Method for manufacturing polyester film, polyester film

Abstract

The objective of the present invention is to provide a method for manufacturing a polyester film that can further suppress the formation of linear defects on the surface of the polyester film. In addition, the objective of the present invention is to provide a polyester film. The method for manufacturing a polyester film according to the present invention has a cooling process in which a uniaxially stretched polyester film is brought into contact with a cooling roll to cool, and the arithmetic mean roughness Ra of the surface of the cooling roll is 0.05 μm or less.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing a polyester film and a polyester film. Background Technology

[0002] Polyester films are used for a wide range of applications in terms of processability, mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance, for example, as supports and protective films for dry film photoresists. Dry film photoresists have a structure formed by laminating a photosensitive resin layer (photoresist layer) onto a support and then laminating a protective film. Recently, dry film photoresists have been used in the touch panel field for etching in the wiring formation process, for forming protective films to protect wiring portions such as copper, ITO (indium tin oxide), and silver nanoparticles, and for interlayer insulating films.

[0003] Patent Document 1 discloses a method for manufacturing a stretched film comprising a longitudinal stretching process for stretching a film made of a strip-shaped thermoplastic resin in a conveying direction, a cooling process for cooling the film by means of a cooling roller, and a side edge removal process for removing both edge portions in the width direction of the film between the longitudinal stretching process and the cooling process. Prior art literature

[0004] Patent Document 1: Japanese Published Patent Application No. 2014-188748 The problem to be solved

[0005] Meanwhile, recently, there is a demand for further precision (fineness) of patterns formed by dry film photoresist (DFR), and higher performance (thinning, low haze, etc.) than conventional methods is also required for supporting materials and protective films.

[0006] The inventors examined the polyester film used as a support and protective film for the DFR and found that when producing the DFR according to the above requirements, faint linear scratches (linear defects) present on the surface of the polyester film may lead to exposure problems.

[0007] The present invention aims to provide a method for manufacturing a polyester film that can further suppress the formation of linear defects on the surface of the polyester film, taking into account the above circumstances.

[0008] In addition, the present invention also has the objective of providing a polyester film. means of solving the problem

[0009] The inventors, after carefully examining the above problem, found that the problem can be solved by the following configuration.

[0010] [1]

[0011] A method for manufacturing a polyester film having a cooling process in which a uniaxially stretched polyester film is brought into contact with a cooling roll to cool, wherein the arithmetic mean roughness Ra of the surface of the cooling roll is 0.05 μm or less.

[0012] [2]

[0013] A manufacturing method described in [1] in which the maximum peak height Rp of the surface of the cooling roll is 0.3 μm or less.

[0014] [3]

[0015] The protrusion density on the surface of the cooling roll is 10,000 pieces / mm 2 The manufacturing method described in [1] or [2] below.

[0016] [4]

[0017] A manufacturing method described in any one of [1] to [3], wherein the cooling rate of the polyester film by the cooling roll in the above cooling process is 150°C / sec or higher.

[0018] [5]

[0019] A manufacturing method described in any one of [1] to [4], wherein the temperature of the polyester film in contact with the cooling roll in the above cooling process is 90°C or higher.

[0020] [6]

[0021] A manufacturing method described in any one of [1] to [5], wherein in the above cooling process, the temperature of the polyester film falling from the cooling roll is 50°C or lower.

[0022] [7]

[0023] A manufacturing method described in any one of [1] to [6], wherein in the above cooling process, the temperature of the polyester film lowered from contact with the cooling roll until it is removed from the cooling roll is 30°C or higher.

[0024] [8]

[0025] A manufacturing method described in any one of [1] to [7], wherein the surface temperature of the cooling roll is 35℃ or lower.

[0026] [9]

[0027] A manufacturing method described in any one of [1] to [8], wherein the conveying speed of the polyester film by the cooling roll is 50 to 150 m / min.

[0028]

[10]

[0029] A manufacturing method described in any one of [1] to [9], further comprising a longitudinal stretching process in which an unoriented polyester film is stretched in a conveying direction using the cooling roll and one or more stretching rolls disposed upstream of the cooling roll in the conveying direction and having a slower conveying speed than the cooling roll to form the uniaxially stretched polyester film, wherein the conveying speed of the unoriented polyester film by the stretching roll is 10 to 50 m / min.

[0030]

[11]

[0031] A manufacturing method described in any one of [1] to

[10] , wherein the arithmetic mean roughness Ra of the surface of the cooling roll is 0.008 μm or more.

[0032]

[12]

[0033] A manufacturing method described in any one of [1] to

[11] , wherein the contact angle of the surface of the cooling roll with water is 10° or more.

[0034]

[13]

[0035] A manufacturing method described in any one of [1] to

[12] , wherein the thickness of the polyester film is 40 μm or less.

[0036]

[14]

[0037] A manufacturing method described in any one of [1] to

[13] , wherein, in the above cooling process, pressure is applied to the polyester film by passing the polyester film between the cooling roll and the opposing roll positioned opposite to the cooling roll.

[0038]

[15]

[0039] A manufacturing method described in

[14] in which the difference between the maximum and minimum values ​​of the pressure applied to the polyester film by the cooling roll and the opposing roll in the width direction is 0.4 MPa or less.

[0040]

[16]

[0041] A manufacturing method described in

[14] or

[15] in which the face average value of the pressure applied to the polyester film by the cooling roll and the opposing roll is 1.1 MPa or more.

[0042]

[17]

[0043] A manufacturing method described in any one of

[14] to

[16] , wherein the face average value of the pressure applied to the polyester film by the cooling roll and the opposing roll is 1.7 MPa or less.

[0044]

[18]

[0045] A manufacturing method described in any one of

[14] to

[17] , wherein, in the above polyester film, the length of the conveying direction of the area where pressure is applied by the cooling roll and the opposing roll is 15 mm or more.

[0046]

[19]

[0047] A manufacturing method described in any one of

[14] to

[18] , wherein the arithmetic mean roughness Ra of the surface of the opposing roll is 1.5 μm or less.

[0048]

[20]

[0049] As a polyester film, the number of linear defects on the surface of the polyester film, wherein the depth is 500 nm or more and the length is 1 mm or more, is 1 m of the polyester film 2 Polyester film, with five or fewer pieces per layer.

[0050]

[21]

[0051] The number of non-uniform defects visible by visually observing reflected light on the surface of the above polyester film is, 1m of the above polyester film 2 Polyester film described in

[20] , with five or fewer pieces per unit.

[0052]

[22]

[0053] The polyester film further has a coating layer provided on its surface, and the number of transfer defects recognizable as pinholes by irradiating light from a side opposite to the coating layer and visually observing the surface on the side of the coating layer is, 1m of the polyester film 2 Polyester film described in

[20] or

[21] , having three or fewer per film. Effects of the invention

[0054] According to the present invention, a method for manufacturing a polyester film can be provided that further suppresses the formation of linear defects on the surface of the polyester film. In addition, according to the present invention, a polyester film can be provided. Brief explanation of the drawing

[0055] Figure 1 is a schematic diagram showing the configuration of a manufacturing apparatus used in a method for manufacturing a polyester film. Specific details for implementing the invention

[0056] The embodiments of the present invention will be described in detail below. Furthermore, the present invention is not limited in any way to the following embodiments, and the present invention may be implemented by making appropriate modifications within the scope of the purpose of the present invention.

[0057] In the present disclosure, a numerical range indicated by "~" refers to a range that includes the values ​​listed before and after "~" as lower and upper limits. In numerical ranges described stepwise in the present disclosure, an upper or lower limit value described as a predetermined numerical range may be substituted with an upper or lower limit value of a numerical range described in another stepwise manner. Furthermore, in numerical ranges described in the present disclosure, an upper or lower limit value described as a predetermined numerical range may be substituted with a value shown in an example.

[0058] In the present disclosure, the amount of each component in the composition refers to the total amount of a plurality of substances present in the composition, unless specifically explained, where a plurality of substances corresponding to each component exist in the composition.

[0059] In the present disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that the intended purpose of the process is achieved.

[0060] In the present disclosure, "mass%" and "weight%" have the same meaning, and "parts of mass" and "parts of weight" have the same meaning.

[0061] In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0062] In the present disclosure, "length direction" refers to the long direction of the polyester film during the manufacture of the polyester film, and has the same meaning as "transport direction" and "machine direction." Additionally, "width direction" refers to a direction perpendicular to the length direction.

[0063] In the present disclosure, the term “orthogonal” is not limited to strict orthogonality but includes approximate orthogonality. “Approximately orthogonal” means intersecting at 90°±5°, preferably intersecting at 90°±3°, and more preferably intersecting at 90°±1°.

[0064] [Method for manufacturing polyester film]

[0065] The method for manufacturing a polyester film according to the present invention comprises a cooling process in which a uniaxially stretched polyester film is brought into contact with a cooling roll to cool. In addition, the arithmetic mean roughness Ra of the surface of the cooling roll used in the cooling process is 0.05 μm or less.

[0066] Hereinafter, a method for manufacturing a polyester film according to the present invention will be described based on specific embodiments, but the present invention is not limited to the following embodiments.

[0067] A method for manufacturing a polyester film according to one embodiment of the present invention (hereinafter also referred to as the "manufacturing method of this embodiment") comprises a process for producing an unoriented polyester film from a raw material polyester by an extrusion molding method (hereinafter also referred to as the "extrusion molding process"), a process for stretching the unoriented polyester film in a conveying direction (hereinafter also referred to as the "longitudinal stretching process"), a process for cooling the uniaxially stretched polyester film obtained by the longitudinal stretching process (hereinafter also referred to as the "cooling process"), and a process for stretching the uniaxially stretched polyester film cooled by the cooling process in the width direction (hereinafter also referred to as the "transverse stretching process").

[0068] [Polyester Raw Material]

[0069] Hereinafter, the polyester used as a raw material for the unoriented polyester film in the manufacturing method of the present embodiment will be described.

[0070] Polyester is a polymer having ester bonds in its main chain. Polyester is often formed by polycondensing a dicarboxylic acid compound and a diol compound, which will be described later.

[0071] As for the polyester, any known polyester may be used without limitation. Examples of polyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalate (PEN), and PET is preferred.

[0072] The intrinsic viscosity of the polyester is preferably 0.50 dl / g or more and less than 0.80 dl / g. More preferably, it is 0.55 dl / g or more and less than 0.70 dl / g.

[0073] The polyester film may contain only one type of polyester, or may contain two or more types of polyester.

[0074] The polyester content is preferably 85 mass% or more, more preferably 90 mass% or more, more preferably 95 mass% or more, and particularly preferably 98 mass% or more, based on the total mass of the polymer in the polyester film.

