Method for manufacturing polyester film, polyester film

Abstract

The object of the present invention is to provide a method for manufacturing a polyester film capable of more suppressing the formation of linear defects on the surface of the polyester film. Further, the object of the present invention is to provide a polyester film. The method for manufacturing a polyester film of the present invention has a cooling step of bringing a uniaxially stretched polyester film into contact with a cooling roll for cooling, and the arithmetic mean roughness Ra of the surface of the cooling roll is 0.05 μm or less.

Description

Technical Field

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

[0002] From the viewpoints of processability, mechanical properties, electrical properties, dimensional stability, transparency, chemical resistance, etc., polyester films are widely used, for example, as a support and a protective film for a dry film photoresist. The dry film photoresist has a structure in which a photosensitive resin layer (photoresist layer) is laminated on a support and then a protective film is further laminated thereon. In recent years, dry film photoresists have been used in the field of touch panels for etching applications in wiring formation processes, for forming protective films for protecting wiring portions such as copper, ITO (indium tin oxide), and silver nanoparticles, and for interlayer insulating film applications.

[0003] Patent Document 1 discloses a method for manufacturing a stretched film, which includes: a longitudinal stretching step of stretching a film made of a strip-shaped thermoplastic resin in the transport direction; a cooling step of cooling the film by a cooling roll; and a side edge portion removing step of removing side edge portions on both sides in the width direction of the film between the longitudinal stretching step and the cooling step.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-188748 Summary of the Invention

[0007] Technical Problem to be Solved by the Invention

[0008] On the other hand, in recent years, further refinement (line thinning) of patterns formed by a dry film photoresist (DFR) has been required, and higher performance (film thinning, low haze, etc.) than in the past has also been required for a temporary support and a protective film.

[0009] As a result of investigations by the present inventors on polyester films used as a temporary support and a protective film for DFR, it has been found that slight linear scratches (linear defects) present on the surface of the polyester film sometimes cause exposure obstacles when manufacturing DFR that meets the above requirements.

[0010] In view of the above circumstances, an object of the present invention is to provide a method for manufacturing a polyester film that can more effectively suppress the formation of linear defects on the surface of the polyester film.

[0011] Moreover, an object of the present invention is to provide a polyester film.

[0012] Means for Solving the Technical Problem

[0013] As a result of the inventors' in-depth exploration of the above problems, it has been found that the above problems can be solved by the following structure.

[0014] 〔1〕A method for manufacturing a polyester film, which has a cooling step of cooling a uniaxially stretched polyester film by bringing it into contact with a cooling roll, wherein the arithmetic mean roughness Ra of the surface of the cooling roll is 0.05 μm or less.

[0015] 〔2〕The manufacturing method according to 〔1〕, wherein

[0016] the maximum peak height Rp of the surface of the cooling roll is 0.3 μm or less.

[0017] 〔3〕The manufacturing method according to 〔1〕 or 〔2〕, wherein

[0018] the protrusion density on the surface of the cooling roll is 10,000 or less per mm 2 hereinafter.

[0019] 〔4〕The manufacturing method according to any one of 〔1〕 to 〔3〕, wherein

[0020] the cooling rate of the polyester film passing through the cooling roll in the cooling step is 150 °C / second or more.

[0021] 〔5〕The manufacturing method according to any one of 〔1〕 to 〔4〕, wherein

[0022] the temperature of the polyester film in contact with the cooling roll in the cooling step is 90 °C or more.

[0023] 〔6〕The manufacturing method according to any one of 〔1〕 to 〔5〕, wherein

[0024] the temperature of the polyester film leaving the cooling roll in the cooling step is 50 °C or less.

[0025] 〔7〕The manufacturing method according to any one of 〔1〕 to 〔6〕, wherein

[0026] the temperature drop of the polyester film from the time of contact with the cooling roll to the time of leaving the cooling roll in the cooling step is 30 °C or more.

[0027] 〔8〕The manufacturing method according to any one of 〔1〕 to 〔7〕, wherein

[0028] the surface temperature of the cooling roll is 35 °C or less.

[0029] 〔9〕The manufacturing method according to any one of 〔1〕 to 〔8〕, wherein

[0030] The conveyance speed of the above-mentioned polyester film through the above-mentioned cooling roll is 50 to 150 m / minute.

[0031] 〔10〕The manufacturing method according to any one of 〔1〕to〔9〕further has a longitudinal stretching step, in the longitudinal stretching step, the above-mentioned cooling roll and one or more stretching rolls arranged on the upstream side in the conveyance direction of the above-mentioned cooling roll and slower than the conveyance speed of the above-mentioned cooling roll are used to stretch the unstretched polyester film in the conveyance direction to form the above-mentioned uniaxially stretched polyester film.

[0032] The conveyance speed of the above-mentioned unstretched polyester film through the above-mentioned stretching roll is 10 to 50 m / minute.

[0033] 〔11〕The manufacturing method according to any one of 〔1〕to〔10〕, wherein

[0034] The arithmetic mean roughness Ra of the surface of the above-mentioned cooling roll is 0.008 μm or more.

[0035] 〔12〕The manufacturing method according to any one of 〔1〕to〔11〕, wherein

[0036] The contact angle of the surface of the above-mentioned cooling roll with respect to water is 10° or more.

[0037] 〔13〕The manufacturing method according to any one of 〔1〕to〔12〕, wherein

[0038] The thickness of the above-mentioned polyester film is 40 μm or less.

[0039] 〔14〕The manufacturing method according to any one of 〔1〕to〔13〕, wherein

[0040] In the above-mentioned cooling step, pressure is applied to the above-mentioned polyester film by passing the above-mentioned polyester film between the above-mentioned cooling roll and an opposing roll arranged to oppose the above-mentioned cooling roll.

[0041] 〔15〕The manufacturing method according to 〔14〕, wherein

[0042] The difference between the maximum value and the minimum value of the pressure applied to the above-mentioned polyester film by the above-mentioned cooling roll and the above-mentioned opposing roll in the width direction is 0.4 MPa or less.

[0043] 〔16〕The manufacturing method according to 〔14〕or〔15〕, wherein

[0044] The surface average value of the pressure applied to the above-mentioned polyester film by the above-mentioned cooling roll and the above-mentioned opposing roll is 1.1 MPa or more.

[0045] 〔17〕The manufacturing method according to any one of 〔14〕to〔16〕, wherein

[0046] The average surface pressure applied to the polyester film by the above-described cooling roll and the above-described opposing roll is 1.7 MPa or less.

[0047] 〔18〕The manufacturing method according to any one of 〔14〕 to 〔17〕, wherein

[0048] In the above polyester film, the length in the conveyance direction of the region where pressure is applied by the above cooling roll and the above opposing roll is 15 mm or more.

[0049] 〔19〕The manufacturing method according to any one of 〔14〕 to 〔18〕, wherein

[0050] The arithmetic mean roughness Ra of the surface of the above opposing roll is 1.5 μm or less.

[0051] 〔20〕A polyester film, wherein

[0052] On the surface of the above polyester film, the number of linear defects having a depth of 500 nm or more and a length of 1 mm or more per 1 m2 of the above polyester film is 5 or less.

[0053] 〔21〕The polyester film according to 〔20〕, wherein

[0054] The number of interference defects visually recognized by observing the reflected light on the surface of the above polyester film per 1 m2 of the above polyester film is 5 or less.

[0055] 〔22〕The polyester film according to 〔20〕 or 〔21〕, further having a coating layer provided on the surface of the above polyester film, and the number of transfer defects visually recognized as pinholes per 1 m2 of the above polyester film by irradiating light from the side opposite to the above coating layer and observing the surface on the above coating layer side is 3 or less.

[0056] Advantages of the Invention

[0057] According to the present invention, it is possible to provide a manufacturing method of a polyester film capable of more suppressing the formation of linear defects on the surface of the polyester film. Further, according to the present invention, it is possible to provide a polyester film. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a schematic diagram showing the structure of a manufacturing apparatus used in the manufacturing method of a polyester film. DETAILED DESCRIPTION OF THE INVENTION

[0059] Hereinafter, embodiments of the present invention will be described in detail. In addition, the present invention is not limited by any of the following embodiments, and within the scope of the object of the present invention, the present invention can be appropriately modified and implemented.

[0060] In the present invention, the numerical range indicated by "~" means the range including the numerical values described before and after "~" as the lower limit value and the upper limit value. In the numerical ranges described stepwise in the present invention, the upper limit value or the lower limit value described in a certain numerical range can be replaced by the upper limit value or the lower limit value of other numerically ranges described stepwise. Moreover, in the numerical ranges described in the present invention, the upper limit value or the lower limit value described in a certain numerical range can be replaced by the value shown in the examples.

[0061] In the present invention, when there are multiple substances corresponding to each component in the composition, unless otherwise specified, the amount of each component in the composition refers to the total amount of the multiple substances present in the composition.

[0062] In the present invention, the term "process" includes not only independent processes, but also includes those that can achieve the intended purpose of the process even when they cannot be clearly distinguished from other processes.

[0063] In the present invention, "mass %" has the same meaning as "weight %", and "parts by mass" has the same meaning as "parts by weight".

[0064] In the present invention, the combination of two or more preferred modes is a more preferred mode.

[0065] In the present invention, the "long side direction" refers to the long strip direction of the polyester film when manufacturing the polyester film, which has the same meaning as the "transport direction" and the "machine direction". Moreover, the "width direction" refers to the direction orthogonal to the long side direction.

[0066] In the present invention, the term "orthogonal" is not limited to strict orthogonality, but includes approximate orthogonality. "Approximate orthogonality" means intersecting at 90° ± 5°, preferably intersecting at 90° ± 3°, and more preferably intersecting at 90° ± 1°.

[0067] [Method for manufacturing a polyester film]

[0068] The method for manufacturing the polyester film of the present invention has a cooling process in which the uniaxially stretched polyester film is brought into contact with a cooling roll for cooling. Moreover, the arithmetic mean roughness Ra of the surface of the cooling roll used in this cooling process is 0.05 μm or less.

[0069] Hereinafter, the method for manufacturing the polyester film of the present invention will be described according to specific embodiments, but the present invention is not limited to the following embodiments.

[0070] A method for manufacturing a polyester film according to an example of an embodiment of the present invention (hereinafter, also referred to as "the manufacturing method of the present embodiment") includes: a step of producing an unstretched polyester film from a raw material polyester by an extrusion molding method (hereinafter, also referred to as "the extrusion molding step"); a step of stretching the unstretched polyester film in the transport direction (hereinafter, also referred to as "the longitudinal stretching step"); a step of cooling the uniaxially stretched polyester film obtained by the longitudinal stretching step (hereinafter, also referred to as "the cooling step"); and a step of stretching the uniaxially stretched polyester film cooled by the cooling step in the width direction (hereinafter, also referred to as "the transverse stretching step").

