Polyester film and image display device using the same

Abstract

This invention provides a polyester film that exhibits high in-plane retardation while maintaining excellent thickness uniformity, resulting in good productivity, workability, and flatness. [Solution] A polyester film is disclosed having an in-plane retardation of 3000 nm to 30000 nm, a plane orientation degree of 0.128 to 0.155, and a thickness variation in the film formation flow direction of 8% or less (the thickness variation is calculated as (maximum thickness - minimum thickness) / average thickness × 100 (%)).

Description

Technical Field

[0001] The present invention relates to a polyester film (for example, a polyester film for optical use). Typically, the present invention relates to a polyester film suitably used for each member of an image display device such as a polarizer protection film, a base film (for example, a transparent electrode base film) such as a touch panel, an anti-scattering film, and a screen surface protection film.

Background Art

[0002] 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 when used in a portion where polarized light passes, an iridescent color unevenness (iridescence) occurs. On the other hand, there are known techniques for eliminating blackout and iridescence when observing an image with polarized sunglasses by providing a high retardation polyester film on the surface of a liquid crystal display device (for example, Patent Document 1), a technique for eliminating iridescence by using it as a polarizer protection film (for example, Patent Document 2), and a technique for using it in combination as a touch panel base material or an anti-scattering film (for example, Patent Document 3). When stretching in only one direction to obtain a high retardation film, the strength and elongation in the direction perpendicular to the stretching direction decrease, so breakage is likely to occur during film formation or processing of the obtained film, and productivity and workability may decrease. Also, by stretching at a low magnification in the direction perpendicular to the main stretching direction first 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 and to secure the required retardation while increasing the production speed. However, when stretching is also performed in the direction perpendicular to the main stretching direction, thickness unevenness may occur and the flatness may deteriorate. A known technique involves stretching the material in the longitudinal direction (MD) by 2.0 times or less, preferably 1.3 times or less, and then stretching it in the width direction (TD) by 4.15 times or more, thereby adjusting the ratio of the longitudinal tensile strength to the width tensile strength to 0.25 to 0.6, and improving the tensile strength and elastic modulus in the MD direction (for example, Patent Document 4). However, this technique still suffers from the problem of poor thickness uniformity and flatness. Furthermore, it has been proposed to use a film that has been stretched 1.0 to 3.4 times in the longitudinal direction (MD) and then 2.5 to 5.0 times in the width direction (TD) as the film for a foldable image display device, with the MD direction as the folding direction (for example, Patent Documents 5 and 6). However, even with this technology, there is still room for improvement in thickness uniformity and flatness. When there is significant thickness variation in the MD direction, the film is prone to breaking not only during deposition but also during slitting. This is especially true when the cutting blade is worn or at high speeds, which tends to reduce productivity and work efficiency. [Prior art documents] [Patent Documents]

[0003] [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 / 159285 [Patent Document 6] International Publication No. 2020 / 162119 [Overview of the project] [Problems that the invention aims to solve]

[0004] 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 various applications of image display devices, has good visibility with less noticeable iridescence, regardless of the type of image display device or light source. [Means for solving the problem]

[0005] The inventors diligently studied and conducted research to achieve this objective, resulting in the completion of the present invention. The present invention encompasses the following aspects. Section 1: In-plane retardation is between 3000nm and 30000nm. The degree of plane orientation is 0.128 or more and 0.155 or less, Thickness variation in the film formation flow direction is 8% or less. This is a polyester film (note that the thickness variation is calculated as (maximum thickness - minimum thickness) / average thickness × 100 (%)).

[0006] Section 2: The polyester film described in item 1, wherein when the thickness measurement data in the film formation flow direction is Fourier transformed and the frequency is replaced with the period of the film length, the ratio A / B, which is the ratio of A to B below, is 5 or less. A: The average amplitude of the top 5 amplitude values ​​for periods of 10 cm or more. B: The average amplitude of the top 5 amplitude values ​​for periods of 10 cm or less.

[0007] Section 3: The polyester film according to item 1 or 2, wherein when the thickness measurement data in the film formation flow direction is Fourier transformed and the frequency is replaced with the period of the film length, the ratio of Amax to B, Amax / B, is 7 or less. Amax: Maximum amplitude for periods of 10 cm or more.

[0008] Section 4: The polyester film according to any one of Items 1 to 3, wherein the NZ coefficient is 1.65 or more and 3 or less.

[0009] Item 5: The polyester film according to any one of Items 1 to 4, wherein the thickness is 25 μm or more and 150 μm or less.

[0010] 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.

[0011] 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 50 MPa or more.

[0012] Item 8: A polarizer protection film made of the polyester film according to any one of Items 1 to 7.

[0013] Item 9: A polarizing plate in which the polarizer protection film according to Item 8 and a polarizer are laminated.

[0014] 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.

[0015] Item 11: A transparent electrode substrate film made of the polyester film according to any one of Items 1 to 7.

[0016] Item 12: A scattering prevention film made of the polyester film according to any one of Items 1 to 7.

[0017] Item 13: A screen surface protection film made of the polyester film according to any one of Items 1 to 7.

[0018] Item 14: An image display device comprising any of the transparent electrode substrate film described in item 11, the shatterproof film described in item 12, and the screen surface protective film described in item 13.

[0019] Section 15: The image display device described in item 14, which is a flexible image display device. [Effects of the Invention]

[0020] The present invention provides a polyester film that exhibits high in-plane retardation while also having excellent thickness uniformity, productivity, workability, and flatness. Furthermore, because iridescence can be suppressed, the polyester film of the present invention is suitably used in polarizer protective films, transparent electrode substrate films for touch panels, shatterproof films, screen surface protective films for image display devices, and other applications, and when used in flexible image display devices, it has excellent bending durability. [Brief explanation of the drawing]

[0021] [Figure 1] This graph shows the results of the frequency analysis of thickness variations in the film formation flow direction for film A. [Figure 2] This graph shows the results of the frequency analysis of thickness variations in the film formation flow direction for film D. [Modes for carrying out the invention]

[0022] Suitable examples of the polyester film of the present invention include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polytetramethylene terephthalate (PBT), and polyethylene naphthalate (PEN), which have the advantage of allowing for large in-plane retardation and having low moisture permeability and hygroscopicity, with PET or PEN being preferred among them. These polyesters may have copolymerized carboxylic acid components and / or glycol components other than the main constituent components, but when the total amount of carboxylic acid components and / or glycol components is set to 100 mol%, the total amount of carboxylic acid components and / or glycol components other than the main constituent components is preferably 10 mol% or less, more preferably 5 mol% or less, and particularly preferably 2 mol% or less.

[0023] 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. In the case of PET, the IV is preferably 0.5 dL / g or more and 1.5 dL / g or less. The lower limit of the IV is more preferably 0.53 dL / g, and even more preferably 0.55 L / g. The upper limit of the IV is more preferably 1.2 dL / g, even more preferably 1 dL / g, and particularly preferably 0.8 dL / g. In the case of PEN, the lower limit of IV is preferably 0.45 dL / g, more preferably 0.48 dL / g, even 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, even more preferably 0.75 dL / g, and particularly preferably 0.7 dL / g. By setting the range as described above, the resulting film has superior mechanical strength, such as impact resistance, making it easier to manufacture a more stable film. Furthermore, it is possible to efficiently produce a film with less thickness variation without placing a heavy load on the equipment.

[0024] In this invention, the lower limit of the in-plane retardation (Re) of the polyester film is preferably 3000 nm, more preferably 4000 nm, even more preferably 4300 nm, particularly preferably 4500 nm, and most preferably 5000 nm. By setting it above the above lower limit, iridescence can be suppressed. The upper limit of Re is preferably 30,000 nm, more preferably 15,000 nm, even more preferably 12,000 nm, particularly preferably 10,000 nm, and most preferably 9,500 nm. By keeping it below the above upper limit, the film does not need to be made thicker than necessary, making it easier to accommodate the thinning of image display devices and the like. Furthermore, in order to widen the angle at which iridescence is suppressed when viewed from an oblique direction, Re is preferably 5500nm or higher, more preferably 6000nm or higher, even more preferably 6000nm or higher, and particularly preferably 6500nm or higher. When a thin film is preferred even if the viewing angle is somewhat narrow, such as in shatterproof films, substrate films for touch panels (e.g., transparent electrode substrate films), screen surface protection films, and foldable films (e.g., PET films), Re is more preferably 7000nm or lower, even more preferably 6500nm or lower, and particularly preferably 6000nm or lower.

