Release film and its applications

Abstract

An object of the present invention is to provide a release film that has excellent winding and unwinding properties, and in which the ceramic green sheets do not stick to the back surface (opposite the release surface) even when the film is wound up with thin ceramic green sheets stacked thereon. [Solution] The present invention relates to a release film having a resin layer A on one side of a polyester film and a resin layer B on the other side, wherein the polyester film contains recycled polyester resin and the resin layer A contains a release agent, and when the amount of charge measured upon peeling the resin layer B from the ceramic green sheet under specified measurement conditions is 16 kV or less.

Description

[Technical Field]

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

[0002] Polyester films, such as polyethylene terephthalate films and polyethylene naphthalate films, are used in a variety of applications because they have excellent properties such as mechanical properties, dimensional stability, flatness, heat resistance, chemical resistance, and optical properties, and also have excellent cost performance.

[0003] Furthermore, polyester films are suitable for various applications, such as release films for forming green sheets for multilayer ceramic capacitors, substrates for releasing interlayer insulating resins, and substrates for dry film resists, taking advantage of the smoothness of the film surface.

[0004] Conventionally, for green sheet molding applications, a release film having a release layer containing a silicone-based release agent on one side of a polyester film has been widely used (Patent Document 1). Furthermore, in order to accommodate applications such as the semiconductor field where contamination with silicon (Si) is undesirable, release films having a release layer using a non-silicone-based release agent have been proposed (Patent Documents 2 and 3). The objective of these documents is to improve the releasability of the release layer from the ceramic green sheet at room temperature or after heat treatment.

[0005] In recent years, as the capacitance of multilayer ceramic capacitors continues to increase, the thickness of ceramic green sheets has also tended to become thinner. In particular, when forming ceramic green sheets with a thickness (after drying) of 2 μm or less, simply reducing the sheet thickness does not make the ceramic green sheets themselves brittle and prone to cracking. Therefore, to ensure ease of handling, measures have been taken to impart appropriate flexibility to the ceramic green sheets themselves by adjusting the composition of the ceramic slurry. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-213590 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-300283 [Patent Document 3] International Publication No. 2022 / 118755 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the inventors have found that when a flexible thin ceramic green sheet is formed using a conventional release film, when the release film is wound into a roll while the thin ceramic green sheet is laminated, and then when the release film is unwound again, the ceramic green sheet may stick to the surface of the film on the side opposite the release surface.

[0008] Therefore, the present invention has been made in consideration of the above-mentioned circumstances, and the problem to be solved is to provide a release film that has excellent winding and unwinding properties, and in which the ceramic green sheets do not stick to the back surface (opposite the release surface) even when the film is wound up in a laminated state with thin ceramic green sheets. [Means for solving the problem]

[0009] Examples of specific embodiments of the present invention are given below.

[0010] [1] A polyester film having a resin layer A on one side and a resin layer B on the other side, The polyester film contains recycled polyester resin, Resin layer A contains a release agent, A release film in which the amount of electrostatic charge measured when peeling the resin layer B from the ceramic green sheet under the following measurement conditions is 16 kV or less; (Measurement conditions) A ceramic green sheet having a thickness of 1.0 μm is formed on resin layer A from a composition containing 39.84 parts by mass of toluene, 39.84 parts by mass of ethanol, 17.65 parts by mass of barium titanate, 1.77 parts by mass of polyvinyl butyral, and 0.90 parts by mass of dioctyl phthalate. The ceramic green sheet and resin layer B are then pressed together at a pressure of 8.2 MPa for 5 hours, and the amount of static electricity is measured when the ceramic green sheet is peeled off from resin layer B; the peel angle when peeling the ceramic green sheet is 90 degrees and the peel speed is 4 cm / sec. [2] The release film according to [1], wherein the resin layer B contains an antistatic agent (C). [3] A polyester film having a resin layer A on one side and a resin layer B on the other side; The polyester film contains recycled polyester resin, Resin layer A contains a release agent, A release film, wherein the resin layer B contains an antistatic agent (C). [4] The release film according to [2] or [3], wherein the antistatic agent (C) is an ion-conductive polymer compound. [5] The release film according to any one of [2] to [4], wherein the antistatic agent (C) is at least one selected from (a1) a polymer in which a compound made of thiophene or a thiophene derivative is doped with another anionic compound, and (a2) a polymer in which a compound made of thiophene or a thiophene derivative has an anionic group and is self-doped. [6] The release film according to any one of [2] to [5], wherein the content of the antistatic agent (C) is 5% by mass or more relative to the total mass of the resin layer B. [7] The release film according to any one of [1] to [6], wherein the resin layer A contains (A) a non-silicone release agent. [8] The release film according to [7], wherein the non-silicone release agent (A) is at least one selected from waxes and compounds containing a long-chain alkyl group. [9] The release film according to any one of [1] to [8], wherein the resin layer B contains (A) a non-silicone release agent.

[10] The release film according to [9], wherein the non-silicone release agent (A) is at least one selected from waxes and compounds containing a long-chain alkyl group.

[11] The release film according to [9] or

[10] , wherein the content of the non-silicone release agent (A) is 5% by mass or more relative to the total mass of the resin layer B.

[12] The release film according to any one of [1] to

[11] , wherein the resin layer B contains a binder resin (B).

[13] The release film according to

[12] , wherein the binder resin (B) is at least one selected from a (meth)acrylic resin and a polyvinyl alcohol.

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

[13] , wherein the resin layer B contains a crosslinking agent (D).

[15] The release film according to

[14] , wherein the crosslinking agent (D) is at least one selected from the group consisting of melamine compounds and oxazoline compounds.

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

[15] , wherein the content of recycled polyester resin relative to the total mass of the resin components in the polyester film is 90 mass % or more.

[17] The release film according to any one of [1] to

[16] , wherein the polyester film has a three-layer structure having a surface layer, an intermediate layer, and a back layer.

[18] The release film according to

[17] , wherein the surface layer contains a chemically recycled polyester resin.

[19] The release film according to

[17] or

[18] , wherein the back surface layer contains a chemically recycled polyester resin.

[20] The release film according to any one of

[17] to

[19] , wherein the intermediate layer contains a polyester resin that is a recycled material.

[21] The release film according to any one of [1] to

[20] , wherein the maximum peak height (Sp) of the resin layer on surface A is 60 nm or less.

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

[21] , wherein the arithmetic mean height (Sa) of the resin layer A side is 5 nm or less.

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

[22] , wherein the thickness of the release film is 9 to 50 μm.

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

[23] , wherein the coefficient of dynamic friction between the resin layer B surface and the resin layer A surface of the release film is 0.2 or less.

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

[24] , which has an air leakage index of 8500 seconds or less.

[26] The release film according to any one of [1] to

[25] , wherein the air leakage index reduction rate calculated by the following formula is 5% or more. Air leakage index reduction rate (%) = 100 - air leakage index of target release film / air leakage index of virgin release film x 100

[27] The release film according to any one of [1] to

[26] , wherein the content of isophthalic acid units is 0.01 to 5 mol % relative to 100 mol % of all dicarboxylic acid units constituting the polyester resin contained in the polyester film.

[28] The release film according to any one of [1] to

[27] , wherein the melting peak temperature (Tm) is 254°C or less.

[29] The release film according to any one of [1] to

[28] , wherein the melting peak heat quantity (ΔHm) is 40 J / g or less.

[30] The gas density is 1.405 g / cm 3

[31] The release film according to any one of [1] to

[30] , wherein the recycled polyester resin is obtained by recycling PET bottles.

[32] The release film according to any one of [1] to

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

[33] A release film with a ceramic green sheet, obtained by laminating a ceramic green sheet on the resin layer A of the release film according to any one of [1] to

[32] .

[34] The release film with a ceramic green sheet according to

[33] , wherein the thickness of the ceramic green sheet (after drying) is 2 μm or less.

[35] A release film with a ceramic green sheet according to

[33] or

[34] , which is used in the manufacturing process of a multilayer ceramic capacitor.

[36] Use of the release film according to any one of [1] to

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

[37] A method for producing a ceramic green sheet, comprising a step of applying a ceramic slurry containing a ceramic component to at least one side of the release film according to any one of [1] to

[32] . [Effects of the Invention]

[0011] According to the present invention, even when thin ceramic green sheets are laminated and wound up, the ceramic green sheets do not stick to the back surface (opposite the release surface), and a release film having excellent winding and unwinding properties can be provided. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view illustrating the configuration of the release film of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Next, an example of an embodiment of the present invention will be described. However, the present invention is not limited to the embodiment described below, and can be implemented with any modifications within the scope of the gist of the present invention. In this specification, when "X to Y" (X and Y are any numbers) is used, unless otherwise specified, it means "X or more and Y or less," and also includes "preferably greater than X" or "preferably less than Y." Furthermore, when "X or more" (X is any number) or "Y or less" (Y is any 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."

[0014] <Release film> A first embodiment of the present invention relates to a release film (hereinafter also referred to as "the present release film") comprising a polyester film (hereinafter also referred to as "the present polyester film") having a resin layer A on one side and a resin layer B on the other side, wherein the polyester film contains a recycled polyester resin and the resin layer A contains a release agent, and when the amount of charge measured at the time of peeling the resin layer B from the ceramic green sheet under the following measurement conditions is 16 kV or less. When measuring the amount of charge, a ceramic green sheet is formed on the resin layer A of the release film under the following conditions, and the resin layer B of the release film is placed on the formed ceramic green sheet so that it is in contact with the ceramic green sheet, and a press treatment is performed, and the amount of charge is then measured. (Measurement conditions) A ceramic green sheet having a thickness of 1.0 μm is formed on resin layer A from a composition containing 39.84 parts by mass of toluene, 39.84 parts by mass of ethanol, 17.65 parts by mass of barium titanate, 1.77 parts by mass of polyvinyl butyral, and 0.90 parts by mass of dioctyl phthalate. The ceramic green sheet and resin layer B are then pressed together at a pressure of 8.2 MPa for 5 hours, and the amount of static electricity is measured when the ceramic green sheet is peeled off from resin layer B; the peel angle when peeling the ceramic green sheet is 90 degrees and the peel speed is 4 cm / sec.

[0015] The charge amount measured under the above measurement conditions may be 16 kV or less, preferably 14 kV or less, more preferably 12 kV or less, even more preferably 10 kV or less, still more preferably 8 kV or less, even more preferably 6 kV or less, still more preferably 4 kV or less, still more preferably 3 kV or less, particularly preferably 2 kV or less, and most preferably 1.5 kV or less. The lower limit of the charge amount is not particularly limited, and may be 0 kV or 0.1 V.

[0016] A second embodiment of the present invention relates to a release film (hereinafter also referred to as "the present release film") comprising a resin layer A on one side of a polyester film (hereinafter also referred to as "the present polyester film") and a resin layer B on the other side, wherein the polyester film contains recycled polyester resin, the resin layer A contains a release agent, and the resin layer B contains an antistatic agent (C).

[0017] As shown in Figure 1, the release film 100 of this embodiment comprises resin layers (hereinafter also referred to as "the present resin layers") formed using a resin composition on both sides of a polyester film 10. Specifically, the present release film is configured to comprise a resin layer A20 on one side of the polyester film 10 and a resin layer B30 on the other side. In this embodiment, the polyester film 10 and the respective resin layers (20, 30) may be laminated so as to be in direct contact with each other, or another layer may be provided between the polyester film 10 and the resin layers (20, 30).

[0018] Because the present release film has the above-described configuration, even when the film is wound up with thin ceramic green sheets stacked thereon, the ceramic green sheets do not stick to the back surface (opposite the release surface), and the film has excellent winding and unwinding properties. In other words, the present release film has excellent anti-sticking properties for ceramic green sheets. Thus, the present release film is suitable for use as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors.

[0019] Furthermore, since the polyester film of this release film contains recycled polyester resin, the air leakage index of the release film can be reduced. As a result, this release film can exhibit appropriate slip properties and improve handleability. For example, a release film with a reduced air leakage index can be easily wound into a roll.

[0020] <<Polyester film>> The polyester film serves as the substrate of the release film. The polyester film contains recycled polyester resin.

[0021] The content of recycled polyester resin relative to the total mass of the resin components in the polyester film is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The upper limit of the recycled polyester resin content in the polyester film is not limited and may be 100% by mass. Because the polyester film can contain a very high proportion of recycled polyester resin, it can also be called a recycled polyester film. Use of such a polyester film can, for example, reduce CO2 emissions and contribute to reducing environmental impact. Furthermore, by setting the recycled polyester resin content within the above range, the smoothness of the polyester film can be improved while imparting the necessary roughness to the polyester film surface, thereby more effectively improving the processability and handleability of the polyester film.

[0022] The polyester film may contain a polyester resin (virgin polyester resin) other than the recycled polyester resin. The content of the polyester resin other than the recycled polyester resin is preferably 50% by mass or less, more preferably 40% by mass or more, even more preferably 30% by mass or more, even more preferably 20% by mass or more, still more preferably 10% by mass or more, and particularly preferably 5% by mass or more, based on the total mass of the resin components in the polyester film. The content of the polyester resin other than the recycled polyester resin may be 0% by mass.

[0023] The maximum peak height (Sp) of at least one surface of the polyester film is preferably 1000 nm or less, more preferably 800 nm or less, even more preferably 500 nm or less, even more preferably 300 nm or less, even more preferably 200 nm or less, even more preferably 150 nm or less, even more preferably 100 nm or less, and particularly preferably 60 nm or less. Furthermore, the maximum peak height (Sp) of at least one surface is preferably 5 nm or more, more preferably 10 nm or more. By keeping the maximum peak height (Sp) of at least one surface within the above range, it is possible to obtain a polyester film with excellent surface smoothness while effectively suppressing the generation of protrusions of unintended sizes on the surface of the polyester film. In this embodiment, it is particularly preferred that the maximum peak height (Sp) of the surface on which the resin layer A is laminated (the surface on which the ceramic green sheet is laminated) be within the above range.

[0024] The arithmetic mean height (Sa) of at least one surface of the polyester film is preferably 15 nm or less, more preferably 10 nm or less, even more preferably 8 nm or less, even more preferably 5 nm or less, and even more preferably 3 nm or less. The arithmetic mean height (Sa) of at least one surface is preferably 0.3 nm or more, more preferably 0.4 nm or more, even more preferably 0.5 nm or more, and particularly preferably 0.6 nm or more. By setting the arithmetic mean height (Sa) of at least one surface to the above upper limit or less, a polyester film with excellent surface smoothness can be obtained. On the other hand, the arithmetic mean height (Sa) of at least one surface is preferably the above lower limit or more, and the surface of the polyester film is preferably provided with a predetermined amount of roughness or more. This provides a rough surface necessary to improve the handleability of the polyester film, thereby reducing the air leakage index of the release film. As a result, the release film can exhibit appropriate slip properties and improve handleability. For example, a release film with appropriate surface roughness can be easily wound into a roll. In this embodiment, it is particularly preferable that the arithmetic mean height (Sa) of the surface on which the resin layer A is laminated (the surface on which the ceramic green sheets are laminated) is within the above range.

[0025] The method for measuring the maximum peak height (Sp) and arithmetic mean height (Sa) of at least one surface of the polyester film is the same as the method for measuring the maximum peak height (Sp) and arithmetic mean height (Sa) of the surface layer, as described below.

[0026] The polyester film may have a single-layer structure or a multi-layer structure. When the polyester film has a multi-layer structure, it may have a two-layer structure, a three-layer structure, or may have four or more layers without departing from the gist of the present invention; the number of layers is not particularly limited. When the polyester film has a multi-layer structure of two or more layers, a two-kind three-layer structure or a three-kind three-layer structure is particularly preferred. In particular, the polyester film preferably has a three-layer structure, and in this case, the polyester film preferably has a three-layer structure having a surface layer, an intermediate layer, and a back layer.

[0027] When the present polyester film is a laminated polyester film having a surface layer, an intermediate layer, and a back layer, all of the surface layer, intermediate layer, and back layer may contain recycled polyester resin. In this embodiment, all of the surface layer, intermediate layer, and back layer may contain chemically recycled polyester resin, or all of the surface layer, intermediate layer, and back layer may contain material recycled polyester resin. In this embodiment, it is also preferable that the surface layer and back layer contain chemically recycled polyester resin, and only the intermediate layer contains material recycled polyester resin. For example, by incorporating a material recycled polyester resin into the intermediate layer, it becomes easy to form fine irregularities in the intermediate layer, and these irregularities propagate to the surface layer, thereby easily forming irregularities that satisfy predetermined conditions in the surface layer while maintaining the smoothness of the surface layer. As a result, the air leakage index of the present release film can be reduced, and the handleability of the release film can be more effectively improved. When incorporating a material recycled polyester resin into the intermediate layer, the degree of propagation of the irregularities in the intermediate layer may be controlled, for example, by appropriately adjusting the thickness of the surface layer.

