WO2023149181A1

WO2023149181A1 - Polyester film production method, polyester film, dry film resist, and release film

Info

Publication number: WO2023149181A1
Application number: PCT/JP2023/001071
Authority: WO
Inventors: 佑記福岡; 年弘尾田; 厳弘森; 怜宮坂; 一仁宮宅
Original assignee: 富士フイルム株式会社
Priority date: 2022-02-03
Filing date: 2023-01-17
Publication date: 2023-08-10
Also published as: TW202340339A

Abstract

The present invention addresses the problem of providing a polyester film production method and a polyester film capable of suppressing optical defects when combined with a photosensitive resin layer or the like and used as a dry film resist. The present invention also addresses the problem of providing a dry film resist and a release film. A polyester film production method according to the present invention comprises: a step 1 in which a polyester resin precursor is continuously polymerized in the presence of a titanium compound, and after the antimony content determined by using inductively coupled plasma mass spectrometry to measure a product containing the produced polyester resin has dropped to 1.0 ppm by mass or less with respect to the product, a polyester resin is obtained; a step 2 in which a melt of the polyester resin is filtered by using a filter medium containing a powdery sintered body and a filter medium containing a fibrous sintered body having a filtration accuracy of 3 μm or less; and a step 3 in which a polyester film is produced using the filtered melt.

Description

Method for producing polyester film, polyester film, dry film resist, and release film

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

A polyester film is produced by melt-extrusion of a polyester resin to form a film, followed by processes such as stretching and heat treatment such as thermal relaxation. In recent years, a polyester film has been widely used as a functional film by applying or attaching a functional material onto the film to impart various functions. For example, by applying a photosensitive composition as a functional material onto a polyester film, it may be used as a dry film resist.
On the other hand, in recent years, with the increasing density of circuit wiring, dry film resists used for forming circuit wiring are required to have higher resolution.
Moreover, the polyester film is also used to produce ceramic green sheets used in the production of laminated ceramic capacitors.

As an attempt to improve resolution, Patent Document 1 discloses a support film containing a resin layer containing fine particles formed on one surface of a biaxially stretched polyester film, and a surface on which a resin layer containing fine particles of the support film is formed. A technique of laminating a photosensitive resin layer on the opposite side is disclosed.

Patent Document 1 discloses a photosensitive element comprising a support film and a photosensitive layer disposed on the support film, wherein the photosensitive layer comprises a binder polymer and a photopolymerizable compound having an ethylenically unsaturated bond. , a photopolymerization initiator, and the number of defects having a diameter of 2 μm or more on the photosensitive layer side surface of the support film is 30 or less per 2 mm ² .

WO2018/100730

With the recent increase in resolution (fineness) of resist patterns, it is often the case that the photosensitive resin layer is patterned through the support film that constitutes the dry film resist. In order to suppress deterioration in performance and transparency, higher performance than ever before is required.
With reference to the technology described in Patent Document 1, the present inventors used a dry film resist having a photosensitive composition on a polyester film to obtain a fine resist pattern with a narrower pattern width (especially 7 μm or less line-and-space (L/S) pattern), it was found that depending on the properties of the polyester film, optical failures such as pinhole defects may occur. It has been known that when an L/S wiring pattern is formed using a dry film resist that causes optical failures, disconnection failure occurs in which the wiring is disconnected, and improvements have been desired.
On the other hand, with the recent increase in capacity and miniaturization of ceramic capacitors, ceramic green sheets are required to be thinner. The present inventors have studied ceramic green sheets, and have found that the properties of the polyester film used to manufacture the ceramic green sheets may affect the performance of the ceramic green sheets.

In view of the above circumstances, an object of the present invention is to provide a method for producing a polyester film and a polyester film that can suppress optical failure when used as a dry film resist in combination with a photosensitive resin layer or the like.
Another object of the present invention is to provide a method for producing a polyester film and a polyester film that can suppress local concave defects when used to produce a ceramic green sheet.
Another object of the present invention is to provide a dry film resist and a release film.

As a result of earnestly examining the above problem, the inventors found that the above problem can be solved by the following configuration.

[1] The content of antimony obtained by continuously polymerizing a polyester resin precursor in the presence of a titanium compound and measuring the product containing the polyester resin produced by inductively coupled plasma mass spectrometry is as described above. Step 1 of obtaining a polyester resin after it has decreased to 1.0 mass ppm or less with respect to the product, and the melt of the polyester resin obtained in the above step 1 is filtered with a filter medium containing a powdery sintered body, and filtered A method for producing a polyester film, comprising step 2 of filtering with a filter medium containing a fibrous sintered body with an accuracy of 3 μm or less, and step 3 of producing a polyester film using the melt filtered in step 2.
[2] The method for producing a polyester film according to [1], wherein the inside of the reaction vessel used for polymerization is washed before continuously polymerizing the polyester resin precursor.
[3] The method for producing a polyester film according to [1] or [2], wherein the polyester film has a polyester base material substantially free of inorganic particles.
[4] The polyester film according to any one of [1] to [3], wherein the polyester resin precursor contains a diol compound and a dicarboxylic acid compound selected from the group consisting of dicarboxylic acids and dicarboxylic acid ester compounds. manufacturing method.
[5] The method for producing a polyester film according to any one of [1] to [4], wherein the polyester film contains at least one element selected from the group consisting of magnesium and phosphorus.
[6] It has a haze of 0.6% or less, an antimony content of 1 mass ppm or less as measured by inductively coupled plasma mass spectrometry, and a diameter of 9 to 20 μm observed with a transmission polarizing microscope. A polyester film having a total number of foreign matter and voids of 10/500 mm ² or less.
[7] The polyester film of [6], which is used for producing a dry film resist.
[8] The polyester film of [6] or [7], wherein the total number of foreign matter and voids having a diameter of 3 μm or more and less than 9 μm observed with a transmission polarizing microscope is 200/500 mm ² or less.
[9] A polyester film in which the total number of foreign matter and voids with a diameter of 9 to 20 μm observed with a transmission polarizing microscope is 1.7/mm ³ or less.
[10] The polyester film of [9], which is for producing a ceramic green sheet.
[11] The polyester film of [9] or [10], which has an antimony content of 1 mass ppm or less as measured by inductively coupled plasma mass spectrometry.
[12] The polyester film according to any one of [9] to [11], wherein the total number of foreign matter and voids having a diameter of 3 μm or more and less than 9 μm observed with a transmission polarizing microscope is 1.7/mm ³ or less.
[13] Contains titanium, magnesium, and phosphorus, and the content of titanium, the content of magnesium, and the content of phosphorus obtained by measurement by inductively coupled plasma mass spectrometry are each included in the total mass of the polyester film. The polyester film according to any one of [6] to [12], which is 1 to 100 ppm by mass.
[14] The polyester film according to any one of [6] to [13], which has a polyester base material substantially free of inorganic particles.
[15] The polyester film according to any one of [6] to [14], which has a polyester base material and a particle-containing layer.
[16] The polyester film according to any one of [6] to [15], wherein the polyester film has a thickness of 1 to 35 μm.
[17] The polyester film according to any one of [9] to [16], which has a haze of 2.0% or less and a thickness of 1 to 35 μm.
[18] A dry film resist comprising the polyester film of any one of [6] to [17] and a photosensitive resin layer.
[19] The dry film resist of [18], wherein the photosensitive resin layer contains a binder polymer, a polymerizable compound having an ethylenically unsaturated bond, and a photopolymerization initiator.
[20] A release film comprising the polyester film of any one of [6] to [17] and a release layer.

According to the present invention, it is possible to provide a method for producing a polyester film and a polyester film that can suppress optical failures when used as a dry film resist in combination with a photosensitive resin layer or the like. Moreover, according to the present invention, it is possible to provide a method for producing a polyester film and a polyester film that can suppress local concave defects when used for producing a ceramic green sheet. Moreover, according to the present invention, a dry film resist and a release film can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows an example of a structure of the manufacturing apparatus of a polyester film. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a filtering device used for filtering melted polyester resin. It is a schematic diagram showing an example of the composition of the filter which a filtering device has.

Hereinafter, embodiments of the present invention will be described in detail. It should be noted that the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the purpose of the present invention.

In this specification, a numerical range indicated using "to" indicates a range including the numerical values before and after "to" as the minimum and maximum values, respectively.
In the numerical ranges described stepwise in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the upper limit or lower limit of another numerical range described stepwise. Moreover, in the numerical ranges described in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the values shown in the examples.

In the present specification, a combination of two or more preferred aspects is a more preferred aspect.
In this specification, when a composition or layer contains a plurality of substances corresponding to each component, unless otherwise specified, the amount of each component in the composition or layer refers to the above-mentioned plurality of substances present in the composition or layer. It means the total amount of substance.
As used herein, the term "step" includes not only independent steps, but also steps in which the intended purpose of the step is achieved even if it cannot be clearly distinguished from other steps.
As used herein, the term “longitudinal direction” means the longitudinal direction of the film during production, and is synonymous with the “conveyance direction” and “machine direction”.
As used herein, "width direction" means a direction perpendicular to the longitudinal direction. In the present disclosure, "orthogonal" is not limited to strictly orthogonal, but includes substantially orthogonal. “Substantially orthogonal” means intersecting at 90°±5°, preferably intersecting at 90°±3°, more preferably intersecting at 90°±1°. The "film width" means the distance between both ends of the film in the width direction.

As used herein, "(meth)acrylic" is a generic term for acrylic and methacrylic, and means "one or more of acrylic and methacrylic". Similarly, "(meth)acrylate" means "one or more of acrylate and methacrylate", and "(meth)acrylic acid" means "one or more of acrylic acid and methacrylic acid".

In this specification, the term “exposure” includes not only exposure using light but also drawing using particle beams such as electron beams and ion beams, unless otherwise specified. Examples of the light used for exposure include the emission line spectrum of a mercury lamp, far ultraviolet rays represented by excimer lasers, extreme ultraviolet rays (EUV light), X-rays, and active rays (active energy rays) such as electron beams. .
As used herein, unless otherwise specified, the refractive index means the refractive index for light with a wavelength of 550 nm measured using an Abbe refractometer (“NAR-2T” manufactured by Atago Co., Ltd.).

In this specification, unless otherwise specified, the weight average molecular weight (Mw) and number average molecular weight (Mn) are TSKgel GMHxL, TSKgel G4000HxL, TSKgel G2000HxL and/or TSKgel Super HZM-N (all manufactured by Tosoh Corporation). (trade name) column) using a gel permeation chromatography (GPC: Gel Permeation Chromatography) analyzer, using THF (tetrahydrofuran) as a solvent, detected by a differential refractometer, molecular weight converted using polystyrene as a standard substance is.

[First embodiment: method for producing a polyester film]
A method for producing a polyester film, which is the first embodiment of the present invention (hereinafter also referred to as "this production method"), is produced by continuously polymerizing a polyester resin precursor in the presence of a titanium compound. Step 1 to obtain a polyester resin after the antimony content obtained by measuring the product containing the polyester resin by inductively coupled plasma mass spectrometry has decreased to 1.0 mass ppm or less with respect to the product; Step 2 of filtering the melt of the polyester resin obtained in Step 2 with a filter medium containing a powdery sintered body and a filter medium containing a fibrous sintered body with a filtration accuracy of 3 μm or less, and the melt filtered in step 2 It is characterized by having a step 3 of manufacturing a polyester film using a material.

By including the above steps 1 to 3, the present production method has the effect of suppressing optical failure when used as a dry film resist in combination with a photosensitive resin layer or the like (hereinafter also referred to as "optical failure suppression effect". Although the details of the reason why a polyester film exhibiting ) can be produced are not clear, the present inventors generally presume as follows.
If there is either a foreign matter or a void in the polyester film used for the dry film resist, it is considered that optical failure occurs because only that portion cannot be exposed. For example, when the photosensitive composition contained in the photosensitive resin layer or the like in the dry film resist is a negative photosensitive composition, when the photosensitive resin layer or the like is exposed through the polyester film, foreign substances and voids of the polyester film are formed. The photocuring reaction does not progress at the location of the photosensitive resin layer or the like corresponding to the location where either is present, and the photosensitive composition contained in the exposed area is removed in the subsequent development process, resulting in an optical failure. is formed.
Therefore, the present inventors confirmed the details of the foreign matter and voids present in such a polyester film. It was also found that voids greatly contribute to the occurrence of optical failures when a photosensitive resin layer or the like is exposed to ultraviolet light. When the present inventors further analyzed each foreign matter, they found that the colored foreign matter contained a component derived from antimony, and the transparent foreign matter was a gel generated during the polymerization process of the polyester resin, or a reaction between magnesium and phosphorus. It was found to be a product of In addition, it was found that the above-mentioned voids were generated around the foreign matter such as the above-mentioned colored foreign matter and transparent foreign matter.
In the method for producing a polyester film according to the present embodiment, a polyester resin having a sufficiently reduced antimony content is supplied, and the melt of the supplied polyester resin is filtered using a specific combination of filter media. It is speculated that the above-mentioned foreign matters and voids contained in the polyester resin, which is the raw material of the polyester film, were suppressed by the above-mentioned method, and thus the optical failure of the dry film resist was suppressed.

