Biaxially oriented polyester film and its manufacturing method

Abstract

To provide: a biaxially oriented polyester film which has excellent transparency, can be easily subjected to secondary fabrication such as coating, vapor deposition and the like, has excellent characteristics after the secondary fabrication, includes a PET bottle, and is eco-friendly in that it uses polyester resins recycled from the market and society, where the biaxially oriented polyester film contains a little foreign matter and has little variation of physical properties in a longitudinal direction even in a case of a long-sized film roll having a long winding length; and a production method of the same.SOLUTION: There is provided, a biaxially oriented polyester film formed of a polyester resin composition, comprising: polyester resins recycled from the market and society including PET bottles; and particles, where at least one surface of the biaxially oriented film satisfies all of following requirements (1) to (3): (1) the number of fine protrusions having a height of less than 3 nm per an area of 4×10-12 m2 is 250 to 600; (2) the number of fine protrusions having a height of 3 nm or more per an area of 4×10-12 m2 is 300 to 600; and (3) an arithmetic average height Sa is 0.01 μm to 0.025 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polyester film and a method for producing the same. More specifically, the present invention relates to a biaxially oriented polyester film that is suitable for secondary processing such as coating or vapor deposition to further enhance the functionality of the biaxially oriented polyester film, is an environmentally friendly polyester film made by using polyester resin recycled from the market or society, including PET bottles (hereinafter, may be referred to as "polyester resin made from recycled PET bottles"), and has little variation in physical properties in the longitudinal direction even in a long film roll with a long wound length, and a method for producing the same. [Background technology]

[0002] Biaxially oriented polyester films have traditionally been used in a wide range of fields, such as packaging materials and industrial materials, due to their excellent mechanical strength, thermal properties, optical properties, etc. Although biaxially oriented polyester films have excellent oxygen barrier properties, there is an increasing demand for oxygen barrier properties and water vapor barrier properties related to the alteration and deterioration of the contents in packaging applications for general foods, retort foods, pharmaceuticals, etc., which can cause the alteration and deterioration of the contents.

[0003] For this reason, biaxially oriented polyester films used in packaging for general food, retort food, pharmaceuticals, etc., have been designed to further improve adhesion to printing inks and gas barrier properties against oxygen, water vapor, etc. For example, methods for improving the gas barrier properties include laminating a film made of a resin with good gas barrier properties, such as polyvinylidene chloride or a polyethylene vinyl alcohol copolymer, onto a biaxially oriented polyester film, coating the film with a solution of such a resin and laminating a thin film on the film surface, or depositing a metal such as aluminum or a metal oxide such as aluminum oxide onto the film surface to form a thin film.

[0004] In particular, vapor-deposited polyester films with metal oxides on the film surface are often used because they are excellent in heat resistance and transparency in addition to gas barrier properties. However, it has not been easy to industrially and stably obtain a vapor-deposited polyester film having a thin metal oxide film such as silicon oxide or aluminum oxide film on its surface, which has good gas barrier properties.

[0005] Therefore, efforts have been made to improve the gas barrier properties of vapor-deposited polyester films by controlling the surface condition of the biaxially oriented polyester film used as the substrate of the vapor-deposited polyester film, and proposals have been made to specify the center plane surface roughness and number of protrusions of the biaxially oriented polyester film (see, for example, Patent Document 1), and to specify the center line surface roughness of the biaxially oriented polyester film (see, for example, Patent Document 2).

[0006] Furthermore, a biaxially oriented polyester film has been proposed in which the number of fine protrusions above a specific height is controlled (see, for example, Patent Document 3).

[0007] These films all focus solely on improving the gas barrier properties after forming a metal oxide thin film, but they have not been able to sufficiently improve the problems of wrinkling in the film roll or adhesion of films within the film roll when wound into a film roll after film production, i.e., blocking. Moreover, the performance after secondary processing such as coating and vapor deposition is also insufficient.

[0008] Furthermore, in recent years, with the growing demand for a recycling-oriented society, the use of recycled raw materials has also been promoted in the materials field. Used PET beverage bottles are recycled for the aforementioned polyester resin, and this utilization method is attracting attention. It is said that using recycled PET bottle raw materials will lead to a reduction in CO2 emissions, and there is a desire to increase the proportion of recycled PET bottle raw materials used, even if only slightly, from the perspective of the global environment.

[0009] For example, Patent Document 4 describes a biaxially oriented polyethylene terephthalate film made from recycled PET bottle materials, which has a melt resistivity of 1.0 × 10 at a temperature of 285 °C. 8 A biaxially oriented polyester film is disclosed in which the resistivity is within Ω·cm and the sodium and potassium contents contained in the film are greater than 0 ppm and 150 ppm or less. This technology makes it possible to obtain a biaxially oriented polyester film that has excellent thermal stability, little residual components of the cleaning solution used in producing recycled PET bottle raw materials, little foreign matter, and stable resistivity when melted, without compromising the productivity or quality of the film.

[0010] However, there has been no mention of vapor-deposited polyester films with good gas barrier properties and coated on their surface with a thin metal oxide film, such as silicon oxide or aluminum oxide. While silica particles with an average particle size of 2.5 μm are used to improve lubricity, this tends to increase the maximum height Sz, and there is a problem of defects or loss of the coating film or inorganic thin film layer on the surface of the biaxially oriented polyester film after secondary processing, which has not been fully considered. Furthermore, no polyester film has yet been realized that is highly transparent, easy to perform secondary processing such as coating or vapor deposition, has excellent properties after secondary processing, and is environmentally friendly by using polyester resin recycled from the market and society, including PET bottles.

[0011] As a means of obtaining an environmentally friendly polyester film that has excellent transparency, is easy to perform secondary processing such as coating or vapor deposition, and has excellent properties after secondary processing, by using polyester resins recycled from the market or society, including PET bottles, it is expected that this can be obtained by biaxially stretching a polyester resin composition in which a polyester resin containing particles is blended with a polyester resin recycled from the market or society, including PET bottles. Generally, a film is formed by mixing resin chips with a normal specific gravity and resin chips with a high specific gravity containing particles. However, because the specific gravity difference between the resin chips containing particles and the normal resin chips is large, segregation of these raw resin chips easily causes variations in the raw material ratio during the mixing and extrusion processes, resulting in differences in physical properties along the longitudinal direction of the film. As a result, there are cases in which a product with uniform physical properties along the longitudinal direction of a long product roll cannot be obtained. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Publication No. 10-119172 [Patent Document 2] Japanese Patent Application Publication No. 11-010725 [Patent Document 3] Patent No. 4834923 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-65282 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0013] The object of the present invention is to overcome the problems of the prior art and to provide a biaxially oriented polyester film and a method for producing the same that is highly transparent, easy to perform secondary processing such as coating or vapor deposition, has excellent properties after secondary processing, and is environmentally friendly by using polyester resin recycled from the market and society, including PET bottles; more preferably, to provide a biaxially oriented polyester film and a method for producing the same that uses a higher proportion of recycled PET bottle raw materials; even more preferably, to provide a biaxially oriented polyester film and a method for producing the same that contains less foreign matter; and particularly preferably, to provide a biaxially oriented polyester film roll and a method for producing the same that has little variation in physical properties in the longitudinal direction, even in long film rolls with a long wound length. [Means for solving the problem]

[0014] The inventors investigated the causes of the deterioration of properties after secondary processing and found that, because biaxially oriented polyester film has electrical insulation properties, it is prone to static marks, which are areas that become locally charged due to contact with or peeling from conveying rolls during the film manufacturing process or secondary processing process, and static mark discharge marks caused by the discharge of accumulated static electricity, and that it is difficult for the coated dissolved resin or evaporated inorganic oxide molecules to form a regular, uniform, and defect-free thin film on the film surface in these areas.

[0015] As a result of extensive research, the inventors have found that in a biaxially oriented polyester film obtained by biaxially stretching a polyester resin composition containing a polyester resin containing particles and a polyester resin recycled from the market or community, including PET bottles, the angle of repose of the particle-containing polyester resin pellets can be set within a specific range. Furthermore, when mixing the raw resin chips, polyester resin chips recycled from the market or community, including PET bottles, are fed into a hopper from above, and particle-containing polyester resin chips are fed through a pipe (hereinafter sometimes referred to as an inner pipe) in the hopper with an outlet directly above the extruder, and the two chips are mixed and melt-extruded to obtain a uniform film with little variation in physical properties in the longitudinal direction of the film. Furthermore, the inventors have found that even when alkaline cleaning is performed to remove foreign matter when producing recycled raw materials from the market or community, including PET bottles, the cleaning solution components used in the present invention are minimal, and the amount of foreign matter is reduced. Furthermore, the use of recycled polyester resins from the market or community, including PET bottles, improves adhesion between the polyester film and the sealant. Furthermore, the inventors discovered that by setting the number of fine protrusions below a certain height on the film surface on which the coating film or vapor deposition film is formed to a specific number or more, it is possible to suppress the occurrence of the aforementioned strongly charged localized areas known as static marks and discharge marks, thereby improving performance after secondary processing, such as gas barrier properties, and that by setting the number of fine protrusions above a certain height and the shape of the protrusions within a specific range, it is possible to improve the sliding properties between films, leading to the completion of the present invention.

[0016] That is, the present invention comprises the following configurations. 1. A biaxially oriented polyester film made from a polyester resin composition containing particles and polyester resin recycled from PET bottles, at least one side of which satisfies all of the following requirements (1) to (3). (1) Area 4×10 -12 m 2 The number of fine protrusions each having a height of less than 3 nm is 250 or more and 600 or less. (2) Area 4×10 -12 m 2 The number of fine protrusions having a height of 3 nm or more per surface is 300 to 600. (3) The arithmetic mean height Sa is 0.010 μm or more and 0.025 μm or less.

[0017] 2. The biaxially oriented polyester film according to 1., wherein the content of isophthalic acid components relative to the total dicarboxylic acid components in the biaxially oriented polyester film is 0.02 mol % or more and 2.0 mol % or less.

[0018] 3. A biaxially oriented polyester film according to 1. or 2., characterized in that the content of polyester resin recycled from PET bottles in the polyester resin composition constituting the biaxially oriented polyester film is 50% by mass or more and 100% by mass or less.

[0019] 4. 1m of film 2 4. The biaxially oriented polyester film according to any one of 1. to 3., characterized in that the number of defects of 1 mm or more per film is less than 1.0.

[0020] 5. The biaxially oriented polyester film according to any one of 1. to 4., wherein the polyester resin recycled from PET bottles has been subjected to alkali washing at least once.

[0021] 6. A biaxially oriented polyester film according to any one of 1. to 5., wherein the coefficient of dynamic friction of the surface of the biaxially oriented polyester film that satisfies all of the requirements (1) to (3) and the opposite surface thereof is 0.20 or more and 0.60 or less.

[0022] 7. The biaxially oriented polyester film according to any one of 1. to 6., wherein the surface of the biaxially oriented polyester film that satisfies all of the requirements (1) to (3) has a wetting tension of 50 mN / m or more.

[0023] 8. The biaxially oriented polyester film according to any one of 1. to 7., wherein the biaxially oriented polyester film has an external haze of 1.8% or less and an internal haze of 2.0% or less.

