Laminated polyester film and its applications

Abstract

The present invention aims to provide a polyester film containing recycled polyester resin and having excellent surface smoothness and film handling properties. The present invention is a laminated polyester film having a surface layer and a back layer, in which the content of recycled polyester resin relative to the total mass of the resin components is 90 mass % or more, and the recycled polyester resin is 50 particles / m² with a particle diameter of 1000 μm or less. 2 The present invention relates to a laminated polyester film comprising the above, wherein the maximum peak height (SpA) of the surface of the surface layer is 90 nm or less, the arithmetic mean height (SaB) of the surface of the back layer is 3 nm or more and 35 nm or less, and the maximum peak height (SpB) of the surface of the back layer is 30 nm or more and 700 nm or less.

Description

[Technical Field]

[0001] The present invention relates to a laminated polyester film, a release film, a laminated polyester film with a ceramic green sheet, use of the laminated 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 cost-effective, and are therefore used in a variety of applications. For example, polyester films, taking advantage of the smoothness of their film surfaces, are suitably used in a variety of applications, such as release films for molding green sheets for multilayer ceramic capacitors, release substrates for interlayer insulating resins, and process films used in the production of dry film resists (DFRs) for forming wiring patterns on electronic circuit boards.

[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] Furthermore, with the advancement of an advanced information society, there is an ever-increasing demand for smaller and lighter IT devices, which in turn has led to a demand for finer and denser printed wiring boards. To achieve finer and denser printed wiring boards, it is important to form fine patterns with extremely small wiring widths and wiring intervals with high precision, and therefore a film with excellent smoothness is required for use in the dry film resist manufacturing process.

[0005] Conventionally, as a support for this type of release film, Patent Document 1 discloses a release film for producing ceramic green sheets, which comprises a substrate having a first side and a second side, a smoothing layer provided on the first side of the substrate, and a release agent layer provided on the side of the smoothing layer opposite the substrate, wherein the smoothing layer is formed by heating and curing a composition for forming a smoothing layer that contains a thermosetting compound having a weight-average molecular weight of 950 or less, and wherein the arithmetic mean roughness Ra1 of the outer surface of the release agent layer is 8 nm or less and the maximum protrusion height Rp1 of the outer surface of the release agent layer is 50 nm or less.

[0006] Patent Document 2 also describes a polyester film for release that has excellent surface smoothness and particularly few fine defects on the film surface, with the number of depression defects of 0.5 μm or more in depth being 5 / m 2 and a release polyester film having a center line average roughness SRa of 15 to 35 nm and a ten-point average roughness SRz of 1000 nm or less on at least one surface thereof.

[0007] Patent Document 3 also describes a polyester film roll obtained by winding up a polyester film, in which slack defects present in the polyester film are removed within 100 m. 2 A polyester film is disclosed in which the number of particles per unit area is less than 5. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-177093 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-7054 [Patent Document 3] Japanese Patent Application Publication No. 2018-90803 Summary of the Invention [Problem to be solved by the invention]

[0009] In recent years, in light of growing environmental concerns and resource conservation, recycling of used PET containers, such as PET bottles, has been promoted, and methods for utilizing them have been attracting attention. However, recycling PET containers involves recovering waste from the market and using them as recycled raw materials, which results in a higher amount of impurities than fossil-fuel-derived PET raw materials (virgin PET raw materials). This has made it difficult to use recycled polyester raw materials for applications requiring excellent surface smoothness, such as polyester film substrates for ceramic green sheet manufacturing and films for DFR manufacturing processes. In addition, while it is desirable to use as much recycled polyester raw materials as possible from an environmental perspective, the above-mentioned challenges associated with using recycled raw materials mean that a certain amount of virgin PET raw materials remains necessary when using recycled polyester raw materials.

[0010] However, when films have high surface smoothness, such as release films used in the production of ceramic green sheets or films used in the DFR manufacturing process, the films are in close contact with each other when stacked, without any gaps between them. In such cases, the film's slipperiness deteriorates, potentially resulting in poor handling. To address this issue, techniques have been proposed that adjust the type and amount of particles incorporated into the surface layer. However, as films become thinner, it has become clear that these techniques are unable to achieve both high surface smoothness and film handling.

[0011] 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 has excellent film surface smoothness and film handling properties, even when it contains a large amount of recycled polyester resin. [Means for solving the problem]

[0012] Examples of specific embodiments of the present invention are given below.

[0013] [1] A laminated polyester film having a surface layer and a back layer, The content of recycled polyester resin relative to the total mass of the resin component is 90% by mass or more, Recycled polyester resin is made of granular particles with a particle size of 1000 μm or less at 50 particles / m 2 Including the above, The maximum peak height (SpA) of the surface of the surface layer is 90 nm or less, A laminated polyester film, wherein the arithmetic mean height (SaB) of the surface of the back layer is 3 nm or more and 35 nm or less, and the maximum peak height (SpB) of the surface of the back layer is 30 nm or more and 700 nm or less. [2] The laminated polyester film according to [1], which satisfies the following (1) or (2): (1) SpA <SpB (2) SaA <SaB Here, SaA is the arithmetic mean height of the surface of the surface layer, SpA is the maximum peak height of the surface of the surface layer, SaB is the arithmetic mean height of the surface of the back layer, and SpB is the maximum peak height of the surface of the back layer. [3] The laminated polyester film according to [1] or [2], wherein the arithmetic mean height (SaA) of the surface of the surface layer is 0.3 nm or more and 5 nm or less, and the maximum peak height (SpA) of the surface of the surface layer is 5 nm or more and 60 nm or less. [4] The laminated polyester film according to any one of [1] to [3], wherein the surface layer contains a chemically recycled polyester resin. [5] The laminated polyester film according to any one of [1] to [4], wherein the laminated polyester film has a surface layer, an intermediate layer, and a back layer, and the surface layer contains a chemically recycled polyester resin. [6] The laminated polyester film according to [5], wherein the intermediate layer contains a polyester resin obtained by material recycling of a finished molded product. [7] The laminated polyester film according to any one of [1] to [6], wherein the back surface layer contains a chemically recycled polyester resin. [8] The laminated polyester film according to any one of [1] to [7], wherein the thickness of the surface layer exceeds 1 μm. [9] The laminated polyester film according to any one of [1] to [8], wherein the surface layer is substantially free of particles.

[10] The laminated polyester film according to any one of [1] to [9], wherein the back surface layer contains particles, and the particles have an average particle size of 2.5 μm or less.

[11] The laminated polyester film according to any one of [5] to

[10] , wherein the thickness of the intermediate layer is 50 to 93% of the total thickness of the film.

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

[11] , which has an air leakage index of 8,500 seconds or less.

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

[12] , wherein the air leakage index reduction rate calculated by the following formula is 13% or more. Air leakage index reduction rate (%) = 100 - air leakage index of target polyester film / air leakage index of virgin polyester film x 100

[14] The laminated polyester film according to any one of [1] to

[13] , wherein the content of isophthalic acid units is 0.01 to 5 mol % relative to 100 mol % of all dicarboxylic acid units constituting the polyester resin contained in the laminated polyester film.

[15] The laminated polyester film according to any one of [1] to

[14] , which has a temperature-raised recrystallization temperature (Tc) of 144.0°C or lower.

[16] The laminated polyester film according to any one of [1] to

[15] , which has a melting peak heat quantity (ΔHm) of 40 J / g or less.

[17] The laminated polyester film according to any one of [1] to

[16] , which has a melting peak temperature (Tm) of 254°C or less.

[18] The laminated polyester film according to any one of [1] to

[17] , wherein the recycled polyester resin is recycled from PET bottles.

[19] The laminated polyester film according to any one of [1] to

[17] , wherein the recycled polyester resin is a recycled polyester film.

[20] The laminated polyester film according to any one of [1] to

[19] , wherein the recycled polyester resin is a chemically recycled polyester resin.

[21] The laminated polyester film according to any one of [1] to

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

[22] The method includes a step of supplying a recycled polyester resin A constituting a surface layer and a recycled polyester resin C constituting a back layer to respective extruders, melting them, and then co-extruding them; The content of recycled polyester resin relative to the total mass of the resin components constituting the surface layer and the back layer is 90% by mass or more, Recycled polyester resin A and recycled polyester resin C are 50 particles / m² of granular material with a particle size of 1000 μm or less. 2 A method for producing a laminated polyester film containing a recycled polyester resin containing the above.

[23] A release film further comprising a release layer on the surface layer side of the laminated polyester film according to any one of [1] to

[21] .

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

[21] .

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

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

[26] A method for producing a ceramic green sheet, comprising a step of applying a ceramic slurry containing a ceramic component to a surface layer side of the laminated polyester film according to any one of [1] to

[21] . [Effects of the Invention]

[0014] According to the present invention, even when a large amount of recycled polyester resin is contained, a polyester film having excellent film surface smoothness and film handling properties can be obtained. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view illustrating the structure of the polyester film of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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."

[0017] (polyester film) The present invention relates to a polyester film in which the content of recycled polyester resin relative to the total mass of the resin components is 90 mass% or more and the maximum peak height (Sp) of at least one surface is 90 nm or less. A preferred embodiment of the present invention is a laminated polyester film having a front layer and a back layer, in which the content of recycled polyester resin relative to the total mass of the resin components is 90 mass% or more and the recycled polyester resin is dispersed in a density of 50 particles / m² with a particle diameter of 1000 μm or less. 2 The present invention relates to a laminated polyester film (hereinafter also referred to as the present film) comprising the above, wherein the maximum peak height (SpA) of the surface of the surface layer is 90 nm or less, the arithmetic mean height (SaB) of the surface of the back layer is 3 nm or more and 35 nm or less, and the maximum peak height (SpB) of the surface of the back layer is 30 nm or more and 700 nm or less. The laminated polyester film of the present embodiment contains a large amount of recycled polyester resin, and is a polyester film that is excellent in film surface smoothness and film handling. In the present embodiment, the recycled polyester resin contains granules with a particle size of 1000 μm or less at a density of 50 particles / m 2 By using a recycled polyester resin containing the above, it is possible to obtain a polyester film that combines surface smoothness and handleability, even without incorporating particles into the surface layer. When particles are not incorporated into the surface layer, particle shedding during the film production process can be suppressed, thereby reducing the inclusion of foreign matter in the film and contamination during the film production process.

[0018] The laminated polyester film of the present embodiment preferably satisfies the following (1) or (2). (1) SpA <SpB (2) SaA <SaB Here, SaA is the arithmetic mean height of the surface of the surface layer, SpA is the maximum peak height of the surface of the surface layer, SaB is the arithmetic mean height of the surface of the back layer, and SpB is the maximum peak height of the surface of the back layer. By satisfying the above condition (1) or (2), the laminated polyester film of the present embodiment can more effectively improve the film surface smoothness and film handling properties.

[0019] The recycled polyester resin content in the present film is preferably 90% by mass or more, more preferably 92% by mass or more, even more preferably 94% by mass or more, even more preferably 95% by mass or more, even more preferably 96% by mass or more, even more preferably 97% by mass or more, and particularly preferably 98% by mass or more, based on the total mass of the resin components contained in the polyester film. The upper limit of the recycled polyester resin content in the present film is not limited and may be 100% by mass. In this embodiment, since a very high proportion of recycled polyester resin can be contained, the film can also be referred to as a recycled polyester film. Using such a polyester film can, for example, reduce CO2 emissions and contribute to reducing environmental impact. Furthermore, by keeping the recycled polyester resin content within the above range, the polyester film surface can be provided with the required roughness while maintaining a maximum peak height (Sp) of 90 nm or less, thereby more effectively improving the processability and handleability of the polyester film.

[0020] In this film, the maximum peak height (Sp) of at least one surface is preferably 90 nm or less, more preferably 85 nm or less, even more preferably 80 nm or less, even more preferably 75 nm or less, even more preferably 70 nm or less, even more preferably 65 nm or less, and particularly preferably 60 nm or less. The lower limit of the maximum peak height (Sp) of at least one surface is not particularly limited, but is preferably, for example, 5 nm or more, more preferably 10 nm or more. By keeping the maximum peak height (Sp) of at least one surface within the above range, it is possible to obtain a polyester film with excellent surface smoothness while effectively suppressing the generation of protrusions of unintended sizes on the surface of the polyester film. In this specification, "at least one surface" preferably refers to "the surface of the surface layer."