[0075] The upper limit of the polyester content is not limited and can be appropriately set within a range of 100 mass% or less relative to the total mass of the polymer in the polyester film.

[0076] The polyester content is preferably 85 mass% or more, 90 mass% or more, 95 mass% or more, and particularly 98 mass% or more, based on the total mass of the polyester film. The upper limit of the polyester content is not limited and can be appropriately set within a range of 100 mass% or less based on the total mass of the polyester film.

[0077] When a polyester film contains polyethylene terephthalate, the content of polyethylene terephthalate is preferably 90 to 100 mass% with respect to the total mass of polyester in the polyester film, more preferably 95 to 100 mass%, more preferably 98 to 100 mass%, and particularly preferably 100 mass%.

[0078] (Method for manufacturing polyester)

[0079] As a method for manufacturing a polyester, known methods may be used without limitation. For example, a polyester can be manufactured by polycondensing at least one dicarboxylic acid compound and at least one diol compound in the presence of a catalyst.

[0080] -catalyst-

[0081] The catalyst used in the manufacture of polyester is not particularly limited, and any known catalyst available for the synthesis of polyester may be used.

[0082] Examples of catalysts include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, germanium compounds, and phosphorus compounds. Among these, titanium compounds are preferred in terms of catalytic activity and cost.

[0083] As a titanium compound, an organic chelated titanium complex is preferred. The organic chelated titanium complex is a titanium compound having an organic acid as a ligand.

[0084] Examples of organic acids include citric acid, lactic acid, trimellitic acid, and malic acid.

[0085] As for titanium compounds, titanium compounds described in paragraphs 0049 to 0053 of Japanese Patent Publication No. 5575671 may also be used, and the contents of the said publication are incorporated by reference into this specification.

[0086] -Dicarboxylic acid compounds-

[0087] Examples of dicarboxylic acid compounds include aliphatic dicarboxylic acid compounds, alicyclic dicarboxylic acid compounds, and aromatic dicarboxylic acid compounds, and aromatic dicarboxylic acids are preferred.

[0088] Examples of aliphatic dicarboxylic acid compounds include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanediionic acid, dimeric acid, eicosanediionic acid, pimetic acid, azelaic acid, methylmalonic acid, and ethylmalonic acid.

[0089] Examples of dicarboxylic acid compounds include adamantein dicarboxylic acid, norbornen dicarboxylic acid, cyclohexane dicarboxylic acid, and decalin dicarboxylic acid.

[0090] Examples of aromatic dicarboxylic acid compounds include, for instance, 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 sulfoisophthalic acid, phenylindene dicarboxylic acid, anthracene dicarboxylic acid, phenanthren dicarboxylic acid, and 9,9'-bis(4-carboxyphenyl)fluorene acid.

[0091] Among them, terephthalic acid or 2,6-naphthalenedicarboxylic acid is preferred, and terephthalic acid is more preferred.

[0092] A single type of dicarboxylic acid compound may be used, or two or more types may be used in combination. When terephthalic acid is used as a dicarboxylic acid compound, terephthalic acid may be used alone, or copolymerized with other aromatic dicarboxylic acids such as isophthalic acid or aliphatic dicarboxylic acids.

[0093] -Diol Compounds-

[0094] Examples of diol compounds include aliphatic diol compounds, alicyclic diol compounds, and aromatic diol compounds, and aliphatic diol compounds are preferred.

[0095] Examples of aliphatic diol compounds include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and neopentyl glycol, and ethylene glycol is preferred.

[0096] Examples of alicyclic diol compounds include cyclohexanedimethanol, spiroglycol, and isosorbide.

[0097] Examples of aromatic diol compounds include bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, and 9,9'-bis(4-hydroxyphenyl)fluorene.

[0098] Diol compounds may be used as a single type, or two or more types may be used in combination.

[0099] -Terminal Sealant-

[0100] In the manufacture of polyester, end sealants may be used as needed. By using end sealants, a structure derived from the end sealant is introduced to the ends of the polyester.

[0101] As for the terminal sealant, known terminal sealants may be used without limitation. Examples of terminal sealants include oxazoline compounds, carbodiimide compounds, and epoxy compounds.

[0102] As for end sealing agents, reference may also be made to paragraphs 0055 to 0064 of Japanese Patent Publication No. 2014-189002, and the contents of said publication are incorporated by reference into this specification.

[0103] -Manufacturing Conditions-

[0104] The reaction temperature is not limited and can be set appropriately depending on the raw material. The reaction temperature is preferably 260 to 300°C, and more preferably 275 to 285°C.

[0105] The pressure is not limited and should be set appropriately according to the raw material. The pressure is 1.33 × 10⁻⁶ -3 ~1.33×10 -5 MPa is desirable, and 6.67×10 -4 ~6.67×10 -5 MPa is more desirable.

[0106] As a method for synthesizing polyester, the method described in paragraphs 0033 to 0070 of Japanese Patent Publication No. 5575671 may also be used, and the contents of the said publication are incorporated by reference into this specification.

[0107] [Manufacturing Equipment]

[0108] The device used in the manufacturing method of the present embodiment is not particularly limited, and a known device may be used.

[0109] FIG. 1 is a schematic diagram showing an example of a manufacturing apparatus used in the manufacturing method of the present embodiment.

[0110] The manufacturing apparatus (100) of a polyester film shown in FIG. 1 comprises a longitudinal stretching section (10) that stretches an unoriented polyester film produced by extrusion molding in a conveying direction, a cooling section (20) that rapidly cools a uniaxially stretched polyester film stretched in the conveying direction from the longitudinal stretching section (10), a transverse stretching section (30) that stretches the polyester film cooled in the cooling section (20) in the width direction, and a winding section (40) that winds the polyester film stretched in the transverse stretching section (30).

[0111] The detailed configuration and function of each of the above-mentioned parts will be described together with the description of each manufacturing process of the manufacturing method of the present embodiment described below.

[0112] Hereinafter, in this specification, the notation "film (F)" and the notation "polyester film" are understood to include all of the unoriented polyester film, the uniaxially stretched polyester film, and the biaxially stretched polyester film.

[0113] [Each Manufacturing Process]

[0114] With reference to the manufacturing apparatus (100) shown in FIG. 1, each process of the manufacturing method of the present embodiment will be explained in detail.

[0115] Extrusion Molding Process

[0116] In the extrusion molding process, an unoriented polyester film is formed from the raw material polyester by the extrusion molding method.

[0117] Extrusion molding is a method of molding raw resin into a desired shape by, for example, extruding the raw resin using an extruder.

[0118] An unoriented polyester film is formed by using an extruder equipped with, for example, one or more screws to heat the above-described polyester to a temperature above its melting point and then rotating the screws to melt and knead. The polyester melts inside the extruder through heating and kneading by the screws to become a melt.

[0119] The molten material is extruded from an extrusion die through a gear pump and a filter, etc. The extrusion die is also simply called a "die" (see JIS B8650:2006, (a) Extrusion molding machine, No. 134). The molten material may be extruded in a single layer or in multiple layers.

[0120] In melt extrusion, it is desirable to nitrogen-substitute the extruder to suppress thermal decomposition (e.g., hydrolysis of polyester) within the extruder. Additionally, a twin-screw extruder is preferred in that the mixing temperature is kept low.

[0121] The molten material extruded from the extrusion die is formed into a film by cooling. For example, the molten material can be formed into a film by bringing it into contact with a casting roll and cooling and solidifying it on the casting roll. In cooling the molten material, it is also desirable to expose the molten material to wind (preferably cold wind).

[0122] The temperature of the casting roll is preferably greater than (Tg-10)℃ and less than or equal to (Tg+30)℃, more preferably (Tg-7) to (Tg+20)℃, and even more preferably (Tg-5) to (Tg+10)℃.

[0123] Additionally, in this specification, "Tg" refers to the glass transition temperature of the polyester constituting the polyester film produced by the manufacturing method of the present embodiment.

[0124] In addition, in the present specification, the temperature of the polyester film and each component in the manufacturing method can be measured using a non-contact thermometer (e.g., a radiation thermometer).

[0125] When using a casting roll in an extrusion molding process, it is desirable to increase the adhesion between the casting roll and the molten metal. Examples of methods to increase adhesion include the electrostatic application method, the air knife method, the air chamber method, the vacuum nozzle method, and the touch roll method.

[0126] A molded body (unoriented polyester film) cooled using a casting roll, etc. is peeled from a cooling member, such as a casting roll, using a peeling member, such as a peeling roll.

[0127] Longitudinal stretching process

[0128] The longitudinal stretching process is a process of stretching an unoriented polyester film in a conveying direction (hereinafter also referred to as "longitudinal stretching"). More specifically, it is a process of stretching an unoriented polyester film in a conveying direction using a device equipped with two or more stretching rolls having different conveying speeds to form a uniaxially stretched polyester film.

[0129] The longitudinal stretching section (10) is an example of a device having two or more stretching rolls with different conveying speeds, and is equipped with a pair of preheating rolls (12), a pair of stretching rolls (14), and a heater (16).

[0130] In the longitudinal stretching section (10), a pair of preheating rolls (12), a pair of stretching rolls (14), and a heater (16) are arranged in this order from the upstream side of the conveying direction.

[0131] The preheating roll (12) conveys the film (F) in the longitudinal direction and also has the function of preheating the film (F) before longitudinal stretching.

[0132] In a longitudinal stretching process using a longitudinal stretching unit (10), an unoriented polyester film is preheated by a preheating roll (12) before longitudinal stretching. By preheating the unoriented polyester film, the polyester film can be easily longitudinally stretched.

[0133] Additionally, the manufacturing apparatus (100) shown in FIG. 1 is equipped with only one pair of preheating rolls (12), but the number of preheating rolls positioned upstream of the stretching roll (14) that performs longitudinal stretching is not particularly limited and can be provided in a number according to the conveying speed of the film (F) and / or the thickness of the film.

[0134] The preheating temperature of the unoriented 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.

[0135] The conveying speed of the film (F) by the preheating roll (12) is not particularly limited, but it is preferable that it be the same as the conveying speed of the film (F) by the stretching roll (14).

[0136] The stretching roll (14) has the function of conveying the film (F) in the longitudinal direction. Here, the conveying speed of the film (F) by the stretching roll (14) is set slower than the conveying speed of the film (F) by the cooling roll (22) described later.

[0137] In the longitudinal stretching section (10), the film (F) is conveyed while applying tension to the film (F) between the stretching roll (14) and the cooling roll (22), which has a faster conveying speed than the stretching roll, thereby performing longitudinal stretching of the unoriented polyester film.

[0138] The conveying speed (main speed) of the film (F) by the stretching roll (14) is not particularly limited as long as it is slower than the cooling roll (22), but 5 to 60 m / min is preferred, 10 to 50 m / min is more preferred, and 15 to 45 m / min is more preferred.

