KR20220158813A - Manufacturing method of polyester film, polyester film - Google Patents

Abstract

The subject of this invention is providing the manufacturing method of the polyester film which can suppress formation of the linear defect in the surface of a polyester film more. Moreover, the subject of this invention is providing a polyester film.
The method for producing a polyester film of the present invention includes a cooling step in which the uniaxially stretched polyester film is brought into contact with a cooling roll to be cooled, and the arithmetic average roughness Ra of the surface of the cooling roll is 0.05 μm or less.

Description

Manufacturing method of polyester film, polyester film

This invention relates to the manufacturing method of a polyester film, and a polyester film.

Polyester films are used in a wide range of applications from the viewpoints of processability, mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance, etc., and are used, for example, as supports and protective films for dry film photoresists. A dry film photoresist has a structure formed by laminating a photosensitive resin layer (photoresist layer) on a support and then further laminating a protective film. Recently, in the touch panel field, dry film photoresists are used for etching in wiring formation processes, for forming protective films for protecting wiring parts such as copper, ITO (indium tin oxide) and silver nanoparticles, and for interlayer insulating films. It is used for purposes, etc.

In Patent Document 1, a longitudinal stretching step of stretching a film made of a belt-shaped thermoplastic resin in the transport direction, a cooling step of cooling the film with a cooling roller, and both sides of the film in the width direction between the longitudinal stretching step and the cooling step. A method for manufacturing a stretched film including a side edge portion removing step of removing an edge portion is disclosed.

Patent Document 1: Japanese Unexamined Patent Publication No. 2014-188748

On the other hand, in recent years, further refinement (thinning) of patterns formed by dry film photoresist (DFR) has been demanded, and high performance (thin film formation, low haze, etc.) ) is required.

As a result of examining the polyester film used as the temporary support and protective film of the present inventors, when producing the DFR that meets the above requirements, faint linear scratches (linear) existing on the surface of the polyester film defect) may lead to exposure failure.

This invention makes it a subject to provide the manufacturing method of the polyester film which can suppress formation of the linear defect in the surface of a polyester film more in view of the said situation.

Moreover, this invention also makes it a subject to provide a polyester film.

MEANS TO SOLVE THE PROBLEM The present inventors discovered that the said subject was solvable by the following structure, as a result of earnestly examining about the said subject.

〔One〕

A method for producing a polyester film comprising a cooling step of cooling the uniaxially stretched polyester film by bringing it into contact with a cooling roll, wherein the arithmetic average roughness Ra of the surface of the cooling roll is 0.05 µm or less.

〔2〕

The manufacturing method according to [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 [1] or [2], wherein the cooling roll has a density of projections on the surface of 10000/mm ² or less.

〔4〕

The manufacturing method according to any one of [1] to [3], wherein a cooling rate of the polyester film by the cooling roll in the cooling step is 150°C/sec or higher.

[5]

The manufacturing method according to any one of [1] to [4], wherein the temperature of the polyester film in contact with the cooling roll in the cooling step is 90°C or higher.

[6]

The manufacturing method according to any one of [1] to [5], wherein the temperature of the polyester film released from the cooling roll in the cooling step is 50°C or lower.

[7]

The manufacturing method according to any one of [1] to [6], wherein the temperature of the polyester film, which is lowered from contacting to the cooling roll to separation from the cooling roll in the cooling step, is 30°C or higher.

〔8〕

The manufacturing method according to any one of [1] to [7], wherein the cooling roll has a surface temperature of 35°C or less.

[9]

The manufacturing method according to any one of [1] to [8], wherein the conveyance speed of the polyester film by the cooling roll is 50 to 150 m/min.

[10]

The unstretched polyester film is stretched in the conveying direction using the cooling roll and one or more stretching rolls disposed upstream of the cooling roll in the conveying direction and having a conveying speed slower than the cooling roll, and the uniaxial stretching is performed. It further has a longitudinal stretching step of forming a stretched polyester film, and the conveyance speed of the unstretched polyester film by the stretching roll is 10 to 50 m / min, [1] The manufacturing method according to any one of [9] .

[11]

The manufacturing method according to any one of [1] to [10], wherein the arithmetic average roughness Ra of the surface of the cooling roll is 0.008 μm or more.

[12]

The manufacturing method according to any one of [1] to [11], wherein the surface of the cooling roll has a contact angle with respect to water of 10° or more.

[13]

The manufacturing method according to any one of [1] to [12], wherein the polyester film has a thickness of 40 µm or less.

[14]

In the cooling step, applying pressure to the polyester film by passing the polyester film between the cooling roll and an opposing roll disposed to face the cooling roll, [1] to [13] The manufacturing method described in any one of them.

[15]

The manufacturing method according to [14], wherein the difference between the maximum value and minimum value in the width direction of the pressure applied to the polyester film by the cooling roll and the counter roll is 0.4 MPa or less.

[16]

The manufacturing method according to [14] or [15], 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.

[17]

The manufacturing method according to any one of [14] to [16], 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.

[18]

The manufacturing method according to any one of [14] to [17], wherein, in the polyester film, a length in a conveyance direction of a region to which pressure is applied by the cooling roll and the counter roll is 15 mm or more.

[19]

The manufacturing method according to any one of [14] to [18], wherein the arithmetic average roughness Ra of the surface of the counter roll is 1.5 µm or less.

[20]

A polyester film, wherein the number of linear defects having a depth of 500 nm or more and a length of 1 mm or more on the surface of the polyester film is 5 or less per 1 m ² of the polyester film.

[21]

The polyester film according to [20], wherein the number of nonuniform defects visually recognized by visually observing reflected light on the surface of the polyester film is 5 or less per 1 m ² of the polyester film.

[22]

A coating layer provided on the surface of the polyester film is further provided, and the number of transfer defects recognized as pinholes by irradiating light from a surface opposite to the coating layer and visually observing the surface on the coating layer side A, the polyester film according to [20] or [21], which is 3 or less per 1 m ² of the polyester film.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the polyester film which can suppress formation of the linear defect in the surface of a polyester film more can be provided. Moreover, according to this invention, a polyester film can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram showing the structure of the manufacturing apparatus used for the manufacturing method of a polyester film.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail. In addition, this invention is not limited at all to the following embodiment, Within the scope of the objective of this invention, this invention can be implemented by adding a change suitably.

In the present disclosure, a numerical range expressed using “to” means a range including the numerical values described before and after “to” as the lower limit and the upper limit. In the numerical ranges stepwise described in this disclosure, the upper limit or lower limit of a predetermined numerical range may be replaced with the upper limit or lower limit of another stepwisely described numerical range. In addition, in the numerical range described in this disclosure, the upper limit value or lower limit value described in the predetermined numerical range may be replaced with the value shown in the examples.

In the present disclosure, the amount of each component in the composition means the total amount of a plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified.

In the present disclosure, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes if the desired purpose of the process is achieved.

In the present disclosure, “mass%” and “weight%” have the same meaning, and “mass parts” and “weight parts” have the same meaning.

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

In this indication, "longitudinal direction" means the long direction of the polyester film at the time of manufacture of a polyester film, and has the same meaning as "conveyance direction" and "machine direction". Moreover, "width direction" means the direction orthogonal to the longitudinal direction.

In this disclosure, the term "orthogonal" is not limited to strictly orthogonal, but includes approximately orthogonal. "Substantially orthogonal" means crossing at 90°±5°, preferably crossing at 90°±3°, and more preferably crossing at 90°±1°.

[Method for producing polyester film]

The method for producing a polyester film according to the present invention includes a cooling step of cooling the uniaxially stretched polyester film by bringing it into contact with a cooling roll. Moreover, the arithmetic average roughness Ra of the surface of the cooling roll used in this cooling process is 0.05 micrometer or less.

Hereinafter, the manufacturing method of the polyester film which concerns on this invention is demonstrated based on specific embodiment, but this invention is not limited to the following embodiment.

A method for producing a polyester film according to an example of an embodiment of the present invention (hereinafter, also referred to as "a production method of this embodiment") is a step of producing an unstretched polyester film from polyester as a raw material by an extrusion molding method. (hereinafter also referred to as “extrusion molding step”), a step of stretching the unstretched polyester film in the transport direction (hereinafter also referred to as a “longitudinal stretching step”), and a uniaxially stretched poly obtained by a longitudinal stretching step A step of cooling the ester film (hereinafter also referred to as a "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 a "transverse stretching step"). have

[Polyester raw material]

Hereinafter, polyester used as a raw material for the unstretched polyester film in the production method of the present embodiment will be described.

Polyester is a polymer having ester bonds in the main chain. Polyester is often formed by polycondensation of a dicarboxylic acid compound and a diol compound described later.

As polyester, it is not restrict|limited, A well-known polyester can be used. Examples of the polyester include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalate (PEN), and PET is preferable.

As for the intrinsic viscosity of polyester, 0.50 dl/g or more and less than 0.80 dl/g are preferable. More preferably, it is 0.55 dl/g or more and less than 0.70 dl/g.

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

The content of the polyester is preferably 85% by mass or more, more preferably 90% by mass or more, still more 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. do.

