WO2022202608A1

WO2022202608A1 - Polyester film and image display device using same

Info

Publication number: WO2022202608A1
Application number: PCT/JP2022/012283
Authority: WO
Inventors: 博史柴野; 潤稲垣; 正太郎西尾; 究河合; 靖佐々木
Original assignee: 東洋紡株式会社
Priority date: 2021-03-24
Filing date: 2022-03-17
Publication date: 2022-09-29
Also published as: KR20230161475A; CN117120242A; JPWO2022202608A1; TW202243861A

Abstract

The present invention provides a polyester film that has excellent uniformity in thickness while ensuring high in-plane retardation and that also provides excellent productivity, workability, and flatness.　Disclosed is a polyester film having an in-plane retardation of 3,000-30,000 nm, a plane orientation degree of 0.128-0.155, and a thickness irregularity of 8% or less (here, the thickness irregularity is a value determined by: (maximum thickness-minimum thickness)/average thickness×100(%)) in a film-forming flow direction.

Description

POLYESTER FILM AND IMAGE DISPLAY DEVICE USING THE SAME

The present invention relates to a polyester film (for example, an optical polyester film). The present invention is typically suitably used for each member of an image display device, such as a polarizer protective film, a base film for a touch panel (e.g., a transparent electrode base film), a scattering prevention film, a screen surface protection film, and the like. It relates to polyester film.

Polyester films are excellent in transparency, mechanical strength, and stability against chemicals, and are used as optical films. These optical polyester films are usually biaxially stretched films and have birefringence. Therefore, it is known that rainbow-like color unevenness (rainbow spots) occurs when used in a portion through which polarized light passes. ing.
On the other hand, by providing a high-retardation polyester film on the surface of a liquid crystal display device, there is a technology that eliminates blackouts and iridescence when viewing images with polarized sunglasses (for example, Patent Document 1), and a polarizer protective film. A technique for eliminating iridescence by using it as a base material (for example, Patent Document 2) and a technique for using it in combination as a touch panel substrate or a scattering prevention film (for example, Patent Document 3) are known.
If the film is stretched in only one direction to obtain a high retardation film, the strength and elongation in the direction perpendicular to the stretched direction will be low, so breakage is likely to occur during film formation and processing of the resulting film. , productivity and workability may decrease. In addition, by first stretching in the direction orthogonal to the main stretching direction at a low magnification and then stretching in the main stretching direction, the strength and elongation in the direction orthogonal to the main stretching direction are increased, and the production speed is increased. Although the required retardation can be ensured, if the film is also stretched in the direction perpendicular to the main stretching direction, unevenness in thickness may occur and flatness may be deteriorated.
Stretched in the longitudinal direction (MD) at 2.0 times or less, preferably at 1.3 times or less, and then stretched in the width direction (TD) at 4.15 times or more to increase the tensile strength in the longitudinal direction. The tensile strength ratio of 0.25 to 0.6 is known to improve the tensile strength and elastic modulus in the MD direction (eg, Patent Document 4). However, this technique still suffers from poor thickness uniformity and flatness.
Furthermore, after stretching 1.0 to 3.4 times in the longitudinal direction (MD), the film stretched 2.5 to 5.0 times in the width direction (TD) is folded with the MD direction as the folding direction. It has been proposed to use it as a film for display devices (for example, Patent Documents 5 and 6). However, even with this technique, there is still room for improvement in the uniformity of thickness and flatness.
If the thickness unevenness in the MD direction is large, it is likely to break not only during film formation but also during slitting, especially when the cutting blade is worn or at high speed, and productivity and workability are poor. tend to become

WO2011/058774 WO2011/162198 WO2014/123209 WO2017/091031 WO2018/159285 WO2020/162119

One object of the present invention is to provide a polyester film that has high in-plane retardation, excellent thickness uniformity, and good productivity, workability, and flatness. A further object of the present invention is to provide a polyester film that, when used as a film for each application of an image display device, has good visibility in which rainbow spots are less noticeable regardless of the type of image display device or the type of light source. is to provide

The present inventor has completed the present invention as a result of intensive studies to achieve this object.
The present invention includes the following aspects.
Item 1:
In-plane retardation is 3000 nm or more and 30000 nm or less,
The degree of plane orientation is 0.128 or more and 0.155 or less,
Thickness unevenness in the film production flow direction is 8% or less,
A polyester film (the thickness unevenness is a value obtained by (maximum thickness - minimum thickness) / average thickness x 100 (%)).

Item 2:
Item 1. The polyester according to item 1, wherein A/B, which is the ratio of A and B below, is 5 or less when Fourier transform is performed on the thickness measurement data in the film production flow direction and the frequency is replaced with the period of the length of the film. the film.
A: Average value of the top 5 amplitude values with a period of 10 cm or more B: Average value of the top 5 amplitude values with a period of 10 cm or less

Item 3:
3. Item 1 or 2, wherein Amax/B, which is the ratio of Amax and B below, is 7 or less when the thickness measurement data in the film production flow direction is Fourier transformed and the frequency is replaced by the period of the length of the film. polyester film.
Amax: The maximum value of amplitude at a period of 10 cm or more

Item 4:
Item 4. The polyester film according to any one of Items 1 to 3, which has a NZ coefficient of 1.65 or more and 3 or less.

Item 5:
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:
Item 6. The polyester film according to any one of items 1 to 5, which has a breaking elongation of 4% or more in the direction of film production.

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

Item 8:
A polarizer protective film comprising the polyester film according to any one of Items 1 to 7.

Item 9:
A polarizing plate in which the polarizer protective film according to Item 8 and a polarizer are laminated.

Item 10:
Item 10. An image display device in which the polarizing plate according to Item 9 is installed on the viewing side of an image display cell.

Item 11:
A transparent electrode substrate film comprising the polyester film according to any one of items 1 to 7.

Item 12:
Item 8. A shatterproof film comprising the polyester film according to any one of items 1 to 7.

Item 13:
A screen surface protection 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 of Item 11, the anti-scattering film of Item 12, and the screen surface protective film of Item 13.

Item 15:
Item 15. The image display device according to Item 14, which is a flexible image display device.

According to the present invention, a polyester film having high in-plane retardation and excellent thickness uniformity, productivity, workability, and flatness can be obtained. Furthermore, since the polyester film of the present invention can suppress iridescence, it is suitably used for a polarizer protective film, a transparent electrode base film for touch panels, a scattering prevention film, a screen surface protective film for an image display device, and the like. It has excellent bending durability when used in a flexible image display device.

4 is a graph showing the results of frequency analysis of thickness unevenness in the film production flow direction for Film A. FIG. 10 is a graph showing the results of frequency analysis of thickness unevenness in the direction of flow of film production for Film D. FIG.

Preferable examples of the polyester film of the present invention include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polytetramethylene terephthalate (PBT), which can increase in-plane retardation and has low moisture permeability and moisture absorption. ), and polyethylene naphthalate (PEN), among which PET or PEN is preferred. These polyesters may be copolymerized with a carboxylic acid component and/or a glycol component other than the main constituent component. is preferably 10 mol % or less, more preferably 5 mol % or less, and particularly preferably 2 mol % or less.

The intrinsic viscosity (IV) of the polyester resin constituting the polyester film of the present invention is preferably 0.45 dL/g or more and 1.5 dL/g or less.
For PET, the IV is preferably 0.5 dL/g or more and 1.5 dL/g or less. The lower limit of IV is more preferably 0.53 dL/g, still more preferably 0.55 L/g. The upper limit of IV is more preferably 1.2 dL/g, still more preferably 1 dL/g, and particularly preferably 0.8 dL/g.
For PEN, the lower limit of IV is preferably 0.45 dL/g, more preferably 0.48 dL/g, still more preferably 0.5 dL/g, and particularly preferably 0.53 dL/g. . The upper limit of IV is more preferably 1 dL/g, more preferably 0.8 dL/g, still more preferably 0.75 dL/g, and particularly preferably 0.7 dL/g.
By setting it in the above range, a film having excellent mechanical strength such as impact resistance can be obtained, more stable film formation can be easily performed, and a film with less thickness unevenness can be efficiently produced without imposing a large load on the equipment. can be done.

