Light-transmitting substrate film and roll thereof

Abstract

Provided is a light-transmitting substrate film that can improve visibility as a result of being used in an image display device, and a roll thereof. Disclosed is a light-transmitting substrate film used in an image display device, said film being characterized in that the width of the film is 500 mm or more and, in a plurality of film pieces cut at lengths of 50 mm to the left and right centered around positions every 100 mm from the center position in the width direction of the film, the average value of the difference (ny-nx) between the length direction refractive index (nx) and the width direction refractive index (ny) is 0.2 or more, the maximum value-the minimum value of (ny-nx) is 0.02 or less, the average value of retardation is 1000 nm or more, and the average value of the degree of elongation at break in the length direction is 50% or more.

Description

Light-transmitting substrate film and roll thereof

[0001] The present invention relates to a light-transmitting substrate film and a roll thereof.

[0002] Polarizing plates used in liquid crystal displays (LCDs) typically consist of a polarizer made of polyvinyl alcohol (PVA) or other materials dyed with iodine sandwiched between two polarizer protective films. Triacetyl cellulose (TAC) films are typically used as polarizer protective films. In recent years, as LCDs have become thinner, thinner polarizing plates have been required. However, reducing the thickness of the TAC films used as polarizer protective films to achieve this result in problems such as insufficient mechanical strength and reduced moisture permeability. Furthermore, TAC films are very expensive, and there is a strong demand for cheaper alternative materials.

[0003] Therefore, in order to make the polarizing plate thinner, it has been proposed to use a polyester film with high retardation instead of a TAC film as a polarizer protective film so that high durability can be maintained even when the film is thin (Patent Documents 1 to 3).

[0004] JP 2004-205773 A JP 2010-244059 A JP 2014-6497 A

[0005] Polyester films have superior durability compared to TAC films. On the other hand, polyester films have extremely high intrinsic birefringence due to the presence of aromatic rings with high polarizability in the molecular chain, and tend to exhibit birefringence due to molecular chain orientation through stretching treatment to impart excellent transparency, heat resistance, and mechanical strength. High-retardation polyester films are typically strongly oriented in one direction, resulting in anisotropy in mechanical strength and requiring careful handling. The inventors conducted various studies and found that high-retardation polyester films have a large difference in refractive index between directions perpendicular to each other, making it difficult to achieve an appropriate relationship between the refractive index in both directions and the refractive index of an antireflection layer, etc. When an optical laminate having an antireflection layer, etc., is installed on the surface of an image display device, the antireflection performance at the surface of the optical laminate may be reduced, resulting in reduced contrast in bright areas. Furthermore, it has been found that when a screen is viewed from a diagonal direction, a decrease in contrast is likely to occur, and that the decrease in contrast is greater depending on whether the long side of the image display device is oriented horizontally or vertically, resulting in a difference in contrast depending on the direction from which the screen is viewed. Here, the optical laminate is a laminate having an optical functional layer on at least one surface of a light-transmitting substrate film. Examples of the optical functional layer include an antireflection layer, a low-reflection layer, and an antiglare layer.

[0006] Furthermore, the inventors have found that even in biaxially oriented polyester films that are excellent in terms of productivity, differences in refractive index tend to occur between the center and edges of the produced film, resulting in differences in contrast within the screen and noticeable rainbow spots.

[0007] An object of the present invention is to provide a light-transmitting substrate film and a roll thereof that can improve visibility when used in an image display device. Here, "improving visibility" means, for example, achieving excellent anti-reflection performance and bright contrast, and further preventing rainbow unevenness.

[0008] As a result of intensive research, the present inventors have found that an image display device having at least excellent anti-reflection performance and bright area contrast can be obtained by reducing the refractive index variation in the width direction of an optically transparent substrate film and setting the average retardation and average breaking elongation within predetermined ranges. Based on this finding, the present inventors have conducted further intensive research and have completed the present invention.

[0009] The present invention encompasses the following embodiments: [Item 1] A roll of light-transmitting substrate film for use in an image display device, wherein the width of the roll is 500 mm or more, the wound length of the roll is 200 m or more, and in a plurality of film pieces cut out in 50 mm lengths to the left and right at positions every 100 mm from the roll center along a direction (width direction) perpendicular to the unwinding direction (longitudinal direction) of the roll, the average value of the difference (ny - nx) between the refractive index in the longitudinal direction (nx) and the refractive index in the width direction (ny) is 0.02 or more, the maximum value - minimum value of (ny - nx) in the width direction is 0.02 or less, the average retardation is 1000 nm or more, and the average breaking elongation in the longitudinal direction is 50% or more. [Item 2] The roll according to Item 1, wherein the absolute value of the angle between the main orientation axis and the width direction at one end of the roll in the width direction is within a range of 0 to 30 degrees, and the absolute value of the angle between the main orientation axis and the width direction at the other end of the roll in the width direction is greater than 0 degrees and not greater than 40 degrees. [Item 3] The roll according to Item 1 or 2, wherein the absolute value of the angle between the main orientation axis and the width direction at one end of the roll in the width direction is greater than 0 degrees and not greater than 30 degrees, and the absolute value of the angle between the main orientation axis and the width direction at the other end of the roll in the width direction is greater than 0 degrees and not greater than 30 degrees. [Item 4] The roll according to Item 1 or 2, wherein the absolute value of the angle between the main orientation axis and the width direction at one end of the roll in the width direction is greater than 0 degrees and not greater than 30 degrees, and the absolute value of the angle between the main orientation axis and the width direction at the other end of the roll in the width direction is greater than 0 degrees and not greater than 40 degrees. [Item 5] The roll according to any one of Items 1 to 4, which has an easy-adhesion layer on at least one surface of the light-transmitting substrate film. [Item 6] The roll according to any one of Items 1 to 5, which is a polyester film, [Item 7] The roll according to any one of Items 1 to 6, which is a biaxially stretched polyethylene terephthalate film, [Item 8] The roll according to any one of Items 1 to 7, which has an antireflection layer and / or a low-reflection layer on at least one surface of the light-transmitting substrate film. [Item 9] The roll according to Item 8, which has an antiglare layer between the antireflection layer or low-reflection layer and the light-transmitting substrate film.[Item 10] The roll according to any one of items 1 to 9, wherein the light-transmitting substrate film is a polarizer protective film. [Item 11] The roll according to item 10, wherein the polarizer protective film is laminated on at least one surface of a polarizer. [Item 12] A light-transmitting substrate film laminated on at least one surface of a polarizer as a polarizer protective film, wherein the width of the light-transmitting substrate film is 500 mm or more, and in a plurality of film pieces cut out along the width direction of the light-transmitting substrate film at positions every 100 mm from a center position and having a length of 50 mm to the left and right, the average value of the difference (ny-nx) between the refractive index (nx) in the longitudinal direction and the refractive index (ny) in the width direction is 0.02 or more, the maximum value-minimum value of (ny-nx) is 0.02 or less, the average value of retardation is 1000 nm or more, and the average value of breaking elongation in the longitudinal direction is 50% or more, the absolute value of the angle between the main alignment axis and the width direction at one end in the width direction of the light-transmitting substrate film is within a range of 0 to 30 degrees, and the absolute value of the angle between the main alignment axis and the width direction at the other end in the width direction of the light-transmitting substrate film is more than 0 degrees and 40 degrees or less. [Item 13] A light-transmitting substrate film laminated on at least one surface of a polarizer as a polarizer protective film, wherein the width of the light-transmitting substrate film is 500 mm or more, and in a plurality of film pieces cut out along the width direction of the light-transmitting substrate film at positions every 100 mm from a center position and having a length of 50 mm to the left and right, the average value of the difference (ny-nx) between the refractive index (nx) in the longitudinal direction and the refractive index (ny) in the width direction is 0.02 or more, the maximum value-minimum value of (ny-nx) is 0.02 or less, the average value of retardation is 1000 nm or more, and the average value of breaking elongation in the longitudinal direction is 50% or more, the absolute value of the angle between the main alignment axis and the width direction at one end in the width direction of the light-transmitting substrate film is more than 0 degrees and 30 degrees or less, and the absolute value of the angle between the main alignment axis and the width direction at the other end in the width direction of the light-transmitting substrate film is more than 0 degrees and 40 degrees or less.

[0010] The present invention can provide a light-transmitting substrate film and a roll thereof that can improve visibility when used in an image display device, for example.

[0011] In one embodiment, the light-transmitting substrate film is preferably used in an image display device, and more preferably in a liquid crystal display device. A liquid crystal display device generally includes a rear module, a liquid crystal cell, and a front module, in this order from the side where a backlight light source (also referred to as a "backlight unit") is disposed (light source side) to the side where an image is displayed (viewing side). The rear module and the front module generally include a transparent substrate, a transparent conductive film on the liquid crystal cell side, and a polarizing plate on the opposite side. The polarizing plate is typically disposed on the light source side in the rear module, and on the viewing side in the front module.

[0012] In one embodiment, the liquid crystal display device includes at least a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates. The backlight source preferably has an emission spectrum with peak tops in the wavelength regions of 400 nm to less than 495 nm, 495 nm to less than 600 nm, and 600 nm to less than 780 nm, each with a half-width of 5 nm or more. The peak wavelengths of blue, green, and red defined in the CIE chromaticity diagram are 435.8 nm (blue), 546.1 nm (green), and 700 nm (red), respectively. The wavelength regions of 400 nm to less than 495 nm, 495 nm to less than 600 nm, and 600 nm to less than 780 nm correspond to the blue region, green region, and red region, respectively.

[0013] Examples of light sources having the above-described emission spectrum include a light source that emits excitation light and a light source that includes at least quantum dots. Other examples of light sources include a phosphor-based white LED light source that combines a phosphor having emission peaks in the R (red) and G (green) regions by excitation light with a blue LED, a three-wavelength white LED light source, and a white LED light source that combines a red laser. Among the phosphors, examples of red phosphors include CaAlSiN ３: Nitride-based phosphors having Eu as a basic composition, CaS: Sulfide-based phosphors having Eu as a basic composition, Ca ２ SiO ４ : silicate-based phosphor with Eu etc. as the basic composition, K ２ SiF ６ : Mn ４＋ Examples of the green phosphors include fluoride phosphors having a basic composition of β-SiAlON:Eu, etc., and sialon phosphors having a basic composition of (Ba, Sr) ２ SiO ４ Examples of suitable phosphors include silicate-based phosphors containing Eu as a basic component.

[0014] In one embodiment, the liquid crystal display device may appropriately include other components in addition to the backlight source, polarizing plate, and liquid crystal cell, such as a color filter, a lens film, a diffusion sheet, an anti-reflection film, and a brightness enhancement film. The brightness enhancement film may be provided between the light-source-side polarizing plate and the backlight source. An example of a brightness enhancement film is a reflective polarizing plate that transmits one linearly polarized light and reflects linearly polarized light perpendicular to the transmitted light. A suitable example of a reflective polarizing plate is a brightness enhancement film from the DBEF (registered trademark) (Dual Brightness Enhancement Film) series manufactured by Sumitomo 3M Limited. Note that the reflective polarizing plate is usually arranged so that the absorption axis of the reflective polarizing plate and the absorption axis of the light-source-side polarizing plate are parallel to each other.

