Polyester film, Polarizer protective film, Polarizing plate, and Image display device

Abstract

This invention provides a polyester film, etc., which can cope with the increasing size of image display devices and exhibit excellent visibility at various positions within the screen (especially suppressing the deterioration of visibility caused by rainbow-like color spots at the edges), and further suppresses display degradation when used outdoors or exposed to ultraviolet light. The polyester film is primarily composed of polyethylene terephthalate (PET), the slow axis direction of the polyester film is approximately parallel to the MD direction, the in-plane birefringence ΔNxy of the polyester film is 0.06 or more and 0.2 or less, the refractive index of the polyester film in the fast axis direction is 1.58 or more and 1.63 or less, the ultraviolet transmittance of the polyester film at 380 nm is 0% or more and 30% or less, and the ratio of the polarization transmittance of the polyester film in the MD direction to the TD direction is 0.95 or less.

Description

Technical Field

[0001] This invention relates to polyester films, polarizing element protective films, polarizing plates, and image display devices (liquid crystal display devices, organic EL displays, etc.). Background Technology

[0002] The polarizing plates used in liquid crystal display (LCD) devices are typically constructed by sandwiching an iodine-dyed polarizing element on materials such as polyvinyl alcohol (PVA) between two protective polarizing films. Triacetyl cellulose (TAC) film is commonly used as the protective film. In recent years, with the thinning and cost reduction of LCDs, there has been a demand for thinner polarizing plates. However, reducing the thickness of the TAC film used as the protective film results in insufficient mechanical strength and deterioration of moisture permeability. Furthermore, TAC film is very expensive, creating a strong demand for inexpensive alternative raw materials. Additionally, the increasing use of digital signage such as LCD devices and OLED displays for outdoor information display in recent years has also increased the demand for UV resistance.

[0003] Polyester film exhibits superior durability compared to TAC film, but unlike TAC film, it possesses birefringence. Therefore, when used as a protective film for polarizers, it suffers from image quality degradation due to optical distortion. Specifically, the birefringence of polyester film results in a defined optical anisotropy (retardation), causing rainbow-like color spots when viewed from an angle, thus degrading image quality. Therefore, Patent Document 1 addresses this rainbow-like color spot by controlling the in-plane retardation of the polyester film within a specific range. Furthermore, Patent Document 1 discloses a countermeasure to suppress ultraviolet-induced degradation of polarizers such as polyvinyl alcohol (PVA) and iodine by including ultraviolet absorbers in the polyester film.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: WO2011-162198 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] One objective of the present invention is to provide a polyester film, a polarizing element protective film, a polarizing plate, and an image display device (liquid crystal display device, organic EL display, etc.) that can cope with the large-scale (i.e., have sufficient mechanical strength) and excellent visibility at all positions within the screen (especially able to suppress the deterioration of visibility caused by rainbow-like color spots at the edges). Preferably, the above objective is to provide a polyester film, a polarizing element protective film, a polarizing plate, and an image display device (liquid crystal display device, organic EL display, etc.) that further suppresses the degradation of the display when used outdoors or exposed to ultraviolet light.

[0009] Solution for solving the problem

[0010] The inventors conducted in-depth research and discovered that by studying stretching conditions, etc., it is possible to provide polyester films, polarizing element protective films, polarizing plates, and image display devices that can cope with the large-scale development of image display devices and have excellent visibility at various positions within the screen (especially at the ends, where rainbow-like color spots can be suppressed). Furthermore, it is possible to provide polyester films, polarizing element protective films, polarizing plates, and image display devices that can further suppress the degradation of the display when used outdoors or exposed to ultraviolet light. Through further repeated research, the present invention was completed.

[0011] The present invention includes embodiments described below.

[0012] [Item 1]

[0013] A polyester film, wherein the polyester of the polyester film is mainly polyethylene terephthalate.

[0014] The slow axis direction of the aforementioned polyester film is approximately parallel to the MD direction.

[0015] The aforementioned polyester film has an in-plane birefringence ΔNxy of 0.06 or higher and 0.2 or lower.

[0016] The aforementioned polyester film has a refractive index in the fast axis direction of 1.58 or higher and 1.63 or lower.

[0017] The aforementioned polyester film has an ultraviolet transmittance of 0% to 30% at 380nm.

[0018] The ratio of the polarization transmittance of the aforementioned polyester film in the MD direction to the TD direction is less than 0.95.

[0019] [Item 2]

[0020] According to item 1, the polyester film has a length of 1m or more in the TD direction.

[0021] The difference between the maximum and minimum values ​​of ΔNxy in the TD direction of the aforementioned polyester film is less than 0.013.

[0022] [Item 3]

[0023] The polyester film according to item 1 or 2, wherein the NZ coefficient of the aforementioned polyester film is 1.5 or more and 2.5 or less.

[0024] [Item 4]

[0025] The polyester film according to any one of items 1 to 3, wherein the thickness of the aforementioned polyester film is 15 μm or more and 60 μm or less.

[0026] [Item 5]

[0027] The polyester film according to any one of items 1 to 4, wherein the angle between the slow axis direction and the MD direction of the aforementioned polyester film is within 10 degrees.

[0028] [Item 6]

[0029] The polyester film according to any one of items 1 to 5, wherein the elastic modulus in the MD direction of the aforementioned polyester film is 3000 MPa or more.

[0030] [Item 7]

[0031] The polyester film according to any one of items 1 to 6, wherein the retardation of the aforementioned polyester film is 700 nm or more and 8000 nm or less.

[0032] [Item 8]

[0033] The polyester film according to any one of items 1 to 7 is a polarizer protective film.

[0034] [Item 9]

[0035] A polarizing plate having a polyester film, as described in any one of claims 1 to 8, laminated on at least one side of a polarizing element, wherein the angle between the absorption axis direction of the aforementioned polarizing element and the MD direction of the aforementioned polyester film is within 10 degrees.

[0036] [Item 10]

[0037] A polarizing plate having a polyester film, as described in any one of claims 1 to 8, laminated on one side of a polarizing element, and having no film laminated on the other side of the polarizing element.

[0038] [Item 11]

[0039] A polarizing plate having a polyester film, as described in any one of claims 1 to 8, laminated on one side of a polarizing element, and a quarter-wavelength plate laminated on the other side of the polarizing element.

[0040] [Item 12]

[0041] An image display device comprising a polarizing plate and a light source as described in any one of claims 9 to 11.

[0042] [Item 13]

[0043] The image display device according to item 12 is a liquid crystal display device.

[0044] [Item 14]

[0045] The image display device according to item 12 is an organic EL display.

[0046] [Item 15]

[0047] The image display device according to item 12 is a QLED display.

[0048] The effects of the invention

[0049] The polyester film, polarizer protective film, polarizer plate, and image display device (liquid crystal display device, organic EL display, etc.) of the present invention exhibit excellent uniformity over a wide area, thus providing good visibility at all positions within the screen in applications with large-area coverage (especially at the edges, where rainbow-like color spots (hereinafter also referred to as "iridescent spots") are suppressed to ensure good visibility). Furthermore, according to the present invention, display degradation can be suppressed when used outdoors or exposed to ultraviolet light. Additionally, according to the present invention, it possesses mechanical strength suitable for thin-film forming, ensuring good processing characteristics. Moreover, according to the present invention, the deterioration of visibility caused by iridescent spots can be significantly suppressed during thin-film forming. Detailed Implementation

[0050] In one embodiment, the polyester film of the present invention preferably satisfies the following (1) to (4).

[0051] (1) The polyester in the aforementioned polyester film is mainly polyethylene terephthalate.

[0052] (2) The slow axis direction of the aforementioned polyester film is roughly parallel to the MD direction.

[0053] (3) The in-plane birefringence ΔNxy of the aforementioned polyester film is above 0.06 and below 0.2.

[0054] (4) The refractive index of the aforementioned polyester film in the fast axis direction is above 1.58 and below 1.63.

[0055] In one embodiment, the polyester film of the present invention preferably satisfies (5) and (6) in addition to (1) to (4) above.

[0056] (5) The ultraviolet transmittance of the aforementioned polyester film at 380nm is above 0% and below 30%.

[0057] (6) The ratio of the polarization transmittance of the aforementioned polyester film in the MD direction to the TD direction is less than 0.95.

[0058] In one embodiment, the polyester film of the present invention preferably satisfies (7) and (8) in addition to (1) to (4) above.

[0059] (7) The length of the aforementioned polyester film in the TD direction is more than 1m.

[0060] (8) The difference between the maximum and minimum values ​​of ΔNxy in the TD direction of the aforementioned polyester film is less than 0.013.

[0061] In one embodiment, the polyester film of the present invention preferably satisfies (1) to (8) above.

