JP2000272003A - Biaxially oriented polyester film and roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film which has a good winding form when a biaxially oriented polyester film is wound into a roll and which can maintain quality and quality for a long period of time. I will provide a. SOLUTION: This is a biaxially oriented polyester film having projections formed by a projection imparting roll on at least one surface near both ends in the width direction, and is deformed by the projection imparting process with respect to a film area in contact with the projection imparting roll. A biaxially oriented polyester film, wherein a ratio of an area where the portion is projected perpendicular to the film surface is 0.01 to 0.25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a biaxially oriented polyester film which has a good roll appearance when the film is wound into a roll and which maintains quality and quality for a long period of time. The present invention relates to a film obtained and a roll having a good winding form when wound up into a roll.

[0002]

2. Description of the Related Art When a film is wound up into a roll, usually, inorganic or organic fine particles are mixed into a raw material resin to form projections on the film surface or to coat a layer containing fine particles. Or to be provided. This plays a role of letting the air out of the roll even if air is entrained between the films due to the flow of air (the accompanying flow) accompanying the running of the film when winding the film.

[0003] However, the recent biaxially oriented polyester film is a substitute for glass or a prism lens sheet (brightness expanding film) used for LCD (liquid crystal display).
Base film, base film for hard coat processing and AR (anti-reflection; anti-glare) film,
It is often used for optical products such as base film of near infrared absorbing film for plasma display, base film of transparent conductive film for touch panel and electroluminescence, and shatterproof film for CRT.
Demands for surface smoothness and transparency have become very strong. In order to satisfy this requirement, the content of the particles contained in the film is reduced or the average particle size is reduced.

However, when the particle content in the film is reduced, the formation of projections on the film surface becomes insufficient,
When the film is wound up in a roll, the accompanying flow cannot be eliminated, resulting in a shift or a large amount of air being locally entangled, resulting in an extremely low product yield. In the case of a film having excellent surface smoothness in which particles having a small average particle size are contained in the film, there is also a problem that the film surface is easily scratched by rubbing between the films.
Such a flaw is recognized as an optical defect when used as a substrate of an optical film, and thus needs to be reduced as much as possible.

Conventionally, in order to avoid the above-mentioned problem, there has been known a method in which unevenness or projections are formed at the end of a film and the film is wound. For example, JP-A-4-85248,
JP-A-4-85249, JP-A-9-124199
Is disclosed. In the related art, by appropriately setting the arrangement direction and distance of the projections and depressions, the air entrained by the accompanying flow in the process of winding the film is released, and the winding displacement and the like can be prevented.

[0006] However, with this technique alone, a good winding appearance can be obtained immediately after winding, but after a long period of time, air gradually escapes from the roll, causing a tightening phenomenon and impairing the flatness of the film. In particular, in the case of a biaxially oriented polyester film having a smooth surface, problems such as scratches due to contact between the films may occur. In particular, the problem was remarkable with a relatively thick film.
The film roll may be stored for a long time in the course of distribution, and the conventional technology cannot guarantee quality for a long time.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems, and to provide a good roll appearance when the biaxially oriented polyester film is wound into a roll, and to obtain a long-term quality and quality. An object of the present invention is to provide a biaxially oriented polyester film from which a held roll can be obtained.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above-mentioned situation, and as a result, have found that when a film having projections applied to both ends in the width direction is rolled up into a roll shape, a projection application roll is used. With respect to the area of the film in contact with, the ratio of the area of the portion deformed by the projection imparting process perpendicularly projected to the film surface is adjusted so that the entrained air is suitable by using a film processed so as to be in the range specified in the present invention. It has a good winding appearance when winding up,
It has been found that a suitable amount of air once caught is retained even after a long period of time, a roll with good roll appearance is obtained, and a roll with no deterioration in flatness or scratches is obtained. Reached.

