Layered polyester film and use thereof

Abstract

The present invention addresses the problem of providing a layered polyester film which contains a recycled polyester resin and exhibits excellent film surface smoothness and handling properties. The present invention relates to a layered polyester film having a front surface layer, an intermediate layer and a back surface layer. The front surface layer and / or the intermediate layer contain(s) a recycled polyester resin. The front surface layer has protrusions that are detected when analysis is performed under prescribed conditions, and the number of protrusions is 70 protrusions / mm2 or more. The present invention also relates to a layered polyester film having a front surface layer, an intermediate layer and a back surface layer. The front surface layer and / or the intermediate layer contain a recycled polyester resin. The front surface layer has protrusions that are detected when analysis is performed under prescribed conditions, and the total area of protrusions is 60 μm2 / mm2 or more.

Description

Laminated polyester film and its applications

[0001] The present invention relates to a laminated polyester film, a release film, a laminated polyester film with a ceramic green sheet, use of the laminated polyester film as a support for a ceramic green sheet, and a method for producing a ceramic green sheet.

[0002] Polyester films, typified by polyethylene terephthalate films and polyethylene naphthalate films, have excellent properties such as mechanical properties, dimensional stability, flatness, heat resistance, chemical resistance, and optical properties, and are also excellent in cost performance, and are therefore used in a variety of applications. For example, by utilizing the smoothness of the film surface, polyester films are suitably used in a variety of applications, such as release films for molding green sheets for multilayer ceramic capacitors, release substrates for interlayer insulating resins, and process films used in the production of dry film resists (DFRs) for forming wiring patterns on electronic circuit boards.

[0003] For example, polyester films are used as supports for release films used to mold green sheets for multilayer ceramic capacitors. In recent years, progress has been made in miniaturizing and increasing the capacity of multilayer ceramic capacitors, leading to the thinning of ceramic green sheets. As ceramic green sheets become thinner, any minute protrusions on the surface of the release film acting as a carrier film can cause pinholes and other defects in the ceramic green sheets. For this reason, release films used to manufacture ceramic green sheets are required to have a high degree of surface smoothness.

[0004] Furthermore, with the advancement of an advanced information society, there is an ever-increasing demand for smaller and lighter IT devices, which in turn has led to a demand for finer and denser printed wiring boards. To achieve finer and denser printed wiring boards, it is important to form fine patterns with extremely small wiring widths and wiring intervals with high precision, and therefore a film with excellent smoothness is required for use in the dry film resist manufacturing process.

[0005] Conventionally, as a support for this type of release film, Patent Document 1 discloses a film having a substrate having a first surface and a second surface, a smoothing layer provided on the first surface side of the substrate, and a release agent layer provided on the surface of the smoothing layer opposite the substrate, the smoothing layer being formed by heating and curing a composition for forming a smoothing layer containing a thermosetting compound having a weight average molecular weight of 950 or less, and the arithmetic mean roughness Ra of the outer surface of the release agent layer is １ is 8 nm or less, and the maximum protrusion height Rp of the outer surface of the release agent layer １ A release film for producing a ceramic green sheet is disclosed, characterized in that the surface roughness is 50 nm or less.

[0006] In addition, Patent Document 2 describes a polyester film for release that is excellent in surface smoothness and has particularly few fine defects on the film surface, and has a number of depression defects of 0.5 μm or more in depth of 5 / m ２ and a release polyester film having a center line average roughness SRa of 15 to 35 nm and a ten-point average roughness SRz of 1000 nm or less on at least one surface thereof.

[0007] In addition, Patent Document 3 discloses a polyester film roll obtained by winding a polyester film, in which slack defects present in the polyester film are removed within 100 m. ２ A polyester film is disclosed in which the number of particles per unit area is less than 5.

[0008] JP 2014-177093 A JP 2013-7054 A JP 2018-90803 A

[0009] In recent years, in light of growing environmental concerns and resource conservation, recycling of used PET containers such as PET bottles has been practiced, and methods for utilizing such containers have been attracting attention. However, recycling PET containers involves recovering waste from the market and using them as recycled raw materials, which results in a higher amount of foreign matter contained in the raw materials compared to PET raw materials derived from fossil fuels (virgin PET raw materials). For this reason, it has been difficult to use recycled polyester raw materials for polyester film substrates for producing ceramic green sheets and films for DFR manufacturing processes, which require particularly high surface smoothness.

[0010] However, when films have high surface smoothness, such as release films used in the production of ceramic green sheets or films used in the DFR manufacturing process, the films are in close contact with each other when stacked together, without any gaps between them. In such cases, the slipperiness of the films deteriorates, which can lead to poor handling, which can be problematic. To address this issue, techniques have been proposed that adjust the type and amount of particles incorporated into the surface layer. However, it has become clear that these techniques are unable to achieve both high surface smoothness and film handling when the film is made thinner.

[0011] Therefore, in order to solve these problems of the conventional technology, the inventors have conducted research with the aim of providing a laminated polyester film that contains recycled polyester resin and has excellent surface smoothness and handleability.

[0012] Examples of specific embodiments of the present invention are given below.

[0013] [1] A laminated polyester film having a surface layer, an intermediate layer, and a back layer, wherein the surface layer and / or the intermediate layer contains recycled polyester resin, and the surface layer has protrusions detected by analysis under the following conditions, and the number of protrusions is 70 / mm ２ or more, or the total area of ​​the protrusions is 60 μm ２ / mm ２ A laminated polyester film having the above structure; (Analysis conditions) The surface texture of the surface is photographed using a laser microscope under conditions of an objective lens magnification of 100x and a viewing angle of 0.15mm x 0.15mm, and the cross-sectional texture is confirmed, and image analysis is performed in areas where there are no concave shapes, using the following procedure. (1) Using image analysis software, the photographed image is converted from a color image to a grayscale image; (2) The threshold is set to 10 to 15, and background processing is performed; (3) The threshold is set to 130 to 230, and density conversion processing is performed; (4) The threshold is set to 0 to 160, and image processing is performed for automatic binarization and morphological hole filling, and the convex shapes observed as a result are regarded as protrusions. [2] The number of protrusions is 2000 / mm ２[3] The laminated polyester film according to [1], wherein the total area of ​​the protrusions is 1000 μm or less. ２ / mm ２ [4] The laminated polyester film according to any one of [1] to [3], wherein the equivalent circle diameter of the protrusions is 0.9 μm or less. [5] The laminated polyester film according to any one of [1] to [4], wherein the average distance between the protrusions is 26 μm or less. [6] The laminated polyester film according to any one of [1] to [5], wherein the total distance between the protrusions is 2050 μm or more. [7] The laminated polyester film according to any one of [1] to [6], wherein the surface layer is substantially free of particles. [8] The laminated polyester film according to any one of [1] to [7], wherein the surface layer has a thickness of 0.5 to 10 μm. [9] The laminated polyester film according to any one of [1] to [8], wherein the thickness of the intermediate layer is 50 to 93% of the total thickness of the film.

[10] The laminated polyester film according to any one of [1] to [9], wherein the air leakage index is 2730 seconds or less.

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

[10] , wherein the surface layer and / or the intermediate layer contains granules.

[12] The recycled polyester resin contains granules with a particle size of 1000 μm or less at a density of 70 particles / m ２The laminated polyester film according to any one of [1] to

[11] , wherein the back surface layer has an arithmetic mean height (Sa) of 3 nm or more and a maximum peak height (Sp) of 30 nm or more and 700 nm or less.

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

[13] , wherein the back surface layer has an arithmetic mean height (Sa) of 3 nm or more and a maximum peak height (Sp) of 30 nm or more and 700 nm or less.

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

[14] , wherein the intermediate layer has an isophthalic acid unit content of 0.01 to 5 mol % relative to 100 mol % of all dicarboxylic acid units constituting the polyester resin.

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

[15] , wherein the recycled polyester resin contained in the surface layer and / or intermediate layer is recycled from PET bottles.

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

[15] , wherein the recycled polyester resin contained in the surface layer and / or intermediate layer is recycled from polyester film.

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

[17] , wherein the recycled polyester resin contained in the surface layer and / or intermediate layer is a chemically recycled polyester resin.

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

[18] , wherein the surface layer and / or intermediate layer contains a polyester resin composed of a biomass-derived raw material.

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

[19] , wherein the laminated polyester film is used as a support for a ceramic green sheet in a manufacturing process of a multilayer ceramic capacitor.

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

[19] , wherein the polyester resin A constituting the surface layer, the polyester resin B constituting the intermediate layer, and the polyester resin C constituting the back layer are supplied to respective extruders, melted, and then co-extruded, wherein the polyester resin A and / or the polyester resin B is in a density of 70 particles per m2 having a particle size of 1000 μm or less. ２

[22] A method for producing a laminated polyester film containing a recycled polyester resin containing the above.

[22] A release film further having a release layer on the surface layer side of the laminated polyester film according to any one of [1] to

[20] .

[23] A laminated polyester film with a ceramic green sheet, in which a ceramic green sheet is laminated on the laminated polyester film according to any one of [1] to

[20] .

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

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

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

[20] .

[0014] According to the present invention, a laminated polyester film containing a recycled polyester resin and having excellent surface smoothness and handleability can be obtained.

[0015] FIG. 1 is a cross-sectional view illustrating the structure of the laminated polyester film of this embodiment.

[0016] The present invention will be described in detail below. The following description may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, when "X to Y" (X and Y are arbitrary numbers) is used, it means "X or more and Y or less," unless otherwise specified, and also includes "preferably greater than X" or "preferably smaller than Y." Furthermore, when "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), it also includes the meaning "preferably greater than X" or "preferably less than Y." In the following description, the terms "film" and "sheet" are not clearly distinguished from each other, and the term "film" includes the term "sheet," and the term "sheet" includes the term "film."

[0017] (Laminated Polyester Film) This embodiment is a laminated polyester film having a surface layer, an intermediate layer, and a back layer, in which the surface layer and / or the intermediate layer contains recycled polyester resin, and the surface layer has protrusions detected by analysis under the following conditions, and the number of protrusions is 70 / mm ２ or more, or the total area of ​​the protrusions is 60 μm ２ / mm ２ The present invention relates to a laminated polyester film (hereinafter also referred to as the present film) as described above. (Analysis Conditions) The surface texture of the surface is photographed using a laser microscope under conditions of an objective lens magnification of 100x and a field of view of 0.15 mm x 0.15 mm, and the cross-sectional texture is confirmed. Image analysis is performed on areas without concave shapes using the following procedure: (1) Using image analysis software, the photographed image is converted from a color image to a grayscale image; (2) A threshold value is set to 10-15, and background processing is performed; (3) A threshold value is set to 130-230, and density conversion processing is performed; (4) A threshold value is set to 0-160, and image processing is performed using automatic binarization and morphological hole filling. The resulting convex shapes observed are considered protrusions. In the above procedure (4), only protrusions having a predetermined size or larger are detected as convex shapes (convex portions); minute protrusions excluded by the threshold values ​​set in procedures (2) to (4) are not detected. The phrase "no concave shape is found when the cross-sectional properties are confirmed" means that no concave shape is found when the cross-section of the film is photographed using a laser microscope with an objective lens magnification of 100x. The image analysis software used for image analysis is not particularly limited as long as it can convert the photographed image from a color image to a grayscale image, and general-purpose analysis software such as WinROOF, ImageJ, and ImageJPro can be used. In this embodiment, image analysis is performed using the WinROOF series, such as "WinROOF2018" manufactured by Mitani Shoji Co., Ltd. Note that in the WinROOF series, such as "WinROOF2018," conversion to a grayscale image may be displayed as conversion to a monochrome image.

[0018] When using image analysis software from the WinROOF series, such as "WinROOF 2018" by Mitani Corporation, image analysis can be performed using steps (1) to (4) above. However, when using other image analysis software, the following steps (A) to (E) can be adopted. (A) Using image analysis software, the captured image is converted from a color image to a grayscale image. (B) Background processing is performed to reduce uneven brightness in the image. (C) Density conversion processing using linear transformation is performed to clarify the contrast between the image background and the object. (D) When the object is considered a black area, the density value that maximizes the degree of separation between the image background and the object is set as the threshold, and binarization is performed to detect protrusions. (E) Morphological hole filling processing is performed, and the detected object is identified as a protrusion. In step (A) above, the captured image (MBP file) is converted from a color image to a grayscale image. Because grayscale images only handle one color component (brightness), the image processing algorithm is simplified, allowing for faster analysis and filtering. It also has the effect of enhancing shape, texture, and contrast between light and shadow, and reducing noise. (B) above is a process for separating objects from backgrounds with density differences and high noise levels. Assuming a pixel size of 0.145 μm, a threshold value 10 to 15 times the average object size (μm) is input to remove brightness variations outside of the object. For example, this threshold value can be set to 10 to 15. (C) above is a process for linearly converting one density range to another, increasing the contrast of the image and facilitating subsequent processing. A range from relatively dark to relatively bright areas within the image is extracted, and this range is then expanded to cover the entire image using linear conversion, resulting in density conversion. For example, this threshold value can be set to 130 to 230. (D) above is a binarization process for detecting protrusions. This process assigns each pixel in an image to one of two colors, "black" or "white," thereby eliminating intermediate tones from the image and clearly distinguishing between the object and the background. If the brightness of a pixel is higher than a set threshold, it is classified as white, and if it is lower than that, it is classified as black. For example, the threshold can be set to a value between 0 and 160.By performing the process (E) above, gaps and small holes in the object can be filled while maintaining the original size of the object. This allows protrusions to be detected. Note that in the steps (A) to (E) above, the conditions for each step are adjusted appropriately with reference to the steps (1) to (4) above.

[0019] In this embodiment, the surface of the laminated polyester film is photographed under the above conditions, and the convex shapes identified by performing image analysis under predetermined conditions are regarded as protrusions. That is, the protrusions in this embodiment are different from those considered to be protrusions in conventional technology, and the present invention identifies the surface properties of the film from a new perspective. In this way, the present invention has succeeded in capturing the surface properties using a new analytical method, and relates to a laminated polyester film that has not been seen before.

[0020] As shown in FIG. 1 , the laminated polyester film 10 of this embodiment (first and second embodiments) has a surface layer 12 on one side of an intermediate layer 14 and a back layer 16 on the other side of the intermediate layer 14. In this embodiment, the intermediate layer 14 and the surface layer 12 are preferably laminated so as to be in direct contact with each other, but another layer may be provided between the intermediate layer 14 and the surface layer 12. Similarly, the intermediate layer 14 and the back layer 16 are preferably laminated so as to be in direct contact with each other, but another layer may be provided between the intermediate layer 14 and the back layer 16. In this specification, the surface layer 12 and the back layer 16 may be the same layer, but are preferably different layers. In this case, the layer with higher surface smoothness can be designated as the surface layer 12 and distinguished from the back layer 16. Note that "higher surface smoothness" means that the arithmetic mean height (Sa), described below, is smaller than that of one surface layer, or the maximum peak height (Sp), described below, is smaller than that of one surface layer.

[0021] In this embodiment, by using recycled polyester resin, it is possible to obtain a laminated polyester film with reduced environmental impact. Furthermore, in this embodiment, by forming protrusions that satisfy predetermined conditions on the surface layer, it is possible to obtain a polyester film with excellent handleability while improving the surface smoothness of the film.

[0022] In this embodiment, it is preferable that the surface layer contains a recycled polyester resin. By containing a recycled polyester resin in the surface layer, it becomes easy to form fine irregularities in the surface layer, and it becomes easy to form protrusions that satisfy predetermined conditions in the surface layer. As a result, the air leakage index of the laminated polyester film of this embodiment can be reduced.

[0023] In this embodiment, it is also preferable that the intermediate layer contains a recycled polyester resin. By containing a recycled polyester resin in the intermediate layer, it becomes easy to form fine irregularities in the intermediate layer, and these irregularities propagate to the surface layer, making it easy to form protrusions that satisfy predetermined conditions in the surface layer. As a result, the laminated polyester film of this embodiment can have a low air leakage index.

[0024] In this embodiment, it is also preferable that both the surface layer and the intermediate layer contain recycled polyester resin. By containing recycled polyester resin in both layers, it becomes easier to form protrusions that satisfy predetermined conditions in the surface layer, and the content ratio of recycled polyester resin can be increased, which is preferable from the viewpoint of environmental issues. From the viewpoint of environmental issues, it is also preferable that the back layer also contains recycled polyester resin.

[0025] In this specification, the larger the value of the air leakage index, the longer it takes for air to leak through the gaps between the films, meaning that the films are in closer contact with each other. On the other hand, a small air leakage index means that there are appropriate gaps between the films. Therefore, a laminated polyester film with a small air leakage index can exhibit appropriate slip properties and has good handleability.

[0026] This embodiment may also relate to a roll (rolled body) obtained by winding the present film. As described above, the present film has appropriate slip properties, strength, and flexibility, and therefore can be stored or distributed as a roll.

