Polyester film, laminate, and method for producing polyester film

Abstract

The present invention addresses the problem of providing a polyester film in which the occurrence of wrinkles on the outer periphery is suppressed when the polyester film is stored in a roll shape, and in which the occurrence of wrinkles is suppressed when the polyester film is heated and conveyed. The present invention also addresses the problem of providing a laminate and a method for producing a polyester film. A polyester film according to the present invention has a thickness of 10-50 μm, the polyester film satisfying both of the following conditions A and B. Condition A: After a polyester film having a size of 100 mm in length and 100 mm in width is heated at 150°C for 30 minutes, the thermal shrinkage of the polyester film is 1.40% or lower. Condition B: After the polyester film having a size of 100 mm in length and 100 mm in width is stored for 24 hours in an environment of 40°C and 90% RH, the humidity expansion coefficient of the polyester film is 0.015% or lower.

Description

Polyester film, laminate, and method for producing polyester film

[0001] The present invention relates to a polyester film, a laminate, and a method for producing a polyester film.

[0002] Biaxially oriented polyester films are used in a wide range of applications from the viewpoints of processability, mechanical properties, electrical properties, dimensional stability, transparency, chemical resistance, etc., and are used in a variety of applications, such as decorative films, supports and protective films for dry film photoresists, magnetic tapes, and release films used in the production of ceramic green sheets for manufacturing multilayer ceramic capacitors.

[0003] For example, Patent Document 1 discloses that, in producing a polyester film, the cooling rate of a heat-relaxed polyester film is set within a predetermined range, and the product of a value derived based on the melting point of the polyester constituting the polyester base material and the heat setting temperature of the polyester film and a value derived based on the stretch ratio of the uniaxially stretched polyester film and the expansion rate of the heat-relaxed polyester film is set within a predetermined range, thereby suppressing unevenness in the thickness of a functional layer provided on the surface of the polyester film.

[0004] International Publication No. 2021 / 261412

[0005] The present inventors produced a polyester film by referring to the description in Patent Document 1, and found that wrinkles sometimes occurred on the outer periphery of the roll when the obtained polyester film was stored in a rolled form, or when the obtained polyester film was heated and transported, and that there was room for improvement.

[0006] In view of the above circumstances, an object of the present invention is to provide a polyester film that is inhibited from generating wrinkles on its periphery when stored in a roll and that is inhibited from generating wrinkles when heated and transported. Another object of the present invention is to provide a laminate and a method for producing the polyester film.

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

[0008] [1] A polyester film having a thickness of 10 to 50 μm, which satisfies both of the following conditions A and B: Condition A: After heating a polyester film measuring 100 mm in length and 100 mm in width at 150°C for 30 minutes, the polyester film has a heat shrinkage rate of 1.40% or less. Condition B: After storing a polyester film measuring 100 mm in length and 100 mm in width in an environment of 40°C and 90% RH for 24 hours, the polyester film has a humidity expansion rate of 0.015% or less. [2] The polyester film according to [1], wherein after storing the polyester film in an environment of 40°C and 90% RH for 24 hours, the polyester film has a moisture content of 1,800 ppm by mass or less. [3] The polyester film according to [1] or [2], which has a crystallinity of 55.0 to 63.0%. [4] The polyester film according to any one of [1] to [3], wherein the polyester film is in a roll form, and after storing the rolled polyester film in an environment of 30°C and 70% RH for 10 days, the rolled polyester film has 10 or fewer wrinkles in an area of ​​100 m periphery × 0.3 m width. [5] The polyester film according to any one of [1] to [4], wherein the polyester film has a maximum protrusion height Sp of 100 nm or less on both sides. [6] The polyester film according to any one of [1] to [5], wherein the polyester film has a surface average roughness Sa of 5 nm or less on both sides. [7] The polyester film according to any one of [1] to [6], wherein the polyester film has a polyester substrate and a particle-containing layer on at least one surface of the polyester substrate. [8] The polyester film according to any one of [1] to [7], wherein the antimony content is 10 ppm by mass or less.[9] When the polyester film has a width of 100 cm or more and a length of 1000 m or more, and a surface region of the polyester film extending from one end in the width direction to 50 cm toward the other end is defined as a first surface region, and a surface region of the polyester film extending from the other end in the width direction to 50 cm toward the one end is defined as a second surface region, the number of fixed foreign particles containing nitrogen atoms and having a major axis of 50 μm or more in the first surface region and the second surface region is 1 particle / 500 m. ２The polyester film according to any one of [1] to [8], which is the following:

[10] A laminated film having the polyester film according to any one of [1] to [9] and a release layer.

[11] The laminated film according to

[10] , wherein the release layer is disposed on one of both surfaces of the polyester film having a lower maximum projection height Sp.

[12] A method for producing a polyester film having a thickness of 10 to 50 μm, comprising: Step A of biaxially stretching an unstretched polyester film to obtain a biaxially oriented polyester film, heating the film to 235 to 245°C, and then heat-relaxing the film at 205 to 225°C; and Step B of cooling the film heat-relaxed in Step A at a cooling rate of 1500°C / min or less, wherein in Step B, the heat-relaxed film is expanded in the width direction at an expansion rate of more than 0% and less than 0.20%.

[13] The method for producing a polyester film according to

[12] , wherein the polyester film is a polyester film having a polyester substrate and a particle-containing layer containing particles on at least one surface of the polyester substrate, and further comprises, before step A, an extrusion molding step of extruding a molten resin containing polyester into a film shape to form the unstretched polyester film containing at least the polyester substrate, a longitudinal stretching step of stretching the unstretched polyester film in a conveying direction to form a uniaxially oriented polyester film, and a transverse stretching step of stretching the uniaxially oriented polyester film in a width direction to form the biaxially oriented polyester film, and further comprises, between the longitudinal stretching step and the transverse stretching step, a step of forming the particle-containing layer using a coating liquid containing the particles, or further comprises, in the extrusion molding step, a step of forming the particle-containing layer by extruding a second melt containing the particles and a binder together with the molten resin.

[14] The method for producing a polyester according to

[12] or

[13] , wherein in step B, both widthwise ends of the heat-relaxed film are gripped with clips, and the clips come into contact with contact members to close the clips, thereby gripping the heat-relaxed film with the clips, and the contact members contain a resin having a melting temperature of 250°C or higher.

[0009] According to the present invention, it is possible to provide a polyester film that is suppressed from generating wrinkles on its outer periphery when stored in a rolled state and that is also suppressed from generating wrinkles when heated and transported. Furthermore, according to the present invention, it is also possible to provide a laminate and a method for producing the polyester film.

[0010] 1 is a cross-sectional view schematically showing an example of the configuration of the polyester film of the present invention; 2 is an observation image of a polyester film in which wrinkles have occurred; 3 is a schematic diagram showing an example of a stretching machine used for producing a polyester film; and 4 is a schematic diagram showing an example of the configuration of a clip provided in the stretching machine.

[0011] Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments and can be practiced with appropriate modifications within the scope of the object of the present invention.

[0012] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples. In this specification, when multiple substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified. In this specification, the term "step" includes not only independent steps, but also steps that cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved. In this specification, a combination of two or more preferred aspects is a more preferred aspect.

[0013] In this specification, the mere term "polyester film" encompasses both a polyester substrate alone and a laminate of a polyester substrate and a particle-containing layer. In this specification, "longitudinal direction" refers to the longitudinal direction of a polyester film during production, and is synonymous with "conveyance direction," "machine direction," and "MD direction." In this specification, "width direction" and "TD direction" refer to directions perpendicular to the longitudinal direction. In this specification, "perpendicular" does not necessarily mean strictly perpendicular, but also includes approximately perpendicular. "Approximately perpendicular" means intersecting at 90°±5°, preferably at 90°±3°, and more preferably at 90°±1°. In addition, in this specification, "film width" refers to the distance between both ends of the polyester film in the width direction. In this specification, "edge" refers to the region including one edge of the film in the width direction and its vicinity.

[0014] In this specification, the width direction of a polyester film can also be determined by measuring the refractive index of the polyester film using an Abbe refractometer. Details of this determination method are provided below. First, a polyester film is cut to obtain a 6 mm x 6 mm square sample 1. Next, the prism of an Abbe refractometer (for example, an "Abbe Refractometer NAR-4T" manufactured by Atago Rikagaku Glass Manufacturing Co., Ltd.) is removed and the sample 1 is placed so that the measurement surface of the sample 1 is in contact with the prism and the measurement direction is perpendicular to the light source. To improve the contact between the measurement surface of the sample 1 and the prism, a methylene iodide solution is used as an intermediate liquid. Next, the sample 1 is rotated in 10° increments from 0 to 180° using the Abbe refractometer, and the refractive index is measured at 10° increments from 0 to 180° for the front surface (one side) of the sample 1. The refractive index value is read to four decimal places. The refractive index of the back surface (the other surface) of Sample 1 is also measured by the above method in 10-degree increments from 0 to 180° in the same direction as the direction measured on the front surface of Sample 1. The average value of the refractive indexes measured in this way in the same direction on the front and back surfaces is calculated, and the direction showing the largest average value of the refractive indexes in 10-degree increments from 0 to 180° is defined as the width direction of Sample 1. The direction of the polyester film corresponding to the width direction of Sample 1 is defined as the width direction of the polyester film.

[0015] [Polyester Film] The polyester film of the present invention (hereinafter also referred to as "the film") is a polyester film having a thickness of 10 to 50 μm, and satisfies both of the following conditions A and B. Condition A: After a 100 mm long x 100 mm wide film of the present invention is heated at 150°C for 30 minutes, the heat shrinkage rate of the film is 1.40% or less. Condition B: After a 100 mm x 100 mm wide film of the present invention is stored in an environment of 40°C and 90% RH for 24 hours, the humidity expansion rate of the film is 0.015% or less. The film of the present invention is preferably a polyester film produced by the "method for producing a polyester film" described below.

[0016] [Structure] The present film preferably has a polyester substrate. The present film may have a single-layer structure consisting of only a polyester substrate formed using a polyester melt, or a multilayer structure having a polyester substrate and a particle-containing layer (i.e., a layer containing particles) containing particles. However, it is more preferable for the present film to have a polyester substrate and the particle-containing layer. The particle-containing layer may be formed on only one surface of the polyester substrate, or on both surfaces of the polyester substrate. The present film may be in the form of a roll obtained by winding up a polyester film.

[0017] Preferably, at least one side of the present film has an uneven surface, and more preferably, only one side has an uneven surface. Here, the uneven surface refers to a surface with a relatively large maximum projection height Sp in the present film, in which the maximum projection height Sp differs between the two surfaces, and a surface with a relatively small maximum projection height Sp is referred to as a "smooth surface." The maximum projection height Sp of the smooth surface is also referred to as "Sp1," and the maximum projection height Sp of the uneven surface is also referred to as "Sp2." FIG. 1 is a cross-sectional view schematically illustrating an example of the configuration of the present film. The polyester film 300 according to this embodiment shown in FIG. 1 has a smooth surface 301 and an uneven surface 302. In the illustrated polyester film 300, the maximum projection height Sp1 of the smooth surface 301 is smaller than the maximum projection height Sp2 of the uneven surface 302. In the film 300 having different maximum projection heights Sp on both surfaces, a functional layer can be laminated on the smooth surface 301 during the production of the laminate film, thereby suppressing transfer marks during storage of the laminate film. Furthermore, since the maximum projection height Sp2 of the uneven surface 302 is relatively large, the slipperiness of the uneven surface 302 is improved, and the transportability of the polyester film and the laminated film can be improved and winding failure can be reduced. The preferred range of the maximum projection height Sp of the present film and the method for measuring it will be described later.

[0018] The smooth surface may be one surface of the polyester substrate, or the surface of another resin layer formed on the surface of the polyester substrate. The maximum projection height Sp1 of the smooth surface can be adjusted, for example, by selecting the type of polyester and the type of additive that constitute the polyester substrate so as to form a smooth film without substantially incorporating particles into the polyester substrate.

[0019] The uneven surface may be the other surface of the polyester substrate or one surface of the particle-containing layer. The maximum projection height Sp2 of the uneven surface can be adjusted, for example, by the following methods: (1) A particle-containing layer is formed on one surface of the polyester substrate, and the height is adjusted by adjusting the size and amount of particles contained in the particle-containing layer and the thickness of the particle-containing layer. Methods for forming the particle-containing layer include forming a coating layer of a particle-containing composition and co-extruding a polyester melt with a second melt containing particles and a binder. (2) Particles are incorporated into the polyester substrate, and the height is adjusted by adjusting the size and amount of the particles. (3) One surface of the polyester substrate is physically treated to make it rough. Examples of physical treatments include plasma treatment. This 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.

[0020] The polyester substrate and the particle-containing layer are each described in more detail below.

[0021] <Polyester substrate> The polyester substrate is a film-like object containing a polyester as the main polymer component. Here, the "main polymer component" refers to the polymer that is contained in the film in the largest amount (by mass). The polyester substrate may contain one type of polyester alone, or may contain two or more types of polyester.

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

[0023] The intrinsic viscosity (IV) of the present film is preferably 0.50 dl / g or more but less than 0.80 dl / g, more preferably 0.55 dl / g or more but less than 0.70 dl / g, and even more preferably 0.60 dl / g or more but less than 0.70 dl / g. The amount of terminal carboxyl groups (terminal COOH content, AV; Acid Value) of the present 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 the terminal COOH content, the more likely the water content is to decrease. The lower limit is, for example, 0.5 eq / ton or more. In this specification, "eq / ton" represents the molar equivalent per ton. Details of the methods for measuring the intrinsic viscosity and terminal COOH content of the present film are as described in the Examples section below. The melting point (Tm) of the polyester is preferably 220 to 270° C., more preferably 245 to 265° C. The glass transition temperature (Tg) of the polyester is preferably 65 to 90° C., more preferably 70 to 85° C.

