CN117120242A - Polyester film and image display device using the same - Google Patents

Abstract

Provided is a polyester film having high in-plane retardation, excellent in thickness uniformity, and excellent in productivity, workability, and planarity. Disclosed is a polyester film having an in-plane retardation of 3000nm to 30000nm, an in-plane orientation degree of 0.128 to 0.155, and a thickness unevenness in the film-forming flow direction of 8% or less (the thickness unevenness is a value obtained by (maximum thickness-minimum thickness)/average thickness x 100 (%)).

Description

Polyester film and image display device using the same

Technical Field

The present invention relates to a polyester film (for example, an optical polyester film). The present invention relates to a polyester film suitable for use in various members of an image display device such as a polarizing material protective film, a base film (for example, a transparent electrode base film) for a touch panel, etc., a scattering preventing film, a screen surface protective film, etc.

Background

Polyester films are excellent in transparency, mechanical strength, and stability against chemicals and the like, and are used as optical films. These optical polyester films are generally biaxially stretched films, and are known to have birefringence, and therefore, when used in a place through which polarized light passes, rainbow-shaped color unevenness (rainbow spots) occurs.

On the other hand, the following techniques are known: a technique of providing a polyester film with high retardation on the surface of a liquid crystal display device to eliminate shadows (blackout) and rainbow spots when an image is observed with polarized sunglasses (for example, patent document 1); a technique of eliminating rainbow spots by using as a polarizer protective film (for example, patent document 2); a technique for combining a touch panel substrate and a scattering preventing film (for example, patent document 3).

When stretching is performed in only one direction to obtain a film with high retardation, the strength elongation in the direction perpendicular to the stretching direction becomes low, and therefore breakage may easily occur during film formation or during processing of the obtained film, and productivity and workability may be lowered. Further, by first stretching in a direction perpendicular to the main stretching direction at a low magnification and then stretching in the main stretching direction, it is possible to increase the strength and elongation in the direction perpendicular to the main stretching direction or to increase the production speed and to secure a necessary retardation, but when stretching is also performed in the direction perpendicular to the main stretching direction, thickness unevenness may occur and flatness may be deteriorated.

The following techniques are known: the ratio of the tensile strength in the longitudinal direction to the tensile strength in the width direction is set to 0.25 to 0.6 by stretching the steel sheet in the longitudinal direction (MD) by a factor of 2.0 or less, preferably 1.3 or less, and then stretching the steel sheet in the width direction (TD) by a factor of 4.15 or more, whereby the tensile strength and elastic modulus in the MD are improved (for example, patent document 4). However, this technique still has a problem of poor thickness uniformity and flatness.

Further, it is proposed that: films obtained by stretching in the longitudinal direction (MD) by 1.0 to 3.4 times and then stretching in the width direction (TD) by 2.5 to 5.0 times are used as films for a folding type image display device, with the MD direction being the folding direction (for example, patent documents 5 and 6). However, in this technique, there is room for improvement in thickness uniformity and flatness.

When the thickness unevenness in the MD direction is large, the following tends to occur: not only the film is easily broken during film formation, but also the cutting is easily broken during cutting, and particularly the cutting edge is easily broken during grinding and at high speed, and productivity and workability are deteriorated.

Prior art literature

Patent literature

Patent document 1: international publication No. 2011/058774

Patent document 2: international publication No. 2011/162198

Patent document 3: international publication No. 2014/123209

Patent document 4: international publication No. 2017/091031

Patent document 5: international publication No. 2018/159885

Patent document 6: international publication No. 2020/162119

Disclosure of Invention

Problems to be solved by the invention

An object of the present invention is to provide a polyester film having a high in-plane retardation, excellent in thickness uniformity, and good in productivity, workability, and flatness. Another object of the present invention is to provide a polyester film having excellent visibility, in which rainbow unevenness is less noticeable, regardless of the type of image display device or the type of light source, when the film is used as a film for various applications of the image display device.

Solution for solving the problem

The present inventors have conducted intensive studies to achieve the object and as a result, have completed the present invention.

The present invention includes the following means.

Item 1:

a polyester film having an in-plane retardation of 3000nm to 30000nm,

the degree of plane orientation is 0.128 or more and 0.155 or less,

the thickness unevenness in the film-forming flow direction was 8% or less.

(wherein, the thickness unevenness is a value obtained by (maximum thickness-minimum thickness)/average thickness×100 (%)).

Item 2:

the polyester film according to item 1, wherein the ratio A/B of A to B is 5 or less when Fourier transform is performed on the thickness measurement data in the film-forming flow direction and the frequency is replaced with the length period of the film.

A: the period is more than 10cm, and the average value of the amplitude of the maximum first 5 values of the amplitude values;

b: the period is 10cm or less, and the average value of the amplitude of the maximum first 5 values of the amplitude values is the average value.

Item 3:

the polyester film according to item 1 or 2, wherein when the film-forming flow direction thickness measurement data is subjected to fourier transform and the frequency is replaced with the film length period, the ratio Amax/B of Amax to B described below is 7 or less.

Amax: the period is more than 10cm, and the amplitude is the maximum value.

Item 4:

the polyester film according to any one of items 1 to 3, wherein the NZ coefficient is 1.65 to 3.

Item 5:

the polyester film according to any one of items 1 to 4, which has a thickness of 25 μm or more and 150 μm or less.

Item 6:

the polyester film according to any one of items 1 to 5, wherein the elongation at break in the film-forming flow direction is 4% or more.

Item 7:

the polyester film according to any one of items 1 to 6, wherein the breaking strength in the film-forming flow direction is 50MPa or more.

Item 8:

a polarizing element protective film formed from the polyester film according to any one of items 1 to 7.

Item 9:

a polarizing plate comprising the polarizing-material protective film according to claim 8 and a polarizing material.

Item 10:

an image display device, wherein the polarizing plate of item 9 is disposed on a visible side of an image display unit.

Item 11:

a transparent electrode substrate film formed from the polyester film according to any one of claims 1 to 7.

Item 12:

a fly-away preventive film comprising the polyester film according to any one of items 1 to 7.

Item 13:

a picture surface protective film comprising the polyester film according to any one of items 1 to 7.

Item 14:

an image display device comprising any one of the transparent electrode base film according to item 11, the anti-scattering film according to item 12, and the screen surface protective film according to item 13.

Item 15:

the image display device according to item 14, which is a flexible image display device.

ADVANTAGEOUS EFFECTS OF INVENTION

The polyester film having high in-plane retardation and excellent in thickness uniformity, productivity, workability and flatness can be obtained by the present invention. Further, the polyester film of the present invention can suppress rainbow unevenness, and therefore, is suitable for a transparent electrode base material film such as a polarizing material protective film and a touch panel, a scattering preventing film, a screen surface protective film of an image display device, and the like, and has excellent bending durability when used in a flexible image display device.

Drawings

Fig. 1 is a graph showing the frequency analysis results of thickness unevenness in the film formation flow direction for film a.

Fig. 2 is a graph showing the frequency analysis results of thickness unevenness in the film formation flow direction for the thin film D.

Detailed Description

Examples of suitable polyester films of the present invention include polyethylene terephthalate (PET), poly (1, 3-propanediol terephthalate) (PTT), poly (1, 4-butanediol terephthalate) (PBT), and polyethylene naphthalate (PEN), and PET or PEN are preferable from the viewpoint of being able to increase in-plane retardation and low in moisture permeability and hygroscopicity. The polyester may be copolymerized with a carboxylic acid component and/or a glycol component other than the main component, and the total amount of the carboxylic acid component and/or the glycol component other than the main component is preferably 10 mol% or less, more preferably 5 mol% or less, and particularly preferably 2 mol% or less, based on 100 mol% of the total amount of the carboxylic acid component and the glycol component.

The Intrinsic Viscosity (IV) of the polyester resin constituting the polyester film of the present invention is preferably 0.45dL/g or more and 1.5dL/g or less.

In the case of PET, the IV is preferably 0.5dL/g or more and 1.5dL/g or less. The lower limit of IV is more preferably 0.53dL/g, still more preferably 0.55L/g. The upper limit of IV is more preferably 1.2dL/g, still more preferably 1dL/g, and particularly preferably 0.8dL/g.

In the case of PEN, the lower limit of IV is preferably 0.45dL/g, more preferably 0.48dL/g, still more preferably 0.5dL/g, and particularly preferably 0.53dL/g. The upper limit of IV is more preferably 1dL/g, still more preferably 0.8dL/g, still more preferably 0.75dL/g, and particularly preferably 0.7dL/g.

By setting the thickness in the above range, a film having more excellent mechanical strength such as impact resistance can be formed, more stable film formation is easy, and a film having less thickness unevenness can be efficiently produced without imposing a significant burden on the machine.

In the present invention, the lower limit of the in-plane retardation (Re) of the polyester film is preferably 3000nm, more preferably 4000nm, further preferably 4300nm, particularly preferably 4500nm, and most preferably 5000nm. By setting the lower limit to be equal to or greater than the above, rainbow unevenness can be suppressed.

The upper limit of Re is preferably 30000nm, more preferably 15000nm, further preferably 12000nm, particularly preferably 10000nm, and most preferably 9500nm. By setting the upper limit or lower, it is not necessary to thicken the film to a desired level or higher, and it is easy to cope with thinning of an image display device or the like.

