Laminated polyester film and application thereof

Abstract

To provide a polyester film that contains a recycled polyester resin and has excellent surface smoothness.SOLUTION: A laminated polyester film includes a surface layer, an intermediate layer, and a rear surface layer. The intermediate layer contains a recycled polyester resin. A maximum peak height (Sp) of the surface layer is 90 nm or less.SELECTED DRAWING: Figure 1

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 also excellent in cost performance, and are therefore used in a variety of applications. For example, by utilizing the smoothness of the film surface, polyester films are suitably used in a variety of applications, such as release films for molding green sheets for multilayer ceramic capacitors, substrates for releasing interlayer insulating resins, and substrates for dry film resists.

[0003] For example, polyester film is used as a support 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. When ceramic green sheets are further thinned to 0.5 μm (thickness after drying) or less, 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 in the production of ceramic green sheets are required to have a high degree of surface smoothness.

[0004] 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.

[0005] 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.

[0006] 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]

[0007] [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]

[0008] 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 foreign matter contained in the raw materials compared to PET raw materials derived from fossil fuels (virgin PET raw materials). For this reason, it has been difficult to use recycled polyester raw materials for polyester film substrates used in the production of ceramic green sheets, which require particularly excellent surface smoothness.

[0009] Therefore, in order to solve the problems of the conventional technology, the present inventors have conducted research with the aim of providing a polyester film that contains recycled polyester resin and has excellent surface smoothness. [Means for solving the problem]

[0010] Examples of specific embodiments of the present invention are given below.

[0011] [1] A laminated polyester film having a surface layer, an intermediate layer, and a back layer, The middle layer contains recycled polyester resin, A laminated polyester film having a maximum peak height (Sp) of 90 nm or less on the surface layer. [2] The laminated polyester film according to [1], wherein the value (Sp / Sa) obtained by dividing the maximum peak height (Sp) of the surface layer by the arithmetic mean height (Sa) of the surface layer is 83 or less. [3] The laminated polyester film according to [1] or [2], wherein the arithmetic mean height (Sa) of the surface layer is 0.9 to 15 nm. [4] The laminated polyester film according to any one of [1] to [3], wherein the thickness of the surface layer exceeds 2 μm. [5] The laminated polyester film according to any one of [1] to [4], further comprising a coating layer on the surface layer. [6] The laminated polyester film according to [5], wherein the total thickness of the surface layer and the coating layer is more than 2 μm. [7] The laminated polyester film according to any one of [1] to [6], wherein the maximum peak height (Sp) of the back surface layer is 10 to 700 nm. [8] The laminated polyester film according to any one of [1] to [7], wherein the back surface layer has an arithmetic mean height (Sa) of 1 to 35 nm. [9] The laminated polyester film according to any one of [1] to [8], wherein the surface layer has an elastic deformation work of 51% or more.

[10] The laminated polyester film according to any one of [1] to [9], which has an air leakage index of 6,800 seconds or less.

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

[10] , which has a temperature-rising recrystallization temperature (Tc) of 145° C. or lower.

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

[11] , which has a maximum chemiluminescence intensity of 7 to 50 CPS / mg.

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

[12] , wherein the intermediate layer contains particulate matter.

[14] Recycled polyester resin is made of granular material with a particle size of 1000 μm or less at 200 particles / m 2 The laminated polyester film according to any one of [1] to

[13] , which comprises the above.

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

[14] , wherein the intrinsic viscosity of the polyester resin contained in the intermediate layer is 0.64 dL / g or more.

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

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

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

[16] , wherein the back surface layer contains particles.

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

[17] , wherein the recycled polyester resin contained in the intermediate layer is recycled from PET bottles.

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

[17] , wherein the recycled polyester resin contained in the intermediate layer is a recycled polyester film.

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

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

[21] 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

[20] .

[22] A laminated 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

[20] .

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

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

[24] 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

[20] . [Effects of the Invention]

[0012] According to the present invention, a polyester film containing recycled polyester resin and having excellent surface smoothness can be obtained. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view illustrating the structure of the laminated polyester film of the present embodiment. [Figure 2] FIG. 2 is a cross-sectional view illustrating the structure of the laminated polyester film of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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."

[0015] (Laminated polyester film) The present embodiment relates to a laminated polyester film (hereinafter also referred to as the present film) having a surface layer, an intermediate layer, and a back layer, in which the intermediate layer contains recycled polyester resin and the maximum peak height (Sp) of the surface layer is 90 nm or less. In the present embodiment, a polyester film containing recycled polyester resin and having excellent surface smoothness can be obtained.

[0016] 1 , the laminated polyester film 10 of this embodiment has a surface layer 12 on one side of an intermediate layer 14 and a back surface layer 16 on the other side of the intermediate layer 14. In this embodiment, the intermediate layer 14 and the surface layer 12 are preferably laminated so as to be in direct contact with each other, but another layer may be provided between the intermediate layer 14 and the surface layer 12. Similarly, the intermediate layer 14 and the back surface layer 16 are preferably laminated so as to be in direct contact with each other, but another layer may be provided between the intermediate layer 14 and the back surface layer 16.

[0017] In this embodiment, the front and back layers may contain recycled polyester resin. However, the recycled polyester resin content is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, based on the total mass of each layer. It is even more preferable that the layers are substantially free of recycled polyester resin. In this specification, "substantially free of recycled polyester resin" means that the recycled polyester resin content is 1% by mass or less, preferably 0.1% by mass or less, based on the total mass of each layer. In this embodiment, the front and back layers, preferably substantially free of recycled polyester resin, are provided on both sides of the intermediate layer containing recycled polyester resin, so that the intermediate layer is not exposed on the surface. This prevents the recycled polyester resin contained in the intermediate layer from adhering to the surface of the surface layer, for example, when the film is wound into a roll. When the film is used as a support (substrate) for ceramic green sheets in the manufacturing process of a multilayer ceramic capacitor, the surface layer must have high surface smoothness, so it is preferable that the recycled polyester resin be contained only in the intermediate layer.

[0018] Furthermore, in this embodiment, the inclusion of recycled polyester resin in the intermediate layer also succeeds in increasing the elastic deformation power of the surface layer of the laminated polyester film. A high elastic deformation power of the surface layer means that the surface layer is easily elastically deformed. For example, when this film is used as a support (substrate) for ceramic green sheets in the manufacturing process of a multilayer ceramic capacitor, the ceramic green sheets laminated on the support may be cut using a cutting blade to peel them off. Appropriate elastic deformation of the surface layer of this film during cutting facilitates separation of the edge (cut portion) of the ceramic green sheet from the film, resulting in the formation of a favorable gap (floating) between the two. This gap (floating) can then be effectively used as a starting point for peeling the ceramic green sheets. Thus, using this film as a support (substrate) for ceramic green sheets in the manufacturing process of a multilayer ceramic capacitor improves the releasability of the ceramic green sheets.

[0019] Furthermore, in this embodiment, by incorporating a recycled polyester resin into the intermediate layer, the air leakage index of the laminated polyester film can be reduced. In this specification, a larger air leakage index value indicates that it takes longer for air to leak through the gaps between the 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 laminated polyester film with a small air leakage index can exhibit appropriate slip properties and has good handleability.

[0020] This embodiment may also relate to a roll (wound 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.

[0021] <Surface layer> This film has a surface layer. The surface layer is a layer containing polyester. When this 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. 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.

