JPH10272678A - Polyester film and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfy an electrical insulating properties as an electrical material, suppress the elution of metal as the inner lining material of a packaging material and of a filling vessel for drinking water, and suppress the occurrence of defect such as pining holes by a method wherein the unevenness of a longitudinal thickness is set to be a specified value, the surface haze of a film is set to be a specified value, and its melt specific resistance is set to be within a specified range. SOLUTION: The unevenness of a longitudinal thickness must be below 20%. If its unevenness exceeds 20%, the unevenness of an insulating properties and poor slitting at working are caused when employed as an electrical material and poor slitting at working is caused as a packaging material and the inner lining material of a filling vessel and poor bonding and separation are caused at the lamination to a metal can as the inner lining material of the filling vessel. The surface haze of a film should be lower than 1.5%. If it is 1.5% or above, the lowering of the adhesion between the metal can as the filling vessel and the film develops and, in addition, the lowering of its shook resistance and its insulating properties develops also. The melt specific resistance of the film must be within the range of 5×10<6> -2×10<10> ω.cm. If its melt specific resistance is outside of the above-mentioned range, elution of metal and poor bonding to a cooling rotary body occur.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polyester film and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, polyester films have been widely used as base materials for magnetic recording media such as video tapes, dielectrics for capacitors, coating materials for insulation, and as packaging materials for foods and drinks and as inner materials for filling containers. Used. For example, Japanese Patent Application Laid-Open No. 63-182351
JP-A-64-194318 and the like, as packaging materials for food and drink and inner lining materials for filling containers, are disclosed in JP-A-64-194318.
Techniques described in Japanese Patent Laid-Open No. 22530, Japanese Patent Laid-Open No. 3-73337, and the like are known.

[0003] In general, when a polyester film is produced, the extruded molten polyester is brought into close contact with a cooling rotator such as a cooling drum or a cooling belt to be cooled and solidified to form a sheet. The so-called “electrostatic application casting method” is adopted in which electrodes for applying static electricity are installed so as to cross the molten polyester and the sheet above or near the point where the rotating body lands, and the molten polyester is charged. doing. For example, JP-B-49-55759 discloses a specific example thereof.

[0004]

However, the above method has the following problems. In general, when a polyester resin is manufactured, various metal compounds such as antimony oxide, cobalt acetate, zinc acetate, magnesium acetate, and manganese acetate are added as a catalyst in order to promote a transesterification reaction or a polymerization reaction. In so-called electric materials such as capacitors and insulating covering materials, the content of metals in the polyester resin is reduced in order to satisfy electric insulation. In addition, even in the case of food and drink packaging materials such as retorts and internal adhesive materials such as beverage metal cans that are filling containers for drinking water, metal in polyester film raw materials is also used to suppress metal elution in food and drink. Has been reduced. As a result, the melting specific resistance of the polyester resin for the above-mentioned applications becomes high, and when the “electrostatic application casting method” is used, the molten polyester sheet becomes insufficiently charged, and the cooling rotation of the cooling drum, cooling belt, etc. Insufficient adhesion to the body. Therefore, the thickness unevenness in the longitudinal direction of the obtained polyester film becomes large,
In addition, there is a problem that a defect called "pinning hole", which occurs when air is caught between the sheet-like material and the cooling rotating body, occurs on the surface of the polyester film. Such a film is not preferable because when used for the above-mentioned applications, the variation in product quality is increased.

[0005] The above problem becomes more remarkable as the rotation speed of the cooling rotator, that is, the so-called "casting speed" becomes higher, and as a result, the production speed cannot be increased. For the purpose of further improving the adhesion between the molten polyester and the cooling rotator, for example, Japanese Patent Publication No. 63-20688 discloses a tape-shaped metal electrode for electrostatic application, which is disclosed in
JP-A-317316 discloses an example in which two linear metal electrodes are used as electrodes for electrostatic application.
No. 2 proposes a method of providing an insulating shield between a linear electrode and a base. However, even if such a method is simply adopted, the molten polyester sheet immediately before being brought into close contact with the cooling rotating body vibrates due to the influence of the electrode vibration and the like, and as a result, unevenness in the thickness in the longitudinal direction occurs. Met.