[0028] The polyester film may be a non-stretched film (sheet) or a stretched film. Among these, the polyester film is preferably a uniaxially or biaxially stretched film. Among these, a biaxially stretched film is more preferred because of its excellent balance of mechanical properties and flatness.

[0029] The total thickness of the polyester film is not particularly limited as long as it is within a range that allows film formation, but is preferably 9 μm or more, more preferably 10 μm or more, and even more preferably 12 μm or more from the viewpoints of mechanical strength, handleability, productivity, etc. The total thickness of the polyester film is preferably 50 μm or less, more preferably 45 μm or less, and even more preferably 42 μm or less.

[0030] (recycled polyester resin) Examples of dicarboxylic acid components that constitute the recycled polyester resin 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.

[0031] Examples of diol components that make up the recycled polyester resin 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.

[0032] When the recycled polyester resin is a homopolyester, it preferably contains structural units derived from an aromatic dicarboxylic acid component and structural units derived from an aliphatic glycol. In this case, examples of aromatic dicarboxylic acids include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of aliphatic glycols include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN), with PET being preferred. Furthermore, examples of recycled polyester resins 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.

[0033] On the other hand, when the recycled polyester resin 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 selected from the group consisting 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 selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol.

[0034] 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 type of recycled raw material, the mode of polycondensation, and other factors. In this specification, 5 mol% or less of diethylene glycol is defined as by-product diethylene glycol, and by-product diethylene glycol is also considered to be included in ethylene glycol and is distinguished from copolymerization components. 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.

[0035] The content of isophthalic acid units relative to 100 mol% of all dicarboxylic acid units constituting the polyester resin contained in the polyester film 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 recycled polyester resin will contain isophthalic acid units within the above range. If the content of isophthalic acid units in the polyester film is equal to or greater than the above lower limit, the flexibility of the polyester film formed from the recycled polyester resin can be improved, making it easier to obtain a polyester film with excellent surface smoothness. On the other hand, if the content of isophthalic acid units is equal to or less than the above upper limit, the gas density of the polyester film can be increased. As a result, even when a thin-film ceramic green sheet is laminated on a release film and then wound up, adhesion of the ceramic green sheet to the back surface (opposite the release surface) can be suppressed, effectively improving winding and unwinding properties. Furthermore, when the polyester 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 polyester film has the advantage that burrs and chips are less likely to be generated when the film is cut with a cutting blade to peel off the ceramic green sheet laminated on the support.

[0036] The recycled polyester resin is obtained by recycling (regenerating) polyester, which is a recycled raw material. The recycled raw material may be, for example, polyester derived from polyester containers (e.g., PET bottles) or polyester derived from polyester films (e.g., processing films). The recycled raw material may also be polyester recovered from the process of producing polyester films or PET bottles without being used as a product. In particular, the recycled polyester resin used in this embodiment is preferably obtained by recycling PET bottles.

[0037] In this specification, polyester (recycled raw material) recovered in the process of producing polyester film or PET bottles is referred to as "self-recovered polyester" or "in-situ recycled polyester." For example, polyester film recovered in the process of producing polyester film used as a support (substrate) for ceramic green sheets in the process of producing multilayer ceramic capacitors can be used as a recycled raw material.

[0038] The self-recovery polyester or in-situ recycled polyester may contain particles. When particles are contained, the particle content is preferably 10 ppm or more by mass, more preferably 20 ppm or more, even more preferably 30 ppm or more, even more preferably 40 ppm or more, and particularly preferably 50 ppm or more. On the other hand, the particle content is preferably 500 ppm or less, more preferably 400 ppm or less, even more preferably 350 ppm or less, even more preferably 300 ppm or less, even more preferably 250 ppm or less, and particularly preferably 200 ppm or less.

[0039] Self-recovery polyester and in-situ recycled polyester use film scraps and film waste generated in the company's own factory, etc., so that the characteristics of the polyester raw material, such as the state of granular matter such as gel, the particle content, intrinsic viscosity, raw material catalyst type, etc., can be accurately determined, making it easier to achieve more stable quality of the obtained film. From this perspective, the use of self-recovery polyester and in-situ recycled polyester is also preferred.

[0040] In this embodiment, a biomass-derived raw material may be used for the polyester, which is the recycled raw material for the recycled polyester resin. In this case, it is preferable that the diol component of the polyester is a biomass-derived raw material. The 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.

[0041] The recycled polyester resin may be a material recycled polyester resin obtained by material recycling of recycled polyester, or may be a chemically recycled polyester resin obtained by chemically recycling recycled polyester. In this embodiment, all of the surface layer, intermediate layer, and back layer may contain a chemically recycled polyester resin, or all of the surface layer, intermediate layer, and back layer may contain a material recycled polyester resin. In particular, in this embodiment, it is preferable that the surface layer and back layer contain a chemically recycled polyester resin. By including a chemically recycled polyester resin in the surface layer and back layer, even when the thin-film ceramic green sheet is wound up in a state where it is laminated on a release film, it is possible to prevent the ceramic green sheet from sticking to the back surface (the surface opposite the release film), and it is possible to effectively improve winding and unwinding properties.

[0042] <<Chemical recycled polyester>> Chemically recycled polyester can be used as the recycled polyester resin. One method for producing chemically recycled polyester resin is to sort, crush, and wash collected PET bottles and polyester films to remove foreign matter, then depolymerize them to break them down into raw materials or intermediate raw materials for polyester resin, purify them, and then repolymerize these raw materials. A feature of chemically recycled polyester resin is that foreign matter and other materials are removed during the depolymerization / repolymerization process, allowing it to be recycled into high-quality polyester resin.

[0043] Depolymerization can be achieved by adding glycol (e.g., ethylene glycol (EG)) to the resin in the presence of a catalyst to convert it back to bishydroxyethyl terephthalate (BHET), an intermediate raw material used in resin production, which is then purified and repolymerized into PET. Alternatively, polyethylene terephthalate is heated 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 polymerized again. In particular, the present embodiment preferably employs a method in which depolymerization to bishydroxyethyl terephthalate (BHET) is followed by repolymerization into PET. Alternatively, the present embodiment also preferably employs a method in which the depolymerized bishydroxyethyl terephthalate (BHET) is subjected to a transesterification reaction with methanol to obtain dimethyl terephthalate (DMT), and then the DMT is polycondensed with a diol component to obtain a repolymerized polyester.

[0044] In this specification, chemically recycled polyester resin (chemically recycled polyester) refers to a polyester resin 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, and the content of structural units derived from monomers obtained by depolymerization contained in the chemically recycled polyester may be 100 mol%.

[0045] When polyester, which is a recycled raw material, is depolymerized to bishydroxyethyl terephthalate (BHET) and then repolymerized to PET, the process for obtaining a chemically recycled polyester resin includes, for example, the following steps. (1) The process of crushing the recovered polyester (2) A process to remove polymer components other than polyester and foreign substances (3) A process in which the ground polyester is introduced into glycol containing a depolymerization catalyst to depolymerize it, thereby obtaining bishydroxyethyl terephthalate (BHET). (4) Solid-liquid separation process, concentration process and / or purification process of bishydroxyethyl terephthalate (BHET) (5) A step of polycondensing bishydroxyethyl terephthalate (BHET) in the presence of a polycondensation catalyst

[0046] When polyester is depolymerized to bishydroxyethyl terephthalate (BHET), dimethyl terephthalate (DMT) is obtained, and then DMT and a diol component are polycondensed, the process for obtaining a chemically recycled polyester resin includes, for example, the following steps. (1') A process for crushing the recovered polyester (2') A process for removing polymer components other than polyester and foreign substances (3') A step of obtaining bishydroxyethyl terephthalate (BHET) by adding the pulverized polyester to glycol containing a depolymerization catalyst and depolymerizing it. (4') Solid-liquid separation process, concentration process and / or purification process of bishydroxyethyl terephthalate (BHET) (5') A step of mixing bishydroxyethyl terephthalate (BHET) with methanol to carry out an ester exchange reaction. (6') Solid-liquid separation process, concentration process and / or purification process of dimethyl terephthalate (DMT) (7') A step of polycondensing dimethyl terephthalate (DMT) and a diol component in the presence of a polycondensation catalyst

[0047] In the above step (1) or (1'), the recovered polyester is washed as necessary and then pulverized into flakes. The pulverization may be performed in water, or the washing step and the pulverization step may be performed simultaneously. The washing step may include alkaline washing or neutral washing.

[0048] In the above step (2) or (2'), polymer components other than polyester (e.g., nylon, polyethylene, polypropylene, polyvinyl chloride, etc.) contained in the pulverized material are removed. For example, methods such as air separation, flotation separation, and centrifugation can be used to remove these polymers. Furthermore, before or after these steps, a foreign matter removal step using a physical or chemical separation method may be performed. Furthermore, a decolorization step may be performed before or after these steps.

[0049] In the above-mentioned process (3) or (3'), bishydroxyethyl terephthalate (BHET) is obtained by adding the ground polyester to glycol containing a depolymerization catalyst and depolymerizing it. Depolymerization using an excess of glycol results in a mixed solution of crude BHET and crude ethylene glycol. Ethylene glycol (EG), 1,3-propanediol, or 1,4-butanediol (BG) is preferred as the glycol, with ethylene glycol (EG) being particularly preferred. In the above-mentioned process (3) or (3'), the ground polyester may be melted and simultaneously hydrolyzed to obtain a polyethylene terephthalate melt with a low degree of polymerization, followed by depolymerization.

[0050] In the above step (3) or (3'), it is preferable to add 0.1 to 50 parts by mass of ethylene glycol (EG) based on the total mass of the ground polyester. The reaction is preferably carried out, for example, at 150 to 260°C under a pressure of 0.1 to 0.5 MPa.

[0051] Examples of the depolymerization catalyst include sodium carbonate, sodium carboxylate, manganese acetate, zinc acetate, etc. The amount of the catalyst used for depolymerization to be added is not particularly limited, but is preferably 0.01 to 10% by mass, for example, relative to the total mass of the recycled raw material.

[0052] Depolymerization may be carried out in the presence of an alkaline compound. Examples of alkaline compounds include tetraethylammonium hydroxide (EAH), potassium hydroxide (KOH), calcium hydroxide, and sodium hydroxide. Among these, tetraethylammonium hydroxide is preferred. By adding an alkaline compound together with glycol in the depolymerization step, the production of by-products such as diethylene glycol (DEG) in the depolymerization reaction can be suppressed. This reduces the DEG content in the polymer polymerized using the low-molecular-weight polymers obtained by depolymerization, thereby improving the polymer quality.

[0053] In the above process (4) or (4'), bishydroxyethyl terephthalate (BHET) undergoes a solid-liquid separation process, a concentration process, and / or a purification process. In the solid-liquid separation process, the ethylene glycol component and the like are removed from the crude BHET to obtain concentrated BHET. After the depolymerization reaction, the two-component mixture of crude BHET and crude ethylene glycol is cooled and filtered to remove solid impurities. Further, adsorption and ion exchange treatments may be performed to remove colored substances and dissolved ions. After the solid-liquid separation process, the two-component mixture of crude BHET and crude ethylene glycol is preferably subjected to distillation or evaporation to separate and distill off the ethylene glycol to obtain concentrated BHET. Alternatively, the two-component mixture may be cooled to 10°C or below to crystallize BHET, followed by solid-liquid separation of the 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. High-purity purified BHET is obtained in this manner. The purified BHET may contain oligomers in addition to BHET.

[0054] In the above step (5), purified BHET is charged into a melt polycondensation reactor to obtain a repolymerized polyester. The polymerization reaction of BHET is preferably carried out at 200 to 300°C and under a pressure of 0.01 to 0.5 MPa. After the polymerization step, a solid-state polymerization step may be provided to adjust the degree of polymerization, as needed.

[0055] Examples of the polycondensation catalyst used in step (5) include antimony compounds, germanium compounds, aluminum compounds, titanium compounds, phosphorus compounds, magnesium compounds, etc. Among these, it is preferable to use at least one selected from antimony compounds, titanium compounds, magnesium compounds, and phosphorus compounds, it is more preferable to use antimony compounds or titanium compounds, and it is even more preferable to use titanium compounds. By using such compounds, particularly titanium compounds, as the polycondensation catalyst, it is possible to reduce the amount of polycondensation catalyst added, which makes it easier to suppress the formation of foreign matter or protrusions derived from the polycondensation catalyst.

[0056] In the above step (5'), bishydroxyethyl terephthalate (BHET) and methanol are mixed and subjected to a transesterification reaction to obtain dimethyl terephthalate (DMT). The transesterification reaction is preferably carried out at 100 to 250°C under a pressure of 0.01 to 0.5 MPa. Examples of the transesterification catalyst include sodium carbonate, magnesium acetate, manganese acetate, and zinc acetate. The amount of the catalyst used for the transesterification is not particularly limited, but is preferably 0.01 to 10% by mass, for example, relative to the total mass of bishydroxyethyl terephthalate (BHET).

[0057] In the above step (6'), dimethyl terephthalate (DMT) obtained by the transesterification reaction is subjected to a solid-liquid separation step, a concentration step, and / or a purification step. This preferably results in purified DMT being obtained from crude DMT. The solid-liquid separation step, concentration step, and / or purification step can be appropriately selected from the same operations as in the above step (4) or (4').

[0058] In the above (7'), dimethyl terephthalate (DMT) and a diol component are polycondensed in the presence of a polycondensation catalyst, and the purified DMT and the diol component are charged into a melt polycondensation reactor to obtain a repolymerized polyester. As the diol component, ethylene glycol (EG), 1,3-propanediol, or 1,4-butanediol (BG) is preferably used, and among these, ethylene glycol (EG) is particularly preferred.

[0059] Examples of the polycondensation catalyst used in step (7') include antimony compounds, germanium compounds, aluminum compounds, titanium compounds, phosphorus compounds, magnesium compounds, etc. Among these, it is preferable to use at least one selected from antimony compounds, titanium compounds, magnesium compounds, and phosphorus compounds, it is more preferable to use antimony compounds or titanium compounds, and it is even more preferable to use titanium compounds. By using such compounds, particularly titanium compounds, as the polycondensation catalyst, it is possible to reduce the amount of polycondensation catalyst added, which makes it easier to suppress the formation of foreign matter or protrusions derived from the polycondensation catalyst.

[0060] The polymerization reaction of dimethyl terephthalate (DMT) and the diol component is preferably carried out, for example, at 200 to 300°C under a pressure of 0.01 to 0.5 MPa. After the polymerization step, a solid-phase polymerization step may be provided to adjust the degree of polymerization, as needed.

[0061] The glycol used in the depolymerization step can be reused and may be circulated within the process or in the repolymerization step.

[0062] <<Material: Recycled Polyester>> Material recycled polyester can be used as the recycled polyester resin. In material recycling, collected used PET bottles and polyester films are first crushed into flakes. These flakes often contain foreign matter, so they are preferably washed, and alkaline washing is more preferable.

[0063] In the process of pelletizing the flakes, an extruder is used to melt, extrude, cool, and granulate the flakes. In the melting process in the extruder, melt kneading is usually carried out at 260 to 300°C. It is preferable that the flakes are sufficiently dried in advance. In addition, the extruder preferably has at least one vacuum vent in the resin melting zone as a degassing means.

[0064] 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.

[0065] 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.

[0066] In addition, during the process of cleaning recovered PET bottles and polyester film, or during the process of melting these raw materials, some of the polyester may be hydrolyzed by the cleaning components or heat, resulting in a decrease in the degree of polymerization of the recycled polyester resin. Depending on the intended use, a decrease in the degree of polymerization may result in poor moldability, strength, transparency, heat resistance, and other properties. To restore the decreased degree of polymerization, a solid-state polymerization process may be performed. 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.

[0067] <<Others>> In this embodiment, a recycled polyester resin with a low oligomer content may be used to suppress the amount of precipitation of oligomer components. Various known methods can be used to produce recycled polyester resins with a low oligomer content, such as a method of solid-state polymerization after polyester production. Furthermore, the polyester may be obtained by esterification or transesterification, followed by melt polycondensation at a higher reaction temperature under reduced pressure.

[0068] 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 recycled polyester resin as needed.