In order to widen the angle at which the iridescence is suppressed when viewed from the oblique direction, re is preferably 5500nm or more, more preferably 6000nm or more, still more preferably 6000nm or more, particularly preferably 6500nm or more. In the case of a film which is thin even when the angle of view is slightly narrow, such as a base film (for example, a transparent electrode base film) of a scatter prevention film, a touch panel or the like, a screen surface protection film, a foldable film (for example, a PET film) or the like, re is more preferably 7000nm or less, still more preferably 6500nm or less, and particularly preferably 6000nm or less.

The lower limit of the degree of plane orientation (Δp) of the polyester film of the present invention is preferably 0.128, more preferably 0.129, still more preferably 0.13, and particularly preferably more than 0.13. The upper limit of the degree of surface orientation is preferably 0.155, more preferably 0.152, and further preferably 0.15. By setting the range as described above, the occurrence of rainbow unevenness is suppressed, and breakage or the like is less likely to occur, so that the film formation stability can be further improved.

In the case of using the film as a polarizer protective film, the upper limit of the degree of plane orientation is more preferably 0.145, still more preferably 0.14, particularly preferably 0.138, and most preferably 0.136 in the case of more effectively controlling rainbow unevenness from an oblique direction, or the like.

In the case of being used for a flexible image display device or the like, for which excellent bending resistance is desired, the lower limit of the degree of plane orientation (Δp) is more preferably 0.135, still more preferably 0.138, and particularly preferably 0.14.

The degree of plane orientation means: the value obtained by (nx+ny)/2-nz is obtained when ny is the refractive index in the slow axis direction, nx is the fast axis (the refractive index in the direction orthogonal to the slow axis direction), and nz is the refractive index in the thickness direction.

The lower limit of the NZ coefficient of the polyester film of the present invention is preferably 1.65, more preferably 1.68, further preferably 1.7, and particularly preferably more than 1.7.

The upper limit of the NZ coefficient is preferably 3, more preferably 2.7, further preferably 2.5, particularly preferably 2.3.

By setting the range as described above, the occurrence of rainbow unevenness is suppressed, and breakage or the like is less likely to occur, so that the film formation stability can be further improved.

In the case of using the film as a polarizer protective film, the upper limit of the NZ coefficient is more preferably 1.9, still more preferably 1.85, and particularly preferably 1.8 in the case of more effectively suppressing rainbow unevenness from an oblique direction or the like.

In the case of being used for a flexible image display device or the like, for which excellent bending resistance is desired, the lower limit of the NZ coefficient is more preferably 1.8, further preferably 1.85, and particularly preferably 1.9.

The NZ coefficient is a value obtained by nz= |ny-nz|/|ny-nx|.

By setting the degree of plane orientation and the NZ coefficient to the above ranges, adhesion to functional layers such as hard coat layers, antireflection layers, antiglare layers, and the like, and adhesion to polarizers and the like can be ensured.

The lower limit of the thickness of the polyester film of the present invention is preferably 25. Mu.m, more preferably 30. Mu.m, 40. Mu.m, 45. Mu.m, 50. Mu.m, 55. Mu.m, in this order.

The upper limit of the thickness is preferably 150. Mu.m, more preferably 130. Mu.m, 100. Mu.m, 90. Mu.m, 85. Mu.m, in this order. In the present specification, the term "a numerical value" is preferably a numerical value whose preferred range is gradually narrowed.

If the thickness is not more than the upper limit, the thickness of the unstretched film becomes thinner when the unstretched film is heated, and therefore, the temperature can be easily increased uniformly in the thickness direction of the film in a short time, and the thickness unevenness can be easily suppressed. In addition, the thickness of the image display device can be easily reduced.

The thickness of the polarizer protective film is preferably 40 to 85 μm, and the thickness of the film is preferably 25 to 70 μm in the case of a base film (for example, a transparent electrode base film) such as a scattering preventing film or a touch panel, or the thickness of the film for protecting the screen surface of a flexible image display device, and the thickness of the film is preferably 60 to 150 μm in the case of a film for protecting the screen surface of a non-flexible image display device.

The thickness can be calculated as follows: for example, the thickness of a film of a predetermined size (for example, about 50mm in width and about 6m in length) is continuously measured at a predetermined speed (for example, at a speed of 1.5 m/min in the MD direction) at a predetermined interval (for example, at an interval of 0.1 seconds) using a contact continuous thickness meter, and a predetermined number of data (for example, 2048 points in succession) is arbitrarily selected based on the obtained data, and calculated based on the average value thereof.

The upper limit of the thickness unevenness in the film forming flow direction (hereinafter, also referred to as the longitudinal direction and the MD direction in some cases, also referred to as the direction orthogonal to the main stretching direction in the case of stretching) of the polyester film of the present invention is preferably 8%, more preferably 7%, still more preferably 6%, particularly preferably 5%, and most preferably 4%.

The thickness unevenness in the MD direction is preferably low, and the lower limit is preferably 0.1%, more preferably 0.5% from the practical viewpoint.

The thickness unevenness is a value obtained by (maximum value of thickness-minimum value)/average value of thickness×100 (%) in the following thickness measurement.

In the present invention, the data obtained by measuring the film thickness in the MD direction is fourier-transformed (for example, fast fourier-transformed), the obtained result is analyzed by the length period in the MD direction of the film (specifically, the frequency is replaced with the length period), a is the average of the maximum first 5 values of the amplitude magnitude with a period of 10cm or more, B is the average of the maximum first 5 values of the amplitude magnitude with a period of less than 10cm, and the lower limit of a/B is preferably 0.5, more preferably 1, still more preferably 1.3, particularly preferably 1.5, and most preferably 1.8.

The upper limit of A/B is preferably 5, more preferably 4.5, further preferably 4, particularly preferably 3.5.

In the above description, when the period is 10cm or more and the maximum value of the amplitude is Amax, the lower limit of Amax/B is preferably 0.7, more preferably 1.4, further preferably 1.8, particularly preferably 2, and most preferably 2.2. The upper limit of Amax/B is 7, more preferably 6, still more preferably 5, particularly preferably 4.5, and most preferably 4.

By setting A/B and/or Amax/B to the above ranges, stable production can be maintained at higher productivity, breakage is less likely to occur even in film formation and post-processing, and a thin film with less likely to be noticeable in chromaticity unevenness can be produced even in a liquid crystal display device obtained by using a light source having a steep peak.

Note that A, amax and B are preferably calculated by the following specific method.

The thickness of the central portion of the film was continuously read at intervals of 0.1 seconds at a speed of 1.5 m/min.

Using the resulting data of 2048 points in succession (an amount of 5.12m in length), frequency analysis was performed using a fast fourier transform.

The frequency of the obtained analysis data is converted into a length period, and the amplitude is obtained.

Among the data having a length period of 10cm or more, 5 points are sequentially selected from the maximum amplitude value, the average value of these points is A, and the maximum amplitude value among these 5 points is Amax.

Among the data having a length period of less than 10cm, 5 points are selected in order from the maximum amplitude value, and the average value of these points is set to B. Note that, the data in the latter half of the frequency analysis data called ghost (ghost) is ignored, and only the analysis data in the former half is used.

According to the studies of the present inventors, in the case where stretching in the MD direction is not performed, the thickness unevenness in the MD direction is often caused by movement of an electrode or vibration of a device used when electrostatically adhering a molten resin to a cooling roll, or by influence of roundness or offset of the cooling roll during casting, or by automatic adjustment of the lip interval of a die. For example, the thickness unevenness caused by movement of the electrode or vibration of the device is often several cm or less in period. However, when the sheet is slightly stretched in the MD direction, the thickness unevenness cannot be sufficiently suppressed even if the sheet is adjusted, and the thickness unevenness having a period of 10cm to m becomes remarkable, and a problem occurs due to the thickness unevenness.

According to further studies by the present inventors, it was found that: in the case of slight stretching in the MD direction, it is necessary to manage the preheating temperature and stretching temperature at the time of stretching to appropriate ranges, and in the case of deviation from the appropriate temperatures, the following phenomenon occurs: uneven stretching occurs, the stretching position is not fixed, stretching is unstable, the film is relaxed, the film is not smoothly peeled off from the roll, uneven thickness of 10cm to m becomes remarkable, and flatness is also deteriorated.

Hereinafter, preferable film forming conditions for obtaining the polyester film of the present invention will be described.

First, a polyester resin (typically, PET) is dried, and then fed into an extruder, melted at 260 to 300 ℃, and extruded from a die in a sheet form onto a cooling roll to obtain an unstretched film. In this case, it is preferable to apply electric charge to the resin or blow air or decompress the inside of the chamber so that the resin rapidly adheres to the cooling roller. At this time, the following operations are preferably performed: adjusting the tension and fixing method of the wire electrode and the strip electrode to reduce the vibration of the electrode; the control is carried out in a mode of stable air flow and decompression; making the casting apparatus less susceptible to vibration of a machine such as a motor, etc.

Then, the unstretched film is preheated to be heated, and finally stretched by applying tension in the MD direction. In this case, the unstretched film is gradually heated in a plurality of stages, and the maximum reached temperature of the film surface in the heating step before the stretching step in which stretching is performed by applying tension is referred to as a preheating temperature, and the maximum reached temperature of the film surface in stretching is referred to as a stretching temperature.

In the MD stretching, the temperature of the film is raised by a plurality of low-speed rolls and the film is stretched by a circumferential speed difference between the high-speed rolls and the low-speed rolls. In this case, as a method for setting the film surface to the final stretching temperature, there are cases where heating is performed by an infrared heater (IR heater) and the like when heating is performed by a final roll (hereinafter, sometimes simply referred to as "final roll") of a low-speed roll.

