TWI876065B - Method for manufacturing polyester film, polyester film, and laminated film - Google Patents

Abstract

The subject of the present invention is to provide a method for manufacturing a polyester film capable of further suppressing the uneven thickness of a functional layer disposed on the surface of the polyester film, and a polyester film and a laminated film capable of further suppressing the uneven thickness of a functional layer disposed on the surface. The method for manufacturing a polyester film of the present invention comprises: an extrusion molding step of extruding a molten resin containing polyester in a film form to form an unstretched polyester film; a longitudinal stretching step of stretching the unstretched polyester film along the conveying direction; a transverse stretching step of stretching a uniaxially oriented polyester film along the width direction; a heat setting step of heating the biaxially oriented polyester film to heat set it; and a step of heating the heat-set polyester film at a temperature lower than that in the heat setting step. A heat relaxation step of heat-relaxing the polyester film by heat-relaxing the polyester film; a cooling step of cooling the heat-relaxed polyester film; an expansion step of expanding the heat-relaxed polyester film in the width direction during the cooling step; and a particle-containing layer forming step of providing a particle-containing layer containing particles on at least one surface of the polyester substrate, wherein the cooling rate V of the polyester film in the cooling step is 2200 to 3500° C./minute and satisfies the specific following condition 1.

Description

Method for producing polyester film, polyester film, laminated film

The present invention relates to a method for manufacturing a polyester film, a polyester film and a laminated film.

Biaxially oriented polyester films are widely used from the viewpoints of processability, mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance, for example, as decorative films, supports and protective films for dry film photoresists, release films used in the production of ceramic green sheets for the manufacture of magnetic tapes and multilayer ceramic capacitors, and many other applications.

On the other hand, in the manufacturing process of biaxially oriented polyester film, as a technology for suppressing the generation of wrinkles (transport wrinkles) generated when the polyester film is transported, there is a known technology of providing a layer containing particles on the surface. For example, Patent Document 1 discloses a polyester film for photoresist, which is a biaxially oriented polyester film having a lubricating resin layer with an average thickness of 3 to 80 nm and a layer without particles having an average particle size greater than 40 nm on the side opposite to the resist coating surface, wherein the 10-point average roughness (SRz), haze, static friction coefficient (μs), and thermal shrinkage stress at 150°C of the lubricating resin layer side of the polyester film are determined.

[Patent Document 1] Japanese Patent Application Publication No. 2004-361446

The inventors of the present invention have studied the method for manufacturing a polyester film having a particle-containing layer by referring to the technology described in Patent Document 1. As a result, they have found that when a functional layer is formed on a biaxially oriented polyester film to manufacture a laminated film, even if no unevenness or wrinkles are visually recognized before the formation of the functional layer, the thickness of the functional layer may be uneven in the laminated film after the functional layer is formed by applying a liquid composition (e.g., a coating liquid) to the surface of the biaxially oriented polyester film and performing a heat treatment. The uneven thickness of the functional layer may, for example, be displayed as uneven color in a decorative film having a decorative layer as a functional layer, thereby reducing the visibility of the decorative film. Furthermore, if thickness unevenness also occurs in other functional layers, there is a possibility that the characteristics or appearance of the functional laminated film will be affected.

In view of the above situation, the subject of the present invention is to provide a method for manufacturing a polyester film capable of further suppressing the uneven thickness of a functional layer provided on the surface of the polyester film. In addition, the subject of the present invention is to provide a polyester film and a laminated film capable of further suppressing the uneven thickness of a functional layer provided on the surface.

As a result of in-depth research on the above-mentioned problem, the inventors of the present invention have found that the above-mentioned problem can be solved by the following structure.

[1] A method for producing a polyester film, comprising: an extrusion molding step of extruding a molten resin containing polyester in a film form to form an unstretched polyester film containing at least a polyester substrate; a longitudinal stretching step of stretching the unstretched polyester film in a conveying direction to form a uniaxially oriented polyester film; a transverse stretching step of stretching the uniaxially oriented polyester film in a width direction to form a biaxially oriented polyester film; a heat setting step of heating the biaxially oriented polyester film to heat set it; and a step of heating the biaxially oriented polyester film at a temperature lower than that in the heat setting step. A heat relaxation step of heating the polyester film heat-set by the heat-setting step at a temperature of 200 to heat-relax it; a cooling step of cooling the polyester film heat-relaxed by the heat relaxation step; an expansion step of expanding the heat-relaxed polyester film along the width direction in the cooling step, wherein the polyester film has a polyester substrate and a particle-containing layer located on at least one surface of the polyester substrate, and in the method for manufacturing the polyester film, a cooling rate V of the polyester film in the cooling step is 2200-3500°C/min and satisfies the condition 1 described later. [2] The manufacturing method as described in [1], wherein the value D calculated from the above-mentioned A, the above-mentioned B and the above-mentioned cooling speed V by the formula (3) described below is 1 to 10000. [3] The manufacturing method as described in [1] or [2], wherein the thickness of the above-mentioned polyester film is less than 50μm. [4] The manufacturing method as described in any one of [1] to [3], wherein between the above-mentioned longitudinal stretching step and the above-mentioned transverse stretching step, there is also a step of forming the above-mentioned particle-containing layer using a coating liquid containing the above-mentioned particles or there is also a step of forming the above-mentioned particle-containing layer by extruding a second melt containing the above-mentioned particles and a binder simultaneously with the above-mentioned molten resin in the above-mentioned extrusion molding step. [5] The manufacturing method as described in any one of [1] to [4], wherein the surface temperature T2 of the polyester film in the thermal relaxation step is 210°C or less. [6] The manufacturing method as described in any one of [1] to [5], wherein the cooling rate V of the polyester film based on the cooling step is 2200 to 3000°C/min. [7] The manufacturing method as described in any one of [1] to [6], wherein the b exceeds 0% and is 1.2% or less. [8] A polyester film comprising a polyester substrate and a particle-containing layer located on at least one surface of the polyester substrate, wherein the polyester film has a thickness of less than 50 μm, and after the polyester film is heated for 20 seconds at a surface temperature of 90°C while being transported at a transport speed of 30 m/min and a tension of 100 N/m in the transport direction, the total area of the stripe-like defect regions observed in the polyester film is 40% or less relative to the total area of the observed regions. [9] The polyester film as described in [8], wherein the expansion rate of the polyester film in the width direction at 90°C is -0.15 to 0.15% relative to the dimension of the polyester film in the width direction at 30°C. [10] The polyester film as described in [8] or [9], wherein the density of the polyester film is 1.39 to 1.41 g/cm ³ . [11] The polyester film as described in any one of [8] to [10], wherein the thickness of the polyester substrate is 3 to 40 μm, and the thickness of the particle-containing layer is 0.001 to 2.5 μm. [12] The polyester film as described in any one of [8] to [11], wherein the particle-containing layer contains particles P having an average particle size of 10 nm or more and less than 1 μm. [13] The polyester film as described in [12], wherein the average particle size of the particles P is greater than the thickness of the particle-containing layer. [14] The polyester film as described in any one of [8] to [13], wherein the particle-containing layer contains particles P1 having an average particle size of 10 to 100 nm. [15] A polyester film as described in any one of [8] to [14], wherein the particle-containing layer contains particles P2 having an average particle size of more than 100 nm and less than 400 nm. [16] A polyester film as described in any one of [8] to [15], wherein the particles contained in the particle-containing layer are resin particles or the particles contained in the particle-containing layer are inorganic particles, and the maximum peak height Rp of at least one surface of the polyester film is 5 to 200 nm. [17] A polyester film as described in any one of [8] to [16], wherein the polyester substrate does not substantially contain particles. [18] A laminated film comprising: a polyester film produced by the production method described in any one of [1] to [7] or a polyester film described in any one of [8] to [17], and having a particle-containing layer only on one surface of a polyester substrate; and a functional layer located on the surface of the polyester substrate opposite to the particle-containing layer and selected from the group consisting of a decorative layer, a photosensitive resin layer and a release layer. [19] The laminated film described in [18], wherein the functional layer is a decorative layer and the laminated film is a decorative film. [20] The laminated film described in [18], wherein the functional layer is a photosensitive resin layer and the laminated film is a photosensitive transfer film. [21] The laminated film as described in [18], wherein the functional layer is a release layer, and the laminated film is a release film for manufacturing ceramic green sheets. [Effects of the Invention]

According to the present invention, a method for manufacturing a polyester film capable of further suppressing uneven thickness of a functional layer disposed on the surface of the polyester film can be provided. In addition, according to the present invention, a polyester film and a laminated film capable of further suppressing uneven thickness of a functional layer disposed on the surface can be provided.

The following is a detailed description of the embodiments of the present invention. The present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the purpose of the present invention.

In the present invention, the numerical range indicated by "～" refers to a range that includes the numerical values recorded before and after "～" as the lower limit and upper limit. In the numerical range recorded in stages in the present invention, the upper limit or lower limit recorded in a certain numerical range can be replaced by the upper limit or lower limit of another numerical range recorded in stages. In addition, in the numerical range recorded in the present invention, the upper limit or lower limit recorded in a certain numerical range can be replaced by the value shown in the embodiment. In the present invention, when there are multiple substances corresponding to each component in the composition, unless otherwise specified, the amount of each component in the composition refers to the total amount of the multiple substances present in the composition. In the present invention, the term "step" includes not only independent steps, but also steps that fulfill the intended purpose even if they cannot be clearly distinguished from other steps. In the present invention, a combination of two or more preferred aspects is a more preferred aspect.

In the present invention, the description of "polyester film" alone includes both the polyester substrate monomer and the laminate of the polyester substrate and the particle-containing layer. In the present invention, "long side direction" refers to the long side direction of the polyester film when the polyester film is manufactured, and has the same meaning as "conveying direction" and "machine direction". In the present invention, "width direction" refers to the direction orthogonal to the long side direction. In the present invention, "orthogonal" is not limited to strict orthogonal, and includes approximately orthogonal. "Approximately orthogonal" means intersecting at 90°±5°, preferably at 90°±3°, and more preferably at 90°±1°. In addition, in the present invention, "film width" refers to the distance between the two ends of the width direction of the polyester film.

[Polyester film] The polyester film of the present invention (hereinafter, also described as "the present film") comprises at least a polyester substrate and a particle-containing layer located on at least one surface of the polyester substrate and containing particles. In one embodiment of the present film, the thickness of the polyester film is less than 50 μm, and the area of the stripe-like defect region observed in the polyester film subjected to the heat treatment described below is less than 40% relative to the total area of the observed region.

[Structure] As described above, the film has a polyester substrate and a particle-containing layer located on at least one surface of the substrate. The particle-containing layer may be formed on only one surface of the polyester substrate or on both surfaces of the polyester substrate. The polyester substrate and the particle-containing layer are described in more detail below.

<Polyester substrate> A polyester substrate is a film-like object containing polyester as the main polymer component. Here, "main polymer component" refers to the polymer with the largest content (mass) among all polymers contained in the film. A polyester substrate may contain a single polyester or two or more polyesters.

(Polyester) Polyester is a polymer having an ester bond in the main chain. Polyester is usually formed by condensing a dicarboxylic acid compound and a diol compound described below. As polyester, there is no particular limitation, and known polyesters can be used. As polyester, for example, polyethylene terephthalate (PET) and polyethylene-2,6 naphthalate (PEN), polypropylene terephthalate (PPT), polybutylene terephthalate (PBT) and copolymers thereof can be cited, among which at least one selected from the group including polyethylene terephthalate (PET), polyethylene-2,6 naphthalate (PEN) and copolymers thereof is preferred, and PET is more preferred.

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

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

-Catalyst- The catalyst used for producing polyester is not particularly limited, and any known catalyst that can be used for synthesizing polyester can be used. As the catalyst, for example, alkali metal compounds (e.g., potassium compounds, sodium compounds), alkali 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 can be cited. Among them, titanium compounds are preferred from the viewpoint of catalyst activity and cost. The catalyst may be used alone or in combination of two or more. It is preferred 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 and a phosphorus compound, and it is more preferred to use a titanium compound and a phosphorus compound.

As the titanium compound, an organic chelate titanium complex is preferred. An organic chelate titanium complex is a titanium compound having an organic acid as a ligand. As the organic acid, for example, citric acid, lactic acid, trimellitic acid, and apple acid can be cited. As the titanium compound, the titanium compound described in paragraphs 0049 to 0053 of Japanese Patent No. 5575671 can also be used, and the contents of the above-mentioned publication are incorporated into this specification.

-Dicarboxylic acid compound- As the dicarboxylic acid compound, dicarboxylic acid or dicarboxylic acid ester is preferred, for example, aliphatic dicarboxylic acid compounds, alicyclic dicarboxylic acid compounds, aromatic dicarboxylic acid compounds and methyl ester compounds or ethyl ester compounds thereof can be cited. Among them, aromatic dicarboxylic acid or aromatic dicarboxylic acid methyl is more preferred.

Examples of aliphatic dicarboxylic acid compounds 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 alicyclic dicarboxylic acid compounds include adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, and decahydronaphthalene dicarboxylic acid.

As aromatic dicarboxylic acid compounds, for example, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 4,4'-diphenyl dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 5-sodium sulfonate of isophthalic acid, phenylindanedicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid and 9,9'-bis(4-dicarboxyphenyl)fluorene acid and their methyl esters can be cited. Among them, terephthalic acid or 2,6-naphthalene dicarboxylic acid is preferred, and terephthalic acid is more preferred.

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 copolymerized with other aromatic dicarboxylic acids such as isophthalic acid or aliphatic dicarboxylic acids.

-Diol compound- As the diol compound, for example, aliphatic diol compounds, alicyclic diol compounds and aromatic diol compounds can be cited, and aliphatic diol compounds are preferred.

Examples of aliphatic diol compounds include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,2-butylene glycol, 1,3-butylene glycol and neopentyl glycol, with ethylene glycol being preferred. Examples of alicyclic diol compounds include cyclohexanedimethanol, spirodiol 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 diol compound may be used, or two or more diol compounds may be used in combination.