[0027] In the past, attempts to impart fine irregularities to the surface layer in order to reduce the air leakage index of a film have been made, and small particles have been added to the surface layer to impart fine irregularities. However, small particles tend to aggregate easily, and this aggregation can cause the formation of coarse protrusions. In contrast, the present invention imparts appropriate irregularities to the surface layer without adding particles to the surface layer by incorporating recycled polyester resin into the surface layer and / or intermediate layer. This makes it possible to reduce the air leakage index while suppressing the formation of coarse protrusions. Furthermore, since the surface layer is substantially free of particles, it is possible to suppress particle detachment from the surface layer, preventing the detached particles from becoming foreign matter or contaminating the process.

[0028] In this embodiment, the content of recycled polyester resin in each of the surface layer, intermediate layer, and back layer is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, still more preferably 40% by mass or more, and particularly preferably 50% by mass or more, based on the total mass of each layer. The content of recycled polyester resin may be 100% by mass based on the total mass of each layer.

[0029] On the other hand, in another embodiment, only the intermediate layer may contain recycled polyester resin, and the front and back layers may be configured to be substantially free of recycled polyester resin. In this specification, "substantially free" means that the content of recycled polyester resin is 1% by mass or less, preferably 0.1% by mass or less, relative to the total mass of each layer. In such a case, for example, when the film is wound into a roll, the recycled polyester resin contained in the intermediate layer can be prevented from adhering to the surface of the front layer.

[0030] <Surface Layer> The present film has a surface layer. The surface layer is a layer containing polyester. When the present film is used as a support (substrate) for ceramic green sheets in the manufacturing process of a multilayer ceramic capacitor, the surface layer is a layer disposed on the side on which the ceramic green sheets are laminated, and preferably has a higher surface smoothness than the back surface. In the manufacturing process of a multilayer ceramic capacitor, for example, a release layer is formed on the surface layer, and then the ceramic green sheets are laminated.

[0031] The surface layer has protrusions detected by analysis under the following conditions, and as described below, the surface layer has preferred numerical ranges for the arithmetic mean height (Sa), maximum peak height (Sp), maximum valley depth (Sv), maximum height (Sz), and root-mean-square height (Sq). The arithmetic mean height (Sa), maximum peak height (Sp), maximum valley depth (Sv), maximum height (Sz), and root-mean-square height (Sq) can be analyzed using the following method. First, the surface texture of the surface layer is photographed using a laser microscope with an objective lens magnification of 100x and a field of view of 0.15 mm x 0.15 mm. From the obtained surface profile curve, the arithmetic mean height (Sa), maximum peak height (Sp), maximum valley depth (Sv), maximum height (Sz), and root-mean-square height (Sq) can be determined. As the laser microscope, for example, an "OPTELICS HYBRID" manufactured by Lasertec Corporation can be used.

[0032] The arithmetic mean height (Sa) of the surface layer measured by the above-mentioned measuring method is preferably 1 nm or more, more preferably 4 nm or more, even more preferably 7 nm or more, even more preferably 9 nm or more, and particularly preferably 11 nm or more. The arithmetic mean height (Sa) of the surface layer is preferably 40 nm or less, more preferably 30 nm or less, even more preferably 26 nm or less, even more preferably 22 nm or less, and particularly preferably 18 nm or less.

[0033] The maximum peak height (Sp) of the surface layer measured by the above-mentioned measurement method is preferably 50 nm or more, more preferably 90 nm or more, even more preferably 120 nm or more, even more preferably 150 nm or more, and particularly preferably 182 nm or more. The maximum peak height (Sp) of the surface layer is preferably 700 nm or less, more preferably 600 nm or less, even more preferably 500 nm or less, even more preferably 400 nm or less, and particularly preferably 300 nm or less.

[0034] The maximum valley depth (Sv) of the surface layer measured by the above measurement method is preferably −300 nm or more, more preferably −200 nm or more, even more preferably −160 nm or more, even more preferably −130 nm or more, and particularly preferably −108 nm or more. The maximum valley depth (Sv) of the surface layer is preferably −10 nm or less, more preferably −20 nm or less, even more preferably −30 nm or less, even more preferably −40 nm or less, and particularly preferably −50 nm or less.

[0035] The maximum height (Sz) of the surface layer measured by the above-mentioned measuring method is preferably 50 nm or more, more preferably 100 nm or more, even more preferably 150 nm or more, even more preferably 200 nm or more, and particularly preferably 230 nm or more. The maximum height (Sz) of the surface layer is preferably 700 nm or less, more preferably 600 nm or less, even more preferably 500 nm or less, even more preferably 400 nm or less, and particularly preferably 350 nm or less.

[0036] The root mean square height (Sq) of the surface layer measured by the above-mentioned measuring method is preferably 2 nm or more, more preferably 5 nm or more, even more preferably 8 nm or more, even more preferably 11 nm or more, and particularly preferably 13.5 nm or more. The root mean square height (Sq) of the surface layer is preferably 50 nm or less, more preferably 40 nm or less, even more preferably 33 nm or less, even more preferably 27 nm or less, and particularly preferably 22 nm or less.

[0037] Furthermore, the relationship between the arithmetic mean height (Sa) and the maximum peak height (Sp) of the surface layer measured by the above-mentioned measurement method, more specifically, the ratio (Sp / Sa) of the maximum peak height (Sp) to the arithmetic mean height (Sa), is preferably 30 or less, more preferably 26 or less, even more preferably 23 or less, even more preferably 20 or less, and particularly preferably 16.5 or less. By having the relationship Sp / Sa between the arithmetic mean height (Sa) and the maximum peak height (Sp) be 30 or less, the maximum peak height (Sp) can be controlled to be low while maintaining the arithmetic mean height (Sa) low, thereby ensuring the processability of the laminated polyester film and achieving high smoothness. As a result, it is particularly easy to form thin ceramic green sheets, making it easier to adapt to thinner ceramic green sheets. The lower limit of Sp / Sa is not particularly limited, but from the viewpoint of imparting high smoothness while ensuring the processability of the laminated polyester film, it is preferably 1 or more, more preferably 3 or more, even more preferably 6 or more, still more preferably 9 or more, and particularly preferably 12 or more.

[0038] In the present embodiment, by setting the values ​​of Sa, Sp, Sv, Sz, and / or Sq within the above ranges, the surface layer can be provided with a required roughness while maintaining high smoothness, thereby more effectively improving the processability and handleability of the laminated polyester film.

[0039] The above-mentioned Sa, Sp, Sv, Sz, and / or Sq can be adjusted, for example, by the type of recycled polyester resin contained in the surface layer and / or intermediate layer, such as its composition, viscosity, molecular weight, thermal properties, the presence or absence of copolymerization components, and the content of the recycled polyester resin, and these adjustments can control the surface properties. They can also be controlled by appropriately incorporating particulate matter or additives into the surface layer and / or intermediate layer. For example, they can be adjusted by appropriately incorporating particles. The content can be adjusted taking into account the type, composition, average particle size, particle size distribution, hardness, affinity with the polyester resin, etc., of the particles used. When two or more types of particles are used in combination, it is preferable to adjust the content ratio taking into account the type of particles and polyester resin used. Furthermore, during polyester film production, it is also effective to control, for example, the stretching ratio (longitudinal and transverse stretching ratios in the case of biaxial stretching), stretching temperature, heat treatment temperature and treatment time (particularly the heat treatment temperature and treatment time after transverse stretching in the case of biaxial stretching).

[0040] The surface layer has protrusions detected by analysis under the following conditions. To detect protrusions, the surface texture of the surface layer is photographed using a laser microscope with an objective lens magnification of 100x and a field of view of 0.15 mm x 0.15 mm. The cross-sectional texture is confirmed, and image analysis is performed on areas without concave shapes using the following procedure: (1) Using image analysis software, the photographed image is converted from a color image to a grayscale image; (2) A threshold value is set to 10-15, and background processing is performed; (3) A threshold value is set to 130-230, and density conversion processing is performed; (4) A threshold value is set to 0-160, and image processing is performed using automatic binarization and morphological hole filling. The resulting convex shapes observed are identified as protrusions. In the above procedure (4), only protrusions having a predetermined size or larger are detected as convex shapes (convex portions), and minute protrusions excluded by the threshold values ​​set in procedures (2) to (4) are not detected. The phrase "no concave shape is found when the cross-sectional characteristics are confirmed" refers to the fact that no concave shape is visually observed when the cross-section of the film is photographed using a laser microscope with an objective lens magnification of 100x. The image analysis software used for image analysis is not particularly limited as long as it can convert the photographed image from a color image to a grayscale image, and general-purpose analysis software such as WinROOF, ImageJ, and ImageJPro can be used. In this embodiment, image analysis is performed using the WinROOF series, such as "WinROOF2018" manufactured by Mitani Shoji Co., Ltd. When using other image analysis software, the above-described steps (A) to (E) can be adopted. In steps (A) to (E), the conditions for each step are appropriately adjusted with reference to steps (1) to (4) above.

[0041] The number of protrusions on the surface layer is 70 / mm ２ It is preferable that the number of particles is 100 or more per mm. ２ More preferably, the number is 120 or more per mm ２ More preferably, the number is 150 / mm or more. ２ More preferably, the number is 170 / mm or more. ２ It is particularly preferable that the number of protrusions is 2000 / mm or more. ２It is preferable that the number of particles is 1000 or less per mm ２ More preferably, the number is 900 or less per mm ２ More preferably, the number is 800 or less per mm ２ It is even more preferable that the number of particles is 700 or less per mm. ２ More preferably, the number is 650 or less per mm ２ It is particularly preferable that the number of protrusions on the surface layer is equal to or greater than the above-mentioned lower limit, and it is preferable that the surface layer has a predetermined amount of roughness or more. This provides a rough surface necessary to improve the handleability of the laminated polyester film, and the air leakage index of the laminated polyester film can be reduced. As a result, the laminated polyester film can exhibit appropriate slip properties and improve handleability. For example, a laminated polyester film with appropriate surface roughness can be easily wound into a roll. Furthermore, by setting the number of protrusions on the surface layer to the above-mentioned upper limit or less, a laminated polyester film with excellent surface smoothness can be obtained.

[0042] The total area of ​​the protrusions on the surface layer is 60 μm ２ / mm ２ Preferably, it is 65 μm or more. ２ / mm ２ More preferably, it is 70 μm or more. ２ / mm ２ More preferably, it is 75 μm or more. ２ / mm ２ More preferably, it is 80 μm or more. ２ / mm ２ It is particularly preferable that the total area of ​​the protrusions is 1000 μm or more. ２ / mm ２ Preferably, it is 500 μm or less. ２ / mm ２ More preferably, it is 400 μm or less. ２ / mm ２ More preferably, it is 300 μm or less. ２ / mm ２ Even more preferably, it is 250 μm or less. ２ / mm ２More preferably, it is 200 μm or less. ２ / mm ２ It is particularly preferable that the total area of ​​the protrusions on the surface layer is equal to or greater than the above-mentioned lower limit, and that a predetermined amount of roughness is imparted. This provides the rough surface necessary to improve the handleability of the laminated polyester film, and the air leakage index of the laminated polyester film can be reduced. As a result, the laminated polyester film can exhibit appropriate slip properties and improve handleability. For example, a laminated polyester film with appropriate surface roughness can be easily wound into a roll. Furthermore, by setting the total area of ​​the protrusions on the surface layer to equal to or less than the above-mentioned upper limit, a laminated polyester film with excellent surface smoothness can be obtained.

[0043] The equivalent circle diameter of the protrusions on the surface layer is preferably 0.9 μm or less, more preferably 0.87 μm or less, even more preferably 0.84 μm or less, even more preferably 0.81 μm or less, and particularly preferably 0.79 μm or less. The equivalent circle diameter of the protrusions is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.3 μm or more, even more preferably 0.4 μm or more, and particularly preferably 0.46 μm or more.

[0044] The average distance between the protrusions of the surface layer is preferably 26 μm or less, more preferably 25 μm or less, and even more preferably 24 nm or less. The average distance between the protrusions is preferably 2 μm or more, more preferably 5 μm or more, even more preferably 7 μm or more, even more preferably 9 μm or more, and particularly preferably 11 μm or more.

[0045] The total distance between the protrusions of the surface layer is preferably 2050 μm or more, more preferably 2100 μm or more, even more preferably 2150 μm or more, and particularly preferably 2200 μm or more. The total distance between the protrusions is preferably 10000 μm or less, more preferably 8000 μm or less, even more preferably 6000 μm or less, even more preferably 5000 μm or less, even more preferably 4500 μm or less, and particularly preferably 4000 μm or less.

[0046] The number of protrusions (protrusion count), total area of ​​protrusions (total protrusion area), and equivalent circle diameter of protrusions (equivalent circle diameter of protrusions) can be determined using a measurement tool. Specifically, for example, these can be determined by selecting "shape features" in the measurement tools of image analysis software ("WinROOF2018" manufactured by Mitani Corporation). The average inter-protrusion distance and total inter-protrusion distance can also be determined using a measurement tool. Specifically, for example, these can be determined by selecting "inter-particle distance" in the measurement tools of image analysis software ("WinROOF2018" manufactured by Mitani Corporation) and measuring the inter-protrusion distance using center-of-gravity distance measurement. The average inter-protrusion distance is the average value of the distance between each protrusion detected in the captured image, and the total inter-protrusion distance is the total distance of the line segments when all protrusions detected in the captured image are connected by straight lines.

[0047] In this embodiment, by setting the circle-equivalent diameter of the protrusions on the surface layer, the average distance between the protrusions, and / or the total distance between the protrusions within the above ranges, it is possible to provide the surface layer with the necessary roughness while maintaining high smoothness, thereby more effectively improving the processability and handleability of the laminated polyester film.

[0048] The number of protrusions, total area of ​​protrusions, equivalent circle diameter of protrusions, average distance between protrusions, and / or total distance between protrusions can be adjusted, for example, by the type of recycled polyester resin contained in the surface layer and / or intermediate layer, such as its composition, viscosity, molecular weight, thermal properties, presence or absence of copolymerization components, particle size and content of particulate matter contained therein, and the content of recycled polyester resin, and these adjustments can control the surface properties. In particular, adjusting the particle size and content of particulate matter contained in the recycled polyester resin contained in the surface layer and / or intermediate layer, and the content of recycled polyester resin, is useful for adjusting the surface properties. Furthermore, the number of protrusions, total area of ​​protrusions, equivalent circle diameter of protrusions, average distance between protrusions, and / or total distance between protrusions can also be adjusted by appropriately blending particulate matter or additives into the surface layer and / or intermediate layer. For example, they can also be adjusted by appropriately incorporating particles. The content can be adjusted taking into account the type, composition, average particle size, particle size distribution, hardness, affinity with the polyester resin to be incorporated, etc. When two or more types of particles are used in combination, it is preferable to adjust the content ratio in consideration of the types of particles and polyester resin used. In addition, during the production of the polyester film, it is also effective to control, for example, the stretching ratio (in the case of biaxial stretching, the stretching ratio in both longitudinal and transverse directions), the stretching temperature, the heat treatment temperature and treatment time (in the case of biaxial stretching, the heat treatment temperature and treatment time after transverse stretching, in particular), etc.

[0049] The arithmetic mean roughness (Ra) of the surface layer measured in accordance with JIS-B0601 (2001) using a stylus-based high-precision microprofile measuring instrument (contact type two-dimensional surface roughness meter) is preferably 0.0001 μm or more, more preferably 0.0003 μm or more, even more preferably 0.0006 μm or more, even more preferably 0.0009 μm or more, and particularly preferably 0.001 μm or more. The arithmetic mean roughness (Ra) of the surface layer is preferably 0.03 μm or less, more preferably 0.01 μm or less, even more preferably 0.007 μm or less, even more preferably 0.005 μm or less, and particularly preferably 0.003 μm or less.

[0050] The maximum peak height (Rp) of the surface layer, measured in accordance with JIS-B0601 (2001) using a high-precision stylus-based microprofile measuring instrument (contact-type two-dimensional surface roughness meter), is preferably 0.0005 μm or more, more preferably 0.0008 μm or more, even more preferably 0.001 μm or more, even more preferably 0.002 μm or more, and particularly preferably 0.003 μm or more. Furthermore, the maximum peak height (Rp) of the surface layer is preferably 0.1 μm or less, more preferably 0.05 μm or less, even more preferably 0.02 μm or less, even more preferably 0.008 μm or less, and particularly preferably 0.005 μm or less.

[0051] The maximum height (Rz) of the surface layer measured in accordance with JIS-B0601 (2001) using a high-precision stylus-based microprofile measuring instrument (contact-type two-dimensional surface roughness meter) is preferably 0.005 μm or more, more preferably 0.01 μm or more, even more preferably 0.03 μm or more, even more preferably 0.05 μm or more, and particularly preferably 0.075 μm or more. The maximum height (Rz) of the surface layer is preferably 1 μm or less, more preferably 0.7 μm or less, even more preferably 0.5 μm or less, even more preferably 0.3 μm or less, and particularly preferably 0.1 μm or less.