When heating is performed by the final roll, the temperature at which the film leaves the final roll becomes the stretching temperature, and the temperature at which the film leaves the low-speed roll (heating roll) immediately before the final roll becomes the preheating temperature. When heating is performed by the IR heater, the highest temperature in the region heated by the IR heater becomes the stretching temperature, and the temperature at the time of leaving from the final roller (heating roller) becomes the preheating temperature.

The preheating temperature for MD stretching is preferably 60 ℃ or higher, more preferably 65 ℃ or higher, and still more preferably 70 ℃ or higher. By setting the preheating temperature to the above range, the temperature difference in the thickness direction of the film can be reduced even if the film formation speed is high, and stable stretching can be achieved.

The preheating temperature for MD stretching is preferably 95 ℃ or less, more preferably 90 ℃ or less, further preferably 85 ℃ or less, particularly preferably 82 ℃ or less, and most preferably 80 ℃ or less. By setting the preheating temperature to the above range, the adhesion between the film and the roller can be suppressed, and stable film travel can be realized. Further, since the film relaxation between the preheating rollers can be suppressed and the tension between the preheating rollers can be reduced, the unnecessary film elongation in the preheating process can be reduced and the thickness unevenness and the reduction in planarity can be suppressed. In addition, when the molecular weight of the polyester is low (in the case of low IV), relaxation of the film or the like is liable to occur, and for example, when the IV is 0.7dl/g or less, it is preferably 90℃or less, and when the IV is 0.65dl/g or less, it is preferably 85℃or less.

The stretching temperature in MD stretching is preferably 86 ℃ or higher, more preferably 88 ℃ or higher, still more preferably 89 ℃ or higher, particularly preferably 90 ℃ or higher, and most preferably 91 ℃ or higher. When the stretching temperature is low, the stress may not rise gradually with respect to the strain in the S-S (stress-strain) characteristic of the unstretched film, and the stretching may be unstable.

The stretching temperature in MD stretching is preferably 110 ℃ or less, more preferably 105 ℃ or less, 102 ℃ or less, 100 ℃ or less, 98 ℃ or less, 96 ℃ or less in this order. By setting the stretching temperature to the above range, the film is not excessively soft, and relaxation during stretching can be suppressed. In particular, when tension is applied, the film is easily stretched from the latter half of 80 ℃, but if the stretching temperature is in the above range, stretching other than the envisaged position can be suppressed, and stretching can be stabilized. Further, as described above, the lower the molecular weight is, the more easily the relaxation is, and therefore, for example, when the IV is 0.7dl/g or less, it is preferably 100℃or less, and when the IV is 0.65dl/g or less, it is preferably 98℃or less.

In MD stretching, the difference between the stretching temperature and the preheating temperature is preferably 11℃or higher, more preferably 12℃or higher, and still more preferably 13℃or higher. The difference between the stretching temperature and the preheating temperature is preferably 24 ℃ or less, more preferably 23 ℃ or less, and still more preferably 22 ℃ or less.

By setting the above-described range, the pseudo stretching during preheating and the sticking of the film to the rollers can be suppressed, and even if the film forming speed is high, the temperature difference in the film thickness direction during stretching can be reduced, and stable stretching can be realized.

In MD stretching, as described above, it is necessary to rapidly raise the film temperature from the preheating temperature to the stretching temperature, but even if the heating is excessively rapid, the temperature difference in the thickness direction of the film becomes large, and it may be difficult to stably stretch. Therefore, in the case of heating by the final roller, it is preferable to increase the holding angle of the film with respect to the final roller and to lengthen the contact time between the final heated roller and the film. The holding angle is preferably 30 degrees or more, more preferably 45 degrees or more, still more preferably 60 degrees or more, particularly preferably 70 degrees or more.

In addition, if an IR heater is used, it is preferable to provide a plurality of heaters along the MD direction, or to use a heater having a wide width in the MD direction.

The rolls used in the preheating step and the rolls used in the stretching step may be rolls having surfaces plated with chromium plating, nickel plating, cobalt plating alloy or the like, and in the case where adhesion of the polyester resin is observed when the roll surfaces reach a high temperature, a roll processed with a fluororesin is preferably used.

It is also important to improve the roundness of the rolls used in the preheating process and the rolls in the stretching process and the accuracy of the offset. The roundness is preferably 30 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less, and usually 0.1 μm or more. The offset is preferably 40 μm or less, more preferably 30 μm or less, still more preferably 20 μm or less, and usually 0.1 μm or more.

The diameter of the rolls is also dependent on the size of the stretching machine, and if a film having a width of about 700 to 2500mm is produced as an unstretched film, it is preferably 100 to 500mm, more preferably 150 to 400mm, still more preferably 170 to 350mm.

The lower limit of the MD stretch ratio is preferably 1.05 times, more preferably 1.08 times, and still more preferably 1.1 times. The upper limit of the MD stretch ratio is preferably 2 times, more preferably 1.8 times, and still more preferably 1.7 times. By setting the range as described above, a film having excellent workability and suppressed rainbow unevenness can be further produced. In the case of using the film as a polarizer protective film, the upper limit of the MD stretching ratio is more preferably 1.25 times, further preferably 1.2 times, and particularly preferably 1.18 times, in the case of more effectively suppressing rainbow unevenness from the oblique direction, or the like. In the case of being used for a flexible image display device or the like, in which excellent bending resistance is desired, the lower limit of the MD stretching ratio is more preferably 1.2 times, further preferably 1.25 times, and particularly preferably 1.3 times.

In the present invention, the upper limit of the thickness unevenness of the film in the direction (TD direction) orthogonal to the film formation flow direction is preferably 5%, more preferably 4%, further preferably 3.5%, and particularly preferably 3%. The thickness unevenness in the TD direction is preferably low, and the lower limit is preferably 0.1%, more preferably 0.5% from the practical viewpoint.

The thickness unevenness in the TD direction can be achieved by, for example, controlling the die lip interval in casting, reducing the unevenness in the temperature of the film in the TD direction during TD stretching, and setting the degree of plane orientation or NZ coefficient to an appropriate range.

In the TD stretching, the film after MD stretching is preheated, preferably stretched at 80 to 130 ℃, more preferably at 90 to 120 ℃. The stretch ratio of the TD stretching is preferably 3 to 6.5 times, more preferably 3.2 to 6.2 times, still more preferably 3.5 to 6.0 times, particularly preferably 3.7 to 5.8 times.

The stretching is preferably followed by thermal fixing. The heat-setting temperature is preferably 150 to 250 ℃, more preferably 170 to 230 ℃. The heat setting time is preferably 3 to 60 seconds, more preferably 5 to 30 seconds.

In the heat setting, it is also preferable to perform the relaxation treatment along the main stretching direction and/or the direction orthogonal thereto. The relaxation treatment is preferably 0.5 to 10%, more preferably 1 to 5%.

The lower limit of the elongation at break in the MD direction of the polyester film of the present invention is preferably 4%, more preferably 5%, 6%, 7%, 8%, 9% and 10% in this order. The upper limit of the elongation at break in the MD direction is preferably 50%, more preferably 40%, further preferably 30%, particularly preferably 25%, and most preferably 20%.

The lower limit of the elongation at break in the TD direction of the polyester film of the present invention is preferably 50%, more preferably 60%. The upper limit of the elongation at break in the TD direction is preferably 200%, more preferably 150%, further preferably 120%, particularly preferably 100%.

The lower limit of the breaking strength in the MD direction of the polyester film of the present invention is preferably 50MPa, more preferably 55MPa, still more preferably 60MPa, particularly preferably 65MPa. The upper limit of the fracture strength in the MD direction is preferably 150MPa, more preferably 130MPa, further preferably 120MPa, particularly preferably 110MPa, and most preferably 100MPa.

The lower limit of the breaking strength in the TD direction of the polyester film of the present invention is preferably 300MPa, more preferably 330MPa, and even more preferably 350MPa.

The upper limit of the fracture strength in the TD direction is preferably 500MPa, more preferably 450MPa, further preferably 420MPa, particularly preferably 400MPa.

When the elongation at break and the breaking strength are within the above ranges, a film having more excellent workability can be formed. The elongation at break and the breaking strength are values measured in accordance with JIS K7113.

Regarding the heat shrinkage rate of the polyester film of the present invention at 150 ℃, the lower limit is preferably-0.5%, more preferably-0.1%, in both the MD direction and the TD direction. Regarding the heat shrinkage at 150 ℃, the upper limit is preferably 3%, more preferably 2.7%, further preferably 2.5%, particularly preferably 2% in both the MD direction and the TD direction.

The transmittance of the polyester film of the present invention at a wavelength of 380nm is preferably 20% or less. The light transmittance at a wavelength of 380nm is more preferably 15% or less, still more preferably 10% or less, particularly preferably 5% or less. If the light transmittance is 20% or less, deterioration of iodine and a dichroic dye in the polarizing layer due to ultraviolet rays can be suppressed. The light transmittance is a value measured in a direction perpendicular to the plane of the film, and may be measured using a spectrophotometer (for example, japanese U-3500). In particular, in the case of using as a polarizer protective film, the transmittance of ultraviolet rays is preferably low.

The transmittance of the polyester film of the present invention at a wavelength of 380nm is set to 20% or less, for example, by adding an ultraviolet absorber to the film, applying a coating liquid containing the ultraviolet absorber to the film surface, and appropriately adjusting the type, concentration, film thickness, and the like of the ultraviolet absorber. The ultraviolet absorber is a known substance. The ultraviolet absorber includes an organic ultraviolet absorber and an inorganic ultraviolet absorber, and is preferably an organic ultraviolet absorber from the viewpoint of transparency.