[0025] The polyester film of the present invention preferably has a lower limit of plane orientation degree (ΔP) of 0.128, more preferably 0.129, even more preferably 0.13, and particularly preferably greater than 0.13. The upper limit of the plane orientation degree is preferably 0.155, more preferably 0.152, and even more preferably 0.15. By setting the plane orientation degree within the above range, it is possible to further improve film formation stability, such as suppressing iridescence while making the film less prone to breakage. When used as a polarizer protective film, and when it is desired to more effectively control iridescence from oblique directions, the upper limit of the plane orientation degree is more preferably 0.145, even more preferably 0.14, particularly preferably 0.138, and most preferably 0.136. When it is desired to provide excellent bending resistance, such as when used in a flexible image display device, the lower limit of the degree of surface orientation (ΔP) is more preferably 0.135, even more preferably 0.138, and particularly preferably 0.14. The degree of surface orientation is calculated as (nx+ny) / 2-nz, where ny is the refractive index in the slow axis direction, nx is the refractive index in the fast axis direction (perpendicular to the slow axis direction), and nz is the refractive index in the thickness direction.

[0026] The polyester film of the present invention preferably has a lower limit of the NZ coefficient of 1.65, more preferably 1.68, even more preferably 1.7, and 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 range as described above, it is possible to further improve film formation stability, such as suppressing iridescence while reducing the likelihood of breakage. When used as a polarizer protective film, and when it is desired to more effectively control iridescence from oblique directions, the upper limit of the NZ coefficient is more preferably 1.9, even more preferably 1.85, and particularly preferably 1.8. When it is desired to provide excellent bending resistance, such as when used in a flexible image display device, the lower limit of the NZ coefficient is more preferably 1.8, even more preferably 1.85, and particularly preferably 1.9. The NZ coefficient is a value calculated using the formula NZ = |ny - nz| / |ny - nx|.

[0027] By setting the plane orientation degree and NZ coefficient within the above range, it is possible to ensure adhesion to functional layers such as hard coat layers, anti-reflective layers, and anti-glare layers, as well as adhesion when bonded to polarizers, etc.

[0028] The lower limit of the thickness of the polyester film of the present invention is preferably 25 μm, and more preferably in the order of 30 μm, 40 μm, 45 μm, 50 μm, and 55 μm. The upper limit of the thickness is preferably 150 μm, and more preferably in the order of 130 μm, 100 μm, 90 μm, and 85 μm. In this specification, "in order of preference" means that values ​​within a narrower range are preferred. If the thickness is below the above upper limit, when the unstretched film is heated, the thickness of the unstretched film also decreases, making it easier to raise the temperature uniformly in the thickness direction of the film in a short time, and thus easier to suppress thickness variations. In addition, it becomes easier to accommodate the thinning of image display devices. For polarizer protective films, a thickness of 40 to 85 μm is preferred. For shatterproof films, base films for touch panels (e.g., transparent electrode base films), or screen surface protective films for flexible image display devices, a thickness of 25 to 70 μm is preferred. For screen surface protective films for non-flexible image display devices, a thickness of 60 to 150 μm is preferred. The thickness can be calculated, for example, by continuously measuring the thickness of a film of a predetermined size (e.g., approximately 50 mm wide and 6 m long) using a contact-type continuous thickness gauge at a predetermined speed (e.g., 1.5 m / min in the MD direction) and at predetermined intervals (e.g., 0.1-second intervals), and then arbitrarily selecting a predetermined number of data points (e.g., 2048 points continuously) from the obtained data and calculating the average of these points.

[0029] The upper limit of the thickness variation in the film formation flow direction of the polyester film of the present invention (hereinafter referred to as the longitudinal direction, MD direction, or the direction perpendicular to the main stretching direction in the case of stretching) is preferably 8%, more preferably 7%, even more preferably 6%, particularly preferably 5%, and most preferably 4%. While a low thickness variation in the MD direction is preferable, in practical terms, the lower limit is preferably 0.1%, and more preferably 0.5%. Note that the thickness variation in the following thickness measurement is calculated as (maximum thickness - minimum thickness) / average thickness × 100 (%).

[0030] In the present invention, data obtained by measuring the thickness of the film in the MD direction is subjected to a Fourier transform (e.g., Fast Fourier Transform), and the obtained results are analyzed in terms of the length period in the MD direction of the film (specifically, the frequency is replaced with the length period). When A is the average of the top 5 points in amplitude magnitude with a period of 10 cm or more, and B is the average of the top 5 points in amplitude magnitude with a period of less than 10 cm, the lower limit of A / B is preferably 0.5, more preferably 1, even 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.

[0031] In the above, when the period is 10 cm or more and the maximum amplitude is Amax, the lower limit of Amax / B is preferably 0.7, more preferably 1.4, even more preferably 1.8, particularly preferably 2, and most preferably 2.2. The upper limit of Amax / B is 7, more preferably 6, even 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 even with liquid crystal display devices using light sources with steep peaks, color unevenness can be made less noticeable.

[0032] Furthermore, it is preferable to calculate A, Amax, and B using the following specific methods. The film is captured at a speed of 1.5 m / min, continuously capturing the thickness of the central part at 0.1-second intervals. The obtained data is used sequentially for 2048 points (length 5.12m) to perform frequency analysis using the Fast Fourier Transform. The frequency of the obtained analysis data is converted to a period, and the amplitude is also determined. From among the points with a period of 10 cm or more, select the five points with the largest amplitude and set their average value as A. The value with the largest amplitude among these five points is set as Amax. From among the points with a period length of less than 10 cm, select the five points with the largest amplitudes and set their average value as B. Note that the latter half of the frequency analysis data, known as ghost data, will be ignored, and only the first half of the analysis data will be used.

[0033] According to the inventors' studies, when stretching in the MD direction is not performed, thickness variations in the MD direction are often caused by the wobble of the electrodes used when electrostatically adhering the molten resin to the cooling roll or by vibration of the equipment, by the effect of the roundness or wobble of the cooling roll during casting, or by the automatic adjustment of the die lip spacing. For example, thickness variations caused by electrode wobble or equipment vibration often have a period of a few centimeters or less. However, when stretching weakly in the MD direction, even if these are adjusted, thickness variations cannot be sufficiently suppressed, and thickness variations with periods of several tens of centimeters to several meters become prominent, leading to problems caused by thickness variations.

[0034] Further investigations by the inventors revealed that when stretching weakly in the MD direction, it is necessary to control the preheating temperature and stretching temperature within an appropriate range. If the temperature is outside the appropriate range, phenomena such as uneven stretching, inconsistent stretching position and unstable stretching occur, film slack occurs, and the film does not peel smoothly from the roll occur. This results in noticeable thickness variations ranging from tens of centimeters to several meters, and also poor flatness.

[0035] The following describes the preferred film-forming conditions for obtaining the polyester film of the present invention.

[0036] First, the polyester resin (typically PET) is dried and then fed into an extruder, melted at 260-300°C, and extruded from the die onto a cooling roll in a sheet form to obtain an unstretched film. At this time, it is preferable to apply an electric charge to the resin, blow air onto it, or reduce the pressure in a chamber so that the resin adheres quickly to the cooling roll. At this time, it is preferable to adjust the tension and fixing method of the wire electrodes and band electrodes to reduce electrode vibration, to control the airflow and pressure reduction to be stable, and to ensure that the casting equipment is less susceptible to the effects of mechanical vibrations such as motors.

[0037] Next, the unstretched film is preheated and its temperature is increased, and finally, tension is applied in the MD direction to stretch it. In this case, the unstretched film is heated in multiple stages, but the highest temperature reached on the film surface during the heating stage before the stretching stage is called the preheating temperature, and the highest temperature reached on the film surface during stretching is called the stretching temperature, and these will be explained separately. To explain with a specific example, in MD stretching, the film is heated by multiple low-speed rolls and then stretched by the difference in peripheral speed between these and subsequent high-speed rolls. In this case, methods for bringing the film surface to the final stretching temperature include heating with the final roll of the low-speed rolls (hereinafter sometimes simply referred to as the "final roll") or heating with an infrared heater (IR heater).

[0038] When heating is done on the final roll, the temperature at which the film separates from the final roll becomes the stretching temperature, and the temperature at which the film separates from the slow roll (heating roll) just before the final roll becomes the preheating temperature. When heating with an IR heater, the highest temperature in the region heated by the IR heater becomes the stretching temperature, and the temperature at which the film separates from the final roll (heating roll) becomes the preheating temperature.

[0039] 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 at a high film formation rate, enabling stable stretching. The preheating temperature for MD stretching is preferably 95°C or lower, more preferably 90°C or lower, even 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, adhesion between the film and the rolls is suppressed, enabling stable film movement. Furthermore, slack in the film between the preheating rolls is suppressed, and the tension between the preheating rolls can be reduced, thereby reducing unnecessary film elongation during the preheating process and suppressing thickness unevenness and a decrease in flatness. Film slack is more likely to occur when the molecular weight of the polyester is low (when the IV is low), and for example, if the IV is 0.7 dl / g or less, it is preferable to set the temperature to 90°C or lower, and if the IV is 0.65 dl / g or less, it is preferable to set the temperature to 85°C or lower.

