Polyester film and application thereof

Abstract

An object of the present invention is to provide a polyester film containing a regenerated polyester resin and capable of extending the life of a cutting blade while exhibiting good cutting properties.SOLUTION: The present invention relates to polyester films containing polyester resins obtained by chemically recycling films or fibers and having a maximum indentation depth of 3.2 μm or more when an indenter is pushed with a 40mN in microhardness measurement, a Martens hardness of 113N / mm2 or less when an indenter is pushed with a 40mN in microhardness measurement, or an indentation modulus of 2710N / mm2 or less when an indenter is pushed with a 40mN in microhardness measurement.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyester film, a release film, a polyester film with a ceramic green sheet, use of the polyester film as a support for a ceramic green sheet, and a method for producing a ceramic green sheet. [Background technology]

[0002] Polyester films, typified by polyethylene terephthalate films and polyethylene naphthalate films, have excellent properties such as mechanical properties, dimensional stability, flatness, heat resistance, chemical resistance, and optical properties, and are also excellent in cost performance, and are therefore used in a variety of applications. For example, by utilizing the smoothness of the film surface, polyester films are suitably used in a variety of applications, such as release films for molding green sheets for multilayer ceramic capacitors, substrates for releasing interlayer insulating resins, and substrates for dry film resists.

[0003] For example, polyester films are used as supports for release films used to mold green sheets for multilayer ceramic capacitors. In recent years, progress has been made in miniaturizing and increasing the capacity of multilayer ceramic capacitors, leading to the thinning of ceramic green sheets. As ceramic green sheets become thinner, any minute protrusions on the surface of the release film acting as a carrier film can cause pinholes and other defects in the ceramic green sheets. For this reason, release films used to manufacture ceramic green sheets are required to have a high degree of surface smoothness.

[0004] In recent years, in light of growing environmental concerns and resource conservation, recycling of used PET containers such as PET bottles has been practiced, and methods for utilizing such containers have been attracting attention. For example, Patent Documents 1 to 3 disclose polyethylene terephthalate films made of polyester resin compositions containing recycled raw materials derived from PET bottles, in which the recycled raw materials are mechanically recycled polyester resins and / or chemically recycled polyester resins. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-56047 [Patent Document 2] Japanese Patent Publication No. 2023-35545 [Patent Document 3] Japanese Patent Application Publication No. 2023-36069 Summary of the Invention [Problem to be solved by the invention]

[0006] However, because recycling PET containers involves collecting waste from the market and turning it into recycled raw material, the amount of foreign matter contained in the raw material is higher than that of PET raw material derived from fossil fuels (virgin PET raw material).This has made it difficult to use recycled polyester raw material for the polyester film substrate used in manufacturing ceramic green sheets, which require particularly excellent surface smoothness.

[0007] In the cutting and peeling process of ceramic green sheets, the ceramic green sheet with a carrier film is fed onto a cutting table equipped with a suction holding function, and while the ceramic green sheet with the carrier is held on the cutting table by suction, a cutting blade is used to cut the ceramic green sheet into a predetermined shape. If the ceramic green sheet is not cut sufficiently during the cutting and peeling process, it may be difficult to peel the ceramic green sheet from the carrier film. For this reason, cutting blades are required to have good cutting properties, and at the same time, cutting blades are also required to have a long life.

[0008] Therefore, in order to solve these problems of the conventional technology, the inventors have conducted research with the aim of providing a polyester film that contains recycled polyester resin, exhibits good cutting properties, and enables a longer life of the cutting blade. [Means for solving the problem]

[0009] Examples of specific embodiments of the present invention are given below.

[0010] [1] Contains polyester resin made from chemically recycled film or fiber, A polyester film whose maximum indentation depth when pressed with an indenter at 40 mN in microhardness measurements is 3.2 μm or more. [2] Contains polyester resins chemically recycled from film or fiber, In microhardness measurements, the Martens hardness was 113N / mm when the indenter was pressed with 40mN. 2 The following is a polyester film. [3] Contains polyester resins chemically recycled from films or fibers, In microhardness measurements, the indentation modulus when the indenter was pressed with 40 mN was 2710 N / mm 2 The following is a polyester film. [4] The polyester film according to any one of [1] to [3], wherein the heat shrinkage in the MD direction when heated at 120°C for 5 minutes divided by the intrinsic viscosity of the polyester film (% / (dL / g)) is less than 1.28% / (dL / g). [5] The polyester film according to any one of [1] to [4], which has a thermal shrinkage rate in the MD direction when heated at 120°C for 5 minutes of less than 0.75%. [6] The polyester film according to any one of [1] to [5], wherein the polyester resin is substantially free of an isophthalic acid unit as a dicarboxylic acid component. [7] The polyester film according to any one of [1] to [6], wherein the content of structural units derived from monomers obtained by depolymerization contained in the polyester resin is 10 mass % or more. [8] The polyester film according to any one of [1] to [7], wherein the total content of structural units derived from monomers obtained by depolymerization and structural units derived from recycled raw materials is 20% by mass or more relative to the content of all monomer units constituting the polyester film. [9] The polyester film according to any one of [1] to [8], which is a laminated polyester film having two or more layers.

[10] The polyester film according to any one of [1] to [9], further comprising a coating layer on at least one surface of the polyester film.

[11] The polyester film according to any one of [1] to

[10] , which has a temperature-raised recrystallization temperature (Tc) of 142.0°C or lower.

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

[11] , which has a heating recrystallization peak calorie (ΔHc) of 31.5 J / g or less.

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

[12] , which is used as a support for a ceramic green sheet in the process of producing a multilayer ceramic capacitor.

[14] A release film comprising the polyester film according to any one of [1] to

[13] , further comprising a release layer on at least one side thereof.

[15] A polyester film with a ceramic green sheet, obtained by laminating a ceramic green sheet on the polyester film according to any one of [1] to

[13] .

[16] Use of the polyester film according to any one of [1] to

[13] as a support for a ceramic green sheet in a process for producing a multilayer ceramic capacitor.

[17] A method for producing a ceramic green sheet, comprising a step of applying a ceramic slurry containing a ceramic component to at least one surface of the polyester film according to any one of [1] to

[13] . [Effects of the Invention]

[0011] According to the present invention, it is possible to obtain a polyester film that contains recycled polyester resin, exhibits good cutting properties, and enables a longer life of the cutting blade. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below. The following description may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, when "X to Y" (X and Y are arbitrary numbers) is used, it means "X or more and Y or less" unless otherwise specified, and also includes "preferably greater than X" or "preferably less than Y." Furthermore, when "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), it also includes the meaning "preferably greater than X" or "preferably less than Y." In the following description, the terms "film" and "sheet" are not clearly distinguished from each other, and the term "film" includes the term "sheet," and the term "sheet" includes the term "film."

[0013] (polyester film) A first embodiment of the present invention relates to a polyester film (hereinafter also referred to as the present film) containing a polyester resin obtained by chemically recycling a film or fiber, and having a maximum indentation depth of 3.2 μm or more when an indenter is pressed with 40 mN in a microhardness measurement. In the first embodiment, the maximum indentation depth when an indenter is pressed with 40 mN in a microhardness measurement is preferably 3.3 μm or more, more preferably 3.4 μm or more, and even more preferably 3.5 μm or more. Furthermore, the maximum indentation depth when an indenter is pressed with 40 mN in a microhardness measurement is preferably 5.5 μm or less, more preferably 5.4 μm or less, and even more preferably 5.3 μm or less. If the maximum indentation depth when an indenter is pressed with 40 mN in a microhardness measurement is equal to or greater than the above-mentioned lower limit, it means that the indenter is pressed to a certain depth or more, and depressions are likely to be formed on the film surface. That is, if the maximum indentation depth when an indenter is pressed with 40 mN in the microhardness measurement is equal to or greater than the lower limit, it indicates that the film surface has high flexibility.

[0014] The second embodiment of the present invention includes a polyester resin obtained by chemically recycling a film or fiber, and in a microhardness measurement, the Martens hardness is 113 N / mm when an indenter is pressed with 40 mN. 2 In the second embodiment, the Martens hardness is 110 N / mm when an indenter is pressed with 40 mN in a microhardness measurement. 2 Preferably, it is less than 105N / mm 2 More preferably, it is 100 N / mm or less. 2 More preferably, it is 95 N / mm or less. 2 More preferably, it is 90 N / mm or less. 2 In addition, in a microhardness measurement, the Martens hardness when an indenter is pressed with 40 mN is 40 N / mm 2 It is preferable that the resistance is 45N / mm or more. 2 More preferably, it is 50N / mm 2More preferably, it is equal to or greater than this.

[0015] The third embodiment of the present invention includes a polyester resin obtained by chemically recycling a film or fiber, and in a microhardness measurement, the indentation modulus is 2710 N / mm when an indenter is pressed with 40 mN. 2 In a third embodiment, the present invention relates to a polyester film (hereinafter also referred to as the present film) having an indentation modulus of 2700 N / mm when an indenter is pressed with 40 mN in a microhardness measurement. 2 Preferably, it is 2500N / mm or less. 2 More preferably, it is 2250 N / mm or less. 2 More preferably, it is 2000 N / mm or less. 2 In addition, in the microhardness measurement, the indentation elastic modulus when the indenter is pressed with 40 mN is 1100 N / mm 2 It is preferable that the resistance is 1300N / mm or more. 2 More preferably, it is 1500N / mm 2 More preferably, it is equal to or greater than this.

[0016] In this specification, the above first to third embodiments may be collectively referred to as "the present embodiment."

[0017] In microhardness measurement, the maximum indentation depth (μm) when the indenter is pressed with 40 mN, and the Martens hardness (N / mm 2 ) and indentation modulus (N / mm 2 ) is a value measured by the following method. First, about 2 to 8 mg of Aron Alpha is dropped onto a glass slide (S1112, manufactured by Matsunami Glass Industry Co., Ltd.), and one side of a polyester film (1.5 cm x 1.5 cm) serving as a sample film is placed on top of it as an adhesive surface and allowed to harden. The glass slide with the sample film attached is then fixed to the sample stage of a hardness tester (dynamic ultra-micro hardness tester (DUH-211S, manufactured by Shimadzu Corporation) and a load-unload test is carried out on the surface of the sample film under the following conditions, and the maximum indentation depth (μm), Martens hardness (N / mm 2) and indentation modulus (N / mm 2 ) is measured. (Measurement conditions) Indenter used: Diamond regular triangular pyramid indenter (edge ​​angle: 115) Measurement mode: Load-unload test Test force: 40.00 mN Minimum test force: 0.20 mN Load rate: 0.5330 mN / sec Load holding time: 0 sec Unload holding time: 0 sec Measurement atmosphere: 23±2°C, relative humidity 50±5%

[0018] In this embodiment, by using a polyester resin obtained by chemically recycling a film or fiber as the recycled polyester resin, the maximum indentation depth (μm) and Martens hardness (N / mm 2 ) and indentation modulus (N / mm 2 ) can be set within a desired range, thereby increasing the flexibility of the film surface. This makes it possible to obtain a polyester film that exhibits good cutting properties and enables a longer life of the cutting blade.