[0071] 〔Polyester raw material〕

[0072] Hereinafter, the polyester used as the raw material of the unstretched polyester film in the manufacturing method of the present embodiment will be described.

[0073] Polyester is a polymer having an ester bond in the main chain. Polyester is mostly formed by polycondensing a dicarboxylic acid compound and a glycol compound described later.

[0074] There is no limitation on the polyester, and known polyesters can be used. Examples of the polyester include polyethylene terephthalate (PET) and polyethylene 2,6-naphthalate (PEN), and PET is preferred.

[0075] 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.

[0076] The polyester film may contain a single polyester or two or more polyesters.

[0077] The content of the polyester is preferably 85% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and particularly preferably 98% by mass or more with respect to the total mass of the polymers in the polyester film.

[0078] There is no limitation on the upper limit of the content of the polyester, and it can be appropriately set within the range of 100% by mass or less with respect to the total mass of the polymers in the polyester film.

[0079] The content of the polyester is preferably 85% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and particularly preferably 98% by mass or more with respect to the total mass of the polyester film. There is no limitation on the upper limit of the content of the polyester, and it can be appropriately set within the range of 100% by mass or less with respect to the total mass of the polyester film.

[0080] When the polyester film contains polyethylene terephthalate, the content of polyethylene terephthalate is preferably 90 to 100% by mass, more preferably 95 to 100% by mass, still more preferably 98 to 100% by mass, and particularly preferably 100% by mass, relative to the total mass of the polyester in the polyester film.

[0081] (Method for producing polyester)

[0082] As the method for producing polyester, there is no limitation, and known methods can be used. For example, in the presence of a catalyst, polyester can be produced by polycondensing at least one dicarboxylic acid compound and at least one glycol compound.

[0083] - Catalyst -

[0084] The catalyst used in the production of polyester is not particularly limited, and known catalysts that can be used for the synthesis of polyester can be used.

[0085] Examples of the catalyst 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 them, titanium compounds are preferred from the viewpoints of catalyst activity and cost.

[0086] As the titanium compound, an organic chelate titanium complex is preferred. An organic chelate titanium complex is a titanium compound having an organic acid as a ligand.

[0087] Examples of the organic acid include citric acid, lactic acid, trimellitic acid, and malic acid.

[0088] As the titanium compound, the titanium compounds described in paragraphs 0049 to 0053 of Japanese Patent No. 5575671 can also be used, and the content of the above-mentioned publication is incorporated into this specification.

[0089] - Dicarboxylic acid compound -

[0090] Examples of the dicarboxylic acid compound include aliphatic dicarboxylic acid compounds, alicyclic dicarboxylic acid compounds, and aromatic dicarboxylic acid compounds, and aromatic dicarboxylic acids are preferred.

[0091] Examples of the aliphatic dicarboxylic acid compound include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, icosanedioic acid, pimelic acid, azelaic acid, methylmalonic acid, and ethylmalonic acid.

[0092] Examples of the alicyclic dicarboxylic acid compound include adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, and decalin dicarboxylic acid.

[0093] As the aromatic dicarboxylic acid compound, for example, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenylether dicarboxylic acid, sodium 5-sulfoisophthalate, phenylindanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, and 9,9'-bis(4-dicarboxyphenyl)fluorene acid can be mentioned.

[0094] Among them, terephthalic acid or 2,6-naphthalenedicarboxylic acid is preferable, and terephthalic acid is more preferable.

[0095] As the dicarboxylic acid compound, only 1 type may be used, or 2 or more types may be used in combination. When terephthalic acid is used as the dicarboxylic acid compound, terephthalic acid may be used alone, or may be copolymerized with other aromatic dicarboxylic acids such as isophthalic acid or aliphatic dicarboxylic acids.

[0096] -Diol compound-

[0097] As the diol compound, for example, aliphatic diol compounds, alicyclic diol compounds, and aromatic diol compounds can be mentioned, and aliphatic diol compounds are preferable.

[0098] As the aliphatic diol compound, for example, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and neopentyl glycol can be mentioned, and ethylene glycol is preferable.

[0099] As the alicyclic diol compound, for example, cyclohexanedimethanol, spirodiol, and isosorbide can be mentioned.

[0100] As the aromatic diol compound, for example, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, and 9,9'-bis(4-hydroxyphenyl)fluorene can be mentioned.

[0101] As the diol compound, only 1 type may be used, or 2 or more types may be used in combination.

[0102] -End capping agent-

[0103] In the production of the polyester, an end capping agent can be used as needed. By using the end capping agent, a structure derived from the end capping agent is introduced at the end of the polyester.

[0104] There is no limitation as the end capping agent, and known end capping agents can be used. As the end capping agent, for example, oxazoline-based compounds, carbodiimide compounds, and epoxy compounds can be mentioned.

[0105] As the end capping agent, the content described in paragraphs 0055 to 0064 of Japanese Patent Application Laid-Open No. 2014-189002 can also be referred to, and the content of the above-mentioned publication is incorporated into this specification.

[0106] - Manufacturing Conditions -

[0107] The reaction temperature is not limited and can be appropriately set according to the raw materials. The reaction temperature is preferably 260 to 300 °C, more preferably 275 to 285 °C.

[0108] The pressure is not limited and can be appropriately set according to the raw materials. The pressure is preferably 1.33×10 to 1.33×10 MPa, more preferably 6.67×10 to 6.67×10 MPa.

[0109] As a method for synthesizing polyester, the method described in paragraphs 0033 to 0070 of Japanese Patent No. 5575671 can also be used, and the content of the above-mentioned publication is incorporated into this specification.

[0110] 〔Manufacturing Apparatus〕

[0111] The apparatus used in the manufacturing method of this embodiment is not particularly limited, and a known apparatus can be used.

[0112] Figure 1 It is a schematic structural diagram showing an example of the manufacturing apparatus used in the manufacturing method of this embodiment.

[0113] Figure 1 The polyester film manufacturing apparatus 100 shown includes: a longitudinal stretching unit 10 that stretches an unstretched polyester film made by an extrusion molding method in the conveying direction; a cooling unit 20 that rapidly cools the uniaxially stretched polyester film stretched in the longitudinal stretching unit 10 in the conveying direction; a transverse stretching unit 30 that stretches the polyester film cooled in the cooling unit 20 in the width direction; and a winding unit 40 that winds the polyester film stretched in the transverse stretching unit 30.

[0114] The detailed structures and functions of the above-mentioned units and the like are described together with the descriptions of the respective manufacturing processes of the manufacturing method of this embodiment described below.

[0115] Hereinafter, in this specification, the notations related to "film F" and a single "polyester film" include all of the unstretched polyester film, the uniaxially stretched polyester film, and the biaxially stretched polyester film.

[0116] 〔Respective Manufacturing Processes〕

[0117] While referring to Figure 1 the manufacturing apparatus 100 shown, the respective processes of the manufacturing method of this embodiment will be specifically described.

[0118] <Extrusion Molding Process>

[0119] In the extrusion molding process, an unstretched polyester film is formed from raw material polyester by an extrusion molding method.

[0120] The extrusion molding method is a method of molding a raw material resin into a desired shape by extruding the raw material resin using an extruder, for example.

[0121] The unstretched polyester film is formed, for example, by heating the above-mentioned polyester to a temperature above the melting point using an extruder equipped with one or more than two screws, and then rotating the screws to perform melt-kneading. The polyester is melted in the extruder by heating and kneading by the screws to become a melt.

[0122] The melt is extruded from the extrusion die through a gear pump, a filter, etc. The extrusion die is also simply referred to as a "die" (refer to JIS B8650:2006, (a) Extrusion molding machine, No. 134). The melt can be extruded in a single layer or in multiple layers.

[0123] In melt extrusion, from the viewpoint of suppressing thermal decomposition (for example, hydrolysis of polyester) in the extruder, it is preferable to replace the inside of the extruder with nitrogen. And from the viewpoint of suppressing the kneading temperature to a lower level, the extruder is preferably a twin-screw extruder.

[0124] The melt extruded from the extrusion die is formed into a film shape by being cooled. For example, by bringing the melt into contact with a casting roll and cooling and solidifying the melt on the casting roll, the melt can be formed into a film shape. In the cooling of the melt, it is preferable to further blow air (preferably cold air) onto the melt.

[0125] The temperature of the casting roll is preferably higher than (Tg - 10) °C and equal to or lower than (Tg + 30) °C, more preferably (Tg - 7) to (Tg + 20) °C, and still more preferably (Tg - 5) to (Tg + 10) °C.

[0126] In addition, in this specification, "Tg" refers to the glass transition temperature of the polyester constituting the polyester film manufactured by the manufacturing method of this embodiment.

[0127] And in this specification, the temperature of the polyester film and each component in the manufacturing method can be measured using a non-contact thermometer (for example, a radiation thermometer).

[0128] When a casting roll is used in the extrusion molding process, it is preferable to improve the adhesion between the casting roll and the melt. As a method for improving the adhesion, for example, an electrostatic application method, an air knife method, an air chamber method, a vacuum nozzle method, and a contact roll method can be cited.

[0129] The molded body (unstretched polyester film) cooled using a casting roll or the like is peeled off from the cooling member such as the casting roll using a peeling member such as a peeling roll.

[0130] <Longitudinal stretching process>

[0131] The longitudinal stretching process is a process of stretching an unstretched polyester film in the conveying direction (hereinafter, also referred to as "longitudinal stretching"). More specifically, it is a process of stretching an unstretched polyester film in the conveying direction using a device having two or more stretching rollers with different conveying speeds to form a uniaxially stretched polyester film.

[0132] The longitudinal stretching unit 10 is an example of a device having two or more stretching rollers with different conveying speeds as described above, and it includes a pair of preheating rollers 12, a pair of stretching rollers 14, and a heater 16.

[0133] In the longitudinal stretching unit 10, a pair of preheating rollers 12, a pair of stretching rollers 14, and the heater 16 are arranged in sequence from the upstream side in the conveying direction.

[0134] The preheating roller 12 has a function of conveying the film F in the long side direction and preheating the film F before longitudinal stretching.