The upper limit of the content of the polyester is not limited, and can be appropriately set in the range of 100% by mass or less with respect to the total mass of the polymer in the polyester film.

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

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, relative to the total mass of polyester in the polyester film, 98-100 mass % is more preferable, and 100 mass % is especially preferable.

(Method for producing polyester)

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

-catalyst-

The catalyst used for producing polyester is not particularly limited, and known catalysts that can be used for synthesizing polyester can be used.

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 catalytic activity and cost.

As a titanium compound, an organic chelate titanium complex is preferable. An organic chelate titanium complex is a titanium compound having an organic acid as a ligand.

As an organic acid, citric acid, lactic acid, trimellitic acid, and malic acid are mentioned, for example.

As a titanium compound, the titanium compound of Paragraph 0049 of Paragraph 0049 - Paragraph 0053 of Unexamined-Japanese-Patent No. 5575671 can also be used, The description content of the said gazette is integrated in this specification.

-Dicarboxylic acid compound-

As a dicarboxylic acid compound, an aliphatic dicarboxylic acid compound, an alicyclic dicarboxylic acid compound, and an aromatic dicarboxylic acid compound are mentioned, for example, Aromatic dicarboxylic acid is preferable.

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

As an alicyclic dicarboxylic acid compound, adamantane dicarboxylic acid, norbornen dicarboxylic acid, cyclohexanedi carboxylic acid, and decalin dicarboxylic acid are mentioned, for example.

As an 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'-diphenyletherdicarboxylic acid, 5-sodium sulfoisophthalic acid, phenylindeindicarboxylic acid, anthracendicarboxylic acid, phenanthrendicarboxylic acid, and 9,9'-bis( 4-carboxyphenyl)fluorenic acid.

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

As for a dicarboxylic acid compound, only 1 type may be used, and 2 or more types may be used together. When terephthalic acid is used as the dicarboxylic acid compound, terephthalic acid alone may be used, or it may be copolymerized with other aromatic dicarboxylic acids or aliphatic dicarboxylic acids such as isophthalic acid.

-Diol compound-

As a diol compound, an aliphatic diol compound, an alicyclic diol compound, and an aromatic diol compound are mentioned, for example, An aliphatic diol compound is preferable.

Examples of the aliphatic diol compound include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, and 1,2-butanediol. , 1,3-butanediol, and neopentyl glycol, and ethylene glycol is preferable.

Examples of the alicyclic diol compound include cyclohexanedimethanol, spiroglycol, and isocarbide.

Examples of the aromatic diol compound include bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, and 9,9'-bis(4-hydroxyphenyl)fluorene.

As for a diol compound, only 1 type may be used and 2 or more types may be used together.

-end sealant-

In the manufacture of polyester, you may use terminal blocker as needed. By using the end capping agent, a structure derived from the end capping agent is introduced to the end of the polyester.

As the end capping agent, it is not limited, and a known end capping agent can be used. As an end capping agent, an oxazoline type compound, a carbodiimide compound, and an epoxy compound are mentioned, for example.

As terminal blocker, Paragraph 0055 of Unexamined-Japanese-Patent No. 2014-189002 - the content described in Paragraph 0064 can also be considered into consideration, and the content of the said gazette is integrated in this specification.

-Manufacturing conditions-

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

The pressure is not limited and may be appropriately set according to the raw material. The pressure is preferably 1.33 × 10 ^-3 to 1.33 × 10 ^-5 MPa, and more preferably 6.67 × 10 ^-4 to 6.67 × 10 ^-5 MPa.

As a method for synthesizing polyester, the method described in Paragraphs 0033 to 0070 of Japanese Patent Publication No. 5575671 can also be used, the contents of which are incorporated herein by reference.

[Manufacturing equipment]

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

1 is a schematic configuration diagram showing an example of a manufacturing apparatus used in the manufacturing method of the present embodiment.

The polyester film manufacturing apparatus 100 shown in FIG. 1 has a longitudinal stretch unit 10 that stretches an unstretched polyester film produced by an extrusion molding method in the conveying direction, and the longitudinal stretch unit 10 stretches it in the conveying direction. In the cooling unit 20 for rapidly cooling the uniaxially stretched polyester film, the horizontal stretching unit 30 for stretching the polyester film cooled in the cooling unit 20 in the width direction, and the horizontal stretching unit 30 A winding unit 40 for winding the stretched polyester film is provided.

The description of the detailed structure and function of each part described above is described together with the description of each manufacturing process included in the manufacturing method of the present embodiment described below.

Hereinafter, in the present specification, the notation "film (F)" and the simple notation "polyester film" refer to an unstretched polyester film, a uniaxially stretched polyester film, and a biaxially stretched polyester film. It is assumed that all films are included.

[Each manufacturing process]

Referring to the manufacturing apparatus 100 shown in FIG. 1, each process of the manufacturing method of this embodiment is demonstrated concretely.

<Extrusion molding process>

In the extrusion molding step, an unstretched polyester film is formed from polyester as a raw material by an extrusion molding method.

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

The unstretched polyester film is formed by, for example, using an extruder equipped with one or two or more screws, heating the above-mentioned polyester to a temperature equal to or higher than the melting point, and then rotating the screw to melt-knead it. . Polyester melts in an extruder by heating and kneading with a screw to become a molten body (melt).

A molten body is extruded from an extrusion die through a gear pump, a filter, and the like. The extrusion die is simply referred to as "die" (refer to JIS B8650:2006, (a) Extruder, No. 134). The melt may be extruded in a single layer or in multiple layers.

In melt extrusion, it is preferable to nitrogen-substitute the inside of an extruder from a viewpoint of suppressing thermal decomposition (for example, hydrolysis of polyester) in an extruder. Moreover, the extruder is preferably a twin-screw extruder from the point where the kneading temperature is suppressed low.

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

The temperature of the casting roll is preferably more than (Tg-10) ° C and less than (Tg + 30) ° C, more preferably (Tg-7) to (Tg + 20) ° C, (Tg-5) to (Tg + 10) °C is more preferred.

In addition, in this specification, "Tg" means the glass transition temperature of the polyester which comprises the polyester film manufactured by the manufacturing method of this embodiment.

In addition, in this specification, the temperature of the polyester film and each member in a manufacturing method can be measured using a non-contact type thermometer (eg, radiation thermometer).

When using a casting roll in the extrusion molding step, it is preferable to enhance the adhesion between the casting roll and the melt. Examples of methods for increasing adhesion include an electrostatic application method, an air knife method, an air chamber method, a vacuum nozzle method, and a touch roll method.

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

<Longitudinal stretching process>

The longitudinal stretching step is a step of stretching the unstretched polyester film in the transport direction (hereinafter, also referred to as "longitudinal stretching"). More specifically, it is a process of extending an unstretched polyester film in a conveyance direction using an apparatus provided with two or more stretching rolls having different conveyance speeds, and forming a uniaxially stretched polyester film.

The longitudinal stretching unit 10 is an example of a device including two or more stretching rolls having different conveying speeds, and includes a pair of preheating rolls 12, a pair of stretching rolls 14, and a heater 16. ) is provided.

In the longitudinal stretching unit 10, a pair of preheating rolls 12, a pair of stretching rolls 14, and a heater 16 are arranged in this order from the upstream side in the conveying direction.

The preheating roll 12 conveys the film F in the longitudinal direction and has a function of preheating the film F before longitudinal stretching.

In the longitudinal stretching step using the longitudinal stretching unit 10, the unstretched polyester film is preheated by the preheating roll 12 before the longitudinal stretching. By preheating the unstretched polyester film, the polyester film can be easily stretched vertically.

The manufacturing apparatus 100 shown in FIG. 1 includes only one pair of preheating rolls 12, but the number of preheating rolls disposed upstream of the stretching rolls 14 for longitudinal stretching is not particularly limited. Instead, the number according to the conveyance speed of the film F and/or the thickness of the film may be provided.

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

The conveyance speed of the film F by the preheating roll 12 is not particularly limited, but is preferably the same as the conveyance speed of the film F by the stretching roll 14 .

The stretching roll 14 has a function of conveying the film F in the longitudinal direction. Here, the conveyance speed of the film F by the stretching roll 14 is set slower than the conveyance speed of the film F by the cooling roll 22 mentioned later.

In the longitudinal stretching unit 10, the film F is conveyed while applying tension to the film F between the stretching roll 14 and the cooling roll 22 having a higher conveyance speed than the stretching roll, thereby unstretched polyester Longitudinal stretching of the film is performed.

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

In addition, 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 the stretching roll 14, but is preferably 40 to 160 m/min, and more preferably 50 to 150 m/min. , 60 to 140 m/min is more preferable.

What is necessary is just to set the draw ratio in a longitudinal stretching process suitably according to a use, but 2.0 to 5.0 times are preferable, 2.5 to 4.0 times are more preferable, and 2.8 to 4.0 times are more preferable.

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

In addition, the stretching roll 14 has a function of preheating the film F. The preferable range of the preheating temperature of the film F by the stretching roll 14 is the same as the preferable range of the preheating temperature of the preheating roll described above.