Examples of the organic ultraviolet absorber include benzotriazole-based, benzophenone-based, cyclic imino ester-based, and combinations thereof, and the like, and the organic ultraviolet absorber is not particularly limited as long as it has a desired absorbance range.

In order to improve slidability, it is also preferable to add particles having an average particle diameter of 0.05 to 2. Mu.m. Examples of the particles include inorganic particles such as titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconium oxide, tungsten oxide, lithium fluoride, and calcium fluoride; and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles.

These particles may be added to the film as a whole or may be made into a skin-core co-extruded multilayer structure and added only to the skin layer. In addition, the film itself preferably contains no particles, but rather particles are added to the easy-to-adhere layer described later.

The polyester film of the present invention may be subjected to a treatment for improving adhesion such as corona treatment, flame treatment, and plasma treatment.

(easy adhesive layer)

The polyester film of the present invention may be provided with an easy-to-adhere layer in order to improve adhesion of the adhesive, coating, etc.

The resin used for the easy-to-adhere layer may be a polyester resin, a polyurethane resin, a polycarbonate resin, an acrylic resin, or the like, and is preferably a polyester resin, a polyester polyurethane resin, a polycarbonate polyurethane resin, or an acrylic resin. The easy-to-adhere layer is preferably crosslinked. Examples of the crosslinking agent include isocyanate compounds, melamine compounds, epoxy resins, and oxazoline compounds. In addition, the addition of a water-soluble resin such as polyvinyl alcohol to the adhesive layer is also a useful means for improving the adhesion to the polarizer.

The easy-to-adhere layer can be provided by applying the resin and, if necessary, a crosslinking agent, particles, or other aqueous coating material to a film and drying the film. Examples of the particles include particles used for the base material.

The easy-to-adhere layer may be provided on the film (for example, stretched film) off-line, and is preferably provided on-line in the film-forming step. When the stretching is performed in an in-line manner, the stretching may be performed before longitudinal stretching (MD stretching) or before transverse stretching (TD stretching), and it is preferable to apply the stretching immediately before transverse stretching, and dry and crosslink the stretching in a preheating, heating, and heat treatment step by a tenter. In the case of performing in-line coating immediately before longitudinal stretching by a roll, it is preferable that the coating is dried by a horizontal dryer after the coating and then guided to a stretching roll.

The coating amount of the easy-to-adhere layer (coating amount after drying) is preferably 0.01 to 1.0g/m ² More preferably 0.03 to 0.5g/m ² 。

(functional layer)

The polyester film of the present invention is also preferably provided with functional layers such as a hard coat layer, an antireflection layer, a low reflection layer, an antiglare layer, an antistatic layer, and the like. The antireflection layer, the low reflection layer, and the antiglare layer are collectively referred to as a reflection reducing layer. The reflection reducing layer also has the following effects: not only prevents external light from being mapped to a display screen and becoming difficult to observe, but also suppresses interface reflection and reduces or makes less noticeable iridescence. In addition, when the film is used as a base film (for example, a transparent electrode base film) for a touch panel or the like, it is preferable to provide a refractive index adjusting layer so that the transparent electrode layer is less noticeable. Among polyester films provided with a functional layer, a film in this state before the functional layer is provided is referred to as a base film. The base film may also contain the above-mentioned adhesive layer.

The upper limit of the reflectance of the polyester film measured from the reflection reducing layer side is preferably 5%, more preferably 4%, further preferably 3%, particularly preferably 2%, and most preferably 1.5%. If the upper limit is less than or equal to the above upper limit, reflection of external light can be reduced, and visibility of the screen can be improved. The lower limit of the reflectance is not particularly limited, but is preferably 0.01%, more preferably 0.1% from the practical viewpoint.

As the reflection reducing layer, there are various types such as a low reflection layer, an antireflection layer, and an antiglare layer.

(Low reflection layer)

The low reflection layer is a layer having the following functions: by providing a low refractive index layer (low refractive index layer) on the surface of the base film, the difference between the refractive index of the base film and that of air is reduced, and the reflectance is reduced.

(anti-reflection layer)

The anti-reflection layer is a layer that controls reflection by controlling the thickness of the low refractive index layer so that reflected light at the interface interferes. The thickness of the low refractive index layer is preferably about (400 to 700 mn)/(refractive index of the low refractive index layer×4) of the wavelength of visible light.

In a preferred embodiment, a high refractive index layer is provided between the antireflection layer and the base film, and the low refractive index layer and/or the high refractive index layer may be provided in 2 or more layers, whereby the antireflection effect can be further improved by multiple interference. The high refractive index layer and the low refractive index layer are sometimes collectively referred to as an antireflection layer.

In the case of the antireflection layer, the upper limit of the reflectance is preferably 2%, more preferably 1.5%, further preferably 1.2%, particularly preferably 1%.

(Low refractive index layer)

The refractive index of the low refractive index layer is preferably 1.45 or less, more preferably 1.42 or less. The refractive index of the low refractive index layer is preferably 1.2 or more, more preferably 1.25 or more.

The refractive index of the low refractive index layer was measured under the condition of a wavelength of 589 nm.

The thickness of the low refractive index layer is not limited, and is usually set appropriately in the range of about 30nm to 1. Mu.m. In the case of using the low refractive index layer as an antireflection layer, the thickness of the low refractive index layer is preferably 70 to 120nm, more preferably 75 to 110nm.

The low refractive index layer may preferably be: (1) A layer formed from a resin composition containing a binder resin and low refractive index particles; (2) A layer formed of a fluorine-based resin as a low refractive index resin; (3) A layer formed from a fluorine-based resin composition containing silica or magnesium fluoride; (4) Films of low refractive index substances such as silica and magnesium fluoride.

The binder resin contained in the resin composition of (1) may be, but not particularly limited to, polyester, polyurethane, polyamide, polycarbonate, acrylic, or the like. Among them, acrylic is preferable, and a resin obtained by polymerizing (crosslinking) a photopolymerizable compound by light irradiation is preferable.

Examples of the photopolymerizable compound include photopolymerizable monomers, photopolymerizable oligomers, and photopolymerizable polymers, and these can be suitably adjusted and used. The photopolymerizable compound is preferably a combination of a photopolymerizable monomer and a photopolymerizable oligomer or a photopolymerizable polymer. The photopolymerizable monomers, photopolymerizable oligomers and photopolymerizable polymers are preferably polyfunctional substances.

Examples of the polyfunctional monomer include pentaerythritol triacrylate (PETA), dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate (PETTA), dipentaerythritol pentaacrylate (DPPA), and the like. In order to adjust the coating viscosity and hardness, a monofunctional monomer may be used in combination.

Examples of the polyfunctional oligomer include polyester (meth) acrylate, urethane (meth) acrylate, polyester- (meth) acrylate, polyether (meth) acrylate, polyol (meth) acrylate, melamine (meth) acrylate, isocyanurate (meth) acrylate, and epoxy (meth) acrylate.

Examples of the polyfunctional polymer include urethane (meth) acrylates, isocyanurate (meth) acrylates, polyester- (meth) acrylates, epoxy (meth) acrylates, and the like.

(1) In addition to the above components, the resin composition of (a) may contain a polymerization initiator, a catalyst for a crosslinking agent, a polymerization inhibitor, an antioxidant, an ultraviolet absorber, a leveling agent, a surfactant, and the like.

The low refractive index particles contained in the resin composition of (1) include silica particles (e.g., hollow silica particles), magnesium fluoride particles, and the like, and among them, hollow silica particles are preferable. Such hollow silica particles can be produced by a production method described in examples of Japanese patent application laid-open No. 2005-099778.

The average particle diameter of primary particles of the low refractive index particles is preferably 5 to 200nm, more preferably 5 to 100nm, and even more preferably 10 to 80nm.

The low refractive index particles are more preferably surface-treated with a silane coupling agent, and among them, the surface-treated with a silane coupling agent having a (meth) acryloyl group is preferable.

The content of the low refractive index particles in the low refractive index layer is preferably 10 to 400 parts by mass, more preferably 10 to 250 parts by mass, still more preferably 50 to 200 parts by mass, particularly preferably 80 to 180 parts by mass, and most preferably 100 to 180 parts by mass, relative to 100 parts by mass of the binder resin.

As the fluorine-based resin of (2), a polymerizable compound having at least a fluorine atom in the molecule or a polymer thereof can be used. The polymerizable compound is not particularly limited, and preferably has a curing reactive group such as a photopolymerizable functional group and a thermosetting polar group. In addition, the compound may be a compound having a plurality of these curing reactive groups at the same time. The polymer does not have the above-mentioned curing reactive group or the like with respect to the polymerizable compound.

As the compound having a photopolymerizable functional group, for example, a fluorine-containing monomer having an ethylenically unsaturated bond can be widely used.

For the purpose of improving the fingerprint resistance, it is also preferable to appropriately add a known polysiloxane-based or fluorine-based antifouling agent to the low refractive index layer.

In order to exhibit antiglare properties, the surface of the low refractive index layer may be a concave-convex surface, and preferably a smooth surface.

When the surface of the low refractive index layer is a smooth surface, the arithmetic average roughness SRa (JIS B0601:1994) of the surface of the low refractive index layer is preferably 20nm or less, more preferably 15nm or less, still more preferably 10nm or less, particularly preferably 1 to 8nm. The ten-point average roughness Rz (JIS B0601:1994) of the surface of the low refractive index layer is preferably 160nm or less, more preferably 50 to 155nm.

