JP7726363B2 - Polyester film - Google Patents

Description

The present invention relates to a polyester film. In particular, it relates to a polyester film used, for example, as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors.

Polyester films, such as polyethylene terephthalate film and polyethylene naphthalate film, have excellent mechanical properties, dimensional stability, flatness, heat resistance, chemical resistance, and optical properties, and are cost-effective. Therefore, they are used in a variety of applications. For example, the smoothness of the film surface is utilized for applications such as interlayer insulating resin release substrates, dry film resist substrates, and release films for forming ceramic green sheets for multi-layered ceramic capacitors (MLCCs).

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

As multilayer ceramic capacitors become smaller and higher capacity, ceramic green sheets are becoming thinner. However, as ceramic green sheets become thinner, there are concerns that tiny protrusions on the surface of the release film may cause pinholes or other defects in the ceramic green sheets. Furthermore, there are concerns that the possibility of breakage or other peeling defects may increase during the process of peeling the ceramic green sheets from the release film.

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

Japanese Patent Application Laid-Open No. 2022-144248

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

The present invention has been developed in consideration of the above circumstances, and provides a polyester film that can improve releasability during the process of peeling a ceramic green sheet from a release film, and also suppresses the occurrence of surface defects such as pinholes.

In light of these circumstances, the inventors conducted extensive research and discovered that the above-mentioned problems can be solved by using a specific polyester film. Specifically, the inventors discovered that, for example, when particles are incorporated, 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 the film-forming conditions.

That is, the present invention provides the following.
[1]
A polyester film having an elastic deformation power of more than 55% on one surface and satisfying the following (1) and (2):
(1) The arithmetic mean height (Sa) is 15 nm or less.
(2) The maximum peak height (Sp) is 150 nm or less.
[2]
The polyester film according to [1], which has a shrinkage rate of 2.8% or less in the longitudinal and transverse directions after heat treatment at 150°C for 5 minutes.
[3]
The polyester film according to [1] or [2], which has a shrinkage rate in the transverse direction of 1.5% or less after heat treatment at 150°C for 5 minutes.
[4]
[4] The polyester film according to any one of [1] to [3], which contains particles, and the content of the particles in the layer in which the particles are contained is 250 ppm to 10,000 ppm by mass.
[5]
[5] The polyester film according to any one of [1] to [4], which contains particles, and the average particle size of the particles is 1 μm or less.
[6]
[6] The polyester film according to any one of [1] to [5], which contains particles, and the particles have a Mohs hardness of 9 or less.
[7]
[6] The polyester film according to any one of [1] to [6], comprising particles, the particles including at least particles (a1) and particles (a2), the particles (a1) being alumina particles, and the particles (a2) being particles other than the particles (a1).
[8]
[8] The polyester film according to any one of [1] to [7], wherein the layer forming one surface contains particles, the particles including at least particles (a1) and particles (a2), and the zeta potentials of the particles (a1) and (a2) at pH 7 are either positive for the particles (a1) and negative for the particles (a2), or negative for the particles (a1) and positive for the particles (a2).
[9]
[8] The polyester film according to [8], wherein the content of the particles having a positive zeta potential at pH 7 is 50 ppm to 5,000 ppm by mass relative to the layer forming the one surface.
[10]
[8] or [9], wherein the content of the particles having a negative zeta potential at pH 7 is 100 ppm or more and 8000 ppm or less by mass relative to the layer forming the one surface.
[11]
[11] The polyester film according to any one of [8] to [10], wherein the particles having a positive zeta potential at pH 7 are alumina particles.
[12]
[12] The polyester film according to any one of [8] to [11], wherein the particles having a negative zeta potential at pH 7 are silica particles or organic particles.
[13]
[13] The polyester film according to any one of [1] to [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 contained in the layer forming the one surface (content of particles having a Mohs hardness of 8 or less/total content of particles) is, in mass ratio, from 0.6 to 0.95.
[14]
[14] The polyester film according to any one of [1] to [13], wherein the layer forming the one surface contains particles, the particles mainly containing particles having a Mohs hardness of 8 or less, and the content of the particles having a Mohs hardness of 8 or less in the layer forming the one surface is less than 1800 ppm by mass.
[15]
[15] The polyester film according to any one of [1] to [14], wherein the maximum peak height (Sp) of the (2) is 100 nm or less.
[16]
[16] The polyester film according to any one of [1] to [15], having a planar orientation degree (ΔP) of 165 or more.
[17]
The polyester film according to any one of [1] to [16], wherein the ratio of the arithmetic mean height (Sa) of one surface to the arithmetic mean height (Sa) of the other surface (arithmetic mean height (Sa) of the other surface/arithmetic mean height (Sa) of the one surface) is 2 or more and 18 or less, provided that the arithmetic mean height (Sa) of the other surface is greater than the arithmetic mean height (Sa) of the one surface.
[18]
[18] The polyester film according to any one of [1] to [17], which consists of at least two layers.
[19]
[19] The polyester film according to any one of [1] to [18], which consists of three layers.
[20]
[19] The polyester film according to [18] or [19], which contains particles, and the content of the particles in one surface layer is 250 ppm or more and 2800 ppm or less by mass.
[21]
[21] The polyester film according to [20], which contains particles, and the content of the particles in the other surface layer is 2000 ppm or more and 8000 ppm or less by mass.
[22]
[22] The polyester film according to any one of [1] to [21], wherein the polyester film comprises a surface layer forming the one surface, an intermediate layer, and a surface layer forming the other surface, in this order, and the thickness of the intermediate layer is greater than the thickness of each of the surface layers.
[23]
[23] The polyester film according to any one of [1] to [22], wherein the polyester film comprises a surface layer forming the one surface, an intermediate layer, and a surface layer forming the other surface, in this order, and the thickness ratio of the layers (thickness of the surface layer:thickness of the intermediate layer:thickness of the surface layer) is 1-10:10-35:1-5.
[24]
The polyester film according to any one of [1] to [23], which is used as a support for a ceramic green sheet in a manufacturing process of a multilayer ceramic capacitor.
[25]
[25] The polyester film according to any one of [1] to [24], which is used as a support for a ceramic green sheet in a process for producing a multilayer ceramic capacitor for an automobile.
[26]
Use of the polyester film according to any one of [1] to [25] as a support for a ceramic green sheet in a process for producing a multilayer ceramic capacitor.
[27]
Use of the polyester film according to any one of [1] to [25] as a support for a ceramic green sheet in a process for producing a multilayer ceramic capacitor for an automobile.
[28]
[26] A method for producing a ceramic green sheet, comprising: applying a ceramic slurry containing a ceramic component to the one surface of the polyester film according to any one of [1] to [25].

