JPH08267684A - Polyester film - Google Patents

Abstract

PURPOSE: To provide a polyester film with good life characteristics of moisture resistance, and also a sliding property and winding up property to be used for condensers. CONSTITUTION: The polyester film includes a skin film with a density of 0.005 or more carboxylic acid formed on at least one surface thereof. A difference in the contact angle of from the reference value of the skin film to water is set above 0 deg. and below 15 deg. or lower. Setting the difference in the contact angle of water into a specific range with respect to a density of the specific surface carboxylic acid and reference value allows the polyester film to be used for condensers to have a good moisture-heat resistive life property, sliding property, element winding up property, and anti-blocking property.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film suitable for capacitors, and more particularly to a metallized film for capacitors having excellent resistance to moisture and heat and a film for laminating, which has excellent adhesiveness and adhesiveness. The present invention relates to a polyester film for capacitors, which has excellent slipperiness and windability.

[0002]

2. Description of the Related Art Conventionally, Japanese Patent Laid-Open No. 5-275276 discloses that a polyester film for capacitors may be coated with various coating materials on its surface and may be subjected to an electric discharge treatment in order to improve adhesion. It is known and it is known to improve the resistance to moisture and heat by coating a specific substance.

Further, Japanese Patent Publication No. 60-23983 proposes to improve adhesion by compounding a carboxyl group having a specific concentration of a specific amount or more.

It is also possible to perform electric discharge machining treatment on the coated polyester film to enhance the adhesiveness.
It is known from Japanese Patent No. 7824.

[0005]

However, although the above-mentioned methods can be expected to have some effects for the respective purposes, in a polyester film having a specific coating layer having a carboxylic acid concentration on the surface having a moisture and heat life resistance, Has good slidability between the film surface and metallized (deposition) surface, but the slidability between the film surface and the metallized surface is poor, and as a result, in the winding process of the capacitor (Including element winding property) is poor and productivity is lowered. As a means for solving these problems, it is possible to improve the slipperiness and the winding property by adding a lubricant or particles, but the wet heat life resistance is reduced,
We couldn't get anything that satisfied both.

Further, in the electric discharge machining treatment, the adhesiveness is improved, but since it is not examined with a specific coating substance as in the present invention, slipperiness, windability (including element winding property) and resistance to moisture and heat life are improved. I couldn't keep both.

It is an object of the present invention to provide a polyester film suitable for a capacitor, which is excellent in the moisture and heat life characteristics in the above-mentioned capacitor application, and is excellent in slipperiness and winding property. .

[0008]

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides a polyester film having the following constitution, that is, a polyester film having a surface carboxylic acid concentration of 0.005 or more on at least one surface thereof. The difference in the contact angle of water from the value is more than 0 ° and 15 ° or less, which is a polyester film.

The polyester resin in the present invention is a crystalline thermoplastic resin composition polymerized by esterification, and such a polyester is obtained by polycondensing a dicarboxylic acid component and a glycol component.

Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid and diphenylethanedicarboxylic acid, and examples of the glycol component include ethylene glycol, propylene glycol, tetramethylene glycol and cyclohexanedimethanol. And so on.
Of these, terephthalic acid and naphthalene-2,6-dicarboxylic acid are preferable as the acid component, and ethylene glycol is preferable as the glycol component.

The melting point of the polyester is preferably 250 ° C. or higher from the viewpoint of heat resistance, and is preferably 300 ° C. or lower from the viewpoint of productivity. Examples of such preferable polyesters include polyethylene terephthalate, polyethylene-2,6-naphthalate, and poly-1,4-cyclohexylene dimethylene terephthalate.

Other components may be copolymerized and blended with these polymers.

The polyester of the present invention has an intrinsic viscosity [η] of 0.50 dl / g or more, preferably 0.6 dl.
/ G or more, more preferably 0.65 dl / g or more, and even more preferably 0.7 dl / g or more is preferable for capacitors in terms of pressure resistance, mechanical characteristics and wet heat resistance characteristics, and is also preferable from the viewpoint of recovery. .

The polyester film is preferably a biaxially stretched film from the viewpoint of mechanical properties, thermal properties and electrical properties.

