Biaxially oriented polyester film, laminate stack, packaging, and top seal member

Abstract

The purpose of the present invention is to provide a biaxially oriented polyester film that is excellent in terms of non-slipperiness of the film surface, transparency, and windability during film processing. Provided is a biaxially oriented polyester film having at least an A layer and a B layer, wherein the A layer and the B layer each contain a polyethylene terephthalate resin as a main constituent component, and the following conditions (a)-(c) are satisfied. (a) The value of the dynamic friction coefficient when the A layer side surface of the biaxially oriented polyester film is brought into contact with a metal plate is 0.20-1.00. (b) The value of the dynamic friction coefficient when the A layer side surface of the biaxially oriented polyester film is brought into contact with the B layer side surface of the biaxially oriented polyester film is 0.35-0.50. (c) The value of haze at a thickness equivalence of 12 μm of the biaxially oriented polyester film is not more than 4.5%.

Description

Biaxially oriented polyester film, laminate, packaging, and top seal material

[0001] The present disclosure relates to a biaxially oriented polyester film, a laminate, a package, and a top seal material used in the packaging field of food, pharmaceuticals, industrial products, etc.

[0002] Aromatic polyesters, such as polyethylene terephthalate (hereinafter sometimes referred to as PET), are widely used as food containers and beverage containers. When using such polyester-based containers, so-called snap-on lids have traditionally been used as lid materials. In recent years, the use of top seal materials as lid materials has been promoted for the purposes of easier opening, standardization of lid materials (i.e., monomaterials), and reduction of waste by reducing thickness.

[0003] Patent Document 1 proposes that a laminated film using a biaxially oriented polyester film as a base layer and offline-coated with a polyester resin layer as a heat-sealable outer layer exhibits good heat-sealability to food trays.

[0004] Japanese Patent Application Laid-Open No. 2017-209996

[0005] With the shift to top-sealing lid materials, it has become impossible to form a groove that matches the shape of the fitting lid, and when plastic containers are stacked and displayed so that the bottoms of the containers are in contact with the top seal material, the containers may slip and collapse. Therefore, the present disclosure aims to provide a biaxially oriented polyester film that has a non-slip film surface and is both transparent and easy to wind during film processing.

[0006] Generally, in order to prevent films from adhering to each other, i.e., to prevent the blocking phenomenon, inorganic or organic lubricants are sometimes added to the film to provide slipperiness. Reducing the amount of lubricant contained in the film reduces the slipperiness, which may result in poor processability during film processing. Therefore, the present inventors have conducted extensive research to achieve the above-mentioned object, and have found that a biaxially oriented polyester film having at least an A layer and a B layer, each of which contains polyethylene terephthalate as a main component, as shown in [1] below, in which the dynamic friction coefficient when the A layer side surface is in contact with a metal plate, the dynamic friction coefficient between the A layer side surface and the B layer side surface, and the haze are controlled within specified ranges, has excellent slipperiness of the film surface, transparency, and winding ability during film processing.

[0007] [1] A biaxially oriented polyester film having at least Layer A and Layer B, each of which contains polyethylene terephthalate resin as a main constituent, and which satisfies the following conditions (a) to (c): (a) the coefficient of dynamic friction when the surface of Layer A of the biaxially oriented polyester film is brought into contact with a metal plate is 0.20 to 1.00; (b) the coefficient of dynamic friction when the surface of Layer A of the biaxially oriented polyester film is brought into contact with the surface of Layer B of the biaxially oriented polyester film is 0.35 to 0.50; and (c) the haze of the biaxially oriented polyester film converted to a thickness of 12 μm is 4.5% or less.

[0008] The present inventors have also found that a biaxially oriented polyester film having at least Layer A and Layer B with different lubricant contents, each layer containing polyethylene terephthalate as a main constituent, in which the content of a lubricant having a predetermined weight average particle size in each layer is controlled within a specified range, and the ratio of haze to the thickness of Layer A is controlled within a specified range, as described in [2] below, has excellent non-slip properties on the film surface, transparency, and winding properties during film processing.

[0009] [2] A biaxially oriented polyester film having at least a layer A and a layer B, wherein the layer A and the layer B each contain a polyethylene terephthalate resin as a main constituent component, the layer A has a lubricant content of 0 to 400 ppm by mass, and the layer B has a lubricant content of 500 to 4,500 ppm by mass, the weight average particle size of the lubricant is 0.5 to 4.0 μm, the biaxially oriented polyester film has a haze value of 4.5% or less when converted to a thickness of 12 μm, and the ratio of the thickness of the layer A to the thickness of the entire biaxially oriented polyester film is 30 to 90%.

[0010] The biaxially oriented polyester film, laminate, packaging material, or top seal material according to the embodiment is preferably any one of the following [3] to

[17] . [3] The biaxially oriented polyester film according to [1] or [2], having a puncture strength of 0.60 to 1.00 N / μm. [4] The biaxially oriented polyester film according to [1] or [3], wherein the ratio of the thickness of Layer A to the total thickness of the biaxially oriented polyester film is 30 to 90%. [5] The biaxially oriented polyester film according to any one of [1] to [4], wherein the biaxially oriented polyester film has an intermediate layer between Layer A and Layer B, the intermediate layer containing 60 to 100% by mass of polyethylene terephthalate resin. [6] The biaxially oriented polyester film according to [5], wherein the lubricant content in the intermediate layer is 0 to 2,500 ppm by mass. [7] The biaxially oriented polyester film according to [5] or [6], wherein the thickness of Layer A is equal to or greater than the thickness of the intermediate layer. [8] The biaxially stretched polyester film according to any one of [1] to [7], wherein the thickness of the B layer is smaller than the thickness of the A layer. [9] The biaxially stretched polyester film according to any one of [2] to [8], wherein the difference between the lubricant content in the A layer and the lubricant content in the B layer is 700 to 4,000 ppm by mass.

[10] The biaxially stretched polyester film according to any one of [2] to [9], wherein the pore volume of the lubricant is 1.0 to 1.7 ml / g.

[11] The biaxially stretched polyester film according to any one of [2] to

[10] , wherein the lubricant contains at least one inorganic lubricant selected from the group consisting of silica, calcium carbonate, and alumina.

[12] The biaxially stretched polyester film according to any one of [1] to

[11] , wherein the haze value of the biaxially stretched polyester film, converted to a thickness of 12 μm, is 0.1 to 4.5%, 0.2 to 4.3%, 0.3 to 4.0%, or 0.4 to 3.8%.

[13] The biaxially stretched polyester film according to any one of [1] to

[12] , wherein the content of the polyethylene terephthalate resin in the A layer is 60 to 100% by mass, and the content of the polyethylene terephthalate resin in the B layer is 60 to 100% by mass.