[0021] In this embodiment, the arithmetic mean height (Sa) of at least one surface is preferably 0.3 nm or more, more preferably 0.4 nm or more, even more preferably 0.5 nm or more, and particularly preferably 0.6 nm or more. Furthermore, the arithmetic mean height (Sa) of at least one surface is preferably 15 nm or less, more preferably 10 nm or less, even more preferably 8 nm or less, and even more preferably 5 nm or less. By setting the arithmetic mean height (Sa) of at least one surface to the above upper limit or less, a polyester film with excellent surface smoothness can be obtained. On the other hand, the arithmetic mean height (Sa) of at least one surface is preferably the above lower limit or more, and the surface of the polyester film is preferably provided with a predetermined amount of roughness or more. This provides a rough surface necessary to improve the handleability of the polyester film, thereby reducing the air leakage index of the polyester film. As a result, the polyester film can exhibit appropriate slip properties and improve handleability. For example, a polyester film with appropriate surface roughness can be easily wound into a roll.

[0022] The value (Sp / Sa) obtained by dividing the maximum peak height (Sp) of at least one surface by the arithmetic mean height (Sa) of the surface is preferably 100 or less, more preferably 95 or less, even more preferably 90 or less, and particularly preferably 85 or less. There are no particular restrictions on the lower limit of the value of Sp / Sa, but for example, it is preferably 5 or more, more preferably 10 or more, even more preferably 15 or more, even more preferably 20 or more, and particularly preferably 25 or more.

[0023] In this film, by controlling the maximum peak height (Sp) to be low while maintaining the arithmetic mean height (Sa) of at least one surface within a certain numerical range, high smoothness is achieved while ensuring processability and handling properties. For example, by using this film as a support (base material) for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor, it becomes easier to form a thin-film ceramic green sheet.

[0024] Note that the method for measuring the maximum peak height (Sp) and the arithmetic mean height (Sa) of at least one surface of this film is the same as the method for measuring the maximum peak height (Sp) and the arithmetic mean height (Sa) of the surface of the surface layer, as described later.

[0025] This film may be a single-layer polyester film, but is preferably a multilayer polyester film having two or more layers, and particularly preferably a multilayer polyester film having a surface layer, an intermediate layer, and a back layer. When this film is a multilayer polyester film having two or more layers, it preferably has a surface layer and a back layer, and the surface layer and the back layer are preferably different layers. In this case, the layer with higher surface smoothness can be distinguished as the surface layer from the back layer. Note that "having higher surface smoothness" means that the arithmetic mean height (Sa) described later is smaller than that of one surface layer, or the maximum peak height (Sp) described later is smaller than that of one surface layer. That is, in this embodiment, SpA < SpB or SaA < SaB (where SaA is the arithmetic mean height of the surface of the surface layer, SpA is the maximum peak height of the surface of the surface layer, SaB is the arithmetic mean height of the surface of the back layer, and SpB is the maximum peak height of the surface of the back layer).

[0026] When this film is a laminated polyester film having a surface layer, an intermediate layer, and a back layer, as shown in FIG. 1, the laminated polyester film 10 of the present embodiment has a surface layer 12 on one surface side of the intermediate layer 14 and a back layer 16 on the other surface side of the intermediate layer 14. In the present embodiment, it is preferable that the intermediate layer 14 and the surface layer 12 are laminated so as to be in direct contact with each other, but other layers may be provided between the intermediate layer 14 and the surface layer 12. Similarly, it is preferable that the intermediate layer 14 and the back layer 16 are laminated so as to be in direct contact with each other, but other layers may be provided between the intermediate layer 14 and the back layer 16. In this specification, it is preferable that the surface layer 12 and the back layer 16 are different layers. In this case, the layer with higher surface smoothness can be distinguished as the surface layer 12 from the back layer 16. Note that "having higher surface smoothness" means that the arithmetic mean height (Sa) described later is smaller than that of one surface layer, or the maximum peak height (Sp) described later is smaller than that of one surface layer. That is, in the present embodiment, SpA < SpB or SaA < SaB (where SaA is the arithmetic mean height of the surface of the surface layer, SpA is the maximum peak height of the surface of the surface layer, SaB is the arithmetic mean height of the surface of the back layer, and SpB is the maximum peak height of the surface of the back layer).

[0027] When this film is a laminated polyester film having two or more layers, it is preferable that the surface layer of the laminated polyester film contains a chemically recycled polyester resin. The surface layer is a layer including the exposed surface of this film. When this film has two layers, the layer with higher surface smoothness becomes the surface layer and the other layer becomes the back layer. Also, when this film is a laminated polyester film having a surface layer, an intermediate layer, and a back layer, it is preferable that at least one of the surface layer and the back layer contains a chemically recycled polyester resin. Among them, it is particularly preferable that the surface layer contains a chemically recycled polyester resin.

[0028] In this embodiment, by incorporating a chemically recycled polyester resin into the surface layer, it is possible to form fine irregularities on the surface layer while increasing the smoothness of the surface layer. As a result, the air leakage index of the polyester film of this embodiment can be reduced. In this specification, a larger air leakage index indicates that it takes longer for air to leak through gaps between films, meaning that the films are in closer contact with each other. On the other hand, a smaller air leakage index indicates that there are appropriate gaps between the films. Therefore, a polyester film with a small air leakage index can exhibit appropriate slip properties and has good handleability.

[0029] When the present film is a laminated polyester film having two or more layers, all of the layers constituting the laminated polyester film may contain chemically recycled polyester resin. For example, when the present film has two layers, it is preferable that both the front layer and the back layer contain chemically recycled polyester resin.

[0030] When the present film is a laminated polyester film having a surface layer, an intermediate layer, and a back layer, all of the surface layer, intermediate layer, and back layer may contain a chemically recycled polyester resin. Furthermore, in this embodiment, the intermediate layer and the back layer may contain a recycled polyester resin other than a chemically recycled polyester resin. In this case, only the surface layer may contain a chemically recycled polyester resin, and the intermediate layer and the back layer may contain a recycled polyester resin other than a chemically recycled polyester resin. It is also preferable that the surface layer and the back layer contain a chemically recycled polyester resin, and only the intermediate layer contains a recycled polyester resin other than a chemically recycled polyester resin. For example, it is more preferable that the surface layer and the back layer contain a chemically recycled polyester resin, and only the intermediate layer contains a material-recycled polyester resin.

[0031] As described above, by incorporating recycled polyester resin into the intermediate layer, it becomes easy to form fine irregularities in the intermediate layer, and these irregularities propagate to the surface layer, making it easy to form irregularities that meet predetermined conditions in the surface layer while maintaining the smoothness of the surface layer. As a result, the air leakage index of the present film can be reduced, and the handleability of the film can be more effectively improved. Furthermore, when recycled polyester resin is incorporated into the intermediate layer, the degree of propagation of the irregularities in the intermediate layer can be controlled, for example, by appropriately adjusting the thickness of the surface layer.

[0032] In the past, attempts to impart fine irregularities to the surface layer to reduce the air leakage index of films have been made, and small particles have been added to the surface layer to impart these irregularities. However, small particles tend to aggregate easily, which can lead to the problem of coarse protrusions. In contrast, the present invention imparts appropriate irregularities to the surface of a polyester film by containing 90% or more recycled polyester resin, even without adding particles to the surface layer. This makes it possible to reduce the air leakage index while suppressing the formation of coarse protrusions. Furthermore, since the surface layer of the polyester film is substantially free of particles, particle detachment from the surface layer can be suppressed, preventing the detached particles from becoming foreign matter or contaminating the process.

[0033] This embodiment may also relate to a roll (rolled body) obtained by winding the present film. As described above, the present film has appropriate slip properties, strength, and flexibility, and therefore can be stored or distributed as a roll.

[0034] <Surface layer> The present film has a surface layer. The present film is preferably a laminated polyester film having a surface layer and a back layer, and more preferably a laminated polyester film having a surface layer, an intermediate layer, and a back layer. The surface layer is a layer containing recycled polyester resin. When the present film is used as a support (substrate) for ceramic green sheets in the manufacturing process of a multilayer ceramic capacitor, the surface layer is a layer disposed on the side on which the ceramic green sheets are laminated, and preferably has a higher surface smoothness than the back layer. In the manufacturing process of a multilayer ceramic capacitor, for example, a release layer is formed on the surface layer, and then the ceramic green sheets are laminated.

[0035] The maximum peak height (Sp (hereinafter, the maximum peak height on the surface of the surface layer may be referred to as SpA)) on the surface of the surface layer is preferably 90 nm or less, more preferably 85 nm or less, even more preferably 80 nm or less, even more preferably 75 nm or less, even more preferably 70 nm or less, even more preferably 65 nm or less, particularly preferably 63 nm or less, and most preferably 60 nm or less. The lower limit of the maximum peak height (SpA) on the surface of the surface layer is not particularly limited, but is preferably, for example, 5 nm or more, more preferably 10 nm or more. By keeping the maximum peak height (SpA) on the surface of the surface layer within the above range, it is possible to effectively prevent protrusions of unintended sizes from occurring on the surface of the polyester film, and a polyester film with excellent surface smoothness can be obtained.

[0036] The arithmetic mean height (Sa (hereinafter, the arithmetic mean height of the surface of the surface layer may be referred to as SaA)) of the surface of the surface layer is preferably 0.3 nm or more, more preferably 0.4 nm or more, even more preferably 0.5 nm or more, and particularly preferably 0.6 nm or more. The arithmetic mean height (SaA) of the surface of the surface layer is preferably 15 nm or less, more preferably 10 nm or less, even more preferably 8 nm or less, and even more preferably 5 nm or less. By setting the arithmetic mean height (SaA) of the surface of the surface layer to the above upper limit or less, a polyester film with excellent surface smoothness can be obtained. On the other hand, the arithmetic mean height (SaA) of the surface of the surface layer is preferably the above lower limit or more, and it is preferable that a predetermined amount or more of roughness is imparted. This provides a rough surface necessary to improve the handleability of the polyester film, thereby reducing the air leakage index of the polyester film. As a result, the polyester film can exhibit appropriate slip properties and improve handleability. For example, a polyester film with appropriate surface roughness can be easily wound into a roll.

[0037] In particular, it is preferable that the arithmetic mean height (SaA) of the surface of the surface layer is 0.3 nm or more and 5 nm or less, and the maximum peak height (SpA) of the surface of the surface layer is 5 nm or more and 60 nm or less, which makes it easier to obtain a laminated polyester film with excellent surface smoothness and handleability.

[0038] The value (SpA / SaA) obtained by dividing the maximum peak height (SpA) of the surface of the surface layer by the arithmetic mean height (SaA) of the surface of the surface layer is preferably 100 or less, more preferably 95 or less, even more preferably 90 or less, and particularly preferably 85 or less. There are no particular restrictions on the lower limit of the SpA / SaA value, but for example, it is preferably 5 or more, more preferably 10 or more, even more preferably 15 or more, even more preferably 20 or more, and particularly preferably 25 or more.

[0039] In this film, by controlling the maximum peak height (SpA) low while maintaining the arithmetic mean height (SaA) of the surface of the surface layer within a certain numerical range, high smoothness is achieved while ensuring processability and ease of handling. For example, by using this film as a support (substrate) for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors, thin ceramic green sheets can be easily formed.

[0040] Arithmetic mean height (Sa) is one of the surface roughness parameters (ISO 25178) and is a three-dimensional extension of the two-dimensional Ra (arithmetic mean roughness of lines), and is calculated by dividing the volume of the area enclosed by the surface shape curve and the mean surface by the measured area, and is calculated using the following formula (1): When the surface is the XY plane and the height direction is the Z axis, A is the defined area (the entire image), and Z(x,y) is the height from the surface at height 0 of the image point (x,y), it can be expressed as in the following formula (1).

[0041]

number

[0042] The maximum peak height (Sp) is one of the surface roughness parameters (ISO 25178) and represents the maximum value of the height from the mean plane of the surface, and is expressed by the following formula (2).