The material forming the coating film of the present invention has a surface carboxylic acid concentration of 0.005 or more, preferably 0.01.
As mentioned above, it is necessary to be more preferably 0.015 to 0.07, and if it is less than 0.005, the resistance to moisture and heat of the capacitor becomes insufficient. Further, if the amount is more than necessary, the resistance to moisture and heat will deteriorate.

As these resins, water-soluble and / or water-dispersible polyester resins, polyurethane resins, acrylic resins and mixtures thereof are preferable in terms of resistance to moisture and heat, retrievability and adhesiveness.

This carboxylic acid is obtained from Japanese Patent Publication No. 60-2398.
As disclosed in JP-A No. 3-5, those utilizing a terminal carboxylic acid are less effective in improving the resistance to moisture and heat life, and those having a carboxylic acid in the side chain or pendant are excellent and preferred.

Further, regarding the polyester resin having a carboxylic acid on its side chain, JP-A-54-46294, JP-A-60-209073, and JP-A-62-
No. 240318, JP-A-53-26828,
JP-A-53-26829, JP-A-53-9833
6, JP-A-56-116718, JP-A-6-
It can be produced by a resin obtained by copolymerizing a polyvalent carboxylic acid having a valence of 3 or more as described in JP-A-1-124684. Moreover, methods other than these may be used.

Specific examples of this resin include terephthalic acid, isophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, adipic acid, trimethyladipic acid, pimelic acid, sebacic acid, fumaric acid, maleic acid as dicarboxylic acids. Examples thereof include itaconic acid and naphthalenedicarboxylic acid. As glycol components, ethylene glycol, diethylene glycol, propylene glycol, neopentyl glycol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl- 1,3
-Propanediol, 1,3-butanediol, 1,4
-Butanediol, 1,5-pentanediol, 1,6
-Hexanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3
-Cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 2,2,4,4-tetramethyl-1,
Examples thereof include 3-cyclobutanediol and 2,5-naphthalenediol.

Specific examples of the trivalent or higher polycarboxylic acid include trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic dianhydride, 4-methylcyclohexene-1,2,3 tricarboxylic acid anhydride. Compounds, trimesic acid and the like, which can be obtained by appropriately combining these and using the production method described above.

Examples of the polyurethane resin include water-soluble and / or water-dispersible resins, and specific examples thereof include polyester polyurethane, polyester polyurethane urea and polyether polyurethane, which have carboxylic acid in their side chains. Specific examples thereof include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, and 2,2-dimethylolvaleric acid. As the manufacturing method, the method described in JP-A-61-228030 is used.

Further, as the acrylic resin, those containing alkyl acrylate or alkyl acrylate as a main component can be mentioned.

Examples of the coating forming method include a composite melt extrusion method, a hot melt coating method, a solvent other than water, an off-line method from a water-soluble and / or water-dispersible resin, and an in-line coating method. It can also be obtained by combining

The above-mentioned water-soluble and / or water-dispersible resin is a resin that can be dissolved and / or dispersed in water, but may contain a trace amount of solvent. However, the one containing an emulsifier such as a surfactant is liable to deteriorate the wet heat resistance. This water-soluble and / or water-dispersible resin is obtained by neutralizing the carboxylic acid of the above-mentioned resin with a neutralizing agent such as ammonia, triethylamine or diethanolamine to obtain a carboxylic acid salt. However, when this carboxylic acid salt is applied to a film and then dried and volatilized but remains in the film, the resistance to moisture and heat is likely to deteriorate. Therefore, the boiling point of this neutralizing agent is 170 ° C. or lower,
It is preferably 150 ° C or lower, more preferably 130 ° C or lower.

The thickness of the coating layer in the present invention is preferably 0.01 to 2.0 μm, more preferably 0.02 to 2.0 μm.
It is 0.5 μm. If it is less than 0.01 μm, the effect of improving the resistance to moisture and heat may be insufficient. Also, 2.0
If the thickness exceeds μm, various electrical characteristics such as dielectric loss and self-healing property are deteriorated in capacitor applications.

The surface of the polyester film of the present invention preferably has a surface roughness of 0.002 to 1.0 .mu.m, and when the surface roughness is less than 0.002 .mu.m, the yield in the manufacturing process of the capacitor is deteriorated and the film is wound. Poor properties are likely to occur. If the thickness exceeds 1.0 μm, problems such as deterioration of wet heat resistance and deterioration of pressure resistance are likely to occur.

