Biaxially oriented polyester film

Abstract

To provide a biaxially oriented polyester film that has excellent mechanical property, transparency, heat resistance, as well as is excellent in suitability for secondary fabrication and print appearance, and to provide a method for producing the same.SOLUTION: Provided is a biaxially oriented polyester film in which at least one film surface satisfies the following (1) and (2), and the film satisfies the following (3) and (4). (1) The maximum protrusion height (SRp) is 1.2 to 1.6 μm. (2) Arithmetic mean roughness (SRa) is 0.024 to 0.045 μm. (3) Tensile strength in longitudinal and transverse directions is 180 to 300 MPa. (4) Haze is 7% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polyester film, and more particularly to a biaxially oriented polyester film that has excellent mechanical properties, transparency, and heat resistance, as well as excellent suitability for secondary processing and excellent print appearance. [Background technology]

[0002] Polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), which are thermoplastic resins with excellent heat resistance and mechanical properties, are used in a wide variety of fields, including plastic films, electronics, energy, packaging materials, and automobiles. Among plastic films, biaxially oriented PET film is widely used in industrial and packaging fields because it offers an excellent balance of mechanical strength, heat resistance, dimensional stability, chemical resistance, optical properties, and cost.

[0003] In the field of industrial films, PET films have excellent transparency and can be used as functional films for flat panel displays (FPDs) such as liquid crystal displays and plasma displays. PET films with hydrolysis resistance are also used as backsheets for solar cells, and are used for a variety of purposes as functional films and base films.

[0004] In the field of packaging films, they are used for food packaging and as gas barrier films. In particular, films with excellent gas barrier properties are used as packaging materials for foods, medicines, electronic components, etc. that require airtightness, or as gas blocking materials, and demand has been increasing in recent years.

[0005] However, polyesters for film have problems such as wrinkles occurring when the produced film is wound into a roll if the film surface is smooth, films stick to each other when overlapped, causing so-called blocking, and defects such as scratches occurring due to poor sliding properties with guide rolls and the like when the rolled film is processed, making the film difficult to handle. In order to solve such problems in handling the film, a method of forming minute protrusions on the surface of the polyester film has been used.

[0006] A technique for incorporating inert particles such as inorganic particles into a polyester film is used as a method for controlling the surface roughness of a polyester film to a certain level. A common method for incorporating inorganic particles into a polyester film is to melt-knead a polyester resin (masterbatch) containing inorganic particles at a concentration higher than the concentration of inorganic particles in the final film into a polyester resin that is substantially free of inorganic particles. On the other hand, if the film surface is rough, so-called printing voids occur after printing on the film, resulting in poor print appearance. For this reason, it has been proposed to keep the surface roughness of the polyester film within a certain range.

[0007] On the other hand, as environmentally friendly or environmentally sustainable materials, recycled resins made from PET bottles and polyester resins made from biomass-derived raw materials have been developed, and films containing large amounts of these resins are in demand. To achieve a high resin content, one method is to use a masterbatch containing a high concentration of inorganic particles. However, when the inorganic particle concentration is high, the particles generally aggregate, which can lead to problems such as missing prints.

[0008] To date, methods have been reported to suppress the aggregation of inorganic particles by setting the particle size, inorganic particle concentration in the masterbatch, and amount of masterbatch added within specific ranges (see, for example, Patent Document 1, etc.). However, these methods are insufficient because the coarse particles are large, at 10 μm or more, and there is a high possibility of print defects occurring.

[0009] Also, a method for improving the insulation resistance of a film capacitor using inorganic particles has been disclosed (see, for example, Patent Document 2). However, there are still problems with mechanical properties, transparency, heat resistance, printing processability and appearance.

[0010] Another report discloses a method of using a masterbatch containing inorganic particles to control the surface roughness and wettability of a film, thereby achieving both adhesion to and releasability from a ceramic slurry (see, for example, Patent Document 3). However, there still remains a problem of missing prints. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. WO13 / 146524 [Patent Document 2] Japanese Patent Application Publication No. 11-40453 [Patent Document 3] Japanese Patent Application Publication No. 2018-83874 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention provides a method for producing a biaxially oriented polyester film that has excellent mechanical properties, transparency, and heat resistance, as well as excellent suitability for secondary processing and excellent print appearance. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention has the following configuration. [1] A biaxially oriented polyester film in which at least one film surface satisfies the following (1) and (2), and the film itself satisfies the following (3) and (4). (1) The maximum protrusion height (SRp) is 1.2 to 1.6 μm. (2) The arithmetic mean roughness (SRa) is 0.024 to 0.045 μm. (3) The tensile strength in the longitudinal and transverse directions is 180 to 300 MPa. (4) Haze is 7% or less.

[0014] [2] The biaxially oriented polyester film according to [1], wherein the film surface satisfies the above (1) and (2) and has a diiodomethane contact angle of 29° or less.

[0015] [3] The biaxially oriented polyester film according to [1] or [2], wherein the biaxially oriented polyester film contains inorganic particles in an amount of 500 to 1500 ppm by mass.

[0016] [4] The biaxially oriented polyester film according to any one of [1] to [3], wherein the inorganic particles are silica particles.

[0017] [5] The biaxially oriented polyester film according to [4], wherein the silica particles have a pore volume of 0.6 to 2.0 ml / g.

[0018] [6] A film roll obtained by winding up the biaxially oriented polyester film according to any one of [1] to [5] above.

[0019] In order to solve the above problems, the present invention further has the following configuration. [7] A method for producing a biaxially oriented polyester film, comprising the steps of: mixing a polyethylene terephthalate resin containing 7,000 ppm by mass or more and 22,000 ppm by mass or less of first inorganic particles with a polyethylene terephthalate resin containing 0 to 50 ppm by mass of second inorganic particles, and melt-extruding the resulting polyester resin composition to contain 500 to 1,500 ppm by mass of inorganic particles; biaxially stretching the unstretched sheet to obtain a biaxially stretched film; and heat-setting the biaxially stretched film at a temperature of 200°C or more and 250°C or less, and then relaxing the biaxially stretched film by 2 to 10% in the width direction while decreasing the temperature to 200°C or less.

[0020] [8] A method for producing a biaxially oriented polyester film, comprising the steps of: mixing a polyethylene terephthalate resin containing 7,000 to 22,000 ppm by mass of first inorganic particles with a polyethylene terephthalate resin containing 0 to 50 ppm by mass of second inorganic particles to form a first polyester resin composition containing 500 to 1,500 ppm by mass; melting each of the first polyester resin composition and the second polyester resin composition; extruding the resulting mixture through a die to form a layer made of the first polyester resin composition / a layer made of the second polyester resin composition to obtain an unstretched sheet; biaxially stretching the unstretched sheet to obtain a biaxially stretched film; and heat-setting the biaxially stretched film at a temperature of 200°C to 250°C, and then relaxing the biaxially stretched film by 2 to 10% in the width direction while decreasing the temperature to 200°C or less. .

[0021] [9] a first polyester resin composition containing 7,000 to 22,000 ppm by mass of first inorganic particles and a second polyester resin composition containing 0 to 50 ppm by mass of second inorganic particles, the first polyester resin composition and the second polyester resin composition being mixed together to form an inorganic particle content of 500 to 1,500 ppm by mass; melting the resulting mixture and co-extruding the resulting mixture through a die to form an unstretched sheet having a structure of a layer made of the first polyester resin composition, a layer made of the second polyester resin composition, and a layer made of the first polyester resin composition; biaxially stretching the unstretched sheet to form a biaxially stretched film; and heat-setting the biaxially stretched film at a temperature of 200°C to 250°C, and then relaxing the film by 2 to 10% in the width direction while decreasing the temperature to 200°C or less.

[0022]

[10] a first polyester resin composition, a second polyester resin composition, and a third polyester resin composition, each containing 500 to 1500 ppm by mass of inorganic particles, are melted and co-extruded through a die to obtain an unstretched sheet having a structure consisting of a layer made of the first polyester resin composition, a layer made of the second polyester resin composition, and a layer made of the third polyester resin composition; a biaxially stretching step of biaxially stretching the unstretched sheet to obtain a biaxially stretched film; and a step of heat-setting the biaxially stretched film at a temperature of 200°C to 250°C, and then relaxing the biaxially stretched film by 2 to 10% in the width direction while decreasing the temperature to 200°C or less.

[0023]

[11] The method for producing a biaxially oriented polyester film according to any one of [7] to

[10] , wherein the step of biaxially stretching the unstretched sheet to obtain a biaxially oriented polyester film is a step of stretching the unstretched sheet in two stages in the machine direction and then stretching it in the transverse direction to obtain a biaxially oriented polyester film.

[0024]

[12] The method for producing a biaxially oriented polyester film according to any one of [7] to

[11] , wherein the first inorganic particles and the second inorganic particles are silica particles.