In addition, when the present production method includes the above steps 1 to 3, when a ceramic green sheet is produced using the produced polyester film, the effect of suppressing local concave defects in the produced ceramic green sheet ( Hereinafter, the details of the reason for achieving the effect of suppressing the concave defect) are not clear, but the present inventors generally presume as follows.
In the method for producing a polyester film according to the present embodiment, a polyester resin having a sufficiently reduced antimony content is supplied, and the melt of the supplied polyester resin is filtered using a specific combination of filter media. It is presumed that the foreign matter and voids contained in the polyester resin, which is the raw material of the polyester film, could be suppressed. As a result, it is speculated that a polyester film having few protrusions on the surface could be produced, and the occurrence of local recessed defects in ceramic green sheets produced using such a polyester film could be further suppressed.
Hereinafter, "the effect of the present invention" means at least one of the optical failure suppressing effect and the concave defect suppressing effect exhibited by each embodiment of the present invention.

Hereinafter, each step of the present production method will be described with reference to a drawing showing an example of a polyester film production apparatus.
FIG. 1 is a schematic diagram showing an example of the configuration of a polyester film manufacturing apparatus used in the present manufacturing method. A film manufacturing apparatus 10 shown in FIG. 1 includes a reaction tank 12 , a film forming process section 14 , a longitudinal stretching process section 16 , a lateral stretching process section 18 for lateral stretching, and a winding section 20 .

The reactor 12 polymerizes a polyester resin precursor to produce a polyester resin.
The film forming process unit 14 includes an extruder 24, a pipe 34, a filtering device 36, a pipe 38, a die 26, and a cast drum 28, and heats and melts the polyester resin produced in the reaction tank 12, The resulting melt is filtered, and polyester film F is produced using the filtered melt.
The longitudinal stretching process section 16 includes a pair of low-speed rollers 30 and a pair of high-speed rollers 32, and stretches the polyester film F produced in the film forming process section 14 in the longitudinal direction.
The transverse stretching process section 18 stretches the longitudinally stretched polyester film F in the transverse direction.
The winding unit 20 winds up the polyester film F stretched in the lateral direction.

[Step 1]
In the reaction tank 12, a step 1 is performed in which a polyester resin precursor is continuously polymerized in the presence of a titanium compound to produce a polyester resin having a predetermined antimony content or less.

As the reaction vessel used in step 1, a known reaction vessel used for synthesis of polyester resin can be used, and is appropriately selected according to the type and amount of the polyester resin and its precursor.
In step 1, it is preferable to use a reaction vessel that has been washed in advance, since the effect of the present invention is more excellent. The method for cleaning the reaction vessel is not particularly limited, and for example, the liquid-contacting part of the reaction vessel (the part where the polyester resin precursor and the polyester resin can contact) is cleaned with a cleaning liquid, and buffing agent and dry ice are used. Polishing treatment using blasting or the like can be mentioned. Examples of the cleaning liquid include organic solvents such as ethylene glycol and triethylene glycol, water or aqueous solutions, acids or alkalis, and combinations thereof, and are appropriately selected according to the polyester resin and its precursor.
Among them, as the cleaning process of the reaction tank, since the effect of the present invention is more excellent, it is heated and washed using an organic solvent such as ethylene glycol and triethylene glycol, and then the wetted part of the reaction tank is subjected to buffing or the like. It is preferable to perform a step of physically removing deposits by performing a polishing treatment. The buffing method is not particularly limited, and any known method can be used.
The step of washing the reactor is always carried out before carrying out the step 1 of continuously polymerizing the polyester resin. The timing of performing the washing step is not particularly limited, but for example, depending on the composition of the polyester resin produced in step 1 (more specifically, the antimony content, etc., described later), step 1 is appropriately interrupted to allow the reaction to proceed. Cleaning of the tank can be performed.

In step 1, a polyester resin is produced by continuously polymerizing a polyester resin precursor in the presence of a titanium compound in the washed reaction vessel. However, only the polyester resin produced after the content of antimony contained in the product containing the polyester resin produced by the continuous polymerization has fallen below a predetermined value is supplied to step 2 described later.
Here, "continuously polymerizing the polyester resin precursor" means that the polyester resin precursor is continuously or intermittently supplied into the reaction vessel, and the reactant is polymerized (polymerized) while being transported within the reaction vessel. condensation reaction) and continuously or intermittently discharging the resulting polymer from the reactor.
The content of antimony contained in the above product is measured by inductively coupled plasma mass spectrometry (ICP-MS). A more specific measuring method will be described in Examples described later.
In this production method, when the content of antimony measured by the ICP-MS method satisfies the condition that the content of antimony is 1.0 ppm by mass or less with respect to the above product, the produced polyester resin is sent to step 2. supply. The condition of the antimony content of the polyester resin to be supplied to step 2 is preferably 0.8 mass ppm or less, more preferably 0.7 mass ppm or less, with respect to the above product, from the viewpoint that the effect of the present invention is more excellent. 0.6 mass ppm or less is more preferable. The lower limit is not particularly limited, and may be 0 mass ppm.

The titanium compound used in step 1 is a compound containing titanium, and examples thereof include known titanium compounds that can be used as catalysts for polymerization of polyester resin precursors.
As the titanium compound, an organic titanium compound is preferred, and an organic chelate titanium complex is more preferred. An organic chelate titanium complex is a titanium compound having an organic acid or its salt as a ligand. Organic acids include, for example, citric acid, lactic acid, trimellitic acid and malic acid. Among them, an organic chelate titanium complex having citric acid or a citrate as a ligand is more preferable.
As the titanium compound, titanium compounds described in paragraphs 0049 to 0053 of Japanese Patent No. 5575671 can also be used, the contents of which are incorporated herein.

The addition amount of the titanium compound used in step 1 is preferably an amount of 1 to 500 mass ppm in terms of the titanium element conversion value with respect to the total mass of the polyester resin precursor, and an amount of 1 to 100 mass ppm. More preferably, the amount of 1 to 30 ppm by mass is more preferable, the amount of 3 to 20 ppm by mass is particularly preferable, and the amount of 5 to 15 ppm by mass is most preferable.

In the polymerization of the polyester resin precursor in step 1, a compound other than the titanium compound may be present together with the titanium compound.
Examples of the other compounds include alkali metal compounds (e.g., potassium compounds, sodium compounds), alkaline earth metal compounds (e.g., calcium compounds, magnesium compounds), zinc compounds, lead compounds, manganese compounds, cobalt compounds, and aluminum. compounds, antimony compounds, germanium compounds and phosphorus compounds.
The other compound is preferably at least one compound selected from the group consisting of magnesium compounds and phosphorus compounds, more preferably both magnesium compounds and phosphorus compounds.

Magnesium compounds include, for example, magnesium oxide, magnesium hydroxide, and magnesium salts such as magnesium alkoxide, magnesium acetate and magnesium carbonate. Among them, magnesium acetate is preferable from the viewpoint of solubility in ethylene glycol.
Phosphorus compounds include, for example, phosphate esters, and pentavalent phosphate esters having no aromatic ring as a substituent are preferred. Examples of the phosphate ester include trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, tris (triethylene glycol) phosphate, methyl acid phosphate, ethyl acid phosphate, and phosphoric acid. Isopropyl acid, butyl acid phosphate, monobutyl phosphate, dibutyl phosphate, dioctyl phosphate and triethylene glycol acid phosphate can be mentioned, with trimethyl phosphate or triethyl phosphate being preferred.

The amount of the other compound added is preferably an amount of 3 to 500 ppm by mass in terms of the metal element or phosphorus element, and an amount of 5 to 100 ppm by mass with respect to the total mass of the polyester resin precursor. more preferred.
When a magnesium compound is used, the amount of the magnesium compound added is 50 ppm by mass or more with respect to the total mass of the polyester resin precursor in terms of the magnesium element conversion value in that it can impart high static electricity to the polyester film. The amount is preferably 50 to 100 mass ppm, more preferably 60 to 90 mass ppm, and particularly preferably 70 to 80 mass ppm.
Further, when a phosphorus compound is used, the amount of the phosphorus compound added is preferably an amount that is 50 to 90 mass ppm with respect to the total mass of the polyester resin precursor, in terms of the phosphorus element, and 60 to 80 mass ppm. is more preferable, and an amount of 65 to 75 ppm by mass is even more preferable.

The content of titanium contained in the polyester resin precursor and the content of elements other than titanium such as magnesium and phosphorus are measured according to the method for measuring the content of antimony contained in the product by the ICP-MS method. Or obtained by measuring the product.

The polyester resin precursor used in step 1 and the polyester resin produced in step 1 will be described in detail in the polyester film according to the second embodiment.

The reaction conditions for producing the polyester resin by polymerizing the polyester resin precursor in step 1 are not particularly limited, and may be appropriately set according to the type of the polyester resin precursor.
The reaction temperature in step 1 is preferably 260 to 300°C, more preferably 275 to 285°C.
The pressure in the reaction vessel in step 1 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 the polyester resin, the method described in [0033] to [0070] of Japanese Patent No. 5575671 can also be used, and the contents of the above publication are incorporated herein.

[Step 2]
In step 2, the polyester resin melt obtained in step 1 is mixed with a filter medium containing a powdery sintered body and a fibrous sintered body with a filtration accuracy of 3 μm or less (hereinafter also referred to as “specific fibrous sintered body” ) through a filter medium containing In the film manufacturing apparatus 10 shown in FIG. 1, step 2 is performed by the extruder 24 and the filtering device 36 of the film forming process section 14 .

The polyester resin obtained in step 2 may be dried by heating before being heated and melted by the extruder 24. In particular, when the polyester resin contains an aromatic polyester resin, the polyester resin produced is dried by heating. After that, it is preferable to heat and melt.
The heating temperature for the heat drying is often 80 to 180° C. for 12 to 36 hours. In particular, when the heating temperature is lower than the glass transition temperature of the polyester resin, it is preferable to dry in a reduced pressure atmosphere.

The polyester resin is melt mixed in the extruder. The conditions for melt-mixing using an extruder are not particularly limited as long as a melt of the polyester resin can be produced.
The inside of the extruder is preferably preheated to a temperature of [Tm+10° C.] to [Tm+70° C.] (preferably [Tm+20° C.] to [Tm+50° C.]) before feeding the polyester resin. "Tm" means the melting point of the polyester resin.
The melt-mixing time of the polyester resin is often 3 minutes or longer, preferably 3 to 20 minutes.
The polyester resin melt obtained in this manner is supplied to a filtering device 36 through a pipe 34 .

The melt melted by the extruder 24 is filtered by a filtering device 36 having a filter medium containing a powdery sintered body and a filter medium containing a specific fibrous sintered body. By filtering the melt using the filtering device 36, dust, unreacted substances, gels, and foreign matter thermally deteriorated in the melt treatment are removed from the melt of the polyester resin.

The filter device 36 is a fibrous sintered body using sintered fibers, and includes a filter medium containing a specific fibrous sintered body with a filtration accuracy of 3 μm or less, and a powdery sintered body using sintered powder. and a filter medium. By filtering using both the filter medium containing the specific fibrous sintered body and the filter medium containing the powdery sintered body, it is possible to remove the gel contained in the polyester resin, which is one of the causes of optical failure. Therefore, it is presumed that when used as a dry film resist in combination with a photosensitive resin layer or the like, a polyester film in which optical failures are further suppressed can be produced.

As long as the filtering device used in step 2 has a filter medium containing a specific fibrous sintered body and a filter medium containing a powdery sintered body, and has a structure in which the molten polyester resin contacts both of these filter media. , its specific configuration is not particularly limited. As the filtering device, for example, a filtering device including at least one filter in which a specific fibrous sintered body and a powdery sintered body are integrated as a filter medium, and at least a filtering device including a specific fibrous sintered body A filtering device that uses one filter and at least one filter containing a powdery sintered body in combination is mentioned. When a filter containing a specific fibrous sintered body and a filter containing a powdery sintered body are used together, the arrangement of both is not particularly limited as long as the melt contacts both. Among them, a filtering device having at least one filter in which a specific fibrous sintered body and a powdery sintered body are integrated is preferable.
A leaf disk type filter is preferable as the filter containing the filter medium. The number and size of the filters including the above-described filter media are appropriately selected according to the type of polyester resin, characteristics such as viscosity, and conditions such as flow rate.

