallinity of the film An infrared spectrophotometer (FT / IR-6100) manufactured by JASCO Corporation was used, and the wavelength was measured at 1340 cm by the reflection method (ATR method). -1 Crystal absorption bands around 1410 cm -1 The absorbance ratio with the correction band (1340 cm -1 / 1410cm -1 ) was used to determine the surface crystallinity. In the present invention, a horizontal prism ATR610RS was used, a diamond prism was used, the angle of incidence was 45°, and the number of accumulations was 64.

[0137] Bending resistance in low temperature environments (pieces / m 2 ) 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 an environment at -10°C, and then subjected to a 200-cycle flex fatigue test (torsion angle: 440°) using a Gelbo Flex Tester (BE-1005, manufactured by Tester Sangyo Co., Ltd.) in an environment at -10°C. The flex fatigue test was conducted in accordance with the ASTM F392 standard, and the number of pinholes was determined for film samples (chuck distance 178 mm, diameter 89 mm) by counting the number of ink-permeated areas on filter paper. Measurements were conducted on three samples, and the measurement was carried out over a 500cm 2 The average number of pinholes per sample was calculated.

[0138] Polyester Resin A <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 at a temperature of 250°C and a pressure of 50 hPa to obtain ethylene terephthalate oligomer (number average degree of polymerization: 5) with an esterification reaction rate of 95%. 50.0 parts by mass of ethylene terephthalate oligomer and 6.0 parts by mass of ethylene glycol were charged into an esterification reactor. Subsequently, with the agitator of the esterification reactor (hereinafter referred to as the "ES can") running, 50.0 parts by mass of BHET was added via a rotary valve. The raw materials were added so that the molar ratio of (total glycol components) / (total acid components) (hereinafter referred to as G / A) was 1.71. The amount of metals (antimony, germanium) contained in the BHET used was 21 ppm. The esterification reaction (step (1)) was then carried out for 1 hour under heat treatment conditions at 250 °C. The reaction product was then pumped into a polycondensation reactor (hereinafter referred to as a PC reactor), and 1.0 × 10 antimony trioxide was added as a polymerization catalyst. -4 mol / unit, and EG slurry of titanium dioxide was added to give a concentration of 0.20 mass%, and the PC can was reduced in pressure, and after 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 (step (2)), to obtain polyester resin A-1 (intrinsic viscosity: 0.66). The metal component content in the obtained polyester resin A-1 was 133 ppm.

[0139] <Polyester resins A-2, A-4, A-5> The amounts of raw materials (BHET, ethylene terephthalate oligomer, terephthalic acid, ethylene glycol), G / A, and reaction temperature in step (1) or step (2) were changed as shown in Table 1 to obtain polyester resins A-2, A-4, and A-5.

[0140] <Polyester resin A-3> 25.0 parts by mass of terephthalic acid was charged into an esterification reactor, and then, with the agitator of the esterification reactor (hereinafter referred to as the "ES can") running, 75.0 parts by mass of BHET was added via a rotary valve. At this time, the raw materials were added so that the molar ratio (total glycol components) / (total acid components) (hereinafter referred to as G / A) was 1.32. The amount of metals (antimony, germanium) contained in the BHET used was 21 ppm. Then, an esterification reaction (step (4)) was carried out for 1 hour under heat treatment conditions at 240°C. The reaction product was then pumped into a polycondensation reactor (hereinafter referred to as a PC reactor), and 1.0 × 10 antimony trioxide was added as a polymerization catalyst. -4 mol / unit, and EG slurry of titanium dioxide was added so as to be 0.20 mass %, and the PC can was reduced in pressure, and after 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 (step (5)), to obtain polyester resin A-3 (intrinsic viscosity: 0.60).

[0141] Table 1 shows the compositions, production conditions, and properties of polyester resins A-1 to A-5.