[0022] The maximum peak height (Sp) of the surface layer is preferably 90 nm or less, more preferably 80 nm or less, even more preferably 70 nm or less, even more preferably 60 nm or less, even more preferably 55 nm or less, even more preferably 50 nm or less, and particularly preferably 45 nm or less. The lower limit of the maximum peak height (Sp) 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 (Sp) of the surface layer within the above range, it is possible to effectively prevent the formation of minute protrusions on the surface of the laminated polyester film, and a laminated polyester film with excellent surface smoothness can be obtained.

[0023] The arithmetic mean height (Sa) of the surface layer is preferably 0.3 nm or more, more preferably 0.5 nm or more, and even more preferably 0.8 nm or more. The arithmetic mean height (Sa) of the surface layer may be 1.2 nm or more, 1.5 nm or more, or even 2 nm or more. The arithmetic mean height (Sa) 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 (Sa) of the surface layer to the above upper limit or less, a laminated polyester film with excellent surface smoothness can be obtained. On the other hand, the arithmetic mean height (Sa) of the surface layer is preferably the above lower limit or more, and a predetermined amount of roughness or more is preferably imparted. This provides a rough surface necessary to improve the handleability of the laminated polyester film, thereby reducing the air leakage index of the laminated polyester film. As a result, the laminated polyester film can exhibit appropriate slip properties and improve handleability. For example, a laminated polyester film with appropriate surface roughness can be easily wound into a roll.

[0024] The value (Sp / Sa) obtained by dividing the maximum peak height (Sp) of the surface layer by the arithmetic mean height (Sa) of the surface layer is preferably 83 or less, more preferably 80 or less, even more preferably 75 or less, still more preferably 70 or less, even more preferably 65 or less, still more preferably 60 or less, particularly preferably 55 or less, and most preferably 50 or less. There are no particular restrictions on the lower limit of the Sp / Sa value, but it is, for example, preferably 5 or more, more preferably 10 or more, even more preferably 15 or more, even more preferably 20 or more, and still more preferably 25 or more.

[0025] In this film, by controlling the maximum peak height (Sp) low while maintaining the arithmetic mean height (Sa) 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.

[0026] 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).

[0027]

number

[0028] 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).

[0029]

number

[0030] The root mean square height (Sq) 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 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 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 back layer is not particularly limited, but is, for example, preferably 1 nm or more, more preferably 3 nm or more.

[0031] 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 back layer by the root mean square height (SqA) 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.

[0032] 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:

[0033]

number

[0034] The 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 kurtosis (Sku) of the surface layer is not particularly limited, but is preferably, for example, 0.5 or more, more preferably 1 or more.

[0035] The kurtosis (Sku) of the back layer of the present film is preferably 18 or less, more preferably 16 or less, even more preferably 15 or less, and particularly preferably 14 or less. The lower limit of the kurtosis (Sku) of the back layer is not particularly limited, but is, for example, preferably 1 or more, more preferably 2 or more.

[0036] 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:

[0037]

number

[0038] The 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 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.

[0039] The skewness (Ssk) of the back surface layer of the present film is preferably 4 or less, more preferably 3.5 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 back surface layer is not particularly limited, but is, for example, preferably 0.5 or more, more preferably 0.8 or more.

[0040] Skewness (Ssk) is one of the surface roughness parameters (ISO 25178) and can be calculated using the following formula:

[0041]

number

[0042] 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 adjusting the content of particles in consideration of the type, composition, average particle size, particle size distribution, hardness, affinity with the polyester to be contained, etc. Also, adjusting the type and content of particles in consideration of the type of polyester to be contained, such as composition, viscosity, molecular weight, thermal properties, and the presence or absence of copolymerization components, is also useful for adjusting 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 to be 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).

[0043] In this embodiment, the elastic deformation power (η it ) is preferably 51% or more, more preferably 52% or more, and even more preferably 53% or more. The elastic deformation power (η it The upper limit of the ratio is not particularly limited, but is preferably 70% or less.

[0044] Elastic deformation power (η it) is calculated using the following formula based on physical quantities measured by nanoindentation (in accordance with ISO 14577). Specifically, a sample film (1.5 cm × 1.5 cm) was placed on a glass slide (S1112, Matsunami Glass Industry Co., Ltd.) with the back layer side of the laminated polyester film as the adhesive surface and allowed to harden. The glass slide with the sample film attached was then fixed to the sample stage of a hardness tester (dynamic ultra-micro hardness tester (DUH-211S, Shimadzu Corporation). A load-unload test was then performed on the surface (surface layer) of the sample film, and the elastic deformation power (η it ) is found. Wtotal = Wplast + Welast (N·m) (Wtotal = total deformation work (N·m), Wplast = plastic deformation work (N·m), Welast = elastic deformation work (N·m)) η it = (Welast / Wplast) x 100 (%) The following conditions can be used as measurement conditions. Indenter used: Diamond regular triangular pyramidal indenter (edge ​​angle: 115) Measurement mode: Load-unload test Test force: 20.00 mN Minimum test force: 0.20 mN Load rate: 0.1464 mN / sec Load holding time: 0 sec Unload holding time: 0 sec Measurement atmosphere: 23 ± 2°C, relative humidity 50 ± 5%

[0045] In this embodiment, the elastic deformation power (η it ) to be equal to or greater than the above lower limit, for example, 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 becomes easier to peel off the ceramic green sheet laminated on the support. More specifically, when cutting the ceramic green sheet laminated on the support with a cutting blade to peel it off, the surface layer of the present film undergoes appropriate elastic deformation, making it easier for the edge (cut portion) of the ceramic green sheet to separate from the present film, and as a result, a good gap (floating) can be formed between the two. This gap (floating) can then be effectively used as a starting point for peeling off the ceramic green sheet. Note that the elastic deformation power (η) of the surface layer it) to be equal to or less than the upper limit, the wear of the cutting blade can be suppressed. In addition, the elastic deformation power (η it ) can be controlled within the above range by appropriately setting the film-forming conditions (particularly, the longitudinal stretching temperature, the transverse stretching ratio, the heat setting temperature, the peripheral speed of the roll, the relaxation rate, etc.), the film-forming raw materials, etc.

[0046] The thickness of the surface layer is preferably greater than 2 μm, more preferably greater than 2.5 μm, even more preferably greater than 3 μm, and particularly preferably greater than 3.5 μm. The thickness of the surface layer is preferably less than 15 μm, more preferably less than 12 μm, even more preferably less than 10 μm, even more preferably less than 9 μm, even more preferably less than 8 μm, even more preferably less than 7 μm, and particularly preferably less than 6 μm. By making the thickness of the surface layer greater than or equal to the lower limit, it becomes easier to control the maximum peak height (Sp) of the film within a desired range, and the surface smoothness can be improved. Furthermore, by making the thickness of the surface greater than or equal to the lower limit, the elastic deformation power (η it ) can be easily controlled within the desired range.

[0047] In order to control the maximum peak height (Sp) of the surface layer within the 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 laminated polyester film, more preferably 8 to 32%, even more preferably 9 to 28%, still more preferably 10 to 24%, even more preferably 11 to 20%, and particularly preferably 12 to 16%.

[0048] The surface layer may or may not contain particles. When particles are blended, by adding an appropriate amount of particles of an appropriate particle size, it is possible to impart an appropriate fine uneven shape to the surface layer, and it is also possible to obtain an effect of preventing scratches on the film surface. When particles are added to the surface layer, the average particle size of the particles to be added is, for example, in accordance with the elastic deformation power (η itFrom the viewpoint of adjusting the particle size and surface smoothness to a desired range, the average particle size is 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 to be 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.