[0135] In the longitudinal stretching process using the longitudinal stretching unit 10, the unstretched polyester film is preheated by the preheating roller 12 before longitudinal stretching. By preheating the unstretched polyester film, the polyester film can be easily longitudinally stretched.

[0136] In addition, Figure 1 The shown manufacturing device 100 only has a pair of preheating rollers 12, but the number of preheating rollers arranged at a position more upstream than the stretching roller 14 for longitudinal stretching is not particularly limited, and a number corresponding to the conveying speed of the film F and / or the thickness of the film may be set.

[0137] The preheating temperature of the unstretched polyester film is preferably (Tg - 30) to (Tg + 40) °C, more preferably (Tg - 20) to (Tg + 30) °C. Specifically, the preheating temperature is preferably 60 to 100 °C, more preferably 65 to 80 °C.

[0138] The conveying speed of the film F through the preheating roller 12 is not particularly limited, and it is preferably the same as the conveying speed of the film F through the stretching roller 14.

[0139] The stretching roller 14 has a function of conveying the film F in the long side direction. Here, the conveying speed of the film F through the stretching roller 14 is set to be slower than the conveying speed of the film F through the cooling roller 22 described later.

[0140] In the longitudinal stretching unit 10, while applying tension to the film F between the stretching roller 14 and the cooling roller 22 whose conveying speed is faster than that of the stretching roller, the film F is conveyed, thereby performing longitudinal stretching of the unstretched polyester film.

[0141] The conveying speed (circumferential speed) of the film F through the stretching roller 14 is not particularly limited as long as it is slower than that of the cooling roller 22, and it is preferably 5 to 60 m / minute, more preferably 10 to 50 m / minute, and further preferably 15 to 45 m / minute.

[0142] Moreover, the conveyance speed (circumferential speed) of the film F by the cooling roll 22 is not particularly limited as long as it is faster than that of the stretching roll 14, preferably 40 to 160 m / min, more preferably 50 to 150 m / min, and still more preferably 60 to 140 m / min.

[0143] The draw ratio in the longitudinal stretching step can be appropriately set according to the use, preferably 2.0 to 5.0 times, more preferably 2.5 to 4.0 times, and still more preferably 2.8 to 4.0 times.

[0144] The stretching speed in the longitudinal stretching step is preferably 800 to 1500% / second, more preferably 1000 to 1400% / second, and still more preferably 1200 to 1400% / second. Here, the "stretching speed" means the value obtained by dividing the length Δd in the conveyance direction of the polyester film stretched in 1 second in the longitudinal stretching step by the length d0 in the conveyance direction of the polyester film before stretching, expressed as a percentage.

[0145] Moreover, the stretching roll 14 has the function of preheating the film F. The preferred range of the preheating temperature of the film F passing through the stretching roll 14 is the same as the preferred range of the preheating temperature of the above-mentioned preheating roll.

[0146] There is no particular limitation on the preheating roll 12 and the stretching roll 14, and known rolls used in the stretching of plastic films can be used. However, the material constituting the surface layer including the surface of each roll is preferably metal, ceramic, or fluororesin, more preferably ceramic. As the metal, chromium is preferred. As the ceramic, chromium oxide or alumina is preferred, and chromium oxide is more preferred. As the fluororesin, polytetrafluoroethylene is preferred.

[0147] The heater 16 has the function of heating the film F (unstretched polyester film) longitudinally stretched by the stretching roll 14 and the cooling roll 22.

[0148] The heating temperature in the longitudinal stretching step by the heater 16 is preferably (Tg - 20) to (Tg + 50)°C, more preferably (Tg - 10) to (Tg + 40)°C, and still more preferably (Tg) to (Tg + 30)°C. Specifically, the heating temperature in the longitudinal stretching step is preferably 70 to 120°C, more preferably 80 to 110°C, and still more preferably 85 to 100°C.

[0149] In addition, in the present embodiment, only one surface of the film F is heated using the heater 16, but both surfaces of the film F can also be heated.

[0150] Moreover, the heating method of the film F in the longitudinal stretching step is not limited to the method using the heater 16, and methods such as heating the film F by the above-mentioned stretching roll 14 or a heated roll other than the stretching roll 14 and blowing warm air onto the film F can be cited.

[0151] Examples of a method for heating each roller include a method of providing a heater inside the roller and a method of providing a pipe inside the roller and flowing a heated fluid into the pipe.

[0152] The uniaxially stretched polyester film used in the production method of the present invention is not limited to the polyester film produced by the above-mentioned longitudinal stretching step.

[0153] For example, in the above-mentioned longitudinal stretching process, the unstretched polyester film is longitudinally stretched by utilizing the difference between the conveying speed of a pair of stretching rollers 14 and the conveying speed of the cooling roller 22. However, instead of the cooling roller 22, one or more high-speed stretching rollers arranged between the stretching roller 14 and the cooling roller 22 and conveying the film F at a faster conveying speed than the stretching roller 14 can be used to longitudinally stretch the unstretched polyester film to produce a uniaxially stretched polyester film.

[0154] Furthermore, as described above, the apparatus used in the longitudinal stretching step may include two or more preheating rollers for preheating the unstretched polyester film before longitudinal stretching, and may include two or more low-speed stretching rollers for longitudinal stretching.

[0155] Furthermore, the preheating roller 12 and stretching roller 14 of the longitudinal stretching section 10 each have a structure in which the film F is conveyed by clamping it between two opposing rollers (a pair of rollers). However, the preheating roller and / or stretching roller used in the longitudinal stretching process may not have opposing rollers but may consist of only one roller in contact with one surface of the polyester film.

[0156] Cooling process

[0157] The cooling step included in the production method of this embodiment is a step of cooling the uniaxially stretched polyester film obtained in the longitudinal stretching step. More specifically, the uniaxially stretched polyester film is cooled by contacting the cooling roller 22 provided in the cooling unit 20.

[0158] In this embodiment, the cooling section 20 for performing the cooling process includes a cooling roller 22, an opposing roller 24 disposed opposite to the cooling roller 22, and three or more second cooling rollers 26. Figure 1 In the embodiment, the second cooling rollers 26 other than the second cooling roller 26 disposed on the most upstream side and the second cooling roller 26 disposed on the most downstream side are omitted.

[0159] (Cooling Roller)

[0160] The cooling roller 22 has a function of cooling the film F. As described above, the cooling roller 22 and the opposing roller 24 rotate while sandwiching the film F and conveying the film F at a predetermined conveying speed, thereby longitudinally stretching the unstretched polyester film.

[0161] Here, the arithmetic mean roughness Ra of the surface of the cooling roll 22 included in the cooling unit 20 is 0.05 μm or less. By using a roll with an arithmetic mean roughness Ra of the surface of 0.05 μm or less to cool the uniaxially stretched polyester film, the number of linear defects generated in the polyester film that shrinks in the width direction during the cooling process can be suppressed.

[0162] From the viewpoint of more excellent effects of the present invention, 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 further preferably 0.02 μm or less. There is no particular limitation on the lower limit of the arithmetic mean roughness Ra of the surface of the cooling roll 22. From the viewpoint of being able to more suppress the generation of interference defects (described later) in the polyester film, it is preferably 0.001 μm or more, more preferably 0.008 μm or more, and further preferably 0.01 μm or more.

[0163] Regarding the arithmetic mean roughness Ra of the surface of the cooling roll, when the cooling roll is a commercially available product and there is a catalog value, the catalog value is adopted. In the case where there is no catalog value, a test piece having the same structure as the cooling roll used is fabricated, and the surface of the obtained test piece is measured at a magnification of 3000 times using a laser microscope (manufactured by KEYENCE Corporation; VK-9510), and the obtained measured value is set as the arithmetic mean roughness Ra of the surface of the cooling roll.

[0164] From the viewpoint of more excellent effects of suppressing linear defects, the maximum peak height Rp of the surface of the cooling roll 22 is preferably 0.4 μm or less, more preferably 0.3 μm or less, and further preferably 0.2 μm or less. There is no particular limitation on the lower limit of the maximum peak height Rp of the surface of the cooling roll 22, and it is preferably 0.01 μm or more.

[0165] Moreover, from the viewpoint of more excellent effects of suppressing linear defects, the protrusion density on the surface of the cooling roll 22 is preferably 10000 pieces / mm2 or less, more preferably 8000 pieces / mm2 or less, and further preferably 6000 pieces / mm2 or less. There is no particular limitation on the lower limit of the protrusion density on the surface of the cooling roll 22, and it is preferably 1000 pieces / mm2 or more.

[0166] The maximum peak height Rp and the protrusion density of the surface of the cooling roll are obtained by the following method: A test piece having the same structure as the cooling roll used is fabricated, and the surface of the obtained test piece is measured under the following conditions using the following micro shape measuring device, and then particle analysis (multiple levels) is performed using the built-in analysis software.

[0167] The measuring machine and measuring conditions are shown below. In the above measurement, the slice levels were set at equal intervals of 10 nm, and the average diameter and density of each slice level were measured 5 times while changing the measurement position, and the average value was calculated and used as each measured value of the maximum peak height Rp and the protrusion density. The test piece was fixed to the specimen stage so that the X direction of the field of view measurement was the width direction of the polyester film.

[0168] · Measuring device: surf-corder ET-4000A manufactured by Kosaka Laboratory Ltd.

[0169] · Analysis software: i-Face model TDA31 Ver2.2.0.4JSIS

[0170] · Radius of the tip of the stylus: 0.5 μm

[0171] · Measuring field of view: X direction: 380 μm, pitch: 1 μm

[0172] Y direction: 280 μm, pitch: 5 μm

[0173] · Stylus pressure: 50 μN

[0174] · Measuring speed: 0.1 mm / s

[0175] · Cutoff value: Low region - 0.8 mm, High region - None

[0176] · Levelling: Entire area

[0177] · Filter: Gaussian filter (2D)

[0178] · Magnification: 100,000 times

[0179] · Particle analysis (multiple levels) conditions

[0180] · Output content setting: Mountain particles

[0181] · Hysteresis width: 5 nm

[0182] · Equal interval of slice levels: 10 nm

[0183] From the viewpoint of more excellent cooling performance of the uniaxially stretched polyester film, the surface temperature of the cooling roll is preferably 40 °C or lower, more preferably 35 °C or lower, and further preferably 30 °C or lower. There is no particular limitation on the lower limit of the surface temperature of the cooling roll, and it is preferably 15 °C or higher.

[0184] From the viewpoint of being able to more suppress the generation of interference defects (described later) in the polyester film, the contact angle of the surface of the cooling roll with respect to water is preferably 10° or more, more preferably 20° or more, and still more preferably 50° or more. There is no particular limitation on the upper limit of the contact angle of the surface of the cooling roll with respect to water, and it is preferably 120° or less.