[0040] The stretching temperature for MD stretching is preferably 86°C or higher, more preferably 88°C or higher, even more preferably 89°C or higher, particularly preferably 90°C or higher, and most preferably 91°C or higher. If the stretching temperature is low, the stress-strain (SS) properties of the unstretched film may not show a gradual increase in stress with respect to strain, resulting in unstable stretching.

[0041] The stretching temperature for MD stretching is preferably 110°C or lower, and more preferably in the order of 105°C or lower, 102°C or lower, 100°C or lower, 98°C or lower, and 96°C or lower. By setting the stretching temperature within the above range, the film does not become too soft, and sagging during stretching can be suppressed. In particular, when tension is applied, the film tends to stretch from the high 80°C range, but if the stretching temperature is within the above range, stretching outside the intended position can be suppressed, and the stretching can be stabilized. Also, as mentioned above, the lower the molecular weight, the more easily it sags, so for example, if the IV is 0.7 dl / g or lower, it is preferable to set the temperature to 100°C or lower, and if the IV is 0.65 dl / g or lower, it is preferable to set the temperature to 98°C or lower.

[0042] In MD stretching, the difference between the stretching temperature and the preheating temperature is preferably 11°C or more, more preferably 12°C or more, and even more preferably 13°C or more. Furthermore, the difference between the stretching temperature and the preheating temperature is preferably 24°C or less, more preferably 23°C or less, and even more preferably 22°C or less. By setting the temperature within the above range, it is possible to suppress pseudo-stretching during preheating and film adhesion to the roll, while minimizing the temperature difference in the thickness direction of the film during stretching, even at high film formation speeds, thus enabling stable stretching.

[0043] In MD stretching, as described above, it is necessary to quickly raise the film temperature from the preheating temperature to the stretching temperature. However, if the film is heated too rapidly, the temperature difference in the thickness direction of the film will become large, which may make stable stretching difficult. Therefore, when heating with the final roll, it is preferable to increase the angle at which the film is held by the final roll to increase the contact time between the final heating roll and the film. The angle at which the film is held is preferably 30 degrees or more, more preferably 45 degrees or more, even more preferably 60 degrees or more, and particularly preferably 70 degrees or more. Furthermore, if an IR heater is used, it is preferable to install multiple heaters in the MD direction or to use a heater with a wide width in the MD direction.

[0044] The rolls used in the preheating process and the rolls used in the stretching process may be rolls with a plated surface such as chrome plating, nickel plating, or cobalt alloy plating. If the roll surface becomes hot and the polyester resin adheres to it, it is preferable to use rolls that have been treated with fluororesin.

[0045] It is also important to improve the accuracy of the roundness and runout 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, and even more preferably 10 μm or less, and is usually 0.1 μm or more. The runout is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less, and is usually 0.1 μm or more. The diameter of the roll depends on the size of the stretching machine, but for producing films with an unstretched film width of about 700 to 2500 mm, it is preferably 100 to 500 mm, more preferably 150 to 400 mm, and even more preferably 170 to 350 mm.

[0046] The lower limit of the MD stretching ratio is preferably 1.05 times, more preferably 1.08 times, and even more preferably 1.1 times. The upper limit of the MD stretching ratio is preferably 2 times, more preferably 1.8 times, and even more preferably 1.7 times. By setting the ratio within the above range, it is possible to obtain a film with even better workability and suppression of iridescence. Furthermore, when used as a polarizer protective film, and when it is desired to more effectively control iridescence from oblique directions, the upper limit of the MD stretching ratio is more preferably 1.25 times, even more preferably 1.2 times, and particularly preferably 1.18 times. When it is desired to provide excellent bending resistance, such as when used in a flexible image display device, the lower limit of the MD stretching ratio is more preferably 1.2 times, even more preferably 1.25 times, and particularly preferably 1.3 times.

[0047] In the present invention, the upper limit of thickness variation in the direction perpendicular to the film formation flow direction (TD direction) is preferably 5%, more preferably 4%, even more preferably 3.5%, and particularly preferably 3%. A lower thickness variation in the TD direction is preferable, but in practical terms, the lower limit is preferably 0.1%, and even more preferably 0.5%. Thickness variations in the TD direction can be achieved, for example, by controlling the lip spacing during casting, reducing variations in film temperature in the TD direction during TD stretching, and setting the degree of surface orientation and NZ coefficient within appropriate ranges.

[0048] In TD stretching, the film after MD stretching is preheated and stretched at a temperature of preferably 80-130°C, more preferably 90-120°C. The stretching ratio for TD stretching is preferably 3-6.5 times, more preferably 3.2-6.2 times, even more preferably 3.5-6.0 times, and particularly preferably 3.7-5.8 times.

[0049] It is preferable to perform heat setting following stretching. The heat setting temperature is preferably 150 to 250°C, and more preferably 170 to 230°C. The heat setting time is preferably 3 to 60 seconds, and more preferably 5 to 30 seconds. In thermal setting, it is also preferable to perform a relaxation treatment in the main stretching direction and / or in a direction perpendicular thereto. The relaxation treatment is preferably 0.5 to 10%, and more preferably 1 to 5%.

[0050] The lower limit of the elongation at break in the MD direction of the polyester film of the present invention is preferably 4%, and more preferably in the order of 5%, 6%, 7%, 8%, 9%, and 10%. The upper limit of the elongation at break in the MD direction is preferably 50%, more preferably 40%, even more preferably 30%, particularly preferably 25%, and most preferably 20%.

[0051] 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%, even more preferably 120%, and particularly preferably 100%.

[0052] 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, even 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.

[0053] 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, and even more preferably 350 MPa. The upper limit of the fracture strength in the TD direction is preferably 500 MPa, more preferably 450 MPa, even more preferably 420 MPa, and particularly preferably 400 MPa. By keeping the elongation at break and tensile strength within the above range, the film becomes even more workable. The elongation at break and tensile strength are values ​​measured in accordance with JIS K 7113.

[0054] The heat shrinkage rate of the polyester film of the present invention at 150°C is preferably -0.5% at the lower limit, more preferably -0.1% in both the MD and TD directions. The heat shrinkage rate at 150°C is preferably 3% at the upper limit, more preferably 2.7% in both the MD and TD directions, even more preferably 2.5%, and particularly preferably 2%.

[0055] The polyester film of the present invention preferably has a light transmittance of 20% or less at a wavelength of 380 nm. More preferably, the light transmittance at a wavelength of 380 nm is 15% or less, even more preferably 10% or less, and particularly preferably 5% or less. If the light transmittance is 20% or less, the deterioration of iodine and dichroic dyes in the polarizing layer due to ultraviolet light can be suppressed. The light transmittance is measured perpendicular to the plane of the film and can be measured using a spectrophotometer (for example, Hitachi U-3500). When used as a polarizer protective film, a low ultraviolet light transmittance is particularly preferable.

[0056] The light transmittance of the polyester film of the present invention at a wavelength of 380 nm can be reduced to 20% or less by, for example, adding an ultraviolet absorber to the film, applying a coating solution containing an ultraviolet absorber to the film surface, or appropriately adjusting the type, concentration, and thickness of the ultraviolet absorber. The ultraviolet absorber is a known substance. Examples of ultraviolet absorbers include organic ultraviolet absorbers and inorganic ultraviolet absorbers, but organic ultraviolet absorbers are preferred from the viewpoint of transparency.

[0057] Examples of organic UV absorbers include benzotriazole-based, benzophenone-based, cyclic iminoester-based, and combinations thereof, but are not particularly limited as long as they fall within the desired absorbance range.

[0058] Furthermore, it is preferable to add particles with an average particle size of 0.05 to 2 μm to the polyester film of the present invention in order to improve its slipperiness. Examples of particles include inorganic particles such as titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, and calcium fluoride, as well as organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. These particles may be added to the entire film, or they may be added only to the skin layer in a co-extruded multilayer skin-core structure. Alternatively, the film itself may not contain particles, and the particles may be added to the easy-adhesion layer described later.

[0059] The polyester film of the present invention may be subjected to treatments that improve adhesion, such as corona treatment, flame treatment, or plasma treatment.

[0060] (Easy adhesion layer) The polyester film of the present invention may be provided with an easy-adhesion layer to improve adhesion with adhesives, coating layers, etc. The resin used in the easy-adhesion layer can be polyester resin, polyurethane resin, polycarbonate resin, or acrylic resin, with polyester resin, polyester polyurethane resin, polycarbonate polyurethane resin, or acrylic resin being preferred. The easy-adhesion layer is preferably crosslinked. Examples of crosslinking agents include isocyanate compounds, melamine compounds, epoxy resins, and oxazoline compounds. Adding a water-soluble resin such as polyvinyl alcohol to the easy-adhesion layer is also a useful method for improving adhesion to the polarizer.

