Laminated Polyester Film

Abstract

A multilayered polyester film which comprises a polyester film and, disposed on at least one surface thereof, a layer X which has a contact angel HX(1) with water of 0-60°, wherein the layer X has a degree of crystallinity C(0) of 0-30%. HX(1): Contact angle at one second after water has come into contact with layer X. A polyester film having excellent recoverability is provided by disposing a layer X on at least one surface of a polyester film, the layer X having a regulated contact angle with water and a regulated degree of crystallinity.

Description

Technical Field

[0001] The present invention relates to a laminated polyester film excellent in removing a layer provided on the laminated polyester film.

Background Art

[0002] Plastics are used in various fields. On the other hand, plastics are regarded as a cause of marine pollution such as microplastics, and it has become an urgent task to reduce the environmental burden caused by plastics. In recent years, due to the evolution of IoT (Internet of Things), the number of electronic devices such as CPUs installed in computers and smartphones has increased rapidly. Along with this, the number of multilayer ceramic capacitors (MLCCs), which are important for driving electronic devices, has also increased explosively. A general manufacturing method of MLCCs has the following steps. A plastic film is used as a base material, and a ceramic green sheet and an electrode are laminated on a release film provided with a release layer on the base material, and then the laminate is peeled off from the release film, and the laminate obtained in that step is laminated in multiple layers and fired. In the above steps, the release film will be discarded as unnecessary during the process.

[0003] That is, the environmental burden caused by an increase in the amount of release films discarded as unnecessary due to the explosive increase in the number of MLCCs in recent years has become an issue. The components of the release layer contained in the release film used in the manufacturing process of MLCCs generally have a composition different from that of the components constituting the film from the viewpoint of releasability. Therefore, when the release film with the release layer is remelted as it is, the components of the release layer exist as foreign substances, so it cannot be reused.

[0004] In Patent Document 1, a technique is disclosed in which wax is kneaded into a film and used as a release film without providing a release layer. Further, in Patent Document 2, a method is disclosed in which a release film having a release layer is washed using a metal brush, and the film from which the release layer has been removed is reused. In Patent Document 3, a method is disclosed in which a water-soluble resin layer is provided between the release layer and the polyester film, and after removing the release layer by washing with water, it is reused.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when using wax as a release agent, the coatability of the ceramic slurry, which is the material of the ceramic green sheet, and the peelability of the green sheet obtained by drying the ceramic slurry are not sufficient. Further, since wax is a substance different from the components constituting the film, there is a problem that it becomes a foreign substance when remelted and reused. In addition, when washing a release film using a metal brush, there are problems such as inability to wash uniformly or insufficient removability of the release layer. Further, the method of providing a water-soluble resin layer between the release layer and the polyester film also has a problem that the removability is not sufficient.

Means for Solving the Problems

[0007] In order to solve the above problems, the present invention has the following configuration. That is, [I] A laminated polyester film having a layer X on at least one surface of the polyester film, the layer X having a water contact angle HX(1) of 0° or more and 60° or less, wherein the layer X has a crystallinity C(0) of 0% or more and 30% or less. HX(1): Contact angle 1 second after water contacts layer X [II] The laminated polyester film according to [I], wherein the crystallinity C(150) of the layer X after heat treatment at 150° C. for 30 minutes is 0% or more and 30% or less. [III] The laminated polyester film according to [I] or [II], wherein the ratio Ra / Xt of the surface roughness Ra (nm) of the polyester film on the side where the layer X is to be provided to the thickness Xt (nm) of the layer X is 0.001 or more and 1.0 or less. [IV] The laminated polyester film according to any one of [I] to [III], wherein the layer X contains a resin having polyvinyl alcohol as the main skeleton. [V] A laminated polyester film according to any one of [I] to [IV], further comprising a layer Y on the side of the layer X opposite to the side in contact with the polyester film, the layer Y having a water contact angle HY(1) of 80° or more and 120° or less, wherein the water contact angles HY(1) (°) and HY(20) (°) of the layer Y of the film satisfy the following formula: 45≦|HY(1)-HY(20)|≦80 HY(1): Contact angle 1 second after water contacts layer Y HY(20): Contact angle of layer Y after 20 seconds of contact with water [VI] The laminated polyester film according to [V], wherein the layer Y contains a resin having dimethylsiloxane as a main skeleton. [VII] The laminated polyester film according to [V] or [VI], wherein a release layer is provided on the surface of the layer Y opposite to the surface in contact with the layer X, and the release layer is peeled off from the layer Y, and the laminated polyester film is used for release purposes. [VIII] The laminated polyester film according to [V] or [VI], which is used for an application in which a release layer is provided on the surface of the layer Y opposite to the surface in contact with the layer X, and the layer X and the layer Y are removed after the release layer is peeled from the layer Y. The laminated polyester film according to [V] or [VI], which is used for the reuse of a polyester film provided with a release layer on the surface opposite to the surface in contact with layer X of layer Y and removing layer X and layer Y after peeling the release layer from layer Y. The laminated polyester film according to any one of [VII] to [IX], wherein the release layer is a ceramic green sheet containing barium titanate as a main component. The laminated polyester film according to any one of [I] to [X], which is used as a release film for the manufacturing process of a multilayer ceramic capacitor (MLCC). A laminated polyester film having a polyester film and layer Y, wherein the contact angles HY(1) (°) and HY(20) (°) of water with layer Y satisfy the following formula. 70 ≦ HY(1) ≦ 120, 10 ≦ |HY(1) - HY(20)| ≦ 80 HY(1): Contact angle 1 second after water contacts layer Y HY(20): Contact angle 20 seconds after water contacts layer Y

Advantages of the Invention

[0008] After using the laminated polyester film of the present invention in industrial applications such as the base material of an adhesive tape or a release film, a laminated polyester film excellent in the removability of layers other than the polyester film can be provided.

Embodiments for Carrying Out the Invention

[0009] The present invention will be described in detail below with specific examples.

[0010] The present invention relates to a laminated polyester film provided with one or more layers on at least one side of a polyester film. The polyester referred to in the present invention has a dicarboxylic acid constituent component and a diol constituent component. In this specification, the constituent component refers to the smallest unit that can be obtained by hydrolyzing the polyester. Examples of the dicarboxylic acid constituent component constituting such a polyester include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, or ester derivatives thereof.