That is, the object of the present invention is achieved by the following means. 1. A biaxially oriented polyester film having projections formed by a projection imparting roll on at least one surface near both ends in the width direction, wherein a film deformed by the projection imparting process with respect to a film area contacted by the projection imparting roll is a film surface. A biaxially oriented polyester film, wherein the ratio of the area projected perpendicular to the film is 0.01 to 0.25. 2. The area obtained by projecting any one of the portions deformed by the projection imparting process perpendicularly to the film surface is 0.01 to 0.2 m.
m. ^{2. The} biaxially oriented polyester film according to the above 1, wherein

[0010] 3. The average height of the portion deformed by the projection imparting process is 1 to 20% of the average film thickness of the non-processed portion.
3. The biaxially oriented polyester film according to any one of the above 1 or 2, wherein 4. The biaxial orientation according to any one of the above items 1 to 3, wherein the non-processed portion has an average film thickness of 30 to 300 µm, and the portion deformed by the projection imparting process has an average height of 3 to 30 µm. Polyester film.

5. The width of the projection-treated portion is 5 to 5.
The biaxially oriented polyester film according to any one of the above items 1 to 4, which is 20 mm. 6. The biaxially oriented polyester film according to any one of the above items 1 to 5, wherein a polymer easy-adhesion layer is provided on at least one surface of the biaxially oriented polyester film.

7. 7. The biaxially oriented polyester film according to the item 6, wherein the high polymer adhesive layer contains inert particles. 8. The polymer easy-adhesion layer has an average particle size of not less than 20 nm and not more than 30.
Inactive particles of less than 0 nm and average particle size of 300 nm or more 1
8. The biaxially oriented polyester film according to the above item 7, which contains inert particles of 000 nm or less.

9. The biaxially oriented polyester film substantially does not contain particles.
Or the biaxially oriented polyester film according to 8. 10. The biaxially oriented polyester film according to any one of the above 1 to 9, wherein the haze value is 1.0% or less.

11. The biaxially oriented polyester film according to any one of the above items 1 to 10, which is used as a substrate of an optical film. 12. A roll obtained by winding up the biaxially oriented polyester film according to any one of the above 1 to 11.

[0015]

Next, the present invention will be described in detail.
In the biaxially oriented polyester film of the present invention, the ratio of the area (projection area ratio) of projecting the portion deformed by the projection applying process perpendicular to the film surface to the film area contacted by the projection applying roll is 0.01. ~
It needs to be 0.25. If the ratio of the projection area is less than 0.01, the flatness of the film is deteriorated when the film roll is stored for a long period of time, and the film surface is undesirably flawed. On the other hand, when the ratio of the protrusion area exceeds 0.25, the disorder of the flatness of the film is deteriorated immediately after winding the film, and the film surface is undesirably flawed.

Area (projection area) where any one of the portions deformed by the projection imparting process is projected perpendicular to the film surface.
Is preferably from 0.01 to 0.2 mm ² from the viewpoint of air retention. The projection area is less than 0.01 mm ^2,
When the film roll is stored for a long period of time, the disorder of the flatness of the film is liable to deteriorate, and the surface of the film is liable to be scratched, which is not preferable. On the other hand, if the protrusion area exceeds 0.2 mm ² , the disorder of the flatness of the film is likely to be deteriorated immediately after winding the film, and the surface of the film is likely to be scratched, which is not preferable.

In order to improve the balance between the rejection and the retention of the trapped air, the average height (B) of the portion deformed by the projection imparting process is determined by the average film thickness (A) of the non-processed portion. ) Is preferably 1 to 20%.
More preferably, it is 2 to 18%. If B / A is less than 1%, scratches are likely to occur immediately after winding the film, which is not preferable. On the other hand, when B / A exceeds 20%, the disorder of the flatness tends to deteriorate when stored for a long time, which is not preferable.

Further, it is preferable that the average thickness of the film in the non-processed portion is 30 to 300 μm, and the average height of the portion deformed by the projection imparting process is 3 to 30 μm. If the average thickness is less than 30 μm or the average height is less than 3 μm, scratches are likely to occur immediately after winding the film, which is not preferable. On the other hand, the average thickness is 300
If it exceeds μm, or if the average height exceeds 30 μm, it is not preferable because the flatness tends to be deteriorated during long-term storage.

Further, from the viewpoint of the exclusion, retention and product loss of entrapped air, the width of the portion provided with the protrusion is
Preferably it is 5 to 20 mm.

It is desirable that the biaxially oriented polyester film of the present invention does not substantially contain inert particles for the purpose of imparting lubricity from the viewpoint of transparency. The fact that substantially no inert particles are contained is particularly effective for obtaining a biaxially oriented polyester having high transparency such that the haze value of the biaxially oriented polyester of the present invention is 1% or less. The fact that substantially no inert particles are contained in the film means that the content of the inert particles is below the detection limit when analyzed by fluorescent X-ray analysis.

