Polyester film

Abstract

To provide a polyester film that can improve releasability in a process of peeling a ceramic green sheet from a release film, and can further prevent formation of surface defects such as pinholes.SOLUTION: The present invention provides a polyester film that contains particles, has an elastic deformation work ratio on one surface of more than 55%, and satisfies the following (1) and (2): (1) an arithmetic mean height (Sa) of 15 nm or less and (2) a maximum peak height (Sp) of 150 nm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyester film, and more particularly to a polyester film used, for example, as a support for a ceramic green sheet in the process of producing a multilayer ceramic capacitor. [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 also have excellent cost performance, so they are used in a variety of applications. For example, by taking advantage of the smoothness of the film surface, they are used as substrates for interlayer insulating resin release films, substrates for dry film resists, and release films for forming ceramic green sheets for multi-layered ceramic capacitors (MLCCs).

[0003] The manufacturing process for multilayer ceramic capacitors begins by coating and drying a release agent on a polyester film to create a release film with a release layer. Then, a ceramic slurry containing ceramic components such as barium titanate and a binder resin is coated and dried on the release film. After that, electrodes are printed and dried using a method such as screen printing to create a ceramic green sheet with printed electrodes. The resulting ceramic green sheet is then cut to a predetermined shape and peeled from the release film. A large number of the peeled ceramic green sheets are stacked and integrated, then cut into individual chips. The internal electrodes and dielectric layers are sintered in a firing furnace to produce a multilayer ceramic capacitor.

[0004] In order to miniaturize and increase the capacity of multilayer ceramic capacitors, ceramic green sheets are becoming thinner. As ceramic green sheets become thinner, there is a concern that minute protrusions on the surface of a release film may cause pinholes or the like in the ceramic green sheets. In addition, there is a concern that the possibility of peeling defects such as breakage may increase during the process of peeling the ceramic green sheets from the release film.

[0005] Patent Document 1 discloses a release film for use in the ceramic green sheet manufacturing process, which has a release agent layer provided on one side of a polyester substrate, and in which a filler such as hydroxyapatite is blended with the release agent layer side of the substrate, and the release film has an elastic deformation power of 45% or more in a load-displacement curve measured when a load of 20 mN is applied using a micro-surface hardness tester, and a two-dimensional arithmetic mean roughness (Ra) of 1 nm or more and 20 nm or less on the surface of the release agent layer opposite the substrate, and a two-dimensional maximum protrusion height (Rp) of 10 nm or more and 200 nm or less. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-144248 Summary of the Invention [Problem to be solved by the invention]

[0007] As ceramic green sheets become thinner in the future, it is expected that there will be greater concerns about the occurrence of surface defects such as pinholes, and that there will also be greater concerns about peeling defects such as breakage in the process of peeling the ceramic green sheet from the release film. Therefore, there is a need to improve the releasability of the release film and to suppress the occurrence of surface defects. However, as a result of extensive investigations by the present inventors, it has become clear that, while it is conceivable to incorporate a specific filler (particles) into the release film, for example, in order to make it easier to peel the ceramic green sheet from the release film, improving the peelability in this manner tends to result in surface defects such as pinholes caused by the filler (particles), and therefore it is difficult to achieve both at a high level. [Means for solving the problem]

[0008] The present invention has been made in consideration of the above circumstances, and provides a polyester film that can improve the releasability in the process of peeling a ceramic green sheet from a release film and further can suppress the occurrence of surface defects such as pinholes.

[0009] In view of the above circumstances, the present inventors have conducted extensive research and found that the above-mentioned problems can be solved by using a specific polyester film. That is, when particles are incorporated, the present inventors have found that the above-mentioned problems can be solved by using a specific polyester film obtained by adjusting various conditions such as the particle composition, average particle size, particle size distribution, hardness, and affinity with polyester, the type of polyester, and film-forming conditions.

[0010] That is, the present invention provides the following. [1] A polyester film having an elastic deformation power of more than 55% on one surface and satisfying the following (1) and (2): (1) The arithmetic mean height (Sa) is 15 nm or less. (2) The maximum peak height (Sp) is 150 nm or less. [2] The polyester film according to [1], which has a shrinkage rate of 2.8% or less in the longitudinal and transverse directions after heat treatment at 150°C for 5 minutes. [3] The polyester film according to [1] or [2], which has a shrinkage rate in the transverse direction of 1.5% or less after heat treatment at 150°C for 5 minutes. [4] The polyester film according to any one of [1] to [3], which contains particles, and the content of the particles in the layer in which the particles are contained is 250 ppm or more and 10,000 ppm or less by mass ratio. [5] The polyester film according to any one of [1] to [4], which contains particles, the average particle size of which is 1 μm or less. [6] The polyester film according to any one of [1] to [5], which contains particles, and the particles have a Mohs hardness of 9 or less. [7] The polyester film according to any one of [1] to [6], comprising particles, the particles including at least particles (a1) and particles (a2), the particles (a1) being alumina particles, and the particles (a2) being particles other than the particles (a1). [8] The polyester film according to any one of [1] to [7], wherein the layer forming one surface contains particles, the particles including at least particles (a1) and particles (a2), and the zeta potentials of the particles (a1) and (a2) at pH 7 are either positive for the particles (a1) and negative for the particles (a2), or negative for the particles (a1) and positive for the particles (a2). [9] [8] The polyester film according to [8], wherein the content of the particles having a positive zeta potential at pH 7 is 50 ppm or more and 5000 ppm or less by mass relative to the layer forming the one surface.

[10] The polyester film according to [8] or [9], wherein the content of the particles having a negative zeta potential at pH 7 is 100 ppm or more and 8000 ppm or less by mass relative to the layer forming the one surface.

[11] The polyester film according to any one of [8] to

[10] , wherein the particles having a positive zeta potential at pH 7 are alumina particles.

[12] The polyester film according to any one of [8] to

[11] , wherein the particles having a negative zeta potential at pH 7 are silica or organic particles.

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

[12] , wherein the layer forming the one surface contains particles, and the ratio of the content of particles having a Mohs hardness of 8 or less to the content of all particles contained in the layer forming the one surface (content of particles having a Mohs hardness of 8 or less / content of all particles) is, in mass ratio, from 0.6 to 0.95.

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

[13] , wherein the layer forming the one surface contains particles, the particles mainly containing particles having a Mohs hardness of 8 or less, and the content of the particles having a Mohs hardness of 8 or less in the layer forming the one surface is less than 1800 ppm by mass.

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

[14] , wherein the maximum peak height (Sp) of the above (2) is 100 nm or less.

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

[15] , which has a planar orientation degree (ΔP) of 165 or more.

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

[16] , wherein the ratio of the arithmetic mean height (Sa) of one surface to the arithmetic mean height (Sa) of the other surface (arithmetic mean height (Sa) of the other surface / arithmetic mean height (Sa) of the one surface) is 2 or more and 18 or less (provided that the arithmetic mean height (Sa) of the other surface>arithmetic mean height (Sa) of the one surface).

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

[17] , which consists of at least two layers.

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

[18] , which consists of three layers.

[20] The polyester film according to

[18] or

[19] , which contains particles, and the content of the particles in one surface layer is 250 ppm or more and 2800 ppm or less by mass. [twenty one]

[20] The polyester film according to

[20] , which contains particles, and the content of the particles in the other surface layer is 2000 ppm or more and 8000 ppm or less by mass ratio. [twenty two] The polyester film according to any one of [1] to

[21] , wherein the polyester film comprises a surface layer forming the one surface, an intermediate layer, and a surface layer forming the other surface, in this order, and the thickness of the intermediate layer is greater than the thickness of each of the surface layers. [twenty three] The polyester film according to any one of [1] to

[22] , wherein the polyester film comprises a surface layer forming the one surface, an intermediate layer, and a surface layer forming the other surface, in this order, and the thickness ratio of the layers (thickness of the surface layer:thickness of the intermediate layer:thickness of the surface layer) is 1-10:10-35:1-5. [twenty four] The polyester film according to any one of [1] to

[23] , which is used as a support for a ceramic green sheet in a process for producing a multilayer ceramic capacitor. [twenty five] The polyester film according to any one of [1] to

[24] , which is used as a support for a ceramic green sheet in a process for producing a multilayer ceramic capacitor for an automobile.

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

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

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

[25] as a support for a ceramic green sheet in the process of producing a multilayer ceramic capacitor for an automobile.

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

[25] . [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a polyester film that can improve the releasability in the step of peeling a ceramic green sheet from a release film and can suppress the occurrence of surface defects such as pinholes. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in more detail below based on embodiments of the present invention, but the present invention is not limited to these embodiments. In this specification, when the expression "X to Y" (X and Y are any numbers) is used, unless otherwise specified, it includes the meaning of "X or more and Y or less," as well as "preferably larger than X" or "preferably smaller than Y." Furthermore, for numerical ranges described in stages in this specification, the upper limit or lower limit of a numerical range in one stage can be arbitrarily combined with the upper limit or lower limit of a numerical range in another stage. Furthermore, in this specification, "X and / or Y (X and Y are any configurations)" means at least one of X and Y, and means three possibilities: X only, Y only, and X and Y. Furthermore, in this specification, the term "film" includes the term "sheet", and the term "sheet" includes the term "film". In addition, in this specification, the term "main component" generally refers to 50% by mass or more of the entire target material, preferably 60% by mass or more, more preferably 70% by mass or more, and may be 80% by mass or more or 90 to 100% by mass.

[0013] As will be described in detail below, a polyester film according to one embodiment of the present invention (hereinafter sometimes referred to as "the film") is a polyester film having an elastic deformation power of more than 55% on one surface and satisfying the following (1) and (2): (1) The arithmetic mean height (Sa) is 15 nm or less. (2) The maximum peak height (Sp) is 150 nm or less.

[0014] The present inventors conducted research and development into a support for ceramic green sheets that can accommodate further thinning of ceramic green sheets (for example, a thickness of 0.5 μm or less after drying) in line with the trend toward smaller size and higher capacity multilayer ceramic capacitors, focusing on the prevention of peeling defects during the peeling process of the ceramic green sheets. In the course of such research, the inventors have found that, for example, when particles are added to a polyester film, the occurrence of peeling defects can be suppressed by controlling the properties of the particles added to the polyester film, but on the other hand, it has been found that this tends to cause surface defects such as pinholes, which have a significant impact on quality and reliability in terms of, for example, short-circuit defects and variations in capacitance.

[0015] The present inventors have conducted further research with a view to solving both of the problems related to the poor release and the surface defects. As a result, they have found that, for example, when particles are blended, a specific polyester film obtained by adjusting the particle composition, average particle size, particle size distribution, hardness, affinity with polyester, type of polyester, and film-forming conditions can improve the releasability in the step of peeling the ceramic green sheet from the release film, thereby suppressing the occurrence of poor release and surface defects such as pinholes.

[0016] The present film newly proposed by the inventors has a specific elastic deformation power (η it ) and specific surface smoothness, and for example, it has high recovery force against deformation that occurs when cutting the ceramic green sheet, resulting in excellent peelability of the ceramic green sheet, and can effectively suppress the occurrence of surface defects such as pinholes, making it extremely excellent in that it can provide a release film, etc. that can guarantee high quality reliability. An embodiment of the film will be described in detail below.

[0017] <<This film>> The present film is suitable for use as a support (substrate) for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors, for example. As described above, the present film is excellent in that it can suppress the occurrence of surface defects such as pinholes and can also suppress the occurrence of peeling defects.