[14] The biaxially oriented polyester film according to any one of [1] and [3] to

[13] , wherein the lubricant content in the layer A is 0 to 400 ppm by mass and the lubricant content in the layer B is 500 to 4,500 ppm by mass.

[15] A laminate comprising the biaxially oriented polyester film according to any one of [1] to

[14] and a sealant film.

[16] A packaging product comprising the biaxially oriented polyester film according to any one of [1] to

[14] .

[17] A top seal material for a container comprising the biaxially oriented polyester film according to any one of [1] to

[14] .

[0011] The above-mentioned configuration makes it possible to obtain a biaxially oriented polyester film having a non-slip surface and excellent transparency and winding properties during film processing. By using the biaxially oriented polyester film as a material for packaging bags or a top seal material for plastic containers, for example, it is possible to prevent products from slipping and collapsing when stacked and displayed.

[0012] Hereinafter, the biaxially stretched polyester film of the embodiment will be described in detail. In this specification, a numerical range expressed using "to" means a range including the numerical values ​​before and after "to" as the lower and upper limits.

[0013] [Biaxially oriented polyester film] The biaxially oriented polyester film of the embodiment is a biaxially oriented polyester film having at least Layer A and Layer B, each of which contains polyethylene terephthalate resin as a main constituent, and which satisfies the following conditions (a) to (c): (a) The dynamic friction coefficient when the surface of Layer A of the biaxially oriented polyester film is in contact with a metal plate is 0.20 to 1.00; (b) The dynamic friction coefficient when the surface of Layer A of the biaxially oriented polyester film is in contact with the surface of Layer B of the biaxially oriented polyester film is 0.35 to 0.50; and (c) The haze value of the biaxially oriented polyester film converted to a thickness of 12 μm is 4.5% or less.

[0014] In another embodiment, the biaxially oriented polyester film has at least Layer A and Layer B, each of which contains polyethylene terephthalate resin as a main component, wherein the lubricant content in Layer A is 0 to 400 ppm by mass, the lubricant content in Layer B is 500 to 4,500 ppm by mass, the weight-average particle size of the lubricant is 0.5 to 4.0 μm, the haze value converted into a biaxially oriented polyester film having a thickness of 12 μm is 4.5% or less, and the ratio of the thickness of Layer A to the thickness of the entire biaxially oriented polyester film is 30 to 90%. The biaxially oriented polyester films of these embodiments are described below.

[0015] The biaxially oriented polyester film preferably has at least a layer A and a layer B. The biaxially oriented polyester film may have a two-layer structure of a layer A and a layer B, or a three-layer structure including one or more intermediate layers between the layer A and the layer B. That is, the biaxially oriented polyester film may consist of a layer A and a layer B, a layer A, a layer B, and an intermediate layer, or a layer A, a layer B, and an intermediate layer.

[0016] Hereinafter, of the surfaces facing the thickness direction of the biaxially oriented polyester film, the surface closer to the A layer than the B layer will be referred to as the A-layer side surface. Also, of the surfaces facing the thickness direction of the biaxially oriented polyester film, the surface closer to the B layer than the A layer will be referred to as the B-layer side surface. The A-layer side surface is preferably the surface of the A layer. Furthermore, the B-layer side surface is preferably the surface of the B layer.

[0017] [Layer A] Layer A of the biaxially oriented polyester film contains polyethylene terephthalate resin (hereinafter, sometimes referred to as PET resin (a)) as a main component. Here, "containing as a main component" means that the content of PET resin (a) in 100% by mass of Layer A is 60% by mass or more, preferably 70% by mass or more, and most preferably 80% by mass or more. By making it 60% by mass or more, the transparency of the biaxially oriented polyester film is improved, making it suitable for printing and also advantageous in terms of cost. In 100% by mass of Layer A, the content of PET resin (a) may be 100% by mass or less, 99.99% by mass or less, 99.98% by mass or less, 99.9% by mass or less, 98% by mass or less, or 95% by mass or less.

[0018] Layer A may contain a polyester resin (b) other than the PET resin (a) for the purpose of adjusting the mechanical properties of the biaxially stretched polyester film. Examples of the polyester resin (b) other than the PET resin (a) include polyester resins such as polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and polypropylene terephthalate (PPT); polyester resins copolymerized with dicarboxylic acids such as isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, and sebacic acid; and polyester resins copolymerized with diol components such as ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol, and polycarbonate diol. The polyester resin (b) is preferably a polyester resin in which at least a dicarboxylic acid and a diol component are copolymerized. These may be used alone or in combination of two or more kinds.

[0019] The lower limit of the intrinsic viscosity of the resin composition constituting Layer A is preferably 0.45 dl / g, more preferably 0.50 dl / g, and most preferably 0.55 dl / g. By setting the intrinsic viscosity at 0.45 dl / g or higher, the intrinsic viscosity of the biaxially oriented polyester film can be maintained high, thereby improving mechanical properties such as puncture strength. The upper limit of the intrinsic viscosity of the resin composition constituting Layer A is preferably 0.80 dl / g, more preferably 0.75 dl / g, and most preferably 0.70 dl / g. Setting the intrinsic viscosity at 0.80 dl / g or lower prevents excessive stress during film stretching, thereby achieving good film formability. Similarly, the intrinsic viscosity of Layer A is preferably 0.45 to 0.80 dl / g, more preferably 0.50 to 0.75 dl / g, and most preferably 0.55 to 0.70 dl / g. The resin composition is PET resin (a) or a mixture of PET resin (a) and other resins. The intrinsic viscosity of the resin composition can be measured, for example, by dissolving 0.2 g of the resin composition in 50 ml of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (60 / 40 (weight ratio)) and using an Ostwald viscometer at 30° C. The same applies to the intrinsic viscosity of the resin composition constituting the B layer and the resin composition constituting the intermediate layer, which will be described later.

[0020] Layer A may contain no lubricant, or may contain a lubricant to the extent that the slipperiness of the film surface can be controlled. The lubricant content, relative to 100% by mass of Layer A, is preferably 0 to 400 ppm by mass, more preferably 0 to 380 ppm by mass, and even more preferably 0 to 350 ppm by mass. By setting the lubricant content to 400 ppm by mass or less, slipperiness of the film surface can be imparted. A lubricant content of 0 ppm by mass in Layer A means that Layer A does not contain a lubricant. In other words, a lubricant content of 0 to 400 ppm by mass in Layer A means that Layer A does not contain a lubricant, or that Layer A contains a lubricant in an amount greater than 0 ppm by mass and less than or equal to 400 ppm by mass. The same applies to the lubricant content in Layer B and the lubricant content in the intermediate layer, which will be described later.