The preheating roll 12 and the stretching roll 14 are not particularly limited, and known rolls used for stretching plastic films can be used. The material constituting the surface layer including the surface of each roll is metal or ceramic. Alternatively, it is preferably a fluororesin, and more preferably a ceramic. As a metal, chromium is preferable. As the ceramic, chromium oxide or alumina oxide is preferable, and chromium oxide is more preferable. As the fluororesin, polytetrafluoroethylene is preferred.

The heater 16 has a function of heating the film F (unstretched polyester film) vertically stretched by the stretching roll 14 and the cooling roll 22 .

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, ( Tg) to (Tg+30)°C is more preferable. Specifically, the heating temperature in the longitudinal stretching step is preferably 70 to 120°C, more preferably 80 to 110°C, still more preferably 85 to 100°C.

In addition, although only one surface of the film F is heated using the heater 16 in this embodiment, you may heat both surfaces of the film F.

In addition, the method of heating the film F in the longitudinal stretching step is not limited to the method using the heater 16, and the film is heated by the stretching roll 14 or a heated roll other than the stretching roll 14 described above. Methods, such as the method of heating (F) and the method of applying warm air to the film (F), are mentioned.

As a method of heating each roll, a method of providing a heater inside the roll, and a method of providing a pipe inside the roll and flowing a heated fluid in the pipe, for example, are exemplified.

The uniaxially stretched polyester film used in the production method according to the present invention is not limited to the polyester film produced by the above longitudinal stretching step.

For example, in the above longitudinal stretching step, the unstretched polyester film is longitudinally stretched using the difference between the conveying speed of the pair of stretching rolls 14 and the conveying speed of the cooling roll 22, but the cooling roll ( 22) Instead, one or more high-speed stretching rolls disposed between the stretching rolls 14 and the cooling rolls 22 and transporting the film F at a faster conveyance speed than the stretching rolls 14 are used, and unstretched The stretched polyester film may be stretched vertically to produce a uniaxially stretched polyester film.

In addition, as described above, the apparatus used in the longitudinal stretching step may include two or more preheating rolls for preheating the unstretched polyester film before longitudinal stretching, or two or more low-speed stretching rolls used for longitudinal stretching. There may be.

In addition, the preheating roll 12 and the stretching roll 14 of the longitudinal stretching unit 10 have a configuration in which the film F is sandwiched and conveyed by two opposing rolls (a pair of rolls), respectively. However, the preheating roll and/or the stretching roll used in the longitudinal stretching step may be composed of only one roll in contact with one surface of the polyester film without having an opposing roll.

<Cooling process>

The cooling process included in the manufacturing method of the present embodiment is a process of cooling the uniaxially stretched polyester film obtained by the longitudinal stretching process. More specifically, the uniaxially stretched polyester film is cooled by bringing it into contact with the cooling roll 22 provided in the cooling unit 20 .

In this embodiment, the cooling unit 20 that performs the cooling process includes a cooling roll 22, an opposing roll 24 disposed to face the cooling roll 22, and three or more second cooling rolls 26 ) is provided. In addition, in FIG. 1, the 2nd cooling roll 26 other than the 2nd cooling roll 26 arrange|positioned most upstream side and the 2nd cooling roll 26 arrange|positioned most downstream side is abbreviate|omitted.

(cooling roll)

While the cooling roll 22 has a function of cooling the film F, as described above, the cooling roll 22 and the counter roll 24 rotate while sandwiching the film F, and the film By conveying (F) at a predetermined conveying speed, it has a function of longitudinally stretching the unstretched polyester film.

Here, the arithmetic mean roughness Ra of the surface of the cooling roll 22 provided in the cooling unit 20 is 0.05 μm or less. By cooling the uniaxially stretched polyester film using a roll having a surface arithmetic average roughness Ra of 0.05 μm or less, the number of linear defects occurring in the polyester film shrinking in the width direction in the cooling step can be suppressed.

The arithmetic average 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 still more preferably 0.02 μm or less, from the viewpoint of more excellent effects of the present invention. The lower limit of the arithmetic average roughness Ra of the surface of the cooling roll 22 is not particularly limited, but is preferably 0.001 µm or more, and is 0.008 from the viewpoint of being able to further suppress the occurrence of non-uniformity defects (described later) in the polyester film. μm or more is more preferable, and 0.01 μm or more is still more preferable.

Regarding the arithmetic average roughness Ra of the surface of the cooling roll, when the cooling roll is a commercial product and a catalog value exists, the catalog value is employed. If the catalog value does not exist, a test piece having the same structure as the cooling roll to be used is prepared, 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). , the obtained measured value is taken as the arithmetic mean roughness Ra of the surface of the cooling roll.

The maximum peak height Rp of the cooling roll 22 is preferably 0.4 μm or less, more preferably 0.3 μm or less, and even more preferably 0.2 μm or less, from the viewpoint of more excellent suppression of linear defects. The lower limit of the maximum peak height Rp of the surface of the cooling roll 22 is not particularly limited, but is preferably 0.01 μm or more.

In addition, since the cooling roll 22 is more excellent in suppression of linear defects, the protrusion density on the surface thereof is preferably 10000 pieces/mm ² or less, more preferably 8000 pieces/mm ² or less, and 6000 pieces/mm 2 or less. It is more preferable that it is 2 pieces/mm ² or less. The lower limit of the density of projections on the surface of the cooling roll 22 is not particularly limited, but is preferably 1000/mm ² or more.

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

A measuring instrument and measurement conditions are shown below. In the above measurement, the slice levels are set at equal intervals of 10 nm, the average diameter and density of each slice level are measured 5 times while changing the measurement position, and the average values are calculated to determine the maximum peak height Rp and protrusion density. as each measured value. The test piece is fixed to the sample stand so that the X direction of the visual field measurement is the width direction of the polyester film.

・Measurement device: surf-corder ET-4000A manufactured by Kosaka Genkyusho

・Analysis software: i-Face model TDA31 Ver2.2.0.4 JSIS

· Tip radius of the stylus: 0.5 μm

・Measuring field of view: X direction: 380 μm, pitch: 1 μm

Y direction: 280μm, Pitch: 5μm

·Pointer pressure: 50 μN

・Measurement speed: 0.1mm/s

・Cutoff value: low frequency - 0.8mm, high frequency - none

Leveling: Global

Filter: Gaussian filter (2D)

Magnification: 100,000 times

・Particle analysis (multiple levels) conditions

・Set output content: acid particle

·Hysteresis width: 5 nm

Slice level equal spacing: 10 nm

The surface temperature of the cooling roll is preferably 40°C or less, more preferably 35°C or less, and still more preferably 30°C or less, from the viewpoint of better cooling performance of the uniaxially stretched polyester film. The lower limit of the surface temperature of the cooling roll is not particularly limited, but is preferably 15°C or higher.

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 more preferably 50° or more, from the viewpoint of being able to further suppress the occurrence of non-uniformity defects (described later) in the polyester film. more preferable The upper limit of the contact angle of the surface of the cooling roll with respect to water is not particularly limited, but is preferably 120° or less.

Regarding the contact angle of the surface of the cooling roll with respect to water, when the cooling roll is a commercial product and a catalog value exists, the catalog value is employed. If there is no catalog value, a test piece having the same structure as the cooling roll used is prepared, and a contact angle meter (DMo-901, manufactured by Kyowa Gamemen Chemical Co., Ltd.) is used to measure the water on the surface of the obtained test piece. The static contact angle (°) for is measured by the droplet method, and the measured value obtained is taken as the contact angle of the surface of the cooling roll with respect to water.

The material constituting the cooling roll is not particularly limited, but it is possible to easily manufacture a cooling roll whose cooling efficiency, surface arithmetic mean roughness Ra, maximum peak height Rp, protrusion density and/or contact angle fall within the above ranges. Therefore, it is preferable that the material constituting the surface layer including at least the surface of the cooling roll is a metal, ceramic or fluororesin. Examples of metals and ceramics include tungsten carbide, hard chromium, and alumina oxide, preferably tungsten carbide or hard chromium, and more preferably tungsten carbide. As the fluororesin, polytetrafluoroethylene is preferred. As a material constituting the cooling roll, among these, tungsten carbide or hard chromium is preferable, and tungsten carbide is more preferable.

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

(opposite roll)

The opposing roll is a member that is arranged to face the cooling roll, rotates in accordance with the rotation of the cooling roll, and has a configuration in which pressure is applied to the cooling roll.

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, from the viewpoint of being able to more suppress the generation of transfer defects (described later) in the polyester film. , more preferably 1.2 μm or less. The lower limit of the arithmetic average roughness Ra of the surface of the counter roll 24 is not particularly limited, but is preferably 0.1 μm or more.

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

A replica material is injected onto the surface of the opposing roll 24 using a replica production kit (manufactured by Microset Products, 101THTHIXO) to bond the surface shape. By measuring the surface of the obtained replica using a laser microscope (manufactured by Keyence Corporation; VK-9510), the arithmetic average roughness Ra of the surface of the counter roll 24 is obtained.

The material constituting the opposing roll is not particularly limited, but an elastic material is preferable. Examples of the elastomer include rubber and thermoplastic elastomer.

