WO2022019113A1

WO2022019113A1 - Polyester film, release film, and method for producing polyester film

Info

Publication number: WO2022019113A1
Application number: PCT/JP2021/025608
Authority: WO
Inventors: 一仁宮宅; 悠樹豊嶋; 泰雄江夏; 佑記福岡
Original assignee: 富士フイルム株式会社
Priority date: 2020-07-20
Filing date: 2021-07-07
Publication date: 2022-01-27
Also published as: CN116137835A; JPWO2022019113A1; KR20230028408A

Abstract

The present invention addresses the problem of providing a polyester film for release film production, that exhibits excellent transportability and excellent release layer coatability and that can suppress the formation of transfer marks in the release layer surface. The present invention also addresses the problem of providing a release film and a method for producing a polyester film. A polyester film according to the present invention is a polyester film for release film production that is provided with a substantially particle-free polyester base material and a particle-containing coating layer disposed on one surface of the polyester base material, that has a first main surface and a second main surface, and that is used to produce a release film by forming a release layer on the first main surface. The second main surface is the surface on the opposite side from the coating layer side of the polyester base material. The maximum projection height Sp of the second main surface is greater than or equal to 1 nm and less than 60 nm, and the surface free energy of the second main surface is 25-60 mJ/m².

Description

Manufacturing method of polyester film, release film, polyester film

The present invention relates to a polyester film for producing a release film, a release film, and a method for producing a polyester film.

Biaxially oriented polyester film is used in a wide range of applications from the viewpoints of workability, mechanical properties, electrical properties, dimensional stability, transparency, chemical resistance, and the like. For example, in the field of laminated ceramic capacitors, a release film formed by laminating a release layer on the surface of a biaxially oriented polyester film is used for producing a ceramic sheet having a dielectric layer for manufacturing a laminated ceramic capacitor.

For example, Patent Document 1 uses a biaxially oriented polyester film composed of two or more layers as a base material, and the base material has a surface layer A containing substantially no particles and a surface layer B containing particles. , The release coating layer is laminated on the surface of the surface layer A, and the smoothing coating layer is laminated on the surface of the surface layer B, and the smoothing coating layer has a specific region surface average roughness (Sa) and A release film for manufacturing a ceramic sheet having a maximum protrusion height (P) is disclosed.

Japanese Unexamined Patent Publication No. 2016-060158

With the recent increase in capacity and miniaturization of ceramic capacitors, further thinning of ceramic sheets is required. On the other hand, as the thinning of the ceramic sheet progresses, it is considered that the surface shape of the release film has a greater influence on the performance of the ceramic sheet. For example, if an uneven shape exists on the peeling surface of the release film, the uneven shape is transferred to the ceramic green sheet when the ceramic green sheet is formed, and the thickness of the ceramic green sheet and the ceramic sheet obtained by firing fluctuates, resulting in ceramic. The performance of condenser products may deteriorate.
Further, not only the peeling surface of the peeling film but also the uneven shape of the transport surface which is the surface opposite to the peeling surface may affect the performance of the ceramic sheet. The transport surface of the release film is often provided with a protrusion shape for the purpose of suppressing wrinkles during high-speed transport, but if this protrusion shape is too large, the release film is transported when it is wound into a roll and stored. The protrusion shape of the surface may be transferred to the peeled surface to form transfer marks. The shape of the transfer marks transferred to the peeled surface is considered to be transferred to the ceramic green sheet and the ceramic sheet and affect the performance of the final product.

The present inventors further examined the release film used for producing the ceramic green sheet with reference to the technique described in Patent Document 1, and found that the formation of transfer marks on the surface of the release layer and the transportability were improved. In addition to the problem, it has been found that depending on the properties of the base film of the release film, the coatability of the release layer such as coating unevenness at the time of forming the release layer and / or defects due to foreign matter may decrease.

In view of the above circumstances, it is an object of the present invention to provide a polyester film for producing a release film, which can suppress the formation of transfer marks on the surface of the release layer and has excellent transportability and coatability of the release layer.
Another object of the present invention is to provide a method for producing a release film and a polyester film.

As a result of diligent studies on the above problems, the present inventors have found that the above problems can be solved by the following configuration.

[1]
It comprises a polyester substrate that is substantially free of particles and a coating layer that contains particles and is disposed on one surface of the polyester substrate, and has a first main surface and a second main surface. A polyester film used for forming a release layer on the first main surface to produce a release film, wherein the second main surface is on the side opposite to the polyester base material side of the coating layer. A polyester film having a maximum protrusion height Sp of 1 nm or more and less than 60 nm of the second main surface, and a surface free energy of the second main surface of 25 to 60 mJ / m ^2.
[2]
When the product (D × Sp) of the density D (unit: piece / μm ² ) of the particles constituting the protrusions on the second main surface and the maximum protrusion height Sp (unit: nm) is 20 or more. The polyester film according to [1].
[3]
The polyester film according to [1] or [2], wherein the polyester film has a thickness of 40 μm or less.
[4]
The polyester film according to any one of [1] to [3], wherein the coating layer further contains polyolefin.
[5]
The polyester film according to any one of [1] to [4], wherein the coating layer further contains a (meth) acrylate resin having an acid value of 30 mgKOH / g or less.
[6]
The average particle size of the particles is 1 to 130 nm, the thickness of the coating layer is 1 to 100 nm, and the average particle size of the particles is larger than the thickness of the coating layer, [1] to [5]. ] The polyester film described in any of.
[7]
The coating layer contains at least one surfactant selected from the group consisting of a hydrocarbon-based surfactant and a fluorine-based surfactant containing a perfluoroalkyl group having 1 to 4 carbon atoms. 1] The polyester film according to any one of [6].
[8]
The description according to any one of [1] to [7], wherein the absolute value of the peeling charge amount between the first main surface and the second main surface of the polyester film corresponding to a circle having a diameter of 1.5 cmφ is 0.12 nC or less. Polyester film.
[9]
The polyester film was heat-treated for 20 seconds under the condition that the temperature of the film surface was 90 ° C. while transporting the polyester film under the conditions of a transport speed of 30 m / min and a tension of 100 N / m in the transport direction. The polyester film according to any one of [1] to [8], wherein the total area of the streaky defect regions observed in the polyester film is 40% or less with respect to the total area of the observation region.
[10]
The polyester film according to any one of [1] to [9], wherein the polyester film has a density of 1.39 to 1.41 g / cm ^3.
[11]
[1] to [10], wherein the expansion rate of the polyester film in the width direction at 90 ° C. is −0.15 to 0.15% with respect to the length of the polyester film in the width direction at 30 ° C. The polyester film described in either.
[12]
The polyester film according to any one of [1] to [11], wherein the surface average roughness Sa of the second main surface is 1 to 10 nm.
[13]
The polyester film according to any one of [1] to [12], wherein the maximum protrusion height Sp of the first main surface is 1 to 60 nm.
[14]
The polyester film according to any one of [1] to [13], wherein the surface free energy of the first main surface is 50 to 70 mJ / m ^2.
[15]
The polyester film according to any one of [1] to [14], wherein the variation in the thickness of the polyester film is 5% or less of the average thickness of the polyester film.
[16]
The polyester film according to any one of [1] to [15], wherein the release film is a release film for producing a ceramic green sheet.
[17]
A release film comprising the polyester film according to any one of [1] to [16] and a release layer arranged on the first main surface of the polyester film.
[18]
The release film according to [17], wherein the maximum protrusion height Sp of the surface of the release layer opposite to the polyester film side is 1 to 60 nm.
[19]
The release film according to [17] or [18], wherein the surface free energy of the surface of the release layer opposite to the polyester film side is 30 mJ / m ^{2 or less.}
[20]
A biaxial stretching step of biaxially stretching an unstretched polyester film having a polyester base material,
It comprises a coating layer forming step of in-line coating using a coating layer forming composition containing particles.
The method for producing a polyester film according to any one of [1] to [16].
[21]
The heat fixing step of heating the polyester film biaxially stretched by the biaxial stretching step at a temperature of less than 240 ° C. and heat-fixing the polyester film heat-fixed by the heat fixing step is performed from the heat fixing step. In the heat relaxation step of heating at a low temperature to relax the heat, the cooling step of cooling the polyester film heat-relaxed by the heat relaxation step, and the cooling step, the heat-relaxed polyester film is expanded in the width direction. The method for producing a polyester film according to [20], wherein the polyester film has a cooling rate of more than 2000 ° C./min and less than 4000 ° C./min in the cooling step.

According to the present invention, it is possible to provide a polyester film for producing a release film, which can suppress the formation of transfer marks on the surface of the release layer and has excellent transportability and coatability of the release layer.
Further, according to the present invention, it is possible to provide a release film and a method for producing a polyester film.

It is sectional drawing which shows an example of the structure of the polyester film which concerns on this disclosure. It is an observation image of a polyester film in which a streak defect region was generated. It is a top view which shows an example of the stretching machine used for manufacturing a polyester film.

Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments, and can be carried out with appropriate modifications within the scope of the object of the present invention.

In the present disclosure, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value. In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described stepwise. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value described in a certain 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 the plurality of substances present in the composition when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified. ..
In the present disclosure, the term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. ..
In the present disclosure, "% by mass" and "% by weight" are synonymous, and "parts by mass" and "parts by weight" are synonymous.
In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

In the present disclosure, the description of a mere "polyester film" includes both a polyester base material alone and a laminate of a polyester base material and a coating layer.
In the present disclosure, the "longitudinal direction" means the long direction of the polyester film at the time of manufacturing the polyester film, and is synonymous with the "transport direction" and the "mechanical direction".
In the present disclosure, the "width direction" means a direction orthogonal to the longitudinal direction. In the present disclosure, "orthogonal" is not limited to strict orthogonality, but includes substantially orthogonality. “Approximately orthogonal” means intersecting at 90 ° ± 5 °, preferably 90 ° ± 3 °, and more preferably 90 ° ± 1 °.
Further, in the present disclosure, the "film width" means the distance between both ends of the polyester film in the width direction.

[Polyester film]
The polyester film according to the present disclosure (hereinafter, also referred to as “this film”) is a coating layer containing particles (hereinafter, “specific coating” arranged on one surface of a polyester base material and a polyester base material). A polyester film having a first main surface and a second main surface, and used for forming a release layer on the first main surface to produce a release film. ..
Further, in this film, the second main surface is the surface opposite to the polyester base material side of the specific coating layer, and the maximum protrusion height Sp of the second main surface is 1 nm or more and less than 60 nm, and the second main surface. The surface free energy of the surface is 25 to 60 mJ / m ² .

〔composition〕
The structure of this film will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of the configuration of this film. The polyester film 1 includes a polyester base material 2 and a specific coating layer 3 arranged on one surface of the polyester base material 2, and has a first main surface 1a and a second main surface 1b.
The specific coating layer 3 contains particles (not shown), while the polyester substrate 2 contains substantially no particles.

The first main surface 1a of the polyester film 1 is a surface for forming a release layer. That is, after the polyester film 1 is manufactured, the release film having the polyester film 1 and the release layer is produced by laminating the release layer on the first main surface 1a.
The second main surface 1b of the polyester film 1 is a surface of the specific coating layer 3 opposite to the surface facing the polyester base material 2. That is, the specific coating layer 3 is the outermost layer of the polyester film 1.
The second main surface 1b of the polyester film 1 has the above-mentioned specific maximum protrusion height Sp and a specific surface free energy.

By having the above-mentioned structure, this film has an effect that the formation of transfer marks on the surface of the release layer can be suppressed, the transportability is excellent, and the coatability of the release layer is excellent (hereinafter, at least one of these effects). This is also referred to as "the effect of the present invention").
The reason why this film exerts the above-mentioned effect of the present invention is not clear, but it is presumed as follows.
When a release layer is formed on the first main surface of this film to produce a release film, the second main surface of this film corresponds to a transport surface which is a surface opposite to the release layer. As described above, the transportability is improved by providing the protrusion shape on the transport surface (second main surface), but if the protrusion shape is too large, transfer marks are formed on the release layer when the release film is stored in a roll. There is a problem that it ends up.
On the other hand, in the polyester film according to the present disclosure, the formation of transfer marks can be suppressed by suppressing the protrusions (maximum protrusion height Sp) of the second main surface of the polyester film, which is the transport surface of the release film, to be small. By keeping the surface free energy of the second main surface low, it is possible to improve the reduced transportability by making the protrusions smaller.
On the other hand, if the maximum protrusion height Sp of the second main surface is made too small, the transportability is significantly reduced, wrinkles are generated during transport, and the peeling layer formed on the first main surface may have uneven thickness. There is sex. Further, if the surface free energy of the second main surface is made too small, the polyester film is likely to be charged, and foreign matter adheres to the first main surface and the second main surface to form a coating film of the composition for forming a release layer. Coating defects may occur. On the other hand, by setting each of the maximum protrusion height Sp and the surface free energy of the second main surface to a specific lower limit value or more, the thickness unevenness and / or the coating defect of the peeling layer is reduced, and the coating property of the peeling layer is reduced. Is presumed to have improved.
Further, in this film, the smoothness of the film is improved by providing the polyester base material substantially free of particles and the coating layer containing particles, so that transfer marks are formed on the surface of the release layer. It is considered that both suppression and transportability are well-balanced and excellent.

This film has the above polyester base material and the specific coating layer, and if the maximum protrusion height Sp and the surface free energy of the second main surface are specified in the above ranges, the specifics thereof. The embodiment is not particularly limited, and may have an embodiment other than the configuration shown in FIG.
For example, in the configuration shown in FIG. 1, the first main surface 1a of the polyester film 1 is a surface opposite to the specific coating layer 3 side of the polyester base material 2, but is different from the specific coating layer side of the polyester base material. On the opposite surface, another layer may be arranged in which one surface is the first main surface 1a.
Further, in the configuration shown in FIG. 1, the specific coating layer 3 is arranged in contact with the surface of the polyester base material 2, but a primer layer or the like may be provided between the specific coating layer and the polyester base material.

Hereinafter, each layer of this film will be described in detail.

<Polyester base material>
The polyester base material is a film-like object containing polyester as a main polymer component. Here, the "main polymer component" means the polymer having the highest content (mass) among all the polymers contained in the film.
The polyester base material may contain one kind of polyester alone or may contain two or more kinds of polyesters.

(polyester)
Polyester is a polymer having an ester bond in the main chain. Polyester is usually formed by polycondensing a dicarboxylic acid compound and a diol compound, which will be described later.
The polyester is not particularly limited, and known polyesters can be used. Examples of the polyester include polyethylene terephthalate (PET), polyethylene-2,6-naphthalate (PEN), polypropylene terephthalate (PPT), polybutylene terephthalate (PBT) and copolymers thereof. Among them, polyester selected from the group consisting of polyethylene terephthalate (PET), polyethylene-2,6-naphthalate (PEN), and copolymers thereof is preferable, and PET is more preferable.

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

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

-catalyst-
The catalyst used for producing the polyester is not particularly limited, and a known catalyst that can be used for synthesizing the polyester can be used.
Examples of the catalyst include alkali metal compounds (for example, potassium compounds and sodium compounds), alkaline earth metal compounds (for example, calcium compounds and magnesium compounds), zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, and antimony compounds. Examples include compounds, titanium compounds, germanium compounds, and phosphorus compounds. Of these, titanium compounds are preferable from the viewpoint of catalytic activity and cost.
Only one type of catalyst may be used, or two or more types may be used in combination. At least one metal catalyst selected from potassium compounds, sodium compounds, calcium compounds, magnesium compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, and germanium compounds, and phosphorus compounds. It is preferable to use in combination with, and it is more preferable to use a titanium compound and a phosphorus compound in combination.

As the titanium compound, an organic chelated titanium complex is preferable. The organic chelated titanium complex is a titanium compound having an organic acid as a ligand.
Examples of the organic acid include citric acid, lactic acid, trimellitic acid, and malic acid.
As the titanium compound, the titanium compounds described in paragraphs 0049 to 0053 of Japanese Patent No. 5575671 can also be used, and the contents of the above publication are incorporated in the present specification.