[0142] [Table 1]

[0143] <Unused polyester resin> Film scraps generated during the production of polyethylene terephthalate resin film were crushed, remelted at 250-290°C, and pelletized. After that, they were dried to obtain unused polyester resin (crystallization temperature on cooling: 179°C) for use in polyester resin film.

[0144] <Virgin polyester resin> In an esterification reactor, terephthalic acid and ethylene glycol were subjected to an esterification reaction 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 chipping. The obtained polyester chips were further dried at 170°C for 2 hours under a nitrogen atmosphere and crystallized. Then, in a batch-type solid-state polymerization apparatus, solid-state polymerization was carried out at 230°C for 6 hours under a nitrogen stream. The solid-phase polymerized polyester was immersed in hot water at 95°C for 4 hours, subjected to water treatment, dehydrated, and dried at 120°C for 2 hours under a nitrogen stream to obtain virgin polyester resin (intrinsic viscosity 0.65, cooling crystallization temperature 180°C).

[0145] <Silica-containing polyester resin (Silica Master)> GS-BR-MG manufactured by Nippon Ester Co., Ltd. was used, which is virgin polyethylene terephthalate resin containing 1.5 mass % of silica with an average particle size of 2.3 μm.

[0146] Example 1 93.5% by mass of polyester resin A-1 and 6.5% by mass of silica masterbatch were mixed and melt-kneaded in an extruder, fed into a T-die, extruded into a sheet, and wound around a metal drum temperature-controlled at 20 ° C., cooled, and wound up to obtain a single-layer unstretched sheet with a thickness of approximately 120 μm. Next, the edges of this unstretched sheet were held with clips in a tenter-type simultaneous biaxial stretching device 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. Thereafter, the sheet was heat-treated at 215 ° C. for 4 seconds with a relaxation rate of 5% in the TD direction, slowly cooled to room temperature, and corona discharge-treated on one side to obtain a biaxially stretched polyester resin film with a thickness of 12 μm.

[0147] Example 2 A biaxially stretched polyester resin film having a thickness of 12 μm was obtained in the same manner as in Example 1, except that an unused polyester resin was mixed and the contents of polyester resin A-1 and silica masterbatch were changed as shown in Table 1.

[0148] Example 3 An 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-type stretching machine, and then, while the edges were held with clips, it was sequentially biaxially stretched at a stretch ratio of 3.6 times in the TD direction at 120°C. Thereafter, it was subjected to a heat treatment at 230°C for 3 seconds with a relaxation rate of 2% in the TD direction, slowly cooled to room temperature, and then subjected to a corona discharge treatment on one side to obtain a biaxially stretched polyester resin film with a thickness of 12 μm.

[0149] Examples 4 and 5 A biaxially stretched polyester resin film having a thickness of 12 μm was obtained by the sequential biaxial stretching method in the same manner as in Example 3, except that the contents of polyester resins A-2, A-3, unadopted polyester resin, and silica masterbatch were changed as shown in Table 1.

[0150] Example 6 A biaxially stretched polyester resin film was obtained by the sequential biaxial stretching method 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 film was stretched 3.5 times in the MD direction at a temperature of 83°C in the roll-type stretching machine, and heat-treated at 228°C for 6 seconds with a relaxation rate of 2% in the TD direction.

[0151] Comparative Examples 1 and 2 A biaxially stretched polyester resin film having a thickness of 12 μm was obtained in the same manner as in Example 5, except that the polyester resin was changed to A-4 or A-5.

[0152] Comparative Example 3 Sequential biaxial stretching was carried out in the same manner as in Example 3, except that 58.5% by mass of polyester resin A-1, 35.0% by mass of virgin polyester resin, and 6.5% by mass of silica masterbatch were mixed and melt-kneaded to obtain a biaxially stretched polyester resin film having a thickness of 12 μm.

[0153] The compositions and physical property evaluation results of the biaxially stretched polyester resin films obtained in each Example and Comparative Example are shown in Tables 2 and 3.

