Polyester film

Abstract

The present invention provides a polyester film which is capable of improving releasability in a step for separating a ceramic green sheet from a release film, and which is also capable of suppressing the occurrence of surface defects such as pinholes.　This polyester film contains particles, has an elastic deformation power of more than 55% on one surface, and satisfies the requirements (1) and (2) described below.　(1) The arithmetic mean height (Sa) is 15 nm or less.　(2) The maximum peak height (Sp) is 150 nm or less.

Description

Polyester film

[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.

[0002] Polyester films, such as polyethylene terephthalate films and polyethylene naphthalate films, have excellent mechanical properties, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, and other characteristics, and are cost-effective. Therefore, they are used in a variety of applications. For example, by taking advantage of the smoothness of their film surfaces, they are used as substrates for release of interlayer insulating resins, substrates for dry film resists, and release films for forming ceramic green sheets for multi-layered ceramic capacitors (MLCCs).

[0003] In the manufacturing process of a multilayer ceramic capacitor, a release agent or the like is first applied to a polyester film and dried to create a release film with a release layer. A ceramic slurry containing ceramic components such as barium titanate and a binder resin is then applied to the release film and dried. After that, electrodes are printed and dried by a method such as screen printing to create a ceramic green sheet with printed electrodes. The resulting ceramic green sheet is then cut into a predetermined shape and peeled from the release film. A large number of the peeled ceramic green sheets are stacked and integrated, and 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 production of ceramic green sheets, which comprises a release agent layer provided on one side of a polyester substrate, and which contains a filler such as hydroxyapatite on the release agent layer side of the substrate, and which 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 which has 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.

[0006] Japanese Patent Application Laid-Open No. 2022-144248

[0007] As ceramic green sheets become thinner in the future, it is expected that there will be an even greater concern about the occurrence of surface defects such as pinholes, and that there will also be an even greater concern about peeling defects such as breakage during the process of peeling the ceramic green sheet from the release film. Therefore, it is necessary to improve the releasability of the release film and to suppress the occurrence of surface defects. However, as a result of extensive research by the present inventors, it has been found that, from the viewpoint of making it easier to peel the ceramic green sheet from the release film, it is conceivable to incorporate a predetermined filler (particles) into the release film. However, improving the releasability in this manner tends to cause surface defects such as pinholes due to the filler (particles), and it has become clear that it is difficult to achieve both of these at a high level.

[0008] One embodiment of the present invention has been made in consideration of the above circumstances, and provides a polyester film that can improve releasability in the step 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 as one embodiment. [I-1] A polyester film having an elastic deformation power of more than 55% on one surface and satisfying the following (1) and (2): (1) an arithmetic mean height (Sa) of 15 nm or less; (2) a maximum peak height (Sp) of 150 nm or less; [I-2] The polyester film according to [I-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; [I-3] The polyester film according to [I-1] or [I-2], which has a shrinkage rate of 1.5% or less in the transverse direction after heat treatment at 150°C for 5 minutes; [I-4] The polyester film according to any one of [I-1] to [I-3], which contains particles, and whose particle content is 250 ppm or more and 10,000 ppm or less by mass relative to the layer in which the particles are contained. [I-5] The polyester film according to any one of [I-1] to [I-4], which contains particles, and the average particle size of the particles is 1 μm or less. [I-6] The polyester film according to any one of [I-1] to [I-5], which contains particles, and the Mohs hardness of the particles is 9 or less. [I-7] The polyester film according to any one of [I-1] to [I-6], which contains particles, and 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). [I-8] The polyester film according to any one of [I-1] to [I-7], wherein the layer forming one surface contains particles, the particles including at least particles (a1) and (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). [I-9] The polyester film according to [I-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 one surface. [I-10] The polyester film according to [I-8] or [I-9], wherein the content of the particles having a negative zeta potential at pH 7 is 100 ppm to 8,000 ppm by mass relative to the layer forming one surface.[I-11] The polyester film according to any one of [I-8] to [I-10], wherein the particles having a positive zeta potential at pH 7 are alumina particles. [I-12] The polyester film according to any one of [I-8] to [I-11], wherein the particles having a negative zeta potential at pH 7 are silica or organic particles. [I-13] The polyester film according to any one of [I-1] to [I-12], 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 total content of particles contained in the layer forming the one surface (content of particles having a Mohs hardness of 8 or less / total content of particles) is 0.6 to 0.95 by mass. [I-14] The polyester film according to any one of [I-1] to [I-13], wherein the layer forming the one surface contains particles, the particles are mainly composed of particles having a Mohs hardness of 8 or less, and the content of the particles having a Mohs hardness of 8 or less is less than 1,800 ppm by mass relative to the layer forming the one surface. [I-15] The polyester film according to any one of [I-1] to [I-14], wherein the maximum peak height (Sp) of (2) is 100 nm or less. [I-16] The polyester film according to any one of [I-1] to [I-15], wherein the planar orientation (ΔP) is 165 or more. [I-17] The polyester film according to any one of [I-1] to [I-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 > the arithmetic mean height (Sa) of the one surface). [I-18] The polyester film according to any one of [I-1] to [I-17], wherein the polyester film consists of at least two layers. [I-19] The polyester film according to any one of [I-1] to [I-18], wherein the polyester film consists of three layers. [I-20] The polyester film according to [I-18] or [I-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.[I-21] The polyester film according to [I-20], which contains particles, and the content of the particles is 2000 ppm to 8000 ppm by mass relative to the other surface layer. [I-22] The polyester film according to any one of [I-1] to [I-21], which comprises a surface layer forming 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 any one of the surface layers. [I-23] The polyester film according to any one of [I-1] to [I-22], which comprises a surface layer forming 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 to 10:10 to 35:1 to 5. [I-24] The polyester film according to any one of [I-1] to [I-23], which is used as a support for a ceramic green sheet in the production process of a multilayer ceramic capacitor. [I-25] The polyester film according to any one of [I-1] to [I-24], which is used as a support for a ceramic green sheet in the production process of an automotive multilayer ceramic capacitor. [I-26] Use of the polyester film according to any one of [I-1] to [I-25], as a support for a ceramic green sheet in the production process of a multilayer ceramic capacitor. [I-27] Use of the polyester film according to any one of [I-1] to [I-25], as a support for a ceramic green sheet in the production process of an automotive multilayer ceramic capacitor. [I-28] A method for producing a ceramic green sheet, comprising a step of applying a ceramic slurry containing a ceramic component to one surface of the polyester film according to any one of [I-1] to [I-25].

[0011] According to one embodiment of 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.

[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, the expression "X to Y" (X and Y are arbitrary numbers) means "X or greater and Y or less," unless otherwise specified, and also includes the meanings of "preferably greater than X" or "preferably smaller than Y." Regarding numerical ranges described in stages in this specification, the upper or lower limit of a numerical range in one stage can be arbitrarily combined with the upper or lower limit of a numerical range in another stage. Furthermore, in this specification, "X and / or Y (X and Y are arbitrary components)" means at least one of X and Y, and can refer to three possibilities: X only, Y only, or X and Y. In this specification, the term "film" also includes "sheet," and the term "sheet" also includes "film." In this specification, the term "main component" typically 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 also refer to 80% by mass or more or 90 to 100% by mass.

[0013] First Embodiment A first embodiment, which is an example of an embodiment of the present invention, will be described below, although the present invention is not limited to the embodiment described below.

[0014] As will be described in detail below, a polyester film according to a first embodiment of the present invention (hereinafter sometimes referred to as "film I") is a polyester film having an elastic deformation power of more than 55% on one surface and satisfying the following requirements (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.

[0015] The present inventors conducted research and development into a ceramic green sheet support that can accommodate further thinning of ceramic green sheets (e.g., 0.5 μm or less after drying) in response to the trend toward smaller and higher-capacity multilayer ceramic capacitors. The inventors focused on preventing peeling defects during the peeling process of ceramic green sheets. During this research, the inventors discovered that, for example, when particles are incorporated into a polyester film, controlling the properties of the particles can prevent peeling defects. However, they also discovered that this approach tends to result in surface defects such as pinholes. Such surface defects significantly affect quality and reliability, resulting in short circuits, capacitance variations, and other problems.

[0016] The present inventors have conducted further research with a view to solving both 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, suppress the occurrence of poor release, and also suppress the occurrence of surface defects such as pinholes.

[0017] The present invention proposes a new film I that has a specific elastic deformation power (η it ) and a specific surface smoothness, and for example, it has a high restoring force against deformation that occurs when the ceramic green sheet is cut, and it has excellent releasability of the ceramic green sheet, and it can effectively suppress the occurrence of surface defects such as pinholes, and is extremely excellent in that it can provide a release film or the like that can ensure high quality reliability. One embodiment of this film I will be described in detail below.

[0018] <<Present Film I>> Present Film I is suitable for use, for example, as a support (substrate) for ceramic green sheets in the production process of multilayer ceramic capacitors. As described above, Present Film I is extremely excellent in that it can suppress the occurrence of surface defects such as pinholes and the occurrence of peeling defects.

[0019] [Elastic deformation power (η it From the viewpoint of effectively suppressing the above-mentioned peeling failure, the present film I has an elastic deformation power (η it ) is preferably more than 55%. it By controlling the elastic deformation power (η ) to a specific range of more than 55%, it is possible to realize a high level of peelability, which is particularly required in the manufacturing process of MLCC using thin ceramic green sheets, and to effectively suppress peel failure. 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. it The upper limit of the ratio is not particularly limited, but may be, for example, about 70%, or about 65%.

[0020] Elastic deformation power of surface A (η it By using the present film I 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 I, and a good gap can be formed between the two. The present film I can be gripped using this gap, making it easy to separate the ceramic green sheet from the present film I.

[0021] Elastic deformation power (η itThe elastic deformation power (η) is calculated by the following formula based on physical quantities measured by nanoindentation (in accordance with ISO 14577). Specifically, it is determined by the method described in the Examples below. it ) = (Welast / Wtotal) × 100 [%] [Wtotal (total deformation work) = Wplast (plastic deformation work) + Welast (elastic deformation work)]

[0022] [Arithmetic mean height (Sa)] In the present film I, for example, the arithmetic mean height (Sa) of one surface, side A, is preferably 15 nm or less. 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, particularly 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 less than 0.3 nm, the film surface becomes extremely flat, the slipperiness of the film decreases, and processability tends to be impaired.

[0023] In order to prevent the roughness of one surface from being transferred to the other surface when the present film I 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 deterioration in transportability or windability due to a decrease in the slipperiness of the film.

[0024] The ratio of the arithmetic mean height (Sa) of side A to that of side B of this film I ("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 even more preferably 14 or less. The ratio (SaB / SaA) can be set appropriately within the above range and is not limited to the following, and 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.

[0025] 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 surface at height 0 of the image point (x, y), it can be expressed as in the following formula (1). More specifically, it can be measured by the method described in the examples below.

[0026]

[0027] [Maximum Peak Height (Sp)] The maximum peak height (Sp) of side A, one of the surfaces of the present film I, is preferably 150 nm or less. If the maximum peak height (Sp) is greater than 150 nm, the surface smoothness will be insufficient, and surface defects such as pinholes will be more likely to occur, making it difficult to achieve 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, and may be, for example, 65 nm or less, 60 nm or less, 40 nm or less, or 30 nm or less.

[0028] The maximum peak height (Sp) of side B, the other surface of this film I, 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 30 nm or more, more preferably 50 nm or more, from the viewpoint of preventing a decrease in transportability or windability due to a decrease in the slipperiness of the film.

[0029] The ratio of the maximum peak heights (Sp) of sides A and B of this film I ("maximum peak height (Sp) of side B (Sp) / 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, still 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.

[0030] 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 formula [Equation 2]. More specifically, it can be measured by the method described in the examples below.

[0031]

[0032] [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 I, 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, which is the other surface of the present film I, 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.

[0033] [Root-mean-square height (Sq)] The root-mean-square height (Sq) of side A, one surface of the present film I, 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 preferably, for example, 0.1 nm or more, more preferably 0.3 nm or more. Furthermore, the root-mean-square height (Sq) of side B, the other surface of the present film I, 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.

[0034] From the viewpoint of achieving a high degree of both surface smoothness and slip resistance, the ratio of the root mean square height (Sq) of side A to the root mean square height (Sq) of side B of this film I ("root mean square height (Sq) of side B / root mean square height (Sq) of side A"; hereinafter, this may be referred to as "SqB / SqA") is preferably 7 or more, more preferably 8 or more, and even more preferably 9 or more. On the other hand, SqB / SqA is preferably 20 or less, more preferably 18 or less, and even more preferably 17 or less.

[0035] 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.

[0036]

[0037] [Kurtosis (Sku)] The kurtosis (Sku) of side A, which is one surface of the present film I, 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.

[0038] The kurtosis (Sku) of side B, the other surface of the present film I, 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.

[0039] Kurtosis (Sku) is one of the surface roughness parameters (ISO 25178) and can be used to evaluate the peakiness (kurtosis) of a histogram of height distribution, and can be calculated using the following formula: [Equation 4]. More specifically, it can be measured by the method described in the Examples below.

[0040]

[0041] [Skewness (Ssk)] The skewness (Ssk) of side A, which is one surface of the present film I, 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.

[0042] The skewness (Ssk) of side B, the other surface of the present film I, 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.

[0043] Skewness (Ssk) is one of the surface roughness parameters (ISO 25178) and can be determined by the following formula: [Equation 5]. More specifically, it can be measured by the method described in the examples below.

[0044]

[0045] 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. Furthermore, 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) and surface properties. When two or more types of particles are used in combination, it is preferable to adjust the content ratio in consideration of the type of particles and polyester used. In addition, during polyester film production, it is also effective to control, for example, the stretching ratio (longitudinal and transverse stretching ratio in the case of biaxial stretching), the stretching temperature, the heat treatment temperature and treatment time (particularly the heat treatment temperature and treatment time after transverse stretching in the case of biaxial stretching). In addition, the same methods as above are also suitable for adjusting other surface properties (root mean square height (Sq), kurtosis (Sku), skewness (Ssk)).

[0046] [Shrinkage after Heat Treatment] The manufacturing process of multilayer ceramic capacitors includes heat treatments, such as drying a release agent coated on a polyester film and drying a ceramic slurry coated on a release film. Therefore, a decrease in heat distortion resistance can lead to coating irregularities and wrinkles. In other words, heat distortion resistance is an important characteristic for ensuring the quality and reliability of the finished product, from intermediate products to finished products in the manufacturing process of multilayer ceramic capacitors, such as the lamination characteristics of ceramic green sheets. To prevent such coating irregularities and wrinkles, the shrinkage of this film I in the machine direction (MD) after heat treatment at 150°C for 5 minutes is preferably 2.8% or less. From the same perspective, the shrinkage 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, and more preferably −0.3% or more.

[0047] Furthermore, the shrinkage percentage in the transverse direction (TD) of this film I 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 percentage in the transverse direction (TD) is about -1%, preferably -0.5% or more, more preferably -0.3% or more. From the viewpoint of realizing a high level of heat distortion resistance that is particularly required in the manufacturing process of MLCCs using thin ceramic green sheets, the shrinkage percentage in the transverse direction (TD) (150°C, 5 minutes) is preferably 1.4% or less, more preferably 1.3% or less. 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.

[0048] 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.

[0049] [Planar orientation degree (ΔP)] In order to suppress the aforementioned peeling defects, the present film I 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.

[0050] The degree of planar orientation (ΔP) is calculated based on the following formula, using JIS K 7142-1996 5.1 (Method A) by measuring the refractive index in the longitudinal direction (nx), the refractive index in the transverse direction (ny), and the refractive index in the thickness direction (nz) with an Abbe refractometer using sodium D line as a light source: degree of planar orientation (ΔP) = ((nx + ny) / 2 - nz) × 1000

[0051] Next, the raw materials and the like used in the embodiment of the present film I will be described.

[0052] <Polyester> Polyester is a raw material of the present film I and refers to a polymer compound having continuous ester bonds in the main chain. The polyester used in the present film I may be a homopolyester or a copolymer polyester. Specific examples include polyesters obtained by polycondensation reaction of a dicarboxylic acid component and a diol component.

[0053] In the present film I, 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 %.

[0054] 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.

[0055] 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.

[0056] When the polyester is a homopolyester, it is preferably one obtained by polycondensation of 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).

[0057] On the other hand, when the polyester is a copolymer polyester, it is preferably a copolymer containing 30 mol% or less of a third component. The third component is a component other than the compound that constitutes the main dicarboxylic acid component constituting the polyester (i.e., the dicarboxylic acid component with the highest content) and the compound that constitutes the main diol component (i.e., the diol component with the highest 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, and neopentyl glycol.

[0058] 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.

[0059] Typically, when polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, diethylene glycol is by-produced from the ethylene glycol. In this specification, this diethylene glycol is referred to as by-product diethylene glycol. The amount of diethylene glycol by-produced from ethylene glycol varies depending on the polycondensation method, 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.

[0060] [Polycondensation catalyst] Examples of polycondensation catalysts used in polycondensing the polyester include antimony compounds, germanium compounds, aluminum compounds, and titanium compounds. Among these, antimony compounds and titanium compounds are preferred, and titanium compounds are particularly preferred. By using the titanium compounds, the number of metal-containing aggregates derived from the titanium compounds, so-called coarse foreign matter, in the film can be reduced, and the surface smoothness can be improved.

[0061] More specifically, it is preferable that the polyester constituting the outermost layer (also referred to as the "surface layer"; for example, the surface layer onto which a release layer is laminated) of the present film I 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, catalyst-induced foreign matter can be reduced without reducing the polyester production efficiency. From the same viewpoint, it is preferable that the content of antimony compounds in the outermost layer of the present film I is 100 ppm or less.