[0011] Examples of the diol constituent component constituting such a polyester include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, alicyclic diols such as cyclohexanedimethanol, spiroglycol, and those in which a plurality of the above-mentioned diols are connected in series. Among them, from the viewpoints of mechanical properties and transparency, polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and those obtained by copolymerizing isophthalic acid or naphthalenedicarboxylic acid into a part of the dicarboxylic acid component of PET, and polyesters obtained by copolymerizing cyclohexanedimethanol, spiroglycol, or diethylene glycol into a part of the diol component of PET are preferably used.

[0012] The laminated polyester film of the present invention needs to have a layer X with a water contact angle HX(1) of 0° or more and 60° or less on at least one side of the polyester film. Here, HX(1) refers to the contact angle 1 second after water contacts layer X when measuring the water contact angle of layer X by the method described later. By setting the water contact angle of layer X within this range, layer X is likely to absorb water, and layer X can be removed from the laminated polyester film by washing with water. It is substantially impossible for it to be less than 0°. Also, when it exceeds 60°, the water absorbency of layer X is poor. HX(1) is more preferably 10° or more and 45° or less.

[0013] Also, when the contact angle 20 seconds after water contacts layer X is defined as HX(20), by setting the absolute value of the difference between HX(20) and HX(1) (|HX(20) - HX(1)|) to 5° or more, preferably 10° or more and 30° or less, the water absorbency of layer X is improved and it becomes easier to wash with water.

[0014] The crystallinity C(0) of layer X of the laminated polyester film of the present invention needs to be 0% or more and 30% or less. Crystallinity generally represents the degree of crystallization of a substance. The higher the crystallinity, the more the substance contains stable crystalline parts in terms of free energy. That is, the higher the crystallinity, the more stable the substance itself becomes, and for example, the elution property with respect to water may decrease. The crystallinity of layer X will not substantially be less than 0%. When it exceeds 30%, the durability against water is improved, and it may become difficult to remove layer X using water. Also, when C(0) is less than 1.0%, it may be difficult to form layer X on the polyester film. Therefore, C(0) is more preferably 1.0% or more and 20% or less, and even more preferably 1.0% or more and 10% or less.

[0015] Further, the crystallinity C(150) of layer X of the laminated polyester film of the present invention after heat treatment at 150°C for 30 minutes is preferably 0% or more and 30% or less. By setting the crystallinity of layer X after heat treatment at 150°C for 30 minutes within the above range, for example, even after heat is applied in the processing step of the object to be released when the laminated polyester film of the present invention is used as a release film provided with a release layer, layer X can be removed using water. C(150) is more preferably 1.0% or more and 20% or less, and even more preferably 1.0% or more and 10% or less. When C(150) is less than 1.0%, the stability of layer X deteriorates due to heat application, and it may be difficult to use the polyester film of the present invention as a release film.

[0016] Layer X of the laminated polyester film of the present invention is preferably a water-soluble substance. By making layer X a water-soluble substance, it becomes easy to set the contact angle HX(1) within a preferable range. Further, when layer X is a water-soluble substance, by washing the laminated film containing layer X with water, layer X dissolves in water and peeling occurs at the interface between the polyester film and layer X, making it easy to take out only the polyester film.

[0017] Examples of water-soluble substances include polyester-based resins having water solubility, polyester urethane-based resins, polyvinyl alcohol-based resins (hereinafter sometimes referred to as polyvinyl alcohol (PVA)), polyvinyl pyrrolidone-based resins (hereinafter sometimes referred to as polyvinyl pyrrolidone (PVP)), and those mainly composed of starch. The water solubility here means that when a solid is immersed in water at 50°C for 10 minutes, the change in the mass of the solid caused by elution in water is 15% or more, and it becomes an aqueous solution. From the viewpoints of affinity with the polyester film, water solubility, heat resistance, durability against organic solvents (hereinafter sometimes referred to as solvent resistance), and crystallinity control, layer X is preferably a polyvinyl alcohol-based resin having a polyvinyl alcohol main skeleton. In particular, PVA is preferable because it has few non-polar sites and contains many hydrophilic groups, so it has high water solubility and solvent resistance.

[0018] When a polyvinyl alcohol resin is used for Layer X, the degree of polymerization is preferably 300 to 1000, more preferably 300 to 800, and even more preferably 400 to 600. If the degree of polymerization exceeds 1000, the molecular chain of the polyvinyl alcohol becomes long, which may result in packing for crystallization even within the molecular chain, resulting in a high degree of crystallization. If the degree of polymerization is less than 200, when Layer X is provided on a polyester film by coating, the coatability may be poor, making it impossible to laminate Layer X, or the coatability may be poor, causing the polyvinyl alcohol forming Layer X to be unevenly distributed on the film and failing to form a layer, resulting in strong molecular interactions and a high degree of crystallization.

[0019] Furthermore, when a polyvinyl alcohol resin is used for layer X, the saponification degree is preferably 30 or more and 88 or less, more preferably 60 or more and 80 or less. Polyvinyl alcohol has hydroxyl groups and acetyl groups as side chains, and the higher the saponification degree, the greater the amount of hydroxyl groups, which are small bulky functional groups. Therefore, when the saponification degree is high, crystallization due to molecular chain packing tends to occur easily. When the saponification degree exceeds 88, the crystallization degree tends to increase. Furthermore, when the saponification degree is less than 30, the acetyl groups are abundant, which may reduce water solubility, making it impossible to set HX(1) within the preferred range, or may reduce resistance to organic solvents.

[0020] In addition, as a side chain of the polyvinyl alcohol-based resin used as layer X, it is also a preferred embodiment to use a copolymerized polyvinyl alcohol obtained by copolymerizing a functional group other than a hydroxyl group or an acetyl group. In particular, by introducing a hydrophilic and bulky functional group, such as a 1,2-ethanediol group, a carboxyl group, a sodium sulfonate group, etc., both HX(1) and C(0) can be easily brought into a preferred range. The copolymerization amount is 3 mol% or more and 20 mol% or less, more preferably 5 mol% or more and 10 mol% or less, based on the total amount of the polyvinyl alcohol resin. When the copolymerization amount exceeds 20 mol%, when layer X is provided on the polyester film by coating, the coatability may deteriorate and it may be difficult to laminate. When it is less than 3 mol%, the effect for making HX(1) and C(0) fall within the preferred range may not be sufficiently obtained.