The filtration accuracy of the filter medium containing the specific fibrous sintered body is preferably 2 μm or less in terms of removing foreign matter with a diameter of 9 to 20 μm and obtaining a superior polyester film due to the effects of the present invention. Although the lower limit is not particularly limited, it is, for example, 1 μm. Here, the filtration accuracy is defined as "the minimum diameter of glass beads that can capture 95% or more by the filter medium". The lower the numerical value of filtration accuracy, the higher the accuracy of the filter medium.

FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a filtering device used for filtering the melted polyester resin in step 2. As shown in FIG.
The filtering device 36 shown in FIG. 2 is composed of a cylindrical housing 44 and a plurality of disk-shaped filters 46 provided inside the housing 44 . The housing 44 also has a supply port 40 that communicates with the pipe 34 to supply the polyester resin melt, and a discharge port 42 that communicates with the pipe 38 and from which the filtered melt is discharged.
In the filtering device 36 , a plurality of filters 46 are arranged side by side in the axial direction of the flow path 48 with a predetermined interval by spacers 54 .

FIG. 3 is a schematic diagram showing an example of the configuration of a filter included in the filtering device.
The disk-shaped filter 46 shown in FIG. 3 has a substantially disk-shaped sintered body 52 having a through hole in the center and is sandwiched between substantially disk-shaped perforated plates 53 having a through hole in the center. It has a configuration in which an annular ring member 50 is attached to the through hole of the. The sintered body 52 has a specific fibrous sintered body and a powdery sintered body.
A side wall of the ring member 50 is provided with a large number of through holes 51 arranged in a circumferential direction, which serve as flow paths for the melt filtered by the sintered body 52 . The hole diameter of the through holes 51 is, for example, 1 to 3 μm or less. The through hole 51 communicates with a channel 48 that is closed at one end and communicates with the discharge port 42 at the other end.
The diameter D of the filter 46 is appropriately set according to the amount of melt supplied from the extruder 24 and the residence time.

As indicated by the arrow in FIG. 2, the melted polyester resin heated and melted in the extruder 24 is supplied from the pipe 34 through the supply port 40 into the housing 44 of the filtering device 36 .
The molten material supplied into the housing 44 is flowed radially outward of the filter by the member 56, flows into the disk-shaped filter 46, is filtered by the sintered body 52, and foreign matters are removed. be done.
The melt that has passed through the sintered body 52 passes through the through hole 51 of the ring member 50 to reach the inside of the channel 48, flows from the open end of the channel 48 through the outlet 42, flows into the pipe 38, and exits from the pipe 38. A die 26 is provided.

Filtration conditions for filtering the melt by the filtration device are not particularly limited, but in order to effectively remove foreign matter, etc., the filtration pressure may be set in the range of 10 to 200 kg/cm ² for filtration. preferable. Moreover, it is preferable that the residence time of the melt staying in the filtering device 36 is 1 minute or more and 30 minutes or less. Furthermore, it is preferable to change the melting temperature and discharge amount of the polyester resin so that the apparent viscosity of the melt at the inlet of the filtering device 36 is 10 to 2000 Pa·s.

It is preferable to wash the filter of the filtering device after use. By washing after use, the filter can be used repeatedly. Examples of the cleaning method include those described in JP-A-2019-013890 and JP-A-2008-037012, the contents of which are incorporated herein.
The filtering device used for filtering the melted polyester resin in step 2 is not limited to the filtering device described above.

[Step 3]
In step 3, the polyester resin melt filtered in step 2 is used to produce a polyester film. In the film manufacturing apparatus 10 shown in FIG. 1 , step 3 is performed by the die 26 and cast drum 28 of the film forming process section 14 , the longitudinal stretching process section 16 and the transverse stretching process section 18 .

First, the polyester resin melt filtered in step 2 is extruded into a film by a die 26, and an unstretched polyester film made of a film-shaped melt (hereinafter, polyester film is simply referred to as " Also referred to as "film F") is formed.
The melt supplied to the die 26 is heated to, for example, [Tm+10° C.] to [Tm+70° C.], cooled and solidified at 30 to 110° C. on the cast drum 28 to form an unstretched film F (amorphous sheet).
The melt may be extruded in a single layer or in multiple layers.
Moreover, a well-known extruder can be used as an extruder for extruding the melt.

Next, the unstretched film F is stretched (longitudinal stretching) in the longitudinal direction (longitudinal direction) by a pair of low-speed rollers 30 and a pair of high-speed rollers 32 provided in the longitudinal stretching section 16 .
When longitudinally stretched, the film F is preferably heated to a temperature of [Tg+5° C.] to [Tg+60° C.] (Tg: glass transition temperature of the polyester resin).
The draw ratio in the longitudinal direction (longitudinal direction) by longitudinal drawing is, for example, 2 to 7 times, preferably 2 to 5 times.

Thereafter, the longitudinally stretched film F is stretched (horizontally stretched) in the transverse direction (film width direction) by the transverse stretching unit 18 to produce a biaxially stretched film (biaxially oriented film). In the lateral stretching process section 18, hot air is sent to the film F, and both width direction end portions of the film F are heated while being held by a tenter.
The heating temperature of the film F during lateral stretching is, for example, [Tg+5° C.] to [Tg+60° C.], preferably [Tg+20° C.] to [Tg+50° C.].
The draw ratio in the transverse direction (longitudinal direction) is, for example, 2 to 7 times, preferably 2 to 5 times.

The film F thus biaxially stretched is finally cooled and then wound up by the winding unit 20 .
The temperature of the stretching step is preferably 120 to 150°C when the polyester resin is polyethylene terephthalate (PET), and preferably 140 to 180°C when the polyester resin is polyethylene-2,6-naphthalate (PEN).
A uniaxially stretched film stretched only in the longitudinal direction can be manufactured by winding the longitudinally stretched film F in the winding section 20 without going through the transverse stretching process section 18 .
For Step 3, the descriptions of [0113] to [0169] of International Publication No. 2020/241692 can be referred to, and the contents thereof are incorporated herein.

The polyester film produced by this production method may have a single-layer structure consisting only of a polyester base material formed using the melt of the polyester resin filtered in step 2, and the polyester film filtered in step 2 A multilayer structure having a polyester base material formed using a resin melt and a particle-containing layer containing particles may also be used.

The polyester base material of the polyester film preferably contains substantially no inorganic particles, more preferably substantially no particles.
The expression “substantially free of the particles” means that the content of the particles in the thermoplastic substrate is determined by quantitative analysis of the elements derived from the particles by X-ray fluorescence spectroscopy. is defined as being 50 mass ppm or less with respect to the total mass of The content of the particles contained in the thermoplastic substrate is more preferably 10 mass ppm or less with respect to the total mass of the thermoplastic substrate, and particularly preferably the detection limit or less.
Even if the particles are not positively added to the polyester base material, contaminant components, raw material resins, or stains adhered to the lines or equipment in the above manufacturing process may peel off and be mixed into the polyester base material. be. For example, the filtration in step 2 above preferably removes unintentionally contaminating particles.

<Particle-containing layer forming step (step 4)>
A polyester film having a polyester substrate and a particle-containing layer can be produced by carrying out a particle-containing layer forming step (step 4) for forming a particle-containing layer at any stage of the present production method.
In step 4, for example, a composition for forming a particle-containing layer containing particles and a resin (hereinafter also referred to as "composition A") is used to form a coating film of composition A by in-line coating, and if necessary and drying accordingly to form a particle-containing layer.
The polyester substrate to which the composition A is applied in step 4 includes, for example, an unstretched polyester substrate and a uniaxially stretched polyester substrate, preferably a uniaxially stretched polyester substrate. That is, it is preferable to perform the step 4 between the longitudinal stretching and the transverse stretching in the above step 3. This is because the adhesion between the polyester substrate and the particle-containing layer can be improved by laterally stretching the uniaxially stretched polyester substrate and the particle-containing layer at the same time.

Composition A can be prepared by mixing particles contained in the particle-containing layer, resin, additives added as necessary, and solvent.
Examples of solvents include water, ethanol, toluene, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether. Among them, water is preferable from the viewpoint of environment, safety and economy.
Composition A may contain a single solvent, or may contain two or more solvents. The content of the solvent is preferably 80 to 99 mass % with respect to the total mass of composition A. That is, the total content of components (solid content) other than the solvent is preferably 0.5 to 20% by mass with respect to the total mass of composition A.

The particles, resins, and additives contained in composition A, including their preferred embodiments, are the same as those described later in the section on the particle-containing layer of the polyester film according to the second embodiment.

The step 4 of forming a particle-containing layer is not limited to the step of forming by applying the above composition A to a polyester substrate, for example, the melt filtered in step 2 and the By co-extrusion of the melt containing the particles and the resin, to form a laminate in which the polyester base material and the particle-containing layer are laminated, and then biaxially stretching the laminate to produce a polyester film. may

The polyester film produced by the present production method described above exhibits an effect of suppressing optical defects when used as a dry film resist in combination with a photosensitive resin layer or the like.
Preferred aspects and uses of the polyester film produced by this production method are the same as those of the polyester films according to the second and third embodiments described below.

[Second embodiment: polyester film (1)]
The polyester film, which is the second embodiment of the present invention, has a haze of 0.6% or less, an antimony content of 1 mass ppm or less as measured by the ICP-MS method, and a transmission polarizing microscope. The number of foreign particles and voids with a diameter of 9 to 20 μm observed is less than 10/500 mm ² .

Although the details of the reason why the polyester film of the present embodiment has the effect of suppressing optical failure due to the above structure are not clear, the present inventors generally presume as follows.
As described above, the present inventors investigated foreign matter and voids present in the polyester film, which are thought to be the cause of optical failures in dry film resists, and found that antimony-derived components among the foreign matter and voids were investigated. It was found that the colored foreign matter contained in the film, and the transparent foreign matter and voids having a diameter of 9 to 20 μm greatly contribute to the occurrence of optical failures when a photosensitive resin layer or the like is exposed to ultraviolet light.
In the polyester film of the present embodiment, by setting the content of antimony to a predetermined value or less, the generation of the colored foreign matter is suppressed, and the content of the foreign matter with a diameter of 9 to 20 μm and the void content is reduced to a predetermined value or less. It is inferred that the optical failure of the dry film resist could be suppressed because of this.

[Characteristics of polyester film]
<Content of antimony>
The content of antimony (Sb) contained in the polyester film of the present embodiment is 1 mass ppm or less with respect to the total mass of the polyester film.
From the viewpoint that the effect of the present invention is more excellent, the antimony content is preferably 0.7 mass ppm or less, more preferably 0.6 mass ppm or less, and 0.5 mass ppm or less with respect to the total mass of the polyester film. is more preferred. The lower limit is not particularly limited, and may be 0 mass ppm.
The content of antimony contained in the polyester film can be measured by ICP-MS. Details of the measurement method will be described in Examples described later.

<Total number of foreign matter and voids>
In the polyester film of the present embodiment, the total number of foreign matter and voids with a diameter of 9 to 20 μm observed with a polarizing microscope is 10/500 mm ² or less.
The unit of "pieces/500 mm ² " means the number of foreign particles or voids per 500 mm ² observation area of the polyester film observed using a polarizing microscope.
The total number of foreign particles and voids with a diameter of 9 to 20 μm contained in the polyester film and the total number of foreign particles and voids with a diameter of 3 μm or more and less than 9 μm are measured using a transmission polarizing microscope. By using a transmission polarizing microscope with a polarizing lens, it is possible to observe the change in color density (refractive index change) of the resin around foreign matter or voids, and accurately count the foreign matter and voids present inside the film. The method for measuring the total number of foreign matter and voids in the polyester film will be described in detail in the examples below.

The total number of foreign particles and voids with a diameter of 9 to 20 μm observed using a polarizing microscope is preferably as small as possible, preferably 7/500 mm ² or less, from the viewpoint of better optical failure suppression effect.
The lower limit of the total number of foreign matter and voids having a diameter of less than 9 to 20 μm is not particularly limited, and may be 0/500 mm ² .

Foreign matter with a diameter of 9 to 20 μm contained in the polyester film includes, for example, transparent foreign matter composed of a gel produced in the process of polymerizing a polyester resin, heat-degraded polyester produced by polymerization, antimony compounds, magnesium compounds, Contaminants originating from either a phosphorus compound or a titanium compound (for example, a phosphate produced by a reaction between a magnesium compound and a phosphorus compound as additives) can be mentioned. In addition, voids having a diameter of 9 to 20 μm contained in the polyester film include voids generated around the above-mentioned foreign matters.
SEM-EDX (Scanning Electron Microscope-Energy dispersive X-ray spectrometry) measurement of the cross section containing the foreign matter of the polyester film can be analyzed by

The total number of foreign matter and voids with a diameter of 3 μm or more and less than 9 μm observed using a polarizing microscope on the polyester film of the present embodiment is preferably 200 / 500 mm ² or less, and 150 It is more preferably 100 pieces/500 mm ² or less, even more preferably 100 pieces/500 mm ² or less, and particularly preferably 70 pieces/500 mm ² or less. The lower limit of the total number of foreign matter and voids with a diameter of 3 μm or more and less than 9 μm is not particularly limited, and may be 0/500 mm ² .