[0062] [Intrinsic Viscosity of Polyester] The intrinsic viscosity of the polyester constituting the present film I is preferably 0.5 dL / g or more, more preferably 0.55 dL / g or more, and even more preferably 0.6 dL / g or more. By using a polyester with an intrinsic viscosity of 0.5 dL / g or more as the polyester constituting the present film I, 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. Furthermore, 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, for example.

[0063] When two or more polyesters having different intrinsic viscosities are used, the intrinsic viscosity of the polyester constituting the present film I means 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.

[0064] The present film I is a film containing polyester as a main component, and the content of polyester contained in the present film I 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. When the present film I is composed of two or more layers, the content of polyester contained 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.

[0065] <Particles> It is preferable to contain particles in the present film I. The type of particles contained in the present film I is not particularly limited, and examples 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.

[0066] Among these, silica, calcium carbonate, and organic particles are preferred as particles to be contained in the present film I. 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 I.

[0067] 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 this case, in the case of non-spherical particles, the average of the longest and shortest diameters can be measured as the diameter of each particle.

[0068] The Mohs hardness of a particle is determined 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, for example, in the range of 1 to 9, and may be, but is not limited to, in the ranges of 1 to 8, 1 to 7, 1 to 5, 1 to 4, 1 to 3, etc. The Mohs hardness is a numerical expression of hardness based on the degree of scratching against a standard substance, and standard substances are designated in order from softest to softest, from 1 to 10, and can be measured by a conventional method using a Mohs hardness scale.

[0069] 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 particle content 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, by mass. Furthermore, the particle content 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.

[0070] 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.

[0071] There are no particular limitations on the method for adding particles to the present film I, 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.

[0072] When particles are incorporated into the present film I, 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.

[0073] A nucleating agent may be contained in the present film I. Examples of the nucleating agent include inorganic nucleating agents and organic nucleating agents, with organic nucleating agents being preferred. The nucleating agents may be used alone or in combination of two or more.

[0074] The organic crystal nucleating agent is preferably, for example, a fatty acid metal salt represented by the following general formula: (CH3(CH2) n COO) m M (wherein 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.)

[0075] In the general formula, M is preferably Na. Furthermore, 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. Furthermore, 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 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.

[0076] 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.

[0077] The content of the nucleating agent in the particle-containing layer is, in mass proportion, 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.

[0078] When a nucleating agent is incorporated into the present film I, it is preferable to provide a surface layer and an intermediate layer and incorporate the nucleating agent in the surface layer. Furthermore, when the film has a three-type, three-layer structure with different front and back designs, it is preferable to incorporate the nucleating agent in one or both of the surface layers.

[0079] 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 I as needed, but the total content of these in the present film I is usually less than 10% by mass.

[0080] <Layer Structure of the Present Film I> The present film I may be a single-layer polyester film or a laminated polyester film having two or more layers. The present film I 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.

[0081] More specifically, in the present invention, when the present film I has a laminated structure having two or more layers, an example thereof is a layered structure having surface layer A and surface layer B forming the outermost layer of the present film I. Another example thereof is a laminated structure having surface layer A and surface layer B forming the outermost layer of the present film I, and one or more intermediate layers C (C1, C2, ...). More specifically, for example, an A / C / B structure consisting of surface layer A, surface layer B, and intermediate layer C is preferred. Note that surface layer A is a surface layer that forms one surface of the present film I, and surface layer B is a surface layer that forms the other surface of the present film I.

[0082] <Preferred Embodiment of the Present Film I> The surface layer A forming one surface of the present film I is a surface layer located on the side of the present film I on which, 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. Furthermore, the surface layer B forming the other surface of the present film I is a surface layer located opposite the side on which the ceramic green sheet or the like is provided. Therefore, for example, the present film I 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 I 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."

[0083] Elastic deformation power (η it Although the method for achieving both high elasticity 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 I, the average particle size of the particles to be contained is set, for example, to a value that satisfies the elastic deformation power (η it From the viewpoint of the surface roughness and the smoothness of the surface layer B, the average particle size is preferably 0.01 μm or more, more preferably 0.03 μm or more, and even more preferably 0.04 μm or more. On the other hand, it 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 the 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 the slipperiness and suppressing the surface roughness of the surface layer B from being transferred to the surface layer A when the surface layer B is 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.

[0084] When particles are contained in the surface layer A constituting the present film I, 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. On the other hand, it is preferably 2800 ppm or less, more preferably 2600 ppm or less, and even more preferably 2500 ppm or less. The particle content to be 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. On the other hand, it is preferably 8000 ppm or less, more preferably 7500 ppm or less, and even more preferably 7000 ppm or less.

[0085] When particles are contained in the surface layer A constituting the present film I, 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.

[0086] In addition, when particles are contained in the surface layer A, the elastic deformation power (η it From the viewpoint of improving the hardness of the surface layer A, 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 appropriately set within the above range and 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.

[0087] In addition, when the surface layer A contains particles with a Mohs hardness of 8 or less, the elastic deformation power (η it ), 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, etc. Elastic deformation power (η it In a preferred embodiment, from the viewpoint of achieving a high degree of both the film resistance and surface smoothness, when at least one type of particle is contained in the surface layer A of the present film I, the particles contained in the surface layer A preferably have an average particle size of 0.4 μm or less and the content of the particles (total content when there are two or more types of particles) is 2800 ppm or less by mass relative to the surface layer A, more preferably the particles contained in the surface layer A have an average particle size of 0.3 μm or less and the content of the particles is 2500 ppm or less by mass relative to the surface layer A, and even more preferably the particles contained in the surface layer A have an average particle size of 0.03 to 0.3 μm and the content of the particles is 250 to 2300 ppm by mass relative to the surface layer A.

[0088] 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 I, aggregation of particles is suppressed, and the elastic deformation power (η it), it is preferable that the surface layer contains two or more types of particles with 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 is positive for particles (a1) and negative for particles (a2), or negative for particles (a1) and positive for particles (a2). That is, at pH 7, due to the difference in charges between particles (a1) and (a2), particles (a1) and (a2) are electrically attracted to each other, and for example, a form can be adopted in which particle (a1) is located around particle (a2). In particles in which particle (a1) is electrically located on particle (a2) (hereinafter sometimes referred to as "composite particles"), since particle (a1) having the same charge exists on the outside, the composite particles repel each other, and the composite particles do not aggregate and maintain high dispersibility, which can suppress the generation of voids and increase 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 particles (a1) located on the outside is smaller than the average particle size of the particles (a2) located on the inside. In other words, a structure is formed in which relatively small particles (a1) are positioned so as to surround relatively large particles (a2), and since the composite particles are electrically repelled from each other, aggregation of the particles (a2) does not occur, and dispersibility is thought to be more likely to be improved. The zeta potential can be measured by electrophoretic light scattering.

[0089] 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.

[0090] The zeta potential of the particles (a1) and (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 the surface treatment agent include silane coupling agents such as vinyltriethoxysilane, vinyltrimethoxysilane, vinyl-tris(β-methoxyethoxy)silane, γ-methacryloyloxypropyltrimethoxysilane, κ-methacryloyloxydodecyltrimethoxysilane, β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, γ-glycidoxypropyl-trimethoxysilane, N-β-(aminoethyl)-γ-aminopropyl-trimethoxysilane, γ-ureidopropyl-triethoxysilane, γ-chloropropyltrimethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, and methyltriethoxysilane, and titanate-based coupling agents. The type and amount of the 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, and preferably 3 to 15 parts by mass, per 100 parts by mass of the particles. The method for treatment with the surface treatment agent is not particularly limited, and known methods can be used. Examples include a method in which the particles and the surface treatment agent are dispersed and mixed in an appropriate solvent using a ball mill or the like, dried in an evaporator or air-dried, and then heated to 50 to 150°C, a method in which the particles and the surface treatment agent are heated and refluxed in a solvent such as alcohol for several hours, and a method in which the surface treatment agent is graft-polymerized onto the particle surfaces.

[0091] 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.

[0092] In addition, from the viewpoint of dispersibility, the content of 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, particularly preferably 200 ppm or more, and even more particularly 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, particularly preferably 800 ppm or less, and especially preferably 500 ppm or less. In addition, from the viewpoint of slipperiness, the content of particles (a1) is, for example, preferably 500 ppm or more, more preferably 1000 ppm or more, 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.

[0093] 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.

[0094] The content of particles (a2) is preferably 100 ppm or more, more preferably 250 ppm or more, even more preferably 500 ppm or more, particularly preferably 700 ppm or more, in terms of surface smoothness, 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 particularly preferably 2000 ppm or less. 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 particularly preferably 3000 ppm or more, in terms of lubricity, 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.

[0095] 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.

[0096] Furthermore, the total content of particles (a1) and particles (a2) is preferably 300 to 10,000 ppm by mass relative to the layer in which they are contained. When the total content is within this range, fine irregularities are formed on the film surface, and the surface of surface layer A is more likely to satisfy the arithmetic mean height (Sa) and maximum peak height (Sp) of (1) and (2) above. In film I, the total content of particles (a1) and particles (a2) in surface layer A is preferably 400 ppm or more by mass, more preferably 800 ppm or more. On the other hand, it is preferably 3,000 ppm or less, and even more preferably 2,000 ppm or less. In film I, the total content of particles (a1) and particles (a2) in surface layer B is preferably 3,000 ppm or more by mass, more preferably 4,000 ppm or more, and even more preferably 5,000 ppm or more. On the other hand, the content is preferably 10,000 ppm or less, more preferably 9,500 ppm or less, and even more preferably 9,000 ppm or less. The present film I may contain particles (a1) and particles (a2) in both the surface layer A and the surface layer B, but may also contain particles (a1) and particles (a2) in the surface layer A and particles (a2) only in the surface layer B, without particles (a1).

[0097] 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.

[0098] 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 more than a predetermined amount of particles (a2) is used, it is preferable to use alumina particles in combination as the particles (a1). Specifically, although not limited to the following, when particles (a2) having a Mohs hardness of 7 or less (for example, silica, organic particles, etc.) are contained in the surface layer A in an amount of 300 ppm or more, for example, 500 to 3000 ppm, as the particles (a2), it is preferable to use alumina particles in combination as the particles (a1), and it is more preferable to use the alumina particles in an amount in the range of 50 to 5000 ppm relative to the surface layer A.

[0099] 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, and the like are the same as those described above.

[0100] 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.

[0101] When a nucleating agent is contained in the surface layer A constituting the present film I, 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.

[0102] When an intermediate layer C is formed in the present film I, 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.

[0103] Furthermore, the intermediate layer C of the present film I may contain recycled polyester raw materials from the viewpoint of reducing CO2 emissions and contributing to a reduction in the burden on the environment. The content of the 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 the recycled polyester raw materials may be 70% by mass or more, 90% by mass or more, or even 100% by mass.

[0104] The total thickness of the present film I 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 I can be appropriately set within the above range, and may be, for example, 30 μm or less or 28 μm or less.

[0105] When the present film I 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.

[0106] When the present film I 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 surface layer A is greater than the thickness of each of the surface layers B.

[0107] When the present film I has a three-layer structure including a surface layer A, an intermediate layer C, and a surface layer B in this order, the ratio of the thicknesses 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.

[0108] The thickness of the surface layer A of the present film I 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 I 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, and particularly preferably 4 μm or less.

[0109] The thickness of the intermediate layer C of the present film I 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.

[0110] <Method for Producing the Present Film I> Next, a specific example of the production of the present film I will be described, but the present film I is not limited to the following production example. 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.

[0111] The resulting unstretched sheet is then biaxially stretched. In this process, the unstretched sheet is first stretched in one direction using a roll or tenter-type stretching machine (primary stretching). The stretching temperature is typically 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is typically 2.5 to 7 times, preferably 3 to 6 times. Next, the sheet is stretched in a direction perpendicular to the first-stage stretching direction. In this case, the stretching temperature is typically 70 to 170°C, and the stretching ratio is typically 3 to 7 times, preferably 3.5 to 6 times. Subsequently, the sheet is heat-treated under tension or relaxation of 30% or less at a temperature of typically 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 with 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 carried out in two or more steps at different temperatures. In the above-mentioned stretching, a method in which unidirectional stretching is carried out in two or more steps may also be employed. In this case, it is preferable to carry out the stretching so that the final stretch ratios in both directions are within the above-mentioned ranges.

[0112] Simultaneous biaxial stretching can also be employed in the production of Film I. In the simultaneous biaxial stretching method, the unstretched sheet is simultaneously stretched and oriented in the machine direction (longitudinal direction) and width direction (transverse direction) under temperature control, typically at 70 to 120°C, and preferably 80 to 110°C. The area stretch ratio is preferably 4 to 50 times, more preferably 7 to 35 times, and even more preferably 10 to 25 times. Subsequently, the sheet is heat-treated under tension or relaxation of 30% or less, typically at a temperature of 170 to 250°C, to obtain a stretched and oriented film. Regarding the simultaneous biaxial stretching apparatus employing the above-described stretching method, conventionally known stretching methods, such as a screw system, a pantograph system, and a linear drive system, can be employed.

[0113] In the manufacturing method of the present film I, the temperature in the primary stretching (longitudinal stretching), the temperature in the heat setting step, 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 In other words, the temperature in the primary stretching (longitudinal stretching), the temperature in the heat setting step, the peripheral speed of the stretching rolls, etc. in the polyester film production process can be easily controlled to control both the elastic deformation power (η 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 deteriorate. Therefore, by further adjusting, for example, the relaxation rate, etc., a high elastic deformation power (η it For example, although not limited to the following, it is preferable to set the temperature in the primary stretching (longitudinal stretching) to a relatively low temperature condition such as 80 to 90°C or 78 to 88°C, and it is also preferable to set the temperature condition in the heat setting step to a temperature condition such as 200 to 240°C or 200 to 230°C, and it is preferable to set the heat treatment time in the heat setting step to 1 to 20 seconds, 2 to 16 seconds, 3 to 13 seconds, 4 to 10 seconds, or the like, and further, it is possible to appropriately set the relaxation rate in the cooling step to, for example, 0 to 20%, 0.5 to 15%, 1 to 10%, or 1.5 to 8%, and thereby it is possible to easily produce a polyester film that can achieve both high elastic deformation power (ηit ) and the heat shrinkage rate after heat treatment can be easily controlled within a desired range.

[0114] The above-described production method typically includes a step of winding the film into a roll using a cylindrical or cylindrical core. 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 above are not limited to the following, but a length of 10,000 m or more is preferred, for example.

[0115] Although the present film I may be an unstretched film (sheet) or a stretched film, it is preferably a uniaxially or biaxially stretched film, and among these, it is preferably a biaxially stretched film in terms of excellent balance of mechanical properties and flatness. Note that a biaxially stretched film means a film in which the refractive index in the longitudinal direction (MD direction) and transverse direction (TD direction) of the film is higher than the refractive index in the thickness direction, and is usually obtained by stretching the film in the longitudinal and transverse directions.

[0116] <<Release Layer>> The present film I is preferably used in a form having a release layer on at least one surface. 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.

[0117] The release layer is laminated to the polyester film directly or via another layer, such as an easy-adhesion coating layer for improving adhesion to the present film I, an antistatic layer, an antiblocking layer, or the like.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] The release layer is formed by coating the present film I 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 outside the system onto a film that has already been produced.

[0122] The release layer can be provided on the present film I by a conventional coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating, or the like.

[0123] The curing conditions for forming the release layer are not particularly limited. When the release layer is formed 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.

[0124] 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.

[0125] The coating amount of the release layer (after drying) is usually 0.005 to 5 g / m from the viewpoint of coating property. 2 , preferably 0.005 to 1 g / m 2 , more preferably 0.005 to 0.1 g / m 2 The coating amount (after drying) is in the range of 0.005 g / m 2 When the coating density is 5 g / m or more, the coating property and stability are good, and a uniform coating film is easily obtained. 2 When the thickness is less than this, the coating adhesion, curing properties, etc. of the release layer itself are not 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.

[0126] <<Applications>> The present film I can be suitably used, for example, in various release applications. For example, it can be used for various release and process applications, such as for dry film resist (DFR), for multilayer circuit boards, and for producing ceramic green sheets for multilayer ceramic capacitors. In release and process applications, the present film I is used, for example, as a support, onto which various materials such as ceramic slurries are coated or laminated.

[0127] In particular, as described above, the present film I is extremely excellent in that it effectively suppresses the occurrence of surface defects such as pinholes and is unlikely to cause peeling problems of ceramic green sheets in the manufacturing process of multilayer ceramic capacitors, and is also unlikely to cause coating spots or wrinkles, for example, when forming 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 I is its use as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors.

[0128] 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 capacitances increase. Therefore, the present film I 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 I is its use as a support for ceramic green sheets in the manufacturing process of automotive multilayer ceramic capacitors.

[0129] As described above, the ceramic green sheet support is used as a film for the process of coating a ceramic slurry, drying (heat treating) the ceramic slurry, solidifying it, and then peeling off the solidified ceramic slurry. Examples of ceramic slurries include those containing ceramic components, binder resins, and solvents. Examples of ceramic components that make up the ceramic slurry include oxides of metals such as titanium, aluminum, barium, lead, zirconium, silicon, and yttrium, and barium titanate. Examples of binder resins that can be used include, but are not limited to, polyurethane resins, urea resins, melamine resins, epoxy resins, vinyl acetate resins, acrylic resins, polyvinyl alcohol, and polyvinyl butyral. Examples of solvents that can be used 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.

[0130] <<Manufacturing Methods Using the Present Film I>> Examples of methods for manufacturing a support for a ceramic green sheet using the present film I include a method for manufacturing a support for a ceramic green sheet that includes a step of forming a release layer on one side of the present film I, which step includes a step of heat treating the applied release agent composition.

[0131] Furthermore, examples of methods for producing ceramic green sheets using the present film I include methods for producing ceramic green sheets that include a step of applying a ceramic slurry containing a ceramic component to one surface of the present film I. Examples of methods for producing ceramic green sheets using the present film I include methods that, in addition to the application step, also include a step of drying the applied ceramic slurry and a step of forming electrodes.