In the present invention, the lower limit of the in-plane retardation (Re) of the polyester film is preferably 3000 nm, more preferably 4000 nm, still more preferably 4300 nm, particularly preferably 4500 nm, most preferably 5000 nm. Iridescent spots can be suppressed by adjusting the content to the above lower limit or higher.
The upper limit of Re is preferably 30000 nm, more preferably 15000 nm, still more preferably 12000 nm, particularly preferably 10000 nm, most preferably 9500 nm. When the thickness is equal to or less than the above upper limit, the thickness of the film is not increased more than necessary, and it becomes easy to cope with thinning of the image display device and the like.
In order to widen the angle at which iris spots are suppressed when viewed obliquely, Re is preferably 5500 nm or more, more preferably 6000 nm or more, even more preferably 6000 nm or more, and particularly preferably 6500 nm or more. Shatterproof film, base film for touch panels (e.g., transparent electrode base film), screen surface protection film, foldable film (e.g., PET film), etc. When thin films are preferable even if the viewing angle is somewhat narrow, Re 7000 nm or less is more preferable, 6500 nm or less is still more preferable, and 6000 nm or less is particularly preferable.

In the polyester film of the present invention, the lower limit of the degree of plane orientation (ΔP) is preferably 0.128, more preferably 0.129, still more preferably 0.13, and more than 0.13. preferably. The upper limit of the degree of plane orientation is preferably 0.155, more preferably 0.152, still more preferably 0.15. By setting the content within the above range, it is possible to further improve the stability of film formation, such as preventing breakage while suppressing iridescence.
When used as a polarizer protective film, when it is desired to more effectively control rainbow spots from oblique directions, etc., the upper limit of the degree of plane orientation is more preferably 0.145, more preferably 0.14, Especially preferred is 0.138, most preferred is 0.136.
When it is desired to provide excellent bending resistance such as for use in a flexible image display device, the lower limit of the degree of plane orientation (ΔP) is more preferably 0.135, more preferably 0.138, and particularly preferably 0. .14.
The degree of planar orientation is (nx+ny)/ It is a value obtained by 2-nz.

In the polyester film of the present invention, the lower limit of the NZ coefficient is preferably 1.65, more preferably 1.68, still more preferably 1.7, particularly preferably greater than 1.7 .
The upper limit of the NZ coefficient is preferably 3, more preferably 2.7, even more preferably 2.5, and particularly preferably 2.3.
By setting the content within the above range, it is possible to further improve the stability of film formation, such as preventing breakage while suppressing iridescence.
When used as a polarizer protective film, when it is desired to more effectively control rainbow spots from oblique directions, etc., the upper limit of the NZ coefficient is more preferably 1.9, more preferably 1.85, and particularly preferably. is 1.8.
The lower limit of the NZ coefficient is more preferably 1.8, still more preferably 1.85, and particularly preferably 1 when it is desired to impart excellent bending resistance such as for use in a flexible image display device. .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 within the above ranges, adhesion to functional layers such as hard coat layers, antireflection layers, and antiglare layers, as well as adhesion to polarizers and the like, are ensured. can also

The lower limit of the thickness of the polyester film of the present invention is preferably 25 µm, more preferably 30 µm, 40 µm, 45 µm, 50 µm and 55 µm in this order.
The upper limit of the thickness is preferably 150 μm, more preferably 130 μm, 100 μm, 90 μm and 85 μm in that order. In the present specification, "preferred in order" means that numerical values with a narrower range are more preferable.
If the thickness is equal to or less than the above upper limit, the thickness of the unstretched film is also reduced when the unstretched film is heated, so it becomes easier to uniformly raise the temperature in the thickness direction of the film in a short time, and it becomes easier to suppress unevenness in thickness. . Moreover, it becomes easy to respond to thinning of the image display device.
In the case of a polarizer protective film, the thickness is preferably 40 to 85 μm. Whether it is a scattering prevention film, a base film for a touch panel (for example, a transparent electrode base film), or a screen surface protective film for a flexible image display device. For example, the thickness is preferably 25 to 70 μm, and the thickness is preferably 60 to 150 μm for a screen surface protective film for a non-flexible image display device.
For the thickness, for example, using a contact-type continuous thickness meter, the thickness of a film of a predetermined size (e.g., width of about 50 mm, length of about 6 m) is measured at a predetermined speed (e.g., 1.5 m / min in the MD direction. speed), continuously measured at predetermined intervals (e.g., 0.1 second intervals), arbitrarily select a predetermined number of data (e.g., 2048 points continuously) from the obtained data, and average them It can be calculated by

The upper limit of the thickness unevenness in the flow direction of the polyester film of the present invention (hereinafter referred to as the longitudinal direction, the MD direction, or the direction perpendicular to the main stretching direction when stretching) is preferably 8%, more preferably. is 7%, more preferably 6%, particularly preferably 5%, most preferably 4%.
The thickness unevenness in the MD direction is preferably as low as possible, but from a practical point of view, the lower limit is preferably 0.1%, more preferably 0.5%.
The unevenness of thickness is a value obtained by (maximum value of thickness - minimum value)/average value of thickness x 100 (%) in the following thickness measurement.

In the present invention, the data obtained by measuring the thickness of the film in the MD direction is subjected to Fourier transform (for example, fast Fourier transform), and the obtained results are analyzed by the length period of the film in the MD direction (specifically, the frequency is changed to the length ), A is the average of the top 5 amplitudes with a period of 10 cm or more, and B is the average of the top 5 amplitudes with a period of less than 10 cm, the lower limit of A/B is It 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, even more preferably 4, and particularly preferably 3.5.

In the above, when the maximum value of amplitude at a period of 10 cm or more is Amax, the lower limit of Amax/B is preferably 0.7, more preferably 1.4, and still more preferably 1.8, Particularly preferred is 2, most preferred is 2.2. The upper limit of Amax/B is 7, preferably 6, still more preferably 5, particularly preferably 4.5, and most preferably 4.
By setting A/B and/or Amax/B within the above range, stable production is possible while maintaining higher productivity, breakage is less likely to occur during film formation and post-processing, and a light source with a sharp peak is used. Even in the case of a liquid crystal display device having a conventional film, the film can be made into a film in which color spots are hardly conspicuous.

In addition, A, Amax and B are preferably calculated by the following specific method.
- The thickness of the central portion of the film is continuously captured at intervals of 0.1 seconds at a speed of 1.5 m/min.
・Continuously use 2048 points (5.12 m in length) of the obtained data to perform frequency analysis by fast Fourier transform.
・Convert the frequency of the obtained analysis data into a length cycle and obtain the amplitude.
・Among the length cycles of 10 cm or more, 5 points with the largest amplitude are selected in descending order, the average value of these is A, and the largest amplitude value among these 5 points is Amax.
・Select 5 points in descending order of amplitude from those with a length period of less than 10 cm, and let B be the average value of these points. Note that data in the second half of the frequency analysis data, which is called ghost, is ignored, and only the analysis data in the first half is used.

According to the studies of the present inventors, when stretching in the MD direction is not performed, the thickness unevenness in the MD direction is caused by the vibration of the electrode or the vibration of the apparatus used when the molten resin is electrostatically adhered to the cooling roll. It is often caused by the effects of chill roll roundness or runout at time, or by the automatic adjustment of the die lip spacing. For example, thickness unevenness caused by electrode blurring or device vibration often has a period of several centimeters or less. However, if the film is weakly stretched in the MD direction, unevenness in thickness cannot be sufficiently suppressed even if these adjustments are made, and unevenness in thickness with a period of several tens of centimeters to several meters becomes noticeable, causing problems due to unevenness in thickness. .

According to further studies by the present inventors, when weakly stretching in the MD direction, it is necessary to control the preheating temperature and stretching temperature during stretching within an appropriate range. , the stretching position is not constant and the stretching is not stable, the film sag occurs, and the film does not peel off smoothly from the roll. , the flatness also deteriorates.

Preferred film forming conditions for obtaining the polyester film of the present invention are described below.

