Polyester film

Abstract

The present invention addresses the problem of providing a polyester film which has excellent coatability with organic-solvent-containing compositions and has a feature wherein a sheet formed on the surface of the release layer can be peeled off at a high speed. This polyester film comprises a release layer and a polyester substrate. The release layer includes an acrylic resin, the surface of the release layer has a water sliding angle of 90° or less, and the release layer has a thickness less than 200 nm.

Description

Polyester film

[0001] The present invention relates to a polyester film.

[0002] Polyester films are used in a variety of applications, such as films for touch panels, films for optical components, substrates for molding, substrates for decorative films, and substrates for photosensitive layers.

[0003] One application of polyester films is as a release film, which is a polyester substrate having a release layer formed thereon, various components being produced in contact with the release layer, and then the components are released.

[0004] Here, when a polyester film is used as a release film, a composition containing an organic solvent (e.g., a ceramic slurry) is applied to the release layer surface of the polyester film, and a sheet (e.g., a ceramic green sheet) is formed on the release layer surface. Therefore, the release layer of the polyester film is required to have excellent coatability for the composition containing an organic solvent. However, when a release layer is formed using a composition such as that described in Patent Document 1 and a composition containing an organic solvent such as a ceramic slurry is applied, repellency defects may occur.

[0005] To address this problem, Patent Document 2 discloses a technique for improving coatability by forming a release layer using a composition containing a specific acrylic resin.

[0006] International Publication No. 2023 / 281972 International Publication No. 2021 / 192896

[0007] According to the technology described in the above-mentioned Patent Document 2, since a composition for forming a release layer that does not contain a silicone resin is used, the coating property tends to be improved. However, when the peeling speed when peeling off the sheet formed on the surface of the release layer is increased (i.e., when the sheet is peeled off at high speed), the sheet's peelability is insufficient. Thus, in the release layer contained in the polyester film, it is difficult to achieve both excellent coating property of the composition containing an organic solvent and excellent high-speed peelability of the sheet formed on the surface of the release layer.

[0008] Therefore, an object of the present invention is to provide a polyester film that has excellent coatability with compositions containing organic solvents and also has excellent high-speed peelability of a sheet formed on the release layer surface.

[0009] The present inventors have conducted extensive research to solve the above problems and have completed the present invention. That is, they have found that the above problems can be solved by the following configuration.

[0010] [1] A polyester film comprising a release layer and a polyester substrate, wherein the release layer contains an acrylic resin, the water sliding angle on the surface of the release layer is 90° or less, and the thickness of the release layer is less than 200 nm. [2] The polyester film according to [1], wherein the silicon atom content on the surface of the release layer is 25 atomic % or less. [3] The polyester film according to [1] or [2], wherein the polyester substrate is substantially free of particles, and the maximum protrusion height Sp on the surface of the release layer is less than 35 nm. [4] The polyester film according to any one of [1] to [3], wherein the thickness of the release layer is less than 90 nm. [5] The release layer is formed from -Si(R) ３wherein R each independently represents an alkyl group or an aryl group. [6] The polyester film according to any one of [1] to [4], wherein the release layer comprises a crosslinked product of an acrylic resin A having a siloxane bond and a crosslinking agent B. [7] The polyester film according to [6], wherein the acrylic resin A comprises a structural unit derived from a monomer A1 that is an acrylic monomer having a siloxane bond, and the molecular weight of the monomer A1 is 4,000 or less. [8] The polyester film according to any one of [1] to [7], wherein the polyester film is used for producing a ceramic green sheet.

[0011] According to the present invention, a polyester film can be provided which has excellent coatability with compositions containing organic solvents and excellent high-speed peelability of a sheet formed on the release layer surface.

[0012] 1 is a side view schematically illustrating an example of a polyester film of the present invention. 2 is a schematic view illustrating an example of a stretching machine used in producing the polyester film of the present invention.

[0013] The present invention will be described in detail below. The following description of the components may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0014] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. Furthermore, in this specification, when two or more types of a component are present, the "content" of that component means the total content of those two or more components. In this specification, in a numerical range described in stages, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in a numerical range described in this specification, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0015] In this specification, "longitudinal direction" refers to the longitudinal direction of the film during film production, and is synonymous with "conveyance direction" and "machine direction." In this specification, "width direction" refers to a direction perpendicular to the longitudinal direction. In this specification, "perpendicular" is not limited to strictly perpendicular, but also includes approximately perpendicular. "Approximately perpendicular" means intersecting within a range of 90°±5°, preferably within a range of 90°±3°, and more preferably within a range of 90°±1°.

[0016] The content (mass%) of each structural unit relative to the total units contained in the acrylic resin was determined by measuring the acrylic resin with proton nuclear magnetic resonance ( １ It is determined by analysis using a H-NMR method.

[0017] [Polyester Film] The polyester film of the present invention is described in detail below. The polyester film of the present invention is a polyester film comprising a release layer and a polyester substrate, wherein the release layer contains an acrylic resin, the water sliding angle of the release layer surface is 90° or less, and the release layer thickness is less than 200 nm.

[0018] The polyester film of the present invention has excellent coatability with compositions containing organic solvents and excellent high-speed releasability of sheets formed on the release layer surface. While the details of the reasons for this are unclear, it is generally assumed as follows. It is presumed that the polyester film of the present invention has excellent coatability with compositions containing organic solvents (e.g., ceramic slurries) because the release layer contains an acrylic resin. It is also presumed that the hardness of the release layer is appropriately controlled by having a thickness of the release layer below a predetermined value, and that the water sliding angle on the release layer surface is below a predetermined value, resulting in excellent high-speed releasability of sheets formed on the release layer surface. In this specification, the term "effects of the present invention" refers to at least one of the coatability with compositions containing organic solvents and the high-speed releasability of sheets formed on the release layer surface.

[0019] The polyester film of the present invention will be described in detail below. FIG. 1 is a side view schematically illustrating an example of the polyester film of the present invention. The polyester film 300 includes a polyester substrate 310 and a release layer 320. The polyester substrate 310 is disposed on one side 321 of the release layer 320. The other side 322 of the release layer 320 is the surface opposite to the side of the release layer 320 on which the polyester substrate 310 is disposed (i.e., one side 321), and may be referred to as the release layer surface or release surface.

[0020] <Polyester substrate> The polyester substrate is a film-like object containing a polyester resin as a main component. Here, the "main component" refers to the component that is contained in the largest amount (by mass) of all the components contained in the film-like object.

[0021] The polyester substrate is preferably a biaxially oriented polyester substrate. "Biaxial orientation" refers to the property of having molecular orientation in two axial directions. The molecular orientation is measured using a microwave transmission molecular orientation meter (for example, MOA-6004, manufactured by Oji Scientific Instruments Co., Ltd.). The angle between the two axial directions is preferably within the range of 90°±5°, more preferably within the range of 90°±3°, and even more preferably within the range of 90°±1°. The molecular orientation changes when stretching is performed, and a biaxially oriented polyester substrate can be produced by performing biaxial stretching.

[0022] The polyester substrate is preferably substantially free of inorganic particles in order to improve the smoothness of the release layer surface. "Substantially free of inorganic particles" is defined as the content of inorganic particles being 50 mass ppm or less, preferably 10 mass ppm or less, more preferably below the detection limit, relative to the total mass of the polyester substrate when elements derived from inorganic particles are quantitatively analyzed by fluorescent X-ray analysis. This is because even if inorganic particles are not actively added to the polyester substrate, contaminants derived from foreign matter, raw resins, or dirt attached to the line or equipment in the manufacturing process of the polyester substrate may peel off and be mixed into the polyester substrate. Here, examples of inorganic particles include inorganic particles that may be contained in the particle-containing layer (protrusion-containing layer) described below.

[0023] Preferably, the polyester substrate is substantially free of particles. Examples of particles include the inorganic particles and organic particles described above. Whether or not the polyester substrate is substantially free of particles can be confirmed by the following procedure. Ten different locations on the cross section of the polyester substrate are observed using a scanning electron microscope to confirm the presence or absence of particles with a size of 10 nm to 10 μm in the cross section of the polyester substrate. The magnification during observation is adjusted to 5,000 to 20,000 times. If particles are observed in any location, this means that particles are contained in the release layer. On the other hand, if particles are not observed in any cross section, this means that particles are not contained in the polyester substrate. Here, examples of organic particles include organic particles contained in the particle-containing layer (protrusion-containing layer) described below.

[0024] (Polyester Resin) The polyester resin contained in the polyester base material is a polymer having an ester bond in the main chain. The polyester resin is usually formed by polycondensation of a dicarboxylic acid compound and a diol compound, which will be described later. There are no particular limitations on the polyester resin, and known polyester resins can be used. Examples of polyester resins include polyethylene terephthalate (PET), polypropylene terephthalate (PPT), polybutylene terephthalate (PBT), polyethylene-2,6-naphthalate (PEN), and copolymers thereof. PET, PEN, and copolymers thereof are preferred, and PET is more preferred.

[0025] The intrinsic viscosity (IV) of the polyester film of the present invention is preferably 0.50 dl / g or more but less than 0.80 dl / g, more preferably 0.55 dl / g or more but less than 0.70 dl / g, and even more preferably 0.60 dl / g or more but less than 0.70 dl / g. The intrinsic viscosity (IV) of the polyester film of the present invention can be determined by dissolving the polyester film of the present invention in a 1,1,2,2-tetrachloroethane / phenol (2 / 3 [mass ratio]) mixed solvent and measuring the solution viscosity at 25°C. The amount of terminal carboxyl groups in the polyester film of the present invention [terminal COOH amount, AV; Acid Value] is preferably 3.5 eq / ton or less, more preferably 3.0 eq / ton or less, and even more preferably 2.8 eq / ton or less. The lower the terminal COOH amount of the polyester film of the present invention, the more likely it is that the water content will decrease. The lower limit is, for example, 0.5 eq / ton or more. The amount of terminal COOH groups can be calculated from the appropriate amount obtained by completely dissolving the polyester film of the present invention in a mixed solvent of benzyl alcohol / chloroform (=2 / 3; volume ratio), titrating the solution with a reference solution (0.01N KOH-benzyl alcohol mixed solution) using phenol red as an indicator. In this specification, "eq / ton" represents the molar equivalent per ton. The melting point (Tm) of the polyester resin is preferably 220 to 270°C, more preferably 245 to 265°C. The glass transition temperature (Tg) of the polyester resin is preferably 65 to 90°C, more preferably 70 to 85°C.

[0026] The method for producing the polyester resin is not particularly limited, and any known method can be used. For example, the polyester resin can be produced by polycondensing at least one dicarboxylic acid compound and at least one diol compound in the presence of a catalyst.

[0027] Catalyst The catalyst used in producing the polyester resin is not particularly limited, and any known catalyst usable in synthesizing polyester resins can be used. Examples of catalysts include alkali metal compounds (e.g., potassium compounds, sodium compounds), alkaline earth metal compounds (e.g., calcium compounds, magnesium compounds), zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, germanium compounds, and phosphorus compounds. Titanium compounds and aluminum compounds are preferred because they are less likely to produce foreign matter or voids in the polyester substrate. A single catalyst may be used, or two or more may be used in combination. It is also preferable to use at least one metal catalyst selected from potassium compounds, sodium compounds, calcium compounds, magnesium compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, and germanium compounds in combination with a phosphorus compound. When using a catalyst in combination, it is preferable to adopt the compounds and amounts described in paragraphs

[0055] to

[0062] of Japanese Patent Publication No. 5,575,671. Furthermore, when the content of the titanium compound in the polyester film is 5 to 15 ppm by mass in terms of Ti element, the content of the magnesium compound used in combination is preferably 60 to 90 ppm by mass in terms of Mg element, and the content of the phosphorus compound used in combination is preferably 5 to 35 ppm by mass in terms of P element.

[0028] The titanium compound is preferably an organic chelate titanium complex. The organic chelate titanium complex is a titanium compound having an organic acid as a ligand. Examples of organic acids include citric acid, lactic acid, trimellitic acid, and malic acid. The titanium compounds described in paragraphs

[0049] to

[0053] of Japanese Patent No. 5575671 can also be used, and the disclosure of this publication is incorporated herein by reference. The content of the titanium compound is preferably 1 to 300 ppm by mass, more preferably 3 to 20 ppm by mass, and even more preferably 5 to 15 ppm by mass, in terms of elemental Ti relative to the total mass of the polyester film. The element content can be measured by inductively coupled plasma mass spectrometry (ICP-MS).

[0029] Examples of the aluminum compound include organoaluminum compounds and partial hydrolysates thereof. The organoaluminum compound is preferably a carboxylate, an inorganic acid salt, or a chelate compound, and more preferably aluminum acetate, basic aluminum acetate, aluminum lactate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride, or aluminum acetylacetonate.

[0030] Dicarboxylic Acid Compound Examples of the dicarboxylic acid compound include dicarboxylic acids such as aliphatic dicarboxylic acid compounds, alicyclic dicarboxylic acid compounds, and aromatic dicarboxylic acid compounds, as well as dicarboxylic acid esters such as methyl ester compounds and ethyl ester compounds of these dicarboxylic acids. Among these, aromatic dicarboxylic acids or aromatic methyl dicarboxylates are preferred.

[0031] Examples of the aliphatic dicarboxylic acid compound include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosanedioic acid, pimelic acid, azelaic acid, methylmalonic acid, and ethylmalonic acid. Examples of the alicyclic dicarboxylic acid compound include adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, and decalindicarboxylic acid.

[0032] Examples of aromatic dicarboxylic acid compounds include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodiumsulfoisophthalic acid, phenylindanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, and 9,9'-bis(4-carboxyphenyl)fluorene acid. Among these, terephthalic acid or 2,6-naphthalenedicarboxylic acid is preferred, and terephthalic acid is more preferred.

[0033] The dicarboxylic acid compound may be used alone or in combination of two or more. When terephthalic acid is used as the dicarboxylic acid compound, terephthalic acid may be used alone or may be copolymerized with other aromatic dicarboxylic acids such as isophthalic acid or aliphatic dicarboxylic acids.

[0034] Diol Compound Examples of the diol compound include an aliphatic diol compound, an alicyclic diol compound, and an aromatic diol compound, and an aliphatic diol compound is preferred.

[0035] Examples of aliphatic diol compounds include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and neopentyl glycol, with ethylene glycol being preferred. Examples of alicyclic diol compounds include cyclohexanedimethanol, spiroglycol, and isosorbide. Examples of aromatic diol compounds include bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, and 9,9'-bis(4-hydroxyphenyl)fluorene. Only one type of diol compound may be used, or two or more types may be used in combination.

[0036] Terminal Capping Agent In the production of the polyester resin, a terminal capping agent may be used as needed. By using the terminal capping agent, a structure derived from the terminal capping agent is introduced into the terminal of the polyester resin. The terminal capping agent is not limited, and known terminal capping agents can be used. Examples of terminal capping agents include oxazoline compounds, carbodiimide compounds, and epoxy compounds. For terminal capping agents, reference can also be made to the contents of paragraphs

[0055] to

[0064] of JP 2014-189002 A, the contents of which are incorporated herein by reference.