[0132] Furthermore, examples of a method for manufacturing a multilayer ceramic capacitor using the present film I 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 I and a release layer provided on one side of the present film I, and the step includes a step of heat treating the applied ceramic slurry.

[0133] The first embodiment of 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 present invention. In the examples, "%" and "ppm" are based on mass.

[0134] <Measurement Methods> First, the various measurement methods used in the following examples are as follows.

[0135] [Elastic deformation power (η it ) On a glass slide (S1112, manufactured by Matsunami Glass Industry Co., Ltd.), approximately 2 to 8 mg of Aron Alpha (registered trademark) (general-purpose, manufactured by Toa Gosei Chemical Industry Co., Ltd.) was dropped. The surface layer B side of a sample film (1.5 cm x 1.5 cm) was placed on top of the drop and cured as an adhesive surface. The slide with the sample film attached was fixed to the sample stage of a hardness tester (Dynamic Ultra-Micro Hardness Tester (DUH-211S, manufactured by Shimadzu Corporation), and then 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) × 100 (%) (Measurement conditions) Indenter used: Diamond regular triangular pyramidal indenter (edge ​​angle: 115) Measurement mode: Load-unload test Test force: 20.00 mN Minimum test force: 0.20 mN Load rate: 0.1464 mN / sec Load holding time: 0 sec Unload holding time: 0 sec Measurement atmosphere: 23±2°C, 50±5% RH Measurement number: 6

[0136] [Shrinkage] A sample film (1.5 cm wide x 15 cm long) was heat-treated for 5 minutes in a hot air oven maintained at a predetermined temperature (150°C) in an untensioned state, 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 taken in both the machine direction (MD) and the transverse direction (TD) of the film. The shrinkage in MD was measured so that the length direction was the MD, and the shrinkage in TD was measured so that the length direction was the TD. Shrinkage (%) = {(length of sample film before heat treatment) - (length of sample film after heat treatment)} ÷ (length of sample film before heat treatment) x 100

[0137] [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 a sample film (2 cm × 1 cm) were measured with an Abbe refractometer using sodium D line as a light source, and the planar orientation degree (ΔP) was calculated based on the following formula: ΔP = ((nx + ny) / 2 - nz) × 1000

[0138] [Arithmetic Mean Height (Sa), Maximum Peak Height (Sp), etc.] The surfaces of surface layer A and surface layer B of a sample film (5 cm × 5 cm) were measured using a surface roughness measuring device (Ametec Corporation, "NewView" (registered trademark)). 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 curves. Specifically, using the surface roughness measuring device, measurements were performed under conditions of an objective lens magnification of 10x, a zoom magnification of 2.0x, and a viewing angle of 0.44 mm × 0.44 mm. After performing the following treatments, the arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk) were determined. Note that measurements were performed 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:200μm

[0139] Next, the polyester raw materials used in the examples and comparative examples are shown in Table I-1. The polyesters in polyester raw materials IA to IO listed in Table I-1 are all homopolyethylene terephthalate. In addition, polyester raw material IM is a recycled raw material made by recovering and recycling waste materials.

[0140]

[0141] [Example I-1] A raw material for the surface layer A was a blend of 88% polyester IA, 8% polyester ID, and 4% polyester IF by mass. A raw material for the intermediate layer C was a blend of 50% polyester IB and 50% polyester IM by mass. A raw material for the surface layer B was a blend of 28% polyester IB, 22% polyester II, and 50% polyester IK by mass. These materials 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-kind, three-layer (A / C / B) structure with the raw materials for the surface layer A and the surface layer B as the outermost layer (surface layer) and the intermediate layer C as the intermediate layer, with a thickness composition ratio of A / C / B = 4 / 19 / 2 under the extrusion conditions. The material was cooled and solidified on a cooling roll with a surface temperature set at 20°C using an electrostatic adhesion method to obtain an amorphous film. Next, the film was stretched 3.6 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%, 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 would be 215°C, and the heat treatment was carried out for 5.1 seconds.

[0142] [Example I-2] A raw material for the surface layer A was a blend of 88% polyester IA, 8% polyester ID, and 4% polyester IF by mass. A raw material for the intermediate layer C was a blend of 50% polyester IB and 50% polyester IM by mass. A raw material for the surface layer B was a blend of 28% polyester IB, 22% polyester II, and 50% polyester IK by mass. These materials 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-kind, three-layer (A / C / B) structure with the raw materials for the surface layer A and the surface layer B as the outermost layer (surface layer) and the intermediate layer C as the intermediate layer, with a thickness composition ratio of A / C / B = 4 / 25 / 2 under the extrusion conditions. The material was cooled and solidified on a cooling roll with a surface temperature set at 20°C using an electrostatic adhesion method to obtain an amorphous film. Next, the film was stretched 3.6 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%, 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 would be 215°C, and the heat treatment was carried out for 5.1 seconds.

[0143] [Example I-3] A raw material for the surface layer A was a blend of 84% polyester IA, 12% polyester ID, and 4% polyester IF by mass. A raw material for the intermediate layer C was 100% polyester IC. A raw material for the surface layer B was a blend of 28% polyester IC, 22% polyester I-H, and 50% polyester I-J by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained, with the raw materials for the surface layer A and the surface layer B as the outermost layers (surface layers) and the intermediate layer C as the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B = 4 / 19 / 2. The film was co-extruded so as to be 25 μm thick, 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 a 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., followed by heat treatment (fixing) at 230° C. and cooling at 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 reached 230° C., and the heat treatment was carried out for 7.8 seconds.

[0144] [Example I-4] A raw material for the surface layer A was a blend of 84% polyester IA, 12% polyester ID, and 4% polyester IF by mass. A raw material for the intermediate layer C was 100% polyester IC. A raw material for the surface layer B was a blend of 28% polyester IC, 22% polyester I-H, and 50% polyester I-J by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer. The thickness composition ratio under the extrusion conditions was A / C / B = 4 / 19 / 2. The film was co-extruded so as to be 25 μm thick, 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 82° C. using the peripheral speed difference with a stretching roll set at a peripheral speed of 14.1 m / min. The machine direction stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105° C., followed by heat treatment (fixing) at 230° C. and cooling at 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 reached 230° C., and the heat treatment was carried out for 7.8 seconds.

[0145] [Example I-5] A raw material obtained by blending 97% polyester I-B and 3% polyester I-G in a mass ratio was used as the raw material for surface layer A, a raw material obtained by blending 100% polyester IC in a mass ratio for intermediate layer C, and a raw material obtained by blending 28% polyester IC, 22% polyester I-H, and 50% polyester I-J in a mass ratio for surface layer B were supplied to a vented extruder and melt-extruded at 280°C. After that, they were co-extruded under the extrusion conditions of a three-kind, three-layer (A / C / B) layer structure in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and intermediate layer C was the intermediate layer, with a thickness composition ratio of A / C / B = 4 / 19 / 2. The film was then cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4.3 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 direction) at a film temperature of 86°C using the peripheral speed difference with the stretching roll set at a peripheral speed of 15.1 m / min. The machine direction stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD direction) 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%, 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 reached 210°C, and the heat treatment was carried out for 7.3 seconds.

[0146] [Example I-6] A raw material obtained by blending 97% polyester I-B and 3% polyester I-L in a mass ratio was used as the raw material for surface layer A, a raw material obtained by blending 100% polyester IC in a mass ratio for intermediate layer C, and a raw material obtained by blending 28% polyester IC, 22% polyester I-H, and 50% polyester I-J in a mass ratio for surface layer B were supplied to a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were used as the outermost layers (surface layers) and the raw materials for intermediate layer C were used as the intermediate layer, and the resulting mixture was co-extruded under extrusion conditions such that the thickness composition ratio was A / C / B = 4 / 19 / 2 to form a three-kind, three-layer (A / C / B) layer structure. The film was then cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4.3 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 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%, yielding 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 carried out for 7.3 seconds.

[0147] [Example I-7] A raw material for the surface layer A was a blend of 88% polyester I-B and 12% polyester I-E in a mass ratio, a raw material for the intermediate layer C was 100% polyester I-B, and a raw material for the surface layer B was a blend of 28% polyester IC, 22% polyester I-I, and 50% polyester I-K in a mass ratio. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, they were co-extruded under the extrusion conditions of a three-kind, three-layer (A / C / B) layer structure in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, with a thickness composition ratio of A / C / B = 4 / 19 / 2. 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 direction) at a film temperature of 86°C using the peripheral speed difference with a stretching roll set at a peripheral speed of 14.1m / min. The machine direction stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD direction) 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 25μm (A / C / B = 4μm / 19μm / 2μm). In 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 7.8 seconds.

[0148] [Example I-8] A raw material obtained by blending 91% polyester I-B and 9% polyester I-D by mass was used as the raw material for surface layer A, a raw material obtained by blending 100% polyester I-M by mass as the raw material for intermediate layer C, and a raw material obtained by blending 28% polyester I-C, 22% polyester I-I, and 50% polyester I-K by mass as the raw material for surface layer B were supplied to a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained, in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the raw materials for intermediate layer C were the intermediate layer, and the extrusion conditions were such that the thickness composition ratio was A / C / B = 8 / 15 / 2. 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 an electrostatic adhesion 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 at a relaxation rate of 5%, yielding 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.

[0149] [Example I-9] A raw material obtained by blending 91% polyester I-B and 9% polyester I-D by mass was used as the raw material for surface layer A, a raw material obtained by blending 100% polyester I-M by mass as the raw material for intermediate layer C, and a raw material obtained by blending 28% polyester I-C, 22% polyester I-I, and 50% polyester I-K by mass as the raw material for surface layer B were supplied to a vented extruder and melt-extruded at 280°C. Thereafter, the raw materials for surface layer A and surface layer B were co-extruded to form a three-kind, three-layer (A / C / B) layer structure in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the raw materials for intermediate layer C were the intermediate layer, with the thickness composition ratio of A / C / B being 8 / 15 / 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 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 (MD) at a film temperature of 86 ° C., and then this machine direction stretched film was introduced into a tenter and stretched 4.2 times in the transverse direction (TD) at 105 ° C., and then heat-treated (fixed) at 230 ° C. in the tenter, and cooled to 140 ° C. at 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 carried out for 5.9 seconds.

[0150] [Example I-10] A raw material obtained by blending 94% polyester I-B and 6% polyester I-D by mass was used as the raw material for surface layer A, a raw material obtained by blending 50% polyester IC and 50% polyester I-M by mass as the raw material for intermediate layer C, and a raw material obtained by blending 28% polyester IC, 22% polyester I-H, and 50% polyester I-J by mass as the raw material for surface layer B were supplied to a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the raw materials for intermediate layer C were the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B=4 / 2. The film was co-extruded to a ratio of 5 / 2, and 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 86°C using the peripheral speed difference with the stretching roll set at a peripheral speed of 14.1m / min. The machine direction 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 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 reached 230°C, and the heat treatment was carried out for 7.8 seconds.

[0151] [Example I-11] A raw material obtained by blending 88% polyester I-B and 12% polyester I-D by mass was used as the raw material for surface layer A, a raw material obtained by blending 50% polyester IC and 50% polyester I-M by mass as the raw material for intermediate layer C, and a raw material obtained by blending 28% polyester IC, 22% polyester I-H, and 50% polyester I-J by mass as the raw material for surface layer B were supplied to a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the raw materials for intermediate layer C were the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B=4 / The film was co-extruded to a ratio of 25 / 2, and 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 86°C using the peripheral speed difference with the stretching roll set at a peripheral speed of 14.1m / min. The machine direction 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 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 reached 230°C, and the heat treatment was carried out for 7.8 seconds.

[0152] [Example I-12] A raw material for the surface layer A was a blend of 78% polyester I-B, 18% polyester I-D, and 4% polyester I-F by mass. A raw material for the intermediate layer C was a blend of 50% polyester I-C and 50% polyester I-M by mass. A raw material for the surface layer B was a blend of 28% polyester I-C, 22% polyester I-H, and 50% polyester I-J by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B. The film was coextruded to a C / B ratio of 4 / 25 / 2, 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 31 μm (A / C / B = 4 μm / 25 μm / 2 μm). The heat-treatment (fixing) step involved applying a temperature gradient to the final temperature of 230°C, and the heat treatment was carried out for 7.8 seconds.

[0153] [Example I-13] A raw material for the surface layer A was a blend of 93% polyester I-B, 4% polyester I-F, and 3% polyester I-G by mass. A raw material for the intermediate layer C was a blend of 50% polyester I-C and 50% polyester I-M by mass. A raw material for the surface layer B was a blend of 28% polyester I-C, 22% polyester I-H, and 50% polyester I-J by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer. The thickness composition ratio under the extrusion conditions was A / C. The film was coextruded to a ratio of A / C / B = 4 / 25 / 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 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 a stretching roll set at a peripheral speed of 14.1 m / min. The machine direction 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 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 reached 230°C, and the heat treatment was carried out for 7.8 seconds.

[0154] [Example I-14] A raw material obtained by blending 90% polyester I-B and 10% polyester I-O by mass was used as the raw material for surface layer A, a raw material obtained by blending 100% polyester I-C by mass was used as the raw material for intermediate layer C, and a raw material obtained by blending 70% polyester I-B and 30% polyester I-G by mass was used as the raw material for surface layer B. These materials were supplied to 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-kind, three-layer (A / C / B) layer structure in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, with the thickness composition ratio under extrusion conditions being A / C / B = 1.55 / 27.9 / 1.55, and the resulting material was subjected to electrostatic application adhesion. Using a method, the film was cooled and solidified on a cooling roll set at a surface temperature of 20 ° C. and a peripheral speed of 5.8 m / min to obtain an amorphous film, and then stretched 3.5 times in the machine direction (MD direction) at a film temperature of 86 ° C. using the peripheral speed difference with a stretching roll set at a peripheral speed of 20.3 m / min. The machine direction stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD direction) at 105 ° C., and 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 31 μm (A / C / B = 1.55 μm / 27.9 μm / 1.55 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 carried out for 5.4 seconds.

[0155] [Comparative Example I-1] A raw material for the surface layer A was a blend of 97% polyester I-B and 3% polyester I-G in a mass ratio, a raw material for the intermediate layer C was 100% polyester IC, and a raw material for the surface layer B was a blend of 28% polyester IC, 22% polyester I-H, and 50% polyester I-J in a mass ratio. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was formed, with the raw materials for the surface layer A and the surface layer B as the outermost layers (surface layers) and the intermediate layer C as the intermediate layer, and the extrusion conditions were such that the thickness composition ratio was A / C / B = 4 / 19 / 2. 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 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 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 so that the final temperature reached 230°C, and the heat treatment was carried out for 7.3 seconds.

[0156] [Comparative Example I-2] A raw material for the surface layer A was a blend of 97% polyester I-B and 3% polyester I-L in a mass ratio, a raw material for the intermediate layer C was 100% polyester IC, and a raw material for the surface layer B was a blend of 28% polyester IC, 22% polyester I-H, and 50% polyester I-J in a mass ratio. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained, with the raw materials for the surface layer A and the surface layer B as the outermost layers (surface layers) and the intermediate layer C as the intermediate layer, and the extrusion conditions were such that the thickness composition ratio was A / C / B = 4 / 19 / 2. 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 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 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 so that the final temperature reached 230°C, and the heat treatment was carried out for 7.3 seconds.

[0157] [Comparative Example I-3] A raw material for the surface layer A was a blend of 90% polyester I-B, 4% polyester I-F, and 6% polyester I-L in a mass ratio. A raw material for the intermediate layer C was 100% polyester IC. A raw material for the surface layer B was a blend of 28% polyester IC, 22% polyester I-H, and 50% polyester I-J in a mass ratio. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was formed, with the raw materials for the surface layer A and the surface layer B as the outermost layers (surface layers) and the intermediate layer C as the intermediate layer, and the extrusion conditions were such that the thickness composition ratio was A / C / B = 4 / 19 / 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 (set) 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). During the heat-treatment (set) step, a temperature gradient was applied so that the final temperature reached 243°C, and the heat treatment was carried out for 7.3 seconds.

[0158] [Comparative Example I-4] A raw material for the surface layer A was a blend of 88% polyester I-B and 12% polyester I-E in a mass ratio, a raw material for the intermediate layer C was 100% polyester I-B, and a raw material for the surface layer B was a blend of 28% polyester IC, 22% polyester I-I, and 50% polyester I-K in a mass ratio. These were fed into a vented extruder and melt-extruded at 280°C. After that, they were co-extruded under the extrusion conditions of a three-kind, three-layer (A / C / B) layer structure in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, with a thickness composition ratio of A / C / B = 4 / 19 / 2. 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 direction) at a film temperature of 86°C using the peripheral speed difference with a stretching roll set at a peripheral speed of 14.1m / min. The machine direction stretched film was then introduced into a tenter and stretched 4.2 times in the transverse direction (TD direction) 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 25μm (A / C / B = 4μm / 19μm / 2μm). In 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 7.8 seconds.

[0159] [Comparative Example I-5] A raw material obtained by blending 87% polyester I-B and 13% polyester I-F by mass was used as the raw material for surface layer A, a raw material obtained by blending 50% polyester IC and 50% polyester I-M by mass as the raw material for intermediate layer C, and a raw material obtained by blending 28% polyester IC, 22% polyester I-H, and 50% polyester I-J by mass as the raw material for surface layer B were supplied to a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the raw materials for intermediate layer C were the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B=4 / 2. The film was co-extruded to a ratio of 5 / 2, and 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 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 15.1 m / min. The machine direction 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 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 reached 230 ° C., and the heat treatment was carried out for 7.3 seconds.