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

[0025] -Catalyst- The catalyst used in the production of polyester is not particularly limited, and known catalysts that can be used in the synthesis of polyesters can be used. Examples of catalysts include alkali metal compounds (e.g., potassium compounds, sodium compounds), alkaline earth metal compounds (e.g., calcium compounds, magnesium compounds), zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, germanium compounds, and phosphorus compounds. Among these, titanium compounds and aluminum compounds are preferred because they are less likely to produce foreign matter in the polyester base material. A single catalyst may be used, or two or more catalysts 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 a combination of catalysts, it is preferable to adopt the types and contents of each compound described in paragraphs 0055 to 0062 of Japanese Patent No. 5,575,671. In the present film, when the content of the titanium compound is 5 to 15 mass ppm in terms of Ti element, the content of the magnesium compound is preferably 60 to 90 mass ppm in terms of Mg element, and the content of the phosphorus compound is preferably 5 to 35 mass ppm in terms of P element.

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

[0027] Examples of the aluminum compound include organoaluminum compounds and partial hydrolysates thereof. The organoaluminum compound is preferably a carboxylate, an inorganic acid salt, or a chelate compound, and more preferably aluminum acetate, basic aluminum acetate, aluminum lactate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride, or aluminum acetylacetonate.

[0028] -Dicarboxylic Acid Compound- The dicarboxylic acid compound is preferably a dicarboxylic acid or a dicarboxylic acid ester, and examples thereof include an aliphatic dicarboxylic acid compound, an alicyclic dicarboxylic acid compound, an aromatic dicarboxylic acid compound, and a methyl ester or ethyl ester thereof. Among these, an aromatic dicarboxylic acid or an aromatic methyl dicarboxylate is more preferred.

[0029] Examples of the aliphatic dicarboxylic acid compound include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosanedioic acid, pimelic acid, azelaic acid, methylmalonic acid, and ethylmalonic acid. Examples of the alicyclic dicarboxylic acid compound include adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, and decalindicarboxylic acid.

[0030] Examples of aromatic dicarboxylic acid compounds include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodiumsulfoisophthalic acid, phenylindanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, 9,9'-bis(4-carboxyphenyl)fluorene acid, and methyl esters thereof. Among these, terephthalic acid or 2,6-naphthalenedicarboxylic acid is preferred, and terephthalic acid is more preferred.

[0031] The dicarboxylic acid compound may be used alone or in combination of two or more. When terephthalic acid is used as the dicarboxylic acid compound, terephthalic acid may be used alone or may be copolymerized with other aromatic dicarboxylic acids such as isophthalic acid or aliphatic dicarboxylic acids.

[0032] -Diol Compound- Examples of the diol compound include aliphatic diol compounds, alicyclic diol compounds, and aromatic diol compounds, with aliphatic diol compounds being preferred.

[0033] Examples of aliphatic diol compounds include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and neopentyl glycol, with ethylene glycol being preferred. Examples of alicyclic diol compounds include cyclohexanedimethanol, spiroglycol, and isosorbide. Examples of aromatic diol compounds include bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, and 9,9'-bis(4-hydroxyphenyl)fluorene. Only one type of diol compound may be used, or two or more types may be used in combination.

[0034] -End-capping agent- In the production of polyester, an end-capping agent may be used as needed. By using the end-capping agent, a structure derived from the end-capping agent is introduced into the end of the polyester. The end-capping agent is not limited, and known end-capping agents can be used. Examples of the end-capping agent include oxazoline compounds, carbodiimide compounds, and epoxy compounds. For end-capping agents, reference can also be made to the contents of paragraphs 0055 to 0064 of JP 2014-189002 A, the contents of which are incorporated herein by reference.

[0035] -Production conditions- The reaction temperature is not limited and may be set appropriately depending on the raw materials. The reaction temperature is preferably 260 to 300°C, more preferably 275 to 285°C. The pressure is not limited and may be set appropriately depending on the raw materials. The pressure is not limited and may be set appropriately depending on the raw materials. －３ ~1.33 x 10 －５ MPa is preferred, and 6.67 × 10 －４ ~6.67 x 10 －５ MPa is more preferred.

[0036] As a method for synthesizing polyester, the method described in paragraphs 0033 to 0070 of Japanese Patent No. 5575671 can also be used, and the contents of the above publication are incorporated herein by reference.

[0037] 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.

[0038] When the polyester substrate contains a polyester formed from ethylene glycol and a dicarboxylic acid, the content of the polyester formed from ethylene glycol and a dicarboxylic acid (hereinafter also referred to as "specific polyester") is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total mass of the polyesters in the polyester substrate. The upper limit of the content of the specific polyester is preferably 100% by mass, based on the total mass of the polyesters in the polyester substrate.

[0039] When the polyester base material contains polyethylene terephthalate, the content of polyethylene terephthalate is preferably 90 to 100 mass %, more preferably 95 to 100 mass %, still more preferably 98 to 100 mass %, and particularly preferably 100 mass % (i.e., the polyester base material is a polyethylene terephthalate base material) relative to the total mass of polyester in the polyester base material.

[0040] The polyester substrate may contain components other than polyester (for example, a catalyst, unreacted raw material components, water, etc.).

[0041] Preferably, the polyester substrate is substantially free of inorganic particles. The term "substantially free of inorganic particles" refers to the fact that, when the polyester substrate is quantitatively analyzed for elements derived from inorganic particles by fluorescent X-ray analysis, the content of inorganic particles is 50 mass ppm or less, preferably 10 mass ppm or less, and more preferably below the detection limit, relative to the total mass of the polyester substrate. This is because, even if inorganic particles are not actively added to the polyester substrate, contaminants derived from foreign matter, raw resins, or dirt adhering to the line or equipment in the polyester substrate manufacturing process may peel off and be mixed into the polyester substrate. Examples of inorganic particles include inorganic particles that may be contained in the particle-containing layer described below.

[0042] It is preferable that the polyester substrate is substantially free of particles. Examples of particles include the inorganic particles and organic particles described above. Whether or not the polyester substrate is substantially free of particles can be confirmed by the following procedure. Ten different locations on the cross section of the polyester substrate are observed using a scanning electron microscope to confirm the presence or absence of particles with a size of 10 nm to 10 μm in the cross section of the polyester substrate. The magnification during observation is adjusted to 5,000 to 20,000 times. If particles are observed in any location, this means that particles are contained in the release layer. On the other hand, if particles are not observed in any location on the cross section, this means that no particles are contained in the polyester substrate. Here, examples of organic particles include organic particles contained in the particle-containing layer described below.

[0043] The thickness of the polyester substrate is preferably 50 μm or less, more preferably 40 μm or less, in order to suppress an increase in haze value. There is no particular lower limit on the thickness, but from the viewpoint of improving strength and processability, it is preferably 10 μm or more, more preferably 15 μm or more. The thickness of the polyester substrate is measured according to the method for measuring the thickness of a polyester film described below.

[0044] <Particle-Containing Layer> The particle-containing layer is a layer containing particles, and is preferably formed on at least one surface of the polyester substrate. The particle-containing layer can form an uneven surface on the surface of the polyester film, thereby improving transportability. More specifically, it can improve winding quality (suppress blocking), suppress the occurrence of scratches and defects during transport, and reduce transport wrinkles. The particle-containing layer may be formed directly on the surface of the polyester substrate or on the surface of the polyester substrate via another layer, but is preferably formed directly on the surface of the polyester substrate because of its superior adhesion. The particle-containing layer is not particularly limited as long as it contains particles, the maximum protrusion height Sp on the surface of the present film satisfies the value described below, the thickness of the present film satisfies the value described below, and the present film satisfies conditions A and B described below. However, it is preferable that the particle-containing layer contains a binder in addition to the particles. The particle-containing layer may also contain additives other than the particles and binder.

[0045] Examples of particles contained in the particle-containing layer include organic particles and inorganic particles. Among these, inorganic particles are preferred from the viewpoint of further improving film winding quality, haze, and durability (e.g., thermal stability). Resin particles are preferred as organic particles. Examples of resins constituting the resin particles include acrylic resins such as polymethyl methacrylate resin (PMMA), polyester resins, silicone resins, and styrene-acrylic resins. Resin particles preferably have a crosslinked structure. Examples of resin particles having a crosslinked structure include divinylbenzene crosslinked particles (e.g., divinylbenzene / styrene copolymer crosslinked particles) having a crosslinked structure derived from divinylbenzene. Resin particles are preferred from the viewpoint of suppressing transfer marks. Examples of inorganic particles include silica particles (silicon dioxide particles), titania particles (titanium oxide particles), calcium carbonate, barium sulfate, and alumina particles (aluminum oxide particles). Among the above, silica particles are preferred as inorganic particles from the viewpoint of further improving haze and durability.

[0046] The shape of the particles is not particularly limited, and examples thereof include rice grain-like, spherical, cubic, spindle-like, scale-like, aggregated, and irregular shapes. "Aggregated" refers to a state in which primary particles are aggregated. The shape of the aggregated particles is not limited, but spherical or irregular shapes are preferred.

[0047] The particle-containing layer is preferably formed by in-line coating using a coating solution containing at least one of aggregated particles and non-aggregated particles, where aggregated particles refer to particles that are in an aggregated state in the coating solution, and non-aggregated particles refer to particles that are not in an aggregated state in the coating solution.

[0048] Preferred examples of the agglomerated particles include fumed silica particles. Available commercially available products include, for example, the Aerosil series manufactured by Nippon Aerosil Co., Ltd. Preferred examples of the non-agglomerated particles include colloidal silica particles. Available commercially available products include, for example, the Snowtex series manufactured by Nissan Chemical Industries, Ltd.

[0049] The particle-containing layer may contain one type of particle or two or more types of particles. From the viewpoints of improving the winding quality of the film and suppressing transfer defects, the particle content is preferably 0.01 to 20% by mass, more preferably 0.5 to 15% by mass, and even more preferably 1 to 10% by mass, relative to the total mass of the particle-containing layer. Furthermore, the particle content is preferably 0.0001 to 0.01% by mass, more preferably 0.0005 to 0.005% by mass, relative to the total mass of the polyester film.

[0050] The particle-containing layer preferably contains particles having an average particle diameter of 1 nm or more and less than 1 μm, from the viewpoint of improving winding quality and suppressing transfer failure. The average particle diameter of the particles is preferably 10 nm or more, more preferably 30 nm or more, from the viewpoint of further improving winding quality. Furthermore, the average particle diameter of the particles is preferably 0.4 μm or less, more preferably 0.25 μm or less, from the viewpoint of further suppressing transfer failure.

[0051] The average particle diameter of the particles contained in the particle-containing layer is determined by the following method using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Specifically, the cross section of the particle-containing layer is observed using the SEM or TEM, and the area of ​​each particle present in a 3 μm × 4 μm field of view is measured using image software. The diameter of a circle having the same area (equivalent-area diameter) is calculated, and the arithmetic mean of the resulting equivalent-area diameters is taken as the average particle diameter of the particles. In measuring the average particle diameter, for aggregated particles, the particle diameter of the secondary particles in the aggregated state (secondary particle diameter) is measured. Furthermore, when the particle-containing layer contains two or more types of particles with different particle diameters, the distribution of equivalent-area diameters measured by the above measurement method will show two or more peaks representing different particle diameters. In this way, when the distribution of equivalent circle area diameters measured by the above-mentioned measurement method has two or more peaks of different particle diameters, the average value of the equivalent circle area diameters is calculated for each peak, and the average particle diameter is calculated for each particle with a different particle diameter.

[0052] (Binder) The particle-containing layer preferably contains a binder. The binder is preferably a resin binder. Examples of the resin binder include acrylic resin, urethane resin, polyester resin, and olefin resin. Non-polyester resins are preferred, and specifically, acrylic resin, urethane resin, or olefin resin is preferred. Known resins can be used as the binder. The resin binder may be an acid-modified resin. The binder contained in the particle-containing layer may have a crosslinked structure. That is, the particle-containing layer may be a crosslinked film.

[0053] The particle-containing layer may contain one type of binder or two or more types of binders. From the viewpoint of durability of the particle-containing layer and / or particle dispersibility, the content of the binder is preferably 30 to 99.8% by mass, more preferably 50 to 99.5% by mass, based on the total mass of the particle-containing layer.

[0054] (Additives) The particle-containing layer may contain additives other than the above-described particles and binder. Examples of additives contained in the particle-containing layer include surfactants, waxes, crosslinking agents, antioxidants, ultraviolet absorbers, colorants, reinforcing agents, plasticizers, antistatic agents, flame retardants, rust inhibitors, and antifungal agents.

[0055] The thickness of the particle-containing layer is preferably 0.001 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, and is preferably 1 to 15 μm, and more preferably 1 to 10 μm. The thickness of the particle-containing layer is determined by preparing a slice having a cross section along the thickness direction of the polyester film and measuring the thicknesses of five points on the slice using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0056] The method for forming the particle-containing layer will be described in detail in the "Particle-containing layer forming step" below.

[0057] The present film may have layers other than the polyester substrate and the particle-containing layer, but preferably consists of a polyester substrate and a particle-containing layer. Also, the present film preferably has only one particle-containing layer formed on one surface of the polyester substrate.

[0058] [Physical Properties, etc.] Next, the physical properties, etc. of the present film will be described.

[0059] <Heat Shrinkage (Condition A)> After heating a 100 mm long x 100 mm wide film at 150°C for 30 minutes, the heat shrinkage of the film is 1.40% or less, preferably 1.30% or less. Thus, the film exhibits a tendency to shrink less when exposed to a high-temperature environment. Here, when providing a functional layer, etc., described below, on the film, the film may be transported while heated. Even in such cases, shrinkage due to heating is less likely to occur, thereby suppressing the occurrence of wrinkles. The lower limit of the heat shrinkage of the film is preferably 0.00% or more, more preferably 0.40% or more, and even more preferably 0.50% or more, in order to suppress the occurrence of wrinkles on the periphery. Details of the method for measuring the heat shrinkage of the film are as described in the Examples section below.