First, after drying a polyester resin (typically PET), it is put into an extruder, melted at 260 to 300°C, and extruded into a sheet from a die onto a cooling roll to obtain an unstretched film. At this time, it is preferable to charge the resin, blow air, or reduce the pressure in a chamber so that the resin can quickly adhere to the chill roll. At this time, adjust the tension and fixing method of the wire electrode and band electrode to reduce electrode vibration, control the air flow and pressure reduction so that it is stable, and make this casting equipment less susceptible to mechanical vibrations such as motors. It is preferable to take measures such as

Next, the unstretched film is preheated to raise the temperature, and finally stretched by applying tension in the MD direction. In this case, the unstretched film is heated in multiple stages. The temperature is called the stretching temperature and will be described separately.
Specifically, in MD stretching, a film is heated by a plurality of low-speed rolls and then stretched with a difference in peripheral speed from the high-speed rolls. In this case, as a method of finally bringing the film surface to the stretching temperature, when heating with a final roll of low speed rolls (hereinafter sometimes simply referred to as "final roll"), when heating with an infrared heater (IR heater) and so on.

When heating with the final roll, the temperature at which the film separates from the final roll is the stretching temperature, and the temperature at which the film separates from the low-speed roll (heating roll) immediately before the final roll is the preheating temperature. In the case of heating with an IR heater, the highest temperature in the region heated by the IR heater is the stretching temperature, and the temperature at the time of separation from the final roll (heating roll) is the preheating temperature.

The preheating temperature for MD stretching is preferably 60° C. or higher, more preferably 65° C. or higher, and even more preferably 70° C. or higher. By setting the preheating temperature within the above range, the temperature difference in the thickness direction of the film can be reduced even if the film-forming speed is high, and stable stretching becomes possible.
The preheating temperature for MD stretching is preferably 95° C. or lower, more preferably 90° C. or lower, still more preferably 85° C. or lower, particularly preferably 82° C. or lower, and most preferably 80° C. or lower. By setting the preheating temperature within the above range, sticking between the film and the roll is suppressed, and stable film running becomes possible. In addition, since the slackness of the film between the preheating rolls can be suppressed and the tension between the preheating rolls can be reduced, unnecessary elongation of the film in the preheating process can be reduced, and thickness unevenness and deterioration of flatness can be reduced. can be suppressed. In addition, when the molecular weight of the polyester is low (when the IV is low), the slack of the film is likely to occur. g or less, it is preferably 85° C. or less.

The stretching temperature for MD stretching is preferably 86°C or higher, more preferably 88°C or higher, still more preferably 89°C or higher, particularly preferably 90°C or higher, and most preferably 91°C or higher. When the stretching temperature is low, the SS (stress-strain) characteristics of the unstretched film may not allow the stress to rise moderately with respect to the strain, resulting in unstable stretching.

The stretching temperature for MD stretching is preferably 110°C or lower, and more preferably 105°C or lower, 102°C or lower, 100°C or lower, 98°C or lower, and 96°C or lower in this order. By setting the stretching temperature within the above range, the film does not become too soft and slack during stretching can be suppressed. In particular, when tension is applied, the film tends to stretch from the latter half of 80° C., but if the stretching temperature is within the above range, stretching at positions other than the assumed positions can be suppressed and stretching can be stabilized. In addition, as described above, since the lower the molecular weight, the easier it is to loosen, for example, when IV is 0.7 dl / g or less, it is preferably 100 ° C. or less, and when IV is 0.65 dl / g or less, it is 98 ° C. or less. is preferably

In MD stretching, the difference between the stretching temperature and the preheating temperature is preferably 11° C. or higher, more preferably 12° C. or higher, still more preferably 13° C. or higher. Also, the difference between the stretching temperature and the preheating temperature is preferably 24° C. or less, more preferably 23° C. or less, still more preferably 22° C. or less.
By setting it to the above range, while suppressing pseudo-stretching during preheating and sticking of the film to the roll, the temperature difference in the thickness direction of the film during stretching can be reduced even if the film-forming speed is high, and stable stretching can be performed. It becomes possible.

In MD stretching, as described above, it is necessary to quickly raise the temperature of the film from the preheating temperature to the stretching temperature. It can be difficult. Therefore, when the film is heated by the final roll, it is preferable to increase the embrace angle of the film to the final roll to prolong the contact time between the final heating roll and the film. The embrace angle is preferably 30 degrees or more, more preferably 45 degrees or more, still more preferably 60 degrees or more, and particularly preferably 70 degrees or more.
In the case of using an IR heater, it is preferable to provide a plurality of heaters in the MD direction or to use a heater with a wide width in the MD direction.

The roll used in the preheating process and the roll in the stretching process may be a roll with a surface plated with chrome plating, nickel plating, cobalt alloy plating, etc., and the surface of the roll becomes hot and sticking of the polyester resin is observed. In such a case, it is preferable to use a fluororesin-coated roll.

It is also important to improve the accuracy of the roundness and deflection of the rolls used in the preheating process and the rolls used in the stretching process. 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 runout 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 roll depends on the size of the stretching machine, but is preferably 100 to 500 mm, more preferably 150 to 400 mm, if the width of the unstretched film is about 700 to 2500 mm. and more preferably 170 to 350 mm.

The lower limit of the MD stretching ratio is preferably 1.05 times, more preferably 1.08 times, and still more preferably 1.1 times. The upper limit of the MD draw ratio is preferably 2 times, more preferably 1.8 times, and still more preferably 1.7 times. By adjusting the content to the above range, it is possible to obtain a film that is more excellent in workability and suppresses iridescence. Further, when used as a polarizer protective film, when it is desired to more effectively control iridescence from an oblique direction, the upper limit of the MD draw ratio is more preferably 1.25 times, more preferably 1.2 times. and particularly preferably 1.18 times. When it is desired to provide excellent bending resistance such as for use in a flexible image display device, the lower limit of the MD draw ratio is more preferably 1.2 times, still more preferably 1.25 times, and particularly preferably 1.25 times. is 1.3 times.

In the present invention, the upper limit of the thickness unevenness in the direction (TD direction) perpendicular to the flow direction of the film is preferably 5%, more preferably 4%, still more preferably 3.5%, particularly Preferably it is 3%. A lower thickness unevenness in the TD direction is preferable, but from a practical point of view, the lower limit is preferably 0.1%, more preferably 0.5%.
Thickness unevenness in the TD direction is achieved, for example, by controlling the lip spacing during casting, reducing unevenness in film temperature in the TD direction during TD stretching, and setting the degree of plane orientation and the NZ coefficient within an appropriate range. be able to.

In TD stretching, the film after MD stretching is preheated and stretched at preferably 80 to 130°C, more preferably 90 to 120°C. The draw ratio for 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, and particularly preferably 3.7 to 5.8 times. Double.

Stretching is preferably followed by heat setting. The heat setting temperature is preferably 150 to 250°C, more preferably 170 to 230°C. The heat setting time is preferably 3 to 60 seconds, more preferably 5 to 30 seconds.
In heat setting, it is also preferable to perform a relaxation treatment in the main drawing direction and/or in a direction perpendicular thereto. The relaxation treatment is preferably 0.5 to 10%, more preferably 1 to 5%.

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

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

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

The lower limit of the breaking strength in the TD direction of the polyester film of the present invention is preferably 300 MPa, more preferably 330 MPa, still more preferably 350 MPa.
The upper limit of the breaking strength in the TD direction is preferably 500 MPa, more preferably 450 MPa, still more preferably 420 MPa, particularly preferably 400 MPa.
By setting the elongation at break and the strength at break within the above ranges, a film with even better workability can be obtained. The breaking elongation and breaking strength are values measured according to JIS K7113.

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

The polyester film of the present invention preferably has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance at a wavelength of 380 nm is more preferably 15% or less, even more preferably 10% or less, and particularly preferably 5% or less. When the light transmittance is 20% or less, deterioration of iodine and dichroic dye in the polarizing layer due to ultraviolet rays can be suppressed. The light transmittance is measured in a direction perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, Hitachi U-3500). Especially when it is used as a polarizer protective film, it preferably has a low ultraviolet transmittance.

The light transmittance of the polyester film of the present invention at a wavelength of 380 nm 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, It can be achieved by appropriately adjusting the type and concentration of the ultraviolet absorbent and the thickness of the film. UV absorbers are known substances. Examples of the UV absorber include organic UV absorbers and inorganic UV absorbers, but organic UV absorbers are preferred from the viewpoint of transparency.

Examples of organic UV absorbers include benzotriazole-based, benzophenone-based, cyclic iminoester-based, and combinations thereof, but are not particularly limited as long as the absorbance is within the desired range.