(high refractive index layer)

The refractive index of the high refractive index layer is preferably 1.55 to 1.85, more preferably 1.56 to 1.7.

The refractive index of the high refractive index layer was measured under the condition of a wavelength of 589 nm.

The thickness of the high refractive index layer is preferably 30 to 200nm, more preferably 50 to 180nm. The high refractive index layer may be a plurality of layers, preferably 2 or less layers, more preferably a single layer. In the case of a plurality of layers, the total thickness of the plurality of layers is preferably within the above range.

When the high refractive index layer is 2 layers, the refractive index of the high refractive index layer on the low refractive index layer side is preferably further increased, specifically, the refractive index of the high refractive index layer on the low refractive index layer side is preferably 1.6 to 1.85, and the refractive index of the other high refractive index layer is preferably 1.55 to 1.7.

The high refractive index layer is preferably formed of a resin composition containing high refractive index particles and a resin.

As the high refractive index particles, antimony pentoxide particles, zinc oxide particles, titanium oxide particles, cerium oxide particles, tin-doped indium oxide particles, antimony-doped tin oxide particles, yttrium oxide particles, zirconium oxide particles, and the like are preferable. Among these, titanium oxide particles and zirconium oxide particles are suitable.

The high refractive index particles may be used in combination of 2 or more. In particular, in order to prevent aggregation, it is also preferable to add the first high refractive index particles and the second high refractive index particles having a smaller surface charge amount than that.

The resin used for the high refractive index layer may be the same resin as that listed for the low refractive index layer, except for a fluorine-based resin.

In order to planarize the low refractive index layer provided on the high refractive index layer, it is preferable that the surface of the high refractive index layer is also planarized. As a method for flattening the surface of the high refractive index layer, a method of flattening the low refractive index layer described above can be used.

The average particle diameter of the high refractive index particles and the primary particles of the high refractive index particles is preferably 5 to 200nm, more preferably 5 to 100nm, and still more preferably 10 to 80nm.

These particles are more preferably surface-treated, and more preferably surface-treated with a silane coupling agent, wherein the surface-treated is preferably with a silane coupling agent having a (meth) acryloyl group.

The content of the high refractive index particles in the high refractive index layer is preferably 10 to 400 parts by mass, more preferably 10 to 250 parts by mass, still more preferably 50 to 200 parts by mass, particularly preferably 80 to 180 parts by mass, and most preferably 100 to 180 parts by mass, relative to 100 parts by mass of the binder resin.

The high refractive index layer and the low refractive index layer can be formed by, for example, applying a resin composition containing a photopolymerizable compound to a base film, drying the resin composition, and then irradiating the resin composition in a film form with light such as ultraviolet rays to polymerize (crosslink) the photopolymerizable compound.

To the resin composition of the high refractive index layer and the low refractive index layer, thermoplastic resin, thermosetting resin, solvent, polymerization initiator, a combination thereof, and the like may be added as necessary. Further, a dispersant, a surfactant, an antistatic agent, a silane coupling agent, a thickener, an anti-coloring agent, a coloring agent (pigment, dye), an antifoaming agent, a leveling agent, a flame retardant, an ultraviolet absorber, an adhesion imparting agent, a polymerization inhibitor, an antioxidant, a surface modifier, an easy-to-lubricate agent, a combination thereof, and the like may be added.

(antiglare layer)

The antiglare layer is a layer that prevents reflection glare in the form of a light source or reduces glare when external light is reflected by a surface by providing irregularities on the surface and diffusely reflecting the surface.

The arithmetic average roughness (SRa) of the surface irregularities of the antiglare layer is preferably 0.02 to 0.25 μm, more preferably 0.02 to 0.15 μm, and still more preferably 0.02 to 0.12 μm.

The ten-point average roughness (Rzjis) of the surface irregularities of the antiglare layer is preferably 0.15 to 2 μm, more preferably 0.2 to 1.2 μm, and even more preferably 0.3 to 0.8 μm.

SRa and Rzjis are calculated from roughness curves measured using a contact type roughness meter in accordance with JIS B0601-1994 or JIS B0601-2001.

Examples of the method for providing the antiglare layer on the base film include the following methods.

Coating material for antiglare layer containing particles (filler) and the like

Curing the antiglare layer resin in contact with a mold having a concave-convex structure

Coating the antiglare layer resin on a mold having a concave-convex structure, and transferring to a base film

Coating material which undergoes decomposition of the Sibinadox during drying and film formation.

The lower limit of the thickness of the antiglare layer is preferably 0.1 μm, more preferably 0.5 μm. The upper limit of the thickness of the antiglare layer is preferably 100. Mu.m, more preferably 50. Mu.m, still more preferably 20. Mu.m.

The refractive index of the antiglare layer is preferably 1.2 to 1.8, more preferably 1.4 to 1.7.

The refractive index of the antiglare layer was measured under the condition of a wavelength of 589 nm.

The antiglare low reflection layer may be formed by providing a low refractive index layer with irregularities, or the antiglare antireflection layer may be formed by providing a hard coat layer or a high refractive index layer with irregularities on the surface thereof and providing an antireflection function with the low refractive index layer thereon.

(hard coat)

The lower layer of the reflection reducing layer is preferably provided with a hard coat layer.

The hard coat layer is preferably H or more, more preferably 2H or more, in terms of pencil hardness. The hard coat layer may be provided by, for example, coating a composition (solution) containing a thermosetting resin or a radiation curable resin and curing it.

Examples of the thermosetting resin include an acrylic resin, a urethane resin, a phenol resin, a urea melamine resin, an epoxy resin, an unsaturated polyester resin, a silicone resin, and a combination thereof. To these curable resins, a curing agent is added as needed in the thermosetting resin composition.

The radiation curable resin is preferably a compound having a radiation curable functional group (radiation curable compound), and examples of the radiation curable functional group include an ethylenically unsaturated bond group such as a (meth) acryloyl group, a vinyl group, an allyl group, an epoxy group, and an oxetanyl group. Among them, the ionizing radiation-curable compound is preferably a compound having an ethylenically unsaturated bond group, more preferably a compound having 2 or more ethylenically unsaturated bond groups, and among them, a polyfunctional (meth) acrylate compound having 2 or more ethylenically unsaturated bond groups is further preferred. The polyfunctional (meth) acrylate compound may be a monomer, an oligomer, or a polymer.

As specific examples thereof, those listed as the binder resin can be used.

In order to achieve the hardness as a hard coat, the difunctional or higher monomer is preferably 50 mass% or higher, more preferably 70 mass% or higher, in the compound having a radiation curable functional group. Further, in the compound having a radiation curable functional group, the trifunctional or higher monomer is preferably 50% by mass or more, more preferably 70% by mass or more.

The compound having a radiation curable functional group may be used singly or in combination of 1 or more than 2.

The thickness of the hard coat layer is preferably in the range of 0.1 to 100. Mu.m, more preferably in the range of 0.8 to 20. Mu.m.

The refractive index of the hard coat layer is more preferably 1.45 to 1.7, and still more preferably 1.5 to 1.6.

The refractive index of the hard coat layer was measured under the condition of a wavelength of 589 nm.

Examples of the method for adjusting the refractive index of the hard coat layer include a method for adjusting the refractive index of the resin and a method for adjusting the refractive index of the particles when the particles are added.

Examples of the particles include particles exemplified as particles of the antiglare layer.

In the present invention, the hard coat layer may be referred to as a reflection reducing layer.

In the case of providing the functional layer, an easy-to-adhere layer may be provided between the functional layer and the base film. The easy-to-adhere layer may be suitably used with a resin, a crosslinking agent, or the like listed in the above-mentioned easy-to-adhere layer. In this case, the adhesive layers may have the same composition or may have different compositions.

(polarizing plate)

The polyester film of the present invention can be suitably used as a polarizer protective film. The polyester film of the present invention may be laminated with a polarizing material to produce a polarizing plate.

(polarizing element)

As the polarizing material, for example, a polarizing material obtained by adsorbing iodine or an organic dichroic dye with uniaxially stretched polyvinyl alcohol (PVA), a liquid crystal polarizing material containing a liquid crystal compound and a substance obtained by aligning an organic dichroic dye or a liquid crystal dichroic dye, a wire grid type polarizing material, or the like can be used without particular limitation.

A film-like polarizing material obtained by adsorbing iodine or an organic dichroic dye with uniaxially stretched polyvinyl alcohol (PVA) may be bonded to a polarizing material protective film wound in a roll form using an adhesive or an adhesive such as PVA or ultraviolet curing, and wound in a roll form. The thickness of the polarizing plate of this type is preferably 5 to 30. Mu.m, more preferably 8 to 25m, and particularly preferably 10 to 20m. The thickness of the adhesive or binder is preferably 1 to 10. Mu.m, more preferably 2 to 5. Mu.m.

In addition, a polarizing material in which PVA is coated on an unstretched substrate such as PET or polypropylene, and uniaxially stretched together with the substrate to adsorb iodine or an organic dichroic dye is also preferably used. In the case of using this polarizer, the polarizer surface (surface on which the base material is not laminated) of the polarizer laminated on the base material is bonded to the polarizer protective film by an adhesive or an adhesive, and thereafter, the base material used for producing the polarizer is peeled off, whereby the polarizer protective film and the polarizer can be bonded. In this case, it is also preferable to attach the sheet in a roll shape and to wind the sheet. The thickness of the polarizing plate of this type is preferably 1 to 10. Mu.m, more preferably 2 to 8. Mu.m, particularly preferably 3 to 6. Mu.m. The thickness of the adhesive or binder is preferably 1 to 10. Mu.m, more preferably 2 to 5. Mu.m.