[0043]

number

[0044] The root mean square height (Sq) of the surface of the surface layer of the present film is preferably 5 nm or less, more preferably 4 nm or less, even more preferably 3.5 nm or less, even more preferably 3 nm or less, and particularly preferably 2.8 nm or less. On the other hand, the lower limit of the root mean square height (Sq) of the two surfaces of the surface layer is not particularly limited, but is, for example, preferably 0.1 nm or more, more preferably 0.3 nm or more. The root mean square height (Sq) of the surface of the back layer of the present film is preferably 40 nm or less, more preferably 38 nm or less, even more preferably 36 nm or less, and particularly preferably 34 nm or less. The lower limit of the root mean square height (Sq) of the surface of the back layer is not particularly limited, but is, for example, preferably 1 nm or more, more preferably 3 nm or more.

[0045] From the viewpoint of achieving both surface smoothness and slip properties, the value (SqB / SqA) obtained by dividing the root mean square height (SqB) of the surface of the back layer by the root mean square height (SqA) of the surface of the front layer is preferably 7 or more, more preferably 8 or more, and even more preferably 9 or more. On the other hand, SqB / SqA is preferably 20 or less, more preferably 18 or less, and even more preferably 17 or less.

[0046] The root mean square height (Sq) is one of the surface roughness parameters (ISO 25178) and is a three-dimensional extension of the two-dimensional Rq. It is the root mean square value of the height data in a defined area, and is a parameter equivalent to the standard deviation of the distance from the mean surface, and can be calculated using the following formula:

[0047]

number

[0048] The surface kurtosis (Sku) of the surface layer of the present film is preferably 100 or less, more preferably 95 or less, and even more preferably 90 or less. On the other hand, the lower limit of the surface kurtosis (Sku) of the surface layer is not particularly limited, but is preferably, for example, 0.5 or more, more preferably 1 or more.

[0049] Kurtosis (Sku) is one of the surface roughness parameters (ISO 25178) that can be used to evaluate the peakiness (kurtosis) of a height distribution histogram and can be calculated using the following formula:

[0050]

number

[0051] The surface skewness (Ssk) of the surface layer of the present film is preferably 5 or less, more preferably 4.5 or less, even more preferably 4.2 or less, and particularly preferably 4 or less. On the other hand, the lower limit of the surface skewness (Ssk) of the surface layer is not particularly limited, but is, for example, preferably 0.2 or more, more preferably 0.4 or more.

[0052] Skewness (Ssk) is one of the surface roughness parameters (ISO 25178) and can be calculated using the following formula:

[0053]

number

[0054] The arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk) can be adjusted, for example, by the type of recycled polyester resin contained in the surface layer and / or intermediate layer, such as its composition, viscosity, molecular weight, thermal properties, the presence or absence of copolymerization components, and the amount of recycled polyester resin. These adjustments can control the surface properties. In particular, adjusting the particle size and amount of particulate matter contained in the recycled polyester resin and the amount of recycled polyester resin is useful for adjusting the surface properties. It is also possible to control these properties by appropriately blending particulate matter or additives into the surface layer and / or intermediate layer. For example, it can also be adjusted by appropriately incorporating particles. These can be adjusted by adjusting the amount of particles used, taking into account the type, composition, average particle size, particle size distribution, hardness, affinity with the polyester, and the like. Adjusting the type and amount of particles, taking into account the type of polyester contained, such as its composition, viscosity, molecular weight, thermal properties, and the presence or absence of copolymerization components, is also useful for adjusting the surface properties. When two or more types of particles are used in combination, it is preferable to adjust the content ratio in consideration of the type of particles and polyester used. In addition, when adjusting the arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk), it is also effective to control, during the production of the polyester film, for example, the stretching ratio (in the case of biaxial stretching, the stretching ratio in both the longitudinal and transverse directions), the stretching temperature, the heat treatment temperature and treatment time (in the case of biaxial stretching, the heat treatment temperature and treatment time, particularly after the transverse stretching).

[0055] The thickness of the surface layer is preferably greater than 1 μm, more preferably 1.2 μm or greater, even more preferably 1.5 μm or greater, even more preferably 2 μm or greater, even more preferably 2.5 μm or greater, and particularly preferably 3 μm or greater. The thickness of the surface layer is preferably 15 μm or less, more preferably 12 μm or less, even more preferably 10 μm or less, even more preferably 9 μm or less, even more preferably 8 μm or less, even more preferably 7 μm or less, and particularly preferably 6 μm or less. By making the thickness of the surface layer greater than or equal to the above-mentioned lower limit, it becomes easier to control the maximum peak height (Sp) of the surface of the present film within the desired range, thereby improving surface smoothness. For example, when the intermediate layer contains recycled polyester resin, the degree of propagation of the unevenness of the intermediate layer can be controlled by appropriately adjusting the thickness of the surface layer.

[0056] In order to control the maximum peak height (SpA) of the surface of the surface layer within a desired range and more effectively improve surface smoothness, the thickness of the surface layer is preferably 6 to 40% of the total thickness of the polyester film, more preferably 7 to 32%, even more preferably 8 to 28%, and even more preferably 9 to 24%.

[0057] The surface layer may or may not contain particles. When the surface layer 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.

[0058] The shape of the particles in the surface layer 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.

[0059] When particles are contained in the surface layer, 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. On the other hand, the average particle size of the particles contained is preferably 1 μm or less, more preferably 0.8 μm or less, even more preferably 0.6 μm or less, still more preferably 0.4 μm or less, and particularly preferably 0.2 μm or less.

[0060] 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, layer, 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.

[0061] When particles are contained in the surface layer, the particle content is preferably more than 200 ppm by mass, more preferably 300 ppm or more, even more preferably 400 ppm or more, still more preferably 500 ppm or more, and particularly preferably 600 ppm or more. On the other hand, the particle content is preferably 2000 ppm or less, more preferably 1800 ppm or less, even more preferably 1600 ppm or less, still more preferably 1400 ppm or less, even more preferably 1200 ppm or less, and particularly preferably 1000 ppm or less.

[0062] In this embodiment, the particle content of the surface layer is preferably 200 ppm or less, more preferably 150 ppm or less, and even more preferably 100 ppm or less. In this embodiment, a configuration in which the surface layer is substantially free of particles is also preferred. The surface layer being substantially free of particles eliminates the risk of coarse protrusions due to particle aggregation or particle shedding, resulting in foreign matter and process contamination. The phrase "substantially free of particles" means that particles are not intentionally included. Specifically, it refers to a particle content (particle concentration) of 50 ppm or less by mass relative to the surface layer, preferably 30 ppm or less, more preferably 10 ppm or less, and even more preferably below the detection limit. The presence or absence of particles and their content can be determined by quantitative analysis of particle-derived elements using, for example, fluorescent X-ray analysis. In this embodiment, by setting the recycled polyester resin content to 90% by mass or more, appropriate unevenness can be imparted to the surface of the polyester film without adding particles to the surface layer. Furthermore, when particles are not added to the surface layer, it is possible to prevent particles from falling off during the film production process, thereby reducing the inclusion of foreign matter in the film and contamination during the film production process.

[0063] The content of recycled polyester resin in the surface layer is preferably 90% by mass or more, more preferably 92% by mass or more, even more preferably 94% by mass or more, still more preferably 95% by mass or more, even more preferably 96% by mass or more, still more preferably 97% by mass or more, and particularly preferably 98% by mass or more, based on the total mass of the resin components contained in the surface layer. The content of recycled polyester resin in the surface layer is most preferably 100% by mass.

[0064] The surface layer contains a recycled polyester resin, and the recycled polyester resin is preferably a chemically recycled polyester resin. When the surface layer contains a chemically recycled polyester resin, the content of the chemically recycled polyester resin is preferably 90% by mass or more, more preferably 92% by mass or more, even more preferably 94% by mass or more, even more preferably 95% by mass or more, even more preferably 96% by mass or more, even more preferably 97% by mass or more, and particularly preferably 98% by mass or more, based on the total mass of the resin components contained in the surface layer. It is most preferable that the content of the chemically recycled polyester resin in the surface layer is 100% by mass.

[0065] In this embodiment, by setting the content of recycled polyester resin in the surface layer within the above range, for example, it is possible to reduce CO2 emissions and contribute to reducing the burden on the environment. Furthermore, by using chemically recycled polyester resin as the recycled polyester resin, it is possible to impart the necessary roughness to the surface layer while keeping the maximum peak height (Sp) of the surface layer below a predetermined value, thereby more effectively improving the processability and handleability of the polyester film.

[0066] The recycled polyester resin contained in the surface layer is obtained by recycling polyester, which is a recycled raw material. The recycled (recycled) polyester may be, for example, polyester derived from polyester containers (e.g., PET bottles) or polyester derived from polyester film (e.g., processing film). Thus, in this embodiment, the recycled polyester resin constituting the surface layer may be recycled polyester resin derived from polyester containers (PET bottles) or recycled polyester resin derived from polyester film. When recycled polyester resin derived from polyester film is used, the recycled polyester film may be a polyester film used as a support (substrate) for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor.

[0067] Note that biomass-derived raw materials may be used as the polymerization components constituting the recycled (regenerated) polyester. For example, biomass-derived ethylene glycol may be used as the diol component. The surface layer may contain a polyester resin made from biomass-derived raw materials, or may contain a polyester resin made from recycled polyester resin and biomass-derived raw materials. For example, the surface layer may contain a chemically recycled recycled polyester resin and a polyester resin made from biomass-derived raw materials.

[0068] <Middle class> The present film is preferably a laminated polyester film having a surface layer, an intermediate layer, and a back layer, and in this case, the intermediate layer preferably functions as the thickest main layer in the present film. Like the surface layer, the intermediate layer also preferably contains recycled polyester resin.

[0069] The thickness of the intermediate layer is preferably 8 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, even more preferably 14 μm or more, still more preferably 16 μm or more, and particularly preferably 18 μm or more. The thickness of the intermediate layer may be 40 μm or less, preferably 34 μm or less, more preferably 32 μm or less, even more preferably 30 μm or less, even more preferably 29 μm or less, and particularly preferably 28 μm or less.

[0070] The thickness of the intermediate layer is preferably 50 to 93% of the total thickness of the polyester film, more preferably 60 to 91%, even more preferably 65 to 90%, still more preferably 70 to 88%, and particularly preferably 75 to 86%.

[0071] The intermediate layer may or may not contain particles. When the intermediate layer 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.

[0072] When particles are contained in the intermediate layer, the particle content is preferably 10 ppm or more, more preferably 20 ppm or more, even more preferably 30 ppm or more, still more preferably 40 ppm or more, and particularly preferably 50 ppm or more by mass, while the particle content is preferably 500 ppm or less, more preferably 400 ppm or less, even more preferably 350 ppm or less, still more preferably 300 ppm or less, even more preferably 250 ppm or less, and particularly preferably 200 ppm or less.

[0073] The recycled polyester resin content in the intermediate layer is preferably 90% by mass or more, more preferably 92% by mass or more, even more preferably 94% by mass or more, even more preferably 95% by mass or more, even more preferably 96% by mass or more, even more preferably 97% by mass or more, and particularly preferably 98% by mass or more. The recycled polyester resin content in the intermediate layer is most preferably 100% by mass. By maintaining the recycled polyester resin content in the intermediate layer within the above range, for example, CO2 emissions can be reduced, contributing to a reduction in the burden on the environment. Furthermore, by incorporating recycled polyester resin into the intermediate layer, the surface layer can be given the necessary roughness while maintaining the maximum peak height (Sp) of the surface layer at a predetermined value or less, thereby more effectively improving the processability and handleability of the polyester film.

[0074] The intermediate layer contains a recycled polyester resin, and the recycled polyester resin may be a material recycled polyester resin made from recycled raw materials, or may be a chemically recycled polyester resin made from recycled raw materials. In particular, the recycled polyester resin that can be contained in the intermediate layer is preferably a material recycled polyester resin made from recycled raw materials. The recycled (recycled) polyester may be, for example, a polyester derived from a polyester container (e.g., a PET bottle) or a polyester film (e.g., a processing film). Thus, in this embodiment, the recycled polyester resin constituting the intermediate layer may be a polyester resin derived from a polyester container (e.g., a PET bottle) or a polyester film. When a recycled polyester resin derived from a polyester film is used, the recycled polyester film may be a polyester film used as a support (substrate) for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor.