[0139] Also, the conveying speed (main speed) of the film (F) by the cooling roll (22) is not particularly limited as long as it is faster than the stretching roll (14), but 40 to 160 m / min is preferred, 50 to 150 m / min is more preferred, and 60 to 140 m / min is more preferred.

[0140] The stretching ratio in the longitudinal stretching process can be set appropriately according to the application, but 2.0 to 5.0 times is preferable, 2.5 to 4.0 times is more preferable, and 2.8 to 4.0 times is more preferable.

[0141] In the longitudinal stretching process, the stretching speed is preferably 800 to 1500% / second, more preferably 1000 to 1400% / second, and more preferably 1200 to 1400% / second. Here, "stretching speed" refers to a value expressed as a percentage obtained by dividing the length Δd of the polyester film in the conveying direction stretched in 1 second in the longitudinal stretching process by the length d0 of the polyester film in the conveying direction before stretching.

[0142] Additionally, the stretching roll (14) has the function of preheating the film (F). The preferred range of the preheating temperature of the film (F) by the stretching roll (14) is the same as the preferred range of the preheating temperature of the preheating roll above.

[0143] As for the preheating roll (12) and the stretching roll (14), any known roll used for stretching plastic film may be used without particular limitation, but the material constituting the surface layer including the surface of each roll is preferably a metal, ceramic, or fluoropolymer, and more preferably a ceramic. As a metal, chromium is preferred. As a ceramic, chromium oxide or alumina oxide is preferred, and chromium oxide is more preferred. As a fluoropolymer, polytetrafluoroethylene is preferred.

[0144] The heater (16) has the function of heating the film (F) (unoriented polyester film) that is longitudinally stretched by the stretching roll (14) and the cooling roll (22).

[0145] The heating temperature in the longitudinal stretching process by the heater (16) is preferably (Tg-20) to (Tg+50)°C, more preferably (Tg-10) to (Tg+40)°C, and more preferably (Tg) to (Tg+30)°C. Specifically, the heating temperature in the longitudinal stretching process is preferably 70 to 120°C, more preferably 80 to 110°C, and more preferably 85 to 100°C.

[0146] In addition, in this embodiment, only one side of the film (F) is heated using the heater (16), but both sides of the film (F) may also be heated.

[0147] In addition, the method of heating the film (F) in the longitudinal stretching process is not limited to the method of using a heater (16), and may include the method of heating the film (F) by the above-mentioned stretching roll (14) or a heated roll other than the stretching roll (14), and the method of applying hot air to the film (F).

[0148] Methods for heating each roll include, for example, providing a heater inside the roll, and providing a pipe inside the roll and flowing a heated fluid through the pipe.

[0149] The uniaxially stretched polyester film used in the manufacturing method according to the present invention is not limited to a polyester film manufactured by the above longitudinal stretching process.

[0150] For example, in the above longitudinal stretching process, an unoriented polyester film is longitudinally stretched using the difference between the conveying speed of a pair of stretching rolls (14) and the conveying speed of a cooling roll (22), but instead of the cooling roll (22), one or more high-speed stretching rolls are placed between the stretching roll (14) and the cooling roll (22) and convey the film (F) at a faster conveying speed than the stretching roll (14), thereby longitudinally stretching the unoriented polyester film to produce a uniaxially stretched polyester film.

[0151] In addition, as described above, the apparatus used for the longitudinal stretching process may be equipped with two or more preheating rolls for preheating the unoriented polyester film before longitudinal stretching, and may be equipped with two or more low-speed stretching rolls used for longitudinal stretching.

[0152] Additionally, the preheating roll (12) and the stretching roll (14) provided by the longitudinal stretching unit (10) each have a configuration for conveying the film (F) between two opposing rolls (a pair of rolls), but the preheating roll and / or stretching roll used in the longitudinal stretching process may not have opposing rolls and may be composed of only one roll in contact with one side of the polyester film.

[0153] <Cooling Process>

[0154] The cooling process of the manufacturing method of the present embodiment is a process of cooling a uniaxially stretched polyester film obtained by a longitudinal stretching process. More specifically, the uniaxially stretched polyester film is cooled by contacting it with a cooling roll (22) provided by the cooling unit (20).

[0155] In this embodiment, the cooling unit (20) performing the cooling process comprises a cooling roll (22), a counter roll (24) positioned opposite the cooling roll (22), and three or more second cooling rolls (26). Additionally, in FIG. 1, second cooling rolls (26) other than the second cooling roll (26) positioned at the uppermost upstream side and the second cooling roll (26) positioned at the lowermost downstream side are omitted.

[0156] (Cooling Roll)

[0157] The cooling roll (22) has the function of cooling the film (F), and as described above, the cooling roll (22) and the opposing roll (24) rotate while holding the film (F) between them, and by conveying the film (F) at a predetermined conveying speed, the unoriented polyester film has the function of longitudinally stretching the film.

[0158] Here, the cooling roll (22) provided by the cooling unit (20) has an arithmetic mean roughness Ra of its surface of 0.05 μm or less. By cooling a uniaxially stretched polyester film using a roll having an arithmetic mean roughness Ra of 0.05 μm or less, the number of linear defects occurring in the polyester film that shrinks in the width direction during the cooling process can be suppressed.

[0159] The arithmetic mean roughness Ra of the surface of the cooling roll (22) is preferably 0.04 μm or less, more preferably 0.03 μm or less, and more preferably 0.02 μm or less, in order to provide a more superior effect of the present invention. The lower limit of the arithmetic mean roughness Ra of the surface of the cooling roll (22) is not particularly limited, but is preferably 0.001 μm or more, more preferably 0.008 μm or more, and more preferably 0.01 μm or more, in order to further suppress the occurrence of non-uniform defects (described later) in the polyester film.

[0160] Regarding the arithmetic mean roughness Ra of the surface of the cooling roll, if the cooling roll is a commercially available product and a catalog value exists, the catalog value is adopted. If a catalog value does not exist, a test piece having the same structure as the cooling roll used is manufactured, and the surface of the obtained test piece is measured at a magnification of 3000x using a laser microscope (Keyence Co., Ltd.; VK-9510), and the obtained measurement value is taken as the arithmetic mean roughness Ra of the surface of the cooling roll.

[0161] The cooling roll (22) preferably has a maximum peak height Rp on its surface of 0.4 μm or less, more preferably 0.3 μm or less, and more preferably 0.2 μm or less, in order to better suppress linear defects. The lower limit of the maximum peak height Rp on the surface of the cooling roll (22) is not particularly limited, but it is preferably 0.01 μm or more.

[0162] Also, the cooling roll (22) has a protrusion density of 10,000 / mm² on its surface, which is superior in suppressing linear defects. 2 It is desirable to be less than or equal to 8,000 pieces / mm 2 It is more desirable to be less than or equal to 6,000 pieces / mm 2 It is more preferable that it be less than or equal to 1000. The lower limit of the density of protrusions on the surface of the cooling roll (22) is not particularly limited, but 1000 / mm 2 Ideally, this is desirable.

[0163] The maximum peak height Rp and protrusion density of the surface of the cooling roll are obtained by fabricating a test piece having the same structure as the cooling roll used, measuring the surface of the obtained test piece under the following conditions using the micro-shape measuring device, and then performing particle analysis (multiple levels) using the built-in analysis software.

[0164] The measuring instrument and measurement conditions are described below. For the above measurement, slice levels are set at equal intervals of 10 nm, and the average diameter and density of each slice level are measured five times while changing the measurement position. The average value is calculated and used as the respective measurement value for the maximum peak height Rp and protrusion density. The test piece is fixed to the sample holder so that the X direction of the field of view measurement is the width direction of the polyester film.

[0165] · Measuring device: Kosaka Genkyusho surf-corder ET-4000A

[0166] · Analysis software: i-Face model TDA31 Ver2.2.0.4 JSIS

[0167] · Stylus tip radius: 0.5μm

[0168] · Measurement field of view: X direction: 380μm, Pitch: 1μm

[0169] Y direction: 280μm, Pitch: 5μm

[0170] · Tracking force: 50μN

[0171] · Measurement speed: 0.1 mm / s

[0172] · Cut-off value: Low - 0.8mm, High - None

[0173] · Leveling: Global

[0174] · Filter: Gaussian filter (2D)

[0175] · Magnification: 100,000x

[0176] · Particle analysis (multiple levels) conditions

[0177] · Output Content Settings: Acid Particles

[0178] · Hysteresis width: 5nm

[0179] · Slice level equidistant: 10nm

[0180] The surface temperature of the cooling roll is preferably 40°C or lower, more preferably 35°C or lower, and even more preferably 30°C or lower, in order to provide superior cooling performance for the uniaxially stretched polyester film. The lower limit of the surface temperature of the cooling roll is not particularly restricted, but is preferably 15°C or higher.

[0181] The contact angle of the surface of the cooling roll to water is preferably 10° or more, more preferably 20° or more, and more preferably 50° or more, in order to further suppress the occurrence of non-uniform defects (described later) of the polyester film. The upper limit of the contact angle of the surface of the cooling roll to water is not particularly limited, but 120° or less is preferred.

[0182] Regarding the contact angle of the surface of the cooling roll with respect to water, if the cooling roll is a commercially available product and a catalog value exists, the catalog value is adopted. If a catalog value does not exist, a test piece having the same structure as the cooling roll to be used is fabricated, and the static contact angle (°) of the surface of the obtained test piece with respect to water is measured by the droplet method using a contact angle meter (manufactured by Kyowa Kaimen Kagaku Co., Ltd., DMo-901), and the obtained measured value is taken as the contact angle of the surface of the cooling roll with respect to water.

[0183] The material constituting the cooling roll is not particularly limited, but in order to easily manufacture a cooling roll in which the cooling efficiency, and the arithmetic mean roughness Ra of the surface, maximum peak height Rp, protrusion density, and / or contact angle of the surface fall within the above ranges, it is preferable that the material constituting the surface layer, including at least the surface of the cooling roll, be a metal, ceramic, or fluoropolymer. Examples of metals and ceramics include tungsten carbide, hard chromium, and alumina oxide, and tungsten carbide or hard chromium is preferred, and tungsten carbide is more preferred. As for the fluoropolymer, polytetrafluoroethylene is preferred. Among the materials constituting the cooling roll, tungsten carbide or hard chromium is preferred, and tungsten carbide is more preferred.

[0184] A cooling roll having a surface layer composed of the above material can be manufactured, for example, by forming a surface layer made of the above material on the outer surface of a known metal roll using a known method such as plating or thermal spraying.

[0185] (Opposing Roll)

[0186] The opposing roll is a member configured to be positioned opposite the cooling roll, rotate in accordance with the rotation of the cooling roll, and apply pressure to the cooling roll.

