Polyester film, laminate film, and method for producing polyester film

Abstract

The present invention addresses the problem of providing: a polyester film capable of suppressing thickness unevenness of a functional layer provided on the surface; a laminate film having the polyester film; and a method for producing the polyester film. A polyester film according to the present invention has a maximum protrusion height Sp of 150 nm or less on both surfaces, has a thickness of not less than 10 µm to less than 30 µm, and has not more than 0.4 streaks / m2 in terms of the number of streaks observed through a polarizing plate.

Description

Polyester film, laminated film, method for manufacturing polyester film

[0001] This invention relates to polyester film, laminated film, and a method for manufacturing polyester film.

[0002] Biaxially oriented polyester films are used in a wide range of applications from the standpoint of processability, mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance. For example, in the field of multilayer ceramic capacitors, release films made by laminating a release layer on the surface of a biaxially oriented polyester film are used to produce ceramic sheets having a dielectric layer for the manufacture of multilayer ceramic capacitors.

[0003] For example, Patent Document 1 discloses a polyester film for manufacturing a release film, comprising a polyester substrate and a coating layer containing particles disposed on one surface of the polyester substrate, wherein the maximum protrusion height Sp and surface free energy of the surface on the coating layer side are within a predetermined range.

[0004] International Publication No. 2022 / 019113

[0005] In laminated films obtained by forming a functional layer on a polyester film, such as the release film for producing the ceramic sheets mentioned above, there is a need for a polyester film that is excellent in terms of the slipperiness of the laminated film and in suppressing transfer marks when the laminated film is stored in roll form or stacked. The present inventors, referring to the technology described in Patent Document 1, further investigated polyester films having a particle-containing layer and found that although transfer marks can be reduced by lowering the maximum protrusion height on both surfaces of the polyester film, there is room for improvement in the thickness unevenness of the functional layer laminated on the polyester film. In particular, it was found that when the thickness of the polyester film is reduced (for example, when the thickness is less than 30 μm), the thickness unevenness of the functional layer laminated on the polyester film may become larger due to the influence of the thickness unevenness of the polyester film itself when the polyester film is used as a carrier film.

[0006] In view of the above circumstances, the present invention aims to provide a polyester film that can suppress thickness unevenness of the functional layer provided on its surface. Furthermore, the present invention aims to provide a laminated film having a polyester film, and a method for manufacturing a polyester film that can suppress thickness unevenness of the functional layer provided on the surface of the polyester film.

[0007] As a result of diligent research into the above problems, the inventors have found that the above problems can be solved by the following configuration.

[0008] [1] The maximum protrusion height Sp on both surfaces is 150 nm or less, the thickness is 10 μm or more and less than 30 μm, and the number of streaks observed through a polarizing plate is 0.4 per m. ２ The following are polyester films: [2] The polyester film according to [1], wherein the maximum height St of both surfaces is less than 50 nm. [3] The polyester film according to [1] or [2], wherein the average surface roughness Sa of both surfaces is 5 nm or less. [4] The polyester film according to any one of [1] to [3], wherein the variation in the thickness of the polyester film is 7% or less of the average thickness of the polyester film. [5] The polyester film according to any one of [1] to [4], comprising a polyester substrate and a particle-containing layer. [6] The polyester film according to any one of [1] to [5], wherein the antimony content in the polyester film obtained by measurement by inductively coupled plasma mass spectrometry is 10 ppm by mass or less. [7] When the width of the polyester film is 100 cm or more, and the length of the polyester film is 1000 m or more, and the surface area from one end to the other end in the width direction of the polyester film is defined as the first surface area, and the surface area from the other end to the first end in the width direction of the polyester film is defined as the second surface area, the number of adhering foreign objects with a major axis of 50 μm or more in the first surface area and the second surface area is 1 per 500 m ２A polyester film according to any one of [1] to [6] below. [8] A laminated film having a polyester film according to any one of [1] to [7] and a release layer. [9] The laminated film according to [8], wherein the release layer is located on a surface in the polyester film where the maximum protrusion height Sp is smaller.

[10] A method for manufacturing a polyester film, comprising: an extrusion molding step of extruding a molten resin containing polyester into a film to form an unstretched polyester film having at least a polyester substrate; a longitudinal stretching step of stretching the unstretched polyester film to a range of 3.30 times or more and less than 3.40 times in the transport direction to form a uniaxially oriented polyester film; a preheating step of preheating the uniaxially oriented polyester film until the surface temperature is 90°C or more and less than 100°C; and a transverse stretching step of stretching the uniaxially oriented polyester film in the width direction to form a biaxially oriented polyester film.

[11] The method for manufacturing a polyester film according to

[10] , further comprising a step of forming a particle-containing layer using a composition containing particles between the longitudinal stretching step and the transverse stretching step, or a step of forming a particle-containing layer in the extrusion molding step by extruding a second molten body containing the particles and a binder simultaneously with the molten resin.

[12] The method for manufacturing a polyester film according to

[10] or

[11] , wherein in the transverse stretching step, both ends of the uniaxially oriented polyester film in the width direction are gripped with clips, the clips come into contact with a contact member and the clips are closed, thereby gripping the uniaxially oriented polyester film with the clips, and the contact member contains a resin with a melting temperature of 250°C or higher.

[0009] According to the present invention, it is possible to provide a polyester film that can suppress thickness unevenness of the functional layer provided on the surface. Furthermore, according to the present invention, it is possible to provide a laminated film having a polyester film, and a method for manufacturing a polyester film that can suppress thickness unevenness of the functional layer provided on the surface of the polyester film.

[0010] This is a schematic diagram showing an example of the configuration of a stretching device. This is a schematic diagram showing an example of the configuration of the clips provided in the stretching device. This is a schematic diagram showing an example of the configuration of the clips provided in the stretching device. This is a schematic cross-sectional view showing an example of the configuration of a polyester film according to an embodiment of the present invention. This is a schematic cross-sectional view showing the configuration of an observation device having a polarizing plate. This is a schematic diagram showing an example of an observation image obtained by observing a polyester film through a polarizing plate.

[0011] 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.

[0012] In this specification, a numerical range expressed using "~" 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 value shown in the example. In this specification, the amount of each component in a composition means the total amount of multiple substances present in the composition if there are multiple substances corresponding to each component in the composition, unless otherwise specified. In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In this specification, "mass%" and "weight%" are synonymous, and "parts by mass" and "parts by weight" are synonymous. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment.

[0013] In this specification, the term "polyester film" encompasses both the polyester substrate alone and laminates of the polyester substrate and particle-containing layer. In this specification, "longitudinal direction" means the longitudinal direction of the polyester film during its manufacture and is synonymous with "conveying direction," "MD," and "machine direction." In this specification, "width direction" and "TD" mean the direction perpendicular to the longitudinal direction. In this specification, "orthogonal" is not limited to strictly orthogonal but includes approximately orthogonal. "Approximately orthogonal" means intersecting at 90° ± 5°, preferably at 90° ± 3°, and more preferably at 90° ± 1°. In this specification, "film width" means the distance between the two ends of the polyester film in the width direction. In this specification, "end" means the region including one end of the film in the width direction and its vicinity.

[0014] In this specification, "(meth)acrylic" is a general term for acrylic and methacrylic, and means "one or more of acrylic and methacrylic." Similarly, "(meth)acrylate" means "one or more of acrylate and methacrylate," and "(meth)acrylic acid" means "one or more of acrylic acid and methacrylic acid." In this specification, unless otherwise specified, refractive index means the refractive index for light with a wavelength of 550 nm, measured using an Abbe refractometer (NAR-2T, manufactured by Atago Co., Ltd.). In this specification, unless otherwise specified, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are determined by gel permeation chromatography (GPC) analysis using columns of TSKgel GMHxL, TSKgel G4000HxL, TSKgel G2000HxL, and / or TSKgel Super HZM-N (all trade names of Tosoh Corporation), using THF (tetrahydrofuran) as the solvent, detection by differential refractometer, and conversion using polystyrene as the standard substance.

[0015] [First Embodiment: Polyester Film] The polyester film according to the first embodiment of the present invention (hereinafter also referred to as "this film") has a maximum protrusion height Sp of 150 nm or less on both surfaces, a thickness of 10 μm or more and less than 30 μm, and the number of streaks (linear streaks with clear differences in color intensity) observed through a polarizing plate is 0.4 streaks / m ２ The following is a polyester film.

[0016] As a result of their investigations, the inventors of the present invention found that when a polyester film is observed through a polarizing plate, linear streaks with clear differences in color intensity (hereinafter also referred to as "streaks" or "linear streaks") can sometimes be detected, and that by using a polyester film in which such streaks are hardly detectable even when observed through a polarizing plate as a carrier film, thickness unevenness of the functional layer (slurry layer, release layer, etc.) laminated on the polyester film can be suppressed even with a thin polyester film (e.g., less than 30 μm). Furthermore, as a result of their investigations, the inventors of the present invention found that by not over-stretching in the longitudinal stretching process in the manufacturing of biaxially oriented polyester film, setting the stretching ratio within a predetermined range, and setting the preheating temperature in the preheating process for preheating the uniaxially oriented polyester film obtained in the longitudinal stretching process within a predetermined range, the number of streaks detected when observing the polyester film through a polarizing plate can be reduced, thus completing the present invention. Hereinafter, the effect of suppressing thickness unevenness of the functional layer provided on the surface of the polyester film will also be referred to as "the effect of the present invention."

[0017] The structure of this film will be described in detail below.

[0018] The film may consist only of a polyester substrate, or it may consist of a polyester substrate and a particle-containing layer containing particles. If the film has a particle-containing layer, one particle-containing layer may be arranged on one side of the polyester substrate, or two particle-containing layers may be arranged on both surfaces of the polyester substrate. In particular, it is preferable that one particle-containing layer is arranged on one side of the polyester substrate. The film may also have layers other than the polyester substrate and the particle-containing layer. Examples of other layers include an adhesion layer, an antistatic layer, and an oligomer precipitation prevention layer. An intermediate layer, such as a primer layer, may be provided between the polyester substrate and the particle-containing layer. The thickness of these other layers is preferably 1 nm to 1 μm, and more preferably 30 to 500 nm. The film may also be in the form of a roll wound into a roll.

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

[0020] <Polyester Substrate> A polyester substrate is a film-like object containing polyester as its main polymer component. Here, "main polymer component" refers to the polymer that has the highest content (mass) among all polymers contained in the film. A polyester substrate may contain one type of polyester or two or more types of polyester.