Foreign matter and voids with a diameter of 3 μm or more and less than 9 μm contained in the polyester film include, for example, transparent foreign matter made of gel formed in the process of polymerizing the polyester resin, colored foreign matter containing Sb-derived components, and a magnesium compound as an additive. voids generated around foreign substances such as phosphates produced by the reaction of phosphorus compounds and colored foreign substances and transparent foreign substances.

In addition, the total number of foreign matter and voids with a diameter of more than 20 μm observed using a polarizing microscope on the polyester film of the present embodiment is preferably less than 1/500 mm ² , and 0/500 mm ² (i.e., not observed) is more preferable.

<Haze>
The haze of the polyester film of this embodiment is 0.6% or less.
The haze of the polyester film is preferably 0.5% or less, more preferably 0.4% or less, and still more preferably less than 0.3%, from the viewpoint of superior transparency and optical failure suppression performance. Although the lower limit is not particularly limited, 0% or more is preferable.
The haze of the polyester film can be measured according to JIS K 7105 using a known haze meter (eg, "NDH-2000" manufactured by Nippon Denshoku Industries Co., Ltd.).

〔composition〕
The polyester film of the present embodiment may have a single-layer structure consisting only of a polyester base material formed using a melt of a polyester resin, and a polyester base material formed using a melt of a polyester resin, It may be a multilayer structure having a particle-containing layer containing particles.
When the polyester film of the present embodiment has a particle-containing layer, one particle-containing layer may be arranged on one side of the polyester substrate, or two particle-containing layers may be arranged on both sides of the polyester substrate. good. Among them, it is preferable that one particle-containing layer is arranged on one side of the polyester base material.
The polyester film of the present embodiment may have layers other than the polyester substrate and the particle-containing layer. Such other layers include adhesion layers, release layers, antistatic layers and oligomer precipitation prevention layers. Further, an intermediate layer such as a primer layer may be provided between the polyester base material and the particle-containing layer. The thickness of these other layers is preferably 1 nm to 1 μm, more preferably 30 to 500 nm.

<Polyester base material>
A polyester substrate is a film-like object containing a polyester resin as a main component. Here, the “main component” means the component with the largest content (mass) among all the components contained in a certain object.
The polyester base material may contain a single polyester resin, or may contain two or more polyester resins.

The polyester base material of the polyester film of the present embodiment preferably does not substantially contain inorganic particles. That is, the content of the inorganic particles is 50 ppm by mass or less with respect to the total mass of the polyester base material when quantitative analysis of the elements derived from the inorganic particles is performed on the polyester base material by fluorescent X-ray analysis. is preferred. Here, examples of the inorganic particles include inorganic particles contained in the particle-containing layer described later.
The content of the particles contained in the polyester base material is more preferably 10 mass ppm or less with respect to the total mass of the polyester base material, and further preferably below the detection limit.

<<polyester resin>>
As the polyester resin, an aromatic polyester resin is preferable because it is excellent in dimensional stability, mechanical strength and transparency.
Examples of aromatic polyester resins include polyethylene terephthalate and polyethylene-2,6-naphthalate.

Representative examples of aromatic polyesters include polyesters whose main monomer units are ethylene terephthalate or ethylene-2,6-naphthalate (that is, polyethylene terephthalate (PET) or polyethylene-2,6-naphthalate (PEN)), and Included are polyesters (copolymers) containing monomer units of both ethylene terephthalate and ethylene-2,6-naphthalate.
The aromatic polyester is preferably an aromatic polyester having repeating units composed of 0 to 40 mol % of ethylene terephthalate units and 60 to 100 mol % of ethylene-2,6-naphthalate units.
Also, the intrinsic viscosity of the aromatic polyester is preferably in the range of 0.50 to 0.80. When the intrinsic viscosity is 0.50 or more, the film is less likely to break even if the draw ratio is increased, and whitening is less likely to occur even if the film is strongly drawn. On the other hand, when the intrinsic viscosity is 0.80 or less, there is no need to greatly improve the molecular weight, so the load in the melt polymerization and solid phase polymerization steps is small, which is preferable from the viewpoint of productivity.

The method for producing the polyester resin is not particularly limited, and known methods can be used. For example, there is a method of producing a polyester resin by subjecting a polyester resin precursor containing at least one dicarboxylic acid compound and at least one diol compound to polycondensation in the presence of a known compound such as a titanium compound. be done.
The materials used for producing the polyester resin are described below.

(Dicarboxylic acid compound)
A dicarboxylic acid compound is a compound selected from the group consisting of dicarboxylic acids and dicarboxylic acid ester compounds.
Examples of dicarboxylic acid compounds 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 these dicarboxylic acids. esters. Among them, aromatic dicarboxylic acid or methyl aromatic dicarboxylate is preferable.

Examples of aliphatic dicarboxylic acid compounds include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalonic acid, and ethylmalonic acid.
Alicyclic dicarboxylic acid compounds include, for example, adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, and decalinedicarboxylic acid.

Examples of aromatic dicarboxylic acid compounds 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, phenylindanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrene dicarboxylic acid, and 9,9′-bis(4- carboxyphenyl)fluoric acid and their methyl esters.
Among them, 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 may be copolymerized with another aromatic dicarboxylic acid such as isophthalic acid, or an aliphatic dicarboxylic acid.

(Diol compound)
Examples of diol compounds include aliphatic diol compounds, alicyclic diol compounds, and aromatic diol compounds, with aliphatic diol compounds being preferred.

Examples of aliphatic diol compounds include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, and neo Pentyl glycol may be mentioned, with ethylene glycol being preferred.
Alicyclic diol compounds include, for example, cyclohexanedimethanol, spiroglycol, and isosorbide.
Examples of aromatic diol compounds include bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, and 9,9′-bis(4-hydroxyphenyl)fluorene.
Only one kind of diol compound may be used, or two or more kinds thereof may be used in combination.

Compounds used for producing polyester resins are not particularly limited, and known compounds that can be used for synthesis of polyester resins can be used.
Compounds include, for example, alkali metal compounds (e.g., potassium compounds, sodium compounds), alkaline earth metal compounds (e.g., calcium compounds, magnesium compounds), zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, germanium compounds, and phosphorus compounds. Among them, titanium compounds are preferable from the viewpoint of catalytic activity and cost.
One of the above compounds may be used alone, or two or more thereof may be used in combination. at least one metal compound 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; It is preferable to use a compound together, and it is more preferable to use a titanium compound and a phosphorus compound together.
When the above compounds are added, the amount of each compound added is generally 1 to 500 ppm by mass with respect to the total mass of the polyester resin in terms of the metal element or phosphorus element, and 1 to 100 An amount that gives ppm by mass is preferred.

The titanium compound, including preferred embodiments, may be the same as the titanium compound used in step 1 of the first embodiment.
In addition, the magnesium compound and the phosphorus compound, including preferred embodiments, may be the same as the magnesium compound and the phosphorus compound, respectively, which are listed as the compounds that may be used in step 1 of the first embodiment.

(Terminal blocking agent)
In the production of the polyester resin, if necessary, a terminal blocker may be used. By using the terminal blocking agent, a structure derived from the terminal blocking agent is introduced to the terminal of the polyester resin.
The terminal blocking agent is not limited, and known terminal blocking agents can be used. Examples of terminal blocking agents include oxazoline-based compounds, carbodiimide-based compounds, and epoxy-based compounds.
As the end blocking agent, the content described in [0055] to [0064] of JP-A-2014-189002 can also be referred to, and the content of the above publication is incorporated herein.

(Other additives)
The polyester resin may contain other metal compounds, nitrogen-containing basic compounds, antioxidants, antistatic agents, ultraviolet absorbers, fluorescent whitening agents, dyes, and the like depending on the purpose.

The method for producing the polyester resin is not particularly limited, and includes known production methods such as batch, semi-batch and continuous methods. Examples of the method for producing the polyester resin include a transesterification method and a direct esterification method.
Among them, as a method for producing a polyester resin, the method described as the step 1 of the first embodiment is particularly preferable.
Furthermore, after these polymerization reactions, a solid phase polymerization reaction may be performed.

The content of the polyester resin in the polyester base is preferably 85% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and 98% by mass with respect to the total mass of the resin in the polyester base. The above are particularly preferred.
The upper limit of the content of the polyester resin is not particularly limited, and can be appropriately set, for example, within a range of 100% by mass or less with respect to the total mass of the resin in the polyester base material.

The polyester base material may contain components other than the polyester resin (for example, the compounds described above, unreacted raw material components, particles, water, and the like).
It is preferable that the polyester base material does not substantially contain inorganic particles, in order to obtain a more excellent effect of the present invention. The inorganic particles contained in the polyester base material include, for example, inorganic particles contained in the particle-containing layer described later, and furthermore, the metal compound and the phosphorus compound used in the step of polymerizing the polyester resin react to Inorganic particles (so-called internal particles) that precipitate as metal phosphates can be mentioned.
Moreover, it is preferable that the polyester base material does not substantially contain organic particles from the viewpoint that the effects of the present invention are more excellent. Organic particles contained in the polyester base material include, for example, organic particles contained in the particle-containing layer described later.

<Particle-containing layer>
The polyester film of the present embodiment preferably has a particle-containing layer on at least one side of the polyester substrate in that the transportability can be improved by imparting slipperiness. Specifically, the winding quality can be improved (blocking can be suppressed), the occurrence of scratches and defects during transportation can be suppressed, and wrinkles during high-speed transportation can be reduced.
The particle-containing layer may be provided directly on the surface of the polyester base material or may be provided via an intermediate layer, but it is preferable to provide it directly on the surface of the polyester base material in terms of better productivity.
The particle-containing layer preferably contains a binder together with the particles. The particle-containing layer may contain additives in addition to the particles and binder.

(particle)
The average particle size of the particles contained in the particle-containing layer is not particularly limited, preferably 1 to 1000 nm, more preferably 40 to 500 nm.
Particles include inorganic particles and organic particles.
Examples of 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).
Examples of organic particles include resin particles. Examples of resins constituting resin particles include acrylic resins such as polymethyl methacrylate resin (PMMA), polyester resins, silicone resins, styrene resins, urethane resins, and styrene-acrylic resins. The resin particles may or may not have a crosslinked structure. Specific examples include non-crosslinked acrylic resin particles, non-crosslinked styrene resin particles, crosslinked acrylic resin particles, crosslinked urethane resin particles, and divinylbenzene crosslinked particles. In addition, in this specification, an acrylic resin means a resin containing structural units derived from acrylate or methacrylate.

From the viewpoint of transportability, the content of particles in the particle-containing layer is preferably 0.1 to 30% by mass, more preferably 1 to 25% by mass, based on the total mass of the particle-containing layer.
Also, the content of the particles is preferably 0.0001 to 0.01% by mass, more preferably 0.0005 to 0.005% by mass, relative to the total mass of the polyester base material.

(binder)
The particle-containing layer preferably contains a binder. As the binder, a resin binder is preferred. As the resin binder, non-polyester resins are preferable, and examples thereof include acrylic resins, urethane resins, polyester resins, and olefin resins, and acrylic resins, urethane resins, and olefin resins are preferable. A known resin can be used as the binder. Also, the resin binder may be an acid-modified resin.
Moreover, the binder contained in the particle-containing layer may have a crosslinked structure. That is, the particle-containing layer may be a crosslinked film.
The particle-containing layer may contain a single binder, or may contain two or more binders.
The binder content is preferably 30 to 99.8% by mass, more preferably 50 to 99.5% by mass, based on the total mass of the particle-containing layer.

(Additive)
Additives contained in the particle-containing layer include, for example, surfactants, waxes, antioxidants, ultraviolet absorbers, colorants, reinforcing agents, plasticizers, antistatic agents, flame retardants, rust inhibitors, and anti-rust agents. Examples include fungicides.

The particle-containing layer preferably contains a surfactant from the viewpoint of improving the smoothness of the surface.
The surfactant is not particularly limited, and includes silicone surfactants, fluorine surfactants, and hydrocarbon surfactants. A fluorine-based surfactant having a fluoroalkyl group) or a hydrocarbon-based surfactant is preferable.
One type of surfactant may be used, or two or more types may be used in combination.
The content of the surfactant is preferably from 0.1 to 10% by mass, more preferably from 0.1 to 5% by mass, based on the total mass of the particle-containing layer, from the viewpoint of better surface smoothness.

The thickness of the particle-containing layer is preferably 1 nm to 1 μm, more preferably 1 to 500 nm, even more preferably 1 to 200 nm, from the viewpoint of low haze.
The thickness of the particle-containing layer is the arithmetic mean of the thicknesses of five locations on the section, which is measured using a scanning electron microscope (SEM) by preparing a section having a section perpendicular to the main surface of the polyester film. value.

