Polyester film

Abstract

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

Description

Technical Field

[0001] The present invention relates to a polyester film. Specifically, for example, it relates to a polyester film used as a support for a ceramic green sheet in the manufacturing process of multilayer ceramic capacitors.

Background Art

[0002] Polyester films typified by polyethylene terephthalate films and polyethylene naphthalate films have excellent properties such as mechanical properties, dimensional stability, flatness, heat resistance, chemical resistance, and optical properties, and are excellent in cost performance. Therefore, they are used in various applications. For example, by utilizing the smoothness of the film surface, they are used as a base material for interlayer insulating resin release, a base material for dry film resist, a release film for forming a ceramic green sheet of a multilayer ceramic capacitor (MLCC), etc.

[0003] In the manufacturing process of multilayer ceramic capacitors, first, a release agent or the like is applied and dried on a polyester film to produce a release film having a release layer. After applying and drying a ceramic slurry containing a ceramic component such as barium titanate and a binder resin on the release film, electrodes are printed and dried by a screen printing method or the like to produce a ceramic green sheet with printed electrodes. Next, the obtained ceramic green sheet is cut into a predetermined shape, and the ceramic green sheet is peeled off from the release film. After laminating and integrating a large number of the peeled ceramic green sheets, they are cut into individual chips, and the internal electrodes and dielectric layers are sintered in a firing furnace to manufacture multilayer ceramic capacitors.

[0004] In the miniaturization and high-capacitance of multilayer ceramic capacitors, the thinning of ceramic green sheets is progressing. If further thinning of the ceramic green sheet occurs, there is concern that if there are minute protrusions on the surface of the release film, pinholes or the like may occur in the ceramic green sheet due to this. Also, in the process of peeling the ceramic green sheet from the release film, there is concern that the possibility of peeling defects such as breakage will increase.

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

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the future, if further thinning of the ceramic green sheet progresses, the concern about the occurrence of surface defects such as pinholes will increase more than ever, and in the process of peeling the ceramic green sheet from the release film, the concern about the occurrence of peeling defects such as breakage will increase more than ever. Therefore, it is required to improve the peelability of the release film and suppress the occurrence of surface defects. However, as a result of extensive studies by the present inventors, from the viewpoint of facilitating peeling from the release film of the ceramic green sheet, for example, it is conceivable to blend a predetermined filler (particles) or the like into the release film. However, when the peelability is improved as described above, surface defects such as pinholes tend to occur due to the filler (particles) or the like. Thus, it has become clear that it is difficult to highly reconcile both.

Means for Solving the Problems

[0008] The present invention has been made in view of the above circumstances, and provides a polyester film capable of improving the peelability in the step of peeling a ceramic green sheet from a release film, and further suppressing the occurrence of surface defects such as pinholes.

[0009] As a result of intensive studies in view of such circumstances, the present inventors have found that the above problems can be solved by using a specific polyester film. That is, the present inventors have found that, for example, when blending particles, the above problems can be solved by using a specific polyester film obtained by adjusting various conditions such as the composition, average particle size, particle size distribution, hardness, and affinity with polyester of the particles, the type of polyester, and film-forming conditions.

[0010] That is, the present invention provides the following. [1] A polyester film having an elastic deformation work rate 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], wherein the shrinkage rates in the longitudinal and transverse directions after heat treatment at 150 ° C. for 5 minutes are 2.8% or less. [3] The polyester film according to [1] or [2], wherein the shrinkage rate in the transverse direction after heat treatment at 150 ° C. for 5 minutes is 1.5% or less. [4] A polyester film according to any one of [1] to [3], which contains particles and the content of the particles is 250 ppm or more and 10,000 ppm or less in terms of mass ratio with respect to the layer to be contained. [5] A polyester film according to any one of [1] to [4], which contains particles and the average particle diameter of the particles is 1 μm or less. [6] A polyester film according to any one of [1] to [5], which contains particles and the Mohs hardness of the particles is 9 or less. [7] A polyester film according to any one of [1] to [6], which contains particles and the particles contain at least particle (a1) and particle (a2), the particle (a1) is alumina particles, and the particle (a2) is particles other than the particle (a1). [8] The layer forming one surface thereof contains particles, the particles contain at least particle (a1) and particle (a2), and the zeta potential of the particles (a1) and (a2) at pH 7 is such that the particle (a1) has a positive value and the particle (a2) has a negative value, or the particle (a1) has a negative value and the particle (a2) has a positive value. A polyester film according to any one of [1] to [7]. [9] The content of the particles having a positive zeta potential at pH 7 is 50 ppm or more and 5,000 ppm or less in terms of mass ratio with respect to the layer forming one surface thereof. A polyester film according to [8].

[10] The content of the particles having a negative zeta potential at pH 7 is 100 ppm or more and 8,000 ppm or less in terms of mass ratio with respect to the layer forming one surface thereof. A polyester film according to [8] or [9].

[11] The particles having a positive zeta potential at pH 7 are alumina particles. A polyester film according to any one of [8] to

[10] .

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

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

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

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

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

[13] , wherein the layer forming one surface contains particles, the main component of the particles is particles having a Mohs hardness of 8 or less, and the content of the particles having a Mohs hardness of 8 or less is less than 1800 ppm by mass ratio with respect to the layer forming one surface.

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

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

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

[15] , wherein the surface orientation degree (ΔP) is 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 one surface) is 2 or more and 18 or less (however, the arithmetic mean height (Sa) of the other surface > the arithmetic mean height (Sa) of one surface).

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

[17] , which comprises at least two layers.

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

[18] , which comprises three layers.

[20] The polyester film according to

[18] or

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

[21] A polyester film according to

[20] , comprising particles, wherein the content of the particles is 2000 ppm or more and 8000 ppm or less by mass ratio with respect to the other surface layer.

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

[21] , comprising a surface layer forming the one surface, an intermediate layer, and a surface layer forming the other surface in this order, wherein the thickness of the intermediate layer is thicker than the thickness of each surface layer.

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

[22] , comprising a surface layer forming the one surface, an intermediate layer, and a surface layer forming the other surface in this order, wherein the ratio of the thicknesses of the respective layers (thickness of the surface layer: thickness of the intermediate layer: thickness of the surface layer) is 1 to 10: 10 to 35: 1 to 5.

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

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

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

[24] , which is used as a support for a ceramic green sheet in the manufacturing process of an automotive multilayer ceramic capacitor.

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

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

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

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

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

[25] . [Effect of the Invention]

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

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in more detail based on embodiments of the present invention, but the present invention is not limited to these embodiments. In addition, when expressed as "X to Y" (X and Y are arbitrary numbers) in this specification, unless otherwise specified, it means "X or more and Y or less", and also includes the meaning of "preferably greater than X" or "preferably less than Y". Also, regarding the numerical ranges described step by step in this specification, the upper limit value or the lower limit value of a certain step's numerical range can be arbitrarily combined with the upper limit value or the lower limit value of another step's numerical range. Furthermore, "X and / or Y (X and Y are arbitrary components)" in this specification means at least one of X and Y, and means three cases: only X, only Y, and X and Y. Also, when referring to "film" in this specification, it includes "sheet", and when referring to "sheet", it includes "film". Also, the "main component" in this specification is usually 50% by mass or more of the entire target material, preferably 60% by mass or more, more preferably 70% by mass or more, and may be 80% by mass or more, or 90 to 100% by mass.

[0013] The polyester film according to one embodiment of the present invention (hereinafter, may be referred to as "this film") is a polyester film in which the elastic deformation work rate of one surface exceeds 55% and satisfies the following (1) and (2), as described in detail below. (1) The arithmetic mean height (Sa) is 15 nm or less. (2) The maximum peak height (Sp) is 150 nm or less.

[0014] In the research and development of a support for a ceramic green sheet that can cope with further thinning of the ceramic green sheet (for example, a thickness of 0.5 μm or less after drying) accompanying the miniaturization and high capacitance of multilayer ceramic capacitors, the inventors focused on suppressing the occurrence of peeling defects in the peeling process of the ceramic green sheet and advanced the research. In the process of such research, for example, when blending particles, the inventors found that the occurrence of peeling defects can be suppressed by controlling the properties of the particles blended in the polyester film. On the other hand, it was found that there is a tendency for surface defects such as pinholes to occur. Such surface defects greatly affect the quality and reliability, for example, in terms of short-circuit defects and variations in capacitance.

[0015] As a result of further research from the perspective of solving both problems regarding the peeling defect and the surface defect, for example, when blending particles, a specific polyester film obtained by adjusting the composition, average particle size, particle size distribution, hardness, and affinity with polyester of the particles, the type of polyester, and film-forming conditions, etc., has improved peelability in the process of peeling the ceramic green sheet from the release film, can suppress the occurrence of peeling defects, and can suppress the occurrence of surface defects such as pinholes.

[0016] The present film newly proposed by the inventors has a specific elastic deformation work rate (η it ) and specific surface smoothness. For example, it has a high restoring force against the deformation that occurs during the cutting of the ceramic green sheet, is excellent in the peelability of the ceramic green sheet, can effectively suppress the occurrence of surface defects such as pinholes, and is very excellent in that it can provide a release film or the like that can ensure a high level of quality and reliability. Hereinafter, a detailed description will be given of an embodiment of the present film.

[0017] <<The Present Film>> This film is suitably used, for example, as a support (base material) for a ceramic green sheet in the manufacturing process of multilayer ceramic capacitors. As described above, this film is very excellent in that it can suppress the occurrence of surface defects such as pinholes and can also suppress the occurrence of peeling failures.

[0018] [Elastic deformation work rate (η it )] From the viewpoint of effectively suppressing the above-mentioned peeling failure, the elastic deformation work rate (η it ) of one surface (hereinafter sometimes referred to as "A surface") of this film is preferably more than 55%. By controlling the elastic deformation work rate (η it ) of the A surface within a specific range of more than 55% like this film, for example, in the manufacturing process of MLCC using a thin-film ceramic green sheet, it is possible to realize the high-level peelability particularly required and effectively suppress the peeling failure. The elastic deformation work rate (η it ) is preferably 55.1% or more, more preferably 55.2% or more, from the same viewpoint. Also, the elastic deformation work rate (η it ) can be appropriately set within the above range and is not limited to the following. For example, it may be 56% or more, 56.2% or more, 56.4% or more, 57% or more, 57.5% or more, etc. Note that the upper limit value of the elastic deformation work rate (η it ) is not particularly limited, but for example, it may be about 70% or about 65%.

[0019] By using this film in which the elastic deformation work rate (η it ) of the A surface is controlled within a specific range of more than 55%, for example, when cutting using a cutting blade to peel the ceramic green sheet, the end of the ceramic green sheet is easily separated from this film, and a good gap can be formed between the two. By using this gap, it becomes easy to grip this film and separate the ceramic green sheet from this film.