The contact angle difference of water from the reference value of the coated surface in the present invention is more than 0 ° and 15 ° or less, preferably 3 °.
It should be in the range of 12 ° to 12 °, more preferably 5 ° to 10 °. At 0 ° or less, the slipperiness between the film surface and the vapor-deposited aluminum (metallized) surface (especially the coefficient of dynamic friction increases)
Deteriorates, the winding property (including the element winding property) deteriorates, the winding defect rate increases, and the productivity deteriorates. On the other hand, if it exceeds 15 °, blocking occurs or slipperiness deteriorates (especially, the coefficient of static friction increases), so that it cannot be used.

As a method of obtaining the contact angle difference of water from the reference value of the coated surface, known methods such as corona discharge treatment and plasma treatment are used in the air or in an inert gas such as nitrogen or carbon dioxide gas and a combination thereof. Arbitrary products can be obtained by changing the treatment strength under the atmosphere.

The treatment strength is 12 to 65 w · min / m ² ,
15 to 50 w · min / m ² is preferable, and 12 is preferable.
If it is less than w · min / m ² , a sufficient coefficient of dynamic friction cannot be obtained and the defective element winding rate is large. Further, if it exceeds 65 w · min / m ² , the coefficient of dynamic friction is improved, but the coefficient of static friction becomes large, the defective element winding rate also becomes large, and there arises a problem that the change over time becomes large.

In this treatment, the film temperature is 70 ° C. or lower, preferably 50 ° C., more preferably 30 ° C. or lower. If the treatment temperature becomes too high, the slipperiness will change over time, and the slipperiness will deteriorate again.

In the film of the present invention, the toner adhesion amount described below is preferably 50 mg / 100 cm ² or less, more preferably 30 mg / 100 c.
It is preferably m ² or less, more preferably 20 mg / 100 cm ² or less. When the amount is 50 mg / 100 cm ² or less, the coefficient of static friction is significantly reduced, the coefficient of dynamic friction is further reduced, preferable slipperiness is obtained, and the adhesion phenomenon to other objects is improved, resulting in excellent workability.

The toner adhesion amount is 50 mg / 100 cm
^{A value of 2} or less can be obtained by destaticizing with a DC and / or AC static eliminator, but an AC static eliminator is more preferable because it reduces the static friction coefficient.

Further, this static elimination is effective only when the contact angle difference of water from the reference value is within a specific range like the surface of the present invention. That is, the above-described effects are not produced until the static electricity is removed in the state where the water has a contact angle difference from a certain reference value as in the present invention.

It is sufficient that the toner adhesion amount on at least one of the surfaces falls within the range of the present invention, but it is preferable that the toner adhesion amount on both surfaces falls within the range of the present invention, because the adhesion to other objects is eliminated. Workability is improved, productivity is improved,
preferable.

Next, the manufacturing method of the present invention will be explained, but the present invention is not necessarily limited to this.

First, polyester as a base material is melt-extruded by an extruder, cooled and cast below a glass transition point,
After heating above the glass transition point, 2.8-in the longitudinal direction
The film is stretched 7.5 times and, if necessary, subjected to corona discharge treatment, coated with the above-mentioned water-soluble and / or water-dispersible coating resin, and further preheated to a temperature not lower than the glass transition point of the base polyester with a stenter. After that, 3.0-12
The film is stretched twice in the width direction and heat-fixed at a temperature lower than the melting point of the base polyester while relaxing if necessary.

As another method, the coating resin may be melt-coated with a hot melt coater.

By subjecting this coated polyester film to a surface treatment, the polyester film for capacitors of the present invention can be obtained.

This surface treatment may be continuous in the steps from the biaxial stretching to the winding described above, but it is a step of slitting to a required width, a step of slitting to the element size, or a step of winding the element. Is also good.

Next, metal vapor deposition to be an internal electrode in the case of a capacitor is obtained by a vacuum vapor deposition method, a metal is vapor deposited from an evaporation source, and a vapor deposition film is formed on the polyester film of the present invention.