[0025]

[13] The method for producing a biaxially oriented polyester film according to

[12] , wherein the pore volume of the silica particles is 0.6 to 2.0 ml / g. [Effects of the Invention]

[0026] According to the present invention, it is possible to provide a biaxially oriented polyester film which has excellent mechanical properties, transparency and heat resistance, and is also excellent in suitability for secondary processing and print appearance. DETAILED DESCRIPTION OF THE INVENTION

[0027] The following describes embodiments of the present invention, but the present invention should not be construed as being limited to the embodiments including the following examples, and various modifications are naturally possible within the scope of achieving the object of the invention and not departing from the gist of the invention.

[0028] (Polyethylene terephthalate resin) The biaxially oriented polyester film of the present invention is composed of a polyethylene terephthalate resin. Here, the polyethylene terephthalate resin contains an ethylene glycol-derived component and a terephthalic acid-derived component as its main components. "Mainly" means that terephthalic acid accounts for 80 mol% or more of 100 mol% of all dicarboxylic acid components, and ethylene glycol accounts for 80 mol% or more of 100 mol% of all glycol components. Other dicarboxylic acid components and glycol components may be copolymerized within a range that does not impair the object of the present invention. The copolymerization amount of the other dicarboxylic acid components and glycol components is less than 20 mol %, preferably 10 mol % or less, and particularly preferably 5 mol % or less, based on the total dicarboxylic acid components or the total glycol components, respectively. Examples of the other dicarboxylic acid components include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphrenedicarboxylic acid, 4,4'-dicarboxybiphenyl, and 5-sodium sulfoisophthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 2,5-norbornenedicarboxylic acid, and tetrahydrophthalic acid; and aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, octadecanedioic acid, fumaric acid, maleic acid, itaconic acid, mesaconic acid, citraconic acid, and dimer acid.

[0029] Examples of the other glycol components include aliphatic glycols such as 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 2-amino-2-ethyl-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol, 1,10-decanediol, dimethyloltricyclodecane, diethylene glycol, and triethylene glycol; alicyclic glycols such as bisphenol A, bisphenol S, bisphenol C, bisphenol Z, bisphenol AP, ethylene oxide adducts or propylene oxide adducts of 4,4'-biphenol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol; polyethylene glycol; and polypropylene glycol.

[0030] As a polymerization method for such a polyethylene terephthalate-based resin, any production method can be used, such as a direct polymerization method in which terephthalic acid and ethylene glycol, and, if necessary, other dicarboxylic acid components and glycol components, are directly reacted, or an ester exchange method in which a dimethyl ester of terephthalic acid (containing a methyl ester of another dicarboxylic acid, if necessary) is subjected to an ester exchange reaction with ethylene glycol (containing another glycol component, if necessary).

[0031] The intrinsic viscosity of the polyethylene terephthalate resin is preferably in the range of 0.30 to 1.20 dL / g, more preferably 0.50 to 1.00 dL / g, and even more preferably 0.55 to 0.90 dL / g. If the intrinsic viscosity is lower than 0.30 dL / g, the polyester film becomes more prone to tearing. If the intrinsic viscosity is higher than 1.20 dL / g, the increase in filtration pressure becomes too great, making high-precision filtration difficult and making it difficult to extrude the resin through the filter. The intrinsic viscosity of the resin in the polyester film is preferably in the range of 0.30 to 1.20 dL / g, more preferably 0.45 to 0.95 dL / g, and even more preferably 0.50 to 0.85 dL / g. If the intrinsic viscosity is lower than 0.30 dL / g, the polyester film becomes more prone to tearing. If the intrinsic viscosity is higher than 1.20 dL / g, the effect of improving mechanical properties tends to become saturated.

[0032] The polyethylene terephthalate resin may be solution polymerized, then chipped, and further subjected to solid-phase polymerization under reduced pressure with heating or in an inert gas stream such as nitrogen, as required.

[0033] As the polyester resin, polyester resins obtained by recycling PET bottle products made of the above-mentioned polyethylene terephthalate resins or polyethylene terephthalate resins made from raw materials derived from biomass can also be used.

[0034] The biaxially oriented polyester film of the present invention may contain other resins such as polyamide, polystyrene, polyolefin, and polyesters other than those mentioned above as constituent components, but from the viewpoint of the mechanical properties and heat resistance of the biaxially oriented polyester film, the content of other resins is preferably 30% by mass or less, more preferably 20% by mass or less, or even 10% by mass or less, and particularly preferably 5% by mass or less, of the total resin components of the polyester film, and most preferably 0% by mass (all resin components constituting the polyester film are essentially polyethylene terephthalate-based resins).

[0035] (Inorganic particles) The biaxially oriented polyester film of the present invention contains inorganic particles as a constituent component. Examples of inorganic particles include calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, and mica. One or more of these particles may be selected and used.

[0036] Among these particles, amorphous silica particles are preferred because they have a refractive index relatively close to that of the resin component and are less likely to form voids around the particles, making it easier to obtain a highly transparent film. In particular, it is preferred that the inorganic particles consist solely of amorphous silica particles.

[0037] Furthermore, when one type of inorganic particle is used, or when two or more types are used, the average particle size of the inorganic particles that make up the main component is 0.5 to 3.0 μm, more preferably 0.8 to 2.8 μm, and even more preferably 1.5 to 2.5 μm. When the particle size is 0.5 μm or greater, it is easy to form surface irregularities, making it easier to achieve an arithmetic mean roughness (SRa) of 0.024 μm or greater on the film surface, and the film's slipperiness is less likely to decrease. On the other hand, when the particle size is 3.0 μm or less, it is easier to achieve a maximum peak height (SRp) of 1.6 μm or less on the film surface. The average particle size of the inorganic particles is measured using a laser diffraction particle size analyzer, model SALD-2200, manufactured by Shimadzu Corporation. The shape of the inorganic particles is not particularly limited, but from the viewpoint of providing easy slipperiness, inorganic particles that are nearly spherical are preferred.

[0038] Furthermore, when the inorganic particles are amorphous silica particles, aggregates of particles with an average primary particle size of 20 to 60 nm are preferred in terms of transparency. This is presumably because the surface layer can be made flat and stable by undergoing the stretching and heat setting steps in the film-forming process. The pore volume of the particle aggregates is preferably 0.6 to 2.0 ml / g, more preferably 1.0 to 1.9 ml / g, and even more preferably 1.2 to 1.8 ml / g. When the pore volume is 0.6 ml / g or more, it is easy to achieve a maximum protrusion height (SRp) of 1.6 μm or less on the film surface. On the other hand, when the pore volume is 2.0 ml / g or less, the inorganic particles do not crumble too much, and it is easy to achieve a maximum protrusion height (SRp) of 1.2 μm or more on the film surface. In addition, since voids are unlikely to form around the particles, it is easy to obtain a highly transparent film. The first inorganic particles and the second inorganic particles in the present invention may be the same or different, for example, they may have the same composition but differ in one or more of particle size, particle size distribution, and pore volume.

[0039] (additives) In addition to inorganic particles, the biaxially oriented polyester film of the present invention may contain one or more of various additives such as inert particles such as heat-resistant polymer particles and crosslinked polymer particles, fluorescent whitening agents, ultraviolet inhibitors, infrared absorbing dyes, heat stabilizers, electrostatic adhesion agents (pinning agents), surfactants, and antioxidants. Examples of antioxidants include aromatic amines, Phenol-based and other antioxidants can be used, and phosphorus-based stabilizers such as phosphoric acid and phosphate ester-based stabilizers, sulfur-based stabilizers, and amine-based stabilizers can be used. Additives other than these inorganic particles can be added to the polyester resin from which the film is formed preferably in a proportion of 3% by weight or less, more preferably 2% by weight or less, and even more preferably 1% by weight or less.

[0040] (Film manufacturing method) Examples of specific configurations of the biaxially oriented polyester film of the present invention will be described below, but the present invention should not be construed as being limited to these examples. It is important that the biaxially oriented polyester film of the present invention is composed of a mixture of a polyethylene terephthalate resin containing 7,000 to 22,000 ppm by mass of first inorganic particles and a polyethylene terephthalate resin containing 0 to 50 ppm by mass of second inorganic particles. The content of the first inorganic particles is preferably 7,000 to 19,000 ppm, more preferably 8,000 to 17,000 ppm, and particularly preferably 9,000 to 15,000 ppm. When the concentration of the first inorganic particles is less than 7,000 ppm, the proportion of the polyethylene terephthalate resin containing the first inorganic particles increases, but the maximum peak height (SRp) of the film surface is easily maintained at 1.2 μm or more without excessively increasing the arithmetic mean roughness (SRa) of the film surface. The proportion of the polyethylene terephthalate resin containing 0 to 50 ppm by mass of second inorganic particles decreases. If the concentration of the first inorganic particles is greater than 22,000 ppm, the maximum projection height (SRp) of the film surface is likely to exceed 1.6 μm.