[0020] Elastic deformation work rate (ηit ) is calculated by the following formula based on the physical quantity measured by the nanoindentation method (conforming to ISO14577). Specifically, it is obtained by the method described in the examples below. Elastic deformation work rate (η it ) = (Welast / Wtotal) × 100 [%] [Wtotal (total deformation work amount) = Wplast (plastic deformation work amount) + Welast (elastic deformation work amount)]

[0021] 〔Arithmetic mean height (Sa)〕 For this film, for example, it is preferable that the arithmetic mean height (Sa) of surface A, which is one of the surfaces, is 15 nm or less. When the arithmetic mean height (Sa) exceeds 15 nm, the surface smoothness becomes insufficient, and for example, surface defects such as pinholes are likely to occur, and it tends to be difficult to cope with the thinning of the ceramic green sheet. From the same viewpoint, the arithmetic mean height (Sa) of surface A is preferably 10 nm or less, more preferably 8 nm or less, still more preferably 6 nm or less, particularly preferably 4 nm or less, especially preferably 3.5 nm or less, still more particularly preferably 3 nm or less, and most preferably 2.5 nm or less. On the other hand, as the lower limit value of the arithmetic mean height (Sa) of surface A, for example, 0.3 nm or more is preferable, and more preferably 0.5 nm or more. When the arithmetic mean height (Sa) is less than 0.3 nm, the film surface becomes extremely flattened, the slipperiness of the film decreases, and the processability tends to be impaired.

[0022] For this film, for example, from the viewpoint of suppressing the transfer of the surface roughness of one surface to the other surface when winding it in a roll shape, it is preferable that the arithmetic mean height (Sa) of surface B, which is the other surface, is 35 nm or less, more preferably 33 nm or less, still more preferably 30 nm or less, and particularly preferably 28 nm or less. The lower limit value of the arithmetic mean height (Sa) of surface B is not particularly limited, but from the viewpoint of suppressing the decrease in transportability or winding property due to the decrease in the slipperiness of the film, for example, 3 nm or more is preferable, and more preferably 5 nm or more.

[0023] The ratio of the arithmetic mean height (Sa) of the A side and the B side of the film (「arithmetic mean height of the B side (Sa) / arithmetic mean height of the A side (Sa)」. Hereinafter, it may be expressed as 「SaB / SaA」) is preferably 2 or more, more preferably 2.5 or more, and even more preferably 3 or more, from the viewpoint of highly achieving both surface smoothness and slipperiness. On the other hand, SaB / SaA is preferably 18 or less, more preferably 16 or less, still more preferably 15 or less, even more preferably 14.5 or less, and particularly preferably 14 or less. In addition, the ratio (SaB / SaA) can be appropriately set within the above range and is not limited to the following. For example, it may be 3.5 or more, 4.5 or more, 5.5 or more, 6.5 or more, 7 or more, 7.4 or more, 7.8 or more, etc.

[0024] The arithmetic mean height (Sa) is one of the surface roughness parameters (ISO 25178), which is an extension of the two-dimensional Ra to three dimensions, and is the volume of the portion surrounded by the surface shape curved surface and the average surface divided by the measurement area. Specifically, when the surface is the XY plane and the height direction is the Z axis, assuming A: the defined area (the entire image), and Z(x,y): the height from the plane of height 0 of the image point (x,y), it is expressed as the formula of [Equation 1]. More specifically, it can be measured by the method described in the following examples.

[0025]

Equation

[0026] 〔Maximum peak height (Sp)〕 The maximum peak height (Sp) of the A side, which is one of the surfaces of the film, is preferably 150 nm or less. When the maximum peak height (Sp) is greater than 150 nm, the surface smoothness becomes insufficient, and for example, surface defects such as pinholes are likely to occur, and it tends to be difficult to cope with the thinning of the ceramic green sheet. From the same perspective, the maximum peak height (Sp) of the A side 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, as the lower limit value of the maximum peak height (Sp) of the A side, for example, 5 nm or more is preferable, and more preferably 10 nm or more. Note that the maximum peak height (Sp) of the A side can be appropriately set within the above range and is not limited to the following. For example, it may be 65 nm or less, 60 nm or less, 40 nm or less, 30 nm or less, etc.

[0027] From the perspective of suppressing the transfer of one surface roughness to the other surface when winding in a roll shape, for example, the maximum peak height (Sp) of the B side, which is the other surface of this film, is usually 700 nm or less, preferably 650 nm or less, more preferably 620 nm or less, even more preferably 600 nm or less, and particularly preferably 570 nm or less. The lower limit value of the maximum peak height (Sp) of the B side is not particularly limited. From the perspective of suppressing the decrease in transportability or winding property due to the decrease in the slipperiness of the film, for example, 30 nm or more is preferable, and more preferably 50 nm or more.

[0028] From the perspective of highly achieving both surface smoothness and slipperiness, the ratio of the maximum peak height (Sp) of the A side and the B side of this film (「the maximum peak height (Sp) of the B side / the maximum peak height (Sp) of the A side」. Hereinafter, it may be expressed 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, even particularly preferably 5.4 or more, and most preferably 5.8 or more. On the other hand, SpB / SpA is preferably 25 or less, more preferably 24.5 or less, and even more preferably 24 or less.

[0029] The maximum peak height (Sp) is one of the surface roughness parameters (ISO 25178), represents the maximum value of the height from the average surface of the surface, and is expressed by the formula of [Equation 2]. More specifically, it can be measured by the method described in the following examples.

[0030]

Equation

[0031] [Ratio of maximum peak height (Sp) to arithmetic mean height (Sa)] The ratio (Sp / Sa) of the maximum peak height (Sp) to the arithmetic mean height (Sa) on surface A, which is one surface of this film, is preferably 70 or less, more preferably 65 or less, and still 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 still more preferably 10 or more. The ratio (Sp / Sa) of the maximum peak height (Sp) to the arithmetic mean height (Sa) on surface B, which is the other surface of this film, is preferably 40 or less, more preferably 35 or less, and still 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 still more preferably 20 or more.

[0032] [Root mean square height (Sq)] The root mean square height (Sq) of surface A, which is one surface of this film, is preferably 5 nm or less, more preferably 4 nm or less, still 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 value of the root mean square height (Sq) of surface A is not particularly limited, but is preferably 0.1 nm or more, more preferably 0.3 nm or more, for example. Also, the root mean square height (Sq) of surface B, which is the other surface of this film, is preferably 40 nm or less, more preferably 38 nm or less, still more preferably 36 nm or less, particularly preferably 34 nm or less. The lower limit value of the root mean square height (Sq) of surface B is not particularly limited, but is preferably 1 nm or more, more preferably 3 nm or more, for example.

[0033] The ratio of the root mean square height (Sq) of the A side and the B side of this film (「root mean square height (Sq) of the B side / root mean square height (Sq) of the A side」. Hereinafter, it may be expressed as 「SqB / SqA」) is preferably 7 or more, more preferably 8 or more, and even more preferably 9 or more from the viewpoint of highly achieving both surface smoothness and slipperiness. On the other hand, SqB / SqA is preferably 20 or less, more preferably 18 or less, and even more preferably 17 or less.

[0034] The root mean square height (Sq) is one of the surface roughness parameters (ISO 25178), and is an extension of two-dimensional Rq to three-dimensional. That is, it is the root mean square value of the height data in the defined area, and is a parameter corresponding to the standard deviation of the distance from the average surface, and can be obtained from the formula of [Equation 3]. More specifically, it can be measured by the method described in the examples below.

[0035]

Equation

[0036] 〔Sku〕 The Sku of the A side, which is one of the surfaces of this 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 value of the Sku of the A side is not particularly limited, but for example, it is preferably 0.5 or more, more preferably 1 or more.

[0037] The Sku of the B side, which is the other surface of this film, is preferably 18 or less, more preferably 16 or less, even more preferably 15 or less, and particularly preferably 14 or less. The lower limit value of the Sku of the B side is not particularly limited, but for example, it is preferably 1 or more, more preferably 2 or more.

[0038] Skewness (Sku) is one of the surface roughness parameters (ISO 25178), which can evaluate the sharpness (kurtosis) of the height distribution histogram and can be obtained from the formula in [Equation 4]. More specifically, it can be measured by the method described in the examples below.

[0039]

Equation

[0040] 〔Skewness (Ssk)〕 The skewness (Ssk) of surface A, which is one surface of this film, is preferably 5 or less, more preferably 4.5 or less, still more preferably 4.2 or less, and particularly preferably 4 or less. On the other hand, the lower limit value of the skewness (Ssk) of surface A is not particularly limited, but for example, 0.2 or more is preferable, and more preferably 0.4 or more.

[0041] The skewness (Ssk) of surface B, which is the other surface of this film, is preferably 4 or less, more preferably 3.5 or less, still more preferably 3 or less, and particularly preferably 2.5 or less. On the other hand, the lower limit value of the skewness (Ssk) of surface B is not particularly limited, but for example, 0.5 or more is preferable, and more preferably 0.8 or more.

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

[0043]

Equation

[0044] Elastic deformation work rate (η itAnd specific surface characteristics (arithmetic mean height (Sa), maximum peak height (Sp)) can be adjusted to a predetermined range, for example, when compounding particles, by adjusting the content in view of the type of particles, specifically, for example, the composition of the particles, average particle size, particle size distribution, hardness, affinity with the polyester to be incorporated, etc. Also, in view of the type of polyester to be incorporated, for example, composition, viscosity, molecular weight, thermal properties, presence or absence of copolymer components, etc., adjusting the type and content of the particles is also useful for adjusting the elastic deformation work rate (η it ) and surface characteristics. When using two or more types of particles in combination, it is preferable to adjust the mixing ratio in view of the types of particles and polyester used. Also, during the production of polyester films, control of, for example, draw ratio (draw ratios in the longitudinal and transverse directions in the case of biaxial drawing), draw temperature, heat treatment temperature and time (especially heat treatment temperature and time after transverse drawing in the case of biaxial drawing) is also effective. Also, the same method as above is suitable when adjusting other surface characteristics (root mean square height (Sq), kurtosis (Sku), skewness (Ssk)).

[0045] 〔Shrinkage rate after heat treatment〕 In the manufacturing process of multilayer ceramic capacitors, since the process includes heat treatment such as drying the release agent coated on the polyester film and drying the ceramic slurry coated on the release film, a decrease in heat resistance deformation can also be a factor inducing coating irregularities and wrinkles. That is, heat resistance deformation is one of the important characteristics for ensuring the quality reliability of intermediate products to final products in the manufacturing process of multilayer ceramic capacitors, such as the lamination characteristics of ceramic green sheets. From the viewpoint of suppressing such coating irregularities and wrinkles, the shrinkage rate in the longitudinal direction (MD) when heat-treated at 150°C for 5 minutes of this film is preferably 2.8% or less. From the same viewpoint, 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. The lower limit value of the shrinkage rate (150°C, 5 minutes) in the longitudinal direction (MD) is about -1% from the same viewpoint, preferably -0.5% or more, and more preferably -0.3% or more.