[0021] As the polyester substrate, a biaxially oriented polyester substrate is preferred. "Biaxial orientation" means the property of having molecular orientation in two axial directions. Molecular orientation is measured using a microwave transmission type molecular orientation meter (for example, 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°. Molecular orientation changes by stretching, and a biaxially oriented polyester substrate can be manufactured by biaxial stretching. A preferred embodiment of the polyester substrate is the polyester substrate described in

[0021] to

[0039] of International Publication No. 2022 / 019113, and the above content is incorporated into this specification.

[0022] (Polyester) Polyester is a polymer having ester bonds in its main chain. Polyester is usually formed by polycondensation of a dicarboxylic acid compound and a diol compound, as described later. There are no particular limitations on the polyester, and known polyesters can be used. Examples of polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalate (PEN), polypropylene terephthalate (PPT), polybutylene terephthalate (PBT), and copolymers thereof. Among these, PET, PEN, or copolymers thereof are preferred, and PET is more preferred.

[0023] The intrinsic viscosity (IV) of this film is preferably 0.50 dl / g or more and less than 0.80 dl / g, more preferably 0.55 dl / g or more and 0.70 dl / g or less, and even more preferably 0.60 dl / g or more and less than 0.70 dl / g. The amount of terminal carboxyl groups (terminal COOH amount, AV; Acid Value) of this film is preferably 3.5 eq / ton or less, more preferably 3.0 eq / ton or less, and even more preferably 2.8 eq / ton or less. The lower limit is, for example, 0.52.8 eq / ton or more. In this specification, "eq / ton" represents the molar equivalent per ton. Details of the method for measuring the intrinsic viscosity and terminal COOH amount of this film are described in the Examples section below. The melting point (Tm) of polyester is preferably 220 to 270°C, and more preferably 245 to 265°C. The glass transition temperature (Tg) of polyester is preferably 65 to 90°C, and more preferably 70 to 85°C.

[0024] The method for producing polyester is not particularly limited, and known methods can be used. For example, polyester can be produced by polycondensation of at least one dicarboxylic acid compound and at least one diol compound in the presence of a catalyst. The catalyst used for producing polyester is not particularly limited, and known catalysts usable for the synthesis of polyester can be used.

[0025] 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 or aluminum compounds are preferred because they are less likely to generate foreign matter in the polyester substrate. Only one type of catalyst may be used, or two or more types may be used in combination. 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 it is more preferable to use a titanium compound and a phosphorus compound in combination. When using multiple catalysts, it is preferable to adopt the types and contents of each compound described in paragraphs 0055 to 0062 of Japanese Patent No. 5575671. In this film, when the titanium compound content is 5 to 15 ppm by mass in terms of Ti element, the magnesium compound content is preferably 60 to 90 ppm by mass in terms of Mg element, and the phosphorus compound content is preferably 5 to 35 ppm by mass in terms of P element.

[0026] As the titanium compound, an organic chelate titanium complex is preferred. An organic chelate titanium complex is a titanium compound having an organic acid as a ligand. Examples of organic acids include citric acid, lactic acid, trimellitic acid, and malic acid. As the titanium compound, the titanium compounds described in paragraphs 0049 to 0053 of Japanese Patent No. 5575671 can also be used, and the contents of the above publication are incorporated herein by reference. Specifically, the titanium compound content is preferably 1 to 300 ppm by mass, more preferably 3 to 20 ppm by mass, and even more preferably 5 to 15 ppm by mass, based on the total mass of the film in terms of Ti element. The content of each element contained in the polyester film can be measured by inductively coupled plasma mass spectrometry (ICP-MS). More specific measurement methods are described in the examples below.

[0027] 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 aromatic dicarboxylic acid methyl are preferred. 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, and 1,8-naphthalenedicarboxylic acid. Dicarboxylic acid compounds may be used individually or in combination of two or more.

[0028] Examples of diol compounds include aliphatic diol compounds, alicyclic diol compounds, and aromatic diol compounds, with aliphatic diol compounds being preferred. 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. Diol compounds may be used individually or in combination of two or more.

[0029] In the manufacture of polyester, end encapsulants may be used as needed. By using an end encapsulant, a structure derived from the end encapsulant is introduced to the end of the polyester. For information on end encapsulants, refer to the contents described in paragraphs

[0055] to

[0064] of Japanese Patent Application Publication No. 2014-189002, which are incorporated herein by reference.

[0030] As a method for synthesizing polyester, the method described in

[0033] to

[0070] of Japanese Patent Publication No. 5575671 can also be used, and the above content is incorporated herein.

[0031] The polyester 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. The upper limit of the polyester content is not limited and can be appropriately set within a range of 100% by mass or less, based on the total mass of the polymer in the polyester substrate.

[0032] When the polyester base material contains PET, the PET 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 in the polyester base material.

[0033] When the polyester base material contains a polyester formed from ethylene glycol and dicarboxylic acid, the polyester content is preferably 80% by mass or more, more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass, based on the total mass of the polyester base material. When the polyester base material contains PET, the PET content is preferably 90 to 100% by mass, more preferably 95 to 100% by mass, even more preferably 98 to 100% by mass, and especially preferably 100% by mass, based on the total mass of the polyester base material.

[0034] The polyester substrate may contain components other than polyester (for example, catalysts, unreacted raw material components, particles, and water). It is preferable that the polyester substrate is substantially free of particles. Examples of particles include those contained in the particle-containing layer described later. "Substantially free of particles" is defined as the particle content being 50 ppm by mass or less relative to the total mass of the polyester substrate when elements derived from particles are quantitatively analyzed by fluorescent X-ray analysis, 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 material resins, or dirt attached to the lines or equipment in the manufacturing process of the polyester substrate may detach and mix into the polyester substrate. Furthermore, it is preferable that the polyester substrate is substantially free of inorganic particles. Examples of inorganic particles include those contained in the particle-containing layer described later.

[0035] When the polyester base material has only the polyester film, the thickness of the polyester base material is 10 μm or more and less than 30 μm. When the polyester film consists of a polyester base material and a particle-containing layer, a polyester base material with a thickness such that the total thickness of the polyester base material and the particle-containing layer is in the range of 10 μm or more and less than 30 μm is used. The thickness of the polyester base material is the arithmetic mean value of the thicknesses of five locations of the polyester base material in the above-mentioned section prepared by making a section having a cross-section perpendicular to the main surface of the polyester film and measured using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0036] <Particle-containing layer> The particle-containing layer is a layer containing particles and is preferably formed on the surface of the polyester base material. By having the particle-containing layer, the transportability of the polyester film and the peeling film described later can be improved. More specifically, the winding quality can be improved (blocking can be suppressed), the occurrence of scratches and defects during transport can be suppressed, and the transport wrinkles in high-speed transport can be reduced.

[0037] The particle-containing layer may be provided directly on the surface of the polyester base material or may be provided on the surface of the polyester base material via another layer. However, in terms of better adhesion, it is preferably provided directly on the surface of the polyester base material. The particle-containing layer is not particularly limited as long as it contains particles and the maximum protrusion height Sp on the surface of the polyester film, the thickness of the polyester film, and the number of streaks satisfy a predetermined range, but it is preferably to contain a binder in addition to the particles. Further, the particle-containing layer may contain additives other than the particles and the binder.

[0038] In terms of improving the winding quality and suppressing transfer failure, the particle-containing layer preferably contains particles with an average particle diameter of 1 nm or more and less than 1 μm. The average particle diameter of the particles is preferably 10 nm or more, more preferably 30 nm or more, in terms of further improving the winding quality. Also, in terms of further suppressing transfer failure, it is preferably 0.4 μm or less, more preferably 0.25 μm or less.

[0039] As the particles contained in the particle-containing layer, one kind alone may be used, or two or more kinds of particles may be used. When the particle-containing layer contains two or more kinds of particles having different particle diameters, the particle-containing layer preferably contains at least one kind of particle having an average particle diameter within the above range, and it is more preferable that all of the two or more kinds of particles having different particle diameters are particles having an average particle diameter within the above range.

[0040] As the particles contained in the particle-containing layer, for example, organic particles and inorganic particles can be mentioned. As the organic particles, resin particles are preferable. Examples of the resin constituting the resin particles include acrylic resins such as polymethyl methacrylate resin (PMMA), polyester resins, silicone resins, and styrene-acrylic resins. The resin particles preferably have a crosslinked structure. Examples of the resin particles having a crosslinked structure include divinylbenzene crosslinked particles. As the inorganic particles, for example, silica particles (silicon dioxide particles, colloidal silica), titania particles (titanium oxide particles), calcium carbonate, barium sulfate, and alumina particles (aluminum oxide particles) can be mentioned.

[0041] The content of the particles in the particle-containing layer is preferably 0.1 to 30% by mass, more preferably 1 to 25% by mass, and still more preferably 1 to 15% by mass with respect to the total mass of the particle-containing layer in terms of better transportability.

[0042] The particle-containing layer preferably contains a binder. Examples of the binder include polyester and non-polyester resins. The polyester includes the polyester contained in the above-mentioned polyester base material. The non-polyester resin is not particularly limited as long as it is a resin other than polyester, and examples thereof include acrylic resins, polyurethanes, polyolefins, polyvinyl alcohol, and polyacrylonitrile butadiene, and acrylic, polyurethane, or polyolefin is preferable. Further, the non-polyester resin may be an acid-modified resin.

[0043] The acrylic resin is a resin containing structural units derived from (meth)acrylate, and may also contain structural units derived from vinyl monomers such as styrene. The acrylic resin preferably contains structural units derived from (meth)acrylate having an alkyl group having 1 to 12 carbon atoms, and more preferably contains structural units derived from (meth)acrylate having an alkyl group having 1 to 8 carbon atoms. In terms of suppressing the precipitation of impurities such as oligomers contained in the polyester substrate, 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 when applied as an aqueous dispersion, 2 mg KOH / g or more is preferred.

[0044] The polyurethane is not limited as long as it is a polymer having urethane bonds in its main chain, and known polyurethanes such as reaction products of polyisocyanate compounds and polyol compounds can be used. The solvent resistance of the particle-containing layer can be improved by adjusting the crosslinking reaction with the organic crosslinking agent, for example, by adjusting the structure and flexibility of the polyol compound and polyisocyanate compound used as raw materials. It is preferable that the polyurethane contains a polyester structure in order to have superior solvent resistance of the particle-containing layer. Examples of commercially available acid group-containing 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.).