[0075] When the intermediate layer contains recycled polyester resin obtained by material recycling, the intermediate layer preferably contains polyester resin obtained by material recycling of a finished molded product. In this specification, a finished molded product refers to a molded product that has been taken out of the manufacturing process (outside the manufacturing plant) as a product. In other words, a finished molded product is distinguished from polyester that is not made into a product but is recovered in the process of manufacturing polyester film or PET bottles, for example. Usually, a finished molded product is discarded after being used for its intended purpose (or after being stored for its intended use). However, in this embodiment, a used and / or stored finished molded product can be recycled and used as a recycled polyester resin.

[0076] Note that biomass-derived raw materials may be used as the polymerization components constituting the recycled (regenerated) polyester. For example, biomass-derived ethylene glycol may be used as the diol component. The intermediate layer may contain a polyester resin made from biomass-derived raw materials, or may contain a polyester resin made from recycled polyester resin and biomass-derived raw materials. For example, the intermediate layer may contain a chemically recycled polyester resin and a polyester resin made from biomass-derived raw materials.

[0077] <Backing layer> The present film has a back surface layer. The present film is preferably a laminated polyester film having a surface layer and a back surface layer, and more preferably a laminated polyester film having a surface layer, an intermediate layer, and a back surface layer. In this case, the back surface layer is a layer disposed on the side opposite to the side on which the ceramic green sheet is laminated. Like the surface layer and the intermediate layer, the back surface layer is preferably a layer containing recycled polyester resin.

[0078] In this embodiment, the maximum peak height (Sp) of the surface of the back layer (hereinafter, the maximum peak height of the surface of the back layer may be referred to as SpB) is preferably 700 nm or less, more preferably 650 nm or less, even more preferably 620 nm or less, even more preferably 600 nm or less, still more preferably 570 nm or less, and particularly preferably 550 nm or less. Furthermore, the maximum peak height (SpB) of the surface of the back layer is preferably 10 nm or more, more preferably 20 nm or more, even more preferably 30 nm or more, and even more preferably 50 nm or more. By setting the maximum peak height (SpB) of the surface of the back layer to the above upper limit value or less, it is possible to prevent the unevenness caused by minute protrusions on the back layer from being transferred to the surface layer when the polyester film is laminated or wound into a roll. On the other hand, by setting the maximum peak height (SpB) of the surface of the back layer to the above lower limit value or more, the necessary roughness is provided on the back surface of the polyester film, thereby improving the handleability of the polyester film.

[0079] The arithmetic mean height (Sa (hereinafter, the arithmetic mean height of the surface of the back layer may be referred to as SaB)) of the surface of the back layer is preferably 1 nm or more, more preferably 3 nm or more, even more preferably 5 nm or more, even more preferably 8 nm or more, and particularly preferably 12 nm or more. The arithmetic mean height (SaB) of the surface of the back layer is preferably 35 nm or less, more preferably 30 nm or less, and even more preferably 25 nm or less. By setting the arithmetic mean height (SaB) of the surface of the back layer to the upper limit or less, it is possible to prevent the uneven shape of the back layer from being transferred to the surface layer. On the other hand, by setting the arithmetic mean height (SaB) of the surface of the back layer to the lower limit or more, a rough surface necessary for improving the handleability of the polyester film is provided, thereby improving the handleability of the polyester film. For example, when the polyester film is wound into a roll, the polyester film can exhibit appropriate slip properties, making it easy to wind into a roll.

[0080] In particular, it is preferable that the arithmetic mean height (SaB) of the surface of the back layer is 3 nm or more and 35 nm or less, and the maximum peak height (SpB) of the surface of the back layer is 30 nm or more and 700 nm or less, which makes it easier to obtain a laminated polyester film with excellent surface smoothness and handleability.

[0081] The value (SpB / SaB) obtained by dividing the maximum peak height (SpB) on the surface of the backing layer by the arithmetic mean height (SaB) on the surface of the backing layer is preferably 100 or less, more preferably 80 or less, even more preferably 50 or less, and particularly preferably 40 or less. The lower limit of the value of SpB / SaB is not particularly limited, but is preferably 5 or more, and may be 10 or more, for example.

[0082] The root mean square height (Sq) of the surface of the back surface layer is preferably 40 nm or less, more preferably 38 nm or less, even more preferably 36 nm or less, and particularly preferably 34 nm or less. The lower limit of the root mean square height (Sq) of the surface of the back surface layer is not particularly limited, but is, for example, preferably 1 nm or more, more preferably 3 nm or more.

[0083] The kurtosis (Sku) of the surface of the back layer is preferably 30 or less, more preferably 25 or less, even more preferably 20 or less, and particularly preferably 14 or less. The lower limit of the kurtosis (Sku) of the surface of the back layer is not particularly limited, but is, for example, preferably 1 or more, more preferably 2 or more.

[0084] The skewness (Ssk) of the surface of the back surface layer is preferably 5 or less, more preferably 4 or less, even more preferably 3 or less, and particularly preferably 2.5 or less. On the other hand, the lower limit of the skewness (Ssk) of the surface of the back surface layer is not particularly limited, but is, for example, preferably 0.5 or more, more preferably 0.8 or more.

[0085] The back surface layer may contain particles, but may also contain particles. The presence of particles in the back surface layer can provide slipperiness and prevent scratches during each process. Furthermore, the presence of particles in the back surface layer makes it easier to control the arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk) within desired ranges. Furthermore, the arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk) of the back surface layer may be controlled within desired ranges by applying a surface treatment or coating to the back surface layer.

[0086] The type of particles contained in the backing layer is not particularly limited as long as they are particles that can impart slipperiness. Specific examples include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, titanium oxide, and barium sulfate, as well as organic particles obtained by polymerizing acrylic acid ester monomers, styrene monomers, silicone monomers, etc., or organic particles obtained by copolymerizing these monomers, acrylic resin particles, melamine resin particles, silicone resin particles, and cross-linked polystyrene particles. Among these, it is preferable to use at least one selected from the group consisting of organic particles, calcium carbonate, silica, and aluminum oxide. Furthermore, precipitated particles obtained by precipitating and finely dispersing a portion of a metal compound such as a catalyst during the polyester production process can also be used.

[0087] In this embodiment, it is also a preferred embodiment that the back surface layer contains both organic and inorganic particles. By using a combination of organic and inorganic particles in the back surface layer, it becomes easy to control the arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk) of the surface of the back surface layer within desired ranges.

[0088] The shape of the particles in the back surface layer is not particularly limited, and any of spherical, blocky, rod-like, flat, etc. may be used. Furthermore, there are no particular limitations on the hardness, specific gravity, color, etc. Two or more types of these particles may be used in combination as needed.

[0089] The average particle size of the particles in the back surface layer is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, even more preferably 2.5 μm or less, and particularly preferably 2 μm or less. The average particle size is preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more. By setting the average particle size within the above range, the surface roughness of the back surface layer does not become too rough, and it is easy to control the arithmetic mean height (Sa), maximum peak height (Sp), root-mean-square height (Sq), kurtosis (Sku), and skewness (Ssk) within desired ranges. Setting the average particle size within the above range also reduces haze, making it easier to ensure transparency for the entire film.

[0090] 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 accumulated volume fraction of 50% (d50) in the equivalent spherical distribution. The average particle size of particles in a film, layer, 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 the case of non-spherical particles, the average of the longest and shortest diameters can be used to measure the diameter of each particle. The average particle size of particles is the primary average particle size.

[0091] The particle content of the back surface layer 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 back surface layer. 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 back surface layer. When two or more types of particles are blended in the back surface layer, the total particle content is preferably within the above range. By setting the particle content to the above lower limit or more, it is possible to effectively impart slipperiness and prevent scratches in each process. Furthermore, by setting the particle content to the above upper limit or less, it is possible to effectively prevent the unevenness caused by minute protrusions on the back surface layer from being transferred to the surface layer.

[0092] The method for adding particles to the polyester film is not particularly limited, and any conventionally known method can be used. For example, particles can be added at any stage in the production of the polyester constituting the back layer, but it is preferable to add them after the completion of the esterification or transesterification reaction.

[0093] The thickness of the back surface layer is preferably 0.5 μm or more, more preferably 0.8 μm or more, even more preferably 1 μm or more, and particularly preferably 1.2 μm or more. The thickness of the back surface layer is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 6 μm or less, and particularly preferably 4 μm or less.

[0094] The thickness of the back layer is preferably 1 to 20% of the total thickness of the polyester film, more preferably 2 to 17%, even more preferably 2.5 to 15%, still more preferably 3 to 13%, and particularly preferably 3 to 10%.

[0095] The content of recycled polyester resin in the back surface layer is preferably 90% by mass or more, more preferably 92% by mass or more, even more preferably 94% by mass or more, still more preferably 95% by mass or more, even more preferably 96% by mass or more, still more preferably 97% by mass or more, and particularly preferably 98% by mass or more, based on the total mass of the resin components contained in the back surface layer. The content of recycled polyester resin in the back surface layer is most preferably 100% by mass.

[0096] The back surface layer contains a recycled polyester resin, and the recycled polyester resin is preferably a chemically recycled polyester resin. When the back surface layer contains a chemically recycled polyester resin, the content of the chemically recycled polyester resin is preferably 90% by mass or more, more preferably 92% by mass or more, even more preferably 94% by mass or more, even more preferably 95% by mass or more, even more preferably 96% by mass or more, even more preferably 97% by mass or more, and particularly preferably 98% by mass or more, based on the total mass of the resin components contained in the back surface layer. The content of the chemically recycled polyester resin in the back surface layer is most preferably 100% by mass.

[0097] In this embodiment, by setting the content of recycled polyester resin in the back surface layer within the above range, for example, it is possible to reduce CO2 emissions and contribute to reducing the burden on the environment. Furthermore, by using a chemically recycled polyester resin as the recycled polyester resin, it is possible to impart the necessary roughness to the back surface layer while keeping the maximum peak height (Sp) of the back surface layer below a predetermined value, thereby more effectively improving the processability and handleability of the polyester film.

[0098] The recycled polyester resin contained in the back surface layer is preferably a polyester obtained by chemically recycling a recycled raw material, polyester. The recycled (recycled) polyester may be, for example, a polyester derived from a polyester container (e.g., a PET bottle) or a polyester film (e.g., a processing film). Thus, in this embodiment, the recycled polyester resin constituting the back surface layer may be a recycled polyester resin derived from a polyester container (a PET bottle) or a recycled polyester resin derived from a polyester film. When a recycled polyester resin derived from a polyester film is used, the recycled polyester film may be a polyester film used as a support (substrate) for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor.

[0099] In this embodiment, the laminated polyester film preferably satisfies the following (1) or (2). (1) SpA <SpB (2) SaA <SaB Here, SaA is the arithmetic mean height of the surface of the surface layer, SpA is the maximum peak height of the surface of the surface layer, SaB is the arithmetic mean height of the surface of the back layer, and SpB is the maximum peak height of the surface of the back layer. That is, it is preferable that the arithmetic mean height of the surface of the back layer and / or the maximum peak height of the surface of the back layer are greater than these values ​​of the surface layer. By satisfying the above condition (1) or (2), the laminated polyester film of this embodiment can more effectively improve the film surface smoothness and film handleability.

[0100] <Recycled polyester resin> Examples of dicarboxylic acid components that constitute the recycled 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.

[0101] Examples of diol components that make up the recycled 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.

[0102] When the recycled 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 recycled polyester resins that can be used include polyethylene terephthalate, which is composed of 80 mol % or more, preferably 90 mol % or more, of ethylene terephthalate units, and polyethylene-2,6-naphthalate, which is composed of ethylene-2,6-naphthalate units.

[0103] On the other hand, when the recycled 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.

[0104] When the recycled polyester resin is a copolymer polyester, the content of isophthalic acid units relative to 100 mol% of all dicarboxylic acid units constituting the recycled polyester resin is preferably 0.01 to 5 mol%, more preferably 0.1 to 4 mol%, even more preferably 0.5 to 3 mol%, and even more preferably 1 to 2.5 mol%. For example, polyesters such as PET bottles recycled from the market or society contain a large amount of isophthalic acid components for the purpose of controlling crystallinity, etc. When such recycled raw materials are used, the recycled polyester resin will contain isophthalic acid units within the above range. If the content of isophthalic acid units is equal to or greater than the above lower limit, the flexibility of the polyester layer formed from the recycled polyester resin can be improved, making it easier to obtain a polyester film with excellent surface smoothness. On the other hand, if the content of isophthalic acid units is equal to or less than the above upper limit, the mechanical strength of the film can be increased. Furthermore, when this film is used as a support (substrate) for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors, the suppressed crystallinity of this film has the advantage that burrs and chips are less likely to be generated when cutting with a cutting blade to peel off the ceramic green sheets laminated on the support.