[0185] Regarding the contact angle of the surface of the cooling roll with respect to water, when the cooling roll is a commercially available product and there is a catalog value, the catalog value is adopted. In the case where there is no catalog value, a test piece having the same structure as the cooling roll used is produced, 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 Interface Science Co., Ltd., DMo-901), and the obtained measurement value is taken as the contact angle of the surface of the cooling roll with respect to water.

[0186] There is no particular limitation on the material constituting the cooling roll. From the viewpoint of being able to easily manufacture a cooling roll in which the cooling efficiency, the arithmetic mean roughness Ra of the surface, the maximum peak height Rp, the protrusion density, and / or the contact angle are within the above ranges, it is preferable that the material constituting at least the surface layer of the cooling roll is metal, ceramic, or fluororesin. Examples of the metal and ceramic include tungsten carbide, hard chromium, and alumina, with tungsten carbide or hard chromium being preferred, and tungsten carbide being more preferred. As the fluororesin, polytetrafluoroethylene is preferred. As the material constituting the cooling roll, tungsten carbide or hard chromium is preferred, and tungsten carbide is more preferred.

[0187] A cooling roll having a surface layer made of the above material can be manufactured, for example, by a known method such as plating and thermal spraying to form a surface layer made of the above material on the outer peripheral surface of a known metal roll.

[0188] (Opposing roll)

[0189] The opposing roll is a component configured to oppose the cooling roll and having a structure that rotates according to the rotation of the cooling roll and applies pressure to the cooling roll.

[0190] From the viewpoint of being able to more suppress the generation of transfer defects (described later) in the polyester film, 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 still more preferably 1.2 μm or less. There is no particular limitation on the lower limit of the arithmetic mean roughness Ra of the surface of the opposing roll 24, and it is preferably 0.1 μm or more.

[0191] The arithmetic mean roughness Ra of the surface of the opposing roll 24 is measured by the following method.

[0192] Using a replica production kit (manufactured by Microset Products, 101THTHIXO), a replica material is injected onto the surface of the opposed roll 24 to imitate the surface shape. The surface of the obtained replica is measured using a laser microscope (manufactured by KEYENCE Corporation; VK-9510), and thereby the arithmetic mean roughness Ra of the surface of the opposed roll 24 is determined.

[0193] There is no particular limitation on the material constituting the opposed roll, and an elastomer is preferred. Examples of the elastomer include rubber and thermoplastic elastomer.

[0194] From the viewpoint of more excellent transfer, the hardness of the opposed roll is preferably 50 to 90 degrees, more preferably 60 to 80 degrees. In addition, the hardness of the opposed roll is the rubber hardness measured using a hardness meter such as a Type A Durometer according to the method described in JIS K6253-3.

[0195] (Cooling conditions)

[0196] As the conditions of the cooling process, the cooling rate of the polyester film passing through the cooling roll, that is, the value obtained by dividing the temperature drop of the polyester film from the time of contact with the cooling roll to the time of separation by the contact time of the polyester film with the cooling roll, is preferably 50°C / second or more, more preferably 120°C / second or more, further preferably 150°C / second or more, and particularly preferably 180°C / second or more. If the cooling rate is within the above range, the generation of interference defects in the polyester film can be more suppressed.

[0197] There is no particular limitation on the upper limit of the above cooling rate, and it is preferably 300°C / second or less.

[0198] The cooling rate of the polyester film passing through the cooling roll can be adjusted by the surface temperature of the cooling roll and the conveyance speed of the film passing through the cooling roll and the opposed roll.

[0199] Regarding the cooling rate of the polyester film passing through the cooling roll, it is determined based on 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 where it separates from the cooling roll (film temperature at separation) measured using a non-contact thermometer, the length of the contact surface of the polyester film with the cooling roll in the conveyance direction, and the conveyance speed of the polyester film passing through the cooling roll and the opposed roll.

[0200] In the cooling process, from the viewpoint that it is excellent when the temperature of the polyester film in contact with the cooling roll is 80°C, it is preferably 90°C or more, more preferably 95°C or more. There is no particular limitation on the upper limit, and it is preferably 120°C or less.

[0201] In the cooling process, from the viewpoint of being able to more effectively suppress the generation of interference defects in the polyester film, the temperature of the polyester film leaving the cooling roll is preferably 80°C or lower, more preferably 50°C or lower. The lower limit is not particularly limited, and is preferably 15°C or higher.

[0202] In the cooling process, from the viewpoint of being able to more effectively suppress the generation of interference defects in the polyester film, the temperature drop of the polyester film from the time of contact with the cooling roll to the time of leaving the cooling roll is preferably 10°C or higher, more preferably 30°C or higher, and further preferably 40°C or higher. The upper limit is not particularly limited, and is preferably 100°C or lower.

[0203] The temperature and temperature change of the polyester film in the cooling process can be measured by the above method using a non-contact thermometer.

[0204] Moreover, in the cooling process using the cooling unit 20, by passing the film F between the cooling roll 22 and the opposing roll 24, pressure is applied to the film F (the film F is pressed). While cooling the uniaxially stretched polyester film with the cooling roll 22, pressing is performed with the cooling roll 22 and the opposing roll 24, whereby the shrinkage amount of the obtained polyester film in the width direction can be reduced.

[0205] In the cooling process, the pressure applied to the polyester film by the cooling roll and the opposing roll is not particularly limited. From the viewpoint of being able to more effectively suppress the generation of linear defects in the obtained polyester film, the surface average value of the above pressure is preferably 0.8 MPa or higher, more preferably 1.1 MPa or higher, and further preferably 1.3 MPa or higher.

[0206] Moreover, from the viewpoint of being able to more effectively suppress the generation of transfer defects and transport wrinkles (described later) in the obtained polyester film, the upper limit of the surface average value of the above pressure is preferably 2.5 MPa or lower, more preferably 2.0 MPa or lower, and further preferably 1.7 MPa or lower.

[0207] In addition, regarding the surface average value of the pressure applied to the polyester film by the above cooling roll and the opposing roll, a pressure measurement film (manufactured by FUJIFILM Corporation, "PRESCALE (registered trademark)"; for ultra-low pressure (LLW)) is used for measurement. More specifically, instead of rotating the cooling roll and the opposing roll, the above pressure measurement film is clamped between the cooling roll and the opposing roll and pressed under the same conditions as in the cooling process. As a result, the region in the pressure measurement film that turns red is regarded as the region (pressing region) where pressure is applied by the cooling roll and the opposing roll.

[0208] Then, using a pressure measuring machine (manufactured by FUJIFILM Corporation; FPD-306), the color density of the colored area appearing in the pressure measuring film is converted into the corresponding pressure value, and the surface average value of the pressure in the pressing area is obtained from the obtained pressure value (total value of the pressure applied to the pressing area / total area of the pressing area).

[0209] Moreover, the difference between the maximum value and the minimum value of the pressure in the width direction in the pressing area of the polyester film (hereinafter, also referred to as "pressure difference in the width direction") is preferably 0.6 MPa or less, more preferably 0.4 MPa or less, and further preferably 0.2 MPa or less. By reducing the pressure difference in the width direction in the pressing area, it is possible to suppress the deviation of the polyester film in the width direction during conveyance, and further suppress the generation of linear defects in the obtained polyester film. The lower limit value is not particularly limited, and preferably 0.01 MPa or more.

[0210] The difference between the maximum value and the minimum value of the pressure in the width direction in the pressing area is obtained by the following method: performing the same method as the measurement method of the surface average value of the above pressure, obtaining the pressure value in the pressing area from the colored area appearing in the pressure measuring film, comparing the average value in the conveyance direction of the obtained pressure values in the width direction, and taking the difference between the maximum value and the minimum value in the width direction.

[0211] The width of the pressing area of the polyester film by the cooling roll and the opposing roll is not particularly limited. From the viewpoint of more excellent suppression of linear defects, the length in the conveyance direction of the pressing area (hereinafter, also referred to as "rolling width") is preferably 12 mm or more, more preferably 15 mm or more, and further preferably 18 mm or more. The upper limit value is not particularly limited, and preferably 30 mm or less.

[0212] The rolling width of the pressing area is obtained by the following method: performing the same method as the measurement method of the surface average value of the above pressure, and measuring the length in the conveyance direction of the colored area appearing in the pressure measuring film. Moreover, the rolling width of the pressing area can be adjusted by 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.

[0213] In the cooling step using the cooling unit 20, the film F is conveyed while applying pressure to the film F by the cooling roll 22 and the opposing roll 24. However, the device used in the cooling step is not particularly limited as long as it has a cooling roll with an arithmetic mean roughness Ra of the surface of 0.05 μm or less.

[0214] For example, the counter roll configured to face the cooling roll may not be provided, and the polyester film may be cooled and conveyed only by the cooling roll that contacts one surface of the polyester film. Further, the apparatus used in the cooling step may include two or more of the above-described cooling rolls.

[0215] (Secondary cooling treatment)

[0216] In the cooling step of 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 with the second cooling roll 26.

[0217] The second cooling roll 26 has a 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 equal to or lower than the surface temperature of the cooling roll 22, and is preferably 15 to 50°C.

[0218] In Figure 1 In the cooling unit 20 shown, three or more second cooling rolls are used, but the number of second cooling rolls may be one or two. Further, a secondary cooling treatment may be performed using an apparatus other than the cooling roll.

[0219] <Transverse stretching step>

[0220] The transverse stretching step is a step of stretching the uniaxially stretched polyester film in the width direction (hereinafter also referred to as "transverse stretching"). More specifically, it is a step of using a transverse stretching machine to stretch the uniaxially stretched polyester film in the width direction to form a biaxially stretched polyester film.

[0221] The transverse stretching unit 30 is an apparatus that stretches the film F in the width direction by applying tension to the film F in the width direction while heating it. As the transverse stretching unit 30, a known transverse stretching machine such as a tenter can be used.

[0222] The tenter is separated by a windbreak curtain and includes a plurality of zones capable of separately adjusting the temperature by hot air or the like. As a specific example of the tenter having these zones, a tenter that sequentially includes a preheating zone, a transverse stretching zone, a heat setting zone, a heat relaxation zone, and a cooling zone from the upstream side in the conveying direction can be cited.

[0223] In the transverse stretching step, it is preferable to preheat the polyester film before transverse stretching. By preheating the polyester film, the polyester film can be easily transversely stretched.