[0021] When using a polyvinyl alcohol-based resin as layer X, it is preferable not to add an acrylic resin or a polyester resin as a binder to layer X, nor a resin having a crosslinking action such as melamine or oxazoline for improving film-forming properties. The binder and the resin having a crosslinking action interact with the hydroxyl groups on the side chains of the polyvinyl alcohol-based resin, and cannot control the crystallinity and the contact angle, and tend not to reach a preferred value.

[0022] As one aspect of the laminated polyester film of the present invention, a laminated polyester film having a polyester film and layer Y can be exemplified, in which the contact angles HY(1) (°) and HY(20) (°) of water on layer Y satisfy the following formula. 80≦HY(1)≦120, 10≦|HY(1)-HY(20)|≦80 HY(1): Contact angle 1 second after water contacts layer Y HY(20): Contact angle 20 seconds after water contacts layer Y By controlling the contact angle with respect to water and having layer Y with HY(1) in the above range, the surface energy of layer Y can be reduced, and as a result, the laminated polyester film having layer Y can be used as a release film.

[0023] In order to make HY(1) a preferable value, it is preferable that layer Y has water repellency. When layer Y is made of a resin, examples of the highly water-repellent resin that can be used for layer Y include silicone compounds having a dimethylsiloxane main skeleton, compounds having a long-chain alkyl group, and compounds having fluorine.

[0024] Also, by changing HY(20) compared to HY(1) and making |HY(1) - HY(20)| within the above range, it becomes possible to change the physical properties of layer Y through water as a medium. That is, by changing the physical properties through water as a medium, the adhesiveness between layer Y and the laminated polyester film is changed, and it becomes easier to remove layer Y from the laminated polyester film using water. If |HY(1) - HY(20)| is small and less than 10°, the change in physical properties may not be sufficient and the removability may be poor. When |HY(1) - HY(20)| exceeds 80°, the physical properties of layer Y are unstable, and it may be difficult to provide layer Y on the polyester film. |HY(1) - HY(20)| is preferably 30° or more and 80° or less, more preferably 45° or more and 80° or less.

[0025] In order to make |HY(1)-HY(20)| of layer Y within the above-mentioned range, it is also a preferred embodiment to provide the aforementioned layer X between the polyester film and layer Y so as to be in contact with the polyester film and layer Y (that is, in a laminated polyester film having layer X with a water contact angle HX(1) of 0° or more and 60° or less on at least one side of the polyester film, a laminated polyester film having layer Y on the surface opposite to the surface in contact with the polyester film of layer X). Since layer X which is easy to absorb water is in contact with layer Y, the water in contact with layer Y permeates through layer Y and is absorbed by layer X, so that the water contact angle of layer Y also changes, and |HY(1)-HY(20)| can be made within a preferred range. The higher the water repellency of layer Y and the higher the water permeability of layer Y, the more |HY(1)-HY(20)| can be made within a preferred range. Examples of the highly water-repellent resin that can be used for layer Y include silicone compounds having a dimethylsiloxane main skeleton, compounds having a long-chain alkyl group, and compounds having fluorine. Among them, silicone having a dimethylsiloxane main skeleton with high water permeability can be preferably used.

[0026] In the laminated polyester film of the present invention, since the contact angle of layer Y with respect to water is large and the surface energy is small, a release layer is provided on the surface opposite to the surface of layer Y in contact with layer X, and it can be preferably used for release applications in which the release layer is peeled off from layer Y. Furthermore, in the laminated polyester film of the present invention, since it is possible to remove layer X and layer Y with water, after peeling off the release object, it is possible to remove layer X and layer Y to obtain only the polyester film. Furthermore, after removing layer X and layer Y from the laminated polyester film of the present invention to obtain a polyester film, it is preferable to reuse the obtained polyester film. Examples of the reuse method include a method of providing layer X and layer Y again on the obtained polyester film and using it as a release film, and a method of remelting the polyester film and molding it into a polyester film again. However, a method of remelting and molding it into a polyester film again with no limitation on the reuse application is preferable.

[0027] When a silicone compound, particularly a compound containing a dimethylsiloxane bond, is used as layer Y of the laminated polyester film of the present invention, the component containing the dimethylsiloxane bond is likely to become a foreign substance when mixed with the polyester film and remelted, which may accelerate the deterioration of the polyester or prevent extrusion molding after melting. Therefore, in order to remelt and reuse the film of the present invention, it is preferable to remove layer Y.

[0028] It is preferable that the ratio Ra / Xt of the surface roughness Ra (nm) on the side where layer X of the polyester film is provided to the thickness Xt (nm) of layer X of the laminated polyester film of the present invention is 0.001 or more and 1.0 or less. When the ratio Ra / Xt exceeds 1.0, layer X cannot cover the entire surface of the polyester film, and high protrusions are exposed. Therefore, when layer Y is further provided on layer X, layer Y is in direct contact with the polyester film, and as a result, water may not be absorbed into layer X through layer Y, and the removability of layer X and layer Y may be poor. When the ratio Ra / Xt is less than 0.001, the polyester film becomes very smooth, resulting in poor affinity with layer X, and it may be impossible to provide layer X by coating. The ratio Ra / Xt is more preferably 0.05 or more and 0.5 or less.

[0029] When the laminated polyester film of the present invention having layer X and layer Y is used as a release film, the object to be released includes an organic adhesive mainly composed of acrylic and an inorganic sheet mainly composed of a metal or a metal oxide. In particular, barium titanate of a metal oxide is essential for manufacturing MLCC, and the usage amount of the release film for the process for manufacturing a barium titanate sheet is increasing. Under such circumstances, by using the film of the present invention having layer X and layer Y in the process of manufacturing a barium titanate sheet, after use in the process of manufacturing a barium titanate sheet, layer X and layer Y can be removed from the laminated polyester film of the present invention, and only the polyester film can be reused, which can contribute to reducing the environmental load.

[0030] A method for manufacturing the laminated polyester film of the present invention will be described below, but the present invention is not limited to the laminated polyester film obtained by this method.

[0031] For the polyester film used in the present invention, if necessary, the dried raw material is heated and melted in an extruder, and a method (melt casting method) of extruding it from a die onto a cooled casting drum and processing it into a sheet shape can be used. The sheet is adhered electrostatically onto a drum cooled to a surface temperature of 20°C or higher and 60°C or lower, and cooled and solidified to produce an unstretched sheet. The temperature of the casting drum is more preferably 20°C or higher and 40°C or lower, and even more preferably 20°C or higher and 30°C or lower.