[0024] 9. A film roll obtained by winding up the biaxially oriented polyester film according to any one of 1. to 8., wherein the area of ​​the sample taken every 1000 m from the surface layer of the film roll to the core in the longitudinal direction of the film is 4 × 10 -12 m 2 The number of microprotrusions less than 3 nm in height per unit area is 4 × 10 -12 m 2 Variation in the number of micro-protrusions with a height of 3 nm or more per and (b) a thickness of the biaxially oriented polyester film roll that is 40% or less. (The variation is expressed by the following formula [1], where the maximum value is Xmax, the minimum value is Xmin, and the average value is Xave. Variation (%) = 100 x (Xmax - Xmin) / Xave [1]

[0025] 10. The biaxially oriented polyester film roll according to 9., characterized in that the variation in arithmetic mean height Sa when samples are taken every 1000 m in the longitudinal direction of the film from the surface layer of the film roll to the core is 40% or less. (The variation is expressed by the following formula [2], where the maximum value of the arithmetic mean height Sa is Xmax, the minimum value is Xmin, and the average value is Xave. Variation (%) = 100 x (Xmax - Xmin) / Xave [2]

[0026] 11. A method for producing a biaxially oriented polyester film according to any one of 1. to 8., comprising a melt-extrusion step of a polyester raw material resin and a biaxial stretching step, wherein in the melt-extrusion step of the polyester raw material resin, raw material resin chips of the polyester resin recycled from PET bottles are supplied to a hopper from above, and raw material resin chips of a polyester resin composition containing the particles having an angle of repose of 30 degrees or more and 40 degrees or less are supplied through a pipe in the hopper having an outlet directly above the extruder, and the two chips are mixed and melt-extruded.

[0027] 12. A method for producing a biaxially oriented polyester film roll according to either 9. or 10., comprising the steps of melt-extruding a polyester raw material resin, biaxially stretching it, and winding up the biaxially stretched film into a roll, wherein the melt-extruding step of the polyester raw material resin comprises supplying raw material resin chips of the polyester resin recycled from PET bottles to a hopper from above, and supplying raw material resin chips of a polyester resin composition containing the particles, the particles having an angle of repose of 30 degrees or more and 40 degrees or less, through a pipe in the hopper having an outlet directly above the extruder, mixing the two chips, and melt-extruding the resulting mixture. [Effects of the Invention]

[0028] The present invention provides a biaxially oriented polyester film and a method for producing the same, which has excellent transparency, is less likely to cause wrinkles in the film roll when wound into a film roll after film production, is easy to perform secondary processing such as coating or vapor deposition due to little adhesion between films in the film roll (the so-called blocking phenomenon), has excellent performance after secondary processing, and is environmentally friendly because it uses polyester resin recycled from the market and society, including PET bottles, more preferably a polyester film with an even higher proportion of recycled PET bottle raw materials, even more preferably has little foreign matter, and particularly preferably has little variation in physical properties in the longitudinal direction even in long film rolls with long wound lengths.

[0029] In particular, in recent years, in order to improve the production efficiency of biaxially oriented polyester films, efforts have been made to increase the width and length of the biaxially oriented polyester film roll (hereinafter referred to as the master roll) that is first wound up after the stretching process.However, even with such large film rolls, it is possible to obtain biaxially oriented polyester films that have little wrinkling and blocking, are easy to process in secondary processing, and have satisfactory performance after secondary processing, such as the gas barrier properties of vapor-deposited films. The same applies to film rolls that are made by slitting the master roll into smaller pieces. [Brief explanation of the drawings]

[0030] [Figure 1] A photograph of the film surface in a state where the strongly charged areas on the surface of the film unwound from the film roll are visualized using charge distribution assessment toner, and static marks are observed. [Figure 2] This is a photograph of the film surface after unwinding from a film roll, where discharge marks are visible using charge distribution assessment toner. Static mark discharge marks can be observed. [Figure 3] FIG. 1 is a diagram showing the arrangement of a biaxially oriented polyester film, a film roll, an anti-static brush, and a meandering prevention device during unwinding. [Figure 4]1 is a schematic diagram illustrating an example of a method for mixing resin chips to produce the biaxially oriented polyester film of the present invention. FIG. [Figure 5] FIG. 5 is a partially enlarged view of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be described in detail below. [Polyester resin made from recycled PET bottles] The biaxially oriented polyester film of the present invention preferably uses polyester resin recycled from the market or society, including the following PET bottles. By using polyester resin recycled from the market or society, including PET bottles, the proportion of recycled materials in the film can be increased, making it possible to obtain an environmentally friendly film.

[0032] The polyester resin recycled from the market or society, including PET bottles, used in the biaxially oriented polyester film of the present invention is mainly recycled containers mainly made of polyethylene terephthalate. For example, recycled beverage containers for tea drinks, soft drinks, etc. are preferably used. They may be appropriately oriented, and colorless ones are preferred, but they may also contain a small amount of coloring components.

[0033] Recycled raw materials from the market or society, including PET bottles, are preferably polyesters manufactured and molded by conventional polymerization and solid-state polymerization methods, preferably composed primarily of polyethylene terephthalate, and may contain other polyester components or copolymer components. They may contain metal compounds such as antimony, germanium, and titanium as catalysts, and phosphorus compounds as stabilizers. Polyesters for PET bottles typically contain germanium as a catalyst, and when recycled PET bottle raw materials are used to make films, the film will contain 1 ppm or more of germanium. However, since this is merely the catalyst content, it is usually no more than 100 ppm, and usually no more than 50 ppm.

[0034] Collected used recycled PET bottles are sorted to prevent contamination with other materials and waste, and after removing labels and other debris, they are crushed into flakes. These flakes often contain foreign matter. Consumers may also fill used PET bottles with chemicals, such as pharmaceuticals and solvents. Examples include dishwashing detergents, insecticides, herbicides, pesticides, and various oils. Because conventional cleaning cannot adequately remove chemicals adsorbed to the surface of PET bottles, alkaline cleaning is preferred. The alkali metal hydroxide solution used in this cleaning process is either sodium hydroxide or potassium hydroxide. In such cleaning processes, a preliminary cleaning may be performed before alkaline cleaning. If alkaline washing is not performed, foreign matter will remain in the raw resin material, which can contaminate the film and cause breakage during film production, reducing productivity. Furthermore, the foreign matter will remain in the film, affecting its appearance and causing printing defects in the subsequent printing process.

[0035] The concentration of the aqueous solution of alkali metal hydroxide used in the washing step is usually in the range of 1 to 10% by weight, although this depends on the temperature, time, and stirring conditions. The washing time is in the range of 10 to 100 minutes, and it is preferable to carry out the washing with stirring to enhance the effect.

[0036] It is preferable to perform rinsing and drying after alkaline cleaning. The alkaline washing step may be repeated several times. If the components of the aqueous solution of alkali metal hydroxide used in washing remain in the flakes, the physical properties of the final film may be affected by the subsequent melt extrusion step in the pelletizing step or the melt extrusion step in the film formation step.

[0037] The sodium and potassium concentrations in the film finally obtained using polyester resins recycled from the market or society, including these PET bottles, are preferably greater than 0 ppm and less than 150 ppm, more preferably 3 to 120 ppm, and even more preferably 5 to 80 ppm. A sodium or potassium concentration greater than 150 ppm in the film is undesirable because it reduces the film's heat resistance and thermal stability and causes coloration. Furthermore, a complete absence of these components is undesirable because it reduces the effect of suppressing the production of diethylene glycol. Furthermore, polyester resins recycled from the market or society, including PET bottles, may contain small amounts of these components, making it difficult to completely eliminate them.

[0038] During this washing process, the PET bottle flakes are partially hydrolyzed by the aqueous solution of alkali metal hydroxide. Furthermore, the degree of polymerization of the resin decreases due to the heat generated during the molding of the PET bottles. Furthermore, after the collected PET bottles are crushed for reuse, they are melted again and pelletized, which reduces the degree of polymerization due to the effects of heat and moisture. While they can be reused as is, depending on their intended use, a decrease in the degree of polymerization can lead to poor moldability, strength, transparency, heat resistance, and other properties, making them unusable as is.

[0039] In such cases, in order to restore the reduced degree of polymerization, it is preferable to crush and wash the PET bottles into flakes or melt the flakes and pelletize them, and then subject them to solid-state polymerization.

[0040] In the solid-state polymerization step, washed flakes or flakes melt-extruded and pelletized can be subjected to continuous solid-state polymerization in an inert gas such as nitrogen gas or a rare gas at 180 to 245°C, preferably 200 to 240°C.

[0041] It is desirable to adjust the flake or pellet conditions so that the polyester resin ultimately has an intrinsic viscosity of 0.55 to 0.90 dL / g, preferably 0.60 to 0.85 dL / g, as a polyester resin recycled from the market or society, including PET bottles.

[0042] The process for pelletizing the flakes will be described below: The flakes are melted, extruded, cooled, and pelletized using an extruder equipped with a degassing means and a filtering means.

[0043] The melting step in the extruder is usually carried out by melt-kneading at 260 to 300°C, preferably 265 to 295°C. The flakes obtained by crushing PET bottles before being added must be sufficiently dried, and drying is preferably carried out under conditions where the moisture content is 5 to 200 ppm, preferably 10 to 100 ppm, and even more preferably 15 to 50 ppm. If the flakes contain a large amount of moisture, a hydrolysis reaction will proceed during the melting step, reducing the intrinsic viscosity of the resulting polyester resin. As a degassing means, it is preferable to have at least one vacuum vent in the resin melting zone.

[0044] The extruder preferably has a filter as a filtering means capable of filtering out solid foreign matter having a particle size of 25 μm or more, preferably 15 μm or more, more preferably 10 μm or more, from the molten resin.

[0045] The molten resin that has passed through the filter passes through a die and is cooled in water, after which it is cut into pellets of the desired shape and granulated. [Polyester resin composition] The biaxially oriented polyester film of the present invention is made of a polyester resin composition containing the following polyester resin as a main component. The polyester resin constituting the biaxially oriented polyester film of the present invention is a polymer synthesized from a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative. Examples include polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, with polyethylene terephthalate being preferred from the viewpoints of mechanical properties, heat resistance, cost, etc. The term "main component" as used herein means that the content in the polyester resin composition is 80% by weight or more, preferably 90% by weight or more, more preferably 95% by weight or more, and most preferably 98% by weight or more.

[0046] These polyester resins may also be copolymerized with other components as long as the objectives of the present invention are not impaired. Specifically, copolymerization components include dicarboxylic acid components such as isophthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, adipic acid, sebacic acid, and their ester-forming derivatives. Diol components include diethylene glycol, hexamethylene glycol, neopentyl glycol, and cyclohexanedimethanol. Polyoxyalkylene glycols such as polyethylene glycol and polypropylene glycol are also included. The copolymerization amount is preferably 10 mol % or less, more preferably 5 mol % or less, and most preferably 3 mol % or less, per constituent repeating unit.

[0047] Examples of methods for producing the polyester resin that constitutes the biaxially oriented polyester film of the present invention include a method in which the above-mentioned dicarboxylic acid or its ester-forming derivative and the diol or its ester-forming derivative are used as main starting materials, and the polyester resin is then subjected to an esterification or transesterification reaction according to a conventional method, followed by a polycondensation reaction at high temperature and reduced pressure.

[0048] The intrinsic viscosity of the polyester resin constituting the biaxially oriented polyester film of the present invention is preferably in the range of 0.50 to 0.9 dl / g, more preferably 0.55 to 0.8 dl / g, from the viewpoints of film formability and recollection.

[0049] The polyester resin composition of the present invention preferably contains at least one type of particle selected from the group consisting of inorganic particles, organic particles, and particles consisting of a mixture thereof, so that at least one surface of the biaxially oriented polyester film of the present invention satisfies all of the following requirements (1) to (3). (1) Area 4×10 -12 m 2 The number of microscopic protrusions each having a height of less than 3 nm is 250 or more. (2) Area 4×10 -12 m 2 The number of micro-protrusions with a height of 3 nm or more per unit is 300 to 600. The following is the result. (3) The arithmetic mean height Sa is 0.010 μm or more and 0.025 μm or less.