[0105] 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.

[0106] Recycled polyester resins are obtained by recycling (regenerating) polyester, which is a recycled raw material. The recycled raw material may be, for example, polyester derived from polyester containers (e.g., PET bottles) or polyester derived from polyester film (e.g., processing film). Polyester recovered from the polyester film or PET bottle manufacturing process without being used as a product can also be used as the recycled raw material. In this specification, polyester (recycled raw material) recovered from the polyester film or PET bottle manufacturing process is referred to as self-recovered polyester or in-situ recycled polyester. For example, polyester film recovered from the process of producing polyester film used as a support (substrate) for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors can be used as the recycled raw material.

[0107] The self-recovery polyester or in-situ recycled polyester may contain particles. When particles are contained, the particle content is preferably 10 ppm or more by mass, more preferably 20 ppm or more, even more preferably 30 ppm or more, even more preferably 40 ppm or more, and particularly preferably 50 ppm or more. On the other hand, the particle content is preferably 500 ppm or less, more preferably 400 ppm or less, even more preferably 350 ppm or less, even more preferably 300 ppm or less, even more preferably 250 ppm or less, and particularly preferably 200 ppm or less.

[0108] Furthermore, since self-recovery polyester and in-situ recycled polyester use film scraps and film waste generated in the company's own factories, the characteristics of the polyester raw material, such as the state of granular matter such as gel, the particle content, intrinsic viscosity, and raw material catalyst type, can be accurately determined, making it easier to stabilize the quality of the resulting film. From this perspective, the use of self-recovery polyester and in-situ recycled polyester is also preferred. When self-recovery polyester or in-situ recycled polyester is used, it is particularly preferred to use it in the intermediate layer.

[0109] The recycled polyester resin may be a polyester derived from a finished molded product. A finished molded product refers to a molded product (e.g., a PET bottle or polyester film) that has been taken out of the manufacturing process (outside the manufacturing plant) as a product. In other words, a finished molded product is distinguished from, for example, self-recovered polyesters that are not used as products during the process of manufacturing polyester film or PET bottles, or in-situ recycled polyesters. Typically, finished molded products are discarded after being used for their intended purpose (or after being stored for use in their intended purpose). However, in this embodiment, used and / or stored finished molded products can be recycled and used as recycled polyester resin. In this embodiment, it is preferable that at least one layer selected from the surface layer and the back surface layer contains polyester derived from the finished molded product. Furthermore, when the laminated polyester film has an intermediate layer, the intermediate layer may contain polyester derived from the finished molded product.

[0110] In this embodiment, a biomass-derived raw material may be used for the polyester, which is the recycled raw material for the recycled polyester resin. 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.

[0111] <<Chemical recycled polyester>> Chemically recycled polyester resins are preferred for recycled polyester resins. Examples of chemically recycled polyester resin production methods include sorting, crushing, and washing collected PET bottles and polyester films to remove foreign matter, then depolymerizing them to break them down into raw materials or intermediate materials for polyester resin, purifying them, and then repolymerizing these materials. Depolymerization can be achieved by adding ethylene glycol (EG) in the presence of a catalyst to return them to bis-2-hydroxyethyl terephthalate (BHET), an intermediate material used in resin production, which is then purified and repolymerized to form PET. Alternatively, polyethylene terephthalate can be heated in a nonaqueous organic solvent in the presence of a catalyst containing oxidized iron to produce terephthalic acid and ethylene glycol, which are then repolymerized. Chemically recycled polyester resins are characterized by the removal of foreign matter and other materials during depolymerization and repolymerization, allowing them to be recycled into polyester resins of similar quality to virgin resins.

[0112] In this specification, chemically recycled polyester refers to polyester containing structural units derived from monomers obtained by depolymerization. The content of structural units derived from monomers obtained by depolymerization contained in the chemically recycled polyester is preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, even more preferably 60 mol% or more, even more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more. All of the monomers constituting the chemically recycled polyester may be monomers obtained by depolymerization, or the content of structural units derived from monomers obtained by depolymerization contained in the chemically recycled polyester may be 100 mol%.

[0113] The collected used PET bottles and polyester films are washed and then crushed into flakes. Crushing may be performed underwater, or the washing and crushing steps may be performed simultaneously. Furthermore, a foreign matter removal step may be performed before or after these steps.

[0114] Next, the polyethylene terephthalate flakes are depolymerized, melted, and simultaneously hydrolyzed to produce a polyethylene terephthalate melt with a low degree of polymerization. Furthermore, it is preferable to depolymerize the flakes using excess ethylene glycol to obtain a two-component mixture solution of crude BHET and crude ethylene glycol. After the depolymerization reaction is complete, the two-component mixture solution of crude BHET and crude ethylene glycol is cooled and filtered to remove solid foreign matter. Further, colored substances and dissolved ions may be removed by adsorption and ion exchange treatment.

[0115] Next, the mixed solution of crude BHET and crude ethylene glycol is preferably subjected to distillation and evaporation to separate and distill off the ethylene glycol to obtain concentrated BHET. Alternatively, the mixed solution 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. Purified bis-β-hydroxyethyl terephthalate is obtained by evaporating the concentrated BHET under specified conditions under vacuum. After obtaining highly purified BHET as described above, the purified BHET can be charged into a melt polycondensation reactor to repolymerize the polyester.

[0116] <<Material: Recycled Polyester>> As the recycled polyester resin, material recycled polyester can be used. In material recycling, collected PET bottles and polyester films are first crushed into flakes. Since these flakes often contain foreign matter, they are preferably washed, and alkaline washing is more preferable.

[0117] 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.

[0118] 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.

[0119] The molten resin that passes through the filter passes through a die, is cooled in water, and then cut into pellets of the desired shape and granulated, yielding recycled polyester resin.

[0120] In addition, in the process of cleaning recovered PET bottles and polyester film, or in the process of melting these raw materials, the polyester may be partially hydrolyzed by the cleaning components or heat, which reduces the degree of polymerization of the recycled polyester resin. Depending on the intended use, a reduced degree of polymerization may result in poor moldability, strength, transparency, heat resistance, and other properties. Therefore, a solid-state polymerization process may be performed to restore the reduced degree of polymerization. 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.

[0121] <<Others>> In this embodiment, a recycled polyester resin with a low oligomer content may be used to suppress the amount of precipitation of oligomer components. Various known methods can be used to produce recycled polyester resins with a low oligomer content, such as a method of solid-state 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.

[0122] In addition to the above-mentioned components, conventionally known ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc. may be added to the recycled polyester resin as needed.

[0123] The recycled polyester resin may further contain a metal component. The metal component may be a metal used as a polycondensation catalyst when producing polyester, which is the recycled raw material for the recycled polyester resin. In other words, the present film may contain a polycondensation catalyst used when producing the polyester to be recycled (regenerated). Examples of metal components include antimony, phosphorus, manganese, calcium, magnesium, cobalt, tin, germanium, zinc, aluminum, and titanium. Among these, the metal component is preferably at least one selected from the group consisting of antimony, germanium, aluminum, and titanium.

[0124] For example, the compounds contained in the film may vary depending on the type of recycled raw material used. For example, because polyester containers such as PET bottles come into direct contact with food, the polycondensation catalysts used in their manufacturing process are limited, and harmful metal elements such as cadmium, palladium, and selenium are generally not detected. Therefore, if cadmium, palladium, selenium, etc. are detected, it can be assumed that polyester food containers were not used as recycled raw materials.

[0125] <<Physical properties of recycled polyester resin>> The intrinsic viscosity of the recycled polyester resin is preferably 0.45 dL / g or more, more preferably 0.5 dL / g or more, even more preferably 0.55 dL / g or more, and even more preferably 0.6 dL / g or more. The viscosity of the recycled polyester resin is preferably 1.2 dL / g or less, more preferably 1 dL / g or less, even more preferably 0.9 dL / g or less, even more preferably 0.8 dL / g or less, and particularly preferably 0.75 dL / g or less. By setting the intrinsic viscosity of the recycled polyester resin to the above-mentioned lower limit or higher, stability during film formation can be improved. On the other hand, by setting the intrinsic viscosity to the above-mentioned upper limit or lower, it is preferable because it is easier to prevent excessive pressure buildup in the film-forming extruder and to easily reduce the thermal shrinkage rate of the film. The intrinsic viscosity of the recycled polyester resin is measured by precisely weighing 1 g of polyester resin, dissolving it in 100 mL of a 50 / 50 (mass ratio) phenol / tetrachloroethane solvent, and measuring the viscosity (IV) at 30° C. The intrinsic viscosity of the polyester film may also be within the above range.

[0126] When the recycled polyester resin is a polyester resin derived from PET bottles, the intrinsic viscosity (IV) of the recycled polyester resin is preferably 0.64 dL / g or more, more preferably 0.66 dL / g or more, even more preferably 0.67 dL / g or more, even more preferably 0.7 dL / g or more, and particularly preferably 0.72 dL / g or more. The intrinsic viscosity (IV) of the recycled polyester resin is preferably 1.2 dL / g or less, more preferably 1 dL / g or less, even more preferably 0.9 dL / g or less, even more preferably 0.85 dL / g or less, and particularly preferably 0.82 dL / g or less.

[0127] When the recycled polyester resin is derived from polyester film, the intrinsic viscosity (IV) of the recycled polyester resin is preferably 0.45 dL / g or more, more preferably 0.5 dL / g or more, even more preferably 0.52 dL / g or more, and particularly preferably 0.54 dL / g or more. The intrinsic viscosity (IV) of the recycled polyester resin is preferably 0.8 dL / g or less, more preferably 0.7 dL / g or less, even more preferably 0.67 dL / g or less, and particularly preferably 0.64 dL / g or less.

[0128] The recycled polyester resin may contain granular matter. In this specification, the granular matter is derived from a gel-like substance formed by aggregation of resin-derived components or foreign matter contained in the recycled raw material. In this case, the recycled polyester resin contains 50 granular matter with a particle size of 1000 μm or less per m. 2 May contain more than 100 pieces / m 2 May contain more than 150 pieces / m 2 May contain more than 200 pieces / m 2 May contain more than 250 pieces / m 2 May contain more than 300 pieces / m 2 May contain more than 350 pieces / m 2 May contain more than 400 pieces / m 2 May contain more than 450 pieces / m 2 May contain more than 500 pieces / m 2 May contain more than 650 pieces / m 2 May contain more than 800 pieces / m 2 May contain more than 1000 pieces / m 2 May contain more than 2000 pieces / m 2 May contain more than 3000 pieces / m 2 The recycled polyester resin may contain granules with a particle size of 1000 μm or less at a density of 6000 particles / m 2 May contain less than 4000 pieces / m 2 May contain less than 2000 pieces / m 2 May contain up to 1700 pieces / m 2 May contain up to 1300 pieces / m2 May contain less than 1000 pieces / m 2 The recycled polyester resin may contain 900 particles / m 2 Preferably, it is 800 pieces / m or less. 2 More preferably, it is 700 particles / m or less. 2 More preferably, it is 600 particles / m or less. 2 More preferably, it is 500 particles / m or less. 2 It is particularly preferable that the particle size is 1000 μm or less. The number of particulate matter having a particle size of 1000 μm or less contained in the present film may also be within the above range. In this specification, the particle size of a particulate matter is the average value of the longest and shortest diameters.