An object of the present invention is to provide a polyester film which pays attention to the above-mentioned problems and suppresses the occurrence of defects such as uneven thickness in the longitudinal direction and pinning holes, and a method for producing the same.

[0007]

In order to solve the above-mentioned problems, according to the present invention, the uneven thickness in the longitudinal direction is less than 20%, the surface haze is less than 1.5%, and the melting specific resistance is 5%.
It is characterized by being in the range of × 10 ^{6 to} 2 × 10 ¹⁰ Ω · cm.

[0008] The method for producing a polyester film of the present invention is a method for producing a polyester film, comprising the steps of: bringing a molten polyester extruded from a die into close contact with a cooling rotator by applying static electricity;
The cross section of the electrode for electrostatic application is such that the major axis is in the range of 2 to 20 mm, the minor axis is in the range of 0.01 to 1 mm, and the ratio of major axis / minor axis is 5
The method is characterized in that the electrode is formed in a shape in the range of 0 to 1000 and the amplitude of vibration of the electrode is controlled to less than 0.5 mm.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The polyester of the present invention includes polyethylene terephthalate
, Polyethylene-2,6-naphthalate, polyethylene α, β-bis (2-chlorophenoxy) ethane 4,4
-Dicarboxylate, polyethylene isophthalate,
Aromatic polyesters such as polybutylene terephthalate are used, but polyethylene terephthalate is generally and preferably used. Here, “mainly” means that the aromatic polyester contains 70 mol% or more. The aromatic polyester may be a homopolyester, a copolyester, or a simple mixture of other components at a ratio of less than 30 mol%.

The polyester film of the present invention preferably has an average thickness in the range of 1 to 50 μm, more preferably 2 to 50 μm, from the viewpoint of workability when the polyester film is used as an electric material or a packaging material. 40μ
m, more preferably in the range of 4 to 30 μm.

The polyester film of the present invention needs to have a melting specific resistance in the range of 5 × 10 ⁶ to 2 × 10 ¹⁰ Ω · cm. That is, the melting specific resistance is 5 × 10 ⁶ Ω · cm
Since the amount of "metal" generated and precipitated from a metal compound added as a polymerization catalyst is large in a polyester film that is less than a so-called electric material such as a capacitor application or an insulating coating material, the electric insulation is significantly reduced. In addition, when the metal is used as a packaging material for food or drink or an inner wrapping material for a filling container, the metal is eluted into the food or drink and the flavor is significantly reduced. On the other hand, the melting specific resistance is 2 × 10 ¹⁰ Ω ·
cm, the amount of charge of the molten polyester due to the application of static electricity is small even when the above method is employed, resulting in insufficient adhesion to the cooling rotating body. The melting specific resistance of this polyester film is preferably 1 × 10
The range is ⁷ to 8 × 10 ⁹ Ω · cm, and more preferably the range is 2 × 10 ^{7 to} 5 × 10 ⁹ Ω · cm. Means for achieving such a melting specific resistance include a method in which an added metal compound is inactivated by an organic and / or inorganic phosphate compound to suppress precipitation as a metal, and a method in which a metal such as germanium oxide is used as a polymerization catalyst. A method using a metal compound which is difficult to precipitate can be used.

The polyester film of the present invention needs to have a surface haze of less than 1.5%. That is, when the film has a surface haze of 1.5% or more, when used as an inner adhesive material of a filling container, a decrease in adhesion to a metal can as a filling container and a decrease in impact resistance are caused.
This is because when used for an electrical material such as a capacitor, a reduction in workability and a reduction in insulation are caused. Such an increase in the surface haze is caused by insufficient adhesion to the cooling rotating body due to insufficient electrostatic application, or roughening of the film surface due to too strong electrostatic application. The surface haze is preferably less than 1%, more preferably less than 0.7%.

[0013] The polyester film of the present invention needs to have a thickness unevenness in the longitudinal direction of less than 20%. That is,
If the thickness unevenness in the longitudinal direction is 20% or more, it causes unevenness in insulation when used as an electrical material and defective slits during processing. Also, when it is used as a packaging material or as an inner ply material for a filling container, it causes slit defects during processing, and especially when it is laminated with a metal can as an inner ply material for a filling container, it causes uneven bonding, resulting in poor adhesion. This is to cause peeling and the like. Here, the thickness unevenness in the longitudinal direction means a difference between the maximum value and the minimum value of the thickness of a sample having a length of 1 m or more arbitrarily sampled from a film, divided by an average thickness, and a percentage (%).
Defined as the value expressed in. In addition, thickness unevenness in the longitudinal direction is
Preferably it is less than 15%, more preferably less than 10%.