[0037] Production Conditions The reaction temperature is not limited and may be set appropriately depending on the raw materials. The reaction temperature is preferably 260 to 300°C, more preferably 275 to 285°C. The pressure is not limited and may be set appropriately depending on the raw materials. The pressure is not limited and may be set appropriately depending on the raw materials. －３ ~1.33 x 10 －５ MPa is preferred, and 6.67 × 10 －４ ~6.67 x 10 －５ MPa is more preferred.

[0038] As a method for synthesizing a polyester resin, the method described in paragraphs

[0033] to

[0070] of Japanese Patent No. 5575671 can also be used, and the contents of the above publication are incorporated herein by reference. As a method for synthesizing a polyester resin, the contents described in paragraphs

[0023] to

[0046] of International Publication No. 2023 / 149181 can also be referenced, and the contents of this publication are incorporated herein by reference.

[0039] The content of the polyester resin in the polyester substrate is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more, based on the total mass of the polyester substrate. The upper limit of the content of the polyester resin is not limited and can be appropriately set within a range of less than 100% by mass based on the total mass of the polyester substrate.

[0040] When the polyester base material contains polyethylene terephthalate, the content of polyethylene terephthalate is preferably 90 to 100 mass%, more preferably 95 to 100 mass%, still more preferably 98 to 100 mass%, and particularly preferably 100 mass%, relative to the total mass of the polyester resin in the polyester base material.

[0041] The polyester substrate may contain components other than the polyester resin (for example, a catalyst, unreacted raw material components, particles, water, etc.).

[0042] The thickness of the polyester substrate is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, still more preferably 40 μm or less, and particularly preferably 35 μm or less. The lower limit of the thickness is not particularly limited, but from the viewpoint of improving strength and processability, it is preferably 1 μm or more, more preferably 3 μm or more, even more preferably 10 μm or more, and particularly preferably 20 μm or more. The thickness of the polyester substrate is determined by preparing a slice having a cross section perpendicular to the main surface of the polyester film and measuring the thickness of five points of the polyester substrate in the slice using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0043] <Release Layer> The polyester film of the present invention has a release layer.

[0044] (Physical Properties of Release Layer) Water Sliding Angle on the Release Layer Surface In the polyester film of the present invention, the water sliding angle on the release layer surface is 90° or less. The water sliding angle on the release layer surface is preferably 85° or less, more preferably less than 80°, even more preferably 75° or less, and particularly preferably 70° or less, from the viewpoint of superior high-speed peelability of the sheet formed on the release layer surface. The lower limit of the water sliding angle on the release layer surface is preferably 5° or more, more preferably 10° or more, from the viewpoint of superior coatability of ceramic slurries, etc. The water sliding angle on the release layer surface can be adjusted, for example, by the composition of the release layer (especially the structure of the acrylic resin contained in the release layer) and the reaction rate with the crosslinking agent. The water sliding angle on the release layer surface can be measured using a contact angle meter. A droplet is attached to the release layer surface, the glass plate is tilted, and the tilt angle at which the droplet begins to move is determined as a movement judgment distance of 50 dots. More specific measurement methods are described in the Examples section below. Here, if the droplet moves within one second after the tilt angle of the glass plate reaches 90°, the "water sliding angle is 90°" and therefore corresponds to "the water sliding angle is 90° or less." However, if the droplet does not move even one second after the tilt angle of the glass plate reaches 90°, this means that the "water sliding angle is 90° or less."

[0045] - Thickness of the Release Layer In the polyester film of the present invention, the thickness of the release layer is less than 200 nm. By having a water sliding angle of 90° or less on the release layer surface and a thickness of less than 200 nm, the high-speed releasability of the sheet formed on the release layer surface is excellent, and the low-speed releasability of the sheet formed on the release layer surface is also excellent. The thickness of the release layer is preferably less than 120 nm, more preferably less than 90 nm, and even more preferably less than 70 nm, from the viewpoint of improving the appearance of the polyester film when rolled (hereinafter simply referred to as "roll appearance"). The lower limit of the thickness of the release layer may be 3 nm or more, but from the viewpoint of improving the effects of the present invention, it is preferably 6 nm or more, more preferably 7 nm or more. The thickness of the release layer is determined by preparing a slice having a cross section perpendicular to the main surface of the polyester film and measuring the thickness of the release layer at five points on the slice using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0046] Silicon atom content The silicon atom content on the release layer surface is preferably 25 atm% or less, more preferably 20 atm% or less, and even more preferably 15 atm% or less, from the viewpoint of better coating properties of the composition containing an organic solvent.In addition, the silicon atom content on the release layer surface is preferably 2 atm% or more, more preferably 3 atm% or more, even more preferably 4 atm% or more, and particularly preferably 6 atm% or more, from the viewpoint of better high-speed peelability and / or low-speed peelability of the sheet formed on the release layer surface.In addition, the silicon atom content on the release layer surface refers to the silicon atom content (atm%) relative to the total number of silicon atoms, carbon atoms, oxygen atoms, nitrogen atoms, and sulfur atoms measured by X-ray photoelectron spectroscopy (XPS).The silicon atom content on the release layer surface can be adjusted by the composition of the release layer (especially the structure of the acrylic resin contained in the release layer) and the thickness of the release layer.

[0047] The silicon atom content can be measured using an XPS analyzer. More specifically, the contents of the following five elements present on the outermost surface of the release layer are measured using an XPS analyzer under the following conditions, and the silicon atom content (atm%) is calculated when the total of the measured atoms is 100 atm%. The arithmetic average of the values ​​obtained by performing the above measurement three times is taken as the silicon atom content (atm%) on the release layer surface. (Measurement conditions) Analytical device: X-ray photoelectron spectrometer, manufactured by Ulvac-PHI X-ray source: monochromated Al-Kα Measurement elements: carbon (C), nitrogen (N), oxygen (O), silicon (Si), sulfur (S) Measurement area: 300 μm × 300 μm Number of measurements: n = 3 Sputtering irradiation ions: argon Energy: 94 eV (0.1 eV step)

[0048] Surface free energy The surface free energy of the release layer surface is 60 mJ / m ２ In many cases, the release energy is 35 mJ / m or less, and from the viewpoint of superior high-speed peelability of the sheet formed on the surface of the release layer, ２ Preferably, 30 mJ / m or less ２ More preferably, 29 mJ / m or less ２The surface free energy of the release layer surface is more preferably 15 mJ / m or less, from the viewpoint of better coatability of a composition containing an organic solvent. ２ More than 17 mJ / m is preferable. ２ More preferably, 20 mJ / m or more ２ The above is more preferable. The surface free energy of the release layer surface can be adjusted, for example, by the silicon atom content of the release layer surface. The method for measuring the surface free energy of the release layer surface is as described in the Examples section below.

[0049] Maximum protrusion height Sp and average surface roughness Sa When the polyester film of the present invention is used to produce high-end ceramic green sheets, it is desirable that the release layer surface be smooth. From this perspective, the maximum protrusion height Sp of the release layer surface is preferably less than 35 nm, more preferably 30 nm or less, even more preferably 25 nm or less, and particularly preferably 20 nm or less. It is further preferably 15 nm or less, more preferably less than 15 nm, even more preferably 13 nm or less, and particularly preferably less than 10 nm. Furthermore, the maximum protrusion height Sp of the release layer surface is often 1 nm or more. When the release layer is formed using the acrylic resin described below, it is easy to adjust the maximum protrusion height Sp of the release layer surface to less than 35 nm. The average surface roughness Sa of the release layer surface is preferably 0 to 10 nm, more preferably 0 to 5 nm, and even more preferably 0 to 2 nm. The maximum protrusion height Sp and surface average roughness Sa of the release layer surface can also be adjusted by selecting the type of polyester and additives constituting the polyester substrate so that the polyester substrate is substantially free of particles and forms a smooth film (for example, by using a polyester resin polymerized with a titanium compound or an aluminum compound). The method for measuring the maximum protrusion height Sp and surface average roughness Sa of the release layer surface is as described in the Examples section below.

[0050] In the polyester film of the present invention, it is preferable that the polyester substrate is substantially free of particles and that the maximum protrusion height (Sp) of the release layer surface is less than 35 nm. This makes the release layer surface smoother, making the polyester film of the present invention suitable for use in the production of high-end ceramic green sheets. The meaning of the polyester substrate being substantially free of particles is as described above.

[0051] The release layer may be provided directly on the surface of the polyester substrate or via an intermediate layer, but it is preferable to provide it directly on the surface of the polyester substrate from the viewpoint of superior productivity. In other words, it is preferable that the polyester substrate and the release layer are adjacent to each other.

[0052] (-Si(R) ３ The release layer is preferably a structure represented by -Si(R) ３ It is preferable that the compound has a structure represented by the formula: —Si(R) ３ In the formula, R each independently represents an alkyl group or an aryl group. Examples of the alkyl group in R include a linear alkyl group having 1 to 10 carbon atoms (preferably 1 to 5 carbon atoms) and a branched or cyclic alkyl group having 3 to 12 carbon atoms (preferably 3 to 6 carbon atoms). Specific examples include a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, an octyl group, an isopropyl group, an isobutyl group, a 2-ethylhexyl group, a tert-butyl group, a tert-octyl group, and a cyclohexyl group. The number of carbon atoms in the aryl group in R is preferably 6 to 30, more preferably 6 to 20, and even more preferably 6 to 12. Specific examples of the aryl group include a phenyl group, a styryl group, a naphthyl group, and a biphenyl group. Among these, from the viewpoint of achieving superior effects of the present invention, R is preferably an alkyl group, more preferably a linear alkyl group having 1 to 5 carbon atoms, still more preferably a methyl group, ethyl group, propyl group, n-butyl group, isopropyl group, isobutyl group, or tert-butyl group, and particularly preferably a methyl group, ethyl group, propyl group, or butyl group. Multiple R may be the same or different.

[0053] -Si(R) ３ The structure represented by the formula: —O—Si(R) is preferred in terms of the effects of the present invention being more excellent. ３ It is preferable that the structure is a partial structure of the structure represented by -Si[-O-Si(R) ３ ] ｎ R １ ３－ｎ and -[Si(R) ２ -O] ｍ -Si(R) ３ In the formula, R is as defined above. １ R each independently represents a hydrogen atom, a hydroxyl group, an alkyl group, or an aryl group. １ The definitions and preferred embodiments of the alkyl group and aryl group represented by are the same as those of the alkyl group and aryl group represented by R. n represents 2 or 3, and preferably 3. m represents an integer of 2 or more, and is preferably an integer of 2 to 100, and more preferably an integer of 5 to 50.

[0054] -Si(R) ３ The structure represented by the formula (I) is preferably possessed by the acrylic resin contained in the release layer, and more preferably by a crosslinked product of acrylic resin A and crosslinking agent B, which will be described later.

[0055] (Acrylic Resin) The release layer contains an acrylic resin. In this specification, "acrylic resin" refers to a resin containing a structural unit derived from a (meth)acrylic acid ester. In this specification, the term "(meth)acrylic acid ester" refers to a concept including a methacrylic acid ester and an acrylic acid ester. The acrylic resin contained in the release layer is preferably a crosslinked acrylic resin synthesized by the reaction of an acrylic resin A and a crosslinking agent B when forming a release layer using a composition containing an acrylic monomer described later, compared to an acrylic resin synthesized by a chain polymerization reaction of an acrylic monomer when forming a release layer using a composition containing an acrylic monomer described later, because the high-speed release property of the sheet formed on the release layer surface is superior. This is because, compared to when a release layer is formed using a composition containing an acrylic monomer, when a release layer is formed using a composition containing an acrylic resin A and a crosslinking agent B described later, the chain polymerization reaction during the formation of the release layer is sufficiently carried out, and the hardening of the release layer often proceeds sufficiently. For example, if the release layer contains residues of a polymerization initiator (e.g., a photopolymerization initiator and a thermal polymerization initiator), it can be determined that the release layer is formed using a composition containing an acrylic monomer and is a layer containing an acrylic resin synthesized by a chain polymerization reaction of the acrylic monomer.

[0056] The acrylic resin contained in the release layer may be crosslinked or not. The release layer preferably contains a crosslinked product formed by the reaction of an acrylic resin A having a reactive group A with a crosslinking agent B having a reactive group B capable of reacting with the reactive group A. The acrylic resin contained in the release layer preferably contains a crosslinked product formed by the reaction of an acrylic resin A having a reactive group A with a crosslinking agent B having a reactive group B capable of reacting with the reactive group A. The acrylic resin contained in the release layer preferably contains a crosslinked product formed by the reaction of an acrylic resin A having a reactive group B capable of reacting with the reactive group A with a crosslinking agent B ... ３ It is preferable that the compound has a structure represented by the formula: ３ It is more preferable that the crosslinked product of the acrylic resin A and the crosslinking agent B has a structure represented by the following formula: The crosslinked product of the acrylic resin A and the crosslinking agent B will be described in more detail below.

[0057] Acrylic Resin A The acrylic resin A is a compound containing a structural unit derived from a (meth)acrylic acid ester and having a reactive group A. Examples of the reactive group A contained in the acrylic resin A include reactive groups containing at least one selected from the group consisting of a carboxy group, a carboxylic acid anhydride group, a carboxylate salt group, and a hydroxyl group. In terms of achieving better effects of the present invention, the reactive group A is preferably a carboxy group or a carboxylate salt which is a carboxylate group.

[0058] The acrylic resin A preferably has a siloxane bond. The siloxane bond is represented by the formula -[O-Si(R) ２ ]- is preferably a structure represented by -[O-Si(R) ２ ]- in which R is -Si(R) ３ It is the same as R in the above formula. It is more preferable that the acrylic resin A has two or more siloxane bonds. In order to improve the high-speed releasability of the sheet formed on the surface of the release layer, it is even more preferable that the acrylic resin A has a linear polysiloxane structure. The linear polysiloxane structure is represented by -[Si(R) ２ -O] ｍ R and m are the same as those of the above-mentioned -[Si(R) ２ -O] ｍ -Si(R) ３ Among them, acrylic resin A has the same meaning as R and m in the structure represented by —Si(R) ３ and as a structure having a siloxane bond, -Si[-O-Si(R) ３ ] ｎ R １ ３－ｎ and -[Si(R) ２ -O] ｍ -Si(R) ３ In view of the superior high-speed releasability of the sheet formed on the surface of the release layer, it is preferable to have at least one selected from the group consisting of structures represented by -[Si(R) ２ -O] ｍ -Si(R) ３ It is more preferable that R, R １, n and m are the same as those of R, R, and R, including preferred embodiments. １ , n and m are synonymous with each other.