[0015] In one embodiment, the light-transmitting substrate film is preferably a polarizer protective film, and the polarizer protective film is preferably laminated on at least one surface of the polarizer. Of the two polarizing plates arranged in the liquid crystal display device, at least one polarizing plate is preferably a polarizer protective film laminated on at least one surface of a polarizer dyed with iodine, such as polyvinyl alcohol (PVA). An optical functional layer is preferably laminated on at least one surface of the light-transmitting substrate film, and from the viewpoint of suppressing rainbow-like color spots, it is preferable that an antireflection layer and / or a low-reflection layer be laminated on at least one surface of the light-transmitting substrate film. When the light-transmitting substrate film is a polarizer protective film, the antireflection layer and / or low-reflection layer may be provided on the side of the polarizer protective film opposite to the surface on which the polarizer is laminated, or on the side of the polarizer protective film on which the polarizer is laminated, or both. However, it is preferable to provide the antireflection layer and / or low-reflection layer on the side of the polarizer protective film opposite to the surface on which the polarizer is laminated. When an antireflection layer and / or a low-reflection layer is provided on the side of the polarizer protective film where the polarizer is laminated, the layer is preferably provided between the polarizer protective film and the polarizer. Furthermore, other layers (e.g., an easy-adhesion layer, a hard coat layer, an antiglare layer, an antistatic layer, an antifouling layer, etc.) may be present between the antireflection layer and / or the low-reflection layer and the light-transmitting substrate film. It is preferable that a film without birefringence, such as a TAC film, an acrylic film, or a norbornene-based film, is laminated on the other side of the polarizer (e.g., a polarizing plate with a three-layer structure), but it is not necessary to laminate a film on the other side of the polarizer (e.g., a polarizing plate with a two-layer structure). Furthermore, the other side may be a protective coating layer such as a hard coat. When polyester films are used as polarizer protective films on both sides of the polarizer, the slow axes of both polyester films are preferably approximately parallel to each other.In this specification, "substantially parallel" means that the inevitable misalignment that occurs when making them parallel is allowed, and means that the absolute value of the angle between the two directions is within the range of 0 to 5 degrees, preferably within the range of 0 to 4 degrees, more preferably within the range of 0 to 3 degrees, even more preferably within the range of 0 to 2 degrees, and even more preferably within the range of 0 to 1 degree.

[0016] The polarizer protective film may be laminated to the polarizer via any adhesive, or may be laminated directly to the polarizer without an adhesive. Any adhesive can be used without any particular limitations. As an example, a water-based adhesive (i.e., an adhesive component dissolved or dispersed in water) can be used. For example, an adhesive containing a polyvinyl alcohol resin and / or a urethane resin as a main component can be used. To improve adhesion, an adhesive further containing an isocyanate compound and / or an epoxy compound, etc., can also be used as needed. As another example, a photocurable adhesive can also be used. In one embodiment, a solventless ultraviolet-curable adhesive is preferred. Examples of photocurable adhesives include those containing a photocurable epoxy resin and a photocationic polymerization initiator.

[0017] The backlight system may be an edge-light system using components such as a light guide plate and a reflector, or a direct-type system. The backlight light source is preferably a "backlight light source having an emission spectrum with peak tops in the wavelength ranges of 400 nm to less than 495 nm, 495 nm to less than 600 nm, and 600 nm to less than 780 nm, with the half-width of each peak being 5 nm or more," with a representative example being a light source that emits excitation light and a backlight light source that includes quantum dots. The quantum dots can be used in the backlight light source, for example, by using a layer containing the quantum dots as the light-emitting layer.

[0018] The application of quantum dot technology to LCDs is a technology that has attracted attention in recent years due to the growing demand for an expanded color gamut. When a backlight source consisting of a light source that emits excitation light and an emission layer containing quantum dots is used, it is possible to reproduce more than 60% of the colors in the spectrum that the human eye can recognize. Examples of quantum dot technology that has been put into practical use include Nanosys' QDEF ＴＭ and QD Vision's Color IQ ＴＭ etc.

[0019] The quantum dot-containing light-emitting layer is a layer that contains quantum dots in a resin material such as polystyrene, and emits light of each color on a pixel-by-pixel basis based on excitation light emitted from a light source. This light-emitting layer may, for example, consist of a red light-emitting layer disposed in a red pixel, a green light-emitting layer disposed in a green pixel, and a blue light-emitting layer disposed in a blue pixel, and the quantum dots in these light-emitting layers of multiple colors generate light of different wavelengths (colors) based on the excitation light.

[0020] Examples of quantum dot materials include CdSe, CdS, ZnS:Mn, InN, InP, CuCl, CuBr, and Si. The particle size (size in one direction) of the quantum dots is, for example, approximately 2 to 20 nm. Among the above quantum dot materials, red-emitting materials include InP, green-emitting materials include CdSc, and blue-emitting materials include CdS. In such light-emitting layers, the emission wavelength can be changed by changing the size (particle size) of the quantum dots or the composition of the material. For example, the size (particle size) and material of the quantum dots can be controlled, mixed with a resin material, and applied separately for each pixel. Furthermore, since the use of heavy metals such as cadmium is being restricted in many applications, it is also preferable to use cadmium-free quantum dots while maintaining the same brightness and stability as conventional quantum dots.

[0021] A blue LED is preferably used as a light source for emitting excitation light, but laser light such as a semiconductor laser may also be used. When the excitation light emitted from the light source passes through the light-emitting layer, an emission spectrum having peak tops in the wavelength regions of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and less than 780 nm is generated. The narrower the half-width of the peak in each wavelength region, the wider the color gamut. However, it is preferable to design the shape of the emission spectrum in consideration of the required balance between the color gamut and the luminous efficiency.

[0022] There are two main mounting methods for quantum dot light sources, but they are not limited to the following. One is the on-edge method, in which quantum dots are mounted along the edge (side) of the backlight's light guide plate. In the on-edge method, quantum dots, which are particles with diameters of several nanometers to several tens of nanometers, are sealed in a glass tube with a diameter of several millimeters and placed between the blue LED and the light guide plate. Light from the blue LED is irradiated onto the glass tube, and the blue light that strikes the quantum dots is converted into green or red light. The on-edge method has the advantage of reducing the amount of quantum dots used, even in large screens. The other is the surface-mount method, in which quantum dots are mounted on the light guide plate. In the surface-mount method, quantum dots are dispersed in resin, formed into a sheet, and then sandwiched and sealed between two barrier films. The quantum dot film is then placed on the light guide plate. The barrier films can prevent deterioration of the quantum dots due to, for example, water or oxygen. As with the on-edge method, the blue LED is placed on the edge (side) of the light guide plate. Light from the blue LED enters the light guide plate and becomes a planar blue light that illuminates the quantum dot film. The surface mount method has at least two advantages. First, because the light from the blue LED passes through the light guide plate and hits the quantum dots, the impact of heat from the LED is minimal, making it easier to ensure reliability. Second, because it is in film form, it can be easily adapted to a wide range of screen sizes, from small to large.

[0023] In one embodiment, the backlight light source preferably has an emission spectrum with peak tops in the wavelength ranges of 400 nm to less than 495 nm, 495 nm to less than 600 nm, and 600 nm to 780 nm, with each peak having a half-width of 5 nm or more. The wavelength range of 400 nm to less than 495 nm is more preferably 430 nm to 470 nm. The wavelength range of 495 nm to less than 600 nm is more preferably 510 nm to 560 nm. The wavelength range of 600 nm to 780 nm is more preferably 600 nm to 750 nm, more preferably 630 nm to 700 nm, and even more preferably 630 nm to 680 nm. The half-width of each peak is preferably 10 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more. From the viewpoint of ensuring an appropriate color gamut, the upper limit of the half-width of each peak is preferably 140 nm or less, preferably 120 nm or less, preferably 100 nm or less, more preferably 80 nm or less, even more preferably 60 nm or less, and even more preferably 45 nm or less. Here, the half-width refers to the peak width (nm) at half the intensity of the peak intensity at the wavelength of the peak top. Any combination of the upper and lower limits of the individual wavelength ranges described herein is envisioned.

[0024] When multiple peaks are present in any of the wavelength regions of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and less than 780 nm, they are considered as follows. When the multiple peaks are independent peaks, it is preferable that the half-width of the peak with the highest peak intensity be within the above range. Furthermore, it is more preferable that the half-width of other peaks having an intensity of 70% or more of the highest peak intensity also be within the above range. For a single independent peak having a shape in which multiple peaks overlap, if the half-width of the peak with the highest peak intensity can be measured directly, that half-width is used. Here, an independent peak is one that has regions on both the short-wavelength side and the long-wavelength side of the peak where the intensity is half the peak intensity. In other words, when multiple peaks overlap and each peak does not have a region where the intensity is half the peak intensity, the multiple peaks are considered as a whole to be a single peak. In the case of a single peak having a shape in which a plurality of peaks overlap, the width (nm) of the peak at half the intensity of the highest peak among them is defined as the half-value width.

[0025] Among the multiple peaks, the peak with the highest peak intensity is defined as the peak top. It is preferable that the peaks with the highest peak intensity in the wavelength region of 400 nm or more and less than 495 nm, the wavelength region of 495 nm or more and less than 600 nm, or the wavelength region of 600 nm or more and less than 780 nm are independent of each other from the peaks in the other wavelength regions. In particular, in terms of color vividness, it is preferable that a region exists in the wavelength region between the peak with the highest peak intensity in the wavelength region of 495 nm or more and less than 600 nm and the peak with the highest peak intensity in the wavelength region of 600 nm or more and less than 780 nm, where the intensity is 1 / 3 or less of the highest peak intensity in the wavelength region of 600 nm or more and less than 780 nm.

[0026] The emission spectrum of the backlight light source can be measured using a spectrometer such as the multi-channel spectrometer PMA-12 manufactured by Hamamatsu Photonics.

[0027] As a result of extensive research, the present inventors have found that in a liquid crystal display device having a backlight source in which the half-width of each peak in the emission spectrum is relatively narrow, such as a light source that emits excitation light and a backlight source that contains quantum dots, by using a polyester film having an antireflection layer and / or a low-reflection layer on at least one surface and having a specific retardation as a polarizer protective film, it is possible to provide a liquid crystal display device in which rainbow spots are suppressed, and a polarizing plate useful for providing such a liquid crystal display device. The mechanism by which the occurrence of rainbow-like color spots is suppressed in the above embodiment is thought to be as follows.

[0028] When an oriented polyester film is disposed on one side of a polarizer, the polarization state of linearly polarized light emitted from a backlight unit or the polarizer changes as it passes through the polyester film. One of the factors that may cause this change in polarization state is thought to be the difference in refractive index at the interface between the air layer and the oriented polyester film, or the difference in refractive index at the interface between the polarizer and the oriented polyester film. When linearly polarized light incident on the oriented polyester film passes through each interface, a portion of the light is reflected due to the difference in refractive index between the interfaces. This change in the polarization state of both the emitted light and the reflected light is thought to be one of the factors that cause rainbow-like color spots. Therefore, by applying an anti-reflection layer or a low-reflection layer to the surface of the oriented polyester film to reduce surface reflection, reflection at the interface between the air layer and the oriented polyester film is suppressed, thereby suppressing rainbow-like color spots.

[0029] As described above, even when a backlight source having a relatively narrow half-width of each peak in the emission spectrum, such as a light source that emits excitation light and a backlight source that includes quantum dots, is combined with a polarizing plate that uses a polyester film as a polarizer protective film, it is possible to suppress rainbow-like color spots and provide good visibility.

[0030] In one embodiment, the light-transmitting substrate film, polarizer protective film, or polyester film that can be used therefor preferably has a retardation of 1000 nm or more and / or a retardation of 8000 nm or less. A retardation within the above range tends to further reduce iridescence, which is preferable. The preferred lower limit is 1500 nm, more preferably 2000 nm, even more preferably 2500 nm, and even more preferably 2800 nm. The preferred upper limit is 5000 nm, more preferably 4000 nm, even more preferably 3500 nm, and particularly preferably 3300 nm. In this specification, retardation refers to in-plane retardation unless otherwise specified. Furthermore, it is preferable that the average retardation of film pieces cut out along the width direction of the film at 50 mm lengths on the left and right sides at positions 100 mm apart from the center position is also within the above range. Within the preferred range of the retardation, it is particularly preferred to set the retardation to 2000 nm or more. By setting the retardation to 2000 nm or more, it becomes possible to obtain a polyester film with well-balanced mechanical properties while easily suppressing iridescence. The polyester film is preferably a biaxially oriented polyester film.