[0187] The arithmetic mean roughness Ra of the surface of the opposing roll (24) is preferably 1.8 μm or less, more preferably 1.5 μm or less, and more preferably 1.2 μm or less, in order to further suppress the occurrence of transfer defects (described later) in the polyester film. The lower limit of the arithmetic mean roughness Ra of the surface of the opposing roll (24) is not particularly limited, but is preferably 0.1 μm or more.

[0188] The arithmetic mean roughness Ra of the surface of the opposing roll (24) is measured by the following method.

[0189] Replica material is injected onto the surface of the opposing roll (24) using a replica production kit (Microset Products, 101THTHIXO) to create a mold of the surface shape. The surface of the obtained replica is measured using a laser microscope (Keyence Co., Ltd.; VK-9510) to obtain the arithmetic mean roughness Ra of the surface of the opposing roll (24).

[0190] As for the material constituting the opposing roll, there are no particular limitations, but an elastomer is preferred. Examples of elastomers include rubber and thermoplastic elastomers.

[0191] The hardness of the opposing roll is preferably 50 to 90 degrees, and more preferably 60 to 80 degrees, as the transfer is superior. In addition, the hardness of the opposing roll is the rubber hardness measured using a durometer such as a Type A durometer in accordance with the method described in JIS K6253-3.

[0192] (Cooling conditions)

[0193] As for the conditions of the cooling process, the cooling rate of the polyester film by the cooling roll, that is, the value obtained by dividing the temperature of the polyester film lowered from the time the polyester film contacts the cooling roll until it detaches by the time the polyester film contacts the cooling roll, is preferably 50°C / second or higher, more preferably 120°C / second or higher, more preferably 150°C / second or higher, and particularly preferably 180°C / second or higher. If the cooling rate is within the above range, the occurrence of non-uniform defects in the polyester film can be further suppressed.

[0194] The upper limit of the above cooling rate is not specifically restricted, but 300℃ / sec or less is preferred.

[0195] The cooling speed of the polyester film by the cooling roll can be adjusted by the surface temperature of the cooling roll and the transport speed of the film by the cooling roll and the opposing roll.

[0196] The cooling rate of the polyester film by the cooling roll is determined from the measured values ​​of the temperature of the polyester film at the position in contact with the cooling roll (film temperature at contact) and the temperature of the polyester film at the position away from the cooling roll (film temperature at separation), measured using a non-contact thermometer, the length of the contact surface between the polyester film and the cooling roll in the conveying direction, and the conveying speed of the polyester film by the cooling roll and the opposing roll.

[0197] In the cooling process, the temperature of the polyester film in contact with the cooling roll is preferably 90°C or higher, and more preferably 95°C or higher, as 80°C is superior. The upper limit is not particularly restricted, but 120°C or lower is preferred.

[0198] In the cooling process, the temperature of the polyester film falling from the cooling roll is preferably 80°C or lower, and more preferably 50°C or lower, in order to further suppress the occurrence of non-uniform defects in the polyester film. The lower limit is not particularly restricted, but 15°C or higher is preferred.

[0199] In the cooling process, the temperature of the polyester film lowered from contact with the cooling roll until it is removed from the cooling roll is preferably 10°C or higher, more preferably 30°C or higher, and even more preferably 40°C or higher, in order to further suppress the occurrence of non-uniform defects in the polyester film. The upper limit is not particularly restricted, but 100°C or lower is preferred.

[0200] The temperature and temperature change of the polyester film during the cooling process can be measured by the above method using a non-contact thermometer.

[0201] In addition, in a cooling process using a cooling unit (20), pressure is applied to the film (F) by passing it between the cooling roll (22) and the opposing roll (24) (the film (F) is compressed). By cooling the uniaxially stretched polyester film with the cooling roll (22) and compressing it with the cooling roll (22) and the opposing roll (24), the amount of shrinkage in the width direction of the polyester film obtained can be reduced.

[0202] In the cooling process, the pressure applied to the polyester film by the cooling roll and the counter roll is not particularly limited, but in order to further suppress the occurrence of linear defects in the obtained polyester film, the face average value of the pressure is preferably 0.8 MPa or higher, more preferably 1.1 MPa or higher, and more preferably 1.3 MPa or higher.

[0203] In addition, the upper limit of the face average value of the above pressure is preferably 2.5 MPa or less, more preferably 2.0 MPa or less, and more preferably 1.7 MPa or less, in order to further suppress the occurrence of transfer defects and return wrinkles (described later) in the obtained polyester film.

[0204] In addition, the face-average value of the pressure applied to the polyester film by the above-mentioned cooling roll and counter roll is measured using a pressure measuring film ("Free Scale" (registered trademark) manufactured by Fujifilm Corporation; for ultra-low pressure (LLW)). More specifically, without rotating the cooling roll and counter roll, the pressure measuring film is placed between the cooling roll and the counter roll under the same conditions as the cooling process and subjected to pressure. As a result, the area that turns red on the pressure measuring film is considered to be the area where pressure is applied by the cooling roll and the counter roll (pressure area).

[0205] In addition, using a pressure measuring instrument (manufactured by Fujifilm Corporation; FPD-306), the color intensity of the color-developed region appearing on the pressure measuring film is converted into a corresponding pressure value, and from the obtained pressure value, the surface average value of the pressure in the pressure region (sum of pressures applied to the pressure region / total area of ​​the pressure region) is calculated.

[0206] In addition, the difference between the maximum and minimum values ​​of pressure in the width direction in the compression region of the polyester film (hereinafter also referred to as the "pressure difference in the width direction") is preferably 0.6 MPa or less, more preferably 0.4 MPa or less, and more preferably 0.2 MPa or less. By reducing the pressure difference in the width direction in the compression region, misalignment of the polyester film in the width direction during transport can be suppressed, and the occurrence of linear defects in the resulting polyester film can be further suppressed. The lower limit is not particularly restricted, but 0.01 MPa or more is preferred.

[0207] The difference between the maximum and minimum values ​​of pressure in the width direction within the pressure region is obtained by performing the same method as the above-described method for measuring the surface average value of pressure, determining the pressure value in the pressure region based on the color-developed area appearing on the pressure measurement film, comparing the average value of the obtained pressure value in the transport direction along the width direction, and taking the difference between the maximum and minimum values ​​in the width direction.

[0208] The width of the compression area of ​​the polyester film by the cooling roll and the opposing roll is not particularly limited, but in terms of superior suppression of linear defects, the length of the compression area in the conveying direction (hereinafter also referred to as "nip width") is preferably 12 mm or more, more preferably 15 mm or more, and more preferably 18 mm or more. The upper limit is not particularly limited, but is preferably 30 mm or less.

[0209] The nip width of the pressure area is obtained by performing the same method as the above method for measuring the face-average value of pressure and measuring the length of the color-developing area in the conveying direction that appears on the pressure measuring film. In addition, the nip width of the pressure area can be adjusted according to the load applied between the cooling roll and the opposing roll, the hardness of the material constituting the opposing roll, and the outer diameters of the cooling roll and the opposing roll.

[0210] In the cooling process using the cooling unit (20), the film (F) is conveyed while applying pressure to the film (F) by means of the cooling roll (22) and the opposing roll (24), but the device used for the cooling process is not particularly limited as long as it is equipped with a cooling roll having an arithmetic mean roughness Ra of 0.05 μm or less on its surface.

[0211] For example, cooling and conveying of the polyester film may be performed using only a cooling roll in contact with one side of the polyester film, without providing a counter roll positioned opposite to the cooling roll. Additionally, the apparatus used for the cooling process may be equipped with two or more of the above-mentioned cooling rolls.

[0212] (Secondary cooling treatment)

[0213] In the cooling process using the cooling unit (20), a secondary cooling treatment is performed on the film (F) cooled by the cooling roll (22) by further cooling it by the second cooling roll (26).

[0214] The second cooling roll (26) has the function of cooling while conveying the film (F). The surface temperature of the second cooling roll is not particularly limited as long as it is lower than or equal to the surface temperature of the cooling roll (22), but is preferably 15 to 50°C.

[0215] In the cooling unit (20) shown in FIG. 1, three or more second cooling rolls are used, but the number of second cooling rolls may be one or two. Also, secondary cooling treatment may be performed using a device other than cooling rolls.

[0216] <Horizontal Stretching Process>

[0217] The transverse stretching process is a process of stretching a uniaxially stretched polyester film in the width direction (hereinafter also referred to as "transverse stretching"). More specifically, it is a process of stretching a uniaxially stretched polyester film in the width direction using a transverse stretching machine to form a biaxially stretched polyester film.

[0218] The transverse stretching unit (30) is a device that stretches the film (F) in the width direction by applying tension in the width direction while heating the film (F). A known transverse stretching machine, such as a tenter, is used as the transverse stretching unit (30).

[0219] The tenter is divided by a wind-blocking curtain and is equipped with a plurality of zones in which the temperature can be individually adjusted by hot air, etc. Specific examples of a tenter equipped with such zones include a tenter equipped with a preheating zone, a transverse stretching zone, a heat fixing zone, a heat relaxation zone, and a cooling zone in order from the upstream side of the conveying direction.

[0220] In the transverse stretching process, it is preferable to preheat the polyester film before transverse stretching. By preheating the polyester film, the polyester film can be easily transversely stretched.

[0221] The preheating temperature is preferably (Tg-10) to (Tg+60)℃, and more preferably (Tg) to (Tg+50)℃. Specifically, the preheating temperature is preferably 80 to 120℃, and more preferably 90 to 110℃.

[0222] It is preferable that the stretching ratio in the transverse stretching process be greater than the stretching ratio in the longitudinal stretching process. The stretching ratio in the transverse stretching process is preferably 3.0 to 6.0 times, more preferably 3.5 to 5.0 times, and more preferably 3.5 to 4.5 times.

[0223] The area ratio, which is the product of the stretching ratio in the longitudinal stretching process and the stretching ratio in the transverse stretching process, 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 greater than or equal to the lower limit value above, the molecular orientation in the film width direction becomes good. Furthermore, if the area ratio is less than or equal to the upper limit value above, it is easy to maintain a state where the molecular orientation is difficult to relax when subjected to heat treatment.

[0224] The heating temperature in the transverse stretching process is preferably (Tg-10) to (Tg+80)°C, more preferably (Tg) to (Tg+70)°C, and more preferably (Tg) to (Tg+60)°C. Specifically, the heating temperature in the transverse stretching process is preferably 100 to 140°C, more preferably 110 to 135°C, and more preferably 115 to 130°C.

[0225] In the transverse stretching process, the stretching speed is preferably 8 to 45% / second, more preferably 10 to 30% / second, and more preferably 15 to 20% / second.