[0069] The recycled polyester resin may further contain a metal component. The metal component may be a metal used as a polycondensation catalyst when producing polyester, which is the recycled raw material for the recycled polyester resin. That is, the polyester film may contain a polycondensation catalyst used when producing the polyester to be recycled (regenerated). Examples of metal components 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.

[0070] For example, the compounds contained in the polyester film may vary depending on the type of recycled raw material used. For example, because polyester containers such as PET bottles come into direct contact with food, the polycondensation catalysts used in their manufacturing process are limited, and harmful metal elements such as cadmium, palladium, and selenium are generally not detected. Therefore, if cadmium, palladium, and selenium are detected, it can be assumed that polyester food containers were not used as recycled raw materials.

[0071] <<Physical properties of recycled polyester resin>> The intrinsic viscosity of the recycled polyester resin is preferably 0.45 dL / g or more, more preferably 0.5 dL / g or more, even more preferably 0.55 dL / g or more, and even more preferably 0.6 dL / g or more. The viscosity 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 0.8 dL / g or less, and particularly preferably 0.75 dL / g or less. By setting the intrinsic viscosity of the recycled polyester resin to the above-mentioned lower limit or higher, stability during film formation can be improved. On the other hand, by setting the intrinsic viscosity to the above-mentioned upper limit or lower, it is preferable because it is easier to prevent excessive pressure buildup in the film-forming extruder and to easily reduce the thermal shrinkage rate of the film. The intrinsic viscosity of the recycled polyester resin is measured by precisely weighing 1 g of polyester resin, dissolving it in 100 mL of a 50 / 50 (mass ratio) phenol / tetrachloroethane solvent, and measuring the viscosity (IV) at 30° C. The intrinsic viscosity of the polyester film may also be within the above range.

[0072] When the recycled polyester resin is 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.

[0073] When the recycled polyester resin is derived from 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.

[0074] <Surface layer> The polyester film is preferably a laminated polyester film having a surface layer, an intermediate layer, and a back layer. When the polyester 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. In the manufacturing process of a multilayer ceramic capacitor, a resin layer A (release layer) is formed on the surface layer, and then the ceramic green sheets are laminated.

[0075] The maximum peak height (Sp) of the surface layer is preferably 1000 nm or less, more preferably 800 nm or less, even more preferably 500 nm or less, even more preferably 300 nm or less, even more preferably 200 nm or less, even more preferably 150 nm or less, even more preferably 100 nm or less, and particularly preferably 60 nm or less. The lower limit of the maximum peak height (Sp) of the surface layer is not particularly limited, but the maximum peak height (Sp) of the surface layer is preferably, for example, 5 nm or more, and more preferably 10 nm or more. By keeping the maximum peak height (Sp) of the surface layer within the above range, it is possible to effectively prevent protrusions of unintended sizes from occurring on the surface of the polyester film, and a polyester film with excellent surface smoothness can be obtained.

[0076] The arithmetic mean height (Sa) of the surface layer is preferably 15 nm or less, more preferably 10 nm or less, even more preferably 8 nm or less, even more preferably 5 nm or less, and even more preferably 3 nm or less. The arithmetic mean height (Sa) of the surface layer is preferably 0.3 nm or more, more preferably 0.4 nm or more, even more preferably 0.5 nm or more, and particularly preferably 0.6 nm or more. By setting the arithmetic mean height (Sa) of the surface layer to the above upper limit or less, a polyester film with excellent surface smoothness can be obtained. On the other hand, the arithmetic mean height (Sa) of the surface layer is preferably the above lower limit or more, and it is preferable that a predetermined amount of roughness or more is imparted. This provides a rough surface necessary to improve the handleability of the polyester film, and the air leakage index of the release film can be reduced. As a result, the release film can exhibit appropriate slip properties and improve handleability. For example, a release film with appropriate surface roughness can be easily wound into a roll.

[0077] 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 lines), and is calculated by dividing the volume of the area enclosed by the surface shape curve and the mean surface by the measured area, and is 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), it can be expressed as in the following formula (1).

[0078]

number

[0079] 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).

[0080]

number

[0081] The arithmetic mean height (Sa) and maximum peak height (Sp) can be easily adjusted by, for example, 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 amount of recycled polyester resin, which is useful for adjusting surface properties. They can also be controlled by appropriately blending particulate matter or additives into the surface layer and / or intermediate layer. For example, they can be adjusted by appropriately incorporating particles. They can be adjusted by adjusting the amount of particles used, taking into account the type, composition, average particle size, particle size distribution, hardness, affinity with the polyester, etc. Adjusting the type and amount of particles, taking into account the type of polyester used, such as its composition, viscosity, molecular weight, thermal properties, and the presence or absence of copolymerization components, is also useful for adjusting surface properties. When two or more types of particles are used in combination, it is preferable to adjust the amount of particles used, taking into account the type of particles and polyester. In addition, when adjusting the arithmetic mean height (Sa) and maximum peak height (Sp), it is also effective to control, during the production of the polyester film, for example, the stretching ratio (in the case of biaxial stretching, the longitudinal and transverse stretching ratios), the stretching temperature, the heat treatment temperature and treatment time (in the case of biaxial stretching, the heat treatment temperature and treatment time, particularly after transverse stretching).

[0082] The thickness of the surface layer is preferably greater than 1 μm, more preferably 1.2 μm or greater, even more preferably 1.5 μm or greater, even more preferably 2 μm or greater, even more preferably 2.5 μm or greater, and particularly preferably 3 μm or greater. 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 9 μm or less, even more preferably 8 μm or less, even more preferably 7 μm or less, and particularly preferably 6 μm or less. By making the thickness of the surface layer greater than or equal to the above-mentioned lower limit, it becomes easier to control the maximum peak height (Sp) of the polyester film within the desired range, thereby improving surface smoothness. For example, when the intermediate layer contains recycled polyester resin, the degree of propagation of the unevenness of the intermediate layer can be controlled by appropriately adjusting the thickness of the surface layer.

[0083] In order to control the maximum peak height (Sp) of the surface layer within the desired range and more effectively improve the surface smoothness, the thickness of the surface layer is preferably 6 to 40% of the total thickness of the polyester film, more preferably 7 to 32%, even more preferably 8 to 28%, and even more preferably 9 to 24%.

[0084] The surface layer may or may not contain particles. When the surface 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. Among these, alumina, silica, calcium carbonate, and organic particles are preferred.

[0085] The shape of the particles in the surface layer is not particularly limited, and any of spherical, blocky, rod-like, flat, etc. may be used. There are also no particular limitations on the hardness, specific gravity, color, etc. Two or more types of these particles may be used in combination as needed.

[0086] When particles are contained in the surface layer, the average particle size of the particles contained 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 contained is preferably 1 μm or less, more preferably 0.8 μm or less, even more preferably 0.6 μm or less, still more preferably 0.4 μm or less, and particularly preferably 0.2 μm or less.

[0087] In the case of powder particles, the average particle size can be determined by measuring the powder using a centrifugal sedimentation particle size distribution analyzer (e.g., Shimadzu Corporation's "SA-CP3 Model") 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) to measure their diameters and calculating the average value. In this case, for non-spherical particles, the average of the longest and shortest diameters can be measured as the diameter of each particle.

[0088] 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.

[0089] In this embodiment, it is also preferable that the surface layer contains substantially no particles. The surface layer contains substantially no particles, which eliminates the risk of coarse protrusions due to particle aggregation or foreign matter or process contamination due to particle shedding. The phrase "substantially does not contain particles" means that particles are not intentionally contained, 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. Because this polyester film contains recycled polyester resin, it is possible to impart appropriate unevenness to the surface of the polyester film without adding particles to the surface layer.

[0090] The content of recycled polyester resin in the surface layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the total mass of the resin components contained in the surface layer. The content of recycled polyester resin in the surface layer is most preferably 100% by mass.

[0091] The surface layer contains a recycled polyester resin, and the recycled polyester resin may be a material recycled polyester resin or a chemically recycled polyester resin. In particular, the recycled polyester resin that can be contained in the surface layer is preferably a chemically recycled polyester resin. 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). By incorporating a chemically recycled polyester resin into the surface layer, even when a thin-film ceramic green sheet is wound up in a laminated state on a release film, adhesion of the ceramic green sheet to the back surface (opposite the release film) can be suppressed, effectively improving winding and unwinding properties. Furthermore, by incorporating a chemically recycled polyester resin into the surface layer, the surface smoothness of the polyester film can be more effectively improved, facilitating the thinning of the ceramic green sheet.

[0092] <Middle class> The polyester film is preferably a laminated polyester film having a surface layer, an intermediate layer, and a back layer, and in this case, the intermediate layer preferably functions as the thickest main layer in the polyester film. Like the surface layer, the intermediate layer also preferably contains a recycled polyester resin.

[0093] 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, still 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.

[0094] The thickness of the intermediate layer is preferably 50 to 93% of the total thickness of the 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%.

[0095] 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.

[0096] When particles are contained in the intermediate layer, the particle content is preferably 10 ppm or more, more preferably 20 ppm or more, even more preferably 30 ppm or more, still more preferably 40 ppm or more, and particularly preferably 50 ppm or more by mass, while the particle content is preferably 500 ppm or less, more preferably 400 ppm or less, even more preferably 350 ppm or less, still more preferably 300 ppm or less, even more preferably 250 ppm or less, and particularly preferably 200 ppm or less.

[0097] The recycled polyester resin content in the intermediate layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The recycled polyester resin content in the intermediate layer is most preferably 100% by mass.

[0098] The intermediate layer contains a recycled polyester resin, and the recycled polyester resin may be a material recycled polyester resin made from recycled raw materials, or may be a chemically recycled polyester resin made from recycled raw materials. Of these, the recycled polyester resin that can be contained in the intermediate layer is preferably a material recycled polyester resin made from recycled raw materials. The recycled (regenerated) polyester may be, for example, a polyester derived from a polyester container (e.g., PET bottles) or a polyester film (e.g., processing film). By incorporating a recycled polyester resin into the intermediate layer, it becomes easy to form fine irregularities in the intermediate layer. These irregularities propagate to the surface layer, thereby easily forming irregularities that satisfy predetermined conditions in the surface layer while maintaining the smoothness of the surface layer. As a result, the air leakage index of the release film can be reduced, and the handleability of the release film can be more effectively improved.

[0099] <Backing layer> The polyester film is preferably a laminated polyester film having a surface layer, an intermediate layer, and a back layer, and in this case, the back layer is a layer disposed on the side opposite to the side on which the ceramic green sheet is laminated. Like the surface layer and the intermediate layer, the back layer is also preferably a layer containing recycled polyester resin.

[0100] In this embodiment, the maximum peak height (Sp) of the back layer is preferably 2500 nm or less, more preferably 2000 nm or less, even more preferably 1800 nm or less, even more preferably 1600 nm or less, even more preferably 1400 nm or less, and particularly preferably 1200 nm or less. The maximum peak height (Sp) of the back layer is preferably 10 nm or more, more preferably 20 nm or more, even more preferably 30 nm or more, even more preferably 40 nm or more, even more preferably 50 nm or more, and particularly preferably 60 nm or more. By setting the maximum peak height (Sp) of the back layer to the above upper limit or less, it is possible to prevent the unevenness caused by minute protrusions on the back layer from being transferred to the front layer when the polyester film is laminated or wound into a roll. On the other hand, by setting the maximum peak height (Sp) of the back layer to the above lower limit or more, the necessary roughness is provided on the back surface of the polyester film, improving the handleability of the polyester film.

[0101] The arithmetic mean height (Sa) of the back surface layer is preferably 100 nm or less, more preferably 80 nm or less, even more preferably 60 nm or less, even more preferably 40 nm or less, even more preferably 30 nm or less, and particularly preferably 25 nm or less. The arithmetic mean height (Sa) of the back surface layer is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. By setting the arithmetic mean height (Sa) of the back surface layer to the upper limit or less, it is possible to prevent the unevenness of the back surface layer from being transferred to the front surface layer. On the other hand, by setting the arithmetic mean height (Sa) of the back surface layer to the lower limit or more, a rough surface necessary for improving the handleability of the polyester film is provided, thereby improving the handleability of the polyester film. For example, when the polyester film is wound into a roll, the polyester film can exhibit appropriate slip properties, making it easy to wind into a roll.

[0102] The back surface layer may not contain particles, but may contain particles. The presence of particles in the back surface layer can provide slipperiness and prevent scratches during each process. Furthermore, the presence of particles in the back surface layer makes it easier to control the arithmetic mean height (Sa) and maximum peak height (Sp) within desired ranges. Furthermore, the arithmetic mean height (Sa) and maximum peak height (Sp) of the back surface layer may be controlled within desired ranges by applying a surface treatment or coating to the back surface layer.

[0103] 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.

[0104] In this embodiment, it is also a preferred embodiment that the back surface layer contains both organic and inorganic particles, which makes it easy to control the arithmetic mean height (Sa) and maximum peak height (Sp) of the back surface layer within desired ranges.

[0105] 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.

[0106] 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 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 height (Sa) and maximum peak height (Sp) within the desired range. Setting the average particle size within the above range also keeps haze low, making it easier to ensure transparency for the polyester film as a whole.

[0107] In the case of powder particles, the average particle size can be determined by measuring the powder using a centrifugal sedimentation particle size distribution analyzer (e.g., Shimadzu Corporation's "SA-CP3 Model") 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) to measure their diameters and calculating the average value. In this case, for non-spherical particles, the average of the longest and shortest diameters can be measured as the diameter of each particle.

[0108] The particle content of the back layer is preferably 200 ppm or more, more preferably 1000 ppm or more, and even more preferably 1500 ppm or more, based on the total mass of the back layer. Furthermore, the particle content 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, based on the total mass of the back layer. When two or more types of particles are blended in the back layer, the total particle content is preferably within the above range.

[0109] 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.

[0110] 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.

[0111] The thickness of the back layer is preferably 1 to 20% of the total thickness of the 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%.

[0112] The content of recycled polyester resin in the back surface layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the total mass of the resin components contained in the back surface layer. The content of recycled polyester resin in the back surface layer is most preferably 100% by mass.

[0113] The back surface layer contains a recycled polyester resin, and the recycled polyester resin may be a material recycled polyester resin or a chemically recycled polyester resin. In particular, the recycled polyester resin that can be contained in the back surface layer is preferably a chemically recycled polyester resin. The recycled (regenerated) polyester may be, for example, a polyester derived from a polyester container (e.g., PET bottles) or a polyester film (e.g., processing film). By including a chemically recycled polyester resin in the back surface layer, even when a thin-film ceramic green sheet is wound up in a state in which it is laminated on a release film, adhesion of the ceramic green sheet to the back surface (opposite the release film) can be suppressed, effectively improving winding and unwinding properties. Furthermore, by including a chemically recycled polyester resin in the back surface layer, the surface smoothness of the polyester film can be more effectively improved.

[0114] <Polyester film manufacturing method> The method for producing a polyester film includes a step of feeding a polyester resin containing a recycled polyester resin into an extruder, melting the polyester resin, and then extruding the melted polyester resin.

[0115] When the polyester film of this embodiment is a laminated polyester film having a surface layer, an intermediate layer, and a back layer, the manufacturing method of the laminated polyester film includes a step of laminating a polyester layer A constituting the surface layer, a polyester layer B constituting the intermediate layer, and a polyester layer C constituting the back layer. In this case, at least one of the polyester layers A, B, and C contains a recycled polyester resin. Alternatively, the manufacturing method of the laminated polyester film of this embodiment includes a step of supplying 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 to respective extruders, melting them, and then co-extruding them. In this case, at least one of the polyester resins A, B, and C contains a recycled polyester resin. In each extruder, the respective polymers are heated to or above their melting points to form molten polymers. 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 polyester film.

[0116] In this embodiment, a step of stretching an unstretched polyester film may be provided. In the stretching step, the unstretched 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.

[0117] 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 polyester film is obtained. The heat setting treatment may be carried out in two or more steps at different temperatures. Furthermore, 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 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.

[0118] <<Resin layer>> This release film has resin layers formed from a resin composition on both sides of a polyester film. Here, the "resin" in the resin composition refers to the main component involved in film formation. More specifically, the "resin" also includes (A) a release agent, (B) a binder resin, and (C) an antistatic agent, which will be described later.

[0119] This release film has a structure in which a resin layer A is provided on one side of a polyester film and a resin layer B is provided on the other side. Resin layer A is made of resin composition A, and resin layer B is made of resin composition B.

[0120] The thickness of the resin layer A is preferably 1 nm or more, more preferably 3 nm or more, even more preferably 6 nm or more, and particularly preferably 10 nm or more, and is preferably 100 nm or less, more preferably 80 nm or less, even more preferably 60 nm or less, and particularly preferably 40 nm or less.