[0018] [Elastic deformation power (η it ) In order to effectively prevent the above-mentioned peeling failure, this film has a high elastic deformation power (η it ) is preferably more than 55%. it ) to a specific range of more than 55%, it is possible to achieve high levels of peelability, which are particularly required in the manufacturing process of MLCCs using thin ceramic green sheets, and to effectively suppress peeling defects. Elastic deformation power (η it From the same viewpoint, the elastic deformation power (η it ) can be appropriately set within the above range and is not limited to the following, but may be, for example, 56% or more, 56.2% or more, 56.4% or more, 57% or more, 57.5% or more, etc. In addition, the elastic deformation power (η it The upper limit of the ratio is not particularly limited, but may be, for example, about 70%, or may be about 65%.

[0019] Elastic deformation power of the A surface (η it By using the present film in which the ratio of the cross-sectional area to the cross-sectional area is controlled to a specific range of more than 55%, for example, when cutting the ceramic green sheet with a cutting blade to peel it off, the edge of the ceramic green sheet can be easily separated from the present film, and a good gap can be formed between the two. This gap can be used to grip the present film, making it easy to separate the ceramic green sheet and the present film.

[0020] Elastic deformation power (ηit ) is calculated by the following formula based on physical quantities measured by nanoindentation method (in accordance with ISO 14577). Specifically, it is determined by the method described in the examples below. Elastic deformation power (η it )=(Welast / Wtotal)×100[%] [Wtotal (total deformation work) = Wplast (plastic deformation work) + Welast (elastic deformation work)]

[0021] [Arithmetic mean height (Sa)] The present film preferably has an arithmetic mean height (Sa) of 15 nm or less on one surface, namely, side A. If the arithmetic mean height (Sa) is greater than 15 nm, the surface smoothness becomes insufficient, and surface defects such as pinholes tend to occur, making it difficult to adapt to thinner ceramic green sheets. From the same viewpoint, the arithmetic mean height (Sa) of side A is preferably 10 nm or less, more preferably 8 nm or less, even more preferably 6 nm or less, particularly preferably 4 nm or less, especially preferably 3.5 nm or less, even more particularly preferably 3 nm or less, and most preferably 2.5 nm or less. On the other hand, the lower limit of the arithmetic mean height (Sa) of side A is, for example, preferably 0.3 nm or more, more preferably 0.5 nm or more. If the arithmetic mean height (Sa) is smaller than 0.3 nm, the film surface becomes too flat, which tends to reduce the slipperiness of the film and impair processability.

[0022] In order to prevent the roughness of one surface from being transferred to the other surface when the film is wound into a roll, the arithmetic mean height (Sa) of the other surface, side B, is preferably 35 nm or less, more preferably 33 nm or less, even more preferably 30 nm or less, and particularly preferably 28 nm or less. The lower limit of the arithmetic mean height (Sa) of side B is not particularly limited, but is preferably 3 nm or more, more preferably 5 nm or more, in order to prevent a decrease in transportability or windability due to a decrease in the slipperiness of the film.

[0023] The ratio of the arithmetic mean height (Sa) of side A to side B of the present film ("arithmetic mean height (Sa) of side B / arithmetic mean height (Sa) of side A"; hereinafter, sometimes referred to as "SaB / SaA") is preferably 2 or more, more preferably 2.5 or more, and even more preferably 3 or more, from the viewpoint of achieving a high degree of both surface smoothness and slip resistance. On the other hand, SaB / SaA is preferably 18 or less, more preferably 16 or less, even more preferably 15 or less, even more preferably 14.5 or less, and particularly preferably 14 or less. Furthermore, the ratio (SaB / SaA) can be set appropriately within the above range, and is not limited to the following, but may be, for example, 3.5 or more, 4.5 or more, 5.5 or more, 6.5 or more, 7 or more, 7.4 or more, 7.8 or more, etc.

[0024] The arithmetic mean height (Sa) is one of the surface roughness parameters (ISO 25178) and is a three-dimensional extension of the two-dimensional Ra, and is calculated by dividing the volume of the area enclosed by the surface shape curved surface and the mean surface by the measured area. Specifically, when the surface is the XY plane and the height direction is the Z axis, where A is the defined area (the entire image) and Z(x, y) is the height from the plane at height 0 of the image point (x, y), it can be expressed as in Equation 1. More specifically, it can be measured by the method described in the Examples below.

[0025]

number

[0026] [Maximum mountain height (Sp)] The maximum peak height (Sp) of one surface of the film, namely, side A, is preferably 150 nm or less. If the maximum peak height (Sp) is greater than 150 nm, the surface smoothness becomes insufficient, and surface defects such as pinholes tend to occur, making it difficult to adapt to thinner ceramic green sheets. From the same viewpoint, the maximum peak height (Sp) of side A is preferably 100 nm or less, more preferably 95 nm or less, even more preferably 90 nm or less, and particularly preferably 86 nm or less. On the other hand, the lower limit of the maximum peak height (Sp) of side A is, for example, preferably 5 nm or more, more preferably 10 nm or more. The maximum peak height (Sp) of side A can be set appropriately within the above range, and is not limited to the following, but may be, for example, 65 nm or less, 60 nm or less, 40 nm or less, 30 nm or less, etc.

[0027] The maximum peak height (Sp) of side B, the other surface of the present film, is usually 700 nm or less, preferably 650 nm or less, more preferably 620 nm or less, even more preferably 600 nm or less, and particularly preferably 570 nm or less, from the viewpoint of preventing the roughness of one surface from being transferred to the other surface when the film is wound into a roll. The lower limit of the maximum peak height (Sp) of side B is not particularly limited, but is preferably, for example, 30 nm or more, more preferably 50 nm or more, from the viewpoint of preventing a decrease in transportability or winding ability due to a decrease in the slipperiness of the film.

[0028] The ratio of the maximum peak heights (Sp) of side A and side B of the present film ("maximum peak height (Sp) of side B / maximum peak height (Sp) of side A"; hereinafter, sometimes referred to as "SpB / SpA") is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, even more preferably 5 or more, particularly preferably 5.4 or more, and most preferably 5.8 or more, from the viewpoint of achieving a high degree of both surface smoothness and slip resistance. On the other hand, SpB / SpA is preferably 25 or less, more preferably 24.5 or less, and even more preferably 24 or less.

[0029] 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: [Equation 2]. More specifically, it can be measured by the method described in the examples below.

[0030]

number

[0031] [Ratio of maximum peak height (Sp) to arithmetic mean height (Sa)] The ratio (Sp / Sa) of the maximum peak height (Sp) to the arithmetic mean height (Sa) on side A, which is one surface of the present film, is preferably 70 or less, more preferably 65 or less, and even more preferably 60 or less. On the other hand, the lower limit of Sp / Sa is not particularly limited, but is preferably 6 or more, more preferably 8 or more, and even more preferably 10 or more. The ratio (Sp / Sa) of the maximum peak height (Sp) to the arithmetic mean height (Sa) on side B, the other surface of the present film, is preferably 40 or less, more preferably 35 or less, and even more preferably 30 or less. On the other hand, the lower limit of Sp / Sa is not particularly limited, but is preferably 10 or more, more preferably 15 or more, and even more preferably 20 or more.

[0032] [Root mean square height (Sq)] The root mean square height (Sq) of side A, one surface of the present film, is preferably 5 nm or less, more preferably 4 nm or less, even more preferably 3.5 nm or less, particularly preferably 3 nm or less, and especially preferably 2.8 nm or less. On the other hand, the lower limit of the root mean square height (Sq) of side A 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 side B, the other surface 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 side B is not particularly limited, but is, for example, preferably 1 nm or more, more preferably 3 nm or more.

[0033] The ratio of the root mean square height (Sq) of side A to side B of the present film ("root mean square height (Sq) of side B / root mean square height (Sq) of side A"; hereinafter, sometimes referred to as "SqB / SqA") is preferably 7 or more, more preferably 8 or more, and even more preferably 9 or more, from the viewpoint of achieving a high degree of both surface smoothness and slip resistance. On the other hand, SqB / SqA is preferably 20 or less, more preferably 18 or less, and even more preferably 17 or less.

[0034] 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. In other words, 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 formula [3]. More specifically, it can be measured by the method described in the examples below.

[0035]

number

[0036] [Kurtosis (Sku)] The kurtosis (Sku) of side A, which is one surface 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 side A is not particularly limited, but is, for example, preferably 0.5 or more, more preferably 1 or more.

[0037] The kurtosis (Sku) of side B, the other surface 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 side B is not particularly limited, but is, for example, preferably 1 or more, more preferably 2 or more.

[0038] Kurtosis (Sku) is one of the surface roughness parameters (ISO 25178) and can be used to evaluate the peakedness (kurtosis) of a histogram of height distribution, and can be calculated using the following formula: [Mathematical formula 4]. More specifically, it can be measured by the method described in the Examples below.

[0039]

number

[0040] [Skewness (Ssk)] The skewness (Ssk) of side A, which is one surface 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 side A is not particularly limited, but is, for example, preferably 0.2 or more, more preferably 0.4 or more.

[0041] The skewness (Ssk) of side B, the other surface 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 side B is not particularly limited, but is, for example, preferably 0.5 or more, more preferably 0.8 or more.

[0042] Skewness (Ssk) is one of the surface roughness parameters (ISO 25178) and can be determined by the formula [5]. More specifically, it can be measured by the method described in the examples below.

[0043]

number

[0044] Elastic deformation power (η it) and specific surface properties (arithmetic mean height (Sa), maximum peak height (Sp)) can be adjusted to a predetermined range, for example, when particles are blended, by adjusting the content in consideration of the type of particles, specifically, for example, the particle composition, average particle size, particle size distribution, hardness, affinity with the polyester to be contained, etc. Also, by adjusting the type and content of particles in consideration of the type of polyester to be contained, for example, the composition, viscosity, molecular weight, thermal properties, presence or absence of copolymerization components, etc., the elastic deformation power (η it When two or more types of particles are used in combination, it is preferable to adjust the content ratio in consideration of the type of particles and polyester used. In addition, during the production of the polyester film, it is also effective to control, for example, the stretching ratio (in the case of biaxial stretching, the longitudinal and transverse stretching ratios), 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 transverse stretching). Furthermore, the same method as above is also suitable for adjusting other surface properties (root mean square height (Sq), kurtosis (Sku), and skewness (Ssk)).

[0045] [Shrinkage rate after heat treatment] The manufacturing process of multilayer ceramic capacitors includes heat treatment steps such as drying the release agent coated on the polyester film and drying the ceramic slurry coated on the release film, so a decrease in heat distortion resistance can lead to coating irregularities and wrinkles. In other words, heat distortion resistance is one of the important properties for ensuring the quality and reliability of the finished product, from intermediate products in the manufacturing process of multilayer ceramic capacitors to the final product, for example, the lamination characteristics of ceramic green sheets. From the viewpoint of suppressing such coating irregularities and wrinkles, the shrinkage rate of the present film in the machine direction (MD) when heat-treated at 150°C for 5 minutes is preferably 2.8% or less. From the same viewpoint, it is more preferably 2.6% or less, even more preferably 2.4% or less, particularly preferably 2.2% or less, and especially preferably 2% or less. From the same viewpoint, the lower limit of the shrinkage rate in the machine direction (MD) (150°C, 5 minutes) is about -1%, preferably -0.5% or more, more preferably -0.3% or more.

[0046] Furthermore, the shrinkage rate in the transverse direction (TD) of this film when heat-treated at 150°C for 5 minutes is preferably 2.8% or less from the viewpoint of suppressing coating irregularities and wrinkles. From the same viewpoint, it is more preferably 2.6% or less, even more preferably 2.4% or less, particularly preferably 2.2% or less, and especially preferably 1.5% or less. From the same viewpoint, the lower limit of the shrinkage rate in the transverse direction (TD) is about -1%, 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 limited to the following, 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.