[0049] When particles are contained in the surface layer, the particle content is preferably 200 ppm or more, 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, by mass. 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.

[0050] When particles are contained in the surface layer, the elastic deformation power (η it From the viewpoint of improving the hardness, the Mohs hardness of the particles is preferably 8 or less, more preferably 1 to 7, even more preferably 2 to 7, and even more preferably 3 to 7.

[0051] 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, of which alumina, silica, calcium carbonate, and organic particles are preferred.

[0052] <Middle class> The film has an intermediate layer. The intermediate layer is a layer containing polyester. The intermediate layer functions as the thickest main layer in the film.

[0053] In this embodiment, the intermediate layer contains recycled polyester resin. The recycled polyester resin content is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on the total mass of the resin constituting the intermediate layer. The recycled polyester resin content may be 60% by mass or more, 70% by mass or more, or even 80% by mass or more. The upper limit of the recycled polyester resin content is not particularly limited and may be 100% by mass based on the total mass of the resin constituting the intermediate layer. By containing recycled polyester resin in the above range, for example, CO2 emissions can be reduced, contributing to a reduction in environmental impact. Furthermore, by containing recycled polyester resin in the intermediate layer, the influence of foreign matter derived from recycled polyester resin on the surface layer can be reduced. Furthermore, by containing recycled polyester resin in the intermediate layer, the arithmetic mean height (Sa) of the surface layer can be set to a certain numerical range, and it is also possible to impart appropriate roughness to the back layer.

[0054] The recycled polyester resin contained in the intermediate layer may be obtained by material recycling of polyester, which is a recycled raw material, or may be obtained by chemically recycling polyester, which is a recycled raw material. In particular, the recycled polyester resin contained in the intermediate layer is preferably obtained by material recycling of polyester, which is a recycled raw material. The recycled (regenerated) polyester may be, for example, polyester derived from polyester containers (e.g., PET bottles) or polyester derived from polyester films (e.g., processing films). Thus, in this embodiment, the recycled polyester resin constituting the intermediate layer may be a recycled polyester resin derived from polyester containers or a recycled polyester resin derived from polyester films. When a recycled polyester resin derived from polyester films is used, the recycled polyester film may be a polyester film used as a support (substrate) for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors.

[0055] The content of isophthalic acid units relative to 100 mol % of all dicarboxylic acid units constituting the polyester resin contained in the intermediate layer 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. When such recycled raw materials are used, the intermediate layer will contain isophthalic acid units within the above range. An isophthalic acid unit content equal to or greater than the above lower limit indicates a high content of recycled resin, such as PET bottles. On the other hand, an isophthalic acid unit content equal to or less than the above upper limit can enhance the mechanical strength of the film. Furthermore, when the present film is used as a support (substrate) for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor, the suppressed crystallinity of the present film has the advantage of reducing the generation of burrs and chips when cutting with a cutting blade to peel off the ceramic green sheet laminated on the support.

[0056] The polymer components constituting the recycled (regenerated) polyester may be derived from biomass, for example, ethylene glycol derived from biomass may be used as the diol component.

[0057] The intermediate layer preferably contains 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 recycled raw materials. In this case, the recycled polyester resin contained in the intermediate layer contains granular matter with a particle size of 1000 μm or less at a density of 200 particles / m 2 May contain more than 500 pieces / m 2 May contain more than 1000 pieces / m 2 May contain more than 1500 pieces / m 2 May contain more than 2000 pieces / m 2 May contain more than 2500 pieces / m 2 May contain more than 3000 pieces / m 2May contain more than 3500 pieces / m 2 May contain more than 4000 pieces / m 2 The recycled polyester resin contained in the intermediate layer may contain granules with a particle size of 1000 μm or less at a density of 10,000 particles / m 2 May contain less than 9000 pieces / m 2 May contain up to 8000 pieces / m 2 May contain up to 7000 pieces / m 2 May contain up to 6000 pieces / m 2 May contain less than 5500 pieces / m 2 May contain less than 5000 pieces / m 2 May contain up to 4500 pieces / m 2 The number of granular particles having a particle size of 1000 μm or less contained in the intermediate layer may also be within the above range. In this specification, the particle size of a granular particle is the average value of the longest diameter and the shortest diameter.

[0058] The recycled polyester resin contained in the middle layer is composed of granular particles with a particle size of 25 μm to 1000 μm at 200 particles / m 2 May contain more than 500 pieces / m 2 May contain more than 1000 pieces / m 2 May contain more than 1500 pieces / m 2 May contain more than 2000 pieces / m 2 May contain more than 2500 pieces / m 2 May contain more than 3000 pieces / m 2 May contain more than 3500 pieces / m 2 May contain more than 4000 pieces / m 2 The recycled polyester resin contained in the intermediate layer may contain granules with a particle size of 25 μm or more and 1000 μm or less at a density of 10,000 particles / m 2 May contain less than 9000 pieces / m 2 May contain up to 8000 pieces / m 2 May contain up to 7000 pieces / m 2 May contain up to 6000 pieces / m 2 May contain less than 5500 pieces / m 2 May contain less than 5000 pieces / m 2May contain up to 4500 pieces / m 2 It may include the following: The recycled polyester resin contained in the intermediate layer may contain 100 to 3000 particles, 300 to 2500 particles, 500 to 2300 particles, 700 to 2100 particles, 800 to 1900 particles, or 900 to 1700 particles having a particle size of 25 μm or more and less than 50 μm. The recycled polyester resin contained in the intermediate layer may contain 50 to 2500 particles, 100 to 2000 particles, 200 to 1500 particles, 250 to 1300 particles, 300 to 1100 particles, 350 to 1000 particles, or 400 to 900 particles having a particle size of 50 μm or more and less than 75 μm. The recycled polyester resin contained in the intermediate layer may contain 30 to 2000 particles, 50 to 1500 particles, 70 to 1000 particles, 100 to 800 particles, 150 to 600 particles, or 200 to 400 particles having a particle size of 75 μm or more and less than 100 μm. The recycled polyester resin contained in the intermediate layer may contain 20 to 2000 particles, 50 to 1500 particles, 70 to 1000 particles, 100 to 800 particles, or 150 to 600 particles having a particle size of 100 μm or more and less than 150 μm. The recycled polyester resin contained in the intermediate layer may contain 15 to 500 particles, 20 to 300 particles, 30 to 200 particles, 40 to 100 particles, or 50 to 80 particles having a particle size of 150 μm or more and less than 200 μm. The recycled polyester resin contained in the intermediate layer may contain 15 to 400 particles, 20 to 200 particles, 30 to 100 particles, 40 to 90 particles, or 50 to 80 particles having a particle size of 200 μm or more and less than 300 μm. The recycled polyester resin contained in the intermediate layer may contain 7 to 100, 9 to 70, 10 to 50, 12 to 30, or 14 to 20 particulate matter having a particle size of 300 μm or more and less than 500 μm.