[0032] Next, the unstretched sheet is biaxially stretched at a temperature T1n (°C) satisfying the following formula (i) by 3.6 times or more in the longitudinal direction (MD) of the film, 3.9 times or more in the width direction (TD) of the film, and 14.0 times or more and 20.0 times or less in terms of area magnification.

[0033] The stretching ratio in the width direction of the film is preferably 4.0 times or more, more preferably 4.3 times or more and 5.0 times or less. By setting the stretching ratio in the width direction of the film to 4.0 times or more, when layer X is applied to the uniaxially stretched film using the in-line coating method described later, the components constituting layer X are stretched and extended following the film, so that the components constituting layer X are prevented from being regularly arranged, and the crystallinity of layer X can be made within a preferable range. If the stretching ratio in the width direction exceeds 5.0 times, the film-forming property of the film may deteriorate. (i) Tg (°C) ≤ T1n (°C) ≤ Tg + 40 (°C) Tg: Glass transition temperature (°C) of the polyester film As the stretching method in the longitudinal direction of the film, a method using a speed difference between rolls is preferably used. At this time, it is also a preferable embodiment to stretch the film in a plurality of sections while fixing the film with nip rolls so that the film does not slip.

[0034] Next, the biaxially stretched film is subjected to a heat setting treatment at a temperature (Th0 (°C)) that satisfies the following formula (ii) for 1 second or more and 30 seconds or less, and after being uniformly slowly cooled, it is cooled to room temperature to obtain a polyester film. (ii) Tmf - 35 (°C) ≤ Th0 (°C) ≤ Tmf (°C) Tmf: Melting point of the film (°C) By obtaining a biaxially stretched film under the conditions that satisfy (ii), an appropriate orientation can be imparted to the film, and the handleability when used as a release film can be improved.

[0035] In order to make the surface roughness of the polyester film of the present invention within the above-mentioned range, in addition to the above-mentioned production method, it is also a preferred embodiment to add particles to the film. As the particles to be added, particles with high hardness are preferable, and crosslinked polystyrene particles, diamond particles, zirconia particles, and aluminum oxide particles are preferably used. The amount of particles added is 0.01% or more and 0.7% or less based on the weight of the polyester film.

[0036] Next, a method for providing layer X and layer Y on the polyester film of the present invention will be described below.

[0037] When layer X is formed of a resin that easily absorbs water, a method of dissolving the resin forming layer X in water and coating it on the polyester film of the present invention is preferably used. As the coating method, general coating methods such as gravure coating, Mayer bar coating, air knife coating, and doctor knife coating can be used. In particular, from the viewpoint of controlling the crystallinity of layer X, an in-line coating method in which the resin of layer X is coated on the surface layer of the polyester film after uniaxially stretching in the longitudinal direction, and layer X is formed simultaneously while the polyester film is stretched in the width direction is preferably used. The thickness of layer X is preferably 50 nm or more and 1000 nm or less. If it is less than 50 nm, the water absorption of layer X may not be fully exhibited, and the removability may be poor. If it exceeds 1000 nm, blocking may occur and the handleability may decrease.

[0038] Next, a method for providing layer Y will be described. Layer Y may be provided simultaneously with layer X or separately. In the case of simultaneous provision, examples include a method of simultaneously coating two layers using a die or the like, or a method of coating using a coating agent in which the components of layer X and layer Y are mixed in advance. In order to improve the lamination accuracy of layer X and layer Y, it is preferable to provide them separately. Using a coating solution in which the components of layer Y are dissolved on the laminated polyester film containing layer X obtained by the above method, it can be coated using a general coating method such as gravure coating, Mayer bar coating, air knife coating, doctor knife coating, etc. The thickness of layer Y is preferably 10 nm or more and 1000 nm or less. If it is less than 10 nm, the function of layer Y may not be exhibited. If it exceeds 1000 nm, the water absorption of layer X may not be exhibited, and |HY(1)-HY(20)| may not be in the preferable range.

[0039] Next, a method for removing layer X and layer Y will be described. Since layer X is water-absorbent, it is a preferred embodiment to wash it with water. For example, a laminated film containing the polyester film of the present invention is subjected to a step of unwinding the laminated film, a step of supplying warm water to the surface of the unwound laminated film and peeling the surface laminate portion from the laminated film, and a step of winding up the polyester film after peeling. The temperature of the warm water is preferably 50°C or higher and 100°C or lower. If it is less than 50°C, sufficient detergency may not be obtained. If it exceeds 100°C, the glass transition temperature of the polyester film may be exceeded, and the film may not be conveyable. The time for which water contacts the surface of the laminated film is 5 seconds or longer, preferably 10 seconds or longer, more preferably 30 seconds or longer and 600 seconds or shorter. The step of supplying warm water to the surface of the unwound laminated film is carried out in a water tank, and examples thereof include a method of covering the entire laminated film and a method of pressurizing the heated water and spraying it onto the film. By supplying water to layer Y of the laminated polyester film, water is absorbed into layer X through layer Y, and as a result, the physical properties of layer Y can be changed, making layer Y more likely to move from the laminated polyester film and improving the detergency. The speed at which the film is conveyed is 5 m / min or higher, preferably 10 m / min or higher, more preferably 20 m / min or higher and 100 m / min or lower. When conveying the laminated film provided with layer X and layer Y in the step of removing layer X and layer Y, it is also important to apply tension to the laminated film. By applying tension, the surface of the laminated film is stretched, and the mobility of layer X and layer Y is improved, resulting in improved detergency. The tension is 5 N / m or higher and 100 N / m or lower, more preferably 20 N / m or higher and 80 N / m or lower, even more preferably 30 N / m or higher and 50 N / m or lower. If it is less than 5 N / m, the surface of the laminated film may not be stretched, and the detergency may be poor. If it exceeds 100 N / m, the film may wrinkle, the surface stretchability may be poor, and the detergency may be poor.

[0040] As described above, the polyester film of the present invention can be used as a release film for processing or other functional laminated films by providing a water-absorbent layer X on at least one side of the polyester film and then providing a release layer Y, and then removing layers X and Y by washing with water to obtain only the polyester film. Therefore, the obtained polyester film can be reused as is, or can be remelted and chipped, used as a recycled raw material for film production, and reused as a film.