[0021] The lubricant can adjust the dynamic friction coefficient of the film, and preferably contains at least one inorganic lubricant selected from the group consisting of silica, calcium carbonate, and alumina, more preferably contains at least one inorganic lubricant selected from the group consisting of silica and calcium carbonate, and most preferably contains silica. In particular, silica makes it easier to achieve both transparency and lubricity. The lubricant may also contain an organic lubricant.

[0022] When Layer A contains a lubricant, the weight average particle size of the lubricant in Layer A may be the same as or different from the weight average particle size of the lubricant in Layer B or the intermediate layer.

[0023] When Layer A contains a lubricant, the weight-average particle size of the lubricant is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1.5 μm or more. On the other hand, the weight-average particle size of the lubricant is preferably 4.0 μm or less, more preferably 3.8 μm or less, and even more preferably 3.5 μm or less. This can reduce haze when Layer A contains a lubricant. The average particle size of the lubricant can be measured, for example, using a laser diffraction particle size distribution analyzer (SALD-2200, manufactured by Shimadzu Corporation). The same applies to the average particle size of the lubricant in Layer B and the average particle size of the lubricant in the intermediate layer, which will be described later.

[0024] When Layer A contains a lubricant, the pore volume of the lubricant is preferably 1.0 ml / g or more, more preferably 1.1 ml / g or more, and even more preferably 1.2 ml / g or more. This allows for an increased dynamic friction coefficient on the surface of Layer A when Layer A contains a lubricant, and also reduces haze. Meanwhile, the pore volume of the lubricant is preferably 1.7 ml / g or less, more preferably 1.6 ml / g or less, and even more preferably 1.5 ml / g or less. The pore volume of the lubricant can be determined, for example, using a high-speed specific surface area / pore distribution analyzer (ASAP 2400) manufactured by Shimadzu Corporation, by integrating the pore volume within a specified pore diameter range (17 to 3000 Å) using the BJH method, which utilizes nitrogen adsorption and desorption (for details, see Shimadzu Review, Vol. 48, No. 1, pp. 35-49). The same applies to the average particle diameter of the pore volume of Layer B and the average particle diameter of the pore volume of the intermediate layer, which will be described later.

[0025] [Layer B] The layer B of the biaxially oriented polyester film contains polyethylene terephthalate resin (hereinafter, sometimes referred to as PET resin (a)) as a main component. Here, "containing as a main component" means that the content of PET resin (a) in 100% by mass of layer B is 60% by mass or more, preferably 70% by mass or more, and most preferably 80% by mass or more. By making it 60% by mass or more, the transparency of the biaxially oriented polyester film is improved, making it suitable for printing and also advantageous in terms of cost. The content of PET resin (a) in 100% by mass of layer B may be 100% by mass or less, 99.99% by mass or less, 99.98% by mass or less, 99.9% by mass or less, 98% by mass or less, or 95% by mass or less.

[0026] Layer B may contain a polyester resin (b) other than the PET resin (a) for the purpose of adjusting the mechanical properties of the biaxially stretched polyester film. Examples of the polyester resin (b) other than the PET resin (a) include polyester resins such as polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and polypropylene terephthalate (PPT); polyester resins copolymerized with dicarboxylic acids such as isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, and sebacic acid; and polyester resins copolymerized with diol components such as ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol, and polycarbonate diol. The polyester resin (b) is preferably a polyester resin in which at least a dicarboxylic acid and a diol component are copolymerized. These may be used alone or in combination of two or more kinds.

[0027] The lower limit of the intrinsic viscosity of the resin composition constituting Layer B is preferably 0.45 dl / g, more preferably 0.50 dl / g, and most preferably 0.55 dl / g. By setting the intrinsic viscosity at 0.45 dl / g or higher, the intrinsic viscosity of the biaxially oriented polyester film can be maintained high, thereby improving mechanical properties such as puncture strength. The upper limit of the intrinsic viscosity of the resin composition constituting Layer B is preferably 0.80 dl / g, more preferably 0.75 dl / g, and most preferably 0.70 dl / g. Setting the intrinsic viscosity at 0.80 dl / g or lower prevents excessive stress during film stretching, resulting in good film formability. Similarly, the intrinsic viscosity of Layer B is preferably 0.45 to 0.80 dl / g, more preferably 0.50 to 0.75 dl / g, and most preferably 0.55 to 0.70 dl / g.

[0028] The polyester resin contained in the B layer may be the same as or different from the polyester resin contained in the A layer.

[0029] Layer B preferably contains a lubricant to improve the slipperiness of the film when Layer A and Layer B are in contact with each other and to improve the quality of winding the roll. The lubricant content, based on 100% by mass of Layer B, is preferably 500 to 4,500 ppm by mass, more preferably 600 to 3,500 ppm by mass, and even more preferably 800 to 2,500 ppm by mass. By setting the lubricant content to 500 ppm by mass or more, the slipperiness during film winding can be improved. On the other hand, by setting the lubricant content to 4,500 ppm by mass or less, the transparency of the film can be improved.

[0030] The lubricant can adjust the dynamic friction coefficient of the film, and preferably contains at least one inorganic lubricant selected from the group consisting of silica, calcium carbonate, and alumina, more preferably contains at least one inorganic lubricant selected from the group consisting of silica and calcium carbonate, and most preferably contains silica. In particular, silica makes it easier to achieve both transparency and lubricity. The lubricant may also contain an organic lubricant.

[0031] When Layer B contains a lubricant, the weight average particle size of the lubricant in Layer B may be the same as or different from the weight average particle size of the lubricant in Layer A or the intermediate layer.

[0032] The weight-average particle size of the lubricant contained in Layer B is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1.5 μm or more. When the particle size is 0.5 μm or more, irregularities can be formed on the surface of Layer B of the biaxially oriented polyester film. Therefore, slipperiness can be imparted to Layer B of the biaxially oriented polyester film. In addition, when the biaxially oriented polyester film is wound into a roll, blocking with Layer A can be suppressed, improving the winding quality of the roll. Meanwhile, the weight-average particle size of the lubricant contained in Layer B is preferably 4.0 μm or less, more preferably 3.8 μm or less, and even more preferably 3.5 μm or less. When the particle size is 4.0 μm or less, the formation of coarse protrusions on the surface of Layer B of the biaxially oriented polyester film can be prevented.