[0129] Recycled polyester resin is made of granular particles with a particle size of 25 μm to 1000 μm at 20 particles / m 2 May contain more than 80 pieces / m 2 May contain more than 150 pieces / m 2 May contain more than 400 pieces / m 2 May contain more than 700 pieces / m 2 May contain more than 1000 pieces / m 2 May contain more than 2000 pieces / m 2 The recycled polyester resin may contain granular particles with a particle size of 25 μm to 1000 μm at a density of 5000 particles / m 2 May contain less than 3000 pieces / m 2 May contain less than 1000 pieces / m 2 May contain up to 700 pieces / m 2 May contain up to 500 pieces / m 2 May contain up to 300 pieces / m 2 It may include the following: Recycled polyester resin is made of granular particles with a particle size of 25 μm or more and less than 50 μm at a rate of 20 to 2500 particles / m 2 May contain 40 to 2000 pieces / m 2 May contain 60 to 1000 pieces / m 2 May contain 100 to 700 pieces / m 2 May contain 200 to 500 pieces / m 2 It may include. Recycled polyester resin is made of granular particles with a particle size of 50 μm or more and less than 75 μm at a rate of 10 to 2000 particles / m 2 May contain 30 to 1500 pieces / m 2 May contain 50 to 1000 pieces / m 2 May contain 70 to 700 pieces / m 2 May contain 90-500 pieces / m 2 It may include. Recycled polyester resin is made of granular particles with a particle size of 75 μm or more and less than 100 μm at a rate of 5 to 1,500 particles / m 2 May contain 20 to 1000 pieces / m 2 May contain 40 to 700 pieces / m 2 It may contain 60 to 500 particles, or 80 to 300 particles / m 2 It may include. Recycled polyester resin is made of granular particles with a particle size of 100 μm or more and less than 150 μm at a rate of 5 to 1,300 particles / m 2 May contain 15 to 1000 pieces / m 2 May contain 30 to 800 pieces / m 2 May contain 50 to 600 pieces / m 2 May contain 70 to 400 pieces / m 2 It may include. Recycled polyester resin is made of granular particles with a particle size of 150 μm or more and less than 200 μm at a rate of 3 to 700 particles / m 2 May contain 8 to 400 pieces / m 2 May contain 13 to 200 pieces / m 2 It may contain 20 to 100 particles, and may contain 40 to 80 particles / m 2 It may include. Recycled polyester resin is made of granular particles with a particle size of 200 μm or more and less than 300 μm, with a density of 1 to 400 particles / m 2 May contain 4 to 200 pieces / m 2 May contain 8 to 100 pieces / m 2 May contain 12 to 70 pieces / m 2 May contain 18 to 50 pieces / m 2 It may include. Recycled polyester resin is made of granular particles with a particle size of 300 μm or more and less than 500 μm, with a density of 1 to 100 particles / m 2May contain 3 to 60 pieces / m 2 May contain 5 to 30 pieces / m 2 May contain 7 to 15 pieces / m 2 It may include.

[0130] Depending on the layer using the recycled polyester resin, a recycled polyester resin having appropriate particulate matter may be appropriately selected. Specifically, from the viewpoint of forming fine irregularities in the surface layer while improving the smoothness of the surface layer, it is preferable to use a recycled polyester resin with a small amount of particulate matter for the surface layer. Furthermore, from the viewpoint of easily forming fine irregularities in the intermediate layer, and by propagating these irregularities to the surface layer, it is easy to form irregularities that satisfy predetermined conditions in the surface layer while maintaining the smoothness of the surface layer, it is also preferable to use a recycled polyester resin with a relatively large amount of particulate matter for the intermediate layer.

[0131] The number of particles having each of the above particle sizes can be measured using a gel counter in the following manner. Specifically, while continuously extruding (recycled) polyester resin into a sheet shape with a width of 10 cm and a thickness of 50 μm, light is applied from above the sheet to an area of ​​approximately 6 cm in the center of the width direction, and a CCD camera is used to photograph the shadows caused by the particles from below the sheet. This allows the number of particles to be counted within 1 m. 2 The number of particles of each particle size present in the gel is measured. The particles are thought to be mainly derived from the gel. The gel counter is composed of a camera system, an extruder, and a chill roll unit, and an "FS-5 Film Scan (camera system), ME-20 / 26 V2 Measuring Extruder (extruder), and CR-7 Chill Roll Unit (chill roll unit)" manufactured by Optical Control Systems can be used as the gel counter. The measurement conditions are as follows: Cooling roll temperature: 30℃ Extruder cylinder temperature: 295℃ Extruder screw speed: 100 rpm Sheet thickness: 50μm

[0132] The particle size and content of particulate matter in the recycled polyester resin can be adjusted, for example, by at least one of the following methods (1) to (4). It is preferable to combine multiple methods, and it is more preferable to use all of the methods. (1) A method of removing metal foreign matter mixed in with collected PET bottles and polyester film using a metal detector. (2) A method of removing foreign matter from collected PET bottles and polyester film by passing them through a precision air classifier. (3) In the process of melting and pelletizing recovered PET bottles and polyester films in an extruder, a method of adjusting the temperature near the raw material inlet of the extruder, the temperature near the outlet, and the temperature difference between the temperature near the inlet and the temperature near the outlet. (4) A method of removing particles other than the desired particle size from the molten recycled polyester resin by passing it through a filter.

[0133] In the above-mentioned method (1) of removing metallic contaminants using a metal detector, a commercially available metal detector can be used to remove the metallic contaminants. A preferred metal detector is one that uses a magnet. For example, a magnetic bar can be attached to the piping used to transport the recycled polyester raw material to the process (2) to remove the metallic contaminants. Failure to remove metallic contaminants can lead to poor thermal stability of the polyester, a high number of contaminants in the resulting film, and reduced transparency.

[0134] In the step (2) of removing foreign matter by passing the raw material through an air classifier, the foreign matter in the raw material that has been through step (1) is further removed using an air classifier. Air classifiers that can be used include gravity classifiers, inertial classifiers, centrifugal classifiers, etc. Commercially available air classifiers can be used, but it is preferable to use a classifier that is capable of precise classification. By using an air classifier, powder and froth-like foreign matter adhering to the surface of recovered PET bottles and polyester film can be separated using a nitrogen or air stream. The powder and froth-like foreign matter adhering to the surface may have a high melting point. If these foreign matter remain attached without being removed using an air classifier, they may not melt during molding, resulting in a reduced transparency of the resulting film.

[0135] In the method (3) above of melting the recovered PET bottles or polyester films in an extruder, it is preferable to melt the materials by setting the temperature near the extruder's raw material inlet to, for example, 290 to 280°C, the temperature near the outlet to, for example, 270 to 260°C, and the temperature difference between the temperature near the inlet and the temperature near the outlet to, for example, 20 to 25°C.

[0136] First, when the raw materials are fed into the extruder, they are melted at a temperature of, for example, 280 to 290°C, and the temperature inside the extruder is gradually lowered, so that the catalyst metal-derived substances melted in the resin act as nuclei, facilitating the precipitation of foreign matter. At this time, the temperature near the extruder outlet is set to, for example, 260 to 270°C, and preferably, the temperature difference between the temperature near the inlet and the temperature near the outlet is set to 20 to 25°C. By setting the temperature near the extruder inlet to 280°C or higher, the precipitation of the above-mentioned foreign matter is facilitated, and by setting the temperature near the extruder inlet to 290°C or lower, decomposition of the polyester resin is suppressed, making it easier to obtain a recycled polyester resin with excellent thermal stability.

[0137] The residence time of the recycled polyester raw material in the extruder is preferably 10 minutes or less, and more preferably 5 minutes or less from the viewpoint of further reducing the carboxyl terminal group concentration and more easily preventing deterioration of the color tone of the polyester.

[0138] In the above method (4), unnecessary foreign matter is removed by passing the molten polyester resin through a filter with a filtration particle size of 10 to 25 μm, for example. By using a filter with a filtration particle size of 25 μm or less, foreign matter can be sufficiently removed, making it easier to obtain a recycled polyester resin with the desired particulate matter. On the other hand, by using a filter with a filtration particle size of 10 μm or more, clogging by foreign matter can be suppressed. By using such a filter, excessively large particulate matter can be removed, and by appropriately adjusting the melting temperature and time, particulate matter that is too small can be allowed to pass through the filter and then grown appropriately, thereby obtaining a recycled polyester resin with the desired amount of particulate matter of the desired particle size.

[0139] The filter that can be used in the above method (4) may be any common filter, such as a screen changer type filter, a leaf disk filter, or a candle type sintered filter.

[0140] <Physical properties of polyester film> The air leakage index of the present film is preferably 8500 seconds or less, more preferably 8000 seconds or less, even more preferably 7500 seconds or less, and particularly preferably 7000 seconds or less. The lower limit of the air leakage index is not particularly limited, but is preferably 100 seconds or more, and may be 300 seconds or more, 500 seconds or more, or 700 seconds or more. The air leakage index of the present film is measured using a DigiBec smoothness tester (manufactured by Toyo Seiki Co., Ltd., "DB-2") in accordance with JIS P8119 at a temperature of 23°C and a relative humidity of 50%. The pressure of the pressurizing device is 100 kPa, and the vacuum container is a 38 ml container. The time (seconds) for 1 mL of air to flow is measured, i.e., the time (seconds) for the pressure inside the container to change from 50.7 kPa to 48.0 kPa. The air leakage index is calculated by multiplying the obtained number of seconds by 10. The sample size of this film is 70 mm square, and 20 sheets of film are stacked with the front and back overlapping to form a test laminate film. A 5 mm diameter hole is drilled in the center of this test laminate film to measure the air leakage index. In this specification, the higher the air leakage index value, the longer it takes for air to leak through the gaps between the films, meaning that the films are more closely contacted. Therefore, an air leakage index below the above upper limit value means that there are appropriate gaps between the films, which improves the slipperiness when the film is wound into a roll and reduces the risk of wrinkles when made into a roll film.

[0141] The air leakage index reduction rate of the present film, calculated by the following formula, is preferably 5% or more, more preferably 10% or more, even more preferably 13% or more, even more preferably 15% or more, and even more preferably 20% or more. Air leakage index reduction rate (%) = 100 - air leakage index of target polyester film / air leakage index of virgin polyester film x 100 The virgin polyester film in the above formula is a film formed by replacing all the recycled polyester resins contained in the target polyester film with virgin polyester resins (polyester resins that have not been recycled). The fact that the air leakage index reduction rate is not less than the above lower limit value means that there is an appropriate gap between the films, which can enhance the slipperiness when winding this film into a roll and reduce the risk of wrinkle generation when forming a roll-shaped film.

[0142] In this embodiment, in order to make the air leakage index and the air leakage index reduction rate within the above ranges, for example, the arithmetic mean height (SaA) and the maximum peak height (SpA) of the surface layer can be set within a predetermined numerical range, or the arithmetic mean height (SaB) and the maximum peak height (SpB) of the back surface layer can be set within a predetermined numerical range, or the surface characteristics can be controlled to satisfy the conditions of SpA < SpB and SaA < SaB. To control the surface characteristics, it is effective to adjust the particle size and content of the particulate matter contained in the recycled polyester resin and the content of the recycled polyester resin.

[0143] The glass transition temperature (Tg) of this film is preferably 65°C or higher, more preferably 70°C or higher, still more preferably 74°C or higher, and even more preferably 77°C or higher. Also, the glass transition temperature (Tg) of this film is preferably 95°C or lower, more preferably 90°C or lower, still more preferably 86°C or lower, and even more preferably 83°C or lower.

[0144] The temperature-rising recrystallization temperature (Tc) of this film is preferably 144°C or lower, more preferably 143.5°C or lower, still more preferably 143°C or lower, even more preferably 140°C or lower, and still more preferably 135°C or lower. The lower limit value of the temperature-rising recrystallization temperature (Tc) of this film is not particularly limited, but for example, it is preferably 110°C or higher, and may be 120°C or higher, 125°C or higher, or 130°C or higher.

[0145] The film preferably has a peak heat of recrystallization (ΔHc) of 10 J / g or more, more preferably 14 J / g or more, even more preferably 18 J / g or more, and even more preferably 22 J / g or more, and preferably has a peak heat of recrystallization (ΔHc) of 45 J / g or less, more preferably 40 J / g or less, even more preferably 37 J / g or less, and even more preferably 35 J / g or less.

[0146] The melting peak temperature (Tm) of the present film is preferably 230° C. or higher, more preferably 235° C. or higher, even more preferably 240° C. or higher, and even more preferably 245° C. or higher. The melting peak temperature (Tm) of the present film is preferably 270° C. or lower, more preferably 260° C. or lower, even more preferably 256° C. or lower, even more preferably 254° C. or lower, and most preferably less than 253° C.

[0147] The film preferably has a peak heat of fusion (ΔHm) of 18 J / g or more, more preferably 22 J / g or more, even more preferably 25 J / g or more, and even more preferably 27 J / g or more, and preferably has a peak heat of fusion (ΔHm) of 50 J / g or less, more preferably 45 J / g or less, even more preferably 40 J / g or less, and even more preferably 36 J / g or less.