[0050] Examples of inorganic particles that can be used include particles made of silica (silicon oxide), alumina (aluminum oxide), titanium dioxide, calcium carbonate, kaolin, and barium sulfate. Examples of organic particles include acrylic resin particles, melamine resin particles, silicone resin particles, and particles made of cross-linked polystyrene. Among these, particles made of silica (silicon oxide), calcium carbonate, or alumina (aluminum oxide), or particles made of polymethacrylate, polymethyl acrylate, or derivatives thereof are preferred, particles made of silica (silicon oxide) or calcium carbonate are more preferred, and inorganic particles made of silica (silicon oxide) are particularly preferred.

[0051] The particle size distribution of the particles used in the present invention is preferably monodisperse. The shape of the inorganic fine particles is not particularly limited, but the closer to a spherical shape, the greater the number of fine protrusions with a height of 3 nm or more, and the greater the number of fine protrusions with a height of less than 3 nm without significantly changing the arithmetic mean height Sa.

[0052] The weight average particle size of the particles in the present invention, as measured with a Coulter counter, is preferably in the range of 0.8 to 1.8 μm. When the weight average particle size of the particles is 0.8 μm or more, the number of fine protrusions less than 3 nm in height and the arithmetic mean height Sa can be easily made equal to or greater than the lower limit values ​​of (1) and (3) above, respectively. When the weight average particle diameter of the particles is 1.8 μm or less, the arithmetic mean height Sa is easily kept below the upper limit value of (3) above, and it is also suitable for keeping the number of fine protrusions less than 3 nm in height above the lower limit value of (1) above.

[0053] The lower limit of the particle content in the particle-containing polyester resin composition (masterbatch) of the present invention is 1000 ppm by weight, more preferably 1300 ppm by weight, and particularly preferably 1400 ppm by weight. When the particle content is 1000 ppm by weight or more, the number of fine protrusions less than 3 nm in height and the number of fine protrusions 3 nm or more in height are likely to be equal to or greater than the lower limit values ​​of (1) and (2) above, respectively. The upper limit of the particle content is preferably 3000 ppm by weight, more preferably 2500 ppm by weight, even more preferably 2200 ppm by weight, and particularly preferably 1800 ppm by weight. The concentration of inorganic particles in the masterbatch is preferably 7,000 to 400,000 ppm, more preferably 8,000 to 350,000 ppm, and particularly preferably 9,000 to 300,000 ppm. If the concentration of inorganic particles in the masterbatch is less than 7,000 ppm, the proportion of masterbatch containing inorganic particles increases, reducing the proportion of polyester resin recycled from the market and society, including PET bottles, the main raw material. This makes it difficult to effectively achieve the resin's low cost and environmentally friendly properties. If the concentration of inorganic particles in the masterbatch is greater than 400,000 ppm, raw material segregation will cause significant fluctuations in the raw material ratio in the longitudinal direction, resulting in significant variation in the longitudinal length of the resulting film. The angle of repose of the master pellets (master batch) is preferably 25 to 40 degrees, and more preferably 30 to 40 degrees. If the angle of repose is greater than 40 degrees, segregation is likely to occur after mixing with polyester resin recycled from the market or society, including PET bottles, before being fed to the extruder, resulting in large longitudinal variations in the resulting film. The angle of repose of the master pellets can be adjusted by changing the shape and size of the pellets. The more spherical the pellets are, the smaller the angle of repose, and the larger the angle of repose if they are elongated. Furthermore, the smaller the pellet size, the smaller the angle of repose.

[0054] As a method for blending the particles into the polyester resin composition of the present invention, for example, the particles can be added at any stage of the esterification stage for producing the polyester resin, after the completion of the transesterification reaction, or before the start of the polycondensation reaction. However, it is preferable to add the particles as a slurry dispersed in ethylene glycol or the like and then proceed with the polycondensation reaction. Alternatively, a method in which a slurry of particles dispersed in ethylene glycol or water is blended with a polyester-based resin raw material using a vented kneading extruder, or a method in which dried particles are blended with a polyester-based resin raw material using a kneading extruder, is also preferred.

[0055] In the process of mixing the particles with the polyester-based resin raw material, it is preferable to minimize particle agglomerations in order to stably obtain the desired surface condition, but the influence of this can be reduced by adjusting the conditions of the film-forming process of the biaxially oriented polyester film after the mixing process.

[0056] Furthermore, the polyester resin composition of the present invention may contain small amounts of other polymers, antioxidants, heat stabilizers, antistatic agents, ultraviolet absorbers, plasticizers, pigments, or other additives, as long as the object of the present invention is not impaired.

[0057] The polyester film obtained as described above preferably contains an isophthalic acid component in an amount of 0.02 mol% to 2.0 mol% based on 100 mol% of all dicarboxylic acid components in the biaxially oriented polyester film. The crystallinity of polyesters generally used in PET bottles is controlled to improve the bottle appearance, and as a result, polyesters containing 10 mol% or less of isophthalic acid components are sometimes used. Therefore, the polyester film of the present invention contains a certain amount of material containing an isophthalic acid component, and by containing a specific amount of isophthalic acid component in the film, the present invention can further improve the adhesive strength when adhered to a sealant. The reason why the inclusion of an isophthalic acid component in the film improves adhesion to the sealant is not clear, but it is thought that this is because isophthalic acid-ethylene glycol units are less likely to crystallize than terephthalic acid-ethylene glycol units, leaving a large amount of amorphous components remaining in the film. As a result, not only is the film more susceptible to modification by surface treatments such as corona treatment, but the very surface of the film is more susceptible to dissolution in solvents, increasing its affinity with the adhesive used to bond it to the sealant.

[0058] The lower limit of the amount of isophthalic acid component relative to the total dicarboxylic acid components constituting the polyester resin contained in the film is preferably 0.02 mol%, more preferably 0.05 mol%, even more preferably 0.1 mol%, and particularly preferably 0.15 mol%. As mentioned above, polyester resins recycled from the market or society, including PET bottles, contain a large amount of isophthalic acid component. Therefore, if the isophthalic acid component constituting the polyester resin in the film is less than 0.02 mol%, it becomes difficult to produce a polyester film with a high proportion of recycled resin, which is not desirable. The upper limit of the amount of isophthalic acid component relative to the total dicarboxylic acid components constituting the polyester resin contained in the film is preferably 2 mol%, more preferably 1.5 mol%, and even more preferably 1.0 mol%. If it exceeds 2.0 mol%, the crystallinity decreases, which may reduce the mechanical strength of the film, which is not desirable. Furthermore, by keeping the content of isophthalic acid component within the above range, it is possible to easily produce a film with excellent lamination strength, shrinkage, and thickness uniformity, which is preferable.

[0059] The upper limit of the intrinsic viscosity of polyester resins recycled from the market or society, including PET bottles, is preferably 0.9 dL / g, more preferably 0.8 dL / g, even more preferably 0.75 dL / g, and particularly preferably 0.69 dL / g. If the intrinsic viscosity exceeds 0.9 dL / g, the resin becomes difficult to extrude from the extruder, which may reduce productivity, and is therefore not preferred.

[0060] In the polyester film of the present invention, the lower limit of the content of polyester resin recycled from the market or society, including PET bottles, relative to the total weight is preferably 50% by weight, more preferably 70% by weight, even more preferably 90% by weight, and particularly preferably 100% by weight. A content of less than 50% by weight results in a poor utilization of recycled resin, which is not desirable in terms of contributing to environmental protection. Here, a recycled polyester resin content of 100% by weight includes a case where particles are contained at 0.5% by weight or less (i.e., a case where the recycled polyester resin content is 99.5% by weight or more). Furthermore, recycled polyester resins, including PET bottles, can also be used as masterbatches (high-concentration resins) when adding lubricants or additives such as inorganic particles to improve film performance.

[0061] [Manufacturing method of biaxially oriented polyester film] The biaxially oriented polyester film of the present invention can be obtained by supplying and mixing polyester resin chips recycled from the market or society, including, for example, the above-mentioned PET bottles, and chips of a polyester resin composition mainly composed of polyester resin into an extruder equipped with a hopper, melt-extruding the mixture through the extruder to form an unstretched sheet, and then stretching the unstretched sheet. Suitable examples are given below, but the present invention is not limited to these.

[0062] The film of the present invention may have a single layer structure of at least one layer, or a laminate structure of two or more layers. It may have two, three, four, or five layers. In the case of a two-layer structure, the structure is laminate part / base layer part, and in the case of a three-layer structure, the structure is laminate part (A) / base layer part / laminate part (B). In the case of a three-layer structure, the laminate part (A) and the laminate part (B) may have the same composition and structure, or may have different compositions, for example, a structure of particle-free layer / base layer / particle-containing layer. Furthermore, they may have substantially the same thickness or different thicknesses. It is preferable to design the laminate part (A) and the laminate part (B) to have the same composition, as this facilitates production.

[0063] Next, it is preferable that at least one of the layers constituting the film of the present invention is biaxially oriented. Of the laminated structures of two or more layers, it is particularly preferable that all layers are biaxially oriented. If all layers are non-oriented or uniaxially oriented, it is difficult to use the film for a label wrapped around a body, and this is not preferable.

[0064] When mixing the raw material resin chips, it is preferable to supply polyester resin chips recycled from the market or society, including PET bottles, to the hopper from above, and supply chips of the polyester resin composition through a pipe (hereinafter sometimes referred to as the "inner pipe") in the hopper with an outlet directly above the extruder, and mix the two chips and melt extrude them. If polyester resin chips recycled from the market or society, including PET bottles, and chips of the polyester resin composition are mixed and placed in the hopper above the extruder, resin chips with different specific gravities and chip shapes may cause raw material segregation in the hopper, especially where the inner wall of the hopper is not vertical (slanted part), raw material segregation is likely to occur. However, if the polyester resin composition is directly supplied to the extruder in the hopper through the inner pipe, raw material segregation can be reduced even if the specific gravities and chip shapes are different, and polyester film can be stably industrially produced.

[0065] An example of a specific mixing procedure is shown in Figure 4. Figure 4 is a schematic diagram showing an example of the relationship between an extruder 2 equipped with a hopper 1 and an inner pipe 3. As shown in Figure 4, resins other than polyester resin chips recycled from the market or society, including PET bottles, which are the main raw material for the polyester film of the present invention, are supplied through the inner pipe 3, and chips of the polyester resin composition are supplied from the top of the hopper 1. Furthermore, because the outlet 4 of the inner pipe 3 is located directly above the extruder (more precisely, directly above the resin supply port 5 of the extruder 2), the mixing ratio of the raw materials can be maintained constant.

[0066] When melt-extruding polyester resins and polyester resin compositions recycled from the market or society, including PET bottles, it is preferable to dry them using a dryer such as a hopper dryer or paddle dryer, or a vacuum dryer. After drying the polyester resins and polyester resin compositions recycled from the market or society, including PET bottles, they are melted and extruded into a film using an extruder at a temperature above the melting point of the polyester resin, i.e., 200 to 300°C. Alternatively, the polyester resin, particles, and optional additives may be fed using separate extruders, merged, melted, and extruded into a sheet. When extruding the molten resin composition, any existing method such as a T-die method or a tubular method can be used.

[0067] The extruded molten polyester resin can then be rapidly cooled to obtain an unstretched sheet. A suitable method for rapidly cooling the molten polyester resin is to cast the molten polyester resin onto a rotating drum from a die and rapidly cool and solidify it to obtain a substantially unoriented resin sheet. The temperature of the rotating drum is preferably set to 40°C or lower.

[0068] Furthermore, the biaxially oriented polyester film of the present invention can be obtained by combining the obtained unstretched sheet with the following processes such as longitudinal and transverse stretching, heat setting, and heat relaxation. The details are explained below: The longitudinal direction means the direction in which the unstretched sheet travels, and the width direction means the direction perpendicular to the longitudinal direction.