[0061] The easy-adhesion layer can be formed by applying and drying a water-based coating containing these resins and, if necessary, crosslinking agents, particles, etc., onto the film. Examples of particles include those used in the aforementioned substrates. The easy-adhesion layer may be applied offline to the film (e.g., a stretched film), but it is preferable to apply it in-line during the film-making process. When applied in-line, it may be applied before longitudinal stretching (MD stretching) or transverse stretching (TD stretching), but it is preferable to apply it immediately before transverse stretching and dry and crosslink it in a preheating, heating, and heat treatment process using a tenter. If in-line coating is applied immediately before longitudinal stretching by rolls, it is preferable to dry the coating in a vertical dryer before guiding it to the stretching rolls. The coating amount of the easy-adhesion layer (coating amount after drying) is 0.01 to 1.0 g / m². 2 Preferably, 0.03~0.5g / m 2 It is preferable.

[0062] (Functional layer) In the present invention, the polyester film may also preferably be provided with functional layers such as a hard coat layer, an anti-reflective layer, a low-reflective layer, an anti-glare layer, and an anti-static layer. The anti-reflective layer, low-reflective layer, and anti-glare layer are collectively referred to as the reflection reduction layer. The reflection reduction layer not only prevents external light from reflecting onto the display screen and making it difficult to see, but also suppresses reflection at the interface, reducing iridescence and making it less noticeable. Furthermore, when used as a base film for touch panels (for example, a transparent electrode base film), it is also preferable to provide a refractive index adjustment layer to make the transparent electrode layer less noticeable. In a polyester film provided with functional layers, the film in the state before the functional layers are provided is called the base film. The base film may also include the above-mentioned easy-adhesion layer.

[0063] The upper limit of the reflectance of the polyester film, measured from the anti-reflective layer side, is preferably 5%, more preferably 4%, even more preferably 3%, particularly preferably 2%, and most preferably 1.5%. Below the above upper limit, the reflection of ambient light can be reduced, and the visibility of the screen can be improved. The lower limit of the reflectance is preferably not particularly defined, but from a practical standpoint, it is preferably 0.01%, and even more preferably 0.1%. There are various types of anti-reflective layers, including low-reflection layers, anti-reflective layers, and anti-glare layers.

[0064] (Low reflective layer) A low-reflectance layer is a layer that reduces reflectivity by minimizing the refractive index difference with air, achieved by providing a low-refractive-index layer on the surface of the base film.

[0065] (Anti-reflection layer) The anti-reflective layer is a layer that controls reflection by interfering with reflected light at the interface by controlling the thickness of the low refractive index layer. Preferably, the thickness of the low refractive index layer is approximately the wavelength of visible light (400-700 mN) / (refractive index of the low refractive index layer × 4). It is also preferable to provide a high refractive index layer between the anti-reflective layer and the base film. Two or more low refractive index layers and / or high refractive index layers may be provided to further enhance the anti-reflective effect through multiple interference. The high refractive index layer and the low refractive index layer together are sometimes referred to as the anti-reflective layer.

[0066] In the case of an anti-reflective layer, the upper limit of the reflectance is preferably 2%, more preferably 1.5%, even more preferably 1.2%, and particularly preferably 1%.

[0067] (Low refractive index layer) The refractive index of the low refractive index layer is preferably 1.45 or less, and more preferably 1.42 or less. Furthermore, the refractive index of the low refractive index layer is preferably 1.2 or more, and more preferably 1.25 or more. Note that the refractive index of the low refractive index layer is the value measured under the condition of a wavelength of 589 nm.

[0068] The thickness of the low refractive index layer is not limited, but it can usually be set appropriately within the range of approximately 30 nm to 1 μm. When used as an anti-reflective layer, the thickness of the low refractive index layer is preferably 70 to 120 nm, and more preferably 75 to 110 nm.

[0069] Examples of low refractive index layers include (1) a layer made of a resin composition containing a binder resin and low refractive index particles, (2) a layer made of a fluororesin which is a low refractive index resin, (3) a layer made of a fluororesin composition containing silica or magnesium fluoride, and (4) a thin film of a low refractive index substance such as silica or magnesium fluoride.

[0070] The binder resin contained in the resin composition of (1) can be polyester, polyurethane, polyamide, polycarbonate, acrylic, etc., without any particular limitations. Among these, acrylic is preferred, and it is preferable that it is obtained by polymerizing (crosslinking) a photopolymerizable compound by light irradiation.

[0071] Examples of photopolymerizable compounds include photopolymerizable monomers, photopolymerizable oligomers, and photopolymerizable polymers, which can be used after being appropriately adjusted. A combination of a photopolymerizable monomer and a photopolymerizable oligomer or photopolymer is preferred as the photopolymerizable compound. These photopolymerizable monomers, photopolymerizable oligomers, and photopolymerizable polymers are preferably polyfunctional.

[0072] Examples of polyfunctional monomers include pentaerythritol triacrylate (PETA), dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate (PETTA), and dipentaerythritol pentaacrylate (DPPA). Monofunctional monomers may also be used in combination to adjust coating viscosity and hardness.

[0073] Examples of polyfunctional oligomers include polyester (meth)acrylate, urethane (meth)acrylate, polyester-urethane (meth)acrylate, polyether (meth)acrylate, polyol (meth)acrylate, melamine (meth)acrylate, isocyanurate (meth)acrylate, epoxy (meth)acrylate, and the like.

[0074] Examples of polyfunctional polymers include urethane (meth)acrylate, isocyanurate (meth)acrylate, polyester-urethane (meth)acrylate, and epoxy (meth)acrylate.

[0075] The resin composition of (1) may also contain, in addition to the above components, a polymerization initiator, a crosslinking catalyst, a polymerization inhibitor, an antioxidant, an ultraviolet absorber, a leveling agent, a surfactant, and the like.

[0076] Examples of low refractive index particles included in the resin composition of (1) include silica particles (e.g., hollow silica particles) and magnesium fluoride particles, with hollow silica particles being preferred. Such hollow silica particles can be produced, for example, by the manufacturing method described in the examples of Japanese Patent Application Publication No. 2005-099778.

[0077] The average particle diameter of the primary particles of the low refractive index particles is preferably 5 to 200 nm, more preferably 5 to 100 nm, and even more preferably 10 to 80 nm. Low refractive index particles are more preferably surface-treated with a silane coupling agent, and among these, those surface-treated with a silane coupling agent having a (meth)acryloyl group are preferred.

[0078] The content of 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, even 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, per 100 parts by mass of binder resin.

[0079] (2) As the fluororesin, a polymerizable compound or polymer thereof containing at least a fluorine atom in its molecule can be used. The polymerizable compound is not particularly limited, but those having curing reactive groups such as photopolymerizable functional groups and thermosetting polar groups are preferred. Compounds having multiple curing reactive groups simultaneously are also acceptable. The polymer of this polymerizable compound does not have the above-mentioned curing reactive groups, etc.

[0080] As compounds having photopolymerizable functional groups, for example, fluorine-containing monomers having ethylenically unsaturated bonds can be widely used.

[0081] To improve fingerprint resistance, it is also preferable to appropriately add known polysiloxane-based or fluorine-based antifouling agents to the low refractive index layer.

[0082] The surface of the low refractive index layer may be uneven to provide anti-glare properties, but a smooth surface is also preferable. When the surface of the low refractive index layer is smooth, 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, even more preferably 10 nm or less, and particularly preferably 1 to 8 nm. Furthermore, the ten-point mean roughness Rz (JIS B0601:1994) of the surface of the low refractive index layer is preferably 160 nm or less, and more preferably 50 to 155 nm.

[0083] (High refractive index layer) The refractive index of the high refractive index layer is preferably 1.55 to 1.85, and more preferably 1.56 to 1.7. Note that the refractive index of the high refractive index layer is the value measured under the condition of a wavelength of 589 nm.

[0084] The thickness of the high refractive index layer is preferably 30 to 200 nm, and more preferably 50 to 180 nm. The high refractive index layer may consist of multiple layers, but two or fewer layers are preferred, and a single layer is more preferred. In the case of multiple layers, it is preferable that the sum of the thicknesses of the multiple layers is within the above range.

[0085] When there are two high refractive index layers, it is preferable to make the refractive index of the high refractive index layer on the low refractive index layer side higher. 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.

[0086] The high refractive index layer is preferably composed of a resin composition containing high refractive index particles and resin. Preferred high refractive index particles include 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, and zirconium oxide particles. Among these, titanium oxide particles and zirconium oxide particles are particularly preferred.