[0060] The heat shrinkage rate of the present film can be adjusted to fall within the above range by, for example, setting various conditions in the production process of the present film, such as the heating temperature in the heat setting step of step A, the heating temperature in the heat relaxation step of step A, the cooling rate in step B (cooling step), and the expansion rate in step B (cooling step), to the conditions shown in the production method of the present film described below.

[0061] <Humidity Expansion Coefficient (Condition B)> After storing a 100 mm long, 100 mm wide film of the present invention in an environment of 40°C and 90% RH for 24 hours, the humidity expansion coefficient of the present film is 0.015% or less, preferably 0.013% or less, and more preferably 0.010% or less. Thus, the present film exhibits a tendency to be resistant to expansion when exposed to a high-humidity environment. Therefore, even when the present film is stored in a rolled form, it is resistant to expansion due to moisture absorption, thereby suppressing the occurrence of wrinkles on the periphery. The lower limit of the humidity expansion coefficient of the present film is preferably −0.100% or more, more preferably −0.050% or more, in order to suppress wrinkles during heating and transport in the subsequent process. Details of the method for measuring the humidity expansion coefficient of the present film are described in the Examples section below.

[0062] The wet thermal expansion coefficient of the present film can be adjusted to fall within the above range by, for example, setting various conditions in the production process of the present film, such as the heating temperature in the heat setting step of step A, the heating temperature in the heat relaxation step of step A, the cooling rate in step B (cooling step), and the expansion rate in step B (cooling step), to the conditions shown in the production method of the present film described below.

[0063] <Moisture Content> After storing the present film for 24 hours in an environment of 40°C and 90% RH, the moisture content of the present film is preferably 1800 mass ppm or less, more preferably 1780 mass ppm or less, and even more preferably 1750 mass ppm or less, in order to further suppress the occurrence of wrinkles on the periphery when stored in a rolled form. The lower limit of the moisture content of the present film is not particularly limited and may be 0 mass ppm, but is often 100 mass ppm or more. In order to adjust the crystallinity appropriately, 1600 mass ppm or more is preferred. Details of the method for measuring the moisture content of the present film are as described in the Examples section below.

[0064] The moisture content of the present film can be adjusted to the above range by, for example, setting various conditions in the production process of the present film, such as the heating temperature in the heat setting step of step A, the heating temperature in the heat relaxation step of step A, the cooling rate in step B (cooling step), and the expansion rate in step B (cooling step), to the conditions shown in the production method of the present film described below.

[0065] <Crystallization degree> The crystallinity of the present film is preferably 55.0 to 63.0% in order to obtain better effects of the present invention. Since the occurrence of wrinkles on the periphery is further suppressed when the film is stored in a rolled form, the crystallinity is preferably 55.0% or more, more preferably 55.5% or more, and even more preferably 56.0% or more. There is no particular upper limit, but it is preferably 63.0% or less, more preferably 62.0% or less, and even more preferably 60.0% or less. Details of the method for measuring the crystallinity of the present film are as described in the Examples section below.

[0066] The crystallinity of the present film can be adjusted to the above range by, for example, setting various conditions in the production process of the present film, such as the heating temperature in the heat setting step of step A, the heating temperature in the heat relaxation step of step A, the cooling rate in step B (cooling step), and the expansion rate in step B (cooling step), to the conditions shown in the production method of the present film described below.

[0067] <Maximum Projection Height Sp, Maximum Height St, Surface Average Roughness Sa> The maximum projection height Sp on both sides of the present film is preferably 150 nm or less, more preferably 100 nm or less, even more preferably less than 90 nm, and particularly preferably less than 60 nm, in order to suppress the occurrence of transfer marks on the surface of a release layer when a release layer is provided on the present film. The lower limit of the maximum projection height Sp on both sides of the present film is not particularly limited, but is often 1 nm or more. The present film preferably has one smooth surface and the other rough surface. When the present film has a smooth surface and a rough surface, the maximum projection height Sp1 on the smooth surface is preferably 60 nm or less, more preferably less than 35 nm, in order to ensure a uniform thickness of a functional layer such as a release layer when provided thereon. The lower limit is not particularly limited, but is often 1 nm or more. The maximum protrusion height Sp2 of the uneven surface is preferably 150 nm or less, more preferably 100 nm or less, even more preferably 80 nm or less, and particularly preferably less than 60 nm, from the viewpoint of suppressing the occurrence of transfer marks on the surface of a release layer when a release layer is provided on the present film. The lower limit is often 1 nm or more, but from the viewpoint of transportability and reduction of winding failure, it is preferably 5 nm or more, more preferably 10 nm or more.

[0068] The maximum height St on both sides of the present film is preferably 150 nm or less, more preferably 100 nm or less, even more preferably less than 60 nm, and particularly preferably less than 50 nm, in order to prevent transfer marks from occurring on the surface of a release layer when a release layer is provided on the present film. The lower limit of the maximum height St on both surfaces is not particularly limited and may be, for example, 1 nm or more. When the present film has a smooth surface and a rough surface, the maximum height St1 of the smooth surface is preferably less than 150 nm, preferably less than 50 nm, and more preferably 30 nm or less, in order to ensure a uniform thickness of the functional layer when a release layer or other functional layer is provided. The lower limit of the maximum height St is not particularly limited and may be, for example, 1 nm or more. The maximum height St2 of the rough surface is preferably 150 nm or less, more preferably 100 nm or less, and even more preferably less than 50 nm, in order to prevent transfer marks from occurring on the surface of the release layer when a release layer is provided on the present 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.

[0069] The surface average roughness Sa on both sides of the present film is preferably 10 nm or less, more preferably 5 nm or less, even more preferably 4 nm or less, and particularly preferably 3 nm or less, from the viewpoint of suppressing the occurrence of transfer marks on the surface of a release layer when a release layer is provided on the present film. The lower limit of the surface average roughness Sa on both sides of the present film is not particularly limited and may be 0 nm. When the present film has a smooth surface and an uneven surface, the surface average roughness Sa1 of the smooth surface is preferably 10 nm or less, more preferably 5 nm or less, and even more preferably 3 nm or less. The lower limit may be 0 nm or more. From the viewpoint of suppressing the occurrence of transfer marks on the surface of a release layer when a release layer is provided on the present film, 0 to 1 nm is most preferable. The surface average roughness Sa2 of the uneven surface is preferably 10 nm or less, more preferably 5 nm or less, and even more preferably 3 nm. The lower limit may be 0 nm or more, but from the viewpoints of transportability and reducing winding failures, it is preferably 1 nm or more, and more preferably 2 nm or more. From the viewpoint of achieving both improvement in winding quality and suppression of transfer marks, a thickness of 2 to 3 nm is most preferable.

[0070] Here, when the present film has a polyester substrate and a particle-containing layer on one surface of the polyester substrate, one of the two surfaces of the present film is the surface of the particle-containing layer, and the other surface is the surface of the polyester substrate on the side where the particle-containing layer is not disposed. When one of the two surfaces of the present film is the surface of the particle-containing layer, the maximum protrusion height Sp2 and average surface roughness Sa2 of the particle-containing layer can be adjusted, for example, by the average particle size and content of the particles contained in the particle-containing layer and the thickness of the particle-containing layer. When the particle-containing layer is formed by coating, the above adjustments can be made more easily. When the other surface of the present film is the surface of the polyester substrate on the side where the particle-containing layer is not disposed, the maximum protrusion height Sp1 and average surface roughness Sa1 of the other surface can be adjusted by selecting the type of polyester and the type of additives constituting the polyester substrate so that the polyester substrate is substantially particle-free and can be formed into a smooth film (e.g., by using a polyester resin polymerized with a titanium compound or an aluminum compound).

[0071] When the present film is constructed by incorporating particles into a polyester substrate, the maximum projection height and other properties can be adjusted by the particle size and amount added. The particles can be the same as those contained in the particle-containing layer. Multiple layers of particle-containing polyester substrates can be formed. When the present film is roughened by physically treating one surface of the polyester substrate (roughening treatment), the maximum projection height and other properties of the uneven surface can be adjusted by appropriately adjusting the conditions of the roughening treatment.

[0072] The maximum protrusion height, average surface roughness, and maximum height on both sides of the film are measured using an optical interferometer (e.g., a Vertscan 3300G Lite manufactured by Hitachi High-Technologies Corporation) under the conditions described in the Examples section, and then analyzed using the built-in data analysis software to determine the maximum protrusion height, average surface roughness, and maximum height on both sides of the film. Specific measurement methods and conditions for the above physical properties are described in the Examples section below.

[0073] <Orientation> The present film is preferably a biaxially oriented polyester film (hereinafter also referred to as "biaxially oriented film"). In this specification, "biaxial orientation" means the property of having molecular orientation in two axial directions. The molecular orientation is measured using a microwave transmission type molecular orientation meter (for example, MOA-6004, manufactured by Oji Scientific Instruments Co., Ltd.). The angle between the two axial directions is preferably 90°±5°, more preferably 90°±3°, and even more preferably 90°±1°. The present film preferably has molecular orientation in the longitudinal direction and the width direction.

[0074] <Number of Wrinkles on the Outer Circumference of Roll> When the present film is in a roll form, after storing the roll form of the present film in an environment of 30°C and 70% RH for 10 days, the number of wrinkles present in an area of ​​100 m on the outer periphery × 0.3 m in width of the roll form of the present film is preferably 10 or less, more preferably 0 to 10, and even more preferably 0. The area of ​​100 m on the outer periphery × 0.3 m in width of the roll form of the present film refers to an area 100 m long and 0.3 m wide from the end of winding to the beginning of winding of the roll form of polyester film.

[0075] As used herein, "wrinkles" refers to wavy wrinkles that appear on the outermost periphery of a rolled film. As described below, wrinkles occur on films after production, and therefore are often irreversible. The wrinkles are not generated during the heat treatment process during film production, but rather are wavy wrinkles that occur when the film is stored in a rolled state. These wrinkles do not occur in rolls from which a 100-m-long outer peripheral portion of the film along the longitudinal direction has been removed, from the end (outermost periphery) of the rolled film to the beginning of the roll. However, if this 100-m-long outer peripheral portion of the film is removed and the rolled film is stored again for 10 days in an environment of 30°C and 70% RH, the wrinkles reappear. It is believed that the wrinkles are generated by humidity expansion of the film during storage of the rolled film.

[0076] Figure 2 shows an image (photograph) of a polyester film in which wrinkles were observed after storage for 10 days in an environment of 30°C and 70% RH. Wrinkles can be seen in the area surrounded by the solid line in Figure 2. The area surrounded by the solid line in Figure 2 has a wavy (uneven) shape along the TD direction. Note that the image (photograph) shown in Figure 2 shows only a portion of the observation area.

[0077] The method for measuring the number of wrinkles on the outer periphery of the roll of the present film is described in detail in the Examples section below.

[0078] The number of wrinkles on the outer periphery of the roll of the present film in roll form can be adjusted to the above range by, for example, setting various conditions in the production process of the present film, such as the heating temperature in the heat setting step of step A, the heating temperature in the heat relaxation step of step A, the cooling rate in step B (cooling step), and the expansion rate in step B (cooling step), to the conditions shown in the production method of the present film described below.

[0079] <Wrinkles on the roll exterior> When the present film is in a roll form, it is preferable that no wrinkles are found on the exterior when the rolled film is stored for 10 days in an environment of 30°C and 70% RH and then the exterior of the rolled film is observed. Wrinkles on the roll exterior refer to wrinkles on the exterior of the roll that are found without unwinding the film from the roll. The definition of wrinkles on the exterior of the present rolled film is the same as the wrinkles explained in the section "Number of wrinkles on the outer periphery of the roll." Details of the method for measuring the number of wrinkles on the exterior of the present rolled film are as described in the Examples section below.

[0080] The occurrence of wrinkles in the roll appearance of the present roll-shaped film can be suppressed by, for example, setting various conditions in the production process of the present film, such as the heating temperature in the heat setting step of step A, the heating temperature in the heat relaxation step of step A, the cooling rate in step B (cooling step), and the expansion rate in step B (cooling step), to the conditions shown in the production method of the present film described below.

[0081] <Antimony Content> The content of antimony (Sb) in the present 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, from the viewpoint of further suppressing the generation of foreign matter. The lower limit of the antimony content in the present film is 0 ppm by mass. Details of the method for measuring the antimony content in the present film are as described in the Examples section below. The antimony content can be adjusted to the above range by using a catalyst other than an antimony compound in the production of the polyester contained in the polyester base material. For methods of reducing the antimony content, reference can also be made to the contents of paragraphs 0023 to 0046 of WO 2023 / 149181, the contents of which are incorporated herein by reference.

[0082] <Specific foreign matter> When the present film has a width of 100 cm or more and a length of 1000 m or more, the surface region from one end of the present film in the width direction toward the other end to 50 cm is defined as a first surface region, and the surface region from the other end of the present film in the width direction toward the one end to 50 cm is defined as a second surface region, and the number of fixed foreign matters containing nitrogen atoms with a major axis of 50 μm or more (hereinafter also referred to as "specific foreign matter") in the first surface region and the second surface region is 1 / 500 m. ２ It is preferable that the number of specific foreign matters in the first surface region and the second surface region is 1 / 500 m or less. ２ If the number of specific foreign matters is less than 50 μm, a polyester film with fewer protrusions on the surface can be produced. Here, "adhering" foreign matters to the surface of the polyester film means that foreign matters such as molten resin adhere to the surface of the polyester film and are not transferred even when contacted with an adhesive roll. "Adhered foreign matters" refers to foreign matters adhering to the surface of the polyester film. "Specific foreign matters" refers to adhering foreign matters containing nitrogen atoms with a major axis of 50 μm or more. There is no particular lower limit for the number of specific foreign matters in the first surface region and the second surface region of the present film, and it is not particularly limited to 0 / 500 m. ２ may be.