[0046] In addition, from the perspective of suppressing coating spots and wrinkles, the shrinkage rate in the transverse direction (TD) when the film is heat-treated at 150°C for 5 minutes is preferably 2.8% or less. From the same perspective, more preferably, it is 2.6% or less, even more preferably 2.4% or less, particularly preferably 2.2% or less, and especially preferably 1.5% or less. The lower limit of the shrinkage rate in the transverse direction (TD) is about -1% from the same perspective, preferably -0.5% or more, and more preferably -0.3% or more. In addition, from the perspective of realizing the high heat resistance to deformation particularly required in the manufacturing process of MLCC using a thin-film ceramic green sheet, the shrinkage rate (at 150°C for 5 minutes) in the transverse direction (TD) is preferably 1.4% or less, and more preferably 1.3% or less. Also, the shrinkage rate (at 150°C for 5 minutes) in the transverse direction (TD) can be appropriately set within the above range and is not limited to the following. For example, it may be 1% or less, 0.8% or less, 0.7% or less, 0.5% or less, 0.4% or less, 0.1% or less, etc.

[0047] Note that, in order to achieve both the elastic deformation work rate (η it ) and the shrinkage rate (heat at 150°C for 5 minutes), for example, by appropriately setting the film-forming conditions (particularly the longitudinal stretching temperature, transverse stretching ratio, heat-fixing temperature, peripheral speed of the roll, relaxation rate, etc.), film-forming raw materials, etc., it can be controlled within the above range. The detailed content will be described later.

[0048] 〔Surface orientation degree (ΔP)〕 For example, from the perspective of suppressing the above-mentioned peeling failure, the surface orientation degree (ΔP) of surface A, which is one of the surfaces of this film, is preferably 165 or more. On the other hand, as the upper limit value of the surface orientation degree (ΔP) of surface A, which is one of the surfaces, for example, 190 or less is preferably, more preferably 185 or less, and even more preferably 180 or less. Note that the surface orientation degree (ΔP) of surface A can be appropriately set within the above range and is not limited to the following. For example, it may be 166 or more, 168 or more, etc.

[0049] The surface orientation degree (ΔP) is calculated based on the following formula by measuring the refractive index in the longitudinal direction (nx), the refractive index in the transverse direction (ny), and the refractive index in the thickness direction (nz) using a sodium D line as the light source and an Abbe refractometer in accordance with JIS K 7142-1996 5.1 (Method A). Surface orientation degree (ΔP) = ((nx + ny) / 2 - nz) × 1000

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

[0051] <Polyester> Polyester is a raw material of this film and refers to a polymer compound having an ester bond continuously in the main chain. The polyester used in this film may be a homopolyester or a copolyester. Specifically, examples include polyesters obtained by polycondensation reaction of a dicarboxylic acid component and a diol component.

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

[0053] Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, and 4,4'-diphenylsulfonedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexanedicarboxylic acid, and ester derivatives thereof.

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

[0055] When the polyester is composed of a homopolyester, it is preferably 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. Typical polyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN).

[0056] On the other hand, when the polyester is a copolyester, 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 becomes the main component of the dicarboxylic acid component (i.e., the dicarboxylic acid component with the highest content) and the compound that becomes the main component of the diol component (i.e., the diol component with the highest content) constituting the polyester. In polyethylene terephthalate, it is a component other than terephthalic acid and ethylene glycol. Examples of the dicarboxylic acid component of the copolyester 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 copolyester include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like.

[0057] In addition, as the polyester, polyethylene terephthalate in which 80 mol% or more, preferably 90 mol% or more, is an ethylene terephthalate unit, polyethylene-2,6-naphthalate in which the unit is ethylene-2,6-naphthalate, and the like are preferable.

[0058] Incidentally, usually, when producing (polycondensing) a polyester using ethylene glycol as one of the raw materials, diethylene glycol is by-produced from ethylene glycol. In this specification, this diethylene glycol is referred to as by-product diethylene glycol. The amount of by-product diethylene glycol from ethylene glycol varies depending on the mode of polycondensation and the like, but is about 5 mol% or less of ethylene glycol. In the present invention, after taking 5 mol% or less of diethylene glycol as by-product diethylene glycol, the by-product diethylene glycol is also included in ethylene glycol and is distinguished from the copolymerization component. On the other hand, depending on the content of diethylene glycol, more specifically, when diethylene glycol is contained in an amount exceeding 5 mol%, diethylene glycol is treated as a copolymerization component rather than by-product diethylene glycol.

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

[0060] More specifically, it is preferable to use a titanium compound as the polycondensation catalyst for the polyester constituting the outermost layer (also referred to as the "surface layer") of this film. For example, the surface layer on which the release layer is laminated. Further, the titanium element content derived from the titanium compound in the outermost layer is preferably 1 ppm or more and 40 ppm or less by mass ratio, and more preferably 2 ppm or more and 35 ppm or less. Within the above range, foreign matters caused by the catalyst can be reduced without reducing the production efficiency of the polyester. Also, from the same viewpoint, the content of the antimony compound in the outermost layer of this film is preferably 100 ppm or less.

[0061] 〔Intrinsic Viscosity of Polyester〕 The intrinsic viscosity of the polyester constituting this film is preferably 0.5 dL / g or more, more preferably 0.55 dL / g or more, and even more preferably 0.6 dL / g or more. By using a polyester with an intrinsic viscosity of 0.5 dL / g or more as the polyester constituting this film, the shear stress during kneading of the polyester increases, and the particles in the polyester resin are likely to be highly dispersed. For example, the surface characteristics of the polyester film tend to be easily within the above range. Also, from the viewpoint of, for example, the fluidity of the particles, the upper limit value 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.

[0062] In addition, when two or more types of polyesters with different intrinsic viscosities are used for the polyester constituting this film, the intrinsic viscosity of these mixed resins shall be meant. Also, the above intrinsic viscosity can be measured according to a conventional method in accordance with JIS K7367-1:2002. For example, it can be measured at 30°C using an Ubbelohde viscometer with phenol:tetrachloroethane = 1:1 as the solvent.

[0063] This film is a film mainly composed of polyester, and the content of polyester contained in this film is, for example, 90% by mass or more, preferably 95% by mass or more, more preferably 98% by mass or more, and particularly preferably 99% by mass or more. Also, when this film is composed of two or more layers, the content of polyester contained in each layer is, for example, 90% by mass or more, preferably 95% by mass or more, more preferably 98% by mass or more, and particularly preferably 99% by mass or more.

[0064] <Particles> It is preferable to contain particles in this film. The types of particles to be contained in this film are not particularly limited. For example, in addition to inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, alumina (aluminum oxide), and titanium oxide, organic particles such as crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, and crosslinked polyester particles can be mentioned.

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

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

[0067] The Mohs hardness of the particles is the elastic deformation work rate (η itFrom the perspective of increasing (η it ), it is preferably 9 or less, more preferably 8 or less. When the Mohs hardness of the particles is greater than the above range, the followability during film stretching decreases and voids are generated, tending to reduce the elastic deformation work rate (η ). From the same perspective, the Mohs hardness of the particles can be appropriately set, for example, in the range of 1 to 9, and is not limited to the following. For example, it may be in the range of 1 to 8, 1 to 7, 1 to 5, 1 to 4, 1 to 3, etc.

[0068] The content of the particles depends on the average particle size as well. From the perspective of increasing the elastic deformation work rate (η it ), in the layer containing the particles, in terms of mass ratio, it is preferably 250 ppm or more, more preferably 300 ppm or more, and even more preferably 500 ppm or more. Also, it is usually 10000 ppm or less, preferably 9000 ppm or less, preferably 8000 ppm or less, and more preferably 7000 ppm or less. When the content of the particles is too high, the particles aggregate with each other and voids are generated, tending to reduce the elastic deformation work rate (η it ).

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

[0070] The method of adding the particles into this film is not particularly limited, and a conventionally known method can be adopted. For example, in the case of a multilayer polyester film, it can be added at any stage of manufacturing the polyester constituting each layer, but it is preferably added after the completion of the esterification or transesterification reaction.

[0071] When the film contains particles, for example, it is preferable to provide a surface layer and an intermediate layer and contain the particles in the surface layer. Further, when making a front-back different design by a three-layer structure of three types or the like, it is preferable to contain the particles in one or both of the surface layers.

[0072] In addition, a crystal nucleating agent can be contained in the film. Examples of the crystal nucleating agent include inorganic crystal nucleating agents and organic crystal nucleating agents, and among them, organic crystal nucleating agents are preferable. The crystal nucleating agent may be used alone or in combination of two or more.

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

[0074] In the above general formula, M is preferably Na. Also, in the above general formula, n is preferably 6 or more, more preferably 8 or more, still more preferably 10 or more, and even more preferably 15 or more. Also, it is preferably 35 or less, more preferably 33 or less, still 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 fatty acids such as 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, arachidic acid, behenic acid, montanic acid, etc. Among them, montanic acid is preferable.

[0075] Further, 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, still more preferably 160°C or higher. Also, it is preferably 260°C or lower, more preferably 250°C or lower, still more preferably 240°C or lower, and even more preferably 230°C or lower. The melting point of the fatty acid metal salt can be measured by TG-DTA.

[0076] The content of the crystal nucleating agent in the layer containing the particles is preferably 2000 ppm or more, more preferably 3000 ppm or more, still more preferably 5000 ppm or more, and even more preferably 6000 ppm or more in terms of mass ratio. Also, it is preferably 28000 ppm or lower, more preferably 25000 ppm or lower, still more preferably 20000 ppm or lower.

[0077] When the crystal nucleating agent is contained in this film, for example, it is preferable to provide a surface layer and an intermediate layer and contain the crystal nucleating agent in the surface layer. Also, when making a front-back different design by a three-layer structure of three types or the like, it is preferable to contain the crystal nucleating agent in one or both of the surface layers.

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

[0079] <The layer structure of this film> This film may be a single-layer polyester film or a polyester film having a laminated structure with two or more layers. From the viewpoint of easily controlling the elastic deformation work rate (η it ) of one surface within the above range and the viewpoint of being suitably used as a support for a process release film used in the manufacturing process of laminated ceramic capacitors, a polyester film composed of at least two layers is preferable, and a polyester film having a three-layer structure is more preferable.

[0080] More specifically, in the present invention, in the case where the 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 layer of the film can be mentioned. Further, for example, a laminated structure having a surface layer A and a surface layer B that constitute the outermost layer of the film and one or more intermediate layers C (C1, C2, etc.) can be mentioned. More specifically, for example, an A / C / B structure composed of a surface layer A, a surface layer B, and an intermediate layer C is preferable. Note that the surface layer A is a surface layer that forms one surface of the film, and the surface layer B is a surface layer that forms the other surface of the film.

[0081] <Preferred Embodiment of the Film> The surface layer A that forms one surface of the film is, in the film, for example, the surface layer located on the side where 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. Further, the surface layer B that forms the other surface of the film is a surface layer located on the side opposite to the side where a ceramic green sheet or the like is provided. Therefore, for example, the 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 film constitutes a part of an intermediate product having a laminated structure of "surface layer B / intermediate layer C / surface layer A / release layer / ceramic green sheet", for example.