The hardness of the opposing roll is preferably 50 to 90 degrees, more preferably 60 to 80 degrees, from the viewpoint of more excellent transfer. In addition, the hardness of the counter roll is a rubber hardness measured using a durometer such as a type A durometer in accordance with the method described in JIS K6253-3.

(cooling conditions)

As a condition of the cooling step, the cooling rate of the polyester film by the cooling roll, that is, the temperature of the polyester film lowered from the time the polyester film comes into contact with the cooling roll until it falls off, the contact between the polyester film and the cooling roll The value divided by time is preferably 50°C/sec or more, more preferably 120°C/sec or more, still more preferably 150°C/sec or more, and particularly preferably 180°C/sec or more. Generation|occurrence|production of the nonuniformity defect in a polyester film can be suppressed more as a cooling rate is in the said range.

Although the upper limit of the said cooling rate is not specifically limited, 300 degrees C/sec or less is preferable.

The cooling rate of the polyester film by the cooling roll can be adjusted by the surface temperature of the cooling roll, and the transport speed of the film by the cooling roll and the opposing roll.

The cooling rate of the polyester film by the cooling roll is the temperature of the polyester film at the position in contact with the cooling roll (film temperature in contact) and the temperature of the polyester film at the position away from the cooling roll, measured using a non-contact thermometer. It is obtained from the measured value of (film temperature during separation), the length of the contact surface of the polyester film and the cooling roll in the conveying direction, and the conveying speed of the polyester film by the cooling roll and the opposing roll.

In the cooling step, the temperature of the polyester film in contact with the cooling roll is preferably 90°C or higher, and more preferably 95°C or higher, since 80°C is more excellent. The upper limit is not particularly limited, but is preferably 120°C or lower.

In the cooling step, the temperature of the polyester film coming off the cooling roll is preferably 80°C or less, and more preferably 50°C or less, from the viewpoint of being able to further suppress occurrence of non-uniformity defects in the polyester film. The lower limit is not particularly limited, but is preferably 15°C or higher.

In the cooling step, the temperature of the polyester film, which is lowered from contact with the cooling roll to separation from the cooling roll, is 10 ° C. or higher from the viewpoint that occurrence of non-uniformity defects in the polyester film can be further suppressed. It is preferable, and it is more preferable that it is 30 degreeC or more, and it is more preferable that it is 40 degreeC or more. The upper limit is not particularly limited, but is preferably 100°C or less.

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

Moreover, in the cooling process using the cooling part 20, pressure is applied to the film F by passing the film F between the cooling roll 22 and the opposing roll 24 (the film F is pressed). By pressing the uniaxially stretched polyester film with the cooling roll 22 and the counter roll 24 while cooling it with the cooling roll 22, the amount of shrinkage in the width direction of the obtained polyester film can be reduced.

In the cooling step, the pressure applied to the polyester film by the cooling roll and the opposing roll is not particularly limited, but from the point of being able to further suppress the generation of linear defects in the resulting polyester film, the pressure The average value is preferably 0.8 MPa or more, more preferably 1.1 MPa or more, and still more preferably 1.3 MPa or more.

In addition, the upper limit of the surface average value of the pressure is preferably 2.5 MPa or less, and more preferably 2.0 MPa or less, from the viewpoint of being able to more suppress generation of transfer defects and conveyance wrinkles (described later) in the resulting polyester film. And, 1.7 MPa or less is more preferable.

In addition, the surface average value of the pressure applied to the polyester film by the cooling roll and the opposing roll is measured using a pressure measuring film (“Free Scale (registered trademark)” manufactured by Fujifilm Corporation; for ultra-low pressure (LLW)). It is measured. More specifically, the pressure measurement film is sandwiched between the cooling roll and the counter roll under the same conditions as in the cooling step, and pressed, without rotating the cooling roll and the counter roll. As a result, a red-colored region in the pressure measurement film is regarded as a region to which pressure is applied by the cooling roll and the opposing roll (pressure region).

Further, using a pressure measuring instrument (manufactured by Fujifilm Co., Ltd.; FPD-306), the color density of the color development region shown on the pressure measurement film is converted into a corresponding pressure value, and from the obtained pressure value, the pressure in the pressure region The surface mean value (the sum of the pressures applied to the pressure area/the total area of the pressure area) is obtained.

Further, the difference between the maximum value and minimum value of the pressure in the pressure region of the polyester film in the width direction (hereinafter, also referred to as “pressure difference in the width direction”) is preferably 0.6 MPa or less, and more preferably 0.4 MPa or less. And, 0.2 MPa or less is more preferable. By reducing the pressure difference in the width direction in the pressing area, the shift in the width direction of the polyester film during conveyance can be suppressed, and generation of linear defects in the polyester film obtained can be further suppressed. The lower limit is not particularly limited, but is preferably 0.01 MPa or more.

The difference between the maximum value and the minimum value of the pressure in the width direction in the pressure region is determined by performing the same method as the method for measuring the surface mean value of the pressure described above, based on the color development region displayed on the pressure measurement film, and determining the pressure value in the pressure region. It is calculated|required by comparing the average value of the conveyance direction of the calculated|required and obtained pressure value along the width direction, and taking the difference of the maximum value and minimum value in the width direction.

The width of the pressing region of the polyester film by the cooling roll and the counter roll is not particularly limited, but the length of the pressing region in the conveying direction (hereinafter also referred to as "nip width") is 12 mm or more in view of better suppression of linear defects. It is preferable, 15 mm or more is more preferable, and 18 mm or more is still more preferable. The upper limit is not particularly limited, but is preferably 30 mm or less.

The nip width of the pressure area is obtained by measuring the length in the conveying direction of the color development area appearing on the pressure measurement film by performing the same method as the method for measuring the surface average value of the pressure described above. In addition, the nip width of the pressing area can be adjusted according to the load applied between the cooling roll and the opposing roll, the hardness of the material constituting the opposing roll, and the outer diameters of the cooling roll and the opposing roll.

In the cooling process using the cooling unit 20, the film F is conveyed while applying pressure to the film F with the cooling roll 22 and the counter roll 24, but the device used for the cooling process is It is not particularly limited as long as it is provided with a cooling roll having an arithmetic mean roughness Ra of 0.05 μm or less.

For example, the polyester film may be cooled and conveyed only with a cooling roll that is in contact with one side of the polyester film, without providing an opposing roll arranged to face the cooling roll. Moreover, the apparatus used for a cooling process may be equipped with two or more of said cooling rolls.

(secondary cooling treatment)

In the cooling process using the cooling part 20, the secondary cooling process of further cooling with the 2nd cooling roll 26 is performed with respect to the film F cooled by the cooling roll 22.

The 2nd cooling roll 26 has a function to cool 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, but is preferably 15 to 50°C.

Although three or more 2nd cooling rolls are used in the cooling part 20 shown in FIG. 1, 1 or 2 may be sufficient as the number of 2nd cooling rolls. In addition, the secondary cooling treatment may be performed using a device other than the cooling roll.

<Horizontal stretching process>

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 forming a biaxially stretched polyester film by stretching the uniaxially stretched polyester film in the width direction using a transverse stretching machine.

The transverse stretching unit 30 is a device that stretches the film F in the width direction by applying tension to the film F in the width direction while heating. As the transverse stretching unit 30, a known transverse stretching machine such as a tenter is used.

The tenter is divided into wind-blocking curtains, and is provided with a large number of zones whose temperature can be individually adjusted by hot air or the like. As a specific example of a tenter provided with such a zone, a tenter provided with a preheating zone, a transverse drawing zone, a heat setting zone, a heat relaxation zone, and a cooling zone sequentially from the upstream side in the conveying direction is mentioned.

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.

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, and more preferably 90 to 110°C.

It is preferable that the draw ratio in the transverse stretch step is larger than the draw ratio in the longitudinal stretch step. The draw ratio in the transverse stretching step is preferably 3.0 to 6.0 times, more preferably 3.5 to 5.0 times, still more preferably 3.5 to 4.5 times.

The area magnification expressed as the product of the draw ratio in the longitudinal stretching step and the draw ratio in the transverse stretching step 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. When the area magnification is equal to or greater than the above lower limit, the molecular orientation in the film width direction becomes good. In addition, if the area magnification is equal to or less than the above upper limit, it is easy to maintain a state in which molecular orientation is difficult to relax when subjected to heat treatment.

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

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

In the case of producing a polyester film having a coating layer, it is preferable to apply a coating liquid for forming a coating layer on the polyester film stretched in the longitudinal direction and then transversely stretch it. By the above method, the adhesion of the coating layer can be improved.

<Heat treatment process>

The manufacturing method of the present embodiment may include a step of heat-treating the polyester film stretched in the width direction by the transverse stretching step (hereinafter, also referred to as a "heat treatment step"). As a heat treatment process, a heat setting process and a thermal relaxation process are mentioned, for example. The heat treatment step preferably includes at least one of a heat setting step and a thermal relaxation step, and more preferably includes both a heat setting step and a thermal relaxation step.

The heat treatment step including the heat setting step and the heat relaxation step is performed using a tenter including a heat setting zone and a heat relaxation zone, exemplified as the transverse stretching unit 30 in the transverse stretching step, for example do.