-Terminal blocking agent- In the production of polyester, an end-blocking agent can be used as needed. By using the end-blocking agent, a structure derived from the end-blocking agent is introduced into the end of the polyester. As the end-blocking agent, there is no limitation, and a known end-blocking agent can be used. As the end-blocking agent, for example, oxazoline compounds, carbodiimide compounds, and epoxy compounds can be cited. As the end-blocking agent, the contents described in paragraphs 0055 to 0064 of Japanese Patent Publication No. 2014-189002 can also be referred to, and the contents of the above-mentioned publication are incorporated into this specification.

-Manufacturing conditions- The reaction temperature is not limited and can be set appropriately according to the raw materials. The reaction temperature is preferably 260-300℃, and more preferably 275-285℃. The pressure is not limited and can be set appropriately according to the raw materials. The pressure is preferably 1.33×10 ^-3 ～1.33×10 ^-5 MPa, and more preferably 6.67×10 ^-4 ～6.67×10 ^-5 MPa.

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 into this specification.

The content of polyester in the polyester substrate is preferably 85% by mass or more relative to the total mass of the polymer in the polyester substrate, more preferably 90% by mass or more, further preferably 95% by mass or more, and particularly preferably 98% by mass or more. The upper limit of the content of polyester is not limited, and can be appropriately set within the range of 100% by mass or less relative to the total mass of the polymer in the polyester substrate.

When the polyester substrate contains polyethylene terephthalate, the content of polyethylene terephthalate relative to the total mass of the polyester in the polyester substrate is preferably 90 to 100 mass %, more preferably 95 to 100 mass %, further preferably 98 to 100 mass %, and particularly preferably 100 mass %.

The polyester substrate may contain components other than polyester (e.g., catalysts, unreacted raw material components, and water, etc.). It is preferred that the polyester substrate contains substantially no particles. Here, "substantially no particles" is defined as the content of particles relative to the total mass of the polyester substrate when both the polyester substrate and the particle-containing layer are quantitatively analyzed for elements derived from particles by fluorescent X-ray analysis, being 50 mass ppm or less, preferably 10 mass ppm or less, and more preferably below the detection limit. This is because, even if particles are not actively added to the substrate film, contamination components derived from foreign impurities or stains attached to the production line or equipment in the step of manufacturing the raw material resin or film may be peeled off and mixed into the film.

From the perspective of being able to suppress the increase in haze value, the thickness of the polyester substrate is preferably 100 μm or less, 50 μm or less is more preferably, and 40 μm or less is more preferably. There is no particular restriction on the lower limit of the thickness. From the perspective of improving strength and processability, 3 μm or more is more preferably, 4 μm or more is more preferably, and 10 μm or more is more preferably. The thickness of the polyester substrate is measured according to the measurement method of the thickness of the polyester film described below.

<Particle-containing layer> The particle-containing layer is a layer containing particles and formed on at least one surface of the polyester substrate. The film can improve the transportability by having a particle-containing layer. More specifically, it can improve the winding quality (suppress adhesion), suppress the occurrence of scratches and defects during transport, and reduce transport wrinkles. The particle-containing layer can be directly provided on the surface of the polyester substrate or provided on the surface of the polyester substrate via another layer, but it is better to provide it directly on the surface of the polyester substrate from the perspective of better adhesion.

As particles contained in the particle-containing layer, for example, organic particles and inorganic particles can be cited. Among them, from the perspective of further improving the film winding quality, haze and durability (for example, thermal stability), inorganic particles are preferred. As organic particles, resin particles are preferred. As resins constituting resin particles, for example, acrylic resins such as polymethyl methacrylate resin (PMMA), polyester resins, silicone resins, and styrene-acrylic resins can be cited. It is preferred that the resin particles have a cross-linked structure. As resin particles having a cross-linked structure, for example, divinylbenzene cross-linked particles having a cross-linked structure derived from divinylbenzene (for example, divinylbenzene/styrene copolymer cross-linked particles) can be cited. From the perspective of suppressing transfer marks, resin particles are preferred. As inorganic particles, for example, silicon dioxide particles, titanium dioxide particles, calcium carbonate, barium sulfate, and aluminum oxide particles can be cited. Among the above, from the perspective of further improving the haze and durability, the inorganic particles are preferably silicon dioxide particles.

The shape of the particles is not particularly limited, and examples thereof include rice grains, spheres, cubes, hammers, scales, aggregates, and irregular shapes. The aggregate state refers to a state in which primary particles are aggregated. The shape of the particles in the aggregate state is not limited, and spherical or irregular shapes are preferred.

In the particle-containing layer, it is preferred that a coating liquid having at least one of agglomerated particles and non-agglomerated particles is formed by an in-line coating method. Here, agglomerated particles refer to particles in an agglomerated state in the coating liquid, and non-agglomerated particles refer to particles that are not in an agglomerated state in the coating liquid.

As agglomerated particles, fumed silica particles are preferably cited. As commercially available products, for example, the AEROSIL series of NIPPON AEROSIL CO., LTD. can be cited. As non-agglomerated particles, colloidal silica particles are preferably cited. As commercially available products, for example, the SNOWTEX series manufactured by Nissan Chemical Industries, Ltd. can be cited.

The particle-containing layer may contain a single type of particle or may contain two or more types of particles. From the viewpoint of improving the winding quality of the film and suppressing transfer defects, the particle content is preferably 0.01 to 20 mass % relative to the total mass of the particle-containing layer, more preferably 0.5 to 15 mass %, and even more preferably 1 to 10 mass %. In addition, the particle content is preferably 0.0001 to 0.01 mass % relative to the total mass of the polyester film, and even more preferably 0.0005 to 0.005 mass %.

(Particles P) From the perspective of improving winding quality and suppressing transfer failures, the particle-containing layer preferably contains particles P having an average particle size of 10 nm or more and less than 1 μm. From the perspective of further improving winding quality, the average particle size of particles P is preferably 0.03 μm or more. Furthermore, from the perspective of further suppressing transfer failures, the average particle size of particles P is preferably 0.4 μm or less, and more preferably 0.25 μm or less. Furthermore, in some embodiments, from the perspective of improving conveying performance and winding quality, it is preferred that the average particle size of particles P is greater than the thickness of the particle-containing layer. In other words, it is preferred that the particle-containing layer contains particles P having an average particle size of 10 nm or more and less than 1 μm and having an average particle size greater than the thickness of the particle-containing layer.

When the particle-containing layer contains two or more particles of different particle sizes, it is preferred that at least one of the two or more particles of different particle sizes is particle P. From the perspective of reducing transfer failures and further improving winding quality, it is more preferred that the particle-containing layer contain two or more particles P of different particle sizes.

The average particle size 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). That is, the cross section of the particle-containing layer is observed by SEM or TEM, and the area of each particle is measured using imaging software for all particles existing in the 3μm×4μm field of view, and the diameter of a circle with the same area (area equivalent circle diameter) is calculated, and the arithmetic mean of the obtained area equivalent circle diameter is taken as the average particle size of the particles. In addition, in the measurement of the average particle size, the particle size of the secondary particles in the aggregated state (secondary particle size) is measured for the aggregated particles. Furthermore, when the particle-containing layer contains two or more particles of different particle sizes, two or more peaks of different particle sizes are observed in the distribution of the area equivalent circle diameter measured by the above measurement method. Thus, when the distribution of the area equivalent circle diameter measured by the above measurement method has two or more peaks of different particle sizes, the average value of the area equivalent circle diameter is calculated for each peak, and the average particle size is calculated for each particle of different particle size.

The particle-containing layer may contain a single particle P or may contain two or more particles P. The content of the particles P, including its preferred form, may be the same as the content of the above-mentioned particles.

In some embodiments, from the perspective of transparency and transfer failure, the particle-containing layer preferably contains particles with a small average particle size (hereinafter also referred to as "particles P1"). Specifically, the particle-containing layer preferably contains particles with an average particle size of 100 nm or less as particles P1, and more preferably contains particles with an average particle size of 70 nm or less. There is no particular lower limit for particles P1, but from the perspective of further improving winding quality, 10 nm or more is preferred.

The particles P1 may be used alone or in combination of two or more. The content of the particles P1 varies depending on the purpose and/or use of the polyester film, but 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.

In some embodiments, from the viewpoint of improving winding quality, the particle-containing layer preferably contains particles with a large average particle size (hereinafter also referred to as "particles P2"). Specifically, the particle-containing layer preferably contains particles with an average particle size of more than 100 nm as particles P2. There is no particular upper limit on the particle P2, but it is preferably less than 1 μm. From the viewpoint of preventing transfer failure and further improving winding quality, it is more preferably less than 400 nm, and even more preferably less than 250 nm.

Particle P2 may be agglomerated particles or non-agglomerated particles. From the perspective of transfer failure, agglomerated particles are preferred. It is preferred that the average secondary particle size of agglomerated particles as particles P2 is greater than 100nm. Moreover, among agglomerated particles, particles with an average primary particle size of 100nm or less are preferably agglomerated. If agglomerated particles with an average primary particle size of less than 100nm and an average secondary particle size of more than 100nm are used, the desired Rp can be set, especially when a particle-containing layer is formed by an in-line coating method, and transfer failure and winding quality can be further improved.

The particles P2 may be used alone or in combination of two or more. The content of the particles P2 varies depending on the purpose and/or use of the polyester film, but is preferably 0.01 to 15% by mass, more preferably 0.05 to 10% by mass, and even more preferably 0.1 to 5% by mass relative to the total mass of the particle-containing layer.

From the viewpoint of further improving transfer failure and winding quality, it is preferred that the particle-containing layer contains at least one type of particle P1 and at least one type of particle P2.

The particles contained in the particle-containing layer can be appropriately selected according to the purpose and/or use. When used as a support for a dry film photoresist for forming a fine pattern, if the particles scatter light during exposure through the support, it will cause pattern defects, so high transparency is required in the support. From the perspective of further improving transparency, the content of particles P1 is preferably 50 to 100 mass % relative to the total content of all particles contained in the particle-containing layer, and 70 to 100 mass % is more preferably. In this case, it is preferred that the remainder is particles P2.

On the other hand, when a higher speed conveying is required for the purpose of improving productivity, high conveying performance is required. From the perspective of further improving conveying performance, the content of particles P2 is preferably 10 to 100 mass %, more preferably 10 to 50 mass %, and even more preferably 10 to 30 mass % relative to the total content of all particles contained in the particle-containing layer. In this case, it is preferred that the remainder is particles P1.

(Binder) The particle-containing layer preferably contains a binder. As the binder, a resin binder is preferred. Examples of the resin binder include polyacrylic acid, polyurethane, polyester, and polyolefin.

As polyacrylic acid, there is no limitation as long as it is a polymer having a constituent unit derived from at least one compound selected from the group including acrylate and methacrylate, and known polyacrylic acid can be used. Polyacrylic acid may have a constituent unit derived from a compound other than acrylate and methacrylate (for example, an olefin compound and a styrene compound). As polyurethane, there is no limitation as long as it is a polymer having a urethane bond, and known polyurethane can be used. Polyurethane is generally produced by reacting an isocyanate compound with a polyol compound. As polyester, the polyester described in the above-mentioned "polyester" item can be applied, and the preferred types are also the same. As polyolefin, there is no limitation, and known polyolefin can be used. As polyolefin, for example, polyethylene and polypropylene can be cited.

The particle-containing layer may contain a single binder or two or more binders. From the perspective of the durability of the particle-containing layer and/or the dispersibility of the particles, the content of the binder is preferably 30 to 99.8 mass % relative to the total mass of the particle-containing layer, and more preferably 50 to 99.5 mass %.

(Additives) The particle-containing layer may contain additives other than the above-mentioned particles and binders. 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, antirust agents, and antimold agents.

There is no particular limitation on the surfactant, and examples thereof include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. One surfactant may be used alone, or two or more surfactants may be used in combination. The content of the surfactant is preferably 0.1 to 10% by mass relative to the total mass of the particle-containing layer.

There is no particular limitation on the wax, and it can be natural wax or synthetic wax. Examples of natural wax include palm wax, candelabra wax, beeswax, lignite wax, stone wax, and petroleum wax. In addition, the lubricant described in [0087] of International Publication No. 2017/169844 can also be used. The wax content is preferably 0 to 10% by mass relative to the total mass of the particle-containing layer.

There is no particular limitation on the crosslinking agent, and known ones can be used. As the crosslinking agent, for example, melamine compounds, oxazoline compounds, epoxy compounds, isocyanate compounds and carbodiimide compounds can be cited, and oxazoline compounds and carbodiimide compounds are preferred. As commercial products, for example, CARBODIIMIDE V-02-L2 (manufactured by Nisshinbo Holdings Inc.) and EPOCROS K-2020E (manufactured by NIPPON SHOKUBAI CO., LTD.) can be cited. For details on epoxy compounds, isocyanate compounds and melamine compounds, refer to [0081] to [0083] of Japanese Patent Publication No. 2015-163457. The crosslinking agent described in [0082] to [0084] of International Publication No. 2017/169844 can also be preferably used. As the carbodiimide compound, reference can be made to [0038] to [0040] of Japanese Patent Publication No. 2017-087421. Regarding the oxazoline compound, the carbodiimide compound and the isocyanate compound, the crosslinking agent described in [0074] to [0075] of International Publication No. 2018/034294 can also be preferably used. The content of the crosslinking agent can be appropriately changed according to the application, and is preferably 0 to 50% by mass relative to the total mass of the particle-containing layer. From the perspective of being suitable as a support for the dry film, the content of the crosslinking agent is preferably 0.1 to 10 mass % relative to the total mass of the particle-containing layer.

The thickness of the particle-containing layer can be 0.001 to 5 μm. From the perspective of manufacturing suitability of the particle-containing layer and reducing haze, 0.001 to 2.5 μm is preferred, 0.005 to 2.0 μm is more preferred, 0.01 to 0.18 μm is further preferred, and 0.01 to 0.1 μm is particularly preferred. The thickness of the particle-containing layer is the arithmetic mean of the thicknesses of five locations measured using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

The method for forming the particle-containing layer will be described in detail in the “particle-containing layer forming step” described later.

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

[Physical properties, etc.] Next, the physical properties, etc. of this film are described.

(Orientation) This film is a biaxially oriented polyester film. In the present invention, "biaxial orientation" refers to the property of having molecular orientation in the biaxial direction. The molecular orientation is measured using a microwave transmission type molecular orientation instrument (for example, MOA-6004, manufactured by Oji Scientific Instruments). The angle formed by the biaxial directions is preferably 90°±5°, more preferably 90°±3°, and further preferably 90°±1°. It is preferred that this film has molecular orientation in the longitudinal direction and the width direction.