[0062] The polyester used in the polyester film of the present invention is preferably polyethylene terephthalate (PET). Here, "predominantly" means PET, which is, for example, 50% or more by mass, preferably 60% or more by mass, more preferably 70% or more by mass, further preferably 80% or more by mass, more preferably 90% or more by mass, particularly preferably 95% or more by mass, and particularly preferably 99% or more by mass, relative to 100% by mass of the polyester. The polyester may consist solely of PET (100% by mass of PET), but the PET content may also be less than 100% by mass, being 99.9% or less by mass, 99.5% or less by mass, or 99% or less by mass. There are no particular limitations on the PET as long as terephthalic acid and ethylene glycol are used as polymerization components, and it may contain any copolymer components. When all acid components in the polyester are set to 100 mol%, and all glycol components are set to 100 mol%, the total amount of copolymer components is preferably 20 mol% or less, more preferably 10 mol% or less, further preferably 5 mol% or less, and particularly preferably 3 mol% or less. This PET exhibits excellent transparency, as well as superior thermal and mechanical properties. It possesses high inherent birefringence, and in-plane birefringence can be easily controlled through stretching. Other polyesters besides PET include, for example, polypropylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polylactic acid (PLA), and copolyesters with these as main components.

[0063] From the viewpoint of suppressing iris spots, the slow axis of the polyester film of the present invention is preferably substantially parallel to the MD direction. The MD direction refers to the direction of travel (flow direction) during film formation, sometimes also referred to as the longitudinal direction. The MD direction is perpendicular to the TD direction. The TD direction refers to the width direction during film formation, sometimes also referred to as the transverse direction. "Substantially parallel" means that the angle between the slow axis direction of the polyester film and the MD direction is preferably within 10 degrees, more preferably within 7 degrees, further preferably within 5 degrees, even more preferably within 3 degrees, particularly preferably within 2 degrees or within 1 degree. The slow axis direction of the polyester film can be determined using a conventional molecular orientation meter (e.g., the MOA-6004 molecular orientation meter manufactured by Oji Measuring Instruments Co., Ltd.).

[0064] From the viewpoint of suppressing iris spots (especially those from the tilted direction), the in-plane birefringence ΔNxy of the polyester film of the present invention is preferably 0.06 or more, more preferably 0.065 or more, further preferably 0.07 or more, even more preferably 0.075 or more, and particularly preferably 0.08 or more. From the viewpoint of maintaining strength suitable for protective applications, ΔNxy is preferably 0.2 or less, more preferably 0.19 or less, and even more preferably 0.18 or less. As an upper limit for ΔNxy, even smaller values ​​are preferred, such as 0.17 or less, 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.1 or less. ΔNxy is the absolute value of the difference between the refractive index (nx) in the slow axis direction and the refractive index (ny) in the fast axis direction. It should be noted that in this specification, the wavelength for measuring the refractive index is 589 nm.

[0065] The length of the polyester film in the TD direction of the present invention is preferably 1 m or more, more preferably 1.1 m or more, and even more preferably 1.2 m or more. The aforementioned length in the TD direction is preferably 4 m or less, more preferably 3.5 m or less, even more preferably 3 m or less, and even more preferably 2.7 m or less. In one embodiment, the length in the TD direction is 1 m or more and 4 m or less.

[0066] From the viewpoint of visibility at various positions within the screen of a large-area display (especially suppressing iris spots at the ends), the difference between the maximum and minimum values ​​of ΔNxy in the TD direction of the polyester film of the present invention (maximum value - minimum value) is preferably 0.013 or less, more preferably 0.0125 or less, and even more preferably 0.012 or less. From the viewpoint of enabling stable film formation, the difference between the maximum and minimum values ​​of ΔNxy in the TD direction is preferably 0 or more, more preferably 0.001 or more, and even more preferably 0.002 or more.

[0067] From the viewpoint of maintaining strength suitable for protective applications, the refractive index (ny) of the polyester film of the present invention in the fast axis direction is preferably 1.58 or more, more preferably 1.584 or more, further preferably 1.585 or more, even more preferably 1.588 or more, and particularly preferably 1.59 or more. From the viewpoint of suppressing iris spots (especially iris spots from the oblique direction), ny is preferably 1.63 or less, more preferably 1.625 or less, further preferably 1.62 or less, even more preferably 1.615 or less, and particularly preferably 1.61 or less. In one embodiment, ny is 1.58 or more and 1.63 or less.

[0068] From the viewpoint of suppressing iris spots (especially those from the tilted direction) by adjusting ny to a desired range, the refractive index (nx) of the polyester film of the present invention in the slow axis direction is preferably 1.66 or more, more preferably 1.664 or more, further preferably 1.665 or more, and even more preferably 1.668 or more. From the viewpoint of maintaining strength suitable for protective applications by adjusting ny to a desired range, nx is preferably 1.72 or less, more preferably 1.716 or less, further preferably 1.715 or less, and even more preferably 1.712 or less. In one embodiment, nx is 1.66 or more and 1.72 or less.

[0069] The refractive index (nz) in the thickness direction of the polyester film of the present invention is preferably 1.5 or more, more preferably 1.505 or more, and even more preferably 1.51 or more. nz is preferably 1.56 or less, more preferably 1.555 or less, and even more preferably 1.55 or less. In one embodiment, nz is 1.5 or more and 1.56 or less.

[0070] The upper limit of the ultraviolet transmittance at 380 nm of the polyester film of the present invention is preferably 30% or less, with the aim of suppressing the deterioration of optical functional pigments such as iodine-based pigments. The lower limit of the aforementioned ultraviolet transmittance is preferably 0% or more, more preferably 0.1% or more. The upper limit of the aforementioned ultraviolet transmittance is preferably 25% or less, more preferably 20% or less, and even more preferably 15% or less. These upper and lower limits can be appropriately combined; for example, the aforementioned ultraviolet transmittance is preferably 0% or more and 30% or less. If the upper limit of the ultraviolet transmittance is 30% or less, the deterioration of optical functional pigments caused by ultraviolet light can be suppressed. The ultraviolet transmittance in the present invention is measured in the vertical direction relative to the plane of the polyester film. The ultraviolet transmittance can be measured, for example, using a spectrophotometer (e.g., Shimadzu UV1800).

[0071] The polyester film of the present invention preferably contains an ultraviolet absorber. In the polyester film of the present invention, the content of the ultraviolet absorber is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.2% by mass or more and 8% by mass or less, further preferably 0.5% by mass or more and 5% by mass or less, even more preferably 0.8% by mass or more and 4% by mass or less, and particularly preferably 1% by mass or more and 2% by mass or less.

[0072] Examples of UV absorbers include triazine-based, benzotriazole-based, benzophenone-based, benzoxazinone-based, salicylic acid ester-based, cyanoacrylate-based, and salicylic acid ester-based UV absorbers, with triazine-based and benzotriazole-based UV absorbers being preferred. Furthermore, as a UV absorber that will not be adversely affected by heat during the manufacture of polyester films, the following UV absorbers can be used, for example.

[0073] 2-(2-hydroxy-4-[1-octoxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine

[0074] 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol,

[0075] 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol,

[0076] Octyl-3-[3-tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl]propionate,

[0077] 2-Ethylhexyl-3-[3-tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl]propionate,

[0078] 2-(2H-benzotriazol-2-yl)-4,6-bis(1-ethyl-1-phenylethyl)phenol,

[0079] phenol,

[0080] 2-(5-chloro-2H-benzotriazol-2-yl)-6-(1,1-dimethylethyl)4-methyl

[0081] 2,2'-Methylenebis(6-(2H-benzotriazol-2-yl)-4-1,1,3,3-tetramethylbutylphenol),

[0082] 2-(4,6-Diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]phenol,

[0083] 2,4-Bis(2-hydroxy-4-butoxyphenyl)-6-(2,4-bis-butoxyphenyl)-1,3,5-triazine

[0084] Phenylacetic acid,

[0085] 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-C7-9 branched and chain alkyl esters,

[0086] 2-(2-hydroxy-5-tert-methylphenyl)-2H-benzotriazole,

[0087] 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol

[0088] 2,2'-Dihydroxy-4-methoxybenzophenone

[0089] 2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-(octoxy)phenol,

[0090] 2-(2'-hydroxy-5'-octylphenyl)benzotriazole.