[0087] Two or more types of high refractive index particles may be used in combination. In particular, adding a first high refractive index particle and a second high refractive index particle with a lower surface charge is preferable to prevent aggregation.

[0088] Resins used in the high refractive index layer include the same resins as those used in the low refractive index layer, with the exception of fluororesins.

[0089] In order to make the low refractive index layer, which is provided on top of the high refractive index layer, flat, it is preferable that the surface of the high refractive index layer is also flat. The method for making the surface of the low refractive index layer flat described above is used as a method for making the surface of the high refractive index layer flat.

[0090] The average particle diameter 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, and even more preferably 10 to 80 nm. These particles are more preferably surface-treated, more preferably surface-treated with a silane coupling agent, and most preferably surface-treated with a silane coupling agent having a (meth)acryloyl group.

[0091] The content of 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, even 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, per 100 parts by mass of binder resin.

[0092] High refractive index layers and low refractive index layers can be formed, for example, by applying a resin composition containing a photopolymerizable compound to a base film, drying it, and then irradiating the resin composition in the form of a coating with light such as ultraviolet light to polymerize (crosslink) the photopolymerizable compound.

[0093] The resin compositions for the high refractive index layer and the low refractive index layer may optionally contain thermoplastic resins, thermosetting resins, solvents, polymerization initiators, or combinations thereof. Furthermore, dispersants, surfactants, antistatic agents, silane coupling agents, thickeners, color inhibitors, colorants (pigments, dyes), defoamers, leveling agents, flame retardants, UV absorbers, adhesion promoters, polymerization inhibitors, antioxidants, surface modifiers, lubrication agents, or combinations thereof may also be added.

[0094] (Anti-glare layer) An anti-glare layer is a layer that reduces glare by creating irregularities on its surface to cause diffuse reflection, thereby preventing the reflection of the light source's shape when external light is reflected off the surface.

[0095] The arithmetic mean roughness (SRa) of the surface irregularities of the anti-glare layer is preferably 0.02 to 0.25 μm, more preferably 0.02 to 0.15 μm, and even more preferably 0.02 to 0.12 μm.

[0096] The ten-point average roughness (Rzjis) of the surface irregularities of the anti-glare 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.

[0097] SRa and Rzjis are calculated from the roughness curve measured using a contact-type roughness meter in accordance with JIS B0601-1994 or JIS B0601-2001.

[0098] Examples of methods for providing an anti-glare layer to a base film include the following: • Apply a paint containing particles (fillers), etc., for anti-glare purposes. The anti-glare layer resin is cured while in contact with a mold having an uneven structure. • The anti-glare layer resin is applied to a mold having an uneven structure and then transferred to a base film. • Apply paints that undergo spinodal decomposition during drying and film formation.

[0099] The lower limit of the anti-glare layer thickness is preferably 0.1 μm, more preferably 0.5 μm. The upper limit of the anti-glare layer thickness is preferably 100 μm, more preferably 50 μm, and even more preferably 20 μm.

[0100] The refractive index of the anti-glare layer is preferably 1.2 to 1.8, and more preferably 1.4 to 1.7. Note that the refractive index of the anti-glare layer is the value measured under conditions of a wavelength of 589 nm. A low refractive index layer may be made uneven to create an anti-glare, low-reflection layer, or the surface of a hard coat layer or a high refractive index layer may be made uneven, and a low refractive index layer may be placed on top of it to provide an anti-reflective function, thereby creating an anti-glare, anti-reflective layer.

[0101] (Hard coat layer) A preferred configuration is to provide a hard coat layer as a layer beneath the above-mentioned anti-reflective layer. The hard coat layer is preferably H or higher on a pencil hardness scale, and more preferably 2H or higher. 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.

[0102] Examples of thermosetting resins include acrylic resins, urethane resins, phenolic resins, urea-melamine resins, epoxy resins, unsaturated polyester resins, silicone resins, and combinations thereof. A curing agent is added to these thermosetting resin compositions as needed.

[0103] Radiation-curable resins are preferably compounds having radiation-curable functional groups (radiation-curable compounds). Examples of radiation-curable functional groups include ethylenically unsaturated bonding groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, as well as epoxy groups and oxetanyl groups. Of these, ionizing radiation-curable compounds are preferably compounds having ethylenically unsaturated bonding groups, more preferably compounds having two or more ethylenically unsaturated bonding groups, and even more preferably polyfunctional (meth)acrylate compounds having two or more ethylenically unsaturated bonding groups. Polyfunctional (meth)acrylate compounds may be monomers, oligomers, or polymers.

[0104] Specific examples of these include the binder resins mentioned above. To achieve the hardness required for a hard coat, it is preferable that the compound having radiation-curable functional groups contains 50% or more by mass of two- or more functional monomers, and more preferably 70% or more by mass. Furthermore, it is preferable that the compound having radiation-curable functional groups contains 50% or more by mass of three- or more functional monomers, and more preferably 70% or more by mass. The above-mentioned compounds having radiation-curable functional groups can be used individually or in combination of two or more.

[0105] The thickness of the hard coat layer is preferably in the range of 0.1 to 100 μm, and more preferably in the range of 0.8 to 20 μm.

[0106] The refractive index of the hard coat layer is more preferably 1.45 to 1.7, and even more preferably 1.5 to 1.6. Note that the refractive index of the hard coat layer is the value measured under conditions of a wavelength of 589 nm.

[0107] Methods for adjusting the refractive index of the hard coat layer include adjusting the refractive index of the resin, or, if particles are added, adjusting the refractive index of the particles. Examples of particles include those used in the anti-glare layer. In this invention, the hard coat layer may also be referred to as the reflection reduction layer.

[0108] When a functional layer is provided, an easy-adhesion layer may be provided between the functional layer and the base film. The easy-adhesion layer preferably uses the resins, crosslinking agents, etc., mentioned above for the easy-adhesion layer. Furthermore, the easy-adhesion layer may be provided on both sides of the base film, in which case the easy-adhesion layers on both sides may have the same composition or different compositions.

[0109] (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 can be laminated with a polarizer to form a polarizing plate. (Polarizer) As polarizers, for example, those made by adsorbing iodine or an organic dichroic dye onto uniaxially stretched polyvinyl alcohol (PVA), those made by oriented a liquid crystal compound and an organic dichroic dye, or liquid crystalline polarizers made of liquid crystalline dichroic dyes, wire grid type polarizers, etc., can be used without particular limitation.

[0110] A polarizer in the form of a film, in which iodine or an organic dichroic dye is adsorbed onto uniaxially stretched polyvinyl alcohol (PVA), and a polarizer protective film wound into a roll can be bonded together using a PVA-based adhesive or adhesive, such as an ultraviolet-curing type, and then wound into a roll. The thickness of this type of polarizer is preferably 5 to 30 μm, more preferably 8 to 25 μm, and particularly preferably 10 to 20 μm. The thickness of the adhesive or adhesive is preferably 1 to 10 μm, more preferably 2 to 5 μm.

[0111] Furthermore, polarizers are also preferably made by coating an unstretched substrate such as PET or polypropylene with PVA, uniaxially stretching it together with the substrate, and adsorbing iodine or an organic dichroic dye. When using this type of polarizer, the polarizer surface (the side not laminated with the substrate) of the polarizer laminated on the substrate and the polarizer protective film are bonded together with an adhesive or adhesive, and then the substrate used to manufacture the polarizer is peeled off, thereby bonding the polarizer protective film and the polarizer. In this case as well, it is preferable to bond them in a roll and then wind them up. The thickness of this type of polarizer is preferably 1 to 10 μm, more preferably 2 to 8 μm, and particularly preferably 3 to 6 μm. The thickness of the adhesive or adhesive is preferably 1 to 10 μm, and more preferably 2 to 5 μm.

[0112] In the case of liquid crystalline polarizers, a polarizer plate can be made by laminating a polarizer protective film with polarizers oriented using a liquid crystal compound and an organic dichroic dye, or by coating the polarizer protective film with a coating liquid containing a liquid crystalline dichroic dye, drying it, and then laminating the polarizers by light or heat curing. Methods for oriented the liquid crystalline polarizers include rubbing the surface of the object to be coated, and curing while irradiating with polarized ultraviolet light to align the liquid crystalline polarizers. The surface of the polarizer protective film may be directly rubbed and then coated with the coating liquid, or the coating liquid may be directly applied to the polarizer protective film and then irradiated with polarized ultraviolet light. It is also preferable to provide an orientation layer on the polarizer protective film before providing the liquid crystalline polarizers (i.e., laminating the liquid crystalline polarizers to the polarizer protective film via an orientation layer). Methods for providing the orientation layer include: A method of coating with polyvinyl alcohol and its derivatives, polyimide and its derivatives, acrylic resin, polysiloxane derivatives, etc., and then rubbing the surface to form an oriented layer (rubbing-oriented layer). A method of applying a coating solution containing a polymer or monomer having photoreactive groups such as cinnamoyl groups and chalcone groups, and a solvent, and irradiating it with polarized ultraviolet light to align and cure it to form an oriented layer (photo-oriented layer). These are some examples.