[0045] The polyolefin can be any resin that contains olefin-derived structural units in its main chain. 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 amount of olefin-derived structural units in the polyolefin is preferably 50 to 99 mol%, and more preferably 60 to 98 mol%, relative to the total structural units of the polyolefin.

[0046] Examples of acid-containing polyolefins include copolymers obtained by modifying the above-mentioned polyolefin with an acid-modifying component such as an unsaturated carboxylic acid or its anhydride. Examples of commercially available acid group-containing polyolefins include the Zaixen® series such as Zaixen AC, A, L, NC, and N (manufactured by Sumitomo Seika Co., Ltd.), the Chemipearl® series such as Chemipearl S100, S120, S200, S300, S650, and SA100 (manufactured by Mitsui Chemicals, Inc.), the Hi-Tec® series such as Hi-Tec S3121 and S3148K (manufactured by Toho Chemical Co., Ltd.), the Arrowbase® series such as Arrowbase SE-1013, SE-1010, SB-1200, SD-1200, SD-1200, DA-1010, and DB-4010 (manufactured by Unitika Ltd.), Hardlen AP-2, NZ-1004, and NZ-1005 (manufactured by Toyobo Co., Ltd.), and Sepolion G315 and VA407 (manufactured by Sumitomo Seika Co., Ltd.). Furthermore, acid-modified polyolefins described in paragraphs

[0022] to

[0034] of Japanese Patent Application Publication No. 2014-076632 can also be preferably used, and this information is incorporated herein.

[0047] The binder contained in the particle-containing layer may have a cross-linked structure. In other words, the particle-containing layer may be a cross-linked film. From the viewpoint of adjusting the maximum protrusion height Sp to a desired range, the binder content in the particle-containing layer 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.

[0048] (Additives) The particle-containing layer may contain additives other than the particles and binders mentioned above. Examples of additives contained in the particle-containing layer include surfactants, waxes, antioxidants, ultraviolet absorbers, colorants, strengthening agents, plasticizers, antistatic agents, flame retardants, rust inhibitors, surfactants, and fungicides.

[0049] The thickness of the particle-containing layer is preferably 1 nm to 15 μm. When the particle-containing layer is formed by coating, the thickness of the particle-containing layer is preferably 1 to 500 nm, more preferably 1 to 200 nm, and even more preferably 5 to 100 nm. When the particle-containing layer is formed by extrusion, the thickness of the particle-containing layer is often greater than 500 nm, preferably 1 to 15 μm, and more preferably 1 to 10 μm. The thickness of the particle-containing layer is determined by preparing a section having a cross-section along the thickness direction of the polyester film and measuring the thickness at five points on the section using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and taking the arithmetic mean of the thicknesses of the above section.

[0050] The method for forming the particle-containing layer will be explained in detail in the [Particle-containing layer formation process] of the second embodiment described later.

[0051] The film may include layers other than the polyester substrate and particle-containing layer described above, but it is preferable that it consists of a polyester substrate and a particle-containing layer.

[0052] (Antimony Content) The antimony (Sb) content in the polyester film is preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less, and even more preferably 1 ppm by mass or less, relative to the total mass of the polyester film, in order to further suppress the generation of foreign matter. The lower limit of the antimony content is not particularly limited and may be 0 ppm by mass relative to the total mass of the polyester film. When manufacturing the polyester film, the antimony content in the polyester film can be reduced by not using compounds containing antimony as raw material polyester, its precursor, catalyst, solvent and additive, as well as in the manufacturing apparatus. For methods of reducing the antimony content, refer to the contents described in

[0023] to

[0046] of International Publication No. 2023 / 149181, which are incorporated herein by reference.

[0053] (Adhered Foreign Matter) This film is a polyester film with a width of 100 cm or more and a length of 1000 m or more. When the surface area from one end to the other end in the width direction of the polyester film is defined as the first surface area, and the surface area from the other end to the first end in the width direction of the polyester film is defined as the second surface area, the number of adhered foreign matter (hereinafter also referred to as "specific foreign matter") with a major axis of 50 μm or more in the first surface area and the second surface area is 1 per 500 m. ２ The following is preferable: The number of specific foreign matter in the first and second surface regions is 1 per 500 m. ２ The following conditions allow for the manufacture of polyester films with fewer protrusions on the surface, further suppressing unevenness in the thickness of the functional layer provided on the surface of the polyester film. Here, "adhering" foreign matter to the surface of the polyester film means that foreign matter such as molten resin adheres to the surface of the polyester film and is not transferred even when an adhesive roll is brought into contact with it. "Adhered foreign matter" refers to foreign matter that has adhered to the surface of the polyester film.

[0054] There is no particular limit to the number of specific foreign objects in the first and second surface regions of the polyester film; the lower limit is 0 objects / 500m. ２ This may also be the case. The method for measuring specific foreign substances on the surface of the polyester film will be described in the examples below.

[0055] The number of specific foreign objects in the first and second surface regions is 1 per 500m. ２ The polyester film described below can be manufactured, for example, by performing a specific transverse stretching process using a stretching apparatus equipped with a contact member containing a resin with a melting temperature of 250°C or higher, which is used as a contact member to close the clip, as described in the second embodiment described later. By using such a contact member, even if small pieces originating from the contact member come into contact with the polyester film when it is brought into contact with the clip, the small pieces are less likely to melt due to subsequent heat treatment, and it is presumed that the number of foreign objects adhering to the surface of the polyester film can be suppressed.

[0056] The specific foreign substance preferably contains components different from those of the polyester film. In particular, a configuration in which the specific foreign substance contains nitrogen atoms and the polyester film does not contain nitrogen atoms is more preferable. This allows for the production of a polyester film with fewer protrusions on its surface, and further suppresses thickness variations in the functional layer provided on the surface of the polyester film. The substances constituting the specific foreign substance can be analyzed by measuring the surface of the polyester film using energy dispersive X-ray spectrometry (EDS).

[0057] [Physical Properties, etc.] Next, the physical properties, etc. of this film will be explained.

[0058] (Maximum protrusion height Sp) In this film, the maximum protrusion height Sp on both surfaces is 150 nm or less. By having the maximum protrusion height Sp on both surfaces within the above range, the occurrence of transfer marks in laminated films obtained by laminating a functional layer onto a polyester film can be suppressed. The maximum protrusion height Sp on both surfaces is preferably 1 to 150 nm, more preferably 1 to 80 nm, and even more preferably 1 nm or more and less than 60 nm, considering the above points and the transportability of the polyester film or laminated film.

[0059] The maximum protrusion height Sp on the surface of the polyester film, as well as the maximum height St and average surface roughness Sa described later, are determined by measuring the surface of the polyester film using an optical interferometer (for example, "Vertscan 3300G Lite" manufactured by Hitachi High-Tech Corporation), and then analyzing the data using the built-in data analysis software. The specific measurement methods and conditions for the above physical properties are described in the examples below.

[0060] In this film, the maximum protrusion height Sp of one surface and the maximum protrusion height Sp of the other surface may be the same or different, but it is preferable that they be different. Hereinafter, in this film in which the maximum protrusion height Sp is different on both surfaces, the surface with a relatively small maximum protrusion height Sp will also be referred to as the "smooth surface," and the surface with a relatively large maximum protrusion height Sp will also be referred to as the "uneven surface." Furthermore, the maximum protrusion height Sp of the smooth surface will also be referred to as "Sp1," and the maximum protrusion height Sp of the uneven surface will also be referred to as "Sp2."

[0061] Figure 3 is a schematic cross-sectional view showing an example of the structure of this film. The polyester film 70 according to this embodiment shown in Figure 3 has a smooth surface 71 and an uneven surface 72. In the illustrated polyester film 70, the maximum protrusion height Sp1 of the smooth surface 71 and the maximum protrusion height Sp2 of the uneven surface 72 are both 150 nm or less, and the maximum protrusion height Sp1 is smaller than the maximum protrusion height Sp2. By laminating a functional layer onto the smooth surface 71 when manufacturing a laminated film, transfer marks during storage of the laminated film can be suppressed. Furthermore, because the maximum protrusion height Sp2 of the uneven surface 72 is relatively large, the slipperiness of the uneven surface 72 is improved, which can improve the transportability of the polyester film and the laminated film, and reduce winding failures.

[0062] The maximum protrusion height Sp1 on the smooth surface and the maximum protrusion height Sp2 on the uneven surface are adjusted as appropriate from the above viewpoint. The maximum protrusion height Sp1 on the smooth surface is, for example, 100 nm or less, preferably 60 nm or less, and more preferably less than 35 nm, in order to ensure that the thickness of the functional layer is uniform when a functional layer such as a release layer is provided. The maximum protrusion height Sp2 on the uneven surface is, for example, 150 nm or less, preferably 130 nm or less, more preferably 100 nm or less, even more preferably 80 nm or less, and particularly preferably less than 60 nm, in order to suppress the occurrence of transfer marks on the surface of the release layer when a release layer is provided on the film. The lower limit is often 1 nm or more, but from the viewpoint of transportability and reduction of winding failures, it is preferably 5 nm or more, and more preferably 10 nm or more.

[0063] The smooth surface may be one surface of the polyester substrate, or it may be the surface of another layer formed on the polyester substrate. The maximum protrusion height Sp1 of the smooth surface can be adjusted, for example, by selecting the type of polyester and additives that constitute the polyester substrate so that the polyester substrate is substantially free of particles and forms a smooth film. The maximum height St1 and average surface roughness Sa1 of the smooth surface, which will be described later, can be adjusted in a similar manner.

[0064] The uneven surface may be the other surface of the polyester substrate, or it may be one surface of the particle-containing layer described above. The maximum protrusion height Sp2 of the uneven surface can be adjusted, for example, by the following methods: (1) Form the particle-containing layer described above on one surface of the polyester substrate and adjust it by the size and amount of particles contained in the particle-containing layer and the thickness of the particle-containing layer. As for the method of forming the particle-containing layer, as described in the [particle-containing formation process] of the second embodiment described later, there is a method of forming a coating layer of a composition containing particles, and a method of co-extruding a second molten body containing particles and a binder together with a molten polyester body. (2) Incorporate particles into the polyester substrate and adjust it by the size and amount of particles. (3) Roughen one surface of the polyester substrate by physical treatment. As for physical treatment, for example, plasma treatment can be used. The maximum height St2 and average surface roughness Sa2 of the uneven surface described later can also be adjusted by the same method. The film has a polyester substrate and a particle-containing layer, and it is preferable that the exposed surface of the polyester substrate is a smooth surface and the exposed surface of the particle-containing layer is an uneven surface.