When the biaxially oriented polyester film of the present invention is used as a film base for optical use, it must have excellent adhesion to a material to be subjected to post-processing such as prism lens processing, hard coating processing, and AR processing. Becomes In order to improve the adhesion between the mating material and the polyester film during such post-processing, at least one surface of the biaxially oriented polyester film is used in combination with a copolymerized polyester resin and a polyurethane resin, or maleic acid. It is preferable to provide an easily polymerizable adhesive layer mainly composed of a polymer resin composition such as a graft polyester.

This polymer easy-adhesion layer can be formed by providing an easy-adhesion layer on at least one surface of an unstretched or uniaxially stretched polyester film, and then laminating by an in-line coating method in which the film is stretched and heat-set in at least one axis direction. preferable. By adding inert particles of an appropriate particle size to the easy-adhesion layer laminated by the in-line coating method, and forming unevenness on the surface of the easy-adhesion layer, it imparts good slipperiness, winding property, and scratch resistance. can do.

For this reason, since it is not necessary to substantially contain inert particles in the biaxially oriented polyester film as the base film, a high haze value of the optically easy-to-adhesive film is 1.0% or less. It is particularly effective for obtaining a transparent film.

As the inert particles to be contained in the easy-adhesion layer, silica is the most preferable because silica has a relatively close refractive index to that of the resin of the easy-adhesion layer and high transparency can be easily obtained. It is also preferable to use composite inorganic oxide particles obtained by combining inorganic oxide particles having a higher refractive index and inorganic oxide particles having a lower refractive index than the resin constituting the easy-adhesion layer. As such particles, for example, there are alumina-silica composite oxide particles, and by optimizing the composition of the raw material alumina and silica, it is possible to obtain a resin having a refractive index similar to that of the resin constituting the easy-adhesion layer. it can.

The average particle size (observed by an electron microscope) of the inert particles added to the aqueous coating solution is 0.01 to 1.0 μm.
m is preferable, and more preferably 0.02 to 0.5 μm
m, particularly preferably 0.03 to 0.1 μm. When the average particle size of the inert particles exceeds 1.0 μm, the surface of the easy-adhesion film tends to be rough, and the transparency of the easy-adhesion film tends to decrease. On the other hand, the average particle size of the inert particles is 0.01
If it is less than μm, the slipperiness of the easily adhesive film tends to be insufficient, which is not preferable.

The content of the inert particles in the coating layer (easy adhesion layer) after drying the coating liquid is 0.01%.
To 60% by weight, particularly preferably 0.1 to 40% by weight.
% By weight. When the content of the inert particles in the coating layer (easy adhesion layer) exceeds 60% by weight, the adhesiveness to the base film may be impaired. On the other hand, if the content of the inert particles is less than 0.01% by weight, the slipperiness of the easily adhesive film becomes insufficient, which is not preferable.

In the present invention, it is preferable that the easy-adhesion layer contains two types of particles (particle A and particle B). Particle A
Has an average particle size of preferably from 20 to less than 300 nm, more preferably from 30 to 100 nm. If the average particle size of the particles A is less than 20 nm, the scratch resistance tends to deteriorate. On the other hand, when the average particle diameter of the particles A exceeds 300 nm, the haze value tends to increase.

Since the particle A alone has insufficient scratch resistance, in order to further improve the scratch resistance,
It is preferable that the particles B are contained in the easy adhesion layer in combination with the particles A. The average particle size of the particles B is 300 to 1000 nm
And more preferably 400 to 800 nm. If the average particle diameter of the particles B is less than 300 nm, the scratch resistance tends to be deteriorated. On the other hand, when the average particle diameter of the particles B exceeds 1000 nm, the haze value tends to be high and the total light transmittance tends to be low.

The biaxially oriented polyester film having such an easy-adhesion layer tends to cause scratches particularly on the coated surface, but by applying the present invention to such a film, a more remarkable effect can be obtained. Obtainable.

By introducing the film of the present invention into the winding step, an appropriate amount of air entrained by the accompanying flow when the film is wound into a roll is discharged out of the roll, and an optimum air layer is formed inside the roll. And a roll having a good winding shape. Further, since the air layer is maintained even after storage for a long period of time, a good rolled shape is maintained for a long period of time, and there is no generation of scratches or the like.