[0226] When manufacturing a polyester film having a coating layer, it is preferable to apply a coating solution for forming the coating layer onto a polyester film stretched in the longitudinal direction, and then stretch it transversely. By the above method, the adhesion of the coating layer can be improved.

[0227] <Heating Process>

[0228] The manufacturing method of the present embodiment may include a process of heat treating a polyester film stretched in the width direction by a transverse stretching process (hereinafter also referred to as a "heat treatment process"). Examples of the heat treatment process include a heat setting process and a heat relaxation process. It is preferable for the heat treatment process to include at least one of the heat setting process and the heat relaxation process, and it is more preferable to include both the heat setting process and the heat relaxation process.

[0229] A heat treatment process including a heat-setting process and a heat-relaxing process is carried out, for example, using a tenter including a heat-setting zone and a heat-relaxing zone, which is exemplified as a transverse stretching part (30) in the transverse stretching process.

[0230] (Heat-fixing process)

[0231] In the heat-setting process, the polyester film stretched in the width direction is heat-set by heating. Since the polyester can be crystallized by heat-setting, the shrinkage of the polyester film can be suppressed.

[0232] The heating temperature in the heat-fixing process is preferably 190 to 240°C, more preferably 200 to 240°C, and more preferably 210 to 230°C.

[0233] In the heat setting process, the non-uniformity of the maximum reached film surface temperature in the film width direction is preferably 0.5 to 10.0°C, more preferably 0.5 to 7.0°C, more preferably 0.5 to 5.0°C, and particularly preferably 0.5 to 4.0°C. By controlling the non-uniformity of the maximum reached film surface temperature in the film width direction to within the above range, non-uniformity of the degree of crystallization in the width direction can be suppressed.

[0234] Examples of heating methods include applying hot air to the film and radiating the film. Examples of devices used in the radiating heating method include infrared heaters.

[0235] The heating time in the heat-setting process is preferably 5 to 50 seconds, more preferably 5 to 30 seconds, and more preferably 5 to 10 seconds.

[0236] (Thermal relaxation process)

[0237] In the heat relaxation process, the polyester film stretched in the width direction is heat-relaxed by heating. Residual distortion of the polyester film can be relieved by heat relaxation.

[0238] The heating temperature in the heat relaxation process is preferably 5°C or lower than the heating temperature in the heat fixation process, more preferably 15°C or lower, more preferably 25°C or lower, and particularly preferably 30°C or lower.

[0239] The lower limit of the heating temperature in the heat relaxation process is preferably 100°C or higher, more preferably 110°C or higher, and more preferably 120°C or higher.

[0240] Examples of heating methods include applying hot air to the film and radiating the film. As for devices used in the radiating heating method, an infrared heater is an example.

[0241] Winding Process

[0242] In the manufacturing method of the present embodiment, the biaxially stretched polyester film that has undergone the above-mentioned transverse stretching process is wound in a winding section (40) to obtain a roll-shaped biaxially stretched polyester film.

[0243] By undergoing the above process, a polyester film in which the occurrence of linear defects on the surface is further suppressed can be manufactured.

[0244] [Polyester Film]

[0245] A polyester film manufactured by the manufacturing method of the present embodiment will be described.

[0246] <Physical properties>

[0247] (Orientation)

[0248] The polyester film produced by the manufacturing method of the present embodiment is a biaxially oriented polyester film. In this specification, "biaxial orientation" means a property having molecular orientation in two axial directions.

[0249] Molecular orientation is measured using a microwave-transmitting molecular orientation system (e.g., MOA-6004, manufactured by Oji Keisoku Kiki Co., Ltd.). The angle formed by the two axial directions is preferably 90°±5°, more preferably 90°±3°, and more preferably 90°±1°. The polyester film manufactured by the manufacturing method of the present embodiment preferably has molecular orientation in the length direction and the width direction.

[0250] (furtherance)

[0251] A polyester film is a film containing polyester as the main polymer component. Here, "main polymer component" refers to the polymer with the highest content (mass) among all polymers contained in the film.

[0252] (Onboard defect)

[0253] In this specification, "linear defect" refers to a scratch formed on the surface of a polyester film that extends linearly along the conveying direction, having a length of 1 mm or more and a maximum depth of 500 nm or more. A linear defect may occur when a polyester film that has undergone longitudinal stretching is cooled, as the polyester film shrinks in the width direction. If a linear defect occurs in the polyester film, there is a possibility that the required performance may not be satisfied, for example, when the polyester film is used as a support and protective film for a DFR, such as causing exposure interference.

[0254] By the manufacturing method according to the present invention, the occurrence of linear defects in a polyester film obtained can be suppressed. The number of linear defects in the polyester film produced by the above manufacturing method is 20 / m 2The following is preferable, 5 pieces / m 2 The following is more preferable, 3 pieces / m 2 The following is more preferable, 1 piece / m 2 The following is particularly desirable. The lower limit is not specifically restricted, but 0.01 pieces / m² 2 Ideally, this is desirable.

[0255] The number of linear defects on the surface of a polyester film is measured by the following method.

[0256] (1) In a dark room, the reflected light of tungsten light from the polyester film and the transmitted light passing through the polyester film are observed with the naked eye while changing the viewing angle, and the location of linear scratches on the surface of the polyester film is determined.

[0257] (2) The length and depth of the observed scratches are measured using a laser microscope (Keyence Co., Ltd.; VK-9510) at a magnification of 300 to 3000 times, and based on the measurement results, scratches with a length of 1 mm or more and a maximum depth of 500 nm or more are classified as linear defects.

[0258] (3) 1 m of polyester film with observed linear defects 2 Number per unit (pieces / m) 2 Measures ).

[0259] (Non-uniform defects)

[0260] In this specification, "non-uniform defect" refers to a rough surface appearance visible by visually observing reflected light on the surface of a polyester film. Non-uniform defects may occur when peeling off a polyester film attached to a roll from a roll during the manufacture of the polyester film.

[0261] The number of non-uniform defects in a polyester film is 30 / m 2 The following is preferable, 10 pieces / m 2 The following is more preferable, 5 pieces / m 2The following is more desirable. The lower limit is not specifically restricted, but 0.01 pieces / m² 2 Ideally, this is desirable.

[0262] The number of non-uniform defects in a polyester film is measured by the following method.

[0263] In a darkroom, a polyester film is placed flat, and the tungsten light reflected from the polyester film is observed visually while changing the viewing angle. As a result of visual observation, areas where the reflected light is uneven and a rough appearance, such as wrinkles or tensiles, is observed on the surface of the polyester film are called non-uniform defects. By counting the number of observed non-uniform defects, 1m of polyester film 2 Number of non-uniform defects per unit (pieces / m) 2 Produces ).

[0264] (Transfer defect)

[0265] In this specification, "transfer defect" refers to a pinhole formed in a coating layer provided on the surface of a polyester film. Preferably, the coating layer is a coating layer formed on the polyester film by an inline coating method in the above manufacturing method. Transfer defects may occur, for example, when a polyester film having a coating layer is loaded onto a pair of rolls and conveyed, if the pressure applied to the polyester film by the pair of rolls is excessively high, or if the surface irregularity of one of the rolls is large.

[0266] The number of transfer defects in polyester film is 10 / m 2 The following is preferable, 3 pieces / m 2 The following is more preferable, 1 piece / m 2 The following is more desirable. The lower limit is not specifically restricted, but 0.01 pieces / m² 2 Ideally, this is desirable.

[0267] The number of transfer defects in a polyester film is measured by the following method.

[0268] (1) A laminated film consisting of a polyester film and a coating layer with a thickness of 0.05 μm is manufactured according to the method described above, except that a coating solution of the following formulation A is applied to the polyester film after longitudinal stretching using a slit nozzle to form a coating film.

[0269] (2) Tungsten light is shone from the side opposite to the side on which the coating layer of the manufactured laminated film is formed, and the coating layer side of the laminated film is observed visually. As a result, the number of transfer defects in the coating layer that are visible as pinholes through which light escapes is counted, and 1 m of polyester film 2 Number of transfer defects per unit (pieces / m) 2 Produces ).

[0270] -Prescription A: Coating solution for forming a coating layer-

[0271] · Polyacrylic (AS-563A, manufactured by Daicel Finechem Co., Ltd., solid content 27.5% by mass): 167 parts by mass

[0272] · Non-ionic surfactant (Naroacty (registered trademark) CL95, manufactured by Sanyo Kasei Kogyo Co., Ltd., solid content 100% by weight): 0.7 parts by weight

[0273] · Anionic surfactant (Rapizol (registered trademark) A-90, manufactured by Nichiyu Co., Ltd., solid content 1% by mass diluted with water): 55.7 parts by mass

[0274] · Carnauba wax dispersion (Cellosol (registered trademark) 524, manufactured by Chukyo Yushi Co., Ltd., solid content 30% by mass): 7 parts by mass

[0275] · Carbodiimide compound (Carbodylite (registered trademark) V-02-L2, manufactured by Nisshinbo Chemical Co., Ltd., 10% by mass solids diluted with water): 20.9 parts by mass

[0276] · Aggregated silica (Aerosil OX50, manufactured by Nippon Aerosil Co., Ltd., solid content 10 mass%, water dispersed, average particle size 40 nm): 2.95 parts by mass

[0277] · Water: 745.8 parts

[0278] (Heize)

[0279] The haze of the polyester film is preferably 3% or less, more preferably 1% or less, more preferably 0.5% or less, and particularly preferably 0.4% or less. Since a lower haze is desirable, there is no limit to the lower limit of the haze. If the lower limit of the haze is set for convenience, it is 0% or more. By making the haze below the upper limit value, scattering of ultraviolet light by the polyester film, which serves as a support for the resist layer, can be reduced when the resist layer is laminated onto the polyester film and then exposed by irradiating with ultraviolet light. Additionally, the condition of the resist pattern wall surface, such as distortion and detachment during resist patterning after development, can be improved, and the transmittance of the polyester film can be improved.

[0280] Haze is measured using a haze meter (e.g., NDH-2000, manufactured by Nippon Tenshoku Kogyo Co., Ltd.) in accordance with the method of JIS K 7105.

[0281] (b * value)

[0282] L * a * b * b in the color system * The value is preferably 0 to 1, more preferably 0 to 0.8, more preferably 0 to 0.6, and particularly preferably 0 to 0.4. L * a * b * b in the color system * Since the value is 0 to 1, the yellowness of the film can be reduced, so the color of the film can be made close to colorless. As a result, the polyester film can be preferably applied in applications requiring high visibility (e.g., display devices).

[0283] L * a * b * b in the color system *The value is measured by the transmission method using a spectrophotometer (e.g., SE-2000, manufactured by Nippon Tenshoku Kogyo Co., Ltd.).