[0059] The number of particles having each of the above particle sizes can be measured using a gel counter in the following manner. The (recycled) polyester resin contained in the intermediate layer is continuously extruded into a sheet having 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 (gel) from below the sheet. This allows the number of particles to be counted over 1 m. 2 The number of particles of each particle size present in the gel is measured. 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

[0060] The intrinsic viscosity of the polyester resin contained in the intermediate layer is preferably 0.64 dL / g or more, more preferably 0.67 dL / g or more, even more preferably 0.7 dL / g or more, and even more preferably 0.72 dL / g or more. The viscosity of the polyester resin contained in the intermediate layer is preferably 1.3 dL / g or less, more preferably 1.1 dL / g or less, even more preferably 0.9 dL / g or less, and even more preferably 0.85 dL / g or less. By setting the intrinsic viscosity at or above the lower limit, film formation is facilitated, even when a large amount of recycled raw materials is used, and it is also easy to control the elastic deformation power at a high level. On the other hand, by setting the intrinsic viscosity at or below the upper limit, it is advantageously possible to easily prevent excessive pressure buildup in the film-forming extruder and to easily reduce the thermal shrinkage of the film. The intrinsic viscosity of the polyester resin contained in the intermediate layer is a value 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 intermediate layer may also be within the above range.

[0061] The intermediate layer may further contain a metal component. The metal component may be one used as a polycondensation catalyst when producing recycled (regenerated) polyester. That is, the intermediate layer may contain a polycondensation catalyst used when producing recycled (regenerated) polyester. 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.

[0062] For example, the compounds contained in the intermediate layer may differ depending on the type of recycled raw material used. For example, since polyester containers such as PET bottles come into direct contact with food, the polycondensation catalysts used in the manufacturing process are limited, and cadmium, palladium, selenium, and other harmful metal components are generally not detected. Therefore, if cadmium, palladium, selenium, and the like are detected, it can be assumed that polyester food containers were not used as recycled raw materials.

[0063] The intermediate layer functions as the thickest main layer. 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, even more preferably 16 μm or more, and particularly preferably 18 μm or more. The thickness of the intermediate layer is 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.

[0064] The thickness of the intermediate layer is preferably 50 to 95% of the total thickness of the laminated polyester film, more preferably 55 to 93%, even more preferably 58 to 90%, still more preferably 60 to 88%, and particularly preferably 62 to 86%.

[0065] 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.

[0066] <Backing layer> The film has a back surface layer. The back surface layer is a layer containing polyester. In this embodiment, the back surface layer is a layer disposed on the side opposite to the side on which the ceramic green sheet is laminated.

[0067] In this embodiment, the maximum peak height (Sp) of the back surface layer 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, and particularly preferably 570 nm or less. The maximum peak height (Sp) of the back surface 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 (Sp) of the back surface layer to the above upper limit or less, it is possible to prevent the unevenness caused by minute protrusions on the back surface layer from being transferred to the front surface layer when the laminated polyester film is laminated or wound into a roll. On the other hand, by setting the maximum peak height (Sp) of the back surface layer to the above lower limit or more, the necessary roughness is provided on the back surface of the laminated polyester film, thereby improving the handleability of the laminated polyester film.

[0068] The arithmetic mean height (Sa) of the back surface 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 (Sa) of the back surface 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 (Sa) of the back surface layer to the upper limit or less, it is possible to prevent the unevenness of the back surface layer from being transferred to the front surface layer. On the other hand, by setting the arithmetic mean height (Sa) of the back surface layer to the lower limit or more, a rough surface is provided that is necessary to improve the handleability of the laminated polyester film, thereby improving the handleability of the laminated polyester film. For example, when the laminated polyester film is wound into a roll, the laminated polyester film can exhibit appropriate slip properties, making it easy to wind into a roll.

[0069] The value (Sp / Sa) obtained by dividing the maximum peak height (Sp) of the back layer by the arithmetic mean height (Sa) of the back layer is preferably 100 or less, more preferably 80 or less, even more preferably 50 or less, and particularly preferably 30 or less. The lower limit of the value of Sp / Sa is not particularly limited, but is preferably 5 or more, and may be 10 or more, for example.

[0070] The back surface layer preferably contains particles. The presence of particles in the back surface layer can provide easy slippage and prevent scratches during each process. Furthermore, the presence of particles in the back surface layer makes it easy to control the maximum peak height (Sp) and arithmetic mean height (Sa) within a desired range. Furthermore, the maximum peak height (Sp) and arithmetic mean height (Sa) may be controlled within a desired range by applying a surface treatment or coating to the back surface layer.

[0071] The type of particles contained in the back surface 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, organic particles, calcium carbonate, silica, aluminum oxide, etc. are preferably used. 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.

[0072] In this embodiment, it is also a preferred embodiment that the back surface layer contains both organic and inorganic particles, which makes it easy to control the arithmetic mean height (Sa) and maximum peak height (Sp) of the back surface layer within desired ranges.

[0073] 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.

[0074] The average particle size of the particles in the back surface layer is preferably 5 μm or less, more preferably 4 μm or less, and even more preferably 3 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 maximum peak height (Sp) and arithmetic mean height (Sa) within the desired range. Furthermore, by setting the average particle size within the above range, haze is kept low, making it easier to ensure transparency for the entire film.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] The thickness of the back layer is preferably 1 to 20% of the total thickness of the laminated polyester film, more preferably 2 to 15%, even more preferably 2.5 to 10%, still more preferably 3 to 8%, and particularly preferably 3 to 5%.

[0080] <Polyester> The polyester constituting each layer of the present film may be a homopolyester or a copolymer polyester. Specific examples include polyesters obtained by polycondensation of a dicarboxylic acid component and a diol component. In the present film, it is preferable to use a polyester containing more than 50 mol% of aromatic dicarboxylic acid or aliphatic dicarboxylic acid units, assuming that the dicarboxylic acid units are 100 mol%.

[0081] Examples of the dicarboxylic acid component 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.

[0082] Examples of diol components 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.

[0083] When the polyester is a homopolyester, it is preferably one obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. In this case, examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative examples of the polyester include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN), with PET being preferred. Furthermore, examples of the polyester 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.

[0084] On the other hand, when the polyester 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.

[0085] Typically, when polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, diethylene glycol is by-produced from 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 polycondensation method, etc., but is approximately 5 mol% or less of the ethylene glycol. In the present invention, 5 mol% or less of diethylene glycol is defined as by-product diethylene glycol, and by-product diethylene glycol is also included in ethylene glycol and is distinguished from a copolymerization component. 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.

[0086] In this embodiment, at least one selected from the dicarboxylic acid component and the diol component constituting the polyester may be a biomass-derived raw material. In particular, it is preferable that the diol component is a biomass-derived raw material. 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 preferably used.

[0087] <<Polycondensation catalyst>> Examples of polycondensation catalysts used in polycondensing the polyester include antimony compounds, germanium compounds, aluminum compounds, and titanium compounds. Among these, it is preferable to use at least one selected from antimony compounds and titanium compounds, and it is more preferable to use a titanium compound. By using a titanium compound as a polycondensation catalyst, it is possible to reduce the amount of polycondensation catalyst added, which makes it easier to suppress the generation of foreign matter or protrusions derived from the polycondensation catalyst.