In order to realize the above-mentioned range of the thickness unevenness in the longitudinal direction, the molten polyester extruded from the die of the present invention is brought into close contact with a cooling rotating body by applying static electricity, and is used for applying static electricity when cooling and solidifying. The electrode must have a major axis in the range of 2 to 20 mm in its cross section. That is, when the major axis is larger than 20 mm, the corona discharge starting voltage for applying the electrostatic force becomes extremely high, so that the electrostatic application voltage must be set high, and as a result, a so-called “spark discharge” is easily generated. This is because a stable electrostatic application state cannot be maintained. In addition, if the major axis is less than 2 mm, handling becomes extremely difficult, which is not practical. Preferably, the major axis is in the range of 3 to 15 mm, more preferably 5 to 10 mm.

Further, the electrode for electrostatic application of the present invention must have a minor axis in the range of 0.01 to 1 mm in its cross section. That is, when the minor axis is larger than 1 mm, the corona discharge starting voltage for applying the electrostatic force also becomes extremely high, so that the electrostatic application voltage must be set high.
As a result, a so-called “spark discharge” is likely to occur, and a stable electrostatic application state cannot be maintained. Also,
If the minor axis is less than 0.01 mm, the electrode will break or vibrate significantly during actual use. Preferably, the minor axis has a diameter of 0.02 to 0.5 mm, more preferably 0.1 to 0.5 mm.
The range is from 03 to 0.2 mm.

The electrode for electrostatic application according to the present invention needs to have a ratio of major axis / minor axis in the cross section in the range of 50 to 1,000. That is, when the ratio of the major axis / minor axis is less than 50, the charge from the electrode does not concentrate on the target molten polyester, and as a result, the electrostatic application becomes insufficient, and the above-described unevenness in the thickness in the longitudinal direction cannot be achieved. Also, when the ratio of the major axis / minor axis is larger than 1000, the torsion and breakage of the electrode and the vibration of the electrode become remarkable in actual use. Preferably, the ratio of major axis / minor axis is from 100 to 50.
0, more preferably in the range of 150 to 350. In order to satisfy the above conditions, it is practical and preferable that the shape of the electrode for electrostatic application of the present invention is a string shape. At this time, the width of the string-shaped electrode corresponds to the “major axis” in the cross section, and the thickness corresponds to the “minor axis” in the cross section.

In the manufacturing method according to the present invention, it is necessary to control the amplitude of the vibration of the electrode for applying electrostatic force to less than 0.5 mm. That is, even if the shape of the electrode is as described above, even if the adhesion of the molten polyester to the cooling rotating body increases, if the electrode itself for electrostatic application is oscillating with an amplitude of 0.5 mm or more, This is because vibration of the molten polyester immediately before the close contact with the cooling rotator is caused, and as a result, it is impossible to make the thickness unevenness in the longitudinal direction of the polyester film within the above range. Preferably, the amplitude of the vibration of the electrode for electrostatic application is controlled to less than 0.2 mm.
In addition. As a method of controlling the amplitude of the vibration of the electrode for electrostatic application as described above, for example, a method of fixing the electrode to a solid support, or applying a tension of 200 MPa or more to both ends of the electrode, Of which two at each end of the electrode
It is realistic and preferable to apply a tension of 00 MPa or more. The tension applied to both ends of the electrode is preferably 300MP.
a or more, more preferably 500 MPa or more.

Further, if necessary, in order to prevent contamination of the electrode, a method in which the electrode is constantly updated while being wound up at a constant speed and an electrode which is not contaminated, or a method in which the electrode is heated to remove contaminants. May be used.

As a method of updating the electrodes while applying the above-mentioned tension, for example, a reel wound around the electrodes is braked by an electromagnetic brake or the like, and the other reel is wound at a constant speed by a motor or the like. A method of shifting can be specifically used.