[0047] In addition, the elastic deformation power (η it In order to achieve both the desired stretching temperature and shrinkage rate (heated at 150°C for 5 minutes), 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., can be appropriately set to be within the above ranges. Details will be described later.

[0048] [Planar orientation degree (ΔP)] In order to suppress the aforementioned peeling defects, the present film preferably has a planar orientation degree (ΔP) of one surface, namely, side A, of 165 or more. On the other hand, the upper limit of the planar orientation degree (ΔP) of one surface, namely, side A, is, for example, preferably 190 or less, more preferably 185 or less, and even more preferably 180 or less. The planar orientation degree (ΔP) of side A can be set appropriately within the above range, and is not limited to the following, and may be, for example, 166 or more, 168 or more, etc.

[0049] The degree of planar orientation (ΔP) is calculated based on the following formula, using JIS K 7142-1996 5.1 (Method A) to measure the refractive index in the vertical direction (nx), the refractive index in the horizontal direction (ny), and the refractive index in the thickness direction (nz) with an Abbe refractometer using sodium D line as a light source. Planar orientation degree (ΔP)=((nx+ny) / 2-nz)×1000

[0050] Next, the raw materials and the like used in the embodiment of the present film will be described.

[0051] <Polyester> Polyester is a raw material of the present film and refers to a polymer compound having continuous ester bonds in the main chain. The polyester used in 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.

[0052] In the present film, it is preferable to use a polyester containing more than 50 mol % of an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid, when the dicarboxylic acid component is taken as 100 mol %.

[0053] 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.

[0054] Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-hexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4-hydroxyethoxyphenyl)propane, isosorbate, and spiroglycol.

[0055] When the polyester is a homopolyester, it is preferably one obtained by polycondensing an aromatic dicarboxylic acid and an aliphatic glycol. 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 polyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN).

[0056] 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 is the main component of the dicarboxylic acid component constituting the polyester (i.e., the dicarboxylic acid component with the largest content) and the compound that is the main component of the diol component (i.e., the diol component with the largest content), and 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, neopentyl glycol, and the like.

[0057] The polyester is preferably polyethylene terephthalate, in which 80 mol % or more, preferably 90 mol % or more, is an ethylene terephthalate unit, or polyethylene-2,6-naphthalate, in which 80 mol % or more, preferably 90 mol % or more, is an ethylene-2,6-naphthalate unit.

[0058] 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 the 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.

[0059] [Polycondensation catalyst] Examples of polycondensation catalysts used in polycondensing the polyester include antimony compounds, germanium compounds, aluminum compounds, titanium compounds, etc. Among these, antimony compounds and titanium compounds are preferred, and titanium compounds are particularly preferred. By using the titanium compound, the number of metal-containing aggregates, so-called coarse foreign matter, originating from the titanium compound in the film can be reduced, and the surface smoothness can be improved.

[0060] More specifically, the polyester constituting the outermost layer of the present film (also referred to as the "surface layer"; for example, the surface layer on which a release layer is laminated) preferably uses a titanium compound as its polycondensation catalyst. Furthermore, the titanium element content derived from the titanium compound in the outermost layer is preferably 1 ppm or more and 40 ppm or less, and more preferably 2 ppm or more and 35 ppm or less, by mass. Within the above range, it is possible to reduce catalyst-induced foreign matter without reducing the polyester production efficiency. From the same viewpoint, the content of antimony compounds in the outermost layer of the present film is preferably 100 ppm or less.

[0061] [Intrinsic Viscosity of Polyester] The polyester constituting the present film preferably has an intrinsic viscosity of 0.5 dL / g or more, more preferably 0.55 dL / g or more, and even more preferably 0.6 dL / g or more. By using a polyester with an intrinsic viscosity of 0.5 dL / g or more as the polyester constituting the present film, the shear stress during kneading of the polyester increases, making it easier to highly disperse particles in the polyester resin, and, for example, making it easier to achieve the surface properties of the polyester film within the above-mentioned range. The upper limit of the intrinsic viscosity of the polyester is preferably 1 dL / g or less, more preferably 0.85 dL / g or less, and even more preferably 0.75 dL / g or less, from the viewpoint of particle fluidity.

[0062] When two or more polyesters with different intrinsic viscosities are used, the intrinsic viscosity of the polyester constituting the present film refers to the intrinsic viscosity 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 using a phenol:tetrachloroethane (1:1) solvent.

[0063] The present film is a film whose main component is polyester, and the content of polyester contained in the present film is, for example, 90% by mass or more, preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably 99% by mass or more. Furthermore, when the present film is composed of two or more layers, the content of polyester in each layer is, for example, 90% by mass or more, preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably 99% by mass or more.

[0064] <Particle> It is preferable that particles are contained in the present film. The type of particles contained in the present film is not particularly limited, and examples thereof include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, alumina (aluminum oxide), and titanium oxide, as well as organic particles such as crosslinked polymers such as crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, and crosslinked polyester particles.

[0065] Among these, silica, calcium carbonate, and organic particles are preferred as particles to be contained in the present film.Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used as particles to be contained in the present film.

[0066] The average particle size of the particles is usually 5 μm or less, preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less. It is also preferably 0.01 μm or more, more preferably 0.02 μm or more, and even more preferably 0.03 μm or more. The average particle size of the particles can be determined by measuring the diameters of 10 or more particles using a scanning electron microscope (SEM) and averaging the measured diameters. In the case of non-spherical particles, the average of the longest and shortest diameters can be measured as the diameter of each particle.

[0067] The Mohs hardness of a particle is calculated by the elastic deformation power (η itFrom the viewpoint of increasing the elastic deformation power (η), it is preferably 9 or less, and more preferably 8 or less. If the Mohs hardness of the particles is greater than the above range, the conformability during film stretching decreases, voids are generated, and the elastic deformation power (η it From the same viewpoint, the Mohs hardness of the particles can be appropriately set within the range of, for example, 1 to 9, and may be, but is not limited to, within the ranges of, for example, 1 to 8, 1 to 7, 1 to 5, 1 to 4, 1 to 3, etc. The Mohs hardness scale is a numerical representation of hardness based on how a material is scratched against a standard material. Standard materials are designated in order of softness from 1 to 10, and the Mohs hardness can be measured using a Mohs hardness tester in the usual way.

[0068] The particle content depends on the average particle size, but the elastic deformation power (η it From the viewpoint of increasing the elastic deformation power (η), the mass ratio of the particles in the layer containing the particles is preferably 250 ppm or more, more preferably 300 ppm or more, and more preferably 500 ppm or more. Furthermore, the mass ratio is usually 10,000 ppm or less, preferably 9,000 ppm or less, preferably 8,000 ppm or less, and more preferably 7,000 ppm or less. If the particle content is too high, the particles aggregate to generate voids, which reduces the elastic deformation power (η it ) tends to decrease.

[0069] The shape of the particles is not particularly limited, and any of spherical, blocky, rod-like, flat, etc. may be used, with spherical being preferred. These particles may be used alone or in combination of two or more types.

[0070] The method for adding particles to the present film is not particularly limited, and any conventionally known method can be used. For example, in the case of a multi-layer polyester film, particles can be added at any stage in the production of the polyester constituting each layer, but it is preferable to add them after the completion of the esterification or transesterification reaction.

[0071] When particles are incorporated into the present film, it is preferable to provide a surface layer and an intermediate layer and incorporate particles into the surface layer. Furthermore, when the film has a three-type, three-layer structure with different front and back layers, it is preferable to incorporate particles into one or both of the surface layers.

[0072] The film may also contain a nucleating agent. Examples of nucleating agents include inorganic and organic nucleating agents, with organic nucleating agents being preferred. The nucleating agents may be used alone or in combination of two or more.

[0073] The organic crystal nucleating agent is preferably, for example, a fatty acid metal salt represented by the following general formula. Formula:(CH3(CH2) n COO) m M (In the general formula, n is an integer of 4 or more, and M is Na, Ca, or Li. Furthermore, m is 1 when M is Na or Li, and 2 when M is Ca.)

[0074] In the general formula, M is preferably Na. In the general formula, n is preferably 6 or more, more preferably 8 or more, even more preferably 10 or more, and even more preferably 15 or more. In addition, n is preferably 35 or less, more preferably 33 or less, even more preferably 30 or less, and even more preferably 28 or less. In the fatty acid metal salt represented by the above general formula, specific examples of the fatty acid include caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, nonadecanoic acid, arachic acid, behenic acid, and montanic acid, and among these, montanic acid is preferred.

[0075] The melting point of the fatty acid metal salt used as the crystal nucleating agent is preferably 140° C. or higher, more preferably 150° C. or higher, and even more preferably 160° C. or higher. It is preferably 260° C. or lower, more preferably 250° C. or lower, even more preferably 240° C. or lower, and even more preferably 230° C. or lower. The melting point of the fatty acid metal salt can be measured by TG-DTA.

[0076] The content of the nucleating agent in the particle-containing layer is preferably 2000 ppm or more, more preferably 3000 ppm or more, even more preferably 5000 ppm or more, and even more preferably 6000 ppm or more, by mass, and is preferably 28000 ppm or less, more preferably 25000 ppm or less, and even more preferably 20000 ppm or less.

[0077] When the present film contains a nucleating agent, it is preferable to provide a surface layer and an intermediate layer and contain the nucleating agent in the surface layer. Also, when the film has a three-type, three-layer structure with different front and back layers, it is preferable to contain the nucleating agent in one or both surface layers.

[0078] In addition to the above-mentioned particles, conventionally known ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc. may be added to the present film as needed, but the total content of these in the present film is usually less than 10% by mass.

[0079] <Layer structure of this film> The film may be a single-layer polyester film or a laminated polyester film having two or more layers. The film has an elastic deformation power (η it ) within the above range and from the viewpoint of suitably using the film as a support for a release film for processing used in the manufacturing process of a multilayer ceramic capacitor, a polyester film consisting of at least two layers is preferred, and a polyester film consisting of three layers is more preferred.

[0080] More specifically, in the present invention, when the present film has a laminated structure having two or more layers, for example, a layer structure having a surface layer A and a surface layer B that form the outermost layers of the present film can be mentioned. Another example is a laminated structure having a surface layer A and a surface layer B that form the outermost layers of the present film, and one or more intermediate layers C (C1, C2, ...). More specifically, for example, an A / C / B structure consisting of a surface layer A, a surface layer B, and an intermediate layer C is preferred. The surface layer A is a surface layer that forms one surface of the present film, and the surface layer B is a surface layer that forms the other surface of the present film.

[0081] <Preferred embodiment of the present film> The surface layer A that forms one surface of the present film is the surface layer located on the side of the present film where, for example, a ceramic green sheet or the like is formed. Specifically, for example, a release layer is formed on the surface of the surface layer A, and a ceramic green sheet is formed on the surface of the release layer. The surface layer B that forms the other surface of the present film is the surface layer located opposite the side where the ceramic green sheet or the like is provided. Therefore, for example, the present film constitutes a part of an intermediate product having a laminated structure of "surface layer B / surface layer A / release layer / ceramic green sheet" in the manufacturing process of a multilayer ceramic capacitor. Similarly, the present film constitutes a part of an intermediate product having a laminated structure of, for example, "surface layer B / intermediate layer C / surface layer A / release layer / ceramic green sheet."