[0031] The retardation can be determined by measuring the refractive index in two axial directions and the thickness, or by using a commercially available automatic birefringence measuring device such as the RETS-100 series (Otsuka Electronics Co., Ltd.). The refractive index can be determined by an Abbe refractometer (measurement wavelength: 589 nm).

[0032] In one embodiment, the light-transmitting substrate film, polarizer protective film, or polyester film that can be used therefor preferably has a film piece (or pieces) cut along the width direction (in the case of a roll, the direction perpendicular to the unwinding direction of the roll) at 50 mm lengths from the center position at positions every 100 mm from the center position, and the average value of the difference (ny - nx) between the refractive index (nx) in the unwinding direction of the roll (longitudinal direction) and the refractive index (ny) in the direction perpendicular thereto (width direction) is preferably 0.02 or more. When the average value of (ny - nx) is equal to or greater than the above range, iridescence tends to be more easily reduced, which is preferable. The preferred lower limit is 0.025, and the more preferred lower limit is 0.03. Furthermore, in order to improve the mechanical properties of the film in the longitudinal direction and improve the balance with the physical properties in the width direction, thereby providing a film with excellent handleability, the upper limit of ny - nx is preferably 0.055, more preferably 0.05, and particularly preferably 0.045. Similarly, if the average value of (ny-nx) is within the above range, the anti-reflection effect can be easily achieved in both the longitudinal and width directions, and contrast can be increased. Furthermore, when the screen is viewed from an oblique angle of 45 to 70 degrees, the reflected light is mainly S-polarized light, but whether the S-polarized light and the fast axis or slow axis of the light-transmitting substrate film are parallel, there is little difference in bright contrast (they appear black in the same way), that is, there is a tendency that no difference in blackness is observed even when the direction from which the screen is viewed is different (there is no difference depending on the axis direction), which is preferable.

[0033] The refractive index of a light-transmitting substrate film (particularly a biaxially stretched film) usually varies across the width of the film due to the influence of the bowing phenomenon. Furthermore, in a wide film (e.g., a width of 500 mm or more), the appearance of rainbow unevenness usually varies across the width of the film. Similarly, in a wide film (e.g., a width of 500 mm or more), contrast tends to vary across the screen, and when S-polarized light and either the fast axis or the slow axis of the film are parallel, differences in bright contrast tend to occur, i.e., differences in blackness tend to be readily apparent across the screen. Therefore, in a plurality of film pieces cut out along the width direction (in the case of a roll, the direction perpendicular to the unwinding direction of the roll) at 50 mm lengths from the center position to the left and right, the maximum value minus the minimum value of (ny-nx) is preferably 0.02 or less, more preferably 0.018 or less, even more preferably 0.016 or less, particularly preferably 0.015 or less, even more preferably 0.14 or less, and most preferably 0.10 or less. From the viewpoint of manufacturing costs, the maximum value-minimum value of (ny-nx) is preferably 0.001 or more, and more preferably 0.005 or more.

[0034] The absolute value of the angle between the longitudinal direction of the light-transmitting substrate film (in the case of a roll, the unwinding direction of the roll) and the transmission axis direction of the polarizer is preferably set within a range of 90 degrees ± 15 degrees (preferably within a range of 90 degrees ± 10 degrees, more preferably within a range of 90 degrees ± 5 degrees, even more preferably within a range of 90 degrees ± 3 degrees, still more preferably within a range of 90 degrees ± 2 degrees, and particularly preferably within a range of 90 degrees ± 1 degree).

[0035] The refractive index ny of the light-transmitting substrate film (or a polyester film that can be used therein) is preferably set to 1.61 or more and 1.76 or less. The upper limit of the refractive index ny is preferably 1.76, more preferably 1.73, even more preferably 1.71, and particularly preferably 1.7. The lower limit of the refractive index ny is preferably 1.61, more preferably 1.63, even more preferably 1.64, and particularly preferably 1.66.

[0036] On the other hand, the refractive index nx of the light-transmitting substrate film (or a polyester film that can be used therein) is preferably set to, for example, 1.6 or more and 1.7 or less. The upper limit of the refractive index nx is more preferably 1.66, and even more preferably 1.65. The lower limit of the refractive index nx is more preferably 1.62, and even more preferably 1.63.

[0037] The direction perpendicular to the longitudinal direction of the light-transmitting substrate film (in the case of a roll, the unwinding direction of the roll) may be approximately parallel to the transmission axis direction of the polarizer. The direction perpendicular to the longitudinal direction of the light-transmitting substrate film can be determined, for example, by measurement using a molecular orientation meter (for example, MOA-6004 molecular orientation meter manufactured by Oji Scientific Instruments Co., Ltd.).

[0038] In one embodiment, the polarizer protective film can be used in both the polarizing plate on the incident light side (light source side) and the polarizing plate on the exit light side (viewing side). In a polarizing plate arranged on the incident light side, the polarizer protective film may be arranged on the incident light side, the liquid crystal cell side, or both sides of the polarizer, but is preferably arranged at least on the exit light side. In a polarizing plate arranged on the exit light side, the polarizer protective film may be arranged on the liquid crystal cell side, the exit light side, or both sides of the polarizer, but is preferably arranged at least on the exit light side.

[0039] The polyester used in the polyester film as the light-transmitting substrate film or polarizer protective film may be polyethylene terephthalate or polyethylene naphthalate, but may also contain other copolymer components. These resins have excellent transparency and excellent thermal and mechanical properties, and retardation can be easily controlled by stretching. In particular, polyethylene terephthalate is the most suitable material because it has a large intrinsic birefringence, and by stretching the film, the refractive index in the direction perpendicular to the stretching direction can be kept low, and large retardation can be relatively easily obtained even with a thin film. In one embodiment, the light-transmitting substrate film or polarizer protective film is preferably a biaxially stretched polyethylene terephthalate film. In polyethylene terephthalate, when the glycol component and the dicarboxylic acid component are each taken as 100 mol %, the total amount of glycol components other than ethylene glycol (e.g., diethylene glycol, trimethylene glycol, tetramethylene glycol) and dicarboxylic acid components other than terephthalic acid (e.g., isophthalic acid) is preferably 10 mol % or less, more preferably 5 mol % or less, and even more preferably 3 mol % or less. In particular, the content of dicarboxylic acid components other than terephthalic acid is preferably 3 mol % or less, more preferably 2 mol % or less, and even more preferably 1.5 mol % or less.

[0040] In one embodiment, the lower limit of the longitudinal breaking elongation of the light-transmitting substrate film, the polarizer protective film, or the polyester film that can be used therefor is preferably 50%, more preferably 80%, and particularly preferably 100%, from the viewpoint of preventing breakage when tension is applied in the processing step. The preferred upper limit is 200%. In addition, the average longitudinal breaking elongation of film pieces cut out in lengths of 50 mm to the left and right at positions every 100 mm from the center position along the width direction of the film is also preferably within the above range.

[0041] In one embodiment, for the purpose of suppressing deterioration of an optically functional dye such as an iodine dye, the light-transmitting substrate film, the polarizer protective film, or the polyester film that can be used therefor desirably has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance is more preferably 15% or less, even more preferably 10% or less, and particularly preferably 5% or less. The light transmittance is measured perpendicular to the plane of the film and can be measured using a spectrophotometer (e.g., Hitachi U-3500 model).

[0042] In order to achieve a light transmittance of 20% or less, it is desirable to appropriately adjust the type, concentration, and film thickness of the ultraviolet absorber. Examples of ultraviolet absorbers include organic and inorganic ultraviolet absorbers, with organic ultraviolet absorbers being preferred from the viewpoint of transparency. Examples of organic ultraviolet absorbers include benzotriazoles, benzophenones, cyclic iminoesters, and combinations thereof, but are not particularly limited as long as the absorbance is within the desired range. From the viewpoint of durability, benzotriazoles, cyclic iminoesters, and combinations thereof are particularly preferred. When two or more ultraviolet absorbers are used in combination, ultraviolet rays of different wavelengths can be simultaneously absorbed, thereby further improving the ultraviolet absorption effect.

[0043] Examples of the benzophenone-based ultraviolet absorber, benzotriazole-based ultraviolet absorber, and acrylonitrile-based ultraviolet absorber include 2-[2'-hydroxy-5'-(methacryloyloxymethyl)phenyl]-2H-benzotriazole, 2-[2'-hydroxy-5'-(methacryloyloxyethyl)phenyl]-2H-benzotriazole, 2-[2'-hydroxy-5'-(methacryloyloxypropyl)phenyl]-2H-benzotriazole, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2,4-di-tert-butyl-6-(5-chlorobenzotriazol-2-yl)phenol, 2-(2'-hydroxybenzotriazole-4,4'-diyl)phenyl Examples of cyclic imino ester-based ultraviolet absorbers include 2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazinon-4-one), 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazin-4-one, and 2-phenyl-3,1-benzoxazin-4-one.

[0044] In addition, it is also a preferred embodiment that the light-transmitting substrate film contains various additives other than the UV absorber, as long as they do not impair the effects of the present invention. Examples of additives include inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light stabilizers, flame retardants, heat stabilizers, antioxidants, antigelling agents, surfactants, etc. In addition, in order to achieve high transparency, it is also preferable that the light-transmitting substrate film does not substantially contain particles. "Substantially not containing particles" means, for example, in the case of inorganic particles, that the content of inorganic elements, when quantified by fluorescent X-ray analysis, is 50 ppm or less, preferably 10 ppm or less, particularly preferably below the detection limit.

[0045] The light-transmitting substrate film may be subjected to corona treatment, coating treatment and / or flame treatment in order to improve adhesion to the polarizer.

[0046] In one embodiment, to improve adhesion to the polarizer, it is preferable that at least one surface of the light-transmitting substrate film has an easy-adhesion layer mainly composed of at least one of polyester resin, polyurethane resin, and polyacrylic resin. Here, the term "main component" refers to a component that accounts for 50% by mass or more of the solid components constituting the easy-adhesion layer. The coating liquid used to form the easy-adhesion layer is preferably an aqueous coating liquid containing at least one of water-soluble or water-dispersible copolymer polyester resin, acrylic resin, and polyurethane resin. Examples of such coating liquids include water-soluble or water-dispersible copolymer polyester resin solutions, acrylic resin solutions, and polyurethane resin solutions disclosed in Japanese Patent Nos. 3,567,927, 3,589,232, 3,589,233, 3,900,191, and 4,150,982.

[0047] The easy-adhesion layer can be obtained, for example, by applying the coating liquid to one or both sides of a uniaxially stretched film in the longitudinal direction, drying the film at 100 to 150°C, and then stretching the film in the transverse direction. The final coating amount of the easy-adhesion layer is set to 0.05 g / m from the viewpoints of adhesion to the polarizer, blocking resistance, etc. ２ 0.20g / m or more ２ It is preferable to control the amount as follows: When easy-adhesion layers are provided on both sides of the light-transmitting substrate film, the coating amounts of the easy-adhesion layers on both sides may be the same or different, and can be set independently within the above ranges.

[0048] It is preferable to add particles to the adhesion layer to impart slipperiness. The average particle size of the particles is preferably 2 μm or less from the viewpoint of preventing falling off. Examples of particles to be contained in the adhesion layer include inorganic particles such as titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, and calcium fluoride, and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. These may be added to the adhesion layer alone or in combination of two or more.

[0049] The coating liquid can be applied by any known method, such as reverse roll coating, gravure coating, kiss coating, roll brushing, spray coating, air knife coating, wire bar coating, and pipe doctor coating, which can be used alone or in combination.

[0050] The average particle size of the particles can be measured by the following method: Particles are photographed with a scanning electron microscope (SEM), and the maximum diameters (the distance between the two most distant points) of 300 to 500 particles are measured at a magnification such that the size of the smallest particle is 2 to 5 mm, and the average value is taken as the average particle size.