[0160] [Comparative Example I-6] A raw material obtained by blending 70% polyester IC and 30% polyester I-N by mass was used as the raw material for the surface layer A, a raw material obtained by blending 45% polyester IC and 55% polyester I-M by mass as the raw material for the intermediate layer C, and a raw material obtained by blending 70% polyester IC and 30% polyester I-N by mass as the raw material for the surface layer B were supplied to a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, and the extrusion conditions were such that the thickness composition ratio was A / C / B = 1 / 23 / 1. The film was co-extruded at 20°C and cooled to a peripheral speed of 5.1 m / min on a cooling roll using an electrostatic contact method to obtain an amorphous film. The film was then stretched 3.47 times in the machine direction (MD) at a film temperature of 85°C using the peripheral speed difference with a stretching roll (17.7 m / min). The stretched film was then introduced into a tenter and stretched 4.2 times in the transverse direction (TD) at 120°C. The film was then heat-treated (fixed) at 219°C and cooled to 125°C with a relaxation rate of 5%, obtaining a polyester film with a thickness of 25 μm (A / C / B = 1 μm / 23 μm / 1 μm). The heat-treatment (fixing) step was performed with a temperature gradient to achieve a final temperature of 219°C, and the heat treatment was performed for 5.3 seconds.

[0161] The properties of each of the films obtained above were measured according to the methods described above, and the results are shown in Tables I-2 and I-3 (Examples I-1 to I-14) and Table I-4 (Comparative Examples I-1 to I-6).

[0162]

[0163]

[0164]

[0165] First, as shown in Tables I-2 and I-3, the polyester films of Examples I-1 to I-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 had 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 I-1 to I-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 is found that when the polyester films of Examples I-1 to I-14 are used as supports for ceramic green sheets used in the manufacturing process of multilayer ceramic capacitors, the polyester films can effectively suppress the occurrence of pinholes and the like in the ceramic green sheets and can also effectively suppress peeling problems of the ceramic green sheets.

[0166] On the other hand, as shown in Table I-4, in Comparative Examples I-1 to I-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 I-1 to I-5 have an elastic deformation power (η it ) is low, the peelability of the ceramic green sheet is unsatisfactory. In addition, the polyester film of Comparative Example I-6 has a large maximum peak height (Sp), and the surface smoothness is unsatisfactory.

[0167] 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 ) and surface smoothness 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 I-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 I-1 to I-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 A comparison between these comparative examples and examples shows that adjusting the heat setting temperature and the transverse stretching ratio, as well as selecting the particle type and content, are also effective for adjusting 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.

[0168] According to one embodiment of the present invention, a polyester film can be provided 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.

[0169] In addition to the first embodiment described above, the present invention discloses the following second to fifth embodiments.

[0170] Second Embodiment A second embodiment, which is an example of an embodiment of the present invention, will be described below, although the present invention is not limited to the embodiment described below.

[0171] As mentioned above, in recent years, with the increasing use of electrical equipment in automobiles and the increasing functionality of smartphones, there has been a demand for smaller multilayer ceramic capacitors with higher capacitance. In response to this demand, efforts have been made to reduce the thickness of ceramic green sheets. However, as ceramic green sheets become thinner, there is concern that the possibility of peeling defects such as breakage occurring in the process of peeling the ceramic green sheets from the release film increases.

[0172] 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 in order to improve the releasability of the ceramic green sheet, and which has an elastic deformation power of 45% or more in a load-displacement curve measured when a load of 20 mN is applied to the release agent layer side using a micro-surface hardness tester.

[0173] It is predicted that multilayer ceramic capacitors will continue to become smaller and have higher capacitance in the future, resulting in a demand for even thinner ceramic green sheets. As ceramic green sheets become thinner, it is expected that there will be greater concerns about peeling defects, such as breakage, occurring during the process of peeling the ceramic green sheet from the release film. Furthermore, there is concern that heat shrinkage of the release film occurs due to the heat treatment for drying the ceramic slurry applied to the release film, resulting in coating irregularities, wrinkles, and the like. Therefore, there is a demand for improving the releasability of the release film while suppressing the occurrence of coating irregularities, wrinkles, and the like.

[0174] However, as a result of extensive investigations by the present inventors, it has been found that, from the viewpoint of making it easier to peel the ceramic green sheet from the release film, it is possible to consider, for example, compounding a predetermined filler (particles) into the release film. However, improving the peelability in this manner tends to result in coating irregularities and wrinkles during the heat treatment step in the manufacturing process of the multilayer ceramic capacitor, and it has become clear that it is difficult to achieve both of these at a high level.

[0175] The second embodiment of the present invention has been made in consideration of the above circumstances, and provides a polyester film that can improve releasability in the step of peeling a ceramic green sheet from a release film and can also suppress the occurrence of coating spots and wrinkles.

[0176] 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.

[0177] That is, the present invention provides the following as one embodiment. [II-1] A polyester film having one surface with an elastic deformation power of more than 55% and a shrinkage rate of 2.8% or less in the longitudinal and transverse directions after heat treatment at 150°C for 5 minutes. [II-2] The polyester film according to [II-1], having a shrinkage rate of 1.5% or less in the transverse direction after heat treatment at 150°C for 5 minutes. [II-3] The polyester film according to [II-1] or [II-2], wherein the one surface satisfies the following (1) and (2): (1) an arithmetic mean height (Sa) of 15 nm or less; (2) a maximum peak height (Sp) of 150 nm or less; [II-4] The polyester film according to any one of [II-1] to [II-3], containing particles, the content of which is 250 ppm or more and 10,000 ppm or less by mass relative to the layer in which the particles are contained. [II-5] The polyester film according to any one of [II-1] to [II-4], which contains particles, and the average particle size of the particles is 1 μm or less. [II-6] The polyester film according to any one of [II-1] to [II-5], which contains particles, and the Mohs hardness of the particles is 9 or less. [II-7] The polyester film according to any one of [II-1] to [II-6], which contains particles, and 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). [II-8] The polyester film according to any one of [II-1] to [II-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). [II-9] The polyester film according to [II-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 one surface.[II-10] The polyester film according to [II-8] or [II-9], wherein the content of the particles having a negative zeta potential at pH 7 is 100 ppm or more and 8,000 ppm or less by mass relative to the layer forming one surface. [II-11] The polyester film according to any one of [II-8] to [II-10], wherein the particles having a positive zeta potential at pH 7 are alumina particles. [II-12] The polyester film according to any one of [II-8] to [II-11], wherein the particles having a negative zeta potential at pH 7 are silica or organic particles. [II-13] The polyester film according to any one of [II-1] to [II-12], 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 in the layer forming one surface (content of particles having a Mohs hardness of 8 or less / total content of particles) is 0.6 or more and 0.95 or less by mass. [II-14] The polyester film according to any one of [II-1] to [II-13], wherein the layer forming one surface contains particles, the particles being mainly composed of particles having a Mohs hardness of 8 or less, and the content of the particles having a Mohs hardness of 8 or less is less than 1,800 ppm by mass relative to the layer forming one surface. [II-15] The polyester film according to [II-3], wherein the maximum peak height (Sp) of (2) is 100 nm or less. [II-16] The polyester film according to any one of [II-1] to [II-15], wherein the degree of planar orientation (ΔP) is 165 or more. [II-17] The polyester film according to any one of [II-1] to [II-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 > the arithmetic mean height (Sa) of the one surface). [II-18] The polyester film according to any one of [II-1] to [II-17], which consists of at least two layers. [II-19] The polyester film according to any one of [II-1] to [II-18], which consists of three layers.[II-20] The polyester film according to [II-18] or [II-19], which contains particles, and the content of the particles is 250 ppm to 2800 ppm by mass relative to one surface layer. [II-21] The polyester film according to [II-20], which contains particles, and the content of the particles is 2000 ppm to 8000 ppm by mass relative to the other surface layer. [II-22] The polyester film according to any of [II-1] to [II-21], which comprises a surface layer forming 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. [II-23] The polyester film according to any one of [II-1] to [II-22], wherein the polyester film comprises a surface layer forming 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. [II-24] The polyester film according to any one of [II-1] to [II-23], which is used as a support for a ceramic green sheet in the production process of a multilayer ceramic capacitor. [II-25] The polyester film according to any one of [II-1] to [II-24], which is used as a support for a ceramic green sheet in the production process of an automotive multilayer ceramic capacitor. [II-26] Use of the polyester film according to any one of [II-1] to [II-25], as a support for a ceramic green sheet in the production process of a multilayer ceramic capacitor. [II-27] Use of the polyester film according to any one of [II-1] to [II-25], as a support for a ceramic green sheet in the production process of an automotive multilayer ceramic capacitor. [II-28] A method for producing a ceramic green sheet, comprising a step of applying a ceramic slurry containing a ceramic component to the one surface of the polyester film according to any one of [II-1] to [II-25].

[0178] According to one embodiment of 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 coating spots and wrinkles.

[0179] The present invention will be described in more detail below based on the second embodiment of the present invention, but the present invention is not limited to these embodiments.

[0180] The polyester film according to the second embodiment of the present invention (hereinafter, sometimes referred to as "the present film II") is a polyester film that satisfies the requirements that the elastic deformation power of one surface is more than 55% and that the shrinkage rates in the longitudinal and transverse directions after heat treatment at 150°C for 5 minutes are 2.8% or less, as will be described in detail below.

[0181] The present inventors conducted research to develop a ceramic green sheet support capable of supporting thinner ceramic green sheets (e.g., 0.5 μm or less after drying) to accommodate the miniaturization and increased capacity of multilayer ceramic capacitors. The inventors conducted research aimed at preventing peeling defects during the peeling process of ceramic green sheets. During this research, the inventors discovered that peeling defects could be prevented by controlling the properties of particles incorporated into polyester films. However, they also discovered that coating defects, such as unevenness and wrinkles, tend to occur during the heat treatment process for drying the ceramic slurry coated on the release film. The occurrence of coating defects and wrinkles during the heat treatment process is an important characteristic in ensuring the quality and reliability of the multilayer ceramic capacitor, from intermediate products to final products, such as the lamination characteristics of ceramic green sheets. This is particularly important for ensuring the quality and reliability required when using thin ceramic green sheets.

[0182] The present inventors have conducted further research with a view to solving both the problems of the above-mentioned peeling defects and the problems of coating spots, wrinkles, etc., and 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, film-forming conditions, etc. can suppress the occurrence of peeling defects in the step of peeling the ceramic green sheet from the release film, and can also suppress the occurrence of coating spots, wrinkles, etc.

[0183] The present invention proposes a new film II that has a specific elastic deformation power (η it ) and specific heat distortion resistance, and for example, has a high recovery force against distortion that occurs when cutting a ceramic green sheet, resulting in excellent releasability of the ceramic green sheet, and is also extremely excellent in that it can effectively suppress the occurrence of coating irregularities and wrinkles in the process of forming a release layer, ceramic green sheet, etc., and can provide a release film, etc. that can ensure high quality reliability. One embodiment of this film II will be described in detail below.

[0184] <<Present Film II>> Present Film II is suitable for use, for example, as a support (substrate) for ceramic green sheets in the production process of multilayer ceramic capacitors. As described above, Present Film II is excellent in that it can suppress the occurrence of coating irregularities and wrinkles and can also suppress the occurrence of peeling defects.

[0185] [Elastic deformation power (η it ) )] In order to effectively suppress the above-mentioned peeling failure, the present film II has an elastic deformation power (η it ) is preferably more than 55%. it By controlling the elastic deformation power (η ) to a specific range of more than 55%, it is possible to realize a high level of peelability, which is particularly required in the manufacturing process of MLCC using thin ceramic green sheets, and to effectively suppress peel failure. itFrom 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. it The upper limit of the ratio is not particularly limited, but may be, for example, about 70%, or about 65%.

[0186] Elastic deformation power of surface A (η it By using the present film II 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 II, and a good gap can be formed between the two. This gap can be used to grip the present film II and easily separate the ceramic green sheet from the present film II.

[0187] Elastic deformation power (η it The elastic deformation power (η) is calculated by the following formula based on physical quantities measured by nanoindentation (in accordance with ISO 14577). Specifically, it is determined by the method described in the Examples below. it ) = (Welast / Wtotal) × 100 [%] [Wtotal (total deformation work) = Wplast (plastic deformation work) + Welast (elastic deformation work)]

[0188] [Shrinkage after heat treatment] From the viewpoint of suppressing the above-mentioned coating irregularities and wrinkles, the shrinkage of Film II 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 in the machine direction (MD) (150°C, 5 minutes) is about -1%, preferably -0.5% or more, more preferably -0.3% or more.

[0189] Furthermore, the shrinkage percentage in the transverse direction (TD) of this film II when heat-treated at 150°C for 5 minutes is preferably 2.8% or less, from the viewpoint of suppressing the aforementioned 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 percentage 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 heat distortion resistance that is particularly required in the manufacturing process of MLCCs using the thin ceramic green sheets, the shrinkage percentage in the transverse direction (TD) (150°C, 5 minutes) is preferably 1.4% or less, more preferably 1.3% or less. 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.

[0190] Elastic deformation power (η it In order to achieve both the desired film thickness and shrinkage rate (heat treatment at 150°C for 5 minutes), the film formation conditions (particularly the longitudinal stretching temperature, transverse stretching ratio, heat setting temperature, roll peripheral speed, relaxation rate, etc.), the film formation raw materials, etc., can be appropriately set to be within the above ranges. The details are as described above.

[0191] [Planar orientation degree (ΔP)] In order to suppress the aforementioned peeling defects, for example, the planar orientation degree (ΔP) of side A, which is one of the surfaces of Film II, is preferably 165 or more. On the other hand, the upper limit of the planar orientation degree (ΔP) of side A, which is one of the surfaces, is preferably, for example, 190, 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.

[0192] The degree of planar orientation (ΔP) is calculated based on the following formula, using JIS K 7142-1996 5.1 (Method A) by measuring the refractive index in the longitudinal direction (nx), the refractive index in the transverse direction (ny), and the refractive index in the thickness direction (nz) with an Abbe refractometer using sodium D line as a light source: degree of planar orientation (ΔP) = ((nx + ny) / 2 - nz) × 1000

[0193] [Arithmetic Mean Height (Sa)] In the present film II, for example, the arithmetic mean height (Sa) of one surface, side A, is preferably 15 nm or less. If the arithmetic mean height (Sa) is greater than 15 nm, the surface smoothness becomes insufficient, and 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, particularly 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 less than 0.3 nm, the film surface becomes extremely flat, which tends to reduce the slipperiness of the film and impair processability.

[0194] In order to prevent the roughness of one surface from being transferred to the other surface when the present film II 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 deterioration in transportability or windability due to a decrease in the slipperiness of the film.

[0195] The ratio of the arithmetic mean height (Sa) of side A to that of side B of this film II ("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 3.5 or more, even more preferably 4.5 or more, even more preferably 5.5 or more, particularly preferably 6.5 or more, especially preferably 7 or more, even more particularly preferably 7.4 or more, and most preferably 7.8 or more, from the viewpoint of achieving a high level 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 even particularly preferably 14 or less.

[0196] 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, obtained 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, A is the defined area (the entire image), and Z(x, y) is the height from the surface at height 0 of the image point (x, y), and it is expressed as in the above-mentioned [Equation 1]. More specifically, it can be measured by the method described in the examples below.

[0197] [Maximum Peak Height (Sp)] The maximum peak height (Sp) of Side A, one of the surfaces of the present film II, is preferably 150 nm or less. If the maximum peak height (Sp) is greater than 150 nm, the surface smoothness will be insufficient, and defects such as pinholes will be more likely 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, and may be, for example, 65 nm or less, 60 nm or less, 40 nm or less, or 30 nm or less.

[0198] The maximum peak height (Sp) of side B, the other surface of this film II, 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 30 nm or more, more preferably 50 nm or more, from the viewpoint of preventing deterioration in transportability or windability due to a decrease in the slipperiness of the film.

[0199] The ratio of the maximum peak heights (Sp) of sides A and B of Film II ("maximum peak height (Sp) of side B (Sp) / 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, still 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.

[0200] 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 above-mentioned [Equation 2]. More specifically, it can be measured by the method described in the examples below.

[0201] [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 II, 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, which is the other surface of the present film II, 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.

[0202] [Root-mean-square height (Sq)] The root-mean-square height (Sq) of side A, one surface of the present film II, 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 preferably, for example, 0.1 nm or more, more preferably 0.3 nm or more. Furthermore, the root-mean-square height (Sq) of side B, the other surface of the present film II, is preferably 40 nm or less, more preferably 38 nm or less, even more preferably 36 nm or less, and especially 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.

[0203] From the viewpoint of achieving a high degree of both surface smoothness and slip resistance, the ratio of the root mean square height (Sq) of side A to the root mean square height (Sq) of side B of this film II ("root mean square height (Sq) of side B / root mean square height (Sq) of side A"; hereinafter, this may be referred to as "SqB / SqA") is preferably 7 or more, more preferably 8 or more, and even more preferably 9 or more. On the other hand, SqB / SqA is preferably 20 or less, more preferably 18 or less, and even more preferably 17 or less.

[0204] 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 above-mentioned formula [3]. More specifically, it can be measured by the method described in the examples below.

[0205] [Kurtosis (Sku)] The kurtosis (Sku) of Side A, which is one surface of the present film II, 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.

[0206] The kurtosis (Sku) of side B, the other surface of the present film II, 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.

[0207] Kurtosis (Sku) is one of the surface roughness parameters (ISO 25178) and can be used to evaluate the peakiness (kurtosis) of a histogram of height distribution, and can be calculated using the above-mentioned formula (4). More specifically, it can be measured by the method described in the examples below.

[0208] [Skewness (Ssk)] The skewness (Ssk) of side A, which is one surface of the present film II, 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.

[0209] The skewness (Ssk) of side B, the other surface of the present film II, 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.

[0210] Skewness (Ssk) is one of the surface roughness parameters (ISO 25178) and can be determined from the above-mentioned formula (5). More specifically, it can be measured by the method described in the examples below.