[0148] 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. The measurement conditions are as follows: the melting peak temperature (Tm: peak-top temperature of the endothermic curve of crystalline melting) and melting peak calorific value (ΔHm: peak calorific value of the endothermic curve of crystalline melting) in (1) are determined, and the glass transition temperature (Tg: midpoint glass transition temperature), temperature-rising recrystallization temperature (Tc: peak-top temperature of the exothermic curve of temperature-rising recrystallization) and melting peak calorific value (ΔHc: peak calorific value of the exothermic curve of temperature-rising recrystallization) in (5) are determined. (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

[0149] The haze of the present film is preferably 15% or less, more preferably 10% or less, even more preferably 7% or less, and even more preferably 5% or less. The lower limit of the haze of the present film is not particularly limited and may be 0%, 0.5%, 1%, 1.5%, or 2.1%. The haze of the film is measured using a haze meter in accordance with JIS K7136:2000.

[0150] The total light transmittance of the present film is preferably 70% or more, more preferably 75% or more, even more preferably 80% or more, and even more preferably 85% or more. The upper limit of the total light transmittance of the present film is not particularly limited and may be 100%, 97%, or 95%. The total light transmittance of the film is measured in accordance with JIS K7136:2000 using a haze meter under a D65 light source.

[0151] 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 a polyester film can lead to coating irregularities and wrinkles. In other words, the heat distortion resistance of a polyester film 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 present film preferably has a machine-direction (MD) heat shrinkage of 2.8% or less, more preferably 2.6% or less, even more preferably 2.4% or less, even more preferably 2.2% or less, and particularly preferably 2% or less, when heat-treated at 150°C for 5 minutes. From the same perspective, the lower limit of the machine-direction (MD) heat shrinkage (150°C, 5 minutes) is preferably −0.5% or more, more preferably −0.3% or more.

[0152] Furthermore, the heat shrinkage of this film in the transverse direction (TD) when heat-treated at 150°C for 5 minutes is preferably 2.8% or less, more preferably 2.6% or less, even more preferably 2.4% or less, even more preferably 2.2% or less, and particularly preferably 1.5% or less, from the viewpoint of suppressing coating irregularities and wrinkles. From the same viewpoint, the lower limit of the heat shrinkage in the transverse direction (TD) is preferably -0.5% or more, more preferably -0.3% or more. Furthermore, from the viewpoint of realizing a high level of thermal distortion resistance, which is particularly required in the manufacturing process of MLCCs using thin-film ceramic green sheets, the thermal shrinkage rate in the transverse direction (TD) (150°C, 5 minutes) is preferably 1.4% or less, more preferably 1.3% or less, and even more preferably 1.2% or less. The thermal shrinkage rate in the transverse direction (TD) (150°C, 5 minutes) can be appropriately set within the above range and is not particularly limited, and may be, for example, 1.4% or less, 1.3% or less, 1.2% or less, 1.1% or less, etc.

[0153] In order to achieve both the desired heat shrinkage rate (heated at 150°C for 5 minutes) of the present film, for example, it is necessary to appropriately set the film-forming conditions (particularly the longitudinal stretching temperature, transverse stretching ratio, heat setting temperature, roll peripheral speed, relaxation rate, etc.), film-forming raw materials, etc. The heat shrinkage rate (heated at 150°C for 5 minutes) of the present film 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

[0154] The total thickness of the present film is not particularly limited as long as it is within a range that allows film formation. However, from the viewpoints of mechanical strength, handleability, and productivity, it is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 18 μm or more. 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 32 μm or less. The total thickness of the present film may be, for example, 30 μm or less, less than 30 μm, 29 μm or less, or 28 μm or less. In conventional laminated polyester films, reducing the overall thickness of the film reduces the thickness of the surface layer, which limits the particle size of the particles incorporated into the surface layer, making it difficult to achieve appropriate surface smoothness (sufficient smoothness while maintaining a moderate degree of roughness). On the other hand, if particles are not incorporated into the surface layer, the film's slipperiness deteriorates and handling becomes poor. That is, in the prior art, when an attempt was made to thin a laminated polyester film, it was difficult to achieve both appropriate surface smoothness and handleability. In contrast, in the present invention, even when the laminated polyester film is made very thin, it has been successful in achieving both appropriate surface smoothness and handleability.

[0155] The gas density of this film is 1.4000 g / cm 3 It is preferable that the density is 1.4015 g / cm or more. 3 More preferably, it is 1.4020 g / cm or more. 3 More preferably, it is 1.4030 g / cm or more. 3 It is even more preferable that the density of the film is 1.4100 g / cm or more. 3 Preferably, it is 1.4075 g / cm or less. 3 More preferably, it is 1.4060 or less, and even more preferably, it is 1.4050 g / cm 3By setting the density of the present film within the above range, the heat resistance, solvent resistance, and flexibility of the polyester film can be all achieved, and a polyester film excellent in processability and surface properties can be easily obtained.

[0156] <Coating layer> In this embodiment, a coating layer may be further provided on the surface layer. The coating layer is preferably a layer formed by applying a coating layer-forming composition (coating liquid) onto the surface 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 the polyester film.

[0157] 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.

[0158] 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.

[0159] <<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 resin composition, one binder resin may be used alone, or two or more binder resins may be used in combination.

[0160] Examples of polyester resins, polyurethane resins, (meth)acrylic resins, and polyvinyl resins used as binder resins include compounds described in WO 2023 / 145952.

[0161] 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.

[0162] <<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.

[0163] Examples of the melamine compound and isocyanate compound used as the crosslinking agent include the compounds described in WO 2023 / 145952.

[0164] 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.

[0165] <<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.

[0166] 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.

[0167] 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.

[0168] The content of the 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 ratio of the total non-volatile components in the composition for forming a coating layer. By setting the content within the above range, the elastic deformation power (η it ) can be easily controlled within the desired range.

[0169] <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.

[0170] In particular, since the present film has excellent surface smoothness 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.

[0171] 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.

[0172] (Production method of polyester film) The present embodiment may relate to a method for producing the above-mentioned polyester film, which includes the steps of supplying a polyester resin containing 90% by mass or more of recycled polyester resin to an extruder, melting the polyester resin, and then extruding the melted polyester resin.

[0173] The method for producing a laminated polyester film of this embodiment preferably includes a step of laminating a recycled polyester layer constituting a surface layer and a recycled polyester layer constituting a back layer. Alternatively, the method for producing a laminated polyester film of this embodiment preferably includes a step of supplying recycled polyester resin A forming the surface layer and recycled polyester resin C forming the back layer to respective extruders, melting them, and then co-extruding them. 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.

[0174] 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 of the laminated polyester film includes a step of laminating a recycled polyester layer A constituting the surface layer, a recycled polyester layer B constituting the intermediate layer, and a recycled polyester layer C constituting the back layer. Alternatively, the manufacturing method of the laminated polyester film of this embodiment includes a step of feeding recycled polyester resin A constituting the surface layer, recycled polyester resin B constituting the intermediate layer, and recycled polyester resin C constituting the back layer into respective extruders, melting them, and then co-extruding them. 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.

[0175] The recycled polyester resin mentioned above is made of granules with a particle size of 1000 μm or less at 50 particles / m 2 That is, the above-mentioned recycled polyester resin A, recycled polyester resin B and recycled polyester resin C each contain 50 particles / m of particles with a particle size of 1000 μm or less. 2 It is preferable that the recycled polyester resin contains at least one particulate material having a predetermined particle size. By using a recycled polyester resin containing particulate material having a predetermined particle size, it becomes easy to control the surface roughness of the resulting laminated polyester film to the desired conditions. The preferred ranges of the particle size and content of the particulate material contained in the recycled polyester resin are the same as the preferred ranges of the particle size and content of the particulate material described in the section "Physical properties of recycled polyester resin."

[0176] 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.

[0177] 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.

[0178] In the present embodiment, when a coating layer is provided on the surface layer, a step of forming the coating layer may be provided. In the step of forming the coating layer, the coating layer is formed by applying a coating layer-forming composition (coating liquid) onto the surface layer.

[0179] (Release film) This embodiment may also relate to a release film further comprising a functional layer such as a release layer on at least one side of the polyester film described above. The surface on which the functional layer is provided preferably has a maximum peak height (Sp) of 90 nm or less.

[0180] 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 further having a functional layer such as a release layer on the surface layer side. That is, for example, the release film has a structure of release layer / surface layer / intermediate layer / back layer. When the present film has a coating layer, it may have a structure of release layer / coating layer / surface layer / intermediate layer / back layer. 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 present film, an antistatic layer, an antiblocking layer, etc. By providing a release layer on the surface layer in this way, when the present 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.

[0181] In this embodiment, the surface layer side of the polyester film may have a functional layer other than the release layer. 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.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] Examples of non-silicone release agents include waxes, compounds containing long-chain alkyl groups, and fluorine compounds.

[0186] 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.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] The release layer is provided by coating the 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.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] (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.

[0196] This 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. This 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 the surface layer side of the polyester film.

[0197] 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 polyester film described above or to the release layer of the release film described above, and then dried to produce a ceramic green sheet (dielectric sheet). The surface of the polyester film to which the ceramic slurry is applied preferably has a maximum peak height (Sp) of 90 nm or less. 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 the release layer of the release film described above. [Example]

[0198] 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 interpreted as being limited by the specific examples shown below. In addition, "ppm" in the tables indicates a percentage based on mass.

[0199] [Polyester raw materials] The polyester raw materials used in the examples and comparative examples are as follows: (1) Polyester A: homopolyethylene terephthalate (titanium catalyst, intrinsic viscosity 0.63 dL / g) (2) Polyester B: Masterbatch (intrinsic viscosity 0.61 dL / g) containing 2.0% by mass of 0.7 μm calcium carbonate particles in homopolyethylene terephthalate (antimony catalyst) (3) Polyester C: Chemically recycled polyethylene terephthalate derived from PET bottles (intrinsic viscosity 0.62 dL / g, isophthalic acid unit content 1.8 mol% relative to 100 mol% of all dicarboxylic acid units, diethylene glycol unit content 1.3 mol% relative to 100 mol% of all diol units) (4) Polyester D: Recycled polyethylene terephthalate from PET bottles, "UK-31" manufactured by Utsumi Recycle Systems (intrinsic viscosity 0.711 dl / g, isophthalic acid unit content 1.4 mol% relative to 100 mol% of total dicarboxylic acid units, diethylene glycol unit content 2.29 mol% relative to 100 mol% of total glycol units) (5) Polyester E: Masterbatch (intrinsic viscosity 0.60 dL / g) containing homopolyethylene terephthalate (titanium catalyst), 1% by mass of 0.1 μm spherical silica particles, and 0.25% by mass of an amide dispersant. (6) Polyester F: Masterbatch (intrinsic viscosity 0.63 dL / g) containing 0.75% by mass of 0.06 μm alumina particles in homopolyethylene terephthalate (titanium catalyst) (7) Polyester G: Polyester G was obtained as follows. The raw materials for surface layers A and C were a blend of 43% by mass of Polyester H (described later), 21% by mass of Polyester B, and 36% by mass of Polyester I (described later). The raw materials for intermediate layer B were 100% by mass of Polyester H. These were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layers A and C were co-extruded to form a three-type, three-layer (A / B / C) structure with the raw materials for surface layers A and C as the outermost layer (surface layer) and intermediate layer B as the intermediate layer, with the thickness composition ratio of A / B / C = 1 / 29 / 1 under the extrusion conditions. The material was then cooled and solidified on a cooling roll with a surface temperature set to 20°C using an electrostatic adhesion method to obtain an amorphous film. Next, the film was stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the difference in roll peripheral speed, and then this machine-stretched film was introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. Heat treatment was then performed at 170°C, 230°C, 230°C, and 140°C in heat treatment (fixing) zones 1, 2, and 3 and cooling zone 4 within the tenter, respectively, to obtain a polyester film with a thickness of 31 μm. The resulting polyester film scraps were collected, crushed, and re-pelletized to obtain a self-recoverable polyester raw material (Polyester G, intrinsic viscosity 0.59 dL / g). (8) Polyester H: homopolyethylene terephthalate (antimony catalyst, intrinsic viscosity 0.65 dL / g) (9) Polyester I: Masterbatch (intrinsic viscosity 0.61 dL / g) containing 0.4% by mass of organic particles with a particle size of 0.8 μm blended with homopolyethylene terephthalate (antimony catalyst)

[0200] (Comparative Example 1) Polyester A was used as the raw material for the surface and intermediate layers. A blend of 80% Polyester A and 20% Polyester B was used as the raw material for the back layer. This raw material was fed into a vented extruder and melt-extruded at 280°C. The raw materials for the surface and back layers were then co-extruded to form a three-type, three-layer structure (surface layer A / intermediate layer / back layer C), with the outermost layers being the raw materials for the surface and back layers. The extrusion conditions were such that the thickness ratio of A / B / C was 3.2 / 26.2 / 1.6. The film was cooled and solidified on a cooling roll set at a surface temperature of 20°C using an electrostatic adhesion method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a temperature of 86°C using the roll peripheral speed differential. This longitudinally stretched film was introduced into a tenter, preheated at 90°C inside the tenter, and then stretched 4.2 times in the transverse direction, i.e., TD, at 105°C. In the heat treatment (fixing) zone inside the tenter, it was heat-treated at 230°C and then cooled to 140°C with a relaxation rate of 2%, resulting in a polyester film with an overall thickness of 31 μm.