[0019] When the film surface is highly flexible, it is possible to prevent a decrease in the penetration speed of the cutting blade penetrating into the film, and the film can more easily follow the cutting edge of the cutting blade, which is thought to improve cutting performance. Furthermore, since the film can more easily follow the cutting edge of the cutting blade, roughness of the cut film cross section can be prevented. In the manufacturing process of multilayer ceramic capacitors, when multiple green sheets are stacked, alignment is performed based on the edge faces, which can cause roughness and burrs on the cut cross section, resulting in poor alignment accuracy. For this reason, using this film, which has excellent cutting properties, as a support is preferable because it can improve alignment accuracy in the manufacturing process of multilayer ceramic capacitors.

[0020] In recent years, there has been a demand for improved yields of good capacitor chips. Therefore, there is a need for polyester films that offer high smoothness and can contribute to the extended life of cutting blades during the cutting and trimming process, thereby contributing to improved yields of good capacitor chips. For example, cutting blades for ceramic green sheets are typically used repeatedly during the cutting process to cut the sheets to a specified size depending on the number of layers of the ceramic green sheet. During this cutting process, the cutting blade penetrates the polyester film substrate immediately below the ceramic green sheet in the thickness direction after passing through the ceramic green sheet. If the surface of the substrate film lacks flexibility, the force (damage) applied to the cutting blade edge becomes significant, resulting in a shortened blade life. The highly flexible surface of this film effectively prevents chipping of the cutting blade, even with repeated cutting, thereby contributing to the extended life of the cutting blade. Thus, this film is a polyester film with excellent cutting properties that can contribute to the extended life of cutting blades.

[0021] In this embodiment, the content of polyester resin obtained by chemically recycling film or fiber relative to the total mass of resin components contained in the polyester film is preferably 20% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. The upper limit of the content of polyester resin obtained by chemically recycling film or fiber is not particularly limited, and may be 100% by mass or 95% by mass. In this manner, since this embodiment can contain a very high proportion of recycled polyester resin, it can also be called a recycled polyester film. Use of such a polyester film can, for example, reduce CO2 emissions and contribute to reducing the burden on the environment. Furthermore, by keeping the content of recycled polyester resin within the above range, the maximum indentation depth (μm) when an indenter is pressed with 40 mN in a microhardness measurement, the Martens hardness (N / mm 2 ) and / or indentation modulus (N / mm 2 ) can be set within a desired range, which can improve the cutting ability of the polyester film and further contribute to extending the life of the cutting blade.

[0022] In this embodiment, the content of the polyester resin obtained by chemically recycling a film or fiber relative to the total mass of the resin components contained in the polyester film may be 2% by mass or more, 4% by mass or more, 6% by mass or more, or 8% by mass or more. The content of the chemically recycled polyester resin may be 60% by mass or less, 55% by mass or less, 50% by mass or less, 45% by mass or less, or 40% by mass or less. By setting the content of the chemically recycled polyester resin to the above-mentioned content ratio, for example, it is possible to further increase the proportion of recycled polyester resin used while suppressing costs, and it is also preferable because a high-quality film can be easily obtained even when recycled polyester resin is used.

[0023] In this embodiment, the sum of the content of structural units derived from monomers obtained by depolymerization and the content of structural units derived from recycled raw materials relative to the content of all monomer units constituting the polyester film is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more. The sum of the content of structural units derived from monomers obtained by depolymerization and the content of structural units derived from recycled raw materials may be 100% by mass. In this specification, the ratio of the sum of the content of structural units derived from monomers obtained by depolymerization and the content of structural units derived from recycled raw materials relative to the content of all monomer units constituting the polyester film is also referred to as the recycle rate.

[0024] The manufacturing process of multilayer ceramic capacitors includes heat treatments, such as drying a release agent coated on a polyester film and drying a ceramic slurry coated on a release film. Therefore, a decrease in the heat distortion resistance of polyester films can lead to coating irregularities and wrinkles. In other words, the heat distortion resistance of polyester films is an important characteristic for ensuring the quality and reliability of the finished product, from intermediate products to finished products in the manufacturing process of multilayer ceramic capacitors, such as the lamination characteristics of ceramic green sheets. To prevent such coating irregularities and wrinkles, the heat shrinkage of the present film in the machine direction (MD) after heat treatment at 120°C for 5 minutes is preferably less than 0.75%, more preferably 0.73% or less, even more preferably 0.70% or less, and even more preferably 0.68% or less. From the same perspective, the heat shrinkage in the machine direction (MD) (120°C, 5 minutes) is preferably 0.1% or more, more preferably 0.2% or more, and even more preferably 0.3% or more.

[0025] Furthermore, the heat shrinkage of this film in the transverse direction (TD) when heat-treated at 120°C for 5 minutes is preferably 0.5% or less, more preferably 0.4% or less, even more preferably 0.35% or less, even more preferably 0.3% or less, and particularly preferably 0.2% or less, from the viewpoint of suppressing coating irregularities and wrinkles. From the same viewpoint, the heat shrinkage in the transverse direction (TD) is preferably -0.5% or more, more preferably -0.4% or more, and even more preferably -0.3% or more.

[0026] The heat shrinkage rate of this film (heated at 120°C for 5 minutes) is calculated using the following formula. Heat shrinkage rate (%) = {(length of evaluation film before heat treatment) - (length of evaluation film after heat treatment)} / (length of evaluation film before heat treatment) × 100

[0027] The intrinsic viscosity of the present film is preferably 0.45 dL / g or more, more preferably 0.48 dL / g or more, even more preferably 0.5 dL / g or more, even more preferably 0.52 dL / g or more, even more preferably 0.55 dL / g or more, and particularly preferably 0.57 dL / g or more. The intrinsic viscosity of the present film is preferably 0.75 dL / g or less, more preferably 0.72 dL / g or less, even more preferably 0.7 dL / g or less, even more preferably 0.68 dL / g or less, and particularly preferably 0.65 dL / g or less. The intrinsic viscosity of the present film was measured at 30°C using a viscosity (IV) measuring device after weighing out 1 g of polyester film and dissolving it in 100 mL of a 50 / 50 (mass ratio) phenol / tetrachloroethane mixed solvent.

[0028] In this embodiment, the value (% / (dL / g)) obtained by dividing the heat shrinkage in the MD direction when heated at 120°C for 5 minutes by the intrinsic viscosity of the film is preferably less than 1.28% / (dL / g), more preferably 1.25% / (dL / g) or less, even more preferably 1.20% / (dL / g) or less, even more preferably 1.17% / (dL / g) or less, and particularly preferably 1.14% / (dL / g) or less. Furthermore, the value (% / (dL / g)) obtained by dividing the heat shrinkage in the MD direction when heated at 120°C for 5 minutes by the intrinsic viscosity of the film is preferably 0% / (dL / g) or more, and may be 0.3% / (dL / g) or more. By setting the value obtained by dividing the heat shrinkage rate in the MD direction when heated at 120°C for 5 minutes by the intrinsic viscosity within the above range, the heat distortion resistance of the polyester film can be more effectively improved, resulting in improved dimensional stability and suppression of coating irregularities, wrinkles, etc.

[0029] The glass transition temperature (Tg), temperature-rising recrystallization temperature (Tc), temperature-rising recrystallization peak calorific value (ΔHc), melting peak temperature (Tm), and melting peak calorific value (ΔHm) of the present film can be measured, for example, using a differential scanning calorimeter (DSC60) manufactured by Shimadzu Corporation under the following measurement conditions. (1) Heat from 20°C to 300°C at 10°C / min (2) Hold at 300°C for 5 minutes (3) Cool down to 20°C at 600°C / min (4) Keep at 20°C for 5 minutes (5) Heat from 20°C to 300°C at 10°C / min (6) Hold at 300°C for 5 minutes (7) Decrease temperature to 20°C at 600°C / min

[0030] The temperature-raised recrystallization temperature (Tc) of the present film in (5) above is preferably 127° C. or higher, more preferably 130° C. or higher, even more preferably 133° C. or higher, even more preferably 136° C. or higher, and particularly preferably 140° C. or higher. The temperature-raised recrystallization temperature (Tc) of the present film in (5) above is, for example, preferably 160° C. or lower, and may be 155° C. or lower, 152° C. or lower, or 148° C. or lower.

[0031] The heat-rising recrystallization peak calorific value (ΔHc) of the film in (5) above is preferably 23 J / g or more, more preferably 26 J / g or more, even more preferably 28 J / g or more, and even more preferably 30 J / g or more. The heat-rising recrystallization peak calorific value (ΔHc) of the film in (5) above is preferably 45 J / g or less, and may be 42 J / g or less, 39 J / g or less, or 36 J / g or less.

[0032] The glass transition temperature (Tg) of the present film in (5) above is preferably 65° C. or higher, more preferably 70° C. or higher, even more preferably 74° C. or higher, and even more preferably 77° C. or higher. The glass transition temperature (Tg) of the present film in (5) above is preferably 95° C. or lower, more preferably 90° C. or lower, even more preferably 86° C. or lower, and even more preferably 83° C. or lower.

[0033] The melting peak temperature (Tm) of the present film in (5) above is preferably 230° C. or higher, more preferably 235° C. or higher, even more preferably 240° C. or higher, even more preferably 245° C. or higher, and particularly preferably 248° C. or higher. The melting peak temperature (Tm) of the present film in (5) above is preferably 270° C. or lower, more preferably 265° C. or lower, even more preferably 260° C. or lower, and even more preferably 257° C. or lower.

[0034] The peak heat of fusion (ΔHm) of the present film in (5) above is preferably 18 J / g or more, more preferably 22 J / g or more, even more preferably 25 J / g or more, even more preferably 27 J / g or more, even more preferably 30 J / g or more, and particularly preferably 33 J / g or more. The peak heat of fusion (ΔHm) of the present film in (5) above is preferably 50 J / g or less, more preferably 47 J / g or less, even more preferably 44 J / g or less, and may be 41 J / g or less.