[0211] 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. Furthermore, 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 ) and surface properties. When two or more types of particles are used in combination, it is preferable to adjust the content ratio in consideration of the type of particles and polyester used. In addition, during polyester film production, it is also effective to control, for example, the stretching ratio (longitudinal and transverse stretching ratio in the case of biaxial stretching), the stretching temperature, the heat treatment temperature and treatment time (particularly the heat treatment temperature and treatment time after transverse stretching in the case of biaxial stretching). In addition, the same methods as above are also suitable for adjusting other surface properties (root mean square height (Sq), kurtosis (Sku), skewness (Ssk)).

[0212] Unless otherwise specified, the raw materials and the like used in the embodiment of Film II are the same as those described in the description of Film I. That is, the descriptions in the description of Film I from the column "Polyester" to the column "Production Methods Using Film I" are also incorporated by reference into the embodiment of Film II.

[0213] [Examples] The second embodiment of 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 present invention. In the examples, "%" and "ppm" refer to mass standards.

[0214] <Measurement Methods> Various measurement methods in the following examples are the same as those described in the examples according to the first embodiment.

[0215] Next, the polyester raw materials used in the examples and comparative examples are shown in Table II-1. The polyesters in polyester raw materials II-A to II-M listed in Table II-1 are all homopolyethylene terephthalate. Furthermore, polyester raw material II-M is a recycled raw material made by recovering and recycling waste materials.

[0216]

[0217] [Example II-1] A raw material for surface layer A was a blend of 88% Polyester II-A, 8% Polyester II-D, and 4% Polyester II-F by mass. A raw material for intermediate layer C was a blend of 50% Polyester II-B and 50% Polyester II-M by mass. A raw material for surface layer B was a blend of 28% Polyester II-B, 22% Polyester II-I, and 50% Polyester II-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-kind, three-layer (A / C / B) structure in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, with the thickness composition ratio of A / C / B being 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 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%, 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 would be 215°C, and the heat treatment was carried out for 5.1 seconds.

[0218] [Example II-2] A raw material for surface layer A was a blend of 88% Polyester II-A, 8% Polyester II-D, and 4% Polyester II-F by mass. A raw material for intermediate layer C was a blend of 50% Polyester II-B and 50% Polyester II-M by mass. A raw material for surface layer B was a blend of 28% Polyester II-B, 22% Polyester II-I, and 50% Polyester II-K by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. The raw materials for surface layer A and surface layer B were then co-extruded to form a three-kind, three-layer (A / C / B) structure with the raw materials for surface layer A and surface layer B as the outermost layers (surface layers) and the raw materials for intermediate layer C as the intermediate layer, with a thickness composition ratio of A / C / B = 4 / 25 / 2 under 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%, 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 would be 215°C, and the heat treatment was carried out for 5.1 seconds.

[0219] [Example II-3] A raw material for surface layer A was a blend of 84% Polyester II-A, 12% Polyester II-D, and 4% Polyester II-F by mass, a raw material for intermediate layer C was 100% Polyester II-C, and a raw material for surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-H, and 50% Polyester II-J by mass, and these were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B=4 / 19 / The film was co-extruded to a thickness of 2 μm (A / C / B=4 μm / 19 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 a 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 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 reached 230° C., and the heat treatment was carried out for 7.8 seconds.

[0220] [Example II-4] A raw material for surface layer A was a blend of 84% Polyester II-A, 12% Polyester II-D, and 4% Polyester II-F by mass, a raw material for intermediate layer C was 100% Polyester II-C, and a raw material for surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-H, and 50% Polyester II-J by mass, and these were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B=4 / 19 / The film was co-extruded to a thickness of 2 μm (A / C / B=4 μm / 19 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 82° C. using the peripheral speed difference with a 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 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 reached 230° C., and the heat treatment was carried out for 7.8 seconds.

[0221] [Example II-5] A raw material for the surface layer A was a blend of 88% Polyester II-B and 12% Polyester II-E in a mass ratio, a raw material for the intermediate layer C was 100% Polyester II-B, and a raw material for the surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-I, and 50% Polyester II-K in a mass ratio. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was formed, with the raw materials for the surface layer A and the surface layer B as the outermost layers (surface layers) and the intermediate layer C as the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B = 4 / 19 / 2. The film was coextruded and cooled to a surface temperature of 20°C and a peripheral speed of 4m / 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 (14.1m / min). The 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 25μm (A / C / B = 4μm / 19μm / 2μm). The heat-treatment (fixing) step was performed with a temperature gradient to achieve a final temperature of 230°C, and the heat treatment was performed for 7.8 seconds.

[0222] [Example II-6] A raw material for the surface layer A was a blend of 91% Polyester II-B and 9% Polyester II-D by mass, a raw material for the intermediate layer C was 100% Polyester II-M, and a raw material for the surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-I, and 50% Polyester II-K by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, they were extruded together under the conditions of a thickness composition ratio of A / C / B=8 / 15 / 2 to form a three-kind, three-layer (A / C / B) structure in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer. The film was extruded, 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 an electrostatic adhesion method to obtain an amorphous film. The film was then stretched 3.8 times in the machine direction (MD direction) 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 direction stretched film was then introduced into a tenter and stretched 4.2 times in the transverse direction (TD direction) at 105°C. The film was then heat-treated (fixed) at 230°C in the tenter and cooled to 140°C at a relaxation rate of 5%, 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 reached 230°C, and the heat treatment was carried out for 5.9 seconds.

[0223] [Example II-7] A raw material for the surface layer A was a blend of 91% Polyester II-B and 9% Polyester II-D by mass, a raw material for the intermediate layer C was 100% Polyester II-M, and a raw material for the surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-I, and 50% Polyester II-K by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, they were co-extruded under the extrusion conditions to form a three-kind, three-layer (A / C / B) structure in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, with a thickness composition ratio of A / C / B = 8 / 15 / 2. The film was then drawn out and 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 an electrostatic adhesion 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 at a relaxation rate of 17%, yielding 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 to achieve a final temperature of 230°C, and the heat treatment was carried out for 5.9 seconds.

[0224] [Comparative Example II-1] A raw material for the surface layer A was a blend of 97% Polyester II-B and 3% Polyester II-G by mass, a raw material for the intermediate layer C was 100% Polyester II-C, and a raw material for the surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-H, and 50% Polyester II-J by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, they were extruded together under the conditions of a thickness composition ratio of A / C / B=4 / 19 / 2 to form a three-kind, three-layer (A / C / B) structure in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer. The film was extruded, 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 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 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%, 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 reached 230°C, and the heat treatment was carried out for 7.3 seconds.

[0225] [Comparative Example II-2] A raw material for the surface layer A was a blend of 97% Polyester II-B and 3% Polyester II-G in a mass ratio, a raw material for the intermediate layer C was 100% Polyester II-C, and a raw material for the surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-H, and 50% Polyester II-J in a mass ratio. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was formed, with the raw materials for the surface layer A and the surface layer B as the outermost layers (surface layers) and the intermediate layer C as the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B = 4 / 19 / 2. Coextrusion was performed using an electrostatic contact method, followed by cooling and solidification 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. Subsequently, the film was 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 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, followed by cooling at 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 reached 210°C, and the heat treatment was performed for 7.3 seconds.

[0226] [Comparative Example II-3] A raw material for the surface layer A was a blend of 97% Polyester II-B and 3% Polyester II-L by mass, a raw material for the intermediate layer C was 100% Polyester II-C, and a raw material for the surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-H, and 50% Polyester II-J by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, they were extruded together under the conditions of a thickness composition ratio of A / C / B=4 / 19 / 2 to form a three-kind, three-layer (A / C / B) structure in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer. The film was extruded, 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 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 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%, 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 reached 230°C, and the heat treatment was carried out for 7.3 seconds.

[0227] [Comparative Example II-4] A raw material for the surface layer A was a blend of 97% Polyester II-B and 3% Polyester II-L in a mass ratio, a raw material for the intermediate layer C was 100% Polyester II-C, and a raw material for the surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-H, and 50% Polyester II-J in a mass ratio. 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 used as the outermost layers (surface layers) and the intermediate layer C was used as the intermediate layer, and the extrusion conditions were such that the thickness composition ratio was A / C / B = 4 / 19 / 2 in a three-kind, three-layer (A / C / B) structure. The film was extruded, 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 adhesion method to obtain an amorphous film, which 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 direction 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%, 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 carried out for 7.3 seconds.

[0228] [Comparative Example II-5] A raw material for surface layer A was a blend of 90% Polyester II-B, 4% Polyester II-F, and 6% Polyester II-L in a mass ratio. A raw material for intermediate layer C was 100% Polyester II-C. A raw material for surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-H, and 50% Polyester II-J in a mass ratio. These were fed into a vented extruder and melt-extruded at 280°C. The resulting mixture had a three-kind, three-layer (A / C / B) structure, with the raw materials for surface layer A and surface layer B as the outermost layers (surface layers) and intermediate layer C as the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B = 4 / 19 / 2. The film was co-extruded to the desired thickness, and 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 adhesion method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD direction) at a film temperature of 86 ° C. using the peripheral speed difference with the stretching roll set at a peripheral speed of 15.1 m / min. The machine direction stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD direction) at 105 ° C. The film was 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 reached 243 ° C., and the heat treatment was carried out for 7.3 seconds.

[0229] [Comparative Example II-6] A raw material containing 100% Polyester II-B was used as the raw material for surface layer A, a raw material containing 100% Polyester II-C was used as the raw material for intermediate layer C, and a raw material for surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-H, and 50% Polyester II-J by mass. These materials were supplied to 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-kind, three-layer (A / C / B) layer structure in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, with the thickness composition ratio of A / C / B being 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 to obtain an amorphous film, which 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, followed by heat treatment (setting) at 230°C in the tenter and cooling at 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 (setting) step, a temperature gradient was applied so that the final temperature was 230°C, and the heat treatment was carried out for 7.3 seconds.

[0230] [Comparative Example II-7] A raw material containing 100% Polyester II-B was used as the raw material for surface layer A, a raw material containing 100% Polyester II-C was used as the raw material for intermediate layer C, and a raw material for surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-H, and 50% Polyester II-J in mass proportions. These materials were supplied to 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-kind, three-layer (A / C / B) layer structure in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, with the thickness composition ratio of A / C / B being 4 / 19 / 2 under the extrusion conditions. Then, an electrostatic application adhesion method was performed. 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, which was then stretched 3.5 times in the machine direction (MD direction) 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 direction stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD direction) at 105 ° C., followed by heat treatment (fixing) at 230 ° C. in the tenter and cooling treatment at 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 carried out for 7.8 seconds.

[0231] [Comparative Example II-8] A raw material for the surface layer A was a blend of 88% Polyester II-B and 12% Polyester II-E in a mass ratio, a raw material for the intermediate layer C was 100% Polyester II-B, and a raw material for the surface layer B was a blend of 28% Polyester II-C, 22% Polyester II-I, and 50% Polyester II-K in a mass ratio. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was formed, with the raw materials for the surface layer A and the surface layer B as the outermost layers (surface layers) and the intermediate layer C as the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B = 4 / 19 / 2. Coextrusion was performed using an electrostatic contact method, and the film was cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4m / 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 a stretching roll set at a peripheral speed of 14.1m / min. The machine-stretched film was then introduced into a tenter and stretched 4.2 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 25μm (A / C / B = 4μm / 19μm / 2μm). In the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature reached 230°C, and the heat treatment was performed for 7.8 seconds.

[0232] The properties of each of the films obtained above were measured according to the methods described above, and the results are shown in Table II-2 (Examples II-1 to II-7) and Table II-3 (Comparative Examples II-1 to II-8).

[0233]

[0234]

[0235] First, as shown in Table II-2, the polyester films of Examples II-1 to II-7 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 had elastic deformation power (η it) and the shrinkage rate after heat treatment are controlled within a specific range. it ) is more than 55%, and the shrinkage rates in both the longitudinal and transverse directions after heat treatment at 150° C. for 5 minutes are 2.8% or less. Therefore, it is clear that the polyester films of Examples II-1 to II-7 are less likely to cause coating irregularities or wrinkles during the process of forming a ceramic green sheet or a peelable layer in the production process of a multilayer ceramic capacitor, and can effectively suppress peeling problems of the ceramic green sheet.

[0236] On the other hand, as shown in Table II-3, in Comparative Examples II-1 to II-8, the elastic deformation power (η it In other words, the polyester films of Comparative Examples II-1 to II-8 have a high elastic deformation power (η it ) is more than 55%, and the shrinkage rate in the longitudinal direction and the transverse direction after heat treatment at 150°C for 5 minutes is 2.8% or less. Specifically, the polyester films of Comparative Examples II-1, II-3, and II-5 to II-8 do not satisfy at least one of the requirements that the elastic deformation power (η it The polyester films of Comparative Examples II-2 and II-4 had a large shrinkage rate after heat treatment and were not satisfactory in terms of heat distortion resistance.

[0237] 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 peeling defects in the process of peeling a ceramic green sheet from a release film, coating spots and wrinkles tend to occur in the heat treatment process in the manufacturing process of a multilayer ceramic capacitor, and the elastic deformation power (η it ) and heat distortion resistance 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 Examples II-1 to II-5, it can be seen that the temperature conditions in the heat setting treatment are it), it is suggested that the temperature conditions in the heat setting process can be adjusted to control the elastic deformation power (η it ) is improved, the shrinkage rate after heat treatment tends to worsen. Similarly, for example, from the results of Comparative Example II-6 and Comparative Example II-7, it can be seen that when the peripheral speed of the stretching roll is increased, the elastic deformation power (η it ), but it is suggested that the elastic deformation power (η it ) is improved, the shrinkage rate (TD direction) after heat treatment tends to worsen. In addition, in Comparative Example II-8, in which the transverse draw ratio was reduced compared to Example II-5 in order to reduce the shrinkage rate after heat treatment, the elastic deformation power (η it ) did not reach 55%. 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.

[0238] According to one embodiment of 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 coating spots and wrinkles. 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.

[0239] Third Embodiment A third embodiment, which is an example of an embodiment of the present invention, will be described below, although the present invention is not limited to the embodiment described below.

[0240] As mentioned above, in recent years, with the increasing use of electrical equipment in automobiles and the increasing functionality of smartphones, there has been a demand for smaller multilayer ceramic capacitors with higher capacitance. In response to this demand, efforts have been made to reduce the thickness of ceramic green sheets. However, as ceramic green sheets become thinner, there is concern that the possibility of peeling defects such as breakage occurring in the process of peeling the ceramic green sheets from the release film increases.

[0241] 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 in order to improve the releasability of the ceramic green sheet, and which has an elastic deformation power of 45% or more in a load-displacement curve measured when a load of 20 mN is applied to the release agent layer side using a micro-surface hardness tester.

[0242] It is predicted that multilayer ceramic capacitors will continue to become smaller and have higher capacitance in the future, which will require even thinner ceramic green sheets. As ceramic green sheets become thinner, it is expected that there will be greater concerns than ever before about peeling defects such as breakage during the process of peeling the ceramic green sheets from the release film, and therefore further improvement in the elastic deformation power mentioned above will be required.

[0243] As a result of extensive research, the inventors have found that there is a correlation between the degree of planar orientation (ΔP) of polyester film and the elastic deformation power. However, it has become clear that, for example, depending on the characteristics of the particles to be blended, satisfactory results cannot be obtained in terms of the elastic deformation power, and that it is extremely difficult to optimize the design and formulation of the release film.

[0244] In view of the above circumstances, the present inventors have conducted extensive research to increase the elastic deformation power of polyester films, and have found that the above problems can be solved by using a specific polyester film.

[0245] That is, the present invention provides the following as one embodiment. [III-1] A polyester film having an elastic deformation power of more than 55% on one surface and a planar orientation degree (ΔP) of the one surface of the polyester film of 165 or more. [III-2] The polyester film according to [III-1], wherein the layer forming the one surface contains particles, the particles being mainly composed of particles having a Mohs hardness of 8 or less. [III-3] The polyester film according to [III-1] or [III-2], wherein the layer forming the one surface contains particles, the ratio of the content of particles having a Mohs hardness of 8 or less to the total content of particles contained in the layer forming the one surface (content of particles having a Mohs hardness of 8 or less / total content of particles) being 0.6 or more by mass. [III-4] The polyester film according to any one of [III-1] to [III-3], wherein the layer forming the one surface contains particles, the particles being mainly composed of particles having a Mohs hardness of 8 or less, the content of the particles having a Mohs hardness of 8 or less being less than 1,800 ppm by mass relative to the layer forming the one surface. [III-5] The polyester film according to any one of [III-1] to [III-4], wherein the one surface 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. [III-6] The polyester film according to any one of [III-1] to [III-5], wherein the ratio of the arithmetic mean height (Sa) of the one surface to the arithmetic mean height (Sa) of the other surface (the arithmetic mean height (Sa) of the other surface / the 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). [III-7] The polyester film according to any one of [III-1] to [III-6], wherein the shrinkage rate in the longitudinal direction and the transverse direction after heat treatment at 150°C for 5 minutes is 2.8% or less. [III-8] The polyester film according to any one of [III-1] to [III-7], which has a shrinkage rate in the transverse direction of 1.5% or less after heat treatment at 150°C for 5 minutes.[III-9] The polyester film according to any one of [III-1] to [III-8], comprising at least particles (a1) and particles (a2), wherein the particles (a1) are alumina particles and the particles (a2) are particles other than the particles (a1). [III-10] The polyester film according to any one of [III-1] to [III-9], comprising at least particles (a1) and particles (a2), wherein the zeta potentials at pH 7 of the particles (a1) and (a2) 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). [III-11] The polyester film according to any one of [III-1] to [III-10], comprising a surface layer forming one surface, an intermediate layer, and a surface layer forming the other surface, in this order, wherein the thickness of the intermediate layer is greater than the thickness of each of the surface layers. [III-12] The polyester film according to any one of [III-1] to [III-11], wherein the polyester film comprises a surface layer forming 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 to 10:10 to 35:1 to 5. [III-13] The polyester film according to any one of [III-1] to [III-12], wherein the surface layer forming the other surface contains particles, in this order, and the particle content of the surface layer forming the other surface is 2000 ppm to 8000 ppm by mass relative to the surface layer forming the other surface. [III-14] The polyester film according to any one of [III-1] to [III-13], wherein the polyester film is used as a support for a ceramic green sheet in the production process of a multilayer ceramic capacitor. [III-15] The polyester film according to any one of [III-1] to [III-13], which is used as a support for a ceramic green sheet in the production process of an automotive multilayer ceramic capacitor.[III-16] Use of the polyester film according to any one of [III-1] to [III-13] as a support for a ceramic green sheet in the process of producing a multilayer ceramic capacitor. [III-17] Use of the polyester film according to any one of [III-1] to [III-13] as a support for a ceramic green sheet in the process of producing an automotive multilayer ceramic capacitor. [III-18] A method for producing a ceramic green sheet, comprising a step of applying a ceramic slurry containing a ceramic component to one surface of the polyester film according to any one of [III-1] to [III-13].