[0121] The thickness of the resin layer B is preferably 1 nm or more, more preferably 3 nm or more, even more preferably 6 nm or more, and particularly preferably 10 nm or more, and is preferably 100 nm or less, more preferably 80 nm or less, even more preferably 60 nm or less, and particularly preferably 40 nm or less.

[0122] <<Resin layer B / resin composition B>> The resin layer B preferably contains an antistatic agent (C) and further contains a release agent (A).

[0123] The total content of the (A) release agent and (C) antistatic agent that may be contained in the resin layer B is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, based on the total mass of the resin layer B. The total content of the (A) release agent and (C) antistatic agent that may be contained in the resin layer B is preferably 90% by mass or less, more preferably 80% by mass or less, and may be 70% by mass or less, or may be 60% by mass or less. When the total content is within this range, it becomes easy to control the amount of charge at the time of peeling the resin layer B and the ceramic green sheet to a predetermined value or less, and the ability to prevent the ceramic green sheet from sticking to the resin layer B is easily exhibited.

[0124] ((A) Mold release agent) The resin layer B preferably contains a release agent (A). The release agent (A) is not particularly limited, and for example, a silicone-based release agent or a non-silicone-based release agent can be used. In particular, the resin layer B preferably contains a non-silicone-based release agent. By using a non-silicone-based release agent, it can be preferably used in applications where contamination with silicon (Si) elements is undesirable, such as in the semiconductor field.

[0125] 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.

[0126] 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.

[0127] Examples of non-silicone release agents include wax, long-chain alkyl group-containing compounds, fluorine compounds, etc. Among these, the (A) release agent is preferably at least one selected from wax and long-chain alkyl group-containing compounds, and more preferably a long-chain alkyl group-containing compound from the viewpoint of preventing sticking of the ceramic green sheet.

[0128] The waxes include natural waxes, synthetic waxes, and modified waxes. Natural waxes include vegetable waxes, animal waxes, mineral waxes and petroleum waxes. Examples of vegetable waxes include candelilla wax, carnauba wax, rice wax, Japan wax, and jojoba oil. Animal waxes include beeswax, lanolin, and spermaceti. Examples of mineral waxes include montan wax, ozokerite, and ceresin. Petroleum waxes include paraffin wax, microcrystalline wax, and petrolatum. Synthetic waxes include synthetic hydrocarbons, modified waxes, hydrogenated waxes, fatty acids, acid amides, amines, imides, ester waxes and ketones.

[0129] 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 the alkyl group 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 in 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.

[0130] 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.

[0131] By including the release agent (A) in the resin layer B, the water- and / or oil-repellent properties of the release agent can enhance the anti-sticking properties of the ceramic green sheet. Furthermore, in this embodiment, by using the antistatic agent (C) in combination, it is possible to more effectively prevent the ceramic green sheet from sticking to the resin layer B, which is thought to be caused by electrostatic charge when the ceramic green sheet is peeled off.

[0132] The content of the (A) release agent in the resin layer B is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, based on the total mass of the resin layer B. The content of the (A) release agent in the resin layer B is preferably 90% by mass or less, more preferably 70% by mass or less, and even more preferably 50% by mass or less. By setting the content of the (A) release agent within the above range, the ability to prevent the ceramic green sheet from sticking to the resin layer B can be more effectively improved.

[0133] ((B) Binder resin) The resin layer B preferably further contains a binder resin (B), which can improve the coatability of the resin composition B when it is used as a coating liquid.

[0134] The binder resin selected as the (B) binder resin is preferably 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), and also having film-forming properties. There are no particular limitations on such binder resins, and conventionally known binder resins can be used. Examples include (meth)acrylic resins, polyvinyl alcohol, polyester resins, and polyurethane resins. Among these, from the viewpoint of high hydrophilicity and film formation, the (B) binder resin is preferably at least one selected from (meth)acrylic resins and polyvinyl alcohols, and more preferably a (meth)acrylic resin. Note that the (B) binder resin may be used alone or in combination of two or more.

[0135] ((Meth)acrylic resin) (Meth)acrylic resins are polymers made of polymerizable monomers including acrylic and methacrylic monomers. These may be homopolymers or copolymers, or copolymers with polymerizable monomers other than acrylic and methacrylic monomers.

[0136] In this specification, when the expression "(meth)acrylic" is used, "(meth)acrylic" means one or both of "acrylic" and "methacrylic". Similarly, "(meth)acrylic acid" means one or both of "acrylic acid" and "methacrylic acid", "(meth)acrylate" means one or both of "acrylate" and "methacrylate", and "(meth)acryloyl" means one or both of "acryloyl" and "methacryloyl". The same applies to other terms.

[0137] The (meth)acrylic resin is a polymer having (meth)acrylic acid or a (meth)acrylic acid alkyl ester as a constituent unit, and may be a copolymer of styrene or a styrene derivative with (meth)acrylic acid or a (meth)acrylic acid alkyl ester. The (meth)acrylic resin may also be a copolymer of such a polymer with another polymer (such as polyester or polyurethane). For example, the (meth)acrylic resin may be a block copolymer or a graft copolymer. That is, the (meth)acrylic resin may be a (meth)acrylic-modified polyester resin or a (meth)acrylic-modified polyurethane resin.

[0138] The (meth)acrylic resin also includes a polymer (or a mixture of polymers, in some cases) obtained by polymerizing a polymerizable monomer, including an acrylic or methacrylic monomer, in a polyester solution or polyester dispersion. Similarly, the (meth)acrylic resin also includes a polymer (or a mixture of polymers, in some cases) obtained by polymerizing the above-mentioned polymerizable monomer in a polyurethane solution or polyurethane dispersion. Similarly, the (meth)acrylic resin also includes a polymer (or a mixture of polymers, in some cases) obtained by polymerizing the above-mentioned polymerizable monomer in another polymer solution or dispersion, and these are also referred to herein as a (meth)acrylic-modified polyester resin or a (meth)acrylic-modified polyurethane resin. The above-mentioned polyesters and polyurethanes used in the (meth)acrylic resin can be appropriately selected from the polyesters and polyurethanes exemplified for use in the binder resin described below. The (meth)acrylic resin may also contain a hydroxy group or an amino group in order to further improve adhesion to the polyester film.

[0139] The polymerizable monomer is not particularly limited, but particularly representative compounds include various carboxyl group-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, and citraconic acid, and salts thereof; various hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, monobutylhydroxyfumarate, and monobutylhydroxyitaconate; and various hydroxyl group-containing monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, and lauryl (meth)acrylate. Examples of such alkyl (meth)acrylates include: various nitrogen-containing compounds such as (meth)acrylamide, diacetone acrylamide, and (meth)acrylonitrile; nitrogen-containing compounds containing a hydroxyl group such as N-methylol (meth)acrylamide; various styrene derivatives such as styrene, α-methylstyrene, divinylbenzene, and vinyltoluene; various vinyl esters such as vinyl propionate; various silicon-containing polymerizable monomers such as γ-methacryloxypropyltrimethoxysilane and vinyltrimethoxysilane; phosphorus-containing vinyl monomers; various vinyl halides such as vinyl chloride and vinylidene chloride; and various conjugated dienes such as butadiene.

[0140] Among the above (meth)acrylic resins, polymers obtained by polymerizing polymerizable monomers including acrylic or methacrylic monomers are preferred, and it is more preferred that the polymerizable monomers include alkyl(meth)acrylic esters. Resin composition B is preferably diluted with a solvent to form a coating solution, as described below. In this case, it is preferred that the solvent is primarily water (50% by mass or more). That is, from the viewpoint of facilitating dissolution or dispersion in an aqueous coating solution, it is preferred that the polymerizable monomers have hydrophilic groups such as hydroxyl groups or carboxyl groups. Therefore, it is also preferred that the (meth)acrylic resin is a polymer obtained by polymerizing alkyl(meth)acrylic esters and polymerizable monomers including hydrophilic group-containing monomers such as hydroxyl group-containing monomers or carboxyl group-containing monomers. The (meth)acrylic resin may also be an emulsion polymer obtained by polymerizing polymerizable monomers in the presence of a surfactant, for example.

[0141] (Polyvinyl alcohol) Polyvinyl alcohol is a compound having a polyvinyl alcohol moiety, and conventionally known polyvinyl alcohols can be used, including modified compounds in which polyvinyl alcohol has been partially acetalized or butyralized. The degree of polymerization of polyvinyl alcohol is not particularly limited, but is preferably 100 or higher, more preferably in the range of 300 to 40,000. A degree of polymerization of 100 or higher is preferred because it ensures water resistance of the resin layer. The degree of saponification of polyvinyl alcohol is not particularly limited, but is preferably 70 mol% or higher, more preferably in the range of 70 to 99.9 mol%, even more preferably 80 to 97 mol%, and even more preferably 86 to 95 mol%, and saponified polyvinyl acetate is practically used.

[0142] (polyester resin) The polyester resin may be composed of, as main components, for example, the following polycarboxylic acids and polyhydroxy compounds. Examples of polycarboxylic acids that can be used include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid, 5-sodium sulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, succinic acid, trimellitic acid, trimesic acid, pyromellitic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, trimellitic acid monopotassium salt, and ester-forming derivatives thereof. Examples of polyhydric hydroxy compounds that can be used include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, and potassium dimethylolpropionate. One or more of these compounds can be appropriately selected and used to synthesize a polyester resin by a conventional polycondensation reaction.

[0143] Alternatively, a polyester resin can be used in which sulfoisophthalic acid is copolymerized as part of the polycarboxylic acid to introduce sulfonic acid groups into the polyester skeleton and then neutralized to make it hydrophilic. In this case, the amount copolymerized is preferably 1 to 13 mol % of the total polycarboxylic acid, more preferably 3 to 10 mol %, and even more preferably 5 to 9 mol %. Introducing an appropriate amount of sulfonic acid groups can increase the hydrophilicity of the resin layer and facilitate the formation of a concave-convex structure. Furthermore, aqueous dispersion stability can be improved.

[0144] (Polyurethane resin) The polyurethane resin is a polymer compound having urethane bonds in the molecule, and is preferably water-dispersible or water-soluble.

[0145] To impart water dispersibility or water solubility, it is preferable to introduce a hydrophilic group such as a hydroxyl group, a carboxyl group, a sulfonic acid group, a sulfonyl group, a phosphate group, or an ether group into the urethane resin. Among the above hydrophilic groups, it is particularly preferable to introduce a carboxyl group or a sulfonic acid group from the viewpoint of adhesion between the resin layer B and the polyester film.

[0146] One method for producing urethane resins is by reacting a hydroxyl group-containing compound with an isocyanate. Polyols are preferably used as raw materials for the hydroxyl group-containing compound, including, for example, polyether polyols, polyester polyols, polycarbonate polyols, polyolefin polyols, and acrylic polyols. These compounds may be used alone or in combination.

[0147] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, and polyhexamethylene ether glycol.

[0148] Examples of polyester polyols include polycarboxylic acids (malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, maleic acid, terephthalic acid, isophthalic acid, etc.) or their acid anhydrides and polyhydric alcohols (ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2 ... 2-butyl-2-ethyl-1,3-propanediol, 2-hexyl-2,4-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-hexyl-1,3-propanediol, cyclohexanediol, bishydroxymethylcyclohexane, dimethanolbenzene, bishydroxyethoxybenzene, alkyldialkanolamine, lactonediol, etc.

[0149] Examples of polycarbonate polyols include polycarbonate diols obtained by dealcoholization reaction of polyhydric alcohols with dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, etc., such as poly(1,6-hexylene) carbonate and poly(3-methyl-1,5-pentylene) carbonate.

[0150] Of these, polyester polyols are preferred.

[0151] Examples of polyisocyanate compounds used to obtain urethane resins include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and tolidine diisocyanate; aliphatic diisocyanates having an aromatic ring such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic diisocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic diisocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and isopropylidenedicyclohexyl diisocyanate. These may be used alone or in combination.

[0152] A chain extender may be used when synthesizing the urethane resin. There are no particular restrictions on the chain extender as long as it has two or more active groups that react with isocyanate groups, and generally, chain extenders having two hydroxyl groups or two amino groups can be mainly used.

[0153] Examples of chain extenders having two hydroxyl groups include glycols such as aliphatic glycols such as ethylene glycol, propylene glycol, and butanediol; aromatic glycols such as xylylene glycol and bishydroxyethoxybenzene; and ester glycols such as neopentyl glycol hydroxypivalate.

[0154] Examples of chain extenders having two amino groups include aromatic diamines such as tolylenediamine, xylylenediamine, and diphenylmethanediamine; aliphatic diamines such as ethylenediamine, propanediamine, hexanediamine, 2,2-dimethyl-1,3-propanediamine, 2-methyl-1,5-pentanediamine, trimethylhexanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,8-octanediamine, 1,9-nonanediamine, and 1,10-decanediamine; and alicyclic diamines such as 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, dicyclohexylmethanediamine, 1,4-diaminocyclohexane, and 1,3-bisaminomethylcyclohexane.

[0155] ((C) Antistatic agent) The resin layer B preferably contains an antistatic agent (C). One example of an antistatic agent is an ion-conductive polymer compound. By containing a predetermined antistatic agent in the resin layer B, it becomes easy to control the amount of charge at the time of peeling the resin layer B from the ceramic green sheet to a predetermined value or less, and the ability to prevent the ceramic green sheet from sticking to the resin layer B is easily exhibited.

[0156] The content of the (C) antistatic agent in the resin layer B is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, based on the total mass of the resin layer B. The content of the (C) antistatic agent in the resin layer B is preferably 60% by mass or less, more preferably 55% by mass or less, even more preferably 50% by mass or less, and even more preferably 45% by mass or less. By keeping the content of the (C) antistatic agent within the above range, it becomes easy to control the amount of charge at the time of peeling the resin layer B and the ceramic green sheet to a predetermined value or less, and the ability to prevent the ceramic green sheet from sticking to the resin layer B is easily exhibited.

[0157] The ion-conductive polymer compound is a polymer compound containing an ion-conductive functional group, and examples thereof include polymer compounds containing an ammonium group, a polyether compound, a sulfonic acid compound, a betaine compound, etc. Among these, ammonium group-containing compounds are particularly preferred from the viewpoint of high polarity and prevention of peeling static electricity.

[0158] The ammonium group-containing compound refers to a compound having an ammonium group in the molecule, and is preferably a polymer compound having an ammonium group. For example, a polymer containing a monomer having an ammonium group and an unsaturated double bond as a component can be used.

[0159] Specific examples of such polymers include polymers having a repeating unit represented by the following formula (1): The ammonium group-containing polymer compound may be a homopolymer or copolymer of these, or may be a copolymer of multiple other components.

[0160] [ka]

[0161] In the above formula (1), R 1 , R 2 are each independently a hydrogen atom, an alkyl group, a phenyl group, or the like, and these alkyl groups and phenyl groups may be substituted with the groups shown below. Examples of the substitutable groups include a hydroxy group, an amide group, an ester group, an alkoxy group, a phenoxy group, a naphthoxy group, a thioalkoxy group, a thiophenoxy group, a cycloalkyl group, a trialkylammonium alkyl group, a cyano group, and a halogen atom. 1 and R 2 may be chemically bonded, and the linked R 1 and R 2 For example, -(CH2) m It may be -(m=an integer of 2 to 5), -CH(CH3)CH(CH3)-, -CH=CH-CH=CH-, -CH=CH-CH=N-, -CH=CH-N=C-, -CH2OCH2-, -(CH2)2O(CH2)2-, or the like.

[0162] X in the above formula (1) - can be appropriately selected within the scope of the present invention. - Examples of the cation include halogen ions, sulfonates, phosphates, nitrates, alkylsulfonates, and carboxylates.

[0163] Among polymers containing a monomer having an ammonium group and an unsaturated double bond as a component, from the viewpoint of improving film-forming properties and obtaining a stable coating, the polymer may contain other monomers as copolymerization components. Examples of other monomers include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate, alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate, and acrylamides such as n-methylolacrylamide.

[0164] However, from the viewpoint of increasing polarity and preventing peeling static electricity, the polymer is preferably a homopolymer having a repeating unit represented by the above formula (1).

[0165] The number-average molecular weight of the ammonium group-containing polymeric compound is preferably 1,000 to 500,000, more preferably 2,000 to 350,000, and even more preferably 5,000 to 200,000. By adjusting the number-average molecular weight of the ammonium group-containing polymeric compound to 1,000 or more, the strength of the coating film can be increased and heat resistance stability can be improved. Furthermore, by adjusting the number-average molecular weight of the ammonium group-containing polymeric compound to 500,000 or less, the viscosity of the coating liquid can be controlled within an appropriate range, improving handleability and coatability.