[0069] The stretching method can be simultaneous biaxial stretching, in which stretching in the longitudinal direction and the width direction is performed simultaneously, or sequential biaxial stretching, in which stretching in either the longitudinal direction or the width direction is performed first. However, sequential biaxial stretching is most preferred from the viewpoints of high productivity due to a fast film-forming speed and excellent thickness uniformity of the final biaxially oriented polyester film. The film-forming speed referred to here means the running speed (m / min) of the biaxially oriented polyester film when it is taken up around a master roll after the stretching step.

[0070] The temperature during stretching of the unstretched sheet in the longitudinal direction is preferably in the range of (Tg+15) to (Tg+55)°C, using the glass transition temperature (hereinafter referred to as Tg) of the polyester resin as an index, and the stretching ratio is preferably in the range of 4.2 to 4.7 times. When the stretching temperature is (Tg+55)°C or lower and 4.2 times or higher, the number of fine protrusions less than 3 nm in height is likely to be equal to or greater than the lower limit of (1) above, the molecular orientation in the longitudinal direction and the width direction is well balanced, and the difference in physical properties between the longitudinal direction and the width direction is small, which is preferable.Furthermore, the flatness of the resulting biaxially stretched polyester film is also good, which is preferable. On the other hand, when the longitudinal stretching temperature is (Tg + 15)°C or higher and the stretching ratio is 4.7 times or less, the arithmetic mean height Sa is easily controlled to be equal to or less than the upper limit of the above (3). This is preferable because the tensile stress (bowing phenomenon) generated in the direction opposite to the running direction of the film during the thermal relaxation step does not become too large.

[0071] Furthermore, in the longitudinal stretching, a method of stretching in two, three, or four or more stages between multiple rolls, rather than in a single stage, is preferred because it allows the stretching ratio in the longitudinal direction to be increased without increasing the stretching speed too much, thereby further reducing the difference in physical properties in the width direction of the film. Two-stage or three-stage stretching is preferred from the standpoints of effectiveness, equipment, and cost.

[0072] The film obtained by stretching the unstretched sheet in the longitudinal direction may be subjected to a surface treatment such as corona treatment or plasma treatment as necessary, and then a resin dispersion or resin solution may be applied to at least one surface of the film to impart functions such as easy slippage, easy adhesion, and antistatic properties.

[0073] When the film obtained by stretching an unstretched sheet in the longitudinal direction is stretched in the width direction, the film is introduced into a tenter device, both ends of the film obtained by stretching the unstretched sheet in the longitudinal direction are held with clips, the film is heated to a predetermined temperature with hot air, and the distance between the clips is increased while the film is transported in the longitudinal direction, thereby stretching the film in the width direction. If the temperature during width direction stretching is Tg+5° C. or higher, the arithmetic mean height Sa is easily adjusted to the upper limit value of the above (3), and breakage during stretching is less likely to occur, which is preferable. Furthermore, when the stretching temperature is Tg+40°C or lower, it is easy to make the number of fine protrusions less than 3 nm in height equal to or greater than the lower limit of (1) above, and uniform stretching in the width direction is facilitated, and thickness unevenness in the width direction is less likely to increase, which is preferable because it reduces the variation in winding hardness of the film roll surface in the width direction. It is more preferably Tg+8°C or higher and Tg+37°C or lower, and even more preferably Tg+11°C or higher and Tg+34°C or lower. The stretching ratio in the width direction of the film obtained by stretching the unstretched sheet in the machine direction is preferably 4.0 times or more and 6 times or less. When the stretching ratio in the width direction is 4.0 times or more, the number of fine protrusions less than 3 nm in height is easily made equal to or greater than the lower limit of (1) above, a high yield is easily obtained in terms of material balance, the mechanical strength is not reduced, thickness unevenness in the width direction is not likely to increase, and variations in winding hardness in the width direction of the film roll are not likely to occur, which is preferable. The stretching ratio in the width direction is more preferably 4.1 times or more, and even more preferably 4.2 times or more. Furthermore, when the stretching ratio in the width direction is 6 times or less, the arithmetic mean height Sa can be easily controlled to the upper limit value of the above (3) or less, and the film is less likely to break during stretching.

[0074] The heat setting step is carried out following the widthwise stretching step, and the heat setting temperature of the film obtained by stretching the unstretched sheet in the longitudinal direction and then stretching it in the widthwise direction is preferably 240°C or higher and 250°C or lower. When the heat setting temperature is 240°C or higher, the number of fine protrusions less than 3 nm in height is easily made equal to or greater than the lower limit of (1) above, and the thermal shrinkage rate in both the longitudinal and transverse directions is not too high, which is preferable because it improves the thermal dimensional stability during vapor deposition processing. On the other hand, if the heat setting temperature is 250° C. or less, bowing is less likely to increase, which is preferable.

[0075] A heat relaxation treatment step is then carried out, which may be carried out separately from the heat setting step after the heat setting step, or may be carried out simultaneously with the heat setting step. The relaxation rate in the film width direction in the heat relaxation treatment step is preferably 4% or more and 8% or less. When the relaxation rate is 4% or more, the heat shrinkage rate in the width direction of the resulting biaxially oriented polyester film does not become too high, and dimensional stability during vapor deposition processing is improved, which is preferable. On the other hand, if the relaxation rate is 8% or less, the tensile stress (bowing phenomenon) generated in the direction opposite to the running direction of the film at the center of the film width direction does not become too large, and the film thickness fluctuation rate in the width direction does not become large, which is preferable.

[0076] In the heat relaxation treatment step, the film obtained by stretching an unstretched sheet in the longitudinal direction is stretched in the width direction, and during the time until the film is stretched in the width direction by heat relaxation, the restraining force in the width direction decreases and the film slackens under its own weight. In addition, the film may expand due to the accompanying air currents of hot air blown out from nozzles installed above and below the film. As a result, the film is in a state in which it is very susceptible to vertical fluctuations, and the amount of change in the orientation angle and the difference in oblique heat shrinkage rate of the resulting biaxially stretched polyester film is likely to vary greatly. To alleviate this, for example, the speed of the hot air blown from the upper and lower nozzles can be adjusted to keep the film parallel.

[0077] The biaxially oriented polyester film for vapor deposition of the present invention may be subjected to corona discharge treatment, glow discharge treatment, flame treatment, or surface roughening treatment, and may also be subjected to known anchor coating treatment, printing, decoration, etc., as long as the object of the present invention is not impaired.

[0078] The wide biaxially oriented polyester film stretched by the above method is wound on a winder to produce a master roll. The width of the master roll is preferably 5,000 mm or more and 10,000 mm or less. A roll width of 5,000 mm or more is preferred because it reduces the cost per film area in subsequent stitching, vapor deposition processing, and printing processing. The master roll preferably has a winding length of 10,000 m or more and 100,000 m or less. A winding length of 5,000 m or more is preferred because it reduces the cost per film area in the subsequent slitting process, vapor deposition process, and printing process. The winding width of the film roll slit from the master roll is preferably 400 mm or more and 3000 mm or less. A winding width of 400 mm or more reduces the need for frequent film roll replacement during the printing process, which is preferable from the standpoint of cost. A longer winding width is preferable, but a width of 3000 mm or less is preferable because the roll width does not become too large and the roll weight does not become too heavy, preventing deterioration in handleability. The film roll length is preferably 2000 m or more and 65000 m or less. A film roll length of 2000 m or more is preferable from the standpoint of cost, as it reduces the need to frequently replace the film roll during the printing process. While a longer film roll length is preferable, a film roll length of 65000 m or less is preferable because it prevents the roll diameter from becoming too large and the roll weight from becoming too heavy, preventing deterioration in handleability.

[0079] [Characteristics of biaxially oriented polyester film] At least one side of the biaxially oriented polyester film made of a polyester resin composition containing polyester resin and particles recycled from the market or society, including the PET bottle of the present invention, preferably satisfies all of the following (1) to (3). Each of these will be described in detail below. (1) Area 4×10 -12 m 2 The number of fine protrusions each having a height of less than 3 nm is 250 or more and 600 or less. (2) Area 4×10 -12 m 2The number of fine protrusions having a height of 3 nm or more per surface is 300 to 600. (3) The arithmetic mean height Sa is 0.010 μm or more and 0.025 μm or less.

[0080] (1) Area 4×10 -12 m 2 Number of microprotrusions less than 3 nm per Because biaxially oriented polyester film has electrical insulation properties, static marks are easily generated due to contact with transport rolls or peeling during the film manufacturing and processing processes, and static marks are generated due to discharge of accumulated static electricity. -12 m 2 When the number of fine protrusions less than 3 nm in height per unit area is 250 or more, static marks and static mark discharge scars are reduced, coating spots are less likely to occur after the coating layer is formed, the gas barrier performance of the formed inorganic thin film layer is improved, and performance after secondary processing is likely to be improved. The reason is that the area is 4 x 10 -12 m 2 If the number of fine protrusions less than 3 nm in height per film is 250 or more, the film and metal roll come into contact with each other with great force during the process of transporting and winding the produced film, and even if the tall protrusions on the film surface are pressed into the film, the area of ​​contact between the film surface and the metal roll becomes extremely small, thereby reducing the amount of charge due to friction and resulting in fewer static marks and static mark discharge scars. It is more preferably 300 or more, more preferably 400 or more, and particularly preferably 500 or more. This tendency also applies to friction caused by contact between films. The number of fine protrusions less than 3 nm in height does not improve the slipperiness of the film or reduce its blocking properties, and is characterized by being less likely to adversely affect the gas barrier properties of the inorganic thin film layer formed on the film surface. Furthermore, even if the number of minute protrusions less than 3 nm in height is in the range of 600 or less, the number of static marks and static mark discharge traces is sufficiently small.

[0081] (2) Area 4×10 -12 m 2 Number of micro-protrusions with a height of 3 nm or more per When the number of microprotrusions having a height of 3 nm or more is 300 or more, the coefficient of dynamic friction between films does not become too small, and since the biaxially oriented polyester film has electrical insulation, it is more difficult to generate static marks, which are areas that have become partially charged due to contact with or peeling from a transport roll during the film manufacturing process or processing process, or static mark discharge marks caused by the discharge of accumulated static electricity, etc. It is even more preferable that the number is 400 or more, and even more preferably 500 or more. If the number of fine protrusions having a height of 3 nm or more is 600 or less, the formed inorganic thin film layer will have sufficient gas barrier properties.

[0082] (3) Arithmetic mean height Sa The arithmetic mean height Sa of at least one surface of the biaxially oriented polyester film of the present invention is preferably 0.010 to 0.025 μm. An arithmetic mean height Sa of 0.010 μm or more is preferable because adhesion (blocking phenomenon) between films and between films in the film roll at recesses between protrusions formed on the film surface is unlikely to occur, allowing for smooth secondary processing of the film, and is even more preferable at 0.013 μm or more, and even more preferable at 0.015 μm or more. An arithmetic mean height Sa of 0.025 μm or less is preferred because the haze, especially the external haze, of the biaxially oriented polyester film is reduced and transparency is excellent, more preferably 0.023 μm or less, even more preferably 0.020 μm or less, and particularly preferably 0.017 μm or less. The arithmetic mean height Sa of the other film surface is also preferably in the same range.