[Physical properties, etc.]
The polyester film of the present embodiment may contain titanium, and preferably contains titanium.
Moreover, the polyester film of the present embodiment may contain an element derived from the compound added to the polyester resin. Among them, the polyester film preferably contains at least one element selected from the group consisting of magnesium and phosphorus, and more preferably contains magnesium and phosphorus.
Moreover, the polyester film of the present embodiment preferably contains at least one element selected from the group consisting of titanium, magnesium and phosphorus, and more preferably contains titanium, magnesium and phosphorus.
The content of each of the above elements is preferably 1 to 500 mass ppm, more preferably 1 to 100 mass ppm, relative to the total mass of the polyester film. The contents of the metal element and phosphorus element contained in the polyester film can be measured by ICP-MS according to the method for measuring the content of antimony.

When the polyester film of the present embodiment contains titanium, the content of the titanium element is preferably 1 to 30 mass ppm, more preferably 3 to 20 mass ppm, and even more preferably 5 to 15 mass ppm.
When the polyester film of the present embodiment contains magnesium, the content of the magnesium element is preferably 50 mass ppm or more with respect to the total mass of the polyester film in that it can impart high static electricity properties, and 50 to 100 mass. ppm is more preferred, 60 to 90 ppm by mass is more preferred, and 70 to 80 ppm by mass is particularly preferred.
When the polyester film of the present embodiment contains phosphorus, the content of the phosphorus element is preferably 50 to 90 mass ppm, more preferably 60 to 80 mass ppm, and 65 to 75 mass ppm, relative to the total mass of the polyester film. is more preferred.

<Thickness>
The thickness of the polyester film of the present embodiment is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 35 μm or less, from the viewpoint of superior optical failure suppression performance. Although the lower limit of the thickness is not particularly limited, it is preferably 1 µm or more, more preferably 5 µm or more, and even more preferably 10 µm or more in terms of improving strength and workability.
The thickness of the polyester film should be measured using a continuous stylus film thickness gauge. Specifically, the thickness of the polyester film is measured over 10 m along the longitudinal direction with a continuous stylus film thickness gauge. This measurement is performed at five different positions in the width direction. Let the arithmetic mean value of the obtained measured value be thickness.
In the case of a polyester film of less than 10 m, the thickness is measured with a stylus type film thickness meter at five different locations arbitrarily selected from the polyester film, and the arithmetic average value of the obtained measured values is taken as the thickness. do.

〔Production method〕
The method for producing the polyester film of the present embodiment is not particularly limited as long as the polyester film having the above configuration can be produced.
As a method for producing a polyester film having a polyester substrate and a particle-containing layer, for example, a polyester resin is melt-extruded to prepare a polyester substrate, and then a particle-containing layer-forming composition containing particles on one side of the polyester substrate. and then stretching, and a method of co-extrusion of a particle-containing layer-forming composition containing a polyester resin melt, particles and a binder and then stretching.

When the polyester film of the present embodiment is used for the production of a dry film resist, a substantially particle-free polyester substrate is prepared by melt extrusion molding, and then a composition containing particles is applied to one side of the polyester substrate. and then stretching to produce a polyester film. As a result, the particles contained in the polyester film can be reduced as much as possible while maintaining the slipperiness, so that the haze of the polyester film can be further reduced and a film with excellent optical failure suppression performance can be produced.
Moreover, as the method for producing the polyester film of the present embodiment, the method described as the method for producing the polyester film according to the above-described first embodiment, including its preferred mode, can be mentioned.

[Use]
Since the polyester film of the present embodiment is excellent in the effect of suppressing optical failures, it is suitably used as a film for producing a dry film resist.
Moreover, since the polyester film of the present embodiment is excellent in transparency, it can be used as an optical film other than for dry film resist production. For example, polyester films can be used for protective films for various applications, support films for various applications such as decorative sheets and decorative sheets, molding films such as decorative layers and resin sheets, films for optical displays, and conductive films. can be done. In addition, since the polyester film of the present embodiment is also excellent in smoothness, it can be used as a release film for various applications such as ceramic green sheet production, a film for semiconductor production process, a film for polarizing plate production process, a film for magnetic tape, and for labels, It can also be used as a separator for adhesive films for medical and office supplies.

[Dry film resist (DFR)]
The dry film resist (DFR) of the present invention has a polyester film and a photosensitive resin layer. DFRs are often used as photosensitive transfer members.
The DFR may have an intermediate layer between the polyester film and the photosensitive resin layer.
Here, the intermediate layer means all layers between the polyester film and the photosensitive resin layer.

The DFR of the present invention has a polyester film. When a polyester film is used as the support, it is preferably a peelable support.
The polyester film has already been described as the polyester film of the second embodiment.
When the particle-containing layer is formed only on one surface of the polyester film, the photosensitive resin layer is preferably formed on the surface of the polyester film opposite to the particle-containing layer.

A known photosensitive resin layer can be used as the photosensitive resin layer. A negative photosensitive resin layer is preferable because it has excellent lamination properties at high speed. Specifically, a binder polymer (preferably a polymer having an acid group), a polymerizable compound having an ethylenically unsaturated bond, and a photosensitive resin layer having a photopolymerization initiator are preferred.
As the photosensitive resin layer, for example, the photosensitive resin layer described in JP-A-2016-224162 may be used. Further, a photosensitive resin layer containing a binder polymer, a polymerizable compound having an ethylenically unsaturated bond, and a photopolymerization initiator described in International Publication No. 2018/105313 is also preferred. A more preferable form is a photosensitive resin layer containing an alkali-soluble acrylic resin having a cyclic structure, a polyfunctional acrylate monomer, and an oxime-based photopolymerization initiator or a bisimidazole-based photopolymerization initiator.

The DFR preferably has a protective film on the surface of the photosensitive resin layer opposite to the support side.
An embodiment using a polyester film as the protective film is also preferred.

[Method for manufacturing DFR]
A method for producing DFR is not particularly limited, and DFR can be produced by a known production method.
As a method for producing a DFR, for example, a step of mixing the constituent components of each layer and a solvent described above to prepare a composition for forming each layer such as a polyester resin composition, and a step of applying the above composition on the surface of the polyester film After applying a substance to form a coating layer, the step of drying the coating layer to form each layer is performed in order according to the desired layer structure, thereby forming a polyester film and an intermediate layer provided as necessary. , and a photosensitive resin layer in this order.

The DFR of the present invention has the excellent effect of being able to form resist patterns with few optical defects even when used to form high-definition resist patterns.
Therefore, the DFR of the present invention is preferably used for manufacturing resist patterns and circuit wiring.

[Third Embodiment: Polyester Film (2)]
The polyester film of the third embodiment of the present invention is characterized in that the total number of foreign matter and voids with a diameter of 9 to 20 μm observed with a transmission polarizing microscope is 1.7/mm ³ or less.

Since the polyester film of the present embodiment has the above structure, the effect of suppressing local concave defects in the ceramic green sheet produced using the polyester film of the present embodiment (hereinafter, also referred to as "defect suppression effect" Although the details of the reason for achieving the above are not clear, polyester films having a density of foreign matter and voids with a diameter of 9 to 20 μm below a predetermined value have few protrusions on the surface. It is presumed that the occurrence of localized concave defects in the ceramic green sheet was further suppressed, and the smoothness was further improved.

[Characteristics of polyester film]
<Total number of foreign matter and voids>
In the polyester film of the present embodiment, the total number of foreign matter and voids with a diameter of 9 to 20 μm observed with a polarizing microscope is 1.7/mm ³ or less.
The unit of "not more than 3 pieces/mm ³ " means the total number of foreign matter or voids per volume of the polyester film observed using a polarizing microscope.
Foreign matter and voids with a diameter of 9 to 20 μm and foreign matter and voids with a diameter of 3 μm or more and less than 9 μm contained in the polyester film are as described in the second embodiment.
In addition, the total number of foreign substances or voids with a diameter of 9 to 20 μm ^per volume of the polyester film is measured by the method described in the second embodiment. After dividing by the "thickness of the polyester film", the obtained value can be obtained by converting the obtained value into a numerical value per 1 mm ³ of the volume of the polyester film. The total number of foreign matter and voids having a diameter of 3 μm or more and less than 9 μm per volume of the polyester film can also be obtained by the same method.

The total number of foreign particles and voids with a diameter of 9 to 20 μm observed using a polarizing microscope is preferably 1.5/mm ³ or less in terms of the effect of suppressing concave defects. The lower limit of the total number of foreign matter and voids having a diameter of less than 9 to 20 μm is not particularly limited, and may be 0/mm ³ .
Means for adjusting the total number of foreign matter and voids with a diameter of 9 to 20 μm within the above range include a method of reducing the content of antimony contained in the polyester film to 1 ppm by mass or less, which will be described later, and when producing the polyester film, the raw material and a method of introducing a step of filtering the melt of the polyester resin used as a by a method according to the step 2 of the first embodiment.

The total number of foreign substances and voids with a diameter of 3 μm or more and less than 9 μm observed with a polarizing microscope on the polyester film is preferably 27.0/mm ³ or less, and 26.0 Pieces/mm ³ or less is more preferable. The lower limit of the total number of foreign matter and voids with a diameter of 3 μm or more and less than 9 μm is not particularly limited, and may be 0/mm ³ .
In addition, the total number of foreign matter and voids with a diameter of more than 20 μm observed on the polyester film using a polarizing microscope is preferably less than 1/500 mm ² , and 0/mm ³ (that is, not observed). is more preferred.

<Content of antimony>
The content of antimony (Sb) contained in the polyester film is preferably 1 mass ppm or less, more preferably 0.7 mass ppm or less, still more preferably 0.6 mass ppm or less, with respect to the total mass of the polyester film. 0.5 mass ppm or less is particularly preferred. By setting the content of antimony within the above range, it is easier to manufacture a polyester film in which the total number of foreign matter and voids with a diameter of 9 to 20 μm observed with a transmission polarizing microscope is 1.7/mm ³ or less. Become.
The lower limit of the antimony content is not particularly limited, and may be 0 mass ppm based on the total mass of the polyester film.
The method for measuring the content of antimony contained in the polyester film is as described in the second embodiment.

<Haze>
The haze of the polyester film of the present embodiment is preferably 5% or less, more preferably 2.0% or less, even more preferably 1.5% or less. Although the lower limit is not particularly limited, 0% or more is preferable.
The method for measuring the haze of the polyester film is as described in the second embodiment.

〔composition〕
The polyester film of the present embodiment may have a single-layer structure consisting only of a polyester base material formed using a melt of a polyester resin, and a polyester base material formed using a melt of a polyester resin, It may be a multilayer structure having a particle-containing layer containing particles.
When the polyester film has a particle-containing layer, one particle-containing layer may be disposed on one side of the polyester substrate, or two particle-containing layers may be disposed on both sides of the polyester substrate. Among them, it is preferable that one particle-containing layer is arranged on one side of the polyester base material.
The polyester film may have layers other than the polyester substrate and the particle-containing layer. Such other layers include adhesion layers, release layers, antistatic layers and oligomer precipitation prevention layers. Further, an intermediate layer such as a primer layer may be provided between the polyester base material and the particle-containing layer. The thickness of these other layers is preferably 1 nm to 1 μm, more preferably 30 to 500 nm.

The polyester base material and particle-containing layer that the polyester film of this embodiment may have, and the physical properties of the polyester film are as described in the second embodiment, except for the following items.

<Thickness>
The thickness of the polyester film of the present embodiment is preferably 75 μm or less, more preferably 50 μm or less, and even more preferably 35 μm or less, in terms of reducing production costs. Although the lower limit of the thickness is not particularly limited, it is preferably 5 µm or more, more preferably 10 µm or more, still more preferably 18 µm or more, and particularly preferably 25 µm or more in terms of improving strength and workability.
The method for measuring the thickness of the polyester film is as described in the second embodiment.

〔Production method〕
The method for producing the polyester film of the present embodiment is not particularly limited as long as the polyester film having the above structure can be produced.
As a method for producing a polyester film having a polyester substrate and a particle-containing layer, for example, a polyester resin is melt-extruded to prepare a polyester substrate, and then a particle-containing layer-forming composition containing particles on one side of the polyester substrate. and then stretching, and a method of co-extrusion of a particle-containing layer-forming composition containing a polyester resin melt, particles and a binder and then stretching.

When the polyester film of the present embodiment is used for the production of a dry film resist, a substantially particle-free polyester substrate is prepared by melt extrusion molding, and then a composition containing particles is applied to one side of the polyester substrate. and then stretching to produce a polyester film. As a result, the particles contained in the polyester film can be reduced as much as possible while maintaining the slipperiness, and a ceramic green sheet can be produced in which local concave defects are further suppressed.
Moreover, as the method for producing the polyester film of the present embodiment, the method described as the method for producing the polyester film according to the above-described first embodiment, including its preferred mode, can be mentioned.