In addition, it is preferable to add particles having an average particle size of 0.05 to 2 μm to the polyester film of the present invention in order to improve slipperiness. As the particles, inorganic particles such as titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride, etc. Examples include organic polymer particles such as styrene, acrylic, melamine, benzoguanamine, and silicone particles.
These particles may be added to the entire film, or may be added only to the skin layer in a skin-core coextruded multilayer structure. Moreover, it is also preferable that the film itself does not contain particles, and particles are added to the easy-adhesion layer to be described later.

The polyester film of the present invention may be subjected to treatments such as corona treatment, flame treatment and plasma treatment to improve adhesiveness.

(Easy adhesion layer)
The polyester film of the present invention may be provided with an easy-adhesion layer in order to improve adhesion to an adhesive, a coat layer, and the like.
Polyester resins, polyurethane resins, polycarbonate resins, acrylic resins, and the like are used as the resins used for the easy-adhesion layer, and polyester resins, polyester-polyurethane resins, polycarbonate-polyurethane resins, and acrylic resins are preferred. The easy-adhesion layer is preferably crosslinked. Examples of cross-linking agents include isocyanate compounds, melamine compounds, epoxy resins, oxazoline compounds, and the like. Addition of a water-soluble resin such as polyvinyl alcohol to the easy-adhesion layer is also a useful means for improving adhesion to the polarizer.

The easy-adhesion layer can be provided by coating and drying the film as a water-based paint containing these resins and, if necessary, a cross-linking agent, particles, and the like. Examples of the particles include those used in the base material described above.
The easy-adhesion layer may be provided on the film (for example, stretched film) off-line, but is preferably provided in-line during the film-forming process. When provided in-line, it may be before the longitudinal stretching (MD stretching) or before the transverse stretching (TD stretching), but it is applied immediately before the transverse stretching, and is dried and crosslinked in the preheating, heating, and heat treatment steps by the tenter. preferably. In the case of in-line coating immediately before longitudinal stretching by rolls, it is preferable to dry the film with a vertical dryer after coating and then guide it to the stretching rolls.
The coating amount (coating amount after drying) of the easily adhesive layer is preferably 0.01 to 1.0 g/m ² , more preferably 0.03 to 0.5 g/m ² .

(functional layer)
It is also a preferred embodiment that the polyester film of the present invention is provided with functional layers such as a hard coat layer, an antireflection layer, a low reflection layer, an antiglare layer and an antistatic layer. The antireflection layer, the low reflection layer, and the antiglare layer are collectively referred to as a reflection reduction layer. The reflection-reducing layer not only prevents external light from being reflected on the display screen and makes it difficult to see, but also has the effect of suppressing reflection at the interface to reduce iridescence or make it less noticeable. Further, when used as a substrate film (for example, a transparent electrode substrate film) for a touch panel or the like, it is also preferable to provide a refractive index adjusting layer in order to make the transparent electrode layer inconspicuous. In addition, in the polyester film provided with the functional layer, the film in the state before the functional layer is provided is referred to as the base film. In addition, the substrate film may contain the above-described easy-adhesion layer.

The upper limit of the reflectance of the polyester film measured from the side of the reflection-reducing layer is preferably 5%, more preferably 4%, even more preferably 3%, particularly preferably 2%, and most preferably 1%. 0.5%. When the thickness is equal to or less than the above upper limit, the reflection of outside light can be reduced, and the visibility of the screen can be improved. Although the lower limit of the reflectance is not particularly defined, it is preferably 0.01%, more preferably 0.1% from a practical point of view.
As the reflection reducing layer, there are various types such as a low reflection layer, an antireflection layer, an antiglare layer, and the like.

(low reflection layer)
The low-reflection layer is a layer having a function of reducing the reflectance by providing a low-refractive-index layer (low-refractive-index layer) on the surface of the base film to reduce the difference in refractive index from air.

(Antireflection layer)
The antireflection layer is a layer that controls reflection by controlling the thickness of the low refractive index layer to interfere the reflected light from the interface. The thickness of the low refractive index layer is preferably about the wavelength of visible light (400 to 700 nm)/(refractive index of low refractive index layer×4).
It is also a preferred form to provide a high refractive index layer between the antireflection layer and the base film, and two or more low refractive index layers and/or high refractive index layers are provided to further enhance the antireflection effect by multiple interference. You can raise it. A combination of the high refractive index layer and the low refractive index layer is sometimes called an antireflection layer.

In the case of the antireflection layer, the upper limit of the reflectance is preferably 2%, more preferably 1.5%, even more preferably 1.2%, and 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. Moreover, 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 is a value measured under the condition of a wavelength of 589 nm.

Although the thickness of the low-refractive-index layer is not limited, it can usually be appropriately set within the range of about 30 nm to 1 μm. When used as an antireflection layer, the thickness of the low refractive index layer is preferably 70 to 120 nm, more preferably 75 to 110 nm.

The low refractive index layer preferably includes (1) a layer made of a resin composition containing a binder resin and low refractive index particles, (2) a layer made of a fluororesin that is a low refractive index resin, (3) silica or (4) a thin film of a low refractive index substance such as silica and magnesium fluoride;

As the binder resin contained in the resin composition (1), polyester, polyurethane, polyamide, polycarbonate, acrylic, etc. can be used without particular limitation. Among them, acrylic is preferred, and one obtained by polymerizing (crosslinking) a photopolymerizable compound by light irradiation is preferred.

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

Examples of polyfunctional monomers include pentaerythritol triacrylate (PETA), dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate (PETTA), and dipentaerythritol pentaacrylate (DPPA). In addition, a monofunctional monomer may be used in combination for adjustment of coating viscosity and hardness.

Polyfunctional oligomers include polyester (meth)acrylate, urethane (meth)acrylate, polyester-urethane (meth)acrylate, polyether (meth)acrylate, polyol (meth)acrylate, melamine (meth)acrylate, and isocyanurate (meth)acrylate. Acrylate, epoxy (meth)acrylate, and the like.

Polyfunctional polymers include urethane (meth)acrylate, isocyanurate (meth)acrylate, polyester-urethane (meth)acrylate, epoxy (meth)acrylate, and the like.

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

Examples of the low refractive index particles contained in the resin composition (1) include silica particles (for example, hollow silica particles), magnesium fluoride particles, etc. Among them, hollow silica particles are preferred. Such hollow silica particles can be produced, for example, by the production method described in Examples of JP-A-2005-099778.

The average particle size of the primary particles of the low refractive index particles is preferably 5 to 200 nm, more preferably 5 to 100 nm, even more preferably 10 to 80 nm.
The low refractive index particles are more preferably surface-treated with a silane coupling agent, and more preferably surface-treated with a silane coupling agent having a (meth)acryloyl group.

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, and further 50 to 200 parts by mass with respect to 100 parts by mass of the binder resin. Preferred is 80 to 180 parts by weight, most preferred is 100 to 180 parts by weight.

As the fluororesin (2), a polymerizable compound containing at least a fluorine atom in the molecule or a polymer thereof can be used. The polymerizable compound is not particularly limited, but preferably has a curing reactive group such as a photopolymerizable functional group or a thermosetting polar group. A compound having these multiple curing reactive groups at the same time may also be used. In contrast to this polymerizable compound, the polymer does not have the above curing reactive groups.

As a 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 anti-fingerprint properties, it is also preferable to appropriately add a known polysiloxane-based or fluorine-based antifouling agent to the low refractive index layer.

The surface of the low-refractive-index layer may be an uneven surface in order to provide anti-glare properties, but it is also preferable that it is a smooth surface.
When the surface of the low refractive index layer is a smooth surface, the arithmetic mean roughness SRa (JIS B0601:1994) of the surface of the low refractive index layer is preferably 20 nm or less, more preferably 15 nm or less, and even more preferably. is 10 nm or less, particularly preferably 1 to 8 nm. The ten-point average roughness Rz (JIS B0601:1994) of the surface of the low refractive index layer is preferably 160 nm or less, more preferably 50 to 155 nm.

(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 is a value measured under the condition of a wavelength of 589 nm.