[0088] <<Intrinsic viscosity>> The intrinsic viscosity (IV) of the polyester constituting the present film is preferably 0.5 dL / g or more, more preferably 0.55 dL / g or more, and even more preferably 0.6 dL / g or more. Using a polyester with an intrinsic viscosity (IV) of 0.5 dL / g or more as the polyester constituting the present film increases the shear stress during kneading of the polyester, facilitating high dispersion of particles in the polyester resin, and, for example, tends to make it easier to achieve the surface properties of the polyester film within the above-mentioned specified range. Furthermore, from the viewpoint of particle flowability, the upper limit of the intrinsic viscosity (IV) of the polyester is preferably 0.85 dL / g or less, more preferably 0.8 dL / g or less, even more preferably 0.75 dL / g or less, even more preferably 0.7 dL / g or less, and particularly preferably 0.67 dL / g or less.

[0089] When two or more polyesters with different intrinsic viscosities (IV) are used, the intrinsic viscosity (IV) of the polyester constituting the present film refers to the intrinsic viscosity (IV) of the mixed resin. The intrinsic viscosity can be measured in accordance with JIS K7367-1:2002 by a conventional method, for example, using an Ubbelohde viscometer at 30°C with a phenol:tetrachloroethane (1:1) solvent.

[0090] When two or more polyesters having different intrinsic viscosities (IV) are used, the term "intrinsic viscosity (IV) of polyester" refers to the intrinsic viscosity (IV) of the mixed resin.

[0091] <<Others>> In this embodiment, in order to suppress the amount of oligomer component precipitation, the polyester film may be produced using a polyester with a low oligomer component content as the raw material. Various known methods can be used to produce a polyester with a low oligomer component content, such as a method of solid-state polymerization after polyester production. Alternatively, the polyester may be obtained by esterification or transesterification, followed by melt polycondensation under reduced pressure at a higher reaction temperature. For example, it is also preferable to suppress the amount of oligomer component precipitation by forming the surface layer of the present film using a polyester raw material with a low oligomer component content.

[0092] 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 present film as needed.

[0093] <Recycled polyester> [Material: Recycled polyester] The recycled polyester resin contained in the intermediate layer may be material recycled polyester. In material recycling, collected used PET bottles and polyester films are first crushed into flakes. These flakes often contain foreign matter attached to or mixed with them, so they are preferably washed, and alkaline washing is more preferred.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] [Chemically recycled polyester] The recycled polyester resin contained in the intermediate layer may be chemically recycled polyester. Examples of methods for producing chemically recycled polyester resin include sorting, crushing, and washing collected PET bottles and polyester films to remove foreign matter, followed by depolymerization 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 into PET. Alternatively, polyethylene terephthalate can be heated in a non-aqueous organic solvent in the presence of a catalyst containing oxidized iron to produce terephthalic acid and ethylene glycol, which are then repolymerized. A distinctive feature of chemically recycled polyester resin is that foreign matter and other materials are removed during the depolymerization and repolymerization process, allowing it to be recycled into a high-quality polyester resin equivalent to virgin resin.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] <Physical properties of laminated polyester film> The air leakage index of this film is preferably 6800 seconds or less, more preferably 6750 seconds or less, and even more preferably 6700 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. The air leakage index of this film is 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 is 100 kPa, and the vacuum container is 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, is measured, and the air leakage index is calculated by multiplying the obtained number of seconds. A sample size of this film is 70 mm square. 20 sheets of film are stacked with the front and back of the film 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 larger the value of the air leakage index, the longer it takes for air to leak through the gaps between the films, meaning that the films are in closer contact with each other. Therefore, an air leakage index of not more than 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 occurring when the film is made into a roll.

[0105] The temperature-rising recrystallization temperature (Tc) of the present film is preferably 145°C or lower, more preferably 140°C or lower, even more preferably 138°C or lower, and particularly preferably 136°C or lower. The lower limit of the temperature-rising recrystallization temperature (Tc) of the present film is not particularly limited, but is preferably 110°C or higher, and may be 120°C or higher, or may be 125°C or higher. The temperature-rising recrystallization temperature (Tc) 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, and the peak top temperature of the heat generation curve of the temperature-rising recrystallization in (5) is taken as the temperature-rising recrystallization temperature (Tc). (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

[0106] Recycled polyester resins, obtained by material recycling of recycled materials such as PET bottles, are generally recycled polyester resins through processes such as crushing collected used PET bottles, cleaning to remove impurities, and high-temperature decontamination. Their recrystallization temperature (Tc) is typically around 130°C, which tends to be lower than that of fossil-fuel-derived polyester resins. The fact that the recrystallization temperature (Tc) of this film falls within the above range indicates that the intermediate layer contains recycled polyester resin. The inclusion of recycled polyester resin in the intermediate layer can contribute to reducing CO2 emissions and other environmental impacts. Furthermore, if the recrystallization temperature falls within the above range, crystallization begins at a lower temperature when the resin is molten, potentially enhancing the film's crystallinity. Another advantage of controlling the recrystallization temperature within the above range is that it facilitates adjustment of the film's shrinkage rate and elastic deformation power.

[0107] The maximum chemiluminescence intensity of this film is preferably 7 CPS / mg or more, more preferably 9 CPS / mg or more, and even more preferably 11 CPS / mg or more. The maximum chemiluminescence intensity of this film is preferably 50 CPS / mg or less, more preferably 40 CPS / mg or less, and even more preferably 30 CPS / mg or less. The maximum chemiluminescence intensity of this film is measured using a chemiluminescence analyzer (Tohoku Electronics Industry Co., Ltd. CLA-FS4). Specifically, the sample film is heated from 50°C to 200°C at a rate of 10°C / min under a nitrogen gas atmosphere, and then held at 200°C for 10 minutes. The chemiluminescence intensity from 50 to 200°C is measured every second at detection wavelengths of 400 nm to 650 nm. Measurements of the aluminum cup are also taken as background values. For data processing, only the temperature rise process (time range 0-900 s) is extracted and the emission profile intensity is analyzed. In subsequent data processing, the background value is subtracted from the measured value of each sample, but for calculations between spectra, Loess (local smoothing) processing is performed in OriginPro2023, and then the maximum chemiluminescence emission intensity is calculated by normalizing by sample mass.

[0108] The full width at half maximum (FWHM) of the chemiluminescence intensity of the present film is preferably 55°C or higher, more preferably 60°C or higher, even more preferably 65°C or higher, even more preferably 70°C or higher, and particularly preferably 73°C or higher. The full width at half maximum (FWHM) of the chemiluminescence intensity is preferably 100°C or lower, more preferably 95°C or lower, even more preferably 90°C or lower, and even more preferably 88°C or lower. The full width at half maximum (FWHM) of the chemiluminescence intensity can be calculated by plotting the temperature increase process from 50°C to 200°C when the present film is heated from 50°C at a rate of 10°C / min in a nitrogen gas atmosphere and held at 200°C for 10 minutes.

[0109] The degree of oxidative degradation of polyester can be evaluated by measuring the amount of light emitted, which is the energy emitted when these excited carbonyls and singlet oxygen return from their excited state to their ground state. In other words, the degree of oxidative degradation of polyester can be determined by measuring the amount of ROOH produced. Therefore, when the maximum luminescence intensity or the full width at half maximum of the chemiluminescence intensity is within the above range, it indicates a large degree of oxidative degradation and means that the intermediate layer uses recycled polyester resin. By containing recycled polyester resin in the intermediate layer, for example, it is possible to reduce CO2 emissions and contribute to reducing the burden on the environment.