[0065] (Maximum height St) In this film, in terms of better suppression stability of the transfer marks of the laminated film, the maximum height St of both surfaces is preferably 150 nm or less, more preferably 100 nm or less, still more preferably less than 60 nm, and particularly preferably less than 50 nm. The lower limit of the maximum height St of both surfaces is not particularly limited and may be, for example, 1 nm or more. When this film has a smooth surface and a concavo-convex surface, the maximum height St1 of the smooth surface is preferably 1 to 100 nm, more preferably more than 1 nm and less than 50 nm, and still more preferably 1 to 30 nm in terms of the thickness of the functional layer such as the release layer being uniform when the functional layer is provided. Also, the maximum height St2 of the concavo-convex surface is, for example, 1 to 150 nm, preferably 10 to 100 nm, and more preferably more than 10 nm and less than 50 nm in terms of achieving both improvement in winding quality and suppression of transfer marks.

[0066] (Surface average roughness Sa) In this film, in terms of better suppression stability of the transfer marks of the laminated film, the surface average roughness Sa of both surfaces is preferably 10 nm or less, more preferably 5 nm or less, still more preferably 4 nm or less, and particularly preferably 3 nm or less. The lower limit of the surface average roughness Sa of both surfaces is not particularly limited and may be 0 nm. When this film has a smooth surface and a concavo-convex surface, the surface average roughness Sa1 of the smooth surface is, for example, 0 to 10 nm, preferably 0 to 5 nm, more preferably 0 to 3 nm, and still more preferably 0 to 1 nm in terms of the thickness of the functional layer such as the release layer being uniform when the functional layer is provided. Also, the surface average roughness Sa2 of the concavo-convex surface is, for example, 0 to 10 nm, preferably 0 to 5 nm, and more preferably 0 to 3 nm. In terms of achieving both improvement in winding quality and suppression of transfer marks, 2 to 3 nm is still more preferably.

[0067] (Streaks) This film is characterized in that the number of streaks observed through a polarizing plate is 0.4 pieces / m ２ or less. When observing a polyester film through a polarizing plate, the number of streaks detected is 0.4 pieces / m ２ or less. Thus, even for a polyester film with a thickness less than 30 μm, unevenness in the thickness of the functional layer (such as a slurry layer, a release layer, etc.) laminated on the polyester film can be suppressed.

[0068] Here, "streaks" observed through a polarizing plate refer to areas that appear as linear regions with a clear difference in color intensity compared to the surrounding area when observing a polyester film through a polarizing plate. "Linear" indicates directionality; the lines may be curved or straight. On the other hand, when observing a polyester film through a polarizing plate, there may be areas where the difference in color intensity compared to the surrounding area is slight, and while there is a difference in intensity, it is difficult to see a clear line that could be called a linear region. These do not fall under the definition of "linear streaks" as described above, and are instead referred to as "blurred streaks." In this specification, "linear streaks" will be defined simply as "streaks." More specific methods for detecting streaks will be described in the examples below.

[0069] The number of streaks in this film is 0.2 per meter, which provides superior effects for the present invention. ２ The following is preferable. The lower limit is not particularly limited, and is 0 pieces / m ２ This may be the case. The number of streaks in the polyester film can be reduced by setting the stretching ratio in the longitudinal stretching process in the manufacture of the biaxially oriented polyester film within a predetermined range, and setting the preheating temperature in the preheating process for preheating the uniaxially oriented polyester film obtained in the longitudinal stretching process within a predetermined range, as described in the second embodiment described later.

[0070] (Thickness) The thickness of this film is 10 μm or more and less than 30 μm. Even if this film is a thin polyester film with a thickness within the above range, it can suppress thickness unevenness in the laminated functional layers (slurry layer, release layer, etc.). The thickness of this film is preferably 15 to 28 μm.

[0071] The thickness variation of this film is preferably 7% or less of the average thickness of the polyester film, more preferably 6% or less, and even more preferably 5% or less, as this provides superior surface smoothness for the functional layer. The lower limit of the thickness variation is not particularly limited and may be 0% or more of the average thickness of the polyester film, and preferably 2% or more.

[0072] The thickness and thickness variation of the polyester film are measured using a spectral interference displacement type multilayer film thickness analyzer (for example, "SI-T80," manufactured by Keyence Corporation). More specific measurement methods are described in the examples below.

[0073] (Film Density) The density of the polyester film is 1.39 to 1.41 g / cm³, which is superior to the effects of the present invention. ３ Preferably, 1.395 to 1.405 g / cm³ ３ More preferably, 1.396 to 1.400 g / cm³ ３ This is even more preferable. The density of the polyester film can be measured using an electronic hydrometer (product name "SD-200L", manufactured by Alpha Mirage).

[0074] [Second Embodiment: Method for Manufacturing Polyester Film] The second embodiment of the present invention, a method for manufacturing polyester film (hereinafter also referred to as "this manufacturing method"), is characterized by comprising: an extrusion molding step of extruding a molten resin containing polyester into a film to form an unstretched polyester film having at least a polyester substrate; a longitudinal stretching step of stretching the unstretched polyester film in the transport direction to a range of 3.30 times or more and less than 3.40 times to form a uniaxially oriented polyester film; a preheating step of preheating the uniaxially oriented polyester film until the surface temperature reaches 90°C or more and less than 100°C; and a transverse stretching step of stretching the uniaxially oriented polyester film in the width direction to form a biaxially oriented polyester film.

[0075] The present manufacturing method may include other steps in addition to the extrusion molding step, the longitudinal stretching step, the preheating step, and the transverse stretching step described above. Preferably, the present manufacturing method includes at least one step selected from the group consisting of, for example, a heat setting step of heating and heat-fixing a biaxially oriented polyester film; a heat relaxation step of heating the polyester film heat-fixed in the heat setting step at a lower temperature than the heat setting step to relieve heat; a cooling step of cooling the polyester film heat-relaxed in the heat relaxation step; an expansion step of expanding the heat-relaxed polyester film in the width direction during the cooling step; and a particle-containing layer formation step of providing a particle-containing layer on one surface of the polyester substrate.

[0076] The steps of this manufacturing method will be described in more detail below. With respect to the manufacturing method, including the steps described below, reference can also be made to paragraphs

[0101] to

[0154] of International Publication No. 2021 / 261412, which are incorporated herein by reference.

[0077] The extrusion molding process is a process in which a molten resin containing polyester as a raw material is extruded into a film shape by an extrusion molding method to form an unstretched polyester film. The polyester raw material is the same as the polyester contained in the polyester substrate of the polyester film of the first embodiment.

[0078] A molten resin containing polyester is formed, for example, by heating the raw polyester material to a temperature above its melting point using an extruder equipped with a screw, and then rotating the screw to melt and knead the material. The polyester melts in the extruder due to heating and kneading with the screw, becoming a molten body (melt). An unstretched resin film made of the film-like molten resin is formed by extruding the polyester-containing molten resin in a film form onto the surface of a cast drum, for example, using an extrusion die. The temperature of the molten resin supplied to the die is, for example, [Tm + 10°C] to [Tm + 70°C] (Tm: melting point of polyester), and it cools and solidifies at 30 to 110°C on the surface of the cast drum. The molten resin may be extruded in a single layer or in multiple layers. Known extruders can be used as the extruder. The temperature of the polyester film and each component can be measured using a non-contact thermometer (e.g., a radiation thermometer). The surface temperature of the polyester film is determined by measuring the temperature of the center of the polyester film in the width direction five times and calculating the average of the obtained measurements.

[0079] In this manufacturing method, as a longitudinal stretching step, an unstretched polyester film is stretched to a range of 3.30 times or more and less than 3.40 times to form a uniaxially oriented polyester film. As the longitudinal stretching step, a known longitudinal stretching method in which the polyester film is stretched in the transport direction (longitudinal direction) can be applied. For example, a uniaxially oriented polyester film can be obtained by applying tension between a pair of low-speed rolls and a pair of high-speed rolls while transporting the unstretched polyester film. In the longitudinal stretching step, the surface temperature of the polyester film is preferably (Tg-20) to (Tg+50)°C (Tg: glass transition temperature of polyester), more preferably (Tg-10) to (Tg+40)°C, and even more preferably (Tg) to (Tg+30)°C. Specifically, the heating temperature in the longitudinal stretching step is preferably 70 to 120°C, more preferably 80 to 110°C, and even more preferably 85 to 100°C.

[0080] In this manufacturing method, a preheating step is performed on the uniaxially oriented polyester film formed by the longitudinal stretching step until the surface temperature of the uniaxially oriented polyester film is 90°C or higher but less than 100°C. Preheating until the surface temperature is 90°C or higher but less than 100°C means that the surface temperature of the uniaxially oriented polyester film at the start of the transverse stretching step is 90°C or higher but less than 100°C. Methods for preheating the uniaxially oriented polyester film include, for example, heating the conveying rolls used to transport the uniaxially oriented polyester film while transporting it, applying hot air to the uniaxially oriented polyester film, and bringing the uniaxially oriented polyester film into contact with a heat source such as a heater, or passing it near a heat source. Methods for heating the conveying rolls include, for example, installing a heater inside the roll, and installing piping inside the roll and flowing heated fluid through the piping.

[0081] The uniaxially oriented polyester film, preheated in the preheating step, is stretched in the width direction (transverse stretching) in the transverse stretching step to produce a biaxially oriented film (biaxially oriented film). The stretching ratio in the width direction due to transverse stretching is, for example, 2 to 7 times, and preferably 2 to 5 times. In the transverse stretching step, it is preferable to heat the polyester film so that its surface temperature is between [Tg - 10°C] and [Tg + 60°C] (more preferably [Tg] to [Tg + 60°C]). Specifically, the heating temperature in the transverse stretching step is preferably 100 to 140°C, more preferably 110 to 135°C, and even more preferably 115 to 130°C.

[0082] In the transverse stretching step of this manufacturing method, when transverse stretching, both ends in the width direction of the uniaxially oriented film, which has been preheated in the preheating step described above, are gripped with clips, and the clips come into contact with a contact member, causing the clips to close, thereby gripping the uniaxially oriented polyester film with the clips. Furthermore, it is preferable that the contact member contains a resin with a melting temperature of 250°C or higher (hereinafter also referred to as the "specific transverse stretching step"). The specific transverse stretching step is performed, for example, using a stretching apparatus that includes clips for gripping both ends in the width direction of the polyester film and a contact member containing a resin with a melting temperature of 250°C or higher. The specific transverse stretching step will be described below with reference to the drawings. Note that the specific transverse stretching step is not limited to a transverse stretching step performed using the stretching apparatus described below, and this manufacturing method is not limited to a manufacturing method having a transverse stretching step performed using the stretching apparatus described below.