The present invention provides a polyester film that can improve releasability during the process of peeling a ceramic green sheet from a release film and suppresses the occurrence of surface defects such as pinholes.

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

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

The present inventors, in researching and developing 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 multilayer ceramic capacitors, conducted research focusing on the viewpoint of suppressing the occurrence of peeling defects in the peeling process of the ceramic green sheet.
In the course of such research, the inventors have found that, for example, when particles are added to a polyester film, the occurrence of peeling defects can be suppressed by controlling the properties of the particles added to the polyester film, but on the other hand, it has been found that this tends to cause surface defects such as pinholes, which have a significant impact on quality and reliability in terms of, for example, short-circuit defects and variations in capacitance.

The inventors conducted further research with the aim of resolving both the issues of poor release and surface defects. As a result, they discovered that, for example, when particles are added, 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 releasability in the process of peeling the ceramic green sheet from the release film, suppressing the occurrence of poor release and also suppressing the occurrence of surface defects such as pinholes.

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

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

[Elastic deformation power (η ^it )]
In order to effectively suppress the aforementioned peeling failure, the elastic deformation power (η ^it ) of one surface (hereinafter sometimes referred to as "side A") of the present film is preferably greater than 55%. By controlling the elastic deformation power (η ^it ) of side A to a specific range of greater than 55%, as in the present film, it is possible to achieve the high level of peelability that is particularly required in the manufacturing process of MLCC using thin ceramic green sheets, and to effectively suppress peeling failure.
From the same viewpoint, the elastic deformation power (η ^it ) is preferably 55.1% or more, more preferably 55.2% or more. The elastic deformation power (η ^it ) can be appropriately set within the above range, and may be, for example, 56% or more, 56.2% or more, 56.4% or more, 57% or more, 57.5% or more, etc., without being limited thereto.
The upper limit of the elastic deformation power (η ^it ) is not particularly limited, but may be, for example, about 70%, or may be about 65%.

By using this film, in which the elastic deformation power (η ^it ) of side A 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 this film, and a good gap can be formed between the two. This gap can be used to grip the film and easily separate the ceramic green sheet and this film.

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

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

In order to prevent the roughness of one surface from being transferred to the other surface when the film is wound into a roll, the arithmetic mean height (Sa) of the other surface, side B, is preferably 35 nm or less, more preferably 33 nm or less, even more preferably 30 nm or less, and particularly preferably 28 nm or less. There are no particular restrictions on the lower limit of the arithmetic mean height (Sa) of side B, but in order to prevent a decrease in transportability or winding ability due to a decrease in the film's slipperiness, it is preferably 3 nm or more, and more preferably 5 nm or more.

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

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. It is calculated by dividing the volume enclosed by the surface shape curve and the mean plane by the measured area. Specifically, when the surface is the XY plane and the height direction is the Z axis, where A is the defined area (the entire image) and Z(x, y) is the height from the plane at height 0 of the image point (x, y), it can be expressed as in [Equation 1]. More specifically, it can be measured using the method described in the examples below.

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

The maximum peak height (Sp) of side B, the other surface of the film, is typically 700 nm or less, preferably 650 nm or less, more preferably 620 nm or less, even more preferably 600 nm or less, and especially 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. There are no particular restrictions on the lower limit of the maximum peak height (Sp) of side B, but from the viewpoint of preventing a decrease in transportability or winding ability due to a decrease in the film's slipperiness, it is preferably, for example, 30 nm or more, more preferably 50 nm or more.

The ratio of the maximum peak heights (Sp) of sides A and B of the film ("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, even more preferably 5 or more, particularly preferably 5.4 or more, and most preferably 5.8 or more, from the perspective of achieving a high level 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.

The maximum peak height (Sp) is one of the surface roughness parameters (ISO 25178) and represents the maximum height from the mean plane of the surface, and is expressed as in the formula [2]. More specifically, it can be measured by the method described in the examples below.

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

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

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

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, a parameter equivalent to the standard deviation of the distance from the mean surface, and can be calculated using the formula [3]. In more detail, it can be measured using the method described in the examples below.

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

The kurtosis (Sku) of side B, the other surface of the film, is preferably 18 or less, more preferably 16 or less, even more preferably 15 or less, and especially preferably 14 or less. There are no particular restrictions on the lower limit of the kurtosis (Sku) of side B, but it is preferably 1 or more, and more preferably 2 or more.

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

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

The skewness (Ssk) of side B, the other surface of this film, is preferably 4 or less, more preferably 3.5 or less, even more preferably 3 or less, and especially 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 preferably 0.5 or more, and more preferably 0.8 or more.

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

The 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, 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 a copolymerization component, etc., is also useful for adjusting 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 to be used.
In addition, during the production of the polyester film, it is also effective to control, for example, the stretching ratio (in the case of biaxial stretching, the longitudinal and transverse stretching ratios), the stretching temperature, the heat treatment temperature and treatment time (in the case of biaxial stretching, the heat treatment temperature and treatment time, particularly after transverse stretching).
The same method as above is also suitable for adjusting other surface properties (root mean square height (Sq), kurtosis (Sku), and skewness (Ssk)).

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

Furthermore, the shrinkage rate in the transverse direction (TD) of this film when heat-treated at 150°C for 5 minutes is preferably 2.8% or less from the viewpoint of suppressing coating irregularities and wrinkles. From the same viewpoint, it is more preferably 2.6% or less, even more preferably 2.4% or less, particularly preferably 2.2% or less, and especially preferably 1.5% or less. From the same viewpoint, the lower limit of the shrinkage rate in the transverse direction (TD) is about -1%, preferably -0.5% or more, more preferably -0.3% or more.
Furthermore, from the viewpoint of realizing a high level of thermal distortion resistance, which is particularly required in the manufacturing process of 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. Furthermore, the shrinkage rate in the transverse direction (TD) (150°C, 5 minutes) can be appropriately set within the above range, and may be, for example, but not limited to, 1% or less, 0.8% or less, 0.7% or less, 0.5% or less, 0.4% or less, 0.1% or less, etc.

In order to achieve both the elastic deformation power (η ^it ) and the shrinkage rate (heated at 150°C for 5 minutes), they can be controlled within the above ranges by appropriately setting, for example, the film-forming conditions (particularly the longitudinal stretching temperature, transverse stretching ratio, heat setting temperature, roll peripheral speed, relaxation rate, etc.), film-forming raw materials, etc. Details will be described later.