[0051] (Hard Coat Layer) When the light-transmitting substrate film of the present invention is used as a surface protection film for protecting an image display device (e.g., a liquid crystal display device) by placing it on the surface, it is preferable that at least one surface of the film has a hard coat layer having the function of an antiglare layer. The hard coat layer is preferably placed on the surface side of the image display device on the light-transmitting substrate film. The resin for forming the hard coat layer can be any resin, including siloxane-based, inorganic hybrid-based, acrylic-based, urethane acrylate-based, polyester acrylate-based, and epoxy-based resins, and is not particularly limited. In addition, two or more materials can be mixed and used, or particles such as inorganic filler or organic filler can be added.

[0052] Resins for forming the hard coat layer include compounds having a (meth)acrylate functional group, such as polyester (meth)acrylate, urethane (meth)acrylate, epoxy (meth)acrylate, and silicone (meth)acrylate, as well as compounds having a functional group with an unsaturated double bond, such as an allyl group or a vinyl group. Furthermore, a polyfunctional monomer may be used in combination to increase the hardness of the hard coat layer. Examples of polyfunctional monomers include trimethylolpropane tri(meth)acrylate, hexanediol (meth)acrylate, tripropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and neopentyl glycol di(meth)acrylate. The above materials may be used alone or in combination.

[0053] When the active energy rays for curing the hard coat layer are ultraviolet rays, it is preferable to add a photopolymerization initiator. The photopolymerization initiator may be a radical polymerization initiator, a cationic polymerization initiator, or a mixed system of a cationic polymerization initiator and a radical polymerization initiator. However, a radical polymerization initiator is particularly preferable because of its high reaction rate and excellent productivity. Examples of ultraviolet radical polymerization initiators include alkylphenones, benzoins, benzophenones, phosphine oxides, ketals, anthraquinones, thioxanthones, azo compounds, peroxides, 2,3-dialkyldione compounds, disulfide compounds, fluoroamine compounds, aromatic sulfonium compounds, titanocenes, and phenyl oxyacetates. These may be used alone or in combination of two or more. Further specific examples include carbonyl compounds such as acetophenone, 2,2-diethoxyacetophenone, p-dimethylacetophenone, p-dimethylaminopropiophenone, benzophenone, 2-chlorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-bisdiethylaminobenzophenone, Michler's ketone, benzil, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, methylbenzoyl formate, p-isopropyl-α-hydroxyisobutylphenone, α-hydroxyisobutylphenone, 2,2-dimethoxy-2-phenylacetophenone, and 1-hydroxycyclohexyl phenyl ketone; sulfur compounds such as tetramethylthiuram monosulfide, tetramethylthiuram disulfide, thioxanthone, 2-chlorothioxanthone, and 2-methylthioxanthone; and peroxide compounds such as benzoyl peroxide and di-t-butyl peroxide. The amount of the photopolymerization initiator added can be in the range of 0.1 parts by mass or more, more preferably 1 part by mass or more, and 30 parts by mass or less, more preferably 20 parts by mass or less, relative to 100 parts by mass of the active energy ray-curable resin. When the amount added is 0.1 parts by mass or more, the hardness of the hard coat layer can be increased, which is preferable. When the amount added is 30 parts by mass or less, there is no risk of yellowing of the hard coat layer, and the hard coat layer is sufficiently cured, which is preferable.

[0054] Furthermore, the hard coat layer may contain various additives to the extent that the performance thereof is not impaired. Examples of the various additives include polymerization inhibitors, crosslinking agents, antistatic agents, adhesion improvers, antioxidants, leveling agents, coupling agents, antifoaming agents, fillers, solvents, antiglare agents, antireflection agents, inorganic fillers, and organic fillers. Among these, antiglare agents, inorganic fillers, and / or organic fillers are preferably used.

[0055] The refractive index of the hard coat layer is preferably smaller than that of the easy-adhesion layer from the viewpoint of suppressing iridescent color (interference fringes) of the hard coat film.

[0056] (Film Thickness of Hard Coat Layer) The film thickness of the hard coat layer is preferably 1 to 50 μm. If it is 1 μm or more, it can be cured sufficiently. In order to increase the pencil hardness, it is more preferably 5 μm or more. Furthermore, by making the thickness 50 μm or less, curling due to cure shrinkage of the hard coat layer can be suppressed, and the handleability of the film can be improved.

[0057] (Coating Method) The hard coat layer can be coated by any method, including a Mayer bar, gravure coater, die coater, knife coater, etc., without any particular limitation, and can be appropriately selected depending on the viscosity, film thickness, etc.

[0058] (Curing Conditions) Methods for curing the hard coat layer include curing methods using energy rays such as ultraviolet rays and electron beams, and heat. To reduce damage to the film, curing methods using ultraviolet rays and electron beams are preferred.

[0059] (Pencil hardness) The pencil hardness of the hard coat layer is preferably 2H or more, more preferably 3H or more. A pencil hardness of 2H or more prevents scratches and does not reduce visibility. Generally, a high pencil hardness of the hard coat layer is preferable, but a pencil hardness of 9H or less, 8H or less, 7H or less, or 6H or less can be used in practice without any problems.

[0060] (Characteristics of hard coat layer) The hard coat layer can be used for the purpose of increasing the pencil hardness of the surface to protect the image display device as described above, and preferably has a high transmittance. The transmittance of the hard coat layer is preferably 85% or more, more preferably 87% or more, and even more preferably 88% or more, from the viewpoint of sufficient visibility. The total light transmittance of the hard coat layer is generally preferably as high as possible, but from the viewpoint of stable production, it is preferably 99% or less, and may be 98% or less or 97% or less.

[0061] The haze of the hard coat layer is preferably 10% or more from the viewpoint of preventing glare when used as a display. The haze of the hard coat layer is more preferably 15% or more, and most preferably 20% or more. If the haze is 10% or more, the visibility of the image can be improved. If the haze is too high, it may affect the clarity and front brightness of the image, so the haze is preferably 60% or less, more preferably 50% or less.

[0062] The hard coat layer may further have other functions added thereto. For example, a hard coat layer having additional functions such as an antiglare antireflection layer, an antireflection layer, a low reflection layer, or an antistatic layer may be preferably used.

[0063] In one embodiment, it is preferable to provide an antireflection layer and / or a low-reflection layer on at least one surface of the light-transmitting substrate film, the polarizer protective film, or the polyester film that can be used therefor. The surface reflectance of the antireflection layer is preferably 2% or less in order to prevent rainbow-like color spots. The surface reflectance of the antireflection layer is more preferably 1.6% or less, even more preferably 1.2% or less, and particularly preferably 1.0% or less. The lower limit of the surface reflectance of the antireflection layer is not particularly limited, but is, for example, 0.01%. The surface reflectance can be measured by any method; for example, a spectrophotometer (Shimadzu Corporation, UV-3150) can be used to measure the light reflectance at a wavelength of 550 nm from the surface on the antireflection layer side.

[0064] The antireflection layer may be a single layer or a multilayer. In the case of a single layer, an antireflection effect can be obtained by forming a low refractive index layer made of a material with a lower refractive index than the polyester film so that the thickness is ¼ wavelength or an odd multiple of the light wavelength. In the case of a multilayer antireflection layer, an antireflection effect can be obtained by alternately forming two or more low refractive index layers and high refractive index layers and laminating them while appropriately controlling the thickness of each layer. Furthermore, a hard coat layer can be laminated between the antireflection layers as needed.

[0065] Examples of methods for forming an antireflection layer include a dry coating method in which an antireflection layer is formed on the surface of a light-transmitting substrate film by vapor deposition or sputtering, a wet coating method in which an antireflection coating liquid is applied to the surface of a light-transmitting substrate film and then dried to form an antireflection layer, and a combined method in which both of these methods are used. The composition of the antireflection layer and the method for forming it are not particularly limited as long as they satisfy the above-mentioned properties.

[0066] Known low-reflection layers can be used. For example, they can be formed by laminating at least one metal or oxide thin film by vapor deposition or sputtering, or by coating one or more organic thin films. A low-reflection layer preferably comprises a single layer of an organic thin film having a lower refractive index than the light-transmitting substrate film or a hard coat layer or the like to be laminated on the light-transmitting substrate film. The surface reflectance of the low-reflection layer is preferably less than 5%, more preferably 4% or less, and even more preferably 3% or less. The lower limit is preferably about 0.8% to 1%.

[0067] The anti-reflection layer and / or low-reflection layer may further be provided with an anti-glare function. This can further suppress iridescence. That is, a combination of an anti-reflection layer and an anti-glare layer, a combination of a low-reflection layer and an anti-glare layer, or a combination of an anti-reflection layer, a low-reflection layer and an anti-glare layer may be used. A combination of a low-reflection layer and an anti-glare layer is particularly preferred. A known anti-glare layer can be used as the anti-glare layer. For example, from the viewpoint of suppressing surface reflection of the film, a preferred embodiment is to laminate an anti-glare layer on a polyester film, and then laminate an anti-reflection layer or a low-reflection layer on the anti-glare layer.

[0068] When providing an antireflection layer or a low-reflection layer, it is preferable to adjust the refractive index of the easy-adhesion layer so that it is close to the geometric mean of the refractive index of the antireflection layer and the refractive index of the light-transmitting substrate film, from the viewpoint of suppressing interference by reflected light. The refractive index of the easy-adhesion layer can be adjusted by using a known method, and can be easily adjusted, for example, by adding a metal species such as titanium, zirconium, germanium, or other metal oxide particles to the binder resin.

[0069] A polyester film that can be used as a light-transmitting substrate film or a polarizer protective film can be produced by a general method for producing a polyester film, for example, by melting a polyester resin, extruding the non-oriented polyester into a sheet, stretching the sheet in the machine direction at a temperature equal to or higher than the glass transition temperature by utilizing a speed difference between rolls, stretching the sheet in the transverse direction using a tenter, and then heat-treating the sheet.

[0070] Specifically, the film-forming conditions for the polyester film are as follows: the longitudinal stretching temperature and the transverse stretching temperature are preferably 80 to 160°C, more preferably 90 to 150°C, and particularly preferably 100 to 140°C. To orient the film so that the slow axis is in the TD direction, the longitudinal stretching ratio is preferably 1 to 4.5 times, more preferably 2.5 to 3.5 times, and particularly preferably 2.7 to 3.3 times. The transverse stretching ratio is preferably 2.5 to 6 times, more preferably 3 to 5.5 times, and particularly preferably 3.5 to 4.7 times.

[0071] In the subsequent heat treatment, the heat treatment temperature (heat setting temperature) is preferably 140 to 250°C, more preferably 180 to 245°C, and particularly preferably 200 to 245°C, to prevent strength reduction and problems during post-processing. Here, the angle between the main orientation axis and the width direction of the biaxially stretched film obtained by stretching typically increases toward both ends of the film due to the influence of the bowing phenomenon. At the center of the width direction of the first winding roll around which the biaxially stretched film is wound, the absolute value of the angle between the main orientation axis and the width direction is within the range of 0 to 10 degrees, while at both ends of the width direction of the first winding roll, the absolute value of the angle between the main orientation axis and the width direction is greater than 0 degrees and 40 degrees or less. The first winding roll can be slit at a predetermined position in the width direction to obtain multiple second winding rolls. For example, if the first winding roll is slit at the center position, two second winding rolls can be obtained. For example, if the first winding roll is slit into thirds in the width direction, three second winding rolls can be obtained. The second winding roll may correspond to the roll of the light-transmitting polyester film in the present invention, and may be simply referred to as a "roll."

[0072] In order to keep the maximum-minimum value of (ny-nx) in the width direction of the film or its roll low, it is preferable to make the longitudinal stretching ratio as small as possible and to keep the heat setting temperature low. Furthermore, it is also preferable to perform transverse stretching and heat setting in separate tenters.