(Stripe-like defect area) In this film, the total area of the stripe-like defect area observed in the polyester film subjected to the following heat treatment is preferably 40% or less relative to the total area of the observation area.

In the present invention, "stripe-like defects" refer to wrinkles that are stretched in a stripe-like manner along the long side direction of the film and appear in a concave-convex form in the width direction of the film. As described later, the stripe-like defects are generated in the film after manufacturing, so they are mostly irreversibly generated wrinkles. The stripe-like defects are not generated during the heat treatment during the manufacturing of the film, but are derived from the wavy wrinkles generated when the film after manufacturing is heat treated, and the above-mentioned wavy wrinkles are solidified by cooling after the heat treatment. In addition, the "stripe-like defect area" refers to the part where the stripe-like defects are generated in the film surface. If a stripe-like defect occurs in a region of the film (i.e., the stripe-like defect occurs locally in the film surface), the functional layer formed on the film may have uneven thickness, which may affect the properties or appearance of the functional layer. In addition, the stripe-like defect region tends to be significantly generated when the film is heated while a tensile load is applied along the long side direction. In contrast, when the total area of the stripe-like defect region observed after the biaxially oriented polyester film is subjected to the following heat treatment is below the above range, the thickness unevenness of the functional layer formed on the film can be reduced.

In this film, the ratio of the total area of the stripe-like defect region generated when heated at 90°C to the total area of the observation area of the polyester film (hereinafter, also referred to as the "area ratio of the stripe-like defect region") is preferably 40% or less, 30% or less is more preferably, and 18% or less is further preferably. The smaller the value of the area ratio of the stripe-like defect region, the better. As a lower limit, for example, 0% can be cited. In addition, in this film, the area ratio of the stripe-like defect region generated when heated at 120°C is preferably 90% or less, 65% or less is more preferably, and 40% or less is further preferably. By making the area ratio of the stripe-shaped defect region below the above range, the thickness unevenness of the functional layer formed on the film can be reduced. The smaller the value of the area ratio of the stripe-shaped defect region, the better. As a lower limit, for example, 0% can be cited. There is no particular limit to the lower limit of the area ratio of the stripe-shaped defect region. When heated at 90°C or 120°C, the smaller the area ratio of the stripe-shaped defect region, the better. No stripe-shaped defect region, that is, 0%, is even better.

The area ratio of the streak defect region generated when heating at 90°C and 120°C was measured by the following method. (1) A polyester film was conveyed at a conveying speed of 30 m/min and a tension of 100 N/m in the conveying direction using a heating conveyor, and a heating treatment was performed at a surface temperature of 90°C or 120°C for 20 seconds. The heating time during the heating treatment was calculated from the moment when the surface temperature of the film reached the target temperature (90°C or 120°C), and heating was continued for 20 seconds from then on. Here, a non-contact thermometer (e.g., a radiation thermometer) can be used to measure the surface temperature of the film. Regarding the surface temperature of the film, the temperature of the center portion approximately equidistant from both ends in the width direction of the film is measured to determine whether it has reached the target temperature. (2) The polyester film subjected to heat treatment is placed on a black flat plate, and then the polyester film is visually observed from the side while changing the viewpoint in the manner of light reflection from a fluorescent lamp (e.g., rupikae-su manufactured by Mitsubishi Electric Corporation (color temperature: 5000K, average color rendering index (Ra): 84)) installed on the ceiling of the room. The area where the reflected image of the fluorescent lamp projected onto the surface of the polyester film by visual observation fluctuates is defined as a stripe-shaped defect area. (3) The number of observed streak-like defect regions is counted, and the periphery of each streak-like defect region existing in the observation area (area of 1 ^m2 ) of the polyester film observed by visual observation is calibrated. Then, among the two parallel tangents circumscribing the periphery of each streak-like defect region, the distance between the two parallel tangents selected so as to maximize the distance between the tangents is measured as the length L of the major axis, and the distance between the two parallel tangents circumscribing the periphery of the streak-like defect region, which are orthogonal to the two parallel tangents given the length L, is measured as the length S of the minor axis. The area of each streak-like defect region is calculated from the obtained lengths L and S by the following formula. The ratio of the total area of the stripe-shaped defect region to the total area of the observation area of the polyester film is calculated from the equivalent values. The length of the long axis of the stripe-shaped defect region L × the length of the short axis of the stripe-shaped defect region S × π = the area of the stripe-shaped defect region. Since the stripe-shaped defect region is often elliptical or circular as described above, the area of the stripe-shaped defect region can be calculated by the calculation method of (3) above.

FIG1 shows an image (photo) of a polyester film observed in a stripe-shaped defect region generated by the heat treatment of (1) above. The region surrounded by a solid line shown in FIG1 is a stripe-shaped defect region. In the stripe-shaped defect region shown in FIG1, a concave-convex shape stretched along the conveying (MD) direction is observed. In addition, the image (photo) shown in FIG1 shows only a portion of the observed area. Thus, the stripe-shaped defect region is mostly elliptical or circular. Furthermore, when a stripe-shaped defect region is generated, it is mostly an elliptical stripe-shaped defect region showing at least one major axis along the conveying direction.

In the method for producing a polyester film, the conditions of each step can be set so that the cooling rate V of the polyester film in the cooling step becomes 2200 to 3500°C/min and the condition 1 described later is satisfied to produce a biaxially oriented polyester film having an area ratio of a stripe-shaped defect region within the above range.

(Expansion rate) The expansion rate of the polyester film in the width direction at 90°C and 120°C is preferably -0.15 to 0.15% relative to the film width at 30°C, -0.10 to 0.10% is more preferred, 0 to 0.10% is further preferred, and 0 to 0.05% is particularly preferred. By adjusting the expansion rate in the width direction of the polyester film at 90°C and 120°C within the above range, not only the expansion of the film in the width direction during the heating process is suppressed, but also the uneven expansion rate of each part of the film surface can be reduced. As a result, it was observed that the generation of stripe-like defect areas caused by heating can be suppressed.

The expansion rate in the width direction at each temperature of 90°C and 120°C is measured by the following method using a thermomechanical analyzer. (1) Prepare a sample adjusted to at least 20 mm in a direction parallel to the width direction of the biaxially oriented film and 4 mm in a direction perpendicular to the width direction of the biaxially oriented film. (2) Using a thermomechanical analyzer (e.g., TMA-60, manufactured by Shimadzu Corporation), apply a tensile load of 0.1 g to a sample having a width of 4 mm and a length (distance between chucks) of 20 mm. (3) The sample is heated from a temperature of 20°C or higher and less than 30°C (preferably 25°C) to 150°C at a heating rate of 5°C/min, thereby obtaining the value of the sample size at each temperature (°C). (4) The following formula is used to calculate the expansion rate in the width direction at each temperature of 90°C and 120°C from the size of the sample at 30°C (L30), the size at 90°C (L90) and the size at 120°C (L120). In the present invention, the expansion rate in the width direction at 90°C and 120°C is set to the arithmetic mean of the expansion rates obtained using 5 samples respectively. In addition, a positive expansion rate refers to expansion, and a negative expansion rate refers to contraction. Formula: Expansion rate (%) = [(L120 or L90) - L30] / L30 × 100

The ratio (E120/E90) of the expansion rate in the width direction at 120°C (E120) to the expansion rate in the width direction at 90°C (E90) is preferably 0 to 1.5, more preferably 0 to 1.1, and even more preferably 0 to 1.05. When E120/E90 is within the above range, the thickness unevenness of the functional layer can be further suppressed. The expansion rate in the width direction at 90°C (E90) and the expansion rate in the width direction at 120°C (E120) are obtained by the method using the above-mentioned thermomechanical analysis device.

The expansion rate in the width direction of the polyester film can be adjusted by, for example, appropriately setting the stretch ratio, heat treatment temperature, and film width during cooling during the production process of the biaxially oriented film.

(Maximum peak height Rp of the surface) From the perspective of further improving the winding quality, the maximum peak height Rp of the particle-containing layer of the polyester film is preferably 0.005μm (5nm) or more, and more preferably 0.01μm (10nm) or more. From the perspective of further suppressing transfer failures, the maximum peak height Rp of the particle-containing layer of the polyester film is preferably 1μm or less, more preferably 0.5μm or less, further preferably 0.25μm (250nm) or less, and particularly preferably 0.2μm (200nm) or less. Among them, when the particle-containing layer contains inorganic particles, the performance of suppressing transfer failures is more significantly manifested, so it is better to set the maximum peak height Rp of the particle-containing layer to the above range. When the particle-containing layer is formed by an in-line coating method, the maximum peak height Rp of the surface of the particle-containing layer can be adjusted by the average particle size of the particles in the particle-containing layer and the thickness of the particle-containing layer.

The maximum peak height Rp of the surface of the polyester film can be obtained as follows: cut out the polyester film to make a test piece, use the following fine shape measurement device to measure the surface of the obtained test piece under the following conditions, and then use the built-in analysis software to perform particle analysis (multiple levels). The measuring machine and measurement conditions are shown below. In the above measurement, the slice level is set at equal intervals of 10nm, and the average diameter and density of each slice level are measured 5 times while changing the measurement position. The average value is calculated and used as the maximum peak height Rp measurement value. The test piece is fixed to the sample stage so that the X direction of the field of view measurement becomes the width direction of the polyester film.

・Measurement device: surf-corder ET-4000A manufactured by Kosaka Laboratory Ltd. ・Analysis software: i-Face model TDA31 Ver2.2.0.4 JSIS ・Stylus tip radius: 0.5μm ・Measurement field of view: X direction: 380μm, pitch: 1μm Y direction: 280μm, pitch: 5μm ・Stylus pressure: 50μN ・Measurement speed: 0.1mm/s ・Cutoff value: low area - 0.8mm, high area - none ・Leveling: Entire area ・Filter: Gaussian filter (2D) ・Magnification: 100,000 times ・Particle analysis (multiple levels) conditions ・Output content setting: mountain particles ・Magnetic hysteresis width: 5nm ・Slice grade interval: 10nm

(Density) From the viewpoint of achieving a more excellent effect of the present invention, the density of the polyester film is preferably 1.39 to 1.41 g/cm ³ , more preferably 1.395 to 1.405 g/cm ³ , and even more preferably 1.398 to 1.400 g/cm ^3. The density of the polyester film can be measured using an electronic densimeter (product name "SD-200L", manufactured by Alfa Mirage Co., Ltd.).

(Haze) When polyester film is used as a support for dry film photoresist, high transparency is required. In particular, when forming fine patterns such as lines and spaces of 50μm or less, higher transparency is required. In this regard, the haze of the polyester film is preferably 1% or less, 0.5% or less is more preferred, 0.4% or less is further preferred, and 0.3% or less is particularly preferred. The smaller the haze, the better, so there is no lower limit for the haze. If the lower limit of the haze is set for convenience, it is 0% or more. By setting the haze below the upper limit, the scattering of ultraviolet light by the support of the photoresist layer, i.e., the polyester film, can be reduced when the photoresist layer is laminated on the polyester film and exposed by ultraviolet light, and the state of the photoresist pattern wall such as distortion and missing in the patterning of the anti-etching agent after development can be improved.

The haze is measured using a haze meter (for example, NDH-2000, manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.) by a method in accordance with JIS K 7105.

(b ^* value) When polyester film is used as a support for dry film photoresist, high transparency is required. In this regard, the b ^* value in the L ^* a ^* b ^* colorimetric system is preferably 0 to 1, more preferably 0 to 0.8, further preferably 0 to 0.6, and particularly preferably 0 to 0.4. By making the b ^* value in the L ^* a ^* b ^* colorimetric system 0 to 1, the yellowness of the film can be reduced, so that the hue of the film can be made close to colorless. As a result, polyester film can be preferably used in applications requiring high visibility (e.g., display devices).

The b ^* value in the L ^* a ^* b ^* colorimetric system is measured by a transmission method using a spectrocolorimeter (for example, SE-2000, manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.).

(Thickness) From the perspective of being able to suppress the increase in haze value and improving lamination adaptability, the thickness of the polyester film is preferably 100μm or less, less than 50μm is more preferably, and 40μm or less is more preferably. There is no particular lower limit for the thickness, but from the perspective of improving strength and processability, 3μm or more is more preferably, 5μm or more is more preferably, and 10μm or more is more preferably. The thickness of the polyester film is the arithmetic mean of the thicknesses of five locations measured by a scanning electron microscope (SEM).

[Manufacturing method] As a manufacturing method of the present film, for example, a method of biaxially stretching an unstretched polyester film can be cited.

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 multiple stages divided into two or more stages. As the form of sequential biaxial stretching, for example, longitudinal stretching → transverse stretching, longitudinal stretching → transverse stretching → longitudinal stretching, longitudinal stretching → longitudinal stretching → transverse stretching, and transverse stretching → longitudinal stretching are cited, and longitudinal stretching → transverse stretching is preferred.

<Stretching machine> The device used for biaxial stretching is not particularly limited, and a known stretching machine can be used. Below, an example of a stretching machine is described with reference to the diagram.

FIG. 2 is a top view showing an example of a stretching machine for manufacturing polyester film. The stretching machine 100 shown in FIG. 2 has a pair of annular rails 60a and 60b and holding members 2a to 21 mounted on each annular rail and movable along the rails. The annular rails 60a and 60b clamp the film 200 and are arranged symmetrically to each other. The stretching machine 100 holds the film 200 by holding members 2a to 21 and moves the holding members 2a to 21 along the rails, thereby being able to stretch the film 200 in the width direction.

The stretching machine 100 has a zone consisting of a preheating section 10, a stretching section 20, a heat setting section 30, a heat relaxation section 40 and a cooling section 50 in order from the upstream side in the conveying direction. The above zones of the stretching machine 100 are separated by wind shields, and the temperature in each zone can be adjusted by hot air, etc.

The preheating portion 10 is a region for preheating the film 200 .

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

The heat setting portion 30 is a region where the film 200 to be stretched is heated and heat-set in a state where the film 200 to be stretched is stretched.