[0083] The number of specific foreign matter in the first surface area and the second surface area is 1 / 500m ２The polyester film described below can be produced, for example, by performing a transverse stretching step using a stretching device equipped with a contact member containing a resin having a melting temperature of 250° C. or higher as the contact member for closing the clip. By using such a contact member, even if small pieces originating from the contact member come into contact with the polyester film when the film is brought into contact with the clip, the small pieces are less likely to melt during the subsequent heat treatment, and it is presumed that the number of specific foreign matters on the surface of the polyester film can be reduced.

[0084] The specific foreign matter preferably contains a component different from the polyester contained in the present film (i.e., the polyester contained in the polyester substrate). The substances constituting the specific foreign matter can be analyzed by measuring the surface of the present film using energy dispersive X-ray spectrometry (EDS). Details of the method for measuring the number of specific foreign matters are as described in the Examples section below.

[0085] <Thickness> The thickness of the present film is 10 to 50 μm, preferably 10 to 40 μm, more preferably 15 to 40 μm, and even more preferably 15 to 35 μm. When the thickness of the present film is within the above range, cost is excellent. The thickness of the present film is the arithmetic average of the thicknesses measured at five locations using a scanning electron microscope (SEM).

[0086] [Method for Producing Polyester Film] The polyester film production method of the present invention (hereinafter also referred to as "the present production method") is a method for producing a polyester film having a thickness of 10 to 50 μm, and includes the following steps A and B. Step A is a step of biaxially stretching an unstretched polyester film to obtain a biaxially oriented polyester film, heating the resulting film to 235 to 245°C, and then heat-relaxing the film at 205 to 225°C. Step B includes a treatment of cooling the film heat-relaxed in step A at a cooling rate of 1500°C / min or less, and a treatment of expanding the heat-relaxed film in the width direction at an expansion ratio of more than 0% and less than 0.20%. The polyester film obtained by this production method has the characteristics of the present film described above. Therefore, this production method is suitable for producing the present film described above.

[0087] The polyester film obtained by this production method is prevented from wrinkles on the periphery when stored in a roll, and also from wrinkles when heated and transported. The details of the reason for this are unclear, but it is generally assumed as follows. It is believed that by performing the above-mentioned steps A and B under the above-mentioned conditions, the crystallinity of the polyester film is improved and amorphous regions with large residual strain are reduced. As a result, it is believed that shrinkage due to heating (thermal shrinkage rate) and dimensional change due to humidity (humidity expansion rate) are also reduced.

[0088] The polyester film obtained by this production method is preferably a polyester film having a polyester substrate and a particle-containing layer containing particles on at least one surface of the polyester substrate. In this case, the production method further comprises, before step A, an extrusion molding step of extruding a molten resin containing polyester into a film shape to form an unstretched polyester film containing at least the polyester substrate, a longitudinal stretching step of stretching the unstretched polyester film in the machine direction to form a uniaxially oriented polyester film, and a transverse stretching step of stretching the uniaxially oriented polyester film in the width direction to form the biaxially oriented polyester film. Preferably, the production method further comprises, between the longitudinal stretching step and the transverse stretching step, a step of forming the particle-containing layer using a coating liquid containing the particles, or a step of forming the particle-containing layer in the extrusion molding step by extruding a second melt containing the particles and a binder together with the molten resin.

[0089] Each step that may be included in this manufacturing method will be described below.

[0090] [Extrusion Molding Step] The present production method may include an extrusion molding step. The extrusion molding step is a step in which a molten resin containing a raw material polyester is extruded into a film shape by extrusion molding to form an unstretched polyester film. The raw material polyester has the same meaning as the polyester described above in the "Polyester" section. The unstretched polyester film formed by the extrusion molding step includes at least a polyester base material.

[0091] The extrusion molding method is a method of molding a raw material resin into a desired shape by extruding a melt of the raw material resin using, for example, an extruder. A molten resin containing a polyester is formed, for example, by using an extruder equipped with one or more screws to heat the polyester to a temperature above its melting point and then melt-kneading the polyester by rotating the screws. The polyester is melted in the extruder by heating and kneading with the screws to form a melt.

[0092] The melt is extruded through an extrusion die via a gear pump, a filter, etc. The extrusion die is also simply referred to as a "die" (see JIS B8650:2006, a, Extrusion Molding Machine, No. 134). For example, the extrusion die described in JP-A-2005-297266, the extrusion die described in JP-A-1-154720, or a combination thereof can be used. The melt may be extruded in a single layer or in multiple layers.

[0093] In the melt extrusion, the atmosphere inside the extruder is preferably replaced with nitrogen in order to suppress thermal decomposition (e.g., hydrolysis of the polyester) in the extruder. Furthermore, the extruder is preferably a twin-screw extruder in order to keep the kneading temperature low.

[0094] The melt extruded from the extrusion die is cooled and formed into a film. For example, the melt can be formed into a film by contacting the melt with a casting roll and cooling and solidifying the melt on the casting roll. In cooling the melt, it is preferable to further blow air (preferably cold air) on the melt.

[0095] The temperature of the casting roll is preferably above (Tg-10)°C and not higher than (Tg+30)°C, more preferably from (Tg-7) to (Tg+20)°C, and even more preferably from (Tg-5) to (Tg+10)°C. The "Tg" mentioned above refers to the glass transition temperature of the polyester constituting the film. Here, the temperatures of the polyester film and each member in this production method can be measured using a non-contact thermometer (e.g., a radiation thermometer). The surface temperature of the film is determined by measuring the temperature at the center of the film in the width direction five times and calculating the average of the obtained measurements.

[0096] When a casting roll is used in the extrusion molding process, it is preferable to increase the adhesion between the casting roll and the melt. Methods for increasing the adhesion include, for example, an electrostatic application method, an air knife method, an air chamber method, a vacuum nozzle method, and a touch roll method.

[0097] The molded product (unstretched polyester film) cooled using a casting roll or the like is peeled off from the cooling member such as the casting roll using a peeling member such as a peeling roll.

[0098] [Stretching Step] The present production method preferably includes a stretching step. In the stretching step, biaxial stretching is preferably performed. The biaxial stretching may be simultaneous biaxial stretching in which longitudinal stretching and transverse stretching are performed simultaneously, or may be sequential biaxial stretching in which longitudinal stretching and transverse stretching are performed in two or more stages. Examples of sequential biaxial stretching include longitudinal stretching → transverse stretching, longitudinal stretching → transverse stretching → longitudinal stretching, longitudinal stretching → longitudinal stretching → transverse stretching, and transverse stretching → longitudinal stretching, with longitudinal stretching → transverse stretching being preferred. One suitable embodiment of the stretching step is an embodiment including the longitudinal stretching step and the transverse stretching step described below.

[0099] <Stretching Machine> The device used for biaxial stretching is not particularly limited, and a known stretching machine can be used. An example of the stretching machine will be described below with reference to the drawings.

[0100] FIG. 3 is a plan view showing an example of a stretching machine used in the production of polyester films. The stretching machine 100 shown in FIG. 3 includes a pair of annular rails 60a and 60b and gripping members 2A to 2L attached to each annular rail and movable along the rails. The annular rails 60a and 60b are arranged symmetrically with respect to each other, sandwiching the film 200. The stretching machine 100 grips the film 200 with the gripping members 2A to 2L and stretches the film 200 in the width direction by moving the gripping members 2A to 2L along the rails. Furthermore, the stretching machine 100 shown in FIG. 3 includes 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 described in the "Clip" section below.

[0101] The stretching machine 100 has zones consisting of, in order from the upstream side in the conveying direction, a preheating zone 10, a stretching zone 20, a heat setting zone 30, a heat relaxing zone 40, and a cooling zone 50. The zones in the stretching machine 100 are separated by windshield curtains, and the temperature in each zone can be adjusted individually by hot air or the like.

[0102] The preheating section 10 is an area where the film 200 is preheated.

[0103] The stretching section 20 is a region where the preheated film 200 is stretched by applying tension in the direction of the arrow TD (width direction), which is perpendicular to the direction of the arrow MD (longitudinal direction). As shown in Figure 3, in the stretching section 20, the film 200 is stretched from width L0 to width L1.

[0104] The heat fixing section 30 is an area where the tensioned film 200 is heated and heat fixed while still being tensioned.

[0105] The thermal relaxation section 40 is a region where the tension of the heat-set film 200 is thermally relaxed by heating the heat-set film 200. As shown in Fig. 3, in the thermal relaxation section 40, the film 200 is reduced (relaxed) from width L1 to width L2.

[0106] Cooling section 50 is an area for cooling thermally relaxed film 200. Cooling film 200 fixes the shape of film 200. Fig. 3 shows that film 200 entering cooling section 50 has a width L2, and film 200 exiting cooling section 50 has a width L3.

[0107] Gripping members 2A, 2B, 2E, 2F, 2I, and 2J are attached to the circular rail 60a and are movable along the circular rail 60a. Gripping members 2C, 2D, 2G, 2H, 2K, and 2L are attached to the circular rail 60b and are movable along the circular rail 60b. Gripping members 2A, 2B, 2E, 2F, 2I, and 2J grip one end of the film 200 in the direction of arrow TD. Gripping members 2C, 2D, 2G, 2H, 2K, and 2L grip the other end of the film 200 in the direction of arrow TD. Gripping members 2A to 2L are often referred to as chucks, clips, or the like. Gripping members 2A, 2B, 2E, 2F, 2I, and 2J move counterclockwise along the circular rail 60a. The gripping members 2C, 2D, 2G, 2H, 2K, and 2L move clockwise along the circular rail 60b.

[0108] Gripping members 2A-2D move along annular rail 60a or 60b while gripping the end of film 200 in preheating section 10, passing through stretching section 20, heat-setting section 30, and heat-relaxing section 40, and then proceeding to cooling section 50. Next, gripping members 2A and 2B, and gripping members 2C and 2D, in that order in the conveying direction, release the end of film 200 at the end downstream of cooling section 50 in the direction of arrow MD (e.g., grip release points P and Q in FIG. 3), and then move further along annular rail 60a or 60b, returning to preheating section 10. In the above process, as film 200 moves in the direction of arrow MD, it is preheated in preheating section 10, stretched in stretching section 20, heat-set in heat-setting section 30, heat-relaxed in heat-relaxing section 40, and cooled in cooling section 50, and then transversely stretched.

[0109] The transport speed of film 200 can be adjusted by adjusting the movement speed of gripping members 2A to 2L. Furthermore, the movement speed of gripping members 2A to 2L can be changed independently of each other.

[0110] As described above, the stretching machine 100 enables transverse stretching in which the film 200 is stretched in the direction of the arrow TD in the stretching section 20. On the other hand, the stretching machine 100 can also stretch the film 200 in the direction of the arrow MD by changing the moving speed of the gripping members 2A to 2L. In other words, simultaneous biaxial stretching can also be performed using the stretching machine 100.

[0111] In addition to the gripping members 2A to 2L, the stretching machine 100 may further include other gripping members (not shown) to support the film 200.

[0112] (Clips) In one preferred embodiment of step B (described in detail below), both widthwise ends of the heat-relaxed film are gripped with clips, and the clips come into contact with contact members to close the clips, thereby gripping the heat-relaxed film with the clips. In this embodiment, the contact members preferably contain a resin having a melting temperature of 250°C or higher. Specific examples of the clips include gripping members 2A to 2L in FIG. 3.

[0113] The structure of the clip will be described in more detail below with reference to Figure 4. Figure 4 is a diagram that schematically shows an example of the configuration of clip 2. Clip 2 in Figure 4 corresponds to holding members 2A to 2L in Figure 3. Figure 4(a) shows clip 2 in a state in which film 200 is released (hereinafter also referred to as the "open state"), and Figure 4(b) shows clip 2 in a state in which film 200 is gripped (hereinafter also referred to as the "closed state").

[0114] The clip 2 includes a clip body 2a, an extension 2b extending inward in the width direction indicated by the arrow TD from above the clip body 2a and having a shaft 2c, an arm 2d rotatably supported by the extension 2b and the shaft 2c, and a clip base 2e extending inward in the width direction from below the clip body 2a and having a top surface facing the lower end of the arm 2d. Although not shown, the clip body 2a is attached to an annular rail 60a or 60b on the outer side of the width direction (the side opposite the extension 2b and clip base 2e). This allows the clip 2 to move in the conveyance direction of the film 200 (the direction penetrating the paper). The tip of the extension 2b extending inward in the width direction is attached near the center of the arm 2d extending vertically via the shaft 2c. 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 state, the film 200 is gripped by the lower end surface of the arm portion 2d and the top surface of the clip base 2e.

[0115] Returning to Figure 3, in the stretching machine 100, a pair of clip closers 3 are disposed upstream in the conveying direction of the film 200, and each is supported by a support member 4. The clip 2 moves along the annular rail 60a or 60b on the upstream side in the conveying direction of the film 200, and when it reaches the position where the clip closer 3 is disposed, the clip closer 3 abuts against the clip 2, and the upper part of the arm portion 2d is pushed outward from the inside in the width direction. As a result, the arm portion 2d rotates clockwise, and the clip 2 enters a closed state in which it can grip the film 200 (see Figure 4(b)).

[0116] In addition, in the stretching machine 100, a pair of clip openers 5 are disposed near the outlet on the downstream side in the conveying direction of the film 200. The clips 2, which come into contact with the clip closers 3 and are in a closed state capable of gripping the film 200, move downstream in the conveying direction. When the clips 2 eventually reach the positions where the clip openers 5 are disposed, the clip openers 5 come into contact with the clips 2, and the upper portions of the arms 2d are pushed inward from the outside in the width direction. As a result, the arms 2d rotate counterclockwise, and the clips 2 change from a closed state gripping the film 200 to an open state releasing the film 200 (see FIG. 4(a)).