[0246] According to one embodiment of the present invention, the elastic deformation power of the polyester film can be increased, and therefore, when the polyester film is used as a support for a ceramic green sheet used in the manufacturing process of a multilayer ceramic capacitor, peeling failure of the ceramic green sheet can be effectively suppressed.

[0247] The present invention will be described in more detail below based on the third embodiment of the present invention, but the present invention is not limited to these embodiments.

[0248] As will be described in detail below, a polyester film according to a third embodiment of the present invention (hereinafter sometimes referred to as "the present film III") preferably has one surface having an elastic deformation power of more than 55% and a planar orientation degree (ΔP) of the one surface of at least 165. More preferably, the layer forming the one surface contains particles, the main component of which is particles having a Mohs hardness of 8 or less.

[0249] In the course of research and development into a support for a ceramic green sheet that can accommodate further thinning of the ceramic green sheet (for example, a thickness of 0.5 μm or less after drying) in line with the trend toward smaller size and higher capacity of multilayer ceramic capacitors, the present inventors have focused on the various properties of the polyester film that serves as the support, particularly the elastic deformation power (η it ) and the elastic deformation power (η itWe have begun research into technologies that will further enhance this.

[0250] In the course of such research, the present inventors have found that, for example, by blending particles, the elastic deformation power (η it However, it was found that it was difficult to obtain satisfactory results. For example, when particles with a Mohs hardness of 9 were blended, the conformability of the film during stretching decreased, voids were generated, and the elastic deformation power (η it ) may not be able to obtain satisfactory results. Furthermore, even if specific particles that can improve the elastic deformation power can be selected, the improvement effect on the elastic deformation power may differ depending on the degree of planar orientation of the release film. it ) It has been found that satisfactory results may not be obtained in some cases. Furthermore, it has also been found that there is a concern that the surface smoothness of the release film may be deteriorated due to particle aggregation.

[0251] The inventors have calculated the elastic deformation power (η it As a result of further research and experiments aimed at increasing the elastic deformation power (η it We have succeeded in discovering a new technology to improve this.

[0252] The present invention has newly proposed film III, which has a high elastic deformation power (η it ) can be provided, which is very advantageous in that, for example, it has a high restoring force against deformation that occurs when cutting the ceramic green sheet and provides excellent peelability of the ceramic green sheet.

[0253] Furthermore, due to the demand for thinner ceramic green sheets, there is a concern that when there are minute protrusions on the surface of a release film, these may cause pinholes or the like to form in the ceramic green sheet. In one embodiment of the present invention, however, the elastic deformation power (η it) and surface smoothness can be highly achieved, which means that, for example, the ceramic green sheet has a high recovery force against deformation that occurs when it is cut, resulting in excellent peelability of the ceramic green sheet, and the occurrence of surface defects such as pinholes can be effectively suppressed, making it extremely excellent in that it can provide a release film or the like that can ensure high quality reliability.

[0254] Furthermore, during the manufacturing process of a multilayer ceramic capacitor, for example, if the release film undergoes thermal shrinkage due to heat treatment for drying the ceramic slurry coated on the release film, there is a concern that coating irregularities and wrinkles may occur. Therefore, release films and the like are required to have heat deformation resistance. However, the inventors have found that increasing the elastic deformation power to suppress the aforementioned peel failure tends to reduce heat deformation resistance. One embodiment of the present invention is excellent in that it can effectively suppress the occurrence of peel failure of ceramic green sheets and also effectively suppress the occurrence of coating irregularities and wrinkles. Below, one embodiment of this film III will be described in detail.

[0255] <<Present Film III>> The present film III is suitably used, for example, as a support (substrate) for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors.

[0256] [Elastic deformation power (η it ) )] From the viewpoint of effectively suppressing the above-mentioned peeling failure, the present film III has an elastic deformation power (η it ) is preferably more than 55%. it By controlling the elastic deformation power (η ) to a specific range of more than 55%, it is possible to realize a high level of peelability, which is particularly required in the manufacturing process of MLCC using thin ceramic green sheets, and to effectively suppress peel failure. 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. it The upper limit of the ratio is not particularly limited, but may be, for example, about 70%, or about 65%.

[0257] Elastic deformation power of surface A (η it By using the present film III 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 III, and a good gap can be formed between the two. This gap can be used to grip the present film III and easily separate the ceramic green sheet from the present film III.

[0258] Elastic deformation power (η it The elastic deformation power (η) is calculated by the following formula based on physical quantities measured by nanoindentation (in accordance with ISO 14577). Specifically, it is determined by the method described in the Examples below. it ) = (Welast / Wtotal) × 100 [%] [Wtotal (total deformation work) = Wplast (plastic deformation work) + Welast (elastic deformation work)]

[0259] [Arithmetic Mean Height (Sa)] In the present film III, for example, the arithmetic mean height (Sa) of one surface, side A, is preferably 15 nm or less. 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, particularly 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 less than 0.3 nm, the film surface becomes too flat, which tends to reduce the slipperiness of the film and impair processability. From the viewpoint of the slipperiness of the film, the lower limit of the arithmetic mean height (Sa) of side A may be 0.8 nm or more, 1 nm or more, 1.5 nm or more, 2 nm or more, etc., but 2 nm or more is particularly preferred.

[0260] In order to prevent the roughness of one surface from being transferred to the other surface when the present film III 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 deterioration in transportability or windability due to a decrease in the slipperiness of the film.

[0261] The ratio of the arithmetic mean height (Sa) of side A to the arithmetic mean height (Sa) of side B of this film III ("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 even more preferably 14 or less. The ratio (SaB / SaA) can be set appropriately within the above range and is not limited to the following, and 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.

[0262] 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, obtained 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, A is the defined area (the entire image), and Z(x, y) is the height from the surface at height 0 of the image point (x, y), and it is expressed as in the above-mentioned [Equation 1]. More specifically, it can be measured by the method described in the examples below.

[0263] [Maximum Peak Height (Sp)] The maximum peak height (Sp) of Side A, one of the surfaces of the present film III, is preferably 150 nm or less. If the maximum peak height (Sp) is greater than 150 nm, the surface smoothness will be insufficient, and surface defects such as pinholes will be more likely to occur, making it difficult to achieve 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, and even more preferably 90 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, and may be, for example, 65 nm or less, 60 nm or less, 40 nm or less, or 30 nm or less.

[0264] The maximum peak height (Sp) of Side B, the other surface of Film III, 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 30 nm or more, more preferably 50 nm or more, from the viewpoint of preventing deterioration in transportability or windability due to a decrease in the slipperiness of the film.

[0265] The ratio of the maximum peak heights (Sp) of sides A and B of Film III ("maximum peak height (Sp) of side B (Sp) / 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, still 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.

[0266] 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 above-mentioned [Equation 2]. More specifically, it can be measured by the method described in the examples below.

[0267] [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 III, 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, which is the other surface of the present film III, 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.

[0268] [Root-mean-square height (Sq)] The root-mean-square height (Sq) of side A, one surface of the present film III, 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 preferably, for example, 0.1 nm or more, more preferably 0.3 nm or more. Furthermore, the root-mean-square height (Sq) of side B, the other surface of the present film III, 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.

[0269] From the viewpoint of achieving a high degree of both surface smoothness and slip resistance, the ratio of the root mean square height (Sq) of side A to the root mean square height (Sq) of side B of this film III ("root mean square height (Sq) of side B / root mean square height (Sq) of side A"; hereinafter, this may be referred to as "SqB / SqA") is preferably 7 or more, more preferably 8 or more, and even more preferably 9 or more. On the other hand, SqB / SqA is preferably 20 or less, more preferably 18 or less, and even more preferably 17 or less.

[0270] 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 above-mentioned formula [3]. More specifically, it can be measured by the method described in the examples below.

[0271] [Kurtosis (Sku)] The kurtosis (Sku) of Side A, which is one surface of the present film III, 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.

[0272] The kurtosis (Sku) of Side B, the other surface of Film III, 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.

[0273] Kurtosis (Sku) is one of the surface roughness parameters (ISO 25178) and can be used to evaluate the peakiness (kurtosis) of a histogram of height distribution, and can be calculated using the above-mentioned formula (4). More specifically, it can be measured by the method described in the examples below.

[0274] [Skewness (Ssk)] The skewness (Ssk) of side A, which is one surface of the present film III, 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.

[0275] The skewness (Ssk) of side B, the other surface of the present film III, 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.

[0276] Skewness (Ssk) is one of the surface roughness parameters (ISO 25178) and can be determined from the above-mentioned formula (5). More specifically, it can be measured by the method described in the examples below.

[0277] The arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk) can be adjusted by, for example, adjusting the content of particles in consideration of the type of particles, specifically, for example, composition, average particle size, particle size distribution, hardness, and affinity with the polyester to be contained. Adjusting the type and content of particles in consideration of the type of polyester to be contained, for example, composition, viscosity, molecular weight, thermal properties, and the presence or absence of a copolymerization component, is also useful for adjusting surface properties. When two or more types of particles are used in combination, it is preferable to adjust the content ratio in consideration of the type of particles and polyester to be used. Furthermore, during polyester film production, it is also effective to control, for example, the stretching ratio (longitudinal and transverse stretching ratios in the case of biaxial stretching), the stretching temperature, and the heat treatment temperature and treatment time (particularly the heat treatment temperature and treatment time after transverse stretching in the case of biaxial stretching).

[0278] [Shrinkage after Heat Treatment] The manufacturing process of multilayer ceramic capacitors includes heat treatments, such as drying a release agent coated on a polyester film and drying a ceramic slurry coated on a release film. Therefore, a decrease in heat distortion resistance can lead to coating irregularities and wrinkles. In other words, heat distortion resistance is an important characteristic for ensuring the quality reliability of the finished product, from intermediate products to the final product in the manufacturing process of multilayer ceramic capacitors, such as the lamination characteristics of ceramic green sheets. To prevent such coating irregularities and wrinkles, the shrinkage of this film III in the machine direction (MD direction) after heat treatment at 150°C for 5 minutes is preferably 2.8% or less. From the same viewpoint, the shrinkage 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 (150° C., 5 minutes) in the machine direction (MD direction) is about −1%, preferably −0.5% or more, and more preferably −0.3% or more.

[0279] Furthermore, the shrinkage rate in the transverse direction (TD) of this film III 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. From the viewpoint of realizing high thermal distortion resistance, which is particularly required in the manufacturing process of MLCC using the thin ceramic green sheet, the shrinkage rate in the transverse direction (TD) (150°C, 5 minutes) is preferably 1.4% or less, more preferably 1.3% or less. 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.

[0280] In addition, the elastic deformation power (η itIn 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-mentioned ranges.

[0281] [Planar Orientation Degree (ΔP)] In order to suppress the aforementioned peeling defects, the present film III 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.

[0282] The degree of planar orientation (ΔP) is calculated based on the following formula, using JIS K 7142-1996 5.1 (Method A) by measuring the refractive index in the longitudinal direction (nx), the refractive index in the transverse direction (ny), and the refractive index in the thickness direction (nz) with an Abbe refractometer using sodium D line as a light source: degree of planar orientation (ΔP) = ((nx + ny) / 2 - nz) × 1000

[0283] Unless otherwise specified, the raw materials and the like used in the embodiment of Film III are the same as those described for Film I. That is, the descriptions in the description of Film I from the column "Polyester" to the column "Production Methods Using Film I" are also applicable to the embodiment of Film III.

[0284] [Examples] The third embodiment of 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 present invention. In the examples, "%" and "ppm" refer to mass standards.

[0285] <Measurement Methods> Various measurement methods in the following examples are the same as those described in the examples according to the first embodiment.

[0286] Next, the polyester raw materials used in the examples and comparative examples are shown in Table III-1. The polyesters in polyester raw materials III-A to III-L listed in Table III-1 are all homopolyethylene terephthalate. Furthermore, polyester raw material III-L is a recycled raw material made by recovering and recycling waste materials.

[0287]

[0288] [Example III-1] A raw material for the surface layer A was a blend of 88% Polyester III-A, 8% Polyester III-D, and 4% Polyester III-E by mass. A raw material for the intermediate layer C was a blend of 50% Polyester III-B and 50% Polyester III-L by mass. A raw material for the surface layer B was a blend of 28% Polyester III-B, 22% Polyester III-H, and 50% Polyester III-J by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. The raw materials for the surface layer A and the surface layer B were co-extruded to form a three-kind, three-layer (A / C / B) structure with the raw materials for the surface layer A and the surface layer B as the outermost layer (surface layer) and the intermediate layer C as the intermediate layer, with a 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 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%, 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 would be 215°C, and the heat treatment was carried out for 5.1 seconds.

[0289] [Example III-2] A raw material for the surface layer A was a blend of 88% Polyester III-A, 8% Polyester III-D, and 4% Polyester III-E by mass. A raw material for the intermediate layer C was a blend of 50% Polyester III-B and 50% Polyester III-L by mass. A raw material for the surface layer B was a blend of 28% Polyester III-B, 22% Polyester III-H, and 50% Polyester III-J by mass. These raw materials were fed into a vented extruder and melt-extruded at 280°C. The raw materials for the surface layer A and the surface layer B were co-extruded to form a three-kind, three-layer (A / C / B) structure with the raw materials for the surface layer A and the surface layer B as the outermost layer (surface layer) and the intermediate layer C as the intermediate layer, with a thickness composition ratio of A / C / B = 4 / 25 / 2 under the extrusion conditions. The resulting material was cooled and solidified on a cooling roll with a surface temperature set at 20°C using an electrostatic adhesion method to obtain an amorphous film. Next, the film was stretched 3.6 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%, 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 would be 215°C, and the heat treatment was carried out for 5.1 seconds.

[0290] [Example III-3] A raw material for surface layer A was a blend of 84% Polyester III-A, 12% Polyester III-D, and 4% Polyester III-E by mass, a raw material for intermediate layer C was 100% Polyester III-C, and a raw material for surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-G, and 50% Polyester III-I by mass, all of which were fed into a vented extruder and melt-extruded at 280°C. The resulting mixture had a three-kind, three-layer (A / C / B) structure, with the raw materials for surface layer A and surface layer B as the outermost layers (surface layers) and intermediate layer C as the intermediate layer, and a thickness composition ratio of A / C / B=4 under the extrusion conditions. The film was co-extruded to a thickness of 19 / 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 adhesion method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD direction) 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 direction stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD direction) 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 reached 230 ° C., and the heat treatment was performed for 7.8 seconds.

[0291] [Example III-4] A raw material for the surface layer A was a blend of 84% Polyester III-A, 12% Polyester III-D, and 4% Polyester III-E in a mass ratio. A raw material for the intermediate layer C was 100% Polyester III-C. A raw material for the surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-G, and 50% Polyester III-I in a mass ratio. These were fed into a vented extruder and melt-extruded at 280°C. The resulting extruded material had a three-kind, three-layer (A / C / B) layer structure, with the raw materials for the surface layer A and the surface layer B as the outermost layers (surface layers) and the intermediate layer C as the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B=4. The film was co-extruded to a thickness of 19 / 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 adhesion method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD direction) at a film temperature of 82 ° C. using the peripheral speed difference with the stretching roll set at a peripheral speed of 14.1 m / min. The machine direction stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD direction) 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.

[0292] [Example III-5] A raw material for the surface layer A was a blend of 97% Polyester III-B and 3% Polyester III-F by mass, a raw material for the intermediate layer C was 100% Polyester III-C, and a raw material for the surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-G, and 50% Polyester III-I by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained, with the raw materials for the surface layer A and the surface layer B as the outermost layers (surface layers) and the intermediate layer C as the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B = 4 / 19 / 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 the stretching roll set at a peripheral speed of 15.1 m / min. The machine direction 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%, 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 reached 210°C, and the heat treatment was carried out for 7.3 seconds.

[0293] [Example III-6] A raw material for the surface layer A was a blend of 97% Polyester III-B and 3% Polyester III-K by mass, a raw material for the intermediate layer C was 100% Polyester III-C, and a raw material for the surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-G, and 50% Polyester III-I by mass, all of which were fed into a vented extruder and melt-extruded at 280°C. The raw materials for the surface layer A and the surface layer B were then extruded under conditions such that the thickness composition ratio of the raw materials for the surface layer A and the surface layer B was 4 / 19 / 2, resulting in a three-kind, three-layer (A / C / B) structure. 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 direction 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%, to obtain 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 so that the final temperature reached 210°C, and the heat treatment was carried out for 7.3 seconds.