[0035] The melting peak temperature (Tm) of the present film in (1) above is preferably 235° C. or higher, more preferably 240° C. or higher, even more preferably 245° C. or higher, even more preferably 248° C. or higher, even more preferably 252° C. or higher, and particularly preferably 254° C. or higher. The melting peak temperature (Tm) of the present film in (1) above is preferably 270° C. or lower, more preferably 267° C. or lower, even more preferably 263° C. or lower, and even more preferably 260° C. or lower.

[0036] The melting peak heat quantity (ΔHm) of the present film in (1) above is preferably 25 J / g or more, more preferably 28 J / g or more, even more preferably 31 J / g or more, even more preferably 34 J / g or more, still more preferably 37 J / g or more, and particularly preferably 40 J / g or more. The melting peak heat quantity (ΔHm) of the present film in (1) above is preferably 55 J / g or less, more preferably 52 J / g or less, even more preferably 48 J / g or less, and may be 46 J / g or less.

[0037] By setting the glass transition temperature (Tg), temperature-rising recrystallization temperature (Tc), temperature-rising recrystallization peak calorific value (ΔHc), melting peak temperature (Tm), and melting peak calorific value (ΔHm) of the present film within the above ranges, stable production tends to be possible without the need to change production conditions such as the melting process and stretching process each time, which is preferable.

[0038] The tensile strength of the present film in the MD direction is preferably 100 MPa or more, more preferably 120 MPa or more, even more preferably 150 MPa or more, even more preferably 170 MPa or more, and particularly preferably 200 MPa or more. The tensile strength of the present film in the MD direction may be 450 MPa or less, 400 MPa or less, 350 MPa or less, or 300 MPa or less. The tensile strength of the present film in the TD direction is preferably 160 MPa or more, more preferably 180 MPa or more, and even more preferably 200 MPa or more. The tensile strength of the present film in the longitudinal direction (TD) may be 400 MPa or less, 350 MPa or less, or 300 MPa or less. The tensile strength refers to the tensile breaking stress according to JIS K 7161-1: 2014. Measurements are performed under conditions of 23°C, 50% relative humidity, a chuck distance of 50 mm for the test piece, and a tensile speed of 200 mm / min.

[0039] The tensile elongation in the MD direction of the present film is preferably 70% or more, more preferably 100% or more, even more preferably 130% or more, even more preferably 160% or more, and particularly preferably 190% or more. The tensile elongation in the longitudinal direction (MD) of the present film may be 300% or less, 280% or less, or 260% or less. The tensile elongation of the present film in the TD direction is preferably 70% or more, more preferably 85% or more, and even more preferably 100% or more, and may be 300% or less, 250% or less, or 200% or less. The tensile elongation refers to the tensile breaking elongation (nominal tensile breaking strain) according to JIS K 7161-1: 2014. The measurement is performed under the conditions of an atmosphere of 23°C and 50% relative humidity, with a chuck distance of 50 mm for the test piece and a pulling speed of 200 mm / min.

[0040] The total thickness of the present film is not particularly limited as long as it is within a range that allows film formation, but from the viewpoints of mechanical strength, handleability, productivity, etc., it is preferably 10 μm or more, more preferably 12 μm or more, and even more preferably 14 μm or more. Furthermore, the total thickness of the present film is preferably 150 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, even more preferably 50 μm or less, even more preferably 38 μm or less, and particularly preferably 35 μm or less. The total thickness of the present film may be, for example, 34 μm or less, or 30 μm or less.

[0041] The film may be a single-layer polyester film, or a laminated polyester film having two or more layers. In this case, the laminated polyester film may be a two-layer laminated polyester film consisting of a first layer and a second layer, or may be a laminated polyester film having a surface layer, an intermediate layer, and a back layer. When the polyester film is a laminated polyester film, other layers may be provided between the layers, but it is preferable that the layers are laminated so that they are in direct contact with each other.

[0042] When the present film is a laminated polyester film having two or more layers, it is sufficient that at least one layer constituting the laminated polyester film contains a polyester resin obtained by chemically recycling a film or fiber. All layers may contain a polyester resin obtained by chemically recycling a film or fiber, or only one of the surface layer or the intermediate layer may contain a polyester resin obtained by chemically recycling a film or fiber.

[0043] This embodiment may also relate to a roll (rolled body) obtained by winding the present film. Because the present film has appropriate strength and flexibility, it can be stored or distributed as a roll.

[0044] <Polyester resin> The present film contains a polyester resin (hereinafter also referred to as the present polyester resin) obtained by chemically recycling a film or fiber.

[0045] Examples of the dicarboxylic acid component constituting the present polyester resin include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, and 4,4'-diphenylsulfonedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexanedicarboxylic acid, and ester derivatives thereof.

[0046] Examples of diol components constituting the present polyester resin include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-hexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4-hydroxyethoxyphenyl)propane, isosorbate, and spiroglycol.

[0047] When the polyester resin is a homopolyester, it preferably contains structural units derived from an aromatic dicarboxylic acid component and structural units derived from an aliphatic glycol. In this case, examples of aromatic dicarboxylic acids include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of aliphatic glycols include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN), with PET being preferred. Furthermore, examples of the polyester resin include polyethylene terephthalate, which contains 80 mol % or more, preferably 90 mol % or more, of ethylene terephthalate units, and polyethylene-2,6-naphthalate, which contains ethylene-2,6-naphthalate units.

[0048] On the other hand, when the polyester resin is a copolymer polyester, it is preferably a copolymer containing 30 mol% or less of a third component. The third component is a component other than the compound that constitutes the main dicarboxylic acid component of the polyester and the compound that constitutes the main diol component. For example, in the case of polyethylene terephthalate, it is a component other than terephthalic acid and ethylene glycol. Examples of the dicarboxylic acid component of the copolymer polyester include one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid. Examples of the glycol component of the copolymer polyester include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol.

[0049] However, it is preferable that the present polyester resin is substantially free of isophthalic acid units as a dicarboxylic acid component. The phrase "the present polyester resin is substantially free of isophthalic acid units" means that the content of isophthalic acid units relative to 100 mol% of all dicarboxylic acid units constituting the present polyester resin is 0.1 mol% or less. The content of isophthalic acid units is preferably 0.05 mol% or less, more preferably 0.01 mol% or less, and even more preferably 0.005 mol% or less. By having the present polyester resin be substantially free of isophthalic acid units, the heat resistance of the present film can be more effectively improved, and the shrinkage rate can be easily kept low.

[0050] For example, polyesters such as PET bottles recycled from the market or society contain a certain amount of isophthalic acid components for the purpose of controlling crystallinity. On the other hand, polyesters that make up films or fibers often do not contain isophthalic acid components. Therefore, by measuring the content of isophthalic acid units in polyester resins, it is possible to identify recycled raw materials for polyester resins.

[0051] Typically, when polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, diethylene glycol is by-produced from the ethylene glycol. In this specification, this diethylene glycol is referred to as by-product diethylene glycol. The amount of diethylene glycol by-produced from ethylene glycol varies depending on the type of recycled raw material, the mode of polycondensation, and other factors. In this specification, 5 mol% or less of diethylene glycol is defined as by-product diethylene glycol, and by-product diethylene glycol is also considered to be included in ethylene glycol and is distinguished from copolymerization components. On the other hand, depending on the diethylene glycol content, more specifically, when diethylene glycol is contained in excess of 5 mol%, diethylene glycol is treated as a copolymerization component rather than as a by-product diethylene glycol.

[0052] This polyester resin is obtained by chemically recycling polyester, a recycled raw material, and the recycled raw material is a film or fiber. The film that can be recycled is not particularly limited, but examples include optical polyester film, packaging polyester film, and polyester film used as a support (substrate) for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors. Furthermore, examples of the fiber that can be recycled include polyester fibers used in clothing (uniforms, rainwear, sportswear, outerwear, underwear, stockings, swimwear, leotards, etc.), fabric products for furniture covering and upholstery (carpets, car seats, sofa upholstery, etc.), gauze, filters, etc.

[0053] The polyester resin constituting the present film may contain polyester resin obtained by material recycling of recycled raw materials in addition to polyester resin obtained by chemically recycling films or fibers. In this case, the content of material recycled polyester resin may be 90% by mass or less, 70% by mass or less, 50% by mass or less, or 30% by mass or less, based on the total mass of the resin components constituting the present film.

[0054] In this embodiment, a biomass-derived raw material may be used for the polyester, which is a recycled raw material. In this case, it is preferable that the diol component of the polyester is a biomass-derived raw material. The biomass-derived ethylene glycol is made from ethanol (biomass ethanol) produced from biomass as a raw material. For example, biomass-derived ethylene glycol can be obtained by converting biomass ethanol into ethylene oxide using a conventionally known method to produce ethylene glycol. Alternatively, commercially available biomass ethylene glycol may be used; for example, biomass ethylene glycol commercially available from India Glycoal Limited can be suitably used. The biomass-derived ethylene glycol may be used as a raw material in the repolymerization step of chemical recycling, which will be described later.

[0055] <<Chemical recycled polyester>> This polyester resin is a polyester resin obtained by chemically recycling film or fiber. One method for producing chemically recycled polyester resin is to sort, crush, and wash collected PET bottles and polyester films to remove foreign matter, then depolymerize them to break them down into raw materials or intermediate raw materials for polyester resin, purify them, and then repolymerize these raw materials. A distinctive feature of chemically recycled polyester resin is that foreign matter and other materials are removed during the depolymerization / repolymerization process, allowing it to be recycled into high-quality polyester resin.

[0056] Depolymerization can be achieved by adding glycol (e.g., ethylene glycol (EG)) to the resin in the presence of a catalyst to convert it back to bishydroxyethyl terephthalate (BHET), an intermediate raw material used in resin production, which is then purified and repolymerized into PET. Alternatively, polyethylene terephthalate is heated in a non-aqueous organic solvent in the presence of a catalyst containing oxidized iron as an essential component to produce terephthalic acid and ethylene glycol, which are then polymerized again. In particular, the present embodiment preferably employs a method in which depolymerization to bishydroxyethyl terephthalate (BHET) is followed by repolymerization into PET. Alternatively, the present embodiment also preferably employs a method in which the depolymerized bishydroxyethyl terephthalate (BHET) is subjected to a transesterification reaction with methanol to obtain dimethyl terephthalate (DMT), and then the DMT is polycondensed with a diol component to obtain a repolymerized polyester.