[0041] [Characteristics evaluation method] A. Surface roughness Ra (nm) of polyester film The three-dimensional surface roughness is measured using the following equipment and conditions, and the arithmetic mean roughness Ra of the surface roughness is calculated using analysis software. The measurement is carried out 10 times at different locations, and the average value is taken as Ra (nm). Equipment: Kosaka Laboratory "surf-corder ET-4000A" Analysis software: i-Face model TDA31 Stylus tip radius: 0.5μm Measurement field of view: X direction: 380 μm Pitch: 1 μm Y direction: 280 μm Pitch: 5 μm Stylus pressure: 50μN Measurement speed: 0.1mm / s Cutoff value: Low frequency - 0.8 mm, High frequency - none Leveling: All areas Filter: Gaussian filter (2D) Magnification: 100,000 times.

[0042] B. Thickness of each layer The thickness of each layer of the laminated film is measured using the following method: A cross section of the film is cut out using a microtome in a direction parallel to the width direction of the film, and the cross section is observed under a scanning electron microscope at a magnification of 5000 times to measure the thickness of each layer of the laminated film.

[0043] C. Intrinsic viscosity (IV) The polyester film of the present invention is dissolved in 100 ml of orthochlorophenol (solution concentration C = 1.2 g / dl), and the viscosity of the solution at 25°C is measured using an Ostwald viscometer. The viscosity of the solvent is also measured in the same manner. Using the obtained solution viscosity and solvent viscosity, [η] (dl / g) is calculated according to the following formula (a), and the obtained value is taken as the intrinsic viscosity (IV). (a) ηsp / C=[η]+K[η] 2 C (Here, ηsp = (solution viscosity (dl / g) / solvent viscosity (dl / g))-1, and K is Huggins' constant (assumed to be 0.343).

[0044] D. Copolymerization amount of layer X (mol%) Using the following equipment: 13 The amount of copolymerization (mol%) is calculated from the peak area of the carbon signal of the modified group introduced in the C NMR spectrum and DEPT135 spectrum. Equipment: ECZ-600R (JEOL RESONANCE Co., Ltd.) Measurement method: Single 13C pulse with inverse gated 1H decoupling Measurement frequency: 150.9MHz Pulse width: 5.25 μs Lock solvent: D2O Chemical shift reference: TSP (0 ppm) Accumulation count: 10,000 times Measurement temperature: 20℃ Sample rotation speed: 15Hz.

[0045] E. Degree of saponification of layer X According to JIS K 6726 (1994) polyvinyl alcohol test method, the amount of acetate groups contained in the sample is determined by titration with an aqueous sodium hydroxide solution and calculated.

[0046] F. Average degree of polymerization of layer X According to JIS K 6726 (1994) polyvinyl alcohol test method, the sample is completely saponified with an aqueous sodium hydroxide solution, and then the viscosity at 25°C is measured using an Ostwald viscometer, and the average degree of polymerization is calculated from the intrinsic viscosity.

[0047] G. Water contact angle (°) Measurements were performed using a Kyowa Interface Science Co., Ltd. DM500 contact angle meter and the accompanying FAMAS analysis software. Under an atmosphere of 23°C and 65% RH, the time when the water droplet contacted the sample surface was set to 0 seconds, and a video of the water droplet shape was recorded for 20 seconds. Measurements were taken five times at different locations, and when the sample surface that the water droplet contacted was layer X, the average contact angles determined from the water droplet shapes after 1 second and 20 seconds were calculated and given as HX(1) and HX(20), respectively. Similarly, when the sample surface that the water droplet contacted was layer Y, the average contact angles were calculated and given as HY(1) and HY(20).

[0048] H. Crystallinity of Layer X (%) The spectrum of layer X is measured by the ATR method of FT-IR using the following device and conditions, and calculation is performed by the method described in a non-patent document (J. Applied Spectroscopy, Vol. 79, No. 4, pp. 521-526 (2012)). Equipment: 670-IR (Varian FT-IR) Light source: Globar Detector: DLatgs (deuterated L-alanine doped triglycine sulfate) Resolution: 4cm -1 Number of times accumulated: 256 Measurement method: Attenuated total reflection method Accessory: Single reflection ATR measurement accessory (The Seagull TM) Germanium is used as the ATR crystal. Incident angle: 60° (unpolarized).

[0049] I. Peelability of the mold to be released A polyester release film with a release object laminated thereon was attached with a polyester adhesive tape (No. 31B, width 19 mm, manufactured by Nitto Denko Corporation), and the 180° peel strength was measured using an adhesion and film peeling analyzer VPA-H200 manufactured by Kyowa Interface Chemical Co., Ltd., and converted to a width of 50 mm. When the peel strength is 50 mN / 50 mm or less, the evaluation is A, and when it exceeds 50 mN / 50 mm, the evaluation is B.

[0050] J. Removability of Layer X and Layer Y Using the polyester film obtained by removing Layer X and Layer Y, the contact angle of water obtained after 1 second was measured according to the above item G, and the determination was made as follows.

[0051] A; 65° or more and less than 80° ° less than B; 80° or more and less than 90°, or less than 65° ° less than, or less than 65° C; 90° or more.

[0052] K. Reusability The polyester film after removing Layer X and Layer Y was pulverized, dried at 180 °C for 2 hours, then put into an extruder, melt-extruded at 280 °C, and formed into a sheet on a cast drum cooled to 25 °C. The intrinsic viscosity of the obtained sheet was measured by the method described in the above item C. The difference (ΔIV) between the intrinsic viscosity IV(R) and the intrinsic viscosity IV(I) of the polyester film was obtained by the following formula (b), and the determination was made as follows. (b) ΔIV = |IV(R) - IV(I)| A; The difference in intrinsic viscosity is 0.05 or less B; The difference in intrinsic viscosity exceeds 0.05 and is less than 0.15 C; The difference in intrinsic viscosity exceeds 0.15.

Examples

[0053] Hereinafter, the present invention will be described with reference to examples, but the present invention is not necessarily limited thereto.

[0054] [Production of PET-1] From terephthalic acid and ethylene glycol, using antimony trioxide and magnesium acetate tetrahydrate as catalysts, polymerization was carried out by a conventional method to obtain melt-polymerized PET. The glass transition temperature of the obtained melt-polymerized PET was 81 °C, the melting point was 255 °C, the intrinsic viscosity was 0.65, and the amount of terminal carboxyl groups was 20 eq. / t.