[0166] The antistatic agent (C) is preferably at least one selected from (a1) a polymer in which a compound made of thiophene or a thiophene derivative is doped with another anionic compound, and (a2) a polymer in which a compound made of thiophene or a thiophene derivative has an anionic group and is self-doped. Examples of such antistatic agents include those obtained by polymerizing a compound represented by the following formula (2) or (3) in the presence of a polyanion.

[0167] [ka]

[0168] In the above formula (2), R 1 and R 2 each independently represents a hydrogen atom, or an aliphatic hydrocarbon group, alicyclic hydrocarbon group, aromatic hydrocarbon group, or the like having 1 to 20 carbon atoms.

[0169] [ka]

[0170] In the above formula (3), n represents an integer of 1 to 4.

[0171] Specific examples of the polymer include polymers having a repeating unit represented by formula (4). The polymer may be a homopolymer or copolymer of these, or may be a copolymer of multiple other components. However, from the viewpoint of improving antistatic properties, the polymer is preferably a homopolymer.

[0172] [ka]

[0173] In the above formula (4), the substituent R 1 is preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R 2 is preferably -O- or -NH-, and R3 is preferably an alkylene group having 1 to 6 carbon atoms or other linking group capable of forming the structure of formula (4), and R 4 , R 5 and R 6 At least one of the substituents is preferably a hydrogen atom, and the other substituents are preferably an alkyl group having 1 to 3 carbon atoms or a hydroxyalkyl group having 2 to 3 carbon atoms in the alkyl group, and X - is preferably an alkylsulfonate ion having an alkyl group having 1 to 4 carbon atoms.

[0174] Examples of polyanions used in polymerization include poly(meth)acrylic acid, polymaleic acid, polystyrene sulfonic acid, polyvinyl sulfonic acid, etc. As a method for producing such a polymer, for example, a method such as that disclosed in JP-A-7-90060 can be used.

[0175] In this embodiment, a compound represented by the above formula (3) in which n is 2 and polystyrene sulfonic acid is used as the polyanion is preferably used.

[0176] When these polyanions are acidic, they may be partially or completely neutralized. The base used for neutralization is preferably ammonia, organic amines, or alkali metal hydroxides.

[0177] ((D) Crosslinking Agent) Resin composition B preferably further contains a crosslinking agent (D), and resin layer B preferably further contains a crosslinking agent (D). The crosslinking agent is not particularly limited, and a conventionally known crosslinking agent can be used. Examples include melamine compounds, oxazoline compounds, epoxy compounds, carbodiimide compounds, isocyanate compounds, and silane coupling compounds. Among these, from the viewpoint of imparting durability to resin layer B, it is preferable to include at least one selected from melamine compounds and oxazoline compounds.

[0178] The content of (D) crosslinking agent in resin composition B is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and even more preferably 20% by mass or more, based on the total mass of the non-volatile components of resin composition B. Furthermore, the content of (D) crosslinking agent in resin composition B is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less, and even more preferably 30% by mass or less. By setting the content of (D) crosslinking agent within the above range, the coatability of resin composition B when used as a coating liquid can be improved. Furthermore, by setting the content of (D) crosslinking agent within the above range, the durability of resin layer B can be more effectively improved.

[0179] (melamine compounds) The melamine compound is a compound having a melamine skeleton within the compound, and examples thereof include alkylolated melamine derivatives, compounds obtained by reacting alkylolated melamine derivatives with alcohol to partially or completely etherify them, and mixtures thereof. Examples of alkylolation include methylolation, ethylolation, isopropylolation, n-butylolation, isobutyrolation, etc. Among these, methylolation is preferred from the viewpoint of reactivity. As the alcohol used for etherification, methanol, ethanol, isopropanol, n-butanol, isobutanol, etc. are preferably used, and among these, methanol is more preferred. The melamine compound may be a monomer or a dimer or higher polymer, or a mixture thereof. Furthermore, melamine may be partially co-condensed with urea or the like, and a catalyst may be further added to the resin composition to increase the reactivity of the melamine compound.

[0180] (Oxazoline compounds) An oxazoline compound is a compound having an oxazoline group in the molecule, and a polymer containing an oxazoline group is particularly preferred. The polymer containing an oxazoline group can be prepared by polymerizing an addition-polymerizable oxazoline group-containing monomer alone or with other monomers. Examples of addition-polymerizable oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline. These monomers can be used alone or in combination. Among these, 2-isopropenyl-2-oxazoline is preferred because it is readily available industrially. The other monomer is not limited as long as it is copolymerizable with the addition-polymerizable oxazoline group-containing monomer, and examples thereof include (meth)acrylic acid esters such as alkyl(meth)acrylate (the alkyl group can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl); unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid, and salts thereof (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); unsaturated nitriles such as acrylonitrile and methacrylonitrile; (meth)acrylamide, N-alkyl(meth)acrylate, N-methyl-N ... Examples of suitable monomers include unsaturated amides such as t)acrylamide and N,N-dialkyl(meth)acrylamide (the alkyl group can be a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a 2-ethylhexyl group, a cyclohexyl group, and the like); vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α,β-unsaturated monomers such as vinyl chloride and vinylidene chloride; and α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene, and one or more of these monomers can be used. The oxazoline compound may have a polyalkylene oxide chain such as a polyethylene oxide chain, and for example, a (meth)acrylate having a polyalkylene oxide chain may be used as another monomer. From the viewpoint of improving the adhesion of the resin layer B to the polyester film, the amount of oxazoline groups in the oxazoline compound is preferably in the range of 0.5 to 10 mmol / g, more preferably 1 to 9 mmol / g, and even more preferably 3 to 8 mmol / g.

[0181] (epoxy compounds) The epoxy compound is a compound having an epoxy group in the molecule, and examples thereof include condensation products of epichlorohydrin, ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A, etc. with a hydroxyl group or an amino group, polyepoxy compounds, diepoxy compounds, monoepoxy compounds, and glycidylamine compounds. Examples of polyepoxy compounds include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris(2-hydroxyethyl)isocyanate, glycerol polyglycidyl ether, and trimethylolpropane polyglycidyl ether. Examples of diepoxy compounds include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcinol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polytetramethylene glycol diglycidyl ether. Examples of monoepoxy compounds include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, and phenyl glycidyl ether, and examples of glycidylamine compounds include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylamino)cyclohexane, etc. From the viewpoint of improving the adhesion of the resin layer B to the polyester film, polyether-based epoxy compounds are preferred. In terms of the amount of epoxy groups, a polyepoxy compound having three or more functional groups is preferred over a difunctional compound.

[0182] (Carbodiimide compounds) The carbodiimide compound is a compound having a carbodiimide structure, and is a compound having one or more carbodiimide structures in the molecule. For better adhesion between the resin layer B and the polyester film, a polycarbodiimide compound having two or more carbodiimide structures in the molecule is more preferred.

[0183] Carbodiimide compounds can be synthesized by conventionally known techniques, and generally involve the condensation reaction of a diisocyanate compound. The diisocyanate compound is not particularly limited, and both aromatic and aliphatic diisocyanates can be used. Specific examples include tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate.

[0184] The content of carbodiimide groups contained in the carbodiimide compound, in terms of carbodiimide equivalent (weight [g] of the carbodiimide compound required to provide 1 mol of carbodiimide groups), is preferably in the range of 100 to 1000, more preferably 250 to 800, and even more preferably 300 to 700. By using within the above range, the durability of the resin layer B is improved.

[0185] Furthermore, within the scope of the present invention, a surfactant may be added to improve the water solubility or water dispersibility of the polycarbodiimide compound, and a hydrophilic monomer such as a polyalkylene oxide, a quaternary ammonium salt of a dialkylamino alcohol, or a hydroxyalkyl sulfonate may be added and used.

[0186] (Isocyanate compounds) The isocyanate compound refers to a compound having an isocyanate or an isocyanate derivative structure, such as a blocked isocyanate. Examples of the isocyanate compound include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate; aliphatic isocyanates having an aromatic ring, such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic isocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic isocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylenebis(4-cyclohexyl isocyanate), and isopropylidenedicyclohexyl diisocyanate. Further examples include polymers and derivatives of these isocyanates, such as biuretized products, isocyanurated products, urethodionated products, and carbodiimide-modified products. These may be used alone or in combination. Among the above isocyanate compounds, aliphatic isocyanates or alicyclic isocyanates are more preferred than aromatic isocyanates in order to prevent yellowing due to ultraviolet rays.

[0187] When used in the form of a blocked isocyanate, examples of the blocking agent include bisulfites; phenolic compounds such as phenol, cresol, and ethylphenol; alcohol compounds such as propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol, and ethanol; active methylene compounds such as methyl isobutanoylacetate, dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, and acetylacetone; mercaptan compounds such as butyl mercaptan and dodecyl mercaptan; lactam compounds such as ε-caprolactam and δ-valerolactam; amine compounds such as diphenylaniline, aniline, and ethyleneimine; acid amide compounds such as acetanilide and acetic acid amide; and oxime compounds such as formaldehyde oxime, acetaldoxime, acetone oxime, methyl ethyl ketone oxime, and cyclohexanone oxime, and these may be used alone or in combination of two or more.

[0188] The isocyanate compound may be used alone or as a mixture or bond with various polymers. In order to improve the dispersibility and crosslinkability of the isocyanate compound, it is preferable to use a mixture or bond with a polyester resin or a urethane resin.

[0189] (Silane coupling compounds) Silane coupling compounds are organosilicon compounds that contain an organic functional group and a hydrolyzable group such as an alkoxy group in one molecule. For example, epoxy group-containing compounds such as 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; vinyl group-containing compounds such as vinyltrimethoxysilane and vinyltriethoxysilane; styryl group-containing compounds such as p-styryltrimethoxysilane and p-styryltriethoxysilane; (meth)acrylic group-containing compounds such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane; 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and N-2-(aminoethyl)-3 amino group-containing compounds such as N-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltriethoxysilane; isocyanurate group-containing compounds such as tris(trimethoxysilylpropyl)isocyanurate and tris(triethoxysilylpropyl)isocyanurate; and mercapto group-containing compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropylmethyldiethoxysilane.

[0190] (Crosslinking catalyst) When the resin layer B contains a crosslinking agent (D), the resin composition B may further contain a crosslinking catalyst. The crosslinking catalyst is used to increase the reactivity of the crosslinking agent, and various known catalysts can be used. Examples include amine compounds, salts of amine compounds, organic acids such as aromatic sulfonic acid compounds (e.g., p-toluenesulfonic acid) and phosphoric acid compounds, and their salts, imine compounds, amidine compounds, guanidine compounds, organometallic compounds, and metal salts such as zinc stearate, zinc myristate, aluminum stearate, and calcium stearate. Among these, amine compounds, salts of amine compounds, and p-toluenesulfonic acid are preferred, and amine compounds and salts of amine compounds are more preferred.

[0191] When resin composition B contains a crosslinking catalyst, the content of the crosslinking catalyst is preferably in the range of 0.01 to 5 mass %, more preferably 0.1 to 4 mass %, and even more preferably 1 to 3 mass %, relative to the total mass of non-volatile components in resin composition B. By setting the content of the crosslinking catalyst in this range, it is possible to suppress a decrease in pot life.

[0192] (fine particles) Resin composition B may further contain fine particles. By using fine particles in combination, a fine uneven structure is formed on the surface of resin layer B, and the convex portions on the surface of the resin layer are less likely to deform even when the release film is rolled, and a good roll appearance can be obtained.

[0193] Examples of fine particles include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, 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. Of these, silica and aluminum oxide are preferred.

[0194] The average particle size (average primary particle size) of the fine particles is preferably 1 to 100 nm, more preferably 2 to 60 nm, and even more preferably 3 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, making it easier to obtain the desired fine uneven structure.

[0195] When resin composition B contains fine particles, the content of the fine particles is preferably in the range of 1 to 50 mass %, more preferably 5 to 45 mass %, and even more preferably 10 to 40 mass %, relative to the total mass of non-volatile components in resin composition B. By setting the content of the fine particles within the above range, a desired fine uneven structure can be obtained.

[0196] ((particularly preferred form)) The combination of compounds contained in Resin Composition B is preferably a combination of (B) binder resin and (C) antistatic agent, more preferably a combination of (B) binder resin, (C) antistatic agent, and (D) crosslinking agent. Most preferably, it is a combination of (B) binder resin and (C) ion-conductive polymer compound, or a combination of (B) binder resin, (C) at least one selected from (a1) polymers in which a compound made of thiophene or a thiophene derivative is doped with another anionic compound, and (a2) polymers in which a compound made of thiophene or a thiophene derivative has an anionic group and is self-doped, and (D) crosslinking agent. Among these, a combination of (A) a release agent, (B) a binder resin, and (C) an ion-conductive polymer compound, or a combination of (B) a binder resin, (C) at least one selected from (a1) a polymer in which a compound made of thiophene or a thiophene derivative is doped with another anionic compound, and (a2) a polymer in which a compound made of thiophene or a thiophene derivative has an anionic group and is self-doped, and (D) a crosslinking agent is particularly preferred.

[0197] <<Resin Layer A / Resin Composition A>> The resin layer A contains a release agent (A). By including the release agent (A) in the resin layer A, the applicability of the ceramic slurry can be improved, and further, the releasability of the ceramic green sheet from the resin layer A can be improved.

[0198] The release agent (A) is not particularly limited, and for example, a silicone-based release agent or a non-silicone-based release agent can be used. However, it is preferable that the resin layer A contains a non-silicone-based release agent. The use of a non-silicone-based release agent allows it to be preferably used in applications where contamination with silicon (Si) elements is undesirable, such as in the semiconductor field. The non-silicone-based release agent is preferably at least one selected from waxes and long-chain alkyl group-containing compounds, and more preferably a long-chain alkyl group-containing compound. Examples of non-silicone-based release agents include the same release agents (A) that may be contained in the resin layer B described above.

[0199] Resin layer A may further contain, as necessary, a (B) binder resin, a (D) crosslinking agent, fine particles, etc. Examples of the (B) binder resin, the (D) crosslinking agent, and the fine particles are the same as the (B) binder resin, the (D) crosslinking agent, and the fine particles that may be contained in resin layer B described above.

[0200] The content of the (A) release agent in the resin layer A is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, based on the total mass of the resin layer A. The content of the (A) release agent in the resin layer A is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less. If the content of the (A) release agent is within the above range, the releasability of the resulting ceramic green sheet is good after the ceramic slurry is applied and dried.

[0201] ((particularly preferred form)) The combination of compounds contained in the resin composition A is preferably a combination of a long-chain alkyl group-containing compound, melamine, and a binder resin, and more preferably a combination of a long-chain alkyl group-containing compound, melamine, and a polyester resin.

[0202] (Other ingredients) In addition to the above components, resin layer A and resin layer B may further contain additives such as antifoaming agents, coatability improvers, surfactants, thickeners, organic lubricants, ultraviolet absorbers, antioxidants, foaming agents, dyes, and pigments, as appropriate, within the scope of the present invention.

[0203] (solvent) Resin composition A and resin composition B may each be diluted with a solvent to form a coating liquid, which may be applied to the polyester film as a liquid coating liquid, and then dried and cured as necessary to form resin layer A and resin layer B, respectively. The components constituting Resin Composition A and Resin Composition B (e.g., (A) release agent, (B) binder resin, (C) antistatic agent, (D) crosslinking agent, and optionally added crosslinking catalyst, fine particles, other components, etc.) may be dissolved in a solvent or dispersed in a solvent.

[0204] When the resin composition is used as a coating liquid, the concentration of all nonvolatile components of the resin composition in the coating liquid is preferably 0.1 to 50% by mass. If the concentration of all nonvolatile components is 0.1% by mass or more, a resin layer of a desired thickness can be efficiently formed. On the other hand, if the concentration of all nonvolatile components is 50% by mass or less, the viscosity during coating can be reduced, thereby improving the appearance of the resin layer and increasing the stability in the coating liquid.