The heat relaxation portion 40 is a region where the tension of the heat-set film 200 is heat-relaxed by heating the heat-set film 200. As shown in FIG. 2 , in the heat relaxation portion 40 , the film 200 is reduced (relaxed) from the width L1 to the width L2.

The cooling section 50 is a region for cooling the thermally relaxed film 200. By cooling the film 200, the shape of the film 200 can be fixed. FIG. 2 shows that the width of the film 200 fed into the cooling section 50 is L2 and the width of the film 200 fed from the cooling section 50 is L3.

The annular guide rail 60a is provided with holding members 2a, 2b, 2e, 2f, 2i and 2j that are movable along the annular guide rail 60a. The annular guide rail 60b is provided with holding members 2c, 2d, 2g, 2h, 2k and 2l that are movable along the annular guide rail 60b. Holding members 2a, 2b, 2e, 2f, 2i and 2j hold the end of one side of the arrow TD direction of the film 200. Holding members 2c, 2d, 2g, 2h, 2k and 2l hold the end of the other side of the arrow TD direction of the film 200. Holding members 2a to 2l are mostly called clamps or clips, etc. The holding members 2a, 2b, 2e, 2f, 2i and 2j move counterclockwise along the annular guide rail 60a. The holding members 2c, 2d, 2g, 2h, 2k and 2l move clockwise along the annular guide rail 60b.

The holding members 2a to 2d move along the circular guide rail 60a or 60b while holding the end of the film 200 in the preheating section 10, and proceed to the cooling section 50 via the stretching section 20, the heat setting section 30, and the heat relaxation section 40. Then, after the ends of the holding members 2a and 2b and the holding members 2c and 2d at the downstream side in the direction of the arrow MD of the cooling section 50 in the conveying direction (for example, the holding release point P and the holding release point Q in FIG. 2) leave the end of the film 200, they move along the circular guide rail 60a or 60b and return to the preheating section 10. In the above process, the film 200 moves along the direction of the arrow MD, thereby being preheated in the preheating section 10, stretched in the stretching section 20, heat-set in the heat-setting section 30, heat-relaxed in the heat-relaxing section 40, and cooled in the cooling section 50 to perform transverse stretching.

By adjusting the moving speed of the holding members 2a to 21, it is possible to adjust the conveying speed of the film 200. In addition, the moving speeds of the holding members 2a to 21 can be changed independently.

As described above, the stretching machine 100 is capable of performing transverse stretching of the film 200 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 holding members 2a to 21. That is, the stretching machine 100 can also perform biaxial stretching simultaneously.

In order to support the film 200 , the stretching machine 100 may include other holding members (not shown) in addition to the holding members 2 a to 2 l .

Next, a method for producing a polyester film (hereinafter also referred to as "the present production method") which is an example of an embodiment of the present invention will be described in detail.

The present production method is a method for producing a biaxially oriented polyester film, and the aforementioned method comprises: an extrusion molding step of extruding a molten resin containing a raw material polyester in a film form to form an unstretched polyester film containing at least a polyester substrate; a longitudinal stretching step of stretching the unstretched polyester film along a conveying direction to form a uniaxially oriented polyester film; a step of stretching the uniaxially oriented polyester film along a width direction to form a biaxially oriented polyester film; A polyester film is stretched transversely; a biaxially oriented polyester film is heated to be heat-set; a heat-relaxation step is performed by heating the polyester film heat-set by the heat-relaxation step at a temperature lower than that in the heat-relaxation step to heat-relax the polyester film; a cooling step is performed by cooling the polyester film heat-relaxed by the heat-relaxation step; and an expansion step is performed by expanding the heat-relaxed polyester film in the width direction during the cooling step. The manufacturing method also has a particle-containing layer forming step of providing a particle-containing layer containing particles on at least one surface of the polyester substrate.

<Extrusion molding step> The extrusion molding step is a step of forming an unstretched polyester film by extruding a molten resin containing a raw material polyester in a film form by an extrusion molding method. The meaning of the raw material polyester is the same as the meaning of the polyester described in the above item (polyester). The unstretched polyester film formed by the extrusion molding step contains at least a polyester base material.

Extrusion molding is a method of molding a raw material resin into a desired shape by, for example, extruding a melt of the raw material resin using an extruder. The molten resin containing polyester is formed by, for example, using an extruder equipped with one or more screws, heating the above polyester to a temperature above the melting point, and then rotating the screws to perform melt kneading. The polyester is melted in the extruder by heating and kneading by the screws to form a molten body (melt).

The molten material is extruded from the extrusion die through a gear pump and a filter. The extrusion die is also referred to as a "die" (see JIS B8650: 2006, a, extrusion molding machine, No. 134). For example, the extrusion die described in Japanese Patent Publication No. 2005-297266, the extrusion die described in Japanese Patent Publication No. 1-154720, and a combination thereof can also be used. The molten material can be extruded in a single layer or in multiple layers.

In melt extrusion, from the viewpoint of suppressing thermal decomposition (for example, hydrolysis of polyester) in the extruder, it is preferable to replace the inside of the extruder with nitrogen. Also, from the viewpoint of suppressing the mixing temperature to a low level, it is preferable that the extruder is a twin-shaft extruder.

The molten material extruded from the extrusion mold is formed into a film shape by being cooled. For example, the molten material can be formed into a film shape by bringing the molten material into contact with a casting roll and cooling and solidifying the molten material on the casting roll. It is preferred that air (preferably cold air) is further blown to the molten material during the cooling of the molten material.

The temperature of the casting roll is preferably higher than (Tg-10)°C and lower than (Tg+30)°C, more preferably (Tg-7) to (Tg+20)°C, and even more preferably (Tg-5) to (Tg+10)°C. The above-mentioned "Tg" refers to the glass transition temperature of the polyester constituting the film. Here, the temperature of the polyester film and each component in the present manufacturing method can be measured using a non-contact thermometer (e.g., a radiation thermometer). The surface temperature of the film is obtained by measuring the temperature of the central portion of the film in the width direction 5 times and calculating the average value of the obtained measured values.

When a casting roll is used in the extrusion molding step, it is better to improve the adhesion between the casting roll and the molten material. Examples of methods for improving the adhesion include electrostatic application, air knife, air chamber, vacuum nozzle, and contact roll.

The molded body (unstretched polyester film) cooled by a casting roll or the like is peeled off from a cooling member such as a casting roll or the like by a peeling member such as a peeling roll or the like.

<Longitudinal stretching step> The longitudinal stretching step is a step of stretching the unstretched polyester film in the conveying direction (hereinafter, also referred to as "longitudinal stretching"). A uniaxially oriented polyester film is formed by the longitudinal stretching step.

In the longitudinal stretching step, it is preferred to preheat the unstretched polyester film before longitudinal stretching. By preheating the unstretched polyester film, the polyester film can be easily stretched longitudinally. 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 roller having a function of preheating the film is arranged on the upstream side of the longitudinal stretching roller, and the unstretched polyester film is preheated while being conveyed.

In addition, the stretching roller can have the function of preheating the film. The preferred range of the preheating temperature of the film by the stretching roller is the same as the preferred range of the preheating temperature of the preheating roller.

The longitudinal stretching can be performed, for example, by applying tension between two or more pairs of stretching rollers arranged in the conveying direction while stretching the unstretched polyester film in the longitudinal direction. For example, when a pair of stretching rollers A are arranged on the upstream side in the conveying direction and a pair of stretching rollers B are arranged on the downstream side in the conveying direction, the rotation speed of the stretching rollers B is made faster than the rotation speed of the stretching rollers A when the unstretched polyester film is conveyed, thereby stretching the unstretched polyester film in the longitudinal direction.

Regarding the conveying speed (circumferential speed) of the film based on a pair of stretching rollers A disposed on the upstream side of the conveying direction and a pair of stretching rollers B disposed on the downstream side of the conveying direction in the longitudinal stretching step, there is no particular restriction as long as the conveying speed of the film based on the stretching roller A is slower than the conveying speed of the film based on the stretching roller B. The conveying speed of the film based on the stretching roller A is, for example, 5 to 60 m/min, preferably 10 to 50 m/min, and more preferably 15 to 45 m/min. The conveying speed of the film based on the stretching roller B is, for example, 40 to 160 m/min, preferably 50 to 150 m/min, and more preferably 60 to 140 m/min.

The stretching ratio in the longitudinal stretching step is appropriately set according to the application, preferably 2.0 to 5.0 times, more preferably 2.5 to 4.0 times, and even more preferably 2.8 to 4.0 times.

The stretching speed in the longitudinal stretching step is preferably 800 to 1500%/second, more preferably 1000 to 1400%/second, and even more preferably 1200 to 1400%/second. Here, the "stretching speed" refers to the value expressed as a percentage of the length Δd in the conveying direction of the polyester film stretched in 1 second in the longitudinal stretching step divided by the length d0 in the conveying direction of the polyester film before stretching.

In the longitudinal stretching step, it is preferred to heat the unstretched polyester film. This is because it is easy to stretch longitudinally by heating. 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 further 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 further preferably 85 to 100°C.

As a method for heating the unstretched polyester film in the longitudinal stretching step, there can be cited a method of heating a stretching roll or the like in contact with the unstretched polyester film. As a method for heating the roll, there can be cited, for example, a method of installing a heater inside the roll and a method of installing a pipe inside the roll and flowing a heated fluid into the pipe. In addition to the above, there can be cited, for example, a method of blowing warm 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 the unstretched polyester film near the heat source.

The longitudinal stretching step of longitudinally stretching the unstretched polyester film is not limited to the above method. In the longitudinal stretching step, the unstretched polyester film is longitudinally stretched by utilizing the difference in the conveying speed of two pairs of stretching rollers, but the unstretched polyester film may be longitudinally stretched using one or more high-speed stretching rollers disposed between the two stretching rollers and conveying the film at a faster conveying speed than the stretching rollers to produce a uniaxially oriented polyester film. In addition, in the longitudinal stretching step, the film is conveyed by sandwiching two rollers (a pair of rollers) facing each other, but the stretching rollers used in the longitudinal stretching step may not have opposing rollers and may consist of only one roller in contact with one surface of the polyester film.

<Transverse stretching step> The transverse stretching step is a step of transversely stretching the uniaxially oriented polyester film. The transverse stretching step is performed, for example, in the transverse stretching section 20 of the above-mentioned stretching machine 100.

In the transverse stretching step, it is preferred to preheat the polyester film before transverse stretching. By preheating the polyester film, the polyester film can be easily stretched transversely. The preheating temperature is preferably (Tg-10) to (Tg+60)°C, and more preferably (Tg) to (Tg+50)°C. Specifically, the preheating temperature is preferably 80 to 120°C, and more preferably 90 to 110°C.

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, and is preferably greater 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 further preferably 3.5 to 4.5 times. When the transverse stretching step is performed in the transverse stretching section 20 of the stretching machine 100, the transverse stretching ratio a is obtained by the ratio (L1/L0) of the film width L1 when it is sent out from the transverse stretching section 20 and the film width L0 when it is sent into the transverse stretching section 20.

The area ratio represented by 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 15.0 times. If the area ratio is above the lower limit, the molecular orientation in the width direction of the film becomes good. If the area ratio is below the upper limit, it is easy to maintain a state in which the molecular orientation is not easily relaxed when subjected to heat treatment.

The heating temperature in the transverse stretching step is preferably (Tg-10) to (Tg+80)°C, more preferably (Tg) to (Tg+70)°C, and further 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 further preferably 115 to 130°C.

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

<Heat setting step> In the present manufacturing method, a heat setting step and a heat relaxation step are performed as a heating treatment of the polyester film stretched transversely by the transverse stretching step. In the heat setting step, the biaxially oriented polyester film obtained by the transverse stretching step is heated to be heat set. The polyester is crystallized by heat setting, thereby suppressing the shrinkage of the polyester film. The heat setting step is performed, for example, in the heat setting section 30 of the stretching machine 100.

The surface temperature of the polyester film in the heat setting step (heat setting temperature T1) is preferably 190 to 240°C, more preferably 200 to 240°C, and even more preferably 210 to 230°C. In the heat setting step, the polyester film is heated while the highest temperature reached on the surface is controlled to be the above-mentioned heat setting temperature T1.

In the heat setting step, the deviation of the 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, further preferably 0.5 to 5.0°C, and particularly preferably 0.5 to 4.0°C. By controlling the variation of the surface temperature in the width direction of the film within the above range, the variation of the degree of crystallization in the width direction can be suppressed.

As the heating method, there are, for example, a method of blowing hot air to the film and a method of radiating the film. As the device used in the radiating heating method, there is, for example, an infrared heater.

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.

<Heat relaxation step> In the heat relaxation step, the polyester film heat-set in the heat setting step is heated at a lower temperature than the heat setting step to perform heat relaxation. The residual strain of the polyester film can be relaxed by heat relaxation. The heat relaxation step is performed, for example, in the heat relaxation section 40 of the stretching machine 100.

The surface temperature of the polyester film in the heat relaxation step (heat relaxation temperature T2) is preferably 5°C or more lower than the heat setting temperature T1, more preferably 15°C or more lower, further preferably 25°C or more lower, and particularly preferably 30°C or more lower. That is, the heat relaxation temperature T2 is preferably 235°C or less, more preferably 225°C or less, further preferably 210°C or less, and particularly preferably 200°C or less. The lower limit of the heat relaxation temperature T2 is preferably 100°C or more, more preferably 110°C or more, and further preferably 120°C or more. In the heat relaxation step, the heat treatment is performed while controlling the highest temperature reached on the surface of the polyester film to the above-mentioned heat relaxation temperature T2.

Examples of the heating method include a method of blowing hot air onto the film and a method of radiantly heating the film. Examples of the device used in the radiantly heating method include an infrared heater.

<Cooling step> This manufacturing method includes a cooling step for cooling the heat-relaxed polyester film. The cooling step and the expansion step described later are performed, for example, in the cooling section 50 of the stretching machine 100.

As a method for cooling the polyester film in the cooling step, for example, there can be cited a method of blowing air (preferably cold air) into the film and a method of bringing the film into contact with a temperature-adjustable member (for example, a temperature-adjusting roller). From the perspective of distinguishing from the heat relaxation step, the cooling temperature in the cooling step is preferably 130°C or less. The cooling temperature is more preferably 30 to 120°C, more preferably 30 to 100°C, and particularly preferably 30 to 80°C.