[0117] In this way, the stretching machine 100 is configured so that, while the clips 2 move along the annular rail 60a or 60b, the clip closers 3 come into contact with the clips 2 to grip both ends of the film 200, the film 200 whose both ends are gripped by the clips 2 is transversely stretched in the stretching region, and the clip openers 5 come into contact with the clips 2 to release the film 200, thereby performing a series of transverse stretching steps. The stretching machine 100 can also perform various processes associated with transverse stretching, such as preheating, transverse stretching, heat setting, heat relaxation, and cooling of the film 200. The stretching machine 100 can also perform longitudinal stretching, in which the film 200 is stretched in the conveying direction, by changing the moving speed of the clips 2. That is, simultaneous biaxial stretching can also be performed using the stretching machine 100.

[0118] The contact member (e.g., clip closer 3 shown in FIG. 3) that contacts the clip to close the clip preferably contains a resin with a melting temperature of 250° C. This makes it difficult for small pieces from the contact member to melt during subsequent heat treatment even if they come into contact with the stretched resin film when the clip is contacted, thereby reducing the number of foreign objects adhering to the produced film.

[0119] Here, the melting temperature of the resin refers to the melting point (Tm) of the resin when the resin contained in the contact member is a crystalline resin, and refers to the glass transition temperature (Tg) of the resin when the resin is a non-crystalline 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, in order to achieve better effects of the present invention. 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 measurement using a differential scanning calorimetry (DSC).

[0120] Examples of resins having a melting temperature of 250°C or higher include polyetheretherketone, polyphenylene sulfide, polyimide, polyamide, and fluororesin. Examples of fluororesin include polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene (ETFE), perfluoroalkoxyalkane (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Among these, polyetheretherketone, polyphenylene sulfide, polyimide, and polytetrafluoroethylene are preferred as resins having a melting temperature of 250°C or higher.

[0121] The clip closer 3 shown in FIG. 3 is disk-shaped and supported by a support member 4 so as to be rotatable around an axis normal to the film 200. This allows the clip closer 3 to rotate when it abuts against the arm portion 2d of the clip 2. The shape of the abutting member used in this manufacturing method is not limited to the clip closer described above, and may be any shape that can abut against the clip to close the clip. The abutting member may, for example, be an elongated, flat plate extending in the conveyance direction, have a contact surface that continuously abuts against the clip, and the contact surface may be inclined from the inner side to the outer side in the width direction as it moves downstream of the film 200. The abutting member is preferably a rotatable disk. In particular, it is more preferable that, in a cross section obtained by cutting the disk-shaped abutting member along its central axis, the side surface that abuts against the clip has two or more line segments with different angles or is a curve such as a circular arc or an elliptical arc.

[0122] Furthermore, the dimensions and arrangement of the contact member are not limited and can be appropriately selected so that the clip switches to a closed state in which it grips the film when the contact member contacts it. The diameter of the disk-shaped contact member may be, for example, within a range of 5 to 30 cm.

[0123] After the film 200 is transversely stretched, a contact member such as the clip opener 5 shown in FIG. 3 is brought into contact with the clip, which has been closed by the contact member to hold both ends of the film 200, thereby releasing the gripping of both ends of the film 200. The shape of the contact member that contacts the clip to change the clip from a closed state to an open state is not particularly limited as long as it can contact the clip and open the clip. The contact member may be, for example, an elongated flat plate extending in the conveying direction, having a contact surface that continuously contacts the clip, and the contact surface may be inclined from the outer side to the inner side in the width direction as it moves downstream of the film 200. The contact member that contacts the clip to open the clip may also be disc-shaped. The material of the contact member that opens the clip is not particularly limited, and examples include resins and metals having a melting temperature of 250°C or higher.

[0124] <Longitudinal Stretching Step> The longitudinal stretching step is a step of stretching an unstretched polyester film in the machine direction (hereinafter also referred to as "longitudinal stretching"), to form a uniaxially oriented polyester film.

[0125] In the longitudinal stretching step, it is preferable to preheat the unstretched polyester film before longitudinal stretching. Preheating the unstretched polyester film allows the polyester film to be easily longitudinally stretched. The preheating temperature of the unstretched polyester film is preferably (Tg-30) to (Tg+40)°C, and more preferably (Tg-20) to (Tg+30)°C. Specifically, the preheating temperature is preferably 60 to 100°C, and more preferably 65 to 80°C. As a method for preheating the unstretched polyester film, for example, a preheating roll having a function of preheating the film is disposed upstream of the stretching rolls used for longitudinal stretching, and the unstretched polyester film is preheated while being transported.

[0126] The stretching rolls may also have a function of preheating the film. The preferred range of the preheating temperature of the film by the stretching rolls is the same as the preferred range of the preheating temperature of the preheating rolls described above.

[0127] The longitudinal stretching can be performed, for example, by applying tension to the unstretched polyester film between two or more pairs of stretching rolls arranged in the transport direction while transporting the film in the longitudinal direction. For example, when a pair of stretching rolls A is arranged on the upstream side in the transport direction and a pair of stretching rolls B is arranged on the downstream side in the transport direction, the unstretched polyester film is stretched in the longitudinal direction by making the rotation speed of the stretching rolls B faster than the rotation speed of the stretching rolls A when transporting the unstretched polyester film.

[0128] In the longitudinal stretching step, the film conveying speed (circumferential speed) by the pair of stretching rolls A provided upstream in the conveying direction and the pair of stretching rolls B provided downstream in the conveying direction is not particularly limited, as long as the film conveying speed by the stretching rolls A is slower than the film conveying speed by the stretching rolls B. The film conveying speed by the stretching rolls A is, for example, 5 to 60 m / min, preferably 10 to 50 m / min, and more preferably 15 to 45 m / min. The film conveying speed by the stretching rolls B is, for example, 40 to 160 m / min, preferably 50 to 150 m / min, and more preferably 60 to 140 m / min.

[0129] The stretching ratio in the longitudinal stretching step is appropriately set depending on the application, but is preferably 2.0 to 5.0 times, more preferably 2.5 to 4.0 times, and even more preferably 2.8 to 4.0 times.

[0130] The stretching speed in the longitudinal stretching step is preferably 800 to 1500% / sec, more preferably 1000 to 1400% / sec, and even more preferably 1200 to 1400% / sec. Here, the "stretching speed" refers to the value obtained by dividing the length Δd of the polyester film in the machine direction stretched per second in the longitudinal stretching step by the length d0 of the polyester film in the machine direction before stretching, expressed as a percentage.

[0131] In the longitudinal stretching step, it is preferable to heat the unstretched polyester film. This is because heating facilitates longitudinal stretching. The heating temperature in the longitudinal stretching step is preferably (Tg-20) to (Tg+50)°C, 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.

[0132]

[0013] Examples of methods for heating the unstretched polyester film in the longitudinal stretching step include heating a roll, such as a stretching roll, that comes into contact with the unstretched polyester film. Examples of methods for heating the roll include providing a heater inside the roll and providing a pipe inside the roll and flowing a heated fluid through the pipe. Other examples include a method of applying hot air to the unstretched polyester film, and a method of heating the unstretched polyester film by bringing the unstretched polyester film into contact with a heat source such as a heater or passing it near a heat source.

[0133] The longitudinal stretching step of longitudinally stretching an unstretched polyester film is not limited to the above-mentioned method. In the longitudinal stretching step, the unstretched polyester film is longitudinally stretched by utilizing the difference in conveying speed between two pairs of stretching rolls. However, a uniaxially oriented polyester film may also be produced by longitudinally stretching the unstretched polyester film using one or more high-speed stretching rolls arranged between the two stretching rolls and conveying the film at a faster conveying speed than the stretching rolls. Furthermore, in the longitudinal stretching step, the film is sandwiched and conveyed between two opposing rolls (a pair of rolls). However, the stretching roll used in the longitudinal stretching step may not have opposing rolls and may consist of only one roll in contact with one side of the polyester film.

[0134] <Transverse Stretching Step> The transverse stretching step is a step of transversely stretching the uniaxially oriented polyester film. The transverse stretching step is carried out, for example, in the transverse stretching section 20 of the stretching machine 100.

[0135] In the transverse stretching step, it is preferable to preheat the polyester film before transverse stretching. Preheating the polyester film allows the polyester film to be easily transversely stretched. The preheating temperature is preferably (Tg-10) to (Tg+60)°C, more preferably (Tg) to (Tg+50)°C. Specifically, the preheating temperature is preferably 80 to 120°C, more preferably 90 to 110°C.

[0136] The stretching ratio in the width direction of the uniaxially oriented polyester film in the transverse stretching step (transverse stretching ratio a) is not particularly limited, but is preferably larger than the stretching ratio in the longitudinal stretching step. The stretching ratio a in the transverse stretching step is preferably 3.0 to 6.0 times, more preferably 3.5 to 5.0 times, and even more preferably 3.5 to 4.5 times. When the transverse stretching step is carried out in the transverse stretching section 20 of the stretching machine 100, the transverse stretching ratio a is calculated from the ratio (L1 / L0) of the film width L1 at the time of discharge from the transverse stretching section 20 to the film width L0 at the time of entry into the transverse stretching section 20.

[0137] The area ratio, which is the product of the stretch ratio in the longitudinal stretching step and the stretch ratio in the transverse stretching step, is preferably 12.8 to 15.5 times, more preferably 13.5 to 15.2 times, and even more preferably 14.0 to 15.2 times. When the area ratio is equal to or greater than the above-mentioned lower limit, molecular orientation in the film width direction is improved. On the other hand, when the area ratio is equal to or less than the above-mentioned upper limit, it is easy to maintain a state in which molecular orientation is not easily relaxed when subjected to heat treatment.

[0138] The heating temperature in the transverse stretching step is preferably (Tg-10) to (Tg+80)°C, more preferably (Tg) to (Tg+70)°C, and even 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.

[0139] The stretching speed in the transverse stretching step is preferably 8 to 45% / sec, more preferably 10 to 30% / sec, and even more preferably 15 to 20% / sec.

[0140] [Step A] Step A is a step in which a biaxially oriented polyester film obtained by biaxially stretching an unstretched polyester film is heated to 235 to 245°C and then heat-relaxed at 205 to 225°C. Of the heat treatments for the biaxially oriented polyester film in step A, the heating to 235 to 245°C is also referred to as the "heat setting step," and the heat-relaxing at 205 to 225°C that is carried out subsequent to the heat setting step is also referred to as the "heat-relaxing step." The heat treatment temperature in step A refers to the surface temperature of the polyester film.

[0141] <Heat Setting Step> In the heat setting step, the biaxially oriented polyester film is heated to heat set it. Heat setting crystallizes the polyester, thereby suppressing shrinkage of the polyester film. The heat setting step is carried out, for example, in the heat setting section 30 of the stretching machine 100.

[0142] The surface temperature of the polyester film in the heat setting step (heat setting temperature T1) is 235 to 245°C, more preferably 236 to 244°C, and even more preferably 237 to 243°C. If the heat setting temperature T1 is 235°C or higher, it is possible to reduce thermal shrinkage and humidity expansion, thereby suppressing the occurrence of wrinkles during heated transport and also suppressing the occurrence of wrinkles on the outer periphery of the roll after storage. Furthermore, if the heat setting temperature T1 is 245°C or lower, hydrolysis of the polyester film can be suppressed, resulting in excellent film formability. In the heat setting step, heat treatment is performed while controlling the maximum temperature reached on the surface of the polyester film to the heat setting temperature T1.

[0143] In the heat setting step, the variation in surface temperature in the width direction of the film is preferably 0.5 to 10.0° C., more preferably 0.5 to 7.0° C., even more preferably 0.5 to 5.0° C., and particularly preferably 0.5 to 4.0° C. By controlling the variation in surface temperature in the width direction of the film within the above range, the variation in crystallinity in the width direction can be suppressed.

[0144] Examples of the heating method include a method of applying hot air to the film and a method of radiating heat to the film. Examples of the device used in the radiating heat method include an infrared heater.

[0145] The heating time in the heat setting step is preferably 5 to 50 seconds, more preferably 5 to 30 seconds, and even more preferably 5 to 10 seconds.

[0146] <Heat Relaxation Step> In the heat relaxation step, the polyester film heat-set in the heat setting step is heat-relaxed by heating at a temperature lower than that in the heat setting step. The heat relaxation can relax the residual strain of the polyester film. The heat relaxation step is carried out, for example, in the heat relaxation section 40 of the stretching machine 100.

[0147] The surface temperature of the polyester film in the heat-relaxing step (heat-relaxing temperature T2) is 205 to 225°C, and more preferably 210 to 220°C. If the heat-relaxing temperature T2 is 205°C or higher, the heat shrinkage rate can be reduced and the heat shrinkage rate can be easily adjusted to the above-mentioned range, thereby suppressing the occurrence of wrinkles during heated transport. Furthermore, if the heat-relaxing temperature T2 is 225°C or lower, the humidity expansion rate can be reduced and the humidity expansion rate can be easily adjusted to the above-mentioned range, thereby suppressing the occurrence of wrinkles on the outer periphery of the roll after storage. In the heat-relaxing step, the heat treatment is performed while controlling the maximum temperature reached on the surface of the polyester film to the above-mentioned heat-relaxing temperature T2.

[0148] Examples of the heating method include a method of applying hot air to the film and a method of radiating heat to the film. Examples of the device used in the radiating heat method include an infrared heater.