(Heat setting process)

In the heat setting step, heat setting is performed by heating the polyester film stretched in the width direction. Since polyester can be crystallized by heat setting, shrinkage of the polyester film can be suppressed.

The heating temperature in the heat setting step is preferably 190 to 240°C, more preferably 200 to 240°C, and still more preferably 210 to 230°C.

In the heat setting step, the unevenness 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, more preferably 0.5 to 5.0 ° C, 0.5-4.0 degreeC is especially preferable. By adjusting the unevenness of the highest attained film surface temperature in the film width direction within the above range, the unevenness in crystallinity in the width direction can be suppressed.

As a heating method, the method of applying hot air to a film, and the method of radiantly heating a film are mentioned, for example. As an apparatus used in the method of radiant heating, an infrared heater is mentioned, for example.

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

(thermal relaxation process)

In the thermal relaxation step, thermal relaxation is performed by heating the polyester film stretched in the width direction. Residual distortion of the polyester film can be alleviated by thermal relaxation.

The heating temperature in the heat-relaxing step is preferably 5°C or more lower than the heating temperature in the heat-setting step, more preferably 15°C or more lower, more preferably 25°C or more lower, and 30°C or more. Temperatures lower than °C are particularly preferred.

The lower limit of the heating temperature in the thermal relaxation step is preferably 100°C or higher, more preferably 110°C or higher, and still more preferably 120°C or higher.

As a heating method, the method of applying hot air to a film and the method of radiantly heating a film are mentioned, for example. As an apparatus used in the method of radiant heating, an infrared heater is mentioned, for example.

<Winding process>

In the manufacturing method of this embodiment, it has a winding-up process which obtains a roll-shaped biaxially stretched polyester film by winding up the biaxially stretched polyester film which performed the said transverse stretching process in the winding-up part 40.

By passing through the above process, the polyester film in which generation|occurence|production of the linear defect in the surface was more suppressed can be manufactured.

[Polyester Film]

The polyester film manufactured by the manufacturing method of this embodiment is demonstrated.

<Physical properties>

(orientation)

The polyester film manufactured by the manufacturing method of this embodiment is a biaxially oriented polyester film. In the present specification, "biaxial orientation" means a property having molecular orientation in a biaxial direction.

Molecular orientation is measured using a microwave transmission type molecular orientation meter (for example, MOA-6004, manufactured by Oji Keisoku Kiki Co., Ltd.). The angle formed by the biaxial directions is preferably 90°±5°, more preferably 90°±3°, and still more preferably 90°±1°. The polyester film produced by the production method of the present embodiment preferably has molecular orientation in the machine direction and width direction.

(Furtherance)

A polyester film is a film containing polyester as a main polymer component. Here, "main polymer component" means the polymer with the largest content (mass) among all the polymers contained in a film.

(shipboard defect)

In this specification, a "linear defect" is a flaw which extends linearly along the conveyance direction formed on the surface of a polyester film, and means the flaw whose length is 1 mm or more and the maximum value of depth is 500 nm or more. Linear defects may occur when the polyester film subjected to longitudinal stretching is cooled, when the polyester film shrinks in the width direction. When linear defects occur in the polyester film, for example, when the polyester film is used as a DFR temporary support and protective film, there is a possibility that the required performance is not satisfied, such as causing exposure problems.

According to the production method according to the present invention, generation of linear defects in the resulting polyester film can be suppressed. The number of linear defects in the polyester film produced by the above production method is preferably 20/m ² or less, more preferably 5/m ² or less, and still more preferably 3/m ² or less. , 1/m ² or less is particularly preferred. The lower limit is not particularly limited, but is preferably 0.01 pieces/m ² or more.

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

(1) In a dark room, the reflected light of the tungsten light by the polyester film and the transmitted light passing through the polyester film are visually observed while changing the viewpoint, and the position of the linear flaw present on the surface of the polyester film is identified. do.

(2) The length and depth of the observed flaw were measured using a laser microscope (manufactured by Keyence Corporation; VK-9510) at a magnification of 300 to 3000, and based on the measurement result, the length was 1 mm or more, and the depth A flaw having a maximum value of 500 nm or more is considered a linear defect.

(3) The number of observed linear defects per 1 m ² of the polyester film (piece/m ² ) is measured.

(non-uniform defect)

In this specification, a "nonuniform defect" refers to the rough appearance of the surface visually recognized by visually observing the reflected light on the surface of the polyester film. A nonuniformity defect may arise when peeling the polyester film affixed to the roll from a roll at the time of manufacture of a polyester film.

The number of nonuniform defects in the polyester film is preferably 30/m ² or less, more preferably 10/m ² or less, and even more preferably 5/m ² or less. The lower limit is not particularly limited, but is preferably 0.01 pieces/m ² or more.

The number of nonuniformity defects in the polyester film is measured by the following method.

In a dark room, the polyester film is placed on a flat surface, and the reflected light of the tungsten light by the polyester film is visually observed while changing the viewpoint. As a result of visual observation, a region in which reflected light is not uniform and a rough appearance such as wrinkles or pulling is observed on the surface of the polyester film is called a non-uniform defect. By counting the number of nonuniformity defects observed, the number of nonuniformity defects per 1 m ² of the polyester film (piece/m ² ) is calculated.

(transfer defect)

In this specification, "transfer defect" means a pinhole formed in the coating layer provided on the surface of the polyester film. It is preferable that the said coating layer is a coating layer formed on the polyester film by the in-line coating method in the said manufacturing method. The transfer defect is, for example, when the polyester film having a coating layer is sandwiched between a pair of rolls and conveyed, when the pressure applied to the polyester film by the pair of rolls is excessively high, or when one of the rolls It can occur when the uneven shape of the surface is large.

The number of transferred defects in the polyester film is preferably 10/m ² or less, more preferably 3/m ² or less, and still more preferably 1/m ² or less. The lower limit is not particularly limited, but is preferably 0.01 pieces/m ² or more.

The number of transfer defects in the polyester film is measured by the following method.

(1) A polyester film and a thickness of 0.05 0.05 in accordance with the method described above except that a coating liquid composed of the following formulation A is applied using a slit-shaped nozzle on the polyester film after longitudinal stretching to form a coating film. A laminated film composed of a coating layer of μm is prepared.

(2) A tungsten light is irradiated from the side opposite to the side on which the coating layer of the manufactured laminated film is formed, and the coating layer side of the laminated film is visually observed. As a result, the number of transfer defects in the coating layer visually recognized as pinholes through which light escapes is counted, and the number of transfer defects per 1 m ² of the polyester film (piece/m ² ) is calculated.

-Recipe A: Coating liquid for coating layer formation-

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

- Nonionic surfactant (Naroacty (registered trademark) CL95, manufactured by Sanyo Kasei Kogyo Co., Ltd., solid content 100% by mass): 0.7 parts by mass

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

-Carnauba wax dispersion (Cellosol (registered trademark) 524, manufactured by Chukyo Chemical Co., Ltd., solid content 30% by mass): 7 parts by mass

Carbodiimide compound (Carbodilite (registered trademark) V-02-L2, manufactured by Nisshinbo Chemical Co., Ltd., solid content 10% by mass diluted with water): 20.9 parts by mass

- Aggregated silica (Aerosil OX50, manufactured by Nippon Aerosil Co., Ltd., solid content 10% by mass, water dispersion, average particle diameter 40nm): 2.95 parts by mass

・Water: 745.8 parts

(Haze)

The haze of the polyester film is preferably 3% or less, more preferably 1% or less, still more preferably 0.5% or less, and particularly preferably 0.4% or less. Since the haze is so preferable that it is small, the lower limit of the haze is not limited. If the lower limit of haze is set for convenience, it is 0% or more. By setting the haze to the above upper limit or less, scattering of ultraviolet rays by the polyester film as a support for the resist layer during exposure by irradiation of ultraviolet rays after laminating the resist layer on the polyester film can be reduced, and the resist after development It is possible to improve the state of the wall surface of the resist pattern, such as distortion and drop-off, in patterning of the film, and also to improve the transmittance of the polyester film.

A haze is measured by a method according to JIS K 7105 using a haze meter (for example, NDH-2000, manufactured by Nippon Denshoku Kogyo Co., Ltd.).

(b ^* value)

The b ^* value in the L ^* a ^* b ^* color system is preferably 0 to 1, more preferably 0 to 0.8, still more preferably 0 to 0.6, and particularly preferably 0 to 0.4. When the b ^* value in the L ^* a ^* b ^* color system is 0 to 1, the yellowness of the film can be reduced, so the color of the film can be made close to colorless. As a result, for example, a polyester film can be suitably applied to applications requiring high visibility (for example, display devices).

The b ^* value in the L ^* a ^* b ^* color system is measured by a transmission method using a spectroscopic color difference meter (for example, SE-2000, manufactured by Nippon Denshoku Kogyo Co., Ltd.).

(thickness)

The thickness of the polyester film is preferably 10 μm to 100 μm, more preferably 10 μm to 50 μm, and even more preferably 12 μm to 40 μm, from the viewpoint of processability (particularly processability when laminating the film). By making the thickness of a polyester film more than the said lower limit, strength can be improved and handling in a processing process can be made easy. Moreover, the raise of a haze value can be suppressed by carrying out thickness below the said upper limit. The thickness of the polyester film is taken as the arithmetic average value of the thicknesses of 5 locations measured by a scanning electron microscope (SEM).