[0083] (dynamic friction coefficient) The coefficient of dynamic friction between one surface of the biaxially oriented polyester film of the present invention and the opposite surface thereof is preferably 0.20 or more and 0.60 or less. If the ratio is 0.20 or more, the films do not slide too much against each other, and wrinkles are less likely to occur in the film roll when the film roll is wound by a winder device during film production or slitting, and secondary processability is less likely to decrease. The ratio is more preferably 0.30 or more, and most preferably 0.45 or more. Furthermore, if the ratio is 0.60 or less, the films will slide against each other, so that when the film roll is wound up by a winder device during film production or slitting, the film roll is less likely to slip, and secondary processability is less likely to deteriorate.The ratio is more preferably 0.50 or less, and most preferably 0.44 or less.

[0084] (coefficient of static friction) The static friction coefficient between one surface of the biaxially oriented polyester film of the present invention and the opposite surface thereof is preferably 0.20 or more and 0.60 or less. If the ratio is 0.20 or more, the films do not slide too much against each other, and wrinkles are less likely to occur in the film roll when the film roll is wound by a winder device during film production or slitting, and secondary processability is less likely to decrease. The ratio is more preferably 0.30 or more, and most preferably 0.45 or more. Furthermore, if the film thickness is 0.60 or less, the films slide against each other, so that when the film roll is wound by a winder device during film production or slitting, the film roll is less likely to slip, and secondary processability is less likely to deteriorate. It is more preferably 0.50 or less, and most preferably 0.44 or less.

[0085] (Maximum height Sz) The maximum height Sz of the surface of the biaxially oriented polyester film of the present invention that satisfies all of the above (1) to (3) is preferably 0.5 μm or more and 2.0 μm or less. If the maximum height Sz is 0.5 μm or more, the amount of air trapped between the contacting films when winding the master roll or when slitting the master roll and winding the biaxially oriented polyester film onto the core is reduced, resulting in less stretching and deformation of the film. Furthermore, the film in the roll is less likely to sag after the air in the film roll is released. If the weight average particle size of the particles contained in the polyester resin is 0.8 μm or more, it is easy to achieve a maximum height Sz of 0.5 μm or more. When the maximum height Sz is 2.0 μm or less, there are fewer defects or missing parts in the coating film or inorganic thin film layer on the surface of the biaxially oriented polyester film after secondary processing. When the temperature during longitudinal stretching is Tg+40°C or less or the stretch ratio is 4.2 times or more, it is easy to achieve a maximum height Sz of 2.0 μm or less. The maximum height Sz of the other film surface is similar.

[0086] (External Haze) The external haze of the biaxially oriented polyester film of the present invention is preferably 1.8% or less. An external haze of 1.8% or less is preferred because it is less likely to impair the smoothness of the film surface, is less likely to cause charging due to contact with or peeling from the transport roll during the film production process, and is less likely to cause quality defects due to charging, such as static marks and static mark discharge scars. It is even more preferred that the external haze is 1.6% or less, even more preferably 1.4% or less, particularly preferably 1.2% or less, and most preferably 1.0% or less.

[0087] (internal haze) The internal haze of the biaxially oriented polyester film of the present invention is preferably 2.5% or less. When the internal haze is 2.5% or less, the transparency is less likely to decrease, which is preferable. It is further preferably 2.0% or less, more preferably 1.8% or less, and particularly preferably 1.6% or less.

[0088] (wetting tension) One surface of the biaxially oriented polyester film of the present invention may be subjected to surface modification by a surface treatment such as low-temperature plasma treatment or corona discharge treatment. In this case, the wetting tension of the surface of the biaxially oriented polyester film of the present invention that satisfies all of the above (1) to (3) is preferably 50 mN / m or more, more preferably 52 mN / m or more. There is no particular upper limit, but even if it is in the range of 55 mN / m or less, the performance after secondary processing coating or vapor deposition thin film is sufficient.

[0089] (film thickness) The biaxially oriented polyester film of the present invention preferably has a film thickness of 5 to 40 μm. A thickness of 5 μm or more is preferable because the strength and stiffness of the film are not reduced and the film roll is less likely to wrinkle when wound up by a winder. On the other hand, a film thickness of 40 μm or less provides sufficient strength and stiffness, and from a cost perspective, it is preferable to make the film thinner. The film thickness is more preferably 8 to 30 μm, and particularly preferably 9 to 20 μm.

[0090] (Number of defects) The biaxially oriented polyester film of the present invention has a thickness of 1 m 2 From the viewpoint of film quality, it is preferable that there is less than one foreign object of 1 mm or more per film, and it can be said that this is a high-quality film even though it is made from recycled polyester raw materials.

[0091] (Vapor deposition film) A gas barrier layer such as an inorganic thin film layer or a metal foil such as aluminum foil can be provided on at least one surface of the biaxially oriented polyester film of the present invention that satisfies all of the following (1) to (3). (1) Area 4×10 -12 m 2 The number of fine protrusions each having a height of less than 3 nm is 250 or more and 600 or less. (2) Area 4×10 -12 m 2 The number of fine protrusions having a height of 3 nm or more per surface is 300 to 600. (3) The arithmetic mean height Sa is 0.01 μm or more and 0.025 μm or less.

[0092] The inorganic thin film layer is a thin film made of a metal or an inorganic oxide. There are no particular limitations on the material forming the inorganic thin film layer as long as it can be made into a thin film, but from the viewpoint of gas barrier properties, inorganic oxides such as silicon oxide (silica), aluminum oxide (alumina), and a mixture of silicon oxide and aluminum oxide are preferred. In particular, a composite oxide of silicon oxide and aluminum oxide is preferred from the viewpoints of achieving both flexibility and density in the thin film layer and transparency.

[0093] In the composite oxide of silicon oxide and aluminum oxide, the mixing ratio of silicon oxide to aluminum oxide is preferably in the range of 20 to 70% Al by weight of the metal content. If the Al concentration is less than 20%, the water vapor gas barrier property may be reduced. On the other hand, if it exceeds 70%, the inorganic thin film layer tends to become hard, and there is a risk that the film will be destroyed during secondary processing such as printing or lamination, resulting in a reduction in gas barrier property. Note that silicon oxide here refers to various silicon oxides such as SiO and SiO2 or mixtures thereof, and aluminum oxide refers to various aluminum oxides such as AlO and Al2O3 or mixtures thereof.

[0094] The inorganic thin film layer has a thickness of usually 1 to 100 nm, preferably 5 to 50 nm. If the thickness of the inorganic thin film layer is less than 1 nm, it may be difficult to obtain satisfactory gas barrier properties. On the other hand, even if the thickness is excessively greater than 100 nm, the corresponding improvement in gas barrier properties cannot be obtained and is actually disadvantageous in terms of flex resistance and production costs.

[0095] The method for forming the inorganic thin film layer is not particularly limited, and any known deposition method, such as physical vapor deposition (PVD) methods such as vacuum deposition, sputtering, and ion plating, or chemical vapor deposition (CVD), may be appropriately employed. A typical method for forming an inorganic thin film layer will be described below, taking silicon oxide / aluminum oxide-based thin films as an example. For example, when using vacuum deposition, a mixture of SiO2 and Al2O3 or a mixture of SiO2 and Al is preferably used as the deposition source. These deposition sources are typically particles, and the particle size is preferably large enough to prevent pressure changes during deposition, with a preferred particle diameter of 1 mm to 5 mm. Heating methods include resistance heating, high-frequency induction heating, electron beam heating, and laser heating. Reactive deposition can also be employed, using reactive gases such as oxygen, nitrogen, hydrogen, argon, carbon dioxide, and water vapor, or by adding ozone or ion-assisted deposition. Furthermore, the deposition conditions can be freely modified by applying a bias to the deposition target (the laminated film to be deposited) or by heating or cooling the deposition target. The deposition material, reactive gas, bias of the deposition target, heating / cooling, etc. can be changed in the same way when the sputtering method or the CVD method is adopted. Furthermore, a printing layer may be laminated on the inorganic thin film layer.

[0096] In the present invention, it is preferable to provide a protective layer on the gas barrier layer. The gas barrier layer made of a metal oxide is not a completely dense film, but has minute defects scattered therein. By forming a protective layer by coating a specific resin composition for a protective layer, which will be described later, on the metal oxide layer, the resin in the resin composition for a protective layer penetrates into the defects in the metal oxide layer, resulting in stable gas barrier properties. In addition, by using a material with gas barrier properties for the protective layer itself, the gas barrier performance of the laminate film is also greatly improved.

[0097] Examples of the protective layer include resins such as urethane-based, polyester-based, acrylic-based, titanium-based, isocyanate-based, imine-based, and polybutadiene-based resins to which curing agents such as epoxy-based, isocyanate-based, and melamine-based curing agents have been added. Examples of solvents used in forming the protective layer include aromatic solvents such as benzene and toluene; alcohol-based solvents such as methanol and ethanol; ketone-based solvents such as acetone and methyl ethyl ketone; ester-based solvents such as ethyl acetate and butyl acetate; and polyhydric alcohol derivatives such as ethylene glycol monomethyl ether.

[0098] The above-mentioned urethane resin is preferred because the polar group of the urethane bond interacts with the inorganic thin film layer and also has flexibility due to the presence of amorphous portions, thereby suppressing damage to the inorganic thin film layer even when a bending load is applied. The acid value of the urethane resin is preferably within the range of 10 to 60 mgKOH / g, more preferably within the range of 15 to 55 mgKOH / g, and even more preferably within the range of 20 to 50 mgKOH / g. When the acid value of the urethane resin is within this range, the liquid stability is improved when the urethane resin is prepared as an aqueous dispersion, and the protective layer can be uniformly deposited on the highly polar inorganic thin film, resulting in a good coat appearance.

[0099] The urethane resin preferably has a glass transition temperature (Tg) of 80° C. or higher, more preferably 90° C. or higher. By making the Tg 80° C. or higher, it is possible to reduce swelling of the protective layer due to molecular motion during the moist heat treatment process (heating, maintaining the temperature, and cooling). From the viewpoint of improving gas barrier properties, it is more preferable to use a urethane resin containing an aromatic or araliphatic diisocyanate component as the main constituent component. Among these, it is particularly preferable to contain a metaxylylene diisocyanate component. By using the above resin, the cohesive strength of the urethane bond can be further increased due to the stacking effect between aromatic rings, resulting in good gas barrier properties. In the present invention, the proportion of aromatic or araliphatic diisocyanate in the urethane resin is preferably 50 mol% or more (50 to 100 mol%) based on 100 mol% of the polyisocyanate component (F). The total proportion of aromatic or araliphatic diisocyanate is preferably 60 to 100 mol%, more preferably 70 to 100 mol%, and even more preferably 80 to 100 mol%. As such a resin, the "Takelac (registered trademark) WPB" series commercially available from Mitsui Chemicals, Inc. can be suitably used. If the total proportion of aromatic or araliphatic diisocyanate is less than 50 mol%, good gas barrier properties may not be obtained.

[0100] The urethane resin preferably contains a carboxylic acid group (carboxyl group) from the viewpoint of improving affinity with the inorganic thin film layer. To introduce a carboxylic acid (salt) group into the urethane resin, for example, a polyol compound having a carboxylic acid group, such as dimethylolpropionic acid or dimethylolbutanoic acid, may be introduced as a copolymerization component. Furthermore, after synthesizing the urethane resin containing a carboxylic acid group, neutralization with a salt-forming agent can produce a water-dispersed urethane resin. Specific examples of salt-forming agents include ammonia; trialkylamines such as trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine, and tri-n-butylamine; N-alkylmorpholines such as N-methylmorpholine and N-ethylmorpholine; and N-dialkylalkanolamines such as N-dimethylethanolamine and N-diethylethanolamine. These may be used alone or in combination of two or more.

[0101] (Laminate) The biaxially oriented polyester film of the present invention may be used as a substrate film to laminate layers of other materials, which may be laminated after the biaxially oriented polyester film is produced or during film production.