In the case of a liquid crystal polarizer, a polarizing plate can be produced by laminating a material obtained by aligning a polarizer containing a liquid crystal compound and an organic dichroic dye on a polarizer protective film, or by applying a coating liquid containing a liquid crystal dichroic dye on a polarizer protective film, and then drying the coating liquid, and photo-curing or thermally curing the coating liquid, and laminating a polarizer. As a method for aligning the liquid crystal polarizer, there is mentioned: a method of brushing the surface of the object to be coated, a method of irradiating polarized ultraviolet rays, and curing a liquid crystal polarizer while aligning it, and the like. The surface of the polarizing element protective film may be directly subjected to brushing treatment and coated with the coating liquid, or the polarizing element protective film may be directly coated with the coating liquid and irradiated with polarized ultraviolet rays. In addition, it is also preferable to provide an alignment layer to the polarizer protective film before providing the liquid crystalline polarizer (i.e., to layer the liquid crystalline polarizer on the polarizer protective film with an alignment layer interposed therebetween). As a method for providing the alignment layer, there can be mentioned:

A method of applying polyvinyl alcohol and its derivatives, polyimide and its derivatives, acrylic resin, polysiloxane derivatives, and the like, and subjecting the surface thereof to a brushing treatment to form an alignment layer (brushing alignment layer);

and a method in which a coating liquid containing a solvent and a polymer or monomer having a photoreactive group such as a cinnamoyl group or a chalcone group is applied, and polarized ultraviolet light is irradiated to be oriented and cured to form an orientation layer (photoalignment layer).

In the above method, the liquid crystal polarizing material is provided on the film having releasability, and the liquid crystal polarizing material surface and the polarizing material film are bonded with an adhesive or an adhesive, and then the film having releasability is peeled off, whereby the polarizing material film and the polarizing material can be bonded.

The thickness of the liquid crystal polarizer is preferably 0.1 to 7. Mu.m, more preferably 0.3 to 5. Mu.m, particularly preferably 0.5 to 3. Mu.m. The thickness of the adhesive or binder is preferably 1 to 10. Mu.m, more preferably 2 to 5. Mu.m.

(lamination of polarizer and polarizer protective film)

The polyester film of the present invention is preferably laminated on the surface of the polarizer opposite to the image display unit side. When a polarizing plate is produced by laminating a polarizing element and a film, the angle between the absorption axis of the polarizing element and the slow axis of the film is preferably about 90 degrees or about 0 degrees. In the present specification, "about" means an error of 7 degrees or less. The error is preferably 5 degrees or less, more preferably 3 degrees or less, particularly preferably 2 degrees or less, and most preferably 1.5 degrees or less. The angle is preferably set in the entire range of the polarizing plate.

In the case where the polarizer is a liquid crystal polarizer or a wire grid type polarizer, the absorption axis of the polarizer is easily inclined with respect to the slow axis of the polyester film, and the angle between the slow axis and the absorption axis may be 30 to 60 degrees, preferably about 45 degrees.

(surface of polarizing element on image display Unit side)

In the case where the polarizing plate is used in a liquid crystal display device, the surface of the polarizing material on the liquid crystal cell side may be in a state where no material is laminated, or may be an adhesive, or may be provided with a cured layer on the polarizing material, or may be provided with a polarizing material protective film different from the polarizing material protective film. The hard coat layer is preferably a cured layer. In the case of the adhesive, a release film may be further laminated. In addition, in the case of an unstacked state, a case of a cured layer, a case of a polarizer protective film, or the like, a releasable protective film may be separately laminated.

Examples of the polarizer protective film on the liquid crystal cell side of the polarizer include a cellulose (TAC) film, an acrylic film, and a polycycloolefin (COP) film. The retardation of the polarizer protective film on the liquid crystal cell side may be substantially zero, or may be a retardation film called an optical compensation film for controlling a change in color tone when the display screen is observed from an oblique direction.

In order to exhibit a desired phase difference using the optical compensation film, there are: stretching the film; or coating a phase difference layer such as a liquid crystal compound on the film; and a method in which a phase difference layer such as a liquid crystal compound is provided on the release film and the phase difference layer is transferred. The liquid crystal compound used for forming the retardation layer is a rod-like liquid crystal compound, a discotic liquid crystal compound, or the like, depending on the desired retardation characteristics. In order to fix the alignment state, the liquid crystal compound preferably has a photocurable reactive group such as a double bond. In order to align the liquid crystal compound to have a retardation, for example, an alignment layer is provided as a lower layer of the retardation layer, and the alignment layer is subjected to a brushing treatment, or polarized ultraviolet rays are irradiated, whereby alignment controllability such that the liquid crystal compound applied thereon is aligned in a specific direction can be imparted.

The retardation of the optical compensation film can be appropriately set by the type of liquid crystal cell used, the degree of viewing angle to be ensured, and the like.

The retardation layer can be provided by applying a composition coating for the retardation layer. The composition coating for the retardation layer may contain a solvent, a polymerization initiator, a sensitizer, a polymerization inhibitor, a leveling agent, a polymerizable non-liquid crystal compound, a crosslinking agent, a combination thereof, and the like. They can use the objects described in the portions of the orientation control layer and the liquid crystal polarizer.

The retardation layer is provided by applying the composition coating for a retardation layer to the release surface or the orientation control layer of the release film, and then drying, heating and curing the composition coating.

As for the conditions, those described in the portions of the alignment control layer and the liquid crystalline polarizer are also used as preferable conditions.

When the polarizer is adhered to the polarizer protective film and the retardation film, an adhesive or an adhesive is used. The adhesive is preferably an aqueous adhesive such as polyvinyl alcohol or a photocurable adhesive. Examples of the photocurable adhesive include acrylic adhesives and epoxy adhesives. The adhesive is preferably an acrylic adhesive.

(liquid Crystal cell)

The liquid crystal cell is obtained by sealing a liquid crystal compound between thin substrates such as glass on which a circuit is formed. When the substrate is glass, the thickness is preferably 1mm or less, more preferably 0.7mm or less, further preferably 0.5mm or less, particularly preferably 0.4mm or less, from the viewpoint of thickness reduction.

The liquid crystal cell is not particularly limited, and VA and IPS modes are modes in which color shift is small when viewed from an oblique direction, and among these modes, the absorption axis of the polarizing plate is parallel or orthogonal to the longitudinal direction of the liquid crystal cell, and thus are preferable modes for application of the present invention.

As the color filter incorporated in the liquid crystal cell, the maximum transmittance and the minimum transmittance of the blue pixel in the wavelength range of 420nm to 460nm are each preferably 80% or more, and more preferably 85% or more. The difference between the maximum transmittance and the minimum transmittance at wavelengths of 420nm to 460nm is preferably 4% or less, more preferably 3% or less.

(liquid Crystal Panel)

Preferably, a polarizing plate is attached to each of the viewing side and the light source side of the liquid crystal cell to form a liquid crystal display panel. The attachment is preferably by means of an adhesive. The adhesive is preferably an acrylic adhesive.

In the liquid crystal panel, the polarizing plate obtained using the polyester film may be either one of a light source-side polarizing plate and a visible-side polarizing plate, and may be two kinds of polarizing plates.

In the case where the image display device is an organic or inorganic electroluminescent unit, a micro LED, or the like, the polarizing plate is preferably a circular polarizing plate. Typically, a circular polarizer is laminated with a 1/4 wavelength layer on the viewing side of the polarizer. The 1/4 wavelength layer includes not only an object having only 1/4 wavelength layer but also an object obtained by combining 1/4 wavelength layer and 1/2 wavelength layer and applying a phase difference layer such as a C plate to them. The phase difference layers such as the 1/4 wavelength layer, the 1/2 wavelength layer and the C plate can be films or coatings. The retardation layer may be an object described in the retardation layer of the polarizing plate if the retardation and the orientation direction of the retardation layer are appropriate.

(transparent electrode substrate film)

The polyester film of the present invention can be suitably used as a transparent electrode base film for a touch panel or the like. The transparent conductive layer may be provided on at least one side of the polyester film, or may be provided on both sides.

Examples of the transparent conductive layer include a mesh print of a conductive paste, a coating layer containing carbon nanotubes, a self-assembled nano silver coating layer, a coating layer containing needle-like conductive filler, and a metal oxide film. Among them, a metal oxide film is preferable, and preferable examples thereof include films of indium oxide, zinc oxide, tin oxide, indium Tin Oxide (ITO), tin antimony oxide, zinc aluminum oxide, indium zinc oxide, and the like.

The transparent conductive layer is preferably formed in a pattern shape such as a line shape or a lattice shape by etching.

The thickness of the transparent conductive layer is preferably 5 to 500nm, more preferably 15 to 250nm, and still more preferably 20 to 100nm. By the above thickness, the conductivity can be ensured and coloring by the conductive layer can be suppressed.

The transparent conductive layer can be formed by a known method such as a vacuum deposition method, a sputtering method, a CVD method, an ion plating method, a spray method, or a sol-gel method.

The transparent conductive layer may be patterned by forming a resist mask having a predetermined pattern by photolithography after forming a film, and then performing etching treatment.

