Polyester film and release film

Abstract

To provide a polyester film and a release film which enable manufacture of a ceramic green sheet where occurrence of uneven defects is suppressed when the release film obtained by using a polyester film after long-term storage is used in manufacture of the ceramic green sheet.SOLUTION: A polyester film in the present invention has a particle-containing layer containing particles, a polyester base material which does not substantially contain particles, and a particle-free layer which does not substantially contain particles, in this order, wherein a release layer is formed on the surface opposite to the polyester base material of the particle-free layer, and is used for manufacturing a release film, and the particle-free layer contains a non-polyester resin other than a polyester resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to polyester films and release films. [Background technology]

[0002] Biaxially oriented polyester films are used in a wide range of applications due to their processability, mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance. For example, release films, which are made by laminating a release layer onto the surface of a biaxially oriented polyester film, are used in the production of ceramic green sheets for the manufacture of multilayer ceramic capacitors.

[0003] For example, Patent Document 1 discloses a release film for manufacturing ceramic sheets, which uses a biaxially oriented polyester film consisting of two or more layers as a base material, the base material having a surface layer A that is substantially free of particles and a surface layer B that contains particles, a release coating layer laminated on the surface of surface layer A and a smoothing coating layer laminated on the surface of surface layer B, the smoothing coating layer having a specific region average surface roughness (Sa) and maximum protrusion height (P). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-060158 [Overview of the project] [Problems that the invention aims to solve]

[0005] With the recent trend towards larger capacitance and smaller size of ceramic capacitors, there is a growing demand for even thinner ceramic green sheets. However, as ceramic green sheets become thinner, the influence of the surface shape of the release film on the performance of the ceramic green sheet is expected to increase. For example, if there are irregularities on the release surface of the release film, these irregularities may be transferred to the ceramic green sheet, causing variations in the thickness of the ceramic green sheet and potentially degrading the performance of the ceramic capacitor product.

[0006] The present inventors have shown that when a release film obtained by forming a release layer on one surface of a polyester film used for manufacturing release films, as described in Patent Document 1, is used in the manufacture of a ceramic green sheet, at least one of minute recesses and protrusions may occur in the ceramic green sheet, indicating that there is room for improvement. In the following, minute recesses and protrusions will be collectively referred to as "unevenness defects."

[0007] In view of the above circumstances, the present invention aims to provide a polyester film and a release film that, when a release film obtained using a polyester film after long-term storage is used in the manufacture of a ceramic green sheet, can produce a ceramic green sheet in which the occurrence of unevenness defects is suppressed. [Means for solving the problem]

[0008] As a result of diligent research to solve the above problems, the inventors of the present invention have found that the desired effect can be obtained when a polyester film is used having, in this order, a particle-containing layer containing particles, a polyester substrate substantially free of particles, and a particle-free layer substantially free of particles and containing a non-polyester resin other than polyester resin, and have arrived at the present invention. In other words, the inventors have found that the above problem can be solved by the following configuration.

[0009] [1] A particle-containing layer containing particles, A polyester substrate that is substantially free of particles, It has, in this order, a particle-free layer that substantially does not contain particles, and A polyester film used to manufacture a release film by forming a release layer on the surface of the particle-free layer opposite to the polyester substrate, A polyester film in which the above particle-free layer contains a non-polyester resin other than polyester resin. [2] The polyester film according to [1], wherein the release film is a release film for manufacturing ceramic green sheets. [3] The polyester film according to [1] or [2], wherein the non-polyester resin contained in the particle-free layer is at least one resin selected from the group consisting of acrylic resin, urethane resin, and olefin resin. [4] The polyester film according to any one of [1] to [3], wherein the particle-containing layer comprises a non-polyester resin other than a polyester resin. [5] The polyester film according to [4], wherein the non-polyester resin contained in the particle-containing layer is at least one resin selected from the group consisting of acrylic resin, urethane resin, and olefin resin. [6] The polyester film according to any one of [1] to [5], wherein, when measured using an optical interferometer at 100 different locations on the surface opposite to the polyester substrate of the particle-free layer, with a measurement area of ​​186 μm × 155 μm per location, the total number of protrusions with a height exceeding 50 nm is 40 or less. [7] A polyester film according to any one of [1] to [6], wherein, when measured using a scanning electron microscope at 40 different locations on the surface of the particle-containing layer opposite to the polyester substrate, with a measurement area of ​​13 μm × 10 μm per location, the total number of foreign objects with a diameter of 1 μm or more is 2 or less. [8] The maximum protrusion height Sp of the surface on the opposite side of the polyester base material of the particle-free layer is 1 to 30 nm, and the maximum protrusion height Sp of the surface on the opposite side of the polyester base material of the particle-containing layer is 10 to 1500 nm, The polyester film according to any one of [1] to [7]. [9] The thickness of the particle-free layer and the thickness of the particle-containing layer are each 1 to 500 nm, The polyester film according to any one of [1] to [8].

[10] The surface free energy of the surface on the opposite side of the polyester base material of the particle-containing layer is 30 to 45 mJ / m 2 The polyester film according to any one of [1] to [9].

[11] The thickness of the polyester film is 40 μm or less, The polyester film according to any one of [1] to

[10] .

[12] A release film having a polyester film according to any one of [1] to

[11] and a release layer disposed on the surface on the opposite side of the polyester base material of the particle-free layer.

[13] When measured using an optical interferometer at 100 different locations on the surface on the opposite side of the particle-free layer of the release layer with a measurement area of 186 μm × 155 μm per location, the total number of protrusions exceeding a height of 50 nm is 40 or less, The release film according to

[12] .

[14] The maximum protrusion height Sp of the surface on the opposite side of the polyester base material of the particle-containing layer is 10 to 1500 nm, and the maximum protrusion height Sp of the surface on the opposite side of the particle-free layer of the release layer is 1 to 30 nm, The release film according to

[12] or

[13] .

Advantages of the Invention

[0010] According to the present invention, when a release film obtained using a polyester film after long-term storage is used in the manufacture of a ceramic green sheet, it is possible to manufacture a ceramic green sheet in which the occurrence of unevenness defects is suppressed. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view showing an example of the structure of the polyester film of the present invention. [Modes for carrying out the invention]

[0012] The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the object of the present invention.

[0013] In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits. In numerical ranges described stepwise in this specification, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Also, in numerical ranges described in this specification, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this specification, the amount of each component in a composition means the total amount of multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition. In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that the intended purpose of the process is achieved. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment.

[0014] In this specification, "longitudinal direction" means the longitudinal direction of the polyester film during the manufacturing of the polyester film, and is synonymous with "conveying direction" and "machine direction." In this specification, "width direction" means the direction perpendicular to the longitudinal direction. In this specification, "orthogonal" is not limited to strictly orthogonal, but includes approximately orthogonal. "Approximately orthogonal" means that the directions intersect within a range of 90° ± 5°, preferably within a range of 90° ± 3°, and more preferably within a range of 90° ± 1°. Furthermore, in this specification, "film width" means the distance between the two ends of the polyester film in the width direction.

[0015] [Polyester film] The polyester film of the present invention (hereinafter also referred to as "this film") comprises, in this order, a particle-containing layer containing particles, a polyester substrate substantially free of particles, and a particle-free layer substantially free of particles. A release layer is formed on the surface of the particle-free layer opposite to the polyester substrate, and it is used to manufacture a release film. Furthermore, in this film, the particle-free layer contains a non-polyester resin other than polyester resin. In this film, the surface opposite the polyester substrate of the particle-free layer is sometimes referred to as the "first main surface," and the surface opposite the polyester substrate of the particle-containing layer is sometimes referred to as the "second main surface."

[0016] When this film is stored for a long period of time, and the resulting release film is used in the manufacture of ceramic green sheets, ceramic green sheets with suppressed surface defects can be obtained. The exact reason for this is not clear, but it is generally presumed to be as follows. Polyester substrates contain impurities such as oligomers, and when polyester films (or release films obtained using polyester films) are stored for a long period of time, protrusions caused by these impurities may precipitate on the surface of the polyester substrate. Here, oligomers are low molecular weight by-products that are generated during the polymerization of polyester resins. It is presumed that in the release film obtained using such a polyester film, at least one of minute recesses and protrusions is formed in the release layer due to protrusions caused by impurities, and that uneven defects based on these minute recesses or protrusions occur in the ceramic green sheet formed on the surface of the release layer. To address this problem, this film has a particle-free layer containing non-polyester resin on the side where the ceramic green sheet is formed. This is presumed to suppress the precipitation of impurities on the surface of the polyester substrate and the growth of impurities that have precipitated on the surface of the polyester substrate. As a result, it is thought that the occurrence of defects in the ceramic green sheet has been suppressed.

[0017] 〔composition〕 The structure of this film will be explained with reference to the diagram. Figure 1 is a cross-sectional view showing an example of the structure of this film. The polyester film 1 has a particle-containing layer 12, a polyester substrate 14 disposed on the particle-containing layer 12, and a particle-free layer 16 disposed on the polyester substrate 14. The particle-containing layer 12 contains particles not shown, while the polyester substrate 14 and the particle-free layer 16 are substantially particle-free. The surface of the particle-free layer 16 opposite to the polyester substrate 14 (the first main surface) is the outermost layer of the polyester film 1 and is the surface for forming the release layer (described later). That is, after the manufacturing of the polyester film 1, a release layer is laminated onto the surface of the particle-free layer 16 opposite to the polyester substrate 14, thereby producing a release film having the polyester film 1 and the release layer. The surface of the particle-containing layer 12 opposite to the polyester substrate 14 (the second main surface) is the outermost layer of the polyester film 1.

[0018] The film has the above-mentioned particle-containing layer, polyester substrate, and particle-free layer, and as long as the particle-free layer contains a non-polyester resin, its specific form is not particularly limited and may have a configuration other than that shown in Figure 1. For example, in the configuration shown in Figure 1, the particle-containing layer 12 is placed in contact with the surface of the polyester substrate 14, but a primer layer or the like may be provided between the particle-containing layer 12 and the polyester substrate 14.

[0019] The following provides a detailed explanation of each layer of this film.

[0020] <Particle-containing layer> The particle-containing layer is a layer containing particles and is formed on one side of the polyester substrate. The surface of the particle-containing layer opposite to the side facing the polyester substrate constitutes the second main surface. This film, by having a particle-containing layer, can improve the transportability of polyester film and release film. More specifically, it can improve winding quality (suppress blocking), suppress the occurrence of scratches and defects during transport, and reduce transport wrinkles during high-speed transport.

[0021] The particle-containing layer may be provided directly on the surface of the polyester substrate, or it may be provided on the surface of the polyester substrate via another layer, but it is preferable to provide it directly on the surface of the polyester substrate in terms of superior adhesion.

[0022] The particle-containing layer is not particularly limited as long as it contains particles, but it is preferable that it contains a non-polyester resin other than polyester resin in addition to the particles. Furthermore, the particle-containing layer may also contain additives other than particles and non-polyester resin.

[0023] The particle-containing layer may be a crosslinked film formed using a crosslinking agent described later.

[0024] (particle) The average particle size of the particles contained in the particle-containing layer is not particularly limited, but is preferably 1 to 400 nm, more preferably 10 to 200 nm, and even more preferably 30 to 130 nm, in terms of having better transportability and suppressing transfer marks. Furthermore, in terms of superior transportability and suppression of transfer marks, it is preferable that the average particle diameter of the particles contained in the particle-containing layer is 10 to 200 nm (more preferably 30 to 130 nm), the thickness of the particle-containing layer is 1 to 200 nm (more preferably 10 to 100 nm), and the average particle diameter of the particles is greater than the thickness of the particle-containing layer.