[0057] In this specification, chemically recycled polyester resin (chemically recycled polyester) refers to a polyester resin containing structural units derived from monomers obtained by depolymerization. The content of structural units derived from monomers obtained by depolymerization contained in the polyester resin obtained by chemically recycling a film or fiber is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, even more preferably 40 mol% or more, even more preferably 50 mol% or more, even more preferably 60 mol% or more, and particularly preferably 70 mol% or more. All of the monomers constituting the chemically recycled polyester may be monomers obtained by depolymerization, and the content of structural units derived from monomers obtained by depolymerization contained in the chemically recycled polyester may be 100 mol%.

[0058] Furthermore, the content of structural units derived from monomers obtained by depolymerization contained in the polyester resin obtained by chemical recycling of films or fibers is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, even more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more. All of the monomers constituting the chemically recycled polyester may be monomers obtained by depolymerization, and the content of structural units derived from monomers obtained by depolymerization contained in the chemically recycled polyester may be 100% by mass.

[0059] When a film or fiber is depolymerized to bishydroxyethyl terephthalate (BHET) and then repolymerized to PET, the process for obtaining a chemically recycled polyester resin includes, for example, the following steps. (1) A process for crushing the recovered film or fiber (2) A process to remove polymer components other than polyester and foreign substances (3) A process in which the ground polyester is introduced into glycol containing a depolymerization catalyst to depolymerize it, thereby obtaining bishydroxyethyl terephthalate (BHET). (4) Solid-liquid separation process, concentration process and / or purification process of bishydroxyethyl terephthalate (BHET) (5) A step of polycondensing bishydroxyethyl terephthalate (BHET) in the presence of a polycondensation catalyst

[0060] When a film or fiber is depolymerized to bishydroxyethyl terephthalate (BHET), dimethyl terephthalate (DMT) is obtained, and then DMT and a diol component are polycondensed, a process for obtaining a chemically recycled polyester resin includes, for example, the following steps. (1') A step of crushing the recovered film or fiber (2') A process for removing polymer components other than polyester and foreign substances (3') A step of obtaining bishydroxyethyl terephthalate (BHET) by adding the pulverized polyester to glycol containing a depolymerization catalyst and depolymerizing it. (4') Solid-liquid separation process, concentration process and / or purification process of bishydroxyethyl terephthalate (BHET) (5') A step of mixing bishydroxyethyl terephthalate (BHET) with methanol to carry out an ester exchange reaction. (6') Solid-liquid separation process, concentration process and / or purification process of dimethyl terephthalate (DMT) (7') A step of polycondensing dimethyl terephthalate (DMT) and a diol component in the presence of a polycondensation catalyst

[0061] In the above step (1) or (1'), the recovered film or fiber is washed as necessary and then crushed into flakes. Crushing may be performed in water, or the washing step and crushing step may be performed simultaneously. The washing step may involve alkaline washing or neutral washing.

[0062] In the above step (2) or (2'), polymer components other than polyester (e.g., nylon, polyethylene, polypropylene, polyvinyl chloride, etc.) contained in the pulverized material are removed. When removing these polymers, methods such as air separation, flotation separation, and centrifugation can be used. Furthermore, before or after these steps, a foreign matter removal step using a physical or chemical separation method may be performed. Furthermore, a bleaching step may be performed before or after these steps. Since polyester fibers are often dyed, in particular, it is preferable to bleach the polyester fibers by treating them with a bleaching treatment solution containing an organic solvent, an alkali agent, a reducing agent, and / or a nonionic surfactant. In the bleaching step, it is preferable to heat the treatment solution to 80°C or higher, if necessary.

[0063] In the above-mentioned process (3) or (3'), bishydroxyethyl terephthalate (BHET) is obtained by adding the ground polyester to glycol containing a depolymerization catalyst and depolymerizing it. Depolymerization using an excess of glycol results in a mixed solution of crude BHET and crude ethylene glycol. Ethylene glycol (EG), 1,3-propanediol, or 1,4-butanediol (BG) is preferred as the glycol, with ethylene glycol (EG) being particularly preferred. In the above-mentioned process (3) or (3'), the ground polyester may be melted and simultaneously hydrolyzed to obtain a polyethylene terephthalate melt with a low degree of polymerization, followed by depolymerization.

[0064] In the above step (3) or (3'), it is preferable to add 0.1 to 50 parts by mass of ethylene glycol (EG) based on the total mass of the ground polyester. The reaction is preferably carried out, for example, at 150 to 260°C under a pressure of 0.1 to 0.5 MPa.

[0065] Examples of the depolymerization catalyst include sodium carbonate, sodium carboxylate, manganese acetate, zinc acetate, etc. The amount of the catalyst used for depolymerization to be added is not particularly limited, but is preferably 0.01 to 10% by mass, for example, relative to the total mass of the recycled raw material.

[0066] Depolymerization may be carried out in the presence of an alkaline compound. Examples of alkaline compounds include tetraethylammonium hydroxide (EAH), potassium hydroxide (KOH), calcium hydroxide, and sodium hydroxide. Among these, tetraethylammonium hydroxide is preferred. By adding an alkaline compound together with glycol in the depolymerization step, the production of by-products such as diethylene glycol (DEG) in the depolymerization reaction can be suppressed. This reduces the DEG content in the polymer polymerized using the low-molecular-weight polymers obtained by depolymerization, thereby improving the polymer quality.

[0067] In the above process (4) or (4'), bishydroxyethyl terephthalate (BHET) undergoes a solid-liquid separation process, a concentration process, and / or a purification process. In the solid-liquid separation process, the ethylene glycol component and the like are removed from the crude BHET to obtain concentrated BHET. After the depolymerization reaction, the two-component mixture of crude BHET and crude ethylene glycol is cooled and filtered to remove solid impurities. Further, adsorption and ion exchange treatments may be performed to remove colored substances and dissolved ions. After the solid-liquid separation process, the two-component mixture of crude BHET and crude ethylene glycol is preferably subjected to distillation or evaporation to separate and distill off the ethylene glycol to obtain concentrated BHET. Alternatively, the two-component mixture may be cooled to 10°C or below to crystallize BHET, followed by solid-liquid separation of the ethylene glycol and BHET to obtain concentrated BHET. This concentrated BHET is then evaporated under vacuum under specified conditions to obtain purified bis-β-hydroxyethyl terephthalate. High-purity purified BHET is obtained in this manner. The purified BHET may contain oligomers in addition to BHET.

[0068] In the above step (5), purified BHET is charged into a melt polycondensation reactor to obtain a repolymerized polyester. The polymerization reaction of BHET is preferably carried out at 200 to 300°C and under a pressure of 0.01 to 0.5 MPa. After the polymerization step, a solid-state polymerization step may be provided to adjust the degree of polymerization, as needed.

[0069] Examples of the polycondensation catalyst used in step (5) include antimony compounds, germanium compounds, aluminum compounds, titanium compounds, phosphorus compounds, magnesium compounds, etc. Among these, it is preferable to use at least one selected from antimony compounds, titanium compounds, magnesium compounds, and phosphorus compounds, it is more preferable to use antimony compounds or titanium compounds, and it is even more preferable to use titanium compounds. By using such compounds, particularly titanium compounds, as the polycondensation catalyst, it is possible to reduce the amount of polycondensation catalyst added, which makes it easier to suppress the formation of foreign matter or protrusions derived from the polycondensation catalyst.

[0070] In the above step (5'), bishydroxyethyl terephthalate (BHET) and methanol are mixed to undergo a transesterification reaction, thereby obtaining dimethyl terephthalate (DMT). The transesterification reaction is preferably carried out at 100 to 250°C under a pressure of 0.01 to 0.5 MPa. Examples of the transesterification catalyst include sodium carbonate, magnesium acetate, manganese acetate, and zinc acetate. The amount of the catalyst used for the transesterification is not particularly limited, but is preferably 0.01 to 10% by mass, for example, relative to the total mass of bishydroxyethyl terephthalate (BHET).

[0071] In the above step (6'), dimethyl terephthalate (DMT) obtained by the transesterification reaction is subjected to a solid-liquid separation step, a concentration step, and / or a purification step. This preferably results in purified DMT being obtained from crude DMT. The solid-liquid separation step, concentration step, and / or purification step can be appropriately selected from the same operations as in the above step (4) or (4').

[0072] In the above (7'), dimethyl terephthalate (DMT) and a diol component are polycondensed in the presence of a polycondensation catalyst, and the purified DMT and the diol component are charged into a melt polycondensation reactor to obtain a repolymerized polyester. As the diol component, ethylene glycol (EG), 1,3-propanediol, or 1,4-butanediol (BG) is preferably used, and among these, ethylene glycol (EG) is particularly preferred.

[0073] Examples of the polycondensation catalyst used in step (7') include antimony compounds, germanium compounds, aluminum compounds, titanium compounds, phosphorus compounds, magnesium compounds, etc. Among these, it is preferable to use at least one selected from antimony compounds, titanium compounds, magnesium compounds, and phosphorus compounds, it is more preferable to use antimony compounds or titanium compounds, and it is even more preferable to use titanium compounds. By using such compounds, particularly titanium compounds, as the polycondensation catalyst, it is possible to reduce the amount of polycondensation catalyst added, which makes it easier to suppress the formation of foreign matter or protrusions derived from the polycondensation catalyst.

[0074] In the above step (7'), the molar ratio of the diol component such as ethylene glycol to dimethyl terephthalate (DMT) is preferably in the range of 1.5 to 2.5, more preferably 1.7 to 2.3, and even more preferably 1.9 to 2.1. By setting the mixing ratio to be equal to or greater than the above lower limit, the transesterification reactivity can be increased, and by setting the mixing ratio to be equal to or less than the above upper limit, the amount of diethylene glycol produced from ethylene glycol can be easily suppressed.

[0075] The polymerization reaction of dimethyl terephthalate (DMT) and the diol component is preferably carried out, for example, at 200 to 300°C under a pressure of 0.01 to 0.5 MPa. After the polymerization step, a solid-phase polymerization step may be provided to adjust the degree of polymerization, as needed.

[0076] The glycol used in the depolymerization step can be reused and may be circulated within the process or in the repolymerization step.