[0033] The pore volume of the lubricant in Layer B is preferably 1.0 ml / g or more, more preferably 1.1 ml / g or more, and even more preferably 1.2 ml / g or more. This can reduce haze when Layer B contains a lubricant. On the other hand, the pore volume of the lubricant in Layer B is preferably 1.7 ml / g or less, more preferably 1.6 ml / g or less, and even more preferably 1.5 ml / g or less. This can reduce the dynamic friction coefficient of the surface on the Layer B side.

[0034] The difference between the lubricant content in Layer A and the lubricant content in Layer B is preferably 700 to 4,000 ppm by mass. Having this difference in the above range makes it easier to achieve both lubrication resistance and excellent winding properties. Furthermore, having the difference be 4,000 ppm by mass or less can reduce haze. The difference is more preferably 800 to 3,000 ppm by mass, and even more preferably 850 to 2,000 ppm by mass.

[0035] The layers A and B of the biaxially stretched polyester film may contain additives other than the lubricant, such as stabilizers, colorants, antioxidants, antistatic agents, and ultraviolet absorbers.

[0036] [Intermediate Layer] The biaxially oriented polyester film may optionally have an intermediate layer between the A layer and the B layer. The intermediate layer preferably contains polyethylene terephthalate resin (hereinafter, sometimes referred to as PET resin (a)) as a main component. Here, "containing as a main component" means that the content of PET resin (a) in 100% by mass of the intermediate layer is 60% by mass or more, preferably 70% by mass or more, and most preferably 80% by mass or more. In 100% by mass of the intermediate layer, the content of PET resin (a) may be 100% by mass or less, 99.99% by mass or less, 99.98% by mass or less, 99.9% by mass or less, 98% by mass or less, or 95% by mass or less.

[0037] The intermediate layer may contain a polyester resin (b) other than the PET resin (a) for the purpose of adjusting the mechanical properties of the biaxially stretched polyester film. Examples of the polyester resin (b) other than the PET resin (a) include polyester resins such as polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), and polypropylene terephthalate (PPT); polyester resins copolymerized with dicarboxylic acids such as isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, and sebacic acid; and polyester resins copolymerized with diol components such as ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, cyclohexanediol, polyethylene glycol, polytetramethylene glycol, and polycarbonate diol. The polyester resin (b) is preferably a polyester resin in which at least a dicarboxylic acid and a diol component are copolymerized. These may be used alone or in combination of two or more kinds.

[0038] The lower limit of the intrinsic viscosity of the resin composition constituting the intermediate layer is preferably 0.45 dl / g, more preferably 0.50 dl / g, and most preferably 0.55 dl / g. By setting the intrinsic viscosity at 0.45 dl / g or higher, the intrinsic viscosity of the biaxially oriented polyester film can be maintained high, thereby improving mechanical properties such as puncture strength. The upper limit of the intrinsic viscosity of the resin composition constituting the intermediate layer is preferably 0.80 dl / g, more preferably 0.75 dl / g, and most preferably 0.70 dl / g. Setting the intrinsic viscosity at 0.80 dl / g or lower prevents excessive stress during film stretching, resulting in good film formability. Similarly, the intrinsic viscosity of the intermediate layer is preferably 0.45 to 0.80 dl / g, more preferably 0.50 to 0.75 dl / g, and most preferably 0.55 to 0.70 dl / g.

[0039] The polyester resin contained in the intermediate layer may be the same as or different from the polyester resin contained in the A layer or B layer.

[0040] The intermediate layer may contain no lubricant, or may contain a lubricant to improve the slipperiness of the film and improve the winding quality of the roll. The lubricant content, based on 100% by mass of the intermediate layer, is preferably 0 to 2,500 ppm by mass, more preferably 0 to 2,000 ppm by mass, and even more preferably 0 to 1,500 ppm by mass. However, since a high silica content may impair the transparency of the film, the total amount of lubricant contained in Layer A, Layer B, and the intermediate layer is preferably 4,500 ppm by mass or less, more preferably 3,500 ppm by mass or less, and even more preferably 2,500 ppm by mass or less, based on the total amount of the biaxially oriented polyester film. On the other hand, the total amount of lubricant contained in Layer A, Layer B, and the intermediate layer is preferably 200 ppm by mass or more, more preferably 500 ppm by mass or more, and even more preferably 1,000 ppm by mass or more, based on the total amount of the biaxially oriented polyester film.

[0041] The lubricant can adjust the dynamic friction coefficient of the film, and preferably contains at least one inorganic lubricant selected from the group consisting of silica, calcium carbonate, and alumina, more preferably contains at least one inorganic lubricant selected from the group consisting of silica and calcium carbonate, and most preferably contains silica. In particular, silica makes it easier to achieve both transparency and lubricity. The lubricant may also contain an organic lubricant.

[0042] When the intermediate layer contains a lubricant, the weight average particle size of the lubricant in the intermediate layer may be the same as or different from the weight average particle size of the lubricant in the A layer or B layer.

[0043] When the intermediate layer contains a lubricant, the weight-average particle size of the lubricant is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1.5 μm or more. On the other hand, the weight-average particle size of the lubricant is preferably 4.0 μm or less, more preferably 3.8 μm or less, and even more preferably 3.5 μm or less. This can reduce haze when the intermediate layer contains a lubricant.

[0044] When the intermediate layer contains a lubricant, the pore volume of the lubricant is preferably 1.0 ml / g or more, more preferably 1.1 ml / g or more, and even more preferably 1.2 ml / g or more. This reduces haze when the intermediate layer contains a lubricant. On the other hand, the pore volume of the lubricant is preferably 1.7 ml / g or less, more preferably 1.6 ml / g or less, and even more preferably 1.5 ml / g or less.

[0045] The intermediate layer may contain additives other than the lubricant, such as a stabilizer, a colorant, an antioxidant, an antistatic agent, an ultraviolet absorber, and the like.

[0046] The thickness of the biaxially stretched polyester film is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 7 μm or more. By setting the thickness to 3 μm or more, the strength of the film can be maintained. The upper limit of the thickness is preferably 100 μm or less, more preferably 75 μm or less, and even more preferably 50 μm or less. Setting the thickness to 100 μm or less makes processing easier.

[0047] The ratio of the thickness of Layer A to the total thickness of the biaxially oriented polyester film is preferably 30 to 90%, more preferably 35 to 70%. Having a thickness ratio of Layer A of 30% or more allows for a high dynamic friction coefficient on the surface of Layer A. This is thought to be due to the fact that when Layer A, which contains PET resin (a) as its main component, is thick to a certain extent, the true contact area of ​​the surface of Layer A under load tends to increase. On the other hand, having a thickness ratio of Layer A of 90% or less makes it easier to ensure the thickness of layers other than Layer A.