[0041] The inorganic particle content in the biaxially oriented polyester film of the present invention is preferably 500 ppm to 1500 ppm, more preferably 700 ppm to 1200 ppm, and particularly preferably 850 ppm to 1000 ppm. If the inorganic particle content exceeds 1500 ppm, particle agglomerations increase, the maximum peak height (SRp) of the film surface is likely to exceed 1.6 μm, and printing defects are likely to occur. On the other hand, if the particle content is less than 500 ppm, the arithmetic mean roughness (SRa) of the film surface is likely to be less than 0.024, which is likely to deteriorate the handleability and roll appearance, such as reduced slip properties and increased wrinkles due to poor air release in the roll.

[0042] In the biaxially oriented polyester film of the present invention, the mixing ratio of the polyethylene terephthalate resin containing 7000 to 22000 ppm by mass of first inorganic particles to the polyethylene terephthalate resin containing 0 to 50 ppm by mass of second inorganic particles is preferably 65% ​​by weight or more, more preferably 75% by weight or more, even more preferably 85% by weight or more, and particularly preferably 90% by weight or more, of the polyethylene terephthalate resin containing 0 to 50 ppm by mass of second inorganic particles relative to the total amount of the mixture of the polyethylene terephthalate resin containing 7000 to 22000 ppm by mass of first inorganic particles and the polyethylene terephthalate resin containing 0 to 50 ppm by mass of second inorganic particles. The polyethylene terephthalate resin containing 0 to 50 mass ppm of second inorganic particles can contain a large amount of polyethylene terephthalate resin recycled from PET bottle products, polyethylene terephthalate resin obtained using biomass-derived raw materials, or polyethylene terephthalate resin containing additives as needed in the film, making it possible to make maximum use of these resins.

[0043] The biaxially oriented polyester film of the present invention may have a laminate structure of two layers, three layers, four or more layers, in addition to the single layer structure described above. When the biaxially oriented polyester film of the present invention has a two-layer structure, one layer is a polyethylene terephthalate film containing first inorganic particles in an amount of 7000 ppm by mass or more and 22000 ppm by mass or less. It is important that the first polyester resin composition is a mixture of a polyethylene terephthalate-based resin and a polyethylene terephthalate-based resin containing 0 to 50 mass ppm of second inorganic particles, and the content of the first inorganic particles is preferably 7,000 to 19,000 ppm, more preferably 8,000 to 17,000 ppm, and particularly preferably 9,000 to 15,000 ppm.

[0044] It is also important that the inorganic particle content in the one outermost layer be 500 ppm to 1500 ppm, preferably 700 ppm to 1200 ppm, and particularly preferably 850 ppm to 1000 ppm. If the inorganic particle content exceeds 1500 ppm, particle agglomerations increase, and the maximum peak height (SRp) of the surface of the one layer is likely to exceed 1.6 μm, resulting in printing defects. On the other hand, if the particle content is less than 500 ppm, the arithmetic mean roughness (SRa) of the film surface is likely to be less than 0.024, which can lead to poor handling and roll appearance, such as reduced slipperiness and increased wrinkles due to poor air release when rolling. The other layer is composed of polyethylene terephthalate resin, inorganic particles, and optionally additives, and resins other than polyethylene terephthalate resin, provided that it is not exactly the same as the one layer.

[0045] When the biaxially oriented polyester film of the present invention has a three-layer structure, it is important that one of the outermost layers is a first polyester resin composition consisting of a mixture of a polyethylene terephthalate resin containing 7,000 to 22,000 ppm by mass of first inorganic particles and a polyethylene terephthalate resin containing 0 to 50 ppm by mass of second inorganic particles, and the content of the first inorganic particles is preferably 7,000 to 19,000 ppm, more preferably 8,000 to 17,000 ppm, and particularly preferably 9,000 to 15,000 ppm.

[0046] It is also important that the inorganic particle content in the one outermost layer be 500 ppm to 1500 ppm, preferably 700 ppm to 1200 ppm, and particularly preferably 850 ppm to 1000 ppm. If the inorganic particle content exceeds 1500 ppm, particle agglomerations increase, and the maximum peak height (SRp) of the surface of the one layer is likely to exceed 1.6 μm, resulting in printing defects. On the other hand, if the particle content is less than 500 ppm, the arithmetic mean roughness (SRa) of the film surface is likely to be less than 0.028, which can lead to poor handling and roll appearance, such as reduced slipperiness and increased wrinkles due to poor air release when rolling. The other outermost layer contains polyethylene terephthalate resin, inorganic particles, and, if necessary, additives and resins other than polyethylene terephthalate resin as constituent components, and may be exactly the same as or different from the one of the layers.

[0047] The intermediate layer is composed of polyethylene terephthalate resin, inorganic particles, and optionally additives, and resins other than polyethylene terephthalate resin, but it need not be exactly the same as the one outermost layer. However, even if inorganic particles are not present, the surface roughness of the film can be controlled by controlling the amount of inorganic particles added only to one outermost layer, which is preferable because it allows the inorganic particle content of the entire film to be reduced. This is because it also improves the problem of odor components escaping through voids (gaps) formed at the boundary between the inorganic particles and the polyester resin, which reduces aroma retention. Furthermore, it is easy to use recycled materials from the edge portions generated during the film-making process or recycled materials from other film-making processes in the intermediate layer, as long as they do not adversely affect the properties of the film surface, which is also advantageous in terms of cost. It is preferable that the other outermost layer has the same composition as the one outermost layer, since this makes production easier.

[0048] When the biaxially oriented polyester film of the present invention has a four-layer structure, one of the outermost layers is It is important that the first polyester resin composition is a mixture of a polyethylene terephthalate resin containing 7,000 to 22,000 ppm by mass of first inorganic particles and a polyethylene terephthalate resin containing 0 to 50 ppm by mass of second inorganic particles, and the content of the first inorganic particles is preferably 7,000 to 19,000 ppm, more preferably 8,000 to 17,000 ppm, and particularly preferably 9,000 to 15,000 ppm.

[0049] It is also important that the inorganic particle content in the one outermost layer be 500 ppm to 1500 ppm, preferably 700 ppm to 1200 ppm, and particularly preferably 850 ppm to 1000 ppm. If the inorganic particle content exceeds 1500 ppm, particle agglomerations increase, and the maximum peak height (SRp) of the surface of the one layer is likely to exceed 1.6 μm, resulting in printing defects. On the other hand, if the particle content is less than 500 ppm, the arithmetic mean roughness (SRa) of the film surface is likely to be less than 0.024, which can lead to poor handling and roll appearance, such as reduced slipperiness and increased wrinkles due to poor air release when rolling. The other outermost layer contains polyethylene terephthalate resin, inorganic particles, and, if necessary, additives and resins other than polyethylene terephthalate resin as constituent components, and may be exactly the same as or different from the one of the layers.

[0050] The two middle layers are composed of polyethylene terephthalate resin, inorganic particles, and optionally additives, and resins other than polyethylene terephthalate resin, but they do not have to be exactly the same as the outermost layer. However, even if inorganic particles are not used, controlling the amount of inorganic particles added to only one of the outermost layers allows the surface roughness of the film to be controlled, and the inorganic particle content in the entire film can be reduced, which is preferable. This is because it also improves the problem of odor components escaping through voids (air gaps) that form at the boundary between the inorganic particles and the polyester resin, resulting in a decrease in aroma retention. Furthermore, it is easy to use recycled materials from the edge portions generated during the film-making process or recycled materials from other film-making processes in the intermediate layer, as long as they do not adversely affect the properties of the film surface, which is also advantageous in terms of cost. It is preferable that the other outermost layer has the same composition as the one outermost layer, since this makes production easier.

[0051] In the biaxially oriented polyester film of the present invention, the proportion of the polyethylene terephthalate resin containing 0 to 50 ppm of the second inorganic particles relative to the mixture of the polyethylene terephthalate resin containing 7,000 to 22,000 ppm of the first inorganic particles by mass and the polyethylene terephthalate resin containing 0 to 50 ppm of the second inorganic particles by mass is preferably 65% ​​by weight or more, more preferably 75% by weight or more, even more preferably 85% by weight or more, and particularly preferably 90% by weight or more. This allows the film to contain a large amount of inexpensive resin, recycled resin from PET bottles, biomass-derived resin, etc., making it possible to maximize the properties of the resin. However, when a polyethylene terephthalate resin containing a high concentration of inorganic particles is melt-extruded, the inorganic particles tend to aggregate, and large particle aggregates of inorganic particles tend to be formed.

[0052] As a method for incorporating inorganic particles into a polyethylene terephthalate-based resin, for example, inorganic particles are dispersed in a predetermined ratio in the form of a slurry in ethylene glycol, which is a diol component, and this ethylene glycol slurry is added at an arbitrary stage before the completion of polyester polymerization. When adding particles, it is preferable to add the aqueous sol or alcohol sol obtained during particle synthesis without first drying it, as this will result in good particle dispersibility and prevent the generation of coarse protrusions. Next, examples of specific methods for processing the biaxially oriented polyester film of the present invention into films will be described, but the present invention should not be construed as being limited to these examples.