[0294] [Example III-7] A raw material for the surface layer A was a blend of 91% Polyester III-B and 9% Polyester III-D in a mass ratio, a raw material for the intermediate layer C was 100% Polyester III-L, and a raw material for the surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-H, and 50% Polyester III-J in a mass ratio. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained, with the raw materials for the surface layer A and the surface layer B as the outermost layers (surface layers) and the intermediate layer C as the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B = 8 / 15 / 2. The film was co-extruded at 20°C and cooled to a peripheral speed of 5.1 m / min on a cooling roll using an electrostatic contact 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 (18.5 m / min). The 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 and cooled to 140°C at a relaxation rate of 17%, obtaining a polyester film with a thickness of 25 μm (A / C / B = 8 μm / 15 μm / 2 μm). The heat-treatment (fixing) step was performed with a temperature gradient to achieve a final temperature of 230°C, and the heat treatment was performed for 5.9 seconds.

[0295] [Example III-8] A raw material for the surface layer A was a blend of 91% Polyester III-B and 9% Polyester III-D by mass, a raw material for the intermediate layer C was 100% Polyester III-L, and a raw material for the surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-H, and 50% Polyester III-J 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 extruded under the conditions of a thickness composition ratio of A / C / B=8 / 15 / 2 to form a three-kind, three-layer (A / C / B) structure in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer. 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 5.1 m / min using an electrostatic contact 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 direction 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 at a relaxation rate of 5%, yielding a polyester film with a thickness of 25 μm (A / C / B = 8 μm / 15 μm / 2 μm). The heat-treatment (fixing) step was performed with a temperature gradient to achieve a final temperature of 230°C for 5.9 seconds.

[0296] [Example III-9] A raw material for the surface layer A was a blend of 94% Polyester III-B and 6% Polyester III-D by mass, a raw material for the intermediate layer C was a blend of 50% Polyester III-C and 50% Polyester III-L by mass, and a raw material for the surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-G, and 50% Polyester III-I by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained, in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B. The film was coextruded to a C / B ratio of 4 / 25 / 2, 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 31 μm (A / C / B = 4 μm / 25 μm / 2 μm). The heat-treatment (fixing) step involved applying a temperature gradient to the final temperature of 230°C, and the heat treatment was carried out for 7.8 seconds.

[0297] [Example III-10] A raw material for the surface layer A was a blend of 88% Polyester III-B and 12% Polyester III-D by mass, a raw material for the intermediate layer C was a blend of 50% Polyester III-C and 50% Polyester III-L by mass, and a raw material for the surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-G, and 50% Polyester III-I by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, and the thickness composition ratio was A under the extrusion conditions. The film was coextruded to a ratio of A / C / B = 4 / 25 / 2, 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 direction 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 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 reached 230°C, and the heat treatment was carried out for 7.8 seconds.

[0298] [Example III-11] A raw material for surface layer A was a blend of 90% Polyester III-B, 4% Polyester III-E, and 6% Polyester III-K by mass, a raw material for intermediate layer C was 100% Polyester III-C, and a raw material for surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-G, and 50% Polyester III-I by mass, all of which were fed into a vented extruder and melt-extruded at 280°C. The resulting extruded material had 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 layers (surface layers) and intermediate layer C as the intermediate layer, and a thickness composition ratio of A / C / B=4 / 1 under the extrusion conditions. The film was co-extruded to a ratio of 9 / 2, and 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 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 15.1 m / min. The machine direction 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 reached 230 ° C., and the heat treatment was carried out for 7.3 seconds.

[0299] [Comparative Example III-1] A raw material containing 100% Polyester III-B was used as the raw material for surface layer A, a raw material containing 100% Polyester III-C was used as the raw material for intermediate layer C, and a raw material for surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-G, and 50% Polyester III-I by mass, which were supplied to 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-kind, three-layer (A / C / B) layer structure in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and intermediate layer C was the intermediate layer, with the thickness composition ratio of A / C / B being 4 / 19 / 2 under the extrusion conditions, and the adhesion was measured by applying electrostatic force. Using a 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, and then stretched 3.5 times in the machine direction (MD direction) 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 direction stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD direction) at 105 ° C., followed by heat treatment (fixing) at 230 ° C. in the tenter and cooling treatment at 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 carried out for 7.3 seconds.

[0300] [Comparative Example III-2] A raw material containing 100% Polyester III-B was used as the raw material for surface layer A, a raw material containing 100% Polyester III-C was used as the raw material for intermediate layer C, and a raw material for surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-G, and 50% Polyester III-I 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-kind, 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 intermediate layer C as the intermediate layer, with the thickness composition ratio of A / C / B being 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 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 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 reached 230°C, and the heat treatment was carried out for 7.8 seconds.

[0301] [Comparative Example III-3] A raw material for the surface layer A was a blend of 90% Polyester III-B, 4% Polyester III-E, and 6% Polyester III-K by mass. A raw material for the intermediate layer C was 100% Polyester III-C. A raw material for the surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-G, and 50% Polyester III-I by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. The resulting extrusions had a three-kind, three-layer (A / C / B) structure, with the raw materials for the surface layer A and the surface layer B as the outermost layers (surface layers) and the intermediate layer C as the intermediate layer. The extrusion conditions were a thickness composition ratio of A / C / B=4 / 1. The film was co-extruded to a ratio of 9 / 2, and 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 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 15.1 m / min. The machine direction 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 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 reached 243°C, and the heat treatment was carried out for 7.3 seconds.

[0302] [Comparative Example III-4] A raw material for the surface layer A was a blend of 87% Polyester III-B and 13% Polyester III-E by mass, a raw material for the intermediate layer C was a blend of 50% Polyester III-C and 50% Polyester III-L by mass, and a raw material for the surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-G, and 50% Polyester III-I by mass. These were fed into a vented extruder and melt-extruded at 280°C. The resulting extruded material had a three-kind, 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 intermediate layer C as the intermediate layer, and a thickness composition ratio of A / C / B was set under the extrusion conditions. The film was coextruded to a C / B ratio of 4 / 25 / 2, 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 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 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 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 reached 230°C, and the heat treatment was carried out for 7.3 seconds.

[0303] [Comparative Example III-5] A raw material for the surface layer A was a blend of 82% Polyester III-B and 18% Polyester III-D in a mass ratio, a raw material for the intermediate layer C was a blend of 50% Polyester III-C and 50% Polyester III-L in a mass ratio, and a raw material for the surface layer B was a blend of 28% Polyester III-C, 22% Polyester III-G, and 50% Polyester III-I in a mass ratio. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, and the thickness composition ratio under the extrusion conditions was A. The film was coextruded to a ratio of A / C / B = 4 / 25 / 2, 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 direction 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 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 reached 230°C, and the heat treatment was carried out for 7.8 seconds.

[0304] The properties of each of the films obtained above were measured according to the methods described above, and the results are shown in Table III-2 (Examples III-1 to III-11) and Table III-3 (Comparative Examples III-1 to III-5).

[0305]

[0306]

[0307] First, as shown in Table III-2, the polyester films of Examples III-1 to III-11 have a planar orientation degree (ΔP) of one surface of 165 or more, and an elastic deformation power (η itTherefore, when the polyester films of Examples III-1 to III-11 are used as supports for ceramic green sheets used in the manufacturing process of multilayer ceramic capacitors, it is clear that they can effectively suppress peeling defects of the ceramic green sheets.

[0308] On the other hand, as shown in Table III-3, the polyester films of Comparative Examples III-1 to III-5 had a planar orientation degree (ΔP) and an elastic deformation power (η it ) is not controlled within a specific range. Specifically, the polyester films of Comparative Examples III-1, III-2, III-4, and III-5 have a planar orientation degree (ΔP) of 165 or more, but the elastic deformation power (η it ) is low, the peelability of the ceramic green sheet is not satisfactory. In addition, the polyester film of Comparative Example III-3 has a low degree of planar orientation (ΔP) and a low elastic deformation power (η it ) is also low, so the peelability of the ceramic green sheet is not satisfactory.

[0309] According to one embodiment of the present invention, a polyester film having a high elastic deformation power can be provided, and therefore, it can be suitably used, for example, as a support for a ceramic green sheet used in the manufacturing process of a multilayer ceramic capacitor. Specifically, since the polyester film can effectively suppress the occurrence of peeling defects in the step of peeling the ceramic green sheet, it is useful as a polyester film used as a support for a ceramic green sheet.

[0310] [Fourth Embodiment] A fourth embodiment, which is an example of an embodiment of the present invention, will be described below, although the present invention is not limited to the embodiment described below.

[0311] As mentioned above, in recent years, with the increasing use of electrical equipment in automobiles and the increasing functionality of smartphones, there has been a demand for smaller multilayer ceramic capacitors with higher capacitance. In response to this demand, efforts have been made to reduce the thickness of ceramic green sheets. However, as ceramic green sheets become thinner, there is concern that the possibility of peeling defects such as breakage occurring in the process of peeling the ceramic green sheets from the release film increases.

[0312] 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 in order to improve the releasability of the ceramic green sheet, and which has an elastic deformation power of 45% or more in a load-displacement curve measured when a load of 20 mN is applied to the release agent layer side using a micro-surface hardness tester.

[0313] It is predicted that multilayer ceramic capacitors will continue to become smaller and have higher capacitance in the future, which will require even thinner ceramic green sheets. As ceramic green sheets become thinner, it is expected that there will be greater concerns than ever before about peeling defects such as breakage during the process of peeling the ceramic green sheets from the release film, and therefore further improvement in the elastic deformation power mentioned above will be required.

[0314] As a result of extensive investigations by the present inventors, it has been found that although it is possible to improve the elastic deformation power by blending, for example, a predetermined filler (particles), there are cases in which it is difficult to obtain the effect of improving the elastic deformation power, for example, depending on the properties of the filler, such as the hardness, etc., whereby the followability during film stretching tends to decrease and voids tend to occur. Furthermore, even if the content of particles is increased so as to obtain the effect of improving the elastic deformation power, there are cases in which it is difficult to obtain the effect of improving the elastic deformation power, such as the tendency for the particles to aggregate and generate voids, and therefore it has become clear that it is very difficult to optimize the design and formulation of the release film.

[0315] In view of the above circumstances, the present inventors have conducted extensive research to increase the elastic deformation power of polyester films, and have found that the above problems can be solved by using a specific polyester film.

[0316] That is, the present invention provides the following as one embodiment. [IV-1] A polyester film, wherein the elastic deformation power of one surface is greater than 55%, and the layer forming the one surface contains particles, the particles being mainly composed of particles having a Mohs hardness of 8 or less. [IV-2] The polyester film according to [IV-1], wherein the content of the particles having a Mohs hardness of 8 or less is less than 1,800 ppm by mass relative to the layer forming the one surface. [IV-3] The polyester film according to [IV-1] or [IV-2], 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 in the layer forming the one surface (content of particles having a Mohs hardness of 8 or less / total content of particles) is 0.6 or more by mass. [IV-4] The polyester film according to any one of [IV-1] to [IV-3], wherein the planar orientation degree (ΔP) of the one surface is 165 or more. [IV-5] The polyester film according to any one of [IV-1] to [IV-4], wherein the one surface 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. [IV-6] The polyester film according to any one of [IV-1] to [IV-5], wherein the ratio of the arithmetic mean height (Sa) of the one surface to the arithmetic mean height (Sa) of the other surface (the arithmetic mean height (Sa) of the other surface / the 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). [IV-7] The polyester film according to any one of [IV-1] to [IV-6], wherein the shrinkage rate in the longitudinal direction and the transverse direction after heat treatment at 150°C for 5 minutes is 2.8% or less. [IV-8] The polyester film according to any one of [IV-1] to [IV-7], which has a shrinkage rate of 1.5% or less in the transverse direction after heat treatment at 150° C. for 5 minutes. [IV-9] The polyester film according to any one of [IV-1] to [IV-8], which contains at least particles (a1) and particles (a2), wherein the particles (a1) are alumina particles and the particles (a2) are particles other than the particles (a1).[IV-10] The polyester film according to any one of [IV-1] to [IV-9], comprising at least particles (a1) and particles (a2), wherein the particles (a1) have a positive zeta potential and the particles (a2) have a negative zeta potential at pH 7, or the particles (a1) have a negative zeta potential and the particles (a2) have a positive zeta potential at pH 7. [IV-11] The polyester film according to any one of [IV-1] to [IV-10], comprising a surface layer forming 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. [IV-12] The polyester film according to any one of [IV-1] to [IV-11], wherein the polyester film comprises a surface layer forming 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 to 10:10 to 35:1 to 5. [IV-13] The polyester film according to any one of [IV-1] to [IV-12], wherein the surface layer forming the other surface contains particles, and the particle content relative to the surface layer forming the other surface is 2000 ppm to 8000 ppm by mass. [IV-14] The polyester film according to any one of [IV-1] to [IV-13], wherein the polyester film is used as a support for a ceramic green sheet in the production process of a multilayer ceramic capacitor. [IV-15] The polyester film according to any one of [IV-1] to [IV-13], which is used as a support for a ceramic green sheet in the production process of an automotive multilayer ceramic capacitor. [IV-16] Use of the polyester film according to any one of [IV-1] to [IV-13], as a support for a ceramic green sheet in the production process of a multilayer ceramic capacitor.[IV-17] Use of the polyester film according to any one of [IV-1] to [IV-13] as a support for a ceramic green sheet in the process of producing an automotive multilayer ceramic capacitor. [IV-18] A method for producing a ceramic green sheet, comprising a step of applying a ceramic slurry containing a ceramic component to one surface of the polyester film according to any one of [IV-1] to [IV-13].

[0317] According to one embodiment of the present invention, the elastic deformation power of the polyester film can be increased, and therefore, when the polyester film is used as a support for a ceramic green sheet used in the manufacturing process of a multilayer ceramic capacitor, peeling failure of the ceramic green sheet can be effectively suppressed.

[0318] The present invention will be described in more detail below based on the fourth embodiment of the present invention, but the present invention is not limited to these embodiments.

[0319] As will be described in detail below, a polyester film according to a fourth embodiment of the present invention (hereinafter, sometimes referred to as "Film IV") preferably has one surface having an elastic deformation power of more than 55%, and a layer forming said one surface contains particles, the particles mainly comprising particles having a Mohs hardness of 8 or less. More preferably, the content of the particles having a Mohs hardness of 8 or less is less than 1800 ppm by mass relative to the layer forming said one surface.

[0320] In the course of research and development into a support for a ceramic green sheet that can accommodate further thinning of the ceramic green sheet (for example, a thickness of 0.5 μm or less after drying) in line with the trend toward smaller size and higher capacity of multilayer ceramic capacitors, the present inventors have focused on the elastic deformation power (η it ) and the elastic deformation power (η it We have begun research into technologies that will further enhance this.

[0321] In the course of such research, the inventors have found that the elastic deformation power (η it ), but it was found that it was difficult to obtain satisfactory results. For example, when particles with a Mohs hardness of 9 were blended, the conformability during film stretching decreased, voids were generated, and the elastic deformation power (η it ) may not be able to obtain satisfactory results, and for example, the elastic deformation power (η it If the particle content is increased in order to increase the elastic deformation power (η it ) It has been found that satisfactory results may not be obtained in some cases. Furthermore, it has also been found that there is a concern that the surface smoothness of the release film may be deteriorated due to the aggregation of such particles.

[0322] The inventors have calculated the elastic deformation power (η it As a result of further research and experiments aimed at increasing the elastic deformation power (η it We have succeeded in discovering a new technology to improve this.

[0323] The present invention proposes a new film IV, which has a high elastic deformation power (η it ) can be provided, which is very advantageous in that, for example, it has a high restoring force against deformation that occurs when cutting the ceramic green sheet and provides excellent peelability of the ceramic green sheet.

[0324] Furthermore, due to the demand for thinner ceramic green sheets, there is a concern that when there are minute protrusions on the surface of a release film, these may cause pinholes or the like to form in the ceramic green sheet. In one embodiment of the present invention, however, the elastic deformation power (η it) and surface smoothness can be highly achieved, which means that, for example, the ceramic green sheet has a high recovery force against deformation that occurs when it is cut, resulting in excellent peelability of the ceramic green sheet, and the occurrence of surface defects such as pinholes can be effectively suppressed, making it extremely excellent in that it can provide a release film or the like that can ensure high quality reliability.

[0325] Furthermore, during the manufacturing process of a multilayer ceramic capacitor, for example, if the release film undergoes thermal shrinkage due to heat treatment to dry the ceramic slurry coated on the release film, there is a concern that coating irregularities and wrinkles may occur. Therefore, release films and the like are required to have heat deformation resistance. However, the inventors have found that increasing the elastic deformation power to suppress the aforementioned peel failure tends to reduce heat deformation resistance. One embodiment of the present invention is excellent in that it can effectively suppress the occurrence of peel failure of the ceramic green sheet and also effectively suppress the occurrence of coating irregularities and wrinkles. Below, one embodiment of this film IV will be described in detail.

[0326] <<Present Film IV>> The present film is suitably used, for example, as a support (substrate) for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors.

[0327] [Elastic deformation power (η it ) )] From the viewpoint of effectively suppressing the above-mentioned peeling failure, this film IV has an elastic deformation power (η it ) is preferably more than 55%. it By controlling the elastic deformation power (η ) to a specific range of more than 55%, it is possible to realize a high level of peelability, which is particularly required in the manufacturing process of MLCC using thin ceramic green sheets, and to effectively suppress peel failure. 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. it The upper limit of the ratio is not particularly limited, but may be, for example, about 70%, or about 65%.

[0328] Elastic deformation power of surface A (η it By using the present film IV 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 IV, and a good gap can be formed between the two. This gap can be used to grip the present film IV and easily separate the ceramic green sheet from the present film IV.

[0329] Elastic deformation power (η it The elastic deformation power (η) is calculated by the following formula based on physical quantities measured by nanoindentation (in accordance with ISO 14577). Specifically, it is determined by the method described in the Examples below. it ) = (Welast / Wtotal) × 100 [%] [Wtotal (total deformation work) = Wplast (plastic deformation work) + Welast (elastic deformation work)]

[0330] [Arithmetic Mean Height (Sa)] In the present film IV, for example, the arithmetic mean height (Sa) of one surface, side A, is preferably 15 nm or less. 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, particularly 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 less than 0.3 nm, the film surface becomes excessively flat, which tends to reduce the slipperiness of the film and impair processability. From the viewpoint of the slipperiness of the film, the lower limit of the arithmetic mean height (Sa) of side A may be 0.8 nm or more, 1 nm or more, 1.5 nm or more, 2 nm or more, etc., but 2 nm or more is particularly preferred.