[0082] Elastic deformation power (η it Although the method for achieving both high degree of hardness and surface smoothness is not limited to the following, for example, a method in which the average particle size, content, Mohs hardness, etc. of the particles are appropriately set within the following preferred ranges is preferred. Specifically, when particles are contained in the surface layer A constituting the present film, the average particle size of the particles to be contained is, for example, itFrom the viewpoint of the thickness and surface smoothness, the thickness 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 thickness is preferably 1 μm or less, more preferably 0.8 μm or less, and even more preferably 0.6 μm or less. The average particle size of the particles contained in surface layer B is preferably 0.1 μm or more, more preferably 0.15 μm or more, and even more preferably 0.2 μm or more, from the viewpoint of, for example, improving lubricity and preventing the surface roughness of surface layer B from being transferred to surface layer A when wound into a roll. On the other hand, it is preferably 1.5 μm or less, more preferably 1.2 μm or less, and even more preferably 1 μm or less.

[0083] When particles are contained in the surface layer A constituting the present film, the particle content is preferably 200 ppm or more, more preferably 250 ppm or more, and even more preferably 300 ppm or more, by mass, and is preferably 2800 ppm or less, more preferably 2600 ppm or less, and even more preferably 2500 ppm or less. The content of particles contained in the surface layer B is preferably 2000 ppm or more, more preferably 2200 ppm or more, and even more preferably 2500 ppm or more, by mass, and is preferably 8000 ppm or less, more preferably 7500 ppm or less, and even more preferably 7000 ppm or less.

[0084] When particles are contained in the surface layer A of this film, the elastic deformation power (η it From the viewpoint of improving the elastic deformation power (η it The particles contained in the surface layer B preferably have a Mohs hardness of 8 or less, more preferably 1 to 7, even more preferably 2 to 6, and particularly preferably 3 to 5.

[0085] In addition, when particles are contained in the surface layer A, the elastic deformation power (η it From the viewpoint of improving the hardness, it is preferable that the main component of the particles be particles having a Mohs hardness of 8 or less. For example, the ratio of the content of particles having a Mohs hardness of 8 or less to the content of all particles contained in the surface layer A (content of particles having a Mohs hardness of 8 or less contained in the surface layer A / content of all particles contained in the surface layer A) is, but is not limited to, 0.429 or more, 0.5 or more, preferably 0.6 or more, more preferably 0.65 or more, and even more preferably 0.7 or more, in mass ratio. The ratio can be set appropriately within the above range, and may be, but is not limited to, for example, 0.75 or more, 0.78 or more, 0.8 or more, etc. Alternatively, it may be, for example, 1 or less, 0.95 or less, 0.9 or less, or 0.88 or less.

[0086] In addition, when the surface layer A contains particles with a Mohs hardness of 8 or less, the elastic deformation power (η it From the viewpoint of improving the surface layer A, the content is preferably less than 1800 ppm by mass relative to the surface layer A. The content can be appropriately set within the above range and is not limited to the following, for example, 1600 ppm or less, 1500 ppm or less, 1300 ppm or less, 1200 ppm or less, or 1000 ppm or less. The content may also be, for example, 200 ppm or more, 300 ppm or more, 400 ppm or more, 500 ppm or more, or the like. Elastic deformation power (η it From the viewpoint of achieving a high degree of both the film resistance and surface smoothness, in a preferred embodiment, for example, when at least one type of particle is contained in the surface layer A constituting the present film, it is preferable that the average particle size of the particles contained in the surface layer A is 0.4 μm or less, and the content of the particles (total content if there are two or more types of particles) is 2800 ppm or less by mass relative to the surface layer A, more preferably, the average particle size of the particles contained in the surface layer A is 0.3 μm or less, and the content of the particles is 2500 ppm or less relative to the surface layer A, and even more preferably, the average particle size of the particles contained in the surface layer A is 0.03 to 0.3 μm, and the content of the particles is 250 to 2300 ppm relative to the surface layer A.

[0087] In addition, for example, in an embodiment in which a plurality of types of particles are contained in the surface layer of the present film, aggregation of the particles is suppressed, and the elastic deformation power (η it From the viewpoint of increasing the zeta potential at pH 7, it is preferable that the surface layer contains two or more types of particles having different positive and negative zeta potentials at pH 7. For example, it is preferable that the surface layer contains particles (a1) and particles (a2), and that the zeta potential at pH 7 of particles (a1) is positive and that of particles (a2) is negative, or that the zeta potential of particles (a1) is negative and that of particles (a2) is positive. That is, at pH 7, due to the difference in charge between particle (a1) and particle (a2), particle (a1) and particle (a2) are electrically attracted to each other, and for example, particle (a1) can be positioned around particle (a2). In particles in which particle (a1) is electrically positioned around particle (a2) (hereinafter sometimes referred to as "composite particles"), the presence of particle (a1) with the same charge on the outside causes the composite particles to repel each other, and the composite particles maintain high dispersibility without agglomeration, thereby suppressing the generation of voids and increasing the elastic deformation power (η it ) is thought to tend to increase. In such composite particles, it is preferable that the average particle size of the outer particles (a1) is smaller than the average particle size of the inner particles (a2). That is, a structure is formed in which the relatively small particles (a1) surround the relatively large particles (a2), and since the composite particles are electrically repelled, aggregation of the particles (a2) does not occur, which is thought to further improve dispersibility. The zeta potential can be measured by electrophoretic light scattering.

[0088] Examples of particles having a positive zeta potential at pH 7 include alumina, cation-modified silica, and rare earth compounds such as ytterbium trifluoride, yttrium fluoride, lanthanum fluoride, yttrium oxide, lanthanum oxide, and ytterbium oxide, with alumina being preferred. Examples of particles having a negative zeta potential at pH 7 include inorganic particles such as metal oxides such as silica, 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, with organic particles and silica being preferred.

[0089] The zeta potential of particles (a1) and particles (a2) at pH 7 may be the zeta potential of the particles themselves, or may be adjusted by modifying the particle surface with a surface treatment agent, etc. Examples of surface treatment agents include silane coupling agents such as vinyltriethoxysilane, vinyltrimethoxysilane, vinyl-tris(β-methoxyethoxy)silane, γ-methacryloyloxypropyltrimethoxysilane, κ-methacryloyloxydodecyltrimethoxysilane, β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-ureidopropyltriethoxysilane, γ-chloropropyltrimethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, and methyltriethoxysilane, as well as titanate-based coupling agents. The type and amount of treatment agent may be appropriately adjusted to achieve the desired zeta potential. The amount of the surface treatment agent used for surface treatment is usually 1 to 30 parts by mass, preferably 3 to 15 parts by mass, per 100 parts by mass of the particles. The method of treatment with the surface treatment agent is not particularly limited, and known methods can be used, such as a method of dispersing and mixing the particles and the surface treatment agent in an appropriate solvent using a ball mill or the like, drying in an evaporator or air drying, and then heating to 50 to 150°C, a method of heating and refluxing the particles and the surface treatment agent in a solvent such as alcohol for several hours, and a method of graft-polymerizing the surface treatment agent onto the particle surfaces.

[0090] The average particle size of the particles (a1) is preferably 0.01 μm or more, more preferably 0.02 μm or more, even more preferably 0.03 μm or more, still more preferably 0.035 μm or more, and particularly preferably 0.04 μm or more, and is preferably 1 μm or less, more preferably 0.8 μm or less, even more preferably 0.5 μm or less, still more preferably 0.3 μm or less, and particularly preferably 0.1 μm or less.

[0091] From the viewpoint of dispersibility, the content of the particles (a1) is, for example, preferably 50 ppm or more, more preferably 100 ppm or more, even more preferably 150 ppm or more, particularly preferably 180 ppm or more, especially preferably 200 ppm or more, and even more especially preferably 250 ppm or more, in terms of mass ratio relative to the surface layer A. On the other hand, it is preferably 5000 ppm or less, more preferably 3000 ppm or less, even more preferably 1000 ppm or less, especially preferably 800 ppm or less, and especially preferably 500 ppm or less. From the viewpoint of lubricity, the content of the particles (a1) is, for example, preferably 500 ppm or more, more preferably 1000 ppm or more, and even more preferably 2000 ppm or more, in terms of mass ratio relative to the surface layer B. On the other hand, it is preferably 5000 ppm or less, more preferably 4500 ppm or less, and even more preferably 4000 ppm or less.

[0092] The average particle size of the particles (a2) is preferably 0.05 μm or more, more preferably 0.07 μm or more, even more preferably 0.08 μm or more, and still more preferably 0.1 μm or more, and is preferably 1 μm or less, more preferably 0.8 μm or less, even more preferably 0.6 μm or less, and still more preferably 0.5 μm or less.

[0093] From the viewpoint of surface smoothness, the content of particles (a2) is preferably 100 ppm or more, more preferably 250 ppm or more, even more preferably 500 ppm or more, and particularly preferably 700 ppm or more, by mass, relative to the surface layer A. On the other hand, for example, it is preferably 8000 ppm or less, more preferably 5000 ppm or less, even more preferably 3000 ppm or less, particularly preferably 2500 ppm or less, and especially preferably 2000 ppm or less. From the viewpoint of slipperiness, the content of particles (a2) is preferably 1000 ppm or more, more preferably 1500 ppm or more, even more preferably 2000 ppm or more, particularly preferably 2500 ppm or more, and especially preferably 3000 ppm or more, by mass, relative to the surface layer B. On the other hand, it is preferably 8000 ppm or less, more preferably 7000 ppm or less, even more preferably 6000 ppm or less, particularly preferably 5500 ppm or less, and especially preferably 5000 ppm or less.

[0094] Furthermore, the relationship between the content of particles (a1) and the content of particles (a2) is preferably such that the content of particles (a2) is equal to or greater than the content of particles (a1).By achieving such a relationship, the roughness of the surface layer A can be adjusted by other particles such as particles (a2), while the effect of particles (a1) in inhibiting (re-)aggregation of other particles can be fully exerted.

[0095] The total content of particles (a1) and particles (a2) is preferably 300 to 10,000 ppm by mass relative to the layer they are contained in. If the total content is within this range, fine irregularities are formed on the film surface, and the surface of surface layer A tends to satisfy the arithmetic mean height (Sa) and maximum peak height (Sp) of (1) and (2) above. In the present film, the total content of particles (a1) and particles (a2) in the surface layer A is preferably 400 ppm or more, more preferably 800 ppm or more, by mass, and is preferably 3000 ppm or less, more preferably 2000 ppm or less. In the present film, the total content of particles (a1) and particles (a2) in the surface layer B is preferably 3000 ppm or more, more preferably 4000 ppm or more, and even more preferably 5000 ppm or more, by mass, and is preferably 10000 ppm or less, more preferably 9500 ppm or less, and even more preferably 9000 ppm or less. The present film may contain particles (a1) and particles (a2) in both surface layer A and surface layer B, respectively. Alternatively, for example, surface layer A may contain particles (a1) and particles (a2), and surface layer B may contain only particles (a2) but not particles (a1).

[0096] It is also preferable to use, for example, alumina particles as the particles (a1), and to use particles other than alumina particles (for example, silica, organic particles, etc.) as the particles (a2). By using alumina particles in combination with particles other than alumina particles, it is possible to suppress the generation of voids due to the aggregation of particles, and the elastic deformation power (η it ) can be effectively increased.

[0097] For example, when the content of the particles (a2) in the surface layer A exceeds a predetermined amount, the particles (a2) tend to aggregate more easily, and voids are generated due to the aggregation of the particles (a2), which reduces the elastic deformation power (η itTherefore, when using more than a predetermined amount of particles (a2), it is preferable to use alumina particles as the particles (a1). Specifically, but not limited to, when the surface layer A contains 300 ppm or more, for example, 500 to 3000 ppm, of particles (a2) having a Mohs hardness of 7 or less (for example, silica, organic particles, etc.), it is preferable to use alumina particles as the particles (a1), and more preferably, the content of the alumina particles is in the range of 50 to 5000 ppm relative to the surface layer A.