[0048] The thickness of Layer A is preferably equal to or greater than the thickness of the intermediate layer. This allows the dynamic friction coefficient of the surface on the Layer A side to be increased. The thickness of Layer A is preferably 1.0 times or more the thickness of the intermediate layer. On the other hand, the thickness of Layer A is preferably 10 times or less the thickness of the intermediate layer, more preferably 6 times or less, and even more preferably 5 times or less. This allows the thickness of the biaxially oriented polyester film to be reduced.

[0049] The thickness of layer B is preferably smaller than that of layer A. This increases the dynamic friction coefficient of the surface on the layer A side and decreases the dynamic friction coefficient of the surface on the layer B side. The thickness of layer B is preferably less than 1.0 times the thickness of layer A, more preferably 0.9 times or less, even more preferably 0.7 times or less, and most preferably 0.6 times or less. On the other hand, the thickness of layer B is preferably 0.1 times or more the thickness of layer A, more preferably 0.2 times or more, even more preferably 0.3 times or more, and most preferably 0.4 times or more. This makes it easier for layer B to retain the lubricant.

[0050] The puncture strength of the biaxially oriented polyester film is preferably 0.60 N / μm or more, more preferably 0.62 N / μm or more, and even more preferably 0.64 N / μm or more. By setting it to 0.60 N / μm or more, for example, when the biaxially oriented polyester film is used as a lid material for plastic containers for food use, it can be used suitably without breaking even when external stress is applied to the lid material. The upper limit of the puncture strength is preferably 1.00 N / μm or less, more preferably 0.97 N / μm or less, and even more preferably 0.94 N / μm or less. By setting it to 1.00 N / μm or less, thermal shrinkage can be suppressed, and processing problems due to film shrinkage in processes such as vapor deposition and printing can be reduced. The puncture strength (N / μm) is the puncture strength converted into a thickness of 1 μm, as described in the examples below.

[0051] The haze value of the biaxially oriented polyester film converted into a thickness of 12 μm is preferably 4.5% or less, more preferably 4.3% or less, even more preferably 4.0% or less, and most preferably 3.8% or less. By setting it to 4.5% or less, transparency is high, and when the biaxially oriented polyester film is used as a lid material or packaging material for plastic containers, the contents can be clearly seen, and printing can be clearly seen, resulting in a good appearance. The haze value of the biaxially oriented polyester film converted into a thickness of 12 μm may be 0.1% or more, 0.2% or more, 0.3% or more, or 0.4% or more.

[0052] When the A layer side surface of the biaxially stretched polyester film is in contact with a metal plate, the dynamic friction coefficient is preferably 0.20 or more, more preferably 0.23 or more, and even more preferably 0.25 or more. The upper limit of the dynamic friction coefficient is not particularly limited, but is preferably 1.00 or less, more preferably 0.80 or less, and even more preferably 0.60 or less. By making it 0.20 or more, the film has excellent surface slip resistance, and for example, when used as a lid material for plastic containers, even when the plastic containers are stacked and displayed so that the bottom and A layer are in contact, the containers are less likely to collapse due to slippage. The dynamic friction coefficient can be measured by the method described in the examples below.

[0053] The dynamic friction coefficient when the B-layer side surface of the biaxially oriented polyester film is in contact with a metal plate is preferably smaller than the dynamic friction coefficient when the A-layer side surface of the biaxially oriented polyester film is in contact with a metal plate. This makes it easier to achieve both slip resistance and excellent winding properties. The dynamic friction coefficient when the B-layer side surface is in contact with a metal plate is preferably 0.9 times or less, more preferably 0.5 times or less, even more preferably 0.3 times or less, and most preferably 0.2 times or less, of the dynamic friction coefficient when the A-layer side surface is in contact with a metal plate. On the other hand, this ratio may be 0.01 times or more, or may be 0.03 times or more.

[0054] The dynamic friction coefficient when the A layer side surface and the B layer side surface of the biaxially stretched polyester film are brought into contact is preferably 0.35 or more, more preferably 0.37 or more, and even more preferably 0.39 or more. It is preferably 0.50 or less, more preferably 0.48 or less, and even more preferably 0.45 or less. By setting the dynamic friction coefficient in the range of 0.35 or more and 0.50 or less, the sliding property between the films is improved, and the winding quality of the film roll is improved. The dynamic friction coefficient can be measured by the method described in the examples below.

[0055] The heat shrinkage of the biaxially stretched polyester film in the machine direction (hereinafter sometimes referred to as MD direction) and width direction (hereinafter sometimes referred to as TD direction) after heat treatment for 15 minutes at 150° C. is preferably 0.1 to 2.5%, more preferably 0.2 to 2.0%, and even more preferably 0.3 to 1.8%. By keeping the heat shrinkage at 2.5% or less, dimensional change when heated in the secondary processing step can be suppressed, and the occurrence of wrinkles can be reduced.

[0056] A printing layer may be laminated on the surface of Layer B of the biaxially oriented polyester film. Aqueous and solvent-based resin-containing printing inks are preferably used to form the printing layer. Examples of resins used in printing inks include acrylic resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate copolymer resins, and mixtures thereof. The printing ink may contain known additives such as antistatic agents, light-blocking agents, UV absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, antifoaming agents, crosslinking agents, antiblocking agents, and antioxidants.

[0057] The printing method for providing the printed layer is not particularly limited, and known printing methods such as offset printing, gravure printing, screen printing, etc. can be used. To dry the solvent after printing, known drying methods such as hot air drying, hot roll drying, and infrared drying can be used.

[0058] The layer B of the biaxially stretched polyester film may be subjected to a smoothing corona discharge treatment, a glow discharge treatment, a flame treatment, or a surface roughening treatment, as long as the purpose of the present disclosure is not impaired, and may also be subjected to a known anchor coating treatment, printing, decoration, etc.

[0059] A layer of another material may be laminated to the layer B of the biaxially oriented polyester film. As a method for this, the biaxially oriented polyester film can be laminated to the layer of another material after film formation, or the biaxially oriented polyester film can be laminated to the layer of another material during film formation.

[0060] The present disclosure further provides a laminate comprising the biaxially oriented polyester film and a sealant film according to an embodiment. The laminate is typically formed by extrusion lamination or dry lamination. The sealant film preferably comprises a heat-sealable resin layer. The thermoplastic copolymer forming the heat-sealable resin layer may be any copolymer capable of sufficiently exhibiting sealant adhesion, including polyethylene resins such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE), polypropylene resin, ethylene-vinyl acetate copolymer, ethylene-α-olefin random copolymer, ionomer resin, polyester resin, and the like. The sealant film may also comprise a heat-sealable resin layer.