[0025] The particles contained in the particle-containing layer may be one type alone, or two or more types of particles may be used. When the particle-containing layer contains two or more particles with different particle sizes, it is preferable that the particle-containing layer contains at least one particle whose average particle size is within the above range, and it is more preferable that all two or more particles with different particle sizes have an average particle size within the above range.

[0026] Examples of particles included in the particle-containing layer include organic particles and inorganic particles. Among these, inorganic particles are preferred from the viewpoint of further improving film winding quality, haze, and durability (e.g., thermal stability). As organic particles, resin particles are preferred. Examples of resins constituting the resin particles include acrylic resins such as polymethyl methacrylate (PMMA), polyester resins, silicone resins, and styrene-acrylic resins. The resin particles preferably have a crosslinked structure. Examples of resin particles having a crosslinked structure include divinylbenzene crosslinked particles. In this specification, "acrylic resin" means a resin containing constituent units derived from acrylate or methacrylate. 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). Among these, silica particles are preferred as the inorganic particles from the viewpoint of improving haze and durability.

[0027] The shape of the particles is not particularly limited and can be, for example, rice grain-shaped, spherical, cubic, spindle-shaped, flaky, aggregated, or irregular. Aggregated means a state in which primary particles are aggregated. The shape of the particles in the aggregated state is not limited, but spherical or irregular shapes are preferred.

[0028] As the aggregated particles, fumed silica particles are preferred. A commercially available example is the Aerosil series from Nippon Aerosil Co., Ltd. Colloidal silica particles are preferred as non-aggregated particles. Examples of commercially available products include the Snowtex series manufactured by Nissan Chemical Corporation.

[0029] From the viewpoint of transportability and coatability of the release layer, the particle content in the particle-containing layer is preferably 0.1 to 30% by mass, more preferably 1 to 25% by mass, and even more preferably 1 to 15% by mass, relative to the total mass of the particle-containing layer. Furthermore, the particle content is preferably 0.0001 to 0.01% by mass, and more preferably 0.0005 to 0.005% by mass, relative to the total mass of the polyester film.

[0030] (Non-polyester resin) The particle-containing layer preferably contains a non-polyester resin. The non-polyester resin can be used as a binder. The non-polyester resin included in the particle-containing layer is not particularly limited as long as it is a resin other than polyester resin, but examples include acrylic resin, urethane resin, olefin resin, polyvinyl alcohol resin, and acrylonitrile butadiene resin. From the viewpoint of superior effects of the present invention, acrylic resin, urethane resin, or olefin resin is preferred, and acrylic resin or olefin resin is more preferred. Here, the solubility parameters (SP values) of acrylic resins and olefin resins are far apart from those of polyester resins. In other words, the compatibility between acrylic resins and olefin resins and polyester resins is insufficient, making it difficult for impurities such as oligomers to precipitate from the polyester substrate. As a result, it is presumed that protrusions caused by impurities contained in the polyester substrate are less likely to form on the surface of the particle-containing layer. Furthermore, among urethane resins, highly hydrophobic urethane resins (i.e., urethane resins whose SP values ​​are sufficiently far apart from those of polyester resins) can also suppress the precipitation of impurities such as oligomers from the polyester substrate for the same reasons as with acrylic resins and olefin resins. The particle-containing layer is preferably formed by coating an aqueous dispersion. In this respect, an acid-modified resin is preferred as the non-polyester resin contained in the particle-containing layer. The acid-modified resin is preferably a copolymer of (meth)acrylate and (meth)acrylic acid, or an olefin resin having a carboxyl group, and more preferably an olefin resin having a carboxyl group.

[0031] Furthermore, as the non-polyester resin included in the particle-containing layer, acrylic resin, olefin resin, or urethane resin is preferred, more preferably acrylic resin or olefin resin, and even more preferably acrylic resin, because it is easy to adjust the surface free energy of the particle-containing layer to a specific range described later. The acrylic resin, olefin resin, and urethane resin are not particularly limited, and known resins can be used. The olefin resin can be any resin that contains constituent units derived from olefins in its main chain. Having an olefin structure in the main chain results in insufficient compatibility with polyester resins, which in turn improves the suppression of defects during long-term storage. The olefin is not particularly limited, but alkenes having 2 to 6 carbon atoms are preferred, ethylene, propylene, or hexene are more preferred, and ethylene is even more preferred. The constituent units derived from olefins in the olefin resin are preferably 50 to 99 mol%, and more preferably 60 to 98%, relative to the total constituent units of the olefin resin.

[0032] As the olefin resin, an acid-modified olefin resin is preferred because it can prevent static charge buildup when applying the release layer. Examples of acid-modified olefin resins include copolymers obtained by modifying the above-mentioned olefin resin with an acid-modifying component such as an unsaturated carboxylic acid or its anhydride. Examples of acid-modified components include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, and crotonic acid, as well as half-esters and half-amides of unsaturated dicarboxylic acids. From the viewpoint of resin dispersion stability, acrylic acid, methacrylic acid, maleic acid, or maleic anhydride are preferred.

[0033] Acidic groups in acid-modified olefin resins include carboxyl groups, sulfol groups, and phosphoric acid groups, which correspond to the acid-modifying components mentioned above, with carboxyl groups being preferred. The acidic groups may form acid anhydrides or be neutralized with at least one selected from alkali metals, organic amines, and ammonia. The acid-modified olefin resin may contain only one type of constituent unit having an acidic group, or it may contain two or more types.

[0034] Examples of commercially available acid-modified olefin resins include the Zaixen® series (manufactured by Sumitomo Seika Co., Ltd.), such as Zaixen AC, A, L, NC, N, etc.; the Chemipearl® series (manufactured by Mitsui Chemicals, Inc.), such as Chemipearl S100, S120, S200, S300, S650, SA100, etc.; and the Hi-Tec® series (manufactured by Mitsui Chemicals, Inc.), such as Hi-Tec S3121, S3148K, etc. Examples include the Arrowbase (registered trademark) series (manufactured by Unitika Ltd.), such as Arrowbase SE-1013, SE-1010, SB-1200, SD-1200, SD-1200, DA-1010, DB-4010, etc. (manufactured by Unitika Ltd.), Hardlen AP-2, NZ-1004, NZ-1005 (manufactured by Toyobo Co., Ltd.), Sepolion G315, VA407 (manufactured by Sumitomo Seika Co., Ltd.). Furthermore, the acid-modified olefin resin described in paragraphs

[0022] to

[0034] of Japanese Patent Publication No. 2014-076632 can also be preferably used.

[0035] Acrylic resin is a resin containing structural units derived from (meth)acrylate, and may be copolymerized with vinyl monomers such as styrene. The acrylic resin is not particularly limited, but it is preferable to contain structural units derived from (meth)acrylate having alkyl groups having 1 to 12 carbon atoms, and more preferable to contain structural units derived from (meth)acrylate having alkyl groups having 1 to 8 carbon atoms. In order to prevent static charge buildup when applying the release layer, the acrylic resin preferably contains an acid-modified component. The acrylic resin preferably contains constituent units derived from (meth)acrylic acid as the acid-modified component. The (meth)acrylic acid may form an acid anhydride or be neutralized with at least one selected from alkali metals, organic amines, and ammonia. When using an aqueous dispersion of acrylic resin in the production of a particle-containing layer, an aqueous dispersion containing acrylic resin and a dispersant is preferably used. The constituent units derived from (meth)acrylate in the acrylic resin are preferably present in an amount of 50 to 100 mol% relative to all constituent units of the acrylic resin. The acid value of the acrylic resin is preferably 30 mg KOH / g or less, and more preferably 20 mg KOH / g or less. The lower limit of the acid value is not particularly limited, for example, 0 mg KOH / g, but from the viewpoint of coating as an aqueous dispersion, 2 mg KOH / g or more is preferred. When an acrylic resin with a solubility parameter (SP value) far removed from that of a polyester resin is used, the compatibility between the acrylic resin and the polyester resin becomes insufficient, and as a result, defect suppression during long-term storage can be further improved. Such an acrylic resin can be obtained, for example, by adjusting it to satisfy at least one of the following: setting the acid value within the above range, and including constituent units derived from (meth)acrylate having an alkyl group having 1 to 12 carbon atoms. In particular, it is preferable that the acrylic resin is obtained by adjusting it to satisfy both of the following conditions: setting the acid value within the above range, and including constituent units derived from (meth)acrylate having an alkyl group having 1 to 12 carbon atoms.

[0036] The urethane resin is not limited as long as it is a polymer having urethane bonds, and known urethane resins such as reaction products of isocyanate compounds and polyol compounds can be used. When using an aqueous dispersion containing urethane resin in the production of a particle-containing layer, it is preferable that the aqueous dispersion contains a urethane resin having an acidic group (e.g., a carboxyl group), or contains a urethane resin and a dispersant. This improves the film-forming properties of the particle-containing layer. The desired SP value of the urethane resin can be achieved by adjusting, for example, at least one of the following: the structure of the raw material polyol compound, the hydrophobicity or hydrophilicity of the raw material polyol, the structure of the raw material isocyanate compound, and the hydrophobicity or hydrophilicity of the raw material isocyanate compound. By using a urethane resin adjusted to be hydrophobic in this way, the compatibility between the urethane resin and the polyester resin becomes insufficient, and as a result, defect suppression during long-term storage can be further improved. Among urethane resins, urethane resins having a polyester structure (polyester-based urethane resins) are preferred because they are hydrophobic and can further improve the suppression of defects during long-term storage. Examples of commercially available polyurethanes include Hydran® AP-20, AP-40N, and AP-201 (all manufactured by DIC Corporation), Takelac® W-605, W-5030, and W-5920 (all manufactured by Mitsui Chemicals, Inc.), Superflex® 210 and 130, and Elastron® H-3-DF, E-37, and H-15 (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

[0037] The particle-containing layer may contain one type of non-polyester resin, or it may contain two or more types of non-polyester resins. The non-polyester resin content is preferably 30 to 99.8% by mass, and more preferably 50 to 99.5% by mass, relative to the total mass of the particle-containing layer, in order to further suppress surface defects.

[0038] (Additives) The particle-containing layer may also contain additives other than the above-mentioned particles and non-polyester resin. Examples of additives included in the particle-containing layer include surfactant waxes, dispersants, antioxidants, UV absorbers, colorants, strengthening agents, plasticizers, antistatic agents, flame retardants, rust inhibitors, and mold inhibitors.

[0039] The particle-containing layer preferably contains a surfactant, as this improves the smoothness of the areas on the second main surface other than those where protrusions formed by the particles exist. By improving the smoothness of the above-mentioned areas on the second main surface and reducing the surface roughness of the second main surface due to factors other than particles, the maximum protrusion height Sp (described later) can be controlled to a desired range, thereby improving the effects of the present invention.

[0040] The surfactant is not particularly limited, and examples include silicone-based surfactants, fluorine-based surfactants, and hydrocarbon-based surfactants. From the viewpoint of suppressing electrostatic charge on the second main surface, hydrocarbon-based surfactants are preferred.