[0053] Pellets of a polyethylene terephthalate resin containing 7,000 to 22,000 ppm by mass of first inorganic particles and a polyethylene terephthalate resin containing 0 to 50 ppm by mass of second inorganic particles are mixed in a predetermined ratio, fed into a vented twin-screw extruder, and melt-extruded. The extruder is preferably filled with a flowing nitrogen atmosphere and the resin temperature is controlled to 265 to 295°C. When the biaxially oriented polyester film of the present invention has a laminated structure of two, three, four or more layers, a multilayering device such as a multilayer feed block, a static mixer, or a multilayer multi-manifold can be used. For example, a method can be used in which thermoplastic resins discharged from different passages using two or more extruders are laminated into multiple layers using a feed block, a static mixer, a multi-manifold die, etc. It is also possible to use only one extruder and introduce the above-mentioned layering device into the melt line from the extruder to the T-die. From the viewpoint of stabilizing the back pressure and suppressing thickness fluctuations, a method in which a static mixer and a gear pump are installed in the polymer flow path is preferred.

[0054] The mixed resin composition is then melted and extruded while being filtered through a filter. Large foreign particles, such as gels formed by oxidation of the polyethylene terephthalate resin and aggregates of inorganic particles, can cause defects in the resulting film, so it is effective to use a filter with a precision that captures 95% or more of foreign particles of 25 μm or larger. Depending on the application of the film, even small foreign particles can be problematic, so it is desirable to use a high-precision filter that captures 95% or more of foreign particles of 10 μm or larger. Using a filter with a higher precision than this can significantly increase the pressure in the filter during extrusion of the molten mixed resin composition, increasing the frequency of filter replacement, which can be disadvantageous in terms of productivity and cost. The filter is not particularly limited, but in the case of a stainless steel sintered body, it is suitable for its excellent ability to remove not only foreign matter such as gel, but also aggregates mainly composed of Si, Ti, Sb, Ge, and Cu derived from additives such as catalysts. The filtration accuracy is preferably 100 μm or less, more preferably 80 μm or less, and particularly preferably 70 μm or less.

[0055] Subsequently, the molten mixed resin composition is extruded into a sheet form through a slit die onto a cooling roll, and is cooled and solidified on the cooling roll to produce an unstretched sheet. Furthermore, when cooling with a cooling roll, the unstretched sheet of the mixed resin composition is adhered to the surface of the cooling roll by a method such as an electrostatic application method in which an electrode to which a high voltage is applied is used to adhere the unstretched sheet of the mixed resin composition to the cooling roll by static electricity, and then cooled and solidified to obtain an unstretched sheet.

[0056] The biaxially oriented polyester film of the present invention is a biaxially oriented film from the viewpoints of the mechanical strength, thickness unevenness, and processing suitability of the film. Methods for stretching an unstretched sheet include simultaneous biaxial stretching and sequential biaxial stretching, but sequential biaxial stretching is preferred from the viewpoints of equipment cost, productivity, etc. The arithmetic mean roughness of the film surface can be prevented from becoming too high by adjusting the inorganic particle content in the film, but in order to prevent the maximum protrusion roughness of the film surface from becoming too high, it is effective to loosen the inorganic particle agglomerates by stress inside the film when stretching the unstretched sheet. When stretching an unstretched sheet, lowering the temperature or multi-stage stretching is effective in increasing the stress inside the film to break up particle agglomerates. If the stress inside the film is too high, the inorganic particles sink into the film, the arithmetic mean roughness decreases, and the film's slipperiness decreases. Furthermore, if the maximum protrusion roughness is too small, the air between the films in the film roll will It is difficult to remove the film, and wrinkles may occur in the film roll. Furthermore, stress increases the formation of voids originating from inorganic particles, which increases haze and odor leakage, so appropriate adjustment is required.

[0057] The obtained unstretched sheet was guided to longitudinal stretching and heated to 40 to 140° C. in the preheating step. At this time, it is desirable to gradually increase the temperature, since if it is heated too quickly, it will stick to the cooling roll. This is followed by the longitudinal stretching step. The longitudinal stretching method can be, but is not limited to, roll stretching or IR stretching. The film is heated to 100 to 140°C between two pairs of rolls operating at different speeds and stretched in the longitudinal direction by 3.6 to 5.0 times, more preferably 3.8 to 4.7 times, and particularly preferably 4.0 to 4.7 times to obtain a longitudinally stretched film. At this time, infrared heaters may be installed on both sides of the film in the middle of the nip rolls as auxiliary film heating devices, and the film may be heated as needed to adjust the longitudinal stretching temperature. Furthermore, the longitudinal stretching may be a one-stage or multi-stage stretching, such as a two-stage or three-stage stretching. In the case of two-stage drawing, the first stage is preferably drawn at a ratio of 1.1 to 3.2 times, and the second stage at a ratio of 1.1 to 3.2 times. In the case of three-stage drawing, the first stage is preferably drawn at a ratio of 1.1 to 1.5 times, the second stage at a ratio of 1.2 to 1.8 times, and the third stage at a ratio of 2.0 to 3.0 times.

[0058] By lowering the heating temperature of the film during the preheating and stretching processes of longitudinal stretching and stretching at a high ratio, inorganic particle aggregates caused by high stress inside the film can be loosened. Furthermore, by stretching while promoting oriented crystallization through multi-stage stretching, it is possible to further improve the internal structure of the film. However, if the stretching ratio is too high, the arithmetic mean roughness decreases and the film's slipperiness decreases. While increasing the stretching ratio improves mechanical strength, it is preferable to keep the longitudinal tensile strength of the resulting biaxially oriented polyester film to 300 MPa or less.

[0059] The obtained longitudinally stretched film may be subjected to a surface treatment such as corona treatment or plasma treatment as necessary, and then a coating liquid may be applied to one side of the film by a coating method to impart properties such as easy slippage, easy adhesion, and antistatic properties.

[0060] Next, both ends of the obtained longitudinally stretched film are gripped with clips and stretched in the transverse direction at 100 to 160°C by 3.9 to 5.0 times, more preferably 4.0 to 4.7 times, and particularly preferably 4.1 to 4.7 times to obtain a biaxially stretched film. As with the longitudinal stretching, a low transverse stretching temperature, a high stretching ratio, and multi-stage stretching can effectively loosen particles, but if the stretching ratio is too high, the arithmetic mean roughness decreases and the film's slipperiness decreases. While a high stretching ratio improves mechanical strength, it is preferable that the resulting biaxially oriented polyester film have a widthwise tensile strength of 300 MPa or less.

[0061] After transverse stretching, the biaxially stretched film is heat-treated. The heat treatment can be carried out by running the biaxially stretched film over heated rolls in an oven. This heat treatment is carried out at a temperature range of 120°C or higher and below the crystalline melting peak temperature of the polyethylene terephthalate resin. The heat treatment time is preferably in the range of 1.6 to 20 seconds. The highest temperature among the heat treatment temperatures is preferably a specific temperature within the temperature range of 200 to 250° C., more preferably 210 to 245° C., and particularly preferably 220 to 245° C. The treatment time at the highest temperature is preferably 0.8 to 10 seconds, more preferably 1 to 5 seconds.

[0062] Following the heat treatment at the maximum temperature, the film is laterally relaxed during the cooling process from the high temperature to the crystallization peak temperature, which also has the effect of breaking up aggregates of inorganic particles caused by stress inside the film. For example, the biaxially stretched film is treated at the highest temperature in the first half of the heat treatment process, and the temperature is Alternatively, the biaxially stretched film may be heat-treated at the highest temperature in the first stage, with the relaxation treatment being carried out while the temperature is being lowered in the second stage, and then heat-treated at a lower temperature in the third stage without relaxation. When lowering the temperature from the maximum temperature, it is desirable to lower the temperature gradually, preferably to a specific temperature within the temperature range of 120 to 210°C from the maximum temperature, more preferably to 130 to 200°C, and particularly preferably to 150 to 200°C.

[0063] The relaxation treatment is preferably 0.5 to 6.5% in the width direction, more preferably 1.0 to 6.0%. If the relaxation treatment is less than 0.5% in the width direction, the thermal dimensional stability, such as the thermal shrinkage rate, is poor, and misalignment and shrinkage during processing are likely to occur. In addition, the particle loosening effect described above is likely to be lost. On the other hand, if it exceeds 6.5%, sagging and other problems are likely to occur, resulting in thickness unevenness. The treatment time for the relaxation treatment is preferably 0.8 to 10 seconds, more preferably 1 to 5 seconds. If the treatment time for the relaxation treatment is less than 0.8 seconds, the film is likely to break. On the other hand, if the treatment time exceeds 10 seconds, sagging and other problems are likely to occur, resulting in thickness unevenness. By gradually lowering the heat treatment temperature after it reaches its maximum, deformation caused by rapid cooling can be suppressed, and this is also effective in reducing thickness unevenness and thermal distortion.