[0055] [Production of Masterbatch (MB)-A] 99 parts by mass of PET-1 and 10 parts by mass of a 10 mass% aqueous slurry of crosslinked polystyrene particles (styrene-acrylate copolymer) with a particle size of 0.1 μm (1 part by mass as crosslinked polystyrene particles) were supplied, the vent hole was maintained at a reduced pressure of 1 kPa or less to remove moisture, and an MB containing 1 wt% of crosslinked polystyrene particles was obtained. The glass transition temperature was 81 °C, the melting point was 255 °C, the intrinsic viscosity was 0.61, and the amount of terminal carboxyl groups was 22 eq. / t.

[0056] [Preparation of MB-B] 99 parts by mass of PET-1 and 1 part by mass of calcium carbonate particles with a particle size of 1.0 μm were supplied, the vent hole was maintained at a reduced pressure of 1 kPa or less to remove moisture, and an MB containing 1 mass% of the particles was obtained. The glass transition temperature was 81 °C, the melting point was 255 °C, the intrinsic viscosity was 0.61, and the amount of terminal carboxyl groups was 22 eq. / t.

[0057] [Production of PEN] From dimethyl 2,6-naphthalenedicarboxylate and ethylene glycol, an ester exchange reaction was carried out using manganese acetate as a catalyst. After completion of the ester exchange reaction, PEN was obtained by a conventional method using antimony trioxide as a catalyst. Also, during polymerization, δ-crystalline alumina particles with a particle size of 0.1 μm were added so that the content became 0.1 mass%. The glass transition temperature of the obtained PEN was 124 °C, the melting point was 265 °C, the intrinsic viscosity was 0.62, and the terminal carboxyl group concentration was 25 eq. / t.

[0058] [Preparation of Coating Agent A] 100 parts by mass of an addition reaction type silicone resin release agent (trade name: LTC750A, manufactured by Toray Dow Corning Silicone Co., Ltd.) and 2 parts by mass of a platinum catalyst (trade name: SRX212, manufactured by Toray Dow Corning Silicone Co., Ltd.) were adjusted to a solid content of 5% by mass using toluene as a solvent to obtain Coating Agent A.

[0059] [Preparation of Coating Agent B] Polyvinyl alcohol “Poval 5-74” (saponification degree: 74, average degree of polymerization: 500) manufactured by Kuraray Co., Ltd. was dissolved in water to a concentration of 4% by mass to obtain Coating Agent B.

[0060] [Preparation of Coating Agent C] Polyvinyl alcohol “Poval LM-25” (saponification degree: 34, average degree of polymerization: 400) manufactured by Kuraray Co., Ltd. was dissolved in water to a concentration of 4% by mass to obtain Coating Agent C.

[0061] [Preparation of Coating Agent D] Polyvinyl alcohol “AYB8041W” (saponification degree: 88, average degree of polymerization: 300, copolymerization amount of 1,2-ethanediol: 3 mol%) manufactured by Mitsubishi Chemical Corporation was dissolved in water to a concentration of 4% by mass to obtain Coating Agent D.

[0062] [Preparation of Coating Agent E] Polyvinyl alcohol “OKS-8089” (saponification degree: 88, average degree of polymerization: 450, copolymerization amount of 1,2-ethanediol: 6 mol%) manufactured by Mitsubishi Chemical Corporation was dissolved in water to a concentration of 4% by mass to obtain Coating Agent E.

[0063] [Preparation of Coating Agent F] Referring to Patent Document JP-A-2004-285143, PVA with a saponification degree of 75, an average degree of polymerization of 500, and a copolymerization amount of 1,2-ethanediol of 6 mol% was prepared. The PVA was dissolved in water to a concentration of 4% by mass to obtain Coating Agent F.

[0064] [Preparation of Coating Agent G] Polyvinyl alcohol “ASP-05” (saponification degree: 88, average degree of polymerization: 500, copolymerized with 1 mol% of sodium sulfonate) manufactured by Nippon Vinyl Poval Co., Ltd. was dissolved in water to a concentration of 4% by mass to obtain Coating Agent G.

[0065] [Preparation of Coating Agent H] Polyvinyl alcohol “GL-05” (saponification degree 88, average degree of polymerization 500) manufactured by Mitsubishi Chemical Corporation was dissolved in water to a concentration of 4% by mass to obtain coating agent H.

[0066] [Preparation of Coating Agent I] Polyvinyl alcohol “NL-05” (saponification degree 99, average degree of polymerization 500) manufactured by Mitsubishi Chemical Corporation was dissolved in water to a concentration of 4% by mass to obtain coating agent I.

[0067] [Preparation of Coating Agent J] To GL-05, a binder polymer (emulsion polymer of methyl methacrylate / ethyl acrylate / acrylonitrile / N-methylol methacrylamide = 45 / 45 / 5 / 5 (molar ratio) (emulsifier: anionic surfactant)), and a crosslinking agent (hexamethoxymelamine crosslinking agent) were adjusted so that the blending ratio of solids was 34 / 24 / 42, and dispersed in water so that the solid content concentration was 4% by mass to obtain coating agent J.

[0068] [Preparation of Coating Agent K] Polyvinyl alcohol “3266” (saponification degree 88, average degree of polymerization 200, 3 mol% copolymerization of sodium sulfonate) manufactured by Mitsubishi Chemical Corporation was dissolved in water to a concentration of 4% by mass to obtain coating agent K.

[0069] [Preparation of Coating Agent L] Polyvinyl alcohol “OKS-1089” (saponification degree 88, average degree of polymerization 2500, copolymerization amount of 1,2-ethanediol 3 mol%) manufactured by Mitsubishi Chemical Corporation was dissolved in water to a concentration of 4% by mass to obtain coating agent L.

[0070] [Preparation of Coating Agent M] Polyvinyl pyrrolidone “KW-30” (average degree of polymerization 30,000) manufactured by Nippon Shokubai Co., Ltd. was dissolved in water to a concentration of 4% by mass to obtain coating M agent.

[0071] [Preparation of Dielectric Paste] 100 parts by weight of barium titanate (product name HPBT-1 manufactured by Fuji Titanium Industry Co., Ltd.), 10 parts by mass of polyvinyl butyral (product name BL-1 manufactured by Sekisui Chemical Co., Ltd.), 5 parts by mass of dibutyl phthalate, and 60 parts by mass of toluene-ethanol (mass ratio 30:30) were taken, and glass beads with a number average particle diameter of 2 mm were added. After mixing and dispersing for 20 hours with a jet mill, filtration was performed to prepare a paste-like dielectric paste.