[0149] [Step B] Step B (cooling step) is a step of cooling the film thermally relaxed in step A at a cooling rate of 1500°C / min or less, and expanding the film in the width direction at an expansion rate of more than 0% and less than 0.20%. By performing cooling and expansion at the above rate in the same cooling step in cooling section 50, strain inherent in the film after cooling is reduced, and the thermal shrinkage rate and humidity expansion rate can be adjusted to desired ranges.

[0150] In step B, the heat-relaxed polyester film is cooled. The cooling and the later-described expansion performed together with the cooling are performed, for example, in the cooling section 50 of the stretching machine 100.

[0151] Methods for cooling the polyester film include, for example, a method of blowing air (preferably cold air) onto the film and a method of bringing the film into contact with a temperature-controllable member (for example, a temperature-control roll). The cooling temperature is preferably 130°C or lower in order to distinguish it from the heat-relaxing step. The cooling temperature is more preferably 30 to 120°C, even more preferably 30 to 100°C, and particularly preferably 30 to 80°C.

[0152] In this production method, cooling is carried out so that the cooling rate of the polyester film is 1500°C / min or less. Adjusting the cooling rate within the above range can suppress the occurrence of wrinkles during heated transport and also suppress the occurrence of wrinkles on the outer periphery of the roll after storage. The details of the mechanism by which specifying the cooling rate range can suppress the occurrence of wrinkles during heated transport and the occurrence of wrinkles on the outer periphery of the roll after storage are not clear, but it is presumed that by efficiently lowering the film temperature and setting the cooling rate to a value that suppresses temperature unevenness in the film, the inherent distortion of the film after cooling is reduced, and the thermal shrinkage rate and humidity expansion rate can be adjusted to the above range. This is presumed to suppress the occurrence of wrinkles on the outer periphery after storage in a rolled form and the occurrence of wrinkles during heated transport. From the above perspectives, the cooling rate is preferably 100 to 1500°C / min, more preferably 100 to 1380°C / min.

[0153] The cooling rate of the polyester film can be measured using a non-contact thermometer. For example, when cooling is performed in the cooling section 50 of the stretching machine 100, the surface temperature of the film 200 transported from the heat-relaxing section 40 to the cooling section 50 and the surface temperature of the film 200 transported from the cooling section 50 are measured to obtain the temperature difference ΔT (°C) between them. The cooling rate can be determined by dividing the obtained temperature difference ΔT (°C) by the residence time ta of the film 200 in the cooling section 50. The cooling rate of the polyester film can be adjusted by the operating conditions of the cooling device and the film transport speed.

[0154] In step B, the heat-relaxed polyester film is cooled at the above-mentioned cooling rate and expanded in the width direction. "Expanding the polyester film in the width direction" in step B means applying tension in the width direction to the polyester film while cooling so that the film width (L3 in Fig. 3 ) at the end of step B is wider than the film width (L2 in Fig. 3 ) of the polyester film at the start of step B.

[0155] In step B, the method for expanding the polyester film in the width direction is not particularly limited. For example, when the present film is produced using the above-mentioned stretching machine 100, the film 200 gripped by each gripping member can be expanded in the width direction in step B by widening the distance between the annular rails 60a and 60b at the end of the cooling section 50 (grip release points P and Q) compared to the distance between the annular rails 60a and 60b at the start of the cooling section 50. The expansion in step B may be carried out continuously or intermittently from the start to the end of step B, or may be carried out only for a certain period during step B, as long as the film width is expanded before and after step B. The expansion in step B is preferably carried out simultaneously with cooling. Therefore, the temperature during expansion in step B is the same as the cooling temperature.

[0156] The widthwise expansion rate of the polyester film, i.e., the ratio of the film width at the end of step B to the film width before the start of step B, is preferably greater than 0%, more preferably 0.001% or greater, and even more preferably 0.01% or greater. The upper limit of the expansion rate (percentage) is less than 0.20%, preferably 0.19% or less, and more preferably 0.18% or less. By setting the film width expansion rate at or below the upper limit, even when a strong tension is applied in the conveying direction to transport the film at high speed during film production (for example, when the tension in the conveying direction is 100 N / m or greater), it is possible to suppress the disruption of the cut surface in the trimming step described below, and furthermore, the breakage of the film due to the disruption of the cut. Furthermore, by setting the film width expansion rate at or below the upper limit, it is possible to adjust the thermal shrinkage rate within the desired range, thereby suppressing the occurrence of wrinkles during heated transport. Furthermore, by setting the expansion rate of the film width to the above-mentioned lower limit or more, the humidity expansion rate can be adjusted to a desired range, and peripheral wrinkles after storage can also be suppressed.

[0157] In the present production method, the heat setting step, heat relaxation step, and cooling step are carried out successively in this order, thereby reducing the load (thermal history) on the polyester film due to repeated heating and cooling, reducing the inherent distortion of the film, adjusting the thermal shrinkage rate and humidity expansion rate to fall within the above-mentioned ranges, and suppressing the generation of wrinkles on the periphery after storage and during heated transport.

[0158] <Particle-Containing Layer Forming Step> The present manufacturing method may include a particle-containing layer forming step of providing a particle-containing layer on at least one surface of a polyester substrate. The particle-containing layer formed by the particle-containing layer forming step is the same as the particle-containing layer described in detail in the above section "Particle-Containing Layer." The particle-containing layer may be formed at any stage of the present manufacturing method. For example, a method of forming a coating film on at least one surface of an unstretched or stretched polyester substrate using a coating liquid containing a material for constituting the particle-containing layer, and drying it as necessary, and a method of forming the particle-containing layer simultaneously with the formation of the polyester substrate by co-extrusion are included.

[0159] First, a method for forming a particle-containing layer using a coating liquid for the particle-containing layer will be described. The coating liquid for the particle-containing layer can be prepared by mixing particles to be contained in the particle-containing layer, binders and additives added as needed, and a solvent. Examples of the solvent 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 viewpoints of environment, safety, and economy.

[0160] The particle-containing layer coating liquid may contain one solvent alone or two or more solvents. The solvent content is preferably 80 to 99% by mass, more preferably 90 to 98% by mass, based on the total mass of the particle-containing layer coating liquid. That is, the total content of components other than the solvent (solid content) in the particle-containing layer coating liquid is preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass, based on the total mass of the particle-containing layer coating liquid. The components other than the solvent in the particle-containing layer coating liquid, including their preferred embodiments, are the same as those described above for the components contained in the particle-containing layer. Furthermore, it is preferable to adjust the content of each component in the coating liquid so that the content of each component relative to the total mass of the solid content of the particle-containing layer coating liquid is the same as the preferred content of each component relative to the total mass of the particle-containing layer.

[0161] The method for applying the coating liquid for the particle-containing layer is not particularly limited, and any known method can be used, such as spray coating, slit coating, roll coating, blade coating, spin coating, bar coating, and dip coating.

[0162] As a method for forming a particle-containing layer using a coating liquid for the particle-containing layer, either a so-called in-line coating method in which a coating liquid is applied to at least one surface of a polyester substrate while the polyester substrate is being transported, or a so-called off-line coating method in which a biaxially oriented polyester substrate is produced and then a coating liquid is applied separately, can be applied, but the in-line coating method is preferred from the viewpoints of being more efficient and imparting transparency. In the in-line coating method, the polyester substrate to which the coating liquid for the particle-containing layer is applied may be an unstretched polyester substrate or a uniaxially oriented polyester substrate, but a uniaxially oriented polyester substrate is preferred.

[0163] Next, a method for forming a particle-containing layer simultaneously with the formation of a polyester substrate by co-extrusion will be described. The method for forming the particle-containing layer by co-extrusion is not particularly limited. For example, a resin composition containing particles and a binder constituting the particle-containing layer, as well as additives added as needed, is prepared, and the resulting resin composition is heated and melt-kneaded according to the method described in the "extrusion molding step" above to produce a melt of the resin composition, which is then extruded together with a melt of polyester using an extruder to form the particle-containing layer.

[0164] The particle-containing layer formation process is preferably an in-line coating process in which a particle-containing layer is formed using a particle-containing layer coating liquid between the longitudinal stretching process and the transverse stretching process, or a co-extrusion molding process in which a polyester substrate and a particle-containing layer are simultaneously formed using a first melt containing a polyester constituting the polyester substrate and a second melt containing particles and a binder, because this process can shorten the heating time of the polyester substrate during the manufacturing process and reduce distortion within the polyester substrate. Among these, it is preferable to form a particle-containing layer by applying the above-mentioned in-line coating method to a uniaxially oriented polyester substrate between the longitudinal stretching process and the transverse stretching process. After forming a particle-containing layer by applying a particle-containing layer coating liquid to at least one surface of the uniaxially oriented polyester substrate, the polyester substrate and the particle-containing layer are simultaneously transversely stretched, thereby improving the adhesion between the polyester substrate and the particle-containing layer. The specific method of transverse stretching in this case is as described above in the transverse stretching process.

[0165] <Other Steps> The present production method may include a winding step of winding the polyester film obtained through the above steps to obtain a roll-shaped polyester film. The present production method may further include a trimming step of continuously cutting the polyester film along the conveyance direction to trim at least one end of the polyester film in the width direction before the winding step.

[0166] The present production method preferably also includes a step of packaging the polyester film (present film) obtained through the above steps (hereinafter also referred to as the "packaging step"). The packaging step is preferably performed after the winding step. The packaging step is preferably a step of covering the entire surface of the rolled present film with packaging material (e.g., a polyethylene sheet, an aluminum-vapor-deposited sheet, or the like). In the packaging step, a known desiccant may be disposed between the polyester film and the sheet. One preferred embodiment of the packaging step includes a step of packaging the entire surface of the rolled present film with a polyethylene sheet (e.g., product name: Lightron NE, product number: E52, manufactured by Sekisui Plastics Co., Ltd.), then attaching a desiccant (e.g., product name: EX-DRY, product number: EX-75SU, manufactured by Sanwa Corporation) to the surface of the package, packaging the package with a tubular aluminum-vapor-deposited sheet (e.g., product name: Aluminum-vapor-deposited tube, manufactured by Takeda Sangyo Kaisha), and sealing the ends with cable ties.

[0167] <Manufacturing Conditions, etc.> The conveying speed of the polyester film in each step other than the longitudinal stretching step in the present manufacturing method is not particularly limited, but when the transverse stretching step, step A, and step B are performed using the stretching machine 100, the conveying speed of the polyester film is preferably 50 to 200 m / min, more preferably 80 to 150 m / min, from the viewpoints of productivity and quality. Furthermore, the conveying speed of the polyester film after being subjected to step B until being taken up in the winding step is preferably 50 to 200 m / min, more preferably 80 to 150 m / min. The conveying speed of the polyester film in the longitudinal stretching step is as described above.

[0168] In each step other than the longitudinal stretching step, the tension in the machine direction applied to the polyester film is not particularly limited, but the tension in the machine direction applied to the polyester film can be adjusted by the stretching conditions when the transverse stretching step, step A, and step B are performed using the stretching machine 100. In addition, the tension in the machine direction applied to the polyester film after being subjected to step B until being taken up in the winding step is preferably 3 to 30 N / m, more preferably 5 to 20 N / m.

[0169] [Laminated Film] The use of the present film is not particularly limited, but it is preferable to further laminate a functional layer to produce a laminated film. That is, the laminated film has the present film and a functional layer. Examples of the functional layer to be laminated on the present film include a decorative layer, a photosensitive resin layer, a magnetic layer, a release layer, an adhesive layer, a conductive layer, a refractive index adjustment layer, and a visibility layer.

[0170] The functional layer (particularly, the release layer) is preferably disposed on the surface of the present film having the lower maximum protrusion height Sp (i.e., the smooth surface). This improves transportability of the laminated film and suppresses wrinkling. Specifically, when the present film has a polyester substrate and a particle-containing layer provided on only one surface of the polyester substrate, and the maximum protrusion height on the surface of the polyester substrate opposite the particle-containing layer is smaller than the maximum protrusion height on the surface of the particle-containing layer, it is preferable that the functional layer (particularly, the release layer) is provided on the surface of the polyester substrate opposite the particle-containing layer.

[0171] More specific examples of laminated films include 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 used as a support for dry film resist, release films in which the functional layer is a release layer (protective films for dry film resists, release films for producing ceramic green sheets, release films for producing semiconductor processes), adhesive films in which the functional layer is an adhesive layer (adhesive films for producing semiconductor processes), 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 adjustment layer.

[0172] Although the method for laminating a functional layer on the surface of the present film is not particularly limited, it is preferable to form the functional layer by applying a coating liquid containing materials that constitute the functional layer to the surface of the present film, and from the viewpoint of superior productivity, it is more preferable to form the functional layer by applying a functional layer coating liquid to the surface of the present film while conveying the present film and then heating the coating film. Even when the present film is subjected to a heat treatment in the functional layer formation step, the occurrence of wrinkles in the present film can be suppressed and unevenness in the thickness of the laminated functional layer can be suppressed.

[0173] The laminated film may have layers other than the present film and the functional layer, such as a base layer containing a binder resin, which is provided for the purpose of improving adhesion between the present film and the functional layer.

[0174] [Release Film] The release film, which is one preferred embodiment of the laminated film, will be described in more detail. This film can be used to produce a release film. More specifically, by providing a release layer on the surface (preferably the smooth surface) of this film, a release film having a polyester film and a release layer can be produced. A preferred embodiment of the release layer is a layer containing a silicone resin.

[0175] The silicone resin means a resin having a silicone structure in the molecule. Examples of the silicone resin include curable silicone resins, silicone graft resins, and modified silicone resins such as alkyl-modified silicone resins, and reactive curable silicone resins are preferred. Examples of the reactive curable silicone resin include addition reaction silicone resins, condensation reaction silicone resins, and ultraviolet or electron beam curable silicone resins. Among these, addition reaction silicone resins having low temperature curing properties or ultraviolet or electron beam curable silicone resins are preferred because they can form a release layer at low temperature.