[0224] The preheating temperature is preferably (Tg - 10) to (Tg + 60)°C, more preferably (Tg) to (Tg + 50)°C. Specifically, the preheating temperature is preferably 80 to 120°C, more preferably 90 to 110°C.

[0225] The draw ratio in the transverse stretching process is preferably larger than that in the longitudinal stretching process described above. The draw ratio in the transverse stretching process is preferably 3.0 to 6.0 times, more preferably 3.5 to 5.0 times, and still more preferably 3.5 to 4.5 times.

[0226] The area ratio represented by the product of the draw ratio in the longitudinal stretching process and the draw ratio in the transverse stretching process is preferably 12.8 to 15.5 times, more preferably 13.5 to 15.2 times, and still more preferably 14.0 to 15.0 times. If the area ratio is above the lower limit value, the molecular orientation in the film width direction becomes good. Also, if the area ratio is below the upper limit value, it is easy to maintain the state where the molecular orientation is not easily relaxed during heat treatment.

[0227] The heating temperature in the transverse stretching process is preferably (Tg - 10) to (Tg + 80) °C, more preferably (Tg) to (Tg + 70) °C, and still 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 still more preferably 115 to 130 °C.

[0228] The stretching speed in the transverse stretching process is preferably 8 to 45% / second, more preferably 10 to 30% / second, and still more preferably 15 to 20% / second.

[0229] In the case of manufacturing a polyester film having a coating layer, it is preferable to apply a coating liquid for forming the coating layer on the polyester film stretched in the longitudinal direction, and then perform transverse stretching. The adhesion of the coating layer can be improved by the above method.

[0230] <Heat treatment process>

[0231] The manufacturing method of the present embodiment may also have a process of heat-treating the polyester film stretched in the width direction by the transverse stretching process (hereinafter, also referred to as "heat treatment process"). As the heat treatment process, for example, a heat setting process and a heat relaxation process can be cited. The heat treatment process preferably has at least one of the heat setting process and the heat relaxation process, and more preferably has both the heat setting process and the heat relaxation process.

[0232] The heat treatment process including the heat setting process and the heat relaxation process is implemented, for example, using a tenter frame including a heat setting region and a heat relaxation region, which is exemplified as the transverse stretching unit 30 in the above transverse stretching process.

[0233] - Heat setting process -

[0234] In the heat setting process, heat setting is performed by heating the polyester film stretched in the above width direction. Since the polyester can be crystallized by heat setting, shrinkage of the polyester film can be suppressed.

[0235] The heating temperature in the heat setting process is preferably 190 to 240 °C, more preferably 200 to 240 °C, and further preferably 210 to 230 °C.

[0236] In the heat setting process, the deviation of the maximum film surface temperature in the film width direction is preferably 0.5 to 10.0 °C, more preferably 0.5 to 7.0 °C, further preferably 0.5 to 5.0 °C, and particularly preferably 0.5 to 4.0 °C. By adjusting the deviation of the maximum film surface temperature in the film width direction within the above range, the deviation of the crystallinity in the width direction can be suppressed.

[0237] As the heating method, for example, a method of blowing hot air onto the film and a method of radiatively heating the film can be cited. As the device used in the radiative heating method, for example, an infrared heater can be cited.

[0238] The heating time in the heat setting process is preferably 5 to 50 seconds, more preferably 5 to 30 seconds, and further preferably 5 to 10 seconds.

[0239] -Heat relaxation process-

[0240] In the heat relaxation process, heat relaxation is performed by heating the biaxially stretched polyester film in the above width direction. The residual strain of the polyester film can be relaxed by heat relaxation.

[0241] The heating temperature in the heat relaxation process is preferably a temperature that is 5 °C or more lower than the heating temperature in the heat setting process, more preferably 15 °C or more lower, further preferably 25 °C or more lower, and particularly preferably 30 °C or more lower.

[0242] The lower limit of the heating temperature in the heat relaxation process is preferably 100 °C or more, more preferably 110 °C or more, and further preferably 120 °C or more.

[0243] As the heating method, for example, a method of blowing hot air onto the film and a method of radiatively heating the film can be cited. As the device used in the radiative heating method, for example, an infrared heater can be cited.

[0244] <Winding process>

[0245] In the manufacturing method of the present embodiment, there is a winding process of obtaining a roll-shaped biaxially stretched polyester film by winding the biaxially stretched polyester film that has undergone the above-described transverse stretching process with the winding unit 40.

[0246] By going through the above processes, a polyester film that more suppresses the generation of linear defects on the surface can be manufactured.

[0247] 〔Polyester film〕

[0248] The polyester film produced by the manufacturing method of this embodiment will be described.

[0249] <Physical properties>

[0250] (Orientation)

[0251] The polyester film produced by the manufacturing method of this embodiment is a biaxially oriented polyester film. In this specification, "biaxially oriented" means having molecular orientation properties in the biaxial direction.

[0252] The molecular orientation is measured using a microwave transmission type molecular orientation meter (for example, MOA-6004, manufactured by Oji Scientific Instruments). The angle formed in the biaxial direction is preferably 90° ± 5°, more preferably 90° ± 3°, and further preferably 90° ± 1°. The polyester film produced by the manufacturing method of this embodiment preferably has molecular orientation in the long side direction and the width direction.

[0253] (Composition)

[0254] The polyester film is a film containing polyester as the main polymer component. Here, "main polymer component" means the polymer with the highest content (mass) among all the polymers contained in the film.

[0255] (Linear defect)

[0256] In this specification, "linear defect" refers to a scratch formed on the surface of the polyester film, extending linearly along the conveying direction, with a length of 1 mm or more and a maximum depth of 500 nm or more. When cooling the longitudinally stretched polyester film, linear defects may be generated by shrinking the polyester film in the width direction. If linear defects are generated on the polyester film, for example, when the polyester film is used as a temporary support and a protective film for DFR, there is a possibility of causing exposure obstacles and other failures to meet the required performance.

[0257] By the manufacturing method of the present invention, the generation of linear defects in the obtained polyester film can be suppressed. The number of linear defects in the polyester film produced by the above manufacturing method is preferably 20 pieces / m 2 More preferably 5 pieces / m or less 2 Further preferably 3 pieces / m or less 2 Particularly preferably 1 piece / m or less 2 or less. The lower limit is not particularly limited, and preferably 0.01 piece / m 2 or more.

[0258] The number of linear defects on the surface of the polyester film is measured by the following method.

[0259] (1) In a dark room, while changing the viewing point, visually observe the reflected light of tungsten light caused by the polyester film and the transmitted light through the polyester film, and determine the position of the linear scratches present on the surface of the polyester film.

[0260] (2) Use a laser microscope (manufactured by KEYENCE Corporation; VK-9510) to measure the length and depth of the observed scratches at magnifications of 300 to 3000 times. According to the measurement results, consider scratches with a length of 1 mm or more and a maximum depth of 500 nm or more as linear defects.

[0261] (3) Measure the number of linear defects observed per 1 m 2 of the polyester film (number / m 2 ).

[0262] (Interference defects)

[0263] In this specification, "interference defects" refer to the rough appearance of the surface visually recognized by observing the reflected light on the surface of the polyester film. When manufacturing the polyester film, interference defects may occur when peeling the polyester film attached to the roller from the roller.

[0264] The number of interference defects in the polyester film is preferably 30 or less per 1 m 2 , more preferably 10 or less per 1 m 2 , and even more preferably 5 or less per 1 m 2 . The lower limit is not particularly limited, and preferably 0.01 or more per 1 m 2 .

[0265] The number of interference defects in the polyester film is measured by the following method.

[0266] In a dark room, place the polyester film on a flat surface and visually observe the reflected light of tungsten light caused by the polyester film while changing the viewing point. As a result of the visual observation, consider the area where the reflected light is uneven and a rough appearance such as wrinkles or twitches is observed on the surface of the polyester film as interference defects. Count the number of observed interference defects and calculate the number of interference defects per 1 m 2 of the polyester film (number / m 2 ).

[0267] (Transfer defects)

[0268] In this specification, "transfer defects" refer to pinholes formed in the coating layer provided on the surface of the polyester film. The above coating layer is preferably a coating layer formed on the polyester film by an in-line coating method in the above manufacturing method. For example, when conveying the polyester film with the coating layer by sandwiching it between a pair of rollers, transfer defects may occur when the pressure applied to the polyester film by the pair of rollers is too high or when the uneven shape of the surface of any one of the rollers is large.

[0269] The number of transfer defects in the polyester film is preferably 10 per m 2 More preferably, it is 3 per m hereinafter 2 Even more preferably, it is 1 per m hereinafter 2 Hereinafter. The lower limit is not particularly limited, and it is preferably 0.01 per m 2 Above.

[0270] The number of transfer defects in the polyester film is measured by the following method

[0271] (1) A coating liquid made of the following Formulation A is applied to the polyester film after longitudinal stretching using a slit-shaped nozzle to form a coating film. Otherwise, a laminated film composed of a polyester film and a coating layer with a thickness of 0.05 μm is manufactured according to the method described above

[0272] (2) Tungsten light is irradiated from the surface opposite to the surface of the coating layer of the manufactured laminated film, and the coating layer side of the laminated film is visually observed. As a result, the number of transfer defects of the coating layer where the pinholes visually recognized as light-transmitting are counted, and the number of transfer defects per 1 m of the polyester film is calculated 2 The number of transfer defects of the polyester film (per m 2 ).

[0273] - Formulation A: Coating liquid for forming a coating layer -

[0274] · Polyacrylic acid (AS - 563A, manufactured by DAICEL FTNECHEM LTD., solid content 27.5% by mass): 167 parts by mass

[0275] · Nonionic surfactant (NAROACTY (registered trademark) CL95, manufactured by SANYO CHEMICAL INDUSTRIES, LTD., solid content 100% by mass): 0.7 parts by mass

[0276] · Anionic surfactant (RAPISOL (registered trademark) A - 90, manufactured by NOF CORPORATION., diluted with water to make the solid content 1% by mass): 55.7 parts by mass

[0277] · Carnauba wax dispersion (Cellulose (registered trademark) 524, manufactured by CHUKYO YUSHI CO., LTD., solid content 30% by mass): 7 parts by mass

[0278] · Carbodiimide compound (CARBODILITE (registered trademark) V - 02 - L2, manufactured by Nisshinbo Chemical Inc., diluted with water to make the solid content 10% by mass): 20.9 parts by mass

[0279] Agglomerated silica (AEROSIL OX50, manufactured by Nippon Aerosil Co., Ltd., solid content 10% by mass, water-dispersible, average particle size 40 nm): 2.95 parts by mass

[0280] Water: 745.8 parts

[0281] (Haze)

[0282] The haze of the polyester film is preferably 3% or less, more preferably 1% or less, further preferably 0.5% or less, and particularly preferably 0.4% or less. A lower haze is preferred, so there is no lower limit for the haze. For convenience, the lower limit of the haze is set to 0% or greater. Setting the haze below the upper limit can reduce scattering of ultraviolet light from the polyester film, the support for the photoresist layer, when a photoresist layer is laminated on the polyester film and exposed to ultraviolet light. This can improve the state of the resist pattern wall, such as distortion and loss during resist patterning after development, and can also improve the transmittance of the polyester film.