[0113] Alternatively, a polarizer can be bonded to a polarizer film by attaching a liquid crystalline polarizer to a release-type film in accordance with the above method, bonding the liquid crystalline polarizer surface and the polarizer film with an adhesive or bonding agent, and then peeling off the release-type film.

[0114] The thickness of the liquid crystalline polarizer is preferably 0.1 to 7 μm, more preferably 0.3 to 5 μm, and particularly preferably 0.5 to 3 μm. The thickness of the adhesive or tack is preferably 1 to 10 μm, more preferably 2 to 5 μm.

[0115] (Lamination of polarizer and polarizer protective film) The polyester film of the present invention is preferably laminated on the side of the polarizer opposite to the image display cell side. When the polarizer and the film are laminated to form a polarizing plate, the angle between the absorption axis of the polarizer and the slow axis of the film is preferably about 90 degrees or about 0 degrees. In this 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. It is preferable that the above angle is maintained over the entire surface of the polarizing plate. Furthermore, if the polarizer is a liquid crystalline polarizer or a wire grid type, it is easy to orient the absorption axis of the polarizer at an angle 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.

[0116] (The side of the polarizer that displays the image cell) When the polarizer is for a liquid crystal display device, the liquid crystal cell side of the polarizer may be unlaminated, coated with an adhesive, or have a hardened layer on it. A polarizer protective film different from the one described above may also be provided. A preferred hardened layer is the hard coat layer mentioned above. If it is coated with an adhesive, a release film may be further laminated. In addition, in the unlaminated state, the case of a hardened layer, or the case of a polarizer protective film, a separate peelable protective film may be laminated.

[0117] Examples of polarizer protective films on the liquid crystal cell side of the polarizer include cellulose-based (TAC) film, acrylic film, and polycyclic olefin (COP) film. The polarizer protective film on the liquid crystal cell side may have nearly zero retardation, or it may be a phase difference film, also known as an optical compensation film, which controls the change in color tone when the display screen is viewed from an oblique angle.

[0118] To achieve the required phase difference in an optical compensation film, methods include stretching the film, coating the film with a phase difference layer such as a liquid crystal compound, or separately, providing a phase difference layer such as a liquid crystal compound on a release film and transferring it. The liquid crystal compound used to form the phase difference layer is selected according to the required phase difference characteristics, such as a rod-shaped liquid crystal compound or a discotic liquid crystal compound. It is preferable that the liquid crystal compound has photocurable reactive groups such as double bonds to fix its orientation state. To orient the liquid crystal compound and create a phase difference, for example, an orientation layer can be provided as a lower layer to the phase difference layer, and the orientation layer can be rubbed or irradiated with polarized ultraviolet light to provide orientation control so that the liquid crystal compound coated on top of it is oriented in a specific direction.

[0119] The phase difference of the optical compensation film can be set appropriately depending on the type of liquid crystal cell used, the required viewing angle, and other factors.

[0120] The phase difference layer can be provided by coating it with a phase difference layer composition coating. The phase difference layer composition coating may contain a solvent, polymerization initiator, sensitizer, polymerization inhibitor, leveling agent, polymerizable non-liquid crystal compound, crosslinking agent, or a combination thereof. These can be those described in the sections on the orientation control layer and the liquid crystalline polarizer.

[0121] A phase difference layer is formed by coating a phase difference layer composition paint onto the release surface or orientation control layer of a release film, followed by drying, heating, and curing.

[0122] These conditions, as well as those described in the sections on the alignment control layer and the liquid crystalline polarizer, are preferred conditions.

[0123] When bonding a polarizer to a polarizer protective film or phase difference film, an adhesive or bonding agent is used. Water-based adhesives such as polyvinyl alcohol-based adhesives or photocurable adhesives are preferably used. Examples of photocurable adhesives include acrylic and epoxy adhesives. Acrylic adhesives are preferably used as the bonding agent.

[0124] (Liquid crystal cell) A liquid crystal cell consists of a liquid crystal compound 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 from the viewpoint of thinning, even more preferably 0.5 mm or less, and particularly preferably 0.4 mm or less.

[0125] While the liquid crystal cell type is not particularly limited, the VA and IPS methods are preferred for applying the present invention because they exhibit minimal color shift when viewed from an oblique direction, and in these methods, the absorption axis of the polarizing plate is parallel to or perpendicular to the long side direction of the liquid crystal cell.

[0126] For the color filter incorporated into the liquid crystal cell, it is preferable that both the maximum and minimum transmittances in the 420nm to 460nm wavelength range of the blue pixels are 80% or higher, and more preferably 85% or higher. The difference between the maximum and minimum transmittances in the 420nm to 460nm wavelength range is preferably 4% or less, and more preferably 3% or less.

[0127] (LCD panel) It is preferable to form a liquid crystal display panel by bonding polarizing plates to both the viewing side and the light source side of the liquid crystal cell. The bonding is preferably done with an adhesive. An acrylic-based adhesive is preferably used.

[0128] In a liquid crystal panel, the polarizing plate using the polyester film described above may be either the polarizing plate on the light source side or the polarizing plate on the viewing side, or it may even be both polarizing plates.

[0129] When the image display device is an organic or inorganic electroluminescent cell, micro-LED, etc., the polarizer is preferably a circular polarizer. Typically, a circular polarizer has a quarter-wavelength layer laminated on the viewing side of the polarizer. The quarter-wavelength layer includes not only a single layer, but also a combination of a quarter-wavelength layer and a half-wavelength layer, and further, a phase difference layer such as a C-plate added to these. The quarter-wavelength layer, half-wavelength layer, and phase difference layer such as a C-plate may be a film or a coating layer. These phase difference layers may be those described in the section on the phase difference layer of a polarizer, as long as the phase difference and its orientation direction are appropriate.

[0130] (Transparent electrode substrate 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, or it may be provided on both sides.

[0131] Examples of transparent conductive layers include mesh prints of conductive paste, carbon nanotube-containing coatings, self-assembled nanosilver coatings, needle-shaped conductive filler-containing coatings, and metal oxide thin films. Among these, metal oxide thin films are preferred, with indium oxide, zinc oxide, tin oxide, indium tin oxide (ITO), tin antimony oxide, zinc aluminum oxide, and indium zinc oxide being preferred examples.

[0132] The transparent conductive layer is preferably formed in a line-like or grid-like pattern shape by etching.

[0133] The thickness of the transparent conductive layer is preferably 5 to 500 nm, more preferably 15 to 250 nm, and even more preferably 20 to 100 nm. This thickness ensures conductivity while suppressing coloration caused by the conductive layer.

[0134] A transparent conductive layer can be formed by known methods such as vacuum deposition, sputtering, CVD, ion plating, spraying, and sol-gel methods.

[0135] After the transparent conductive layer is fabricated, a resist mask with a predetermined pattern can be formed using photolithography, followed by etching to create the pattern.

[0136] The transparent conductive layer may be amorphous, but it is preferable to heat-treat the amorphous transparent conductive layer at 130-180°C for 0.5-2 hours to grow crystals and create a crystalline transparent conductive layer, thereby improving conductivity.

[0137] It is also preferable to provide a hard coat layer and a refractive index adjustment layer as layers beneath the transparent conductive layer. The refractive index adjustment layer may be a layer with a refractive index close to that of the transparent conductive layer (high refractive index layer), and 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.

[0138] The polyester film of the present invention is preferably used as a shatterproof film. When a glass plate is used as a substrate for a touch panel or screen surface cover, the shatterproof film is laminated to the glass plate to prevent fragments from damaging the internal structure or scattering and exposing the outside when the glass plate breaks. The shatterproof film may be laminated on either the viewing side or the non-viewing side of the glass plate. When laminated to a glass plate, it is preferable to use an optical substrate-less adhesive called OCA.

[0139] 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 an image display device, and can protect the internal image display cells from external impacts and prevent the surface from being scratched. The screen surface protective film is preferably attached to the image display area using an adhesive. It is also preferable that the screen surface protective film is located on the outermost surface of the image display area and can be peeled off and replaced if it is scratched. In this case, it is preferable that the adhesive has an adhesive strength that allows it to be peeled off by hand.

[0140] The polyester film of the present invention is also preferably used in flexible image display devices, and is used as a polarizer protective film, back cover film, transparent electrode substrate film, screen surface protective film, etc. of flexible image display devices. In particular, it is preferably used as a back cover film and a screen surface protective film. The flexible image display device may be V-shaped, double-door type, W-shaped, etc., in which the image display section can be folded, or it may be rolled up into a roll. When used in a flexible image display device, it is preferable to position the slow axis of the polyester film perpendicular to the folding direction, or in other words, to position it so that the fold becomes the slow axis.