[0098] When alumina particles are used as particles (a1), examples of particles (a2) to be used in combination include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, and titanium oxide; 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, organic particles and silica are preferred. Note that even when alumina particles are used as particles (a1) and particles other than alumina particles (e.g., organic particles) are used as particles (a2), the preferred ranges for average particle size, shape, content, etc. are the same as those described above.

[0099] The method for producing alumina particles is not particularly limited, but examples thereof include a thermal decomposition method, i.e., a method of flame hydrolysis using anhydrous aluminum chloride as a raw material, and an ammonium alum thermal decomposition method, i.e., a method of reacting aluminum hydroxide as a raw material with sulfuric acid to form aluminum sulfate, and then reacting it with ammonium sulfate to form ammonium alum, which is then calcined.

[0100] When a nucleating agent is contained in the surface layer A constituting the present film, the content of the nucleating agent is, by mass, preferably 2000 ppm or more, more preferably 3000 ppm or more, even more preferably 5000 ppm or more, and even more preferably 6000 ppm or more, and is preferably 28000 ppm or less, more preferably 25000 ppm or less, and even more preferably 20000 ppm or less.

[0101] When an intermediate layer C is formed in the present film, from the viewpoint of reducing costs, it is preferable that the intermediate layer C does not substantially contain particles. Note that "substantially does not contain" means that particles are not intentionally contained, and specifically means that the particle content is 200 ppm or less, more preferably 150 ppm or less, by mass.

[0102] Furthermore, the intermediate layer C of the present film may contain recycled polyester raw materials in order to reduce CO2 emissions and contribute to reducing the burden on the environment. The content of recycled polyester raw materials is preferably 40% by mass or more, more preferably 50% by mass or more, relative to the intermediate layer C. The content of recycled polyester raw materials may be 70% by mass or more, 90% by mass or more, or even 100% by mass.

[0103] 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, even more preferably 18 μm or more, and particularly preferably 19 μm or more. It is also preferably 150 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, particularly preferably 50 μm or less, especially preferably 38 μm or less, and most preferably 32 μm or less. The total thickness of the present film can be set appropriately within the above range, and may be, for example, 30 μm or less, or 28 μm or less.

[0104] When the present film has a three-layer structure including a surface layer A, an intermediate layer C, and a surface layer B in this order, it is preferable that the thickness of the intermediate layer C is greater than the thickness of each of the surface layers A.

[0105] When the present film has a three-layer structure including a surface layer A, an intermediate layer C, and a surface layer B in this order, the thickness of the surface layer A is preferably greater than the thickness of each of the surface layers B.

[0106] When the present film has a three-layer structure having a surface layer A, an intermediate layer C, and a surface layer B in this order, the thickness ratio of the layers (thickness of surface layer A:thickness of intermediate layer C:thickness of surface layer B) is preferably 1-10:10-35:1-5, more preferably 2-8:10-32:1-3, and even more preferably 3-6:10-30:1-2.

[0107] The thickness of the surface layer A of the present film is preferably 0.8 μm or more, more preferably 1 μm or more, even more preferably 1.5 μm or more, particularly preferably 2 μm or more, and most preferably 2.5 μm or more, and is preferably 15 μm or less, more preferably 13 μm or less, even more preferably 11 μm or less, and particularly preferably 10 μm or less. The thickness of the surface layer B of the present film is preferably 0.5 μm or more, more preferably 0.8 μm or more, even more preferably 1 μm or more, particularly preferably 1.2 μm or more, and is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 6 μm or less, particularly preferably 4 μm or less.

[0108] The thickness of the intermediate layer C of the present film is preferably 8 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, particularly preferably 14 μm or more, and is preferably 35 μm or less, more preferably 30 μm or less, even more preferably 28 μm or less, particularly preferably 26 μm or less.

[0109] <Manufacturing method of this film> Next, specific examples of the production of the present film will be described, but the present invention is not limited to these examples. For example, when producing a biaxially stretched film, a preferred method is to extrude dried pellets of the polyester raw material described above as a molten sheet from a die using a melt extrusion device such as an extruder, and then cool and solidify the molten sheet on a cooling roll such as a rotating cooling drum to obtain an unstretched sheet. In this case, it is preferable to increase the adhesion between the sheet and the cooling roll to improve the flatness of the sheet, and an electrostatic application adhesion method and / or a liquid coating adhesion method are preferably used.

[0110] The unstretched sheet is then biaxially stretched. In this case, the unstretched sheet is first stretched in one direction using a roll or tenter type stretching machine (primary stretching). The stretching temperature is usually 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is usually 2.5 to 7 times, preferably 3 to 6 times. Next, the film is stretched in a direction perpendicular to the first-stage stretching direction, and in this case, the stretching temperature is usually 70 to 170° C., and the stretching ratio is usually 3 to 7 times, preferably 3.5 to 6 times. Subsequently, the film is heat-treated under tension or relaxation of 30% or less at a temperature of 180 to 270°C to obtain a biaxially stretched film. This heat treatment is also called a heat setting step. The heat treatment may be performed in two or more steps at different temperatures. The heat treatment time in the heat setting step is preferably 1 to 20 seconds, more preferably 2 to 16 seconds, even more preferably 3 to 13 seconds, and even more preferably 4 to 10 seconds. After the heat treatment, the film may be cooled in a cooling zone under a relaxation of 0 to 20%, 0.5 to 15%, preferably 1 to 10%, and more preferably 1.5 to 7%. The cooling temperature in the cooling step is preferably higher than the glass transition temperature (Tg) of the polyester constituting the film, more specifically, preferably in the range of 100 to 160°C. This cooling may be performed in two or more steps at different temperatures. In the stretching, a method of stretching in one direction in two or more stages can be adopted, in which case it is preferable to perform the stretching so that the final stretching ratios in both directions are within the above ranges.

[0111] The film can also be produced by simultaneous biaxial stretching, which involves simultaneously stretching and orienting the unstretched sheet in the machine direction (longitudinal direction) and width direction (transverse direction) under temperature control, typically at 70 to 120°C, and preferably at 80 to 110°C, with the area stretch ratio being preferably 4 to 50 times, more preferably 7 to 35 times, and even more preferably 10 to 25 times. Subsequently, the film is subjected to a heat treatment under tension or relaxation of 30% or less at a temperature of typically 170 to 250°C to obtain a stretched and oriented film. Regarding the simultaneous biaxial stretching device employing the above-mentioned stretching method, any conventionally known stretching method such as a screw method, a pantograph method, or a linear drive method can be employed.

[0112] In the manufacturing method of the present film, the temperature in the primary stretching (longitudinal stretching), the temperature in the heat setting process, the peripheral speed of the roll, and the relaxation rate are adjusted as main conditions, thereby making it possible to control the elastic deformation power (η it ) and the heat shrinkage rate after heat treatment can be easily controlled within a desired range. That is, the temperature in the primary stretching (longitudinal stretching) during the polyester film manufacturing process, the temperature in the heat setting process, the peripheral speed of the stretching roll, etc. it ) are the main factors that control the elastic deformation power (η it ) can be improved, but the shrinkage rate after heat treatment tends to worsen. Therefore, by further adjusting, for example, the relaxation rate, etc., a high elastic deformation power (η itIt becomes easy to produce a polyester film that can achieve both excellent heat distortion resistance and high elastic deformation power (η it ) and the heat shrinkage rate after heat treatment can be easily controlled within a desired range.

[0113] The manufacturing method typically includes a step of winding a cylindrical or cylindrical core into a roll. Examples of the core include paper tubes, metal tubes, and resin tubes, with resin tubes being preferred. The inner diameter and width of the core are not particularly limited, but the inner diameter is typically within the range of 3 to 20 inches, with 4 to 8 inches being preferred. The length and width of the polyester film constituting the film roll obtained as described above are not limited to the following, but for example, a length of 10,000 m or more is preferred.

[0114] The present film may be an unstretched film (sheet) or a stretched film, but is preferably a uniaxially or biaxially stretched film, and among these, a biaxially stretched film is preferred in terms of excellent balance of mechanical properties and flatness. Note that a biaxially stretched film refers to a film in which the refractive index in the machine direction (MD) and the cross direction (TD) of the film is higher than the refractive index in the thickness direction, and is usually obtained by stretching the film in the machine direction and the cross direction.

[0115] <<Release layer>> The present film is preferably used in a form having a release layer on at least one side thereof. For example, when the surface layer A is used on the side on which the ceramic green sheet is laminated, the release layer is preferably laminated on the surface of the surface layer A.

[0116] The release layer is laminated on the polyester film directly or via another layer, such as an easy-adhesion coating layer for improving adhesion to the film, an antistatic layer, or an antiblocking layer.

[0117] The release layer is formed from a release agent composition containing a release agent. From the viewpoint of obtaining good release performance, the release agent composition preferably contains a silicone resin. Specifically, it is preferable that the release agent composition contains a type containing a curable silicone resin as a main component, a silicone type modified by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin, or a fluorosilicone resin. Among these, it is more preferable that the release layer contains a curable silicone resin.

[0118] The curable silicone resin may be any of the existing curing reaction types, such as a heat-curable type (addition type, condensation type, etc.) or an electron beam-curable type (ultraviolet curable type, etc.), or a combination of multiple types of curable silicone resins may be used. The form of application of the curable silicone resin when forming the release layer is not particularly limited, and the resin may be dissolved in an organic solvent, in the form of an aqueous emulsion, or in a solventless form.

[0119] 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, and the like.

[0120] The release layer is formed by coating the film with a release agent composition. The coating method may be 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 to a film that has already been produced outside the system.

[0121] 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.

[0122] 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.

[0123] If necessary, the heat treatment may be combined with irradiation with active energy rays such as ultraviolet rays. As the energy source for curing by irradiation with active energy rays, known devices and energy sources may be used.

[0124] The coating amount of the release layer (after drying) is usually 0.005 to 5 g / m from the viewpoint of coating properties. 2 , preferably 0.005 to 1 g / m 2 , more preferably 0.005 to 0.1 g / m 2 The coating amount (after drying) is in the range of 0.005 g / m 2 If the coating density is 5 g / m or more, the coating property and stability are good, and it is easy to obtain a uniform coating film. 2 If the thickness is less than this, the coating adhesion, curing properties, etc. of the release layer itself will not be reduced. The coating amount is calculated from the liquid mass per coating time (before drying), the non-volatile content of the coating liquid, the coating width, the stretching ratio, the line speed, etc.

[0125] <<Applications>> The present 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, the present film is used, for example, as a support on which various materials such as ceramic slurries are coated or laminated.

[0126] In particular, as described above, the present film is extremely excellent in that it effectively suppresses the occurrence of surface defects such as pinholes and is less likely to cause peeling problems of ceramic green sheets in the manufacturing process of multilayer ceramic capacitors, and is also less likely to cause coating spots or wrinkles when forming, for example, a release layer or ceramic green sheet, making it particularly suitable for use as a support for ceramic green sheets. That is, a preferred embodiment of the present film is its use as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors.

[0127] Furthermore, in the future, as automotive multilayer ceramic capacitors become increasingly electrified, it is predicted that the ceramic green sheets used will become thinner, particularly as the capacitors become smaller and their capacitance increases. Therefore, the present film can be particularly suitably used as a support for ceramic green sheets used in automotive multilayer ceramic capacitors. That is, a preferred embodiment of the present film is its use as a support for ceramic green sheets in the manufacturing process of automotive multilayer ceramic capacitors.