[0059] ...Constituent Units Derived from Monomer A1 The acrylic resin A preferably contains constituent units derived from monomer A1, which is an acrylic monomer having a siloxane bond. The above-mentioned acrylic monomer represents a concept including both (meth)acrylic acid esters and (meth)acrylic acid. The (meth)acrylic acid represents a concept including methacrylic acid and acrylic acid. The monomer A1 is preferably a (meth)acrylic acid ester having a siloxane bond. Furthermore, the monomer A1 preferably contains a -Si(R) ３ It is also preferred that the monomer A1 has a group represented by the formula: ３ ] ｎ R １ ３－ｎ and a group represented by —[Si(R) ２ -O] ｍ -Si(R) ３ It is preferable that the compound has at least one group selected from the group consisting of groups represented by —[Si(R) ２ -O] ｍ -Si(R) ３ It is more preferable that the alkyl group has a group represented by the following formula:

[0060] The molecular weight of monomer A1 is preferably 5,000 or less, more preferably 4,000 or less, and even more preferably 3,000 or less, from the viewpoint of achieving better high-speed releasability of the sheet formed on the surface of the release layer. The lower limit is often 100 or more, preferably 500 or more, and more preferably 700 or more. Details of the method for measuring the molecular weight of monomer A1 are as described in the Examples section. Here, when monomer A1 is a mixture of monomers with different molecular weights, the peak with the greatest intensity detected by MS spectrometry (MS spectrum) is read, and this molecular weight is taken as the molecular weight of monomer A1.

[0061] The monomer A1 is preferably a compound represented by the following formula (A1-1): CH ２ = C(R １１ ) C(O)O-L １１-Rh (A1-1)

[0062] In formula (A1-1), R １１ is a hydrogen atom or a methyl group.

[0063] In formula (A1-1), L １１ is an alkylene group which may have a substituent. １１ The alkylene group in may be linear, branched, or cyclic, but is preferably linear or branched, and more preferably linear. １１ The number of carbon atoms in the alkylene group in the formula (I) is preferably 1 to 10, more preferably 1 to 7, and even more preferably 1 to 5. Specific examples of the substituent that the alkylene group may have include a halogen atom, an alkoxy group (preferably having 1 to 5 carbon atoms), and a carboxy group. １１ is preferably an alkylene group having no substituent, more preferably a propylene group, an ethylene group, or a methylene group.

[0064] In formula (A1-1), Rh is a substituent having a siloxane bond. Rh is —Si(R) ３ It is also preferable that Rh has one or more groups represented by the following formula: ３ ] ｎ R １ ３－ｎ or a group represented by -[Si(R) ２ -O] ｍ -Si(R) ３ Preferably, it is a group represented by -[Si(R) ２ -O] ｍ -Si(R) ３ It is more preferable that R and R are groups represented by the following formula: １ , n, and m are as described above.

[0065] Specific examples of Monomer A1 include organosilyl group-containing monomers such as 3-[tris(trimethylsilyloxy)silyl]propyl (meth)acrylate, Silaplane FM-0711 (manufactured by JNC Corporation), Silaplane FM-0721 (manufactured by JNC Corporation), Silaplane FM-0725 (manufactured by JNC Corporation), Silaplane TM-0701T (manufactured by JNC Corporation), X-22-174ASX (manufactured by Shin-Etsu Chemical Co., Ltd.), X-22-174BX (manufactured by Shin-Etsu Chemical Co., Ltd.), KF-2012 (manufactured by Shin-Etsu Chemical Co., Ltd.), X-22-2426 (manufactured by Shin-Etsu Chemical Co., Ltd.), and X-22-2404 (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0066] When the acrylic resin A has a structural unit derived from monomer A1, the content of the structural unit derived from monomer A1 is preferably 10 to 90% by mass, more preferably 15 to 85% by mass, and even more preferably 20 to 80% by mass, relative to the total structural units (100% by mass) of the acrylic resin A. When the content of the structural unit derived from monomer A1 is 10% by mass or more, the release properties of the sheet formed on the release layer surface are superior. Furthermore, when the content of the structural unit derived from monomer A1 is 90% by mass or less, the coatability of the composition containing an organic solvent is superior.

[0067] ...Constituent Units Derived from Monomer A2 The acrylic resin A preferably contains a constituent unit derived from monomer A2 containing at least one of a carboxy group, a carboxylic acid anhydride group, and a carboxylic acid salt group. This results in superior water solubility and curability of the resin. Monomer A2 preferably does not contain a siloxane bond. When the acrylic resin A contains a constituent unit derived from monomer A2, a crosslinked product of the acrylic resin A and crosslinking agent B (preferably a reactive group B) described below can be formed by reaction of at least one selected from the group consisting of a carboxy group, a carboxylic acid anhydride group, and a carboxylic acid salt group with a crosslinking agent B described below (preferably a reactive group B described below). Examples of the carboxylic acid anhydride group include groups based on acid anhydrides such as maleic anhydride and itaconic anhydride. Examples of the carboxylic acid salt group include alkali metal salts of a carboxy group, organic amine salts of a carboxy group, and ammonium salts of a carboxy group.

[0068] Examples of the monomer A2 include carboxy group-containing monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and crotonic acid, and salts thereof (for example, sodium salts, potassium salts, ammonium salts, and tertiary amine salts); acid anhydride monomers such as maleic anhydride and itaconic anhydride; and (meth)acrylic acid esters having a carboxy group or a carboxylic acid salt group.

[0069] Specific examples of the (meth)acrylic acid ester having a carboxy group or a carboxylate salt group include carboxy group-containing (meth)acrylic acid esters such as 2-methacryloyloxyethyl succinate, 2-acryloyloxyethyl hexahydrophthalate, and ω-carboxy-polycaprolactone monoacrylate.

[0070] When the acrylic resin A has a structural unit derived from monomer A2, the content of the structural unit derived from monomer A2 is preferably 1 to 40% by mass, more preferably 3 to 35% by mass, and even more preferably 5 to 30% by mass, relative to the total structural units (100% by mass) of the acrylic resin A. When the content of the structural unit derived from monomer A2 is 5% by mass or more, the water solubility and curability of the resin are superior. Furthermore, when the content of the structural unit derived from monomer A2 is 30% by mass or less, the releasability of the sheet formed on the surface of the release layer is superior.

[0071] Structural Unit Derived from Monomer A3: It is preferable that the acrylic resin A further contains a structural unit derived from Monomer A3 having a ClogP value of 0.8 or more. This improves the high-speed releasability of the sheet formed on the surface of the release layer. It is preferable that Monomer A3 does not have any of a siloxane bond, a carboxy group, a carboxylic anhydride group, and a carboxylic acid salt group.

[0072] The ClogP value of Monomer A3 is preferably 1.0 or more, more preferably 1.2 or more, from the viewpoint of superior high-speed releasability of the sheet formed on the surface of the release layer. The ClogP value of Monomer A3 is preferably 6.0 or less, more preferably 5.0 or less, and even more preferably 4.0 or less, from the viewpoint of suitability for synthesis of Acrylic Resin A. Here, the ClogP value is the value obtained by calculating the common logarithm logP of the partition coefficient P between 1-octanol and water. Known methods and software can be used to calculate the ClogP value, but unless otherwise specified, the ClogP program incorporated into Cambridgesoft's ChemBioDraw Ultra 13.0 will be used in the present invention.

[0073] From the viewpoint of copolymerizability with Monomer A1 and Monomer A2, Monomer A3 preferably has a polymerizable group such as a (meth)acryloyloxy group or a vinyl group. The (meth)acryloyloxy group represents a concept including an acryloyloxy group and a methacryloyloxy group.

[0074] Specific examples of Monomer A3 include (meth)acrylic acid esters such as 2-methoxyethyl acrylate (MEA), 2-hydroxy-3-phenoxypropyl acrylate (HPPA), ethylene glycol monoacetoacetate monomethacrylate (EGMM), t-butyl acrylate (tBA), benzyl methacrylate (BnMA), phenoxyethyl acrylate (PEA), n-butyl acrylate (nBA), cyclohexyl acrylate (CyHA), tetrahydrofurfuryl methacrylate (THFMA), cyclohexyl methacrylate (CyHMA), methyl methacrylate (MMA) caprolactone-modified methacrylate, 2-acryloyloxyethyl-2-hydroxyethyl phthalate, dicyclopentanyl methacrylate, and isobornyl methacrylate; styrene (St), α-methylstyrene, and the like.

[0075] When the acrylic resin A has a structural unit derived from monomer A3, the content of the structural unit derived from monomer A3 is preferably 5 to 30% by mass, more preferably 7 to 25% by mass, and even more preferably 10 to 20% by mass, relative to the total structural units (100% by mass) possessed by monomer A3. When the content of the structural unit derived from monomer A3 is 5% by mass or more, the high-speed releasability of the sheet formed on the surface of the release layer is superior. Furthermore, when the content of the structural unit derived from monomer A3 is 30% by mass or less, the high-speed releasability of the sheet formed on the surface of the release layer is superior.

[0076] --Structural Units Derived from Other Monomers The acrylic resin A may have structural units derived from monomers other than the monomers A1 to A3 (hereinafter also referred to as "other monomers").

[0077] A specific example of the other monomer is a (meth)acrylic acid ester containing a polyalkylene oxide chain. Specific examples of the polyalkylene oxide chain include polymethylene oxide, polyethylene oxide, polypropylene oxide, and polybutylene oxide. The number of repeating units of the polyalkylene oxide chain is preferably 3 to 100.

[0078] Examples of (meth)acrylic acid esters containing a polyalkylene oxide chain include methoxypolyethylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, and ethoxypolypropylene glycol (meth)acrylate.

[0079] Specific examples of monomers other than (meth)acrylic acid esters containing a polyalkylene oxide chain include: hydroxyl group-containing monomers such as 2-hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, glycerol monomethacrylate, and 4-hydroxybutyl (meth)acrylate; epoxy group-containing monomers such as glycidyl (meth)acrylate and allyl glycidyl ether; sulfonic acid group-containing monomers such as styrene sulfonic acid and salts thereof; phosphate group-containing monomers such as 2-methacryloyloxyethyl acid phosphate and salts thereof; Amide group-containing monomers such as (meth)acrylamide, N-alkyl(meth)acrylamide, N,N-dialkyl(meth)acrylamide, N,N-dialkyl(meth)acrylate (examples of the alkyl group: methyl group, ethyl group, n-butyl group, isobutyl group, etc.), acryloylmorpholine, N-methylol(meth)acrylamide, N-isopropylacrylamide, diacetone acrylamide, and N-phenyl(meth)acrylamide; vinyl isocyanate, allyl isocyanate, vinyl methyl ether, vinyl ethyl ether, vinyl trialkoxysilane, alkyl maleic acid monoester, alkyl fumaric acid monoester, alkyl itaconic acid monoester, (meth)acrylonitrile vinylidene chloride, ethylene, propylene, vinyl chloride, vinyl acetate, and butadiene.

[0080] When the acrylic resin A has a structural unit derived from another monomer, the content of the structural unit derived from the other monomer is preferably 1 to 30 mass%, more preferably 2 to 20 mass%, and even more preferably 5 to 15 mass%, relative to all structural units (100 mass%) contained in the acrylic resin A.

[0081] Preferred embodiment of acrylic resin A One preferred embodiment of the acrylic resin A is an embodiment containing a structural unit derived from monomer A1 and a structural unit derived from monomer A2, and more preferably an embodiment containing a structural unit derived from monomer A1, a structural unit derived from monomer A2, and a structural unit derived from monomer A3. This provides better effects of the present invention. An embodiment in which the structural unit derived from monomer A1 has a siloxane bond is even more preferred.

[0082] The acid value of acrylic resin A is preferably 0.3 to 6.0 mmol / g, more preferably 0.5 to 4.5 mmol / g, even more preferably 0.5 to 3.0 mmol / g, and particularly preferably 0.5 to 2.5 mmol / g. The hydroxyl value of acrylic resin A is preferably 0 to 3.0 mmol / g, more preferably 0 to 2.5 mmol / g, and even more preferably 0 to 2.0 mmol / g. If the acid value or hydroxyl value is equal to or greater than the above lower limit, the water solubility and curability of acrylic resin A are superior. If the acid value or hydroxyl value is equal to or less than the above lower limit, the high-speed releasability and low-speed releasability of the sheet formed on the release layer surface are superior. The method for calculating the acid value and hydroxyl value is as described in the Examples section below.

[0083] The weight average molecular weight (Mw) of acrylic resin A is preferably 5,000 to 100,000, more preferably 7,000 to 80,000, and even more preferably 10,000 to 50,000. If the Mw of acrylic resin A is 5,000 or more, the release layer has better coating suitability for production. Furthermore, if the Mw of acrylic resin A is 100,000 or less, the high-speed releasability of the sheet formed on the surface of the release layer is better. The method for measuring the Mw of acrylic resin A is as described in the Examples section below.

[0084] Only one type of acrylic resin A may be contained, or two or more types may be contained. The content of acrylic resin A is preferably 20 to 90 mass %, more preferably 30 to 80 mass %, and even more preferably 50 to 80 mass %, relative to the total mass of the release layer. Note that, when the release layer contains a crosslinked product of acrylic resin A and crosslinking agent B described below, the content of the structure derived from acrylic resin A preferably satisfies the above range.

[0085] Crosslinking agent B Crosslinking agent B is a compound having a reactive group B capable of reacting with the reactive group A possessed by acrylic resin A. Crosslinking agent B is preferably water-soluble, since it facilitates the formation of a release layer by in-line application. The crosslinked product of acrylic resin A and crosslinking agent B can be formed, for example, by the reaction of the reactive group A possessed by acrylic resin A with the reactive group B possessed by crosslinking agent B when a release layer is formed using a composition containing acrylic resin A and crosslinking agent B.

[0086] When the acrylic resin A has a carboxy group, a carboxylic acid anhydride group, or a carboxylic acid salt group, the reactive group B is preferably an oxazoline group, a carbodiimide group, an epoxy group, a methylol group, an isocyanate group, or a blocked isocyanate group, because of its excellent reactivity with the carboxy group, etc. Among them, an oxazoline group, an epoxy group, or a carbodiimide group is more preferred, an oxazoline group or an epoxy group is even more preferred, and an oxazoline group is particularly preferred, because of its excellent high-speed releasability of the sheet formed on the release layer surface. Here, the blocked isocyanate group refers to a group in which an isocyanate group is blocked with a blocking agent (e.g., a compound having an active hydrogen group). When the acrylic resin A has a hydroxyl group, the reactive group B is preferably an isocyanate group, a methylol group, or a blocked isocyanate group, because of its excellent reactivity with the hydroxyl group.

[0087] The crosslinking agent B having a reactive group B is not particularly limited, and examples thereof include one or more crosslinking agents selected from the group consisting of oxazoline compounds, isocyanate compounds, carbodiimide compounds, melamine compounds, and epoxy compounds. The isocyanate compound may be a compound having a blocked isocyanate group in which the isocyanate group is blocked with a blocking agent. Among these, oxazoline compounds, epoxy compounds, or carbodiimide compounds are preferred, oxazoline compounds or epoxy compounds are more preferred, and oxazoline compounds are even more preferred, in view of the superior high-speed releasability of the sheet formed on the release layer surface.

[0088] Oxazoline-based compounds The oxazoline-based compounds are not particularly limited as long as they are compounds having an oxazoline group, and may be low-molecular-weight compounds having a weight-average molecular weight (Mw) of 1,000 or less, or high-molecular-weight compounds having a weight-average molecular weight (Mw) of more than 1,000. However, high-molecular-weight compounds are preferred because they provide superior high-speed releasability for the sheet formed on the surface of the release layer.