[0082] Elastic deformation work rate (η it ) As a method of highly achieving both surface smoothness, although not limited to the following, for example, a method of appropriately setting the average particle diameter, content, Mohs hardness, etc. of the particles within the following preferable ranges is preferable. Specifically, when the surface layer A constituting the film contains particles, the average particle diameter of the particles to be contained is, for example, the elastic deformation work rate (η itFrom the viewpoints of slipperiness and surface smoothness, it is preferably 0.01 μm or more, more preferably 0.03 μm or more, and still more preferably 0.04 μm or more. On the other hand, it is preferably 1 μm or less, more preferably 0.8 μm or less, and still more preferably 0.6 μm or less. The average particle diameter of the particles contained in the surface layer B is preferably 0.1 μm or more, more preferably 0.15 μm or more, and still more preferably 0.2 μm or more, from the viewpoints of enhancing slipperiness and suppressing the transfer of the surface roughness of the surface layer B to the surface layer A when winding into a roll shape. On the other hand, it is preferably 1.5 μm or less, more preferably 1.2 μm or less, and still more preferably 1 μm or less.

[0083] When particles are contained in the surface layer A constituting the film, the content of the particles is preferably 200 ppm or more, more preferably 250 ppm or more, and still more preferably 300 ppm or more, in terms of mass ratio. On the other hand, it is preferably 2800 ppm or less, more preferably 2600 ppm or less, and still more preferably 2500 ppm or less. The content of the particles contained in the surface layer B is preferably 2000 ppm or more, more preferably 2200 ppm or more, and still more preferably 2500 ppm or more, in terms of mass ratio. On the other hand, it is preferably 8000 ppm or less, more preferably 7500 ppm or less, and still more preferably 7000 ppm or less.

[0084] When particles are contained in the surface layer A constituting the film, from the viewpoint of improving the elastic deformation work rate (η it ), the Mohs hardness of the particles is preferably 8 or less, more preferably 1 to 7. When the Mohs hardness of the particles is greater than the above range, the followability during film stretching decreases and voids are generated, tending to reduce the elastic deformation work rate (η it ). Also, the Mohs hardness of the particles contained in the surface layer B is preferably 8 or less, more preferably 1 to 7, still more preferably 2 to 6, and particularly preferably 3 to 5.

[0085] Also, when particles are contained in the surface layer A, from the viewpoint of improving the elastic deformation work rate (η it ), it is preferable that the main component of the particles is 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 total 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 / total content of all particles contained in the surface layer A) is not limited to the following, but in terms of mass ratio, it is 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. Also, the above ratio can be appropriately set within the above range and is not limited to the following. For example, it may be 0.75 or more, 0.78 or more, 0.8 or more, etc. Also, for example, it may be 1 or less, 0.95 or less, 0.9 or less, 0.88 or less.

[0086] Also, when the surface layer A contains particles with a Mohs hardness of 8 or less, from the viewpoint of improving the elastic deformation work rate (η it ), the content thereof is preferably less than 1800 ppm in terms of mass ratio with respect to the surface layer A. Also, the above content can be appropriately set within the above range and is not limited to the following. For example, it may be 1600 ppm or less, 1500 ppm or less, 1300 ppm or less, 1200 ppm or less, etc., and may also be 1000 ppm or less. Also, for example, it may be 200 ppm or more, 300 ppm or more, 400 ppm or more, 500 ppm or more, etc. From the viewpoint of highly achieving both the elastic deformation work rate (η it ) and the surface smoothness, as a preferred embodiment, for example, when at least one kind of particle is contained in the surface layer A constituting the present film, the average particle diameter of the particles contained in the surface layer A is 0.4 μm or less, and the content of the particles (total content in the case of two or more kinds) is preferably 2800 ppm or less in terms of mass ratio with respect to the surface layer A. More preferably, the average particle diameter 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 with respect to the surface layer A. Even more preferably, the average particle diameter 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 with respect to the surface layer A.

[0087] Also, for example, in an embodiment where a plurality of types of particles are contained in the surface layer of the present film, from the viewpoint of suppressing aggregation of the particles and increasing the elastic deformation work rate (η it ), it is preferable to include 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 particle (a1) and particle (a2), and the zeta potential at pH 7 is such that particle (a1) has a positive value and particle (a2) has a negative value, or particle (a1) has a negative value and particle (a2) has a positive value. That is, at pH 7, due to the different charges of particle (a1) and particle (a2), particle (a1) and particle (a2) are electrically attracted to each other and can take a form such that particle (a1) is located around particle (a2), for example. Particles (hereinafter sometimes referred to as "composite particles") in which particle (a1) is electrically located on particle (a2) have particles (a1) with the same charge on the outside, so the composite particles repel each other and the composite particles are maintained with high dispersibility without aggregation, so the generation of voids can be suppressed, and it is considered that there is a tendency to increase the elastic deformation work rate (η it ). In such composite particles, it is preferable that the average particle diameter of the outer particle (a1) is smaller than the average particle diameter of the inner particle (a2). That is, it becomes a structure in which relatively small particle (a1) is located so as to cover relatively large particle (a2). Since the composite particles repel each other electrically, aggregation of particle (a2) does not occur, and it is considered that the dispersibility is more likely to be improved. The zeta potential can be measured by the electrophoretic light scattering method.

[0088] Examples of particles having a positive zeta potential at pH 7 include alumina, cation-modified silica, and rare earth compounds such as ytterbium trifluoride, yttrium fluoride, lanthanum fluoride, yttrium oxide, lanthanum oxide, and ytterbium oxide. Among these, alumina is preferred. Examples of particles having a negative zeta potential at pH 7 include 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 like silica-zirconium oxide, silica-titanium oxide, silica-titanium oxide-barium oxide, silica-titanium oxide-zirconium oxide, borosilicate glass, aluminosilicate glass, and fluoroaluminosilicate glass; and organic particles having a carboxy group or a sulfonic acid group. Organic particles and silica are preferred.

[0089] The zeta potential at pH 7 of particles (a1) and particles (a2) may be the zeta potential of the particles themselves, or it can also be adjusted by modifying the particle surface with a surface treatment agent or the like. 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 coupling agents. The type and amount of the treatment agent may be appropriately adjusted to obtain the desired zeta potential. The surface treatment amount of the surface treatment agent is usually 1 to 30 parts by mass, preferably 3 to 15 parts by mass, per 100 parts by mass of the particles. The treatment method using the surface treatment agent is not particularly limited, and known methods can be adopted. For example, a method of dispersing and mixing particles and a surface treatment agent in a suitable solvent using a ball mill or the like, drying by an evaporator or air drying, and then heating to 50 to 150°C; a method of heating and refluxing particles and a surface treatment agent in a solvent such as alcohol for about several hours; a method of graft-polymerizing a surface treatment agent on the particle surface, etc. can be mentioned.

[0090] As for the average particle diameter of the particles (a1), 0.01 μm or more is preferable, more preferably 0.02 μm or more, still more preferably 0.03 μm or more, even more preferably 0.035 μm or more, particularly preferably 0.04 μm or more. On the other hand, 1 μm or less is preferable, more preferably 0.8 μm or less, still more preferably 0.5 μm or less, even more preferably 0.3 μm or less, particularly preferably 0.1 μm or less.

[0091] Also, from the viewpoint of dispersibility, the content of the particles (a1) is preferably 50 ppm or more, more preferably 100 ppm or more, still 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, for example, in terms of mass ratio with respect to the surface layer A. On the other hand, it is preferably 5000 ppm or less, more preferably 3000 ppm or less, still more preferably 1000 ppm or less, particularly preferably 800 ppm or less, especially preferably 500 ppm or less. Also, from the viewpoint of slipperiness, the content of the particles (a1) is preferably 500 ppm or more, more preferably 1000 ppm or more, still more preferably 2000 ppm or more, for example, in terms of mass ratio with respect to the surface layer B. On the other hand, it is preferably 5000 ppm or less, more preferably 4500 ppm or less, still more preferably 4000 ppm or less.

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

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

[0094] Furthermore, the relationship between the content of the particles (a1) and the content of the particles (a2) is preferably such that the content of the particles (a2) is equal to or more than the content of the particles (a1). By setting such a relationship, while adjusting the roughness of the surface layer A by other particles such as the particles (a2), the effect of suppressing (re)aggregation of other particles by the particles (a1) can be sufficiently exerted.

[0095] Also, the total content of the particles (a1) and the particles (a2) is preferably 300 to 10000 ppm in terms of mass ratio with respect to the layer to be contained. If the total content is within the above range, fine irregularities are formed on the film surface, and the surface of the surface layer A is likely to satisfy the arithmetic mean height (Sa) and the maximum peak height (Sp) of (1) and (2) above. In this 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 ratio. On the other hand, it is preferably 3000 ppm or less, and more preferably 2000 ppm or less. In this film, the total content of particles (a1) and particles (a2) in the surface layer B is preferably 3000 ppm or more, more preferably 4000 ppm or more, and even more preferably 5000 ppm or more, by mass ratio. On the other hand, it is preferably 10000 ppm or less, more preferably 9500 ppm or less, and even more preferably 9000 ppm or less. Note that this film may contain particles (a1) and particles (a2) in both the surface layer A and the surface layer B. For example, the surface layer A contains particles (a1) and particles (a2), and the surface layer B may contain only particles (a2) and not contain particles (a1).

[0096] Also, as the particles (a1), for example, alumina particles are preferably used, and as the particles (a2), particles other than alumina particles (for example, silica, organic particles, etc.) are preferably used. By using alumina particles and particles other than alumina particles in combination, the generation of voids due to aggregation of the particles can be suppressed, and the elastic deformation work rate (η it ) can be effectively increased.

[0097] Note that, for example, when the content of the particles (a2) exceeds a predetermined amount with respect to the surface layer A, the tendency for the particles (a2) to aggregate with each other increases, voids are generated due to the aggregation of the particles (a2), and the elastic deformation work rate (η it) may have an impact such as a decrease. Therefore, when using particles (a2) exceeding a predetermined amount, it is preferable to use alumina particles in combination as the particles (a1). Specifically, although not limited to the following, for example, when the surface layer A contains 300 ppm or more, for example, 500 to 3000 ppm of particles (such as silica, organic particles, etc.) with a Mohs hardness of 7 or less as the particles (a2), it is preferable to use alumina particles in combination as the particles (a1). Moreover, it is more preferable to use the content of such alumina particles in the range of 50 to 5000 ppm with respect to the surface layer A.

[0098] When using alumina particles as the particles (a1), examples of the 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 polymer particles 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 resin. Among these, organic particles and silica are preferable. In addition, even when using alumina particles as the particles (a1) and particles other than alumina particles (such as organic particles) as the particles (a2), the preferable ranges of the average particle size, shape, content, etc. are the same as those described above.

[0099] The production method of alumina particles is not particularly limited. For example, there can be mentioned a thermal decomposition method, that is, a method of flame hydrolysis using anhydrous aluminum chloride as a raw material, or an ammonium alum thermal decomposition method, that is, a method of reacting aluminum hydroxide with sulfuric acid to form aluminum sulfate, and then reacting with ammonium sulfate to form ammonium alum and firing it.

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

[0101] When forming the intermediate layer C in the film, from the viewpoint of cost reduction, it is preferable that the intermediate layer C substantially does not contain particles. Note that "substantially does not contain" means not intentionally containing, and specifically means that the content of particles is 200 ppm or less, more preferably 150 ppm or less in terms of mass ratio.