[0052] The arithmetic mean roughness (Ra), maximum peak height (Rp), and maximum height (Rz) of the surface layer are measured using a contact-type two-dimensional surface roughness meter in the longitudinal direction (MD) of the film under the following conditions: stylus tip radius 0.5 mm, evaluation length 2.5 mm, longitudinal magnification 20,000, lateral magnification 10, cutoff value 0.08 mm, and measurement speed 0.1 mm / sec. In this film, by setting the arithmetic mean roughness (Ra), maximum peak height (Rp), and / or maximum height (Rz) of the surface layer within the above ranges, it is possible to provide the necessary rough surface while maintaining high smoothness of the surface layer, thereby more effectively improving the processability and handleability of the laminated polyester film.

[0053] The above-mentioned Ra, Rp, and Rz can be adjusted, for example, by the type of recycled polyester resin contained in the surface layer and / or intermediate layer, such as its composition, viscosity, molecular weight, thermal properties, the presence or absence of copolymerization components, and the content of the recycled polyester resin, and these adjustments can control the surface properties. They can also be controlled by appropriately incorporating particulate matter or additives into the surface layer and / or intermediate layer. For example, they can be adjusted by appropriately incorporating particles. The content can be adjusted taking into account the type, composition, average particle size, particle size distribution, hardness, and affinity with the polyester resin used. When two or more types of particles are used in combination, it is preferable to adjust the content ratio taking into account the type of particles and polyester resin used. Furthermore, during polyester film production, it is also effective to control, for example, the stretching ratio (longitudinal and transverse stretching ratios in the case of biaxial stretching), stretching temperature, and heat treatment temperature and treatment time (particularly the heat treatment temperature and treatment time after transverse stretching in the case of biaxial stretching).

[0054] The arithmetic mean height (Sa) of the surface layer calculated from a surface profile curve measured using a surface roughness measuring instrument is preferably 0.1 nm or more, more preferably 0.2 nm or more, even more preferably 0.3 nm or more, even more preferably 0.5 nm or more, and particularly preferably 0.6 nm or more. The arithmetic mean height (Sa) of the surface layer is preferably 8 nm or less, more preferably 6 nm or less, even more preferably 4 nm or less, even more preferably 2 nm or less, and particularly preferably 1 nm or less.

[0055] The maximum peak height (Sp) of the surface layer calculated from a surface profile curve measured using a surface roughness measuring instrument is preferably 3 nm or more, more preferably 6 nm or more, even more preferably 9 nm or more, even more preferably 12 nm or more, and particularly preferably 15 nm or more. The maximum peak height (Sp) of the surface layer is preferably 90 nm or less, more preferably 80 nm or less, even more preferably 70 nm or less, even more preferably 60 nm or less, and particularly preferably 50 nm or less.

[0056] The maximum height (Sz) of the surface layer calculated from a surface profile curve measured using a surface roughness measuring instrument is preferably 5 nm or more, more preferably 8 nm or more, even more preferably 12 nm or more, even more preferably 16 nm or more, and particularly preferably 20 nm or more. The maximum height (Sz) of the surface layer is preferably 110 nm or less, more preferably 90 nm or less, even more preferably 75 nm or less, even more preferably 60 nm or less, and particularly preferably 50 nm or less.

[0057] Furthermore, the relationship between the arithmetic mean height (Sa) and the maximum peak height (Sp) of the surface layer calculated from a surface profile curve measured using a surface roughness measuring instrument, more specifically, the ratio (Sp / Sa) of the maximum peak height (Sp) to the arithmetic mean height (Sa), is preferably 50 or less, more preferably 40 or less, even more preferably 37 or less, even more preferably 34 or less, and particularly preferably 31 or less. By having the relationship Sp / Sa between the arithmetic mean height (Sa) and the maximum peak height (Sp) be 50 or less, the maximum peak height (Sp) can be controlled to be low while maintaining a low arithmetic mean height (Sa), thereby ensuring high smoothness while ensuring the processability of the laminated polyester film. As a result, it is easy to form particularly thin ceramic green sheets, making it easier to adapt to thinner ceramic green sheets. The lower limit of Sp / Sa is not particularly limited, but from the viewpoint of imparting high smoothness while ensuring the processability of the laminated polyester film, it is preferably 3 or more, more preferably 7 or more, even more preferably 10 or more, still more preferably 15 or more, and particularly preferably 20 or more.

[0058] Arithmetic mean height (Sa) is one of the surface roughness parameters (ISO 25178) and is a three-dimensional extension of the two-dimensional Ra (arithmetic mean roughness of a line), and is found by dividing the volume of the area enclosed by the surface shape curved surface and the mean surface by the measured area, and can be calculated using the following formula (1): When the surface is the XY plane and the height direction is the Z axis, A is the defined area (the entire image), and Z(x, y) is the height from the surface at height 0 of the image point (x, y), then it can be expressed as in the following formula (1).

[0059]

[0060] The maximum peak height (Sp) is one of the surface roughness parameters (ISO 25178), and represents the maximum value of the height from the mean plane of the surface, and is expressed by the following formula (2).

[0061]

[0062] The maximum height (Sz) is one of the surface roughness parameters (ISO 25178) and is expressed as Sz = Sp + Sv. It represents the distance from the highest point to the lowest point on the surface, and is the maximum height (Rz) extended to the surface.

[0063] The arithmetic mean height (Sa), maximum peak height (Sp), and maximum height (Sz) are measured using a surface roughness measuring instrument under the conditions of an objective lens magnification of 10x, a zoom magnification of 2.0x, and a viewing angle of 0.44 mm x 0.44 mm, and the arithmetic mean height (Sa), maximum peak height (Sp), and maximum height (Sz) are determined after the following processing is performed: Filter Type: Spline Filter: High Pass Type: Robust Gaussian Spline Fixed Cutoffs Mode: Period Long Period: 200 μm

[0064] In the present film, by setting the arithmetic mean height (Sa), maximum peak height (Sp) and / or maximum height (Sz) of the surface layer within the above ranges, it is possible to provide the necessary rough surface while maintaining high smoothness of the surface layer, thereby more effectively improving the processability and handleability of the laminated polyester film.

[0065] The above-mentioned Sa, Sp, and Sz can be adjusted, for example, by the type of recycled polyester resin contained in the surface layer and / or intermediate layer, such as its composition, viscosity, molecular weight, thermal properties, the presence or absence of copolymerization components, and the content of the recycled polyester resin, and these adjustments can control the surface properties. They can also be controlled by appropriately incorporating particulate matter or additives into the surface layer and / or intermediate layer. For example, they can be adjusted by appropriately incorporating particles. The content can be adjusted taking into account the type, composition, average particle size, particle size distribution, hardness, and affinity with the polyester resin used. When two or more types of particles are used in combination, it is preferable to adjust the content ratio taking into account the type of particles and polyester resin used. Furthermore, during polyester film production, it is also effective to control, for example, the stretching ratio (longitudinal and transverse stretching ratios in the case of biaxial stretching), stretching temperature, and heat treatment temperature and treatment time (particularly the heat treatment temperature and treatment time after transverse stretching in the case of biaxial stretching).

[0066] The thickness of the surface layer is preferably 0.5 μm or more, more preferably 0.8 μm or more, even more preferably 1 μm or more, and particularly preferably 1.2 μm or more. The thickness of the surface layer is preferably 15 μm or less, more preferably 12 μm or less, even more preferably 10 μm or less, even more preferably 8 μm or less, even more preferably 6 μm or less, even more preferably 5 μm or less, particularly preferably 4 μm or less, and most preferably 3 μm or less. By making the thickness of the surface layer equal to or greater than the above-mentioned lower limit, it becomes easy to control the number and total area of ​​the protrusions on the surface layer within the desired range, and the processability and handleability of the laminated polyester film can be more effectively improved while maintaining high smoothness of the surface layer.

[0067] In order to control the number and total area of ​​the protrusions on the surface layer within the desired range, the thickness of the surface layer is preferably 1 to 22%, more preferably 2 to 19%, even more preferably 2.5 to 16%, still more preferably 3 to 13%, and particularly preferably 5 to 10% of the total thickness of the laminated polyester film.

[0068] In this embodiment, it is preferable that the surface layer is substantially free of particles. The surface layer being substantially free of particles eliminates the risk of large protrusions due to particle aggregation, or of particles falling off, resulting in foreign matter and process contamination. The phrase "substantially free of particles" means that particles are not intentionally included, and specifically refers to a particle content (particle concentration) of 200 ppm or less, more preferably 150 ppm or less, even more preferably 100 ppm or less, and particularly preferably 50 ppm or less, by mass, relative to the surface layer.

[0069] In another embodiment, the surface layer may contain particles. When particles are blended, by adding an appropriate amount of particles of an appropriate particle size, it is possible to impart an appropriate fine uneven shape to the surface layer and also to obtain an effect of preventing scratches on the film surface. When particles are added to the surface layer, the average particle size of the particles to be added is, for example, preferably 0.01 μm or more, more preferably 0.03 μm or more, and even more preferably 0.04 μm or more. On the other hand, the average particle size of the particles to be added is preferably 1 μm or less, more preferably 0.8 μm or less, even more preferably 0.6 μm or less, even more preferably 0.4 μm or less, and particularly preferably 0.2 μm or less.

[0070] When particles are contained in the surface layer, the particle content is preferably more than 200 ppm by mass, more preferably 300 ppm or more, even more preferably 400 ppm or more, still more preferably 500 ppm or more, and particularly preferably 600 ppm or more. On the other hand, the particle content is preferably 2000 ppm or less, more preferably 1800 ppm or less, even more preferably 1600 ppm or less, still more preferably 1400 ppm or less, even more preferably 1200 ppm or less, and particularly preferably 1000 ppm or less.

[0071] The particles are not particularly limited, and examples thereof include inorganic particles such as metal oxides such as alumina, silica, calcium carbonate, titanium oxide, ceria, zirconium oxide, barium oxide, chromium oxide, iron oxide, and tungsten oxide; composite oxides such as silica-zirconium oxide, silica-titanium oxide, silica-titanium oxide-barium oxide, silica-titanium oxide-zirconium oxide, borosilicate glass, aluminosilicate glass, and fluoroaluminosilicate glass; and organic particles having a carboxy group or a sulfonic acid group, of which alumina, silica, calcium carbonate, and organic particles are preferred.

[0072] It is also preferable that the surface layer contains a recycled polyester resin that may be contained in the intermediate layer, as described later. The recycled polyester resin that may be contained in the surface layer can be the same as the recycled polyester resin contained in the intermediate layer, as described later. For example, the recycled polyester resin contained in the surface layer may be recycled from PET bottles or recycled polyester film. Furthermore, the recycled polyester resin may be a polyester resin obtained by chemically recycling recycled raw materials such as PET bottles and polyester film. By containing a recycled polyester resin in the surface layer, the number of protrusions on the surface layer and the total area of ​​the protrusions may be within a desired range. Furthermore, by containing a recycled polyester resin in the surface layer, for example, CO ２ This will reduce emissions and contribute to reducing the burden on the environment.

[0073] When the surface layer contains recycled polyester resin, the content of recycled polyester resin is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, relative to the total mass of the resin constituting the surface layer. The content of recycled polyester resin may be 60% by mass or more, 70% by mass or more, or even 80% by mass or more. The upper limit of the content of recycled polyester resin is not particularly limited, and may be 100% by mass, relative to the total mass of the resin constituting the surface layer. By containing recycled polyester resin in the above range in the surface layer, for example, CO ２This can reduce emissions and contribute to reducing the burden on the environment. Furthermore, by incorporating recycled polyester resin into the surface layer, the number and total area of ​​the protrusions on the surface layer can be adjusted to a desired range, making it easy to impart appropriate roughness to the surface layer. This improves the slipperiness of the laminated polyester film, thereby more effectively improving processability and handleability.

[0074] Biomass-derived raw materials may be used as the polymerization components constituting the recycled (regenerated) polyester. For example, biomass-derived ethylene glycol may be used as the diol component. The surface layer may contain a polyester resin composed of biomass-derived raw materials, or may contain a polyester resin composed of recycled polyester resin and biomass-derived raw materials. For example, the surface layer may contain a chemically recycled polyester resin and a polyester resin composed of biomass-derived raw materials.

[0075] The surface layer preferably contains granular matter. In this specification, the granular matter is derived from a gel-like substance formed by aggregation of resin-derived components or foreign matter contained in recycled raw materials. In this case, the recycled polyester resin that can be contained in the surface layer contains granular matter with a particle size of 1000 μm or less at a density of 50 particles / m ２ It may contain more than 70 pieces / m ２ It may contain more than 75 pieces / m ２ It may contain more than 100 pieces / m ２ It may contain more than 150 pieces / m ２ It may contain more than 175 pieces / m ２ It may contain more than 200 pieces / m ２ The recycled polyester resin that can be contained in the surface layer may contain particles having a particle size of 1000 μm or less at a density of 4000 particles / m ２ It may contain up to 3000 pieces / m ２ It may contain up to 2000 pieces / m ２ It may contain up to 1500 pieces / m ２ It may contain up to 1000 pieces / m ２ It may contain up to 600 pieces / m２ The number of granular particles having a particle size of 1000 μm or less contained in the surface layer may also be within the above range. In this specification, the particle size of the granular particles is the average value of the longest diameter and the shortest diameter.

[0076] The recycled polyester resin that can be contained in the surface layer is 50 particles / m2 with a particle size of 25 μm or more and 1000 μm or less. ２ It may contain more than 70 pieces / m ２ It may contain more than 75 pieces / m ２ It may contain more than 100 pieces / m ２ It may contain more than 150 pieces / m ２ It may contain more than 175 pieces / m ２ It may contain more than 200 pieces / m ２ The recycled polyester resin contained in the surface layer may contain granules having a particle size of 25 μm or more and 1000 μm or less at a density of 4000 particles / m ２ It may contain up to 3000 pieces / m ２ It may contain up to 2000 pieces / m ２ It may contain up to 1500 pieces / m ２ It may contain up to 1000 pieces / m ２ It may contain up to 600 pieces / m ２ The recycled polyester resin that can be contained in the surface layer may contain particles having a particle size of 25 μm or more and less than 50 μm at a density of 15 to 1500 particles / m ２ may contain 20 to 1000 particles / m ２ may contain 25 to 600 particles / m ２ may contain 30 to 300 particles / m ２ may contain 40 to 100 particles / m ２ The recycled polyester resin that can be contained in the surface layer has a particle size of 50 μm or more and less than 75 μm at a density of 10 to 700 particles / m ２ may contain 15 to 500 particles / m ２ may contain 20 to 300 particles / m ２ may contain 22 to 200 particles / m ２ May contain 25 to 100 pieces / m ２The recycled polyester resin that can be contained in the surface layer has a particle size of 75 μm or more and less than 100 μm at a density of 5 to 300 particles / m ２ may contain 10 to 200 particles / m ２ may contain 15 to 100 particles / m ２ It may contain 18 to 70 particles, and may contain 20 to 50 particles / m ２ The recycled polyester resin that can be contained in the surface layer has a particle size of 100 μm or more and less than 150 μm at a density of 5 to 250 particles / m ２ may contain 10 to 200 particles / m ２ may contain 15 to 100 particles / m ２ may contain 18 to 70 pieces / m ２ may contain 20 to 50 pieces / m ２ The recycled polyester resin that can be contained in the surface layer has a particle size of 150 μm or more and less than 200 μm at a density of 1 to 80 particles / m ２ may contain 2 to 50 pieces / m ２ may contain 3 to 40 pieces / m ２ It may contain 4 to 30 particles, and may contain 5 to 20 particles / m ２ The recycled polyester resin that can be contained in the surface layer has a particle size of 200 μm or more and less than 300 μm at a density of 1 to 50 particles / m ２ may contain 2 to 40 pieces / m ２ may contain 3 to 30 pieces / m ２ may contain 4 to 20 pieces / m ２ may contain 5 to 15 pieces / m ２ The recycled polyester resin contained in the surface layer may contain granules having a particle size of 300 μm or more and less than 500 μm at a density of 1 to 30 particles / m ２ may contain 2 to 20 pieces / m ２ may contain 3 to 10 pieces / m ２ may contain 4 to 8 pieces / m ２ It may include.

[0077] The number of particles having each of the above particle sizes can be measured using a gel counter as follows: The (recycled) polyester resin contained in the surface layer is continuously extruded into a sheet having a width of 10 cm and a thickness of 50 μm, and light is applied from above to an area of ​​approximately 6 cm in the center of the width direction of the sheet, and a CCD camera is used to photograph the shadows caused by the particles (gel) from below the sheet. ２ The number of particles having each particle size present in the gel is measured. The gel counter is composed of a camera system, an extruder, and a chill roll unit. As the gel counter, an "FS-5 Film Scan (camera system), ME-20 / 26 V2 Measuring Extruder (extruder), CR-7 Chill Roll Unit (chill roll unit)" manufactured by Optical Control Systems can be used. The measurement conditions are as follows: Chill roll temperature: 30°C, Extruder cylinder temperature: 295°C, Extruder screw rotation speed: 100 rpm, Sheet thickness: 50 μm

[0078] The particle size and content of the particulate matter in the recycled polyester resin can be adjusted by the same method as that for adjusting the particle size and content of the particulate matter in the recycled polyester resin contained in the intermediate layer.