[0283] The haze is measured using a haze meter (for example, NDH-2000, manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.) by a method in accordance with JIS K 7105.

[0284] (b * value)

[0285] L * a * b * b in the color system * The value is preferably 0 to 1, more preferably 0 to 0.8, further preferably 0 to 0.6, and particularly preferably 0 to 0.4. * a * b * b in the color system * A value of 0 to 1 can reduce the yellowness of the film, thereby making the hue of the film close to colorless. As a result, polyester films can be preferably used in applications requiring high visibility (for example, display devices).

[0286] For L * a * b * b in the color system * The values are measured by a transmission method using a spectrocolorimeter (for example, SE-2000, manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.).

[0287] (thickness)

[0288] From the viewpoint of processability (especially, processability during lamination of the film), the thickness of the polyester film is preferably 10 to 100 μm, more preferably 10 to 50 μm, and further preferably 12 to 40 μm. By setting the thickness of the polyester film to be not less than the above lower limit value, the strength can be improved and the operations in the processing steps can be easily performed. Also, by setting the thickness to be not more than the above upper limit value, an increase in the haze value can be suppressed. The thickness of the polyester film is set to the arithmetic average of the thicknesses at five positions measured by a scanning electron microscope (SEM: Scanning Electron Microscope).

[0289] (Dimensional change rate)

[0290] In the polyester film, if the dimensional change rate is within the following range, deformation and wrinkle generation due to thermal shrinkage in the DFR processing step can be suppressed, and thus it is preferred. The dimensional change rate can be appropriately adjusted by known methods such as relaxation and heat treatment conditions during film formation. The dimensional change rate at 150 °C is preferably less than 3% in the long side direction and less than 2.5% in the width direction, more preferably 0.5% or more and less than 2% in the long side direction and 1% or more and less than 2% in the width direction. Also, the dimensional change rate at 100 °C is preferably less than 1% in both the long side direction and the width direction, more preferably less than 0.8%. If the dimensional change rate is lower than the lower limit of the above range, poor planarity will occur due to relaxation when coating the photoresist layer, and if it exceeds the upper limit, zinc-plated iron-like shrinkage marks will occur due to shrinkage when coating the photoresist layer, resulting in poor planarity. In any case, spots will occur in the coating thickness of the photoresist layer.

[0291] (F-5 value)

[0292] In the polyester film, the strength (F-5 value) when stretched by 5% in the long side direction is preferably 0 MPa or more and less than 150 MPa. When the F-5 value in the long side direction is less than 70 MPa, the processability may sometimes deteriorate due to insufficient strength and the generation of scratches, etc. On the other hand, when the F-5 value in the long side direction is 150 MPa or more, it may sometimes be difficult to achieve compatibility with the F-5 value in the width direction. The F-5 value in the long side direction is more preferably 80 MPa or more and less than 140 MPa, and further preferably 90 MPa or more and less than 130 MPa.

[0293] The F-5 value in the width direction is preferably 80 MPa or more and less than 160 MPa. When the F-5 value in the width direction is less than 80 MPa, the processing characteristics may sometimes deteriorate due to scratches caused by insufficient strength. When it is 160 MPa or more, it may sometimes be difficult to achieve compatibility with the F-5 value in the long side direction. The F-5 value in the width direction is more preferably 90 MPa or more and less than 150 MPa, and further preferably 100 MPa or more and less than 140 MPa.

[0294] (Breaking strength)

[0295] In the polyester film, the breaking strength in the long side 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.

[0296] The F-5 value and the breaking strength of the polyester film can be achieved by appropriately adjusting the stretching temperature and stretching ratio in the longitudinal and transverse directions.

[0297] <Structure>

[0298] The polyester film may have a single-layer structure or a laminated structure. When the polyester film has a laminated structure, it preferably has a base material containing polyester and a coating layer containing particles on at least one surface of the above base material and having a plurality of protrusions on the surface. By having a coating layer on the polyester film, the winding quality can be improved.

[0299] (Coating layer)

[0300] There is no particular limitation on the coating layer when the polyester film has a laminated structure. The coating layer may or may not contain particles.

[0301] The coating layer preferably contains particles and has a plurality of protrusions on the surface.

[0302] Examples of the particles include organic particles and inorganic particles. Among the above, from the viewpoints of film winding quality, haze, and durability (e.g., thermal stability), the particles are preferably inorganic particles.

[0303] As the organic particles, resin particles are preferred. Examples of the resin particles include acrylic resin particles, polyester resin particles, silicone resin particles, and styrene-acrylic resin particles. The resin particles preferably have a crosslinked structure.

[0304] As inorganic particles, for example, silicon dioxide particles, titanium dioxide particles (titanium oxide particles), calcium carbonate, barium sulfate, and aluminum oxide particles can be cited. Among the above, from the viewpoints of haze and durability, silicon dioxide particles are preferred as the inorganic particles.

[0305] There is no particular limitation on the average particle diameter of the particles. From the viewpoints of improving the winding quality and suppressing transfer defects, it is preferably 0.01 to 0.4 μm, more preferably 0.04 to 0.2 μm.

[0306] The average particle diameter of the particles is obtained by arithmetically averaging the particle diameters of 50 particles arbitrarily selected from the images of a scanning electron microscope (SEM).

[0307] The coating layer may contain a single type of particle or two or more types of particles.

[0308] From the viewpoints of improving the winding quality of the film and suppressing transfer defects, the content of the particles is preferably 0.01 to 15% by mass, more preferably 0.1 to 10% by mass, and further preferably 0.5 to 6% by mass relative to the total mass of the coating layer.

[0309] When the polyester film has a coating layer, the content of the particles is preferably 0.0001 to 0.01% by mass, more preferably 0.0005 to 0.005% by mass relative to the total mass of the polyester film.

[0310] The coating layer preferably contains an adhesive. As the adhesive, a resin adhesive is preferred. As the resin adhesive, for example, polyacrylic acid, polyurethane, polyester, and polyolefin can be cited.

[0311] As for polyacrylic acid, as long as it is a polymer having a structural unit derived from at least one compound selected from acrylate and methacrylate, there is no limitation, and a known polyacrylic acid can be used. The polyacrylic acid may have a structural unit derived from a compound other than acrylate and methacrylate (for example, an olefin compound and a styrene compound).

[0312] As for polyurethane, as long as it is a polymer having a urethane bond, there is no limitation, and a known polyurethane can be used. Polyurethane is mostly manufactured by reacting an isocyanate compound with a polyol compound.

[0313] As for polyester, the polyester described in the item of "polyester" above can be applied, and the preferred types are also the same.

[0314] As for polyolefin, there is no limitation, and a known polyolefin can be used. As the polyolefin, for example, polyethylene and polypropylene can be cited.

[0315] The coating layer may contain a single type of binder or two or more types of binders.

[0316] From the viewpoints of the durability of the coating layer and / or the dispersibility of the particles, the content of the binder is preferably 30 to 80% by mass, more preferably 40 to 70% by mass, and still more preferably 45 to 65% by mass relative to the total mass of the coating layer.

[0317] Regarding the plurality of protrusions in the coating layer, the preferred modes also include the same protrusions as those described in the item of "protrusion density" above.

[0318] From the viewpoint of the manufacturability of the coating layer, the thickness of the coating layer is preferably 0.01 to 0.3 μm, more preferably 0.02 to 0.1 μm, and still more preferably 0.02 to 0.06 μm. The thickness of the coating layer is set as the arithmetic average of the thicknesses of five portions measured by a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0319] As a method for forming the coating layer, for example, a method using a coating liquid for forming the coating layer can be cited. For example, the coating layer can be formed by coating the coating liquid for forming the coating layer on a polyester film substrate and drying it as needed. Also, the coating layer can be formed simultaneously with the formation of the unstretched polyester film in the extrusion forming process by co-extrusion.

[0320] The coating liquid for forming the coating layer can be prepared by mixing the above-mentioned respective components and a solvent. As the solvent, for example, water, hexane, acetone, ethanol, tetrahydrofuran, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether can be cited. Among them, water is preferred from the viewpoints of the environment, safety, and economy.

[0321] The coating liquid for forming the coating layer may contain a single type of solvent or two or more types of solvents.

[0322] The content of the solvent is preferably 80 to 99% by mass, more preferably 90 to 98% by mass relative to the total mass of the coating liquid for forming the coating layer.

[0323] The coating method of the coating liquid for forming the coating layer is not limited, and known methods can be used. As the coating method, for example, spraying method, slit coating method, roll coating method, knife coating method, spin coating method, bar coating method, and dip coating method can be cited.

[0324] When forming the coating layer using the coating liquid for forming the coating layer, the substrate coated with the coating liquid for forming the coating layer can be an unstretched polyester film, a uniaxially stretched polyester film, or a biaxially stretched polyester film.

[0325] From the viewpoint of the adhesion between the base material and the coating layer, the method for forming the coating layer preferably involves applying a coating liquid for forming the coating layer onto a uniaxially stretched polyester film. For example, after forming the coating layer by applying the coating liquid for forming the coating layer onto the surface of the uniaxially stretched polyester film, the uniaxially stretched polyester film and the coating layer are stretched simultaneously, thereby improving the adhesion between the base material and the coating layer. The specific method of stretching is as described above.

[0326] <Usage>

[0327] The use of the polyester film produced by the manufacturing method of the present invention is not particularly limited. For example, it can be cited as a support and a protective film for a dry film photoresist, a release film for the manufacturing process of a multilayer ceramic capacitor (MLCC), and a film for a transparent conductive substrate.