[0077] <<Material: Recycled Polyester>> The polyester resin constituting the present film may contain polyester resin obtained by material recycling of recycled raw materials. In material recycling, collected used PET bottles, polyester film, and polyester fibers are first crushed into flakes. These flakes often contain foreign matter attached to or mixed in, so they are preferably washed, and alkaline washing is more preferable.

[0078] In the process of pelletizing the flakes, an extruder is used to melt, extrude, cool, and granulate the flakes. In the melting process in the extruder, melt kneading is usually carried out at 260 to 300°C. It is preferable that the flakes are sufficiently dried in advance. In addition, the extruder preferably has at least one vacuum vent in the resin melting zone as a degassing means.

[0079] It is also preferable that a filtering means is provided downstream of the extruder, and the filtering means preferably has a filter capable of filtering out solid foreign matter contained in the molten resin.

[0080] The molten resin that has passed through the filter passes through a die, is cooled in water, and then cut into pellets of the desired shape and granulated, thereby obtaining the recycled polyester resin.

[0081] In addition, during the process of cleaning recovered used PET bottles, polyester film, and polyester fibers, or during the process of melting these raw materials, the polyester may be partially hydrolyzed by the cleaning components or heat, resulting in a decrease in the degree of polymerization of the recycled polyester resin. Depending on the intended use, a decrease in the degree of polymerization may result in poor moldability, strength, transparency, heat resistance, and other properties. To restore the decreased degree of polymerization, a solid-state polymerization process may be performed. In the solid-state polymerization process, flakes may be melt-extruded and pelletized, and then continuously solid-state polymerized in an inert gas such as nitrogen gas or a rare gas at 180 to 245°C.

[0082] <<Physical properties of this polyester resin>> The intrinsic viscosity of the polyester resin constituting the present film is preferably 0.5 dL / g or more, more preferably 0.53 dL / g or more, even more preferably 0.56 dL / g or more, and even more preferably 0.6 dL / g or more. The viscosity of the polyester resin constituting the present film is preferably 0.8 dL / g or less, more preferably 0.76 dL / g or less, even more preferably 0.73 dL / g or less, even more preferably 0.7 dL / g or less, and particularly preferably 0.68 dL / g or less. In particular, the intrinsic viscosity of polyester resins obtained by chemically recycling films or fibers is preferably within the above range. By setting the intrinsic viscosity of the polyester resin at or above the above lower limit, stability during film formation can be improved. On the other hand, setting the intrinsic viscosity at or below the above upper limit is preferred, as it facilitates the prevention of excessive pressure buildup in the film-forming extruder and the reduction of the thermal shrinkage of the film. The intrinsic viscosity of the polyester resin was measured at 30°C using a viscosity (IV) measuring device after precisely weighing 1 g of polyester resin and dissolving it in 100 mL of a mixed solvent of phenol / tetrachloroethane = 50 / 50 (mass ratio).

[0083] When the polyester resin is a polyester resin obtained by chemically recycling a film, the intrinsic viscosity (IV) of the polyester resin is preferably 0.5 dL / g or more, more preferably 0.53 dL / g or more, even more preferably 0.56 dL / g or more, and particularly preferably 0.6 dL / g or more. The intrinsic viscosity (IV) of the polyester resin obtained by chemically recycling a film is preferably 0.8 dL / g or less, more preferably 0.76 dL / g or less, even more preferably 0.73 dL / g or less, even more preferably 0.7 dL / g or less, and particularly preferably 0.68 dL / g or less.

[0084] When the polyester resin is a polyester resin obtained by chemically recycling fibers, the intrinsic viscosity (IV) of the polyester resin is preferably 0.5 dL / g or more, more preferably 0.53 dL / g or more, even more preferably 0.56 dL / g or more, and particularly preferably 0.6 dL / g or more. The intrinsic viscosity (IV) of the polyester resin obtained by chemically recycling fibers is preferably 0.78 dL / g or less, more preferably 0.75 dL / g or less, even more preferably 0.7 dL / g or less, even more preferably 0.67 dL / g or less, and particularly preferably 0.65 dL / g or less.

[0085] In this embodiment, a polyester resin having a low content of oligomer components may be used to suppress the amount of precipitation of oligomer components. Various known methods can be used to produce a polyester resin having a low content of oligomer components, such as a method of solid-phase polymerization after polyester production. Furthermore, the polyester may be obtained by esterification or transesterification, followed by melt polycondensation at a higher reaction temperature under reduced pressure.

[0086] <Optional ingredients> In addition to the polyester resin obtained by chemically recycling film or fibers, the present film may contain conventionally known ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc., as necessary.

[0087] The present film may further contain a metal component. The metal component may be a metal used as a polycondensation catalyst when producing polyester, which is a recycled raw material for polyester resin. That is, the present film may contain a polycondensation catalyst used when producing polyester to be recycled (regenerated). Examples of metal components include antimony, phosphorus, manganese, calcium, magnesium, cobalt, tin, germanium, zinc, aluminum, and titanium. Of these, the metal component is preferably at least one selected from the group consisting of antimony, germanium, aluminum, and titanium.

[0088] For example, the compounds contained in the film may vary depending on the type of recycled raw material used. For example, because food packaging polyester films come into direct contact with food, the polycondensation catalysts used in the manufacturing process are limited, and cadmium, palladium, selenium, and other harmful metal components are generally not detected. Therefore, if cadmium, palladium, selenium, and the like are detected, it can be assumed that the food packaging polyester film was not used as a recycled raw material.

[0089] The present film may contain particles. When the present film contains particles, the particles are not particularly limited, and examples thereof include inorganic particles such as metal oxides such as alumina, silica, calcium carbonate, titanium oxide, ceria, zirconium oxide, barium oxide, chromium oxide, iron oxide, and tungsten oxide, composite oxides such as silica-zirconium oxide, silica-titanium oxide, silica-titanium oxide-barium oxide, silica-titanium oxide-zirconium oxide, borosilicate glass, aluminosilicate glass, and fluoroaluminosilicate glass, and organic particles having a carboxy group or a sulfonic acid group. Among these, alumina, silica, calcium carbonate, and organic particles are preferred.

[0090] The shape of the particles in the present film is not particularly limited, and any of spherical, blocky, rod-like, flat, etc. may be used. There are also no particular limitations on the hardness, specific gravity, color, etc. Two or more types of these particles may be used in combination as needed.

[0091] When particles are contained in the present film, the average particle size of the particles contained is, for example, preferably 0.01 μm or more, more preferably 0.03 μm or more, and even more preferably 0.04 μm or more, while the average particle size of the particles contained is preferably 5 μm or less, more preferably 4 μm or less, and even more preferably 3 μm or less.

[0092] In the case of powder particles, the average particle size can be determined by measuring the powder using a centrifugal sedimentation particle size distribution analyzer (e.g., Shimadzu Corporation's "SA-CP3 Model") and determining the particle size at an integrated volume fraction of 50% (d50) in the equivalent spherical distribution. The average particle size of particles in a film or resin can be determined by observing 10 or more particles with a scanning electron microscope (SEM) to measure their diameters and calculating the average value. In this case, for non-spherical particles, the average of the longest and shortest diameters can be measured as the diameter of each particle.

[0093] The particle content of the present film is preferably 200 ppm or more, more preferably 1000 ppm or more, and even more preferably 1500 ppm or more, based on the total mass of the film. Furthermore, the particle content is preferably 20,000 ppm or less, more preferably 15,000 ppm or less, even more preferably 10,000 ppm or less, and even more preferably 8,000 ppm or less, based on the total mass of the film. When two or more types of particles are blended in the present film, the total particle content is preferably within the above range.

[0094] The method for adding the optional components to the present film is not particularly limited, and any conventionally known method can be used. For example, the optional components can be added at any stage in the production of the polyester constituting the present film, but are preferably added after the completion of the esterification or transesterification reaction.

[0095] <Coating layer> In this embodiment, a coating layer may be further provided on at least one surface of the present film. The coating layer is preferably a layer formed by applying a coating layer-forming composition (coating liquid) to the surface of the present film, but may also be a layer formed by laminating a pre-formed resin layer. The coating layer can be formed by in-line coating or off-line coating, but is preferably formed by in-line coating. This can improve the production efficiency of polyester films.

[0096] The thickness of the coating layer is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more, and is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less.

[0097] The coating layer-forming composition preferably contains a binder resin and a crosslinking agent. The total content of the binder resin and crosslinking agent contained in the coating layer-forming composition is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, as non-volatile components. The coating layer-forming composition also preferably contains particles, a catalyst, etc.

[0098] <<Binder resin>> The coating layer-forming composition preferably contains a binder resin. The binder resin is a polymer compound having a number-average molecular weight (Mn) of 1,000 or more as measured by gel permeation chromatography (GPC) in accordance with the "Flow Scheme for the Safety Evaluation of Polymeric Compounds" (November 1985, sponsored by the Chemical Substances Council). Among these, those with film-forming properties are preferred. There are no particular limitations on the binder resin, and conventionally known binder resins such as polyester resins, polyurethane resins, (meth)acrylic resins, polyvinyl resins (e.g., polyvinyl alcohol, vinyl chloride-vinyl acetate copolymers), polyalkylene glycols, polyalkyleneimines, methyl cellulose, hydroxycellulose, and starches can be used. From the viewpoints of film-forming properties and adhesion to polyester films, the composition preferably contains at least one selected from the group consisting of polyester resins, polyurethane resins, and (meth)acrylic resins, and more preferably at least one selected from the group consisting of polyester resins and polyurethane resins. In the coating layer-forming composition, one binder resin may be used alone, or two or more binder resins may be used in combination.

[0099] Examples of polyester resins, polyurethane resins, (meth)acrylic resins, and polyvinyl resins used as binder resins include compounds described in WO 2023 / 145952.

[0100] The content of the binder resin in the coating layer-forming composition is preferably 5 to 95% by mass, more preferably 10 to 80% by mass, even more preferably 20 to 70% by mass, and even more preferably 30 to 60% by mass, as a proportion of all nonvolatile components in the coating layer-forming composition. By keeping the content within the above range, it is possible to easily form a film that has film-forming properties and contains particles. Furthermore, by improving adhesion to the polyester film, it is possible to prevent the coating film from falling off.

[0101] <<Crosslinking agent>> The coating layer-forming composition preferably contains a crosslinking agent. The crosslinking agent is not particularly limited, and conventionally known crosslinking agents can be used. Examples of crosslinking agents include melamine compounds, isocyanate compounds, oxazoline compounds, epoxy compounds, carbodiimide compounds, and silane coupling compounds. Among these, it is preferable to contain a melamine compound from the viewpoint of increasing the strength of the coating layer and improving adhesion to the polyester film. In the coating layer-forming composition, the crosslinking agent may be used alone or in combination of two or more types.