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

When two high refractive index layers are used, the refractive index of the high refractive index layer on the low refractive index layer side is preferably higher. Specifically, the refractive index of the high refractive index layer on the low refractive index layer side is The index 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 made of a resin composition containing high refractive index particles and a resin.
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 as the high refractive index particles. Among these, titanium oxide particles and zirconium oxide particles are preferred.

Two or more kinds of high refractive index particles may be used in combination. In particular, 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 to prevent aggregation.

The resins used for the high refractive index layer include the same resins as those listed for the low refractive index layer, except for fluorine-based resins.

In order to flatten 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 flat. As a method for flattening the surface of the high refractive index layer, the above method for flattening the low refractive index layer is used.

The average particle size of the high refractive index particles and the primary particles of the high refractive index particles is preferably 5 to 200 nm, more preferably 5 to 100 nm, even more preferably 10 to 80 nm.
These particles are more preferably surface-treated, more preferably surface-treated with a silane coupling agent, and more preferably surface-treated 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, and further 50 to 200 parts by mass with respect to 100 parts by mass of the binder resin. Preferred is 80 to 180 parts by weight, most preferred is 100 to 180 parts by weight.

For the high refractive index layer and the low refractive index layer, for example, a resin composition containing a photopolymerizable compound is applied to a base film, dried, and then the coated resin composition is irradiated with light such as ultraviolet rays. can be formed by polymerizing (crosslinking) the photopolymerizable compound.

If necessary, a thermoplastic resin, a thermosetting resin, a solvent, a polymerization initiator, a combination thereof, or the like may be added to the resin composition of the high refractive index layer and the low refractive index layer. In addition, dispersants, surfactants, antistatic agents, silane coupling agents, thickeners, anti-coloring agents, coloring agents (pigments, dyes), antifoaming agents, leveling agents, flame retardants, UV absorbers, adhesion imparting agents agents, polymerization inhibitors, antioxidants, surface modifiers, lubricants, combinations thereof, and the like may be added.

(Antiglare layer)
The anti-glare layer is a layer that prevents reflection of the shape of a light source when external light is reflected on the surface and reduces glare, by providing irregularities on the surface to cause diffuse reflection.

The arithmetic mean roughness (SRa) of the irregularities on the surface of the antiglare layer is preferably 0.02 to 0.25 μm, more preferably 0.02 to 0.15 μm, still more preferably 0.02 to 0. .12 μm.

The ten-point average roughness (Rzjis) of unevenness on the surface of the antiglare layer is preferably from 0.15 to 2 μm, more preferably from 0.2 to 1.2 μm, and still more preferably from 0.3 to 0.3 μm. 8 μm.

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

Examples of methods for providing the antiglare layer on the base film include the following methods.
・Apply anti-glare layer paint containing particles (filler), etc. ・Cure anti-glare layer resin while it is in contact with a mold with uneven structure. It is applied to the mold that has it and transferred to the base film. ・A paint that causes spinodal decomposition 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 µm, more preferably 50 µm, and still more preferably 20 µm.

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 is a value measured under the condition of a wavelength of 589 nm.
The low refractive index layer may be provided with unevenness to form an antiglare and low reflective layer, and the surface of the hard coat layer or high refractive index layer may be uneven, and the low refractive index layer may be provided thereon to provide an antireflection function. may be used as an antiglare and antireflection layer.

(Hard coat layer)
It is also a preferred form to provide a hard coat layer as a lower layer of the reflection reducing layer.
The hard coat layer preferably has a pencil hardness of H or more, more preferably 2H or more. The hard coat layer can be provided, for example, by applying and curing a composition (solution) containing a thermosetting resin or a radiation-curable resin.

Thermosetting resins include acrylic resins, urethane resins, phenolic resins, urea melamine resins, epoxy resins, unsaturated polyester resins, silicone resins, and combinations thereof. If necessary, a curing agent is added to these curable resins in the thermosetting resin composition.

The radiation-curable resin is preferably a compound having a radiation-curable functional group (radiation-curable compound). A saturated bond group, an epoxy group, an oxetanyl group, and the like can be mentioned. Among these, as the ionizing radiation-curable compound, a compound having an ethylenically unsaturated bond group is preferable, and a compound having two or more ethylenically unsaturated bond groups is more preferable. Polyfunctional (meth)acrylate compounds having the above are more preferable. A polyfunctional (meth)acrylate compound may be a monomer, an oligomer, or a polymer.

As specific examples thereof, those mentioned as the binder resin are used.
In order to achieve hardness as a hard coat, the difunctional or higher monomer content in the compound having a radiation-curable functional group is preferably 50% by mass or more, more preferably 70% by mass or more. Furthermore, in the compound having a radiation-curable functional group, the trifunctional or higher monomer preferably accounts for 50% by mass or more, more preferably 70% by mass or more.
The compounds having a radiation-curable functional group can be used singly or in combination of two or more.

The thickness of the hard coat layer is preferably in the range of 0.1-100 μm, more preferably in the range of 0.8-20 μm.

The hard coat layer preferably has a refractive index of 1.45 to 1.7, more preferably 1.5 to 1.6.
The refractive index of the hard coat layer is a value measured at a wavelength of 589 nm.

Examples of adjusting the refractive index of the hard coat layer include a method of adjusting the refractive index of the resin, and a method of adjusting the refractive index of the particles when particles are added.
Examples of the particles include those exemplified as the particles of the antiglare layer.
In addition, in this invention, it may be called a reflection reduction layer including a hard-coat layer.

When the functional layer is provided, an easily adhesive layer may be provided between the functional layer and the base film. For the easy-adhesion layer, the resins, cross-linking agents, and the like mentioned for the easy-adhesion layer are preferably used. Also, the easy-adhesion layers may be provided on both sides of the substrate film, and in that case, the easy-adhesion layers on both sides may have the same composition or different compositions.

(Polarizer)
The polyester film of the present invention can be suitably used as a polarizer protective film. The polyester film of the present invention can be laminated with a polarizer to form a polarizing plate.
(Polarizer)
As a polarizer, for example, uniaxially stretched polyvinyl alcohol (PVA) to which iodine or an organic dichroic dye is adsorbed, a liquid crystal compound and an organic dichroic dye that are aligned, or a liquid crystalline A liquid crystalline polarizer composed of a dichroic dye, a wire grid type polarizer, and the like can be used without particular limitation.

A film-shaped polarizer made by adsorbing iodine or an organic dichroic dye to uniaxially stretched polyvinyl alcohol (PVA) and a roll-shaped polarizer protective film are adhered by PVA-based, UV-curable, etc. It can be laminated using an adhesive or adhesive and wound into a roll. The thickness of this type of polarizer is preferably 5 to 30 μm, more preferably 8 to 25 m, particularly preferably 10 to 20 m. The thickness of the adhesive or adhesive is preferably 1-10 μm, more preferably 2-5 μm.

Also, a polarizer obtained by coating an unstretched base material such as PET or polypropylene with PVA and uniaxially stretching it together with the base material to adsorb iodine or an organic dichroic dye is also preferably used. When using this polarizer, the polarizer surface of the polarizer laminated on the substrate (the surface on which the substrate is not laminated) and the polarizer protective film are attached together with an adhesive or adhesive, and then the polarizer is attached. The polarizer protective film and the polarizer can be bonded together by peeling off the base material used for the production. Also in this case, it is preferable to stick together in a roll form and take up the roll. The thickness of this type of polarizer is preferably 1 to 10 μm, more preferably 2 to 8 μm, particularly preferably 3 to 6 μm. The thickness of the adhesive or adhesive is preferably 1-10 μm, more preferably 2-5 μm.

In the case of a liquid crystalline polarizer, a polarizer protective film is laminated with an oriented polarizer consisting of a liquid crystal compound and an organic dichroic dye, or a liquid crystalline dichroic material is laminated on the polarizer protective film. A polarizing plate can be obtained by applying a coating liquid containing a polar dye, drying it, photocuring or thermally curing it, and laminating a polarizer. Examples of the method for orienting the liquid crystalline polarizer include a method of rubbing the surface of the object to be coated and a method of irradiating polarized ultraviolet rays to cure the liquid crystalline polarizer while aligning it. The surface of the polarizer protective film may be directly rubbed and coated with the coating liquid, or the polarizer protective film may be directly coated with the coating liquid and irradiated with polarized ultraviolet rays. It is also a preferable method to provide an orientation layer on the polarizer protective film before providing the liquid crystalline polarizer (that is, to laminate the liquid crystalline polarizer on the polarizer protective film via the orientation layer). As a method for providing the orientation layer,
- A method of coating polyvinyl alcohol and its derivatives, polyimide and its derivatives, acrylic resin, polysiloxane derivative, etc., and rubbing the surface thereof to form an alignment layer (rubbing alignment layer);
- A method of applying a coating solution containing a polymer or monomer having a photoreactive group such as a cinnamoyl group or a chalcone group and a solvent, and irradiating polarized ultraviolet rays to harden the alignment layer (photoalignment layer), etc. is mentioned.