[0073] Furthermore, in order to keep the maximum-minimum value of (ny - nx) in the width direction of the film or its roll low, it is preferable to suppress the bowing phenomenon and ensure uniform crystallization during heat setting. Here, to suppress the bowing phenomenon, it is preferable to lower the molecular tension in the MD direction compared to the TD direction after TD stretching is completed. For example, the following methods are available. It is preferable to make the longitudinal stretching ratio smaller than the transverse stretching ratio. The MD / TD stretching ratio ratio is preferably 0.5 or more, more preferably 0.55 or more, even more preferably 0.6 or more, particularly preferably 0.63 or more, and most preferably 0.65 or more. The MD / TD stretching ratio ratio is preferably 0.9 or less, more preferably 0.87 or less, even more preferably 0.85 or less, particularly preferably 0.82 or less, and most preferably 0.8 or less. The stretching temperature during MD stretching is preferably 100°C to 140°C. To prevent rapid cooling between the low-speed rolls and the high-speed rolls, the ambient temperature is preferably 30° C. to 50° C. After MD stretching, the film is preferably heated to relax the film in the MD direction, for example, by 1% to 10%.

[0074] Furthermore, during TD stretching and heat setting, the temperature at the edges tends to be lower than that at the center due to the influence of the clips. Therefore, it is preferable to maintain a uniform temperature across the width of the film as much as possible by adjusting the wind speed in the TD direction during these processes.

[0075] Furthermore, if crystallization progresses rapidly during heat setting, (ny - nx) tends to become non-uniform. It is preferable to suppress a rapid temperature increase by gradually increasing the temperature in the heat setting zone or by adjusting the air volume. When gradually increasing the temperature in the heat setting zone, it is preferable to provide a temperature region ranging from the tenter temperature at the end of the stretching step + 20°C or more to the maximum tenter temperature in the heat setting step - 20°C or less. In particular, when the heat setting temperature is 200°C or more, it is preferable to provide a temperature region ranging from the tenter temperature at the end of the stretching step + 30°C or more to the maximum tenter temperature in the heat setting step - 30°C or less.

[0076] In order to suppress fluctuations in retardation, it is preferable that the thickness unevenness of the film is small. Since the stretching temperature and stretching ratio have a significant effect on the thickness unevenness of the film, it is preferable to optimize the film-forming conditions from the viewpoint of reducing the thickness unevenness.

[0077] In one embodiment, the thickness unevenness of the light-transmitting substrate film, polarizer protective film, or polyester film that can be used therefor is preferably 5% or less, more preferably 4.5% or less, even more preferably 4% or less, and particularly preferably 3% or less. The thickness unevenness of the film can be measured as follows. A tape-shaped film sample (3 m) is taken, and the thickness is measured at 100 points at 1 cm intervals using a Millitron 1240 electronic micrometer manufactured by Seiko EM Corporation. The maximum thickness (dmax), minimum thickness (dmin), and average thickness (d) are determined from the measured values, and the thickness unevenness (%) is calculated using the following formula. It is preferable to perform the measurement three times and calculate the average value. Thickness unevenness (%) = ((dmax - dmin) / d) × 100

[0078] As described above, the retardation can be controlled within a specific range by appropriately setting the stretching ratio, stretching temperature, and film thickness. For example, the higher the stretching ratio, the lower the stretching temperature, and the thicker the film, the easier it is to obtain a high retardation. Conversely, the lower the stretching ratio, the higher the stretching temperature, and the thinner the film, the easier it is to obtain a low retardation. From the viewpoint of thickness direction retardation, it is desirable to appropriately set the film thickness within the range described below. In addition to controlling the retardation, it is preferable to set the final film-forming conditions taking into account the physical properties required for processing.

[0079] In one embodiment, the thickness of the light-transmitting substrate film, the polarizer protective film, or the polyester film that can be used therefor is not particularly limited, but is preferably 15 μm or more, more preferably 20 μm or more, and even more preferably 25 μm or more. The thickness is preferably 150 μm or less, more preferably 120 μm or less, and even more preferably 100 μm or less. By setting the thickness within the above range, the strength required for the polarizer protective film can be ensured, and the film can be prevented from becoming thicker than necessary.

[0080] Furthermore, as a method for incorporating an ultraviolet absorber into a polyester film that can be used as a light-transmitting substrate film or a polarizer protective film, a combination of known methods can be adopted. For example, the ultraviolet absorber can be incorporated by a method in which a dried ultraviolet absorber and a polymer raw material are blended in advance using a kneading extruder to prepare a masterbatch, and then the predetermined masterbatch and the polymer raw material are mixed during film formation.

[0081] In this case, the concentration of the ultraviolet absorber in the masterbatch is preferably 5 to 30% by mass in order to disperse the ultraviolet absorber uniformly and to compound economically. The masterbatch is prepared using a kneading extruder, and the extrusion temperature is preferably from the melting point of the polyester raw material to 290°C inclusive for 1 to 15 minutes in order to prevent a decrease in the amount of ultraviolet absorber and a decrease in the viscosity of the masterbatch. A stabilizer, a color tone adjuster, and / or an antistatic agent may be added as needed.

[0082] In one embodiment, it is preferable that the polyester film has a multilayer structure of at least three layers, and that an ultraviolet absorber be added to the intermediate layer of the film. A three-layer film containing an ultraviolet absorber in the intermediate layer can be specifically produced as follows: Polyester pellets alone for the outer layer and a masterbatch containing an ultraviolet absorber and polyester pellets for the intermediate layer are mixed in a predetermined ratio, dried, and then fed into a known melt lamination extruder, extruded into a sheet through a slit die, and cooled and solidified on a casting roll to produce an unstretched film. That is, using two or more extruders, a three-layer manifold, or a merging block (e.g., a merging block having a rectangular merging portion), film layers constituting both outer layers and a film layer constituting the intermediate layer are laminated, and the three-layer sheet is extruded through a die and cooled on a casting roll to produce an unstretched film. High-precision filtration is preferably performed during melt extrusion to remove foreign matter contained in the raw polyester that may cause optical defects. The filtering particle size (initial filtering efficiency 95%) of the filter medium used for high-precision filtering of molten resin is preferably 15 μm or less from the viewpoint of removing foreign matter.

[0083] In one embodiment, the light-transmitting substrate film is a light-transmitting substrate film laminated on at least one surface of a polarizer as a polarizer protective film, wherein the width of the light-transmitting substrate film is 500 mm or more, and in a plurality of film pieces cut out along the width direction of the light-transmitting substrate film at positions every 100 mm from a center position and having a length of 50 mm to the left and right, the average value of the difference (ny-nx) between the refractive index (nx) in the longitudinal direction and the refractive index (ny) in the width direction is 0.02 or more, the maximum value-minimum value of (ny-nx) is 0.02 or less, the average value of retardation is 1000 nm or more, and the average value of breaking elongation in the longitudinal direction is 50% or more, and the absolute value of the angle between the main alignment axis and the width direction at one end in the width direction of the light-transmitting substrate film is within a range of 0 to 30 degrees (preferably within a range of 0 to 20 degrees, 0 to 15 degrees, or 0 to 10 degrees), Preferably, the light-transmitting substrate film is characterized in that the absolute value of the angle between the main orientation axis and the width direction at the other end in the width direction of the light-transmitting substrate film is more than 0 degrees and 40 degrees or less (preferably 10 degrees or more, 15 degrees or more, or 20 degrees or more, and / or 37 degrees or less or 35 degrees or less).

[0084] In one embodiment, the light-transmitting substrate film is a light-transmitting substrate film laminated on at least one surface of a polarizer as a polarizer protective film, wherein the width of the light-transmitting substrate film is 500 mm or more, and in a plurality of film pieces cut out along the width direction of the light-transmitting substrate film at positions every 100 mm from a center position and having a length of 50 mm to the left and right, the average value of the difference (ny-nx) between the refractive index (nx) in the longitudinal direction and the refractive index (ny) in the width direction is 0.02 or more, the maximum value-minimum value of (ny-nx) is 0.02 or less, the average value of retardation is 1000 nm or more, and the average value of breaking elongation in the longitudinal direction is 50% or more, and the absolute value of the angle formed between the main alignment axis and the width direction at one end in the width direction of the light-transmitting substrate film is more than 0 degree and 30 degrees or less (preferably 5 degrees or more, 10 degrees or more, or 15 degrees or more, and / or 25 degrees or less or 20 degrees or less), Preferably, the light-transmitting substrate film is characterized in that the absolute value of the angle between the main orientation axis and the width direction at the other end in the width direction of the light-transmitting substrate film is more than 0 degrees and 40 degrees or less (preferably 10 degrees or more, 15 degrees or more, or 20 degrees or more, and / or 37 degrees or less or 35 degrees or less).

[0085] The light-transmitting substrate film and the polarizer protective film may be in the form of a roll. The width of the roll is preferably 500 mm or more from the viewpoint of production efficiency, and preferably 2500 mm or less from the viewpoint of equipment constraints. The wound length of the roll is preferably 200 m or more from the viewpoint of production efficiency, and preferably 20000 m or less from the viewpoint of equipment constraints. The upper limit of the width of the roll is more preferably 2300 mm, and even more preferably 2000 mm. The lower limit of the width of the roll is more preferably 650 mm, and even more preferably 800 mm.

[0086] In one embodiment, the absolute value of the angle between the main orientation axis and the width direction at one end of the roll in the width direction is preferably within a range of 0 to 30 degrees, more preferably within a range of 0 to 20 degrees, even more preferably within a range of 0 to 15 degrees, and particularly preferably within a range of 0 to 10 degrees.

[0087] In one embodiment, the absolute value of the angle between the main orientation axis and the width direction at one end of the roll in the width direction is preferably more than 0 degrees and not more than 30 degrees. The absolute value of this angle is particularly preferably 5 degrees or more, 10 degrees or more, or 15 degrees or more, and / or 25 degrees or less, or 20 degrees or less.

[0088] At the other end of the roll in the width direction, the absolute value of the angle between the main orientation axis and the width direction is preferably more than 0 degrees and not more than 40 degrees. The absolute value of this angle is more preferably not more than 37 degrees, and even more preferably not more than 35 degrees. The absolute value of this angle is also preferably not less than 10 degrees, more preferably not less than 15 degrees, and particularly preferably not less than 20 degrees.

[0089] For example, when the first winding roll is slit at the center (when two second winding rolls are obtained), the absolute value of the angle between the main orientation axis and the width direction at one end of the second winding roll in the width direction is preferably within the range of 0 to 10 degrees, more preferably within the range of 0 to 5 degrees, and particularly preferably within the range of 0 to 3 degrees. Similarly, in this case, the absolute value of the angle between the main orientation axis and the width direction at the other end of the second winding roll in the width direction is the same as the range described above for the other end.

[0090] On the other hand, when the first winding roll is slit into thirds in the width direction (when three second winding rolls are obtained), it is preferable that the absolute value of the angle between the main orientation axis and the width direction at one end in the width direction of the second winding roll located in the center is more than 0 degrees and not more than 30 degrees, and the absolute value of the angle between the main orientation axis and the width direction at the other end in the width direction of the second winding roll located in the center is more than 0 degrees and not more than 30 degrees. It is also preferable that the absolute value of the angle between the main orientation axis and the width direction at one end in the width direction of the second winding roll located on both sides is more than 0 degrees and not more than 30 degrees, and the absolute value of the angle between the main orientation axis and the width direction at the other end in the width direction of the second winding roll located on both sides is more than 0 degrees and not more than 40 degrees.

[0091] When the absolute value of the angle between the main orientation axis and the width direction at one end of the roll in the width direction and the absolute value of the angle between the main orientation axis and the width direction at the other end of the roll in the width direction are within these ranges, the physical properties of the film are made uniform in the width direction of the roll. Specifically, the maximum value-minimum value of (ny-nx) in the width direction of the roll can be easily adjusted to 0.02 or less.