[0064] In the biaxially oriented polyester film of the present invention, a polyethylene terephthalate resin containing 7000 to 2200 ppm by mass of first inorganic particles and a polyethylene terephthalate resin containing 0 to 50 ppm by mass of second inorganic particles are mixed to form a resin composition containing 500 to 1500 ppm by mass of inorganic particles. The thickness of the layer made of this resin composition is preferably 0.5 to 30 μm, more preferably 0.5 to 20 μm, even more preferably 0.5 to 10 μm, and more preferably 0.5 to 8 μm. A layer thickness of 30 μm or less facilitates achieving an arithmetic mean roughness (SRa) of 0.024 μm or more on the surface of the film.

[0065] The total thickness of the biaxially oriented polyester film of the present invention is preferably 9 to 75 μm, more preferably 9 to 50 μm, and even more preferably 9 to 25 μm. When the total thickness of the film is 9 μm or more, the rigidity of the film can be easily increased and processing is facilitated. In addition, the film is less likely to wrinkle when rolled. When the total thickness of the film is 75 μm or less, the film is not too rigid and is less likely to wrinkle when rolled.

[0066] (Film characteristics) It is important that the biaxially oriented polyester film of the present invention and the surface of the layer made of a polyester resin composition containing 500 to 1500 ppm by mass of inorganic particles, which is obtained by mixing a polyethylene terephthalate resin containing 7000 to 22000 ppm by mass of first inorganic particles with a polyethylene terephthalate resin containing 0 to 50 ppm by mass of second inorganic particles, satisfy the following properties (1) and (2). (1) The maximum projection height (SRp) is 1.2 to 1.6 μm or less. (2) The arithmetic mean roughness (SRa) is 0.024 to 0.045 μm.

[0067] When the maximum projection height (SRp) is 1.2 μm or less, air can easily escape between the films when the film is wound into a film roll, making it less likely for wrinkles or streaks to form on the film roll. Furthermore, the film's slipperiness improves, facilitating secondary processing such as printing, which is likely to be advantageous in terms of quality and processing costs. When the maximum projection height (SRp) is 1.6 μm or less, there are fewer print voids and the print appearance is good, which is advantageous in terms of design, and it is less likely for misalignment to occur when rolled, making storage easier and likely improving production efficiency. The maximum projection height (SRp) is more preferably 1.2 to 1.5 μm or less, and even more preferably 1.2 to 1.4 μm. When the arithmetic mean roughness (SRa) is 0.024 μm or more, the film has improved slip properties. Secondary processing such as printing is easy to perform, which tends to be advantageous in terms of quality and processing costs. If the arithmetic mean roughness (SRa) is 0.045 μm or less, printing defects are reduced, the print appearance is good, and it is advantageous in terms of design. The arithmetic mean roughness (SRa) is more preferably 0.024 to 0.040 μm, and even more preferably 0.024 to 0.035 μm.

[0068] It is important that the biaxially oriented polyester film of the present invention satisfy the following properties (3) and (4) in addition to the above properties (1) and (2). (3) The tensile strength in the longitudinal and transverse directions is 180 to 300 MPa. (4) Haze is 7% or less. By appropriately controlling the tensile strength and haze, it is possible to further improve printability and print appearance.

[0069] When the tensile strength in the longitudinal and width directions is 180 MPa or more, the film is less likely to deform or break when tension is applied to the film, not only during printing processing, etc. The lower limits of the tensile strength in the longitudinal and width directions of the film are preferably 190 MPa or more, more preferably 200 MPa or more, and particularly preferably 210 MPa or more. If the tensile strength is 300 MPa or less, the stress during stretching of the unstretched sheet or longitudinally stretched film is likely to be kept from becoming too high, the inorganic particles are unlikely to sink into the film, the film surface roughness is likely to increase, and voids are unlikely to form around the inorganic particles in the film, making it easy to reduce haze. The tensile strength is preferably 290 MPa or less, more preferably 280 MPa or less, and particularly preferably 270 MPa or less.

[0070] When the film haze is 7% or less, the appearance of the print is improved, and even in high-speed processing, it becomes easier to detect foreign matter using X-rays or the like, making it easier to obtain sufficient quality. The film haze is preferably 6% or less, more preferably 5% or less, and particularly preferably 4% or less.

[0071] The film is dissolved in a 6 / 4 (weight ratio) mixed solvent of phenol / 1,1,2,2-tetrachloroethane, and the intrinsic viscosity (IV) measured at a temperature of 30°C is preferably in the range of 0.5 to 0·7 (g / dl).

[0072] The contact angle measured on the film surface using a DropMaster 500 manufactured by Kyowa Interface Science Co., Ltd., in an environment of 20°C and 50% RH, by extruding 2 μL of diiodomethane from a needle with an outer diameter of 0.7 mm onto the measurement surface of the film (the measurement was performed 10 times at different positions and the average value was calculated), is preferably 29° or less, more preferably 28° or less, and even more preferably 27° or less. If the contact angle on the film surface is 29° or less, printing ink loss tends to be reduced under 5% halftone dot conditions.

[0073] The air release time measured by the method described in the examples is preferably 14 seconds or less, more preferably 13 seconds or less, and even more preferably 12 seconds or less. When the air release time is 14 seconds or less, the air is released quickly when the film is wound into a film roll, and wrinkles are less likely to occur and there is less slippage when the film is wound.

[0074] When the produced biaxially oriented polyester film is wound up to a width of 800 mm and a length of 12,000 m, the surface of the roll is visually evaluated to have slight wrinkles. However, applying a tension of about 20 N / m to the unwound film will preferably remove the wrinkles, and it is preferable that there are no wrinkles at all.

[0075] In the printing evaluation performed by the method described in the examples, the number of ink dots printed was 100%. It is preferred that the clear printed dots be 95% or more, and more preferably 98% or more.

[0076] It is preferable that the proportion of polyethylene terephthalate resin containing 0 to 50 mass ppm of inorganic particles is 80% by weight or more, since this enhances the environmental friendliness of recycled polyester resin from PET bottle products and polyester resin made from biomass-derived raw materials. The proportion is more preferably 80% by weight or more, even more preferably 85% by weight or more, and particularly preferably 90% by weight or more. [Example]

[0077] (1) Composition of polyethylene terephthalate resin Polyethylene terephthalate resins and films can be dissolved in hexafluoroisopropanol (HFIP) and the content of each monomer residue component and by-product diethylene glycol can be quantified using 1H-NMR and 13C-NMR. In the case of laminated films, each layer of the film can be scraped off depending on the laminate thickness, allowing the components that make up each layer to be sampled and evaluated.

[0078] (2) Intrinsic viscosity (IV) of polyethylene terephthalate resin Polyethylene terephthalate resin was dissolved in a 6 / 4 (weight ratio) mixed solvent of phenol / 1,1,2,2-tetrachloroethane, and the measurement was carried out at a temperature of 30°C.

[0079] (3) Glass transition temperature (Tg) and melting point (Tm) of polyethylene terephthalate resin Measurement was performed using a differential scanning calorimeter (DSC) manufactured by SII, with a sample weight of 10 mg and a heating rate of 20°C / min. The glass transition onset temperature obtained from the DSC curve was taken as the glass transition temperature, and the melting endothermic peak temperature was taken as the melting point.

[0080] (4) Film thickness, layer thickness The film was embedded in epoxy resin, and the cross section of the film was cut out with a microtome. The cross section was observed with a transmission electron microscope (JEM2100 manufactured by JEOL Ltd.) to determine the thickness of the film and the thickness of the polyester layer.

[0081] (5) Inorganic particle content in each film layer The layer to be measured was scraped off from the film, 0.9 g of which was added to 1.0 liter of 0-chlorophenol and heated at 120°C for 3 hours, then centrifuged at 30,000 rpm for 40 minutes, and the resulting particles were vacuum dried at 100°C. When the microparticles were measured using DSC, if a dissolution peak corresponding to the polymer was observed, 0-chlorophenol was added to the microparticles, and after heating and cooling, the particles were centrifuged again. When the dissolution peak was no longer observed, the microparticles were considered to be particles. Usually, two centrifugation steps are sufficient. The ratio (ppm) of the obtained particles to the total weight was taken as the inorganic particle content.

[0082] (6) Content of inorganic particles in all layers of the film The polyester film was analyzed using a fluorescent X-ray analyzer (Rigaku Corporation, Supermini 200 model) using a previously prepared calibration curve.

[0083] (7) Hayes Measurement was carried out at 23° C. in accordance with JIS K 7105. Measurement was carried out using a haze meter (300A, manufactured by Nippon Denshoku Industries Co., Ltd.) The measurement was carried out twice, and the average value was calculated.

[0084] (8) Tensile strength of film Measurement was performed in accordance with JIS K 7127. The film was measured in a 10 mm width in the longitudinal and transverse directions. A 180 mm long sample was cut out using a razor. After leaving it in an atmosphere of 23°C and 65% RH for 12 hours, measurements were taken under conditions of 23°C and 65% RH, with a chuck distance of 100 mm and a pulling speed of 200 mm / min. The average value of five measurement results was used. The measurement device used was an Autograph AG5000A manufactured by Shimadzu Corporation.