[0284] (thickness)

[0285] From the perspective of processability (especially processability when laminating the film), the thickness of the polyester film is preferably 10 to 100 μm, more preferably 10 to 50 μm, and more preferably 12 to 40 μm. By making the thickness of the polyester film greater than or equal to the lower limit value above, strength can be improved, making it easier to handle during the processing process. In addition, by making the thickness less than or equal to the upper limit value above, an increase in the haze value can be suppressed. The thickness of the polyester film is the arithmetic mean of the thicknesses at five locations measured by a scanning electron microscope (SEM).

[0286] (Rate of change in dimensions)

[0287] For polyester films, it is desirable that the dimensional change rate be within the following ranges, as this can suppress the occurrence of distortion and wrinkles caused by thermal shrinkage during the DFR processing process. The dimensional change rate can be achieved by appropriately adjusting conditions such as relaxation and heat treatment in the film-forming conditions using known methods. At 150°C, the dimensional change rate is preferably less than 3% in the longitudinal direction and less than 2.5% in the width direction, and more preferably 0.5% or more and less than 2% in the longitudinal direction and 1% or more and less than 2% in the width direction. In addition, at 100°C, the dimensional change rate is preferably less than 1% in both the longitudinal and width directions, and more preferably less than 0.8%. If the dimensional change rate falls below the lower limit of the above range, flatness defects due to sagging occur when applying the resist layer, and if it exceeds the upper limit, uneven shrinkage in a wavy pattern occurs due to shrinkage when applying the resist layer, resulting in flatness defects; in either case, unevenness in the thickness of the resist layer may occur.

[0288] (F-5 value)

[0289] It is preferable that the polyester film has a strength (F-5 value) of 0 MPa or more and less than 150 MPa when elongated by 5% in the longitudinal direction. If the F-5 value in the longitudinal direction is less than 70 MPa, processing characteristics may deteriorate due to the occurrence of scratches, etc., caused by insufficient strength. On the other hand, if the F-5 value in the longitudinal direction is 150 MPa or more, it may be difficult to achieve compatibility with the F-5 value in the width direction. More preferably, the F-5 value in the longitudinal direction is 80 MPa or more and less than 140 MPa, and even more preferably 90 MPa or more and less than 130 MPa.

[0290] It is preferable that the width-direction F-5 value be 80 MPa or more and less than 160 MPa. If the width-direction F-5 value is less than 80 MPa, processing characteristics may deteriorate due to the occurrence of scratches caused by insufficient strength, and if it is 160 MPa or more, it may be difficult to achieve compatibility with the length-direction F-5 value. More preferably, the width-direction F-5 value is 90 MPa or more and less than 150 MPa, and even more preferably 100 MPa or more and less than 140 MPa.

[0291] (Break strength)

[0292] For the polyester film, the breaking strength in the longitudinal direction is preferably 200 MPa or more and less than 360 MPa, and more preferably 220 MPa or more and less than 340 MPa. Regarding the breaking strength in the width direction, it is preferably 260 MPa or more and less than 420 MPa, and more preferably 280 MPa or more and less than 400 MPa.

[0293] The F-5 value and breaking strength of the polyester film can be achieved by appropriately adjusting the stretching temperature and stretching ratio in the longitudinal and transverse directions.

[0294] Structure

[0295] The polyester film may have a single-layer structure or a laminated structure. When the polyester film has a laminated structure, it is preferable to have a substrate containing polyester and a coating layer on at least one surface of the substrate that contains particles and has a plurality of protrusions on its surface. By having a coating layer, the winding quality of the polyester film can be improved.

[0296] (Covering layer)

[0297] When the polyester film has a laminated structure, the coating layer is not particularly limited. The coating layer may or may not contain particles.

[0298] It is preferable that the coating layer contains particles and also has a plurality of protrusions on its surface.

[0299] Examples of particles include organic particles and inorganic particles. Among the above, inorganic particles are preferred in terms of film winding quality, haze, and durability (e.g., thermal stability).

[0300] As for the organic particles, resin particles are preferred. Examples of resin particles include acrylic resin particles, polyester resin particles, silicone resin particles, and styrene-acrylic resin particles. It is preferable for the resin particles to have a cross-linked structure.

[0301] Examples of inorganic particles include silica particles (silicon dioxide particles), titania particles (titanium oxide particles), calcium carbonate, barium sulfate, and alumina particles (aluminum oxide particles). Among the above, silica particles are preferred as inorganic particles in terms of haze and durability.

[0302] The average particle size of the particles is not particularly limited, but 0.01 to 0.4 μm is preferred and 0.04 to 0.2 μm is more preferred in terms of improving winding quality and suppressing transfer defects.

[0303] The average particle size of the particles is obtained by arithmetically averaging the particle sizes of 50 randomly selected particles from an image of a scanning electron microscope (SEM).

[0304] The coating layer may contain only one type of particle, or may contain two or more types of particles.

[0305] The particle content is preferably 0.01 to 15 mass% with respect to the total mass of the coating layer, more preferably 0.1 to 10 mass%, and more preferably 0.5 to 6 mass%, in terms of improving the winding quality of the film and suppressing transfer defects.

[0306] When the polyester film has a coating layer, the particle content is preferably 0.0001 to 0.01 mass% with respect to the total mass of the polyester film, and more preferably 0.0005 to 0.005 mass%.

[0307] The coating layer preferably contains a binder. As the binder, a resin binder is preferred. Examples of resin binders include polyacrylic, polyurethane, polyester, and polyolefin.

[0308] As for the polyacrylate, known polyacrylates may be used, provided that they are polymers having constituent units derived from at least one compound selected from the group consisting of acrylic acid esters and methacrylic acid esters. The polyacrylate may also have constituent units derived from compounds other than acrylic acid esters and methacrylic acid esters (e.g., olefin compounds and styrene compounds).

[0309] As for the polyurethane, any known polyurethane can be used, provided it is a polymer having urethane bonds. Polyurethane is often prepared by reacting an isocyanate compound with a polyol compound.

[0310] As for the polyester, the polyester described in the item "Polyester" above may be used, and the preferred type is also the same.

[0311] As for the polyolefin, known polyolefins may be used without limitation. Examples of polyolefins include polyethylene and polypropylene.

[0312] The coating layer may contain only one type of binder, or may contain two or more types of binders.

[0313] The binder content is preferably 30 to 80 mass% with respect to the total mass of the coating layer, more preferably 40 to 70 mass%, and more preferably 45 to 65 mass%, in terms of the durability of the coating layer and / or the dispersibility of the particles.

[0314] Regarding the multiple protrusions in the coating layer, including preferred embodiments, they are identical to the protrusions described in the item "protrusion density" above.

[0315] The thickness of the coating layer is preferably 0.01 to 0.3 μm, more preferably 0.02 to 0.1 μm, and more preferably 0.02 to 0.06 μm from the perspective of the suitability of manufacturing the coating layer. The thickness of the coating layer is the arithmetic mean of the thicknesses at five locations measured by a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0316] As a method for forming a coating layer, for example, a method using a coating solution for forming a coating layer may be used. For example, a coating layer can be formed by applying a coating solution for forming a coating layer onto a polyester film substrate and drying it as needed. Alternatively, the coating layer may be formed simultaneously with the formation of the unoriented polyester film in the extrusion forming process by a co-extrusion method.

[0317] A coating solution for forming a coating layer can be prepared by mixing each of the above components and a solvent. Examples of solvents include water, hexane, acetone, ethanol, tetrahydrofuran, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether. Among these, water is preferred from the perspective of environment, safety, and economic feasibility.

[0318] The coating solution for forming a coating layer may contain only one type of solvent, or may contain two or more types of solvents.

[0319] The solvent content is preferably 80 to 99 mass% with respect to the total mass of the coating solution for forming the coating layer, and more preferably 90 to 98 mass%.

[0320] The method of applying the coating solution for forming a coating layer is not limited and known methods may be used. Examples of application methods include spray coating, slit coating, roll coating, blade coating, spin coating, bar coating, and dip coating.

[0321] When forming a coating layer using a coating solution for forming a coating layer, the substrate to which the coating solution for forming a coating layer is applied may be an unoriented polyester film, a uniaxially stretched polyester film, or a biaxially stretched polyester film.

[0322] Regarding the method of forming the coating layer, it is preferable to apply a coating solution for forming the coating layer onto a uniaxially stretched polyester film in terms of adhesion between the substrate and the coating layer. For example, the adhesion between the substrate and the coating layer can be improved by forming a coating layer by applying a coating solution for forming the coating layer to the surface of a uniaxially stretched polyester film, and then simultaneously stretching the uniaxially stretched polyester film and the coating layer. The specific method of stretching is as described above.

[0323] <Uses>

[0324] The uses of the polyester film produced by the manufacturing method according to the present invention are not particularly limited, and examples include a support and protective film for a dry film photoresist, a release film for a multilayer ceramic capacitor (MLCC) manufacturing process, and a film for a transparent conductive substrate.

[0325] Examples

[0326] The present disclosure is explained more specifically below with reference to examples. The materials, usage amounts, ratios, processing details, and processing procedures shown in the following examples may be appropriately modified without departing from the spirit of the present disclosure. Accordingly, the scope of the present disclosure is not limited to the specific examples shown below. Furthermore, unless specifically stated otherwise, "parts" and "%" are based on mass.

[0327] [Example 1]

[0328] Extrusion Molding Process

[0329] Polyethylene terephthalate pellets were prepared using a titanium compound (citrate chelate titanium complex, VERTEC AC-420, manufactured by Johnson & Matty) described in Japanese Patent Publication No. 5575671 as a polymerization catalyst. The obtained pellets were dried until the moisture content was 50 ppm or less, then fed into the hopper of a 30 mm diameter single-screw kneading extruder, and subsequently melted and extruded at 280°C. The molten material was passed through a filter (hole diameter 3 μm) and then extruded from a die onto a cooling drum at 25°C to obtain an unoriented film. Additionally, the extruded molten material was adhered to the cooling drum by an electrostatic application method.

[0330] Longitudinal stretching process and cooling process

[0331] For the above-mentioned unoriented film, a longitudinal stretching process was performed by the following method.

[0332] A uniaxially stretched film was produced by passing an unoriented film, preheated by a preheating roll, between a pair of stretching rolls (made of ceramic) and then between a cooling roll C1 (product name "WC-12Co", manufactured by Praxair Kogaku Co., Ltd.) having a surface layer composed of tungsten carbide on the outer surface of a metal roll and a counter roll N1 (product name "90A70W", manufactured by Kinyosha, hardness 70 degrees) to stretch the film in the longitudinal direction (conveying direction). In addition, the longitudinal stretching process was carried out under conditions where the preheating temperature was 75°C, the stretching temperature was 90°C, the stretching ratio was 3.4 times, and the stretching speed was 1300% / second. The conveying speed of the unoriented film when passing through a pair of stretching rolls was 30 m / min, and the conveying speed of the uniaxially stretched film when passing between cooling roll C1 and opposing roll N1 was 100 m / min.