[0110] The manufacturing process of multilayer ceramic capacitors includes heat treatments, such as drying a release agent coated on a polyester film and drying a ceramic slurry coated on a release film. Therefore, a decrease in the heat distortion resistance of polyester films can lead to coating irregularities and wrinkles. In other words, the heat distortion resistance of polyester films is an important characteristic for ensuring the quality and reliability of the finished product, from intermediate products to finished products in the manufacturing process of multilayer ceramic capacitors, such as the lamination characteristics of ceramic green sheets. To prevent such coating irregularities and wrinkles, the shrinkage rate of the present film in the machine direction (MD) after heat treatment 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 2% or less. From the same perspective, the lower limit of the shrinkage rate in the machine direction (MD) (150°C, 5 minutes) is preferably −0.5% or more, more preferably −0.3% or more.

[0111] Furthermore, the shrinkage rate in the transverse direction (TD) of the present film 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, still 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 shrinkage rate 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 shrinkage rate in the transverse direction (TD) (150°C, 5 minutes) is preferably 1.4% or less, more preferably 1.3% or less. Furthermore, the 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% or less, 0.8% or less, 0.7% or less, 0.5% or less, 0.4% or less, 0.1% or less, etc.

[0112] In addition, the elastic deformation power of this film (η it In order to achieve both the desired stretching temperature and shrinkage rate (heating at 150°C for 5 minutes), 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.), the film-forming raw materials, etc.

[0113] The total thickness of the present film is not particularly limited as long as it is within a range that allows film formation, but from the viewpoints of mechanical strength, handleability, productivity, etc., it is preferably 10 μm or more, more preferably 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, or 28 μm or less.

[0114] <Coating layer> In this embodiment, a coating layer may be further provided on the surface layer. For example, as shown in FIG. 2, the laminated polyester film 10 of this embodiment may further have a coating layer 18 provided on the surface layer 12. In this embodiment, the coating layer 18 is preferably a layer formed by applying a coating layer-forming composition (coating liquid) onto the surface layer 12. The coating layer 18 can be formed by in-line coating or offline coating, but is preferably formed by in-line coating. This can improve the production efficiency of the laminated polyester film 10.

[0115] 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.

[0116] When a coating layer is further provided on the surface layer, the total thickness of the surface layer and coating layer is preferably greater than 2 μm, more preferably greater than 2.5 μm, even more preferably greater than 3 μm, and particularly preferably greater than 3.5 μm. Furthermore, the total thickness of the surface layer and coating layer is preferably less than 15.5 μm, more preferably less than 12.5 μm, even more preferably less than 10.5 μm, even more preferably less than 9.5 μm, even more preferably less than 8.5 μm, even more preferably less than 7.5 μm, and particularly preferably less than 6.5 μm. By making the total thickness of the surface layer and coating layer greater than or equal to the above lower limit, it becomes easier to control the maximum peak height (Sp) of the film within the desired range, thereby improving surface smoothness. Furthermore, by making the total thickness of the surface layer and coating layer greater than or equal to the above lower limit, the elastic deformation power (η it ) can be easily controlled within the desired range.

[0117] 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.

[0118] <<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.

[0119] Examples of polyester resins, polyurethane resins, (meth)acrylic resins, and polyvinyl resins used as binder resins include compounds described in WO 2023 / 145952.

[0120] 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.

[0121] <<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.

[0122] Examples of the melamine compound and isocyanate compound used as the crosslinking agent include the compounds described in WO 2023 / 145952.

[0123] 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.

[0124] <<Particle>> The coating layer-forming composition preferably contains particles. Examples of the 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.

[0125] 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.

[0126] 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.

[0127] 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 (ηit ) can be easily controlled within the desired range.

[0128] <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.

[0129] In particular, as described above, the present film has excellent surface smoothness, allowing for the thinning of ceramic green sheets, and is therefore preferably used as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors. That is, the laminated polyester film of this embodiment is preferably a laminated polyester film for manufacturing multilayer ceramic capacitors. The laminated polyester film of this embodiment contains recycled polyester resin, but has a maximum peak height (Sp) of 90 nm or less in the surface layer, thereby suppressing the formation of minute protrusions on the surface of the laminated polyester film, which serves as a support for ceramic green sheets. This prevents defects such as pinholes from occurring in ceramic green sheets, even when manufacturing thin ceramic green sheets. Furthermore, surface defects such as pinholes in ceramic green sheets are problematic because they significantly affect quality and reliability in terms of short circuits, capacitance variations, and so on.

[0130] 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.

[0131] (Method of manufacturing laminated polyester film) This embodiment may relate to a method for producing the laminated polyester film described above. The method for producing a laminated polyester film of this embodiment includes a step of laminating a polyester layer A constituting a surface layer, a polyester layer B constituting an intermediate layer containing recycled polyester resin, and a polyester layer C constituting a back layer. Alternatively, the method for producing a laminated polyester film of this embodiment includes a step of supplying polyester resin A constituting the surface layer, polyester resin B constituting the intermediate layer containing recycled polyester resin, and polyester resin C constituting 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 laminated polyester film.

[0132] In this embodiment, a step of stretching an unstretched laminated polyester film may be provided. In the stretching step, the unstretched laminated 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 used.

[0133] 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 laminated 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 laminated 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.

[0134] In this embodiment, a step of forming a coating layer on the surface layer may be provided. In the step of forming a coating layer, a coating layer-forming composition (coating liquid) is applied onto the surface layer to form the coating layer.

[0135] When forming a coating layer by applying a coating layer-forming composition (coating liquid) onto a surface layer, the coating layer-forming composition (coating liquid) is applied onto the surface layer, and if necessary, the applied resin composition is subjected to treatments such as drying, curing, heat treatment, etc. In this embodiment, at least heat treatment is preferably performed.

[0136] The composition for forming a coating layer is not particularly limited. The method for applying the composition for forming a coating layer is not particularly limited, and any conventionally known coating method can be used, such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, or curtain coating.

[0137] The coating layer can be formed by in-line coating or offline coating. The method for heat-treating the applied coating layer-forming composition is not particularly limited, and when forming the coating layer by offline coating, the heat treatment is typically carried out at 80 to 200°C for 3 to 40 seconds, preferably at 100 to 180°C for 3 to 40 seconds. On the other hand, when forming the coating layer by in-line coating, the heat treatment is typically carried out at 70 to 280°C for 3 to 200 seconds. The heat treatment may be carried out in two or more steps at different temperatures within the above temperature range. At least a part of the heat treatment may be carried out by heating during stretching. Furthermore, drying and curing may be carried out simultaneously by heating in the heat treatment.

[0138] The coating layer is preferably formed by in-line coating, which treats the film surface during the polyester film production process. In-line coating is a method of coating within the polyester film production process, specifically, a method of coating at any stage from melt extrusion of polyester to stretching, heat setting, and winding up. Typically, the coating is applied to any of the following: an unstretched sheet obtained by melting and quenching, a stretched uniaxially stretched film, a biaxially stretched film before heat setting, or a film after heat setting and before winding up.

[0139] For example, when sequential biaxial stretching is performed, a method in which a composition for forming a coating layer is coated onto a uniaxially stretched film stretched in the longitudinal direction (machine direction), and then stretched in the transverse direction is advantageous. This method allows film formation and coating layer formation to be carried out simultaneously, which is advantageous in terms of production costs. In addition, since stretching is carried out after coating, the thickness of the coating layer can be changed by adjusting the stretching ratio, and thin film coating can be carried out more easily than with offline coating films.