[0085] (9) Static friction coefficient (μs) The resulting film was cut into a 400mm x 100mm area to create a sample film. This was then aged for 12 hours at 23°C and 65% RH. The sample was divided into a 300mm x 100mm slide and a 100mm x 100mm slide. The slide was set on the slide, and the load was attached with tape to the metal surface of the 1.5kg load, with the opposite sides in contact. The static friction coefficient (μs) was measured at a pulling speed of 200mm / min, 23°C, and 65% RH, and the average of three measurements was calculated. The measurements were performed using a Tensilon RTG-1210 (AND Corporation) and calculated in accordance with JIS-7125. The static friction coefficient of the film is preferably 0.15 to 0.8, more preferably 0.2 to 0.7, and even more preferably 0.25 to 0.7. If the friction coefficient is less than 0.15, the film may be too slippery to maintain a rolled state, or may slip when unwound during printing, resulting in poor processability. If the static friction coefficient is higher than 0.8, defects such as wrinkles on the roll and scratches on the metal roll may occur.

[0086] (10) SRa and SRp of the film surface The surface roughness of the film was measured by the following method. Confocal observation equipment: Scanning confocal laser microscope (Olympus LEXT) Laser type: 405nm semiconductor laser Objective lens: 50x magnification Shooting mode: High precision Confocal images of the measurement surface were captured using the above equipment and conditions. Surface Roughness Analysis Measurement range: 256μm x 256μm Analysis software: OLS4100 No cutoff Surface roughness analysis was performed under the above conditions, and the arithmetic mean roughness (SRa) and maximum protrusion height (SRp) were measured. Measurements were performed 10 times at different measurement positions, and the average values ​​were calculated. However, if partial abnormalities such as scratches or foreign matter were clearly visible in the image, they were not included in the measurement, and the measurement was repeated, avoiding the abnormal areas.

[0087] (11) Wetting tension of film surface Using a DropMaster500 manufactured by Kyowa Interface Science Co., Ltd., 2 μL of diiodomethane was extruded onto the film surface from a needle with an outer diameter of 0.7 mm at 20°C and 50% RH to measure the contact angle. The measurement was performed 10 times at different positions, and the average value was calculated.

[0088] (12) Air release time As shown in Figure 1, film 4 is placed on base plate 1. Next, film holder 2 is placed on top of film 4 and fixed in place, applying tension to film 4. Next, film 5 is placed on top of film holder 2, with the side opposite the top surface of film 4 placed on base plate 1 facing downwards. Next, film holder 8 is placed on top of film 5, and screws 3 are used to secure film holders 8 and 2 to base plate 1. Next, the cavity 2a in the film holder 2 is connected to the vacuum pump 6 via the small holes 2c in the film holder 2 and the pipe 7. When the vacuum pump 6 is driven, the film 5 is sucked into the cavity 2a, and tension is applied to the film 5. At the same time, the overlapping surfaces of the films 4 and 5 are also sucked into the small holes 2c formed in the film holder 2 in a circumferential shape. The pressure is reduced via d, and the films 4 and 5 begin to adhere to each other from the outer periphery at their overlapping surfaces. The state of adhesion can be easily determined by observing the interference fringes from above the overlapping surfaces. The time (seconds) from when interference fringes appear on the periphery of the overlapping surfaces of films 4 and 5 to when they spread to the front of the overlapping surfaces and stop moving is measured, and this time (seconds) is taken as the air release time. The measurement is repeated five times by replacing the two films, and the average value is used. In other words, the shorter the time (seconds), the better the film's winding characteristics.

[0089] (13) Wrinkle evaluation of film roll The biaxially oriented polyester film thus produced was wound up to a width of 800 mm and a length of 12,000 m, and the wrinkles on the surface of the roll were visually evaluated according to the following criteria. ◯ and △ were judged to be pass. ○: No wrinkles △: There are slight wrinkles, but the wrinkles disappear when a tension of about 20 N / m is applied to the pulled-out film. ×: There are strong wrinkles, and the wrinkles do not disappear even when a tension of about 20 N / m is applied to the pulled-out film.

[0090] (14) Printing evaluation Gravure printing was performed on the film using a gravure printing machine (manufactured by Higashiya Iron Works Co., Ltd.) at a speed of 100 m / min with a halftone dot density of 5%. The ink used was gravure printing ink (manufactured by Toyo Ink Co., Ltd.: product name Finestar R92 ink) mixed with a dilution solvent (manufactured by Toyo Ink Co., Ltd.: product name SL302) in a ratio of 77:23. The resulting printed sample was observed under an optical microscope and evaluated according to the following criteria within an area of ​​2 cm length x 2 cm width. The evaluation was based on the average of the results from five different positions. A rating of ○ or △ was considered pass.

[0091] ○: 95% or more of the total ink dots are painted cleanly △: Less than 90-95% of the total ink dots are clean. ×: Less than 90% of the total ink dots are cleanly applied

[0092] (15) Ratio of polyethylene terephthalate resin containing 0 to 50 mass ppm of inorganic particles The environmental friendliness is enhanced by using a high ratio of recycled polyester resin from PET bottle products and polyester resin made from biomass-derived raw materials in a polyethylene terephthalate resin containing 0 to 50 mass ppm of inorganic particles.Environmental friendliness was evaluated based on the ratio of use.

[0093] 1: Use ratio of 90% by weight or more, excellent 2: Use ratio of 85% by weight or more, excellent 3: Use ratio of 80% by weight or more, good 4: Usage ratio of 70% by weight or more, acceptable 5: Usage ratio of 65% by weight or more, not allowed 6: Usage ratio less than 65% by weight, defective

[0094] (Production of polyethylene terephthalate resin) The polyethylene terephthalate resin used for film formation was prepared as follows. (Polyethylene terephthalate resin 1) Magnesium acetate tetrahydrate was added to a mixture of terephthalic acid and ethylene glycol, and the esterification reaction was carried out at atmospheric pressure and a temperature of 255°C. Antimony trioxide and trimethyl phosphate were then added, and the reaction was further carried out at a temperature of 260°C. Subsequently, the reaction product was transferred to a polycondensation reaction tank. The reaction system was gradually depressurized while being heated and polycondensation was carried out at 280°C under a reduced pressure of 133 Pa (1 mmHg) by conventional methods, yielding polyester chips with an IV of 0.62 dl / g. This is designated polyethylene terephthalate resin 1. The composition of the resulting polyethylene terephthalate resin 1 was terephthalic acid component / isophthalic acid component / ethylene glycol component / diethylene glycol component = 100 / 0 / / 98 / 2 (mol%), with a glass transition temperature of 80°C and a melting point of 255°C.

[0095] (Polyethylene terephthalate resin 2) After washing away residual beverage and other impurities from PET beverage bottles, the resulting flakes were crushed and melted in an extruder. The resulting flakes were filtered twice using successively smaller mesh filters to remove finer impurities, and then filtered a third time using a filter with the smallest mesh size (50 μm), yielding recycled polyester material with an IV of 0.70 dL / g. This is designated polyethylene terephthalate resin 2. The resulting polyethylene terephthalate resin 2 had a composition of terephthalic acid component / isophthalic acid component / ethylene glycol component / diethylene glycol component = 98 / 2 / / 98 / 2 (mol%), a glass transition temperature of 76°C, and a melting point of 252°C.

[0096] (Polyethylene terephthalate resin 3) Polyester chips with an IV of 0.62 dL / g were obtained using the same method as for polyethylene terephthalate resin 1, except that ethylene glycol extracted from a plant source was used. This is designated polyethylene terephthalate resin 3. The composition of the obtained polyethylene terephthalate resin 3 was terephthalic acid component / isophthalic acid component / ethylene glycol component / diethylene glycol component = 100 / 0 / / 98 / 2 (mol %), with a glass transition temperature of 80°C and a melting point of 255°C. The biomass content of this polyester 3 was measured according to ASTM D6866 and was found to be 17%.

[0097] (Polyethylene terephthalate resin containing inorganic particles) (Polyethylene terephthalate resin containing inorganic particles 1) When preparing the polyethylene terephthalate resin 1, an ethylene glycol slurry of amorphous silica particles (manufactured by Fuji Silysia Chemical Ltd., product name: Sylysia 310) with an average particle size of 2.4 μm and a pore volume of 1.6 ml / g was added to a polycondensation reaction tank so that the silica concentration was 7,200 ppm in the polyethylene terephthalate resin 1, and then polycondensation was carried out to obtain polyester chips with an IV of 0.62. This is designated polyethylene terephthalate resin 1 containing inorganic particles.

[0098] (Polyethylene terephthalate resin containing inorganic particles 2) Polyester chips with an IV of 0.62 were obtained under the same conditions as in polyethylene terephthalate resin 1 containing inorganic particles, except that silica was added to the polyester to a concentration of 1500 ppm. This is designated polyethylene terephthalate resin 2 containing inorganic particles.