[0061] The sealant film or heat-sealable resin layer may be a single layer or a multilayer, and the structure may be selected depending on the required function. The sealant film or heat-sealable resin 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 total thickness of the sealant film is preferably 5 to 100 μm, more preferably 10 to 60 μm.

[0062] The biaxially oriented polyester film and laminate of the embodiment can be used in the packaging field of foods, medicines, industrial products, etc. In particular, they can be suitably used as top seal materials for packaging containers.

[0063] The present disclosure further provides a top seal material comprising the biaxially oriented polyester film of the embodiment. When using the top seal material, it is preferable to use it with the surface of Layer B facing the packaging container and the surface of Layer A facing the outer surface of the top seal material. The layer configuration of the top seal material for packaging containers, where the layer boundary is represented by / , can be, for example, a non-slip surface layer / sealant layer, a non-slip surface layer / gas barrier layer / protective layer, a non-slip surface layer / gas barrier layer / protective layer / adhesive layer / sealant layer, a non-slip surface layer / gas barrier layer / protective layer / adhesive layer / resin layer / adhesive layer / sealant layer, a non-slip surface layer / adhesive layer / resin layer / gas barrier layer / protective layer / adhesive layer / sealant layer, a non-slip surface layer / gas barrier layer / protective layer / printing layer / adhesive layer / sealant layer, or a non-slip surface layer / printing layer / gas barrier layer / protective layer / adhesive layer / sealant layer, non-slip surface layer / gas barrier layer / protective layer / adhesive layer / resin layer / printing layer / adhesive layer / sealant layer, non-slip surface layer / adhesive layer / resin layer / printing layer / gas barrier layer / protective layer / adhesive layer / sealant layer, non-slip surface layer / printing layer / gas barrier layer / protective layer / adhesive layer / resin layer / adhesive layer / sealant layer, non-slip surface layer / printing layer / adhesive layer / resin layer / gas barrier layer / protective layer / adhesive layer / sealant layer, non-slip surface ...printing layer / adhesive layer / sealant layer, etc.

[0064] The present disclosure further provides a package including the biaxially oriented polyester film of the embodiment. Examples of the package include packaging products, various label materials, lid materials, sheet molded products, laminated tubes, etc. Examples of the packaging products include packaging bags, etc.

[0065] (Method for Producing Biaxially Stretched Polyester Film) There are no particular limitations on the method for obtaining a biaxially stretched polyester film, but the T-die method is preferred from the viewpoint of thickness accuracy. With the inflation method, the stretch ratio is difficult to increase due to the manufacturing method, and thickness defects in the width direction may occur. Here, a typical manufacturing process for the T-die method will be described. The T-die method includes: (1) a step of melt-extruding a polyester resin composition into a sheet and cooling it on a cooling roll to form an unstretched sheet; (2) a stretching step of stretching the formed unstretched sheet in the MD direction and in the TD direction perpendicular to the MD direction; (3) a heat-setting step of heating and crystallizing the film after the stretching; (4) a heat-relaxing step (sometimes referred to as a relaxation step) of removing residual strain in the heat-set film; and (5) a cooling step of cooling the film after heat-relaxing.

[0066] The upper limit of the resin melting temperature in the extruder is preferably 310°C, more preferably 300°C. If the temperature is 310°C or lower, decomposition of the resin can be suppressed, preventing the film from becoming brittle and also preventing deterioration of film quality due to heat degradation products. The lower limit of the resin melting temperature in the extruder is preferably 230°C, more preferably 240°C. If the temperature is 230°C or higher, not only can the resin be extruded, but discharge is stable and thickness accuracy is good.

[0067] The upper limit of the chill roll temperature is preferably 40°C, and more preferably 20°C or lower. If the temperature is 40°C or lower, the crystallinity of the molten polyester resin composition does not become too high when it is cooled and solidified, making it easier to stretch, and also suppressing a decrease in transparency due to crystallization. The lower limit of the chill roll temperature is preferably 0°C. If the temperature is 0°C or higher, the effect of suppressing crystallization when the molten polyester resin composition is cooled and solidified can be fully exerted. Furthermore, when the chill roll temperature is set within the above range, it is preferable to reduce the humidity of the environment near the chill roll to prevent condensation.

[0068] The thickness of the unstretched sheet is preferably in the range of 15 to 2500 μm, more preferably 500 μm or less, and most preferably 300 μm or less.

[0069] The stretching method will now be described. The stretching method can be either simultaneous biaxial stretching or sequential biaxial stretching, but in order to increase the piercing strength, it is necessary to increase the degree of planar orientation, and in this respect sequential biaxial stretching is preferred.

[0070] The lower limit of the MD stretching temperature is preferably 90°C, more preferably 95°C, and particularly preferably 100°C. At 90°C or higher, breakage can be further suppressed. The upper limit of the MD stretching temperature is preferably 140°C, more preferably 135°C, and particularly preferably 130°C. At 140°C or lower, the degree of planar orientation can be increased, and puncture strength can be increased.

[0071] The lower limit of the stretching ratio in the MD direction is preferably 2.8 times, more preferably 2.9 times, and particularly preferably 3.0 times. When it is 2.8 times or more, the degree of planar orientation can be increased, and the puncture strength can be increased. Furthermore, when it is 2.8 times or more, thickness unevenness can be suppressed, and slack in the film roll can be prevented. The upper limit of the stretching ratio in the MD direction is preferably 4.5 times, more preferably 4.4 times, and particularly preferably 4.3 times. When it is 4.5 times or less, the effects of improving mechanical strength and thickness unevenness can be sufficiently obtained.

[0072] The lower limit of the stretching temperature in the TD direction is preferably 100°C, more preferably 105°C, and particularly preferably 110°C. If the temperature is 100°C or higher, breakage can be made less likely to occur. The upper limit of the stretching temperature in the TD direction is preferably 140°C, more preferably 135°C, and particularly preferably 130°C. If the temperature is 140°C or lower, the degree of planar orientation can be increased, and the puncture strength can be increased.

[0073] The lower limit of the stretching ratio in the TD direction is preferably 3.8 times, more preferably 3.9 times, and particularly preferably 4.0 times. If it is 3.8 times or more, the degree of planar orientation can be increased, and the puncture strength can be increased. The upper limit of the stretching ratio in the TD direction is preferably 5.0 times, more preferably 4.9 times, and particularly preferably 4.8 times. If it is 5.0 times or less, the effects of improving mechanical strength and thickness unevenness can be sufficiently obtained.

[0074] The lower limit of the heat setting temperature is preferably 170°C, more preferably 180°C, and particularly preferably 190°C. If the temperature is 170°C or higher, the heat shrinkage rate can be further reduced. The upper limit of the heat setting temperature is preferably 240°C, more preferably 230°C, and particularly preferably 220°C. If the temperature is 240°C or lower, melting of the film can be suppressed, and the degree of planar orientation can be increased, thereby increasing the puncture strength.