[0041] The silicone-based surfactant is not particularly limited as long as it is a surfactant having a silicon-containing group as a hydrophobic group, and examples include polydimethylsiloxane, polyether-modified polydimethylsiloxane, and polymethylalkylsiloxane. Examples of commercially available silicone-based surfactants include BYK(registered trademark)-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-347, BYK-348, and BYK-349 (all manufactured by BYK), as well as KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, and KF-6017 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0042] The fluorine-based surfactant is not particularly limited as long as it is a surfactant having a fluorine-containing group as a hydrophobic group, and examples include perfluorooctanesulfonic acid and perfluorocarboxylic acid. Examples of commercially available fluorine-based surfactants include Megafac® F-114, F-410, F-440, F-447, F-553, and F-556 (all manufactured by DIC Corporation), and Surflon® S-211, S-221, S-231, S-233, S-241, S-242, S-243, S-420, S-661, S-651, and S-386 (manufactured by AGC Seimi Chemical Co., Ltd.). Furthermore, as a fluorine-based surfactant, from the viewpoint of improving environmental suitability, surfactants derived from alternative materials of compounds having linear perfluoroalkyl groups with 7 or more carbon atoms, such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), are preferred.

[0043] Examples of hydrocarbon-based surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Examples of anionic surfactants include alkyl sulfates, alkylbenzene sulfons, alkyl phosphates, and fatty acid salts. Examples of nonionic surfactants include polyalkylene glycol mono- or dialkyl ethers, polyalkylene glycol mono- or dialkyl esters, and polyalkylene glycol monoalkyl esters / monoalkyl ethers. Examples of cationic surfactants include primary to tertiary alkylamine salts and quaternary ammonium compounds. Examples of amphoteric surfactants include surfactants that have both anionic and cationic sites within their molecule.

[0044] Examples of commercially available anionic surfactants include Rapizole® A-90, A-80, BW-30, B-90, and C-70 (all manufactured by NOF Corporation), Nikkol® OTP-100 (all manufactured by Nikko Chemical Co., Ltd.), Kohacool® ON, L-40, and Phosphanol® 702 (all manufactured by Toho Chemical Industry Co., Ltd.), and Viewlight® A-5000 and SSS (all manufactured by Sanyo Chemical Industries, Ltd.). Examples of commercially available nonionic surfactants include Naroacty® CL-95 and HN-100 (product name: manufactured by Sanyo Chemical Industries, Ltd.), Risolex BW400 (product name: manufactured by Kofu Alcohol Industry Co., Ltd.), EMALEX® ET-2020 (all manufactured by Nippon Emulsion Co., Ltd.), and Surfinol® 104E, 420, 440, 465, and Dynol® 604, 607 (all manufactured by Nisshin Chemical Industry Co., Ltd.).

[0045] When used in combination with an acid-modified resin, at least one of an anionic surfactant and a nonionic surfactant is preferred, and an anionic surfactant is more preferred, from the viewpoint of forming a coating layer with a smooth surface without inhibiting the dispersion of the resin. That is, as a surfactant, an anionic hydrocarbon surfactant is more preferred from the viewpoint of improving surface smoothness.

[0046] Anionic hydrocarbon surfactants are preferable to have multiple hydrophobic end groups in that they have improved smoothness. The hydrophobic end groups may be some of the hydrocarbon groups that the hydrocarbon surfactant has. For example, a hydrocarbon surfactant having a branched-chain hydrocarbon group at its end will have multiple hydrophobic end groups. Examples of anionic hydrocarbon surfactants having multiple hydrophobic end groups include sodium di-2-ethylhexyl sulfosuccinate (having four hydrophobic end groups), sodium di-2-ethyloctyl sulfosuccinate (having four hydrophobic end groups), and branched-chain alkylbenzene sulfonates (having two hydrophobic end groups).

[0047] One type of surfactant may be used, or two or more types may be used in combination. The surfactant content is preferably 0.1 to 10% by mass relative to the total mass of the particle-containing layer, more preferably 0.1 to 5% by mass, and even more preferably 0.5 to 2% by mass, for superior surface smoothness.

[0048] The wax is not particularly limited and may be either natural or synthetic. Examples of natural waxes include carnauba wax, candelilla wax, beeswax, montan wax, paraffin wax, and petroleum wax. In addition, the lubricants described in section

[0087] of International Publication No. 2017 / 169844 may also be used. The wax content is preferably 0 to 10% by mass relative to the total mass of the particle-containing layer.

[0049] (thickness) The particle-containing layer can be formed, for example, by coating a particle-containing composition onto one surface of a polyester substrate, and its thickness is often 1 μm or less. Alternatively, the particle-containing layer may be formed by co-extruding the polyester substrate and the resin used to form the particle-containing layer, in which case the thickness of the particle-containing layer is often 1 to 10 μm. From the viewpoint of suitability for manufacturing the particle-containing layer and haze reduction, the thickness of the particle-containing layer is preferably 1 to 500 nm, more preferably 1 to 250 nm, even more preferably 10 to 100 nm, and particularly preferably 20 to 100 nm. The thickness of the particle-containing layer is determined by preparing a section of the polyester film with a cross-section perpendicular to the main surface, and measuring the thickness at five points on the section using a scanning electron microscope (SEM) or transmission electron microscope (TEM). The arithmetic mean of these thicknesses is then used. If the particle-containing layer is soft and it is difficult to reliably prepare cross-sectional sections, a refractometer may be used for measurement. Specifically, the thickness of the particle-containing layer can be determined by fitting the measured reflectance spectrum to the film thickness and refractive index of the particle-containing layer and the polyester substrate.

[0050] The method for forming the particle-containing layer will be explained in detail in the "Particle-Containing Layer Formation Process" section below.

[0051] <Polyester base material> A polyester substrate is a film-like object that contains polyester resin as its main polymer component and is substantially free of particles. Here, "main polymer component" refers to the polymer that is present in the largest quantity (by mass) of all polymers contained in the film. "Substantially particle-free" is defined as a polyester substrate in which, when elements derived from particles are quantitatively analyzed by X-ray fluorescence analysis, the particle content is 50 ppm by mass or less relative to the total mass of the polyester substrate, preferably 10 ppm by mass or less, and more preferably below the detection limit. This is because even without actively adding particles to the polyester substrate, contaminants derived from foreign substances, raw resins, or dirt adhering to the lines or equipment in the manufacturing process of the polyester substrate may detach and become mixed into the polyester substrate. Examples of particles include those contained in the particle-containing layer described above. The polyester substrate may contain one type of polyester resin, or it may contain two or more types of polyester resins.

[0052] (Polyester resin) Polyester resins are polymers having ester bonds in their main chain. Polyester resins are usually formed by polycondensation of dicarboxylic acid compounds and diol compounds, as described later. The polyester resin is not particularly limited, and any known polyester resin can be used. Examples of polyester resins include polyethylene terephthalate (PET), polyethylene-2,6-naphthalate (PEN), and copolymers thereof, with PET being preferred.

[0053] The intrinsic viscosity of the polyester resin is preferably 0.50 dl / g or more and less than 0.80 dl / g, and more preferably 0.55 dl / g or more and less than 0.70 dl / g. The melting point (Tm) of the polyester resin is preferably 220 to 270°C, and more preferably 245 to 265°C. The glass transition temperature (Tg) of the polyester resin is preferably 65 to 90°C, and more preferably 70 to 85°C.

[0054] The method for producing polyester resin is not particularly limited, and known methods can be used. For example, polyester resin can be produced by polycondensation of at least one dicarboxylic acid compound and at least one diol compound in the presence of a catalyst.

[0055] -catalyst- The catalyst used in the production of polyester resin is not particularly limited, and any known catalyst usable for the synthesis of polyester resin 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. Among these, titanium compounds are preferred from the viewpoint of catalytic activity and cost. The catalyst may be used alone or in combination of two or more. It is 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, and more preferably to use a titanium compound and a phosphorus compound in combination.

[0056] As the titanium compound, organic chelate titanium complexes are preferred. Organic chelate titanium complexes are titanium compounds that have an organic acid as a ligand. Examples of organic acids include citric acid, lactic acid, trimellitic acid, and malic acid. As a titanium compound, the titanium compounds described in paragraphs

[0049] to

[0053] of Japanese Patent Publication No. 5575671 can also be used, and the contents of the above publication are incorporated herein by reference.

[0057] -Dicarboxylic acid compounds- Examples of dicarboxylic acid compounds include 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 methyl aromatic dicarboxylic acids are preferred.

[0058] Examples of aliphatic dicarboxylic acid compounds include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedionic acid, dimer acid, eicosanedionic acid, pimelic acid, azelaic acid, methylmalonic acid, and ethylmalonic acid. Examples of alicyclic dicarboxylic acid compounds include adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, and decalindicarboxylic acid.

[0059] 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-sodium sulfisoisophthalic acid, phenylindanedicarboxylic acid, anthracenedicarboxylic acid, phenantradicarboxylic acid, and 9,9'-bis(4-carboxyphenyl)fluorenic acid. Among these, terephthalic acid or 2,6-naphthalenedicarboxylic acid is preferred, and terephthalic acid is more preferred.

[0060] Dicarboxylic acid compounds may be used individually or in combination of two or more. When terephthalic acid is used as the dicarboxylic acid compound, it may be used alone or copolymerized with other aromatic dicarboxylic acids or aliphatic dicarboxylic acids such as isophthalic acid.

[0061] -Diol compounds- Examples of diol compounds include aliphatic diol compounds, alicyclic diol compounds, and aromatic diol compounds, with aliphatic diol compounds being preferred.

[0062] 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. Diol compounds may be used individually or in combination of two or more.

[0063] -End-capturing agent- In the manufacture of polyester resin, end encapsulants may be used as needed. By using end encapsulants, structures derived from the end encapsulant are introduced to the ends of the polyester resin. The end-captive agent is not limited, and known end-captive agents can be used. Examples of end-captive agents include oxazoline compounds, carbodiimide compounds, and epoxy compounds. As an end-capturing agent, see

[0055] ~ of Japanese Patent Publication No. 2014-189002.

[0064] You may also refer to the contents described in the above publication, and the contents of the above publication are incorporated herein by reference.

[0064] -Manufacturing conditions- The reaction temperature is not limited and can be set appropriately depending on the raw materials. A reaction temperature of 260-300°C is preferred, and 275-285°C is more preferred. The pressure is not limited and should be set appropriately according to the raw materials. The pressure is 1.33 × 10⁻⁶. -3 ~1.33 × 10 -5 MPa is preferred, 6.67 × 10 -4 ~6.67×10 -5 MPa is more preferable.

[0065] As a method for synthesizing polyester resin, the method described in paragraphs

[0033] to

[0070] of Japanese Patent Publication No. 5575671 can also be used, and the contents of the above publication are incorporated herein by reference.

[0066] The polyester substrate is preferably a biaxially oriented polyester substrate. "Biaxial orientation" refers to the property of having molecular orientation in two axial directions. Molecular orientation is measured using a microwave transmission molecular orientation meter (e.g., MOA-6004, manufactured by Oji 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°.

[0067] The polyester resin content 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 polymer in the polyester substrate. There is no upper limit to the polyester resin content, and it can be appropriately set within a range of 100% by mass or less relative to the total mass of the polymer in the polyester substrate.

[0068] When the polyester substrate contains polyethylene terephthalate, the polyethylene terephthalate content is preferably 90 to 100% by mass, more preferably 95 to 100% by mass, even more preferably 98 to 100% by mass, and particularly preferably 100% by mass, relative to the total mass of polyester resin in the polyester substrate.