-Dicarboxylic acid compound-
Examples of the dicarboxylic acid compound include dicarboxylic acids such as aliphatic dicarboxylic acid compounds, alicyclic dicarboxylic acid compounds, and aromatic dicarboxylic acid compounds, and dicarboxylic acids such as methyl ester compounds and ethyl ester compounds of the dicarboxylic acids. Esther can be mentioned. Of these, aromatic dicarboxylic acid or methyl 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, dodecandionic acid, dimer acid, eicosandionic acid, pimelic acid, azelaic acid, and methylmalonic acid. And ethylmalonic acid.
Examples of the alicyclic dicarboxylic acid compound include adamantandicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, and decalindicarboxylic acid.

Examples of the aromatic dicarboxylic acid compound include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 1,8-naphthalenedicarboxylic acid. , 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodium sulfoisophthalic acid, phenylindandicarboxylic acid, anthracendicarboxylic acid, phenanthrangecarboxylic acid, 9,9'-bis (4-carboxyphenyl) ) Dicarboxylic acids and their methyl ester forms are mentioned.
Of these, terephthalic acid or 2,6-naphthalenedicarboxylic acid is preferable, and terephthalic acid is more preferable.

Only one type of dicarboxylic acid compound may be used, or two or more types may be used in combination. When terephthalic acid is used as the dicarboxylic acid compound, terephthalic acid may be used alone, or it may be copolymerized with another aromatic dicarboxylic acid such as isophthalic acid or an aliphatic dicarboxylic acid.

-Diol compound-
Examples of the diol compound include an aliphatic diol compound, an alicyclic diol compound, and an aromatic diol compound, and an aliphatic diol compound is preferable.

Examples of the aliphatic diol compound include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and neo. Examples include pentyl glycol, preferably ethylene glycol.
Examples of the alicyclic diol compound include cyclohexanedimethanol, spiroglycol, and isosorbide.
Examples of the aromatic diol compound include bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, and 9,9'-bis (4-hydroxyphenyl) fluorene.
Only one kind of diol compound may be used, or two or more kinds may be used in combination.

-End sealant-
In the production of polyester, an end-capping agent may be used if necessary. By using the end sealant, a structure derived from the end sealant is introduced into the end of the polyester.
As the terminal encapsulant, a known end encapsulant can be used without limitation. Examples of the terminal encapsulant include oxazoline compounds, carbodiimide compounds, and epoxy compounds.
As the terminal encapsulant, the contents described in paragraphs 0055 to 0064 of JP-A-2014-189002 can also be referred to, and the contents of the above-mentioned publication are incorporated in the present specification.

-Manufacturing conditions-
The reaction temperature is not limited and may be appropriately set according to the raw material. The reaction temperature is preferably 260 to 300 ° C, more preferably 275 to 285 ° C.
The pressure is not limited and may be set appropriately according to the raw material. The pressure is ^{preferably 1.33 × 10 -3} to 1.33 × 10 ^-5 MPa, more preferably 6.67 × 10 ^-4 to 6.67 × 10 ^-5 MPa.

As a method for synthesizing polyester, the methods described in paragraphs 0033 to 0070 of Japanese Patent No. 5575671 can also be used, and the contents of the above publication are incorporated in the present specification.

The polyester content in the polyester base material is preferably 85% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, still more preferably 98% by mass, based on the total mass of the polymer in the polyester base material. The above is particularly preferable.
The upper limit of the polyester content is not limited and can be appropriately set within a range of 100% by mass or less with respect to the total mass of the polymer in the polyester substrate.

When the polyester base material contains polyethylene terephthalate, the content of polyethylene terephthalate is preferably 90 to 100% by mass, more preferably 95 to 100% by mass, and 98 to 90 to the total mass of the polyester in the polyester base material. 100% by mass is more preferable, and 100% by mass is particularly preferable.

The polyester substrate may contain components other than polyester (eg, catalyst, unreacted raw material components, particles, water, etc.).
The polyester substrate is substantially free of particles. Examples of the particles include particles contained in the specific coating layer described later. The phrase "substantially free of particles" means that the content of particles is 50 with respect to the total mass of the polyester substrate when the elements derived from the particles are quantitatively analyzed by fluorescent X-ray analysis. It is defined as having a mass of ppm or less, preferably 10% by mass or less, and more preferably not more than the detection limit. This means that even if the particles are not actively added to the polyester base material, the contamination component derived from foreign matter, the raw material resin, or the dirt adhering to the line or device in the manufacturing process of the polyester base material is peeled off, and the polyester is polyester. This is because it may be mixed in the base material.

The thickness of the polyester base material is preferably 100 μm or less, more preferably 50 μm or less, still more preferably 40 μm or less, in that the peelability can be controlled. The lower limit of the thickness is not particularly limited, but 3 μm or more is preferable, 4 μm or more is more preferable, and 10 μm or more is further preferable, in terms of improving the strength and the workability.
The thickness of the polyester base material is measured according to the method for measuring the thickness of the polyester film described later.

<Specific coating layer>
The specific coating layer is a layer containing particles and is formed on one surface of a polyester base material. Further, the surface of the specific coating layer opposite to the surface facing the polyester base material constitutes the second main surface.
By having a specific coating layer, this film can improve the transportability of the polyester film and the release film. More specifically, it is possible to improve the winding quality (suppress blocking), suppress the occurrence of scratches and defects during transport, and reduce transport wrinkles during high-speed transport.

The specific coating layer may be provided directly on the surface of the polyester base material or may be provided on the surface of the polyester base material via another layer, but the specific coating layer may be provided directly on the surface of the polyester base material in terms of better adhesion. It is preferable to provide it. That is, it is preferable that the surface of the specific coating layer on the first main surface side is in contact with the polyester base material.

The specific coating layer is not particularly limited as long as it contains particles and the second main surface has a specific maximum protrusion height Sp and surface free energy, but it is preferable to contain a binder in addition to the particles. Further, the specific coating layer may contain additives other than particles and a binder.

(particle)
The average particle size of the particles contained in the specific coating layer is not particularly limited, and is preferably 1 to 250 nm, more preferably 10 to 200 nm, and more preferably 30 to 130 nm in terms of better transportability and suppression of transfer marks. Is more preferable.
Further, the average particle diameter of the particles contained in the specific coating layer is 10 to 250 nm (more preferably 30 to 130 nm) in terms of better transportability and suppression of transfer marks, and the thickness of the specific coating layer. Is 1 to 200 nm (more preferably 10 to 100 nm), and the average particle size of the particles is preferably larger than the thickness of the specific coating layer.

As the particles contained in the specific coating layer, one type of particles may be used alone, or two or more types of particles may be used.
When the specific coating layer contains two or more kinds of particles having different particle diameters, the specific coating layer preferably contains at least one kind of particles having an average particle diameter within the above range, and two kinds having different particle diameters. It is more preferable that all of the above particles are particles having an average particle diameter within the above range.

The average particle size of the particles contained in the specific coating layer is determined by the following method using a scanning electron microscope (SEM). That is, the second main surface of the polyester film is observed at a magnification of 20000 times using SEM. Observation is performed on 10 arbitrarily selected fields of view, and the area of each particle is measured using image software for particles that can be identified as protrusions in each field of view (particles that are visible as protrusions protruding from the base surface). Then, the diameter of a circle having the same area (diameter equivalent to the area circle) is calculated. The arithmetic mean value of the obtained area circle equivalent diameter is defined as the average particle diameter of the particles. At this time, even if dust and / or coarse agglomerated particles of 1 μm or more are present, the dust and coarse agglomerated particles are not counted when calculating the average particle size.
In the measurement of the average particle size, for the agglomerated particles, the particle size (secondary particle size) of the secondary particles in the agglomerated state shall be measured.
Further, when the specific coating layer contains two or more kinds of particles having different particle diameters, two or more peaks having different particle diameters can be seen in the distribution of the area equivalent circle diameter measured by the above measuring method. In this way, when the distribution of the area circle equivalent diameter measured by the above measurement method has two or more peaks with different particle diameters, the average value of the area circle equivalent diameter is calculated for each peak. Therefore, the average particle size shall be calculated for each particle with a different particle size.

Examples of the particles contained in the specific coating layer include organic particles and inorganic particles. Among them, inorganic particles are preferable from the viewpoint of further improving film winding quality, haze, and durability (for example, thermal stability).
As the organic particles, resin particles are preferable. Examples of the resin constituting the resin particles include acrylic resin such as polymethyl methacrylate resin (PMMA), polyester resin, silicone resin, and styrene-acrylic resin. The resin particles preferably have a crosslinked structure. Examples of the resin particles having a crosslinked structure include divinylbenzene crosslinked particles.
Examples of the inorganic particles include silica particles (silicon dioxide particles, colloidal silica), titania particles (titanium oxide particles), calcium carbonate, barium sulfate, and alumina particles (aluminum oxide particles). Among the above, the inorganic particles are preferably silica particles from the viewpoint of further improving haze and durability.

The shape of the particles is not particularly limited, and examples thereof include rice granules, spheres, cubes, spindles, scales, agglutinates, and indefinite shapes. The aggregated state means a state in which the primary particles are aggregated. The shape of the aggregated particles is not limited, but a spherical or irregular shape is preferable.

As the agglomerated particles, fumed silica particles are preferably mentioned. Examples of commercially available products include Aerosil series manufactured by Nippon Aerosil Co., Ltd.
Preferred examples of the non-aggregated particles include colloidal silica particles. Examples of commercially available products include the Snowtex series manufactured by Nissan Chemical Industries, Ltd.

The content of the particles in the specific coating layer is preferably 0.1 to 30% by mass, preferably 1 to 25% by mass, based on the total mass of the specific coating layer from the viewpoint of transportability and coatability of the release layer. More preferably, 1 to 15% by mass is further preferable.
The content of the particles is preferably 0.0001 to 0.01% by mass, more preferably 0.0005 to 0.005% by mass, based on the total mass of the polyester film.

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

The specific coating layer is preferably formed by coating an aqueous dispersion containing a binder. In that respect, an acid-modified resin is preferable as the binder. Examples of the acid-modified resin include a copolymer of (meth) acrylate and (meth) acrylic acid, a polyolefin having a carboxyl group, and an acid-modified polyurethane, and a copolymer of (meth) acrylate and (meth) acrylic acid. Or, a polyolefin having a carboxyl group is preferable, and a polyolefin having a carboxyl group is more preferable.
Further, the binder is preferably a (meth) acrylate resin, polyolefin or polyurethane, and more preferably a (meth) acrylate resin or polyolefin, in that the surface free energy of the specific coating layer can be easily adjusted to the above-mentioned specific range. Preferably, polyolefin is even more preferred. The (meth) acrylate resin, polyolefin and polyurethane are not particularly limited, and known resins can be used.

The polyolefin may contain a structural unit derived from an olefin in the main chain, and preferably contains a structural unit derived from an olefin as a main component. Having an olefin structure in the main chain results in insufficient compatibility with the polyester substrate, and as a result, transfer marks after long-term storage can be further improved. The olefin is not particularly limited, but an alkene having 2 to 6 carbon atoms is preferable, ethylene, propylene, or hexene is more preferable, and ethylene is further preferable.
In addition, in this specification, "having a constituent unit derived from a certain monomer as a main component" means that the constituent unit is 50 mol% or more with respect to all the constituent units of the polymer.
The constituent unit derived from the olefin of the polyolefin is preferably 50 to 99 mol%, more preferably 60 to 98%, based on all the constituent units of the polyolefin.

As the polyolefin, an acid-modified polyolefin is preferable because it can prevent charging when the release layer is applied. Examples of the acid-modified polyolefin include a copolymer obtained by modifying the above-mentioned polyolefin with an acid-modified component such as an unsaturated carboxylic acid or an anhydride thereof. The form of polymerization of this copolymer is not particularly limited, and examples thereof include random copolymerization, block copolymerization, and graft copolymerization.
Examples of the acid-modifying component include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, and crotonic acid, and half esters and half amides of unsaturated dicarboxylic acids. From the viewpoint of dispersion stability of the resin, crotonic acid, methacrylic acid, maleic acid, or maleic anhydride is preferable.

Examples of the acidic group contained in the acid-modified polyolefin include a carboxyl group, a sulfo group, and a phosphoric acid group, which are acidic groups corresponding to the above-mentioned acid-modified component, and a carboxyl group is preferable. The acidic group may form an acid anhydride or may be neutralized with at least one selected from alkali metals, organic amines and ammonia. The acid-modifying component is preferably neutralized with an alkali metal in terms of suppressing charge and improving the coatability of the release layer.
The acid-modified polyolefin may contain only one type of structural unit having an acidic group, or may contain two or more types. Examples of the structural unit having an acidic group include a structural unit derived from the above-mentioned acid-modifying component monomer and a structural unit derived from the above-mentioned olefin monomer obtained by grafting the acid-modified component. The content of the structural unit having an acidic group is not particularly limited, but is preferably 0.1 to 30 mol% with respect to all the structural units of the acid-modified polyolefin.

Examples of commercially available acid-modified polyolefins include Zyxen (registered trademark) series (manufactured by Sumitomo Seika Co., Ltd.) such as Zyxen AC, A, L, NC, and N, Chemipearl S100, S120, S200, S300, and S650. Chemipearl (registered trademark) series such as SA100 (manufactured by Mitsui Kagaku Co., Ltd.), Hi-Tech (registered trademark) series such as Hi-Tech S3121 and S3148K (manufactured by Toho Kagaku Co., Ltd.), Arrow Base SE-1013, SE-1010 , SB-1200, SD-1200, SD-1200, DA-1010, DB-4010, etc. Arrow Base (registered trademark) series (manufactured by Unitika Co., Ltd.), Hardlen AP-2, NZ-1004, NZ-1005 ( Examples thereof include Toyobo Co., Ltd., Seporjon G315, and VA407 (Sumitomo Seika Co., Ltd.).
Further, the acid-modified polyolefin described in paragraphs 0022 to 0034 of JP-A-2014-076632 can also be preferably used.

The (meth) acrylate resin is a resin containing a structural unit derived from (meth) acrylate, and may be copolymerized with a vinyl monomer such as styrene. The (meth) acrylate resin is not particularly limited, but preferably contains a structural unit derived from a (meth) acrylate having an alkyl group having 1 to 12 carbon atoms, and has an alkyl group having 1 to 6 carbon atoms (meth). ) It is more preferable to contain a structural unit derived from acrylate.
The (meth) acrylate resin preferably has an acid-modifying component in that it can prevent charging when the release layer is applied. The (meth) acrylate resin preferably contains a structural unit derived from (meth) acrylic acid as an acid-modifying component. The (meth) acrylic acid may form an acid anhydride or may be neutralized with at least one selected from alkali metals, organic amines and ammonia. The (meth) acrylic acid is preferably neutralized with an alkali metal in that it suppresses charging and improves the coatability of the release layer.
The content of the structural unit having an acid-modifying group is 0.1 to 10% by mass with respect to all the structural units of the (meth) acrylate resin in that the charge is suppressed and the coatability of the release layer is improved. It is preferably present, and the constituent unit composed of (meth) acrylic acid is more preferably 0.1 to 10% by mass. By setting the content of the structural unit having an acid-modifying group within the above range, the acid value can be lowered and the surface free energy can be adjusted to a desired range. Further, as the aqueous dispersion of the (meth) acrylate resin, an aqueous dispersion containing the (meth) acrylate resin and the dispersant is also preferable.