[0102] For example, the biaxially oriented polyester film of the present invention, or a biaxially oriented polyester film of the present invention provided with an inorganic vapor deposition layer, can be further coated with a heat-sealable resin layer called a sealant and used as a packaging material. The heat-sealable resin layer is usually formed by extrusion lamination or dry lamination. The thermoplastic polymer forming the heat-sealable resin layer may be any polymer that can exhibit sufficient sealant adhesiveness, and examples of such polymers include polyethylene resins such as HDPE, LDPE, and LLDPE, polypropylene resins, ethylene-vinyl acetate copolymers, ethylene-α-olefin random copolymers, and ionomer resins.

[0103] The sealant layer may be a single-layer film or a multilayer film, and may be selected depending on the required function. For example, to provide moisture resistance, a multilayer film containing a resin such as an ethylene-cyclic olefin copolymer or polymethylpentene may be used. The sealant layer may also contain various additives such as a flame retardant, a slip agent, an antiblocking agent, an antioxidant, a light stabilizer, and a tackifier. The thickness of the sealant layer is preferably 10 to 100 μm, more preferably 20 to 60 μm.

[0104] Examples of layer structures of a laminate for a packaging material using the biaxially oriented polyester film of the present invention as a base film include base film / gas barrier layer / protective layer, base film / gas barrier layer / protective layer / adhesive layer / sealant layer, base film / gas barrier layer / protective layer / adhesive layer / resin layer / adhesive layer / sealant layer, base film / adhesive layer / resin layer / gas barrier layer / protective layer / adhesive layer / sealant layer, base film / gas barrier layer / protective layer / printing layer / adhesive layer / sealant layer, and base film / printing layer / gas barrier layer / protective layer / adhesive layer. Examples include adhesive layer / sealant layer, base film / gas barrier layer / protective layer / adhesive layer / resin layer / printing layer / adhesive layer / sealant layer, base film / adhesive layer / resin layer / printing layer / gas barrier layer / protective layer / adhesive layer / sealant layer, base film / printing layer / gas barrier layer / protective layer / adhesive layer / resin layer / adhesive layer / sealant layer, base film / printing layer / adhesive layer / resin layer / gas barrier layer / protective layer / adhesive layer / sealant layer, base film / adhesive layer / resin layer / gas barrier layer / protective layer / adhesive layer / sealant layer, and base film / adhesive layer / resin layer / gas barrier layer / protective layer / printing layer / adhesive layer / sealant layer.

[0105] Laminates using the biaxially oriented polyester film of the present invention can be suitably used for applications such as packaging products, various label materials, lid materials, sheet molded products, laminated tubes, etc. In particular, they are used for packaging bags (for example, pillow bags, standing pouches, four-sided pouches, and other pouches). The thickness of the laminate can be appropriately determined depending on the application. For example, it is used in the form of a film or sheet having a thickness of about 5 to 500 μm, preferably about 10 to 300 μm. [Example]

[0106] The present invention will be described in more detail below using examples, but the present invention is not limited to the embodiments of these examples and can be modified as appropriate within the scope of the invention.

[0107] A. The polyester resin was evaluated as follows: [Glass transition temperature (Tg)] Using a differential scanning calorimeter (DSC6220 model, manufactured by SII NanoTechnology Inc.), 5 mg of the resin sample was melted to 280°C under a nitrogen atmosphere, held at that temperature for 5 minutes, then rapidly cooled with liquid nitrogen. Measurements were then performed at a heating rate of 20°C / min from room temperature.

[0108] [Intrinsic viscosity (IV)] 0.2 g of polyester resin was dissolved in 50 ml of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (60 / 40 (weight ratio)), and the viscosity was measured using an Ostwald viscometer at 30° C. The unit is dl / g.

[0109] [Content of terephthalic acid and isophthalic acid components in raw polyester and polyester that constitutes the film] A sample solution was prepared by dissolving chloroform D (manufactured by Eurisop) and trifluoroacetic acid D1 (manufactured by Eurisop) in a 10:1 (volume ratio) mixture, and proton NMR of the sample solution was measured using an NMR (GEMINI-200; manufactured by Varian) at a temperature of 23°C and an accumulation count of 64. In the NMR measurement, the peak intensity of a predetermined proton was calculated, and the content (mol %) of terephthalic acid components and isophthalic acid components in 100 mol % of acid components was calculated.

[0110] [Angle of repose of raw material pellets] The pellets were dropped into the center of the end face of a metal cylinder with a diameter of 50 mm and a height of 10 mm using a polyethylene funnel (10 mm diameter). The angle of repose was measured using a protractor and was the angle formed by the plane of the metal cylinder and the ridge line of the pellet.

[0111] B. The polyester film was evaluated as follows. [Film thickness] Measurement was carried out using a dial gauge in accordance with JIS K7130-1999 Method A.

[0112] [External haze, internal haze, total haze] A piece measuring 5 cm in the vertical direction and 5 cm in the horizontal direction was cut out from the obtained film, and the total haze was measured at 25°C for all wavelengths of visible light in accordance with JIS-K7136 using a turbidity meter (NDH5000) manufactured by Nippon Denshoku Industries Co., Ltd. Similarly, the haze of a laminate in which only Zedel oil was sandwiched between two quartz glass plates (hereinafter referred to as "haze H1") and the haze of a laminate in which a polyester film whose surface was uniformly wetted with Zedel oil was sandwiched between two quartz glass plates (hereinafter referred to as "haze H2") were measured. Next, the internal haze is calculated according to the following formula. Internal haze = haze (H2) - haze (H1) Equation 1 The external haze is the value obtained by subtracting the internal haze from the total haze. The total haze, internal haze, and external haze are all measured against all wavelengths of visible light. He points to Hayes.

[0113] [Arithmetic mean height Sa, maximum height Sz] A piece measuring 10 cm in the vertical direction and 10 cm in the horizontal direction was cut out from the obtained film, and a white laser interferometer (NEW VIEW8300) manufactured by Zygo was used. A 20x lens was attached to the interferometer, scanning was performed, and the arithmetic mean height (μm) and maximum height (μm) were measured. The measurement was performed over a range of 0.82μm in the MD direction and 0.82μm in the width direction on one surface, and the surface was the target, excluding foreign matter such as unmelted material and dust. Measurements were taken at 10 randomly selected points on a 10 cm x 10 cm sample, and the average values ​​were taken as the arithmetic mean height Sa and the maximum height Sz, respectively. The variation (%) of the arithmetic mean height Sa was measured by sampling the obtained polyester film roll (width 2080 mm, wound length 63,000 m) in the longitudinal direction every 1000 m from the surface of the film roll to the core. Measurements were carried out for each sampled film under the above conditions. The maximum value of the obtained arithmetic mean height Sa was designated Xmax(N), the minimum value was designated Xmin(N), and the average value was designated Xave, and the variation in the longitudinal direction was calculated using the following formula [1]:

[0114] [Kinematic friction coefficient, static friction coefficient,] The resulting film was cut into a piece measuring 400 mm in length and 100 mm in width to prepare a sample film. This was aged for 12 hours in an atmosphere of 23°C and 65% RH, and then divided into a test piece measuring 300 mm in length and 100 mm in width for the test table and a test piece measuring 100 mm in length and 100 mm in width for the sliding piece. The test piece for the test table was set on the test table, and the test piece for the sliding piece was the bottom surface (area size 39.7 mm) of a metal sliding piece with a load of 1.5 kg. 2 , square) with double-sided tape so that the surfaces that had contacted the casting drum faced each other. The dynamic friction coefficient and static friction coefficient were measured under the conditions of a sliding speed of 200 mm / min, 23°C, and 65% RH, and other conditions were in accordance with JIS K-7125. The average of three measurements was used.

[0115] [Film surface area 4 x 10 -12 m 2 Number of micro-projections in A piece measuring 10 mm in the longitudinal direction and 10 mm in the width direction was cut out from the obtained film, and measurements were carried out using a scanning probe microscope (SPM-9700) manufactured by Shimadzu Corporation under the following observation conditions, and images of the measurement surface were captured. The obtained image (height trace) was subjected to image processing under the following conditions. Using the SPM-9700 series particle analysis software, the threshold value for particles to be extracted under the following particle analysis conditions was set to 3 nm, and the number of particles 3 nm or larger (protrusion count) and particles smaller than 3 nm (protrusion count) were counted on an area of ​​4 x 10 -12 m 2 The number of particles (protrusions) smaller than 3 nm was counted as those 0.01 nm or larger. The measurement was carried out five times at different locations, and the number of microprojections was calculated by excluding the highest and lowest counts and averaging the remaining three counts. (Observation conditions) Cantilever: Made of Si (silicon) Scanning mode: Phase mode Scanning speed: 2Hz Scanning range: 2μm Resolution: 256 x 256 Offset X: 0 μm Offset Y: 0 μm Scanning angle: 0° Operating point: 1.0V P-Gain: 0.001 I Gain: 1500 Offset Z: 0 μm Z Range: x2 Scanning mode: constant force (Image Processing) Tilt correction: average value in X direction (X), average value in Y direction (Y), line fit (L) Noise line removal: Mode (range specification), Auto selection (particle analysis) Target Shape: Particle XY Threshold: 30% Number of pixels to ignore: 5 The variation (%) in the number of fine protrusions was measured by sampling the obtained polyester film roll (width 2080 mm, wound length 63,000 m) in the longitudinal direction every 1000 m from the surface layer of the film roll to the winding core. Measurements were carried out for each sampled film under the conditions described above. The maximum number of obtained fine protrusions was designated Xmax(N), the minimum value Xmin(N), and the average value Xave, and the variation in the longitudinal direction was calculated using the following formula [1].

[0116] [Frictional charging voltage] A sample film measuring 80 mm in length and 50 mm in width was cut from the obtained film. This was aged for 16 hours in an atmosphere of 23°C and 50% RH. The frictional electrification voltage was measured using a frictional electrification voltage measuring instrument (RST-300a) manufactured by Daiei Scientific Instruments Co., Ltd. The sample was fixed to a rotating device and rubbed against a metal plate at a drum rotation speed of 400 rpm for 60 seconds, and the generated static electricity was measured, and the maximum value was taken as the frictional electrification voltage. The measured frictional electrification voltage was evaluated according to the following criteria. ◎: Frictional charging voltage less than 200V ○: Frictional charging voltage 200V or more, less than 500V △: Frictional charging voltage 500V or more, less than 1000V ×: Frictional charging voltage 1000V or more

[0117] [Static Mark Evaluation] The resulting biaxially oriented polyester was wound to a length of 550 mm in the width direction and 500 m in the length direction. The film roll was rewound using a slitter (FN105E type) manufactured by Nishimura Manufacturing Co., Ltd. at a speed of 15 m / min and a winding tension of 100 N / m (unit tension setting). To remove static electricity at this time, the static electricity removal device attached to the slitter was turned on, and static removal brushes (Achilles "NSP-2S") were placed on the top and bottom sides of the film between the unwinding roll and the tilt adjustment roller. The film was unwound from the outermost edge of the obtained film roll, and after removing 2 m from the edge, the film was sampled at a length of 10 cm from the center in the width direction and 10 cm in the longitudinal direction, and the charge state of the film surface was visualized using a charge distribution assessment toner manufactured by Kasuga Electric Co., Ltd. The chargeability of the film roll was evaluated according to the following criteria. ⊚: No static marks, static mark discharge marks or toner adhesion. ◯: No static marks or static mark discharge marks are observed, but toner is attached. ×: Static marks or static mark discharge marks are observed. [Foreign substances in film (number of defects)] The obtained film was cut into an area of ​​250 mm in the longitudinal direction × 250 mm in the width direction to prepare a sample film. This was observed using a microscope with a scale from a direction perpendicular to the film surface, and the number of foreign particles having a diameter of 1 mm or more was counted on the area of ​​250 mm in the longitudinal direction × 250 mm in the width direction (0.0625 mm).2 This is done for 20 sample films, and the total number of foreign particles obtained is counted over the total observation area (1.25 m 2 ) and divide by 1m 2 Number of foreign objects per unit (pieces / m 2 The number of foreign matters in the measured film was evaluated according to the following criteria. ◯: Number of foreign objects (defects) in the film: 1.0 / m 2 less than ×: Number of foreign particles (defects) in the film: 1.0 / m 2 End