[0091] The lower limit of the polarization transmittance ratio R of the polyester film of the present invention, which is the ratio of the polarization transmittance in the MD direction to the TD direction, is preferably 0.5 or more, more preferably 0.6 or more, even more preferably 0.7 or more, even more preferably 0.75 or more, and particularly preferably 0.8 or more. The upper limit of the ratio R is preferably 0.99 or less, more preferably 0.97 or less, even more preferably 0.96 or less, even more preferably 0.95 or less, and particularly preferably 0.93 or less. These upper and lower limits can be appropriately combined, and the ratio R is, for example, preferably 0.5 or more and 0.99 or less, more preferably 0.6 or more and 0.97 or less, even more preferably 0.7 or more and 0.96 or less, even more preferably 0.75 or more and 0.95 or less, and particularly preferably 0.8 or more and 0.93 or less. The polarization transmittance is expressed using the orthogonal biaxial polarization transmittance in the length direction (MD direction) and width direction (TD direction) at a wavelength of 390 nm, where 30% of the total light transmission is displayed. Polarization transmittance can be measured using a UV-Vis spectrophotometer (Shimadzu UV1800) with a measurement wavelength range of 190–1100 nm. Polarization transmittance in each direction can be measured by inserting a polarizing plate (SHC-YL38, Nippon Kayaku) that allows the ultraviolet wavelength region to pass through the detector side of the spectrophotometer, and measuring the light transmitted through the polarizing plate. To eliminate the influence of the polarizing plate's orientation, it is preferable to rotate the film 90° after measuring the polarized transmittance in the longitudinal direction to extract the polarized transmittance in the transverse direction.

[0092] Ultraviolet absorbers are oriented along the stretching direction as the polyester film is stretched, resulting in anisotropic transmittance. In the polyester film of the present invention, by oriented along the MD direction, the molecular chains of the ultraviolet absorber are also oriented along the MD direction, thereby improving the absorption capacity in the MD direction. When the absorption axis of the isopolarizing element is oriented along the MD direction in a roll-to-roll bonding manner, the polyester film of the present invention absorbs more ultraviolet light in the MD direction, thereby suppressing the deterioration of the polarizing element.

[0093] Based on the above viewpoints, the slow axis direction of the polyester film of the present invention is approximately parallel to the MD direction of the polyester film, and the absorption axis direction of the polarizer is also preferably approximately parallel to the MD direction of the polyester film. The angle between the slow axis direction of the polyester film and the MD direction is preferably within 10 degrees, more preferably within 7 degrees, further preferably within 5 degrees, even more preferably within 3 degrees, and particularly preferably within 2 degrees or 1 degree. The angle between the absorption axis direction of the polarizer and the MD direction of the polyester film is preferably within 10 degrees, more preferably within 7 degrees, further preferably within 5 degrees, even more preferably within 3 degrees, and particularly preferably within 2 degrees or 1 degree.

[0094] From the viewpoint of exhibiting anisotropy, the angle between the slow axis direction and the MD direction of the polyester film of the present invention is preferably within 10 degrees, and when it is within 5 degrees, it further exhibits anisotropy. In addition, from the viewpoint of suppressing the deterioration of the polarizer, it is preferable to bond the polarizer with the absorption axis direction of the polarizer and the MD direction of the polyester film at an angle of within 10 degrees, and when it is within 5 degrees, the deterioration of the polarizer can be further suppressed.

[0095] From the viewpoint of maintaining strength suitable for protective applications, the thickness of the polyester film of the present invention is preferably 10 μm or more, more preferably 15 μm or more, further preferably 20 μm or more, even more preferably 25 μm or more, and particularly preferably 30 μm or more. From the viewpoint of producing a polarizing plate of desired thickness, the above-mentioned thickness is preferably 100 μm or less, more preferably 90 μm or less, even more preferably 80 μm or less, even more preferably 70 μm or less, and particularly preferably 60 μm or less or 55 μm or less. In one embodiment, the above-mentioned thickness is 10 μm or more and 100 μm or less. In a preferred embodiment, the above-mentioned thickness is 15 μm or more and 60 μm or less.

[0096] From the viewpoint of maintaining strength suitable for protective applications, the Nz coefficient of the polyester film of the present invention is preferably 1.5 or more, more preferably 1.6 or more, and even more preferably 1.7 or more. From the viewpoint of suppressing iris spots (especially iris spots from the oblique direction), the Nz coefficient is preferably 2.5 or less, more preferably 2.4 or less, and even more preferably 2.3 or less. In a preferred embodiment, the Nz coefficient is 1.5 or more and 2.5 or less.

[0097] The Nz coefficient can be calculated as follows. Using a conventional molecular orientation meter (e.g., the MOA-6004 molecular orientation meter manufactured by Oji Instruments Co., Ltd.), the orientation principal axis direction (slow axis direction) of the thin film is determined. Then, using a conventional Abbe refractometer (e.g., the NAR-4T manufactured by ATAGO, with a measurement wavelength of 589 nm), the biaxial refractive indices (refractive index nx in the slow axis direction, refractive index ny in the fast axis direction, where nx > ny) and the refractive index (nz) in the thickness direction are determined. Substituting the thus determined nx, ny, and nz into the formula expressed as |nx - nz| / |nx - ny|, the Nz coefficient can be calculated.

[0098] From the viewpoint of suppressing iris spots, the retardation of the polyester film of the present invention is preferably 700 μm or more, more preferably 1000 μm or more, even more preferably 1200 μm or more, even more preferably 1500 μm or more, and particularly preferably 2000 μm or more. The retardation is preferably 8000 nm or less, more preferably 7000 nm or less, even more preferably 6000 nm or less, even more preferably 5500 nm or less, and particularly preferably 5000 nm or less. In a preferred embodiment, the retardation is 700 μm or more and 8000 μm or less.

[0099] From the perspective of controlling the shrinkage (mainly shrinkage in the absorption axis direction) of polarizing elements such as PVA films and the resulting warping of the image display device, the elastic modulus in the MD direction of the polyester film of the present invention is preferably 3000 MPa or more, more preferably 3500 MPa or more, further preferably 4000 MPa or more, and particularly preferably 4500 MPa or more. The elastic modulus in the MD direction is preferably 10000 MPa or less, more preferably 8000 MPa or less, and further preferably 7000 MPa or less. In one embodiment, the elastic modulus in the MD direction is 3000 MPa or more and 10000 MPa or less.

[0100] The polyester film of the present invention can be in the form of a roll. The length of the roll is preferably 500 m or more, more preferably 1000 m or more, even more preferably 1500 m or more, and even more preferably 2000 m or more. The length of the roll is preferably 10000 m or less, more preferably 7000 m or less, even more preferably 6000 m or less, and even more preferably 5000 m or less. In one embodiment, the length of the roll is 500 m or more and 10000 m or less.

[0101] In the polyester film of the present invention, it is preferable to contain various additives other than catalysts, without impairing 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, ultraviolet absorbers (e.g., benzotriazole, benzophenone, cyclic imine esters, etc.), antistatic agents, lightfast agents, flame retardants, heat stabilizers, antioxidants, anti-gelling agents, surfactants, etc. Furthermore, to achieve high transparency, it is preferable that the polyester film is substantially free of particles. "Substantially free of particles" means, for example, in the case of inorganic particles, a content of 50 ppm or less, preferably 10 ppm or less, and particularly preferably below the detection limit when the inorganic elements are quantified by X-ray fluorescence analysis.

[0102] For the purpose of preventing reflection, suppressing glare, and suppressing scratches, it is also a preferred method to coat the surface of the polyester film of the present invention with various hard coatings.

[0103] Furthermore, in this invention, in order to ensure good adhesion to polarizing elements and various hard coatings, the polyester film can also be subjected to corona treatment, coating treatment, flame treatment, etc.

[0104] Preferably, at least one side of the polyester film of the present invention has an easy-to-adhere layer with at least one of a resin selected from polyester resin, polyurethane resin, and polyacrylic resin as its main component. Here, "main component" refers to a component that accounts for 50% or more by mass of the solid components constituting the easy-to-adhere layer. The coating liquid used to form the easy-to-adhere layer is preferably an aqueous coating liquid containing at least one of a water-soluble or water-dispersible copolyester resin, acrylic resin, and polyurethane resin. Examples of such coating liquids include, for example, water-soluble or water-dispersible copolyester resin solutions, acrylic resin solutions, and polyurethane resin solutions disclosed in Japanese Patent Nos. 3567927, 3589232, 3589233, 3900191, and 4150982.

[0105] The easy-to-adhesive layer can be obtained, for example, by applying a coating liquid to at least one surface of the film in any step of the polyester film manufacturing process, followed by drying at a temperature above 100°C and below 150°C. From the viewpoint of adhesion and anti-blocking properties, the coating amount of the final easy-to-adhesive layer is preferably controlled at 0.05 g / m². 2 Above and 0.2g / m 2 The following applies. When an easy-adhesive layer is provided on both sides of a polyester film, the coating amount of the easy-adhesive layer on both sides can be the same or different, and can be set independently within the above-mentioned range.

[0106] To impart slipperiness to the easy-to-adhere layer, it is preferable to add particulate matter. From the viewpoint of preventing detachment, the particulate matter is preferably microparticles with an average particle size of 2 μm or less. Examples of particulate matter contained in the easy-to-adhere layer include inorganic particles such as titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, lithium montmorillonite, zirconium oxide, tungsten oxide, lithium fluoride, and calcium fluoride, as well as organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and organosilicon-based particles. These can be added to the easy-to-adhere layer alone or in combination of two or more.