The transparent conductive layer may be amorphous, and preferably, the amorphous transparent conductive layer is heat-treated at 130 to 180 ℃ for 0.5 to 2 hours to grow crystals, thereby producing a crystalline transparent conductive layer and improving conductivity.

The lower layer of the transparent conductive layer is also preferably provided with a hard coat layer or a refractive index adjusting layer. The refractive index adjustment layer may be a layer having a refractive index close to that of the transparent conductive layer (high refractive index layer), or a high refractive index layer and a low refractive index layer may be provided in this order. It is particularly preferable to provide a high refractive index layer and a low refractive index layer in this order.

The polyester film of the present invention is preferably used as a fly-away preventing film. When a glass plate is used as a base material of a touch panel or the like, a screen display cover layer, or the like, the scattering preventing film is adhered to the glass plate for use, and when the glass plate is broken, fragments can be prevented from damaging the internal structure or scattering or exposing to the outside. The anti-scatter film may be laminated on either one of the visible side and the reverse visible side of the glass plate. When laminated on a glass plate, it is preferable to adhere the glass plate using an optical base-free adhesive called OCA.

The polyester film of the present invention is preferably used as a picture surface protective film. The screen surface protective film is laminated on the visual side of the screen of the image display device, and can protect the internal image display unit from external impact or prevent surface damage. The screen surface protective film is preferably attached to the image display unit using an adhesive. The screen surface protective film is also preferably a type which is positioned on the outermost surface of the image display section and can be peeled off and replaced when damaged. In this case, the adhesive is preferably an adhesive force to such an extent that it can be peeled off by hand.

The polyester film of the present invention is also preferably used for a flexible image display device, and can be used in the form of a polarizer protective film, a back cover film, a transparent electrode base film, a screen surface protective film, and the like of a flexible image display device. Among them, the film is preferably used as a back cover film or a screen surface protective film.

The flexible image display device may be configured such that the image display unit is folded in a V-shape, a left-right side-by-side shape, a W-shape, or the like, or may be wound in a roll shape.

In the case of being used for a flexible image display device, it is preferable that the polyester film is arranged such that the slow axis of the polyester film is orthogonal to the folding direction, in other words, such that the fold line becomes the slow axis.

When the film is used as a transparent electrode base film, a scattering preventing film, a screen surface protecting film, or the like on the visible side of a polarizing plate of an image display device, it is preferable that the film be arranged such that the slow axis of the polyester film is 30 to 60 degrees, preferably about 45 degrees, with respect to the absorption axis of the polarizing plate, and that no shadow or rainbow-mark be generated when observed by sunglasses.

Examples

The present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples described below, and may be implemented with appropriate modifications within the scope of the gist of the present invention, and all of them fall within the technical scope of the present invention. The evaluation methods of physical properties and the like in the following examples are as follows.

(1) Refractive index of polyester film

The slow axis direction of the film was determined by using a molecular orientation meter (model MOA-6004 molecular orientation meter, manufactured by prince measuring instruments Co., ltd.) and a rectangle of 4cm X2 cm was cut so that the slow axis direction was parallel to the long side, and the film was used as a sample for measurement. For this sample, the refractive index of the perpendicular biaxial (refractive index in the slow axis direction: ny, fast axis (refractive index in the direction perpendicular to the slow axis direction): nx) and refractive index in the thickness direction (nz) were obtained by using an Abbe refractometer (manufactured by ATAGO Co., NAR-4T, measurement wavelength 589 nm).

(2) In-plane retardation (Re)

The in-plane retardation is a parameter defined by the product (Δnxy×d) of the refractive index anisotropy (Δnxy= |nx-ny|) of orthogonal biaxial on the film and the film thickness d (nm), and is a scale representing optical isotropy and anisotropy. By the method of the above (1), the absolute value of the refractive index difference of the biaxial (nx-ny|) is calculated as the anisotropy of the refractive index of the biaxial (Δnxy). The in-plane retardation (Re) was obtained by multiplying the anisotropy of refractive index (ΔNxy) by the thickness d (nm) of the thin film (ΔNxy×d).

(3) Thickness direction retardation (Rth)

The thickness direction retardation is a parameter indicating a retardation average value obtained by multiplying two birefringence Δ Nxz (= |nx-nz|) and Δ Nyz (= |ny-nz|) by the film thickness d, respectively, when viewed from a cross section in the film thickness direction. Nx, ny, and nz were obtained by the method of (1) above, and the average value of (Δ Nxz ×d) and (Δ Nyz ×d) was calculated to obtain the thickness-direction retardation (Rth).

(4) Degree of plane orientation

The degree of orientation of the surface was obtained by substituting nx, ny and nz into the formula represented by |nx+ny|/2-nz.

(5) NZ coefficient

The NZ coefficients were obtained by substituting nx, ny and NZ into the formula of |ny-nz|/|ny-nx|.

(6) Absorption axis of polarizer

A polarizing filter having a known absorption axis was placed on a surface light source while being superposed on a polarizing material, and a direction in which the direction of the absorption axis of the polarizing filter in the darkest state by rotating the polarizing filter was 90 degrees was set as the absorption axis direction of the polarizing material. In the case of a long polarizing material in which PVA is stretched in the longitudinal direction, the longitudinal direction is the absorption axis direction, and therefore, the longitudinal direction may be the absorption axis direction.

(7) Slow axis direction of film

The measurement was performed by a molecular orientation meter (model MOA-6004 molecular orientation meter, manufactured by prince measuring instruments Co.).

(8) Transmittance at 380nm wavelength

The light transmittance at 380nm was determined by measuring the light transmittance in the wavelength range of 300 to 500nm using a spectrophotometer (model U-3500 manufactured by Hitachi Ltd.) with the air layer as a standard.

(9) Intrinsic viscosity

Sample 0.2g was dissolved in 50ml of a mixed solvent of phenol/1, 2-tetrachloroethane (60/40 (weight ratio)), and measured at 30℃using an Ostwald viscometer.

(10) Film thickness and frequency characteristics after Fourier transform

Using a contact continuous thickness meter (manufactured by the electric company of An Li as a thickness meter part) by MIKURON meter co., a sample having a width of about 50mm in the MD and a length of about 6m was cut out from the center portion in the width direction of the obtained film, and the thickness was measured at a speed of 1.5 m/min in the MD, and data were continuously read at 0.1 second intervals.

2048 points (the amount of 5.12m in length) were arbitrarily selected continuously from the obtained data, and the average value of the thicknesses thereof was taken as the film thickness. In the measurement data, the value obtained by (maximum thickness-minimum thickness)/average thickness×100 was used as the MD-direction thickness unevenness (%).

Further, based on the selected 2048 points data, a frequency analysis was performed by a fast fourier transform using EXCEL (registered trademark) which is a form calculation software of microsoft corporation. Further, the frequency of the obtained analysis data is converted into a length period, and the respective amplitudes are obtained.

5 points are selected from the values with large amplitude among the values with a length period of 10cm or more, the average value of the values is A, and the maximum value of the amplitude among the 5 points is Amax. Further, 5 points were selected from among the values with a length period of less than 10cm and with a large amplitude, and the average value was defined as B. The length period ignores the data of the latter half of the frequency analysis data of the phantom, and uses only the analysis data of the former half.

A/B and Amax/B were obtained from the obtained values of A, amax and B. The TD-direction thickness unevenness was obtained as follows: the center portion of the film after film formation was cut to a width of 1000mm, and a sample having a width of 1000mm×50mm in the TD direction was obtained by measuring the film with a continuous thickness meter in the same manner, and the film was obtained as (maximum thickness-minimum thickness)/average thickness×100 from the obtained data.

The length period of 10cm or more corresponds to a frequency of 0.25Hz or less.

(11) Breaking strength and elongation at break

Based on JIS K7113. A sample having a width of 10mm and a length of 100mm in the longitudinal direction and the width direction of the film was cut out using a razor as a sample. After the sample was left to stand at 23℃under an atmosphere of 65% RH for 12 hours, the measurement was performed at 23℃under an atmosphere of 65% RH, with a distance between chucks of 100mm and a stretching speed of 200 mm/min, and an average value of the results of 5 times was used. As a measurement device, autograph AG5000A manufactured by shimadzu corporation was used.

(12) Film temperature

The measurement was performed by inserting a detection unit from the side of the film forming machine using a radiation thermometer (IR-BZPHGN 1 manufactured by CHINO corporation). The measured data were smoothed for 10 seconds.

(13) Productivity of

The evaluation was performed based on the number of breaks when the central portion of the obtained film was cut to a width of 1000 mm. The cutting blade for cutting was used for cutting a conventional film corresponding to the comparative example, and the sample removed in excess of the predetermined amount was again grasped at a speed of 90% of the maximum design speed of the slitter.

O: the number of breaks for 1 day was 0.

Delta: the number of breaks for 1 day was 1.

X: the number of breaks per 1 day is 2 or more.

(14) Planarity of

Ion exchange water was dropped onto a flat glass plate, and a sample obtained by cutting a 1000mm wide film into 2000mm long pieces was placed thereon, and the film was stuck by a roller so that the water layer became uniform. The fluorescent lamp was observed to be projected from an oblique direction to the ceiling of the film, and the flatness was evaluated.

O: the reflected fluorescent lamp has less bending and good flatness.

Delta: the reflected fluorescent lamp is bent but acceptable.

X: the reflected fluorescent lamp has large bending and poor flatness.