[0201] (Comparative Example 2) In Comparative Example 1, polyester D was used as the raw material for the surface layer and intermediate layer, and a raw material blended with 80% polyester D and 20% polyester B by mass was used as the raw material for the back layer. The same procedure as in Comparative Example 1 was repeated to obtain a polyester film with a total thickness of 31 μm.

[0202] Example 1 In Comparative Example 1, polyester C was used as the raw material for the surface layer and intermediate layer, and a raw material blended with 80% polyester C and 20% polyester B by mass was used as the raw material for the back layer. The same procedure as in Comparative Example 1 was repeated to obtain a polyester film with a total thickness of 31 μm.

[0203] Example 2 A polyester film having a total thickness of 31 μm was obtained in the same manner as in Example 1, except that the raw material for the intermediate layer was changed to Polyester D.

[0204] Example 3 A polyester film having a total thickness of 31 μm was obtained in the same manner as in Example 2, except that the raw material for the surface layer was a blend of 90% polyester C and 10% polyester E by mass.

[0205] Example 4 A polyester film having a total thickness of 31 μm was produced in the same manner as in Example 2, except that the raw material for the surface layer was a blend of 90% polyester C and 10% polyester F by mass.

[0206] Example 5 A polyester film having a total thickness of 31 μm was obtained in the same manner as in Example 4, except that the raw material for the intermediate layer was changed to Polyester G.

[0207] <Measurement and evaluation methods> (1) Arithmetic mean height (Sa), maximum peak height (Sp) The surfaces of the front and back layers of the evaluation film (5 cm x 5 cm) were measured using a surface roughness measuring device (Ametec Co., Ltd., "NewView" (registered trademark)), and the arithmetic mean height (Sa) and maximum peak height (Sp) were calculated from the obtained surface profile curve. Specifically, measurements were taken using the above-mentioned surface roughness measuring instrument under conditions of an objective lens magnification of 10x, a zoom magnification of 2.0x, and a viewing angle of 0.44mm x 0.44mm, and the arithmetic mean height (Sa) and maximum peak height (Sp) were determined after the following processing. Measurements were taken at 12 points, and the average of the 10 points excluding the maximum and minimum values ​​was used as the measured value. FilterType:Spline Filter: High Pass Type:Robust Gaussian Spline Fixed Cutoffs Mode: Period Long Period: 200 μm

[0208] (2) Air leakage index The air leakage index was measured using a DigiBec smoothness tester ("DB-2" manufactured by Toyo Seiki Co., Ltd.) in accordance with JIS P8119 at a temperature of 23°C and a relative humidity of 50%. The pressure of the pressure device was 100 kPa, and the vacuum container was a 38 ml container. The time (seconds) for 1 mL of air to flow, i.e., the time (seconds) for the pressure inside the container to change from 50.7 kPa to 48.0 kPa, was measured, and the air leakage index was calculated by multiplying the measured time by 10. Twenty polyester film samples, each 70 mm square, were stacked with the front and back of the film facing each other to form a test laminate film. A 5 mm diameter hole was then drilled in the center of this test laminate film, and the air leakage index was measured as described above. A higher air leakage index value indicates a longer time for air to leak through the gaps between the films, indicating a tighter film contact and a greater likelihood of wrinkling when rolled. In addition, the air leakage index reduction rate was calculated using the following formula. Air leakage index reduction rate (%) = 100 - air leakage index of target polyester film / air leakage index of virgin polyester film x 100 The air leakage index of the virgin polyester film in the above formula is the air leakage index of the polyester film obtained in Comparative Example 1.

[0209] (3) Tc (heat-raised recrystallization temperature), Tm (melting peak temperature), ΔHm (melting peak heat quantity) An 8 mg sample cut out from the evaluation film 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 melting peak temperature (Tm: the peak top temperature of the endothermic curve of crystalline melting) and melting peak heat quantity (ΔHm: the peak heat quantity of the endothermic curve of crystalline melting) in (1) were determined, and the temperature-rising recrystallization temperature (Tc: the peak top temperature of the exothermic curve of temperature-rising recrystallization) in (5) was determined.

[0210] (4) Gas density The gas density was measured using an Accupyc1330 (dry-type automatic density meter) manufactured by Shimadzu Corporation under the following measurement conditions, and each film sample was vacuum-dried for 30 minutes or more before measurement. ·Measurement temperature: 23℃ Measurement cell: 10cm 3 Gas used: Helium gas (purity > 99.99995% by volume)

[0211] (5) Haze Measurement was carried out in accordance with JIS K7136:2000 using a haze meter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd.

[0212] (6) Total light transmittance The total light transmittance was measured in accordance with JIS K7136:2000 using a haze meter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. under a D65 light source.

[0213] (7) Heat shrinkage rate An evaluation film (1.5 cm wide x 15 cm long) was heat-treated for 5 minutes in a hot air oven maintained at a specified temperature (150°C) in an untensioned state, and the length of the evaluation 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 both the machine direction (MD) and the transverse direction (TD) of the film. The MD heat shrinkage was measured so that the machine direction coincided with the MD, and the TD heat shrinkage was measured so that the machine direction coincided with the TD. 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

[0214] (8) 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.

[0215] (9) Number and average particle size of granules Polyesters A, C, and D were continuously extruded into a sheet of 10 cm width and 50 μm thickness. Light was applied from above to an area of ​​approximately 6 cm in the center of the width direction of the sheet, and a CCD camera was used from below the sheet to photograph the shadows caused by the granular matter (gel). 2 The number of particulate matter present in the gel was measured. The gel counter consisted of a camera system, an extruder, and a chill roll unit, and the gel counter used was an "FS-5 Film Scan (camera system), ME-20 / 26 V2 Measuring Extruder, and CR-7 Chill Roll Unit" manufactured by Optical Control Systems. The measurement conditions were as follows. The number of particulate matter and average particle size were as shown in Table 2. Cooling roll temperature: 30℃ Extruder cylinder temperature: 295℃ Extruder screw speed: 100 rpm Sheet thickness: 50μm

[0216] [Table 1]

[0217] [Table 2]

[0218] In the examples, polyester films containing 90% by mass or more of recycled polyester resin were obtained, and since the surface layer did not have large protrusions, extremely excellent surface smoothness was achieved. Furthermore, in the examples, the air leakage index was small, indicating that the polyester film had good handleability.

[0219] On the other hand, Comparative Example 1 does not contain recycled polyester resin, which places a heavy burden on the environment. Furthermore, Comparative Example 1 tended to have a high air leakage index and was poor in handleability. Comparative Example 2 had large protrusions on the surface layer, which is undesirable because they directly lead to pinholes in the ceramic sheet. [Industrial Applicability]

[0220] The polyester film of the present invention contains recycled polyester resin and has excellent surface smoothness and handleability. Therefore, it contributes to reducing the burden on the environment and is useful, for example, as a support (substrate) in the manufacturing process of multilayer ceramic capacitors and DFRs. When used as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors, it is possible to form a uniform, thin dielectric layer with reduced pinhole defects. The polyester film of the present invention is particularly suitable for use as a support for ceramic green sheets used in multilayer ceramic capacitors for automobiles. [Explanation of symbols]

[0221] 10 Polyester film 12 Surface layer 14 Middle Class 16 Back layer

Claims

1. A laminated polyester film having a surface layer and a back layer, The proportion of recycled polyester resin relative to the total mass of the resin components is 90% by mass or more. The recycled polyester resin contains 50 granular particles with a particle size of 1000 μm or less per square meter. ２ Including the above, The maximum peak height (SpA) of the surface layer is 90 nm or less. A laminated polyester film in which the arithmetic mean height (SaB) of the surface of the back layer is 3 nm or more and 35 nm or less, and the maximum peak height (SpB) of the surface of the back layer is 30 nm or more and 700 nm or less.

2. A laminated polyester film according to claim 1, satisfying either (1) or (2) below; (1) SpA<SpB (2) SaA<SaB However, SaA is the arithmetic mean height of the surface of the surface layer, SpA is the maximum peak height of the surface of the surface layer, SaB is the arithmetic mean height of the surface of the back layer, and SpB is the maximum peak height of the surface of the back layer.

3. The laminated polyester film according to claim 1, wherein the arithmetic mean height (SaA) of the surface of the surface layer is 0.3 nm or more and 5 nm or less, and the maximum peak height (SpA) of the surface of the surface layer is 5 nm or more and 60 nm or less.

4. The laminated polyester film according to claim 1, wherein the surface layer contains a chemically recycled polyester resin.

5. The laminated polyester film according to claim 1, wherein the laminated polyester film is a laminated polyester film having a surface layer, an intermediate layer and a back layer, and the surface layer contains a chemically recycled polyester resin.

6. The laminated polyester film according to claim 5, wherein the intermediate layer contains a polyester resin obtained by material recycling of a finished molded product.

7. The laminated polyester film according to claim 1, wherein the back layer contains a chemically recycled polyester resin.

8. The laminated polyester film according to claim 1, wherein the thickness of the surface layer is greater than 1 μm.

9. The laminated polyester film according to claim 1, wherein the surface layer substantially does not contain particles.

10. The laminated polyester film according to claim 1, wherein the back layer contains particles, and the average particle size of the particles is 2.5 μm or less.

11. The laminated polyester film according to claim 5, wherein the thickness of the intermediate layer is 50 to 93% of the total film thickness.

12. The laminated polyester film according to claim 1, wherein the air leakage index is 8500 seconds or less.

13. The laminated polyester film according to claim 1, wherein the air leakage index reduction rate calculated by the following formula is 13% or more. Air leakage index reduction rate (%) = 100 - Air leakage index of the target polyester film / Air leakage index of the virgin polyester film × 100

14. The laminated polyester film according to claim 1, wherein the content of isophthalic acid units relative to 100 mol% of the total dicarboxylic acid units constituting the polyester resin contained in the laminated polyester film is 0.01 to 5 mol%.

15. The laminated polyester film according to claim 1, wherein the temperature rise recrystallization temperature (Tc) is 144.0°C or lower.

16. The laminated polyester film according to claim 1, wherein the peak melting heat (ΔHm) is 40 J / g or less.

17. The laminated polyester film according to claim 1, wherein the melting peak temperature (Tm) is 254°C or less.

18. The laminated polyester film according to claim 1, wherein the recycled polyester resin is made from recycled PET bottles.

19. The laminated polyester film according to claim 1, wherein the recycled polyester resin is obtained by recycling polyester film.

20. The laminated polyester film according to claim 1, wherein the recycled polyester resin is a chemically recycled polyester resin.

21. The laminated polyester film according to claim 1, used as a support for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor.

22. A release film further having a release layer on the surface layer side of the laminated polyester film according to any one of claims 1 to 21.

23. A polyester film with a ceramic green sheet, wherein a ceramic green sheet is laminated onto a laminated polyester film according to any one of claims 1 to 21.

24. Use of the laminated polyester film according to any one of claims 1 to 21 as a support for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor.

25. A method for manufacturing a ceramic green sheet, comprising the step of coating the surface layer side of a laminated polyester film according to any one of claims 1 to 21 with a ceramic slurry containing a ceramic component.