[0176] Examples of silicone resins based on addition reactions include those obtained by reacting and curing polydimethylsiloxanes having vinyl groups introduced at the terminals or side chains with hydrogen siloxanes using a platinum catalyst. Examples of silicone resins based on condensation reactions include those having a three-dimensional crosslinked structure formed by condensing polydimethylsiloxanes having OH groups at the terminals with polydimethylsiloxanes having H groups at the terminals using an organotin catalyst. Examples of silicone resins based on ultraviolet curing include those that utilize the same radical reaction as silicone rubber crosslinking, those that introduce unsaturated groups to be photocured, those that decompose onium salts with ultraviolet or electron beams to generate strong acids and then cleave epoxy groups to crosslink, and those that crosslink via the addition reaction of thiols to vinyl siloxanes. More specifically, examples include acrylate-modified polydimethylsiloxanes and glycidoxy-modified polydimethylsiloxanes.

[0177] The release layer may contain additives other than the resins described above. Examples of additives that may be added include light release additives and heavy release additives for adjusting the release force, adhesion improvers, and antistatic agents. The resins contained in the release layer may be used alone or in combination of two or more.

[0178] The thickness of the release layer may be set depending on the intended use and is not particularly limited, but is preferably 0.005 to 2.0 μm, more preferably 0.005 to 1.0 μm, in order to achieve a good balance between release performance and smoothness of the release layer surface.

[0179] The method for providing a release layer on the surface (preferably the smooth surface) of the present film is not particularly limited, but examples include a method in which a coating liquid for forming a release layer, which is prepared by dissolving or dispersing a release agent in a solvent, is applied to the surface of the present film, the solvent is removed by drying, and if necessary, heating or light irradiation is performed to form a cured product.

[0180] The coating method of the release layer-forming coating solution is not particularly limited, and known methods can be used. Examples of the coating method include spray coating, slit coating, roll coating, blade coating, spin coating, bar coating, and dip coating. The heating temperature in forming the release layer is preferably 180°C or less, more preferably 150°C or less, and even more preferably 120°C or less. The lower limit is not particularly limited, and may be 60°C or more.

[0181] The coating liquid for forming a release layer contains the above-mentioned resin and solvent, and may contain the above-mentioned additives and / or the above-mentioned catalyst used for curing the resin, if necessary.The coating liquid for forming a release layer can be prepared by mixing these components.The solvent can be, for example, 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, and organic solvents are preferred.The coating liquid for forming a release layer may contain one solvent alone, or may contain two or more solvents.

[0182] <Applications> A release film including the present film has excellent transportability, can suppress the formation of transfer marks during roll storage, etc., and can suppress unevenness in the thickness of the release layer, so it is preferably used as a release film (carrier film) for producing ceramic green sheets. Ceramic green sheets produced using the above release film can be suitably used for producing ceramic capacitors, which are required to have multilayer internal electrodes in line with the trend toward smaller size and larger capacity.

[0183] The method for producing a ceramic green sheet using the release film is not particularly limited and can be carried out by a known method. Examples of methods for producing a ceramic green sheet include a method in which a prepared ceramic slurry is applied to the release layer surface of the release film and the solvent contained in the ceramic slurry is dried and removed. The method for applying the ceramic slurry is not particularly limited, and known methods can be applied, such as a method in which a ceramic slurry obtained by dispersing ceramic powder and a binder in a solvent is applied by a reverse roll method and the solvent is removed by heating and drying. The binder is not particularly limited, and examples thereof include polyvinyl butyral. The solvent is also not particularly limited, and examples thereof include ethanol and toluene.

[0184] The present disclosure will be further described in detail below with reference to examples. The materials, amounts used, ratios, processing details, and processing procedures shown in the following examples can be changed as appropriate without departing from the spirit of the present disclosure. Therefore, the scope of the present disclosure is not limited to the specific examples shown below. Unless otherwise specified, "parts" and "%" are based on mass.

[0185] Hereinafter, in the present examples, the mere expression "film" includes both a polyester substrate alone and an embodiment having a polyester substrate and a particle-containing layer, and also includes all of an unstretched film, a uniaxially oriented film, and a biaxially oriented film. In each step of the present examples, the temperature of the center of the film in the width direction was measured five times using a non-contact thermometer (AD-5616 (product name), manufactured by A&D, emissivity 0.95), and the arithmetic mean of the obtained measurements was used as the measured surface temperature of the film.

[0186] [Example 1] In the same manner as in Example 1 (paragraphs 0166 to 0174) of WO 2021 / 261412, an unstretched polyester film made of polyethylene terephthalate was longitudinally stretched, a composition (coating solution) was applied in-line to one side of the uniaxially stretched film, and the formed coating film was dried with hot air to form a particle-containing layer. The particle-containing layer-attached film was then subjected to a transverse stretching process, etc., to produce a polyester film comprising a polyester substrate and a particle-containing layer. At this time, by adjusting the thickness of the unstretched film in the extrusion molding process and adjusting the amount of composition applied in-line, a 30 μm-thick polyester film having a 15 nm-thick particle-containing layer was produced. The resulting polyester film had a width of 2.0 m and a winding length of 7000 m. The transverse stretching process was also carried out using a transverse stretching apparatus having the configuration shown in FIG. 3. The clip closer of the transverse stretching device was a disk-shaped member made of polyether ether ketone (PEEK) with a diameter of 150 mm and a thickness of 13 mm. Furthermore, the composition to be in-line coated was changed to the following composition X1, and the film-forming conditions for the polyester film were changed as follows.

[0187] (Composition X1) Acid-modified polyolefin (Zaixen (registered trademark) NC, manufactured by Sumitomo Seika Chemicals Co., Ltd., aqueous dispersion prepared by adding water to a solids content of 25% by mass): 157 parts Anionic hydrocarbon surfactant (Rapisol (registered trademark) A-90, di-2-ethylhexyl sodium sulfosuccinate, manufactured by NOF Corporation, water dilution with a solids content of 1% by mass): 56 parts Particles (Snowtex (registered trademark) ZL, manufactured by Nissan Chemical Industries, Ltd., colloidal silica, aqueous dispersion with a solids content of 40% by mass): 14 parts Water: 776 parts When preparing composition X1 and compositions X2 to X5 described below, the components were mixed and then subjected to filtration using a filter having a pore size of 6 μm (F20, manufactured by Mahle Filter Systems Co., Ltd.) and membrane degassing (2×6 Radial Flow Superphobic, manufactured by Polypore Corporation).

[0188] (Longitudinal stretching conditions) Preheating temperature: 75°C, stretching temperature: 90°C, stretch ratio: 3.5 times, stretching speed: 1340% / sec (Transverse stretching conditions) Preheating temperature: 100°C, stretching temperature: 120°C, stretch ratio: 4.3 times, stretching speed: 40% / sec <Step A> (Heat setting conditions) Heat setting temperature: as shown in Table 1 below, heat setting time: 5.2 seconds (Heat relaxation conditions) Heat relaxation temperature: 214°C, heat relaxation rate: as shown in Table 1 below <Step B> (Cooling conditions) Cooling rate: as shown in Table 1 below, cooling time ta: 6 seconds, expansion rate ΔL: as shown in Table 1 below

[0189] [Examples 2 and 3] Polyester films were produced in accordance with the method described in Example 1, except that the heat setting temperature in the heat setting step, the heat relaxation rate in the heat relaxation step, the cooling rate in step B (cooling step), and the expansion rate ΔL in step B (cooling step) were controlled to be the values ​​shown in Table 1 below.

[0190] [Examples 4 to 7] Polyester films were produced according to the method described in Example 1, except that the following compositions X2 to X4 were used in the particle-containing layer-forming step and the thickness of the particle-containing layer was adjusted to the values ​​shown in Table 1.

[0191] (Composition X2) Acid-modified polyolefin (Zaixen (registered trademark) NC, manufactured by Sumitomo Seika Chemicals Co., Ltd., aqueous dispersion prepared by adding water to a solid content of 25% by mass): 157 parts Anionic hydrocarbon surfactant (Rapisol (registered trademark) A-90, di-2-ethylhexyl sodium sulfosuccinate, manufactured by NOF Corporation, aqueous dilution of 1% by mass solid content): 56 parts Particles (Snowtex (registered trademark) ZL, manufactured by Nissan Chemical Industries, Ltd., colloidal silica, aqueous dispersion of 40% by mass solid content): 22 parts Water: 776 parts

[0192] (Composition X3) - Aqueous dispersion of acrylic resin (acrylic resin copolymerized with a composition of methyl methacrylate / styrene / 2-ethylhexyl acrylate / 2-hydroxyethyl methacrylate / acrylic acid = 59:8:23:5:5 (mass ratio)) (solid content concentration 27.5 mass%): 167 parts - Nonionic surfactant (Naloracty CL95, manufactured by Sanyo Chemical Industries, Ltd., solid content 100 mass%): 0.7 parts - Anionic surfactant (Rapisol A-90, manufactured by NOF Corporation, solid content 1 mass%, water-diluted explanation): 55.7 parts Carnauba wax dispersion (Cellosol 524, manufactured by Chukyo Yushi Co., Ltd., solid content 30% by mass): 7 parts Carbodiimide compound (Carbodilite V-02-L2, manufactured by Nisshinbo Co., Ltd., solid content 10% by mass, diluted with water): 20.9 parts Particles (Snowtex XL, manufactured by Nissan Chemical Co., Ltd., solid content 40% by mass): 2.8 parts Aggregated particles (Aerosil OX50, manufactured by Nippon Aerosil Co., Ltd., solid content 10% by mass, water dispersion, median diameter 0.2 μm): 2.95 parts Water: 743 parts

[0193] (Composition X4) Acid-modified polyolefin (Zaixen (registered trademark) NC, manufactured by Sumitomo Seika Chemicals Co., Ltd., aqueous dispersion prepared by adding water to a solid content of 25% by mass): 157 parts Anionic hydrocarbon surfactant (Rapisol (registered trademark) A-90, di-2-ethylhexyl sodium sulfosuccinate, manufactured by NOF Corporation, water dilution of 1% by mass solid content): 56 parts Particles (Snowtex (registered trademark) ZL, manufactured by Nissan Chemical Industries, Ltd., colloidal silica, aqueous dispersion of 40% by mass solid content): 11 parts Oxazoline compound (Epocross (registered trademark) WS-700, manufactured by Nippon Shokubai Co., Ltd., aqueous solution of 25% by mass solid content): 15 parts by mass Water: 776 parts

[0194] Examples 8 to 10 Polyester films were prepared in the same manner as in Example 1.

[0195] [Comparative Example 1] A polyester film was produced in exactly the same manner as in Example 1 of WO 2021 / 261412.

[0196] [Comparative Example 2] A polyester film was produced in exactly the same manner as in Comparative Example 1 of WO 2021 / 261412.

[0197] [Film Properties] <Heat Shrinkage> The polyester films produced in each Example and Comparative Example were cut to a size of 100 mm in the width direction (TD direction) and 100 mm in the direction perpendicular to the width direction (MD direction) to obtain square samples. The dimensions in the MD and TD directions before heating were measured using a measuring microscope (product name "MM-800", manufactured by Nikon Corporation), and the arithmetic mean value was designated as Ls. The sample was then placed on a sample holder and placed in a thermostatic chamber set to 150°C. After 30 minutes had passed since the placement, the sample was removed, and the dimensions in the MD and TD directions after heating were measured using the measuring microscope, and the arithmetic mean value was designated as Ll. The heat shrinkage of the polyester film was calculated using the following formula (1). A positive value for the heat shrinkage indicates shrinkage, and a negative value indicates expansion. Heat shrinkage (%) = {(Ls - Ll) / Ls} x 100 (1)

[0198] <Humidity Expansion Coefficient> The polyester films produced in each Example and Comparative Example were cut to a dimension of 100 mm in the width direction (TD direction) and 100 mm in the direction perpendicular to the width direction (MD direction) to obtain square samples. The obtained samples were stored in an environment of room temperature (25°C) and 40% RH as described in the "Storage Period" in Table 1 below. After the storage period, the dimensions in the MD direction and TD direction before humidification were measured using a measuring microscope (product name "MM-800", manufactured by Nikon Corporation), and the arithmetic mean value thereof was calculated as Ls ２ Then, the sample was placed on a sample holder and placed in a constant temperature and humidity chamber (product name "PH-2KT", manufactured by Espec Corporation) set at 40°C and 90% RH. 24 hours after placement, the sample was removed and the dimensions in the MD and TD directions after humidification were measured using a measuring microscope, and the arithmetic mean values ​​were calculated as L1. ２ The humidity expansion coefficient of the polyester film was calculated by the following formula (2). A positive value of the humidity expansion coefficient indicates shrinkage, and a negative value indicates expansion. Humidity expansion coefficient (%) = {(Ls ２ -Ll ２ ) / Ls ２} x 100 (2)

[0199] <Moisture Content> The polyester films produced in each Example and Comparative Example were cut into samples measuring 50 mm (TD) x 10 mm (MD) to prepare 100 or more samples, which were then stored in a thermo-hygrostat chamber at 40°C and 90% RH for 24 hours. After 24 hours, 3 g of the samples were removed from the thermo-hygrostat chamber, and the moisture content was measured using a Karl Fischer moisture meter (device name: ADP-611, MKC-610, manufactured by Kyoto Electronics Manufacturing Co., Ltd.) to determine the moisture content.