(Dimension change rate)

In a polyester film, since generation|occurrence|production of distortion and wrinkles by heat shrinkage in a DFR processing process can be suppressed when the rate of dimensional change is within the following range, it is preferable. The rate of dimensional change can be achieved by appropriately adjusting conditions such as relaxation and heat treatment in the film forming conditions by a known method. The rate of dimensional change at 150°C is preferably less than 3% in the longitudinal direction and less than 2.5% in the width direction, more preferably 0.5% or more and less than 2% in the longitudinal direction, and more preferably 1% or more and less than 2% in the width direction. Moreover, as for the dimensional change rate at 100 degreeC, less than 1% is preferable in both the longitudinal direction and the width direction, and it is more preferable in it being less than 0.8%. If the rate of dimensional change is less than the lower limit of the above range, flatness defects due to sagging occur when the resist layer is applied, and if it exceeds the upper limit, shrinkage unevenness occurs in a wavy shape due to shrinkage when the resist layer is applied, resulting in poor flatness. It becomes a defect, and in any case, non-uniformity may occur in the coating thickness of the resist layer.

(F-5 value)

It is preferable that the strength (F-5 value) of the polyester film when stretched by 5% in the longitudinal direction is 0 MPa or more and less than 150 MPa. When the F-5 value in the longitudinal direction is less than 70 MPa, processing characteristics may be deteriorated due to scratches and the like due to lack of strength. On the other hand, if the F-5 value in the longitudinal direction is 150 MPa or more, compatibility with the F-5 value in the width direction may become difficult. The F-5 value in the longitudinal direction is more preferably 80 MPa or more and less than 140 MPa, and still more preferably 90 MPa or more and less than 130 MPa.

It is preferable that the F-5 value of the width direction is 80 MPa or more and less than 160 MPa. If the F-5 value in the width direction is less than 80 MPa, processing characteristics may deteriorate due to scratches due to insufficient strength, and if it is 160 MPa or more, compatibility with the F-5 value in the longitudinal direction may be difficult. The F-5 value in the width direction is more preferably 90 MPa or more and less than 150 MPa, and still more preferably 100 MPa or more and less than 140 MPa.

(breaking strength)

In the polyester film, the breaking strength in the longitudinal direction is preferably 200 MPa or more and less than 360 MPa, and more preferably 220 MPa or more and less than 340 MPa. The breaking strength in the width direction is preferably 260 MPa or more and less than 420 MPa, and more preferably 280 MPa or more and less than 400 MPa.

The F-5 value and breaking strength of the polyester film can be achieved by appropriately adjusting the stretching temperature and stretching ratio in the machine direction and the transverse direction.

<structure>

The polyester film may have a single layer structure or may have a laminated structure. When the polyester film has a laminated structure, it is preferable to have a base material containing polyester and a coating layer containing particles and having a plurality of projections on the surface on at least one surface of the base material. When a polyester film has a coating layer, winding quality can be improved.

(coating layer)

The coating layer in case the polyester film has a laminated structure is not particularly limited. The coating layer may or may not contain particles.

It is preferable that the coating layer contains particles and has a plurality of protrusions on the surface.

Examples of the particles include organic particles and inorganic particles. Among the above, inorganic particles are preferable for the particles from the viewpoints of film winding quality, haze, and durability (for example, thermal stability).

As organic particles, resin particles are preferable. Examples of the resin particles include acrylic resin particles, polyester resin particles, silicone resin particles, and styrene-acrylic resin particles. It is preferable that the resin particle has a crosslinked structure.

Examples of the inorganic particles include silica particles (silicon dioxide particles), titania particles (titanium oxide particles), calcium carbonate, barium sulfate, and alumina particles (aluminum oxide particles). Among the above, inorganic particles are preferably silica particles from the viewpoints of haze and durability.

The average particle size of the particles is not particularly limited, but is preferably 0.01 to 0.4 μm, more preferably 0.04 to 0.2 μm, from the viewpoint of improving winding quality and suppressing transfer defects.

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

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

The content of the particles is preferably 0.01 to 15% by mass, more preferably 0.1 to 10% by mass, and 0.5 to 6% by mass, based on the total mass of the coating layer, from the viewpoint of improving the winding quality of the film and suppressing transfer defects. Mass % is more preferred.

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

The coating layer preferably contains a binder. As the binder, a resin binder is preferable. Examples of the resin binder include polyacrylic, polyurethane, polyester and polyolefin.

The polyacryl is not limited as long as it is a polymer having structural units derived from at least one compound selected from the group consisting of acrylic acid esters and methacrylic acid esters, and known polyacrylic materials can be used. Polyacrylic acid may have structural units derived from compounds other than acrylic acid ester and methacrylic acid ester (for example, an olefin compound and a styrene compound).

The polyurethane is not particularly limited as long as it is a polymer having a urethane bond, and a known polyurethane can be used. In many cases, polyurethane is produced by reacting an isocyanate compound with a polyol compound.

As the polyester, the polyester described in the above section of "Polyester" can be applied, and the preferred types are also the same.

The polyolefin is not particularly limited, and known polyolefins can be used. As polyolefin, polyethylene and polypropylene are mentioned, for example.

The coating layer may contain a single binder or may contain two or more binders.

The content of the binder is preferably 30 to 80% by mass, more preferably 40 to 70% by mass, and 45 to 65% by mass with respect to the total mass of the coating layer, from the viewpoint of durability of the coating layer and/or dispersibility of particles. more preferable

The plurality of protrusions in the coating layer are the same as the protrusions described in the section of "density of protrusions", including preferred embodiments.

The thickness of the coating layer is preferably from 0.01 to 0.3 µm, more preferably from 0.02 to 0.1 µm, and still more preferably from 0.02 to 0.06 µm, from the viewpoint of manufacturing aptitude of the coating layer. The thickness of the coating layer is taken as the arithmetic average value of the thicknesses of 5 locations measured by a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

As a method of forming the coating layer, a method using a coating liquid for forming the coating layer is exemplified. For example, a coating layer can be formed by applying a coating liquid for forming a coating layer on a polyester film substrate and drying it as needed. Moreover, you may form a coating layer simultaneously with formation of the unstretched polyester film in the extrusion formation process by the co-extrusion method.

The coating liquid for forming a coating layer can be prepared by mixing each of the above components and a solvent. Examples of the solvent include water, hexane, acetone, ethanol, tetrahydrofuran, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, and propylene glycol. Monoethyl ether is mentioned. Among them, water is preferred from the viewpoints of environment, safety and economy.

The coating liquid for coating layer formation may contain the solvent of single 1 type, and may contain 2 or more types of solvents.

80-99 mass % is preferable with respect to the total mass of the coating liquid for coating layer formation, and, as for content of a solvent, 90-98 mass % is more preferable.

The method of applying the coating liquid for forming the coating layer is not limited, and a known method can be used. Examples of the coating method include a spray coating method, a slit coating method, a roll coating method, a blade coating method, a spin coating method, a bar coating method, and a dip coating method.

When the coating layer is formed using the coating liquid for forming the coating layer, the substrate to which the coating liquid for forming the coating layer is applied may be an unstretched polyester film, a uniaxially stretched polyester film, or a biaxially stretched polyester film. .

The method for forming the coating layer is preferably a method of applying a coating liquid for forming a coating layer on a uniaxially stretched polyester film from the viewpoint of adhesion between the base material and the coating layer. For example, after forming a coating layer by applying a coating liquid for forming a coating layer to the surface of a uniaxially stretched polyester film, the adhesion between the substrate and the coating layer can be improved by simultaneously stretching the uniaxially stretched polyester film and the coating layer. . The specific method of stretching is as described above.

<Use>

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

Example

The present disclosure will be described in more detail by way of examples below. Materials, amount of use, ratio, processing content, and processing procedure shown in the following examples can be appropriately changed without departing from the spirit of the present disclosure. Accordingly, the scope of the present disclosure is not limited to the specific examples shown below. In addition, "part" and "%" are based on mass unless there is particular notice.

[Example 1]

<Extrusion molding process>

Pellets of polyethylene terephthalate were prepared using a titanium compound (citric acid chelate titanium complex, VERTEC AC-420, manufactured by Johnson Matthey) as a polymerization catalyst described in Japanese Patent Publication No. 5575671. After drying the obtained pellets until the moisture content was 50 ppm or less, they were fed into a hopper of a single screw kneading extruder having a diameter of 30 mm, and then melted and extruded at 280°C. After passing the molten body (melt) through a filter (hole diameter: 3 µm), an unstretched film was obtained by extruding from a die to a cooling drum at 25°C. Further, the extruded molten body (melt) was brought into close contact with the cooling drum by an electrostatic application method.

<Longitudinal stretching process and cooling process>

About the said unstretched film, the longitudinal stretching process was implemented by the following method.