The polyester of the biaxially oriented polyester film of the present invention is not particularly limited, but the use of a polyester containing polyethylene terephthalate as a main component is most effective. Furthermore, other polyesters may be mixed, or another acid component or glycol component may be copolymerized as long as the present invention is not impaired.

Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 schematically shows a state in which an end portion of a biaxially oriented polyester film is subjected to a projection imparting process. In FIG. 1, reference numeral 1 denotes a biaxially oriented polyester film that is running continuously; Reference numeral 2 denotes a projection imparting roll, 2 ′ denotes a backup roll, and 3 denotes a rolled-up biaxially oriented polyester film roll.
As the projection applying roll 2, a metal roll having a large number of projections on its surface is preferably used. More preferably, a hardening process (for example, a nitriding process) is performed. Further, the backup roll 2 ′ is a flat roll, and its material is preferably a metal, and the surface thereof is desirably rust-proofed (for example, hard chrome plated).

Further, it is desirable that the projection imparting roll 2 and the backup roll 2 ′ are arranged to face each other, and each of them has a structure operated by an air cylinder. The projection is imparted by nipping the biaxially oriented polyester film 1. be able to.

FIG. 2 is a diagram schematically showing an enlarged portion of the projection application processing portion. In FIG. 2, reference numeral 4 denotes a portion where the film is deformed by the projection applying process, and reference numeral 5 denotes a portion where the projection applying roll is in contact with the film.

In order to realize the state of the projections shown in the present invention, there are a method of appropriately setting the size, shape and interval of the projections of the projection applying roll, and a method of appropriately setting the processing pressure. It may be realized by the method described above.

[0036]

The present invention will be described below in detail with reference to examples. The present invention is not limited by the embodiments. The results in Examples and Comparative Examples are collectively shown in Table 1.

The biaxially oriented polyester films obtained in Examples and Comparative Examples were evaluated by the following methods.

1) Proportion of the area where the portion deformed by the projection application is perpendicularly projected on the film surface to the area of the film contacted by the projection application roll (ratio of the projection area) Optical fiber microscope (manufactured by Keyence Corporation; VH-6110)
The image obtained by magnifying the projection-provided portion of the film by 20 times was printed using a color video printer (CVP-M3, manufactured by Sony Corporation). Each of the ten deformed portions due to the projection imparting process was approximated by a square, and the vertical and horizontal lengths were respectively measured. The area of each deformed portion was determined from the product, and the average value of 10 pieces was defined as the average area (A: mm ² / piece) per deformed portion by the projection imparting process. Of the portions contacted by the projection applying roll, the length in the width direction (W: mm) and the length in the longitudinal direction 1
The number of protrusions (N: number) within the range of 00 mm was obtained, and the ratio of the protrusion area was calculated by the following equation (1).

Ratio of protrusion area = (N × A) / (100 × W) (1)

2) Average film thickness In a non-processed portion of the film, an arbitrary thickness of 20 points was measured by a digital micrometer (manufactured by Sony Magnescale;
M-30), and the average value was taken as the average film thickness (μm).

3) Average height of the portion deformed by the projection imparting process The apparent thickness of the projection imparting portion and the thickness of the non-processed portion immediately adjacent to the measurement portion were measured by a digital micrometer (manufactured by Sony Magnescale; M-30). Each was measured at 20 points, and the average of the difference was taken as the average height (μm) of the portion deformed by the projection imparting process.

4) Air content ratio The ratio of the cross-sectional area (A2) occupied by air to the cross-sectional area (A1) occupied by the film roll is represented by the air content ratio (A1 / A).
2:%).

Here, the cross-sectional area (A1: mm ² ) occupied by the film roll is calculated by first calculating the roll diameter from the peripheral length of the film roll, then calculating the roll cross-sectional area (mm ² ) from the roll diameter, The cross-sectional area (mm ² ) of the core is calculated and can be obtained by the following equation (2).