[0140] (Release film) This embodiment may also relate to a release film further comprising a release layer on the surface layer side of the laminated polyester film described above. That is, the release film has a structure of release layer / surface layer / intermediate layer / back surface layer. When the present film has a coating layer, it may have a structure of release layer / coating layer / surface layer / intermediate layer / back surface layer. The release layer is laminated to the laminated 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, and the like. 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.

[0141] 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.

[0142] 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.

[0143] 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 be used in combination.

[0144] Examples of non-silicone release agents include waxes, compounds containing long-chain alkyl groups, and fluorine compounds.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] The release layer is provided by coating the present film with a release agent composition. Either in-line coating, which is carried out during the film production process, or so-called off-line coating, in which the release agent composition is applied outside the system onto a film that has already been produced, may be employed.

[0151] 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.

[0152] 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.

[0153] 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 / m2 , 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.

[0154] (Laminated polyester fill with ceramic green sheet) This embodiment may relate to a laminated polyester film with a ceramic green sheet, in which a ceramic green sheet is laminated on the laminated polyester film described above, or may relate 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 laminated polyester film of this embodiment is suitable for manufacturing thin ceramic green sheets, for example, the thickness of the ceramic green sheet after drying may be 2 μm or less, 1 μm or less, or 0.5 μm or less.

[0155] This embodiment may relate to the use of the laminated polyester film as a support for a ceramic green sheet in the process of 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 laminated polyester film.

[0156] When manufacturing the laminated polyester film with ceramic green sheet of this embodiment, a ceramic slurry containing ceramic components and a binder resin can be applied to the surface layer or coating layer of the above-mentioned laminated polyester film, or to the release layer of the above-mentioned release film, and then dried to produce a ceramic green sheet (dielectric sheet). [Example]

[0157] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0158] [Polyester raw materials] The polyester raw materials used in the examples and comparative examples are shown in Table 1.

[0159] [Table 1]

[0160] The polyesters in polyester raw materials A to E listed in Table 1 are all homopolyethylene terephthalate. Polyester raw material F is a recycled raw material derived from PET bottles, and is a polyester raw material "UK-31" manufactured by Utsumi Recycle Systems Co., Ltd. (intrinsic viscosity 0.711 dl / g, content of isophthalic acid units relative to 100 mol% of all carboxylic acid units is 1.4 mol%, and content of diethylene glycol units relative to 100 mol% of all glycol units is 2.29 mol%).

[0161] (Comparative Example 1) The surface layer was made from a blend of 87% polyester A and 13% polyester B by mass, the middle layer was made from 100% polyester C, and the back layer was made from a blend of 28% polyester C, 50% polyester D, and 22% polyester E by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. The surface and back layer materials were then co-extruded into a three-layer structure (surface layer A / middle layer / back layer C) with the outermost layers being the materials for the surface layer and back layer. The thickness ratio of the extrusion conditions was A / B / C = 2 / 27 / 2. The mixture was cooled and solidified on a cooling roll with a surface temperature set at 20°C using an electrostatic adhesion method to obtain an amorphous film. Next, the film was stretched 3.5 times in the longitudinal direction, i.e., in the MD direction, at a film temperature of 86°C using the difference in roll peripheral speed. Then, this longitudinally stretched film was introduced into a tenter and stretched 4.5 times in the transverse direction, i.e., in the TD direction, at 105°C. Heat treatment was performed at 170°C, 230°C, and 230°C in heat treatment (fixing) zones 1, 2, and 3 within the tenter, respectively, and a cooling treatment was performed at 140°C with a relaxation rate of 2%, resulting in a laminated polyester film with an overall thickness of 31 μm.

[0162] (Comparative Example 2) A laminated polyester film having a total thickness of 31 μm was produced in the same manner as in Comparative Example 1, except that the raw material for the intermediate layer was changed to a raw material obtained by blending 50% polyester C and 50% polyester F by mass.

[0163] Example 1 A laminated polyester film having a total thickness of 31 μm was produced in the same manner as in Comparative Example 2, except that the thickness composition ratio in Comparative Example 2 was A / B / C=4 / 25 / 2.

[0164] Example 2 A laminated polyester film having a total thickness of 31 μm was produced in the same manner as in Comparative Example 2, except that the thickness composition ratio of A / B / C was 8 / 21 / 2.

[0165] Example 3 The surface layer was made from a blend of 87% polyester A and 13% polyester B by mass. The middle layer was made from a blend of 50% polyester C and 50% polyester F by mass. The back layer was made from a blend of 28% polyester C, 50% polyester D, and 22% polyester E by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. The materials for the surface and back layers were then co-extruded to form a three-type, three-layer structure (surface layer A / middle layer / back layer C), with the outermost layers being the materials for the surface and back layers. The thickness ratio of the co-extrusion was A / B / C = 2 / 27 / 2. The film was cooled and solidified on a cooling roll set at 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 to produce a uniaxially stretched film. A coating solution having the following composition was applied to one side of this uniaxially stretched film so that the coating thickness (after drying and stretching) would be 100 nm to form a coating layer. The longitudinally stretched film with the coating layer was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C, followed by heat treatments at 170°C, 230°C, and 230°C in heat treatment (fixing) zones 1, 2, and 3 within the tenter, respectively, followed by cooling to 140°C at a relaxation rate of 2%, to obtain a laminated polyester film with an overall thickness of 31.1 μm.

[0166] [Coating layer forming composition (coating liquid)] Polyester resin water dispersion 30% by mass Monomer composition: (acid component) terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / / (diol component) ethylene glycol / 1,4-butanediol / diethylene glycol = 56 / 40 / 4 / / 70 / 20 / 10 (mol%) Melamine compound: hexamethoxymethylol melamine 70% by mass Lubricant: 0.3% by mass of silica particles with an average particle size of 0.07 μm Catalyst: 2-amino-2-methylpropanol hydrochloride 0.5% by mass

[0167] Example 4 A laminated polyester film having a total thickness of 31.24 μm was obtained in the same manner as in Example 3, except that the thickness of the coating layer was changed to 240 nm.

[0168] <Measurement and evaluation methods> (1) Maximum peak height (Sp) · Arithmetic mean height (Sa) The surface roughness of the front and back layers of the sample film (5 cm x 5 cm) was 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 the 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 calculated after the following processing. Measurements were taken at at least 12 points, and the average was used as the measured value. FilterType:Spline Filter: High Pass Type:Robust Gaussian Spline Fixed Cutoffs Mode: Period Long Period: 200 μm

[0169] (2) Intrinsic viscosity 1 g of polyester was precisely weighed and dissolved in 100 mL of a 50 / 50 (mass ratio) phenol / tetrachloroethane mixed solvent, and the viscosity (IV) was measured at 30°C using a VMS-022UPC·F10 viscosity (IV) measuring device (manufactured by Rigo Co., Ltd.).

[0170] (3) Content of terephthalic acid and isophthalic acid components 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.

[0171] (4) Number and average particle size of granules The raw material F used for the middle layer was continuously extruded into a sheet with a width of 10 cm and a thickness of 50 μm. Light was applied from above the sheet to an area of ​​approximately 6 cm in the center of the width direction, and a CCD camera was used from below the sheet to photograph the shadows caused by the granular material (gel). 2 The number of particles 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 (extruder), and CR-7 Chill Roll Unit (chill roll unit)" manufactured by Optical Control Systems. The measurement conditions were as follows: Cooling roll temperature: 30℃ Extruder cylinder temperature: 295℃ Extruder screw speed: 100 rpm Sheet thickness: 50μm

[0172] (5) 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. The laminated polyester film sample size was 70 mm square. Twenty sheets were stacked with the front and back of the film overlapping 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.