[0102] Further, the intermediate layer C of the film may contain a recycled polyester raw material from the viewpoint of reducing CO2 emissions and contributing to reducing the environmental load. The content of the recycled polyester raw material is preferably 40% by mass or more, more preferably 50% by mass or more with respect to the intermediate layer C. Note that the content of the recycled polyester raw material may be 70% by mass or more, 90% by mass or more, or 100% by mass.

[0103] The total thickness of the film is not particularly limited as long as it can 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, still more preferably 18 μm or more, and particularly preferably 19 μm or more. Further, it is preferably 150 μm or less, more preferably 100 μm or less, still 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 film can be appropriately set within the above range, for example, it may be 30 μm or less, 28 μm or less.

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

[0105] Further, when the film has a three-layer structure including a surface layer A, an intermediate layer C, and a surface layer B in this order, it is preferable that the thickness of the surface layer A is greater than the thickness of each surface layer B.

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

[0107] The thickness of the surface layer A of the 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, particularly preferably 10 μm or less. The thickness of the surface layer B of the film is preferably 0.5 μm or more, more preferably 0.8 μm or more, even more preferably 1 μm or more, particularly preferably 1.2 μm or more, and is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 6 μm or less, particularly preferably 4 μm or less.

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

[0109] <Manufacturing method of the film> Next, manufacturing examples of this film will be specifically described, but the present invention is not limited to the following manufacturing examples. For example, when manufacturing a biaxially stretched film, it is preferable to use a melting and extrusion device such as an extruder to extrude the dried pellets of the polyester raw material described above from a die as a molten sheet, and then cool and solidify it with a cooling roll such as a rotary cooling drum to obtain an unstretched sheet. In this case, it is preferable to enhance the adhesion between the sheet and the cooling roll in order to improve the flatness of the sheet, and an electrostatic printing adhesion method and / or a liquid coating adhesion method are preferably adopted.

[0110] Next, the obtained unstretched sheet is stretched in two axial directions. In that case, first, the above-mentioned unstretched sheet is stretched in one direction by 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. Subsequently, stretching is performed in a direction perpendicular to the stretching direction of the first stage. In that 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. Then, subsequently, heat treatment is carried out at a temperature of usually 180 to 270°C under tension or with relaxation within 30% to obtain a biaxially stretched film. This heat treatment is also called a heat setting step. The heat treatment may be carried out in two or more steps with different temperatures. The heat treatment time in the heat setting step is preferably 1 to 20 seconds, more preferably 2 to 16 seconds, still more preferably 3 to 13 seconds, and even more preferably 4 to 10 seconds. Also, after the heat treatment, cooling may be carried out in a cooling zone with 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, and more specifically, it is preferably in the range of 100 to 160°C. This cooling may be carried out in two or more steps with different temperatures. In the above stretching, a method of performing the one-direction stretching in two or more stages can also be adopted. In that case, it is preferable to perform the stretching so that the final biaxial stretching ratios are respectively within the above ranges.

[0111] Also, the simultaneous biaxial stretching method can be adopted in the production of this film. The simultaneous biaxial stretching method is a method of simultaneously stretching and orienting the above-mentioned unstretched sheet in the machine direction (longitudinal direction) and the width direction (lateral direction) while controlling the temperature at usually 70 to 120°C, preferably 80 to 110°C. As the stretching ratio, the area ratio is preferably 4 to 50 times, more preferably 7 to 35 times, and still more preferably 10 to 25 times. Then, subsequently, heat treatment is carried out at a temperature of usually 170 to 250°C under tension or under relaxation within 30% to obtain a stretched and oriented film. Regarding the simultaneous biaxial stretching device adopting the above-mentioned stretching method, conventionally known stretching methods such as a screw method, a pantograph method, and a linear drive method can be adopted.

[0112] In addition, in the manufacturing method of this film, by adjusting the temperature in the primary stretching (longitudinal stretching), the temperature in the heat setting process, the peripheral speed of the roll, and the relaxation rate as the main conditions, it becomes easy to control both the elastic deformation work rate (η it ) and the heat shrinkage rate after the heat treatment within a desired range. That is, the temperature in the primary stretching (longitudinal stretching) during the manufacturing process of the polyester film, the temperature in the heat setting process, the peripheral speed of the stretching roll, etc. are the main factors for controlling the elastic deformation work rate (η it ). By appropriately adjusting these, the elastic deformation work rate (η it ) can be improved. On the other hand, since the shrinkage rate after the heat treatment tends to deteriorate, further, for example, by appropriately adjusting the relaxation rate, etc., a high elastic deformation work rate (η it) It becomes easy to manufacture a polyester film that can achieve both excellent heat resistance and heat distortion resistance. For example, although not limited to the following, it is preferable to set the temperature in the primary stretching (longitudinal stretching) to a relatively low temperature condition such as 80 to 90 °C, 78 to 88 °C, etc., and it is also preferable to set the temperature condition in the heat setting process 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 process to 1 to 20 seconds, 2 to 16 seconds, 3 to 13 seconds, 4 to 10 seconds, etc. Furthermore, by appropriately setting the relaxation rate in the cooling process within a range such as 0 to 20%, 0.5 to 15%, 1 to 10%, 1.5 to 8%, etc., it becomes easy to control both the elastic deformation work rate (η it ) and the heat shrinkage rate after heat treatment within a desired range.

[0113] In the manufacturing method, usually, there is a step of winding in a roll shape using a columnar or cylindrical core. Examples of the core include tubes such as paper tubes, metal tubes, and resin tubes, and resin tubes are preferable. Also, the inner diameter and width of the core are not particularly limited, but the inner diameter is usually within the range of 3 to 20 inches, and 4 to 8 inches is preferable. 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 preferable.

[0114] This film may be an unstretched film (sheet) or a stretched film, but it is preferably a film stretched in a uniaxial or biaxial direction. Among them, in terms of excellent balance of mechanical properties and flatness, a biaxially stretched film is preferable. Note that a biaxially stretched film means a film in a state where the refractive indices in the longitudinal direction (MD direction) and the transverse direction (TD direction) of the film are higher than the refractive index in the thickness direction, and it is usually obtained by stretching the film in the longitudinal and transverse directions.

[0115] <<Release layer>> This film is preferably used in a form having a release layer on at least one side. When the release layer is used on the side where the surface layer A is laminated with a ceramic green sheet, for example, it is preferably laminated on the surface of the surface layer A.

[0116] The release layer is laminated on the polyester film directly or via another layer. Examples of other layers include an easy-adhesion coating layer for improving the adhesion to this film, an antistatic layer, a blocking prevention layer, and the like.

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

[0118] As the curable silicone resin, any existing curing reaction type such as a thermosetting type such as an addition type or a condensation type, or an electron beam curing type such as an ultraviolet curing type can be used, and a plurality of types of curable silicone resins can be used in combination. Also, there is no particular limitation on the coating form of the curable silicone resin when forming the release layer, and it may be in a form dissolved in an organic solvent, an aqueous emulsion form, or a solvent-free form.

[0119] In addition to the above, the release agent composition for forming the release layer may also contain, as necessary, a binder, an antifoaming agent, a coating property improver, a thickener, inorganic particles, organic particles, an organic lubricant, an antistatic agent, a conductive agent, an ultraviolet absorber, an antioxidant, a foaming agent, dyes, pigments, and the like.

[0120] The release layer is provided by coating the release agent composition on this film. As the coating method, either in-line coating performed within the film forming process or so-called off-line coating where the coating is applied outside the system on the once manufactured film may be adopted.

[0121] As methods for providing a release layer on this film, conventionally known coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating, etc. can be mentioned.

[0122] Regarding the curing conditions when forming the release layer, there is no particular limitation. When providing the release layer by off-line coating, usually, heat treatment is preferably carried out with a temperature of 80°C or higher for 10 seconds or more, preferably at 100 - 200°C for 3 - 40 seconds, more preferably at 120 - 180°C for 3 - 40 seconds as a guide.

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

[0124] The coating amount (after drying) of the release layer is usually 0.005 - 5 g / m 2 , preferably 0.005 - 1 g / m 2 , more preferably 0.005 - 0.1 g / m 2 within the range. When the coating amount (after drying) is 0.005 g / m 2 or more, the coatability is good and the stability is excellent, and it is easy to obtain a uniform coating film. On the other hand, when it is 5 g / m 2 or less, the coating film adhesion, curability, etc. of the release layer itself do not decrease. The coating amount is calculated from the liquid mass (before drying) per unit time of coating, the non-volatile content concentration of the coating liquid, the coating width, the draw ratio, the line speed, etc.

[0125] <<Applications>> This film can be suitably used, for example, in various release applications. For example, it can be used in various release and process applications such as for dry film resist (DFR), for multilayer circuit boards, for manufacturing ceramic green sheets of multilayer ceramic capacitors, etc. In release applications and process applications, this film is used, for example, as a support, and various materials such as ceramic slurries are coated, laminated, etc. on the support.

[0126] In particular, as described above, this film can effectively suppress the occurrence of surface defects such as pinholes, and is very excellent in that peeling failure of the ceramic green sheet hardly occurs in the manufacturing process of multilayer ceramic capacitors. Moreover, for example, when forming a release layer or a ceramic green sheet, coating unevenness and wrinkles hardly occur, so it can be particularly suitably used as a support for ceramic green sheets. That is, as a preferred embodiment of this film, there is the use of this film as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors.

[0127] In addition, in multilayer ceramic capacitors for automobiles where electrification will progress in the future, in particular, it is predicted that as the capacitors are miniaturized and have increased capacitance, the ceramic green sheets used will become thinner. Therefore, in particular, this film can be suitably used as a support for ceramic green sheets used in multilayer ceramic capacitors for automobiles. That is, as a preferred embodiment of this film, there is the use of this film as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors for automobiles.

[0128] As described above, the support for ceramic green sheets is used as a film for the process of coating a ceramic slurry, drying (heat-treating) the ceramic slurry, solidifying it, and then peeling the solidified ceramic slurry. Examples of the ceramic slurry include those containing a ceramic component, a binder resin, and a solvent. As ceramic components constituting the ceramic slurry, for example, oxides composed of metals such as titanium, aluminum, barium, lead, zirconium, silicon, yttrium, etc., and barium titanate can be used. The binder resin is not particularly limited, and examples include polyurethane resin, urea resin, melamine resin, epoxy resin, vinyl acetate resin, acrylic resin, polyvinyl alcohol, polyvinyl butyral, etc. The solvent is not particularly limited, and examples include water, toluene, ethanol, methyl ethyl ketone, isopropyl alcohol, γ-butyrolactone, etc. Further, a plasticizer, a dispersant, an antistatic agent, a surfactant, etc. may be added to the ceramic slurry as necessary.

[0129] <<Each manufacturing method using this film>> As a method for manufacturing a support of a ceramic green sheet using this film, there is a method for manufacturing a support of a ceramic green sheet including a step of forming a release layer on one side of this film, and the step includes a step of performing heat treatment on the applied release agent composition.