[0079] <Intermediate Layer> The present film has an intermediate layer. The intermediate layer is a layer containing polyester. The intermediate layer functions as the thickest main layer in the present film.

[0080] In this embodiment, the intermediate layer preferably contains recycled polyester resin. The content of recycled polyester resin is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, relative to the total mass of the resin constituting the intermediate layer. The content of recycled polyester resin may be 60% by mass or more, 70% by mass or more, or even 80% by mass or more. The upper limit of the content of recycled polyester resin is not particularly limited, and may be 100% by mass, relative to the total mass of the resin constituting the intermediate layer. By containing recycled polyester resin in the above range in the intermediate layer, for example, CO２ This can reduce emissions and contribute to reducing the burden on the environment. Furthermore, by incorporating recycled polyester resin into the intermediate layer, the number and total area of ​​the protrusions on the surface layer can be adjusted to desired ranges, making it easier to impart appropriate roughness to the surface layer. This improves the slipperiness of the laminated polyester film, thereby more effectively improving its processability and handling.

[0081] The recycled polyester resin that can be contained in the intermediate layer may be a material recycled polyester, which is a recycled raw material, or may be a chemically recycled polyester. In particular, the recycled polyester resin that can be contained in the intermediate layer is preferably a chemically recycled polyester, which is a recycled raw material. The recycled (regenerated) polyester may be, for example, a polyester derived from a polyester container (e.g., a PET bottle) or a polyester film (e.g., a processing film). Thus, in this embodiment, the recycled polyester resin constituting the intermediate layer may be a recycled polyester resin derived from a polyester container or a recycled polyester resin derived from a polyester film. When a recycled polyester resin derived from a polyester film is used, the recycled polyester film may be a polyester film used as a support (substrate) for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor.

[0082] The content of isophthalic acid units relative to 100 mol% of all dicarboxylic acid units constituting the polyester resin that can be contained in the intermediate layer is preferably 0.01 to 5 mol%, more preferably 0.1 to 4 mol%, even more preferably 0.5 to 3 mol%, and even more preferably 1 to 2.5 mol%. For example, polyesters such as PET bottles recycled from the market or society contain a large amount of isophthalic acid components for the purpose of controlling crystallinity. When such recycled raw materials are used, the intermediate layer will contain isophthalic acid units within the above range. An isophthalic acid unit content equal to or greater than the above lower limit indicates a high content of recycled resin, such as PET bottles. On the other hand, an isophthalic acid unit content equal to or less than the above upper limit can enhance the mechanical strength of the film. Furthermore, when the present film is used as a support (substrate) for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor, the suppressed crystallinity of the present film has the advantage of reducing the generation of burrs and chips when cutting with a cutting blade to peel off the ceramic green sheet laminated on the support.

[0083] Biomass-derived raw materials may be used as the polymerization components constituting the recycled (regenerated) polyester. For example, biomass-derived ethylene glycol may be used as the diol component. The intermediate layer may contain a polyester resin composed of biomass-derived raw materials, or may contain a polyester resin composed of recycled polyester resin and biomass-derived raw materials. For example, the intermediate layer may contain a chemically recycled polyester resin and a polyester resin composed of biomass-derived raw materials.

[0084] The intermediate layer preferably contains granular matter. In this specification, the granular matter is derived from a gel-like substance formed by aggregation of resin-derived components or foreign matter contained in recycled raw materials. In this case, the recycled polyester resin that can be contained in the intermediate layer contains granular matter with a particle size of 1000 μm or less at a density of 50 particles / m ２ It may contain more than 70 pieces / m ２It may contain more than 75 pieces / m ２ It may contain more than 100 pieces / m ２ It may contain more than 150 pieces / m ２ It may contain more than 175 pieces / m ２ It may contain more than 200 pieces / m ２ The recycled polyester resin that can be contained in the intermediate layer may contain particles having a particle size of 1000 μm or less at a density of 4000 particles / m ２ It may contain up to 3000 pieces / m ２ It may contain up to 2000 pieces / m ２ It may contain up to 1500 pieces / m ２ It may contain up to 1000 pieces / m ２ It may contain up to 600 pieces / m ２ The number of granular particles having a particle size of 1000 μm or less contained in the intermediate layer may also be within the above range. In this specification, the particle size of a granular particle is the average value of the longest diameter and the shortest diameter.

[0085] The recycled polyester resin that can be contained in the intermediate layer is 50 particles / m2 with a particle size of 25 μm or more and 1000 μm or less. ２ It may contain more than 70 pieces / m ２ It may contain more than 75 pieces / m ２ It may contain more than 100 pieces / m ２ It may contain more than 150 pieces / m ２ It may contain more than 175 pieces / m ２ It may contain more than 200 pieces / m ２ The recycled polyester resin contained in the intermediate layer may contain granules having a particle size of 25 μm or more and 1000 μm or less at a density of 4000 particles / m ２ It may contain up to 3000 pieces / m ２ It may contain up to 2000 pieces / m ２ It may contain up to 1500 pieces / m ２ It may contain up to 1000 pieces / m ２ It may contain up to 600 pieces / m ２ The recycled polyester resin that can be contained in the intermediate layer may contain particles having a particle size of 25 μm or more and less than 50 μm at a density of 15 to 1500 particles / m ２may contain 20 to 1000 particles / m ２ may contain 25 to 600 particles / m ２ may contain 30 to 300 particles / m ２ may contain 40 to 100 particles / m ２ The recycled polyester resin that can be contained in the intermediate layer has a particle size of 50 μm or more and less than 75 μm at a density of 10 to 700 particles / m ２ may contain 15 to 500 particles / m ２ may contain 20 to 300 particles / m ２ may contain 22 to 200 particles / m ２ May contain 25 to 100 pieces / m ２ The recycled polyester resin that can be contained in the intermediate layer has a particle size of 75 μm or more and less than 100 μm at a density of 5 to 300 particles / m ２ may contain 10 to 200 particles / m ２ may contain 15 to 100 particles / m ２ It may contain 18 to 70 particles, and may contain 20 to 50 particles / m ２ The recycled polyester resin that can be contained in the intermediate layer has a particle size of 100 μm or more and less than 150 μm at a density of 5 to 250 particles / m ２ may contain 10 to 200 particles / m ２ may contain 15 to 100 particles / m ２ may contain 18 to 70 pieces / m ２ may contain 20 to 50 pieces / m ２ The recycled polyester resin that can be contained in the intermediate layer has a particle size of 150 μm or more and less than 200 μm at a density of 1 to 80 particles / m ２ may contain 2 to 50 pieces / m ２ may contain 3 to 40 pieces / m ２ It may contain 4 to 30 particles, and may contain 5 to 20 particles / m ２ The recycled polyester resin that can be contained in the intermediate layer has a particle size of 200 μm or more and less than 300 μm at a density of 1 to 50 particles / m ２ may contain 2 to 40 pieces / m ２ may contain 3 to 30 pieces / m ２ may contain 4 to 20 pieces / m ２may contain 5 to 15 pieces / m ２ The recycled polyester resin contained in the intermediate layer may contain granules having a particle size of 300 μm or more and less than 500 μm at a density of 1 to 30 particles / m ２ may contain 2 to 20 pieces / m ２ may contain 3 to 10 pieces / m ２ may contain 4 to 8 pieces / m ２ It may include.

[0086] The number of particles having each of the above particle sizes can be measured using a gel counter as follows: The (recycled) polyester resin contained in the intermediate layer is continuously extruded into a sheet having a width of 10 cm and a thickness of 50 μm, and light is applied from above to an area of ​​approximately 6 cm in the center of the width direction of the sheet, and a CCD camera is used to photograph the shadows caused by the particles from below the sheet. ２ The number of particulates having each particle size present in the film is measured. The particulates are considered to be mainly derived from the gel. The gel counter is composed of a camera system, an extruder, and a chill roll unit. As the gel counter, an "FS-5 Film Scan (camera system), ME-20 / 26 V2 Measuring Extruder (extruder), CR-7 Chill Roll Unit (chill roll unit)" manufactured by Optical Control Systems can be used. The measurement conditions are as follows: - Chill roll temperature: 30°C - Extruder cylinder temperature: 295°C - Extruder screw rotation speed: 100 rpm - Sheet thickness: 50 μm

[0087] The particle size and content of particulate matter in recycled polyester resin can be adjusted by, for example, at least one of the following methods (1) to (4), and it is preferable to combine a plurality of methods, and it is more preferable to use all of them: (1) A method of removing metallic foreign matter present in recovered PET bottles and polyester films using a metal detector; (2) A method of removing foreign matter present in recovered PET bottles and polyester films by passing them through a precision air classifier; (3) A method of adjusting the temperature near the raw material inlet of the extruder, the temperature near the outlet, and the temperature difference between the temperature near the inlet and the outlet in a process of melting recovered PET bottles and polyester films in an extruder and pelletizing them, etc.; (4) A method of removing particulate matter of a particle size other than the desired particle size from molten recycled polyester resin by passing it through a filter.

[0088] In the above-mentioned method (1) of removing metallic contaminants using a metal detector, the metallic contaminants may be removed using a commercially available metal detector. A preferred metal detector is one that uses a magnet. For example, a method of removing metallic contaminants by attaching a magnetic bar to a pipe when blowing the recycled polyester raw material to the step (2) is exemplified. If metallic contaminants are not removed, the thermal stability of the polyester tends to be reduced, the number of contaminants in the resulting film tends to increase, and transparency tends to be reduced.

[0089] In the step (2) of removing foreign matter by passing the raw material through an air classifier, foreign matter in the raw material that has been through step (1) is further removed using an air classifier. As the air classifier, a gravity classifier, an inertial classifier, a centrifugal classifier, etc. can be used, and commercially available ones can be used, but it is preferable to use a classifier that is capable of precise classification. By using an air classifier, powder and froth-like foreign matter attached to the surface of recovered PET bottles and polyester films can be separated with a nitrogen or air stream. The powder and froth-like foreign matter attached to the surface may have a high melting point, and if they remain attached without being removed using an air classifier, these foreign matter will not melt during molding, which may reduce the transparency of the resulting film.

[0090] In the above method (3) of melting the recovered PET bottles or polyester films in an extruder, it is preferable to melt the materials by setting the temperature near the raw material inlet of the extruder to, for example, 290 to 280°C, the temperature near the outlet to, for example, 270 to 260°C, and the temperature difference between the temperature near the inlet and the temperature near the outlet to, for example, 20 to 25°C.

[0091] First, when the raw materials are fed into the extruder, they are melted at a temperature of, for example, 280 to 290°C, and the temperature inside the extruder is gradually lowered, so that the catalyst metal-derived substances melted in the resin act as nuclei, facilitating the precipitation of foreign matter. At this time, the temperature near the extruder outlet is set to, for example, 260 to 270°C, and preferably, the temperature difference between the temperature near the inlet and the temperature near the outlet is set to 20 to 25°C. By setting the temperature near the extruder inlet to 280°C or higher, the precipitation of the above-mentioned foreign matter is facilitated, and by setting the temperature near the extruder inlet to 290°C or lower, decomposition of the polyester resin is suppressed, making it easier to obtain a recycled polyester resin with excellent thermal stability.

[0092] The residence time of the recycled polyester raw material in the extruder is preferably 10 minutes or less, and more preferably 5 minutes or less from the viewpoint of further suppressing the carboxyl terminal group concentration and more easily suppressing deterioration in the color tone of the polyester.

[0093] In the above method (4), unnecessary foreign matter is removed by passing the molten polyester resin through a filter with a filtration particle size of 10 to 25 μm, for example. By using a filter with a filtration particle size of 25 μm or less, foreign matter can be sufficiently removed, making it easier to obtain a recycled polyester resin with the desired particulate matter. On the other hand, by using a filter with a filtration particle size of 10 μm or more, clogging by foreign matter can be suppressed. By using such a filter, excessively large particulate matter can be removed, and by appropriately adjusting the melting temperature and time, particulate matter that is too small can be allowed to pass through the filter and then grown appropriately, thereby obtaining a recycled polyester resin with the desired amount of particulate matter of the desired particle size.

[0094] The filter that can be used in the above method (4) may be any common filter, such as a screen changer type filter, a leaf disk filter, or a candle type sintered filter.

[0095] The intrinsic viscosity of the polyester resin contained in the intermediate layer is preferably 0.55 dL / g or more, more preferably 0.57 dL / g or more, even more preferably 0.59 dL / g or more, and even more preferably 0.61 dL / g or more. The viscosity of the polyester resin contained in the intermediate layer is preferably 1.3 dL / g or less, more preferably 1.1 dL / g or less, even more preferably 0.9 dL / g or less, even more preferably 0.8 dL / g or less, and particularly preferably 0.75 dL / g or less. Setting the intrinsic viscosity at or above the lower limit mentioned above facilitates stable film formation even when a large amount of recycled raw materials is used. On the other hand, setting the intrinsic viscosity at or below the upper limit mentioned above is advantageous in that it is easy to prevent excessive pressure buildup in the film-forming extruder and easy to reduce the thermal shrinkage rate of the film, which is preferable. The intrinsic viscosity of the polyester resin contained in the intermediate layer is a value measured by precisely weighing 1 g of polyester resin, adding 100 mL of a mixed solvent of phenol / tetrachloroethane = 50 / 50 (mass ratio) to dissolve the resin, and measuring the viscosity (IV) at 30°C using a viscosity (IV) measuring device. The intrinsic viscosity of the intermediate layer may also be within the above range.

[0096] The intermediate layer may further contain a metal component. The metal component may be a metal used as a polycondensation catalyst when producing the polyester to be recycled (regenerated). That is, the intermediate layer may contain a polycondensation catalyst used when producing the polyester to be recycled (regenerated). Examples of the metal component include antimony, phosphorus, manganese, calcium, magnesium, cobalt, tin, germanium, zinc, aluminum, and titanium. Among these, the metal component is preferably at least one selected from the group consisting of antimony, germanium, aluminum, and titanium.

[0097] For example, the compounds contained in the intermediate layer may differ depending on the type of recycled raw material used. For example, since polyester containers such as PET bottles come into direct contact with food, the polycondensation catalysts used in the manufacturing process are limited, and cadmium, palladium, selenium, and other harmful metal components are generally not detected. Therefore, if cadmium, palladium, selenium, and the like are detected, it can be assumed that polyester food containers were not used as recycled raw materials.

[0098] The intermediate layer functions as the thickest main layer. The thickness of the intermediate layer is preferably 8 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, even more preferably 14 μm or more, even more preferably 16 μm or more, and particularly preferably 18 μm or more. The thickness of the intermediate layer may be 40 μm or less, preferably 34 μm or less, more preferably 32 μm or less, even more preferably 30 μm or less, even more preferably 29 μm or less, and particularly preferably 28 μm or less.

[0099] The thickness of the intermediate layer is preferably 50 to 93% of the total thickness of the laminated polyester film, more preferably 60 to 91%, even more preferably 65 to 90%, still more preferably 70 to 88%, and particularly preferably 75 to 86%.

[0100] The intermediate layer may or may not contain particles. When the intermediate layer contains particles, the particles are not particularly limited, and examples thereof include inorganic particles such as metal oxides such as alumina, silica, calcium carbonate, titanium oxide, ceria, zirconium oxide, barium oxide, chromium oxide, iron oxide, and tungsten oxide, composite oxides such as silica-zirconium oxide, silica-titanium oxide, silica-titanium oxide-barium oxide, silica-titanium oxide-zirconium oxide, borosilicate glass, aluminosilicate glass, and fluoroaluminosilicate glass, and organic particles having a carboxy group or a sulfonic acid group.

[0101] <Back surface layer> The present film has a back surface layer. The back surface layer is a layer containing polyester. In this embodiment, the back surface layer is a layer disposed on the side opposite to the side on which the ceramic green sheet is laminated.

[0102] The arithmetic mean roughness (Ra) of the back surface layer, measured in accordance with JIS-B0601 (2001) using a high-precision stylus-based microprofile measuring instrument (contact-type two-dimensional surface roughness meter), is preferably 0.001 μm or more, more preferably 0.003 μm or more, even more preferably 0.006 μm or more, and even more preferably 0.01 μm or more. The arithmetic mean roughness (Ra) of the back surface layer is preferably 0.1 μm or less, more preferably 0.07 μm or less, even more preferably 0.05 μm or less, and even more preferably 0.03 μm or less.