[0044] The cross-sectional area (A2) occupied by air can be obtained from the following formula (3) from the product of the cross-sectional area (A1) occupied by the film roll, the film winding length (m), and the average film thickness (μm). Cross-sectional area occupied by air (A2) = cross-sectional area occupied by film roll (A1)-film winding length (m) x average film thickness (μm) (3)

5) Disorder of Film Flatness A film having a length of 3 m was unwound from the film roll in the longitudinal direction, spread on a flat table, and visually judged in three stages. ◎: There is no disorder in flatness. ：: There is a slight disorder in flatness. ×: The flatness is disturbed.

6) Presence or Absence of Scratches A 1 m film is unwound in the longitudinal direction from the film roll, and a video photographing light (LPL Co., Ltd.
Using VIDEO LIGHT VL-302, halogen lamp 100V-300W), the presence or absence of flaws was visually observed on both sides of the film while observing the light source at an oblique angle to the entire surface of the film.

7) Accelerated treatment for long-term storage Assuming long-term storage, the film is held in a room at 40 ° C. and 70% RH for 30 days with the film roll supported at both ends of the core (the film is not in direct contact with the floor). Accelerated treatment was performed. Thereafter, the air content, the disorder of flatness, and the presence or absence of scratches were evaluated according to the above-described method.

Example 1 (1) Preparation of coating solution 95 parts of dimethyl terephthalate, 95 parts of dimethyl isophthalate, 35 parts of ethylene glycol, 145 parts of neopentyl glycol, 0.1 part of zinc acetate and 0.1 part of antimony trioxide were used. The mixture was charged in a reaction vessel and transesterification was performed at 180 ° C. for 3 hours. Next, 6.0 parts of 5-sodium isophthalic acid was added, and the esterification reaction was carried out at 240 ° C. for 1 hour.
The polycondensation reaction was performed at ~ 0.3 hPa for 2 hours to obtain a copolymerized polyester resin (A) having a molecular weight of 19,500 and a softening point of 60 ° C.

The copolymerized polyester resin (A) of 30
6.7 parts of a 20% aqueous dispersion, and 40 parts of a 20% aqueous solution of a self-crosslinkable polyurethane resin (B) containing an isocyanate group blocked with sodium bisulfite (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: Elastron H-3). 0.5 parts of Elastron catalyst (manufactured by Daiichi Kogyo Seiyaku Co., Ltd .: Cat64) and 4 parts of water
4.3 parts and 5 parts of isopropyl alcohol were mixed, 0.6 part of a 10% aqueous solution of an anionic surfactant was added, and spherical silica particles A (Nissan Chemical Industries, Ltd .: Snowtex OL, average particle size 40 nm) ) And 1.8 parts of a 4% aqueous dispersion of dry-processed silica particles B (manufactured by Nippon Aerosil Co., Ltd., Aerosil OX50, average particle diameter 500 nm, average primary particle diameter 40 nm) are added. A coating solution was obtained.

(2) Production of Easy Adhesive Film As a film raw material, polyethylene terephthalate resin pellets having an intrinsic viscosity of 0.62 dl / g and substantially containing inert particles were dried under reduced pressure at 135 ° C. for 6 hours ( (1.3 hPa), and then fed to an extruder to obtain about 28
It was melt-extruded into a sheet at 0 ° C. and quenched and solidified on a metal roll maintained at a surface temperature of 20 ° C. to obtain a cast film having a thickness of 1750 μm.

At this time, a stainless sintered filter medium having a filter particle size (initial filtration efficiency of 95%) of 10 μm was used as a filter medium for removing foreign matters from the molten resin. Next, the cast film was heated for 100 hours by a heated roll group and an infrared heater.
C., and then stretched 3.5 times in the longitudinal direction with a group of rolls having a difference in peripheral speed to obtain a uniaxially oriented PET film.

Thereafter, the coating solution was subjected to precision filtration with a filter material made of felt type polypropylene having a filtration particle size (initial filtration efficiency: 95%) of 25 μm, applied to one surface of a uniaxially oriented PET film by a reverse roll method, and dried. The coating amount (solid content weight) at this time was 0.07 g / m ² . Subsequently, the end of the film is gripped with a clip and
3. Guided to a hot air zone heated to ℃, and dried in the width direction after drying.
The film was stretched to 0 times, subsequently heat-set at 240 ° C., and further subjected to a 3% transverse relaxation at 200 ° C., to obtain a biaxially oriented polyethylene terephthalate film having a 125 μm-thick easily adhesive layer. The coating amount of the easy-adhesion layer after drying was 0.10 g / m ² as a solid content.