[0107] As a method for applying the coating liquid, known methods can be used. Examples include reverse roller coating, gravure coating, coincidence coating, roller brush coating, spraying, air knife coating, wire bar coating, and tube doctor blade coating. These methods can be used individually or in combination.

[0108] The average particle size of the above particles was determined by the following method: The particles were photographed using a scanning electron microscope (SEM), and the maximum diameter (distance between the two furthest points) of 300 to 500 particles was measured at a magnification of 2 to 5 mm for the smallest particle. The average value of these measurements was taken as the average particle size.

[0109] The polyester film of the present invention is preferably a biaxially stretched film. Examples of methods for biaxially stretched films include: melting polyester resin, stretching an extruded sheet of non-oriented polyester along the MD and TD directions at a temperature above the glass transition temperature, and performing heat treatment.

[0110] When the MD direction is the dominant stretching direction, it is preferable to stretch in the TD direction as well to prevent the film from cracking. However, to reduce the refractive index in the fast axis direction, it is also necessary to increase the stretching ratio in the MD direction. When performing such a large area ratio stretching, the following problems may arise.

[0111] • In the successive biaxial stretching method, which stretches along the MD direction and then along the TD direction, the MD direction and the slow axis direction tend to shift at the ends of the film formed by the bowing phenomenon.

[0112] • In the successive biaxial stretching method, which involves stretching along the TD direction followed by stretching along the MD direction, it is difficult to achieve uniform stretching along the TD direction.

[0113] • In simultaneous biaxial stretching, the film is prone to cracking between the fixtures. In order to reduce stress, the stretching temperature is increased, but uneven stretching (difference in refractive index) is likely to occur.

[0114] The reasons why uneven stretching is prone to occur during simultaneous biaxial stretching are as follows: the film softens rapidly as the temperature rises, and even slight temperature changes cause a large change in the film's softness, resulting in relaxation, film vibration (especially in the width), etc., which makes it impossible to apply the stretching force stably to the whole.

[0115] In order to avoid causing these problems and to obtain polyester films that satisfy (1)~(4) and (5)~(6) and / or (7)~(8) above, it is preferable to perform stretching in multiple stages, including stretching in the MD direction. In the first half of the stretching, stretching is performed along the two axes of the MD direction and the TD direction, and in the second half, stretching is mainly performed along the MD direction. However, it is also possible not to separate the first half and the second half of the stretching, but to gradually change into the main body of stretching in the MD direction as the stretching progresses.

[0116] Biaxial stretching in the MD and TD directions can be performed sequentially, but to further reduce orientation deviations and uneven stretching, and to achieve stable production, simultaneous biaxial stretching is preferred. It should be noted that repeated micro-stretching in the MD and TD directions using a simultaneous biaxial stretching machine is also included within the scope of simultaneous biaxial stretching.

[0117] Simultaneous biaxial stretching in both the MD and TD directions, and stretching primarily in the MD direction, can be performed in the same tenter frame or in different tenter frames. Alternatively, after simultaneous biaxial stretching in both the MD and TD directions using a tenter frame, stretching primarily in the MD direction can be performed using roller stretching.

[0118] In multi-stage stretching, the number of stretching steps (segments) is preferably 2 or more. Furthermore, from the viewpoint of ease of setting and controlling the stretching conditions, the number of stretching steps is preferably 10 or less, more preferably 7 or less, even more preferably 5 or less, even more preferably 4 or less, and particularly preferably 3 or less. In one embodiment, the number of stretching steps is 2 or more and 10 or less.

[0119] In multi-stage stretching, from the viewpoint of film formation stability, the stretching temperature in the first stretching region is preferably 90°C or higher, more preferably 95°C or higher, even more preferably 98°C or higher, and even more preferably 100°C or higher. Furthermore, from the viewpoint of film formation properties and suppressing uneven stretching, the stretching temperature in the first stretching region is preferably 120°C or lower, more preferably 115°C or lower, even more preferably 112°C or lower, and even more preferably 110°C or lower. In one embodiment, the stretching temperature in the first stretching region is 90°C or higher and 120°C or lower.

[0120] From the viewpoint of uniform film formation in the width direction, the area ratio of the stretching in the first stretching region is preferably 7 or more, more preferably 7.5 or more, even more preferably 8 or more, even more preferably 8.5 or more, and particularly preferably 9 or more. From the viewpoint of being able to form a film without breakage and stably, the above-mentioned area ratio is preferably 14 or less, more preferably 13.5 or less, even more preferably 13 or less, even more preferably 12.5 or less, and particularly preferably 12 or less. In one embodiment, the above-mentioned area ratio is 7 or more and 14 or less.

[0121] The stretching ratio in the TD direction of the first stretching region can accommodate large-scale applications through uniform stretching. From the viewpoint of improving productivity, it is preferably 1.4 or more, more preferably 1.5 or more, further preferably 1.6 or more, even more preferably 1.8 or more, and particularly preferably 2 or more. From the viewpoint of suppressing the refractive index of the fast axis, the stretching ratio in the TD direction is preferably 3.7 or less, more preferably 3.5 or less, even more preferably 3.2 or less, even more preferably 3 or less, and particularly preferably 2.8 or less. In one embodiment, the stretching ratio in the TD direction is 1.4 or more and 3.7 or less.

[0122] From the viewpoint of uniform stretching, the stretch ratio in the MD direction of the first stretching region is preferably 2 or more, more preferably 2.1 or more, further preferably 2.2 or more, even more preferably 2.3 or more, and particularly preferably 2.4 or more. From the viewpoint of being able to form a film without breakage and stably, the stretch ratio in the MD direction is preferably 5 or less, more preferably 4.9 or less, even more preferably 4.8 or less, even more preferably 4.7 or less, and particularly preferably 4.6 or less. In one embodiment, the stretch ratio in the MD direction is 2 or more and 5 or less.

[0123] The ratio of the stretching ratio in the MD direction to that in the TD direction in the first stretching region is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.7 or more. The aforementioned ratio is preferably 3 or less, more preferably 2.5 or less, even more preferably 2.2 or less, and even more preferably 2 or less. In one embodiment, the aforementioned ratio is 0.5 or more and 3 or less.

[0124] In multi-stage stretching, from the viewpoint of film formation stability, the stretching temperature in the second stretching region is preferably 90°C or higher, more preferably 95°C or higher, even more preferably 98°C or higher, and even more preferably 100°C or higher or 105°C or higher. Furthermore, from the viewpoint of film formation properties and suppression of stretching unevenness, the stretching temperature in the second stretching region is preferably 120°C or lower, more preferably 115°C or lower, even more preferably 112°C or lower, and even more preferably 110°C or lower. In one embodiment, the stretching temperature in the second stretching region is 90°C or higher and 120°C or lower. In another embodiment, the stretching temperature in the second stretching region is higher than the stretching temperature in the first stretching region. The absolute value of the difference between the stretching temperature in the second stretching region and the stretching temperature in the first stretching region can be, for example, 1°C or higher, 2°C or higher, 3°C or higher, 4°C or higher, or 5°C or higher, and can be 20°C or lower, 15°C or lower, or 10°C or lower, and can be 1°C or higher and 20°C or lower.

[0125] From an aesthetic point of view, the area ratio of the stretching in the second stretching region is preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.3 or more, even more preferably 1.4 or more, and particularly preferably 1.5 or more. From the viewpoint of film formation stability, the above-mentioned area ratio is preferably 6 or less, more preferably 5.8 or less, even more preferably 5.6 or less, even more preferably 5.4 or less, and particularly preferably 5 or less. In one embodiment, the above-mentioned area ratio is 1.1 or more and 6 or less.

[0126] From an aesthetic point of view, the stretch ratio in the TD direction of the second stretching region is preferably 0.7 or more, more preferably 0.75 or more, even more preferably 0.8 or more, even more preferably 0.85 or more, and particularly preferably 0.9 or more. From the point of view of film formation stability, the stretch ratio in the TD direction is preferably 2 or less, more preferably 1.95 or less, even more preferably 1.9 or less, even more preferably 1.85 or less, and particularly preferably 1.8 or less. In one embodiment, the stretch ratio in the TD direction is 0.7 or more and 2 or less.

[0127] From the viewpoint of balancing the refractive indices of the slow and fast axes, the stretching ratio in the MD direction of the second stretching region is preferably 1.5 or more, more preferably 1.55 or more, further preferably 1.6 or more, even more preferably 1.65 or more, and particularly preferably 1.7 or more. From the viewpoint of film formation stability, the stretching ratio in the MD direction is preferably 5 or less, more preferably 4.9 or less, even more preferably 4.8 or less, even more preferably 4.7 or less, and particularly preferably 4.6 or less. In one embodiment, the stretching ratio in the MD direction is 1.5 or more and 5 or less.