[0333] In addition, as a cooling process, the above-mentioned uniaxially stretched film was cooled by contacting it with cooling roll C1. Also, pressure was applied to the uniaxially stretched film by passing it between cooling roll C1 and opposing roll N1.

[0334] For the surface of cooling roll C1, the arithmetic mean roughness Ra is 0.02 μm, the maximum peak height Rp is 0.187 μm, and the protrusion density is 3647 pieces / mm² 2 The contact angle with water was 68.1°, and the temperature was 25℃.

[0335] The arithmetic mean roughness Ra of the surface of the opposing roll N1 was 1.1 μm.

[0336] The average value of the pressure applied to the uniaxially stretched film by the cooling roll C1 and the opposing roll N1 in the width direction was 1.3 MPa, and the difference between the maximum and minimum values ​​of the pressure in the width direction was 0.08 MPa. The length of the pressure area in the conveying direction formed by the pressure of the cooling roll C1 and the opposing roll N1 (hereinafter also referred to as the "nip width of the pressure area") was 20 mm.

[0337] In addition, the temperature of the uniaxially stretched film at the position in contact with the cooling roll was 100°C, and the temperature of the uniaxially stretched film at the position separated from the cooling roll was 50°C. From these temperatures, the cooling rate of the uniaxially stretched film by the cooling roll was calculated to be 200°C / second.

[0338] The measurement method for each of the above physical properties is described below.

[0339] -Measurement of the arithmetic mean roughness Ra of the cooling roll surface-

[0340] Regarding the arithmetic mean roughness Ra of the surface of the cooling roll, if the cooling roll is a commercially available product and a catalog value exists, the catalog value was adopted. If a catalog value does not exist, a test piece having the same structure as the cooling roll used was fabricated, and the surface of the obtained test piece was measured at a magnification of 3000x using a laser microscope (Keyence Co., Ltd.; VK-9510) to obtain the arithmetic mean roughness Ra of the surface of the cooling roll.

[0341] -Measurement of maximum mountain height Rp and protrusion density-

[0342] The maximum peak height Rp and protrusion density of the surface of the cooling roll were obtained by fabricating a test piece having the same structure as the cooling roll used, measuring the surface of the obtained test piece under the following conditions using the micro-shape measuring device, and then performing particle analysis (multiple levels) using the built-in analysis software.

[0343] The measuring instrument and measurement conditions are described below. For the above measurements, slice levels were set at equal intervals of 10 nm, and the average diameter and density of each slice level were measured five times while changing the measurement position. The average values ​​were calculated and used as the respective measurements for the maximum peak height Rp and protrusion density. Additionally, the test piece was fixed to the sample holder so that the X direction of the field of view measurement was the width direction of the polyester film.

[0344] · Measuring device: Kosaka Genkyusho surf-corder ET-4000A

[0345] · Analysis software: i-Face model TDA31 Ver2.2.0.4 JSIS

[0346] · Stylus tip radius: 0.5μm

[0347] · Measurement field of view: X direction: 380μm, Pitch: 1μm

[0348] Y direction: 280μm, Pitch: 5μm

[0349] · Tracking force: 50μN

[0350] · Measurement speed: 0.1 mm / s

[0351] · Cut-off value: Low - 0.8mm, High - None

[0352] · Leveling: Global

[0353] · Filter: Gaussian filter (2D)

[0354] · Magnification: 100,000x

[0355] · Particle analysis (multiple levels) conditions

[0356] · Output Content Settings: Acid Particles

[0357] · Hysteresis width: 5nm

[0358] · Slice level equidistant: 10nm

[0359] -Measurement of Contact Angle-

[0360] Regarding the contact angle of the cooling roll surface with respect to water, if the cooling roll is a commercially available product and a catalog value exists, the catalog value was adopted. If a catalog value does not exist, a test piece having the same structure as the cooling roll used was fabricated, and the static contact angle (°) of the surface of the test piece with respect to water was measured by the droplet method using a contact angle meter (manufactured by Kyowa Kaimen Kagaku Co., Ltd., DMo-901) and used as the contact angle of the cooling roll surface with respect to water.

[0361] -Measurement of the arithmetic mean roughness Ra of the opposing roll surface-

[0362] Replica material was injected onto the surface of a counter roll using a replica production kit (Microset Products, 101THTHIXO) to create a mold of the surface shape. The surface of the obtained replica was measured at a magnification of 3000x using a laser microscope (Keyence Co., Ltd.; VK-9510) to obtain the arithmetic mean roughness Ra of the surface of the counter roll.

[0363] -Pressure conditions-

[0364] In the above cooling process, the pressure applied to the uniaxially stretched film by the cooling roll and the counter roll was measured using a pressure measuring film (Fujifilm Corporation “Free Scale (registered trademark”); for ultra-low pressure (LLW)). Specifically, without rotating the cooling roll and the counter roll, the pressure measuring film was placed between the cooling roll and the counter roll and pressed under the same conditions as the above cooling process. As a result, a red-colored area appeared on the pressure measuring film. The colored area on the pressure measuring film corresponds to the area where pressure was applied by the cooling roll and the counter roll (i.e., the pressure area).

[0365] Next, the pressure measuring film was removed, and using a pressure measuring instrument (Fujifilm Corporation; FPD-306), the color intensity of the color-developed region appearing on the pressure measuring film was converted into a corresponding pressure value. From the obtained pressure value, the average value of the pressure in the width direction in the pressure region and the difference between the maximum and minimum values ​​in the width direction were calculated.

[0366] In addition, the length of the color development area in the return direction shown on the pressure measuring film was measured using a ruler. This measurement was performed every 100 mm in the width direction, and the average value of the obtained measurements was taken as the nip width of the pressure area formed by the pressure of the cooling roll C1 and the opposing roll N1.

[0367] -Measurement of film temperature-

[0368] Using a non-contact thermometer (AD-5616 (product name), manufactured by A&D, emissivity 0.95), the temperature of the uniaxially stretched film at the position in contact with the cooling roll (film temperature at contact) and the temperature of the uniaxially stretched film at the position away from the cooling roll (film temperature at separation) were measured. For each temperature measurement, the temperature of the center of the film in the width direction was measured five times, and the average value was taken as the measured value of the film temperature at contact and the film temperature at separation.

[0369] In addition, the time the uniaxially stretched film is in contact with the cooling roll was determined as the cooling time ta from the longitudinal length of the contact surface where the uniaxially stretched film is in contact with the cooling roll and the rotation speed of the cooling roll. The temperature difference Ta (°C) between the film temperature at contact and the film temperature at separation was divided by the cooling time ta (Ta / ta) to determine the cooling rate (°C / sec) of the uniaxially stretched film by the cooling process.

[0370] <Horizontal Stretching Process>

[0371] A uniaxially stretched film subjected to the above cooling process was transversely stretched using a tenter under the following conditions to obtain a biaxially stretched film.

[0372] -condition-

[0373] Preheating temperature: 100℃

[0374] Stretching temperature: 120℃

[0375] Stretch magnification: 4.2x

[0376] Stretching speed: 50% / sec

[0377] <Thermal Fixing and Thermal Relaxation Process>

[0378] The biaxially stretched film subjected to the above transverse stretching process was heat-set under the following conditions. In addition, after heat-setting, the tenter width was reduced and heat-relaxed under the following conditions, followed by cooling.

[0379] (Heat fixation conditions)

[0380] Heat fixing temperature: 227℃

[0381] Heat lock time: 6 seconds

[0382] (Thermal relaxation conditions)

[0383] Thermal relaxation temperature: 190℃

[0384] Thermal relaxation rate: 4%

[0385] (Cooling conditions)

[0386] Cooling rate: 2500℃ / min

[0387] Winding Process

[0388] The ends of the film in the width direction, after undergoing the above heat-setting and heat-relaxation processes, were trimmed, and subsequently, the ends of the film in the width direction were subjected to extrusion processing (knurling) to a width of 10 mm, and then the stretched film was wound with a tension of 40 kg / m. By the above method, a biaxially oriented film with a thickness of 30 μm was obtained. The width of the obtained biaxially oriented film was 1.5 m, and the winding length was 7000 m.

[0389] [Example 2]

[0390] A biaxially oriented film was obtained by the same method as in Example 1, except that in the cooling process, the pressure (average value in the width direction) applied to the uniaxially stretched film by the cooling roll C1 and the opposing roll N1 was adjusted to 1.0 MPa.

[0391] The nip width of the pressure area in the cooling process of Example 2 was 17 mm.

[0392] [Example 3]

[0393] A biaxially oriented film was obtained by the same method as in Example 1, except that in the cooling process, a counter roll N2 (product name "90A80W", manufactured by Kinyosha) was used instead of a counter roll N1, and the pressure (average value in the width direction) applied to the uniaxially stretched film by the cooling roll C1 and the counter roll N2 was adjusted to 2.1 MPa.

[0394] The hardness of the opposing roll N2 was 80 degrees. Also, the nip width of the pressing area in the cooling process of Example 3 was 17 mm.

[0395] [Example 4]

[0396] A biaxially oriented film was obtained by the same method as in Example 1, except that in the cooling process, a counter roll N3 (product name "90A70W", manufactured by Kinyosha) was used instead of a counter roll N1.

[0397] In the cooling process of Example 4, the difference between the maximum and minimum values ​​in the width direction of the pressure applied to the uniaxially stretched film by the cooling roll C1 and the opposing roll N3 was 0.49 MPa, and the nip width of the pressure area was 20 mm. In addition, this pressure difference and nip width are thought to be caused by distortion of the roll fixing part.

[0398] [Example 5]

[0399] A biaxially oriented film was obtained by the same method as in Example 1, except that in the cooling process, a counter roll N4 (product name "90A70W", manufactured by Kinyosha) was used instead of a counter roll N1.

[0400] In addition, since the opposing roll N4 had deteriorated over time, the arithmetic mean roughness Ra of its surface was 1.8 μm.

[0401] [Example 6]

[0402] A biaxially oriented film was obtained by the same method as in Example 1, except that in the cooling process, a cooling roll C2 (manufactured by Nomura Mekki Co., Ltd.) having a hard chromium plating treatment layer on the outer surface of a metal roll was used instead of cooling roll C1.

[0403] The plating layer of cooling roll C2 has an arithmetic mean surface roughness Ra of 0.008 μm, a maximum peak height Rp of 0.113 μm, and a maximum protrusion density of 2284 protrusions / mm² 2 It had a surface with a contact angle with water of 15.5°.