Further, the electrode for electrostatic application of the present invention is preferably made of a conductive material having a Young's modulus of 20 GPa or more. That is, if the tension is less than 20 GPa, the electrode is deformed or broken when the above-described tension is applied. The Young's modulus of the electrode is more preferably 40 GPa or more, and further preferably 80 GPa or more. Specifically, a simple metal such as iron, nickel, molybdenum, tungsten, titanium, cobalt, chromium, and zirconium, an alloy containing at least one of the above components (eg, stainless steel, duralumin, etc.), A simple substance or an alloy plated may be used, of which stainless steel, which is inexpensive, is realistic and preferred.

Next, a method for producing the polyester film according to the present invention will be described, but the method is not necessarily limited thereto. First, the melting specific resistance is 5 × 10 ⁶ to
A polyester of 2 × 10 ¹⁰ Ω · cm is melt-extruded at a temperature exceeding its melting point by a conventional extruder, and is adhered to a cooling drum or a cooling belt by electrostatic application to be cooled and solidified to form a sheet. In this case, the electrode for electrostatic application is a string-shaped metal electrode having a major axis of 2 to 20 mm in cross section and a minor axis of 0.01 to 1 mm, and the electrode is a landing point of the molten polyester to the cooling rotator. And placed at a distance of 3 to 15 mm from the lower end of the electrode and the molten polyester so as to cross the molten polyester.
Electrostatic application is performed with a high voltage by applying a tension of 00 MPa or more.

Thereafter, the film is heated to a temperature equal to or higher than the glass transition temperature and stretched 2.8 to 7.5 times in the longitudinal direction. Subsequently, it is heated to a glass transition temperature or higher by a stenter, stretched 3 to 6 times in the width direction, and subsequently heat-treated at a temperature of 100 to 400 ° C. for 5 seconds or more, and finally cut into a predetermined width. Products.
If necessary, a treatment such as coating or corona discharge may be performed before, during, or after the stretching.

The polyester film thus obtained is suitably used as an electric material such as a capacitor, a packaging material and an inner wrapping material of a filling container. For example, when a capacitor is used, an aluminum vapor-deposited film serving as an internal electrode of the capacitor is provided on at least one side of the polyester film by a method such as vapor deposition, and then the above-described vapor deposition is performed in a stripe shape having a margin portion running in the longitudinal direction. ,
A blade is inserted into the center of each vapor deposition section and the center of each margin section, slit, and wound into a reel having a margin at the left end or the right end. The obtained left margin reel and right margin reel are wound one on top of the other so that the respective vapor deposition portions protrude beyond the other margin portion in the width direction. Remove the core material from the wound body,
Pressing is performed at a temperature of 100 to 200 ° C. under a pressure of 0.2 to 2 MPa for 1 to 30 minutes. A method can be used in which metallikon is sprayed on both ends to form external electrodes, and a lead wire is welded to the metallikon to form a film capacitor.

When the polyester film is used as an inner adhesive material, for example, a method in which an adhesive is applied to one surface of the polyester film and laminated on a metal plate such as aluminum or stainless steel can be used. [Method for Evaluating Physical Property Values] (1) Measurement of Melting Specific Resistance The polyester film was melted at 280 ° C. in a nitrogen atmosphere, a pair of electrodes was inserted, and the applied voltage V ( V), the measured current I (A), the distance D (cm) between the electrodes, and the area S (cm ² ) of the electrodes were obtained from the following equation. Melting specific resistance = V × S / (I × D)

(2) Measurement of Average Thickness Ten films are stacked, and the thickness of an arbitrary portion is measured with a μ-mate micrometer manufactured by Sony Corporation. Divide the obtained value by 10 to obtain the thickness per sheet. Using this method, 10 points were arbitrarily measured, and the average value was obtained.

(3) Measurement of surface haze, edited by The Society of Polymer Science, Baifukan, “Testing methods and evaluation of polymer materials”,
In accordance with the method described in JIS-K6718, 6.4, the total haze (Ht) of the film was measured using an integrating sphere light transmittance measuring device HGM-2DP manufactured by Suga Test Instruments Co., Ltd. and a direct reading haze computer. I asked. Subsequently, the film was immersed in tetralin having the same refractive index as the film, and the internal haze (Hi) was determined from the above measurement. The surface haze (Hs) is changed from the total haze (Ht) to the internal haze (Ht).
i) was subtracted.