In the present manufacturing method, the cooling step is performed in such a manner that the cooling rate V of the polyester film becomes 2200 to 3500°C/minute. By adjusting the cooling rate V within the above range, the thickness unevenness of the functional layer laminated on the biaxially oriented film can be reduced. Although the details of the mechanism for reducing the thickness unevenness of the functional layer by determining the range of the cooling rate V are unclear, it can be inferred that the reason is that by effectively reducing the temperature of the film surface and setting the cooling rate to suppress the temperature unevenness of the film surface, the inherent strain in the film after cooling can be reduced, thereby suppressing the generation of ripples accompanying the high temperature treatment when the functional layer is laminated. Considering the above viewpoints, the cooling rate V in the cooling step is preferably 2200-3000℃/min, and more preferably 2300-2600℃/min.

The cooling rate V of the polyester film in the cooling step can be measured using a non-contact thermometer. For example, when the cooling step is performed in the cooling section 50 of the stretching machine 100, the surface temperature of the film 200 fed into the cooling section 50 from the heat relaxation section 40 and the surface temperature of the film 200 fed out of the cooling section 50 are measured to obtain the temperature difference ΔT (°C). The cooling rate V is obtained by dividing the obtained temperature difference ΔT (°C) by the retention 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 conveying speed of the film.

The heat setting step, heat relaxation step and cooling step in the manufacturing method are preferably performed sequentially and continuously. This is because the repeated load (thermal history) of heating and cooling the polyester film is reduced, the inherent strain in the film is reduced, and the generation of streak defects can be suppressed.

<Expansion step> This manufacturing method has an expansion step of expanding the heat-relaxed polyester film in the above-mentioned cooling step in the width direction. In the cooling step, "expanding the polyester film in the width direction" means that tension is applied to the polyester film in the width direction during the cooling step in such a way that the film width at the end of the cooling step (L3 in FIG. 2) is wider than the film width of the polyester film at the start of the cooling step (L2 in FIG. 2).

There is no particular limitation on the method of expanding the polyester film in the width direction during the cooling step. For example, when the biaxially oriented polyester film is manufactured using the above-mentioned stretching machine 100, the distance between the annular rails 60a and 60b at the end point (holding release point P and holding release point Q) of the cooling section 50 is made wider than the distance between the annular rails 60a and 60b at the start point of the cooling section 50, thereby expanding the film 200 held by each holding member in the width direction during the cooling step. As long as the film width is expanded before and after the cooling step, the expansion step can be performed continuously or intermittently from the beginning of the cooling step to the end, or it can be performed only during a period of time during the cooling step. The expansion step is preferably performed below 130°C. Among them, 30-120°C is more preferred, 30-100°C is further preferred, and 30-80°C is particularly preferred.

If the expansion rate of the polyester film in the width direction based on the expansion step, that is, the ratio of the film width at the end of the cooling step to the film width before the start of the cooling step is greater than 0, there is no special restriction, but from the perspective of the better effect of the present invention, the percentage b of the above expansion rate is preferably 0.001% or more, and 0.01% or more is more preferably. There is no special restriction on the upper limit, and the percentage b of the above expansion rate is preferably 1.3% or less, 1.2% or less is more preferably, and 1.0% or less is further preferably. By setting the expansion rate of the film width below the above upper limit, even when a strong tension is applied in the conveying direction in order to convey the film at high speed during production (for example, when the tension in the conveying direction is 100 N/m or more), it is possible to suppress the disorder of the cut surface in the cutting step described later and the breakage of the film accompanying the disordered cutting.

<Particle-containing layer forming step> The present manufacturing method has a particle-containing layer forming step of providing a particle-containing layer on at least one surface of a polyester substrate. The meaning of the particle-containing layer formed by the particle-containing layer forming step is the same as the meaning of the particle-containing layer described in detail in the above-mentioned <Particle-containing layer>. The particle-containing layer can be formed at any stage in 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 constituting the particle-containing layer and drying it as needed, and a method of forming a particle-containing layer simultaneously with the formation of the polyester substrate by a co-extrusion method.

First, a method for forming a particle-containing layer using a coating liquid for a particle-containing layer is described. The coating liquid for a particle-containing layer can be prepared by mixing particles contained in the particle-containing layer, a binder and an additive added as needed, and a solvent. As the solvent, for example, water, ethanol, toluene, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether can be cited. Among them, water is preferred from the viewpoints of environment, safety, and economy.

The coating liquid for the particle-containing layer may contain a single solvent or two or more solvents. The content of the solvent is preferably 80 to 99 mass % relative to the total mass of the coating liquid for the particle-containing layer, and more preferably 90 to 98 mass %. That is, in the coating liquid for the particle-containing layer, the total content of the components (solid components) other than the solvent is preferably 0.5 to 20 mass % relative to the total mass of the coating liquid for the particle-containing layer, and more preferably 1 to 10 mass %. The components other than the solvent in the coating liquid for the particle-containing layer, including the preferred embodiment, are the same as the contents described for the components contained in the above-mentioned 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 components of the coating liquid for the particle-containing layer is the same as the preferred content of each component relative to the total mass of the above-mentioned particle-containing layer. The average particle size of the particles contained in the coating liquid for the particle-containing layer is measured using a laser diffraction/scattering particle size distribution measuring device ("LA-950", manufactured by HORIBA, Ltd.). In addition, when commercially available particles are used, the average particle size of the particles may be a catalog value.

The coating method of the particle-containing layer coating liquid is not particularly limited, and a known method can be used. Examples of the coating method include spray coating, slit coating, roll coating, blade coating, spin coating, rod coating, and dip coating.

As a method for forming a particle-containing layer using a coating liquid for a particle-containing layer, either the so-called on-line coating method in which the coating liquid is applied to at least one surface of the polyester substrate while the polyester substrate is transported, or the so-called off-line coating method in which the coating liquid is applied separately after manufacturing a biaxially oriented polyester substrate, can be applied. However, from the perspective of higher efficiency and the perspective of imparting transparency, the on-line coating method is preferred. In the on-line coating method, the polyester substrate on which the coating liquid for the particle-containing layer is applied can be an unstretched polyester substrate or a uniaxially oriented polyester substrate, and a uniaxially oriented polyester substrate is preferred.

Next, a method for forming a particle-containing layer simultaneously with the formation of a polyester substrate by co-extrusion is described. The method for forming a particle-containing layer by co-extrusion is not particularly limited. For example, a particle-containing layer can be formed by preparing a resin composition containing particles constituting the particle-containing layer and a binder and additives added as needed, heating and melt-kneading the obtained resin composition according to the method described in the above <Extrusion Forming Step>, thereby preparing a melt of the resin composition, and extruding it together with the melt of the polyester using an extruder.

As the particle-containing layer forming step, from the viewpoint of being able to shorten the heating time of the polyester substrate in the manufacturing step and being able to reduce the strain inside the polyester substrate, it is preferable to use an online coating method step of forming the particle-containing layer between the longitudinal stretching step and the transverse stretching step using a coating liquid for the particle-containing layer or a co-extrusion molding step of simultaneously forming the polyester substrate and the particle-containing layer using a first melt containing polyester constituting the polyester substrate and a second melt containing particles and a binder. Among them, it is preferable to apply the above-mentioned online coating method to form the particle-containing layer on a uniaxially oriented polyester substrate between the longitudinal stretching step and the transverse stretching step. After the particle-containing layer is formed by applying a coating liquid to at least one surface of a uniaxially oriented polyester substrate, the polyester substrate and the particle-containing layer are stretched transversely at the same time, thereby improving the adhesion between the polyester substrate and the particle-containing layer. The specific method of transverse stretching at this time is described in the above transverse stretching step.

The present manufacturing method may include a winding step of obtaining a roll-shaped biaxially oriented polyester film by winding the biaxially oriented polyester film obtained in the above step. In addition, the present manufacturing method may also include a cutting step of continuously cutting the polyester film along the conveying direction to cut at least one end of the polyester film in the width direction before the winding step is performed.

<Manufacturing conditions> This manufacturing method satisfies the following condition 1. Condition 1: When the melting point of the polyester constituting the polyester substrate is set to Tm (°C), the heat setting temperature in the heat setting step is set to T1 (°C), the stretching ratio of the uniaxially oriented polyester film in the transverse stretching step is set to a, and the percentage of the expansion rate in the width direction of the heat-relaxed polyester film in the expansion step is set to b (%), the value C of the product (A×B) of A calculated by the following formula (1) and B calculated by the following formula (2) is -4.0 to 4.0. However, the case where one of A and B is 0 is excluded. A=Tm-T1-30   (1) B=a/5-b   (2)

Although the details of the mechanism for reducing the uneven thickness of the functional layer by setting the conditions of each step in a manner that satisfies the above condition 1 are not clear, it is speculated that this is because excessive crystallization of the polyester is suppressed in the heat setting step, and the polyester is expanded in the width direction at a predetermined expansion rate in the cooling step, thereby increasing the proportion of the polyester molecular chain in the width direction, thereby reducing the dimensional change rate due to heating in the subsequent step, and as a result, the generation of stripes accompanying the high temperature treatment in the step of laminating the functional layer can be suppressed. From the above viewpoints, the absolute value of the above value C is preferably 0.1 to 0.7, and the above value C is more preferably 0.1 to 0.5. In addition, as mentioned above, when one of A and B is 0, condition 1 is not satisfied, but when both A and B are 0, condition 1 is satisfied.

In the present production method, the melting point of the polyester constituting the polyester substrate is further set to Tm (°C), the heat setting temperature in the heat setting step is set to T1 (°C), the stretching ratio of the uniaxially oriented polyester film in the transverse stretching step is set to a, the percentage of the expansion rate in the width direction of the heat-relaxed polyester film in the expansion step is set to b (%), and the cooling rate in the cooling step is set to V (°C/minute). It is preferred that A calculated by the above formula (1), B calculated by the above formula (2) and D calculated by the cooling rate V by the following formula (3) is 1 to 10000. D = (A × B) ² × V (3)

Although the details of the mechanism for reducing the thickness unevenness of the functional layer by setting the conditions of each step so that the value D becomes the above range are not clear, it is estimated to be the same mechanism as the mechanism for reducing the thickness unevenness by determining the range of the cooling speed V and the range of the value C. From the above viewpoint, the value D is preferably 0.1 to 6000, and more preferably 1 to 1500.

There is no particular restriction on the conveying speed of the polyester film in each step of the manufacturing method except the longitudinal stretching step. When the above-mentioned stretching machine 100 is used to perform the transverse stretching step, the heat setting step, the heat relaxation step, the cooling step and the expansion step, the conveying speed of the polyester film is preferably 50 to 200 m/min, and more preferably 80 to 150 m/min from the perspective of productivity and quality. In addition, after the cooling step, the conveying speed of the polyester film until it is wound in the above-mentioned winding step is preferably 50 to 200 m/min, and more preferably 80 to 150 m/min. The conveying speed of the polyester film in the longitudinal stretching step is as described above.

In addition, in each step except the longitudinal stretching step, there is no particular restriction on the tension in the transport direction applied to the polyester film. When the above-mentioned stretching machine 100 is used to perform the transverse stretching step, the heat setting step, the heat relaxation step, the cooling step and the expansion step, the tension in the transport direction applied to the polyester film can be adjusted by the stretching conditions. In addition, after the cooling step, the tension in the transport direction applied to the polyester film until it is wound in the above-mentioned winding step is preferably 3 to 30 N/m, and more preferably 5 to 20 N/m.

[Laminated film] The use of the present film is not particularly limited, and it is preferred to further laminate a functional layer to produce a laminated film. As the functional layer laminated on the present film, for example, a decorative layer, a photosensitive resin layer, a magnetic layer, a peeling layer, an adhesive layer, a conductive layer, a refractive index adjustment layer, and a visibility layer can be cited. As a laminated film, in order to maintain the slipperiness (transportability) based on the particle-containing layer, it is preferred that the particle-containing layer is provided only on one surface of the polyester substrate and the functional layer is provided on the surface of the polyester substrate opposite to the particle-containing layer.

As more specific examples of laminated films, the following can be cited: a decorative film whose functional layer is a decorative layer, a photosensitive transfer film whose functional layer is a photosensitive resin layer and is used as a support for a dry film photoresist, a release film whose functional layer is a release layer (a protective film for dry film photoresist, a release film for ceramic green sheet manufacturing, a release film for semiconductor step manufacturing), a functional layer Adhesive film for adhesive layer (adhesive film for semiconductor manufacturing step), film for transparent conductive substrate whose functional layer is transparent conductive layer, photosensitive transfer film for forming etching resist film whose functional layer is photosensitive resin layer and visibility layer, and photosensitive transfer film for forming protective film for touch panel whose functional layer is photosensitive resin layer and refractive index adjustment layer.

The method of laminating the 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 a material constituting the functional layer on the surface of the biaxially oriented polyester film. From the viewpoint of better productivity, it is more preferable to form the functional layer by applying the coating liquid for the functional layer on 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 heat treatment in the step of forming the functional layer, the generation of stripe-shaped defective areas in the biaxially oriented polyester film can be suppressed and the thickness unevenness of the laminated functional layer can be suppressed.

The laminated film may have layers other than the present film and the functional layer. Examples of the layers other than the present film and the functional layer include a base layer containing an adhesive resin provided for the purpose of improving the adhesion between the present film and the functional layer.

The film is preferably used as a support for dry film photoresist. A photosensitive resin layer can be provided as a functional layer, and then a decorative layer, a refractive index adjustment layer and/or a visibility layer can be laminated. If there are multiple functional layers, there is a tendency for uneven thickness to occur due to heating each time the layers are laminated, but the problem of uneven thickness can be solved by using the film. There is no particular restriction on the photosensitive resin layer, and the negative type is preferred. Specifically, the adhesive polymer, ethylenically unsaturated compound or photopolymerization initiator described in the International Publication No. 2018/105313 can be cited as a preferred form. The photosensitive resin layer is preferably a layer having an alkaline soluble acrylic resin with a ring structure, a multifunctional acrylate, an oxime-based photopolymerization initiator or a bisimidazole-type photopolymerization initiator.