The biaxially oriented polyester film having a thickness of 125 μm was treated with a projection-providing roll, the ratio of the projection area was 0.18, and the area of the portion deformed by the projection-imparting process perpendicular to the film surface was 0.1 mm. 12mm
^2. The average height of the part deformed by the projection imparting process is 1
A 0 μm treated film was obtained. Following this treatment, the winding tension is 10 kg / m and the winding surface pressure is 2.5 kg / m.
And wound up. Immediately after the winding and after the long-term storage assumed acceleration processing, the air content was 0.06, there was no disturbance in flatness, and no scratch was observed.

Comparative Example 1 A biaxially oriented polyester film and a film roll were obtained in the same manner as in Example 1 except that the ratio of the projection area was 0.008. No problem occurred immediately after winding, but after accelerated processing for long-term storage assumption, the air content decreased (before treatment: 0.06 → after treatment: 0.02), the flatness was disturbed, and scratches were observed. Was.

Examples 2 to 5 and Comparative Example 2 Biaxially oriented polyester films and rolls were obtained in the same manner as in Example 1 except that the conditions shown in Table 1 were used.

[0056]

[Table 1]

[0057]

As described above, by introducing the biaxially oriented polyester film of the present invention into the winding step, a suitable amount of air is taken out of the roll by the accompanying flow when it is wound into a roll. A good roll is obtained that is discharged and contains an optimal amount of air layer inside the roll. Furthermore, since an appropriate air layer is maintained even after storage for a long period of time, a good rolled shape is maintained for a long period of time, and no scratch is generated. Therefore, the degree of freedom in adjusting the production schedule is greatly increased, and operational losses such as brand switching are reduced. Further, the quality of the product roll itself is improved, and it is possible to reduce troubles for customers. Further, it is suitable as a base material for an optical film.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a state in which a biaxially oriented polyester film is subjected to a projection imparting process.

FIG. 2 is an enlarged view schematically illustrating a processed portion for providing a projection.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Biaxially oriented polyester film 2 Projection provision roll 2 'Backup roll 3 Film roll 4 Part deformed by projection provision processing 5 Part in which projection provision roll contacted the film

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) B29K 67:00 B29L 7:00 C08L 67:02

Claims (12)

[Claims] 1. A biaxially oriented polyester film having projections formed by a projection imparting roll on at least one surface near both ends in the width direction, wherein a film area in contact with the projection imparting roll is deformed by the projection imparting process. Biaxially oriented polyester film, characterized in that the ratio of the area of the projected portion perpendicular to the film surface is 0.01 to 0.25. 2. An area obtained by projecting any one of the portions deformed by the projection providing process perpendicularly to the film surface is 0.02.
The biaxially oriented polyester film of claim 1, wherein it is 1~0.2mm ^2. 3. An average height of a portion deformed by the projection imparting process is 1 to 20% of an average film thickness of a non-processed portion.
The biaxially oriented polyester film according to claim 1, wherein 4. An average film thickness of a non-processed portion of 30 to
The biaxially oriented polyester film according to any one of claims 1 to 3, wherein the biaxially oriented polyester film has a thickness of 300 µm and an average height of a portion deformed by the projection imparting process is 3 to 30 µm. 5. The width of the portion subjected to the projection application processing is 5 to 20.
The biaxially oriented polyester film according to any one of claims 1 to 4, wherein 6. The biaxially oriented polyester film according to claim 1, wherein a high polymer adhesive layer is provided on at least one surface of the biaxially oriented polyester film. 7. The biaxially oriented polyester film according to claim 6, wherein the high polymer adhesive layer contains inert particles. 8. The polymer easy-adhesion layer has an average particle size of 20 nm.
Inert particles having an average particle diameter of at least 300 nm
The biaxially oriented polyester film according to claim 7, which contains inert particles of m or more and 1000 nm or less. 9. The biaxially oriented polyester film according to claim 7, wherein the biaxially oriented polyester film contains substantially no particles. 10. The biaxially oriented polyester film according to claim 1, wherein the haze value is 1.0% or less. 11. The biaxially oriented polyester film according to claim 1, which is used as a substrate of an optical film. 12. A roll obtained by winding up the biaxially oriented polyester film according to any one of claims 1 to 11.