[0075] The lower limit of the relaxation rate in the heat relaxation is preferably 0.5%, more preferably 1.0%, and particularly preferably 2.0%. If it is 0.5% or more, the thermal shrinkage rate in the TD direction can be kept low. The upper limit of the relaxation rate is preferably 10%, more preferably 8%, and particularly preferably 6%. If it is 10% or less, the occurrence of slack and the like can be prevented, and flatness can be improved.

[0076] This application claims the benefit of priority based on Japanese Patent Application No. 2023-108659, filed on June 30, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-108659, filed on June 30, 2023, are incorporated herein by reference.

[0077] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to the following examples and may be modified within the scope of the above-mentioned and below-mentioned aims. The biaxially stretched polyester films were evaluated using the following measurement methods. Unless otherwise specified, measurements were carried out in a measurement room at 23°C and a relative humidity of 65%.

[0078] [Film Puncture Strength] The value measured by a test method in accordance with JIS Z1707 (2019) was calculated in terms of 1 μm using the following formula: Puncture strength (N / μm) = Measured puncture strength value (N) / Film thickness (μm)

[0079] [Film Haze] According to JIS K7136 (2000), the film was cut into a square shape with a side length of 10 cm, and the haze was measured using a haze meter NDH8000 manufactured by Nippon Denshoku Co., Ltd. Measurements were performed at three locations, and the average value was taken as the actual haze measurement value. The haze (% / 12 μm) was calculated as the haze (%) converted to 12 μm using the following formula: Haze (% / 12 μm) = Actual haze measurement value × 12 / Film thickness (μm)

[0080] [Film Thickness] The thickness was measured using a dial gauge in accordance with JIS K7130 (1999) Method A.

[0081] [Dynamic Friction Coefficient Between the A-Layer Surface of the Film and a Metal Plate] In accordance with JIS K-7125 (1999 edition), the A-Layer surface of the film was brought into contact with a metal plate using a tensile tester (Tensilon RTG-1210 manufactured by A&D Co., Ltd.) in an environment of 23°C and 65% RH to determine the dynamic friction coefficient. Specifically, the film was wrapped around a thread (weight) so that the A-Layer surface was exposed, and this was placed on a SUS plate, which was a metal plate, to bring the A-Layer surface into contact with the metal plate. The mass of the thread (weight) around which the upper film was wrapped was 3.5 kg, and the size of the base area of ​​the thread was 39.7 mm ２ The tensile speed during measurement of the coefficient of friction was 200 mm / min. The coefficient of dynamic friction thus determined is referred to as "coefficient of dynamic friction (layer A / metal plate)" in the examples and tables.

[0082] [Dynamic Friction Coefficient Between the A-Layer Surface and the B-Layer Surface of the Film] In accordance with JIS K-7125 (1999 edition), the A-Layer surface and the B-Layer surface of a biaxially stretched polyester film were brought into contact with each other using a tensile tester (Tensilon RTG-1210 manufactured by A&D Co., Ltd.) under an environment of 23°C and 65% RH to determine the dynamic friction coefficient. Specifically, two pieces were cut out from the biaxially stretched polyester film, and one piece was wrapped around a thread (weight) so that the A-Layer surface was exposed. This was then placed on the B-Layer surface of the other piece, bringing the A-Layer surface and the B-Layer surface into contact with each other. The weight of the thread (weight) around which the upper film was wrapped was 1.5 kg, and the base area of ​​the thread was 39.7 mm ２ The tensile speed during measurement of the coefficient of friction was 200 mm / min. The coefficient of dynamic friction thus determined is referred to as "coefficient of dynamic friction (Layer A / Layer B)" in the examples and tables.

[0083] [Heat Shrinkage of Film] The heat shrinkage was measured by a dimensional change test method in accordance with JIS C2151 (2019), except that the test temperature was 150°C and the heating time was 15 minutes.

[0084] [Evaluation of Inclined Sliding] The surface of the layer A of the biaxially oriented polyester film was brought into contact with the bottom of a plastic container, and a load was applied to the plastic container. The angle when the container was placed on a flat surface was defined as 0°, and the container was tilted at 2 m / min to determine the inclination angle (°) at which the container began to slide. The plastic containers used and the loads used during measurement are listed below. Polystyrene lunch container ("PS container") Length 230 mm x Width 195 mm x Height 25 mm (manufactured by Fukusuke Kogyo Co., Ltd.), Load 200 g Polypropylene tray container ("PP container") Length 190 mm x Width 140 mm x Height 31 mm (manufactured by Chuo Kagaku Co., Ltd.), Load 200 g A-PET clean cup container ("A-PET container") Diameter φ101 mm x Height 35 mm (manufactured by Rispack Co., Ltd.), Load 100 g The angle at which the container began to slide was evaluated according to the following criteria: ○: The angle at which the container began to slide was 26° or more ×: The angle at which the container began to slide was less than 26°

[0085] [Evaluation of Film Winding Properties] The produced biaxially stretched polyester films were wound up to a width of 800 mm and a winding length of 1500 m, and the winding quality was evaluated as follows: Good: Good slippage between layers A and B of the film, no winding defects Poor: Poor slippage between layers A and B of the film, winding defects

[0086] [Example 1] A PET resin (PET resin composed of terephthalic acid / ethylene glycol = 100 / / 100 (mol%), intrinsic viscosity 0.62 dL / g, no silica particles added) was used as the resin composition constituting the A layer. A PET resin (PET resin composed of terephthalic acid / ethylene glycol = 100 / / 100 (mol%), intrinsic viscosity 0.62 dL / g, no silica particles added) was used as the resin composition constituting the intermediate layer. A PET resin (PET resin composed of terephthalic acid / ethylene glycol = 100 / / 100 (mol%), intrinsic viscosity 0.62 dL / g, silica particles added) was used as the resin composition constituting the B layer. The compositions were the same except for the inclusion of silica particles. Silica particles used were Sylysia 310 (average particle size 2.7 μm, pore volume 1.60 ml / g) manufactured by Fuji Silysia Corporation. Using an apparatus consisting of three extruders and a 380 mm wide coextrusion T-die, each resin composition was melted at 280 °C, laminated in a layer A / intermediate layer / B configuration using a feedblock method, cast from a T-die at 280 °C, and adhered to a 10 °C chill roll using an electrostatic adhesion method to obtain an unstretched sheet. The resulting unstretched sheet was then stretched 3.5 times in the MD direction at 115 °C, then passed through a tenter and stretched 4.0 times in the TD direction at 120 °C, followed by heat setting at 215 °C for 3 seconds and relaxation at 7% for 1 second to obtain a 12 μm thick biaxially oriented polyester film. The physical properties and evaluation results of the resulting film are shown in Table 1.