[0173] (6) Elastic deformation power Approximately 2 to 8 mg of Aron Alpha (registered trademark) (general-purpose, manufactured by Toa Gosei Chemical Industry Co., Ltd.) was dropped onto a glass slide (S1112, manufactured by Matsunami Glass Industry Co., Ltd.). A sample film (1.5 cm x 1.5 cm) was placed on top of the drop with the back layer side of the laminated polyester film as the adhesive surface and allowed to harden. The slide with the sample film attached was then fixed to the sample stage of a hardness tester (Dynamic Ultra-Micro Hardness Tester (DUH-211S, manufactured by Shimadzu Corporation) and a load-unload test was performed on the surface (surface layer) of the sample film. The elastic deformation power (η it ) was calculated (the average of five measurements, excluding the first one, was taken from n=6). Wtotal = Wplast + Welast (N·m) (Wtotal = total deformation work (N·m), Wplast = plastic deformation work (N·m), Welast = elastic deformation work (N·m)) η it= (Welast / Wplast) x 100 (%) (measurement conditions) Indenter used: Diamond regular triangular pyramidal indenter (edge ​​angle: 115) Measurement mode: Load-unload test Test force: 20.00 mN Minimum test force: 0.20 mN Load rate: 0.1464 mN / sec Load holding time: 0 sec Unload holding time: 0 sec Measurement atmosphere: 23 ± 2°C, relative humidity 50 ± 5% Number of measurements: 6

[0174] (7) Temperature-raised recrystallization temperature (Tc) 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 peak top temperature of the exothermic peak curve of the temperature-programmed recrystallization in (5) was taken as the temperature-programmed recrystallization temperature (Tc).

[0175] (8) Maximum chemiluminescence intensity Six laminated polyester films (approximately 50 mg each) were stacked in a 20 mm diameter aluminum cup using a chemiluminescence analyzer (Tohoku Electronics Industry Co., Ltd. CLA-FS4). The temperature was raised from 50°C to 200°C at a rate of 10°C / min under a nitrogen atmosphere, and the chemiluminescence intensity was measured every second at detection wavelengths of 400 nm to 650 nm while the temperature was held at 200°C for 10 minutes. The aluminum cup measurements were also used as background values. For data processing, only the temperature rise period was extracted (time range 0–900 s) and the intensity of the emission profile was analyzed. Subsequent data processing involved subtracting the background value from the measured values ​​for each sample. For spectral calculations, the maximum chemiluminescence intensity was calculated by performing Loess (local smoothing) processing in OriginPro 2023 and normalizing by sample mass.

[0176] (9) 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 shrinkage ratio was calculated using the following formula. The shrinkage ratios were measured in both the machine direction (MD) and the transverse direction (TD) of the film. The MD shrinkage ratio was measured so that the machine direction was the MD, and the TD shrinkage ratio was measured so that the machine direction was the TD. Shrinkage rate (%) = {(length of evaluation film before heat treatment) - (length of evaluation film after heat treatment)} / (length of evaluation film before heat treatment) × 100

[0177] [Table 2]

[0178] In the examples, laminated polyester films containing recycled polyester resins 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 laminated polyester film had good handleability. Furthermore, in the examples, the elastic deformation power value was large, indicating good peelability of the ceramic sheet.

[0179] On the other hand, in Comparative Example 1, since the intermediate layer did not contain recycled polyester resin, the air leakage index tended to be high and handling was poor. Furthermore, in Comparative Example 1, the value of the elastic deformation power was low, raising concerns about poor peeling of the ceramic sheet. In Comparative Example 2, large protrusions were formed on the surface layer, which is undesirable because such large protrusions directly lead to pinholes in the ceramic sheet. [Industrial Applicability]

[0180] The laminated polyester film of the present invention is a polyester film containing recycled polyester resin and having excellent surface smoothness. Therefore, it contributes to reducing the burden on the environment and is useful as a support (substrate) for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors. 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 laminated 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]

[0181] 10. Laminated polyester film 12 Surface layer 14 Middle Class 16 Back layer 18 Coating layer

Claims

1. A laminated polyester film having a surface layer, an intermediate layer, and a back layer, the intermediate layer contains recycled polyester resin, A laminated polyester film, wherein the maximum peak height (Sp) of the surface layer is 90 nm or less.

2. 2. The laminated polyester film according to claim 1, wherein a value (Sp / Sa) obtained by dividing the maximum peak height (Sp) of the surface layer by the arithmetic mean height (Sa) of the surface layer is 83 or less.

3. 2. The laminated polyester film according to claim 1, wherein the surface layer has an arithmetic mean height (Sa) of 0.9 to 15 nm.

4. 2. The laminated polyester film according to claim 1, wherein the thickness of the surface layer is greater than 2 μm.

5. The laminated polyester film according to claim 1 , further comprising a coating layer on the surface layer.

6. The laminated polyester film according to claim 5 , wherein the total thickness of the surface layer and the coating layer is more than 2 μm.

7. 2. The laminated polyester film according to claim 1, wherein the back surface layer has a maximum peak height (Sp) of 10 to 700 nm.

8. The laminated polyester film according to claim 1, wherein the back surface layer has an arithmetic mean height (Sa) of 1 to 35 nm.

9. 2. The laminated polyester film according to claim 1, wherein the surface layer has an elastic deformation work of 51% or more.

10. 2. The laminated polyester film according to claim 1, which has an air leakage index of 6,800 seconds or less.

11. 2. The laminated polyester film according to claim 1, which has a temperature-raised recrystallization temperature (Tc) of 145°C or lower.

12. 2. The laminated polyester film according to claim 1, wherein the maximum chemiluminescence intensity is 7 to 50 CPS / mg.

13. The laminated polyester film of claim 1 , wherein the intermediate layer comprises particulate matter.

14. The recycled polyester resin contains 200 particles per m of particles having a particle diameter of 1000 μm or less. ２ The laminated polyester film according to claim 1, comprising:

15. 2. The laminated polyester film according to claim 1, wherein the intrinsic viscosity of the polyester resin contained in the intermediate layer is 0.64 dL / g or more.

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

17. The laminated polyester film according to claim 1 , wherein the backing layer contains particles.

18. 2. The laminated polyester film according to claim 1, wherein the recycled polyester resin contained in the intermediate layer is recycled from PET bottles.

19. 2. The laminated polyester film according to claim 1, wherein the recycled polyester resin contained in the intermediate layer is a recycled polyester film.

20. 2. The laminated polyester film according to claim 1, which is used as a support for a ceramic green sheet in the production process of a multilayer ceramic capacitor.

21. A release film, further comprising a release layer on the surface layer side of the laminated polyester film according to any one of claims 1 to 20.

22. A laminated polyester film with a ceramic green sheet, comprising the laminated polyester film according to any one of claims 1 to 20 and a ceramic green sheet laminated thereon.

23. Use of the laminated polyester film according to any one of claims 1 to 20 as a support for a ceramic green sheet in the process of producing a multilayer ceramic capacitor.

24. A method for producing a ceramic green sheet, comprising a step of applying a ceramic slurry containing a ceramic component to the surface layer side of the laminated polyester film according to any one of claims 1 to 20.

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