[0102] Examples of the melamine compound and isocyanate compound used as the crosslinking agent include the compounds described in WO 2023 / 145952.

[0103] The content of the crosslinking agent in the coating layer-forming composition is preferably 5 to 50 mass %, more preferably 8 to 40 mass %, even more preferably 10 to 35 mass %, and particularly preferably 15 to 30 mass %, as a proportion of all nonvolatile components in the coating layer-forming composition. By keeping the content within the above range, it is possible to easily form a film containing particles with film-forming properties. Furthermore, by improving adhesion to the polyester film, it is possible to prevent the coating film from falling off.

[0104] <<Particle>> The coating layer-forming composition may contain particles to the extent that the properties and effects of the present invention are not impaired. Examples of particles include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, zirconium oxide, aluminum oxide, and titanium oxide, as well as crosslinked polymers such as crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, and crosslinked polyester particles, and organic particles such as calcium oxalate and ion exchange resins. Among these, zirconium oxide, titanium oxide, and silica are preferred, and zirconium oxide and silica are more preferred. The particles may be used alone or in combination of two or more types.

[0105] The shape of the particles used may be spherical, blocky, rod-like, flat, chain-like, etc. Among these, spherical particles are preferred from the viewpoint of facilitating uniform distribution in the resin composition.

[0106] The average particle size is preferably 0.5 to 300 nm, more preferably 1 to 250 nm, even more preferably 2 to 200 nm, even more preferably 2.5 to 200 nm, even more preferably 3 to 150 nm, even more preferably 3.5 to 100 nm, even more preferably 4 to 60 nm, and particularly preferably 4.5 to 30 nm. An average particle size within this range can prevent the generation of coarse protrusions due to particle aggregation and process contamination due to particle dropout. The average particle size can be measured by a method that calculates it from the specific surface area measured by a specific surface area measuring device and the particle density, a method that calculates the particle diameter after observation with a transmission electron microscope (TEM) or scanning electron microscope (SEM), or a method that determines it by measurement using dynamic light scattering. The average particle size can be measured by a method that is appropriate for the particle size.

[0107] The content of particles in the composition for forming a coating layer is preferably in the range of 0.01 to 20 mass%, more preferably 0.05 to 15 mass%, and even more preferably 0.1 to 10 mass%, as a proportion of all non-volatile components in the composition for forming a coating layer.

[0108] <Application> This film can be suitably used for various release applications, such as dry film resist (DFR), multilayer circuit boards, and the production of ceramic green sheets for multilayer ceramic capacitors. In release and process applications, this film can be used, for example, as a support, onto which various materials such as ceramic slurries can be applied or laminated.

[0109] In particular, since the present film has excellent cuttability as described above and can accommodate thinner ceramic green sheets, it is preferably used as a support for ceramic green sheets in the production process of multilayer ceramic capacitors. That is, the polyester film of this embodiment is preferably a polyester film for producing multilayer ceramic capacitors.

[0110] Furthermore, as electrification continues to increase in automobiles, it is predicted that the ceramic green sheets used will become thinner as capacitors become smaller and higher capacity. Therefore, this film is suitable for use as a support for ceramic green sheets in the manufacturing process of automotive ceramic capacitors.

[0111] (Polyester film manufacturing method) The present embodiment may relate to a method for producing the above-mentioned polyester film. The method for producing a polyester film includes a step of supplying a polyester resin obtained by chemically recycling a film or fiber to an extruder, melting the polyester resin, and then extruding the melted polyester resin.

[0112] When the polyester film of this embodiment is a laminated polyester film having a surface layer, an intermediate layer, and a back layer, the manufacturing method for the laminated polyester film includes a step of laminating a polyester layer A constituting the surface layer, a polyester layer B constituting the intermediate layer, and a polyester layer C constituting the back layer. Here, at least one of the polyester layers A to C contains a polyester resin obtained by chemically recycling a film or fiber. Alternatively, the manufacturing method for the laminated polyester film of this embodiment includes a step of supplying the polyester resin A constituting the surface layer, the polyester resin B constituting the intermediate layer, and the polyester resin C constituting the back layer to respective extruders, melting them, and then co-extruding them. Here, at least one of the polyester resins A to C contains a polyester resin obtained by chemically recycling a film or fiber. In each extruder, each polymer is heated to above its melting point to form a molten polymer. The molten polymer is then extruded through a die and cooled and solidified on a rotating cooling drum to a temperature below the glass transition point of the polymer, thereby obtaining an unstretched polyester film.

[0113] In this embodiment, a step of stretching an unstretched polyester film may be provided. In the stretching step, the unstretched polyester film is first stretched in one direction using a roll or tenter-type stretching machine. In this case, the stretching temperature is usually 25 to 120°C, preferably 35 to 100°C, and the stretching ratio is usually 2.5 to 7 times, preferably 2.8 to 6 times. Next, it is preferable to stretch the film in a direction perpendicular to the first-stage stretching direction. In this case, the stretching temperature is usually 50 to 140°C, and the stretching ratio is usually 3.0 to 7 times, preferably 4.0 times or more, more preferably 4.5 to 5.0 times. In the stretching step, a method in which unidirectional stretching is performed in two or more stages may also be employed.

[0114] Subsequently, it is preferable to carry out a heat setting treatment at a temperature of 180 to 220°C under tension or under relaxation of 30% or less. In this way, a biaxially stretched polyester film is obtained. The heat setting treatment may be carried out in two or more steps at different temperatures. Furthermore, cooling may be carried out in a cooling zone after the heat setting treatment. The cooling temperature is preferably higher than the glass transition temperature (Tg) of the polyester resin constituting the polyester film, more specifically, preferably in the range of 100 to 160°C. This cooling may be carried out in two or more steps at different temperatures.

[0115] In this embodiment, when the film has a coating layer on at least one surface, a step of forming the coating layer may be provided. In the step of forming the coating layer, a coating layer is formed by applying a coating layer-forming composition (coating liquid) onto the surface of the film.

[0116] (Release film) The present embodiment may also relate to a release film further having a functional layer such as a release layer on at least one surface of the above-mentioned polyester film.

[0117] When the polyester film of this embodiment is a laminated polyester film having a surface layer, an intermediate layer, and a back layer, it may also relate to a release film that further has a functional layer such as a release layer on the surface layer side. The release layer is laminated to the polyester film directly or via another layer. Examples of other layers include an easy-adhesion coating layer for improving adhesion to the film, an antistatic layer, an antiblocking layer, etc. By providing a release layer on the polyester film in this way, when the film is used as a support (substrate) for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor, it is possible to easily peel off the ceramic green sheet laminated on the release layer.

[0118] In this embodiment, the polyester film may have a functional layer other than the release layer on at least one side thereof. Examples of the functional layer other than the release layer include a tacky adhesive layer, a hard coat layer, a decorative layer, a light-shielding layer, an ultraviolet-shielding layer, an easy-adhesion layer (primer layer), an antistatic layer, a refractive index adjusting layer, an oligomer sealing layer, and an antiblocking layer.

[0119] The release layer is formed from a release agent composition containing a release agent, and the release agent composition preferably contains a silicone-based release agent or a non-silicone-based release agent.

[0120] Examples of silicone-based release agents include release agents containing a curable silicone resin as a main component, modified silicone release agents obtained by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin, and fluorosilicone release agents. Of these, it is more preferable that the silicone-based release agent contains a curable silicone resin.

[0121] As the curable silicone resin, any of the existing curing reaction types can be used, such as heat-curable types such as addition types and condensation types, and electron beam-curable types such as ultraviolet-curable types, and multiple types of curable silicone resins can also be used in combination.

[0122] Examples of non-silicone release agents include waxes, compounds containing long-chain alkyl groups, and fluorine compounds.

[0123] The waxes include natural waxes, synthetic waxes, and modified waxes. Natural waxes include vegetable waxes, animal waxes, mineral waxes and petroleum waxes. Examples of vegetable waxes include candelilla wax, carnauba wax, rice wax, Japan wax, and jojoba oil. Animal waxes include beeswax, lanolin, and spermaceti. Examples of mineral waxes include montan wax, ozokerite, and ceresin. Petroleum waxes include paraffin wax, microcrystalline wax, and petrolatum. Synthetic waxes include synthetic hydrocarbons, modified waxes, hydrogenated waxes, fatty acids, acid amides, amines, imides, ester waxes and ketones.

[0124] The long-chain alkyl group-containing compound is a compound having a linear or branched alkyl group with 6 or more carbon atoms, preferably 8 or more carbon atoms, and more preferably 12 or more carbon atoms. Examples of the alkyl group include hexyl, octyl, decyl, lauryl, octadecyl, and behenyl groups. Examples of compounds having an alkyl group include various long-chain alkyl group-containing polymeric compounds, long-chain alkyl group-containing amine compounds, long-chain alkyl group-containing ether compounds, and long-chain alkyl group-containing quaternary ammonium salts. Polymeric compounds having a long-chain alkyl group in the side chain can be obtained by reacting a polymer having a reactive group with a compound having an alkyl group capable of reacting with the reactive group. Examples of the reactive group include hydroxyl, amino, carboxy, and acid anhydrides. Examples of compounds having these reactive groups include polyvinyl alcohol, polyethyleneimine, polyethyleneamine, reactive group-containing polyester resins, and reactive group-containing poly(meth)acrylic resins. Among these, polyvinyl alcohol is preferred for ease of handling.

[0125] The fluorine compound is a compound containing fluorine atoms. As the fluorine compound, an organic fluorine compound is preferably used, for example, a perfluoroalkyl group-containing compound, a polymer of an olefin compound containing a fluorine atom, an aromatic fluorine compound such as fluorobenzene, etc.

[0126] There are no particular limitations on the form of application of the release agent composition when forming the release layer. The release agent composition preferably contains a solvent in addition to the release agent. The release agent composition may be in the form of a solution in an organic solvent, in the form of an aqueous emulsion, or in the form of a solventless composition.

[0127] The release agent composition for forming the release layer may further contain, as necessary, a binder, an antifoaming agent, a coatability improver, a thickener, inorganic particles, organic particles, an organic lubricant, an antistatic agent, a conductive agent, an ultraviolet absorber, an antioxidant, a foaming agent, a dye, a pigment, or the like.