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

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

Next, we will explain the raw materials used in this film embodiment.

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

In this film, it is preferable to use a polyester that contains more than 50 mol% of aromatic dicarboxylic acid or aliphatic dicarboxylic acid, assuming the dicarboxylic acid component is 100 mol%.

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.

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.

When the polyester is a homopolyester, it is preferably one obtained by polycondensing an aromatic dicarboxylic acid and an aliphatic glycol.
Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol.
Representative polyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN).

On the other hand, when the polyester is a copolymer polyester, it is preferably a copolymer containing 30 mol % or less of a third component. The third component is a component other than the compound that is the main component of the dicarboxylic acid component constituting the polyester (i.e., the dicarboxylic acid component with the largest content) and the compound that is the main component of the diol component (i.e., the diol component with the largest content), and in the case of polyethylene terephthalate, it is a component other than terephthalic acid and ethylene glycol.
Examples of the dicarboxylic acid component of the copolymer polyester include one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid.
Examples of the glycol component of the copolymer polyester include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like.

Preferred polyesters include polyethylene terephthalate, which contains 80 mol % or more, and preferably 90 mol % or more, of ethylene terephthalate units, and polyethylene-2,6-naphthalate, which contains ethylene-2,6-naphthalate units.

Usually, when polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, diethylene glycol is by-produced from the ethylene glycol. In this specification, this diethylene glycol is referred to as by-product diethylene glycol. The amount of diethylene glycol by-produced from ethylene glycol varies depending on the type of polycondensation, 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 this by-product diethylene glycol is also considered to be 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.

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

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

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

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

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

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

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

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 can be determined by measuring the diameters of 10 or more particles using a scanning electron microscope (SEM) and averaging the measured diameters. In the case of non-spherical particles, the average of the longest and shortest diameters can be used to measure the diameter of each particle.

From the viewpoint of increasing the elastic deformation power (η ^it ), the Mohs hardness of the particles 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 tends to decrease, resulting in the generation of voids and a decrease in 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 scale is a numerical representation of hardness based on how a material is scratched against a standard material. Standard materials are designated with numbers 1 to 10, in order of softness, and can be measured using a Mohs hardness scale in the usual way.

The particle content depends on the average particle size, but from the viewpoint of increasing the elastic deformation power (η ^it ), the particle content is preferably 250 ppm or more, more preferably 300 ppm or more, and more preferably 500 ppm or more, by mass ratio, in the layer containing the particles. 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 tend to aggregate to generate voids, which reduces the elastic deformation power (η ^it ).

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.

There are no particular limitations on the method for adding particles to the film, 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 that makes up each layer, but it is preferable to add them after the esterification or transesterification reaction is complete.

When incorporating particles into the present film, it is preferable to provide a surface layer and an intermediate layer, and incorporate particles into the surface layer. Furthermore, when using a three-type, three-layer structure or other structure with different front and back layers, it is preferable to incorporate particles into one or both surface layers.

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

The organic crystal nucleating agent is preferably, for example, a fatty acid metal salt represented by the following general formula.
Formula: (CH ₃ (CH ₂ ) _n COO) _m M
(In the above general formula, n is an integer of 4 or more, and M is Na, Ca, or Li. Furthermore, m is 1 when M is Na or Li, and 2 when M is Ca.)

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

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 also 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 using TG-DTA.

The content of the nucleating agent in the particle-containing layer is preferably 2,000 ppm or more by mass, more preferably 3,000 ppm or more, even more preferably 5,000 ppm or more, and even more preferably 6,000 ppm or more. It is also preferably 28,000 ppm or less, more preferably 25,000 ppm or less, and even more preferably 20,000 ppm or less.

When incorporating a nucleating agent into the present film, it is preferable to provide a surface layer and an intermediate layer, and incorporate the nucleating agent into the surface layer. Furthermore, when using a three-layer structure with different front and back layers, it is preferable to incorporate the nucleating agent into one or both surface layers.

In addition to the particles described above, conventionally known additives such as ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, and pigments can be added to the film as needed, but the total content of these additives in the film is usually less than 10% by mass.

<Layer structure of this film>
The present film may be a single-layer polyester film or a laminated polyester film having two or more layers. From the viewpoint of easily controlling the elastic deformation power (η ^it ) of one surface within the above range and from the viewpoint of suitable use as a support for a process release film used in the production process of a multilayer ceramic capacitor, the present film is preferably a polyester film consisting of at least two layers, and more preferably a polyester film consisting of three layers.

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

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

Methods for achieving a high degree of both elastic deformation power (η ^it ) and surface smoothness are not limited to the following, but a preferred method is to appropriately set the average particle size, content, Mohs hardness, etc. of the particles within the following preferred ranges.
Specifically, when particles are contained in the surface layer A constituting the present film, the average particle size of the particles to be contained is preferably 0.01 μm or more, more preferably 0.03 μm or more, and even more preferably 0.04 μm or more, from the viewpoints of, for example, the elastic deformation power (η ^it ) and surface smoothness, and is preferably 1 μm or less, more preferably 0.8 μm or less, and even more preferably 0.6 μm or less.
The average particle size of the particles contained in surface layer B is preferably 0.1 μm or more, more preferably 0.15 μm or more, and even more preferably 0.2 μm or more, from the viewpoint of, for example, improving lubricity and suppressing the transfer of the surface roughness of surface layer B to surface layer A when wound into a roll. On the other hand, it is preferably 1.5 μm or less, more preferably 1.2 μm or less, and even more preferably 1 μm or less.

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

When particles are contained in the surface layer A constituting the present film, from the viewpoint of improving the elastic deformation power (η ^it ), the Mohs hardness of the particles is preferably 8 or less, more preferably 1 to 7. If the Mohs hardness of the particles is greater than the above range, the conformability during film stretching tends to decrease, resulting in the generation of voids and a decrease in the elastic deformation power (η ^it ). Furthermore, the Mohs hardness of the particles contained in the surface layer B is preferably 8 or less, more preferably 1 to 7, even more preferably 2 to 6, and particularly preferably 3 to 5.

Furthermore, when particles are contained in the surface layer A, from the viewpoint of improving the elastic deformation power (η ^it ), it is preferable that the main component of the particles be particles with a Mohs hardness of 8 or less. For example, the ratio of the content of particles with a Mohs hardness of 8 or less to the content of all particles contained in the surface layer A (content of particles with 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. Furthermore, 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.