[0103] The maximum peak height (Rp) of the back surface layer, measured in accordance with JIS-B0601 (2001) using a high-precision stylus-based microprofile measuring instrument (contact-type two-dimensional surface roughness meter), is preferably 0.005 μm or more, more preferably 0.01 μm or more, even more preferably 0.02 μm or more, and even more preferably 0.04 μm or more. The maximum peak height (Rp) of the back surface layer is preferably 0.4 μm or less, more preferably 0.3 μm or less, even more preferably 0.2 μm or less, and even more preferably 0.15 μm or less.

[0104] The maximum height (Rz) of the back surface layer, measured in accordance with JIS-B0601 (2001) using a high-precision stylus-based microprofile measuring instrument (contact-type two-dimensional surface roughness meter), is preferably 0.01 μm or more, more preferably 0.03 μm or more, even more preferably 0.05 μm or more, and even more preferably 0.07 μm or more. The maximum height (Rz) of the back surface layer is preferably 1.5 μm or less, more preferably 1 μm or less, even more preferably 0.7 μm or less, and even more preferably 0.4 μm or less.

[0105] The arithmetic mean roughness (Ra), maximum peak height (Rp), and maximum height (Rz) of the back layer are measured using a contact-type two-dimensional surface roughness meter in the longitudinal direction (MD) of the film under the following conditions: stylus tip radius 0.5 mm, evaluation length 2.5 mm, longitudinal magnification 20,000, lateral magnification 10, cutoff value 0.08 mm, and measurement speed 0.1 mm / sec. In this film, by setting the arithmetic mean roughness (Ra), maximum peak height (Rp), and / or maximum height (Rz) of the back layer within the above ranges, it is possible to prevent the transfer of unevenness caused by minute protrusions on the back layer to the front layer when the laminated polyester film is laminated or wound into a roll. Furthermore, by setting the arithmetic mean roughness (Ra), maximum peak height (Rp), and / or maximum height (Rz) of the back layer within the above ranges, the back surface of the laminated polyester film is provided with the necessary roughness, thereby improving the handleability of the laminated polyester film. The method for adjusting the Ra, Rp, and Rz of the back surface layer is the same as the method for adjusting the Ra, Rp, and Rz of the front surface layer, and is as described above.

[0106] The arithmetic mean height (Sa) of the back surface layer calculated from a surface profile curve measured using a surface roughness measuring instrument is preferably 1 nm or more, more preferably 3 nm or more, even more preferably 5 nm or more, even more preferably 8 nm or more, even more preferably 10 nm or more, and particularly preferably 11 nm or more. The arithmetic mean height (Sa) of the back surface layer is preferably 35 nm or less, more preferably 30 nm or less, and even more preferably 25 nm or less.

[0107] The maximum peak height (Sp) of the back surface layer calculated from a surface profile curve measured using a surface roughness measuring instrument is preferably 10 nm or more, more preferably 20 nm or more, even more preferably 30 nm or more, and even more preferably 50 nm or more. The maximum peak height (Sp) of the back surface layer is preferably 700 nm or less, more preferably 650 nm or less, even more preferably 600 nm or less, even more preferably 550 nm or less, and particularly preferably 500 nm or less.

[0108] The maximum height (Sz) of the back surface layer calculated from a surface profile curve measured using a surface roughness measuring device is preferably 3 nm or more, more preferably 5 nm or more, even more preferably 10 nm or more, and even more preferably 15 nm or more. The maximum height (Sz) of the back surface layer is preferably 80 nm or less, more preferably 60 nm or less, even more preferably 50 nm or less, and even more preferably 40 nm or less.

[0109] In this embodiment, the maximum peak height (Sp) of the back surface layer calculated from a surface profile curve measured using a surface roughness measuring device is preferably 3 nm to 35 nm and 30 nm to 700 nm, thereby providing the necessary rough surface on the back surface of the laminated polyester film and more effectively improving the handleability of the laminated polyester film.

[0110] The arithmetic mean height (Sa), maximum peak height (Sp), and maximum height (Sz) are measured using a surface roughness measuring instrument under conditions of an objective lens magnification of 10x, a zoom magnification of 2.0x, and a viewing angle of 0.44 mm x 0.44 mm, and the arithmetic mean height (Sa), maximum peak height (Sp), and maximum height (Sz) are determined after the following processing is performed: Filter Type: Spline Filter: High Pass Type: Robust Gaussian Spline Fixed Cutoffs Mode: Period Long Period: 200 μm

[0111] In this film, by setting the arithmetic mean height (Sa), maximum peak height (Sp), and / or maximum height (Sz) of the back layer within the above ranges, it is possible to prevent the unevenness caused by the minute protrusions of the back layer from being transferred to the front layer when the laminated polyester film is laminated or wound into a roll. Furthermore, by setting the arithmetic mean height (Sa), maximum peak height (Sp), and / or maximum height (Sz) of the back layer within the above ranges, the back surface of the laminated polyester film is provided with the necessary roughness, thereby improving the handleability of the laminated polyester film. The method for adjusting Sa, Sp, and Sz of the back layer is the same as the method for adjusting Sa, Sp, and Sz of the front layer, as described above.

[0112] The back surface layer may not contain particles, but may contain particles. The presence of particles in the back surface layer can provide easy slippage and prevent scratches during each process. Furthermore, the presence of particles in the back surface layer makes it easy to control the arithmetic mean roughness (Ra), maximum peak height (Rp), maximum height (Rz), arithmetic mean height (Sa), maximum peak height (Sp), and maximum height (Sz) of the back surface layer within desired ranges. Furthermore, the arithmetic mean roughness (Ra), maximum peak height (Rp), maximum height (Rz), arithmetic mean height (Sa), maximum peak height (Sp), and maximum height (Sz) of the back surface layer may be controlled within desired ranges by subjecting the back surface layer to a surface treatment or coating.

[0113] The type of particles contained in the back surface layer is not particularly limited as long as they are particles that can impart slipperiness. Specific examples include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, titanium oxide, and barium sulfate, as well as organic particles obtained by polymerizing acrylic acid ester monomers, styrene monomers, silicone monomers, etc., or organic particles obtained by copolymerizing these monomers, acrylic resin particles, melamine resin particles, silicone resin particles, and cross-linked polystyrene particles. Among these, organic particles, calcium carbonate, silica, aluminum oxide, etc. are preferably used. Furthermore, precipitated particles obtained by precipitating and finely dispersing a portion of a metal compound such as a catalyst during the polyester production process can also be used.

[0114] In this embodiment, it is also a preferred embodiment that the back surface layer contains both organic and inorganic particles. By using a combination of organic and inorganic particles in the back surface layer, it becomes easy to control the arithmetic mean roughness (Ra), maximum peak height (Rp), maximum height (Rz), arithmetic mean height (Sa), maximum peak height (Sp), and maximum height (Sz) of the back surface layer within desired ranges.

[0115] The shape of the particles in the back surface layer is not particularly limited, and any of spherical, blocky, rod-like, flat, etc. may be used. Furthermore, there are no particular limitations on the hardness, specific gravity, color, etc. Two or more types of these particles may be used in combination as needed.

[0116] The average particle size of the particles in the back surface layer is preferably 5 μm or less, more preferably 4 μm or less, and even more preferably 3 μm or less. The average particle size of the particles is preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more. By setting the average particle size within the above range, the surface roughness of the back surface layer does not become too rough, and it is easy to control the arithmetic mean roughness (Ra), maximum peak height (Rp), maximum height (Rz), arithmetic mean height (Sa), maximum peak height (Sp), and maximum height (Sz) of the back surface layer within the desired range. Furthermore, by setting the average particle size within the above range, haze is kept low, making it easier to ensure transparency of the entire film.

[0117] In addition, when the particles are in the form of a powder, the average particle size of the particles can be determined by measuring the powder using a centrifugal sedimentation particle size distribution analyzer (e.g., the "SA-CP3" model manufactured by Shimadzu Corporation) and determining the particle size at an integrated volume fraction of 50% (d50) in the equivalent spherical distribution. The average particle size of particles in a film, layer, or resin can be determined by observing 10 or more particles with a scanning electron microscope (SEM), measuring the particle diameters, and calculating the average value. In this case, in the case of non-spherical particles, the average value of the longest and shortest diameters can be measured as the diameter of each particle.

[0118] The content of particles contained in the back surface layer is preferably 200 ppm or more, more preferably 1000 ppm or more, and even more preferably 1500 ppm or more, relative to the total mass of the back surface layer. Furthermore, the content of particles is preferably 20,000 ppm or less, more preferably 15,000 ppm or less, even more preferably 10,000 ppm or less, and even more preferably 8,000 ppm or less, relative to the total mass of the back surface layer. When two or more types of particles are blended in the back surface layer, the total content of the particles is preferably within the above range. By setting the particle content to the above lower limit or more, it is possible to effectively impart slipperiness and prevent scratches in each process. Furthermore, by setting the particle content to the above upper limit or less, it is possible to effectively prevent the unevenness caused by minute protrusions on the back surface layer from being transferred to the surface layer.

[0119] The method for adding particles to the polyester film is not particularly limited, and any conventionally known method can be used. For example, particles can be added at any stage in the production of the polyester constituting the back layer, but it is preferable to add them after the completion of the esterification or transesterification reaction.

[0120] The thickness of the back surface layer is preferably 0.5 μm or more, more preferably 0.8 μm or more, even more preferably 1 μm or more, and particularly preferably 1.2 μm or more. The thickness of the back surface layer is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 6 μm or less, and particularly preferably 4 μm or less.

[0121] The thickness of the back layer is preferably 1 to 20% of the total thickness of the laminated polyester film, more preferably 2 to 17%, even more preferably 2.5 to 15%, still more preferably 3 to 13%, and particularly preferably 3 to 10%.

[0122] It is also preferable that the back surface layer contains a recycled polyester resin that can be contained in the intermediate layer as described above. The recycled polyester resin that can be contained in the back surface layer can be the same as the recycled polyester resin contained in the intermediate layer described above. By containing a recycled polyester resin in the back surface layer, the surface roughness of the back surface layer can be set to a desired range. In addition, by containing a recycled polyester resin in the back surface layer, for example, CO ２ This will reduce emissions and contribute to reducing the burden on the environment.

[0123] When the back surface layer contains recycled polyester resin, the content of recycled polyester resin is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, relative to the total mass of the resin constituting the back surface layer. The content of recycled polyester resin may be 60% by mass or more, 70% by mass or more, or 80% by mass or more. The upper limit of the content of recycled polyester resin is not particularly limited, and may be 100% by mass, relative to the total mass of the resin constituting the back surface layer. By containing recycled polyester resin in the above range in the back surface layer, for example, CO ２ This can reduce emissions and contribute to reducing the burden on the environment. Furthermore, by incorporating recycled polyester resin into the back surface layer, the surface roughness of the back surface layer can be adjusted to a desired range, making it easy to impart appropriate roughness to the back surface layer. This improves the slipperiness of the laminated polyester film, thereby more effectively improving processability and handleability.

[0124] <Polyester> The polyester constituting each layer of the present film may be a homopolyester or a copolymer polyester. Specific examples include polyesters obtained by polycondensation of a dicarboxylic acid component and a diol component. In the present film, it is preferable to use a polyester containing more than 50 mol% of aromatic dicarboxylic acid or aliphatic dicarboxylic acid units, assuming that the dicarboxylic acid units are 100 mol%.

[0125] 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.

[0126] Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-hexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4-hydroxyethoxyphenyl)propane, isosorbate, and spiroglycol.

[0127] When the polyester is a homopolyester, it is preferably one obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. In this case, examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative examples of the polyester include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN), with PET being preferred. Furthermore, examples of the polyester that can be used include polyethylene terephthalate, which is composed of 80 mol % or more, preferably 90 mol % or more, of ethylene terephthalate units, and polyethylene-2,6-naphthalate, which is composed of ethylene-2,6-naphthalate units.

[0128] On the other hand, when the polyester is a copolymer polyester, it is preferably a copolymer containing 30 mol% or less of a third component. The third component is a component other than the compound that constitutes the main dicarboxylic acid component of the polyester and the compound that constitutes the main diol component. For example, in the case of polyethylene terephthalate, it is a component other than terephthalic acid and ethylene glycol. Examples of the dicarboxylic acid component of the copolymer polyester include one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid. Examples of the glycol component of the copolymer polyester include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol.

[0129] Typically, when polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, diethylene glycol is by-produced from the ethylene glycol. In this specification, this diethylene glycol is referred to as by-product diethylene glycol. The amount of diethylene glycol by-produced from ethylene glycol varies depending on the polycondensation method, but is approximately 5 mol% or less of the ethylene glycol. In the present invention, 5 mol% or less of diethylene glycol is defined as by-product diethylene glycol, and the by-product diethylene glycol is also included in ethylene glycol and is distinguished from a copolymerization component. On the other hand, depending on the diethylene glycol content, more specifically, when diethylene glycol is contained in excess of 5 mol%, diethylene glycol is treated as a copolymerization component rather than as a by-product diethylene glycol.

[0130] In this embodiment, at least one selected from the dicarboxylic acid component and the diol component constituting the polyester may be a biomass-derived raw material. In particular, the diol component is preferably a biomass-derived raw material. Biomass-derived ethylene glycol is made from ethanol (biomass ethanol) produced from biomass as a raw material. For example, biomass-derived ethylene glycol can be obtained by converting biomass ethanol into ethylene oxide using a conventionally known method to produce ethylene glycol. Alternatively, commercially available biomass ethylene glycol may be used; for example, biomass ethylene glycol commercially available from India Glycoal Limited can be suitably used.

[0131] <<Polycondensation Catalyst>> Examples of polycondensation catalysts used in polycondensing the polyester include antimony compounds, germanium compounds, aluminum compounds, and titanium compounds. Among these, it is preferable to use at least one selected from antimony compounds and titanium compounds, and it is more preferable to use a titanium compound. By using a titanium compound as the polycondensation catalyst, it is possible to reduce the amount of polycondensation catalyst added, which makes it easier to suppress the generation of foreign matter or protrusions derived from the polycondensation catalyst.

[0132] <<Intrinsic Viscosity>> The intrinsic viscosity (IV) of the polyester constituting the present film is preferably 0.5 dL / g or more, more preferably 0.55 dL / g or more, and even more preferably 0.6 dL / g or more. Using a polyester with an intrinsic viscosity (IV) of 0.5 dL / g or more as the polyester constituting the present film increases the shear stress during kneading of the polyester, making it easier to highly disperse particles in the polyester resin, and, for example, tends to make it easier to achieve the surface properties of the polyester film within the above-mentioned specified range. Furthermore, from the viewpoint of particle fluidity, the upper limit of the intrinsic viscosity (IV) of the polyester is preferably 0.85 dL / g or less, more preferably 0.8 dL / g or less, even more preferably 0.75 dL / g or less, even more preferably 0.7 dL / g or less, and particularly preferably 0.67 dL / g or less.

[0133] When two or more polyesters having different intrinsic viscosities (IV) are used, the intrinsic viscosity (IV) of the polyester constituting the present film refers to the intrinsic viscosity (IV) of the mixed resin. The intrinsic viscosity can be measured in accordance with JIS K7367-1:2002 by a conventional method, for example, using an Ubbelohde viscometer at 30°C using a phenol:tetrachloroethane (1:1) solvent.

[0134] When two or more polyesters having different intrinsic viscosities (IV) are used, the term "intrinsic viscosity (IV) of polyester" refers to the intrinsic viscosity (IV) of the mixed resin.

[0135] <<Others>> In this embodiment, in order to reduce the amount of oligomer component precipitation, the polyester film may be produced using a polyester with a low oligomer component content as the raw material. Various known methods can be used to produce a polyester with a low oligomer component content, such as a method of solid-state polymerization after polyester production. Alternatively, the polyester may be obtained by esterification or transesterification, followed by melt polycondensation under reduced pressure at a higher reaction temperature. For example, it is also preferable to reduce the amount of oligomer component precipitation by forming the surface layer of the present film using a polyester raw material with a low oligomer component content.

[0136] In addition to the above-mentioned components, conventionally known ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc. may be added to the present film as needed.

[0137] <Recycled Polyester> [Chemically Recycled Polyester] The recycled polyester resin used in this embodiment is preferably a chemically recycled polyester. Examples of methods for producing chemically recycled polyester resin include sorting, crushing, and washing collected PET bottles and polyester films to remove foreign matter, followed by depolymerization to decompose and purify them into raw materials or intermediate materials for polyester resin, and then repolymerizing these raw materials. Examples of depolymerization methods include adding ethylene glycol (EG) and, in the presence of a catalyst, returning the material to bis-2-hydroxyethyl terephthalate (BHET), an intermediate material used in resin production, which is then purified and repolymerized into PET; and methods include heat-treating polyethylene terephthalate in a non-aqueous organic solvent in the presence of a catalyst containing oxidized iron as an essential component to produce terephthalic acid and ethylene glycol, which are then repolymerized. A characteristic of chemically recycled polyester resin is that foreign matter and other materials are removed during depolymerization and repolymerization, allowing it to be recycled into a polyester resin of similar high quality to virgin resin.