After passing the unstretched film preheated by the preheating roll between a pair of stretching rolls (ceramic), a cooling roll C1 having a surface layer made of tungsten carbide on the outer peripheral surface of the metal roll (product name "WC-12Co", It was stretched in the machine direction (conveyance direction) by passing it between a counter roll N1 (product name "90A70W", manufactured by Kinyosha, hardness: 70 degrees) and a counter roll N1 (manufactured by Praxair Kogaku Co., Ltd.) to prepare a uniaxially stretched film. In addition, the longitudinal stretching step was performed under the conditions of a preheating temperature of 75°C, a stretching temperature of 90°C, a draw ratio of 3.4 times, and a stretching speed of 1300%/sec. The conveyance speed of the unstretched film when passing through a pair of stretching rolls was 30 m/min, and the conveyance speed of the uniaxially stretched film when passing between the cooling roll C1 and the counter roll N1 was 100 m/min. .

Moreover, as a cooling process, it cooled by making said uniaxially stretched film contact with cooling roll C1. Moreover, pressure was applied to the uniaxially stretched film by passing the uniaxially stretched film between the cooling roll C1 and the counter roll N1.

For the surface of the cooling roll C1, the arithmetic average roughness Ra was 0.02 μm, the maximum peak height Rp was 0.187 μm, the asperity density was 3647/mm ² , the contact angle to water was 68.1°, and the temperature was 25° C. .

The arithmetic mean roughness Ra of the surface of the counter roll N1 was 1.1 µm.

The average value in the width direction of the pressure applied to the uniaxially stretched film by the cooling roll C1 and the counter roll N1 was 1.3 MPa, and the difference between the maximum value and minimum value of the pressure in the width direction was 0.08 MPa. The length of the conveying direction of the pressing area formed by the pressing of the cooling roll C1 and the counter roll N1 (hereinafter also referred to as “nip width of the pressing area”) was 20 mm.

Moreover, the temperature of the uniaxially stretched film at a position in contact with the cooling roll was 100°C, and the temperature of the uniaxially stretched film at a position separated from the cooling roll was 50°C. From these temperatures, the cooling rate of the uniaxially stretched film by the cooling roll was calculated to be 200°C/sec.

Hereinafter, methods for measuring each of the above physical property values are described.

-Measurement of the arithmetic mean roughness Ra of the surface of the cooling roll-

Regarding the arithmetic mean roughness Ra of the surface of the cooling roll, when the cooling roll was a commercial product and a catalog value existed, the catalog value was employed. If the catalog value does not exist, a test piece having the same structure as the cooling roll used is prepared, 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). , the arithmetic mean roughness Ra of the surface of the cooling roll was obtained.

-Measurement of maximum mountain height Rp and asperity density-

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

A measuring instrument and measurement conditions are shown below. In the above measurement, the slice levels are set at equal intervals of 10 nm, the average diameter and density of each slice level are measured 5 times while changing the measurement position, and the average values are calculated to determine the maximum peak height Rp and protrusion density. It was set as each measured value. In addition, the test piece was fixed to the sample stand so that the X direction of the visual field measurement was the width direction of the polyester film.

・Measurement device: surf-corder ET-4000A manufactured by Kosaka Genkyusho

・Analysis software: i-Face model TDA31 Ver2.2.0.4 JSIS

· Tip radius of the stylus: 0.5 μm

・Measuring field of view: X direction: 380 μm, pitch: 1 μm

Y direction: 280μm, Pitch: 5μm

·Pointer pressure: 50 μN

・Measurement speed: 0.1mm/s

・Cutoff value: low frequency - 0.8mm, high frequency - none

Leveling: Global

Filter: Gaussian filter (2D)

Magnification: 100,000 times

・Particle analysis (multiple levels) conditions

・Set output content: acid particle

·Hysteresis width: 5 nm

Slice level equal spacing: 10 nm

-Measurement of contact angle-

Regarding the contact angle of the surface of the cooling roll with respect to water, when the cooling roll was a commercial product and a catalog value existed, the catalog value was employed. If there is no catalog value, a test piece having the same structure as the cooling roll to be used is prepared, and a contact angle meter (DMo-901, manufactured by Kyowa Gamemen Chemical Co., Ltd.) is used to measure the water on the surface of the obtained test piece. The static contact angle (°) was measured by the droplet method, and was taken as the contact angle of the surface of the cooling roll with water.

-Measurement of the arithmetic average roughness Ra of the surface of the opposing roll-

Using a replica production kit (manufactured by Microset Products, 101THTHIXO), a replica material was injected onto the surface of the opposing roll to bond the surface shape. The surface of the obtained replica was measured at a magnification of 3000 times using a laser microscope (manufactured by Keyence Corporation; VK-9510), and the arithmetic mean roughness Ra of the surface of the counter roll was obtained.

-Pressure conditions-

In the cooling step, the pressure applied to the uniaxially stretched film by the cooling roll and the opposing roll is measured using a pressure measuring film ("Free Scale (registered trademark)" manufactured by Fujifilm Corporation; for ultra-low pressure (LLW)) Measured. Specifically, the pressure measurement film was sandwiched between the cooling roll and the counter roll and pressed under the same conditions as in the cooling step, without rotating the cooling roll and the counter roll. As a result, a region colored in red appeared on the pressure measurement film. The color development area in the pressure measurement film corresponds to the area to which pressure is applied by the cooling roll and the counter roll (ie, the pressing area).

Next, the pressure measurement film was taken out, and the color density of the color development region shown on the pressure measurement film was converted into a corresponding pressure value using a pressure measuring instrument (FPD-306 manufactured by Fujifilm Corporation). From the obtained pressure values, the average value of the pressure in the pressure area in the width direction and the difference between the maximum value and minimum value in the width direction were determined.

In addition, the length of the conveying direction of the color development region appearing on the pressure measurement film was measured using a ruler. This measurement was performed every 100 mm in the width direction, and the average value of the obtained measured values was made into the nip width of the pressing area|region formed by the pressing of the cooling roll C1 and the counter roll N1.

-Measurement of film temperature-

Using a non-contact thermometer (AD-5616 (product name), manufactured by A&D, emissivity 0.95), the temperature of the uniaxially stretched film at the position in contact with the cooling roll (film temperature at contact) and the uniaxially stretched film at the position away from the cooling roll The temperature of the film (film temperature during separation) was measured. In the measurement of each temperature, the temperature of the central part in the width direction of the film was measured 5 times, and the average value thereof was used as the measured value of the film temperature during contact and the film temperature during separation.

Further, the time during which the uniaxially stretched film is in contact with the cooling roll was determined as the cooling time ta from the longitudinal length of the contact surface of the uniaxially stretched film in contact with the cooling roll and the rotational speed of the cooling roll. 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./sec) of the uniaxially stretched film by the cooling process.

<Horizontal stretching process>

About the uniaxially stretched film which performed the said cooling process, it transversely stretched on condition of the following using a tenter, and obtained the biaxially stretched film.

-Condition-

Preheating temperature: 100℃

Stretching temperature: 120°C

Stretching ratio: 4.2 times

Stretching speed: 50%/sec

<Heat setting and heat relaxation process>

The biaxially stretched film subjected to the transverse stretching step was heat-set under the following conditions. Further, after heat-setting, the tenter width was reduced, heat-relaxed under the following conditions, and then cooled.

(heat setting condition)

Heat setting temperature: 227℃

Heat setting time: 6 seconds

(thermal relaxation condition)

Thermal relaxation temperature: 190 ℃

Thermal relaxation rate: 4%

(cooling conditions)

Cooling rate: 2500°C/min

<Winding process>

Both ends in the width direction of the film subjected to the heat setting and thermal relaxation steps are trimmed, and then extrusion processing (knurling) is performed on both ends in the film width direction to a width of 10 mm, and then the stretched film is stretched at a tension of 40 kg/m. wound up By the above method, a biaxially oriented film having a thickness of 30 μm was obtained. The obtained biaxially oriented film had a width of 1.5 m and a winding length of 7000 m.

[Example 2]

In the cooling step, the biaxially oriented film was prepared in the same manner as in Example 1, except that the pressure (average value in the width direction) applied to the uniaxially oriented film by the cooling roll C1 and the counter roll N1 was adjusted to 1.0 MPa. got it

The nip width of the pressing area|region in the cooling process of Example 2 was 17 mm.

[Example 3]

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

The hardness of the opposing roll N2 was 80 degrees. Moreover, the nip width of the pressing area|region in the cooling process of Example 3 was 17 mm.

[Example 4]

In the cooling step, a biaxially oriented film was obtained in the same manner as in Example 1, except that counter roll N3 (product name "90A70W", manufactured by Kinyo) was used instead of counter roll N1.

In the cooling step of Example 4, the difference between the maximum value and minimum value in the width direction of the pressure applied to the uniaxially stretched film by the cooling roll C1 and the counter roll N3 was 0.49 MPa, and the nip width of the pressing region was 20 mm. In addition, it is considered that this pressure difference and nip width are caused by distortion of the roll fixing part.

[Example 5]

In the cooling step, a biaxially oriented film was obtained in the same manner as in Example 1, except that counter roll N4 (product name "90A70W", manufactured by Kinyo Co., Ltd.) was used instead of counter roll N1.

In addition, since counter roll N4 deteriorated with age, the arithmetic average roughness Ra of the surface was 1.8 micrometers.