[0205] The solvent used for dilution is not particularly limited, and either water or an organic solvent can be used. From the viewpoint of environmental protection, it is preferable to use water as the main solvent (50% by mass or more). The water content is preferably 60% by mass or more, more preferably 70% by mass or more. The aqueous coating liquid may contain a small amount of organic solvent. The specific amount of organic solvent should be less than that of water on a mass basis, and for example, it is preferably less than 50% by mass of the solvent, more preferably less than 30% by mass, and even more preferably less than 20% by mass. Examples of organic solvents used in combination with water include alcohols such as ethanol, isopropanol, ethylene glycol, and glycerin; ethers such as ethyl cellosolve, t-butyl cellosolve, propylene glycol monomethyl ether, and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate; and amines such as dimethylethanolamine. These can be used alone or in combination. By appropriately selecting and adding these organic solvents to the aqueous coating solution as needed, the stability and coatability of the coating solution can sometimes be improved.

[0206] Furthermore, when only an organic solvent is used as the solvent, examples of such organic solvents include aromatic hydrocarbons such as toluene, aliphatic hydrocarbons such as hexane, heptane, isooctane, esters such as ethyl acetate, butyl acetate, ketones such as ethyl methyl ketone, isobutyl methyl ketone, alcohols such as ethanol, 2-propanol, ethers such as diisopropyl ether, dibutyl ether, etc. These may be used alone or in combination, taking into consideration solubility, coatability, boiling point, etc.

[0207] The components in the resin layer (e.g., (A) release agent, (B) binder resin, (C) antistatic agent, (D) crosslinking agent, optionally added crosslinking catalyst and fine particles, unreacted materials such as other components, reacted compounds, or mixtures thereof) can be analyzed by, for example, TOF-SIMS, ESCA, fluorescent X-ray, etc.

[0208] <Method of forming resin layers A and B> The method for forming resin layers A and B (hereinafter also simply referred to as "resin layers") is not particularly limited, and conventionally known coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, and curtain coating can be used. Methods for forming resin layers include in-line coating and offline coating. Drying and curing conditions are not particularly limited. For example, when forming a resin layer by offline coating, heat treatment is preferably carried out at 80 to 200°C for 3 to 40 seconds, more preferably at 100 to 180°C for 3 to 40 seconds. On the other hand, when forming a resin layer by in-line coating, heat treatment is preferably carried out at 70 to 280°C for 3 to 200 seconds.

[0209] In particular, the resin layer is preferably formed by in-line coating, which treats the film surface during the polyester film production process. In-line coating is a method of coating within the polyester film production process, specifically, a method of coating at any stage from melt extrusion of polyester to stretching, heat setting, and winding up. Typically, the coating is performed on any of the following: an unstretched sheet obtained by melting and quenching, a stretched uniaxially stretched film, a biaxially stretched film before heat setting, and a film after heat setting and before winding up. Forming the resin layer by in-line coating can improve the production efficiency of release films.

[0210] For example, when a resin layer is formed by in-line coating, a method in which a uniaxially stretched film that has been stretched in the longitudinal direction (machine direction) is coated and then stretched in the transverse direction is particularly advantageous in sequential biaxial stretching. This method has advantages in terms of production costs because film production and resin layer formation can be carried out simultaneously. In addition, because stretching is carried out after coating, the thickness of the resin layer can be changed by adjusting the stretch ratio, and thin film coating can be carried out more easily than with offline coating films.

[0211] Furthermore, by providing a resin layer on the film before stretching, the resin layer can be stretched together with the polyester film, thereby allowing the resin layer to be firmly adhered to the polyester film.

[0212] Furthermore, in the production of biaxially stretched polyester films, by stretching the film while gripping its edges with clips or the like, the film can be constrained in both the longitudinal and transverse directions, and high temperatures can be applied in the heat setting process while maintaining flatness and preventing wrinkles. This allows the heat treatment performed after coating to be performed at a high temperature that cannot be achieved by other methods, improving the film-forming properties of the resin layer and enabling stronger adhesion between the resin layer and the polyester film. Furthermore, a strong resin layer can be formed, improving performance such as migration resistance and moist heat resistance to various functional layers that may be formed on the resin layer.

[0213] Regardless of whether off-line coating or in-line coating is used, heat treatment and irradiation with active energy rays such as ultraviolet radiation may be used in combination as needed. The polyester film constituting the present release film may be previously subjected to a surface treatment such as a corona treatment or a plasma treatment.

[0214] The coating amount of the non-volatile component of the resin layer (after drying and stretching) is preferably 0.005 to 1.0 g / m 2 , more preferably 0.01 to 0.5 g / m 2 , and more preferably 0.03 to 0.2 g / m 2 If the coating amount is within this range, the desired performance (releasability or anti-sticking property of the ceramic green sheet) can be exhibited. The coating amount can be calculated from the concentration of nonvolatile components in the coating liquid, the coating amount before drying derived from the consumption amount of the coating liquid, the transverse stretching ratio, etc.

[0215] <<<Release film properties>>> [Maximum mountain height (Sp)] The maximum peak height (Sp) of the resin layer A side of the present release film is preferably 1000 nm or less, more preferably 800 nm or less, even more preferably 500 nm or less, even more preferably 300 nm or less, even more preferably 200 nm or less, even more preferably 150 nm or less, even more preferably 100 nm or less, and particularly preferably 60 nm or less. Furthermore, the maximum peak height (Sp) of the resin layer A side of the present release film is preferably, for example, 5 nm or more, more preferably 10 nm or more. By setting the maximum peak height (Sp) of the resin layer A side of the present release film within the above range, it is possible to obtain a release film with excellent surface smoothness while effectively suppressing the generation of protrusions of unintended sizes on the surface of the release film. As a result, it becomes easier to reduce the thickness of the ceramic green sheet.

[0216] The maximum peak height (Sp) of the resin layer B side of the present release film is preferably 2500 nm or less, more preferably 2000 nm or less, even more preferably 1800 nm or less, even more preferably 1600 nm or less, even more preferably 1400 nm or less, and particularly preferably 1200 nm or less. Furthermore, the maximum peak height (Sp) of the resin layer B side of the present release film is preferably 10 nm or more, more preferably 20 nm or more, even more preferably 30 nm or more, even more preferably 40 nm or more, even more preferably 50 nm or more, and particularly preferably 60 nm or more. By setting the maximum peak height (Sp) of the resin layer B side of the present release film within the above range, the release film is provided with a rough surface necessary to improve its handleability, and the air leakage index of the present release film can be reduced. As a result, the present release film can exhibit appropriate slip properties, improving its handleability. For example, a release film with appropriate surface roughness can be easily wound into a roll. Furthermore, by setting the maximum peak height (Sp) on the resin layer B surface within the above range, the ability to prevent the ceramic green sheet from sticking to the resin layer B can be more effectively improved.

[0217] [Arithmetic mean height (Sa)] The arithmetic mean height (Sa) of the resin layer A side of the present release film is preferably 15 nm or less, more preferably 10 nm or less, even more preferably 8 nm or less, even more preferably 5 nm or less, and even more preferably 3 nm or less. The arithmetic mean height (Sa) of the resin layer A side of the present release film is preferably 0.3 nm or more, more preferably 0.4 nm or more, even more preferably 0.5 nm or more, and particularly preferably 0.6 nm or more. By setting the arithmetic mean height (Sa) of the resin layer A side to the above upper limit or less, a polyester film with excellent surface smoothness can be obtained. As a result, it is easy to reduce the thickness of the ceramic green sheet. On the other hand, the arithmetic mean height (Sa) of the resin layer A side is preferably the above lower limit or more, and the surface of the release film is preferably provided with a predetermined amount of roughness or more. This provides a rough surface necessary to improve the handleability of the release film, thereby reducing the air leakage index of the present release film. As a result, the present release film can exhibit appropriate slip properties and improve handleability.

[0218] The arithmetic mean height (Sa) of the resin layer B side of the present release film is preferably 100 nm or less, more preferably 80 nm or less, even more preferably 60 nm or less, even more preferably 40 nm or less, even more preferably 30 nm or less, and particularly preferably 25 nm or less. The arithmetic mean height (Sa) of the resin layer B side of the present release film is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. By setting the arithmetic mean height (Sa) of the resin layer B side within the above range, the surface smoothness can be improved while more effectively improving the anti-sticking properties of the ceramic green sheet. The arithmetic mean height (Sa) of the resin layer B side is preferably equal to or greater than the above lower limit, and the surface of the release film is preferably provided with a predetermined amount of roughness or more. This provides a rough surface necessary to improve the handleability of the release film, thereby reducing the air leakage index of the present release film. As a result, the present release film can exhibit appropriate slip properties and improve handleability.

[0219] The ratio Sp / Sa of the maximum peak height (Sp) to the arithmetic mean height (Sa) of the resin layer A side of the release film is preferably 5 or more, more preferably 10 or more, even more preferably 20 or more, and even more preferably 25 or more. Sp / Sa is also preferably 400 or less, more preferably 200 or less, even more preferably 100 or less, even more preferably 70 or less, even more preferably 50 or less, and particularly preferably 30 or less. By setting Sp / Sa of the resin layer A side within the above range, it becomes easier to form a thin ceramic green sheet.

[0220] The ratio Sp / Sa of the maximum peak height (Sp) to the arithmetic mean height (Sa) on the resin layer B side of the release film is preferably 10 or more, more preferably 20 or more, and even more preferably 30 or more. Sp / Sa is also preferably 150 or less, more preferably 110 or less, even more preferably 90 or less, and even more preferably 70 or less. By setting Sp / Sa on the resin layer B side within the above range, the ability to prevent the ceramic green sheet from sticking to the resin layer B can be more effectively improved.

[0221] [Water droplet contact angle] The water droplet contact angle on the surface of resin layer B is preferably 105° or less, more preferably 103° or less, and even more preferably 100° or less. By setting the water droplet contact angle on the surface of resin layer B within the above range, it is possible to more effectively prevent the ceramic green sheet from sticking to resin layer B. There is no particular limitation on the lower limit of the water droplet contact angle on the surface of resin layer B, but it is preferably 20°, more preferably 30°, and may be 40°. When measuring the water droplet contact angle on the surface of resin layer B, the release film is conditioned for 24 hours or more in an environment of 23°C and a relative humidity of 50%, and then the water droplet contact angle on the surface of resin layer B (side B) of the release film is measured after 60 seconds using an automatic contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., model DMo-501).

[0222] [Tape peeling force] The peel strength of the resin layer B surface against acrylic adhesive tape is preferably 2000 mN / cm or less, more preferably 1500 mN / cm or less, even more preferably 1300 mN / cm or less, even more preferably 1100 mN / cm or less, and particularly preferably 1000 mN / cm or less. By setting the peel strength within the above range, it is possible to more effectively prevent the ceramic green sheet from sticking to the resin layer B from the viewpoint of physical factors. When measuring the peel strength of the resin layer B surface against acrylic adhesive tape, a 50 μm thick adhesive tape (Nitto Denko Corporation's "No. 31B" tape) is pressed back and forth once with a 2 kg rubber roller to the surface of the resin layer B (side B) of the release film. After leaving it at room temperature for 1 hour, the tape is peeled at a 180° angle using Shimadzu Corporation's "AGX-plus" tape at a pulling speed of 300 mm / min to measure the peel strength.

[0223] [Surface resistivity] The surface resistivity of the resin layer B surface (23°C ± 2°C, relative humidity 50 ± 10%) is 1.0 × 10 12 It is preferably Ω or less, and more preferably 1.0×10 11 Ω or less, more preferably 1.5×10 10 Ω or less. By setting the surface resistivity of the resin layer B surface within the above range, it is possible to more effectively prevent the ceramic green sheet from sticking to the resin layer B due to static electricity. When measuring the surface resistivity of the resin layer B surface, the release film is conditioned for 30 minutes in an environment of 23°C and a relative humidity of 50%, and then a high-resistance resistivity meter: Hiresta UX MCP-HT800 and a measuring electrode: UR-100 manufactured by Nitto Seiko Analytech Co., Ltd. are used to apply a voltage of 500 V to the surface (side B) of the resin layer B of the release film, and measurement is performed, and the value after 1 minute is taken as the surface resistivity.

[0224] [Static friction coefficient] The static friction coefficient between the surface of resin layer A and the surface of resin layer B is preferably 0.5 or less, more preferably 0.25 or less, even more preferably 0.23 or less, still more preferably 0.2 or less, and even more preferably 0.18 or less. In addition, the static friction coefficient between the surface of resin layer A and the surface of resin layer B is preferably 0.05 or more. By setting the static friction coefficient within the above range, the handleability of the release film can be improved.

[0225] [Dynamic friction coefficient] The dynamic friction coefficient between the resin layer A surface and the resin layer B surface is preferably 0.4 or less, more preferably 0.25 or less, even more preferably 0.22 or less, even more preferably 0.19 or less, and even more preferably 0.17 or less. Furthermore, the dynamic friction coefficient between the resin layer A surface and the resin layer B surface is preferably 0.05 or more. By setting the dynamic friction coefficient within the above range, the handleability of the release film can be improved. When measuring the static friction coefficient and dynamic friction coefficient between the resin layer A surface and the resin layer B surface, a release film is attached to a smooth glass plate having a width of 10 mm and a length of 100 mm, and another piece of release film cut to a width of 18 mm and a length of 120 mm is slid over the release film to measure the friction force between the resin layer A surface (side A) and the resin layer B surface (side B). Specifically, another release film is pressed against a metal pin with a diameter of 8 mm, and the metal pin is slid longitudinally across the glass plate at a speed of 40 mm / min with a load of 30 g to measure the friction force. The maximum value immediately after the pin starts to slide is regarded as the static friction coefficient, and the average value of the friction coefficient between 4 mm and 6 mm of sliding is evaluated as the kinetic friction coefficient.

[0226] [Thickness] The total thickness of the release film is preferably 9 μm or more, more preferably 10 μm or more, and even more preferably 12 μm or more. The total thickness of the release film is preferably 50 μm or less, more preferably 45 μm or less, and even more preferably 42 μm or less. By setting the thickness of the release film within the above range, the handleability of the release film can be improved. Furthermore, by setting the thickness of the release film within the above range, the ability to prevent the ceramic green sheet from sticking to the resin layer B can be more effectively improved.

[0227] [Air leakage index] The air leakage index of the release film is preferably 8500 seconds or less, more preferably 8000 seconds or less, even more preferably 7500 seconds or less, and particularly preferably 7000 seconds or less. The lower limit of the air leakage index is not particularly limited, but is preferably 100 seconds, and may be 300 seconds, 500 seconds, or 700 seconds, for example. The air leakage index of the release 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 pressure 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 inside 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 release film is 70 mm square, and 20 sheets of the film are stacked with the front and back overlapping to form a test laminate film. A 5 mm diameter hole 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 more closely contacted. Therefore, an air leakage index below the above upper limit value means that there are appropriate gaps between the films, which improves the slipperiness when the release film is wound into a roll and reduces the risk of wrinkles when made into a roll film.

[0228] [Air leakage index reduction rate] The air leakage index reduction rate of the present release film, calculated by the following formula, is preferably 5% or more, more preferably 10% or more, even more preferably 13% or more, even more preferably 15% or more, and even more preferably 20% or more. The upper limit of the air leakage index reduction rate is not particularly limited, but may be, for example, 90%, 80%, or 70%. Air leakage index reduction rate (%) = 100 - air leakage index of target release film / air leakage index of virgin polyester film x 100 The virgin polyester film in the above formula is a film constructed by replacing all of the recycled polyester resin contained in the polyester film with virgin polyester resin (non-recycled polyester resin). An air leakage index reduction rate of equal to or greater than the above lower limit means that there are appropriate gaps between films, which improves the slipperiness when the release film is wound into a roll and reduces the risk of wrinkles occurring when the film is made into a roll.

[0229] [Melting peak temperature (Tm)] The melting peak temperature (Tm) of the present release 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 release film is preferably 270° C. or lower, more preferably 260° C. or lower, even more preferably 256° C. or lower, and particularly preferably 254° C. or lower. By setting the melting peak temperature (Tm) of the present release film within the above range, the ability to prevent the ceramic green sheet from sticking to the resin layer B can be more effectively improved.

[0230] [Melting peak heat (ΔHm)] The peak heat of fusion (ΔHm) of the present release film is preferably 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. The peak heat of fusion (ΔHm) of the present release film is preferably 50 J / g or less, more preferably 45 J / g or less, even more preferably 40 J / g or less, even more preferably 38 J / g or less, and particularly preferably 36 J / g or less. By setting the peak heat of fusion (ΔHm) of the present release film within the above range, the ability to prevent the ceramic green sheet from sticking to the resin layer B can be more effectively improved.