[0128] As described above, the ceramic green sheet support is used as a film for the process of applying a ceramic slurry, drying (heat treating) the ceramic slurry, solidifying it, and then peeling off the solidified ceramic slurry. Examples of the ceramic slurry include those containing ceramic components, a binder resin, and a solvent. Examples of ceramic components constituting the ceramic slurry include oxides of metals such as titanium, aluminum, barium, lead, zirconium, silicon, and yttrium, as well as barium titanate. Examples of binder resins include, but are not limited to, polyurethane resin, urea resin, melamine resin, epoxy resin, vinyl acetate resin, acrylic resin, polyvinyl alcohol, and polyvinyl butyral. Examples of solvents include, but are not limited to, water, toluene, ethanol, methyl ethyl ketone, isopropyl alcohol, and γ-butyl lactone. Plasticizers, dispersants, antistatic agents, surfactants, and the like may also be added to the ceramic slurry as needed.

[0129] <<Manufacturing methods using this film>> Examples of a method for producing a support for a ceramic green sheet using the present film include a method for producing a support for a ceramic green sheet that includes a step of forming a release layer on one side of the present film, and the step includes a step of performing heat treatment on the applied release agent composition.

[0130] Furthermore, a method for producing a ceramic green sheet using the present film includes a method for producing a ceramic green sheet that includes a step of applying a ceramic slurry containing a ceramic component to one surface of the present film. Furthermore, a method for producing a ceramic green sheet using the present film may include, in addition to the coating step, a step of drying the coated ceramic slurry, and a step of forming an electrode.

[0131] Furthermore, examples of methods for manufacturing a multilayer ceramic capacitor using the present film include a method for manufacturing a multilayer ceramic capacitor that includes a step of forming a ceramic green sheet on one side of a ceramic green sheet support having the present film and a release layer provided on one side of the film, the step including a step of heat treating the applied ceramic slurry. [Example]

[0132] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "%" and "ppm" are based on mass.

[0133] <Measurement method> First, various measurement methods in the following examples are as follows.

[0134] [Elastic deformation power (η it ) Approximately 2 to 8 mg of Aron Alpha (registered trademark) (general-purpose, manufactured by Toa Gosei Chemical Industry Co., Ltd.) was dropped onto a slide glass (S1112, manufactured by Matsunami Glass Industry Co., Ltd.). The surface layer B side of a sample film (1.5 cm x 1.5 cm) was placed on top of the drop and allowed to harden as an adhesive surface. The slide glass 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), after which a load-unload test was performed on the surface (surface layer A) of the sample film, and the elastic deformation power (η it ) was calculated (average value of 5 measurements excluding the first one out of 6 measurements). 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 / Wtotal) x 100 (%) (Measurement conditions) Indenter used: Diamond regular triangular pyramid indenter (edge ​​angle: 115) Measurement mode: Load-unload test Test force: 20.00mN Minimum test force: 0.20 mN Load speed: 0.1464mN / sec Load holding time: 0sec Unloading holding time: 0sec Measurement atmosphere: 23±2℃, 50±5%RH Number of measurements: 6

[0135] [Shrinkage rate] A sample film (1.5 cm wide x 15 cm long) was heat-treated in an untensioned state for 5 minutes in a hot air oven maintained at a specified temperature (150°C), and the length of the sample film in the longitudinal direction was measured before and after the treatment, and the shrinkage was calculated using the following formula. Measurements were made in both the machine direction (MD) and the transverse direction (TD) of the film. The shrinkage in MD was measured so that the machine direction was the MD, and the shrinkage in TD was measured so that the machine direction was the TD. Shrinkage rate (%) = {(length of sample film before heat treatment) - (length of sample film after heat treatment)} ÷ (length of sample film before heat treatment) × 100

[0136] [Planar orientation degree (ΔP)] According to JIS K 7142-1996 5.1 (Method A), the refractive index in the longitudinal direction (nx), the refractive index in the width direction (ny), and the refractive index in the thickness direction (nz) of the surface layer A of the sample film (2 cm × 1 cm) were measured using an Abbe refractometer with sodium D line as a light source, and the degree of planar orientation (ΔP) was calculated based on the following formula. ΔP=((nx+ny) / 2-nz)×1000

[0137] [Arithmetic mean height (Sa), maximum peak height (Sp), etc.] The surfaces of surface layer A and surface layer B of the sample film (5 cm × 5 cm) were measured using a surface roughness measuring device (Ametec Co., Ltd., "NewView" (registered trademark)), and the arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk) were determined from the obtained surface profile curve. Specifically, measurements were made using the surface roughness measuring instrument described above under conditions of an objective lens magnification of 10x, a zoom magnification of 2.0x, and a viewing angle of 0.44mm x 0.44mm, and the arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk) were determined after the following treatments were performed. Measurements were made 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

[0138] Next, the polyester raw materials used in the examples and comparative examples are shown in Table 1. The polyesters in polyester raw materials A to O listed in Table 1 are all homopolyethylene terephthalate. In addition, polyester raw material M is a recycled raw material obtained by collecting and recycling waste materials.

[0139] [Table 1]

[0140] [Example 1] The raw material for surface layer A was a blend of 88% Polyester A, 8% Polyester D, and 4% Polyester F by mass. The raw material for middle layer C was a blend of 50% Polyester B and 50% Polyester M by mass. The raw material for surface layer B was a blend of 28% Polyester B, 22% Polyester I, and 50% Polyester K by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-type, three-layer (A / C / B) structure with the raw materials for surface layer A and surface layer B as the outermost layer (surface layer) and the raw materials for middle layer C as the middle layer, with the thickness composition ratio of A / C / B = 4 / 19 / 2 under the extrusion conditions. The material was then 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 3.6 times in the machine direction (MD) at a film temperature of 85°C using the roll peripheral speed difference, and then this machine-stretched film was introduced into a tenter and stretched 4.2 times in the transverse direction (TD) at 120°C, followed by heat treatment (fixing) at 215°C in the tenter and cooling treatment at 125°C with a relaxation rate of 5%, to obtain a polyester film with a thickness of 25μm (A / C / B = 4μm / 19μm / 2μm). In the heat treatment (fixing) step, a temperature gradient was applied so that the final temperature was 215°C, and the heat treatment was carried out for 5.1 seconds.

[0141] [Example 2] The raw material for surface layer A was a blend of 88% Polyester A, 8% Polyester D, and 4% Polyester F by mass. The raw material for middle layer C was a blend of 50% Polyester B and 50% Polyester M by mass. The raw material for surface layer B was a blend of 28% Polyester B, 22% Polyester I, and 50% Polyester K by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-type, three-layer (A / C / B) structure with the raw materials for surface layer A and surface layer B as the outermost layer (surface layer) and the raw materials for middle layer C as the middle layer, with the thickness composition ratio of A / C / B = 4 / 25 / 2 under the extrusion conditions. The material was then 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 3.6 times in the machine direction (MD direction) at a film temperature of 85°C using the roll peripheral speed difference, and then this machine-stretched film was introduced into a tenter and stretched 4.2 times in the transverse direction (TD direction) at 120°C, and then heat-treated (fixed) at 215°C in the tenter and cooled to 125°C with a relaxation rate of 5%, obtaining a polyester film with a thickness of 31μm (A / C / B = 4μm / 25μm / 2μm). In the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature would be 215°C, and the heat treatment was carried out for 5.1 seconds.

[0142] [Example 3] The raw material for surface layer A was a blend of 84% polyester A, 12% polyester D, and 4% polyester F by mass, the raw material for middle layer C was 100% polyester C, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, they were co-extruded to form a three-type, three-layer (A / C / B) structure with the raw materials for surface layer A and surface layer B as the outermost layer (surface layer) and the raw materials for middle layer C as the middle layer, with the thickness composition ratio of A / C / B being 4 / 19 / 2 under the extrusion conditions. The film was then cooled and solidified on a cooling roll set at a surface temperature of 20 ° C and a peripheral speed of 4 m / min 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 film temperature of 86 ° C using the peripheral speed difference with the stretching roll set at a peripheral speed of 14.1 m / min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105 ° C. The film was then heat-treated (fixed) at 230 ° C. in the tenter and cooled to 140 ° C. with a relaxation rate of 2% to obtain a polyester film with a thickness of 25 μm (A / C / B = 4 μm / 19 μm / 2 μm). In the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature was 230 ° C., and the heat treatment was performed for 7.8 seconds.

[0143] [Example 4] The raw material for surface layer A was a blend of 84% polyester A, 12% polyester D, and 4% polyester F by mass, the raw material for middle layer C was 100% polyester C, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, they were co-extruded to form a three-type, three-layer (A / C / B) structure with the raw materials for surface layer A and surface layer B as the outermost layer (surface layer) and the raw materials for middle layer C as the middle layer, with the thickness composition ratio of A / C / B being 4 / 19 / 2 under the extrusion conditions. The film was then cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4m / min 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 film temperature of 82°C using the peripheral speed difference with a stretching roll set at a peripheral speed of 14.1m / min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. The film was then heat-treated (fixed) at 230°C in the tenter and cooled to 140°C with a relaxation rate of 2%, resulting in a polyester film with a thickness of 25μm (A / C / B = 4μm / 19μm / 2μm). During the heat-treatment (fixing) step, a temperature gradient was applied to achieve a final temperature of 230°C, and the heat treatment was carried out for 7.8 seconds.

[0144] [Example 5] The raw material for surface layer A was a blend of 97% polyester B and 3% polyester G by mass, the raw material for middle layer C was 100% polyester C, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-type, three-layer (A / C / B) structure with the outermost layer (surface layer) made of the raw materials for surface layer A and surface layer B and the middle layer C as the middle layer, with the thickness composition ratio of A / C / B = 4 / 19 / 2 under the extrusion conditions. Electrostatic application was performed. Using the adhesion method, the film was cooled and solidified on a cooling roll set at a surface temperature of 20 ° C. and a peripheral speed of 4.3 m / min to obtain an amorphous film. Then, using the peripheral speed difference with the stretching roll set at a peripheral speed of 15.1 m / min, the film was stretched 3.5 times in the machine direction, i.e., in the MD direction, at a film temperature of 86 ° C., and then this machine-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., and then heat-treated (fixed) at 210 ° C. in the tenter and cooled to 140 ° C. with a relaxation rate of 2%, to obtain a polyester film with a thickness of 25 μm (A / C / B = 4 μm / 19 μm / 2 μm). In the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature was 210 ° C., and the heat treatment was performed for 7.3 seconds.

[0145] [Example 6] The raw material for surface layer A was a blend of 97% polyester B and 3% polyester L by mass, the raw material for middle layer C was 100% polyester C, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-type, three-layer (A / C / B) structure with the outermost layer (surface layer) and the middle layer C as the middle layer, with the thickness composition ratio of A / C / B=4 / 19 / 2 under the extrusion conditions. The film was cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4.3 m / min using a deposition method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the peripheral speed difference with a stretching roll set at a peripheral speed of 15.1 m / min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. The film was then heat-treated (fixed) at 210°C in the tenter and cooled to 140°C with a relaxation rate of 2%, obtaining a polyester film with a thickness of 25 μm (A / C / B = 4 μm / 19 μm / 2 μm). During the heat-treatment (fixing) step, a temperature gradient was applied to achieve a final temperature of 210°C, and the heat treatment was performed for 7.3 seconds.