Furthermore, when particles having a Mohs hardness of 8 or less are contained in the surface layer A, from the viewpoint of improving the elastic deformation power (η ^it ), the content thereof is preferably less than 1800 ppm by mass relative to the surface layer A. Furthermore, 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. Furthermore, the content may be, for example, 200 ppm or more, 300 ppm or more, 400 ppm or more, 500 ppm or more, etc.
From the viewpoint of achieving a high degree of both elastic deformation power (η ^it ) and surface smoothness, in a preferred embodiment, for example, when at least one type of particle is contained in the surface layer A constituting the present film, it is preferable that the average particle size of the particles contained in the surface layer A is 0.4 μm or less, and the content of the particles (total content if there are two or more types) is 2800 ppm or less by mass relative to the surface layer A, more preferably, the average particle size of the particles contained in the surface layer A is 0.3 μm or less, and the content of the particles is 2500 ppm or less relative to the surface layer A, and even more preferably, the average particle size of the particles contained in the surface layer A is 0.03 to 0.3 μm, and the content of the particles is 250 to 2300 ppm relative to the surface layer A.

Furthermore, for example, in an embodiment in which the surface layer of the present film contains multiple types of particles, from the viewpoint of suppressing particle aggregation and increasing the elastic deformation power (η ^it ), it is preferable to contain two or more types of particles having different positive and negative zeta potentials at pH 7. For example, it is preferable that the surface layer contains particles (a1) and particles (a2), and 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 electric charges between the particles (a1) and (a2), the particles (a1) and (a2) are electrically attracted to each other, and for example, a form can be taken in which the particle (a1) is located around the particle (a2). In particles in which the particle (a1) is electrically located on the particle (a2) (hereinafter sometimes referred to as "composite particles"), the presence of the particle (a1) with the same electric charge on the outside causes the composite particles to repel each other, and the composite particles do not aggregate and maintain high dispersibility, which is thought to suppress the generation of voids and tend to increase the elastic deformation power (η ^it ).
In such composite particles, it is preferable that the average particle size of the outer particles (a1) is smaller than the average particle size of the inner particles (a2). That is, a structure is formed in which the relatively small particles (a1) are positioned so as to surround the 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 further improved. The zeta potential can be measured by electrophoretic light scattering.

Particles with a positive zeta potential at pH 7 include, for example, 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. Particles with a negative zeta potential at pH 7 include, for example, metal oxides such as silica, titanium oxide, ceria, zirconium oxide, barium oxide, chromium oxide, iron oxide, and tungsten oxide, inorganic particles such as composite oxides of 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 carboxyl groups or sulfonic acid groups, with organic particles and silica being preferred.

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, preferably 3 to 15 parts by mass, per 100 parts by mass of the particles.
The method of treatment with the surface treatment agent is not particularly limited, and known methods can be employed, such as a method of dispersing and mixing the particles and the surface treatment agent in an appropriate solvent using a ball mill or the like, drying in an evaporator or by air drying, and then heating to 50 to 150°C, a method of heating the particles and the surface treatment agent in a solvent such as alcohol for several hours under reflux, and a method of graft-polymerizing the surface treatment agent onto the particle surfaces.

The average particle size of 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. On the other hand, it 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.

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

The average particle size of 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 even more preferably 0.1 μm or more. On the other hand, it is preferably 1 μm or less, more preferably 0.8 μm or less, even more preferably 0.6 μm or less, and even more preferably 0.5 μm or less.

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

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 surface layer A can be adjusted by other particles such as particles (a2), while particles (a1) can fully exert their effect of inhibiting (re-)agglomeration of other particles.

The total content of the particles (a1) and the particles (a2) is preferably 300 to 10,000 ppm by mass relative to the layer they are contained in. If the total content is within this range, fine irregularities are formed on the film surface, and the surface of the surface layer A tends to satisfy the arithmetic mean height (Sa) and maximum peak height (Sp) of (1) and (2) above.
In the present film, the total content of particles (a1) and particles (a2) in the surface layer A is preferably 400 ppm or more, more preferably 800 ppm or more, by mass, and is preferably 3000 ppm or less, more preferably 2000 ppm or less.
In the present film, the total content of particles (a1) and particles (a2) in the surface layer B is preferably 3,000 ppm or more, more preferably 4,000 ppm or more, and even more preferably 5,000 ppm or more, by mass, and 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 may contain particles (a1) and particles (a2) in both the surface layer A and the surface layer B, respectively. Alternatively, for example, the surface layer A may contain particles (a1) and particles (a2), and the surface layer B may contain only particles (a2) but not particles (a1).

It is also preferable to use, for example, alumina particles as the particles (a1) and 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 aggregation of particles, and it is possible to effectively increase the elastic deformation power (η ^it ).

Note that, for example, if the content of particles (a2) in the surface layer A exceeds a predetermined amount, the particles (a2) tend to aggregate more easily, which may result in the generation of voids due to the aggregation of the particles (a2), resulting in a decrease in the elastic deformation power (η ^it ), and therefore, when using particles (a2) in an amount exceeding a predetermined amount, it is preferable to use alumina particles in combination as the particles (a1). Specifically, but not limited to, for example, when the surface layer A contains 300 ppm or more, for example, 500 to 3000 ppm, of particles (a2) having a Mohs hardness of 7 or less (e.g., silica, organic particles, etc.), it is preferable to use alumina particles in combination as the particles (a1), and more preferably, the content of such alumina particles in combination is in the range of 50 to 5000 ppm relative to the surface layer A.

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.

The method for producing alumina particles is not particularly limited, but examples include thermal decomposition, i.e., a method in which anhydrous aluminum chloride is used as a raw material and subjected to flame hydrolysis, or ammonium alum thermal decomposition, i.e., a method in which aluminum hydroxide is used as a raw material and reacted with sulfuric acid to produce aluminum sulfate, which is then reacted with ammonium sulfate to produce ammonium alum, which is then calcined.

When a nucleating agent is contained in the surface layer A constituting the present film, the content of the nucleating agent is preferably 2,000 ppm or more by mass, more preferably 3,000 ppm or more, even more preferably 5,000 ppm or more, and even more preferably 6,000 ppm or more. It is also preferably 28,000 ppm or less, more preferably 25,000 ppm or less, and even more preferably 20,000 ppm or less.

When an intermediate layer C is formed in this film, it is preferable that the intermediate layer C be substantially free of particles from the perspective of reducing costs. Note that "substantially free of particles" means that particles are not intentionally included, and specifically means that the particle content is 200 ppm or less, more preferably 150 ppm or less, by mass.

Furthermore, the intermediate layer C of the present film 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 100% by mass.