[0128] The ratio of the stretching ratio in the MD direction to that in the TD direction in the second stretching region is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.7 or more. The aforementioned ratio is preferably 3 or less, more preferably 2.5 or less, even more preferably 2.2 or less, and even more preferably 2 or less. In one embodiment, the aforementioned ratio is 0.5 or more and 3 or less.

[0129] From the viewpoint of uniform stretching, the total stretching ratio in the TD direction of the first and second stretching regions is preferably 1.4 or more, more preferably 1.5 or more, further preferably 1.6 or more, even more preferably 1.8 or more, and particularly preferably 2 or more. From the viewpoint of suppressing the refractive index of the fast axis, the total stretching ratio in the TD direction is preferably 3.7 or less, more preferably 3.5 or less, even more preferably 3.2 or less, even more preferably 3 or less, and particularly preferably 2.8 or less. In one embodiment, the total stretching ratio in the TD direction is 1.4 or more and 3.7 or less.

[0130] From the viewpoint of balancing the refractive indices of the slow and fast axes, the ratio of the stretching ratio in the TD direction of the first stretching region to the total stretching ratio in the TD direction of the first and second stretching regions is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.7 or more. From the viewpoint of appearance, the above ratio is preferably 1.4 or less, more preferably 1.3 or less, even more preferably 1.2 or less, and even more preferably 1.1 or less. In one embodiment, the above ratio is 0.5 or more and 1.4 or less.

[0131] From an optical property perspective, the total stretching ratio in the MD direction of the first and second stretching regions is preferably 5 or more, more preferably 5.1 or more, even more preferably 5.3 or more, even more preferably 5.5 or more, and particularly preferably 6 or more. From the viewpoint of film formation stability, the total stretching ratio in the MD direction is preferably 7.5 or less, more preferably 7.4 or less, even more preferably 7.3 or less, even more preferably 7.2 or less, and particularly preferably 7.1 or less. In one embodiment, the total stretching ratio in the MD direction is 5 or more and 7.5 or less.

[0132] From the viewpoint of balancing the refractive indices of the slow and fast axes, the ratio of the stretching ratio in the MD direction of the first stretching region to the total stretching ratio in the MD direction of the first and second stretching regions is preferably 0.2 or more, more preferably 0.25 or more, even more preferably 0.3 or more, and even more preferably 0.35 or more. From the viewpoint of balancing the refractive indices of the slow and fast axes, the above ratio is preferably 0.8 or less, more preferably 0.75 or less, even more preferably 0.7 or less, even more preferably 0.65 or less, and particularly preferably 0.63 or less or 0.6 or less. In one embodiment, the above ratio is 0.2 or more and 0.8 or less.

[0133] From the viewpoint of balancing the refractive indices of the slow and fast axes, the ratio of the total stretching ratio in the MD direction of the first and second stretching regions to the total stretching ratio in the TD direction of the first and second stretching regions is preferably 1.7 or more, more preferably 1.75 or more, even more preferably 1.8 or more, even more preferably 1.9 or more, and particularly preferably 2 or more. From the viewpoint of film formation stability, the above ratio is preferably 7.5 or less, more preferably 7.4 or less, even more preferably 7.3 or less, even more preferably 7.2 or less, and particularly preferably 7.1 or less. In one embodiment, the above ratio is 1.7 or more and 7.5 or less.

[0134] From the viewpoint of uniform stretching, the total area ratio of the stretching in the first and second stretching regions is preferably 10 or more, more preferably 11 or more, further preferably 12 or more, even more preferably 13 or more, and particularly preferably 14 or more. From the viewpoint of film formation stability, the above-mentioned total area ratio is preferably 30 or less, more preferably 27 or less, even more preferably 25 or less, and even more preferably 23 or less. In one embodiment, the above-mentioned total area ratio is 10 or more and 30 or less.

[0135] The heat treatment temperature (heat setting temperature) after stretching is preferably 150°C or higher, more preferably 160°C or higher, and even more preferably 170°C or higher. The above-mentioned treatment temperature is preferably 250°C or lower, more preferably 240°C or lower, and even more preferably 230°C or lower. In one embodiment, the above-mentioned treatment temperature is 150°C or higher and 250°C or lower.

[0136] The heat treatment time (heat setting time) after stretching is preferably 1 second or more, more preferably 2 seconds or more. The aforementioned treatment time is preferably 15 seconds or less, more preferably 14 seconds or less. In one embodiment, the aforementioned treatment time is 1 second or more and 15 seconds or less.

[0137] The relaxation treatment is preferably performed after heat curing. The relaxation rate is preferably 0.1% or more and 5% or less. The easing temperature is preferably 150°C or more and 250°C or less.

[0138] The polyester film of the present invention can be used as a protective film for polarizing components.

[0139] This invention includes a polarizing plate on which the aforementioned polyester film (or polarizing element protective film) is laminated on at least one side of a polarizing element (e.g., a polarizing element dyed with iodine on PVA, etc.). In a preferred embodiment, the aforementioned polarizing element protective film is laminated on one side of the polarizing element, and a non-birefringent polarizing element protective film or optical compensation film, such as a TAC film, norbornene film, or acrylic film, is laminated on the other side of the polarizing element. Alternatively, in another preferred embodiment, the aforementioned polarizing element protective film is laminated on one side of the polarizing element, and no film is laminated on the other side of the polarizing element (the film is not attached as a separate unit on the other side of the polarizing element). In this embodiment, a coating layer (a hard coating layer, an anti-glare layer, an anti-reflection layer, a low-reflection layer, a moisture-resistant layer (which can be formed from an organic or inorganic material), or a layer combining these functions) may be provided on the side of the polarizing element opposite to the side on which the aforementioned polarizing element protective film is laminated.

[0140] From the viewpoints of suppressing iris spots and suppressing warping of the liquid crystal panel, the polarizing plate of the present invention is preferably stacked with the absorption axis direction of the polarizing element and the slow axis direction of the polyester film substantially parallel. "Substantially parallel" means that the angle between the absorption axis direction of the polarizing element and the slow axis direction of the polyester film is preferably within 10 degrees, more preferably within 7 degrees, further preferably within 5 degrees, even more preferably within 3 degrees, particularly preferably within 2 degrees or within 1 degree.

[0141] This invention includes an image display device containing the aforementioned polyester film (or polarizing element protective film). The image display device includes liquid crystal displays, organic EL displays, QLED displays, micro LED displays, and other devices that include a polarizing plate inside the image display device.

[0142] Generally, a liquid crystal panel (LCD) consists of a rear surface module, liquid crystal cells, and a front surface module, arranged in order from the side opposite to the backlight source towards the side displaying the image (viewable side). The rear and front surface modules typically consist of a transparent substrate, a transparent conductive film formed on the side surface of the liquid crystal cell, and a polarizing plate disposed on the opposite side. Here, the polarizing plate is usually disposed in the rear surface module on the side opposite to the backlight source, and in the front surface module on the side displaying the image (viewable side).

[0143] The liquid crystal display device preferably includes at least a backlight source and liquid crystal cells disposed between two polarizing plates as constituent components. In addition, it may also have other components besides these, such as color filters, lens films, diffusers, anti-reflective films, etc.

[0144] The configuration of the polyester film (or polarizer protective film) of the present invention is not particularly limited. In the case of a liquid crystal display device comprising a polarizer plate disposed on the incident light side (light source side), a liquid crystal cell, and a polarizer plate disposed on the emitted light side (viewable side), the polarizer protective film on the incident light side of the polarizer plate disposed on the incident light side and / or the polarizer protective film on the emitted light side of the polarizer plate disposed on the emitted light side are preferably the polyester film of the present invention. In a preferred embodiment, the polarizer protective film on the incident light side of the polarizer plate disposed on the incident light side is used as the polyester film of the present invention.

[0145] As a backlight component, it can be a side-lighting method that uses light guide plates, reflectors, etc. as components, or it can be a direct-lighting method.

[0146] White light-emitting diodes (LEDs) are preferably used as the backlight source for liquid crystal display devices. A white LED is an element that emits white light by combining a blue LED (using a compound semiconductor) or an ultraviolet LED with a phosphor. Examples of phosphors include yttrium aluminum garnet (YAG) based yellow phosphors and terbium aluminum garnet (TERB) based yellow phosphors. White LEDs, which combine a blue LED using a compound semiconductor with a yttrium aluminum garnet (YAG) based yellow phosphor, have a continuous and broad emission spectrum and excellent luminous efficiency. Here, "continuous emission spectrum" means that there are no wavelengths with zero light intensity in the visible light region. Furthermore, the method of this invention allows for the widespread use of white LEDs with low power consumption, thus achieving energy savings.