(4) Measurement of thickness unevenness in the longitudinal direction Electronic micrometer (FILM THICKN manufactured by Anritsu Corporation)
According to ESS TESTER KG601A), the film was continuously run in the longitudinal direction under the following conditions, and thickness unevenness was measured. Measurement conditions Range: 5 μm, high cut: 25 Hz, film take-up speed: 1.5 m / min, chart speed: 60 cm
/ Min, measurement length: 10 m If the film length is less than 10 m, the maximum length that can be taken is taken as the measurement length.

(5) Measurement of Young's Modulus of Electrode A sample of the electrode was cut to a length of 150 mm, and the distance between the chucks was 100 m.
m, pulling speed 300m / min, chart speed 500mm
At / min, pull with an Instron type universal tensile tester. The Young's modulus is determined from the tangent at the rising portion of the obtained load-elongation curve.

(6) Measurement of Electrode Tension The center of an electrode having a length L (mm) is fixed to a fixed length x (m) by push-pull in a direction perpendicular to the direction in which the electrode is stretched.
m) Pull, read the load F (N) at that time, and obtain the tension T (N) from the following equation. T = FL / 4x The obtained tension was divided by the cross-sectional area of the electrode, and converted to a tension per unit cross-sectional area (MPa).

(7) Measurement of the amplitude of the vibration of the electrode As a non-contact electro-optical displacement measuring device,
Using an Optofollow Model 1000 manufactured by KK, the amplitudes of the vertical and horizontal vibrations of the center of the electrode were measured.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. Example 1 A polyethylene terephthalate having a melting specific resistance of 5 × 10 ⁹ Ω · cm was melt-extruded at 280 ° C., discharged from a T-die, and cast by a cooling drum by an electrostatic application casting method under the following conditions. I got a sheet. -Electrode for electrostatic application Material: Stainless steel of SUS304H Shape: String of 0.03 mm thick x 8 mm wide-Electrostatic application condition Applied voltage: 12 kV with + DC voltage Tension applied to electrode: 600 MPa Casting speed: 35 m / Min Distance between the molten polyester and the lower end of the electrode: 7 mm This sheet is heated to 120 ° C, stretched 6 times in the longitudinal direction, heated to 140 ° C and stretched 3.7 times in the width direction, and subsequently 230 ° C At 8% to give a 4.4 μm biaxially stretched film. The polyester film thus obtained had small unevenness in thickness, and was good without defects caused by “pinning holes”.

Example 2 A film was obtained in the same manner as in Example 1 except that the following conditions were changed.・ Electrostatic application condition Applied voltage: 13 kV at + DC voltage Casting speed: 38 m / min Distance between the molten polyester and the lower end of the electrode: 5 mm Also in this case, a good polyester film with little unevenness in thickness and no surface defects is obtained. Was done.

Example 3 A film was obtained in the same manner as in Example 1 except that the following conditions were changed. -Electrode for electrostatic application Material: Stainless steel of SUS304H Shape: String shape of thickness 0.04 mm x 7.5 mm-Electrostatic application condition Applied voltage: 12 kV at + DC voltage Between molten polyester and lower end of electrode Distance: 6 mm Also in this case, a good polyester film having small thickness unevenness and no surface defects was obtained.

Example 4 Polyethylene terephthalate having a melt specific resistance of 15 × 10 ⁸ Ω · cm and containing 15 mol% of an isophthalate component as a copolymer component was melt-extruded at 280 ° C.
The sheet was discharged from a die and cast by a cooling drum under the following conditions by an electrostatic application casting method to obtain a sheet. -Electrode for electrostatic application Material: Stainless steel of SUS304H Shape: String of 0.03 mm thickness x 8 mm width-Electrostatic application condition Applied voltage: 12 kV with + DC voltage Tension applied to electrode: 500 MPa Casting speed: 30 m / Min Distance between the molten polyester and the lower end of the electrode: 5 mm This sheet was heated to 105 ° C., stretched three times in the longitudinal direction, heated to 110 ° C., stretched three times in the width direction, and then stretched at 185 ° C. to 3 times. % Relaxation treatment to obtain a 20 μm biaxially stretched film. The polyester film thus obtained also had a small thickness unevenness in the longitudinal direction, and was a good result without surface defects.