The acid value of the (meth) acrylate resin is preferably 30 mgKOH / g or less, more preferably 20 mgKOH / g or less. The lower limit of the acid value is not particularly limited and is, for example, 0 mgKOH / g, but 2 mgKOH / g or more is preferable from the viewpoint of application as an aqueous dispersion. The acid value of the (meth) acrylate resin is adjusted to be in the above range, and the acid value is adjusted to satisfy at least one of the above range and the inclusion of a structural unit derived from the (meth) acrylate having an alkyl group having 1 to 12 carbon atoms. Thereby, the surface free energy can be adjusted to a desired range. When the polyester film of the present invention is stored for a long period of time to form a release film for producing a ceramic green sheet, the points that defects can be suppressed are that the acid value of the acrylic resin is within the above range and that the number of carbon atoms is 1 to 12. It is preferable to satisfy both of containing a structural unit derived from a (meth) acrylate having an alkyl group.

The polyurethane is not limited as long as it is a polymer having a urethane bond in the main chain, and known polyurethane such as a reaction product of an isocyanate compound and a polyol compound can be used.
As described above, acid-modified polyurethane is preferable in that an aqueous dispersion can be easily prepared. The acid-modified polyurethane means a polyurethane having an acidic group. Examples of the acidic group include the groups mentioned as the acidic group contained in the above-mentioned acid-modified polyolefin. Further, as the aqueous dispersion of polyurethane, an aqueous dispersion containing polyurethane and a dispersant is also preferable.
The polyurethane contained in the specific coating layer has, for example, the surface free energy of the specific coating layer within a specific range by adjusting the structure and hydrophobicity (hydrophilicity) of each of the polyol compound and / or the isocyanate compound as a raw material. Can be controlled.
Commercially available polyurethane products include, for example, Hydran (registered trademark) AP-20, AP-40N and AP-201 (all manufactured by DIC Corporation); Takelac (registered trademark) W-605, W-5030 and W- 5920 (above, manufactured by Mitsui Chemicals, Inc.); and Superflex (registered trademark) 210 and 130, Elastron (registered trademark) H-3-DF, E-37 and H-15 (above, Dai-ichi Kogyo Seiyaku Co., Ltd.) Made by Co., Ltd.).

The specific coating layer may contain one kind of binder alone, or may contain two or more kinds of binders. When the polyolefin or (meth) acrylate resin is used in combination with a resin other than the polyolefin and the (meth) acrylate resin in order to control the surface free energy, the polyurethane is preferable as the resin to be used in combination.
The content of the binder is preferably 30 to 99.8% by mass, more preferably 50 to 99.5% by mass, based on the total mass of the specific coating layer, from the viewpoint of adjusting Sp to a desired range.

(Additive)
The specific coating layer may contain additives other than the above particles and binder.
Additives contained in the specific coating layer include, for example, surfactants, waxes, cross-linking agents, antioxidants, UV absorbers, colorants, strengthening agents, plasticizers, antistatic agents, flame retardants, and rust preventives. , And antistatic agents.

The specific coating layer preferably has a surfactant on the second main surface in that the smoothness of the region other than the portion where the protrusions formed by the particles are present is improved. By improving the smoothness of the above-mentioned region of the second main surface and reducing the surface roughness of the second main surface due to factors other than particles, Sp can be controlled within a desired range and the effect of the present invention can be improved. Can be done.

The surfactant is not particularly limited, and examples thereof include a silicone-based surfactant, a fluorine-based surfactant, and a hydrocarbon-based surfactant. Hydrocarbon-based surfactants are preferable in that the coatability of the peeling layer can be improved by suppressing the charge on the first main surface and suppressing the generation of defects due to foreign substances when the peeling layer is applied.

The silicone-based surfactant is not particularly limited as long as it is a surfactant having a silicon-containing group as a hydrophobic group, and examples thereof include polydimethylsiloxane, polyether-modified polydimethylsiloxane, and polymethylalkylsiloxane.
Commercially available products of silicone-based surfactants include, for example, BYK®-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, BYK-347, BYK-348, and , BYK-349 (all manufactured by BYK), and KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, Examples thereof include KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, and KF-6017 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

The fluorine-based surfactant is not particularly limited as long as it is a surfactant having a fluorine-containing group as a hydrophobic group, and examples thereof include perfluorooctanesulfonic acid and perfluorocarboxylic acid.
Commercially available products of fluorine-based surfactants include, for example, Megafuck (registered trademark) F-114, F-410, F-440, F-447, F-553, and F-556 (all manufactured by DIC Corporation). ), And Surfron® S-211, S-221, S-231, S-233, S-241, S-242, S-243, S-420, S-661, S-651, and Examples thereof include S-386 (manufactured by AGC Seimi Chemical Co., Ltd.).

The fluorine-based surfactant has a linear perfluoroalkyl group having 7 or more carbon atoms, such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), from the viewpoint of improving environmental suitability. It is preferable to use a surfactant derived from a substitute material for the compound, and more preferably to use a surfactant derived from a substitute material for a compound having a linear perfluoroalkyl group having 6 or more carbon atoms.
More specifically, a perfluoroalkyl group having 1 to 4 carbon atoms can improve the coatability of the release layer as compared with a surfactant having a linear perfluoroalkyl group having 6 or more carbon atoms. It is preferable to use a surfactant having the above. The perfluoroalkyl group having 1 to 4 carbon atoms may be linear or branched. Among them, a surfactant having a linear perfluoroalkyl group having 1 to 4 carbon atoms or a branched perfluoroalkyl group having 3 carbon atoms is more preferable, and a perfluoroalkyl group having 1 or 2 carbon atoms is more preferable. A surfactant having a group or a branched perfluoroalkyl group having 3 carbon atoms is more preferable.
Examples of the perfluoroalkyl group, for _{_{_{_{example, CF 3 - *, C 2}}}} F 5 - *, C 3 F 7 - *, n-C 4 F 9 - *, _and, _(CF 3) 2 CF- * is Can be mentioned. Here, * indicates a bond position with a carbon atom other than the carbon atom substituted with the fluorine atom. The carbon atom bonded to these perfluoroalkyl groups preferably has either a hydrogen atom or is bonded only to a carbon atom.

Commercially available products of fluorine-based surfactants having a perfluoroalkyl group having 1 to 4 carbon atoms include, for example, Futergent (registered trademark) 100, 100C, 110, 150, 150H, 212M, 215M, 250, 251, 222F. , 245F, 208G, FTX-218, DFX-18, 300, 310, 320, 400SW, 710FL, 683, 601AD, 602A, and 681, (all manufactured by Neos Co., Ltd.), and PF-136A, PF- Examples thereof include 156A, PF-151N, PF-636, PF-6320, PF-656, PF-6520, and PF-652-NF (all manufactured by OMNOVA).

When a surfactant having a perfluoroalkyl group having 1 to 4 carbon atoms is used, the coatability of the release layer is higher than that when a surfactant having a linear perfluoroalkyl group having 6 or more carbon atoms is used. Although but no reason is uncertain to improve, surfactants having a perfluoroalkyl group having 1 to 4 carbon atoms, to include a number of low CF ₃ group surface tension per weight, the second main with a small amount The surface free energy of the surface can be reduced. As a result, the transportability of the polyester film can be improved, and since the composition of the specific coating layer does not change significantly, it is presumed that the peeling charge described later can be suppressed and the coating property of the peeling layer can be improved. ing.

Examples of the hydrocarbon-based surfactant include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants.
Examples of the anionic surfactant include alkyl sulfates, alkylbenzene sulfonates, alkyl phosphates, and fatty acid salts.
Examples of the nonionic surfactant include polyalkylene glycol mono or dialkyl ether, polyalkylene glycol mono or dialkyl ester, and polyalkylene glycol monoalkyl ester / monoalkyl ether.
Examples of the cationic surfactant include primary to tertiary alkylamine salts, quaternary ammonium compounds and the like.
Examples of amphoteric surfactants include surfactants having both anionic and cationic moieties in the molecule.

Examples of commercially available anionic surfactants include Lapizol (registered trademark) A-90, A-80, BW-30, B-90, and C-70 (all manufactured by Nichiyu Co., Ltd.). NIKKOL (registered trademark) OTP-100 (above, manufactured by Nikko Chemical Co., Ltd.), Kohakul (registered trademark) ON, L-40, and Phosphanol (registered trademark) 702 (above, manufactured by Toho Chemical Industries, Ltd.) ), Viewlight (registered trademark) A-5000, and SSS (all manufactured by Sanyo Chemical Industries, Ltd.).
Commercially available nonionic surfactants include, for example, Naroacty (registered trademark) CL-95, HN-100 (trade name: manufactured by Sanyo Chemical Industries, Ltd.), and Lisolex BW400 (trade name: higher alcohol industry). EMALEX® ET-2020 (all manufactured by Nippon Emulsion Co., Ltd.), and Surfinol® 104E, 420, 440, 465, and Dynol® 604, 607 (above, manufactured by Nisshin Chemical Industry Co., Ltd.).

When used in combination with an acid-modified resin, anionic surfactants and / or nonionic surfactants are preferable and anionic surfactants are preferable because they can form a coating layer having a smooth surface without inhibiting the dispersion of the resin. Activators are more preferred. That is, as the surfactant, an anionic hydrocarbon-based surfactant is more preferable in terms of improving the surface smoothness and the coatability of the release layer.

The anionic hydrocarbon-based surfactant preferably has a plurality of hydrophobic end groups in terms of further improving smoothness. The hydrophobic end group may be a part of the hydrocarbon group contained in the hydrocarbon-based surfactant. For example, a hydrocarbon-based surfactant having a hydrocarbon group having a branched chain structure at the end will have a plurality of hydrophobic end groups.
Examples of anionic hydrocarbon-based surfactants having a plurality of hydrophobic end groups include di-2-ethylhexyl sulfosuccinate (having four hydrophobic end groups) and di-2-ethyloctyl sulfosuccinate (sodium sulfosuccinate). (Has four hydrophobic end groups) and branched chain alkylbenzene sulfonate (has two hydrophobic end groups).

One type of surfactant may be used, or two or more types may be used in combination.
The content of the surfactant is preferably 0.1 to 10% by mass with respect to the total mass of the specific coating layer, and is 0.1 in that it is excellent in antistatic property at the time of forming the release layer and surface smoothness. It is more preferably to 5% by mass, and even more preferably 0.5 to 2% by mass.

The wax is not particularly limited, and may be a natural wax or a synthetic wax. Examples of the natural wax include carnauba wax, candelilla wax, beeswax, montan wax, paraffin wax, and petroleum wax. In addition, the slip agent described in [0087] of International Publication No. 2017/169844 can also be used.
The wax content is preferably 0 to 10% by mass with respect to the total mass of the specific coating layer.

The cross-linking agent is not particularly limited, and known ones can be used.
Examples of the cross-linking agent include melamine compounds, oxazoline compounds, epoxy compounds, isocyanate compounds, and carbodiimide-based compounds, and oxazoline-based compounds and carbodiimide-based compounds are particularly preferable. Examples of commercially available products include Carbodilite V-02-L2 (manufactured by Nisshinbo Co., Ltd.) and Epocross K-2020E (manufactured by Nippon Shokubai Co., Ltd.). For details of the epoxy-based compound, the isocyanate-based compound, and the melamine-based compound, the description of [0081] to [0083] of JP2015-163457 can be referred to. The cross-linking agent described in [2002] to [0084] of International Publication No. 2017/169844 can also be preferably used. As the carbodiimide compound, the description of [0038] to [0040] of JP-A-2017-087421 can be referred to.
As for the oxazoline compound, the carbodiimide compound, and the isocyanate compound, the cross-linking agent described in [0074] to [0075] of International Publication No. 2018/034294 can also be preferably used.
The content of the cross-linking agent is preferably 0 to 50% by mass with respect to the total mass of the specific coating layer.

(thickness)
The specific coating layer is often formed to have a thickness of 1 μm or less by coating a composition containing particles on one surface of a polyester base material.
The thickness of the specific coating layer is preferably 1 to 200 nm, more preferably 10 to 100 nm, and even more preferably 20 to 100 nm, from the viewpoint of manufacturing suitability of the specific coating layer and reduction of haze.
The thickness of the specific coating layer is measured by preparing a section having a cross section perpendicular to the main surface of the polyester film and using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The arithmetic average value of the thickness at 5 points of the above section is used.
If the specific coating layer is soft and it is difficult to stably prepare a cross-sectional section, measurement may be performed using a refractive index meter. Specifically, the film thickness of the specific coating layer can be obtained by fitting the measured reflectance spectrum with the film thickness and the refractive index of the specific coating layer and the polyester base material.

The method for forming the specific coating layer will be described in detail in the "specific coating layer forming step" described later.

This film may include a layer other than the polyester base material and the specific coating layer described above, but is more preferably composed of the polyester base material and the specific coating layer.

[Physical characteristics, etc.]
Next, the physical characteristics of this film will be described.

(Surface free energy of the second main surface)
In this film, the surface free energy of the second main surface is 25 to 60 mJ / m ² . Since the surface free energy of the second main surface is in the above range, polyester has excellent transportability and excellent coatability of the release layer even if the maximum protrusion height Sp of the second main surface is in the above range. A film is obtained.
The surface free energy of the second main surface is preferably ^{25 to 50 mJ / m 2 in} that the formation of transfer marks on the surface of the release layer of the release film after long-term storage can be further suppressed. Further, from the viewpoint of the coating property of the transportability and the release layer, the surface free energy of the second main surface is more preferably 30 ~ 50 mJ / ^{m 2,} more preferably ^{30 ~ 45mJ / m 2, 40} ~ 45mJ / m ² is particularly preferred.
The surface free energy of the second main surface (the surface of the specific coating layer) can be adjusted by selecting, for example, the particles constituting the specific coating layer, the above-mentioned binder, the additive, and the like.

The surface free energy of the second main surface of the polyester film is the second main surface (specific coating layer) under the condition of 25 ° C. using a contact angle meter (for example, "DROPMASTER-501" manufactured by Kyowa Interface Chemistry Co., Ltd.). Droplets of purified water, methylene iodide, and ethylene glycol were dropped onto the surface on the side), and the contact angle 1 second after the droplets adhered to the surface was measured. It is obtained by calculating according to the method of the field.
The "surface free energy" obtained by the above method is the total of the polar component and the hydrogen bond component of the surface free energy.

(Surface free energy of the first main surface)
From the viewpoint of antistatic when winding the film, the surface free energy of the first main surface is preferably ^{50 to 70 mJ / m 2.}
Further, it is preferable that the difference between the surface free energy of the first main surface and the surface free energy of the second main surface is wide because the film is less likely to be charged. The difference between the surface free energy of the surface free energy and a second major surface of the first main surface is preferably 1 ~ 35 mJ / ^{m 2,} more preferably 5 ~ 35 mJ / ^{m 2,} more preferably 10 ~ 30 mJ / ^{m 2} ..
The surface free energy of the first main surface can be adjusted by the type of resin and additive forming the layer having the first main surface. For example, when the first main surface is the surface opposite to the specific coating layer side of the polyester base material, the surface free energy of the first main surface can be adjusted depending on the type of resin and additive forming the polyester base material. ..

(Maximum protrusion height Sp of the second main surface, surface average roughness Sa)
In this film, the maximum protrusion height Sp of the second main surface is 1 nm or more and less than 60 nm. When the maximum protrusion height Sp of the second main surface is within the above range, it is possible to produce a release film having a good balance of suppression of transfer marks and transportability on the surface of the release layer.
From the above viewpoint, the maximum protrusion height Sp of the second main surface is preferably 10 to 50 nm, more preferably 20 to 50 nm.

Further, in this film, the surface average roughness Sa of the second main surface is preferably 1 to 10 nm, more preferably 1 to 9 nm, in that the suppression stability of the transfer marks is more excellent. It is more preferably 1 to 8 nm.

The maximum protrusion height Sp and surface average roughness Sa of the second main surface (specific coating layer surface) depend on, for example, the average particle size and content of the particles contained in the specific coating layer, and the thickness of the specific coating layer. , Can be adjusted. When the specific coating layer is formed by in-line coating, the above adjustment can be performed more easily.