[0083] Figure 1 is a schematic plan view showing an example of the configuration of a stretching machine used in the manufacture of polyester film. The stretching machine 100 shown in Figure 1 comprises a pair of annular rails 60a and 60b, and gripping members 2A to 2L attached to each annular rail and movable along the rails. The annular rails 60a and 60b are arranged symmetrically with respect to the film 200 (polyester film). The stretching machine 100 can stretch the film 200 in the width direction by gripping the film 200 with the gripping members 2A to 2L and moving the gripping members 2A to 2L along the rails. Furthermore, the stretching machine 100 shown in Figure 1 comprises a clip closer 3, a support member 4 that supports the clip closer 3, and a clip opener 5. Details of these components will be explained later in the section on [clips].

[0084] The stretching machine 100 has regions consisting of, in order from the upstream side in the conveying direction, a preheating section 10, a stretching section 20, a heat setting section 30, a heat relaxation section 40, and a cooling section 50. These regions of the stretching machine 100 are separated by windbreak curtains, and the temperature within each region can be adjusted individually using hot air or the like.

[0085] The preheating section 10 is the region for preheating the film 200.

[0086] The stretching section 20 is a region in which the preheated film 200 is stretched by applying tension in the direction of arrow TD (width direction), which is perpendicular to the direction of arrow MD (longitudinal direction). As shown in Figure 1, in the stretching section 20, the film 200 is stretched (laterally stretched) from width L0 to width L1.

[0087] The heat-setting section 30 is a region in which the tensioned film 200 is heated and heat-set while maintaining that tension.

[0088] The heat relaxation section 40 is a region in which the tension of the heat-fixed film 200 is thermally relaxed by heating the heat-fixed film 200. As shown in Figure 1, in the heat relaxation section 40, the film 200 is reduced (relaxed) from a width L1 to a width L2.

[0089] The cooling section 50 is a region for cooling the heat-relaxed film 200. By cooling the film 200, the shape of the film 200 can be fixed. Figure 1 shows that the width of the film 200 being fed into the cooling section 50 is L2, and the width of the film 200 being discharged from the cooling section 50 is L3.

[0090] 2A, 2B, 2E, 2F, 2I, and 2J are attached to the annular rail 60a, and gripping members 2A, 2B, 2E, 2F, 2I, and 2J are attached to the annular rail 60a, and gripping members 2C, 2D, 2G, 2H, 2K, and 2L are attached to the annular rail 60b, and gripping members 2A, 2B, 2E, 2F, 2I, and 2J grip one end of the film 200 in the direction of arrow TD. 2C, 2D, 2G, 2H, 2K, and 2L grip the other end of the film 200 in the direction of arrow TD. 2A to 2L are often referred to as chucks or clips. 3A, 2B, 2E, 2F, 2I, and 2J move counterclockwise along the annular rail 60a. The gripping members 2C, 2D, 2G, 2H, 2K, and 2L move clockwise along the annular rail 60b.

[0091] The gripping members 2A to 2D move along the annular rail 60a or 60b while gripping the end of the film 200 in the preheating section 10, and proceed through the stretching section 20, the heat-setting section 30, and the heat-relaxing section 40 to the cooling section 50. Next, the gripping members 2A and 2B and the gripping members 2C and 2D release the end of the film 200 at the downstream end in the direction of arrow MD of the cooling section 50 (for example, grip release point P and grip release point Q in Figure 1), in order of the transport direction, and then move further along the annular rail 60a or 60b to return to the preheating section 10. In the above process, as the film 200 moves in the direction of arrow MD, it undergoes preheating in the preheating section 10, stretching in the stretching section 20, heat-setting in the heat-setting section 30, heat-relaxing in the heat-relaxing section 40, and cooling in the cooling section 50, and is stretched laterally.

[0092] The transport speed of the film 200 can be adjusted by adjusting the movement speed of the gripping members 2A to 2L. Furthermore, the movement speed of each gripping member 2A to 2L can be changed independently.

[0093] As described above, the stretching machine 100 enables lateral stretching of the film 200 in the direction of arrow TD in the stretching section 20.

[0094] The stretching machine 100 may have additional gripping members (not shown) in addition to the gripping members 2A to 2L to support the film 200.

[0095] [Clip] The structure of clip 2 will be explained in more detail below with reference to Figures 2A and 2B. Figures 2A and 2B are schematic diagrams showing an example of the configuration of clip 2. Clip 2 in Figures 2A and 2B corresponds to gripping members 2A to 2L in Figure 1. Figure 2A shows clip 2 in the open state (hereinafter also referred to as the "open state"), and Figure 2B shows clip 2 in the closed state (hereinafter also referred to as the "closed state") that grips the film 200.

[0096] The clip 2 comprises a clip body 2a, an extension 2b extending inward in the width direction indicated by arrow TD above the clip body 2a and having an axis 2c, an arm portion 2d rotatably supported by the extension 2b and axis 2c, and a clip base 2e extending inward in the width direction below the clip body 2a and having a top surface facing the lower end of the arm portion 2d. The clip body 2a is attached to an annular rail 60a or 60b on its outer side in the width direction (opposite to the extension 2b and clip base 2e), although not shown in the figure. This allows the clip 2 to move in the direction of transporting the film 200 (the direction that penetrates the paper surface). The tip of the extension 2b extending inward in the width direction is attached via axis 2c to the vicinity of the center of the arm portion 2d which extends in the vertical direction. An edge (not shown) is provided on the lower end surface of the arm portion 2d, and when the clip 2 is in the closed position, the film 200 is gripped by the lower end surface of the arm portion 2d and the top surface of the clip base 2e.

[0097] Returning to Figure 1, in the stretching machine 100, a pair of clip closers 3 are positioned upstream of the film 200 in the transport direction, and each is supported by a support member 4. The clip 2 moves along the annular rail 60a or 60b upstream of the film 200 in the transport direction, and when it reaches the position where the clip closer 3 is positioned, the clip closer 3 comes into contact with the clip 2, and the upper part of the arm portion 2d is pushed out from the inside to the outside in the width direction. As a result, the arm portion 2d rotates clockwise, and the clip 2 becomes closed, capable of gripping the film 200 (see Figure 2B).

[0098] Furthermore, in the stretching machine 100, a pair of clip openers 5 are positioned near the exit on the downstream side in the transport direction of the film 200. The clip 2, which has come into contact with the clip closer 3 and is in a closed state capable of gripping the film 200, moves downstream in the transport direction. Eventually, when the clip 2 reaches the position where the clip opener 5 is located, the clip opener 5 comes into contact with the clip 2, and the upper part of the arm portion 2d is pushed out from the outside in the width direction toward the inside. As a result, the arm portion 2d rotates counterclockwise, and the clip 2 changes from a closed state that grips the film 200 to an open state that releases the film 200 (see Figure 2A).

[0099] Thus, the stretching machine 100 is configured such that, as the clip 2 moves along the annular rail 60a or 60b, the clip closer 3 comes into contact with it, gripping both ends of the film 200 with the clip 2. In the stretching area, the film 200 gripped at both ends by the clip 2 is stretched laterally, and the clip opener 5 comes into contact with it, releasing the film 200 from the clip 2, thereby performing a series of later stretching processes. Furthermore, the stretching machine 100 can perform various processes such as a preheating process, a later stretching process, a heat setting process, a heat relaxation process, and a cooling process.

[0100] In a stretching apparatus used in a specific transverse stretching process, it is preferable that the contact member (for example, the clip closer 3 shown in Figure 1) that closes the clip by contacting it contains a resin with a melting temperature of 250°C or higher. By using a contact member containing a resin with a melting temperature of 250°C or higher, even if small pieces originating from the contact member come into contact with the film 200 when it is brought into contact with the clip, the small pieces are less likely to melt due to subsequent heat treatment. As a result, the number of foreign objects adhering to the polyester film can be suppressed, and it is presumed that a polyester film with fewer protrusions on the surface can be manufactured, further suppressing thickness unevenness of the functional layer provided on the surface of the polyester film.

[0101] Here, the melting temperature of the resin refers to the melting point (Tm) of the resin if the resin contained in the contact member is a crystalline resin, and to the glass transition temperature (Tg) of the resin if the resin is an amorphous resin. The melting temperature of the resin contained in the contact member is preferably 270°C or higher, more preferably 300°C or higher, and even more preferably 330°C or higher. The upper limit is not particularly limited and may be 400°C or lower. The glass transition temperature (Tg) of the resin and the melting point (Tm) of the crystalline resin can be determined by measuring with a differential scanning calorimetry (DSC).

[0102] Examples of resins with a melting temperature of 250°C or higher include polyether ether ketone, polyphenylene sulfide, polyimide, polyamide, and fluororesin. Examples of fluororesin include polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene (ETFE), perfluoroalkoxyalkane (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Among these, polyether ether ketone, polyphenylene sulfide, polyimide, or polytetrafluoroethylene are preferred as resins with a melting temperature of 250°C or higher.

[0103] The clip closer 3 shown in Figure 1 is disc-shaped and is rotatably supported by a support member 4 with respect to the direction normal to the film 200. As a result, the clip closer 3 rotates upon contact with the arm portion 2d of the clip 2. The shape of the contact member is not limited to the clip closer described above, and any shape that can contact the clip and close it is acceptable. The contact member may be, for example, an elongated flat plate extending in the transport direction, having a contact surface that continuously contacts the clip, and the contact surface may be inclined from the inside to the outside in the width direction as it moves downstream of the film 200. The contact member is preferably a rotatable disc shape. In particular, in the cross-section obtained by cutting the disc-shaped contact member along its central axis, the side portion that contacts the clip is more preferably a curve such as a circular arc or an elliptical arc, having two or more line segments with different angles.

[0104] Furthermore, the dimensions and arrangement of the contact members are not limited and can be appropriately selected so as to cause the clip to switch to a closed state where it grips the film when the contact members are in contact. The diameter of the disc-shaped contact member may be, for example, in the range of 5 to 30 cm.