[0141] When used on the viewing side of an image display device from the polarizing plate, such as as a transparent electrode substrate film, a shatterproof film, or a screen surface protective film, it is preferable to position the slow phase axis of the polyester film at 30 to 60 degrees, preferably about 45 degrees, with respect to the absorption axis of the polarizing plate, so that blackout does not occur and no iridescence is produced when viewed with sunglasses. [Examples]

[0142] The present invention will be described more specifically below with reference to examples, but the present invention is not limited by the following examples, and can be implemented with appropriate modifications within the scope that is consistent with the spirit of the present invention, and all such modifications are included within the technical scope of the present invention. The evaluation methods for physical properties, etc., in the following examples are as follows.

[0143] (1) Refractive index of polyester film Using a molecular orientation meter (MOA-6004, manufactured by Oji Instruments Co., Ltd.), the slow phase axis direction of the film was determined, and a 4cm x 2cm rectangle was cut out so that the slow phase axis direction was parallel to the longer side, and this was used as a sample for measurement. For this sample, the refractive index in two orthogonal axes (refractive index in the direction of the slow phase axis: ny, and refractive index in the direction perpendicular to the slow phase axis: nx), and the refractive index in the thickness direction (nz) were determined using an Abbe refractometer (NAR-4T, manufactured by Atago, measurement wavelength 589nm).

[0144] (2) In-plane retardation (Re) In-plane retardation is a parameter defined by the product (△Nxy × d) of the anisotropy of the refractive indices of two orthogonal axes on the film (△Nxy = |nx - ny|) and the film thickness d (nm), and is a measure of optical isotropy and anisotropy. Using the method described in (1) above, the absolute value of the difference in refractive index between the two axes (|nx - ny|) was calculated as the anisotropy of the refractive index of the two axes (△Nxy). The in-plane retardation (Re) was determined by the product (△Nxy × d) of the refractive index anisotropy (△Nxy) and the film thickness d (nm).

[0145] (3) Thickness direction retardation (Rth) Thickness retardation is a parameter that represents the average retardation obtained by multiplying the two birefringences △Nxz (=|nx-nz|) and △Nyz (=|ny-nz|) as viewed from a cross-section in the thickness direction of the film by the film thickness d. Using the method described in (1) above, nx, ny, and nz were determined, and the thickness retardation (Rth) was obtained by calculating the average value of (△Nxz×d) and (△Nyz×d).

[0146] (4) Degree of plane orientation The degree of surface orientation was calculated by substituting nx, ny, and nz into the formula |nx+ny| / 2-nz.

[0147] (5) NZ coefficient The NZ coefficient was calculated by substituting nx, ny, and nz into the expression |ny-nz| / |ny-nx|.

[0148] (6) CLIA axis of the polarizer A polarizing filter and a polarizer with known absorption axes were superimposed and placed on a surface light source. The polarizing filter was rotated until it was darkest, and the direction of the polarizer's absorption axis was set to 90 degrees from the direction of the polarizing filter's absorption axis. In the case of a long polarizer made of PVA stretched in the longitudinal direction, the longitudinal direction is the absorption axis, so the longitudinal direction can be considered the absorption axis.

[0149] (7) The slow axis direction of the film The measurements were taken using a molecular orientation analyzer (MOA-6004 molecular orientation analyzer, manufactured by Oji Instruments Co., Ltd.).

[0150] (8) Light transmittance at a wavelength of 380 nm Using a spectrophotometer (Hitachi, Ltd., U-3500 model), the light transmittance in the wavelength range of 300-500 nm was measured with an air layer as the standard, and the light transmittance at a wavelength of 380 nm was determined.

[0151] (9) Intrinsic viscosity 0.2 g of the sample was dissolved in 50 ml of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (60 / 40 (weight ratio)) and measured using an Ostwald viscometer at 30°C.

[0152] (10) Film thickness and frequency characteristics after Fourier transform Using a contact-type continuous thickness gauge manufactured by Micron Measuring Instruments Co., Ltd. (the thickness gauge portion was manufactured by Anritsu Electric Co., Ltd.), a sample approximately 50 mm wide and 6 m long was cut from the center of the obtained film in the width direction in the MD direction. The thickness was measured in the MD direction at a speed of 1.5 m / min, and data was continuously acquired at 0.1-second intervals. From the obtained data, 2048 points (a length of 5.12 m) were arbitrarily selected consecutively, and the average of their thicknesses was defined as the film thickness. Among the measured data, the value obtained by (maximum thickness - minimum thickness) / average thickness × 100 was defined as the MD direction thickness variation (%). Furthermore, frequency analysis was performed using Fast Fourier Transform (FFT) on the selected 2048 data points, employing Microsoft Excel® spreadsheet software. Additionally, the frequencies of the obtained analysis data were converted to periodic lengths, and their respective amplitudes were determined. From the data with a period of 10 cm or more, the five points with the largest amplitudes were selected, and their average value was defined as A. The largest amplitude value among these five points was defined as Amax. Furthermore, from the data with a period of less than 10 cm, the five points with the largest amplitudes were selected, and their average value was defined as B. For the period analysis, the data in the latter half of the frequency analysis data, known as ghost data, was ignored, and only the analysis data in the first half was used. From the obtained values ​​of A, Amax, and B, A / B and Amax / B were determined. The TD direction thickness variation was calculated by slitting the central part of the film in the TD direction to a width of 1000 mm, cutting a 1000 mm x 50 mm sample in the TD direction of this film, measuring it similarly with a continuous thickness gauge, and calculating (maximum thickness - minimum thickness) / average thickness × 100 based on the obtained data. Note that a period length of 10 cm or more corresponds to a frequency of 0.25 Hz or less.

[0153] (11) Breaking strength and elongation at break The procedure conformed to JIS K 7113. Samples measuring 10 mm in width and 100 mm in length were cut from the film using a razor blade in both the longitudinal and lateral directions. After being left for 12 hours in an atmosphere of 23°C and 65% RH, measurements were performed in an atmosphere of 23°C and 65% RH, with a chuck distance of 100 mm and a tensile speed of 200 mm / min. The average value of five measurement results was used. A Shimadzu Autograph AG5000A was used as the measuring instrument.

[0154] (12) Film temperature A radiation thermometer (Chino IR-BZPHGN1) was used, and the detection unit was inserted from the side of the film deposition machine to take measurements. The measurement data was smoothed for 10 seconds.

[0155] (13) Productivity The evaluation was based on the number of breaks when the central part of the obtained film was slit to a width of 1000 mm. The cutting blade used for slitting was one that had been used to cut a conventional film equivalent to the comparative example, and had been removed after exceeding the specified usage limit, and was reassembled. The running speed was 90% of the slitter's design maximum speed. ○: The number of fractures per day is 0. △: The number of fractures per day is 1. ×: The number of fractures in a single day is two or more.

[0156] (14) Flatness Deionized water was dropped onto a flat glass plate, and a 1000mm wide film cut to a length of 2000mm was placed on top. A roller was then used to ensure a uniform layer of water. The flatness of the film was evaluated by observing the reflection of the ceiling fluorescent lights on the film from an oblique angle. ○: The reflected fluorescent light shows little curvature and has good flatness. △: Although there is some distortion in the reflected fluorescent light, it is acceptable. ×: The reflected fluorescent light is significantly curved, and its flatness is poor.

[0157] • Polyester A (PET(A)) Polyethylene terephthalate with an intrinsic viscosity of 0.62 dl / g • Polyester B (PET(B)) A molten mixture of 10 parts by mass of the ultraviolet absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazinon-4-one) and 90 parts by mass of PET(A).

[0158] (Preparation of adhesive modifying coating solution) Transesterification and polycondensation reactions were carried out by conventional methods to prepare a water-dispersible sulfonic acid metal base-containing copolymer polyester resin with the following composition: dicarboxylic acid components (relative to the total dicarboxylic acid components): 46 mol% terephthalic acid, 46 mol% isophthalic acid, and 8 mol% sodium 5-sulfonaisophthalate; and glycol components (relative to the total glycol components): 50 mol% ethylene glycol and 50 mol% neopentyl glycol. Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellsolve, and 0.06 parts by mass of a nonionic surfactant were mixed, and the mixture was heated and stirred until it reached 77°C. Then, 5 parts by mass of the above water-dispersible sulfonic acid metal base-containing copolymer polyester resin was added, and stirring continued until there were no more clumps of resin. After that, the resin aqueous dispersion was cooled to room temperature to obtain a uniform water-dispersible copolymer polyester resin liquid with a solid content of 5.0% by mass. Furthermore, 3 parts by mass of aggregated silica particles (Silysia 310, manufactured by Fuji Silysia Co., Ltd.) were dispersed in 50 parts by mass of water. Then, 0.54 parts by mass of the aqueous dispersion of Silysia 310 was added to 99.46 parts by mass of the above-mentioned water-dispersible copolymer polyester resin liquid, and 20 parts by mass of water was added while stirring to obtain an adhesive modification coating solution.