[0118] [Wetting tension] A piece measuring 400 mm in the longitudinal direction and 300 mm in the transverse direction was cut out from the obtained film, and after aging for 24 hours at a temperature of 23°C and a relative humidity of 50%, the corona-treated surface was measured according to the following procedure in accordance with JIS-K-7100, except that the test room atmosphere was a temperature of 23°C and a relative humidity of 50%. Place the test specimen on the hand coater substrate, drop a few drops of the test mixture onto the specimen, and immediately spread it by pulling the wire bar. If using a cotton swab or brush to spread the test mixture, the liquid should be at least 6 cm 2 Spread the liquid quickly over the above area. The amount of liquid should be enough to form a thin layer without creating any puddles. The wetting tension is determined by observing the liquid film of the test mixture in a bright place and checking the state of the liquid film after 3 seconds. If the liquid film remains in the same state as when it was applied for 3 seconds or more without breaking, it is considered to be wet. If the wetting persists for more than 3 seconds, proceed to the mixture with the next highest surface tension. Conversely, if the liquid film breaks in 3 seconds or less, proceed to the next mixed liquid with a lower surface tension. Repeat this process to select a mixed liquid that can accurately wet the surface of the test piece in 3 seconds. Use a new cotton swab for each test. Brushes or wire burrs should be cleaned with methanol and dried after each use, as residual liquid will change composition and surface tension upon evaporation. The procedure is repeated at least three times to select a mixture that can wet the corona-treated surface in 3 seconds, and the surface tension of the mixture thus selected is reported as the wetting tension of the film.

[0119] [Preparation of laminate for evaluation] A 70 μm thick unstretched polypropylene film (P1147 manufactured by Toyobo Co., Ltd.) was laminated onto a polyester film by dry lamination using a urethane-based two-component curing adhesive (Mitsui Chemicals' "Takelac® A525S" and "Takenate® A50" blended in a 13.5:1 (weight ratio)) as a heat-sealable resin layer, and the laminate was then aged at 40°C for 4 days to obtain a laminate. The thickness of the adhesive layer formed with the urethane-based two-component curing adhesive after drying was approximately 4 μm in all cases.

[0120] [Laminate strength] The laminate was cut into test pieces 15 mm wide and 200 mm long, and the laminate strength was measured using a Tensilon universal material testing machine (Tensilon UMT-II-500, manufactured by Toyo Baldwin Co., Ltd.) under conditions of a temperature of 23°C and a relative humidity of 65%. The lamination strength was determined as the strength when the laminated film and the heat-sealable resin layer were peeled at a peel angle of 180 degrees at a pulling speed of 200 mm / min.

[0121] The raw resin chips used in the present examples and comparative examples are described in detail below. (Polyester Resin A) The PET resin recycled from PET bottles used in the production of the biaxially stretched polyester film described below was synthesized using the following method. After washing the remaining beverage and other foreign matter from the PET beverage bottles, they were crushed to obtain flakes. The resulting flakes were washed with a 3.5 wt% sodium hydroxide solution at a flake concentration of 10 wt% at 85°C for 30 minutes under stirring. After the alkaline wash, the flakes were removed and washed with distilled water at a flake concentration of 10 wt% at 25°C for 20 minutes under stirring. This water wash was repeated two more times, each time changing the distilled water. After washing, the flakes were dried and melted in an extruder. The finer foreign matter was further filtered out twice using filters with successively smaller mesh sizes, and finally filtered out a third time using a filter with the smallest mesh size (50 μm), yielding a polyester resin A with an intrinsic viscosity of 0.69 dl / g, an isophthalic acid content of 2 mol%, and an angle of repose of 46°. (Polyester resin B) Polyester resin B having an intrinsic viscosity of 0.69 dl / g, an isophthalic acid content of 2 mol%, and an angle of repose of 46 degrees was obtained in the same manner as in the production process of polyester resin A, except that alkali washing was not performed. (Polyester resin C) The fossil fuel-derived PET resin used in the production of the biaxially oriented polyester film described below was terephthalic acid / ethylene glycol = 100 / / 100 (mol %) (manufactured by Toyobo Co., Ltd., intrinsic viscosity 0.62 dl / g, angle of repose 45 degrees). (Polyester resin D) The esterification reactor was heated to 200°C, and a slurry consisting of 86.4 parts by mass of terephthalic acid and 64.4 parts by mass of ethylene glycol was added. While stirring, antimony trioxide (0.017 parts by mass) and triethylamine (0.16 parts by mass) were added as catalysts. The temperature was then increased by heating, and a pressurized esterification reaction was carried out at a gauge pressure of 0.34 MPa and 240°C. The pressure inside the esterification reactor was then returned to normal, and magnesium acetate tetrahydrate (0.071 parts by mass) and trimethyl phosphate (0.014 parts by mass) were added. The temperature was then increased to 260°C over 15 minutes, after which trimethyl phosphate (0.012 parts by mass) and sodium acetate (0.0036 parts by mass) were added. After 15 minutes, the mixture was dispersed using a high-pressure disperser. An ethylene glycol slurry of irregular silica particles with an average particle size of 1.3 μm was then added (3.0 parts by weight, based on the particle content). These silica particles were obtained by first preparing an ethylene glycol slurry, centrifuging it to remove 35% of the coarse particles, and then filtering it through a metal filter with a 5 μm mesh size. After 15 minutes, the resulting esterification reaction product was transferred to a polycondensation reactor and subjected to a polycondensation reaction under reduced pressure at 280°C to obtain a polyester resin D with an intrinsic viscosity of 0.60 dL / g and an angle of repose of 37°. (Polyester resin E~P) Polyester resins E to P were obtained in the same manner as for polyester resin D, except that the shape, average particle size and content of the silica particles were changed.

[0122] The raw resin chips are as shown in Table 1. The abbreviations in the table are as follows: TPA: Terephthalic acid EG: Ethylene glycol

[0123] [Table 1]

[0124] [Example 1] Three extruders were used to produce a three-layer film. The base layer (B) consisted of 98.7% by mass of polyester resin A and 1.3% by mass of polyester resin D, and the surface layer (A) consisted of 93.3% by mass of polyester resin A and 6.7% by mass of polyester resin D. Here, polyester resin D was introduced using an inner pipe as shown in Figure 4 so that it was mixed with the other raw materials before entering the extruder. After drying each raw resin, the mixed resin forming the surface layer (A) was melt-extruded from the first and third extruders at a resin temperature of 285°C, and the mixed resin forming the base layer (B) was melted from the second extruder at a resin temperature of 285°C.The layers were then merged and laminated in a T-die in the order of surface layer (A) / base layer (B) / surface layer (A) from the side contacting the casting drum so that the thickness ratio was 1 / 10 / 1 (μm), extruded from a T-shaped nozzle, and cooled and solidified on a casting drum with a surface temperature of 30°C to obtain an unstretched polyethylene terephthalate sheet. At this time, static electricity was applied using a wire electrode with a diameter of 0.15 mm, and the film was brought into close contact with a cooling drum to obtain a three-layer unstretched film. The resulting unstretched film was heated to 115°C and stretched in the longitudinal direction at a total stretch ratio of 4.5 times in three stages: 1.24 times in the first stage, 1.4 times in the second stage, and 2.6 times in the third stage. Subsequently, the film was stretched in the width direction at a temperature of 140°C and a stretch ratio of 4.3 times, heat-set at 245°C, and subjected to a 5% thermal relaxation treatment in the width direction. The surface of layer A that came into contact with the chill roll was then stretched at 40 W·min / m 2 The film was then wound up into a roll using a winder to produce a master roll (26,000 m long, 8,000 mm wide) of biaxially oriented polyester film with a thickness of 12 μm. The biaxially oriented polyester film was unwound from the obtained master roll and slit to a width of 2200 mm onto a core with a diameter of 6 inches (152.2 mm). The film roll was wound up while applying surface pressure to the film roll with a contact roll and tension to the film with a two-axis turret winder. The raw material composition and film-forming conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 2. The film was evaluated on the surface of Layer A, which was in contact with the chill roll.

[0125] [Example 2] A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials for the surface layer (A) were changed to 95.0% by mass of polyester resin A and 5.0% by mass of polyester resin D, to obtain a biaxially oriented polyester film having a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 2. The film was evaluated on the surface of Layer A that came into contact with the chill roll.

[0126] [Example 3] A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials for the surface layer (A) were changed to 96.0% by mass of polyester resin A and 4.0% by mass of polyester resin E, to obtain a biaxially oriented polyester film having a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 2. The film was evaluated on the surface of Layer A on the side that came into contact with the chill roll.

[0127] [Example 4] A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials for the surface layer (A) were changed to 92.0% by mass of polyester resin A and 8.0% by mass of polyester resin F, to obtain a biaxially oriented polyester film having a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 2. The film was evaluated on the surface of Layer A on the side that came into contact with the chill roll.

[0128] [Comparative Example 1] A biaxially stretched film was produced in the same manner as in Example 1, except that the polyester resin of the surface layer (A) was changed to polyester resin C as the raw material, to obtain a biaxially oriented polyester film having a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 2. The film was evaluated on the surface of Layer A on the side that came into contact with the chill roll.

[0129] Comparative Example 2 A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials for the surface layer (A) were changed to 95.0% by mass of polyester resin A and 5.0% by mass of polyester resin G, to obtain a biaxially oriented polyester film having a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 2. The film was evaluated on the surface of Layer A on the side that came into contact with the chill roll.

[0130] Comparative Example 3 A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials for the surface layer (A) were changed to 95.0% by mass of polyester resin A and 5.0% by mass of polyester resin H, to obtain a biaxially oriented polyester film having a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 2. The film was evaluated on the surface of Layer A on the side that came into contact with the chill roll.

[0131] [Example 5] A biaxially stretched film was produced in the same manner as in Comparative Example 1, except that the polyester resin of the surface layer (A) was changed to polyester resin B as the raw material, to obtain a biaxially oriented polyester film having a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 2. The film was evaluated on the surface of Layer A on the side that came into contact with the chill roll.

[0132] [Reference example 1] As in Example 1, a three-layer film was produced using three extruders. The base layer (B) contained 98.7 mass% polyester resin A and 1.3 mass% polyester resin D, and the surface layer (A) contained 93.3 mass% polyester resin A and 6.7 mass% polyester resin D. However, polyester resin A and polyester resin D were all mixed together and fed into the extruder. In other words, polyester resin D was mixed at the top of the hopper and fed into the extruder without using an inner pipe. After drying the raw resins, the mixed resin forming the surface layer (A) was melt-extruded from the first and third extruders at a resin temperature of 285°C, and the mixed resin forming the base layer (B) was melted from the second extruder at a resin temperature of 285°C. The layers were then laminated in a T-die in the order of surface layer (A) / base layer (B) / surface layer (A) from the side contacting the casting drum to a thickness ratio of 1 / 10 / 1 (μm), extruded from a T-shaped die, and cooled and solidified on a casting drum with a surface temperature of 30°C to obtain an unstretched polyethylene terephthalate sheet. A 0.15 mm diameter wire electrode was used to apply static electricity, and the film was tightly attached to the cooling drum to obtain a three-layer unstretched film. The resulting unstretched film was heated to 115°C and stretched in the longitudinal direction at a total stretch ratio of 4.5 times in three stages: 1.24 times in the first stage, 1.4 times in the second stage, and 2.6 times in the third stage. Subsequently, the film was stretched in the width direction at a temperature of 140°C and a stretch ratio of 4.3 times, heat-set at 245°C, and subjected to a 5% thermal relaxation treatment in the width direction. The surface of layer A that came into contact with the chill roll was then stretched at 40 W·min / m 2 The film was then wound up into a roll using a winder to produce a master roll (26,000 m long, 8,000 mm wide) of biaxially oriented polyester film with a thickness of 12 μm. The biaxially oriented polyester film was unwound from the obtained master roll and slit to a width of 2200 mm onto a core with a diameter of 6 inches (152.2 mm). The film roll was wound up while applying surface pressure to the film roll with a contact roll and tension to the film with a two-axis turret winder. The raw material composition and film-forming conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 2. The film was evaluated on the surface of Layer A, which was in contact with the chill roll.