[0130] Further, as a method for manufacturing a ceramic green sheet using this film, there is a method for manufacturing a ceramic green sheet having a step of coating a ceramic slurry containing a ceramic component on one surface of this film. Further, as a method for manufacturing a ceramic green sheet using this film, there is a manufacturing method having a step of drying the coated ceramic slurry in addition to the coating step, and further having a step of forming an electrode.

[0131] In addition, as a method for manufacturing a multilayer ceramic capacitor using this film, there is provided a method for manufacturing a multilayer ceramic capacitor including a step of forming a ceramic green sheet on one side of a support of a ceramic green sheet having this film and a release layer provided on one side of this film, wherein the step includes a step of performing a heat treatment on the applied ceramic slurry.

Example

[0132] Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the examples, “%” and “ppm” mean mass basis.

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

[0134] 〔Elastic deformation work rate (η it )〕 About 2 to 8 mg of Aron Alpha (registered trademark) (for general use, manufactured by Toagosei Co., Ltd.) was dropped onto a slide glass (S1112, manufactured by Matsunami Glass Industry Co., Ltd.). On top of that, the surface layer B side of the sample film (1.5 cm × 1.5 cm) was covered as the adhesive surface and cured. After fixing the slide glass with the sample film to the sample stage of a hardness tester (Dynamic ultra-micro hardness tester (DUH-211S, manufactured by Shimadzu Corporation)), a load-unloading test was performed on the surface (surface layer A) of the sample film, and the elastic deformation work rate (η it ) was obtained using the following formula (average value of 5 measurements excluding the first point out of 6 measurements). Wtotal = Wplast + Welast (N·m) (Wtotal = total deformation work amount (N·m), Wplast = plastic deformation work amount (N·m), Welast = elastic deformation work amount (N·m)) η it =(Welast / Wtotal)×100 (%) (Measurement conditions) Indenter used: Diamond regular triangular pyramid indenter (inter-edge angle: 115) Measurement mode: Loading-unloading test Test force: 20.00 mN Minimum test force: 0.20 mN Loading speed: 0.1464 mN / sec Loading hold time: 0 sec Unloading hold time: 0 sec Measurement atmosphere: 23 ± 2 °C, 50 ± 5% RH Number of measurements: 6

[0135] 〔Shrinkage rate〕 A sample film (width 1.5 cm × length 15 cm) was heat-treated for 5 minutes in a hot air oven maintained at a predetermined temperature (150 °C) in a tension-free state, and the lengths in the longitudinal direction of the sample film before and after the heat treatment were measured, and the shrinkage rate was calculated using the following formula. The measurements were taken for both the longitudinal direction (MD) and the transverse direction (TD) of the film. The shrinkage rate of MD was measured with the longitudinal direction being MD, and the shrinkage rate of TD was measured with the longitudinal direction being TD. Shrinkage rate (%) = { (Length of the sample film before heat treatment) - (Length of the sample film after heat treatment)} ÷ (Length of the sample film before heat treatment) × 100

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

[0137] 〔Arithmetic mean height (Sa), maximum peak height (Sp), etc.〕 Using a surface roughness measuring instrument (manufactured by Ametek, "NewView" (registered trademark)), the surfaces of the surface layer A and the surface layer B of the sample film (5 cm × 5 cm) were measured, and from the obtained surface profile curves, the arithmetic mean height (Sa), the maximum peak height (Sp), the root mean square height (Sq), the kurtosis (Sku), and the skewness (Ssk) were obtained. Specifically, using the above surface roughness measuring instrument, measurements were taken under the conditions of an objective lens magnification of 10 times, a zoom magnification of 2.0 times, and a field angle of 0.44 mm × 0.44 mm. After performing the following processes, the arithmetic mean height (Sa), maximum peak height (Sp), root mean square height (Sq), kurtosis (Sku), and skewness (Ssk) were obtained. Note that the measurement was performed at least at 12 points or more, and the average value was taken as the measured value. FilterType:Spline Filter:High Pass Type:Robust Gaussian Spline Fixed Cutoffs Mode:Period Long Period:200μm

[0138] Next, the polyester raw materials used in the examples and comparative examples are shown in Table 1. The polyesters in the polyester raw materials A to O described in Table 1 are all homopolyethylene terephthalate. Also, the polyester raw material M is a recycled raw material obtained by recovering and reusing end materials.

[0139]

Table 1

[0140] [Example 1] A raw material obtained by blending polyester A at 88%, polyester D at 8%, and polyester F at 4% by mass was used as the raw material for surface layer A. A raw material obtained by blending polyester B at 50% and polyester M at 50% by mass was used as the raw material for intermediate layer C. A raw material obtained by blending polyester B at 28%, polyester I at 22%, and polyester K at 50% by mass was used as the raw material for surface layer B. The raw materials were supplied to an extruder with a vent, melt-extruded at 280°C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio was A / C / B = 4 / 19 / 2 under the extrusion conditions. The film was cooled and solidified on a cooling roll with the surface temperature set at 20°C using the electrostatic printing adhesion method to obtain an amorphous film. Next, using the roll peripheral speed difference, the film was stretched 3.6 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 85°C. Then, this longitudinally stretched film was led into a tenter and stretched 4.2 times in the transverse direction, i.e., the TD direction, at 120°C. Heat treatment (fixing) was performed at 215°C in the tenter, and cooling treatment was performed at 125°C with a relaxation rate of 5% 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) process, a temperature gradient was applied so that the final temperature reached 215°C, and heat treatment was performed for 5.1 seconds.

[0141] [Example 2] A raw material obtained by blending polyester A at 88%, polyester D at 8%, and polyester F at 4% by mass was used as the raw material for surface layer A. A raw material obtained by blending polyester B at 50% and polyester M at 50% by mass was used as the raw material for intermediate layer C. A raw material obtained by blending polyester B at 28%, polyester I at 22%, and polyester K at 50% by mass was used as the raw material for surface layer B. These were supplied to an extruder with a vent, melt-extruded at 280°C, and then co-extruded in a three-layer (A / C / B) layer configuration with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio was A / C / B = 4 / 25 / 2 under the extrusion conditions. Cooling and solidification were carried out on a cooling roll with the surface temperature set at 20°C using the electrostatic printing adhesion method to obtain an amorphous film. Next, using the roll peripheral speed difference, the film was stretched 3.6 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 85°C. Then, this longitudinally stretched film was led into a tenter and stretched 4.2 times in the transverse direction, i.e., the TD direction, at 120°C. Heat treatment (fixing) was performed at 215°C in the tenter, and cooling treatment was performed at 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) process, a temperature gradient was applied so that the final temperature reached 215°C, and heat treatment was performed for 5.1 seconds.

[0142] [Example 3] A raw material obtained by blending 84% of polyester A, 12% of polyester D, and 4% of polyester F by mass was used as the raw material for surface layer A. A raw material with 100% of polyester C was used as the raw material for intermediate layer C. A raw material obtained by blending 28% of polyester C, 22% of polyester H, and 50% of polyester J by mass was used as the raw material for surface layer B. The materials were supplied to an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer under extrusion conditions such that the thickness composition ratio was A / C / B = 4 / 19 / 2. The film was cooled and solidified on a cooling roll set at a surface temperature of 20 °C and a peripheral speed of 4 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Subsequently, the film was stretched 3.5 times in the longitudinal direction, i.e., 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 14.1 m / min. Then, this longitudinally stretched film was led into a tenter and stretched 4.5 times in the transverse direction, i.e., the TD direction, at 105 °C. Heat treatment (fixing) was performed at 230 °C in the tenter, and a cooling treatment was performed 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) process, a temperature gradient was applied so that the final temperature reached 230 °C, and the heat treatment was performed for 7.8 seconds.

[0143] [Example 4] A raw material blend consisting of 84% polyester A, 12% polyester D, and 4% polyester F was used as the raw material for surface layer A. A raw material of 100% polyester C was used as the raw material for intermediate layer C. A raw material blend consisting of 28% polyester C, 22% polyester H, and 50% polyester J was used as the raw material for surface layer B. The materials were fed into an extruder with a vent, melt-extruded at 280°C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer. The thickness composition ratio was set to A / C / B = 4 / 19 / 2 under the extrusion conditions. The film was cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Then, the film was longitudinally stretched 3.5 times at a film temperature of 82°C, i.e., in the MD direction, using the peripheral speed difference with a stretching roll set at a peripheral speed of 14.1 m / min. The longitudinally stretched film was then led into a tenter and stretched 4.5 times at 105°C in the transverse direction, i.e., the TD direction. Heat treatment (fixing) was performed at 230°C in the tenter, and a relaxation rate of 2% was used for cooling treatment at 140°C 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) process, a temperature gradient was applied so that the final temperature reached 230°C, and the heat treatment was performed for 7.8 seconds.

[0144] [Example 5] A raw material obtained by blending polyester B at a mass ratio of 97% and polyester G at a mass ratio of 3% is used as the raw material for surface layer A. A raw material with 100% polyester C is used as the raw material for intermediate layer C. A raw material obtained by blending polyester C at a mass ratio of 28%, polyester H at a mass ratio of 22% and polyester J at a mass ratio of 50% is used as the raw material for surface layer B. The materials are supplied to an extruder with vents, melt-extruded at 280°C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio is A / C / B = 4 / 19 / 2 under the extrusion conditions. After cooling and solidifying on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4.3 m / min using the electrostatic printing adhesion method to obtain an amorphous film, the film is then longitudinally, i.e., in the MD direction, stretched 3.5 times 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. This longitudinally stretched film is then led into a tenter and stretched 4.5 times at 105°C in the transverse direction, i.e., the TD direction. Heat treatment (fixing) is carried out at 210°C in the tenter, and a cooling treatment is carried out 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) process, a temperature gradient is applied so that the final temperature reaches 210°C, and the heat treatment is carried out for 7.3 seconds.

[0145] [Example 6] A raw material obtained by blending polyester B at a mass ratio of 97% and polyester L at a mass ratio of 3% is used as the raw material for surface layer A. A raw material with 100% polyester C is used as the raw material for intermediate layer C. A raw material obtained by blending polyester C at a mass ratio of 28%, polyester H at a mass ratio of 22% and polyester J at a mass ratio of 50% is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio is A / C / B = 4 / 19 / 2 under the extrusion conditions. The film is cooled and solidified on a cooling roll with the surface temperature set at 20 °C and the peripheral speed set at 4.3 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Then, using the peripheral speed difference with a stretching roll with the peripheral speed set at 15.1 m / min, the film is stretched 3.5 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 86 °C. Subsequently, this longitudinally stretched film is guided into a tenter and stretched 4.5 times in the transverse direction, i.e., the TD direction, at 105 °C, and heat-treated (fixed) at 210 °C in the tenter. A cooling treatment is performed 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) process, a temperature gradient is applied so that the final temperature reaches 210 °C, and the heat treatment is performed for 7.3 seconds.