[0138] In this specification, chemically recycled polyester refers to polyester containing structural units derived from monomers obtained by depolymerization. The content of structural units derived from monomers obtained by depolymerization contained in the chemically recycled polyester is preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, even more preferably 60 mol% or more, even more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more. All of the monomers constituting the chemically recycled polyester may be monomers obtained by depolymerization, or the content of structural units derived from monomers obtained by depolymerization contained in the chemically recycled polyester may be 100 mol%.

[0139] The collected used PET bottles and polyester films are washed and then crushed into flakes. Crushing may be performed underwater, or the washing and crushing steps may be performed simultaneously. Furthermore, a foreign matter removal step may be performed before or after these steps.

[0140] Next, the polyethylene terephthalate flakes are depolymerized, melted, and simultaneously hydrolyzed to produce a polyethylene terephthalate melt with a low degree of polymerization. Furthermore, it is preferable to depolymerize the flakes using excess ethylene glycol to obtain a two-component mixed solution of crude BHET and crude ethylene glycol. After the depolymerization reaction is complete, the two-component mixed solution of crude BHET and crude ethylene glycol is cooled and filtered to remove solid foreign matter. Further, colored materials and dissolved ions may be removed by adsorption / ion exchange treatment.

[0141] Next, it is preferable to subject the two-component mixed solution of crude BHET and crude ethylene glycol to distillation and separation to obtain concentrated BHET. Alternatively, the two-component mixed solution may be cooled to 10°C or below to crystallize BHET, followed by solid-liquid separation of ethylene glycol and BHET to obtain concentrated BHET. This concentrated BHET is then evaporated under vacuum under specified conditions to obtain purified bis-β-hydroxyethyl terephthalate. After obtaining high-purity purified BHET as described above, this purified BHET can be charged into a melt polycondensation reactor to obtain a repolymerized polyester.

[0142] [Material Recycled Polyester] The recycled polyester resin used in this embodiment may be material recycled polyester. In material recycling, first, collected used PET bottles and polyester films are crushed into flakes. Since these flakes often contain foreign matter attached or mixed in, they are preferably washed, and more preferably washed with an alkali.

[0143] In the process of pelletizing the flakes, an extruder is used to melt, extrude, cool, and pelletize the flakes. In the melting process in the extruder, melt kneading is usually carried out at 260 to 300°C. It is preferable to thoroughly dry the flakes in advance. In addition, the extruder preferably has at least one vacuum vent in the resin melting zone as a degassing means.

[0144] It is also preferable that a filtering means is provided downstream of the extruder, and the filtering means preferably has a filter capable of filtering out solid foreign matter contained in the molten resin.

[0145] The molten resin that passes through the filter passes through a die, is cooled in water, and then cut into pellets of the desired shape and granulated, yielding recycled polyester resin.

[0146] In addition, in the process of cleaning recovered PET bottles and polyester films and the process of melting these raw materials, the polyester may be partially hydrolyzed by the cleaning components or heat, which reduces the degree of polymerization of the recycled polyester resin. Depending on the intended use, a reduced degree of polymerization may result in poor moldability, strength, transparency, heat resistance, and the like. Therefore, a solid-state polymerization process may be provided to restore the reduced degree of polymerization. In the solid-state polymerization process, flakes may be melt-extruded and pelletized, and then continuously solid-state polymerized in an inert gas such as nitrogen gas or a rare gas at 180 to 245°C.

[0147] When the recycled polyester resin is a polyester resin derived from PET bottles, the intrinsic viscosity (IV) of the recycled polyester resin is preferably 0.64 dL / g or more, more preferably 0.66 dL / g or more, even more preferably 0.67 dL / g or more, even more preferably 0.7 dL / g or more, and particularly preferably 0.72 dL / g or more. The intrinsic viscosity (IV) of the recycled polyester resin is preferably 1.2 dL / g or less, more preferably 1 dL / g or less, even more preferably 0.9 dL / g or less, even more preferably 0.85 dL / g or less, and particularly preferably 0.82 dL / g or less.

[0148] When the recycled polyester resin is derived from a polyester film, the intrinsic viscosity (IV) of the recycled polyester resin is preferably 0.45 dL / g or more, more preferably 0.5 dL / g or more, even more preferably 0.52 dL / g or more, and particularly preferably 0.54 dL / g or more. The intrinsic viscosity (IV) of the recycled polyester resin is preferably 0.8 dL / g or less, more preferably 0.7 dL / g or less, even more preferably 0.67 dL / g or less, and particularly preferably 0.64 dL / g or less.

[0149] <Physical Properties of Laminated Polyester Film> The air leakage index of the present film is preferably 2730 seconds or less, more preferably 2700 seconds or less, even more preferably 2600 seconds or less, and particularly preferably 2500 seconds or less. The lower limit of the air leakage index is not particularly limited, but is preferably 100 seconds or more, and may be 300 seconds or more, 500 seconds or more, or 700 seconds or more. The air leakage index of the present film is measured using a DigiBec smoothness tester (manufactured by Toyo Seiki Co., Ltd., "DB-2") in accordance with JIS P8119 at a temperature of 23°C and a relative humidity of 50%. The pressure of the pressurizing device is 100 kPa, and the vacuum container is a container with a volume of 38 ml. The time (seconds) for 1 mL of air to flow is measured, i.e., the time (seconds) for the pressure in the container to change from 50.7 kPa to 48.0 kPa. The air leakage index is calculated by multiplying the obtained number of seconds by 10. The sample size of this film is 70 mm square, and 20 sheets of the film are laminated so that the front and back of the film overlap to form a test laminate film. A hole with a diameter of 5 mm is drilled in the center of this test laminate film to measure the air leakage index. In this specification, the higher the air leakage index value, the longer it takes for air to leak through the gaps between the films, meaning that the films are in closer contact with each other. Therefore, an air leakage index of less than the above upper limit value means that there are appropriate gaps between the films, which improves the slipperiness when the film is wound into a roll and reduces the risk of wrinkles when made into a roll film.

[0150] The dynamic friction coefficient of the present film is preferably 0.2 or more, more preferably 0.25 or more, even more preferably 0.3 or more, and even more preferably 0.35 or more, and is preferably 0.7 or less, more preferably 0.65 or less, even more preferably 0.6 or less, and even more preferably 0.55 or less.

[0151] The static friction coefficient of the present film is preferably 0.3 or more, more preferably 0.35 or more, even more preferably 0.4 or more, and even more preferably 0.45 or more. The static friction coefficient of the present film is also preferably 0.8 or less, more preferably 0.75 or less, even more preferably 0.7 or less, and even more preferably 0.65 or less. By controlling the friction coefficient of the present film to fall within the above range, the slipperiness can be improved when the present film is wound into a roll, when a functional layer such as a release layer or a ceramic green sheet is laminated, or when the film is unwound from the roll, and the risk of wrinkles occurring when the film is made into a roll can be reduced.

[0152] When measuring the coefficient of friction of this film, after conditioning the film, one side of the film is held in contact with the other side for 15 seconds before starting the test, and measurement is carried out in the longitudinal direction (MD) under the following conditions: Apparatus: Parallel movement friction tester (MCS-300) manufactured by Yokohama Systems Research Institute Slider: Total mass 104 g (contact area is a square with one side of 12 mm) Test speed: 20 mm / min Temperature: 23°C ± 2°C Relative humidity: 50% ± 10%

[0153] The glass transition temperature (Tg) of the present film is preferably 65° C. or higher, more preferably 70° C. or higher, even more preferably 74° C. or higher, and even more preferably 77° C. or higher. The glass transition temperature (Tg) of the present film is preferably 95° C. or lower, more preferably 90° C. or lower, even more preferably 86° C. or lower, and even more preferably 83° C. or lower.

[0154] The thermal recrystallization temperature (Tc) of the present film is preferably 155° C. or lower, more preferably 150° C. or lower, even more preferably 148° C. or lower, and even more preferably 146° C. or lower. The lower limit of the thermal recrystallization temperature (Tc) of the present film is not particularly limited, but is preferably 110° C. or higher, and may be 120° C. or higher, 125° C. or higher, or 130° C. or higher, for example.

[0155] The film preferably has a peak heat of recrystallization (ΔHc) of 10 J / g or more, more preferably 14 J / g or more, even more preferably 18 J / g or more, and even more preferably 22 J / g or more, and preferably has a peak heat of recrystallization (ΔHc) of 45 J / g or less, more preferably 40 J / g or less, even more preferably 37 J / g or less, and even more preferably 33 J / g or less.

[0156] The melting peak temperature (Tm) of the present film is preferably 230° C. or higher, more preferably 235° C. or higher, even more preferably 240° C. or higher, and even more preferably 245° C. or higher. The melting peak temperature (Tm) of the present film is preferably 270° C. or lower, more preferably 260° C. or lower, even more preferably 256° C. or lower, and even more preferably lower than 253° C.

[0157] The film preferably has a peak heat of fusion (ΔHm) of 18 J / g or more, more preferably 22 J / g or more, even more preferably 25 J / g or more, and even more preferably 27 J / g or more, and preferably has a peak heat of fusion (ΔHm) of 50 J / g or less, more preferably 45 J / g or less, even more preferably 40 J / g or less, and even more preferably less than 35 J / g.

[0158] The glass transition temperature (Tg), temperature-rising recrystallization temperature (Tc), temperature-rising recrystallization peak calorific value (ΔHc), melting peak temperature (Tm), and melting peak calorific value (ΔHm) of the present film can be measured, for example, using a differential scanning calorimeter (DSC60) manufactured by Shimadzu Corporation. The measurement conditions are as follows, and the glass transition temperature (Tg: midpoint glass transition temperature), temperature-rising recrystallization temperature (Tc: peak-top temperature of the exothermic curve of temperature-rising recrystallization), temperature-rising recrystallization peak calorific value (ΔHc: peak calorific value of the exothermic curve of temperature-rising recrystallization), melting peak temperature (Tm: peak-top temperature of the endothermic curve of crystalline melting), and melting peak calorific value (ΔHm: peak calorific value of the endothermic curve of crystalline melting) in (5) are determined. (1) Heat from -70°C to 280°C at 10°C / min. (2) Hold at 280°C for 5 minutes. (3) Cool to -70°C at 600°C / min. (4) Hold at -70°C for 5 minutes. (5) Heat from -70°C to 280°C at 10°C / min. (6) Hold at 300°C for 5 minutes. (7) Cool to -70°C at 600°C / min.

[0159] The haze of the present film is preferably 15% or less, more preferably 10% or less, even more preferably 7% or less, and even more preferably 5% or less. The lower limit of the haze of the present film is not particularly limited, and may be 0%, 0.5%, 1%, 1.5%, or 2.1%. The haze of the film is measured using a haze meter in accordance with JIS K7136:2000.

[0160] The tensile strength of the present film in the machine direction (MD) is preferably 100 MPa or more, more preferably 150 MPa or more, and even more preferably 200 MPa or more. The tensile strength of the present film in the machine direction (MD) may be 450 MPa or less, 400 MPa or less, or 350 MPa or less. The tensile strength of the present film in the cross direction (TD) is preferably 150 MPa or more, more preferably 200 MPa or more, and even more preferably 250 MPa or more. The tensile strength of the present film in the machine direction (MD) may be 500 MPa or less, 450 MPa or less, or 400 MPa or less. Tensile strength refers to the tensile stress at break as defined in JIS K 7161-1:2014. Measurements are performed in an atmosphere of 23°C and 50% relative humidity, with a test specimen chuck distance of 50 mm and a pulling speed of 200 mm / min.

[0161] The tensile elongation in the machine direction (MD) of the present film is preferably 70% or more, more preferably 100% or more, and even more preferably 130% or more. The tensile elongation in the machine direction (MD) of the present film may be 300% or less, 250% or less, or 200% or less. The tensile elongation in the cross direction (TD) of the present film is preferably 30% or more, more preferably 50% or more, and even more preferably 70% or more. The tensile elongation in the machine direction (MD) of the present film may be 250% or less, 200% or less, or 150% or less. The tensile strength refers to the tensile elongation at break (nominal tensile break strain) according to JIS K 7161-1:2014. Measurements are performed in an atmosphere of 23°C and 50% relative humidity, with a chuck distance of 50 mm for the test specimen, and a pulling rate of 200 mm / min.

[0162] The manufacturing process of multilayer ceramic capacitors includes heat treatments, such as drying a release agent coated on a polyester film and drying a ceramic slurry coated on a release film. Therefore, a decrease in the heat distortion resistance of a polyester film can lead to coating irregularities and wrinkles. In other words, the heat distortion resistance of a polyester film is an important characteristic for ensuring the quality reliability of the finished product, from intermediate products to finished products in the manufacturing process of multilayer ceramic capacitors, such as the lamination characteristics of ceramic green sheets. To prevent such coating irregularities and wrinkles, the heat shrinkage rate of the present film in the machine direction (MD direction) when heat-treated at 150°C for 5 minutes is preferably 2.8% or less, more preferably 2.6% or less, even more preferably 2.4% or less, even more preferably 2.2% or less, and particularly preferably 2% or less. From the same perspective, the lower limit of the machine direction (MD direction) heat shrinkage rate (150°C, 5 minutes) is preferably -0.5% or more, more preferably -0.3% or more.

[0163] Furthermore, the heat shrinkage rate in the transverse direction (TD) of this film when heat-treated at 150°C for 5 minutes is preferably 2.8% or less, more preferably 2.6% or less, even more preferably 2.4% or less, even more preferably 2.2% or less, and particularly preferably 1.5% or less, from the viewpoint of suppressing coating irregularities and wrinkles. From the same viewpoint, the lower limit of the heat shrinkage rate in the transverse direction (TD) is preferably -0.5% or more, more preferably -0.3% or more. Furthermore, from the viewpoint of realizing a high level of heat distortion resistance that is particularly required in the manufacturing process of MLCCs using the thin ceramic green sheets, the heat shrinkage rate in the transverse direction (TD) (150°C, 5 minutes) is preferably 1.4% or less, more preferably 1.3% or less. The thermal shrinkage rate (150°C, 5 minutes) in the transverse direction (TD) can be appropriately set within the above range and is not particularly limited, but may be, for example, 1% or less, 0.8% or less, 0.7% or less, 0.5% or less, 0.4% or less, 0.1% or less, etc.

[0164] In order to achieve a desired heat shrinkage rate (heated at 150°C for 5 minutes) for the present film, for example, the film-forming conditions (particularly the longitudinal stretching temperature, transverse stretching ratio, heat setting temperature, roll peripheral speed, relaxation rate, etc.), the film-forming raw materials, etc. may be appropriately set. The heat shrinkage rate (heated at 150°C for 5 minutes) for the present film is calculated using the following formula: Heat shrinkage rate (%) = {(length of evaluation film before heat treatment) - (length of evaluation film after heat treatment)} / (length of evaluation film before heat treatment) x 100

[0165] The total thickness of the present film is not particularly limited as long as it is within a range that allows film formation. However, from the viewpoints of mechanical strength, handleability, and productivity, it is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 18 μm or more. Furthermore, the total thickness of the present film is preferably 150 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, even more preferably 50 μm or less, even more preferably 38 μm or less, and particularly preferably 32 μm or less. The total thickness of the present film may be, for example, 30 μm or less, less than 30 μm, 29 μm or less, or 28 μm or less. In conventional laminated polyester films, reducing the total thickness of the film also reduces the thickness of the surface layer, which limits the particle size of the particles incorporated into the surface layer, making it impossible to achieve appropriate surface smoothness (sufficient smoothness while maintaining a moderate degree of roughness). On the other hand, if particles are not incorporated into the surface layer, the film's slipperiness deteriorates and handling becomes poor. That is, in the prior art, when an attempt was made to thin a laminated polyester film, it was difficult to achieve both appropriate surface smoothness and handleability. In contrast, in the present invention, even when the laminated polyester film is made very thin, it has been successful in achieving both appropriate surface smoothness and handleability.

[0166] <Coating Layer> In this embodiment, a coating layer may be further provided on the surface layer. The coating layer is preferably a layer formed by applying a coating layer-forming composition (coating liquid) on the surface layer. The coating layer can be formed by in-line coating or offline coating, but is preferably formed by in-line coating. This can improve the production efficiency of the laminated polyester film.

[0167] The thickness of the coating layer is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more, and is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less.

[0168] The coating layer-forming composition preferably contains a binder resin and a crosslinking agent. The total content of the binder resin and the crosslinking agent contained in the coating layer-forming composition is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, as non-volatile components. The coating layer-forming composition also preferably contains particles, a catalyst, etc.