[0089] Examples of low molecular weight compounds having an oxazoline group include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2,2'-bis-(2-oxazoline), 2,2'-methylene-bis-(2-oxazoline), 2,2'-ethylene-bis-(2-oxazoline), 2,2'-trimethylene-bis- (2-oxazoline), 2,2'-tetramethylene-bis-(2-oxazoline), 2,2'-hexamethylene-bis-(2-oxazoline), 2,2'-octamethylene-bis-(2-oxazoline), 2,2'-ethylene-bis-(4,4'-dimethyl-2-oxazoline), 2,2'-p-phenylene-bis-(2-oxazoline), 2,2'-m-phenylene-bis-(2-oxazoline), 2,2'-m-phenylene-bis-(4,4'-dimethyl-2-oxazoline), bis-(2-oxazolinylcyclohexane)sulfide, and bis-(2-oxazolinylnorbornane)sulfide are examples of the oxazolinyl compounds.

[0090] When the oxazoline compound is a polymer compound, it is sufficient that the polymer compound has an oxazoline group, and examples thereof include copolymers containing the above-mentioned low molecular weight compound having an oxazoline group as a constituent unit.

[0091] The polymer compound having an oxazoline group is preferably an acrylic polymer having an oxazoline group, and more preferably an acrylic polymer containing an oxazoline group and a polyalkylene oxide chain. When the polymer compound having an oxazoline group contains a polyalkylene oxide chain, the water solubility of the crosslinking agent B can be improved, and the in-line coating suitability can be further improved.

[0092] Examples of the polyalkylene oxide chain include polymethylene oxide, polyethylene oxide, polypropylene oxide, and polybutylene oxide. The polyalkylene oxide chain preferably has 3 to 100 repeating units.

[0093] Examples of (meth)acrylic acid esters containing a polyalkylene oxide chain include methoxypolyethylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, and ethoxypolypropylene glycol (meth)acrylate.

[0094] The polymer compound having an oxazoline group may contain a constituent unit derived from a low molecular weight compound having an oxazoline group and a constituent unit derived from a monomer other than the constituent unit derived from a (meth)acrylic acid ester containing a polyalkylene oxide chain.

[0095] Other monomers include alkyl group-containing monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate; hydroxy-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and glycerol monomethacrylate; epoxy group-containing monomers such as glycidyl (meth)acrylate and allyl glycidyl ether; styrene sulfonic acid, potassium 3-sulfopropyl methacrylate, 2-acrylic acid, and the like. Examples of the other monomers include sulfo group-containing monomers such as mido-2-methylpropanesulfonic acid; amide group-containing monomers such as (meth)acrylamide, N-alkyl(meth)acrylamide, N,N-dialkyl(meth)acrylamide, N,N-dialkyl(meth)acrylate (examples of the alkyl group: methyl group, ethyl group, n-butyl group, isobutyl group, etc.), acryloylmorpholine, N-methylol(meth)acrylamide, and N-phenyl(meth)acrylamide; vinyl isocyanate, allyl isocyanate, styrene, α-methylstyrene, vinyl methyl ether, vinyl ethyl ether, vinyltrialkoxysilane, alkyl maleic acid monoester, alkyl fumaric acid monoester, alkyl itaconic acid monoester, (meth)acrylonitrile vinylidene chloride, ethylene, propylene, vinyl chloride, vinyl acetate, butadiene, and the compound represented by the above formula (A1-1). Among these, the compound represented by the above formula (A1-1) is preferred as the other monomer in terms of achieving the effects of the present invention.

[0096] The polymer compound having an oxazoline group is preferably water-soluble from the viewpoint of environmental load.

[0097] The weight average molecular weight (Mw) of the polymer compound having an oxazoline group is not particularly limited, but is preferably 3,000 or more, more preferably 5,000 to 200,000, and even more preferably 7,000 to 150,000. The weight average molecular weight (Mw) is measured by the method described in the Examples section below.

[0098] The polymer compound having an oxazoline group may be a commercially available product, such as EPOCROS (registered trademark, the same applies hereinafter) K-2010E, EPOCROS K-2020E, EPOCROS K-2030E, EPOCROS WS-700, and EPOCROS WS-300 (all manufactured by Nippon Shokubai Co., Ltd.).

[0099] Isocyanate Compounds The isocyanate compounds are compounds having an isocyanate group or a blocked isocyanate group. The isocyanate compounds are preferably blocked isocyanate compounds (i.e., compounds having a blocked isocyanate group). Blocked isocyanate compounds are compounds in which the isocyanate group of a polyisocyanate is protected (i.e., blocked) with a blocking agent, and are included in the isocyanate compounds in this specification. Examples of blocking agents in blocked isocyanates include ester compounds, phenol compounds, alcohol compounds, oxime compounds, mercaptan compounds, lactam compounds, amine compounds, acid amide compounds, pyrazole compounds, triazole compounds, and bisulfite compounds.

[0100] Examples of ester compounds include malonic acid diesters such as dimethyl malonate and diethyl malonate, and acetoacetic acid esters such as methyl acetoacetate and ethyl acetoacetate. Among these, diethyl malonate is preferred due to its availability. Examples of phenolic compounds include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol, and ethylphenol. Examples of alcohol compounds include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, propylene glycol monomethyl ether, ethylene glycol, and benzyl alcohol. Examples of oxime compounds include acetoxime, methyl ethyl ketone oxime, acetaldoxime, formaldoxime, diacetyl monooxime, and cyclohexane oxime, with acetoxime or methyl ethyl ketone oxime being preferred.

[0101] Examples of mercaptan compounds include butyl mercaptan and dodecyl mercaptan. Examples of lactam compounds include ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam, with ε-caprolactam being preferred. Examples of amine compounds include diphenylaniline, aniline, and ethyleneimine. Examples of acid amide compounds include acetanilide and acetic acid amide. Examples of pyrazole compounds include methylpyrazole (e.g., 2-methylpyrazole, 3-methylpyrazole, 4-methylpyrazole), dimethylpyrazole (e.g., 2,4-dimethylpyrazole, 2,5-dimethylpyrazole, 3,4-dimethylpyrazole, 3,5-dimethylpyrazole), 4-nitro-3,5-dimethylpyrazole, and 4-bromo-3,5-dimethylpyrazole, with methylpyrazole or dimethylpyrazole being preferred. An example of the triazole compound is 1,2,4-triazole.

[0102] Examples of polyisocyanates whose isocyanate groups are protected by a blocking agent include polyfunctional polyisocyanates in the form of an adduct (also called an adduct body) obtained by adding 3 moles of diisocyanate to 1 mole of trimethylolpropane, a biuret (also called a biuret body) obtained by reacting 3 moles of diisocyanate with 1 mole of water, or an isocyanurate (also called an isocyanurate body) obtained by polymerizing 3 moles of diisocyanate. The polyisocyanate whose isocyanate groups are protected by a blocking agent may also be a polyurethane polyisocyanate obtained by reacting a polyisocyanate with a polyol (e.g., polyester polyol, polyether polyol, low molecular weight polyol). Examples of diisocyanates include aromatic diisocyanates, aliphatic diisocyanates, and alicyclic isocyanates. From the viewpoint of producing ceramic green sheets with reduced defects and without generating recessed defects on the peeled surface, aliphatic diisocyanates are preferred, and hexamethylene diisocyanate is more preferred.

[0103] Examples of aromatic diisocyanates include 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, tetraalkyldiphenylmethane diisocyanate, dialkyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, polymeric diphenylmethane diisocyanate, tolylene diisocyanate (2,4- or 2,6-tolylene diisocyanate), 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 1,5-naphthylene diisocyanate, and naphthalene diisocyanate.

[0104] Examples of aliphatic diisocyanates that are examples of diisocyanates include hexamethylene diisocyanate, trimethylene diisocyanate, trimethylhexamethylene diisocyanate (2,2,4- or 2,4,4-trimethylhexamethylene diisocyanate), lysine diisocyanate, xylylene diisocyanate, 1,2-propylene diisocyanate, butylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, and 1,5-pentamethylene diisocyanate.

[0105] Examples of diisocyanates, such as alicyclic isocyanates, include 1,3-cyclopentane diisocyanate, 1,3-cyclopentene diisocyanate, cyclohexane diisocyanate (1,3- or 1,4-cyclohexane diisocyanate), 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate, methylcyclohexane diisocyanate (-2,4- or -2,6-methylcyclohexane diisocyanate), and norbornane diisocyanate.

[0106] Among these, from the viewpoints of availability and ease of synthesis, an isocyanurate of hexamethylene diisocyanate, a biuret of hexamethylene diisocyanate, or an adduct of hexamethylene diisocyanate is preferred.

[0107] As the blocked isocyanate, commercially available products may be used, examples of which include 2554, 2507, and BI-301 from the Coronate series manufactured by Tosoh Corporation, SBN-70D, SBN-70P, MF-B60B, 17B-60P, TPA-B80E, and E402-B80B from the Duranate series manufactured by Asahi Kasei Corporation, and B-830, B-815N, B-820NSU, B-842N, B-846N, B870N, B874N, and B882N from the Takenate series manufactured by Mitsui Chemicals, Inc.

[0108] Carbodiimide Compounds Carbodiimide compounds are compounds having a carbodiimide group. Carbodiimide compounds can be synthesized by a conventionally known method. For example, a condensation reaction of a diisocyanate compound is used. The diisocyanate compound is not particularly limited, and may be any of aromatic diisocyanates, aliphatic diisocyanates, and alicyclic diisocyanates. Specific examples of aromatic diisocyanates, aliphatic diisocyanates, and alicyclic diisocyanates are the same as the specific examples of diisocyanates described in the section on isocyanate compounds.

[0109] The carbodiimide equivalent (the mass [g] of the carbodiimide compound required to provide 1 mole of carbodiimide groups) is preferably 100 to 1,000 g / mol, more preferably 250 to 800 g / mol, and even more preferably 300 to 700 g / mol.

[0110] Melamine-based compounds In this specification, the melamine-based compounds include melamine and —NH ２ The melamine compound is not particularly limited, but may be obtained by condensing melamine with formaldehyde, and may be a melamine derivative in which the hydrogen atom of the -NH ２ One or more of the hydrogen atoms of the group is a methylol group (-CH ２ Examples of the melamine compounds include methylol melamine compounds substituted with hydroxyl groups (OH). Examples of the melamine compounds also include etherified methylol melamine compounds obtained by etherifying the above-mentioned methylol melamine with an alcohol compound through dehydration condensation. Specific examples of the melamine compounds include trimethylol melamine, hexamethylol melamine, trimethoxymethyl melamine, and hexamethoxymethyl melamine.

[0111] Epoxy Compounds There are no particular limitations on the epoxy compound as long as it is a compound having an epoxy group. It is preferable that the epoxy compound has two or more epoxy groups in the molecule. The epoxy group in the epoxy compound may be an epoxy group contained in a glycidyl group, or an epoxy group contained in an alicyclic epoxy group. An alicyclic epoxy group refers to, for example, a group such as a 3,4-epoxycyclohexyl group.

[0112] The epoxy compound may be a commercially available product, such as Cyclomer (registered trademark) M100, Celloxide (registered trademark) 2000, Celloxide (registered trademark) 2021P, 2081, Epolead (registered trademark) GT401, or EHPE (registered trademark) 3150 (manufactured by Daicel Corporation).

[0113] The epoxy-based compound is not particularly limited as long as it is a compound having an epoxy group, and may be a low molecular weight compound having a weight average molecular weight (Mw) of 1000 or less, or a high molecular weight compound having a weight average molecular weight (Mw) of more than 1000. However, a high molecular weight compound is preferred because it provides superior high-speed releasability for the sheet formed on the surface of the release layer.

[0114] When the epoxy compound is a low molecular weight compound, examples of the low molecular weight compound include "Denacol-EX-521" (trade name, polyglycerol polyglycidyl ether), "Denacol EX-512" (trade name, polyglycerol polyglycidyl ether), and "Denacol EX-830" (trade name, polyethylene glycol diglycidyl ether), all of which are manufactured by Nagase ChemteX Corporation.

[0115] When the epoxy compound is a polymer compound, it may be any polymer compound having an epoxy group, such as a polymer compound obtained by polymerizing a monomer having an epoxy group, and among these, an acrylic polymer having an epoxy group is preferred, and an acrylic polymer having an epoxy group and a polyalkylene oxide chain is more preferred. When the epoxy compound contains a polyalkylene oxide chain, the water solubility of the crosslinking agent B can be improved, and the in-line coating suitability is further improved.

[0116] Specific examples of the monomer having an epoxy group include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, and phenyl glycidyl ether, and among these, glycidyl acrylate and glycidyl methacrylate are preferred.

[0117] When the epoxy compound is an acrylic polymer containing an epoxy group and a polyalkylene oxide chain, the acrylic polymer may contain a structural unit derived from a (meth)acrylic acid ester containing a polyalkylene oxide chain. Specific examples of the (meth)acrylic acid ester containing a polyalkylene oxide chain are the same as the (meth)acrylic acid ester containing a polyalkylene oxide chain described above in connection with the polymer compound having an oxazoline group.

[0118] The polymer compound having an epoxy group may contain a constituent unit derived from a monomer other than the constituent unit derived from the compound having an epoxy group and the constituent unit derived from a (meth)acrylic acid ester containing a polyalkylene oxide chain. Specific examples of the other monomers are the same as those described above for the polymer compound having an oxazoline group.

[0119] The weight average molecular weight (Mw) of the polymer compound having an epoxy group is not particularly limited, but is preferably 3,000 or more, more preferably 4,000 to 100,000, and even more preferably 5,000 to 50,000. The weight average molecular weight (Mw) is measured by the method described in the Examples section below.

[0120] Preferred Embodiments of Crosslinking Agent B The crosslinking agent B is preferably an acrylic resin having a reactive group B in its side chain, from the viewpoint of providing superior high-speed releasability of the sheet formed on the release layer surface. Specific examples of acrylic resins having a reactive group B in their side chains include the above-mentioned polymeric compounds having an oxazoline group (specifically, a copolymer containing a structural unit derived from the above-mentioned low-molecular-weight compound having an oxazoline group and a structural unit derived from a (meth)acrylic acid ester containing a polyalkylene oxide chain), and the above-mentioned polymeric compounds having an epoxy group (specifically, a copolymer containing a structural unit derived from a compound having an epoxy group and a structural unit derived from a (meth)acrylic acid ester containing a polyalkylene oxide chain). Among these, the acrylic resin having a reactive group B in its side chain is preferably the above-mentioned polymeric compound having an oxazoline group, from the viewpoint of providing superior high-speed releasability of the sheet formed on the release layer surface.

[0121] Only one type of crosslinking agent B may be used, or two or more types may be used. The content of crosslinking agent B is preferably 1 to 80% by mass, more preferably 1 to 70% by mass, even more preferably 1 to 60% by mass, and still more preferably 10 to 50% by mass, relative to the total mass of the release layer, from the viewpoint of the reactivity of acrylic resin A. Note that, when the release layer contains a crosslinked product of acrylic resin A and crosslinking agent B described below, it is preferable that the content of the structure derived from crosslinking agent B satisfies the above range.