The total thickness of the present film is not particularly limited as long as it is within the range that allows it to be formed into a film, but from the viewpoints of mechanical strength, handleability, productivity, etc., it is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 18 μm or more, and particularly preferably 19 μm or more. It is also preferably 150 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, particularly preferably 50 μm or less, especially preferably 38 μm or less, and most preferably 32 μm or less. The total thickness of the present film can be set appropriately within the above range, and may be, for example, 30 μm or less, or 28 μm or less.

When the present film has a three-layer structure comprising 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.

Furthermore, when the present film has a three-layer structure having a surface layer A, an intermediate layer C, and a surface layer B in this order, it is preferable that the thickness of the surface layer A is thicker than the thickness of each of the surface layers B.

When the present film has a three-layer structure comprising surface layer A, intermediate layer C, and 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.

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

The thickness of the intermediate layer C of this film is preferably 8 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, and 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, and particularly preferably 26 μm or less.

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

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

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

In addition, in the manufacturing method of this film, by adjusting the temperature in the first stretching (longitudinal stretching), the temperature in the heat setting process, the peripheral speed of the roll, and the relaxation rate as main conditions, it becomes easy to control both the elastic deformation power (η ^it ) and the thermal shrinkage rate after heat treatment within the desired range.
In other words, the temperature during the primary stretching (longitudinal stretching) during the polyester film manufacturing process, the temperature during the heat-setting process, the peripheral speed of the stretching roll, etc. are the main factors that control the elastic deformation power (η ^it ).By appropriately adjusting these, the elastic deformation power (η ^it ) can be improved, but the shrinkage rate after heat treatment tends to deteriorate.Therefore, by further appropriately adjusting, for example, the relaxation rate, etc., it becomes easier to produce a polyester film that can achieve both a high elastic deformation power (η ^it ) and excellent heat distortion resistance. For example, but not limited to, 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, 78 to 88°C, etc., 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, 200 to 230°C, etc., 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, etc., and further, by appropriately setting the relaxation rate in the cooling step to, for example, 0 to 20%, 0.5 to 15%, 1 to 10%, 1.5 to 8%, etc., it becomes easy to control both the elastic deformation power (η ^it ) and the heat shrinkage rate after heat treatment within the desired range.

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

This film may be an unstretched film (sheet) or a stretched film, but is preferably a uniaxially or biaxially stretched film, and of these, a biaxially stretched film is preferred due to its excellent balance of mechanical properties and flatness. A biaxially stretched film is a film in which the refractive index in the machine direction (MD) and cross direction (TD) of the film is higher than the refractive index in the thickness direction, and is typically obtained by stretching the film in both the machine direction and cross direction.

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

The release layer is laminated to the polyester film directly or via another layer. Examples of other layers include an easy-adhesion coating layer to improve adhesion to the film, an antistatic layer, an antiblocking layer, etc.

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 whose main component is a curable silicone resin, a modified silicone type obtained 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.

The curable silicone resin can be any of the existing curing reaction types, such as heat-curable types (addition type, condensation type, etc.) or electron beam-curable types (UV-curable type, etc.), and multiple types of curable silicone resins can be used in combination. There are also no particular restrictions on the form in which the curable silicone resin is applied when forming the release layer; it can be dissolved in an organic solvent, in the form of an aqueous emulsion, or in a solvent-free form.

The release agent composition that forms the release layer may also contain binders, antifoaming agents, coatability improvers, thickeners, inorganic particles, organic particles, organic lubricants, antistatic agents, conductive agents, UV absorbers, antioxidants, foaming agents, dyes, pigments, and the like, as needed.

The release layer is formed by coating the film with a release agent composition. The coating method may be either inline coating, which is performed during the film production process, or so-called off-line coating, in which the composition is applied outside the system onto a film that has already been produced.

Methods for providing a release layer on this film include conventional coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, and curtain coating.

There are no particular restrictions on the curing conditions when forming the release layer. When forming the release layer by offline coating, the heat treatment is usually carried out at 80°C or higher for 10 seconds or more, preferably at 100-200°C for 3-40 seconds, and more preferably at 120-180°C for 3-40 seconds.

If necessary, heat treatment may be combined with irradiation with active energy rays such as ultraviolet light. Known devices and energy sources can be used as the energy source for curing by irradiation with active energy rays.

From the viewpoint of coatability, the coating weight (after drying) of the release layer is usually in the range of 0.005 to 5 g/m ² , preferably 0.005 to 1 g/m ² , and more preferably 0.005 to 0.1 g/m ² . When the coating weight (after drying) is 0.005 g/m ² or more, good coatability and stability are achieved, and a uniform coating film is easily obtained. On the other hand, when it is 5 g/m ² or less, the coating film adhesion, curing properties, etc. of the release layer itself are not reduced. The coating weight is calculated from the liquid mass per coating time (before drying), the nonvolatile content of the coating liquid, the coating width, the stretching ratio, the line speed, etc.

<<Applications>>
The present film can be suitably used, for example, in various mold release applications. For example, it can be used for various mold 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 mold release and process applications, the present film is used, for example, as a support, onto which various materials such as ceramic slurries are coated or laminated.

In particular, as mentioned above, this film effectively suppresses the occurrence of surface defects such as pinholes, and is extremely excellent in that it is less likely to cause peeling problems for ceramic green sheets during the manufacturing process of multilayer ceramic capacitors. Furthermore, it is also less likely to cause coating spots or wrinkles when forming release layers or ceramic green sheets, making it particularly suitable for use as a support for ceramic green sheets. In other words, a preferred embodiment of this film is its use as a support for ceramic green sheets during the manufacturing process of multilayer ceramic capacitors.

Furthermore, as automotive multilayer ceramic capacitors become increasingly electrified, it is predicted that the ceramic green sheets used will become thinner as these capacitors become smaller and higher capacity. Therefore, this film is particularly suitable as a support for ceramic green sheets used in automotive multilayer ceramic capacitors. In other words, a preferred embodiment of this film is its use as a support for ceramic green sheets in the manufacturing process of automotive multilayer ceramic capacitors.

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

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

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

Another example of a method for manufacturing a multilayer ceramic capacitor using this film is 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 this film and a release layer provided on one side of the film, and the step includes a step of heat treating the applied ceramic slurry.