The evaporation source may be a resistance heating type boat, a radiant or high frequency heating crucible type,
There is a method using electron beam heating, but the method is not particularly limited. The conditions may be any ordinary method.
The metals used for this vapor deposition include Al, Zn, Mg, S
Metals such as n are preferable, but Ti, In, Cr, Ni,
Cu, Pb, Fe, etc. can also be used. These metals are preferably processed into a granular, rod-shaped, tablet-shaped, wire-shaped or crucible-shaped material having a purity of 99% or more, preferably 99.5% or more.

In the case of this vapor deposition, aluminum is particularly preferable in terms of productivity and cost, and aluminum is vapor-deposited on at least one side to provide an aluminum vapor deposition film. At this time, for example, nickel, copper, Other metal components such as gold, silver, chromium, zinc can also be deposited.

Although the thickness of the aluminum depends on the purpose of use, it is preferably 20 to 1000 angstroms from the viewpoint of capacitor characteristics.

Further, for use in capacitors, it is preferable that the aluminum oxidation index on the surface of the vapor-deposited aluminum film is 1.65 or less, preferably 1.45 to 1.60, because the wet heat resistance is further improved.

Although the application of the film of the present invention to the vapor deposition film has been described above, in order to improve the slipperiness and the element winding property, the film of the present invention is applied only to the coated polyester surface which is in contact with the vapor deposition surface. If used, the effect can be sufficiently exerted, and when used in the element winding of one side vapor deposition, by making the surface of the vapor deposition surface the film of the present invention,
The effect is fully exerted. When a double-sided vapor deposition film and a coated polyester film (referred to as a laminated film) are used to form a capacitor element, the effect of the present invention is sufficiently exerted only by the laminated film.

[0046]

【Evaluation methods】

(1) Intrinsic viscosity of polyester [η] Dissolve polyester in orthochlorophenol,
It was measured at ° C.

(2) Surface roughness of film Measured according to Ra JIS B6010.

(3) Aluminum oxidation index of aluminum vapor deposition film surface The surface of the vapor deposition film is analyzed by soft X-ray photoelectron spectroscopy. If the sample is a capacitor, disassemble it and expose the vapor deposition surface to the air to obtain a sample. From the ratio of the number of atoms obtained by correcting the peak area ratio obtained by the measurement with the relative sensitivity factor of each atom and the component ratio obtained by dividing the peak shifted depending on the bonding state of each atom, the aluminum oxidation index O / Al was calculated. It is calculated by the equation (1).

O / Al = [O (Al oxide) / Al (Total)] / [Al (III) / Al (Total)] (1) where [Al (III) / Al (Total)] is an aluminum atom. Abundance ratio of Al (III) obtained by dividing the peak of
(Al oxide) / Al (Total)] is calculated by subtracting the oxygen concentration combined with oxygen alone and the elements other than aluminum from the total oxygen concentration with respect to aluminum. That is, for example, the concentration of oxygen bound to carbon is obtained by dividing the carbon peak. At this time, if there are some functional groups containing oxygen, or if the binding energy is so close that separation is not possible, etc., the most oxygen is bound to carbon if the amount of oxygen cannot be specified. Estimate. Similarly, the amount of bound oxygen is obtained for oxygen bound to other elements, and the summed value is subtracted from the total oxygen concentration. The measurement conditions are shown below.

Device: Shimadzu ESCA750 Excited X-ray: MgKα1.2 line (1253.6 eV) Energy correction: The binding energy of the C1S main peak is set to 284.6 eV.

Photoelectron escape angle: 90 ° (4) Moisture and heat resistance of the capacitor The capacitor is 400 V in an atmosphere of 60 ° C. and 95% RH.
DC was applied and aging was performed to measure the rate of change in capacitance. The time until the capacitance change rate ΔC / C decreased by 10% was shown, and the result was the moisture resistance life test result. The longer this time, the better the resistance to moisture and heat. Here, C is the capacitance before aging, and ΔC is the amount of capacitance change before and after aging.

(5) Two pieces of blocking film are cut into 3 × 7 cm, 3 × 4 cm portions of the surfaces to be measured (covered surfaces) are overlapped, and a load of 500 g is applied to the entire area. 40 ℃ 85%
After being left for 24 hours in a temperature-controlled and humidity-controlled RH, the non-overlapping ends are subjected to a tensile tester, and the shearing force is measured. A value of 50 g / 12 cm ² or less was shown as ◯ without blocking, and a value of 100 g / 12 cm ² or more was blocked, and x was shown as unusable. In addition, the intermediate ones are shown as Δ because they can be partially used.