[0087] [Examples 2 to 4] In Examples 2 to 4, biaxially stretched polyester films having a thickness of 12 μm were obtained by film formation in the same manner as in Example 1, except that the content of silica particles contained in the resin compositions constituting Layer A, the intermediate layer, and Layer B, and the layer thickness ratio (Layer A / Intermediate layer / Layer B) were changed as shown in Table 1. The physical properties and evaluation results of the obtained films are shown in Table 1.

[0088] [Example 5] A biaxially stretched polyester film having a thickness of 12 μm was obtained by film formation in the same manner as in Example 1, except that the silica particles in Example 5 were changed to Sylysia 420 (average particle size 3.1 μm, pore volume 1.25 ml / g) manufactured by Fuji Silysia Ltd. The physical properties and evaluation results of the obtained film are shown in Table 1.

[0089]

[0090] Comparative Example 1 Comparative Example 1 was carried out in the same manner as in Example 1, except that the content of silica particles in Layer B was changed to the content of silica particles shown in Table 2. The physical properties and evaluation results of the obtained film are shown in Table 2. The dynamic friction coefficient (Layer A / Layer B) of the obtained film was too large to be measured. In addition, the film winding property was also poor.

[0091] Comparative Example 2 Comparative Example 2 was carried out in the same manner as in Example 1, except that the content of silica particles in Layer A was changed to the content of silica particles shown in Table 2. The physical properties and evaluation results of the obtained film are shown in Table 2. The obtained film had a small dynamic friction coefficient (Layer A / metal plate) and lost its slip resistance. In addition, the start angle of inclined sliding was small for all plastic containers, and the results were poor.

[0092] Comparative Example 3 Comparative Example 3 was carried out in the same manner as in Example 1, except that the layer thickness ratio of Layer A to Layer B was changed to the thickness ratio shown in Table 2. The physical properties and evaluation results of the obtained film are shown in Table 2. Because Layer A was thin, the obtained film had a small dynamic friction coefficient (Layer A / metal plate), and the film lost its slip resistance. In addition, the start angle of inclined sliding was small for all plastic containers, and the film was poor.

[0093] Comparative Example 4 Comparative Example 4 was carried out in the same manner as in Example 1, except that the content of silica particles in Layer B was changed to the content of silica particles shown in Table 2. The physical properties and evaluation results of the obtained film are shown in Table 2. The obtained film had a high content of silica particles, and as a result, the haze was deteriorated.

[0094] Comparative Example 5 Comparative Example 5 was carried out in the same manner as in Example 1, except that the silica particles were changed to Sylysia 530 (average particle size 2.7 μm, pore volume 0.80 ml / g) manufactured by Fuji Silysia Ltd. The physical properties and evaluation results of the obtained film are shown in Table 2. The obtained film had a poor haze because the pore volume of the silica particles was small and coarse protrusions were likely to form.

[0095] Comparative Example 6 Comparative Example 6 was carried out in the same manner as in Example 1, except that the silica particles were changed to Sylysia 250 (average particle size 5.0 μm, pore volume 1.80 ml / g) manufactured by Fuji Silysia Ltd. The physical properties and evaluation results of the obtained film are shown in Table 2. The obtained film had a large pore volume of the silica particles and was easily crushed, so the dynamic friction coefficient (layer A / layer B) was too large to be measured. In addition, the film winding property was also poor.

[0096]

Claims

1. A biaxially oriented polyester film having at least a layer A and a layer B, each of which contains a polyethylene terephthalate resin as a main component, and which satisfies the following conditions (a) to (c): (a) the dynamic friction coefficient when the surface of the biaxially oriented polyester film on the layer A side is brought into contact with a metal plate is 0.20 to 1.00; (b) the dynamic friction coefficient when the surface of the biaxially oriented polyester film on the layer A side is brought into contact with a surface of the biaxially oriented polyester film on the layer B side is 0.35 to 0.50; and (c) the haze value of the biaxially oriented polyester film converted to a thickness of 12 μm is 4.5% or less.

2. A biaxially oriented polyester film having at least a layer A and a layer B, each of which contains polyethylene terephthalate resin as a main component, wherein the layer A has a lubricant content of 0 to 400 ppm by mass and the layer B has a lubricant content of 500 to 4,500 ppm by mass, the weight average particle size of the lubricant is 0.5 to 4.0 μm, the haze value calculated based on a thickness of 12 μm of the biaxially oriented polyester film is 4.5% or less, and the ratio of the thickness of the layer A to the thickness of the entire biaxially oriented polyester film is 30 to 90%.

3. The biaxially oriented polyester film according to claim 1 or 2, which has a puncture strength of 0.60 to 1.00 N / μm.

4. The biaxially oriented polyester film according to claim 1, wherein the ratio of the thickness of said layer A to the total thickness of said biaxially oriented polyester film is 30 to 90%.

5. The biaxially oriented polyester film according to claim 1 or 2, wherein the biaxially oriented polyester film has an intermediate layer between the layer A and the layer B, the intermediate layer containing 60 to 100% by mass of a polyethylene terephthalate resin.

6. The biaxially oriented polyester film according to claim 5, wherein the lubricant content in the intermediate layer is 0 to 2,500 ppm by mass.

7. The biaxially oriented polyester film according to claim 5, wherein the thickness of said layer A is equal to or greater than the thickness of said intermediate layer.

8. The biaxially oriented polyester film according to claim 1 or 2, wherein the thickness of said layer B is smaller than the thickness of said layer A.

9. The biaxially oriented polyester film according to claim 2, wherein the difference between the lubricant content in the A layer and the lubricant content in the B layer is 700 to 4,000 ppm by mass.

10. The biaxially oriented polyester film according to claim 2, wherein the pore volume of the lubricant is 1.0 to 1.7 ml / g.

11. The biaxially oriented polyester film according to claim 2, wherein the lubricant comprises at least one inorganic lubricant selected from the group consisting of silica, calcium carbonate, and alumina.

12. The biaxially oriented polyester film according to claim 1 or 2, wherein the haze value of the biaxially oriented polyester film is 0.1 to 4.5% when calculated based on a thickness of 12 μm.

13. A laminate comprising the biaxially oriented polyester film according to claim 1 or 2 and a sealant film.

14. A package comprising the biaxially oriented polyester film according to claim 1 or 2.

15. A top seal material for a container, comprising the biaxially oriented polyester film according to claim 1 or 2.

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