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

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

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

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

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

[Arithmetic mean height (Sa), maximum peak height (Sp), etc.]
The surfaces of the surface layer A and the surface layer B of the sample film (5 cm × 5 cm) were measured using a surface roughness measuring device (manufactured by Ametec Co., Ltd., "NewView" (registered trademark)), and the arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk) were determined from the obtained surface profile curve.
Specifically, measurements were carried out using the surface roughness measuring instrument described above under conditions of an objective lens magnification of 10x, a zoom magnification of 2.0x, and a viewing angle of 0.44mm x 0.44mm, and the arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk) were determined after the following treatments were carried out. Note that measurements were taken at at least 12 points, and the averages were used as the measured values.
FilterType: Spline
Filter: High Pass
Type: Robust Gaussian Spline Fixed

Cutoffs
Mode: Period
Long Period: 200μm

Next, the polyester raw materials used in the examples and comparative examples are shown in Table 1. All of the polyesters in polyester raw materials A to O listed in Table 1 are homopolyethylene terephthalate. In addition, polyester raw material M is a recycled raw material made by recovering and recycling waste materials.

[Example 1]
The raw material for surface layer A was a blend of 88% Polyester A, 8% Polyester D, and 4% Polyester F by mass. The raw material for intermediate layer C was a blend of 50% Polyester B and 50% Polyester M by mass. The raw material for surface layer B was a blend of 28% Polyester B, 22% Polyester I, and 50% Polyester K by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-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 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.

[Example 2]
The raw material for surface layer A was a blend of 88% Polyester A, 8% Polyester D, and 4% Polyester F by mass. The raw material for intermediate layer C was a blend of 50% Polyester B and 50% Polyester M by mass. The raw material for surface layer B was a blend of 28% Polyester B, 22% Polyester I, and 50% Polyester K by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-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 = 4/25/2 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.

[Example 3]
The raw material for surface layer A was a blend of 84% polyester A, 12% polyester D, and 4% polyester F by mass, the raw material for intermediate layer C was 100% polyester C, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, they were co-extruded 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 the thickness composition ratio of A/C/B being 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.

[Example 4]
The raw material for surface layer A was a blend of 84% polyester A, 12% polyester D, and 4% polyester F by mass, the raw material for intermediate layer C was 100% polyester C, and the raw material for surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, they were co-extruded 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 the thickness composition ratio of A/C/B being 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 82°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.

[Example 5]
A raw material for the surface layer A was a blend of 97% polyester B and 3% polyester G by mass, a raw material for the intermediate layer C was 100% polyester C, and a raw material for the surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for the surface layer A and the surface layer B were co-extruded to form 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, with the thickness composition ratio under the extrusion conditions being A/C/B = 4/19/2, and electrostatic application was performed. Using the contact 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. Subsequently, using the peripheral speed difference with the stretching roll set at a peripheral speed of 15.1 m/min, the film was stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C. 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%, 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.

[Example 6]
A raw material for the surface layer A was a blend of 97% polyester B and 3% polyester L in a mass ratio, a raw material for the intermediate layer C was 100% polyester C, and a raw material for the surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester 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 co-extruded to form 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, with the thickness composition ratio under the extrusion conditions being 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 a deposition method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the peripheral speed difference with a stretching roll set at a peripheral speed of 15.1 m/min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. The film was then heat-treated (fixed) at 210°C in the tenter and cooled to 140°C with a relaxation rate of 2%, 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.

[Example 7]
A raw material for the surface layer A was a blend of 88% polyester B and 12% polyester E in a mass ratio, a raw material for the intermediate layer C was 100% polyester B, and a raw material for the surface layer B was a blend of 28% polyester C, 22% polyester I, and 50% polyester K 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 co-extruded to form 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, with the thickness composition ratio under the extrusion conditions being A/C/B = 4/19/2, and electrostatic application was performed. Using the adhesion method, the film was cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4m/min to obtain an amorphous film. Subsequently, using the peripheral speed difference with the stretching roll set at a peripheral speed of 14.1m/min, the film was stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C. 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 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.

[Example 8]
The raw material for the surface layer A was a blend of 91% polyester B and 9% polyester D by mass, the raw material for the intermediate layer C was 100% polyester M, and the raw material for the surface layer B was a blend of 28% polyester C, 22% polyester I, and 50% polyester K by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for 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 the thickness composition ratio of A/C/B being 8/15/2 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 5.1 m/min using a deposition method to obtain an amorphous film. The film was then stretched 3.8 times in the machine direction (MD 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-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%, obtaining 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.

[Example 9]
The raw material for the surface layer A was a blend of 91% polyester B and 9% polyester D by mass, the raw material for the intermediate layer C was 100% polyester M, and the raw material for the surface layer B was a blend of 28% polyester C, 22% polyester I, and 50% polyester K by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for the surface layer A and the surface layer B were co-extruded to form 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, with the thickness composition ratio of A/C/B being 8/15/2 under the extrusion conditions, and the resulting laminate 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 5.1 m / min to obtain an amorphous film, and then stretched 3.8 times in the machine direction, i.e., in the 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-stretched film was then introduced into a tenter and stretched 4.2 times in the transverse direction, i.e., in the TD direction, at 105 ° C., and heat-treated (fixed) at 230 ° C. in the tenter. Then, a cooling treatment at 140 ° C. with a relaxation rate of 17% was performed to obtain a polyester film with a thickness of 25 μm (A / C / B = 8 μm / 15 μm / 2 μm). In the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature was 230 ° C., and the heat treatment was performed for 5.9 seconds.

[Example 10]
A raw material for the surface layer A was a blend of 94% polyester B and 6% polyester D in a mass ratio, a raw material for the intermediate layer C was a blend of 50% polyester C and 50% polyester M in a mass ratio, and a raw material for the surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester 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 extruded under conditions such that the outermost layer (surface layer) was the raw material for the surface layer A and the intermediate layer C was the intermediate layer, resulting in 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 the thickness composition ratio under the extrusion conditions was A/C/B = 4/25/2. The film was coextruded as shown above, cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4 m/min using an electrostatic contact method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the peripheral speed difference with 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). The heat-treatment (fixing) step was performed with a temperature gradient to achieve a final temperature of 230°C for 7.8 seconds.

[Example 11]
A raw material blended with 88% polyester B and 12% polyester D in a mass ratio was used as the raw material for surface layer A, a raw material blended with 50% polyester C and 50% polyester M in a mass ratio was used as the raw material for intermediate layer C, and a raw material blended with 28% polyester C, 22% polyester H, and 50% polyester J in a mass ratio was used as the raw material for surface layer B. These were fed into a vented extruder and melt-extruded at 280°C, resulting in a three-kind, three-layer (A/C/B) layer structure with the raw materials for surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, and the thickness composition ratio under the extrusion conditions was A/C/B = 4/25/2. The film was coextruded as shown in Fig. 1, and cooled and solidified on a cooling roll set at a surface temperature of 20 ° C and a peripheral speed of 4 m/min using an electrostatic contact method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86 ° C using the peripheral speed difference with 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. 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.