[0122] Preferred embodiment of crosslinked product The release layer preferably contains a crosslinked product of an acrylic resin A having a siloxane bond and a crosslinking agent B. Among these, at least one of the cases where the acrylic resin A having a siloxane bond is the preferred embodiment described above and the case where the crosslinking agent B is the preferred embodiment described above is more preferred, and the case where the acrylic resin A having a siloxane bond is the preferred embodiment described above and the crosslinking agent B is the preferred embodiment described above is even more preferred.

[0123] When the release layer contains a crosslinked product of acrylic resin A and crosslinking agent B, the content of the crosslinked product of acrylic resin A and crosslinking agent B is preferably 98 to 100 mass %, and more preferably 98.5 to 100 mass %, relative to the total mass of the release layer, in terms of more excellent effects of the present invention.

[0124] (Additives) The release layer may contain additives other than those described above. Examples of additives include light release additives and heavy release additives for adjusting the release force, surfactants, adhesion improvers, and antistatic agents. In particular, it is preferable that the release layer contains a surfactant. Specific examples of surfactants are the same as the specific examples of surfactants that can be contained in the protrusion-containing layer described below. When the release layer contains an additive, the content of the additive is preferably 0.1 to 3 mass %, and more preferably 0.1 to 2 mass %, relative to the total mass of the release layer.

[0125] <Protrusions and protrusion-containing layer> The polyester film preferably has protrusions on the surface of the polyester film facing the polyester substrate (the surface of the polyester film opposite the release surface, hereinafter also referred to as the "smooth surface"). When the polyester film has protrusions on the smooth surface, the polyester film has excellent slip properties and can improve transportability.

[0126] The maximum protrusion height (Sp) of the smooth surface may be 1 nm or more, but from the viewpoint of transportability and reduction of winding trouble, it is preferably 10 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more.In addition, the maximum protrusion height (Sp) of the smooth surface is preferably 1.0 μm or less, more preferably 600 nm or less, and even more preferably 300 nm or less.In order to prevent winding trouble such as winding slippage when winding the polyester film, it is more preferably 150 nm or less, particularly preferably 100 nm or less, and most preferably less than 60 nm.When the maximum protrusion height (Sp) of the smooth surface is below the above range, the smoothness of the release layer surface can be improved.

[0127] The surface average roughness (Sa) of the smooth surface is preferably 5 nm or less, more preferably 3 nm or less. The lower limit may be 0 nm or more. From the viewpoint of suppressing transfer marks and improving the smoothness of the release layer surface, the surface average roughness (Sa) of the smooth surface is preferably 2 to 3 nm. The maximum projection height (Sp) and surface average roughness (Sa) of the smooth surface can be measured in the same manner as the maximum projection height and surface average roughness of the release layer, except that the smooth surface is measured.

[0128] The protrusions may be formed directly on the polyester substrate, or may be formed by a protrusion-containing layer that is a separate layer from the polyester substrate. That is, the polyester film may have a protrusion-containing layer on the side opposite the release layer of the polyester substrate. In other words, the polyester film may have a release layer, a polyester substrate, and a protrusion-containing layer in this order. The protrusion-containing layer refers to a layer having protrusions on at least one surface thereof. The protrusion-containing layer may be provided directly on the surface of the polyester substrate or via an intermediate layer, but from the viewpoint of superior productivity, it is preferable to provide it directly on the surface of the polyester substrate. That is, the polyester film is composed of a release layer, a polyester substrate, and a protrusion-containing layer, and it is preferable that the release layer and the polyester substrate are adjacent to each other, and that the polyester substrate and the protrusion-containing layer are adjacent to each other.

[0129] The maximum protrusion height (Sp) of the smooth surface can be adjusted, for example, by the following methods. (1) A particle-containing layer is formed on one surface of a polyester substrate, and the size and amount of particles contained in the particle-containing layer and the thickness of the particle-containing layer are adjusted. Methods for forming the particle-containing layer include forming a coating layer of a particle-containing composition and co-extruding a polyester melt with a second melt containing particles and a binder. (2) Particles are incorporated into the polyester substrate, and the size and amount of the particles are adjusted. (3) One surface of the polyester substrate is physically treated to make it rough. Examples of physical treatments include plasma treatment. Preferably, the polyester film has a particle-containing layer on one surface of the polyester substrate, and the exposed surface of the particle-containing layer is the smooth surface. In an embodiment in which the exposed surface of the particle-containing layer is the smooth surface, the maximum protrusion height (Sp) of the smooth surface is adjusted by method (1).

[0130] The method for forming the protrusion-containing layer is not particularly limited as long as protrusions are formed on at least one surface of the protrusion-containing layer. For example, a method can be used in which a layer containing particles (hereinafter also referred to as a "particle-containing layer") is provided as the protrusion-containing layer on the surface opposite to the release surface of the polyester film. Hereinafter, the particle-containing layer will be described as an example of the protrusion-containing layer.

[0131] (Particle-Containing Layer) The particle-containing layer is not particularly limited as long as it contains particles. The particle-containing layer preferably contains a binder in addition to the particles. The particle-containing layer may further contain an additive.

[0132] The average particle size of the particles contained in the particle-containing layer is not particularly limited, but is preferably 1 to 1,000 nm, and more preferably 40 to 500 nm. Examples of the particles include inorganic particles and organic particles. Examples of inorganic particles include silica particles (silicon dioxide particles, colloidal silica), titania particles (titanium oxide particles), calcium carbonate, barium sulfate, and alumina particles (aluminum oxide particles). Examples of the organic particles include resin particles. Examples of the resins constituting the resin particles include acrylic resins such as polymethyl methacrylate resin (PMMA), polyester resins, silicone resins, styrene resins, urethane resins, and styrene-acrylic resins. The resin particles may or may not have a crosslinked structure. Specific examples include non-crosslinked acrylic resin particles, non-crosslinked styrene resin particles, crosslinked acrylic resin particles, crosslinked urethane resin particles, and divinylbenzene crosslinked particles.

[0133] The content of particles in the particle-containing layer is preferably 0.1 to 30% by mass, more preferably 1 to 25% by mass, based on the total mass of the particle-containing layer, from the viewpoint of transportability.

[0134] By adjusting the type, particle size, content, etc. of particles in the particle-containing layer, the coefficient of dynamic friction between the release surface and the slippery surface (the surface of the particle-containing layer opposite the polyester substrate side) can be adjusted.

[0135] The binder that the particle-containing layer may contain is preferably a resin binder. Examples of resin binders include acrylic resins, urethane resins, polyester resins, and olefin resins. Non-polyester resins are preferred, specifically acrylic resins, urethane resins, or olefin resins. Known resins can be used as binders. The resin binder may also be an acid-modified resin. The binder contained in the particle-containing layer may have a crosslinked structure. In other words, the particle-containing layer may be a crosslinked film. The particle-containing layer may contain only one type of binder, or may contain two or more types of binders. The binder content is preferably 30 to 99.8% by mass, more preferably 50 to 99.5% by mass, based on the total mass of the particle-containing layer.

[0136] Examples of additives contained in the particle-containing layer include surfactants, waxes, antioxidants, ultraviolet absorbers, colorants, reinforcing agents, plasticizers, antistatic agents, flame retardants, rust inhibitors, and antifungal agents.

[0137] The particle-containing layer preferably contains a surfactant in order to improve the surface smoothness. The surfactant is not particularly limited, and examples thereof include silicone-based surfactants, fluorine-based surfactants, and hydrocarbon-based surfactants. Fluorine-based surfactants (particularly, fluorine-based surfactants having a perfluoroalkyl group having 1 to 4 carbon atoms) or hydrocarbon-based surfactants are preferred. Only one type of surfactant may be used, or two or more types may be used in combination. The content of the surfactant is preferably 0.1 to 10% by mass, based on the total mass of the particle-containing layer, and more preferably 0.1 to 5% by mass in order to achieve better surface smoothness.

[0138] The thickness of the particle-containing layer is preferably 1 nm to 1 μm, more preferably 1 to 500 nm, and even more preferably 1 to 200 nm, from the viewpoint of the smoothness of the surface of the release layer. The thickness of the particle-containing layer is determined by preparing a slice having a cross section perpendicular to the main surface of the polyester film and measuring the thickness of the particle-containing layer at five points in the slice using a scanning electron microscope (SEM).

[0139] <Characteristics of Polyester Film> The polyester film of the present invention preferably exhibits various characteristics, which will now be described.

[0140] The thickness of the polyester film is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, particularly preferably 40 μm or less, and most preferably 35 μm or less, from the viewpoint of excellent cost efficiency. The lower limit of the thickness is not particularly limited, but from the viewpoint of improved strength and improved processability, it is preferably 1 μm or more, more preferably 3 μm or more, even more preferably 10 μm or more, particularly preferably 18 μm or more, and most preferably 20 μm or more. The thickness of the polyester film is measured at five different arbitrarily selected locations using a stylus film thickness meter, and the arithmetic mean of the measured values ​​obtained is defined as the thickness.

[0141] In the polyester film, the dynamic friction coefficient is preferably 0.2 or more. The dynamic friction coefficient in the polyester film refers to the friction coefficient on both sides of the polyester film, more specifically, the dynamic friction coefficient between the release layer surface and the surface of the polyester film opposite to the release layer surface (a smooth surface, for example, the surface opposite the polyester substrate side of the protrusion-containing layer). If the dynamic friction coefficient is 0.2 or more, the polyester film is less likely to slip when wound into a roll. Furthermore, the dynamic friction coefficient is preferably less than 1.0. If the dynamic friction coefficient is less than 1.0, blocking is less likely to occur when the polyester film is wound into a roll. The dynamic friction coefficient can be measured in accordance with ASTM D 1894-95. The detailed procedure for measuring the dynamic friction coefficient shall follow the method described in the Examples below.

[0142] The heat shrinkage of the polyester film in both the machine direction and width direction, measured in an environment at 150°C, is preferably -1.0 to 3.0%, more preferably -0.5 to 2.0%, and even more preferably 0 to 1.5%. When the heat shrinkage of the polyester film is within the above range, the dimensional stability of the ceramic green sheet formed on the release layer surface of the polyester film and the dimensional stability when the ceramic green sheet is peeled from the polyester film and then laminated is good, making electronic components less susceptible to failure. The method for measuring each of the above heat shrinkage rates is described in the Examples section below. The heat shrinkage rate of the polyester film can be adjusted by selecting the heating or cooling conditions during production of the polyester film. More specifically, it can be adjusted by changing at least one of the conditions of the heat setting process, heat relaxation process, and cooling process described below.

[0143] <Method for producing polyester film> The polyester film of the present invention can be produced by a known method. The method for producing the polyester film of the present invention preferably includes a step of applying a release layer-forming composition (hereinafter also referred to as "composition L") to at least one side of the polyester base material.

[0144] (Composition L) Composition L is a composition capable of forming the above-described release layer. Composition L preferably contains an acrylic resin, and preferably contains an acrylic resin and a crosslinking agent. Furthermore, composition L more preferably contains acrylic resin A. Composition L further preferably contains acrylic resin A (particularly preferably acrylic resin A having a siloxane bond) and crosslinking agent B. Details of acrylic resin A and crosslinking agent B are as described above. Note that, when composition L contains acrylic resin A, it is intended that acrylic resin A is already present in the form of a resin in composition L. In other words, it is not intended that the acrylic resin A is a resin that exists as a monomer composed of a (meth)acrylic acid ester in composition L and is polymerized when forming the release layer.

[0145] The content of acrylic resin A is preferably 20 to 90% by mass, more preferably 30 to 80% by mass, and even more preferably 50 to 80% by mass, based on the components other than the solvent (solid content) of composition L. From the viewpoint of the reactivity of acrylic resin A, the content of crosslinking agent B is preferably 1 to 70% by mass, more preferably 1 to 60% by mass, and even more preferably 10 to 50% by mass, based on the components other than the solvent (solid content) of composition L. The total content of acrylic resin A and crosslinking agent B is preferably 98 to 100% by mass, based on the components other than the solvent (solid content) of composition L.

[0146] Composition L preferably contains a solvent. The solvent preferably contains water from the viewpoint of excellent in-line applicability. The solvent may contain only water, or may contain water and an alcohol. Specific examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, propylene glycol, and propylene glycol monomethyl ether. Only one type of alcohol may be used, or two or more types may be used.

[0147] The water content is preferably 50 to 100% by mass, more preferably 70 to 100% by mass, and even more preferably 80 to 99% by mass, relative to the total mass of the solvent. When the solvent contains alcohol, the alcohol content is preferably 0.5 to 50% by mass, more preferably 0.5 to 30% by mass, even more preferably 0.5 to 15% by mass, and particularly preferably 1 to 10% by mass, relative to the total mass of the solvent. The solvent content is preferably 80 to 99.5% by mass, more preferably 90 to 99.0% by mass, relative to the total mass of Composition L. That is, the total solid content in Composition L is preferably 0.5 to 20% by mass, more preferably 1.0 to 10% by mass, relative to the total mass of Composition L.

[0148] Composition L may further contain the additives contained in the release layer described above. When composition L contains the additives, the content of the additives is preferably 0.1 to 20 mass %, more preferably 0.5 to 10 mass %, based on the total mass of the components (solid content) other than the solvent of composition L.

[0149] The composition L is preferably applied by an in-line coating method. The in-line coating method refers to a method in which the composition L is applied to at least one surface of the polyester substrate during the polyester film production process. When the polyester film is produced using the stretching machine shown in FIG. 2 described below, an example of a method for forming a release layer by the in-line coating method is shown below. First, before the polyester substrate is transported to the stretching section 20, the composition L is applied to the surface of the polyester substrate to obtain a polyester substrate with a coating film. Here, the polyester substrate to which the composition L is applied may be an unstretched polyester substrate or a longitudinally stretched polyester substrate. Next, the polyester substrate with the coating film is transported to the stretching section 20, where the polyester substrate with the coating film is stretched transversely while the coating film is dried. In this way, a stretched polyester substrate with a release layer is obtained. Note that if the polyester substrate with the coating film transported to the stretching section 20 is unstretched, longitudinal stretching may be performed before transverse stretching in the stretching section 20.

[0150] One preferred embodiment of the polyester film manufacturing method involves melt-extruding a polyester resin to prepare an unstretched polyester substrate, stretching the unstretched polyester substrate longitudinally, applying composition L to one side of the longitudinally stretched polyester substrate, and then stretching the resulting polyester substrate transversely to produce a polyester film. Furthermore, when composition L contains an acrylic resin A having a reactive group A and a crosslinking agent B having a reactive group B, the method may include a release layer formation step in which the acrylic resin A contained in the coating film reacts with the crosslinking agent B. As described above, when performing transverse stretching in the stretching section 20, it is preferable that drying of the coating film and the release layer formation step are performed simultaneously. Below, each step that may be included in the polyester film manufacturing method of the present invention is described.

[0151] (Stretching Step) The method for producing a polyester film preferably includes a stretching step. In the stretching step, biaxial stretching is preferably performed. The biaxial stretching may be simultaneous biaxial stretching in which longitudinal stretching and transverse stretching are performed simultaneously, or may be sequential biaxial stretching in which longitudinal stretching and transverse stretching are performed in two or more stages. Examples of sequential biaxial stretching include longitudinal stretching → transverse stretching, longitudinal stretching → transverse stretching → longitudinal stretching, longitudinal stretching → longitudinal stretching → transverse stretching, and transverse stretching → longitudinal stretching, with longitudinal stretching → transverse stretching being preferred. One preferred embodiment of the stretching step is an embodiment including the longitudinal stretching step and the transverse stretching step described below.