[0128] The release layer is provided by coating the present film with a release agent composition. Either in-line coating, which is carried out during the film production process, or so-called off-line coating, in which the release agent composition is applied outside the system onto a film that has already been produced, may be employed.

[0129] The release layer can be provided on the film by any of the conventional coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, and curtain coating.

[0130] The curing conditions for forming the release layer are not particularly limited. When forming the release layer by offline coating, the heat treatment is usually carried out at 80°C or higher for 10 seconds or more, preferably at 100 to 200°C for 3 to 40 seconds, and more preferably at 120 to 180°C for 3 to 40 seconds.

[0131] The coating amount of the release layer (after drying) is usually 0.005 to 5 g / m from the viewpoint of coating properties. 2 , preferably 0.005 to 1 g / m 2 , more preferably 0.005 to 0.1 g / m 2 The coating amount (after drying) is in the range of 0.005 g / m 2 When the amount is 5 g / m or more, good stability can be obtained in terms of coating properties, and a uniform coating film can be obtained. 2 If it is below this level, the release layer itself can have good coating adhesion, curability, etc.

[0132] (Polyester film with ceramic green sheet) This embodiment may relate to a polyester film with a ceramic green sheet obtained by laminating a ceramic green sheet on the above-mentioned polyester film, or to a release film with a ceramic green sheet used in the manufacturing process of an automotive ceramic capacitor. The release film with a ceramic green sheet is obtained in the manufacturing process of a multilayer ceramic capacitor. Since the polyester film of this embodiment is suitable for manufacturing thin ceramic green sheets, the thickness of the ceramic green sheets after drying may be, for example, 2 μm or less, 1 μm or less, or 0.5 μm or less.

[0133] The present embodiment may relate to use of the polyester film as a support for a ceramic green sheet in a process for producing a multilayer ceramic capacitor. The present embodiment may also relate to a method for producing a ceramic green sheet, which includes a step of applying a ceramic slurry containing a ceramic component to at least one surface of the polyester film.

[0134] When producing the polyester film with a ceramic green sheet of this embodiment, a ceramic slurry containing a ceramic component and a binder resin is applied to at least one side of the above-mentioned polyester film or to the release layer of the above-mentioned release film, and then dried to produce a ceramic green sheet (dielectric sheet). Furthermore, when the polyester film is a laminated polyester film having a surface layer, an intermediate layer, and a back layer, it is preferable to apply the ceramic slurry containing a ceramic component and a binder resin to the surface layer or to the release layer of the above-mentioned release film. [Example]

[0135] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0136] Example 1 <Depolymerization reaction of polyethylene terephthalate film> 301 parts by mass of Mitsubishi Chemical Corporation's polyethylene terephthalate film "Diafoil T369" (thickness: 25 μm) and 2,700 parts by mass of ethylene glycol were placed in a separable flask, and 0.71 parts by mass of sodium carbonate as an ester exchange catalyst was added. Depolymerization was carried out for 5 hours under conditions of normal pressure and 200°C, yielding an ethylene glycol solution containing bishydroxyethyl terephthalate (BHET). This solution was cooled to 55°C and filtered through a 1 μm membrane filter to obtain 2954 parts by mass of a filtrate. This solution was cooled to 3°C to obtain an ethylene glycol liquid-containing solid containing bishydroxyethyl terephthalate (BHET) as the main component. The ethylene glycol liquid-containing solid was washed with water at 3°C ​​to obtain 302 parts by mass of a water-containing solid. This water-containing solid was dissolved in water at 85°C to a solid content of 20% by mass, and filtered through a 1 μm membrane filter to obtain 1508 parts by mass of an aqueous solution. This solution was cooled to 20°C, and the resulting solid was filtered and dried to obtain 253 parts by mass of a depolymerized composition containing bishydroxyethyl terephthalate (BHET). This depolymerized composition contained 92.9% by mass of bishydroxyethyl terephthalate (BHET), 0.2% by mass of monohydroxyethyl terephthalate, and 6.9% by mass of oligomers.

[0137] <Melt polycondensation reaction> 197.5 parts by mass of bishydroxyethyl terephthalate (BHET) obtained by the film depolymerization described above was placed in a polycondensation reactor equipped with a torque meter and a stirrer. After the system was purged with nitrogen, the raw materials were dissolved in an oil bath (constant at 260°C). Hereinafter, the time from the start of raw material dissolution is designated as time 0. After 60 minutes, complete dissolution of the raw materials was confirmed, and stirring at 150 rpm was initiated. 0.32 parts by mass of ethyl phosphate solution in ethylene glycol (7 ppm phosphorus atoms relative to the polymer produced), 1.00 parts by mass of magnesium acetate tetrahydrate solution (11 ppm magnesium atoms relative to the polymer produced), and 0.38 parts by mass of tetra-n-butoxy titanate solution (5.3 ppm titanium atoms relative to the polymer produced) were added. After adding the auxiliary and catalyst, 5 minutes of stirring was added for each step. After 75 minutes, the reactor was depressurized, and after 90 minutes, the reactor temperature was increased. The pressure was reduced to 133 Pa over 70 minutes, with the logarithm of the pressure increasing inversely proportional to time. The temperature was increased from 225°C to 280°C over 70 minutes. After 2 hours and 40 minutes from the start of raw material dissolution, the temperature was kept constant at 280°C, and melt polymerization was carried out to achieve an intrinsic viscosity between 0.55 and 0.65 dL / g. After the polycondensation reaction at 280°C, the pressure was returned to normal to terminate the reaction. The polycondensate was extruded from the bottom of the reactor in the form of strands, which were cut while cooled with water. This yielded a polyester resin (polyethylene terephthalate pellets) obtained by chemically recycling polyethylene terephthalate film. The content of structural units derived from the monomer obtained by depolymerization was 100% by mass.

[0138] <Preparation of polyester film> The polyethylene terephthalate pellets were dried in a nitrogen atmosphere for 3 hours at 180°C. The dried pellets were formed into a sheet using a heat press (manufactured by Shinto Metal Mining Co., Ltd.) with a metal frame measuring 70 mm in length, 70 mm in width, and 200 μm in thickness, and a hot plate set at 290°C. The sheet was then cooled and solidified to produce an unstretched polyethylene terephthalate film. The unstretched film was stretched 3.0 times in the longitudinal direction at 90°C using a batch stretching machine (IMC-11A9 model manufactured by Imoto Manufacturing Co., Ltd.), and then stretched 3.0 times in the width direction perpendicular to the longitudinal direction at 90°C to produce a biaxially stretched film. This biaxially stretched film was heat-set at 220°C for 20 seconds to obtain a polyethylene terephthalate film with a thickness of 25 μm.

[0139] Example 2 <Transesterification reaction> Fifty parts by mass of chemically recycled dimethyl terephthalate (DMT) obtained by depolymerization of polyethylene terephthalate fiber and 32 parts by mass of fossil-derived ethylene glycol were fed into an esterification reactor and dissolved. Then, 0.673 parts by mass of magnesium acetate tetrahydrate solution dissolved in ethylene glycol (97 ppm by mass of magnesium atoms relative to the polymer produced) was added. The transesterification reaction was initiated at 150°C under atmospheric pressure, and the time from the start of the transesterification reaction was defined as reaction time 0. The transesterification reaction was carried out by raising the temperature of the reactor to 225°C after 3 hours and maintaining the temperature at 225°C for 4 hours and 15 minutes, during which the resulting methanol was distilled off. The reaction mixture was then transferred to a polycondensation reactor.

[0140] <Melt polycondensation reaction> To the above transfer reaction liquid, 0.289 parts by mass of ethyl phosphate solution dissolved in ethylene glycol (89 ppm by mass of phosphorus atoms relative to the polymer produced) and 2.04 parts by mass of diantimony trioxide solution (336 ppm by mass of antimony atoms relative to the polymer produced) were added. After the addition of the coagent and catalyst, 5 minutes of stirring was added for each step. Approximately 4 hours and 30 minutes after the start of the reaction, the reactor was depressurized, and 4 hours and 45 minutes later, the reactor temperature was increased. The pressure was reduced to 400 Pa over 85 minutes, with the logarithm of the pressure increasing inversely proportional to time. The temperature was increased from 225 °C to 280 °C over 80 minutes. After 6 hours and 5 minutes of reaction, the temperature was kept constant at 280 °C, and melt polymerization was carried out to achieve an intrinsic viscosity between 0.55 and 0.65 dL / g. After the polycondensation reaction was carried out at 280°C, the pressure was returned to normal to terminate the reaction, and the polycondensate was extruded in the form of strands from the bottom of the reactor, which were then cut while being cooled with water to obtain polyester resin (polyethylene terephthalate pellets) obtained by chemically recycling polyethylene terephthalate fibers. The content of structural units derived from the monomer obtained by depolymerization was 70% by mass.

[0141] <Preparation of polyester film> The polyethylene terephthalate pellets were dried at 180°C for 3 hours under a nitrogen atmosphere. The dried pellets were fed into an extruder (Labo Plastomill "4C150" manufactured by Toyo Seiki Seisaku-sho, Ltd.) and melted at 280°C. The resulting molten polymer was extruded from a die into a sheet, and then brought into contact with a casting drum to cool and solidify, producing an unstretched film. The unstretched film was stretched 3.0 times in the longitudinal direction at 90°C using a batch stretching machine (IMC-11A9 model manufactured by Imoto Manufacturing Co., Ltd.), and then stretched 3.0 times in the direction perpendicular to the longitudinal direction at 90°C to produce a biaxially stretched film. This biaxially stretched film was heat-set at 220°C for 20 seconds to produce a polyethylene terephthalate film with a thickness of 16 μm.

[0142] Example 3 Material recycling was carried out on film scraps from the production of Mitsubishi Chemical Corporation's polyethylene terephthalate film "T100F" (thickness: 38 μm) with a coating layer. Specifically, the collected film scraps were crushed and re-pelletized to obtain polyethylene terephthalate pellets 1. The intrinsic viscosity of the resulting polyester resin was 0.58 dL / g.