[0072] [Preparation of Adhesive] 97 parts by mass of butyl acrylate, 3 parts by mass of acrylic acid, 0.2 parts by mass of azobisisobutyronitrile as a polymerization initiator, and 233 parts by mass of ethyl acetate were added. Then, nitrogen gas was passed through, and nitrogen substitution was carried out for about 1 hour while stirring. Thereafter, the flask was heated to 60 °C and reacted for 7 hours to obtain an acrylic polymer with a weight average molecular weight (Mw) of 1.1 million. To this acrylic polymer solution (with 100 parts by mass of solid content), 0.8 parts by mass of trimethylolpropane triisocyanate (product name "Coronate L", manufactured by Nippon Polyurethane Industry Co., Ltd.) as an isocyanate-based crosslinking agent and 0.1 parts by mass of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) were added to prepare an adhesive composition mainly composed of acrylic.

[0073] (Example 1) 80 parts by mass of PET-1 and 20 parts by mass of MB-A were mixed, vacuum-dried at 160 °C for 2 hours, then put into an extruder, melted at 280 °C, and extruded onto a casting drum with a surface temperature of 25 °C through a die to produce an unstretched sheet. Subsequently, the sheet was preheated with a group of heated rolls, then stretched 3.8 times in the longitudinal direction (MD direction) at a temperature of 90 °C, and then cooled with a group of rolls at a temperature of 25 °C to obtain a uniaxially stretched film. Coating agent B was applied to the obtained uniaxially stretched film by the bar coating method so that the coating thickness after drying was 100 nm. Subsequently, while gripping both ends of the film with clips, it was stretched 4.3 times in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 100 °C in a tenter. Furthermore, subsequently, heat fixation was performed at a temperature of 235 °C for 10 seconds in a heat treatment zone in the tenter. Then, after uniformly slow cooling in a cooling zone, it was wound up to obtain a laminated polyester film with layer X laminated. The properties of the obtained polyester film and layer X were as described in Tables 1 and 2.

[0074] On the surface of the obtained laminated polyester film opposite to the surface in contact with the polyester film of layer X, coating agent A was applied by the gravure coating method so that the thickness was 0.1 μm as layer Y to obtain a laminated polyester film. The properties of layer Y were as described in Table 3.

[0075] On the obtained laminated polyester film, as a release object, a dielectric paste was applied by the die coating method so that the thickness after drying was 1.0 μm. Then, from the obtained laminate, a release film roll for the process of releasing the dielectric and peeling the release object was obtained. The film roll was introduced into a water washing device equipped with an unwinding and winding device, washed with water at 100 °C for 2 minutes under a tension of 30 N / m, and a polyester film with layer X and layer Y removed was recovered.

[0076] Since the water contact angle HX(1) and crystallinity C(0) of layer X were in a preferable range, and the water contact angle of layer Y was also in a preferable range, the releasability of the release object and the removability of layer X and layer Y were both good, and the film reused according to the above item K was also practically problem-free (Table 3).

[0077] (Examples 2 to 6) A laminated polyester film was produced in the same manner as in Example 1, except that Coating C was used for Layer X in Example 2, Coating D in Example 3, Coating E in Example 4, Coating F in Example 5, and Coating G in Example 6. Then, Layer X and Layer Y were removed, and the polyester film was reused (Tables 1, 2, and 3).

[0078] In Example 2, since the degree of saponification was slightly low, although the crystallinity C(0) of Layer X was low, the solvent resistance was slightly reduced. As a result, the contact angle HY(1) of Layer Y was slightly small and the peelability of the release object was slightly reduced, but it was within a range without practical problems.

[0079] In Examples 3 and 6, since the amount of the copolymer component was small, although the crystallinity C(0) of Layer X was slightly large, there were no practical problems with the peelability of the release object, the removability of Layers X and Y, and the reusability of the polyester film.

[0080] In Examples 4 to 5, as a result of being able to suppress the crystallinity C(0) and C(150) of Layer X to be small, good removability of Layers X and Y and reusability of the polyester film were shown.

[0081] (Example 7) A laminated polyester film was produced in the same manner as in Example 4, except that the polyester raw material used was PEN and the film-forming conditions were as described in the table. Then, Layer X and Layer Y were removed, and the polyester film was reused (Tables 1, 2, and 3). As a result of being able to suppress the crystallinity C(0) and C(150) of Layer X to be small, good removability of Layers X and Y and reusability of the polyester film were shown.

[0082] (Example 8) A laminated polyester film was produced in the same manner as in Example 4, except that the polyester raw materials used were 80 parts by mass of PET-1 and 20 parts by mass of MB-B, and the thickness of Layer X was as described in the table. Then, Layer X and Layer Y were removed, and the polyester film was reused (Tables 4, 5, and 6).

[0083] As the surface roughness of the polyester film was large and Ra / Xt was large, as a result, the contact angle HY(20) of layer Y became slightly large, and although the removability of layer X and layer Y and the reusability of the polyester film were slightly inferior, they were within the range where there were no practical problems.

[0084] (Example 9) A laminated polyester film was produced in the same manner as in Example 1 except that coating agent M was used as layer X, layer X and layer Y were removed, and the polyester film was reused (Tables 4, 5, 6). Although the crystallinity C(0) of layer X was low, since polyvinylpyrrolidone has nonpolar sites, it has a high affinity for organic solvents and its solvent resistance was slightly low. Therefore, although the contact angle HY(1) of layer Y became slightly small and the peelability of the release object decreased slightly, it was within the range where there were no practical problems.

[0085] (Example 10) In Example 5, an adhesive was used as the release object and applied by the die coating method so that the thickness after drying was 10 μm. Then, from the obtained laminate, a release film roll for the step of releasing the adhesive and peeling the release object was obtained. The film roll was introduced into a water washing device having an unwinding and winding device, and washed with water at 100 °C for 2 minutes under a tension of 30 N / m to recover a polyester film from which layer X and layer Y were removed (Tables 4, 5, 6).

[0086] As a result of being able to suppress the crystallinity C(0) and C(150) of layer X to be small, good removability of layer X and layer Y and reusability of the polyester film were shown.

[0087] (Comparative Examples 1 to 5) A laminated polyester film was produced in the same manner as in Example 1 except that coating agent H was used in Comparative Example 1, coating agent I was used in Comparative Example 2, coating agent J was used in Comparative Example 3, coating agent K was used in Comparative Example 4, and coating agent L was used in Comparative Example 5. Layer X and layer Y were removed, and the polyester film was reused (Tables 4, 5, 6).