The maximum protrusion height Sp and surface average roughness Sa of the second main surface of the polyester film are set on the surface of the polyester film on the specific coating layer side with an optical interferometer (for example, "Vertscan 3300G Lite" manufactured by Hitachi High-Tech Co., Ltd.). It is obtained by measuring under the following conditions using the above and then analyzing with the built-in data analysis software.
In the measurement of the maximum protrusion height Sp, the measurement is performed 5 times by changing the measurement position, and the maximum value of the obtained measured value is the measured value of the maximum protrusion height Sp (denoted as P in the built-in data analysis software). Ru). Further, in the measurement of the surface average roughness Sa, the measurement is performed 5 times by changing the measurement position, and the average value of the obtained measured values is used as the measured value of the surface average roughness Sa.
(Measurement condition)
-Measurement mode: WAVE mode-Objective lens: 50x-Measurement area: 186 μm x 155 μm

(Maximum protrusion height Sp of the first main surface, surface average roughness Sa)
In terms of smoothing the release layer, it is preferable that the first main surface is as smooth as possible. Specifically, the maximum protrusion height Sp of the first main surface is preferably 1 to 60 nm, and more preferably 5 to 30 nm. The surface average roughness Sa of the first main surface is preferably 0 to 10 nm, more preferably 0 to 5 nm.
The maximum protrusion height Sp and surface average roughness Sa of the first main surface are the types and additions of polyesters constituting the polyester base material so that particles are not substantially contained in the polyester base material and the film is formed smoothly. It can be adjusted by a method such as selecting the type of agent.
The maximum protrusion height Sp and the surface average roughness Sa of the first main surface can be measured according to the above-mentioned measuring methods of the maximum protrusion height Sp and the surface average roughness Sa of the second main surface.

(The product of the maximum protrusion height Sp of the second main surface and the particle density D)
In this film, the density D (unit: piece / μm ² , also referred to as “particle density D”) of the particles constituting the protrusions on the second main surface and the above-mentioned second are in terms of being more excellent in transportability. The product (D × Sp) with the maximum protrusion height Sp (unit: nm) of the main surface is preferably 1 or more, more preferably 20 or more, and further preferably 50 or more. The upper limit is not particularly limited, but 400 or less is preferable, and 300 or less is more preferable, in that the suppression of transfer marks is more excellent.
The product (D × Sp) is an index showing how large the protrusions are present on the second main surface at what density, and the product (D × Sp) is within the above range. It is preferable because the protrusions, which are preferable from the viewpoint of suppressing transfer marks and transportability, are present on the second main surface in an appropriate amount, and the effects of suppressing transfer marks and transportability are further excellent.

The particle density D depends on, for example, the average particle size and content of the particles contained in the specific coating layer, and the thickness of the specific coating layer, similarly to the maximum protrusion height Sp and the surface average roughness Sa. , Can be adjusted. When the specific coating layer is formed by in-line coating, the above adjustment can be performed more easily.

Further, the particle density D of the particles constituting the protrusions on the second main surface of the polyester film can be obtained by the same method as the method for measuring the average particle diameter of the particles using SEM. That is, the surface of the polyester film on the specific coating layer side is observed at a magnification of 20000 times. Observation is performed on 10 arbitrarily selected fields of view, and the number of individual particles is measured using image software for particles that can be identified as protrusions in each field of view (particles that are visible as protrusions protruding from the base surface). do. The calculated value obtained by dividing the total number of particles measured in the entire field of view by the total area of the entire field of view is defined as the particle density D (unit: particles / μm ² ).

(Orientation)
This film is a biaxially oriented polyester film. In the present disclosure, "biaxial orientation" means a property having molecular orientation in the biaxial direction.
The molecular orientation is measured using a microwave transmission type molecular orientation meter (for example, MOA-6004, manufactured by Oji Measuring Instruments Co., Ltd.). The angle formed in the biaxial direction is preferably 90 ° ± 5 °, more preferably 90 ° ± 3 °, and even more preferably 90 ° ± 1 °. This film preferably has molecular orientation in the longitudinal direction and the width direction.

(Streak defect area)
In the present disclosure, the "streak defect" means a wrinkle that extends in a streak shape along the longitudinal direction of the film and appears as unevenness in the width direction of the film. As will be described later, since the streak defects occur in the film after production, they are often wrinkles that occur irreversibly. The streak defects do not occur in the heat treatment during the production of the film, but are derived from the wrinkles generated in the heat treatment for the film after the production, and the wrinkles are solidified by cooling after the heat treatment. The "streak defect region" means a portion in the film surface where the streak defect has occurred.
When a streak defect region is generated (that is, a streak defect is partially generated in the film surface), the peeling layer becomes uneven in thickness, and the coatability of the peeling layer is deteriorated, resulting in the ceramic capacitor. May affect performance. Further, the streak defect region tends to be remarkably generated when the film is heated in a state where a tensile load is applied in the longitudinal direction of the film.

The ratio of the total area of the streak defect region generated when heated at 90 ° C. to the total area of the observation region of the polyester film (hereinafter, also referred to as “area ratio of the streak defect region”) is the coatability of the release layer. 40% or less is preferable, 30% or less is more preferable, and 20% or less is further preferable.
The lower limit of the area ratio of the streak defect region is not particularly limited, but the area ratio of the streak defect region generated when heated at 90 ° C. is preferably small, and there is no streak defect region, that is, 0%. Is more preferable.

The area ratio of the streak defect region is measured by the following method.
(1) Using a heating and transporting device, heat the polyester film under the conditions of a transport speed of 30 m / min and a tension of 100 N / m in the transport direction while the surface temperature of the film is 90 ° C. The process is performed for 20 seconds. The heating time in the heat treatment is calculated from the time when the surface temperature of the film reaches the target temperature (90 ° C.), and the film is heated for 20 consecutive seconds from there. The method for measuring the surface temperature of the film will be described later.
(2) A heat-treated polyester film was placed on a black flat plate, and then a fluorescent lamp installed on the ceiling of the room [For example, Lupica Ace manufactured by Mitsubishi Electric Co., Ltd. (color temperature: 5000K, average color rendering index) ( The polyester film is visually observed from an angle while changing the viewpoint so that the light of Ra): 84)] is reflected. The region where the reflected image of the fluorescent lamp reflected on the surface of the polyester film, which is visually observed, is undulating is defined as a streak defect region.
(3) The number of observed streak defect regions is counted, and the outer circumference of each streak defect region existing in ^{the visually observed observation region (area 1 m 2) of the polyester film is marked.} Next, of the two parallel tangents circumscribing the outer periphery of each streak defect region, the distance between the two parallel tangents selected so as to maximize the distance between the tangents is defined as the length L of the major axis. The distance between two parallel tangents orthogonal to the two parallel tangents giving the length L and circumscribing the outer periphery of the streak defect region is measured with the length S of the minor axis. From the obtained lengths L and S, the area of each streak defect region is calculated by the following formula. From these values, the ratio of the total area of the streak defect region to the total area of the polyester film is calculated.
Length of the major axis of the streak defect region L × Length of the minor axis of the streak defect region S × π = Area of the streak defect region The streak defect region is often elliptical or circular as described above. Therefore, the area of the streak defect region can be calculated by the calculation method of (3) above.

FIG. 2 shows an image (photograph) of a polyester film in which a streak defect region generated by the heat treatment of (1) above is observed. The region surrounded by the solid line shown in FIG. 2 is the streak defect region. In the streak defect region shown in FIG. 2, an uneven shape extending in the transport (MD) direction is observed. The image (photograph) shown in FIG. 2 shows only a part of the observation area.
As described above, the streak defect region is often elliptical or circular. Further, when a streak defect region is generated, at least one elliptical streak defect region whose long axis direction is along the transport direction often appears.

The biaxially oriented polyester film having the area ratio of the streak defect region in the above range is used in the heat fixing temperature in the heat fixing step, the cooling rate of the polyester film in the cooling step, and the expansion step in the polyester film manufacturing method described later. It can be manufactured by adjusting the expansion ratio of the polyester film in the width direction.

(Expansion rate)
The expansion rate of the polyester film in the width direction at 90 ° C. is preferably −0.15 to 0.15%, preferably −0.10 to 0.10%, based on the film width at 30 ° C. Is more preferable, 0 to 0.10% is further preferable, and 0 to 0.05% is particularly preferable.
By adjusting the expansion coefficient in the width direction of the polyester film at 90 ° C. within the above range, not only the expansion of the film in the width direction in the heating process can be suppressed, but also the expansion coefficient unevenness in each place on the film surface can be reduced. As a result, it is presumed that the generation of streaky defect regions due to heating can be suppressed.

The coefficient of expansion in the width direction at 90 ° C. is measured by the following method using a thermomechanical analyzer.
(1) Prepare a sample adjusted to a length of at least 20 mm in a direction parallel to the width direction of the biaxially oriented film and 4 mm in a direction orthogonal to the width direction of the biaxially oriented film.
(2) Using a thermomechanical analyzer (for example, TMA-60, manufactured by Shimadzu Corporation), a tensile load of 0.1 g is applied to a sample having a width of 4 mm and a length (distance between chucks) of 20 mm.
(3) The value of the length of the sample at each temperature (° C.) by raising the temperature of the above sample from a temperature of 20 ° C. or higher and lower than 30 ° C. (preferably 25 ° C.) to 150 ° C. at a heating rate of 5 ° C./min. To get.
(4) From the sample length (L30) at 30 ° C. and the length (L90) at 90 ° C., the expansion coefficient in the width direction at 90 ° C. is obtained using the following formula. In the present disclosure, the coefficient of expansion in the width direction is an arithmetic mean value of the coefficient of expansion obtained using five samples. A positive expansion rate means expansion, and a negative expansion rate means contraction.
Equation: Expansion rate (%) = (L90-L30) / L30 × 100

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

(Film density)
The density of the polyester film, in view of more excellent effects of the present invention, preferably 1.39 ~ 1.41g / cm ^3, more preferably ^{1.395 ~ 1.405g / cm 3, 1.398} ~ 1.400g / cm ³ is more preferred.
The density of the polyester film can be measured using an electronic hydrometer (product name "SD-200L", manufactured by Alpha Mirage Co., Ltd.).

(thickness)
The thickness of the polyester film is preferably 100 μm or less, more preferably 50 μm or less, still more preferably 40 μm or less, in that the peelability is more excellent. The lower limit of the thickness is not particularly limited, but 3 μm or more is preferable, 5 μm or more is more preferable, and 10 μm or more is further preferable, from the viewpoint of excellent handleability.
The thickness of the polyester film shall be the arithmetic mean value of the thicknesses at five points measured by the continuous stylus type film thickness meter.

Further, the variation in the thickness of the polyester film is preferably 7% or less, more preferably 5% or less of the average thickness of the polyester film in that the surface smoothness of the first main surface forming the release layer is more excellent. The lower limit of the thickness variation is not particularly limited, and may be 0% or more of the average thickness of the polyester film.
The thickness variation can be obtained by the following measuring method. Using a continuous stylus film thickness meter, the thickness of the polyester film is measured over 10 m along the longitudinal direction. This measurement is performed at five locations where the positions in the width direction are different. From the obtained measured values, the value obtained by dividing the difference between the maximum value and the minimum value by the arithmetic mean value of all the measured values ((maximum thickness-minimum thickness) / average thickness) is defined as the thickness variation. do.

(Peeling charge amount)
The polyester film is a polyester corresponding to a circle with a diameter of 1.5 cmφ measured in an environment of a temperature of 23 ° C. and a relative humidity (RH) of 20% by the following measurement method in that the coatability of the release layer is improved. The absolute value of the peel charge amount between the first main surface and the second main surface of the film is preferably 0.12 nc (nanocoolon) or less, more preferably 0.11 nc or less, and 0.1 nc or less. Is more preferable. Here, the unit nc (nanocoulomb) is ^10-9 coulombs.

The method for measuring the peeling charge amount of the polyester film is as follows.
As a measuring device, a reference sample is placed by placing a reference sample of polyester film (first main surface on the upper surface) and ascending and descending along the vertical direction while holding the measurement sample (second main surface on the lower surface). A device equipped with a head capable of repeatedly crimping and peeling the second main surface of the measurement sample against the first main surface of the measurement sample and an electrometer connected to the head and capable of measuring the charge amount of the measurement sample is used. do.
A polyester film is cut into a circle with a diameter of 1.5 cm to prepare a sample for measuring the peeling charge, and a rectangular with a size of 13 cm × 4 cm is cut to prepare a sample as a reference for measuring the peeling charge. To make. Next, the obtained polyester film sample is left to stand in advance under the above-mentioned measurement temperature and humidity environment for 2 hours or more. After that, the reference sample is placed on the base of the measuring device, and the measurement sample is attached to the head. At this time, in the reference sample to be placed on the table so that the first main surface of the reference sample and the second main surface of the measurement sample face each other, the first main surface is on the upper surface side and the second main surface of the measurement sample is mounted on the head. The main surface is arranged on the lower surface side, respectively.
After static elimination of the measurement sample, the head is raised or lowered, and the reference film is repeatedly crimped and peeled off from the measurement sample. Using the same measurement sample, the charge amount of the measurement sample is measured after the first to fifth peeling, and the average value of the measured values is calculated. While changing the measurement sample, the position where the measurement sample contacts in the reference sample is changed for each measurement sample, and the measurement is performed with a total of four samples, and the average of all is taken as the peeling charge amount.
Regarding the method for measuring the peeling charge amount of the polyester film, the contents described in JP-A-2003-194865 (particularly [0053] to [0067]) can also be referred to, and the contents described in the above publication are incorporated in the present specification. ..

The amount of peeling charge can be adjusted by selecting the type and amount of components such as the binder and the surfactant contained in the polyester base material and the specific coating layer. More specifically, the peel charge amount can be adjusted within the above range by selecting a material closer in the charging column for the two selected from the group consisting of the polyester substrate, the binder and the surfactant.

〔Production method〕
As a method for producing this film, for example, a method including a biaxial stretching step of biaxially stretching an unstretched polyester film having a polyester base material and a specific coating layer forming step of forming a specific coating layer containing particles. Can be mentioned.

The biaxial stretching may be simultaneous biaxial stretching in which longitudinal stretching and transverse stretching are performed at the same time, or sequential biaxial stretching in which longitudinal stretching and transverse stretching are divided into two or more stages. Examples of the form of sequential biaxial stretching include longitudinal stretching → transverse stretching, longitudinal stretching → transverse stretching → longitudinal stretching, longitudinal stretching → longitudinal stretching → transverse stretching, and transverse stretching → longitudinal stretching, and longitudinal stretching → transverse stretching. Is preferable.

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

FIG. 3 is a plan view showing an example of a stretching machine used for manufacturing a polyester film.
The stretching machine 100 shown in FIG. 3 includes a pair of

annular rails

60a and 60b, and gripping members 2a to 2l attached to each annular rail and movable along the rails. The

annular rails

60a and 60b are arranged symmetrically with respect to each other with the film 200 interposed therebetween. The stretching machine 100 can stretch the film 200 in the width direction by gripping the film 200 with the gripping members 2a to 2l and moving the gripping members 2a to 2l along the rail.

The stretching machine 100 has a region including a preheating section 10, a stretching section 20, a heat fixing section 30, a heat relaxing section 40, and a cooling section 50 in this order from the upstream side in the transport direction.
The above-mentioned region of the stretching machine 100 is divided by a windbreak curtain, and the temperature in the region can be individually adjusted by hot air or the like.

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

The stretched portion 20 is a region in which the preheated film 200 is stretched by applying tension in the direction of the arrow TD (width direction), which is a direction orthogonal to the direction of the arrow MD (longitudinal direction). As shown in FIG. 3, in the stretched portion 20, the film 200 is stretched from the width L0 to the width L1.

The heat fixing portion 30 is a region where the film 200 to which tension is applied is heated and heat-fixed while being tensioned.

The heat relaxation unit 40 is a region for heat relaxation of the tension of the heat-fixed film 200 by heating the heat-fixed film 200.
As shown in FIG. 3, in the heat relaxation unit 40, the film 200 is reduced (relaxed) from the width L1 to the width L2.