[0099] (Polyethylene terephthalate resin containing inorganic particles 3) Polyester chips with an IV of 0.62 were obtained under the same conditions as in polyethylene terephthalate resin 1 containing inorganic particles, except that silica was added to polyethylene terephthalate resin 1 so that the concentration was 12,000 ppm. This is designated polyethylene terephthalate resin 3 containing inorganic particles.

[0100] (Polyethylene terephthalate resin containing inorganic particles 4) The same procedure was carried out under the same conditions except that silica was added to the polyethylene terephthalate resin 1 containing inorganic particles so that the content was 20,000 ppm in the polyethylene terephthalate resin 1, and polyester chips with an IV of 0.62 were obtained. Phthalate resin 4.

[0101] (Polyethylene terephthalate resin containing inorganic particles 5) Polyester chips with an IV of 0.62 were obtained under the same conditions as in polyethylene terephthalate resin 1 containing inorganic particles, except that silica was added to polyethylene terephthalate resin 1 so that the content was 23,000 ppm. This is designated polyethylene terephthalate resin 5 containing inorganic particles.

[0102] (Polyester resin containing additives) (Polyethylene terephthalate resin containing additives 1) 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 (0.025 parts by mass) and triethylamine (0.16 parts by mass) were added as catalysts. The temperature was then increased, 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 (0.34 parts by mass) was added as an electrostatic adhesive, followed by trimethyl phosphate (0.042 parts by mass). The temperature was then raised to 260°C over 15 minutes, after which trimethyl phosphate (0.036 parts by mass) and sodium acetate (0.0036 parts by mass) were added. The resulting esterification reaction product was transferred to a polycondensation reactor, where the temperature was gradually increased from 260°C to 280°C under reduced pressure, and the polycondensation reaction was carried out at 285°C. After the polycondensation reaction was completed, the mixture was filtered through a sintered stainless steel filter with a pore size of 5 μm (initial filtration efficiency of 95%), and the resulting polycondensation reaction product was pelletized. This was designated as polyethylene terephthalate resin 1 containing additives.

[0103] Example 1 The raw materials used were a mixture of polyethylene terephthalate resin 1 / polyethylene terephthalate resin containing inorganic particles / polyethylene terephthalate resin containing additives = 76.5 / 12.5 / 11.0 (mass%) for the surface layer (A), and polyethylene terephthalate resin 1 / polyethylene terephthalate resin containing inorganic particles / polyethylene terephthalate resin containing additives = 84.1 / 4.9 / 11.0 (mass%) for the base layer (B). Two melt extruders were used, and the first extruder melt-extruded the mixed resin forming the surface layer (A) at a resin temperature of 285 °C, and the second extruder melt-extruded the mixed resin forming the base layer (B) at a resin temperature of 285 °C. Each extruder used a filter that captured more than 95% of foreign matter larger than 25 μm. The layers were laminated in a T-die in the order of surface layer (A) / base layer (B) / surface layer (A) from the side contacting the chill roll so that the thickness ratio was 1 / 10 / 1 (μm), and then extruded into a sheet onto a chill roll whose temperature was controlled at 35° C. At this time, static electricity was applied using a wire electrode with a diameter of 0.15 mm, and the film was adhered to the chill roll to obtain a three-layer unstretched film.

[0104] The unstretched film obtained was sent to a longitudinal stretching preheating process. In the longitudinal stretching preheating process, the film was preheated using a group of rolls whose roll temperatures were gradually increased from 70 to 134°C. The film was then stretched in the longitudinal direction by 1.2 times between two pairs of nip rolls heated to 134°C and operating at different speeds. Using the same method, the film was stretched in the longitudinal direction by 1.5 times in the second stage and 2.5 times in the third stage, for a total stretching of 4.5 times. Next, in a tenter-type transverse stretching machine, the film was stretched 4.3 times in a zone where the temperature was gradually increased from 143 to 154°C. Thereafter, heat treatment by heat setting was performed in two separate parts: the first half, where the temperature was 245°C and the film was heat-treated for 1.5 seconds; the second half, where the temperature was gradually decreased from 227 to 150°C, was used to perform heat treatment for 2.3 seconds. In this second half of the heat treatment, a 4.4% relaxation treatment was performed in the width direction. The film was then cooled to room temperature, approximately 23°C. Thus, a biaxially oriented polyester film with a film thickness of 12 μm was obtained. The film was evaluated on the layer A on the side that came into contact with the cooling roll.

[0105] Example 2 A biaxially oriented polyester film having a film thickness of 12 μm was obtained in the same manner as in Example 1, except that the raw materials for the surface layer (A) were mixed so that polyethylene terephthalate resin 1 / polyethylene terephthalate resin containing inorganic particles 1 / polyethylene terephthalate resin containing additives 1 = 80.7 / 8.3 / 11.0 (mass%). Evaluation was performed in the same manner as in Example 1.

[0106] Example 3 A biaxially oriented polyester film having a film thickness of 12 μm was obtained in the same manner as in Example 1, except that the raw materials for the surface layer (A) were mixed so that the ratio of polyethylene terephthalate resin 1 / polyethylene terephthalate resin containing inorganic particles 1 / polyethylene terephthalate resin containing additives was 72.3 / 16.7 / 11.0 (mass%). Evaluation was performed in the same manner as in Example 1.

[0107] Example 4 A biaxially oriented polyester film having a film thickness of 16 μm was obtained in the same manner as in Example 1, except that the thickness of the base layer (B) was changed to 14 μm, the heat treatment temperature in the first half of the heat setting was changed to 242°C, and the treatment time was changed to 2 seconds in the first half and 3 seconds in the second half. It was evaluated in the same manner as in Example 1.

[0108] Example 5 As raw materials, a polyethylene terephthalate resin 1 / polyethylene terephthalate resin 3 containing inorganic particles / polyethylene terephthalate resin containing additives was used as the surface layer (A) in a ratio of 181.5 / 7.5 / 11.0 (mass%), and a polyethylene terephthalate resin 1 / polyethylene terephthalate resin 3 containing inorganic particles / polyethylene terephthalate resin 1 containing additives was used as the base layer (B) in a ratio of 86.1 / 2.9 / 11.0 (mass%). A biaxially oriented polyester film having a film thickness of 12 μm was obtained in the same manner as in Example 1. Evaluation was performed in the same manner as in Example 1.

[0109] Example 6 As raw materials, the base layer (B) was made of the same polyethylene terephthalate resin 2 / polyethylene terephthalate resin containing inorganic particles 1 / polyethylene terephthalate resin containing additives 1 = 86.3 / 10.0 / 3.7 (mass%) as the surface layer (A), with a one-type, three-layer structure, and the film-forming conditions were changed as shown in Table 1. A biaxially oriented polyester film with a film thickness of 12 μm was obtained in the same manner as in Example 1. The preheating temperature before longitudinal stretching was kept constant at 75°C, and the longitudinal stretching was performed as a two-stage stretching by IR. Evaluation was performed in the same manner as in Example 1.

[0110] Example 7 As raw materials, the surface layer (A) was made up of polyethylene terephthalate resin 3 / polyethylene terephthalate resin 1 containing inorganic particles / polyethylene terephthalate resin 1 containing additives = 85.0 / 10.4 / 4.6 (mass%), and the base layer (B) was made up of polyethylene terephthalate resin 3 / polyethylene terephthalate resin 1 containing inorganic particles / polyethylene terephthalate resin 1 containing additives = 93.6 / 1.4 / 5.0 (mass%). They were mixed and laminated in a T-die to a thickness ratio of 3 / 6 / 3 (μm). Except for changing the film production conditions as shown in Table 1, a biaxially oriented polyester film with a film thickness of 12 μm was obtained in the same manner as in Example 1. Note that the longitudinal stretching was performed using two-stage stretching with rolls. Evaluation was performed in the same manner as in Example 1.

[0111] (Comparative Example 1) As raw materials, the surface layer (A) is made of polyethylene terephthalate resin 1 / polyethylene terephthalate resin containing inorganic particles. A biaxially oriented polyester film having a film thickness of 12 μm was obtained in the same manner as in Example 1, except that the polyethylene terephthalate resin 1 / polyethylene terephthalate resin containing additive 1 were mixed so as to be 82.7 / 6.3 / 11.0 (mass %). Evaluation was performed in the same manner as in Example 1.

[0112] (Comparative Example 2) A biaxially oriented polyester film having a film thickness of 12 μm was obtained in the same manner as in Example 1, except that the raw materials for the surface layer (A) were mixed so that the ratio of polyethylene terephthalate resin 1 / polyethylene terephthalate resin containing inorganic particles 1 / polyethylene terephthalate resin containing additives was 66.8 / 22.2 / 11.0 (mass%). Evaluation was performed in the same manner as in Example 1.