[0088] In Comparative Example 1 in which the PVA constituting Layer X has no copolymerization component, HX(1) and the crystallinity C(0) are large, and since the contact angle of Layer Y is not in a preferable range, the removability of Layers X and Y is poor. Thereafter, in accordance with item K above, when the pulverized polyester film was melt-extruded, Layers X and Y could not be removed and remained, resulting in deterioration in the extruder and the inability to form a sheet.

[0089] In Comparative Example 2 in which the saponification degree of the PVA constituting Layer X is large, HX(1) and the crystallinity C(0) are large, and since the contact angle of Layer Y is not in a preferable range, the removability of Layers X and Y is poor. Thereafter, in accordance with item K above, when the pulverized polyester film was melt-extruded, Layers X and Y could not be removed and remained, resulting in deterioration in the extruder and the inability to form a sheet.

[0090] In Comparative Example 3 in which the PVA content as a component constituting Layer X is small and further contains a resin having a crosslinking action with a binder, HX(1) and the crystallinity C(0) are large, and since the contact angle of Layer Y is not in a preferable range, the removability of Layers X and Y is poor. Thereafter, in accordance with item K above, when the pulverized polyester film was melt-extruded, Layers X and Y could not be removed and remained, resulting in deterioration in the extruder and the inability to form a sheet.

[0091] In Comparative Example 4 in which the average polymerization degree of the PVA constituting Layer X is small, the crystallinity C(0) is large, and since the contact angle of Layer Y is not in a preferable range, the removability of Layers X and Y is poor. Thereafter, in accordance with item K above, when the pulverized polyester film was melt-extruded, Layers X and Y could not be removed and remained, resulting in deterioration in the extruder and the inability to form a sheet.

[0092] In Comparative Example 5 where the average degree of polymerization of PVA constituting Layer X was large, HX(1) and the crystallinity C(0) were large, and the contact angle of Layer Y was not within the preferable range, resulting in poor removability of Layers X and Y. Subsequently, when the pulverized polyester film was melt-extruded according to the above-mentioned item K, Layers X and Y could not be removed and remained, causing deterioration in the extruder and preventing the formation of a sheet.

[0093]

Table 1

[0094]

Table 2

[0095]

Table 3

[0096]

Table 4

[0097]

Table 5

[0098]

Table 6

Industrial Applicability

[0099] Since the crystallinity of layer X in the laminated polyester film of the present invention is low and the water absorption is excellent, the removability of layer Y laminated in contact with layer X by water is excellent. Further, by making layer Y of the present invention a water-repellent material, it can be suitably used as a release film for the manufacturing process of a multilayer ceramic capacitor (MLCC) using a dielectric paste as a release object. In addition, since the polyester film can be easily recovered from the release film after use in the MLCC manufacturing process, the polyester film can be easily reused as a raw material for melt film formation.

Claims

1. A laminated polyester film having a layer X with a water contact angle HX(1) of 0° or more and 60° or less on at least one side of a polyester film, wherein |HX(20) - HX(1)| is 5° or more, and the crystallinity C(0) of the layer X is 0% or more and 30% or less. HX(1): Contact angle 1 second after water contacts layer X HX(20): Contact angle 20 seconds after water contacts layer X |HX(20) - HX(1)|: Absolute value of the difference between the contact angle 1 second after water contacts layer X and the contact angle 20 seconds after water contacts layer X

2. The laminated polyester film according to Claim 1, wherein the crystallinity C(150) of the layer X after heat treatment at 150°C for 30 minutes is 0% or more and 30% or less.

3. The laminated polyester film according to Claim 1 or 2, wherein the ratio Ra / Xt of the surface roughness Ra (nm) of the surface on which the layer X of the polyester film is provided to the thickness Xt (nm) of the layer X is 0.001 or more and 1.0 or less.

4. The laminated polyester film according to any one of Claims 1 to 3, wherein the layer X contains a resin having polyvinyl alcohol as a main skeleton.

5. A laminated polyester film further having a layer Y with a water contact angle HY(1) of 80° or more and 120° or less on the surface opposite to the surface in contact with the polyester film of the layer X, wherein the water contact angles HY(1) (°) and HY(20) (°) of the layer Y of the film satisfy the following formula. The laminated polyester film according to any one of Claims 1 to 4. 45 ≤ |HY(1) - HY(20)| ≤ 80 HY(1): Contact angle 1 second after water contacts layer Y HY(20): Contact angle 20 seconds after water contacts layer Y

6. The laminated polyester film according to Claim 5, wherein the layer Y contains a resin having dimethylsiloxane as a main skeleton.

7. The laminated polyester film according to Claim 5 or 6, wherein a release layer is provided on the surface opposite to the surface in contact with the layer X of the layer Y, and it is used for a release application in which the release layer is peeled off from the layer Y.

8. The laminated polyester film according to Claim 5 or 6, wherein a release layer is provided on the surface opposite to the surface in contact with the layer X of the layer Y, and after the release layer is peeled off from the layer Y, it is used for an application in which the layer X and the layer Y are removed.

9. The laminated polyester film according to claim 5 or 6, which is used for the purpose of reusing a polyester film in which a release layer is provided on a surface opposite to the surface in contact with layer X of layer Y, and after peeling the release layer from layer Y, layers X and Y are further removed.

10. The laminated polyester film according to any one of claims 7 to 9, wherein the release layer is a ceramic green sheet mainly composed of barium titanate.

11. The laminated polyester film according to any one of claims 1 to 10, which is used as a release film for a manufacturing process of a multilayer ceramic capacitor (MLCC).

12. The laminated polyester film according to claim 1, wherein layer X contains a resin having a polyvinyl alcohol with a degree of polymerization of 300 to 1000 and a saponification degree of 30 or more and 88 or less as a main skeleton, and the resin having a polyvinyl alcohol as a main skeleton has a copolymerization component of 3 to 20 mol%.

13. The laminated polyester film according to claim 12, wherein the copolymerization component is a 1,2-ethanediol group or a sodium sulfonate group.

14. The laminated polyester film according to claim 12 or 13, further having layer Y on a surface opposite to the surface in contact with the polyester film of layer X, and layer Y contains a resin having a dimethylsiloxane as a main skeleton.

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