[0146] [Example 7] A raw material obtained by blending polyester B at a mass ratio of 88% and polyester E at a mass ratio of 12% is used as the raw material for surface layer A. A raw material with 100% polyester B is used as the raw material for intermediate layer C. A raw material obtained by blending polyester C at a mass ratio of 28%, polyester I at a mass ratio of 22% and polyester K at a mass ratio of 50% is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, so that the thickness composition ratio is A / C / B = 4 / 19 / 2 under the extrusion conditions. It is cooled and solidified on a cooling roll with the surface temperature set at 20 °C and the peripheral speed set at 4 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Then, using the peripheral speed difference with a stretching roll with the peripheral speed set at 14.1 m / min, it is stretched 3.5 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 86 °C. After that, this longitudinally stretched film is led into a tenter and stretched 4.5 times in the transverse direction, i.e., the TD direction, at 105 °C, and heat-treated (fixed) at 230 °C in the tenter, and then cooled 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) process, a temperature gradient is applied so that the final temperature reaches 230 °C, and the heat treatment is carried out for 7.8 seconds.

[0147] [Example 8] A raw material obtained by blending polyester B at a mass ratio of 91% and polyester D at a mass ratio of 9% is used as the raw material for surface layer A. A raw material with 100% polyester M is used as the raw material for intermediate layer C. A raw material obtained by blending polyester C at 28%, polyester I at 22% and polyester K at 50% by mass is used as the raw material for surface layer B. The materials are fed into an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer under extrusion conditions such that the thickness composition ratio is A / C / B = 8 / 15 / 2. The film is 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 the electrostatic printing adhesion method to obtain an amorphous film. Subsequently, the film is stretched 3.8 times in the longitudinal direction, i.e., 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. Then, this longitudinally stretched film is led into a tenter and stretched 4.2 times in the transverse direction, i.e., the TD direction, at 105 °C, and heat-treated (fixed) at 230 °C in the tenter. A relaxation rate of 5% is applied and a cooling treatment is performed at 140 °C 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) process, a temperature gradient is applied so that the final temperature reaches 230 °C, and the heat treatment is performed for 5.9 seconds.

[0148] [Example 9] A raw material obtained by blending polyester B at a mass ratio of 91% and polyester D at a mass ratio of 9% is used as the raw material for surface layer A. A raw material with 100% polyester M is used as the raw material for intermediate layer C. A raw material obtained by blending polyester C at a mass ratio of 28%, polyester I at a mass ratio of 22% and polyester K at a mass ratio of 50% is used as the raw material for surface layer B. The materials are fed into an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio is A / C / B = 8 / 15 / 2 under the extrusion conditions. The film is cooled and solidified on a cooling roll with the surface temperature set at 20 °C and the peripheral speed set at 5.1 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Subsequently, the film is stretched 3.8 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 86 °C by utilizing the peripheral speed difference with a stretching roll with the peripheral speed set at 18.5 m / min. Then, this longitudinally stretched film is guided into a tenter and stretched 4.2 times in the transverse direction, i.e., the TD direction, at 105 °C, and heat-treated (fixed) at 230 °C in the tenter. A cooling treatment is performed at 140 °C with a relaxation rate of 17% to obtain a polyester film with a thickness of 25 μm (A / C / B = 8 μm / 15 μm / 2 μm). In the heat treatment (fixing) process, a temperature gradient is applied such that the final temperature reaches 230 °C, and the heat treatment is performed for 5.9 seconds.

[0149] [Example 10] A raw material obtained by blending polyester B at a mass ratio of 94% and polyester D at a mass ratio of 6% is used as the raw material for surface layer A. A raw material obtained by blending polyester C at a mass ratio of 50% and polyester M at a mass ratio of 50% is used as the raw material for intermediate layer C. A raw material obtained by blending polyester C at a mass ratio of 28%, polyester H at a mass ratio of 22% and polyester J at a mass ratio of 50% is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio is A / C / B = 4 / 25 / 2 under the extrusion conditions. The film is cooled and solidified on a cooling roll with the surface temperature set at 20 °C and the peripheral speed set at 4 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Then, the film is stretched 3.5 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 86 °C using the peripheral speed difference with a stretching roll with the peripheral speed set at 14.1 m / min. Subsequently, this longitudinally stretched film is guided into a tenter and stretched 4.5 times in the transverse direction, i.e., the TD direction, at 105 °C, and heat-treated (fixed) at 230 °C in the tenter. A relaxation treatment is performed at 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) process, a temperature gradient is applied such that the final temperature reaches 230 °C, and the heat treatment is performed for 7.8 seconds.

[0150] [Example 11] A raw material obtained by blending polyester B at a mass ratio of 88% and polyester D at a mass ratio of 12% is used as the raw material for surface layer A. A raw material obtained by blending polyester C at a mass ratio of 50% and polyester M at a mass ratio of 50% is used as the raw material for intermediate layer C. A raw material obtained by blending polyester C at a mass ratio of 28%, polyester H at a mass ratio of 22% and polyester J at a mass ratio of 50% is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280°C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio is A / C / B = 4 / 25 / 2 under the extrusion conditions. The film is cooled and solidified on a cooling roll set at a surface temperature of 20°C and a peripheral speed of 4 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Then, using the peripheral speed difference with a stretching roll set at a peripheral speed of 14.1 m / min, the film is stretched 3.5 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 86°C. After that, this longitudinally stretched film is guided into a tenter and stretched 4.5 times in the transverse direction, i.e., the TD direction, at 105°C. Heat treatment (fixing) is performed at 230°C in the tenter, and a relaxation treatment at 2% is carried out with cooling at 140°C 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) process, a temperature gradient is applied so that the final temperature reaches 230°C, and the heat treatment is carried out for 7.8 seconds.

[0151] [Example 12] A raw material obtained by blending polyester B at a mass ratio of 78%, polyester D at 18%, and polyester F at 4% is used as the raw material for surface layer A. A raw material obtained by blending polyester C at 50% and polyester M at 50% by mass is used as the raw material for intermediate layer C. A raw material obtained by blending polyester C at 28%, polyester H at 22%, and polyester J at 50% by mass is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, with the thickness composition ratio of A / C / B = 4 / 25 / 2 under the extrusion conditions. The film is cooled and solidified on a cooling roll with the surface temperature set at 20 °C and the peripheral speed set at 4 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Then, using the peripheral speed difference with a stretching roll with the peripheral speed set at 14.1 m / min, the film is stretched 3.5 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 86 °C. After that, the longitudinally stretched film is led into a tenter and stretched 4.5 times in the transverse direction, i.e., the TD direction, at 105 °C, and heat-treated (fixed) at 230 °C in the tenter. A relaxation rate of 2% is used for a cooling treatment at 140 °C 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) process, a temperature gradient is applied so that the final temperature reaches 230 °C, and the heat treatment is carried out for 7.8 seconds.

[0152] [Example 13] A raw material obtained by blending polyester B at a mass ratio of 93%, polyester F at 4%, and polyester G at 3% is used as the raw material for surface layer A. A raw material obtained by blending polyester C at 50% and polyester M at 50% by mass is used as the raw material for intermediate layer C. A raw material obtained by blending polyester C at 28%, polyester H at 22%, and polyester J at 50% by mass is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio is A / C / B = 4 / 25 / 2 under the extrusion conditions. The film is cooled and solidified on a cooling roll set at a surface temperature of 20 °C and a peripheral speed of 4 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Then, using the peripheral speed difference with a stretching roll set at a peripheral speed of 14.1 m / min, the film is stretched 3.5 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 86 °C. Subsequently, this longitudinally stretched film is led into a tenter and stretched 4.5 times in the transverse direction, i.e., the TD direction, at 105 °C. Heat treatment (fixing) is performed at 230 °C in the tenter, and a cooling treatment is performed at 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) process, a temperature gradient is applied so that the final temperature reaches 230 °C, and the heat treatment is performed for 7.8 seconds.

[0153] [Example 14] A raw material obtained by blending polyester B at 90% and polyester O at 10% by mass is used as the raw material for surface layer A, a raw material with 100% polyester C is used as the raw material for intermediate layer C, and a raw material obtained by blending polyester B at 70% and polyester G at 30% by mass is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer. The thickness composition ratio is set to A / C / B = 1.55 / 27.9 / 1.55 under the extrusion conditions. The film is cooled and solidified on a cooling roll with the surface temperature set at 20 °C and the peripheral speed set at 5.8 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Then, using the peripheral speed difference with a stretching roll with the peripheral speed set at 20.3 m / min, the film is stretched 3.5 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 86 °C. After that, this longitudinally stretched film is led into a tenter and stretched 4.5 times in the transverse direction, i.e., the TD direction, at 105 °C, and heat-treated (fixed) at 230 °C in the tenter. A cooling treatment is performed at 140 °C with a relaxation rate of 2% to obtain a polyester film with a thickness of 31 μm (A / C / B = 1.55 μm / 27.9 μm / 1.55 μm). In the heat treatment (fixing) process, a temperature gradient is applied so that the final temperature reaches 230 °C, and the heat treatment is performed for 5.4 seconds.

[0154] [Comparative Example 1] A raw material obtained by blending polyester B at a mass ratio of 97% and polyester G at a mass ratio of 3% is used as the raw material for surface layer A, a raw material with 100% polyester C is used as the raw material for intermediate layer C, and a raw material obtained by blending polyester C at a mass ratio of 28%, polyester H at a mass ratio of 22% and polyester J at a mass ratio of 50% is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio is A / C / B = 4 / 19 / 2 under the extrusion conditions. Cooling and solidification are carried out on a cooling roll with the surface temperature set at 20 °C and the peripheral speed set at 4.3 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Subsequently, the film is stretched 3.5 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 86 °C using the peripheral speed difference with a stretching roll with the peripheral speed set at 15.1 m / min. Then, this longitudinally stretched film is guided into a tenter and stretched 4.5 times in the transverse direction, i.e., the TD direction, at 105 °C, and heat treatment (fixing) is carried out at 230 °C in the tenter, followed by a 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) process, a temperature gradient was applied so that the final temperature reached 230 °C, and the heat treatment was carried out for 7.3 seconds.

[0155] [Comparative Example 2] A raw material obtained by blending polyester B at a mass ratio of 97% and polyester L at a mass ratio of 3% is used as the raw material for surface layer A, a raw material with 100% polyester C is used as the raw material for intermediate layer C, and a raw material obtained by blending polyester C at a mass ratio of 28%, polyester H at a mass ratio of 22% and polyester J at a mass ratio of 50% is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280°C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio is A / C / B = 4 / 19 / 2 under the extrusion conditions. The film is cooled and solidified on a cooling roll with the surface temperature set at 20°C and the peripheral speed set at 4.3 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Subsequently, the film is stretched 3.5 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 86°C using the peripheral speed difference with a stretching roll with the peripheral speed set at 15.1 m / min. Then, this longitudinally stretched film is led into a tenter and stretched 4.5 times in the transverse direction, i.e., the TD direction, at 105°C, and heat-treated (fixed) at 230°C in the tenter. A cooling treatment is performed 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) process, a temperature gradient is applied so that the final temperature reaches 230°C, and the heat treatment is performed for 7.3 seconds.