[Use]
Since the polyester film of the present embodiment is excellent in the effect of suppressing concave defects, it is suitably used as a film for producing ceramic green sheets.
In addition, since the polyester film of the present embodiment has excellent smoothness, it is used as a film for semiconductor manufacturing processes, a film for polarizing plate manufacturing processes, a film for magnetic tapes, and an adhesive film for labels, medical and office supplies. It can also be used as a separator.
Furthermore, since the polyester film of the present embodiment is excellent in transparency and an effect of suppressing optical failure, it can also be used as an optical film. For example, films for producing dry film resists, protective films for various applications, decorative sheets and support films for various applications such as decorative sheets, molding films such as decorative layers and resin sheets, films for optical displays, and conductive films For example, a polyester film can be used.

[Method for producing ceramic green sheet]
A method for producing a ceramic green sheet using the polyester film of the present embodiment is not particularly limited, and a known method can be used. As a method for producing a ceramic green sheet, for example, the prepared ceramic slurry is applied to one main surface of the release film having the polyester film of the present embodiment, and the solvent contained in the ceramic slurry is removed by drying. A method of forming a green sheet is included.

The configuration of the release film has the polyester film of the present embodiment, and as long as the formed ceramic green sheet can be released from the main surface (hereinafter also referred to as "release surface") to which the ceramic slurry is applied, There are no particular restrictions. The release film may be a laminated film having the polyester film of the present embodiment and a release layer.
Further, when the ceramic green sheet to be formed can be peeled off (for example, when the ceramic green sheet has peeling performance), the release film having the polyester film of the present embodiment may have no release layer. , the polyester film of the present embodiment may be used alone as a release film.

As the release film, a laminate film having the polyester film of the present embodiment and a release layer is preferable.
In the laminated film, the release layer is arranged as the outermost layer, and one main surface of the release layer serves as the release surface on which the ceramic green sheet is formed. When the particle-containing layer is formed only on one surface of the polyester film, the release layer is preferably formed on the surface of the polyester film opposite to the particle-containing layer.
The laminate film may have an intermediate layer between the polyester film and the release layer. Here, the intermediate layer means all layers between the polyester film and the release layer. Examples of the intermediate layer include a non-polyester resin layer that suppresses precipitation of oligomers from the polyester base material, an antistatic layer, and the like.

The release film can be produced, for example, by providing a release layer on one main surface of the polyester film. The release layer may be provided directly on the surface of the polyester base material, or may be provided on the polyester base material via another layer.
The release layer is preferably provided directly on the surface of the polyester base material in terms of better smoothness. Also, if necessary, a release layer may be laminated on the polyester film via the intermediate layer.

The composition of the release layer is not particularly limited as long as the ceramic green sheet can be manufactured in a separable manner, but the release layer preferably contains a resin as a release agent.
The resin contained in the release layer is not particularly limited, and examples thereof include silicone resins, fluororesins, alkyd resins, acrylic resins, various waxes, and aliphatic olefins. Silicone resins are preferred in terms of superior release properties of the ceramic green sheet. preferable. The release layer is also preferably a cured layer obtained by curing components contained in the release layer.
The release layer may contain other components such as a resin other than the release agent and additives, in addition to the resin used as the release agent. Additives include light and heavy release additives to adjust release force, adhesion improvers, and antistatic agents.

A silicone resin means a resin having a silicone structure in its molecule. Examples of silicone resins include curable silicone resins, silicone graft resins, and modified silicone resins such as alkyl-modified silicone resins, and reactive curable silicone resins are preferred.
Examples of reactive curable silicone resins include addition reaction silicone resins, condensation reaction silicone resins, and ultraviolet or electron beam curable silicone resins.

The thickness of the release layer is preferably from 10 to 1000 nm, more preferably from 30 to 700 nm, in terms of excellent balance between release performance and smoothness of the release layer surface.
The thickness of the release layer is measured using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) by preparing a section having a cross section perpendicular to the main surface of the release film. Arithmetic mean value of the thickness at each point.

As a method of forming a release layer on a polyester film, for example, a release layer forming composition is applied to the surface of the polyester film, the coating film is dried to remove the solvent, and if necessary, heating or irradiation with light is performed. method.
As the release layer-forming composition, a known release layer-forming composition can be used. The release layer-forming composition can be prepared, for example, by mixing a release agent, a solvent, and other components added as necessary. Examples of solvents include water, alcohol solvents, ether solvents, ketone solvents, and aromatic hydrocarbon solvents. The release layer-forming composition may contain a single solvent, or may contain two or more solvents.
The content of the solvent is preferably 80 to 99.5% by mass with respect to the total mass of the release layer-forming composition. The total content of components (solid content) other than the solvent in the release layer-forming composition is preferably 0.5 to 20% by mass with respect to the total mass of the release layer-forming composition.

The method for applying the release layer-forming composition and the method for drying the coating film are not particularly limited, and known methods can be used. Specific examples of the coating method include the in-line coating method mentioned in step 4 in the method for producing a polyester film, and the offline coating method in which a separate coater is used after the polyester film is produced. Examples of the coating method include gravure coating, bar coating, spray coating, spin coating, knife coating, roll coating, and die coating.
In order to improve the adhesion between the polyester film and the release layer, the surface of the polyester film may be subjected to pretreatment such as anchor coating, corona treatment and plasma treatment before providing the release layer.

The method of applying the ceramic slurry to the release surface of the release film is not particularly limited. For example, a method of applying a ceramic slurry obtained by dispersing ceramic powder and a binder agent in a solvent and removing the solvent by heating and drying. can be applied. Binder agents include, for example, polyvinyl butyral. Examples of solvents include ethanol and toluene.

The produced ceramic green sheets are used to manufacture ceramic capacitors. A known method can be applied as a method of manufacturing a ceramic capacitor using a ceramic green sheet, and examples thereof include the following method.
First, internal electrodes are provided on the laminate of the release film and the ceramic green sheets produced by the above method by applying or printing a conductive paste. Next, the release film is removed from the laminate of ceramic green sheets, the ceramic green sheets with internal electrodes are successively laminated, and the resulting laminate is pressed to produce an intermediate laminate. After cutting the intermediate laminate into a desired shape, the cut intermediate laminate is fired to obtain a ceramic body. Next, a ceramic capacitor is obtained by forming external electrodes electrically connected to the internal electrodes on the two end surfaces of the fired intermediate laminate using a conductive paste such as silver.

The release film having the polyester film of the present embodiment includes a protective film for dry film resist, a film for sheet molding such as a decorative layer and a resin sheet, a release film for process manufacturing such as a semiconductor manufacturing process, and a polarizing plate manufacturing process. It can also be used as a release film, and as a separator for adhesive films for labels, medical and office supplies.

The present invention will be described in more detail based on examples below.
The materials, amounts used, proportions, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed as limited by the examples shown below. Unless otherwise specified, "parts", "ppm" and "%" are based on mass.

In the present examples, the expression "film" includes both aspects of a polyester base material only and aspects of a polyester film having a polyester base material and a particle-containing layer. Moreover, the notation of "film" shall include all unstretched films, uniaxially stretched films, and biaxially stretched films.

First, the method for producing the films used in each example and comparative example will be described.

[Example 1]
[Production of polyester pellets before washing]
Using terephthalic acid and ethylene glycol as raw materials, an antimony compound was used to conduct an esterification reaction and a polycondensation reaction in a continuous polymerization apparatus to produce polyester pellets. The continuous polymerization apparatus has a mixing tank, a first esterification reaction tank, a second esterification reaction tank, a first polycondensation reaction tank, a second polycondensation reaction tank and a third polycondensation reaction tank in this order. Hereinafter, the first esterification reaction tank, the second esterification reaction tank, the first polycondensation reaction tank, the second polycondensation reaction tank, and the third polycondensation reaction tank are also collectively referred to as "reaction tanks". The production of polyester pellets was carried out according to the method described in (1) and (2) of [Production of polyester film] described later, except that an antimony compound was added in place of the titanium compound. After the continuous production of polyester pellets was completed, the reactor provided in the continuous polymerization apparatus was washed as described below.

[Cleaning of reaction tank]
An amount of triethylene glycol corresponding to 70% by volume of the reaction vessel was added as a cleaning liquid to the reaction vessel used for the polymerization of the polyester resin, and the headspace of the reaction vessel was replaced with nitrogen. °C. After the washing liquid was stirred at 270° C. for 6 hours, it was cooled to room temperature and then the washing liquid was discharged. The piping connecting the reactors for transporting the product was cleaned by flowing a mixture of triethylene glycol and water. When the inside of the reaction vessel was visually checked, it was confirmed that stains still remained.
Next, the wetted part of the reaction tank was cleaned by buffing with no solvent until the dirt in the reaction tank was removed and the wetted part of the reaction tank regained its metallic luster. After that, the inside of the reaction tank was completely cleaned by high-pressure water washing.
All tanks and pipes used for the polymerization of polyethylene terephthalate were washed in the same manner as the above-described method for washing the reaction tank.

[Production of polyester film]
A polyester film was continuously produced by the following procedures (1) to (3) using a continuous polymerization apparatus equipped with a washed reaction vessel.

(1) Esterification Reaction A mixing tank was charged with 4.7 tons of high-purity terephthalic acid and 1.8 tons of ethylene glycol as polyester resin precursors, and the mixture was mixed for 90 minutes to form a slurry. The resulting slurry was continuously supplied from the mixing tank to the first esterification reactor at a flow rate of 3800 kg/h. Furthermore, an ethylene glycol solution of citric acid chelate titanium complex (VERTEC AC-420, manufactured by Johnson Matthey) in which citric acid is coordinated to Ti element was continuously supplied to the first esterification reaction tank, and the temperature in the tank was 251 ° C. , under stirring with an average residence time of about 4.3 hours. At this time, the citric acid chelate titanium complex was continuously added so that the added amount of Ti in terms of element was 7 ppm with respect to the total amount of the polyester resin precursor. At this time, the obtained oligomer had an acid value of 500 eq/ton.

The reactant obtained in the first esterification reaction tank was transferred to the second esterification reaction tank and reacted under stirring at an internal tank temperature of 250° C. for 1.2 hours with an average residence time of 190 eq/ton. was obtained. The inside of the second esterification reactor is partitioned into three zones consisting of a first zone, a second zone and a third zone in the order in which the oligomers are supplied. Continuously supplied so that the amount added was 75 ppm with respect to the total amount of the oligomer in terms of elements, and then from the third zone, an ethylene glycol solution of trimethyl phosphate was added. It was continuously supplied so as to be 65 ppm with respect to the total amount.

(2) Polycondensation Reaction The esterification reaction product obtained above is continuously supplied to the first polycondensation reaction tank and stirred at a reaction temperature of 270° C. and a tank pressure of 20 torr (2.67×10 ^{−3 )} . MPa) with an average residence time of about 1.8 hours.
Furthermore, the intermediate polymer obtained in the first polycondensation reaction tank was transferred to the second polycondensation reaction tank, and under stirring, the temperature in the tank was 276 ° C. and the pressure in the tank was 3.0 torr (3.99 × 10 ^-4 MPa). ) under conditions of a residence time of about 1.2 hours (polycondensation).
Next, the intermediate polymer obtained in the second polycondensation reaction tank was further transferred to the third polycondensation reaction tank, and the temperature in the tank was 278 ° C. and the pressure in the tank was 1.0 torr (1.33 × 10 ^-4 MPa). , the reaction (polycondensation) was carried out under the conditions of a residence time of 1.5 hours, and polyethylene terephthalate (PET) was discharged from the third polycondensation reactor as a product.
The resulting product was analyzed for Sb content using an ICP-MS analyzer (manufactured by Agilent Technologies, "Agilent 7800 ICP-MS"). It was 0.9 ppm.

Next, the obtained product was extruded into cold water in the form of a strand and immediately cut to prepare polyester resin pellets <cross section: about 4 mm long axis, about 2 mm short axis, length: about 3 mm>.
The steps from charging the polyester resin precursor, discharging the product from the third polycondensation reactor, and producing pellets were continuously carried out. That is, after starting to produce pellets of the product obtained by polymerization of the polyester resin precursor when charging was started, pellets were continuously produced.