[0147] As a backlight source, a white light source having emission spectral peaks in each wavelength region—between 400 nm and 495 nm (B region), between 495 nm and 600 nm (G region), and between 600 nm and 780 nm (R region)—is preferred. Examples include white light sources utilizing quantum dot technology, white LED light sources using phosphors that emit emission peaks in the R (red) and G (green) regions and blue LEDs respectively, three-wavelength white LED light sources, white LED light sources incorporating red lasers, and light sources using, for example, a composition of K2SiF6:Mn. 4+Fluoride phosphors (also known as "KSF") and white LED light sources, such as blue LEDs, are used. These white light sources have attracted attention as backlight sources for liquid crystal display devices with wide color gamuts. Compared with the light sources composed of white LEDs, which are light-emitting elements composed of blue LEDs and yttrium aluminum garnet-based yellow phosphors, which have been used in the past, these white light sources have narrower peak half-widths. When using backlight sources composed of these white light sources, compared with the backlight sources composed of white LEDs, which are light-emitting elements composed of blue LEDs and yttrium aluminum garnet-based yellow phosphors, if a polyester film with retardation is used as a component of the polarizer, i.e., a polarizer protective film, there is a tendency to generate iris spots. However, with the polarizer protective film of the present invention, iris spots can be significantly suppressed.

[0148] Organic EL elements can be appropriately selected from those known in the art. The use of organic EL elements is preferred in terms of wide viewing angle, high contrast, and high-speed response. A typical organic EL element is a light-emitting body (organic electroluminescent body) having a structure in which an anode as a transparent electrode, an organic light-emitting layer, and a cathode as a metal electrode are sequentially stacked on a transparent substrate. The organic EL unit emits light by recombination of holes injected from the anode with electrons injected from the cathode within the organic light-emitting layer when a voltage is applied between the anode and cathode.

[0149] As the aforementioned transparent substrate, any transparent substrate can be used. For example, the transparent substrate can be selected from the group consisting of glass substrate, ceramic substrate, semiconductor substrate, metal substrate, and plastic substrate. As a specific plastic substrate, a transparent resin film conventionally used can be cited as an example. A surface treatment layer can be provided on the transparent substrate as needed. Examples of surface treatment layers include moisture-proof layers, gas-barrier layers, hard coatings, and primer coatings.

[0150] Materials constituting the anode and cathode include, for example, metals, metal oxides, alloys, conductive compounds, and mixtures thereof. More specific materials constituting the anode include conductive transparent materials such as gold, silver, chromium, nickel, copper iodide, indium tin oxide (ITO), tin oxide, and zinc oxide. More specific materials constituting the cathode include magnesium, aluminum, indium, lithium, sodium, cesium, silver, magnesium-silver alloys, magnesium-indium alloys, and lithium-aluminum alloys.

[0151] The thicknesses of the anode and cathode can be arbitrarily set according to the materials constituting the anode and cathode. For example, the thickness of the anode can be appropriately set in the range of 10 nm to 200 nm, preferably 10 nm to 100 nm. For example, the thickness of the cathode can be appropriately set in the range of 10 nm to 1000 nm, preferably 10 nm to 200 nm.

[0152] An organic light-emitting layer is a layer that provides sites for the recombination of holes and electrons when a voltage is applied, thereby emitting light. This organic light-emitting layer contains organic light-emitting materials and can be a single-layer structure or a stacked structure of two or more layers. In the case of a stacked structure, each layer can emit light in a different color. The thickness of the organic light-emitting layer is arbitrary, for example, it can be appropriately set in the range of 3 nm to 3 μm.

[0153] The organic light-emitting material used in the organic light-emitting layer can be appropriately selected from any light-emitting material. Specifically, it can be appropriately selected from the group consisting of: olefinic light-emitting materials such as 4,4'-(2,2-diphenylvinyl)biphenyl; 9,10-bis(2-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene, 9,10-bis(9,9-dimethylfluorenyl)anthracene, 9,10-(4-(2,2-diphenylvinyl)phenyl)anthracene, 9,10'-bis(2-biphenyl) Anthracene-based luminescent materials include 9,9'-bis(anthracene), 9,10,9'10'-tetraphenyl-2,2'-bianthracene, and 1,4-bis(9-phenyl-10-anthracene)benzene; spiroluminescent materials include 2,7,2',7'-tetra(2,2-diphenylvinyl)spirodifluorene; carbazole-based luminescent materials include 4,4'-dicarbazole biphenyl and 1,3-dicarbazole phenylene; and pyrene-based luminescent materials include 1,3,5-tripyrene phenylene.

[0154] To isolate the organic EL element, which consists of an anode, an organic light-emitting layer, and a cathode on the aforementioned substrate, from external gases, the organic EL element may be equipped with a sealing member formed to cover the organic EL element. By providing a sealing member, the degradation of the light-emitting properties of the organic light-emitting layer due to moisture and oxygen in the external gas can be prevented.

[0155] Organic EL devices can also have any components (e.g., hole injection layer, hole transport layer, electron injection layer and / or electron transport layer) at any appropriate location.

[0156] When using an organic EL cell as an image display unit, it is preferable to have a polarizing plate on its visible side. Since the thickness of the organic light-emitting layer is as thin as, for example, about 10 nm, external light is reflected by the metal electrodes and emitted again towards the visible side. When viewed from the outside, the display surface of the organic EL display device sometimes appears mirror-like. To block such specular reflection of external light, it is preferable to provide a polarizing plate on the visible side of the organic EL cell, and then provide a quarter-wave plate between the organic EL cell and the polarizing plate. The polarizing plate described above can be used, and it is preferable to laminate the polyester film (or polarizing element protective film) of the present invention on the visible side of the polarizing element. Alternatively, it is preferable to laminate the quarter-wave plate onto the polarizing element instead of the protective film on the organic EL element side of the polarizing element. By combining these visible-side polarizing plates and the quarter-wave plate to form a circular polarizing plate, the external light specularly reflected by the metal electrodes of the organic EL cell is blocked by the circular polarizing plate, thus suppressing the reduction in the visibility of the image display device. Alternatively, a half-wavelength plate or the like can be further stacked on the organic EL element side or polarizer side of the quarter-wavelength plate. Preferably, the half-wavelength plates or the like are stacked on the organic EL element side of the quarter-wavelength plate in such a way that their optical axes form an angle, as disclosed in Japanese Patent Application Publication No. 10-68816 and Japanese Patent Application Publication No. 2017-97379.

[0157] QLED displays, similar to organic EL in that they utilize the self-illumination of quantum dots when an electric current is applied, are attracting attention as a next-generation display.

[0158] Example

[0159] The present invention will be described in more detail below with examples, but the present invention is not limited to the following examples. It can also be implemented with appropriate modifications within the scope that can conform to the spirit of the present invention, and these modifications are all included in the technical scope of the present invention.

[0160] The methods for evaluating physical properties in the following embodiments are described below.

[0161] (1) Evaluation of the slow axis direction of the thin film

[0162] The slow axis orientation of the thin film was evaluated using a molecular orientation meter (manufactured by Oji Instruments Co., Ltd., MOA-6004 type molecular orientation meter).

[0163] (2) Δn and delay (Re)

[0164] The retardation is a parameter defined by the product of the anisotropy of the orthogonal biaxial refractive index on the thin film (Δn = |nx - ny|) and the film thickness d (nm) (Δn × d). It is a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (Δn) is determined by the following method: Using a molecular orientation meter (manufactured by Oji Instruments Co., Ltd., MOA-6004 type molecular orientation meter), the slow axis direction of the thin film is determined. A 4cm × 2cm rectangle is cut out with the slow axis direction parallel to the long side of the sample to be measured, which serves as the sample for measurement. For this sample, the orthogonal biaxial refractive indices (refractive index along the slow axis: nx, and refractive index in the direction orthogonal to the slow axis in the plane (i.e., the refractive index along the fast axis): ny) and the thickness direction (nz) were determined using an Abbe refractometer (Atago, NAR-4T, measurement wavelength 589 nm). The absolute value of the difference between these biaxial refractive indices (|nx-ny|) was taken as the anisotropy of the refractive index (Δn). The film thickness d (nm) was measured using an electrical micrometer (Feinpruf GmbH, Millitron 1245D), and the units were converted to nm. The retardation (Re) was calculated by the product of the anisotropy of the refractive index (Δn) and the film thickness d (nm) (Δn×d).

[0165] (3) The difference between the maximum and minimum values ​​of Δn in the width direction

[0166] Using a 1000mm long roll in the TD direction, and employing the same method as described in (2) above, cut a total of 5 4cm×2cm samples from the center of the TD direction toward each end, with a center-to-end spacing of 200mm. Measure Δn. Calculate the difference between the maximum and minimum values ​​of Δn obtained from the measurements.

[0167] (4) NZ coefficient

[0168] Substitute the values ​​of nx, ny, and nz measured by the Abbe refractometer in (2) above into |nx-nz| / |nx-ny| to obtain the NZ coefficient.

[0169] (5) Planar orientation degree ΔP

[0170] Substitute the values ​​of nx, ny, and nz measured by the Abbe refractometer in (2) above into (nx+ny) / 2-nz to calculate the surface orientation degree ΔP.