[0152] - Stretching Machine The device used for biaxial stretching is not particularly limited, and a known stretching machine can be used. An example of the stretching machine will be described below with reference to the drawings.

[0153] FIG. 2 is a plan view showing an example of a stretching machine used in the production of polyester films. The stretching machine 100 shown in FIG. 2 includes a pair of annular rails 60a and 60b and gripping members 2A to 2L attached to each annular rail and movable along the rails. The annular rails 60a and 60b are arranged symmetrically with respect to each other, sandwiching the film 200. The stretching machine 100 can stretch the film 200 in the width direction by gripping the film 200 with the gripping members 2A to 2L and moving the gripping members 2A to 2L along the rails. Furthermore, the stretching machine 100 shown in FIG. 2 includes a clip closer 3, a support member 4 that supports the clip closer 3, and a clip opener 5.

[0154] The stretching machine 100 has zones consisting of, in order from the upstream side in the conveying direction, a preheating zone 10, a stretching zone 20, a heat setting zone 30, a heat relaxing zone 40, and a cooling zone 50. The zones in the stretching machine 100 are separated by windshield curtains, and the temperature in each zone can be adjusted individually by hot air or the like.

[0155] The preheating section 10 is an area where the film 200 is preheated.

[0156] The stretching section 20 is a region where the preheated film 200 is stretched by applying tension in the direction of the arrow TD (width direction), which is perpendicular to the direction of the arrow MD (longitudinal direction). As shown in Figure 2, in the stretching section 20, the film 200 is stretched from width L0 to width L1.

[0157] The heat fixing section 30 is an area where the tensioned film 200 is heated and heat fixed while still being tensioned.

[0158] The thermal relaxation section 40 is a region where the tension of the heat-set film 200 is thermally relaxed by heating the heat-set film 200. As shown in Fig. 2, in the thermal relaxation section 40, the film 200 is reduced (relaxed) from width L1 to width L2.

[0159] Cooling section 50 is an area for cooling thermally relaxed film 200. By cooling film 200, the shape of film 200 can be fixed. In Fig. 2, the width of film 200 fed into cooling section 50 is L2, and the width of film 200 fed out of cooling section 50 is L3.

[0160] Gripping members 2A, 2B, 2E, 2F, 2I, and 2J are attached to the circular rail 60a and are movable along the circular rail 60a. Gripping members 2C, 2D, 2G, 2H, 2K, and 2L are attached to the circular rail 60b and are movable along the circular rail 60b. Gripping members 2A, 2B, 2E, 2F, 2I, and 2J grip one end of the film 200 in the direction of arrow TD. Gripping members 2C, 2D, 2G, 2H, 2K, and 2L grip the other end of the film 200 in the direction of arrow TD. Gripping members 2A to 2L are often referred to as chucks, clips, or the like. Gripping members 2A, 2B, 2E, 2F, 2I, and 2J move counterclockwise along the circular rail 60a. The gripping members 2C, 2D, 2G, 2H, 2K, and 2L move clockwise along the circular rail 60b.

[0161] Gripping members 2A-2D move along annular rail 60a or 60b while gripping the end of film 200 in preheating section 10, passing through stretching section 20, heat-setting section 30, and heat-relaxing section 40, and then proceeding to cooling section 50. Next, gripping members 2A and 2B, and gripping members 2C and 2D, in that order in the conveying direction, release the end of film 200 at the end downstream of cooling section 50 in the direction of arrow MD (e.g., grip release points P and Q in FIG. 2), and then move further along annular rail 60a or 60b, returning to preheating section 10. In the above process, as film 200 moves in the direction of arrow MD, it is preheated in preheating section 10, stretched in stretching section 20, heat-set in heat-setting section 30, heat-relaxed in heat-relaxing section 40, and cooled in cooling section 50, and then transversely stretched.

[0162] The transport speed of film 200 can be adjusted by adjusting the movement speed of gripping members 2A to 2L. Furthermore, the movement speed of gripping members 2A to 2L can be changed independently of each other.

[0163] As described above, the stretching machine 100 enables transverse stretching in which the film 200 is stretched in the direction of the arrow TD in the stretching section 20. On the other hand, the stretching machine 100 can also stretch the film 200 in the direction of the arrow MD by changing the moving speed of the gripping members 2A to 2L. In other words, simultaneous biaxial stretching can also be performed using the stretching machine 100.

[0164] In addition to the gripping members 2A to 2L, the stretching machine 100 may further include other gripping members (not shown) to support the film 200.

[0165] Longitudinal Stretching Step The polyester film manufacturing method preferably includes a longitudinal stretching step of longitudinally stretching an unstretched polyester substrate. Longitudinal stretching can be performed, for example, by conveying the unstretched polyester substrate in the machine direction while applying tension between two or more pairs of stretching rolls arranged in the conveying direction. The stretching ratio in the longitudinal stretching step is appropriately set depending on the application, but is preferably 2.0 to 5.0 times, more preferably 2.5 to 4.0 times, and even more preferably 2.8 to 4.0 times.

[0166] Transverse Stretching Step The polyester film manufacturing method preferably includes a transverse stretching step in which the polyester substrate is transversely stretched. Transverse stretching refers to a process in which the polyester substrate is stretched in the width direction. For example, when using the stretching machine 100 shown in FIG. 2, it is performed in the stretching section 20. The heating temperature in the transverse stretching step is preferably 100 to 140°C, more preferably 110 to 135°C, and even more preferably 115 to 130°C. The stretch ratio in the width direction of the polyester substrate in the transverse stretching step (transverse stretching ratio) is not particularly limited, but is preferably larger than the stretch ratio in the longitudinal stretching step. The stretch ratio in the transverse stretching step is preferably 3.0 to 6.0 times, more preferably 3.5 to 5.0 times, and even more preferably 3.5 to 4.5 times.

[0167] (Coating Film Forming Step) The polyester film manufacturing method preferably includes a coating film forming step of forming a coating film of composition L. Specifically, the coating film forming step is a step of applying composition L to at least one surface of a polyester substrate to form a coating film. The coating film forming step may be in-line coating or offline coating, but in-line coating is preferred from the viewpoint of improving the smoothness of the release layer surface. The in-line coating is preferably a method of applying composition L to one surface of a longitudinally stretched polyester substrate. In in-line coating, for example, when using the stretching machine 100 shown in FIG. 2, the polyester substrate coated with composition L (polyester substrate with a coating film) is stretched transversely in the stretching section 20, and at this time, the coating film is cured simultaneously with the transverse stretching. Here, "curing" refers to drying of the coating film, but it is preferable that curing by a crosslinking reaction also proceed. In other words, when composition L contains an acrylic resin A having a reactive group A and a crosslinking agent B having a reactive group B, it is preferable that the reaction between the acrylic resin A and the crosslinking agent B also proceeds. Among these, it is more preferable that curing proceeds by forming a crosslinked structure through reaction between the reactive group A of the acrylic resin A and the reactive group B of the crosslinking agent B. From the viewpoint of forming a sufficiently cured coating film (release layer), it is preferable that drying and the crosslinking reaction proceed simultaneously. Furthermore, since the crosslinking reaction is carried out in the stretching section 20 of FIG. 2 , it is preferable that sufficient crosslinking occurs at the heating temperature of the transverse stretching step described above. To achieve superior high-speed releasability, it is preferable to select reactive groups A and B that are sufficiently crosslinked at the heating temperature of the transverse stretching step. The coating method for composition L is not particularly limited, and known methods can be used. Examples of coating methods include spray coating, slit coating, roll coating, blade coating, spin coating, bar coating, and dip coating.

[0168] <Applications> The polyester film can be used in various applications. For example, the polyester film is preferably used as a release film (carrier film) for producing ceramic green sheets. The ceramic green sheets produced using the polyester film can be suitably used for producing ceramic capacitors, which require multilayer internal electrodes in response to miniaturization and increased capacitance.

[0169] The method for producing a ceramic green sheet using the polyester film is not particularly limited and can be carried out by a known method. Examples of methods for producing a ceramic green sheet include a method in which a prepared ceramic slurry is applied to the release layer surface of the polyester film and the solvent contained in the ceramic slurry is dried and removed. The method for applying the ceramic slurry is not particularly limited, and known methods can be applied, such as a method in which a ceramic slurry obtained by dispersing ceramic powder and a binder in a solvent is applied by a reverse roll method and the solvent is removed by heating and drying. The binder is not particularly limited, and examples thereof include polyvinyl butyral. The solvent is also not particularly limited, and examples thereof include ethanol and toluene.

[0170] The produced ceramic green sheet is used to manufacture a ceramic capacitor. Known methods can be used to manufacture a ceramic capacitor using the ceramic green sheet, including, for example, the following method. First, internal electrodes are provided on a laminate of a polyester film and a ceramic green sheet by coating or printing a conductive paste. Next, the polyester film is removed from the laminate, and ceramic green sheets with internal electrodes are sequentially stacked. The resulting laminate is pressed to produce an intermediate laminate. The intermediate laminate is cut into a desired shape, and the cut intermediate laminate is fired to obtain a ceramic element. Next, external electrodes electrically connected to the internal electrodes are formed on each of the two end faces of the fired intermediate laminate using a conductive paste such as silver, thereby obtaining a ceramic capacitor.

[0171] The polyester film can also be used as a protective film for dry film resist, a film for sheet molding such as a decorative layer and a resin sheet, a release film for process manufacturing such as a semiconductor manufacturing process, a battery manufacturing process, and a polarizing plate manufacturing process, and a separator for an adhesive film for labels, medical use, and office supplies.

[0172] The present invention will be described in more detail below with reference to examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below.

[0173] [Production of Polyester Film] Example 1 An unstretched polyester substrate was produced with reference to the conditions described in paragraphs

[0160] to

[0169] of WO 2020 / 158316. The obtained unstretched polyester substrate was longitudinally stretched. The following protrusion-containing layer-forming composition X1 was applied to one side of the longitudinally stretched polyester substrate, and the following composition L1 was applied to the opposite side. Each of the formed coating films was dried with hot air at 100°C to form a protrusion-containing layer and a release layer. That is, protrusion-containing layer-forming composition X1 and composition L1 were applied in-line. At this time, the application amounts of protrusion-containing layer-forming composition X1 and composition L1 were adjusted so that the thickness of the protrusion-containing layer was 60 nm and the thickness of the release layer was 15 nm. When preparing each composition, the components were mixed and then filtered using a depth-pleated filter (SHPH010, manufactured by Roki Techno Co., Ltd.) with a pore size of 1 μm, followed by membrane degassing (2x6 Radial Flow Superphobic, manufactured by Polypore Co., Ltd.). The resulting coated film was stretched transversely to produce a biaxially oriented polyester film with a width of 1500 mm, which was then wound up at 7000 m intervals without knurling. The thickness of the produced biaxially oriented polyester film (polyester film of Example 1) was 31 μm. The biaxially oriented polyester film (polyester film of Example 1) had an intrinsic viscosity of 0.63 dl / g and a terminal COOH content in the range of 2.6 to 2.8 eq / ton. The polyester substrate in the polyester film was substantially free of particles. Furthermore, the biaxially stretched polyester film (polyester film of Example 1) had an Sb content of 0 to 1 mass ppm, a Ti content of 7 ppm, an Mg content of 75 ppm, and a P content of 65 ppm, based on the total mass of the biaxially stretched polyester film (polyester film of Example 1). The measurements were carried out using an ICP-MS analyzer "Agilent 7800 ICP-MS" (manufactured by Agilent Technologies).

[0174] (Protrusion-Containing Layer-Forming Composition X1) The components shown below were mixed, and then the above-mentioned filtration treatment and membrane degassing were carried out to obtain protrusion-containing layer-forming composition X1. - Aqueous solution of aqueous primer (Hydran AP-40N, manufactured by DIC Corporation) with a solids concentration of 35% by mass: 112.1 parts by mass - Water-diluted solution of anionic hydrocarbon surfactant (Rapisol (registered trademark) A-90, manufactured by NOF Corporation) with a solids concentration of 1% by mass: 55.7 parts by mass - Aqueous dispersion of colloidal silica (Snowtex ZL, manufactured by Nissan Chemical Industries, Ltd.) with a solids concentration of 40.5% by mass: 11.1 parts by mass - Water: 821.1 parts by mass

[0175] (Method for preparing composition L1) The components shown below were mixed, and then subjected to the above-mentioned filtration and membrane degassing to obtain composition L1 (composition L1 for forming a release layer). Acrylic resin A1 (solid content concentration 20% by mass): 82.5 parts by mass (16.5 parts by mass in terms of solid content) Crosslinker B1 (aqueous solution containing an oxazoline compound, an acrylic polymer with 2-isopropenyl-2-oxazoline-derived structural units / methoxypolyethylene glycol acrylate-derived structural units / ethyl acrylate-derived structural units / methyl methacrylate-derived structural units = 48 / 10 / 2 / 40 (molar ratio), solid content concentration 25% by mass aqueous solution, weight average molecular weight Mw: 23,000, oxazoline value = 4.8) (referred to as "B1 (oxazoline)" in the table): 44 parts by mass (11 parts by mass in terms of solid content) Water: 873.5 parts by mass

[0176] - Method for synthesizing acrylic resin A1 1-propanol (92.83 g) was placed in a 1-liter three-neck flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, and the temperature was raised to 80°C under a nitrogen stream. Mixed solution 1, which was a mixture of 2.16 g of V-601 (a radical polymerization initiator; manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 30.94 g of 1-propanol, 20.00 g of methacrylic acid (MAA), methacrylic-modified silicone oil (CH ２ =C(CH ３ )-C(O)O-L １１ -[Si(CH ３ ) ２ -O] ｍ -SiR １ (CH ３ ) ２L in the formula １１ The definition of is defined as R in the above formula (A1-1). １１ and L １１ The definitions of m and R in the formula are the same as those of １ The definition of -[Si(R ３ ) ２ -O] ｍ -SiR １ (R ２ ) ２ m and R in the group represented by １ The definition is the same as that of the above. Molecular weight: approximately 1000. In the tables below, this is referred to as "SiMA-1." Mixed solution 2, prepared by mixing 70.00 g of methyl methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name "M-90G"; in the tables below, this is referred to as "M-90G"), 10.00 g of methoxypolyethylene glycol methacrylate, 0.66 g of dodecyl mercaptan, and 30.94 g of 1-propanol, was added dropwise at a constant rate under dropping conditions such that the dropwise addition was completed within 3 hours. After the dropwise addition of the mixed solution was completed, a mixed solution prepared by mixing 0.32 g of V-601 and 2 g of 1-propanol was added to the resulting reaction mixture, and the mixture was heated and stirred for 6 hours. To the resulting reaction mixture was added 49.39 g of ethanol, and then 16.57 g of dimethylaminoethanol (neutralizing agent) (DMAE) was added dropwise using a dropping funnel, and water was added to adjust the solid content to 20%, thereby obtaining a solution of acrylic resin A1.