[0154] [Table 2]

[0155] [Table 3]

[0156] Examples 1 to 6 are biaxially oriented polyester resin films containing 60 mass% or more of polyester resin A produced under specific conditions, i.e., polyester resin A having a diethylene glycol content of 4.0 mol% or less when the total amount of all glycol components is 100 mol%. Therefore, even though the films were thin, less than 50 μm in thickness, they had excellent flex resistance in a low-temperature environment of -10°C, and the amount of foreign matter in the polyester resin A used was small, making them excellent for continuous production.

[0157] On the other hand, the biaxially stretched polyester resin films of Comparative Examples 1 and 2 had poor flex resistance in low-temperature environments and many pinholes because the diethylene glycol content of the polyester resin used in film formation exceeded the range specified in the present invention. Furthermore, the tensile elongation was low, the amount of foreign matter was increased, breakage problems were easily caused during the stretching process, and long-term continuous productivity was poor.

[0158] The biaxially stretched polyester resin film of Comparative Example 3 had a content of polyester resin A with a diethylene glycol content of 4.0 mol% or less less than 60 mass% when the total amount of all glycol components was 100 mol%, so it had poor bending resistance in low-temperature environments and produced many pinholes.

Claims

1. A polyester resin film containing 60% by mass or more of a polyester resin A having a diethylene glycol content of 4.0 mol% or less when the total amount of all glycol components is 100 mol%, After 200 repeated bending fatigue tests using a Gelbo flex tester in a -10°C atmosphere, the number of pinholes was 10 / 500cm ２ That is: A biaxially oriented polyester resin film characterized by:

2. 2. The biaxially stretched polyester resin film according to claim 1, wherein the biaxially stretched polyester resin film crystallizes at a temperature of 160 to 180°C when, in differential scanning calorimetry (DSC), the film is heated 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.

3. 2. The biaxially oriented polyester resin film according to claim 1, having a haze of 10.0% or less.

4. 2. The biaxially stretched polyester resin film according to claim 1, wherein the carboxyl terminal group concentration is 20 to 60 equivalents / t.

5. 2. The biaxially stretched polyester resin film according to claim 1, wherein the surface crystallinity determined by attenuated total reflectance infrared spectroscopy (ATR-IR) is 1.1 to 1.

4.

6. 2. The biaxially oriented polyester resin film according to claim 1, which has a thickness of 50 μm or less and a tensile elongation of 100% or more in both the MD and TD directions.

7. The biaxially oriented polyester resin film according to claim 1, wherein the b* value is 0 or less.

8. A packaging material comprising the biaxially oriented polyester resin film according to any one of claims 1 to 7.

9. A method for producing a biaxially oriented polyester resin film, comprising: (1) A step of adding bis-2-hydroxyethyl terephthalate to a mixture containing ethylene terephthalate oligomer and ethylene glycol, and carrying out an esterification reaction under heat treatment conditions of 200 to 280°C to obtain a reaction product. (2) A step of adding a polymerization catalyst to the reaction product and subjecting it to a polycondensation reaction at a temperature of 260 to 285°C and a reduced pressure of 1.0 hPa or less to obtain a polyester resin A. (3) a step of producing an unstretched film using a starting material containing the polyester resin A, and then biaxially stretching the unstretched film; The method for producing the biaxially oriented polyester resin film according to claim 1, comprising:

10. A method for producing a biaxially oriented polyester resin film, comprising: (4) A step of adding terephthalic acid to bis-2-hydroxyethyl terephthalate and carrying out an esterification reaction under heat treatment conditions of 200 to 250°C to obtain a reaction product. (5) A step of adding a polymerization catalyst to the reaction product and subjecting it to a polycondensation reaction at a temperature of 260 to 285°C and a reduced pressure of 1.0 hPa or less to obtain a polyester resin A. (6) a step of producing an unstretched film using a starting material containing the polyester resin A, and then biaxially stretching the unstretched film; The method for producing the biaxially oriented polyester resin film according to claim 1, comprising:

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