[0171] (6) Ultraviolet transmittance

[0172] Prepare a polyester film measuring 8 mm in width (TD) and 40 mm in mechanical flow direction (MD) as a sample. Using a spectrophotometer (Shimadzu UV1800), set the sample with the direction of gravity parallel to the direction of mechanical flow (MD) and measure the transmittance at a wavelength of 380 nm.

[0173] (7) Ultraviolet transmittance anisotropy (polarization transmittance anisotropy)

[0174] Ultraviolet transmittance anisotropy is expressed using the biaxial ultraviolet transmittance at a wavelength of 390 nm, where the total light transmittance of the sample is 30%, orthogonal to the length direction (MD direction) and the width direction (TD direction). 390 nm is a wavelength where anisotropy is easily measured. The anisotropy of ultraviolet transmittance was measured using a UV-Vis spectrophotometer (Shimadzu UV1800) with a measurement wavelength range of 190–1100 nm. Regarding the transmittance in each stretching direction, a polarizing plate (SHC-YL38) allowing the ultraviolet wavelength region to pass through was inserted into the detector side of the spectrophotometer, and the light transmitted through the polarizing plate was measured. To eliminate the influence of the polarizing plate's orientation, after measuring the polarized transmitted light in the length direction, the film was rotated 90° to extract the polarized transmitted light in the width direction. It should be noted that the transmittance anisotropy (i.e., the ratio of polarized transmittance in the MD direction to that in the TD direction) is calculated using the following equation (A).

[0175] (Transmittance anisotropy) = (Transmittance along the long side (%)) / (Transmittance along the width (%)) …(A)

[0176] (8) Optical evaluation in large-area images (liquid crystal display devices)

[0177] A roll of a polarizing element containing iodine and polyvinyl alcohol film, manufactured by uniaxial stretching in the MD direction, is bonded to a roll of PET film of the PET film described later in parallel in the MD direction. Additionally, a roll of TAC film (manufactured by Fujifilm Corporation, 40 μm thick) is similarly bonded to the other side of the polarizing element in a roll-to-roll manner to create a polarizing plate composed of PET film / polarizing element / TAC film.

[0178] The obtained polarizing plates were respectively placed on the incident light side and the emitted light side of a liquid crystal display device using a white LED (Nichia Chemical, NSPW500CS) as the light source. The white LED is a light-emitting element composed of a blue light-emitting diode and a yttrium aluminum garnet-based yellow phosphor. The polarizing plate on the incident light side was set with a polyester film as the light source side, and the polarizing plate on the emitted light side was set with a polyester film as the viewable side. Five observers visually observed the polarizing plates of the liquid crystal display device with a large screen area (50 inches in this example) from the front and tilted directions, and determined the presence or absence of iris spots as follows.

[0179] (8A) Optical properties (optical properties correspond to Δn (in-plane birefringence.)

[0180] 〇: The number of people who are judged to not see the rainbow even when viewed from an angle is 4 or more.

[0181] △: The number of people who did not see the rainbow when viewing the image from an angle is determined to be less than 3, and even if the rainbow is determined to be seen, it is not to the extent that the visibility is deteriorated.

[0182] ×: When viewing the image from an angle, the number of people who did not see the rainbow was less than 3, and when they did see the rainbow, a deterioration in visibility was observed.

[0183] (8B) Homogeneity (homogeneity corresponds to the difference between the maximum and minimum values ​​of in-plane birefringence in the width direction)

[0184] 〇: The number of people who were determined not to have iris spots caused by different positions on the screen of a large-area display is 4 or more.

[0185] △: The number of people who did not see the iris caused by different positions in the large-area display screen is determined to be less than 3, and even if the iris is determined to be seen, it is not to the extent that it deteriorates the visibility.

[0186] ×: The number of people who did not see the iris caused by different positions in the large-area display screen is determined to be less than 3, and when the iris was determined to be seen, the visibility was deteriorated.

[0187] (8C) Comprehensive Evaluation (The comprehensive evaluation is a comprehensive assessment of 8A and 8B above.)

[0188] 〇: The number of people who are judged to have no visible iris when viewed from any angle on the entire screen is 4 or more.

[0189] △: The number of people who do not see the rainbow when viewed from any angle is less than 3, and even if the rainbow is seen faintly when viewed from an angle, it is not considered to have deteriorated the visibility.

[0190] ×: If the number of people who do not see the rainbow when viewed from any angle on the entire screen is less than 3, and if the rainbow is seen on part or the entire screen, a deterioration in visibility is observed.

[0191] (9) Durability evaluation of polarizing plate

[0192] A polarizing plate is fabricated by laminating the PET film and polarizing element of each embodiment described later in a roll-to-roll manner. Similarly, the comparative and reference examples described later also involve laminating the PET film and polarizing element in a roll-to-roll manner to fabricate polarizing plates. Here, the angle between the slow axis direction of the PET film and the MD direction is within 10 degrees. Furthermore, the polarizing element is laminated with the absorption axis direction of the PET film at an angle within 10 degrees to the MD direction. This allows the PET film to absorb more ultraviolet light in the MD direction.

[0193] Using a UV irradiation testing machine (Iwasaki Electric Co., Ltd., Eye Super UV Tester, SUV-W151), for each polarizing plate, at an irradiation intensity of 100W / m², 2 Under conditions of black panel temperature (60℃) and relative humidity (60%RH) below, after 500 hours of ultraviolet irradiation, visually observe for discoloration. No discoloration indicates exceptionally good durability, rated "0". Slight discoloration indicates good durability, rated "△". Significant discoloration indicates poor durability, rated "×".

[0194] (10) Film-forming properties

[0195] Starting from one hour after the start of film formation, the number of breaks in the following hour is compared to determine the film formation properties of the film.

[0196] ○: The number of fractures is less than 3

[0197] △: The number of fractures is more than 3 but less than 6

[0198] ×: The number of fractures is 6 or more.

[0199] (Manufacturing Example 1 - Polyester A)

[0200] The esterification reactor was heated to 200°C, at which point 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were added. While 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 added as catalysts. Next, the reactor was pressurized and heated to 240°C at a gauge pressure of 0.34 MPa. After the pressurized esterification reaction, the reactor was returned to atmospheric pressure, and 0.014 parts by mass of phosphoric acid were added. The temperature was further increased to 260°C over 15 minutes, and 0.012 parts by mass of trimethyl phosphate were added. After 15 minutes, the mixture was dispersed using a high-pressure disperser. After another 15 minutes, the resulting esterification product was transferred to a polycondensation reactor and subjected to reduced pressure polycondensation at 280°C.

[0201] After the polycondensation reaction, the product was filtered through a Naslon filter with a 95% diameter cutoff of 5 μm, extruded into a filament from a nozzle, and cooled and cured using pre-filtered cooling water (pore size: less than 1 μm). The resulting polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl / g and a diethylene glycol (DEG) content of 1.5 mol%, and was substantially free of inactive particles and internally precipitated particles. (Hereinafter referred to as PET(A)).

[0202] (Manufacturing Example 2 - Polyester B)

[0203] Ten parts by weight of dried ultraviolet absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazin-4-one) and 90 parts by weight of particulate-free PET(A) (intrinsic viscosity 0.62 dl / g) were mixed and extruded using a compounding extruder to obtain polyethylene terephthalate resin (B) containing the ultraviolet absorber. (Hereinafter referred to as PET(B)).

[0204] (Example 3 - Preparation of adhesive-modified coating liquid)

[0205] A water-dispersible copolyester resin containing sulfonic acid metal salts was prepared by transesterification and polycondensation using conventional methods. The resin composition was as follows: 46 mol% terephthalic acid, 46 mol% isophthalic acid, and 8 mol% sodium isophthalate-5-sulfonate as dicarboxylic acid components (relative to the total dicarboxylic acid components); and 50 mol% ethylene glycol and 50 mol% neopentyl glycol as diol components (relative to the total diol components). Next, 51.4 parts by weight of water, 38 parts by weight of isopropanol, 5 parts by weight of n-butyl cellosolve, and 0.06 parts by weight of nonionic surfactant were mixed and heated to 77°C. Then, 5 parts by weight of the above-mentioned water-dispersible copolyester resin containing sulfonic acid metal salts were added, and stirring continued until the resin lumps disappeared. The resin dispersion was then cooled to room temperature to obtain a uniform water-dispersible copolyester resin solution with a solid content of 5.0% by weight. Subsequently, after dispersing 3 parts by mass of aggregated silica particles (manufactured by Fuji Silysia Chemical, Ltd., SYLYSIA 310) in 50 parts by mass of water, 0.54 parts by mass of the aqueous dispersion of SYLYSIA 310 was added to 99.46 parts by mass of the above-mentioned water-dispersible copolyester resin liquid, and 20 parts by mass of water was added while stirring to obtain an adhesive-modified coating liquid.