[0143] 50 parts by mass of the polyethylene terephthalate pellets obtained in Example 2 and 50 parts by mass of the polyethylene terephthalate pellets 1 obtained above were dried at 180°C for 3 hours under a nitrogen atmosphere. The dried pellets obtained were fed to an extruder (Labo Plastomill "4C150" manufactured by Toyo Seiki Seisaku-sho, Ltd.) and melted at 280°C. The resulting molten polymer was extruded from a die in the form of a sheet, and then brought into contact with a casting drum to cool and solidify, producing an unstretched film. The unstretched film was stretched 3.0 times in the longitudinal direction at 90°C using a batch stretching machine (IMC-11A9 model manufactured by Imoto Manufacturing Co., Ltd.), and then stretched 3.0 times in the direction perpendicular to the longitudinal direction at 90°C to produce a biaxially stretched film. This biaxially stretched film was heat-set at 220°C for 20 seconds to produce a polyethylene terephthalate film with a thickness of 20 μm.

[0144] (Comparative Example 1) A polyethylene terephthalate film having a thickness of 33 μm was obtained in the same manner as in Example 2, except that polyethylene terephthalate pellets 1 were used instead.

[0145] (Comparative Example 2) A 33 μm thick polyethylene terephthalate film was obtained in the same manner as in Example 2, except that chemically recycled polyethylene terephthalate derived from PET bottles (intrinsic viscosity 0.62 dL / g, isophthalic acid unit content of 1.8 mol% relative to 100 mol% of all dicarboxylic acid units, diethylene glycol unit content of 1.3 mol% relative to 100 mol% of all diol units, and structural unit content derived from monomers obtained by depolymerization of 72 mass%) was used.

[0146] (Comparative Example 3) A polyethylene terephthalate film having a thickness of 36 μm was obtained in the same manner as in Example 2, except that virgin polyethylene terephthalate derived from fossil fuel (intrinsic viscosity 0.63 dL / g, antimony-based catalyst) was used.

[0147] <Measurement and evaluation methods> (1) Intrinsic viscosity (IV) 1 g of raw polyester or polyester film was precisely weighed and dissolved in 100 mL of a 50 / 50 (mass ratio) phenol / tetrachloroethane mixed solvent. The viscosity (IV) was measured at 30°C using a VMS-022UPC·F10 viscosity (IV) measuring device (Rigo Co., Ltd.).

[0148] (2) Maximum indentation depth (μm), Martens hardness (N / mm 2 ), indentation modulus (N / mm 2 ) Approximately 2 to 8 mg of Aron Alpha (registered trademark) (general-purpose, manufactured by Toa Gosei Chemical Industry Co., Ltd.) was dropped onto a slide glass (S1112, manufactured by Matsunami Glass Industry Co., Ltd.). One side of a polyester film (1.5 cm × 1.5 cm) was placed on top of the sample film as an adhesive surface and allowed to harden. The slide glass with the sample film attached was fixed to the sample stage of a hardness tester (Dynamic Ultra-Micro Hardness Tester (DUH-211S, manufactured by Shimadzu Corporation), and a load-unload test was performed on the surface of the sample film to measure the maximum indentation depth (μm) and Martens hardness (N / mm 2 ) and indentation modulus (N / mm 2 ) was measured. (The average value of 10 measurements, excluding the first point, was calculated from n=11.) (Measurement conditions) Indenter used: Diamond regular triangular pyramidal indenter (edge ​​angle: 115) Measurement mode: Load-unload test Test force: 40.00 mN Minimum test force: 0.20 mN Load rate: 0.5330 mN / sec Load holding time: 0 sec Unload holding time: 0 sec Measurement atmosphere: 23±2°C, relative humidity 50±5% Number of measurements: 11

[0149] (3) Tg (glass transition temperature), Tc (temperature-rising recrystallization temperature), ΔHc (heat-rising recrystallization peak calorific value), Tm (melting peak temperature), ΔHm (melting peak calorific value) 8 mg of a sample cut out from the polyester film obtained in each of the examples and comparative examples was measured using a differential scanning calorimeter (DSC8500) manufactured by Shimadzu Corporation. The sample temperature is (1) Heat from 20°C to 300°C at 10°C / min (2) Hold at 300°C for 5 minutes (3) Cool down to 20°C at 600°C / min (4) Keep at 20°C for 5 minutes (5) Heat from 20°C to 300°C at 10°C / min (6) Hold at 300°C for 5 minutes (7) Decrease temperature to 20°C at 600°C / min The results were analyzed in the order of (1), Tm (peak melting temperature) and ΔHm (peak melting calorific value) in (1), and Tg (glass transition temperature), Tc (heat-rising recrystallization temperature), ΔHc (heat-rising recrystallization peak calorific value), Tm (peak melting temperature), and ΔHm (peak melting calorific value) in (5). The results measured in (1) were used as the results measured in DSC-1st, and the results measured in (5) were used as the results measured in DSC-2nd.

[0150] (4) Heat shrinkage rate The polyester films (1.5 cm wide x 15 cm long) obtained in the examples and comparative examples were heat-treated for 5 minutes in a hot air oven maintained at a predetermined temperature (120°C) in an untensioned state, and the length of the film in the longitudinal direction was measured before and after the treatment, and the heat shrinkage was calculated using the following formula. The heat shrinkage was measured in the machine direction (MD) of the film, with the MD being the longitudinal direction of the film. Heat shrinkage rate (%) = {(length of evaluation film before heat treatment) - (length of evaluation film after heat treatment)} / (length of evaluation film before heat treatment) × 100

[0151] (5) Tensile strength and elongation Test pieces measuring 15 mm across (TD) x 150 mm in length (MD) were cut from the test film, and the tensile strength (tensile breaking stress) and tensile elongation (tensile breaking nominal strain) were measured in the MD using a Shimadzu Autograph AGX-V tensile tester in accordance with JIS K 7161-1 (2014). Measurements were performed at 23°C, 50% relative humidity, with gauge marks at 50 mm intervals in the center of each test piece, at a chuck distance of 50 mm, and at a tensile speed of 200 mm / min.

[0152] (6) Content of terephthalic acid and isophthalic acid components contained in polyester A sample solution was prepared by dissolving the raw polyester in a solvent consisting of a 10:1 (volume ratio) mixture of chloroform D (manufactured by Eurisop) and trifluoroacetic acid D1 (manufactured by Eurisop). The sample solution was then subjected to proton NMR measurement using an NMR (GEMINI-200; manufactured by Varian) at a temperature of 23°C and an accumulation count of 64. In the NMR measurement, the peak intensity of a specific proton was calculated, and the content (mol %) of terephthalic acid and isophthalic acid components in 100 mol % of the acid component was calculated.

[0153] (7) Recycling rate The total mass ratio of the content of structural units derived from monomers obtained by depolymerization (chemical recycling) and structural units derived from material-recycled raw materials to the total monomer units constituting the polyester films obtained in the Examples and Comparative Examples was calculated as the recycling rate.

[0154] [Table 1]

[0155] In Table 1, "Film" indicates a film-derived material, "Fiber" indicates a fiber-derived material, "Bottle" indicates a bottle-derived material, and "Fossil" indicates a fossil-derived material. Also, "CR" indicates a chemically recycled material, and "MR" indicates a material that has been material recycled.

[0156] [Table 2]

[0157] In the examples, the maximum indentation depth was greater than or equal to a predetermined value, and the Martens hardness and indentation modulus were less than or equal to a predetermined value, resulting in polyester films with excellent surface flexibility. This improves cutting performance during cutting and contributes to a longer life of the cutting blade. Therefore, the polyester films obtained in the examples are suitable as supports for ceramic green sheets, for example. [Industrial Applicability]

[0158] The polyester film of the present invention contains recycled polyester resin and exhibits good cutting properties while enabling a longer life of the cutting blade. Therefore, it is useful as a support (substrate) for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors while contributing to a reduction in environmental impact. When used as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors, it is preferable because it can prevent roughness of the cut film cross section during cutting and improve alignment accuracy. Furthermore, it can effectively prevent chipping of the cutting blade during cutting, thereby contributing to a longer life of the cutting blade.

Claims

1. It contains polyester resin made from chemically recycled film or fiber, A polyester film having a maximum indentation depth of 3.2 μm or more when an indenter is pressed with a force of 40 mN in a microhardness measurement.

2. It contains polyester resin made from chemically recycled film or fiber, In microhardness measurement, the Martens hardness was 113 N / mm when the indenter was pressed with 40 mN. ２ The following is a polyester film.

3. It contains polyester resin made from chemically recycled film or fiber, In microhardness measurement, the indentation elastic modulus when the indenter was pressed with 40 mN was 2710 N / mm ２ The following is a polyester film.

4. 4. The polyester film according to claim 1, wherein the heat shrinkage in the machine direction when heated at 120°C for 5 minutes divided by the intrinsic viscosity of the polyester film (% / (dL / g)) is less than 1.28% / (dL / g).

5. The polyester film according to any one of claims 1 to 3, which has a heat shrinkage rate in the machine direction when heated at 120°C for 5 minutes of less than 0.75%.

6. The polyester film according to any one of claims 1 to 3, wherein the polyester resin is substantially free of an isophthalic acid unit as a dicarboxylic acid component.

7. The polyester film according to any one of claims 1 to 3, wherein the content of structural units derived from monomers obtained by depolymerization in the polyester resin is 10 mass% or more.

8. 4. The polyester film according to claim 1, wherein the sum of the content of structural units derived from monomers obtained by depolymerization and the content of structural units derived from recycled raw materials is 20% by mass or more, based on the content of all monomer units constituting the polyester film.

9. The polyester film according to any one of claims 1 to 3, which is a laminated polyester film having two or more layers.

10. The polyester film according to any one of claims 1 to 3, further comprising a coating layer on at least one surface of the polyester film.

11. The polyester film according to any one of claims 1 to 3, which has a temperature-raised recrystallization temperature (Tc) of 142.0°C or lower.

12. The polyester film according to any one of claims 1 to 3, having a heating recrystallization peak calorie (ΔHc) of 31.5 J / g or less.

13. The polyester film according to any one of claims 1 to 3, which is used as a support for a ceramic green sheet in a process for producing a multilayer ceramic capacitor.

14. A release film comprising the polyester film according to any one of claims 1 to 3, further comprising a release layer on at least one side thereof.

15. A polyester film with a ceramic green sheet, comprising the polyester film according to any one of claims 1 to 3 and a ceramic green sheet laminated thereon.

16. Use of the polyester film according to any one of claims 1 to 3 as a support for a ceramic green sheet in the process of producing a multilayer ceramic capacitor.

17. A method for producing a ceramic green sheet, comprising a step of applying a ceramic slurry containing a ceramic component to at least one surface of the polyester film according to any one of claims 1 to 3.

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