[0069] The polyester substrate may contain components other than polyester resin (for example, catalysts, unreacted raw material components, particles, and water).

[0070] The thickness of the polyester substrate is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 40 μm or less, in order to control the peelability. There is no particular lower limit to the thickness, but in order to improve strength and processability, it is preferably 3 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. The thickness of the polyester substrate can be determined by subtracting the thickness of the particle-containing layer (measured by the method described above) and the thickness of the particle-free layer (measured by the method described below) from the thickness of the film (measured by the method described below).

[0071] <Particle-free layer> The particle-free layer is a layer that is substantially free of particles and is formed on the other side of the polyester substrate. The surface of the particle-free layer opposite to the side facing the polyester substrate constitutes the first main surface. "Substantially free of particles" is defined as a particle content of 50 ppm or less by mass relative to the total mass of the particle-free layer, when quantitatively analyzing elements derived from particles by X-ray fluorescence analysis, preferably 10 ppm or less by mass, and more preferably below the detection limit. Examples of particles in this case include the particles contained in the particle-containing layer described above.

[0072] The particle-free layer is not particularly limited as long as it contains a non-polyester resin other than polyester resin. The particle-free layer may also contain additives other than non-polyester resins.

[0073] The particle-free layer may be a crosslinked film formed using a crosslinking agent described later.

[0074] (Non-polyester resin) The non-polyester resin included in the particle-free layer is not particularly limited as long as it is a resin other than polyester resin, but examples include acrylic resin, urethane resin, olefin resin, polyvinyl alcohol resin, and acrylonitrile butadiene resin. From the viewpoint of superior effects of the present invention, acrylic resin, urethane resin, or olefin resin is preferred, and acrylic resin or olefin resin is more preferred. When acrylic resin or olefin resin is used, from the viewpoint of the SP value with the polyester resin mentioned above, protrusions caused by impurities contained in the polyester substrate are less likely to occur on the surface of the particle-free layer. Furthermore, even with highly hydrophobic urethane resins, the precipitation of impurities such as oligomers from the polyester substrate can be suppressed for the same reasons as with acrylic resin and olefin resin. The olefin resin, urethane resin, and acrylic resin may be the same as the olefin resin, urethane resin, and acrylic resin described as non-polyester resins included in the particle-containing layer described above, including their preferred embodiments.

[0075] The particle-free layer may contain additives in addition to the non-polyester resin. Examples of the additives include surfactants, waxes, antioxidants, ultraviolet absorbers, colorants, reinforcing agents, plasticizers, antistatic agents, flame retardants, rust preventives, and antifungal agents. Regarding the surfactant, it may be the same as the surfactant contained in the above particle-containing layer, including its preferred embodiments.

[0076] The thickness of the particle-free layer is often 1 μm or less, preferably 1 to 500 nm, more preferably 1 to 200 nm, still more preferably 10 to 100 nm, and particularly preferably 20 to 100 nm. The thickness of the particle-free layer can be measured in the same manner as the thickness of the particle-containing layer.

[0077] The particle-free layer is preferably provided on the surface of the polyester substrate by in-line coating. When providing the particle-free layer by in-line coating, it is preferably provided immediately before or after the particle-containing layer forming step described later, or simultaneously with the particle-containing layer forming step. Also, the polyester substrate and the resin used for forming the particle-free layer may be co-extruded to provide the particle-free layer on the surface of the polyester substrate.

[0078] This film may include layers other than the above particle-containing layer, polyester substrate, and particle-free layer, but preferably has a layer structure composed of the particle-containing layer, polyester substrate, and particle-free layer.

[0079] 〔Physical properties, etc.〕 Next, the physical properties, etc. of this film will be described.

[0080] (Surface free energy of the first main surface) The surface free energy of the first main surface of this film (that is, the surface on the opposite side of the polyester substrate from the particle-free layer) is preferably 25 to 65 mJ / m 2 more preferably 30 to 45 mJ / m 2 still more preferably 30 to 40 mJ / m 2 The surface free energy of the first main surface is 30 to 45 mJ / m 2Because it falls within this range, the SP value of the polyester resin is further separated, making it less likely for impurities such as oligomers to precipitate from the polyester substrate, thus resulting in superior effects of the present invention. The surface free energy of the first main surface can be adjusted, for example, by selecting the type of non-polyester resin and additives contained in the particle-free layer.

[0081] The surface free energy of the first principal surface of this film is determined according to the method described in the Examples section below.

[0082] (Surface free energy of the second principal surface) The surface free energy of the second main surface of this film (i.e., the surface opposite to the polyester substrate of the particle-containing layer) is 25-65 mJ / m². 2 Preferably, 30-45 mJ / m 2 More preferably, 35-45 mJ / m 2 This is even more preferable. The surface free energy of the second principal surface is 30-45 mJ / m². 2 By being within this range, it is possible to suppress oligomers generated from the polyester substrate from passing through the particle-containing layer and precipitating as particulate matter on the surface of the second main surface. As a result, when this film is wound into a roll for storage, it is possible to suppress particles adhering to the surface of the second main surface from adhering to the first main surface. The surface free energy of the second principal surface can be adjusted, for example, by selecting a non-polyester resin and additives. The surface free energy of the second principal surface of this film is determined according to the method described in the Examples section below.

[0083] (Maximum projection height Sp of the first principal surface, average surface roughness Sa, number of local projections) From the viewpoint of smoothing the release layer, it is preferable that the first main surface (i.e., the surface opposite to the polyester substrate of the particle-free layer) be as smooth as possible. Specifically, the maximum protrusion height Sp of the first main surface is preferably 1 to 60 nm, more preferably 1 to 50 nm, even more preferably 1 to 30 nm, and particularly preferably 1 to 20 nm. The average surface roughness Sa of the first main surface is preferably 0 to 10 nm, more preferably 0 to 5 nm, and even more preferably 0 to 2 nm.

[0084] The number of local protrusions on the first main surface is preferably 70 or less in terms of suppressing the occurrence of defects after long-term storage, preferably 40 or less, more preferably 20 or less, and even more preferably 10 or less in terms of smoothing the peeling layer. The lower limit of the number of local protrusions on the first main surface is preferably 0. Here, the number of local protrusions on the first main surface refers to the total number of protrusions with a height exceeding 50 nm, and is measured according to the method described in the Examples section below.

[0085] The maximum protrusion height Sp, average surface roughness Sa, and number of local protrusions on the first main surface can be adjusted by not introducing particles into the particle-free layer, selecting the type of non-polyester resin and additive (such as a surfactant) used to form the particle-free layer, and forming a smooth coating layer.

[0086] The maximum protrusion height Sp, average surface roughness Sa, and number of local protrusions of the first main surface of this film are measured according to the method described in the Examples section below.

[0087] Note that "a surface average roughness Sa of 0 nm" means that the surface average roughness Sa measured by the measurement method described later is below the measurement limit.

[0088] (Maximum protrusion height Sp of the second main surface, average surface roughness Sa, number of foreign particles) When a release layer is formed on the first main surface of this film to produce a release film, the second main surface of this film corresponds to the transport surface, which is the surface opposite to the release layer. While providing a protruding shape on the transport surface (second main surface) improves transportability, if the protrusions are too large, transfer marks may be formed on the release layer when the release film is stored in a roll. Therefore, it is preferable that the maximum protrusion height Sp of the second main surface be within a predetermined range from the viewpoint of suppressing transfer marks on the surface of the release layer and improving transportability. Specifically, the maximum protrusion height Sp of the second main surface is preferably 10 to 2300 nm, more preferably 10 to 2000 nm, even more preferably 10 to 1500 nm, particularly preferably 10 to 500 nm, and most preferably 20 to 60 nm.

[0089] The number of foreign objects on the second main surface is preferably 7 or less, more preferably 4 or less, even more preferably 2 or less, and particularly preferably 1 or less, in order to suppress the occurrence of defects after long-term storage. The lower limit for the number of foreign objects on the second main surface is preferably 0. Here, the number of foreign matter particles on the second main surface refers to the total number of foreign matter particles with a diameter of 1 μm or more, and is measured according to the method described in the Examples section below. Furthermore, "foreign matter" refers to granular material other than the aforementioned particles contained in the particle-containing layer, such as the oligomers mentioned above.

[0090] Furthermore, in terms of further suppressing transfer marks, the average surface roughness Sa of the second main surface is preferably 1 to 15 nm, more preferably 1 to 10 nm, and even more preferably 3 to 8 nm.

[0091] The maximum protrusion height Sp and average surface roughness Sa of the second main surface can be adjusted, for example, by selecting the average particle diameter and content of particles in the particle-containing layer, the thickness of the particle-containing layer, and the types of non-polyester resins and additives (such as surfactants) that may be included in the particle-containing layer. When forming the particle-containing layer by in-line coating, the above adjustments can be made more easily. The maximum protrusion height Sp and the average surface roughness Sa of the second main surface are measured according to the method described in the Examples section below.

[0092] (thickness) The thickness of this film is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 40 μm or less, in terms of superior peelability. There is no particular lower limit to the thickness, but in terms of superior handling performance, it is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more. The thickness of this film shall be the arithmetic mean of the thicknesses measured at five points using a continuous stylus-type film thickness gauge.

[0093] [Manufacturing method] A first embodiment of the method for manufacturing this film includes a biaxial stretching step of biaxially stretching an unstretched polyester substrate, a particle-containing layer formation step of forming a particle-containing layer containing particles, and a particle-free layer formation step of forming a particle-free layer substantially free of particles.

[0094] Biaxial stretching may be simultaneous biaxial stretching, where longitudinal stretching and transverse stretching are performed at the same time, or it may be sequential biaxial stretching, where 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.

[0095] This manufacturing method includes, for example, an extrusion molding step of extruding a molten resin containing a raw polyester resin into a film to form an unstretched polyester substrate; a biaxial stretching step consisting of a longitudinal stretching step of stretching the unstretched polyester substrate in the transport direction to form a uniaxially oriented polyester substrate and a transverse stretching step of stretching the uniaxially oriented polyester substrate in the width direction to form a biaxially oriented polyester substrate; a heat setting step of heating and heat-fixing the biaxially oriented polyester substrate; a heat relaxation step of heating the polyester substrate heat-fixed in the heat setting step at a lower temperature than the heat setting step to heat-relax it; a cooling step of cooling the polyester substrate heat-relaxed in the heat relaxation step; an expansion step of expanding the heat-relaxed polyester substrate in the width direction during the cooling step; a particle-containing layer formation step of providing a particle-containing layer on one side of the polyester substrate by an in-line coating method using a particle-containing layer-forming composition containing particles; and a particle-free layer formation step of providing a particle-free layer on the other side of the polyester substrate by an in-line coating method using a particle-free layer-forming composition that substantially does not contain particles.

[0096] <Extrusion molding process> The extrusion molding process is a process in which molten resin containing polyester resin as a raw material is extruded into a film using the extrusion molding method to form an unstretched polyester substrate. The polyester resin used as a raw material is the same as the polyester resin described in the (Polyester Resin) section above.

[0097] Extrusion molding is a method of molding raw material resin into a desired shape by, for example, using an extruder to push out a molten raw material resin. The molten material extruded from the extrusion die is formed into a film by cooling. For example, the molten material can be formed into a film by bringing it into contact with a casting roll and cooling and solidifying it on the casting roll. In cooling the molten material, it is preferable to further apply air (preferably cold air) to the molten material.