Polyester A (PET (A))

Polyethylene terephthalate with an intrinsic viscosity of 0.62dl/g

Polyester B (PET (B))

10 parts by mass of an ultraviolet absorber (2, 2' - (1, 4-phenylene) bis (4H-3, 1-benzoxazin-4-one) and 90 parts by mass of PET (A).

(preparation of adhesive modified coating liquid)

The ester interchange reaction and the polycondensation reaction were carried out by a conventional method to prepare a water-dispersible copolymerized polyester resin containing a sulfonic acid metal salt, which had a composition of 46 mol% of terephthalic acid, 46 mol% of isophthalic acid and 8 mol% of 5-sodium sulfonate of isophthalic acid as dicarboxylic acid components (relative to the entire dicarboxylic acid components), and 50 mol% of ethylene glycol and 50 mol% of neopentyl glycol as diol components. Then, after mixing 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve and 0.06 parts by mass of a nonionic surfactant, the mixture was heated and stirred, 5 parts by mass of the water-dispersible and metal sulfonate-containing copolyester resin was added after the temperature reached 77 ℃, and after continuing stirring until solidification of the resin did not disappear, the aqueous resin dispersion was cooled to room temperature, to obtain a uniform water-dispersible copolyester resin liquid having a solid content of 5.0% by mass. Further, 3 parts by mass of aggregate silica particles (SYLYSIA 310, manufactured by Fuji-Silysia Co.) were dispersed in 50 parts by mass of water, and then 0.54 part by mass of an aqueous dispersion of SYLYSIA 310 was added to 99.46 parts by mass of the water-dispersible copolyester resin liquid, followed by stirring and adding 20 parts by mass of water, to obtain an adhesive modified coating liquid.

(polarizing element)

A rolled polyvinyl alcohol film of 80 μm thickness, which was continuously dyed in an aqueous iodine solution, was stretched 5 times in the transport direction, treated in a boric acid solution, washed with water, and dried to obtain a long polarizing element.

(polyester films A to H)

As a raw material for the intermediate layer of the base film, 10 parts by mass of PET (B) resin pellets containing 90 parts by mass of PET (a) resin pellets and an ultraviolet absorber, which were free of particles, were dried under reduced pressure (1 Torr) at 135 ℃ for 6 hours, and then fed into an extruder 2 (for the intermediate layer II layer), and PET (a) was dried by a conventional method, fed into an extruder 1 (for the outer layer I layer and the outer layer III layer), respectively, and dissolved at 285 ℃. The two polymers were each filtered through a stainless steel sintered filter medium (to remove particles having a 95% nominal filtration accuracy of 10 μm), laminated with 2 kinds of 3-layer joint blocks, formed into a sheet from a tube head, extruded, and wound around a casting drum having a surface temperature of 30℃by an electrostatic casting method, and cooled and solidified to prepare an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the layer I, the layer II, and the layer III became 10:80:10.

The unstretched PET film was introduced into an MD stretcher consisting of a low-speed roll and a high-speed roll. The film is heated to a preheating temperature by a plurality of low-speed rolls, and further, is heated to a stretching temperature by an infrared heater located between the low-speed rolls and the high-speed rolls, and is stretched by a difference in peripheral speed between the low-speed rolls and the high-speed rolls.

The preheating temperature, stretching temperature and stretching ratio are shown in table 1. The number of the turned-on lamps of the infrared heater is the number of the rows of the infrared heater which are set in the MD direction and are turned on by the heating.

The rolls of the MD stretcher were each formed by plating chromium on the surface of 180 to 250mm in diameter, and had a roundness of 10 μm or less and a deflection of 20 μm or less.

Next, the coating amount after drying was 0.08g/m on both sides of the MD-stretched film ² The above-mentioned adhesion-modifying coating liquid is applied and dried. The resulting film having the coating layer formed thereon was introduced into a tenter stretcher, and stretched in the width direction while holding the end of the film with a jig, and introduced into the tenter at 100 ℃. Then, the stretched PET film was obtained by maintaining the width in the width direction, performing a treatment at 200 ℃ for 10 seconds in the heat-setting region, and further performing a relaxation treatment of 2% in the width direction.

(films I and J)

The above-mentioned unstretched PET film was introduced into an MD stretching machine, heated by a plurality of rolls, and heated to a preheating temperature by a 2 nd roll from a final roll of a low-speed roll, and heated to a stretching temperature by a final low-speed roll. The film is stretched by a peripheral speed difference from the high speed roll. The final low-speed roller and the roll provided on the final low-speed roller are rollers having a surface subjected to a fluororesin process. Thereafter, TD stretching and heat setting were performed in the same manner as described above to obtain a stretched PET film.

The film forming conditions and the characteristic values such as thickness unevenness of these films are shown in table 1. The transmittance at 380nm was in the range of 2.3 to 2.5% except that the film H was 8.5%.

As an example of a graph of the frequency analysis results of the thickness unevenness, the results of the film a are shown in fig. 1, and the results of the film D are shown in fig. 2.

TABLE 1

From table 1 it can be seen that: film a may have a low MD stretching temperature and a large thickness unevenness, but by increasing the MD stretching temperature as in film B and film C, the thickness unevenness in the MD direction is reduced, and the value of a/B and the like is also reduced. This is also known from the fact that when the frequency of film A is 0.25Hz or less (cycle is 10cm or more) and the amplitude of film A is larger than the amplitude of frequency exceeding 0.25Hz (cycle is less than 10 cm) in comparison with the frequency of film D in FIG. 1 (film A).

On the other hand, when the MD stretching temperature is too high as in the film E, the stretching position may be relaxed and irregular, and the thickness in the MD direction may become large. In addition, the preheating temperature of the film F is high, and in some cases, the film is loosened during the preheating step, and the film is stuck to the roller, and the thickness unevenness in the MD direction becomes large.

As in the films G and H, even if the MD stretching ratio is increased, the thickness unevenness in the MD direction can be suppressed as long as the preheating temperature and the stretching temperature are appropriate. In the stretching by the roller heating, too, when the preheating temperature is too high and the stretching temperature is too low, as in the film I, the thickness unevenness is large, but by optimizing the temperature, the thickness unevenness can be reduced.

Films B to D, E to G and J can be suitably used for, for example, a polarizing element protective film. The film H can be suitably used as, for example, a transparent electrode base film, a scattering preventing film, and a screen surface protecting film of a flexible image display device.

(production of polarizing plate)

Among the polyester films produced in the examples, films C, D and J having particularly good thickness unevenness were used to produce polarizing plates as follows.

The polyester film produced as described above was adhered to one side of the polarizing material by roll-to-roll, and a cellulose triacetate film (thickness: 40 μm) was adhered to the opposite side, to thereby produce a polarizing plate. An ultraviolet-curable adhesive was used for the adhesion. The slow axis of the polyester film and the absorption axis of the polarizer are both 90 degrees, and the offset is less than 0.5 degrees.

(evaluation of image display device)

The obtained polarizing plate was cut and replaced with a commercially available 42-type liquid crystal television visible side polarizing plate. Any polarizing plate has no rainbow unevenness even when viewed from an oblique direction, and has good visibility.

Industrial applicability

The present invention provides a polyester film having high in-plane retardation, excellent thickness uniformity, and good productivity, workability, and planarity. The polyester film is not easy to be obvious in rainbow spots regardless of the type of the image display device and the type of the light source, has good visibility, and can be suitable for various purposes of the image display device.

Claims (15)

1. A polyester film having an in-plane retardation of 3000nm to 30000nm,

the degree of plane orientation is 0.128 or more and 0.155 or less,

the thickness unevenness in the film-forming flow direction was 8% or less,

the thickness unevenness is a value obtained by (maximum thickness-minimum thickness)/average thickness×100 (%).

2. The polyester film according to claim 1, wherein the ratio A/B of A to B is 5 or less when Fourier transform is performed on the thickness measurement data in the film-forming flow direction and the frequency is replaced with the length period of the film,

a: the period is more than 10cm, and the average value of the amplitude of the maximum first 5 values of the amplitude values;

b: the period is 10cm or less, and the average value of the amplitude of the maximum first 5 values of the amplitude values is the average value.

3. The polyester film according to claim 1 or 2, wherein when the film-forming flow direction thickness measurement data is subjected to Fourier transform and the frequency is replaced with the film length period, the ratio Amax/B of Amax to B is 7 or less,

amax: the period is more than 10cm, and the amplitude is the maximum value.

4. The polyester film according to any one of claims 1 to 3, having an NZ coefficient of 1.65 or more and 3 or less.

5. The polyester film according to any one of claims 1 to 4, which has a thickness of 25 μm or more and 150 μm or less.

6. The polyester film according to any one of claims 1 to 5, wherein the elongation at break in the film-forming flow direction is 4% or more.

7. The polyester film according to any one of claims 1 to 6, which has a breaking strength of 50MPa or more in the film-forming flow direction.

8. A polarizing element protective film formed from the polyester film according to any one of claims 1 to 7.

9. A polarizing plate comprising the polarizing material protective film according to claim 8 and a polarizing material.

10. An image display device in which the polarizing plate of claim 9 is provided on a visible side of an image display unit.

11. A transparent electrode substrate film formed from the polyester film according to any one of claims 1 to 7.

12. A fly-away prevention film formed of the polyester film according to any one of claims 1 to 7.

13. A picture surface protective film formed from the polyester film according to any one of claims 1 to 7.

14. An image display device comprising any one of the transparent electrode base film according to claim 11, the anti-scattering film according to claim 12, and the screen surface protective film according to claim 13.

15. The image display device of claim 14, being a flexible image display device.