[0133] As shown in Table 2, the films of Examples 1 to 4 had a number of fine protrusions 3 nm or more in height, a number of fine protrusions less than 3 nm in height, and an arithmetic mean height Sa that were within the specified ranges, and therefore had few quality defects due to static marks and static mark discharge scars and other static mark defects, had excellent performance after secondary processing such as coating and vapor deposition, and were environmentally friendly polyester films using polyester resin recycled from the market and society, including PET bottles, had little foreign matter, and had little variation in physical properties in the longitudinal direction even in long film rolls with long wound lengths.

[0134] In Comparative Example 1, the number of fine protrusions 3 nm or more in height, the number of fine protrusions less than 3 nm in height, and the arithmetic mean height Sa of the obtained film were all within the specified ranges, so there were few quality defects due to static marks and static mark discharge marks, and the film had excellent performance after secondary processing such as coating and vapor deposition.However, because the film was made of a conventional polyester resin derived from fossil fuels, it was inferior as an environmentally friendly polyester film.

[0135] In Comparative Example 2, although the number of microprotrusions 3 nm or more in height was within the range, the number of microprotrusions less than 3 nm in height was small, resulting in a high frictional electrification voltage and a poor static mark evaluation. Moreover, the arithmetic mean height Sa was too large, resulting in high external haze and poor transparency.

[0136] In Comparative Example 3, although the number of fine protrusions 3 nm or more in height of the obtained film was within the range, the number of fine protrusions less than 3 nm in height was low, so the frictional electrification voltage was high and the static mark evaluation was poor.

[0137] In Example 5, the number of fine protrusions 3 nm or more in height, the number of fine protrusions less than 3 nm in height, and the arithmetic mean height Sa of the obtained film were all within the specified ranges, so there were few quality defects due to static marks and static mark discharge marks, and the film had excellent performance after secondary processing such as coating and vapor deposition. However, because the film used polyester resin recycled from the market and society, including PET bottles that had not been subjected to alkaline cleaning, there was a lot of foreign matter in the film.

[0138] In Reference Example 1, an inner pipe was not used to supply the raw materials, and the raw material ratio fluctuated greatly in the longitudinal direction due to segregation of the raw materials. As a result, the number of fine protrusions 3 nm or more in height and the number of fine protrusions less than 3 nm in height varied greatly in the longitudinal direction of the obtained film. Although a good film having physical properties equivalent to those of Examples 1 to 4 was obtained in some parts of the film roll, the film was inferior as a film roll.

[0139] [Table 2A]

[0140] [Table 2B]

[0141] [Example 6] A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials were changed so that the polyester resin A in the surface layer (A) was 98.0 mass% and the polyester resin I was 2.0 mass%, and the polyester resin A in the base layer (B) was 99.6 mass% and the polyester resin I was 0.4 mass%, to obtain a biaxially oriented polyester film with a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 3. The film was evaluated on the surface of Layer A that came into contact with the chill roll.

[0142] [Example 7] A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials were changed so that the polyester resin A in the surface layer (A) was 99.33 mass% and the polyester resin J was 0.67 mass%, and the polyester resin A in the base layer (B) was 99.87 mass% and the polyester resin J was 0.13 mass%, to obtain a biaxially oriented polyester film with a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 3. The film was evaluated on the surface of Layer A on the side that came into contact with the chill roll.

[0143] [Example 8] A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials were changed so that the polyester resin A in the surface layer (A) was 99.5% by mass and the polyester resin J was 0.5% by mass, and the polyester resin A in the base layer (B) was 99.87% by mass and the polyester resin J was 0.13% by mass, to obtain a biaxially oriented polyester film with a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 3. The film was evaluated on the surface of Layer A on the side that came into contact with the chill roll.

[0144] [Example 9] A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials were changed so that the polyester resin A in the surface layer (A) was 99.6% by mass and the polyester resin M was 0.4% by mass, and the polyester resin A in the base layer (B) was 99.87% by mass and the polyester resin M was 0.13% by mass, to obtain a biaxially oriented polyester film with a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 3. The film was evaluated on the surface of Layer A that came into contact with the chill roll.

[0145] [Example 10] A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials were changed so that the polyester resin A in the surface layer (A) was 99.2% by mass and the polyester resin N was 0.8% by mass, and the polyester resin A in the base layer (B) was 99.87% by mass and the polyester resin N was 0.13% by mass, to obtain a biaxially oriented polyester film with a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 3. The film was evaluated on the surface of Layer A that came into contact with the chill roll.

[0146] Comparative Example 4 A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials were changed so that the polyester resin A in the surface layer (A) was 99.5% by mass and the polyester resin O was 0.5% by mass, and the polyester resin A in the base layer (B) was 99.87% by mass and the polyester resin O was 0.13% by mass, to obtain a biaxially oriented polyester film with a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 3. The film was evaluated on the surface of Layer A that came into contact with the chill roll.

[0147] Comparative Example 5 A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials were changed to 99.5% by mass of polyester resin A and 0.5% by mass of polyester resin P for the surface layer (A), and 99.87% by mass of polyester resin A and 0.13% by mass of polyester resin P for the base layer (B), to obtain a biaxially oriented polyester film with a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 3. The film was evaluated on the surface of Layer A that came into contact with the chill roll.

[0148] [Example 11] A biaxially stretched film was produced in the same manner as in Example 1, except that the raw materials were changed to 90.0 mass% polyester resin A and 10.0 mass% polyester resin K for the surface layer (A), and 97.4 mass% polyester resin A and 2.6 mass% polyester resin K for the base layer (B), to obtain a biaxially oriented polyester film with a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 3. The film was evaluated on the surface of Layer A that came into contact with the chill roll.

[0149] [Reference example 2] A biaxially stretched film was produced in the same manner as in Example 6, except that the polyester resin of the surface layer (A) and base layer (B) was changed to polyester resin L, to obtain a biaxially oriented polyester film with a thickness of 12 μm. The raw material composition and film production conditions of the obtained film, as well as the physical properties and evaluation results of the obtained film, are shown in Table 3. The film was evaluated on the surface of Layer A, which was in contact with the chill roll.

[0150] As shown in Table 3, the films of Examples 5 to 9 had a number of fine protrusions 3 nm or more in height, a number of fine protrusions less than 3 nm in height, and an arithmetic mean height Sa that were within the specified range, and therefore had few quality defects due to static marks and static mark discharge marks and other electrostatic charges, and had excellent performance after secondary processing such as coating and vapor deposition.In addition, the films used polyester resin recycled from the market and society, including PET bottles, and by further increasing the proportion of recycled PET bottle raw materials used, they were environmentally friendly polyester films, had little foreign matter, and had little variation in physical properties in the longitudinal direction, even in long film rolls with long wound lengths.

[0151] In Comparative Example 4, although the number of micro-protrusions having a height of 3 nm or more was within the range, the number of micro-protrusions having a height of less than 3 nm was small, so the frictional electrification voltage was high and the static mark evaluation was poor. Moreover, because the arithmetic mean height Sa was too large, the external haze was large and the transparency was poor.

[0152] In Comparative Example 5, although the number of fine protrusions 3 nm or more in height was within the range, the number of fine protrusions less than 3 nm in height was low, resulting in a high frictional electrification voltage and a poor static mark evaluation.

[0153] In Example 11, the particle content of the polyester resin composition containing particles was low, so the proportion of recycled PET bottle raw materials used was slightly reduced, but the film and film roll had good physical properties similar to those of Examples 6 to 10.

[0154] In Reference Example 2, the angle of repose of the pellets of the polyester resin composition containing particles was large, and as a result of the segregation of the raw materials, the raw material ratio fluctuated greatly in the longitudinal direction, and as a result, the number of fine protrusions 3 nm or more in height and the number of fine protrusions less than 3 nm in height varied greatly in the longitudinal direction of the obtained film. Although a good film having physical properties equivalent to those of Examples 6 to 10 in some parts of the film roll was obtained, the film roll was inferior.

[0155] [Table 3A]

[0156] [Table 3B] [Industrial Applicability]

[0157] The biaxially oriented polyester film of the present invention has excellent transparency, is less likely to cause wrinkles in the film roll during film production or when wound onto a film roll after slitting, and is easy to unwind from the film roll, making it easy to perform secondary processing such as coating and vapor deposition. Furthermore, since there are fewer quality defects due to static marks and static mark discharge scars caused by static charging, the polyester film has excellent performance after secondary processing such as coating and vapor deposition, and is an environmentally friendly polyester film made using polyester resin recycled from the market and society, including PET bottles.It is also possible to provide a biaxially oriented polyester film and a method for producing the same, which has few foreign matter and little variation in physical properties in the longitudinal direction even in long film rolls with long wound lengths. Therefore, it is useful for food packaging applications, particularly for applications in films with gas barrier properties, and is expected to make a significant contribution to the industrial world.

Claims

1. A biaxially oriented polyester film having a thickness of 5 μm or more and 40 μm or less, which is made of a polyester resin composition containing recycled polyethylene terephthalate and particles, and at least one surface of the biaxially oriented polyester film satisfies all of the following requirements (1) to (4): (1) Area 4×10 -12 m 2 The number of fine protrusions each having a height of less than 3 nm is 250 or more and 600 or less. (2) Area 4×10 -12 m 2 The number of fine protrusions having a height of 3 nm or more per surface is 300 to 600. (3) The arithmetic mean height Sa is 0.010 μm or more and 0.025 μm or less. (4) The content of the isophthalic acid component relative to 100 mol % of all dicarboxylic acid components in the polyester resin composition is 0.02 mol % or more and 2.0 mol % or less.

2. 2. The biaxially oriented polyester film according to claim 1, wherein the content of recycled polyethylene terephthalate in the polyester resin composition constituting the biaxially oriented polyester film is 50% by mass or more and 100% by mass or less.

3. 1m of film 2 3. The biaxially oriented polyester film according to claim 1, wherein the number of defects of 1 mm or more per film is less than 1.

0.

4. 4. The biaxially oriented polyester film according to claim 1, wherein the recycled polyethylene terephthalate has been subjected to alkali washing at least once.

5. The surface of the biaxially oriented polyester film that satisfies all of the requirements (1) to (3) and 5. The biaxially oriented polyester film according to claim 1, wherein the coefficient of dynamic friction between the facing surfaces is 0.2 or more and 0.60 or less.

6. 6. The biaxially oriented polyester film according to claim 1, wherein the surface of the biaxially oriented polyester film that satisfies all of the requirements (1) to (3) has a wetting tension of 50 mN / m or more.

7. The biaxially oriented polyester film according to any one of claims 1 to 6, wherein the biaxially oriented polyester film has an external haze of 1.8% or less and an internal haze of 2% or less.

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