[0092] The one end of the roll in the width direction is a portion less than 200 mm from one end of the roll in the width direction. Similarly, the other end of the roll in the width direction is a portion less than 200 mm from the other end of the roll in the width direction. In other words, the end may be a region corresponding to the remainder when a piece of film is cut out to the extreme end in lengths of 50 mm on both sides, centered at positions 100 mm apart from the roll center position.

[0093] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples, and appropriate modifications can be made within the scope of the present invention, and all such modifications are included in the technical scope of the present invention. The physical properties in the following examples were evaluated as follows.

[0094] (1) Refractive Index of Polyester Film Each film piece was cut at 50 mm intervals on both sides along the width direction (direction perpendicular to the unwinding direction (longitudinal direction) of the roll, centered at positions every 100 mm from the roll center position, to serve as a molecular orientation measurement sample. The slow axis direction of each film piece was determined using a molecular orientation meter (MOA-6004 molecular orientation meter, manufactured by Oji Scientific Instruments Co., Ltd.). Next, each film piece (molecular orientation measurement sample) was further cut into a 4 cm x 2 cm rectangle so that the slow axis direction was parallel to the short side, to serve as a refractive index measurement sample. In this case, the width center of the molecular orientation measurement sample was aligned with the width center of the refractive index measurement sample. Each film piece (refractive index measurement sample) was then measured using an Abbe refractometer (manufactured by Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm) to determine the refractive index of two perpendicular axes (refractive index in the slow axis direction: Ny, refractive index in the direction perpendicular to the slow axis direction: Nx), and the refractive index in the thickness direction (Nz).

[0095] (2) Retardation (Re) Each film piece was cut out at 50 mm intervals on both sides, centered on a position every 100 mm from the roll center position, along the direction (width direction) perpendicular to the unwinding direction (longitudinal direction) of the roll, and used as a measurement sample. Retardation is a parameter defined by the product (Δnxy × d) of the anisotropy of the refractive index of two orthogonal axes on the film (Δnxy = |nx - ny|) and the film thickness d (nm), and is a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (Δnxy) was determined by the method described in (1) above, and the absolute value of the difference in the refractive index of the two axes (|nx - ny|) was calculated as the refractive index anisotropy (Δnxy). The thickness d (nm) of the films of Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-4 was measured using an electric micrometer (Militron 1245D, manufactured by Fine Leaf Co., Ltd.), and the thickness d (nm) of the films of Examples 2-1 to 2-15 was measured using an electronic micrometer, Millitron 1240, manufactured by Seiko EM Co., Ltd., and the units were converted to nm. The retardation (Re) was calculated from the product (Δnxy × d) of the refractive index anisotropy (Δnxy) and the film thickness d (nm).

[0096] (3) Breaking Elongation Each film piece was cut out at 50 mm intervals on both sides of the roll center at 100 mm intervals from the roll center along the direction (width direction) perpendicular to the unwinding direction (longitudinal direction) of the roll, to serve as a measurement sample. Test samples measuring 15 mm wide and 100 mm long were cut out from each film piece in accordance with JIS K 7127. The test samples were subjected to a tensile test using a tensile tester (Shimadzu Corporation, Autograph AG-I) under conditions of a gauge length of 50 mm and a tensile speed of 200 mm / min. The breaking elongation of the test sample was calculated from the obtained stress-strain curve. The breaking elongation in the unwinding direction (MD) of the roll was measured.

[0097] (4) Iridescence Observation The liquid crystal display devices obtained in Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-4 were visually observed in a dark place from the front and from an oblique direction, and the presence or absence of iris spots was judged as follows. Here, "oblique direction" means a range of 30 to 60 degrees from the normal direction to the screen of the liquid crystal display device. ∘: Iridescence spots were not observed, or were observed only slightly. ×: Iridescence spots were observed. XX: Iridescence spots were significantly observed. The liquid crystal display devices obtained in Examples 2-1 to 2-15 were visually observed in a dark place from the front and from an oblique direction, and the presence or absence of iris spots was judged as follows. Here, "oblique direction" means a range of 30 to 60 degrees from the normal direction to the screen of the liquid crystal display device. ⊚: Iridescence spots were not observed at all. ∘: Iridescence spots were observed, but were slight and negligible. ×: Iridescence spots were observed. XX: Iridescence spots were significantly observed.

[0098] (5) Reflectance Using a spectrophotometer (Shimadzu Corporation, UV-3150), the 5-degree reflectance at a wavelength of 550 nm was measured from the surface on the antireflection layer side (or low reflection layer side). The surface of the polyester film opposite to the side on which the antireflection layer (or low reflection layer) was provided was coated with black marker and then black vinyl tape (Kyowa Vinyl Tape HF-737, width 50 mm) was attached thereto.

[0099] (6) Bright Light Contrast An optical laminate was placed on the polarizing element on the viewing side of a Sony BRAVIA KDL-40W920A liquid crystal display device (having a light source that emits excitation light and a backlight source containing quantum dots) so that the relationship between S-polarized light and the fast axis of the light-transmitting substrate film during reflectance measurement was the same, with the optical functional layer facing the viewing side. The bright light contrast of the display screen was evaluated visually from an oblique direction at an ambient illuminance of 400 lux (bright light). During this evaluation, the direction of the light incident surface and the fast axis of the light-transmitting substrate film were perpendicular. This optical laminate also had an optical functional layer on one side of the light-transmitting substrate film. This light-transmitting substrate film was obtained by cutting a light-transmitting polyester film roll described below to fit the size of the screen. Specifically, bright light contrast is expressed by the following formula. Generally, the rate of change in bright light white luminance is small and the rate of change in bright light black luminance is large, so bright light contrast is dominated by bright light black luminance. Furthermore, since the panel's inherent black luminance is small compared to the bright black luminance and can be ignored, the blackness (bright black luminance) was evaluated in the following manner, which was essentially used to evaluate the bright contrast. That is, a liquid crystal display device A was installed with one optical laminate so that the long side direction (width direction) of the screen was the TD direction of the light-transmitting substrate film, and sensory evaluation was performed by 15 monitors. In this sensory evaluation, the liquid crystal display device A displaying black was visually observed from a position 50 to 60 cm away from the first direction in which S-polarized light and the fast axis of the light-transmitting substrate film were parallel, and from a second direction in which S-polarized light and the slow axis of the light-transmitting substrate film were parallel, and whether it appeared black was evaluated. Bright contrast: CR = LW / LB Bright white luminance (LW): luminance when the liquid crystal display device displays white in a bright place with external light (ambient illuminance 400 lux) Bright black luminance (LB): luminance when the liquid crystal display device displays black in a bright place with external light (ambient illuminance 400 lux)

[0100] (Production Example 1 - Polyethylene terephthalate resin (A)) An esterification reactor was heated to 200°C, and 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were charged. Then, with stirring, 0.017 parts by mass of antimony trioxide, 0.064 parts by mass of magnesium acetate tetrahydrate, and 0.16 parts by mass of triethylamine were charged as catalysts. The temperature was then increased under pressure, and a pressurized esterification reaction was carried out at a gauge pressure of 0.34 MPa and 240°C. The esterification reactor was then returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. The temperature was then increased to 260°C over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. After 15 minutes, the mixture was dispersed using a high-pressure disperser. After 15 minutes, the resulting esterification reaction product was transferred to a polycondensation reactor, and a polycondensation reaction was carried out under reduced pressure at 280°C.

[0101] After the polycondensation reaction was completed, the mixture was filtered through a Naslon filter with a 95% cutoff diameter of 5 μm, extruded from a nozzle in the form of a strand, cooled with pre-filtered cooling water (pore diameter: 1 μm or less), solidified, and cut into pellets. The resulting polyethylene terephthalate resin (A) (hereinafter referred to as PET (A)) had an intrinsic viscosity of 0.62 dl / g and contained substantially no inert particles or internally precipitated particles.

[0102] (Production Example 2 - Polyethylene terephthalate resin (B)) 10 parts by mass of dried ultraviolet absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazinon-4-one) and 90 parts by mass of particle-free PET (A) (intrinsic viscosity of 0.62 dl / g) were mixed and extruded using a kneading extruder to obtain ultraviolet absorber-containing polyethylene terephthalate resin (B) (hereinafter abbreviated as PET (B)).

[0103] (Production Example 3 - Preparation of Adhesion-Modifying Coating Liquid) By carrying out a transesterification reaction and a polycondensation reaction by a conventional method, the dicarboxylic acid component (relative to the total dicarboxylic acid component) was 46 mol% terephthalic acid, 46 mol% isophthalic acid, and 8 mol% sodium 5-sulfonatoisophthalate, and the glycol component (relative to the total glycol component) was 50 mol% ethylene glycol and 50 mol% neopentyl glycol. A water-dispersible sulfonate metal base-containing copolymerized polyester resin of this composition was prepared. Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of a nonionic surfactant were mixed, and the mixture was heated and stirred. When the temperature reached 77 ° C., 5 parts by mass of the water-dispersible sulfonate metal base-containing copolymerized polyester resin was added, and the mixture was stirred until no lumps of resin remained. The resin aqueous dispersion was then cooled to room temperature to obtain a uniform water-dispersible copolymerized polyester resin solution having a solids concentration of 5.0% by mass. Furthermore, 3 parts by mass of aggregated silica particles (Sylysia 310, manufactured by Fuji Silysia Co., Ltd.) were dispersed in 50 parts by mass of water, and then 0.54 parts by mass of an aqueous dispersion of Sylysia 310 was added to 99.46 parts by mass of the water-dispersible copolymer polyester resin liquid, and 20 parts by mass of water was added while stirring to obtain an adhesive property-modifying coating liquid.

[0104] (Production Example 4 - Preparation of High Refractive Index Coating Agent) 80 parts by mass of methyl methacrylate, 20 parts by mass of methacrylic acid, 1 part by mass of azoisobutyronitrile, and 200 parts by mass of isopropyl alcohol were charged into a reaction vessel and reacted for 7 hours at 80°C under a nitrogen atmosphere to obtain an isopropyl alcohol solution of a polymer having a weight average molecular weight of 30,000. The obtained polymer solution was further diluted with isopropyl alcohol to a solids content of 5% by mass to obtain acrylic resin solution B. Next, the obtained acrylic resin solution B was mixed with the following components to obtain a coating liquid for forming a high refractive index layer.

[0105] Acrylic resin solution B 5 parts by mass Bisphenol A diglycidyl ether 0.25 parts by mass Titanium oxide particles having an average particle size of 20 nm 0.5 parts by mass Triphenylphosphine 0.05 parts by mass Isopropyl alcohol 14.25 parts by mass

[0106] (Production Example 5 - Preparation of low refractive index coating agent) 2,2,2-trifluoroethyl acrylate (45 parts by mass), perfluorooctylethyl acrylate (45 parts by mass), acrylic acid (10 parts by mass), azoisobutyronitrile (1.5 parts by mass), and methyl ethyl ketone (200 parts by mass) were charged into a reaction vessel and reacted at 80°C for 7 hours under a nitrogen atmosphere to obtain a methyl ethyl ketone solution of a polymer having a weight average molecular weight of 20,000. The obtained polymer solution was diluted with methyl ethyl ketone to a solids concentration of 5% by mass to obtain fluoropolymer solution C. The obtained fluoropolymer solution C was mixed as follows to obtain a coating liquid for forming a low refractive index layer.