The cooling unit 50 is a region for cooling the heat-relaxed film 200. By cooling the film 200, the shape of the film 200 can be fixed.
FIG. 3 shows that the width of the film 200 carried into the cooling unit 50 is L2, and the width of the film 200 carried out from the cooling unit 50 is L3.

The annular rail 60a is attached with gripping

members

2a, 2b, 2e, 2f, 2i, and 2j that are movable along the annular rail 60a. The annular rail 60b is attached with gripping

members

2c, 2d, 2g, 2h, 2k, and 2l that are movable along the annular rail 60b.
The gripping

members

2a, 2b, 2e, 2f, 2i, and 2j grip one end of the film 200 in the direction of the arrow TD. The gripping

members

2c, 2d, 2g, 2h, 2k, and 2l grip the other end of the film 200 in the direction of the arrow TD. The gripping members 2a to 2l are generally referred to as chucks, clips and the like.
The gripping

members

2a, 2b, 2e, 2f, 2i, and 2j move counterclockwise along the annular rail 60a. The gripping

members

2c, 2d, 2g, 2h, 2k, and 2l move clockwise along the annular rail 60b.

The gripping members 2a to 2d move along the

annular rail

60a or 60b while gripping the end portion of the film 200 in the preheating portion 10, pass through the stretching portion 20, the heat fixing portion 30, and the heat relaxing portion 40, and then the cooling portion. Proceed to 50. Next, the gripping

members

2a and 2b and the gripping

members

2c and 2d are end portions on the downstream side in the direction of the arrow MD of the cooling unit 50 (for example, the gripping release point P and the grip release point Q in FIG. 3) in the order of transport direction. After separating the end portion of the film 200 at), the film further moves along the

annular rail

60a or 60b and returns to the preheating portion 10. In the above process, by moving the film 200 in the direction of the arrow MD, preheating in the preheating section 10, stretching in the stretching section 20, heat fixing in the heat fixing section 30, heat relaxation in the heat relaxing section 40, And cooling is performed by the cooling unit 50, and the film is laterally stretched.

By adjusting the moving speed of the gripping members 2a to 2l, the transport speed of the film 200 can be adjusted. Further, the gripping members 2a to 2l can independently change the moving speed.

As described above, the stretching machine 100 enables lateral stretching in the stretching portion 20 to stretch the film 200 in the direction of the arrow TD. On the other hand, the stretching machine 100 can also stretch the film 200 in the direction of the arrow MD by changing the moving speed of the gripping members 2a to 2l. That is, it is also possible to perform simultaneous biaxial stretching using the stretching machine 100.

The stretching machine 100 may further have other gripping members in addition to the gripping members 2a to 2l in order to support the film 200 (not shown).

Next, this manufacturing method will be specifically described.
The manufacturing method includes, for example, an extrusion molding step of extruding a molten resin containing a raw material polyester into a film to form an unstretched polyester film having a polyester base material, and stretching the unstretched polyester film in a transport direction. A biaxial stretching step consisting of a longitudinal stretching step of forming a uniaxially oriented polyester film and a transverse stretching step of stretching the uniaxially oriented polyester film in the width direction to form a biaxially oriented polyester film, and a biaxially oriented polyester film. The heat was relaxed by a heat fixing step of heating and heat fixing, a heat relaxation step of heating the polyester film heat-fixed by the heat fixing step at a temperature lower than that of the heat fixing step, and heat relaxation. A cooling step for cooling the polyester film, an expansion step for expanding the heat-relaxed polyester film in the width direction in the cooling step, and a polyester substrate by an in-line coating method using a composition for forming a specific coating layer containing particles. Examples thereof include a method having a specific coating layer forming step of providing a specific coating layer on one surface.

<Extrusion molding process>
The extrusion molding step is a step of extruding a molten resin containing polyester as a raw material into a film by an extrusion molding method to form an unstretched polyester film. The raw material polyester has the same meaning as the polyester described in the above item (polyester).

The extrusion molding method is a method of molding a raw material resin into a desired shape by extruding a melt of the raw material resin using, for example, an extruder.
For the molten resin containing polyester, for example, using an extruder equipped with one or more screws, the polyester described above is heated to a temperature equal to or higher than the melting point, and the screw is rotated to melt and knead. Is formed by. Polyester is melted in an extruder by heating and kneading with a screw to form a melt.

The melt is extruded from the extrusion die through a gear pump, a filter, etc. The extrusion die is also simply referred to as a "die" (see JIS B8650: 2006, a, extruder, number 134). For example, the extruded die described in JP-A-2005-297266, the extruded die described in JP-A-1-154720, and a combination thereof can also be used. The melt may be extruded in a single layer or in multiple layers.

In melt extrusion, it is preferable to replace the inside of the extruder with nitrogen from the viewpoint of suppressing thermal decomposition (for example, hydrolysis of polyester) in the extruder. Further, the extruder is preferably a twin-screw extruder because the kneading temperature can be kept low.

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

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

When a casting roll is used in the extrusion molding process, it is preferable to improve the adhesion between the casting roll and the melt. Examples of the method for improving the 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 product (unstretched polyester film) cooled using a casting roll or the like is stripped from the cooling member such as a casting roll by using a stripping member such as a stripping roll.

<Biaxial stretching process>
The biaxial stretching step is a longitudinal stretching step of stretching the unstretched polyester film in the transport direction (hereinafter, also referred to as “longitudinal stretching”) to form a uniaxially oriented polyester film, and a longitudinal stretching step of forming the uniaxially oriented polyester film in the width direction. It has a transverse stretching step of forming a biaxially oriented polyester film by stretching (hereinafter, also referred to as “lateral stretching”).

(Vertical stretching process)
In the longitudinal stretching step, it is preferable to preheat the unstretched polyester film before longitudinal stretching. By preheating the unstretched polyester film, the polyester film can be easily stretched vertically.
The preheating temperature of the unstretched polyester film is preferably (Tg-30) to (Tg + 40) ° C, more preferably (Tg-20) to (Tg + 30) ° C. Specifically, the preheating temperature is preferably 60 to 100 ° C, more preferably 65 to 80 ° C.
As a method for preheating the unstretched polyester film, for example, a method of arranging a preheating roll having a function of preheating the film on the upstream side of the vertically stretched stretch roll and preheating while transporting the unstretched polyester film can be mentioned. Be done.

Further, the stretched roll may have a function of preheating the film. The preferable range of the preheating temperature of the film by the stretch roll is the same as the preferable range of the preheating temperature of the preheating roll described above.

Longitudinal stretching can be performed, for example, by applying tension between two or more pairs of stretch rolls installed in the transport direction while transporting the unstretched polyester film in the longitudinal direction. For example, when a pair of stretched rolls A and a pair of stretched rolls B are installed on the upstream side in the transport direction, the rotation speed of the stretched rolls B is set when the unstretched polyester film is transported. By increasing the rotation speed of A, the unstretched polyester film is stretched in the longitudinal direction.

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

The draw ratio in the longitudinal stretching step is appropriately set depending on the application, but is preferably 2.0 to 5.0 times, more preferably 2.5 to 4.0 times, still more preferably 2.8 to 4.0 times. ..

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

In the longitudinal stretching step, it is preferable to heat the unstretched polyester film. This is because longitudinal stretching becomes easier by heating.
The heating temperature in the longitudinal stretching step is preferably (Tg-20) to (Tg + 50) ° C, more preferably (Tg-10) to (Tg + 40) ° C, and even more preferably (Tg) to (Tg + 30) ° C. Specifically, the heating temperature in the longitudinal stretching step is preferably 70 to 120 ° C, more preferably 80 to 110 ° C, and even more preferably 85 to 100 ° C.

Examples of the method of heating the unstretched polyester film in the longitudinal stretching step include a method of heating a roll such as a stretched roll in contact with the unstretched polyester film. Examples of the method for heating the roll include a method of providing a heater inside the roll and a method of providing a pipe inside the roll and allowing the heated fluid to flow in the pipe. In addition to the above, for example, a method of applying warm air to the unstretched polyester film, and heating the unstretched polyester film by bringing the unstretched polyester film into contact with a heat source such as a heater or passing it in the vicinity of the heat source. The method can be mentioned.

The longitudinal stretching step of longitudinally stretching the unstretched polyester film is not limited to the above method.
In the above-mentioned longitudinal stretching step, the unstretched polyester film is longitudinally stretched by utilizing the difference in the transport speeds of the two stretched rolls, but it is arranged between the two stretched rolls and is faster than those stretched rolls. A uniaxially oriented polyester film may be produced by longitudinally stretching an unstretched polyester film using one or more high-speed stretching rolls that transport the film at a transport speed.
Further, in the above-mentioned longitudinal stretching step, the film is sandwiched and conveyed by two rolls (a pair of rolls) facing each other, but the stretching rolls used in the longitudinal stretching step have the opposing rolls. It may be composed of only one roll in contact with one surface of the polyester film.

(Transverse stretching process)
The transverse stretching step is a step of transversely stretching a uniaxially oriented polyester film. The transverse stretching step is carried out, for example, in the transverse stretching portion 20 of the stretching machine 100.

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

The stretching ratio (transverse stretching ratio) in the width direction of the uniaxially oriented polyester film in the transverse stretching step is not particularly limited, but is preferably larger than the stretching ratio in the longitudinal stretching step. The stretching 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.
When the transverse stretching step is carried out in the transverse stretching portion 20 of the stretching machine 100, the transverse stretching ratio is the ratio of the film width L1 at the time of carrying out from the transverse stretching portion 20 to the film width L0 at the time of carrying in the transverse stretching portion 20 (L1). It is obtained from / L0).

The area magnification represented by the product of the stretching ratio in the longitudinal stretching step and the stretching ratio in the transverse stretching step is preferably 12.8 to 15.5 times, more preferably 13.5 to 15.2 times, and 14. It is more preferably 0 to 15.0 times. When the area magnification is at least the above lower limit value, the molecular orientation in the film width direction becomes good. Further, when the area magnification is not more than the above upper limit value, it is easy to maintain a state in which the molecular orientation is difficult to be relaxed when subjected to the 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 even more preferably (Tg) to (Tg + 60) ° C. Specifically, the heating temperature in the transverse stretching step is preferably 100 to 140 ° C, more preferably 110 to 135 ° C, and even more preferably 115 to 130 ° C.

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

<Heat fixing process>
In this production method, it is preferable to perform a heat fixing step and a heat relaxation step as a heat treatment for the polyester film laterally stretched by the transverse stretching step.
In the heat fixing step, the biaxially oriented polyester film obtained by the transverse stretching step can be heated and heat-fixed. By crystallizing the polyester by heat fixing, shrinkage of the polyester film can be suppressed.
The heat fixing step is carried out, for example, in the heat fixing portion 30 of the stretching machine 100.

The surface temperature (heat fixing temperature) of the polyester film in the heat fixing step is not particularly limited, but is preferably less than 240 ° C., more preferably 235 ° C. or lower, still more preferably 230 ° C. or lower. The lower limit is not particularly limited, but is preferably 190 ° C. or higher, more preferably 200 ° C. or higher, and even more preferably 210 ° C. or higher.
In the heat fixing step, the heat treatment is performed while controlling the maximum temperature reached on the surface of the polyester film to be the above heat fixing temperature.

In the heat fixing step, the variation in the surface temperature in the film width direction is preferably 0.5 to 10.0 ° C, more preferably 0.5 to 7.0 ° C, still more preferably 0.5 to 5.0 ° C. 0.5 to 4.0 ° C. is particularly preferable. By controlling the variation in the surface temperature in the film width direction within the above range, the variation in the crystallinity in the width direction can be suppressed.

Examples of the heating method include a method of applying hot air to the film and a method of radiant heating of the film. Examples of the device used in the method of radiant heating include an infrared heater.

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

<Heat relaxation process>
In the heat relaxation step, it is preferable to heat the polyester film heat-fixed by the heat-fixing step at a temperature lower than that of the heat-fixing step to heat-relax. Residual strain of the polyester film can be alleviated by heat relaxation.
The heat relaxation step is carried out, for example, in the heat relaxation unit 40 of the stretching machine 100.

The surface temperature (heat relaxation temperature) of the polyester film in the heat relaxation step is preferably 5 ° C. or higher lower than the heat fixation temperature, more preferably 15 ° C. or higher, further preferably 25 ° C. or higher, and 30 ° C. or higher. Low temperatures are particularly preferred. That is, the heat relaxation temperature is preferably 235 ° C. or lower, more preferably 225 ° C. or lower, further preferably 210 ° C. or lower, and particularly preferably 200 ° C. or lower.
The lower limit of the heat relaxation temperature is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, and even more preferably 120 ° C. or higher.
In the heat relaxation step, the heat treatment is performed while controlling the maximum temperature reached on the surface of the polyester film to be the above heat relaxation temperature.

<Cooling process>
The production method preferably includes a cooling step of cooling the heat-relaxed polyester film. The cooling step and the expansion step described later are carried out, for example, in the cooling unit 50 of the stretching machine 100.

Examples of the method for cooling the polyester film in the cooling step include a method of blowing air (preferably cold air) on the film and a method of bringing the film into contact with a temperature-adjustable member (for example, a temperature control roll).

The cooling rate of the polyester film in the cooling step is not particularly limited, but the thickness unevenness of the release layer laminated on the biaxially oriented film is reduced, and the coatability of the release layer is more excellent. Less than / min is preferred, 2000-3500 ° C / min is more preferred, more than 2200 ° C / min and less than 3000 ° C / min is even more preferred, and 2300-2800 ° C / min is particularly preferred.

The cooling rate of the polyester film in the cooling step can be measured using a non-contact thermometer. For example, when the cooling step is carried out in the cooling unit 50 of the stretching machine 100, the surface temperature of the film 200 carried from the heat relaxation unit 40 to the cooling unit 50 and the surface temperature of the film 200 carried out from the cooling unit 50 Is measured to obtain the temperature difference ΔT (° C.) between the two. The cooling rate is obtained by dividing the obtained temperature difference ΔT (° C.) by the residence time ta of the film 200 in the cooling unit 50.
The cooling speed of the polyester film can be adjusted by the operating conditions of the cooling device and the transport speed of the film.

It is preferable that the above-mentioned heat fixing step, heat relaxation step and cooling step in this manufacturing method are continuously carried out in this order. This is because the load (heat history) due to repeated heating and cooling of the polyester film can be reduced, the strain inherent in the film can be reduced, and the occurrence of streak defects can be suppressed.

<Expansion process>
In the cooling step, it is also preferable to have a step of expanding the heat-relaxed polyester film in the width direction.
"Expanding the polyester film in the width direction" in the cooling step means the film width at the end of the cooling step (L2 in FIG. 3) rather than the film width of the polyester film at the start of the cooling step (L2 in FIG. 3). It means applying tension in the width direction to the polyester film during the cooling step so that L3) becomes wider.

In the expansion step, the method of expanding the polyester film in the width direction is not particularly limited. For example, when a biaxially oriented polyester film is manufactured using the above-mentioned stretching machine 100, the end point of the cooling unit 50 (grip release point P and gripping release point P) is more than the distance between the

annular rails

60a and 60b at the start point of the cooling unit 50. By increasing the distance between the

annular rails

60a and 60b at the release point Q), the film 200 gripped by each gripping member can be expanded in the width direction.
The expansion step may be carried out continuously or intermittently from the start to the end of the cooling step as long as the film width is expanded before and after the cooling step, or may be carried out only at one time during the cooling step.

The expansion ratio of the polyester film in the width direction by the expansion step, that is, the ratio of the film width to the film width before the start of the cooling step at the end of the cooling step is preferably 0% or more, more preferably 0.001% or more. 0.01% or more is more preferable.
The upper limit of the expansion rate is not particularly limited, but is preferably 1.3% or less, more preferably 1.2% or less, still more preferably 1.0% or less. When a strong tension is applied in the transport direction in order to transport the film at high speed by setting the expansion rate of the film width to the above upper limit value or less (for example, when the tension in the transport direction is 100 N / m or more). ), It is possible to suppress the disorder of the cut surface in the trimming step described later, and further, the breakage of the film due to the cutting disorder.