[0177] Examples 2 to 45 Biaxially stretched films (polyester films) of Examples 2 to 45 were obtained by replacing composition L1 used to form the release layer with compositions L2 to L36, in which the components were changed as shown in the table below. The amount of each component in compositions L2 to L36 was adjusted so that the solids concentration was the same as that of composition L1. In Examples 20 to 28, the amount of composition L2 applied was adjusted so that the thickness of the release layer was as shown in the table below. Of the components used in preparing compositions L2 to L36, the components other than those used in composition L1 are as follows. The components in parentheses at the end of each component are the abbreviations for each component listed in the table below.

[0178] (Monomers used in the synthesis of acrylic resin A) 3-[tris(trimethylsilyloxy)silyl]propyl methacrylate (TrisMA) 3-[tris(trimethylsilyloxy)silyl]propyl acrylate (TrisA) Methacrylic-modified silicone oil (CH ２ =C(CH ３ )-C(O)O-L １１ -[Si(CH ３ ) ２ -O] ｍ -SiR １ (CH ３ ) ２ L in the formula １１ The definition of is defined as R in the above formula (A1-1). １１ and L １１ The definitions of m and R in the formula are the same as those of １ The definition of -[Si(R ３ ) ２ -O] ｍ -SiR １ (R ２ ) ２ m and R in the group represented by １ The molecular weight is about 2000.) (SiMA-2) Methacrylic modified silicone oil (CH ２ =C(CH ３ )-C(O)O-C ３ H ６ -[Si(CH ３ ) ２ -O] ｍ -Si(CH ３ ) ２ (C ４ H ９ The definition of m in the formula is the same as that of —[Si(R ３ ) ２ -O] ｍ -SiR １ (R ２ ) ２ The definition of m is the same as that of the group represented by the formula (1). Molecular weight: about 5000.) (SiMA-3) Methacrylic-modified silicone oil (CH ２ =C(CH ３ )-C(O)O-C ３ H ６ -[Si(CH ３ ) ２-O] ｍ -Si(CH ３ ) ２ (C ４ H ９ The definition of m in the formula is the same as that of —[Si(R ３ ) ２ -O] ｍ -SiR １ (R ２ ) ２ The definition of m is the same as that of the group represented by the formula: Molecular weight: about 1,000. ) (SiMA-4) Acrylic acid (AA) 2-methacryloyloxyethyl succinate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Ester HO-MS") (HO-MS) Hydroxyethyl methacrylate (HEMA) Methoxytetraethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name "NK Ester M-40G") (M-40G) Methoxypolyethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name "NK Ester M-230G") (M-230G) 2-Methoxyethyl acrylate (MEA) Diacetone acrylamide (DAAM) Ethylene glycol monoacetoacetate monomethacrylate (EGMM) t-Butyl acrylate (tBA) 2-Hydroxy-3-phenoxypropyl acrylate (HPPA) 4-Hydroxybutyl acrylate (HBA) Phenoxyethyl acrylate (PEA) Benzyl methacrylate (BnMA) Cyclohexyl acrylate (CyHA) Cyclohexyl methacrylate (CyHMA) Tetrahydrofurfuryl methacrylate (THFMA) Styrene (St) n-Butyl acrylate (nBA) Methyl methacrylate (MMA) Stearyl methacrylate (MMA)

[0179] The molecular weight of the monomer was measured by MALDI-MS (matrix-assisted laser desorption / ionization mass spectrometry) as follows. Specifically, 10 μL of a diluted monomer solution (1 mg / mL, THF (tetrahydrofuran) solution) was mixed with 10 μL of DHB (2,5-dihydroxybenzoic acid) (10 mg / mL, THF solution) and 5 μL of NaTFA (sodium trifluoroacetate) (1 mg / mL, THF solution) to obtain a mixed solution. MS spectra of 1 μL of the obtained mixed solution were measured using a mass spectrometer (Ultraflextreme manufactured by Bruker) that employs MALDI-MS as the measurement principle. The measurements were performed with n=2. The peak with the strongest intensity in the obtained MS spectrum was taken as the molecular weight.

[0180] (Neutralizing agent) Diisopropylethylamine (DIPEA) 28% aqueous ammonia (NH3aq)

[0181] (Crosslinking agent B) Crosslinking agent B2 (aqueous solution containing an oxazoline compound, an acrylic polymer having a molar ratio of 2-isopropenyl-2-oxazoline-derived structural units / ethyl acrylate-derived structural units / methyl methacrylate-derived structural units of 75 / 5 / 20, an aqueous solution with a solids concentration of 10% by mass, a weight-average molecular weight Mw: 60,000, and an oxazoline value of 7.5) (B2 (oxazoline)). Crosslinking agent B3 (an acrylic polymer having an oxazoline group synthesized by the method described below (a copolymer represented by formula (B3) described below), a weight-average molecular weight Mw: 14,200) (B3 (oxazoline)). Crosslinking agent B4 (an acrylic polymer having an oxazoline group synthesized by the method described below (a copolymer represented by formula (B4) described below), a weight-average molecular weight Mw: 12,300) (B4 (oxazoline)).

[0182] The weight average molecular weight Mw of the crosslinking agent B was determined in the same manner as the weight average molecular weight Mw of the acrylic resin A1 described below.

[0183] Synthesis Method of Crosslinking Agent B3 1-propanol (54.41 g) was placed in a 500-milliliter three-neck flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, and the temperature was raised to 80° C. under a nitrogen stream. To this, mixed solution 1, which was a mixture of 0.62 g of V-601 (radical polymerization initiator; manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 15.54 g of 1-propanol, and mixed solution 2, which was a mixture of 20.00 g of 2-isopropenyl-2-oxazoline, 10.00 g of 3-[tris(trimethylsilyloxy)silyl]propyl methacrylate (TrisMA), 20.00 g of methoxytetraethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name "M-40G"), 0.88 g of dodecyl mercaptan, and 7.77 g of 1-propanol, were each added dropwise at a constant rate under conditions such that the dropwise addition was completed within 3 hours. After the dropwise addition of the mixed solution was completed, a mixed solution of 0.60 g of V-601 and 1 g of 1-propanol was added to the resulting reaction mixture, and the mixture was heated and stirred for 5 hours to obtain a solution of crosslinker B3. The solid content of B3 was 40% by mass.

[0184]

[0185] Crosslinking agent B3 has a mass ratio of the structural units, from left to right, of 20:40:40.

[0186] Synthesis of Crosslinker B4: A solution of crosslinker B4 was obtained in the same manner as for synthesis of crosslinker B3, except that the amounts of the compounds added were adjusted so that the mass ratios of the structural units were as shown below. The solid content of B4 was 40 mass%.

[0187]

[0188] Crosslinking agent B4 has a mass ratio of the structural units, from left to right, of 40:20:40.

[0189] Comparative Example 1 A biaxially stretched film (polyester film) of Comparative Example 1 was obtained in the same manner as in Example 1, except that the following composition LX1 (composition LX1 for forming a release layer) was used instead of composition L1. Here, composition LX1 is the coating liquid used in Example 14 of JP 2021-11081 A, and contains silicone (referred to as "CX1" in the tables described below) but does not contain an acrylic resin.

[0190] (Release Layer Forming Composition LX1) Emulsion (I) and emulsion (II) were prepared according to the following procedure. (A) 50 parts by mass of a vinyl-containing polydimethylsiloxane in which both ends are each blocked with a dimethylvinylsilyl group, (B) 0.5 parts by mass of a platinum-vinylsiloxane complex solution having a platinum content of 1% by mass, (C) 0.11 parts by mass of 1-ethynyl-1-cyclohexanol (manufactured by Nissin Chemical Industry Co., Ltd.), (D) 6.6 parts by mass of a nonionic surfactant ("Naroacty CL-95" manufactured by Sanyo Chemical Industries, Ltd.), and (E) 44 parts by mass of purified water were mixed and stirred to prepare emulsion (I). The platinum content was 100 ppm by mass relative to the mass of polydimethylsiloxane (A). Furthermore, 35 parts by mass of (F) a methylhydrogenpolysiloxane having SiH groups in its side chains and both molecular chain terminals blocked with trimethylsiloxy groups, 5 parts by mass of (G) a nonionic surfactant ("Naroacty CL-95" manufactured by Sanyo Chemical Industries, Ltd.), and 60 parts by mass of (H) purified water were mixed and stirred to prepare emulsion (II). Next, emulsion (I) and emulsion (II) were mixed and further diluted with purified water to a solids concentration of 40% by mass, thereby obtaining a composition. When preparing the composition, the mixing ratio of emulsion (I) and emulsion (II) was adjusted so that the ratio of the total number of moles of SiH groups in component (F) to the total number of moles of alkenyl groups in component (A) was 2.9. To 92.5 parts by mass of the above composition (37 parts by mass in terms of solid content), 5 parts by mass of a silane coupling agent (KBE-403, manufactured by Shin-Etsu Chemical Co., Ltd.) and 2 parts by mass of a nonionic surfactant ("Naloacty CL-95" manufactured by Sanyo Chemical Industries, Ltd.) were added and mixed, and the mixture was further diluted with purified water to a solid content concentration of 1% by mass, thereby obtaining composition LX1.

[0191] <Comparative Example 2> Instead of composition L1, the following composition LX2 (composition LX2 for forming a release layer) was used to obtain a biaxially stretched film (polyester film) of Comparative Example 2 according to the procedure described in Example 6 of WO 2018 / 150255. The polyester film of Comparative Example 2 was produced without employing an in-line coating method. Here, composition LX2 is the coating liquid used in Example 6 of WO 2018 / 150255, and contains an acrylic resin having a siloxane bond (referred to as "AX1" in the formula described below), and its composition is as shown in the table. In addition, crosslinking agent BX1 (isocyanate) is the isocyanate-based crosslinking agent (SUR200, manufactured by Toyo Ink Co., Ltd.) used in Example 6 of WO 2018 / 150255. CX2 is an acrylic resin (b) (YL455, manufactured by Toyo Ink Co., Ltd.) having no siloxane bond, used in Example 6 of WO 2018 / 150255.

[0192] <Comparative Example 3> A biaxially stretched film (polyester film) of Comparative Example 3 was obtained in the same manner as in Example 1, except that the following composition LX3 (composition LX3 for forming a release layer) was used instead of composition L1. Here, composition LX3 is the composition of the following composition used in Example 1 of WO 2021 / 192896. The acrylic resin AX2 contained in composition LX3 is the acrylic resin A-1 used in Example 1 of WO 2021 / 192896, and is an acrylic resin synthesized using 100 parts by mass of hydroxyethyl methacrylate (HEMA), 8 parts by mass of methacrylic acid (MAA), 33 parts by mass of stearyl methacrylate (SMA), and 3 parts by mass of methyl methacrylate (MMA). The acrylic resin AX2 does not have a siloxane bond. The oxazoline crosslinking agent BX2 (oxazoline) contained in composition LX3 is the oxazoline crosslinking agent C-1 used in Example 1 of WO 2021 / 192896. The polyether-modified polydimethylsiloxane DX1 contained in composition LX3 is the additive E-1 used in Example 1 of WO 2021 / 192896.

[0193] (Composition LX3) Water: 45.76 parts by mass Isopropyl alcohol: 28.20 parts by mass Acrylic resin AX2 (solid content concentration 20% by mass): 14.00 parts by mass Oxazoline-based crosslinking agent BX2 (solid content concentration 10% by mass): 12.00 parts by mass Polyether-modified polydimethylsiloxane DX1,67 Additive (solid content concentration 100% by mass, manufactured by Dow Corning Toray Co., Ltd.): 0.04 parts by mass

[0194] <Comparative Example 4> Instead of composition L1, the following composition LX4 (composition LX4 for forming a release layer) was used to obtain a biaxially stretched film (polyester film) of Comparative Example 4 according to the procedure described in Example 8 of WO 2020 / 050081. The polyester film of Comparative Example 4 was produced without employing an in-line coating method. Here, composition LX4 is the coating liquid used in Example 8 of WO 2020 / 050081. The acrylic resin AX3 contained in composition LX4 is the silicone group-containing acrylic polyol used in Example 8 of WO 2020 / 050081. The melamine-based crosslinking agent BX3 (melamine) contained in composition LX4 is the crosslinking agent (hexamethoxymethylolmelamine) used in Example 8 of WO 2020 / 050081. Furthermore, the polyether-modified polydimethylsiloxane DX2 contained in composition LX4 is the silicone mold release agent used in Example 8 of WO 2020 / 050081.

[0195] [Physical Properties of Acrylic Resin A] <Acid Value and Hydroxyl Value> The following table shows the theoretical values ​​of the acid value and hydroxyl value of Acrylic Resin A calculated from the amounts of monomers charged in the production of Acrylic Resin A. When the acid value of Acrylic Resin A was measured by the following measurement method, the measured value was almost the same as the theoretical value described above.

[0196] (Method for Measuring Acid Value) 1.0 g of sample (acrylic resin A) was weighed into a 200 mL beaker, and the weight was recorded. 95 mL of a mixed solvent of THF (tetrahydrofuran) / water (5 / 1 (volume ratio)) was added to dissolve the sample. This solution (sample solution) was subjected to potentiometric titration (automatic titration apparatus AT-510, manufactured by Kyoto Electronics Manufacturing Co., Ltd.) with 0.1 N aqueous sodium hydroxide while stirring with a magnetic stirrer, and the titration volume was determined from the endpoint (performed with N=2). A blank test was conducted in the same manner, and the acid value was calculated using the following formula: Acid value (mmol / g) = 0.1 (mol / L) × f × (titration volume of sample solution (mL) - titration volume of blank (mL)) × weighed value of sample (g) × solids concentration (%) × 0.01 In the formula, f represents the titrant factor of the aqueous sodium hydroxide solution.

[0197] <Weight average molecular weight Mw> The weight average molecular weight (Mw) was measured by gel permeation chromatography (GPC). Measurement by gel permeation chromatography (GPC) was performed using an HLC (registered trademark)-8320GPC (manufactured by Tosoh Corporation) as a measuring device, two TSKgel (registered trademark) Super Multipore HZ-M (4.6 mm ID × 15 cm, manufactured by Tosoh Corporation) as columns, and THF (tetrahydrofuran) as an eluent. The measurement was performed using a RI (Refractive Index) detector at a sample concentration of 0.3 mass%, a flow rate of 0.35 mL / min, a sample injection amount of 10 μL, and a measurement temperature of 40 ° C. The calibration curve was prepared from 12 samples of "Standard Sample TSK Standard, Polystyrene" manufactured by Tosoh Corporation: "F-128", "F-80", "F-40", "F-20", "F-10", "F-4", "F-2", "F-1", "A-5000", "A-2500", "A-1000", and "A-500".

[0198] [Film Properties] <Surface Free Energy> The surface free energy of the release layer surface was measured by the following method. Using a contact angle meter (DROPMASTER-501, manufactured by Kyowa Interface Science Co., Ltd.), a droplet was dropped onto the release layer surface of a polyester film at 25°C, and the contact angle was measured 1 second after the droplet adhered to the release layer surface. 2 μL of purified water, 1 μL of methylene iodide, and 1 μL of ethylene glycol were used as droplets, and the surface free energy was calculated from the measured contact angles using the Kitazaki-Hata method.