[0404] [Example 7]

[0405] A biaxially oriented film was obtained by the same method as in Example 1, except that in the cooling process, the cooling rate was adjusted to 100℃ / sec.

[0406] At this time, the temperature of the uniaxially stretched film at the position separated from the cooling roll C1 was 75℃.

[0407] [Comparative Example 1]

[0408] A biaxially oriented film was obtained by the same method as in Example 1, except that in the cooling process, a cooling roll C3 (product name "LC-4", manufactured by Praxair Kogaku Co., Ltd.) having a surface layer composed of chromium oxide on the outer surface of a metal roll was used instead of cooling roll C1.

[0409] The surface layer of cooling roll C3 has an arithmetic mean surface roughness Ra of 0.08 μm, a maximum peak height Rp of 0.323 μm, and a maximum protrusion density of 4,549 protrusions / mm² 2 It had a surface with a contact angle with water of 100.6°.

[0410] [evaluation]

[0411] For each of the biaxially oriented films of Examples 1 to 7 and Comparative Example 1, the following evaluation was performed. The evaluation results are shown in Table 1.

[0412] [Linear defects]

[0413] In a darkroom, using tungsten light as a light source, the reflected light from the biaxially aligned film and the transmitted light passing through the biaxially aligned film were observed visually while changing the viewing angle, and the locations of linear scratches present on the surface of the biaxially aligned film were identified. Next, the length and depth of the observed scratches were measured using a laser microscope (Keyence Co., Ltd.; VK-9510) at magnifications of 300 to 3000 times. Based on the measurement results, scratches with a length of 1 mm or more and a maximum depth of 500 nm or more were defined as linear defects, and the biaxially aligned film 1 m 2 Number of on-board defects (pieces / m) 2) was measured. Also, the area of ​​1m² in the biaxially oriented film 2 An area was randomly selected, and the maximum depth (unit: nm) of the longest linear defect in the selected area was measured.

[0414] [Non-uniform defects]

[0415] In a darkroom, a biaxially aligned film was placed flat, and the tungsten light reflected from the biaxially aligned film was observed visually while changing the viewing angle. As a result of the visual observation, the reflected light was non-uniform; areas where a rough appearance was observed on the surface of the biaxially aligned film, causing the reflected light from the light source to scatter, were defined as non-uniform defects. The observed non-uniform defects were counted, and 1 m of the biaxially aligned film 2 Number of non-uniform defects per unit (pieces / m) 2 ) produced.

[0416] [Transfer Defect]

[0417] A biaxially oriented film having a coating layer was prepared according to the method described in Examples 1 to 7 and Comparative Example 1, except that a coating solution composed of the above formulation A was applied using a slit nozzle onto a polyester film after performing longitudinal stretching by the above longitudinal stretching process to form a coating layer with a thickness of 0.05 μm.

[0418] Tungsten light was irradiated from the side opposite to the side on which the coating layer was formed on the biaxially oriented film with the coating layer, and the presence or absence of pinholes (transfer defects) in the coating layer was observed visually. The number of observed transfer defects was counted, and 1 m of the biaxially oriented film 2 Number of transfer defects per unit (pieces / m) 2 ) produced.

[0419] [Return pleat]

[0420] In the cooling process, the transport condition of the uniaxially stretched film on the cooling roll was observed and evaluated according to the following criteria. If the evaluation is A, it can be said that there are no practical problems. In addition, "both ends in the width direction" refers to the area up to 30 mm from both ends in the width direction of the uniaxially stretched film. Also, the transport wrinkles often have a shape that extends diagonally with respect to the transport direction.

[0421] (standard)

[0422] A: No wrinkles occur at both ends of the uniaxially stretched film in the width direction on the cooling roll.

[0423] B: Wrinkles occur at both ends of the uniaxially stretched film in the width direction on the cooling roll.

[0424] Table 1 shows the cooling process performed in each example and comparative example and the evaluation results for each, respectively.

[0425] In Table 1, the "surface material" column of the "cooling roll" indicates the material constituting the surface of the cooling roll, and "material A" means tungsten carbide, "material B" means hard chromium (plating layer), and "material C" means ceramic (chromium oxide), respectively.

[0426] [Table 1]

[0427]

[0428] [Table 2]

[0429]

[0430] From Table 1, it was confirmed that Examples 1 to 7, in which the arithmetic mean roughness Ra of the surface of the cooling roll is 0.05 μm or less, can suppress the occurrence of linear defects on the surface of the polyester film compared to Comparative Example 1.

[0431] It was confirmed that when the face average value of the pressure applied to the polyester film by the cooling roll and the opposing roll is 1.1 MPa or higher, the occurrence of linear defects on the surface of the polyester film can be further suppressed (comparison of Example 1 and Example 2).

[0432] In addition, it was confirmed that when the face average value of the pressure applied to the polyester film by the cooling roll and the opposing roll is 2.0 MPa or less, the occurrence of transfer defects and return wrinkles in the polyester film can be further suppressed (comparison of Example 1 and Example 3).

[0433] It was confirmed that when the difference between the maximum and minimum values ​​of pressure in the width direction in the area where pressure is applied by the cooling roll and the opposing roll in the polyester film is 0.4 MPa or less, the occurrence of linear defects on the surface of the polyester film can be further suppressed (comparison of Example 1 and Example 4).

[0434] It was confirmed that when the arithmetic mean roughness Ra of the surface of the opposing roll is 1.5 μm or less, the occurrence of transfer defects on the surface of the polyester film can be suppressed (comparison of Example 1 and Example 5).

[0435] It was confirmed that when the contact angle of the surface of the cooling roll with water is 20° or greater, the occurrence of non-uniform defects on the surface of the polyester film can be suppressed (comparison of Example 1 and Example 6).

[0436] It was confirmed that when the cooling rate of the polyester film by the cooling roll is 120°C / sec or higher, the occurrence of non-uniform defects on the surface of the polyester film can be suppressed (comparison of Example 1 and Example 7). Explanation of the symbols

[0437] 10-year-old bride 12 preheating rolls 14 consecutive rolls 16 heaters 20 cooling unit 22 cooling rolls 24 Large Roll 26 Second cooling roll 30 horizontal extensions 40 winding section 100 manufacturing devices F film

Claims

Claim 1 A method for manufacturing a polyester film comprises a cooling process in which a uniaxially stretched polyester film is brought into contact with a cooling roll to cool, wherein the arithmetic mean roughness Ra of the surface of the cooling roll is 0.05 μm or less, and further comprises a longitudinal stretching process in which an unoriented polyester film is stretched in a conveying direction using the cooling roll and one or more stretching rolls disposed upstream of the cooling roll in the conveying direction and having a conveying speed slower than that of the cooling roll to form the uniaxially stretched polyester film, and the polyester film obtained by the manufacturing method further comprises a coating layer provided on the surface of the polyester film, wherein the number of transfer defects recognizable as pinholes by visually observing the surface of the coating layer side by irradiating light from a side opposite to the coating layer is such that 1 m of the polyester film 2 A method for manufacturing a polyester film, having three or fewer per layer. Claim 2 A manufacturing method according to claim 1, wherein the maximum peak height Rp of the surface of the cooling roll is 0.3 μm or less. Claim 3 In claim 1 or claim 2, the density of protrusions on the surface of the cooling roll is 10,000 pieces / mm² 2 Lee Ha-in, manufacturing method. Claim 4 A manufacturing method according to claim 1 or claim 2, wherein the cooling rate of the polyester film by the cooling roll in the cooling process is 150°C / sec or higher. Claim 5 A manufacturing method according to claim 1 or claim 2, wherein the temperature of the polyester film in contact with the cooling roll in the cooling process is 90°C or higher. Claim 6 A method of manufacturing according to claim 1 or claim 2, wherein the temperature of the polyester film falling from the cooling roll in the cooling process is 50°C or lower. Claim 7 A method of manufacturing according to claim 1 or claim 2, wherein the temperature of the polyester film lowered during the cooling process from contact with the cooling roll until it is removed from the cooling roll is 30°C or higher. Claim 8 A manufacturing method according to claim 1 or claim 2, wherein the surface temperature of the cooling roll is 35°C or lower. Claim 9 A method of manufacturing according to claim 1 or claim 2, wherein the conveying speed of the polyester film by the cooling roll is 50 to 150 m / min. Claim 10 A method of manufacturing according to claim 1 or claim 2, wherein the conveying speed of the unoriented polyester film by the stretching roll is 10 to 50 m / min. Claim 11 A manufacturing method according to claim 1 or claim 2, wherein the arithmetic mean roughness Ra of the surface of the cooling roll is 0.008 μm or more. Claim 12 A manufacturing method according to claim 1 or claim 2, wherein the contact angle of the surface of the cooling roll with water is 10° or more. Claim 13 A method of manufacturing according to claim 1 or claim 2, wherein the thickness of the polyester film is 40 μm or less. Claim 14 A manufacturing method according to claim 1 or claim 2, wherein in the cooling process, pressure is applied to the polyester film by passing the polyester film between the cooling roll and the opposing roll positioned opposite to the cooling roll. Claim 15 A manufacturing method according to claim 14, wherein the difference between the maximum and minimum values ​​of the pressure applied to the polyester film by the cooling roll and the opposing roll in the width direction is 0.4 MPa or less. Claim 16 A manufacturing method according to claim 14, wherein the face average value of the pressure applied to the polyester film by the cooling roll and the opposing roll is 1.1 MPa or more. Claim 17 A manufacturing method according to claim 14, wherein the face average value of the pressure applied to the polyester film by the cooling roll and the opposing roll is 1.7 MPa or less. Claim 18 A manufacturing method according to claim 14, wherein the length of the conveying direction of the area where pressure is applied by the cooling roll and the opposing roll in the polyester film is 15 mm or more. Claim 19 A manufacturing method according to claim 14, wherein the arithmetic mean roughness Ra of the surface of the opposing roll is 1.5 μm or less. Claim 20 As a polyester film, the number of linear defects on the surface of the polyester film, wherein the depth is 500 nm or more and the length is 1 mm or more, is 1 m of the polyester film 2 The number of transfer defects is five or fewer per unit, and further comprises a coating layer provided on the surface of the polyester film, wherein the number of transfer defects recognizable as pinholes by irradiating light from a side opposite to the coating layer and visually observing the surface on the side of the coating layer is, 1m of the polyester film 2 Polyester film, with three or fewer pieces per layer. Claim 21 In claim 20, the number of non-uniform defects visible by visually observing reflected light on the surface of the polyester film is 1m of the polyester film 2 Polyester film, with five or fewer pieces per layer. Claim 22 delete

Images