[0328] Examples

[0329] Examples are given below to further illustrate the present invention in detail. The materials, amounts used, ratios, treatment contents, and treatment sequences shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0330] 〔Example 1〕

[0331] <Extrusion molding process>

[0332] As a polymerization catalyst, a titanium compound (citric acid chelated titanium complex, VERTEC AC-420, manufactured by Johnson Matthey) described in Japanese Patent No. 5575671 was used to produce poly(ethylene terephthalate) pellets. After drying the obtained pellets to a moisture content of 50 ppm or less, they were put into the hopper of a single-screw kneading extruder with a diameter of 30 mm, and then melted and extruded at 280°C. After passing the melt through a filter (pore size 3 μm), it was extruded from the die onto a cooling drum at 25°C, thereby obtaining an unstretched film. In addition, the extruded melt was brought into close contact with the cooling drum by the electrostatic application method.

[0333] <Longitudinal stretching process and cooling process>

[0334] For the above-mentioned unstretched film, the longitudinal stretching process was carried out by the following method.

[0335] After passing the unstretched film preheated by the preheating roller between a pair of stretching rollers (made of ceramics), it passes between a cooling roller C1 (product name "WC-12Co", manufactured by Praxair Surface Technologies) having a surface layer made of tungsten carbide on the outer peripheral surface of a metal roller and an opposing roller N1 (product name "90A70W", manufactured by KINYOSHA CO,., LTD., hardness 70 degrees), and is thus stretched in the longitudinal direction (transport direction) to produce a uniaxially stretched film. In addition, the longitudinal stretching process was carried out under the conditions of a preheating temperature of 75 °C, a stretching temperature of 90 °C, a stretching ratio of 3.4 times, and a stretching speed of 1300% / second. The transport speed of the unstretched film when passing through a pair of stretching rollers was 30 m / minute, and the transport speed of the uniaxially stretched film when passing between the cooling roller C1 and the opposing roller N1 was 100 m / minute.

[0336] And, as the cooling process, the above-mentioned uniaxially stretched film was cooled by contacting the cooling roller C1. And by passing the uniaxially stretched film between the cooling roller C1 and the opposing roller N1, pressure was applied to the uniaxially stretched film.

[0337] Regarding the surface of the cooling roller 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 / mm 2 , the contact angle with water is 68.1°, and the temperature is 25 °C.

[0338] The arithmetic mean roughness Ra of the surface of the opposing roller N1 is 1.1 μm.

[0339] The average value of the pressure applied to the uniaxially stretched film by the cooling roller C1 and the opposing roller N1 in the width direction is 1.3 MPa, and the difference between the maximum value and the minimum value of the pressure in the width direction is 0.08 MPa. The length of the pressing area formed by the pressing of the cooling roller C1 and the opposing roller N1 in the transport direction (hereinafter also referred to as "the rolling width of the pressing area.") is 20 mm.

[0340] And, the temperature of the uniaxially stretched film at the position where it contacts the cooling roller is 100 °C, and the temperature of the uniaxially stretched film at the position where it separates from the cooling roller is 50 °C. From these temperatures, the cooling rate of the uniaxially stretched film passing through the cooling roller is calculated to be 200 °C / second.

[0341] Hereinafter, the measurement methods of the above-mentioned various physical property values are described.

[0342] -Measurement of the arithmetic mean roughness Ra of the surface of the cooling roller-

[0343] Regarding the arithmetic mean roughness Ra of the surface of the cooling roll, when the cooling roll is a commercially available product and there is a catalog value, the catalog value is adopted. In the case where there is no catalog value, a test piece having the same structure as the cooling roll used is fabricated, and the arithmetic mean roughness Ra of the surface of the cooling roll is obtained by measuring it at a magnification of 3000 times using a laser microscope (manufactured by KEYENCE Corporation; VK-9510).

[0344] -Measurement of maximum peak height Rp and protrusion density-

[0345] The maximum peak height Rp and protrusion density of the surface of the cooling roll are determined by the following method: A test piece having the same structure as the cooling roll used is fabricated, and the surface of the obtained test piece is measured under the following conditions using the following micro shape measuring device, and then particle analysis (multiple levels) is performed using the built-in analysis software.

[0346] The measuring machine and measuring conditions are shown below. In the above measurement, the section levels are set at equal intervals of 10 nm, and the average diameter and density of each section level are measured 5 times while changing the measuring position, and these average values are calculated and used as the respective measured values of the maximum peak height Rp and protrusion density. Also, the test piece is fixed to the specimen stage so that the X direction of the field of view measurement becomes the width direction of the polyester film.

[0347] · Measuring device: surf-corder ET-4000A manufactured by Kosaka Laboratory Ltd.

[0348] · Analysis software: i-Face model TDA31 Ver2.2.0.4JSIS

[0349] · Stylus tip radius: 0.5 μm

[0350] · Measuring field of view: X direction: 380 μm, pitch: 1 μm

[0351] Y direction: 280 μm, pitch: 5 μm

[0352] · Needle pressure: 50 μN

[0353] · Measuring speed: 0.1 mm / s

[0354] · Cutoff value: Low region - 0.8 mm, High region - None

[0355] · Levelling: Entire area

[0356] · Filter: Gaussian filter (2D)

[0357] · Magnification: 100,000 times

[0358] · Particle analysis (multiple levels) conditions

[0359] · Output content setting: Mountain particles

[0360] · Hysteresis width: 5 nm

[0361] · Slice level equal interval: 10 nm

[0362] - Measurement of contact angle

[0363] Regarding the contact angle of the surface of the cooling roll with respect to water, when the cooling roll is a commercially available product and there is a catalog value, the catalog value is adopted. In the case where there is no catalog value, a test piece having the same structure as the cooling roll used is produced, 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 Interface Scienee Co., Ltd.; DMo-901), and this is taken as the contact angle of the surface of the cooling roll with respect to water.

[0364] - Measurement of the arithmetic mean roughness Ra of the surface of the opposed roll

[0365] A replica production kit (manufactured by Microset Products Company; 101THTHIXO) is used to inject a replica material onto the surface of the opposed roll to imitate the surface shape. Using a laser microscope (manufactured by KEYENCE Corporation; VK-9510), the surface of the obtained replica is measured at a magnification of 3000 times, and the arithmetic mean roughness Ra of the surface of the opposed roll is obtained.

[0366] - Pressing conditions

[0367] In the above cooling process, the pressure applied to the uniaxially stretched film by the above cooling roll and the opposed roll was measured using a pressure measurement film (manufactured by FUJIFILM Corporation, "PRESCALE (registered trademark)"; for ultra-low pressure (LLW)). Specifically, instead of rotating the cooling roll and the opposed roll, the pressure measurement film was clamped between the cooling roll and the opposed roll and pressed under the same conditions as the above cooling process. As a result, a red-colored region appeared on the pressure measurement film. The colored region in the pressure measurement film corresponds to the region where pressure is applied by the cooling roll and the opposed roll (i.e., the pressing region).

[0368] Next, the pressure measurement film was taken out, and using a pressure measuring machine (manufactured by FUJIFILM Corporation; FPD-306), the color density of the colored area appearing on the pressure measurement film was converted into the corresponding pressure value. The average value of the pressure in the width direction and the difference between the maximum and minimum values in the width direction of the pressure in the pressing area were obtained from the obtained pressure values.

[0369] Moreover, a ruler was used to measure the length of the colored area appearing on the pressure measurement film in the conveyance direction. This measurement was performed every 100 mm in the width direction, and the average value of the obtained measurement values was taken as the rolling width of the pressing area formed by pressing through the cooling roll C1 and the opposing roll N1.

[0370] -Measurement of film temperature-

[0371] Using a non-contact thermometer (AD-5616 (product name), manufactured by A&D Company, 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 where it separates from the cooling roll (film temperature at separation) were measured. In the measurement of each temperature, the temperature at the center of the width direction of the film was measured 5 times, and the average value of these was taken as the measured value of the film temperature at contact and the film temperature at separation.

[0372] Moreover, based on the length in the longitudinal direction of the contact surface between the uniaxially stretched film and the cooling roll and the rotation speed of the cooling roll, the contact time between the uniaxially stretched film and the cooling roll was obtained as the cooling time ta. The temperature difference Ta (°C) between the measured film temperature at contact and the film temperature at separation was divided by the cooling time ta (Ta / ta) to obtain the cooling rate (°C / second) of the uniaxially stretched film through the cooling process.

[0373] <Transverse stretching process>

[0374] The uniaxially stretched film that had undergone the above cooling process was transversely stretched using a tenter under the following conditions to obtain a biaxially stretched film.

[0375] -Conditions-

[0376] Preheating temperature: 100 °C

[0377] Stretching temperature: 120 °C

[0378] Stretching ratio: 4.2 times

[0379] Stretching speed: 50% / second

[0380] <Heat setting and heat relaxation processes>

[0381] The biaxially stretched film that had undergone the above-described transverse stretching process was heat-set under the following conditions. Further, after heat-setting, the width of the tenter was reduced and heat relaxation was performed under the following conditions, followed by cooling.

[0382] (Heat-setting conditions)

[0383] Heat-setting temperature: 227 °C

[0384] Heat-setting time: 6 seconds

[0385] (Heat-relaxation conditions)

[0386] Heat-relaxation temperature: 190 °C

[0387] Heat-relaxation rate: 4%

[0388] (Cooling conditions)

[0389] Cooling rate: 2500 °C / minute

[0390] <Winding process>

[0391] The both ends in the width direction of the film that had undergone the above heat-setting and heat-relaxation processes were trimmed. Then, after extrusion processing (knurling) of the both ends in the width direction of the film with a width of 10 mm, 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 roll length was 7000 m.

[0392] [Example 2]

[0393] 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 opposed roll N1 was adjusted to 1.0 MPa. Except for this, a biaxially stretched film was obtained by the same method as in Example 1.

[0394] The rolling width of the pressing area in the cooling process of Example 2 was 17 mm.

[0395] [Example 3]

[0396] In the cooling process, the opposed roll N2 (product name "90A80W", manufactured by KINYOSHA CO,., LTD.) was used instead of the opposed roll N1, and the pressure (average value in the width direction) applied to the uniaxially stretched film by the cooling roll C1 and the opposed roll N2 was adjusted to 2.1 MPa. Except for this, a biaxially oriented film was obtained by the same method as in Example 1.

[0397] The hardness of the opposed roll N2 was 80 degrees. And the rolling width of the pressing area in the cooling process of Example 3 was 1Tmmm.

[0398] 〔Example 4〕

[0399] In the cooling step, opposed roll N3 (product name: “90A70W”, manufactured by KINYOSHA CO,., LTD.) was used instead of opposed roll N1, and a biaxially oriented film was obtained in the same manner as in Example 1 except for this.