[Example 12]
A raw material for the surface layer A was a blend of 78% polyester B, 18% polyester D, and 4% polyester F by mass, a raw material for the intermediate layer C was a blend of 50% polyester C and 50% polyester M by mass, and a raw material for the surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C, resulting in a three-kind, three-layer (A/C/B) layer structure with the raw materials for 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 under the extrusion conditions. The film was coextruded to a thickness of 1/2, 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 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%, yielding 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 reach a final temperature of 230°C, and the heat treatment was carried out for 7.8 seconds.

[Example 13]
The raw material for the surface layer A was a blend of 93% polyester B, 4% polyester F, and 3% polyester G by mass, the raw material for the intermediate layer C was a blend of 50% polyester C and 50% polyester M by mass, and the raw material for the surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These were fed into a vented extruder and melt-extruded at 280°C, resulting in a three-kind, three-layer (A/C/B) layer structure with the raw materials for 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 the thickness composition ratio under the extrusion conditions being A/C/B=4/25/ The film was co-extruded to a thickness of 2 μm (A/C/B=4 μm/25 μm/2 μm), and cooled and solidified on a cooling roll set at a surface temperature of 20° C. and a peripheral speed of 4 m/min using an electrostatic adhesion method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86° C. using the peripheral speed difference with 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 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.

[Example 14]
A raw material for the surface layer A was a blend of 90% polyester B and 10% polyester O by mass, a raw material for the intermediate layer C was 100% polyester C, and a raw material for the surface layer B was a blend of 70% polyester B and 30% polyester G by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for the surface layer A and the surface layer B were co-extruded to form a three-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, with a thickness composition ratio of A/C/B = 1.55/27.9/1.55 under the extrusion conditions. The film was cooled and solidified on a cooling roll with a surface temperature of 20°C and a peripheral speed of 5.8 m/min to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the difference in peripheral speed with a stretching roll with a peripheral speed of 20.3 m/min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. The film was then heat-treated (fixed) at 230°C 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). 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 5.4 seconds.

[Comparative Example 1]
A raw material for the surface layer A was a blend of 97% polyester B and 3% polyester G by mass, a raw material for the intermediate layer C was 100% polyester C, and a raw material for the surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester J by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for the surface layer A and the surface layer B were co-extruded to form 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, 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 using a deposition method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the peripheral speed difference with a stretching roll set at a peripheral speed of 15.1 m/min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. The film was then heat-treated (fixed) at 230°C in the tenter and cooled to 140°C with a relaxation rate of 2%, 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.

[Comparative Example 2]
A raw material for the surface layer A was a blend of 97% polyester B and 3% polyester L in a mass ratio, a raw material for the intermediate layer C was 100% polyester C, and a raw material for the surface layer B was a blend of 28% polyester C, 22% polyester H, and 50% polyester 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 co-extruded to form 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, with the thickness composition ratio under the extrusion conditions being 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 a deposition method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction (MD) at a film temperature of 86°C using the peripheral speed difference with a stretching roll set at a peripheral speed of 15.1 m/min. The machine-stretched film was then introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105°C. The film was then heat-treated (fixed) at 230°C in the tenter and cooled to 140°C with a relaxation rate of 2%, 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.

[Comparative Example 3]
A raw material for surface layer A was a blend of 90% Polyester B, 4% Polyester F, and 6% Polyester L by mass, a raw material for intermediate layer C was 100% Polyester C, and a raw material for surface layer B was a blend of 28% Polyester C, 22% Polyester H, and 50% Polyester J by mass. These materials were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for surface layer A and surface layer B were co-extruded to form a three-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 being A/C/B = 4/19/2 under the extrusion conditions. Using the electrostatic adhesion method, the film was cooled and solidified on a cooling roll set at a surface temperature of 20 ° C. and a peripheral speed of 4.3 m / min to obtain an amorphous film. Then, using the peripheral speed difference with the stretching roll set at a peripheral speed of 15.1 m / min, the film was stretched 3.5 times in the machine direction (MD) at a film temperature of 86 ° C., and then this machine-stretched film was introduced into a tenter and stretched 4.5 times in the transverse direction (TD) at 105 ° C., followed by heat treatment (fixing) at 243 ° 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 243 ° C., and the heat treatment was carried out for 7.3 seconds.

[Comparative Example 4]
A raw material for the surface layer A was a blend of 88% polyester B and 12% polyester E in a mass ratio, a raw material for the intermediate layer C was 100% polyester B, and a raw material for the surface layer B was a blend of 28% polyester C, 22% polyester I, and 50% polyester K 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 co-extruded to form 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, with the thickness composition ratio under the extrusion conditions being A/C/B = 4/19/2, and electrostatic application was performed. Using the adhesion method, the film was cooled and solidified on a cooling roll set at a surface temperature of 20 ° C and a peripheral speed of 4 m / min to obtain an amorphous film, 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 4.2 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.

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

[Comparative Example 6]
A raw material for the surface layer A was a blend of 70% polyester C and 30% polyester N by mass, a raw material for the intermediate layer C was a blend of 45% polyester C and 55% polyester M by mass, and a raw material for the surface layer B was a blend of 70% polyester C and 30% polyester N by mass. These were fed into a vented extruder and melt-extruded at 280°C. After that, the raw materials for the surface layer A and the surface layer B were co-extruded to form a three-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 being A/C/B = 1/23/1 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 17.7 m / min, the film was stretched 3.47 times in the machine direction, i.e., in the MD direction, at a film temperature of 85 ° C., and then this machine-stretched film was introduced into a tenter and stretched 4.2 times in the transverse direction, i.e., in the TD direction, at 120 ° C., and then heat-treated (fixed) at 219 ° C. in the tenter and cooled to 125 ° C. with a relaxation rate of 5%, to obtain a polyester film with a thickness of 25 μm (A / C / B = 1 μm / 23 μm / 1 μm). In the heat-treatment (fixing) step, a temperature gradient was applied so that the final temperature was 219 ° C., and the heat treatment was carried out for 5.3 seconds.