[0231] The melting peak temperature (Tm) and melting peak calorific value (ΔHm) of the present release film can be measured, for example, using a differential scanning calorimeter (DSC60) manufactured by Shimadzu Corporation. The measurement conditions are as follows, and the 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 (1) are determined. (1) Heat from 20°C to 300°C at 10°C / min (2) Hold at 300°C for 5 minutes (3) Cool down to 20°C at 600°C / min (4) Keep at 20°C for 5 minutes (5) Heat from 20°C to 300°C at 10°C / min (6) Hold at 300°C for 5 minutes (7) Decrease temperature to 20°C at 600°C / min

[0232] [Gas density] The gas density of this release film is 1.4000 g / cm 3 It is preferable that the density is 1.4015 g / cm or more. 3 More preferably, it is 1.4020 g / cm or more. 3 It is more preferable that the density of the release film is 1.4100 g / cm or more. 3 Preferably, it is 1.4075 g / cm or less. 3More preferably, it is 1.4060 or less, and even more preferably, it is 1.4050 g / cm 3 It is even more preferable that the density of the present release film is within the above range. By setting the density of the present release film within the above range, the heat resistance, solvent resistance, and flexibility of the polyester film can be all achieved, and a polyester film with excellent processability and surface properties can be easily obtained. As a result, the ability to prevent the ceramic green sheet from sticking to the resin layer B can be more effectively improved. Furthermore, although the use of recycled raw materials tends to lower the gas density of the present release film, by controlling the gas density so that it does not become too low, it becomes easier to suppress a decrease in the anti-sticking properties of the ceramic green sheet. Specifically, by using a raw material containing a chemically recycled polyester resin as the raw material, it becomes easier to suppress a decrease in the gas density of the present release film, which is preferable.

[0233] [Heat shrinkage rate] The manufacturing process of multilayer ceramic capacitors includes heat treatments, such as drying a resin composition coated on a polyester film or 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 release film is an important characteristic for ensuring the quality and reliability of the finished product, from intermediate products to finished products in the manufacturing process of multilayer ceramic capacitors, such as the lamination characteristics of ceramic green sheets. To prevent such coating irregularities and wrinkles, the release film preferably has a thermal shrinkage in the machine direction (MD) when heat-treated at 150°C for 5 minutes. This thermal shrinkage is preferably 5% or less, more preferably 4% or less, even more preferably 3% or less, even more preferably 2.5% or less, and particularly preferably 2% or less. From the same perspective, the lower limit of the thermal shrinkage in the machine direction (MD) (150°C, 5 minutes) is preferably −0.5% or more, more preferably −0.3% or more.

[0234] Furthermore, the heat shrinkage rate of the present release film in the transverse direction (TD) when heat-treated at 150°C for 5 minutes is preferably 3% or less, more preferably 2.5% or less, even more preferably 2% or less, even more preferably 1.5% or less, and particularly preferably 1% 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.

[0235] In order to achieve a desired heat shrinkage rate (heated at 150°C for 5 minutes) for the present release film, for example, it is necessary to appropriately set the film-forming conditions (particularly the longitudinal stretching temperature, transverse stretching ratio, heat setting temperature, roll peripheral speed, relaxation rate, etc.), film-forming raw materials, etc. The heat shrinkage rate (heated at 150°C for 5 minutes) for the present release 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) × 100

[0236] When this release film is heated at 150°C for 5 minutes, the heat shrinkage in the MD direction is divided by the intrinsic viscosity of the polyester film (% / (dL / g)) and is preferably 1% / (dL / g) or more, more preferably 2% / (dL / g) or more, and even more preferably 2.8% / (dL / g) or more. Furthermore, the heat shrinkage in the MD direction is preferably 8% / (dL / g) or less, more preferably 6% / (dL / g) or less, even more preferably 4% / (dL / g) or less, and even more preferably 3.5% / (dL / g) or less.

[0237] When this release film is heated at 150°C for 5 minutes, the heat shrinkage in the TD direction divided by the intrinsic viscosity of the polyester film (% / (dL / g)) is preferably 0.5% / (dL / g) or more, more preferably 1% / (dL / g) or more, and even more preferably 1.7% / (dL / g) or more. Furthermore, the heat shrinkage in the TD direction divided by the intrinsic viscosity of the polyester film (% / (dL / g)) is preferably 6% / (dL / g) or less, more preferably 4% / (dL / g) or less, even more preferably 3% / (dL / g) or less, and even more preferably 2.5% / (dL / g) or less. By setting the value obtained by dividing the heat shrinkage rate in each direction when heated at 150°C for 5 minutes by the intrinsic viscosity within the above range, the heat distortion resistance of the polyester film can be more effectively improved, resulting in improved dimensional stability and suppressing the occurrence of coating spots, wrinkles, etc. Furthermore, by setting the value obtained by dividing the heat shrinkage rate in each direction when heated at 150°C for 5 minutes by the intrinsic viscosity within the above range, the ability to prevent the ceramic green sheet from sticking to the resin layer B can be more effectively improved.

[0238] <<<Application>>> The release film of this embodiment is suitable for use in molding ceramic green sheets. The release film of this embodiment is preferably used as a support for ceramic green sheets in the manufacturing process of multilayer ceramic capacitors. In particular, the release film of this embodiment is preferably used as a support for ceramic green sheets in the manufacturing process of automotive ceramic capacitors. The release film of this embodiment is particularly suitable for use in molding thin-film ceramic green sheets, and the thickness of the thin-film ceramic green sheets (after drying) may be 2 μm or less, 1 μm or less, or 0.5 μm or less.

[0239] In particular, even when the release film of this embodiment is wound up with a thin film ceramic green sheet having a thickness (after drying) of 2 μm or less laminated thereon, the ceramic green sheet does not stick to the back surface (opposite the release surface), and the release film has excellent winding and unwinding properties. In this embodiment, the thin film ceramic green sheet is laminated on resin layer A of the release film. When the film is wound up into a roll in this state, the thin film ceramic green sheet and resin layer B are laminated together, but in this embodiment, the ceramic green sheet is prevented from sticking to resin layer B. Therefore, a release film with excellent winding and unwinding properties and handleability can be provided.

[0240] Furthermore, since the release film of this embodiment has a small air leakage index, when used for molding a ceramic green sheet, the film can be easily wound into a roll. Furthermore, by reducing the air leakage index of the release film, the film can be easily wound into a roll, and wrinkles are less likely to occur.

[0241] Furthermore, since the release film of this embodiment has a moderately thin thickness, it can also be used to make long release films, which can also contribute to improving productivity by reducing the frequency of switching release film rolls during processing.

[0242] This embodiment may relate to a release film with a ceramic green sheet, in which a ceramic green sheet is laminated on the resin layer A of the above-mentioned release film, 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 used in the manufacturing process of a multilayer ceramic capacitor. Furthermore, 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.

[0243] This embodiment may relate to use of the polyester film as a support for a ceramic green sheet in a process for 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 polyester film. [Example]

[0244] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples as long as it does not deviate from the gist of the present invention.

[0245] <Evaluation method> (1) Intrinsic viscosity (IV) of polyester film One gram of polyester film, from which components incompatible with polyester had been removed, was precisely weighed and dissolved in 100 mL of a 50 / 50 (mass ratio) phenol / tetrachloroethane mixed solvent. The intrinsic viscosity (IV) was measured at 30°C using a viscosity measuring device "VMS-022UPC·F10" (manufactured by Rigo Co., Ltd.).

[0246] (2) Average particle size (average primary particle size) The average particle size of particles was determined by observing and measuring the diameters of 10 or more particles using a scanning electron microscope (SEM) and taking the average value. In the case of non-spherical particles, the average value of the longest and shortest diameters was taken as the diameter of each particle.

[0247] (3) Resin layer thickness measurement method The surface of the resin layer was stained with RuO4 and embedded in epoxy resin. Then, sections prepared by ultrathin sectioning were stained with RuO4, and the thickness of the resin layer cross section was measured using a TEM (Hitachi High-Technologies Corporation H-7650, accelerating voltage 100V).

[0248] (4) Water droplet contact angle The release film was conditioned for 24 hours or more in an environment of 23°C and a relative humidity of 50%. After that, the water droplet contact angle on the surface of resin layer B (side B) of the release film was measured after 60 seconds using an automatic contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., model DMo-501).

[0249] (5) Tape peeling strength An adhesive tape (Nitto Denko Corporation's "No. 31B", 50 μm thick) was pressed back and forth once onto the surface (side B) of resin layer B of the release film using a 2 kg rubber roller, and the tape was left at room temperature for 1 hour before measuring the peel strength. The peel strength was measured using Shimadzu Corporation's "AGX-plus" tape, with a 180° peel angle at a tensile speed of 300 mm / min.

[0250] (6)Surface specific resistance The release film was conditioned for 30 minutes in an environment of 23°C and relative humidity of 50%. Then, using a high-resistance resistivity meter: Hiresta UX MCP-HT800 and a measurement electrode: UR-100 manufactured by Nitto Seiko Analytech Co., Ltd., a voltage of 500 V was applied to the surface of resin layer B (side B) of the release film, and measurements were performed, and the value after 1 minute was taken as the surface resistivity value. If the resistance value exceeded the upper limit of the measurable range, it was deemed unmeasurable.

[0251] (7) Arithmetic mean height (Sa), maximum peak height (Sp) The arithmetic mean height (Sa) and maximum peak height (Sp) of the measurement surfaces (resin layer A surface and resin layer B surface) were measured as follows. Using a non-contact surface / layer cross-sectional shape measurement system, VertScan® R550GML, manufactured by Ryoka Systems Co., Ltd., a 640 μm × 480 μm measurement surface area was measured using a Sony HR-50 1 / 3' CCD camera, a 20x objective lens, a 1X body lens barrel, a no-relay zoom lens, a 530 white wavelength filter, and measurement mode: Wave. Using output from a fourth-order polynomial correction, the arithmetic mean height (Sa) and maximum peak height (Sp) of each surface were averaged over 10 points.

[0252] (8) Static friction coefficient / dynamic friction coefficient The static friction coefficient between the resin layer A surface (side A) and the resin layer B surface (side B) of a release film was determined using the following method. A release film was attached to a smooth glass plate measuring 10 mm wide and 100 mm long, and another release film cut to a width of 18 mm and a length of 120 mm was slid over the release film to measure the friction force between the resin layer A surface (side A) and the resin layer B surface (side B). Specifically, another release film was pressed against an 8 mm diameter metal pin, and the metal pin was slid longitudinally across the glass plate at a load of 30 g and a speed of 40 mm / min to measure the friction force. The maximum value immediately after the start of sliding was defined as the static friction coefficient, and the average value of the friction coefficients over the sliding distance of 4 mm to 6 mm was defined as the kinetic friction coefficient. Measurements were performed at room temperature (23 ± 1°C) and a relative humidity of 50 ± 0.5%. Ten measurements (N) were performed, and the average value was used. Static friction coefficient (μs) = Fs / weight load (In the above formula, the units of Fs and Fd are g-force, and the unit of weight load is g-force) In the comparative example in which the resin layer B was not provided, the exposed surface of the polyester film was used in place of the B surface for evaluation.

[0253] (9) Ceramic green sheet sticking prevention A composition consisting of the materials listed below was stirred and mixed, and dispersed for 60 minutes using a paint shaker with zirconia beads of 0.5 mm diameter as a dispersoid to obtain a ceramic slurry. Toluene 39.84 parts by mass Ethanol 39.84 parts by mass Barium titanate (HPBT-1 manufactured by Fuji Titanium Industry Co., Ltd.) 17.65 parts by mass Polyvinyl butyral (S-LEC BM-S manufactured by Sekisui Chemical Co., Ltd.) 1.77 parts by mass DOP (dioctyl phthalate) 0.90 parts by mass The resulting ceramic slurry was then applied to the resin layer A surface (release surface) of a release film using an applicator to a dry thickness of 1.0 μm, followed by drying at 90°C for 2 minutes to form a ceramic green sheet on the resin layer A surface. Two sample sheets each having a resin layer B / polyester film / resin layer A / ceramic green sheet configuration were stacked in the same direction, and a pressure of 8.2 MPa was applied from above and below for 5 hours. After that, the two sheets were peeled off, and the degree of peeling (anti-sticking property) between the ceramic green sheet and resin layer B was evaluated sensorily according to the following criteria. In the comparative example without resin layer A, the ceramic slurry was applied to the exposed surface of the polyester film instead of surface A. (Judgment criteria) A: Ceramic green sheet can be easily peeled off from resin layer B B: The ceramic green sheet can be peeled off from the resin layer B, but in rare cases it cannot be peeled off. C: The ceramic green sheet is difficult to peel off from the resin layer B (sticking can be seen)

[0254] (10) Charge amount when peeling off ceramic green sheet Using the two-ply sample prepared in (9), the amount of static electricity when peeling the ceramic green sheet from the resin layer B was measured using a KSD-1000 device manufactured by Kasuga Electric Co., Ltd. The maximum amount of static electricity when peeling was taken as the amount of charge when peeling the ceramic green sheet. The peel angle when peeling the ceramic green sheet was 90 degrees, and the peel speed was 4 cm / sec. The amount of charge was measured in an environment of 20°C and relative humidity of 50%. The amount of charge when the ceramic green sheet was peeled off was measured 10 times, and the average value was calculated.

[0255] (11) Air leakage index The air leakage index of release films was measured in accordance with JIS P8119 using a DigiBec smoothness tester ("DB-2" manufactured by Toyo Seiki Co., Ltd.) at a temperature of 23°C and a relative humidity of 50%. The pressure of the pressure device was 100 kPa, and the vacuum container was a 38 ml container. The time (seconds) for 1 mL of air to flow, i.e., the time (seconds) for the pressure inside the container to change from 50.7 kPa to 48.0 kPa, was measured, and the air leakage index was calculated by multiplying the measured number of seconds by 10. The release film sample size was 70 mm square, and 20 sheets were stacked with the front and back of the release film overlapping to form a test laminate film. A 5 mm diameter hole was then drilled in the center of this test laminate film, and the air leakage index was measured as described above. A higher air leakage index value indicates a longer time for air to leak through the gaps between the films, indicating a tighter contact between the films and a greater likelihood of wrinkling when rolled. In addition, the air leakage index reduction rate was calculated using the following formula. Air leakage index reduction rate (%) = 100 - air leakage index of target release film / air leakage index of virgin release film x 100 The air leakage index of the virgin release film in the above formula is the air leakage index of the polyester film obtained in Comparative Example 5.

[0256] (12) Tm (melting peak temperature), ΔHm (melting peak heat quantity) An 8 mg sample cut from the release film was measured using a differential scanning calorimeter (DSC8500) manufactured by Shimadzu Corporation. The sample temperature is (1) Heat from 20°C to 300°C at 10°C / min (2) Hold at 300°C for 5 minutes (3) Cool down to 20°C at 600°C / min (4) Keep at 20°C for 5 minutes (5) Heat from 20°C to 300°C at 10°C / min (6) Hold at 300°C for 5 minutes (7) Decrease temperature to 20°C at 600°C / min The melting peak temperature (Tm: peak top temperature of the endothermic curve of crystalline melting) and melting peak heat quantity (ΔHm: peak heat quantity of the endothermic curve of crystalline melting) in (1) were determined.

[0257] (13) Gas density The gas density of the release film was measured using an Accupyc1330 (dry automatic density meter) manufactured by Shimadzu Corporation. The measurement conditions were as follows: Each release film sample was vacuum dried for 30 minutes or more before measurement. ·Measurement temperature: 23℃ Measurement cell: 10cm 3 Gas used: Helium gas (purity > 99.99995% by volume)

[0258] (14) Heat shrinkage rate A release film (1.5 cm wide x 15 cm long) was used as the evaluation film and subjected to heat treatment 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 was calculated using the following formula. The heat shrinkage was measured in both the machine direction (MD) and the transverse direction (TD) of the release film. The heat shrinkage in MD was measured so that the machine direction was the MD, and the heat shrinkage in TD was measured so that the machine direction was 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) × 100

[0259] (15) Content of terephthalic acid and isophthalic acid components contained in polyester film A sample solution was prepared by dissolving the raw polyester in a solvent consisting of a 10:1 (volume ratio) mixture of chloroform D (manufactured by Eurisotop) and trifluoroacetic acid D1 (manufactured by Eurisotop). The sample solution was then subjected to proton NMR measurement using an NMR (GEMINI-200; manufactured by Varian) at a temperature of 23°C and an accumulation count of 64. In the NMR measurement, the peak intensity of a predetermined proton was calculated, and the content (mol %) of terephthalic acid and isophthalic acid components in 100 mol % of the acid component was calculated.