[0113] (Comparative Example 3) As raw materials, the surface layer (A) was polyethylene terephthalate resin 3 / polyethylene terephthalate resin 1 containing inorganic particles / polyethylene terephthalate resin 1 containing additives = 84.6 / 10.4 / 5.0 (mass%), and the base layer (B) was polyethylene terephthalate resin 3 / polyethylene terephthalate resin 1 containing inorganic particles / polyethylene terephthalate resin 1 containing additives = 84.5 / 12.5 / 5.0 (mass%). Two types of two-layer film, surface layer (A) / base layer (A'), were laminated together in a T-die to a thickness ratio of 11 / 1 (μm) from the chill roll contact side. A biaxially oriented polyester film with a film thickness of 12 μm was obtained in the same manner as in Example 1, except that the film production conditions were changed as shown in Table 1. The preheating temperature before longitudinal stretching was constant at 78 ° C, and the longitudinal stretching was one-stage stretching by IR. Evaluation was performed in the same manner as in Example 1.

[0114] Comparative Example 4 As raw materials, a polyethylene terephthalate resin 1 / polyethylene terephthalate resin 5 containing inorganic particles / polyethylene terephthalate resin 1 containing additives = 85.1 / 3.9 / 11.0 (mass%) was used for the surface layer (A), and a polyethylene terephthalate resin 1 / polyethylene terephthalate resin 5 containing inorganic particles / polyethylene terephthalate resin 1 containing additives = 87.5 / 1.5 / 11.0 (mass%) was used for the base layer (B). A biaxially oriented polyester film with a film thickness of 12 μm was obtained in the same manner as in Example 1. Evaluation was performed in the same manner as in Example 1.

[0115] (Comparative Example 5) A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1, except that the film-forming conditions were changed as shown in Table 1.

[0116] (Comparative Example 6) As raw materials, the surface layer (A) was polyethylene terephthalate resin 1 / polyethylene terephthalate resin 2 containing inorganic particles / polyethylene terephthalate resin 1 containing additives = 29.0 / 60.0 / 11.0 (mass%), and the base layer (B) was polyethylene terephthalate resin 1 / polyethylene terephthalate resin 2 containing inorganic particles / polyethylene terephthalate resin 1 containing additives = 65.7 / 23.3 / 11.0 (mass%). Further, except for changing the film formation conditions as shown in Table 1, a biaxially oriented polyester film with a film thickness of 12 μm was obtained in the same manner as in Example 1. Note that the preheating temperature before longitudinal stretching was constant at 78 ° C, and the longitudinal stretching was one-stage stretching by IR. Evaluation was performed in the same manner as in Example 1.

[0117] (Comparative Example 7) As raw materials, the base layer (B) uses the same polyethylene terephthalate resin 1 / polyethylene terephthalate resin containing inorganic particles 3 = 95.0 / 5.0 (mass%) as the surface layer (A). A biaxially oriented polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1, except that a single-type, three-layer structure was used and the film-forming conditions were changed as shown in Table 1. The preheating temperature before longitudinal stretching was constant at 100°C, and the one-stage longitudinal stretching using rolls and the latter half of the heat treatment in heat setting were constant at 200°C. Evaluation was performed in the same manner as in Example 1.

[0118] (Comparative Example 8) As raw materials, a mixture of polyethylene terephthalate resin 1 / polyethylene terephthalate resin containing inorganic particles 4 was used for the surface layer (A) at a ratio of 96.0 / 4.0 (mass%), and these were laminated in a T-die to a thickness ratio of 2 / 16 / 2 (μm). A biaxially oriented polyester film with a film thickness of 20 μm was obtained in the same manner as in Example 1, except that the film production conditions were changed as shown in Table 1. The preheating temperature before longitudinal stretching was constant at 100°C, and longitudinal stretching was one-stage stretching using rolls. Heat treatment in heat setting was constant at 200°C in the first half and 220°C in the second half, and relaxation treatment was performed in the first and second half of the heat treatment. Evaluation was performed in the same manner as in Example 1.

[0119] As shown in the results in Table 1, Examples 1 to 7 were good in the roll wrinkle evaluation and print evaluation, and the polyester resin, which is the main raw material, was added at a ratio of 80% or more, which effectively exhibited the resin properties.

[0120] The results for Comparative Examples 1 to 8 are as shown in Table 2. In Comparative Example 1, the inorganic particle concentration in layer A was low, so both SRa and SRp were low, the deairing time was long, and strong wrinkles occurred on the roll.

[0121] In Comparative Example 2, the concentration of inorganic particles in the surface A layer was high, so that both SRa and SRp were high, the contact angle was high, and the print evaluation was poor.

[0122] In Comparative Example 3, even though the inorganic particle concentration was within the range, both SRa and SRp were high, the contact angle was high, and the print evaluation was poor. The reasons for this are speculation, but it is thought that the thick surface A layer caused particles inside the film to affect the surface irregularities and make it prone to becoming rough, and that the longitudinal stretching was performed in one stage and the temperature of the relaxation treatment was high, which resulted in insufficient particle loosening.

[0123] In Comparative Example 4, the concentration of inorganic particles in the masterbatch was too high, which resulted in increased SRp due to large protrusions, and the print evaluation was poor.

[0124] In Comparative Example 5, the longitudinal and transverse stretching temperatures were low and the stretching ratio was high, resulting in excessive stress, causing the inorganic particles on the surface to sink into the film, resulting in low SRa and SRp. As a result, the film did not vent properly, causing wrinkles on the roll. In addition, many voids originating from the inorganic particles were formed inside the film, resulting in high haze.

[0125] In Comparative Example 6, the inorganic particle concentration in the masterbatch was lowered, longitudinal stretching was performed in one stage, and the temperature of the relaxation treatment was increased, thereby reducing the effect of loosening the particles. However, this resulted in fewer coarse protrusions, a lower SRp, and a poor de-airing time, which is thought to have resulted in a poor wrinkle evaluation using a roll. In addition, the proportion of the polyethylene terephthalate resin, which is the main raw material, was low, so the resin properties could not be effectively obtained.

[0126] In Comparative Example 7, the inorganic particle concentration in the masterbatch was high, and longitudinal stretching was performed using a single-stage roll at a relatively low magnification, which is thought to have resulted in insufficient loosening of the inorganic particles and large protrusions, resulting in a poor print evaluation. Furthermore, perhaps due to the large thickness, the haze was also high.

[0127] In Comparative Example 8, the longitudinal and transverse stretching ratios were low, the longitudinal stretching was performed using one roll, and the temperature of the relaxation treatment was high, so the loosening effect was insufficient and large protrusions were formed, resulting in a poor print evaluation. The tensile strength in the direction was insufficient.

[0128] [Table 1]

[0129] [Table 2] [Industrial Applicability]

[0130] The present invention provides a biaxially oriented polyester film that has excellent mechanical properties, transparency, and heat resistance, as well as excellent suitability for secondary processing and print appearance, a method for producing the same, and a film roll obtained by winding up the biaxially oriented polyester film. This is useful in the field of industrial films, and particularly in the field of packaging films for food packaging and gas barrier film applications, and since it is possible to increase the blending ratio of inexpensive resins, recycled resins, biomass resins, etc., it becomes possible to effectively obtain the properties of the resin. In particular, as there is a strong desire these days to reduce the environmental impact, the present invention is one effective means of responding to this need and is believed to be of great value.

Claims

1. A biaxially oriented polyester film having a single layer or a laminate structure, wherein at least an outermost layer of the single layer or the laminate structure is composed of a composition containing, as constituent components, a polyethylene terephthalate resin containing 98 mol% or more of terephthalic acid in 100 mol% of dicarboxylic acid components and 98 mol% or more of ethylene glycol in 100 mol% of glycol components, and inorganic particles having an average particle size of 0.5 to 3.0 μm, and both outermost layers are composed of the same composition, and the content of inorganic particles in the composition constituting the single layer or both outermost layers is 500 ppm or more and 1500 ppm or less, A biaxially oriented polyester film, at least one of the film surfaces of which satisfies the following (1) and (2), and the film itself satisfies the following (3) to (5). (1) The maximum protrusion height (SRp) is 1.2 to 1.6 μm. (2) The arithmetic mean roughness (SRa) is 0.024 to 0.045 μm. (3) The tensile strength in the longitudinal and transverse directions is 180 to 300 MPa. (4) The haze is 7% or less. (5) The thickness of the film is 9 to 75 μm.

2. 2. The biaxially oriented polyester film according to claim 1, wherein the polyethylene terephthalate-based resin comprises a recycled polyester resin from PET bottle products and / or a polyester resin using biomass-derived raw materials.

3. 3. The biaxially oriented polyester film according to claim 1, wherein the film surface satisfies the conditions (1) and (2) and has a diiodomethane contact angle of 29° or less.

4. 4. The biaxially oriented polyester film according to claim 1, wherein the inorganic particles are silica particles.

5. 5. The biaxially oriented polyester film for packaging according to claim 4, wherein the pore volume of the silica particles is 0.6 to 2.0 ml / g.

6. A film roll obtained by winding up the biaxially oriented polyester film according to any one of claims 1 to 5.

Images