Example 5 A film was obtained in the same manner as in Example 4 except that the following conditions were changed.・ Electrostatic application conditions Applied voltage: 13 kV at a DC voltage of + Casting speed: 38 m / min In this case also, a good polyester film having little unevenness in the thickness in the longitudinal direction and no surface defects was obtained.

Example 6 A film was obtained in the same manner as in Example 4 except that the following conditions were changed. -Electrode for electrostatic application Material: Stainless steel of SUS304H Shape: String of 0.02 mm thick x 6 mm wide Also in this case, a good polyester film with small unevenness in the longitudinal direction and no surface defects was obtained.

Comparative Example 1 A film was obtained in the same manner as in Example 1 except that the following conditions were changed. -Electrode for electrostatic application Material: Tungsten Shape: Linear shape of 0.1 mm in diameter-Electrostatic application condition Tension applied to the electrode: 700 MPa This polyester film resulted in large thickness unevenness in the longitudinal direction.

Comparative Example 2 A film was obtained in the same manner as in Example 1 except that the following conditions were changed. -Electrode for electrostatic application Material: Stainless steel of SUS304H Shape: String of 1.5 mm thick x 8 mm wide Also in this case, the polyester film had large unevenness in the longitudinal direction and many surface defects.

Comparative Example 3 A film was obtained in the same manner as in Example 1 except that the following conditions were changed. -Electrode for electrostatic application Material: SUS304H stainless steel Shape: 0.005 mm thick x 8 mm wide string In this case, the electrode was twisted and broken immediately after the start of the experiment, and no polyester film was obtained.

Comparative Example 4 A film was obtained in the same manner as in Example 4 except that the following conditions were changed.・ Electrostatic application conditions Tension applied to the electrode: 100 MPa The polyester film in this case had no defects caused by “pinning holes” and the surface was clean, but the electrode was vibrating with an amplitude of 1.4 mm, so that the longitudinal direction was used. Resulted in a large thickness unevenness.

Comparative Example 5 In Example 4, the melting specific resistance of the polyester resin was 2
A film was obtained in the same manner as in Example 4 except that the film thickness was changed to × 10 ⁶ Ω · cm. Although this product had no unevenness in thickness in the longitudinal direction and had no defects, it was inconvenient when processed into a capacitor, resulting in poor insulation.

[0042]

[Table 1]

[0043]

According to the present invention, it is possible to provide a polyester film having less unevenness in thickness and suppressing occurrence of defects, which is suitable for an electric material, a packaging material, an inner wrapping material of a filling container, and the like.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08J 5/18 CFD C08J 5/18 CFD C08L 67/02 C08L 67/02 // H01G 4/18 330 H01G 4/18 330Z B29K 67:00 B29L 7:00

Claims (8)

[Claims] 1. The thickness unevenness in the longitudinal direction is less than 20%,
A polyester film having a surface haze of less than 1.5% and a melting specific resistance in a range of 5 × 10 ⁶ to 2 × 10 ¹⁰ Ω · cm. 2. The polyester film according to claim 1, wherein the average thickness is in the range of 1 to 50 μm. 3. The thickness unevenness in the longitudinal direction is less than 10%,
The polyester film according to claim 1, wherein a melting specific resistance is in a range of 1 × 10 ⁷ to 8 × 10 ⁹ Ω · cm. 4. The polyester film according to claim 1, wherein the surface haze is less than 1%. 5. The polyester film according to claim 1, which is used for an electric material. 6. The polyester film according to any one of claims 1 to 4, wherein the polyester film is used as an adhesive material for food and drink in a container. 7. A method for producing a polyester film, comprising a step of bringing a molten polyester extruded from a die into close contact with a cooling rotator by applying static electricity to cool and solidify the molten polyester. ~ 20mm,
It is required that the minor axis is in the range of 0.01 to 1 mm, the ratio of the major axis / minor axis is in the range of 50 to 1000, and the amplitude of the vibration of the electrode is controlled to less than 0.5 mm. A method for producing a polyester film. 8. The method for producing a polyester film according to claim 7, wherein the shape of the electrode for applying static electricity is a string shape.