When used in a dry film photoresist support for forming an electrode protective film for a touch panel, it is preferred to have a refractive index adjustment layer laminated separately from the photosensitive resin layer. As a preferred form of the refractive index adjustment layer, the second curable transparent resin layer described in Japanese Patent Publication No. 2014-108541 can be cited. The refractive index of the refractive index adjustment layer is preferably 1.6 or more, and the refractive index adjustment layer preferably has metal oxide particles with a high refractive index such as titanium oxide and zirconium oxide.

When used to form a dry film photoresist support for decorative patterns, the photosensitive resin layer is preferably colored. The colored photosensitive resin layer is preferably formed from the photosensitive resin composition described in the specification of International Publication No. 2017/208849. The colored photosensitive resin layer is preferably a layer having a pigment as a colorant, and more preferably a layer having a pigment, a binder polymer, a multifunctional acrylate, and a photopolymerization initiator.

When used as a dry film photoresist support for etching resist used in forming a fine pattern of less than 50μm, it is preferred to have a visible layer separately from the photosensitive resin layer. By having a visible layer, it is possible to visually identify the pattern in the step of confirming the latent image.

The film is preferably used as a peeling film for manufacturing ceramic green sheets. In the case of a peeling film, a peeling layer is often provided as a functional layer. As a preferred form of the peeling layer, a layer having a polysilicone resin can be cited. [Example]

The following examples are given to further illustrate the present invention. The materials, usage amounts, ratios, processing contents and processing sequences shown in the following examples can be appropriately changed as long as they do not deviate from the purpose of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. In addition, unless otherwise specified, "parts" and "%" are based on mass.

Hereinafter, in this embodiment, the labeling of a single "film" includes both the polyester substrate monomer and the state having the polyester substrate and the particle-containing layer, and includes all of the unstretched film, the uniaxially oriented film, and the biaxially oriented film. In addition, in each step of this embodiment, a non-contact thermometer (AD-5616 (product name), manufactured by A&D, emissivity 0.95) is used to measure the temperature of the center portion in the width direction of the film 5 times, and the arithmetic average of the obtained measured values is set as the measured value of the surface temperature of the film.

[Example 1] <Extrusion molding step> Using the titanium compound described in Japanese Patent No. 5575671 (citric acid chelated titanium complex, VERTEC AC-420, manufactured by Johnson Matthey Co., Ltd.) as a polymerization catalyst, polyethylene terephthalate particles were produced. Specifically, 1 ton (1000 kg) of terephthalic acid was mixed with 390 kg of ethylene glycol and 9 mass ppm of Ti atoms relative to the polyethylene terephthalate produced by the titanium compound. The obtained mixture was continuously supplied to a reaction device for esterification reaction. In addition, magnesium acetate tetrahydrate in an amount of 81 mass ppm of Mg atoms relative to the generated polyethylene terephthalate and trimethyl phosphate in an amount of 73 mass ppm of P atoms relative to the generated polyethylene terephthalate were added to the mixture to carry out polycondensation reaction to produce polyethylene terephthalate pellets. The obtained pellets were dried to a moisture content of 50 ppm or less, and then put into the hopper of a single-axis kneading extruder with a diameter of 30 mm, and then melted and extruded at 280°C. After passing the melt through a filter (pore size 3μm), it was extruded from a die onto a cooling drum at 25°C to obtain an unstretched film made of polyethylene terephthalate. In addition, the extruded molten body (melt) is brought into close contact with a cooling roller by electrostatic application. The melting point (Tm) of the polyethylene terephthalate constituting the unstretched film is 258°C, and the glass transition temperature (Tg) is 80°C.

<Longitudinal stretching step> The above-mentioned unstretched film was subjected to a longitudinal stretching step by the following method. Under the following conditions, the preheated unstretched film was passed between two pairs of rolls with different circumferential speeds and stretched in the longitudinal direction (transport direction), thereby producing a uniaxially oriented film. (Longitudinal stretching conditions) Preheating temperature: 75°C Stretching temperature: 90°C Stretching ratio: 3.4 times Stretching speed: 1300%/second

<Particle-Containing Layer Formation Step> The particle-containing layer coating liquid described below was applied to one side of a longitudinally stretched uniaxially oriented film (polyester substrate) by a rod coater so that the solid content weight of the coating film relative to the surface area of the uniaxially oriented film became 5.6 g/m ² .

(Coating liquid for particle-containing layer) A coating liquid for a particle-containing layer (coating liquid A) was prepared by mixing the components shown below. A coating liquid for a particle-containing layer (coating liquid A) was prepared by mixing the components shown below. The prepared coating liquid A was filtered using a filter with a pore size of 6 μm (F20, manufactured by MAHLE Filter Systems Japan Corp.) and subjected to membrane degassing (2x6 radial flow super hydrophobic, manufactured by Polypore International Inc.), and then applied to the surface of a uniaxially oriented film and dried in hot air at 100°C to form a slippery coating layer. ・Acrylic resin (as a solid component, an aqueous dispersion of a copolymer composed of methyl methacrylate, styrene, 2-ethoxyhexyl acrylate, 2-hydroxyethyl methacrylate and acrylic acid (containing in a mass ratio of 59:8:26:5:2) at 27.5% by mass): 167 parts ・Non-ionic surfactant ("NAROACTY (registered trademark) CL95", manufactured by Sanyo Chemical Industries, Ltd., polyoxyalkylene alkyl ether, solid content 100% by mass): 0.7 parts ・Anionic surfactant ("RAPISOL (registered trademark) A-90", manufactured by NOF CORPORATION, solid content 1% by mass aqueous dilution): 55.7 parts ・Wax ("Cellosol (registered trademark) 524", manufactured by CHUKYO YUSHI CO., LTD., ester wax dispersion, solid content 30 mass%): 7 parts ・ Crosslinking agent ("CARBODIIMIDE (registered trademark) V-02-L2", Nisshinbo Chemical Inc., carbodiimide compound, solid content 10 mass% water dilution): 20.9 parts ・ Non-agglomerated particles ("SNOWTEX XL", average particle size 50nm, colloidal silica, Nissan Chemical Industries, Ltd., solid content 40 mass% water dispersion): 2.8 parts ・ Agglomerated particles ("AEROSILOX50", average secondary particle size 200nm, agglomerated silica, average primary particle size 40nm, NIPPON AEROSIL CO., LTD., solid content 10 mass% water dispersion): 2.95 parts ・ Water: 743 parts

<Transverse stretching step> The film subjected to the longitudinal stretching step and the particle-containing layer forming step was stretched in the width direction using a tenter under the following conditions to produce a biaxially oriented film. (Transverse stretching conditions) Preheating temperature: 100°C Stretching temperature: 120°C Stretching ratio: 4.3 times Stretching speed: 50%/second

<Heat-setting step> The biaxially oriented film subjected to the above-mentioned transverse stretching step was heated under the following conditions using a tenter, thereby performing a heat-setting step of the heat-setting film. (Heat-setting conditions) Heat-setting temperature T1: 227°C Heat-setting time: 6 seconds

<Heat relaxation step> Next, the heat-set film was heated under the following conditions to perform a heat relaxation step to relax the film. In the heat relaxation step, the film width was reduced by narrowing the distance between the holding members of the tenter holding both ends of the film (tenter width) compared with the end of the heat setting step. The following heat relaxation rate ΔLr was calculated from the film width L2 at the end of the heat relaxation step relative to the film width L1 at the start of the heat relaxation step by the formula Lr=(L1-L2)/L1×100. (Thermal relaxation conditions) Thermal relaxation temperature T2: 190℃ Thermal relaxation rate Lr: 4%

<Cooling step and expansion step> A cooling step for cooling the heat-relaxed film was performed under the following conditions. In the cooling step, an expansion step for expanding the width of the film by expanding the width of the tenter was performed to compare the film width at the end of the heat-relaxation step. The cooling speed V described below was obtained by setting the retention time from the film being fed into the cooling section 50 of the stretching machine 100 to being fed out as the cooling time ta, and dividing the temperature difference ΔT (°C) between the film surface temperature measured when the film was fed into the cooling section 50 and the film surface temperature measured when the film was fed out of the cooling section 50 by the cooling time ta. In addition, the following expansion rate ΔL is obtained from the film width L3 at the end of the cooling step relative to the film width L2 of the polyester film at the beginning of the cooling step by the formula ΔL=(L3-L2)/L2×100. (Cooling conditions) Cooling rate V: 2500℃/min Cooling time ta: 3.1 seconds (Expansion conditions) Expansion rate ΔL: 0.6%

<Winding step> The film cooled by the cooling step was cut continuously along the conveying direction at 20 cm from both ends of the film in the width direction using a cutting device to cut both ends of the film. Then, after extrusion processing (rolling) was performed on the area from both ends of the film to 10 mm in the width direction, the film was rolled up at a tension of 40 kg/m. By the above method, a biaxially oriented film was produced. The obtained biaxially oriented film had a thickness of 31 μm, a width of 1.5 m, and a winding length of 7000 m. In addition, the thickness of the particle-containing layer of the obtained biaxially oriented film was 40 nm. In addition, the results of the measurement in the above method confirmed that the particle-containing layer of the obtained biaxially oriented film contained particles with an average particle size of 50nm and particles with an average particle size of 200nm.

[Example 2] As a coating liquid for the particle-containing layer, a coating liquid B having the same composition as coating liquid A except that it does not contain non-agglomerated particles was used. In addition, a biaxially oriented film was prepared according to the method described in Example 1.

[Examples 3 to 11] The heat setting temperature T1 in the heat setting step, the cooling speed V in the cooling step, and the expansion rate ΔL in the expansion step were controlled to the values described in Table 1 described later. In addition, a biaxially oriented film was produced according to the method described in Example 1.

[Examples 12 to 17] Biaxially oriented films were prepared according to the method described in Example 1 except that the particles listed in Table 1 were used as non-agglomerated particles without containing agglomerated particles and the thickness of the layer containing the particles was adjusted to the value listed in Table 1. The details of the particles listed in Table 1 are shown below. 450nm non-agglomerated particles: SNOWTEX MP-4540M, manufactured by Nissan Chemical Industries, Ltd., average particle size 450nm, colloidal silica 200nm non-agglomerated particles: SNOWTEX MP-2040, manufactured by Nissan Chemical Industries, Ltd., average particle size 200nm, colloidal silica 100nm non-agglomerated particles: SNOWTEX ZL, manufactured by Nissan Chemical Industries, Ltd., average particle size 100nm, colloidal silica 50nm non-agglomerated particles: SNOWTEX XL, manufactured by Nissan Chemical Industries, Ltd., average particle size 50nm, colloidal silica 300nm non-agglomerated particles: divinylbenzene/styrene copolymer crosslinked particles, average particle size 300nm

[Example 18] Instead of the extrusion molding step performed in Example 1, the melt produced in the extrusion molding step of Example 1 and the melt of the following resin H were co-extruded through a cooling column at 25°C to produce an unstretched film composed of polyethylene terephthalate and a particle-containing layer, and in addition, a biaxially oriented film was produced according to the method described in Example 1. In addition to mixing divinylbenzene/styrene copolymer crosslinked particles having an average particle size of 300nm, particles of resin H containing non-agglomerated particles were produced according to the method for producing particles of polyethylene terephthalate in Example 1. The obtained pellets were dried until the moisture content was less than 50 ppm, and then put into the hopper of a 30 mm diameter uniaxial kneading extruder, and then melted at 280°C to produce a melt of resin H. The thickness of the obtained biaxially oriented film was 31 μm, and the thickness of the particle-containing layer was 2 μm.

[Examples 19 to 21] In the extrusion molding step, the thickness of the unstretched film made of polyethylene terephthalate was adjusted so that the thickness of the produced biaxially oriented polyester film became the value described in Table 1. In addition, a biaxially oriented film was produced according to the method described in Example 1. In addition, in Example 20, the above-mentioned coating liquid F was used as a coating liquid for the particle-containing layer.

[Example 22] In the heat setting step, the heat setting temperature T1 was controlled to be the value described in Table 1. In addition, a biaxially oriented film was prepared according to the method described in Example 1.

[Comparative Examples 1 to 5] The heat setting temperature T1 in the heat setting step, the cooling speed V in the cooling step, and the expansion rate ΔL in the expansion step were controlled to the values described in Table 1 described later, and the above-mentioned coating liquid B was used as the coating liquid for the particle-containing layer in Comparative Examples 1 to 4. In addition, a biaxially oriented film was produced according to the method described in Example 1.

[Measurement of physical properties] The following physical properties were measured for each biaxially oriented film of Examples 1 to 25 and Comparative Examples 1 to 6. The measurement results are shown in Table 1. In addition, according to the above-mentioned measurement method, the thickness of the particle-containing layer and the average particle size of the particles contained in the particle-containing layer were measured for each biaxially oriented film of Examples 2 to 25 and Comparative Examples 1 to 6. These measurement results are also shown in Table 1.

<Density> The density (g/cm ³ ) of the biaxially oriented film was measured using an electronic densitometer (product name “SD-200L”, manufactured by Alfa Mirage Co., Ltd.).

<Stripe defect area (90℃, 120℃)> The biaxially oriented film was heat treated at 90℃ or 120℃ for 20 seconds while being transported at a transport speed of 30m/min and a tension of 100N/m in the transport direction using a heating conveyor. The heating temperature during the heat treatment refers to the surface temperature of the film. The heating time during the heat treatment is calculated from the moment when the surface temperature of the film reaches the target temperature (90℃ or 120℃). The heat-treated biaxially oriented film was placed on a black flat plate, and then the biaxially oriented film was visually observed from the side while changing the viewpoint of light reflection from a fluorescent lamp [Rupikae-su manufactured by Mitsubishi Electric Corporation (color temperature: 5000K, average color rendering rating (Ra): 84)] installed on the ceiling of the room. By visually observing an area of 1m×1m, the area where the reflection image of the fluorescent lamp on the surface of the biaxially oriented film fluctuated was defined as a stripe-shaped defect area. Then, the ratio (area ratio) of the total area of the observed stripe-shaped defect areas to the total area of the observed area of the biaxially oriented film was calculated by the method described above (see the item "Stripe-shaped defect area" above).