<Specific coating layer forming process>
The present production method preferably includes a specific coating layer forming step of in-line coating using a composition for forming a specific coating layer containing particles (hereinafter, also referred to as “composition A”). The specific coating layer formed on one surface of the polyester base material by the specific coating layer forming step has the same meaning as the layer described in detail in the above item <Specific coating layer>.
The specific coating layer may be formed at any stage of the present production method. For example, a method of forming a coating film on one surface of an unstretched or stretched polyester substrate and drying it if necessary. Can be mentioned.

First, a method of forming a specific coating layer using the composition A will be described.
The composition A can be prepared by mixing the particles contained in the specific coating layer, the binder and additives added as necessary, and the solvent.
Examples of the solvent include water, ethanol, toluene, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether. Of these, water is preferable from the viewpoint of environment, safety and economy.

The composition A may contain one kind of solvent alone, or may contain two or more kinds of solvents.
The content of the solvent is preferably 80 to 99% by mass, more preferably 90 to 98% by mass, based on the total mass of the composition A.
That is, in the composition A, the total content of the components (solid content) other than the solvent is preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass, based on the total mass of the composition A.

The particles, binders and additives contained in the composition A, including their preferred embodiments, are as described in detail in the above item <Specific coating layer>.
For each component other than the solvent in the composition A, the content of each component with respect to the total mass of the solid content of the composition A is the same as the preferable content of each component with respect to the total mass of the above-mentioned specific coating layer. , It is preferable to adjust the content of each component in the coating liquid.

The method of applying the composition A is not particularly 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.

In the specific coating layer forming step, an in-line coating method in which a coating liquid is applied to one surface of the polyester substrate while transporting the polyester substrate is applied. By applying the in-line coating method, the heating time of the polyester base material in the manufacturing process is shortened and the heat history is not applied, so that the streak defect region can be reduced, and as a result, the coatability of the release layer can be further improved.
In the in-line coating method, the polyester base material to which the composition A is applied may be an unstretched polyester base material or a uniaxially oriented polyester base material, but the uniaxially oriented polyester base material may be used. It is preferably a base material. That is, it is preferable to perform the specific coating layer forming step by the in-line coating method between the longitudinal stretching step and the transverse stretching step. This is because the adhesion between the polyester base material and the specific coating layer can be improved by simultaneously laterally stretching the uniaxially oriented polyester base material and the specific coating layer.

The present manufacturing method may include a winding step of obtaining a roll-shaped biaxially oriented polyester film by winding the biaxially oriented polyester film obtained through the above steps.
Further, the present manufacturing method further includes a trimming step of continuously cutting the polyester film along the transport direction and cutting off at least one end in the width direction of the polyester film before carrying out the winding step. You may.

The transport speed of the polyester film in each step other than the longitudinal stretching step of this production method is not particularly limited, but the transverse stretching step, the heat fixing step, the heat relaxation step, the cooling step and the expansion step are performed by using the stretching machine 100. In this case, 50 to 200 m / min is preferable, and 80 to 150 m / min is more preferable in terms of productivity and quality. The transport speed of the polyester film in the longitudinal stretching step is as described above.

Further, in each step other than the longitudinal stretching step, the tension applied to the polyester film in the transport direction is not particularly limited, but the transverse stretching step, the heat fixing step, the heat relaxation step, the cooling step and the expansion step are performed on the stretching machine. When 100 is used, the tension applied to the polyester film in the transport direction can be adjusted by the stretching conditions.
Further, the tension applied to the polyester film in the transport direction after the cooling step is applied until the polyester film is taken up in the above winding step is preferably 3 to 30 N / m, more preferably 5 to 20 N / m.

In the method for producing the present film specifically described above, a combination of two or more preferred embodiments is a more preferred embodiment.
Among them, the manufacturing method having two or more combinations selected from the group consisting of the following manufacturing conditions is for adjusting the area ratio of the streaky defect region of the biaxially oriented film to be manufactured and the expansion rate in the width direction. It can be said that this is a preferable embodiment in that it serves as an index of.
-The stretching ratio in the transverse stretching step is 3.0 to 6.0 times, preferably 3.5 to 5.0 times, and more preferably 3.5 to 4.5 times.
The heat fixing temperature in the heat fixing step is less than 240 ° C., preferably 190 ° C. or higher and lower than 240 ° C., more preferably 200 to 230 ° C., still more preferably 210 to 230 ° C.
The heat relaxation temperature in the heat relaxation step is lower than the heat fixing temperature, preferably 5 ° C. or higher, more preferably 15 ° C. or higher, further preferably 25 ° C. or higher, and particularly preferably 30 ° C. or higher.
The cooling rate of the polyester film in the cooling step is more than 2000 ° C./min and less than 4000 ° C./min, preferably 2000 to 3500 ° C./min, more preferably more than 2200 ° C./min and less than 3000 ° C./min, still more preferably 2300 to. It should be 2800 ° C / min.
The expansion ratio of the polyester film in the width direction in the expansion step is 0 to 1.3%, preferably 0.001 to 1.2%, and more preferably 0.01 to 1.0%. ..

The area ratio of the streaky defect region and the expansion rate in the width direction of the biaxially oriented film differ depending on the materials constituting the polyester base material and the specific coating layer, and the manufacturing conditions other than the above. It is not always possible to produce a polyester film having an area ratio of a desired streak defect region and / or an expansion rate in the width direction by a production method having two or more combinations selected from the group consisting of production conditions. .. Further, the method for producing a polyester film having a desired area ratio of streaky defect regions and / or an expansion rate in the width direction is not limited to a method having two or more of the above production conditions.

[Release film]
The above polyester film can be used for producing a release film. More specifically, by providing the release layer on the first main surface of the polyester film, a release film having the polyester film and the release layer arranged on the first main surface of the polyester film can be manufactured.

The release layer contains at least a resin as a release agent. The resin contained in the release layer is not particularly limited, and examples thereof include silicone resin, fluororesin, alkyd resin, acrylic resin, various waxes, and aliphatic olefins, and silicone resin is preferable.

The silicone resin means a resin having a silicone structure in the molecule. Examples of the silicone resin include curable silicone resins, silicone graft resins, modified silicone resins such as alkyl-modified, and reactive curable silicone resins are preferable.
Examples of the reactive curable silicone resin include an addition reaction type silicone resin, a condensation reaction type silicone resin, and an ultraviolet ray or electron beam curable type silicone resin. Of these, an addition reaction type silicone resin having low temperature curability or an ultraviolet or electron beam curable silicone resin is preferable because the release layer can be formed at a low temperature.

Examples of the addition reaction type silicone resin include a resin obtained by reacting polydimethylsiloxane having a vinyl group introduced at the terminal or side chain with hydrodienesiloxane using a platinum catalyst and curing the resin.
The silicone resin of the condensation reaction system is, for example, three-dimensionally formed by subjecting a polydimethylsiloxane having an OH group at the terminal and a polydimethylsiloxane having an H group at the terminal to a condensation reaction using an organic tin catalyst. Examples thereof include a resin having a crosslinked structure.
UV-curable silicone resins include those that utilize the same radical reaction as silicone rubber cross-linking, those that are photo-cured by introducing unsaturated groups, and those that decompose onium salts with ultraviolet rays or electron beams to generate strong acids, and epoxys. Examples thereof include those in which the group is cleaved and crosslinked, and those in which the group is crosslinked by the addition reaction of thiol to vinylsiloxane. More specifically, acrylate-modified polydimethylsiloxane, glycidoxy-modified polydimethylsiloxane, and the like can be mentioned.

The release layer may contain an additive in addition to the above resin. As the additive, a light peeling additive, a heavy peeling additive, an adhesion improving agent, an additive such as an antistatic agent, and the like for adjusting the peeling force may be added.
The resin contained in the release layer may be used alone or in combination of two or more.
The content of the resin in the release layer is preferably 50 to 99% by mass, more preferably 60 to 98% by mass, based on the total mass of the release layer. The remainder of the release layer other than the resin may be the above-mentioned additive and / or a residue such as a solvent and a catalyst contained in the release layer forming coating liquid used for forming the release layer.

The thickness of the peeling layer may be set according to the purpose of use and is not particularly limited, but 0.005 to 2.0 μm is preferable and 0 is preferable in that the peeling performance and the smoothness of the peeling layer surface are well-balanced. More preferably, it is 0.05 to 1.0 μm.

(Surface free energy of peeled surface)
From the viewpoint of antistatic when the release film is wound, the surface free energy of the surface (also referred to as the release surface) of the release layer opposite to the polyester substrate side ^{is preferably 30 mJ / m 2} or less. more preferably ~ is 30 mJ / ^{m 2,} further preferably 10 ~ 30mJ / ^{m 2.}
Further, it is preferable that the difference between the surface free energy of the peeling surface of the peeling layer and the surface free energy of the second main surface of the polyester film is wide because the film is less likely to be charged. Difference between the surface free energy of the second main surface of the surface free energy and the polyester film of the release surface of the release layer is preferably 1 ~ 50 mJ / ^{m 2,} more preferably ^{1 ~ 40mJ / m 2, 1} ~ 35mJ / m ² is more preferable, 5 to 30 mJ / m ² is particularly preferable, and 10 to 25 mJ / m ² is most preferable.
The surface free energy of the peeling surface of the peeling layer can be adjusted by the type of resin forming the peeling layer and the additive.

(Maximum protrusion height Sp of peeled surface, surface average roughness Sa)
The peeled surface is preferably as smooth as possible in terms of smoothing the functional layer such as the ceramic green sheet formed on the peeled layer. Specifically, the maximum protrusion height Sp of the peeled surface is preferably 1 to 60 nm, and more preferably 1 to 40 nm. The surface average roughness Sa of the peeled surface is preferably 0 to 10 nm, more preferably 0 to 5 nm.
The maximum protrusion height Sp and surface average roughness Sa of the peeled surface can be adjusted by not putting particles in the peeled layer when providing the peeled layer and by selecting the resin and the additive forming the peeled layer. ..
The maximum protrusion height Sp and the surface average roughness Sa of the peeled surface can be measured according to the above-mentioned measuring method of the maximum protrusion height Sp and the surface average roughness Sa of the second main surface.

The method of providing the release layer on the first main surface of the film is not particularly limited, but a release layer forming coating liquid obtained by dissolving or dispersing the release agent in a solvent is applied to the first main surface of the film. Examples thereof include a method of removing the solvent by drying and, if necessary, heating or irradiating with light to form a cured product.

The method of applying the coating liquid for forming the release layer is not particularly 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.
The heating temperature for forming the release layer is preferably 180 ° C. or lower, more preferably 150 ° C. or lower, and even more preferably 120 ° C. or lower. The lower limit is not particularly limited and may be 60 ° C. or higher.

The coating liquid for forming a release layer may contain the above-mentioned resin and solvent, and may contain the above-mentioned additive and / or the above-mentioned catalyst used for curing the resin, if necessary. The coating liquid for forming a release layer can be prepared by mixing these components.
Examples of the solvent include water and organic solvents such as toluene, methyl ethyl ketone, ethanol, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether, and organic solvents are preferable.

The coating liquid for forming a release layer may contain one type of solvent alone, or may contain two or more types of solvents.
The content of the solvent is preferably 80 to 99.5% by mass, more preferably 90 to 99% by mass, based on the total mass of the coating liquid for forming the release layer.
That is, the total content of the components (solid content) other than the solvent in the coating liquid for forming the release layer is preferably 0.5 to 20% by mass, preferably 1 to 10% by mass, based on the total mass of the coating liquid for forming the release layer. More preferably by mass.

Further, in order to improve the adhesion between the film and the release layer, the first main surface of the film is subjected to pretreatment such as anchor coating, corona treatment, and plasma treatment before the release layer is provided. May be good.

<Use>
The release film provided with this film has excellent transportability, can suppress the formation of transfer marks during roll storage, and can suppress uneven thickness and / or coating defects of the release layer. Therefore, it is a release film for manufacturing a ceramic green sheet. It is preferable to use it as a (carrier film). The ceramic green sheet manufactured by using the above-mentioned release film can be suitably used for manufacturing a ceramic capacitor, which is required to have multiple layers of internal electrodes due to miniaturization and large capacity.

The method for producing a ceramic green sheet using the release film is not particularly limited, and a known method can be used. Examples of the method for producing the ceramic green sheet include a method in which the prepared ceramic slurry is applied to the surface of the release layer of the release film and the solvent contained in the ceramic slurry is dried and removed.
The method for applying the ceramic slurry is not particularly limited, and for example, a known method of applying a ceramic slurry in which a ceramic powder and a binder are dispersed in a solvent by a reverse roll method and removing the solvent by heating and drying is known. The method can be applied. The binder agent is not particularly limited, and examples thereof include polyvinyl butyral and the like. Further, the solvent is not particularly limited, and examples thereof include ethanol and toluene.

The release film provided with this film includes a protective film for dry film resist, a sheet forming film such as a decorative layer and a resin sheet, a release film for a semiconductor manufacturing process, a release film for a polarizing plate manufacturing process, and a label. It can be used as a separator for adhesive films for medical and office supplies.

The present disclosure will be described in more detail with reference to examples below. The materials, amounts, ratios, treatment contents, and treatment procedures shown in the following examples may be appropriately changed as long as they do not deviate from the gist of the present disclosure. Therefore, the scope of the present disclosure is not limited to the specific examples shown below. Unless otherwise specified, "parts" and "%" are based on mass.

Hereinafter, in the present embodiment, the term "film" includes both a polyester base material alone and an embodiment having a polyester base material and a specific coating layer, and an unstretched film, a uniaxially oriented film, and the like. And all of the biaxially oriented films shall be included.
Further, in each step of this embodiment, a non-contact thermometer (AD-5616 (product name), manufactured by A & D Co., Ltd., emissivity 0.95) is used to measure the temperature of the central portion in the width direction of the film five times. Then, the arithmetic mean value of the obtained measured values was used as the measured value of the surface temperature of the film.

[Example 1]
<Extrusion molding process>
Pellets of polyethylene terephthalate were produced using a titanium compound (citrate chelated titanium complex, VERTEC AC-420, manufactured by Johnson Matthey) described in Japanese Patent No. 5575671 as a polymerization catalyst. The obtained pellets were dried to a water content of 50 ppm or less, charged into a hopper of a uniaxial kneading extruder having a diameter of 30 mm, and then melted and extruded at 280 ° C. The melt was passed through a filter (pore diameter 3 μm) and then extruded from the die into a cooling drum at 25 ° C. to obtain an unstretched film made of polyethylene terephthalate. The extruded melt was brought into close contact with the cooling drum by the electrostatic application method.
The melting point (Tm) of polyethylene terephthalate constituting the unstretched film was 258 ° C., and the glass transition temperature (Tg) was 80 ° C.

<Vertical stretching process>
The unstretched film was subjected to a longitudinal stretching step by the following method.
A uniaxially oriented film was produced by passing a preheated unstretched film between two pairs of rolls having different peripheral speeds and stretching the film in the vertical direction (conveyance direction) under the following conditions.
(Vertical stretching conditions)
Preheating temperature: 75 ° C
Stretching temperature: 90 ° C
Stretching ratio: 3.4 times Stretching speed: 1300% / sec

<Specific coating layer forming process>
The following composition A (composition for forming a specific coating layer) is applied to one side of a vertically stretched uniaxially oriented film (polyester base material) with a bar coater, and the formed coating film is blown with hot air at 100 ° C. It was dried to form a specific coating layer. At this time, the coating amount of the composition A was adjusted so that the thickness of the formed specific coating layer was 60 nm.