[0159] (Polarizer) A roll of polyvinyl alcohol film with a thickness of 80 μm, which was continuously stained in an iodine aqueous solution, was stretched five times in the transport direction, treated in a boric acid solution, washed with water, and dried to obtain a long polarizer.

[0160] (Polyester film A~H) As raw materials for the intermediate layer of the base film, 90 parts by mass of particle-free PET(A) resin pellets and 10 parts by mass of PET(B) resin pellets containing an ultraviolet absorber were dried under reduced pressure (1 Torr) at 135°C for 6 hours, and then supplied to extruder 2 (for intermediate layer II). PET(A) was dried by a conventional method and supplied to extruder 1 (for outer layer I and outer layer III), respectively, and melted at 285°C. These two polymers were filtered using a stainless steel sintered filter medium (nominal filtration accuracy, 95% particle cut of 10 μm particles), laminated in a 2-layer 3-combination block, extruded into a sheet from a die, and then cooled and solidified using an electrostatic casting method on a casting drum with a surface temperature of 30°C to produce an unstretched film. At this time, the discharge rate of each extruder was adjusted so that the thickness ratio of layers I, II, and III was 10:80:10.

[0161] This unstretched PET film was fed into an MD stretching machine consisting of low-speed and high-speed rolls. The film was heated to a preheating temperature by multiple low-speed rolls, and then further heated to a stretching temperature by an infrared heater located between the low-speed and high-speed rolls. Stretching was then performed using the difference in peripheral speed between the low-speed and high-speed rolls. The preheating temperature, stretching temperature, and stretching ratio are shown in Table 1. The number of infrared heaters lit refers to the number of rows of infrared heaters installed in multiple rows in the MD direction that were lit for heating. The rolls used in the MD stretching machine were chrome-plated on the surface, with a diameter of 180 to 250 mm, and all had a roundness of 10 μm or less and a runout of 20 μm or less.

[0162] Next, apply a dry coating of 0.08 g / m² to both sides of the MD-stretched film. 2 The above adhesive modification coating solution was applied and dried. The resulting coated film was guided to a tenter stretcher, and while holding the ends of the film with clips, it was guided to a 100°C tenter and stretched in the width direction. Next, while maintaining the width stretched in the width direction, it was treated in a heat setting zone at 200°C for 10 seconds, and then a 2% relaxation treatment was performed in the width direction to obtain a stretched PET film.

[0163] (Films I and J) The unstretched PET film described above was fed into an MD stretching machine and heated by multiple rolls. The second-to-last roll of the low-speed rolls was used to raise the temperature to the preheating temperature, and the final low-speed roll was used to heat the film to the stretching temperature. The film was stretched using the difference in peripheral speed between the high-speed and low-speed rolls. The final low-speed roll and the nip roll installed on the final low-speed roll were coated with fluororesin on their surfaces. Then, TD stretching and heat fixing were performed in the same manner as described above to obtain a stretched PET film.

[0164] Table 1 shows the characteristics of these films, including the film formation conditions and thickness variations. The light transmittance at a wavelength of 380 nm was within the range of 2.3-2.5% for all films except film H, which had a transmittance of 8.5%. Furthermore, as examples of graphs showing the results of frequency analysis of thickness variations, Figure 1 shows the results for film A, and Figure 2 shows the results for film D.

[0165] [Table 1]

[0166] As is clear from Table 1, film A had large thickness variations, possibly due to its low MD stretching temperature. However, by increasing the MD stretching temperature, as seen in films B and C, the MD-direction thickness variations decreased, and values ​​such as A / B also decreased. This can also be seen by comparing Figure 1 (film A) and Figure 2 (film D), where film A shows a larger amplitude at frequencies below 0.25 Hz (periods of 10 cm or more) compared to amplitudes at frequencies above 0.25 Hz (periods of less than 10 cm). On the other hand, when the MD stretching temperature was too high, as with film E, the thickness variation in the MD direction increased, possibly due to slack and irregular stretching positions. Also, with film F, the preheating temperature was high, and slack occurred during the preheating process, and the film sometimes stuck to the roll, resulting in a large thickness variation in the MD direction. As with films G and H, even with a high MD stretching ratio, MD-direction thickness variation was suppressed if the preheating and stretching temperatures were appropriate. In stretching with roll heating, as with film I, thickness variation was large when the preheating temperature was too high and the stretching temperature was too low, but by optimizing the temperatures, the thickness variation could be reduced. Films B-D, E-G, and J can be suitably used, for example, as polarizer protective films. Film H can also be suitably used, for example, as a transparent electrode substrate film, a shatterproof film, or a screen surface protective film for a flexible image display device.

[0167] (Fabrication of polarizing plates) Using films C, D, and J, which exhibited particularly good thickness variation among the polyester films produced in the examples, polarizing plates were fabricated as follows. A polarizing plate was fabricated by laminating the polyester film prepared above to one side of a polarizer and a triacetyl cellulose film (40 μm thick) to the opposite side using a roll-to-roll method. An ultraviolet-curing adhesive was used for lamination. In all cases, the angle between the slow axis of the polyester film and the absorption axis of the polarizer was 90 degrees, and the misalignment was 0.5 degrees or less.

[0168] (Evaluation of image display devices) The obtained polarizing plates were cut and replaced with the viewfinder polarizing plates of a commercially available 42-inch LCD television. No iridescence was observed when viewing from an oblique angle with either polarizing plate, and good visibility was maintained. [Industrial applicability]

[0169] The present invention provides a polyester film that exhibits high in-plane retardation while maintaining excellent thickness uniformity, resulting in good productivity, workability, and flatness. This polyester film has good visibility with minimal iridescence regardless of the type of image display device or light source, and is suitable for various applications of image display devices.

Claims

1. In-plane retardation is between 3000 nm and 30000 nm. The NZ coefficient is between 1.65 and 3. Thickness variation in the film formation flow direction is 8% or less. When the thickness measurement data in the film formation flow direction is Fourier transformed and the frequency is replaced with the period of the film length, the ratio A / B, which is the ratio of A to B below, is 5 or less. A: The average amplitude of the top 5 points with a period of 10 cm or more. B: The average amplitude of the top 5 amplitude values ​​for periods of 10 cm or less. This is a polyester film (the thickness variation is calculated as (maximum thickness - minimum thickness) / average thickness × 100 (%)).

2. In-plane retardation is between 3000 nm and 30000 nm. The NZ coefficient is between 1.65 and 3. Thickness variation in the film formation flow direction is 8% or less. When the thickness measurement data in the film formation flow direction is Fourier transformed and the frequency is replaced with the period of the film length, the ratio of Amax to B, Amax / B, is 7 or less. This is a polyester film (the thickness variation is calculated as (maximum thickness - minimum thickness) / average thickness × 100 (%)). Amax: Maximum amplitude with a period of 10 cm or more. B: The average amplitude of the top 5 amplitude values ​​for periods of 10 cm or less.

3. In-plane retardation is between 3000 nm and 30000 nm. The NZ coefficient is between 1.65 and 3. Thickness variation in the film formation flow direction is 8% or less. Breakage elongation in the film formation flow direction is 4% or more This is a polyester film (the thickness variation is calculated as (maximum thickness - minimum thickness) / average thickness × 100 (%)).

4. In-plane retardation is between 3000 nm and 30000 nm. The NZ coefficient is between 1.65 and 3. Thickness variation in the film formation flow direction is 8% or less. Breaking strength in the film formation flow direction is 50 MPa or higher. This is a polyester film (the thickness variation is calculated as (maximum thickness - minimum thickness) / average thickness × 100 (%)).

5. A polyester film according to any one of claims 1 to 4, wherein the thickness is 25 μm or more and 150 μm or less.

6. A polarizer protective film made of a polyester film according to any one of claims 1 to 5.

7. A polarizing plate comprising a polarizer protective film and a polarizer laminated together as described in claim 6.

8. An image display device in which the polarizing plate according to claim 7 is installed on the viewing side of the image display cell.

9. A transparent electrode substrate film made of a polyester film according to any one of claims 1 to 5.

10. A shatterproof film made of a polyester film according to any one of claims 1 to 5.

11. A screen surface protective film made of a polyester film according to any one of claims 1 to 5.

12. An image display device comprising any one of the transparent electrode substrate film according to claim 9, the shatterproof film according to claim 10, and the screen surface protective film according to claim 11.

13. The image display device according to claim 12, which is a flexible image display device.

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