<Expansion rate (90°C, 120°C)> The expansion rate of the biaxially oriented film in the width direction at 90°C and 120°C was measured using a thermomechanical analyzer (TMA-60, manufactured by Shimadzu Corporation) according to the above method (see the item "Expansion rate" above).

<Maximum peak height Rp> The maximum peak height Rp of the surface of the biaxially oriented film is obtained as follows: a test piece is cut out of the manufactured biaxially oriented film, and the surface of the obtained test piece is measured under the conditions described above using the micro-shape measuring device described above, and then particle analysis (multiple levels) is performed using the built-in analysis software. In the measurement of the maximum peak height Rp, the slice level is set to an equal interval of 10nm, and the average diameter and density of each slice level are measured 5 times while changing the measurement position, and the average value is calculated and set as the measured value of the maximum peak height Rp. The test piece is fixed to the sample stand so that the X direction of the field of view measurement becomes the width direction of the polyester film.

[Evaluation] The following evaluations were performed on each biaxially oriented film of Examples 1 to 22 and Comparative Examples 1 to 5. The evaluation results are shown in Table 1.

[Thickness Unevenness] While conveying the biaxially oriented film produced in each embodiment and comparative example, a coating liquid for a base layer composed of the following formula A was applied to the surface of the biaxially oriented film using a slit nozzle, and the coated film was dried at a temperature of 90°C to form a base layer. Next, while conveying the biaxially oriented film formed with the base layer, a coating liquid for a black layer composed of the following formula B was applied to the base layer, and the coated film was dried at a temperature of 90°C to form a black layer. The conveying speed of the biaxially oriented film when forming the base layer and the black layer was 70 m/min. The biaxially oriented film provided with a base layer and a black layer was placed on a light workbench, and the color unevenness of the black layer was visually observed at a position 1m away from the biaxially oriented film. The drying temperature conditions when forming the base layer and the black layer were changed to 120°C. In addition, a biaxially oriented film provided with a base layer and a black layer was formed according to the above method and visually observed. Based on the observation results of each biaxially oriented film manufactured with the drying temperature condition of the coating film set to 90°C or 120°C, the thickness unevenness of the biaxially oriented film was evaluated according to the following criteria.

(Formula A: Base layer coating liquid) ・PVA205 (polyvinyl alcohol, manufactured by Kuraray Co., Ltd., alkalization degree 88%, polymerization degree 550): 32.2 parts by mass ・Polyvinyl pyrrolidone (manufactured by Information System Products Co., Ltd., K-30): 14.9 parts by mass ・Distilled water: 524 parts by mass ・Methanol: 429 parts by mass

(Formula B: coating liquid for black layer) ・Resin-coated carbon black prepared according to paragraphs 0036 to 0042 of Japanese Patent Gazette No. 5320652: 13.1 parts by mass ・Dispersant: Dispersant 1 described in paragraph [0103] of International Publication No. 2017/208849   0.65 parts by mass ・Polymer (random copolymer of benzyl methacrylate/methacrylic acid = 72/28 molar ratio, weight average molecular weight 37,000): 6.72 parts by mass ・Propylene glycol monomethyl ether acetate: 79.53 parts by mass

(Evaluation criteria) A: No color unevenness was observed in the black layer at either 90°C or 120°C. B: Slight color unevenness was observed in the black layer at either 90°C or 120°C. C: Color unevenness was observed in the black layer at only 120°C. D: Color unevenness was observed in the black layer at either 90°C or 120°C.

[Transfer failure] The two ends were cut so that the width of the biaxially oriented film with a base layer and a black layer produced in the above-mentioned thickness unevenness evaluation became 45 cm. Then, the cut biaxially oriented film was rolled into an ABS (acrylonitrile-butadiene-styrene) resin core with a diameter of 3 inches (1 inch = 2.54 cm) while pressing the contact roller with a tension of 11.5 kg/m. The length of the long side direction of the rolled biaxially oriented film was 100 m. The obtained test sample was left at 25°C and 50% RH for 30 days. After 30 days, the surface of the black layer in the biaxially oriented film wound on the core was observed under a fluorescent lamp [Rupikae-su manufactured by Mitsubishi Electric Corporation (color temperature: 5000K, average color rendering index (Ra): 84)]. The unevenness of the film surface was visually observed using the reflected light of the fluorescent lamp, and the transfer failure was evaluated according to the following criteria.

(Evaluation criteria) A: No surface irregularities are visible, which is an extremely good condition. B: Some surface irregularities can be visually identified, but they are very slight. C: Slight surface irregularities can be visually identified.

Table 1 shows the evaluation results of each embodiment and comparative example. In Table 1, the "Formation method" column of "particle-containing layer" means that the particle-containing layer is formed by the following method in the particle-containing layer formation step in each embodiment and comparative example. A: After the longitudinal stretching step and before the transverse stretching step, the coating liquid is applied to the uniaxially oriented film to form (online coating method). B: Formed by co-extrusion molding, simultaneously with the unstretched film.

【Table 1】 Manufacturing conditions Layer containing particles Heat setting temperature T1 [℃] Cooling speed V [℃/min] Expansion rate ΔL [%] Value C Value D Coating liquid or resin Agglomerated particle size Non-agglomerated particle size Formation method thickness Embodiment 1 227 2500 0.6 0.3 169 A 200nm 50nm A 40nm Embodiment 2 227 2500 0.6 0.3 169 B 200nm without A 40nm Embodiment 3 235 2500 0.6 -1.8 8282 A 200nm 50nm A 40nm Embodiment 4 231 2500 0.6 -0.8 1521 A 200nm 50nm A 40nm Embodiment 5 229 2500 0.6 -0.3 169 A 200nm 50nm A 40nm Embodiment 6 227 2200 0.6 0.3 149 A 200nm 50nm A 40nm Embodiment 7 227 3500 0.6 0.3 237 A 200nm 50nm A 40nm Embodiment 8 227 3000 0.6 0.3 203 A 200nm 50nm A 40nm Embodiment 9 227 2500 0.2 0.7 1089 A 200nm 50nm A 40nm Embodiment 10 227 2500 0.8 0.1 9 A 200nm 50nm A 40nm Embodiment 11 227 2500 1.2 -0.3 289 A 200nm 50nm A 40nm Embodiment 12 227 2500 0.6 0.3 169 C without 450nm A 200nm Embodiment 13 227 2500 0.6 0.3 169 D without 200nm A 100nm Embodiment 14 227 2500 0.6 0.3 169 E without 100nm A 40nm Embodiment 15 227 2500 0.6 0.3 169 F without 50nm A 40nm Embodiment 16 227 2500 0.6 0.3 169 F without 50nm A 60nm Embodiment 17 227 2500 0.6 0.3 169 G without 300nm A 150nm Embodiment 18 227 2500 0.6 0.3 169 H without 300nm B 2μm Embodiment 19 227 2500 0.6 0.3 169 A 200nm 50nm A 40nm Embodiment 20 227 2500 0.6 0.3 169 F without 50nm A 40nm Embodiment 21 227 2500 0.6 0.3 169 A 200nm 50nm A 40nm Embodiment 22 215 2500 0.6 3.4 28564 A 200nm 50nm A 40nm Comparison Example 1 240 2500 0.4 -5.5 76185 B 200nm without A 40nm Comparison Example 2 220 3500 0.0 6.9 165670 B 200nm without A 40nm Comparison Example 3 227 2000 0.6 0.8 1217 B 200nm without A 40nm Comparison Example 4 227 4000 0.6 0.8 2434 B 200nm without A 40nm Comparison Example 5 235 2500 0.0 -6.0 90612 A 200nm 50nm A 40nm

【Table 2】 Table 1 (continued) Polyester film (physical properties) Reviews thickness density 90℃ Stripe defect area 120℃ Stripe defect area 90℃ expansion rate[%] 120℃ expansion rate [%] Rp [nm] Uneven thickness Transfer failure Embodiment 1 31μm 1.400 10% twenty four% 0.040 0.040 110nm A A Embodiment 2 31μm 1.400 10% twenty four% 0.040 0.040 110nm A B Embodiment 3 31μm 1.403 39% 88% 0.102 0.224 11 0nm C A Embodiment 4 31μm 1.401 32% 84% 0.071 0.132 110nm C A Embodiment 5 31μm 1.401 twenty four% 60% 0.055 0.086 110nm B A Embodiment 6 31μm 1.400 twenty four% 60% 0.040 0.100 110nm B A Embodiment 7 31μm 1.400 38% 97% 0.040 0.040 110nm C A Embodiment 8 31μm 1.400 25% 63% 0.040 0.040 110nm B A Embodiment 9 31μm 1.400 20% 52% 0.084 0.160 110nm B A Embodiment 10 31μm 1.400 10% twenty four% 0.040 -0.020 110nm A A Embodiment 11 31μm 1.400 10% 63% 0.040 -0.140 110nm B A Embodiment 12 31μm 1.400 10% twenty four% 0.040 0.040 250nm A C Embodiment 13 31μm 1.400 10% twenty four% 0.040 0.040 100nm A B Embodiment 14 31μm 1.400 10% twenty four% 0.040 0.040 60nm A A Embodiment 15 31μm 1.400 10% twenty four% 0.040 0.040 10nm A A Embodiment 16 31μm 1.400 10% twenty four% 0.040 0.040 5nm A A Embodiment 17 31μm 1.400 10% twenty four% 0.040 0.040 150nm A A Embodiment 18 31μm 1.400 10% twenty four% 0.040 0.040 250nm A A Embodiment 19 20μm 1.400 15% 35% 0.040 0.040 110nm A A Embodiment 20 20μm 1.400 15% 35% 0.040 0.040 10nm A A Embodiment 21 16μm 1.400 18% 39% 0.040 0.040 110nm A A Embodiment 22 31μm 1.397 10% 100% 0.040 -0.300 110nm C A Comparison Example 1 31μm 1.404 43% 100% 0.162 0.399 110nm D B Comparison Example 2 31μm 1.398 41% 29% 0.150 0.059 110nm D B Comparison Example 3 31μm 1.400 100% 63% 0.040 0.040 110nm D B Comparison Example 4 31μm 1.400 60% 100% 0.100 0.100 110nm D B Comparison Example 5 31μm 1.403 45% 100% 0.168 0.404 110nm D A

Table 1 shows that the cooling rate V of the polyester film in the cooling step is within the range of 2200-3500°C/min, and Examples 1-22 satisfying the above-mentioned condition 1 can suppress the uneven thickness of the laminated functional layer compared with Comparative Examples 1-5. In addition, Table 1 shows that after a specific heat treatment, Examples 1-22 in which the area of the stripe-shaped defect region observed in the polyester film is 40% or less relative to the total area of the observed region can suppress the uneven thickness of the laminated functional layer compared with Comparative Examples 1-5.

Among them, from the comparison of Examples 1 to 5 and 9 to 11, it is confirmed that when the absolute value of the product value C of A calculated by formula (1) and B calculated by formula (2) is 0.1 to 0.7, the thickness unevenness of the deposited functional layer can be further suppressed. It is confirmed that when the above value C is 0.1 to 0.5, the thickness unevenness of the deposited functional layer can be further suppressed.

Furthermore, from the comparison between Examples 1 and 6 to 8, it was confirmed that when the cooling rate V in the cooling step was 2200 to 3000°C, the thickness unevenness of the deposited functional layer could be further suppressed, and it was confirmed that when it was 2300 to 2600°C/min, the thickness unevenness of the deposited functional layer could be further suppressed.

Furthermore, from the comparison between Examples 1 and 12 to 17, it is confirmed that when the maximum peak height Rp of the surface of the particle-containing layer is 0.2 μm or less, the transfer failure can be further suppressed. Furthermore, from the comparison between Examples 12 and 18, it is confirmed that when the particles contained in the particle-containing layer are resin particles, the transfer failure can be further suppressed. Furthermore, from the comparison between Examples 1 and 12 to 17, it is confirmed that when the particles have an average particle size of 0.4 μm or less, the transfer failure can be further suppressed.

[Example 23] The biaxially oriented film prepared in Example 1 was used as a support, and a transfer film for decoration was prepared by the following procedure. The thermoplastic (non-photosensitive) resin layer coating liquid described in [0106] of International Publication No. 2017/208849 was applied to the surface of the biaxially oriented film prepared in Example 1 on the side opposite to the particle-containing layer, and dried at 80°C to form a thermoplastic (non-photosensitive) resin layer. Then, a base layer coating liquid composed of the above-mentioned formula A was applied and dried at 120°C to form a base layer. A photosensitive resin layer-forming composition consisting of the following formula C was applied thereon and dried at 90°C to form a photosensitive resin layer. The thickness of the base layer was 1.6 μm, and the thickness of the photosensitive resin layer was 2.0 μm. Finally, a polypropylene film with a thickness of 12 μm was pressed onto the surface of the photosensitive resin layer as a protective film to produce a decorative transfer film. The obtained decorative transfer film had no color unevenness and no transfer failure and had good characteristics. In addition, the obtained decorative transfer film was used to form a decorative pattern according to the description of [0109] of the International Publication No. 2017/208849, and a good pattern was formed.

<Formula C: Photosensitive resin layer forming composition> ・The above-mentioned black pigment dispersion 180.9 parts ・A-NOD-N (Shin-Nakamura Chemical Co., Ltd., 2-functional, molecular weight 226) 3.29 parts ・A-DCP (Shin-Nakamura Chemical Co., Ltd., 2-functional, molecular weight 304) 9.9 parts ・8UX-015A (TAISEI FINE CHEMICAL CO,.LTD., 15-functional) 6.59 parts ・A-DPH (Shin-Nakamura Chemical Co., Ltd., 6-functional, molecular weight 578) 2.20 parts ・Binder (copolymer of benzyl methacrylate/methacrylic acid, 70/30 mass%, weight average molecular weight (Mw) = 5000, solid content = 40.5 mass%) 141.2 parts ・Polymerization initiator OXE-02 (BASF, IRGACURE OXE 02, ethyl ketone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-, 1-(0-acetyl oxime)) 6.75 parts ・Propylene glycol monomethyl ether acetate 250 parts ・Methyl ethyl ketone 404.2 parts

[Example 24] The biaxially oriented film prepared in Example 21 was used as a support, and a dry film for forming a touch panel protective film was prepared by the following procedure. The coating liquid for forming the second transparent transfer layer composed of the following formula D was applied to the surface of the biaxially oriented film prepared in Example 21 on the side opposite to the particle-containing layer, and dried at 90°C to form the second transparent transfer layer. Then, the coating liquid for forming the first transparent transfer layer composed of the following formula E was applied to the second transparent transfer layer, and dried at 70°C to form the first transparent transfer layer. The thickness of the second transparent transfer layer is 5.0 μm, and the thickness of the first transparent transfer layer is about 80 nm. Finally, a polyethylene terephthalate film with a thickness of 16 μm was pressed onto the surface of the first transparent transfer layer as a protective film to produce a transfer film for forming a touch panel protective film. The obtained transfer film has no refractive index change due to uneven thickness and no transfer failure, and has good properties. For the obtained transfer film, referring to [0122] to [0128] of the specification of International Publication No. 2018/186428, the results of forming contact holes can form a good pattern.