(Composition A)
Composition A was prepared by mixing each of the components shown below. Filtration treatment of the prepared composition A using a filter having a pore size of 6 μm (F20, manufactured by Mahle Filter Systems Co., Ltd.) and membrane degassing (2x6 radial flow superphobic, manufactured by Polypore Co., Ltd.). After that, the obtained composition A was applied to the surface of the uniaxially oriented film.
-Acid-modified polyolefin (Zyxen (registered trademark) NC, manufactured by Sumitomo Seika Co., Ltd., aqueous dispersion prepared by adding water to a solid content of 25% by mass): 157 parts-Anionic hydrocarbon-based surfactant (rapizol (rapizol) Registered trademark) A-90, di-2-ethylhexyl sulfosuccinate, manufactured by Nichiyu Co., Ltd., solid content 1% by mass water diluted solution): 56 parts / particles (Snowtex (registered trademark) ZL, Nissan Chemical Co., Ltd.) Made, colloidal silica, solid content 40% by mass aqueous dispersion): 11 parts, water: 776 parts

<Transverse stretching process>
The film subjected to the longitudinal stretching step and the specific coating layer forming step was stretched in the width direction using a tenter under the following conditions to prepare a biaxially oriented film.
(Transverse stretching conditions)
Preheating temperature: 100 ° C
Stretching temperature: 120 ° C
Stretching ratio: 4.2 times Stretching speed: 50% / sec

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

<Heat relaxation process>
Next, the heat-fixed film was heated under the following conditions to perform a heat relaxation step of relaxing the tension of the film. Further, in the heat relaxation step, the film width was reduced as compared with the end of the heat fixing step by narrowing the distance (tenter width) between the gripping members of the tenter that grips both ends of the film. The following heat relaxation rate Lr was obtained from the film width L2 at the end of the heat relaxation step with respect to the film width L1 at the start of the heat relaxation step by the formula Lr = (L1-L2) / L1 × 100.
(Heat relaxation conditions)
Heat relaxation temperature: 190 ° C
Heat relaxation rate Lr: 4%

<Cooling process and expansion process>
A cooling step of cooling the heat-relaxed film under the following conditions was performed. Further, in the cooling step, an expansion step was carried out in which the film width was expanded as compared with the time when the heat relaxation step was completed by widening the tenter width.
The following cooling rates are the film surface temperature measured at the time of carrying into the cooling unit 50 and the cooling unit 50, with the residence time from the time the film is carried into the cooling unit 50 of the stretching machine 100 to being carried out as the cooling time ta. It was obtained by dividing the temperature difference ΔT (° C.) from the film surface temperature measured at the time of carrying out by the cooling time ta.
Further, the following expansion ratio ΔL was obtained from the film width L3 at the end of the cooling step with respect to the film width L2 of the polyester film at the start of the cooling step by the formula ΔL = (L3-L2) / L2 × 100.
(Cooling conditions)
Cooling rate: 2500 ° C / min (expansion condition)
Expansion rate ΔL: 0.6%

<Rolling process>
With respect to the film cooled by the cooling step, the film was continuously cut along the transport direction at a position 20 cm from both ends in the width direction of the film using a trimming device, and both ends of the film were trimmed. Next, an extrusion process (knurling) was performed on a region from both ends of the film to 10 mm in the width direction, and then the film was wound up at a tension of 40 kg / m.
A biaxially oriented film was produced by the above method. The thickness of the obtained biaxially oriented film was 31 μm, the width was 1.5 m, and the winding length was 7000 m. Moreover, when the thickness of the specific coating layer of the obtained biaxially oriented film was measured using SEM, the thickness of the specific coating layer was 60 nm. Specifically, a biaxially oriented film is cut using a microtome to prepare a sample having a cross section along the thickness direction of the biaxially oriented film, and the obtained sample is etched with Ar ions and subjected to Pt. After the vapor deposition treatment of the above, the cross section of the sample was observed using SEM (“S-4800” manufactured by Hitachi High-Tech Co., Ltd.). From the obtained observation image, the thickness of the specific coating layer was measured at five points, and the measured values were arithmetically averaged to obtain the thickness of the specific coating layer.

[Example 2]
In the preparation of composition A, "Snowtex MP2040" (manufactured by Nissan Chemical Industries, Ltd., colloidal silica, solid content 40% by mass aqueous dispersion) was used instead of "Snowtex ZL" as particles, and A biaxially oriented film was produced according to the method described in Example 1 except that the thickness of the specific coating layer was adjusted to 160 nm.

[Example 3]
A biaxially oriented film was produced according to the method described in Example 1 except that the thickness of the specific coating layer was adjusted to 50 nm.

[Example 4]
A biaxially oriented film was prepared according to the method described in Example 1 except that the amount of particles (“Snowtex ZL”) added was changed from 11 parts to 22 parts in the preparation of the composition A.

[Example 5]
A biaxially oriented film was prepared according to the method described in Example 1 except that the amount of particles (“Snowtex ZL”) added was changed from 11 parts to 1.1 parts in the preparation of the composition A.

[Example 6]
In the preparation of the composition A, "Snowtex XL" (manufactured by Nissan Chemical Industries, Ltd., colloidal silica, solid content 40% by mass aqueous dispersion) was used instead of "Snowtex ZL" as the particles. A biaxially oriented film was produced according to the method described in Example 1 except that the addition amount was changed from 11 parts to 3 parts and the thickness of the specific coating layer was adjusted to 40 nm.

[Example 7]
A biaxially oriented film was prepared according to the method described in Example 1 except that 40 parts of the following additive (crosslinking agent) was further added to the composition A.
-A dispersion prepared by adding water to a cross-linking agent (isocyanate compound, "Duranate (registered trademark) WM44L70" manufactured by Asahi Kasei Chemicals Co., Ltd. (solid content 70% by mass) so that the solid content concentration becomes 10% by mass. )

[Example 8]
A biaxially oriented film was prepared according to the method described in Example 1 except that the amount of the anionic hydrocarbon-based surfactant added was changed from 56 parts to 112 parts in the preparation of the composition A.

[Example 9]
In the preparation of the composition A, instead of the anionic hydrocarbon-based surfactant, a silicone-based surfactant (BYK-346, solid content 52% by mass, manufactured by BYK) was added to water so as to have a solid content of 1% by mass. A biaxially oriented film was prepared according to the method described in Example 1 except that 56 parts of the obtained diluted solution was used.

[Example 10]
In the preparation of the composition A, instead of the anionic hydrocarbon-based surfactant, a fluorine-based surfactant (Surflon S-211, solid content 50% by mass, manufactured by AGC Seimi Chemical Co., Ltd.) was used as a solid content 1% by mass. A biaxially oriented film was prepared according to the method described in Example 1 except that 56 parts of the obtained diluted solution was used.

[Examples 11 to 13 and 23]
In the preparation of the composition A, instead of "Zyxen NC" as the resin, "Zyxen L" (manufactured by Sumitomo Seika Co., Ltd., acid-modified polyolefin, solid content 25% by mass aqueous dispersion) (Example 11), ""ZyxenA" (manufactured by Sumitomo Seika Co., Ltd., acid-modified polyolefin, water dispersion with a solid content of 25% by mass) (Example 12) and "Chemipal S120" (manufactured by Mitsui Chemicals Co., Ltd., acid-modified polyolefin, solid) 25% by mass water dispersion) (Example 13), acrylic resin (methyl methacrylate, styrene, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate and acrylic acid polymerized at a mass ratio of 59: 8: 26: 5: 2. Biaxially oriented film according to the method described in Example 1 except that the water dispersion of the polyolefin, the solid content concentration of 25% by mass, and the acid value of 16 mgKOH / g) (Example 23) were used. Was produced.

[Examples 14 to 22]
2 An axial alignment film was prepared.

[Example 24]
In the preparation of composition A, instead of "Zyxen NC" as a resin, "Takelac W605" (manufactured by Mitsui Chemicals, Inc., polyurethane, solid content 30% by mass aqueous dispersion) was used as a binder for the total mass of composition A. A biaxially oriented film was prepared according to the method described in Example 1, except that the films used had the same content.

[Example 25]
In the preparation of the composition A, instead of the resin "Zyxen NC", "Hydran AP-40N" (manufactured by DIC Corporation, polyurethane, solid content 35% by mass aqueous dispersion) was used with respect to the total mass of the composition A. A biaxially oriented film was prepared according to the method described in Example 1 except that the binders were used in the same amount.

[Example 26]
According to the method described in Example 25, except that 5 parts of a fluorine-based surfactant (Futergent 215M, manufactured by Neos Co., Ltd., diluted with water having a solid content of 1% by mass) was added in the preparation of the composition A. A biaxially oriented film was produced.

[Example 27]
Except for the addition of 20 parts of a water-diluted solution (solid content 1% by mass) of a fluorine-based surfactant (Surflon S-211, solid content 50% by mass, manufactured by AGC Seimi Chemical Co., Ltd.) in the preparation of composition A. Made a biaxially oriented film according to the method described in Example 25.

[Comparative Example 1]
In the preparation of the composition A, "Snowtex MP2040" was used instead of "Snowtex ZL" as the particles, the thickness of the specific coating layer was adjusted to 100 nm, and the heat in the heat fixing step was used. A biaxially oriented film was produced according to the method described in Example 1 except that the fixed temperature, the cooling rate in the cooling step, and the expansion rate in the expansion step were controlled to be the values shown in Table 1 described later. did.

[Comparative Example 2]
In the preparation of the composition A, an aqueous dispersion of an acrylic resin (methyl methacrylate, 2-hydroxyethyl methacrylate and methacrylic acid) is polymerized at a mass ratio of 28:48:24 instead of "Zyxen NC" as the resin. An aqueous dispersion obtained by neutralizing the polymer) (solid content 25% by mass, acid value 157 mgKOH / g) was used, and the heat fixing temperature in the heat fixing step and the cooling rate in the cooling step are described later in Table 1 A biaxially oriented film was produced according to the method described in Example 1, except that the values were controlled to be as described in 1.

[Comparative Example 3]
In the preparation of the composition A, "Snowtex MP2040" is used instead of "Snowtex ZL" as the particles, and "Simac US-480" (Toa Synthetic Co., Ltd.) is used instead of "Zyxen NC" as the resin. Made of silicone modified acrylic resin, solid content 25% by mass), the thickness of the specific coating layer was adjusted to 100 nm, the heat fixing temperature in the heat fixing process, the cooling rate in the cooling process, A biaxially oriented film was produced according to the method described in Example 1 except that the expansion rate in the expansion step was controlled to be the numerical value shown in Table 1 described later.

[Measurement of physical properties]
The following physical properties were measured for each of the biaxially oriented films of Examples 1 to 27 and Comparative Examples 1 to 3. The measurement results are shown in Table 1.

<Maximum protrusion height Sp, surface average roughness Sa>
The maximum protrusion height Sp and the surface average roughness Sa of the second main surface of the specific coating layer of the biaxially oriented film were measured by the following methods.
The surface of the manufactured biaxially oriented film on the specific coating layer side is measured using an optical interferometer (Vertscan 3300G Lite, manufactured by Hitachi High-Tech Co., Ltd.) under the following conditions, and then the built-in data analysis software ( By analysis by VS-Measure5), the maximum protrusion height Sp and the surface average roughness Sa of the second main surface of the specific coating layer were obtained.
In the measurement of the maximum protrusion height Sp, the maximum value of the measured value obtained by 5 measurements with different measurement positions is adopted, and in the measurement of the surface average roughness Sa, it is obtained by 5 measurements with different measurement positions. The average value of the measured values to be measured was adopted.
(Measurement condition)
-Measurement mode: WAVE mode-Objective lens: 50x-Measurement area: 186 μm x 155 μm
In the same manner, the maximum protrusion height Sp and the surface average roughness Sa of the first main surface of the biaxially oriented film were measured. In each example, Sp was 20 nm and Sa was 3 nm.

<Surface free energy>
The surface free energy of the second main surface of the specific coating layer of the biaxially oriented film was measured by the following method.
Using a contact angle meter (DROPMASTER-501 manufactured by Kyowa Surface Chemistry Co., Ltd.), droplets are dropped on the surface of the manufactured biaxially oriented film on the specific coating layer side under the condition of 25 ° C., and the droplets are surfaced. The contact angle was measured 1 second after adhering to. Using 2 μL of purified water, 1 μL of methylene iodide and 1 μL of ethylene glycol as droplets, the surface free energy was calculated by the method of Kitazaki and Hata from each measured contact angle.
The surface free energy of the first main surface of the biaxially oriented film was measured by the same method. In each example, it was 59.7 mJ / m ² .

<Thickness variation>
A sample having a length of 10 m in the longitudinal direction was taken from the produced biaxially oriented film. The thickness of this sample was measured over 10 m along the longitudinal direction using a continuous stylus type film thickness meter (TOF-6R001, manufactured by Yamabun Co., Ltd.). This measurement was performed at 5 locations with different positions in the width direction. From the obtained measured values, the value obtained by dividing the difference between the maximum value and the minimum value by the arithmetic mean value of all the measured values ((maximum thickness-minimum thickness) / average thickness) is used as the thickness variation. Calculated.

<Film density>
The density (g / cm ³ ) of the biaxially oriented film was measured using an electronic hydrometer (product name "SD-200L", manufactured by Alpha Mirage Co., Ltd.).

<Streak defect area>
The biaxially oriented film was heat-treated at 90 ° C. for 20 seconds while being conveyed at a transfer speed of 30 m / min and a tension of 100 N / m in the transfer direction using a heat transfer device. The heating temperature in the heat treatment refers to the surface temperature of the film. The heating time in the heat treatment was calculated from the time when the surface temperature of the film reached the target temperature (90 ° C.). The heat-treated biaxially oriented film was placed on a black flat plate, and then a fluorescent lamp installed on the ceiling of the room [Lupica Ace manufactured by Mitsubishi Electric Corporation (color temperature: 5000K, average color rendering index (Ra): 84). )] The biaxially oriented film was visually observed from an angle while changing the viewpoint so that the light was reflected. A region of 1 m × 1 m was visually observed, and a region where the reflected image of the fluorescent lamp was undulating on the surface of the biaxially oriented film was defined as a streak defect region. Next, the ratio (area ratio) of the total area of the observed streaky defect regions to the total area of the observation region of the biaxially oriented film is calculated by the method described above (see the item of "streaky defect region" above). did.

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

<Average particle size, particle density D>
The average particle diameter and the particle density D of the particles contained in the specific coating layer were measured by the following methods.
Using a scanning electron microscope (SEM, manufactured by Hitachi High-Tech, S4700), the surface of the biaxially oriented film on the specific coating layer side was observed at a magnification of 20000 times to obtain an observation image of 10 fields of view. For particles that can be identified as protrusions from the obtained image data, the area of each particle is measured using image software and converted into the diameter of a circle having the same area (diameter equivalent to the area circle). After obtaining the diameter, the arithmetic average value of all particles was calculated.
Further, the value obtained by dividing the number of particles that can be identified from the image data of each visual field by the visual field area was calculated as the particle density D (unit: individual / μm ² ).

<Measurement of peeling charge>
The amount of peeling charge of each biaxially oriented film manufactured rises along the vertical direction while holding the table on which the reference sample (first main surface is on the upper surface) and the measurement sample (second main surface is on the lower side). A measuring device provided with a head capable of repeatedly crimping and peeling the measurement sample against the upper surface of the reference sample by lowering and lowering, and an electrometer connected to this head and capable of measuring the charge amount of the measurement sample. Used and measured.
First, each of the manufactured biaxially oriented films is cut into a circle with a diameter of 1.5 cm to prepare a sample for measuring the amount of peeling charge, and then cut into a rectangle with a size of 13 cm × 4 cm as a reference. Samples were prepared and each sample was left for 2 hours or more in an environment of a temperature of 23 ° C. and a relative humidity (RH) of 20%.
The obtained reference sample was placed on the table of the measuring device, and the measurement sample was attached to the head. At this time, in the reference sample to be placed on the table so that the first main surface of the reference sample and the second main surface of the measurement sample face each other, the first main surface is on the upper surface side and the second main surface of the measurement sample is mounted on the head. The main surface was arranged on the lower surface side, respectively. After static elimination of the measurement sample, the head was raised or lowered, and crimping and peeling of the measurement sample against the reference sample were repeated 5 times (contact pressure was 566 g / cm ² , contact time was 2 seconds). The charge amount of the measurement sample was measured after each of the first to fifth peeling, and the average value of the measured values was calculated. While changing the measurement sample, the position where the measurement sample came into contact with the reference sample was changed for each measurement sample, and measurement was performed with a total of four samples, and the average of all was obtained as the peel charge amount.