[0156] [Comparative Example 3] A raw material obtained by blending 90% of polyester B, 4% of polyester F, and 6% of polyester L by mass is used as the raw material for surface layer A. A raw material with 100% of polyester C is used as the raw material for intermediate layer C. A raw material obtained by blending 28% of polyester C, 22% of polyester H, and 50% of polyester J by mass is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio is A / C / B = 4 / 19 / 2 under the extrusion conditions. The film is 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 the electrostatic printing adhesion method to obtain an amorphous film. Subsequently, the film is stretched 3.5 times in the longitudinal direction, i.e., 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 15.1 m / min. Then, this longitudinally stretched film is led into a tenter and stretched 4.5 times in the transverse direction, i.e., the TD direction, at 105 °C, and heat-treated (fixed) at 243 °C in the tenter. A relaxation rate of 2% is used for a cooling treatment at 140 °C 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) process, a temperature gradient is applied so that the final temperature reaches 243 °C, and the heat treatment is performed for 7.3 seconds.

[0157] [Comparative Example 4] A raw material obtained by blending polyester B at a mass ratio of 88% and polyester E at a mass ratio of 12% is used as the raw material for surface layer A, a raw material with 100% polyester B is used as the raw material for intermediate layer C, and a raw material obtained by blending polyester C at a mass ratio of 28%, polyester I at a mass ratio of 22% and polyester K at a mass ratio of 50% is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio is A / C / B = 4 / 19 / 2 under the extrusion conditions. Cooling and solidification are carried out on a cooling roll with the surface temperature set at 20 °C and the peripheral speed set at 4 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Subsequently, the film is stretched 3.5 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 86 °C using the peripheral speed difference with a stretching roll with the peripheral speed set at 14.1 m / min. Then, this longitudinally stretched film is guided into a tenter and stretched 4.2 times in the transverse direction, i.e., the TD direction, at 105 °C, and heat treatment (fixing) is carried out at 230 °C in the tenter, followed by a 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) process, a temperature gradient is applied so that the final temperature reaches 230 °C, and the heat treatment is carried out for 7.8 seconds.

[0158] [Comparative Example 5] A raw material obtained by blending polyester B at a mass ratio of 87% and polyester F at a mass ratio of 13% is used as the raw material for surface layer A, a raw material obtained by blending polyester C at a mass ratio of 50% and polyester M at a mass ratio of 50% is used as the raw material for intermediate layer C, and a raw material obtained by blending polyester C at a mass ratio of 28%, polyester H at a mass ratio of 22% and polyester J at a mass ratio of 50% is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280 °C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, such that the thickness composition ratio is A / C / B = 4 / 25 / 2 under the extrusion conditions. The film is cooled and solidified on a cooling roll where the surface temperature is set to 20 °C and the peripheral speed is set to 4.3 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Then, using the peripheral speed difference with a stretching roll where the peripheral speed is set to 15.1 m / min, the film is stretched 3.5 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 86 °C. Subsequently, this longitudinally stretched film is led into a tenter and stretched 4.5 times in the transverse direction, i.e., the TD direction, at 105 °C, and heat-treated (fixed) at 230 °C in the tenter. A cooling treatment is performed at 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) process, a temperature gradient is applied such that the final temperature reaches 230 °C, and the heat treatment is performed for 7.3 seconds.

[0159] [Comparative Example 6] A raw material obtained by blending polyester C at 70% and polyester N at 30% by mass is used as the raw material for surface layer A, a raw material obtained by blending polyester C at 45% and polyester M at 55% by mass is used as the raw material for intermediate layer C, and a raw material obtained by blending polyester C at 70% and polyester N at 30% by mass is used as the raw material for surface layer B. The materials are supplied to an extruder with a vent, melt-extruded at 280°C, and then co-extruded in a three-layer (A / C / B) layer structure with surface layer A and surface layer B as the outermost layer (surface layer) and intermediate layer C as the intermediate layer, so that the thickness composition ratio is A / C / B = 1 / 23 / 1 under the extrusion conditions. Cooling and solidification are carried out on a cooling roll with the surface temperature set at 20°C and the peripheral speed set at 5.1 m / min using the electrostatic printing adhesion method to obtain an amorphous film. Then, using the peripheral speed difference with a stretching roll with the peripheral speed set at 17.7 m / min, the film is stretched 3.47 times in the longitudinal direction, i.e., the MD direction, at a film temperature of 85°C. After that, this longitudinally stretched film is led into a tenter and stretched 4.2 times in the transverse direction, i.e., the TD direction, at 120°C, and heat treatment (fixing) is carried out at 219°C in the tenter, followed by a cooling treatment at 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) process, a temperature gradient was applied so that the final temperature reached 219°C, and the heat treatment was carried out for 5.3 seconds.

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

[0161]

Table 2

[0162]

Table 3

[0163]

Table 4

[0164] First, as shown in Tables 2 and 3, the polyester films of Examples 1 to 14 are specific polyester films obtained by adjusting the type of polyester such as the composition, average particle size, particle size distribution, hardness, and affinity with polyester of the particles, as well as film-forming conditions, etc. The elastic deformation work rate (η it ), as well as the arithmetic mean height (Sa) and the maximum peak height (Sp) are controlled within a specific range. Specifically, in the polyester films of Examples 1 to 14, the elastic deformation work rate (η it ) on one surface is more than 55%, the arithmetic mean height (Sa) is 15 nm or less, and the maximum peak height (Sp) is 150 nm or less. Therefore, it can be understood that when the polyester films of Examples 1 to 14 are used as the support of the ceramic green sheet in the manufacturing process of, for example, multilayer ceramic capacitors, the generation of pinholes and the like in the ceramic green sheet can be effectively suppressed, and the peeling failure of the ceramic green sheet can be effectively suppressed.

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

[0166] In addition, from the results shown in the examples and comparative examples, for example, when trying to suppress the occurrence of peeling failure in the process of peeling the ceramic green sheet from the release film, on the other hand, surface defects such as pinholes tend to occur, suggesting that the elastic deformation work rate (η it ) and the surface smoothness are contradictory characteristics. However, in terms of being able to balance such contradictory characteristics, it can be said that the technical value of the present invention is very high. That is, for example, from the results of Comparative Example 6, when the content of the particles contained in the surface layer A is large, although the elastic deformation work rate (η it ) can be improved to a sufficient level, the maximum peak height (Sp) is high, suggesting a tendency for insufficient surface smoothness. On the other hand, from the results of Comparative Examples 1 to 5, etc., when the content of the particles contained in the surface layer A is small, although the surface smoothness is within a good range, the elastic deformation work rate (η it ) tends to be insufficient. Furthermore, it can be understood from the comparison between these comparative examples and the examples that adjusting the elastic deformation work rate (η it ) is also effective by adjusting the heat setting temperature and the transverse stretching ratio, and by selecting the particle type and content. Thus, in the polyester film containing particles, there is a tendency for the elastic deformation work rate (η it ) and the surface smoothness to be in conflict. However, according to the present invention, it can be said that the technical value is extremely high in that a polyester film capable of achieving both such conflicting characteristics can be provided.

Industrial Applicability

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

Claims

Claim 1 A polyester film containing particles, wherein the elastic deformation work rate of one surface exceeds 55% and satisfies 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. Claim 2 The polyester film according to claim 1, wherein the shrinkage rates in the longitudinal and transverse directions after heat treatment at 150 °C for 5 minutes are 2.8% or less. Claim 3 The polyester film according to claim 1 or 2, wherein the shrinkage rate in the transverse direction after heat treatment at 150 °C for 5 minutes is 1.5% or less. Claim 4 The polyester film according to claim 1 or 2, wherein the content of the particles is 250 ppm or more and 10,000 ppm or less by mass ratio with respect to the layer to be contained. Claim 5 The polyester film according to claim 1 or 2, wherein the average particle diameter of the particles is 1 μm or less. Claim 6 The polyester film according to claim 1 or 2, wherein the Mohs hardness of the particles is 9 or less. Claim 7 The polyester film according to claim 1 or 2, wherein the particles contain at least particle (a1) and particle (a2), the particle (a1) is an alumina particle, and the particle (a2) is a particle other than the particle (a1). Claim 8 The layer forming the one surface contains particles, the particles contain at least particle (a1) and particle (a2), and the zeta potential of the particles (a1) and (a2) at pH 7 is such that the particle (a1) has a positive value and the particle (a2) has a negative value, or the particle (a1) has a negative value and the particle (a2) has a positive value. The polyester film according to claim 1 or 2. Claim 9 The polyester film according to claim 8, wherein the content of the particles having a positive zeta potential at pH 7 is 50 ppm or more and 5,000 ppm or less by mass ratio with respect to the layer forming the one surface. Claim 10 The polyester film according to claim 8, wherein the content of the particles having a negative zeta potential at pH 7 is 100 ppm or more and 8,000 ppm or less by mass ratio with respect to the layer forming the one surface. Claim 11 The polyester film according to claim 8, wherein the particles having a positive zeta potential at pH 7 are alumina particles. Claim 12 The polyester film according to claim 8, wherein the particles having a negative zeta potential at pH 7 are silica or organic particles. Claim 13 The layer forming the 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 the 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 terms of mass ratio. The polyester film according to claim 1 or 2.

14. The layer forming the one surface contains particles, the main component of the particles is particles with a Mohs hardness of 8 or less, and the content of the particles with a Mohs hardness of 8 or less is less than 1800 ppm in terms of mass ratio with respect to the layer forming the one surface. The polyester film according to claim 1 or 2.

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

16. The surface orientation degree (ΔP) is 165 or more. The polyester film according to claim 1 or 2.

17. The ratio of the arithmetic mean height (Sa) of the 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. The polyester film according to claim 1 or 2 (provided that the arithmetic mean height (Sa) of the other surface > the arithmetic mean height (Sa) of the one surface).

18. The polyester film according to claim 1 or 2, which comprises at least two layers.

19. The polyester film according to claim 1 or 2, which comprises three layers.

20. The content of the particles is 250 ppm or more and 2800 ppm or less in terms of mass ratio with respect to the one surface layer. The polyester film according to claim 18.

21. The content of the particles is 2000 ppm or more and 8000 ppm or less in terms of mass ratio with respect to the other surface layer. The polyester film according to claim 20.

22. The polyester film includes 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 thicker than the thickness of each surface layer. The polyester film according to claim 1 or 2.

23. The polyester film includes a surface layer forming the one surface, an intermediate layer, and a surface layer forming the other surface in this order, and the ratio of the thicknesses of the respective layers (thickness of the surface layer: thickness of the intermediate layer: thickness of the surface layer) is 1 to 10: 10 to 35: 1 to 5. The polyester film according to claim 1 or 2.

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

25. The polyester film according to claim 1 or 2, which is used as a support for a ceramic green sheet in the manufacturing process of an automotive multilayer ceramic capacitor.

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

27. Use of the polyester film according to claim 1 or 2 as a support for a ceramic green sheet in the manufacturing process of an automotive multilayer ceramic capacitor.

28. A method for manufacturing a ceramic green sheet, comprising a step of coating a ceramic slurry containing a ceramic component on the one surface of the polyester film according to claim 1 or 2.

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