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

First, as shown in Tables 2 and 3, the polyester films of Examples 1 to 14 are specific polyester films obtained by adjusting the type of polyester, such as particle composition, average particle size, particle size distribution, hardness, and affinity with polyester, as well as the film-forming conditions, and the elastic deformation power (η ^it ), arithmetic mean height (Sa), and maximum peak height (Sp) are controlled within specific ranges. Specifically, the polyester films of Examples 1 to 14 have an elastic deformation power (η ^it ) of one surface exceeding 55%, an arithmetic mean height (Sa) of 15 nm or less, and a maximum peak height (Sp) of 150 nm or less.
Therefore, it can be seen that when the polyester films of Examples 1 to 14 are used, for example, as supports for ceramic green sheets used in the manufacturing process of multilayer ceramic capacitors, they 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.

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

Furthermore, from the results shown in the examples and comparative examples, it is suggested that, for example, when trying to suppress the occurrence of peeling defects in the process of peeling a ceramic green sheet from a release film, surface defects such as pinholes tend to occur, and that the elastic deformation power (η ^it ) and surface smoothness are contradictory properties. However, the technical value of the present invention can be said to be extremely high in that it can achieve both of these contradictory properties.
That is, for example, the results of Comparative Example 6 suggest that when the content of particles contained in surface layer A is large, the elastic deformation power (η ^it ) can be improved to a sufficient level, but the maximum peak height (Sp) tends to be high and the surface smoothness tends to be insufficient, while the results of Comparative Examples 1 to 5, etc. suggest that when the content of particles contained in surface layer A is small, the surface smoothness is in a good range, but the elastic deformation power (η ^it ) tends to be insufficient. Furthermore, comparison between these Comparative Examples and Examples shows that adjustment of the heat setting temperature and transverse draw ratio, and selection of particle type and content are also effective for adjusting the elastic deformation power (η ^it ).
Thus, in polyester films containing particles, the elastic deformation power (η ^it ) and surface smoothness tend to be in conflict with each other. However, the present invention can be said to be of great technical value in that it can provide a polyester film that can achieve both of these contradictory properties.

The present invention provides a polyester film that can suppress the occurrence of peeling defects during the process of peeling a ceramic green sheet from a release film and also suppresses the occurrence of surface defects such as pinholes. Therefore, the film can be suitably used, for example, as a support for ceramic green sheets used in the manufacturing process of multilayer ceramic capacitors.

Claims (27)

1. A polyester film containing particles, having an elastic deformation power of more than 55% on one surface, and satisfying the following (1) and (2) , the polyester film being used as a support for a ceramic green sheet in a manufacturing process for a multilayer ceramic capacitor .
(1) The arithmetic mean height (Sa) is 15 nm or less.
(2) The maximum peak height (Sp) is 150 nm or less. The polyester film of 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. 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. The polyester film according to claim 1 or 2, wherein the 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. The polyester film according to claim 1 or 2, wherein the particles have an average particle size of 1 μm or less. The polyester film according to claim 1 or 2, wherein the particles have a Mohs hardness of 9 or less. The polyester film according to claim 1 or 2, 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). The polyester film according to claim 1 or 2, 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). 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. The polyester film according to claim 8, wherein the content of particles having a negative zeta potential at pH 7 is 100 ppm or more and 8000 ppm or less by mass relative to the layer forming the one surface. The polyester film according to claim 8, wherein the particles having a positive zeta potential at pH 7 are alumina particles. The polyester film according to claim 8, wherein the particles having a negative zeta potential at pH 7 are silica or organic particles. The polyester film according to claim 1 or 2, wherein the layer forming one surface contains particles, and the ratio of the content of particles with a Mohs hardness of 8 or less to the content of all particles contained in the layer forming one surface (content of particles with a Mohs hardness of 8 or less/content of all particles) is 0.6 or more and 0.95 or less, in mass ratio. The polyester film according to claim 1 or 2, wherein the layer forming one surface contains particles, the particles mainly comprising particles with a Mohs hardness of 8 or less, and the content of the particles with a Mohs hardness of 8 or less relative to the layer forming one surface is less than 1800 ppm by mass. The polyester film according to claim 1 or 2, wherein the maximum peak height (Sp) of (2) is 100 nm or less. The polyester film according to claim 1 or 2, having a degree of planar orientation (ΔP) of 165 or more. The polyester film according to claim 1 or 2, 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). The polyester film according to claim 1 or 2, which consists of at least two layers. The polyester film according to claim 1 or 2, which consists of three layers. 19. The polyester film according to claim 18, wherein the polyester film comprises at least a surface layer forming the one surface and a surface layer forming the other surface, the surface layer forming the one surface contains particles, and the particle content of the surface layer forming the one surface is 250 ppm to 2800 ppm by mass. 21. The polyester film according to claim 20 , wherein the surface layer forming the other surface contains particles, and the content of the particles in the surface layer forming the other surface is 2000 ppm to 8000 ppm by mass. The polyester film according to claim 1 or 2, wherein the polyester film comprises, in this order, a surface layer forming one surface, an intermediate layer, and a surface layer forming the other surface, and the thickness of the intermediate layer is greater than the thickness of each of the surface layers. The polyester film according to claim 1 or 2, 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 (surface layer thickness: intermediate layer thickness: surface layer thickness) is 1-10:10-35:1-5. 1. A polyester film used as a support for a ceramic green sheet in a manufacturing process for an automotive multilayer ceramic capacitor. 2. A polyester film used as a support for a ceramic green sheet in a manufacturing process for an automotive multilayer ceramic capacitor.
(1) The arithmetic mean height (Sa) is 15 nm or less.
(2) The maximum peak height (Sp) is 150 nm or less. 1. Use of a polyester film containing particles, having an elastic deformation power of more than 55% on one surface, and satisfying the following (1) and (2) as a support for a ceramic green sheet in a process for producing a multilayer ceramic capacitor.
(1) The arithmetic mean height (Sa) is 15 nm or less.
(2) The maximum peak height (Sp) is 150 nm or less. 1. Use of a polyester film containing particles, having an elastic deformation power of more than 55% on one surface, and satisfying the following (1) and (2) as a support for a ceramic green sheet in a manufacturing process for an automotive multilayer ceramic capacitor.
(1) The arithmetic mean height (Sa) is 15 nm or less.
(2) The maximum peak height (Sp) is 150 nm or less. A method for producing a ceramic green sheet , comprising: applying a ceramic slurry containing a ceramic component to one surface of a polyester film containing particles, the polyester film having an elastic deformation power of more than 55% on one surface, and the polyester film satisfying the following (1) and (2) :
(1) The arithmetic mean height (Sa) is 15 nm or less.
(2) The maximum peak height (Sp) is 150 nm or less.