[0169] <<Binder Resin>> The coating layer-forming composition preferably contains a binder resin. The binder resin is a polymer compound having a number-average molecular weight (Mn) of 1,000 or more as measured by gel permeation chromatography (GPC) in accordance with the "Flow Scheme for the Safety Evaluation of Polymeric Compounds" (November 1985, sponsored by the Chemical Substances Council). Of these, those having film-forming properties are preferred. Such binder resins are not particularly limited, and conventionally known binder resins such as polyester resins, polyurethane resins, (meth)acrylic resins, polyvinyl resins (polyvinyl alcohol, vinyl chloride-vinyl acetate copolymers, etc.), polyalkylene glycols, polyalkyleneimines, methyl cellulose, hydroxycellulose, and starches can be used. Among these, from the viewpoints of film-forming properties and adhesion to polyester films, the binder resin preferably contains one or more resins selected from the group consisting of polyester resins, polyurethane resins, and (meth)acrylic resins, and more preferably contains one or more resins selected from the group consisting of polyester resins and polyurethane resins. In the present resin composition, one type of binder resin may be used alone, or two or more types may be used in combination.

[0170] Examples of the polyester resin, polyurethane resin, (meth)acrylic resin, and polyvinyl resin used as the binder resin include the compounds described in WO 2023 / 145952.

[0171] The content of the binder resin in the coating layer-forming composition is preferably 5 to 95% by mass, more preferably 10 to 80% by mass, even more preferably 20 to 70% by mass, and even more preferably 30 to 60% by mass, as a proportion of all non-volatile components in the coating layer-forming composition. By setting the content within the above range, it is possible to easily form a film that has film-forming properties and contains particles. Furthermore, by improving adhesion to the polyester film, it is possible to prevent the coating film from falling off.

[0172] <<Crosslinking Agent>> The composition for forming a coating layer preferably contains a crosslinking agent. The crosslinking agent is not particularly limited, and conventionally known crosslinking agents can be used. Examples of the crosslinking agent include melamine compounds, isocyanate compounds, oxazoline compounds, epoxy compounds, carbodiimide compounds, and silane coupling compounds. Among these, it is preferable to contain a melamine compound from the viewpoint of increasing the strength of the coating layer and improving adhesion to the polyester film. In the composition for forming a coating layer, the crosslinking agent may be used alone or in combination of two or more types.

[0173] Examples of the melamine compound and isocyanate compound used as the crosslinking agent include the compounds described in WO 2023 / 145952.

[0174] The content of the crosslinking agent in the coating layer-forming composition is preferably 5 to 50% by mass, more preferably 8 to 40% by mass, even more preferably 10 to 35% by mass, and particularly preferably 15 to 30% by mass, as a proportion of all non-volatile components in the coating layer-forming composition. By setting the content within the above range, it is possible to easily form a film that has film-forming properties and contains particles. Furthermore, by improving adhesion to the polyester film, it is possible to prevent the coating film from falling off.

[0175] <<Particles>> The coating layer-forming composition may contain particles to the extent that the properties and effects of the present invention are not impaired. Examples of particles include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, zirconium oxide, aluminum oxide, and titanium oxide, as well as crosslinked polymers such as crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, and crosslinked polyester particles, and organic particles such as calcium oxalate and ion exchange resins. Among these, zirconium oxide, titanium oxide, and silica are preferred, and zirconium oxide and silica are more preferred. The particles may be used alone or in combination of two or more types.

[0176] The shape of the particles used may be spherical, blocky, rod-like, flat, chain-like, etc. Among these, spherical particles are preferred from the viewpoint of facilitating uniform distribution in the resin composition.

[0177] The average particle size of the particles is preferably 0.5 to 300 nm, more preferably 1 to 250 nm, even more preferably 2 to 200 nm, still more preferably 2.5 to 200 nm, even more preferably 3 to 150 nm, even more preferably 3.5 to 100 nm, even more preferably 4 to 60 nm, and particularly preferably 4.5 to 30 nm. When the average particle size is within this range, the generation of coarse protrusions due to particle aggregation and process contamination due to particle dropout can be suppressed. The average particle size of the particles can be measured by a method that calculates the particle size from the specific surface area measured by a specific surface area measuring device and the particle density, a method that calculates the particle diameter by observing the particles with a transmission electron microscope (TEM) or scanning electron microscope (SEM), or a method that determines the particle size by dynamic light scattering measurement. The particle size can be measured by a method that is appropriate for the particle size.

[0178] The content of the particles in the coating layer-forming composition is preferably in the range of 0.01 to 20% by mass, more preferably 0.05 to 15% by mass, and even more preferably 0.1 to 10% by mass, as a proportion of all non-volatile components in the coating layer-forming composition. By setting the content within the above range, the elastic deformation power (η it ) can be easily controlled within the desired range.

[0179] <Applications> The present film can be suitably used for various release applications. For example, it can be used for various release and process applications such as dry film resist (DFR), multilayer circuit boards, and the production of ceramic green sheets for multilayer ceramic capacitors. In release and process applications, the present film can be used, for example, as a support, onto which various materials such as ceramic slurries can be applied or laminated.

[0180] In particular, since the present film has excellent surface smoothness as described above and can accommodate thinner ceramic green sheets, it is preferably used as a support for ceramic green sheets in the production process of multilayer ceramic capacitors. That is, the multilayer polyester film of the present embodiment is preferably a multilayer polyester film for producing multilayer ceramic capacitors.

[0181] Furthermore, in the future, as electrification of automobiles progresses, it is predicted that the ceramic green sheets used will become thinner as capacitors become smaller and higher in capacity. Therefore, the present film is preferably used as a support for ceramic green sheets in the manufacturing process of automotive ceramic capacitors.

[0182] (Method for producing laminated polyester film) This embodiment may relate to a method for producing the laminated polyester film described above. The method for producing a laminated polyester film of this embodiment includes a step of laminating a polyester layer A constituting a surface layer, a polyester layer B constituting an intermediate layer, and a polyester layer C constituting a back layer. In this embodiment, the polyester layer A and / or the polyester layer B contains a recycled polyester resin. Alternatively, the method for producing a laminated polyester film of this embodiment includes a step of supplying a polyester resin A constituting the surface layer, a polyester resin B constituting the intermediate layer, and a polyester resin C constituting the back layer to respective extruders, melting them, and then co-extruding them. In this embodiment, the polyester resin A and / or the polyester resin B contains a recycled polyester resin. In each extruder, each polymer is heated to a temperature above its melting point to form a molten polymer. The molten polymer is then extruded through a die and cooled and solidified on a rotating cooling drum to a temperature below the glass transition point of the polymer, thereby obtaining an unstretched laminated polyester film.

[0183] The polyester resin A and / or polyester resin B preferably contains a recycled polyester resin containing granules, and the granules have a particle size of 1000 μm or less at a density of 70 particles / m ２In a more preferred embodiment, the polyester resin C preferably contains a recycled polyester resin containing granules, and the granules have a particle size of 1000 μm or less at a rate of 70 particles / m ２ It is particularly preferred that the polyester resin A and / or polyester resin B contain a recycled polyester resin containing particulate matter. When polyester resin A and / or polyester resin B contains a recycled polyester resin containing particulate matter, it becomes easier to adjust the number of protrusions and the total area of ​​protrusions in the surface layer of the obtained laminated polyester film to a desired range. The preferred ranges for the particle size and content of the particulate matter contained in the recycled polyester resin are the same as the preferred ranges for the particle size and content of the particulate matter contained in the recycled polyester resin of the <intermediate layer>.

[0184] In this embodiment, a step of stretching an unstretched laminated polyester film may be provided. In the stretching step, the unstretched laminated polyester film is first stretched in one direction using a roll or tenter-type stretching machine. In this case, the stretching temperature is usually 25 to 120°C, preferably 35 to 100°C, and the stretching ratio is usually 2.5 to 7 times, preferably 2.8 to 6 times. Next, it is preferable to stretch the film in a direction perpendicular to the first-stage stretching direction. In this case, the stretching temperature is usually 50 to 140°C, and the stretching ratio is usually 3.0 to 7 times, preferably 4.0 times or more, more preferably 4.5 to 5.0 times. In the stretching step, a method in which unidirectional stretching is performed in two or more stages may also be employed.

[0185] Subsequently, it is preferable to carry out a heat setting treatment at a temperature of 180 to 220°C under tension or under relaxation of 30% or less. In this way, a biaxially stretched laminated polyester film is obtained. The heat setting treatment may be carried out in two or more steps at different temperatures. Alternatively, cooling may be carried out in a cooling zone after the heat setting treatment. The cooling temperature is preferably higher than the glass transition temperature (Tg) of the polyester resin constituting the laminated polyester film, more specifically, preferably in the range of 100 to 160°C. This cooling may be carried out in two or more steps at different temperatures.

[0186] In the present embodiment, when a coating layer is provided on the surface layer, a step of forming the coating layer may be provided. In the step of forming the coating layer, the coating layer is formed by applying a coating layer-forming composition (coating liquid) onto the surface layer.

[0187] (Release Film) This embodiment may relate to a release film further comprising a functional layer, such as a release layer, on the surface layer side of the laminated polyester film described above. That is, for example, the release film may have a structure of release layer / surface layer / intermediate layer / back surface layer. When the present film has a coating layer, the structure may be release layer / coating layer / surface layer / intermediate layer / back surface layer. The release layer is laminated to the laminated polyester film directly or via another layer. Examples of other layers include an easy-adhesion coating layer for improving adhesion to the present film, an antistatic layer, an antiblocking layer, and the like. By providing a release layer on the surface layer in this way, when the present film is used as a support (substrate) for a ceramic green sheet in the manufacturing process of a multilayer ceramic capacitor, it is possible to easily peel off the ceramic green sheet laminated on the release layer.

[0188] In this embodiment, the surface layer side of the laminated polyester film may have a functional layer other than the release layer, such as a tacky adhesive layer, a hard coat layer, a decorative layer, a light-shielding layer, an ultraviolet-shielding layer, an easy-adhesion layer (primer layer), an antistatic layer, a refractive index adjusting layer, an oligomer sealing layer, an antiblocking layer, etc.

[0189] The release layer is formed from a release agent composition containing a release agent, and the release agent composition preferably contains a silicone-based release agent or a non-silicone-based release agent.

[0190] Examples of silicone-based release agents include release agents containing a curable silicone resin as a main component, modified silicone release agents obtained by graft polymerization with an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin, and fluorosilicone release agents. Of these, it is more preferable that the silicone-based release agent contains a curable silicone resin.

[0191] As the curable silicone resin, any of the existing curing reaction types can be used, such as heat-curable types such as addition types and condensation types, and electron beam-curable types such as ultraviolet-curable types, and multiple types of curable silicone resins can be used in combination.

[0192] Examples of non-silicone release agents include waxes, compounds containing long-chain alkyl groups, and fluorine compounds.

[0193] Examples of waxes include natural waxes, synthetic waxes, and modified waxes. Examples of natural waxes include plant-based waxes, animal-based waxes, mineral waxes, and petroleum waxes. Examples of plant-based waxes include candelilla wax, carnauba wax, rice wax, Japan wax, and jojoba oil. Examples of animal-based waxes include beeswax, lanolin, and spermaceti wax. Examples of mineral waxes include montan wax, ozokerite, and ceresin. Examples of petroleum waxes include paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include synthetic hydrocarbons, modified waxes, hydrogenated waxes, fatty acids, acid amides, amines, imides, ester waxes, and ketones.

[0194] The long-chain alkyl group-containing compound is a compound having a linear or branched alkyl group with 6 or more carbon atoms, preferably 8 or more carbon atoms, and more preferably 12 or more carbon atoms. Examples of alkyl groups include hexyl, octyl, decyl, lauryl, octadecyl, and behenyl groups. Examples of compounds having an alkyl group include various long-chain alkyl group-containing polymeric compounds, long-chain alkyl group-containing amine compounds, long-chain alkyl group-containing ether compounds, and long-chain alkyl group-containing quaternary ammonium salts. Polymeric compounds having a long-chain alkyl group on the side chain can be obtained by reacting a polymer having a reactive group with a compound having an alkyl group capable of reacting with the reactive group. Examples of the reactive group include hydroxyl, amino, carboxy, and acid anhydrides. Examples of compounds having these reactive groups include polyvinyl alcohol, polyethyleneimine, polyethyleneamine, reactive group-containing polyester resins, and reactive group-containing poly(meth)acrylic resins. Among these, polyvinyl alcohol is preferred for ease of handling.

[0195] The fluorine compound is a compound containing fluorine atoms. As the fluorine compound, an organic fluorine compound is preferably used, for example, a perfluoroalkyl group-containing compound, a polymer of an olefin compound containing a fluorine atom, an aromatic fluorine compound such as fluorobenzene, etc.

[0196] There are no particular limitations on the form of application of the release agent composition when forming the release layer. The release agent composition preferably contains a solvent in addition to the release agent. The release agent composition may be in the form of a solution in an organic solvent, in the form of an aqueous emulsion, or in the form of a solventless composition.

[0197] The release agent composition for forming the release layer may further contain, as necessary, a binder, an antifoaming agent, a coatability improver, a thickener, inorganic particles, organic particles, an organic lubricant, an antistatic agent, a conductive agent, an ultraviolet absorber, an antioxidant, a foaming agent, a dye, a pigment, or the like.

[0198] The release layer is provided by coating the present film with a release agent composition. Either in-line coating, which is carried out during the film production process, or so-called off-line coating, in which the release agent composition is applied outside the system onto a film that has already been produced, may be employed.

[0199] The release layer can be provided on the film by any of the conventional coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, and curtain coating.

[0200] The curing conditions for forming the release layer are not particularly limited. When the release layer is formed by offline coating, the heat treatment is usually carried out at 80°C or higher for 10 seconds or more, preferably at 100 to 200°C for 3 to 40 seconds, and more preferably at 120 to 180°C for 3 to 40 seconds.

[0201] The coating amount of the release layer (after drying) is usually 0.005 to 5 g / m from the viewpoint of coating property. ２ , preferably 0.005 to 1 g / m ２ , more preferably 0.005 to 0.1 g / m ２ The coating amount (after drying) is in the range of 0.005 g / m ２ When the amount is 5 g / m or more, good stability can be obtained in terms of coating properties, and a uniform coating film can be obtained. ２ If it is below this level, the release layer itself can have good coating adhesion, curability, etc.

[0202] (Laminated Polyester Film with Ceramic Green Sheet) This embodiment may relate to a laminated polyester film with a ceramic green sheet obtained by laminating a ceramic green sheet on the laminated polyester film described above, or may relate to a release film with a ceramic green sheet used in the manufacturing process of an automotive ceramic capacitor. The release film with a ceramic green sheet is obtained in the manufacturing process of a multilayer ceramic capacitor. Since the laminated polyester film of this embodiment is suitable for manufacturing thin ceramic green sheets, for example, the thickness of the ceramic green sheet after drying may be 2 μm or less, 1 μm or less, or 0.5 μm or less.

[0203] This embodiment may relate to the use of the laminated polyester film as a support for a ceramic green sheet in the process of producing a multilayer ceramic capacitor. This embodiment may also relate to a method for producing a ceramic green sheet, which includes a step of applying a ceramic slurry containing a ceramic component to the surface layer side of the laminated polyester film.

[0204] When producing the laminated polyester film with a ceramic green sheet of this embodiment, a ceramic slurry containing a ceramic component and a binder resin can be applied to the surface layer of the above-mentioned laminated polyester film or the release layer of the above-mentioned release film, and then dried to produce a ceramic green sheet (dielectric sheet).

[0205] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0206] [Polyester Raw Materials] The polyester raw materials used in the examples and comparative examples are as follows. (1) Polyester A: homopolyethylene terephthalate (titanium catalyst, intrinsic viscosity 0.63 dL / g) (2) Polyester B: masterbatch obtained by blending 1.0 mass% of 0.3 μm organic particles into homopolyethylene terephthalate (titanium catalyst, intrinsic viscosity 0.63 dL / g) (3) Polyester C: chemically recycled polyethylene terephthalate derived from PET bottles (intrinsic viscosity 0.62 dL / g, isophthalic acid unit content 1.8 mol% relative to 100 mol% of all carboxylic acid units, diethylene glycol unit content 1.3 mol% relative to 100 mol% of all diol units) (4) Polyester D: biomass-derived polyethylene terephthalate with a biocontent of 30%, Indorama's "BF3067B" (intrinsic viscosity 0.63 dL / g, biomass-derived ethylene glycol units 98 mol% relative to 100 mol% of all diol units, biomass-derived diethylene glycol units 2 mol%, biomass-derived units 50 mol% of the total diol units and dicarboxylic acid units)

[0207] Comparative Example 1: Polyester A was used as the raw material for the surface layer and intermediate layer. A raw material obtained by blending 65% Polyester A and 35% Polyester B by mass was used as the raw material for the back layer. This raw material was fed into a vented extruder and melt-extruded at 280°C. The raw materials for the surface layer and back layer were then co-extruded to form a three-type, three-layer structure (surface layer A / intermediate layer / back layer C), with the raw materials for the surface layer and back layer as the outermost layers. The extrusion conditions for the thickness composition ratio were A / B / C = 2 / 2 1 / 2. The film was cooled and solidified on a cooling roll with a surface temperature set to 20°C using an electrostatic adhesion method to obtain an amorphous film. The film was then stretched 3.5 times in the machine direction, i.e., in the MD direction, at a film temperature of 86°C using the roll peripheral speed difference. This longitudinally stretched film was introduced into a tenter, preheated at 90°C in the tenter, and then stretched 4.4 times in the transverse direction, i.e., the TD direction, at 105°C. In the heat treatment (fixing) zone in the tenter, it was heat-treated at 230°C and then cooled to 140°C with a relaxation rate of 2%, to obtain a laminated polyester film with an overall thickness of 25 μm.