(6) Production of Capacitor Aluminum was vacuum-deposited on both surfaces of the film of the present invention so that the surface resistance value was 2Ω. At that time, vapor deposition was performed in a stripe shape having a margin portion running in the longitudinal direction (the vapor deposition portion width was 8.0 mm, and the margin portion width was 1.0 mm). Next, the back side was also displaced by 4.5 mm and vapor-deposited in the same manner. A blade was put in the center of the vapor deposition section and the center of each margin section and slitted to form a take-up reel in the form of a tape having a width of 4.5 mm and a margin of 0.5 mm to the left or right.
The reel thus obtained and one undeposited laminated film (film of the present invention) were superposed and wound to obtain a wound body having an electrostatic capacity of about 0.047 μF. Remove the core material from this wound body and leave it at 150 ° C, 10 kg / cm ² temperature,
Pressed with pressure for 5 minutes. Metallicon was thermally sprayed on both end faces of this to form external electrodes, and lead wires were welded to the metallicon to obtain a wound-type capacitor element.

(7) Element winding property In the capacitor manufacturing method of (6), in the step of winding from the reel (element winding step), it was judged whether or not there was winding deviation of the wound element.

Those having no winding deviation are regarded as good, and are indicated by ○.
Those in which winding misalignment was recognized were regarded as defective and indicated by x.

(8) Adhesion to other objects In the capacitor manufacturing method of (6), the undeposited film (combined film) was pulled out from the reel and evaluated by performing filming. Pulling (adhering) due to electrification to the device
Indicated by △, ×, x indicates extremely poor workability and cannot be used, and △ indicates workability which is a little poor due to adhesion, but is fully usable.

In addition, those which did not cause adhesion due to electrification were evaluated as good and indicated by ◯.

(9) Concentration of Carboxylic Acid on Surface Using ESCA750 manufactured by Shimadzu Corporation, measurement was carried out under the following conditions.

Excited X-ray: MgKα1,2 ray (1253.6 eV) Photoelectron escape angle θ: 90 ° A polyacrylic acid (PAA) film was used as a standard sample.

The following gas phase chemical modification reaction was carried out for both the standard sample and the measurement sample.

[0061]

[Formula 1] Approximately 1c of the sample film and the standard sample PAA film
Cut into m-squares and esterify the carboxylic acid on the film surface with trifluoroethanol (TFE) using pyridine and dicyclohexylcarbodiimide (DCC) as catalysts in an air atmosphere in a desiccator (sample film and PAA film are in the same batch). I did it in).

From the PAA standard sample, the reaction rate (r) with TFE and the residual rate (m) of DCC used as the reaction catalyst were determined, and the peak areas of C1S and F1S of each sample were taken into consideration with r and m, and the film surface was examined. Carboxylic acid concentration (-COOH / C [tota
l]).

(10) Method for vapor deposition of metal vapor deposition (or metallization) film After vacuum evacuation of an electron beam heating type vacuum vapor deposition machine to 2 × 10 ^-3 Pascal, carbon dioxide gas was introduced to a pressure of 4 × 10 ^-1 Pascal. Using a coaxial cylindrical magnetron electrode, low-temperature plasma treatment was performed at an intensity of E value of 200 W · min / m ² , followed by vacuum deposition of aluminum. Alumina crucible (manufactured by Japan Carbon Serum Co., Ltd.)
Granular aluminum (manufactured by Vacuum Metallurgy Co., Ltd., purity 99.9)
9%) and aluminum was heated and melted by an electron beam to form an aluminum film having a thickness of 30 nm.
The temperature of the film cooling drum at this time was 30 ° C. to obtain an aluminum vapor deposition film.

(11) Difference in contact angle of water from reference value The contact angle of water was determined using a contact angle meter CA-D type (manufactured by Kyowa Interface Science Co., Ltd.) under the conditions of 23 ° C. and 65% RH. .

The reference value is the contact angle of water after heat treatment at 230 ° C. for 3 minutes.

The contact angle difference of water from the reference value is shown by subtracting the reference value from the contact angle of water on the film surface.

(12) Coefficient of friction Measured according to ASTM D 1894.