A liquid crystalline polarizer is provided on a releasable film according to the above method, the liquid crystalline polarizer surface and the polarizer film are bonded together with an adhesive or a pressure-sensitive adhesive, and then a releasable film is attached. A polarizer film and a polarizer can also be bonded together by peeling.

The thickness of the liquid crystalline polarizer is preferably 0.1 to 7 μm, more preferably 0.3 to 5 μm, particularly preferably 0.5 to 3 μm. The thickness of the adhesive or adhesive is preferably 1-10 μm, more preferably 2-5 μm.

(Lamination of polarizer and polarizer protective film)
The polyester film of the present invention is preferably laminated on the opposite side of the polarizer to the image display cell side. When a polarizer and a film are laminated to form a polarizing plate, the angle formed by the absorption axis of the polarizer and the slow axis of the film is preferably about 90 degrees or about 0 degrees. As used herein, "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, most preferably 1.5 degrees or less. It is preferable that the above angle is provided over the entire range of the polarizing plate.
If the polarizer is a liquid crystalline polarizer or a wire grid type polarizer, it is easy to make the absorption axis of the polarizer oblique to the slow axis of the polyester film. The angle between them may be 30-60 degrees, preferably about 45 degrees.

(Surface of the polarizer on the image display cell side)
When the polarizing plate is for a liquid crystal display device, the surface of the polarizer on the liquid crystal cell side may be in a state in which nothing is laminated, or may be an adhesive, and a cured layer is provided on the polarizer. A polarizer protective film different from the above polarizer protective film may be provided. A preferable cured layer includes the hard coat layer described above. When it is an adhesive, a release film may be further laminated. In addition, in a non-laminated state, in the case of a cured layer, or in the case of a polarizer protective film, a separate peelable protective film may be laminated.

The polarizer protective film on the liquid crystal cell side of the polarizer includes cellulose-based (TAC) film, acrylic film, polycyclic olefin (COP) film, and the like. The polarizer protective film on the side of the liquid crystal cell may have a retardation of almost zero, and has a phase difference called an optical compensation film for controlling color tone changes when the display screen is viewed from an oblique direction. It may be a film.

In order to obtain the necessary retardation in the optical compensation film, the film should be stretched, or a retardation layer such as a liquid crystal compound should be applied on the film. is provided and transferred. A liquid crystal compound for forming the retardation layer may be a rod-like liquid crystal compound, a discotic liquid crystal compound, or the like, depending on the required retardation characteristics. The liquid crystal compound preferably has a photocurable reactive group such as a double bond in order to fix the alignment state. In order to align the liquid crystal compound and provide a retardation, for example, an alignment layer is provided as a lower layer of the retardation layer, and the alignment layer is rubbed or irradiated with polarized ultraviolet rays, and then coated thereon. It is possible to impart alignment controllability such that the liquid crystal compound to be aligned is aligned in a specific direction.

The retardation of the optical compensation film can be set as appropriate depending on the type of liquid crystal cell used and the viewing angle to be secured.

The retardation layer can be provided by applying a composition paint for retardation layer. The composition paint for retardation layer may contain a solvent, a polymerization initiator, a sensitizer, a polymerization inhibitor, a leveling agent, a polymerizable non-liquid crystal compound, a cross-linking agent, a combination thereof, and the like. For these, the ones described in the alignment control layer and the liquid crystalline polarizer can be used.

A retardation layer is provided by coating the composition paint for retardation layer on the release surface of the release film or the orientation control layer, followed by drying, heating, and curing.

As for these conditions, the conditions described in the section on the alignment control layer and the liquid crystalline polarizer are used as preferable conditions.

An adhesive or pressure-sensitive adhesive is used when bonding a polarizer to a polarizer protective film or a retardation film. As the adhesive, a water-based adhesive such as a polyvinyl alcohol-based adhesive or a photocurable adhesive is preferably used. Examples of photocurable adhesives include acrylic adhesives and epoxy adhesives. An acrylic adhesive is preferably used as the adhesive.

(liquid crystal cell)
A liquid crystal cell is a cell in which a liquid crystal compound is sealed between thin substrates such as glass on which circuits are formed. When the substrate is glass, the thickness is preferably 1 mm or less, more preferably 0.7 mm or less, further preferably 0.5 mm or less, and particularly preferably 0.4 mm or less from the viewpoint of thinning.

The method of the liquid crystal cell is not particularly limited. This is a preferred method for applying the present invention because it is parallel or orthogonal to the long side direction of the .

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

(liquid crystal panel)
A liquid crystal display panel is preferably formed by bonding polarizing plates to the viewing side and the light source side of the liquid crystal cell. Bonding is preferably performed with an adhesive. An acrylic adhesive is preferably used as the adhesive.

In the liquid crystal panel, the polarizing plate using the polyester film may be either the polarizing plate on the light source side or the polarizing plate on the viewing side, or may be both polarizing plates.

When the image display device is an organic or inorganic electroluminescence cell, micro LED, or the like, the polarizing plate is preferably a circularly polarizing plate. A circular polarizer typically has a quarter-wave layer laminated on the viewing side of a polarizer. The quarter-wave layer includes not only one quarter-wave layer but also a combination of a quarter-wave layer and a half-wave layer, and a retardation layer such as a C plate. Including added ones. A retardation layer such as a quarter-wave layer, a half-wave layer, and a C plate may be a film or a coat layer. These retardation layers may be the same as those described for the retardation layer of the polarizing plate, as long as the retardation and the orientation direction thereof are appropriate.

(Transparent electrode base film)
The polyester film of the present invention is suitably used as a transparent electrode substrate film for touch panels and the like. The transparent conductive layer is provided on at least one side of the polyester film, and may be provided on both sides.

Examples of transparent conductive layers include conductive paste mesh prints, carbon nanotube-containing coats, self-assembled nano-silver coats, acicular conductive filler-containing coats, metal oxide thin films, and the like. Among them, metal oxide thin films are preferable, and preferable examples include thin films of indium oxide, zinc oxide, tin oxide, indium tin oxide (ITO), tin antimony oxide, zinc aluminum oxide, and indium zinc oxide.

The transparent conductive layer is preferably formed into 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 500 nm, more preferably 15 to 250 nm, even more preferably 20 to 100 nm. Due to the above thickness, it is possible to suppress the tint caused by the conductive layer while ensuring conductivity.

A 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.

After forming the transparent conductive layer, a resist mask with a predetermined pattern can be formed by photolithography, and then an etching process can be performed to form a pattern or the like.

The transparent conductive layer may be amorphous, but the amorphous transparent conductive layer is heat-treated at 130 to 180° C. for 0.5 to 2 hours to grow crystals to form a crystalline transparent conductive layer, It is preferable to increase the conductivity.

It is also a preferred form to provide a hard coat layer and a refractive index adjusting layer as a lower layer of the transparent conductive layer. The refractive index adjusting 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. In particular, it is preferable to provide the high refractive index layer and the low refractive index layer in this order.

The polyester film of the present invention is preferably used as a shatterproof film. When a glass plate is used as a base material for a touch panel or as a screen surface cover, the shatterproof film is used by bonding it to the glass plate. It can prevent scattering and exposure to the outside. The anti-scattering film may be laminated on either the viewing side or the anti-viewing side of the glass plate. When laminating on a glass plate, it is preferable to use an optical substrate-less pressure-sensitive adhesive called OCA.

The polyester film of the present invention is preferably used as a screen surface protective film. The screen surface protective film is laminated on the viewing side of the screen of the image display device, and can protect the internal image display cells from external shocks and prevent the surface from being damaged. The screen surface protective film is preferably attached to the image display portion using an adhesive. It is also preferable that the screen surface protective film is positioned on the outermost surface of the image display portion and is of a type that can be peeled off and replaced when damaged. In this case, it is preferable that the adhesive has such an adhesive strength that it can be peeled off by hand.