[0146] [Example 7] The raw material for surface layer A was a blend of 88% polyester B and 12% polyester E by mass, the raw material for middle layer C was 100% polyester B, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester I, and 50% polyester K by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-type, three-layer (A / C / B) structure with the outermost layer (surface layer) made of the raw materials for surface layer A and surface layer B and the middle layer C as the middle layer, with the thickness composition ratio under extrusion conditions being A / C / B = 4 / 19 / 2, and electrostatic application was performed. Using the adhesion method, the film was cooled and solidified on a cooling roll set at a surface temperature of 20 ° C and a peripheral speed of 4 m / min to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86 ° C using the peripheral speed difference with the stretching roll set at a peripheral speed of 14.1 m / min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105 ° C. The film was then heat-treated (fixed) at 230 ° C. in the tenter and cooled to 140 ° C. with a relaxation rate of 2% to obtain a polyester film with a thickness of 25 μm (A / C / B = 4 μm / 19 μm / 2 μm). In the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature was 230 ° C., and the heat treatment was performed for 7.8 seconds.

[0147] [Example 8] The raw material for surface layer A was a blend of 91% polyester B and 9% polyester D by mass, the raw material for middle layer C was 100% polyester M, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester I, and 50% polyester K by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-type, three-layer (A / C / B) structure with the outermost layer (surface layer) and the middle layer C as the middle layer, with the thickness composition ratio of A / C / B = 8 / 15 / 2 under the extrusion conditions. The density of the surface layer was measured under electrostatic application. The film was cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 5.1 m / min using a deposition method to obtain an amorphous film. The film was then stretched 3.8 times in the machine direction (MD) at a film temperature of 86°C using the peripheral speed difference with a stretching roll set at a peripheral speed of 18.5 m / min. The machine-stretched film was then introduced into a tenter and stretched 4.2 times in the transverse direction (TD) at 105°C. The film was then heat-treated (fixed) at 230°C in the tenter and cooled to 140°C with a relaxation rate of 5%, obtaining a polyester film with a thickness of 25 μm (A / C / B = 8 μm / 15 μm / 2 μm). During the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature reached 230°C, and the heat treatment was carried out for 5.9 seconds.

[0148] [Example 9] The raw material for surface layer A was a blend of 91% polyester B and 9% polyester D by mass, the raw material for middle layer C was 100% polyester M, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester I, and 50% polyester K by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-type, three-layer (A / C / B) structure with the outermost layer (surface layer) made of the raw materials for surface layer A and surface layer B and the middle layer C as the middle layer, with the thickness composition ratio of A / C / B = 8 / 15 / 2 under the extrusion conditions, and the materials were adhered by applying electrostatic force. Using the method, the film was cooled and solidified on a cooling roll set at a surface temperature of 20 ° C. and a peripheral speed of 5.1 m / min to obtain an amorphous film. Then, using the peripheral speed difference with the stretching roll set at a peripheral speed of 18.5 m / min, the film was stretched 3.8 times in the machine direction, i.e., in the MD direction, at a film temperature of 86 ° C., and then this machine-stretched film was introduced into a tenter and stretched 4.2 times in the transverse direction, i.e., in the TD direction, at 105 ° C., and then heat-treated (fixed) at 230 ° C. in the tenter and cooled to 140 ° C. with a relaxation rate of 17%, to obtain a polyester film with a thickness of 25 μm (A / C / B = 8 μm / 15 μm / 2 μm). In the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature was 230 ° C., and the heat treatment was performed for 5.9 seconds.

[0149] [Example 10] The raw material for surface layer A was a blend of 94% polyester B and 6% polyester D by mass, the raw material for middle layer C was a blend of 50% polyester C and 50% polyester M by mass, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C, resulting in a three-kind, three-layer (A / C / B) layer structure with the raw materials for surface layer A and surface layer B as the outermost layer (surface layer) and the raw materials for middle layer C as the middle layer, with the thickness composition ratio of A / C / B=4 / 25 / 2 under the extrusion conditions. The film was coextruded as shown above, cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4 m / min using an electrostatic contact method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the peripheral speed difference with the stretching roll set at a peripheral speed of 14.1 m / min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. The film was then heat-treated (fixed) at 230°C in the tenter and cooled to 140°C with a relaxation rate of 2%, yielding a polyester film with a thickness of 31 μm (A / C / B = 4 μm / 25 μm / 2 μm). During the heat-treatment (fixing) step, a temperature gradient was applied to achieve a final temperature of 230°C, and the heat treatment was carried out for 7.8 seconds.

[0150] [Example 11] The raw material for surface layer A was a blend of 88% polyester B and 12% polyester D by mass, the raw material for middle layer C was a blend of 50% polyester C and 50% polyester M by mass, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C, resulting in a three-type, three-layer (A / C / B) layer structure with the raw materials for surface layer A and surface layer B as the outermost layer (surface layer) and middle layer C as the middle layer, and the thickness composition ratio under the extrusion conditions was A / C / B = 4 / 25 / 2. The film was coextruded as shown above, cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4 m / min using an electrostatic contact method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the peripheral speed difference with the stretching roll set at a peripheral speed of 14.1 m / min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. The film was then heat-treated (fixed) at 230°C in the tenter and cooled to 140°C with a relaxation rate of 2%, obtaining a polyester film with a thickness of 31 μm (A / C / B = 4 μm / 25 μm / 2 μm). During the heat-treatment (fixing) step, a temperature gradient was applied to achieve a final temperature of 230°C, and the heat treatment was carried out for 7.8 seconds.

[0151] [Example 12] The raw material for surface layer A was a blend of 78% polyester B, 18% polyester D, and 4% polyester F by mass. The raw material for middle layer C was a blend of 50% polyester C and 50% polyester M by mass. The raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C. After this, the raw materials for surface layer A and surface layer B were used as the outermost layer (surface layer) and the raw materials for middle layer C were used as the middle layer, resulting in a three-type, three-layer (A / C / B) layer structure (A / C / B), with the raw materials for surface layer A and surface layer B as the outermost layer (surface layer) and the raw materials for middle layer C as the middle layer. The extrusion conditions were such that the thickness composition ratio was A / C / B=4 / 25. The film was coextruded to a thickness of 2 / 2, and cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4 m / min using an electrostatic contact method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the peripheral speed difference with the stretching roll set at a peripheral speed of 14.1 m / min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. The film was then heat-treated (set) at 230°C in the tenter and cooled to 140°C with a relaxation rate of 2%, resulting in a polyester film with a thickness of 31 μm (A / C / B = 4 μm / 25 μm / 2 μm). During the heat-treatment (set) step, a temperature gradient was applied to achieve a final temperature of 230°C, and the heat treatment was performed for 7.8 seconds.

[0152] [Example 13] The raw material for surface layer A was a blend of 93% polyester B, 4% polyester F, and 3% polyester G by mass, the raw material for middle layer C was a blend of 50% polyester C and 50% polyester M by mass, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C, resulting in a three-type, three-layer (A / C / B) layer structure with the raw materials for surface layer A and surface layer B as the outermost layer (surface layer) and the raw materials for middle layer C as the middle layer, with the thickness composition ratio under the extrusion conditions being A / C / B=4 / 25 / The film was co-extruded to a thickness of 2 μm (A / C / B = 4 μm / 25 μm / 2 μm), and cooled and solidified on a cooling roll set at a surface temperature of 20 ° C and a peripheral speed of 4 m / min 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 film temperature of 86 ° C using the peripheral speed difference with the stretching roll set at a peripheral speed of 14.1 m / min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105 ° C. The film was then heat-treated (fixed) at 230 ° C. and cooled to 140 ° C. with a relaxation rate of 2% to obtain a polyester film with a thickness of 31 μm (A / C / B = 4 μm / 25 μm / 2 μm). In the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature was 230 ° C., and the heat treatment was performed for 7.8 seconds.

[0153] [Example 14] The raw material for surface layer A was a blend of 90% polyester B and 10% polyester O by mass, the raw material for middle layer C was 100% polyester C, and the raw material for surface layer B was a blend of 70% polyester B and 30% polyester G by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-type, three-layer (A / C / B) structure with the outermost layer (surface layer) made of the raw materials for surface layer A and surface layer B and the middle layer C as the middle layer, with the thickness composition ratio under extrusion conditions being A / C / B = 1.55 / 27.9 / 1.55, and the resulting material was then adhered to the surface using an electrostatic application adhesion method. The film was cooled and solidified on a cooling roll with a surface temperature of 20 ° C and a peripheral speed of 5.8 m / min to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86 ° C using the peripheral speed difference with the stretching roll (20.3 m / min). The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105 ° C. The film was then heat-treated (fixed) at 230 ° C. and cooled to 140 ° C. with a relaxation rate of 2% to obtain a polyester film with a thickness of 31 μm (A / C / B = 1.55 μm / 27.9 μm / 1.55 μm). During the heat treatment (fixing) step, a temperature gradient was applied to achieve a final temperature of 230 ° C., and the film was heat-treated for 5.4 seconds.

[0154] [Comparative Example 1] The raw material for surface layer A was a blend of 97% polyester B and 3% polyester G by mass, the raw material for middle layer C was 100% polyester C, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-type, three-layer (A / C / B) structure with the outermost layer (surface layer) and the middle layer C as the middle layer, with the thickness composition ratio of A / C / B=4 / 19 / 2 under the extrusion conditions. The density of the surface layer was measured by applying electrostatic pressure. The film was cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4.3 m / min using a deposition method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the peripheral speed difference with a stretching roll set at a peripheral speed of 15.1 m / min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. The film was then heat-treated (fixed) at 230°C in the tenter and cooled to 140°C with a relaxation rate of 2%, obtaining a polyester film with a thickness of 25 μm (A / C / B = 4 μm / 19 μm / 2 μm). During the heat-treatment (fixing) step, a temperature gradient was applied to achieve a final temperature of 230°C, and the heat treatment was carried out for 7.3 seconds.

[0155] Comparative Example 2 The raw material for surface layer A was a blend of 97% polyester B and 3% polyester L by mass, the raw material for middle layer C was 100% polyester C, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-type, three-layer (A / C / B) structure with the outermost layer (surface layer) and the middle layer C as the middle layer, with the thickness composition ratio of A / C / B=4 / 19 / 2 under the extrusion conditions. The film was cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4.3 m / min using a deposition method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the peripheral speed difference with a stretching roll set at a peripheral speed of 15.1 m / min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. The film was then heat-treated (fixed) at 230°C in the tenter and cooled to 140°C with a relaxation rate of 2%, obtaining a polyester film with a thickness of 25 μm (A / C / B = 4 μm / 19 μm / 2 μm). During the heat-treatment (fixing) step, a temperature gradient was applied to achieve a final temperature of 230°C, and the heat treatment was carried out for 7.3 seconds.

[0156] Comparative Example 3 The raw material for surface layer A was a blend of 90% polyester B, 4% polyester F, and 6% polyester L by mass, the raw material for middle layer C was 100% polyester C, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-type, three-layer (A / C / B) layer structure with the raw materials for surface layer A and surface layer B as the outermost layer (surface layer) and the raw materials for middle layer C as the middle layer, with the thickness composition ratio being A / C / B = 4 / 19 / 2 under the extrusion conditions. Using the electrostatic adhesion method, the film was cooled and solidified on a cooling roll set at a surface temperature of 20 ° C and a peripheral speed of 4.3 m / min to obtain an amorphous film. Then, using the peripheral speed difference with the stretching roll set at a peripheral speed of 15.1 m / min, the film was stretched 3.5 times in the machine direction, i.e., in the MD direction, at a film temperature of 86 ° C., and then this machine-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., and then heat-treated (fixed) at 243 ° C. in the tenter and cooled to 140 ° C. with a relaxation rate of 2%, to obtain a polyester film with a thickness of 25 μm (A / C / B = 4 μm / 19 μm / 2 μm). In the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature was 243 ° C., and the heat treatment was performed for 7.3 seconds.