[0098] <Biaxial stretching process> The biaxial stretching process includes a longitudinal stretching step in which an unstretched polyester substrate is stretched in the transport direction (hereinafter also referred to as "longitudinal stretching") to form a uniaxially oriented polyester substrate, and a transverse stretching step in which the uniaxially oriented polyester substrate is stretched in the width direction (hereinafter also referred to as "transverse stretching") to form a biaxially oriented polyester substrate.

[0099] (Longitudinal stretching process) Longitudinal stretching can be performed, for example, by conveying an unstretched polyester substrate in the longitudinal direction while applying tension between two or more stretching rolls installed in the conveying direction. The stretching ratio in the longitudinal stretching process is set appropriately 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. The stretching speed in the longitudinal stretching process is preferably 800 to 1500% / second, more preferably 1000 to 1400% / second, and even more preferably 1200 to 1400% / second. Here, "stretching speed" is the value obtained by dividing the length Δd of the polyester substrate stretched in the transport direction per second in the longitudinal stretching process by the length d0 of the polyester substrate in the transport direction before stretching, expressed as a percentage. In the longitudinal stretching process, it is preferable to heat the unstretched polyester substrate. This is because heating facilitates longitudinal stretching.

[0100] (lateral stretching process) The transverse stretching process is a process of transversely stretching a uniaxially oriented polyester substrate. In the transverse stretching process, it is preferable to preheat the polyester substrate before transverse stretching. Preheating the polyester substrate allows for easier transverse stretching. The stretching ratio in the width direction (lateral stretching ratio) of the uniaxially oriented polyester substrate in the transverse stretching process is not particularly limited, but it is preferably greater than the stretching ratio in the longitudinal stretching process. The stretching ratio in the transverse stretching process 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. When the transverse stretching process is carried out in the stretching section of a stretching machine, the transverse stretching ratio is determined from the ratio (L1 / L0) of the polyester substrate width L1 at the time of discharge from the stretching section to the polyester substrate width L0 at the time of loading into the stretching section. The stretching speed in the transverse stretching process is preferably 8 to 45% / second, more preferably 10 to 30% / second, and even more preferably 15 to 20% / second.

[0101] <Heat setting process> In this manufacturing method, it is preferable to perform a heat setting step as a heat treatment for the polyester substrate that has been horizontally stretched in the horizontal stretching step. In the heat-setting process, the biaxially oriented polyester substrate obtained in the transverse stretching process can be heated and heat-set. By crystallizing the polyester resin through heat-setting, shrinkage of the polyester substrate can be suppressed. The surface temperature of the polyester substrate in the heat-setting process (heat-setting temperature) is not particularly limited, but is preferably less than 240°C, more preferably 235°C or less, and even more preferably 230°C or less. The lower limit is not particularly limited, but is preferably 190°C or higher, more preferably 200°C or higher, and even more preferably 210°C or higher. The heating time in the heat setting process is preferably 5 to 50 seconds, more preferably 5 to 30 seconds, and even more preferably 5 to 10 seconds.

[0102] <Thermal relaxation process> In the thermal relaxation process, it is preferable to thermally relax the polyester substrate, which has been thermally fixed in the thermal fixing process, by heating it at a lower temperature than that of the thermal fixing process. Thermal relaxation can alleviate residual strain in the polyester substrate. In the heat relaxation process, the surface temperature of the polyester substrate (heat relaxation temperature) is preferably 5°C or more lower than the heat fixing temperature, more preferably 15°C or more lower, even more preferably 25°C or more lower, and particularly preferably 30°C or more lower. That is, the heat relaxation temperature is preferably 235°C or lower, more preferably 225°C or lower, even more preferably 210°C or lower, and particularly preferably 200°C or lower. The lower limit of the thermal relaxation temperature is preferably 100°C or higher, more preferably 110°C or higher, and even more preferably 120°C or higher.

[0103] <Cooling process> This manufacturing method preferably includes a cooling step for cooling the heat-relaxed polyester substrate. The cooling rate of the polyester substrate in the cooling process is not particularly limited, but it is preferably more than 2000°C / min and less than 4000°C / min, more preferably between 2000 and 3500°C / min, even more preferably between 2200°C / min and less than 3000°C / min, and particularly preferably between 2300 and 2800°C / min, as this reduces thickness unevenness of the release layer laminated on the film and improves the applicability of the release layer.

[0104] <Expansion Process> In the above cooling process, it is also preferable to include a step of expanding the heat-relaxed polyester substrate in the width direction. The expansion rate in the width direction of the polyester substrate due to the expansion process, that is, the ratio of the polyester substrate width at the end of the cooling process to the polyester substrate width before the start of the cooling process, is preferably 0% or more, more preferably 0.001% or more, and even more preferably 0.01% or more. There is no particular upper limit to the expansion rate, but it is preferably 1.3% or less, more preferably 1.2% or less, and even more preferably 1.0% or less.

[0105] <Particle-containing layer formation process> The present manufacturing method preferably includes a particle-containing layer formation step in which a particle-containing layer formation composition containing particles (hereinafter also referred to as "Composition B") is used for in-line coating. The particle-containing layer formed on one surface of the polyester substrate by the particle-containing layer formation step is the same as the layer described in detail in the <Particle-containing layer> section above. The particle-containing layer may be formed at any stage of this manufacturing method. For example, a coating film may be formed on one surface of an unstretched or stretched polyester substrate, and then dried as necessary.

[0106] First, we will explain the method for forming a particle-containing layer using composition B. Composition B can be prepared by mixing particles contained in the particle-containing layer, non-polyester resins and additives added as needed, and a solvent. Examples of solvents include water and ethanol.

[0107] Composition B may contain one solvent or two or more solvents. The solvent content is preferably 80 to 99.5% by mass, and more preferably 90 to 99.0% by mass, based on the total mass of composition B. In other words, in composition B, the total content of components other than the solvent (solids) is preferably 0.5 to 20% by mass, and more preferably 1 to 10% by mass, relative to the total mass of composition B.

[0108] The particles, non-polyester resin, and additives contained in composition B, including their preferred embodiments, are as described in detail in the section on <particle-containing layer> above. With respect to each component other than the solvent in composition B, it is preferable to adjust the content of each component in the coating solution so that the content of each component relative to the total mass of solids in composition B is the same as the preferred content of each component relative to the total mass of the particle-containing layer described above.

[0109] Composition B may contain a crosslinking agent. There are no particular restrictions on the crosslinking agent; known agents can be used. Examples of crosslinking agents include melamine compounds, oxazoline compounds, epoxy compounds, isocyanate compounds, and carbodiimide compounds, with oxazoline compounds or carbodiimide compounds being preferred. Examples of commercially available products include Carbodilite V-02-L2 (manufactured by Nisshinbo Inc.) and Epocross K-2020E (manufactured by Nippon Shokubai Inc.). For details on epoxy compounds, isocyanate compounds, and melamine compounds, refer to sections

[0081] to

[0083] of Japanese Patent Application Publication No. 2015-163457. Crosslinking agents described in sections

[0082] to

[0084] of International Publication No. 2017 / 169844 can also be preferably used. For carbodiimide compounds, refer to sections

[0038] to

[0040] of Japanese Patent Application Publication No. 2017-087421. For oxazoline compounds, carbodiimide compounds, and isocyanate compounds, the crosslinking agents described in sections

[0074] to

[0075] of International Publication No. 2018 / 034294 can also be preferably used. The crosslinking agent content is preferably 0 to 50% by mass relative to the total mass of solids in composition B.

[0110] If composition B contains a non-polyester resin, it is preferable that composition B is a latex in which particles of the non-polyester resin are dispersed in water. In this case, the average particle size of the non-polyester resin particles is preferably 10 to 1000 nm, more preferably 20 to 500 nm, and even more preferably 50 to 200 nm. If the average particle size of the non-polyester resin particles is 50 nm or more, the number of local protrusions on the second main surface can be reduced, thus improving the effectiveness of the present invention. If the average particle size of the non-polyester resin is 200 nm or less, the coatability of composition B is excellent. The average particle size of non-polyester resin particles is the 50th percentile value (D50), which is calculated by determining the volume average from the particle size distribution measured using a laser diffraction / scattering particle size distribution analyzer ("LA-950", manufactured by Horiba, Ltd.).

[0111] The method of applying composition B is not particularly limited, and known methods can be used. Examples of application methods include spray coating, slit coating, roll coating, blade coating, spin coating, bar coating, and dip coating.

[0112] In the particle-containing layer formation process, it is preferable to apply an in-line coating method in which the coating solution is applied to one surface of the polyester substrate while the polyester substrate is being transported. By applying the in-line coating method, the heating time of the polyester substrate in the manufacturing process is shortened and no thermal history is applied, thus reducing the area of ​​streaky defects. In the in-line coating method, the polyester substrate to which composition B is applied may be an unstretched polyester substrate or a uniaxially oriented polyester substrate, but a uniaxially oriented polyester substrate is preferred. That is, it is preferable that the particle-containing layer formation step is a coating step performed between the longitudinal stretching step and the transverse stretching step. This is because the adhesion between the polyester substrate and the particle-containing layer can be improved by simultaneously transversely stretching the uniaxially oriented polyester substrate and the particle-containing layer.

[0113] <Particle-free layer formation process> This manufacturing method preferably includes a particle-free layer formation step in which a particle-free layer formation composition (hereinafter also referred to as "Composition A") substantially contains no particles is used for in-line coating. The particle-free layer formed on the other surface of the polyester substrate by the particle-free layer formation step is synonymous with the layer described in detail in the <Particle-Free Layer> section above. The particle-free layer may be formed at any stage of the manufacturing method, for example, by forming a coating film on the other surface of an unstretched or stretched polyester substrate and drying it as necessary. The particle-free layer formation step is the same as the particle-containing layer formation step described above, except that a particle-free layer is formed on the other surface of the polyester substrate using composition A.

[0114] Composition A can be prepared by mixing a non-polyester resin, additives as needed, and a solvent.

[0115] The solvent is as described in the section above, <Particle-containing layer formation process>, including preferred embodiments.

[0116] The non-polyester resin and additives contained in composition A, including their preferred embodiments, are as described in detail in the section on <particle-free layer> above. With respect to each component other than the solvent in composition A, it is preferable to adjust the content of each component in the coating solution so that the content of each component relative to the total mass of solids in composition A is the same as the preferred content of each component relative to the total mass of the particle-free layer described above.

[0117] Composition A may contain a crosslinking agent. The crosslinking agent contained in Composition A is the same as the crosslinking agent contained in Composition B, including preferred embodiments.

[0118] Composition A is preferably a latex in which non-polyester resin particles are dispersed in water. In this case, the preferred range for the average particle size of the non-polyester resin particles is the same as that for the non-polyester resin particles in Composition B described above.

[0119] This manufacturing method may include a winding step to obtain a roll-shaped biaxially oriented polyester substrate by winding up the biaxially oriented polyester substrate obtained through the above steps.

[0120] The conveying speed of the polyester substrate in each step of this manufacturing method other than the longitudinal stretching step is not particularly limited, but when performing the transverse stretching step, heat setting step, heat relaxation step, cooling step and expansion step, a speed of 50 to 200 m / min is preferred, and 80 to 150 m / min is more preferred, in terms of productivity and quality.