[evaluation]
A release film was prepared using each of the biaxially oriented films of Examples 1 to 27 and Comparative Examples 1 to 3, and the obtained release film was evaluated as follows. The evaluation results are shown in Table 1.

[Preparation of release film]
The biaxially oriented film produced in each Example and Comparative Example was sent out, and a coating liquid consisting of the following formulation A was applied to the surface of the biaxially oriented polyester film opposite to the particle-containing layer by a slot die method. The coating film was dried using a hot air dryer at 120 ° C. and wound to prepare a roll-shaped release film (biaxially oriented film provided with a release layer). The thickness of the peeled layer after drying was 0.5 μm.

[Transfer mark evaluation 1]
The obtained release film cut into 3.5 cm squares was stacked 10 sheets in a direction in which the release layer and the specific coating layer were in contact with each other to obtain a sample of a laminated body. This sample was kept in an oven at 40 ° C. for 3 days with a weight of 84 kg. The sample was taken out of the oven and the release film was peeled off one by one from the sample. The surface of the release layer of the release film was observed at 20000 times using a scanning electron microscope (SEM, manufactured by Hitachi High-Tech, Ltd., S4700), and transfer marks were evaluated from the presence of dents according to the following criteria.

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

(Evaluation criteria)
A: No dents were observed, and the surface was smooth.
B: A dent was observed, and the surface of the release layer was roughened.

[Transfer mark evaluation 2: Evaluation after long-term storage]
A long-term storage test was conducted in which the release film prepared by the method described in the above [Preparation of release film] was stored in a normal temperature and humidity environment for 3 months. Except for using the release film after storage, the transfer marks formed on the release film were evaluated according to the method described in [Transfer Mark Evaluation 1] described above.
The evaluation criteria in the transfer mark evaluation 2 are shown below.

(Evaluation criteria)
A: No dents were observed, and the surface was smooth.
B: Only one of the 10 release films was dented, but the remaining 9 had a smooth surface.
C: A dent was observed on two or more of the 10 release films, and the surface of the release layer was roughened.

[Transportability]
In each Example and Comparative Example, the biaxially oriented film subjected to the above cooling step was conveyed under the following conveying conditions before being wound according to the method described in the above winding step. At this time, the state of wrinkles appearing on the biaxially oriented film transported by the transport roll was visually observed, and the transportability was evaluated according to the following criteria.
(Transport conditions)
Transport roll material: Stainless steel (SUS)
Transport roll wrap angle: 130 ° (coated surface)
Transport speed: 100 m / min Transport tension: 100 N / m

(Evaluation criteria)
A: No wrinkles were observed during transportation.
B: Wrinkles were observed only in the vicinity of the transport roll.
C: Wrinkles were constantly observed even on the downstream side of the transport roll.

[Applicability of release layer]
The release film produced in the evaluation of the transfer marks was cut out in the longitudinal direction to a length of 30 m. Under a three-wavelength fluorescent lamp, the surface of the obtained sample on the peeling layer side was visually observed, and the number of streaky coating unevenness and defects due to foreign matter observed by the reflected light was measured. From the measurement results, the applicability of the release layer was evaluated according to the following criteria.

(Evaluation criteria)
A: No coating unevenness or defects were observed.
B: Coating unevenness and / or defects were observed, but were within the permissible range.
C: Coating unevenness and / or defects exceeding the allowable range were observed.

Table 1 shows the evaluation results of each Example and Comparative Example.
In Table 1, resins 1 to 9 in the "resin" column, W-1 to W-4 in the "surfactant" column, cross-linking agents in the "additive" column, and particles in the "type" column of "particles". 1 to 3 indicate that the following components were used, respectively.
(resin)
Resin 1: Zyxen NC (manufactured by Sumitomo Seika Chemical Co., Ltd., acid-modified polyolefin, aqueous dispersion)
Resin 2: Zyxen L (manufactured by Sumitomo Seika Chemical Co., Ltd., acid-modified polyolefin, aqueous dispersion)
Resin 3: Zyxen A (manufactured by Sumitomo Seika Chemical Co., Ltd., acid-modified polyolefin, aqueous dispersion)
Resin 4: Chemipearl S120 (manufactured by Mitsui Chemicals, Inc., acid-modified polyolefin, aqueous dispersion)
Resin 5: Acrylic resin (an aqueous dispersion obtained by polymerizing methyl methacrylate, 2-hydroxyethyl methacrylate and methacrylic acid at a mass ratio of 28:48:24 to neutralize a copolymer).
Resin 6: Cymac US-480 (manufactured by Toagosei Co., Ltd., silicone-modified acrylic resin, aqueous dispersion)
Resin 7: Acrylic resin (copolymer obtained by polymerizing methyl methacrylate, styrene, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate and acrylic acid at a mass ratio of 59: 8: 26: 5: 2, an aqueous dispersion)
Resin 8: Takelac W605 (manufactured by Mitsui Chemicals, Inc., polyurethane, aqueous dispersion)
Resin 9: Hydran AP-40N (manufactured by DIC Corporation, polyurethane, aqueous dispersion)
(Surfactant)
W-1: Anionic hydrocarbon-based surfactant (Lapisol A-90, manufactured by NOF CORPORATION)
W-2: Silicone-based surfactant (BYK-346, manufactured by BYK)
W-3: Fluorosurfactant (Surflon S-211, manufactured by AGC Seimi Chemical Co., Ltd., structure containing a linear perfluoroalkyl group having 6 or more carbon atoms)
W-4: Fluorosurfactant (Futergent 215M, manufactured by Neos Co., Ltd., a structure containing a perfluoroisopropyl group and not containing a linear perfluoroalkyl group having 6 or more carbon atoms)
(Additive)
Crosslinking agent: Isocyanate compound, "Duranate (registered trademark) WM44L70" manufactured by Asahi Kasei Chemicals Co., Ltd. (particles)
Particle 1: Snowtex ZL (manufactured by Nissan Chemical Industries, Ltd., colloidal silica, aqueous dispersion)
Particle 2: Snowtex MP2040, (manufactured by Nissan Chemical Industries, Ltd., colloidal silica, aqueous dispersion)
Particle 3: Snowtex XL (manufactured by Nissan Chemical Industries, Ltd., colloidal silica, aqueous dispersion)

From Table 1, it was confirmed that the biaxially oriented polyester films of Examples 1 to 27 according to the present invention were more excellent in the effect of the present invention than those of Comparative Examples 1 to 3.

[Comparative Example 4]
As the polyester film of Comparative Example 4, a polyethylene terephthalate film (“Cosmo Shine (registered trademark) A-1517”, manufactured by Toyobo Co., Ltd.) in which a resin layer containing particles is laminated on one main surface of a polyethylene terephthalate base material. , Thickness 16 μm) was prepared. The polyester film of Comparative Example 4 has a relatively flat first surface (corresponding to the first main surface of the present film) and a second surface having an uneven shape (corresponding to the second main surface of the present film). Was. The maximum protrusion height Sp of the uneven surface of the polyester film of Comparative Example 4 was 63 nm.
Using the polyester film of Comparative Example 4, a roll-shaped release film was produced by providing a release layer on the first surface according to the method described in the above [Preparation of release film]. When the transfer marks on the surface of the release layer were evaluated by the method described in the above [Transfer mark evaluation 1] using the obtained release film, dents were observed and the release layer was roughened (evaluation B). ..
Further, when the transfer marks on the surface of the release layer were evaluated by the method described in the above [Transfer mark evaluation 2] using the obtained release film, dents were found on the surface of two or more of the ten release films. It was observed that the peeled layer was roughened (evaluation C).

It was confirmed that when the average particle size of the particles contained in the specific coating layer was 130 nm or less, the transportability was more excellent (comparison between Examples 1 and 2).

Further, the product (D × Sp) of the particle density D (unit: piece / μm ² ) of the particles constituting the protrusions on the second main surface and the maximum protrusion height Sp (unit: nm) on the second main surface. ) Is 20 or more, it is confirmed that the transportability is more excellent (comparison between Examples 2, 5 and 6 and other Examples).

When the area ratio of the streak defect region generated when heated at 90 ° C. was 20% or less, it was confirmed that the applicability of the release layer was more excellent (Examples 1, 20 to 22 and Examples 14 to 14). Comparison of 19).

It was confirmed that when the cooling rate of the polyester film in the cooling step was more than 2200 ° C./min and less than 3000 ° C./min, the coatability of the release layer was more excellent (comparison between Examples 1 and 17-19).

It was confirmed that when the specific coating layer contains a hydrocarbon-based surfactant, the coating property of the release layer is more excellent (comparison between Examples 1 and 9 to 10).
When the specific coating layer contains a fluorine-based surfactant having a perfluoroalkyl group having 1 to 4 carbon atoms, it contains a fluorine-based surfactant having a linear perfluoroalkyl group having 6 or more carbon atoms. It was confirmed that the coatability of the release layer was superior to that of the case (comparison of Examples 26 and 27).

Further, it was confirmed that when the absolute value of the peeling charge amount of the biaxially oriented film measured by the above measuring method was 0.12 nC or less, the coatability of the peeling layer was more excellent (Examples 9 to 10). Comparison with Examples 1-8, 11-13, 23, 25, 26).

When the surface free energy of the second main surface was 50 mJ / m ² or less, it was confirmed that the formation of transfer marks on the surface of the release layer could be further suppressed even after the release film was stored for a long period of time (Example). 24 and comparison with other examples).

[Example 101: Production of ceramic green sheet]
A ceramic slurry having the following formulation K is applied onto the release layer of the release film prepared in each of Examples 1 to 26 so that the thickness after drying becomes 0.5 μm, and then obtained. The resulting slurry coating film was dried at 90 ° C. The ceramic slurry was prepared by mixing each of the raw materials described in the following formulation and dispersing them with a ball mill. The two release films with a slurry coating film produced by the above method were superposed so that the surface of the slurry coating film and the surface of the specific coating film were in contact with each other, and a load of ^{1 kg / cm 2 was applied for 10 minutes.} Then, the release film was peeled off from the release film with the slurry coating film to obtain a ceramic green sheet.
The obtained ceramic green sheet had good characteristics without foreign matter or transfer failure.

<Prescription K: Ceramic Rally>
・ Polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd., Eslek BX-5) 5 parts ・ Barium titanate (manufactured by Fuji Titanium Industry Co., Ltd., HPBT) 100 parts ・ Toluene and ethanol 6: 4 mixed solvent 45 parts

1: Polyester film 1a: First main surface 1b: Second main surface 2: Polyester base material 2a to 2l: Gripping member 3: Specific coating layer 10: Preheating part 20: Stretched part 30: Heat fixing part 40: Heat relaxation part 50: Cooling

parts

60a, 60b: Circular rail 100: Stretching machine 200: Film P, Q: Gripping release point MD: Transport direction (longitudinal direction)
TD: Width direction L0, L1, L2, L3: Film width

Claims

With a polyester substrate that contains virtually no particles,
A coating layer containing particles, which is arranged on one surface of the polyester substrate, is provided.
It has a first main surface and a second main surface,
A polyester film used for producing a release film by forming a release layer on the first main surface.
The second main surface is a surface of the coating layer opposite to the polyester base material side.
The maximum protrusion height Sp of the second main surface is 1 nm or more and less than 60 nm.
A polyester film having a surface free energy of 25 to 60 mJ / m 2 on the second main surface.
When the product (D × Sp) of the density D (unit: piece / μm 2 ) of the particles constituting the protrusions on the second main surface and the maximum protrusion height Sp (unit: nm) is 20 or more. The polyester film according to claim 1.
The polyester film according to claim 1 or 2, wherein the polyester film has a thickness of 40 μm or less.
The polyester film according to any one of claims 1 to 3, wherein the coating layer further contains polyolefin.
The polyester film according to any one of claims 1 to 4, wherein the coating layer further contains a (meth) acrylate resin having an acid value of 30 mgKOH / g or less.
The average particle size of the particles is 1 to 130 nm, and the particles have an average particle diameter of 1 to 130 nm.
The thickness of the coating layer is 1 to 100 nm, and
The polyester film according to any one of claims 1 to 5, wherein the average particle diameter of the particles is larger than the thickness of the coating layer.
The coating layer contains at least one surfactant selected from the group consisting of a hydrocarbon-based surfactant and a fluorine-based surfactant containing a perfluoroalkyl group having 1 to 4 carbon atoms. Item 6. The polyester film according to any one of Items 1 to 6.
The invention according to any one of claims 1 to 7, wherein the absolute value of the peeling charge amount between the first main surface and the second main surface of the polyester film corresponding to a circle having a diameter of 1.5 cmφ is 0.12 nC or less. Polyester film.
The polyester film was heat-treated for 20 seconds under the condition that the temperature of the film surface was 90 ° C. while transporting the polyester film under the conditions of a transport speed of 30 m / min and a tension of 100 N / m in the transport direction. The polyester film according to any one of claims 1 to 8, wherein the total area of the streaky defect regions observed in the polyester film is 40% or less with respect to the total area of the observation region.
The polyester film according to any one of claims 1 to 9, wherein the polyester film has a density of 1.39 to 1.41 g / cm 3.
Any of claims 1 to 10, wherein the expansion rate of the polyester film in the width direction at 90 ° C. is −0.15 to 0.15% with respect to the length of the polyester film in the width direction at 30 ° C. The polyester film according to item 1.
The polyester film according to any one of claims 1 to 11, wherein the surface average roughness Sa of the second main surface is 1 to 10 nm.
The polyester film according to any one of claims 1 to 12, wherein the maximum protrusion height Sp of the first main surface is 1 to 60 nm.
The polyester film according to any one of claims 1 to 13, wherein the surface free energy of the first main surface is 50 to 70 mJ / m 2.
The polyester film according to any one of claims 1 to 14, wherein the variation in the thickness of the polyester film is 5% or less of the average thickness of the polyester film.
The polyester film according to any one of claims 1 to 15, wherein the release film is a release film for manufacturing a ceramic green sheet.
A release film comprising the polyester film according to any one of claims 1 to 16 and a release layer arranged on the first main surface of the polyester film.
The release film according to claim 17, wherein the maximum protrusion height Sp of the surface of the release layer opposite to the polyester film side is 1 to 60 nm.
The release film according to claim 17 or 18, wherein the surface free energy of the surface of the release layer opposite to the polyester film side is 30 mJ / m 2 or less.
A biaxial stretching step of biaxially stretching an unstretched polyester film having a polyester base material,
It comprises a coating layer forming step of in-line coating using a coating layer forming composition containing particles.
The method for producing a polyester film according to any one of claims 1 to 16.
A heat fixing step of heating and fixing the polyester film biaxially stretched by the biaxial stretching step at a temperature of less than 240 ° C.
A heat relaxation step of heating the polyester film heat-fixed by the heat-fixing step at a temperature lower than that of the heat-fixing step to heat-relax the polyester film.
A cooling step of cooling the polyester film heat-relaxed by the heat-relaxation step, and a cooling step of cooling the polyester film.
The cooling step includes an expansion step of expanding the heat-relaxed polyester film in the width direction.
The method for producing a polyester film according to claim 20, wherein the cooling rate of the polyester film in the cooling step is more than 2000 ° C./min and less than 4000 ° C./min.