[0199] <Maximum protrusion height Sp, average surface roughness Sa> The maximum protrusion height Sp and average surface roughness Sa of the release layer surface of the polyester film were measured by the following method. The release layer surface of the polyester film was measured under the following conditions using an optical interferometer (Vertscan 3300G Lite, manufactured by Hitachi High-Tech Corporation), and then analyzed using the built-in data analysis software (VS-Measure5) to determine the maximum protrusion height Sp and average surface roughness Sa of the release layer surface n. In measuring the maximum protrusion height Sp, the maximum value of the measured values ​​obtained from five measurements at different measurement positions was used, and in measuring the average surface roughness Sa, the average value of the measured values ​​obtained from five measurements at different measurement positions was used. (Measurement conditions) Measurement mode: WAVE mode Objective lens: 50x Measurement area: 186 μm × 155 μm

[0200] The maximum protrusion height Sp of the release layer surface of the polyester film measured by the above method is shown in the table below. Furthermore, the surface average roughness Sa of the release layer surface of the polyester film measured by the above method was in the range of 0.5 to 2.0 nm in all examples. The maximum protrusion height Sp and surface average roughness Sa of the smooth surface of the polyester film were measured using the same method as above. In all examples, the maximum protrusion height Sp of the smooth surface was in the range of 10 to 60 nm, and the surface average roughness Sa of the smooth surface was in the range of 2 to 3 nm.

[0201] <Sliding Angle of Water on Release Layer Surface> Measurements were made using a contact angle meter (Kyowa Interface Science Co., Ltd., fully automatic contact angle meter DM-701) in an environment of 23°C and 50% humidity. Specifically, a polyester film was placed on a flat glass substrate, and a 10.0 μL droplet of water was dropped onto the release layer surface. The glass plate began to tilt 1 second after the dropped droplet adhered to the release layer surface, and the glass plate was tilted from an inclination angle of 0° to 90° at a tilt speed of 1.0° / sec. The movement judgment distance was 50 dots, and the inclination angle at which the droplet began to move was taken as the measured value of the sliding angle. Measurements were made twice in total, and the arithmetic mean value of the measured values ​​was adopted as the sliding angle. The measurement results for the sliding angle are shown in the table below. Note that if the droplet did not move even 1 second after the inclination angle of the glass plate reached 90°, it was recorded as "not falling."

[0202] <Silicon atom content> For the polyester films of the examples and comparative examples, the silicon atom content (atm %) on the release layer surface was calculated by the method described above using an analyzer (X-ray photoelectron spectroscopy analyzer, manufactured by Ulvac-PHI) that uses XPS (X-ray photoelectron spectroscopy) as its measurement principle. The calculated silicon atom content is shown in the "Surface Si ratio" column in the table below. Note that when the silicon atom content was below the detection limit, it was marked "0" in the table.

[0203] <Heat Shrinkage Rate> The polyester film of each example was cut to a dimension of 100 mm in the width direction and 100 mm in the direction perpendicular to the width direction to obtain a square sample. The longitudinal and width dimensions before heating were measured using a measuring microscope (product name "MM-800" manufactured by Nikon Corporation), and the arithmetic mean value was designated as Ls. The sample was then placed on a sample holder and placed in a thermostatic chamber set to 150°C. After 30 minutes had passed since placement, the sample was removed, and the longitudinal and width dimensions after heating were measured using the measuring microscope, and the arithmetic mean value was designated as Ll. The heat shrinkage rate of the polyester film was calculated using the following formula (1). A positive value for the heat shrinkage rate indicates shrinkage, and a negative value indicates expansion. Heat Shrinkage Rate (%) = {(Ls - Ll) / Ls} × 100 (1) The heat shrinkage rates of the polyester films produced in the examples were all in the range of 0.95 to 1.15%.

[0204] <Dynamic Friction Coefficient> For the polyester film of each example, the coefficient of friction between the release surface (surface of the release layer) and the protrusion surface (surface of the protrusion-containing layer) was measured in accordance with ASTM D 1894-95. As a measurement condition, the distance over which the flat indenter was moved in the longitudinal direction of the fixed test specimen was set to 130 mm. The force (test force) required to move the flat indenter was recorded using a measuring instrument, and a plot was created with the movement distance (unit: mm) on the horizontal axis and the test force (unit: N) on the vertical axis. The dynamic friction coefficient was calculated from the measured values ​​of the test force plotted above. The above operation was repeated five times, and the average value of the dynamic friction coefficients for each of the five measurements was calculated. The average value of the dynamic friction coefficient is shown in the table below as the dynamic friction coefficient. As a result, the dynamic friction coefficients of the polyester films of each example were all in the range of 0.3 to 0.5.

[0205] [Performance] <Coating Defects> A polyester film was cut into a length of 2 m, and the surface of the release layer was visually observed to evaluate coating defects (cissing) according to the following criteria: A: Less than 3 coating defects (cissing) B: 3 to less than 10 coating defects (cissing) C: 10 or more coating defects (cissing)

[0206] <Roll Appearance> The appearance of the rolled polyester films obtained by winding the polyester film in Examples and Comparative Examples was visually observed and evaluated according to the following criteria: A: No wrinkles were observed immediately after winding, and no wrinkles were observed even after one week of storage. B: No wrinkles were observed immediately after winding, but wrinkles were observed after one week of storage. C: Wrinkles were observed immediately after winding.

[0207] <Method for producing ceramic green sheets and evaluation> (Preparation of ceramic slurry) Barium titanate powder (BaTiO ３A mixed solution was prepared by mixing 100 parts by weight of a binder (manufactured by Sakai Chemical Industry Co., Ltd., product name "BT-03"), 8 parts by weight of a polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name "S-LEC (registered trademark) B.K BM-2") as a binder, 4 parts by weight of dioctyl phthalate (manufactured by Kanto Chemical Co., Ltd., dioctyl phthalate, Deer Grade 1) as a plasticizer, and 135 parts by weight of a mixed solution of toluene and ethanol (5:5 by weight ratio). Zirconia beads were added to the mixed solution, and dispersed in the barium titanate powder mixed solution using a ball mill to prepare a dispersion. The zirconia beads were removed from the resulting dispersion to obtain a ceramic slurry. The ceramic slurry is a composition containing an organic solvent.

[0208] (Coatability (Cleaning) of Ceramic Slurry) The ceramic slurry was applied to the surface of the release layer of a polyester film using an applicator so that the thickness of the dried ceramic green sheets would be 1.0 μm, 0.5 μm, and 0.2 μm, respectively. After drying at 80° C. for 1 minute, a ceramic green sheet was formed on the surface of the release layer of the polyester film. The surface condition of the ceramic green sheet was visually confirmed, and the coatability was evaluated according to the following criteria. A: Coating was successful at both 1.0 μm and 0.5 μm without cissing or the like. Furthermore, coating was successful at 0.2 μm without cissing or the like. B: Coating was successful at both 1.0 μm and 0.5 μm without cissing or the like. However, cissing occurred in some areas at 0.2 μm. C: Coating was successful at 1.0 μm without cissing or the like. However, cissing occurred in some areas at 0.2 μm and 0.5 μm.

[0209] (Slow-Speed ​​Peelability) The ceramic slurry was applied to the release layer surface of a polyester film using an applicator so that the thickness of the dried ceramic green sheet would be 0.2 μm. After drying at 90°C for 1 minute, a ceramic green sheet was formed on the release layer surface of the polyester film. Using a peel tester (VPA-2S, manufactured by Kyowa Interface Science Co., Ltd., load cell load 1N), the ceramic green sheet formed on the release layer surface was peeled at a peel angle of 90°, a peel temperature of 25°C, and a peel speed of 0.3 m / min. The peel direction was as follows: double-sided adhesive tape (No. 535A, manufactured by Nitto Denko Corporation) was attached to a stainless steel (SUS) plate attached to the peel tester, and the polyester film with the ceramic green sheet was fixed on the double-sided tape by adhering the ceramic green sheet side to the tape. The polyester film side was then pulled to peel the sheet. The average peel force of the measured values ​​obtained over peel distances of 20 mm to 50 mm was calculated, and this value was designated as the peel force. The measurement was performed five times, and the average peel strength was used as the peel strength of the ceramic green sheet. Based on the peel strength of the ceramic green sheet, the low-speed peelability was evaluated according to the following criteria: AA: Peel strength ≦ 0.10 N / 25 mm; A: 0.10 N / 25 mm < peel strength ≦ 0.15 N / 25 mm; B: 0.15 N / 25 mm < peel strength ≦ 0.25 N / 25 mm; C: 0.25 N / 25 mm < peel strength ≦ 0.35 N / 25 mm; D: Peel strength exceeds 0.35 N / 25 mm, or the ceramic green sheet breaks during peeling.

[0210] (High-Speed ​​Removal Property) The high-speed removability was evaluated based on the peel strength of the ceramic green sheet in the same manner as in the evaluation method for low-speed removability, except that the peel speed was changed from 0.3 m / min to 3 m / min, and according to the following criteria: AA: Peel strength ≦ 0.10 N / 25 mm A: 0.10 N / 25 mm < peel strength ≦ 0.15 N / 25 mm B: 0.15 N / 25 mm < peel strength ≦ 0.25 N / 25 mm C: 0.25 N / 25 mm < peel strength ≦ 0.35 N / 25 mm D: Peel strength exceeds 0.35 N / 25 mm, or the ceramic green sheet breaks during peeling.

[0211] The measurement results of the above physical properties and the evaluation results of the performance are shown in the table below. In the table below, monomers A1 to A4 and a neutralizing agent are components used in the synthesis of the acrylic resin. Monomers A1 to A3 are defined as above, and monomer A4 refers to a monomer that does not fall under the category of monomers A1 to A3. In the table below, A / B means "content of acrylic resin A / content of crosslinking agent B" in the composition for forming a release layer. In the table below, A / C / B / D means "content of acrylic resin A / content of other polymer C / content of crosslinking agent B / content of other additive D" in the composition for forming a release layer. In the table below, the "maximum projection height Sp (nm)" column indicates the maximum projection height Sp (unit: nm) on the surface of the release layer.

[0212] The ratio (mass ratio) of the constituent units of each acrylic resin A was measured by proton nuclear magnetic resonance ( １ The ratio of the amount of the monomers charged was determined by H-NMR, and was found to be equivalent to the ratio of the amount of the monomers charged. All of the release layers in the examples were formed from a composition containing an acrylic resin A having structural units derived from monomer A2 and a crosslinking agent B, and since heating was performed during the formation of the release layer, it can be said that they have a crosslinked structure.

[0213]

[0214]

[0215]

[0216] As shown in the table above, a polyester film comprising a release layer and a polyester substrate, wherein the release layer contains an acrylic resin, the water sliding angle of the release layer surface is 90°C or less, and the thickness of the release layer is less than 200 nm, has been shown to have excellent coatability with a composition containing an organic solvent (ceramic slurry), and also has excellent high-speed peelability of a sheet (ceramic green sheet) formed on the surface of the release layer (Example).

[0217] Comparison of Examples 1 to 19 showed that when an acrylic resin A having a structural unit derived from monomer A3 with a ClogP value of 0.8 or more was used, the high-speed releasability of the sheet (ceramic green sheet) formed on the surface of the release layer was superior. Comparison of Examples 2 and 20 to 28 showed that when the release layer thickness was 7 nm or more, the high-speed and low-speed releasability of the sheet (ceramic green sheet) formed on the surface of the release layer was superior. Furthermore, comparison of Examples 2 and 20 to 28 showed that when the release layer thickness was less than 90 nm, the appearance (roll appearance) of the polyester film when rolled was superior, and further, when the release layer thickness was less than 70 nm, the roll appearance was even superior. Comparison of Examples 1 and 32 showed that when the surface Si ratio (silicon atom content on the surface of the release layer) was 2 atm% or more, the high-speed and low-speed releasability of the sheet (ceramic green sheet) formed on the surface of the release layer was superior. Comparison of Examples 2 and 32 to 35 showed that when an acrylic resin A having an acid value of 4.5 mmol / g or less was used, the high-speed releasability of the sheet (ceramic green sheet) formed on the release layer surface was superior, while when an acrylic resin A having an acid value of 3.0 mmol / g or less was used, the low-speed releasability of the sheet (ceramic green sheet) formed on the release layer surface was superior. Comparison of Examples 1, 36, 37, and 45 showed that when an acrylic resin A containing a structural unit derived from a monomer A1 having a molecular weight of 4000 or less was used, the high-speed releasability of the sheet formed on the release layer surface was superior. Comparison of Examples 1, 38, 39, and 45 showed that when an acrylic resin A having a linear polysiloxane structure was used, the high-speed releasability of the sheet formed on the release layer surface was superior. Comparison of Examples 1, 40, and 41 showed that when an acrylic resin A having a structural unit derived from methacrylic acid was used, the low-speed releasability of the sheet formed on the release layer surface was superior.

[0218] In contrast, when the release layer does not contain acrylic resin, the water sliding angle on the release layer surface is not 90° or less ("does not fall off"), or the thickness of the release layer is 200 nm or more, it was shown that at least one of the coatability of the composition containing an organic solvent (ceramic slurry) and the releasability of the sheet (ceramic green sheet) formed on the surface of the release layer is poor (Comparative Examples 1 to 4).

[0219] 2A to 2L: Gripping member 3: Clip closer 4: Support member 5: Clip opener 10: Preheating section 20: Stretching section 30: Heat setting section 40: Heat relaxation section 50: Cooling section 60a, 60b: Circular rail 100: Stretching machine 200: Film 300: Polyester film 310: Polyester base material 320: Release layer 321: One side 322: Other side (release layer surface, release surface) P, Q: Grip release point MD: Machine direction (longitudinal direction) TD: Width direction L0, L1, L2, L3: Film width

Claims

1. A polyester film comprising a release layer and a polyester substrate, wherein the release layer comprises an acrylic resin, the water sliding angle of the release layer surface is 90° or less, and the thickness of the release layer is less than 200 nm.

2. The polyester film according to claim 1, wherein the silicon atom content in the surface of the release layer is 25 atm % or less.

3. The polyester film according to claim 1 or 2, wherein the polyester substrate is substantially free of particles, and the maximum peak height (Sp) of the release layer surface is less than 35 nm.

4. The polyester film according to claim 1 or 2, wherein the release layer has a thickness of less than 90 nm.

5. The release layer is -Si(R) ３ The polyester film according to claim 1 or 2, having a structure represented by the following formula: wherein each R independently represents an alkyl group or an aryl group.

6. The polyester film according to claim 1 or 2, wherein the release layer comprises a crosslinked product of an acrylic resin A having a siloxane bond and a crosslinking agent B.

7. The polyester film according to claim 6, wherein the acrylic resin A contains a structural unit derived from a monomer A1 which is an acrylic monomer having a siloxane bond, and the molecular weight of the monomer A1 is 4,000 or less.

8. The polyester film according to claim 1 or 2, which is used for producing a ceramic green sheet.

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