[0260] <Materials used> The polyesters used in the examples and comparative examples are as follows:

[0261] (1) Polyester A: 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 dicarboxylic acid units, diethylene glycol unit content 1.3 mol% relative to 100 mol% of all diol units) (2) Polyester B: Recycled polyethylene terephthalate from PET bottles, "UK-31" manufactured by Utsumi Recycle Systems (intrinsic viscosity 0.711 dl / g, isophthalic acid unit content 1.4 mol% relative to 100 mol% of total dicarboxylic acid units, diethylene glycol unit content 2.29 mol% relative to 100 mol% of total glycol units) (3) Polyester C: Masterbatch (intrinsic viscosity 0.61 dL / g) containing 2.0% by mass of 0.7 μm calcium carbonate particles in homopolyethylene terephthalate (antimony catalyst) (4) Polyester D: homopolyethylene terephthalate (titanium catalyst, intrinsic viscosity 0.63 dL / g)

[0262] Next, resin compositions obtained by mixing with stirring the components in the formulations shown in Table 1 below were diluted with water to prepare coating solutions 1 to 8.

[0263] [Table 1]

[0264] (1) A1: Compound containing a long-chain alkyl group A compound containing a long-chain alkyl group, in which octadecyl isocyanate is added to polyvinyl alcohol with an average degree of polymerization of 500 and a degree of saponification of 88 mol%.

[0265] (2) A2: Wax A wax emulsion obtained by the following method. 300 g of oxidized polyethylene wax having a melting point of 105°C, an acid value of 16 mgKOH / g, a density of 0.93 g / mL, and an average molecular weight of 5000, 650 g of ion-exchanged water, 50 g of decaglycerin monooleate surfactant, and 10 g of 48% aqueous potassium hydroxide solution were placed in a 1.5 L emulsification facility equipped with a stirrer, thermometer, and temperature controller, and after purging with nitrogen, the facility was sealed and stirred at high speed at 150°C for 1 hour, cooled to 130°C, passed through a high-pressure homogenizer under 400 atmospheres, and cooled to 40°C to obtain a wax emulsion.

[0266] (3) A3: Fluorine compounds A water dispersion of a fluorine compound polymerized according to the following composition: Octadecyl acrylate / perfluorohexylethyl methacrylate / vinyl chloride = 66 / 17 / 17 (mass%)

[0267] (4) B1: Binder resin (acrylic resin) Aqueous dispersion of acrylic resin polymerized according to the following composition. Emulsion polymer of ethyl acrylate / n-butyl acrylate / methyl methacrylate / N-methylolacrylamide / acrylic acid = 65 / 21 / 10 / 2 / 2 (mass%) (emulsifier: anionic surfactant)

[0268] (5) B2: Binder resin (acrylic resin) A water dispersion of a mixture of an acrylic resin and an oxazoline compound polymerized in the following composition. A mixture of 90 parts by mass of an acrylic resin formed from methyl methacrylate / ethyl acrylate = 64 / 36 (mass%) and 10 parts by mass of an oxazoline compound.

[0269] (6) B3: Binder resin (polyester resin) A water dispersion of a polyester resin copolymerized with the following composition: Monomer composition: (acid component) terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / / (diol component) ethylene glycol / 1,4-butanediol / diethylene glycol = 56 / 40 / 4 / / 70 / 20 / 10 (mol%)

[0270] (7) B4: Binder resin (urethane resin) When (C1a) is a polyester polyol containing 282 parts by mass of terephthalic acid, 282 parts by mass of isophthalic acid, 62 parts by mass of ethylene glycol, and 250 parts by mass of neopentyl glycol, a polyester polyurethane containing 876 parts by mass of (C1a), 244 parts by mass of tolylene diisocyanate, 81 parts by mass of ethylene glycol, and 67 parts by mass of dimethylolpropionic acid was neutralized with ammonia and dispersed in water (concentration 20% by mass, viscosity at 25°C 50 mPa s).

[0271] (8) B5: Binder resin (PEO resin) A compound in which an average of 40 polyethylene oxide molecules are added to the polyglycerin skeleton where n=2 in the formula below. [ka]

[0272] (9) B6: Binder resin (polyester resin) A water dispersion of a polyester resin copolymerized with the following composition: Monomer composition: (acid component) terephthalic acid / isophthalic acid / sulfoisophthalic acid / / (diol component) ethylene glycol / neopentyl glycol = 49 / 48 / 3 / / 50 / 50 (mol%)

[0273] (10) B7: Binder resin (polyester resin) A water dispersion of a polyester resin copolymerized with the following composition: Monomer composition: (acid component) 2,6-naphthalenedicarboxylic acid / 5-sodium sulfoisophthalic acid / / (diol component) ethylene glycol / diethylene glycol = 92 / 8 / / 80 / 20 (mol%)

[0274] (11) B8: Binder resin (PEO resin) Polyglycerol in the following formula where n=4. [ka]

[0275] (12) C1: Antistatic agent A polymer having a pyrrolidinium ring in the main chain, polymerized with the following composition. Diallyldimethylammonium chloride / dimethylacrylamide / N-methylolacrylamide = 90 / 5 / 5 (mol%). Number average molecular weight: approximately 30,000.

[0276] (13) C2: Antistatic agent PEDOT / PSS Conductive agent (Orgacon ICP1010 manufactured by Agfa-Gevaert) consisting of polyethylenedioxythiophene and polystyrene sulfonic acid was neutralized with concentrated aqueous ammonia to pH = 9 (non-volatile component: 1.2 mass%, solvent: water).

[0277] (14) D1: Crosslinking agent Melamine compound: hexamethoxymethylolmelamine

[0278] (15) D2: Crosslinking agent Epoxy compound: Polyglycerol polyglycidyl ether

[0279] (16) E1: Surfactant A nonionic surfactant having a structure having polyethylene oxide in the side chain, as shown in the following formula: [ka]

[0280] (17) E2: Surfactant A fluorine-based nonionic surfactant with a structure that has a branched perfluoroalkenyl group in the hydrophobic group and a polyethylene oxide chain (average chain length 8 units) in the hydrophilic group.

[0281] (18)F: Particle Silica particles with an average particle size (average primary particle size) of 0.07 μm

[0282] (Example 1: Polyester film No. 1) The surface layer was made of 100% polyester A, the middle layer was made of 100% polyester B, and the back layer was made of a blend of 80% polyester A and 20% polyester C by mass. These materials were fed into a vented extruder and melted at 280°C. The resulting mixture was then co-extruded to form a three-layer (A / B / C) structure consisting of a surface layer, a middle layer, and a back layer, with a thickness ratio of A / B / C = 3.2 / 26.2 / 1.6. The mixture was cooled and solidified on a chill roll set at 25°C using an electrostatic adhesion method to obtain an amorphous film. The back layer was the side in contact with the chill roll.

[0283] Next, the film was stretched 3.5 times in the machine direction, i.e., in the MD direction, at a film temperature of 86°C using the difference in roll peripheral speed, and both sides of the film were coated with Coating Solution 1 and Coating Solution 2 listed in Table 1. Thereafter, the machine-stretched film was introduced into a tenter, preheated at 90°C in the tenter, and then stretched 4.2 times in the transverse direction, i.e., in the TD direction, at 105°C. Each film was heat-treated at 230°C in the heat treatment (fixing) zone of the tenter, and then cooled to 140°C with a relaxation rate of 2%, to obtain a release film with an overall thickness of approximately 31 μm.

[0284] (Comparative Example 1: Polyester Film No. 1) A release film (polyester film) having a thickness of 31 μm was obtained in the same manner as in Example 1, except that Coating Liquid 1 and Coating Liquid 2 were not applied and Resin Layer A and Resin Layer B were not provided.

[0285] (Examples 2 to 6 and Comparative Example 2: Polyester Film No. 1) A release film having a thickness of about 31 μm was obtained in the same manner as in Example 1, except that the coating liquid 2 used in Example 1 was changed to the coating liquid shown in Table 2.

[0286] (Example 7: Polyester film No. 2) A release film with an overall thickness of approximately 31 μm was obtained in the same manner as in Example 1, except that a material containing 100% polyester B was used as the material for the surface layer, a material containing 100% polyester B was used as the material for the middle layer, and a material blended with 80% polyester B and 20% polyester C in a mass ratio was used as the material for the back layer.

[0287] (Comparative Example 3: Polyester Film No. 2) A release film (polyester film) having a thickness of 31 μm was obtained in the same manner as in Example 7, except that Coating Liquid 1 and Coating Liquid 2 were not applied and Resin Layer A and Resin Layer B were not provided.

[0288] (Examples 8 to 12 and Comparative Example 4: Polyester Film No. 2) A release film having a thickness of approximately 31 μm was obtained in the same manner as in Example 7, except that the coating liquid 2 used in Example 7 was changed to the coating liquid shown in Table 3.

[0289] (Comparative Example 5: Polyester film No. 3) A release film with an overall thickness of 31 μm was obtained in the same manner as in Comparative Example 1, except that a material containing 100% polyester D was used as the material for the surface layer, a material containing 100% polyester D was used as the material for the middle layer, and a material blended with 80% polyester D and 20% polyester C in a mass ratio was used as the material for the back layer.

[0290] (Comparative Example 6: Polyester Film No. 3) A release film with an overall thickness of 31 μm was obtained in the same manner as in Comparative Example 2, except that a material containing 100% polyester D was used as the material for the surface layer, a material containing 100% polyester D was used as the material for the middle layer, and a material blended with 80% polyester D and 20% polyester C in a mass ratio was used as the material for the back layer.

[0291] [Table 2]

[0292] [Table 3]

[0293] [Table 4]

[0294] From the results shown in Tables 2 to 4, it was found that the examples had a good effect of preventing sticking to the back surface (opposite to the release surface) of the thin ceramic green sheet. Therefore, even when the release film of this embodiment is wound into a roll, the ceramic green sheet does not stick to the back surface (opposite to the release surface) of the release film, and the unwinding property is good. On the other hand, in all of the comparative examples, it was difficult to prevent the ceramic green sheet from sticking to the back surface (opposite the release surface).Furthermore, in comparative examples 1, 3 and 5, the releasability of the ceramic green sheet was also poor.

[0295] The present invention has discovered a new problem that had not been considered a problem in the past: "sticking of a thin ceramic green sheet to the non-release surface (back surface) of a release film," which is caused by the unique flexibility of a thin ceramic green sheet, particularly one having a thickness (after drying) of, for example, 2 μm or less.The present invention has solved this problem by configuring the release film of this embodiment, leading to the completion of the present invention.

[0296] Furthermore, in the present invention, since the polyester film contains recycled polyester resin, the air leakage index of the release film is small, indicating that the handleability of the release film is good. [Industrial Applicability]

[0297] The release film of this embodiment is useful for molding thin ceramic green sheets. In this embodiment, the film can be wound into a roll while ceramic green sheets are laminated on it, and even when thin ceramic green sheets having a thickness (after drying) of 2 μm or less are used, the ceramic green sheets do not stick to the back surface (opposite the release surface), providing a release film with excellent handleability. [Explanation of symbols]

[0298] 10 Polyester film 20 Resin layer A 30 Resin layer B 100 Release Film

Claims

1. A polyester film is provided with a resin layer A on one side and a resin layer B on the other side, the polyester film contains recycled polyester resin, the resin layer A contains a release agent, a release film having an electrostatic charge of 16 kV or less when the resin layer B and the ceramic green sheet are separated from each other under the following measurement conditions: (Measurement conditions) A ceramic green sheet having a thickness of 1.0 μm was formed on resin layer A from a composition containing 39.84 parts by mass of toluene, 39.84 parts by mass of ethanol, 17.65 parts by mass of barium titanate, 1.77 parts by mass of polyvinyl butyral, and 0.90 parts by mass of dioctyl phthalate. The ceramic green sheet and resin layer B were then treated at a press pressure (8.2 MPa) for 5 hours, and the amount of static electricity was measured when peeling the ceramic green sheet from resin layer B; the peel angle when peeling the ceramic green sheet was 90 degrees and the peel speed was 4 cm / sec.

2. The release film according to claim 1 , wherein the resin layer B contains an antistatic agent (C).

3. A polyester film is provided with a resin layer A on one side and a resin layer B on the other side, the polyester film contains recycled polyester resin, the resin layer A contains a release agent, The release film, wherein the resin layer B contains an antistatic agent (C).

4. The release film according to claim 2 or 3, wherein the antistatic agent (C) is an ion-conductive polymer compound.

5. 4. The release film according to claim 2 or 3, wherein the (C) antistatic agent is at least one selected from (a1) a polymer in which a compound made of thiophene or a thiophene derivative is doped with another anionic compound, and (a2) a polymer in which a compound made of thiophene or a thiophene derivative has an anionic group and is self-doped.

6. 4. The release film according to claim 2, wherein the content of the antistatic agent (C) is 5% by mass or more based on the total mass of the resin layer (B).

7. The release film according to claim 1 or 3, wherein the resin layer A comprises (A) a non-silicone release agent.

8. 8. The release film according to claim 7, wherein the non-silicone release agent (A) is at least one selected from the group consisting of waxes and long-chain alkyl group-containing compounds.

9. The release film according to claim 1 or 3, wherein the resin layer B contains (A) a non-silicone release agent.

10. 10. The release film according to claim 9, wherein the non-silicone release agent (A) is at least one selected from the group consisting of waxes and long-chain alkyl group-containing compounds.

11. 10. The release film according to claim 9, wherein the content of the non-silicone release agent (A) is 5% by mass or more relative to the total mass of the resin layer (B).

12. The release film according to claim 1 or 3, wherein the resin layer B comprises a binder resin (B).

13. 13. The release film according to claim 12, wherein the binder resin (B) is at least one selected from a (meth)acrylic resin and a polyvinyl alcohol.

14. The release film according to claim 1 or 3, wherein the resin layer B contains (D) a crosslinking agent.

15. 15. The release film according to claim 14, wherein the crosslinking agent (D) is at least one selected from the group consisting of a melamine compound and an oxazoline compound.

16. 4. The release film according to claim 1, wherein the content of the recycled polyester resin relative to the total mass of resin components in the polyester film is 90 mass% or more.

17. The release film according to claim 1 or 3, wherein the polyester film has a three-layer structure having a surface layer, an intermediate layer, and a back layer.

18. 18. The release film of claim 17, wherein the surface layer comprises a chemically recycled polyester resin.

19. 18. The release film of claim 17, wherein the backing layer comprises a chemically recycled polyester resin.

20. 18. The release film according to claim 17, wherein the intermediate layer comprises a material recycled polyester resin.

21. The release film according to claim 1 or 3, wherein the maximum peak height (Sp) of the resin layer A side is 60 nm or less.

22. The release film according to claim 1 or 3, wherein the arithmetic mean height (Sa) of the resin layer A surface is 5 nm or less.

23. The release film according to claim 1 or 3, wherein the thickness of the release film is 9 to 50 μm.

24. 4. The release film according to claim 1, wherein a dynamic friction coefficient between the resin layer B surface and the resin layer A surface of the release film is 0.2 or less.

25. 4. The release film according to claim 1, wherein the air leakage index is 8,500 seconds or less.

26. 4. The release film according to claim 1, wherein the air leakage index reduction rate calculated by the following formula is 5% or more. Air leakage index reduction rate (%) = 100 - air leakage index of target release film / air leakage index of virgin release film × 100

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

28. 4. The release film according to claim 1, wherein the release film has a melting peak temperature (Tm) of 254°C or less.

29. 4. The release film according to claim 1, wherein the heat of fusion peak (ΔHm) is 40 J / g or less.

30. Gas density is 1.405 g / cm ３ The release film according to claim 1 or 3, wherein the release film is as described above.

31. 4. The release film according to claim 1, wherein the recycled polyester resin is a recycled polyester (PET) bottle.

32. 4. The release film according to claim 1, which is used as a support for a ceramic green sheet in the process of producing a multilayer ceramic capacitor.

33. A release film with a ceramic green sheet, comprising the release film according to claim 1 or 3, and a ceramic green sheet laminated on the resin layer A of the release film.

34. 34. The release film with a ceramic green sheet according to claim 33, wherein the ceramic green sheet has a thickness (after drying) of 2 μm or less.

35. The ceramic green sheet-attached release film according to claim 33, which is used in a manufacturing process of a multilayer ceramic capacitor.

36. 4. Use of the release film according to claim 1 or 3 as a support for a ceramic green sheet in the process of producing a multilayer ceramic capacitor.

37. A method for producing a ceramic green sheet, comprising a step of applying a ceramic slurry containing a ceramic component to at least one surface of the release film according to claim 1 or 3.

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