[0400] In the cooling step of Example 4, the difference between the maximum value and the minimum value in the width direction of the pressure applied to the uniaxially stretched film by cooling roll C1 and opposed roll N3 was 0.49 MPa, and the rolling width of the pressing area was 20 mm. In addition, it is considered that this pressure difference and rolling width were caused by the deformation of the roll mounting portion.

[0401] 〔Example 5〕

[0402] In the cooling step, opposed roll N4 (product name: “90A70W”, manufactured by KINYOSHA C0,., LTD.) was used instead of opposed roll N1, and a biaxially oriented film was obtained in the same manner as in Example 1 except for this.

[0403] In addition, opposed roll N4 aged over time, and thus the arithmetic mean roughness Ra of its surface was 1.8 μm.

[0404] 〔Example 6〕

[0405] In the cooling step, cooling roll C2 (manufactured by NOMURA PLATING CO., LTD.) having a hard chromium plating treatment layer on the outer peripheral surface of a metal roll was used instead of cooling roll C1, and a biaxially oriented film was obtained in the same manner as in Example 1 except for this.

[0406] The plating treatment layer of cooling roll C2 had a surface with an arithmetic mean roughness Ra of 0.008 μm, a maximum peak height Rp of 0.113 μm, a maximum protrusion density of 2284 pieces / mm 2 and a contact angle with water of 15.5°.

[0407] 〔Example 7〕

[0408] In the cooling step, the cooling rate was adjusted to 100 °C / second, and a biaxially oriented film was obtained in the same manner as in Example 1 except for this.

[0409] At this time, the temperature of the uniaxially stretched film at the position separated from cooling roll C1 was 75 °C.

[0410] 〔Comparative Example 1〕

[0411] In the cooling process, instead of the cooling roll C1, a cooling roll C3 (product name "LC-4", manufactured by Praxair Surface Technologies) having a surface layer made of chromium oxide on the outer peripheral surface of a metal roll was used. Except for this, a biaxially oriented film was obtained by the same method as in Example 1.

[0412] The surface layer of the cooling roll C3 has a surface arithmetic mean roughness Ra of 0.08 μm, a maximum peak height Rp of 0.323 μm, and a maximum protrusion density of 4549 pieces / mm 2 and a surface with a contact angle with water of 100.6°.

[0413] [Evaluation]

[0414] The following evaluations were performed on the biaxially oriented films of Examples 1 to 7 and Comparative Example 1. The evaluation results are shown in Table 1.

[0415] [Linear defects]

[0416] In a dark room, using tungsten light as the light source, while changing the viewing angle, the reflected light of the tungsten light caused by the biaxially oriented film and the transmitted light passing through the biaxially oriented film were visually observed, and the positions of the linear scratches existing on the surface of the biaxially oriented film were determined. Then, using a laser microscope (manufactured by KEYENCE Corporation; VK-9510), the length and depth of the observed scratches were measured 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 regarded as linear defects, and the number of linear defects per 1 m 2 of the biaxially oriented film (pieces / m2) was measured. And, an area of 1 m 2 in the biaxially oriented film was arbitrarily selected, and the maximum depth (unit: nm) of the longest linear defect in the selected area was measured.

[0417] [Interference defects]

[0418] In a dark room, the biaxially oriented film was placed on a plane, and while changing the viewing angle, the reflected light of the tungsten light caused by the biaxially oriented film was visually observed. As a result of the visual observation, an area with uneven reflected light and a rough appearance where the reflected light of the interference light source was observed on the surface of the biaxially oriented film was regarded as an interference defect. The observed interference defects were counted, and the number of interference defects per 1 m 2 of the biaxially oriented film (pieces / m 2 ) was calculated.

[0419] [Transfer defects]

[0420] The coating liquid prepared from the above-mentioned Formulation A was applied to the polyester film after longitudinal stretching by the above-mentioned longitudinal stretching process using a slit-shaped nozzle, thereby forming a coating layer with a thickness of 0.05 μm. In addition, a biaxially oriented film with a coating layer was manufactured according to the methods described in the above-mentioned Examples 1 to 7 and Comparative Example 1.

[0421] Tungsten light was irradiated from the surface on the side opposite to the surface of the biaxially oriented film (with the coating layer provided) where the coating layer was formed, and the presence or absence of pinholes (transfer defects) in the coating layer was visually observed. The number of the observed transfer defects was counted, and the number of transfer defects per 1 m 2 of the biaxially oriented film (pieces / m 2 ) was calculated.

[0422]

[0423] In the cooling process, the transfer state of the uniaxially stretched film on the cooling roll was observed and evaluated according to the following criteria. If the evaluation was A, it could be said that there was no practical problem. In addition, the "both end portions in the width direction" refers to the region from both ends in the width direction of the uniaxially stretched film to 30 mm. And the transfer wrinkles mostly have a shape extending in an inclined direction with respect to the transfer direction.

[0424] (Criteria)

[0425] A: No wrinkles were generated at both end portions in the width direction of the uniaxially stretched film on the cooling roll.

[0426] B: Wrinkles were generated at both end portions in the width direction of the uniaxially stretched film on the cooling roll.

[0427] Table 1 shows the cooling processes and the respective evaluation results carried out in each of the Examples and Comparative Examples.

[0428] In Table 1, the "surface material" column of the "cooling roll" shows the material constituting the surface of the cooling roll. "Material A" refers to tungsten carbide, "Material B" refers to hard chromium (coating layer), and "Material C" refers to ceramic (chromium oxide).

[0429]

[0430] It was confirmed from Table 1 that, compared with Comparative Example 1, Examples 1 to 7 in which the arithmetic mean roughness Ra of the surface of the cooling roll was 0.05 μm or less were able to suppress the generation of linear defects on the surface of the polyester film.

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

[0432] ​Moreover, it was confirmed that when the average surface pressure applied to the polyester film by the cooling roll and the opposing roll was 2.0 MPa or less, generation of transfer defects and transport wrinkles in the polyester film could be more suppressed (comparison between Example 1 and Example 3).

[0433] It was confirmed that when the difference between the maximum value and the minimum value in the width direction of the pressure in the region where the pressure was applied to the polyester film by the cooling roll and the opposing roll was 0.4 MPa or less, generation of linear defects on the surface of the polyester film could be more suppressed (comparison between Example 1 and Example 4).

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

[0435] It was confirmed that when the contact angle of the surface of the cooling roll with respect to water was 20° or more, generation of interference defects on the surface of the polyester film could be suppressed (comparison between Example 1 and Example 6).

[0436] It was confirmed that when the cooling rate of the polyester film passing through the cooling roll was 120°C / second or more, generation of interference defects on the surface of the polyester film could be suppressed (comparison between Example 1 and Example 7).

[0437] Symbol Explanation

[0438] 10 - Longitudinal stretching section, 12 - Preheating roll, 14 - Stretching roll, 16 - Heater, 20 - Cooling section, 22 - Cooling roll, 24 - Opposing roll, 26 - Second cooling roll, 30 - Transverse stretching section, 40 - Winding section, 100 - Manufacturing apparatus, F - Film.

Claims

1. A method for manufacturing a polyester film, which has a cooling step of cooling the uniaxially stretched polyester film by bringing it into contact with a cooling roll, wherein the arithmetic mean roughness Ra of the surface of the cooling roll is 0.05 μm or less, in the cooling step, pressure is applied to the polyester film by passing the polyester film between the cooling roll and an opposing roll arranged to oppose the cooling roll, and the arithmetic mean roughness Ra of the surface of the opposing roll is 1.5 μm or less.

2. The 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.

3. The manufacturing method according to claim 1 or 2, wherein, The density of protrusions on the surface of the cooling roller is 10,000 / mm 2 the following.

4. The manufacturing method according to claim 1 or 2, wherein, the cooling rate of the polyester film passing through the cooling roll in the cooling step is 150 °C / second or more.

5. The manufacturing method according to claim 1 or 2, wherein, the temperature of the polyester film in contact with the cooling roll in the cooling step is 90 °C or more.

6. The manufacturing method according to claim 1 or 2, wherein, the temperature of the polyester film leaving the cooling roll in the cooling step is 50 °C or less.

7. The manufacturing method according to claim 1 or 2, wherein, the temperature drop of the polyester film from the time of contact with the cooling roll to the time of leaving the cooling roll in the cooling step is 30 °C or more.

8. The manufacturing method according to claim 1 or 2, wherein, the surface temperature of the cooling roll is 35 °C or less.

9. The manufacturing method according to claim 1 or 2, wherein, the conveyance speed of the polyester film passing through the cooling roll is 50 m / minute to 150 m / minute.

10. The manufacturing method according to claim 1 or 2, which further has a longitudinal stretching step, in which the unstretched polyester film is stretched in the conveyance direction using the cooling roll and one or more stretching rolls arranged upstream of the cooling roll in the conveyance direction and slower than the conveyance speed of the cooling roll to form the uniaxially stretched polyester film, and the conveyance speed of the unstretched polyester film passing through the cooling roll is 10 m / minute to 50 m / minute.

11. The manufacturing method according to claim 1 or 2, wherein, the arithmetic mean roughness Ra of the surface of the cooling roll is 0.008 μm or more.

12. The manufacturing method according to claim 1 or 2, wherein, the contact angle of the surface of the cooling roll with respect to water is 10° or more.

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

14. The manufacturing method according to claim 1 or 2, wherein, the difference between the maximum value and the minimum value 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.

15. The manufacturing method according to claim 1 or 2, wherein, the surface average value of the pressure applied to the polyester film by the cooling roll and the opposing roll is 1.1 MPa or more.

16. The manufacturing method according to claim 1 or 2, wherein, The surface average value of the pressure applied to the polyester film by the cooling roll and the opposing roll is 1.7 MPa or less.

17. The manufacturing method according to claim 1 or 2, wherein: In the polyester film, a length in the conveyance direction of a region to which pressure is applied by the cooling roll and the counter roll is 15 mm or more.

18. A polyester film, wherein On the surface of the polyester film, per 1 m 2 In the polyester film, the number of linear defects with a depth of 500 nm or more and a length of 1 mm or more is 5 or less. The polyester film further comprises a coating layer provided on the surface of the polyester film. Per 1 m 2 In the polyester film, the number of transfer defects visually recognized as pinholes is 3 or less by irradiating light from the surface on the side opposite to the coating layer and visually observing the surface on the coating layer side.

19. The polyester film according to claim 18, wherein, Per 1 m 2 In the polyester film, the number of interference defects visually recognizable by observing the reflected light on the surface of the polyester film is 5 or less.

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