[0208] (Example 1) A laminated polyester film having a total thickness of 25 μm was produced in the same manner as in Comparative Example 1, except that the raw materials for the intermediate layer were changed to 50% Polyester A and 50% Polyester C in terms of mass ratio.

[0209] Example 2 A laminated polyester film having a total thickness of 25 μm was produced in the same manner as in Comparative Example 1, except that the raw material for the intermediate layer was changed to Polyester C.

[0210] Example 3 A laminated polyester film having a total thickness of 25 μm was produced in the same manner as in Comparative Example 1, except that the raw material for the surface layer and the intermediate layer was changed to Polyester C.

[0211] (Example 4) A laminated polyester film having a total thickness of 25 μm was produced in the same manner as in Example 3, except that the raw materials for the intermediate layer were changed to 50% Polyester C and 50% Polyester D by mass ratio.

[0212] <Measurement and Evaluation Methods> (1) Arithmetic Mean Roughness (Ra), Maximum Peak Height (Rp), and Maximum Height (Rz) Using a high-precision, stylus-based, fine-profile measuring instrument (contact-type two-dimensional surface roughness meter), the arithmetic mean roughness (Ra), maximum peak height (Rp), and maximum height (Rz) were measured in accordance with JIS-B0601 (2001). Specifically, using a contact-type two-dimensional surface roughness meter (Surf Coder SE3500) manufactured by Kosaka Laboratory Co., Ltd., measurements were performed in the longitudinal direction (MD) of the evaluation film under the following conditions: stylus tip radius 0.5 mm, evaluation length 2.5 mm, longitudinal magnification 20,000, lateral magnification 10, cutoff value 0.08 mm, and measurement speed 0.1 mm / sec, and the arithmetic mean roughness Ra, maximum peak height Rp, and maximum height Rz were determined. Note that the measurement was performed 12 times, and the average value of 10 points obtained by dividing the maximum and minimum values ​​was used as the measured value.

[0213] (2) Arithmetic Mean Height (Sa), Maximum Peak Height (Sp), and Maximum Height (Sz) The surfaces of the front and back layers of the evaluation film (5 cm × 5 cm) were measured using a surface roughness measuring device (manufactured by Ametec Co., Ltd., "NewView" (registered trademark)), and the arithmetic mean height (Sa), maximum peak height (Sp), and maximum height (Sz) were determined from the obtained surface profile curves. Specifically, using the above-mentioned surface roughness measuring device, measurements were performed under conditions of an objective lens magnification of 10x, a zoom magnification of 2.0x, and a viewing angle of 0.44 mm × 0.44 mm, and the arithmetic mean height (Sa), maximum peak height (Sp), and maximum height (Sz) were determined after performing the following treatments. Note that measurements were performed at at least 12 points, and the average was used as the measured value. FilterType:Spline Filter:High Pass Type:Robust Gaussian Spline Fixed Cutoffs Mode:Period Long Period:200μm

[0214] (3) Roughness Analysis Using a Laser Microscope The surface properties of the surface layer and the surface of the back layer of the evaluation film (5 cm x 5 cm) were photographed using a laser microscope ("OPTELICS HYBRID" manufactured by Lasertec Corporation), and the arithmetic mean height (Sa), maximum peak height (Sp), maximum valley depth (Sv), maximum height (Sz), and root mean square height (Sq) were determined from the obtained surface profile curve. Specifically, using the above laser microscope, measurements were performed under conditions of an objective lens magnification of 100x and a viewing angle of 0.15 mm x 0.15 mm, and the arithmetic mean height (Sa), maximum peak height (Sp), maximum valley depth (Sv), maximum height (Sz), and root mean square height (Sq) were determined. Measurements were taken at three different locations, and the average was used as the measured value.

[0215] (4) Image analysis of protrusions using a laser microscope. The surface characteristics of the surface layer and the surface of the back layer of the evaluation film (5 cm x 5 cm) were photographed using a laser microscope ("OPTELICS HYBRID" manufactured by Lasertec Corporation). The cross-sectional characteristics were confirmed, and in areas without concave shapes, image analysis of the surface protrusions was performed using the following procedure. When the cross section of this film was photographed using a laser microscope at an objective lens magnification of 100x, areas where no concave shapes were visible were selected as "areas without concave shapes." Specifically, image analysis was performed by converting the captured image (MBP file) from a color image to a monochrome image using image analysis software ("WinROOF2018" manufactured by Mitani Shoji Co., Ltd.). Subsequently, to reduce brightness unevenness, a "threshold value" of 10-15 was set, and image processing for "background processing" was performed. Furthermore, to clarify the contrast between the background and the object in the image, a "threshold value" of 130-230 was set, and image processing for "density conversion" was performed using linear conversion. Next, in order to detect protrusions, a "threshold value" of 0 to 160 was set and "binarization" was performed. Next, small holes were filled using the "morphological hole filling" process, and these image processing steps were used to detect protrusions on the film surface. Finally, "shape features" was selected in the measurement tool, and the number of protrusions (protrusion count), total area of ​​the protrusions (total protrusion area), and circle equivalent diameter of the protrusions (protrusion circle equivalent diameter) were determined. Additionally, "inter-particle distance" was selected in the measurement tool, and the distance between protrusions was determined by measuring the distance between the centers of gravity, and then the average distance between protrusions and the total distance between protrusions were calculated.

[0216] (5) Air Leakage Index Using a DigiBec smoothness tester (manufactured by Toyo Seiki Co., Ltd., "DB-2"), the air leakage index was measured in accordance with JIS P8119 under an atmosphere of 23 ° C. and 50% relative humidity. The pressure of the pressure device was 100 kPa, and the vacuum container was a container with a volume of 38 ml. The time for 1 mL of air to flow, i.e., the time (seconds) until the pressure in the container changed from 50.7 kPa to 48.0 kPa, was measured, and 10 times the obtained number of seconds was used as the air leakage index. The sample size of the laminated polyester film was 70 mm square, and 20 sheets were laminated so that the front and back of the film overlapped to form a test laminate film. Then, a 5 mm diameter hole was drilled in the center of this test laminate film, and the air leakage index was measured as described above. The higher the value of this air leakage index, the longer it takes for air to leak through the gap between the films, indicating that the films are in closer contact with each other and that wrinkles are more likely to occur when the film is made into a rolled film.

[0217] (6) Coefficient of Friction An evaluation film measuring 15 x 160 mm was cut out from the laminated polyester film, and the dynamic friction coefficient and static friction coefficient between one side of the evaluation film and the other side were measured. Specifically, one side of the evaluation film was held in contact with the other side for 15 seconds before the start of the test, and then measurement was performed in the longitudinal direction (MD) under the following conditions. The evaluation film was humidified for at least 6 hours before measurement. - Apparatus: Parallel movement type friction tester (MCS-300) manufactured by Yokohama Systems Research Institute - Sliding piece: Total mass 104 g (contact area is a square with one side of 12 mm) - Test speed: 20 mm / min - Temperature: 23°C ± 2°C - Relative humidity: 50% ± 10%

[0218] (7) Tg (glass transition temperature), Tc (heat-rised recrystallization temperature), ΔHc (heat-rised recrystallization peak calorific value), Tm (melting peak temperature), ΔHm (melting peak calorific value) An 8 mg sample cut out from the evaluation film was measured using a differential scanning calorimeter (DSC8500) manufactured by Shimadzu Corporation. The sample temperature was scanned in the following order: (1) heating from -70°C to 280°C at 10°C / min, (2) holding at 280°C for 5 minutes, (3) cooling to -70°C at 600°C / min, (4) holding at -70°C for 5 minutes, (5) heating from -70°C to 280°C at 10°C / min, (6) holding at 300°C for 5 minutes, and (7) cooling to -70°C at 600°C / min. The glass transition temperature (Tg: midpoint glass transition temperature), temperature-rising recrystallization temperature (Tc: peak-top temperature of the exothermic curve of temperature-rising recrystallization), peak heat of temperature-rising recrystallization (ΔHc: peak heat of the exothermic curve of temperature-rising recrystallization), peak melting temperature (Tm: peak-top temperature of the endothermic curve of crystalline melting), and peak heat of melting (ΔHm: peak heat of the endothermic curve of crystalline melting) were determined at (5).

[0219] (8) Haze: Measured in accordance with JIS K7136:2000 using a haze meter DH-2000 manufactured by Nippon Denshoku Industries Co., Ltd.

[0220] (9) Intrinsic Viscosity 1 g of raw material polyester or laminated polyester film for evaluation was precisely weighed, dissolved in 100 mL of a mixed solvent of phenol / tetrachloroethane = 50 / 50 (mass ratio), and the intrinsic viscosity was measured at 30°C using a viscosity (IV) measuring device "VMS-022UPC-F10" (manufactured by Rigo Co., Ltd.).

[0221] (10) Tensile strength and tensile elongation Sample pieces measuring 15 mm in the width direction (TD) and 150 mm in the length direction (MD) were taken from the evaluation film, and the tensile strength (tensile breaking stress) and tensile elongation (tensile breaking nominal strain) were measured in the longitudinal direction (MD) and the transverse direction (TD) using a Shimadzu Autograph AGX-V tensile tester in accordance with JIS K 7161-1 (2014). Measurements were performed in an atmosphere of 23°C and 50% relative humidity, with gauge marks placed at 50 mm intervals in the center of each test piece, at a chuck distance of 50 mm, and at a tensile speed of 200 mm / min.

[0222] (11) Heat Shrinkage Rate An evaluation film (width 1.5 cm x length 15 cm) was heat-treated for 5 minutes in a hot air oven maintained at a predetermined temperature (150°C) in an untensioned state, and the length of the evaluation film in the longitudinal direction was measured before and after the treatment, and the heat shrinkage rate was calculated using the following formula. The heat shrinkage rates were measured for both the machine direction (MD) and the transverse direction (TD) of the film. The heat shrinkage rate in MD was measured so that the length direction coincided with the MD, and the heat shrinkage rate in TD was measured so that the length direction coincided with the TD. Heat shrinkage rate (%) = {(length of evaluation film before heat treatment) - (length of evaluation film after heat treatment)} / (length of evaluation film before heat treatment) x 100

[0223] (12) Contents of Terephthalic Acid and Isophthalic Acid Components in Polyester A sample solution was prepared by dissolving raw material polyester in a solvent prepared by mixing chloroform D (manufactured by Eurisop) and trifluoroacetic acid D1 (manufactured by Eurisop) in a volume ratio of 10:1. The proton NMR of the sample solution was measured using an NMR (GEMINI-200; manufactured by Varian) under the measurement conditions of a temperature of 23°C and an accumulation number of 64. In the NMR measurement, the peak intensity of a predetermined proton was calculated, and the contents (mol %) of the terephthalic acid component and the isophthalic acid component in 100 mol % of the acid component were calculated.

[0224] (13) Number and average particle size of granules Polyesters C and D used in the intermediate layer were continuously extruded into a sheet having a width of 10 cm and a thickness of 50 μm. Light was applied from above the sheet to an area of ​​approximately 6 cm from the center in the width direction, and shadows caused by the granules (gel) were photographed from below the sheet with a CCD camera. ２The number of particulates present in the gel was measured. The gel counter was composed of a camera system, an extruder, and a chill roll unit. The gel counter used was an "FS-5 Film Scan (camera system), ME-20 / 26 V2 Measuring Extruder (extruder), and CR-7 Chill Roll Unit (chill roll unit)" manufactured by Optical Control Systems. The measurement conditions were as follows. The number of particulates and average particle size were as shown in Table 3. Chill roll temperature: 30°C Extruder cylinder temperature: 295°C Extruder screw rotation speed: 100 rpm Sheet thickness: 50 μm

[0225]

[0226]

[0227]

[0228] In the examples, laminated polyester films containing recycled polyester resin were obtained, and the laminated polyester films had excellent surface smoothness and moderate surface roughness. Therefore, the air leakage index was small in the examples, indicating that the handling properties of the laminated polyester films were good.

[0229] On the other hand, Comparative Example 1 did not contain recycled polyester resin in the surface layer or intermediate layer, and therefore tended to have a high air leakage index and was inferior in handleability.

[0230] The laminated polyester film of the present invention contains a recycled polyester resin and can be obtained as a polyester film having excellent surface smoothness and handleability. Furthermore, since the surface of the laminated polyester film of the present invention has high smoothness, it is useful as a support (substrate) for ceramic green sheets in the production process of multilayer ceramic capacitors or as a film for the DFR production process. The laminated polyester film of the present invention is particularly suitable for use as a support for ceramic green sheets used in automotive multilayer ceramic capacitors.

[0231] 10: Laminated polyester film 12: Surface layer 14: Intermediate layer 16: Back layer

Claims

1. A laminated polyester film having a surface layer, an intermediate layer, and a back layer, wherein the surface layer and / or the intermediate layer contains recycled polyester resin, the surface layer has protrusions detected by analysis under the following conditions, and the number of protrusions is 70 / mm ２ or more, or the total area of ​​the protrusions is 60 μm ２ / mm ２ The laminated polyester film described above; (Analysis conditions) The surface texture of the surface is photographed using a laser microscope under conditions of an objective lens magnification of 100x and a viewing angle of 0.15 mm x 0.15 mm, and the cross-sectional texture is confirmed, and image analysis is performed in areas where there are no concave shapes, using the following procedures: (1) Using image analysis software, the photographed image is converted from a color image to a grayscale image; (2) A threshold value is set to 10 to 15, and background processing is performed; (3) A threshold value is set to 130 to 230, and density conversion processing is performed; (4) A threshold value is set to 0 to 160, and image processing is performed for automatic binarization and morphological hole filling, and any convex shapes observed as a result are regarded as protrusions.

2. The number of the protrusions is 2000 / mm ２ The laminated polyester film according to claim 1, wherein:

3. The total area of ​​the protrusions is 1000 μm ２ / mm ２ The laminated polyester film according to claim 1, wherein:

4. The laminated polyester film according to claim 1, wherein the projections have an equivalent circle diameter of 0.9 μm or less.

5. The laminated polyester film according to claim 1, wherein the average distance between the protrusions is 26 μm or less.

6. The laminated polyester film according to claim 1, wherein the total distance between the protrusions is 2050 μm or more.

7. The laminated polyester film according to claim 1, wherein the surface layer is substantially free of particles.

8. The laminated polyester film according to claim 1, wherein the surface layer has a thickness of 0.5 to 10 μm.

9. The laminated polyester film according to claim 1, wherein the thickness of the intermediate layer is 50 to 93% of the total thickness of the film.

10. The laminated polyester film according to claim 1, having an air leakage index of 2730 seconds or less.

11. The laminated polyester film according to claim 1, wherein the surface layer and / or the intermediate layer contains particulate matter.

12. The recycled polyester resin has a particle size of 1000 μm or less at 70 particles / m ２ The laminated polyester film according to claim 1, comprising:

13. The laminated polyester film according to claim 1, wherein the back surface layer has an arithmetic mean height (Sa) of 3 nm or more and 35 nm or less, and a maximum peak height (Sp) of 30 nm or more and 700 nm or less.

14. The laminated polyester film according to claim 1, having a total thickness of less than 30 μm.

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

16. The laminated polyester film according to claim 1, wherein the recycled polyester resin contained in the surface layer and / or the intermediate layer is recycled from PET bottles.

17. The laminated polyester film according to claim 1, wherein the recycled polyester resin contained in the surface layer and / or the intermediate layer is a recycled polyester film.

18. The laminated polyester film according to claim 1, wherein the recycled polyester resin contained in the surface layer and / or the intermediate layer is a chemically recycled polyester resin.

19. The laminated polyester film according to claim 1, wherein the surface layer and / or the intermediate layer contains a polyester resin made from a biomass-derived material.

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

21. A method for producing a polyester resin film comprising: supplying a polyester resin A constituting a surface layer, a polyester resin B constituting an intermediate layer, and a polyester resin C constituting a back layer to respective extruders, melting them, and then co-extruding them; wherein the polyester resin A and / or the polyester resin B is a granular material having a particle diameter of 1000 μm or less at a density of 70 particles / m ２ A method for producing a laminated polyester film containing a recycled polyester resin containing the above.

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

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

24. Use of the laminated polyester film according to any one of claims 1 to 20 as a support for ceramic green sheets in the manufacturing process of a laminated ceramic capacitor.

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

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