[0107] Fluorine polymer solution C 44 parts by mass 1,10-bis(2,3-epoxypropoxy)-2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorodecane (Fluorite FE-16, manufactured by Kyoeisha Chemical Co., Ltd.) 1 part by mass Triphenylphosphine 0.1 parts by mass Methyl ethyl ketone 19 parts by mass

[0108] (Production Example 6 - Preparation of Antiglare Layer Coating Agent-1) An unsaturated double bond-containing acrylic copolymer CYCLOMER P ACA-Z250 (manufactured by Daicel Chemical Industries, Ltd.) (49 parts by mass), cellulose acetate propionate CAP482-20 (number average molecular weight 75,000) (manufactured by Eastman Chemical Company) (3 parts by mass), acrylic monomer AYARAD DPHA (manufactured by Nippon Kayaku Co., Ltd.) (49 parts by mass), acrylic-styrene copolymer (average particle size 4.0 μm) (manufactured by Sekisui Plastics Co., Ltd.) (2 parts by mass), and IRGACURE 184 (manufactured by BASF) (10 parts by mass) were added to a mixed solvent of methyl ethyl ketone:1-butanol=3:1 so as to give a solid content of 35% by mass, thereby obtaining antiglare layer coating agent-1.

[0109] (Production Example 7 - Preparation of Antiglare Layer Coating Agent-2) An unsaturated double bond-containing acrylic copolymer CYCLOMER P ACA-Z250 (manufactured by Daicel Chemical Industries, Ltd.) (49 parts by mass), cellulose acetate propionate CAP482-0.5 (number average molecular weight 25,000) (manufactured by Eastman Chemical Company) (3 parts by mass), acrylic monomer AYARAD DPHA (manufactured by Nippon Kayaku Co., Ltd.) (49 parts by mass), acrylic-styrene copolymer (average particle size 4.0 μm) (manufactured by Sekisui Plastics Co., Ltd.) (4 parts by mass), and IRGACURE 184 (manufactured by BASF) (10 parts by mass) were added to a mixed solvent of methyl ethyl ketone:1-butanol=3:1 so as to give a solid content of 35% by mass, thereby obtaining antiglare layer coating agent-2.

[0110] (Production Example 8 - Preparation of Antiglare Layer Coating Agent-3) An unsaturated double bond-containing acrylic copolymer CYCLOMER P ACA-Z250 (manufactured by Daicel Chemical Industries, Ltd.) (49 parts by mass), cellulose acetate propionate CAP482-0.2 (number average molecular weight 15,000) (manufactured by Eastman Chemical Company) (3 parts by mass), acrylic monomer AYARAD DPHA (manufactured by Nippon Kayaku Co., Ltd.) (49 parts by mass), acrylic-styrene copolymer (average particle size 4.0 μm) (manufactured by Sekisui Plastics Co., Ltd.) (2 parts by mass), and IRGACURE 184 (manufactured by BASF) (10 parts by mass) were added to a mixed solvent of methyl ethyl ketone:1-butanol=3:1 so as to give a solid content of 35% by mass, thereby obtaining antiglare layer coating agent-3.

[0111] [Example 1-1] (Light-transmitting polyester film roll 1-1) As the raw material for the intermediate layer of the base film, 90 parts by mass of PET (A) resin pellets containing no particles and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber were dried under reduced pressure (1 Torr) for 6 hours at 135 ° C., and then fed to extruder 2 (for intermediate layer II layer), and PET (A) was dried by a conventional method and fed to extruder 1 (for outer layer I layer and outer layer III), respectively, and melted at 285 ° C. These two polymers were each filtered with a stainless steel sintered filter material (nominal filtration accuracy 10 μm particles 95% cut) and stacked in a two-kind three-layer confluence block, and then extruded into a sheet form from a die, and then wrapped around a casting drum with a surface temperature of 30 ° C. using an electrostatic casting method, cooled and solidified, and made an unstretched film. At this time, the discharge rates of the extruders were adjusted so that the ratio of the thicknesses of the I layer, II layer, and III layer was 10:80:10.

[0112] The resulting unstretched sheet was introduced into a longitudinal stretching step, preheated by a group of rolls, and then stretched 3.2 times in the longitudinal direction at 100°C.

[0113] Next, a coating amount of 0.08 g / m2 was applied to both sides of the unstretched PET film by the reverse roll method. ２ After the adhesiveness modifying coating liquid was applied so that the thickness of the coated film became 1 / 2 mm, the coated film was dried at 80° C. for 20 seconds.

[0114] The unstretched film bearing this coating layer was introduced into a tenter stretching machine, and while holding the film's edges with clips, it was introduced into a hot air zone at 125°C and stretched 4.2 times in the width direction. Next, while maintaining the width stretched width, the film was heat-set at 240°C for 10 seconds and then further relaxed 3.0% in the width direction to obtain a biaxially stretched PET film with a film thickness of approximately 75 μm. The angle between the orientation axis and the width direction of the biaxially stretched film obtained by stretching increases due to the influence of the bowing phenomenon as it approaches both ends of the film. At the center of the width direction of the first winding roll that winds this biaxially stretched film, the absolute value of the angle between the orientation axis and the width direction was within the range of 0 to 10 degrees, and at both width direction ends of the first winding roll, the absolute value of the angle between the orientation axis and the width direction was greater than 0 degrees and 40 degrees or less. In Example 1-1, the width of the first winding roll was 2000 mm. This first winding roll was slit at the center to obtain two light-transmitting polyester film rolls 1-1 (rolls 1-1A and 1-1B) with a winding length of 1,000 m and a width of 1,000 mm. Rolls 1-1A and 1-1B are also referred to as second winding rolls. Rolls 1-1A and 1-1B correspond to examples of light-transmitting polyester film rolls in the present invention. At one end of roll 1-1A in the width direction, the absolute value of the angle between the main orientation axis and the width direction was within the range of 0 to 10 degrees, and at the other end of roll 1-1A in the width direction, the absolute value of the angle between the main orientation axis and the width direction was 30 to 35 degrees. Similarly, at one end of roll 1-1B in the width direction, the absolute value of the angle between the main orientation axis and the width direction was within the range of 0 to 10 degrees, and at the other end of roll 1-1B in the width direction, the absolute value of the angle between the main orientation axis and the width direction was 30 to 35 degrees.

[0115] [Example 2-1] (Light-transmitting polyester film roll 2-1) The first winding roll of Example 1-1 was slit widthwise into approximately three equal sections to obtain three light-transmitting polyester film rolls 2-1 (rolls 2-1A, 2-1B, and 2-1C) with a winding length of 1,000 m and a width of 666 mm. Rolls 2-1A, 2-1B, and 2-1C are also referred to as second winding rolls. Rolls 2-1A, 2-1B, and 2-1C correspond to examples of the light-transmitting polyester film rolls of the present invention. Roll 2-1B is a roll located between roll 2-1A and roll 2-1C. Roll 2-1A and roll 2-1C are rolls located on both sides of roll 2-1B. At one widthwise end of roll 2-1A, the absolute value of the angle between the main orientation axis and the width direction was 15 to 25 degrees, and at the other widthwise end of roll 2-1A, the absolute value of the angle between the main orientation axis and the width direction was 30 to 35 degrees. At one widthwise end of roll 2-1B, the absolute value of the angle between the main orientation axis and the width direction was 15 to 25 degrees, and at the other widthwise end of roll 2-1B, the absolute value of the angle between the main orientation axis and the width direction was 15 to 25 degrees. At one widthwise end of roll 2-1C, the absolute value of the angle between the main orientation axis and the width direction was 15 to 25 degrees, and at the other widthwise end of roll 2-1C, the absolute value of the angle between the main orientation axis and the width direction was 30 to 35 degrees.

[0116] [Example 1-2] (Light-transmitting polyester film roll 1-2) Two light-transmitting polyester film rolls 1-2 (rolls 1-2A and 1-2B) with a film thickness of approximately 75 μm were obtained by film formation in the same manner as in the light-transmitting polyester film roll 1-1, except that the heat setting temperature was changed to 250°C.

[0117] [Example 2-2] (Light-Transmitting Polyester Film Roll 2-2) Three light-transmitting polyester film rolls 2-2 (rolls 2-2A, 2-2B, and 2-2C) with a film thickness of approximately 75 μm were obtained by film formation in the same manner as in the light-transmitting polyester film roll 2-1, except that the heat setting temperature was changed to 250°C.

[0118] [Example 1-3] (Light-Transmitting Polyester Film Roll 1-3) Two light-transmitting polyester film rolls 1-3 (rolls 1-3A and 1-3B) with a film thickness of approximately 75 μm were obtained by film formation in the same manner as in the light-transmitting polyester film roll 1-1, except that the heat setting temperature was changed to 230°C.

[0119] [Example 2-3] (Light-Transmitting Polyester Film Roll 2-3) Three light-transmitting polyester film rolls 2-3 (rolls 2-3A, 2-3B, and 2-3C) with a film thickness of approximately 75 μm were obtained by film formation in the same manner as in the light-transmitting polyester film roll 2-1, except that the heat setting temperature was changed to 230°C.

[0120] [Example 1-4] (Light-transmitting polyester film roll 1-4) Two light-transmitting polyester film rolls 1-4 (rolls 1-4A and 1-4B) with a film thickness of approximately 75 μm were obtained by film production in the same manner as in the light-transmitting polyester film roll 1-1, except that the longitudinal stretching ratio was set to 2.8 times.

[0121] [Example 2-4] (Light-transmitting polyester film roll 2-4) Three light-transmitting polyester film rolls 2-4 (rolls 2-4A, 2-4B, and 2-4C) with a film thickness of approximately 75 μm were obtained by film production in the same manner as in the light-transmitting polyester film roll 2-1, except that the longitudinal stretching ratio was set to 2.8 times.

[0122] [Example 1-5] (Light-Transmitting Polyester Film Roll 1-5) Two light-transmitting polyester film rolls 1-5 (rolls 1-5A and 1-5B) with a film thickness of approximately 75 μm were obtained by film formation in the same manner as in the light-transmitting polyester film roll 1-4, except that the heat setting temperature was 215°C.

[0123] [Example 2-5] (Light-Transmitting Polyester Film Roll 2-5) Three light-transmitting polyester film rolls 2-5 (rolls 2-5A, 2-5B, and 2-5C) with a film thickness of approximately 75 μm were obtained by film formation in the same manner as in the light-transmitting polyester film roll 2-4, except that the heat setting temperature was set to 215°C.

[0124] Comparative Example 1-1 (Light-Transmitting Polyester Film Roll 1-6) Two light-transmitting polyester film rolls 1-6 (rolls 1-6A and 1-6B) with a film thickness of approximately 75 μm were obtained by the same method as for the light-transmitting polyester film roll 1-1, except that the film was stretched to 1.7 times in the longitudinal direction at 95°C and to 4.2 times in the width direction at a temperature of 110°C and the heat setting temperature was set to 220°C.

[0125] Comparative Example 1-2 (Light-Transmitting Polyester Film Roll 1-7) Two light-transmitting polyester film rolls 1-7 (rolls 1-7A and 1-7B) with a film thickness of approximately 75 μm were obtained by the same method as for the light-transmitting polyester film roll 1-1, except that the film was stretched to 1.0 times in the longitudinal direction at 95°C and to 4.2 times in the width direction at a temperature of 110°C and the heat setting temperature was 220°C.

[0126] (Light-Transmitting Polyester Film Roll 1-8) Two light-transmitting polyester film rolls 1-8 (rolls 1-8A and 1-8B) with a film thickness of approximately 75 μm were obtained by the same method as for the light-transmitting polyester film roll 1-1, except that the stretching ratio in the longitudinal direction was 3.5 times, the stretching ratio in the width direction was 3.8 times, and the heat setting temperature was 250°C.

[0127] (Light-transmitting polyester film rolls 1-1 to 1-5 and 1-8 with antireflection layer) The high refractive index layer-forming coating liquid was applied to one coating surface of a light-transmitting polyester film roll (1-1A, 1-1B, 1-2A, 1-2B, 1-3A, 1-3B, 1-4A, 1-4B, 1-5A, 1-5B, 1-8A, 1-8B), and dried at 150 ° C. for 2 minutes to form a high refractive index layer with a film thickness of 0.1 μm. The low refractive index layer-forming coating liquid obtained by the above method was applied to this high refractive index layer, and dried at 150 ° C. for 2 minutes to form a low refractive index layer with a film thickness of 0.1 μm, and two light-transmitting polyester film rolls 1-1 to 1-5 and 1-8 with an antireflection layer laminated thereon were obtained.