[0121] <Other embodiments of the method for manufacturing this film> A second embodiment of the method for manufacturing this film includes a step of forming a laminate X in which an unstretched polyester substrate and a particle-containing layer are laminated by co-extruding a molten resin containing a raw polyester resin for forming an unstretched polyester substrate and a particle-containing molten resin containing particles and a non-polyester resin for forming a particle-containing layer (laminate X formation step), and a particle-free layer formation step in which a particle-free layer substantially free of particles is formed by coating.

[0122] The raw materials, polyester resin, particles, and non-polyester resin, are as described in the first embodiment. The co-extrusion method in the laminate X formation process can be the same as the extrusion molding process in the first embodiment, except that a particle-containing molten resin is used together with the molten resin.

[0123] It is preferable to use the laminate X to carry out each of the processes described in the first embodiment, such as the biaxial stretching process, the heat setting process, the heat relaxation process, the cooling process, and the expansion process.

[0124] The particle-free layer formation step can be carried out in the same manner as the particle-free layer formation step in the first embodiment.

[0125] A third embodiment of the method for manufacturing this film includes a step (laminate Y formation step) in which a molten resin containing a raw polyester resin for forming an unstretched polyester substrate, a particle-containing molten resin containing particles and a non-polyester resin for forming a particle-containing layer, and a non-polyester molten resin containing a non-polyester resin for forming a particle-free layer are co-extruded to form a laminate Y in which the particle-free layer, the unstretched polyester substrate, and the particle-containing layer are laminated in this order.

[0126] The raw materials, polyester resin, particles, and non-polyester resin, are as described in the first embodiment. The co-extrusion method in the laminate Y formation process can be the same as the extrusion molding process in the second embodiment, except that a particle-containing molten resin and a non-polyester molten resin are used together with the molten resin.

[0127] It is preferable to use the laminate Y to carry out each of the processes described in the first embodiment, such as the biaxial stretching process, the heat setting process, the heat relaxation process, the cooling process, and the expansion process.

[0128] In the method for manufacturing this film, reference can be given to the contents of sections

[0113] to

[0169] of International Publication No. 2020 / 241692, and these contents are incorporated into the present specification.

[0129] In the film manufacturing method described above, a combination of two or more preferred embodiments is a more preferred embodiment.

[0130] [Release film] This film can be used in the manufacture of release films. More specifically, by providing a release layer on the first main surface of this film (the surface opposite to the polyester substrate of the particle-free layer), a release film can be manufactured having this film and a release layer disposed on the first main surface of this film.

[0131] The release layer contains at least a resin as a release agent. The resin contained in the release layer is not particularly limited and includes, for example, silicone resin, fluororesin, alkyd resin, acrylic resin, various waxes, and aliphatic olefins. From the viewpoint of release properties of the ceramic green sheet, silicone resin is preferred.

[0132] Silicone resin refers to a resin that has a silicone structure within its molecule. Examples of silicone resins include curable silicone resins, silicone graft resins, and modified silicone resins such as alkyl-modified resins, with reactive curable silicone resins being preferred. Examples of reactive curable silicone resins include addition reaction-type silicone resins, condensation reaction-type silicone resins, and ultraviolet or electron beam curable silicone resins. Among these, addition reaction-type silicone resins or ultraviolet or electron beam curable silicone resins are preferred because they have low-temperature curing properties, allowing for the formation of a release layer at low temperatures.

[0133] Examples of silicone resins used in addition reactions include resins obtained by reacting polydimethylsiloxane, which has vinyl groups introduced to its terminals or side chains, with hydrodienesiloxane using a platinum catalyst and then curing the reaction. Examples of silicone resins used in condensation reactions include resins having a three-dimensional crosslinked structure, formed by condensing polydimethylsiloxane having OH groups at its ends with polydimethylsiloxane having H groups at its ends using an organotin catalyst. Examples of UV-curable silicone resins include those that utilize the same radical reaction as silicone rubber crosslinking, those that are photocured by introducing unsaturated groups, those that decompose onium salts with ultraviolet light or electron beams to generate strong acids, which then cleave epoxy groups and cause crosslinking, and those that are crosslinked by the addition reaction of thiols to vinylsiloxane. More specifically, examples include acrylate-modified polydimethylsiloxane and glycidoxy-modified polydimethylsiloxane.

[0134] The release layer may contain additives other than the resin mentioned above. These additives may include light and heavy release additives for adjusting the release force, adhesion enhancers, curing agents (crosslinking agents), and antistatic agents. The resin contained in the release layer may be used alone or in combination of two or more types. The resin content in the release layer is preferably 50 to 99% by mass, and more preferably 60 to 98% by mass, relative to the total mass of the release layer. The remainder of the release layer other than the resin may consist of at least one of the above-mentioned additives and residues such as solvents and catalysts contained in the coating liquid used to form the release layer.

[0135] The thickness of the release layer can be set according to its intended use and is not particularly limited, but a thickness of 0.005 to 2.0 μm is preferred, and 0.05 to 1.0 μm is more preferred, as it provides a good balance between release performance and surface smoothness of the release layer.

[0136] (Surface free energy of the delamination surface) From the perspective of preventing static electricity when winding the release film, the surface free energy of the surface of the release layer opposite the particle-free layer (also called the release surface) is 30 mJ / m 2 The following are preferred: 1 to 30 mJ / m 2 More preferably, 10-30 mJ / m 2 That is even more preferable. The surface free energy of the delamination surface of the delamination layer can be adjusted by the type of resin and additives used to form the delamination layer.

[0137] (Maximum protrusion height Sp of the delamination surface, average surface roughness Sa, number of local protrusions) In order to smooth the functional layer, such as the ceramic green sheet, formed on the release layer, it is preferable that the release surface be as smooth as possible. Specifically, the maximum protrusion height Sp of the release surface is preferably 1 to 60 nm, more preferably 1 to 40 nm, and even more preferably 1 to 30 nm. Furthermore, the average surface roughness Sa of the peeled surface is preferably 0 to 10 nm, and more preferably 0 to 5 nm. Furthermore, the number of local protrusions on the peeled surface is preferably 70 or less, preferably 40 or less, more preferably 20 or less, and even more preferably 10 or less, in terms of improving the smoothness of the peeled surface. The lower limit of the number of local protrusions on the peeled surface is preferably 0. The maximum protrusion height Sp, average surface roughness Sa, and number of local protrusions on the release surface can be adjusted, for example, by not including particles in the release layer when forming it, and by selecting the resin and additives that form the release layer. Alternatively, the maximum protrusion height Sp, average surface roughness Sa, and number of local protrusions of the particle-free layer can also be adjusted within the aforementioned ranges. The maximum protrusion height Sp, average surface roughness Sa, and number of local protrusions on the peeled surface are measured according to the method described in the Examples section below.

[0138] The method for providing a release layer on the first main surface of the film is not particularly limited, but one method involves applying a coating solution for forming a release layer, which is obtained by dissolving or dispersing a release agent in a solvent, to the first main surface of the film, removing the solvent by drying, and forming a cured product by heating or irradiating with light as necessary. The release layer is preferably a cured product hardened by light (e.g., ultraviolet light) or heat.

[0139] The method of applying the coating solution for forming the release layer is not particularly limited, and known methods can be used. Examples of application methods include spray coating, slit coating, roll coating, blade coating, spin coating, bar coating, and dip coating. The heating temperature for forming the release layer is preferably 180°C or lower, more preferably 150°C or lower, and even more preferably 120°C or lower. The lower limit is not particularly limited and may be 60°C or higher.

[0140] The coating solution for forming the release layer contains the above-mentioned resin and solvent, and may optionally contain at least one of the above-mentioned additives and the above-mentioned catalyst used for curing the resin. The coating solution for forming the release layer can be prepared by mixing these components. Examples of solvents include water, as well as organic solvents such as toluene, methyl ethyl ketone, ethanol, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether, with organic solvents being preferred.

[0141] The coating solution for forming the release layer may contain one solvent or two or more solvents. The solvent content is preferably 80 to 99.5% by mass, and more preferably 90 to 99% by mass, relative to the total mass of the coating solution for forming the release layer. In other words, in the coating solution for forming the release layer, the total content of components other than the solvent (solids) is preferably 0.5 to 20% by mass, and more preferably 1 to 10% by mass, relative to the total mass of the coating solution for forming the release layer.

[0142] Furthermore, in order to improve the adhesion between the film and the release layer, pretreatment such as anchor coating, corona treatment, and plasma treatment may be applied to the first main surface of the film before the release layer is applied.

[0143] <Application> The release film having this film is preferably used as a release film (carrier film) for the manufacture of ceramic green sheets. The ceramic green sheets manufactured using the above release film can be suitably used in the manufacture of ceramic capacitors and multilayer inductors, where multilayering of internal electrodes is required due to miniaturization and increased capacitance. Furthermore, release films containing this film may be used as protective films for dry film resists, release films for process manufacturing, and the like.

[0144] The method for producing a ceramic green sheet using the above-mentioned release film is not particularly limited and can be carried out by known methods. For example, a method for producing a ceramic green sheet may involve applying a prepared ceramic slurry to the surface of the release layer of the release film and drying off the solvent contained in the ceramic slurry. The method for applying the ceramic slurry is not particularly limited. For example, known methods such as applying a ceramic slurry, which is prepared by dispersing ceramic powder and a binder agent in a solvent, using a reverse roll method and removing the solvent by heating and drying can be applied. The binder agent is not particularly limited, and an example is polyvinyl butyral. The solvent is also not particularly limited, and an example is ethanol and toluene. [Examples]

[0145] The present disclosure will be further explained with reference to the following examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples may be modified as appropriate, as long as they do not deviate from the spirit of the present disclosure. Therefore, the scope of the present disclosure is not limited to the following specific examples. Unless otherwise specified, "parts" and "%" are based on mass.

[0146] [Example 1] <Extrusion molding process> A titanium compound (titanium citrate chelate complex, VERTEC AC-420, manufactured by Johnson Matthey) described in Japanese Patent No. 5575671 was used as a polymerization catalyst to produce polyethylene terephthalate pellets. The obtained pellets were dried until the moisture content was 50 ppm or less, then placed into the hopper of a twin-screw compounding extruder described in Japanese Patent No. 6049648, and subsequently melted and extruded at 280°C. The molten material was passed through a filter (pore size 3 μm) and then extruded from the die into a cooling drum at 25°C to obtain an unstretched film made of polyethylene terephthalate. The extruded molten material was then brought into close contact with the cooling drum by electrostatic application. The melting point (Tm) of polyethylene terephthalate, which constitutes the unstretched film, was 258°C, and the glass transition temperature (Tg) was 80°C.

[0147] <Longitudinal stretching process> The above unstretched film was subjected to a longitudinal stretching process using the following method. A uniaxially oriented film was produced by stretching a preheated, unstretched film in the longitudinal direction (conveying direction) by passing it between two pairs of rolls with different peripheral speeds under the following conditions. (Longitudinal extension conditions) Preheating temperature: 75℃ Stretching temperature: 90℃ Stretching ratio: 3.4 times Stretching speed: 1300% / sec

[0148] <Coating layer formation process (particle-free layer formation process and particle-containing layer formation process)> Composition A-1 (composition for forming a particle-free layer) was applied to the cooling drum surface of a longitudinally stretched uniaxially oriented film (polyester substrate) during film formation using a bar coater, and composition B-1 (composition for forming a particle-containing layer) was applied to the opposite surface. The formed coated films were dried with hot air at 100°C to form a particle-containing layer on one surface of the polyester substrate and a particle-free layer on the other surface. At this time, the amount of composition A-1 and B-1 applied was adjusted so that the thickness of the formed particle-containing layer and particle-free layer was 60 nm, respectively.