<Formula D: Coating liquid for forming the second transparent transfer layer> ・ARONIX TO-2349 (TOAGOSEI CO., LTD., carboxylic acid-containing monomer) 0.93 parts ・A-DCP (Shin-Nakamura Chemical Co., Ltd., bifunctional, molecular weight 304) 5.6 parts ・8UX-015A (TAISEI FINE CHEMICAL CO,.LTD., urethane acrylate) 2.80 parts ・Binder (copolymer of cyclohexyl methacrylate/methyl methacrylate/methacrylic acid/methacrylic acid glycidyl methacrylate adduct, 51.5/2/26.5/20%, weight average molecular weight (Mw) = 29000, acid value = 95 mgKOH) 15.59 parts ・Polymerization initiator IRGACURE OXE-02 (BASF) 0.11 parts ・Polymerization initiator IRGACURE 907 (BASF, 2-methyl-1-(4-methylthiophenyl)-2-hydroxypropane-1-one) 0.21 parts ・N-phenylglycine 0.03 parts ・Blocked isocyanate (Asahi Kasei Chemicals Co., Ltd., Duranate WT32-B75P) 3.63 parts ・Benzimidazole 0.09 parts ・Surfactant (DIC CORPORATION, MEGAFACE F-551) 0.02 parts ・1-methoxy-2-propyl acetate 31.08 parts ・Methyl ethyl ketone 40.0 parts

<Formula E: Coating liquid for forming the first transparent transfer layer> ・NanoUse OZ-S30M (ZrO2 particle methanol dispersion, Nissan Chemical Industries, LTD., non-volatile component 30.5%) 4.34 parts ・Ammonia water (25%) 7.82 parts ・Monoisopropanolamine 0.02 parts ・Binder (allyl methacrylate/methacrylic acid copolymer, 40/60 mol%, weight average molecular weight (Mw) = 38000) 0.24 parts ・ARONIX TO-2349 (TOAGOSEI CO., LTD.) 0.03 parts ・Benzotriazole 0.03 parts ・Surfactant (DIC CORPORATION, MEGAFACE F-444) 0.01 parts ・Ion exchange water 21.5 parts ・Methanol 66.0 parts

[Example 25] The biaxially oriented film prepared in Example 21 was used as a support, and a dry film for forming an etching resist was prepared by the following procedure. The coating liquid for forming a thermoplastic resin layer composed of the following formula F was applied to the surface of the biaxially oriented film prepared in Example 21 on the side opposite to the particle-containing layer, and dried at 80°C to form a thermoplastic resin layer. Then, the coating liquid for forming a water-soluble resin layer composed of the following formula G was applied to the thermoplastic resin layer, and then dried at 80°C to form a water-soluble resin layer. In addition, a coating liquid for forming a photosensitive resin layer composed of the following formula H was applied on the water-soluble resin layer and then dried at 80°C to form a photosensitive resin layer. The thickness of the thermoplastic resin layer was 2μm, the thickness of the water-soluble resin layer was 1μm, and the thickness of the photosensitive resin layer was 2μm. Finally, a polyethylene terephthalate film with a thickness of 16μm was pressed onto the surface of the photosensitive resin layer as a protective film to prepare a transfer film for forming an etching resist. The obtained transfer film was exposed according to [0429] to [0430] of International Publication No. 2019/151534, and the visibility results were confirmed, and the line and space patterns could be clearly visually identified.

<Formula F: Coating liquid for forming thermoplastic resin layer> ・Benzyl methacrylate/methacrylic acid/acrylic acid polymer (75/10/15 mass%, molecular weight 30,000, solid content 30%) 22.7 parts ・3,6-bis(diphenylamino) fluorescent yellow matrix 0.12 parts ・A-1 described in paragraph 0227 of Japanese Patent Publication No. 2013-047765, oxime sulfonate type photoacid generator 0.2 parts ・Tricyclodecanedimethanol diacrylate 3.32 parts ・8UX-015A (TAISEI FINE CHEMICAL CO,.LTD., 15-functional) 1.66 parts ・ARONIX TO-2349 (TOAGOSEI CO.,LTD.) 0.55 parts ・Surfactant (DIC CORPORATION, MEGAFACE F-552) 0.02 parts

<Formula G: Coating liquid for forming a water-soluble resin layer> ・Polyvinyl alcohol (KURARAY POVAL4-88LA, manufactured by Kuraray Co., Ltd.) 3.22 parts ・Polyvinyl pyrrolidone (K-30 manufactured by NIPPON SHOKUBAI CO., LTD.) 1.49 parts ・Surfactant (MEGAFACE F-444, manufactured by DIC CORPORATION) 0.0035 parts ・Methanol (manufactured by MITSUBISHI GAS CHEMICAL COMPANY, INC.) 57.1 parts ・Ion exchange water 38.12 parts

<Formula H: Coating liquid for forming a photosensitive resin layer> ・Polymer of styrene/methacrylic acid/methyl methacrylate (52/29/19 mass%, molecular weight 60,000, solid content 30%) 25.2 parts ・Colorless crystal violet 0.06 parts ・Photopolymerization initiator (2-(2-chlorophenyl)-4,5-diphenylimidazole dimer) 1.03 parts ・4,4'-bis(diethylamino)benzophenone 0.04 parts ・N-phenylaminomethyl-N-carboxymethylaniline 0.02 parts ・Ethoxylated bisphenol A dimethacrylate NK ESTER BPE-500 (manufactured by Shin-Nakamura Chemical Co., Ltd.) 5.61 parts ・ARONIX M-270 (TOAGOSEI CO.,LTD.) 0.58 parts ・Phenothiocyanate 0.04 parts ・4-Hydroxymethyl-4-methyl-1-phenyl-3-pyrazolone 0.002 parts ・Surfactant (DIC CORPORATION, MEGAFACE F-552) 0.048 parts ・Propylene glycol monomethyl ether acetate 19.7 parts ・Methyl ethyl ketone 43.8 parts

[Example 26] The biaxially oriented film produced in Example 1 was used as a support, and a peeling film for producing ceramic green sheets was produced by the following procedure. A coating liquid for forming a peeling layer composed of the following formula J was applied to the surface of the biaxially oriented film produced in Example 1 on the side opposite to the particle-containing layer, and dried at 120°C to form a peeling layer. The thickness of the peeling layer was 0.1μm. Next, a ceramic slurry composed of the following formula K was applied to the glass layer so that the thickness after drying became 0.5μm, and then dried at 90°C. The slurry surface and the particle-containing layer were overlapped, and after applying a load of 1 kg/ ^cm2 for 10 minutes, the peeling film was peeled off to obtain a ceramic green sheet. The obtained ceramic green sheet had no uneven thickness and no transfer failure and had good characteristics.

<Formula J: Coating liquid for peeling layer formation> ・Polysilicone resin (SRX-345, addition reaction type polysilicone manufactured by Dow Corning Toray Co., Ltd.) 10 parts ・Platinum catalyst (SRX-212, manufactured by Dow Corning Toray Co., Ltd.) 0.1 parts ・Toluene/methyl ethyl ketone mixed solvent 490 parts

<Formula K: Ceramic slurry> ・Polyvinyl butyral (S-LEC BH-3 manufactured by SEKISUI CHEMICAL CO., LTD.) 5 parts ・Barium titanium oxide (HPBT manufactured by FUJI TITANIUM INDUSTRY CO., LTD.) 50 parts ・Toluene/ethanol mixed solvent 45 parts

2a～2l: Holding member 10: Preheating section 20: Stretching section 30: Heat setting section 40: Heat relaxation section 50: Cooling section 60a, 60b: Ring guide 100: Stretching machine 200: Film P, Q: Holding release point MD: Transport direction (longitudinal direction) TD: Width direction L0, L1, L2, L3: Film width

Figure 1 is an observation image of a polyester film with stripe-shaped defect areas. Figure 2 is a top view showing an example of a stretching machine used to manufacture polyester film.

Claims (21)

A method for producing a polyester film comprises: an extrusion molding step of extruding a molten resin containing polyester in a film form to form an unstretched polyester film containing at least a polyester substrate; a longitudinal stretching step of stretching the unstretched polyester film along a conveying direction to form a uniaxially oriented polyester film; a transverse stretching step of stretching the uniaxially oriented polyester film along a width direction to form a biaxially oriented polyester film; and a heating step of heating the biaxially oriented polyester film. A heat setting step for orienting a polyester film to heat set it; a heat relaxation step for heating the polyester film heat set by the heat setting step at a temperature lower than that of the heat setting step to heat relax it; a cooling step for cooling the polyester film heat relaxed by the heat relaxation step; and an expansion step for expanding the heat relaxed polyester film in the width direction in the cooling step, wherein the polyester film has a polyester substrate and a The particle-containing layer on at least one surface of the polyester substrate, wherein in the method for producing the polyester film, the cooling rate V of the polyester film in the cooling step is 2200-3500°C/min, and the following condition 1 is satisfied: condition 1: the melting point of the polyester is set to Tm (°C), the heat setting temperature in the heat setting step is set to T1 (°C), and the transverse stretching step is set to When the stretching ratio of the uniaxially oriented polyester film in the stretching step is a and the percentage of the expansion rate in the width direction of the heat-relaxed polyester film in the expansion step is b (%), the value C of the product of A calculated by the following formula (1) and B calculated by the following formula (2) is -4.0 to 4.0, except when one of A and B is 0, A=Tm-T1-30 (1) B=a/5-b (2). A method for producing a polyester film as described in claim 1, wherein the value D calculated from the aforementioned A, the aforementioned B and the aforementioned cooling rate V by the following formula (3) is 1~10000, D=(A×B) ² ×V (3). A method for manufacturing a polyester film as described in claim 1 or claim 2, wherein the thickness of the polyester film is less than 50 μm. The method for producing a polyester film as described in claim 1 or claim 2, wherein between the longitudinal stretching step and the transverse stretching step, there is a step of forming the particle-containing layer using a coating liquid containing the particles, or there is a step of forming the particle-containing layer by extruding a second melt containing the particles and a binder simultaneously with the molten resin in the extrusion molding step. A method for manufacturing a polyester film as described in claim 1 or claim 2, wherein the surface temperature T2 of the polyester film in the thermal relaxation step is below 210°C. A method for manufacturing a polyester film as described in claim 1 or claim 2, wherein the cooling rate V of the aforementioned polyester film based on the aforementioned cooling step is 2200~3000℃/minute. A method for manufacturing a polyester film as described in claim 1 or claim 2, wherein the aforementioned b exceeds 0% and is less than 1.2%. A polyester film, comprising: a polyester substrate, the polyester substrate comprising polyethylene terephthalate; and a particle-containing layer comprising particles located on at least one surface of the polyethylene terephthalate substrate, wherein the thickness of the polyester film is less than 50 μm, and the polyester film is transported at a transport speed of 30 m/min and a tension of 100 N/m in the transport direction, and is heated for 20 seconds at a temperature of 90° C. on the surface of the film, and the total area of the stripe-shaped defective areas observed in a 1 m×1 m area of the polyester film when visually observed is less than 40% relative to the total area of the 1 m×1 m area. The polyester film as described in claim 8, wherein the expansion rate of the aforementioned polyester film in the width direction at 90°C is -0.15~0.15% relative to the dimension of the aforementioned polyester film in the width direction at 30°C. The polyester film as claimed in claim 8 or claim 9, wherein the density of the polyester film is 1.39-1.41 g/cm ³ . The polyester film as described in claim 8 or claim 9, wherein the thickness of the aforementioned polyester substrate is 3-40 μm, and the thickness of the aforementioned particle-containing layer is 0.001-2.5 μm. The polyester film as described in claim 8 or claim 9, wherein the aforementioned particle-containing layer contains particles P having an average particle size of not less than 10 nm and less than 1 μm. The polyester film as described in claim 12, wherein the average particle size of the aforementioned particles P is greater than the thickness of the aforementioned particle-containing layer. The polyester film as described in claim 8 or claim 9, wherein the aforementioned particle-containing layer contains particles P1 with an average particle size of 10 to 100 nm. The polyester film as described in claim 8 or claim 9, wherein the aforementioned particle-containing layer contains particles P2 having an average particle size of more than 100 nm and less than 400 nm. The polyester film as described in claim 8 or claim 9, wherein the particles contained in the aforementioned particle-containing layer are resin particles or the particles contained in the aforementioned particle-containing layer are inorganic particles, and the maximum peak height Rp of at least one surface in the aforementioned polyester film is 5 to 200 nm. The polyester film as described in claim 8 or claim 9, wherein the polyester substrate substantially does not contain particles. A laminated film comprising: a polyester film, which is a polyester film produced by the method for producing a polyester film described in any one of claims 1 to 7 or a polyester film described in any one of claims 8 to 17, and has a particle-containing layer only on one surface of a polyester substrate; and a functional layer, which is located on the surface of the polyester substrate opposite to the particle-containing layer and is selected from the group consisting of a decorative layer, a photosensitive resin layer and a release layer. The laminated film as described in claim 18, wherein the aforementioned functional layer is a decorative layer, and the aforementioned laminated film is a decorative film. The laminated film as described in claim 18, wherein the aforementioned functional layer is a photosensitive resin layer, and the aforementioned laminated film is a photosensitive transfer film. The laminated film as described in claim 18, wherein the aforementioned functional layer is a peeling layer, and the aforementioned laminated film is a peeling film for manufacturing ceramic green sheets.