[0157] Comparative Example 4 The raw material for surface layer A was a blend of 88% polyester B and 12% polyester E by mass, the raw material for middle layer C was 100% polyester B, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester I, and 50% polyester K by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-type, three-layer (A / C / B) structure with the outermost layer (surface layer) made of the raw materials for surface layer A and surface layer B and the middle layer C as the middle layer, with the thickness composition ratio under extrusion conditions being A / C / B = 4 / 19 / 2, and electrostatic application was performed. Using the adhesion method, the film was cooled and solidified on a cooling roll set at a surface temperature of 20 ° C and a peripheral speed of 4 m / min to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86 ° C using the peripheral speed difference with the stretching roll set at a peripheral speed of 14.1 m / min. The machine-stretched film was then introduced into a tenter and stretched 4.2 times in the transverse direction (TD) at 105 ° C. The film was then heat-treated (fixed) at 230 ° C. in the tenter and cooled to 140 ° C. with a relaxation rate of 2% to obtain a polyester film with a thickness of 25 μm (A / C / B = 4 μm / 19 μm / 2 μm). In the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature was 230 ° C., and the heat treatment was performed for 7.8 seconds.

[0158] Comparative Example 5 The raw material for surface layer A was a blend of 87% polyester B and 13% polyester F by mass, the raw material for middle layer C was a blend of 50% polyester C and 50% polyester M by mass, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C, resulting in a three-kind, three-layer (A / C / B) layer structure with the raw materials for surface layer A and surface layer B as the outermost layer (surface layer) and the raw materials for middle layer C as the middle layer, with the extrusion conditions being such that the thickness composition ratio was A / C / B = 4 / 25 / 2. The film was coextruded as shown above, cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4.3 m / min using an electrostatic contact method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the peripheral speed difference with a stretching roll set at a peripheral speed of 15.1 m / min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. The film was then heat-treated (fixed) at 230°C in the tenter and cooled to 140°C with a relaxation rate of 2%, yielding a polyester film with a thickness of 31 μm (A / C / B = 4 μm / 25 μm / 2 μm). During the heat-treatment (fixing) step, a temperature gradient was applied to achieve a final temperature of 230°C, and the heat treatment was carried out for 7.3 seconds.

[0159] Comparative Example 6 A raw material for the surface layer A was a blend of 70% polyester C and 30% polyester N by mass, a raw material for the middle layer C was a blend of 45% polyester C and 55% polyester M by mass, and a raw material for the surface layer B was a blend of 70% polyester C and 30% polyester N by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for the surface layer A and the surface layer B were co-extruded to form a three-type, three-layer (A / C / B) layer structure with the raw materials for the surface layer A and the surface layer B as the outermost layer (surface layer) and the middle layer C as the middle layer, with the thickness composition ratio under the extrusion conditions being A / C / B = 1 / 23 / 1. Using the electrostatic adhesion method, the film was cooled and solidified on a cooling roll set at a surface temperature of 20 ° C and a peripheral speed of 5.1 m / min to obtain an amorphous film. Then, using the peripheral speed difference with the stretching roll set at a peripheral speed of 17.7 m / min, the film was stretched 3.47 times in the machine direction, i.e., in the MD direction, at a film temperature of 85 ° C., and then this machine-stretched film was introduced into a tenter and stretched 4.2 times in the transverse direction, i.e., in the TD direction, at 120 ° C., and then heat-treated (fixed) at 219 ° C. in the tenter and cooled to 125 ° C. with a relaxation rate of 5%, to obtain a polyester film with a thickness of 25 μm (A / C / B = 1 μm / 23 μm / 1 μm). In the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature was 219 ° C., and the heat treatment was performed for 5.3 seconds.

[0160] The various properties of each of the films obtained above were measured according to the methods described above, and the results are shown in Tables 2 and 3 (Examples 1 to 14) and Table 4 (Comparative Examples 1 to 6).

[0161] [Table 2]

[0162] [Table 3]

[0163] [Table 4]

[0164] First, as shown in Tables 2 and 3, the polyester films of Examples 1 to 14 were specific polyester films obtained by adjusting the particle composition, average particle size, particle size distribution, hardness, affinity with polyester, type of polyester, film-forming conditions, etc., and the elastic deformation power (η it ), as well as the arithmetic mean height (Sa) and the maximum peak height (Sp) are controlled within specific ranges. Specifically, the polyester films of Examples 1 to 14 have the elastic deformation power (η it ) is more than 55%, the arithmetic mean height (Sa) is 15 nm or less, and the maximum peak height (Sp) is 150 nm or less. Therefore, it can be seen that when the polyester films of Examples 1 to 14 are used, for example, as a support for a ceramic green sheet used in the manufacturing process of a multilayer ceramic capacitor, they can effectively suppress the occurrence of pinholes and the like in the ceramic green sheet and can also effectively suppress peeling problems of the ceramic green sheet.

[0165] On the other hand, as shown in the table, in Comparative Examples 1 to 6, the elastic deformation power (η it ), and at least one of the arithmetic mean height (Sa) and the maximum peak height (Sp) is not controlled within a specific range. Specifically, the polyester films of Comparative Examples 1 to 5 have a low elastic deformation power (η it ) is low, the peelability of the ceramic green sheet is unsatisfactory. In addition, the polyester film of Comparative Example 6 has a large maximum peak height (Sp), and the surface smoothness is unsatisfactory.

[0166] It should be noted that, from the results shown in the Examples and Comparative Examples, it can be seen that, for example, when an attempt is made to suppress the occurrence of poor peeling in the process of peeling a ceramic green sheet from a release film, surface defects such as pinholes tend to occur, and the elastic deformation power (η it It is suggested that the surface smoothness and the surface roughness are contradictory properties, but the technical value of the present invention is very high in that it can achieve both of these contradictory properties. That is, for example, from the results of Comparative Example 6, when the content of particles contained in the surface layer A is large, the elastic deformation power (η it ) can be improved to a sufficient degree, but the maximum peak height (Sp) is high, suggesting a tendency for the surface smoothness to be insufficient. On the other hand, from the results of Comparative Examples 1 to 5, when the content of particles contained in the surface layer A is small, the surface smoothness is in a good range, but the elastic deformation power (η it ) tends to be insufficient. it Comparison between these comparative examples and examples shows that adjustment of the heat setting temperature and transverse draw ratio, as well as selection of particle type and content, are also effective in adjusting the film thickness. In this way, in the polyester film containing particles, the elastic deformation power (η it The present invention is of great technical value in that it can provide a polyester film that can satisfy both of these contradictory properties. [Industrial Applicability]

[0167] According to the present invention, it is possible to provide a polyester film that can suppress the occurrence of peeling defects in the step of peeling a ceramic green sheet from a release film and can also suppress the occurrence of surface defects such as pinholes. Therefore, the polyester film can be suitably used, for example, as a support for a ceramic green sheet used in the manufacturing process of a multilayer ceramic capacitor.

Claims

1. A polyester film containing particles, having an elastic deformation power of more than 55% on one surface, and satisfying the following (1) and (2): (1) The arithmetic mean height (Sa) is 15 nm or less. (2) The maximum peak height (Sp) is 150 nm or less.

2. 2. The polyester film according to claim 1, which has a shrinkage rate of 2.8% or less in the longitudinal and transverse directions after heat treatment at 150°C for 5 minutes.

3. 3. The polyester film according to claim 1, which has a shrinkage rate in the transverse direction of 1.5% or less after heat treatment at 150°C for 5 minutes.

4. 3. The polyester film according to claim 1, wherein the content of the particles is 250 ppm to 10,000 ppm by mass relative to the layer in which the particles are contained.

5. 3. The polyester film according to claim 1, wherein the particles have an average particle size of 1 μm or less.

6. 3. The polyester film according to claim 1, wherein the particles have a Mohs hardness of 9 or less.

7. 3. The polyester film according to claim 1, wherein the particles include at least particles (a1) and particles (a2), the particles (a1) being alumina particles, and the particles (a2) being particles other than the particles (a1).

8. 3. The polyester film according to claim 1, wherein the layer forming one surface contains particles, the particles including at least particles (a1) and particles (a2), and the zeta potentials of the particles (a1) and (a2) at pH 7 are either positive for the particles (a1) and negative for the particles (a2), or negative for the particles (a1) and positive for the particles (a2).

9. 9. The polyester film according to claim 8, wherein the content of the particles having a positive zeta potential at pH 7 is 50 ppm to 5,000 ppm by mass relative to the layer forming the one surface.

10. 9. The polyester film according to claim 8, wherein the content of the particles having a negative zeta potential at pH 7 is 100 ppm to 8000 ppm by mass relative to the layer forming the one surface.

11. 9. The polyester film according to claim 8, wherein the particles having a positive zeta potential at pH 7 are alumina particles.

12. 9. The polyester film according to claim 8, wherein the particles having a negative zeta potential at pH 7 are silica or organic particles.

13. 3. The polyester film according to claim 1, wherein the layer forming one surface contains particles, and the ratio of the content of particles having a Mohs hardness of 8 or less to the content of all particles contained in the layer forming the one surface (content of particles having a Mohs hardness of 8 or less / content of all particles) is 0.6 to 0.95, in mass ratio.

14. 3. The polyester film according to claim 1, wherein the layer forming one surface contains particles, the particles mainly comprising particles having a Mohs hardness of 8 or less, and the content of the particles having a Mohs hardness of 8 or less relative to the layer forming the one surface is less than 1,800 ppm by mass.

15. 3. The polyester film according to claim 1, wherein the maximum peak height (Sp) of the (2) is 100 nm or less.

16. 3. The polyester film according to claim 1, having a planar orientation degree (ΔP) of 165 or more.

17. 3. The polyester film according to claim 1, wherein the ratio of the arithmetic mean height (Sa) of one surface to the arithmetic mean height (Sa) of the other surface (arithmetic mean height (Sa) of the other surface / arithmetic mean height (Sa) of the one surface) is 2 or more and 18 or less, provided that the arithmetic mean height (Sa) of the other surface is greater than the arithmetic mean height (Sa) of the one surface.

18. 3. The polyester film according to claim 1, which consists of at least two layers.

19. 3. The polyester film according to claim 1, which consists of three layers.

20. 19. The polyester film according to claim 18, wherein the content of the particles in one surface layer is 250 ppm to 2800 ppm by mass.

21. The polyester film according to claim 20, wherein the content of the particles in the other surface layer is 2000 ppm to 8000 ppm by mass.

22. 3. The polyester film according to claim 1, wherein the polyester film comprises a surface layer forming the one surface, an intermediate layer, and a surface layer forming the other surface, in that order, and the thickness of the intermediate layer is greater than the thickness of each of the surface layers.

23. 3. The polyester film according to claim 1, wherein the polyester film comprises a surface layer forming the one surface, an intermediate layer, and a surface layer forming the other surface, in this order, and the thickness ratio of the layers (thickness of the surface layer:thickness of the intermediate layer:thickness of the surface layer) is 1-10:10-35:1-5.

24. 3. The 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.

25. 3. The polyester film according to claim 1, which is used as a support for ceramic green sheets in the production process of multilayer ceramic capacitors for automobiles.

26. 3. Use of the polyester film according to claim 1 or 2 as a support for ceramic green sheets in the process of producing a multilayer ceramic capacitor.

27. 3. Use of the polyester film according to claim 1 or 2 as a support for ceramic green sheets in the process of producing multilayer ceramic capacitors for automobiles.

28. 3. A method for producing a ceramic green sheet, comprising the step of applying a ceramic slurry containing a ceramic component to the one surface of the polyester film according to claim 1.

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