[0149] (Composition A-1, B-1) Compositions A-1 and B-1 were prepared by mixing the components listed below. After filtration using a filter with a pore size of 6 μm (F20, manufactured by MAHLE FILES SYSTEMS, Inc.) and membrane degassing (2x6 radial flow superphobic, manufactured by POLIPORE, Inc.), the obtained compositions A-1 and B-1 were simultaneously coated on both sides of a uniaxially oriented film. (Composition A-1) • Acrylic resin (aqueous dispersion of a copolymer obtained by polymerizing methyl methacrylate, styrene, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, and acrylic acid in a mass ratio of 59:8:26:5:2, solid content concentration 25% by mass): 212 parts by mass • Anionic hydrocarbon surfactant (Rapizol® A-90, sodium di-2-ethylhexyl sulfosuccinate, manufactured by NOF Corporation, 1% solids by mass diluted with water): 12 parts by mass • Carbodiimide-based crosslinking agent (Carbodilite® V-02-L2, manufactured by Nisshinbo Industries Ltd., an aqueous crosslinking agent in which hydrophilic segments are imparted to polycarbodiimide resin, solid content concentration 40% by mass) 10 parts by mass ·Water: 766 parts by mass (Composition B-1) • Acid-modified olefin resin (Zyxen® NC, manufactured by Sumitomo Seika Co., Ltd., aqueous dispersion of olefin resin, solid content concentration 28% by mass): 140 parts by mass • Anionic hydrocarbon surfactant (Rapizol® A-90, sodium di-2-ethylhexyl sulfosuccinate, manufactured by NOF Corporation, 1% solids by mass diluted with water): 56 parts by mass • Particles (Snowtex® ZL, manufactured by Nissan Chemical Corporation, colloidal silica, 40% by mass aqueous dispersion): 11 parts by mass ·Wednesday: 793 copies

[0150] <Horizontal stretching process> A biaxially oriented film was prepared by stretching the film in the width direction using a tenter under the following conditions, after the longitudinal stretching process and the coating layer formation process had been performed. (lateral stretching conditions) Preheating temperature: 100℃ Stretching temperature: 120℃ Stretching ratio: 4.2x Stretching speed: 50% / sec

[0151] <Heat setting process> The biaxially oriented film subjected to the above transverse stretching process was then subjected to a heat setting process by heating it with a tenter under the following conditions to heat-set the film. (Heat fixation conditions) Heat fixing temperature: 227℃ Thermal setting time: 6 seconds

[0152] <Thermal relaxation process> Next, a thermal relaxation process was performed on the heat-fixed film by heating it under the following conditions to relieve tension in the film. In addition, during the thermal relaxation process, the distance between the gripping members of the tenter that grips both ends of the film (tenter width) was narrowed, thereby reducing the film width compared to the end of the thermal fixing process. The thermal relaxation rate Lr shown below was calculated using the formula Lr = (L1 - L2) / L1 × 100, where Lr is the film width at the end of the thermal relaxation process and L1 is the film width at the start of the thermal relaxation process. (Thermal relaxation conditions) Thermal relaxation temperature: 190℃ Thermal relaxation rate Lr: 4%

[0153] <Cooling process and expansion process> A cooling process was performed on the heat-relaxed film under the following conditions. In addition, an expansion process was carried out during the cooling process to widen the tenter width, thereby expanding the film width compared to the end of the heat relaxation process. The cooling rate shown below was calculated by dividing the temperature difference ΔT (°C) between the film surface temperature measured when the film was loaded into the cooling section of the stretcher and the film surface temperature measured when it was removed from the cooling section by the cooling time ta, with the cooling time ta being the time the film stayed in the cooling section from when it was loaded into the cooling section until it was removed from the cooling section. Furthermore, the expansion ratio ΔL shown below was calculated using the formula ΔL = (L3 - L2) / L2 × 100, where L3 is the film width of the polyester film at the end of the cooling process and L2 is the film width of the polyester film at the start of the cooling process. (Cooling conditions) Cooling rate: 2500℃ / min (Extended conditions) Expansion rate ΔL: 0.6%

[0154] <Winding process> After the film had been cooled in the cooling process, a trimming device was used to continuously cut the film along the transport direction at a position 20 cm from both ends in the width direction, thereby trimming both ends of the film. Next, an extrusion process (knurling) was performed on the area from both ends of the film up to 10 mm in the width direction, and then the film was wound up with a tension of 40 kg / m. Using the method described above, a biaxially oriented film (polyester film) was prepared in which a particle-free layer, a polyester substrate, and a particle-containing layer were laminated in that order. The obtained biaxially oriented film had a thickness of 31 μm, a width of 1.5 m, and a roll length of 7000 m. Furthermore, the thicknesses of the particle-free layer and particle-containing layer of the obtained biaxially oriented film were measured using a scanning electron microscope (S-4800, Hitachi High-Tech Corporation) after cross-sectioning with a microtome, etching with Ar ions, and Pt deposition. The thicknesses of the particle-free layer and particle-containing layer were found to be 60 nm, respectively.

[0155] [Measurement of physical properties of biaxially oriented films] The following physical properties were measured for the biaxially oriented film of Example 1.

[0156] <Maximum protrusion height Sp, average surface roughness Sa> The average surface roughness Sa and maximum protrusion height Sp of the particle-free layer side and the particle-containing layer side of the biaxially oriented film were measured by the following method. The surface of the manufactured biaxially oriented film was measured using an optical interferometer (Vertscan 3300G Lite, manufactured by Hitachi High-Tech Corporation) under the following conditions, and then analyzed using the built-in data analysis software (VS-Measure5). For measuring the average surface roughness Sa, the average value of measurements obtained from five measurements taken at different measurement positions was adopted. Similarly, for measuring the maximum protrusion height Sp (denoted as P in the built-in data analysis software), the average value of measurements obtained from five measurements taken at different measurement positions was adopted. (Measurement conditions) • Measurement mode: WAVE mode • Objective lens: 50x ·Measurement area: 186μm×155μm

[0157] <Number of localized processes> For the surface of the particle-free layer of the biaxially oriented film, the total number of protrusions with a height exceeding 50 nm was determined in the same manner as described above for maximum protrusion height Sp and average surface roughness Sa, except that 100 measurements were taken with different measurement positions.

[0158] <Number of foreign objects> The number of foreign particles on the surface of the particle-containing layer of the biaxially oriented film was measured using the following method. The surface of the particle-containing layer was observed using a scanning electron microscope (S-4800, Hitachi High-Tech Corporation) to obtain a 10,000x magnified image. The number of foreign particles with a diameter of 1 μm or larger present in a measurement area (field of view) of 13 μm × 10 μm was measured. This procedure was performed in a total of 40 fields of view with arbitrarily changed measurement positions to determine the total number of foreign particles with a diameter of 1 μm or larger. Here, a foreign object with a diameter of 1 μm or more means that the diameter of the circumscribed circle of the foreign object is 1 μm or more. Furthermore, the observed foreign substance was analyzed for elemental distribution using EDS (Energy Dispersive X-ray Spectroscopy) analysis with the same analytical instrument, and was identified as an oligomer (a low molecular weight by-product generated during the polymerization of polyester resin). In addition, the observed foreign substance was subjected to detailed compositional analysis using TOF-SIM (Time-of-Flight Secondary Ion Mass Spectrometry) to reconfirm that it was an oligomer.

[0159] <Surface free energy> The surface free energies of the particle-free layer and the particle-containing layer of the biaxially oriented film were measured using the following method. Using a contact angle meter (Kyowa Interface Chemical Co., Ltd., DROPMASTER-501), droplets were dropped onto the surface of either the particle-free layer or the particle-containing layer of a manufactured biaxially oriented film at 25°C, and the contact angle was measured 1 second after the droplet adhered to the 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. The "surface free energy" obtained by the above method is the sum of the polar component and the hydrogen bonding component of the surface free energy.

[0160] [Uneven surface defects (Evaluation 1)] <Preparation of ceramic slurry> A ceramic slurry was prepared by mixing 100 parts by mass of barium titanate powder (BaTiO3; manufactured by Sakai Chemical Industry Co., Ltd., product name "BT-03"), 8 parts by mass of polyvinyl butyral resin as a binder (manufactured by Sekisui Chemical Co., Ltd., product name "Eslec B·K BM-2"), and 4 parts by mass of dioctyl phthalate as a plasticizer (manufactured by Kanto Chemical Co., Ltd., dioctyl phthalate grade 1), with 135 parts by mass of a mixture of toluene and ethanol (mass ratio 6:4), in the presence of zirconia beads using a ball mill, dispersing the mixture, and then removing the beads. <Preparation and evaluation of samples for measuring surface defects> After leaving a roll of wound biaxially oriented film at room temperature and humidity for one week, a release layer (1 μm thick) was formed on the surface of the particle-free layer of the biaxially oriented film after the period of storage to obtain a release film. Here, the release layer was prepared according to the method for forming a release agent layer using the release layer forming material described in Example 1 of Japanese Patent Application Publication No. 2015-195291. The above ceramic slurry was applied to the surface of the release layer of the release film in a die coater over an area of ​​250 mm in width and 10 m in length, so that the film thickness after drying would be 1 μm. The film was then dried in a dryer at 80°C for 1 minute. For the laminated film of the ceramic green sheet and the release film, a fluorescent lamp was shone from the release film side, and all molded ceramic green sheet surfaces were visually inspected. The surface defects were evaluated according to the following criteria. A: No irregularities or defects were found in the ceramic green sheet. B: 1 to 5 irregularities were found in the ceramic green sheet. C: 6 to 30 irregularities were found in the ceramic green sheet. D: More than 31 irregularities were found in the ceramic green sheet.

[0161] [Uneven surface defects (evaluation 2)] Except for using a biaxially oriented film that had been left at room temperature and humidity for three months, a laminated film prepared in the same manner as for surface defects (Evaluation 1) was used, and the same evaluation as for surface defects (Evaluation 1) was performed.

[0162] [Measurement of physical properties of release film] Using the release film obtained in "Irregular Defects (Evaluation 1)" described above, the maximum protrusion height Sp, average surface roughness Sa, and number of local protrusions were measured on the release surface of the release film (the surface opposite to the particle-free layer side of the release layer) in the same manner as the physical property measurement of the biaxially oriented film described above.