[0105] After the film 200 is stretched laterally, the clip, which is in a closed state by gripping both ends of the film 200 with the above-mentioned contact member, is brought into contact with the clip opener 5 shown in Figure 1, thereby releasing the gripping state of both ends of the film 200. The shape of the contact member that comes into contact with the clip to open the clip from a closed state is not particularly limited as long as it is a shape that can come into contact with the clip and open the clip. The contact member may be, for example, an elongated flat plate extending in the transport direction, having a contact surface that continuously contacts the clip, and the contact surface may be a member that slopes from the outside in the width direction to the inside as it moves downstream of the film 200. Alternatively, the shape of the contact member that comes into contact with the clip and opens the clip may be a disc shape. The material constituting the contact member that opens the clip is not particularly limited, and examples include resins and metals with a melting temperature of 250°C or higher.

[0106] In this manufacturing method, it is preferable to perform the above-mentioned heat setting, heat relaxation, cooling, and expansion steps after the transverse stretching step. This manufacturing method may also include a winding step to obtain a roll-shaped biaxially oriented polyester film by winding up the biaxially oriented polyester film obtained through the above steps. Furthermore, this manufacturing method may further include a trimming step before performing the winding step, in which the polyester film is continuously cut along the conveying direction to cut off at least one end of the polyester film in the width direction.

[0107] The polyester film produced by this manufacturing method may be a single-layer structure consisting only of a polyester substrate formed using a molten polyester, or it may be a multilayer structure having a polyester substrate and a particle-containing layer containing particles. Preferably, at least one surface of the polyester film produced by this manufacturing method is uneven, and more preferably, one surface is smooth and the other surface is uneven. The uneven and smooth surfaces, including more preferred embodiments, are as described in the first embodiment. Furthermore, if the polyester film produced by this manufacturing method is a single-layer structure consisting only of a polyester substrate, an uneven surface can be formed on at least one surface of the polyester film, for example, according to methods (2) and (3) described in the first embodiment as a method for adjusting the maximum protrusion height Sp2 of the uneven surface.

[0108] [Particle-containing layer formation process] A polyester film having a polyester substrate and a particle-containing layer can be manufactured by performing a particle-containing layer formation process at any stage of this manufacturing method. Examples of the particle-containing layer formation process include a step of forming a particle-containing layer using a particle-containing layer formation composition containing particles (hereinafter also referred to as "composition A"), and a step of forming a particle-containing layer by extruding a second molten body containing particles and a binder simultaneously with the molten resin in an extrusion formation process.

[0109] First, the step of forming a particle-containing layer using composition A (hereinafter also referred to as "step A") will be described. Step A may be performed at any stage of this manufacturing method. For example, step A may be performed after the extrusion molding step by an in-line coating method to form a particle-containing layer on the surface of an unstretched polyester substrate, or it may be performed between the longitudinal stretching step and the preheating step to form a particle-containing layer on the surface of a uniaxially stretched polyester substrate. Preferably, step A is performed between the longitudinal stretching step and the preheating step to form a coating film on one surface of the uniaxially stretched polyester substrate, and to form a particle-containing layer by drying the coating film as needed. This is because the adhesion between the polyester substrate and the particle-containing layer can be improved by simultaneously stretching the uniaxially stretched polyester substrate and the particle-containing layer laterally.

[0110] Composition A can be prepared by mixing particles contained in a particle-containing layer, a binder, additives added as needed, and a solvent. Examples of solvents include water, ethanol, toluene, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether. Among these, water is preferred from the viewpoint of environmental impact, safety, and economic efficiency. Composition A may contain one solvent or two or more solvents. The solvent content is preferably 80 to 99% by mass of the total mass of Composition A. That is, the total content of components other than the solvent (solids) is preferably 0.5 to 20% by mass of the total mass of Composition A.

[0111] The particles, binder, and additives contained in composition A are the same as those described in the section on the particle-containing layer of the polyester film according to the first embodiment, including their preferred embodiments.

[0112] The method of applying composition A 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.

[0113] The particle-containing layer formation step may be a step in which a particle-containing layer is formed by co-extrusion, in which a second molten body containing particles and a binder is extruded simultaneously with a molten polyester resin. After forming a laminate in which a polyester substrate and a particle-containing layer are laminated by co-extrusion, a polyester film may be manufactured by performing the above-mentioned longitudinal stretching step, preheating step, and transverse stretching step on the laminate. Co-extrusion can be carried out in the same manner as the extrusion molding step already described, except that a composition containing particles and a binder is melted to produce a second molten body, and the obtained second molten body is extruded together with the molten resin by a known co-extrusion method. The particles and binder contained in the second molten body are the same as those described in the section on the particle-containing layer of the polyester film according to the first embodiment, including their preferred embodiments.

[0114] [Laminated Film] The polyester film according to the first embodiment and the polyester film manufactured by the manufacturing method according to the second embodiment (hereinafter, both are collectively referred to as "the film") are not particularly limited in their use, but it is preferable to manufacture a laminated film by further laminating a functional layer on the surface of the film. Examples of functional layers to be laminated on the film include a release layer, a decorative layer, a photosensitive resin layer, a magnetic layer, a conductive layer, a refractive index adjusting layer, and a visibility layer. As for the laminated film, it is preferable that the functional layer is provided on the surface (smooth surface) of the two surfaces of the film where the maximum protrusion height Sp is smaller.

[0115] More specific examples of laminated films include release films in which the functional layer is a release layer (protective films for dry film resists, release films for manufacturing ceramic capacitors), decorative films in which the functional layer is a decorative layer, photosensitive transfer films in which the functional layer is a photosensitive resin layer and are used as supports for dry film resists, films for transparent conductive substrates in which the functional layer is a transparent conductive layer, photosensitive transfer films for forming etching resist films in which the functional layers are a photosensitive resin layer and a visibility layer, and photosensitive transfer films for forming protective films for touch panels in which the functional layers are a photosensitive resin layer and a refractive index adjusting layer.

[0116] The method for laminating the functional layer onto the surface (preferably a smooth surface) of this film is not particularly limited, but it is preferable to form the functional layer by applying a coating solution containing the materials constituting the functional layer to the surface of this film. In terms of superior productivity, it is even more preferable to form the functional layer by applying the coating solution for the functional layer to the surface of this film while transporting the film, and then heating the coating film. This film can suppress thickness unevenness of the laminated functional layer even when heat treatment is performed in the functional layer formation process.

[0117] The laminated film may have layers other than the main film and the functional layer. Examples of layers other than the main film and the functional layer include a base layer containing a binder resin, which is provided for the purpose of improving the adhesion between the main film and the functional layer.

[0118] [Release Film] A release film, which is an example of a preferred form of laminated film, will be described in more detail. This film can be used in the manufacture of release films. More specifically, by providing a release layer on the surface (preferably a smooth surface) of this film, a release film having a polyester film and a release layer can be manufactured.

[0119] 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 resins, fluororesins, alkyd resins, acrylic resins, various waxes, and aliphatic olefins, with silicone resins being preferred.

[0120] 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 with low-temperature curing properties, or ultraviolet or electron beam curable silicone resins, are preferred because they allow for the formation of a release layer at low temperatures.

[0121] Addition reaction-type silicone resins include, for example, resins obtained by reacting polydimethylsiloxane with vinyl groups introduced to the terminals or side chains with hydrodienesiloxane using a platinum catalyst and curing the reaction. Condensation reaction-type silicone resins include, for example, resins having a three-dimensional crosslinked structure formed by condensing polydimethylsiloxane having OH groups at the terminals with polydimethylsiloxane having H groups at the terminals using an organotin catalyst. UV-curing-type 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 and cleave epoxy groups to crosslink, and those that are crosslinked by the addition reaction of thiols to vinylsiloxane. More specifically, examples include acrylate-modified polydimethylsiloxane and glycidoxy-modified polydimethylsiloxane.

[0122] 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, and antistatic agents. The resin 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 the additives mentioned above, and / or residues of solvents and catalysts contained in the coating solution used to form the release layer.

[0123] The thickness of the release layer can be set according to its intended use and is not particularly limited, but it is preferably 0.005 to 2.0 μm, and more preferably 0.005 to 1.0 μm, in that it provides a good balance between release performance and surface smoothness of the release layer.

[0124] The method for forming a release layer on the surface (preferably a smooth 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 surface of the film, removing the solvent by drying, and forming a cured product by heating or irradiating with light as necessary.

[0125] 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.

[0126] The coating solution for forming the release layer contains the above-mentioned resin and solvent, and may optionally contain the above-mentioned additives and / or 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, and 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.

[0127] 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, based on the total mass of the coating solution for forming the release layer. That is, the total content of components other than solvents (solids) in the coating solution for forming the release layer is preferably 0.5 to 20% by mass, and more preferably 1 to 10% by mass, based on the total mass of the coating solution for forming the release layer.

[0128] 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 surface of the film before applying the release layer.

[0129] <Applications> The release film equipped with this film has excellent transportability, can suppress the formation of transfer marks during roll storage, and can suppress thickness unevenness of the release layer, so it is preferable to use it as a release film (carrier film) for the manufacture of ceramic green sheets. The ceramic green sheet manufactured using the above release film can be suitably used in the manufacture of ceramic capacitors, where multilayering of internal electrodes is required due to miniaturization and increased capacitance.

[0130] 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 involves 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, a known method such as applying a ceramic slurry, which comprises ceramic powder and a binder agent dispersed in a solvent, by a reverse roll method and removing the solvent by heating and drying can be applied. The binder agent is not particularly limited and can be, for example, polyvinyl butyral. The solvent is also not particularly limited and can be, for example, ethanol and toluene.

[0131] The release film comprising this film can be used as a protective film for dry film resists, a decorative layer and a film for sheet molding such as resin sheets, a release film for semiconductor manufacturing processes, a release film for polarizing plate manufacturing processes, and a separator for adhesive films such as labels, medical and office supplies.

[0132] The present disclosure will be further described with reference to the following examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate, as long as they do not depart from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the following specific examples. Unless otherwise specified, "parts" and "%" are based on mass.

[0133] In each step of this embodiment, a non-contact thermometer (THERMOMETER CThot (product name), manufactured by Micro-Epsilon, emissivity 0.95) was used to measure the temperature of the center of the film in the width direction five times, and the arithmetic mean of the obtained measurements was taken as the measured surface temperature of the film.