[0331] In order to prevent the roughness of one surface from being transferred to the other surface when the present film IV 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 deterioration in transportability or windability due to a decrease in the slipperiness of the film.

[0332] The ratio of the arithmetic mean height (Sa) of side A to the arithmetic mean height (Sa) of side B of this film IV ("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 even more preferably 14 or less. The ratio (SaB / SaA) can be set appropriately within the above range and is not limited to the following, and 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.

[0333] 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 surface at height 0 of the image point (x, y), it can be expressed as in the above-mentioned [Equation 1]. More specifically, it can be measured by the method described in the examples below.

[0334] [Maximum Peak Height (Sp)] The maximum peak height (Sp) of Side A, one of the surfaces of the present film IV, is preferably 150 nm or less. If the maximum peak height (Sp) is greater than 150 nm, the surface smoothness will be insufficient, and surface defects such as pinholes will be more likely to occur, making it difficult to achieve 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, and even more preferably 90 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, and may be, for example, 65 nm or less, 60 nm or less, 40 nm or less, or 30 nm or less.

[0335] The maximum peak height (Sp) of side B, the other surface of this film IV, 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 30 nm or more, more preferably 50 nm or more, from the viewpoint of preventing deterioration in transportability or windability due to a decrease in the slipperiness of the film.

[0336] The ratio of the maximum peak heights (Sp) of sides A and B of this film IV ("maximum peak height (Sp) of side B (Sp) / 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, still 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.

[0337] 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 above-mentioned [Equation 2]. More specifically, it can be measured by the method described in the examples below.

[0338] [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 IV, 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, which is the other surface of the present film IV, 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.

[0339] [Root-mean-square height (Sq)] The root-mean-square height (Sq) of side A, one surface of the present film IV, 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 preferably, for example, 0.1 nm or more, more preferably 0.3 nm or more. Furthermore, the root-mean-square height (Sq) of side B, the other surface of the present film IV, 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.

[0340] From the viewpoint of achieving a high degree of both surface smoothness and slip resistance, the ratio of the root mean square height (Sq) of side A to that of side B of this film IV ("root mean square height (Sq) of side B / root mean square height (Sq) of side A"; hereinafter, this may be referred to as "SqB / SqA") is preferably 7 or more, more preferably 8 or more, and even more preferably 9 or more. On the other hand, SqB / SqA is preferably 20 or less, more preferably 18 or less, and even more preferably 17 or less.

[0341] 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 above-mentioned formula [3]. More specifically, it can be measured by the method described in the examples below.

[0342] [Kurtosis (Sku)] The kurtosis (Sku) of side A, which is one surface of the present film IV, 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.

[0343] The kurtosis (Sku) of side B, the other surface of the present film IV, 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.

[0344] Kurtosis (Sku) is one of the surface roughness parameters (ISO 25178) and can be used to evaluate the peakiness (kurtosis) of a histogram of height distribution, and can be calculated using the above-mentioned formula (4). More specifically, it can be measured by the method described in the examples below.

[0345] [Skewness (Ssk)] The skewness (Ssk) of side A, which is one surface of the present film IV, 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.

[0346] The skewness (Ssk) of side B, the other surface of the present film IV, 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.

[0347] Skewness (Ssk) is one of the surface roughness parameters (ISO 25178) and can be determined from the above-mentioned formula (5). More specifically, it can be measured by the method described in the examples below.

[0348] The arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk) can be adjusted by, for example, adjusting the content of particles in consideration of the type of particles, specifically, for example, composition, average particle size, particle size distribution, hardness, and affinity with the polyester to be contained. Adjusting the type and content of particles in consideration of the type of polyester to be contained, for example, composition, viscosity, molecular weight, thermal properties, and the presence or absence of a copolymerization component, is also useful for adjusting surface properties. When two or more types of particles are used in combination, it is preferable to adjust the content ratio in consideration of the type of particles and polyester to be used. Furthermore, during polyester film production, it is also effective to control, for example, the stretching ratio (longitudinal and transverse stretching ratios in the case of biaxial stretching), the stretching temperature, and the heat treatment temperature and treatment time (particularly the heat treatment temperature and treatment time after transverse stretching in the case of biaxial stretching).

[0349] [Shrinkage after Heat Treatment] The manufacturing process of multilayer ceramic capacitors includes heat treatments, such as drying a release agent coated on a polyester film and drying a ceramic slurry coated on a release film. Therefore, a decrease in heat distortion resistance can lead to coating irregularities and wrinkles. In other words, heat distortion resistance is an important characteristic for ensuring the quality and reliability of the finished product, from intermediate products to the final product, such as the lamination characteristics of ceramic green sheets, during the manufacturing process of multilayer ceramic capacitors. To prevent such coating irregularities and wrinkles, the shrinkage of Film IV in the machine direction (MD) after heat treatment at 150°C for 5 minutes is preferably 2.8% or less. From the same perspective, the shrinkage 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 (150° C., 5 minutes) in the machine direction (MD direction) is about −1%, preferably −0.5% or more, and more preferably −0.3% or more.

[0350] Furthermore, the shrinkage rate in the transverse direction (TD) of this film IV 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. From the viewpoint of achieving high thermal distortion resistance, which is particularly required in the manufacturing process of MLCCs using thin 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. 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.

[0351] In addition, the elastic deformation power (η itIn 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-mentioned ranges.

[0352] [Planar Orientation Degree (ΔP)] In order to suppress the aforementioned peeling defects, for example, the planar orientation degree (ΔP) of side A, which is one of the surfaces of Film IV, is preferably 165 or more. On the other hand, the upper limit of the planar orientation degree (ΔP) of side A, which is one of the surfaces, 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.

[0353] The degree of planar orientation (ΔP) is calculated based on the following formula, using JIS K 7142-1996 5.1 (Method A) by measuring the refractive index in the longitudinal direction (nx), the refractive index in the transverse direction (ny), and the refractive index in the thickness direction (nz) with an Abbe refractometer using sodium D line as a light source: degree of planar orientation (ΔP) = ((nx + ny) / 2 - nz) × 1000

[0354] Unless otherwise specified, the raw materials and the like used in the embodiment of Film IV are the same as those described in the description of Film I. That is, the descriptions in the description of Film I from the column "Polyester" to the column "Manufacturing Methods Using Film I" are also incorporated by reference into the embodiment of Film IV.

[0355] [Examples] The fourth embodiment of 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 present invention. In the examples, "%" and "ppm" refer to mass standards.

[0356] <Measurement Methods> Various measurement methods in the following examples are the same as those described in the examples according to the first embodiment.

[0357] Next, the polyester raw materials used in the examples and comparative examples are shown in Table IV-1. The polyesters in polyester raw materials IV-A to IV-L listed in Table IV-1 are all homopolyethylene terephthalate. Furthermore, polyester raw material IV-L is a recycled raw material made by recovering and recycling waste materials.

[0358]

[0359] [Example IV-1] A raw material for surface layer A was a blend of 88% Polyester IV-A, 8% Polyester IV-D, and 4% Polyester IV-E by mass. A raw material for intermediate layer C was a blend of 50% Polyester IV-B and 50% Polyester IV-L by mass. A raw material for surface layer B was a blend of 28% Polyester IV-B, 22% Polyester IV-H, and 50% Polyester IV-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-kind, 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 intermediate layer C as the intermediate layer, with a thickness composition ratio of A / C / B = 4 / 19 / 2 under extrusion conditions. The material was cooled and solidified on a cooling roll with a surface temperature set at 20°C using an electrostatic adhesion method to obtain an amorphous film. Next, the film was stretched 3.6 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%, 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 would be 215°C, and the heat treatment was carried out for 5.1 seconds.

[0360] [Example IV-2] A raw material for surface layer A was a blend of 88% Polyester IV-A, 8% Polyester IV-D, and 4% Polyester IV-E by mass. A raw material for intermediate layer C was a blend of 50% Polyester IV-B and 50% Polyester IV-L by mass. A raw material for surface layer B was a blend of 28% Polyester IV-B, 22% Polyester IV-H, and 50% Polyester IV-J by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was formed, with the raw materials for surface layer A and surface layer B as the outermost layer (surface layer) and the raw materials for intermediate layer C as the intermediate layer, with a thickness composition ratio of A / C / B = 4 / 25 / 2 under extrusion conditions. The material was cooled and solidified on a cooling roll with a surface temperature set at 20°C using an electrostatic adhesion method to obtain an amorphous film. Next, the film was stretched 3.6 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%, 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 would be 215°C, and the heat treatment was carried out for 5.1 seconds.

[0361] [Example IV-3] A raw material for surface layer A was a blend of 84% Polyester IV-A, 12% Polyester IV-D, and 4% Polyester IV-E by mass, a raw material for intermediate layer C was 100% Polyester IV-C, and a raw material for surface layer B was a blend of 28% Polyester IV-C, 22% Polyester IV-G, and 50% Polyester IV-I by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B=4 / 19 / The film was co-extruded to a thickness of 2 μm (A / C / B=4 μm / 19 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 a 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 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 reached 230° C., and the heat treatment was carried out for 7.8 seconds.

[0362] [Example IV-4] A raw material for surface layer A was a blend of 84% Polyester IV-A, 12% Polyester IV-D, and 4% Polyester IV-E by mass, a raw material for intermediate layer C was 100% Polyester IV-C, and a raw material for surface layer B was a blend of 28% Polyester IV-C, 22% Polyester IV-G, and 50% Polyester IV-I by mass, all of which were fed into a vented extruder and melt-extruded at 280°C. The resulting material had 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 layers (surface layers) and intermediate layer C as the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B=4 / 19 / The film was co-extruded to a thickness of 2 μm (A / C / B=4 μm / 19 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 82° C. using the peripheral speed difference with a 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 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 reached 230° C., and the heat treatment was carried out for 7.8 seconds.

[0363] [Example IV-5] A raw material for surface layer A was a blend of 97% Polyester IV-B and 3% Polyester IV-F by mass, a raw material for intermediate layer C was 100% Polyester IV-C, and a raw material for surface layer B was a blend of 28% Polyester IV-C, 22% Polyester IV-G, and 50% Polyester IV-I by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was formed, with the raw materials for surface layer A and surface layer B as the outermost layers (surface layers) and intermediate layer C as the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B = 4 / 19 / 2. Coextrusion was performed using an electrostatic contact method, followed by cooling and solidification 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. Subsequently, the film was 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 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, followed by cooling at 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 reached 210°C, and the heat treatment was performed for 7.3 seconds.

[0364] [Example IV-6] A raw material for the surface layer A was a blend of 97% Polyester IV-B and 3% Polyester IV-K by mass, a raw material for the intermediate layer C was 100% Polyester IV-C, and a raw material for the surface layer B was a blend of 28% Polyester IV-C, 22% Polyester IV-G, and 50% Polyester IV-I 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 mixed together to form a three-kind, three-layer (A / C / B) layer structure in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, with the thickness composition ratio of A / C / B being 4 / 19 / 2 under the extrusion conditions. The film was extruded, 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 adhesion method to obtain an amorphous film, which 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 direction 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%, 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 carried out for 7.3 seconds.

[0365] [Example IV-7] A raw material for the surface layer A was a blend of 91% Polyester IV-B and 9% Polyester IV-D by mass, a raw material for the intermediate layer C was 100% Polyester IV-L, and a raw material for the surface layer B was a blend of 28% Polyester IV-C, 22% Polyester IV-H, and 50% Polyester IV-J by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, they were co-extruded under the extrusion conditions such that the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, resulting in a three-kind, three-layer (A / C / B) layer structure with a thickness composition ratio of A / C / B = 8 / 15 / 2. The film was then drawn out and 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 an electrostatic adhesion 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 at a relaxation rate of 17%, yielding 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 to achieve a final temperature of 230°C, and the heat treatment was carried out for 5.9 seconds.

[0366] [Example IV-8] A raw material for the surface layer A was a blend of 91% Polyester IV-B and 9% Polyester IV-D by mass, a raw material for the intermediate layer C was 100% Polyester IV-L, and a raw material for the surface layer B was a blend of 28% Polyester IV-C, 22% Polyester IV-H, and 50% Polyester IV-J 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 used as the outermost layers (surface layers) and the intermediate layer C was used as the intermediate layer, and the extrusion conditions were such that the thickness composition ratio was A / C / B = 8 / 15 / 2 to form a three-kind, three-layer (A / C / B) structure. The film was extruded, 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 an electrostatic adhesion method to obtain an amorphous film. The film was then stretched 3.8 times in the machine direction (MD direction) 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 direction stretched film was then introduced into a tenter and stretched 4.2 times in the transverse direction (TD direction) at 105°C. The film was then heat-treated (fixed) at 230°C in the tenter and cooled to 140°C at a relaxation rate of 5%, 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 reached 230°C, and the heat treatment was carried out for 5.9 seconds.

[0367] [Example IV-9] A raw material for the surface layer A was a blend of 94% Polyester IV-B and 6% Polyester IV-D by mass, a raw material for the intermediate layer C was a blend of 50% Polyester IV-C and 50% Polyester IV-L by mass, and a raw material for the surface layer B was a blend of 28% Polyester IV-C, 22% Polyester IV-G, and 50% Polyester IV-I by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B. The film was coextruded to a ratio of 4 / 25 / 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 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 a 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 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 reached 230°C, and the heat treatment was carried out for 7.8 seconds.

[0368] [Example IV-10] A raw material for the surface layer A was a blend of 88% Polyester IV-B and 12% Polyester IV-D by mass, a raw material for the intermediate layer C was a blend of 50% Polyester IV-C and 50% Polyester IV-L by mass, and a raw material for the surface layer B was a blend of 28% Polyester IV-C, 22% Polyester IV-G, and 50% Polyester IV-I by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for the surface layer A and the surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B. The film was coextruded to a ratio of 4 / 25 / 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 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 a 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 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 reached 230°C, and the heat treatment was carried out for 7.8 seconds.

[0369] [Example IV-11] A raw material for surface layer A was a blend of 90% Polyester IV-B, 4% Polyester IV-E, and 6% Polyester IV-K by mass, a raw material for intermediate layer C was 100% Polyester IV-C, and a raw material for surface layer B was a blend of 28% Polyester IV-C, 22% Polyester IV-G, and 50% Polyester IV-I by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, a three-kind, three-layer (A / C / B) layer structure was obtained in which the raw materials for surface layer A and surface layer B were the outermost layers (surface layers) and the intermediate layer C was the intermediate layer, and the thickness composition ratio under the extrusion conditions was A / C / B=4 / 19 / 2. The film was co-extruded to the desired thickness, and 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 adhesion method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD direction) at a film temperature of 86 ° C. using the peripheral speed difference with the stretching roll set at a peripheral speed of 15.1 m / min. The machine direction stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD direction) 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 temperatur...

Claims

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

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

5. The polyester film according to any one of claims 1 to 4, wherein the particles have an average particle size of 1 µm or less.

6. The polyester film according to any one of claims 1 to 5, wherein the particles have a Mohs hardness of 9 or less.

7. The polyester film according to any one of claims 1 to 6, wherein the particles include at least particles (a1) and particles (a2), the particles (a1) are alumina particles, and the particles (a2) are particles other than the particles (a1).

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

10. The polyester film according to claim 8 or 9, wherein the content of particles having a negative zeta potential at pH 7 is 100 ppm or more and 8,000 ppm or less by mass relative to the layer forming the one surface.

11. The polyester film according to any one of claims 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 claims 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 claims 1 to 12, wherein the layer forming one of the surfaces 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 of the surfaces (content of particles having a Mohs hardness of 8 or less / total content of particles) is, in mass proportion, from 0.6 to 0.

95.

14. The polyester film according to any one of claims 1 to 13, wherein the layer forming the one surface contains particles, the main component of the particles being 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 1,800 ppm by mass.

15. The polyester film according to any one of claims 1 to 14, wherein the maximum peak height (Sp) of (2) is 100 nm or less.

16. The polyester film according to any one of claims 1 to 15, having a planar orientation degree (ΔP) of 165 or more.

17. The polyester film according to any one of claims 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 one surface) is 2 or more and 18 or less, provided that the arithmetic mean height (Sa) of the other surface > the arithmetic mean height (Sa) of the one surface.

18. The polyester film according to any one of claims 1 to 17, which consists of at least two layers.

19. The polyester film according to any one of claims 1 to 18, which consists of three layers.

20. The polyester film according to claim 18 or 19, wherein the particle content in one of the surface layers is 250 ppm or more and 2,800 ppm or less by mass.

21. The polyester film according to claim 20, wherein the content of the particles in the other surface layer is 2,000 ppm or more and 8,000 ppm or less by mass.

22. The polyester film according to any one of claims 1 to 21, comprising a surface layer forming the one surface, an intermediate layer, and a surface layer forming the other surface, in that order, and the intermediate layer is thicker than each of the surface layers.

23. The polyester film according to any one of claims 1 to 22, comprising a surface layer forming the one surface, an intermediate layer, and a surface layer forming the other surface, in that order, and the ratio of thicknesses 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. The polyester film according to any one of claims 1 to 23, which is used as a support for a ceramic green sheet in the production process of a multilayer ceramic capacitor.

25. The polyester film according to any one of claims 1 to 24, which is used as a support for a ceramic green sheet in the process of producing a multilayer ceramic capacitor for an automobile.

26. Use of the polyester film according to any one of claims 1 to 25 as a support for a ceramic green sheet in the production process of a multilayer ceramic capacitor.

27. Use of the polyester film according to any one of claims 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 said one surface of the polyester film according to any one of claims 1 to 25.

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