[0128] (Light-transmitting polyester film rolls 2-1 to 2-5 with antireflection layer) The high refractive index layer-forming coating liquid was applied to one coating surface of the light-transmitting polyester film rolls (2-1A, 2-1B, 2-1C, 2-2A, 2-2B, 2-2C, 2-3A, 2-3B, 2-3C, 2-4A, 2-4B, 2-4C, 2-5A, 2-5B, 2-5C), and dried at 150 ° C. for 2 minutes to form a high refractive index layer with a film thickness of 0.1 μm. The low refractive index layer-forming coating liquid obtained by the above method was applied onto this high refractive index layer, and dried at 150 ° C. for 2 minutes to form a low refractive index layer with a film thickness of 0.1 μm, and three light-transmitting polyester film rolls 2-1 to 2-5 with an antireflection layer laminated thereon were obtained.

[0129] (Light-Transmitting Polyester Film Rolls 1-1 to 1-5 and 1-8 with Antiglare Layer) Antiglare layer coating agent-2 was applied to one coating surface of each of the light-transmitting polyester film rolls (1-1A, 1-1B, 1-2A, 1-2B, 1-3A, 1-3B, 1-4A, 1-4B, 1-5A, 1-5B, 1-8A, and 1-8B) so that the film thickness after curing would be 8 μm, and the coating was dried in an oven at 80° C. for 60 seconds. Thereafter, the coating was exposed to an ultraviolet ray irradiation device (Fusion UV Systems Japan, light source H bulb) at an irradiation dose of 300 mJ / cm. ２ An antiglare layer was then laminated on the antiglare layer in the same manner as in the antiglare layer-attached light-transmitting polyester film roll 1-1, thereby obtaining two antiglare layer-attached polarizer protective film rolls 1-1 to 1-5 and 1-8.

[0130] (Light-Transmitting Polyester Film Rolls 2-1 to 2-5 with Antiglare Layer) Antiglare layer coating agent-2 was applied to one coating surface of each of the light-transmitting polyester film rolls (2-1A, 2-1B, 2-1C, 2-2A, 2-2B, 2-2C, 2-3A, 2-3B, 2-3C, 2-4A, 2-4B, 2-4C, 2-5A, 2-5B, and 2-5C) so that the film thickness after curing would be 8 μm, and the coating was dried in an oven at 80° C. for 60 seconds. Thereafter, the coating was exposed to an ultraviolet ray irradiation device (Fusion UV Systems Japan, light source H bulb) at an irradiation dose of 300 mJ / cm. ２An antiglare layer was then laminated on the antiglare layer in the same manner as in the antiglare layer-attached light-transmitting polyester film roll 2-1, to obtain three antiglare layer-attached polarizer protective film rolls 2-1 to 2-5.

[0131] Using the light-transmitting polyester film roll with an antireflection layer and the light-transmitting polyester film roll with an antiglare layer, polarizing plates and liquid crystal displays were produced as described below, and rainbow unevenness was evaluated.

[0132] Examples 1-6 to 1-15 A film from each of the antireflection-layer-attached light-transmitting polyester film rolls 1-1 to 1-5 and the antiglare-layer-attached light-transmitting polyester film rolls 1-1 to 1-5 was attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer and the fast axis of the film (roll unwinding direction) were perpendicular, and a TAC film (thickness: 80 μm) was attached to the opposite side to produce antireflection-layer-attached polarizing plate rolls 1-1 to 1-5 and antiglare-layer-attached polarizing plate rolls 1-1 to 1-5. A polarizer was laminated on the side of the light-transmitting polyester film on which the antireflection layer was not laminated to produce a polarizing plate. A liquid crystal display device was fabricated by replacing the polarizing plate on the viewing side of a Sony BRAVIA KDL-40W920A (a liquid crystal display device having a light source that emits excitation light and a backlight source containing quantum dots) with the above polarizing plates 1-1 to 1-5 so that the polyester film was on the opposite side (distal) from the liquid crystal cell, and rainbow unevenness was evaluated. The polarizing plates were replaced so that the direction of the transmission axis of the polarizing plates 1-1 to 1-5 was the same as the direction of the transmission axis of the polarizing plate before replacement. The polarizing plates were fabricated from rolls A and B, respectively, to measure 1000 mm x 1000 mm, and rainbow unevenness was observed at all positions in the width direction.

[0133] Examples 2-6 to 2-15 A film from each of the antireflection-layer-attached light-transmitting polyester film rolls 2-1 to 2-5 and the antiglare-layer-attached light-transmitting polyester film rolls 2-1 to 2-5 was attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer and the fast axis of the film (roll unwinding direction) were perpendicular, and a TAC film (thickness: 80 μm) was attached to the opposite side to produce antireflection-layer-attached polarizing plate rolls 2-1 to 2-5 and antiglare-layer-attached polarizing plate rolls 2-1 to 2-5. Note that a polarizer was laminated on the side of the light-transmitting substrate film on which the antireflection layer was not laminated to produce a polarizing plate. A liquid crystal display device was fabricated by replacing the polarizing plate on the viewing side of a Sony BRAVIA KDL-40W920A (a liquid crystal display device having a light source that emits excitation light and a backlight source containing quantum dots) with the above polarizing plates 2-1 to 2-5 so that the polyester film was on the opposite side (distal) from the liquid crystal cell, and rainbow unevenness was evaluated. The polarizing plates were replaced so that the direction of the transmission axis of the polarizing plates 2-1 to 2-5 was the same as the direction of the transmission axis of the polarizing plate before replacement. Polarizing plates were fabricated from rolls A, B, and C, respectively, to measure 1000 mm x 666 mm, and rainbow unevenness was observed at all positions in the width direction.

[0134] Comparative Examples 1-3 and 1-4 A polarizing plate roll 1-8 with an antireflection layer and a polarizing plate roll 1-8 with an antiglare layer were produced using a light-transmitting polyester film roll 1-8 with an antireflection layer and a light-transmitting polyester film roll 1-8 with an antiglare layer in the same manner as in Examples 1-6 to 1-15, respectively, and liquid crystal displays were produced, and then the rainbow unevenness was evaluated.

[0135] The results of Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-4 are shown in Tables 1 to 4 below. In the bright light contrast evaluations in Tables 1 to 4, ◯ and × represent the following evaluations: ◯: 12 or more people out of 15 judged the screen to be uniformly black in both the first and second directions. ×: 11 or fewer people out of 15 judged the screen to be uniformly black in both the first and second directions.

[0136] The results of Examples 2-1 to 2-15 are shown in Tables 5 to 7 below. In the bright light contrast evaluations in Tables 5 to 7, ◎, ◯, and × represent the following evaluations: ◎: The number of people who judged the screen to be uniformly black in both the first and second directions was 14 or more out of 15 people. ◯: The number of people who judged the screen to be uniformly black in both the first and second directions was 12 to 13 out of 15 people. ×: The number of people who judged the screen to be uniformly black in both the first and second directions was 11 or less out of 15 people.

[0137]

[0138]

[0139]

[0140]

[0141]

[0142]

[0143]

[0144] When used in an image display device, the light-transmitting substrate film of the present invention can ensure good visibility with rainbow-like color unevenness significantly suppressed at any angle, making a great contribution to the industry.

Claims

1. A roll of a light-transmissive substrate film used in an image display device, wherein the width of the roll is 500 mm or more, the winding length of the roll is 200 m or more, and along the direction (width direction) perpendicular to the unwinding direction (longitudinal direction) of the roll, in a plurality of film pieces cut out with a length of 50 mm to the left and right centered at positions every 100 mm from the roll center position, the average value of the difference (ny - nx) between the refractive index (nx) in the longitudinal direction and the refractive index (ny) in the width direction is 0.02 or more, the maximum value - minimum value of (ny - nx) is 0.02 or less, the average value of retardation is 1000 nm or more, and the average value of the elongation at break in the longitudinal direction is 50% or more. The roll is characterized by the above.

2. The roll according to claim 1, wherein the absolute value of the angle formed by the main axis of orientation and the width direction at one end in the width direction of the roll is in the range of 0 degrees to 30 degrees, and the absolute value of the angle formed by the main axis of orientation and the width direction at the other end in the width direction of the roll exceeds 0 degrees and is 40 degrees or less.

3. The roll according to claim 1, wherein the absolute value of the angle formed by the main axis of orientation and the width direction at one end in the width direction of the roll exceeds 0 degrees and is 30 degrees or less, and the absolute value of the angle formed by the main axis of orientation and the width direction at the other end in the width direction of the roll exceeds 0 degrees and is 30 degrees or less.

4. The roll according to claim 1, wherein the absolute value of the angle formed by the main axis of orientation and the width direction at one end in the width direction of the roll exceeds 0 degrees and is 30 degrees or less, and the absolute value of the angle formed by the main axis of orientation and the width direction at the other end in the width direction of the roll exceeds 0 degrees and is 40 degrees or less.

5. The roll according to claim 1, having an easy-adhesion layer on at least one surface of the light-transmissive substrate film.

6. The roll according to claim 1, wherein the light-transmissive substrate film is a polyester film.

7. The roll according to claim 1, wherein the light-transmissive substrate film is a biaxially stretched polyethylene terephthalate film.

8. The roll according to claim 1, having an antireflection layer and / or a low-reflection layer on at least one surface of the light-transmissive substrate film.

9. The roll according to claim 8, having an antiglare layer between the antireflection layer or low-reflection layer and the light-transmissive substrate film.

10. The roll according to any one of claims 1 to 9, wherein the light-transmissive substrate film is a polarizer protection film.

11. The roll according to claim 10, wherein the polarizer protection film is laminated on at least one surface of the polarizer.

12. As the polarizer protection film, a light-transmissive base film laminated on at least one surface of the polarizer, wherein the width of the light-transmissive base film is 500 mm or more, and along the width direction of the light-transmissive base film, in a plurality of film pieces cut out with a length of 50 mm to the left and right centered at positions every 100 mm from the center position, the average value of the difference (ny - nx) between the refractive index (nx) in the longitudinal direction and the refractive index (ny) in the width direction is 0.02 or more, the maximum value - minimum value of (ny - nx) is 0.02 or less, the average value of retardation is 1000 nm or more, the average value of the elongation at break in the longitudinal direction is 50% or more, at one end in the width direction of the light-transmissive base film, the absolute value of the angle formed by the principal axis of orientation and the width direction is within the range of 0 degrees to 30 degrees, and at the other end in the width direction of the light-transmissive base film, the absolute value of the angle formed by the principal axis of orientation and the width direction exceeds 0 degrees and is 40 degrees or less. A light-transmissive base film characterized by this.

13. As the polarizer protection film, a light-transmissive base film laminated on at least one surface of the polarizer, wherein the width of the light-transmissive base film is 500 mm or more, and along the width direction of the light-transmissive base film, in a plurality of film pieces cut out with a length of 50 mm to the left and right centered at positions every 100 mm from the center position, the average value of the difference (ny - nx) between the refractive index (nx) in the longitudinal direction and the refractive index (ny) in the width direction is 0.02 or more, the maximum value - minimum value of (ny - nx) is 0.02 or less, the average value of retardation is 1000 nm or more, the average value of the elongation at break in the longitudinal direction is 50% or more, at one end in the width direction of the light-transmissive base film, the absolute value of the angle formed by the principal axis of orientation and the width direction exceeds 0 degrees and is 30 degrees or less, and at the other end in the width direction of the light-transmissive base film, the absolute value of the angle formed by the principal axis of orientation and the width direction exceeds 0 degrees and is 40 degrees or less. A light-transmissive base film characterized by this.

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