[0134] [Production of Polyester Film] [Example 1] Similar to the method described in Example 1 (

[0190] to

[0198] ) of International Publication No. 2022 / 019113, an unstretched polyester film made of polyethylene terephthalate was longitudinally stretched, and the following composition X1 was applied in-line to one side of the uniaxially oriented film. The formed coating film was dried with hot air to form a particle-containing layer, and a transverse stretching process was performed on the film with the particle-containing layer to produce a polyester film containing a polyester substrate and a particle-containing layer. At this time, by adjusting the thickness of the unstretched film and the amount of composition X1 applied in the extrusion molding process, a polyester film with a thickness of 25 μm and a particle-containing layer with a thickness of 15 nm was produced. The width was 2.0 m and the roll length was 7000 m. The transverse stretching process was performed using a transverse stretching apparatus having the configuration shown in Figure 1. The clip closer in the above transverse stretching apparatus was made of polyetheretherketone (PEEK) and was a disc-shaped member with a diameter of 150 mm and a thickness of 13 mm. Furthermore, the film formation conditions for the polyester film were changed as follows. Note that "preheating temperature before transverse stretching" refers to the surface temperature of the uniaxially oriented polyester film at the time preheating before transverse stretching is completed. (Longitudinal stretching conditions) Preheating temperature: 75°C, stretching temperature: 90°C, stretching ratio: as shown in Table 1 below (Transverse stretching conditions) Preheating temperature before transverse stretching: as shown in Table 1 below, stretching temperature: 120°C, stretching ratio: 4.2 times, stretching speed: 50% / second (Thermal fixation conditions) Thermal fixation temperature: 220°C, thermal fixation time: 6 seconds (Thermal relaxation conditions) Thermal relaxation temperature: 190°C, thermal relaxation rate Lr: 3.9% (Cooling conditions and expansion conditions in the cooling process) Cooling rate: 2500°C / min, expansion rate ΔL: 0.36%

[0135] (Composition X1) - Acid-modified polyolefin (Zyxene® NC, manufactured by Sumitomo Seika Co., Ltd., aqueous dispersion prepared by adding water to 25% solids): 157 parts - Anionic hydrocarbon surfactant (Rapizol® A-90, sodium di-2-ethylhexyl sulfosuccinate, manufactured by NOF Corporation, aqueous dilution with 1% solids): 56 parts - Particles (Snowtex® ZL, manufactured by Nissan Chemical Corporation, colloidal silica, aqueous dispersion with 40% solids): 14 parts - Water: 776 parts When preparing composition X1 and compositions X2 to X5 described later, each component was mixed, and then subjected to 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 Polypore, Inc.).

[0136] [Examples 2-6] The release films of Examples 2-6 were prepared in the same manner as in Example 1, except that the stretching ratio in the longitudinal stretching process and / or the preheating temperature before transverse stretching in the transverse stretching process were changed to the values ​​shown in Table 1 below.

[0137] [Example 7] A release film of Example 7 was prepared in the same manner as in Example 3, except that the amount of composition X1 applied was adjusted to form a particle-containing layer with a thickness of 40 nm.

[0138] [Examples 8-11] Release films for Examples 8-10 were prepared in the same manner as in Example 3, except that compositions X2-X4 were used instead of composition X1. Furthermore, a release film for Example 11 was prepared in the same manner as in Example 1, except that composition X5 was used instead of composition X1. The compositions of compositions X2-X5 are shown below.

[0139] (Composition X2) - Acid-modified polyolefin (Zyxene® NC, manufactured by Sumitomo Seika Co., Ltd., aqueous dispersion prepared by adding water to 25% solids): 157 parts - Anionic hydrocarbon surfactant (Rapizol® A-90, sodium di-2-ethylhexyl sulfosuccinate, manufactured by NOF Corporation, aqueous dilution with 1% solids): 56 parts - Particles (Snowtex® ZL, manufactured by Nissan Chemical Corporation, colloidal silica, aqueous dispersion with 40% solids): 22 parts - Water: 776 parts

[0140] (Composition X3) 167 parts of aqueous dispersion of acrylic resin (acrylic resin copolymerized with the composition methyl methacrylate / styrene / 2-ethylhexyl acrylate / 2-hydroxyethyl methacrylate / acrylic acid = 59:8:23:5:5 (mass ratio)) (solid content concentration 27.5% by mass) 0.7 parts of nonionic surfactant (Naroacty CL95, manufactured by Sanyo Chemical Industries, Ltd., solid content 100% by mass) Anionic surfactant (Rapizol A-90, manufactured by NOF Corporation, solid content 1% by mass) 55.7 parts (percent volume, diluted with water), 7 parts carnauba wax dispersion (Cellosol 524, manufactured by Chukyo Oil & Fat Co., Ltd., solids content 30% by mass), 20.9 parts carbodiimide compound (Carbodilite V-02-L2, manufactured by Nisshinbo Inc., solids content 10% by mass, diluted with water), 2.8 parts particles (Snowtex XL, manufactured by Nissan Chemical Corporation, solids content 40% by mass), 2.95 parts aggregated particles (Aerosil OX50, manufactured by Nippon Aerosil Co., Ltd., solids content 10% by mass, water dispersion, median diameter 0.2 μm), 743 parts water

[0141] (Composition X4) - Acid-modified polyolefin (Zyxene® NC, manufactured by Sumitomo Seika Co., Ltd., aqueous dispersion prepared by adding water to 25% solids): 157 parts - Anionic hydrocarbon surfactant (Rapizol® A-90, sodium di-2-ethylhexyl sulfosuccinate, manufactured by NOF Corporation, aqueous dilution with 1% solids): 56 parts - Particles (Snowtex® ZL, manufactured by Nissan Chemical Corporation, colloidal silica, aqueous dispersion with 40% solids): 11 parts - Oxazoline compound (Epocross® WS-700, manufactured by Nippon Shokubai Co., Ltd., aqueous solution with 25% solids): 15 parts by mass - Water: 776 parts

[0142] (Composition X5) ・35% by mass aqueous dispersion of urethane resin (Superflex® 210, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 115 parts by mass ・1% by mass aqueous dilution of anionic hydrocarbon surfactant (Rapizol® A-90, manufactured by NOF Corporation): 36 parts by mass ・20% by mass aqueous dispersion of non-crosslinked styrene resin particles (Nipol® UFN1008, manufactured by Nippon Zeon Co., Ltd.): 11.2 parts by mass ・5% by mass aqueous dispersion of particles (PMMA resin particles, MP1000, manufactured by Soken Chemical Co., Ltd.): 179.2 parts by mass ・25% by mass aqueous solution of crosslinking agent (oxazoline compound, Epocross® WS-700, manufactured by Nippon Shokubai Co., Ltd.): 32.2 parts by mass ・Water: 622 parts by mass

[0143] [Comparative Example 1] Similar to the method described in Example 19 (

[0179] ) of International Publication No. 2022 / 2641219113, an unstretched polyester film made of polyethylene terephthalate was longitudinally stretched, composition X3 was applied in-line to one side of the uniaxially oriented film, the formed coating film was dried with hot air to form a particle-containing layer, and a transverse stretching process was performed on the film with the particle-containing layer to produce a polyester film containing a polyester substrate and a particle-containing layer. At this time, the film-forming conditions for the polyester film were changed in the same manner as in Example 1. The stretching ratio in the longitudinal stretching process and the preheating temperature before transverse stretching in the transverse stretching process were changed to the values ​​shown in Table 1 described later.

[0144] [Physical Property Measurement] The following physical properties were measured for each polyester film of Examples 1 to 11 and Comparative Example 1. The measurement results are shown in Table 1.

[0145] <Maximum protrusion height Sp, maximum height St, average surface roughness Sa> The maximum protrusion height Sp, maximum height St, and average surface roughness Sa of both surfaces of the polyester film were measured using the following method. The surface of the polyester film was measured using an optical interferometer (Vertscan 3300G Lite, manufactured by Hitachi High-Tech Corporation) under the following conditions, and then the maximum protrusion height Sp, maximum height, and average surface roughness Sa of the surface were determined by analyzing the data using the built-in data analysis software (VS-Measure 5). For the measurement of the maximum protrusion height Sp and maximum height St, the maximum value obtained from five measurements taken at different measurement positions was adopted, and for the measurement of the average surface roughness Sa, the average value obtained from five measurements taken at different measurement positions was adopted. (Measurement conditions) ・Measurement mode: WAVE mode ・Objective lens: 50x ・Measurement area: 186 μm × 155 μm

[0146] Table 1, described later, shows the maximum protrusion height Sp2, maximum height St2, and average surface roughness Sa2 of the uneven surface (the surface on the particle-containing layer side) of the polyester film measured by the method described above. Furthermore, the maximum protrusion height Sp1, maximum height St1, and average surface roughness Sa1 of the smooth surface (the surface on the substrate side) of the polyester film were measured by the method described above, and in all examples, Sp1 was in the range of 10 to 20 nm, St1 was in the range of 10 to 20 nm, and Sa1 was in the range of 1 to 2 nm.

[0147] <Thickness and Thickness Variation of Polyester Film> Before winding the manufactured polyester film, the thickness was measured at 60,000 points along the longitudinal direction over a length of 106 m using a spectral interference displacement type multilayer film thickness analyzer ("SI-T80", manufactured by Keyence Corporation) at the center of the width direction of the polyester film. The average value obtained by arithmetic mean of the obtained thickness measurements was taken as the thickness of the polyester film. In addition, 6σ was calculated from the obtained thickness measurements, and the percentage of 6σ relative to the average thickness (6σ / average value × 100 (%)) was calculated as the thickness variation. In each example, the thickness variation of the polyester film was in the range of 2 to 6% relative to the average thickness.

[0148] The Sb content and other elements were measured for the polyester films obtained in each example using an ICP-MS analyzer (Agilent Technologies, "Agilent 7800 ICP-MS"). As a result, the Sb content relative to the total mass of the polyester film was 0.8 ppm. The Ti content was 7 ppm, the Mg content was 75 ppm, and the P content was 65 ppm.

[0149] For each example of polyester film obtained, the number of adhering foreign objects (specific foreign objects) with a major axis of 50 μm or more adhering to both surfaces was counted using a film surface inspection device (manufactured by MEC Corporation, device name "LSC-6000") over a 1000 m transport direction of the polyester film, in a first surface region extending 50 cm from one end to the other in the width direction, and in a second surface region extending 50 cm from the other end to the first in the width direction. Here, "major axis of 50 μm or more" for adhering foreign objects means that the diameter of the circumscribed circle of the adhering foreign object is 50 μm or more. If specific foreign objects were detected by the above inspection, the elemental distribution of the detected specific foreign objects was analyzed using EDS to confirm whether the specific foreign objects contained components different from the components of the film. Furthermore, it was confirmed that the specific foreign objects detected by the above inspection were adhering foreign objects that were not transferred even when an adhesive roll (manufactured by teknek, p-type adhesive roll) was brought into contact with them. As a result, the number of specific foreign substances on both surfaces of the polyester film obtained in each example was 0 per 500m. ２ That was the case.