(3) Formation of film After drying the pellets obtained in (2) above until the moisture content is 50 ppm or less, they are put into a hopper of a single-screw kneading extruder with a diameter of 30 mm, and the pellets are heated to 280°C. and extruded the molten pellets. The extruded melt was passed through a filtration device A described later, extruded from a die to a cooling cast drum at 25° C., and brought into close contact with the cast drum using an electrostatic application method. A particle-free unstretched polyester film was obtained by peeling the film using a stripping roll placed opposite the casting drum.
In Example 1, the time for continuous polymerization from the start of charging of the polyester resin precursor to the preparation of polyester pellets by the methods described in (1) and (2) above (hereinafter simply " An unstretched polyester film was produced using the pellets produced after 72 hours had elapsed.
The filtering device A is a filtering device having the same configuration as the filtering device 36 shown in FIG. 145 laminated filters are provided in which the porosity and layer thickness of the sintered body are adjusted so that the filtration accuracy of the fibrous metal sintered body is 3 μm. It was a filtering device with

With reference to the conditions described in [0160] to [0169] of International Publication No. WO 2020/158316, the obtained unstretched polyester film is longitudinally stretched and the particle-containing layer-forming composition is applied to the surface of the film to obtain. The resulting particle-containing layer-attached film was stretched to prepare a biaxially stretched polyester film, which was wound up every 7000 m. The thickness of the produced biaxially stretched polyester film was 16 μm (including a particle-containing layer with a thickness of 40 nm).
The obtained polyester film was analyzed using an ICP-MS analyzer in the same manner as described above, and the content of each element contained in the film was measured. As a result, the Sb content was 0.8 ppm, the Ti content was 7 ppm, the Mg content was 75 ppm, and the P content was 65 ppm with respect to the total mass of the polyester film.

[Examples 2 to 5]
The use of the filter B in which the filtration accuracy of the fibrous metal sintered body in the filter A was changed to 2 μm, and the fact that the filter was discharged from the third condensation reaction tank after the elapsed time shown in Table 1 has passed. Biaxially stretched polyester films of Examples 2 to 5 were produced in the same manner as in Example 1, except that polyester pellets produced using the product obtained from the above were used.

[Examples 6-7]
In the film manufacturing process, the same as in Example 5, except that the amount of melted polyester pellets extruded from the die to the cast drum was changed so that the thickness of the biaxially stretched polyester film was the thickness shown in Table 1. to produce biaxially stretched films of Examples 6 and 7, respectively.

[Examples 8-9]
In the production of polyester pellets before washing, the titanium compound described in (1) of [Production of polyester film] in Example 1 was used instead of the antimony compound, and the elapsed time described in Table 1 passed. The biaxially stretched polyester films of Examples 8 and 9 were prepared in the same manner as in Example 2, except that the polyester pellets made using the product discharged from the third condensation reaction tank were used. manufactured.

[Comparative Example 1]
In [Production of polyester film] of Example 1, instead of the citric acid chelate titanium complex, an antimony compound (antimony trioxide, diantimony trioxide, Nippon Seiko Co., Ltd. "PATOX-C") was continuously added to the first esterification reactor to continuously produce polyester pellets in the same manner as in Example 5, Comparative Example 1 A biaxially oriented polyester film was produced.

[Comparative Example 2]
A biaxially stretched polyester film was produced in the same manner as in Example 5, except that in the production of the polyester film, the melted polyester pellets were passed through a filtration device C described later.
Here, the filter device C is provided with 145 filters "NF2M-4C" (manufactured by Nippon Seisen Co., Ltd.) having a fibrous metal sintered body and a filter medium with a filtration accuracy of 4 μm attached. It is a device with

[Comparative Example 3]
A biaxially stretched polyester film of Comparative Example 3 was produced in the same manner as in Example 5, except that the reaction tank was not washed before producing the polyester film.

[Reference Examples 1 and 2]
A three-layer structure biaxially stretched PET film "Lumirror 16FB40" (manufactured by Toray Industries, Inc.) having layers containing particles on both front and back surfaces was prepared (Reference Example 1).
In addition, a three-layer structure biaxially stretched PET film "Lumirror 16KS40" (manufactured by Toray Industries, Inc.) having layers containing fine particles on both front and back surfaces was prepared (Reference Example 2).

The products used in the production of the films in Examples 2-9 and Comparative Examples 1-3, the films produced in Examples 2-9 and Comparative Examples 1-3, and the 2 used in Reference Examples 1-2 Each axially stretched PET film was analyzed using an ICP-MS analyzer in the same manner as in Example 1 to measure the content of each element. Table 1 shows the measurement results of the Sb element content in each. In each of Examples 2 to 9 and Comparative Examples 1 to 3, the Ti content was 7 ppm, the Mg content was 75 ppm, and the P content was 65 ppm with respect to the total mass of the polyester film.
Further, none of the unstretched polyester films produced in Examples 1-9 and Comparative Examples 1-3 contained inorganic particles and organic particles.

[Film measurement]
<Total number of foreign matter and voids>
Visible light is irradiated from the smooth surface side of each film (surface roughness is measured with an optical interference type roughness meter, and the surface with smaller roughness), and a transmission polarizing microscope (BX51, manufactured by OLYMPUS) is used. Observe a 5 mm × 5 mm square visual field range of each film at a magnification of 100 times, and the number of foreign substances and voids with a diameter of 9 to 20 μm and foreign substances and voids with a diameter of 3 μm or more and less than 9 μm in the thickness direction of the film. counted.
In the measurement of foreign matter and voids, a transmission polarizing microscope with a polarizing lens is used to observe the change in color density (refractive index change) of the resin around the foreign matter or voids, thereby identifying foreign matter and voids present inside the film. counted. Further, application software (manufactured by OLYMPUS, "XD 2D Measurement") was used to enlarge the field of view on the monitor for observation, thereby measuring minute foreign matters and voids.
For each film, perform the above observation in 20 arbitrarily selected fields of view, and measure the foreign matter and voids, calculate the ^total number of measured foreign substances and voids, The total number of foreign matter and voids was taken as the total number.

In addition, from the volume obtained by multiplying the result of calculation of the total number of foreign matter and voids measured by the above method by the observation field of view and the thickness of each film, foreign matter with a diameter of 9 to 20 μm per volume of each film And the total number of voids (pieces/mm ³ ), and the total number of foreign matter and voids having a diameter of 3 μm or more and less than 9 μm per volume of each film (pieces/mm ³ ) were calculated.
In addition, according to the above method, foreign matter and voids with a diameter of more than 20 μm were measured, but no foreign matter and voids with a diameter of more than 20 μm were observed in any of the films.

<Haze measurement>
The haze of the film produced or prepared in each example was measured by a method according to JIS K 7105 using a haze meter (NDH-2000, manufactured by Nippon Denshoku Industries Co., Ltd.). Table 1 shows the measurement results.

<Preparation of photosensitive transfer member>
The film obtained in each example was applied as a support for a photosensitive transfer member. That is, a thermoplastic resin layer-forming coating liquid having the following formulation F is applied to the surface of the obtained film opposite to the particle-containing layer, and the obtained coating film is dried at 80° C. to form a thermoplastic resin layer. formed. Next, a coating liquid for forming a water-soluble resin layer having the following formulation G was applied onto the thermoplastic resin layer, and the resulting coating film was dried at 80° C. to form a water-soluble resin layer. Further, a coating solution for forming a photosensitive resin layer having the following formulation H was applied onto the water-soluble resin layer, and the resulting coating film was dried at 80° C. to form a photosensitive resin layer. Finally, a PET film (Lumirror 16KS40, manufactured by Toray Industries, Inc.) was press-bonded to the surface of the photosensitive resin layer as a protective film, and the resulting laminate was wound up to produce a roll-shaped photosensitive transfer member.
The above photosensitive transfer member is an example of DFR, and has a layer structure consisting of support/thermoplastic resin layer/water-soluble resin layer/photosensitive resin layer/protective film. The thickness of the thermoplastic resin layer was 2 μm, the thickness of the water-soluble resin layer was 1 μm, and the thickness of the photosensitive resin layer was 2 μm.
For the films of Reference Examples 1 and 2, a thermoplastic resin layer, a water-soluble resin layer, a photosensitive resin layer and a protective film were laminated on the smoother surface by the method described above.

(Prescription F: Coating liquid for forming thermoplastic resin layer)
22.7 parts of a copolymer obtained by polymerizing benzyl methacrylate, methacrylic acid and acrylic acid (mass ratio of each monomer = 75:10:15, molecular weight of 30,000, solid content concentration of 30%) 22.7 parts , 6-Bis (diphenylamino) fluorane: 0.12 parts Oxime sulfonate-type photoacid generator (synthesized according to paragraph 0227 of JP-A-2013-047765): 0.2 parts Tricyclodecanedimethanol di Acrylate: 3.32 parts ・UV curable urethane acrylate oligomer (Taisei Fine Chemical Co., Ltd. “8UX-015A”, 15 functional): 1.66 parts ・Multifunctional acrylate monomer (Toagosei Co., Ltd. “Aronix (registered Trademark) TO-2349"): 0.55 parts Surfactant (manufactured by DIC Corporation "Megafac (registered trademark) F-552"): 0.02 parts

(Prescription G: Coating liquid for forming water-soluble resin layer)
・Polyvinyl alcohol (“Kuraray Poval (registered trademark) 4-88LA” manufactured by Kuraray Co., Ltd.): 3.22 parts ・Polyvinylpyrrolidone (“K-30” manufactured by Nippon Shokubai Co., Ltd.): 1.49 parts ・Surfactant Agent ("Megafac F-444" manufactured by DIC Corporation): 0.0035 parts Methanol (manufactured by Mitsubishi Gas Chemical Co., Ltd.): 57.1 parts Ion-exchanged water: 38.12 parts

(Prescription H: Coating liquid for forming photosensitive resin layer)
・Copolymer obtained by polymerizing styrene, methacrylic acid and methyl methacrylate (mass ratio of each monomer = 52:29:19, molecular weight of 60,000, aqueous dispersion with solid concentration of 30%): 25.2 parts ・Leuco crystal violet: 0.06 parts Photopolymerization initiator (2-(2-chlorophenyl)-4,5-diphenylimidazole dimer): 1.03 parts 4,4'-bis (diethylamino) benzophenone: 0 .04 parts N-phenylcarbamoylmethyl-N-carboxymethylaniline: 0.02 parts Ethoxylated bisphenol A dimethacrylate (“NK Ester BPE-500” manufactured by Shin-Nakamura Chemical Co., Ltd.): 5.61 parts Polyfunctional acrylate monomer (“Aronix M-270” manufactured by Toagosei Co., Ltd.): 0.58 parts Phenothiazine: 0.04 parts 4-Hydroxymethyl-4-methyl-1-phenyl-3-pyrazolidone: 0. 002 parts Surfactant ("Megafac F-552" manufactured by DIC Corporation): 0.048 parts Propylene glycol monomethyl ether acetate: 19.7 parts Methyl ethyl ketone: 43.8 parts

[Optical failure evaluation (pinhole evaluation)]
A PET substrate with a copper layer was produced by forming a copper layer with a thickness of 200 nm on a polyethylene terephthalate (PET) film with a thickness of 100 μm by a sputtering method.
The roll-shaped photosensitive transfer member prepared above was unwound, and the protective film was peeled off from the photosensitive transfer member. Next, the photosensitive transfer member and the PET substrate with the copper layer were laminated together so that the photosensitive resin layer exposed by peeling off the protective film and the copper layer were in contact with each other to obtain a laminate. This bonding step was performed under conditions of a roll temperature of 100° C., a linear pressure of 1.0 MPa, and a linear velocity of 4.0 m/min.

The support of the obtained laminate (the film produced or prepared in each example, not the PET substrate of the copper layer-attached PET substrate) is irradiated with an ultra-high pressure mercury lamp (main exposure wavelength: 365 nm) to make it photosensitive. The entire surface of the resin layer was exposed with an exposure amount of 180 mJ/cm ² .
After peeling the support from the exposed laminate, 1.0% at a liquid temperature of 25° C. is applied to the surface of the laminate on which the thermoplastic resin layer, water-soluble resin layer and photosensitive resin layer are laminated. Shower development was performed for 30 seconds using an aqueous sodium carbonate solution. After performing shower development, the entire surface of the exposed photosensitive resin layer was observed to confirm the presence or absence of pinholes. Pinholes in the photosensitive resin layer after exposure are caused by foreign substances or voids contained in the support that cause unexposed areas in the photosensitive resin layer. It is thought that this is caused by removing the water-soluble resin layer and the thermoplastic resin layer laminated on the part. When a pinhole was generated in the photosensitive resin layer after exposure, the pinhole diameter was measured.
As a result of observation of the laminate, if no pinholes were confirmed in the photosensitive resin layer, or if pinholes were confirmed in the photosensitive resin layer but the pinhole diameter was 3 μm or less, the allowable range shall be included in

Table 1 below shows the production process of the film, the Sb content of the pellets used in the production of the film, the composition and physical properties of the produced film, and the above evaluation results for each example.
In the table, the "metal compound" column represents the metal compound used in (1) the esterification reaction in polyester film production, the notation "Ti" indicates that a titanium compound was used, and "Sb" and indicates that an antimony compound was used.
In the table, the notation "Yes" in the "Reaction vessel cleaning" column indicates that polyester pellets were produced using the cleaned reaction vessel, and the notation "No" indicates the reaction vessel that was not cleaned. It shows that polyester pellets were produced using.
The column "manufactured product type before washing" represents the metal compound used during the esterification reaction in the production of polyester pellets before washing the reaction tank, and the notation "Ti" indicates that a titanium compound was used. The notation "Sb" indicates that an antimony compound was used.
The "elapsed time" column indicates how much time has elapsed since the start of charging of the polyester resin precursor, among the polyester pellets used in the production of the film, among the polyester pellets that were continuously produced using the reaction tank. Indicates whether the polyester pellet was manufactured at the time point.