The polyester film of the present invention is also preferably used in flexible image display devices, such as polarizer protective films, back cover films, transparent electrode substrate films, and screen surface protective films of flexible image display devices. Among them, it is preferably used as a back cover film and a screen surface protective film.
The flexible image display device may be of a V type, a double door type, a W type, or the like with a foldable image display portion, or may be wound into a roll.
When used in a flexible image display device, it is preferable to arrange the slow axis of the polyester film so as to be orthogonal to the folding direction, in other words, to arrange so that the crease becomes the slow axis.

When used as a transparent electrode base film, a scattering prevention film, a screen surface protective film, etc. on the viewing side of the polarizing plate of an image display device, the slow axis of the polyester film is 30 to 60 degrees with respect to the absorption axis of the polarizing plate. , preferably about 45 degrees, so that blackout and iridescence do not occur when viewed with sunglasses.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited by the following examples, and can be carried out with appropriate modifications within the scope of the gist of the present invention. Both of them are included in the technical scope of the present invention. The methods for evaluating physical properties and the like in the following examples are as follows.

(1) Refractive index of polyester film
Using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Keisoku Co., Ltd.), the slow axis direction of the film was determined, and the slow axis direction was parallel to the long side. A rectangle was cut out and used as a sample for measurement. For this sample, the refractive index in the orthogonal biaxial direction (refractive index in the slow axis direction: ny, fast axis (refractive index in the direction perpendicular to the slow axis direction): nx), and the refractive index in the thickness direction ( nz) was determined by an Abbe refractometer (NAR-4T manufactured by Atago Co., measuring wavelength 589 nm).

(2) In-plane retardation (Re)
The in-plane retardation is defined as the product (ΔNxy×d) of the refractive index anisotropy (ΔNxy=|nx−ny|) and the film thickness d (nm) on the film. It is a parameter and a measure of optical isotropy and anisotropy. The absolute value of the biaxial refractive index difference (|nx−ny|) was calculated as the biaxial refractive index anisotropy (ΔNxy) by the above method (1). The in-plane retardation (Re) was obtained from the product (ΔNxy×d) of the refractive index anisotropy (ΔNxy) and the film thickness d (nm).

(3) Thickness direction retardation (Rth)
The retardation in the thickness direction refers to the two birefringences ΔNxz (=|nx-nz|) and ΔNyz (=|ny-nz|) when viewed from the cross section in the film thickness direction, and the film thickness d It is a parameter indicating the average retardation obtained by multiplication. nx, ny, and nz were obtained by the method (1) above, and the average value of (ΔNxz×d) and (ΔNyz×d) was calculated to obtain the retardation in the thickness direction (Rth).

(4) The degrees of planar orientation nx, ny, and nz were substituted into the formula represented by |nx+ny|/2−nz to determine the degree of planar orientation.

(5) NZ Coefficient The NZ coefficient was obtained by substituting nx, ny, and nz into the expression |ny-nz|/|ny-nx|.

(6) Absorption axis of polarizer A polarizing filter with a known absorption axis and a polarizer are placed on top of a surface light source, and the polarizing filter is rotated to obtain the darkest absorption axis of the polarizing filter. The direction of 90 degrees was taken as the absorption axis direction of the polarizer. In the case of a long polarizer in which PVA is stretched in the longitudinal direction, the longitudinal direction is the absorption axis direction, so the longitudinal direction can be regarded as the absorption axis direction.

(7) Slow axis direction of film Measured with a molecular orienter (MOA-6004 type molecular orienter manufactured by Oji Instruments Co., Ltd.).

(8) Light transmittance at a wavelength of 380 nm
Using a spectrophotometer (U-3500, manufactured by Hitachi, Ltd.), the light transmittance in the wavelength range of 300 to 500 nm was measured with the air layer as a standard, and the light transmittance at a wavelength of 380 nm was obtained.

(9) Intrinsic viscosity 0.2 g of a sample was dissolved in 50 ml of a mixed solvent of phenol/1,1,2,2-tetrachloroethane (60/40 (weight ratio)), and measured at 30°C using an Ostwald viscometer. It was measured.

(10) Film thickness and frequency characteristics after Fourier transform MD from the center in the width direction of the obtained film using a contact-type continuous thickness meter by Micron Keiseki Co., Ltd. A sample with a width of about 50 mm and a length of about 6 m was cut in the direction, and the thickness was measured in the MD direction at a speed of 1.5 m/min, and the data was continuously captured at 0.1 second intervals.
From the obtained data, 2048 points (for a length of 5.12 m) were continuously selected arbitrarily, and the average value of the thickness was taken as the film thickness. Among the measurement data, the value obtained by (maximum thickness−minimum thickness)/average thickness×100 was taken as MD direction thickness unevenness (%).
Further, from the selected 2048 points of data, frequency analysis was performed by fast Fourier transform using Microsoft's Excel (registered trademark) spreadsheet software. Furthermore, the frequency of the obtained analysis data was converted into a length period, and each amplitude was obtained.
Among those with a length period of 10 cm or more, 5 points with the largest amplitude were selected, and the average value of these was designated as A, and the largest value of amplitude among these 5 points was designated as Amax. Furthermore, among those with a length period of less than 10 cm, five points with the largest amplitude were selected, and B was the average value of these five points. The data in the second half of the frequency analysis data, which is said to be a ghost of the length period, was ignored, and only the analysis data in the first half was used.
A/B and Amax/B were obtained from the obtained values of A, Amax, and B. The TD direction thickness unevenness is obtained by slitting the central portion of the TD direction of the film after film formation to a width of 1000 mm, cutting out a sample of 1000 mm × width 50 mm in the TD direction of this film, and measuring with a continuous thickness meter in the same manner. Based on the data obtained, it was obtained as (maximum thickness - minimum thickness) / average thickness x 100.
A length cycle of 10 cm or more corresponds to a frequency of 0.25 Hz or less.

(11) Breaking strength and breaking elongation Conforming to JIS K7113. A sample having a width of 10 mm and a length of 100 mm was cut out using a razor to obtain a sample. After being left for 12 hours in an atmosphere of 23°C and 65% RH, measurement was performed in an atmosphere of 23°C and 65% RH under the conditions of a chuck distance of 100 mm and a pulling speed of 200 mm/min. values were used. Autograph AG5000A manufactured by Shimadzu Corporation was used as a measuring device.

(12) Film temperature A radiation thermometer (IR-BZPHGN1 manufactured by Chino Co., Ltd.) was used to measure the temperature by inserting the detection part from the side of the film forming machine. The measured data were smoothed for 10 seconds.

(13) Productivity Evaluation was made by the number of breaks when slitting the central portion of the obtained film to a width of 1000 mm. The cutting blade used for slitting was used for cutting the conventional film, which is equivalent to the comparative example, and was removed after exceeding the specified amount of use, and then reassembled. It ran at 90% speed.
◯: The number of ruptures per day is 0.
Δ: The number of ruptures per day is 1.
x: The number of ruptures per day is 2 or more.

(14) Planarity Ion-exchanged water was dropped on a flat glass plate, and a film with a width of 1000 mm cut into a length of 2000 mm was placed on this and pasted with a roller so that the water layer was uniform. . The fluorescent lamp on the ceiling reflected on the film was observed from an oblique direction to evaluate the flatness.
◯: The reflected fluorescent lamp has little curvature, and the flatness is good.
Δ: Although the reflected fluorescent lamp is curved, it is acceptable.
x: The curvature of the reflected fluorescent lamp is large, and the planarity is poor.

・Polyester A (PET (A))
Polyethylene terephthalate/polyester B (PET (B)) with an intrinsic viscosity of 0.62 dl/g
A molten mixture of 10 parts by weight of an ultraviolet absorber (2,2′-(1,4-phenylene)bis(4H-3,1-benzoxazinone-4-one) and 90 parts by weight of PET (A).