[0163] [Examples 2-7] Compositions B-2 to B-7 were obtained by replacing some of the materials in composition B-1 with the following materials. Except for using one of compositions B-2 to B-7 instead of composition B-1, the above-mentioned physical property measurements and evaluation of each surface defect were performed in the same manner as in Example 1. (Composition B-2) The acid-modified olefin resin was replaced with the following acrylic resin. • Acrylic resin (an aqueous dispersion of a copolymer obtained by polymerizing methyl methacrylate, styrene, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, and acrylic acid in a mass ratio of 59:8:26:5:2, solid content concentration 25% by mass) (Composition B-3) The acid-modified olefin resin was replaced with the following urethane resin A. • Urethane resin A (Hydran® AP-40N, manufactured by DIC Corporation, polyester-based urethane aqueous dispersion, solid content concentration 35% by mass adjusted to 25% by mass with water) (Composition B-4) The acid-modified olefin resin was replaced with the following urethane resin B. • Urethane resin B (Superflex® 210, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., ester-based urethane aqueous dispersion, solid content concentration of 35% by mass adjusted to 25% by mass with water) (Composition B-5) The acid-modified olefin resin was replaced with the following urethane resin C. • Urethane resin C (ADEKA Bonditer® HUX-370, manufactured by ADEKA Corporation, urethane aqueous dispersion, solid content concentration 35% by mass adjusted to 25% by mass with water) (Composition B-6) The acid-modified olefin resin was replaced with the following PVA resin. • PVA resin (Kuraray Poval® PVA-117H, manufactured by Kuraray Co., Ltd., PVA aqueous solution, solid content concentration 25% by mass) (Composition B-7) The acid-modified olefin resin was replaced with the following NBR (acrylonitrile butadiene resin). • NBR resin (Nipol® LX-407C5, manufactured by Nippon Zeon Co., Ltd., acrylonitrile butadiene rubber aqueous dispersion, solid content concentration 40% by mass adjusted to 25% by mass with water)

[0164] [Examples 8-13] Compositions A-2 to A-7 were obtained by replacing some of the materials in composition A-1 with the following materials. Except for using one of compositions A-2 to A-7 instead of composition A-1, the above-mentioned physical property measurements and evaluation of each surface defect were performed in the same manner as in Example 1. (Composition A-2) The acrylic resin was replaced with the following acid-modified olefin resin. • Acid-modified olefin resin (Zyxen® NC, manufactured by Sumitomo Seika Co., Ltd., aqueous dispersion of olefin resin, solid content concentration of 28% by mass adjusted to 25% by mass with water) (Composition A-3) The acrylic resin was replaced with the above-mentioned urethane resin A. (Composition A-4) The acrylic resin was replaced with the above-mentioned urethane resin B. (Composition A-5) The acrylic resin was replaced with the above-mentioned urethane resin C. (Composition A-6) The acrylic resin was replaced with the PVA resin mentioned above. (Composition A-7) The acrylic resin was changed to the NBR resin mentioned above.

[0165] [Examples 14-16] Compositions B-8 to B-10 were prepared using composition B-1 as follows. Except for using one of compositions B-8 to B-10 instead of composition B-1, the above-mentioned physical property measurements and evaluation of each surface defect were performed in the same manner as in Example 1. (Composition B-8) NIPGEL® AZ-204 (manufactured by Tosoh Silica Co., Ltd.) was added in an amount equal to the solid content of Snowtex ZL. (Composition B-9) NIPGEL® AZ-204 (manufactured by Tosoh Silica Co., Ltd.) was added in an amount 10 times that of the solid content of Snowtex ZL. (Composition B-10) NIPGEL® AZ-204 (manufactured by Tosoh Silica Co., Ltd.) was added in an amount equivalent to 20 times the solid content of Snowtex ZL.

[0166] [Example 17] Except for adjusting the amount of composition B-9 applied so that the thickness of the formed particle-containing layer was 120 nm, the above-mentioned physical property measurements and evaluation of each surface defect were performed in the same manner as in Example 15.

[0167] [Example 18] Except for using composition A-8 instead of composition A-1, the above-mentioned physical property measurements and evaluation of each surface defect were performed in the same manner as in Example 1. (Composition A-8) • Acrylic resin (aqueous dispersion of a copolymer obtained by polymerizing methyl methacrylate, styrene, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, and acrylic acid in a mass ratio of 59:8:26:5:2, solid content concentration 25% by mass): 141 parts by mass • Urethane resin B (Superflex® 210, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., ester-based urethane aqueous dispersion, solid content concentration 35% by mass): 38 parts by mass • Anionic hydrocarbon surfactant (Rapizol® A-90, sodium di-2-ethylhexyl sulfosuccinate, manufactured by NOF Corporation, 1% solids by mass diluted with water): 12 parts by mass • Carbodiimide-based crosslinking agent (Carbodilite® V-02-L2, manufactured by Nisshinbo Industries Ltd., an aqueous crosslinking agent in which hydrophilic segments are imparted to polycarbodiimide resin, solid content concentration 40% by mass) 20 parts by mass • Benzyl alcohol: 4 parts by mass ·Water: 785 parts by mass

[0168] [Example 19] Except for using composition B-11 instead of composition B-1, the above-mentioned physical property measurements and evaluation of each surface defect were performed in the same manner as in Example 18. (Composition B-11) • Organic particles A (MP1000, manufactured by Soken Chemical Co., Ltd., non-crosslinked acrylic particles, solid content 100% by mass): 8 parts by mass • Organic particles B (Nipol® UFN1008, manufactured by Nippon Zeon Co., Ltd., polystyrene aqueous dispersion, solid content 20% by mass): 8 parts by mass • Acrylic resin (aqueous dispersion of a copolymer obtained by polymerizing methyl methacrylate, styrene, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, and acrylic acid in a mass ratio of 59:8:26:5:2, solid content concentration 25% by mass): 141 parts by mass • Urethane resin B (Superflex® 210, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., ester-based urethane aqueous dispersion, solid content concentration 35% by mass): 38 parts by mass • Anionic hydrocarbon surfactant (Rapizol® A-90, sodium di-2-ethylhexyl sulfosuccinate, manufactured by NOF Corporation, 1% solids by mass diluted with water): 12 parts by mass • Carbodiimide-based crosslinking agent (Carbodilite® V-02-L2, manufactured by Nisshinbo Industries Ltd., an aqueous crosslinking agent in which hydrophilic segments are imparted to polycarbodiimide resin, solid content concentration 40% by mass) 20 parts by mass • Benzyl alcohol: 4 parts by mass ·Water: 769 parts by mass

[0169] [Comparative Example 1] Except that a particle-free layer was not formed on the other surface of the polyester substrate, various physical property measurements and evaluations of each concavo-convex defect were performed in the same manner as in Example 1. The release layer was formed on the surface of the polyester substrate opposite to the particle-containing layer.

[0170] [Comparative Example 2] In Example 1, the acrylic resin contained in Composition A-1 was changed to the polyester aqueous dispersion Aw-1 described in International Publication No. 2017 / 199774 to obtain Composition C-1. Except that Composition C-1 was used instead of Composition A-1, various physical property measurements and evaluations of each concavo-convex defect were performed in the same manner as in Example 1.

[0171] [Table 1]

[0172] In Table 1, "Surface E" means "surface free energy".

[0173] As shown in Table 1, when the release films obtained by long-term storage of the polyester films (biaxially oriented polyester films) of Examples 1 to 17 according to the present invention were used in the production of ceramic green sheets, it was shown that the generation of concavo-convex defects could be suppressed as compared with Comparative Examples 1 and 2.

[0174] From the comparison of Examples 1 to 7, if the non-polyester resin contained in the particle-containing layer is at least one resin selected from the group consisting of an acrylic resin, a urethane resin, and an olefin resin, the concavo-convex defects of the ceramic green sheet can be more suppressed (Examples 1 to 5). From the comparison of Examples 3 to 5, if the surface free energy of the surface of the particle-containing layer opposite to the polyester substrate is 30 to 45 mJ / m 2 the concavo-convex defects of the ceramic green sheet can be more suppressed (Examples 3 and 4). A comparison of Examples 1, 8-13, 18, and 19 shows that if the non-polyester resin contained in the particle-free layer is at least one resin selected from the group consisting of acrylic resin, urethane resin, and olefin resin, the unevenness defects (Evaluation 1) of the ceramic green sheet can be further suppressed (Examples 1, 8-11, 18, and 19). From a comparison of Examples 9-11, the surface free energy of the surface opposite the polyester substrate of the particle-free layer is 30-45 mJ / m². 2 Therefore, the unevenness defects (evaluation 2) of the ceramic green sheet could be further suppressed (Examples 9 and 10). Comparing Example 1 with Examples 14-17, it was found that if the maximum protrusion height Sp on the surface opposite to the polyester substrate of the particle-containing layer was 10-1500 nm, the unevenness defects of the ceramic green sheet could be further suppressed (Examples 1, 14-16). When acrylic resin and urethane resin were used in combination to form the particle-free layer (Examples 18 and 19), the number of local protrusions in the release layer was zero (no local protrusions were observed), which was confirmed to be particularly good. [Explanation of symbols]

[0175] 1: Polyester film 12: Particle-containing layer 14: Polyester base material 16: Particle-free layer

Claims

1. A particle-containing layer containing particles, A polyester substrate that is substantially free of particles, It has, in this order, a particle-free layer that substantially does not contain particles, and A polyester film used to manufacture a release film by forming a release layer on the surface of the particle-free layer opposite to the polyester substrate, The particle-free layer contains a non-polyester resin other than a polyester resin, and the non-polyester resin contained in the particle-free layer is at least one resin selected from the group consisting of acrylic resin, urethane resin, and olefin resin. A polyester film in which the surface free energy of the particle-free layer on the surface opposite to the polyester substrate is 25 to 55 mJ / m².

2. The polyester film according to claim 1, wherein the release film is a release film for manufacturing ceramic green sheets.

3. The polyester film according to claim 1 or 2, wherein the particle-containing layer comprises a non-polyester resin other than a polyester resin.

4. The polyester film according to claim 3, wherein the non-polyester resin contained in the particle-containing layer is at least one resin selected from the group consisting of acrylic resin, urethane resin, and olefin resin.

5. The polyester film according to claim 1 or 2, wherein when measured using an optical interferometer at 100 different locations on the surface of the particle-free layer opposite to the polyester substrate, with a measurement area of ​​186 μm × 155 μm per location, the total number of protrusions with a height exceeding 50 nm is 40 or less.

6. The polyester film according to claim 1 or 2, wherein when a scanning electron microscope is used to measure 40 different locations on the surface of the particle-containing layer opposite to the polyester substrate, with a measurement area of ​​13 μm × 10 μm per location, the total number of foreign objects with a diameter of 1 μm or more is 2 or less.

7. The maximum protrusion height Sp on the surface of the particle-free layer opposite to the polyester substrate is 1 to 30 nm, and The polyester film according to claim 1 or 2, wherein the maximum protrusion height Sp on the surface of the particle-containing layer opposite to the polyester substrate is 10 to 1500 nm.

8. The polyester film according to claim 1 or 2, wherein the thickness of the particle-free layer and the thickness of the particle-containing layer are each 1 to 500 nm.

9. The surface free energy of the particle-containing layer on the surface opposite to the polyester substrate is 30 to 45 mJ / m ２ The polyester film according to claim 1 or 2.

10. The polyester film according to claim 1 or 2, wherein the thickness of the polyester film is 40 μm or less.

11. A release film comprising a polyester film according to claim 1 or 2, and a release layer disposed on the surface of the particle-free layer opposite to the polyester substrate.

12. The release film according to claim 11, wherein when measured using an optical interferometer at 100 different locations on the surface of the release layer opposite to the particle-free layer, with a measurement area of ​​186 μm × 155 μm per location, the total number of protrusions with a height exceeding 50 nm is 40 or less.

13. The maximum protrusion height Sp on the surface of the particle-containing layer opposite to the polyester substrate is 10 to 1500 nm, and The release film according to claim 11, wherein the maximum protrusion height Sp on the surface of the release layer opposite to the particle-free layer is 1 to 30 nm.

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