Measurement environment: 25 ° C., 65% RH The sample of the present invention was used as it was / vapor-deposited on the same sample (that is, measured by the friction coefficient of the film surface / aluminum surface. (13) Toner adhesion amount, manufactured by Fujitsu Ltd. Toner for printer F6700D,
Toray Engineering Co., Ltd. printer T8400
After spraying each of the toners for 10 cm on the entire surface of each film, hold the end face of the film and shake it off about 10 times. The weight of the film after being shaken off is measured, and the weight of the film before being sprinkled is subtracted to obtain the toner adhesion weight.

[0069]

EXAMPLES The present invention will be described below based on examples.

Example 1 Using polyethylene terephthalate having an IV of 0.62,
It was vacuum dried at 180 ° C., supplied to an extruder, melted at 290 ° C., discharged from a T die, and cast on a cooling drum.

This film was heated to 90 ° C., stretched 3.5 times in the longitudinal direction, and "Hydran" AP40 (manufactured by Dainippon Ink and Chemicals, Inc.) on both sides of this uniaxially stretched film.
Was applied, preheated to 90 ° C., further heated to 100 ° C., stretched in the width direction by 3.6 times, and subsequently subjected to 4% relaxation treatment at 240 ° C. to obtain a 5.4 μm biaxially stretched film. . The coat thickness was 0.1 μm.

The processing strength of this film is 20 w.min.
Corona discharge treatment was performed so as to be / mm ² . The contact angle of water was 59.5 °. The reference value of the contact angle of water on this film was 62.5 °. The difference in the contact angle of water from the reference value was 3 °.

Comparative Example 1 A biaxially stretched film was obtained in the same manner as in Example 1 except that no coating layer was provided and no corona discharge treatment was performed. The difference in contact angle of water from the reference value was 0 °.

Examples 2 to 4 and Comparative Examples 2 to 3 "HYDRAN" HW350 (manufactured by Dainippon Ink and Chemicals, Inc.) was used for the coating layer, and Comparative Example 2 was not subjected to corona discharge treatment, and Examples 2 to 2 were used. 4, Comparative Example 3 was obtained in the same manner as in Example 1 except that the corona discharge treatment strength was changed in the order of ²⁰ , 40, 60, 75 w · min / mm ² to obtain a biaxially stretched film. The characteristics of each are shown in the table.

As is clear from this result, when the surface carboxylic acid concentration is 0.005 or more and the difference between the contact angle of water and the reference value is within the specific range, excellent wet heat resistance is obtained.
What was excellent in slipperiness, element winding property, and blocking resistance was obtained.

Examples 5 to 6 The film obtained in Example 3 was further subjected to 2.0 by AC deelectromechanical treatment,
A biaxially stretched film was obtained in the same manner as in Example 3 except that the charge was removed at 3.5 and 5.0 KV. The characteristics of each are shown in the table.

As is clear from this result, when the surface carboxylic acid concentration is 0.005 or more and the difference in the contact angle of water from the reference value is within the specified range, excellent wet heat resistance is obtained,
It has excellent slipperiness, element winding property, and blocking resistance, and when the toner adhesion amount is 50 mg / 10 mm ² or less (per surface), electrostatic adhesion to other objects is eliminated and friction is reduced. The coefficient, particularly the coefficient of static friction, is reduced, and the workability and element winding property are further improved.

[0078]

[Table 1]

[0079]

EFFECTS OF THE INVENTION The polyester film for capacitors of the present invention is excellent in wet heat life resistance, slip property, and element winding property by setting the contact angle difference of water between the specific surface carboxylic acid concentration and the reference value within a specific range. The one having excellent blocking resistance was obtained.

Claims (4)

[Claims] 1. A polyester film having a coating film having a carboxylic acid concentration of 0.005 or more on at least one surface, wherein the contact angle difference of water from the reference value of the coating surface exceeds 0 °. A polyester film having a temperature of 15 ° or less. 2. The polyester film according to claim 1, wherein the coating resin comprises a polyester resin, a polyurethane resin, an acrylic resin and a mixture thereof. 3. The toner adhesion amount is 50 mg / 100 cm ^2.
The polyester film according to claim 1 or 2, which has the following (per surface). 4. The polyester film according to claim 1, which is used for a capacitor.