[0200] <Degree of Crystallinity> The density (g / cm 3 ) of the polyester film produced in each example and comparative example was ３ ) was measured using an electronic densitometer (product name "SD-200L", manufactured by Alpha Mirage). From the obtained density, the crystallinity was calculated using the following formula (3): Xc = [{Z × (X - Y)} / {X × (Z - Y)}] × 100 (3), where Xc is the crystallinity (%) and X is the density of the polyester film (g / cm ３ ) Y: Density of PET film at crystallinity 0% (g / cm ３ ) Z: density of PET film at 100% crystallinity (g / cm ３ )

[0201] <Measurement of Intrinsic Viscosity (IV) and Terminal COOH Content (AV)> The intrinsic viscosity (IV) of the polyester films produced in each Example and Comparative Example was determined by dissolving each polyester film in a 1,1,2,2-tetrachloroethane / phenol (2 / 3 [mass ratio]) mixed solvent and measuring the solution viscosity at 25°C. The resulting viscosity of the polyester films in each Example and Comparative Example was 0.63 [dl / g]. The terminal COOH content (AV) of the polyester films produced in each Example and Comparative Example was determined by completely dissolving each polyester film in a benzyl alcohol / chloroform (2 / 3 [volume ratio]) mixed solvent and titrating the resulting solution with a standard solution (0.01 N KOH-benzyl alcohol mixed solution) using phenol red as an indicator. The terminal COOH content of the polyester films in each Example and Comparative Example was calculated from the titration volume. The terminal COOH content of each polyester film was found to be within the range of 2.6 to 2.8 [eq / ton].

[0202] <Content of Elements Such as Antimony> The antimony content in the polyester films produced in each Example and Comparative Example was measured by inductively coupled plasma mass spectrometry (ICP-MS). An ICP-MS analyzer "Agilent 7800 ICP-MS" (manufactured by Agilent Technologies) was used for the measurement. As a result, in all Examples and Comparative Examples, the Sb content was in the range of 0 to 1 ppm by mass, relative to the total mass of the polyester film. The Ti content was 7 ppm by mass, the Mg content was 75 ppm by mass, and the P content was 65 ppm by mass.

[0203] <Number of Specific Foreign Matter> The number of specific foreign matter in the polyester film produced in each example was measured as follows. First, the polyester film was unwound from a roll, and the number of adhered foreign matter particles with a major axis of 50 μm or more adhered to both sides of the film surface was counted over 1,000 m in the film conveyance direction using a film surface inspection device (manufactured by MEC Corporation, device name "LSC-6000") for a first surface region extending from one end of the film toward the other end in the width direction of the film and a second surface region extending from the other end of the film toward the one end in the width direction of the film. Here, "a major axis of 50 μm or more" for adhered foreign matter means that the diameter of the circumscribed circle of the adhered foreign matter is 50 μm or more. If specific foreign matter was detected by the above inspection, the detected specific foreign matter was analyzed for elemental distribution using EDS to confirm whether the specific foreign matter contained components different from those of the film. Furthermore, it was confirmed that the specific foreign matter detected by the above test was a fixed foreign matter that was not transferred even when contacted with an adhesive roll (a p-type adhesive roll manufactured by Teknek). Then, the number of fixed foreign matters containing nitrogen atoms (specific foreign matter) was counted. As a result, the number of specific foreign matters in the polyester films of the examples was zero.

[0204] [Physical Properties of Protrusion-Containing Layer] <Maximum Protrusion Height Sp, Maximum Height St, Surface Average Roughness Sa> The maximum protrusion height Sp, maximum height St, and surface average roughness Sa of both surfaces of the polyester films produced in each Example and Comparative Example were measured using the following method. Both surfaces of the polyester film were measured under the following conditions using an optical interferometer (Vertscan 3300G Lite, manufactured by Hitachi High-Tech Corporation), and then analyzed using the built-in data analysis software (VS-Measure5) to determine the maximum protrusion height Sp, maximum height St, and surface average roughness Sa of both surfaces. In measuring the maximum protrusion height Sp and maximum height St, the maximum measured value obtained from five measurements taken at different measurement positions was used, and in measuring the surface average roughness Sa, the average measured value obtained from five measurements taken at different measurement positions was used. (Measurement conditions) Measurement mode: WAVE mode Objective lens: 50x Measurement area: 186 μm × 155 μm The maximum projection height Sp2, maximum height St2, and surface average roughness Sa2 of the uneven surface of the polyester film (surface on the particle-containing layer side) measured by the above method are shown in Table 1 below. Furthermore, the maximum projection height Sp1, maximum height St1, and surface average roughness Sa1 of the smooth surface of the polyester film (surface on the polyester substrate side) were measured by the above method, and as a result, 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 0 to 1 nm.

[0205] [Evaluation] <Wrinkles on Roll Outer Circumference> The rolled polyester films produced in each Example and Comparative Example were stored in a rolled state in an environment of 30°C and 70% RH for 10 days. After storage, the rolled biaxially oriented film was unwound, and an area of ​​100 m periphery × 0.3 m width was visually observed, and the number of wrinkles was counted. Specifically, the area of ​​100 m periphery × 0.3 m width of the polyester film was visually observed obliquely while changing the viewpoint so that the light from a fluorescent lamp [Lupica Ace (color temperature: 5000 K, average color rendering index (Ra): 84) manufactured by Mitsubishi Electric Corporation] installed on the ceiling in the room was reflected.

[0206] <Roll Appearance> The roll-shaped polyester films produced in each Example and Comparative Example were stored in the rolled state in an environment of 30°C and 70% RH for 10 days. After storage, the roll appearance was visually observed without unwinding to check for the presence or absence of wrinkles.

[0207] <Transfer Marks> The polyester films produced in each Example and Comparative Example were fed out, and a coating solution consisting of the following formulation A was applied to the surface of the polyester film opposite the particle-containing layer using a slot die method. The coating film was then dried using a hot air dryer at 120°C and wound up to produce a roll-shaped release film (a polyester film provided with a release layer). The thickness of the release layer after drying was 0.5 μm. Ten of the resulting release films were cut into 3.5 cm squares and stacked with the release layer and particle-containing layer in contact to obtain a laminate sample. This sample was kept in an oven at 40°C for 3 days under a load of 84 kg. The sample was removed from the oven, and the release film was peeled off one by one. 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 of dents was evaluated for transfer marks according to the following criteria.

[0208] (Evaluation Criteria) A: No dents were observed. B: Dent was observed.

[0209] (Formulation A: Coating liquid for forming release layer) Addition reaction type silicone (SRX-345, release agent, manufactured by Toray Dow Corning Co., Ltd.): 10 parts Mixed solvent of toluene and methyl ethyl ketone (mixing ratio = 7:3 (mass ratio)): 490 parts Platinum catalyst (SRX-212, manufactured by Toray Dow Corning Co., Ltd.): 0.1 part The coating liquid for forming the release layer was prepared by stirring and mixing the above components.

[0210] <Heat Wrinkles in the Next Step> While transporting the polyester films produced in each Example and Comparative Example, a primer layer coating liquid having the following formulation B was applied to the surface of the polyester film using a slit nozzle, and the coated film was then dried at a temperature of 90°C to form a primer layer. Next, while transporting the polyester film on which the primer layer had been formed, a black layer coating liquid having the following formulation C was applied onto the primer layer, and the coated film was then dried at a temperature of 90°C to form a black layer. The transport speed of the polyester film during the formation of the primer layer and black layer was 70 m / min. The polyester film provided with the primer layer and black layer was placed on a light table, and color unevenness in the black layer was visually observed at a position 1 m away from the polyester film and evaluated according to the following evaluation criteria.

[0211] (Evaluation criteria) A: No color unevenness in the black layer was observed. B: Color unevenness in the black layer was observed. If no color unevenness in the black layer was observed, it indicates that the thickness of the black layer was uniform, that is, no thickness unevenness occurred. Note that if no color unevenness in the black layer was observed, it can be said that no wrinkles were generated in the polyester film due to heating during transportation when forming the base layer and black layer.

[0212] (Formulation B: Coating liquid for undercoat layer) PVA205 (polyvinyl alcohol, manufactured by Kuraray Co., Ltd., saponification degree 88%, polymerization degree 550): 32.2 parts by weight Polyvinylpyrrolidone (manufactured by ISP Japan Co., Ltd., K-30): 14.9 parts by weight Distilled water: 524 parts by weight Methanol: 429 parts by weight

[0213] (Formulation C: Coating liquid for black layer) Resin-coated carbon black prepared according to the description in paragraphs 0036 to 0042 of Japanese Patent No. 5,320,652: 13.1 parts by mass Dispersant: Dispersant 1 described in paragraph

[0103] of WO 2017 / 208,849: 0.65 parts by mass Polymer (random copolymer of benzyl methacrylate / methacrylic acid in a molar ratio of 72 / 28, weight-average molecular weight of 37,000): 6.72 parts by mass Propylene glycol monomethyl ether acetate: 79.53 parts by mass

[0214]

[0215]

[0216] As shown in the above table, it was confirmed that, when the manufacturing method for a polyester film satisfies the manufacturing conditions in the above-mentioned steps A and B, the occurrence of wrinkles on the periphery is suppressed when the film is stored in a rolled form, and the occurrence of wrinkles is also suppressed when the film is heated and transported (Examples). Comparing Examples 1 and 4 to 6, it was found that when the maximum projection height Sp of the side with the larger maximum projection height (i.e., the maximum projection height Sp2 of the projection-containing layer) was less than 90 nm, the occurrence of transfer marks could be further suppressed (Examples 1, 4, and 6).

[0217] In contrast, it was confirmed that if the polyester film manufacturing method does not satisfy either of the manufacturing conditions in the above-mentioned process A or process B, at least one of the occurrence of wrinkles on the periphery when stored in a rolled form and the occurrence of wrinkles when heated and transported cannot be sufficiently suppressed (Comparative Example).

[0218] 2A to 2L: Gripping member 2: Clip 2a: Clip body 2b: Extension portion 2c: Shaft 2d: Arm portion 2e: Clip base 3: Clip closer 4: Support member 5: Clip opener 10: Preheating section 20: Stretching section 30: Heat setting section 40: Heat relaxation section 50: Cooling section 60a, 60b: Circular rail 100: Stretching machine 200: Film 300: Polyester film 301: Smooth surface 302: Textured surface P, Q: Gripping release point MD: Convex direction (longitudinal direction) TD: Width direction L0, L1, L2, L3: Film width

Claims

A polyester film having a thickness of 10 to 50 μm, A polyester film that satisfies both of the following conditions A and B. 　 Condition A: After heating a polyester film having a length of 100 mm and a width of 100 mm at 150° C. for 30 minutes, the heat shrinkage rate of the polyester film is 1.40% or less. Condition B: After storing the polyester film having a size of 100 mm length and 100 mm width in an environment of 40° C. and 90% RH for 24 hours, the humidity expansion coefficient of the polyester film is 0.015% or less. 　 The polyester film according to claim 1 , wherein the polyester film has a moisture content of 1800 ppm by mass or less after being stored in an environment of 40° C. and 90% RH for 24 hours.

2. The polyester film according to claim 1, wherein the crystallinity is 55.0 to 63.0%. 　 The polyester film is in a roll form, 2. The polyester film according to claim 1, wherein after storing the rolled polyester film in an environment of 30°C and 70% RH for 10 days, the rolled polyester film has 10 or fewer wrinkles in an area of ​​100 m around its periphery and 0.3 m wide.

2. The polyester film according to claim 1, wherein the maximum projection heights Sp on both surfaces of the polyester film are 100 nm or less. 　 The polyester film according to claim 1 , wherein the average surface roughness Sa of both surfaces of the polyester film is 5 nm or less.

10. The polyester film of claim 1, wherein the polyester film comprises a polyester substrate and a particle-containing layer on at least one surface of the polyester substrate.

2. The polyester film according to claim 1, wherein the antimony content is 10 ppm by mass or less. 　 The polyester film has a width of 100 cm or more and a length of 1000 m or more, When a surface region of the polyester film extending from one end to the other end in the width direction thereof to 50 cm is defined as a first surface region, and a surface region of the polyester film extending from the other end to one end in the width direction thereof to 50 cm is defined as a second surface region, The number of adhered foreign particles containing nitrogen atoms having a major axis of 50 μm or more in the first surface region and the second surface region is 1 / 500 m. ２ 2. The polyester film according to claim 1, wherein: 　 A laminated film comprising the polyester film according to any one of claims 1 to 9 and a release layer. 　 The laminated film according to claim 10 , wherein the release layer is disposed on one of the two surfaces of the polyester film having a lower maximum projection height Sp. 　 A method for producing a polyester film having a thickness of 10 to 50 μm, comprising: A step A includes biaxially stretching an unstretched polyester film to obtain a biaxially oriented polyester film, heating the resulting biaxially oriented polyester film to 235 to 245°C, and then heat-relaxing the film at 205 to 225°C; and a step B of cooling the film thermally relaxed in the step A at a cooling rate of 1500°C / min or less, In the step B, the heat-relaxed film is expanded in the width direction at an expansion rate of more than 0% and less than 0.20%. 　 the polyester film has a polyester substrate and a particle-containing layer containing particles on at least one surface of the polyester substrate; Before the step A, an extrusion molding step of extruding a molten resin containing a polyester into a film shape to form the unstretched polyester film containing at least a polyester base material; a longitudinal stretching step of stretching the unstretched polyester film in a machine direction to form a uniaxially oriented polyester film; and a transverse stretching step of stretching the uniaxially oriented polyester film in the width direction to form the biaxially oriented polyester film, The method further comprises a step of forming the particle-containing layer using a coating liquid containing the particles between the longitudinal stretching step and the transverse stretching step, or The method for producing a polyester film according to claim 12 , further comprising the step of forming the particle-containing layer by extruding a second molten material containing the particles and the binder together with the molten resin in the extrusion molding step. 　 In the step B, both ends of the heat-relaxed film in the width direction are gripped with clips, and the clips come into contact with contact members to close the clips, thereby gripping the heat-relaxed film with the clips, The method for producing a polyester according to claim 12 or 13, wherein the contact member contains a resin having a melting temperature of 250°C or higher.

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