[0206] As an example, we will explain the case of using a simultaneous biaxial stretching machine to perform stretching in two stages.

[0207] [Reference Example 1]

[0208] Ninety parts by weight of particle-free PET(A) resin granules and ten parts by weight of PET(B) resin granules containing UV absorbers, used as raw materials for the intermediate layer of the substrate film, were dried under reduced pressure (1 Torr) at 135°C for 6 hours and then fed to extruder 2 (for intermediate layer II). Meanwhile, PET(A) was dried using conventional methods and fed to extruder 1 (for outer layer I and outer layer III), where it was dissolved at 285°C. Both polymers were filtered separately using stainless steel sintered filter media (with a nominal filtration accuracy of 10μm particles, retaining 95% of the particles). Two three-layer confluence blocks were stacked and extruded from the die into sheets. These sheets were then electrostatically cast onto a casting drum at a surface temperature of 30°C for cooling and curing to produce an unstretched film. The discharge rate of each extruder was adjusted to a thickness ratio of 10:80:10 for layers I, II, and III.

[0209] Next, the coating amount after drying is 0.08 g / m² using the reverse roller method. 2 The adhesive-modified coating liquid was applied to both sides of the unstretched PET film and then dried at 80°C for 20 seconds.

[0210] The unstretched film with the coating layer is fed into a biaxial stretching machine. While holding the ends of the film with clamps, it is fed into hot air zone 1 at a first stretching temperature of 100°C, where it is stretched 3.9 times in the flow direction and 2.2 times in the width direction. Next, it is fed into hot air zone 2 at a second stretching temperature of 105°C, where it is stretched 1.7 times in the flow direction and 1.0 times in the width direction. While maintaining the stretched width, it is treated at a heat-fixing temperature of 220°C for 30 seconds to obtain a biaxially oriented PET film with a thickness of 40 μm. This film is then wound into a roll to form a film roll (1000 mm in length in the TD direction and 500 m in length in the MD direction).

[0211] [Examples 1-3, 5 and 6, Comparative Examples 1, 5 and 7, and Reference Examples 2-4]

[0212] The stretching ratios in the flow direction and width direction of hot air zone 1 were changed to the ratios shown in Table 1, and the stretching ratio in the flow direction of hot air zone 2 was changed to the ratios shown in Table 1. Otherwise, the same procedure as in Reference Example 1 was followed to obtain a biaxially oriented PET film (roll).

[0213] [Example 4]

[0214] By changing the flow direction ratio of hot air zone 1 to 4.2 times and the stretch ratio in the width direction to 2.0 times, the same procedure as in Reference Example 1 was followed to obtain a biaxially oriented PET film (roll).

[0215] [Examples 7 and 8]

[0216] By changing the thickness to 60 μm or 30 μm, and otherwise operating in the same manner as in Example 1, a biaxially oriented PET film (roll) was obtained.

[0217] [Example 9]

[0218] The temperature of hot air zone 1 (first stretching temperature) was changed to 105°C, and the temperature of hot air zone 2 (second stretching temperature) was changed to 110°C. Otherwise, the same procedure as in Example 1 was followed to obtain a biaxially oriented PET film (roll).

[0219] [Example 10]

[0220] By changing the flow direction ratio of hot air zone 1 to 3.3 times and the stretch ratio in the width direction to 3.0 times, and changing the flow direction stretch ratio of hot air zone 2 to 2.0 times and the stretch ratio in the width direction to 1.1 times, the same procedure as in Reference Example 1 was followed to obtain a biaxially oriented PET film (roll).

[0221] [Example 11]

[0222] As raw materials for the intermediate layer of the substrate film, 80 parts by weight of PET(A) resin granules without particles and 20 parts by weight of PET(B) resin granules containing ultraviolet absorbers were used. Otherwise, the operation was the same as in Example 1 to obtain a biaxially oriented PET film (roll).

[0223] [Example 12]

[0224] As raw materials for the intermediate layer of the substrate film, 80 parts by weight of PET(A) resin granules without particles and 20 parts by weight of PET(B) resin granules containing ultraviolet absorbers were used. Otherwise, the operation was the same as in Example 3 to obtain a biaxially oriented PET film (roll).

[0225] [Example 13]

[0226] As raw materials for the intermediate layer of the substrate film, 80 parts by weight of PET(A) resin granules without particles and 20 parts by weight of PET(B) resin granules containing ultraviolet absorbers were used. Otherwise, the operation was the same as in Example 6 to obtain a biaxially oriented PET film (roll).

[0227] [Example 14]

[0228] As the raw material for the intermediate layer of the substrate film, 70 parts by weight of PET(A) resin granules without particles and 30 parts by weight of PET(B) resin granules containing ultraviolet absorbers were used. The thickness of the biaxially oriented PET film was set to 30 μm. Otherwise, the operation was the same as in Example 8 to obtain a biaxially oriented PET film (roll).

[0229] [Example 15]

[0230] As the raw material for the intermediate layer of the substrate film, 60 parts by weight of PET(A) resin granules without particles and 40 parts by weight of PET(B) resin granules containing ultraviolet absorbers were used. The thickness of the biaxially oriented PET film was set to 20 μm. Otherwise, the operation was the same as in Example 1 to obtain a biaxially oriented PET film (roll).

[0231] [Comparative Example 6]

[0232] The flow direction ratio of hot air zone 1 was changed to 3.1 times, and the stretch ratio of the flow direction of hot air zone 2 was changed to 1.3 times. Otherwise, the same procedure as in Reference Example 1 was followed to obtain a biaxially oriented PET film (roll).

[0233] [Refer to Example 8]

[0234] The temperature of hot air zone 1 (first stretching temperature) was changed to 125°C, the stretching ratio in the flow direction was changed to 6.5 times, stretching was not performed in hot air zone 2, and the heat setting temperature was changed to 225°C. Otherwise, the same operation as in Reference Example 1 was performed to obtain a biaxially oriented PET film (roll).

[0235] [Table 1A]

[0236]

[0237] [Table 1B]

[0238]

[0239] [Table 1C]

[0240]

[0241] [Table 1D]

[0242]

[0243] [Table 2A]

[0244]

[0245] [Table 2B]

[0246]

[0247] [Table 2C]

[0248]

[0249] [Table 3A]

[0250]

[0251] [Table 3B]

[0252]

[0253] [Table 3C]

[0254]

[0255] It should be noted that the above example is a two-stage example, but it can be modified within the scope of the above-mentioned stretching considerations. For example, weak MD stretching or TD stretching can be applied before and after the first and second stretching, or the first and second stretching can be further divided into multiple stages. Alternatively, the first and second halves of the stretching can not be separated, but can gradually change to be dominated by MD stretching as the stretching progresses.

Claims

1. A polyester film, wherein, The polyester film is primarily made of polyethylene terephthalate. The slow axis direction of the polyester film is approximately parallel to the MD direction. The in-plane birefringence ΔNxy of the polyester film is greater than 0.06 and less than 0.

2. The polyester film has a refractive index of 1.58 or higher and 1.63 or lower along its fast axis. The polyester film has an ultraviolet transmittance of 0% or more and 30% or less at 380 nm. The ratio of the polarization transmittance of the polyester film in the MD direction to the TD direction is less than 0.

95.

2. The polyester film according to claim 1, wherein, The polyester film has a length of 1m or more in the TD direction. The difference between the maximum and minimum values ​​of ΔNxy in the TD direction of the polyester film is less than 0.

013.

3. The polyester film according to claim 1, wherein, The NZ coefficient of the polyester film is above 1.5 and below 2.

5.

4. The polyester film according to claim 1, wherein, The thickness of the polyester film is 15 μm or more and 60 μm or less.

5. The polyester film according to claim 1, wherein, The angle between the slow axis direction and the MD direction of the polyester film is within 10 degrees.

6. The polyester film according to claim 1, wherein, The elastic modulus in the MD direction of the polyester film is above 3000 MPa.

7. The polyester film according to claim 1, wherein, The delay of the polyester film is above 700 nm and below 8000 nm.

8. The polyester film according to claim 7, which is a protective film for polarizing components.

9. A polarizing plate having a polyester film of claim 8 laminated on at least one side of a polarizing element, wherein the angle between the absorption axis direction of the polarizing element and the MD direction of the polyester film is within 10 degrees.

10. A polarizing plate having a polyester film of claim 8 laminated on one side of a polarizing element, and no film laminated on the other side of the polarizing element.

11. A polarizing plate having a polyester film of claim 8 laminated on one side of a polarizing element and a quarter-wavelength plate laminated on the other side of the polarizing element.

12. An image display device comprising a light source and a polarizing plate according to any one of claims 9 to 11.

13. The image display device according to claim 12, wherein it is a liquid crystal display device.

14. The image display device according to claim 12, wherein it is an organic EL display.

15. The image display device according to claim 12, wherein it is a QLED display.

Images