The “Sb [ppm]” column of “Pellets” indicates the Sb content (unit: mass ppm) relative to the total mass of polyester pellets analyzed using an ICP-MS analyzer.
The "melt filter" column shows the filtration accuracy (unit: μm) of the fibrous metal sintered body contained in the filter medium.

The "3 to 9 μm foreign matter and voids" column in "Film" indicates the total number of foreign matter and voids with a diameter of 3 μm or more and less than 9 μm per 500 mm ² of the film measured by the above method. indicates the total number of foreign particles and voids with a diameter of 9 to 20 μm per 500 mm ² of film measured by the method described above.
The numerical values of foreign matter and voids in Reference Examples 1 ^and 2 are reference values. In Reference Example 2, the total number of foreign matter and voids with a diameter of 5 μm or more per 500 mm ² of film measured according to the above method is shown.

From Table 1, it is confirmed that the polyester films of Examples 1 to 9 according to the present invention are more effective in suppressing the occurrence of optical defects appearing as pinholes than Comparative Examples 1 to 3 and Reference Examples 1 and 2. was done.

It was also confirmed that when the total number of foreign matter and voids with a diameter of 3 μm or more and less than 9 μm is 100/500 mm ² or less, the effect of suppressing the occurrence of optical defects is further excellent (comparison of Examples 1 to 9).
It was confirmed that when the total number of foreign matter and voids with a diameter of 9 to 20 μm was 7 pieces/500 mm ² or less, the effect of suppressing the occurrence of optical defects was further excellent (comparison with Examples 1 to 9).
When the Sb content in the polyester pellet is 0.8 mass ppm or less, the effect of suppressing the occurrence of optical defects is further excellent, and when it is 0.6 mass ppm or less, the effect of suppressing the occurrence of optical defects is particularly excellent. Confirmed (comparison of Examples 1-9).
When the Sb content in the polyester film is 0.7 mass ppm or less, the effect of suppressing the occurrence of optical defects is further excellent, and when it is 0.5 mass ppm or less, the effect of suppressing the occurrence of optical defects is particularly excellent. Confirmed (comparison of Examples 1-9).

[Example 11]
In the method described in "(3) Film formation" of Example 1, the following composition A as a composition for forming a particle-containing layer was applied to the surface of a longitudinally stretched polyester film to obtain a film with a particle-containing layer. A biaxially stretched polyester film having a thickness of 31 μm was obtained in the same manner as in Example 1, except that the film was stretched and wound without knurling. The thickness of the particle-containing layer was 60 nm.
The variation in thickness over the entire length and width of the obtained polyester film was 3.5% when calculated from the average value measured with an optical film thickness meter using the following formula.
Thickness variation (%) = {6σ (thickness standard deviation)} / (thickness average value) × 100

(Composition A)
Composition A was prepared by mixing each component shown below. The prepared composition A was subjected to filtration treatment using a filter with 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.). carried out.
・ Acid-modified polyolefin (Zaixen (registered trademark) NC, manufactured by Sumitomo Seika Co., Ltd., aqueous dispersion prepared by adding water to 25% by mass of solid content): 157 parts ・ Anionic hydrocarbon surfactant (Rapisol (registered Trademark) A-90, di-2-ethylhexyl sodium sulfosuccinate, manufactured by NOF Corporation, solid content 1% by mass diluted with water): 56 parts Particles (Snowtex (registered trademark) ZL, manufactured by Nissan Chemical Co., Ltd., Colloidal silica, solid content 40% by mass aqueous dispersion): 11 parts Water: 776 parts

[Examples 12 to 17, Comparative Example 4]
The above composition A was applied as a composition for forming a particle-containing layer on the surface of a longitudinally stretched polyester film, and the obtained film with a particle-containing layer was stretched and wound without knurling. A biaxially stretched polyester film having a thickness of 31 μm was obtained in the same manner as in Example 1. The thickness of the particle-containing layer was 60 nm.
Examples 2-5, 8-9, And, in the same manner as in Comparative Example 1, biaxially stretched polyester films of Examples 12 to 17 and Comparative Example 4 were produced.

[Example 18]
A biaxially stretched polyester film was produced in the same manner as in Example 15, except that the thickness of the biaxially stretched polyester film was 25 μm.

[Examples 19-20]
Example 19 in the same manner as in Example 11 except that polyester pellets made using the product discharged from the third condensation reactor after the elapsed time shown in Table 1 was used. ∼20 biaxially oriented polyester films were produced respectively.

[Film measurement]
The films produced in Examples 11 to 20 and Comparative Example 4 were analyzed using an ICP-MS analyzer in the same manner as in Example 1 to measure the content of each element. Table 2 shows the measurement results of the Sb element content in each. In addition, in each of Examples 11 to 20 and Comparative Example 4, the Ti content was 7 ppm, the Mg content was 75 ppm, and the P content was 65 ppm with respect to the total mass of the polyester film.
Moreover, none of the unstretched polyester films produced in Examples 11 to 20 and Comparative Example 4 contained inorganic particles or organic particles.

In addition, for each film produced in Examples 11 to 20 and Comparative Example 4, in the same manner as in Examples 1 to 9, etc., the total number of foreign substances and voids with a diameter of 9 to 20 μm present in the thickness direction of the film (pieces / 500 mm ² ), and the total number of foreign matter and voids with a diameter of 3 μm or more and less than 9 μm (pieces/500 mm ² ), and the total number of foreign matter and voids with a diameter of 9 to 20 μm per film volume (pieces/mm ³ ), and the diameter The total number (pieces/mm ³ ) of foreign matter and voids of 3 μm or more and less than 9 μm was measured. Each measurement result is shown in Table 2. In any of the films produced in Examples 11 to 20 and Comparative Example 4, no foreign matter with a diameter exceeding 20 μm and voids were observed.
In addition, the haze of the films produced in Examples 11 to 20 and Comparative Example 4 was measured by the method described above. Table 2 shows the measurement results.

Table 2 below shows the film manufacturing process, the Sb content of the pellets used in the film manufacturing, and the above measurement results for Examples 11 to 20 and Comparative Example 4.
Each notation in the table is as described above.

[Defect evaluation]
<Preparation of ceramic slurry>
Barium titanate powder (BaTiO ₃ ; manufactured by Sakai Chemical Industry Co., Ltd., product name “BT-03”) 100 parts by mass, polyvinyl butyral resin as a binder (manufactured by Sekisui Chemical Co., Ltd., product name “S-Lec (registered trademark) B・K BM-2”) 8 parts by mass, 4 parts by mass of dioctyl phthalate as a plasticizer (manufactured by Kanto Chemical Co., Ltd., dioctyl phthalate Deer 1st grade), and a mixture of toluene and ethanol (mass ratio 6:4) ) 135 parts by mass were mixed. The obtained mixture was dispersed in a ball mill in the presence of zirconia beads, and then the beads were removed from the mixture to prepare a ceramic slurry.

<Production and evaluation of sample for defect measurement>
The film roll of the wound biaxially stretched polyester film is peeled by forming a release layer (thickness 1 μm) on the surface of the biaxially stretched polyester film on the polyester substrate side (that is, the surface where the particle-containing layer does not exist). got the film. Here, the release layer was produced according to the method of forming a release agent layer using the release layer-forming material described in Example 1 of JP-A-2015-195291.
The above ceramic slurry is applied to the surface of the release layer of the release film over a width of 250 mm and a length of 10 m so that the film thickness after drying is 1 μm with a die coater, and then dried at 80 ° C. dried for a minute. The laminated film of the ceramic green sheet and the release film was illuminated with fluorescent light from the release film side, and the light transmitted through the laminated film from the ceramic green sheet side was visually inspected over all surfaces of the molded ceramic green sheet. . The ceramic green sheet is peeled off from the defective portion where the color is different from that of the surrounding area such as a pinhole, and the peeled film at the defective portion is observed with a transmission polarizing microscope. The number of defect locations (concave defects) in which foreign matter was present inside the release film at the defect locations was counted.

For the films produced in Examples 11 to 19, the number of concave defects was zero. For the film made in Example 20, two concave defects were present. For the film made in Comparative Example 4, there were 5 concave defects.
From the above, it was confirmed that the polyester films of Examples 11 to 20 according to the present invention have fewer local concave defects occurring in the ceramic green sheet than Comparative Example 4, and have a more excellent concave defect suppressing effect.

REFERENCE SIGNS LIST 10 film manufacturing apparatus 12 reaction tank 14 film forming process unit 16 longitudinal stretching process unit 18 transverse stretching process unit 20 winding unit 24 extruder 26 die 28 cast drum 30 low speed roller 32 high speed roller 34 pipe 36 filter device 38 pipe 40 supply port 42 outlet 44 housing 46 filter 48 channel 50 ring member 51 through hole 52 sintered body 53 perforated plate 54 spacer 56 member F film (polyester film)

Claims

The content of antimony obtained by continuously polymerizing a polyester resin precursor in the presence of a titanium compound and measuring the product containing the polyester resin produced by inductively coupled plasma mass spectrometry is in the product. Step 1 of obtaining a polyester resin after decreasing to 1.0 ppm by mass or less,
A step 2 of filtering the melt of the polyester resin obtained in the step 1 with a filter medium containing a powdery sintered body and a filter medium containing a fibrous sintered body with a filtration accuracy of 3 μm or less;
A method for producing a polyester film, comprising a step 3 of producing a polyester film using the melt filtered in the step 2.
The method for producing a polyester film according to claim 1, wherein the inside of the reaction vessel used for polymerization is washed before continuously polymerizing the polyester resin precursor.
The method for producing a polyester film according to claim 1 or 2, wherein the polyester film has a polyester base material that does not substantially contain inorganic particles.
The method for producing a polyester film according to claim 1 or 2, wherein the polyester resin precursor contains a diol compound and a dicarboxylic acid compound selected from the group consisting of dicarboxylic acid and dicarboxylic acid ester compounds.
The method for producing a polyester film according to claim 1 or 2, wherein the polyester film contains at least one element selected from the group consisting of magnesium and phosphorus.
haze is 0.6% or less,
The content of antimony obtained by measurement by inductively coupled plasma mass spectrometry is 1 mass ppm or less,
A polyester film in which the total number of foreign matter and voids with a diameter of 9 to 20 μm observed with a transmission polarizing microscope is 10/500 mm 2 or less.
The polyester film according to claim 6, which is for dry film resist production.
The polyester film according to claim 6 or 7, wherein the total number of foreign matter and voids having a diameter of 3 µm or more and less than 9 µm observed with a transmission polarizing microscope is 200/500 mm2 or less.
A polyester film in which the total number of foreign matter and voids with a diameter of 9 to 20 μm observed with a transmission polarizing microscope is 1.7/mm 3 or less.
The polyester film according to claim 9, which is used for producing ceramic green sheets.
The polyester film according to claim 9 or 10, wherein the content of antimony obtained by measurement by inductively coupled plasma mass spectrometry is 1 ppm by mass or less.
The polyester film according to claim 9 or 10, wherein the total number of foreign matter and voids having a diameter of 3 μm or more and less than 9 μm observed with a transmission polarizing microscope is 27.0/mm 3 or less.
containing titanium, magnesium and phosphorus,
Each of the titanium content, magnesium content, and phosphorus content measured by inductively coupled plasma mass spectrometry is 1 to 100 ppm by mass with respect to the total mass of the polyester film. Item 9. The polyester film according to Item 6 or 9.
The polyester film according to claim 6 or 9, which has a polyester base material that does not substantially contain inorganic particles.
The polyester film according to claim 6 or 9, which has a polyester base material and a particle-containing layer.
The polyester film according to claim 6 or 9, wherein the polyester film has a thickness of 1 to 35 µm.
The polyester film according to claim 9 or 10, which has a haze of 2.0% or less and a thickness of 1 to 35 µm.
A dry film resist comprising the polyester film according to claim 6 or 9 and a photosensitive resin layer.
The dry film resist according to claim 18, wherein the photosensitive resin layer contains a binder polymer, a polymerizable compound having an ethylenically unsaturated bond, and a photopolymerization initiator.
A release film comprising the polyester film according to claim 6 or 9 and a release layer.