[Example 6]

In the cooling step, a biaxially oriented film was prepared in the same manner as in Example 1, except that a cooling roll C2 (manufactured by Nomura Mekki Co., Ltd.) having a hard chromium plating layer on the outer circumferential surface of the metal roll was used instead of the cooling roll C1. got it

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

[Example 7]

In the cooling step, a biaxially oriented film was obtained in the same manner as in Example 1, except that the cooling rate was adjusted to 100°C/sec.

The temperature of the uniaxially stretched film at the position separated from the cooling roll C1 at this time was 75°C.

[Comparative Example 1]

In the cooling step, instead of cooling roll C1, the cooling roll C3 (product name "LC-4", manufactured by Praxair Kogaku Co., Ltd.) having a surface layer made of chromium oxide on the outer circumferential surface of the metal roll was used, but the same as in Example 1. A biaxially oriented film was obtained by the method.

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

[evaluation]

The following evaluation was performed about each biaxially oriented film of Examples 1-7 and Comparative Example 1. Table 1 shows the evaluation results.

[shipboard defect]

In a dark room, using tungsten light as a light source, observe the reflected light by the biaxially oriented film of the tungsten light and the transmitted light passing through the biaxially oriented film with the naked eye while changing the viewpoint, and present on the surface of the biaxially oriented film The position of the flaw on the line to be specified was specified. Next, the length and depth of the scratches observed were measured at a magnification of 300 to 3000 using a laser microscope (manufactured by Keyence Corporation; VK-9510). Based on the measurement results, a flaw having a length of 1 mm or more and a maximum depth of 500 nm or more was referred to as a linear defect, and the number of linear defects per 1 m ² of the biaxially oriented film (piece/m ² ) was measured. Further, a region having 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 region was measured.

[Non-uniformity defect]

In a dark room, the biaxially oriented film was placed on a flat surface, and the reflected light of the tungsten light by the biaxially oriented film was visually observed while changing the viewpoint. As a result of visual observation, the reflected light was not uniform, and the area where the surface of the biaxially oriented film had a rough appearance that disturbed the reflected light of the light source was observed as a non-uniform defect. The observed nonuniform defects were counted, and the number of nonuniform defects per 1 m ² of the biaxially oriented film (piece/m ² ) was calculated.

[transcription defect]

Examples 1 to 7 above, except that a coating layer having a thickness of 0.05 μm was formed by applying a coating liquid composed of the above formulation A using a slit-shaped nozzle on the polyester film after longitudinal stretching in the above longitudinal stretching step. And according to the method described in Comparative Example 1, a biaxially oriented film having a coating layer was produced.

A biaxially oriented film provided with a coating layer was irradiated with tungsten light from the side opposite to the side on which the coating layer was formed, and the presence or absence of pinholes (transfer defects) in the coating layer was visually observed. The number of observed transfer defects was counted, and the number of transferred defects per 1 m ² of the biaxially oriented film (pcs/m ² ) was calculated.

[Conveyance wrinkles]

In the cooling process, the conveyance state of the uniaxially stretched film on the cooling roll was observed and evaluated according to the following criteria. If the evaluation is A, it can be said that there is no problem in practical use. In addition, "the width direction both ends" means the area|region from both ends of the uniaxially stretched film in the width direction to 30 mm. Moreover, conveyance wrinkles often have a shape extending obliquely with respect to the conveyance direction.

(standard)

A: Wrinkles do not occur at both ends in the width direction of the uniaxially stretched film on the cooling roll.

B: Wrinkles are generated at both ends in the width direction of the uniaxially stretched film on the cooling roll.

In Table 1, the cooling process and each evaluation result performed in each Example and Comparative Example are respectively shown.

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

[Table 1]

[Table 2]

From Table 1, it was confirmed that Examples 1 to 7 in which the arithmetic average roughness Ra of the surface of the cooling roll was 0.05 μm or less could suppress the generation of linear defects on the surface of the polyester film compared to Comparative Example 1. .

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 occurrence of linear defects on the surface of the polyester film could be more suppressed (Example 1 and Example 1). comparison of Example 2).

In addition, 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 2.0 MPa or less, the occurrence of transfer defects and conveyance wrinkles in the polyester film could be more suppressed (Examples 1 and Example 3).

When the difference between the maximum value and the minimum value of the pressure in the width direction in the area where the pressure is applied by the cooling roll and the counter roll in the polyester film is 0.4 MPa or less, generation of linear defects on the surface of the polyester film is prevented. It was confirmed that it could be suppressed more (comparison of Example 1 and Example 4).

When the arithmetic mean roughness Ra of the surface of the opposing roll was 1.5 µm or less, it was confirmed that occurrence of transfer defects on the surface of the polyester film could be suppressed (comparison between Example 1 and Example 5).

When the contact angle of the cooling roll surface to water was 20° or more, it was confirmed that occurrence of non-uniformity defects on the surface of the polyester film could be suppressed (comparison between Example 1 and Example 6).

When the cooling rate of the polyester film by the cooling roll was 120 ° C./sec or higher, it was confirmed that occurrence of non-uniformity defects on the surface of the polyester film could be suppressed (comparison between Example 1 and Example 7).

10 vertical stretch section
12 preheat roll
14 stretch rolls
16 heater
20 cooling section
22 cooling rolls
24 facing rolls
26 second cooling roll
30 transverse stretching unit
40 winding part
100 manufacturing units
F film

Claims (22)

A cooling step of bringing the uniaxially stretched polyester film into contact with a cooling roll to cool it,
The manufacturing method of the polyester film whose arithmetic mean roughness Ra of the surface of the said cooling roll is 0.05 micrometer or less. The method of claim 1,
The manufacturing method in which the maximum peak height Rp of the surface of the cooling roll is 0.3 μm or less. According to claim 1 or claim 2,
The manufacturing method in which the density of protrusions on the surface of the cooling roll is 10000 pieces/mm ² or less. The method according to any one of claims 1 to 3,
The manufacturing method in which the cooling rate of the said polyester film by the said cooling roll in the said cooling process is 150 degrees C/sec or more. The method according to any one of claims 1 to 4,
The manufacturing method in which the temperature of the said polyester film which contacts the said cooling roll in the said cooling process is 90 degreeC or more. The method according to any one of claims 1 to 5,
The manufacturing method in which the temperature of the polyester film released from the cooling roll in the cooling step is 50°C or lower. The method according to any one of claims 1 to 6,
The manufacturing method in which the temperature of the said polyester film which fell from contacting to the said cooling roll in the said cooling process until it separated from the said cooling roll is 30 degreeC or more. According to any one of claims 1 to 7,
The manufacturing method in which the surface temperature of the said cooling roll is 35 degrees C or less. The method according to any one of claims 1 to 8,
The manufacturing method in which the conveyance speed of the said polyester film by the said cooling roll is 50-150 m/min. The method according to any one of claims 1 to 9,
The unstretched polyester film is stretched in the conveying direction using the cooling roll and one or more stretching rolls disposed upstream of the cooling roll in the conveying direction and having a conveying speed slower than the cooling roll, and the uniaxial stretching is performed. It further has a longitudinal stretching process of forming a polyester film,
The manufacturing method in which the conveyance speed of the said unstretched polyester film by the said stretching roll is 10-50 m/min. The method according to any one of claims 1 to 10,
The manufacturing method in which the arithmetic average roughness Ra of the surface of the said cooling roll is 0.008 micrometer or more. According to any one of claims 1 to 11,
The manufacturing method according to claim 1 , wherein a contact angle of the surface of the cooling roll with respect to water is 10° or more. According to any one of claims 1 to 12,
The manufacturing method in which the thickness of the said polyester film is 40 micrometers or less. The method according to any one of claims 1 to 13,
In the cooling step, pressure is applied to the polyester film by passing the polyester film between the cooling roll and an opposing roll disposed to face the cooling roll. The method of claim 14,
The manufacturing method in which the difference between the maximum value and minimum value in the width direction of the pressure applied to the polyester film by the cooling roll and the counter roll is 0.4 MPa or less. According to claim 14 or claim 15,
The manufacturing method in which 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. The method according to any one of claims 14 to 16,
The manufacturing method in which 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. The method according to any one of claims 14 to 17,
The manufacturing method of the said polyester film WHEREIN: The length of the conveyance direction of the area|region to which the pressure is applied by the said cooling roll and the said counter roll is 15 mm or more. The method according to any one of claims 14 to 18,
The manufacturing method in which the arithmetic average roughness Ra of the surface of the counter roll is 1.5 μm or less. A polyester film, wherein the number of linear defects having a depth of 500 nm or more and a length of 1 mm or more on the surface of the polyester film is 5 or less per 1 m ² of the polyester film. The method of claim 20
The polyester film in which the number of nonuniform defects visually recognized by visually observing reflected light on the surface of the polyester film is 5 or less per 1 m ² of the polyester film. According to claim 20 or claim 21,
Further having a coating layer provided on the surface of the polyester film,
The number of transfer defects recognized as pinholes by irradiating light from a surface opposite to the coating layer and visually observing the surface on the coating layer side is 3 or less per 1 m ² of the polyester film. Polyester film.

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