[0150] <Measurement of Intrinsic Viscosity (IV) and End-Tier COOH Content (AV)> The intrinsic viscosity (IV) of the polyester films obtained in each example was determined by dissolving the polyester film in a 1,1,2,2-tetrachloroethane / phenol (= 2 / 3 [mass ratio]) mixed solvent and measuring the viscosity of the solution at 25°C. As a result, the intrinsic viscosity of the polyester films in Examples 1 to 11 was 0.63. The end-tier COOH content (AV) of the polyester films obtained in each example was calculated by completely dissolving the polyester film in a benzyl alcohol / chloroform (= 2 / 3 [volume ratio]) mixed solution, titrating the solution with a standard solution (0.01 NKOH-benzyl alcohol mixed solution) using phenol red as an indicator, and determining the appropriate amount. As a result, the end-tier COOH content of the polyester films in Examples 1 to 11 was in the range of 2.6 to 2.8.

[0151] <Streaks> The polyester films produced in each example and comparative example were observed through the polarizing plate using the following measuring device equipped with a polarizing plate, and the presence and number of streaks were confirmed. Figure 4 is a schematic cross-sectional view showing the configuration of the observation device 80 used to observe the polyester film. The observation device 80 consisted of a light source 81, a white translucent substrate 82, a first polarizing film 83, and a second polarizing film 84. The light source 81 was a fluorescent lamp, and multiple light sources 81 were arranged about 15 cm apart below the white translucent substrate. The translucent substrate 82 had a size of 2.5 m x 2.5 m. The light source 81 and the translucent substrate 82 were components of a lighting fixture called a Schaukasten. The first polarizing film 83 and the second polarizing film 84 were both TAC films. As shown in the figure, the first polarizing film 83 and the second polarizing film 84 were arranged apart from each other, and the absorption axis of the first polarizing film 83 and the absorption axis of the second polarizing film 84 were orthogonal to each other.

[0152] From the 2 m wide polyester film produced in each example and comparative example, a sample S with a longitudinal length of 30 m was taken and wound up using a winding core. Subsequently, as shown in Figure 4, the wound sample S was placed between the first polarizing film 83 and the second polarizing film 84, without contact with either the first polarizing film 83 or the second polarizing film 84, and at a distance of 0 to 10 cm from the first polarizing film 83. With the sample S positioned between the first polarizing film 83 and the second polarizing film 84, the sample S was visually observed from above in the vertical direction. When observing the sample S, if there was a difference in color intensity at a certain point in the sample S compared to the surrounding area, a double-line mark was placed at the boundary of the color intensity difference. A second sample with dimensions of 20 cm in the longitudinal direction (MD) and 2 m in the width direction (TD), including the marked area, was cut from the sample S. Using a strain analyzer ("TYPE-25W", manufactured by Shinto Kagaku Co., Ltd.), we observed whether the marked areas on the second sample corresponded to streaks. Specifically, the second sample was placed on the lower polarizing plate of the strain analyzer, and the upper polarizing plate was positioned above the second sample so that the absorption axes of the lower and upper polarizing plates were perpendicular to each other. Next, the intensity of polarization in and around the marked areas was observed from above the upper polarizing plate in the vertical direction, and based on the following criteria, we distinguished whether the marked areas were linear streaks or blurred streaks, and counted the number of each (unit: streaks / m). ２ The following measurements were taken: (Evaluation criteria) Linear streaks: There is a clear difference in color intensity between the marked area and its surroundings, and the area of ​​intensity difference is linear. Blurred streaks: There is only a slight difference in color intensity between the marked area and its surroundings, and although there is an intensity difference, a clear line is difficult to see.

[0153] Figure 5 is an illustrative diagram showing an example of an observation image obtained by observing the second sample using the method described above. As shown by the two black lines in Figure 5, linear streaks are observed as areas of clear color intensity differences that are linear in shape.

[0154] [Evaluation] The polyester films produced in each example and comparative example were evaluated as follows. The evaluation results are shown in Table 1.

[0155] [Transfer Mark Evaluation] A polyester film was fed out, and a coating solution consisting of the following formulation A was applied to the smooth surface of the polyester film using a slot die method. The coating film was then dried using a hot air dryer at 120°C, wound up, and a roll-shaped release film (polyester film with a release layer) was produced. The thickness of the release layer after drying was 0.5 μm.

[0156] The obtained release film was cut into 3.5 cm squares, and 10 of these were stacked in a direction where the release layer and the particle-containing layer were in contact to obtain a laminated sample. This sample was subjected to a load of 84 kg and kept in a 40°C oven for 3 days. After removing the sample from the oven, the release film was peeled off one sheet at a time. The surface of the release layer of the release film was observed at 20,000x magnification using a scanning electron microscope (SEM, Hitachi High-Tech Corporation, S4700), and the presence and degree of indentations were observed to evaluate the transfer traces according to the following criteria.

[0157] (Formulation A: Coating solution for forming a release layer) - Addition reaction type silicone (manufactured by Toray Dow Corning Co., Ltd., SRX-345, release agent): 10 parts - Mixed solvent of toluene and methyl ethyl ketone (mixing ratio = 7:3 (mass ratio)): 490 parts - Platinum catalyst (manufactured by Toray Dow Corning Co., Ltd., SRX-212): 0.1 parts The coating solution for forming a release layer was prepared by stirring and mixing the above components.

[0158] (Evaluation Criteria) A: No dents were observed. B: Slight dents were observed. C: Clear dents were observed.

[0159] [Thickness Variation of the Release Layer] Similar to the [Transfer Mark Evaluation] above, a release layer with a thickness of 0.5 μm was applied to the smooth surface of the polyester film. The thickness of the release layer was continuously measured along the longitudinal direction for 106 m using a spectral interference displacement type multilayer film thickness analyzer ("SI-T80", manufactured by Keyence Corporation). From the obtained thickness measurements, the maximum value, minimum value, and arithmetic mean of all measurements were calculated, and the thickness variation of the release layer was determined using the formula ((maximum value - minimum value) / mean value).

[0160] Table 1 shows the manufacturing conditions for the polyester film, the characteristics of the particle-containing layer, the measurement results, and the evaluation results of the transfer marks for each example and comparative example. In the table, "Sp2 (nm)", "St2 (nm)", and "Sa2 (nm)" represent the maximum protrusion height Sp2, maximum height St2, and average surface roughness Sa2 of the surface (uneven surface) of the particle-containing layer, respectively.

[0161]

[0162] Furthermore, the evaluation of the thickness of the release layer showed that the thickness unevenness of the release layer in the polyester films of Examples 1 to 11 was smaller and better than that of the polyester film of Comparative Example 1. Therefore, it was confirmed that the polyester films of Examples 1 to 11 according to the present invention exhibit superior effects compared to Comparative Example 1.

[0163] It was confirmed that transfer marks can be further suppressed when the maximum height St of the uneven surface (surface of the particle-containing layer) of the polyester film is less than 50 nm (comparison of Examples 3, 8, 9 and 10).

[0164] 2A-2L Gripping member 2 Clip 2a Clip body 2b Extension part 2c Shaft 2d Arm part 2e Clip base 3 Clip closer 4 Support member 5 Clip opener 10 Preheating part 20 Stretching part 30 Heat setting part 40 Heat relaxation part 50 Cooling part 60a, 60b Annular rail 70 Polyester film 71 Smooth surface 72 Uneven surface 80 Observation device 81 Light source 82 Translucent substrate 83 First polarizing film 84 Second polarizing film 100 Stretcher 200 Film (polyester film) S Sample

Claims

1. The maximum protrusion height Sp on both surfaces is 150 nm or less, the thickness is 10 μm or more and less than 30 μm, and the number of streaks observed through a polarizing plate is 0.4 per meter. ２ The following is a polyester film.

2. The polyester film according to claim 1, wherein the maximum height St of both surfaces is less than 50 nm.

3. The polyester film according to claim 1, wherein the average surface roughness Sa of both surfaces is 5 nm or less.

4. The polyester film according to claim 1, wherein the variation in the thickness of the polyester film is 7% or less of the average thickness of the polyester film.

5. The polyester film according to claim 1, comprising a polyester substrate and a particle-containing layer.

6. The polyester film according to claim 1, wherein the antimony content in the polyester film, as measured by inductively coupled plasma mass spectrometry, is 10 ppm by mass or less.

7. When the width of the polyester film is 100 cm or more, and the length of the polyester film is 1000 m or more, and the surface area from one end to the other end in the width direction of the polyester film is defined as the first surface area, and the surface area from the other end to the first end in the width direction of the polyester film is defined as the second surface area, then the number of adhering foreign objects with a major axis of 50 μm or more in the first surface area and the second surface area is 1 per 500 m. ２ The polyester film according to claim 1, which is as follows:

8. A laminated film having a polyester film according to any one of claims 1 to 7 and a release layer.

9. The laminated film according to claim 8, wherein the release layer is located on a surface in the polyester film where the maximum protrusion height Sp is smaller.

10. A method for manufacturing a polyester film, comprising: an extrusion step of extruding a molten resin containing polyester into a film to form an unstretched polyester film having at least a polyester substrate; a longitudinal stretching step of stretching the unstretched polyester film to a range of 3.30 times or more and less than 3.40 times in the transport direction to form a uniaxially oriented polyester film; a preheating step of preheating the uniaxially oriented polyester film until its surface temperature is 90°C or more and less than 100°C; and a transverse stretching step of stretching the uniaxially oriented polyester film in the width direction to form a biaxially oriented polyester film.

11. The method for producing a polyester film according to claim 10, further comprising a step of forming a particle-containing layer using a composition containing particles between the longitudinal stretching step and the transverse stretching step, or further comprising a step of forming a particle-containing layer in the extrusion molding step by extruding a second molten body containing the particles and a binder together with the molten resin.

12. The method for manufacturing a polyester film according to claim 10 or 11, wherein in the transverse stretching step, both ends of the uniaxially oriented polyester film in the width direction are gripped with clips, the clips come into contact with a contact member and the clips are closed, thereby gripping the uniaxially oriented polyester film with the clips, and the contact member contains a resin having a melting temperature of 250°C or higher.

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