(Preparation of adhesion-improving coating liquid)
A transesterification reaction and a polycondensation reaction were carried out by a conventional method to obtain 46 mol % of terephthalic acid, 46 mol % of isophthalic acid and 8 mol % of sodium 5-sulfonatoisophthalate as dicarboxylic acid components (relative to the total dicarboxylic acid components). A water-dispersible sulfonic acid metal base-containing copolymer polyester resin was prepared having a composition of 50 mol % ethylene glycol and 50 mol % neopentyl glycol as the glycol component (relative to the total glycol component). Next, 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 is heated and stirred, and when the temperature reaches 77°C, After adding 5 parts by mass of the water-dispersible sulfonic acid metal group-containing copolymer polyester resin and continuing to stir until the lumps of the resin disappear, the aqueous resin dispersion is cooled to room temperature and the solid content concentration is 5.0% by mass. A homogeneous water-dispersible copolyester resin liquid was obtained. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (manufactured by Fuji Silysia Co., Ltd., Silysia 310) in 50 parts by mass of water, Silysia 310 was added to 99.46 parts by mass of the water-dispersible copolymer polyester resin liquid. 0.54 parts by mass of the aqueous dispersion was added, and 20 parts by mass of water was added while stirring to obtain an adhesion-improving coating liquid.

(Polarizer)
A roll-shaped polyvinyl alcohol film with a thickness of 80 μm that was continuously dyed in an iodine aqueous solution was stretched 5 times in the conveying direction, treated in a boric acid solution, washed with water, and dried to obtain a long polarizer. .

(Polyester film A to H)
After drying under reduced pressure (1 Torr) at 135° C. for 6 hours, 90 parts by mass of PET (A) resin pellets containing no particles and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber as raw materials for the base film intermediate layer. , supplied to extruder 2 (for intermediate layer II layer), and PET (A) was dried by a conventional method, supplied to extruder 1 (for outer layer I layer and outer layer III), and melted at 285 ° C. . These two types of polymers are each filtered with a stainless sintered filter material (nominal filtration accuracy: 10 μm, 95% cut of particles), laminated in a two-type, three-layer confluence block, extruded in a sheet form from a nozzle, An unstretched film was produced by winding the film around a casting drum having a surface temperature of 30° C. and solidifying it by cooling using an electrostatic casting method. At this time, the discharge rate of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

This unstretched PET film was led to an MD stretching machine consisting of low speed rolls and high speed rolls. The film was heated to a preheating temperature with a plurality of low-speed rolls, further heated to a stretching temperature with an infrared heater between the low-speed rolls and the high-speed rolls, and stretched using the difference in peripheral speed between the low-speed rolls and the high-speed rolls.
Table 1 shows the preheating temperature, stretching temperature, and stretching ratio. The number of infrared heaters to be turned on is the number of the infrared heaters that are turned on for heating among the infrared heaters arranged in a plurality of rows in the MD direction.
Each roll of the MD stretching machine had a diameter of 180 to 250 mm, a surface chromium plating, and a roundness of 10 μm or less and a runout of 20 μm or less.

Subsequently, the adhesion-improving coating solution was applied to both surfaces of the MD-stretched film so that the coating amount after drying was 0.08 g/m ² and dried. The obtained film having the coating layer formed thereon was guided to a tenter stretching machine, and while holding the ends of the film with clips, it was guided to a tenter at 100° C. and stretched in the width direction. Next, while maintaining the stretched width in the width direction, the film was treated in a heat setting zone at 200° C. for 10 seconds, and further subjected to a relaxation treatment of 2% in the width direction to obtain a stretched PET film.

(Films I and J)
The above unstretched PET film was guided to an MD stretching machine, heated by a plurality of rolls, heated to a preheating temperature by the penultimate low-speed roll, and heated to a stretching temperature by a final low-speed roll. The film was stretched using the difference in peripheral speed between the high-speed rolls. The surface of the final low-speed roll and the nip roll installed on the final low-speed roll were treated with fluorine resin. After that, TD stretching and heat setting were performed in the same manner as above to obtain a stretched PET film.

Table 1 shows the film-forming conditions and characteristic values such as uneven thickness of these films. The light transmittance at a wavelength of 380 nm was in the range of 2.3 to 2.5% for all films except for Film H which was 8.5%.
As examples of graphs of the results of frequency analysis of thickness unevenness, the results of film A are shown in FIG. 1, and the results of film D are shown in FIG.

As is clear from Table 1, film A had large thickness unevenness, probably because the MD stretching temperature was low. , A/B, etc. also decreased. Comparing FIG. 1 (Film A) and FIG. 2 (Film D), it can be seen that Film A has a frequency of 0.25 Hz or less (period 10 cm or more) is larger.
On the other hand, when the MD stretching temperature was too high as in Film E, the thickness unevenness in the MD direction became large, probably because slackness and stretching positions became irregular. Moreover, the preheating temperature of the film F was high, and the film sometimes slackened during the preheating process and stuck to the roll, resulting in large thickness unevenness in the MD direction.
As in Films G and H, even if the MD draw ratio was increased, if the preheating and drawing temperatures were appropriate, the thickness unevenness in the MD direction was suppressed. Even in stretching with roll heating, thickness unevenness is large when the preheating temperature is too high and the stretching temperature is too low as in Film I, but the thickness unevenness can be reduced by optimizing the temperature. .
Films BD, EG, and J can be suitably used, for example, as polarizer protective films. Moreover, the film H can be suitably used as, for example, a transparent electrode substrate film, a scattering prevention film, and a screen surface protection film for a flexible image display device.

(Preparation of polarizing plate)
Among the polyester films produced in Examples, films C, D, and J, which had particularly good unevenness in thickness, were used to produce polarizing plates as follows.
A polarizing plate was produced by laminating the polyester film prepared above on one side of a polarizer and a triacetyl cellulose film (40 μm in thickness) on the opposite side by roll-to-roll. An ultraviolet curable adhesive was used for bonding. In both cases, the angle between the slow axis of the polyester film and the absorption axis of the polarizer was 90 degrees, and the deviation was 0.5 degrees or less.

(Evaluation of image display device)
The resulting polarizing plate was cut and replaced with a viewing side polarizing plate of a commercially available 42-inch liquid crystal television. All of the polarizing plates had good visibility with no iridescence observed even when viewed from an oblique direction.

The present invention can provide a polyester film that has high in-plane retardation, is excellent in thickness uniformity, and has good productivity, workability, and flatness. The polyester film has good visibility with inconspicuous iridescence regardless of the type of image display device and the type of light source, and is suitably used for various applications of the image display device.

Claims

In-plane retardation is 3000 nm or more and 30000 nm or less,
The degree of plane orientation is 0.128 or more and 0.155 or less,
A polyester film having thickness unevenness in the flow direction of film formation of 8% or less (the thickness unevenness is a value obtained by (maximum thickness−minimum thickness)/average thickness×100(%)).
2. The method according to claim 1, wherein A/B, which is the ratio of A and B below, is 5 or less when Fourier transform is performed on the thickness measurement data in the flow direction of film formation and the frequency is replaced with the period of the length of the film. polyester film.
A: Average value of the top 5 amplitude values with a period of 10 cm or more B: Average value of the top 5 amplitude values with a period of 10 cm or less
3. The ratio of Amax and B described below, Amax/B, is 7 or less when Fourier transform is performed on the thickness measurement data in the film production flow direction and the frequency is replaced with the period of the length of the film. polyester film.
Amax: The maximum value of amplitude at a period of 10 cm or more
4. The polyester film according to any one of claims 1 to 3, which has a NZ coefficient of 1.65 or more and 3 or less.
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.
The polyester film according to any one of claims 1 to 5, which has a breaking elongation of 4% or more in the direction of film production.
7. The polyester film according to any one of claims 1 to 6, which has a breaking strength of 50 MPa or more in the film-forming flow direction.
A polarizer protective film comprising the polyester film according to any one of claims 1 to 7.
A polarizing plate in which the polarizer protective film according to claim 8 and a polarizer are laminated.
An image display device in which the polarizing plate according to claim 9 is installed on the viewing side of an image display cell.
A transparent electrode substrate film comprising the polyester film according to any one of claims 1 to 7.
A shatterproof film made of the polyester film according to any one of claims 1 to 7.
A screen surface protective film comprising the polyester film according to any one of claims 1 to 7.
An image display device comprising any one of the transparent electrode substrate 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, which is a flexible image display device.